A perspective on DRT applications for the analysis of solid oxide cell electrodes

Conventional electrochemical impedance spectroscopy (EIS) is a popular in-situ technique for electrochemical analysis and has been widely applied in solid oxide cells (SOCs), including solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), to determine the polarization resistance of electrodes. To interpret the EIS, equivalent circuit models (ECMs) are widely used, however, usually pre-defined without careful evaluation of the electrochemical processes, such as some elemental processes might overlap in frequency domain. On this background, distribution of relaxation times (DRT) converted from impedance spectra has been developed, that can effectively separate the polarization processes with a high resolution. Rational ECMs can be obtained by calculating and analyzing the characteristics of DRT spectra. The DRT method has been successfully used to SOFCs and SOECs, enabling much clearer understandings of the corresponding electrochemical reaction mechanism of the cells. Although the DRT method has been explored in SOFCs and SOECs for more than ten years, while it is still in its infancy and faces some challenges. Here, we present a review for the status of DRT applications in SOFCs and SOECs. On the basis of rational interpretation of DRT spectra, we believed that the DRT analysis can facilitate the design of key materials for SOFCs and SOECs with high efficiency and excellent performance.