A nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst, and a preparation method and application thereof

Abstract

The application discloses a nitrogen-doped MXene loaded Mo monatomic / sub-nanoparticle catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: adding lithium fluoride powder and titanium aluminum carbide powder into a hydrochloric acid solution and reacting under stirring, centrifuging, washing and precipitating to ink green, so as to obtain ink green precipitate; dispersing the ink green precipitate in a solvent, then ultrasonic treating, centrifuging, taking the upper liquid and drying, so as to obtain few-layer MXene; adding melamine and ammonium molybdate tetrahydrate into the few-layer MXene suspension and stirring uniformly, so as to obtain a suspension; freeze-drying the suspension, so as to obtain a precursor, and then heat-treating the precursor under a protective gas; and the application can anchor atomic clusters and single-atom state dispersed electrocatalytic active materials on the surface of the few-layer MXene, so that the prepared catalyst can be applied to hydrogen production as a hydrogen evolution catalyst, and has excellent electrochemical performance under acidic conditions.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalysts, in particular to a nitrogen-doped MXene loaded Mo single atom / sub-nanoparticle catalyst and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen energy, as a green energy in the 21st century, plays an important role in future sustainable energy due to its characteristics of cleanness, easy storage and resource abundance. The electrochemical hydrogen evolution reaction is considered as an effective method for hydrogen production, and a catalyst plays a dominant role in the process. At present, platinum group nanomaterials and their alloys with high selectivity and low overpotential have been proved to be effectively used for electrocatalytic hydrogen evolution reaction, but high cost, scarcity and low stability seriously hinder their large-scale industrial application. Under this background, designing and developing high energy density, low-cost and sustainable green electrochemical catalysts has become a research hotspot at present.

[0003] Compared with noble metals, non-noble metal single atom catalysts with relatively low price, most of which are concentrated in 3D transition metal single atom catalysts such as iron, cobalt and nickel, and there are still few reports on non-3D transition metal single atoms. As a 4D transition metal element with variable oxidation state and coordination number, molybdenum has shown great potential in electrocatalysis. In recent years, single atom catalysts (SACs) have become a research hotspot in the field of heterogeneous catalysis due to their high atom utilization rate and unique catalytic performance. The activation of water molecules by Mo SACs is not ideal, which hinders the transportation of intermediates at the electrolyte / electrode interface, thereby reducing the catalytic activity.

[0004] In view of this, the application is proposed. SUMMARY

[0005] The application aims to provide a nitrogen-doped MXene loaded Mo single atom / sub-nanoparticle catalyst and a preparation method and application thereof. The few-layer MXene prepared by the preparation method is subjected to etching treatment by an acidic solvent, a large number of defect sites are formed on the surface, and the defect sites can be used to anchor active metal single atoms, so that the loading capacity is improved. The electrocatalytic active material in the form of atom clusters and single atom state anchored on the surface of the few-layer MXene can be used as a hydrogen evolution catalyst and applied to hydrogen production, and has excellent electrochemical performance under acidic conditions.

[0006] In order to achieve the above-mentioned purpose of the application, the following technical scheme is adopted:

[0007] The application provides a preparation method of a nitrogen-doped MXene loaded Mo single atom / sub-nanoparticle catalyst.

[0008] (a) adding lithium fluoride powder and titanium aluminum carbide powder into a hydrochloric acid solution and reacting under stirring, centrifuging, washing the precipitate to greenish black, to obtain a greenish black precipitate;

[0009] (b) dispersing the greenish black precipitate in a solvent, then ultrasonic treatment, centrifuging, and taking the supernatant for drying, to obtain a few-layer MXene;

[0010] (c) adding melamine and ammonium molybdate tetrahydrate into the few-layer MXene suspension and stirring evenly, to obtain a suspension;

[0011] (d) freeze-drying the suspension to obtain a precursor, and then heat-treating the precursor under a protective gas to obtain the nitrogen-doped MXene supported Mo single atom / sub-nanoparticle catalyst.

[0012] Preferably, in the step (a), the mass ratio of lithium fluoride powder and titanium aluminum carbide powder is (6-9):(4-7).

[0013] Preferably, in the step (a), the concentration of the hydrochloric acid solution is 6-12 mol / L; the stirring rate is 200-600 r / min; the reaction temperature is constant at 30-50℃, and the reaction time is 25-35 h.

[0014] Preferably, in the step (a), the centrifugal speed is 2000-4000 rpm, and the centrifugal time is 4-8 min.

[0015] Preferably, in the step (b), the ultrasonic treatment time is 0.5-1.5 h; the centrifugal speed is 2000-4000 rpm, and the centrifugal time is 20-30 min.

[0016] Preferably, in the step (b), the solvent is deionized water, and the mass-volume ratio of lithium fluoride powder to the solvent is 0.012-0.0225.

[0017] Preferably, in the step (c), the concentration of the few-layer MXene suspension is 0.4-0.8 mg / ml; and the mass ratio of melamine, ammonium molybdate tetrahydrate and few-layer MXene is (8-12):(1-3):5.

[0018] Preferably, in the step (d), the freeze-drying is freeze-treating the suspension for 10-15 h, and then treating in a freeze-drying box for 20-30 h.

[0019] Preferably, in the step (d), the protective gas flow rate is 200-500 sccm, and the protective gas includes argon.

[0020] Preferably, in the step (d), the heat treatment is heating to 600-900 DEG C at a rate of 3-7 DEG C / min and holding for 1-3 h.

[0021] The second aspect of the present application provides a nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared by the above preparation method.

[0022] The third aspect of the present application provides an application of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared by the above preparation method in water electrolysis for hydrogen production.

[0023] Compared with the prior art, the present application has at least the following beneficial effects:

[0024] The preparation method combines the preparation of few-layer MXene by acid etching method with the preparation of MXene supported Mo monatomic / sub-nanoparticle by high-temperature pyrolysis method, and a novel nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst is prepared, which has simple and feasible process and low cost.

[0025] The few-layer MXene prepared by the preparation method is etched by an acid solvent, a large number of defect sites are formed on the surface, and can be used to anchor active metal monatomic to improve the loading capacity; the active material in the form of atomic clusters and single atoms is anchored on the surface of the few-layer MXene, so that the prepared catalyst can be used as a hydrogen evolution catalyst for hydrogen production, and has excellent electrochemical performance under acidic conditions. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0027] Figure 1 A transmission electron microscope image of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared in Example 1 of the present application;

[0028] Figure 2 A spherical aberration-corrected high-resolution transmission electron microscope image of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared in Example 1 of the present application;

[0029] Figure 3 A hydrogen evolution linear sweep voltammetry curve of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared in Example 1 of the present application in 0.5M H2SO4 electrolyte;

[0030] Figure 4 The chronopotentiometric stability test curve of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared in Embodiment 1 is shown in the following figure. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described in detail below with reference to the embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0032] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present application should be understood as the usual meanings understood by the skilled person in the field to which the present application belongs.

[0033] Embodiment 1

[0034] The present embodiment is a preparation method of a nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst, which comprises the following steps:

[0035] (a) 1.6 g of lithium fluoride powder and 1 g of titanium aluminum carbide powder are added to a 9 mol / L hydrochloric acid solution and reacted at 400 r / min and a constant temperature of 40℃ for 30 h, then centrifuged at 3500 rpm for 5 min, and the precipitate is washed to a dark green color to obtain a dark green precipitate;

[0036] (b) The dark green precipitate is dispersed in 100 ml of deionized water, then ultrasonically treated for 1 h, centrifuged at 3500 rpm for 20 min, and the upper liquid is taken and dried to obtain a few-layer MXene;

[0037] (c) 50 mg of the few-layer MXene is taken and ultrasonically treated in deionized water for 30 min to obtain a 0.6 mg / ml few-layer MXene suspension, 100 mg of melamine and 20 mg of ammonium molybdate tetrahydrate are added to the few-layer MXene suspension and stirred for 30 min to obtain a suspension;

[0038] (d) The suspension is subjected to freezing treatment for 12 h, then placed in a freeze-drying box for 24 h of freeze-drying treatment to obtain a precursor, and the precursor is heated to 750℃ at a rate of 5℃ / min under the protection of 300 sccm of argon gas and kept for 2 h to obtain the above-mentioned nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst.

[0039] Embodiment 2

[0040] The present embodiment is a preparation method of a nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst, which comprises the following steps:

[0041] (a) 1.2 g of lithium fluoride powder and 0.8 g of titanium aluminum carbide powder were added to a 6 mol / L hydrochloric acid solution and reacted at 600 r / min and a constant temperature of 30°C for 35 h, then centrifuged at 2000 rpm for 8 min, and the precipitate was washed to greenish black to obtain a greenish black precipitate;

[0042] (b) The greenish black precipitate was dispersed in 80 ml of deionized water, then ultrasonically treated for 1.5 h, centrifuged at 2000 rpm for 30 min, and the upper liquid was taken and dried to obtain few-layer MXene;

[0043] (c) 50 mg of few-layer MXene was taken and ultrasonically treated in deionized water for 30 min to obtain a 0.4 mg / ml few-layer MXene suspension, 80 mg of melamine and 30 mg of ammonium molybdate tetrahydrate were added to the few-layer MXene suspension and stirred for 30 min to obtain a suspension;

[0044] (d) The suspension was subjected to freezing treatment for 10 h, then placed in a freeze-drying box and freeze-dried for 20 h, to obtain a precursor, which was heated to 900°C at a rate of 7°C / min under the protection of 500 sccm of argon gas and kept for 1 h to obtain the above-mentioned nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst.

[0045] Example 3

[0046] The present embodiment is a preparation method of a nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst, which comprises the following steps:

[0047] (a) 1.8 g of lithium fluoride powder and 1.4 g of titanium aluminum carbide powder were added to a 12 mol / L hydrochloric acid solution and reacted at 200 r / min and a constant temperature of 50°C for 25 h, then centrifuged at 4000 rpm for 4 min, and the precipitate was washed to greenish black to obtain a greenish black precipitate;

[0048] (b) The greenish black precipitate was dispersed in 100 ml of deionized water, then ultrasonically treated for 0.5 h, centrifuged at 4000 rpm for 20 min, and the upper liquid was taken and dried to obtain few-layer MXene;

[0049] (c) 50 mg of few-layer MXene was taken and ultrasonically treated in deionized water for 30 min to obtain a 0.8 mg / ml few-layer MXene suspension, 120 mg of melamine and 10 mg of ammonium molybdate tetrahydrate were added to the 0.8 mg / ml few-layer MXene suspension and stirred for 20 min to obtain a suspension;

[0050] (d) the suspension is subjected to freeze treatment for 15 h, and then freeze-dried in a freeze-drying box for 30 h to obtain a precursor; the precursor is heated to 600 ℃ at a rate of 3 ℃ / min and kept for 3 h under the protection of 200 sccm of argon gas, to obtain the above-mentioned nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst.

[0051] Experimental Example

[0052] The nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst is prepared according to the method of Example 1.

[0053] The nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared above is subjected to transmission electron microscopy scanning, and the transmission electron microscopy image is as shown in Figure 1 .

[0054] It can be seen from Figure 1 that the few-layer MXene still maintains the morphology of nanosheets, and thin nitrogen-doped carbon layers can be seen on the nanoframework, and there are obvious metal particles.

[0055] The nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared above is subjected to spherical aberration correction high-resolution transmission electron microscopy observation, and the observation result is as shown in Figure 2 .

[0056] It can be seen from Figure 2 that many sub-nanometer Mo particles with an average diameter of 1.87 nm can be observed on the surface of the MXene, and the existence of monatomic Mo in the MXene framework can be directly observed beside the clusters.

[0057] The nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared above and the commercial Pt / C (purchased from Beijing Inokai Reagent, item number A07498) are subjected to hydrogen evolution testing in a 0.5M H2SO4 electrolyte; the hydrogen evolution result is as shown in Figure 3 .

[0058] It can be seen from Figure 3 that in the 0.5M H2SO4 electrolyte, when the catalyst of the water electrolysis testing system is the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared in Example 1 of the present application, only a low overpotential of 75 mV is needed to make the current density of the reaction system reach 10 mA / cm -2 , close to the commercial platinum-carbon catalyst. At the same time, as the current density increases, the gap between the two catalysts becomes smaller and smaller, and the advantage of the Mo monatomic / sub-nanoparticle hydrogen evolution electrocatalyst becomes more and more obvious.

[0059] The stability of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared above was tested by chronoamperometric stability test, and the test results are shown in Figure 4

[0060] As can be seen from Figure 4 , under a current density of 10 mA / cm -2 , the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst of the present embodiment can ensure almost no decay of catalytic activity within 15 h, and the potential drop speed is slower, indicating that its stability is significantly better than that of commercial Pt / C. This indicates that the catalyst has excellent potential for practical use. At the same time, the Mo element is cheap and easy to obtain, and has extremely high economic benefits.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application.​

Claims

1. A method for preparing a nitrogen-doped MXene-supported Mo monatomic / subnanoparticle catalyst, characterized in that, The method comprises the following steps: (a) adding lithium fluoride powder and titanium aluminum carbide powder into a hydrochloric acid solution and reacting under stirring, centrifuging, washing the precipitate to greenish black, and obtaining a greenish black precipitate; (b) dispersing the greenish black precipitate in a solvent, then ultrasonic treatment, centrifuging, and taking the supernatant liquid to dry, and obtaining few-layer MXene; (c) adding melamine and ammonium molybdate tetrahydrate into the few-layer MXene suspension and stirring uniformly, and obtaining a suspension; (d) freeze-drying the suspension to obtain a precursor, and then heat-treating the precursor under a protective gas to obtain the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst; In the step (a), the mass ratio of lithium fluoride powder and titanium aluminum carbide powder is (6-9):(4-7); the concentration of the hydrochloric acid solution is 6-12 mol / L; the stirring rate is 200-600 r / min; the reaction temperature is constant at 30-50℃, and the reaction time is 25-35 h; In the step (b), the ultrasonic treatment time is 0.5-1.5 h; the centrifugal speed is 2000-4000 rpm, and the centrifugal time is 20-30 min; In the step (c), the concentration of the few-layer MXene suspension is 0.4-0.8 mg / ml; the mass ratio of melamine, ammonium molybdate tetrahydrate and few-layer MXene is (8-12):(1-3):5; In the step (d), the freeze-drying is to freeze the suspension for 10-15 h, and then place it in a freeze-drying box for 20-30 h; the protective gas flow rate is 200-500 sccm, and the protective gas includes argon; the heat treatment is to heat to 600-900℃ at a rate of 3-7℃ / min and keep for 1-3 h.

2. The nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared by the preparation method of claim 1.

3. The application of the nitrogen-doped MXene supported Mo monatomic / sub-nanoparticle catalyst prepared by the preparation method of claim 1 in electrolytic water hydrogen production.

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