Effects of oxygen reduction on nickel deposition from unbuffered aqueous solutions. II: Characterization of the electrode interface in electrodeposition

Contrary to the reactive electrodeposition of cobalt, porous nickel is not easily produced by electrodeposition from neutral aqueous solutions in the presence of dissolved oxygen. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) examination of the electrode surface detected the presence of a highly stable metal hydroxide layer of the same characteristics as precipitated Ni(OH) 2 . The hydroxide layer inhibits the nucleation of nickel nuclei and increases the irreversibility in electrodeposition. For reactive deposition to result in a porous deposit, the hydroxide layer should have only moderate stability so that it can be continuously removed and reinstated by interfacial chemical and electrochemical reactions. The surface Ni(OH) 2 formed in neutral solutions lacks the reactivity for such dynamism. Nonetheless, the stability of surface Ni(OH) 2 could be lowered by increasing the acidity of the deposition medium. Careful pH control seems to be a requirement for nickel reactive electrodeposition to produce porous metal deposits