Preparation and Properties of Composite Proton Exchange Membranes from Troger's Base-based Polyimides/Polybenzimidazoles for Fuel Cells Operating in a Wide Temperature Range

For proton exchange membranes used in fuel cells, it is critical to develop materials that can withstand a wide range of industrially relevant temperatures. In this work, novel polybenzimidazole (TB-PBI-N) containing Troger's base (TB) units was synthesized and used as a filler to be blended with TB-based polyimide (PI-TB-N) for five types of phosphoric acid-doped composite proton exchange membranes. The chemical structures, mechanical properties, thermal and oxidative stability, acid adsorption, swelling ratios, proton conductivity (s) and power density of H2O/air fuel cells (PD) of the composite membranes were characterized by Fourier transform infrared spectroscopy ( FTIR), magnetic resonance spectroscopy (1H-NMR), thermogravimetric analysis (TGA), and tensile tests. The effect of incorporated TB-PBI-N filler on the properties of the composite membranes were investigated in details. The results showed that the tensile strength of the composite membranes without phosphoric acid doping were 87.3-129.5 MPa, and 3.7-9.5 MPa for the acid doped membranes. The phosphonic acid uptake were 235.3%-288.7% after doping with the swelling ratios ranging between 13.9%-25.0%, and the composite membranes can conduct protons at wide temperature range from 30. to 160 degrees C. The maximum sigma and PD of the composite membranes reached up to 94.3 mS/cm and 334.6 mW/cm(2), respectively. Furthermore, it was found that the introduction of TB- PBI- N filler improved the mechanical properties and the dimensional stability for the phosphoric acid doped membranes. In addition, the TB units in TB-PBI-N have additional base sites, which enhanced acid adsorption capacity and greatly improved the s values of the membranes. Among the five membrane types, the TB-PI-5PBI membrane showed a tensile strength of 116.8 MPa, proton conductivity of 67.7 mS/cm (160., 0% RH). More importantly, the PD values of the fuel cells reached 58.9, 224.7 and 334.6 mW/cm(2) at 30, 80 and 160., respectively, indicating excellent application prospect in a wide temperature range under non-humidity environment.