It has been shown that the mechanism of the water oxidation reaction on BiVO 4 surface depends on the pH of the electrolyte. At low pH, the water oxidation reaction is initiated mainly through the dehydrogenation of adsorbed water molecules, involve the the H 2 O• + radical cation as an intermediate. While at high pH, the reaction is initiated through the oxidation of OH - (OH -/OH•). Based on observations here, the Bi 7f -(OH 2 ) 2 structure may more favorable to the formation of H 2 O• + in acidic conditions. However, the desorption of terminal adsorbed water is a disadvantage to generate H 2 O• + at alkaline conditions. This leaves the opportunity for Bi 7f OH -to combine hole and formate OH• at high pH. This is in line with the role of negative surface charge in hole selectivity reported by recent experiments and ionized oxygen vacancy proposed by theoretical calculations. .