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

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.