Determination of the rate-determining step of the oxygen reduction reaction of La0.8Sr0.2MnO3(LSM)- 8mol% yttria-stabilized zirconia(YSZ): Composition and microstructure

Abstract In this study, LSM-YSZ composite cathodes were analyzed by changing the firing temperature, composition, and operating temperature to determine the contribution of each step of the oxygen reduction reaction (ORR). The overall resistance of the cathode reaction was characterized by fitting the AC impedance spectra with an equivalent circuit model. It was found that initial reactions of ORR (dissociative adsorption) are the main rate-determining step (RDS) regardless of operating or sintering temperature, while reactions on LSM surface become the main RDS when the ratio of LSM catalysts has a relatively small proportion. The [LSM-YSZ]5:5 cathode fired at 1100 °C showed the best microstructure and lowest resistance in the ORR at an operating temperature of 700 °C (RHF: 0.18 Ωcm2, RMF: 0.20 Ω cm2, RLF: 0.25 Ωcm2, Rcathode: 1.14 Ωcm2). This demonstrates the potential use of LSM-YSZ cathodes for IT/LT-SOFC without the use of expensive materials, such as LSCF and BSCF.