Interestingly, it is observed that more than one water molecule adsorbed to the same Bi 7f site at positively charged BiVO 4 /NaCl interface (Fig. ). That means the adsorption of interfacial water is enhanced by the electric field in EDL at low pH. On the contrary, the adsorbed water molecules partly desorbed into the electrolyte at negatively charged BiVO 4 /NaCl interface (Fig. ). The results indicate that the adsorption of interfacial water is weakened by the the electric field in EDL at high pH.