The electrochemical behaviour of nanocrystalline nickel: A comparison with polycrystalline nickel under the same experimental condition

The main objective of this work was to study the effect of nanocrystalline (nc) grain size on the electrochemical behaviour of solid-state and interfacial processes in the Ni | oxide film | electrolyte system inside the potential region between hydrogen and oxygen evolutions. Nc–Ni thin films were deposited by magnetron sputtering onto alumina ceramic substrates. The study was performed in a pH 8.4 borate buffer solution by using the following in situ techniques: voltammetry, electrochemical impedance spectroscopy (EIS), and electrochemical quartz crystal nanobalance (EQCN) methods. Both the significant increase in the charge storage ability during anodic polarization inside the potential region of Ni(OH)2 formation and a shift of the onset potential for hydrogen evolution to the positive potentials due to the small grain size and the high volume fraction of grain boundaries in comparison to polycrystalline Ni have been observed. The oxide film properties were discussed in terms of the point defect model and the Mott–Schottky theory. The passive film behaves as a p-type semiconductor.