Gaurav Raut

 

Modeling of equivalent circuits and their distribution of relaxation times to describe elementary processes in SOFC / SOEC

(a) Nyquist plot and (b) corresponding distribution of relaxation times Copyright: G. Raut (a) Nyquist plot and (b) corresponding distribution of relaxation times

Different challenges like electrode degradation or optimization of cell performance can be solved by studying distinct processes happening in an electrochemical system. The Electrochemical Impedance Spectroscopy (EIS) is one of the non-destructive methods to characterize these processes of electrochemical systems. Generally, in this method small perturbations of voltage/current are applied to an electrochemical system and the resulting current/voltage as well as the impedance with its corresponding frequency is recorded. Then Equivalent Circuit Models (ECM) are designed to fit with the experimental results of the impedance measurements. The Distribution of Relaxation Times (DRT) method can be used to separate the different processes as per their individual relaxation times if experimental data allow for that. But the experimental DRT data always have some redundancies due to which several ECMs can fit the experimental DRT data.

Several attempts have been made to find the equivalent circuit model which closely represents the thermodynamic and kinetic behaviour of Solid Oxide Fuel/Electrolysis Cells (SOFC/SOEC) under consideration. The various simple to complex ECMs can be designed to represent theoretical physico-chemical processes. The redundancy of DRT data could only be reduced by background measurements of the electrochemical system which is not possible in our case. Therefore, a precise characterization of the behaviour of DRT data from known ECMs is necessary. A database of DRT spectra from these different modelled ECMs will be created and compared with experimental DRT spectra to find out the best suitable model.