Anhydrous Proton-Conducting Membranes Based on Protic Polymerized Ionic Liquids for Intermediate-Temperature Proton Exchange Membrane Fuel Cells

Anhydrous proton exchange membranes (PEMs) are pivotal for intermediate-temperature proton exchange membrane fuel cells (IT-PEMFCs), requiring stable mechanical properties and high proton conductivity under anhydrous conditions at elevated temperatures. This study introduces a series of innovative PEMs developed from composites of a polymerized poly(diallylmethylammonium) bis(trifluoromethanesulfonyl)imide (protic polyIL) and 1-methylimidazolium bis(trifluoromethylsulfonyl)imide (protic IL). These composites are tailored to serve as proton exchange membranes in hydrogen fuel cells operating between 80 and 120 °C. By adjusting the mix ratios of protic polyIL to protic IL (60:40, 75:25, 90:10 wt %), we observed that the latter functions as a plasticizer in the composite, reducing its glass transition temperature (Tg) and enhancing ionic conductivity. Spectroscopic analysis revealed that the incorporation of protic IL into protic polyIL forms a hydrogen bond between the bis(trifluoromethanesulfonyl)imide (TFSI–) anions and the proton from the cations. This interaction facilitates fast exchange of protons between protic IL and protic polyIL, leading to a high proton diffusion coefficient within the membranes. This study underscores the potential of anhydrous proton exchange membranes based on protic polyIL and protic IL for high-performance, intermediate-temperature PEM fuel cells.