Mildly regulated intrinsic faradaic layer at the oxide/water interface for improved photoelectrochemical performance

Metal oxides are widely used in different fields, including photoelectrocatalysis, photocatalysis, dye-sensitized solar cells, photoinduced superhydrophilicity and so on. It is well-known that there are intrinsic hydrated layers on the surfaces of metal oxides in ambient air or electrolyte. Generally, interface layers between metal oxides and solution have significant effects on the performances in these applications. However, the exact roles of the intrinsic hydrated layers are still unclear. In this study, taking TiO2 and Fe2O3 as model materials, we propose a mild heat-treatment to increase the hydroxyl content in the hydrated surface layers of the oxides, which improves their photoelectrochemical performance remarkably. Moreover, we find that the heat-regulated hydrated layer plays a role as a hole transfer mediator between oxides and electrolyte, which can accelerate both interface charge collection and oxygen evolution reaction kinetics in acid solution. The new insights on the intrinsic hydrated interface layer on oxides can offer guidance not only in photoelectrocatalysis, but also the other applications mentioned above.