Hydrogen evolution on iridium oxide cathodes

Abstract

IrO _x electrodes prepared by thermal decomposition of IrCl₃ dissolved in water have been prepared at temperatures betweeen 300 and 500°C. They have been characterized by voltammetric curves before and after each experiment to monitor changes in surface conditions. Hydrogen evolution from 1 mol dm⁻³ constant ionic strength perchlorate solutions at pH between 0 and 1 has been studied by quasi-stationary potentiostatic curves and reaction order determination. A Tafel slope close to 40 mV and a reaction order of 1.5 with respect to H⁺ are explained with a mechanism involving a step of reduction of the active sites and a pH dependence of the potential at the reaction plane which is typical of the acid-base properties of oxide surfaces. The results indicate that wetting-dewetting phenomena of the electrode surface, depending on the magnitude of the current, are operative during hydrogen evolution, and that the oxide surface is never reduced down to the metal, while no bulk reduction whatsoever takes place.