Ce-mof doped nafion composite proton exchange membrane, and preparation method and use thereof

Abstract

The present application relates to a kind of Ce-MOF doped Nafion composite proton exchange membrane and its preparation method and purposes, the Ce-MOF doped Nafion composite proton exchange membrane includes Nafion composite proton exchange membrane and Ce-MOF;Metal site in the Ce-MOF is Ce;The amino group is contained in the Ce-MOF.By introducing Ce element, using Ce as radical quencher, effectively eliminate free radicals, reversible redox pair Ce 3+ And Ce 4+ , inhibit polymer chain chemical degradation, help to improve the durability of proton exchange membrane, improve the oxidation resistance of proton exchange membrane.Simultaneously through MOF skeleton anchoring Ce ion position, effectively solve the problem of Ce loss after long time work, while introducing amino and sulfonic acid group on Nafion chain form proton transport channel, ensure the proton conductivity of membrane.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane electrolysis for hydrogen production, and particularly to a Ce-MOF-doped Nafion composite proton exchange membrane, its preparation method, and its applications. Background Technology

[0002] Proton exchange membrane electrolysis (PEMWE) is considered a promising technology for producing green hydrogen due to its high efficiency, high reliability, and rapid response. Currently, the most widely used proton exchange membrane (PEM) is the perfluorosulfonic acid (Nafion) membrane developed by DuPont. This membrane features high proton conductivity at room temperature and good mechanical stability, but it also suffers from drawbacks such as complex manufacturing processes, high cost, and poor stability.

[0003] Metal-organic frameworks (MOFs) have been among the most attractive porous materials since their inception, possessing excellent characteristics such as tunable pore size, regular void cages, and tunable surface properties. As potential novel proton conductors, they have been used to modify and improve existing proton exchange membranes, enhancing their proton conductivity and other properties. Among the tetravalent metals that can be used to form M-MOFs (M = Ti, Zr, Hf, Ce, U, Th, etc.), Ce(IV) has a low-occupancy 4f orbital, which can accelerate charge transfer from ligands to the metal. It also possesses the ability to switch between oxidized (IV) and reduced (III) states, utilizing the switching between different valence states to scavenge free radicals. Therefore, it can be introduced into proton exchange membranes as a free radical quencher, enhancing the membrane's chemical stability.

[0004] CN117603543A discloses a de-MOF / Nafion composite membrane, its preparation method, and its applications. The secondary structural units of de-MOF possess inorganic polyacid properties and can be used as proton sources to dope into Nafion membranes. A dynamic hydrogen bond network is formed within the Nafion membrane, enabling water storage and efficient proton transfer via a hopping mechanism, thereby improving the proton conductivity of the Nafion membrane. This composite membrane is obtained by immersing a Nafion membrane in a de-MOF dispersion and stirring for two days. However, it suffers from problems such as easy MOF loss and does not address the study of water absorption, swelling, and antioxidant properties of the composite membrane under different temperature conditions.

[0005] CN117209825A discloses a polymer hybrid proton exchange membrane modified with a metal-organic framework (MOF-NH2) functionalized with a -PO3H2 / -NH2 acid-base pair. The proton exchange membrane incorporates a -PO3H2 / -NH2 acid-base pair functionalized MOF-NH2 to hybridize the polymer. The porous structure of P-MOF-NH2 and the modification with hydrophilic groups -PO3H2 and -NH2 give P-MOF-NH2 high water affinity, significantly enhancing the membrane's water retention capacity and thus promoting proton conduction. This composite membrane exhibits good conductivity and stability, but it does not address the issue of resisting free radical attack to improve the chemical stability of the proton exchange membrane.

[0006] Existing technologies suffer from drawbacks such as complex preparation processes, low electrical conductivity of Nafion membranes at high temperatures, and poor chemical durability. Therefore, improving the electrical conductivity and chemical durability of Nafion composite proton exchange membranes has become an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a Ce-MOF-doped Nafion composite proton exchange membrane, its preparation method, and its applications. The Ce-MOF-doped Nafion composite proton exchange membrane of the present invention exhibits high proton transport rate and redox capability, and high catalytic activity and stability within an operating temperature range of 25-130℃.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a Ce-MOF-doped Nafion composite proton exchange membrane, wherein the Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and a Ce-MOF; the metal site in the Ce-MOF is Ce; and the Ce-MOF contains amino groups.

[0010] To address the issue of Nafion membranes being easily degraded by free radicals during use, this invention introduces Ce as a free radical quencher, effectively scavenging free radicals and providing reversible redox reactions with Ce. 3+ and Ce 4+ It inhibits the chemical degradation of polymer chains, which is beneficial to improving the durability of proton exchange membranes and enhancing their antioxidant properties.

[0011] On the other hand, considering the disadvantage of easy migration of Ce ions, this invention uses an MOF framework to anchor the Ce ion position, effectively solving the problem of Ce loss after long-term operation. At the same time, it introduces amino groups and sulfonic acid groups on the Nafion chain to form proton transport channels, ensuring the proton conductivity of the membrane.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] Preferably, the mass fraction of the Ce-MOF is 1wt%-9wt%, for example, it can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, or 9wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 4wt%-6wt%.

[0014] The present invention further adjusts the mass fraction of Ce-MOF to 1wt%-9wt%, so that the Ce-MOF-doped Nafion composite proton exchange membrane has better conductivity, which can significantly improve the Fenton mass loss rate. In addition, the prepared composite proton exchange membrane has high mechanical properties and exhibits high electrolysis current in the process of water electrolysis to produce hydrogen. If the mass fraction of Ce-MOF is less than 1 wt%, the interaction between -NH2 and -SO3H caused by the small amount of doping makes it difficult to form a continuous hydrogen bond network, increasing the uncertainty of proton transport and reducing the conductivity of the Ce-MOF-doped Nafion composite proton exchange membrane. If the mass fraction of Ce-MOF is higher than 9 wt%, the Ce-MOF powder inside the composite membrane is severely agglomerated, which disrupts the orderly establishment of proton transport channels inside the membrane, increases the number of defect sites, and leads to a decrease in the conductivity of the Ce-MOF-doped Nafion composite proton exchange membrane. The composite membrane becomes more brittle, and the tensile strength and electrolysis voltage also decrease. The present invention further optimizes the Ce-MOF mass fraction in the Ce-MOF-doped Nafion composite proton exchange membrane to be 4 wt%-6 wt%, at which point the overall performance is the best.

[0015] Preferably, the Ce-MOF includes UIO-66.

[0016] The Ce-MOF of this invention includes UIO-66. Compared with the conventional method of anchoring CeO2 on fibers and nanotubes, the strong bonding between the metal ions and organic ligands of the MOF solves the problem of Ce ion migration. Furthermore, by utilizing the tunable surface properties of UIO-66 and through the synergistic effect of the loaded -NH2 and -SO3H functional groups, the conductivity of the proton exchange membrane is also guaranteed.

[0017] In a second aspect, the present invention provides a method for preparing a Ce-MOF-doped Nafion composite proton exchange membrane as described in the first aspect, the method comprising the following steps:

[0018] (1) Mix cerium salt, amino-containing organic ligand, water and ethanol, and react in the first reaction to obtain amino-containing Ce-MOF;

[0019] (2) Mix the amino-containing Ce-MOF with Nafion solution, and carry out a second reaction to obtain a dispersion. After casting and annealing, the dispersion is used to obtain the Ce-MOF-doped Nafion composite proton exchange membrane.

[0020] In the preparation of metal-organic frameworks, this invention uses amino-containing organic ligands as organic ligands to prepare metal-organic frameworks with amino groups. Subsequently, the interaction between the amino groups and the sulfonic acid groups on the Nafion chain facilitates the formation of proton transport channels with low steric hindrance, ensuring the proton conductivity of the membrane. The preparation method of the Ce-MOF-doped Nafion composite proton exchange membrane of this invention is simple, low-cost, mild, and environmentally friendly.

[0021] Preferably, the cerium salt comprises a tetravalent cerium salt.

[0022] Preferably, the tetravalent cerium salt includes any one or a combination of at least two of cerium ammonium nitrate, cerium acetate, or cerium sulfate, wherein typical but non-limiting combinations include a combination of cerium ammonium nitrate and cerium acetate, a combination of cerium acetate and cerium sulfate, a combination of cerium ammonium nitrate and cerium sulfate, or a combination of cerium ammonium nitrate, cerium acetate, and cerium sulfate.

[0023] Preferably, the amino-containing organic ligand includes 2-aminoterephthalic acid.

[0024] Preferably, the molar ratio of the cerium salt to the amino-containing organic ligand is (3-5):(2-8), for example, it can be 3:2, 3.4:3, 3.5:3.2, 4:3, 4.5:5.7, 4:7 or 5:8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] This invention regulates the structure of the Ce-MOF generated by further controlling the molar ratio of cerium salt to amino-containing organic ligands to satisfy (3-5):(2-8), resulting in a more complete structure with suitable pore structure. This also affects the conductivity and mechanical properties of the prepared Ce-MOF-doped Nafion composite proton exchange membrane. If the molar ratio of cerium salt or amino-containing organic ligands is too large or too small, it will lead to a decrease in the number of crystal nuclei, or even no nucleation at all.

[0026] Preferably, acetic acid is added before the first reaction.

[0027] In this invention, acetic acid can maintain the acid-base environment of the reaction system, promote the formation of UIO-66 structure, and the addition of acetic acid is more conducive to the formation of a uniform solution, ensuring the uniform distribution of metal ions and suppressing side reactions, which helps to achieve better and purer crystal growth.

[0028] Preferably, the volume ratio of acetic acid, water, and ethanol is (5-10):(15-30):(30-60), for example, it can be 5:15:30, 5:20:30, 6:15:30, 6:20:40, 7:15:30, 7:20:30, 7:20:35, 7:20:40, 8:25:30, 8:30:30, 8:20:35, 8:20:40, 8:25:40, 8:25:50, 9:25:30, 9:30:30, 9:20:35, 10:20:40, 10:25:40, 10:25:50, 10:25:60, or 10:30:60, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] In this invention, ethanol acts as a medium during the synthesis process, affecting the dispersion and assembly of cerium ions and amino-containing organic ligand molecules. The presence of ethanol molecules helps to generate ordered structures, thereby affecting the pore structure and specific surface area of ​​MOFs.

[0030] Step (1) after the first reaction also includes washing and a first drying.

[0031] Preferably, the washing steps are as follows: washing with water and / or ethanol 3 to 6 times, for example, 3, 4, 5 or 6 times.

[0032] Preferably, the first drying includes vacuum drying.

[0033] Preferably, the temperature of the first drying is 60℃-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the first drying time is 12h-24h, for example, it can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the method for preparing the Nafion solution includes: drying the Nafion aqueous alcohol solution to obtain Nafion resin, and mixing the Nafion resin with a solvent to obtain the Nafion solution.

[0036] Preferably, the Nafion aqueous alcohol solution includes any one or a combination of at least two of Nafion D2020 solution, Nafion D1020 solution, or Nafion D520 solution, wherein typical but non-limiting combinations include combinations of Nafion D2020 solution and Nafion D1020 solution, combinations of Nafion D1020 solution and Nafion D520 solution, combinations of Nafion D2020 solution and Nafion D520 solution, and combinations of Nafion D2020 solution, Nafion D1020 solution, and Nafion D520 solution.

[0037] Preferably, the drying temperature is 60℃-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0038] Preferably, the solvent comprises any one or a combination of at least two of anhydrous ethanol, isopropanol, N,N-dimethylformamide, or N,N-dimethylacetamide, wherein typical but non-limiting combinations include combinations of anhydrous ethanol and isopropanol, combinations of isopropanol and N,N-dimethylformamide, combinations of N,N-dimethylformamide and N,N-dimethylacetamide, combinations of anhydrous ethanol, isopropanol, and N,N-dimethylformamide, and combinations of anhydrous ethanol, isopropanol, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0039] Preferably, the mass fraction of Nafion resin in the Nafion solution is 5wt%-20wt%, for example, it can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the temperature of the second reaction in step (2) is 60℃-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the reaction time in step (2) is 12h-24h, for example, it can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, step (2) after the second reaction includes ultrasonic dispersion for 0.5h-1h, for example, 0.5h, 0.6h, 0.8h or 1h, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0043] Preferably, step (2) includes a second drying process after pouring.

[0044] Preferably, the temperature of the second drying is 60℃-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0045] Preferably, the second drying time is 12h-24h, for example, it can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the annealing temperature is 100℃-150℃, for example, it can be 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Preferably, the annealing time is 2h-12h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0049] (1) A mixture of cerium ammonium nitrate, 2-aminoterephthalic acid, acetic acid, water and ethanol is prepared, wherein the molar ratio of cerium ammonium nitrate to 2-aminoterephthalic acid is (3-5):(2-8); and the volume ratio of acetic acid, water and ethanol is (5-10):(15-30):(30-60). The mixture is subjected to a first reaction, and washed 3-6 times with water and / or ethanol respectively. The mixture is then vacuum dried at 60℃-80℃ for 12-24h to obtain an amino-containing Ce-MOF.

[0050] (2) Nafion water-alcohol solution was dried at 60℃-80℃ to obtain Nafion resin. Nafion resin was mixed with solvent and stirred at 70℃-80℃ for 12h-24h to obtain Nafion solution with a mass fraction of 5wt%-20wt%.

[0051] (3) The amino-containing Ce-MOF from step (1) and the Nafion solution from step (2) are mixed and subjected to a second reaction at 60℃-80℃ for 12h-24h, followed by ultrasonic dispersion for 0.5h-1h to obtain a dispersion. The dispersion is then poured into a 7.5cm×7.5cm glass tank, dried at 60℃-80℃ for 12h-24h, and annealed at 100℃-150℃ for 2h-12h to obtain the Ce-MOF-doped Nafion composite proton exchange membrane.

[0052] Thirdly, the present invention provides a use of the Ce-MOF-doped Nafion composite proton exchange membrane as described in the first aspect, wherein the Ce-MOF-doped Nafion composite proton exchange membrane is used for hydrogen production by water electrolysis.

[0053] This invention relates to a Ce-MOF-doped Nafion composite proton exchange membrane for hydrogen production via water electrolysis, which improves proton conductivity and enhances membrane chemical stability. The simple functionalization of MOFs allows for effective modification of hydrophilic groups, providing active sites for proton transport. Simultaneously, the strength of their metal-oxygen bond and unique geometry significantly preserves Ce ion content. The Ce-MOF-doped Nafion composite proton exchange membrane improves proton conductivity, thermal stability, and chemical and physical durability. These properties contribute to increased efficiency and reduced cost in water electrolysis for hydrogen production. Furthermore, it broadens the operating temperature range and lifespan of the proton exchange membrane, reduces water absorption and swelling, and ensures dimensional stability of the composite membrane.

[0054] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) This invention introduces Ce element and utilizes Ce as a free radical quencher to effectively scavenge free radicals. Reversible redox reactions with Ce 3+ and Ce 4+ Inhibiting the chemical degradation of polymer chains is beneficial to improving the durability and antioxidant performance of proton exchange membranes. On the other hand, considering the easy migration of Ce ions, this invention uses Ce-MOF containing amino groups to anchor Ce ion positions through the MOF framework, effectively solving the problem of Ce loss after long-term operation. At the same time, the introduction of amino groups and sulfonic acid groups on the Nafion chain forms proton transport channels, ensuring the proton conductivity of the membrane.

[0057] (2) In the process of preparing metal-organic frameworks, 2-aminoterephthalic acid is used as an organic ligand to prepare metal-organic frameworks with amino groups. Subsequently, the interaction between the amino group and the sulfonic acid group on the Nafion chain is beneficial to the formation of proton transport channels with low steric hindrance, thus ensuring the proton conductivity of the membrane. The preparation method of Ce-MOF-doped Nafion composite proton exchange membrane of the present invention is simple, low-cost, mild, and environmentally friendly.

[0058] (3) The Ce-MOF-doped Nafion composite proton exchange membrane of this invention is used to improve proton conductivity and enhance the chemical stability of the membrane in water electrolysis for hydrogen production. The simple functionalization of MOFs allows them to effectively modify hydrophilic groups, providing active sites for proton transfer. At the same time, the strength of their metal ion-oxygen ion bonds and their unique geometric structure greatly preserve the Ce ion content. The Ce-MOF-doped Nafion composite proton exchange membrane improves proton conductivity, thermal stability, and chemical and physical durability. These properties help to improve the efficiency of water electrolysis for hydrogen production and reduce costs. It also broadens the operating temperature range and service life of the proton exchange membrane, reduces water absorption and swelling rate, and ensures the dimensional stability of the composite membrane. Attached Figure Description

[0059] Figure 1 This is the XRD pattern of the amino-containing Ce-MOF prepared in Example 1 of this invention;

[0060] Figure 2 This is the infrared spectrum of the amino-containing Ce-MOF prepared in Example 1 of this invention;

[0061] Figure 3 These are the conductivity graphs of the Nafion composite proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1 and 2 of this invention as a function of temperature.

[0062] Figure 4These are the swelling rate and water absorption rate spectra of the Nafion composite proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1 and 2 of this invention;

[0063] Figure 5 These are the Fenton mass loss rate variation spectra of the Nafion composite proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1 and 2 of this invention;

[0064] Figure 6 This is a comparison of the stretching ratios of the Nafion composite proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1 and 2 of this invention.

[0065] Figure 7 These are polarization curves of water electrolysis to produce hydrogen using Nafion composite proton exchange membranes prepared in Examples 1-5 and Comparative Examples 1 and 2 of this invention.

[0066] Figure 8 This is the XRD pattern of Ce-MOF prepared in Comparative Example 3 of this invention. Detailed Implementation

[0067] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0068] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0069] Example 1

[0070] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, wherein the Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and Ce-MOF; the metal site in the Ce-MOF is Ce, the Ce-MOF contains amino groups, and the mass fraction of the Ce-MOF is 5 wt%.

[0071] The method for preparing the Ce-MOF-doped Nafion composite proton exchange membrane provided in this embodiment includes the following steps:

[0072] (1) A first reaction was carried out by mixing cerium ammonium nitrate, 2-aminoterephthalic acid, acetic acid, water and ethanol. The molar ratio of cerium ammonium nitrate to 2-aminoterephthalic acid was 3.4 mmol:3 mmol; the volume ratio of acetic acid, water and ethanol was 6 mL:16 mL:40 mL. A brown solid was obtained by solid-liquid separation. The brown solid was washed three times with water and ethanol respectively, and dried under vacuum at 70 °C for 12 h to obtain Ce-MOF containing amino groups.

[0073] (2) Nafion D2020 solution was dried at 70°C for 12 hours to obtain Nafion resin. Nafion resin was mixed with N,N-dimethylformamide and stirred at 70°C for 12 hours to obtain a Nafion solution with a mass fraction of 5wt%.

[0074] (3) The amino-containing Ce-MOF from step (1) and the Nafion solution from step (2) were mixed and reacted at 70°C for 12 hours. The mixture was then ultrasonically dispersed for 0.5 hours to obtain a dispersion. The dispersion was poured into a 7.5cm×7.5cm glass tank and dried at 80°C for 12 hours. After annealing at 130°C for 2 hours, the composite membrane was cooled to room temperature and then peeled off from the glass tank to obtain the Nafion composite proton exchange membrane with a Ce-MOF doping amount of 5wt%.

[0075] The XRD pattern of the prepared Ce-MOF is shown in the figure. Figure 1 As shown, from Figure 1 As can be seen from the figure, the structure of the MOF in Ce-MOF conforms to the expected crystal structure of UIO-66. In the figure, 7.13° corresponds to the (111) crystal plane and 8.19° corresponds to the (002) crystal plane.

[0076] The infrared spectrum of the prepared Ce-MOF is shown below. Figure 2 As shown, from Figure 2 As can be seen from this, Ce-MOF contains amino groups.

[0077] Example 2

[0078] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, wherein the Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and Ce-MOF; the metal site in the Ce-MOF is Ce, the Ce-MOF contains amino groups, and the mass fraction of the Ce-MOF is 1 wt%.

[0079] The method for preparing the Ce-MOF-doped Nafion composite proton exchange membrane provided in this embodiment includes the following steps:

[0080] (1) A first reaction was carried out by mixing cerium ammonium nitrate, 2-aminoterephthalic acid, acetic acid, water and ethanol. The molar ratio of cerium ammonium nitrate and 2-aminoterephthalic acid was 4 mmol:3.5 mmol. The volume ratio of acetic acid, water and ethanol was 10 mL:16 mL:45 mL. After stirring and solid-liquid separation, a brown solid was obtained. The brown solid was washed three times with water and ethanol respectively, and dried under vacuum at 60 °C for 20 h to obtain Ce-MOF containing amino groups.

[0081] (2) Nafion D1020 solution was dried at 80°C for 12 hours to obtain Nafion resin. Nafion resin was mixed with anhydrous ethanol and stirred at 80°C for 12 hours to obtain a Nafion solution with a mass fraction of 10wt%.

[0082] (3) The amino-containing Ce-MOF from step (1) and the Nafion solution from step (2) were mixed and reacted at 60°C for 24 hours. The mixture was then ultrasonically dispersed for 0.5 hours to obtain a dispersion. The dispersion was poured into a 7.5cm×7.5cm glass tank and dried at 80°C for 12 hours. After annealing at 100°C for 12 hours, the composite membrane was cooled to room temperature and then peeled off from the glass tank to obtain the Nafion composite proton exchange membrane with a Ce-MOF doping amount of 1wt%.

[0083] Example 3

[0084] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, wherein the Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and Ce-MOF; the metal site in the Ce-MOF is Ce, the Ce-MOF contains amino groups, and the mass fraction of the Ce-MOF is 3wt%.

[0085] The method for preparing the Ce-MOF-doped Nafion composite proton exchange membrane provided in this embodiment includes the following steps:

[0086] (1) A first reaction was carried out by mixing cerium ammonium nitrate, 2-aminoterephthalic acid, acetic acid, water and ethanol. The molar ratio of cerium ammonium nitrate and 2-aminoterephthalic acid was 4 mmol:4.5 mmol. The volume ratio of acetic acid, water and ethanol was 6 mL:16 mL:40 mL. A brown solid was obtained by solid-liquid separation. The brown solid was washed three times with water and ethanol respectively. It was then dried under vacuum at 70 °C for 12 h to obtain Ce-MOF containing amino groups.

[0087] (2) Nafion D520 solution was dried at 70°C for 12 hours to obtain Nafion resin. Nafion resin was mixed with isopropanol and stirred at 70°C for 12 hours to obtain a Nafion solution with a mass fraction of 10wt%.

[0088] (3) The amino-containing Ce-MOF from step (1) and the Nafion solution from step (2) were mixed and reacted at 70°C for 12 hours. The mixture was then ultrasonically dispersed for 0.5 hours to obtain a dispersion. The dispersion was poured into a 7.5cm×7.5cm glass tank and dried at 80°C for 12 hours. After annealing at 150°C for 2 hours and cooling to room temperature, the composite membrane was peeled off from the glass tank to obtain the Nafion composite proton exchange membrane with a Ce-MOF doping amount of 3wt%.

[0089] Example 4

[0090] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, wherein the Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and Ce-MOF; the metal site in the Ce-MOF is Ce, the Ce-MOF contains amino groups, and the mass fraction of the Ce-MOF is 7 wt%.

[0091] The method for preparing the Ce-MOF-doped Nafion composite proton exchange membrane provided in this embodiment includes the following steps:

[0092] (1) A first reaction was carried out by mixing cerium ammonium nitrate, 2-aminoterephthalic acid, acetic acid, water and ethanol. The molar ratio of cerium ammonium nitrate and 2-aminoterephthalic acid was 3 mmol:2 mmol. The volume ratio of acetic acid, water and ethanol was 6 mL:20 mL:45 mL. A brown solid was obtained by solid-liquid separation. The brown solid was washed 5 times with water and ethanol respectively, and dried under vacuum at 70 °C for 12 h to obtain Ce-MOF containing amino groups.

[0093] (2) Nafion D2020 solution was dried at 70°C for 12 hours to obtain Nafion resin. Nafion resin was mixed with N,N-dimethylacetamide and stirred at 70°C for 12 hours to obtain a Nafion solution with a mass fraction of 5wt%.

[0094] (3) The amino-containing Ce-MOF from step (1) and the Nafion solution from step (2) were mixed and reacted at 70°C for 12 hours. The mixture was then ultrasonically dispersed for 0.5 hours to obtain a dispersion. The dispersion was poured into a 7.5cm×7.5cm glass tank and dried at 80°C for 12 hours. After annealing at 120°C for 2 hours and cooling to room temperature, the composite membrane was peeled off from the glass tank to obtain the Nafion composite proton exchange membrane with a Ce-MOF doping amount of 7wt%.

[0095] Example 5

[0096] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, wherein the Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and Ce-MOF; the metal site in the Ce-MOF is Ce, the Ce-MOF contains amino groups, and the mass fraction of the Ce-MOF is 9 wt%.

[0097] The method for preparing the Ce-MOF-doped Nafion composite proton exchange membrane provided in this embodiment includes the following steps:

[0098] (1) A first reaction was carried out by mixing cerium ammonium nitrate, 2-aminoterephthalic acid, acetic acid, water and ethanol. The molar ratio of cerium ammonium nitrate and 2-aminoterephthalic acid was 5 mmol:4.5 mmol; the volume ratio of acetic acid, water and ethanol was 10 mL:25 mL:50 mL. A brown solid was obtained by solid-liquid separation. The brown solid was washed 6 times with water and 6 times with ethanol respectively, and dried under vacuum at 70 °C for 12 h to obtain Ce-MOF containing amino groups.

[0099] (2) Nafion D2020 solution was dried at 70°C for 12 hours to obtain Nafion resin. Nafion resin was mixed with N,N-dimethylformamide and stirred at 70°C for 12 hours to obtain a Nafion solution with a mass fraction of 5wt%.

[0100] (3) The amino-containing Ce-MOF from step (1) and the Nafion solution from step (2) were mixed and reacted at 70°C for 12 hours. The mixture was then ultrasonically dispersed for 0.5 hours to obtain a dispersion. The dispersion was poured into a 7.5cm×7.5cm glass tank and dried at 80°C for 12 hours. After annealing at 130°C for 2 hours, the composite membrane was cooled to room temperature and then peeled off from the glass tank to obtain the Nafion composite proton exchange membrane with a Ce-MOF doping amount of 9wt%.

[0101] Example 6

[0102] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, which differs from Embodiment 1 only in that the mass fraction of Ce-MOF is 0.5 wt%.

[0103] Example 7

[0104] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane, which differs from Embodiment 1 only in that the mass fraction of Ce-MOF is 10 wt%.

[0105] Example 8

[0106] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane. The only difference from Example 1 is that the molar ratio of cerium ammonium nitrate and 2-aminoterephthalic acid is 1 mmol:3 mmol when preparing the Ce-MOF-doped Nafion composite proton exchange membrane.

[0107] Example 9

[0108] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane. The only difference from Example 1 is that the molar ratio of cerium ammonium nitrate and 2-aminoterephthalic acid is 6 mmol:1 mmol when preparing the Ce-MOF-doped Nafion composite proton exchange membrane.

[0109] Example 10

[0110] This embodiment provides a Ce-MOF-doped Nafion composite proton exchange membrane. The only difference from Embodiment 1 is that acetic acid was not added in step (1) when preparing the Ce-MOF-doped Nafion composite proton exchange membrane.

[0111] Comparative Example 1

[0112] This comparative example provides a Nafion composite proton exchange membrane, which differs from Example 1 only in that step (1) is not performed when preparing the Nafion composite proton exchange membrane and Ce-MOF containing amino groups is not added in step (3).

[0113] Comparative Example 2

[0114] This comparative example provides a CeO2-doped Nafion composite proton exchange membrane. The only difference from Example 1 is that step (1) is omitted when preparing the CeO2-doped Nafion composite proton exchange membrane, and the Ce-MOF in step (3) is replaced with an equal mass of CeO2.

[0115] Comparative Example 3

[0116] This comparative example provides a Nafion composite proton exchange membrane, which differs from Example 1 only in that, when preparing the Nafion composite proton exchange membrane, 2-aminoterephthalic acid in step (1) is replaced with an equimolar amount of 2,2'-bipyridine-4,4'-dicarboxylic acid.

[0117] The obtained Ce-MOF was subjected to XRD testing, and the results are as follows: Figure 8 As shown in the figure, the MOF crystal form is not UIO-66, and the structure was not successfully synthesized.

[0118] Application Examples 1-9

[0119] Electrolysis experiments were conducted on the Ce-MOF-doped Nafion composite proton exchange membranes prepared in Examples 1-9. The specific procedures were as follows: CCM (Catalyst Coating Method): A catalyst layer was prepared by spraying cathode and anode catalyst slurries onto both sides of the Nafion composite proton exchange membrane using an ultrasonic sprayer. The catalyst slurry included anode (IrO2) or cathode (60% Pt / C) catalyst, deionized water, D520 Nafion ionomer, and IPA. The performance of the membrane electrodes in Examples 1-9 was tested under constant current conditions at 80°C. Before testing the electrolysis performance, all membrane electrodes were activated at a constant current density for 0.5 h. The current density was measured in the range of 1.3 V to 2.0 V using an electrochemical workstation (Gamry 3000).

[0120] The current density for hydrogen production via water electrolysis is shown in Table 1.

[0121] Comparative Application Examples 1-3

[0122] The Nafion composite proton exchange membranes prepared in Comparative Examples 1-3 were subjected to water electrolysis experiments. The experimental methods were the same as those in Application Examples 1-9. The current densities for hydrogen production by water electrolysis are shown in Table 1.

[0123] Test methods: The proton exchange membranes prepared in the above examples and comparative examples were tested for conductivity, water absorption, swelling rate and mechanical strength. The test results are shown in Table 1 below.

[0124] The conductivity was measured using an electrochemical impedance spectroscopy (EIS) CHI 660E (Shanghai Chenhua Instrument Co., Ltd.). Before testing, the composite proton exchange membrane was activated at 80℃ using the following steps: 1) Heating with 3% H₂O₂ for 1 hour to remove organic impurities, followed by washing with deionized water; 2) Heating with 0.5M H₂SO₄(aq) for 1 hour to activate the active sites of the polymer. +Completely replace, then rinse with deionized water; 3) Soak in deionized water for 1 hour to fully remove excess H2SO4. The sample was cut into rectangular strips of 10mm × 30mm. Ten measuring points were selected to measure the film thickness and average D value. In the frequency range of 0.1Hz to 1MHz, the surface resistance R (Ω) of the sample under different temperatures and full humidity was measured to obtain the proton conductivity σ (S / cm), which can be obtained from Equation 1:

[0125]

[0126] L (cm) is the distance between the two electrodes (here the distance is 1cm), S (cm) 2 ) is the cross-sectional area of ​​the composite membrane strip (the product of the width and thickness of the composite membrane).

[0127] The water absorption rate was tested as follows: Each membrane was activated with 0.5 M H₂SO₄(aq) at 60°C for 24 h, rinsed with deionized water, and then dried in an oven at 80°C for 24 h until the mass was constant. The initial mass W1 was recorded. The membrane was then placed in an aqueous environment and heated to the test temperature for 24 h until equilibrium was reached. The surface water of the sample was then quickly removed, and the test mass W2 was recorded. The experimental results were calculated according to Equation 2:

[0128]

[0129] The method for testing the swelling rate is the same as that for testing the water absorption rate, except that the recorded mass changes W1 and W2 are replaced with area changes A1 and A2, and the experimental results are calculated according to Equation 3:

[0130]

[0131] The mechanical strength test method is as follows: The mechanical properties of the thin film are tested using an electronic universal testing machine. During the test, the sample is cut into rectangular strips of 15mm × 45mm, and the measurement is performed at a test speed of 50mm / min at room temperature.

[0132] The Fenton mass loss rate test method is as follows: 20 ppm Fe 2+ Fenton's reagent was prepared by adding 0.02 g of ferrous sulfate to 100 ml of 3 wt% H₂O₂. Initially, the sample was dried at 80 °C for 24 hours, and the initial mass W1 was recorded. Then, a 2 cm × 4 cm proton exchange membrane was immersed in Fenton's reagent at 80 °C. Every 24 hours, the sample was removed, rinsed with deionized water, and dried again in a vacuum oven at 80 °C for 24 hours. The sample weight W2 was recorded, and the Fenton's reagent was replaced. The experimental results after 120 hours of Fenton testing were calculated according to Equation 4:

[0133]

[0134] The conductivity of the prepared Nafion composite proton exchange membrane changes with temperature as follows: Figure 3 As shown, from Figure 3 As can be seen from the data, Example 1 achieved the highest conductivity of 0.22 S / cm at 80°C and 100% RH, which is the largest improvement in proton conduction performance compared to Comparative Examples 1 and 2.

[0135] The swelling ratio and water absorption rate of the prepared Nafion composite proton exchange membrane are shown in the following graphs. Figure 4 As shown, from Figure 4 As can be seen, after doping with Ce-MOF, the water absorption rate and swelling rate of the composite films in Examples 1-5 are reduced, and their dimensional stability is improved to a certain extent. Among them, the water absorption rate and swelling rate of Example 1 are the smallest, at 10.78% and 9.54%, respectively.

[0136] The variation spectrum of the Fenton mass loss rate of the prepared Nafion composite proton exchange membrane is shown in the figure below. Figure 5 As shown, from Figure 5 As can be seen, after 120 hours of Fenton testing, Example 1 retained the most residual mass at 97.16%, and the introduction of Ce-MOF effectively improved the antioxidant properties of the composite membrane.

[0137] The elongation comparison spectrum of the prepared Nafion composite proton exchange membrane is shown in the figure below. Figure 6 As shown, from Figure 6 As can be seen, the interaction between the -NH2 and -SO3H functional groups also helps to form a dense structure within the membrane, thereby enhancing the mechanical properties of the composite membrane. Example 1 showed a maximum tensile strength of 19.501 MPa.

[0138] The polarization curve of the prepared Nafion composite proton exchange membrane for hydrogen production by water electrolysis is shown in the figure below. Figure 7 As shown, from Figure 7 As can be seen from the data, Example 1 exhibits the best in-plane proton conductivity during the water electrolysis hydrogen production process, demonstrating 2.63 A / cm². 2 High current density.

[0139] Table 1

[0140]

[0141] The test results show that:

[0142] (1) As can be seen from Examples 1-5, the present invention, by introducing the element Ce, utilizes Ce as a free radical quencher to effectively scavenge free radicals, and the reversible redox reaction of Ce... 3+ and Ce 4+Inhibiting the chemical degradation of polymer chains is beneficial to improving the durability and antioxidant performance of proton exchange membranes. The prepared Ce-MOF-doped Nafion composite proton exchange membrane was applied to the electrolysis of water for hydrogen production. A continuous hydrogen bond network was constructed within the membrane, exhibiting high current density. Example 1, with the best overall performance, showed a conductivity of 0.22 S / cm at 80℃ and 100% RH, a maximum tensile strength of 19.501 MPa, and retained 97.16% of its mass after a 120-hour Fenton test. Compared to Comparative Example 1, it exhibited the lowest water absorption and swelling rate and the highest current density of 2.63 A / cm. 2 .

[0143] (2) By comparing Example 1 with Examples 6-7, it can be seen that by further controlling the mass fraction of Ce-MOF to 1wt%-9wt%, the present invention makes the Ce-MOF-doped Nafion composite proton exchange membrane have better conductivity, which can significantly improve the Fenton mass loss rate. In addition, the prepared composite proton exchange membrane has high mechanical properties. The interaction between -NH2 and -SO3H caused by a small amount of doping makes it difficult to form a continuous hydrogen bond network, which increases the uncertainty of proton transport and reduces the conductivity of Ce-MOF-doped Nafion composite proton exchange membrane. If the mass fraction of Ce-MOF is higher than 9wt%, the Ce-MOF powder inside the composite membrane is severely agglomerated, which destroys the orderly establishment of proton transport channels in the membrane, increases the defect sites, and leads to a decrease in the conductivity of Ce-MOF-doped Nafion composite proton exchange membrane. The composite membrane becomes more brittle and the tensile strength also deteriorates.

[0144] (3) A comparison of Examples 1 and 8-9 shows that the present invention further controls the molar ratio of cerium salt to amino-containing organic ligands to satisfy (3-5):(2-8), thereby regulating the structure of the Ce-MOF generated in the reaction, making the resulting structure more complete and having a suitable pore structure. This also affects the conductivity and mechanical properties of the prepared Ce-MOF-doped Nafion composite proton exchange membrane. If the molar ratio of cerium salt or amino-containing organic ligands is too large or too small, it will lead to the inability to form a stable UIO-66 crystal form, resulting in structural collapse.

[0145] (4) By comparing Example 1 and Example 10, it can be seen that the addition of acetic acid in the present invention can maintain the acid-base environment of the reaction system, promote the formation of UIO-66 structure, and the addition of acetic acid is more conducive to the formation of a uniform solution, ensuring the uniform distribution of metal ions, suppressing side reactions, and helping to grow better and purer crystals.

[0146] (5) As can be seen from Example 1 and Comparative Examples 1-2, the present invention, by introducing Ce element and utilizing Ce as a free radical quencher, effectively scavenges free radicals, and reversibly redox-resistant Ce... 3+ and Ce 4+ This process inhibits the chemical degradation of polymer chains, which is beneficial to improving the durability and antioxidant performance of the proton exchange membrane. Simultaneously, the interaction between the -NH2 and -SO3H groups forms a continuous hydrogen bond network within the membrane, improving proton transport efficiency. However, when Ce-MOF is not doped or CeO2 is introduced, the conductivity of the proton exchange membrane and the performance of water electrolysis for hydrogen production will deteriorate, failing to achieve the technical effects of this invention.

[0147] (6) As can be seen from Example 1 and Comparative Example 3, the present invention uses 2-aminoterephthalic acid as an organic ligand to prepare a metal-organic framework with Ce-UIO-66-NH2 structure. However, if other organic ligands are used, it is impossible to prepare a metal-organic framework with Ce-UIO-66-NH2 structure, and its efficiency in producing hydrogen by electrolysis of water will also decrease significantly.

[0148] In summary, this invention, by introducing Ce element and utilizing Ce as a free radical quencher, effectively scavenges free radicals, and reversibly redox-mediated Ce... 3+ and Ce 4+ This inhibits the chemical degradation of polymer chains, which is beneficial to improving the durability and antioxidant performance of the proton exchange membrane. On the other hand, considering the easy migration of Ce ions, this invention adopts a Ce-UIO-66 structure, anchoring the Ce ion position through the MOF framework, effectively solving the problem of Ce loss after long-term operation. At the same time, the introduction of amino groups and sulfonic acid groups on the Nafion chain to form proton transport channels ensures the proton conductivity of the membrane and significantly improves the current density during water electrolysis to produce hydrogen.

[0149] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A Ce-MOF-doped Nafion composite proton exchange membrane for hydrogen production via water electrolysis, characterized in that it improves proton transport rate and redox capability, and is further characterized in that... The Ce-MOF-doped Nafion composite proton exchange membrane comprises a Nafion composite proton exchange membrane and Ce-MOF; The metal sites in the Ce-MOF are Ce; The Ce-MOF contains amino groups; The mass fraction of the Ce-MOF is 4wt%-6wt%.

2. The Ce-MOF-doped Nafion composite proton exchange membrane according to claim 1, characterized in that, The Ce-MOF includes UIO-66.

3. A method for preparing a Ce-MOF-doped Nafion composite proton exchange membrane as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) Mix cerium salt, amino-containing organic ligand, water and ethanol, and react in the first reaction to obtain amino-containing Ce-MOF; (2) Mix the amino-containing Ce-MOF with Nafion solution, and carry out a second reaction to obtain a dispersion. After casting and annealing, the dispersion is used to obtain the Ce-MOF-doped Nafion composite proton exchange membrane.

4. The preparation method according to claim 3, characterized in that, The cerium salts include tetravalent cerium salts.

5. The preparation method according to claim 4, characterized in that, The tetravalent cerium salt includes cerium ammonium nitrate.

6. The preparation method according to claim 3, characterized in that, The amino-containing organic ligands include 2-aminoterephthalic acid.

7. The preparation method according to claim 3, characterized in that, The molar ratio of the cerium salt to the amino-containing organic ligand is (3-5):(2-8).

8. The preparation method according to claim 3, characterized in that, The first reaction also includes the addition of acetic acid.

9. The preparation method according to claim 3, characterized in that, The volume ratio of water to ethanol is (15-30):(30-60).

10. The preparation method according to claim 8, characterized in that, The volume ratio of acetic acid, water and ethanol is (5-10):(15-30):(30-60).

11. The preparation method according to claim 3, characterized in that, Step (1) includes washing and a first drying process following the first reaction.

12. The preparation method according to claim 11, characterized in that, The specific washing steps are as follows: wash with water and / or ethanol 3 to 6 times respectively.

13. The preparation method according to claim 11, characterized in that, The first drying process is vacuum drying.

14. The preparation method according to claim 11, characterized in that, The temperature for the first drying process is 60℃-80℃.

15. The preparation method according to claim 11, characterized in that, The first drying time is 12h-24h.

16. The preparation method according to claim 3, characterized in that, The method for preparing the Nafion solution includes: drying the Nafion aqueous alcohol solution to obtain Nafion resin, and mixing the Nafion resin with a solvent to obtain the Nafion solution.

17. The preparation method according to claim 16, characterized in that, The Nafion hydroalcoholic solution includes any one or a combination of at least two of Nafion D2020 solution, Nafion D1020 solution, or Nafion D520 solution.

18. The preparation method according to claim 16, characterized in that, The drying temperature is 60℃-80℃.

19. The preparation method according to claim 16, characterized in that, The solvent includes any one or a combination of at least two of anhydrous ethanol, isopropanol, N,N-dimethylformamide, or N,N-dimethylacetamide.

20. The preparation method according to claim 16, characterized in that, The mass fraction of Nafion resin in the Nafion solution is 5wt%-20wt%.

21. The preparation method according to claim 3, characterized in that, In step (2), the temperature of the second reaction is 60℃-80℃.

22. The preparation method according to claim 3, characterized in that, The reaction time in step (2) is 12h-24h.

23. The preparation method according to claim 3, characterized in that, Step (2) The second reaction is followed by ultrasonic dispersion for 0.5-1 h.

24. The preparation method according to claim 3, characterized in that, Step (2) includes a second drying process after pouring.

25. The preparation method according to claim 24, characterized in that, The second drying temperature is 60℃-80℃.

26. The preparation method according to claim 24, characterized in that, The second drying time is 12h-24h.

27. The preparation method according to claim 3, characterized in that, The annealing temperature is 100℃-150℃.

28. The preparation method according to claim 3, characterized in that, The annealing time is 2h-12h.

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