Transport-reaction modeling of the impedance response of a fuel cell

by Coignet, Philippe.

Electrochemical impedance spectroscopy (EIS) is a technique consisting of the application of a small perturbing current or voltage to an electrochemical system and measuring the response of the system. The response of the system can be described through the notion of impedance, Z, which is defined as the transfer function between the voltage and the current signal. By describing the impedance, one can gain insight into the interpretation of EIS experiments for the measurement of fundamental physical properties (eg diffusion coefficients). The impedance responses of electrochemical systems have been described in the past as an arrangement of ideal equivalent-circuit elements. Simple lumped-parameter circuits and more complex finite-transmission-line circuits have been used in the past, but the disadvantage of this approach is the difficulty in interpreting the equivalent-circuit parameters in terms of fundamental properties. It is then interesting to determine impedance by describing mathematically the fundamental physical processes that govern the response of the system. By describing and predicting analytically the impedance response induced by the perturbing current signal, one can: (i) gain considerable insight into the electrochemical process of interest, (ii) make explicit use of the modeling approach to address operational issues such as process design optimization, monitoring, diagnostics and control, and (iii) offer an interpretation to carefully designed EIS experiments for the measurement of fundamental physical properties such as diffusion coefficients or surface of active catalyst. - 3 -