Photoelectrochemical (PEC) water splitting is a promising way to convert solar energy into hydrogen energy, but the efficiency is limited by severe charge recombination especially in photoanodes. Herein, to reduce the charge recombination in the bulk phase and at the surface of the BiVO4 photoanodes, oxygen vacancy introduction and cocatalyst loading were realized simultaneously by one-step photocathode deposition. A unique re-BiVO4/FeOOH photoanode was obtained by the photocathodic reduction of BiVO4 in an electrolyte containing Fe3+, where the oxygen vacancies were introduced during the reduction process and the deposition of the FeOOH cocatalyst on the surface was induced by the generated OH-. When used for PEC water oxidation, the obtained re-BiVO4/FeOOH photoanode achieved an excellent PEC performance with a photocurrent density of 5.35 mA/cm2 at 1.23 V versus RHE under AM 1.5G illumination, which was considerably higher than those for the pristine BiVO4 photoanode (2.88 mA/cm2) and the re-BiVO4 photoanode obtained by photocathodic reduction without Fe3+ (4.32 mA/cm2). After further modification with a cobalt silicate (Co-Sil) cocatalyst, the resultant re-BiVO4/FeOOH/Co-Sil photoanode exhibited a photocurrent density as high as 6.10 mA/cm2 at 1.23 V versus RHE and a remarkable applied bias photon-to-current efficiency of 2.25%. The outstanding performance of the re-BiVO4/FeOOH/Co-Sil photoanode could be attributed to the coexistence of plenty of oxygen vacancies in BiVO4 reducing recombination of photogenerated carriers, the FeOOH cocatalyst interlayer as a hole-transport layer, and the outer Co-Sil cocatalyst with a high activity toward oxygen evolution. This work may open a new avenue toward multifunctional modifications of photoanode systems for efficient solar conversion.
Keywords: BiVO4 photoanodes; cocatalyst; oxygen vacancy; photoelectrochemical water splitting; photoelectrodeposition.