High-performance triazine-structured polymeric ionic liquid cross-linking membranes with superior proton conductivity and phosphoric acid retention for high-temperature PEMFCs

Polymeric ionic liquids (PILs) serve as excellent modifying materials in the field of high-temperature proton exchange membranes, with the ability to notably enhance phosphoric acid retention capacity via ion-pair interactions. In this study, the triazine structure is introduced that increases the membrane's free volume and enables the incorporation of high-density quaternary ammonium (QA) groups. By crosslinking this triazine-ring hydroxyethyl ionic liquid at various concentrations (HIL x , x =5–20 wt%) with N-H-free polybenzimidazole (NbPBI), we fabricated a series of HT-PEMs that preserve the polymer backbone while improving PA retention and proton conductivity. This approach not only improves the retention rate of phosphoric acid (PA) but also enhances proton conductivity without depleting the sites of main-chain N–H. The optimized NbPBI-HIL 15 membrane achieved a proton conductivity of 104.5 mS cm -1 at 180 °C, while the NbPBI-HIL 20 membrane retained 81% of its PA at 80 °C and 40% relative humidity (RH). In fuel cell tests, the NbPBI-HIL 15 membrane achieved a peak power density of 737 mW cm -2 at 160 °C without back pressure. These results demonstrate that NbPBI-HIL x composite membranes are expected to be potential materials for high-temperature proton exchange membranes (HT-PEMs).