Acceleration of Electroless Silver Deposition from Solutions Containing Cobalt(II) as Reducing Agent

By using cobalt(II) complexes with ammonia or organic amines as reducing agents electroless silver plating solutions of high stability were developed; the deposition of high quality Ag layers with plating rate 1 – 3 μm/h are known [1-3].

In this work, the possibilities to increase silver plating rate without changing of concentration of reactants and temperature were studied. The additives enhancing the partial electrochemical reactions of the electroless plating process – anodic Co(II) oxidation and cathodic Ag(I) reduction – were applied. The effect of chloride and bromide ions was studied by electrochemical and chemical kinetics methods, including electrochemical quartz crystal microgravimetry (EQCM).

Electrochemical measurements showed that the Co(II) anodic oxidation on silver electrode is enhanced  by the presence of halide ions. At 1 mM level, KCl additive change the rate of Co(II) oxidation only little, while KBr and KI increase the rate considerably. Accelerating effect of halides corresponds to the increase in adsorption ability of halides in the sequence Cl^-<Br^-<I^-, the adsorbed halide ions could facilitate the electron transfer through the halide bridge. The electroless silver deposition was shown to increase by factor of 2-3 at chloride concentrations 20 – 50 mM at satisfactory solution stability. The enhancing effect is related to anodic cobalt(II) oxidation reaction. AFM images of the silver surface showed absence of considerable changes of real surface area, and the rate increase is obviously not caused by development of catalytic surface.

References

1. 1. A. Vaškelis, E. Norkus, Electrochim. Acta 44 (1999) 3667.

2. A.Vaškelis, J. Jaciauskiene, A. Jagminiene, E. Norkus, Solid State Sci. 4 (2002) 1299.

3. E. Norkus, A. Vaškelis, A. Jagminiene, L. Tamašauskaite-Tamašiûnaite, J. Appl. Electrochem. 31 (2001) 1061.