Engineering of microstructure and design of a planar porous composite SOFC cathode: A numerical analysis

Abstract

The electrochemical performance of a SOFC cathode depends not only on the activity of the cathode, but also on the relative facility by which the reaction participants are transported to the reaction site. The microstructure and the geometry of the cathode influence the relevant transport and reaction characteristics, and thereby the distribution of current density, in a complex manner. In this study, the influence of electrode porosity and thickness as well as current collector layer thickness and interconnect coverage was examined using a 2-dimensional across-the-channel model of a planar SOFC LSM-YSZ composite cathode. The results indicate that for a fixed functional layer thickness for the electrode, increasing the porosity of the electrode actually reduces the electrochemical performance but improves the oxygen distribution. Addition of a porous current collector layer improved both oxygen distribution and overall electrochemical performance. The results of varying interconnect coverage were very interesting in that an improved performance was observed upon reduction of coverage from 50% to 25% but no further change was observed upon further reduction to 12.5%. A closer examination of current density distribution for the cases of 25 and 12.5% coverages showed that a reduction of the coverage from 25% to 12.5% results in improving mass transport limitations under the interconnect but reduces electron transport under the channel. However, the electron transport limitation is offset by enhancement in oxygen distribution. The study highlights the need for simultaneous optimization of electrode microstructure and geometry.