Intermodulated non-linear analysis of a redox couple in solution. 1. The model

The use of intermodulated nonlinear analysis is important in the study of electrochemical systems, in order to separate the effects of kinetic (alpha, and i(0)), mass transport (D-red and D-ox), and capacitive contributions within a single measurement at open circuit potential. The advantage of such treatment is that no assumption on the potential dependence of the parameters is required. In this paper, the mathematical framework for the analysis of the differential immittance spectra of the redox couple is extensively presented. The shape of the differential conductance and susceptance is discussed in connection to the faradaic and capacitive parameters, in order to guide the reader through the understanding of the system. It was observed that, by choosing the proper probe frequency, it is possible to emphasize one contribution with respect to the others. Thus, intermodulated differential immittance spectroscopy (IDIS) performed at different probe frequencies can help understanding in great detail the nonlinear behaviour of the electrochemical system. (C) 2015 Elsevier Ltd. All rights reserved.