| In recent years,energy shortage and environmental pollution have gotten worse.It is imperative to look for a new category and purifying of energy to alleviate the current pressure.High efficiency and zero emissions of fuel cell,is considered to be one of the options for improving the environment and achieving sustainable energy development.The development of anion exchange membranes with excellent ion conductivity and alkali resistance stability is the key to improving the life and energy conversion efficiency of fuel cells.Traditional polymer membranes exhibit low ion conductivity and poor alkali resistance stability due to their single structure,which limits their development in fuel cells.In response to the above problems,this paper takes the optimization of the microstructure of the membrane and the improvement of the macroscopic performance as the starting point,and proposes different modification strategies to achieve simultaneous improvement of the ion conductivity and alkali resistance stability of the anion exchange membrane.The main work is divided into the following three parts:(1)Carbon quantum dots were prepared by hydrothermal synthesis using citric acid and ethylenediamine as raw materials,and they were characterized and analyzed by Fourier Transform Infrared Spectrometer(FTIR).Using polysulfone as the organic polymer backbone,flexible side chains were introduced through chloromethylation and quaternization reactions to construct a series of side chain anion exchange membranes with different carbon quantum dots content,and explore the effect of carbon quantum dots on the performance of side chain anion exchange membranes.In addition,for the application of fuel cells,the membrane has been tested for water uptake and swelling ratio,OH~-conductivity and single cell.The experimental results show that the introduction of carbon quantum dots significantly improves the water uptake of the membrane,from 27.9%of the pure membrane to 35.6%of the hybrid membrane.Compared with the pure membrane,the OH~-conductivity of the hybrid membrane can reach 42.03 m S·cm-1 at 80o C.In addition,the mechanical strength increased from 24.0 MPa for the pure membrane to 31.7 MPa for the hybrid membrane,a stable increase of 32%.(2)Using tertiary amine groups at both ends and flexible hydrophobic chains in the middle as crosslinking agents,the polysulfone matrix was crosslinked.A series of cross-linked anion exchange membranes with different carbon quantum dot contents were constructed.The ionic conductivity of the cross-linked hybrid membrane an reach 61.1 m S·cm-1at 80°C,which is higher than the ionic conductivity of the side-chain hybrid membrane(42.03 m S·cm-1)at 80°C.The mechanical strength increased from 40.7 MPa for the pure membrane to 49.3 MPa for the hybrid membrane.The hybrid membrane remains intact and the remaining OH~-conductivity is 61.1%,shows outstanding alkali stability.(3)In order to enhance the compatibility and stability between the carbon quantum dots and the polysulfone matrix,adjust the time and temperature of hydrothermal synthesis to prepare modified carbon quantum dots.With polysulfone as the polymer backbone,modified carbon quantum dots were grafted by quaternization reaction to construct a series of graft-type anion exchange membranes with different carbon quantum dots contents.The experimental results show that the modified carbon quantum dots have a rich surface structure and form a positively charged ion-conducting group after being branched with the polysulfone main link.The OH~-conductivity of the hybrid membrane can reach 39.8 m S·cm-1at 80o C,which is better than the pure membrane.The mechanical strength increased from 19.0 MPa of the pure membrane to 35.4 MPa of the hybrid membrane,an increase of 86.3%,and it has excellent mechanical properties. |
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