A highly oxygen-permeable ionomer with sterically hindered groups, its preparation method and application

Abstract

This invention discloses a highly oxygen-permeable ionomer with large steric hindrance groups, its preparation method, and its application, belonging to the field of fuel cell technology. The preparation method of this invention includes 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. After the reaction, the ionomer is recovered; (2) The ionomer is washed in a strong alkaline solution and filtered to obtain the product; (3) The product is protonated, and after completion, the highly oxygen-permeable ionomer with large steric hindrance groups is recovered. This method has the advantages of convenient process, convenient post-processing, batch preparation, and suitability for industrial production. The highly oxygen-permeable ionomer with large steric hindrance groups, when used in proton exchange membrane fuel cells, optimizes the peak power density and improves mass transfer performance. Especially in the high current density region, it exhibits excellent battery output performance and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a highly oxygen-permeable ionomer with large steric hindrance groups, its preparation method, and its application. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is a highly efficient and clean energy conversion device. Ionomers are a crucial component of PEMFCs. After protons are generated at the anode, they are transferred to the proton exchange membrane via ionomers in the anode catalyst layer, and then transported to the cathode catalyst surface via ionomers in the cathode catalyst layer to react. Ideally, ionomers should possess good proton conductivity and chemical stability. They also need high oxygen permeability to ensure efficient oxygen transport in the cathode catalyst layer. Currently, commonly used ionomers are perfluorosulfonic acid ionomers, which consist of a stable and hydrophobic polytetrafluoroethylene (PTFE) backbone and strongly acidic perfluorosulfonic acid side chains, exhibiting excellent proton conductivity and chemical stability. However, the sulfonic acid side chains of these ionomers have strong adsorption properties on the platinum catalyst surface. This not only occupies reaction sites but also pulls the backbone to accumulate into a dense film on the platinum surface, significantly hindering oxygen transport.

[0003] To address the problems caused by perfluorosulfonic acid ionomers, the development of novel 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. obtained perfluorosulfonyl fluoride resins with high oxygen permeability through free radical copolymerization of perfluoro(2-methylene-4-methyl-1,3-dioxolane) monomers and perfluorosulfonyl fluoride monomers, thus improving oxygen transport. However, the introduction of cyclic monomers on the main chain is not conducive to the formation of microphase separation and proton conduction, and the oxygen transport efficiency still needs to be improved. Currently, research in this area is still relatively scarce.

[0004] Chinese invention patent CN113314722A discloses a method for reducing the poisoning of Pt catalysts by sulfonic acid groups in the catalyst layer of fuel cells. This invention first ultrasonically disperses Nafion ionomers in isopropanol solvent, then adds a highly hindered alcohol to interact with the Nafion ionomers. The dispersion of the mixture of the highly hindered alcohol and Nafion ionomers is then added to a commercial Pt-based catalyst wetted with deionized water. After ultrasonic dispersion, a catalyst slurry modified with the highly hindered alcohol is obtained. Finally, the catalyst slurry modified with the highly hindered alcohol is coated onto a commercial proton exchange membrane and dried to obtain a catalyst layer that can mitigate the poisoning effect of sulfonic acid groups. In Chinese invention patent CN118738419A, the inventors provide a proton exchange membrane fuel cell membrane electrode catalyst layer, its preparation method, and its application. This method premixes a dispersion of hydroxyl-rich polysaccharide porous molecules with a catalyst and an organic solvent, modifies the catalyst surface with a layer of hydroxyl-rich polysaccharide porous molecules, and then adds a perfluorosulfonic acid electrolyte solution and mixes thoroughly to obtain a catalyst layer slurry.

[0005] When sterically hindered alcohols or other hydroxyl compounds are introduced into polymer molecular chains, although large substituents will increase the local free volume to some 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 they are adjacent to other oxygen- or nitrogen-containing groups; these hydrogen bonds may enhance the interaction between molecular chains, resulting in a more compact stacking; (2) Although excessively sterically hindered groups increase steric hindrance, they also restrict the rotational freedom of the molecular chains, making the overall chain conformation relatively fixed and difficult to effectively disperse to form more free volume.

[0006] In Chinese invention patent CN117476951A, the inventors disclosed a proton exchange membrane fuel cell catalyst slurry, its preparation method, and its application. The slurry mainly comprises a catalyst, a perfluorosulfonic acid electrolyte, a solvent, and also includes a porphyrin macrocyclic compound rich in hydroxyl groups. On one hand, the interaction between the hydroxyl groups and the perfluorosulfonic acid electrolyte weakens the adsorption and poisoning of sulfonic acid groups on the catalyst surface and improves the phase separation degree of the perfluorosulfonic acid electrolyte; on the other hand, the oxygen enrichment characteristics of the macrocyclic compound itself can further promote oxygen transport at the catalyst / ionomer interface. However, directly adding the compound and utilizing the interaction between the groups has the drawback of easy loss, and its application effect needs further optimization.

[0007] In summary, proposing a suitable process scheme to solve the technical problems existing in the current technology, further improve the mass transfer capacity of ionomers in proton exchange membrane fuel cells, and enhance the output performance of the cells are of great significance for expanding the application of proton exchange membrane fuel cells. Summary of the Invention

[0008] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a method for preparing a highly oxygen-permeable ionomer with large steric hindrance groups is provided, which is convenient in process, easy in post-processing, can be mass-produced and is suitable for industrial production, comprising the following steps:

[0009] (1) In a solution environment, perfluorosulfonyl fluoride resins and aminobenzenesulfonic acid compounds undergo nucleophilic substitution reaction under the action of an acid-binding agent. After the reaction is completed, the ionomer is recovered.

[0010] (2) The ionomer was washed in a strong alkaline solution and filtered to obtain the product;

[0011] (3) The product is protonated and then recovered to obtain a highly oxygen-permeable ionomer with large steric hindrance groups.

[0012] Preferably, in step (1), the perfluorosulfonyl fluoride resin includes at least one of Nafion R-1100, 3M PFSO2F, and Aquivion PFSO2F.

[0013] Those skilled in the art can select suitable perfluorosulfonyl fluoride resins based on actual conditions and application requirements, such as Nafion R-1100, 3M PFSO2F, and Aquivion PFSO2F used in proton exchange membrane fuel cells. Nafion R-1100 exhibits high proton conductivity, excellent resistance to chemical attack, particularly in acidic and oxidizing environments, and maintains physical strength and durability over a wider temperature and humidity range. 3M PFSO2F resin has a lower production cost and achieves higher proton conductivity through specific molecular design, especially under low humidity conditions. Aquivion PFSO2F, a perfluorosulfonyl fluoride resin produced by Solvay and specifically designed for PEMFC applications, possesses strong mechanical and dimensional stability and exhibits excellent proton conductivity under both high and low humidity conditions. The above types of perfluorosulfonyl fluoride resins are particularly suitable raw material types for the process of this invention.

[0014] 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.

[0015] Preferably, in step (1), the molar ratio of perfluorosulfonyl fluoride resin to aminobenzenesulfonic acid compound is 1:1-4.

[0016] The benzene ring is an electron-donating group that increases the electron density of the carbon atom on the amino group through resonance. This makes the sulfonyl fluoride group more susceptible to nucleophilic attack, thus greatly enhancing the activity of the nucleophilic substitution reaction. Therefore, the process of this invention does not require an additional catalyst, reducing the reaction difficulty while achieving the grafting of the target group, achieving multiple benefits in one step.

[0017] Preferably, in step (1), the solution environment is created by a reaction solvent, which includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and perfluorobenzene.

[0018] 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.

[0019] Preferably, in step (1), the molar ratio of the acid-binding agent to the perfluorosulfonyl fluoride resin is 2-4:1.

[0020] 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.

[0021] Preferably, in 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.

[0022] In the preparation method of this invention, there are various ways to recover the ionomer, and those skilled in the art can choose a suitable product collection method according to the scale of production and actual conditions. For example, the crude product can be concentrated and then precipitated in its unsuitable solvent (water, acetonitrile, ethanol, methanol, etc.). This method has the advantages of relatively simple operation, low cost, and high purity.

[0023] Preferably, in step (2), the strong alkali solution is an aqueous solution of a strong alkali; the strong alkali includes at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0024] Preferably, in step (2), the concentration of the strong alkali solution is 0.5-2 mol / L.

[0025] After washing, the products can be separated by filtration or other methods.

[0026] 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.

[0027] More preferably, the concentration of the inorganic acid is 0.5-2 mol / L.

[0028] Treatment with inorganic acids can improve the conductivity of ionomers, enhance their chemical stability and environmental adaptability. Those skilled in the art can select appropriate concentrations of inorganic acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, perchloric acid, etc., to achieve the protonation objective of this invention.

[0029] After the product is protonated, the crude product can be washed and dried (e.g., treated at 80-100 °C for 12-36 h) to recover the target product. Those skilled in the art can also use other means or methods to achieve the recovery.

[0030] In a second aspect of the present invention, a highly oxygen-permeable ionomer having sterically hindered groups is provided, which is prepared using the preparation method provided in the first aspect of the present invention.

[0031] In a third aspect of the invention, the application of the highly oxygen-permeable ionomer with large steric hindrance groups of the second aspect of the invention is provided, specifically, its application to the cathode catalyst layer of a proton exchange membrane fuel cell.

[0032] Based on the above technical solutions, the design concept and principle of this invention are as follows:

[0033] The preparation method of the present invention involves reacting sulfonyl fluoride with amino groups through a nucleophilic substitution reaction to form sulfonamide bonds, grafting benzenesulfonic acid groups onto the side chains of a perfluorosulfonyl fluoride resin, and then protonating the ionomer. Without the need for additional catalysts, a perfluoro ionomer with sterically hindered groups at the end of the side chains formed by the nucleophilic substitution reaction was successfully prepared.

[0034] Compared to existing methods that introduce sterically hindered alcohols or hydroxyl-rich polymer groups, this invention grafts sterically hindered benzenesulfonic acid groups to increase the free volume of the polymer, reduce the local oxygen transport resistance in the ionomer layer, and promote oxygen transport in the ionomer layer, thereby improving mass transfer polarization at high current densities. Furthermore, the covalent grafting method has the advantage of being less prone to loss compared to direct addition. The resulting highly oxygen-permeable ionomer with sterically hindered groups utilizes the steric hindrance effect to suppress the adsorption of sulfonic acid groups on the platinum surface, which is beneficial for improving catalyst activity.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] This invention provides a method for preparing highly oxygen-permeable ionomers with large steric hindrance groups, which has the advantages of convenient process, convenient post-processing, batch preparation and suitability for industrial production.

[0037] This invention provides a highly oxygen-permeable ionomer with large steric hindrance groups, which utilizes the steric hindrance effect to inhibit the adsorption of sulfonic acid groups on the platinum surface, thereby improving the activity of the catalyst.

[0038] This invention provides an application of a highly oxygen-permeable ionomer with large steric hindrance groups in proton exchange membrane fuel cells, which optimizes peak power density and greatly improves mass transfer performance, especially in the high current density region, exhibiting excellent battery output performance and has broad application prospects. Attached Figure Description

[0039] Figure 1 The 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 are shown.

[0040] Figure 2 The polarization curves and power density curves of Example 1 and Comparative Example 1 under hydrogen-oxygen, 100%RH, and 150 kPa back pressure are shown.

[0041] Figure 3 The polarization curves and power density curves of Example 1 and Comparative Example 1 under hydrogen air, 100%RH, and 150 kPa back pressure are shown.

[0042] Figure 4 The bar chart shows the local oxygen transport impedance values ​​for Example 1 and Comparative Example 1. Detailed Implementation

[0043] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0044] Example 1

[0045] The preparation method of highly oxygen-permeable ionomers (PFBSA ionomers) with sterically hindered groups includes the following steps:

[0046] (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. The mixture was refluxed at 80 °C for 3 days. When the reaction was finished, the reaction solution was concentrated and precipitated by dropping it into water at room temperature. The solid was collected by filtration, washed with deionized water, and dried under vacuum at 80 °C to obtain the ionomer.

[0047] (2) Add the ionomer to a 1M NaOH aqueous solution, heat at 80 °C for 12 h, and filter to separate the product after washing;

[0048] (3) The protonation process was completed in 1M hydrochloric acid aqueous solution at 80 °C, followed by vacuum filtration, washing with ultrapure water and drying to obtain PFBSA ionomer.

[0049] In this embodiment, the obtained PFBSA ionomer was applied to the fabrication of a membrane electrode assembly (MEA), and the local oxygen transport impedance and performance of the PFBSA ionomer in a fuel cell were tested to study its practical application effect.

[0050] The preparation method of MEA is as follows:

[0051] Weigh the PFBSA ionomer and commercial Pt / C catalyst according to a PFBSA ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain a catalyst-coated membrane (CCM) electrode. Assemble the CCM electrode and a commercial gas diffusion layer together to obtain the membrane electrode assembly.

[0052] The local oxygen transport resistance of PFBSA ionomers in fuel cells was tested as follows:

[0053] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open circuit voltage (OCV) of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using linear sweep voltammetry (LSV).

[0054] The performance of PFBSA ionomers in fuel cells was tested as follows:

[0055] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, under an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0056] Example 2

[0057] The preparation method of highly oxygen-permeable ionomers (PFBSA ionomers) with sterically hindered groups includes the following steps:

[0058] (1) Dissolve 3M PFSO2F and 4-aminobenzenesulfonic acid in 5 mL of anhydrous N,N-dimethylacetamide in a molar ratio of 1:1.2, then add 0.001 mol of triethylamine and reflux at 90 °C for 3 days; when the reaction is finished, concentrate the reaction solution, precipitate it by dropping it into water at room temperature, filter and collect the solid, wash it with deionized water, and dry it under vacuum at 80 °C to obtain the ionomer;

[0059] (2) Add the ionomer to a 1M KOH aqueous solution, heat at 80 °C for 12 h, and filter to separate the product after washing;

[0060] (3) The protonation process was completed in 1M sulfuric acid aqueous solution at 80 °C, followed by vacuum filtration, washing with ultrapure water and drying to obtain PFBSA ionomer.

[0061] In this embodiment, the obtained PFBSA ionomer was applied to the preparation of MEA, and the local oxygen transport impedance and performance of the PFBSA ionomer in the fuel cell were tested to study its practical application effect.

[0062] The preparation method of MEA is as follows:

[0063] Weigh the PFBSA ionomer and commercially available Pt / C catalyst according to a PFBSA ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain the CCM electrode. Assemble the CCM electrode and a commercially available gas diffusion layer together to obtain the membrane electrode assembly.

[0064] The local oxygen transport resistance of PFBSA ionomers in fuel cells was tested as follows:

[0065] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open-circuit voltage of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using a current-limited linear sweep voltammetry method.

[0066] The performance of PFBSA ionomers in fuel cells was tested as follows:

[0067] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, and an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0068] Example 3

[0069] The preparation method of highly oxygen-permeable ionomers (PFBSA ionomers) with sterically hindered groups includes the following steps:

[0070] (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. The mixture was refluxed at 100 °C for 2 days. When the reaction was finished, the reaction solution was concentrated and precipitated by dropping it into water at room temperature. The solid was collected by filtration, washed with deionized water, and dried under vacuum at 80 °C to obtain the ionomer.

[0071] (2) Add the ionomer to a 1M RbOH aqueous solution, heat at 80 °C for 12 h, and filter to separate the product after washing;

[0072] (3) The protonation process was completed in 1M perchloric acid aqueous solution at 80 °C, followed by vacuum filtration, washing with ultrapure water and drying to obtain PFBSA ionomer.

[0073] In this embodiment, the obtained PFBSA ionomer was applied to the preparation of MEA, and the local oxygen transport impedance and performance of the PFBSA ionomer in the fuel cell were tested to study its practical application effect.

[0074] The preparation method of MEA is as follows:

[0075] Weigh the PFBSA ionomer and commercially available Pt / C catalyst according to a PFBSA ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain the CCM electrode. Assemble the CCM electrode and a commercially available gas diffusion layer together to obtain the membrane electrode assembly.

[0076] The local oxygen transport resistance of PFBSA ionomers in fuel cells was tested as follows:

[0077] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open-circuit voltage of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using a current-limited linear sweep voltammetry method.

[0078] The performance of PFBSA ionomers in fuel cells was tested as follows:

[0079] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, and an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0080] Example 4

[0081] The preparation method of highly oxygen-permeable ionomers (PFBSA ionomers) with sterically hindered groups includes the following steps:

[0082] (1) Dissolve Nafion R-1100 and potassium 4-aminobenzenesulfonate in 5 mL of anhydrous perfluorobenzene at a molar ratio of 1:3, then add 0.0015 mol of potassium carbonate and reflux at 100 °C for 3 days; when the reaction is finished, concentrate the reaction solution, precipitate it by dropping it into water at room temperature, filter and collect the solid, wash it with deionized water, and dry it under vacuum at 80 °C to obtain the ionomer;

[0083] (2) Add the ionomer to a 1M NaOH aqueous solution, heat at 80 °C for 12 h, and filter to separate the product after washing;

[0084] (3) The protonation process was completed in 1M phosphoric acid aqueous solution at 80 °C, followed by vacuum filtration, washing with ultrapure water and drying to obtain PFBSA ionomer.

[0085] In this embodiment, the obtained PFBSA ionomer was applied to the preparation of MEA, and the local oxygen transport impedance and performance of the PFBSA ionomer in the fuel cell were tested to study its practical application effect.

[0086] The preparation method of MEA is as follows:

[0087] Weigh the PFBSA ionomer and commercially available Pt / C catalyst according to a PFBSA ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain the CCM electrode. Assemble the CCM electrode and a commercially available gas diffusion layer together to obtain the membrane electrode assembly.

[0088] The local oxygen transport resistance of PFBSA ionomers in fuel cells was tested as follows:

[0089] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open-circuit voltage of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using a current-limited linear sweep voltammetry method.

[0090] The performance of PFBSA ionomers in fuel cells was tested as follows:

[0091] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, and an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0092] Example 5

[0093] The preparation method of highly oxygen-permeable ionomers (PFBSA ionomers) with sterically hindered groups includes the following steps:

[0094] (1) Dissolve 3M PFSO2F and 3-aminobenzenesulfonic acid in 5 mL of anhydrous N,N-dimethylformamide in a molar ratio of 1:1.5, then add 0.001 mol of potassium carbonate and reflux at 100 °C for 2 days; when the reaction is finished, concentrate the reaction solution, precipitate it by dropping it into water at room temperature, filter and collect the solid, wash it with deionized water, and dry it under vacuum at 80 °C to obtain the ionomer;

[0095] (2) Add the ionomer to a 1M KOH aqueous solution, heat at 80 °C for 12 h, and filter to separate the product after washing;

[0096] (3) The protonation process was completed in 1M hydrochloric acid aqueous solution at 80 °C, followed by vacuum filtration, washing with ultrapure water and drying to obtain PFBSA ionomer.

[0097] In this embodiment, the obtained PFBSA ionomer was applied to the preparation of MEA, and the local oxygen transport impedance and performance of the PFBSA ionomer in the fuel cell were tested to study its practical application effect.

[0098] The preparation method of MEA is as follows:

[0099] Weigh the PFBSA ionomer and commercially available Pt / C catalyst according to a PFBSA ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain the CCM electrode. Assemble the CCM electrode and a commercially available gas diffusion layer together to obtain the membrane electrode assembly.

[0100] The local oxygen transport resistance of PFBSA ionomers in fuel cells was tested as follows:

[0101] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open-circuit voltage of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using a current-limited linear sweep voltammetry method.

[0102] The performance of PFBSA ionomers in fuel cells was tested as follows:

[0103] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, and an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0104] Example 6

[0105] The preparation method of highly oxygen-permeable ionomers (PFBSA ionomers) with sterically hindered groups includes the following steps:

[0106] (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. The mixture was refluxed at 90 °C for 3 days. When the reaction was finished, the reaction solution was concentrated and precipitated by dropping it into water at room temperature. The solid was collected by filtration, washed with deionized water, and dried under vacuum at 80 °C to obtain the ionomer.

[0107] (2) Add the ionomer to a 1M RbOH aqueous solution, heat at 80 °C for 12 h, and filter to separate the product after washing;

[0108] (3) The protonation process was completed in 1M hydrochloric acid aqueous solution at 80 °C, followed by vacuum filtration, washing with ultrapure water and drying to obtain PFBSA ionomer.

[0109] In this embodiment, the obtained PFBSA ionomer was applied to the preparation of MEA, and the local oxygen transport impedance and performance of the PFBSA ionomer in the fuel cell were tested to study its practical application effect.

[0110] The preparation method of MEA is as follows:

[0111] Weigh the PFBSA ionomer and commercially available Pt / C catalyst according to a PFBSA ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain the CCM electrode. Assemble the CCM electrode and a commercially available gas diffusion layer together to obtain the membrane electrode assembly.

[0112] The local oxygen transport resistance of PFBSA ionomers in fuel cells was tested as follows:

[0113] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open-circuit voltage of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using a current-limited linear sweep voltammetry method.

[0114] The performance of PFBSA ionomers in fuel cells was tested as follows:

[0115] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, and an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0116] Comparative Example 1

[0117] In this comparative example, a conventional Nafion ionomer (PFSA ionomer) membrane electrode was prepared, and the steps are as follows:

[0118] Weigh out the Nafion ionomer and commercial Pt / C catalyst according to a ionomer:catalyst mass ratio of 1:3.33. Wet the catalyst with a trace amount of water, then add an appropriate amount of isopropanol:water mixed solvent (4:1), and then add the weighed ionomer solution to prepare an ink with a mass concentration of 2.5 mg / mL. After ultrasonic dispersion at room temperature for 60 min, spray the uniformly dispersed ink onto both sides of the proton exchange membrane to obtain the CCM electrode. Assemble the CCM electrode and the commercial gas diffusion layer together to obtain the membrane electrode assembly.

[0119] The local oxygen transport impedance of Nafion ionomers in fuel cells was tested as follows:

[0120] The membrane electrode assembly, flow field plate, and end plate were assembled into a single fuel cell. At a cell temperature of 80 °C, 100% RH, and an open-circuit voltage of 0.15 V, N2 / O2 (X) was injected into the cathode at a flow rate of 600 mL / min. O2 A mixture of 1%, 2%, 3%, and 4% hydrogen gas was injected into the anode at a flow rate of 600 mL / min, and the oxygen transport impedance was determined using a current-limited linear sweep voltammetry method.

[0121] The performance of Nafion ionomers in fuel cells was tested as follows:

[0122] The membrane electrode assembly, flow field plate, and end plate are assembled into a single fuel cell. Fuel cell testing is conducted at a cell temperature of 80 °C, with pure oxygen or air at the cathode, pure hydrogen at the anode, and a gas flow rate of 300 mL / min for both, and an applied back pressure of 150 kPa. Polarization curves and power density curves are measured under different humidity levels.

[0123] Test Example 1

[0124] This test case presents the test results of representative embodiments of the present invention, namely, Embodiment 1 and Comparative Example 1.

[0125] Figure 1 The figures show the polarization and power density curves of Example 1 and Comparative Example 1 under conditions of 100% RH, hydrogen at the anode, oxygen at the cathode, and no back pressure. As can be seen from the figures, when PFBSA ionomer is used as the ionomer in the cathode catalyst layer of the fuel cell, the single cell exhibits an extremely high power density, with a peak power density of 1688 mW / cm². 2 It is significantly higher than that of PFSA ionomers.

[0126] Figure 2 The figures show the polarization and power density curves of Example 1 and Comparative Example 1 under the conditions of 100% RH, hydrogen at the anode and oxygen at the cathode (150 kPa back pressure). As can be seen from the figures, when a back pressure of 150 kPa is applied to the fuel cell, the single cell prepared using PFBSA ionomer exhibits a superior peak power density compared to the PFSA ionomer, and the mass transfer polarization is significantly improved.

[0127] Figure 3 The graphs show the polarization and power density curves of Example 1 and Comparative Example 1 under conditions of 100% RH, hydrogen at the anode, and air at the cathode (150 kPa back pressure). Figure 2 In contrast, the performance improvement of PFBSA ionomers is more significant when the fuel cell cathode is switched from oxygen to air. This is because the low oxygen concentration in air places higher demands on the oxygen permeability of the ionomers. This further illustrates the beneficial effect of PFBSA ionomers on local oxygen diffusion.

[0128] Figure 4 The bar chart shows the local oxygen transport impedance values ​​for Example 1 and Comparative Example 1. As can be seen from the figure, the PFBSA ionomer exhibits good oxygen permeability, with a local oxygen transport impedance value of 0.369 s / cm, lower than that of the conventional commercial PFSA ionomer (0.564 s / cm).

[0129] Based on the above embodiments and test results, the preparation method of the present invention does not require an additional catalyst. It forms a perfluorinated ionomer with sterically hindered groups at the end of the side chains through a nucleophilic substitution reaction. This structure helps increase the free volume of the polymer and promotes oxygen transport in the ionomer layer. The covalent grafting method avoids the problem of easy loss when added directly. This method is simple, convenient for post-processing, and can be mass-produced, making it suitable for industrial production.

[0130] In the highly oxygen-permeable ionomer with sterically hindered groups prepared in this invention, the benzenesulfonic acid groups utilize the steric hindrance effect to suppress the adsorption of sulfonic acid groups on the platinum surface, which is beneficial to improving the activity of the catalyst. In proton exchange membrane fuel cells, it exhibits an astonishing peak power density, greatly improving mass transfer performance, especially in the high current density region, where it demonstrates superior battery output performance. This invention provides a new solution to existing technical problems and has broad application prospects.

[0131] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a highly oxygen-permeable ionomer with sterically hindered groups, characterized in that, Includes the following steps: (1) In a solution environment, perfluorosulfonyl fluoride resins and aminobenzenesulfonic acid compounds undergo nucleophilic substitution reaction under the action of an acid-binding agent. After the reaction is completed, the ionomer is recovered. Perfluorosulfonyl fluoride resins include at least one of Nafion R-1100, 3M PFSO2F, and Aquivion PFSO2F; aminobenzenesulfonic acid compounds include 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, and m-phenylenediamine-4,6-disulfonic acid. The compound contains at least one of the following: 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; the acid-binding agent includes at least one of sodium hydride, triethylamine, potassium carbonate, cesium carbonate, pyridine, N,N-diisopropylethylamine, and 4-dimethylaminopyridine; the molar ratio of the acid-binding agent to the perfluorosulfonyl fluoride resin is 2-4:1; (2) The ionomer was washed in a strong alkaline solution and filtered to obtain the product; (3) The product is protonated and then recovered to obtain a highly oxygen-permeable ionomer with large steric hindrance groups.

2. The method for preparing a highly oxygen-permeable ionomer with sterically hindered groups according to claim 1, characterized in that: In step (1), the solution environment is created by a reaction solvent, which includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and perfluorobenzene.

3. The method for preparing a highly oxygen-permeable ionomer with sterically hindered groups according to claim 1, characterized in that: In step (1), the temperature of the nucleophilic substitution reaction is 80-100 °C; the time of the nucleophilic substitution reaction is 1-3 days.

4. The method for preparing a highly oxygen-permeable ionomer with sterically hindered groups according to claim 1, characterized in that: In 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.

5. The method for preparing a highly oxygen-permeable ionomer with sterically hindered groups according to claim 1, characterized in that: In step (2), the strong alkali solution is an aqueous solution of a strong alkali; the strong alkali includes at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, and cesium hydroxide; the concentration of the strong alkali solution is 0.5-2 mol / L.

6. The method for preparing a highly oxygen-permeable ionomer with sterically hindered groups according to claim 1, characterized in that: In step (3), the product is protonated using an inorganic acid; the inorganic acid includes at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and perchloric acid; the concentration of the inorganic acid is 0.5-2 mol / L.

7. A highly oxygen-permeable ionomer with sterically hindered groups, characterized in that: It is prepared by the preparation method described in any one of claims 1-6.

8. An application of the highly oxygen-permeable ionomer with sterically hindered groups as described in claim 7, characterized in that: High oxygen-permeable ionomers with large steric hindrance groups are applied to the cathode catalyst layer of proton exchange membrane fuel cells.

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