Borate and iron hydroxide co-modified BiVO4 photoanodes for high-performance photoelectrochemical water oxidation

Abstract

• β-FeOOH-B-BiVO 4 with oxygen vacancies are fabricated by a two-step solution method. • β-FeOOH-B-BiVO 4 is used as photoanode for water oxidation. • β-FeOOH-B-BiVO 4 shows an outstanding photocurrent density of 4.96 mA cm −2 . • β-FeOOH-B-BiVO 4 exhibits a sustainable photostability by electrolyte tuning. • A possible mechanism for O 2 evolution over β-FeOOH-B-BiVO 4 is proposed. BiVO 4 has attracted tremendous attention as a promising photoanode material for photoelectrochemical (PEC) water oxidation, but the serious surface charge recombination and the slow water oxidation kinetics restrict its progress. To settle this problem, a two-step simple solution impregnation method is developed for fabricating a high-performance photoanode by anchoring an ultrathin β-FeOOH nanolayer with enriched active sites on borate-post-treated nanoporous BiVO 4 (B-BiVO 4 ). The resultant β-FeOOH-B-BiVO 4 photoanode shows an extremely high photocurrent density of 4.96 mA cm −2 at 1.23 V vs. RHE (1 sun illumination), over 3-fold larger than that of pure BiVO 4 (1.45 mA cm −2 ) and also superior to that of B-BiVO 4 (3.80 mA cm −2 ). The half-cell solar-to-hydrogen conversion efficiency and the surface charge transfer efficiency of β-FeOOH-B-BiVO 4 photoanode are determined as 1.94% (ca. 0.62 V vs. RHE) and 90.2% (1.23 V vs. RHE), respectively. These PEC property enhancement is systematially confirmed to be ascribed to restrain surface charge recombination of BiVO 4 , accelerated hole transfer from B-BiVO 4 to the catalytic sites of β-FeOOH, and abundant oxygen vacancies from ultrathin β-FeOOH nanolayers. Further, a sustainable photostability is gained for the β-FeOOH-B-BiVO 4 photoanode only by tuning electrolyte composition. This study offers a viable route to fabricate low-cost and high-performance catalysts for solar water splitting.