Cross-Linking of Bromo-Pillar[5]arenes and Sulfonated Poly(Aryl Ether Ketone Sulfone) Enhances Proton Conductivity of Membranes at Low Ion Exchange Capacity

Improving the overall performance of proton exchange membranes while maintaining high proton conductivity represents a persistent challenge. Bromo-functionalized pillar[5]arene (BrP5) is introduced as a multiarm cross-linker in sulfonated poly(aryl ether ketone sulfone) for the first time. Unlike traditional cross-linkers sacrificing proton conductivity, our pillararene-cross-linked membranes (SPAEKS-CL-QP5) retain cross-linking advantages without compromising conductivity, such as excellent oxidation stability (SPAEKS-CL-QP5-7% retained 84.2% after 24 h), low water absorption (9.7–18.4%), and low swelling (8.7–12.2%) at 80 °C, while exhibiting a high tensile strength of 50.4 MPa. SPAEKS-CL-QP5-7% exhibited a twice conductivity value per unit of ion exchange capacity (133.4 mS g cm–1 mmol–1) compared to the control Am-SPAEKS (65.2 mS g cm–1 mmol–1). The rigid pillar structure of pillararene macrocycles is critical to these performance improvements.