Engineering BiVO₄ and Oxygen Evolution Cocatalyst Interfaces with Rapid Hole Extraction for Photoelectrochemical Water Splitting

Tailoring the oxygen evolution cocatalyst (OEC)/BiVO₄ interfaces with a hole transfer layer (HTL) is expected to suppress the interfacial charge recombination, thus achieving highly efficient photoelectrochemical (PEC) water splitting. Herein, Co₃O₄ nanoparticles are inserted between the NiOOH OEC and BiVO₄ as an HTL for the design of NiOOH/Co₃O₄/BiVO₄ photoanodes. A champion photoanode achieves a photocurrent density of 6.4 mA cm^-2 at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G illumination (100 mW cm^-2). Stable PEC water splitting is realized for up to 90 h. Being highly dispersed at the surfaces of BiVO₄, the p-type Co₃O₄ nanoparticles form p-n junctions with BiVO₄, thus providing an extra driving force for the extraction of the photogenerated holes from BiVO₄ to the NiOOH OEC, which efficiently suppresses charge recombination at the BiVO₄/NiOOH interfaces and accelerates the surface water oxidation kinetics. A charge separation efficiency of 95.6% and a surface charge transfer efficiency of 97.7% are achieved at 1.23 V vs RHE. The strategy is applicable to other OEC (e.g., MnO_x and FeOOH)/BiVO₄ photoanodes. This work may inspire the rational design of high-performance photoanodes for feasible solar energy conversion.