Bimetal borohydride system as well as preparation method and application thereof

Abstract

The invention discloses a bimetallic borohydride system. The bimetallic borohydride system comprises a Li / KBH4 eutectic system and graphene loaded with Ni3B nanoparticles, and the Li / KBH4 eutectic system is infiltrated into gaps of the lamellar graphene loaded with the Ni3B nano particles through melting, so that a novel sandwich structure consisting of the Li / KBH4 eutectic system, the graphene and the nano Ni3B is constructed. According to the bimetal hydroboron system disclosed by the invention, the hydrogen absorption and desorption temperature of the system can be remarkably reduced and the dynamic performance and the cycling stability of the system can be improved under the premise of keeping the high hydrogen storage capacity of the system by utilizing the synergistic effect of the graphene and the Ni3B nanoparticles.

Description

Technical Field

[0001] The technical field of hydrogen storage materials of the present invention particularly relates to a bimetallic borohydride system and a preparation method and application thereof. Background Art

[0002] As a new type of energy, hydrogen energy has the advantages of abundant resources, clean and environmentally friendly, high energy density and renewable nature. The safe and efficient storage of hydrogen is the key to realizing hydrogen energy applications. Among the three major types of hydrogen storage technologies currently under development, namely high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage and solid-state hydrogen storage, solid-state hydrogen storage has high density, good safety and relatively low cost, making it an ideal hydrogen storage method. The bimetallic borohydride system composed of a mixture of light alkali metal or alkaline earth metal borohydrides has attracted widespread attention in the field of solid hydrogen storage materials due to its high mass hydrogen storage density and low eutectic melting point. However, this system generally has problems such as slow kinetics and poor reversibility, which limit its promotion in practical hydrogen storage applications. Therefore, the hydrogen storage performance of the bimetallic borohydride system still needs to be further improved. Catalysis and nano-sizing are two effective ways to improve the hydrogen storage performance of this system.

[0003] In terms of nanoscaling, the low eutectic melting point of bimetallic borohydride systems makes them ideal for nanoconfinement within porous framework materials via melt infiltration. This approach not only effectively shortens hydrogen diffusion distances and provides rapid diffusion pathways through numerous interfaces, but also inhibits particle aggregation and growth during the hydrogen absorption and desorption cycles, significantly improving the desorption kinetics and reversibility.

[0004] For example, F.Peru et al. (F.Peru, S.Payandeh, G.Charalambopoulou, TRJensen, T.Steriotis, Hydrogen sorption and reversibility of the LiBH4-KBH4 eutectic system confined in a CMK-3 type carbon via melt infiltration, C–J.Carbon Res.6(2020)19.), nanoconfining the 0.725LiBH4-0.275KBH4 system in CMK-3 can reduce the hydrogen desorption peak temperature of the system by 120°C. However, due to the limitation of the pore volume of the confined support, the loading amount of bimetallic borohydride in the confined system is only 38.6wt%, resulting in its overall hydrogen storage capacity dropping to 2.6wt% H2.

[0005] Catalysis is another common method for improving the hydrogen absorption and desorption performance of bimetallic borohydride systems. This is typically achieved by introducing transition metals (such as Ni, Co, and Zn) and their oxides, halides, or borides into the system as catalysts to provide nucleation sites or act as charge transfer media, thereby lowering the kinetic energy barrier during the reaction and improving hydrogen absorption and desorption performance. However, existing catalysts typically have large particle sizes. While some can reach nanometer sizes, their tendency to aggregate easily during hydrogen absorption and desorption results in relatively low catalytic efficiency.

[0006] Therefore, there is an urgent need to develop a feasible technical solution to combine nano-sizing with catalysis, achieving effective dispersion and high loading of bimetallic borohydrides while maintaining high catalytic activity. This is of great significance for the development and application of high-performance hydrogen storage materials. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention discloses a bimetallic borohydride system, which utilizes the synergistic effect of graphene and Ni3B nanoparticles to significantly reduce the hydrogen absorption and desorption temperature of the system while maintaining the high hydrogen storage capacity of the system, thereby improving its kinetic performance and cyclic stability.

[0008] The specific technical solutions are as follows:

[0009] A bimetallic borohydride system comprising a Li / KBH4 eutectic system and graphene loaded with Ni3B nanoparticles;

[0010] The Li / KBH4 eutectic system penetrates into the lamellar gaps of the graphene loaded with Ni3B nanoparticles, thereby constructing a novel sandwich structure consisting of the Li / KBH4 eutectic system, graphene and nano-Ni3B.

[0011] Preferred:

[0012] The particle size of the Ni3B nanoparticles is 5 to 100 nm;

[0013] More preferably, the particle size of the Ni3B nanoparticles is 10 to 20 nm; more preferably, the particle size is 15 nm.

[0014] Preferred:

[0015] The molar ratio of LiBH4 to KBH4 in the Li / KBH4 eutectic system is 0.725:0.275; the Li / KBH4 eutectic system prepared at this ratio has a lower melting point.

[0016] Preferred:

[0017] In the graphene loaded with Ni3B nanoparticles, the loading amount of Ni3B nanoparticles is 10-30wt%;

[0018] Further preferably, the loading amount of Ni3B nanoparticles is 20-30 wt%;

[0019] More preferably, the loading amount of Ni3B nanoparticles is 20 wt%;

[0020] Experiments have shown that the bimetallic borohydride system prepared by graphene with a loading of 20 wt% Ni3B nanoparticles has the best hydrogen storage performance.

[0021] Preferred:

[0022] In the bimetallic borohydride system, the mass proportion of graphene loaded with Ni3B nanoparticles is 10-40%;

[0023] More preferably, the mass proportion of the graphene loaded with Ni3B nanoparticles is 20%.

[0024] The bimetallic borohydride system disclosed in the present invention has an initial hydrogen release temperature of 182-223°C, a main hydrogen release peak temperature of 278-313°C, a hydrogen release amount of not less than 8.5wt% H2 when kept at 350°C for 30 minutes, an initial hydrogen absorption temperature of 102-170°C, and a hydrogen release amount of not less than 6.9wt% H2 after fifty hydrogen absorption and desorption cycles.

[0025] The present invention also discloses a method for preparing the bimetallic borohydride system, comprising:

[0026] S1, mixing nickel precursor, graphene, sodium borohydride and water, undergoing redox reaction and then sintering at high temperature to obtain graphene loaded with Ni3B nanoparticles, denoted as Ni3B / G;

[0027] S2, mixing LiBH4 and KBH4 by ball milling to obtain a Li / KBH4 eutectic system;

[0028] S3. Fully mix the Li / KBH4 eutectic system with Ni3B / G, and heat the Li / KBH4 eutectic system so that it is in a molten liquid state and fully contacts and mixes with Ni3B / G to obtain the bimetallic borohydride system, which is recorded as Li / KBH4@(Ni3B / G) composite system.

[0029] In step S1:

[0030] Preferably, the nickel precursor is selected from common types in the art, such as one or more of nickel chloride, nickel sulfate, nickel nitrate, and nickel oxide;

[0031] Preferably, the molar ratio of the nickel precursor to sodium borohydride is 3:1, based on the molar number of nickel in the nickel precursor. This molar ratio can ensure sufficient reaction and prepare Ni3B nanoparticles.

[0032] Preferably, the mass ratio of the nickel precursor to graphene is 1:(1-8), more preferably 1:3. By adjusting the mass ratio of the nickel precursor to graphene, Ni3B / G materials with different Ni3B doping amounts can be prepared, denoted as xNi3B / G.

[0033] Preferably, the redox reaction is carried out at room temperature;

[0034] In order to control the reaction process of the redox reaction and ensure that Ni3B nanoparticles with smaller particle size are prepared, it is further preferred that a nickel precursor solution (graphene is added to the nickel precursor solution) and a sodium borohydride solution are prepared separately, and then the two are mixed by dropwise addition.

[0035] Preferably, the temperature of the high-temperature sintering is 300-600°C.

[0036] In step S2:

[0037] Preferably, the molar ratio of LiBH4 to KBH4 is 0.725:0.275.

[0038] In step S3:

[0039] Preferably, the mass ratio of the Li / KBH4 eutectic system to Ni3B / G is (1.5-9):1; more preferably, it is 4:1.

[0040] Preferably, the heating temperature is 105-150° C., so that the Li / KBH 4 eutectic system is in a molten liquid state.

[0041] The invention also discloses the application of the bimetallic borohydride system in solid-state hydrogen storage.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention discloses a bimetallic borohydride system, comprising a Li / KBH4 eutectic system and graphene loaded with Ni3B nanoparticles. The Li / KBH4 eutectic system penetrates into the gaps between the lamellar graphene of Ni3B / G, thereby constructing a novel sandwich structure consisting of the Li / KBH4 eutectic system, graphene, and nano-Ni3B. Utilizing the synergistic effect of the graphene and the Ni3B nanoparticles, the initial hydrogen desorption temperature and the peak hydrogen desorption temperature of the Li / KBH4@(Ni3B / G) composite system can be significantly reduced to 182° C. and 278° C., respectively. The hydrogen desorption amount can reach 8.5 wt% H2 when kept at 350° C. for 30 minutes. The system has a lower apparent activation energy for hydrogen desorption, thereby exhibiting better hydrogen desorption kinetics. Furthermore, the system has better cyclic stability, with the hydrogen desorption amount still exceeding 6.9 wt% H2 after fifty hydrogen absorption and desorption cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 XRD patterns of graphene loaded with Ni3B nanoparticles prepared in Examples 1 to 3, respectively. The graphs of graphene and Ni3B are also given for comparison.

[0045] Figure 2 The SEM images of graphene loaded with Ni3B nanoparticles prepared in Examples 1 to 3 are provided, and the SEM image of graphene is provided for comparison;

[0046] Figure 3 TEM images of graphene loaded with Ni3B nanoparticles prepared in Examples 1 to 3, respectively. In the figures, (b) is a TEM image of the composite material prepared in Example 1, and (d) is a HRTEM image of the dotted area in (b); (a) is a TEM image of the composite material prepared in Example 2; (c) is a TEM image of the composite material prepared in Example 3;

[0047] Figure 4 XRD patterns of the bimetallic borohydride systems prepared in Examples 1 to 3, the Li / KBH4 eutectic system prepared in step S2 of Example 1, the bimetallic borohydride system prepared in Comparative Example 1, and pristine LiBH4;

[0048] Figure 5 FTIR spectra of the bimetallic borohydride systems prepared in Examples 1 to 3, the Li / KBH4 eutectic system prepared in step S2 of Example 1, the bimetallic borohydride system prepared in Comparative Example 1, and pristine LiBH4;

[0049] Figure 6SEM images (a), TEM images (b, c), HRTEM images (d), TEM, STEM–HAADF images, and EDS surface scanning element distribution maps (e, f) of the bimetallic borohydride system prepared in Example 1;

[0050] Figure 7 TEM image of Ni3B nanoparticles prepared in step S1 of Comparative Example 2;

[0051] Figure 8 TPD-MS curves of the bimetallic borohydride systems prepared in Examples 1 to 3 and Comparative Examples 1 to 2, as well as the Li / KBH4 eutectic system and the original LiBH4;

[0052] Figure 9 Temperature-dependent hydrogen release curves of the bimetallic borohydride systems prepared in Examples 1 to 3 and Comparative Examples 1 to 2, as well as the Li / KBH4 eutectic system and the original LiBH4;

[0053] Figure 10 The temperature-dependent hydrogen absorption curves of the systems prepared in Example 1 and Comparative Examples 1-2, the Li / KBH4 eutectic system, and the original LiBH4;

[0054] Figure 11 The isothermal hydrogen desorption curves of the Li / KBH4@(20Ni3B / G) system prepared in Example 1 at 250°C, 300°C and 350°C;

[0055] Figure 12 The isothermal hydrogen desorption curves of the Li / KBH4@G system and the Li / KBH4 eutectic system and the single LiBH4 prepared in Comparative Example 1 at 350°C are shown;

[0056] Figure 13 Kissinger linear fitting diagrams of the systems prepared in Example 1 and Comparative Example 1, respectively. The insets are TPD–MS curves at different heating rates.

[0057] Figure 14 The cyclic hydrogen release curve (a) and cyclic hydrogen absorption curve (b) of the system prepared in Example 1. DETAILED DESCRIPTION

[0058] The present invention will be further described in detail below with reference to examples and comparative examples, but the embodiments of the present invention are not limited thereto.

[0059] Example 1

[0060] S1. Dissolve 500 mg of nickel chloride hexahydrate in 50 mL of deionized water and stir for 1 h, dissolve 1.504 g of graphene in the nickel chloride solution, and continue stirring for 30 min; dissolve 500 mg of sodium borohydride in 10 mL of deionized water and stir for 1 h, and add the prepared sodium borohydride solution dropwise to the above solution using a disposable dropper at a drop rate of 1 drop / 10 s. After the end, continue stirring for 3 h; centrifuge, filter, and dry after stirring; finally, sinter the sample in an Ar gas atmosphere from room temperature to 400 ° C at a heating rate of 10 ° C / min, keep warm for 3 h, and obtain graphene loaded with Ni3B nanoparticles after cooling, which is recorded as 20Ni3B / G;

[0061] S2. Using an XQM-4L vertical semicircular planetary ball mill, LiBH4 and KBH4 were subjected to high-energy ball milling at a molar ratio of 0.725:0.275 to prepare a Li / KBH4 eutectic system. The ball-to-material ratio used was 120:1, the rotation speed was 500 rpm, and 5 MPa of H2 was injected into the milling tank before milling to prevent decomposition of the borohydride hydrogen storage material during the long milling process. The milling time was 4 h. During the milling process, the forward direction was run for 12 min and the pause was 6 min, and then the reverse direction was run for 12 min and the pause was 6 min to minimize the temperature rise during the milling process and avoid overheating of the sample.

[0062] S3. The Li / KBH4 eutectic system prepared in step S2 and the 20Ni3B / G prepared in step S1 were hand-grinded in a mortar for 15 minutes to mix them evenly. The amount of 20Ni3B / G added was 20 wt% based on the total mass of the Li / KBH4 eutectic system and 20Ni3B / G. The mixture was then loaded into a reactor and kept warm at 110°C for 30 minutes to allow the Li / KBH4 to fully contact and mix with the 20Ni3B / G in a molten liquid state to obtain a bimetallic borohydride system, which was recorded as Li / KBH4@(20Ni3B / G).

[0063] Example 2

[0064] The preparation process is basically the same as that in Example 1, except that in step S1, the mass of graphene added is replaced by 3.384 g, and the prepared graphene loaded with Ni3B nanoparticles is recorded as 10Ni3B / G; the finally prepared bimetallic borohydride system is recorded as Li / KBH4@(10Ni3B / G).

[0065] Example 3

[0066] The preparation process is basically the same as that in Example 1, except that in step S1, the mass of graphene added is replaced with 0.877 g, and the prepared graphene loaded with Ni3B nanoparticles is recorded as 30Ni3B / G; the finally prepared bimetallic borohydride system is recorded as Li / KBH4@(30Ni3B / G).

[0067] Comparative Example 1

[0068] S1. Using an XQM-4L vertical semicircular planetary ball mill, LiBH4 and KBH4 were milled to a molar ratio of 0.725:0.275 to prepare a Li / KBH4 eutectic system. The ball-to-material ratio was 120:1, the rotation speed was 500 rpm, and 5 MPa of H2 was injected into the milling tank before milling to prevent decomposition of the borohydride hydrogen storage material during the long milling process. The milling time was 4 h. During the milling process, the forward direction was run for 12 min and the pause was 6 min, and then the reverse direction was run for 12 min and the pause was 6 min to minimize the temperature rise during the milling process and avoid overheating of the sample.

[0069] S2. The Li / KBH4 eutectic system prepared in step S2 and graphene were hand-grinded in a mortar for 15 minutes to mix uniformly, and the added amount of graphene was 20 wt% based on the total mass of the Li / KBH4 eutectic system and graphene. The mixture was then loaded into a reactor, and then kept warm at 110° C. for 30 minutes to allow the Li / KBH4 to fully contact and mix with the graphene in a molten liquid state to obtain a bimetallic borohydride system, which was recorded as Li / KBH4@G.

[0070] Comparative Example 2

[0071] S1. Dissolve 500 mg of nickel chloride hexahydrate in 50 mL of deionized water and stir for 1 hour; dissolve 500 mg of sodium borohydride in 10 mL of deionized water and stir for 1 hour, then add the prepared sodium borohydride solution dropwise to the above solution using a disposable dropper at a rate of drop / 10 seconds, and continue stirring for 3 hours after the end; after stirring, centrifuge, filter, and dry; and cool to obtain Ni3B nanoparticles;

[0072] S2. Using an XQM-4L vertical semicircular planetary ball mill, LiBH4 and KBH4 were subjected to high-energy ball milling at a molar ratio of 0.725:0.275 to prepare a Li / KBH4 eutectic system. The ball-to-material ratio used was 120:1, the rotation speed was 500 rpm, and 5 MPa of H2 was injected into the milling tank before milling to prevent decomposition of the borohydride hydrogen storage material during the long milling process. The milling time was 4 h. During the milling process, the forward direction was run for 12 min and the pause was 6 min, and then the reverse direction was run for 12 min and the pause was 6 min to minimize the temperature rise during the milling process and avoid overheating of the sample.

[0073] S3. The Li / KBH4 eutectic system prepared in step S2 and the Ni3B nanoparticles prepared in step S1 were hand-grinded in a mortar for 15 minutes to mix them evenly. The amount of Ni3B nanoparticles added was 20 wt% based on the total mass of the Li / KBH4 eutectic system and the Ni3B nanoparticles. The mixture was then loaded into a reactor and kept warm at 110°C for 30 minutes to allow the Li / KBH4 to fully contact and mix with the Ni3B in a molten liquid state to obtain a bimetallic borohydride system, which was recorded as Li / KBH4@Ni3B.

[0074] Figure 1 The XRD patterns of graphene loaded with Ni3B nanoparticles, prepared in Examples 1-3, are shown. The graphene and Ni3B patterns are also shown for comparison. All composite materials exhibit diffraction peaks characteristic of Ni3B (PDF#72–9062), and the relative intensity of these peaks increases with increasing Ni3B addition. This demonstrates that highly crystalline Ni3B nanoparticles have been successfully synthesized on graphene through wet chemical synthesis and solid-phase sintering.

[0075] Figure 2 The SEM images of graphene loaded with Ni3B nanoparticles prepared in Examples 1 to 3 are shown, and the SEM images of graphene are given as a comparison. Figure 2 (a) has a typical multilayered sheet structure. In all composite materials, Ni3B particles with a size of tens of nanometers can be observed, which are dispersed on the surface of the graphene sheets. As the amount of Ni3B loading increases, the number of nanoparticles loaded on the graphene increases accordingly. When 10wt% Ni3B is added ( Figure 2 (Fig. 2(b)), the Ni3B nanoparticles on the graphene surface are relatively sparse, and more uncovered areas are exposed on the graphene surface. When the Ni3B loading increases to 20wt% ( Figure 2 (c) in the graph), the graphene surface is largely covered by Ni3B and exhibits good dispersion. When the Ni3B loading is further increased to 30wt% ( Figure 2 In the middle (d) figure, the graphene surface is basically covered by Ni3B particles, and a small amount of Ni3B nanoparticles have agglomerated and grown, as shown by the dotted circles in the figure.

[0076] Figure 3TEM images of graphene loaded with Ni3B nanoparticles prepared in Examples 1 to 3, respectively. In the figure, (b) is a TEM image of the composite material prepared in Example 1, (d) is a HRTEM image of the dotted area in (b); (a) is a TEM image of the composite material prepared in Example 2; (c) is a TEM image of the composite material prepared in Example 3. It was observed that under the conditions of Ni3B loading of 10 and 20 wt% ( Figure 3 In (a, b), the particle size of Ni3B is basically between 10 and 20 nm. When the loading is 30 wt%, Figure 3 As shown in Figure (c), the size of Ni3B nanoparticles has increased, and a certain degree of agglomeration has occurred between the particles. The HRTEM morphology analysis of the 20Ni3B / G composite material ( Figure 3 In the middle (d) figure, the lattice fringes of the Ni3B (121) crystal plane and the graphene (002) crystal plane can be clearly observed, and the interplanar spacings are 0.230nm and 0.335nm, respectively. The size of the Ni3B nanoparticles is about 15nm.

[0077] Figure 4 The XRD patterns of the bimetallic borohydride systems prepared in Examples 1 to 3, the Li / KBH4 eutectic system prepared in Example 1 S2, the bimetallic borohydride system prepared in Comparative Example 1, and the original LiBH4. It was observed that in the Li / KBH4, Li / KBH4@G and Li / KBH4@(xNi3B / G) (x=10, 20, 30) systems, LiK(BH4)2(PDF#76–9291) was the main phase. In the XRD patterns of these three systems, only the weak diffraction peak of LiBH4(PDF#81–9183) was observed, and no diffraction peak of KBH4 was detected, indicating that a Li / KBH4 eutectic system composed of LiK(BH4)2 and LiBH4 was generated after ball milling. This phase composition is consistent with the phase of the 0.725LiBH4–0.275KBH4 eutectic system in the LiBH4–KBH4 binary phase diagram at room temperature. Figure 1 Furthermore, the XRD patterns of the Li / KBH4@(xNi3B / G) system show distinct diffraction peaks of Ni3B (PDF#72–9062) at 38.50°, 45.96°, and 46.93°, respectively, indicating that the infiltration of Li / KBH4 into Ni3B / G in the molten state has no significant effect on the crystal structure of Ni3B. No graphene diffraction peaks were detected in the XRD patterns of either the Li / KBH4@G or Li / KBH4@(xNi3B / G) systems, indicating that the graphene exists in an amorphous state after infiltration.

[0078] Figure 5The FTIR spectra of the bimetallic borohydride system prepared in Examples 1 to 3, the Li / KBH4 eutectic system prepared in Example 1 and S2, the bimetallic borohydride system prepared in Comparative Example 1, and the original LiBH4 are shown in Figure 1. –1 and 1125cm –1 Similar stretching and bending vibrations appear at the α-H bond, consistent with the B–H bond in LiK(BH4)2 and LiBH4. This indicates that the chemical environments of the B–H bonds in LiK(BH4)2 and LiBH4 in different systems are almost identical, that is, the infiltration mixing process of Li / KBH4 in liquid state and Ni3B / G does not significantly affect the chemical environment of the B–H bonds.

[0079] Figure 6 The SEM images (a), TEM images (b, c), HRTEM images (d), TEM, STEM-HAADF images, and EDS surface scanning element distribution maps (e, f) of the bimetallic borohydride system prepared in Example 1 are shown. It was observed that the borohydride in the bimetallic borohydride system prepared in this example fully penetrated into the gaps of the lamellar graphene loaded with nano-Ni3B, and constructed a sandwich structure consisting of lamellar graphene, Ni3B nanoparticles, and Li / KBH4. From the TEM morphology of the bimetallic borohydride system ( Figure 6 As can be seen in Figures (b, c), graphene plays a good role in dispersing and supporting Li / KBH4; the large number of dispersed nanoparticles in the figure should be Ni3B, and the size of the nanoparticles is about 15nm. Further HRTEM observation and analysis of the bimetallic borohydride system ( Figure 6 (d) It was found that the interplanar spacing of the particles with a size of about 15 nm in the system was 0.230 nm, which corresponds to the Ni3B (121) crystal plane, further explaining that the Ni3B nanocrystals are dispersed in the Li / KBH4@(20Ni3B / G) system; HRTEM did not observe the lattice fringes of graphene, which may be due to its amorphous state, which is consistent with the above XRD results. In addition, the high-angle annular dark field TEM image (STEM–HAADF) of the bimetallic borohydride system and its corresponding EDS surface scanning element distribution map ( Figure 6 Analysis of Figures (e and f) reveals that the areas where Ni and B overlap well are Ni3B nanoparticles, further demonstrating that the Ni3B nanoparticles are uniformly dispersed in the system. The B signal that does not overlap with Ni originates from Li / KBH4. These results demonstrate that the melt infiltration method can uniformly mix the Li / KBH4 system with the Ni3B / G composite.

[0080] Figure 7This is a TEM image of the Ni3B nanoparticles prepared in step S1 of Comparative Example 2. It is observed that the synthesized Ni3B particles are agglomerated and have a large particle size of about 30 to 50 nm.

[0081] Performance testing:

[0082] 1. Hydrogen absorption and desorption performance test with temperature

[0083] (1) TPD-MS curve test method: The hydrogen desorption temperature of the system was tested using the temperature-programmed desorption method. High-purity argon was used as the carrier gas at a flow rate of 20 mL / min. The system was heated from room temperature to 600°C at a heating rate of 2°C / min.

[0084] Figure 8The TPD-MS curves of the bimetallic borohydride systems prepared in Examples 1-3 and Comparative Examples 1-2, respectively, as well as the Li / KBH4 eutectic system and pristine LiBH4, are shown. Observations show that the single Li / KBH4 eutectic system exhibits a three-step dehydrogenation process: the first step exhibits a peak dehydrogenation temperature of approximately 343°C, with a relatively broad peak shape; the second and third steps exhibit peak dehydrogenation temperatures of 451°C and 533°C, respectively, representing the primary dehydrogenation steps. When Ni3B is added to the Li / KBH4 eutectic system (Li / KBH4@Ni3B system), the system still exhibits a three-step dehydrogenation process similar to the single Li / KBH4 system, but the peak dehydrogenation temperatures for each step decrease compared to the single Li / KBH4 system, dropping to 334°C, 415°C, and 510°C, respectively. This indicates that the addition of Ni3B alone can catalyze the dehydrogenation reaction in the Li / KBH4 system. The Li / KBH4@G system, unlike the dehydrogenation processes of the single Li / KBH4 and Li / KBH4@Ni3B systems, exhibits a two-step dehydrogenation process. The first step is the primary dehydrogenation step, which, based on the dehydrogenation reaction process of Li / KBH4, corresponds to the dehydrogenation of LiBH4. The peak temperature is significantly reduced to 335°C, a 116°C decrease compared to the peak temperature of single Li / KBH4. The second dehydrogenation step is the dehydrogenation of KBH4, with a peak temperature of 428°C, a 105°C decrease compared to the corresponding dehydrogenation peak temperature of single Li / KBH4. Furthermore, compared to single Li / KBH4, both the initial and final dehydrogenation temperatures of this system are significantly lower. This indicates that the introduction of graphene has a certain improvement in the dehydrogenation performance of Li / KBH4, which is due to the fact that graphene, to a certain extent, acts as a confinement agent for Li / KBH4. The Li / KBH4@(10Ni3B / G) system exhibits a distinct two-step dehydrogenation process: the peak dehydrogenation temperatures for the first and second steps are 313°C and 417°C, respectively, 138°C and 116°C lower than those for the Li / KBH4 system. The onset dehydrogenation temperature for this system is approximately 223°C, 55°C lower than that for the Li / KBH4 system. Furthermore, the dehydrogenation process is nearly complete at approximately 452°C, 140°C lower than that for the Li / KBH4 system. When the Ni3B loading is 20wt% (Li / KBH4@(20Ni3B / G) system), unlike the Li / KBH4@G and Li / KBH4@(10Ni3B / G) systems, the two hydrogen desorption peaks of this system overlap to a large extent, with the peak temperature of the main hydrogen desorption peak dropping to 278°C, and the peak temperature of the other weaker hydrogen desorption peak at 357°C, which is further reduced by 35°C and 60°C compared to the Li / KBH4@(10Ni3B / G) system. In addition, compared with the Li / KBH4@(10Ni3B / G) system, the starting and ending hydrogen desorption temperatures of this system are also significantly reduced.This shows that Ni3B, as the catalytically active phase in the composite material (xNi3B / G), plays a significant role in promoting the dehydrogenation of the Li / KBH4 system under the condition of a loading of 20wt%. However, the addition amount of Ni3B with a loading of 10wt% is too low, and it is observed to be sparsely distributed on the graphene in the aforementioned SEM morphology, resulting in a limited contact surface between it and Li / KBH4 and insufficient catalytic effect. When the loading amount of Ni3B is increased to 30wt%, the dehydrogenation performance of the system is not further improved. On the contrary, the initial dehydrogenation temperature and the peak dehydrogenation temperature are slightly higher than those of the Li / KBH4@(20Ni3B / G) system. This is mainly due to the growth and agglomeration of some Ni3B nanoparticles in the 30Ni3B / G composite material, which causes its catalytic activity to decrease slightly compared with the 20Ni3B / G composite material. However, the major hydrogen release of each Li / KBH4@(xNi3B / G) system was basically completed before 400℃, which was much lower than that of other systems, indicating the efficient catalytic effect of graphene-dispersed Ni3B on Li / KBH4.

[0085] (2) Temperature-dependent hydrogen release curve test method: Temperature-dependent hydrogen release adopts the volumetric method to test the hydrogen release amount of the system. The test procedure is to set the initial vacuum degree to 1×10 -3 Under the condition of 1000 Torr, the temperature was increased from room temperature to 450 °C at a heating rate of 2 °C / min.

[0086] Figure 9The following are the temperature-dependent hydrogen desorption curves for the bimetallic borohydride systems prepared in Examples 1-3 and Comparative Examples 1-2, as well as the Li / KBH4 eutectic system and pristine LiBH4. Observations show that the primary hydrogen desorption process in the Li / KBH4@G system shifts significantly toward lower temperatures compared to the single Li / KBH4 eutectic system and pristine LiBH4. The addition of Ni3B further lowers the desorption temperature. When heated to 230°C, the Li / KBH4@(xNi3B / G) systems (x = 10, 20, and 30 wt%) release 1.4, 3.0, and 2.4 wt% H2, respectively, significantly exceeding the 0.7 wt% H2 release of the Li / KBH4@G, Li / KBH4@Ni3B, and Li / KBH4 systems. In contrast, single LiBH4 barely begins to desorb hydrogen under these conditions. The dehydrogenation performance of the Li / KBH4@G system consistently outperforms that of the Li / KBH4 system at dehydrogenation temperatures exceeding 230°C. This is attributed to the confinement of Li / KBH4 by graphene, which reduces its particle size and thus improves its dehydrogenation performance. At 340°C, the Li / KBH4@(20Ni3B / G) system releases 6.2 wt% H2, slightly higher than the 5.8 wt% H2 released by the Li / KBH4@(10Ni3B / G) and Li / KBH4@(30Ni3B / G) systems at this temperature, and close to the theoretical dehydrogenation capacity (5.6 wt% H2) of LiBH4 dehydrogenated to LiH and B in the Li / KBH4@(xNi3B / G) system. At this point, the hydrogen release rate of the Li / KBH4@G system was 4.0 wt% H2. The hydrogen release curve of the Li / KBH4@Ni3B system under these conditions almost overlaps with that of the Li / KBH4 eutectic system, indicating that the two systems release nearly identical amounts of hydrogen within this temperature range, only 1.7 wt% H2. When the dehydrogenation temperature exceeds 340°C, the introduction of Ni3B improves the dehydrogenation performance of the Li / KBH4 system, confirming its catalytic effect on the dehydrogenation process. Upon further heating to 450°C, the Li / KBH4@(xNi3B / G) systems (x=10, 20, and 30 wt%) release 7.8, 8.1, and 7.7 wt% H2, respectively, reaching 92%, 95%, and 91% of the theoretical hydrogen storage capacity (8.5 wt% H2, corresponding to the dehydrogenation products LiH, K, and B), indicating that dehydrogenation is essentially complete. It can be seen that the confinement effect of graphene on the Li / KBH4 system and the catalytic effect of Ni3B show an efficient synergistic promotion effect in the hydrogen desorption process of the Li / KBH4 system.

[0087] (3) Temperature-dependent hydrogen absorption curve test method: Temperature-dependent hydrogen absorption adopts the volume method to test the hydrogen absorption capacity of the system. The test procedure is to heat from room temperature to 500℃ at a heating rate of 2℃ / min under the condition of an initial hydrogen pressure of 10MPa.

[0088] Figure 10 The temperature-dependent hydrogen absorption performance curves for the Li / KBH4@(xNi3B / G) system, Li / KBH4@G system, Li / KBH4@Ni3B system, Li / KBH4 eutectic system, and pristine LiBH4 are shown for comparison. Observations show that the hydrogen absorption performance of all Li / KBH4@(xNi3B / G) systems is significantly improved compared to the pristine LiBH4 and Li / KBH4 eutectic systems. Furthermore, the composite system with a Ni3B loading of 20wt% exhibits the lowest onset hydrogen absorption temperature and the highest hydrogen absorption capacity. This is because, compared to 10wt% and 30wt%, the 20wt% Ni3B loading in the xNi3B / G composite material provides the best Ni3B dispersion and the largest contact area with the Li / KBH4 system, effectively leveraging the Ni3B nanoparticles' enhanced hydrogen absorption performance. The Li / KBH4@Ni3B system exhibits a 75°C lower onset hydrogen absorption temperature of 313°C compared to the pure Li / KBH4 system. The initial hydrogen absorption temperature of the Li / KBH4@G system is 246°C, which is significantly lower than that of the single Li / KBH4 system by 142°C, indicating that the dispersion effect of graphene can improve the hydrogen absorption performance of the system to a certain extent. The Li / KBH4@(20Ni3B / G) system begins to absorb hydrogen at about 102°C, which is 144°C lower than that of the Li / KBH4@G system and 211°C lower than that of the Li / KBH4@Ni3B system. The results show that the addition of Ni3B alone has a certain catalytic effect on the hydrogen absorption and desorption reaction of the Li / KBH4 system, but when Ni3B is not dispersed with graphene, the synthesized Ni3B particles agglomerate and the particle size is large ( Figure 7 ), resulting in limited contact with the Li / KBH4 system, thus failing to fully exert its catalytic effect. However, the well-dispersed Ni3B nanoparticles within the graphene exhibit excellent bidirectional catalysis for the Li / KBH4 hydrogen absorption and desorption reactions. As the temperature rises to 400°C, the hydrogen absorption reaches 4.7 wt% H2. The absorption rate increases with further increases in temperature, reaching a total of 8.0 wt% H2 at 500°C, corresponding to 99% of the initial hydrogen desorption.

[0089] 2. Isothermal hydrogen release performance test

[0090] (1) Isothermal hydrogen desorption curve test method: The isothermal hydrogen desorption performance of the system at different temperatures was tested using the volumetric method. -3 The samples were heated to 250°C, 300°C and 350°C at a heating rate of 10°C / min under 0.1 Torr and kept at this temperature for 40 min for isothermal hydrogen release.

[0091] Figure 11The isothermal hydrogen desorption curves of the Li / KBH4@(20Ni3B / G) system prepared in Example 1 at 250°C, 300°C and 350°C; Figure 12 Isothermal hydrogen desorption curves at 350°C for the Li / KBH4@G system, the Li / KBH4 eutectic system, and single LiBH4 prepared in Comparative Example 1. When heated to 350°C at a heating rate of 10°C / min, the Li / KBH4@(20Ni3B / G) system rapidly released 6.7 wt% H2. Holding at 350°C for 30 minutes resulted in complete hydrogen desorption, with the decomposition products being LiH, K, and B, for a total of 8.5 wt% H2. Even at lower temperatures of 250°C and 300°C, the Li / KBH4@(20Ni3B / G) system released 3.8 and 6.6 wt% H2, respectively, within 60 minutes (including heating time). In contrast, the Li / KBH4@G system released 5.5 wt% H2 over 60 minutes at 350°C (including the heating process), while the LiBH4 and Li / KBH4 systems released only 1.5 and 2.3 wt% H2 after the same 30-minute heating at 350°C, respectively. Therefore, the introduction of Ni3B / G significantly improved the hydrogen desorption kinetics of Li / KBH4.

[0092] (2) Apparent activation energy of hydrogen release: High-purity argon was used as the carrier gas at a flow rate of 20 mL / min. The system was heated from room temperature to 600°C at different heating rates to obtain TPD-MS curves at different heating rates. The activation energy of hydrogen release was calculated according to the Kissinger equation: d(lnβ / T p 2 ) / d(1 / T p )=-E a / R, where β is the heating rate, T p is the main hydrogen desorption peak temperature under the heating rate, R is the ideal gas constant, expressed as lnβ / T p 2 is the vertical axis, 1 / T p Draw a graph for the horizontal axis and perform a linear fit. The slope of the fitted line is -E a / R, from which the apparent activation energy of hydrogen decomposition of the system can be calculated.

[0093] Figure 13 The Kissinger linear fitting diagrams of the systems prepared in Example 1 and Comparative Example 1 are shown, and the illustrations are TPD–MS curves at different heating rates. As shown in the figure, the Li / KBH4@(20Ni3B / G) system ( Figure 13 The apparent activation energy of hydrogen release in (a) is 102±2 kJ mol –1 , compared with Li / KBH4@G system ( Figure 13Middle (b), 122 ± 1 kJ mol –1 ) and Li / KBH4 system (176±4kJ mol –1 ) were reduced by 16% and 42% respectively. The introduction of Ni3B / G significantly reduced the hydrogen desorption kinetics barrier of the Li / KBH4 system and greatly improved the hydrogen desorption kinetics of the system.

[0094] 3. Cycle performance test

[0095] The initial vacuum degree is 1×10 -3 Under the conditions of 2000 Nm / min, the reactor was heated to 350°C at a rate of 10°C / min, kept warm for 30 minutes for isothermal hydrogen release, cooled to room temperature, and then heated to 400°C at a rate of 10°C / min, filled with 10 MPa H2, and kept warm for 120 minutes for isothermal hydrogen absorption; the cycle was repeated in this manner.

[0096] Figure 14 The partial isothermal hydrogen desorption curves (Figure (a)) and hydrogen absorption curves (Figure (b)) of the Li / KBH4@(20Ni3B / G) system prepared in Example 1 over 50 cycles under the above conditions are shown. As shown, the initial hydrogen release of the Li / KBH4@(20Ni3B / G) system is 8.5 wt% H2, and after 50 cycles, the hydrogen release remains at 6.9 wt% H2, with a total cycle capacity retention rate of 81.2%. The system exhibits rapid hydrogen absorption and desorption during each cycle, demonstrating its excellent kinetic performance during cycling.

[0097] Table 1 below shows the hydrogen desorption capacity and capacity retention rate data of different systems at different cycle numbers.

[0098] Table 1

[0099]

[0100]

[0101] Combined with Table 1, it can be seen that the confinement effect of graphene flakes on Li / KBH4 and the catalytic effect of Ni3B nanoparticles synergistically promote the significant improvement of the comprehensive hydrogen storage performance of the Li / KBH4 system.

[0102] The above-mentioned embodiments are preferred embodiments, but the protection scope of the present invention is not limited thereto. Ordinary technicians in this field can easily understand the spirit of the present invention based on the above-mentioned embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A bimetallic borohydride system, characterized in that: including Li / KBH4 eutectic system and graphene loaded with Ni3B nanoparticles; The Li / KBH4 eutectic system is melted and infiltrated into the lamellar gaps of the graphene loaded with Ni3B nanoparticles, thereby constructing a novel sandwich structure consisting of the Li / KBH4 eutectic system, graphene and nano-Ni3B.

2. The bimetallic borohydride system according to claim 1, characterized in that The particle size of the Ni3B nanoparticles is 5 to 100 nm.

3. The bimetallic borohydride system according to claim 1, characterized in that: The molar ratio of LiBH4 to KBH4 in the Li / KBH4 eutectic system is 0.725:0.275; In the graphene loaded with Ni3B nanoparticles, the loading amount of Ni3B nanoparticles is 10-30wt%; In the bimetallic borohydride system, the mass proportion of graphene loaded with Ni3B nanoparticles is 10-40%.

4. The bimetallic borohydride system according to claim 1, characterized in that: The initial hydrogen decomposition temperature is 182-223°C, the main hydrogen decomposition peak temperature is 278-313°C, the hydrogen decomposition amount is not less than 8.5wt% H2 when kept at 350°C for 30 minutes, the initial hydrogen absorption temperature is 102-170°C, and the hydrogen decomposition amount after fifty cycles of hydrogen absorption and decomposition is not less than 6.9wt% H2.

5. A method for preparing a bimetallic borohydride system according to any one of claims 1 to 4, characterized in that: include: S1, mixing nickel precursor, graphene, sodium borohydride and water, undergoing redox reaction and then sintering at high temperature to obtain graphene loaded with Ni3B nanoparticles, denoted as Ni3B / G; S2, mixing LiBH4 and KBH4 by ball milling to obtain a Li / KBH4 eutectic system; S3. Fully mix the Li / KBH4 eutectic system with Ni3B / G, and heat the Li / KBH4 eutectic system so that it is in a molten liquid state and fully contacts and mixes with Ni3B / G to obtain the bimetallic borohydride system, which is recorded as Li / KBH4@(Ni3B / G) composite system.

6. The method for preparing a bimetallic borohydride system according to claim 5, characterized in that: In step S1: The nickel precursor is selected from one or more of nickel chloride, nickel sulfate, nickel nitrate, and nickel oxide; The molar ratio of the nickel precursor to sodium borohydride is 3:1, based on the molar number of nickel in the nickel precursor; The mass ratio of nickel precursor to graphene is 1:(1-8).

7. The method for preparing a bimetallic borohydride system according to claim 5, wherein: In step S1: The redox reaction is carried out at room temperature; The temperature of the high-temperature sintering is 300-600°C.

8. The method for preparing a bimetallic borohydride system according to claim 5, wherein: In step S2: The molar ratio of LiBH4 and KBH4 is 0.725:0.

275.

9. The method for preparing a bimetallic borohydride system according to claim 5, wherein: In step S3: The mass ratio of Li / KBH4 eutectic system to Ni3B / G is (1.5-9):1; The heating temperature is 105-150°C.

10. Use of the bimetallic borohydride system according to any one of claims 1 to 4 in solid-state hydrogen storage.

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