AN EXPLANATION FOR DEPRESSED SEMICIRCULAR ARCS IN INTERFACIAL IMPEDANCE PLOTS OF THE INTERFACE BETWEEN METAL AND ELECTROLYTE

A new electrical equivalent circuit accounting for metal/solution interface about the surface heterogeneity of electrodes was proposed instead of the known semi-circular law. The present equivalent model consists of a ladder network of elements, where each element is made of a solution resistance in series with a parallel combination of double layer of capacitance and charge transfer resistance. The parameter-sigma, the standard deviation of normal distribution of double layer capacitance affected the depressed semi-circular arcs of different extent, which may be caused by various heterogeneities of the surface reactivity. The circuit which gives a depressed semi-circular arc is in agreement with the results of electrodeposition of copper from acidic copper sulphate solution.