Triple-phase boundary and surface transport in mixed conducting patterned electrodes

The mathematical framework required to account for a triple-phase boundary (TPB) and the accompanying surface transport was added to a two-dimensional numerical model of a mixed conducting thin film by considering appropriate kinetic rate and mass-transport expressions. Approximate parameters were chosen so that the model qualitatively matched experimental results for patterned La(1-x)Sr(x)MnO(3 +/-delta) (LSM) electrodes, including trends with respect to thickness, active area, cathodic polarization, and sheet resistance. The rate of the TPB reaction was predicted to decrease due to sheet-resistance limitation, although it is expected to be independent of the active area and thickness of the film electrode when the effect of sheet resistance is insignificant. The addition of this feature is vital to the interpretation of patterned electrode experiments and to precise determination of parameters for better prediction of the electrochemical response of patterned LSM electrodes. The implementation and validation of this model is the next step in the development of continuum models useful to a variety of multiscale investigations of SOFC electrodes. (c) 2008 The Electrochemical Society.