Multifunctional poly(ionic liquid)s cross-linked polybenzimidazole membrane with excellent long-term stability for high temperature-proton exchange membranes fuel cells

Novel high temperature-proton exchange membranes (HT-PEMs) are prepared based on norbornene-type PBI (NbPBI) and double bond ionic liquids. For comparison, three ionic liquids are selected to prepare NbPBI-PIL membranes. Herein, the ionic liquids are synthesized into poly(ionic liquid)s (PILs) by in-situ free radical polymerization. Simultaneously, the PILs also react with the norbornene monomer of NbPBI to form a cross-linked network. After acid-base doping, the Br− or Cl− of PILs are successfully replaced with H2PO4− to promote proton transport. Notably, the NbPBI-PIL membranes exhibit high proton conductivity and enhanced phosphoric acid retention, especially the NbPBI-MPIm membrane has a proton conductivity of 0.074 S cm−1 at 170 °C and phosphoric acid retention of 87.2% and 73.8% under 160 °C and 80 °C/40 RH%, respectively. The single-cell with NbPBI-TPAm membrane obtains the highest power density of 385 mW cm−2 at 160 °C and negligible single-cell voltage decay after the 200-h test.