Fluorine-free proton exchange membrane, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a fluorine-free proton exchange membrane, and a preparation method therefor and the use thereof. The composition of the fluorine-free proton exchange membrane of the present invention comprises a polyoxometallate molecular cluster and a fluorine-free oxygen-containing organic polymer, wherein the mass ratio of the polyoxometallate molecular cluster to the fluorine-free oxygen-containing organic polymer is (0.8-5):1. The preparation method for the fluorine-free proton exchange membrane of the present invention comprises the following steps: dispersing a polyoxometallate molecular cluster and a fluorine-free oxygen-containing organic polymer in a solvent to prepare a coating solution, forming a membrane from the coating solution on a substrate, and drying same, so as to obtain a fluorine-free proton exchange membrane. The fluorine-free proton exchange membrane provided in the present invention has a characteristic phase-separated continuous phase structure formed under induction by means of interaction between supramolecules of the molecular cluster, and has high ion transmission efficiency, good conductivity, high thermal stability, good mechanical properties and high levels of safety, and a manufacturing process therefor is green and simple, and is low in terms of production costs; therefore, the fluorine-free proton exchange membrane has very broad application prospects.

Description

A fluorine-free proton exchange membrane and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of hydrogen proton exchange membrane fuel cells, and in particular to a fluorine-free proton exchange membrane and a preparation method and application thereof. Background Art

[0002] A hydrogen proton exchange membrane fuel cell is a proton exchange membrane fuel cell that uses hydrogen as fuel and air or oxygen as oxidant. It has the advantages of high energy conversion efficiency, long cycle life, and no pollution. It is expected to become the preferred option for the next generation of energy generation technology in the future.

[0003] The proton exchange membrane (PEM) is a key component of hydrogen PEM fuel cells, conducting protons and blocking gaseous fuels, ultimately determining the cell's performance. Currently, the most widely used PEMs in commercial applications are perfluorosulfonic acid (PFSA) membranes (e.g., Nafion membranes manufactured by DuPont and Gore Enhanced Membrane manufactured by W.L. Gore). These materials consist of a perfluorocarbon backbone and fluoroether side chains terminated with sulfonic acid groups. They can self-assemble in aqueous conditions to form a unique hydrophilic-hydrophobic microphase separation structure, where continuous hydrophilic regions enable efficient ion conduction. Consequently, PFSA membranes offer advantages such as high proton conductivity, chemical stability, and mechanical strength, making them a mainstream membrane material. However, the high conductivity of perfluorosulfonic acid proton exchange membranes can only be achieved under relatively mild conditions. For example, the Nafion membrane needs to be fully hydrated and at a moderate temperature (<90°C). Moreover, since perfluorosulfonic acid proton exchange membranes are rich in fluorine, the process of fluorinating polymers will cause environmental pollution. In addition, the preparation process of perfluorosulfonic acid proton exchange membranes is complex and costly.

[0004] Therefore, it is of great significance to develop a fluorine-free proton exchange membrane with high cost performance, green and streamlined manufacturing process, and the ability to be used in a wide temperature range.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a fluorine-free proton exchange membrane and a preparation method and application thereof.

[0007] The technical solution adopted by the present invention is:

[0008] A fluorine-free proton exchange membrane comprises polyoxometalate molecular clusters and fluorine-free oxygen-containing organic polymers, wherein the mass ratio of the polyoxometalate molecular clusters to the fluorine-free oxygen-containing organic polymer is (0.8-5):1.

[0009] Preferably, the polyoxometalate molecular cluster is at least one of a Keggin-type polyoxometalate molecular cluster, a Dawson-type polyoxometalate molecular cluster, and a pentavanadate-type polyoxometalate molecular cluster.

[0010] Preferably, the general structural formula of the Keggin-type polyoxometalate molecular cluster is as follows: n [XM 12 O 40 ] n- ·mH2O, wherein X represents the central atom, X is selected from at least one of P, Si, Co, and Al, Y represents the counter ion, Y is selected from at least one of H, Li, Na, and K, M represents the coordinating atom, M is selected from at least one of Nb, W, and Mo, m represents the number of crystal waters, the number of m depends on the self-bound water and the specific environmental humidity, m is an integer from 0 to 40, and n represents the number of charges carried by the polyanion / the number of counter ions, and n is 3, 4, or 6.

[0011] Further preferably, the Keggin type polyoxometalate molecular cluster is a silicotungstic acid molecular cluster (X4[SiW 12 O 40 ] 4- ·mH2O), cobalt tungstate molecular clusters (X6[CoW 12 O 40 ] 6- ·mH2O), phosphotungstic acid molecular clusters (X3[PW 12 O 40 ] 3- ·mH2O).

[0012] More preferably, the Keggin-type polyoxometalate molecular cluster is a silicotungstic acid molecular cluster H4SiW 12 O 40 ·mH2O (abbreviated as SiW 12 ), cobalt tungstate molecular cluster H6CoW 12 O 40 mH2O (abbreviated as CoW 12 ), phosphotungstic acid molecular cluster H3PW 12 O 40 mH2O (abbreviated as PW 12 ) at least one of.

[0013] Preferably, the general structural formula of the Dawson type polyoxometalate molecular cluster is as follows: n [X2M 18 O 62 ] n-·mH2O, wherein X represents the central atom, X is selected from at least one of P, Si, Co, and Al, Y represents the counter ion, Y is selected from at least one of H, Li, Na, and K, M represents the coordinating atom, M is selected from at least one of Nb, W, and Mo, m represents the number of crystallization waters, the number of m depends on the self-bound water and the specific environmental humidity, m is an integer from 0 to 60, and n represents the number of charges carried by the polyanion / the number of counter ions, and n is 3, 4, 6, or 8.

[0014] Preferably, the structural formula of the pentavanadate-type polyoxometalate molecular cluster is Li7[V 15 O 36 (CO3)]·39H2O.

[0015] Preferably, the fluorine-free oxygen-containing organic polymer is at least one of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, chitosan, and carboxymethyl cellulose.

[0016] Preferably, the weight average molecular weight of the fluorine-free oxygen-containing organic polymer is 50,000 g / mol to 250,000 g / mol.

[0017] A method for preparing the fluorine-free proton exchange membrane as described above comprises the following steps: dispersing polyoxometalate molecular clusters and fluorine-free oxygen-containing organic polymers in a solvent to prepare a coating solution, forming a film of the coating solution on a substrate, and drying the film to obtain the fluorine-free proton exchange membrane.

[0018] Preferably, the dispersing method is stirring.

[0019] Preferably, the dispersing is performed at 45°C to 55°C.

[0020] Preferably, the solvent is at least one of N,N-dimethylformamide, dimethyl sulfoxide, methanol, water, ethanol, and acetic acid.

[0021] Preferably, the mass fraction of the polyoxometalate molecular clusters in the coating solution is 3% to 20%.

[0022] Preferably, the film forming method is one of spin coating, drop coating, blade coating, and pull coating.

[0023] Preferably, the substrate is a silicone substrate.

[0024] Preferably, the specific operation of the drying is: first drying at 55°C to 60°C for 12 hours to 24 hours, and then vacuum drying at 50°C to 60°C for 4 hours to 8 hours.

[0025] A hydrogen proton exchange membrane fuel cell comprises the above-mentioned fluorine-free proton exchange membrane.

[0026] The beneficial effects of the present invention are: the fluorine-free proton exchange membrane of the present invention has a characteristic phase-separated continuous phase structure induced by the supramolecular interaction of molecular clusters, high ion transmission efficiency, good electrical conductivity, high thermal stability, good mechanical properties, high safety, and its manufacturing process is green and streamlined, the production cost is low, and it has a very broad application prospect.

[0027] Specifically:

[0028] 1) The polyoxometalate molecular clusters (hydrophilic) and the fluorine-free oxygen-containing organic polymer (hydrophobic) in the fluorine-free proton exchange membrane of the present invention have good compatibility. The oxygen-containing groups in the fluorine-free oxygen-containing organic polymer can provide binding sites that strongly interact with the polyoxometalate molecular clusters. The polyoxometalate molecular clusters are uniformly dispersed in the fluorine-free oxygen-containing organic polymer through hydrogen bonding. The polyoxometalate molecular clusters serve as a hydrophilic phase and a high proton source to form continuous ion conduction channels. The fluorine-free proton exchange membrane has a clear microphase structure, can exert high hydration capacity and effectively transfer protons under high humidity. At the same time, the strong binding energy between the fluorine-free oxygen-containing organic polymer and the polyoxometalate molecular clusters effectively solves the problem of the easy leakage of incorporated small molecule acids from the polymer matrix in existing organic-inorganic blend composite proton exchange membrane materials, thereby ensuring efficient ion transfer.

[0029] 2) The fluorine-free proton exchange membrane of the present invention is in a uniform solid film state in a dry state, has high ion transmission efficiency, good electrical conductivity, high thermal stability, good mechanical properties, and high safety, and is suitable for use in hydrogen proton exchange membrane fuel cells;

[0030] 3) The fluorine-free oxygen-containing organic polymer in the fluorine-free proton exchange membrane of the present invention can provide a structural support skeleton for the fluorine-free proton exchange membrane, thereby endowing the fluorine-free proton exchange membrane with high thermal stability and mechanical strength;

[0031] 4) The synthesis process of the fluorine-free proton exchange membrane of the present invention is simple and easy. It only requires dissolving the polyoxometalate molecular clusters and the fluorine-free oxygen-containing organic polymer in a solvent to form a uniform solution, and then casting the solution into a membrane. The product process quality is easy to control, and the production cost is greatly reduced compared to the commercial Nafion proton exchange membrane, which is conducive to industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a physical picture of the fluorine-free proton exchange membrane of Example 1.

[0033] Figure 2 shows the fluorine-free proton exchange membrane of Example 2, the fluorine-free proton exchange membrane of Example 3, and PW 12 SAXS spectrum of .

[0034] 3A is a TEM image of a polyvinyl butyral membrane; FIG. 3B is a TEM image of a fluorine-free proton exchange membrane of Example 2; and FIG. 3C is a TEM image of a fluorine-free proton exchange membrane of Example 3C.

[0035] FIG4 is a conductivity-temperature curve of the fluorine-free proton exchange membrane of Example 2, the fluorine-free proton exchange membrane of Example 3, and the Nafion membrane of the comparative example.

[0036] FIG5 is a polarization curve of a fuel cell assembled with the fluorine-free proton exchange membrane of Example 3 and the Nafion membrane of the comparative example.

[0037] FIG6 is a graph showing the operating stability test results of a fuel cell assembled with a fluorine-free proton exchange membrane according to Example 3.

[0038] FIG7 is a TG curve of the fluorine-free proton exchange membrane of Example 3. DETAILED DESCRIPTION

[0039] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0040] Example 1

[0041] A fluorine-free proton exchange membrane, the preparation method of which comprises the following steps:

[0042] 1) Phosphotungstic acid molecular cluster H3PW 12 O 40 ·mH2O(PW 12 ) and chitosan with a weight average molecular weight of 50000 g / mol were added to acetic acid, stirred at 55°C until uniform and transparent, and then concentrated at 70°C to obtain a coating solution with a mass fraction of 15% (PW 12 , chitosan mass ratio is 1:1);

[0043] 2) The coating liquid was spin-coated on a silica gel substrate, dried at 60° C. for 12 h, peeled off from the silica gel substrate, and vacuum-dried at 50° C. for 7 h to obtain a fluorine-free proton exchange membrane (thickness of about 100 μm).

[0044] A physical picture of the fluorine-free proton exchange membrane of this embodiment is shown in FIG1 .

[0045] As shown in Figure 1, the fluorine-free proton exchange membrane has a uniform texture, is bendable, and has good mechanical properties, and can be used as a diaphragm material in fuel cells.

[0046] Example 2

[0047] A fluorine-free proton exchange membrane, the preparation method of which comprises the following steps:

[0048] 1) Silicate tungstic acid molecular cluster H4SiW 12 O 40·mH2O(SiW 12 ) and polyvinyl butyral with a weight average molecular weight of 120,000 g / mol were added to ethanol, stirred at 55°C until uniform and transparent, and then concentrated at 70°C to obtain a coating solution with a mass fraction of 20% (SiW 12 , polyvinyl butyral (the mass ratio is 2:1);

[0049] 2) The coating liquid was spin-coated on a silica gel substrate, dried at 55° C. for 24 h, peeled off from the silica gel substrate, and vacuum-dried at 55° C. for 4 h to obtain a fluorine-free proton exchange membrane (thickness of about 100 μm).

[0050] Example 3

[0051] A fluorine-free proton exchange membrane, the preparation method of which comprises the following steps:

[0052] 1) Phosphotungstic acid molecular cluster H3PW 12 O 40 ·mH2O(PW 12 ) and polyvinyl butyral with a weight average molecular weight of 170000 g / mol were added to ethanol, stirred at 55°C until uniform and transparent, and then concentrated at 70°C to obtain a coating solution with a mass fraction of 40% (PW 12 , polyvinyl butyral (the mass ratio is 4:1);

[0053] 2) The coating liquid was spin-coated on a silica gel substrate, dried at 55° C. for 24 h, peeled off from the silica gel substrate, and vacuum-dried at 55° C. for 4 h to obtain a fluorine-free proton exchange membrane (thickness of about 100 μm).

[0054] Comparative Example

[0055] A Nafion membrane, the preparation method of which comprises the following steps:

[0056] 1) Dimethyl sulfoxide was added to a Nafion dispersion (model Nafion-D520, wherein the mass fraction of the resin was 5%) at a mass ratio of 1:9, and then concentrated at 80°C to obtain a 20% mass fraction Nafion solution (the mass fraction of the resin was 20%).

[0057] 2) The Nafion solution was spin-coated on a glass substrate, dried at 90°C for 36 h, peeled off from the glass substrate, activated with a 1 mol / L HCl aqueous solution at 60°C for 5 h, rinsed with deionized water several times (to rinse away residual HCl), and dried at 60°C for 12 h to obtain a Nafion membrane (about 100 μm thick).

[0058] Performance Testing

[0059] 1) Fluorine-free proton exchange membrane of Example 2, fluorine-free proton exchange membrane of Example 3 and phosphotungstic acid molecular cluster H3PW 12 O 40 ·mH2O(PW 12 ) is shown in Figure 2.

[0060] As shown in FIG2 , the phosphotungstic acid molecular clusters are uniformly dispersed in the fluorine-free proton exchange membranes of Examples 2 and 3.

[0061] 2) Transmission electron microscopy (TEM) images of the polyvinyl butyral membrane, the fluorine-free proton exchange membrane of Example 2, and the fluorine-free proton exchange membrane of Example 3 are shown in FIG3A , FIG3B , and FIG3C .

[0062] As can be seen from Figures 3A, 3B and 3C, the hydrophilic molecular clusters (dark areas in the figures) and the hydrophobic parts of the polymer (light areas in the figures) in the fluorine-free proton exchange membranes of Examples 2 and 3 form a microphase separation structure, while there is no phase separation structure in the polyvinyl butyral membrane, indicating that the hydrophilic molecular clusters can be combined with various groups on the hydrophobic polymer to induce the formation of two phases of hydrophilic molecular clusters and hydrophobic polymer. Among them, the molecular clusters act as proton donors and carriers, enabling protons to be efficiently transmitted in the channel, and the conductivity of the fluorine-free proton exchange membrane is greatly improved.

[0063] 3) The conductivity-temperature relationship curves of the fluorine-free proton exchange membrane of Example 2, the fluorine-free proton exchange membrane of Example 3, and the Nafion membrane of the comparative example (applying a small-amplitude AC potential wave of different frequencies to the electrochemical system, measuring the ratio of the AC potential to the current signal (i.e., the impedance of the system) as the sine wave frequency ω changes, or the phase angle Φ of the impedance changes as ω, and then calculating the ionic conductivity σ of the film sample) are shown in Figure 4. The conductivity test results of the fluorine-free proton exchange membranes of Examples 1 to 3 and the Nafion membrane of the comparative example at a temperature of 80°C and a relative humidity of 100% RH are shown in Table 1:

[0064] Table 1 Conductivity test results of fluorine-free proton exchange membranes of Examples 1 to 3 and Nafion membranes of comparative example

[0065] As shown in Figure 4 and Table 1, the fluorine-free proton exchange membranes of Examples 2 and 3 have high ionic conductivity in a medium temperature and high humidity environment of 30°C to 80°C, effectively realizing ion transfer in the molecular cluster ion conduction pathway of the proton exchange membrane in a hydrated environment.

[0066] 4) The fluorine-free proton exchange membrane of Example 3 and the Nafion membrane of the comparative example were assembled into a sandwich-type membrane electrode assembly (with the membrane in the middle and electrodes on both sides, with the attached catalyst layer facing inward and in contact with the membrane) by hot pressing with two gas diffusion electrodes (i.e., electrodes composed of a gas diffusion layer with a platinum catalyst loaded on a carbon paper substrate). The fuel cell was installed in a fuel cell experimental device for testing. The polarization curve obtained by the test is shown in Figure 5.

[0067] As shown in Figure 5, the power density of the fuel cell assembled with the fluorine-free proton exchange membrane of Example 3 is 1050 mW·cm at a temperature of 70°C and a relative humidity of 100%. -2 (open circuit potential is 0.96 V), which is greater than the 1019 mW·cm of the fuel cell assembled with the Nafion membrane in the comparative example. -2 (the open circuit potential is 0.90 V), indicating that the fluorine-free proton exchange membrane of the present invention can replace the Nafion membrane.

[0068] After testing (testing method is the same as above), the power density of the fuel cell assembled with the fluorine-free proton exchange membrane of Example 1 is 450mW·cm under the conditions of temperature of 70°C and relative humidity of 100%. -2 (open circuit potential is 0.94 V), the power density of the fuel cell assembled with the fluorine-free proton exchange membrane of Example 2 is 420 mW·cm under the conditions of temperature of 70°C and relative humidity of 100%. -2 (The open circuit potential is 0.92V).

[0069] 5) The results of the working stability test of the fuel cell assembled with the fluorine-free proton exchange membrane of Example 3 (under the conditions of temperature of 70° C. and relative humidity of 100%, with an external current of 0.25 A applied and continuous operation for 200 h) are shown in FIG6 .

[0070] As shown in FIG6 , the voltage of the fuel cell assembled with the fluorine-free proton exchange membrane of Example 3 only slightly decreases after continuous operation for 200 hours, indicating that the fluorine-free proton exchange membrane of the present invention has good working stability.

[0071] 6) The thermogravimetric (TG) curve of the fluorine-free proton exchange membrane of Example 3 is shown in FIG7 (the heating rate is 10° C. / min, and the set temperature range is 30° C. to 800° C.).

[0072] As shown in FIG7 , the extrapolated onset temperature of the fluorine-free proton exchange membrane of Example 3 is above 150° C., indicating that it has good thermal stability.

[0073] 7) The Young's modulus of the fluorine-free proton exchange membranes of Examples 1 to 3 and the Nafion membrane of the comparative example (measured by tensile testing at a tensile rate of 10 mm / min) is shown in Table 2:

[0074] Table 2 Young's modulus of the fluorine-free proton exchange membranes of Examples 1 to 3 and the Nafion membrane of the comparative example

[0075] It can be seen from Table 2 that the fluorine-free proton exchange membranes of Examples 1 to 3 have strong mechanical strength and mechanical properties.

[0076] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A fluorine-free proton exchange membrane, characterized in that: It comprises polyoxometalate molecular clusters and fluorine-free oxygen-containing organic polymers; the mass ratio of the polyoxometalate molecular clusters to the fluorine-free oxygen-containing organic polymer is (0.8-5):

1.

2. The fluorine-free proton exchange membrane according to claim 1, characterized in that: The polyoxometalate molecular cluster is at least one of a Keggin-type polyoxometalate molecular cluster, a Dawson-type polyoxometalate molecular cluster, and a pentavanadate-type polyoxometalate molecular cluster.

3. The fluorine-free proton exchange membrane according to claim 2, characterized in that: The general structural formula of the Keggin type polyoxometalate molecular cluster is as follows: n [XM 12 O 40 ] n- ·mH2O, wherein X represents the central atom, X is selected from at least one of P, Si, Co, and Al, Y represents the counter ion, Y is selected from at least one of H, Li, Na, and K, M represents the coordinating atom, M is selected from at least one of Nb, W, and Mo, m represents the number of crystal waters, the number of m depends on the self-bound water and the specific environmental humidity, m is an integer of 0 to 40, and n represents the number of charges carried by the polyanions / the number of counter ions, and n is 3, 4, or 6.

4. The fluorine-free proton exchange membrane according to claim 2, characterized in that: The general structural formula of the Dawson type polyoxometalate molecular cluster is as follows: n [X2M 18 O 62 ] n- ·mH2O, wherein X represents the central atom, X is selected from at least one of P, Si, Co, and Al, Y represents the counter ion, Y is selected from at least one of H, Li, Na, and K, M represents the coordinating atom, M is selected from at least one of Nb, W, and Mo, m represents the number of crystal waters, the number of m depends on the self-bound water and the specific environmental humidity, m is an integer of 0 to 60, and n represents the number of charges carried by the polyanions / the number of counter ions, and n is 3, 4, 6, or 8.

5. The fluorine-free proton exchange membrane according to claim 2, characterized in that: The structural formula of the pentavanadate-type polyoxometalate molecular cluster is Li7[V 15 O 36 (CO3)]·39H2O.

6. The fluorine-free proton exchange membrane according to any one of claims 1 to 5, characterized in that: The fluorine-free oxygen-containing organic polymer is at least one of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, chitosan and carboxymethyl cellulose.

7. The fluorine-free proton exchange membrane according to claim 6, characterized in that: The weight average molecular weight of the fluorine-free oxygen-containing organic polymer is 50,000 g / mol to 250,000 g / mol.

8. A method for preparing a fluorine-free proton exchange membrane according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: dispersing polyoxometalate molecular clusters and fluorine-free oxygen-containing organic polymers in a solvent to prepare a coating liquid, forming a film of the coating liquid on a substrate, and drying the film to obtain a fluorine-free proton exchange membrane.

9. The preparation method according to claim 8, characterized in that: The solvent is at least one of N,N-dimethylformamide, dimethyl sulfoxide, methanol, water, ethanol and acetic acid.

10. A hydrogen proton exchange membrane fuel cell, characterized in that: A fluorine-free proton exchange membrane comprising any one of claims 1 to 7.

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