Electrochemical study of the activating solution for electroless plating of polymers

This paper presents an electrochemical study about the activating solutions of the electroless plating of polymers, containing Pd(II), Sn(II) and Sn(IV) mixtures in HCl as main components. The objective of the study is the voltammetric characterization of these solutions by cyclic and linear voltammetry in order to study the recovery of tin and palladium from these solutions. The effect of concentration and rotation rate on the current−potential curves was studied using the RDE technique. The electrochemical behaviour of solutions prepared in the laboratory was performed as a prior step to the further study of real activating rinsing solutions. The electrochemical reduction of Pd(II) takes place in two one-electron transfer steps which are mass transport controlled. The electrochemical reduction of Sn(II) and Sn(IV) is also mass transport controlled and takes place with direct formation of metallic tin, although the electrochemical reduction of Sn(IV) only takes place in solutions with HCl concentrations higher than 1 M. The presence of additives in the real solutions prevent the chemical reduction of Pd(II) and the formation of Sn(IV) hydroxylated complexes. This causes the appearance of well defined diffusion waves attributable to the electrochemical reduction of Pd(II) and Sn(IV). Hence, the recovery of both species simultaneously as well as separately could be carried out, if appropriate conditions are selected.