Synergistic Enhancement of Proton Conductivity in Proton Exchange Membranes via Acid–Base Cross-Linked Dual Proton Channels

Proton exchange membranes possessing a high proton conductivity and robust mechanical stability are essential for achieving high power density and long-term durability in fuel cells. To address the challenge of balancing mechanical stability and proton conductivity in proton exchange membranes, this study presents a cost-effective and easily fabricated strategy for constructing fluorine-free composite membranes. Using sulfonated polyarylene ether nitrile (SPEN) as the polymer matrix and amino-functionalized silica as the functional filler, an acid–base ion-pair cross-linked network is established. This structure simultaneously creates dual proton channels while enhancing the mechanical integrity. The resulting composite membranes exhibit both a high proton conductivity and excellent dimensional stability. Compared with the widely used commercial Nafion membranes, the developed SPEN-SN composite membranes exhibit enhanced mechanical properties and proton conduction. The tensile strength and modulus of the SPEN-SN composite membranes both surpass those of the pure SPEN membrane. Besides, its tensile strength reaches 57.5 MPa, which is 2.42 times that of the Nafion membrane in the dry state. The proton conductivity of the SPEN-SN-5 membrane reaches 0.162 S/cm at 80 °C. Remarkably, the conductivity remains nearly unchanged over a 120 h stability test, demonstrating exceptional operational stability. Furthermore, when applied in an H2/O2 fuel cell with a low Pt loading (0.2 mg/cm2), the membrane achieves a peak power density of 405 mW/cm2. These results underscore the potential of SPEN-SN composite membranes as promising alternatives for fuel-cell applications.