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Experiments are described in which the nature of surface oxidation processes at Ru electrodes are investigated and compared with those of other noble metals. Surface oxidation of Ru is much more irreversible than at Pt, Au, or Rh and the oxide formed in sweeps taken to 1.4V can only be reduced in the H region, usually with some coevolution of . However, surface oxidation already begins at potentials in, or close to, the H region; this behavior is somewhat similar to that of Pt in alkaline solutions. Upon repeated cycling into the oxide region up to , a new state of the oxidized Ru surface is generated which exhibits remarkable reversibility of the i‐V profile in anodic and cathodic sweeps taken to any potential in the range 1.4V. This effect is associated with a reversible redox process in the oxide film, probably between Ru(IV) and Ru(III), but reduction back to the metallic surface does not occur as it does in the initial sweeps. The behavior is somewhat similar to that previously observed with Ir. Time‐dependent growth of the oxide film at Ru is observed, as at other noble metals, and the direct logarithmic law applies. Similarities to the surface oxidation behavior of other noble metals, especially iridium, are pointed out and depend on anion adsorption.
̄i‐Jordanov et al. (Fri,) studied this question.