Comparison of Forward and Reverse Reactions in Hydrogen Generation between GaN, InGaN, Nanocrystalline TiO2 and Pt Electrodes during Water Electrolysis

The electron transport between n-, p-GaN, and p-In0.12Ga0.88N electrodes and electrolyte Solution is studied by cyclic voltammetry under dark conditions, and compared with that between Pt and nanocrystalline TiO2/Ti electrodes. Both forward and reverse reactions of 2H(+) + 2e(-) = H-2 occur for Pt and TiO2/Ti electrodes. In contrast. in n-, p-GaN and p-In0.12Ga0.88N electrodes, only the forward reaction of 2H(+) + 2e(-) -> H-2 occurs and no reverse reaction is observed. These results are consistent with the finding that the conduction band-edge potentials of n-, p-GaN, and p-In0.12Ga0.88N are higher than the reduction potential of H+(aq) in electrolyte, determined by flat-band potential measurement. These differences in potential work as,in energy barrier for the reverse electron transfer from H-2 molecules to electrodes. These results also support the experimental results of spontaneous H-2 generation caused by the band-gap excitation of p-GaN and p-In0.12Ga0.88N electrodes without applying bias voltage. [DOI: 10.1143/JJAP.47.8793]