Study of electrochemically formed Ni(OH)(2) layers by EIS

Passive layers formed in KOH and Ni(OH)(2) layers deposited under various conditions in Ni(NO3)(2) neutral solutions are studied by EIS in 1 M KOH. They act as a cpe considered in first approximation as a capacitance in a frequency range depending both on potential and on the formation conditions of the layer. Influence of formation conditions and ageing with time or potential on the p-semiconductive properties of passive layers are examined in relation to the stabilisation of the film. The capacitance of alpha-Ni(OH)(2) deposits decreases with thickness corresponding to insulating properties. Impedance results are consistant with an insulating porous layer covering the inner semiconductive passive layer. The difference in the electronic conductivity of deposits and passive layers may result from their different ionic conductivity: ionic species that easily diffuse into deposits, react with the electronic acceptor defects and the intrinsic semiconductivity is reached. On some thick deposits at Ni(OH)(2)/NiOOH equilibrium potential, the diffusion coefficient is deduced from the characteristic frequency in the low frequency range.