CN101787141A - Method for preparing proton exchange membrane with polyvinylidene fluoride grafted and grafting copolymerized with 2-acrylamido-2-methylpropanesulfonic acid - Google Patents

Abstract

The invention relates to a preparation method of a polyvinylidene fluoride graft blended poly 2-acrylamide-2-methylpropanesulfonic acid proton exchange membrane, belonging to the field of battery electrolyte materials. In the present invention, the silicon compound is first dissolved in an aqueous N-methylpyrrolidone solution, then polyvinylidene fluoride PVDF and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) are added to the solution, and an initiator is added. heating and stirring, casting the solution onto a clean glass plate, drying, and stripping to obtain a modified polyvinylidene fluoride and poly 2-acrylamide-2-methylpropanesulfonic acid graft copolymer film; prepared by the present invention The proton exchange membrane not only has a good proton conductor, but also facilitates large-scale production.

Description

Preparation method of polyvinylidene fluoride graft blended poly 2-acrylamido-2-methylpropanesulfonic acid proton exchange membrane

technical field

The invention relates to a preparation method of a polyvinylidene fluoride graft blended poly 2-acrylamide-2-methylpropanesulfonic acid proton exchange membrane, belonging to the field of battery electrolyte materials.

Background technique

In proton exchange membrane fuel cells and direct methanol fuel cells, the proton exchange membrane electrolyte is the key material in the battery, and the performance of the proton exchange membrane will directly affect the performance of the battery. Therefore, the proton exchange membrane has always been a key topic in the research and development of fuel cells. At present, the widely used proton exchange membrane is mainly the perfluorosulfonic acid ion exchange membrane (Nafion membrane) produced by DuPont Company of the United States. This kind of proton exchange membrane has good proton conductivity, but because it is a perfluorinated ion exchange membrane, the production cost is relatively expensive, especially this kind of proton exchange membrane has poor barrier property to liquid fuels such as methanol and has a large swelling rate, which is not conducive to production Fuel cells for organic fuels. In order to solve this problem, some new proton exchange membranes have been developed, such as polyvinylidene fluoride sulfonic acid proton exchange membrane, which not only has good proton conductivity, but also has low methanol permeability, Therefore, it is an ideal proton exchange membrane for direct methanol fuel cells.

The key issue in the preparation of polyvinylidene fluoride sulfonic acid membrane is how to remove HF from polyvinylidene fluoride to generate active points. The current method is to use methyl pyrrolidone as solvent first, and pour polyvinylidene fluoride into the film by solution casting. Make a film, and then irradiate it with high-energy electron radiation to generate free radicals. Immediately after the free radicals are generated, the film is placed in a solution of styrene with an initiator for grafting. After a certain period of time, the grafted The membrane is sulfonated to obtain a proton exchange membrane grafted with polyvinylidene fluoride and polystyrene sulfonic acid. The proton conductivity of the membrane and the methanol permeability of the membrane are different according to the radiation time and the grafting time. Under a suitable condition, the grafted film has high proton conductivity. Therefore, this membrane is considered to be an ideal electrolyte material for proton exchange membrane fuel cells.

In the above proton exchange membrane fuel cell, the proton exchange membrane has always been the key material affecting the fuel cell. The proton exchange membrane not only plays the role of conducting ions, but also plays the role of isolating fuel. However, methanol is used as fuel in direct methanol fuel cells, so the proton exchange membrane in the battery is required not only to have high proton conductivity, but also to have very low methanol permeability, which makes the widely used perfluorosulfur Acid proton exchange membranes are no longer suitable. In order to obtain a proton exchange membrane suitable for direct methanol fuel cells, it is proposed to use polyvinylidene fluoride grafted polystyrene sulfonic acid membrane, but this membrane must use radiation to excite free radicals, on the other hand grafted to polystyrene sulfonic acid membrane. The polystyrene on the vinylidene fluoride film needs sulfonation, which is complex and unfavorable for large-scale production.

Contents of the invention

The object of the present invention is to provide a kind of 2-acrylamido-2-methyl propanesulfonic acid that utilizes silicon compound to make polyvinylidene fluoride produce free radicals, and directly grafts and blends, so that not only can simplify the production process of the film A method for preparing a polyvinylidene fluoride graft blended poly 2-acrylamido-2-methylpropanesulfonic acid proton exchange membrane capable of controlling the grafting amount and electrical conductivity at the same time.

Technical solution: The raw materials of the present invention include: sodium orthosilicate, 2-acrylamido-2-methylpropanesulfonic acid, ammonium persulfate and polyvinylidene fluoride;

The preparation method is as follows: (1) Dissolve 5wt% to 12wt% sodium orthosilicate in water-containing 3wt% to 5wt% N-methylpyrrolidone solution by weight percentage, and stir for 1 to 3 hours to obtain solution A, wherein: One gram of polyvinylidene fluoride requires 5-6 mL of liquid N-methylpyrrolidone; (2) pour 53wt%-72wt% polyvinylidene fluoride PVDF into solution A and stir for 1-2 hours to obtain mixed solution B; (3) weigh 1wt% ~ 2wt% ammonium persulfate, measure 20wt% ~ 30wt% 2-acrylamido-2-methylpropanesulfonic acid, add it to the mixed solution B, and continue to electrokinetic in a water bath at 80°C ~ 90°C in a nitrogen atmosphere. Stir for 1-2 hours and let stand for 3 hours to obtain solution C; (4) Cast solution C on a clean glass plate, control the thickness of the casting film to 0.08mm-0.1mm, and volatilize at 80°C-90°C for 5- After 7 hours, dry and remove the film to obtain a modified polyvinylidene fluoride and poly 2-acrylamide-2-methylpropanesulfonic acid graft copolymer film; (5) the obtained film was extracted with deionized water for 24 hours Above, the 2-acrylamido-2-methylpropanesulfonic acid homopolymer was completely removed.

The membrane was soaked in deionized water for 6-12 hours before use.

The invention grafts poly(2-acrylamido-2-methylpropanesulfonic acid) on the polyvinylidene fluoride to form free radicals on the polyvinylidene fluoride, and then uses a free radical initiator. Its effect: the proton exchange membrane prepared by the present invention has lower methanol permeability (on the order of 10 ^-7 cm ² /min), and has good proton conductivity (conductivity reaches the order of 10 ^-2 S/cm) , the swelling rate is low, compared with DuPont's Nafion117 membrane, the permeability to methanol is reduced by an order of magnitude (in the order of 10 ^-7 cm ² /min), the swelling rate is reduced by 10%, and the conductivity is increased by 1 to 2 times. At the same time, the production cost is low, and it is convenient for large-scale production.

Detailed ways

Example:

Dissolve 0.4g of powdered sodium orthosilicate in 16mL of N-methylpyrrolidone with a water content of 3% to 5%, and stir for 1 hour to obtain solution A, which is a homogeneous solution; then 3.1g of polyvinylidene fluoride PVDF powder Pour into the stirred solution A and stir for 2 hours to obtain solution B; weigh 0.08g of ammonium persulfate, weigh 1.5g of 2-acrylamido-2-methylpropanesulfonic acid AMPS, add it to solution B under nitrogen Continue electric stirring for 1 hour in a water bath with an atmosphere of 80°C, and let stand for 3 hours to obtain solution C. Cast solution C onto a clean glass plate, volatilize at 90°C for 5 hours, dry, and remove the film to obtain modified polybias Vinyl fluoride and poly 2-acrylamido-2-methylpropanesulfonic acid graft copolymer membrane; the resulting membrane was extracted with deionized water for more than 24 hours to completely remove 2-acrylamido-2-methylpropanesulfonic acid Homopolymer. The membrane needs to be soaked in deionized water for 6-12 hours before use. The electrical conductivity was measured by the two-electrode AC impedance method, and the swelling behavior of the film was characterized by the degree of swelling ( _SD ). In the methanol aqueous solution of L ^-1 , take it out after fully swelling for 48 hours, measure the size of the wet film, obtain the area S _W , and calculate the swelling degree SD of the film by the following formula: $\mathrm{SD}=\frac{S_W-S_d}{S_d}\×100\%;$ Methanol permeability of the membrane was determined by the membrane diffusion method.

Comparative example As a comparison, we used Nafion117 membrane to compare its methanol permeability, swelling rate and electrical conductivity. Nafion117 membrane was soaked in deionized water for several hours, and its electrical conductivity was measured by two-electrode AC impedance method; To characterize the swelling behavior of the film, the dry film was first cut into a rectangular film (area Sd) with a size of about 3 cm × 4 cm, immersed in 1 mol L ^-1 methanol aqueous solution, fully swollen for 48 hours, and then taken out. Measure the size of the wet film to obtain the area S _W , and calculate the swelling degree SD of the film by the following formula: $\mathrm{SD}=\frac{S_W-S_d}{S_d}\×100\%;$ Methanol permeability of the membrane was determined by the membrane diffusion method.

Table 1 Comparison of performance of modified polyvinylidene fluoride graft blended 2-acrylamido-2-methylpropanesulfonic acid (AMPS) proton exchange membrane with Nafion membrane at 25°C

sample number Conductivity (10 ^-2 S/cm) Swelling rate in water (%) Methanol permeability (10 ^-6 cm ² /min) Nafion117 1.76 33.4 2.0 sample 4.274 20.4 0.6

Claims (2)

1. The preparation method of polyvinylidene fluoride graft blending poly 2-acrylamide-2-methylpropanesulfonic acid proton exchange membrane, is characterized in that, the raw material of the present invention comprises: sodium orthosilicate, 2-acrylamide - 2-Methylpropanesulfonic acid, ammonium persulfate and polyvinylidene fluoride; The preparation method is as follows: (1) Dissolve 5wt% to 12wt% sodium orthosilicate in water-containing 3wt% to 5wt% N-methylpyrrolidone solution by weight percentage, and stir for 1 to 3 hours to obtain solution A, wherein: One gram of polyvinylidene fluoride requires 5-6 mL of liquid N-methylpyrrolidone; (2) pour 53wt%-72wt% polyvinylidene fluoride PVDF into solution A and stir for 1-2 hours to obtain mixed solution B; (3) weigh 1wt% ~ 2wt% ammonium persulfate, measure 20wt% ~ 30wt% 2-acrylamido-2-methylpropanesulfonic acid AMPS, add to the mixed solution B and continue in a nitrogen atmosphere at 80°C ~ 90°C in a water bath Electric stirring for 1 to 2 hours, and standing for 3 hours to obtain solution C. (4) Cast solution C on a clean glass plate, control the thickness of the casting film to 0.08mm to 0.1mm, and volatilize at a temperature of 80°C to 90°C for 5 After ~7 hours, dry and remove the film to obtain a modified polyvinylidene fluoride and poly 2-acrylamide-2-methylpropanesulfonic acid graft copolymer film; (5) the obtained film is extracted with deionized water for 24 After more than 1 hour, the 2-acrylamido-2-methylpropanesulfonic acid homopolymer was completely removed. 2. the preparation method of polyvinylidene fluoride graft blending poly-2-acrylamido-2-methylpropanesulfonic acid proton exchange membrane according to claim 1, is characterized in that, membrane is carried out before using Soak in deionized water for 6-12 hours.