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

Abstract

Abstract BiVO 4 is one of the most promising candidates for photoanodes in solar water splitting. However, the poor charge‐separation yield in BiVO 4 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 BiVO 4 , hydrogen‐treated BiVO 4 (H‐BiVO 4− 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–B i ) complex on the H‐BiVO 4− x surface as an oxygen evolution catalyst to improve the water oxidation kinetics. The Ni–B i /H‐BiVO 4− 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‐BiVO 4− x , and the role of Ni–B i as a hole conductor, facilitating photogenerated electron mobilization.