Photoelectrolysis of water at high current density - Use of laser light excitation of semiconductor-based photoelectrochemical cells

Results are given for the ultraviolet (351, 364 nm) laser light irradiation of the photoanode (Sn02, KTa0 .7?Nbo. 2303 , SrTi03, or Ti02) in a cell for the light driven electrolysis of H20. Irradiation intensities up to 380 W/cm have been used, and the general finding is that the properties of anode materials are independent of light intensity. Conversion of ultraviolet light to stored chemical energy in the form of H2/^02 from H20 has been driven at a rate of up to -30 W/cm. High 02 evolution rates at the irradiated anodes without change in current-voltage curves is hypothesized to be a consequence of the excess oxidizing power associated with photogenerated holes. A test for this sort of hypothesis for H2 evolution at p-type materials is proposed. INTRODUCTION Conversion of laser light energy to chemical and/or electrical energy (ref. 1-20) using photoelectrochemical cells is possible. In the last several years there has been considerable interest in n-type semiconductorbased cells configured as in Scheme I, Fig. 1, for converting light to electricity or as in Scheme II, Fig. 2, for producing storable, high energy density fuel from H20. In such cells the n-type semiconductor serves as a photoanode, and the key fact is that the oxidation occurs at electrode potentials which are more negative than thermodynamically possible at reversible, but dark, electrodes. Thus, the light-driven electrolysis of H20 according to equation (1) is