Electrochemical Formation of BiVO ₄ /BiPO ₄ Photoanodes for Enhanced Selectivity toward H ₂ O ₂ Generation

Abstract Two‐electron water oxidation to generate H 2 O 2 is a promising alternative to oxygen evolution in solar water splitting, as it enhances reaction kinetics and improves its economic competitiveness. However, competition with oxygen evolution remains challenging due to its higher thermodynamic potential. Several materials with preference for two‐electron oxidation are identified, but finding ones with enhanced selectivity toward H 2 O 2 production remains critical. Here, we systematically investigate and control the surface transformation from BiVO 4 to BiVO 4 /BiPO 4 photoanode via external bias in potassium phosphate. Varying BiPO 4 on the surface via bias duration, we find increased faradaic efficiency (FE) for H 2 O 2 production with higher surface transformation. By combining density functional theory calculations with experimental results, we find that both BiVO 4 and BiPO 4 exhibit a stronger FE dependence on HCO 3 − concentration compare to OH − . Particularly, the HCO 3 − adsorption energy on BiPO 4 is stronger than that on BiVO 4 , leading to a higher local concentration and likely explaining the enhanced FE observed. This work identifies BiPO 4 , not previously explored in two‐electron water oxidation, as a promising catalyst. More generally beyond BiPO 4 , this study demonstrates that HCO 3 − adsorption plays a more critical role than OH − and should be prioritized in the design of materials for H 2 O 2 production.