Thursday, 27 July 2017: 14:40
Atlantic Ballroom 3 (The Diplomat Beach Resort)
Electrochemical impedance spectroscopy (EIS) is a powerful technique to characterize the performance of solid oxide fuel cells (SOFCs). Given a proper analysis technique, EIS data can shed light on the different contributions to the total impedance. The most common analysis technique is equivalent circuit modelling (ECM), where a combination of resistors, capacitors, constant phase elements, etc. represents the physical response of the sample. ECM has its known drawbacks, e.g. non-uniqueness and obscure physical meaning of the chosen model. Using impedance spectroscopy genetic programming (ISGP), based on evolutionary programming, those challenges are better tackled. Our analysis focuses on finding the distribution function of relaxation times (DFRT). The analysis procedure using ISGP yields a DFRT model comprised of known mathematical peaks. Each peak in the model is characterized by its height, width and relaxation time. It is possible to assign each peak to one or more process, and to calculate its area. Thus, we are able to determine the contribution of each process to the total impedance. By plotting the DFRT as a function of frequency it is possible to identify the different polarization processes and gain additional information, which may be convoluted and therefore undetected in other analysis techniques.
Here, we report the electrochemical performance of perovskite-type Co-free cathodes such as Ba0.5Sr0.5Fe0.91Al0.09O3-δ, Ba0.5Sr0.5Fe0.8Cu0.2O3-δ, and Ba0.5Sr0.5Fe0.8Nb0.2O3-δ with oxide ion conducting La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) and proton conducting Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3-δ electrolytes have been investigated by ISGP. Composites of cathode with electrolytes were screen printed on both sides of electrolyte in order to get symmetrical cells for evaluating cathode performances. EIS of symmetrical cells at different experimental conditions were analyzed by ISGP. Thus, by changing parameters and monitoring corresponding changes in the peaks’ relaxation times and areas, in-depth understanding of the operation of various components of the symmetrical cells such as the oxygen reduction reactions, mass transfer limitations and the electrolyte ionic conductivity can be achieved.