Photoelectrochemical production of hydrogen peroxide (H2O2) via the two-electron water oxidation pathway has attracted much attention as a promising energy conversion strategy. Recent studies have shown that certain electrolyte ions can significantly enhance the selectivity of H2O2 formation over the competing oxygen evolution reaction (OER). However, the mechanistic basis for this enhancement remains largely unknown. In this work, we utilize density functional theory (DFT) based static and molecular dynamics simulations to investigate the role of bicarbonate ions (HCO3-) from solution in promoting H2O2 production on BiVO4 photoanodes. Our computational results suggest that adsorbed HCO3- species can act as electrocatalytic centers, facilitating the formation of an HCO4- intermediate that improves both the activity and selectivity of the water oxidation reaction toward H2O2 generation. Furthermore, mobile hole polarons on the photoanode play a crucial role in stabilizing the transient reaction intermediates. Our results provide key mechanistic insights into the role of bicarbonate ions at the photoelectrochemical interface, offering a potential electrolyte engineering strategy to enhance H2O2 selectivity in water oxidation processes.
