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

Abstract

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.