Dual (oxy)hydroxide Cocatalyst Synergistically Boosts Solar Water Splitting of BiVO₄ Photoanode

Bismuth oxide (BiVO₄) is considered one of the most promising semiconductors for photoelectrochemical (PEC) water splitting due to its highly theoretical photocurrent of 7.5 mA cm^-2. However, its sluggish kinetics and severe photocorrosion still hinder the real application of a large-area BiVO₄ photoanode. Herein, a room-temperature immersion method has been used to fabricate a dual cocatalyst-coated BiVO₄ film, namely the BiVO₄/FeOOH/Co(OH)₂ photoanode. This composite photoanode delivers a photocurrent density of 2.56 mA cm^-2, which is 2.7 times that of pure BiVO₄. After a long-term testing of 10 h, its retention rate of photocurrent reaches 71.63 %, which is 4.6 times that of BiVO₄. The kinetic studies illustrate that dual cocatalyst can significantly lower the charge transfer resistance, improve the charge injection efficiency, and reduce the Tafel slope. Specifically, FeOOH plays a role in transporting photogenerated holes, while Co(OH)₂ facilitates water oxidation reactions. In addition, the dual cocatalyst coating can slow down vanadium ion dissolution and improve PEC stability. This immersion method can easily be applied to large-area photoelectrodes.