Simulations of Nanomaterials: Carbon
Nanotubes, Graphene and Gold
Nanoclusters
Iván Cabria, María J. López, Luis M. Molina,
Nicolás A. Cordero, P. A. Marcos, A. Mañanes and
Julio A. Alonso
Dpto. de Física Teórica, Universidad de Valladolid,
47005 Valladolid, Spain
Group of Physics of Nanostructures
http://www.nanostructures.uva.es/indexenglidh.hyml
Group of Physics of Nanostructrures
University of Valladolid
J. A. Alonso
I. Cabria
M. J. López
L. M. Molina
Group of Simulations of Materials
University of Burgos
N. A. Cordero
P. A. Marcos
University of Cantabria
A. Mañanes
Universidad de Valladolid
Other collaborators
UAM Mexico: J. Arellano
Univ. Guanajuato Mexico: J. Robles
DIPC San Sebastian: A. Rubio
University of Pennsylvania: L.A. Girifalco,
K. Mahadevan, J. Fischer
Instituto del Carbón, CSIC, Oviedo:
Nacho Paredes, Juan M. Tascón
Argonne National Laboratory: Stefan Vajda
Main Lines of Research
Related with Nanomaterials and Nanotechnology
Can be focused on Materials and/or on Technological
Applications
Simulations of Properties and Dynamics of
Nanomaterials
Main Lines of Research
- Carbon Nanotubes
- Hydrogen Storage for Hydrogen Cars
- New Catalysts made of Gold
Nanoclusters
The discovery of Carbon nanotubes
After the C60 fullerene discovered in 1985
CNTs are the new breakthrough of carbon, discovered in 1991
Multiwall Carbon Nanotubes
(MWCNTs) were produced
by the arc discharge
technique
• Nested cylinders of Carbon
• 4-30 nm in diameter
3 nm
• 1 µm in length
Iijima, Nature 354, 56 (1991)
Ebbesen, Ajayan, Nature 358, 220 (1992)
Single Wall Carbon nanotubes
produced by the arc discharge technique with a
metal catalyst
cobalt catalyst
Bethune et al, Nature 363, 605 (1993)
iron catalyst
Iijima, Ichihashi, Nature 363, 603 (1993)
Geometrical Construction of SWCNTs
by wrapping around a graphene strip in a seamless cylinder
Chiral vector: Ch
Ch  n a1  m a2
(n,m) uniquely specifies all
posssible tube structures
Translation vector: T
Chiral angle: θ
θ = angle ( a1 , Ch )
Hamada et al, Phys Rev Lett 68, 1579 (1992)
Saito et al, Appl Phys Lett 60, 2204 (1992)
Types of CNTs structures
(5,5) Armchair, θ = 30º
(9,0) Zigzag, θ = 0º
(10,5) Chiral, 0º <θ< 30º
Hamada et al, Phys Rev Lett 68, 1579 (1992)
Saito et al, Appl Phys Lett 60, 2204 (1992)
Conducting character of SWCNTs
n = m  metallic
n - m = 3q  small gap
semiconductor
n – m ≠ 3q  moderate gap
semiconductor
Hamada et al, Phys Rev Lett 68, 1579 (1992)
Saito et al, Appl Phys Lett 60, 2204 (1992)
Carbon Nanotubes
Application of finite nanotubes to
Spintronic: electrical current with spin
polarization
Separation of nanotubes by its
metallic or semiconducting character
Microelectronics needs nanotubes of the same electronic character
Surfactants and nitronium molecular ions are used to attack selectively
and separate the nanotubes in the bundles
Carbon Nanotubes
Chemical sensors based on nanotubes very sensitive to
different gases
Funcionalization of nanotubes with molecules and/or clusters
Changes of the electrical conductivity of nanotubes due to extremely small
amounts of gases adsorbed on the surface of the nanotubes
Applications: environmental, medical, clean room control, etc.
Hydrogen Economy
- Hydrogen could be an alternative to conventional fossil-fuel
sources of energy
- Hydrogen is abundant and non contaminant
- Hydrogen is NOT a primary source of energy but an energy
vector
Three Aspects of an Economy based on
Hydrogen
 Production
 Hydrogen Storage
 Use: Fuel Cell
Hydrogen Economy
Production
 Natural Gas: 50 %
Production, most common
 Water electrolysis: for
cheap electricity
 Biomass, pirolysis,
photobiological processes
(bacteria)
Electrolysis of water
Hydrogen Economy
Production: Prices
1 Kg
Hydrogen
Natural gas
reforming 2003
5.0 USD Untaxed
1 Kg
Hydrogen
Electrolitic H,
3.3 USD Untaxed
4.02 L
Gasoline
Spain, July 2010
6.1 USD Taxed taxes=49 %
4.02 L
Gasoline
USA, September
2010
2.9 USD Taxed taxes=18 %
May 2006
1 Kg hydrogen contains the same energy than 4.02 L of gasoline
1 Kg hydrogen occupies 1/0.000089 = 11200 L at normal conditions
http://www.nanostructures.uva.es/~cabria/hydrogeneconomyandothers.html
Hydrogen Economy
Storage
 Onboard (cars) and in situ (buildings)
storage
 Storage methods
Liquid Hydrogen
Compressed Hydrogen
Stored in a solid
Hydrogen Fuel Cell Cars
Hydrogen Car: Electric Car powered by a Hydrogen Fuel
Cell instead of batteries
Fuel Cell Electric Vehicle in California
Hydrogen Fuel Cell Cars
Technological goal: Hydrogen cars equivalent to Fossil Fuel
Cars
Bottlenecks: fuel cell efficiency and onboard storage
Onboard hydrogen storage targets for 2010:
6 weight % of hydrogen
0.045 Kg H2/L
at room temperature and
moderate pressures, 40-100 atms
Hydrogen Fuel Cell Cars
Types of Hydrogen Storage: gas, liquid and solid
Mechanisms of Solid Hydrogen Storage:
physisorption, chemisorption and chemical reactions
Materials that store by physisorption: nanotubes, nanoporous
carbons (CDCs, ACs, GNFs, etc.), porous materials such as
MOFs, COFs, porous polymers, etc., and metal-doped
carbons
Hydrogen Fuel Cell Cars
Electric Cars powered by Hydrogen Fuel
Cells instead of batteries
Compressed hydrogen
100-200 km of autonomy vs 500 km of gasoline cars
About 2.5 times more expensive than gasoline cars
Hydrogen at 350 bars in Japan, at 700 bars in Europe
No room for luggage: Tank with 110 H2 liters at 350 bars
110 CV vs 200-300 CV of gasoline
Norway, Fall 2006: First European public hydrogen station
Hydrogen Onboard Storage
One of the main Hydrogen economy challenges
Hydrogen Storage is one of the bottlenecks of present
technology of Hydrogen Fuel Cell Cars
Hydrogen has a high energy density by mass: 120 MJ/kg
(LHV) 140 MJ/kg (HHV) (gasoline: 44 MJ/kg)
But it has a low energy density by volume: 1.5 MJ/L at
150 bars, 0.01 MJ/L at 1 atm and 300 K, 8.4 MJ/L liquid
H2 (gasoline: 35 MJ/L)
LHV: Lower Heating Value; HHV: Higher Heating Value
Hydrogen Onboard Storage
One of the main Hydrogen economy challenges
A Storage Capacity of 5-10 kg of hydrogen is needed to
provide a range of 480 km for a electric-fuel cell car
60 L of gasoline for 480 km
1 kg H2 = 4.02 L gasoline
15 kg H2
15 kg H2
Fuel cell eficiency = 2-3  5-10 kg H2
Hydrogen Onboard Storage
DOE targets for 2010
 Specific energy: 7.2 MJ/kg
 Gravimetric capacity: 7.2/120 kg H2/kg =
0.06 kg H2/kg = 6 weight %
 Energy density: 5.4 MJ/L
 Volumetric capacity: 5.4/120 kg H2/L = 0.045 kg H2/L
Reversible Hydrogen Storage
Note: energy density of hydrogen is 120 MJ/kg for DOE, the LHV value
Hydrogen Onboard Storage
DOE targets for 2010
 Operating temperature: 250 – 320 K
 Delivery pressure: 2.5 bars
 Refueling rate: 1.5 Kg/min or 7 minutes
Hydrogen Onboard Storage
Reference gasoline car
 Mass fuel storage system: 74 Kg
 Volume fuel storage system: 107 L
 75 L of gasoline or 55.4 Kg of gasoline
 600 Km of autonomy
 75 L gasoline × 35 MJ/L gasoline = 2625 MJ
 Specific energy: 2625/74 + Fuel cell eficiency=2-5 7.2 MJ/kg
 Energy density: 2625/107 + Fuel cell eficiency=2-5 5.4 MJ/L
Hydrogen Onboard Storage
?
No current hydrogen storage technology meets the targets
Materials for Hydrogen Onboard Storage
GOAL: Find new materials that fulfill the DOE
targets for onboard hydrogen storage
Light Materials
Porous Materials
Binding energy of H2 to surface: 0.3-0.4 eV/molecule
- Graphene Slitpores, Nanoporous Carbons, Carbide-Derived
Carbons
- Li doped Graphene Slitpores
- Pd doped Graphene Slitpores
- Molecular Organic Frameworks, MOFs
Simulation of Slitpores
Slitpore of width D: two parallel flat layers at distance D
Van der Waals
interaction of a
molecule with
the surface
Single Layer
Slitpore
Relationship between pore size and shape and storage capacity
Models for different pore shapes
Two parallel graphene layers:
slitpore
CNTs:
cylidrical pores
Fullerenes:
spherical pores
Storage capacities from the slitpore model
Y. Gogotsi, et al. JACS 127, 16006 (2005)
Jordá-Beneyto,et al. Carbon 45,293 (2007)
The measured storage capacities can be mimicked through
slitpores of a single size or a combination of sizes
Pure Graphene Slitpores
- Optimal Slitpore Width: around 6 Å
- Volumetric and gravimetric goals ARE
REACHED above 10 MPa at 300 K
- Volumetric and gravimetric goals are reached
at moderate pressures at 77 K and for slitpore
widths larger than 5.5 Å
Concavity and Li doping
electronic density
redistribution
H2
= dark +2, white -2
10- 4 e/au3
Eb = 190-200 meV
Li
= green:+1, yellow -1,
Li
10- 3 e/au3
H2
Eb = 310-330 meV
Metal impurities increase binding energy and hydrogen storage
Near Li inside: 0.30 eV/molecule!!
JCP 128, 144704 (2008) and JCP 123, 204721 (2003)
A binding energy of 0.3-0.4 eV/H2 molecule is required for reversible
uptake and release at room T Li et al., JCP 119, 2376-2385 (2003)
Burgos, November 6th 2009, Project Meeting
Interaction of H2 with Pd doped Graphene
molecular adsorption
Metal Organic Frameworks (MOFs)
MOFs: New family of highly porous, crystalline materials
 inorganic metal oxide cluster + organic linker
High Specific Surface Area,
SSA = 2000 – 4700 m 2 /g
High porosity volume = 80%
High Specific Pore Volume = 1 cm 3 /g
 Promise for hydrogen storage:
• tunable pore size: changing the linker
• tunable functionality: changing the metal
Yaghi & coworkers, Nature 402 276 (1999)
MOF-5 structure
crystalline lattice: fcc
forms cubes:
corners: OZn 4 clusters
edges: BDC organic linkers
Lattice parameter = 25.65 Å
Porosity: two types of pores of
15 Å and 12 Å
MOF-5 cube
red: Zn
blue: O
gray: C
white: H
MOF-5 adsorption sites
Direct determination of the adsorption sites using inelastic neutron diffraction:
• Yaghi & coworkers, Science 300, 1127 (2003)
2 sites: one associated with the Zn and one with the BDC linker
• Yildirim & Hartman, Phys. Rev. Lett. (2005)
2 more sites are identified around the Zn-oxide cluster
Theoretical investigation find three main adsorption sites:
 CUP between three Ocore-Zn-O-C-O-Zn hexagons
 O 3 plane above Zn
 Benzene
Adsorption around the Zn-oxide cluster should be responsible for the high
storage capacity of MOFs
Comparison of MOFs with other nanoporous materials
MOFs perform better than Activated Carbons
and Carbide Derived Carbons at moderate
pressures
AC from Linares, CDC from Gogotsi, MOF from Yaghi
New Catalysts made of Gold Nanoclusters
Gold is noble metal, chemically inactive
But small clusters and nanostructures of gold have catalytic
properties
They are very efficient for different chemical reactions of
industrial interest
GOAL: Design new catalysts made of gold
nanoparticles for each specific chemical reaction
New Catalysts made of Gold Nanoclusters
We have shown the
selective oxidation
of propene to form
propylene oxide,
used in the
production of
polyurethane
Model for Aun/Al2O3
Clusters are supported on different
surfaces and environments and
these change their catalytic
properties
Perspectives
Bimetallic Au-Ag alloy nanoparticles
1ML of Ag1.83O on top of Au(111) corresponds to the situation of
a bimetallic alloy with high Au concentration.
Parallel MD Algorithm applied
to Economic Organization of Recycling
- European Directive February 2003: take-back
and treatment (recycling) of 4 kg of electronic
waste per inhabitant and year
- Organization of the take-back
- Optimization of take-back costs
- Molecular dynamics algorithm applied to this
economic problem
Parallel MD Algorithm applied
to Economic Organization of Recycling
Interest of Research
The results of our research are
useful for new technologies and
materials related to important
activity sectors of our region
such as automotive and clean
energies
Acknowledgments
- Ministerio de Educación y Ciencia de España y FSE, Programa
“Ramón y Cajal”, http://www.mec.es/ciencia/jsp/plantilla.jsp?area=cajal&id=11
- Ministerio de Educación y Ciencia de España: Programa Nacional de
Investigación. Planes Nacionales I+D/I+D+I, MAT2005-06544-C0301 and MAT2008-06483-C02-01
- Junta de Castilla y León, Programa Gral. de Apoyo a Proyectos de
Investigación, VA039A05, VA017A08 and GR23
Thanks for your attention