Novel Nanostructured Photocatalysts for Hydrogen Production by Solar Light Driven Water Splitting

Aniruddh Mukherji (2011). Novel Nanostructured Photocatalysts for Hydrogen Production by Solar Light Driven Water Splitting PhD Thesis, School of Chemical Engineering, The University of Queensland.

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Author Aniruddh Mukherji
Thesis Title Novel Nanostructured Photocatalysts for Hydrogen Production by Solar Light Driven Water Splitting
School, Centre or Institute School of Chemical Engineering
Institution The University of Queensland
Publication date 2011-02
Thesis type PhD Thesis
Supervisor A. Prof. Lianzhou Wang
Prof. Max Lu
Total pages 202
Total colour pages 48
Total black and white pages 154
Subjects 03 Chemical Sciences
Abstract/Summary Since the first energy crisis in the early 1970s, much research has been devoted to the development of efficient systems that would enable the absorption and conversion of solar light into useful chemical energy sources. Hydrogen generated from renewable sources of energy has the potential to replace fossil fuels in the future, whereas renewable hydrogen production is not popular yet because the cost is still high. Since the pioneering work of Fujishima and Honda on photoelectrochemical water splitting for Hydrogen generation, a lot of research has been devoted to photocatalyst research. Hydrogen can be produced from the splitting of water into Hydrogen and Oxygen using the energy of light. This process of photocatalysis or artificial photosynthesis has been considered as one of the ultimate solutions in solving the world’s energy concerns. This thesis investigates the use of layered perovskite type materials as photocatalysts for visible light driven water splitting. This treatise focuses on the synthesis and characterization of photocatalysts which are suitable for production of hydrogen from solar light irradiation in photoreactor. Two major shortcomings in the photocatalytic water splitting process were identified from the literature review of the extensive work that was done in the field. The first issue was that of lack of visible light absorption in most photocatalysts. This was tackled in the earlier chapters of this work (namely 3,4 and 5). Transition metal oxide photocatalysts with perovskite structures typically tantalum oxides which were anion doped and visible light absorption and visible light activity was achieved. A detailed analysis of nitrogen species in particular was carried. Extensive characterization including UV Vis spectroscopy, XPS, SEM, TEM, XRD, were used to analyse these materials. Theoretical calculations and modelling namely DOS and DFT were used to understand the enhanced hydrogen production activity of these novel nitrogen doped tantalum oxides. These studies indicated that the success and the extent of anion doping relied on the overall crystal structure of the photocatalyst and metal oxides with intergallery spacings or tunnelled structures showed homogenous nitrogen doping which translated into higher visible light activity. The efficiencies of the doped species in simulated sunlight were recorded to be higher (upto doubling of efficiencies in some cases) than their undoped analogues. The second drawback in the photocatalytic water splitting process was identified to be the high rate of charge carrier recombination. This issue was addressed by the novel use of conductive carbon scaffolds loaded with co-catalysts (Pt) in conjunction with the anion doped visible light active photocatalyst material. Graphene and multi-walled carbon nanotubes (MWNT) were used as typical conductive carbon scaffolds with nitrogen doped Sr2Ta2O7. It was demonstrated that the use of these scaffolds did demonstrate better activity because it reduced the rate of charge carrier recombination by acting as an electron highway. Charge transfer characteristics were studied and the electron transfer scheme was shown through characterization methods including UV-Vis spectroscopy, FTIR and XPS. However the loading amounts of these carbon scaffolds in the photocatalyst composites was an important criterion since there was a threshold limit beyond which the effect of loading these conductive carbon species was detrimental. This was attributed to the fact that the carbon materials started absorbing more light beyond a certain threshold loading limit which resulted in lesser light absorbance for the active photocatalyst and thus lowered the efficiency of the photocatalyst.
Keyword Water splitting, solar hydrogen, photocatalysis
Additional Notes 18, 30, 32, 37, 38, 39, 41, 44, 45, 47, 48, 55, 58, 88, 93, 98, 108, 109, 110, 111, 120, 124, 128, 140, 141, 142, 143,144, 145, 157, 159, 160, 161, 163, 165, 166, 168, 176, 177, 178, 179, 180, 181, 187, 188, 189, 190, 191

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Created: Thu, 02 Jun 2011, 17:37:43 EST by Mr Aniruddh Mukherji on behalf of Library - Information Access Service