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.