Understanding the Roles of NiO_x in Enhancing the Photoelectrochemical Performance of BiVO₄ Photoanodes for Solar Water Splitting

Solar water oxidation is considered as a promising method for efficient utilization of solar energy and bismuth vanadate (BiVO₄) is a potential photoanode. Catalyst loading on BiVO₄ is often used to tackle the limitations of charge recombination and sluggish kinetics. In this study, amorphous nickel oxide (NiO_x) is loaded onto Mo-doped BiVO₄ by photochemical metal–organic deposition method. The resulting NiO_x/Mo:BiVO₄ photoanodes demonstrate a two-fold improvement in photocurrent density (2.44 mA cm⁻²) at 1.23 V versus reversible hydrogen electrode (RHE) compared with the uncatalyzed samples. After NiO_x modification the charge-separation and charge-transfer efficiencies improve significantly across the entire potential range. It is further elucidated by open-circuit photovoltage (OCP), time-resolved-microwave conductivity (TRMC), and rapid-scan voltammetry (RSV) measurements that NiO_x modification induces larger band bending and promotes efficient charge transfer on the surface of BiVO₄. This work provides insight into designing BiVO₄-catalyst assemblies by using a simple surface-modification route for efficient solar water oxidation.