Study On Synthesis And Proton Conduction Of Metal-organic Framework/Chitosa Hybrid Proton Exchange Membranes

The proton-exchange membrane（PEM） is an essential part of the proton-exchange membrane fuel cell（PEMFC）. The anode and cathode are separated by the membrane, which is permeable to protons but not to electrons. The proton-exchange membrane（PEM） allows H+ions generated at the anode to migrate to the cathode, the membrane therefore acts as a salt bridge. The PEM greatly affects the life and property of the fuel cell. Therefore, the research of the PEM is the hot spot of the PEMFC all the time. In recent years, the organic metal frameworks with a specific function still can receive extensive attention of chemists. The MOF material based on better characteristic of thermostability, structure can be designed, pore space can be functionalized modifications as well as the larger specific surface area, shows a tempting prospects in many fields, for example optical material, magnetic materials,gas adsorption and separation, heterogeneous catalysis and electrical materials, etc.The metal organic framework materials with hole cavity or the proton affinity groups,having unique structure and proton transport channel, have obtained the certain development in proton conductivity. The research of introducing the complexes into the proton exchange membrane not only greatly promotes the MOF materials to the practical application, but also offers a new way for proton exchange membrane modification. In this paper, we synthetize two mesoporous complexes: one is chromium（III） oxoterephthalate [Cr₃O（H₂O）₃（bdc）₃]（MIL-101）, and the other is[Cr₃O（H₂O）₃（STA）₃]·n H₂O（S-MIL-101）. Meanwhile, we get H₂SO₄@MIL-101,H₃PO₄@MIL-101 and CF₃-SO₃H@MIL-101 with the method of putting MIL-101 into acids. Using chitosan（CS） as substrate, we can get a series of protons composite membrane by blending method and solvent casting method. We test the electrical conductivity of all membranes, and learn the characteristics of these membranes by FT-IR, thermogravimetric, elemental analysis, scanning electron microscopy and transmission electron microscopy. Finally, we also explore the proton transfering mechanism.The main work includes two parts as follows:1. Two mesoporous coordination complexes [Cr₃O（H₂O）3（bdc）₃]（MIL-101）（1）and [Cr₃（H₂O）₃（STA）₃]·n H₂O（S-MIL-101）（2） were synthesized under solvothermal condition through the Cr（NO₃）₃·9H₂O with rigid terephthalic acid（Hbdc） and 2-sulfoterephthalate ligand（STSA）. Through XRD, we can confirm that the structure of products in accordance with reported, MIL-101 and S-MIL-101 have similar geometry configuration namely the Cr³⁺ adopts the same coordination mode. The difference between 1 and 2 is that the S-MIL-101 has many free sulfonic acid groups.Then we get a series of proton composite membranes by the method of mixing and casting: CS/MIL-101-X1 and CS/S-MIL-101-X（X1, X respectively represents the percentage of MIL-101 and S-MIL-101 by weight）. In this paper, we test conductivity of all the membranes. Then we can find that CS/MIL-101-X1 and CS/S-MIL-101-X hybrid membranes show higher proton conductivity than pure CS membrane,especially the conductivity of CS/S-MIL-101-4 is up to 0.064 S·cm-1, which is 120%higher than pure CS（0.029 S·cm-1）. Furthermore, all of the composite membranes’ thermal stability was studied, and we infered the possible mechanism of the proton transferring in these two kinds of membranes by means of various characterizations.2. We successfully get H₂SO₄@MIL-101, H₃PO₄@MIL-101 and CF₃-SO₃H@MIL-101 with synthesized MIL-101 and H₂SO₄,H₃PO₄ and CF₃-SO₃ H which are difficult to volatile by the method of acid steeping. The morphology of them is observed by FESEM. Through the XRD characterization, we ensure that the MIL-101 can still maintain the stability of the structure after being treated by these three acids. Then we produce three types of protons composite membranes by using the same method: CS/H₂SO₄@MIL-101-X, CS/H₃PO₄@MIL-101-X and CS/CF₃-SO₃H@MIL-101-X, in which X（X=1,2,4,6,8,10,12,14,16） represents the percentage of seperated joining three quality to total quality. Interestingly, the proton conductivity of all membranes is obviously enhanced, escepcially in the condition of100 oC, 100% RH, the proton conductivity is up to 0.095 S·cm-1（which is 227%higher than pristine CS membrane）. In addition, we also study the proton transfer mechanism of the composite membrane.