Résumé
Small angle neutron scattering experiments were performed on a Proton Exchange Membrane Fuel Cell in order to determine the transversal water concentration profile, within the polymer electrolyte. This is determined, for the first time, under the state of art operating conditions. From the scattering spectra, different concentration profiles were deduced and discussed in term of a competition between electro-osmosis and back-diffusion. For steady states, the balance between these driving forces is modified by the current density. It is also demonstrated that this equilibrium is laterally non-uniform in the fuel cell. This is especially pronounced between the gas inlets and outlets, in a co-flow geometry.