Ultra-microporous cr-mof material, method of preparation and proton conduction applications thereof

Abstract

The application belongs to the technical field of metal organic framework material preparation, and particularly relates to a super-microporous Cr-MOF material, a preparation method thereof and proton conduction application. 15 H 11 Cr 3.5 O 16.5 X 3.5 , X is one of OH or Cl, the ligand is uniform benzene tetraformic acid, the three-dimensional structure contains gourd-shaped pore channels, the pore wall is rich in uncoordinated-COOH, X functional groups and coordinated water, is easy to form a continuous hydrogen bond network, realizes efficient proton conduction. The material has a thermal stability of 330 DEG C or above, and has excellent water and acid stability. The application is synthesized by a solvent-free mechanical grinding-thermal reaction method. The method does not need organic solvents, and is suitable for large-scale production. The material has excellent proton conduction performance, and is suitable for fields such as proton exchange membrane fuel cells.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework material preparation technology, specifically relating to an ultramicroporous Cr-MOF material, its preparation method, and its proton conduction application. Background Technology

[0002] The performance of proton exchange membrane fuel cells (PEMFCs) has long been limited by their core proton conduction materials. Traditional perfluorosulfonic acid membranes (such as Nafion®) suffer from a sharp drop in proton conductivity due to membrane dehydration in high-temperature (>80°C) or low-humidity environments, and also have drawbacks such as high cost, fuel permeation, and high-temperature mechanical performance degradation, making them unable to meet the requirements of harsh operating conditions.

[0003] To overcome these bottlenecks, researchers have turned to structure-designable metal-organic frameworks (MOFs). However, most MOFs suffer from inherent limitations: they are based on Zn... 2+ Cu 2+ Metal MOFs have poor stability and are prone to framework decomposition in humid, acidic, and heated environments. Their proton conduction relies heavily on hydrogen bond networks formed by physically adsorbed water, making them extremely sensitive to humidity. They also lack ordered intrinsic proton sources (such as -SO3H and -PO3H2), making it difficult to conduct efficiently in low humidity conditions. In addition, insufficient pore design and functionalization also hinder the construction of continuous, low-resistivity proton transport pathways.

[0004] For chromium-based MOF systems with high stability potential, the traditional solvothermal synthesis method has become an obstacle to performance improvement. This method requires the use of a large amount of organic solvents, which is costly, environmentally unfriendly, and has a long reaction cycle. In addition, solvent molecules may interfere with the optimal construction of proton transport sites, and the synthesis efficiency and atom economy are also insufficient, which is not conducive to large-scale preparation.

[0005] Therefore, it is of great necessity and urgency to develop a green and efficient synthesis strategy to avoid the defects of traditional solvothermal methods and to directionally prepare a chromium-based MOF material with both excellent stability and high proton conduction performance. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an ultramicroporous Cr-MOF material, its preparation method, and its proton conduction application. This invention prepares Cr-MOF materials through a solvent-free mechanical grinding synthesis method. The solvent-free method improves the utilization rate of raw materials and increases the yield of Cr-MOF materials. The Cr-MOF material exhibits excellent proton conductivity.

[0007] This invention is achieved through the following technical solution: A microporous Cr-MOF material with the chemical formula C 15 H 11 Cr3.5 O 16.5 X 3.5 X is either OH or Cl, and the ligand is pyromellitic acid H4BETC, with the following structural formula: ; The ultraporous Cr-MOF material has a three-dimensional topological structure.

[0008] Furthermore, the space group of the ultramicroporous Cr-MOF material is C2 / c Each asymmetric unit contains 0.5 Cr3O(COO)6X clusters, 1 Cr2(OH)(COO)2X3(H2O)3 cluster, and 1 BETC cluster. 4- and 0.5 H2BETC 2- BETC 4- and H2BETC 2- -COO - Both are coordinated with Cr in a bidental coordination mode. 3+ Coordination links form a three-dimensional structure.

[0009] Furthermore, the three-dimensional network structure of the ultraporous Cr-MOF material contains a gourd-shaped channel structure, H2BETC 2- Containing two uncoordinated carboxylic acid groups (-COOH), it can provide protons to improve proton conductivity. At the same time, the distance between the X (X is OH or Cl) functional groups on the pore walls and between them and the coordinated water molecules is extremely small, which is conducive to the formation of a continuous hydrogen bond network after the adsorption of water molecules, ultimately leading to excellent proton conduction performance.

[0010] A solvent-free preparation method for ultramicroporous Cr-MOF materials includes the following steps: Step 1: Pyromellitic acid and chromium salt are ground and mixed to obtain a premix; Step 2: The premixed material is subjected to thermal reaction. After cooling, the product is washed with anhydrous ethanol. After washing, the supernatant is transparent and colorless after centrifugation. The precipitate after centrifugation is collected and vacuum dried at 60-80℃ for 6-18 hours to obtain chromium-based metal-organic framework material.

[0011] Furthermore, in step one, the chromium salt is one of chromium acetate trihydrate, chromium acetylacetone, chromium chloride hexahydrate, and chromium nitrate nonahydrate.

[0012] Furthermore, the molar ratio of pyromellitic acid to chromium salt is 1:2-8.

[0013] Furthermore, the grinding time in step one is 10-20 minutes.

[0014] Furthermore, in step two, the thermal reaction conditions are 190-240℃ for 24-36 hours.

[0015] Application of a chromium-based metal-organic framework material in proton conductivity.

[0016] Beneficial technical effects of the present invention: (1) This invention reports for the first time an ultraporous Cr-MOF material with high proton conductivity, which forms a "-O-Cl-O-Cl" proton hopping route, thereby improving proton conductivity.

[0017] (2) The Cr-MOF contains gourd-shaped channels with uncoordinated -COOH groups on the channel walls. The -COOH, coordinated water, and coordinated X groups (X is OH or Cl) contained in the channels are very close together. After adsorbing water molecules, they can form a continuous hydrogen bond network, thereby efficiently conducting protons.

[0018] (3) The product of this invention uses high-charge chromium ions to synthesize metal-organic framework materials, which have outstanding water stability, acid and alkali stability and thermal stability, and can be used in harsher working environments.

[0019] (4) This application adopts a solvent-free preparation process, which directly synthesizes raw materials by grinding and mixing them (without solvent) and reacting them with high-temperature solid-state reaction (190–240℃). On the one hand, the mechanical grinding method does not introduce solvents, thereby avoiding the pollution of the environment by potentially harmful organic solvents, and also reducing the cost of raw materials. On the other hand, the solvent-free method theoretically incorporates all the raw materials used in the synthesis reaction into the final product, which makes the reaction yield significantly higher than that of the solvent method, satisfying the atom economy and making this method applicable to large-scale industrial-scale reactions. Attached Figure Description

[0020] Figure 1 XRD results of the ultramicroporous Cr-MOF material; Figure 2 A schematic diagram of the asymmetric structural unit of the ultramicroporous Cr-MOF material; Figure 3 This is a schematic diagram of the three-dimensional structure of the ultramicroporous Cr-MOF material; Figure 4 A schematic diagram of the pore structure of ultramicroporous Cr-MOF material; Figure 5 Infrared spectrum of ultra-microporous Cr-MOF material; Figure 6 SEM image of the ultramicroporous Cr-MOF material; Figure 7 EDS results for the ultramicroporous Cr-MOF material; Figure 8 Thermogravimetric analysis results of the ultramicroporous Cr-MOF material are shown in the figure. Figure 9 H after dissolution of ultramicroporous Cr-MOF materials and ligands 1 NUM spectrum; Figure 10 XRD results of stability testing of ultramicroporous Cr-MOF materials; Figure 11 The graph shows the impedance test results of the ultramicroporous Cr-MOF material as a function of temperature at 100% relative humidity. Figure 12 The figure shows the activation energy fitting results for the ultraporous Cr-MOF material. Detailed Implementation

[0021] Example 1

[0022] A solvent-free preparation method for ultramicroporous Cr-MOF materials includes the following steps: S1. Weigh 254 mg (1 mmol) of pyromellitic acid and 1600 mg (4 mmol) of chromium nitrate nonahydrate and place them in a mortar. Use a pestle to mix and grind the reactants thoroughly for 10 min to obtain a premix.

[0023] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave, heated to 240°C and reacted for 24 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 60°C for 12 hours to obtain the chromium-based metal-organic framework material.

[0024] Example 2

[0025] A solvent-free preparation method for ultramicroporous Cr-MOF materials includes the following steps: S1. Weigh 254 mg (1 mmol) of pyromellitic acid and 1745 mg (5 mmol) of chromium acetylacetonate and place them in a mortar. Use a pestle to mix and grind the reactants thoroughly for 15 minutes to obtain a premix.

[0026] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave and heated to 220°C at a rate of 5°C / min for 36 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 60°C for 12 hours to obtain the chromium-based metal-organic framework material.

[0027] Example 3

[0028] A solvent-free preparation method for ultramicroporous Cr-MOF materials includes the following steps: S1. Weigh 254 mg (1 mmol) pyromellitic acid and 1698 mg (6 mmol) chromium acetate trihydrate and place them in a mortar. Use a pestle to mix and grind the reactants thoroughly for 20 minutes to obtain a premix.

[0029] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave, heated to 190°C and reacted for 24 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 60°C for 14 hours to obtain the chromium-based metal-organic framework material.

[0030] Example 4

[0031] A solvent-free preparation method for ultramicroporous Cr-MOF materials includes the following steps: S1. Weigh 254 mg (1 mmol) of pyromellitic acid and 2128 mg (8 mmol) of chromium chloride hexahydrate (8 mmol) and place them in a mortar. Use a pestle to mix and grind the reactants thoroughly for 20 minutes to obtain a premix.

[0032] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave, heated to 190°C and reacted for 24 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 60°C for 14 hours to obtain the chromium-based metal-organic framework material.

[0033] The materials obtained in Examples 1-4 have the same structure. The materials obtained in Examples 1-4 were characterized, and the results are as follows: Figure 1 The image shows the XRD results of the ultramicroporous Cr-MOF material. In the freshly prepared sample, the XRD pattern shows narrow diffraction peaks, indicating that the material has good crystallinity and basically meets the requirements of structural analysis. The fact that the XRD measured by the sample is basically consistent with the simulation results also indicates the purity of the sample, providing a benchmark for subsequent performance testing.

[0034] Figure 2 This is a schematic diagram of the asymmetric unit structure of the ultramicroporous Cr-MOF material; it can be seen that each asymmetric unit contains 0.5 Cr3O(COO)6X (X is OH or Cl) clusters, 1 Cr2(OH)(COO)2X3(H2O)3 (X is OH or Cl), and 1 BETC 4- and 0.5 H2BETC 2- BETC 4- and H2BETC 2- -COO - Both are coordinated with Cr in a bidental coordination mode. 3+ Coordination links form a three-dimensional structure (see) Figure 3 ).

[0035] The three-dimensional structure of the Cr-MOF material contains a gourd-shaped channel structure, H2BETC 2- Containing two uncoordinated carboxylic acid groups (-COOH), it can provide protons to improve proton conductivity. Simultaneously, the extremely small distances between the X (OH or Cl) functional groups on the pore walls and between them and the coordinated water molecules facilitate the formation of a continuous hydrogen bond network after water molecule adsorption, ultimately leading to excellent proton conductivity. Figure 4 ).

[0036] Figure 5 The Fourier transform infrared spectrum of the ultramicroporous Cr-MOF material verifies the performance at 860 cm⁻¹. -1 The band shift observed was attributed to the deprotonation of the -COOH group to generate Cr-O bonds.

[0037] Figure 6 and Figure 7 The images show the SEM and EDS results of the microporous Cr-MOF material, confirming its crystallographic characteristics and demonstrating the material's morphology and uniform elemental distribution.

[0038] Figure 8 The image shows the thermogravimetric analysis (TGA) results of the ultramicroporous Cr-MOF material. The thermal stability of the material in air was evaluated by TGA, and it remained stable at temperatures up to 330°C.

[0039] Figure 9 H is a mixture of ultra-microporous Cr-MOF material and pyromellitic acid solution. 1 The NUM spectrum confirmed the integrity of the pyromellitic ligand.

[0040] Figure 10 The images show the XRD results of Cr-MOF materials after treatment under different conditions. For practical applications in proton conduction, the stability of MOFs is crucial. In freshly prepared samples, the XRD patterns show high-intensity diffraction peaks, indicating good crystallinity and providing a benchmark for subsequent stability tests. Various conditions were applied to the material to demonstrate its chemical and thermal stability. PXRD measurements were performed on samples immersed in different solutions. The PXRD patterns remained largely unchanged, indicating that the crystal structure remained unchanged after treatment, fully demonstrating the material's chemical stability.

[0041] The materials obtained in Examples 1-3 were subjected to proton conductivity tests. Using a custom mold, at 1,000 kg cm -2 Under pressure, approximately 70 mg of MOF powder was pressed into a rectangular plate (approximately 0.2 × 0.4 × 1.0 cm). 3The time is 90 s. Two surfaces of the rectangular prism plate (0.2 × 0.4 cm) are... 2 All were fixed to silver wires with silver paste and sealed in a double-walled glass chamber. Temperature was regulated by temperature-controlled circulating water within the double-walled glass chamber. Impedance plots were obtained using a Zennium Pro electrochemical workstation with a tuning frequency range of 1 Hz to 8 MHz and an AC potential of 100 mV. Proton conductivity (σ, S cm⁻¹) was also measured. -1 The following formula is used (l, 1.0 cm; R, measured impedance, Ω; S, ca. 0.2 × 0.4 cm). 2 ): σ = l / (RS) The activation energy (Ea) is derived using proton conductivity data from 25 to 90°C at 100% RH and the Arrhenius equation (T, absolute temperature, K; A, pre-exponential factor; kB, Boltzmann constant): ln(σT) = lnA−Ea / (k B T) The result is: Figure 11 This shows that the material's impedance changes uniformly with temperature; Figure 12 The activation energy of the material is 0.15 eV, indicating that proton transfer mainly follows the Grotthuss mechanism (jumping mechanism, Ea < 0.4 eV).

Claims

1. A microporous Cr-MOF material, characterized in that: The chemical formula and molecular formula are C 15 H 11 Cr 3.5 O 16.5 X 3.5 X is either OH or Cl, and the ligand is pyromellitic acid H4BETC, with the following structural formula: ； The ultraporous Cr-MOF material has a three-dimensional network topology; The space group of the ultramicroporous Cr-MOF material is C2 / c Each asymmetric unit contains 0.5 Cr3O(COO)6X clusters, 1 Cr2(OH)(COO)2X3(H2O)3 cluster, and 1 BETC cluster. 4- and 0.5 H2BETC 2- BETC 4- and H2BETC 2- -COO - Both are coordinated with Cr in a bidental coordination mode. 3+ Coordination links form a three-dimensional network topology; The three-dimensional network topology of the ultraporous Cr-MOF material contains gourd-shaped channels, H2BETC 2- It contains two uncoordinated carboxylic acid groups -COOH, and the pore walls have OH or Cl functional groups; The solvent-free preparation method of the ultraporous Cr-MOF material includes the following steps: Step 1: Pyromellitic acid and chromium salt are ground and mixed to obtain a premix; Step 2: The premixed material is subjected to a thermal reaction at 190-240℃ for 24-36 hours. After cooling, the product is washed with anhydrous ethanol until the supernatant is transparent and colorless after centrifugation. The precipitate after centrifugation is collected and vacuum dried at 60-80℃ for 6-18 hours to obtain Cr-MOF material.

2. The ultraporous Cr-MOF material according to claim 1, characterized in that: In step one, the chromium salt is one of chromium acetate trihydrate, chromium acetylacetone, chromium chloride hexahydrate, and chromium nitrate nonahydrate.

3. The ultraporous Cr-MOF material according to claim 1, characterized in that: The molar ratio of pyromellitic acid to chromium salt is 1:2-8.

4. The ultraporous Cr-MOF material according to claim 1, characterized in that: The grinding time in step one is 10-20 minutes.

5. The application of the ultramicroporous Cr-MOF material as described in claim 1 in proton conductivity.

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