Understanding the electrochemical behaviour of LSM-based SOFC cathodes. Part II - Mechanistic modelling and physically-based interpretation

摘要

This study presents a physically-based model for the impedance simulation of the oxygen reduction reaction inudporous strontium-doped lanthanum manganite (LSM) cathodes. The model describes the surface mechanismudonly, taking into account the co-limited adsorption/diffusion of oxygen and the charge-transfer reaction at theudthree-phase boundary (TPB). After calibration with experimental impedance spectra, themodel is used to identifyudthe transition of kinetic regime fromthe surface to the bulk pathmechanism,which occurs at cathodic dc biasudof ca. 0.2 V within 700–800 °C. The transition is highlighted by a significant decrease in impedance and the appearanceudof a low-frequency inductive loop. The model consistently reproduces the impedance spectra beforeudthe transition of kinetic regime with a single set of parameters, allowing for the deconvolution of two features,udone associated with the co-limited adsorption/diffusion process (ca. 5 Hz) and another minor contribution dueudto the charge-transfer at the TPB (ca. 35 Hz). The model and its parameters, which quantitatively agree withudthe literature, can be used as a basis to optimize the microstructural and surface properties of technical LSMbasedudcathodes, showing that the TPB length is not the main parameter to be maximized.