A covalent organic framework JUC-505-loaded Co-B composite material and its preparation method and application

Abstract

The present invention discloses a composite material based on a covalent organic framework JUC-505 loaded with Co-B. First, a covalent organic framework JUC-505 with a small granular shape and an average size of 50 nm is prepared by a solvothermal method. Then, JUC-505 is used as a carrier to load spherical Co-B nanoparticles by a chemical reduction method. Co-B is loaded on the surface of JUC-505 to obtain a specific surface area of ​​389.78 m 2 / g, magnetic Co-B / JUC-505. The preparation method includes the following steps: 1. Preparation of JUC-505; 2. Preparation of Co-B / JUC-505. The maximum hydrogen production rate is 10000-15000mL·min ‑1 ·g ‑1 When the hydrogen release time is 40-70s, the hydrogen release amount reaches 100% of the theoretical value; the activation energy is E a =21.6-26.2 kJ·mol ‑1 7 recycling / repeated cycles retain 84.4-87.8% of the initial catalytic activity. The advantages include: 1. Improved material micromorphology, enhanced uniformity, suppressed agglomeration, increased contact area, and increased active sites; 2. High thermal stability and high cycling stability; 3. Magnetic properties, which improve cycling performance through magnetic recycling.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic hydrolysis of sodium borohydride to produce hydrogen, and in particular to a covalent organic framework JUC-505-based loaded Co-B composite material, a preparation method thereof, and applications thereof. Background Art

[0002] Among hydrogen storage materials, NaBH4 has a very high hydrogen storage density, reaching 10.8 wt.%. Furthermore, the hydrogen produced by the hydrolysis of NaBH4 is highly pure, free of impurities such as CO and CO2, meeting the purity requirements of fuel cells. Furthermore, it offers advantages such as easy reaction control, high safety, and non-toxicity. However, the hydrolysis rate of borohydride alone is extremely slow. Therefore, it is necessary to prepare catalysts with large specific surface areas and high stability to improve the hydrogen production performance of borohydride hydrolysis.

[0003] The precious metal-based sodium borohydride hydrolysis hydrogen production catalyst is difficult to achieve long-term promotion in practical applications due to its high cost and limited reserves. Among the non-precious metal-based sodium borohydride hydrolysis hydrogen production catalysts, transition metals Co, Ni, Cu and Fe have relatively excellent performance. Among them, Co-based catalysts have the characteristics of low cost, higher activity and better cycle stability. For example, the existing document 1 (Jeong SU, Kim RK, Cho EA, et al. Astudy on hydrogen generation from NaBH4 solution using the high-performance Co-B catalyst [J]. Journal of Power Sources, 2005, 144 (1): 129-134.) synthesized the Co-B catalyst by chemical reduction method, and the maximum hydrogen production rate was only 1100 mL min -1 ·g -1 The existing technical problem is that the Co-B particles are agglomerated, and the contact area with the sodium borohydride solution during the reaction is small, resulting in a low maximum hydrogen production rate.

[0004] Currently, the main method to solve agglomeration is to add suitable carrier materials and protective layers to enhance the hydrogen production performance and cyclic stability of the material. The carrier materials reported in the literature mainly include carbon materials, metal organic frameworks, TiO2, etc.

[0005] Among them, the existing literature 2 (Zhang H, Wei Q, Wu G, et al. Zn-MOF-74-derived graphene nanosheets supporting CoB alloys for promoting hydrolytic dehydrogenation of sodium borohydride [J]. Journal of Alloys and Compounds, 2023, 930: 167486.) prepared a Co-B / GNS catalyst by loading Co-B particles on Zn-MOF-74 derived graphene nanosheets by chemical reduction, with a maximum hydrogen production rate of 7937 mL min -1 ·g -1 , and maintained at 66.8% of the initial value after 7 cycles. This technical solution reduces the agglomeration of Co-B particles by introducing MOF as a carrier, and at the same time, the specific surface area of ​​Co-B is increased from 35.1m 2 / g increased to 66.7m 2 / g, thereby improving the hydrogen production performance and cycle stability of the material. However, the technical problem of this technical solution is that due to the poor stability of the MOFs material itself, the structure collapses during the cycle, which ultimately affects the cycle stability of the catalyst.

[0006] Therefore, the existing technology currently has the following technical problems:

[0007] 1. Sodium borohydride hydrolysis hydrogen production catalyst has poor stability and suffers from agglomeration, oxidation, and shedding problems, which directly lead to poor catalytic activity and recyclability;

[0008] 2. The catalyst carrier material has poor stability and its structure is prone to collapse, resulting in poor catalyst recyclability.

[0009] In order to solve the above problems, covalent organic framework COFs materials can be used as carriers to solve them. Compared to MOFs materials, COFs materials are not only stable, crystalline and porous, but also have the advantages of high thermal stability and large specific surface area. The above characteristics can be supported by existing literature 4 (Freund R, Zaremba O, Arnauts G, et al. The current status of MOF and COF applications [J]. Angewandte Chemie International Edition, 2021, 60 (45): 23975-24001.). This technical solution utilizes the characteristics of COFs materials having higher chemical stability than MOFs materials to successfully improve the stability of composite materials.

[0010] In addition, according to the currently available literature, there is no technical solution for applying COFs materials to NaBH4 hydrolysis. Summary of the Invention

[0011] The present invention aims to provide a covalent organic framework JUC-505-loaded Co-B composite material and a preparation method and application thereof.

[0012] Taking advantage of the large specific surface area and high stability of COFs materials, more active sites are provided for loading Co-B, inhibiting the agglomeration phenomenon during the Co-B synthesis process; and overcoming the problem of material structure collapse during the reaction process and catalytic cycle.

[0013] Furthermore, according to the present invention, research has revealed that not all COFs can achieve the aforementioned objectives. Therefore, the present invention selected JUC-505, a highly stable polyarylene ether COF material linked by ether bonds, as the carrier to maintain its high structural stability in boiling water, strong acids, strong bases, strong oxidants, strong reducing agents, and most organic solvents.

[0014] The specific principles and methods involved include:

[0015] 1. Use JUC-505 carrier to load Co-B particles to improve the microstructure of the material, increase uniformity, avoid agglomeration, thereby increasing the contact area between Co-B and NaBH4 and improving catalytic performance;

[0016] 2. Use JUC-505 carrier to load Co-B particles to increase the specific surface area of ​​Co-B, increase active sites, and improve catalytic performance.

[0017] 3. The JUC-505 carrier has high stability, which reduces the collapse of the material structure during the hydrolysis reaction and improves the cyclic stability of the material.

[0018] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0019] A JUC-505-loaded Co-B composite material is prepared by a solvothermal method, and then the JUC-505 is used as a carrier to load Co-B nanoparticles via a chemical reduction method to obtain a JUC-505-loaded Co-B composite material, referred to as Co-B / JUC-505.

[0020] The raw materials for preparing JUC-505 are anhydrous potassium carbonate, tetrafluoroterephthalonitrile, hexahydroxytriphenylene, mesitylene and 1-methylpyrrolidine;

[0021] The raw materials for loading Co-B are citric acid monohydrate, cobalt sulfate heptahydrate and sodium borohydride;

[0022] The microscopic morphology of the Co-B / JUC-505 is that JUC-505 is in the form of small grains with an average size of 50 nm, and Co-B is in the form of spherical particles, and Co-B is loaded on the surface of JUC-505;

[0023] The specific surface area of ​​Co-B / JUC-505 is 389.78 m 2 / g;

[0024] The Co-B / JUC-505 has magnetic properties.

[0025] A method for preparing a Co-B composite material based on a covalent organic framework JUC-505, comprising the following steps:

[0026] Step 1, preparation of JUC-505: first, 2,3,6,7,10,11-hexahydroxytriphenylene and tetrafluoroterephthalonitrile are ground and mixed to obtain a mixture A; then, the obtained mixture A, anhydrous potassium carbonate, mesitylene, and 1-methylpyrrolidone are mixed to obtain a mixture B; then, the mixture B is degassed; after the degassed operation is completed, a reaction is carried out under certain conditions; finally, the reaction product is soaked and washed, solvent exchanged, filtered, and vacuum dried to obtain JUC-505;

[0027] In the step 1, 2,3,6,7,10,11-hexahydroxytriphenylene, tetrafluoroterephthalonitrile, anhydrous potassium carbonate, mesitylene and 1-methylpyrrolidone satisfy the following ratio: 2,3,6,7,10,11-hexahydroxytriphenylene: tetrafluoroterephthalonitrile: anhydrous potassium carbonate: mesitylene: 1-methylpyrrolidone = 1 mol: (0.5-2) mol: (0.5-10) mol: 0.2 L: (0.05-0.8) L;

[0028] In step 1, the degassing operation is to first freeze with liquid nitrogen, then evacuate, and finally melt, and the degassing operation is repeated 3-5 times;

[0029] In step 1, the reaction conditions are: under vacuum conditions, the reaction temperature is 120-180° C., and the reaction time is 3-7 days;

[0030] In step 1, the soaking and washing method is to soak and wash with N,N-dimethylformamide, water and tetrahydrofuran in sequence, the solvent is replaced with acetone, and the vacuum drying conditions are as follows: the drying temperature is 60-80°C and the drying time is 6-12h;

[0031] Step 2, preparation of Co-B / JUC-505, placing the JUC-505 obtained in step 1, citric acid monohydrate, and cobalt sulfate heptahydrate in deionized water, and performing an ultrasonication and then standing operation under certain conditions to obtain a mixture C; then, under certain conditions, adding a sodium borohydride solution dropwise to the mixture C, and then standing. The resulting product is thoroughly washed with alcohol, filtered, and then vacuum dried under certain conditions to obtain a covalent organic framework JUC-505-loaded Co-B composite material, named Co-B / JUC-505;

[0032] In step 2, the mass ratio of JUC-505, citric acid monohydrate and cobalt sulfate heptahydrate is (1-4):0.5:14;

[0033] In step 2, the ultrasonic conditions are as follows: ultrasonic time is 0.5-1h, and standing time is 12-24h;

[0034] In step 2, the sodium borohydride is added dropwise at a rate of 3-5 seconds per drop under stirring, and the concentration of the sodium borohydride is 1-1.25 mol / L;

[0035] In step 2, the drying conditions are as follows: the drying temperature is 60-80° C. and the drying time is 6-12 hours.

[0036] A covalent organic framework JUC-505-loaded Co-B composite material is used as a catalyst for hydrogen production from sodium borohydride hydrolysis, providing a maximum hydrogen production rate of 10,000-15,000 mL min at 303 K. -1 ·g -1 , when the hydrogen release time is 40-70s, the hydrogen release amount reaches 100% of the theoretical value;

[0037] The activation energy of catalytic hydrogen evolution is E a =21.6-26.2 kJ·mol -1 ;

[0038] At 303 K, 84.4–87.8% of the initial catalytic activity was retained after 7 recycling / reuses.

[0039] The technical effects of the present invention can be seen from the following tests:

[0040] XRD analysis showed that the characteristic peaks of Co-B / JUC-505 were the same as those of JUC-505, indicating that JUC-505 was successfully synthesized.

[0041] SEM examination showed that the microstructure of Co-B / JUC-505 was that spherical particles grew on the surface of JUC-505 grains;

[0042] EDS testing shows that Co-B / JUC-505 contains not only the C, O, and N elements of JUC-505, but also Co and B elements. Combined with XRD and SEM test results, it can be proved that the Co-B particles are successfully loaded.

[0043] BET test shows that the specific surface area of ​​Co-B / JUC-505 material is 389.78m 2 / g;

[0044] Magnetic testing shows that Co-B / JUC-505 is a magnetic material, which is conducive to recycling and improves the recycling performance;

[0045] The results of the hydrolysis hydrogen production test showed that the maximum hydrogen production rate at 303K was 14946mL·min -1 ·g -1 , when the hydrogen release time is 43s, the hydrogen release amount reaches 100% of the theoretical value;

[0046] The reaction kinetics performance test shows that the apparent activation energy E of the reaction is a =21.6 kJ·mol -1 ;

[0047] The cyclic performance test showed that after 7 cycles at 303K, the catalyst still retained 87.8% of its initial catalytic activity for the hydrolysis of NaBH4.

[0048] Therefore, the present invention has the following advantages:

[0049] 1. The present invention uses JUC-505 carrier to load Co-B, which improves the material micromorphology, increases the material uniformity, inhibits agglomeration, effectively increases the contact area between Co-B and NaBH4, and thus increases the hydrogen production rate of the catalyst.

[0050] 2. The present invention uses JUC-505 as a carrier to load Co-B particles, which increases the specific surface area of ​​Co-B, exposes more active sites, and thus increases the hydrogen production rate of the catalyst;

[0051] 3. The JUC-505 carrier used in the present invention has high thermal stability. During the hydrolysis reaction, the catalyst structure is not prone to collapse, thereby improving the cyclic stability of the material.

[0052] 4. The present invention uses non-precious metal Co instead of precious metal as a catalyst and supports it with a JUC-505 carrier, thereby increasing the hydrogen production rate of the catalyst while also reducing the cost of the material.

[0053] 5. The present invention has magnetism, and magnetic recovery replaces the traditional filtration recovery method, which can effectively improve the problems of oxidation and shedding during its use, greatly reducing the process difficulty of the recovery process and the damage to the micromorphology of the material, and improving the stability of the catalyst.

[0054] Therefore, compared with the prior art, the present invention has better catalytic performance for producing hydrogen by hydrolyzing sodium borohydride, improves the stability of the catalyst, and has broad application prospects in the fields of hydrogen production materials, fuel cells, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 XRD patterns of JUC-505, Co-B, and Co-B / JUC-505 composite materials in Example 1;

[0056] Figure 2 is the SEM image of JUC-505 in Example 1;

[0057] Figure 3 is the SEM image of Co-B / JUC-505 in Example 1;

[0058] Figure 4 is the backscattered electron image of Co-B / JUC-505 in Example 1;

[0059] Figure 5 This is the EDS image corresponding to the backscattered electron image of Co-B / JUC-505 in Example 1;

[0060] Figure 6 BET diagrams of Co-B / JUC-505 and Co-B in Example 1 and Comparative Example 1;

[0061] Figure 7 This is a graph showing the hydrogen production from sodium borohydride catalyzed by Co-B / JUC-505 at different temperatures in Example 1;

[0062] Figure 8 is the activation energy diagram of Co-B / JUC-505 in Example 1;

[0063] Figure 9 This is a diagram of Co-B / JUC-505 adsorbed on the surface of a magnetic stirring bar in the cyclic test of Example 1;

[0064] Figure 10 This is a graph showing the cyclic performance of Co-B / JUC-505 in Example 1 after 7 cycles of catalytic sodium borohydride hydrolysis at 303 K.

[0065] Figure 11 is the SEM image of Co-B in Comparative Example 1;

[0066] Figure 12This is a comparison chart of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 catalyzing the hydrolysis and hydrogenation of sodium borohydride at a temperature of 303K. DETAILED DESCRIPTION

[0067] The present invention is further described in detail through embodiments and in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0068] Example 1

[0069] A method for preparing a Co-B composite material based on a covalent organic framework JUC-505, the specific steps are as follows:

[0070] Step 1, preparation of JUC-505, first, 32.4 mg of 2,3,6,7,10,11-hexahydroxytriphenylene and 30.0 mg of tetrafluoroterephthalonitrile were ground and mixed to obtain a mixture A; then, the obtained mixture A, 138.2 mg of anhydrous potassium carbonate, 0.3 mL of mesitylene, and 0.6 mL of 1-methylpyrrolidone were mixed to obtain a mixture B; then, the mixture B was degassed; after the degassed operation was completed, the reaction was carried out under vacuum conditions at a reaction temperature of 120° C. and a reaction time of 3 days; finally, the reaction product was soaked and washed, solvent exchanged, filtered, and vacuum dried to obtain JUC-505;

[0071] The degassing operation is to first freeze with liquid nitrogen, then evacuate, and finally melt, and the degassing operation is repeated three times;

[0072] The soaking and washing method is to soak and wash in N, N-dimethylformamide, water and tetrahydrofuran in sequence, the solvent is replaced with acetone, and the vacuum drying conditions are as follows: the drying temperature is 80° C. and the drying time is 6 hours;

[0073] In order to prove the crystal structure of JUC-505 obtained in step 1, XRD test was performed. The test results are as follows Figure 1 As shown in the figure, the peak of JUC-505 is consistent with the standard peak of JUC-505 reported in the literature. The test results show that JUC-505 was successfully synthesized.

[0074] In order to verify the microstructure of JUC-505 obtained in step 1, SEM test was performed. The test results are as follows Figure 2 As shown, JUC-505 is in the form of small grains with an average size of 50 nm.

[0075] In order to verify the specific surface area of ​​JUC-505 obtained in step 1, N2 isothermal adsorption / desorption BET test was performed. The test results are shown in Figure 2. Figure 6 As shown, the specific surface area of ​​JUC-505 is 583.89 m2 / g.

[0076] Step 2, preparation of Co-B / JUC-505, 150 mg of JUC-505 obtained in step 1, 25 mg of citric acid monohydrate and 70.28 mg of cobalt sulfate heptahydrate were placed in 80 mL of deionized water, and an ultrasonic time of 1 hour and a standing time of 24 hours were performed to obtain a mixture C; then, under stirring, a sodium borohydride solution with a concentration of 1.25 mol / L was added dropwise to the mixture C at a rate of 3 seconds per drop, and then the mixture was allowed to stand for 3 hours. The resulting product was thoroughly washed with alcohol and filtered, and then vacuum dried at a drying temperature of 60°C and a drying time of 12 hours to obtain a covalent organic framework JUC-505-loaded Co-B composite material, named Co-B / JUC-505.

[0077] In order to prove the composition of Co-B / JUC-505 obtained in step 2, XRD test was performed. The test results are as follows Figure 1 As shown in the figure, the characteristic peaks of Co-B / JUC-505 are the same as those of JUC-505. The test results show that the loading of Co-B particles has no effect on the crystal structure of JUC-505.

[0078] In order to verify the microstructure of Co-B / JUC-505 obtained in step 2 and the successful loading of Co-B particles, SEM and EDS tests were performed.

[0079] SEM test results are as follows Figure 3 As shown, the microscopic morphology of Co-B / JUC-505 is that spherical particles grow on the surface of JUC-505 grains;

[0080] EDS test results are as follows Figure 4 and Figure 5 As shown in the figure, Co-B / JUC-505 contains not only the C, O, and N elements of JUC-505, but also Co and B. Combining the XRD and SEM test results, it can be proved that the Co-B particles are successfully loaded.

[0081] In order to demonstrate the effect of step 2 on the specific surface area of ​​Co-B / JUC-505, the Co-B / JUC-505 obtained in step 2 was subjected to BET test. Figure 6 As shown, the specific surface area of ​​Co-B / JUC-505 is 389.78m 2 Compared with the JUC-505 obtained in step 1, it can be seen that the reason for the decrease in the specific surface area of ​​the material is the loading of Co-B particles.

[0082] To demonstrate the hydrogen production performance of the Co-B / JUC-505 obtained in step 2 as a sodium borohydride hydrolysis catalyst, hydrolysis hydrogen production tests were conducted on the JUC-505 obtained in step 1 and the Co-B / JUC-505 obtained in step 2. The specific method for the hydrolysis hydrogen production test was as follows: a solution containing 1.5 wt.% NaBH4 and 5 wt.% NaOH was placed in a constant temperature water bath under the set temperature. After reaching equilibrium at the set temperature, 10 mL of the solution was removed and added to a wide-mouth bottle containing the catalyst. The volume of hydrogen generated per unit time was collected and recorded by the water displacement method to obtain the hydrogen release rate. The temperature was 303 K unless otherwise specified.

[0083] The test results of JUC-505 for hydrogen production by hydrolysis are as follows Figure 12 As shown in the figure, under the condition of 303K, the maximum hydrogen production rate is 0, that is, JUC-505 has no catalytic effect on the hydrolysis of sodium borohydride to produce hydrogen;

[0084] The test results of hydrolysis hydrogen production of Co-B / JUC-505 are shown in Table 1 and Figure 7 As shown in Figure 2, at 303K, the maximum hydrogen production rate is 14946 mL min -1 ·g -1 When the hydrogen release time is 43s, the hydrogen release amount reaches 100% of the theoretical value.

[0085] The test results of hydrolysis hydrogen production show that JUC-505 itself does not have catalytic effect; after the introduction of Co-B, the composite material has catalytic activity; therefore, the role of JUC-505 in the technical solution is a carrier.

[0086] Table 1 Hydrogen production rate and activation energy of NaBH4 hydrolysis catalyzed by different catalysts

[0087]

[0088] Note: The reference numbers in Table 1 correspond to the following documents:

[0089] [1] Yang F, Zou Y, Xiang C, et al. Synthesis of “needle-cluster” NiCo2O4carbon nanofibers and loading of Co-B nanoparticles for hydrogen production through the hydrolysis ofNaBH4. Journal of Alloys and Compounds, 2022,911:165069.

[0090] [2]Peng C, Li T, Zou Y, et al. Bacterial cellulose derived carbon as asupport for catalytically active Co–B alloy for hydrolysis of sodiumborohydride. International Journal of Hydrogen Energy, 2021, 46(1): 666-675.

[0091] [3]Muir SS,Chen Z.,Wood BJ,Wang LZ,Lu GQNew electrolessplating method for preparation of highly active Co-B catalysts for NaBH4hydrolysis.International Journal of Hydrogen Energy,2014,39,414-425.

[0092] [4] Shi L, Chen Z, Jian Z, et al. Carbon nanotubes-promoted Co-B catalysts for rapid hydrogen generation via NaBH4 hydrolysis. International Journal of Hydrogen Energy, 2019, 44(36): 19868-19877.

[0093] Furthermore, in order to prove the reaction kinetics of Co-B / JUC-505, hydrolysis hydrogen production tests were carried out at 298K, 308K, and 313K. The test results were fitted with the Arrhenius equation as shown in Table 1 and Figure 8 As shown, the apparent activation energy E of the reaction a =21.6 kJ·mol -1 At the same time, in order to compare with the existing technology, the data of the references are summarized in Table 1.

[0094] Through the above test results and comparative analysis with existing references, the following conclusions can be drawn preliminarily:

[0095] 1. References [1], [2], [3] and [4] use different materials as carriers, and their performances vary greatly;

[0096] 2. By comparing references [3] and [4], it can be seen that using Ni as a carrier can significantly increase the maximum hydrogen production rate, but the reduction in the reaction activation energy is negligible; using CNT as a carrier can significantly reduce the reaction activation energy, but the improvement in the maximum hydrogen production rate is limited, that is, common carriers can only improve the single performance of the sodium borohydride hydrolysis reaction;

[0097] 3. Through the comparison of CNF carbon nanofibers and CNT carbon nanotubes in references [1] and [4], it can be seen that even if they are the same carbon materials, the performance of the resulting composite materials is very different due to the different specific materials;

[0098] Based on the above analysis, the reasons for the significant improvement in catalytic performance of the present invention compared with the prior art are as follows:

[0099] 1. The present invention uses JUC-505 as a carrier to increase the specific surface area of ​​Co-B particles, obtain more active sites, and thus effectively increase the hydrogen production rate;

[0100] 2. The present invention uses JUC-505 as a carrier to improve the uniformity of Co-B particle loading while also inhibiting the agglomeration of Co-B particles, that is, improving the dispersion of Co-B particles, so that the catalyst activity changes very little with temperature, thereby effectively reducing the reaction activation energy.

[0101] According to the previous research results of the inventor's research group, the catalyst can be efficiently separated from the reaction liquid by magnetic recovery of the catalyst. In order to prove that the Co-B / JUC-505 composite material has magnetic properties, a magnetic test was conducted. The magnetic test results are as follows: Figure 9 As shown, Co-B / JUC-505 is attached to the surface of the magnetic stirring bar. The test results show that Co-B / JUC-505 has magnetism, that is, the catalyst can be recovered by magnetic force.

[0102] In order to prove the cycle performance of Co-B / JUC-505, a cycle performance test was conducted. The specific method of the cycle performance test is: the Co-B / JUC-505 that has been subjected to the hydrogen release test is magnetically recovered and then subjected to the aforementioned hydrolysis hydrogen production test again to obtain the hydrogen release rate after the cycle. The cycle performance of Co-B / JUC-505 can be obtained by simple calculation. The test results are shown in Table 2 and Figure 10 As shown in Figure 2, after 7 cycles at 303 K, 87.8% of the initial catalytic activity was retained. In addition, in order to compare with the existing technology, the data of the references are summarized in Table 2.

[0103] Table 2 Cycle number and cycle performance of NaBH4 hydrolysis catalyzed by different catalysts

[0104]

[0105]

[0106] Note: The corresponding literature for the reference numbers in Table 2 is as follows:

[0107] [5] Wang X, Liao J, Li H, et al. Highly active porous Co–B nanoalloy synthesized on liquid-gas interface for hydrolysis of sodium borohydride. International Journal of Hydrogen Energy, 2018, 43(37): 17543-17555.

[0108] [6] Saka C, Eygii MS, Balbay A. Cobalt loaded organic acid modified kaolin clay for the enhanced catalytic activity of hydrogen release via hydrolysis of sodium borohydride. International Journal of Hydrogen Energy, 2021, 46(5): 3876-3886.

[0109] [7] Rakap M. Hydrolysis of sodium borohydride and ammonia borane for hydrogen generation using highly efficient poly(N-vinyl-2-pyrrolidone)-stabilized Ru–Pd nanoparticles as catalysts. International journal of green energy, 2015, 12(12): 1288-1300.

[0110] [8]Li H, Li B, Zou Y, et al. Modulating valence band to enhance the catalytic activity of Co-Cr-B / NG for hydrolysis of sodium borohydride. Journal of Alloys and Compounds, 2022,924:166556.

[0111] [9] Luo X, Sun L, Xu F, et al. Metal boride-decorated CoNi layered doublehydroxides supported on muti-walled carbon nanotubes as efficient hydrolysiscatalysts for sodium borohydride. Journal of Alloys and Compounds, 2022:167339.

[0112] As shown in Table 2, the present invention retained 87.8% of its initial catalytic activity after 7 recycling cycles, and 54.5% after 15 recycling cycles. Compared with references [5]-[9], the cycling performance of Co-B / JUC-505 after repeated use is significantly better.

[0113] From the above analysis, it can be seen that the significant improvement in the cycle performance of the present invention can be attributed to the following reasons:

[0114] 1. The polyarylether covalent organic framework JUC-505 has excellent stability and can maintain structural stability under conditions such as strong acid, strong base, strong reducing agent or strong oxidizing agent. After JUC-505 is used as a carrier to load Co-B particles, the structure is not easy to collapse, which effectively enhances the structural stability of the catalyst;

[0115] 2. JUC-505 as a carrier effectively inhibits the agglomeration of Co-B particles and improves the cyclic stability of the catalyst during the reaction process;

[0116] 3. The JUC-505 carrier-loaded Co-B particle catalyst is magnetic, which allows it to be quickly recovered using a magnetic stirrer during the cyclic test, reducing the mass loss and morphological damage of Co-B / JUC-505 during the cyclic process, and effectively enhancing the stability of the catalyst during the cyclic process.

[0117] The role of Co-B in the technical solution has been demonstrated through Example 1. Comparative Example 1, which uses a Co-B material without a JUC-505 carrier, demonstrates the role of JUC-505 as a carrier in the technical solution.

[0118] Comparative Example 1

[0119] A method for preparing a Co-B catalyst without a JUC-505 carrier, wherein the steps not specifically described are the same as those in Example 1, except that step 2 is performed directly without performing step 1, and no JUC-505 is added in step 2. The resulting material is named Co-B.

[0120] The SEM test results of Co-B are as follows Figure 11 As shown in Figure 1, Co-B is in the form of granular aggregates. Combined with the SEM test results of Co-B / JUC-505, it can be seen that the introduction of JUC-505 as a carrier can change and adjust the micromorphology of the composite material, achieving the technical effect of preventing agglomeration.

[0121] The BET test results of Co-B are as follows Figure 6 As shown, the specific surface area of ​​Co-B is 20.39 m 2 Combined with the BET test results of Co-B / JUC-505, it can be seen that the introduction of JUC-505 as a carrier can significantly increase the specific surface area by 1845%.

[0122] The test results of Co-B hydrolysis hydrogen production are as follows Figure 12 As shown in Figure 2, at 303K, the maximum hydrogen production rate is 2387.8 mL·min -1 ·g -1 When the hydrogen release time is 96 seconds, the hydrogen release rate reaches 100% of the theoretical value. Combined with the test results of Co-B / JUC-505 hydrolysis hydrogen production, it can be seen that although Co-B can achieve a hydrogen release rate of 100%, the introduction of JUC-505 as a carrier can significantly reduce the hydrogen release time and increase the maximum hydrogen release rate by 526%.

[0123] By comparing Comparative Example 1 with Example 1, the following conclusion can be drawn: by introducing JUC-505 as a carrier, the micromorphology of the composite material is directly adjusted, agglomeration is avoided, the specific surface area is significantly increased, and the maximum hydrogen release rate is significantly increased, which proves the role of the carrier in the technical solution.

[0124] The role of the carrier in the technical solution has been demonstrated through Comparative Example 1. Comparative Example 2, using the Co-B / COF-1 material with COF-1 as the carrier, demonstrates the role of different carriers in the technical solution.

[0125] Comparative Example 2

[0126] A COF-1-loaded Co-B particle composite material was prepared. The steps not specifically described were the same as those in Example 1, except that the preparation of COF-1 was substituted for the preparation of JUC-505 in step 1, and in step 2, COF-1 was substituted for JUC-505. The resulting material was designated Co-B / COF-1.

[0127] The specific method for preparing COF-1 is as follows: first, 25 mg of DBA, 0.5 mL of mesitylene, and 0.5 mL of dioxane are mixed and dissolved to obtain a mixture D; then, the mixture D is reacted at a reaction temperature of 120° C. and a reaction time of 72 h; finally, the reaction product, a white solid, is centrifuged and repeatedly washed with acetone three times, and then vacuum dried at a drying temperature of 50° C. and a drying time of 24 h to obtain COF-1.

[0128] The results of the hydrolysis hydrogen production test of Co-B / COF-1 are as follows Figure 12 As shown in Figure 2, at 303K, the maximum hydrogen production rate is 2000mL·min -1 ·g -1 When the hydrogen release time is 115s, the hydrogen release amount reaches 100% of the theoretical value. Combined with the test results of Comparative Example 1, it can be seen that COF-1 as a carrier not only fails to improve the catalytic performance of Co-B, but instead reduces its performance.

[0129] The principle is that when COF-1 is used as a carrier, due to the use of chemical reduction method, when loading Co-B particles, the imine bond in COF-1 will be reduced by sodium borohydride, which directly leads to the collapse of the carrier structure and ultimately makes it impossible to improve the catalytic performance of the composite material.

[0130] Therefore, the test results show that although COF-1 and JUC-505 are both covalent organic framework materials, they play different roles in the two technical solutions. In other words, those skilled in the art cannot obtain technical insights from the common knowledge related to covalent organic framework materials based on the existing technology. Combined with the performance data of different carriers in Table 1, this further proves that those skilled in the art cannot achieve the technical effects and technical insights of the present invention by simply replacing the carrier material.

[0131] In order to demonstrate the effect of the amount of JUC-505 added on the catalytic performance, comparative examples 3, 4 and 5 are provided, ie, composite catalysts with JUC-505 added in amounts of 50 mg, 100 mg and 200 mg, respectively.

[0132] Comparative Example 3

[0133] A JUC-505-loaded Co-B particle composite material was prepared. The steps not specifically described were the same as those in Example 1, except that 50 mg of JUC-505 was added in step 1. The resulting material was designated Co-B / JUC-505-50.

[0134] The test results of Co-B / JUC-505-50 for hydrogen production by hydrolysis are as follows Figure 12 As shown in Figure 2, at 303K, the maximum hydrogen production rate is 10545mL·min -1 ·g -1 When the hydrogen release time is 61s, the hydrogen release amount reaches 100% of the theoretical value. By comparison with Example 1, it can be seen that the hydrogen production performance of Example 1 is improved by 41.7% compared with Comparative Example 3.

[0135] Comparative Example 4

[0136] A JUC-505-loaded Co-B particle composite material was prepared. The steps not specifically described were the same as those in Example 1, except that 100 mg of JUC-505 was added in step 1. The resulting material was designated Co-B / JUC-505-100.

[0137] The test results of Co-B / JUC-505-100 for hydrogen production by hydrolysis are as follows Figure 12 As shown, at 303K, the maximum hydrogen production rate is 12116mL·min -1 ·g -1 When the hydrogen release time is 53s, the hydrogen release amount reaches 100% of the theoretical value. By comparison with Example 1, it can be seen that the hydrogen production performance of Example 1 is improved by 23.4% compared with Comparative Example 4.

[0138] Comparative Example 5

[0139] A JUC-505-loaded Co-B particle composite material was prepared. The steps not specifically described were the same as those in Example 1, except that 200 mg of JUC-505 was added in step 1. The resulting material was designated Co-B / JUC-505-200.

[0140] The test results of Co-B / JUC-505-200 for hydrogen production by hydrolysis are as follows Figure 12 As shown, at 303K, the maximum hydrogen production rate is 10039mL·min -1 ·g -1 When the hydrogen release time is 64s, the hydrogen release amount reaches 100% of the theoretical value. By comparison with Example 1, it can be seen that the hydrogen production performance of Example 1 is improved by 48.9% compared with Comparative Example 5.

[0141] It can be seen from Example 1 and Comparative Examples 3, 4 and 5 that the addition amount of JUC-505 has a significant effect on the catalytic performance, which can be briefly summarized as follows:

[0142] When the amount of JUC-505 added is small, the agglomeration of Co-B particles is improved with the increase of JUC-505 addition, so the morphology of Co-B / JUC-505 composite material becomes uniform and its catalytic performance is enhanced;

[0143] However, when too much JUC-505 is added, although JUC-505 provides more active sites and enhanced cycling stability for the composite material due to its high specific surface area and high stability, due to its poor electrical conductivity, when too much JUC-505 is added, the overall electrical conductivity of the composite material also decreases, which directly has an adverse effect on electron transport during the sodium borohydride hydrolysis reaction, and is further reflected in the reduction of the final catalytic performance.

[0144] Therefore, according to the test results, when the addition amount of JUC-505 is 150 mg, the catalytic performance of the catalyst is the best.

Claims

1. A Co-B composite material based on the covalent organic framework JUC-505, characterized by: First, the covalent organic framework JUC-505 is prepared by a solvothermal method. Then, JUC-505 is used as a carrier to load Co-B nanoparticles through a chemical reduction method to obtain a covalent organic framework JUC-505-loaded Co-B composite material, referred to as Co-B / JUC-505. The raw materials for preparing JUC-505 are anhydrous potassium carbonate, tetrafluoroterephthalonitrile, hexahydroxytriphenylene, mesitylene and 1-methylpyrrolidone; The raw materials for loading Co-B are citric acid monohydrate, cobalt sulfate heptahydrate and sodium borohydride; The microscopic morphology of the Co-B / JUC-505 is that JUC-505 is in the form of small grains with an average size of 50 nm, and Co-B is in the form of spherical particles, and Co-B is loaded on the surface of JUC-505; The specific surface area of ​​Co-B / JUC-505 is 389.78 m 2 / g.

2. The covalent organic framework JUC-505-loaded Co-B composite material according to claim 1, characterized in that: The Co-B / JUC-505 has magnetic properties.

3. The covalent organic framework JUC-505-loaded Co-B composite material according to claim 1, characterized in that: As a catalyst for hydrogen production from sodium borohydride hydrolysis, the maximum hydrogen production rate provided at 303K is 10000-15000mL·min -1 ·g -1 , when the hydrogen release time is 40-70s, the hydrogen release amount reaches 100% of the theoretical value; The activation energy of catalytic hydrogen evolution is E a =21.6-26.2 kJ·mol -1 ; At 303 K, 84.4–87.8% of the initial catalytic activity was retained after 7 recycling / reuses.

4. A method for preparing a covalent organic framework JUC-505-loaded Co-B composite material, characterized in that The following steps are involved: Step 1, preparation of JUC-505: first, 2,3,6,7,10,11-hexahydroxytriphenylene and tetrafluoroterephthalonitrile are ground and mixed to obtain a mixture A; then, the obtained mixture A, anhydrous potassium carbonate, mesitylene, and 1-methylpyrrolidone are mixed to obtain a mixture B; then, the mixture B is degassed; after the degassed operation is completed, a reaction is carried out under certain conditions; finally, the reaction product is soaked and washed, solvent exchanged, filtered, and vacuum dried to obtain JUC-505; In the step 1, 2,3,6,7,10,11-hexahydroxytriphenylene, tetrafluoroterephthalonitrile, anhydrous potassium carbonate, mesitylene and 1-methylpyrrolidone satisfy the following ratio: 2,3,6,7,10,11-hexahydroxytriphenylene: tetrafluoroterephthalonitrile: anhydrous potassium carbonate: mesitylene: 1-methylpyrrolidone = 1 mol: (0.5-2) mol: (0.5-10) mol: 0.2 L: (0.05-0.8) L; In step 1, the degassing operation is to first freeze with liquid nitrogen, then evacuate, and finally melt, and the degassing operation is repeated 3-5 times; In step 1, the reaction conditions are: under vacuum conditions, the reaction temperature is 120-180° C., and the reaction time is 3-7 days; In step 1, the soaking and washing method is to soak and wash with N,N-dimethylformamide, water and tetrahydrofuran in sequence, the solvent is replaced with acetone, and the vacuum drying conditions are as follows: the drying temperature is 60-80°C and the drying time is 6-12h; Step 2, preparation of Co-B / JUC-505, placing the JUC-505 obtained in step 1, citric acid monohydrate, and cobalt sulfate heptahydrate in deionized water, and performing an ultrasonication and then standing operation under certain conditions to obtain a mixture C; then, under certain conditions, adding a sodium borohydride solution dropwise to the mixture C, and then standing. The resulting product is thoroughly washed with alcohol, filtered, and then vacuum dried under certain conditions to obtain a covalent organic framework JUC-505-loaded Co-B composite material, named Co-B / JUC-505; In step 2, the ultrasonic conditions are as follows: ultrasonic time is 0.5-1h, and standing time is 12-24h; In step 2, the sodium borohydride is added dropwise at a rate of 3-5 seconds per drop under stirring, and the concentration of the sodium borohydride is 1-1.25 mol / L; In step 2, the drying conditions are as follows: the drying temperature is 60-80° C. and the drying time is 6-12 hours.

Images