Effect of carbonate salt addition on the photocatalytic decomposition of liquid water over Pt-TiO2 catalyst

It has been found that an addition of carbonate salts to Pt-loaded TiO2 suspensions led to highly efficient stoichiometric photocatalytic decomposition of liquid water into H-2 and O-2. Neither the pH nor cation directly contributes to the water splitting, and the presence of a high concentration of carbonate ions is essential for the catalytic photodecomposition of water. The carbonate ion affects both the Pt particles and the TiO2 surface. The Pt was covered with some titanium hydroxide compounds and, therefore, the rate of the back reaction (H2O formation from H-2 and O-2) on the Pt was suppressed effectively in the presence of carbonate ions. On the other hand, the TiO2 surface was readily covered with several types of carbonate species. It is considered that these carbonate species aid desorption of O-2 from the TiO2 surface. A new reaction mechanism involving peroxocarbonates has been proposed.