The transition to renewable energy requires efficient hydrogen production and utilization technologies, where proton exchange membranes (PEMs) play a critical role in water electrolysis and fuel cells. Conventional perfluorosulfonic acid (PFSA)-based membranes, such as Nafion, offer high proton conductivity and chemical stability, but suffer from high cost, environmental concerns, and performance limitations under low humidity. Therefore, research has shifted toward nonfluorinated PEMs, which face a persistent trade-off between proton conductivity and mechanical stability. This review critically examines recent strategies aimed at mitigating this compromise, including polymer backbone modification, polymer blending, cross-linking, and mixed matrix membranes. Backbone modification approaches such as sulfonation of ether-based polymers, incorporation of nitrogen-containing structures, and development of ether-free frameworks are discussed with emphasis on conductivity–stability balance. Blending strategies leveraging acid–acid and acid–base interactions, as well as advanced cross-linking techniques, are evaluated for their impact on dimensional integrity and durability. Finally, mixed matrix membranes incorporating functional fillers, such as metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and carbon-based nanomaterials are discussed for their ability to enhance proton transport while reinforcing mechanical strength. Comparative analysis of conductivity, tensile strength, and swelling behavior reveals that ether-free backbones and COF-based composite membranes offer the most promising pathway toward high-performance, PFSA-free PEMs. This review concludes with design recommendations for next-generation membranes targeting simultaneous improvements in conductivity, chemical stability, and mechanical robustness.
Keulen et al. (Fri,) studied this question.