CN115101790A - A kind of composite electrolyte membrane with high electrical conductivity and preparation method thereof - Google Patents

Abstract

The invention provides a composite electrolyte membrane with high conductivity and a preparation method thereof, wherein the preparation method comprises the following steps: s1: dissolving polybenzimidazole and polyvinylidene chloride in a polar organic solvent; s2: adding a cross-linking agent into S1, and uniformly stirring to obtain a polymer solution, wherein the cross-linking agent is a binary or multi-element halide R-X; s3: casting the polymer solution of S2 in a mould, drying and then carrying out heat treatment to obtain a polybenzimidazole film; s4: and (3) immersing the polybenzimidazole membrane obtained in the step (S3) in phosphoric acid, standing, and taking out the polybenzimidazole membrane after standing to obtain the composite electrolyte membrane. The preparation method has the advantages of simple preparation process, easy implementation, low cost, no change of PBI resin synthesis process and reaction conditions, no modification requirement on film forming equipment, very simple process, low raw material cost, and easy batch production, and the composite film obtained by the preparation method.

Description

A kind of composite electrolyte membrane with high electrical conductivity and preparation method thereof

technical field

The invention relates to the field of preparation of a composite electrolyte membrane, and more particularly to a composite electrolyte membrane with high electrical conductivity and a preparation method thereof.

Background technique

Nowadays, fossil energy is decreasing day by day and the environmental problems caused by the use of fossil energy are becoming more and more prominent. Hydrogen energy is considered to be a good substitute for fossil energy, and the use of hydrogen energy requires energy conversion. The proton exchange membrane fuel cell (PEMFC), as an energy conversion device, can be used in the energy device of mobile equipment such as new energy vehicles. Proton exchange membrane PEM, also known as proton membrane or hydrogen ion exchange membrane, is an ion-selective permeable membrane that functions in batteries to provide channels for proton migration and transport, to separate gaseous reactants, and to block electrolytes.

One of the most widely studied in PEM is polybenzimidazole (PBI) and its derivatives. Polybenzimidazole (PBI) is a linear heterocyclic polymer containing polybenzimidazole groups in repeating units. It has good thermal and chemical stability and high mechanical strength, but polybenzimidazole itself does not. There is no proton conductivity, so it needs to be compounded with phosphoric acid to obtain higher proton conductivity. Usually, a higher doping amount of phosphoric acid is required to obtain higher battery performance, but at the same time, it will also cause the mechanical properties of the film-forming material to decline. At the same time, when the phosphoric acid doping amount of the membrane material is too large, a large amount of "free acid" that is easily lost will be generated, and the loss of phosphoric acid will also cause problems such as performance degradation, size reduction and electrode corrosion of the membrane material.

At present, in order to cope with the problem that the mechanical strength of the phosphoric acid is too large, cross-linking modification is generally used to strengthen the linking modification. Copolymerization crosslinking occurs in the process of synthesizing PBI resin, which is a crosslinking modified polymer obtained by reacting 3,3'-diaminobenzidine and isophthalic acid with polyacid compounds such as trimesic acid. This polymer has a hyperbranched structure. The covalent crosslinking modification occurs after the synthesis of PBI, and the PBI resin and a suitable crosslinking agent are dissolved in an organic solvent at the same time, so that the crosslinking agent and the N-H on the imidazole ring on the PBI structure undergo a substitution reaction. At present, the commonly used cross-linking agents include dichloromethyl hypophosphorous acid, benzoxazole, dibromotoluene and epoxy resin, etc. These cross-linking agents usually need to participate in the PBI resin synthesis reaction process, which is unfavorable to the PBI resin synthesis reaction. In addition, the prepared resin is not easily soluble in organic solvents due to cross-linking, which brings inconvenience to film formation. Therefore, there is a need to improve existing processes.

SUMMARY OF THE INVENTION

In order to solve the problem that the existing electrolyte membrane loses mechanical strength due to the excessive amount of doped phosphoric acid, a composite electrolyte membrane with high conductivity and a preparation method thereof are provided.

The specific technical solutions are as follows:

A method for preparing a composite electrolyte membrane with high electrical conductivity, comprising the following steps:

S1: Dissolve polybenzimidazole and polyvinylidene chloride in polar organic solvent;

S2: Add the cross-linking agent to S1, stir evenly to obtain a polymer solution, the cross-linking agent is a binary or polyvalent halogenated hydrocarbon R-X, and the modification occurs after the PBI synthesis, so it does not participate in the PBI resin synthesis reaction , will not adversely affect the synthesis reaction of PBI resin, and will not bring about the problem of difficult film formation of composite films;

S3: casting the polymer solution described in S2 in a mold, and performing heat treatment after drying to obtain a polybenzimidazole film;

S4: the polybenzimidazole film obtained in S3 is immersed in phosphoric acid and then left to stand, and then taken out to obtain a composite electrolyte membrane.

After the polybenzimidazole film is doped with phosphoric acid, a large number of phosphoric acid molecules will enter between the polymer chains to break the hydrogen bonds. And the "strong plasticization" effect of the incorporated phosphoric acid molecules will significantly reduce the mechanical properties of the membrane material, resulting in dimensional swelling. Crosslinking generally refers to the process of forming a network structure in a polymer, which is a common polymer modification method. Mechanical behavior. When swelling occurs, the interchain force of the polymer can be enhanced, so that the membrane material exhibits higher dimensional stability. At the same time, the formation of a cross-linked network can provide greater resistance to phosphoric acid loss and improve its phosphoric acid retention capacity.

The mass ratio of polybenzimidazole, polyvinylidene chloride and organic solvent in the S1 is 1:(100-400).

The mass ratio of the cross-linking agent in the S2 to the mass ratio of polybenzimidazole and polyvinylidene chloride is 1: (10-100). Compared with the ionic cross-linking structure, the formed covalent cross-linking structure is very important for the mechanical properties of the membrane. The performance improvement is more obvious, which means that it can withstand higher phosphoric acid doping levels, but at the same time, as the crosslinking degree increases, the polymer chains will be packed more tightly, which limits the doping ability of phosphoric acid. Therefore, it is necessary to control and optimize the amount of cross-linking agent to achieve the optimal effect.

The temperature at which the heat treatment is performed in the S3 is 150-200°C.

The drying temperature in S3 is 80-120°C.

X in the halide R-X is Cl, Br or I.

The organic solvent in S1 is a mixture of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone in any proportion.

The standing time in S4 is 1-12 hours.

A composite electrolyte membrane with high electrical conductivity is prepared by the above preparation method.

Beneficial effects:

(1) A composite electrolyte membrane with high electrical conductivity and a preparation method thereof provided by the present invention, in view of the problem that the mechanical strength of the composite membrane is reduced, a cross-linking agent is used to modify it. The cross-linking agent used in the preparation method is: Binary or polyhalogenated compounds, and the modification occurs after PBI synthesis, so it does not participate in the PBI resin synthesis reaction, does not adversely affect the PBI resin synthesis reaction, and does not bring about the problem of difficulty in forming a composite film.

(2) The polymer backbone has a grid-like structure by adding a cross-linking agent, and at the same time, the composite film has a higher mechanical strength by optimizing the addition ratio of the cross-linking agent.

(3) The amount of the crosslinking agent added in this preparation method is 1%-10% of the mass of PBI/PVDF, which neither limits the doping ability of phosphoric acid, but also enables the composite membrane to obtain excellent mechanical properties.

(4) The preparation process of the present invention is simple, easy to implement, low in cost, does not change the PBI resin synthesis process and reaction conditions, and has no requirement for modification of film-forming equipment, the process is very simple, the cost of raw materials is low, and it is a process that is easy to mass-produce .

Description of drawings

Figure 1 shows the tensile curves of PVDF/polybenzimidazole films with different crosslinking ratios.

Figure 2 shows the proton conductivity of PVDF/polybenzimidazole/phosphoric acid composite membranes with different crosslinking ratios.

Detailed ways

In order to deepen the understanding of the present invention, the present invention will be described in further detail below with reference to the embodiments and the accompanying drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

Example 1

A preparation method of a composite electrolyte membrane with high electrical conductivity mainly comprises the following steps:

(1) dissolve 0.6g of polybenzimidazole in 100g of N,N-dimethylformamide;

(2) after the polybenzimidazole in step (1) is completely dissolved, the polymer solution is cast in a flat mold, and dried at 100° C. to volatilize the organic solvent;

(3) after the organic solvent in step (2) is completely volatilized, heat treatment at 180° C. to form a polybenzimidazole film;

(4) Immerse the polybenzimidazole film in concentrated sulfuric acid at 130° C. and let it stand for 12 hours.

Example 2

A preparation method of a composite electrolyte membrane with high electrical conductivity mainly comprises the following steps:

(1) dissolve 0.6g of polybenzimidazole in 100g of N,N-dimethylformamide;

(2) after the polybenzimidazole in step (1) is completely dissolved, add the halogenated hydrocarbon of 0.024g, and stir to obtain a uniform and stable polybenzimidazole solution;

(3) casting the polymer solution in a flat mold, drying at 100°C to volatilize the organic solvent;

(4) after the organic solvent in step (3) is completely volatilized, heat treatment at 180° C. to form a polybenzimidazole film;

(5) Immerse the polybenzimidazole film in concentrated sulfuric acid at 130° C. and let it stand for 12 hours.

Example 3

A preparation method of a composite electrolyte membrane with high electrical conductivity mainly comprises the following steps:

(1) dissolve 0.6g of polybenzimidazole in 100g of N,N-dimethylformamide;

(2) after the polybenzimidazole in step (1) is completely dissolved, add the halogenated hydrocarbon of 0.042g, and stir to obtain a uniform and stable polybenzimidazole solution;

(3) casting the polymer solution in a flat mold, drying at 100°C to volatilize the organic solvent;

(4) after the organic solvent in step (3) is completely volatilized, heat treatment at 180° C. to form a polybenzimidazole film;

(5) Immerse the polybenzimidazole film in concentrated sulfuric acid at 130° C. and let it stand for 12 hours.

The composite films prepared by the above-mentioned three groups of embodiments are tested for performance:

(1) Mechanical performance test

Test method: Before the test, all samples are cut into samples of a certain size. The composite electrolyte membrane during operation must have certain mechanical properties to withstand the pressure generated by the gas flow on both sides. Therefore, a tensile test is performed on the membrane samples to evaluate its performance. Mechanical properties, Figure 1 is the tensile curve of the composite film prepared by using different ratios of cross-linking agents. It can be seen from Figure 1 that because no cross-linking agent is added in Example 1, after phosphoric acid doping treatment, a large amount of The phosphoric acid molecules enter the polymer to play the role of "strong plasticization", which makes the composite film show lower mechanical strength. In Example 3, when the proportion of crosslinking agent is 7% of the mass of PBI, the Tensile strength is the best.

(2) Proton conductivity test

The composite membrane samples prepared in the three groups of examples were cut into the same specifications, and the cut samples were used for proton conductivity test. The test was carried out during the cooling process from 180°C to 100°C to remove the influence of water. The impedance value (R) of the sample was measured by the four-electrode AC impedance method, and the proton conductivity σ was obtained by calculation. The formula is: σ=L/ (A×R); where L is the distance between the two electrodes; A is the cross-sectional area of the film sample. Figure 2 shows the proton conductivity of composite membranes prepared with different ratios of cross-linking agents. It can be seen from the figure that the conductivity is the best when the ratio of cross-linking agent is 4% of the mass of PBI.

As a further improvement, the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall include within the protection scope of the present invention.

Claims (9)

1. a preparation method of the composite electrolyte membrane of high electrical conductivity, is characterized in that, comprises the following steps: S1: Dissolve polybenzimidazole and polyvinylidene chloride in polar organic solvent; S2: adding a cross-linking agent to S1, stirring uniformly to obtain a polymer solution, and the cross-linking agent is a binary or polyvalent halogenated hydrocarbon R-X; S3: casting the polymer solution described in S2 in a mold, and performing heat treatment after drying to obtain a polybenzimidazole film; S4: the polybenzimidazole film obtained in S3 is immersed in phosphoric acid and then left to stand, and then taken out to obtain a composite electrolyte membrane. 2. the preparation method of the composite electrolyte membrane of a kind of high electrical conductivity according to claim 1, is characterized in that, in described S2, the mass ratio of the quality of crosslinking agent to polybenzimidazole and polyvinylidene chloride is 1 : (10 to 100). 3. the preparation method of the composite electrolyte membrane of a kind of high electrical conductivity according to claim 1, is characterized in that, in described S1, the mass ratio of polybenzimidazole, polyvinylidene chloride and organic solvent is 1:(100 ~400). 4 . The method for preparing a composite electrolyte membrane with high electrical conductivity according to claim 1 , wherein the temperature of the heat treatment in the S3 is 150-200° C. 5 . 5 . The method for preparing a composite electrolyte membrane with high electrical conductivity according to claim 1 , wherein the drying temperature in the S3 is 80-120° C. 6 . 6 . The method for preparing a composite electrolyte membrane with high electrical conductivity according to claim 1 , wherein X in the halide R-X is Cl, Br or I. 7 . 7. The method for preparing a composite electrolyte membrane with high electrical conductivity according to claim 1, wherein the organic solvent in the S1 is N,N-dimethylformamide, N,N-dimethylformamide A mixture of acetamide, dimethyl sulfoxide and N-methylpyrrolidone in any ratio. 8 . The method for preparing a composite electrolyte membrane with high electrical conductivity according to claim 1 , wherein the standing time in the S4 is 1-12 hours. 9 . 9. A composite electrolyte membrane with high electrical conductivity, characterized in that, the electrolyte membrane is prepared by the method according to any one of claims 1-8.

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