Kinetics of electrode reactions in liquid ammonia. Part 4.—The CuII/CuI/Cu0 system in acid solution

Abstract

The Cu^II/Cu^I redox system is fully reversible on gold or platinum electrodes and quasi-reversible on vitreous carbon. When the metal electrodes are anodically oxidised prior to the measurements, the redox process is inhibited and curvature in the polarisation data indicate that the electrodes behave as p-type semi-conductors. The system Cu^I/Cu⁰ possesses unusual features. Whereas the dissolution of Cu⁰ to Cu^I is quasi reversible (k₀= 8 × 10^–5 cm s^–1) the deposition reaction is severely inhibited by the formation of unidentified insulating films which also retard the reduction of Cu^II to Cu^I. This result explains the poor quality of electrodeposits of copper from ammonia solutions described in the older literature.