(Invited) Pulse Current Currents Transient Curve Study: Hydrogen Discharge and Modeling Attempts

Abstract

Pulse currents and periodic reverse currents have proven to be of great interest for improving plating rate and coatings properties. Virtually all metals are sensitive to this technique. Pulse plating operates a periodically interrupted direct current. [1] Every short (usually a few milliseconds) cathodic pulse is followed by a short time-off, where no current is applied. Reverse plating implements an additional reverse current, periodically applied to the electrode [2]. Nevertheless, the optimum choice of the pulse current sequence parameters requires preliminary studies. Among them, the use of transient curves in response to pulse currents represents an interesting strategy. In the case of electrolytes with high Faradic yields, a succession of characteristic patterns may be observed. Particularly, two typical plateaus are noticeable, the first corresponds to the Faradic reduction of the metallic species involved below the diffusion limit, while the second, at higher potential, is attributed to the local resistance induced by the depletion of the concentration of the concentration of metal close to the interface. This situation called “diffusion limited range” interferes with the metal reduction, promoting the competitive hydrogen production. A recent work performed with copper during electroforming process show a large influence of the various steps on the hydrogen trapping into the coating [3]. On the contrary, electrolytes with low Faradic yields does not exhibit these two patterns, because the hydrogen discharge starts almost immediately with the current increase. In this case, reverse pulse is a possible solution to keep the possibility to modify the coating properties as for example the microstructure. In this case, the strategy for parameters determination is less obvious. In both situations, modeling constitutes a great help to seek for optimization. [1] J. Cl. Puippe and N. Ibl, J. Appl. Electrochem., 10, (1980) [2] E. J. Taylor, C. Zhou, and J. J. Sun, USPTO Patent Grants, (2005) [3] L. Lain Amador, J Rolet, M-L Doche, P. Massuti-Ballester, M-P Gigandet, V. Moutarlier, M. Taborelli, L. M. A. Ferreira, P. Chiggiato, J-Y Hihn, ECS trans. ECS Transactions 85(13): 815-822 (2018)