Cadmium reduction process on paraffin impregnated graphite electrode studied by elimination voltammetry with linear scan

This paper describes the process of cadmium reduction by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and elimination voltammetry with linear scan (EVLS). Experiments were performed on paraffin impregnated graphite electrode (PIGE) or hanging mercury drop electrode (HMDE) in aqueous solutions with different supporting electrolytes. The EVLS, as a new mathematical model for deeper interpretation of electrode processes, requires experimental voltammetric curves measured at different scan rates. By using chosen elimination functions this method enables certain current components to be eliminated and unknown processes to be revealed. While the LSV current responses of cadmium were quite similar for both electrodes, the EVLS curves showed substantial differences. In each of the electrolytes (NO3-, Cl−, and SO42-) there were differences in EVLS functions between HMDE and PIGE, due to the different behavior of anions in the electrode double layer. On PIGE a kinetically controlled process was identified. The effect of electrode surface roughness and scan rate on this process was investigated. Voltammetric results were complemented with electrochemical impedance spectroscopy (EIS), and the reduction process of Cd2+ was discussed on the basis of calculated heterogeneous rate constants and charge transfer coefficients.