Integration of an Electron Transport Layer and a p‐n Heterojunction in a ZnO photoanode for Photoelectrochemical Water Oxidation

Zinc oxide (ZnO) has received extensive attention in the field of photoelectrochemical water splitting (PEC-WS). However, ZnO has a narrow absorption range for visible light, easy recombination of photogenerated electrons and holes, and slow kinetics of surface water oxidation, limiting its further practical application. In this work, a FTO/TiO2/ZnO/NiO photoanode with a micro-nano structure is built with ZnO as nanosheet clusters, TiO2 as the electron transport layer, and NiO for forming p-n heterojunction between NiO and ZnO. This photoanode exhibits a photocurrent density of 1.91 mA/cm2 at 1.23 VRHE, which is three times that of the pure ZnO photoanode (0.65 mA/cm2). The detailed mechanism investigations demonstrate that the introduced TiO2 can reduce the interface defects between ZnO and FTO, and Ti doping to ZnO improves the conductivity, which simultaneously reduces the bottom surface and bulk charge recombination. The constructed p-n heterojunction further significantly increases the carrier transfer efficiency.