Second harmonic ac voltammetry study of a fast faradaic process in the presence of the uncompensated resistance

A procedure is presented for the analysis of faradaic admittance obtained by the second harmonic ac voltammetry in the presence of the uncompensated resistance. The procedure involves the analysis of the equivalent circuit with a current source at the double frequency and normalization of the second harmonic faradaic current to the square of the interfacial potential. A system was developed for both instrument control and data acquisition in order to implement this method. The procedure was applied to an ac quasi-reversible (over the frequency range 100 Hz to 1 kHz) case for a freely diffusing redox species Ru(NH3)63+. The validity of the suggested method was established by comparison of the parameters derived from the first and second harmonic faradaic admittance data.