Constrained hydrocarbon-based ionomers in porous Poly(tetrafluoroethylene) supports for enhanced durability of polymer electrolyte membrane fuel cells and water electrolyzers

Abstract

The dimensional stability of proton exchange membranes in the moisture involved energy conversion devices polymer electrolyte membranes fuel cells (PEMFCs) and water electrolyzers (PEMWEs) is a critical property to prolong the cell life span. Here, highly water swellable sulfonated poly(arylene ether sulfone) (SPAES) ionomers are incorporated into mechanically tough porous poly(tetrafluoroethylene) (PTFE) to reduce the dimensional change in water. Three different SAPAES with a degree of sulfonation ranging from 40 to 60 are synthesized, and their composites with PTFE are prepared. The reinforced SPAES membranes show enhanced dimensional and mechanical properties due to the mechanical stress of the PTFE supports (∼28 MPa) that oppose ionomer dilatation in water, which is evaluated from a thermodynamic perspective. The dimensionally stable composites show higher chemical stability in the ex situ Fenton's test and yield more stable long-term performance in both PEMFC and PEMWE, possibly due to reduced gas permeability and enhanced interfacial stability of the membrane electrode assembly. In the PEMFCs, the durability against wet–dry cycle at 80 °C is enhanced 3−4-fold, and in PEMWEs, the voltage increase over time at a constant current density of 2 A/cm2 is significantly reduced by suppressing the ionomer's swelling in the confined PTFE frames.