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 BiVO₄ films is essential to enhance the photoelectrochemical performance of BiVO₄ photoanodes. Herein, we report a novel dual chemical bath deposition and drop-casting strategy for fabricating pinhole-free CoV₂O₆/BiVO₄ 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 CoV₂O₆/BiVO₄ 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 CoV₂O₆/BiVO₄ photoanodes exhibited a fivefold increase in photocurrent compared to pristine BiVO₄ 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 BiVO₄. The enhanced photoelectrocatalytic performance is primarily attributed to the formation of the pinhole-free CoV₂O₆/BiVO₄ 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.