Electrochemical Behavior of Nickel in Acidic Sulfate Electrolytes

The electrochemical behaviour of Nickel in sulphuric acid electrolytes was studied by various electrochemical means. Under cathodic polarization, Nickel forms metastable hydrides under cathodic charging; the successive egress of hydrogen is controlled by solid state diffusion of hydrogen atoms. The nature of these hydrides evolves with electrochemical aging of the samples, as judged by their electrochemical signature. The nature of the (hydro)oxides formed during anodic polarization also evolves with aging. Anodic polarization and investigation of electrochemical oscillations in the transpassive region show that defect states which constitute preferred dissolution sites assume a wider energy range with increasing aging, indicating a high degree of inhomogeneity of the surface. The catalytic activity of Nickel increases after aging under both cathodic and anodic conditions, due to the formation of an inhomogeneous surface.