Biomass-based organic-inorganic composite proton exchange membrane and preparation method thereof

Abstract

The invention relates to the field of fuel cells, and particularly discloses a biomass-based organic-inorganic composite proton exchange membrane and a preparation method thereof. The biomass-based organic-inorganic composite proton exchange membrane comprises a chitosan matrix and a sulfonated metal organic framework anchored with CeO2, the sulfonated metal organic framework anchored with CeO2 is dispersed in the chitosan matrix, and the addition amount of the sulfonated metal organic framework anchored with CeO2 is 0.5 wt.%-10 wt.% of chitosan. The preparation method comprises the following steps: 1) synthesizing nano cerium dioxide (CeO2) through a hydrothermal method; (2) preparing an aminated metal organic framework for anchoring CeO2; (3) preparing a sulfonated metal organic framework anchored with CeO2; 4) dispersing the sulfonated metal organic framework anchored with CeO2 into a chitosan solution, and casting to form a membrane, and 5) cross-linking the dry membrane with sulfuric acid to obtain the biomass-based organic-inorganic composite proton exchange membrane.The prepared composite membrane has significantly increased proton conductivity and oxidation stability, and the mechanical strength is obviously higher than that of an unmodified pure membrane.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and in particular to a biomass-based organic-inorganic composite proton exchange membrane and a preparation method thereof. Background Art

[0002] A fuel cell is an energy conversion device that can directly convert the chemical energy of a fuel (such as methanol, hydrogen, natural gas, etc.) into electrical energy. With its advantages of high energy conversion rate and low pollution, it meets the needs of the development of the times and has become one of the most promising power generation technologies. Among all types of fuel cells, proton exchange membrane fuel cells are the most widely studied, and the proton exchange membrane is the heart of the proton exchange membrane fuel cell. In the battery, it not only plays the role of transmitting protons, isolating electrons, and preventing oxygen and fuel from penetrating and contacting the positive and negative poles, but also has a high proton transmission capacity and maintains excellent proton conductivity and mechanical strength under high temperature and low humidity working conditions. The most widely used proton exchange membrane on the market is the perfluorosulfonic acid membrane produced by General Motors of the United States. A series of membranes have high conductivity at saturated humidity, but at high temperatures (>100°C) the membrane loses water, causing a sharp drop in conductivity, making them difficult to use in medium- and high-temperature fuel cells. Furthermore, the preparation process for these membranes is extremely complex and expensive, and the fuel permeation problem caused by methanol permeation is also very serious. Therefore, it is particularly important to find a proton exchange membrane with high proton conductivity and mechanical strength, relatively low price, and no serious fuel permeation.

[0003] Chitosan (CS) is a biomass polysaccharide that can be extracted from chitin. Chitin (also known as chitin) is widely found in the shells of marine arthropods such as crabs and shrimps, the shells of insects, the cell membranes of fungi and algae, the shells and bones of mollusks, and the cell walls of higher animals. It is inexpensive and has good film-forming properties. The film-forming process is simple and environmentally friendly (no organic solvents are required). The ring structure on the chitosan molecule ensures the thermochemical stability of the chitosan film. However, the dry chitosan film without modification has a thermal stability of only 10 -9The electrical conductivity of chitosan is 0.05 S / cm, which is equivalent to that of insulating materials, and its mechanical strength needs to be further improved. Although studies have shown that the proton conductivity of uncrosslinked and unmodified chitosan dry membranes at room temperature is not high, the presence of a large number of hydroxyl and amino groups in the chitosan molecular chain provides the possibility for its modification. There are generally two common methods for modifying chitosan for proton exchange membranes, namely chemical modification and organic-inorganic composite. Compared with chemical modification, the organic-inorganic composite method does not destroy the structure of the chitosan molecule, so it does not bring about the disadvantage of loss of mechanical properties. At the same time, the organic-inorganic composite method can significantly improve the mechanical properties of the chitosan membrane by uniformly dispersing inorganic particles in the chitosan matrix; at the same time, functionalized inorganic particles can also improve other properties of the chitosan membrane. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a biomass-based organic-inorganic composite proton exchange membrane and a preparation method thereof.

[0005] Metal organic framework (MOF) is a widely used ultra-porous nanomaterial. Through design and synthesis, a series of MOFs with specific functional groups can be prepared. The amino-containing MIL-101 chromium-based MOF (NH2-MIL-101-Cr) was synthesized by using chromium nitrate nonahydrate and 2-aminoterephthalic acid. 3+ Chitosan has good compatibility with this type of MOF due to its good adsorption effect. In addition, this type of MOF can be sulfonated through the ring-opening reaction of 1,3-propane sultone, that is, a sulfonic acid group is grafted on the amino group as a proton transfer site. Incorporating the sulfonated MOF into chitosan as a proton exchange membrane can not only improve the mechanical properties of the matrix, but also improve its proton conductivity. However, in the working environment of the fuel cell, a large number of free radicals will be generated. These free radicals will attack the chitosan molecules, resulting in degradation and fragmentation of the chitosan membrane. Cerium dioxide (CeO2) has a unique oxygen vacancy mechanism, which enables Ce(III) and Ce(IV) in it to convert into each other and consume free radicals. Therefore, cerium dioxide is also often used as a free radical scavenger in various fields. In this application, CeO2 is coupled and anchored to NH2-MIL-101-Cr generated in situ during the hydrothermal reaction through a hydrothermal reaction, and sulfonated to prepare a sulfonated metal organic framework anchoring CeO2, which is then composited with chitosan to improve the mechanical properties, proton conductivity and antioxidant properties of the chitosan membrane.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides a biomass-based organic-inorganic composite proton exchange membrane, wherein the biomass-based organic-inorganic composite proton exchange membrane comprises a chitosan matrix and a sulfonated metal organic framework Ce-MNS anchored with CeO2, wherein the Ce-MNS is dispersed in the chitosan matrix and its addition amount is 0.5wt.%-10wt.% of the chitosan;

[0007] The Ce-MNS is prepared by the following method: CeO2 nanoparticles and a MIL-101 type chromium-based MOF precursor with amino groups are prepared by an in-situ hydrothermal method to prepare an amino metal organic framework anchoring CeO2; then, sulfonic acid groups are grafted onto the amino metal organic framework anchoring CeO2 through a ring-opening reaction to prepare Ce-MNS.

[0008] The present invention also provides a method for preparing the above-mentioned biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0009] (1) Preparation of CeO2-anchored amino metal-organic frameworks

[0010] Chromium nitrate nonahydrate, 2-aminoterephthalic acid, and NaOH are added to deionized water and stirred thoroughly until the chromium nitrate nonahydrate is completely dissolved. CeO2 nanoparticles are then added and dispersed evenly to obtain a mixed solution. The mixture is subjected to a hydrothermal reaction at 140-180°C for 24-48 hours. The resulting crude product is washed and dried (preferably in a vacuum oven at 100°C for 10-24 hours) to obtain an amino metal organic framework anchored with CeO2.

[0011] (2) Preparation of CeO2-anchored sulfonated metal organic frameworks

[0012] 1,3-propane sultone is added to a dispersion of an amino metal organic framework anchored with CeO2, and the mixture is stirred and reacted at 80-120°C for 24-48 hours. After the reaction is cooled to room temperature, the mixture is poured into a solvent (preferably acetone or anhydrous ethanol) to dissolve unreacted 1,3-propane sultone, and the precipitate is collected by centrifugation. The precipitate is immersed in sulfuric acid (preferably 0.5M sulfuric acid) and acidified in an ice-water bath. Finally, the residual acid is removed by centrifugation and washing, and the sulfonated metal organic framework Ce-MNS anchored with CeO2 is obtained after drying (preferably at 80°C for 24 hours);

[0013] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g: 50-150 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:1-4;

[0014] (3) dispersing the Ce-MNS obtained in step (2) into a chitosan solution to obtain a uniform dispersion, and casting the dispersion into a film, wherein the Ce-MNS accounts for 0.5% to 10% of the mass of the chitosan;

[0015] (4) cross-linking the cast membrane obtained in step (3) with dilute sulfuric acid (preferably at a concentration of 0.5 to 2 M), and washing and drying the cross-linked membrane to obtain the biomass-based organic-inorganic composite proton exchange membrane.

[0016] Furthermore, the preparation method of the CeO2 nanoparticles is as follows: dissolve cerium nitrate hexahydrate in deionized water, and adjust the pH value to 8-10 with ammonia water, so that the solution changes from transparent to milky white, add the obtained solution into a hydrothermal reactor, seal it, and react at 120-180°C for 12-24h, cool it to room temperature, centrifuge, wash, dry, grind, and then calcine in a muffle furnace (preferably calcining at 500°C for 5h) to obtain CeO2 nanoparticles.

[0017] Furthermore, the washing operation in (1) is as follows: the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2 hours, centrifuged, and then dispersed in anhydrous ethanol, and refluxed at 80°C for 2 hours.

[0018] Furthermore, the molar concentration of chromium nitrate in the mixed solution (1) is 0.01-0.05M, the molar concentration of 2-aminoterephthalic acid is 0.01-0.05M, and the molar concentration of NaOH is 0.02-0.10M; and the molar ratio of CeO2 nanoparticles to chromium nitrate nonahydrate is 1:1.

[0019] Furthermore, in said (2), under nitrogen protection, the CeO2-anchored amino metal organic framework prepared in step (1) is stirred and dispersed in N,N-dimethylformamide to obtain a dispersion of the CeO2-anchored amino metal organic framework.

[0020] Furthermore, in (3), chitosan is dissolved in a 1-3 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 0.5 wt.% to 5 wt.%.

[0021] The present invention also provides the use of the above-mentioned biomass-based organic-inorganic composite proton exchange membrane or the biomass-based organic-inorganic composite proton exchange membrane prepared by the above-mentioned method in the preparation of a proton exchange membrane fuel cell.

[0022] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects and advantages compared with the existing technology:

[0023] 1. The chitosan-based composite proton exchange membrane modified by the sulfonated metal organic framework anchored with CeO2 provided by the present invention has a high conductivity and high refractive index. 3+ Good adsorption effect, so the chromium-based metal organic framework has good compatibility with the chitosan matrix, and the introduced sulfonic acid group can form an acid-base pair with the amino group in the chitosan structure, further promoting the good dispersion of the sulfonated metal organic framework anchored CeO2 in chitosan, and can increase the mechanical properties of the chitosan membrane (the tensile strength of the composite membrane increased by 13.2% to 72.5% compared with the pure chitosan membrane; under the same addition amount, the tensile strength of the composite membrane increased by 30.2% compared with the chitosan / metal organic framework composite membrane).

[0024] 2. The biomass-based organic-inorganic composite proton exchange membrane provided by the present invention can serve as a new proton transfer site in the composite membrane by introducing sulfonic acid groups on the amino metal organic framework anchored by CeO2, thereby playing a role in transferring protons, thereby improving the proton conductivity of the composite membrane (compared with the pure chitosan phase membrane, the conductivity of the composite membrane increased by 52% to 185%; under the same addition amount, the proton conductivity of the composite membrane increased by 71% compared with the chitosan / metal organic framework composite membrane, and increased by 63.3% compared with the chitosan / metal organic framework composite membrane anchored by CeO2).

[0025] 3. The biomass-based organic-inorganic composite proton exchange membrane provided by the present invention can effectively scavenge various free radicals (such as ·OOH and ·OH) generated during the battery reaction by anchoring cerium dioxide with free radical scavenging ability on the metal organic framework, thereby preventing free radicals from attacking chitosan molecules and causing membrane degradation, and effectively improving the oxidative stability of the composite membrane (the oxidative stability of the composite membrane is 1 to 2.3 times higher than that of the pure chitosan membrane; under the same addition amount, the oxidative stability of the composite membrane is increased by 73.3% compared with the chitosan / metal organic framework composite membrane and by 62.5% compared with the chitosan / sulfonated metal organic framework composite membrane).

[0026] In summary, the biomass-based organic-inorganic composite proton exchange membrane prepared by chitosan and sulfonated metal organic framework anchored CeO2 is expected to have broad application prospects in proton exchange membrane fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The infrared spectra of the CeO2-anchored amino metal organic framework and the CeO2-anchored sulfonated metal organic framework prepared in Example 1;

[0028] Figure 2Scanning electron micrographs of the CeO2-anchored amino metal-organic framework and the CeO2-anchored sulfonated metal-organic framework prepared in Example 1 (a and b are the CeO2-anchored amino metal-organic framework; c and d are the CeO2-anchored sulfonated metal-organic framework). DETAILED DESCRIPTION

[0029] The applicant will now further explain the technical solution of the present invention in detail with reference to specific embodiments and accompanying drawings, in order to enable those skilled in the art to have a clearer understanding and recognition of the present application.

[0030] The following specific embodiments should not be understood or interpreted in any way as limiting the scope of protection requested by the claims of this application.

[0031] The molecular weight of chitosan used in the following examples is 500,000.

[0032] Example 1: A method for preparing a biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0033] (1) 1.0 g of Ce(NO3)3·6H2O was dissolved in 45 mL of deionized water and the pH value was adjusted to 9 with ammonia. The solution changed from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 160°C for 18 h. After cooling to room temperature (25°C, the same below), the reaction was centrifuged and washed three times with deionized water. After drying and grinding, the solution was calcined in a muffle furnace at 500°C for 5 h (the heating rate of the muffle furnace was 10°C / min, the same below) to obtain CeO2 nanoparticles.

[0034] (2) Cr(NO3)3·9H2O, 2-aminoterephthalic acid, and NaOH were added to 10 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO2 nanoparticles obtained in step (1) were added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 24 h. After cooling to room temperature, the crude product was obtained by centrifugation and refluxed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal organic framework anchored with CeO2, wherein the amino metal organic framework is a MIL-101 type chromium-based MOF with an amino group.

[0035] In the mixed solution, the molar concentration of chromium nitrate is 0.015M, the molar concentration of 2-aminoterephthalic acid is 0.015M, and the molar concentration of NaOH is 0.03M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the reflux washing with N,N-dimethylformamide and anhydrous ethanol specifically comprises dispersing the crude product in N,N-dimethylformamide, refluxing at 90°C for 2h, centrifuging, and then dispersing in ethanol (all referring to anhydrous ethanol), refluxing at 80°C for 2h, and collecting the centrifuged product.

[0036] (3) The CeO2-anchored amino metal organic framework prepared in step (2) was stirred and dispersed in N,N-dimethylformamide at room temperature (25°C, the same below) under nitrogen protection to obtain a dispersion, and then 1,3-propane sultone was added to the dispersion, and the reaction was stirred at 90°C for 24 hours. After cooling to room temperature, the mixture was poured into acetone to dissolve the unreacted 1,3-propane sultone, and the precipitate was collected by centrifugation and immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid was removed by centrifugation and washing, and the mixture was dried at 80°C for 24 hours to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS.

[0037] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g:150 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:2.

[0038] (4) Chitosan was dissolved in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 2 wt.%, and the Ce-MNS obtained in step (3) was dispersed in the chitosan solution (wherein the mass of Ce-MNS was 4.5% of the mass of chitosan) to obtain a uniform dispersion, which was then cast into a membrane.

[0039] (5) The cast membrane obtained in step (4) was cross-linked with 0.5M dilute sulfuric acid (specifically, the cast membrane was immersed in dilute sulfuric acid for 2 hours, the same below). The cross-linked membrane was repeatedly rinsed with deionized water and then dried (dried in a 60°C oven for 24 hours, the same below) to obtain a biomass-based organic-inorganic composite proton exchange membrane. Comparative Example 1: Preparation of pure chitosan membrane, the steps are as follows:

[0040] Chitosan was dissolved in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 2 wt.%, and cast into a membrane; the cast membrane was cross-linked with 0.5 M dilute sulfuric acid, and the cross-linked membrane was repeatedly rinsed with deionized water and dried to obtain a pure chitosan membrane.

[0041] Comparative Example 2: Preparation of chitosan / metal organic framework composite membrane, the process is as follows:

[0042] (1) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 10 mL of deionized water and stirred thoroughly until the chromium nitrate nonahydrate was completely dissolved. The mixture was then transferred to a 100 mL hydrothermal reactor, sealed, and reacted at 160°C for 24 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain a metal-organic framework.

[0043] The molar concentration of chromium nitrate in the mixed solution is 0.015M, the molar concentration of 2-aminoterephthalic acid is 0.015M, and the molar concentration of NaOH is 0.03M; the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0044] (2) Dissolving chitosan in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 2 wt.%, dispersing the metal organic framework obtained in step (1) into the chitosan solution (wherein the mass of the metal organic framework is 4.5% of the mass of the chitosan) to obtain a uniform dispersion, and casting it into a membrane.

[0045] (3) cross-linking the cast membrane obtained in step (2) with 0.5M dilute sulfuric acid, repeatedly rinsing the cross-linked membrane with deionized water and then drying to obtain a chitosan / metal organic framework composite proton exchange membrane.

[0046] Comparative Example 3: Preparation of chitosan / sulfonated metal organic framework composite membrane, the process is as follows:

[0047] (1) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 10 mL of deionized water and stirred thoroughly until the chromium nitrate nonahydrate was completely dissolved. The mixture was then transferred to a 100 mL hydrothermal reactor, sealed, and reacted at 160°C for 24 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino-metal organic framework.

[0048] The molar concentration of chromium nitrate in the mixed solution is 0.015M, the molar concentration of 2-aminoterephthalic acid is 0.015M, and the molar concentration of NaOH is 0.03M; the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0049] (2) The amino metal organic framework prepared in step (1) is dispersed in N,N-dimethylformamide under nitrogen protection at room temperature with stirring to obtain a dispersion, and then 1,3-propane sultone is added to the dispersion, and the reaction is stirred at 90°C for 24 hours. After the reaction is cooled to room temperature, the mixture is poured into a large amount of acetone, the precipitate is collected by centrifugation, and the precipitate is immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid is removed by centrifugation and washing, and the mixture is dried at 80°C for 24 hours to obtain a sulfonated metal organic framework.

[0050] The ratio of the amino metal organic framework to N,N-dimethylformamide is 1 g:150 mL, and the molar ratio of the amino metal organic framework to 1,3-propane sultone is 1:2.

[0051] (3) Dissolving chitosan in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 2 wt.%, dispersing the sulfonated metal organic framework obtained in step (2) into the chitosan solution (wherein the mass of the sulfonated metal organic framework is 4.5% of the mass of the chitosan) to obtain a uniform dispersion, and casting it into a membrane.

[0052] (3) The cast membrane obtained in step (2) was cross-linked with 0.5M dilute sulfuric acid. The cross-linked membrane was repeatedly rinsed with deionized water and then dried to obtain a chitosan / sulfonated metal organic framework composite proton exchange membrane. Comparative Example 4: Preparation of a chitosan / anchored CeO2 metal organic framework composite membrane, the process is as follows:

[0053] (1) 1.0 g of Ce(NO₃)₃·6H₂O was dissolved in 45 mL of deionized water and the pH was adjusted to 9 with aqueous ammonia. The solution turned from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 160°C for 18 h. After cooling to room temperature, the reaction was centrifuged and washed three times with deionized water. After drying and grinding, the solution was calcined in a muffle furnace at 500°C for 5 h to obtain CeO₂ nanoparticles.

[0054] (2) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 10 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO₂ nanoparticles obtained in step (1) were then added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 24 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal-organic framework anchored with CeO₂.

[0055] In the mixed solution, the molar concentration of chromium nitrate is 0.015M, the molar concentration of 2-aminoterephthalic acid is 0.015M, and the molar concentration of NaOH is 0.03M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0056] (3) Dissolve chitosan in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 2 wt.%, disperse the CeO2-anchored amino metal organic framework obtained in step (2) into the chitosan solution (wherein the mass of the CeO2-anchored amino metal organic framework is 4.5% of the mass of the chitosan) to obtain a uniform dispersion, and cast it into a film.

[0057] (4) The cast membrane obtained in step (3) is cross-linked with 0.5M dilute sulfuric acid, and the cross-linked membrane is repeatedly rinsed with deionized water and then dried to obtain a chitosan / anchored CeO2 metal organic framework composite proton exchange membrane.

[0058] The performance test results of the films prepared in Example 1 and Comparative Examples 1-4 are shown in Table 1 (the thickness of each film is 60-80 μm).

[0059] Table 1

[0060]

[0061] from Figure 1 It can be seen that compared with the infrared spectrum of the CeO2-anchored amino metal organic framework, the characteristic peaks attributed to the sulfonic acid group in the infrared spectrum of the CeO2-anchored sulfonated metal organic framework appear at 1049 and 1209 cm -1 The sulfonic acid groups were successfully grafted onto the CeO2-anchored metal organic framework. The micromorphology of the metal organic framework and the sulfonated metal organic framework anchored CeO2 was characterized by SEM, as shown in Figure 2. Figure 2 As shown, it can be clearly observed that the metal organic framework exhibits a typical octahedral structure, which is consistent with the structure reported in the literature; the sulfonated metal organic framework anchored with CeO2 also exhibits an octahedral structure, indicating that the addition of CeO2 does not destroy the original structure of the metal organic framework, and there are many nanoparticles on the surface of the octahedron, which are CeO2 nanoparticles evenly distributed on the surface of the metal organic framework.

[0062] Example 2: A method for preparing a biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0063] (1) 1.0 g of Ce(NO₃)₃·6H₂O was dissolved in 30 mL of deionized water and the pH was adjusted to 8 with aqueous ammonia. The solution turned from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 180°C for 12 h. After cooling to room temperature, the reaction was centrifuged and washed three times with deionized water. After drying and grinding, the solution was calcined in a muffle furnace at 500°C for 5 h to obtain CeO₂ nanoparticles.

[0064] (2) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 50 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO₂ nanoparticles obtained in step (1) were then added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 36 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal-organic framework anchored with CeO₂.

[0065] In the mixed solution, the molar concentration of chromium nitrate is 0.01M, the molar concentration of 2-aminoterephthalic acid is 0.01M, and the molar concentration of NaOH is 0.02M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0066] (3) The CeO2-anchored amino metal organic framework prepared in step (2) was dispersed in N,N-dimethylformamide under nitrogen protection at room temperature with stirring to obtain a dispersion, and then 1,3-propanesulfonic acid lactone was added to the dispersion, and the reaction was stirred at 90°C for 48 hours. After the reaction was cooled to room temperature, the mixture was poured into a large amount of acetone, the precipitate was collected by centrifugation, and the precipitate was immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid was removed by centrifugation and washing, and the mixture was dried at 80°C for 24 hours to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS.

[0067] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g:50 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:1.

[0068] (4) Chitosan was dissolved in a 1 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 0.5 wt.%, and the Ce-MNS obtained in step (3) was dispersed in the chitosan solution (wherein the mass of Ce-MNS was 10% of the mass of chitosan) to obtain a uniform dispersion, which was then cast into a membrane.

[0069] (5) The cast membrane obtained in step (4) is cross-linked with 1.0 M dilute sulfuric acid, and the cross-linked membrane is repeatedly rinsed with deionized water and then dried to obtain a biomass-based organic-inorganic composite proton exchange membrane.

[0070] Example 3: A method for preparing a biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0071] (1) 1.0 g of Ce(NO₃)₃·6H₂O was dissolved in 60 mL of deionized water and the pH was adjusted to 10 with aqueous ammonia. The solution turned from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 120°C for 24 h. After cooling to room temperature, the reaction was centrifuged and washed three times with deionized water. After drying and grinding, the solution was calcined in a muffle furnace at 500°C for 5 h to obtain CeO₂ nanoparticles.

[0072] (2) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 25 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO₂ nanoparticles obtained in step (1) were then added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 48 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal-organic framework anchored with CeO₂.

[0073] In the mixed solution, the molar concentration of chromium nitrate is 0.05M, the molar concentration of 2-aminoterephthalic acid is 0.05M, and the molar concentration of NaOH is 0.10M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0074] (3) The CeO2-anchored amino metal organic framework prepared in step (2) was dispersed in N,N-dimethylformamide under nitrogen protection at room temperature with stirring to obtain a dispersion, and then 1,3-propane sultone was added to the dispersion, and the reaction was stirred at 90°C for 36 hours. After the reaction was cooled to room temperature, the mixture was poured into a large amount of acetone, the precipitate was collected by centrifugation, and the precipitate was immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid was removed by centrifugation and washing, and the mixture was dried at 80°C for 24 hours to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS.

[0075] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g:100 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:4.

[0076] (4) Chitosan was dissolved in a 3 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 5 wt.%, and the Ce-MNS obtained in step (3) was dispersed in the chitosan solution (wherein the mass of Ce-MNS was 0.5% of the mass of chitosan) to obtain a uniform dispersion, which was then cast into a membrane.

[0077] (5) The cast membrane obtained in step (4) is cross-linked with 2M dilute sulfuric acid, and the cross-linked membrane is repeatedly rinsed with deionized water and then dried to obtain a biomass-based organic-inorganic composite proton exchange membrane.

[0078] Example 4: A method for preparing a biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0079] (1) 1.0 g of Ce(NO₃)₃·6H₂O was dissolved in 50 mL of deionized water and the pH was adjusted to 9 with ammonia. The solution turned from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 150°C for 20 h. After cooling to room temperature, the solution was centrifuged and washed three times with deionized water. After drying and grinding, the solution was calcined in a muffle furnace at 500°C for 5 h to obtain CeO₂ nanoparticles.

[0080] (2) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 40 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO₂ nanoparticles obtained in step (1) were then added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 40 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal-organic framework anchored with CeO₂.

[0081] In the mixed solution, the molar concentration of chromium nitrate is 0.03M, the molar concentration of 2-aminoterephthalic acid is 0.03M, and the molar concentration of NaOH is 0.06M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the crude product is refluxed and rinsed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0082] (3) The CeO2-anchored amino metal organic framework prepared in step (2) was dispersed in N,N-dimethylformamide under nitrogen protection at room temperature with stirring to obtain a dispersion, and then 1,3-propanesulfonic acid lactone was added to the dispersion, and the reaction was stirred at 90°C for 40 hours. After the reaction was cooled to room temperature, the mixture was poured into a large amount of acetone, the precipitate was collected by centrifugation, and the precipitate was immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid was removed by centrifugation and washing, and the mixture was dried at 80°C for 24 hours to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS.

[0083] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g:80 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:3.

[0084] (4) Chitosan was dissolved in a 1.5 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 1 wt.%, and the Ce-MNS obtained in step (3) was dispersed in the chitosan solution (wherein the mass of Ce-MNS was 2% of the mass of chitosan) to obtain a uniform dispersion, which was then cast into a membrane.

[0085] (5) The cast membrane obtained in step (4) is cross-linked with 1.5M dilute sulfuric acid, and the cross-linked membrane is repeatedly rinsed with deionized water and then dried to obtain a biomass-based organic-inorganic composite proton exchange membrane.

[0086] Example 5: A method for preparing a biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0087] (1) 1.0 g of Ce(NO₃)₃·6H₂O was dissolved in 40 mL of deionized water and the pH was adjusted to 9 with ammonia. The solution changed from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 160°C for 12 h. After cooling to room temperature, the reaction was centrifuged and repeatedly washed with deionized water. After drying and grinding, the solution was calcined at 500°C in a muffle furnace for 5 h to obtain CeO₂ nanoparticles.

[0088] (2) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 50 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO₂ nanoparticles obtained in step (1) were then added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 30 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal-organic framework anchored with CeO₂.

[0089] In the mixed solution, the molar concentration of chromium nitrate is 0.04M, the molar concentration of 2-aminoterephthalic acid is 0.04M, and the molar concentration of NaOH is 0.08M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0090] (3) The CeO2-anchored amino metal organic framework prepared in step (2) was dispersed in N,N-dimethylformamide under nitrogen protection at room temperature with stirring to obtain a dispersion, and then 1,3-propane sultone was added to the dispersion, and the reaction was stirred at 90°C for 24 hours. After the reaction was cooled to room temperature, the mixture was poured into a large amount of acetone, the precipitate was collected by centrifugation, and the precipitate was immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid was removed by centrifugation and washing, and the mixture was dried at 80°C for 24 hours to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS.

[0091] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g:120 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:2.

[0092] (4) Chitosan was dissolved in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 3 wt.%, and the Ce-MNS obtained in step (3) was dispersed in the chitosan solution (wherein the mass of Ce-MNS was 6% of the mass of chitosan) to obtain a uniform dispersion, which was then cast into a membrane.

[0093] (5) The cast membrane obtained in step (4) is cross-linked with 1.0 M dilute sulfuric acid, and the cross-linked membrane is repeatedly rinsed with deionized water and then dried to obtain a biomass-based organic-inorganic composite proton exchange membrane.

[0094] Example 6: A method for preparing a biomass-based organic-inorganic composite proton exchange membrane, comprising the following steps:

[0095] (1) 1.0 g of Ce(NO₃)₃·6H₂O was dissolved in 50 mL of deionized water and the pH was adjusted to 9 with ammonia. The solution changed from transparent to milky white. The resulting solution was added to a 100 mL hydrothermal reactor, sealed, and reacted at 160°C for 20 h. After cooling to room temperature, the reaction was centrifuged and repeatedly washed with deionized water. After drying and grinding, the solution was calcined in a muffle furnace at 500°C for 5 h to obtain CeO₂ nanoparticles.

[0096] (2) Cr(NO₃)₃·9H₂O, 2-aminoterephthalic acid, and NaOH were added to 25 mL of deionized water and stirred thoroughly until chromium nitrate nonahydrate was completely dissolved. The CeO₂ nanoparticles obtained in step (1) were then added and uniformly dispersed. The mixture was then transferred to a hydrothermal reactor and reacted at 160°C for 40 h. After cooling to room temperature, the crude product was obtained by centrifugation and rinsed with N,N-dimethylformamide and anhydrous ethanol. The solid product was collected and dried in a vacuum oven at 100°C for 10 h to obtain an amino metal-organic framework anchored with CeO₂.

[0097] In the mixed solution, the molar concentration of chromium nitrate is 0.02M, the molar concentration of 2-aminoterephthalic acid is 0.02M, and the molar concentration of NaOH is 0.04M; the amount of CeO2 nanoparticles added is: CeO2: chromium nitrate nonahydrate = 1:1 (molar ratio); the crude product is refluxed and washed with N,N-dimethylformamide and anhydrous ethanol, specifically, the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2h, centrifuged, and then dispersed in ethanol, refluxed at 80°C for 2h, and the centrifuged product is collected.

[0098] (3) The CeO2-anchored amino metal organic framework prepared in step (2) was dispersed in N,N-dimethylformamide under nitrogen protection at room temperature with stirring to obtain a dispersion, and then 1,3-propane sultone was added to the dispersion, and the reaction was stirred at 90°C for 24 hours. After the reaction was cooled to room temperature, the mixture was poured into a large amount of acetone, the precipitate was collected by centrifugation, and the precipitate was immersed in 0.5M sulfuric acid for ice-water bath acidification. Finally, the residual acid was removed by centrifugation and washing, and the mixture was dried at 80°C for 24 hours to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS.

[0099] The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g:60 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1:2.

[0100] (4) Chitosan was dissolved in a 2 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 1 wt.%, and the Ce-MNS obtained in step (3) was dispersed in the chitosan solution (wherein the mass of Ce-MNS was 8% of the mass of chitosan) to obtain a uniform dispersion, which was then cast into a membrane.

[0101] (5) The cast membrane obtained in step (4) is cross-linked with 2M dilute sulfuric acid, and the cross-linked membrane is repeatedly rinsed with deionized water and then dried to obtain a biomass-based organic-inorganic composite proton exchange membrane.

[0102] The performance test results of the films prepared in Examples 1 to 6 are shown in Table 2 (the thickness of each film is 60-80 microns).

[0103] Table 2

[0104]

[0105] As can be seen from Table 2, the proton conductivity and tensile strength of the composite membranes prepared in Examples 1-6 are better than those of the pure chitosan membrane, wherein the proton conductivity is increased by 52% to 185% compared with the pure chitosan membrane, the tensile strength is increased by 13.7% to 72.5% compared with the pure chitosan membrane, and the oxidative stability is increased by 1 to 2.3 times compared with the pure chitosan membrane.

[0106] Membrane performance test method:

[0107] (1) Tensile strength: The film sample was cut into rectangular strips with a length × width = 40 × 10 mm. A tensile test was performed on a universal material testing machine at room temperature using a tensile rate of 2 mm / min. The maximum tensile stress to which the film sample was subjected until it broke was recorded as the tensile strength.

[0108] (2) Proton conductivity: The resistance of the membrane was tested on a frequency response analyzer with a frequency sweep range of 1-10 6 Hz, with an AC signal amplitude of 50 mV. A cut membrane (length × width = 3 cm × 2 cm) was tested using a two-electrode AC impedance method. Prior to testing, the membrane sample was saturated in room-temperature deionized water. The membrane's proton conductivity, σ (S / cm), was calculated using the following formula:

[0109]

[0110] Where L and A are the distance between the two electrodes and the effective cross-sectional area of ​​the membrane to be measured between the two electrodes, respectively; R is the resistance of the membrane, which is obtained from the Nyquist plot obtained from the AC impedance test.

[0111] (3) Oxidative Stability: Oxidative stability was characterized by using Fenton's reagent (2 ppm FeSO₄ in a 3 wt.% H₂O₂ solution) to simulate the operating environment of a fuel cell. Composite membranes were cut to the same size (1.5 cm × 4 cm). The specimens were then immersed in the Fenton's solution at 80°C, and the time required for them to break was recorded. The measurement was repeated three or more times, and the average value was calculated.

[0112] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principles of the present invention shall be deemed equivalent replacements and included within the scope of protection of the present invention.

Claims

1. A biomass-based organic-inorganic composite proton exchange membrane, comprising a chitosan matrix and a sulfonated metal organic framework (Ce-MNS) anchored with CeO2, wherein the Ce-MNS is dispersed in the chitosan matrix and added in an amount of 0.5 wt.% to 10 wt.% of the chitosan matrix; The Ce-MNS is prepared by the following method: CeO2 nanoparticles and a MIL-101 type chromium-based MOF precursor with amino groups are prepared by an in-situ hydrothermal method to prepare an amino metal organic framework anchoring CeO2; then, sulfonic acid groups are grafted onto the amino metal organic framework anchoring CeO2 through a ring-opening reaction to prepare Ce-MNS.

2. The method for preparing the biomass-based organic-inorganic composite proton exchange membrane according to claim 1, comprising the following steps: (1) Preparation of CeO2-anchored amino metal-organic frameworks Chromium nitrate nonahydrate, 2-aminoterephthalic acid, and NaOH were added to deionized water and stirred thoroughly until the chromium nitrate nonahydrate was completely dissolved. CeO2 nanoparticles were then added and dispersed evenly to obtain a mixed solution. The mixture was hydrothermally reacted at 140-180°C for 24-48 hours. The resulting crude product was washed and dried to obtain an amino metal organic framework anchored with CeO2. (2) Preparation of sulfonated metal organic framework anchored with CeO2 Then, 1,3-propane sultone is added to the dispersion of the CeO2-anchored amino metal organic framework, and the reaction is stirred at 80-120°C for 24-48 hours. After the reaction is cooled to room temperature, the mixture is poured into a solvent to dissolve the unreacted 1,3-propane sultone, and the precipitate is collected and immersed in sulfuric acid for ice-water bath acidification. After removing the residual acid, the precipitate is dried to obtain the CeO2-anchored sulfonated metal organic framework Ce-MNS. The ratio of the CeO2-anchored amino metal organic framework to N,N-dimethylformamide is 1 g: 50 ~ 150 mL, and the molar ratio of the CeO2-anchored amino metal organic framework to 1,3-propane sultone is 1: 1 ~ 4; (3) dispersing the Ce-MNS obtained in step (2) into a chitosan solution to obtain a uniform dispersion, and casting the dispersion into a film, wherein the Ce-MNS accounts for 0.5% to 10% of the mass of the chitosan; (4) cross-linking the cast membrane obtained in step (3) with dilute sulfuric acid, and washing and drying the cross-linked membrane to obtain the biomass-based organic-inorganic composite proton exchange membrane.

3. The preparation method according to claim 2, characterized in that The solvent is acetone or anhydrous ethanol.

4. The preparation method according to claim 2, characterized in that The washing operation in (1) is as follows: the crude product is dispersed in N,N-dimethylformamide, refluxed at 90°C for 2 h, centrifuged, and then dispersed in anhydrous ethanol and refluxed at 80°C for 2 h.

5. The preparation method according to claim 2, characterized in that The molar concentration of chromium nitrate in the mixed solution (1) is 0.01-0.05 M, the molar concentration of 2-aminoterephthalic acid is 0.01-0.05 M, and the molar concentration of NaOH is 0.02-0.10 M; the molar ratio of CeO2 nanoparticles to chromium nitrate nonahydrate is 1:

1.

6. The preparation method according to claim 2, characterized in that In the above (2), under nitrogen protection, the CeO2-anchored amino metal organic framework prepared in step (1) is stirred and dispersed in N,N-dimethylformamide to obtain a dispersion of the CeO2-anchored amino metal organic framework.

7. The preparation method according to claim 2, characterized in that In the above (3), chitosan is dissolved in a 1-3 vol.% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 0.5 wt.%-5 wt.%.

8. Use of the biomass-based organic-inorganic composite proton exchange membrane according to claim 1 or the biomass-based organic-inorganic composite proton exchange membrane obtained by the preparation method according to any one of claims 2 to 7 in the preparation of a proton exchange membrane fuel cell.

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