Characterizing transport mechanism of cathodic oxygen ions in SOFC by molecular dynamics

This paper investigates the oxygen ion conductivity (OIC) of cathodic materials in Solid Oxide Fuel Cells (SOFCs) by molecular dynamics simulation. Although the oxygen diffusion coefficient (ODC) is known to be one of the major factors associated with the ion conductivity of cathodic materials in the SOFC, other major process factors are remained to be further investigated so that the related oxygen ion conductivity can be fully characterized and enhanced. In order to search for significant factors that affect the OIC in cathode, the characteristics of doping effect and temperature change are simulated via Molecular Dynamics approach and the results are presented in details in this study. Based upon the modeling results, it is realized that the OIC at 773 K can be greatly improved by using the catalyst of Gd_1-xBa_xCo_yFe_1-y (GBCF). And also, the highest OIC at 973 K can be greatly enhanced by using the catalyst of La_1-xSr_xCo_yFe_1-y (LSCF). In addition, the modeling results also indicate that both the doping ratio and operating temperature are of significant factors for both ODC and OIC. Although ODC is a metrics that can be used to evaluate the mobility of oxygen ions inside the catalyst for cathode materials, it does not comprehend the characters of materials. In order to be able to fully characterize the conductivity of cathodic materials in SOFC, significant factors of OIC including the lattice structure of materials, the concentration of oxygen vacancy, and the operating temperature are fully explored in this paper for detailed system characterization. The modeling results clearly indicate that as the working temperature increasing from 773K to 973K, the largest OIC change is given by LSCF, and the smallest OIC change is provided by GBCF. Also, the ODC curve of the GBCF possesses highest ODC values in medium working temperature range due to large numbers of oxygen vacancy generated by the cathode.