Determination of Redox Currents in Electroless Systems: Correct Application of Mixed Potential Analysis

Abstract

Electroless processes have traditionally been modeled by way of the ‘mixed potential theory’, stipulating that the electroless process operates at a potential where the anodic and cathodic currents are of equal magnitude. The latter are typically measured in separate systems, with compositions similar to the process chemistry, however, absent either the oxidized or the reduced species. While valid for some processes, this application of the mixed potential theory fails in many others. A new method for characterizing electroless processes is presented here. Applying external current to the complete electroless chemistry, both the oxidation and reduction processes proceed in parallel, via the external current and through the electroless process. Monitoring the external current and the amount of deposited metal, the correct anodic and cathodic polarization curves in the actual system are determined and applied to the mixed potential theory. Using this method, excellent agreement was found in characterizing the process of electroless copper reduction by glyoxylic acid, a system which the classical mixed potential theory fails to correlate. Although applied here just to the copper - glyoxylic acid system, this technique for generating polarization curves in complete electroless systems is general and can be extended to other electroless and redox processes.