Photoassisted Electrolysis of Water by Irradiation of a Titanium Dioxide Electrode

Ultraviolet irradiation (351, 364 nm) of the n-type semiconductor TiO2as the single crystal electrode of an aqueous electrochemical cell evolves O2at the TiO2electrode and H2at the Pt electrode. The gases are typically evolved in a two: one (H2:O2) volume ratio. The photo-assisted reaction seems to require applied voltages, but values as low as 0.25 V do allow the photoassisted electrolysis to proceed. Prolonged irradiation in either acid or base evolves the gaseous products in amounts which clearly demonstrate that the reaction is catalytic with respect to the TiO2. The wavelength response of the TiO2and the correlation of product yield and current are reported. The results support the claim that TiO2is a true photo-assistance agent for the electrolysis of water. Minimum optical storage efficiencies of the order of 1% can be achieved by the production of H2.