Micro-scale modelling of solid oxide fuel cells with micro-structurally graded electrodes

A mathematical model was developed for modelling the performance of solid oxide fuel cell (SOFC) with functionally graded electrodes at the micro-scale level. The model considered all forms of overpotentials and was able to capture the coupled electrochemical reactions and mass transfer involved in the SOFC operation. The model was validated by comparing the simulation results with experimental data from the literature. Additional modelling analyses were conducted to gain better understanding of the SOFC working mechanisms at the micro-scale level and to quantify the performance of micro-structurally graded SOFC. It was found that micro-structural grading could significantly enhance the gas transport but had negligible effects on the ohmic and activation overpotentials, especially for thick electrodes. However, for thin electrodes with large particles, too much grading should be avoided as the increased activation overpotentials may result in higher overall overpotentials at a medium or low current density. Among all the cases tested in the present study, the micro-structurally graded SOFC showed significantly higher power density than conventional SOFC of uniform porosity and particle size. The difference between micro-structurally graded SOFC and conventional SOFC is more pronounced for smaller electrode-electrolyte (EE) interfacial particles. Particle size grading is generally more effective than porosity grading and it can increase the maximum power density by one-fold in comparison with conventional SOFC. The present study reveals the working mechanisms of SOFC at the micro-scale level and demonstrates the promise of the use of micro-structural grading to enhance the SOFC performance.