Hybrid nanostructure designs facilitated by M13 virus
for lithium ion battery and lithium air battery electrodes
By
Dahyun Oh
B.S. Materials Science and Engineering, Seoul National University, Korea, 2008
SUBMITTED TO THE DEPARTMENT OF
MATERIALS SCIENCE AND ENGINEERING
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
JANUARY 2014
0 2014 Massachusetts Institute of Technology. All rights reserved.
-MASSAHUStTS
TE
OF TECHNOLOGY
MAY 14 2014
LIBRARIES
Signature of Author:
Department of M
rials Science and Engineering
January 1 7 th 2014
Certified by:
Angela M. Belcher
Materials Science and Engineering and Biological Engineering
Thesis Supervisor
Accepted by:
Chair, Departmental C
on
Hybrid nanostructure designs facilitated by M 13 virus for
lithium ion battery and lithium air battery electrodes
By
Dahyun Oh
B.S. Materials Science and Engineering, Seoul National University, Korea, 2008
Submitted to the Department of Materials Science and Engineering on Jan 17 th, 2014 in Partial
Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Materials Science and
Engineering at the Massachusetts Institute of Technology
ABSTRACT
The development of technology and population growth will demand 56 percent increase of
the energy consumption in 30 years. An efficient energy storage system will be necessary to meet
these increased needs to deliver and store the energy. After the first release of commercial Li ion
batteries in 1991, they were widely adapted to various applications from small portable devices to
electric vehicles. However, the current Li ion battery can only store -250 Wh/kgcelj of gravimetric
energy, a far limited energy storage capability especially to replace gasoline in powering vehicles.
This limitation originated either from the incomplete utilization of active materials or their low
theoretical energy density. Therefore, a rational design of electrodes as well as the new battery
chemistry needs to be investigated to further develop the current energy storage system.
In this thesis, high theoretical energy density batteries are investigated. First, the power
performance of conversion reaction cathode materials, bismuth oxyfluorides, was improved. By
rationally designing genetic sequences of the M13 virus, graphene sheets were homogeneously
distributed throughout bismuth oxyfluorides cathodes as conducting paths. Second, large surface
area cathodes were developed with virus-templated manganese oxide nanowires. These electrodes
were applied to Li-0
2
battery systems to achieve large capacities and a long cycle life.
Furthermore, the chemical composition of virus-templated inorganic nanowires was easily tuned
to study the catalytic behavior of transition metal oxides in Li-0
2
batteries. These bio-directed
methods to develop high performance battery electrodes, in conclusion, suggest an eco-friendly
and cost effective way to manufacture energy storage devices. The design strategy established in
this thesis could be applied not only to batteries but also to electronic devices requiring
sophisticated nanoscale controls.
Thesis advisor: Angela M. Belcher
Title: W.M. Keck Professor of Energy
1
ACKNOWLEDGEMENT
It was a great journey to complete Ph.D. program at MIT, full of excitement, curiosity
and endurance. For five years of study, Prof. Angela M. Belcher, who is my teacher and advisor,
has led me to learn science and technology but also life. I would like to send my sincere thanks to
Angie for her strong support, encouragement and passion. In addition to my advisor, it was a
great pleasure to meet many insightful scholars at MIT including my thesis committee members,
Prof. Gerbrand Ceder, Prof. Paula T. Hammond and my course work teacher, Prof. Michael J.
Demkowicz, Prof. Samuel M. Allen. I appreciate their efforts and time to guide me to
successfully finish my thesis and course work. As a graduate student researcher, I had many great
opportunities to communicate and discuss about the research with Prof. Yang Shao-Horn and
Prof. Jing Kong. Their feedback and guidance has directed me to find excitements in research.
In addition to leading investigators, I would like to thank to my colleagues, collaborators
and friends at MIT. I spent most of my school life at CMSE and ISN, with the help from Dr.
Yong Zhang, Dr. Scott Speakman and Mr. William F. DiNatale. My lab mates, Prof. Yun Jung
Lee, Dr. Hyunjung Yi, Prof. Debadyuti Ghosh, Dr. Gaelen Hess and my neighbor Mr. John
Patrick Casey have kindly shared all of my joy, sadness and worries for my graduate life.
Furthermore, I am thankful to Dr. Jifa Qi, Prof. Yi-Chun Lu, Dr. Nimrod Heldman, Prof. Seung
Woo Lee and Prof. Byungwoo Kang for their scientific feedback and kind answers to my endless
questions. My Korean classmates, Eun Seon, YJ, Yong-cheol and international classmates, Billy,
Jo, Kevin, Marco, Sophie, thank you all to spend the most exciting MIT course 3 graduate life
together. I am thankful to my friend at MIT, Jouha, Sungmin, Chris, Yunna, Su, Dong Sook, Eun
hee to mentally support my graduate life. Finally, I appreciate the financial support from
Kwanjeong Educational Foundation and Prof. Anne Mayes.
Most of all, I would like to send my sincere thank to my family, Rosia, George, Ann,
Dongho for their kind greetings and welcoming during my vacation in US. I appreciate the
support from my lovely aunts in Korea as well. I am sending my greatest love to my only one
sister, Jihyun for sharing all pains, love and encouragements. I am also sending my deepest sorry,
love and thank to my parents in Korea for their firmness, health, support and love. In final, I am
grateful to God, who is the start and the end, to lead me to his love.
2
BIOGRAPHICAL NOTE
EDUCATION
2008.09 ~ present Ph. D. at Department of Materials Science and Engineering
Massachusetts Institute of Technology (MIT), Massachusetts, USA
Advisor: Angela M. Belcher
Ph. D. thesis title: Hybrid nanostructure designs facilitated by M 13 virus for
lithium ion battery and lithium air battery electrodes
2004.03 ~ 2008.01 B.S. at Department of Materials Science and Engineering
Seoul National University, Seoul, Korea
Graduated with honors (Summa cum laude)
AWARDS AND SCHOLARSHIPS
2013
2011
2008-2013
2008
2007
2006
2005
2004
Graduate Student Award, Silver, Fall MRS Meeting, Boston, USA
Outstanding Poster Award, Fall MRS Meeting, Boston, USA
Kwanjeong Educational Foundation graduate student fellowship, Seoul, Korea
Mayes fellowship, MIT, USA
Korea Semiconductor Industry Association fellowship, Seoul, Korea
Korea Federation of Textile Industries fellowship, Seoul, Korea
Honors and fellowship for top student, SNU, Seoul, Korea
Korea Science and Engineering Foundation fellowship, Seoul, Korea
PUBLICATION
Journal Publications
1.
Dahyun Oh, Jifa Qit, Geran Zhang, Thomas Carney, Yang Shao-Horn* and Angela M.
Belcher* (*Equal contribution)
Variations of oxygen reduction/oxygen evolution reactions in Li-0 2 batteries with biotemplated
multi-component (Mn,Co) transition metal oxide nanowires, In preparation, 2014
2.
Dahyun Oh, Jifa Qit, Yi-Chun Lu, Yong Zhang, Yang Shao-Horn* and Angela M.
Belcher* ( Equal contribution)
Biologically enhanced cathode design for improved capacity and cycle life for Li-oxygen
batteries, Nature communications, 2013, 4, 2756 DOI: 10.1038/ncomms3756
3.
Dahvun Oh, Xiangnan Dang, Hyunjung Yi, Mark A. Allen, Kang Xu, Yun Jung Lee*
and Angela M. Belcher*
Graphene sheets stabilized on genetically engineered M 13 viral templates as Conducting
Frameworks for Hybrid Energy-Storage Materials, Small, 2012, 8 (7), pp 1006-1011 DOI:
10.1002/smll.20 1102036
4.
Yun Jung Leet, Youjin Leet, Dahyun Oh, Tiffany Chen, Gerbrand Ceder* and Angela
M. Belcher* (tEqual contribution)
Biologically Activated Noble Metal Alloys at the Nanoscale: For Lithium Ion Battery Anodes
Nano Letters, 2010, 10 (7), pp 2433-2440 DOI: 10.1021/n11005993
3
Conference Proceedings
1.
Kang Xu*, Dahvun Oh, Hyunjung Yi, Jifa Qi, Alice Xu, James Snyder and Angela M.
Belcher, ECS transaction, 2012, 41 (41), pp 55-64 DOI: 10. 1149/1.4717963
Genetically Programming Interfaces between Active Materials, Conductive Pathway and Current
Collector in Li Ion Batteries
PATENT
1.
Dahvun Oh, Jifa Qi, Yang Shao-Horn and Angela M. Belcher
M 13 bacteriophage templated nanocomposites of transition metal oxides and metal nanoparticles
for high performance lithium air batteries, US patent filed.
4
TABLE OF CONTENTS
Abstract ............................................................................................................................................
Acknow ledgem ent ...........................................................................................................................
Biographical note .............................................................................................................................
L ist of Tables ...................................................................................................................................
Lisgt of Figures ..................................................................................................................................
I
2
3
6
6
Chapter 1. Introduction ....................................................................................................................
1. 1 Background ...........................................................................................................................
1.2 Scopeofw ork .....................................................................................................................
1.3 References ...........................................................................................................................
8
9
12
13
Chapter 2. Integrating graphene based conducting frameworks into Lithium ion battery cathodes
(Bism uth oxyfluorides, BiOo. 5F 2) by genetic engineering of M 13 virus ...................................
15
2.1 Introduction .........................................................................................................................
16
2.2 Experim ental .......................................................................................................................
18
2.3 Results and discussion .....................................................................................................
23
2.4 Conclusion ...........................................................................................................................
30
2.5 Figures and tables ................................................................................................................
31
2.6 References ............................................................................................................................
43
Chapter 3. Li-0 2 battery hybrid nanocatalyst formed with M 13 virus templated Manganese oxides
nanow ires and noble m etal nanoparticles ..................................................................................
46
3.1 Introduction .........................................................................................................................
47
3.2 Experim ental .......................................................................................................................
49
3.3 Results and discussion .....................................................................................................
54
3.4 Conclusion ...........................................................................................................................
64
3.5 Figures and tables ................................................................................................................
65
3.6 References ............................................................................................................................
84
Chapter 4. Investigation of catalytic behavior of M13 virus templated MnCo30 4 (x = 0, 1,2)
nanow ires for Li-0 2 battery cathodes .......................................................................................
89
4.1 Introduction .........................................................................................................................
90
4.2 Experim ental ........................................................................................................................
92
4.3 Results and discussion .....................................................................................................
96
4.4 Conclusion .........................................................................................................................
100
4.5 Figures and tables ..............................................................................................................
101
4.6 References ..........................................................................................................................
106
Chapter 5. Ongoing work: Probing graphene defects with genetic modifications of M13 virus
......................................................................................................................................................
4.1
4.2
4.3
4.4
4.5
Introduction .......................................................................................................................
Experim ental .....................................................................................................................
Results and discussion .......................................................................................................
Figures and tables ..............................................................................................................
References .........................................................................................................................
5
10 8
109
110
II1
112
115
List of tables
Table 2.1. XRD peaks table for synthesized bismuth oxyfluoride from 20-70 degree (2 Theta)
with Rietveld refinement results for compound .......................................................................
42
Table 2.2. Atomic concentration (%) of bismuth oxyfluoride by XPS analysis .......................
42
Table 3.1. The Gas Chromatography (GC) data of Pd (3 wt %)/bio MO nanowires electrodes after
the first galvanostatic discharge/charge at 0.4 A g-'c with 0.1 M LiCIO
4
in DME ...................
83
Table 3.2. The discharge/charge capacity (mAh g'c) for the first and second cycle of different
electrodes galvanostatically tested at 0.4 A g-1, with 0.1 M LiCIO
4
in DME under I atm of 02
.......................................................................................................................................................
83
List of figures
Figure 2. 1. Characterizations of graphene.................................................................................
31
Figure 2.2. Determination of virus mass by Thermogravimetric analysis (TGA) ....................
32
Figure 2.3. The graphene/M 13 virus complex with the enhanced colloidal stability for the hybrid
graphene/nanoparticle nanocom posites .....................................................................................
33
Figure 2.4. Characterizations of the bismuth oxyfluoride nucleated on the graphene/virus complex
.......................................................................................................................................................
35
Figure 2.5. Characterizations of bismuth oxyfluoride with an electrochemical method and X RD
........................................................................................................................................................
36
Figure 2.6. The power performance of the graphene/bismuth oxyfluoride nanocomposites with
the genetically engineered M 13 virus .......................................................................................
37
Figure 2.7. Electrochemical performance and characterization of bismuth oxyfluoride/graphene
nanocomposites and bismuth oxyfluoride on FC#2 ..................................................................
39
Figure 2.8. XRD patterns of control samples ...........................................................................
40
Figure 2.9. The first five cycles galvanostatic data of bismuth oxyfluoride/graphene (2.4 wt%)
nanocomposites (BOF-GP) with FC# 2 and control samples ...................................................
41
Figure 3.1. Schematic of a nanocomposite structure.................................................................
65
Figure 3.2. Electron microscope images of bio MO nanowires .................................................
66
Figure 3.3. Crystallographic property of bio MO nanowires .....................................................
67
Figure 3.4. XPS spectra of bio MO nanowires and manganese oxide (MO) nanoparticles...........68
Figure 3.5. Stabilization effect of PAA wrapping on bio MO nanowires.................................
69
Figure 3.6. Pd/Au nanoparticles loading on bio MO nanowires ...............................................
70
Figure 3.7. Elemental mapping of Pd/Au nanoparticles loaded bio MO nanowires...................71
6
Figure 3.8. TGA data and galvanostatic profile of bio MO nanowires and control samples.........72
Figure 3.9. Microstructure analysis of MO nanoparticles and bio MO nanowires ....................
73
Figure 3.10. Li-0
2
battery operation of MO nanoparticles and bio MO nanowires...................74
Figure 3.11. Li-0
2
battery operation of Au, Pd nanoparticle loaded bio MO nanowires electrodes
........................................................................................................................................................
Figure 3.12. The improved specific capacity of Li-0
2
75
battery with the rationally designed catalyst
electro des ........................................................................................................................................
Figure 3.13. The improvement of Li-0
2
76
battery cycling performance with the rationally designed
catalyst electrodes...........................................................................................................................77
Figure 3.14. The cycling performance of low carbon Li-0
2
batteries with the fixed discharge
capacity of 4,000 mAh g-I (400 mAh g-c+catalyst)...........................................................................78
Figure 3.15. The cycling voltage profile of low carbon Li-0
capacity of 2,000 mAh g-Ic (200 mAh g-
2
+catalyst)...........................................................................79
Figure 3.16. The cycling voltage profile of high carbon Li-0
capacity of 727 mAh g-'c (400 mAh
batteries with the fixed discharge
2
batteries with the fixed discharge
g- c+catalyst)............................................................................81
Figure 4.1. M13 virus mediated synthesis of various Li-0
2
battery materials for Li-0
2
batteries
......................................................................................................................................................
10 1
Figure 4.2. HRTEM images of biotemplated MCO nanowires....................................................
102
Figure 4.3. The electrochemical performance of bio MCO nanowires in Li-0
2
batteries ........... 103
Figure 4.4. C haracterizations of N i N Ps.......................................................................................
Figure 4.5. The electrochemical performances of bio MnxCo 3
xO4
104
(x=l, 2) nanowires in Li-02
b atteries.........................................................................................................................................
1 05
Figure 5.1 Scheme of Ml 3 virus-based graphene defects detector..............................................
112
Figure 5.2 Scanning electron microscope (SEM) image of graphene flakes ...............................
113
3
Figure 5.3 p sequences of M 13 virus clones selected from bio-panning against graphene flakes
......................................................................................................................................................
7
1 14
Chapter 1. Introduction
8
1.1
Background
The word to describe the post X-generation has changed from 'Global' generation to 'Tech',
'Digital', even to 'Wii'
generation. Thus, storing electrical energy into pockets becomes
important and Li ion batteries met the needs to power small portable devices. From 1970s,
rechargeable Li ion batteries operating with 'intercalation' mechanism at room temperature' have
been studied. Intercalation reactions in Li ion batteries refer to the insertion/de-insertion of Li ion
into crystalline phase of active materials. 2 Theoretical capacities of these intercalation materials
remain low since the number of electron transferred between the positive electrode and the
negative electrode is mostly limited to around one per active 3d metal (e.g. LiCoO 2 , LiFePO 4,
LiTiS 2 etc). The amount of energy stored (or dissipated) in batteries is proportional to the number
of electron associated in reactions and the cell potential as the following equation shows
|AGI= nFE|
(n: mol, number of moles of electron passed per mole of reactants, F: 96,485 C/mol, magnitude of
electric charge per mole of electron, E: V, potential difference between a cathode and an anode).
Thus, finding the battery reaction chemistry accompanying multiple numbers of electrons and a
high potential difference is necessary to achieve high energy density batteries. In this thesis,
conversion reaction
system and Li-oxygen battery system
were selected to meet those
requirements to develop next generation energy storage devices with high energy densities.
1.1.1 Conversion reaction materials for Li-ion battery cathodes
Among the high energy density batteries, the conversion reaction mechanism is promising
since each chemical formula of the conversion materials reacts with multiple lithium ions and
electrons
(MaXb +
(b-n)Li
-> aM + bLinX). They have great possibilities due to their larger
theoretical capacity than the conventional intercalation materials. Compared to other conversion
reaction materials including sulfides, oxides, nitrides and phosphides,'0 fluoride materials''
9
provide high reduction potentials above 2 V vs. Li/Li+, which is applicable to cathodes due to the
highly ionic characteristic of metal-fluorine bonds. However, the application of conversion
reaction materials has been limited by their small practical capacity because of low conductivity
and poor reversibility of electrochemical reactions. Thus, there have been several efforts to
increase the conductivity of fluorides. One of the reported methods is to partially replace the
fluorine with oxygen' 2
13
to induce covalent characteristic to the compound. For other methods,
fluorides have been composited with carbon materials through a high-energy ball milling. With
this method, the active materials particle size is reduced to nanoscale thus it has decreased ionic
and electronic
reactions.
diffusion path resulting
in the improved reversibility of electrochemical
Here, we expect the genetically engineered M 13 virus can improve the power and the
reversibility of conversion materials based cathodes. By nanocompositing conducting materials,
graphene and bismuth oxyfluorides (BiOO. 5F 2) using M 13 virus, homogeneous graphene based
conductive framework that contacts to active materials can result in a significant improvement in
the electrochemical performance of a model conversion reaction material, bismuth oxyfluoride.
1.1.2 Li-oxygen batteries for high energy density storage systems
Li-oxygen batteries are attractive next generation energy storage systems as they can
increase the gravimetric energy density of fully packaged batteries by 2-3 times that of
conventional Li-ion cells. 5 In the operation of rechargeable Li-oxygen batteries with nonaqueous electrolytes, Li 2 02is deposited (oxygen reduction reaction; ORR) during discharging and
decomposed back into Li+ and 02 (oxygen evolution reaction, OER) during charging at the
catalyst electrode (2Li++O 2+2eLi
20 2 ).
Although their high theoretical energy density (3,505
Wh kg') is extremely advantageous, current Li-oxygen batteries suffer from a high voltage
hysteresis, a low power performance and a short cycle life. These poor performances of Lioxygen batteries were mainly originated from the instability of electrolytes due to the high
reactivity of reduced oxygen or discharge products, Li 20 2 .16'
10
17
In addition to electrolytes, the
cathodes still remain as a barrier to fully utilize the advantage of Li-oxygen batteries. The
catalytic efficiency of Li-oxygen battery cathodes needs to be improved, as they form or
decompose highly insulating Li 2 0 2 throughout the electrode during the operation. Furthermore, in
recent studies, the cathodes were made with high cost (e.g. Au 18 , Pd, Pt)' 9 or rare (e.g. RuO
20
2 2,
Lao. 7 5Sro.2 5 MnO 321) elements, impeding the commercialization of Li-oxygen batteries. Therefore,
developing a highly functional and cost efficient catalyst electrode is necessary to achieve high
energy density battery systems. In this thesis, the M 13 virus can be applied to form a
nanocomposite structure for Li-oxygen battery cathodes with a high surface area and cost
efficiency. By developing a synthetic method to homogeneously distribute the functional
nanoparticles, the amount of noble metal can be lowered and the surface mediated reaction
between lithium ions, oxygen molecules and electrons can be facilitated.
1.1.3 The property of M13 Virus and its electronic device applications
This thesis focuses on developing high energy density
battery systems with the
biomolecule, M 13 virus, to expand the application of batteries into electric vehicles. The M 13
virus is a filamentous bacteriophage, with a length of - 880 nm and a diameter of - 6.5 nm.3 This
high aspect ratio virus particle has been used as a nanowire template for the functional inorganic
nanomaterials growth such as semiconductors, 4 photovoltaic cells,5 perovskites6 and Li-ion
battery electrodes.','8 9 In addition, the single-stranded DNA encapsulated inside the coat proteins
can be modified to express specific peptide sequences on the surface of the virus to enhance the
interaction with materials of interest. 4' 9 By taking advantages of these two properties of M 13
virus, high energy density battery electrodes can be rationally designed and fabricated with a
precise control at the nanoscale.
11
1.2
Scope of work
The main focus of this thesis lies on the rational design of nanomaterials for Li-ion battery
and Li-oxygen battery electrodes. Nanocomposite structures were suggested with the genetic
engineering of M 13 virus by taking into account the reaction mechanism and current limitations
of Li-ion battery and Li-oxygen battery. The transportation of two key elements in the operation
of battery, lithium ion and electron, was improved by decreasing the active material size into
nanoscale and by compositing carbon-based materials or conductive metals. In chapter 2, the
M 13 virus was used as a template of BiO0 .5F 2 as well as a stabilizer of graphene. The new M 13
virus clone was selected and further modified, called FC#2, to play the dual functionality in
forming Li-ion battery cathodes. The M 13 virus mediated graphene/BiOO. 5F 2 nanocomposites
improved the power performance, round trip efficiency of conversion reaction materials, BiOo. F .
5 2
In chapter 3, the synthesis of spherulitic surface morphology of bio-templated manganese oxide
(bio MO) nanowires was described. They improved the capacity and cycle life of Li-oxygen
batteries at six times higher current density than previously reported manganese oxide based
cathodes. Moreover, the surface of bio MO nanowires was further engineered to control the
binding affinity with oxygen molecules by decorating a small amount of (3-5 wt % of electrodes)
novel metal nanoparticles, Au or Pd. In chapter 4, we were able to easily tune the composition of
nanowire with M 13 virus templates, resulting in various transition metal based nanowires,
MnCo3 O 4 (x
=
0, 1, 2) for the application to Li-oxygen battery cathodes. The different
electrochemical behaviors in Li-oxygen batteries were observed with this compositional set of
spinel oxides thus enabling us to frame a design principle for future Li-oxygen batteries. In
chapter 5, the M 13 virus based graphene defect detector is introduced and its preliminary result
is included as ongoing work.
12
1.3
Reference
I.
Whittingham MS. Electrical Energy-Storage and Intercalation Chemistry. Science 192,
1126-1127 (1976).
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Whittingham MS. History, Evolution, and Future Status of Energy Storage. P Ieee 100,
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III CFB, Burton DR, Scott JK, Silverman GJ. Phage display: a laboratory manual.Cold
Spring Harbor Laboratory Press: Cold Spring Harbor, New York, 2001.
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Mao CB, Solis DJ, Reiss BD, Kottmann ST, Sweeney RY, Hayhurst A, et al. Virus-based
toolkit for the directed synthesis of magnetic and semiconducting nanowires. Science
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Dang XN, Yi HJ, Ham MH, Qi JF, Yun DS, Ladewski R, et al. Virus-templated selfassembled single-walled carbon nanotubes for highly efficient electron collection in
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Nuraje N, Dang XN, Qi JF, Allen MA, Lei Y, Belcher AM. Biotemplated Synthesis of
Perovskite Nanomaterials for Solar Energy Conversion. Adv Mater 24, 2885-2889
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Nam KT, Kim DW, Yoo PJ, Chiang CY, Meethong N, Hammond PT. et al. Virusenabled synthesis and assembly of nanowires for lithium ion battery electrodes. Science
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Lee YJ, Yi H, Kim WJ, Kang K, Yun DS, Strano MS, et al. Fabricating Genetically
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Lee YJ, Lee Y, Oh D, Chen T, Ceder G, Belcher AM. Biologically Activated Noble
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Cabana J, Monconduit L, Larcher D, Palacin MR. Beyond Intercalation-Based Li-Ion
Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through
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Amatucci GG, Pereira N. Fluoride based electrode materials for advanced energy storage
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Gocheva ID, Tanaka I, Doi T, Okada S, Yamaki J. A new iron oxyfluoride cathode active
material for Li-ion battery, Fe2OF4. Electrochem Commun 11, 1583-1585 (2009).
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Bervas M, Klein LC, Amatucci GG. Reversible conversion reactions with lithium in
bismuth oxyfluoride nanocomposites. JElectrochem Soc 153, A 159-A 170 (2006).
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Bervas M, Badway F, Klein LC, Amatucci GG. Bismuth fluoride nanocomposite as a
positive electrode material for rechargeable lithium batteries. Electrochem Solid-State
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Bruce PG, Freunberger SA, Hardwick LJ, Tarascon JM. Li-O-2 and Li-S batteries with
high energy storage. Nat Mater 11, 19-29 (2012).
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McCloskey BD, Speidel A, Scheffler R, Miller DC, Viswanathan V, Hummelshoj JS, et
al. Twin Problems of Interfacial Carbonate Formation in Nonaqueous Li-O-2 Batteries. J
Phys Chem Lett 3, 997-1001 (2012).
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McCloskey BD, Bethune DS, Shelby RM, Girishkumar G, Luntz AC. Solvents' Critical
Role in Nonaqueous Lithium-Oxygen Battery Electrochemistry. JPhys Chem Lett 2,
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18.
Peng ZQ, Freunberger SA, Chen YH, Bruce PG. A Reversible and Higher-Rate Li-O-2
Battery. Science 337, 563-566 (2012).
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Lu YC, Gasteiger HA, Shao-Horn Y. Catalytic Activity Trends of Oxygen Reduction
Reaction for Nonaqueous Li-Air Batteries. JAm Chem Soc 133, 19048-19051 (2011).
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Jung HG, Jeong YS, Park JB, Sun YK, Scrosati B, Lee YJ. Ruthenium-Based
Electrocatalysts Supported on Reduced Graphene Oxide for Lithium-Air Batteries. Acs
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Xu JJ, Xu D, Wang ZL, Wang HG, Zhang LL, Zhang XB. Synthesis of Perovskite-Based
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14
Chapter 2. Integrating graphene based conducting frameworks into
Lithium ion battery cathodes (Bismuth oxyfluorides,
BiOo. 5F 2) by genetic engineering of M 13 virus*
- The content in this chapter was reprinted with permission from Small. Copyright C 2012 WILEY-VCH
Verlag GmbH & Co. KGaA, Weinheim
15
2.1 Introduction
Single-layer graphene sheets have significantly broadened the horizon of nanotechnology
with their unique electronic, optical, quantum mechanical and mechanical properties associated
with the two-dimensional atomic crystal structure.' To best utilize this material for practical
applications, it is crucial to prevent the spontaneous aggregation between individual graphene
sheets during composite materials formations. Numerous efforts have been made to stabilize
functionalized graphene sheets on molecular2 '
3
or polymeric species.4'
Biomolecules such as
DNA 6 and proteins 7 have also been grafted onto graphene planes for applications of biosensors ,8
controlled drug-delivery9 as well as cancer imaging.1' In addition to biomedical applications,
graphene sheets can also be hybridized with biomolecules into energy storage devices to increase
the conductivity of active materials that are often insulators. In previous work, ultrasonication" or
chemical reduction,' 2 followed by heat treatment, 13 ' 14, " have been adopted to achieve composites
between graphene and various materials (LiFePO 4 1" and SnO 2 16). However, due to the nonspecific nature of interactions between the graphene templates and active materials, it is expected
that only random and inhomogeneous contacts were created, leaving the segregation on nano- or
even sub-micron levels. Ideally, the performance of these active materials, such as the accessible
capacity and the rate capability, can be maximized only if atomic level contacts can be realized
between the conductive phase (graphene) and the active phase.
In order to expand the range of graphene based hybrid materials, methods to prevent
aggregation around the limit of colloidal stability need to be developed. The stability of aqueous
colloidal dispersion of functionalized graphene is usually maintained at high pH and low ionic
strength due to the charges on the functionalized surface.' 7 Substrate specificity of ligands in
biomolecules can improve the colloidal stability of graphene and strengthen the interaction
between graphene and functional materials, thereby providing a genetically tunable hybrid
building block and a desired conducting frame. The Ml 3 bacteriophage has been demonstrated as
16
a genetically engineerable biological toolkit to develop nanostructured hybrid materials to
enhance the performance of energy storage and conversion devices.''
19
Here, we show that the
non-covalent binding between the engineered M13 virus and graphene increased the dispersion
stability of graphene sheets at pH as low as 3 and an increased ionic strength environment. In
addition, using this biological approach, we were able to take a DNA sequence that coded for
peptides that could bind graphene and modify this sequence to further broaden the stability
window of aqueous colloid of graphene sheets. With the improved stability of graphene in
aqueous media, inorganic nanoparticles nucleated on the M13 virus were able to intimately
interface with graphene sheets and fully utilized the excellent electronic conductivity of graphene,
although the incorporation of graphene might lower the packing density. As a result, we achieved
an efficient conducting matrix throughout the hybrid material with the genetically engineered
M13 virus, which simultaneously stabilizes graphene
sheets and mineralizes the active
nanoparticles. We also demonstrated that the electrochemical utilization of the originally
insulating active materials could be improved in the composite network consisting of active
nanoparticles and conductive graphene sheets.
17
2.2 Experimental
2.2.1 Synthesis of bio-templated bismuth oxyfluorides and their composites with graphene
FC#2 viruses (2x1013 ) were incubated with the graphene solution (64 ml, 2.3 [tg mlr).
Bi(N
3 )3 -5H 2 0
(0.8m1, 200 mM, dissolved in 10% HNO 3) was added to this mixture to make the
final solution (400 ml, 0.4 mM). LiF solution (171 ml, 50 mM) was added and stirred at room
temperature for 3 hours. Graphene solution (40 ml, 50 [tg mlr)
was further added into the
nanocomposites. The final products were filtered, washed and dried under vacuum at 50'C
overnight. With the same method, wild type viruses were used for bismuth oxyfluoride/graphene
nanocomposites and virus addition and incubation steps were excluded for composites without
virus.
2.2.2 Synthesis of SWNTs/bio-templated bismuth oxyfluoride nanocomposites
The SWNT/FC#2 complexes were constructed by dialyzing the mixture of FC#2 (2x 101)
and SWNTs (0.094 mg in 2 wt% sodium cholate aqueous solution) against D.I. water with
gradual increase of salt (KCI) concentration of media from 10 mM to 80 mM, while maintaining
pH 9 using NaOH for two days. Bismuth oxyfluoride was synthesized by adding Bi(NO ) -5H 0
3 3
2
(0.8 ml, 200 mM, dissolved in 10% HNO 3) to complex solution giving final volume to 400 ml.
After an hour, LiF (171 ml, 50 mM) was added and rested for 2 hours. The final products were
washed and dried under vacuum at 50*C overnight.
2.2.3 Electrochemical tests with coin cell type batteries
Active materials were mixed mechanically with Super P (TIMCAL, SUPER PO Li) for 20
minutes and polytetrafluoroethylene (PTFE) was added. (Active materials : virus : graphene :
Super P : PTFE (mass ratio) = 68.8 : 8.8 : 2.4 : 15 : 5). Mixed powders were rolled out and
punched in 4.08 mg cm 2 and dried under vacuum at 120'C overnight. Inside the Ar-filled glove
18
box, the electrodes were assembled into coin cells with Li metal foils as the counter electrodes
and I M LiPF6 in EMC was used as the electrolyte. Three layers of microporous polymer
separator (Celgard 2325) were used. Assembled coin cells were tested with a Solatron Analytical
1 470E potentiostat at room temperature.
2.2.4 FC#2 gene construction
The p8cs#3 clone was selected by a bio-panning method with a pVIlI library previously
reported by this group.' 9 Using QuikChange Lightning site-directed mutagenesis kit (Stratagene,
catalog#210518), K was first mutated to E, and N to D then to E, producing EFE virus. The
primer sequences used to change K to E are 5' CAG GGA GTT AAA GGC CGC TTC TGC
GGG ATC CGG CAG CGC 3' and 5' GCG CTG CCG GAT CCC GCA GAA GCG GCC TTT
AAC TCC CTG 3'; for N to D, primers of 5' GTC GCTGA GGCTT GCAGG GAGTC AAAGG
CCGCT TTTGC GGG 3' and 5' CCC GCAAA AGCGG CCTTT GACTC CCTGC AAGCC
TCAGC GAC 3' were used; for D to E, primers, 5' GC TGA GGC TTG CAG GGA CTC AAA
GGC CGC TTC TGC 3' and 5' GCA GAA GCG GCC TTT GAG TCC CTG CAA GCC TCA
GC 3' were used. Previously reported SWNT-binding peptide MC#2,18 was fused to pill of EFE
virus. The oligonucleotides used to introduce SWNT-binding functionality to the minor pill coat
protein are 5 [Phos]' GTA CCT TTC TAT TCT CAC TCT GAT ATG CCG CGT ACT ACT
ATG TCT CCG CCG CCG CGT GGT GGA GGT TC 3' and 5 [Phos]' GGC CGA ACC TCC
ACC ACG CGG CGG CGG AGA CAT AGT AGT ACG CGG CAT ATC AGA GTG AGA
ATA GAA AG -3' and they were annealed to form a DNA duplex. The cloning vector was
extracted from EFE virus using standard miniprep kit (QIAGEN) and was digested with Eag I
and Acc65 I enzymes, dephosphorylated, and purified with agarose-gel. Purified vector and DNA
duplex were ligated using T4 DNA ligase at 16*C overnight, and electrotransformed to XL-l blue
cells. Transformed cells were incubated for one hour, plated, and incubated at 37'C overnight.
19
2.2.5 Synthesis of water-soluble graphene2
Graphene oxide (GO) was synthesized by Hummer's method.2 ' 75 mg of GO was dispersed
in 75 ml of water by bath-sonication for one hour followed by centrifugation (3,000 rpm). The pH
was adjusted to 10 with 5 wt% sodium carbonate (Sigma-Aldrich) solution. Then 600 mg of
sodium borohydride (Sigma-Aldrich) in 15 ml of water was added to partially reduce GO at 80*C
for one hour followed by centrifugation (20,000 rpm). After washing with water, the partially
reduced GO was dispersed again in 75 ml of water by sonication. The diazonium salt for
sulfonation was made with 46 mg of sulfanilic acid (Alfa-Aesar) and 18 mg of sodium nitrite
(Alfa-Aesar) in 10 ml of water and 0.5 ml of I M HCl solution in an ice bath. The diazonium salt
solution was added to the partially reduced GO in an ice bath for 2 hours. To completely reduce
the sulfonated graphene, 2 g of hydrazine (Acros) in 5 ml water was added kept at 100 C for 24
hours. I ml of 5 wt% sodium carbonate solution was then added into the mixture to precipitate the
graphene. After centrifuging (25,000 rpm) and washing with water, the lightly sulfonated
graphene was dried under vacuum at room temperature for 24 hours.
2.2.6 Characterization of graphene.
The water-soluble graphene was characterized by transmission electron microscopy (TEM) in
Figure 2.1.a and atomic force microscopy (AFM) in Figure 2.1.b. For TEM, JEOL 2010F TEM
was used with accelerating voltage of 200 kV. For AFM, the graphene on mica (Ted Pella)
substrate was achieved by drying graphene dispersion and Veeco Nanoscope IV under tapping
mode was used.
2.2.7 Zeta potential measurement of virus and graphene.
The concentration of virus solution was
1012
m-I in water with 10 mM NaCl. The stock
solution of virus (- 1014 m-) was initially dissolved in 10 mM Tris, 15 mM NaCI before diluting
in 10 mM NaCl in ddH20. The amount of solution used to generate curve was 30 ml. The ionic
20
concentration of the solution was set to 10 mM NaCl for all samples to minimize the fluctuation
of ionic strength during pH adjustment. The pH was then adjusted using NaOH until the pH was
around 10. For graphene zeta potential measurement (Figure 2.1.c), the concentration was 40 mg
ml' in water and the pH of graphene dispersion was adjusted to around 11 by NaOH. The zeta
potential of both virus and graphene were then measured at an accumulation time of 10 with 5
measurements per sample at 20 V using DelsaNano (Beckman Coulter). Electrophoretic mobility
was calculated using the Smoluchowski approximation (used for particles larger than 0.2 ptm in I
mM or greater salt solution). The pH of solution was then adjusted with HCL.
2.2.8 Characterization of bismuth oxyfluoride and graphene nanocomposites by XRD, XPS
and TGA.
The crystal structure was confirmed by X-Ray Diffraction (PANanalytical Multipurpose
Diffractometer, Cu Ka radiation) and Rietveld refinement was conducted (Table 2.1) by
changing the atomic occupancy of oxygen and fluorine. Since oxygen can take a place in fluorine
site, we changed the occupancy of fluorine positions (F l: 0.5,0.5,0.5 and F2: 0.25,0.25,0.25) to fit
the calculation to the data. For the electrode discharged to 1.5 V, the coin cell was disassembled
inside Ar-filled glove box and the discharged electrode was covered by Kapton* tape to prevent
any air contamination. X-ray photoelectron spectroscopy (XPS, Kraots AXIS) was conducted
with pass energy 20 eV and step size 0.1 eV and the atomic ratio between bismuth and fluorine
were
measured.
To
quantify
the
virus
mass
of the
composites
(Figure 2.2.a,
b),
thermogravimetric analysis (TGA, Q50 TA instrument) was used with increasing temperature
with rate of I 0 0 C min" under nitrogen.
21
2.2.9
Characterization
of
bismuth
oxyfluoride
and
graphene/bismuth
oxyfluoride
nanocomposite by electron microscope.
The bismuth oxyfluoride was characterized by high-resolution TEM (HRTEM) using JEOL
201 OF TEM with an accelerating voltage of 200 kV. The graphene/bismuth oxyfluoride
nanocomposites were also characterized by using JEOL 200CX TEM operating at an accelerating
voltage of 120 kV.
22
2.3 Results and discussion
We utilized an M13 virus to synthesize a graphene/virus complex to function as a building
block for a conducting framework. The M 13 virus is a filamentous bacteriophage, with a length
of -880 nm and a diameter of -6.5 nm.22 The single-stranded DNA encapsulated inside the coat
proteins can be modified to express specific peptide sequences on the surface of the virus to
enhance the interaction with materials of interest.23 '
24
To fabricate a virus-mediated graphene
framework with inorganic nanoparticles, two factors must be addressed; the colloidal stability of
graphene and the interface between the active materials and the graphene. In designing an M13
virus, the major coat protein (pVIII) was chosen as a major interacting motif to maximize the
attraction between the graphene and the virus, so that every particle templated on the virus was
forced to contact the graphene (Figure 2.3.a). First, the graphene-binding virus, with an 8-mer
peptide insert, DVYESALP, fused to the amino-terminus of the pVIII major coat protein (this
virus is called p8cs#3), was identified through a bio-panning method using a pVIlI library
previously reported by this group.19 The aromatic residue, tyrosine (Y), of the selected sequence
is expected to interact with graphene, as well as single-walled carbon nanotubes (SWNTs),
through jT-n interaction. In addition to the aromatic residue, the hydrophobicity plot of the
sequence, calculated based on the Hopp-Woods scale with the averaging group size 5,
25
shows a
hydrophobic moiety between two hydrophilic regions (Figure 2.3.b inset) suggesting that the
virus can bind graphene by hydrophobic-hydrophobic interaction. Second, to facilitate the
nucleation of nanoparticles, we introduced two additional carboxyl groups on each pVIII protein
of p8cs#3 virus, in which the thirteenth amino acid, lysine (K), and the seventeenth amino acid,
asparagine (N), were changed to the glutamic acid (E), using site-directed mutagenesis (Figure
2.3.b top) (this site-mutated virus is called EFE). Since the thirteenth and seventeenth amino
acids of an M 13 virus are known to be exposed on the surface and accessible to ligands, 2 6 these
carboxyl groups of glutamic acid can chelate metal ions and catalyze the mineralization. The zeta
23
potential of EFE was measured and compared with that of the control virus, p8cs#3, to confirm
the effect of the site-directed mutation on the surface charge of the virus (Figure 2.3.b bottom).
It was observed that the isoelectric point of the virus shifted to a lower pH by the addition of two
glutamic acids on the pVIII protein. The increased negative charges associated with the carboxyl
groups have additional advantages in enhancing the colloidal stability of the graphene/virus
complex. Finally, the pIII minor coat protein was also engineered to increase the binding affinity
between the virus and the graphene (see the experimental section). We designate this virus clone
as FC#2 and use it for further research on stabilizing graphene, nucleating functional materials
and improving the performance of lithium ion batteries. The stability of the graphene/virus
complex was tested by adding bismuth nitrate (the precursor for the material of interest for
lithium ion batteries) at pH 3. The stability of graphene dispersion by the virus was maintained
after 24 hours of incubation with bismuth nitrate as shown in Figure 2.3.c. This is in contrast to
the control sample under the same salt concentration and pH without the virus, where the
graphene aggregated. We also observed the graphene/virus (FC#2) complex by atomic force
microscopy (AFM) (Figure 2.3.d). The thickness of the graphene in the solution was around 0.8
nm as indicated in Figure 2.3.d inset. An area with the relatively lower coverage of the virus on
the graphene compared to the approximate calculation was selected to clearly visualize the
interaction of the virus and the graphene. The geometrical quantification of graphene and virus
(FC#2) was achieved by following method. The total mass of graphene is 64 ml
147.2 mg. For 2
x
10
1
viruses, there is 147.2 mg / (2
virus, corresponding to 7.36
x
1018 g / 12 g molr
x
x
6.02
1013) = 7.36
x
x
x
2.3 mg ml- =
10-" g of graphene per
1021 moP' = 3.7
x 105
carbon atoms.
Considering a hexagonal packed structure of carbon atoms, each carbon atom contribute to an
area of 0.5
x
(0.142 nm) 2
x
sin(p/3)
x3
= 0.0262 nm 2 . Also considering the graphene thickness is
around 0.8 nm, which is close to the thickness of a two-layer graphene, each virus covers an area
of graphene of 0.0262 nm 2
x
x
3.7
x10
5
=9.7
3
x 10
nm 2 . The cross section area of a virus is 6.5 nm
2
880 nm = 5720 nm 2 . Thus, the coverage of virus on graphene is expected to be 5720 nm / 9700
24
nm 2 = 59%. This calculation is based on the assumption that every single virion of virus binds
graphene.
Leveraging the enhanced colloidal stability of the genetically programmed graphene/virus
complex, we assembled
bismuth oxyfluoride
on the graphene/virus
template.
Bismuth
oxyfluoride is a conversion reaction cathode material with an open circuit voltage of 2.8 V vs
Li/Li+, a high theoretical specific capacity of 210 mAh g- (for BiOo.5F 2, from LiF formation) and
an attractive volumetric energy density of 5056 Wh 1-,
which can be synthesized in aqueous
solution under low pH conditions. Among the candidates of cathode materials for next generation
lithium ion batteries, bismuth oxyfluoride was chosen as a model material, since we found the
synthetic condition for this material under a weak acidic environment, suitable for demonstrating
the improved colloidal stability of the graphene. Since the M13 virus helped maintain the
colloidal stability of the graphene during the nucleation of inorganic nanoparticles under low pH,
it is now possible to form hybrid nanostructures of the graphene/BiOo. 5 F2 . We first developed an
aqueous solution-based approach to synthesize bismuth oxyfluoride nanoparticles on the virus
under a weakly acidic condition at room temperature, using LiF as a milder precursor than
hydrofluoric acid" and ammonium fluoride.
Nanoparticles, thus synthesized along the virus,
have a diameter of around 40 nm (Figure 2.4.a,b). The virus-mediated synthesis increased the
reaction yield (the mass of final products of each synthesis was measured and the yield of
products was calculated as, yield (%) = (mass of BiOO. 5F 2 without virus mass)/(number of moles
of bismuth precursor
x
molecular weight of BiOO. 5F 2 )
x100,
thus, the yield was increased from
17% without virus to 63% with virus, both without graphene) and decreased the particle size of
the material compared with the previous report.27 To fabricate the nanocomposites of the watersoluble graphene and bismuth oxyfluoride, the graphene was first complexed and stabilized by
the FC#2 virus, and then bismuth oxyfluoride was grown on the virus/graphene complex. In order
to visualize the hybrid structure with graphene, we used a lowered concentration of the precursor
to show that more bismuth oxyfluoride was nucleated along the virus than on the surface of
25
graphene (Figure 2.4.c). The chemically modified graphene possesses functional groups, which
also act as nucleation sites, but the graphene-assisted nucleation is not as efficient as the virusassisted nucleation. Two control hybrid materials with the graphene were synthesized without
using the virus or with a wild type virus (M13KE, denoted in our work as a wild type virus). In
addition to the reduced colloidal stability as shown in Figure 2.3.c, the yield of bismuth
oxyfluoride of the reaction without the virus (42%) was much lower than the yield of the reaction
aided by the FC#2 (68%). For the nanocomposites made with the wild type virus, the graphene
was initially stabilized by non-specific interaction, but the graphene aggregation and the
separation between the graphene and active materials eventually prevailed as the nucleation
proceeded (Figure 2.4.d). Furthermore, the positive surface charge from the wild type virus
under weakly acidic conditions (pH 3) did not facilitate the nucleation of bismuth oxyfluoride and
the yield was similar to the reaction without the virus.
The crystal structure of the virus-templated bismuth oxyfluoride was confirmed as cubic (Fm3m) by high-resolution transmission electron microscopy (HRTEM) (Figure 2.4.b) and X-ray
diffraction (XRD) (Figure 2.5.a), with a lattice parameter of 5.8160(1)
photoelectron
spectroscopy
(XPS)
elemental
A. From X-ray
analysis, the bismuth-to-fluorine
ratio was
determined to be 1:2.02 (Table 2.2), giving a chemical formula of BiOO.4 9F 2 .02 . The galvanostatic
measurement (at a current density of 6 mA g-) further confirmed the composition of fluorine and
oxygen based on the fact that oxygen and fluorine in bismuth oxyfluoride react with the lithium at
different potentials of 1.8 V and 2.6 V (vs Li/Li+). 2 9 In Figure 2.5.b, the ratio of discharge
capacity in the plateau regions around 2.7 V and 1.9 V was calculated to be 1.95:1.05. Because
the ethyl methyl carbonate (EMC) electrolyte is believed to be inert to Bi nanocrystals,30 the solid
electrolyte interphase formation does not occur under 2 V, therefore does not contribute to the
capacity. Since each fluorine atom reacts with one lithium atom and each oxygen atom reacts
with two lithium atoms, the galvanostatic measurement gave a chemical formula of BiOo.5 25 F,.95 ,
in fairly good agreement with the XPS analysis result. Therefore we concluded with a reasonable
26
approximation that the chemical formula of the synthesized bismuth oxyfluoride was close to
BiOO.5F2.
The advantage of incorporating well-dispersed graphene into lithium ion battery cathodes was
demonstrated by making electrodes with the graphene/bismuth oxyfluoride nanocomposites
assembled with a biologically engineered virus. With a small amount (2.4 wt%) of graphene
incorporated into the bismuth oxyfluoride, the specific capacity of the virus-templated bismuth
oxyfluoride was increased from 124 mAh g- to 174 mAh g-1 at a current density of 30 mA g(C/7) (Figure 2.6.a and Figure 2.6.b). The second cycle capacity (206 mAh g-,
at C/7) of the
virus templated bismuth oxyfluoride with 2.4 wt% of graphene in Figure 2.7.a corresponds to
98% of theoretical capacity, which is the highest reported for this material to date. Moreover, the
rate performance has also been improved, showing a specific capacity of 131 mAh g(corresponding to 711 W kg', with an energy density of 316 Wh kg-, 2718 Wh 1-) at a current
density of 300 mA g-
(1.4 C) compared to 67 mAh g-
for the virus-templated bismuth
oxyfluoride without graphene. These results represent a significant improvement in the
electrochemical performance of bismuth oxyfluoride compared to the previous report, as
indicated by the increased active mass loading in the electrode (from 50 wt% to 70 wt%) and the
improved specific capacity at a 20 times higher current density. In addition, the presence of the
graphene also significantly decreased the voltage hysteresis between the charge and the discharge
profiles (Figure 2.7.a), which became more pronounced at a higher discharging rate (Figure
2.6.a). This reduction in the electrode overpotential stems from the excellent electric wiring
achieved at the atomic level by graphene sheets, which connects active nanoparticles with the cell
current collector through a homogeneously distributed percolating conductive network.
To study the beneficial effect of specific interaction between the genetically engineered virus
and the graphene in the formation of a conducting framework, control experiments have been
done with graphene/bismuth oxyfluoride nanocomposites synthesized in the absence of the virus
or in the presence of the wild type virus. The bismuth oxyfluoride synthesized in the control
27
experiments had the same chemical and crystallographic properties as that formed with FC#2
(Figure 2.8 shows XRD patterns for each composite). As shown in Figure 2.6.a, c and d, the
specific capacity (174 mAh g-' at C/7) of nanocomposites using FC#2 was higher than that of
nanocomposites using the wild type virus (145 mAh g- at C/7) and without the virus (102 mAh gI at C/7). Moreover, the superior electrochemical performance of the nanocomposites
using FC#2
was more apparent at a high rate of 600 mA g- (110 mAh g- for FC#2, 67 mAh g- for the wild
type virus and 64 mAh g- without the virus), indicating accelerated electrode kinetics for the cell
reactions in those nanocomposites benefiting from the specific interaction between the graphene
and FC#2 virus. The poor electrochemical activities of the nanocomposites in the presence of the
wild type virus and in the absence of the virus are caused by the agglomeration of graphene
during the active material synthesis. Based on these observations, we conclude that the increased
interaction of graphene with the active material particles aided by the genetically engineered virus
results in an efficient conducting network. This was made possible by maintaining the colloidal
stability of complex during the synthesis. Moreover, we achieved both higher capacity utilization
of the active materials and a much reduced kinetic barrier between charge and discharge
reactions, as compared with the previous report.2 9
The superior formation of a percolating network with two-dimensional conducting sheets
enabled by the genetically engineered virus has also been demonstrated by comparing the effects
of graphene and SWNTs on the electrochemical performance of bismuth oxyfluoride. The
SWNTs were evenly dispersed inside the electrode by the virus complexation method' 9 and
bismuth oxyfluoride was synthesized on this template. When the same amount of graphene and
SWNTs (0.5 wt%) were incorporated into the nanocomposites, the specific capacities of 128
mAh g-
for the SWNTs/bismuth oxyfluoride nanocomposites
and 181 mAh g-
for the
graphene/bismuth oxyfluoride nanocomposites were obtained respectively, at a current density of
30 mA g- (Figure 2.6.e). The graphene improves the kinetics of the conversion reaction more
effectively than SWNTs. Although the SWNTs are known to be advantageous for constructing a
28
percolating network because of their high aspect ratio,31 when a small quantity of carbon is used,
the interconnectivity between the one-dimensional SWNTs could be limited compared to the twodimensional graphene. In the bismuth oxyfluoride system, the graphene appears to be more
effective in facilitating the electrochemical reaction.
29
2.4 Conclusion
In summary, using a genetically engineered M 13 virus, we broadened the stability
window of graphene in aqueous media, which enabled an environment-friendly approach to
establish a graphene/virus nanotemplate. By designing the M13 virus for simultaneously
stabilizing the graphene and nucleating bismuth oxyfluoride, we fabricated the graphene/bismuth
oxyfluoride
nanocomposites
in
which
both
phases
were
intimately
interwoven.
The
graphene/virus complex formed a homogeneously distributed conducting framework and the
kinetics of electron transfer inside the battery electrodes was improved, demonstrating the
increased specific capacity of bismuth oxyfluoride at a high current density (131 mAh g-' at 300
mA g-') and the reduced overpotentials for both charging and discharging cell reactions. This
study demonstrates the importance of well-dispersed graphene in aqueous media for synthesizing
composite materials and this general method could be extended to other materials for applications
including biosensors, supercapacitors, catalysts and energy conversion applications.
30
2.5 Figure and Tables
Oil
C.1
-25
-
>-30* 40.
j45-
50.
-
----------------
-00.
65.
i")
1,
pH
Figure 2.1. Characterizations of graphene. (a) TEM image of the chemically reduced graphene
with a selected area electron diffraction (SAED) pattern. AFM image (b) and Zeta potential data
(c) of water-soluble graphene, the size of the AFM image is 2 mm by 2 mm.
31
100
--
100
-
8W
vWpqylIC iss
i f loss
from vrus
a--
94
-2
-
90
92
Bismuth oxyfluoride
90
Bismuth oxyfluoride-graphene
on FC#2, under nitrogen
--
on FC#2, under nitrogen
100
200
300
400
500
100
Temperature CC)
200
300
400
500
600
Temperature ( 0 C)
Figure 2.2. Determination of virus mass by Thermogravimetric analysis (TGA). (a)
TGA
data of bismuth oxyfluoride grown on FC#2 showing that virus accounts for 11 wt% of the final
hybrid nanowire. (b) TGA data for the analysis of virus mass inside the graphene-bismuth
oxyfluoride nanocomposites formed by FC#2 (before adding 2.4 wt%
of additional graphene),
which shows the similar quantity as bismuth oxyfluoride grown on virus.
32
b pcst3
IAl DI VI YI E S A LPDPA
K A A F
Site mutation
EFE
A D
YESAL
N
.
4
C
D P A E A A F E .
20
-VVYGSALP
10
02
01
-10
-20
-30
Amino Acl
-40
0
N
-50
-60
-- EFE
p8cs#p
-70
3
4
5
6
7
8
9
10
11
10 nm
-pH
0 nm
33
Figure 2.3. The graphene/M13 virus complex with the enhanced colloidal stability for the
hybrid graphene/nanoparticle nanocomposites. (a) Scheme of the inorganic nanoparticle
nucleation on the graphene/virus template. The virus enables a close contact between inorganic
nanoparticles and the graphene. (b) Top: The peptide sequence of pVIIl protein of p8cs#3 and
EFE. Bottom: The zeta potential of EFE and p8cs#3. Inset: The hydrophobicity plot of the pVIIl
major coat proteins of p8cs#3 virus as a function of the amino acid location. (c) The left vial is
the graphene solution after 24 hours of incubation with bismuth nitrate, showing the aggregation
of graphene on top. The right vial is the graphene/FC#2 complex solution after 24 hours of
incubation with bismuth nitrate without any aggregation. (d) AFM image of the graphene/virus
(FC#2) complex. Inset: The height profile of line A showing the thickness of graphene as ~0.8
nm.
34
a
500 nm
C
300 nm
d
-
--
iif
+-Graphone
5
nm
Figure 2.4. Characterizations of the bismuth oxyfluoride nucleated on the graphene/virus
complex. (a) TEM image of bismuth oxyfluoride nucleated on FC#2. (b) HRTEM image of a
bismuth oxyfluoride nanoparticle with the Fm-3m crystal system, (200) d=2.9
(220)
d=2.1
A (left arrow) and
A (right arrow). (c) TEM image of the bismuth oxyfluoride/graphene
nanocomposites with FC#2 virus for battery electrodes. The bismuth oxyfluoride/FC#2 virus
complexes are shown exclusively on the graphene. Inset: Catalyzed nucleation of bismuth
oxyfluoride on FC#2 virus was observed by lowering the precursor concentration in the
composite synthesis with a scale bar of 400 nm. Background is the graphene in the inset. (d) TEM
image of the bismuth oxyfluoride/graphene nanocomposites formed with the wild type virus
showing the separation of graphene and bismuth oxyfluoride.
35
4.0
a
Bismuth oxyftuoride
on virus (FC#2)
-
-
Bismuth oxyfluoridelgraphene (2.4 wt%j
with FC#2
3.5
03.0
(.4
C
LiF formation
L~ILf
02.S
00
20
25
30
35
40
45
50
55
0 2.0
Li 2 O formtion
C;
60 65
70
2 Theta (degree)
15
0
30
60
90 120 150 180 210 240 270 300
Specific capacity (mAhlg)
Figure 2.5. Characterizations of bismuth oxyfluoride with an electrochemical method and
XRD. (a) XRD pattern of bismuth oxyfluoride nanoparticles. (b) Galvanostatic data of bismuth
oxyfluoride/graphene nanocomposites (2.4 wt% of graphene addition) under constant current
density (6 mA g-)
until 1.5 V.
36
a3.2 -aj
---
2.8
60 mA/g
150 mA/g'
300 mA/g,
---
00 mAILg
---
Bismuth oxyfluoride/graphone
b,3.
b nooositr
20 40
(2.4
wt%)
s with FC#2
60
80 100 120 140160 180
2.8-
2.
Bismuth oxyfluorid. on virus (FC#2)
20 40 60
C 3 .2
80 100 120 140 160 180
2.8-
2.4
Bismuth oxyfluoridIelgraphone (2.4 wt%)
d 3.2
20 40
60
80 100120140160180
2.8
Bismuth oxyfluoridelgraphone (2.4 wt%)
compositswt wild typ virus
3.2
20
40
60
80 100 120 140 160 180
2.0
2.8
Bismuth oxyfluoride/graphenes 0.5
---
1.6
Bi m t
020
40
xfy
60 80
d*8
t
N *05w%
100 120 140 160 180 200
Specific capacity (mAhlg)
Figure 2.6. The power performance of the graphene/bismuth oxyfluoride nanocomposites
with the genetically engineered M13 virus. (a-d) The first discharge of bismuth oxyfluoride at
different current densities; (a) the bismuth oxyfluoride/graphene nanocomposites with FC#2, (b)
the
bismuth
oxyfluoride
templated
on
FC#2
37
without
graphene,
(c)
the
bismuth
oxyfluoride/graphene composites in the absence of virus, (d) the bismuth oxyfluoride/graphene
composites in the presence of the wild type virus. (e) Comparison between the graphene and
SWNTs: The first discharge of the bismuth oxyfluoride/graphene composites and the bismuth
oxyfluoride/SWNTs composites formed with FC#2 viruses having the same mass percentage of
carbon (0.5 wt% of electrodes) at a 30 mA g- of current density.
38
a
. . .
.
oxyfluoridelgraphene
4.8
. .
Bismuth
4.4-
Bismuth oxyfluoride on FC#2
2.4
b
wt%
. .,IIeg.
*
O3.2
t
-
.
. .
50
55 60
Bismuth oxyfluoride-graphene
nanocomposite after discharge
.
Bi metal
2deys
nn
2 ycle
-
2
cyce
2.48
2.0
0
20 40 60 80 100 120 140 160 180 200 220
2025
Specific capacity (mAh/g)
Figure
2.7.
Electrochemical
30
35
40
45
65
70
2 Theta (degree)
performance
and
characterization
of
bismuth
oxyfluoride/graphene nanocomposites and bismuth oxyfluoride on FC#2. (a) First (straight)
and second (dashed) cycles of bismuth oxyfluoride/graphene (2.4 wt%) nanocomposites with FC#
2 and bismuth oxyfluoride on FC#2 at a current density of 30 mA g-1. (b) XRD patterns of the
bismuth oxyfluoride-graphene nanocomposites (2.4 wt% addition) electrode after discharging to
1.5 V with constant current density of 6 mA g-.
Bi metal is detected, however, Bi 20
observed and this could be due to small particle sizes.29
39
3
was not
a
D--
-
Bismuth oxyfluoridelgraphone
(2.4 wt%) with FC#2 (a=5.8160 A
-
C
Bismuth oxyftuoride/SWNTs
(0.5 wt%) with FC#2 (a-5.8213 A)
Bismuth oxyftuorld./grsphone
(2.4 wt%) without virus (a=5.8158 A
--
d
-
Bismuth oxyfluoridelgraphen.
(2.4 wt%) with wild type virus
(az5.8145 A)
20 25 30 35 40 45 50 55 60
65
70
2 Theta (degree)
Figure
2.8.
XRD
patterns
of
control
samples.
(a)
bismuth
oxyfluoride/graphene
nanocomposites formed with FC#2, (b) bismuth oxyfluoride/SWNTs nanocomposites formed
with FC#2, (c) bismuth oxyfluoride-graphene composites formed without the virus, (d) bismuth
oxyfluoride-graphene nanocomposites formed with the wild type virus.
40
4
AA4
40
312
25
14
2.0
80 5f Gaphtna w4th F C*2
B
40
2.4
0
0B
Graphene w'thOu virus
C 4.0
36
28
0
20
40 60890 1001201404601802W0220240
Specific capacity (mAh/g)
Figure 2.9. The first five cycles galvanostatic data of bismuth oxyfluoride/graphene (2.4
wt%)
nanocomposites
oxyfluoride/graphene
(BOF-GP)
(2.4
wt%)
with
FC# 2
nanocomposites
and
control
(BOF-GP)
samples.
with
FC#,
(A)
bismuth
(B)
bismuth
oxyfluoride/graphene (2.4 wt%) nanocomposites without virus, (C) bismuth oxyfluoride/graphene
(2.4 wt%) nanocomposites with wild type virus under constant current (30 mA g-).
41
Table 2.1. XRD peaks table for synthesized bismuth oxyfluoride from 20-70 degree (2
Theta) with Rietveld refinement results for compound.
(h k I )
2T(cal)
2T(cor)
2T(obs)
Delta
d(cal)
d(cor)
d(obs)
Del-d
1%
( 1 1)
26.547
26.547
26.609
0
3.3549
3.355
3.3472
0
100
(2 0 0)
30.748
30.747
30.809
0.001
2.9054
2.9055
2.8998
0.0001
42.2
(220)
44.041
44.042
44.101
-0.001
2.0545 2.0544 2.0518
0
62.7
(3 11)
52.164
52.163
52.221
0
1.7521
1.7521
1.7503
0
55.6
(2 2 2)
54.671
54.669
54.726
0.002
1.6775
1.6775
1.6759
0.0001
16
(400)
64.044
64.038
64.093
0.006
1.4527
1.4528
1.4517
0.0001
7
(cal=Calculated, obs=Observed, cor=Corrected)
Table 2.2. Atomic concentration (%) of bismuth oxyfluoride by XPS analysis.
Elements
Atomic concentration (%)
Bi
23.09
F
46.79
42
2.6 References
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Li F, Zhou GM, Wang DW, Zhang LL, Li N, Wu ZS, et al. Graphene-Wrapped
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SnO2/graphene nanocomposite and their application as anode material for lithium ion
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Li D, Muller MB, Gilje S, Kaner RB, Wallace GG. Processable aqueous dispersions of
graphene nanosheets. Nat Nano 3, 101-105 (2008).
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Engineered High-Power Lithium-Ion Batteries Using Multiple Virus Genes. Science 324,
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Dang X, Yi H, Ham MH, Qi J, Yun DS, Ladewski R, et al. Virus-templated selfassembled single-walled carbon nanotubes for highly efficient electron collection in
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III CFB, Burton DR, Scott JK, Silverman GJ. Phage display: a laboratorymanual. Cold
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Mao CB, Solis DJ, Reiss BD, Kottmann ST, Sweeney RY, Hayhurst A, et al. Virus-based
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Lee YJ, Lee Y, Oh D, Chen T, Ceder G, Belcher AM. Biologically Activated Noble
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Kneissel S, Queitsch I, Petersen G, Behrsing 0, Micheel B, Dubel S. Epitope structures
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45
Chapter 3. Li-0 2 battery hybrid nanocatalyst formed with M 13
virus templated Manganese oxides nanowires and noble
metal nanoparticles*
- The content in this chapter was reprinted with permission from Nature Communications. Copyright ©
2013, Rights Managed by Nature Publishing Group
46
3.1 Introduction
Rechargeable Li-0
2
batteries operate through the reversible reaction between lithium ions
and oxygen molecules." 2 ' 3 When Li-0
2
batteries discharge in non-aqueous electrolytes, Li' reacts
with reduced oxygen (oxygen reduction reaction; ORR) yielding the reaction product, mainly
Li 2 0
2
that is deposited on the catalyst electrode at a thermodynamic voltage of 2.96 V (vs.
Li/Li+).4'5'6 Upon charging, the electrical energy is stored by decomposing Li 20 2 back into Li+
and 02(oxygen evolution reaction, OER). To promote these ORR and OER for Li-0
2
batteries,
several materials have been investigated as catalyst electrodes, such as noble metals (e.g. Au, Pt,
Ru, Pd),'''
9
transition metal oxides (e.g. a-MnO 2,'" Co 30 4 ," MnCo 2 0 4 ,'2 RuO 2,") and carbon-
based materials (e.g. graphene 415,
'
carbon fiber,' 6 doped carbon nanotube' 7 ). However, these
materials suffer either from high material costs, low conductivities or side reactions with
electrolytes, which limits their use as high performance Li-0
difficulties restrain the capability of Li-0
2
2
battery electrodes. Although these
batteries, the rational design and selection of electrode
materials may fully deliver these battery chemistries to a high gravimetric energy storage system.
To enhance structural functionality, organisms in nature form skeletal tissues from soft
to hard through the interactions between nucleating protein matrices and inorganic ions.18,
19,20
Inspired by these biominerals researchers have fabricated novel nanoarchitectures using peptides
or proteins as scaffolds applied in various functional structures.2 For example, numerous types of
platforms such as synthetic peptide nanofibers,22 nanorings,23 and ferritin cages 24 provide simple
and uniform ways to synthesize interesting materials at the nanoscale. In electrochemical energy
storage devices, nanostructured materials enhance Li ion batteries by shortening the diffusion
length of Li ions,
29
For Li-0
2
25,26,27
and benefit capacitors by providing electrodes with large surface areas. 28,
batteries, since the oxygen is in principle derived from the air, both the oxygen flow
into electrodes and the high efficiency to promote discharge/charge reactions are additional
important factors.
30
Constructing a new catalyst that combines porous nanostructures and high
catalytic activity would allow us to harness the advantages of Li-0
47
2
batteries for practical
applications, such as long-range electric vehicles. Here, we built the catalyst structures to achieve
high Li-0
2
battery performances by forming a nanocomposite of biotemplated manganese oxide
nanowires (bio MO nanowires) with incorporation of a small weigh percent (3 wt %) of Pd
nanoparticles (Fig. 3.1). We believe this is the first bio-directed synthetic method demonstrated
for Li-0
2
battery applications.
48
3.2 Experimental
3.2.1 Synthesis of bio MO nanowires and their nanocomposites with Au or Pd nanoparticles
Manganese sulfate monohydrate (MnSO 4-H 20, Sigma-Aldrich, 2.4 ml of 50 mM) and
sodium sulfate (Na 2 SO 4 , Sigma-Aldrich, 2.4 ml of 50 mM) solutions were added together into 50
ml of D.I. water. FC#2 viruses (1.63x]01)
were added into this solution and stirred at room
temperature overnight. After the overnight incubation, potassium permanganate (KMnO 4, Alfa
Aesar, 16 ml of 10 mM) solution was added and stirred at room temperature overnight. The final
products were washed with D.I. water by centrifugation and collected after lyophilization. To
incorporate the noble metal nanoparticles (Pd, Au), the bio MO solution was dialyzed against D.I.
water overnight and diluted with D.I. water to make a final solution volume of 200 ml. PAA
(MW: 2,000, 0.6g in 20 ml of D.I. water) was added and stirred overnight. The PAA wrapped bio
MO nanowires were collected by centrifugation and dispersed again with 240 ml of D.I. water.
Au/Pd precursor solutions were added into the previous solution (For Au: gold (III) chloride
trihydrate, HAuCl4e3H 20, 2.17 ml of 25.4 mM for 1.7 wt % of Au in the final Au/bio MO
nanowire composite electrodes. For Pd: sodium tetrachloropalladate (II), Na 2PdCI 4, SigmaAldrich, 0.612 ml of 34 mM for 3 wt % (0.408 ml of 34 mM for 1.1 wt %) of Pd in the final
Pd/bio MO nanowire composite electrodes) and stirred overnight at room temperature. To reduce
the metal ion, 3 ml of ethylene glycol was added to each Au/bio MO nanowire and Pd/bio MO
nanowire solution for 24 hours inside a brown bottle due to light sensitivity. The solution was
washed three times by centrifugation with D.I. water and lyophilized.
3.2.2 Characterizations of MO nanoparticles, bio MO nanowires and Au,Pd/bio MO
nanowires
For SEM images, FEG-SEM 6700F (JEOL) was used under 5 kV with 5.9 mm of
working distance (or 0.5 kV with 3 mm of WD) after coating the sample with Pd. High-resolution
transmission electron microscopy (HRTEM) images were obtained with 2100, 2010 FEG (JEOL)
49
under an accelerating voltage of 200 kV. The sample was loaded on formvar/carbon or quantifoil
grids
(Electron
microscopy
sciences).
X-Ray
Diffraction
(PANanalytical
Multipurpose
Diffractometer, Cu Ka radiation) patterns were collected with 0.18 */min scan speeds under the
following settings: 20 of anti-scatter slit, 6 mm of irradiated length of automatic mode and 0.04
rad of soller slit. The discharged/charged samples were collected after disassembling batteries
inside an Ar-filled glove box and were covered by Kaptono tape to prevent any air contamination.
Inductively coupled plasma atomic emission spectroscopy (ICP-AES,
Horiba Jobin Yvon
ACTIVA-S) was used to determine the atomic ratio between manganese, gold, palladium ions of
Au/bio MO nanowires and Pd/bio MO nanowires. The sample was dissolved in nitric acid at 50
C overnight and diluted with D.I. water (ACS reagent grades) to make the final nitric acid
concentration of 2 % v/v for ICP measurements. X-ray photoelectron spectroscopy (XPS,
Physical Electronics Versaprobe 11) was measured with the monochromatic Al X-ray source (K0,
1486.6 eV) under the pass energy of 23.5 eV and the step size of 0.1 eV. The acquired XPS
spectra were calibrated with adventitious carbon peak (Is) as a reference positioned at 284.8 eV.
To quantify the PAA mass of the metal nanoparticles/bio
MO nanowires composites,
thermogravimetric analysis (TGA, Q50 TA instrument) was used with 10 *C min-' increasing
temperature rate under nitrogen.
3.2.3 Chemical titration for Mn oxidation state determination
The average oxidation state of MO was determined by two separate chemical titration
steps reported in the literature. 3 1 The color change indicator (sodium diphenylamine-4-sulfonate,
C, 2 HIONNaO 3S, Alfa Aesar) was further added during the titration. MO nanoparticles were used
for titrations because the manganese oxidation state is expected to be similar to bio MO
nanowires from XPS analysis and the protein residue of bio MO nanowires would cause
significant errors during the titration.
50
3.2.4 Electrochemical tests
The lyophilized catalyst materials were further dried in a vacuum oven at 90 'C
overnight before electrode preparations. The Li-0
2
electrodes were composed of Ketjan black
(EC600JD, AkzoNobel), catalyst materials, LiTHionTm dispersion (Ion Power, USA) with the
mass ratio of 44 : 36 : 20 for high carbon containing (44 wt %) electrodes and the mass ratio of 8 :
72 : 20 for low carbon containing (8 wt %) electrodes. These three components were dissolved
into 2-propanol and mixed overnight using a bath sonicator to get homogeneous slurry mixtures.
The mixture was spread on the separator (Celgard, PP2075) by tape casting methods and dried in
a vacuum oven at 80'C for 2 hours. The dried slurry was punched into circle electrodes with
diameters of 1.27 cm and the mass of each electrode was measured (0.1-0.3 mg/cm 2 ) following
further drying in vacuum oven at 80'C overnight before the electrochemical test. Inside the Arfilled glove box, the catalyst electrode was soaked with the electrolyte in advance (0.1 M LiCIO
in DME, Novolyte) and assembled into the Li-0
2
4
battery cell designed by our lab. Metallic Li
foils (negative electrode), two layers of separators, catalyst electrodes and a positive electrode
current collector (316 stainless steel mesh) were sequentially put on the cell and additional
electrolyte (100 ptl) was added. After the assembly, the Li-0 2 battery cell was purged with oxygen
(Airgas, UPC grade) and closed at 1.08 atm. The purged cell was allowed to rest at least 2 hours
before the electrochemical test. The first cycle of Li-0
2
battery cell was tested by galvanostatic
measurements at 0.4 A/ge with a Solartron Analytical 1470E potentiostat. For the cycling tests,
the pressure of the Li-0 2 battery cell was adjusted again to 1.08 atm after 16 cycles and I A/ge of
current was applied.
51
3.2.5 The true electrode surface area specific capacity
Here we make estimation in calculating the thickness of the discharge product, Li 20 2. It
is assumed that Li 2 0
2
is formed as films throughout the overall catalyst electrode with the
volumetric capacity, 2698.6 mAh cm- . First, the true electrode surface area was calculated. The
BET surface area of bio MO nanowires is 271.7 m 2
Ketjan black (EC600JD, AkzoNobel) is 1,400 m2
-1 and the reported BET surface area of
-1. Thus, the true surface area can be obtained
by considering the weight percentage (catalyst: Ketjan black = 36 : 44) of each component in
electrode, resulting in 271.7 m 2 g- * 0.36 +1,400 m 2
-' * 0.44
=
713.8 mtrue 2
-c+catalyst.
As
13,347 mAh g'c corresponds to 7,340.8 mAh g- c+catalyst, the true electrode surface area specific
capacity is -1.0
tAh cm2true.
3.2.6 The Gas Chromatography (GC) of Pd/bio MO nanowires electrodes after the first
galvanostatic discharge/charge
Two separate Pd (3 wt %)/bio MO nanowires cells were prepared to collect the gaseous
sample after discharge/charge steps. After the first galvanostatic discharge under I atm of
02,
the
cells were disassembled in Ar glove box and purged with Ar to remove 02. These cells were then
taken out from the Ar glove box and one of them was charged to 4.15 V at 0.4 A g-1, resulting in
the 02 evolution. 250 Rl of gas sample was collected from each discharged and charged cells with
an airtight syringe. These samples were analyzed with 7980A GC system (Agilent Technologies)
with two sequential separating columns (80/100 Hayesep N (13067-U) and 45/60 molecular sieve
(13069-U,
Sigma-Aldrich)) and thermal conductivity detector (TCD). The retention time was
calibrated with the standard reference sample (H 2 = 0.8 min, 02= 1.1 min, N 2
4.5 min). We observed higher composition of
02
=
1.2 min, CO 2
=
in addition to the air introduced during the
sample injection in charged cells than discharged cells indicating the 02 evolution reaction from
52
Li 2O 2 oxidations. A small amount of H 2 could be due to the reaction of H 20 with the Li metal
anode.
53
3.3 Results and discussion
3.3.1 M13 virus mediated synthesis of manganese oxide nanowires
Bio MO nanowires with spherulitic surface morphology were synthesized through a
facile and moderate chemical reaction by utilizing the biomolecule, M13 virus. M13 viruses have
been used as versatile templates for high aspect ratio nanowire synthesis (e.g. semiconductors,3 2
metal oxides3 3' 34'35) under environmentally benign conditions. Among the five different types of
capsid proteins on this virus template, p8 is a major coat protein with 2,700 copies surrounding
the single-stranded DNA. In addition to the material specificity of these surface proteins (p8 or
five copies of minor proteins existing at one end of virus particle, p3), electrostatic interactions
between the opposite charge of precursor ions and functional groups of p8 coat protein broaden
the template functionality. In this work, the virus clone with the p8 peptide sequences
ADVYESALPDPAEAAFE
(named FC#2) 36 was used because it has two additional negative
functional groups (-COOH from glutamic acid on
13 th
and
1 7 th)
than Ml3KE (New England
Biolabs) under basic conditions. Using this clone, bio MO nanowires were synthesized by first
binding Mn2
ions to the FC#2 virus p8 proteins followed by reacting with KMnO 4 at room
temperature. From this simple aqueous biotemplating reaction, homogeneous bio MO nanowires
with high aspect ratio (-80 nm in diameter and -
[tm in length) were obtained. These nanowires
showed spherulitic surface morphology (TEM image in Fig. 3.2.a, b, c). While the flower-like
the nucleation of MO along the virus particle
spheres of MO were previously synthesized,'
developed this spherulitic surface of materials into higher dimensional nanowires. Thus, the
hierarchical nanostructures of these bio MO nanowires are expected to be advantageous in Li-0
2
battery performances. While previous studies utilized smooth surface MO nanowires for Li-0
2
battery electrodes 0 ' 39, the rough surface of these bio MO nanowires can provide large catalytic
area as well as enough storage space for discharge products. To the best of our knowledge, this is
the first report of M13 virus directed synthesis of manganese oxide nanowires, which is
54
applicable not only to Li-0
2
battery electrodes but also to various applications such as
electrochemical capacitors 0 , Li ion battery electrodes 4' and water purifications. 4 2
With the aqueous, room temperature approach using M 13 virus templates, multi-valent
(Mn 3+/Mn4 ), birnessite-like MO nanowires were developed. The crystallographic and chemical
properties of bio MO nanowires were investigated with X-ray diffraction (XRD), high-resolution
transmission
electron microscopy (HRTEM),
the chemical
titration method, and X-ray
photoelectron spectroscopy (XPS). First, the XRD pattern of virus-templated MO nanowires
showed three broad peaks centered at 37', 53.5* and 65.5* (20 of Fig. 3.3.a), partially matching
to 8-MnO 2 (birnessite, space group C2/m, powder diffraction file (PDF) no. 01-073-2509) XRD
pattern. Also, the surface morphology of bio MO nanowires was similar to that of typical
birnessites43, as can be seen in the TEM image (Fig. 3.2.b). The crystal sizes of bio MO
nanowires were 2-5 nm and the co-existing amorphous phase was observed by HRTEM (Fig.
3.3.b). The average oxidation state of bio MO nanowires was determined to be 3.51 by chemical
titration methods, 3' suggesting a multi-valence state (Mn 3+/Mn4
=
0.96) of nanowires. This
mixed-valence property of MO was also observed from XPS spectra in Fig. 3.4. We confirmed
that the average oxidation state of bio MO nanowires lies between Mn 3+ and Mn4 by observing
two features, the peak position of Mn
2
P3/2
and the multiplet splitting of Mn 3s. First, the Mn
2
P3/2
4±
peak position of bio MO nanowires (642.1 eV in Fig. 3.4.a) was close to that of MnO 2 (Mn ,
642.2
-
642.4 eV) as reported in the literature.44' 45 However, the width of Mn 3s multiplet
splitting (5.2 eV in Fig. 3.4.b) of bio MO nanowires showed a larger separation than that of
MnO 2 (4.5 ~ 4.7 eV) but close to that of Mn 2 O 3 (5.2 ~ 5.4 eV)."'
45
Since it is known that the
separation between Mn 3s splitting peaks becomes larger as the oxidation state of Mn is lower, 4 6
the larger separations of Mn 3s splitting compared to Mn4 imply the presence of a lower valence
state in bio MO nanowires.
55
3.3.2 Nanocompositing ORR catalyst on bio MO nanowires
To enhance the ORR activity and surface conductivity of porous bio MO nanowires for
Li-0
2
battery electrodes, 1-3 wt % of ORR catalytic metal nanoparticles were homogeneously
incorporated onto the surface of the nanowires. It is reported that noble metal nanoparticles (e.g.
Pd, Pt, Ru and Au) have higher intrinsic ORR activities compared to carbon with 0.1 M lithium
perchlorate (LiCIO 4) in dimethoxyethane (DME) electrolyte.' In particular, very recent studies
reported a great stability (Au) 47 and high ORR catalytic activity (Pd)7 in Li-0
2
battery
applications. However, those electrodes contained 40-100 wt % of noble metal nanoparticles,
making them less practical due to cost efficiency. Thus, we suggest the composite structure of bio
MO nanowires combined with noble metal nanoparticles to decrease the loading of precious
metals in cathodes while maximizing the catalytic activity of Li-0
2
batteries.
The nanocomposites were designed to nucleate the metal nanoparticle on the surface of
the bio MO nanowire templates to maximize the contact with discharge products in Fig. 3.1 (red
lines, right middle). In addition, the homogeneous distribution of ORR metal catalyst along the
bio MO nanowires was important in maintaining the porous structure of the electrodes. To
facilitate these requirements, poly acrylic acid (PAA) was incorporated around the bio MO
nanowires to nucleate the metal nanoparticle. The PAA wrapped nanowires increased the
colloidal stability of the nanowires during the synthesis so that a more homogeneous solution of
bio MO nanowires was observed (Fig. 3.5.a). Control experiment without PAA wrapping resulted
in free Pd nanoparticle formation and aggregated MO nanowires as shown in the TEM image
(Fig. 3.5.b). This composite synthesis method was applied to two different ORR metal catalysts,
Au or Pd (Au/Pd). To nucleate these metal nanoparticles on PAA wrapped bio MO nanowires,
ethylene glycol was used as a mild and selective reducing agent to react with noble metal
precursors (HAuCl 4 , Na 2PdCI 4) slowly, avoiding reactions with virus-templated MO nanowires.
56
This metal nanoparticle incorporation method by stabilizing and trapping precursor ions with
PAA is expected to be applicable not only to biotemplated nanowires but also to various
nanosized substrates, such as nanofibers.
The homogeneous distribution of Au/Pd nanoparticles (with a diameter of 2-6 nm, Fig.
3.6) was observed by elemental mapping using scanning transmission electron microscopy
(STEM) in Fig. 3.7. The amount of PAA used to form the composite nanostructure was
determined with thermogravimetric analysis (TGA) to be 2.5 wt % of the electrode by comparing
the weight loss difference between bio MO nanowires and Pd incorporated bio MO nanowires at
500*C (Fig. 3.8.a). 48 The amount of Au/Pd nanoparticle incorporated in the bio MO nanowires
was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis
and varied approximately 1-3 wt % of the total electrode, depending on the metal precursor
amount that was added during synthesis.
3.3.3 Improved Li-0
2
battery performances with bio MO nanowires
The virus-templated MO Li-0
mAh/gc+catayst+L202)
2
battery cathodes showed a 9,196 mAh/g, (955
first discharge capacity with 92.6 % of coulombic efficiency at a current
density of 0.4 A/ge. The electrochemical tests were performed with 0.1 M LiCIO 4/DME
electrolyte under 1 atm of oxygen (further details on measurement methods are described in the
experimental section). Although ether-based electrolytes may undergo some side reactions during
Li-0
2
battery charging49 , it is one of the most stable electrolytes against the oxygen electrode for
Li-0
2
batteries known to date
without the reactivity with Li metal like DMSO has.47 Further
control experiments with different electrolytes were included in the following section and Fig.
3.8.b. For galvanostatic tests, the operating voltage was limited to 2.2-4.15 V (vs. Li/Li+) to
minimize possible parasitic reactions. First, the effect of MO electrode structures on Li-0
2
battery
performance was studied by varying the architecture from nanoparticles to bio MO nanowires.
Under the same synthetic conditions, MO nanoparticles (60 nm diameter) were synthesized
57
without viruses and their morphology was compared to bio MO nanowires with scanning electron
images (Fig. 3.9.a,b). The surface area of both the nanoparticles and
microscope (SEM)
nanowires was measured by the Brunauer-Emmett-Teller (BET) method giving 98.5 m 2 /g and
271.7 m2/g, respectively. Bio MO nanowires showed a 40 % improvement of Li 2O 2 storage
capability (9,196 mAh/gc at 0.4 A/ge) compared to MO nanoparticles (6,545 mAh/ge), as can be
seen from the first discharge capacity in Fig. 3.10.a. In addition, the discharge voltage of the bio
MO nanowires (-2.68 V) is higher than that of MO nanoparticles (-2.6 V) by -80 mV and the
charge voltage of the bio MO nanowires (-3.65 V) is lower than that of MO nanoparticles (-3.77
V) by -120 mV. In other words, the bio MO nanowires showed decreased discharge and charge
overpotentials compared to the MO nanoparticles. Since the oxidation state of both the MO
nanoparticles and nanowires was determined to be similar by XPS analysis (Fig. 3.4.a, b), the
difference in Li-0
2
battery discharge capacity was mainly attributed to their different surface
area 5 ' and morphologies. Since MO nanoparticles agglomerate during the synthesis, the low
surface area electrode materials (Fig. 3.9.a) limit the surface mediated reaction so that it results in
a poor specific discharge capacity. In our biotemplated system, the high aspect ratio as well as
larger surface areas (Fig. 3.9.b) formed highly active Li-0
2
battery cathodes where the electrode
spaces can be fully utilized while minimizing the effect of discharge product blocking the
electrodes.
The major discharge product obtained after the first discharge of bio MO nanowire
electrodes was Li 2 0
2
confirmed by XRD in Fig. 3.10b. The XRD data of discharged electrode
matches well to the reference XRD pattern of Li 2 0
2
(orange star, PDF no. 01-074-0115). There
was no other major discharge product observed except Li 2 O 2. In previous reports, MOs have been
shown to produce a LiOH phase during the discharge 39'
residues. The Li-0
2
49
due to the structural water or hydroxyl
battery performance of dehydrated (thermal treatments at 160*C for 2 hours)
bio MO nanowires was investigated to eliminate any possible contributions from water molecules
or hydroxyl groups. The thermally treated nanowires showed a similar discharge capacity of
58
9,206 mAh/ge at 0.4 A/g, (Fig. 3.8.b) compared to nanowires without heat treatments, although
structural water decreased from 3.2 to 1.5 wt % of electrodes after heat treatment (Fig. 3.8.a).
Thus, the LiOH formation is negligible in this Li-0
3.3.4 The Li-0
2
2
battery performance.
battery performance with different electrolytes
The first galvanostatic cycle of bio MO nanowires was tested with I M lithium triflate
(LiCF 3SO 3) in tetra (ethylene) glycol dimethyl ether (TEGDME) to investigate the Li-0
performance
dependence
on
electrolytes.
Here,
bio
MO
nanowire
electrodes
2
with
LiCF 3SO 3/TEGDME exhibited higher charging overpotential as well as lower first discharge
capacity (Fig. 3.8.b, red, 8,766 mAh g'e at 0.4 A g-e). Furthermore, the coulombic efficiency of
nanowire electrodes dropped from 92.6 % (0.1 M LiC1O 4 in DME) to 61.5 % (1 M LiCF 3SO 3 in
TEGDME) at the same charging cut off voltage, 4.15 V. Since increasing the test voltage
windows higher than 4.15 V may evoke the electrolyte decomposition, DME was suitable for bio
MO nanowire electrodes in order to achieve higher coulombic efficiency in lower voltage ranges.
3.3.5 Li-0
2
battery performances of Pd/Au loaded bio MO nanowires
The hybrid nanostructure composed of Pd nanoparticles and bio MO nanowires exhibited
improvement of the Li-0
2
battery discharge capacity. The first galvanostatic cycle of Au/bio MO
nanowires and Pd/bio MO nanowires were compared with approximately the same amount of Au
(1.7 wt %) and Pd (1.1 wt %) incorporations in each nanocomposited electrode. After the addition
of only -I wt % of Au or Pd nanoparticles, the first discharge capacities of Au/bio MO nanowires
and Pd/bio MO nanowires (cut off voltage at 2.2 V vs Li/Lie) were improved by 8 % (Au) and
15.5 % (Pd) respectively, compared to bare bio MO nanowires (at 0.4 A/gc, Fig. 3.11.a, Au: green
straight, Pd: red dashed). In addition, the Pd/bio MO nanowire electrodes showed approximately
60 mV higher discharge voltage than Au/bio MO nanowires as can be observed from Fig. 3.11.a.
The higher discharge voltage of Pd/bio MO nanowires than Au/bio MO nanowires in the first
59
galvanostatic cycle of Li-0
and oxygen.
2
electrodes may be attributed to the attractive interaction between Pd
Also, although Pd has a lower contrast than Au on TEM observation due to its
lower atomic mass, large (higher than 5 nm) Pd nanoparticles on bio MO nanowires were rarely
observed than Au nanoparticles decorated bio MO nanowires (Fig. 3.6) so the smaller
nanoparticle distribution of Pd/bio MO nanowires in a given synthetic conditions may improve
the battery performances. Thus, the surface electrocatalytic functionality of bio MO nanowires
was easily tuned by the composite synthesis method developed here.
The capability to store lithium peroxide was further improved by increasing Pd
incorporations from 1.1 wt % to 3 wt % of Pd/bio MO nanowires electrodes. With 3 wt % of Pd
incorporation, a 45 % improvement of the first specific capacity of bio MO nanowires (Fig.
3.11.a, red straight, 13,347 mAh/gc, 1,008
mAh/gc+cataystLi20 2 )
was achieved at 0.4 A/gc. This is
the highest specific capacity under a high applied current (0.4 A/ge, 0.22
A/gc+catalyst)
among all
manganese-oxide-based electrodes reported to date.39' 3 The formation of Li 2 0 2 after discharge
and its decomposition during the charge (oxygen evolution was detected by Gas Chromatography
(GC) in Table. 3.1) with Pd/bio MO nanowire electrodes was also confirmed by Raman
spectroscopy in Fig. 3.11.b. No significant amount of side product (e.g., Li 2 CO 3) can be detected
by XRD and Raman, suggesting that DME is largely stable during discharge.
We believe the
enhanced discharge capacity of Pd/bio MO nanowires originated from the better utilization of
porous electrode spaces by improving the electrochemical active surface area and surface
conductivity of bio MO nanowires. The Pd nanoparticles located on the surface of the bio MO
nanowires facilitated ORR reactions and improved the electronic conduction throughout the Li 2 02
layers allowing further discharge product depositions.
The differences in the charging profile of the 3 wt % Pd-MO nanowires compared to the
bare bio MO nanowires (Fig. 3.10.a) can be associated with the increased thickness of Li 2 02
layer of the 3 wt % Pd/bio MO nanowires (-4 nm Li 2 0 2 ) compared to the bare bio MO nanowires
(-2.6 nm Li 2 O 2 ) due to larger discharge capacity. However, the charging potential of Pd/bio MO
60
nanowires after decomposing 0.05 IAAh/cmtre
2
of Li 2O 2 was still -100 mV lower than that of
catalyst-free, carbon electrode55 at the same depth of discharge, -1 rtAh/cmtme2 (the true electrode
surface area specific capacities, the detail calculation method is the experimental section). This
lower OER potential compared with catalyst-free electrodes suggests the catalytic function of
Pd/bio MO nanowires even after the deep discharge in Li-0
2
battery. The following (second)
cycle profile of MO nanoparticles, bio MO nanowires, Au (1.7 wt%)/bio MO nanowires, Pd (1.1
wt%)/bio MO nanowires and Pd (3 wt%)/bio MO nanowires are included in Fig. 3.12.a. The
second charging profile showed enhanced performance than previous manganese-oxides-based
electrode at -6 times higher current density3 9 and further studies to improve the cycle life after
the deep discharge remains as future work.
To clarify the role of Pd nanoparticles, PAA wrapped bio MO nanowires were tested as
Li-0
2
battery electrodes under the same test conditions. The first discharge capacity of the
PAA/bio MO nanowires electrode was 9,722 mAh/gc (Fig. 3.8.b, green), which is only a 5 %
improvement of bio MO nanowire electrodes. This small improvement of discharge capacity
could be attributed to the decreased aggregation between bio MO nanowires after PAA
stabilization. The average value of discharge specific capacity can be seen in Fig. 3.12.b.
Therefore, the increased first discharge capacity of Pd/bio MO nanowire composites originated
from Pd nanoparticle incorporation onto bio MO nanowires, not from the PAA wrapping. We
expect that this methodology can be easily applied to other promising ORR or OER candidate
materials to develop efficient catalyst structures for Li-0
2
batteries in future studies.
3.3.6 Lowered carbon amounts in Pd/bio MO nanowires cycling electrodes
The catalyst nanostructure designed in this work, Pd/bio MO nanowires, allowed for an
electrode with greatly decreased carbon content (8 wt %) in the catalyst electrodes to improve
cycle life of Li-0
2
battery. Although carbon functions as a conducting agent and an ORR catalyst,
it can also reduce the cycle life because side products can be formed at the carbon/electrolyte or
61
carbon/Li 2O 2 interface in electrodes with ether-based electrolytes.56 By reducing carbon amounts
in our electrodes, cycle life of Li-0
A/gc+catalyst)
2
batteries was enhanced at high current densities (1 A/ge; 0.1
even under relatively low charging cutoff voltage (4.15 V). The cycling tests were
conducted by limiting the discharge capacity to 2,000 mAh/g, (200 mAh/gcatalyst) or 4,000
mAh/gc (400 mAh/gc+cataIyst, 299 mAh/gc+catayst+Li202) following the previous works method.:' '
Similar to the first discharge specific capacity, the cycle life of Li-0
2
batteries was gradually
enhanced as the catalyst structure changed from MO nanoparticles to nanowires and finally to
composite Pd/bio MO nanowires (Fig. 3.13-16). In particular, the OER overpotential was lowered
as the surface area of catalyst electrodes as well as the surface conductivity of bio MO nanowires
was improved by Pd incorporation (Fig. 3.13.a) after being discharge to 4,000 mAh g-'c (400
mAh g-'c+catalyst). Thus, the first cycling round trip efficiencies of MO nanoparticles, bio MO
nanowires and Pd/bio MO nanowires was improved from 75 %, 77.7 % to 79.2 %, respectively,
as the cathode was rationally designed. The aggregated microstructure of MO nanoparticles
limited the Li-0
A/ge (0.1
2
battery cycle life to 10 cycles with 4,000 mAh/gc (299
A/gc+cataiyst).
mAh/gc+catayst-Li2o2)
at I
The bio MO nanowires showed cycle retentions up to 20 cycles due to the
high porosity and large catalytic surface area of the electrodes. After incorporating Pd
nanoparticles, the discharge capacity of Li-0
2
batteries maintained stable to 50 cycles (Fig.
3.13.b, 3.14). When the depth of discharge capacity was fixed to 2,000 mAh/ge (at I A/ge; 0.1
A/gc+catalyst),
these electrodes showed a longer cycle life with a similar cycling performance trend.
Each MO nanoparticles, bio MO nanowires and Pd/bio MO maintained the 2,000 mAh/gc of
discharge capacity up to 22, 47 and 58 cycles, respectively (Fig. 3.13.b, 3.15). The reversible
cycling number with Pd/bio MO nanowires electrodes is smaller than the recently reported,3' 47
which might be due to the instability of electrolyte or the reactivity between carbon and oxygen
reduction intermediates.56 ,
7
This can be observed from the charging cycle profile in Fig. 3.14-16,
resulting in the faster decay of charging capacity than the discharging capacity as cycling number
62
increased in Fig. 3.13.b. Ongoing and future work will be focused on developing stable
electrolytes and carbon-free electrodes to enhance the cycling of these electrodes.
To investigate the effect of carbon in cycle of Li-0
2
batteries, electrodes were prepared
with 44 wt % of carbon. The cycle life of bio MO nanowires and Pd/bio MO nanowires decayed
faster than those of low carbon electrodes under the same fixed discharge capacity (728 mAh/ge,
400 mAh/g+catajys,) and current density (I A/ge, 0.1 A/gc+catayst). The observed cycle number was
17, 21 and 30 for MO nanoparticles, bio MO nanowires and Pd/bio MO nanowires, respectively
(Fig. 3.16). Although the electronic conductivity was higher for 44 wt % versus 8 wt % carbon
electrodes, side products can be formed in the high carbon electrodes during cycling 56
counteracting the kinetic advantage in Li-0
2
battery performance. Therefore, we believe Pd/bio
MO nanowires are a viable materials platform for long lasting, high capacity Li-0
63
2
batteries.
3.4 Conclusion
Using a biological template, a new catalyst electrode was developed that increased
capacity (13,350 mAh/gc; 7,340
mAh/gc; 400
mAh/gc+catajyst
at 0.4 A/gc) and cycle life (50 cycles with 4,000
mAh/gc+catalyst
at I A/gc; 0.4
A/g+catayst)
of Li-0 2 batteries at the highest gravimetric
current density compared with other transition metal oxide based electrodes in literatures.'
39
These templates allowed the formation of high aspect ratio manganese oxide nanowires wrapped
in 3 wt % Pd nanoparticles facilitating compositional control that outperforms materials made by
mechanical mixing.; These high aspect ratio bio MO nanowires formed a porous network that
maximizes the interaction between the catalyst and the discharge products (Li 2 0 2 ) thus increasing
reversibility and generating a stable cycle life of Li-0
2
batteries. Furthermore, the Pd/bio MO
nanowires allowed the implementation of low carbon electrodes batteries improving battery cycle
life. We believe this template is readily adaptable for other materials combinations and can
provide a platform to test various catalytic electrode materials for Li-0
2
batteries and other
catalytic systems. In addition, the application of biomaterials will broaden the material selection
scope into diverse areas in designing Li-0
2
development of energy storage systems.
64
battery electrodes
thus contributing to the
3.5 Figure and Tables
Biotemplating
MnOx
Carbon
particle
M13 virus
8I
ADVYESALPDPAEAAFESL..
Porous biotemplated
NWs electrodes
02
PAA wrapping
on biotemplated
MnO NWs
Incorporation of
metal NPs
Figure 3.1.
Schematic
of a
nanocomposite
Porous and catalytic
biotemplated
NWs electrodes
structure. Synthesis step
of the
metal
nanoparticle/M 13 virus-templated manganese oxide nanowires (bio MO nanowires) and
the
operational reaction inside Li-0
2
battery cells.
65
a
C
-
200 nm
Figure 3.2. Electron microscope images of bio MO nanowires. TEM images of Ml 3 virustemplated MO nanowires (a) at low magnitude (b) zoomed at the end of an individual bio MO
nanowire or the whole nanowire (c).
66
Biotemplated MnO NWs
AL
10
20
30
40
50
2 Theta (degree)
60
70
Figure 3.3. Crystallographic property of bio MO nanowires. (a) XRD pattern of bio MO
nanowires with the weak and broad peak signals due to the poorly crystalline phase of nanowires.
The orange triangle marks (2 theta at 37*, 53.50, 65.50) correspond to the lattice spacing observed
from HRTEM FFT image (Fig. 3.2b). (b) HRTEM image showing amorphous phase mixed with
crystalline phase (Inset: the Fast Fourier Transform (FFT) pattern with two major rings matching
to the atomic planes with the spacing of 2.4
A and 1.6 A, respectively).
67
a - 2
b
Mn 2p,
Mn 2p
Mn 3s
5.2 eV
Mn 2p.
C
C
b~ W~
C
MnOx NPs
Bkoemplated MnOx NWs
660
656
652
PnOx NPs
Boemplaed MnOx NWs
648
644
640
636
96
94
92
Binding energy (eV)
90
88
86
84
82
80
78
76
Binding energy (eV)
C
Bomplated MnO. NWs
C
040
C
1,100
1.00
900
800
700
600
500
400
Binding energy (eV)
300
200
100
0
Figure 3.4. XPS spectra of bio MO nanowires and manganese oxide (MO) nanoparticles.
The high resolution spectra of bio MO nanowires at (a) Mn 2p region, (b) Mn 3s regions showing
5.2 eV of 3s multiplet splitting. (c) The full range survey XPS spectrum of bio MO nanowires
indicates that no element other than Mn is present within the bio MO nanowires.
68
Figure 3.5. Stabilization effect of PAA wrapping on bio MO nanowires. (a) The digital
camera image of PAA wrapped bio MO nanowire solutions (left) and bare bio MO nanowire
solutions (right). (b) TEM image of bio MO nanowires composited with Pd nanoparticles without
PAA wrappings.
69
Figure 3.6. Pd/Au nanoparticles loading on bio MO nanowires. HRTEM image of (a) Pd/bio
MO nanowires showing high contrast round shape particles (Pd) with 2.2
A of lattice spacing that
corresponds to (111) planes of Pd. (b) Au/bio MO nanowires with dark round particles (Au)
having 2.3
A of lattice spacing that corresponds to (I 11) planes of Au.
70
I
Figure 3.7. Elemental mapping of Pd/Au nanoparticles loaded bio MO nanowires. (a) STEM
image of Pd/bio MO nanowires (left) and the corresponding Energy Dispersive X-ray (EDX)
elemental mapping images of manganese (Mn, red, upper right) and palladium (Pd, green, lower
right, scale bars, 100 nm). (b) STEM image of Au/bio MO nanowires (left) and the corresponding
EDX elemental mapping images of manganese (Mn, red, upper right) and gold (Au, yellow,
lower right, scale bars, 50 nm).
71
0
Specific capacity (mAh/gc)
2,000 4,000 6,000 8.000
10.000
a100
4.0903.5
800
3.0
2
70-
only
Biotemplated MnOx NWs
Mno
-
2.0
Biotemplated MnOx NWs with heat treatments
Biotemplated MnO NWs with PAA/Pd NPs
50
100
0
500
300
400
200
Temperature (celsius)
1.5
Biotemplated MnOx NWs
1M LiCF3SO 3 TEGDME
Heat treatment
PAA wrapping
0
600
Ketjan black
1,000 2.000 3000 4.000 5,000 6,000
Specific capacity (mAhlgc+catalyst)
Figure 3.8. TGA data and galvanostatic profile of bio MO nanowires and control samples.
(a) TGA curve of MO nanoparticles, bio MO nanowires, bio MO nanowires after heat treatment
at 160*C for 2 h and Pd/bio MO nanowires. Since there is almost no difference in weight percent
59
between MO nanoparticles and bio MO nanoparticles at 500 C , the mass percentage of virus in
bio MO nanoparticles is negligible. In addition, 1.623x 10"3 of virus particles (one virus particle
weighs ~17 MD) were consumed to produce 24 mg of bio MO nanoparticles. Therefore,
(2.82x10-
4
x
1.623x10" )/24 x100%=1.9 %, which is 0.68 % of mass in electrode thus we can
almost neglect the mass percentage of virus in Li-0
cycle (at 0.4 A g-', under I atm of
02)
2
battery electrodes. (b) The first galvanostatic
of bio MO nanowires tested with the electrolyte composed
of I M LiCF 3SO 3/TEGDME (red), bio MO nanowires after heat treatment at 160*C for 2 h (blue,
with 0.1 M LiCIO 4 /DME) and the PAA wrapped bio MO nanowires (green, with 0.1 M
LiClO 4/DME).
72
a
BET surface area: 271.7 m2 /g
BET surface area: 98.5 m2/g
Figure 3.9. Microstructure analysis of MO nanoparticles and bio MO nanowires. The SEM
image and BET surface area of (a) MO nanoparticle showing bulky phase of aggregated particles
(Scale bar corresponds to 1 pm) and (b) homogeneously dispersed bio MO nanowires with larger
pores (scale bars, I pm). The two BET surface areas are 98.5 and 271.7 m 29-, respectively.
73
a
0
Specific capacity (rnAhlgc)
2.000 4,000 6.000
8,000
10.000
- U.I.
4.5
4.0Charged
3.5
S3.0
25
**D
ed
Biotemplated MnO NWs
MnO NPs
2 0 -
~
Biotemplated MnO NWs electrodes
1.5 .
0
1,000 2000 3000 4,000 5.000
Specific capacity (mAh/gc+catalyst)
Figure 3.10. Li-0
2
2 Theta (degree)
battery operation of MO nanoparticles and bio MO nanowires. (a) The
first galvanostatic Li-0
2
battery cycle of MO nanoparticles (green) and bio MO nanowires (red)
at a current density of 0.4 A/ge (-0.044 mA/cm 2 ) with 0.1 M LiClO 4/DME electrolytes under I
atm of oxygen. (b) XRD patterns of bio MO nanowire electrodes at the pristine state (blue), the
end of the first full discharge until 2.2 V (green) and the end of the first full charge until 4.15 V
(red) tested under 0.4 A/ge of current density. The XRD data of discharged electrode matches
well to the reference XRD pattern of Li2 0
2
(orange star, PDF no. 01-074-0115). There was no
other major discharge product observed except Li 2 O 2 .
74
a
Specific
0
3.000
4'5
capacity (mAh/gc)
9,000 12.000
6,000
15.000
-
I
-
Biotemplated MnO. NWs nanocomposites
I
40
3.5-
Dischargled
Charged
Charged
D pak
G peak
2.52.
0-0
20 --PAA/Au NPs (1.7 wt%)
PAA'Pd NPs (1 1 wt/a)
PAA/Pd NPs (3 wt%)
o
2,000
4,000
6,000
Specific capacity (mAhlgc+catalyst)
Figure 3.11. Li-0
2
8000
800
1.000 1,200 1,400 1.600
Raman Shift cm 1 .
1800
battery operation of Au, Pd nanoparticle loaded bio MO nanowires
electrodes. (a) The first galvanostatic cycle of bio MO nanowires with the similar weight percent
of the different type of metal nanoparticle composites (Pd nanoparticles: red dash, Au
nanoparticles: green straight) tested under the current density of 0.4 A/g. Further improvement
was observed with 3 wt % addition of Pd NPs (red straight) onto bio MO nanowires. (b) Pd (3 wt
%)/bio MO nanowires electrodes after the discharge (red) and charge (blue) tested under the
current density of 0.4 mA g-1, with 0.1M LiCIO 4/DME electrolyte.
75
a
Specific capacity (mAhigc)
4
5 -.
4
0
0
3,000
6:000
9000
12.000
15.000
b
000
1000
12-000
1.0001
3
>
-8.000
S4
000
=2.5
,0
C
O NPS
B", *
i
Botempiated MiO NWs
2.0
2.000
PAAAw NP, 11.7 wtyBrto MO NWs
NPs 1 1wtV iOMO NWs
NP- 13 wto
MO NWs
U
-- -PAAPd
-PAAPd
0
2,000
4.000
6,000
Specific capacity (mAh/9c+catatyst)
4.000
2,000-
0
0
Biotempt ted Btemp[
8,000
Biotemplated
d
Mn0 NWs MnO, NWs/PAA
MnO NWs
with
Figure 3.12. The improved specific capacity of Li-0
2
PAAPd NP,
battery with the rationally designed
catalyst electrodes. (a) The second galvanostatic cycle (at 0.4 A g-' under I atm of 02) of
various electrodes MO nanoparticles (green), bio MO nanowires (blue), PAA/Au NPs (1.7
wt%)/Bio MO nanowires (yellow), PAA/Pd NPs (1.1 wt%)/Bio MO nanowires (red dash) and
PAA/Pd NPs (3 wt%)/Bio MO nanowires (red straight) were tested with the electrolyte, 0.1 M
LiC1O 4 /DME. These are the following second cycles of the first cycle of Fig. 3.10a and Fig.
3.11a. (b) The specific capacities of electrodes with MO nanoparticles (orange), bio MO
nanowires (blue), bio MO nanowires with PAA wrapping (green), Pd/bio MO nanowires (red)
including standard deviations error bars (154-854 mAh/ge). Each sample type was made and
tested at least triplicate.
76
a
Specific capacity (mAh/g.)
1.000
0
2.000
3,000
b
4.000
45
500~--
2.
.
Eectrodes with 8 wt % of carbon
Electrodes with 8 wt % of Carbon
)uI oi
2 4004
4.0-
4.000
300
3
>
3,0-
-2,000
MnOX NPs
25-
MnOX NWs
Bonemplated MnOX NWs with PAA'Pd NPs
0
S 0
-~-Betemplated
--
0
200
300
400
Specific capacity (mAh/gc+catalyst)
100
Boterp afed MnO
10
1.000
rrr
MnO NWs
-~-MOps.
Bolwmplated
20
NWs
w,
PAA!Pd NPs
30
40
Cycle number
50
60
0
70
Figure 3.13. The improvement of Li-0 2 battery cycling performance with the rationally
designed catalyst electrodes. (a) The first cycling voltage profile of Li-0
2
batteries with the
fixed discharge capacity of 4,000 mAh/g, (400 mAh/gccatalys,) for MO nanoparticles (blue), bio
MO nanowires (green) and Pd/bio MO nanowires (red) at the current density of I A/ge. Each
electrode was composed of 8 wt % of carbon and was cycled in 2-4.15 V voltage windows. (b)
The cycling performance of Li-0
2
battery electrodes composed of MO nanoparticles (blue), bio
MO nanowires (green) and Pd/bio MO nanowires (red) at the current density of I A/ge (0.1
A/gc+catalyst) with the two different fixed discharge capacities of 2,000 mAh/g, and 4,000 mAh/g,
(200, 400 mAh/g+catalyst). The circular shape indicates discharge capacities (for both, 2,000 and
4,000 mAh/ge), the triangle indicates charge capacities (until 4.15 V) for 2,000 mAh/ge and the
inverted triangle indicates charge capacities for 4,000 mAh/gc. Each electrode was composed of 8
wt % carbon. All of electrochemical tests reported in this work were repeated for at least six
different devices.
77
4.5-
4
Specific capacity (mAhjg)
1.000
2.000 3000 4.000
0
Electrodes with 8 wt
of carbor
5,000
-
-J' cycae
0
35-
'03,0
>
0
25
2.0
MnOx NPs
0
b
45.
0
100
200
300
400
Specific capacity (mAhigc+caataysI)
500
Specific capacity (mAh/gc)
1000
2,000
3,000 4,000
Electrodes with 8 *t
of carbon
5,000
c
--
10 cyde
'41 Cycle
335
-6 3,0 5 30
20
0tm ated Mo0 NWs
0
C
0
45
100
200
300
400
Specific capacity (mAhgqc+catatys I
500
Specific capacity imAhigci
1,000
2.000
3,000
iectrodes witn 8 W" of carbon
4.000
5,000
(;yde
-
1()
2r
40 .
'13'
y
cycle
50' cycle
o3
20
.BoKempIeodMno NWs with PAA]PO NPs
0
100
200
300
400
Specific capacity (mAh/gccatayt)
500
Figure 3.14. The cycling performance of low carbon Li-0 2 batteries with the fixed discharge
capacity of 4,000 mAh g~'c (400 mAh g'c+catayst). (a) MO nanoparticles, (b) bio MO nanowires
and (c) Pd/bio MO nanowires at the current density of I A g-'c. Each electrode was composed of
8 wt % of carbon and was cycled in 2-4.15 V voltage windows.
78
a
Spebftc cpartly (mArlgc )
500
1.000
1,500 2.000
0
4.5
of caboi
Electodes mdh 8 1M
-
4,0
>
2 500
1
-
i c0ycle
--
35
S3.01
20- Mno NP,
50
0
100
Specific capaCdty
150
200
Specic capac y (mAqC)
1500
1000
500
0
wctodes
wh
S wt I^f
250
(mmh,'C,4rays
arbxor
2.500
2.000
1
--
eyde
36
5
2
WCn a
SpoI
0
C
),Mo
50
100
1 0
Specfir capacity (mAhIy,+,
0
CaOacity
500
1000
NWb,
200
250
, yst)
4
OTI(mAh 0 P
1,500 2.000
2.50,)
4.5
ctrodes
E
wi
8 w-Ii o
cadx
C
20
225
2V0 Bvte
0
+
iiated MnO.
51
250
NNs wth
PAA PO
100
150
NPs
200
250
2,500
E
5.
ectrcdt,,,,
*d
8 wt
%of rcarbor
200
150
2.000
L0
B0 tempatea MnirO, NWs
-- jotemptateduno, NWs wePAAPd NPs
0
to
2'
300
15
50
60
Cyrte numftr
Figure 3.15. The cycling voltage profile of low carbon Li-02 batteries with the fixed
discharge capacity of 2,000 mAh gc (200 mAh g~' +,tyt).(a) MO
79
nanoparticles, (b) bio MO
nanowires, (c) Pd/bio MO nanowires at the current density of 1 A g~',. Each electrode was
composed of 8 wt % of carbon and was cycled in 2-4.15 V voltage windows.
80
ImAh/gc)
500 600 700 8W0
Specific capacity
a4 .5
0
100 200 300 400
with 44 WF% of carbon
ElecIrodoa
900
-cycl
4,0
0
3.014
2.5
2.0-'
MnO NPs
0
500
100
200
300
400
Specific capac4y (mAh!gc+calatlyst
Specific capacity (mAh/g.)
b
100 200 300 400 500 600 700 800 900
0
Electrodes
wfth 44 W % of carbon
1 cycle
10 Cycle
20 cyde
403+5-
3,0-
-6
2 0-
B.empadf
0
C
WnOW NW%
200
300
400
Specific capac;ty (mAh!gc+catalys)
500
100
Specific capacity (mAh/c)
100 200 300 400 500 600 700 800 900
0
4.5
Electrodes with 44
W
of carbon
iy'.yde
--
20
cyce
cycle
___30
cxde
10
40
4
0
~3Q.
20
1
oafnplated MnOx NW wi th PAA(Pd NPs
0
100
d
200
300
400
500
Specific capablty mAhgC ctalyst)
500
Electrories with 44 Wi
-
%1
800
of
Co
400.
6(00
,00
400
200
U10
NW'.
Brk+iplaled MnO,
NW' wilh PAA;Pd NPs
-
0
200 e
nO AP
Biolerrplated MnO,
- ,
0
-
-
-
- -
10
20
Cycle number
- -
-
- 0
30
81
Figure 3.16. The cycling voltage profile of high carbon Li-0 2 batteries with the fixed
discharge capacity of 727 mAh g-' (400 mAh g~'c+catalyst). (a) MO nanoparticles, (b) bio MO
nanowires, (c) Pd/bio MO nanowires and (d) cycle life of MO nanoparticles, bio MO nanowires
and Pd/bio MO nanowires at the current density of I A g-c. Each electrode was composed of 44
wt % of carbon and was cycled in 2-4.15 V voltage windows.
82
Table 3.1. The Gas Chromatography (GC) data of Pd (3 wt %)/bio MO nanowires
electrodes after the first galvanostatic discharge/charge at 0.4 A g~', with 0.1 M LiClO in
4
DME.
Sample name
Retention Time
(min)
Gas Type
Bio MO NWs
with PAA/Pd NPs
(3 wt%)
discharged
Bio MO NWs
with PAA/Pd NPs
(3 wt%) charged
0.801
1.127
1.274
H2
02
~4.5
CO 2
0.794
1.119
1.270
H2
02
N2
-4.5
CO 2
Area %
1.594
28.682
69.722
Not detected
3.716
36.251
60.031
Not detected
N2
Area ratio
normalized with
N2
0.022
0.411
1
0.061
0.603
1
-
Table 3.2. The discharge/charge capacity (mAh g~',) for the first and second cycle of
different electrodes galvanostatically tested at 0.4 A g-' with 0.1 M LiClO 4 in DME under 1
atm of 02.
Sample name
MnOx NPs
Biotemplated MnOx NWs
Bio MO NWs with
PAA/Au NPs (1.7 wt%)
Bio MO NWs with
I" Discharge
Is Charge
capacity
capacity
capacity
capacity
6695.1
9196.5
9935.5
4524.8
8516.5
7196.5
5781.6
10528.8
11264.1
1853.3
4367.4
3268.9
10620.1
8549.9
13378.2
3328.4
12267.6
_
3276.7
2 nd
Discharge
2 "dCharge
PAA/Pd NPs (1.1 wt%)
Bio MO NWs with
PAA/Pd NPs (3 wt%)
13347.2
9839.1
_
_
83
_
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88
Chapter 4. Investigation of catalytic behavior of M 13 virus
templated MnxCo.O
4
02 battery cathodes
89
(x
=
0, 1, 2) nanowires for Li-
4.1 Introduction
The practical energy density of future battery pack can be improved to ~1,000 Wh kgwith the non-aqueous Li-0
2
battery system.' This potential improvement is promising, since the
current Li-ion battery can only deliver 100~140 Wh kg-' (-100 miles of driving range with a
single charge), impeding the replacement of gasoline powered vehicles (-300 miles of driving
range with a refueling). 2 Despite of this attractive energy density, the current state of non-aqueous
Li-0
2
batteries is preliminary. They suffer from the large voltage hysteresis, low power, poor
cycle life and the absence of efficient filter that selectively passes oxygen molecules. Many recent
studies achieved significant improvements with a novel approach to solve those limitations of Li02
battery systems. Some researchers applied a redox mediator to achieve 100 cycles at the high
current density3 (at I mA cm 2 ) and the other utilized the gel cathode/solid catholyte structure to
cycle the Li-0
2
battery (at 0.16 mA cm 2 ) for 100 times in ambient air 4 . In addition to employing
these advances in Li-0
2
battery systems, a systematic study to select good cathode materials
among various compounds is also important to develop a better performing Li-0
Although there are many reports focusing on a single material as a Li-0
Nao. 4 4 MnO 2 , 5 Lao.75Sro.2 5MnO 3, 6 TiC, 7 Ru0
8
2
2
2
battery.
battery cathode (e.g.
), direct comparisons between different materials
were hardly made. Therefore, a versatile tool to screen the possible candidate for an efficient Li02 battery cathode is required to produce a high energy density storage system.
Spinel oxides have shown many interesting physicochemical properties with a diverse
combination of elements, AB 2 0 4 (A: metal cation occupying tetrahedral sites, B: metal cation
occupying octahedral sites) applicable to magnetism,9 electrocatalyst'
1112
system. 1
and energy storage
In particular, cobalt manganese spinel oxides (MnCo 3.,0 4, x = 0-3, here we
designate them as MCO) have presented considerable catalytic activities for oxygen reduction
reaction (ORR) and oxygen evolution reactions (OER) in alkaline solutions. 3 ' 14 These spinel
oxides were also studied in previous reports as a cost effective electrocatalyst for Zn-airl and Liair batteries but with carbonate based electrolytes
90
5
which decompose during Li-air battery
operations.1 6 Here we first report the biomolecule directed synthesis of MCO to investigate their
functionality as Li-0
2
battery cathodes with ether based electrolytes. While the conventional
synthetic methods generated random sizes of particle'',
plate'
and spheres' 9 of MCO, the Ml3
virus enabled us to form homogeneously distributed high-aspect ratio MCO nanowires (25-50
nm of diameter and ~1 tm of length). Thus, we could observe the correlation between the Li-0
2
battery performance and the chemical composition of bio MCO nanowires while confining the
geometry of cathode materials in a similar scale.
M13 bacteriophage is a filamentous virus with a single-stranded DNA encapsulated by
various major and minor coat proteins. It is approximately 880 nm long and 6 nm in diameter
(Fig. 4.1).
The viral capsid is composed of 2,700 copies of helically arranged major coat
proteins, p8, and 5-7 copies of p3, p6, p9 and p7, located at either ends of the M 13 virus. The
genetic sequence of these proteins can be modified to display short (<8-12 amino acid) peptide
sequences at their own locations on the M 13 virus. In particular, the E3/E4 virus clone (having a
sequence of AEEEE (E4) or AEEE (E3) at the N-terminus of each p8) was used as an effective
2
versatile template for the nucleation of a wide variety of metal oxides such as Co 30 4 ,' , 20
perovskite oxides (SrTiO 3, BiFeO 3).21 Since negatively charged virus surfaces make them easily
interact with cationic metal precursors, metal oxide nanomaterials were formed with a high
production yield. We recently synthesized MnOx nanowires for Li-0
2
battery cathodes using a
M 13 virus clone ADVYESALPDPAEAAFE at p8, presenting negatively charged virus surfaces
originated from Aspartate (D) and Glutamate (E). 22 In this study, we extended the bio-directed
synthesis of Li-0
2
battery cathodes to different metal cations (Co, Mn) with their diverse
stoichiometries (Fig. 4.1) using a versatile clone, E3/E4.
91
4.2 Experimental
4.2.1 Biotemplated synthesis of CoO, nanowires
The Co precursor solution was prepared by sequentially adding D.l. water (14 mL),
NH3-H 20 solution (4 mL, 28 %) and hydrogen peroxide (2 mL) solution into a glass flask with 10
mmol of cobalt (II) acetate tetrahydrate ((CH 3COO) 2 Co-4H 2 0, 98 %, 500 mM) solution with a
vigorous stirring. This Co precursor solution (0.5 mL, 500 mM) was added slowly into the E3/E4
virus solution (150 mL, l.Ox101 pfu mUl, pH 9). After stirring this solution at room temperature
more than 6 hours, NH 3 -H20 solution (1 mL, 10%) was added and stirred for one hour. Hydrogen
peroxide solution (0.1 mL, I M) was added and reacted for one hour at room temperature. The
temperature of this solution was increased to 60'C and was stirred for 12 hours. The final product,
M 13 virus-templated cobalt oxide nanowires with the smooth surface morphology, was obtained.
The as-synthesized biotemplated cobalt oxide nanowire solution was washed with D.I. water by
centrifugation, at least repeating twice.
4.2.2 Biotemplated synthesis of Mn,Co 3 ,0
4
(x=1, 2) nanowires
Aqueous Co, Mn precursor solutions were prepared by mixing the cobalt (II) sulfate
heptahydrate
aqueous solution
(CoSO 4 -7H 2 0,
>99%, 500 mM),
manganese
(II)
sulfate
monohydrate aqueous solution (MnSO 4 -H 20, >99%, 500 mM) in Mn:Co molar ratio of 2:1 and
1:2 for CoMn 2O 4, MnCo 20 4, respectively. For bio-MC20 NWs: 0.32 mmol of Co and 0.16 mmol
of Mn, for bio-CM20 NWs: 0.16 mmol of Co and 0.32 mmol of Mn was added slowly to E3
virus solutions (100 mL, 5.Ox1012 /mL) with vigorous stirring. The solution was kept stirring at
room temperature more than 2 hours, and then NH 3*H 20 solution (5%) was added to adjust the
pH of solution between 9 and 10. The color of solution quickly changed from light red to light
green and gradually evolved to dark brown with the time for bio-CO NWs. For bio-MC20 and
CM20 NWs, the color of solution changed from light red to yellow brown instantly. After one
hour, hydrogen peroxide solution (H 2 0 2 , I M, 0.48 mL for bio-CO NWs, 0.32mL for bio-MC20
92
and CM20 NWs) was added while stirring at room temperature for 2 hours. To increase the yield
and rate of bio-CO NWs formation, the solution can be further heated up to 80 0C in oil bath with
stirring. The final product can be collected by centrifugation at 3,300 rpm. The product was
washed at least twice, with 70 v/v % ethanol and span at 3,300 rpm for 20 min.
4.2.3 Synthesis of Ni nanoparticles
The synthesis was carried out under oxygen free environment. In a typical
synthesis
of
Ni
NPs,
0.1
mmol
of
nickel
(II)
acetylacetonate
(Ni(CH 3COCHCOCH 3) 2(H20) 2, 95%, Ni(acac) 2 ) and 0.3 mmol of Tert-butylamineborane (TBAB, dissolved in 2 mL of oleylamine (OAm, >70%)) were dissolved in a
mixture of oleic acid (OA, 90%, 0.2 mL) and OAm (10 mL) at room temperature with
stirring. The temperature of this mixture was maintained to 160 'C for 30 min under
vacuum to dehydrate the precursor and remove trace water in solvents. Under argon gas
flowing over the solution in flask, the temperature of solution was further increased to
270 'C with a constant heating rate of 15 'C min-,
and kept for 20 min. Then, the
solution was cooled down. A mixture of 3-mercaptopropionic acid (6 [l) and hexane (0.5
mL) was injected to the solution under stirring when temperature went below 90 'C. The
final product was washed with ethanol and separated by centrifugation (10,000 rpm for
15 min), and then dispersed in ethanol.
4.2.4 Bio CO/Ni nanoparticles nanocomposite formation
Bio CO/Ni nanoparticles nanocomposites were obtained by binding the preformed metal
nanoparticles on the surface of cobalt oxide nanowires. The bio CO nanowire solution (100 mL)
and Ni nanoparticles dispersion (in ethanol, or ethanol/water, 1.8 mmol) was mixed overnight.
93
The weight percent of Ni in nanocomposites was calculated as 1.76 wt %. The final product was
washed with water and collected with centrifugation.
4.2.5 Characterizations of biotemplated MnCo3 ..,0
Biotemplated MnCo 3.,0
4
(x=O, 1, 2) nanowires
4
(x=0, 1, 2) nanowires were imaged with high-resolution
transmission electron microscopy (HRTEM, 2010 FEG, JEOL) under an accelerating voltage of
200 kV. X-Ray Diffraction (PANanalytical Multipurpose Diffractometer, Cu Kca radiation)
patterns of bio MCO nanowires were collected with 0.41 '/min scan speeds under the following
settings: 2' of anti-scatter slit, 6 mm of irradiated length of automatic mode and 0.04 rad of soller
slit. The surface areas of bio-MCO nanowires were measured with Brunauer-Emmett-Teller
(BET) method (Micromeritics, ASAP 2020) after one hour of degassing at 50 'C.
4.2.6 Electrochemical tests
The final products of biotemplated MnCo 3 .,0
4
(x=0, 1, 2) and bio CO/Ni nanoparticles
nanocomposites were lyophilized and further dried in a vacuum oven at 90 C overnight. The Li02electrodes were prepared with the same method described in chapter 3. The spinel oxide based
electrodes were made with Ketjan black (EC600JD, AkzoNobel), catalyst materials, LiTHionTM
dispersion (Ion Power, USA) with the mass ratio of 44 : 36 : 20 or 8 : 72 : 20. These three
components were mixed with 2-propanol using a bath sonicator overnight. This mixture was tape
casted on the separator (Celgard, PP2075) and dried in a vacuum oven at 80*C for 2 hours. These
electrodes were punched into circle with diameters of 1.27 cm and the mass of each electrode was
about 0.1-0.3 mg/cm 2 . Before the electrochemical test, these electrodes were further dried in
vacuum oven at 80'C overnight and were soaked with the electrolyte in advance (0.1 M LiC1O 4
in DME, Novolyte) inside the Ar-filled glove box. Li-0
2 batteries
were assembled with metallic
Li foils (negative electrode), two layers of separators, additional electrolyte (100 [d), catalyst
94
electrodes and a current collector (316 stainless steel mesh) sequentially. After taking the cell
from Ar-filled glove box, the Li-0 2 battery cell was purged with oxygen (Airgas, UPC grade) and
closed at 1.08 atm. The cell was rested at least 2 hours before the electrochemical test. The
galvanostatic test was conducted at 0.4 A/ge with a Solartron Analytical 1470E potentiostat. In
cycling tests at 1 A/ge (100
mA/g+catalyst)
of current, the pressure of the Li-0
adjusted again to 1.08 atm after 16 cycles.
95
2
battery cell was
4.3 Results and discussion
Biotemplated MCO nanowires were synthesized by two-step reactions, decoration of
precursor metal ions along the M 13 virus and oxidation of these ions afterwards. First, the E3/E4
virus solution was incubated with a stoichiometric mixture of metal cation precursors, Co2+ and
Mn2+. The biotemplated MCO nanowires were formed along the M 13 virus after the hydrolysis
and condensation with the addition of ammonia solution or H20 2 while adjusting pH from 8 to 10.
The bio MCO nanowires were characterized by High-resolution transmission electron microscopy
(HRTEM) (Fig. 4.2.A-D). We observed the particle shape growth of Co 3 O 4 /Co(OH) 2 (designated
as CO) after the oxidation of Co 2 + stained virus (Fig. 4.2.A). While there was no significant
crystalline peak observed for bio CO nanowires synthesized at room temperature, they changed to
crystalline phase of bio Co 30 4 (Co 30
4
PDF no. 00-043-1003, cubic) nanowires after annealing at
400 *C for 10 minutes (Fig. 4.2.E). The annealing temperature was adjusted to be long enough
for further crystallization but not too long to destroy nanowires morphology. Furthermore, the
BET surface area of biotemplated C030
4
nanowires increased from 59 to 90.2 m2 /g after
annealing. This increase of surface area might be originated from the roughened surface of bio
Co 30
4
nanowires after heat treatment as can be observed by TEM images (Fig. 4.2.A,B). The
surface roughness of bio MCO increased as Mn ion involved during the nanowire nucleation.
Incorporation of Mn during the synthesis developed nanosheet structures along the biotemplate
(Fig. 4.2.C, D), resulting in the additional surface area of nanowires. While as synthesized bio
MnCo 3.,0
4
, (x
=
0, 1) nanowires were amorphous or poorly crystalline, CoMn 20 4 showed
perfect crystalline phase matching to the reference card (CoMn 2O 4 PDF no. 00-055-0685,
tetragonal) (Fig. 4.2E). The surface area of bio MnCo 204and bio CoMn2 O 4 was measured with
BET method, showing 104 and 95.6 m 2 g', respectively.
The Li-0
2
battery performance of bio CO and heat-treated bio C030
4
nanowires was
investigated with ether based electrolyte, 0.1 M LiClO 4 in DME. The specific capacity of bio CO
nanowires was improved by 30 % after thermal treatments of bio Co3O 4 nanowires, from 11,000
96
mAh/gc (6,050 mAh/gc+catalyst) to 14,340 mAh/gc (7,890 mAh/gc+cata
1 yst) (Fig. 4.3.A). These Li-0
batteries were tested at the current density of 400 mA/ge (220
mA/gc+catalyst)
2
with the custom
designed cell having closed pure oxygen (Airgas, UPC grade) environment at I atm. To the best
of our knowledge, this is the highest specific capacity achieved under highest gravimetric current
density with Co 3 0 4 based Li-0 2 battery electrodes up to date. In addition to the improvement of
specific capacity, heat-treated bio C0 30 4 nanowires showed higher coulombic efficiency (91.5 %)
than as synthesized bio CO nanowires (83 %) within the relatively lower cut-off voltage windows
(2.2-4.15 V, vs Li/Li+) than other works. These improvements in electrochemical performance of
Li-0
2
battery after thermal treatment of bio Co 30
4
nanowires could be originated from the
increased surface area (from 59.9 to 90.2 m2 /g) of catalyst materials. High surface area electrodes
provide enough electrocatalytic reaction sites thus resulting in a higher capacity as well as a better
coulombic efficiency.
Here we further functionalized bio CO nanowires by hybridizing preformed Ni
nanoparticles on the surface of nanowires. The successful synthesis of Ni nanoparticles was
confirmed with HRTEM showing around 5 nm of their diameter and XRD, as can be seen from
Fig. 4.4. After the incorporation of Ni nanoparticles on bio CO nanowires, the specific capacity
of Li-0
2
battery was slightly improved to 11,830 mAh/gc (6,500
mAh/gc+catajyst
for bio Ni/CO
nanowires) and 14,830 mAh/gc (6,500 mAh/g.catayst for bio Ni/CO nanowires after heat
treatment). More interestingly, the charging profile of Ni composited electrode was different from
that of bio CO nanowires based electrodes. While a single step charging profile was observed for
bio CO nanowires electrodes, two flat voltage regions around 3.3 V and 3.9 V were observed for
bio Ni/CO nanowires electrodes during charging (Fig. 4.3.B). Since the amount of discharge
product for bio CO nanowires and bio Ni/CO nanowires was approximately similar, the different
charging profile might be resulted from the surface mediated electrochemical reaction not from
the different thickness of discharge products. In Fig. 4.3.A, the charging voltages after
decomposing 500 mAh/gc of discharge products were 3.34 V (for bio CO nanowires) and 3.31 V
97
(for heat treated bio Co 30
4
nanowires). We observed the decrease of charging voltages after 500
mAh/gc of Li 2O 2 decomposition for Ni composited bio CO nanowires electrodes, 3.18 V and for
heat treated bio Ni/CO nanowires, 3.24 V in Fig. 4.3.B. Therefore, these decreases of charging
potential after the incorporation of Ni nanoparticles in electrodes can suggest a better
electrocatalyst design for Li-0
2
battery electrodes.
The improved OER activity after incorporating Ni nanoparticles on bio CO nanowires
was more clearly observed when the same amount of discharge product was oxidized (Fig.
4.3.C). At the given thickness of Li 20
2
(8,000 mAh/gc corresponding to -2.5
nm of Li 2O 2 if it
formed homogeneous layer on catalyst electrode), heat-treated bio Ni/CO nanowires showed a
lower charging potential than bio CO nanowires, heat-treated bio Co 30
Ni/Co 30
4
4
nanowires, and bio
nanowires. Since the overall surface area of catalyst electrodes would be similar after
heat treatment or Ni nanoparticle decoration, the lowered charging profile of heat-treated bio
Ni/CO nanowires might be due to the improved surface conductivity with Ni nanoparticles
incorporation. The better OER activity after heat-treatments than as synthesized Ni/bio CO
nanocomposites could be originated from the improved contact between Ni nanoparticles and bio
CO nanowires with annealing. In addition, heat-treated Ni/bio CO nanowires showed a longer
cycle life maintained to 32 cycles than that of bare bio C0 30
The cycling performance of Li-0
mAh/gc (200
The
mAh/gc+catayst)
4
nanowires, 17 cycles (Fig. 4.3.D).
battery electrodes was tested with a fixed capacity of 2,000
at I A/ge (100 mA/ge).
electrochemical
composition (MnCo 3.0
2
4
performance
of biotemplated
spinel
, x=0, 1, 2) was investigated as Li-0
2
oxides with
different
battery electrodes. As the
morphology changes to urchin-like shape with the addition of Mn to bio CO nanowires, the
specific capacity of bio MnCo 2 0 4 and CoMn 20
4
nanowires was larger than that of bio CO
nanowires by 14-17 % (Fig. 4.5.A), which might be originated from the improved surface area of
bio MCO nanowires. Moreover, the charging profile of bio MCO nanowires evolved in two steps
while bio CO nanowires showed only a single step during charging. While bio CoMn 204
98
nanowires showed a larger sloppy region than bio MnCo 2O 4 nanowires during charging in the
first full cycle, both bio MCO nanowires showed similar charging behaviors when they were
charged after cutting the discharge capacity to 8,000 mAh/ge (Fig. 4.5.B). Although the charging
behavior of bio MnCo 2 0 4 and CoMn 20 4 nanowires was similar, bio MnCo 20
presented a longer cycle life to 16 cycles than bio CoMn 20
4
4
nanowires
nanowires which could be cycled
only 10 times with a fixed capacity of 2,000 mAh/g, (200 mAh/g+catalyst) at I A/ge (100 mA/ge)
(Fig. 4.5.C).
99
4.4 Conclusion
We formed a various compositional set of spinel oxides, MnxCo 3.xO
4
(x=0, 1, 2)
nanowires by using biomolecule, the M 13 virus. All of these three different cobalt manganese
oxides can be simply synthesized by two-step reaction and they shared the similar geometrical
scale around -50 nm of diameter, -1
[tm of length. We observed two different nanowire
morphology evolutions with each chemical component, the particle shape growth with cobalt and
the planar shape growth with manganese along the M 13 virus. These cobalt manganese spinel
oxides were applied to Li-0
2
battery cathodes to investigate their electrocatalytic behavior. The
modification of these nanowires with thermal treatments, Ni nanoparticles incorporations showed
improvements of Li-0
2
battery performances. This biologically formed nanowires suggest an
easy route to frame the selection criterion for high performance Li-0
100
2
battery cathode materials.
4.5 Figures and tables
0
0
0
0
0
C0304
000*
M13 virus
0
x= 2,3
0
MnCo 20 4
0 Oxygen
* Manganese
* Cobalt
CoMn 2 O4
Figure 4.1. M13 virus mediated synthesis of various Li-0 2 battery materials for Li-0
2
batteries. Through the interaction between transition metal ions (Co+, Mn+) and the major
surface protein of M13 virus (left side), here we synthesized three different compositions of
MnCo 3.,0
4
(x
=
0, 1, 2) nanowires to utilize them as Li-0
101
2
battery electrodes.
E Bio Co 0 NWs
Bio Co.O4 NWs after heat treatment
o
CO
3
.(00-043-1003)
-Bio
MnvCo, O, NWs
S,000231237)
Bio CoMn2qO NWs
ACOWn,0 (0"-55-M65)
20
30
40
50
60
70
2 Theta (degree)
Figure 4.2. HRTEM images of biotemplated MCO nanowires. The scale bars in A-D
correspond to 50 nm. (A) bio CO nanowires, (B) heat-treated (400 *C for 10 minutes) bio C0 30 4
nanowires, (C) bio MnCo 204nanowires and (D) bio CoMn 2O4 nanowires. (E) XRD patterns of
bio CO nanowires (green), heat-treated (400 *C for 10 minutes) bio C0 30 4 nanowires (violet), bio
MnCo 2O 4 nanowires (blue) and bio CoMn2 O4 nanowires (orange).
102
Specific capacity (mAh/gc)
A45
0
6,000
3,000
9,000
Specific capacity (mAh/gc)
12,000 15000
B
0
8,000
9000
12M0
15,000
45
40-
40
35-
35
3.31V
3.34 V$
P3
3000
3.24 V
M
3.0-
3.18 V
3.02: 5
2.5Bi
C030 4 NWs
-
BK C030 4 NWs after heat treatment
20-
0
2,0
--
2,000
4.000
6,000
8,00
Specific capacity (mAh/gc+catalyst)
-
Bo Ni.Co 3 0 4 Nws
Ba NiCo3 0 4 NWs after heal treatment
0
4.000
2000
6000
8.000
Specific capacity (mAh/gc+catalyst)
Specific capacty (mAh/gcI
C4 5
0
2.000
4000
6.000
8,000
I
D 2500
250
Electrodes with Ketjan 8 wt %
4,01
(/,
2000
-200
E 1500
150
0h
3.5
8
3
3.0 4
1000-
100 >
1o Cc 3 0 4 NWs
2.51
500.U
s
--
L
,o0
0
--
iA O
m
3 4 Nwls aftr h"I irii"ine
Ni co30 4 NWW after heat ieatmni
1.000
2.000
3.000
4.000
)
BiO Co 3O4 NWs after heat treatment
Ba Ni/Co 30 4 NWs after heat treatment
5
10
15
20
Cycle number
Specific capacity (mAhIgc+catalyst)
25
30
Figure 4.3. The electrochemical performance of bio MCO nanowires in Li-0
C) The first galvanostatic cycle of Li-0
2
2
-50
0
35
batteries. (A-
batteries tested with 0.1 M LiC104 in DME electrolytes
within a cut-off voltage 2.2-4.15 V at the current density of 400 mA/ge under I atm of
02.
The
discharge/charge profile of (A) bio CO nanowires (dashed) and heat-treated (400 *C for 10
minutes) bio C0 30
Ni/Co 30
4
4
nanowires (straight), (B) bio Ni/CO nanowires (dashed) and heat-treated bio
nanowires (straight). (C) Voltage profiles of Li-0
2
batteries tested with the fixed
discharge capacity (8,000 mAh/ge). (D) The discharge capacity (fixed with 2,000 mAh/ge;200
mAh/g+catalyst) against cycle number for bio Ni/CO nanowires (orange circle) and heat-treated bio
Ni/Co 30
4
nanowires (blue triangle) tested at 1 A/ge (100 mA/g+atalyst) under I atm of 02. The
electrodes were formed with 8 wt % of carbon and 72 wt % of catalyst materials.
103
B
--
Ni (00-004-0850)
~M5
-
Ni NPs
'
20
30
40
50
2 Theta
60
70
Figure 4.4. Characterizations of Ni NPs. (A) the HRTEM image and (B) the XRD pattern of Ni
NPs.
104
A
0
45
Specific capacity (mAhtg)
3,000
6.000 9,000 12,000 15,000
B
45=
0
Specific capacity (mAh/g.)
2000
4,000
6,000
8.000
4.0
3.5
3.5
3.0
3.0
2.5
Bio0Co
U
NWs
2.5-
Rio MnCo 0 NWs
-
Bi CoMn 0, NWs
2.0
0
2,000
4, )00
6,000
Specific capacit) (mAhIg,
)
C 2. 500
20
8,000
4--....
.....-
2200
NWs
Bio MnCo
Bia CoMn
O,NWs
O,NWs
1,000
2,0 DO
3,000
4,00
Specific capac
,
I
Electrodes with Ketjan 8 wt %
2, 000 -
-
Bio CoO
I
250
-200
..
0
E
500-
150
U:)
2.
000
100
"C
tF
1.
5O0
--
0
50
Rio MnCo,O nanowires
u
nZ
Bio CoMnO, nanowires
3
12
I0
15
18
Cycle number
Figure 4.5. The electrochemical performances of bio MnCo3 .0
4
(x=1, 2) nanowires in Li-
02 batteries. (A) The first galvanostatic cycle of bio CO (yellow), MnCo 2O 4 (straight pink) and
bio CoMn 20
4
(straight green) nanowires at 400 mA/&. (B) The Li-0
2
batteries voltage profiles of
bio MnCo 2O 4 nanowires (dashed pink) and bio CoMn 20 4 nanowires (dashed green) tested with
the fixed discharge capacity (8,000 mAh/ge). (C) The cycle life (fixed with 2,000 mAh/g; 200
mAh/g+caalyst) bio MnCo 2 0 4 nanowires (pink triangle) and bio CoMn 0
2
4
nanowires (green dot)
tested at 1 A/ge (100 mA/gcaalyst) under I atm of 02. The electrodes were formed with 8 wt % of
carbon and 72 wt % of catalyst materials.
105
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107
Chapter 5. Ongoing work: Probing graphene defects with
phage display
108
5.1
Introduction
Graphene
has showed its great potential with its excellent electrical',
quantum
mechanical2 and mechanical3' 4 properties. In particular, mass production of defect free graphene
sheets in large scale
(~M2)
is crucial in flexible display, solar panel and electronic device
fabrications.5 However, currently available methods to detect the graphene defect are limited to
scanning
techniques, such as Atomic force microscope
(AFM), 6 Transmission
electron
microscopy (TEM) 7 and Raman spectroscopy 8 . Thus, an easy and single-step toolkit to screen the
impurity of graphene needs to be developed to expand its application into industrial scale.
The material specific affinity of protein assembly can be used to detect the impurity of
products,9 for example, graphene defects. Here, a M 13 virus based graphene defect detector is
proposed by implementing the dual functionality in a single biomolecule. As each type of M13
virus coat protein can be separately designed with a different functionality, the detector and signal
producer can be equipped into p3 and p8 of M 13 virus (Fig. 5.1). By selecting a specific peptide
sequence that favorably binds to graphene defects from M13 virus p3 library, this clone can be
used to detect nanoscale defect on one layer of graphene sheet. Since the perfect graphene sheet
exhibits stronger hydrophobicity than defect region (e.g. -COOH, -OH), we expect the interaction
mechanism between graphene defect and peptide sequence can be easily used to differentiate the
defect region. In addition, once the virus attached to the imperfect carbon bonds, the position of
virus can be easily detected by applying fluorescence molecules on the body of M13 virus. This
would help to detect the graphene defects with a single optical image of the products rather than
using time-consuming analysis techniques.
109
5.2
Experimental
5.2.1 Selecting the graphene flake-binding genetic sequence by bio-panning method
The graphene flake sample with an area of 0.5x0.5 cm 2 was prepared on a cupper foil.
This sample was held on the 24-well plate with double sticky tapes and washed with I ml of TBS
(IX) solution. The blocking buffer was added to completely cover (1 ml) the sample area and
incubated for 1 hr with gentle rocking at room temperature. After the incubation, the sample was
washed 6 times rapidly with TBST (0.1 % v/v, 300 [d). From the library stock solution (NEB,
Ph.D.TM -C7C library), 2x10" phage was diluted with 390 [d of TBST (0.1 % v/v) and incubated
with the graphene flake sample for 1 hr with gentle rocking at room temperature. Unbound phage
was discarded after the incubation and the sample was washed with I ml of TBST (0.1 % v/v,
from the second round, increase to 0.2 % v/v) with 10 times. The elution buffer (I ml of 0.2 M
Glycine-H Cl, pH 2.2, 1 mg/ml of BSA) was added for 20 min with gentle rocking at room
temperature and collected for neutralization with 150 [l of 1 M Tris-HCI (pH 9.1). For E.coli
elution, 100 [l of mid-log culture was incubated for 5 min and directly followed for titrations.
From each eluted phage solution (Glycine buffer and E.coli elution), 10 [d of virus was collected
and amplified with 20 ml scale. In each round, the number of phage in library was fixed to
2x10". After the amplification, the phage solution was titered using agar plates containing Xgal/isopropyl-#f-D- I -thiogalactopyranoside (IPTG)/tetracycline. The DNA from each plaque was
extracted using QlAprep* Miniprep Kit (Qiagen) and sequenced in the Biopolymers laboratory at
MIT.
110
5.3
Results and discussion
To select the genetic sequence having affinity towards graphene defects from Ph.D.TM -
C7C library, graphene flakes were grown on Cu foil by a low pressure chemical vapor deposition
(CVD) method (Fig. 5.2). The synthetic condition was adjusted to form graphene flakes rather
than the perfect graphene layer because the flake has a high concentration of graphene edges or
broken bonds. These flakes can be easily transferred to Si wafer so that we can disregard the
interaction between the protein assembly and substrate materials. These graphene flakes samples
with two different substrates (Cu, Si) will be applied alternatively for each round to minimize the
substrate-mediated binding.
The first round of bio-panning with C7C library was conducted against Cu-graphene
flakes. To collect the bound phages, the acid elution was first applied and the E.coli solution was
further added afterwards to harvest remaining phages. These phages were DNA sequenced by
selecting the random plaques after titrations. The sequence results of phages eluted by E.coli
solution and acid are included in Fig. 5.3. We observed the high frequency of Histidine (H),
which functioned as the hydrophobic-hydrophobic interaction moiety with carbon-based
materials,' 0 among the selected phages. The diversity of library was maintained after the first
round as can be seen from the various combinations of sequences in Fig. 5.3. On the second
round, the amplified library from the first round was added with the fixed number of phages.
Unbound phages were washed with more harsh conditions (TBST, 0.2 % v/v) for the second
round. However, the sequencing result after the second round of bio-panning converges into few
clones that dominate in the population. This can be due to the difference of phage growth speed
during the amplification after the selection. Thus, the amplification duration can be adjusted to
the point where the library diversity maintains.
111
5.4
Figures
M13 virus
p8: Signal
producer (Dye
conjugated)
p3: Graphene
defect detector
Figure 5.1. Scheme of M13 virus-based graphene defects detector. Ml13 virus based graphene
defects detector (left) with dual functionality (p 8 : signal producer, p 3 : graphene defect detector)
and the operation mechanism of this biosensor (right).
112
Figure 5.2. Scanning electron microscope (SEM) image of graphene flakes. The graphene
flakes were grown with Cu-mediated low pressure CVD method by Mr. Yong Cheol Shin. The
image credit goes to Mr. Shin.
113
1 st
Round
Gly
C
C
G
V
S
L
A
G
C
C
C
C
C
C
C
C
C
T
L
G
L
Q
K
R
T
F
T
K
M
A
V
P
R
E
P
A
Q
R
T
T
L
A
I
G
N
Q
P
L
S
G
N
K
T
S
G
D
N
A
E
A
F
I
p
A
Q
L
G
N
K
M
A
G
T
F
P
N
S
D
S
A
D
E
A
C
K
S
T
E
T
A
S
C
N
T
G
S
p
Y
E
C
E
R
F
N
Q
G
L
C
N
E
p
K
p
R
L
C
C
C
T
G
p
A
R
R
2"d Round
E.coli
Figure 5.3. p3 sequences of M13 virus clones selected from bio-panning against graphene
flakes. The sequencing result after the first and second round of bio-panning against graphene
flakes on Cu foil. The left column indicates the elution method. Each sequence contains two
Cysteines in the beginning and at the end that form the ring in p3.
114
5.5
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