Niobium-based MXene catalyst for lithium borohydride hydrogen storage as well as preparation and application of niobium-based MXene catalyst

Abstract

The invention relates to a niobium-based MXene catalyst for lithium borohydride hydrogen storage as well as preparation and application of the niobium-based MXene catalyst. The expressions of the niobium-based MXene catalyst are Nb2C and TiNbC MXene respectively. The preparation method comprises the following steps: dissolving Nb2AlC MAX in a hydrofluoric acid solution, dissolving TiNbAlC MAX in a mixed solution of hydrogen chloride and lithium fluoride, cleaning and drying to obtain Nb2C and TiNbC MXene with layered structures. According to the preparation method of the niobium-based MXene catalyst for lithium borohydride hydrogen storage, Nb2C of a layered structure, TiNbC MXene and lithium borohydride are mixed and prepared by adopting a high-energy ball milling method, a LiBH4 + xwt% Nb2C composition and a LiBH4 + xwt% TiNbCTx composition are synthesized, the preparation method of the niobium-based MXene catalyst for lithium borohydride hydrogen storage has high catalytic performance, and the hydrogen desorption performance of lithium borohydride is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen storage materials, and relates to a niobium-based MXene catalyst for lithium borohydride hydrogen storage, its preparation and application. Background Art

[0002] Lithium borohydride (LiBH 4 ) has received extensive attention as an excellent hydrogen storage material due to its extremely high hydrogen storage capacity (LiBH 4 : 18.5 wt%; Mg(BH 4 ) 2 : 14.8 wt%; Ca(BH 4 ) 2 : 11.6 wt%). However, the main hydrogen release process of LiBH 4 occurs at about 400 °C, and the hydrogen release products LiH and B of pure LiBH 4 need to be hydrogenated under very harsh conditions, such as hydrogen absorption conditions of 600 °C and 35 MPa hydrogen pressure. A series of problems such as poor thermodynamic and kinetic properties and low reversibility of LiBH 4 severely limit the development of LiBH4.

[0003] Commonly used hydrogen storage modification methods for LiBH 4 include adding catalysts, nanoconfinement, and forming composite systems with other hydrogen storage materials. MXene is a newly emerging two-dimensional material with highly active transition metal sites, a layered structure, and excellent specific surface area. In recent years, it has also been widely used in solid-state hydrogen storage materials to improve their hydrogen storage performance.

[0004] Related reports (Improving the hydrogen storage performance of lithium borohydride by Ti 3 C 2 MXene, International Journal of Hydrogen Energy, 44(2019)29297-29303) prepared LiBH 4 -xTi 3 C 2 composites by ball milling method, where LiBH 4 -40 wt% Ti 3 C 2 starts to release hydrogen at 120 °C and can release 5.37 wt% of hydrogen within 1 hour at 350 °C, indicating that the addition of Ti 3 C 2 significantly improves the hydrogen storage performance of LiBH4 The hydrogen desorption performance, and its mechanism mainly includes the following three aspects: 1) LiBH 4 and Ti 3 C 2 MXene generates TiB-containing 2 active substances during the hydrogen desorption process, which is beneficial to reducing the peak hydrogen desorption temperature; in addition, the fluorine groups remaining during the etching process of Ti 3 C 2 MXene partially replace the hydrogen ions in LiBH 4 and LiH, which is beneficial to reducing the initial hydrogen desorption temperature; finally, the layered structure of Ti 3 C 2 provides more contact area, accelerating the process of the hydrogen desorption reaction. Related reports (In Situ Introduction ofLi 3 BO 3 and NbHLeads to Superior Cyclic Stability and Kinetics of a LiBH4-Based HydrogenStorage System, ACS Applied Materials&Interfaces, 12(2019)893-903) use niobium ethoxide as the niobium source to in-situ generate Li 4 BO 3 and NbH active substances during the ball milling and heat treatment processes with LiBH 3 . The obtained LiBH 4 -0.04(Li 3 BO 3 +NbH) composite has the initial and peak hydrogen desorption temperatures decreased by 200 and 90 °C respectively, and 9.2 wt% of hydrogen can be released when heated to 400 °C, and its hydrogen desorption performance is significantly improved. However, the initial hydrogen desorption temperature of the above hydrogen storage material composite is still above 100 °C, and the hydrogen desorption amount below 400 °C is less than 11 wt%. At the same time, although the introduction of Ti 3 C 2 and Li 3 BO 3 significantly improves the hydrogen desorption performance of LiBH 4 , the above LiBH 4 composite still has problems of high hydrogen desorption temperature and low hydrogen desorption capacity. Summary of the Invention

[0005] The purpose of the present invention is to provide a niobium-based MXene catalyst for lithium borohydride hydrogen storage, its preparation and application, which have the advantages of low initial and peak hydrogen desorption temperatures, high hydrogen desorption capacity, and excellent re-hydrogenation performance.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] In one aspect, the present invention provides a niobium-based MXene catalyst for lithium borohydride hydrogen storage, and its expression is Nb 2 C MXene or TiNbC MXene.

[0008] In a second aspect, the present invention provides a preparation method of a niobium-based MXene catalyst for lithium borohydride hydrogen storage. The niobium-based MXene catalyst is Nb 2 C MXene, and its preparation method includes the following steps:

[0009] (1) Weigh aluminum niobium carbide and dissolve it in a hydrogen fluoride solution, stir and react to mix, and obtain a mixed solution;

[0010] (2) Centrifuge the mixed solution in step (1) once or several times at room temperature until a viscous precipitate appears, remove the upper liquid, and vacuum dry the collected viscous precipitate to obtain layered structure Nb 2 C MXene powder, which is the target niobium-based MXene catalyst.

[0011] Furthermore, in step (1), the addition ratio of aluminum niobium carbide to the hydrogen fluoride solution is 2 g:(25 - 35) mL, and the mass concentration of the hydrogen fluoride solution is 47 - 49%.

[0012] Furthermore, in step (1), the temperature of the stirring reaction is 45 - 55 °C, and the time is 70 - 80 h.

[0013] Furthermore, in step (2), the rotation speed of centrifugation is 8000 - 9000 rpm, and the time for each centrifugation is 5 - 8 min; preferably, the number of centrifugations is 7 - 8 times.

[0014] Furthermore, in step (2), the pH of the upper liquid is 6 - 7.

[0015] Furthermore, in step (2), the temperature of vacuum drying is 40 - 50 °C, and the time is 5 - 8 h.

[0016] Further, the niobium-based MXene catalyst is TiNbC MXene, and its preparation method includes the following steps:

[0017] (A) Weigh titanium niobium carbide and dissolve it in a solution of hydrogen chloride and lithium fluoride, stir and react to obtain a mixed solution;

[0018] (B) Centrifuge the mixed solution once or several times at room temperature to obtain a black precipitate at the bottom;

[0019] (C) Vacuum dry the black precipitate to obtain layered structure TiNbC MXene powder, which is the target niobium-based MXene catalyst.

[0020] Furthermore, in step (A), the addition ratio of the solution of aluminum titanium niobium carbide, hydrogen chloride and lithium fluoride is 2 g : (35 - 45) mL. In the solution of hydrogen chloride and lithium fluoride, the molar concentration of hydrogen chloride is 8 - 9 mol / L, and the addition amount of lithium fluoride is (3 - 3.2) g / (35 - 45) mL.

[0021] Furthermore, in step (A), the temperature of the stirring reaction is 35 - 45 °C, and the time is 40 - 50 h;

[0022] In step (B), the centrifugation speed is 4000 - 6000 rpm, and the time for each centrifugation is 5 - 10 min.

[0023] Furthermore, in step (C), the temperature of the vacuum drying is 45 - 55 °C, and the time is 12 - 18 h.

[0024] In a third aspect, the present invention provides an application of a niobium-based MXene catalyst for lithium borohydride hydrogen storage in using as a hydrogen storage material for lithium borohydride hydrogen storage.

[0025] During specific application, after uniformly mixing the niobium-based MXene catalyst and LiBH 4 and then using high-energy ball milling method for mixing preparation to synthesize LiBH 4 +xwt% Nb 2 C composite and LiBH 4 +xwt% TiNbC composite (10 ≤ x ≤ 50). When the addition amount is 40 wt%, the composites can start to release hydrogen below 70 °C and complete the main hydrogen release process before 400 °C. Preferably, during mixing, control the environment O 2 <0.01 ppm, H 2 O < 0.01 ppm.

[0026] Preferably, the particle size of the used aluminum niobium carbide (Nb2AlC) and titanium niobium aluminum carbide (TiNbAlC) is 300 - 400 mesh, and the purity is 99%.

[0027] Preferably, the mixing adopts high-energy ball milling method, the ball milling speed is 300 - 500 rmp, the time is 8 - 12 hours, and the ball-to-material ratio is 100 - 200∶1.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) The preparation method of the niobium-based MXene catalyst for lithium borohydride hydrogen storage has a layered structure with a high specific surface area, providing more active sites for the reaction, thereby reducing the thermodynamic stability and enhancing its thermodynamic performance;

[0030] (2) During the dehydrogenation process of the lithium borohydride-MXene composite, Li 3 BO 3 is in-situ generated. The active center Li + can weaken the Li-B ionic bond, and the highly electronegative oxygen atom can weaken the B-H covalent bond;

[0031] (3) During the ball milling and dehydrogenation process of lithium borohydride and MXene, as well as the active substances containing Ti and Nb, they play a "hydrogen pump" role, changing the dehydrogenation path, thereby enhancing the dehydrogenation performance of lithium borohydride;

[0032] (4) The coexistence of multiple active substances provides more grain boundaries for the diffusion and transport of hydrogen atoms, enhancing the dehydrogenation kinetic performance.

[0033] (5) The preparation method of the composite material is simple, the operation is simple, the addition ratio of MXene is flexible, and it can significantly improve the dehydrogenation performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the XRD patterns of different catalyst components prepared in Example 1 and Example 2 of the present invention;

[0035] Figure 2 It is the temperature-programmed desorption curve (TPD) of the LiBH 4 + 40wt% TiNbC composite in Example 1 of the present invention;

[0036] Figure 3 It is the XRD patterns of the LiBH 4 + 40wt% TiNbC composite in different states in Example 1 of the present invention;

[0037] Figure 4 It is the Ti2p and Nb 3d XPS spectra of the dehydrogenation product of the LiBH 4 + 40wt% TiNbC composite at 500°C in Example 1 of the present invention;

[0038] Figure 5 It is the temperature-programmed desorption curve (TPD) of the LiBH 4 + 40wt% Nb 2 C composite in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives the detailed implementation manner and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0040] In the following embodiments, the TiNbAlC and Nb 2 AlC used are all commercially available products, purchased from Foshan New En Technology Co., Ltd.

[0041] For the remaining raw materials or processing technologies without special instructions, it means that they are all conventional commercially available raw materials or conventional processing technologies in the art.

[0042] Example 1

[0043] A niobium-based MXene catalyst for lithium borohydride, the catalyst composition expression of which is TiNbC MXene, is prepared by the following method:

[0044] (1) Prepare an etching solution by dissolving 3 g of lithium fluoride in 40 mL of a hydrochloric acid solution with a concentration of 9 mol / L. After stirring well, dissolve 2 g of titanium niobium aluminum carbide (TiNbAlC) in the above solution and mix at 45 °C for 48 hours to remove the aluminum layer;

[0045] (2) Centrifuge the mixture at a speed of 3500 rpm at room temperature for about 3 min, repeat 7-8 times, and obtain a black precipitate at the bottom;

[0046] (3) Dry the precipitate in a vacuum drying oven at 50 °C for 12 hours to obtain layered TiNbC MXene powder.

[0047] (4) In a glove box, uniformly mix the layered TiNbC MXene with LiBH 4 and then prepare the mixture by high-energy ball milling to synthesize LiBH 4 +xwt% TiNbC composite (indicating that the addition amount of TiNbC is xwt% of LiBH 4 , where x = 40). The ball milling speed is 400 rpm, the time is 10 hours, and the ball-to-material ratio is 150:1. The composite can start to release hydrogen at 69 °C, complete the main hydrogen release process at 371 °C, release 11.65 wt% of hydrogen, and the final hydrogen release amount is 12.61 wt% when the temperature is raised to 500 °C.

[0048] Figure 1In (b) and (c) are the XRD curves of TiNbAlC and TiNbC, respectively. As shown in the figure, the peak intensity corresponding to the (0 0 2) crystal plane with 2θ = 12.88° in TiNbAlC decreases significantly and shifts to a smaller angle to 2θ = 5.87° of TiNbC, indicating that the aluminum layer is removed and the interlayer spacing increases.

[0049] Figure 2 is pure LiBH 4 and LiBH 4 + 40 wt% TiNbC composite temperature-programmed desorption curve (TPD), as shown in the figure. Pure LiBH4 starts to release hydrogen at 270 °C, the peak hydrogen release temperature is about 405 °C, and 11.30 wt% of hydrogen can be released when heated to 500 °C. While the LiBH 4 + 40 wt% TiNbC composite can start to release hydrogen at 69.02 °C, complete the main hydrogen release process at 371.36 °C, release 11.79 wt% of hydrogen, and the final hydrogen release amount is 12.61 wt% when heated to 500 °C.

[0050] Figure 3 is the XRD patterns of the LiBH 4 + 40 wt% TiNbC composite in different states: Ⅰ) ball milling; Ⅱ) hydrogen release at 300 °C; Ⅲ) hydrogen release at 500 °C. As shown in the figure, no new phase formation is found in the XRD patterns after ball milling and hydrogen release at 300 °C. However, after hydrogen release at 500 °C, the XRD pattern changes significantly, and TiNbC and LiBH 4 react to form LiF, Li 3 BO 3 、Ti and NbH x active substances.

[0051] Figure 4 is the XPS spectra of Ti 2p and Nb 3d of the hydrogen release product of the LiBH 4 + 40 wt% TiNbC composite at 500 °C. As shown in the figure, during the hydrogen release process, LiBH 4 and TiNbC react to form Ti / TiB 2 、Nb / NbH x 、LiF and Li 3 BO 3 active substances, further catalyzing the hydrogen release reaction of LiBH 4 .

[0052] Example 2

[0053] A niobium-based MXene catalyst for lithium borohydride, the catalyst composition expression is Nb 2 C MXene, which is prepared by the following method:

[0054] (1) Dissolve 2 grams of niobium aluminum carbide (Nb 2 AlC) in 30 ml of hydrogen fluoride solution with a concentration of 49%, and mix at 50 °C for 72 hours to obtain a mixed solution after removing the aluminum layer;

[0055] (2) Centrifuge the mixed solution at 8500 rpm for 5 minutes at room temperature, repeat 7 - 8 times until a viscous precipitate appears, the pH of the upper liquid is 6 - 7, and remove the upper liquid to obtain a viscous precipitate;

[0056] (3) Dry the precipitate in a vacuum drying oven at 40 °C for 5 hours to obtain layered structure Nb 2 C MXene powder;

[0057] (4) In a glove box, mix the layered structure Nb 2 C MXene with LiBH 4 uniformly, and then use high - energy ball milling method for mixing preparation to synthesize LiBH 4 +xwt% Nb 2 C composite (10 ≤ x ≤ 50, x = 40 in this example). The ball - milling speed is 400 rpm, the time is 10 hours, and the ball - to - powder ratio is 150:1. The composite can start to release hydrogen at 56.9 °C, complete the main hydrogen - release process at 437.7 °C, release 12.73 wt% of hydrogen, and the final hydrogen - release amount is 13.40 wt% when heated to 500 °C.

[0058] Figure 1 JCPDS#00 - 030 - 0033 in 2 is the standard PDF card of Nb Figure 1 (a) To obtain the XRD curve of Nb 2 C MXene, the peak at 2θ = 7.67° corresponds to the (0 0 2) crystal plane of Nb 2 C MXene, indicating that the aluminum layer is removed and the layer spacing increases. At the same time, there are still some peaks of Nb 2 in the XRD pattern of Nb 2 AlC, indicating that there is still some Nb 2 AlC MAX phase in the obtained Nb 2 C MXene

[0059] Figure 5 is the temperature - programmed desorption curve (TPD) of pure LiBH 4 and LiBH 4 +40wt% TiNbC composite. As shown in the figure, pure LiBH 4Hydrogen release starts at 270 °C, the peak hydrogen release temperature is about 405 °C, and 11.30 wt% of hydrogen can be released when heated to 500 °C. For the LiBH 4 + 40 wt% Nb 2 composite, hydrogen release starts at 52.95 °C, the main hydrogen release process is completed at 440.11 °C, and 12.62 wt% of hydrogen is released. When heated to 500 °C, the final hydrogen release amount is 13.40 wt%, and the hydrogen release performance is significantly improved.

[0060] As described in the background art above, the prior art also discloses introducing niobium-containing materials and MXene layered structure materials to improve the hydrogen absorption and desorption performance of LiBH 4 , and the hydrogen absorption and desorption performance of LiBH 4 has also been significantly improved. The main innovation of the present invention is that using the TiNbC MXene layered structure material as a reactant, through ball milling and hydrogen release processes, LiBH 4 reacts with TiNbC to generate various active substances such as Ti / TiB 2 , Nb / NbH x , Li 3 BO 3 , and LiF. Among them, Ti / TiB 2 improves its hydrogen desorption kinetic performance by changing the hydrogen desorption path of LiBH 4 ; Nb / NbH x plays the role of a "hydrogen pump" to accelerate the transmission and diffusion of hydrogen atoms; Li 3 BO 3 weakens the Li-B ionic bond with Li + as the active center, and the highly electronegative oxygen atom attracts the B atom in [BH 4 - to weaken the B-H covalent bond. Finally, since the electronegativity of fluorine atoms is higher than that of hydrogen atoms, the residual F in the TiNbC etching process replaces the H in LiH to form LiF, which also contributes to the decomposition of LiBH 4 . Finally, the coexistence of various active substances provides more grain boundaries for the diffusion and transmission of hydrogen atoms, thus significantly improving the hydrogen desorption performance of LiBH 4 .

[0061] Combined with the characterization experimental data of the above embodiments, it can be seen that compared with the hydrogen release materials mentioned in the background art, the LiBH 4 -40 wt% TiNbC composite prepared in the present invention has an initial hydrogen release temperature as low as 69.02 °C, which is significantly lower than 120 °C of LiBH 4 -40 wt% Ti 3 C 2 and 120 °C of LiBH 4 -33 wt% Li​3 BO 3 at 105 °C. In addition, there are also obvious advantages in terms of hydrogen storage capacity. LiBH 4 -40 wt% TiNbC composite can release 11.79 wt% of hydrogen at about 370 °C, which is significantly higher than that of LiBH 4 -40 wt% Ti 3 C 2 at 8 wt% (400 °C) and LiBH 4 -33 wt% Li 3 BO 3 at 11 wt% (400 °C). Therefore, compared with the addition of the single catalyst mentioned above, the coexistence of multiple active substances in the present invention shows better catalytic effect in improving the hydrogen release performance of LiBH 4

[0062] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.​

Claims

1. A niobium-based MXene catalyst for lithium borohydride hydrogen storage, characterized in that: Its expression is Nb2C MXene or TiNbC MXene.

2. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 1, characterized in that: The niobium-based MXene catalyst is Nb2C MXene, and its preparation method comprises the following steps: (1) weighing niobium aluminum carbide and dissolving it in a hydrogen fluoride solution, stirring and reacting to obtain a mixed solution; (2) The mixed solution in step (1) is centrifuged once or several times at room temperature until a viscous precipitate appears, the upper liquid is removed, and the collected viscous precipitate is vacuum dried to obtain a layered Nb2C MXene powder, which is the target product, a niobium-based MXene catalyst.

3. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 2, characterized in that: In step (1), the ratio of the added amount of niobium aluminum carbide to the hydrogen fluoride solution is 2g: (25-35)mL, and the mass concentration of the hydrogen fluoride solution is 47-49%.

4. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 2, characterized in that: In step (1), the stirring reaction temperature is 45 to 55° C. and the time is 70 to 80 hours.

5. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 2, characterized in that: In step (2), the centrifugal speed is 8000-9000 rpm, and the time of each centrifugation is 5-8 min; The pH of the upper liquid is 6-7; The vacuum drying temperature is 40-50°C and the time is 5-8 hours.

6. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 2, characterized in that: The niobium-based MXene catalyst is TiNbC MXene, and its preparation method comprises the following steps: (A) weighing titanium niobium aluminum carbide and dissolving it in a solution of hydrogen chloride and lithium fluoride, stirring for reaction, and obtaining a mixed solution; (B) centrifuging the mixed solution once or several times at room temperature to obtain a black precipitate at the bottom; (C) The black precipitate is vacuum dried to obtain a layered TiNbC MXene powder, which is the target product, a niobium-based MXene catalyst.

7. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 6, characterized in that: In step (A), the ratio of the added amount of titanium niobium aluminum carbide, hydrogen chloride and lithium fluoride solution is 2g: (35-45)mL, and the molar concentration of hydrogen chloride in the hydrogen chloride and lithium fluoride solution is 8-9mol / L, and the added amount of lithium fluoride is (3-3.2)g / (35-45)mL.

8. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 6, characterized in that: In step (A), the stirring reaction temperature is 35 to 45° C. and the time is 40 to 50 hours; In step (B), the centrifugal speed is 4000-6000 rpm, and the time of each centrifugation is 5-10 minutes.

9. The method for preparing a niobium-based MXene catalyst for lithium borohydride hydrogen storage according to claim 6, characterized in that: In step (C), the vacuum drying temperature is 45 to 55° C. and the time is 12 to 18 hours.

10. Use of the niobium-based MXene catalyst for lithium borohydride hydrogen storage as claimed in claim 1 as a hydrogen storage material for lithium borohydride hydrogen storage.

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