Oxygen-Rich Carbon Nitride Quantum Dots Engineered Bismuth Vanadate Photoanode Surface to Achieve Highly Efficient Solar Water Oxidation

This study proposes a strategy for passivating intrinsic oxygen vacancies (Ovac) on BiVO₄ photoanodes through surface modification with carbon nitride quantum dots (CNQDs). The BiVO₄-CNQDs photoanode was fabricated via chemical bath deposition and calcination, achieving significant Ovac suppression without compromising the crystallinity of the BiVO₄ framework. This Ovac reduction critically alters the thermodynamic landscape of water oxidation by modulating intermediate adsorption energetics, steering the reaction pathway toward selective H₂O₂ generation. The optimized BiVO₄-CNQDs photoanode demonstrates a 24.91% average Faradaic efficiency (FE) for H₂O₂ production, representing a 1.38-fold enhancement over the pristine BiVO₄ photoanode. By integrating an In₂O₃ passivation layer, a BiVO₄-CNQDs-In₂O₃ photoanode was formed, and the average FE of H₂O₂ preparation reached 28.16%, achieving further performance improvement. The generated electrons and holes can be more effectively transferred from BiVO₄ to the In₂O₃ passivation layer before participating in subsequent electrochemical reactions. This dual modification synergistically promotes the quasi-Fermi level of holes to move toward the anode and reduces band bending, synergistically driving photo generated holes toward the higher oxidation potentials to accelerate the selective conversion of H₂O to H₂O₂. The BiVO₄-CNQDs-In₂O₃ photoanode achieves a 1.58-fold improvement in average H₂O₂ FE within the 1.2–2.4 V versus reversible hydrogen electrode (RHE) range compared to unmodified BiVO₄. This work establishes an innovative approach for modulating inherent Ovac in BiVO₄ photoanode and optimizing the preparation pathway of H₂O₂ through the vacancy engineering.