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.