A bifunctional catalyst, its preparation method and application

Abstract

This invention provides a bifunctional catalyst, its preparation method, and its applications. Specifically, it relates to a bifunctional catalyst that improves both magnesium-based hydrogen storage and hydrogen production performance. The bifunctional catalyst comprises Ni3Fe and Ti3C2 in a mass ratio of 3–6:1. Its structure is a supported structure of Ni3Fe particles loaded on the surface of lamellar Ti3C2, exhibiting strong inter-component interactions and excellent dispersion of the supported material. In the field of magnesium-based hydrogen storage, this catalyst requires only 5 wt.% to reduce the effective hydrogen absorption temperature from 200°C to 50°C and the peak dehydrogenation temperature from 384.5°C to 279.9°C. In the field of magnesium-based hydrogen production, this catalyst requires only 0.5 wt.% to achieve a 94.7% conversion rate for hydrogen production from magnesium hydrolysis within 30 seconds, meeting practical application requirements over a wide temperature range.

Description

Technical fields:

[0001] This invention relates to a catalyst, its preparation method, and its application, specifically to a bifunctional catalyst that improves both magnesium hydrogen storage and hydrogen production performance, its preparation method, and its application. This material has strong inter-component interactions and excellent dispersion of the supported material, and can simultaneously improve the kinetic performance of the magnesium hydrogen storage and hydrolysis hydrogen production dual system. Background technology:

[0002] Hydrogen energy boasts advantages such as high calorific value, zero pollution, and recyclability. It can be converted into electricity through fuel cells, enabling large-scale peak shaving of the power grid and cross-seasonal, cross-regional energy storage; alternatively, it can be converted into heat energy through combustion. Both energy conversions ultimately produce only water, accelerating the decarbonization of industry, construction, and transportation. While hydrogen energy is characterized by its recyclability, zero emissions, storability, and energy interconnectivity, its efficient production and storage technologies have received widespread attention. However, hydrogen's extremely low volumetric density makes its portable storage a major obstacle to its practical application and widespread adoption.

[0003] Magnesium can absorb or release hydrogen through heating (pyrolysis), with a theoretical hydrogen storage density as high as 7.6 wt.%, far exceeding most metallic hydrogen storage materials. Furthermore, magnesium is abundant in the Earth's crust, relatively inexpensive, and exhibits good reversibility in hydrogen absorption and desorption reactions, making it suitable for large-scale hydrogen storage stations and on-board hydrogen storage systems. However, the strong binding force between Mg and H, requiring an activation energy of up to 160 kJ / mol for dehydrogenation, means that high operating temperatures and slow absorption / desorption rates are the main factors limiting its practical application. In addition, magnesium can directly release hydrogen through hydrolysis (reaction with water), making it suitable for small-scale applications requiring portable clean hydrogen sources. However, the kinetics of magnesium hydrolysis for hydrogen production are very slow, with low conversion rates; and due to the non-recyclability of hydrolysis-based hydrogen production, the system's economy and portability are crucial. Doping magnesium with trace amounts of transition metals through ball milling is an effective way to improve its hydrogen storage and hydrolysis hydrogen production performance, significantly enhancing kinetic performance while avoiding excessive capacity loss. Ni-based transition metals are commonly used catalysts. Cheng et al. (Int J Hydrogen Energy, 2019, 44: 10777-87) deposited Pd and Ni nanoparticles onto the surface and interior of mesoporous carbon using a simple impregnation and high-temperature reduction method. This bimetallic catalyst significantly improved the hydrogen storage performance of MgH2, releasing approximately 6 wt% hydrogen at 561 K. However, metallic Pd is relatively expensive. Yao et al. (J Phys Chem B, 2006, 110: 11697–703) found that the FeTi-CNT complex had a more significant impact on the hydrogen absorption rate of Mg compared to single-element catalysts. The ternary complex of Mg-FeTi-CNT could absorb 5 wt% hydrogen within 10 min at 200 °C, but the long grinding time (30-60 hours) and high hydrogen absorption temperature were not conducive to large-scale applications. Transition metals and their oxides have a significant promoting effect on the hydrolysis performance of Mg. Huang et al. (Int. J. Hydrogen Energy, 2017, 42(35): 22305-11) reported the effects of Fe2O3, CaO, MoO3, Fe3O4, Nb2O5, and TiO2 on the hydrolysis performance of Mg. Among them, Mg-MoO3 and Mg-Fe2O3 showed the highest hydrolysis performance, reaching 888 mL g. -1 min -1 The hydrogen production rate is high, with a hydrogen conversion rate of 95.2% within 10 minutes.

[0004] Clearly, metal catalysts exhibit excellent catalytic performance in both magnesium-based hydrogen storage and production systems. However, few studies have focused on developing a high-performance transition metal-based catalyst with the dual function of promoting both magnesium hydrogen storage and hydrogen production through the common hydrogen movement characteristics in both processes. In large-scale magnesium hydrogen storage systems, the required hydrogen absorption and desorption temperatures are currently high, so performance modification should aim to lower the operating temperature. In magnesium hydrogen production systems, due to the irreversible nature of hydrolysis, performance modification should focus on reducing the catalyst dosage to meet economic requirements. Currently, in magnesium hydrogen storage systems, the catalytic effects of Ni and Fe are far from meeting practical application requirements. In magnesium hydrogen production systems, the small specific surface area of ​​metal catalysts means that low dosages cannot demonstrate catalytic performance. Ti3C2, as a two-dimensional material, can significantly increase the specific surface area of ​​metal catalysts, but metal catalysts are difficult to anchor on its surface, and metal supports often exhibit detachment and aggregation. Summary of the Invention:

[0005] The purpose of this invention is to improve upon existing technologies by providing a bifunctional catalyst that enhances both magnesium hydrogen storage and hydrogen production performance, addressing the poor kinetics of magnesium hydrogen storage / hydrogen production. Another objective is to provide a method for preparing the catalyst, and a further objective is to provide applications of the catalyst. The catalyst comprises Ni3Fe and Ti3C2 in a mass ratio of 3–6:1; its structure is a supported structure of Ni3Fe particles supported on the surface of lamellar Ti3C2, exhibiting strong inter-component interactions and excellent dispersion of the supported material. Adding 5 wt.% of this catalyst reduces the effective hydrogen absorption temperature of magnesium hydrogen storage from 200°C to 50°C and the peak dehydrogenation temperature from 384.5°C to 279.9°C. Adding 0.5 wt.% of this catalyst enables a 94.7% conversion rate for magnesium hydrogen production via hydrolysis within 30 seconds, meeting practical application requirements over a wide temperature range.

[0006] The technical solution adopted in this invention is: a bifunctional catalyst, characterized in that the bifunctional catalyst components include Ni3Fe and Ti3C2 in a mass ratio of 3 to 6:1; the structure is a supported structure in which Ni3Fe particles are supported on the surface of Ti3C2 sheets.

[0007] This invention also provides a method for preparing the above-mentioned bifunctional catalyst. The method involves electrostatically combining a NiFe-LDH-Ti3C2 colloidal solution, centrifuging and drying it to obtain a self-assembled (NiFe-LDH)-Ti3C2 precursor, followed by thermal reduction of the (NiFe-LDH)-Ti3C2 precursor to obtain the Ni3Fe-Ti3C2 bifunctional catalyst. Ni3Fe-Ti3C2 is then combined with MgH2 / Mg via a ball milling process. Based on corresponding hydrogen storage and hydrolysis hydrogen production performance tests, it is demonstrated that Ni3Fe-Ti3C2 has an excellent promoting effect on both magnesium hydrogen storage and hydrogen production performance, and exhibits synergistic catalytic characteristics among the catalyst components.

[0008] The specific steps are as follows:

[0009] (1) A certain proportion of Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, urea and NH4F were added to a methanol solution and mixed. The mixture was then solvothermal in a high-pressure reactor for a certain time. After centrifugation, washing and drying, flower-shaped NiFe-LDH was obtained.

[0010] (2) Etching Ti3AlC2 to obtain a product suspension, then performing ultrasonic centrifugation to peel off the upper colloidal solution to obtain a Ti3C2 colloidal solution;

[0011] (3) The NiFe-LDH from step (1) is added to the Ti3C2 colloidal solution from step (2) in portions, and then sealed ultrasonic dispersion, centrifugal washing and drying are performed in sequence to obtain the (NiFe-LDH)-Ti3C2 precursor; (4) The (NiFe-LDH)-Ti3C2 precursor from step (3) is calcined and reduced to obtain the Ni3Fe-Ti3C2 bifunctional catalyst.

[0012] In preferred step (1), the molar ratio of Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, urea and NH4F is 6:2:(12~15):(0.5~1); the solvothermal temperature is 90~120℃, the holding time is 8~12h; the centrifugal washing speed is 6000~8000rpm, the centrifugal washing time is 10~30min; the drying temperature is 40~50℃, and the drying time is 24~48h.

[0013] In step (2), the product suspension was prepared by etching Ti3AlC2 with a LiF-HCl mixture, referring to the invention patent CN114843700A.

[0014] The preferred parameters for ultrasonic centrifugal peeling in step (2) are: ultrasonic temperature of 0-5℃, ultrasonic power of 300-400W, ultrasonic treatment time of 1-3h; centrifugal peeling speed of 3000-4000rpm, and centrifugal peeling time of 1-3h.

[0015] In the preferred step (3), the number of times the ultrasonic treatment is performed is 8 to 10 times; the ultrasonic temperature is 0 to 5°C, the ultrasonic power is 300 to 400W, and the ultrasonic treatment time is 1 to 3 hours; the centrifugal washing speed is 6000 to 8000 rpm, and the centrifugal washing time is 10 to 30 minutes; the drying temperature is 40 to 50°C, and the drying time is 24 to 48 hours.

[0016] The preferred step (4) is to use a calcination and reduction temperature of 500-600°C, a calcination and reduction time of 1-3 hours, and a calcination and reduction atmosphere of pure hydrogen or a hydrogen-argon mixture with a hydrogen volume concentration of 5%-10%.

[0017] This invention also provides the application of the above-mentioned Ni3Fe-Ti3C2 bifunctional catalyst in metal hydrogen storage. Its characteristic is that Ni3Fe-Ti3C2 and MgH2 are mixed by ball milling, and the ball milling loading and unloading processes are both carried out in an argon atmosphere glove box, wherein the mass of the catalyst added is 3% to 10% of the total mass of MgH2 and the catalyst. This invention also provides the application of the above-mentioned Ni3Fe-Ti3C2 bifunctional catalyst in metal hydrogen production. Its characteristic is that Ni3Fe-Ti3C2 and Mg are mixed by ball milling, and the ball milling loading and unloading processes are both carried out in an argon atmosphere glove box, wherein the catalyst accounts for 0.5 wt.% to 8 wt.% of the total mass of Mg and the catalyst.

[0018] The NiFe-LDH prepared in this invention exhibits a positive charge in solution and a negative charge in Ti3C2 colloidal solution. By slowly adding a certain amount of NiFe-LDH to the Ti3C2 solution, a supported structure of NiFe-LDH on the Ti3C2 surface is formed through electrostatic adsorption and self-assembly. Further calcination in a reducing atmosphere yields a supported Ni3Fe-Ti3C2 catalyst. A synergistic catalytic effect is observed between Ni3Fe and Ti3C2. This catalyst significantly reduces the operating temperature during magnesium hydrogen storage and significantly increases the hydrogen production rate and conversion rate during magnesium hydrolysis hydrogen production, demonstrating a dual-function catalytic effect that simultaneously promotes magnesium hydrogen storage and production.

[0019] Beneficial effects:

[0020] (1) Compared with ordinary metal catalyst support systems, the bifunctional catalyst provided by the electrostatic self-assembled precursor of the present invention has the characteristics of strong inter-component interaction and excellent dispersion of the support without falling off.

[0021] (2) Compared with the single function of ordinary catalysts (hydrogen storage or water electrolysis hydrogen production system), the bifunctional catalyst provided by the present invention exhibits component synergy through the supported structure, thereby possessing strong magnesium hydrogen storage and water electrolysis hydrogen production dual system catalytic effect.

[0022] (3) The Ni3Fe-Ti3C2 bifunctional catalyst reduces the operating temperature of magnesium hydrogen absorption from 200℃ to 50℃, and the hydrogen absorption capacity is as high as 4.56wt.%, providing a broad prospect for the application of magnesium hydrogen storage system.

[0023] (4) Only 0.5 wt.% of Ni3Fe-Ti3C2 bifunctional catalyst is required to achieve a hydrogen production conversion rate of 94.7% for micron-sized magnesium hydrolysis within 30s; at the same time, it meets a wide range of hydrolysis temperatures, which meets the actual application requirements of metal hydrolysis hydrogen production. Attached image description:

[0024] Figure 1 The XRD patterns of the Ni3Fe-Ti3C2 (Ni3Fe to Ti3C2 mass ratio of 3:1, 4:1, 5:1, 6:1) bifunctional catalysts prepared in Examples 1-4 are shown.

[0025] Figure 2 DSC curves for MgH2-5 wt.%Ni3Fe-Ti3C2 (mass ratio of Ni3Fe to Ti3C2 is 3:1, 4:1, 5:1, 6:1) prepared in Example 2;

[0026] Figure 3 SEM images of the (NiFe-LDH)-Ti3C2 precursor (a) and Ni3Fe-Ti3C2 (5:1) (b) samples prepared in Example 3;

[0027] Figure 4 DSC curves of MgH2-5 wt.%Ni3Fe-Ti3C2(5:1) prepared in Example 3 and samples from Comparative Examples 1, 2 and 3 are shown.

[0028] Figure 5 Isothermal hydrogen absorption curves of MgH2-5 wt.% Ni3Fe-Ti3C2 (5:1) prepared in Example 3 and Comparative Example 3 at different temperatures;

[0029] Figure 6 Hydrogen production curves of Mg-y wt.% Ni3Fe-Ti3C2(5:1) (y=0.5,1,2,5,8) prepared in Example 4 at 30℃;

[0030] Figure 7 Hydrogen production curves of Mg-5wt.%Ni3Fe-Ti3C2(5:1) prepared in Example 5 at different temperatures;

[0031] Figure 8 Hydrogen production curves at 0 °C were obtained for the Mg-5wt.%Ni3Fe-Ti3C2 (5:1) prepared in Example 5 and for the samples of Comparative Examples 4, 5 and 6. Detailed implementation method:

[0032] The present invention will be further described in detail below with reference to specific embodiments. The embodiments and application examples given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0033] Unless otherwise specified, the experimental methods in the following embodiments and application examples are conventional methods.

[0034] Unless otherwise specified, the materials and reagents used in the following examples and application examples are commercially available.

[0035] Example 1

[0036] (1) 6 mmol Ni(NO3)2·6H2O, 2 mmol Fe(NO3)3·9H2O, 12 mmol urea and 0.5 mmol NH4F were added to 50 ml methanol solution. After dissolution, the solution was placed in a reaction vessel, sealed, and reacted at 120 °C for 8 h. After the reaction, the product was washed three times by alternating centrifugation with deionized water and ethanol. The centrifugation speed was 6000 rpm and the centrifugation time was 30 min. Then, the product was dried in an oven at 40 °C for 24 h to obtain NiFe-LDH.

[0037] (2) Referring to Example 1 of the invention patent CN114843700A, 2g LiF was added to 40mL of 9M HCl under constant stirring, and then 2g Ti3AlC2 was added to it. The above solution was then placed in a 40℃ water bath and stirred for 24h to obtain the etching product. Subsequently, it was washed with ultrapure water until the pH value was 6.

[0038] (3) The above product was sealed at 5°C, sonicated at 300W power for 3h, and centrifuged at 4000rpm for 1h. The dark green solution on the upper layer of the product was collected as the obtained Ti3C2 colloidal solution.

[0039] (4) NiFe-LDH was added to the Ti3C2 colloidal solution in 8 batches with stirring according to the mass ratio of Ni3Fe to Ti3C2 of 3:1. The solution was sealed at 5°C, ultrasonically dispersed at 300W power for 3h, centrifuged at 6000rpm for 30min, and then dried in an oven at 40°C for 24h to obtain the (NiFe-LDH)-Ti3C2 catalyst precursor.

[0040] (5) The above (NiFe-LDH)-Ti3C2 catalyst precursor was then calcined in a hydrogen atmosphere at 500°C for 1 h to obtain Ni3Fe-Ti3C2 (3:1) catalyst.

[0041] Example 2

[0042] (1) 6 mmol Ni(NO3)2·6H2O, 2 mmol Fe(NO3)3·9H2O, 13 mmol urea and 0.7 mmol NH4F were added to 50 ml of methanol solution. After dissolution, the solution was placed in a reaction vessel, sealed, and reacted at 100 °C for 10 h. After the reaction, the product was washed three times by alternating centrifugation with deionized water and ethanol. The centrifugation speed was 7000 rpm and the centrifugation time was 25 min. Then, the product was dried in an oven at 40 °C for 48 h to obtain NiFe-LDH.

[0043] (2) Referring to Example 2 of the invention patent CN114843700A, 2g of LiF was added to 40mL of 9M HCl under constant stirring, and then 2g of Ti3AlC2 was added to it. The above solution was then placed in a 35°C water bath and stirred for 30h to obtain the etching product. Subsequently, it was washed with ultrapure water until the pH value was 6.

[0044] (3) The above solution was sealed at 3°C, sonicated at 350W power for 2 hours, and centrifuged at 3500rpm for 2 hours. The dark green solution on the upper layer of the product was collected as the obtained Ti3C2 colloidal solution.

[0045] (4) NiFe-LDH was added to the Ti3C2 colloidal solution in 9 batches with stirring according to the mass ratio of Ni3Fe to Ti3C2 of 4:1. The solution was sealed at 3°C, ultrasonically dispersed at 350W power for 2h, centrifuged at 7000rpm for 25min, and then dried in an oven at 40°C for 48h to obtain the (NiFe-LDH)-Ti3C2 catalyst precursor.

[0046] (5) The above (NiFe-LDH)-Ti3C2 catalyst precursor was then calcined in a hydrogen-argon mixed atmosphere at 550℃ (hydrogen volume concentration of 5%) for 1 h to obtain Ni3Fe-Ti3C2 (4:1) catalyst.

[0047] Example 3

[0048] (1) 6 mmol Ni(NO3)2·6H2O, 2 mmol Fe(NO3)3·9H2O, 14 mmol urea and 0.8 mmol NH4F were added to 50 ml of methanol solution. After dissolution, the solution was placed in a reaction vessel, sealed, and reacted at 90 °C for 12 h. After the reaction, the product was washed three times by alternating centrifugation with deionized water and ethanol. The centrifugation speed was 8000 rpm and the centrifugation time was 10 min. Then, the product was dried in an oven at 50 °C for 24 h to obtain NiFe-LDH.

[0049] (2) Referring to Example 3 of the invention patent CN114843700A, 2g of LiF was added to 40mL of 9M HCl under constant stirring, and then 2g of Ti3AlC2 was added to it. The above solution was then placed in a 45℃ water bath and stirred for 20h to obtain the etching product. Subsequently, it was washed with ultrapure water until the pH value was 7.

[0050] (3) The above solution was sealed at 0℃, sonicated at 400W power for 1h, and centrifuged at 3000rpm for 3h. The dark green solution on the upper layer of the product was collected as the obtained Ti3C2 colloidal solution.

[0051] (4) NiFe-LDH was added to the Ti3C2 colloidal solution in 10 batches with stirring according to the mass ratio of Ni3Fe to Ti3C2 of 5:1. The solution was sealed at 0℃, ultrasonically dispersed at 400W power for 1h, centrifuged at 8000rpm for 10min, and then dried in an oven at 50℃ for 24h to obtain the (NiFe-LDH)-Ti3C2 catalyst precursor.

[0052] (5) Subsequently, the above (NiFe-LDH)-Ti3C2 catalyst precursor was calcined in a hydrogen-argon mixed atmosphere at 600℃ (hydrogen volume concentration of 10%) for 2h to obtain Ni3Fe-Ti3C2 (5:1) catalyst.

[0053] Example 4

[0054] (1) 6 mmol Ni(NO3)2·6H2O, 2 mmol Fe(NO3)3·9H2O, 15 mmol urea and 1 mmol NH4F were added to 50 ml of methanol solution. After dissolution, the solution was placed in a reaction vessel, sealed, and reacted at 110 °C for 9 h. After the reaction, the product was washed three times by alternating centrifugation with deionized water and ethanol. The centrifugation speed was 7000 rpm and the centrifugation time was 20 min. Then, the product was dried in an oven at 45 °C for 36 h to obtain NiFe-LDH.

[0055] (2) Referring to Example 4 of the invention patent CN114843700A, 2g of LiF was added to 40mL of 9M HCl under constant stirring, and then 2g of Ti3AlC2 was added to it. The above solution was then placed in a 40℃ water bath and stirred for 24h to obtain the etching product. Subsequently, it was washed with ultrapure water until the pH value was 6.

[0056] (3) The above solution was sealed at 1°C, sonicated at 350W for 3h, and centrifuged at 3500rpm for 3h. The dark green solution on the upper layer of the product was collected as the obtained Ti3C2 colloidal solution.

[0057] (4) NiFe-LDH was added to the Ti3C2 colloidal solution in 10 batches with stirring according to the mass ratio of Ni3Fe to Ti3C2 of 6:1. The solution was sealed at 1℃, ultrasonically dispersed at 350W power for 3h, centrifuged at 7000rpm for 20min, and then dried in an oven at 45℃ for 36h to obtain the (NiFe-LDH)-Ti3C2 catalyst precursor.

[0058] (5) The above (NiFe-LDH)-Ti3C2 catalyst precursor was then calcined in a hydrogen-argon mixed atmosphere at 550℃ (hydrogen volume concentration of 10%) for 3h to obtain Ni3Fe-Ti3C2 (6:1) catalyst.

[0059] The results are as follows:

[0060] Figure 1 The XRD patterns of Ni3Fe-Ti3C2 (mass ratio of Ni3Fe to Ti3C2 of 3:1, 4:1, 5:1, 6:1) obtained by thermal reduction of the (NiFe-LDH)-Ti3C2 catalyst precursor prepared in Examples 1-4 above are shown. As can be seen from the figure, characteristic diffraction peaks of Ni3Fe and Ti3C2 appear in all cases under the current process, proving that Ni3Fe-Ti3C2 of different proportions was successfully prepared.

[0061] Application Example 1

[0062] (1) Preparation of MgH2-x wt.% Ni3Fe-Ti3C2 (3:1) (x=3,5,8,10) hydrogen storage material by ball milling: Ni3Fe-Ti3C2 (3:1) prepared in Example 1 above was mixed with MgH2 by ball milling. The mass ratio of MgH2 to Ni3Fe-Ti3C2 (3:1) bifunctional catalyst was 97:3, 95:5, 92:8, and 90:10, respectively. The ball milling time was 10 hours, the ball-to-material mass ratio was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading process was carried out in an argon atmosphere glove box.

[0063] (2) The composite hydrogen storage material prepared above was subjected to DSC testing. The test conditions were as follows: the sample mass for each test was 10 mg, the test atmosphere was argon, the pressure was 27 kPa, and the heating rate was 10 °C / min. Considering both kinetic performance and hydrogen storage capacity, the DSC results showed that MgH2-5 wt.%Ni3Fe-Ti3C2 (3:1) exhibited the best hydrogen storage performance. Therefore, when the mass ratio of MgH2 to the bifunctional catalyst was 95:5, i.e., the catalyst content was 5 wt.%, it was considered the preferred option.

[0064] Application Example 2

[0065] Preparation of MgH2-5 wt.% Ni3Fe-Ti3C2 (Ni3Fe to Ti3C2 mass ratio of 3:1, 4:1, 5:1, 6:1) hydrogen storage material by ball milling: The Ni3Fe-Ti3C2 (Ni3Fe to Ti3C2 mass ratio of 3:1, 4:1, 5:1, 6:1) prepared in Examples 1-4 above was mixed with MgH2 by ball milling. The mass ratio of MgH2 to Ni3Fe-Ti3C2 (Ni3Fe to Ti3C2 mass ratio of 3:1, 4:1, 5:1, 6:1) bifunctional catalyst was 95:5. The ball milling time was 10 hours, the ball-to-material mass ratio was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation followed by 6 minutes of rest. The ball milling loading and unloading processes were all carried out in an argon atmosphere glove box.

[0066] Figure 2 The DSC curves for MgH2-5 wt.% Ni3Fe-Ti3C2 (Ni3Fe to Ti3C2 mass ratios of 3:1, 4:1, 5:1, and 6:1) are shown. The peak dehydrogenation temperatures for MgH2-5 wt.% Ni3Fe-Ti3C2 (3:1) are 274.9℃ and 347.7℃, respectively; the peak dehydrogenation temperatures for MgH2-5 wt.% Ni3Fe-Ti3C2 (4:1) are 278.7℃ and 347.7℃, respectively.

[0067] The peak dehydrogenation temperatures of MgH2-5 wt.% Ni3Fe-Ti3C2 (6:1) were 276.9℃ and 301.2℃, respectively; while MgH2-5 wt.% Ni3Fe-Ti3C2 (5:1) exhibited the best dehydrogenation performance, showing only one peak dehydrogenation temperature, which was only 279.9℃. Therefore, the Ni3Fe-Ti3C2 (5:1) bifunctional catalyst showed the best performance.

[0068] Figure 3 SEM images of the (NiFe-LDH)-Ti3C2 catalyst precursor and the Ni3Fe-Ti3C2 (5:1) catalyst are shown. The SEM images show that Ti3C2 has a layered structure, with Ni3Fe micron particles of approximately 1–2 μm supported on the layered Ti3C2 to form a supported structure.

[0069] Application Example 3

[0070] (1) Preparation of MgH2-5 wt.%Ni3Fe-Ti3C2(5:1) hydrogen storage material by ball milling: Ni3Fe-Ti3C2(5:1) prepared in Example 3 above was mixed with MgH2 by ball milling. The mass ratio of MgH2 to Ni3Fe-Ti3C2(5:1) bifunctional catalyst was 95:5. The ball milling time was 10 hours, the ball-to-material mass ratio was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading process was carried out in an argon atmosphere glove box.

[0071] (2) The composite hydrogen storage material prepared above was subjected to DSC test. The test conditions were: the mass of the sample was 10 mg each time, the test atmosphere was argon atmosphere, the pressure was 27 kPa, and the heating rate was 10 °C / min.

[0072] (3) The composite hydrogen storage material prepared above was subjected to isothermal hydrogen absorption test. The test conditions were: isothermal hydrogen absorption test temperature of 50, 100 and 150℃, and hydrogen absorption pressure of 3MPa.

[0073] The results are as follows:

[0074] Figure 4 The DSC curves of the prepared MgH2-5 wt.%Ni3Fe-Ti3C2 (5:1), MgH2-5 wt.%Ni3Fe in Comparative Example 1, MgH2-5 wt.%Ti3C2 in Comparative Example 2, and MgH2 in Comparative Example 3 are shown. The figures show that MgH2-5 wt.%Ni3Fe-Ti3C2 (5:1) exhibits the best performance, with a dehydrogenation peak temperature of 279.9℃. The dehydrogenation peak temperatures of MgH2-5 wt.%Ni3Fe and MgH2-5 wt.%Ti3C2 are 317.2℃ and 350.1℃, respectively, while the dehydrogenation peak temperature of MgH2 without a catalyst reaches as high as 384.5℃. Therefore, Ni3Fe-Ti3C2 exhibits a synergistic effect among its components.

[0075] Figure 5 The isothermal hydrogen absorption curves of the prepared MgH2-5 wt.% Ni3Fe-Ti3C2 (5:1) and MgH2 in Comparative Example 3 are shown. As can be seen from the figure, at 50℃, MgH2-5 wt.% Ni3Fe-Ti3C2 (5:1) can achieve a hydrogen absorption capacity of ~4.56 wt.%, while MgH2 without a catalyst only exhibits effective hydrogen absorption performance at 200℃.

[0076] Application Example 4

[0077] (1) Preparation of Mg-y wt.% Ni3Fe-Ti3C2(5:1) (y=0.5,1,2,5,8) hydrolysis hydrogen production material by ball milling: The Ni3Fe-Ti3C2(5:1) catalyst prepared in Example 3 above was mixed with Mg by ball milling. The mass ratio of Mg to Ni3Fe-Ti3C2(5:1) bifunctional catalyst was 99.5:0.5, 99:1, 98:2, 95:5 and 92:8, respectively. The ball milling time was 1 hour, the ball-to-material mass ratio was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading process was carried out in an argon atmosphere glove box.

[0078] (2) The above-mentioned hydrolysis hydrogen production material was placed in a 3.5% NaCl solution at 30℃ to test its hydrolysis hydrogen production performance. The results are as follows:

[0079] Figure 6 To obtain Mg-y Hydrogen production curves of wt.% Ni3Fe-Ti3C2(5:1) (y=0.5,1,2,5,8) at 30℃; among them, Mg-0.5wt.% Ni3Fe-Ti3C2(5:1) reached a saturated hydrogen production of 873.3mL / g within 30s, Mg-1wt.% Ni3Fe-Ti3C2(5:1) reached a saturated hydrogen production of 877.4mL / g within 25s, Mg-2wt.% Ni3Fe-Ti3C2(5:1) reached a saturated hydrogen production of 873.2mL / g within 25s; Mg-5wt.% Ni3Fe-Ti3C2(5:1) reached a saturated hydrogen production of 866.5mL / g within 25s; Mg-8wt.% Ni3Fe-Ti3C2(5:1) reached a saturated hydrogen production of 843.8mL / g within 25s. Therefore, only 0.5 wt.% Ni3Fe-Ti3C2 is needed for magnesium to exhibit sufficiently efficient hydrogen production through hydrolysis.

[0080] Application Example 5

[0081] (1) Preparation of Mg-5wt.%Ni3Fe-Ti3C2(5:1) hydrolysis hydrogen production material by ball milling: The Ni3Fe-Ti3C2(5:1) catalyst prepared in Example 3 above was mixed with Mg by ball milling. The mass ratio of Mg to Ni3Fe-Ti3C2(5:1) bifunctional catalyst was 95:5. The ball milling time was 1 hour, the ball-to-material mass ratio was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading process was carried out in an argon atmosphere glove box.

[0082] (2) The above-mentioned hydrolysis hydrogen production materials were placed in 3.5% NaCl solutions at 0, 10, 20, 30 and 40°C to test their hydrolysis hydrogen production performance.

[0083] The results are as follows:

[0084] Figure 7 Hydrogen production curves of Mg-5wt.%Ni3Fe-Ti3C2(5:1) at different temperatures were shown. Mg-5wt.%Ni3Fe-Ti3C2(5:1) produced 835.6, 863.8, 865.2, 865.6, and 867.3 mL / g of hydrogen gas within 15 s at temperatures of 0, 10, 20, 30, and 40 °C, respectively. Therefore, Mg-5wt.%Ni3Fe-Ti3C2(5:1) still exhibits excellent hydrogen production performance through hydrolysis over a wide range of practical application temperatures.

[0085] Figure 8 The figures show the hydrogen production curves of the prepared Mg-5wt.%Ni3Fe-Ti3C2 (5:1), as well as the Mg-5wt.%Ni3Fe in Comparative Example 4, the Mg-5wt.%Ti3C2 in Comparative Example 5, and the Mg sample in Comparative Example 6. As can be seen from the figures, at 0℃, the Mg-5wt.%Ni3Fe-Ti3C2 (5:1) exhibits the best hydrogen production performance through hydrolysis, producing 857.4 mL / g of hydrogen within 20 s. Under the same conditions, the Mg-5wt.%Ni3Fe, Mg-5wt.%Ti3C2, and Mg samples only produced 690.5, 49.3, and 27.7 mL / g of hydrogen, respectively. Therefore, Ni3Fe-Ti3C2 demonstrates excellent component synergistic effects.

[0086] Comparative Example 1:

[0087] (1) Preparation of Ni3Fe catalyst: 6 mmol Ni(NO3)2·6H2O, 2 mmol Fe(NO3)3·9H2O, 14 mmol urea and 1 mmol NH4F were added to 50 ml of methanol solution. After dissolution, the solution was placed in a sealed reactor and reacted at 90 °C for 12 hours. After the reaction, the product was washed three times by alternating centrifugation with deionized water and ethanol. The centrifugation speed was 6000 rpm and the centrifugation time was 30 min. Then, the product was dried in an oven at 40 °C for 24 hours to obtain NiFe-LDH. Next, NiFe-LDH was calcined at 500 °C under a hydrogen atmosphere for 1 hour to obtain Ni3Fe catalyst.

[0088] (2) Preparation of MgH2-5 wt.%Ni3Fe hydrogen storage material by ball milling: Ni3Fe catalyst and MgH2 were mixed by ball milling. The mass ratio of MgH2 to Ni3Fe catalyst was 95:5. The ball milling time was 10 hours, the mass ratio of ball to material was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading process was carried out in an argon atmosphere glove box.

[0089] Comparative Example 2:

[0090] (1) Preparation of Ti3C2 catalyst: Ti3C2 colloidal solution was filtered and dried in an oven at 40°C for 24 hours.

[0091] (2) Preparation of MgH2-5 wt.%Ti3C2 hydrogen storage material by ball milling: Ti3C2 catalyst and MgH2 were mixed by ball milling. The mass ratio of MgH2 to Ti3C2 catalyst was 95:5. The ball milling time was 10 hours, the mass ratio of ball to material was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading process was carried out in an argon atmosphere glove box.

[0092] Comparative Example 3:

[0093] Ball milling preparation of MgH2 hydrogen storage material: The ball milling time was 10 hours, the ball-to-material mass ratio was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation followed by 6 minutes of rest. The ball milling loading and unloading processes were all carried out in an argon atmosphere glove box.

[0094] Comparative Example 4:

[0095] Preparation of Mg-5wt.%Ni3Fe hydrolysis hydrogen production material by ball milling: Ni3Fe catalyst and Mg were mixed by ball milling with a mass ratio of Mg to Ni3Fe catalyst of 95:5, a ball milling time of 1 hour, a ball-to-material mass ratio of 30:1, a ball milling speed of 400 r / min, and alternating between 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading processes were carried out in an argon atmosphere glove box.

[0096] Comparative Example 5

[0097] Preparation of Mg-5wt.%Ti3C2 hydrolysis hydrogen production material by ball milling: Ti3C2 catalyst and Mg were mixed by ball milling. The mass ratio of Mg to Ti3C2 catalyst was 95:5. The ball milling time was 1 hour, the mass ratio of ball to material was 30:1, the ball milling speed was 400 r / min, and the process was repeated with 30 minutes of operation and 6 minutes of rest. The ball milling loading and unloading processes were carried out in an argon atmosphere glove box.

[0098] Comparative Example 6

[0099] Ball milling preparation of Mg hydrolysis hydrogen production materials: ball milling time was 1 hour, ball-to-material mass ratio was 30:1, ball milling speed was 400 r / min, running for 30 minutes and stopping for 6 minutes alternately, and the ball milling loading and unloading processes were all carried out in an argon atmosphere glove box.

Claims

1. A bifunctional catalyst, characterized in that, The bifunctional catalyst comprises Ni3Fe and Ti3C2 in a mass ratio of 3–6:1; its structure is a supported structure of Ni3Fe particles supported on the surface of Ti3C2 sheets, and it is prepared by the following method, the specific steps of which are as follows: (1) A certain proportion of Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, urea and NH4F were added to a methanol solution and mixed. The mixture was then solvothermal in a high-pressure reactor for a certain time. After centrifugation, washing and drying, flower-shaped NiFe-LDH was obtained. (2) Etching Ti3AlC2 to obtain a product suspension, then performing ultrasonic centrifugation to peel off the upper colloidal solution to obtain a Ti3C2 colloidal solution; (3) The NiFe-LDH in step (1) is added to the Ti3C2 colloidal solution in step (2) in portions, and then sealed ultrasonic dispersion, centrifugal washing and drying are performed in sequence to obtain (NiFe-LDH)-Ti3C2 precursor; (4) The (NiFe-LDH)-Ti3C2 precursor in step (3) is subjected to calcination and reduction treatment to obtain the Ni3Fe-Ti3C2 bifunctional catalyst.

2. The bifunctional catalyst according to claim 1, characterized in that... In step (1), the molar ratio of Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, urea and NH4F is 6:2:(12~15):(0.5~1); the solvothermal temperature is 90~120℃, the holding time is 8~12h; the centrifugal washing speed is 6000~8000rpm, the centrifugal washing time is 10~30min; the drying temperature is 40~50℃, and the drying time is 24~48h.

3. The bifunctional catalyst according to claim 1, characterized in that... The ultrasonic centrifugal peeling parameters in step (2) are as follows: ultrasonic temperature is 0-5℃, ultrasonic power is 300-400W, ultrasonic treatment time is 1-3h; centrifugal peeling speed is 3000-4000rpm, and centrifugal peeling time is 1-3h.

4. The bifunctional catalyst according to claim 1, characterized in that... In step (3), the number of times is 8 to 10; the ultrasonic temperature is 0 to 5℃, the ultrasonic power is 300 to 400W, and the ultrasonic treatment time is 1 to 3 hours; the centrifugal washing speed is 6000 to 8000 rpm, and the centrifugal washing time is 10 to 30 minutes; the drying temperature is 40 to 50℃, and the drying time is 24 to 48 hours.

5. The bifunctional catalyst according to claim 1, characterized in that... In step (4), the calcination and reduction temperature is 500-600℃, the calcination and reduction time is 1-3h, and the calcination and reduction atmosphere is pure hydrogen or a hydrogen-argon mixture with a hydrogen volume concentration of 5%-10%.

6. The application of the Ni3Fe-Ti3C2 bifunctional catalyst as described in claim 1 in metal hydrogen storage.

7. The application according to claim 6, characterized in that: Ni3Fe-Ti3C2 and MgH2 are mixed by ball milling. The ball milling loading and unloading processes are carried out in an argon atmosphere glove box. The mass of the catalyst added is 3% to 10% of the total mass of MgH2 and the catalyst.

8. The application of the Ni3Fe-Ti3C2 bifunctional catalyst as described in claim 1 in metal hydrogen production.

9. The application of the Ni3Fe-Ti3C2 bifunctional catalyst according to claim 8 in metal hydrogen production, characterized in that: Ni3Fe-Ti3C2 and Mg are mixed by ball milling. The ball milling loading and unloading processes are carried out in an argon atmosphere glove box. The catalyst accounts for 0.5% to 8% of the total mass of Mg and catalyst.

Images