Photoassisted electrolysis of water by irradiation of a titanium dioxide electrode.

Ultraviolet irradiation (351, 364 nm) of the n-type semiconductor TiO(2) as the single crystal electrode of an aqueous electrochemical cell evolves O(2) at the TiO(2) electrode and H(2) at the Pt electrode. The gases are typically evolved in a two: one (H(2):O(2)) volume ratio. The photoassisted 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 TiO(2). The wavelength response of the TiO(2) and the correlation of product yield and current are reported. The results support the claim that TiO(2) is a true photoassistance agent for the electrolysis of water. Minimum optical storage efficiencies of the order of 1% can be achieved by the production of H(2).