An oxygen-vacancy-rich BiVO4/TiO2/Co2P2O7 heterojunction photoanode with Ti3C2Tx-derived TiO2 for enhanced photoelectrochemical water oxidation

Constructing BiVO₄/TiO₂ heterojunction and introducing oxygen vacancies (O_V) are effective strategies to increase the photoelectrochemical (PEC) performance of BiVO₄. In this work, an oxygen-vacancy-rich BiVO₄/TiO₂ heterojunction is synthesized through a simple hydrothermal method using Ti₃C₂T_x MXene as the precursor for TiO₂. During the reaction, Ti₃C₂T_x MXene is oxidized to TiO₂ by water and surface chemisorbed oxygen of BiVO₄ to form a heterojunction with BiVO₄. Meanwhile, BiVO₄ is reduced by Ti₃C₂T_x MXene to produce O_V. The as-synthesized BiVO₄/TiO₂ heterojunction delivers a high photocurrent density of 2.73 mA cm⁻² at 1.23 V_RHE, which is 2-fold higher than the BiVO₄ (1.36 mA cm⁻²). In addition, the carrier transfer in the BiVO₄/TiO₂ heterojunction is investigated through density functional theory (DFT) calculations. The photogenerated electrons will transfer to the BiVO₄, while the photogenerated holes will migrate to the TiO₂. The BiVO₄ and TiO₂ form a type II heterojunction, leading to efficient separation of electron-hole pairs. After loading Co₂P₂O₇ nanosheets as an oxygen evolution cocatalyst, a considerable photocurrent density of 4.57 mA/cm² at 1.23 V_RHE can be achieved. This work presents a novel strategy of constructing BiVO₄/TiO₂ heterojunctions and introducing O_V, which may be used to fabricate other TiO₂-constituted heterojunctions and synchronously introduce O_V.