| Proton exchange membrane (PEM) fuel cells are a proven technology to produce portable energy from hydrogen and thus are a vital element in the development of a hydrogen economy. An understanding of proton transport within perfluorosulfonic acid (PFSA) membranes is crucial to improve the efficiency of PEM fuel cells. Proton transport occurs through water channels created in hydrophilic pores in the membranes. This transport is a multiscale phenomenon, with the negatively charged polymer side chains, the morphology of the water channels, and the processing history of the polymer membrane all modulating the transport.;Using reactive molecular dynamics simulations, we have examined proton transport in hydrated PFSA materials. We have examined the effect of changing the length of the polymer side chain, and in so doing discovered the importance of a previously ignored proton transport pathway. We have also investigated the impact of the confinement and caging of the excess protons and water molecules within the hydrophilic pore and compared this to small amphiphilic molecules. Finally, we have built larger, more physically representative systems using information from small-angle x-ray scattering experiments and found the hydrated regions have a propensity to form locally flat yet generally tortuous morphologies with minimal surface area.;The lessons learned from this research will help design the next generation of PEM membrane materials, as well as informing the development of coarse-grained models to look at proton transport at much larger length scales. |
