Materials Letters
Volume 53, Issues 1-2 , March 2002, Pages 91-101

doi:10.1016/S0167-577X(01)00459-1    How to cite or link using doi (opens new window) Cite or link using doi
Copyright © 2002 Elsevier Science B.V. All rights reserved.

Impedance spectroscopy study of nickel electrodeposits

H. S. Karayiannia, Corresponding Author Contact Information, E-mail The Corresponding Author, G. S. Patermarakisa and J. C. Papaioannoub

a Section of Materials Science and Engineering, Department of Chemical Engineering, National Technical University of Athens, Iroon Polytechniou 9, Zografou 157 80, Athens, Greece
b Laboratory of Physical Chemistry, Department of Chemistry, University of Athens, Panepistimioupolis 157 71, Athens, Greece

Received 28 August 2000;  revised 19 June 2001;  accepted 21 June 2001.  Available online 30 January 2002.


Nickel electrodeposits prepared in NiSO4 and NiCl2 electrolytes with thicknesses of 43–49.4 small mu, Greekm 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 RaCa elements characterised by a single relaxation time, 8.27×10-6 s, combined in series with another Rb element, Rb<<Ra. 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 NiSO4–Ni and NiCl2–Ni deposits. The diffusion coefficient of hydrogen, 1.25×10-11 cm2 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.

Author Keywords: Nickel electrodeposits; Impedance spectroscopy; Hydrogen hopping/diffusion conduction mechanism; Microstructure model