Micro scale dynamic modeling of LSM/YSZ composite cathodes

•Numerical model for oxygen reduction reaction on LSM–YSZ composite cathodes•Prediction of contribution from bulk and surface pathways for oxygen reduction•Assessment of sensitivity of the predictions to model parameters•Accurate capture of experimental trends by the model

In this study, a detailed reaction mechanism for oxygen reduction on LSM/YSZ is applied to dynamic one-dimensional micro-scale modeling of LSM–YSZ composite cathodes. The model incorporates the effects of cathode microstructural properties on the local transport phenomena and electrochemistry inside the cathode. The reaction mechanism used in the model features two parallel routes for bulk gas oxygen conversion to electrolyte lattice oxygen, namely two-phase boundary (2 PB) and three-phase boundary (3 PB) pathways. The model predicts field distributions of local thermodynamic values, over-potential, Faradaic current and other parameters relevant to cathode performance. Electrochemical impedance simulations are performed in the time domain to analyze the contribution of specific mechanistic steps to the overall impedance. A parametric study was performed to assess the sensitivity of the model predictions to selected model parameters and cathode micro-structural properties. Results reveal that the relative contribution from 3 PB and 2 PB pathways to the total charge transfer is dependent upon operating conditions. Parametric sensitivities observed in the impedance results are compared with polarization simulations to assess the physical plausibility of the proposed reaction and transport model. Simulation results are further compared to experimental findings reported in literature.