CN105406091B - A kind of preparation method of Kynoar heteropoly acid chitosan compound proton exchange membrane - Google Patents

Abstract

The invention relates to the technical field of fuel cells, and specifically discloses a method for preparing a polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane. In this method, the polyvinylidene fluoride fiber membrane is first obtained by electrospinning, and then the heteropolyacid is coated on the surface of the fiber by polydopamine with strong adhesion, and then the positively charged natural polymer chitosan is filled into the fiber. The pores of the membrane can effectively prevent the loss of heteropolyacid during battery use by using the strong electrostatic interaction between chitosan and heteropolyacid, and can also greatly increase the mechanical properties of the fiber membrane. The composite membrane exhibits high proton conductivity and mechanical properties at both room temperature and high temperature. The polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane of the invention is expected to have broad application prospects in the field of proton exchange membrane fuel cells.

Description

A kind of preparation method of polyvinylidene fluoride-heteropoly acid-chitosan composite proton exchange membrane

technical field

The invention relates to the technical field of fuel cells, in particular to a preparation method of a polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane.

Background technique

Proton exchange membrane fuel cells have broad application prospects in electric vehicles and portable power supplies due to their advantages such as room temperature start-up, high energy conversion efficiency, and compact structure. As one of the key components of a proton exchange membrane fuel cell, the proton exchange membrane can separate fuel and oxidant, allowing protons to pass through, but insulating electrons, and it is also the substrate of electrolytes and catalysts. Therefore, an excellent proton exchange membrane must have high Proton conductivity and excellent mechanical properties. What is commonly used at present is the Nafion series perfluorosulfonic acid proton exchange membrane developed by DuPont Company, but it will cause a sharp drop in proton conductivity due to strong dehydration under high temperature and low humidity, poor alcohol resistance and high price. The widespread commercial use of Nafion membranes is limited. Therefore, it is urgent to research and develop the substitute of Nafion membrane.

The electrospinning method is a method in which a polymer solution or melt is sprayed and stretched by electrostatic action to obtain continuous micro-nano-scale fibers. The research group of Professor Pintauro in the United States [Macromolecules, 2008, 41, 4569.] used electrospinning technology to prepare a three-dimensional interpenetrating sulfonated polyarylethersulfone nanofiber membrane, and then filled it with an inert polymer with excellent mechanical properties. In order to improve the alcohol resistance and mechanical properties in the voids of the fiber membrane, the proton conductivity of the final membrane can be comparable to that of the commercial Nafion 117 membrane, but the phase-separated nano-morphological structure has not reached the expected ideal state, and it has a negative effect on the properties of the polyelectrolyte solution. The relationship with electrospinning performance was not explored. Domestic Professor Na Hui's research group [Journal of Membrane Science, 2006, 281:1.] also used electrospinning technology to prepare sulfonated polyetheretherketone (SPEEK) membranes. In the process, it is easier to gather to form ion clusters, but its follow-up research and battery performance have not been reported. Meng Yuezhong from Sun Yat-Sen University [Chinese patent ZL201110393309.8] dissolved the sulfonated polymer and another non-sulfonated polymer separately and then electrospun to obtain a chemically heterogeneous electrospun fiber membrane. The composite membrane has a high chemical stability and proton conductivity. In general, most of the current research focuses on the preparation of proton exchange membranes by electrospinning sulfonated polymers, but due to the strong repulsion interference between the ionic groups on the sulfonated polymer molecules, the polymers in solution It presents a rod-like conformation, the conditions of electrospinning are not easy to control, and it is difficult to produce on a large scale.

Polyvinylidene fluoride (PVDF) is a semi-crystalline fluoropolymer with excellent comprehensive properties, such as excellent mechanical properties, electrochemical and thermal stability, high dielectric constant, and easy electrospinning to form films. And after film formation, the strength and flexibility are excellent, but PVDF itself does not have proton conductivity, so compounding PVDF with inorganic proton conductors such as heteropolyacids is an effective way to improve its proton conductivity, but heteropolyacids are easily soluble in water , during the operation of proton exchange membrane fuel cells, it is easy to lose with the water generated by the electrodes. Therefore, how to solve the loss of heteropolyacids in electrospun membranes is the key issue for the practical application of such membranes.

Contents of the invention

Aiming at the deficiencies in the prior art, the object of the present invention is to provide a method for preparing a polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane.

In order to realize the above-mentioned purpose of the invention, the present invention has taken following technical measures:

A preparation method of polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane, the method comprises the following steps in sequence:

(1) Dissolving polyvinylidene fluoride in a mixed organic solvent to prepare an electrospinning solution with a polyvinylidene fluoride concentration of 5wt% to 30wt%;

The polyvinylidene fluoride is preferably polyvinylidene fluoride of brand HSV900;

The mixed organic solvent is composed of an amide solvent and a ketone solvent, wherein the volume percentage of the ketone solvent in the mixed organic solvent is 2-40%;

The amide solvent is N,N-dimethylformamide or N,N-dimethylacetamide, and the ketone solvent is acetone or butanone;

(2) Add the electrospinning solution obtained in step (1) into the syringe of the electrospinning device, the ambient temperature is 10-30°C, the spinning voltage is 20-40kV, and the flow rate of the spinning needle is 0.1-1mL/h Electrospinning is carried out under certain conditions to obtain a polyvinylidene fluoride electrospun fiber membrane;

(3) configuration tris (hydroxymethyl) aminomethane concentration is the Tris-HCl buffer solution of 1～10mmol/L, and described Tris-HCl buffer solution pH value is 8.0～9.0, and step (2) gained polyvinylidene fluoride The electrospun fiber membrane is soaked in the Tris-HCl buffer;

(4) Add dopamine hydrochloride to the Tris-HCl buffer solution that step (3) gained is soaked with polyvinylidene fluoride electrospinning fiber membrane, the ratio of dopamine hydrochloride and Tris-HCl buffer solution is (0.5～8 )mg: 1mL, magnetically stir at room temperature to oxidatively polymerize dopamine for 10-48 hours, and obtain a polydopamine-treated polyvinylidene fluoride electrospun fiber membrane;

(5) Add the polyvinylidene fluoride electrospun fiber membrane treated with polypamine obtained in step (4) into a heteropolyacid aqueous solution with a concentration of 2wt% to 25wt%, soak at room temperature for 8 to 24h, take out the fiber membrane, and Polyvinylidene fluoride-heteropolyacid film is obtained by washing and drying with deionized water; the heteropolyacid is phosphotungstic acid, phosphomolybdic acid or silicotungstic acid;

(6) configuration acetic acid concentration is the acetic acid aqueous solution of 0.5wt%～3wt%, then chitosan is dissolved in this acetic acid aqueous solution and is made into the chitosan solution that chitosan concentration is 0.2wt%～5wt%, step ( 5) The obtained polyvinylidene fluoride-heteropoly acid film is added to the chitosan solution, soaked at room temperature for 15-45 minutes, taken out to dry, then repeated soaking and drying for 2-6 times, and finally dried to obtain polyvinylidene fluoride -Heteropolyacid-chitosan composite proton exchange membrane.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. Compared with directly doping heteropoly acid into polyvinylidene fluoride, the present invention adopts a super-adhesive polydopamine as the intermediate layer, which can firmly wrap heteropoly acid on polyvinylidene fluoride The surface of the fiber (see accompanying drawing 3);

2. Compared with only filling the pores of the electrospun fiber membrane with inert polymers to increase the mechanical properties of the membrane, the present invention fills the pores of the fiber membrane with positively charged natural polymer chitosan, and utilizes chitosan and hetero The strong electrostatic interaction between polyacids can effectively prevent the loss of heteropolyacids during battery use, and chitosan filling can also greatly increase the mechanical properties of electrospun membranes;

3. The composite membrane prepared by the present invention has high proton conductivity due to the introduction of inorganic proton conductor heteropolyacid;

4. The preparation process of the present invention is simple, and the cost of the prepared composite proton exchange membrane is much lower than that of Nafion commercial membrane, which is easy to be industrialized and can promote the development of fuel cells.

In summary, the polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane prepared by the present invention is expected to have broad application prospects in the field of proton exchange membrane fuel cells.

Description of drawings

Figures 1 and 2 are scanning electron micrographs and energy spectrum diagrams of the polyvinylidene fluoride electrospun fiber membrane prepared in Example 1, respectively;

Figures 3 and 4 are scanning electron microscope images and energy spectrum images of the polyvinylidene fluoride-phosphotungstic acid fiber membrane coated with phosphotungstic acid prepared in Example 1, respectively.

It can be seen from Figure 1 that the diameter of the polyvinylidene fluoride fiber membrane prepared by electrospinning is relatively uniform, and the diameter is basically about 500nm; in Figure 2, there are only C and F elements in the fiber membrane detected by the energy spectrum; it can be seen from Figure 3 After being coated with chitosan, the surface of the fiber is evenly covered with a thick shell layer; the appearance of obvious P, W, O and other elements in the energy spectrum in Figure 4 can prove that the coating layer is phosphotungstic acid.

detailed description

Below, the applicant will further describe the technical solution of the present invention in detail in combination with specific embodiments, in order to enable those skilled in the art to have a clearer understanding and understanding of the present application.

The following specific examples should not be understood or interpreted as limiting the protection scope of the claims of the present application to any extent.

Among the following examples 1-5:

The raw material polyvinylidene fluoride (brand name HSV900) was purchased from Acma, France; chitosan (deacetylation degree 92.5%, molecular weight 100,000) was purchased from Zhejiang Aoxing Biotechnology Co., Ltd.

All other reagents and raw materials are commercially available.

Example 1

A preparation method of polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane, the steps are as follows:

Dissolve 5g of polyvinylidene fluoride in a mixed solvent of N,N-dimethylacetamide and acetone with a volume ratio of 9.5:0.5 to prepare a 10wt% polyvinylidene fluoride electrospinning solution; The solution was added to the syringe of the electrospinning device, and the electrospinning was carried out under the conditions of the ambient temperature of 25°C, the spinning voltage of 25kV, and the flow rate of the spinning needle of 0.3mL/h to obtain polyvinylidene fluoride electrospun fibers Membrane; configuration tris (hydroxymethyl) aminomethane concentration is the Tris-HCl buffer solution of 4mmol/L, and the pH value of the Tris-HCl buffer solution is 8.5, then the polyvinylidene fluoride electrospun fiber membrane is soaked in this buffer In the solution, add 4mg/mL dopamine hydrochloride (this ratio is the solid-to-liquid ratio of dopamine hydrochloride and Tris-HCl buffer solution, the following examples are the same, do not repeat them) to the buffer solution, and magnetically stir at room temperature for 24h Finally, the polydopamine-treated polyvinylidene fluoride electrospun fiber membrane is obtained; then the polydopamine-treated polyvinylidene fluoride electrospun fiber membrane is added to a phosphotungstic acid aqueous solution with a concentration of 15 wt%, soaked at room temperature for 12 hours, and taken out fiber membrane, and washed and dried with deionized water to obtain polyvinylidene fluoride-phosphotungstic acid membrane; configure the acetic acid aqueous solution with acetic acid concentration of 1wt%, and then dissolve chitosan in the acetic acid aqueous solution to form a chitosan concentration of 1wt% chitosan solution, then add polyvinylidene fluoride-phosphotungstic acid film into the chitosan solution, soak at room temperature for 30min, take it out and dry in the air, repeat soaking and drying for 5 times, and finally dry to obtain the polyvinylidene fluoride-phosphotungstic acid film. Vinylidene fluoride-phosphotungstic acid-chitosan composite proton exchange membrane. The performance test results of the film are shown in Table 1.

Table 1

It can be seen from the results in Table 1 that the proton conductivity of the polyvinylidene fluoride-phosphotungstic acid-chitosan composite proton exchange membrane prepared in this example is higher than that of the Nafion 112 membrane at room temperature and high temperature (80°C). Especially at 80°C, the proton conductivity is about three times that of Nafion 112 membrane under the same conditions; at the same time, the mechanical properties of the composite proton exchange membrane are greatly improved compared with the polyvinylidene fluoride-phosphotungstic acid membrane not filled with chitosan. This composite membrane is expected to be used in proton exchange membrane fuel cells.

Example 2

A preparation method of polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane, the steps are as follows:

Dissolve 5g of polyvinylidene fluoride in a mixed solvent of N,N-dimethylformamide and butanone at a volume ratio of 9.8:0.2 to prepare a 5wt% polyvinylidene fluoride electrospinning solution; The silk solution was added to the syringe of the electrospinning device, and the electrospinning was carried out under the conditions of the ambient temperature of 10°C, the spinning voltage of 20kV, and the flow rate of the spinning needle of 1mL/h to obtain polyvinylidene fluoride electrospun fibers Membrane; configuration tris (hydroxymethyl) aminomethane concentration is the Tris-HCl buffer solution of 1mmol/L, and the pH value of the Tris-HCl buffer solution is 8.0, then the polyvinylidene fluoride electrospun fiber membrane is soaked in this buffer solution, and then add 0.5 mg/mL dopamine hydrochloride to the buffer solution, and after magnetic stirring at room temperature for 10 hours, obtain polydopamine-treated polyvinylidene fluoride electrospun fiber membrane; then polydopamine-treated polyvinylidene fluoride Add the ethylene electrospun fiber membrane to the phosphomolybdic acid aqueous solution with a concentration of 2wt%, soak it at room temperature for 24 hours, take out the fiber membrane, wash and dry it with deionized water to obtain the polyvinylidene fluoride-phosphomolybdic acid membrane; configure the concentration of acetic acid as 0.5wt% acetic acid aqueous solution, and then dissolving chitosan in this acetic acid aqueous solution is made into the chitosan solution that chitosan concentration is 0.2wt%, then adds polyvinylidene fluoride-phosphomolybdic acid film to this chitosan Soak in the sugar solution for 15 minutes at room temperature, take it out and dry it in the air, repeat the soaking and drying for 6 times, and finally dry it to obtain the polyvinylidene fluoride-phosphomolybdic acid-chitosan composite proton exchange membrane.

Example 3

A preparation method of polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane, the steps are as follows:

Dissolve 5g of polyvinylidene fluoride in a mixed solvent of N,N-dimethylformamide and butanone at a volume ratio of 6:4 to prepare a 30wt% polyvinylidene fluoride electrospinning solution; The silk solution was added to the syringe of the electrospinning device, and the electrospinning was carried out under the conditions of the ambient temperature of 30°C, the spinning voltage of 40kV, and the flow rate of the spinning needle of 0.1mL/h to obtain polyvinylidene fluoride electrospinning Fiber membrane; configuration tris (hydroxymethyl) aminomethane concentration is the Tris-HCl buffer solution of 10mmol/L, and the pH value of the Tris-HCl buffer solution is 9.0, then the polyvinylidene fluoride electrospun fiber membrane is immersed in the 8 mg/mL dopamine hydrochloride was added to the buffer solution, and after magnetic stirring at room temperature for 48 hours, the polydopamine-treated polyvinylidene fluoride electrospun fiber membrane was obtained; the polydopamine-treated polyvinylidene fluoride Add the ethylene electrospun fiber membrane to the aqueous solution of silicotungstic acid with a concentration of 25wt%, soak it at room temperature for 12 hours, take out the fiber membrane, wash and dry it with deionized water to obtain the polyvinylidene fluoride-silicotungstic acid membrane; configure the concentration of acetic acid as 3wt% acetic acid aqueous solution, then dissolving chitosan in this acetic acid aqueous solution is made into the chitosan solution that chitosan concentration is 5wt%, then adds polyvinylidene fluoride-silicotungstic acid film to this chitosan solution , soaked at room temperature for 45 minutes, took it out to dry, repeated soaking and drying twice, and finally dried to obtain polyvinylidene fluoride-silicotungstic acid-chitosan composite proton exchange membrane.

Example 4

A preparation method of polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane, the steps are as follows:

Dissolve 5g of polyvinylidene fluoride in a mixed solvent of N,N-dimethylacetamide and butanone at a volume ratio of 8:2 to prepare a 15wt% polyvinylidene fluoride electrospinning solution; The silk solution was added to the syringe of the electrospinning device, and the electrospinning was carried out under the conditions of the ambient temperature of 20°C, the spinning voltage of 30kV, and the flow rate of the spinning needle of 0.5mL/h to obtain polyvinylidene fluoride electrospinning Fiber membrane; configuration tris (hydroxymethyl) aminomethane concentration is the Tris-HCl buffer solution of 6mmol/L, and the pH value of the Tris-HCl buffer solution is 8.2, then the polyvinylidene fluoride electrospun fiber membrane is soaked in this 5 mg/mL dopamine hydrochloride was added to the buffer solution, and after magnetic stirring at room temperature for 16 hours, a polydopamine-treated polyvinylidene fluoride electrospun fiber membrane was obtained; then the polydopamine-treated polyvinylidene fluoride Add the ethylene electrospun fiber membrane to the phosphotungstic acid aqueous solution with a concentration of 10wt%, soak it at room temperature for 16 hours, take out the fiber membrane, wash and dry it with deionized water to obtain the polyvinylidene fluoride-phosphotungstic acid membrane; configure the concentration of acetic acid as 2wt% acetic acid aqueous solution, then dissolving chitosan in the acetic acid aqueous solution to form a chitosan solution with a chitosan concentration of 2wt%, and then adding the polyvinylidene fluoride-phosphotungstic acid film to the chitosan solution , soaked at room temperature for 25 minutes, took it out to dry, repeated soaking and drying 3 times, and finally dried to obtain polyvinylidene fluoride-phosphotungstic acid-chitosan composite proton exchange membrane.

Example 5

A preparation method of polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane, the steps are as follows:

Dissolve 5g of polyvinylidene fluoride in a mixed solvent of N,N-dimethylformamide and acetone with a volume ratio of 7:3 to prepare a 25wt% polyvinylidene fluoride electrospinning solution; The solution was added to the syringe of the electrospinning device, and the electrospinning was carried out under the conditions of the ambient temperature of 25°C, the spinning voltage of 35kV, and the flow rate of the spinning needle of 0.8mL/h to obtain polyvinylidene fluoride electrospun fibers Membrane; configuration tris (hydroxymethyl) aminomethane concentration is the Tris-HCl buffer solution of 2mmol/L, and the pH value of the Tris-HCl buffer solution is 8.2, then the polyvinylidene fluoride electrospun fiber membrane is soaked in this buffer solution, then add 2mg/mL dopamine hydrochloride to the buffer solution, and after magnetic stirring at room temperature for 30h, obtain polydopamine-treated polyvinylidene fluoride electrospun fiber membrane; then polydopamine-treated polyvinylidene fluoride The electrospun fiber membrane was added to a 20wt% phosphomolybdic acid aqueous solution, soaked at room temperature for 8 hours, the fiber membrane was taken out, washed and dried with deionized water to obtain a polyvinylidene fluoride-phosphomolybdic acid membrane; the concentration of acetic acid was 1.5 Wt% acetic acid aqueous solution, then dissolving chitosan in this acetic acid aqueous solution is made into the chitosan solution that chitosan concentration is 3wt%, then polyvinylidene fluoride-phosphomolybdic acid film is added to this chitosan solution , soaked at room temperature for 35 minutes, took it out to dry, repeated soaking and drying 4 times, and finally dried to obtain polyvinylidene fluoride-phosphomolybdic acid-chitosan composite proton exchange membrane.

Table 2 lists the performance index data of the polyvinylidene fluoride-heteropolyacid-chitosan composite proton exchange membrane prepared in Examples 2-5.

Table 2

The film performance test conditions prepared by each of the above embodiments are described in a unified manner as follows:

(1) Proton conductivity: The resistance of the membrane was tested on a frequency response analyzer, the frequency scanning range was 1-10 ⁷ Hz, and the amplitude of the AC signal was 100mV. The cut film (4cm×5cm) was tested by four-electrode AC impedance method. Before the test, the film sample was placed in deionized water at room temperature to reach saturation. The proton conductivity σ (S/cm) of the membrane was calculated by the following formula:

In the formula, L and A are the distance between the two electrodes and the effective cross-sectional area of the film to be tested between the two electrodes, respectively, and R is the resistance of the film, which is obtained from the Nyquist diagram obtained from the AC impedance test.

(2) Tensile strength and elongation at break: Cut the film into a rectangular strip with a length of 50 mm and a width of 20 mm, and test it on an electronic tensile machine at a tensile speed of 2 mm/min.

(3) Loss rate of heteropoly acid: first weigh the mass of the dry film as W ₁ , then soak the film in deionized water at room temperature for 24 hours, take it out, dry it to constant weight, and weigh its mass as W ₂ , the mass of the heteropoly acid The churn rate for is calculated by the following formula:

The above examples are preferred implementations of the present invention, but the implementation of the present invention is not limited by the above examples. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention shall be regarded as equivalent replacements, and shall be included in the protection scope of the present invention.

Claims (1)

1. a kind of preparation method of Kynoar-heteropoly acid-chitosan compound proton exchange membrane, this method includes following successively Step：

（1）Kynoar is dissolved in mixed organic solvents, is made into the electrostatic that Kynoar concentration is 5wt% ~ 30wt% Spinning solution；

The mixed organic solvents are made up of amide solvent and ketones solvent, wherein, ketones solvent is in mixed organic solvents Volume percent content be 2 ~ 40%；

The amide solvent is DMF or DMA, and ketones solvent is acetone or butanone；

（2）By step（1）Gained electrostatic spinning solution is added in the syringe of electrostatic spinning apparatus, environment temperature be 10 ~ 30 DEG C, spinning voltage be 20 ~ 40 kV, spinning syringe needle flow carry out electrostatic spinning under conditions of being 0.1 ~ 1 mL/h, obtain poly- inclined PVF electrospun fibers film；

（3）Configuration three（Methylol）Aminomethane concentration is 1 ~ 10 mmol/L Tris-HCl buffer solutions, and the Tris-HCl delays Fliud flushing pH value is 8.0 ~ 9.0, by step（2）Gained Kynoar electrospun fibers film is soaked in the Tris-HCl buffer solutions In；

（4）Toward step（3）Gained in the Tris-HCl buffer solutions of Kynoar electrospun fibers film immersed with adding DOPA The ratio of amine hydrochlorate, dopamine hydrochloride and Tris-HCl buffer solutions is 0.5 ~ 8 mg：1mL, room temperature magnetic agitation make DOPA After 10 ~ 48h of amine oxidation polymerization, the Kynoar electrospun fibers film of poly-dopamine processing is obtained；

（5）By step（4）A Kynoar electrospun fibers film for poly- bar of amine processing of gained be added to concentration for 2wt% ~ In the 25wt% heteropoly acid aqueous solution, 8 ~ 24h of soaking at room temperature, tunica fibrosa is taken out, and poly- inclined fluorine is drying to obtain through deionized water washing Ethene-heteropoly acid film；

The heteropoly acid is one kind in phosphotungstic acid, phosphomolybdic acid or silico-tungstic acid；

（6）The acetic acid aqueous solution that acetic acid concentration is 0.5wt% ~ 3wt% is configured, is then dissolved chitosan in the acetic acid aqueous solution The chitosan solution that chitosan concentration is 0.2wt% ~ 5wt% is made into, by step（5）Gained Kynoar-heteropoly acid film adds Into the chitosan solution, 15 ~ 45min of soaking at room temperature, taking-up is dried, and is repeated immersion, is dried 2 ~ 6 times, finally dry to gather Vinylidene-heteropoly acid-chitosan compound proton exchange membrane.