Impact of a Compressive Stress on Water Sorption and Diffusion in Ionomer Membranes for Fuel Cells. A 1H NMR Study in Vapor-Equilibrated Nafion

Abstract

The electrolyte membrane is exposed to high compression loads when operating in a proton exchange membrane fuel cell (PEMFC). It was reported in the literature that compression impacts the membrane properties when immersed in liquid water but little is known about the quantitative effects of stress on water sorption and its dynamical properties when the membrane is at equilibrium with a humid gas. In this work, we investigated the influence of a static normal stress on the properties of Nafion® by pulsed field gradient NMR (PFGNMR) with a NMR compatible compression device. The results demonstrated a reduction in water content due to compression at high relative humidity (≥ 90% RH) and much more moderate effects at low hydration (≤ 85% RH). The changes observed on the diffusion properties are more pronounced and related to both water loss and a reversible modification of the membrane structure effective at the micrometric scale.