Electrochemical and Structural Characterization of Recast Aquivion® EW720 Polymer Electrolyte Membranes for Proton Exchange Membrane Fuel Cell (PEMFC) Applications

Polymer electrolyte membranes based on Aquivion® polymer dispersion (D72-25BS), produced by Syensqo, were prepared using a standardized in-house Doctor-Blade casting technique for application in H2/air PEM fuel cells (PEMFCs). The study aimed to identify the optimal preparation method for low-equivalent-weight (EW = 720 g/eq) Aquivion®, a copolymer of TetraFluoroEthylene (TFE) and Sulfonyl Fluoride Vinyl Ether (SFVE), known as Short-Side-Chain (SSC) ionomer. SSC ionomers offer higher ion-exchange capacity (IEC) and proton conductivity compared to Long-Side-Chain (LSC) perfluorosulphonic counterparts. Comprehensive characterization was performed using in-situ X-ray Diffraction (XRD), micro-Raman spectroscopy, water retention, IEC, Dynamic-Mechanical Analysis (DMA), proton conductivity and electrochemical tests to assess the influence of casting methods and post-casting treatments. Two recast Aquivion® membranes were developed and compared to a pilot-scale e-PTFE reinforced Aquivion® membrane supplied by Syensqo. The recast Aqu10 membrane, thermally-treated at 155°C and subsequently acid-treated, showed an excellent proton conductivity of about 0.073 S/cm under harsh conditions (110°C; 50%RH) outperforming both the e-PTFE-reinforced reference membrane and the Aqu1 membrane, which was thermally treated at a higher temperature (190 °C). Moreover, the recast Aqu10 membrane achieved a power density of 0.67 W/cm2 (@0.6V) compared to 0.43 W/cm2 (@0.6V) under PEMFC operating drastic conditions (95°C; 50%RH) confirming the effectiveness of the selected preparation method and making this membrane a promising prototype for PEMFC applications.