Enhancements on oxygen vacancy and light absorption of alkaline-etched BiVO₄ for photoelectrochemical water oxidation

Designing the favorable morphology with large surface area and abundant oxygen vacancies for BiVO4 can enhance its electron diffusion lengths and improve its photocatalytic ability toward photoelectrochemical water oxidation. The ex-situ alkaline etching process is reported to be facile for enhancing the light absorption and oxygen vacancy of BiVO4, but the systematic study of alkaline etching on the photocatalytic ability of BiVO4 is rare. In this study, alkaline-etched BiVO4 is firstly fabricated using a hydrothermal process with different durations as the photocatalyst of water oxidation. The BiVO4 etched by alkaline for longer durations presents rougher surface, more oxygen vacancies and higher light absorption. The larger carrier densities and the smaller charge-transfer resistances are also achieved for the alkaline etched BiVO4. The largest photocurrent density of 2.38 mA/cm2 is achieved at 1.23 V versus reversible hydrogen electrode in the Na2SO4 electrolyte for BiVO4 etched by alkaline for 45 min, while the pristine BiVO4 electrode only shows a photocurrent density of 0.59 mA/cm2. The photocurrent retention of 81% is also obtained for the alkaline etched BiVO4 electrode after continuous illumination for 6000 s. The results imply the feasibility of applying the alkaline etching process on refining the photoelectrochemical catalytic ability of BiVO4.