A polynorbornene-based anion exchange ionomer having dual domain coupled ion channels and methods of making and using the same

Abstract

The application belongs to the technical field of fuel cell application, and discloses a polynorbornene-based anion exchange ionomer with double-domain coupled ion channels, a preparation method and application thereof. The polynorbornene-based anion exchange ionomer simultaneously constructs an ion domain rich in cation groups and a synergistic functional domain rich in oxygen-containing functional groups at a molecular scale, the two types of domains are coupled with each other in the material and form a continuous double-domain ion transmission network, so that the ionomer can still maintain a stable and continuous hydrogen and oxygen ion transmission channel under the conditions of a thin layer state of a cathode catalyst layer and limited hydration, and effectively improves the ion transmission connectivity and catalyst utilization efficiency of the catalyst layer interface. The ionomer is suitable for being used as an ion-conducting bonding material of a cathode of an alkaline membrane fuel cell, can improve the oxygen reduction reaction performance of the cathode, and provides a new material and structural design idea for a low-noble metal loading and high-power density fuel cell electrode structure design.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell application technology, and relates to a polynorbornene-based anion exchange polymer with dual-domain coupled ion channels, its preparation method, and its application. Background Technology

[0002] As a core technology of the hydrogen economy, anion exchange membrane fuel cells (FEFCs) can utilize non-precious metal catalysts in alkaline environments, offering advantages in cost and resources. However, their overall performance is still susceptible to limitations imposed by the slow kinetics of the oxygen reduction reaction at the cathode. Within the catalyst layer, the anion exchange polymer plays a crucial role in catalyst bonding, hydroxide ion transport, and the construction of the three-phase interface; its structural design directly impacts the accessibility of active sites and interfacial transport efficiency.

[0003] Most studies directly apply high-performance anion exchange membrane materials to ionomer systems without specifically optimizing the structure of ionomers in the ultrathin film state within the catalyst layer. Although ionomers and anion exchange membranes share similar chemical compositions, their operating states differ significantly. Anion exchange membranes achieve transmembrane ion transport through dense membranes, while ionomers typically form thin films tens of nanometers thick on the surface of catalyst particles. In the thin film state, ionomers often exhibit reduced water content, limited swelling, and weakened microphase separation structures, easily leading to interruptions in ion transport pathways and affecting electrode performance. Therefore, under ultrathin film and low hydration conditions, a single ionic structural domain often struggles to maintain a continuous and stable conduction pathway. Literature reports that in polybenzimidazole basic membranes, the synergistic introduction of ether bonds, ionic groups, and tertiary amine structures helps form ion clusters and hydrogen bond networks, thereby constructing nearly universally connected ion conduction channels and significantly enhancing ion conductivity.

[0004] Furthermore, while constructing multi-domain synergistic ion transport, alkaline ionomer films must still maintain excellent chemical stability. Previous studies on anion exchange membranes have shown that, under alkaline conditions, structures containing aryl ethers and aryl sulfones are affected by OH groups. - The chemical degradation that occurs during the attack also produces acidic phenols that neutralize OH groups. - Ions are detrimental to battery performance. In contrast, polynorbornene exhibits excellent chemical stability due to its all-carbon backbone, and its monomers are readily available and its functionalization is flexible, making it a promising class of ionomer materials. Summary of the Invention

[0005] This invention provides a polynorbornene-based anion-exchange ionomer with a dual-domain coupled ion channel. The ionomer is characterized by comprising an ionic domain containing cationic groups and a cooperating functional domain rich in oxygen functional groups. The ionic domain provides a charge conduction pathway for hydroxide ions, while the cooperating functional domain containing oxygen functional groups can form a hydrogen bond network, thereby promoting OH- ion exchange.- Grotthuss transport. The two types of structural domains mentioned above are coupled to each other within the material and form a connected multidimensional ion transport network, enabling the ionomer to maintain stable and continuous ion conduction ability even in the confined environment of the catalyst layer, thereby improving the interfacial transport efficiency and electrochemical performance of the cathode catalyst layer.

[0006] The technical solution of the present invention: A polynorbornene-based anion-exchange ionomer with a dual-domain coupled ion channel has the following structure: in: R1 is C 1-10 Alkylene or oxyalkylene, preferably C4 1-6 Alkylene or oxyalkylene; R2 is a cationic functional group selected from one of quaternized trimethylamine, triethylamine, tri-n-propylamine, and N-methylpiperidine; The ratio of m to n is 1:99 ~ 99:1, preferably 1:(3 ~ 20); m and n are selected from 10 to 500, preferably 20 to 300.

[0007] A method for preparing a polynorbornene-based anion-exchange ionomer with dual-domain coupled ion channels includes the following steps: S1. Synthesize precursor polymers rich in hydroxyl functional groups through ring-opening metathesis polymerization; The norbornene monomer was dissolved in a solvent to prepare solution A, and then Grubbs catalyst was added. The reaction was stirred under an inert gas environment. After the reaction was completed, the reaction was quenched with vinyl ether, concentrated, and added to a precipitant to precipitate the precursor polymer.

[0008] The norbornene monomer has the following structure: The solvent is tetrahydrofuran, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide.

[0009] The concentration of the norbornene monomer in the reaction system is 0.01-5 M.

[0010] The Grubbs catalyst mentioned above refers to the first-generation Grubbs catalyst, the second-generation Grubbs catalyst, and the third-generation Grubbs catalyst.

[0011] The molar ratio of norbornene monomer to Grubbs catalyst is 10:1 to 10000:1.

[0012] The stirring reaction time is 5 min to 7 days.

[0013] The precursor polymer has the structure shown in the following formula: S2. Hydrogenation reaction of the precursor polymer to saturate the carbon-carbon double bonds in the main chain with hydrogen; The precursor polymer obtained in step S1 was dissolved in a high-boiling-point solvent to prepare solution B. Then, 4-toluenesulfonyl trap was added, and the reaction was stirred, refluxed, and stirred in an inert gas environment. After the reaction was completed, a precipitant was added to precipitate the polymer, and the hydrogenated saturated polymer was obtained. The high-boiling-point solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide.

[0014] The concentration of the precursor polymer in solution B is 0.01-5 M.

[0015] The molar ratio of the precursor polymer to 4-toluenesulfonyl trap is 1:1 to 1:1000.

[0016] The inert gas is nitrogen, argon, helium, or neon.

[0017] The temperature of the condensation reflux reaction is 90-160°C. o C.

[0018] The condensation reflux reaction takes 5 hours to 10 days.

[0019] The hydrogen-saturated polymer has the structure shown in the following formula: S3. Grafting cationic functional groups onto the hydrogen-saturated polymer to obtain an ionomer; The polymer saturated by hydrogenation in step S2 is dissolved in an anhydrous high-boiling solvent to prepare solution C. Then, an alkali and an alkyl or oxyalkyl halide with a cationic group are added and stirred in an inert gas environment. After the reaction is completed, a precipitant is added to precipitate the polymer, resulting in a polynorbornene anion exchange polymer with dual-domain coupled ion channels.

[0020] The anhydrous high-boiling-point solvent is anhydrous dimethylacetamide, anhydrous dimethylformamide, anhydrous N-methylpyrrolidone, or anhydrous dimethyl sulfoxide.

[0021] The concentration of the hydrogenated polymer in solution C is 0.01-5 M.

[0022] The alkali is sodium hydride, potassium hydride, lithium diisopropylamine hydride, or lithium hexamethyldisilazane.

[0023] The preferred molar ratio of the hydrogenated saturated polymer, the base, and the alkyl or oxyalkyl halide with a cationic group is 1:1:1 to 1:100:100.

[0024] The temperature of the stirring reaction is 25-80°C. o C.

[0025] The stirring reaction takes 1-20 days.

[0026] The alkyl or oxyalkyl halide containing a cationic group has a chain length of C2. 1-10 The alkylene or oxyalkyl group has a cationic group that is one of quaternized trimethylamine, triethylamine, tri-n-propylamine, or N-methylpiperidine, and the halogen in the halogenated product is Cl, Br, or I.

[0027] The application of the aforementioned polynorbornene-based anion-exchange polymer with dual-domain coupled ion channels in the fabrication of membrane electrodes for fuel cells includes the following steps: After dissolving the ionomer in an organic solvent, a catalyst is added to prepare an ink slurry. The ink slurry is then sprayed onto a gas diffusion layer or membrane to form a catalyst layer using a catalyst-coated substrate method or a catalyst-coated membrane method.

[0028] The catalyst refers to a Pt / C catalyst with a platinum loading of 5-80 wt%.

[0029] The organic solvent is N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide; the organic solvent is a mixture of ethanol and dimethyl sulfoxide, ethanol and N-methylpyrrolidone, isopropanol and water, or a mixture of N,N-dimethylacetamide, isopropanol and water.

[0030] The mass ratio of the catalyst in the ink slurry to the polynorbornene anion exchange ionomer with dual-domain coupled ion channels is 20:1 to 1:1, more preferably 10:1 to 3:1.

[0031] The mass fraction of the polynorbornene anion exchange ionomer with dual-domain coupled ion channels in the reaction system is preferably 0.1% to 10%.

[0032] The catalyst loading in the catalyst layer is preferably 0.05~2.0 mg / cm³. 2 More preferably 0.1 ~ 1.0 mg / cm³ 2 .

[0033] The membrane electrode is obtained by spraying a catalyst onto a gas diffusion layer using a catalyst coating substrate method. The gas diffusion layer includes at least one of carbon paper, carbon felt, porous stainless steel mesh, nickel mesh, nickel felt, and nickel foam.

[0034] The beneficial effects of this invention are: This invention achieves precise construction of the molecular structure of polynorbornene ionomers through ring-opening metathesis polymerization, main-chain hydrogenation treatment, and controllable grafting of quaternized side chains. At the molecular scale, it synergistically forms ionic structural domains rich in cationic groups and synergistic functional structural domains rich in oxygen-containing functional groups, enabling the ionomer to form a continuous and interconnected dual-domain coupled ion transport network on the catalyst particle surface. This ionomer, existing as a thin layer covering the cathode catalyst layer and maintaining stable hydroxide ion transport channels under low hydration conditions, effectively alleviates the problem of decreased catalyst utilization caused by discontinuous ion channels and insufficient interfacial ion connectivity in traditional ionomers within the catalyst layer, thereby improving the interfacial transport efficiency and electrochemical performance of the cathode oxygen reduction reaction.

[0035] Meanwhile, the physical entanglement or physical cross-linking structure formed between the oxygen-containing functional groups in the molecular chain helps to suppress excessive water absorption and structural instability of the ionomer in the electrode environment. The non-aromatic polynorbornene backbone has both good chemical stability and gas transport potential. Combined with a structurally tunable, mild and reproducible synthesis process, the ionomer is suitable as an ion-conducting binder material for the cathode catalyst layer of alkaline membrane fuel cells. Attached Figure Description

[0036] Figure 1 This illustrates the interaction between N and -OH groups in the polynorbornene ionomer of the dual-domain coupled ion transport channel in Example 1 of this invention. Figure 2 The above is the 1H NMR spectrum of the polynorbornene ionomer with dual-domain coupled ion transport channels m / n=1:3 in Example 1 of this invention. Figure 3 The polarization curves of the polynorbornene ionomer with dual-domain coupled ion transport channels in Example 1 are shown. Figure 4 The power density curve of the polynorbornene ionomer hydrogen fuel cell with dual-domain coupled ion transport channels in Example 1 is shown. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0038] Example 1 This example provides a method for preparing quaternized polynorbornene ionomer (QA-HPNB-X%), as follows: As shown in the above procedure, under a nitrogen atmosphere, 0.01 mol of 5-norbornene-2-methanol was dissolved in 100 mL of dry tetrahydrofuran to prepare a 0.1 M solution. Then, 3 mol of Grubbs third-generation catalyst was added to the dry tetrahydrofuran and stirred vigorously at room temperature for 15 minutes. After that, vinyl ether was added to quench the reaction, and the mixture was concentrated naturally at room temperature. The precipitate was then deposited into ethyl acetate. The resulting white solid was dissolved again in tetrahydrofuran and precipitated into ethyl acetate for further purification of the polymer.

[0039] 0.01 mol of the purified polymer from ring-opening metathesis polymerization was dissolved in 150 mL of N,N-dimethylformamide to prepare a 0.067 M solution. Then, 0.06 mol of 4-toluenesulfonyl sulfide was added to the solution. The reaction was carried out in a 250 mL three-necked flask with a reflux condenser. Before the reaction, the gas in the single-necked flask was first evacuated using a vacuum pump through a double-row tube and replaced with argon three times to ensure an argon atmosphere. The reaction was carried out at 120 °C for 3 days. After the reaction was completed, the precipitate was precipitated in ethyl acetate, washed three times with ethyl acetate, and dried at room temperature.

[0040] 0.001 mol of the hydrogenated polymer was dissolved in 50 mL of anhydrous dimethyl sulfoxide to prepare a 0.02 M solution. Then, 0.015 mol of sodium hydride was added. The reaction was maintained in an argon environment by purging the solution three times with a double-row tube and a vacuum pump. The reaction was carried out at room temperature for 8 hours until no gas was produced. Then, 0.04 mol of 3-bromopropyltrimethylammonium bromide was added, and the reaction was carried out at 40 °C for 1 day, 3 days, and 5 days. After the reaction was completed, the mixture was poured into deionized water to precipitate the polymer. After washing with deionized water several times, the polymer was dried to obtain polynorbornene ionomers with grafting degrees of 5%, 15%, and 25% (QA-HPNB-5%, QA-HPNB-15%, QA-HPNB-25%).

[0041] Its structural formula is shown below: The ratios of m to n are 1:19, 3:17, and 1:3.

[0042] Example 2 This example provides a method for preparing piperidinized polynorbornene ionomers, as follows: 0.001 mol of the hydrogenated polymer was dissolved in 50 mL of anhydrous N-methylpyrrolidone to prepare a 0.02 M solution. Then, 0.015 mol of sodium hydride was added. The mixture was purged three times with argon using a double-row tube and a vacuum pump to ensure an argon atmosphere. The reaction was carried out at room temperature for 8 hours until no gas was produced. Then, 0.04 mol of 1,6-dibromohexane was added, and the reaction was carried out at 40 °C for 3 days. After the reaction was completed, the mixture was poured into deionized water to precipitate the precipitate. The precipitate was then washed several times with deionized water and dried.

[0043] 0.001 mol of the polymer with brominated side chains was dissolved in 50 mL of anhydrous dimethyl sulfoxide to prepare a 0.02 M solution. Then, 0.015 mol of sodium hydride was added. The mixture was purged three times with argon using a double-row tube and a vacuum pump to ensure an argon atmosphere. The reaction was carried out at room temperature for 8 hours until no gas was produced. Then, 0.04 mol of 1-methylpiperidine was added, and the reaction was carried out at room temperature for 5 days. After the reaction was completed, the mixture was poured into deionized water to precipitate the precipitate. The precipitate was then washed several times with deionized water and dried.

[0044] Its structural formula is shown below: Example 3 This example provides a method for preparing piperidinized polynorbornene ionomers, as follows: 0.002 mol of the hydrogenated polymer was dissolved in 50 mL of anhydrous dimethyl sulfoxide to prepare a 0.04 M solution. Then, 0.03 mol of potassium hydride was added. The nitrogen environment was maintained by purging the solution three times with argon using a double-row tube and a vacuum pump. The reaction was carried out at room temperature for 8 hours until no gas was produced. Then, 0.08 mol of 1,2-bis(2-chloroethoxy)ethane was added, and the reaction was carried out at room temperature for 4 days. After the reaction was completed, the mixture was poured into deionized water to precipitate the precipitate. The precipitate was then washed several times with deionized water and dried.

[0045] 0.0005 mol of the polymer with brominated side chains was dissolved in 50 mL of anhydrous dimethyl sulfoxide to prepare a 0.01 M solution. Then, 0.0075 mol of potassium hydride was added. The nitrogen environment was maintained by purging the solution three times with argon using a double-row tube and a vacuum pump. The reaction was carried out at room temperature for 10 hours until no gas was produced. Then, 0.02 mol of 1-methylpiperidine or trimethylamine, triethylamine, or tri-n-propylamine was added, and the reaction was carried out at 40 °C for 3 days. After the reaction was completed, the mixture was poured into deionized water to precipitate the precipitate. The mixture was then washed several times with deionized water and dried.

[0046] Its structural formula is shown below: Example 4 When preparing the QA-HPNB-X ionomer of Example 1, the concentration of norbornene monomer was 0.2 M, while other parameters remained unchanged.

[0047] Example 5 When preparing the QA-HPNB-X ionomer of Example 1, the Grubbs second-generation catalyst was selected, and other parameters remained unchanged.

[0048] Example 6 When preparing the QA-HPNB-X ionomer of Example 1, the molar ratio of norbornene monomer to Grubbs catalyst was selected as 1:500, while other parameters remained unchanged.

[0049] Example 7 When preparing the QA-HPNB-X ionomer of Example 1, the reaction time in step S1 was 60 min, and the other steps remained unchanged.

[0050] Example 8 This embodiment provides fuel cell data for a polynorbornene-based anion exchange ionomer with a dual-domain coupled ion channel. The ionomer used is the one prepared in Example 1; the membrane used is the commercially available PiperION A20.

[0051] Membrane electrodes (MEAs) were prepared using the gas diffusion electrode (GDE) method, specifically as follows: Pt / C was used as the anode and cathode catalysts, and carbon paper was used as the substrate. Ink slurry was sprayed onto the anode and cathode substrates, respectively, with a Pt loading of 0.5 mg / cm³. 2 .

[0052] The anolyte and cathode catalyst layers and the anion exchange membrane were immersed in 1 M KOH for 24 hours to convert them to OH-. - The sample was then thoroughly rinsed with deionized water to remove residual alkali before being assembled into a battery. On the HTS-125 fuel cell test system (Hephas Energy Co., Ltd.), at 80... o At a temperature of C, at 1.0 L / min -1 The performance of the H2 / O2 battery was tested at gas flow rate and 100% relative humidity, and the battery voltage and power density at various current densities were recorded.

Claims

1. A polynorbornene-based anion-exchange polymer with dual-domain coupled ion channels, characterized in that, The polynorbornene-based anion-exchange polymer has the following structure: in: R1 is C 1-10 Alkylene or oxyalkylene, preferably C4 1-6 Alkylene or oxyalkylene; R2 is a cationic functional group selected from one of quaternized trimethylamine, triethylamine, tri-n-propylamine, and N-methylpiperidine; The ratio of m to n is 1:99 to 99:1; m and n are selected from 10 to 500.

2. A method for preparing a polynorbornen-based anion-exchange polymer with a dual-domain coupled ion channel, characterized in that, Includes the following steps: S1. Synthesize precursor polymers rich in hydroxyl functional groups through ring-opening metathesis polymerization; The norbornene monomer was dissolved in a solvent to prepare solution A. Then, Grubbs catalyst was added and the reaction was stirred under an inert gas environment. After the reaction was completed, the reaction was quenched with vinyl ether. After concentration, the solution was added to a precipitant to precipitate the precursor polymer. S2. Hydrogenation reaction of the precursor polymer to saturate the carbon-carbon double bonds in the main chain with hydrogen; The precursor polymer obtained in step S1 was dissolved in a high-boiling-point solvent to prepare solution B. Then, 4-toluenesulfonyl trap was added, and the reaction was stirred, refluxed, and stirred in an inert gas environment. After the reaction was completed, a precipitant was added to precipitate the polymer, and the hydrogenated saturated polymer was obtained. S3. Grafting cationic functional groups onto the hydrogen-saturated polymer to obtain an ionomer; The polymer saturated by hydrogenation in step S2 is dissolved in an anhydrous high-boiling solvent to prepare solution C. Then, an alkali and an alkyl or oxyalkyl halide with a cationic group are added and stirred in an inert gas environment. After the reaction is completed, a precipitant is added to precipitate the polymer, resulting in a polynorbornene anion exchange polymer with dual-domain coupled ion channels.

3. The preparation method according to claim 2, characterized in that, In step S1, The norbornene monomer has the following structure: The solvent is tetrahydrofuran, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide; The concentration of the norbornene monomer in the reaction system is 0.01-5 M; The Grubbs catalyst mentioned above refers to the first-generation Grubbs catalyst, the second-generation Grubbs catalyst, and the third-generation Grubbs catalyst. The molar ratio of norbornene monomer to Grubbs catalyst is 10:1 to 10000:1; The stirring reaction time is 5 min to 7 days; The precursor polymer has the structure shown in the following formula: 。 4. The preparation method according to claim 2, characterized in that, In step S2, The high-boiling-point solvent is dimethylacetamide, dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide; The concentration of the precursor polymer in solution B is 0.01-5 M; The molar ratio of the precursor polymer to 4-toluenesulfonyl trap is 1:1 to 1:1000; The inert gas is nitrogen, argon, helium, or neon; The temperature of the condensation reflux reaction is 90-160°C. o C; The condensation reflux reaction takes 5 hours to 10 days. The hydrogen-saturated polymer has the structure shown in the following formula: 。 5. The preparation method according to claim 2, characterized in that, In step S3, The anhydrous high-boiling-point solvent is anhydrous dimethylacetamide, anhydrous dimethylformamide, anhydrous N-methylpyrrolidone, or anhydrous dimethyl sulfoxide; The concentration of the hydrogenated saturated polymer in solution C is 0.01-5 M; The alkali is sodium hydride, potassium hydride, lithium diisopropylamine hydride, or lithium hexamethyldisilazane; The preferred molar ratio of the hydrogenated polymer, the base, and the alkyl or oxyalkyl halide with a cationic group is 1:1:1 to 1:100:

100. The temperature of the stirring reaction is 25-80°C. o C; The stirring reaction takes 1-20 days; The alkyl or oxyalkyl halide containing a cationic group has a chain length of C2. 1-10 The alkylene or oxyalkyl group has a cationic group that is one of quaternized trimethylamine, triethylamine, tri-n-propylamine, or N-methylpiperidine, and the halogen in the halogenated product is Cl, Br, or I.

6. The application of a polynorbornene-based anion-exchange polymer with dual-domain coupled ion channels in the fabrication of membrane electrodes in fuel cells, characterized in that... Includes the following steps: After dissolving the ionomer in an organic solvent, a catalyst is added to prepare an ink slurry. The ink slurry is then sprayed onto a gas diffusion layer or membrane to form a catalyst layer using a catalyst-coated substrate method or a catalyst-coated membrane method.

7. The application according to claim 6, characterized in that, The catalyst refers to a Pt / C catalyst with a platinum loading of 5-80 wt%. The organic solvent is N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide; the organic solvent is a mixture of ethanol and dimethyl sulfoxide, ethanol and N-methylpyrrolidone, isopropanol and water, or a mixture of N,N-dimethylacetamide, isopropanol and water. The mass ratio of the catalyst in the ink slurry to the polynorbornene anion exchange ionomer with dual-domain coupled ion channels is 20:1 to 1:

1. The mass fraction of the polynorbornene-based anion-exchange ionomer with dual-domain coupled ion channels in the reaction system is 0.1% to 10%. The catalyst loading in the catalyst layer is preferably 0.05~2.0 mg / cm³. 2 ; The membrane electrode is obtained by spraying a catalyst onto a gas diffusion layer using a catalyst coating substrate method. The gas diffusion layer includes at least one of carbon paper, carbon felt, porous stainless steel mesh, nickel mesh, nickel felt, and nickel foam.

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