Interpenetrating Network Polymer Electrolyte Membranes for Durable Fuel Cells

Hydrogen fuel cells utilize polymer electrolyte membranes (PEMs) to conduct protons while blocking electrons, hydrogen, and oxygen molecules. However, the cyclic swelling and contraction due to fluctuating water production during fuel cell operation can lead to fatigue crack growth in the membranes, limiting their lifespan. This study introduces an innovative approach to enhancing the fatigue resistance of electrolyte membranes by forming an interpenetrating network of Nafion, a plastic electrolyte, and perfluoropolyether (PFPE), a rubbery polymer. The Nafion-PFPE composite membranes were prepared by absorbing the PFPE precursor into the pristine Nafion membrane and then curing it to form a robust interpenetrating network.<br/>The introduction of the PFPE network modestly reduces the electrochemical performance of the membrane but significantly enhances its fatigue resistance. Compared to the pristine Nafion, the Nafion-PFPE composite membrane showed a 20% reduction in maximum power density but an impressive 175% increase in fatigue threshold. Under the wet/dry accelerated stress test, the lifespan of the Nafion-PFPE membrane was 410 hours, which is 1.7 times longer than that of the Nafion membrane.<br/>The study details the preparation process, where Nafion is submerged in a PFPE precursor, followed by UV curing to form an interpenetrating network. Mechanical characterization showed that Nafion-PFPE membranes have significantly higher fatigue threshold compared to pristine Nafion. For instance, the Nafion-PFPE-50 (50% saturation with PFPE) exhibited a fatigue threshold of 275 J m^-2, compared to pristine Nafion’s 100 J m^-2. Electrochemical tests demonstrated that Nafion-PFPE-50 maintained a current density of 0.574 A cm^-2 at 0.6 V, which is slightly lower than Nafion’s 0.892 A cm^-2 but still functional. The membrane also showed a moderate increase in hydrogen crossover, attributed to the increased permeability of the PFPE component. Despite this, the Nafion-PFPE-50 membrane displayed a comparable ohmic resistance to Nafion, indicating that the interpenetrating network does not significantly impede proton conduction. Further in situ wet/dry accelerated stress tests, which mimic real fuel cell operations with cyclic relative humidity changes, confirmed the enhanced durability of the Nafion-PFPE membranes. The open circuit voltage and hydrogen crossover indicated a 69% extension in operational lifespan for Nafion-PFPE-50 compared to Nafion. These findings suggest that the interpenetrating network of PFPE and Nafion significantly enhances the fatigue resistance and overall durability of PEMs in fuel cells.<br/>In conclusion, the development of Nafion-PFPE composite membranes offers a promising solution to the fatigue issues in PEMs, providing a balance between maintaining electrochemical performance and enhancing mechanical durability. This approach could lead to more durable and reliable fuel cells, contributing to the advancement of sustainable energy technologies.