Investigations on the mixed oxide material TiO2-In2O3in regard to photoelectrolytic hydrogen production

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Abstract
A new photoelectrode system TiO2-In2O3 for photo-assisted electrolysis of water is described. The mixed oxide electrodes have been synthesised by solid-state sintering. These sintered electrode discs exhibited enhanced photovoltage and photocurrent of 0.78 V, 14 mA cm-2 whereas for TiO2 they were 0.8 V, 5 mA cm-2 respectively. X-ray diffraction and scanning electron microscopy investigations of the mixed oxide electrodes have been carried out to monitor their bulk and surface characteristics. EDAX analysis has been done to explore the chemical stoichiometry. These studies indicate microcrystalline-like surface characteristics and a cation doping ('In' up to approximately 2%) for the TiO2-In2O3 electrodes. The Mott-Schottky plots (1/c2-V) in 1 M NaOH solution and temperature variation of electronic conductivity (In sigma -1/T) for TiO2 as well as TiO2-In2O3 have been evaluated. These investigations suggest decrease in band gap and slight shift in the flat-band potential of the mixed oxide electrode compared with TiO2. The relative enhancement in hydrogen evolution under photo-assisted mode of electrolysis of TiO2 and mixed oxide (TiO2-In2O3) electrodes has been found to be from 1.2 to 1.8 ml h-1. The probable causes of the enhancements in photoactivity and hydrogen evolution have been suggested as: (i) 'In' cation doping in TiO2 lattice; (ii) increased surface area with In2O3 inclusion; (iii) decrease in the band gap and enhanced range of absorption of mixed oxide electrode; and (iv) catalytic activity of In2O3.