High Conductive and Dimensional Stability Sulfonated Polyimide/Expanded Polytetrafluoroethylene (ePTFE) Composite Proton Exchange Membranes for Methanol Fuel Cells

To address swelling, reduced mechanical strength, and high methanol permeability in sulfonated polyimide (SPI) proton exchange membranes, a composite membrane was developed by incorporating phenolic amine-modified porous expanded polytetrafluoroethylene (ePTFE) as a reinforcing skeleton within the SPI matrix. The resulting membrane (pore size: 0.1 μm) demonstrates a proton conductivity of 0.42 S/cm at 80 °C, low swelling rates (4% surface, 10% thickness), high tensile strength (33 MPa), and reduced methanol permeability (0.11 × 10–6 cm2/s). The ePTFE skeleton enhances mechanical strength, limits water absorption, and ensures continuous proton transport. Additionally, hydrogen bonding between the phenolamine groups on ePTFE and the sulfonic acid groups of SPI further improves the membrane’s performance. This study presents a straightforward strategy for developing high-performance SPI membranes.