The separation membrane is a key component in Polymer electrolyte fuel cells. It must be both an ionic conductor and an electronic insulator. Cellulose nanofibrill membranes (CNM) are promising in this respect while being thermally and mechanically stable at high temperature and high humidity. They are cheaper and environmentally benign, and have better gas barrier properties but one order of magnitude lower proton conductivities than the commercial alternatives, Nafion. With surface functional groups, CNMs may interact differently with water molecules that transport protons in porous nanostructures. So, to further improve CNMs’ proton conductivity, we propose to use quasielastic neutron scattering (QENS) to study how surface functional groups of CNMs influence the water dynamics. Multiscale dynamics is expected and will be analyzed based on existing models developed for Nafion by QENS