This project aims to improve our understanding of degradation phenomena in proton exchange membrane fuel cell (PEMFC) catalysts using operando scattering techniques. With the present proposal, we will combine two AST protocols for operando measurements, to make them more comparable to a “real-life application” and at the same time reduce the required measurement time substantially. We will apply the new concept of operando SAXS / WAXS measurements in a grazing incidence configuration allowing “catalyst-depth depending” information. We will compare a bimodal Pt/C catalysts with the respective monomodal catalysts. The combination of operando SAXS / WAXS measurements and ex-situ TEM analysis will be used to develop fitting models that will allow us to obtain probability functions similar to size histograms obtained in TEM analysis. Most importantly the model should not require the assumption of log-normal size distributions that does not take degradation phenomena into account.