Covalent grafted heteropoly acid modified perfluorosulfonic acid membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of proton exchange membranes, and provides a covalent grafted heteropoly acid modified perfluorosulfonic acid membrane as well as a preparation method and application thereof. According to the invention, polypropylene glycol monoalkyl ether and Keggin type vacancy heteropoly acid are subjected to covalent grafting, and then the obtained covalent grafted heteropoly acid is used as an additive to modify the perfluorosulfonic acid membrane, so that the leakage problem of heteropoly acid in the proton exchange membrane can be effectively relieved, and meanwhile, the excellent proton conduction performance of heteropoly acid is also retained; moreover, the polypropylene glycol monoalkyl ether has relatively large molecular weight, so that the heteropoly acid can be anchored more firmly in the perfluorosulfonic acid membrane, and the proton conduction capability of the heteropoly acid is fully exerted. The result of the embodiment shows that the covalent grafted heteropoly acid modified perfluorosulfonic acid membrane provided by the invention shows excellent proton conduction performance and chemical stability, and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of proton exchange membranes, and in particular to a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane and a preparation method and application thereof. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) and proton exchange membrane water electrolyzers (PEMWEs) are the most promising candidates for future clean energy technologies. As the core components of PEMFCs and PEMWEs, proton exchange membranes (PEMs) play a vital role in battery performance. Perfluorosulfonic acid membranes represented by Nafion are well-known ionomers with excellent chemical stability and high ion transport properties. However, it is difficult for Nafion to simultaneously achieve improvements in proton conductivity and mechanical stability, and the perfluoro chain of Nafion is chemically inert, making it difficult to modify by directly changing the molecular structure of Nafion.

[0003] At present, the method of heteropoly acid modification is usually used to obtain Nafion modified membranes with enhanced performance. The high proton conductivity of heteropoly acid can effectively improve the proton conductivity of Nafion membrane. However, due to the high hydrophilicity and oxygen-rich surface of heteropoly acid, it is easy for heteropoly acid to be separated from the system under solvent conditions, resulting in leakage from the membrane, which is not conducive to the long-term operation of PEMFCs and PEMWEs. There are related reports on the modification of Nafion by introducing heteropoly acid, but because the heteropoly acid is not stable enough in the system, the performance improvement of the modified Nafion membrane is limited. How to achieve stable immobilization of heteropoly acid in Nafion system has become an urgent problem to be solved. Summary of the invention

[0004] In view of this, the present invention provides a covalently grafted heteropoly acid modified perfluorosulfonic acid membrane and a preparation method and application thereof. The present invention uses polypropylene glycol monoalkyl ether and vacant heteropoly acid for covalent grafting, which can firmly anchor the heteropoly acid in the perfluorosulfonic acid membrane, better exert the proton conduction ability of the heteropoly acid, and the obtained modified perfluorosulfonic acid membrane exhibits excellent proton conduction performance and chemical stability.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A covalently grafted heteropolyacid modified perfluorosulfonic acid membrane comprises a perfluorosulfonic acid membrane and an additive hybridized in the perfluorosulfonic acid membrane; the additive is a hydrogen-type covalently grafted heteropolyacid; the hydrogen-type covalently grafted heteropolyacid is a Keggin-type vacancy heteropolyacid grafted with polypropylene glycol monoalkyl ether trimethoxysilane; the mass of the additive is 1% to 5% of the mass of the perfluorosulfonic acid membrane.

[0007] Preferably, the polypropylene glycol monoalkyl ether trimethoxysilane includes methyl polypropylene glycol monoalkyl ether trimethoxysilane and / or propyl polypropylene glycol monoalkyl ether trimethoxysilane.

[0008] Preferably, the Keggin-type vacant heteropoly acid is vacant silicotungstic acid or vacant phosphotungstic acid.

[0009] The present invention also provides a method for preparing the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane described in the above scheme, comprising the following steps:

[0010] The perfluorosulfonic acid resin, the hydrogen-type covalently grafted heteropoly acid and the organic solvent are mixed to obtain a film casting solution;

[0011] The casting solution is cast into a membrane to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane.

[0012] Preferably, the preparation method of the hydrogen-type covalently grafted heteropolyacid comprises:

[0013] The polypropylene glycol monoalkyl ether trimethoxysilane, potassium-type Keggin-type vacant heteropoly acid, hydrochloric acid solution and organic solvent are mixed to carry out grafting reaction to obtain potassium-type covalently grafted heteropoly acid;

[0014] The potassium-type covalently grafted heteropolyacid is subjected to hydrogen ion replacement to obtain a hydrogen-type covalently grafted heteropolyacid.

[0015] Preferably, the molar ratio of the polypropylene glycol monoalkyl ether trimethoxysilane to the potassium Keggin type vacant heteropoly acid is 2:(0.8-1.2); the molar ratio of the potassium Keggin type vacant heteropoly acid to the hydrochloric acid in the hydrochloric acid solution is 1:(4-5);

[0016] The grafting reaction time is 5 to 10 hours.

[0017] Preferably, the hydrogen ion replacement method is ion chromatography or reverse precipitation;

[0018] The ion chromatography method is to use hydrogen-type ion exchange resin to replace hydrogen ions;

[0019] The reverse precipitation method comprises: dissolving the potassium-type covalently grafted heteropoly acid in N,N-dimethylformamide, and precipitating the obtained solution in a hydrochloric acid solution to obtain the hydrogen-type covalently grafted heteropoly acid.

[0020] Preferably, the preparation method of the polypropylene glycol monoalkyl ether trimethoxysilane comprises:

[0021] Polypropylene glycol monoalkyl ether, chloroalkyl trimethoxysilane, sodium hydride and an organic solvent are mixed to carry out a substitution reaction to obtain the polypropylene glycol monoalkyl ether trimethoxysilane.

[0022] Preferably, the weight average molecular weight of the polypropylene glycol monoalkyl ether is 800 to 2000 g / mol;

[0023] The molar ratio of the polypropylene glycol monoalkyl ether to the chloroalkyltrimethoxysilane is 1:(1-2); the chloroalkyltrimethoxysilane is chloromethyltrimethoxysilane and / or chloropropyltrimethoxysilane;

[0024] The molar ratio of the polypropylene glycol monoalkyl ether to sodium hydride is 1:(1-2);

[0025] The temperature of the substitution reaction is 20-80° C., and the reaction time is 4-72 hours.

[0026] The present invention also provides the use of the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane described in the above scheme or the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane prepared by the preparation method described in the above scheme as a proton exchange membrane.

[0027] The invention provides a covalently grafted heteropolyacid modified perfluorosulfonic acid membrane, comprising a perfluorosulfonic acid membrane and an additive hybridized in the perfluorosulfonic acid membrane; the additive is a hydrogen-type covalently grafted heteropolyacid; the hydrogen-type covalently grafted heteropolyacid is a Keggin-type vacancy heteropolyacid grafted with polypropylene glycol monoalkyl ether trimethoxysilane; the mass of the additive is 1% to 5% of the mass of the perfluorosulfonic acid membrane. Heteropolyacid is an inorganic proton conductor with high proton conductivity. It can provide protons in a hydrated state, increase the proton concentration of the system and provide proton hopping sites, thereby improving the proton conductivity of the system. However, due to its good water solubility, it may have leakage problems in the membrane. Polypropylene glycol (PPG) monoalkyl ether is a commercial polymer electrolyte material soluble in water, which can be assembled with other matrices to form a stable structure and improve the stability of the material. However, compared with traditional electrolytes, polypropylene glycol monoalkyl ether itself has lower conductivity and insufficient proton conductivity. The present invention effectively alleviates the leakage problem of heteropolyacid in the proton exchange membrane by covalent grafting of polypropylene glycol monoalkyl ether and absent heteropolyacid, while retaining the excellent proton conductivity of heteropolyacid. In addition, polypropylene glycol monoalkyl ether has a large molecular weight, which can make the heteropolyacid anchored more firmly in the perfluorosulfonic acid membrane, thereby giving full play to the proton conductivity of the heteropolyacid. The results of the examples show that the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane provided by the present invention exhibits excellent proton conductivity and chemical stability. When the mass fraction of the additive is 2%, the conductivity of the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane at 80°C can reach 252 mS cm -1 , and after repeated conductivity performance tests, there was no cracking or dissolution, indicating that it has good long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1This is a comparison chart of the proton conductivity of Nafion212 membrane and the covalently grafted heteropolyacid modified perfluorosulfonic acid membrane prepared in Example 2. DETAILED DESCRIPTION

[0029] The invention provides a covalently grafted heteropolyacid modified perfluorosulfonic acid membrane, comprising a perfluorosulfonic acid membrane and an additive hybridized in the perfluorosulfonic acid membrane; the additive is a hydrogen-type covalently grafted heteropolyacid; the hydrogen-type covalently grafted heteropolyacid is a Keggin-type vacancy heteropolyacid grafted with polypropylene glycol monoalkyl ether trimethoxysilane; the mass of the additive is 1% to 5% of the mass of the perfluorosulfonic acid membrane.

[0030] In the present invention, the mass of the additive can be 1%, 2%, 3%, 4% or 5% of the mass of the perfluorosulfonic acid membrane. The present invention controls the mass fraction of the additive within the above range to obtain a modified perfluorosulfonic acid membrane with excellent proton conductivity and chemical stability.

[0031] In the present invention, the polypropylene glycol monoalkyl ether trimethoxysilane includes methyl polypropylene glycol monoalkyl ether trimethoxysilane and / or propyl polypropylene glycol monoalkyl ether trimethoxysilane; the polypropylene glycol monoalkyl ether trimethoxysilane is prepared from polypropylene glycol monoalkyl ether and chloroalkyl trimethoxysilane, and the carbon number of the alkyl group in the polypropylene glycol monoalkyl ether is preferably 1 to 8, more preferably 1 to 6, and further preferably 1 to 4; in a specific embodiment of the present invention, the polypropylene glycol monoalkyl ether is polypropylene glycol monobutyl ether. The present invention uses polypropylene glycol monoalkyl ether trimethoxysilane to graft Keggin type vacancy heteropoly acid, which can make the heteropoly acid anchor more firmly in the perfluorosulfonic acid membrane and give full play to the proton conduction ability of the heteropoly acid.

[0032] In the present invention, the Keggin type vacant heteropoly acid is vacant silicotungstic acid or vacant phosphotungstic acid.

[0033] In the present invention, the perfluorosulfonic acid membrane is preferably a Nafion membrane; the perfluorosulfonic acid membrane is formed by a perfluorosulfonic acid resin, the perfluorosulfonic acid resin has a perfluoro main chain, a fluoroether side chain and a hydrophilic sulfonic acid end group, and the main chain, the side chain and the sulfonic acid end group undergo self-assembled microphase separation, so that the hydrated ion phase region in the membrane forms a three-dimensional interwoven network structure. In the present invention, the perfluorosulfonic acid resin is specifically a perfluorosulfonic acid-polytetrafluoroethylene copolymer.

[0034] In the present invention, the thickness of the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane is preferably 20 to 100 μm, specifically 20 μm, 50 μm, 80 μm or 100 μm.

[0035] The present invention also provides a method for preparing the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane described in the above scheme, comprising the following steps:

[0036] Mix perfluorosulfonic acid resin, hydrogen-type covalently grafted heteropolyacid and an organic solvent to obtain a casting solution;

[0037] Cast the casting solution into a film to obtain the obtained covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane.

[0038] In the present invention, the preparation method of the hydrogen-type covalently grafted heteropolyacid preferably includes:

[0039] Mix polypropylene glycol monoalkyl ether trimethoxysilane, potassium-type Keggin-type lacunary heteropolyacid, hydrochloric acid solution (denoted as the first hydrochloric acid solution) and an organic solvent to carry out a grafting reaction to obtain potassium-type covalently grafted heteropolyacid;

[0040] Perform hydrogen ion replacement on the potassium-type covalently grafted heteropolyacid to obtain the hydrogen-type covalently grafted heteropolyacid.

[0041] In the present invention, polypropylene glycol monoalkyl ether alkyltrialkoxysilane, potassium-type Keggin-type lacunary heteropolyacid, hydrochloric acid solution and an organic solvent (denoted as the first organic solvent) are mixed to carry out a grafting reaction to obtain potassium-type covalently grafted heteropolyacid. In the present invention, the potassium-type Keggin-type lacunary heteropolyacid is preferably potassium-type lacunary silicotungstic acid (K8[SiW 11 O 39 ) or potassium-type lacunary phosphotungstic acid; the preparation method of the potassium-type lacunary silicotungstic acid preferably includes: dissolving sodium silicate and sodium tungstate in hydrochloric acid solution (denoted as the second hydrochloric acid solution), boiling and then cooling to room temperature, then adding potassium chloride to the obtained material solution until precipitation is complete, and then performing filtration and drying to obtain the potassium-type lacunary silicotungstic acid; the molar ratio of sodium silicate to sodium tungstate is preferably 11:1; the concentration of the second hydrochloric acid solution is preferably 4 mol / L, the boiling time is preferably 1 h; the drying is preferably room temperature drying. The present invention has no special requirements for the preparation method of the potassium-type lacunary phosphotungstic acid, and those well-known to those skilled in the art can be used.

[0042] In the present invention, the preparation method of the polypropylene glycol monoalkyl ether trimethoxysilane preferably comprises: mixing polypropylene glycol monoalkyl ether, chloroalkyl trimethoxysilane, sodium hydride and an organic solvent (referred to as the second organic solvent) for substitution reaction to obtain the polypropylene glycol monoalkyl ether trimethoxysilane; the weight average molecular weight of the polypropylene glycol monoalkyl ether is preferably 800 to 2000 g / mol, specifically 800 g / mol, 1000 g / mol, 1300 g / mol, 1500 g / mol, 1800 g / mol or 2000 g / mol. mol; the molar ratio of the polypropylene glycol monoalkyl ether to the chloroalkyltrimethoxysilane is preferably 1:(1-2), specifically 1:1, 1:1.5 or 1:2; the chloroalkyltrimethoxysilane is preferably chloromethyltrimethoxysilane and / or chloropropyltrimethoxysilane; the molar ratio of the polypropylene glycol monoalkyl ether to sodium hydride is preferably 1:(1-2), specifically 1:1, 1:1.5 or 1:2; the second organic solvent is preferably tetrahydrofuran, and the volume ratio of the second organic solvent to the polypropylene glycol monoalkyl ether is preferably (10-20):1.

[0043] In the present invention, the temperature of the substitution reaction is preferably 20 to 80° C., specifically 20° C., 30° C., 40° C. or 80° C., and the reaction time is preferably 4 to 72 hours, more preferably 8 to 48 hours. During the substitution reaction, sodium hydride captures the proton on the terminal hydroxyl group of the polypropylene glycol monoalkyl ether to generate sodium alkoxide, and the sodium alkoxide undergoes a substitution reaction with the chloroalkyltrialkoxysilane to generate the polypropylene glycol monoalkyl ether alkyltrialkoxysilane.

[0044] After the substitution reaction is completed, the present invention preferably centrifuges the obtained product liquid, and evaporates the obtained supernatant to obtain a concentrated solution; the concentrated solution is precipitated in n-hexane, and then allowed to stand for stratification, and the lower layer is the polypropylene glycol monoalkyl ether trimethoxysilane; the volume ratio of the concentrated solution to n-hexane is preferably 1:100.

[0045] In the present invention, the molar ratio of the polypropylene glycol monoalkyl ether trimethoxysilane to the potassium-type Keggin-type vacant heteropolyacid is preferably 2:(0.8-1.2), specifically 2:0.8, 2:1, 2:1.1 or 2:1.2; the molar ratio of the potassium-type Keggin-type vacant heteropolyacid to the hydrochloric acid in the first hydrochloric acid solution is preferably 1:(4-5), and the concentration of the first hydrochloric acid solution is preferably 0.5-2 mol / L, more preferably 1 mol / L; the first organic solvent is preferably acetonitrile; the dosage ratio of the first organic solvent to the potassium-type Keggin-type vacant heteropolyacid is preferably (20-100) mL:1 mmol.

[0046] In the present invention, the grafting reaction time is preferably 5 to 10 hours, specifically 5 hours, 6 hours, 8 hours or 10 hours; the grafting reaction can be carried out at room temperature. During the grafting reaction, hydrochloric acid hydrolyzes the polypropylene glycol monoalkyl ether trimethoxysilane, and the hydrolysis product of the polypropylene glycol monoalkyl ether trimethoxysilane reacts with the potassium-type Keggin-type vacancy heteropolyacid to form a potassium-type covalently grafted heteropolyacid.

[0047] After the grafting reaction is completed, the present invention preferably filters the obtained reaction solution, and rotary evaporates the obtained filtrate to obtain the potassium-type covalently grafted heteropoly acid.

[0048] After obtaining the potassium-type covalently grafted heteropoly acid, the present invention performs hydrogen ion replacement on the potassium-type covalently grafted heteropoly acid to obtain the hydrogen-type covalently grafted heteropoly acid. In the present invention, the hydrogen ion replacement method is preferably ion chromatography or reverse precipitation; the ion chromatography preferably uses a hydrogen-type ion exchange resin to replace hydrogen ions; the present invention has no special requirements for the specific operation method of the ion chromatography, and it can be used by those skilled in the art.

[0049] In the present invention, the reverse precipitation method preferably includes: dissolving the potassium-type covalently grafted heteropolyacid in N, N-dimethylformamide, precipitating the resulting solution in a hydrochloric acid solution (referred to as the third hydrochloric acid solution) to obtain a hydrogen-type covalently grafted heteropolyacid; the concentration of the third hydrochloric acid solution is preferably 1 mol / L; after precipitation in the third hydrochloric acid solution is completed, the present invention preferably takes the precipitate and dissolves it again with N, N-dimethylformamide, then drips it into chloroform for precipitation, and then centrifuges it, and the resulting precipitate is the hydrogen-type covalently grafted heteropolyacid. After precipitation in the hydrochloric acid solution is completed, the resulting solid contains a large amount of water that is not easy to remove. If high-temperature water removal is easy to destroy the product structure, the present invention reversely precipitates the resulting precipitate into chloroform with a low boiling point, thereby achieving the removal of the solvent under mild conditions and avoiding the product from being destroyed by high temperature.

[0050] After obtaining the hydrogen-type covalently grafted heteropoly acid, the present invention mixes the perfluorosulfonic acid resin, the hydrogen-type covalently grafted heteropoly acid and an organic solvent (referred to as the third organic solvent) to obtain a casting solution. In the present invention, the perfluorosulfonic acid resin is preferably obtained by drying a perfluorosulfonic acid resin solution; the perfluorosulfonic acid resin solution is preferably a commercially available Nafion solution; the drying temperature is preferably 60° C., and the drying time is preferably 24 hours.

[0051] In the present invention, the third organic solvent is preferably a polar solvent, more preferably one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and N-methylpyrrolidone (NMP), further preferably DMAc and / or DMF.

[0052] Preferably, the perfluorosulfonic acid membrane is first dissolved in a third organic solvent to obtain a perfluorosulfonic acid resin solution, and then a hydrogen-type covalently grafted heteropolyacid is added for dissolution; the concentration of the perfluorosulfonic acid resin in the perfluorosulfonic acid resin solution is preferably 50-100 mg / mL, more preferably 80-90 mg / mL.

[0053] After obtaining the casting solution, the present invention casts the casting solution into a film to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane. In the present invention, the casting into a film preferably includes: casting the casting solution onto a glass plate, and then drying to remove the solvent to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane; the casting temperature is preferably 80 °C; the drying temperature is preferably 80 °C, and the time is preferably 15 h.

[0054] The present invention also provides the application of the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane described in the above solution or the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane prepared by the preparation method described in the above solution as a proton exchange membrane. The present invention has no special requirements on the specific manner of the application, and the application can be carried out by using the methods well-known to those skilled in the art.

[0055] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0056] The raw materials used in the following examples are: perfluorosulfonic acid-polytetrafluoroethylene copolymer (Nafion, Chemours D520). Polypropylene glycol monobutyl ether (PPG, CAS No.: 9003-13-8). Sodium hydride (NaH, CAS No.: 7646-69-7). Chloromethyltrimethoxysilane (CAS No.: 5926-26-1). Chloropropyltrimethoxysilane (CAS No.: 2530-87-2). Sodium silicate (CAS No.: 1344-09-8). Sodium tungstate (CAS No.: 10213-10-2). Hydrochloric acid (CAS No.: 7647-01-0).

[0057] The preparation method of the Nafion resin is: drying the Nafion solution (commercially available, 20%, w / w) in a forced-air drying oven at 60 °C for 24 h to obtain the Nafion resin.

[0058] Example 1

[0059] In a round-bottom flask, add 50 mL of tetrahydrofuran and 6 g of polypropylene glycol monobutyl ether (molecular weight is 1000 g / mol, 6 mmol), add 0.1728 g (7.2 mmol) of sodium hydride, and then add 2.048 g (12 mmol) of chloromethyltrimethoxysilane, and stir to react at 40°C for 8 hours; centrifuge the solution after the reaction at a speed of 10000 r / min for 15 minutes, and evaporate the obtained supernatant at 40°C under vacuum conditions. The obtained concentrated solution is added dropwise to n-hexane, and the volume ratio of n-hexane to the concentrated solution is 100:1. Let stand to separate the layers, and the obtained lower layer is methyl-type polypropylene glycol monobutyl ether trimethoxysilane.

[0060] 3.3 g (1 mmol) of potassium Keggin-type vacant silicotungstic acid (K8[SiW 11 O 39 ]) was added to a round-bottom flask, and 5mmol hydrochloric acid (1mol / L), 50mL acetonitrile and 1mL methyl polypropylene glycol monobutyl ether trimethoxysilane were added. The reaction was carried out at room temperature for 8h. The product was filtered and the acetonitrile solvent was removed by rotary evaporation at 50°C under vacuum conditions to obtain potassium polypropylene glycol monobutyl ether trimethoxysilane grafted Keggin type vacant heteropoly acid (referred to as potassium grafted silicotungstic acid). After the potassium grafted silicotungstic acid was completely dissolved with 1mL DMF, it was precipitated into 10mL of 1mol / L hydrochloric acid solution, the bottom precipitate was taken and completely dissolved with 1mL DMF again, and then dropped into 50mL of chloroform for precipitation, and the solution was centrifuged at a speed of 10000r / min for 15min. The bottom precipitate obtained was hydrogen polypropylene glycol monobutyl ether trimethoxysilane grafted Keggin type vacant heteropoly acid (i.e. hydrogen grafted silicotungstic acid).

[0061] 0.25 g Nafion resin was dissolved in 3 mL DMAc solvent and stirred to dissolve, and then 2.5 mg hydrogen-grafted silicotungstic acid was added and stirred to dissolve; the resulting mixture was cast into a membrane at 80°C and dried at 80°C for 15 h to obtain a covalently grafted heteropolyacid modified perfluorosulfonic acid membrane with a membrane thickness of 50±3 μm, in which the hybridization mass fraction of hydrogen-grafted silicotungstic acid was 1%, recorded as PPG-SiW@Nafion-Me-1%.

[0062] The proton conductivity of the obtained covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane was tested at different temperatures. The test method is as follows:

[0063] The conductivity of the prepared covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane was tested by using an AC impedance meter. All membranes were immersed in water at different temperatures (30-80°C) for 7 days, and the conductivity was measured in the fully wet state in the water. During the immersion process, it was found that no covalently grafted silicotungstic acid leakage was found in all the prepared modified proton exchange membranes. The test results are shown in Table 1.

[0064] Table 1 Proton Conductivity of PPG-SiW@Nafion-Me-1% Modified Membrane

[0065] Temperature (°C) 30 40 50 60 70 80 <![CDATA[σ (mScm -1 )]]> 104 133 158 181 200 223

[0066] As can be seen from the results in Table 1, the covalently grafted heteropolyacid modified perfluorosulfonic acid membrane of the present invention has excellent proton conductivity at different temperatures, and there are no phenomena such as cracking and dissolution after repeated conductivity tests, indicating its good long-term stability.

[0067] Example 2

[0068] Prepare hydrogen-type grafted silicotungstic acid according to the method of Example 1.

[0069] Dissolve 0.25 g of Nafion resin in 3 mL of DMAc solvent, stir to dissolve, then add 5.0 mg of hydrogen-type grafted silicotungstic acid and stir to dissolve; cast the obtained mixed solution into a membrane at 80 °C and dry it at 80 °C for 15 h to obtain a covalently grafted heteropolyacid modified perfluorosulfonic acid membrane with a membrane thickness of 50 ± 3 μm, where the mass fraction of hydrogen-type grafted silicotungstic acid is 2%, denoted as PPG-SiW@Nafion-Me-2%. Test the proton conductivity of the obtained covalently grafted heteropolyacid modified perfluorosulfonic acid membrane at different temperatures according to the method in Example 1, and the results are shown in Table 2.

[0070] Table 2 Proton Conductivity of PPG-SiW@Nafion-Me-2% Modified Membrane

[0071] Temperature (°C) 30 40 50 60 70 80 <![CDATA[σ(mScm -1 )]]> 117 151 174 203 231 252

[0072] As can be seen from the results in Table 2, the covalently grafted heteropolyacid modified perfluorosulfonic acid membrane of the present invention has excellent proton conductivity at different temperatures, and there are no phenomena such as cracking and dissolution after repeated conductivity tests, indicating its good long-term stability.

[0073] Example 3

[0074] Prepare hydrogen-type grafted silicotungstic acid according to the method of Example 1.

[0075] 0.25 g Nafion resin was dissolved in 3 mL DMAc solvent and stirred to dissolve, and then 7.5 mg hydrogen-grafted silicotungstic acid was added and stirred to dissolve; the resulting mixed solution was cast into a membrane at 80° C. and dried at 80° C. for 15 h to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane with a membrane thickness of 50±3 μm, wherein the hybridization mass fraction of hydrogen-grafted silicotungstic acid was 3%, recorded as PPG-SiW@Nafion-Me-3%. The proton conductivity of the obtained covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane at different temperatures was tested according to the method in Example 1, and the results are shown in Table 3.

[0076] Table 3 Proton conductivity performance of PPG-SiW@Nafion-Me-3% modified membrane

[0077] Temperature (°C) 30 40 50 60 70 80 <![CDATA[σ (mScm -1 )]]> 102 129 156 179 197 217

[0078] According to the results in Table 3, it can be seen that the covalently grafted heteropolyacid modified perfluorosulfonic acid membrane of the present invention has excellent proton conductivity at different temperatures, and no cracking or dissolution occurs after repeated conductivity performance tests, indicating that it has good long-term stability.

[0079] Example 4

[0080] Add 50 mL of tetrahydrofuran and 6 g of polypropylene glycol monobutyl ether (molecular weight of 1000 g / mol, 6 mmol) into a round-bottom flask, add 0.1728 g (7.2 mmol) of sodium hydride, and then add 2.4 g (12 mmol) of chloropropyltrimethoxysilane, and stir the reaction at 40°C for 8 hours; centrifuge the solution after the reaction at a speed of 10000 r / min for 15 minutes, and evaporate the obtained supernatant at 40°C under vacuum conditions. The obtained concentrated solution is added dropwise to n-hexane at a volume ratio of n-hexane to the concentrated solution of 100:1. Let stand to separate the layers, and the obtained lower layer is propyl-type polypropylene glycol monobutyl ether trimethoxysilane.

[0081] 3.3 g (1 mmol) of potassium Keggin-type vacant silicotungstic acid (K8[SiW 11 O 39]) was added to a round-bottom flask, and 5mmol hydrochloric acid (1mol / L), 50mL acetonitrile and 1mL propyl type polypropylene glycol monobutyl ether trimethoxysilane were added, and the reaction was carried out at room temperature for 8h. The product was filtered, and the acetonitrile solvent was removed by rotary evaporation at 50°C under vacuum conditions to obtain potassium type polypropylene glycol monobutyl ether trimethoxysilane grafted Keggin type vacant heteropoly acid (recorded as potassium type grafted silicotungstic acid). After the potassium type grafted silicotungstic acid was completely dissolved with 1mL DMF, it was precipitated into 10mL of 1mol / L hydrochloric acid aqueous solution, and the bottom precipitate was taken and completely dissolved with 1mL DMF again, and then dropped into 50mL of chloroform for precipitation, and the solution was centrifuged at a speed of 10000r / min for 15min. The bottom precipitate obtained was hydrogen type polypropylene glycol monobutyl ether trimethoxysilane grafted Keggin type vacant heteropoly acid (recorded as hydrogen type grafted silicotungstic acid).

[0082] 0.25 g Nafion resin was dissolved in 3 mL DMAc solvent and stirred to dissolve, and then 2.5 mg hydrogen-grafted silicotungstic acid was added and stirred to dissolve; the resulting mixed solution was cast into a membrane at 80° C. and dried at 80° C. for 15 h to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane with a membrane thickness of 50±3 μm, wherein the hybridization mass fraction of hydrogen-grafted silicotungstic acid was 1%, recorded as PPG-SiW@Nafion-Pr-1%. The proton conductivity of the obtained covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane was tested at different temperatures according to the method in Example 1, and the results are shown in Table 4.

[0083] Table 4 Proton conductivity performance of PPG-SiW@Nafion-Pr-1% modified membrane

[0084] Temperature (°C) 30 40 50 60 70 80 <![CDATA[σ (mScm -1 )]]> 110 143 167 192 207 218

[0085] According to the results in Table 4, it can be seen that the covalently grafted heteropolyacid modified perfluorosulfonic acid membrane of the present invention has excellent proton conductivity at different temperatures, and no cracking or dissolution occurs after repeated conductivity performance tests, indicating that it has good long-term stability.

[0086] Example 5

[0087] The hydrogen-type grafted silicotungstic acid was prepared according to the method of Example 4.

[0088] Dissolve 0.25 g of Nafion resin in 3 mL of DMAc solvent, stir to dissolve, then add 5.0 mg of hydrogen-form grafted silicotungstic acid, and stir to dissolve; pour the obtained mixed solution into a film at 80 °C, dry at 80 °C for 15 h to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane with a film thickness of 50 ± 3 μm, where the hybrid mass fraction of grafted silicotungstic acid is 2%, denoted as PPG-SiW@Nafion-Pr-2%. Test the proton conduction performance of the obtained covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane at different temperatures according to the method in Example 1, and the results are shown in Table 5.

[0089] Table 5 Proton Conduction Performance of PPG-SiW@Nafion-Pr-2% Modified Membrane

[0090] Temperature (°C) 30 40 50 60 70 80 <![CDATA[σ(mScm -1 )]]> 113 145 170 198 214 221

[0091] According to the results in Table 5, it can be seen that the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane of the present invention has excellent proton conduction performance at different temperatures, and there are no phenomena such as cracking and dissolution after repeated conduction performance tests, indicating its good long-term stability.

[0092] Comparative Example 1

[0093] Dissolve 0.25 g of Nafion resin in 3 mL of DMAc solvent, stir to dissolve, pour the obtained mixed solution into a film at 80 °C, dry at 80 °C for 15 h to obtain a recast Nafion membrane with a film thickness of 50 ± 3 μm. Test the proton conduction performance of the obtained covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane at different temperatures according to the method in Example 1, and the results are shown in Table 6.

[0094] Table 6 Proton Conduction Performance of Recast Nafion Membrane

[0095] Temperature (°C) 30 40 50 60 70 80 <![CDATA[σ (mScm -1 )]]> 96 125 151 176 196 213

[0096] According to the data in Examples 1-5 and Comparative Example 1, it can be seen that after modifying the perfluorosulfonic acid membrane with the hydrogen-form covalently grafted heteropolyacid of the present invention, the proton conduction performance of the obtained modified membrane is greatly improved.

[0097] Comparative Example 2

[0098] Use the commercially available Nafion 212 membrane as Comparative Example 2.

[0099] Figure 1 Figure for comparing the proton conductivities of the Nafion 212 membrane and the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane prepared in Example 2. According to Figure 1 It can be seen that the proton conductivity of the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane prepared by the present invention is significantly higher than that of the commercially available Nafion 212 membrane.

[0100] It can be seen from the above embodiments that the present invention uses polypropylene glycol monobutyl ether and Keggin type vacancy heteropolyacid for covalent grafting, and then uses the obtained covalently grafted heteropolyacid as an additive to modify the perfluorosulfonic acid membrane, which can effectively improve the proton conductivity of the perfluorosulfonic acid membrane while ensuring good compatibility between the additive and the perfluorosulfonic acid membrane, and the additive is not easy to leak, and the modified perfluorosulfonic acid membrane has long-term conductive stability.

[0101] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane, characterized in that, The invention comprises a perfluorosulfonic acid membrane and an additive hybridized in the perfluorosulfonic acid membrane; the additive is a hydrogen-type covalently grafted heteropoly acid; the hydrogen-type covalently grafted heteropoly acid is a Keggin-type vacancy heteropoly acid grafted with polypropylene glycol monoalkyl ether trimethoxysilane; the mass of the additive is 1% to 5% of the mass of the perfluorosulfonic acid membrane.

2. The covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane according to claim 1, wherein The polypropylene glycol monoalkyl ether trimethoxysilane includes methyl polypropylene glycol monoalkyl ether trimethoxysilane and / or propyl polypropylene glycol monoalkyl ether trimethoxysilane.

3. The covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane according to claim 1, wherein The Keggin type vacant heteropoly acid is vacant silicotungstic acid or vacant phosphotungstic acid.

4. The preparation method of the covalently grafted heteropolyacid modified perfluorosulfonic acid membrane according to any one of claims 1 to 3, characterized in that, The following steps are involved: The perfluorosulfonic acid resin, the hydrogen-type covalently grafted heteropoly acid and the organic solvent are mixed to obtain a film casting solution; The casting solution is cast into a membrane to obtain a covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane.

5. The preparation method according to claim 4, characterized in that, The preparation method of the hydrogen-type covalently grafted heteropoly acid comprises: The polypropylene glycol monoalkyl ether trimethoxysilane, potassium-type Keggin-type vacant heteropoly acid, hydrochloric acid solution and organic solvent are mixed to carry out grafting reaction to obtain potassium-type covalently grafted heteropoly acid; The potassium-type covalently grafted heteropolyacid is subjected to hydrogen ion replacement to obtain a hydrogen-type covalently grafted heteropolyacid.

6. The preparation method according to claim 5, characterized in that, The molar ratio of the polypropylene glycol monoalkyl ether trimethoxysilane to the potassium Keggin type vacant heteropoly acid is 2:(0.8-1.2); the molar ratio of the potassium Keggin type vacant heteropoly acid to the hydrochloric acid in the hydrochloric acid solution is 1:(4-5); The grafting reaction time is 5 to 10 hours.

7. The preparation method according to claim 5, characterized in that, The method of hydrogen ion replacement is ion chromatography or reverse precipitation; The ion chromatography method is to use hydrogen-type ion exchange resin to replace hydrogen ions; The reverse precipitation method comprises: dissolving the potassium-type covalently grafted heteropoly acid in N,N-dimethylformamide, and precipitating the obtained solution in a hydrochloric acid solution to obtain the hydrogen-type covalently grafted heteropoly acid.

8. The preparation method according to claim 5, characterized in that, The preparation method of the polypropylene glycol monoalkyl ether trimethoxysilane comprises: Polypropylene glycol monoalkyl ether, chloroalkyl trimethoxysilane, sodium hydride and an organic solvent are mixed to carry out a substitution reaction to obtain the polypropylene glycol monoalkyl ether trimethoxysilane.

9. The preparation method according to claim 8, wherein, The weight average molecular weight of the polypropylene glycol monoalkyl ether is 800 to 2000 g / mol; The molar ratio of the polypropylene glycol monoalkyl ether to the chloroalkyltrimethoxysilane is 1:(1-2); the chloroalkyltrimethoxysilane is chloromethyltrimethoxysilane and / or chloropropyltrimethoxysilane; The molar ratio of the polypropylene glycol monoalkyl ether to sodium hydride is 1:(1-2); The temperature of the substitution reaction is 20-80° C., and the reaction time is 4-72 hours.

10. Use of the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane according to any one of claims 1 to 3 or the covalently grafted heteropolyacid-modified perfluorosulfonic acid membrane prepared by the preparation method according to any one of claims 4 to 9 as a proton exchange membrane.

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