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

BiVO4 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-B-i) 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 mAcm(-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.