Behavior of surface peroxo species in the photoreactions at titanium dioxide

TLDR: The electrochemical behavior of the surface species photogenerated at a polycrystalline titanium dioxide film electrode in alkaline solution was investigated by means of cyclic voltammetry as discussed by the authors.

Abstract: The electrochemical behavior of the surface species photogenerated at a polycrystalline titanium dioxide film electrode in alkaline solution was investigated by means of cyclic voltammetry. The obtained results are consistent with the same surface peroxo titanium species being formed when an illuminated TiO/sub 2/ electrode is subjected to an anodic bias or left in open circuit both in the presence and in the absence of oxygen. The decay of these species after the cutoff of illumination was observed to occur relatively slowly, about half of their initial amount being still detectable after 16 h of electrode immersion in sodium hydroxide solution. It was shown that the cathodic reduction of the surface peroxo species, photogenerated at the TiO/sub 2/ electrode, takes place at distinctly more negative potentials than that of dissolved molecular oxygen and that of both preadsorbed and dissolved hydrogen peroxide. The latter species (present mainly as HO/sub 2//sup -/ ions) were also observed to undergo rapid photooxidation at the TiO/sub 2/ photoanode, competing efficiently for positive holes with OH/sup -/ ions. These findings do not support the earlier postulated involvement of the hydrogen peroxide as an intermediate of the photoreaction leading to oxygen evolution. The pathways for the photooxidationmore » reactions at TiO/sub 2/ are briefly discussed in connection with the proposed mechanism of formation of the surface peroxo titanium species. Their role in controlling the surface electron-hole recombination, particularly at dispersed TiO/sub 2/ photocatalysts, is pointed out.« less