V₂CT_x MXene suppresses V⁵⁺ dissolution and boosts the stability and performance of BiVO₄ for solar water splitting

The BiVO₄ photoanode shows great potential as a key component of photoelectrochemical (PEC) devices for converting solar energy and water into green hydrogen. However, it faces challenges due to surface-hole accumulation, leading to diminished PEC performance and photocorrosion accompanied by V⁵⁺ loss. Adding vanadium ions to the electrolyte is proposed to suppress V⁵⁺ dissolution; however, the surface modification of BiVO₄ with vanadium-based materials has not been fully explored. Herein, we have introduced, for the first time, vanadium-containing MXene (i.e. V₂CT_x MXene) between the BiVO₄ photoanode and the Co-Pi co-catalyst. Consequently, the V⁵⁺ dissolution is suppressed, and the PEC performance is significantly boosted, achieving photocurrent density values of 3.20 and 4.72 mA cm⁻² at bias potentials of 0.6 and 1.23 V_RHE, respectively, with an outstanding photostability for over 56 h. Thorough spectroscopic and dynamic analyses reveal that the high PEC performance arises from V₂CT_x MXene's ability to efficiently extract and store photogenerated holes, enabling many of them to reach the Co-Pi co-catalyst for efficient PEC water oxidation.