Investigating the influence of the side-chain pendants of perfluorosulfonic acid membranes in a PEMFC by molecular dynamics simulations

Abstract

In this study, we used full atomistic molecular dynamics (MD) simulations to evaluate the influence of the side-chain pendants of the PFSA polymer in membranes composed of Nafion or Aquivion ionomers. Despite the lower equivalent weight of the Aquivion ionomer, the Nafion and Aquivion ionomers exhibit similar densities at both room (298.15 K) and operating (353.15 K) temperatures, which leads to higher sulfonic-group/sulfonic-group and sulfonic-group/water-molecule correlations in the Aquivion membrane. We also found that the Aquivion membrane exhibits higher diffusion coefficients for water, hydronium ions, and oxygen molecules than the Nafion membrane. These results are in good agreement with the volume-analysis results, which reveal that the solvent volume is higher in the Aquivion membrane than in the Nafion membrane, which leads to favorable water channels and improved small-molecule diffusion. This study provides PFSA membrane-design insight that can improve PEMFC performance.