Comparative Potentiodynamic Study of Nickel in Still and Stirred Sulfuric Acid‐Potassium Sulfate Solutions in the 0.4–5.7 pH Range

Abstract

The potentiodynamic behavior of polycrystalline nickel disk electrodes in the potential range of the active to passive transition was investigated in still and stirred sulfuric acid solutions containing potassium sulfate in the range. Voltammetric data derived with a nickel rotating disk electrode allow a distinction between the main competing processes associated with the active to passive transition of nickel in acid, through their different dependences on the potential sweep rate and on the rotation speed. The first process corresponds to the formation of a nickel hydroxide solid phase through a relatively simple mechanism initially involving adsorbed (OH) species. The second process comprises the chemical dissolution and precipitation of nickel hydroxide, producing the thickening of the anodic layer. At high positive potentials, this anodic layer progressively transforms into the passive layer. The overall reaction is discussed in terms of a complex reaction pathway in which the participation of water plays a fundamental role.