Microelectrode-based transient amperometry of O2 adsorption and desorption on a SrTiO3 photocatalyst excited under water

Abstract

Oxygen evolution at water–solid interfaces is a key reaction for sustainable energy production. Although some intermediate states have been detected in transient absorption spectroscopy, the O₂ evolution kinetics after the multi-step, four-electron oxidation of water remain unknown. In this study, transient amperometry with a microelectrode was applied to operando O₂ detection over Al-doped SrTiO₃ particles doubly loaded with RhCrO_x and CoO_y cocatalysts, an efficient photocatalyst for the overall water-splitting reaction. Electrochemical O₂ detection at intervals of 0.1 s unexpectedly indicated instantaneous O₂ adsorption and desorption in addition to steady, photocatalytic O₂ evolution on the photocatalyst modified under intense light irradiation. We hypothesized that electrons excited in the conduction band were transferred to O₂ in water thorough Ti cations neighboring an oxygen anion vacancy on the modified Al-doped SrTiO₃. The negatively charged O₂ was then bound to the Ti cations. It was neutralized and released when shaded through electron back-transfer to the conduction band. The hypothesized mechanism for O₂ adsorption and desorption was compared with the photoinduced O₂ desorption known to occur on anion vacancies of TiO₂(110). The microelectrode-based transient amperometry demonstrated in this paper will be applied to many other phenomena at liquid–solid interfaces.