Modeling of the Area-specific Resistance of SOFC Cathodes by Application of a Square Grain Model Involving Grain Boundaries

A square grain model is proposed for the calculation of the area‐specific resistance (ASR) of porous cathodes for solid oxide fuel cells (SOFCs) by means of the finite element approach. The grains and pores are represented by squares of equal side length. The grain boundaries are assumed to be thin slabs of uniform thickness. Both blocking conditions for the ionic current and fast transport of oxide ions along the grain boundaries have been taken into account. The results of the simulation suggest that highly active cathode materials could be developed by increasing the grain boundary ionic conductivity. In the case of an average grain size of 0.1 μm, a remarkable decrease of the ASR is predicted, if the ionic conductivity of the grain boundaries exceeds that of the bulk by a factor of 100. The model has been applied to simulate the increase of the ASR due to degradation of La0.6Sr0.4CoO3–δ in dry and humid atmospheres at 600 °C. A rapid increase of the ASR is predicted in H2O‐containing atmospheres. The effect of Cr‐poisoning on the ASR has been modeled for dry and humid atmospheres at 600 °C. The degradation owing to Cr‐poisoning is most pronounced in atmospheres containing water vapor.