Impedance spectroscopy study of nickel electrodeposits

Nickel electrodeposits prepared in NiSO 4 and NiCl 2 electrolytes with thicknesses of 43–49.4 μm were examined by the impedance spectroscopy (IS) method for a–c frequencies 1 Hz–100 kHz. The Nyquist diagrams were single, almost perfect semicircles, suggesting the applicability of the in parallel combination of the R a– C a elements characterised by a single relaxation time, 8.27×10 −6 s, combined in series with another R b element, R b≪ R a. This relaxation time predicted that the incorporated hydrogen atoms are involved in the process of conduction by a hopping/diffusion mechanism, which is differentiated in the cases of NiSO 4–Ni and NiCl 2–Ni deposits. The diffusion coefficient of hydrogen, 1.25×10 −11 cm 2 s −1, was determined. The microstructure of Ni electrodeposits was also studied and characterised by electron microscopy. Finally, a general model for the microstructure of Ni electrodeposits, consistent with the results of impedance spectroscopy, was formulated.