Modeling of Proton Conductivity through Perfluorosulfonate Acid Electrolyte Membranes

Abstract

Proton conductivity through perfluorosulfonate acid (PFSA) polymer electrolyte membranes was investigated using a nanoporous network model to describe transport of charged species through PFSA membranes. The membrane was modeled as an indeterminate network of random fractal nanopores with the PFSA anionic groups fixed along the pore wall according to a distribution determined by the equivalent weight and dry membrane density. The transport of the hydronium ions inside the pore was expressed using the Nernst-Einstein equation. Continuum percolation theory and a fractal structural model were used to determine a relevant diffusion coefficient and to illustrate the possible transport mechanisms. The conductivity of the membrane was deduced in terms of the following quantities: water content, equivalent weight, temperature, and the architecture of PFSA polymer. Theoretical predictions of the model for varying water content and temperature were compared against experimental conductivity data of four commercial PFSA membranes.