The catalysis of the electrochemical reduction of cadmium ions by chloride ions

From the rate data obtained with impedance and demodulation voltammetry at varied concentrations of chloride ion acting as the catalyst, it is concluded that the cadmium ion reduction proceeds according to a CECEC mechanism. The second and third “chemical” steps show up because the catalyst accelerates specifically the first chemical and the first electrochemical step and because it does not affect the other steps to a significant extent. It is argued that the addition of a catalyst may serve as a general tool to unraveling the mechanism of an electrode reaction in a way that has some resemblance to variation of the electrode potential. The rate data, after correction for the Frumkin effect and complex formation, are treated as a function of the concentration, the surface excess and the surface activity of the catalyst, leading to a preference for the latter quantity. The way in which the catalyst exerts its activity is found to be greatly different from the results obtained earlier in this laboratory with thiourea catalyzing the Cd(II) reduction and with iodide ions catalyzing the Zn(II) reduction.