Preparation And Characterization On Ionic Liquid 1-Buty-3-Methylimidazolium Hexafluorophosphate And The New Anhydrous Conducting Membranes Based On Polymers Of Sulfonated Poly (Ether Ether) Ketone And Polyvinylidenefluoride

PEM is the key component of proton exchange membrane fuel cell (PEMFC). For solving the problems such as low conductivity, critical water and thermal managements and catalyst poisoning by fuel impurities in the case of PEMFCs working at temperatures lower than 100℃. Developing the high temperature PEMFCs working at temperatures above 110℃has been the focus in the field. Recently, low melting point,high conductivity and thermal stable ionic liquids,are collecting keen interests to be used as proton conductors for high temperature PEM.In this work, the ionic liquid of 1-buty-3-methylimidazolium hexafluorophosphate (BMIMPF6) was synthesized from N-methylimidazole, 1-chlorobutane and hexafluorophosphoric acid.BMIMPF6 was employed to prepare anhydrous conducting membranes based on sulfonated poly (ether ether) ketone (SPEEK) and polyvinylidenefluoride (PVDF) by solution casting method, respectively. And BMIMPF6/Nafion composite membrane was prepared by immersing Nafion membrane in BMIMPF6.The conductivity of BMIMPF6 and its composite membranes as well as the mechanical strength of the membrane were investigated at temperatures above 100℃and under anhydrous conditions.The conductivity of BMIMPF6 and the composite membranes were investigated above 110℃and the mechanical characters of the composite membranes were also tested at 25℃,110℃and 130℃, respectively.The conductivity of BMIMPF6 was 0.118 S/cm at 240℃.Under anhydrous conditions,the conductivity of BMIMPF6/Nafion composite membrane was 0.0030 S/cm at 200℃.For a membrane containing 60wt% BMIMPF6 in PVDF, the conductivity was 0.023 S/cm.The conductivity was 0.0015 S/cm for the membrane containing 40wt% BMIMPF6 in SPEEK with a sulfonation degree of 70% at 160℃, and which was raised up to 0.0051 S/cm and 0.0136 S/cm when porous SiO2-P2O5 and TFMSA were added, separately. At the same temperature and mass percents of BMIMPF6 in BMIMPF6/polymer, the mechanical strength of BMIMPF6/PVDF was better than that of BMIMPF6/SPEEK. For example, the percent of BMIMPF6 was 40% in both the two composite membranes,the stress of BMIMPF6/PVDF was 3.7 MPa, comparing to 0.45 MPa of the BMIMPF6/SPEEK with the sulfonation degree of 45% at 130℃. The mechanical strength of BMIMPF6/SPEEK composite membranes can be strengthened by the cross linkers of glycol and glycerol.The effects of mass percents of BMIMPF6 and temperature on the mechanical properties were also investigated.