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

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 attributed to bulk charge transfer process.