X-ray photoelectron spectroscopic studies of the iridium electrode system

X-ray photoelectron spectroscopy has been used to investigate the surface of iridium electrodes studied under both steady-state and cyclic conditions in 0.5 and 5 mol dm–3 sulphuric acid solutions. The results show that pulsing into the anodic region produced very small amounts of oxide in 0.5 mol dm–3 acid and slightly more in the 5 mol dm–3 solutions. The oxide is thought to be predominantly IrO2. When the electrode has been cycled up to 1.5 V (vs RHE) substantial amounts of oxide were observed, the amount being dependent upon the number of cycles and the sweep rate. The oxide was not a simple as in the case of polarization, but is explained as a mixture of iridium oxy/hydroxide species. Two other sweep limits (1.2 and 1.8 V) were briefly investigated. Possible mechanisms explaining these results are discussed. The pure-metal spectra (including angle-resolved studies) have been examined at ambient and elevated temperatures with particular emphasis upon the O 1s region and the methods for removing any residual oxide from the metal surface.