MECHANISMS OF COMPETITIVE PHOTOELECTROCHEMICAL OXIDATION OF I - AND H2O AT n-TiO2 ELECTRODES: A KINETIC APPROACH.

The competitive photo-oxidation of H//2O and I** minus on a polycrystalline n-tiO//2 electrode was studied by the rotating ring-disk electrode technique. The photo-oxidation efficiency was measured as a function of the illumination intensity, electrode potential, iodide concentraiton, and electrolyte pH. In the low photocurrent range, where photo-oxidation reactions are not limited by diffusion of electrolyte reduced species, iodide was photo-oxidized in preference to water in acidic solutions (pH 4) and at low light intensities. A monotonic decrease of the iodide photo-oxidation efficiency, PHI //1-, with increasing photocurrent was also observed at pH 4. The iodine reactivity was found to decrease considerably by increasing the electrolyte pH.