AN INVESTIGATION OF OXIDE-FILMS ON PLATINUM IN SULFURIC-ACID-SOLUTION BY ELECTROCHEMICAL AND PHOTOELECTROCHEMICAL TECHNIQUES

The measurement of photocurrents at polycrystalline platinum electrodes oxidized to different extents in 0.5 mol dm-3 sulphuric acid solution is reported. Small anodic photocurrents were detected in the potential region where the thin alpha-oxide film begins to grow on platinum. The photocurrent conversion efficiency PHI reached values of the order of 10(-5) at 5.0 eV. PHI was found to depend exponentially on photon energy for an oxide film grown at 1.6 V/RHE, and plots of log10PHI vs. hnu were linear over the range 2.2-5 eV with slopes close to 1 eV per decade. The photoelectrochemical behaviour of thicker oxide films (alpha and beta) formed by galvanostatic oxidation of platinum in the oxygen evolution region was also examined, and cathodic photocurrents with much higher conversion efficiencies were observed. The photocurrent measured during potentiodynamic experiments on the thicker oxide films has been related to the reduction of the underlying alpha-oxide phase and of the outer beta-oxide phase. The results indicate that both oxide phases are photoactive.