Photoelectrochemical studies of semiconducting photoanodes for hydrogen production via water dissociation

Abstract

Single crystals of various n-type semiconducting oxides have been investigated in order to better understand the relationship between their photoelectrochemical behavior and their optical properties. The single crystals used in this study were all n-type and consisted of: KTaO_3, BaTiO_3, SrTiO_3, and ZnO. Current density vs applied potential measurements indicated that all of the crystals exhibited diodic properties when in contact with a highly basic electrolyte (8.5 M NaOH at room temperature). The ZnO electrodes, however, exhibited some degradation after exposure to the operational cell environment. Results indicate that the spectral quantum yield of the crystals is related to the penetration depth of the incident light, meaning that electron–hole pairs formed far from the semiconductor–liquid junction are less likely to be collected than those formed near the surface (e.g. inside the depletion regions). Additionally the quantum yield was found to decrease with time. In the case of KTaO_3, the decay of the quantum yield was fit to a double exponential, which suggests that a complicated process is operative for this material. Ongoing research is directed toward understanding the influence of both temperature variations and the surface/electrolyte interface on the effects observed in the case of KTaO_3.