A method for improving the hydrogen storage performance of MgH2 by catalysis with graphene oxide supported dzhalindite

Abstract

The present invention relates to the field of solid-state hydrogen storage materials, and particularly to a method for improving the hydrogen storage performance of MgH2 by catalyzing with graphene oxide supported VS4. The present invention synthesizes a GO@VS4 nanoparticle composite catalyst by a hydrothermal method assisted by an ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), and then prepares MgH2 doped with GO@VS4 by a ball milling method. The VS4, a transition metal sulfide catalyst prepared in the present invention, has unsaturated d electrons and high conductivity. By introducing a graphene oxide supported VS4 (GO@VS4) catalyst into MgH2, the hydrogen absorption and desorption reaction kinetics and cycle stability of MgH2 can be effectively improved. The activation energy of the desorption kinetics of MgH2 is reduced from 122.7 kJ / mol to 63.8 kJ / mol, and the mass hydrogen desorption capacity remains unchanged after 100 cycles. The preparation process is simple, has low requirements for equipment, is easy to operate, and has commercial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of solid-state hydrogen storage materials, and particularly to a method for enhancing the hydrogen storage performance of MgH2 by catalyzing with graphene oxide supported greenockite. Technical Background

[0002] As a new type of energy with high reserves, high energy density, clean, environmentally friendly and renewable, hydrogen energy has become an important development direction for replacing fossil fuels. At present, the large-scale utilization of hydrogen energy mainly involves three nodes: hydrogen production, storage and application. Developing safe, efficient and economical hydrogen storage technologies is one of the bottlenecks for the large-scale application of hydrogen energy. Hydrogen storage technologies can be divided into high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage and solid-state hydrogen storage. Compared with high-pressure gaseous hydrogen storage materials, solid-state hydrogen storage materials have high safety, good stability, large hydrogen storage capacity of hydrogen storage materials, low storage and transportation hydrogen and hydrogenation costs, and are bound to become the most ideal materials for future large-scale hydrogen energy application hydrogen storage systems. At present, the research on solid-state hydrogen storage materials is continuously developing towards high-hydrogen storage density light high-capacity hydride hydrogen storage systems, mainly including light metal hydrides, etc. The mass hydrogen storage density of MgH2 is 7.6 wt%, and at the same time, it has good reversibility, rich sources and low costs, and is currently a research hotspot of light metal hydrides.

[0003] However, commercial MgH2 needs to release hydrogen at temperatures above 300 °C, and during the hydrogen absorption and desorption cycle process, there will be obvious attenuation of the hydrogen storage capacity. Therefore, to use it as a commercial hydrogen storage material, it is necessary to solve the problems of high hydrogen release temperature and decline in cycle stability. The main reasons for the high hydrogen release temperature of MgH2 include the increase in the endothermic enthalpy of hydrogen release thermodynamics and the slow hydrogen release kinetics. Introducing a catalyst is one of the effective means to solve the kinetic problems faced by MgH2 hydrogen release.

[0004] Among many catalysts, vanadium elements are beneficial to the dehydrogenation of MgH2. Therefore, in the prior art, there have been studies on compounding transition metal vanadium-based catalysts with MgH2 to solve the kinetic problems faced by MgH2 hydrogen release. Currently, the research on vanadium-based catalysts mainly includes: by ball milling, introducing vanadium-based oxides and double-metal salts to reduce the reversible hydrogen absorption and desorption temperature of MgH2. For example, in the document with the application number "202310745955.9", a method for catalyzing and enhancing the hydrogen storage performance of MgH2 by vanadium oxide (vanadium pentoxide@carbon, V2O5@C) is disclosed; in the document with the application number "202410670564.X", a method for catalyzing and enhancing the hydrogen storage performance of MgH2 by copper vanadate is disclosed. However, the problems of the above solutions are: low electron conductivity oxygen-containing substance catalysts will react with MgH2 during the hydrogen absorption and desorption process of MgH2 to form MgO, reducing the hydrogen storage capacity of the system, and at the same time, the hydrogen release temperature is high and the cycle stability declines. Therefore, it is very necessary to develop some other vanadium-based compound catalysts. Summary of the Invention

[0005] To solve the problems of high dehydrogenation temperature, decline in cycle stability, and low hydrogen storage capacity existing in the prior art, the present invention provides a method for catalytically enhancing the hydrogen storage performance of MgH2 based on graphene oxide supported VS4.

[0006] To achieve the purpose of the present invention, the present invention provides a method for catalytically enhancing the hydrogen storage performance of MgH2 based on graphene oxide (GO) supported VS4, comprising the following steps:

[0007] Step 1: GO and 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) are ultrasonically and uniformly dispersed in deionized water to obtain a mixed solution;

[0008] Step 2: Na3VO4·12H2O and C2H5NS (TAA) are added to the mixed solution, and the stirred mixed solution is transferred into a reaction kettle for hydrothermal reaction.

[0009] Step 3: After the reaction solution is cooled to room temperature, the product is collected by centrifugation, washed several times with deionized water and absolute ethanol respectively, and dried in vacuum at 60 °C to obtain a catalyst labeled as GO@VS4.

[0010] Step 4: MgH2 and the prepared GO@VS4 catalyst are mixed and ball-milled to prepare a composite material of MgH2 and GO@VS4.

[0011] In the above step 4, the mass ratio of MgH2 to GO@VS4 is 80-95:5-20.

[0012] In the above step 4, the preferred mass ratio of MgH2 to GO@VS4 is 85:15.

[0013] In the above step 1, 15 mg of GO and 2 mmol of 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) are ultrasonically dispersed in 15 mL of deionized water for 6 h.

[0014] In the above step 1, the ultrasonic time is 5-8 h.

[0015] In the above step 2, 0.5 mmol of Na3VO4·12H2O and 10 mmol of C2H5NS (TAA) are successively added to the mixed solution, and stirring is continued for 1-2 h.

[0016] In the above step 2, the hydrothermal reaction temperature is 160-180 °C and the time is 20-24 h.

[0017] In the above step 4, MgH2 and GO@VS4 are loaded into the ball milling jar, filled with 50 bar of hydrogen, and then ball milled. During ball milling, a two-way operation mode is adopted. First, it rotates forward for 12 minutes, then pauses for 6 minutes, then rotates backward for 12 minutes, and then pauses for 6 minutes, and so on in a cycle.

[0018] In the above step 4, the ball milling speed is 400 rpm, and the mass ratio of the grinding balls to the material is 120:1.

[0019] In the above step 4, the ball milling beads are made of stainless steel and come in three sizes with diameters of 16 mm, 12 mm, and 6 mm respectively, and are proportioned according to a mass ratio of 51:42:27.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] 1) Sulfides of vanadium have higher electronic conductivity compared to oxides of vanadium and vanadium-containing salts, and MgO will not be generated during the hydrogen absorption and desorption process, which can improve the hydrogen storage capacity of MgH2 while enhancing its hydrogen storage performance.

[0022] 2) In the present invention, the GO@VS4 nanoparticle composite catalyst is synthesized by a hydrothermal method assisted by the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIm]Cl). By the hydrothermal method assisted by the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), the size of the VS4 nanoparticles can be controlled at about 10 nm.

[0023] 3) The metastable phase of the transition metal sulfide catalyst prepared in the present invention, VS4, has unsaturated d electrons and high conductivity. By introducing the graphene oxide supported VS4 (GO@VS4) catalyst into MgH2, the hydrogen absorption and desorption reaction kinetics and cycle stability of MgH2 can be effectively improved. The activation energy for dehydrogenation kinetics of MgH2 is reduced from 122.7 kJ / mol to 63.8 kJ / mol, and the mass dehydrogenation capacity remains unchanged after 100 cycles.

[0024] 4) The preparation process of the catalyst and the corresponding composite material provided by the present invention is simple, has low requirements for equipment, and is easy to operate;

[0025] 5) The obtained composite material has excellent dehydrogenation performance and stable cycle performance, and has commercial application prospects. Description of the Drawings

[0026] Figure 1 is the SEM photograph of the GO@VS4 catalyst;

[0027] Figure 2 is the XRD pattern of the GO@VS4 catalyst;

[0028] Figure 3It is the TEM image of the GO@VS4 catalyst;

[0029] Figure 4 It is the HRTEM of the GO@VS4 catalyst;

[0030] Figure 5 It is the SEM image of MgH2-10wt% GO@VS4;

[0031] Figure 6 It is the SEM image of MgH2-15wt% GO@VS4;

[0032] Figure 7 It is the XRD pattern of pristine MgH2, GO@VS4, MgH2-10wt% GO@VS4, and MgH2-10wt% GO@VS4;

[0033] Figure 8 It is the hydrogen desorption performance diagram of pristine MgH2, the composite material with 10wt% GO@VS4 added, and the composite material with 15wt% GO@VS4 added as a function of temperature;

[0034] Figure 9 It is the DSC curve of pristine MgH2 and MgH2-15wt% GO@VS4;

[0035] Figure 10 It is the isothermal hydrogen desorption performance diagram of MgH2-15wt% GO@VS4;

[0036] Figure 11 It is the hydrogen desorption performance diagram of MgH2-15wt% GO@VS4 after 100 cycles;

[0037] Figure 12 It is the activation energy of pristine MgH2 and MgH2-15wt% GO@VS4 samples;

[0038] Figure 13 It is the XRD pattern of the sample of MgH2-15wt% GO@VS4 after the first hydrogen desorption, the second hydrogen desorption, and 100 cycles of hydrogen desorption;

[0039] Figure 14 It is the XRD pattern of the sample of MgH2-15wt% GO@VS4 after the first hydrogen absorption, the second hydrogen absorption, and 100 cycles of hydrogen absorption. Specific implementation method

[0040] The technical solution of the present invention will be further described below through specific examples and drawings.

[0041] The preparation process of the present invention is as follows: The GO@VS4 nanoparticle composite catalyst is synthesized by an ionic liquid-assisted hydrothermal method, and then the GO@VS4-doped MgH2 is prepared by ball milling.

[0042] Example 1: A method for improving the hydrogen storage performance of MgH2 by catalyzing with graphene oxide supported VS4 includes the following steps:

[0043] Step 1: 15 mg of GO and 2 mmol of 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) are ultrasonically dispersed in 15 mL of deionized water for 6 h to obtain a mixed solution.

[0044] Step 2: 0.5 mmol of Na3VO4·12H2O and 10 mmol of C2H5NS (TAA) are successively added to the mixed solution. After continuous stirring for 1 h, the formed mixed solution is transferred into a 30 mL stainless steel autoclave with a polytetrafluoroethylene liner and reacted at 160 °C for 24 h to obtain a reaction solution.

[0045] Step 3: After the reaction solution is cooled to room temperature, the product is collected by centrifugation, washed several times with deionized water and anhydrous ethanol respectively, and dried in vacuum at 60 °C. The obtained catalyst is labeled as GO@VS4.

[0046] As Figure 1 shown, VS4 nanoparticles are tightly attached to the wrinkled and curled GO nanosheets, and there are clear gaps between the particles.

[0047] The phase and purity of the GO@VS4 composite material are characterized by XRD. As Figure 2 shown, the diffraction peak at about 26.5° is the diffraction peak of GO, and the other diffraction peaks correspond to VS4 (JCPDS No. 87-0603). No diffraction peaks of other substances are observed.

[0048] As Figure 3 shown, the low-magnification TEM image further shows that a large number of highly dispersed VS4 nanoparticles are anchored on the GO nanosheets.

[0049] As Figure 4 shown, the HRTEM image shows that the size of the VS4 nanoparticles is about 10 nm.

[0050] Step 4: MgH2 is weighed according to a mass ratio of 90:10, and the GO@VS4 catalyst prepared in Step 3 is loaded into a ball milling tank. After filling with 50 bar of hydrogen, ball milling is carried out. The prepared sample is labeled as MgH2-10wt% GO@VS4 (see Figure 5)。During ball milling, a two-way operation mode is adopted. First, it rotates forward for 12 minutes, then pauses for 6 minutes, then rotates backward for 12 minutes, and then pauses for 6 minutes, and this cycle repeats. The ball milling speed is 400 rpm, and the mass ratio of the grinding balls to the material is 120:1. The ball milling tank is made of stainless steel, with a volume of about 170 mL, and there is a valve connected to the lid for convenient gas charging and discharging. The ball milling beads used are also made of stainless steel, and there are three sizes, with diameters of 16 mm, 12 mm, and 6 mm respectively. According to the mass ratio of 51:42:27, a total mass of 120 g is weighed.

[0051] Example 2. A method for improving the hydrogen storage performance of MgH2 by catalyzing with graphene oxide supported VS4 provided by the present invention includes the following steps:

[0052] Steps 1-3 are the same as those in Example 1;

[0053] Step 4. Weigh MgH2 and the GO@VS4 catalyst prepared in Step 3 according to a mass ratio of 85:15, and prepare the sample MgH2-15wt% GO@VS4 according to the steps of Example 1 (see Figure 6 ).

[0054] The preparation process of the MgH2 is as follows:

[0055] Take 6 grams of Mg powder and put it into the reactor. Connect the reactor containing Mg powder to the hydrogen storage test stand for synthesizing MgH2, evacuate it for half an hour, fill it with hydrogen pressure up to 50 bar, heat it to 580 °C, keep it warm for 2 h, then slowly cool it down to 340 °C, and keep it warm for 8 h. Transfer the powder in the reactor to the ball milling tank, fill the ball milling tank with hydrogen pressure of 50 bar, and the ball milling parameters are: 400 rpm, 8 h. Re-fill the ball-milled powder into the reactor and connect it to the special hydrogen storage test stand for synthesizing MgH2 again, and fill it with hydrogen pressure up to 50 bar after evacuating. Heat it to 380 °C and keep it warm for 12 h to prepare the original MgH2, marked as Pristine MgH2.

[0056] Figure 7 The XRD patterns show that after ball milling and mixing, the XRD diffraction peaks of the MgH2-10wt% GO@VS4 and MgH2-15wt% GO@VS4 samples completely match the diffraction peaks of MgH2.

[0057] See Figure 8, the main hydrogen desorption of the original MgH2 is concentrated between 320 and 380 °C. Adding 10 wt% GO@VS4 catalyst can reduce the hydrogen desorption temperature range of MgH2 to 250 - 350 °C. Compared with the original MgH2, the hydrogen desorption temperature is reduced by 70 °C, and the hydrogen desorption amount at 400 °C is about 6.5 wt%. Adding 15 wt% GO@VS4 catalyst can reduce the hydrogen desorption temperature range of MgH2 to 180 - 320 °C. Compared with the original MgH2, the hydrogen desorption temperature is reduced by 140 °C, and the hydrogen desorption amount when heated to 400 °C is about 6.2 wt%.

[0058] Since the performance of the composite material with 15 wt% GO@VS4 catalyst added is better than that of the composite material with 10 wt% GO@VS4 catalyst added, it can be seen that Example 2 is the best. Therefore, the hydrogen desorption performance and reaction mechanism of the composite material in Example 2 - adding 15 wt% GO@VS4 catalyst were further analyzed.

[0059] From Figure 9 It can be seen that adding GO@VS4 can significantly reduce the hydrogen desorption temperature of MgH2. The original MgH2 without catalyst starts to desorb hydrogen from ~320 °C, and the peak temperature is 348 °C. After adding 15 wt% GO@VS4 catalyst, the peak temperature of the main strong peak of hydrogen desorption of MgH2 is 220 °C, which is 128 °C lower than that of the original MgH2. See Figure 10 , at 270 °C, the MgH2 - 15 wt% GO@VS4 sample can quickly desorb 5 wt% H2 within 10 min.

[0060] See Figure 11 , the hydrogen desorption amount of the sample after 100 cycles is 6.1 wt%, showing good cycle stability.

[0061] The Kissinger method was used to calculate the hydrogen desorption activation energy of the original MgH2 and GO@VS4 - modified MgH2. See Figure 12 are the DSC curves of the two at different heating rates. As the heating rate increases, the hydrogen desorption curve of the sample gradually shifts to higher temperatures. According to the Kissinger equation fitting, the hydrogen desorption activation energy of the original MgH2 is 122.7 kJ / mol, while that of the MgH2 - 15 wt% GO@VS4 sample is 63.8 kJ / mol, only 52% of the original MgH2. Therefore, the GO@VS4 catalyst greatly improves the hydrogen absorption and desorption kinetics of MgH2.

[0062] See Figure 13, in the XRD patterns of all the samples after hydrogen release, the hexagonal phase Mg is the main phase, and the diffraction peaks of MgS and MgO are observed simultaneously. During the first hydrogen release process, VS4 reacts with MgH2 to form MgS. In addition, compared with the sample after the first hydrogen release, the diffraction peaks of the sample after hydrogen release after 100 cycles show basically no shift, indicating that the addition of the catalyst can reduce the operating temperature during the cycling of the sample, inhibit the grain growth of the sample and the agglomeration growth of the particles, and thus improve the cycling stability of the sample.

[0063] See Figure 14 , in the XRD patterns of all the samples after hydrogen absorption, the hexagonal phase MgH2 is the main phase, and the diffraction peaks of MgS and MgO are observed simultaneously. The MgS formed during the first hydrogen release stably exists throughout the hydrogen absorption and release process. In addition, compared with the sample after the first hydrogen absorption, the diffraction peaks of the sample after hydrogen absorption after 100 cycles show basically no shift, indicating that the addition of the catalyst can reduce the operating temperature during the cycling of the sample, inhibit the grain growth of the sample and the agglomeration growth of the particles, and thus improve the cycling stability of the sample.

[0064] The above are only specific embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the hydrogen storage performance of MgH2 based on graphene oxide supported green sulfur vanadium catalysis, comprising the following steps: Step 1: 15 mg of GO and 2 mmol of chloro-1-butyl-3-methylimidazolium salt were uniformly dispersed in 15 mL of deionized water by ultrasonication for 6 h to obtain a mixed solution; Step 2: 0.5 mmol of Na3VO4·12H2O and 10 mmol of C2H5NS were successively added to the mixed solution, and after stirring for 1 h, the mixed solution was transferred to a 30 mL stainless steel reactor lined with polytetrafluoroethylene, and reacted at 160°C for 24 h to obtain a reaction solution; Step 3: After the reaction solution is cooled to room temperature, the product is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and dried under vacuum at 60°C. The obtained catalyst is labeled as GO@VS4. Step 4: Weigh MgH2 at a mass ratio of 85:15 and put it into a ball mill with the GO@VS4 catalyst prepared in step 3. Fill it with 50 bar of hydrogen and then perform ball milling to prepare a sample labeled MgH2-15wt% GO@VS4.

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