Improving the durability of electrochemical energy conversion devices, such as PEM fuel cells or electrolyzers, is a crucial topic on their way to commercialization. In that context, simulation plays an important role, since building real prototypes and hardware testing is cumbersome and expensive. 3D CFD (computational fluid dynamics) simulation is the method of choice when it comes to the optimization of geometry features and operating conditions. To be able to simulate a realistic aging behavior of fuel cells, physical degradation models are needed. Those models should ideally be fully coupled with the performance models in order to close the feedback loop between degradation and performance: Local stressors, e.g. potential, affect the degradation rates and, vice versa, degradation rates affect the performance via modification of material properties. In this work, a fully coupled degradation model for the catalyst layer and the membrane of PEM fuel cells [1, 2] is presented. The model accounts for catalyst dissolution and redeposition, particle detachment and agglomeration, carbon oxidation, catalyst oxidation, carbon corrosion and chemical ionomer degradation. The model is applied to a number of use cases, such as accelerated stress tests with voltage cycles or an air start-up scenario (see Figure 1).