DESC0024975

There is a national need for a comprehensive energy portfolio to build a sustainable hydrogen-based economy while addressing the climate crisis. The governmental goal to achieve carbon pollution-free electricity by 2035, and further, to achieve net-zero emission by 2050, will rely on the development of electrochemically driven membrane technologies. Among these technologies are fuel cells which electrochemically converts hydrogenĺs chemical energy into electrical energy without combustion. For heavy-duty applications, higher temperature operation (120 ľ 200 °C) is desirable for improved catalyst activity, higher tolerance to fuel impurities such as carbon monoxide, and a greatly simplified thermal and water management system. However, costly perfluorosulfonic acid ionomers are the prevailing membrane used in fuel cells and they cannot function at these temperatures due to its polymer structure and dependance on humidification for proton conductivity. Therefore, new durable membranes and membrane electrode assemblies that possess high conductivity thatĺs independent of humidification, mechanical and thermal stability, and stable fuel cell performance 120 - 200 °C are needed. The objective of this program is to develop and demonstrate non-perfluorinated, thermally stable aromatic membranes that meet the chemical, thermal, and mechanical properties necessary to qualify for the demanding environments within a high temperature proton exchange membrane fuel cell for heavy duty applications, like long haul trucks. The approach involves the synthesis of novel high molecular weight aromatic hydrocarbon membranes that possess polar moieties along the polymer backbone and pendant quaternary ammonium groups. Membrane electrode assemblies shall be fabricated and evaluated for fuel cell performance. During the Phase I, aromatic polymers with pendant quaternary ammonium groups shall be synthesized and utilized to fabricate stable phosphoric acid imbibed membrane composites. Specifically, high molecular weight poly(thioether benzonitrile) copolymers with pendant quaternary ammonium groups shall be synthesized using functionalized monomers to afford tailorable copolymer compositions. The copolymer will be controllably imbibed with phosphoric acid to create mechanically robust membranes based on the ion pair concept. A stable ion pair is formed because the phosphoric acid associates with the quaternary ammonium groups at energies comparable to ionic compounds capable of operating at 120 ľ 200 °C. The benzonitrile moiety offers an additional polar interaction to the phosphoric acid, which helps to stabilize the composite to increase phosphoric acid retention. The controlled imbibing process and concept design does not prepare gel membranes. The Benzonitrile- Phosphoric Acid ion pair membranes will be characterized for their physical and mechanical properties, including mechanical (tensile) strength, dimensional stability (swelling), and proton conductivity as a function of temperature and humidity. Membrane electrode assemblies will be prepared and evaluated for preliminary single cell performance, which will afford validation of a Technology Readiness Level 3. TRL 5 shall be reached via membrane incorporation into membrane electrode assemblies and the cell performance evaluation.