Study of the Hydrogen Electrode Reaction on Iridium Electrodes Covered by a Hydrous Oxide Film

M.A. MONTERO; M.R. GENNERO DE CHIALVO; A.C. CHIALVO

Buenos Aires

Congreso; 20th Topical Meeting of the International Society of Electrochemistry (ISE): Advances in Lithium and Hydrogen Electrochemical Systems for Energy Conversion and Storage; 2017

ISE

The iridium electrode, unlike the rest of the noble metals, has a great ability to form thick films of hydrous oxides. Moreover, the film obtained exhibits a markedly different behaviour with respect to the other noble metals. The most important characteristics are: (i) oxide layer grows with the increase of the number of applied potentiodynamic cycles, it is amorphous, its stoichiometry is undefined and it is inhomogeneous in depth. (ii) Oxide exhibits highly reversible redox behaviour, being the cathodic peak almost a mirror image of the anodic peak. (iii) Hydrous Ir oxide exhibits electrochromism, originated in the proton flow to or from the oxide layer during the oxidation/reduction process. (iv) The process of adsorption/desorption of underpotentially deposited hydrogen (HUPD) still takes place although the electrode surface is completely covered by the iridium hydrous oxide, and it only disappears when the oxide film reaches significantly high thickness values. On the other hand, it is well known that the inhibition of the HUPD adsorption sites is always accompanied by a decrease in the reaction rate of the hydrogen evolution, although the surface sites involved are different. All these aspects emphasize the role played by the Ir electrode pretreatment on its electrocatalytic activity towards hydrogen electrode reaction (HER). In this context, the objective of the present work is the study of the HER in acid solution on iridium electrodes covered by a hydrous oxide film, with special emphasis in the changes in the oxide structure with the variation of the film thickness.