Preparation method of magnesium-based hydrogen storage composite material

Abstract

A preparation method of a magnesium-based hydrogen storage composite material, the magnesium-based hydrogen storage alloy composite material is M-Ta2C / CNTs, 1) Ta2C material is obtained by etching Ta2AlC; 2) a mixed precursor material is obtained by grinding Ta2C, Co salt, Ni salt and melamine in a certain proportion; 3) the mixed precursor material is calcined and reduced at high temperature to obtain M-Ta2C / CNTs catalyst; 4) the M-Ta2C / CNTs catalyst is mixed with MgH2 and then ball milled to obtain the magnesium-based hydrogen storage alloy composite material. The problems that the existing hydrogen storage material cannot absorb and release hydrogen under mild conditions and has poor cycle performance are solved.

Description

Technical Field

[0001] This invention belongs to the field of solid-state hydrogen storage technology and relates to a magnesium-based hydrogen storage composite material, specifically to a magnesium-based hydrogen storage composite material based on an M-Ta2C / CNTs catalyst and its preparation. Background Technology

[0002] Driven by the goals of energy security and carbon neutrality, the global energy system's transition to clean and sustainable energy is imperative. With the exponential growth of societal energy demand, the depletion of fossil fuel resources and environmental pollution are becoming increasingly prominent issues. Hydrogen energy, with its abundant sources, high energy density, and the fact that its combustion product is only water, has become a key to breaking this deadlock and is one of the most promising alternative energy sources. The core bottleneck for its large-scale application lies in breakthroughs in high-performance, safe, and reliable hydrogen storage technology.

[0003] Among various solid-state hydrogen storage materials, magnesium-based hydrogen storage alloys are considered the preferred candidate materials for lightweight hydrogen storage systems due to their significant advantages, such as an ultra-high theoretical hydrogen storage capacity of 7.6 wt.%, abundant magnesium resources in the Earth's crust, and low preparation cost. However, pure-phase MgH2 has severe performance shortcomings: it has strong kinetic inertness, requiring hydrogen absorption under high temperature and high pressure conditions, and hydrogen release temperature is as high as 400℃ or more, far exceeding the mildness requirements of practical applications; at the same time, although existing modification strategies (such as catalytic modification, nano-processing, alloying, etc.) can improve local performance to a certain extent, they all have inherent defects: nanoparticles are prone to sintering and agglomeration, and the loss of active sites during cycling leads to a continuous decline in hydrogen storage performance, making it difficult to balance mild hydrogen absorption and desorption conditions with long-term cycling stability.

[0004] Therefore, it is crucial to develop a magnesium-based composite hydrogen storage material that exhibits mild hydrogen absorption and desorption conditions, structural stability during cycling, and controllable performance degradation. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing magnesium-based hydrogen storage composite materials, which solves the problems of existing hydrogen storage materials being unable to release hydrogen under mild conditions, having slow hydrogen absorption and desorption kinetic rates, and poor cycle performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a magnesium-based hydrogen storage composite material includes the following steps:

[0008] Step 1: Obtain Ta2C material by etching Ta2AlC;

[0009] Step 2: Grind Ta2C, Co salt, Ni salt and melamine in a certain proportion to obtain a mixed precursor material;

[0010] Step 3: Calcine and reduce the uniformly mixed precursor material at high temperature to obtain the M-Ta2C / CNTs catalyst;

[0011] Step 4: Mix the M-Ta2C / CNTs catalyst with MgH2 and then ball mill to obtain a magnesium-based hydrogen storage alloy composite material.

[0012] The magnesium-based hydrogen storage alloy composite material is a composite material of M-Ta2C / CNTs (where M is one or both of Co and Ni) and MgH2.

[0013] The M-Ta2C / CNTs catalyst is a composite material of transition metal and in-situ grown carbon nanotubes doped in tantalum carbide, wherein M is one or both of Co and Ni. Its structural features are: two-dimensional tantalum carbide nanosheets are used as substrates, and interwoven carbon nanotube networks are grown in-situ on their surface. Transition metal (Co, Ni or their alloys) nanoparticles are confined and anchored at the interface between tantalum carbide and carbon nanotubes.

[0014] In the M-Ta2C / CNTs catalyst, the mass ratio of tantalum carbide, transition metal elements (derived from the corresponding chlorides), and melamine as a carbon and nitrogen source is 1:(0.1-0.3):(2-5).

[0015] The preparation method of the M-Ta2C / CNTs catalyst includes the following steps:

[0016] Step 1: Preparation of Ta2C: Place Ta2AlC powder in hydrofluoric acid aqueous solution, etch at 30-50℃ for 48-96 hours, wash until neutral and dry to obtain two-dimensional Ta2C material;

[0017] Step 2, Mixing precursors: Grind the Ta2C, cobalt chloride hexahydrate and / or nickel chloride hexahydrate obtained in step S1 together in proportion to obtain a uniform mixed precursor powder;

[0018] Step 3, In-situ Pyrolysis Composite: The mixed precursor is heated to 600-800℃ in an Ar / H2 mixed atmosphere containing 5% H2 at a rate of 2-10℃ / min and held at this temperature for 1-4 hours. During this process, the metal salt is reduced to nanoparticles and anchored on the Ta2C surface. As melamine pyrolyzes, carbon nanotubes grow in situ from the metal nanoparticles, ultimately forming an M-Ta2C / CNTs composite catalyst.

[0019] The magnesium-based composite hydrogen storage material is synthesized by high-energy ball milling with the above-mentioned M-Ta2C / CNTs composite catalyst as a modifier and MgH2. The mass ratio of catalyst to MgH2 is 1:(5-15). The high-energy ball milling conditions are: ball-to-material ratio (30:1)-(50:1), rotation speed 400-500 rpm, and total ball milling time 6-12 hours.

[0020] The beneficial effects of this invention are:

[0021] The method described in this invention solves the problems of existing hydrogen storage materials being unable to absorb and desorb hydrogen under mild conditions and having poor cycling performance. By synthesizing transition metal carbon nanotubes loaded onto tantalum carbide composite materials, the hydrogen desorption kinetics and temperature of pure magnesium hydride can be greatly optimized. Compared with single transition metal loading, the synergistic effect between the two transition metals can form more active sites to promote the dissociation of Mg-H bonds, resulting in a 150°C reduction in the initial hydrogen desorption temperature of pure magnesium hydride, releasing 5.29 wt.% of hydrogen within 954 s at 270°C. Furthermore, after 30 hydrogen absorption and desorption cycles, the hydrogen storage capacity decreases by only 3.9%, exhibiting excellent cycling stability. Attached Figure Description

[0022] Figure 1 The non-isothermal hydrogen desorption curves of the composite materials prepared in Examples 1-3 and Comparative Example 1 are compared (heating rate 2℃ / min).

[0023] Figure 2 The graphs show the isothermal hydrogen release at different temperatures of the CoNi-Ta2C / CNTs-MgH2 composite material prepared in Example 1.

[0024] Figure 3 The graphs show the isothermal hydrogen release at different temperatures of the Co-Ta2C / CNTs-MgH2 composite material prepared in Example 2.

[0025] Figure 4 These are isothermal hydrogen desorption diagrams of the Ni-Ta2C / CNTs-MgH2 composite material prepared in Example 3 at different temperatures.

[0026] Figure 5 This is an isothermal hydrogen absorption diagram of the CoNi-Ta2C / CNTs-MgH2 composite material prepared in Example 1 at different temperatures.

[0027] Figure 6 This is an isothermal hydrogen absorption diagram of the Co-Ta2C / CNTs-MgH2 composite material prepared in Example 2 at different temperatures.

[0028] Figure 7 The graphs show the isothermal hydrogen absorption at different temperatures of the Ni-Ta2C / CNTs-MgH2 composite material prepared in Example 3.

[0029] Figure 8 The curves show the cyclic performance test curves of the CoNi-Ta2C / CNTs-MgH2 composite material prepared in Example 1.

[0030] Figure 9 The images show the XRD patterns of the CoNi-Ta2C / CNTs catalysts prepared in Examples 1-3. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0032] Example 1: Preparation of NiCo-Ta2C / CNTs catalyst and its composite hydrogen storage material

[0033] As the core support for the catalyst, the exfoliation quality of two-dimensional tantalum carbide (Ta2CMXene) directly affects the exposure efficiency of subsequent catalytic active sites. Its preparation process is as follows:

[0034] 3.0 g of ternary layered ceramic powder Ta2AlC was weighed and placed in a polytetrafluoroethylene reaction vessel. Then, 40 mL of a 40 wt.% hydrofluoric acid aqueous solution was slowly poured into the vessel. After sealing, the vessel was placed in a 40°C constant temperature water bath and continuously stirred for 72 h to ensure complete dissolution of the interlayer Al elements. After the reaction, the mixture was centrifuged in a centrifuge tube with deionized water at 9000 rpm for 6 min, and the supernatant was discarded. This process was repeated until the pH of the supernatant stabilized at around 7. The product obtained by centrifugation was dried overnight in a vacuum drying oven at 100°C to finally obtain two-dimensional tantalum carbide powder.

[0035] The specific preparation process of the NiCo-Ta2C / CNTs composite catalyst is as follows:

[0036] In an inert atmosphere-protected glove box, 0.10 g of the prepared Ta2C powder, 0.05 g of cobalt chloride hexahydrate, 0.05 g of nickel chloride hexahydrate, and 0.40 g of melamine were weighed and ground in an agate mortar for 15 min until no obvious particles were felt, obtaining a uniformly mixed precursor powder. The uniformly mixed precursor powder was spread evenly on a ceramic boat and placed in a tube furnace. A mixed gas consisting of 5% hydrogen and 95% argon was introduced into the furnace at a flow rate of 50 ml / min for 30 min to completely purge the air from the furnace. The furnace temperature was raised to 700°C at a heating rate of 5°C / min and calcined at this temperature for 2 h to finally obtain the NiCo-Ta2C / CNTs composite catalyst.

[0037] The preparation process of NiCo-Ta2C / CNTs-MgH2 composite hydrogen storage material is as follows:

[0038] In an inert atmosphere-protected glove box, 0.10 g of the prepared NiCo-Ta2C / CNTs catalyst and 0.90 g of commercial magnesium hydride powder were weighed and placed together with stainless steel grinding balls into a stainless steel ball mill jar, which was then sealed. The total mass ratio of grinding balls to materials (catalyst + MgH2) was set to 40:1. The ball mill jar was fixed on a planetary ball mill, and mechanical ball milling was performed at a speed of 450 rpm / min for a total duration of 8 hours, with a 0.5-hour cooling pause every 1 hour of operation. After ball milling, the product was removed from the glove box, yielding the final target material, the NiCo-Ta2C / CNTs-MgH2 composite hydrogen storage material.

[0039] Example 2: Preparation of Co-Ta2C / CNTs catalyst and its composite hydrogen storage material

[0040] To investigate the effect of single transition metal doping on catalytic performance, this embodiment simplified the composition of the transition metal source, using only cobalt salt as the single doping component, while maintaining the same preparation process as in Example 1. Specifically, in the catalyst preparation stage, only 0.05 g of cobalt chloride hexahydrate was used as the transition metal source, without adding nickel salt; the mixing and grinding process still used 0.10 g Ta₂C, 0.05 g CoCl₂·6H₂O, and 0.40 g melamine, and the heat treatment conditions (700℃, 2 h, 5% H₂ / Ar) and the composite ball milling process with MgH₂ (0.10 g catalyst and 0.90 g MgH₂, ball-to-material ratio 40:1, rotation speed 450 rpm, total duration 8 h, intermittent cooling) were exactly the same as in Example 1. Finally, a Co-Ta₂C / CNTs-MgH₂ composite hydrogen storage material was obtained, used to compare the catalytic effects of single cobalt doping and bimetallic doping.

[0041] Example 3: Preparation of Ni-Ta2C@CNTs catalyst and its composite hydrogen storage material

[0042] Corresponding to Example 2, this example uses nickel salt as a single transition metal source to clarify the catalytic effect of single nickel doping. The remaining preparation steps are completely consistent with Example 1. In the mixing and grinding stage of catalyst preparation, only 0.05g of nickel chloride hexahydrate is used as the transition metal source, and no cobalt salt is added. The other material ratios (0.10g Ta2C and 0.40g melamine), heat treatment conditions, and composite ball milling process with MgH2 remain unchanged. Finally, Ni-Ta2C / CNTs-MgH2 composite hydrogen storage material is obtained. By comparing the performance with Examples 1 and 2, the synergistic effect of single and double doping of Ni and Co can be clearly clarified.

[0043] Comparative Example 1: Catalyst-free composite MgH2

[0044] To visually verify the effect of the catalyst of this invention on the performance of magnesium-based hydrogen storage materials, this comparative example was set up as a blank control. 1.00 g of commercial magnesium hydride powder was taken directly into an inert atmosphere glove box and ball-milled separately under the same conditions as the composite ball milling in Example 1 (ball-to-powder ratio 40:1, rotation speed 450 rpm / min, total time 8 h, intermittent cooling). The resulting product served as a control sample without any catalyst, and its performance data will provide a benchmark reference for evaluating the effect of the catalyst.

[0045] Take 0.2g of each of the composite materials prepared in Examples 1-3 and Comparative Example 1, and place them sequentially into a self-made multifunctional hydrogen absorption and desorption performance evaluation device. After evacuation and leak detection, start the hydrogen desorption kinetic test. The heating furnace is heated to 500℃ at a rate of 2℃ / min through a program.

[0046] Figure 1 Comparison of the hydrogen desorption curves of all composite materials and pure MgH2 shows that the addition of transition metals to two-dimensional Ta2C, and the provision of nitrogen and carbon-catalyzed carbon nanotube composite materials after melamine pyrolysis, can significantly reduce the initial hydrogen desorption temperature of MgH2. NiCo-Ta2C / CNTs, Ni-Ta2C / CNTs, and Co-Ta2C / CNTs reduce the initial hydrogen desorption temperature of MgH2 to 159℃, 163℃, and 184℃, respectively. Among them, the CoNi dual transition metal composite catalyst has better catalytic performance than the single transition metal composite catalyst, indicating that the electronic and chemical synergistic effect of bimetallic CoNi can further enhance the catalytic activity.

[0047] The heating furnace was rapidly raised to 330℃, 300℃, and 270℃ and then held at these temperatures. Isothermal hydrogen desorption tests were then conducted on the NiCo-Ta2C / CNTs-MgH2 composite material prepared in Example 1 at different temperatures. The results are as follows: Figure 2 As shown, CoNi-Ta2C / CNTs-MgH2 can release 5.29 wt.% hydrogen gas within 954 s at 270 °C. The isothermal hydrogen release test results for Examples 2 and 3 under the same conditions are as follows... Figure 3 and Figure 4 As shown, at 270℃, the Co-Ta2C / CNTs prepared in Example 2 only released 1.45 wt.% hydrogen gas within 3000 s, while the Ni-Ta2C / CNTs prepared in Example 3 released 5.21 wt.% hydrogen gas within 1500 s. The isothermal hydrogen release performance test further demonstrates that the synergistic effect of the Co and Ni bimetals can significantly improve the hydrogen release performance of magnesium hydride.

[0048] After all the hydrogen was released from the composite material, the temperature was increased under vacuum conditions. The furnace was rapidly raised to 330°C, 300°C, and 270°C using a program and then held. Isothermal hydrogen absorption tests were performed on Examples 1-3 at different temperatures, and the results are as follows: Figure 5-7 As shown, all materials can absorb H2 to near saturation within 150s at 330℃. Among them, the CoNi-Ta2C / CNTs-MgH2 bimetallic composite material can absorb to saturation in an astonishing 56s, which is faster than that of the single metal composite material.

[0049] The furnace was rapidly heated to 300°C using a program and then maintained at that temperature for 30 cycles of hydrogen absorption and desorption. The test results are as follows: Figure 5 As shown, after 30 cycles, the prepared NiCo-Ta2C / CNTs-MgH2 composite material can stably and rapidly absorb and desorb hydrogen. At the same time, the hydrogen storage capacity of the composite material decreased from 5.79 wt.% to 5.62 wt.%, with a capacity retention rate of 97.1%. This further verifies its excellent hydrogen absorption and desorption performance after long-term continuous use.

[0050] Phase analysis of the catalysts prepared in Examples 1-3 is as follows: Figure 6 As shown in the XRD pattern, compared with Co–Ta2C / CNTs and Ni–Ta2C / CNTs, the CoNi–Ta2C / CNTs composite exhibits alloy-induced diffraction peak shift, as well as peak broadening and intensity decrease. This indicates the formation of a CoNi alloy phase with smaller grains and better dispersion. After ball milling with magnesium hydride, it has a larger contact interface, more hydrogen dissociation active sites, and a shorter hydrogen diffusion path, which makes the CoNi–Ta2C / CNTs-MgH2 composite exhibit optimal performance. In contrast, the Ni phase in Ni–Ta2C / CNTs has higher crystallinity and larger particles, while the effective Co metal phase in Co–Ta2C / CNTs is less. This difference in the structure of the active metal phase directly leads to a sequentially weakening promoting effect on the hydrogen adsorption and desorption kinetics of MgH2.

[0051] By comparing the performance exhibited in Examples 1-3 and Comparative Example 1, it can be seen that synthesizing transition metal carbon nanotubes loaded onto tantalum carbide composites can significantly optimize the hydrogen desorption kinetics and temperature of pure magnesium hydride. Compared to single transition metal loading, the synergistic effect between the two transition metals can form more active sites to promote the dissociation of Mg-H bonds, resulting in a 150°C decrease in the initial hydrogen desorption temperature of pure magnesium hydride, releasing 5.29 wt.% of hydrogen within 954 s at 270°C. Furthermore, after 30 hydrogen adsorption / desorption cycles, the hydrogen storage capacity only decreased by 3.9%, demonstrating excellent cycle stability.

Claims

1. A method for preparing a magnesium-based hydrogen storage composite material, characterized in that, Includes the following steps: Step 1: Selectively etch the aluminum layer in the ternary layered ceramic material to obtain tantalum carbide two-dimensional material, which is divided into the following steps; 1) Place the ternary layered ceramic material Ta2AlC powder in a hydrofluoric acid solution and etch it at 30-50℃ for 48-96 hours to ensure that the aluminum element between the layers is fully dissolved. The concentration of the hydrofluoric acid solution is 40-50%, and the mass-volume ratio of Ta2AlC powder to hydrofluoric acid solution is 1g:(10-15)ml. 2) After etching, the product is repeatedly centrifuged and washed with deionized water until the supernatant is neutral. 3) The washed product is dried under vacuum at 80-120℃ to obtain tantalum carbide two-dimensional material; Step 2: The two-dimensional tantalum carbide material, transition metal source, and nitrogen-containing organic precursor obtained in step (1) are mechanically mixed to obtain a homogeneous mixture, wherein the mass ratio of the two-dimensional tantalum carbide material, transition metal source, and nitrogen-containing organic precursor is 1:(0.1-0.3):(2-5). Step 3: The mixture obtained in step (2) is heated to 600-800℃ at a heating rate of 2-10℃ / min under a reducing atmosphere, and held at this temperature for 1-4 hours for heat treatment. The nitrogen-containing organic precursor is pyrolyzed to reduce the transition metal ions and catalyze the generation of carbon nanotubes anchored on the surface of tantalum carbide, thereby obtaining a transition metal-derived carbon nanotube-anchored tantalum carbide composite material. Step 4: The transition metal-derived carbon nanotube-anchored tantalum carbide composite material obtained in step (3) is used as a catalyst and combined with magnesium-based hydrogen storage material by high-energy ball milling. The mass ratio of the catalyst to the hydrogen storage matrix material is 1:(5-15), and magnesium-based hydrogen storage composite material M-Ta2C / CNTs is obtained.

2. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The centrifugation speed in step (1) is 8000-10000 rpm, and the centrifugation time is 5-8 minutes.

3. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, In step (2), the transition metal source is a cobalt salt and / or a nickel salt.

4. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1 as described in claim 3, characterized in that, The transition metal source is cobalt chloride hexahydrate and / or nickel chloride hexahydrate.

5. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The nitrogen-containing organic precursor in step (2) is melamine.

6. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, In step (2), mechanical mixing is performed by manual grinding or ball milling, and the mixing time is 10-30 minutes.

7. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, In step (3), the reducing atmosphere is a mixture of hydrogen and argon, wherein the hydrogen gas fraction is 2%-10%.

8. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The transition metal-derived carbon nanotube-anchored tantalum carbide composite material obtained in step 3 has a two-dimensional tantalum carbide nanosheet as its substrate. A carbon nanotube network and a nitrogen-doped carbon layer are grown in situ and entangled on the transition metal active sites thereon. The transition metal nanoparticles are uniformly loaded on the carbon nanotube nodes and the tantalum carbide surface in the form of alloys or elements.

9. The transition metal-derived carbon nanotube-anchored tantalum carbide composite material according to claim 8, characterized in that, The transition metal is an alloy formed from one or two of cobalt and nickel.

10. The method for preparing a magnesium-based hydrogen storage composite material according to claim 1, characterized in that, The process conditions for the high-energy ball mill are: ball-to-material ratio of (30:1) to (50:1), rotation speed of 400-500 rpm, and milling time of 6-12 hours.

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