We propose a continuation experiment of our QENS study of water dynamics in the ionomer thin film (less than 10 nm) coated on the carbon grains of catalyst layers (CL) used for fuel cells. The CL is a complex multi-component system: porous carbon grains, Pt nanoparticles (catalyst), ionomer (Nafion) and water. The Nafion films in CL play a fundamental role: they collect protons and transfer them to the fuel cell electrolyte (Nafion membrane 25 mm thick). A molecular understanding of the water and proton dynamics in these CL's Nafion thin films is crucial to improve the design of optimized CL. We have shown in the past that coupled IN5/IN16 experiments allow to detect and analyse the proton dynamics in the Nafion thin layers without disturbance from the carbon support. We have already investigated the effect of carbon porosity, hydration level and Pt amount. In this proposal we want now to evaluate the effect of two other important parameters : the ionomer content and the functional groups density. This is an important issue to reduce the amount of Pt, which is one major industrial target for fuel cells development.