An Imidazolium Type Ionic Liquid Functionalized Ether-Free Poly(terphenyl piperidinium) Membrane for High Temperature Polymer Electrolyte Membrane Fuel Cell Applications

Development of high temperature polymer electrolyte membranes is essential for advanced energy conversion and storage technologies. Herein, an imidazolium type ionic liquid (BPMIm) with a long side-chain of 5-bromopentyl is synthesized and employed as the quaternization reagent for ether-free poly(p-terphenyl-co-N-methyl-piperidine) (PTP). Grafting the flexible long side-chain imidazolium group into the ether-free polymer backbone not only improves the polymer solubility in organic solvents but also provides acid-base interaction sites for the following phosphoric acid doping that supports proton conductivity at above 100 °C. Compared with pure and iodomethane quaternized PTP membranes (i.e. PTP and PTP-Me), the prepared imidazolium ionic liquid grafted PTP membrane (i.e. PTP-PMIm) exhibits an enhanced phosphoric acid uptake and hence a superior anhydrous proton conductivity of 138 mS cm⁻¹ at 180 °C. The technical feasibility of the PTP-PMIm membrane is demonstrated in H₂-air fuel cells at temperatures from 160 °C–200 °C, which reaches a high peak power density of around 456 mW cm⁻² at 200 °C at ambient pressure.