Nanofabrication and characterization of ZnO nanorods and nanoplatellets

1
Synthesis of Iron Oxides nanorods for water
splitting application
Cebo. Ndlangamandla
iThemba LABS/ UniZulu
Energy Postgraduate Conference 2013
2
OUTLINE

• Introduction
• What has been done
• Why Iron Oxide?
• Experimental Approach
• Results Discussion
• Conclusion

3
INTRODUCTION

• Energy Crisis The worlds 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

4
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 DEOs 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

5
Principle of water splitting
6
M. Gratzel et al, ChemSusChem (2011)
7
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.

• Challenges
• Carrier transport
• Valence Band Edge
• Water Oxidation Kinetics
• Low optical absorption

• 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

• Shift of Band Position
• Quantum size effect
• Transition metal doping

8
(No Transcript)
9
BACK CONTACT IN DEFERENT MORPHOLOGY
10

• 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.

11
Synthesis (Aqueous Chemical growth)
Vaysseries et al (2001)
12
SEM images of doped and undoped Fe2O3 nanorods
grown onto FTO.
13
X-RAY POWDER DIFFRACTION (XRD).
Hematite has a trigonal/rhombohedra structure
with approximately hexagonal close-packed array
of oxygen. Fe3 ions occupy two thirds of
octahedral sites between oxygens 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
14
RAMAN MEASUREMENTS
Raman Study on Hematite samples Raman Study on Hematite samples Raman Study on Hematite samples
modes Beattie et al 1970 (cm-1) Massey et al 1990 (cm-1) Shim et al 2001 (cm-1) This Study (cm-1)
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
Eu 659 658
2Eu 1320 1316 1312
15
Optical measurements of Fe2O3 thin film deposited
on FTO.
16
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.