Probing Oxygen Reduction Reaction Kinetics of Sr-Doped LaMnO[sub 3] Supported on Y[sub 2]O[sub 3]-Stabilized ZrO[sub 2]

Dense microelectrodes fabricated with well-defined microstructures and geometries using microelectronic fabrication techniques were studied using electrochemical impedance spectroscopy (EIS) to investigate the rate-limiting reaction step(s) for oxygen reduction reaction (ORR) on the (LSM)/ -stabilized (8YSZ) system. At least four distinct reaction processes were observed for ORR on LSM/8YSZ under ambient and at intermediate temperatures, which have been assigned tentatively to: (i) ion transport in 8YSZ with an average activation energy of , (ii) a surface diffusion process on LSM with activation energy in the range from , (iii) at least one surface chemical process on LSM with activation energies in the range from and an average capacitance value of , and (iv) a mixed bulk/three-phase boundary (TPB) charge transfer process with activation energies in the range from and an average capacitance value of . This study suggests that the overall ORR rate may be limited by mixed bulk/TPB charge transfer processes below and surface chemical reactions above . The ORR current contributions from the bulk oxide ion transport and TPB incorporation path was estimated by correlating microelectrode geometry to impedance data.