Integrated description of electrode/electrolyte interfaces based on equivalent circuits and its verification using impedance measurements.

An integrated theory describing both faradaic and nonfaradaic currents obtained upon potential step at an electrified electrode/electrolyte interface has been developed based on equivalent circuits that had been used to explain electrochemical reactions and experimentally verified. The faradaic current is shown to consist of the mass transport-dependent and -independent parts, which is in general agreement with the expression previously derived from the diffusion equations. The decay of the capacitive current is determined by the time constant represented by the product of the resistance obtained from the parallel connection of the solution and polarization resistances and the double layer capacitance; this is not consistent with the current understanding of the capacitive current decay, which takes into account the double layer capacitance and the solution resistance only. Many insights into the electron-transfer reactions are discussed based on the interpretation of impedance representation of the system, which would not have been possible without the present theory.