Analysis:
A: It is mainly used for manufacturing fuel cells.
Improvement and application of proton exchange membrane materials
Proton exchange membrane fuel cell (PEMFC) has the advantages of low working temperature, fast start-up, high specific power, simple structure and convenient operation, and is recognized as the preferred energy source for electric vehicles and fixed power stations. Inside the fuel cell, the proton exchange membrane provides a channel for the migration and transportation of protons, so that protons can reach the cathode from the anode through the membrane, and form a loop with the electron transfer of the external circuit to provide current to the outside world. Therefore, the performance of proton exchange membrane plays a very important role in the performance of fuel cells, and its quality directly affects the service life of the cells.
Up to now, the most commonly used proton exchange membrane (PEMFC) is Nafion from DuPont. The membrane has the advantages of high proton conductivity and good chemical stability. At present, most PEMFC adopt Nafion? PEM used to assemble PEMFC in China mainly depends on imports. But Nafion? Membrane-like materials still have the following disadvantages: (1) it is difficult to make and the cost is high, the synthesis and sulfonation of perfluoro materials are very difficult, and hydrolysis and sulfonation in the process of film formation are easy to denature and degrade the polymer, which makes film formation difficult and leads to high cost; (2) High requirements on temperature and water content, Nafion? The optimum working temperature of this series of membranes is 70 ~ 90℃. If it exceeds this temperature, the water content and conductivity of the membrane will decrease rapidly, which hinders the improvement of electrode reaction speed and the overcoming of catalyst poisoning by properly increasing the working temperature. (3) Some hydrocarbons, such as methanol, have high permeability and are not suitable for proton exchange membrane (DMFC) in direct methanol fuel cells.
Therefore, in order to improve the performance of proton exchange membrane, the improvement of proton exchange membrane is under way. According to the literature reports in recent two years, the following methods can be adopted for improvement:
(1) The organic/inorganic nanocomposite proton exchange membrane improves the water retention capacity of the composite membrane by virtue of the characteristics of small nanoparticle size and large specific surface area, thus achieving the purpose of expanding the working temperature range of proton exchange membrane fuel cells;
(2) Improvement of proton exchange membrane skeleton materials, aiming at Nafion? The shortcomings of the membrane are still in Nafion? Improvement of membrane base, or selection of new skeleton materials;
(3) Adjust the internal structure of the membrane, especially increase the micropores in it, so as to facilitate the membrane formation and solve the problem of catalyst poisoning.
In addition, in addition to these three improvements, many existing studies have adopted nanotechnology to a greater or lesser extent, making materials smaller and better in performance.
The following is a brief introduction to the literature using these three methods.
(1) organic/inorganic nanocomposite proton exchange membrane
The world patent WO * * * * * * * * published by Columbia Chemical Company on February 4, 2003 discloses a sulfonic acid conductor polymer grafted carbon material. Its manufacturing method is oxidative polymerization and sulfonation grafting of conductor polymer monomer containing heteroatoms in carbon materials. The method can further metallize polymer grafted carbon materials. The carbon-containing material can be carbon black, graphite, nano-carbon or fullerene. The polymer is polyaniline, polypyrrole, etc. Its proton conductivity is 8.9× 10-2S/cm (measured by Nafion- sulfonic polyaniline).
Many domestic patents adopt similar methods. For example, in Tsinghua University China patent CN 1476 1 13 published in June, 2003, aromatic heterocyclic polymers with sulfonic acid side groups in the membrane matrix are added into a solvent to form a uniform mixture, and then inorganic substances are added to form a suspension. The suspension was pulverized by nano-pulverization technology to obtain evenly dispersed slurry, and the film was made by tape casting. The film structure formed by it is uniform and quite dense. It not only has good methanol permeability resistance, but also has good chemical stability and proton conductivity, and the methanol permeability is less than 5%.
(2) Polymer materials with improved membrane skeleton.
The Journal of Membrane Science published a paper published by the University of Hong Kong in 2005. Nafion and polymerized furfuryl alcohol were polymerized by in-situ acid catalysis. The proton exchange membrane made of this material obviously improves the flow rate of reducing methanol, and its proton conductivity is 0.0848S/cm.
The patent CN 1585 153 published by Sun Yat-sen University in China in 2004 introduced a preparation method of modified proton exchange membrane for direct alcohol fuel cells. Proton exchange membrane was prepared by using sulfonated resin as raw material, adding inorganic nano-materials, and by film-forming methods such as casting, calendering, slurry coating or impregnation.
(3) adjusting the internal structure of the membrane
In 2004, Journal of Electrochemistry published the paper of Gwangju Institute of Science and Technology, Korea. An improved polymer was used as proton exchange membrane, and sulfonated polystyrene -b- poly (ethylene-γ-butene) -b- polystyrene * * * polymer (SSEBS) was selected. Under the microscope, the proton exchange membrane is more resistant to electricity than ordinary ones, showing nano-structured ion channels.
China invention patent CN141085 published and applied by Huazhong University of Science and Technology on 200 1 085 has a plurality of orderly distributed micropores on a ceramic film structure with a thickness of h≤ 1mm and an aperture of n ≤ 2 mm, and the micropores are distributed all over the ceramic film. The pore size n is preferably in the order of nanometers. The preparation method of proton exchange membrane comprises the following steps: firstly, preparing ordered micropores on a metal membrane with the thickness of h≤ 1mm; Then oxidized into ceramic membrane by electrochemical method or other means; Then the micropores of the ceramic membrane are filled with electrolyte with high conductivity. This method has the characteristics of easy film formation and low manufacturing cost. By increasing the working temperature of proton exchange membrane, the problem of catalyst poisoning can be solved.
In addition, some methods of manufacturing proton exchange membranes reported abroad recently include:
Wo * * * * * * * is a patent on ion conductor composite proton exchange membrane submitted by Renault Company on May 19, 2005, which discloses a manufacturing method of ion conductor composite membrane, including a) combining electrons and ion non-conductor polymers, or mixing low melting point salts with at least two polymers in solution or molten state; B) combine with that organic precursor of silicon dioxide hydrolysis; C) mixing with an appropriate heteropoly acid organic solution, and casting into a film, especially a film with a thickness of 5-500 microns and a smooth surface, and the pore channels of the ion conductor are nano-scale. Wherein, the polymer is polysulfone and polyimide resin. The final proton conductivity is 433k, which reaches (1.1~ 3.8) ×10-2s/cm when tested at 100%RH.
The world patent WO * * * * * * * * published by Sabanz University on March 10, 2005 uses a metal-coated nanofiber, and also relates to the metal-coated process of electrospun nanofibers.
Table 1 and table 2 list the materials, proton conductivity and performance of the final fuel cell respectively.
However, the research on the new method is not mature at present, and some shortcomings need to be further improved. For example, after adding inorganic substances, the composite membrane will become brittle and hard, and the film-forming property will become worse, so the proper ratio of organic substances and inorganic substances in the composite membrane becomes particularly important, which is also one of the future research directions. In addition, after adding nanoparticles, the research on the comprehensive properties of the membrane, such as dispersion of nanoparticles and control of reaction energy, deserves further attention.