OXYGEN REDUCTION AT PT0.65CR0.35, PT0.2CR0.8 AND ROUGHENED PLATINUM

Oxygen reduction in 0. 5M H//2SO//4 has been investigated at Pt//0//. //6//5Cr//0//. //3//5, Pt//0//. //2Cr//0//. //8 and at surfaces produced from them by selective dissolution of the Cr component. Rotating disk electrodes (RDE) were used to examine the oxygen reduction reaction (ORR). The published (1-2) surface analysis using x-ray photoelectron spectroscopy (XPS) combined with sputter profiling and Rutherford backscattering spectrometry (RBS) convincingly demonstrated that the surface region can be selectively depleted of the Cr component by electrochemical excursions to potentials positive of approximately plus 1. 25V vs. RHE. For the more Cr-rich alloy very severe depletion ( greater than 500 Angstrom) occurs upon prolonged potential excursions above plus 1. 25V. For the Pt// 0//. //6//5Cr//0//. //3//5 sample, the surface depletion extends about 2-3 monolayers into the surface.