On the Influence of the Extent of Oxidation on the Kinetics of the Hydrogen Electrode Reactions on Polycrystalline Nickel

摘要

The influence of the extent of oxidation of Ni electrodes on the kinetics of the hydrogen oxidation (HOR) and evolution (HER) reactions has been explored by combining an experimental cyclic voltammetry and chronoamperometry study with microkinetic modeling. The HOR/HER specific activity of the Ni/NiOx electrodes follows a volcano-type dependence with a maximum at 30% NiOx coverage corresponding to a 14-fold increase (nominally from 2.2 to 32.8 mu A cm(Ni)(-2)) of the specific activity calculated as the exchange current density normalized by the electrochemical surface area of Ni active sites. The kinetic model suggests that the experimentally observed changes in the shape of current-potential curves as well as the HOR/HER specific activities are mostly due to the NiOx coverage-dependent strength of adsorption of hydrogen atoms. The latter is accompanied by an increase of the rate of the Volmer step and a decrease of the potential of OHad adsorption on Ni centers in the vicinity of surface Ni oxides.