UHV AND ELECTROCHEMICAL STUDIES OF THE SURFACE-PROPERTIES OF RU+PT+TI MIXED-OXIDE ELECTRODES

The surface properties of Ru0.3PT0.4Ti0.3Ox, prepared by thermal decomposition of the respective chlorides on Ti in the temperature range 400-600 degrees C, have been studied by XPS, AES and cyclic voltammetry in 1 M HClO4 solutions. The material loss during potential cycling has been determined by ICEPS of the electrolyte solution. Results have shown that, in the fresh electrodes, Pt is in the oxidation state of ca. +2, with a trend to decrease upon potential cycling. At the same time, Pt segregates to the surface and the voltammetric curve increasingly resembles that of a polycrystalline Pt electrode. XPS has confirmed that the surface concentration of Pt increases with the number of potential cycles, at the expense of that of Ru which is found preferentially dissolved in solution. The fact that the accumulation of metallic species in solution stops after a few tens of potential cycles suggests that (mechanical) erosion probably plays a predominant role with freshly prepared surfaces. Increasing the temperature of calcination improves the electrode stability, which has also been observed to be sensitive to the negative limit of the potential window.