Preparation And Characterization Of The Proton Exchange Membrane Incorporated By Ionic Liquids

Proton exchange membrane (PEM) is the core component of proton exchangemembrane fuel cell (PEMFC) which is an environmental friendly and effective powersource. At present, the development of PEM with high conductivity under operatingconditions (e.g. high temperature and low humidity) has become a hotspot anddifficulty. Ionic liquid (IL) as the promising anhydrous proton conductor has attractedconsiderable attention in recent years due to their advantages, including nonvolatile,good themal and chemical stabilities, and high ionic conductivity. In this thesis, thecomposite membranes with high performances under high temperature and anhydrousconditions were prepared by incorporating IL into membrane matrix. Sulfonated poly(ether ether ketone)(SPEEK) with controllable degree of sulfonated (DS) wassynthesized by changing the reaction time. The composite membranes were preparedby in suit method and immersing method. The membrane was characterized by meansof SEM, FTIR, SAXS, XRD, TGA, and tensile test. The porfermances wereinvestigated through the measurements of proton conductivity, swelling test, and ILlose weight. The influence of the control membrane structure, preparation method andconditions upon the loading amont of ionic liquid was investigated systematically;and the relationship between the membrane structure/IL loading amount and protonconductivity was explored in detail. The details were summarized as follows:(1) The SPEEK control membrane with different degree of sulfonation wasfabricated by solution casting method. The influence of degree of sulfonation on themembrane structure was studied. It was found that the channel dimension and protonconductivity of plain membrane increased with the increase of DS. For instance, at100%relative humidity and25℃, the proton conductivity of SP-43, SP-54, SP-62,and SP-75were11.1,14.3,23.5and32.3mS/cm; the mass lose of SPEEK membraneis below9%before260℃, suggesting that it has good thermostability, and has thepotential as the high temperature PEM.(2) The composite membrane was prepared by in situ method. The study focusedon the regulation of the IL on the membrane structure. With the increases of IL loading amount, the proton conductivity increased. For instance, when the loadingamounts were16%,25%,32%, and43%at140℃, the proton conductivities were3.6,4.6,6.1and8.5mS/cm, respectively.(3) The composite membrane was prepared via immersing method. The IL loadingamount can be regulated by changing the ultrasonic power, immersingtemperatureand time as well as other conditions. The study focuses on the regulationof the IL upon membrane structure and the influence of preparation conditions uponthe IL loading amount. It was found that the ultrasonic treatment had little influenceon the IL loading amount. The area swelling and channel dimension increased withthe increase of immersing temperature and time. As the loading amount increased, theproton conductivity increased. For instance, when the loading amounts were16%,25%,32%, and43%at140℃, the proton conductivities were5.2,6.1,7.4and9.3mS/cm, respectively, and the value increases more than1000times.(4) By comparison of the proton conductivity, structure and performance ofsoaking membrane and in suit membrane, results show that the thermal properties ofboth are similar, but the resistance to swelling performance mechanical property andproton transmission capacity of soaking membrane are better.