Enhanced Photocatalytic Efficiency Through Oxygen Vacancy-Driven Molecular Epitaxial Growth of Metal–Organic Frameworks on BiVO4

Efficient charge separation at the semiconductor/cocatalyst interface is crucial for high-performance photoelectrodes, as it directly influences the availability of surface charges for solar water oxidation. However, establishing strong molecular-level connections between these interfaces to achieve superior interfacial quality presents significant challenges. This study introduces an innovative electrochemical etching method that generates a high concentration of oxygen vacancy sites on BiVO₄ surfaces (Ov-BiVO₄), enabling interactions with the oxygen-rich ligands of MIL-101. This reduces the formation energy and promotes conformal growth on BiVO₄. The Ov-BiVO₄/MIL-101 composite exhibits an ideal semiconductor/cocatalyst interface, achieving an impressive photocurrent density of 5.91 mA cm⁻² at 1.23 V_RHE, along with excellent stability. This high-performing photoanode enables an unbiased tandem device with an Ov-BiVO₄/MIL-101-Si solar cell system, achieving a solar-to-hydrogen efficiency of 4.33%. The molecular-level integration mitigates surface states and enhances the internal electric field, facilitating the migration of photogenerated holes into the MIL-101 overlayer. This process activates highly efficient Fe catalytic sites, which effectively adsorb water molecules, lowering the energy barrier for water oxidation and improving interfacial kinetics. Further studies confirm the broad applicability of oxygen vacancy-induced molecular epitaxial growth in various MOFs, offering valuable insights into defect engineering for optimizing interfaces and enhancing photocatalytic activity.