DEPOLARIZATION BY MERCAPTOACETIC ACID DURING ELECTRODEPOSITION OF COPPER

Abstract

Mercaptoacetic acid (MAA) in acid copper sulphate electrolyte decreased the cathode polarization throughout the course of electrolysis at all concentrations up to 20 mgm./liter. Addition of small amounts of chloride caused further depolarization. When present together with cystine, MAA showed an independence of action. The depolarization caused by MAA was ascribed to a decreased activation overpotential due to substitution of a more readily dischargeable MAA–copper complex for the aquo–copper complex. The additional depolarization due to chloride was ascribed to formation of a still more readily dischargeable chloro–MAA–copper complex. The depolarization in both cases increased with time during prolonged electrolysis, apparently due to surface roughening with, presumably, a consequent increase in surface area and decrease in true current density.