Fuel cells are an environmentally friendly alternative to combustion engines since they use hydrogen to generate electric power. To assure the fulfilment of the lifetime targets, extensive aging tests are required. In order to reduce the amount and costs of these tests, it is necessary to use a predictive simulation model. A performance model has been developed by ZSW using Matlab®. This model is now being extended to include the degradation model. There are many processes which cause degradation in the cell components. The focus of this work is on the electrochemical aging behavior of catalyst layer, including also first aspects of carbon corrosion and dehydrophobization effects. The catalyst consists of the support material carbon and the catalyst material platinum. On the surface platinum and carbon oxidation and corrosion occurs, Pt ions dissolve and move into the membrane, particles detach and agglomerate. The result of these mechanisms is the reduction of the electrochemical active surface area which leads to performance loss. Additionally, the reduced ionomer coverage of the catalyst and carbon corrosion results in a decreasing contact angle, leading to dehydrophobization and thereby to a limited O2 mass transport. The degradation is calculated using an ODE system based on the particle radii and size distribution for every time step. At the beginning, the size of the particle radii and the distribution are defined. The change in these two variables is then calculated in the ODE system and the active surface area of platinum is computed as one influencing aging factor.