Hydrated water-soluble dendrimer-grafted polymer membranes for application to polymer electrolyte membrane fuel cells

We investigate a new molecular architecture in which water-soluble dendrimers are grafted onto a linear polymer for application to polymer electrolyte membrane fuel cells (PEMFC). Using full-atomistic MD simulations, we examined the nanophase-segregation and transport properties in hydrated membranes with this new architecture. In order to determine how the nature of the linear polymer backbone might affect membrane properties, we considered three different types of linear polymers: poly (epichlorohydrin) (PECH), poly (styrene) (PS) and poly (tetrafluoroethylene) (PTFE) in combination with the second-generation sulfonic poly aryl ether dendrimer to form PECH-D2, PS-D2, and PTFE-D2. Our simulations show that the extent of nanophase-segregation in the membrane increases in order of PECH-D2 (∼20 Å) < PS-D2 (∼35 Å) < PTFE-D2 (∼40 Å) at the same water content, which can be compared to 30~50 Å for Nafion and ∼30 Å for Dendrion at the same water content. We find that the structure and dynamics of the water molecules and transport of protons are strongly affected by the extent of nanophase segregation and water content of the membrane. As the nanophase-segregation scale increases, the structure in water phase, the water dynamics and the proton transport approach those to those in bulk water. Based on the predicted proton and water transport rates, we expect that the PTFE-D2 may have a performance comparable with Nafion and Dendrion.