Polybenzimidazole containing ether units as electrolyte for high temperature proton exchange membrane fuel cells

• A flexible polybenzimidazole containing ether units (OPBI) was synthesized.
• OPBI was synthesized by a liquid–phase method under microwave irradiation.
• A H2SO4/OPBI hybrid membrane with high acid doping level was developed.
• The highest proton conductivity of the membrane is 190 mS cm−1 at 160 °C.

A rapid method to synthesize poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) through a solution polycondensation under microwave irradiation is explored. Synthesis parameters affecting the molecular weight (Mw) of OPBI, including the mass ratio of solvent to P2O5, the monomer concentration, and reaction time, are optimized. The main characteristics of OPBI are studied, and the corresponding membrane is prepared through a solvent casting process. A series of sulfuric acid doped OPBI (H2SO4/OPBI) hybrid membranes with different acid doping levels (ADLs) are developed. The effects of H2SO4 on microstructure, ADL and electrochemical properties of these membranes are explored. Herein, the hybrid membrane shows high proton conductivity (190 mS cm−1) at elevated temperature (160 °C) and anhydrous conditions, high ADL (18.73 mol of H2SO4 for OPBI per repeat unit, i.e., ADL = 18.73 mol PRU−1) and excellent dimensional stability (40.3%). All these properties demonstrated that H2SO4/OPBI hybrid membrane can be used as an alternative membrane for high temperature proton exchange membrane fuel cells (HT-PEMFCs).