| Due to the serious problem of resource constraints, and shortage of energy in modern society, research for new energy sources attracts more and more academic and industrial attentions now. Proton exchange membrane fuel cell (PEMFC) is a new type of energy. Compare with the traditional energy sources, there are a lot of advantages of the PEMFC, such as fast initiation, efficient energy transformation, high power density, high specific energy and low pollution. So PEMFCs are suitable for portable and distributed power applications. Proton exchange membrane (PEM) is the key part of the PEMFC. It directly influences the cost and the efficiency of the PEMFC. Research for the PEM will be helpful to much more widely use of the PEMFC.Additionally, a variety of natural materials extensively exist in the earth, such as chitosan, alginate acid. However, most of them are generally discarded as industrial waste around the world. Application of these polymers in electrical devices would be attractive not only in terms of product cost and environmental safety but also from the point of view of materials science. Chitosan is the deacetylated form of chitin, which is the second most abundant biopolymer in nature. Its modified products have been also widely study by many investigators. Further and effectively use of such a natural material is an important problem.Standing on the previous research and existing conditions, we synthesized N-methylene phosphonic chitosan proton exchange membranes, and characterized the structure of the products. Additionally, molecular simulation was used, and a model of phosphonic chitosan PEM was built according to the results of chemical experiments and references. The details are shown as follows:1. N-methylene phosphonic chitosan was synthesized by homogeneous reaction. A self-supporting, light yellow transparent amphibious proton exchange membrane was prepared by adding polyvinyl alcohol1799into the previous compound and phosphorylating together. The structures of products were characterized by Fourier-transform infrared (FT-IR) spectroscopy and Elemental analysis (EA).2. Film-forming capacity of PEMs was investigated. Thermal stability, proton conductivity was analysis by thermal gravimetric analysis (TGA) and exchanges impedance analysis (EIS), respectively. The results show the membranes were thermally stabilized up to180℃. And the proton conducting property of these membranes was investigated under both hydrous and anhydrous conditions. The relationship between structure and properties was studied, and the mechanism of proton transfer was also discussed.3. Molecular mechanics (MM) and molecular dynamics (MD) method were used in the molecular simulation. The amphibious proton exchange membrane with three-dimensional periodic boundary conditions was established by step-by-step modeling approach and optimized according to experimental results and data from references. The applicability of COMPASS force field was examined, and equilibrium time and parameters was studied.4. Molecular simulation model of the PEM was optimized by NVT, NPT molecular dynamics method. Non-bond interactions, movement capabilities of polymer chain were calculated, so the relationship between structure and properties was explained from the microscopic point of view. The possibility of the existence of the so-called "hydrogen bridge" structure was certified.In this study, amphibious proton exchange membrane was successfully synthesized by using of the natural material, chitosan. Chemical experiments and molecular modeling methods were used to characterize the structure and properties. And the relationship between structure and properties was also studied.With further research and progress in technology, the structure, properties, and the proton transfer mechanism of proton exchange membrane will be much clearer. And proton exchange membrane fuel cells will be widely applied in future life. |
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