Dual Chemical Bath and Drop‐Casting Strategy for CoV₂O₆/BiVO₄ Heterostructure Fabrication to Improve Charge Separation and Boost Photoelectrochemical Water Splitting

Developing a facile approach for the fabrication of high‐quality BiVO 4 films is essential to enhance the photoelectrochemical performance of BiVO 4 photoanodes. Herein, we report a novel dual chemical bath deposition and drop‐casting strategy for fabricating pinhole‐free CoV 2 O 6 /BiVO 4 heterostructure. First, a Co(OH) 2 layer was grown on an FTO substrate via chemical bath deposition. Then, a Bi/V precursor mixture was drop‐cast and annealed to obtain high‐quality CoV 2 O 6 /BiVO 4 photoanodes. This dual‐deposition approach was crucial for preventing pinhole formation and thereby minimizing the solution‐mediated back‐reduction reaction at the FTO back contact. Photoelectrochemical measurements revealed that the CoV 2 O 6 /BiVO 4 photoanodes exhibited a fivefold increase in photocurrent compared to pristine BiVO 4 photoanodes. After modification with water oxidation cocatalysts, the photoanodes delivered a stable photocurrent density of 4.55 mA cm −2 at 1.23 V RHE . They demonstrated a Faradaic efficiency of 95% and achieved an applied bias photon‐to‐current efficiency of 1.45%, representing a sevenfold improvement over pristine BiVO 4 . The enhanced photoelectrocatalytic performance is primarily attributed to the formation of the pinhole‐free CoV 2 O 6 /BiVO 4 heterostructure, which suppresses surface recombination and extends the lifetime of photogenerated holes, as confirmed by transient photocurrent and intensity‐modulated photocurrent spectroscopy measurements. The developed dual‐deposition strategy is facile and can be applied to other metal oxide‐based photoanodes.