Oxygen Transport Kinetics in Infiltrated SOFCs Cathode by Electrical Conductivity Relaxation Technique

Abstract

Infiltration has attracted increasing attention as an effective technique to modify SOFC cathodes to improve cell electrochemical performance while maintaining material compatibility and long-term stability. However, the infiltrated material's effect on oxygen transport is still not clear and detailed knowledge of the oxygen reduction reaction in infiltrated cathodes is lacking. In this work, the technique of electrical conductivity relaxation (ECR) is used to evaluate oxygen exchange in two common infiltrated materials, Ce0.8Sm0.2O1.9 and La0.6Sr0.4CoO3-δ. The ECR technique is also used to examine the transport processes in a composite material formed with a backbone of La0.6Sr0.4Co0.2Fe0.8O3-δ and possessing a thin, dense surface layer composed of the representative infiltrate material. Both the surface oxygen exchange process and the oxygen exchange coefficient at infiltrate/LSCF interface are reported. ECR testing results indicate that the application of infiltrate under certain oxygen partial pressure conditions produces a measureable increase in the fitted oxygen exchange parameter. It is presently only possible to generate hypotheses to explain the observation. However the correlation between improved electrochemical performance and increased oxygen transport measured by ECR is reliably demonstrated. The simple and inexpensive ECR technique is utilized as a direct method to optimize the selection of specific infiltrate/backbone material systems for superior performance.