Evolutionary programming based approach for SOFC cathode characterization: A case study on co-free mixed conducting perovskites

Cobalt-free perovskites were investigated in this work, in order to find more economical and chemically stable materials to serve as cathodes for intermediate temperature solid oxide fuel cells. The electrochemical performance of Ba_0.5Sr_0.5Fe_0.91Al_0.09O_3-δ and Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3-δ with oxide ion conducting La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ and proton conducting Ba_0.5Sr_0.5Ce_0.6Zr_0.2Gd_0.1Y_0.1O_3-δ electrolytes was studied using nondestructive electrochemical impedance spectroscopy. The measured data was analyzed by impedance spectroscopy genetic programming (ISGP), which results in a unique model that requires no a-priori knowledge of the tested system. In-depth cathode operation mechanism is shown by finding the distribution function of relaxation times (DFRT) using ISGP. By monitoring the changes in the DFRT models at different temperatures, we are able to de-convolute the oxygen reduction reaction to its several polarization processes. Using our analysis approach, it is possible to gain additional information, which may be convoluted and therefore undetected in conventional impedance analysis.