Significance of Hydroxyl Radical in Photoinduced Oxygen Evolution in Water on Monoclinic Bismuth Vanadate

Understanding the details of the mechanism of water photo-oxidation on monoclinic bismuth vanadate (m-BiVO₄) is intriguing for efficient oxygen (O₂) evolution under solar light. Hydroxyl (OH) radical was confirmed in a photocatalytic system of m-BiVO₄ powders. OH radical is highly reactive to dimerize into hydrogen peroxide (H₂O₂), which is further oxidized into O₂ molecule. Therefore, O₂ evolution from OH radicals could be one of the plausible mechanisms. In the present study, to clarify the significance of O₂ evolution from OH radicals, O₂ molecules and OH radicals were generated by photoelectrochemical water oxidation on m-BiVO₄ electrode. The amounts of O₂ molecules and OH radicals were quantified by using an oxygen meter and a fluorescence probe method, respectively. The current efficiency of the photocurrent for the formation of OH radicals (∼0.06%) was much smaller than that for O₂ evolution (∼100%), indicating that O₂ evolution from OH radicals was not significant on m-BiVO₄.