AC-IMPEDANCE OF THE AMALGAMATED ZINC ELECTRODE

The dissolution kinetics of amalgamated zinc has been studied by imped ance spectroscopy. A single relaxation is observed in the complex impe dance diagram. Two plausible mechanisms are considered, the one-step t wo-electron transfer and the two-step consecutive mechanism with one a dsorbed intermediate. The impedance behaviour of these mechanisms was simulated and compared to the experimental results. For the two-electr on transfer mechanism a good agreement between experimental and theore tical data is observed at anodic potentials. However, in the cathodic region a disagreement occurs, and the reason for this is discussed. Fo r the two-step mechanism, with the first step in equilibrium, it was s hown that, if this mechanism prevails, the single relaxation observed descends from the intermediate adsorbed on the surface. This is due to the fact that the charge-transfer resistance becomes negligible compa red to the polarisation resistance when the first step is in pseudo eq uilibrium. The potential dependencies of the time constants involved a re discussed.