Fabrication of methanol barrier layer on the sulfonated poly(ether sulfone) proton exchange membrane via interfacial polymerization

Proton exchange membrane (PEM) plays a critical role in conducting protons and mitigating methanol crossover in direct methanol fuel cells (DMFCs). In recent years, sulfonated poly(ether sulfone) (SPES) membrane has been extensively studied in DMFCs, while its methanol permeability is still unsatisfied. In this work, a methanol barrier layer was fabricated on the SPES membrane via interfacial polymerization to prevent methanol permeation. The interfacial polymerized polyamide layer has a dense structure that could prevent methanol permeation across the membrane, and the methanol permeability decreases with an increasing number of interfacial polymerization cycles. It is demonstrated that the optimized SPES-PA 5 membrane achieves a methanol permeability of 0.986 × 10 −7  cm 2  s −1 , which is much smaller than the SPES membrane (2.17 × 10 −7  cm 2  s −1 ). And it is noteworthy that the SPES-PA 5 membrane still exhibits a high proton conductivity of 0.12 S cm −1 at 20 °C. This work provides a feasible approach to reduce methanol permeability and preserve the high proton conductivity of PEMs.