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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.
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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
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 INTRODUCTION
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%
Potentiostat Ag/AgCL reference electrode Pt Counter electrode e- e- H2O h+ 300W Xe-Lamp or Solar Simulator H2 O2 Photoelectrode Principle of water splitting
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. • Challenges • Carrier transport • Valence Band Edge • Water Oxidation Kinetics • Low optical absorption • 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
E/eV -1 0 1 2 3 -4 -5 -6 -7 -8 H2/H+ H2O/O2 2.2 eV 3.0 eV 2.8 eV 3.2 eV Fe2O3 TiO2 rutile ZnO WO3
SUN e e BACK CONTACT IN DEFERENT MORPHOLOGY 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 NaNO3is 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.
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 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 groupR-3C. Vayssieres et al, Adv. Mater.,Vol 17, 2320-2323
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.
