Synergistic Effects of Ferrihydrite and Cobalt (Oxy)Hydroxide on BiVO₄for Unbiased Photoelectrochemical Water Splitting

Charge carrier recombination and photocorrosion are perceived as detrimental factors that profoundly impede the photoelectrochemical (PEC) water splitting performance of bismuth vanadate (BiVO₄). Herein, dual hole transporting layers of ferrihydrite (Fh) and cobalt (oxy)hydroxide (Co(O)OH) formed a synergistic effect with BiVO₄, improving the photoinduced charge carrier separation and transfer efficiency, as well as accelerating the water oxidation kinetics of the BiVO₄photoanode. An exemplary photocurrent density of 3.20 mA cm^–2was achieved by the Co(O)OH/Fh/BiVO₄photoanode at 1.23 V vs the reversible hydrogen electrode (V_RHE) under AM 1.5 G irradiation, which is 2.66-fold higher than that of pristine BiVO₄. Attributed by the improved fill factor of the Co(O)OH/Fh/BiVO₄photoanode, an unbiased solar-driven water splitting system was successfully constructed by integrating it with a commercial silicon solar cell, achieving a solar-to-hydrogen (STH) conversion efficiency of 1.38%, with demonstrated photostability over 24 h. This work represents a pivotal advancement in the design of a high-performing photoanode for self-driven green hydrogen production via the water splitting reaction.