Impedance Studies of Thin-film and Patterned Sr-doped LaMnO3 on Yttria- Stabilized Zirconia to Probe Oxygen Reduction Kinetics

Abstract

Sr-doped LaMnO3 (LSM)/Yttria-stabilized Zirconia (YSZ) are the conventional cathode/electrolyte materials for SOFCs. However, the mechanisms that occur during oxygen reduction reaction (ORR) at the cathode/electrolyte interface are still unclear and have been a roadblock for further enhancement of SOFC performance, especially at low-temperatures. For this study, LSM is fabricated on sputtered and single crystal YSZ by thin-film techniques and patterned via photolithography to obtain precise microelectrodes. EIS results on thin-film LSM microeletrodes supported on thin-film YSZ showed at least four distinct processes during ORR, which were tentatively assigned to (i)surface chemical reaction on LSM, (ii)surface diffusion on LSM, (iii)electrolyte ion transport and (iv)bulk+three-phase boundary (TPB) charge transfer process. It should be noted that the resistance associated with bulk+three-phase boundary charge transfer was highly dependent on LSM electrode thickness. In contrast, thin-film LSM microelectrodes supported on single-crystal YSZ exhibited one distinct process, which is be attributed to bulk charge transfer process.