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

Applications of single-phase TiO 2 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) TiO 2 nanowire arrays (NWAs) (ZnO/TiO 2 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 TiO 2 NWAs and the holes to be transferred from TiO 2 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/TiO 2 2D/1D NS-NWA photoanode exhibits remarkable enhancement for hydrogen generation in a neutral electrolyte solution. The H 2 generation rate of the ZnO/TiO 2 2D/1D NS-NWA photoanode is 3-fold that of the bare TiO 2 NWA photoanode. Moreover, the ZnO/TiO 2 2D/1D NS-NWA photoanode shows excellent photostability after irradiation with light for 5 h. Applications of single-phase TiO 2 and ZnO in the field of photoelectrochemical (PEC) solar hydrogen generation are limited by their high recombination rate of photogenerated charge carriers.