Efficient Photoelectrochemical Water Oxidation over Hydrogen‐Reduced Nanoporous BiVO4 with Ni–Bi Electrocatalyst

Abstract

AbstractBiVO4 is one of the most promising candidates for photoanodes in solar water splitting. However, the poor charge‐separation yield in BiVO4 has limited its photochemical activity. Here, we overcome this limitation by constructing a nanoporous morphology that effectively inhibits bulk carrier recombination as well as undergoes controlled introduction of oxygen vacancies through hydrogenation. In comparison to pristine BiVO4, hydrogen‐treated BiVO4 (H‐BiVO4−x) exhibits a superior photocurrent and electron‐hole separation yield, owing to enhanced carrier density and conductivity. In addition, we adopt a layer of nickel–borate (Ni–Bi) complex on the H‐BiVO4−x surface as an oxygen evolution catalyst to improve the water oxidation kinetics. The Ni–Bi/H‐BiVO4−x photoanode results in a large cathodic shift (350 mV) in the onset potential for water oxidation at pH 9. Moreover, the photoanodes exhibit high performance in the low‐bias regime and achieve a maximum power point of 0.82 % (photon‐to‐current efficiency) for solar water oxidation at potentials as low as 0.79 V versus RHE with a photocurrent of 2.26 mA cm−2. We attribute these improved photoelectrochemical performances to the enhanced charge separation, higher carrier density, better conductivity of H‐BiVO4−x, and the role of Ni–Bi as a hole conductor, facilitating photogenerated electron mobilization.