Synthesis Of Ionic Liquid 2,3-dimethyl-1-ethylimidazolium Dihydrogenphosphate And Preparation And Characterization Of Its Composite Membranes

Taking proton exchange membrane materials as the research content in this work, a high-temperature PEM proton exchange membrane which can be used above 110℃was prepared in order to overcome the shortcoming that proton conductivity of Nafion decreases significantly due to the water loss of the membrane at temperatures above 100℃.Ionic liquids, which exhibit excellent properties, such as high ionic conductivity, immeasurable low vapor pressure, good thermal and electrochemical stability, are suitable for incorporation into proton exchange membranes.In this work, the room temperature ionic liquid of 2,3-dimethyl-1-ethylimidazolium dihydrogenphosphate (DMEtImH2PO4)was synthesized through a two-step method from 1,2-dimethyimidazole,1-bromoethane(C2H5Br) and potassium dihydrophosphate (KH2PO4). Characterization of DMEtImH2PO4 was made by infrared spectra (IR), thermogravimetric analysis (TGA) and conductivities measurement. The conductivity of DMEtImH2PO4 was 177.3 mS/cm at 200℃.SPEEK/DMEtImH2PO4 membranes were prepared by introducing DMEtImH2PO4 in sulfonated poly (ether ether) ketone (SPEEK) and with a method of solution casting. The conductivity of the composite membrane SPEEK/DMEtImH2PO4 was measured under anhydrous conditions within a temperature range from 80℃to 170℃.The mechanical properties of the composite membrane SPEEK/DMEtImH2PO4 was studied at room temperature.The conductivity was 8.33 mS/cm for the SPEEK/DMEtImH2PO4 composite membrane containing 50 wt% DMEtImH2PO4 in SPEEK with a sulfonation degree of 70% at 170℃.Doping H3PO4 in SPEEK(SD=70%)/DMEtImH2PO4 composite membrane, the conductivity of the composite membrane could be enhanced. Introducing of ZSM-5 in SPEEK/DMEtImH2PO4 composite membrane could improve its mechanical properties. With a mass percent of 10% of ZSM-5 in the membrane, the tensile strength of the membrane reached 18.03 MPa at room temperature. The mechanical properties of the SPEEK/PVDF/DMEtImH2PO4 composite membrane were improved obviously in the presence of polyvinylidene fluoride (PVDF) at elevated temperatures.The tensile strength at break of SPEEK/PVDF(7:3)/(30wt%)DMEtImH2PO4 composite membrane with a sulfonation degree of 74% for SPEEK reached 1.73 MPa, elongation was 51.76% at 110℃.