Multi-scale solid oxide fuel cell materials modeling

Performance and degradation of fuel cell components are discussed in a multi-scale framework in this paper. Electrochemical reactions in a solid oxide fuel cell occur simultaneously as charge and gas pass through the anode, electrolyte, and cathode to produce electric power. Since fuel cells typically operate at high temperatures for long periods of time, performance degradation due to aging of the fuel cell materials should be examined. This phenomenon is treated in a multi-scale framework by considering how microstructure evolution affects the performance at the macro-scale. Mass and charge conservation equations and electrochemical kinetic equations are solved to predict the overall cell performance using the local properties calculated at the micro-scale. Separately, the microstructures assigned to the macroscopic integration points are evolved via the Cahn-Hilliard equation using an experimentally calibrated kinetic parameter. The effective properties of the evolving microstructure are obtained by homogenization and incorporated in the macro-scale calculation. The proposed model is applied to a solid oxide fuel cell system with a nickel/yttria stabilized zirconia (Ni/YSZ) cermet anode. Our model predicts performance degradation after extended hours of operation related to nickel particle coarsening and the resulting decrease in triple phase boundary (TPB) density of the anode material. The investigation of the microstructural effects on TPB density suggests that using Ni and YSZ particles of similar size may retard performance degradation due to anode aging.