| As an environmental friendly new energy technology, fuel cells have gained wide attention and research for their high energy conversion efficiency, great power density and low pollution. Compared to the hydrogen, methanol is easier for storage and transport. There should be greater opportunity and potential for the development of direct methanol fuel cell(DMFC). Currently, DMFC has already used as a kind of portable power source in some areas such as mobile phone and electric vehicle.However, there are two major problems of DMFC. On one hand, the recently mature research results of proton exchange membrane fuel cell(PEMDMFC) must use noble metal catalyst such as Pt, which makes the cost difficult to control. On the other hand,high methanol permeability of proton exchange membrane leads to the loss of fuel which degrades the battery performance. Anion exchange membrane direct methanol fuel cell(AEMDMFC) can effectively solve these problems. In alkaline conditions, a high reaction kinetics of cell cathode allow AEMDMFC to use non-precious metal catalysts in order to reduce cost. Furthermore, the transport direction of OH- is opposite to the methanol permeation, which can suppress on the permeation of methanol fuel to a certain extent. Therefore, anion exchange membrane(AEM) has become one of the hotspots in domestic and foreign research.As an electrolyte membrane, anion exchange membrane have some shortcomings such as low conductivity and poor stability. Thus, improving the overall performance of AEM is significance to promote the development of AEMDMFC. In this paper, considering the advantages of a rigid bicyclic structure of its main chain,anion exchange membrane material with great thermal and chemical stability, good mechanical properties, low methanol permeability and excellent dielectric properties is expected to be prepared through the designing of polymer structure and functional modification of addition polynorbornene material.Firstly, 5-norbornene-2-methylene-heptyl ether(HN) and the functionalized norbornene monomer 3-(5-norbornene-2-methoxyl)-N, N-dimethyl Propanamine(NA) are prepared successfully. Addition-type norbornene copolymer P(HN/NA) aresynthesized via the vinyl addition copolymerization of HN and NA by using a bis-(benzocyclohexan-ketonabenzylimino)nickel(II)/B(C6F5)3 binary catalytic system.Copolymers of different insertion rates are obtained by changing the feed ratios of monomers. This catalytic system exhibites high activity and the obtained copolymers have high molecular weight. Anion-exchange Membranes which can conduct OH- are obtained by quaternary ammonium functional modification and alkalization. The QBnP(HN/NA) membranes have a high thermal stability, excellent methanol permeability, good chemical stability and mechanical properties. The highest ion conductivity is up to 3.58×10-3 S/cm at 80 oC.Then, through adding the N-Trimethoxysilylpropyl-N,N,N-Trimethylammonium Chloride(TSPCA) with quaternary ammonium functional groups to the polynorbornene by a sol-gel method, a composite quaternized polynorbornene/nano-silica(QPDN/SiO2) anion exchange membrane with higher thermal stability,greater chemical stability, and better ion conductivity can be prepared. The obtained QPDN/SiO2-25(25 wt. % of TSPCA to QPDN in the membrane matrix) exhibits the best performance with the highest ion conductivity of 9.33×10-3S/cm, and the methanol permeability of this membrane is 2.89×10-7 cm2/s, which is lower than that of Nafion(2.37×10-6 cm2/s). The membrane electrode assembly(MEA) is fabricated using the QPDN/SiO2-25, the open circuit voltage of QPDN/SiO2-25 is 0.65 V in methanol/air at 80 oC, and its power density is 32 m W/cm2. Experiments show that the uniform introduction of the inorganic nanoparticles in the polymer matrix of the film can improve the comprehensive performance of the membrane. By further optimization of conductivity and stability, the AEM films are expected to be applied to direct methanol fuel cells. |
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