Porous CuBi2O4 photocathodes with rationally engineered morphology and composition towards high-efficiency photoelectrochemical performance

CuBi2O4 with a suitable optical bandgap and positive onset potential is a promising photocathode material for solar hydrogen evolution, while fine control of the morphology and chemical composition (Cu/Bi ratio) is currently still highly desirable for pursuing its high photoelectrochemical performance. Here, we demonstrate the facile synthesis of high-quality nanoporous CuBi2O4 films through spin coating with a vividly controlled morphology and Cu/Bi composition. Through systematic analysis of energy bands, we found that the electronic structure of CuBi2O4 was much sensitive to the variation of the Cu/Bi ratio, which could result in different photoelectrochemical performances. The nanoporous CuBi2O4 films with enhanced light absorption and a shortened carrier diffusion pathway exhibited a high photocurrent density of up to 2.45 mA cm(-2) at 0.6 V vs. the reversible hydrogen electrode with H2O2 as a sacrificial agent. By further optimizing the chemical compositions, the photocurrent density of the film with a Cu/Bi ratio of 0.55 could increase to 2.66 mA cm(-2), which is among the top recorded values of CuBi2O4 based photocathodes. This work reveals the significance of rational control of the morphology and chemical composition for the development of highly efficient CuBi2O4 photoelectrodes.