Sulfonated poly(p-phenylene)-based ionomer/PTFE composite membrane with enhanced performance and durability for energy conversion devices

Proton exchange membranes (PEMs) have to be fabricated as thin as possible to minimize the ohmic loss in the cell voltage of proton exchange membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs). Additionally, the dimensional and mechanical stabilities of the PEMs must be maintained because they are critical for prolonging the cell lifespan in energy conversion devices that are used in moist environments. Herein, a sulfonated poly(p-phenylene)-based (SPP) multiblock ionomer is impregnated into a porous polytetrafluoroethylene (PTFE) substrate as a practical strategy for fabricating a mechanically robust and thin membrane. A five-layered structure is fabricated using two PTFE substrates as the composite membrane to increase the interfacial area between the SPP ionomer and PTFE; PTFE is treated with n-propyl alcohol to mediate the interfacial interactions between the two incompatible components. The composite membrane exhibits enhanced dimensional stability and mechanical properties compared with those of the pristine membrane owing to the SPP ionomer interlocking with PTFE. Regarding the electrochemical properties, the cell performance of the composite membrane displays a high current density of 1.52 A/cm² at 0.5 V and 7.90 A/cm² at 1.9 V for PEMFC and PEMWE, respectively; these densities are 32% and 16% greater, respectively, than that of Nafion212.