Short-side-chain proton conducting perfluorosulfonic acid ionomers: Why they perform better in PEM fuel cells
Abstract
Short-side-chain (SSC) perfluorosulfonic acid ionomers (Dow 840 and Dow 1150) are characterised with respect to water sorption, transport (proton conductivity, electroosmotic water drag and water diffusion) and visco-elastic properties as a function of temperature and degree of hydration. The data are compared to those of Nafion 117, and the implications for the use of such ionomers as separator materials in direct methanol and hydrogen fuel cells are discussed. For this, a scheme is used which allows for the simulation of the water distribution and the resulting solvent (water, methanol) fluxes and potential losses across the membranes under transient and steady state conditions. The simulation results provide a rational for the lower solvent (water, methanol) cross-over in direct methanol fuel cells and the smaller potential losses in hydrogen fuel cells. The present comparison also demonstrates that combining high ion exchange capacity and high mechanical stability (elastic modulus and crystallinity) is a promising approach to improve membrane performance in both direct methanol and PEM fuel cells.