Degradation of formic acid was investigated using a novel photoelectrocatalytic reactor with a porous titanium plate as an air distributor as well as an electrode. By the comparison of the COD removal efficiencies from the solution containing formic acid for three processes, direct electro-oxidation, photocatalysis and photoelectrocatalysis, a significant photoelectrochemical synergetic effect was observed in the photoelectrocatalysis process. The synergetic effect was assessed with a new parameter, synergetic factor (SF). The effects of various operating conditions, such as applied cell voltage, treating time, airflow, initial pH value, catalyst amounts and conductivity of solution, on the SF were investigated as well. It was found that the SF was considerably dependent on these operating conditions, moreover, not simply proportional to them.

A platinised TiO2/ITO film, Pt-TiO2/ITO, was prepared by a dip-coating and subsequent photodeposition procedure. Compared with bare TiO2/ITO film, Pt-TiO2/ITO film not only possesses a relative high photocatalytic activity but also shows a rather non-photocatalytic activity towards HCOOH degradation at room temperature and atmosphere pressure. The non-photocatalytic effect of platinised TiO2 was partly responsible for degradation of formic acid in the photocatalytic process. The non-photocatalytic activity of Pt-TiO2/ITO film is very dependent on its preparation method.

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 1.48V 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.

Ag-TiO2 composite film supported on indium-tin oxide (ITO) glass was used as photoanodes to investigate the feasibility of a hybrid technology of Ag deposition combined with the application of an external electric field. The results showed that the deposited Ag and applied anodic bias have an apparent additive effect for suppressing the recombination between the photogenerated charge carriers and enhancing the photocatalytic oxidation of formic acid.