Transport Properties and Morphology of Cerium Oxide Composite Sulfonated(Poly Arylene Ether Sulfone) Membranes for Application in Heavy-Duty Fuel Cell Vehicles

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Fuel cells for Heavy Duty Vehicles (HDVs) offer easy scalability and the potential for critical reduction in CO2 emissions. During the drive cycles of HDVs, the fuel cells will operate over a range of temperatures, with increases while climbing up steep gradients. Operating temperatures above 90°C will be necessary, along with low relative humidity (RH) due to the need to avoid pressurization of gases. Therefore, Proton Exchange Membranes (PEMs) for HDV applications need to be suitable over this range of conditions, including functioning at high temperatures and low relative humidity. Moreover, the membranes should not swell extensively when more water is present.In this study, sulfonated poly (arylene ether sulfone) multiblock copolymers were modified with the incorporation of clusters of modified cerium oxide nanoparticles to form composites. These synthesized novel membranes approach operational proton conductivity requirements for HDV vehicles, with conductivity of 15mS/cm at 120°C and 25% relative humidity, remarkably avoiding the typical large decrease in conductivity observed below 70% RH in non-fluorinated PEMs. One purpose of this study is to understand the water, proton, and polymer interactions within these membranes. The cerium nanoparticles and sulfonamide clusters play a critical role in the membrane, affecting conductivity, and water transport, especially at high temperatures and low relative humidity, while also suppressing swelling of the membrane. Membrane proton conductivity is also strongly influenced by physical properties such as water uptake and dimensional swelling behavior, which is further impacted by polymer morphology. To probe the dynamics of the components, the diffusion coefficient and relaxation time of water in the membrane and the protonic conductivity of the membrane as functions of membrane water content are analyzed using nuclear magnetic resonance (NMR) measurements and water uptake measurements. Film property and morphology changes are evaluated using Transmission Electron Microscopy (TEM) and Small-Angle X-ray Scattering (SAXS). This study demonstrates the advantageous and non-linear benefits of closely packed acid clusters with cerium oxide composites on membrane functionality under HDV operating conditions.