Photostable 3D heterojunction photoanode made of ZnO nanosheets coated onto TiO2 nanowire arrays for photoelectrochemical solar hydrogen generation

Applications of single-phase TiO2 and ZnO in the field of photoelectrochemical (PEC) solar hydrogen generation are limited by their high recombination rate of photogenerated charge carriers. Herein, a novel three-dimensional (3D) architecture comprising two-dimensional (2D) ZnO nanosheets (NSs) coated onto one-dimensional (1D) TiO2 nanowire arrays (NWAs) (ZnO/TiO2 2D/1D NSs-NWAs) is designed as an efficient photoelectrode for PEC solar hydrogen production. A type II band alignment established in the photoanode enables the electrons to be efficiently transported from ZnO NSs to TiO2 NWAs and the holes to be transferred from TiO2 NWAs to ZnO NSs, efficiently suppressing the recombination of electrons and holes. Additionally, the 3D architecture offers large areas for harvesting light energy, large interfacial contact areas with the electrolyte, and more pathways for rapid transfer and separation of charge carriers. The ZnO/TiO2 2D/1D NS-NWA photoanode exhibits remarkable enhancement for hydrogen generation in a neutral electrolyte solution. The H2 generation rate of the ZnO/TiO2 2D/1D NS-NWA photoanode is 3-fold that of the bare TiO2 NWA photoanode. Moreover, the ZnO/TiO2 2D/1D NS-NWA photoanode shows excellent photostability after irradiation with light for 5 h.