Physically-based modelling and distribution of relaxation times: tools for electrochemical reactions investigation and electrodes optimization in solid oxide cells

Understanding the phenomena involved in electrode kinetics is a key factor in the solid oxide cells (SOCs) development. We describe the effectiveness of physically-based modelling coupled with experimental results from electrochemical impedance spectroscopy (EIS) and 3D tomography, for both cathode and anode materials. Its application allows identifying the elementary kinetic mechanisms as well as the relationship between microstructural factors (e.g. three-phase boundary extension) and electrochemical performance, thus enabling electrode optimization and assessment of long-term stability [1-3]. The whole approach benefits from the integration of the distribution of relaxation times (DRT), which is a deconvolution method able to separate the overlapped contributions of EIS data. Conventional DRT algorithms suffer from numerical issues and the main drawback is the formation of artificial peaks in spectra. Here, a new algorithm is presented with an extension of the frequency domain by zero-padding technique to overcome such a problem. This solution improves the DRT stability, reducing the distortion of DRT curves, also when applied to critical EIS data set (e.g. noise, EIS curve does not close on real-impedance axis) [4]. Increasing the quality in evaluating characteristic frequencies of involved phenomena helps their identification, reinforcing the physically-based modelling hypotheses. These results underline the advantages of combining complementary tools able to separate impedance contributions in SOC electrodes.