Universal Fluorine‐Free Proton Exchange Polymers for High‐Performance and Durable Fuel Cells Operable Under Severe Conditions

ABSTRACT Fluorine‐free proton exchange membranes (PEMs) could offer a promising alternative to perfluorosulfonic acid (PFSA) membranes, addressing challenges such as negative environmental impact, high cost, and limited performance under harsh conditions. However, fluorine‐free PEMs inherently suffer from low proton conductivity due to weaker acidity and poorly developed hydrophilic/hydrophobic phase‐separation, along with limited mechanical and chemical stability. Here, we report a novel and universal fluorine‐free PEMs featuring aliphatic chains in the backbone, which for the first time to dissolve all the issues mentioned, such as 2.6 times higher proton conductivity than PFSAs. Further physical reinforcement (SP‐PAC12 ₆₇ ‐QP‐4.5‐PE‐7) effectively extended their lifetime to 335.1 times of the original SP‐PAC12 ₆₇ ‐QP‐3.5, and exceeded 1.3 times of the state‐of‐the‐art fluorinated Nafion XL reinforced membrane, in the severely accelerated durability test. Furthermore, the fluorine‐free PEMs exhibited outstanding performance than Nafion XL, especially at elevated temperatures, proving their practical applicability as a promising alternative to the fluorinated counterparts.