Does photoelectrocatalysis by TiO2 work?

BACKGROUND: This paper examines TiO2 photoelectrocatalysis (PEC), a process that increases the efficiency of TiO2 photocatalysis (PC) by applying a potential to separate the UV-generated charge carriers whose recombination typically limits photonic efficiencies of conventional photocatalysis. RESULTS: Four representative photoelectrocatalytic reactions, nitrophenol oxidation, oxalate degradation, E. coli inactivation and dye decolouration were considered. For all four, a small applied potential raised the rate of pollutant removal by TiO2 electrodes. Because the improvements were probably insufficient to make PEC technologically viable except in niche applications, rates of pollutant removal by PEC and by PC using TiO2 particle dispersions were directly compared. PEC rates were not significantly larger than rates of PC by dispersions. CONCLUSION: Discussions of the implications of these conclusions focus on whether PEC is currently limited by reactor design (irradiation geometry, or mass transfer) or by electrode materials. It is inferred that the performance of present electrodes is not limited significantly by mass transfer constraints. Since the choice of electrode materials (sol-gel or thermal electrodes) has been shown to influence PEC efficiency, recent results on titania nanotubes (TNT) are reviewed. It is concluded that the enhancement factors - the PEC : PC ratio - of TNT electrodes are no higher than those of conventional materials. (C) 2011 Society of Chemical Industry