Investigation of Oxygen Reduction Mechanisms Using Cathode Microelectrodes, Part II: Analytical Modelling of La1−xSrxMnO3−d Electrochemical Impedance Spectrum

The oxygen reduction reactions (ORR) on La 1-x Sr x MnO 3-d (LSM) are not well understood at the molecular level. We couple the kinetic modeling of the oxygen reduction process with experiments on patterned microelectrode cathodes for analyzing the electrochemical impedance spectroscopy (EIS) response to investigate ORR. This paper presents the analytical modeling of EIS response due to specified oxygen reduction mechanisms on LSM. A model for ORR as proposed in literature with surface adsorption, electronation, diffusion and electrolyte diffusion is considered as a likely realistic reaction mechanism and is examined here. The intrinsic electrochemical properties for LSM are partially retrieved from literature. The EIS response of this model implies that the electrode surface processes can govern the high frequency region and the electrode surface and electrolyte bulk diffusion can govern the low frequency region in the EIS. A comparison of the simulated and experimental EIS as a function of P O2 indicates discrepancy between the two. The ORR model requires modifications and alternatives are proposed for further investigation.