Preparation and Properties of Composite Proton Exchange Membranes from Tr?ger'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 Tröger'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(σ)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 ℃.The maximum σ and PD of the composite membranes reached up to 94.3 mS/cm and 334.6 mW/cm2,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 σ 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/cm2 at 30,80 and 160 ℃,respectively,indicating excellent application prospect in a wide temperature range under non-humidity environment.
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