Sulfonated Poly(fluorene alkylene)s Containing Dual Hydrophilic and Hydrophobic Side Chains for High-Performance Proton Exchange Membranes

Proton exchange membranes (PEMs) based on aromatic hydrocarbon polymers are considered promising alternatives to Nafion membranes. However, insufficient proton conductivity and stability hinder practical applications of hydrocarbon PEMs. Herein, we propose a series of aryl ether-free PEMs based on sulfonated poly(fluorene alkylene)s (SHF-HHF-x) by simultaneously incorporating dual hydrophilic and hydrophobic side chains. Benefiting from the featured side-chain structure, a well-defined microphase separation was formed within the SHF-HHF-x membranes. As a result, the SHF-HHF-x membranes exhibit high proton conductivity (up to 213.1 mS cm^–1 at 80 °C), as well as a low swelling ratio (<30%). In addition, these membranes demonstrated excellent oxidative stability with a high residual weight (>86%), after soaking in Fenton’s reagent (3% H₂O₂ and 4 ppm Fe²⁺) for 10 h. The H₂–O₂ single cell assembled with the SHF-HHF-70 PEM reached a peak power density of 941.6 mW cm^–2 at 80 °C. This study offers a design strategy for the preparation of high-performance PEMs.