Design and Evaluation of Hydrocarbon-Based Polymeric Ion-Exchange Membranes for Fuel Cell and Electrolyzer Applications

The advancement of a sustainable hydrogen economy hinges on the development of efficient, affordable materials for energy conversion technologies. Although perfluorinated membranes such as Nafion® are widely used in state-of-the-art fuel cells and water electrolyzers due to their superior conductivity, their high cost, environmental concerns, and reduced performance at elevated temperatures pose significant challenges. This work tackles these issues by developing, synthesizing, and evaluating a new generation of ion-exchange membranes through a dual-path investigative approach. Initially, the study assesses a novel linear polymer, poly(terphenyl-co-3-bromo-1,1,1-trifluoroacetone) (PTBFA), for potential use as both proton and anion exchange membranes (PEMs and AEMs). The sulfonated PTBFA was unsuitable for PEMs owing to a low ion-exchange capacity. After assessing the performance of proton exchange membranes and finding them limited by low ion-exchange capacity and water uptake, attention was redirected to anion exchange membranes. Although structural modifications led to some improvements in ion-exchange and hydration properties, the overall performance of PTBFA-based anion exchange membranes remained inadequate. The most noteworthy progress was achieved with the design of a branched poly(terphenyl piperidinium) (b-PTP), which, upon quaternization with iodomethane. This architecture exhibited exceptional thermo-mechanical robustness, with dynamic mechanical analysis (DMA) indicating a storage modulus of 108-109 Pa sustained up to 200 °C. Enhanced water diffusivity in the hydroxide form further supported the development of an interconnected conductive network. At the same time, ionic conductivity reached 35.76 mS/cm in the HCO3- and 32 mS/cm in the I- form at room temperature. In general, these results position the cost-effective branched poly(terphenyl piperidinium) membrane as a strong contender to replace conventional materials, providing a credible route to more economical and robust alkaline fuel cells and water electrolyzers for the next generation of sustainable energy devices.