A Practical Method for Modeling of Solid Oxide Fuel Cell Stack Degradation

In this paper, the influences of area specific resistance (ASR), current density, temperature and thermal cycle (TC) on solid oxide fuel cell (SOFC) degradation were analyzed and quantified. The cell degradation equation and its influence equations with ASR, current density, temperature and thermal cycles were derived. Based on these equations, several ideal cases were studied. Meanwhile, a practical method considering three types of SOFC stack degradation behaviors based on empirical data were employed. This was done using an inhouse SOFC dynamic-link library as an input into a computational fluid dynamics (CFD) tool for modeling voltage decay and end of life (EOL) performance. It allows for a detailed 3-D study of a solid oxide fuel cell stack. It is revealed that the operating current density and cell ASR are two factors directly determining the degradation rate of individual cells. In addition, the operating temperature has a significant influence on the lumped ASR, thus also influencing cell degradation rate. The influence of contact ASR on cell degradation can be superior to that of temperature in that a contact resistance increment due to a thermal cycle, or other event, can cause a step change with a cell temperature increase and cell voltage decrease. It is suggested to run a stack below a certain critical peak internal temperature is favored, and if the contact loss is around 0.1 Ωcm², one may offset the cell degradation by increasing operating temperature about 30°C. However, if the stack is operated above the cell critical peak temperature, it may cause an ineluctable increase in degradation.