Assessment of ex-situ degradation of perfluorosulfonic acid membranes in water electrolysis

Abstract

The escalating energy demands and environmental concerns associated with fossil fuel consumption have resulted in various national policies and technical targets for green hydrogen production as a viable energy carrier and green chemical feedstock. Proton Exchange Membrane Water Electrolysis (PEMWE) is a promising technology for hydrogen production due to its high efficiency and compact design. However, the operational lifetime of PEMWE systems is hindered by the degradation of components, including PFSA membranes, under oxidising, acidic operating conditions.This study investigates the chemical degradation of PFSA membranes via an ex-situ ASTusing Fenton's reagent. Nafion® 115 and 117 membranes were subjected to varying ferrous (Fe2+) concentrations and exposure durations to simulate degradation caused by metallic impurities and radical species. Changes in key membrane properties, including Ion Exchange Capacity (IEC), Fluoride Release Rate (FRR), and surface morphology, were analysed. The in-situ performance of degraded membranes in PEMWE cells was also evaluated, focusing on polarisation behaviour, charge-transfer resistance, and ohmic resistance.Multi-modal characterisation revealed a dose-dependent degradation mechanism characterised by concurrent side-chain and main-chain scission, evidenced by a Fluoride-toSulfur ratio of ~18.6:1, at 30ppm Fe2+, and the simultaneous loss of backbone (728 cm-1) and side-chain (1060 cm-1) Raman signals. Profilometry identified a chemo-mechanical synergy, in which mechanical defects from cutting methods served as initiation sites for radical attack. In-situ testing of degraded membranes confirmed that these chemical and structural defects manifest as nonlinear increases in ohmic resistance and potential failure.The findings provide insights into the degradation mechanisms and establish correlations between ex-situ chemical degradation markers and the in-situ electrochemical performance of PEMWE cells.