Proton Solvation and Transport in Realistic Proton Exchange Membrane Morphologies

Understanding the role of morphology of perfluorosulfonic acid (PFSA) membranes in defining their proton transport behavior is crucial for the development of the next generation of proton exchange membrane fuel cells. In this study, we build large-scale simulation models of three of the most realistic PFSAs morphologies proposed from the results of SAXS experiments and then examine the cation solvation and transport properties of these models. Upon equilibration with molecular dynamics, we find that the bundle morphology immediately flattens into ribbons, in agreement with the locally flat model. The lamellar model, the extreme version of the locally flat model, shows much too fast dynamical properties and too low density. The random model shows acceptable agreement with experiment; however, the bundle model shows the best overall agreement. The addition of sodium as a co-ion to the system makes the water less structured, and while this does not affect water transport it does slows all ionic transport.