Cross-linked high temperature proton exchange membrane and preparation method thereof

Abstract

The application discloses a crosslinking type high-temperature proton exchange membrane and a preparation method thereof, and is used for a high-temperature proton exchange membrane fuel cell. The high-temperature proton exchange membrane is prepared from linear aromatic ether type polybenzimidazole (OPBI) as raw material and 2,6-pyridine dimethyl alcohol as a crosslinking agent, and is obtained through in-situ covalent crosslinking film formation by a flow casting method. The imidazole-2,6-pyridine dimethyl alcohol is obtained through nucleophilic substitution reaction of imidazole and 2,6-pyridine dimethyl alcohol. The application has the advantages of simple preparation process, low raw material cost, and the like. After doping phosphoric acid, the crosslinking structure film has the advantages of strong proton conduction capacity, good chemical stability and the like, and has a wide application prospect in the high-temperature proton exchange membrane fuel cell.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer materials and fuel cell technology, and relates to a material for a high-temperature proton exchange membrane fuel cell proton exchange membrane with a cross-linked network structure and a preparation method thereof. BACKGROUND

[0002] Proton exchange membrane fuel cell (PEMFC) is a kind of high-efficiency, clean and environmentally friendly power generation device, which is an ideal power source for electric vehicles, and can also be used as a military power source for distributed power stations, submarines and spacecraft, and a portable power source, etc., and has a very broad application prospect. Due to the limitation of the working temperature of PEMFC, it faces problems such as poor CO tolerance and difficult water and heat management of the system in actual application. Therefore, increasing the operating temperature of PEMFC to above 100℃ can effectively overcome the above problems of traditional Nafion-based PEMFC, and this type of fuel cell (FC) is usually called high-temperature proton exchange membrane fuel cell (HT-PEMFC), which is an important development direction of PEMFC technology. Nowadays, PBI, as the most outstanding polymer-based material in engineering thermoplastics, shows great effectiveness and feasibility in being used as a high-temperature proton exchange membrane for HT-PEMFC. However, so far, one of the key problems to obtain excellent performance of HT-PEMFC based on PBI is the trade-off between proton conductivity and mechanical strength. PBI is a kind of heterocyclic polymer, and each repeating unit contains two imidazole groups. These basic groups are easily doped with phosphoric acid (PA) molecules. The doping of a large number of PA molecules can make the PBI membrane have excellent proton conductivity. However, the doping of PA also reduces the interaction force between PBI polymer chains, and the mechanical strength of the PBI membrane deteriorates sharply with the increase of the acid doping level. Therefore, the modification of polybenzimidazole membrane should improve the mechanical properties while ensuring excellent proton conductivity.

[0003] Recently, a variety of cross-linking methods have been developed to improve the performance of PBI membranes, for example, (1) ion cross-linking process relying on the acid-base interaction between basic benzimidazole and acidic groups; (2) covalent cross-linking strategy based on Friedel-Crafts reaction or N-substitution reaction. However, a better covalent cross-linking strategy is now urgently needed to explore for obtaining high-performance PA-PBI membranes combining high proton conductivity and excellent fuel cell performance. At present, two key factors limit the performance of covalently cross-linked PBI membranes: (1) the introduction of a small molecule cross-linking agent in an amount of more than 10% in the PBI membrane generally leads to a decrease in the concentration of proton-conducting imidazole units, thereby resulting in a decrease in proton conductivity; (2) the excessively tight cross-linked network in the PBI membrane inhibits the uptake of PA (phosphoric acid). These two factors result in low proton conductivity of conventional cross-linked PBI membranes. SUMMARY

[0004] The technical problem solved by the present application is to overcome the shortcomings of the prior art and provide a cross-linked high-temperature proton exchange membrane and a preparation method thereof.

[0005] The technical solution of the present application is:

[0006] A cross-linked high-temperature proton exchange membrane comprises the following raw materials:

[0007] and polybenzimidazole, wherein x=1-3 and y=1-3.

[0008] The polybenzimidazole is any one or more of OPBI and F6-PBI.

[0009] The structural formula of the OPBI is The structural formula of the F6-PBI is .

[0010] When x and y are both 1, 2,6-pyridine dimethyl alcohol, and the molar ratio of the repeating unit of the polybenzimidazole to the 2,6-pyridine dimethyl alcohol is 1: (5-20%).

[0011] The polybenzimidazole, are used as raw materials to form a film through in-situ covalent cross-linking by a casting method.

[0012] The polybenzimidazole is OPBI, wherein x=y=1.

[0013] The polybenzimidazole and 2,6-pyridine dimethyl alcohol are respectively dissolved in a polar aprotic solvent, the two solutions are uniformly mixed and stirred, and then a film is formed through a casting method, and in the evaporation process of the solvent, in-situ nucleophilic substitution reaction of -OH and imidazole occurs, thereby cross-linking to obtain a cross-linked polybenzimidazole film.

[0014] The polar aprotic solvent is any one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0015] The polybenzimidazole is dissolved in a polar aprotic solvent to obtain an OPBI solution, and the mass percentage of the OPBI in the OPBI solution is 2-6%; the 2,6-pyridine dimethyl alcohol is dissolved in a polar aprotic solvent to obtain a cross-linking agent solution, and the mass percentage of the 2,6-pyridine dimethyl alcohol in the cross-linking agent solution is 8-12%.

[0016] Through the above technical solution, within the raw material concentration range specified in this application, the OPBI slurry exhibits good film-forming properties, resulting in a relatively smooth and even film without obvious defects, and good film uniformity. When the concentration of polybenzimidazole and / or 2,6-pyridinediethanol in the solvent is too high, the solution is difficult to spread on the film-forming substrate and is prone to undissolved particles. When the concentration is too low, the film-forming properties are poor, resulting in a thick wet film that is prone to flow, leading to uneven dry film after drying.

[0017] The temperature of the evaporating solvent is controlled by a gradient, maintaining 60-80℃ for 5-12 hours and 120-140℃ for 6-12 hours to allow for full cross-linking.

[0018] The molar ratio of the repeating unit of OPBI to 2,6-pyridinediethanol is 1:(5-20%).

[0019] The degree of crosslinking is controlled by adjusting the proportion of the bis(hydroxymethyl) crosslinking agent 2,6-pyridinediethanol, so that the reactivity of the imidazole group in polybenzimidazole is 5-20%. When the amount of 2,6-pyridinediethanol is too large, excessive crosslinking network structure will be formed, which will significantly reduce solubility and film formation. Excessive crosslinking degree leads to the formation of dense crosslinking network, which hinders phosphoric acid adsorption and retention and reduces proton conductivity. When the amount of O2 and 6-pyridinediethanol is too small, a crosslinking network structure of a certain density cannot be formed, and the performance improvement is not significant.

[0020] The structural characteristics of the 2,6-pyridinediethanol are as follows:

[0021] (1) 2,6-pyridinediethanol has a highly efficient cross-linking reaction, which can not only reduce the consumption of cross-linking agent and proton-conductive imidazole units on the PBI main chain, but also reduce the high density of cross-linking structure from hindering PA absorption.

[0022] (2) The pyridine ring on the crosslinking agent contains Lewis basic N atoms that can interact with phosphoric acid molecules to promote phosphoric acid absorption and increase proton conductivity.

[0023] In summary, this application includes at least the following beneficial technical effects:

[0024] 1. This invention introduces a cross-linked structure into the polybenzimidazole membrane through covalent cross-linking modification, which greatly improves the mechanical properties and dimensional stability of the membrane. When the cross-linked high-temperature proton exchange membrane of this invention is impregnated with phosphoric acid, the phosphoric acid doping amount per unit volume is increased. Due to the increase in phosphoric acid doping amount per unit volume, its proton conductivity is also improved.

[0025] 2. The novel crosslinking agent of the present invention is suitable for mass production, the crosslinking process is very simple and suitable for large-scale industrial production, and the prepared crosslinked polybenzimidazole high-temperature proton exchange membrane has excellent performance when applied to high-temperature fuel cells. Attached Figure Description

[0026] Figure 1 This is a comparison of the mechanical properties of the polybenzimidazole high-temperature proton exchange membrane materials with cross-linked network structures prepared in Examples 1-4 with those of commercial polybenzimidazole membranes before and after phosphoric acid doping. Figure 1 a is the tensile stress-strain curve of undoped phosphoric acid. Figure 1 b is the tensile stress-strain curve of the wet film after doping with phosphoric acid.

[0027] Figure 2 The figures show the proton conductivity curves of the polybenzimidazole high-temperature proton exchange membrane materials with cross-linked network structures prepared in Examples 1-4 and commercial polybenzimidazole membranes under non-humidification conditions in the range of 110-180°C.

[0028] Figure 3 This is a comparison of the phosphoric acid doping amount and dimensional stability of the high-temperature proton exchange membrane materials prepared in Examples 1-4 with those of commercial polybenzimidazole membranes.

[0029] Figure 4 This section compares the thermodynamic properties of the high-temperature proton exchange membrane materials prepared in Examples 1-4 with those of commercially available polybenzimidazole membranes. Figure 4 a represents the thermogravimetric curve of the undoped phosphate film. Figure 4 b is the thermogravimetric curve of the film after phosphate doping. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0031] Example 1: The preparation method of C-PBI-5% high-temperature proton exchange membrane material is as follows:

[0032] Polybenzimidazole (OPBI) was added to an N-methylpyrrolidone solution, heated and stirred to dissolve, yielding a 10 wt% polymer solution. 2,6-pyridinediethanol was added to the N-methylpyrrolidone solution and stirred to dissolve, yielding a 4 wt% crosslinking agent solution. The molar ratio of 2,6-pyridinediethanol to the imidazole ring in polybenzimidazole was controlled at 1:20, meaning 5% of the imidazole ring underwent nucleophilic substitution. The 2,6-pyridinediethanol solution was added dropwise to the polybenzimidazole solution to obtain a homogeneous solution containing the crosslinking agent. A film was formed using a casting method, casting the homogeneous crosslinking agent solution onto a glass plate, heating at 80°C for 10 h, then at 140°C for 6 h, and evaporating the solvent to obtain a crosslinked polybenzimidazole membrane. The crosslinked membrane was then immersed in 85 wt% phosphoric acid at 120°C for 12 h before being removed, yielding the desired crosslinked high-temperature proton exchange membrane.

[0033] Example 2: The preparation method of C-PBI-10% high-temperature proton exchange membrane material is as follows:

[0034] Polybenzimidazole (OPBI) was added to an N-methylpyrrolidone solution, heated and stirred to dissolve, yielding a 10 wt% polymer solution. 2,6-pyridinediethanol was added to the N-methylpyrrolidone solution and stirred to dissolve, yielding a 4 wt% crosslinking agent solution. The molar ratio of 2,6-pyridinediethanol to the imidazole ring in polybenzimidazole was controlled at 1:10, meaning 10% of the imidazole ring underwent nucleophilic substitution. The 2,6-pyridinediethanol solution was added dropwise to the polybenzimidazole solution to obtain a homogeneous solution containing the crosslinking agent. A film was formed using a casting method, casting the homogeneous crosslinking agent solution onto a glass plate, heating at 80°C for 10 h, then at 140°C for 6 h, and evaporating the solvent to obtain a crosslinked polybenzimidazole membrane. The crosslinked membrane was then immersed in 85 wt% phosphoric acid at 120°C for 12 h before being removed, yielding the desired crosslinked high-temperature proton exchange membrane.

[0035] Example 3: The preparation method of C-PBI-15% high-temperature proton exchange membrane material is as follows:

[0036] Polybenzimidazole (OPBI) was added to an N-methylpyrrolidone solution, heated and stirred to dissolve, yielding a 10 wt% polymer solution. 2,6-pyridinediethanol was added to the N-methylpyrrolidone solution and stirred to dissolve, yielding a 4 wt% crosslinking agent solution. The molar ratio of 2,6-pyridinediethanol to the imidazole ring in polybenzimidazole was controlled at 1:7, meaning 15% of the imidazole ring underwent nucleophilic substitution. The 2,6-pyridinediethanol solution was added dropwise to the polybenzimidazole solution to obtain a homogeneous solution containing the crosslinking agent. A film was formed using a casting method, casting the homogeneous crosslinking agent solution onto a glass plate, heating at 80°C for 10 h, then at 140°C for 6 h, and evaporating the solvent to obtain a crosslinked polybenzimidazole membrane. The crosslinked membrane was then immersed in 85 wt% phosphoric acid at 120°C for 12 h before being removed, yielding the desired crosslinked high-temperature proton exchange membrane.

[0037] Example 4: The preparation method of C-PBI-20% high-temperature proton exchange membrane material is as follows:

[0038] Polybenzimidazole (OPBI) was added to an N-methylpyrrolidone solution, heated and stirred to dissolve, yielding a 10 wt% polymer solution. 2,6-pyridinediethanol was added to the N-methylpyrrolidone solution and stirred to dissolve, yielding a 4 wt% crosslinking agent solution. The molar ratio of 2,6-pyridinediethanol to the imidazole ring in polybenzimidazole was controlled at 1:5, meaning 20% ​​of the imidazole ring underwent nucleophilic substitution. The 2,6-pyridinediethanol solution was added dropwise to the polybenzimidazole solution to obtain a homogeneous solution containing the crosslinking agent. A film was formed using a casting method, casting the homogeneous crosslinking agent solution onto a glass plate, heating at 80°C for 10 h, then at 140°C for 6 h, and evaporating the solvent to obtain a crosslinked polybenzimidazole membrane. The crosslinked membrane was then immersed in 85 wt% phosphoric acid at 120°C for 12 h before being removed, yielding the desired crosslinked high-temperature proton exchange membrane.

[0039] Example 5

[0040] The difference from Example 1 is that OPBI is replaced with F6-PBI with an equal molar amount of repeating units. Polybenzimidazole (F6-PBI) was added to an N-methylpyrrolidone solution, heated and stirred to dissolve, yielding a 10 wt% polymer solution. 2,6-pyridinediethanol was added to the N-methylpyrrolidone solution and stirred to dissolve, yielding a 4 wt% crosslinking agent solution. The molar ratio of 2,6-pyridinediethanol to the imidazole ring in F6-PBI was controlled at 1:5, meaning 20% ​​of the imidazole ring underwent nucleophilic substitution. The 2,6-pyridinediethanol solution was added dropwise to the polybenzimidazole solution to obtain a homogeneous solution containing the crosslinking agent. A film was formed using a casting method, casting the homogeneous crosslinking agent solution onto a glass plate, heating at 80°C for 10 h, then at 140°C for 6 h, and evaporating the solvent to obtain a crosslinked polybenzimidazole membrane. The crosslinked membrane was then immersed in 85 wt% phosphoric acid at 120°C for 12 h before being removed, yielding the desired crosslinked high-temperature proton exchange membrane.

[0041] Comparative Example 1

[0042] The difference from Example 1 is as follows: 2,6-pyridinediethanol is replaced with p-dichlorobenzyl; polybenzimidazole (OPBI) is added to an N-methylpyrrolidone solution, heated and stirred to dissolve, resulting in a 10 wt% polymer solution; p-dichlorobenzyl is added to an N-methylpyrrolidone solution, stirred to dissolve, resulting in a 4 wt% crosslinking agent solution; the molar ratio of p-dichlorobenzyl to the imidazole ring in OPBI is controlled at 1:20, i.e., 5% of the imidazole ring undergoes nucleophilic substitution reaction; the p-dichlorobenzyl solution is added dropwise to the polybenzimidazole solution to obtain a homogeneous solution containing the crosslinking agent; a film is formed by casting, the homogeneous solution containing the crosslinking agent is cast onto a glass plate, heated at 80°C for 10 h, then heated at 140°C for 6 h, and the solvent is evaporated to obtain a crosslinked polybenzimidazole membrane; the crosslinked membrane is immersed in 85 wt% phosphoric acid at 120°C for 12 h and then removed to obtain the desired crosslinked high-temperature proton exchange membrane.

[0043] Comparative Example 2

[0044] Currently, commercially available polybenzimidazole membranes are mainly produced and sold by foreign companies, such as FuMATech's fumapem AP proton exchange membrane and BASF's Celtec® high-temperature proton exchange membrane. This article compares the commercially available high-temperature proton exchange membrane with FuMATech's fumapem AP proton exchange membrane. The commercial membrane was cut to the required size, immersed in 85wt% phosphoric acid at 120°C for 12 hours, and then removed to obtain the desired phosphoric acid-doped high-temperature proton exchange membrane.

[0045] Performance testing

[0046] According to GB / T6425-2008, the cross-linked high-temperature proton exchange membranes obtained in the above examples and comparative examples were subjected to thermodynamic performance testing.

[0047] According to GB / T20042, the proton conductivity of the cross-linked high-temperature proton exchange membranes obtained in the above embodiments and comparative examples was tested.

[0048] According to GB / T12160, the mechanical properties of the cross-linked high-temperature proton exchange membranes obtained in the above embodiments and comparative examples were tested.

[0049] The dimensional stability of the cross-linked high-temperature proton exchange membranes obtained in the above embodiments and comparative examples was tested by volume deformation measurement.

[0050] The phosphoric acid doping content of the cross-linked high-temperature proton exchange membranes obtained in the above embodiments and comparative examples was detected by mass weighing.

[0051] The test results of Examples 1-4 and Comparative Example 2 are shown in the appendix to the instruction manual. Figures 1-4 .

[0052] The detection results of Examples 1 and 5 and Comparative Example 1 are shown in Table 1.

[0053] Table 1 Test Results

[0054]

[0055] According to Examples 1-4 and Figures 1-4 It can be seen that the mechanical tensile strength of the cross-linked OPBI film gradually increases with the increase of cross-linking degree. This trend can be observed in both the dry film and the film doped with phosphoric acid. The proton conductivity shows a trend of first increasing and then decreasing, with the highest proton conductivity value at a cross-linking degree of 5%. The proton conductivity of cross-linked films with cross-linking degrees of 5%, 10%, and 15% is higher than that of commercial PBI films, but the proton conductivity of the 20% cross-linked film is lower than that of commercial PBI films. This may be because the excessively dense cross-linking network hinders the migration and adsorption of phosphoric acid, thereby reducing the proton conductivity. The phosphoric acid adsorption capacity and volume swelling rate of the cross-linked film also decrease with the increase of cross-linking degree. The 5% cross-linked film has the highest phosphoric acid doping amount and the highest volume swelling rate. All cross-linked films have high thermal stability. Before 500℃, there is no significant mass change except for the evaporation of a small amount of water and solvent in the film.

[0056] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A cross-linked high-temperature proton exchange membrane, characterized in that... It includes the following raw materials: And polybenzimidazole, where x=1-3, y=1-3, As a crosslinking agent, it crosslinks the polybenzimidazole backbone to form a network structure; When both x and y are 1 The molar ratio of the repeating unit of polybenzimidazole to 2,6-pyridinediethanol is 1:(5-20%).

2. The cross-linked high-temperature proton exchange membrane according to claim 1, characterized in that: The polybenzimidazole is any one or more of OPBI and F6-PBI.

3. A method for preparing a cross-linked high-temperature proton exchange membrane, characterized in that: With polybenzimidazole, The film is obtained by in-situ covalent crosslinking using the raw material and a casting method. in As a crosslinking agent, it crosslinks the polybenzimidazole backbone to form a network structure; The polybenzimidazole is OPBI. In the case of x=y=1; The molar ratio of the repeating unit of OPBI to 2,6-pyridinediethanol is 1:(5-20%).

4. The method for preparing a cross-linked high-temperature proton exchange membrane according to claim 3, characterized in that: The polybenzimidazole and 2,6-pyridinediethanol are dissolved in polar aprotic solvents respectively. After the two solutions are mixed and stirred evenly, a film is formed by casting. During the solvent evaporation process, -OH undergoes an in-situ nucleophilic substitution reaction with imidazole, thereby crosslinking, to obtain a crosslinked polybenzimidazole film.

5. The method for preparing a cross-linked high-temperature proton exchange membrane according to claim 4, characterized in that: The polar aprotic solvent is any one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

6. The method for preparing a cross-linked high-temperature proton exchange membrane according to claim 4, characterized in that: The polybenzimidazole is dissolved in a polar aprotic solvent to obtain an OPBI solution, wherein the mass percentage of OPBI in the OPBI solution is 2-6%; 2,6-pyridinediethanol is dissolved in a polar aprotic solvent to obtain a crosslinking agent solution, wherein the mass fraction of 2,6-pyridinediethanol in the crosslinking agent solution is 8-12%.

7. The method for preparing a cross-linked high-temperature proton exchange membrane according to claim 4, characterized in that: The temperature of the evaporating solvent is controlled by a gradient: 60-80℃ for 5-12 hours and 120-140℃ for 6-12 hours.

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