A new computational approach for SOFC impedance from detailed electrochemical reaction-diffusion models

A new computational approach for simulating impedance spectra of electrochemical systems from detailed models of elementary reactions and diffusion processes is presented. It is based on transient numerical simulations of the dynamics of the reaction-diffusion system when a periodic variation of overpotential is imposed. Impedance is calculated in the time domain maintaining the full nonlinearity of the system. This represents a numerical experiment of impedance measurements using frequency response analyzers. Combined with data fitting, the method yields chemical and physical parameters without the necessity of applying equivalent circuit models. The method is compared to the state-space modeling approach of Bieberle and Gauckler [Solid State Ionics 146, 23-41 (2002)] by applying it to the same six-step surface reaction model of the hydrogen oxidation reaction at an SOFC Ni/YSZ pattern anode. Good agreement is obtained between simulated impedance and literature experimental data. Advantages and limitations of the new approach are discussed.