Oxygen-Deficient Bi ₂ Mo ₂ O ₉ /BiVO ₄ Composite Photoanode for Efficient Photoelectrochemical Hydrogen Peroxide Synthesis via Two-Electron Water Oxidation

The photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4) in hydrogen peroxide (H2O2) generation via two-electron water oxidation reaction (2e–WOR) necessitates improvement. In this study, bismuth molybdate (Bi2Mo2O9) was chosen to create a composite photoanode with BiVO4. Furthermore, by calcinating in an argon atmosphere, additional oxygen vacancies were introduced beyond the intrinsic ones (denoted as Ar–Bi2Mo2O9/BiVO4). In comparison to BiVO4, Ar–Bi2Mo2O9/BiVO4 exhibits a substantial enhancement in both Faradaic efficiency (FE) and generation rate for PEC H2O2 production. At a potential of 1.53 V vs RHE, there is an increase in FE from 9.2% to 21.8%, and an elevation in H2O2 generation rate from 0.06 to 0.19 μmol·min–1·cm–2. Moreover, the PEC stability of the photoanode is significantly improved. The mechanistic analysis suggests that calcination in argon atmosphere enhances the separation efficiency of photogenerated carriers in the composite photoanode; it amplifies the Fermi level splitting, which increases the energy of the hole quasi-Fermi level, thereby accelerating the 2e–WOR. The leaching of vanadium ions from BiVO4 is significantly mitigated through the passivation process with Bi2Mo2O9, consequently augmenting the PEC stability of BiVO4. Additionally, the feasibility and potential of the photoanode for PEC H2O2 production via 2e–WOR in seawater electrolytes is confirmed.