A two-dimensional model and numerical treatment for mixed conducting thin films

A two-dimensional simulation was developed for thin-film, mixed ionic-electronic conductor (MIEC) electrodes. The equations for the steady-state (nonlinear) dc case are derived and solved through a finite volume discretization that enables a linear solver while preserving the nonlinear characteristics of the problem. Using parametric data for La1-xSrxMnO3 +/-delta (LSM) collected from the literature, we found that the simulation is limited by electrochemically activated ionic transport at low cathodic overpotentials and co-limited by ionic and electronic resistance at high overpotentials. The current-voltage curves generated are similar in shape to most reported in the literature for thin LSM films. However, the simulation is much more resistive. While the cause for the discrepancy has yet to be validated, it seems clear that the sheet resistance of a thin-film electrode can critically influence its electrocatalytic behavior. This effect becomes more pronounced with the amplitude of polarization and the decrease in dimension, implying that it can be significant in patterned or nanostructured electrodes. (c) 2007 The Electrochemical Society.