A photoelectrochemical study on the features of carbonate-catalyzed water oxidation at illuminated TiO2/Solution interface

Photoelectrochemical (PEC) measurements were performed to investigate the catalytic effect of carbonate on water splitting over TiO2 nanotube photoanode at low applied potentials. The photocurrent measured with the presence of carbonate with a low concentration of 5 x 10(-3) M in 0.5 M NaClO4 solution of pH = 6-13 was ca. two to seven times of that measured in the absence of carbonate in solution. By adding a small amount of formate as a precursor of in situ generated carbonate in solution, the significant catalytic effect of carbonate was further evidenced. The features of the photocurrents measured under both potential dynamic and potentiostatic conditions indicated that the existence of carbonate in solution can effectively prevent the surface recombination of the photogenerated electron-hole pairs occurring at the TiO2/solution interface, which was regarded as the main reason for the catalytic effect of carbonate on the PEC water splitting in this work. The related charge transfer processes during water photooxidation at the TiO2/solution interface were discussed.