The electrochemical behavior of (100) IrO 2 single‐crystal electrodes in 0.5 mol / dm 3 H 2 SO 4 has been studied using linear potential scan cyclic voltammetry. A highly irreversible behavior of the main electrochemical process of hydrogen or hydronium ion injection/ejection has been found in the potential range 360–580 mV ( vs. Ag / AgCl reference). The obtained voltammograms have been compared with those for RuO 2 single crystals possessing similar electrocatalytic properties and the same crystallographic structure and also with the behavior of sputtered and anodic IrO 2 films. It has been found that the energy of major interaction of hydrogen species with the IrO 2 single‐crystal structure is close to that observed for sputtered IrO 2 films but differs by ca. 29 kJ/mol (corresponding to 300 mV in the potential scale) from that for the anodic IrO 2 films. The penetration depth for hydrogen is highly minimized in the case of single‐crystal IrO 2 electrodes and involves at most one or two monolayers. Thus, the coloration/bleaching process described for the IROX films cannot develop on nonhydrated single‐crystal IrO 2 electrodes unless their crystallographic structure is damaged by cycling in a wide potential range.
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Hepel et al. (1985) studied this question.