High-oxygen-permeability ionomer with large steric hindrance group as well as preparation method and application of high-oxygen-permeability ionomer

Abstract

The invention discloses a high-oxygen-permeability ionomer with a large steric hindrance group as well as a preparation method and application of the high-oxygen-permeability ionomer, and belongs to the technical field of fuel cells. The preparation method comprises the following steps: (1) in a solution environment, carrying out nucleophilic substitution reaction on perfluorosulfonyl fluoride resin and an aminobenzene sulfonic acid compound under the action of an acid-binding agent, and recovering to obtain an ionomer after the reaction is finished; (2) washing the ionomer in a strong alkali solution, and filtering to obtain a product; and (3) carrying out protonation treatment on the product, and recovering to obtain the high-oxygen-permeability ionomer with the large steric hindrance group after the protonation treatment is completed. The method has the advantages that the process is convenient, post-treatment is convenient, batch preparation can be achieved, and the method is suitable for industrial production. The high-oxygen-permeability ionomer with the large steric hindrance group is used for a proton exchange membrane fuel cell, the peak power density is optimized, the mass transfer performance is improved, and the high-oxygen-permeability ionomer shows excellent cell output performance especially in a large-current-density area and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of fuel cells, and in particular to a high oxygen permeability ionomer with a large steric hindrance group, and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cell (PEMFC) is an efficient and clean energy conversion device. Ionomer is an important component of PEMFC. After protons are generated at the anode, they are transferred to the proton exchange membrane through the ionomer in the anode catalyst layer, and then transferred to the cathode catalyst surface through the ionomer in the cathode catalyst layer to react. The ideal ionomer should have good proton conductivity and chemical stability. At the same time, it is also required to have a high oxygen permeability to ensure the efficient transmission of oxygen in the cathode catalyst layer. The commonly used ionomers are perfluorosulfonic acid ionomers, which are composed of a stable and hydrophobic polytetrafluoroethylene (PTFE) main chain and a strongly acidic perfluorosulfonic acid side chain, and have excellent proton conductivity and chemical stability. However, the sulfonic acid side chain of this type of ionomer has strong adsorption on the catalyst platinum surface, which not only occupies the reaction site, but also pulls the main chain to accumulate into a dense film on the platinum surface, greatly hindering oxygen transmission.

[0003] In order to solve the problems caused by the above-mentioned perfluorosulfonic acid ionomers, the development of new ionomers has become a recent research hotspot. For example, in the literature (Adlai Katzenberg et al, J. Am. Chem. Soc. 2020, 142, 3742-3752), Adlai Katzenberg et al. free radical copolymerized perfluoro(2-methylene-4-methyl-1,3-dioxolane) monomer and perfluorosulfonyl fluoride monomer to obtain a perfluorosulfonyl fluoride resin with high oxygen permeability, which improved the transmission of oxygen. However, the introduction of cyclic monomers on the main chain is not conducive to the formation of microphase separation and the conduction of protons, and the oxygen transmission efficiency still needs to be improved. At present, research in this area is still relatively scarce.

[0004] The Chinese invention patent with publication number CN113314722A discloses a method for reducing the poisoning of Pt catalyst by sulfonic acid groups in the catalyst layer of a fuel cell. The invention first ultrasonically disperses Nafion ionomer in an isopropanol solvent, then adds a high-steric alcohol to interact with the Nafion ionomer, then adds the dispersion of the mixture of high-steric alcohol and Nafion ionomer to a commercial Pt-based catalyst moistened with deionized water, obtains a catalyst slurry modified with high-steric alcohol after ultrasonic dispersion, and finally coats the catalyst slurry modified with high-steric alcohol on a commercial proton exchange membrane, and obtains a catalyst layer that can reduce the poisoning effect of sulfonic acid groups after drying. In the Chinese invention patent with publication number CN118738419A, the inventor team provides a membrane electrode catalyst layer for a proton exchange membrane fuel cell and its preparation method and application. It premixes a dispersion of hydroxyl-rich polysaccharide porous molecules with a catalyst and an organic solvent, modifies a layer of hydroxyl-rich polysaccharide porous molecules on the catalyst surface, and then adds a perfluorosulfonic acid electrolyte solution and fully mixes to obtain a catalyst layer slurry.

[0005] When introducing highly hindered alcohol compounds or other hydroxyl compounds into polymer molecular chains, although the bulky substituents will increase the local free volume to a certain extent, the overall effect is still not as expected due to the following reasons: (1) Hydroxyl groups are prone to participate in the formation of hydrogen bonds, especially when adjacent to other oxygen- or nitrogen-containing groups; these hydrogen bonds may enhance the interaction between molecular chains and lead to tighter stacking; (2) Although overly hindered groups increase steric hindrance, they also limit the rotational freedom of the molecular chain, making the overall chain conformation relatively fixed and difficult to effectively disperse to form more free volume.

[0006] In the Chinese invention patent with publication number CN117476951A, the inventor team disclosed a proton exchange membrane fuel cell catalyst layer slurry and its preparation method and application. The slurry mainly includes a catalyst, a perfluorosulfonic acid electrolyte, a solvent, and a hydroxyl-rich porphyrin macrocyclic compound. On the one hand, the interaction between the hydroxyl group and the perfluorosulfonic acid electrolyte weakens the adsorption and poisoning of the sulfonic acid group on the catalyst surface and improves the phase separation of the perfluorosulfonic acid electrolyte; on the other hand, the oxygen enrichment characteristics of the macrocyclic compound itself can further promote oxygen transfer at the catalyst / ionomer interface. However, the method of directly adding compounds and utilizing the interaction between groups has the defect of easy loss, and its application effect needs to be optimized.

[0007] In summary, proposing a suitable process scheme to solve the technical problems existing in the prior art, further improve the mass transfer capacity of the ionomer in the proton exchange membrane fuel cell, and improve the battery output performance is of great significance for expanding the application of proton exchange membrane fuel cells. Summary of the invention

[0008] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, a method for preparing a highly oxygen-permeable ionomer having a large steric hindrance group is provided, which has a convenient process, convenient post-treatment, can be prepared in batches and is suitable for industrial production, comprising the following steps: (1) In a solution environment, a perfluorosulfonyl fluoride resin and an aminobenzenesulfonic acid compound undergo a nucleophilic substitution reaction under the action of an acid-binding agent, and after the reaction is completed, an ionomer is recovered; (2) washing the ionomer in a strong alkaline solution and filtering to obtain the product; (3) The product is protonated and then recovered to obtain a highly oxygen-permeable ionomer having a large steric hindrance group.

[0009] Preferably, in step (1), the perfluorosulfonyl fluoride resin includes at least one of Nafion R-1100, 3M PFSO2F, and Aquivion PFSO2F.

[0010] Those skilled in the art can select suitable perfluorosulfonyl fluoride resins according to actual conditions and application requirements, such as Nafion R-1100, 3M PFSO2F, Aquivion PFSO2F and other types used in the field of proton exchange membrane fuel cells. Nafion R-1100 has high proton conductivity and excellent chemical corrosion resistance, especially in acidic and oxidizing environments, and can maintain physical strength and durability in a wider range of temperature and humidity. The production cost of 3M PFSO2F resin is lower, and it achieves higher proton conductivity through specific molecular design, especially excellent performance under low humidity conditions. Aquivion PFSO2F is a perfluorosulfonic acid resin designed for PEMFC applications produced by Solvay, which has strong mechanical and dimensional stability and exhibits excellent proton conductivity under high humidity and low humidity conditions. The above types of perfluorosulfonyl fluoride resins are particularly suitable for the raw material types of the process of the present invention.

[0011] Preferably, in step (1), the aminobenzenesulfonic acid compound includes at least one of 4-aminobenzenesulfonic acid, sodium 4-aminobenzenesulfonate, potassium 4-aminobenzenesulfonate, 3-aminobenzenesulfonic acid, sodium 3-aminobenzenesulfonate, 2,4-diaminobenzenesulfonic acid, sodium 2,4-diaminobenzenesulfonate, 2-aminotoluene-5-sulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, sodium 1-naphthylamine-4-sulfonate, aniline-2,4-disulfonic acid, 1-amino-8-naphthol-4,6-disulfonic acid, m-phenylenediamine-4,6-disulfonic acid, 1-naphthylamine-4,6,8-trisulfonic acid, barium diphenylamine sulfonate, m-toluidine p-sulfonic acid, diphenylamine-4-sulfonic acid, and 1-amino-8-naphthol-4,6-disulfonic acid.

[0012] Preferably, in step (1), the molar ratio of the perfluorosulfonyl fluoride resin to the aminobenzenesulfonic acid compound is 1:1-4.

[0013] The benzene ring is an electron-donating group, which increases the electron density of the carbon atom on the amino group through the resonance effect, which makes the sulfonyl fluoride group more susceptible to attack by nucleophilic reagents, thereby greatly enhancing the activity of the nucleophilic substitution reaction. Therefore, no additional catalyst is required in the process of the present invention, and the difficulty of the reaction is reduced while achieving the grafting target group, achieving the purpose of killing two birds with one stone.

[0014] Preferably, in step (1), the solution environment is created by a reaction solvent, and the reaction solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and perfluorobenzene.

[0015] Preferably, in step (1), the acid-binding agent includes at least one of sodium hydride, triethylamine, potassium carbonate, cesium carbonate, pyridine, N,N-diisopropylethylamine, and 4-dimethylaminopyridine.

[0016] Preferably, in step (1), the molar ratio of the acid binding agent to the perfluorosulfonyl fluoride resin is 2-4:1.

[0017] Preferably, in step (1), the temperature of the nucleophilic substitution reaction is 80-100° C.; and the time of the nucleophilic substitution reaction is 1-3 days.

[0018] Preferably, in the step (1), after the reaction is completed, the crude product is concentrated and precipitated in a solvent to obtain an ionomer; the solvent comprises at least one of water, acetonitrile, ethanol and methanol.

[0019] In the preparation method of the present invention, there are various ways to recover the ionomer, and those skilled in the art can select a suitable product collection method according to the scale of production and actual conditions. For example, the crude product is concentrated and then precipitated in a poor solvent (water, acetonitrile, ethanol, methanol, etc.), which has the advantages of relatively simple operation, low cost, high purity, etc.

[0020] Preferably, in step (2), the strong alkali solution is an aqueous solution of a strong alkali; the strong alkali comprises at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0021] Preferably, in step (2), the concentration of the strong alkaline solution is 0.5-2 mol / L.

[0022] After washing is completed, the product can be separated by filtration or the like.

[0023] Preferably, in step (3), an inorganic acid is used to protonate the product; the inorganic acid includes at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and perchloric acid.

[0024] Further preferably, the concentration of the inorganic acid is 0.5-2 mol / L.

[0025] The use of inorganic acid treatment can improve the conductivity of the ionomer and enhance its chemical stability and environmental adaptability. Those skilled in the art can use inorganic acids of appropriate concentrations, such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, perchloric acid, etc. for treatment, which can achieve the purpose of protonation of the present invention.

[0026] After the product is protonated, the crude product can be washed and dried (for example, at 80-100°C for 12-36 hours) to recover the target product. Those skilled in the art may also use other means or methods to achieve the purpose of recovery.

[0027] In the second aspect of the present invention, a high oxygen permeability ionomer having a large steric hindrance group is provided, which is prepared by the preparation method provided by the first aspect of the present invention.

[0028] In the third aspect of the present invention, there is provided an application of the high oxygen permeability ionomer having a large steric hindrance group according to the second aspect of the present invention, specifically, applying the ionomer to the cathode catalyst layer of a proton exchange membrane fuel cell.

[0029] Based on the above technical solutions, the design concept and principle of the present invention are as follows: The preparation method of the present invention uses a nucleophilic substitution reaction to react sulfonyl fluoride with an amino group to form a sulfonamide bond, grafts a benzenesulfonic acid group onto the side chain of a perfluorosulfonyl fluoride resin, and then protonates the ionomer without the need for an additional catalyst, thereby successfully preparing a perfluoroionomer with a large steric hindrance group at the end of the side chain formed by a nucleophilic substitution reaction.

[0030] Compared with the existing introduction of high steric hindrance alcohol compounds or hydroxyl-rich polymer groups, the grafting of large steric hindrance benzene sulfonic acid groups in the present invention can increase the free volume of the polymer, reduce the local oxygen transmission resistance of oxygen diffusion in the ionomer layer, promote the transmission of oxygen in the ionomer layer, and thus improve the mass transfer polarization under high current density. In addition, the form of covalent bond grafting has the advantage of not being easy to lose compared to direct addition. The obtained high oxygen permeability ionomer with large steric hindrance groups uses the steric effect to inhibit the adsorption of sulfonic acid groups on the platinum surface, which is beneficial to improve the activity of the catalyst.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects: The invention provides a method for preparing a high oxygen permeability ionomer with a large steric hindrance group, which has the advantages of convenient process, convenient post-treatment, batch preparation and applicability to industrial production.

[0032] The invention provides a high oxygen permeability ionomer with a large steric hindrance group, which utilizes the steric hindrance effect to inhibit the adsorption of sulfonic acid groups on the surface of platinum, thereby facilitating the improvement of the activity of the catalyst.

[0033] The present invention provides an application of a highly oxygen-permeable ionomer with a large steric hindrance group for use in a proton exchange membrane fuel cell, which optimizes the peak power density and greatly improves the mass transfer performance, especially in the high current density region, exhibits excellent battery output performance, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Polarization curves and power density curves of Example 1 and Comparative Example 1 under hydrogen and oxygen, 100% relative humidity (RH), and no back pressure; Figure 2 Polarization curves and power density curves of Example 1 and Comparative Example 1 under hydrogen and oxygen, 100% RH, and 150 kPa back pressure; Figure 3 Polarization curves and power density curves of Example 1 and Comparative Example 1 under hydrogen air, 100% RH, and 150 kPa back pressure; Figure 4 It is a bar graph of the local oxygen transfer impedance values ​​of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0035] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0036] Example 1 The preparation method of the high oxygen permeability ionomer (PFBSA ionomer) with large steric hindrance groups comprises the following steps: (1) Nafion R-1100 and 4-aminobenzenesulfonic acid in a molar ratio of 1:4 were dissolved in 5 mL of anhydrous N,N-dimethylformamide, and then 0.001 mol of potassium carbonate was added, and the mixture was refluxed at 80 °C for 3 days. When the reaction was completed, the reaction solution was concentrated, dropped into water at room temperature for precipitation, and the solid was collected by filtration, washed with deionized water, and vacuum dried at 80 °C to obtain an ionomer. (2) adding the ionomer to a 1 M NaOH aqueous solution, heating at 80 °C for 12 h, and filtering and separating the product after washing; (3) The PFBSA ionomer was obtained by protonation treatment in a 1 M hydrochloric acid aqueous solution at 80 °C, followed by vacuum filtration, ultrapure water washing, and drying.

[0037] In this example, the obtained PFBSA ionomer is applied to the preparation of membrane electrode assembly (MEA), and the local oxygen transfer impedance of the PFBSA ionomer in the fuel cell and the performance in the fuel cell are tested to study its practical application effect.

[0038] The preparation method of MEA is as follows: Weigh the mass of PFBSA ionomer and commercial Pt / C catalyst according to the mass ratio of PFBSA ionomer to catalyst of 1:3.33. Wet the catalyst with a small amount of water, add an appropriate amount of isopropanol: water mixed solvent of 4:1, and then add the weighed ionomer solution to it to make an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the evenly dispersed ink on both sides of the proton exchange membrane to obtain a catalyst coated membrane (CCM) electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain a membrane electrode assembly.

[0039] The local oxygen transfer impedance of PFBSA ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage (OCV) was 0.15 V, N2 / O2 (X O2 =1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by linear sweep voltammetry (LSV) using the current limiting method.

[0040] The performance tests of PFBSA ionomers in fuel cells are as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 ℃, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, plus a back pressure of 150 kPa, to test the polarization curve and power density curve under different humidity.

[0041] Example 2 The preparation method of the high oxygen permeability ionomer (PFBSA ionomer) with large steric hindrance groups comprises the following steps: (1) 3M PFSO2F and 4-aminobenzenesulfonic acid in a molar ratio of 1:1.2 were dissolved in 5 mL of anhydrous N,N-dimethylacetamide, and then 0.001 mol of triethylamine was added and refluxed at 90 °C for 3 days; when the reaction was completed, the reaction solution was concentrated and dropped into water at room temperature for precipitation, the solid was collected by filtration, washed with deionized water, and vacuum dried at 80 °C to obtain an ionomer; (2) adding the ionomer to a 1 M KOH aqueous solution, heating at 80 °C for 12 h, and filtering and separating the product after washing; (3) The PFBSA ionomer was obtained by protonation treatment in a 1 M sulfuric acid aqueous solution at 80 °C, followed by vacuum filtration, ultrapure water washing, and drying.

[0042] In this example, the obtained PFBSA ionomer is applied to the preparation of MEA, and the local oxygen transfer impedance of the PFBSA ionomer in the fuel cell and the performance in the fuel cell are tested to study its practical application effect.

[0043] The preparation method of MEA is as follows: Weigh the mass of PFBSA ionomer and commercial Pt / C catalyst according to the mass ratio of PFBSA ionomer to catalyst of 1:3.33. Wet the catalyst with a small amount of water, add an appropriate amount of isopropanol: water mixed solvent of 4:1, and then add the weighed ionomer solution to it to make an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the evenly dispersed ink on both sides of the proton exchange membrane to obtain a CCM electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain a membrane electrode assembly.

[0044] The local oxygen transfer impedance of PFBSA ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage was 0.15 V, N2 / O2 (X O2 =1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by current-limiting linear sweep voltammetry.

[0045] The performance tests of PFBSA ionomers in fuel cells are as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 °C, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, and the external back pressure is 150 kPa, and the polarization curve and power density curve under different humidity are tested.

[0046] Example 3 The preparation method of the high oxygen permeability ionomer (PFBSA ionomer) with large steric hindrance groups comprises the following steps: (1) Aquivion PFSO2F and sodium 4-aminobenzenesulfonate in a molar ratio of 1:2 were dissolved in 5 mL of anhydrous dimethyl sulfoxide, and then 0.001 mol of cesium carbonate was added and refluxed at 100 °C for 2 days. When the reaction was completed, the reaction solution was concentrated and dropped into water at room temperature for precipitation. The solid was collected by filtration, washed with deionized water, and vacuum dried at 80 °C to obtain an ionomer. (2) adding the ionomer to a 1 M RbOH aqueous solution, heating at 80 °C for 12 h, and filtering and separating the product after washing; (3) The PFBSA ionomer was obtained by protonation treatment in a 1 M perchloric acid aqueous solution at 80 °C, followed by vacuum filtration, ultrapure water washing, and drying.

[0047] In this example, the obtained PFBSA ionomer is applied to the preparation of MEA, and the local oxygen transfer impedance of the PFBSA ionomer in the fuel cell and the performance in the fuel cell are tested to study its practical application effect.

[0048] The preparation method of MEA is as follows: Weigh the mass of PFBSA ionomer and commercial Pt / C catalyst according to the mass ratio of PFBSA ionomer to catalyst of 1:3.33. Wet the catalyst with a small amount of water, add an appropriate amount of isopropanol: water mixed solvent of 4:1, and then add the weighed ionomer solution to it to make an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the evenly dispersed ink on both sides of the proton exchange membrane to obtain a CCM electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain a membrane electrode assembly.

[0049] The local oxygen transfer impedance of PFBSA ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage was 0.15 V, N2 / O2 (X O2=1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by current-limiting linear sweep voltammetry.

[0050] The performance tests of PFBSA ionomers in fuel cells are as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 °C, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, and the external back pressure is 150 kPa, and the polarization curve and power density curve under different humidity are tested.

[0051] Example 4 The preparation method of the high oxygen permeability ionomer (PFBSA ionomer) with large steric hindrance groups comprises the following steps: (1) Nafion R-1100 and potassium 4-aminobenzenesulfonate in a molar ratio of 1:3 were dissolved in 5 mL of anhydrous perfluorobenzene, and then 0.0015 mol of potassium carbonate was added, and the mixture was refluxed at 100 °C for 3 days. When the reaction was completed, the reaction solution was concentrated, dropped into water at room temperature for precipitation, and the solid was collected by filtration, washed with deionized water, and vacuum dried at 80 °C to obtain an ionomer. (2) adding the ionomer to a 1 M NaOH aqueous solution, heating at 80 °C for 12 h, and filtering and separating the product after washing; (3) The PFBSA ionomer was obtained by protonation treatment in a 1 M phosphoric acid aqueous solution at 80 °C, followed by vacuum filtration, ultrapure water washing, and drying.

[0052] In this example, the obtained PFBSA ionomer is applied to the preparation of MEA, and the local oxygen transfer impedance of the PFBSA ionomer in the fuel cell and the performance in the fuel cell are tested to study its practical application effect.

[0053] The preparation method of MEA is as follows: Weigh the mass of PFBSA ionomer and commercial Pt / C catalyst according to the mass ratio of PFBSA ionomer to catalyst of 1:3.33. Wet the catalyst with a small amount of water, add an appropriate amount of isopropanol: water mixed solvent of 4:1, and then add the weighed ionomer solution to it to make an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the evenly dispersed ink on both sides of the proton exchange membrane to obtain a CCM electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain a membrane electrode assembly.

[0054] The local oxygen transfer impedance of PFBSA ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage was 0.15 V, N2 / O2 (X O2 =1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by current-limiting linear sweep voltammetry.

[0055] The performance tests of PFBSA ionomers in fuel cells are as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 °C, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, and the external back pressure is 150 kPa, and the polarization curve and power density curve under different humidity are tested.

[0056] Example 5 The preparation method of the high oxygen permeability ionomer (PFBSA ionomer) with large steric hindrance groups comprises the following steps: (1) 3M PFSO2F and 3-aminobenzenesulfonic acid in a molar ratio of 1:1.5 were dissolved in 5 mL of anhydrous N,N-dimethylformamide, and then 0.001 mol of potassium carbonate was added, and the mixture was refluxed at 100 °C for 2 days; when the reaction was completed, the reaction solution was concentrated, dropped into water at room temperature for precipitation, and the solid was collected by filtration, washed with deionized water, and vacuum dried at 80 °C to obtain an ionomer; (2) adding the ionomer to a 1 M KOH aqueous solution, heating at 80 °C for 12 h, and filtering and separating the product after washing; (3) The PFBSA ionomer was obtained by protonation treatment in a 1 M hydrochloric acid aqueous solution at 80 °C, followed by vacuum filtration, ultrapure water washing, and drying.

[0057] In this example, the obtained PFBSA ionomer is applied to the preparation of MEA, and the local oxygen transfer impedance of the PFBSA ionomer in the fuel cell and the performance in the fuel cell are tested to study its practical application effect.

[0058] The preparation method of MEA is as follows: Weigh the mass of PFBSA ionomer and commercial Pt / C catalyst according to the mass ratio of PFBSA ionomer to catalyst of 1:3.33. Wet the catalyst with a small amount of water, add an appropriate amount of isopropanol: water mixed solvent of 4:1, and then add the weighed ionomer solution to it to make an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the evenly dispersed ink on both sides of the proton exchange membrane to obtain a CCM electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain a membrane electrode assembly.

[0059] The local oxygen transfer impedance of PFBSA ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage was 0.15 V, N2 / O2 (X O2 =1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by current-limiting linear sweep voltammetry.

[0060] The performance tests of PFBSA ionomers in fuel cells are as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 °C, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, and the external back pressure is 150 kPa, and the polarization curve and power density curve under different humidity are tested.

[0061] Example 6 The preparation method of the high oxygen permeability ionomer (PFBSA ionomer) with large steric hindrance groups comprises the following steps: (1) Aquivion PFSO2F and 1-amino-2-naphthol-4-sulfonic acid in a molar ratio of 1:3 were dissolved in 5 mL of anhydrous N,N-dimethylacetamide, and then 0.002 mol of N,N-diisopropylethylamine was added and refluxed at 90 °C for 3 days. When the reaction was completed, the reaction solution was concentrated and dropped into water at room temperature for precipitation. The solid was collected by filtration, washed with deionized water, and vacuum dried at 80 °C to obtain an ionomer. (2) adding the ionomer to a 1 M RbOH aqueous solution, heating at 80 °C for 12 h, and filtering and separating the product after washing; (3) The PFBSA ionomer was obtained by protonation treatment in a 1 M hydrochloric acid aqueous solution at 80 °C, followed by vacuum filtration, ultrapure water washing, and drying.

[0062] In this example, the obtained PFBSA ionomer is applied to the preparation of MEA, and the local oxygen transfer impedance of the PFBSA ionomer in the fuel cell and the performance in the fuel cell are tested to study its practical application effect.

[0063] The preparation method of MEA is as follows: Weigh the mass of PFBSA ionomer and commercial Pt / C catalyst according to the mass ratio of PFBSA ionomer to catalyst of 1:3.33. Wet the catalyst with a small amount of water, add an appropriate amount of isopropanol: water mixed solvent of 4:1, and then add the weighed ionomer solution to it to make an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the evenly dispersed ink on both sides of the proton exchange membrane to obtain a CCM electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain a membrane electrode assembly.

[0064] The local oxygen transfer impedance of PFBSA ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage was 0.15 V, N2 / O2 (X O2 =1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by current-limiting linear sweep voltammetry.

[0065] The performance tests of PFBSA ionomers in fuel cells are as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 °C, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, and the external back pressure is 150 kPa, and the polarization curve and power density curve under different humidity are tested.

[0066] Comparative Example 1 In this comparative example, a conventional Nafion ionomer (PFSA ionomer) membrane electrode was prepared, and the steps were as follows: The mass of Nafion ionomer and commercial Pt / C catalyst was weighed according to the mass ratio of ionomer to catalyst of 1:3.33. The catalyst was soaked with a small amount of water, and then an appropriate amount of isopropanol: water mixed solvent of 4:1 was added, and then the weighed ionomer solution was added thereto to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, the uniformly dispersed ink was sprayed on both sides of the proton exchange membrane to obtain a CCM electrode, and the CCM electrode and the commercial gas diffusion layer were assembled together to obtain a membrane electrode assembly.

[0067] The local oxygen transport impedance of Nafion ionomer in fuel cells was tested as follows: The membrane electrode assembly, flow field plate and end plate were assembled into a single fuel cell. When the cell temperature was 80 °C, 100% RH and the open circuit voltage was 0.15 V, N2 / O2 (X O2 =1%, 2%, 3% and 4%) mixed gas, pure hydrogen was injected into the anode at a flow rate of 600 mL / min, and the oxygen transfer impedance was measured by current-limiting linear sweep voltammetry.

[0068] The performance of Nafion ionomers in fuel cells is tested as follows: The membrane electrode assembly, flow field plate and end plate are assembled into a single fuel cell. The fuel cell battery test is carried out at a battery temperature of 80 °C, with pure oxygen or air as the cathode and pure hydrogen as the anode, and the gas flow rate is 300 mL / min, and the external back pressure is 150 kPa, and the polarization curve and power density curve under different humidity are tested.

[0069] Test Example 1 This test example presents the test results of representative embodiments of the present invention, namely, embodiment 1 and comparative example 1.

[0070] Figure 1 The polarization curves and power density curves of Example 1 and Comparative Example 1 under 100% RH, hydrogen at the anode and oxygen at the cathode, and no back pressure are shown in the figure. It can be seen from the figure that when PFBSA ionomer is used as an ionomer in the cathode catalyst layer of a fuel cell, the single cell exhibits an ultra-high power density, and its peak power density is 1688 mW / cm 2 , significantly higher than that of PFSA ionomer.

[0071] Figure 2 The polarization curves and power density curves of Example 1 and Comparative Example 1 under 100% RH, hydrogen at the anode and oxygen at the cathode (150 kPa back pressure) are shown. It can be seen from the figure that when the fuel cell is subjected to a back pressure of 150 kPa, the single cell made with PFBSA ionomer exhibits a better peak power density than that made with PFSA ionomer, and the mass transfer polarization is significantly improved.

[0072] Figure 3 The polarization curves and power density curves of Example 1 and Comparative Example 1 under the conditions of 100% RH, hydrogen as the anode and air as the cathode (150 kPa back pressure). Figure 2In contrast, when the fuel cell cathode is switched from oxygen to air, the performance improvement of PFBSA ionomer is more obvious, because the oxygen concentration in air is low, which requires higher oxygen permeability of ionomer. This further illustrates the beneficial effect of PFBSA ionomer on local oxygen diffusion.

[0073] Figure 4 The figure is a bar graph of the local oxygen transfer impedance values ​​of Example 1 and Comparative Example 1. It can be seen from the figure that the PFBSA ionomer has good oxygen permeability, and the local oxygen transfer impedance value of the ionomer is 0.369 s / cm, which is lower than the traditional commercial PFSA ionomer (0.564 s / cm).

[0074] Based on the above examples and test results, the preparation method of the present invention does not require additional catalysts, and forms a perfluoroionomer with a large steric hindrance group at the end of the side chain through a nucleophilic substitution reaction. This structure helps to increase the free volume of the polymer and promote the transmission of oxygen in the ionomer layer. The covalent grafting method avoids the problem of easy loss of direct addition. The method is simple, convenient for post-processing, can be prepared in batches, and is suitable for industrial production.

[0075] In the high oxygen permeability ionomer with large steric hindrance groups prepared by the present invention, the benzenesulfonic acid group inhibits the adsorption of the sulfonic acid group on the platinum surface by utilizing the steric hindrance effect, which is beneficial to improving the activity of the catalyst. In the proton exchange membrane fuel cell, it exhibits an amazing peak power density, greatly improves the mass transfer performance, especially in the high current density region, and has a more excellent battery output performance. The present invention proposes a new solution to the existing technical problems and has broad application prospects.

[0076] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a highly oxygen permeable ionomer having a large steric hindrance group, characterized in that: The steps include: (1) In a solution environment, a perfluorosulfonyl fluoride resin and an aminobenzenesulfonic acid compound undergo a nucleophilic substitution reaction under the action of an acid-binding agent, and after the reaction is completed, an ionomer is recovered; (2) washing the ionomer in a strong alkaline solution and filtering to obtain the product; (3) The product is protonated and then recovered to obtain a highly oxygen-permeable ionomer having a large steric hindrance group.

2. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (1), the perfluorosulfonyl fluoride resin includes Nafion R-1100, 3M PFSO2F, Aquivion At least one of PFSO2F; in the step (1), the aminobenzenesulfonic acid compound includes at least one of 4-aminobenzenesulfonic acid, sodium 4-aminobenzenesulfonate, potassium 4-aminobenzenesulfonate, 3-aminobenzenesulfonic acid, sodium 3-aminobenzenesulfonate, 2,4-diaminobenzenesulfonic acid, sodium 2,4-diaminobenzenesulfonate, 2-aminotoluene-5-sulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, sodium 1-naphthylamine-4-sulfonate, aniline-2,4-disulfonic acid, 1-amino-8-naphthol-4,6-disulfonic acid, m-phenylenediamine-4,6-disulfonic acid, 1-naphthylamine-4,6,8-trisulfonic acid, barium diphenylamine sulfonate, m-toluidine p-sulfonic acid, diphenylamine-4-sulfonic acid, and 1-amino-8-naphthol-4,6-disulfonic acid; the molar ratio of the perfluorosulfonyl fluoride resin to the aminobenzenesulfonic acid compound is 1:1-4.

3. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (1), the solution environment is created by a reaction solvent, and the reaction solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and perfluorobenzene.

4. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (1), the acid binding agent includes at least one of sodium hydride, triethylamine, potassium carbonate, cesium carbonate, pyridine, N,N-diisopropylethylamine, and 4-dimethylaminopyridine; and the molar ratio of the acid binding agent to the perfluorosulfonyl fluoride resin is 2-4:

1.

5. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (1), the temperature of the nucleophilic substitution reaction is 80-100° C.; and the time of the nucleophilic substitution reaction is 1-3 days.

6. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (1), after the reaction is completed, the crude product is concentrated and precipitated in a solvent to obtain an ionomer; the solvent includes at least one of water, acetonitrile, ethanol and methanol.

7. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (2), the strong alkali solution is an aqueous solution of a strong alkali; the strong alkali comprises at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, and cesium hydroxide; and the concentration of the strong alkali solution is 0.5-2 mol / L.

8. The method for preparing a highly oxygen permeable ionomer having a large steric hindrance group according to claim 1, characterized in that: In the step (3), an inorganic acid is used to protonate the product; the inorganic acid includes at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and perchloric acid; and the concentration of the inorganic acid is 0.5-2 mol / L.

9. A highly oxygen permeable ionomer having a large steric hindrance group, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An application of the high oxygen permeability ionomer with large steric hindrance groups as claimed in claim 9, characterized in that: A highly oxygen permeable ionomer with large steric hindrance groups is applied to the cathode catalyst layer of a proton exchange membrane fuel cell.

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