Effects of the electrochemically grown hydrous oxide on the hydrogen electrode reaction on iridium electrode

•Influence of oxide layers on the hydrogen electrode reaction on iridium•At low thickness, hydrous oxide layer increases the electroactive surface area.•At high thickness, an inner anhydrous oxide layer is formed.•The inner oxide layer decreases the electrocatalytic activity.

The hydrogen electrode reaction was studied on iridium electrodes covered by a hydrous oxide film in acid solution. The IrOx·nH2O film was prepared by the application of repetitive cyclic voltammetry and it was characterized by the charge of the broad voltammetric peak at 0.97 V. It was observed for charges lower than 720 μC cm− 2 a slight increase of both, the HUPD electroadsorption and the steady state limiting current of hydrogen oxidation, with respect to Ir metal. For higher oxide charge values, both variables decrease while a small anodic peak appears at 0.65 V. This behaviour was explained on the basis of the formation of two types of Ir oxide depending on the film thickness and the water concentration profile, which changes the site where the hydrogen reaction takes place.

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