Synthesis of Iron Oxides nanorods
for water splitting application
Cebo. Ndlangamandla
iThemba LABS/ UniZulu
Energy Postgraduate Conference 2013
OUTLINE
• Introduction
• What has been done
• Why Iron Oxide?
• Experimental Approach
• Results Discussion
• Conclusion
INTRODUCTION
Energy Crisis: The world’s economy depend on fossil fuel and
countries without fossil fuel depend to those with it.
Very Expensive so renewable Energy (cheap) is a need.
Non-Renewable Resources for the Production of Energy are limited.
Global warming: is due to the continuous emission of green house
gases. so environmental friendly energy production systems are
needed. The Fossil fuel need to be substituted
Nanosystems for water splitting
Photo catalysis of water first reported by Honda and co-worker in 1970
and now has received interest since it offers a renewable nonpolluting
approach of hydrogen production. US DEO’s target for photo
electrochemical hydrogen production for solar hydrogen conversion
efficiency is (8% by 2010 and 10% by 2015).
Solar Hydrogen at Tungsten Trioxide, Vaysseries et al (2001)
Solar Hydrogen at Titanium Dioxide, Honda et al (1970)
Solar Hydrogen at nano-composite semiconductors, Yoshihiro et al
(2006)
Hydrogen System nanodevices, Vaysseries et al (2005)
Hydrogen System on ZnO, Levey-Clement et al (2003)
In all systems, the efficiency is still less than 6%
Principle of water splitting
Potentiostat
Ag/AgCL reference
electrode
Pt Counter
electrode
e-
e-
H2O
h+
300W Xe-Lamp or Solar
Simulator
H2
O2
Photoelectrode
M. Gratzel et al, ChemSusChem (2011)
Iron Oxide
Iron Oxide is a commonly-found material with band gap well-suited for the
direct solar water splitting of water but its performance has been severely
limited by opto-electronic properties. This material is promising because of
Photo Oxidation of water for hydrogen production, transparent electronics
applications.
Promise
Band gaps ~ 2.2 eV (it absorb up to
40% of solar light).
Abundant and inexpensive
High Stability in electrolytes
Thermodynamically stable.
PEC increase
Growth of crystalline Oxide
Direct growth along the
preferred electron conduction
paths (orientation)
High surface area material
Challenges
Carrier transport
Valence Band Edge
Water Oxidation Kinetics
Low optical absorption
Shift of Band Position
Quantum size effect
Transition metal doping
E/eV
-1
-4
0 H2/H+
-5
1
-6
2.2 eV
3.0 eV
2.8 eV
H2O/O2
3.2 eV
2
-7
Fe2O3
-8
3
TiO2
rutile
WO3
ZnO
BACK CONTACT IN DEFERENT MORPHOLOGY
SUN
e
e
e
e
EXPERIMENTAL APPROACH
ACG uses simple equipments, low temperature
deposition and the reaction is less hazardous,
Template-less, Surfactant-free and there is no need to
use the metal catalysts.
The size, shape and the orientation of the
nanostructure can be easily being tailored. The
coverage and the growth of the nanostructures on the
substrate can be monitored.
An aqueous solution of FeCl3
and NaNO3 is used and
parameters such as Time, pH can be controlled. 95oC was
used for deposition.
Synthesis (Aqueous Chemical growth)
Vaysseries et al (2001)
SEM images of doped and undoped Fe2O3 nanorods grown onto
FTO.
Pure
0.006
g
0.01
8g
0.030
g
(214)
(300)
(024)
(122)
intensity (a.u)
(012)
(113)
(116)
(110)
(104)
X-RAY POWDER DIFFRACTION (XRD).
A
B
C
D
20
30
40
2
50
60
70
Hematite has a trigonal/rhombohedra structure with approximately hexagonal close-packed array
of oxygen. Fe3+ ions occupy two thirds of octahedral sites between oxygen’s each FeO6 octahedron
shares a face with another in the layer above or below. Iron atoms lie on planes spaced
approximately one third and two-thirds the distance between oxygen layers. Belong to the space
group R-3C.
Vayssieres et al, Adv. Mater.,Vol 17, 2320-2323
RAMAN MEASUREMENTS
Raman Study on Hematite samples
modes
Beattie et al
1970 (cm-1)
Massey et al
1990 (cm-1)
Shim et al
2001 (cm1)
A1g(1)
226
228
224
219
A1g(1)
245
246
243
243
A1g(1)
293
294
290
293
A1g(1)
298
300
297
388
A1g(1)
413
412
408
408
A1g(2)
500
496
496
496
A1g(1)
612
614
609
608
659
658
1316
1312
Eu
2Eu
1320
This Study
(cm-1)
Optical measurements of Fe2O3 thin film deposited on FTO.
1.2m
pure
0.03
0.018
0.006
hv
2
800.0µ
400.0µ
0.0
1.5
2.0
2.5
Eg (eV)
3.0
CONCLUSION
Randomly perpendicular oriented nanorods were
obtained by adjusting the solution pH. This
orientation is preferred to avoid recombination.
Spherical may not provide a good electrical
pathway for the photo-generated electron to
travel to the FTO back contact.
The band gap of hematite can be tailored by growth
parameters such doping.