Oxide based earth abundant semiconductors and oxygen evolving catalysts for photoelectrochemical and PV driven water splitting

In the first part of this dissertation , photosplitting of water on the surface of semiconductor electrodes was investigated. Stability consideration favors metal oxide based semiconductors, hence titania and iron oxide were selected. High band gap for n-TiO2 and low charge career mobility for n-Fe2O3 hinders their utilization for efficient water splitting. To enhance the spectral response of these semiconductors, nonmetal impurities such as hydrogen and carbon were used as doping elements. Hydrogen modification of n-TiO2 was carried out by cathodic reduction of rutile thin film in basic electrolyte under dark conditions. Carbon modification of n-TiO2 and n-Fe2O3 was carried out by flame oxidation of a clean Ti and Fe substrates where the carbon source is the combustion products of CH4 and O2. Flame temperature and gas flow rates were optimized. Iron oxide suffers high recombination rate of the photogenerated electron-hole pair. To overcome this limitation, n-Fe2O3 nanowires were successfully synthesized by thermal oxidation of Fe metal sample under optimum oxidation temperature and time.;Inspired by the natural photosynthesis, in the second part, leaf-like amorphous silicon (a-Si) based photo-electrochemical cells (PECs) were synthesized for monolithic water splitting. The fundamental limitation of silicon, such as instability in electrolyte solution, was overcame by covering a-Si with TiO2 as a visible light transparent thin film. While a-Si provides the necessary photovoltage, TiO2 layer protects a-Si and provides the favorable valence band for water oxidation. These PECs were further protected by an ultra-thin film of Mn-oxide for long term operations.;In the third part, solar driven water electrolysis to generate H 2 was investigated. In this study we particularly investigated transition metal oxides such as porous Ni-Co3O4 and Ni-Co-mixed oxides as efficient oxygen evolving catalysts. The synthesis of the highly porous Ni-Co3O4 electrodes was carried out by mixing an appropriate amount of Ni and Co3O4 powders. Spray pyrolysis was used for the synthesis of transition metal mixed oxides on a conductive substrate, this was carried out by mixing different volume ratios of Ni(NO3)2 and Co(NO3)2 aqueous solutions. The activity of these transition metal oxides thin films was investigated for oxygen evolution during water electrolysis.