VOLTAMMETRY AND ANODIC STABILITY OF A HYDROUS OXIDE FILM ON A NICKEL ELECTRODE IN ALKALINE-SOLUTION

A hydrous oxide film on a nickel electrode was formed electrolytically by square-wave cycling in 1 mol dm-3 NaOH solution. The reproducibility of a second scan in a voltammetric experiment depended on holding the potential at a negative value (-1.1 V vs SCE) and on the positive potential limit. The hydrous oxide film, with a charge enhancement factor of 19, exhibited two stages of oxide reduction. Coulometric data showed that the majority of the oxide (80-90%) was reduced in Ni(III)/Ni(II) transition almost reversibly at potentials where the higher oxide was formed while, depending on the potential of formation, about 10-20% of the NiOOH was irreversibly reduced in the potential region of the hydrogen evolution reaction. An anodic stability test in the oxygen evolution reaction was carried out at 0.1 A cm-2. The hydrous oxide layer was stable over 14 days of electrolysis with an unchanged charge enhancement factor. The electrocatalytic activity of the electrode, however, expressed through the overpotential at the same current density, was not maintained.