The enhanced PC and PEC oxidation of formic acid in aqueous solution using a Cu-TiO2/ITO film.

The photocatalytic (PC) and photoelectrocatalytic (PEC) activity of Cu-TiO2/ITO films for degrading formic acid in aqueous solution was investigated in this study. Compared with a TiO2/ITO film, the degradation efficiency of formic acid on the Cu-TiO2 films increased markedly in both the PC and PEC oxidation processes. However, it was found that the photodeposited Cu metal on the Cu-TiO2 films could electrochemically dissolute during the PEC reaction, while an electrical bias with the voltage higher than 1.48 V was applied. It is believed this is a common problem occurred for several metals deposition on the TiO2 films, which results in a poor stability of the metal-deposited TiO2 electrode in PEC processes. To improve the stability of the Cu-TiO2 electrode, an alternative process between PC and PEC reactions was investigated. It was found that the dissolute Cu metal during the PEC process was re-deposited on the Cu-TiO2 film again during the PC process. The experiments with repeated runs demonstrated that this alternative process could not only overcome the loss of Cu, but also enhance the PEC oxidation efficiency of the Cu-TiO2 films.