CN113877620A - Mo2N/NC composite material and preparation method thereof - Google Patents

Mo2N/NC composite material and preparation method thereof Download PDF

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CN113877620A
CN113877620A CN202111204404.9A CN202111204404A CN113877620A CN 113877620 A CN113877620 A CN 113877620A CN 202111204404 A CN202111204404 A CN 202111204404A CN 113877620 A CN113877620 A CN 113877620A
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composite material
preparation
graphene oxide
mixed solution
hydrazine hydrate
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冯其
孙彦兵
赵景
莫代泽
郑得洲
王付鑫
靳柄军
曾庆光
徐维
张业龙
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Wuyi University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/24—Nitrogen compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/615—100-500 m2/g
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Abstract

The invention discloses Mo2The preparation method comprises the steps of taking a graphene oxide solution, a molybdenum source and hydrazine hydrate as raw materials, stirring, standing for aging, freeze-drying, pyrolyzing and calcining in one step and the like to obtain Mo with a porous sheet structure2N/NC composite material. According to the preparation method, the graphene oxide solution is used as a carbon source and a template, dangerous ammonia gas is not needed, and the high-purity two-dimensional flaky Mo can be obtained through one-step pyrolysis method2The N/NC composite material has the advantages of safe and reliable whole preparation process, simple and easily-controlled process conditions and lower production cost, and is suitable for industrial large-scale production; the obtained flaky Mo2The N/NC composite material has a particle diameterSmall size, high purity and large specific surface area, shows good catalytic activity similar to platinum, and can be widely applied to the field of catalysis.

Description

Mo2N/NC composite material and preparation method thereof
Technical Field
The invention belongs to the technical field of material processing, and particularly relates to Mo2An N/NC composite material and a preparation method thereof.
Background
Noble metals such as platinum are widely used in catalytic processes in the fields of petrochemical industry, organic synthesis, fuel cells, automobiles, electronic industry, and the like because of their catalytic effects, but on the one hand, such noble metals are very small in reserves on the earth and are decreasing, and on the other hand, they are very expensive and have high application costs. As such, new catalytic materials that can replace noble metal catalysts such as platinum have been sought.
The transition metal nitride is an interstitial compound or alloy generated by filling N element into the transition metal lattice. After the non-metal N element enters gaps among transition metal atoms, the metal atom spacing is increased, the crystal lattice is expanded, the transition metal d band is contracted, and the Fermi level state density is increased. This modulation makes the surface properties and adsorption characteristics of transition metal nitrides very similar to those of platinum group noble metals. Wherein, molybdenum nitride (Mo)2N) due to its good chemical and thermodynamic stability, high electronic conductivity and platinum-like electronic structure, Mo2The catalytic performance of N is similar to that of noble metals such as Pt, Rh and the like, so that the N is known as a quasi-platinum catalyst, and has wide application prospect in the fields of hydrodesulfurization, hydrodenitrogenation, electro-catalytic hydrogen evolution and the like.
At present, Mo2The conventional process for preparing N is by molybdenum oxide and ammonia (NH)3) Reacting and synthesizing under high temperature. But Mo prepared by the method2The N has large particle size and small specific surface area, and limits Mo2Catalytic activity of N. For increasing Mo2Specific surface area and conductivity of N, in general Mo2N is supported on a porous carbon material, but this physical mixing method, Mo2The bonding force between N and carbon is weak, and the catalyst is easy to fall off and lose efficacy in the catalytic process. Ordinary carbon source, nitrogen source and molybdenum source are calcined at high temperature in inert atmosphere due to molybdenum carbide (Mo)2C) Thermodynamic enthalpy transformation ratio Mo2Small N (in the high-temperature pyrolysis process, Mo)2C is more easily formed), it is generally difficult to obtain high purity molybdenum nitride/carbon (Mo)2N/C) composite material. Therefore, Mo with simple development process, high purity and high specific surface area2The N/C chemistry is an important challenge.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention provides a molybdenum nitride/nitrogen-doped carbon (Mo)2N/NC) composite material and a preparation method thereof, aiming at solving the technical problems of low catalytic activity, weak binding force and low purity of the existing molybdenum nitride composite material. The preparation method can obtain high-purity porous flaky Mo2The N/NC composite material shows good catalytic activity similar to platinum, has simple process and low cost, and can be widely applied to the field of catalysis.
In order to achieve the purpose, the invention adopts the following technical scheme:
one aspect of the present invention provides a Mo2N/NC composite material.
Another aspect of the present invention provides Mo2The preparation method of the N/NC composite material comprises the following steps:
adding a molybdenum source into a graphene oxide solution to obtain a first mixed solution;
adding hydrazine hydrate into the first mixed solution, stirring, standing and aging to obtain a second mixed solution;
carrying out freeze drying treatment on the second mixed solution to obtain precursor powder;
calcining the precursor powder in an inert atmosphere to obtain Mo2N/NC composite material.
Another aspect of the present invention provides Mo2The application of the N/NC composite material in the field of catalysts.
Yet another aspect of the present invention provides a capacitor including Mo2Catalyst of N/NC composite material.
The invention has the following beneficial effects:
(1) the Mo provided by the invention2The preparation method of the N/NC composite material adopts the graphene oxide solution as a carbon source and a template, does not need dangerous ammonia gas, and can obtain high-purity two-dimensional porous flaky Mo through one-step pyrolysis2N/NC composite material. In the preparation process, molybdate ions are loaded on graphene oxide with rich groups, and the graphene oxide serving as a carbon template plays a role in space confinement in the high-temperature sintering process, so that Mo is limited2Coarsening the N particle size. Hydrazine hydrate is used as a nitrogen source, and strong reduction is provided in the high-temperature sintering process to nitride molybdenum (Mo) to form Mo2N。
(2) The preparation method can obtain high-purity porous flaky Mo2The N/NC composite material has the advantages of safe and reliable whole preparation process, simple and easily-controlled process conditions and low production cost. Finally, the flaky Mo obtained by the preparation method2The N/NC composite material has the characteristics of small particle size, high purity and large effective specific surface area, shows good catalytic activity similar to platinum, and can be widely applied to the field of catalysis.
Drawings
The invention is further described with reference to the following figures and examples, in which:
FIG. 1 shows Mo prepared in example 1 of the present invention2X-ray powder diffraction (XRD) profile of the N/NC composite material;
FIG. 2 is an X-ray powder diffraction (XRD) plot of a composite prepared according to comparative example 1 of the present invention;
FIG. 3 shows Mo prepared in example 1 of the present invention2Scanning Electron Microscope (SEM) images of the N/NC composite material;
FIG. 4 shows Mo prepared in example 1 of the present invention2The polarization curves of hydrogen evolution reaction of the N/NC composite material and the composite material prepared in the comparative example 1 as a catalyst are compared.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
One aspect of the present invention provides a Mo2N/NC composite material.
In some embodiments, the Mo2The N/NC composite material is a porous sheet structure.
In some embodiments, Mo2The specific surface area of N is 200-450m2 g-1。
In some embodiments, Mo2The specific surface area of N can be 250-450m2 g-1。
In some embodiments, Mo2The specific surface area of N can be 300-450m2 g-1。
Preferably, Mo is2The particle size of N is 1-20 nm.
Mo2In N/NC composite materials, Mo2The N is tightly wrapped by the carbon nano-sheets. And the carbon-based nanosheets contain a small amount of nitrogen, and the mass fraction of the nitrogen is 0.5-5%.
In some embodiments, Mo2The mass fraction of N in the composite material is 5-60%; preferably, Mo is2The mass fraction of N in the composite material is 10-50%; preferably, Mo is2The mass fraction of N in the composite material is 20-40%. Wherein, Mo2The catalytic effect of N with the mass fraction of about 30 percent is better, and at the moment, Mo2The particle size and distribution of N in the carbon nano-sheet are more reasonable.
Preferably, the size of the carbon-based nanosheet in the composite material is 100 nm-5 microns.
In another aspect of the present invention, there is provided Mo2The preparation method of the N/NC composite material comprises the following steps:
adding a molybdenum source into a graphene oxide solution to obtain a first mixed solution;
adding hydrazine hydrate into the first mixed solution, stirring, standing and aging to obtain a second mixed solution;
carrying out freeze drying treatment on the second mixed solution to obtain precursor powder;
calcining the precursor powder in an inert atmosphere to obtain Mo2N/NC composite material.
The Mo provided by the invention2The preparation method of the N/NC composite material comprises the steps of taking a graphene oxide solution, a molybdenum source and hydrazine hydrate as raw materials, and adding the molybdenum source into the graphene oxide solution to obtain a first mixed solution. And then adding a certain amount of hydrazine hydrate, stirring to uniformly mix, standing and aging to obtain a second mixed solution. Then, the second mixed solution is subjected to freeze drying treatment, and the solvent is volatilized to obtain precursor powder. The precursor powder is calcined at high temperature in one step in inert atmosphere to obtain porous flaky Mo2N/NC composite material.
Molybdenum nitride usually contains Mo2N, MoN and Mo5N6And the like, and various phases are easily generated in the process of preparing the molybdenum nitride. In the preparation method, molybdate ions are loaded on graphene oxide with rich groups, and the graphene oxide serving as a carbon template plays a role in space confinement in a high-temperature sintering process, so that Mo is limited2Coarsening the N particle size. Hydrazine hydrate is used as a nitrogen source, and strong reduction is provided in the high-temperature sintering process, so that Mo is nitrided to form Mo2N, thereby obtaining Mo of high purity2N/NC composite material. Wherein, Mo2N is compared with MoN and Mo5N6Phase, its electronic structure is closer to that of noble metal platinumAnd has better catalytic effect.
In some embodiments, agitation, sonication, may be employed in order to achieve sufficient dissolution of the molybdenum source for subsequent reaction. Namely, a molybdenum source can be added into the graphene oxide solution, and ultrasonic stirring is carried out for 10-30 min.
In some embodiments, hydrazine hydrate is added into the first mixed solution and stirred for 0.3-24 hours, so as to form a fully dissolved mixed solution; preferably, the stirring time is 0.5 to 20 hours, for example, 0.5 hour, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours or 20 hours.
Preferably, the standing and aging time is 1-48 h; preferably, the standing and aging time is 6-42 h; preferably, the standing and aging time is 12-36 h, for example, 12h, 16h, 20h, 24h, 28h, 32h or 36 h.
The process of stirring, standing and aging can ensure that the components are fully mixed to form a complex. If the solution does not undergo a standing aging process, the mixed solution cannot sufficiently generate a complex, and the subsequent reaction cannot generate a two-dimensional sheet structure with uniform appearance.
In some embodiments, the step of freeze-drying comprises: freezing the second mixed solution at-20 to-50 ℃ for 20 to 28 hours; then, carrying out vacuum freeze drying on the frozen product for 64-80 h; the vacuum degree of the vacuum freeze drying is 0.1-1 Pa, and the temperature is-30 to-60 ℃.
Preferably, the freezing temperature is from-25 ℃ to-45 ℃, and may be, for example, -25 ℃, -30 ℃, -35 ℃, -40 ℃ or-45 ℃.
Preferably, the freezing time is 22-26 h.
Preferably, the vacuum freeze-drying time is 68-76 h, for example, 68h, 70h, 72h, 74h or 76 h.
Preferably, the temperature of the vacuum freeze-drying is-35 to-55 ℃, and may be, for example, -35 ℃, -40 ℃, -45 ℃, -50 ℃ or-55 ℃.
The composite material obtained by freeze drying treatment can be recrystallized better to form a porous two-dimensional sheet structure. If ordinary drying or vacuum drying is used only, and recrystallization and setting processes are lacked, a porous two-dimensional sheet-like structure material cannot be obtained.
In some embodiments, the calcination treatment is a one-step pyrolysis calcination.
Preferably, the temperature of the calcining treatment is 700-1000 ℃; preferably, the temperature of the calcination treatment is 750 to 950 ℃, for example, 750 ℃, 800 ℃, 850 ℃, 900 ℃ or 950 ℃.
In the process, hydrazine hydrate can be used as a nitrogen source and can provide strong reduction effect in the high-temperature pyrolysis process, so that Mo is nitrided to form Mo2N, further obtaining high-purity Mo2N/NC composite material.
Preferably, the calcining treatment time is 1-5 h; preferably, the calcining treatment time is 2-4 h;
preferably, the temperature rise rate of the calcination treatment is 1-10 ℃/min; preferably, the temperature rise rate of the calcination treatment is 3-8 ℃/min;
in some embodiments, the calcination treatment is performed in an inert atmosphere, which is one or more of nitrogen, argon, helium, or a mixed atmosphere containing 5% hydrogen/95% nitrogen, 5% hydrogen/95% argon, and 5% hydrogen/95% helium by volume. For example, 5% hydrogen/95% nitrogen means that the mixed atmosphere contains 5% hydrogen and 95% nitrogen by volume.
In some embodiments, the graphene oxide solution has a concentration of 0.5-10 mg/mL; preferably, the concentration of the graphene oxide solution is 1 to 9mg/mL, and may be, for example, 1mg/mL, 2mg/mL, 3mg/mL, 4mg/mL, 5mg/mL, 6mg/mL, 7mg/mL, 8mg/mL, or 9 mg/mL.
Further, the graphene oxide solution is generally an aqueous solution.
Preferably, the molybdenum source is soluble in the graphene oxide solution; specifically, the molybdenum source is at least one of ammonium tetramolybdate, ammonium heptamolybdate, ammonium phosphomolybdate and molybdic acid.
In some embodiments, the mass ratio of the molybdenum source to graphene oxide is 1: 0.2 to 10; preferably, the mass ratio of the molybdenum source to the graphene oxide is 1: 0.3 to 8; preferably, the mass ratio of the molybdenum source to the graphene oxide is 1: 0.5 to 5;
preferably, the mass ratio of the volume of the hydrazine hydrate to the graphene oxide is 1 mL: 5-15 mg; preferably, the mass ratio of the volume of hydrazine hydrate to the graphene oxide is 1 mL: 6-13 mg; preferably, the mass ratio of the volume of hydrazine hydrate to the graphene oxide is 1 mL: 8-12 mg.
In the invention, molybdate ions are loaded on graphene oxide with rich groups, and the graphene oxide serving as a carbon template plays a role in space confinement in a high-temperature sintering process, so that Mo can be effectively limited2Coarsening the N particle size.
Another aspect of the present invention provides Mo2The application of the N/NC composite material in the field of catalysts.
Yet another aspect of the present invention provides a capacitor including Mo2Catalyst of N/NC composite material.
The embodiment of the invention provides the Mo2The preparation method of the N/NC composite material does not need to introduce NH with high risk in the whole process3Gas, i.e. obtaining porous sheet Mo2The N/NC composite material has safe and reliable whole production process, simple and easily-controlled process conditions and low production cost, and is suitable for industrial large-scale production. The obtained final product is subjected to corresponding performance detection, specifically including XRD, SEM and electrochemical hydrogen evolution performance tests, and the composite material has the characteristics of small particle size, high purity, large effective specific surface area and the like, and shows catalytic activity similar to platinum, so that the composite material can be widely applied to the catalytic fields of hydrodesulfurization, hydrodenitrogenation, hydrogen evolution, hydrogenolysis, oxygen reduction, carriers and the like.
Specifically, the Mo2The invention is further described in detail by taking a part of test results as reference, and the following is described in detail by combining specific examples. The experimental materials used in the invention are available from conventional sources, and the hydrazine hydrate used is analytically pure (volume concentration is 80%). The method is common unless otherwise specifiedThe method is disclosed.
Example 1
This example provides a Mo2The preparation method of the N/NC composite material comprises the following steps:
(1) taking 100mL of 1mg/mL graphene oxide aqueous solution, adding 150mg of ammonium molybdate tetrahydrate into the graphene oxide aqueous solution, and ultrasonically stirring for 20min until the ammonium molybdate is completely dissolved to obtain a first mixed solution;
(2) adding 10mL of hydrazine hydrate into the solution obtained in the step (1), stirring for 30min, standing and aging for 24h to obtain a second mixed solution;
(3) freezing the second mixed solution in a freezer cabinet of a refrigerator at-30 ℃ for 24h, and then placing the frozen product in a vacuum freeze dryer with the vacuum degree of 0.1Pa and the freeze drying temperature of-45 ℃ for freeze drying for 72h to obtain dried precursor solid powder;
(4) placing the dried precursor solid powder in a nitrogen atmosphere for calcination treatment, wherein the temperature rise rate of calcination is 5 ℃/min, raising the temperature to 800 ℃, calcining at the constant temperature of 800 ℃ for 3h, and then naturally cooling to obtain Mo2N/NC product.
The specific surface area of example 1 was 327.2m according to the conventional BET test2 g-1The obtained product has rich micropore and mesoporous structures and higher specific surface area, and is beneficial to increasing the active sites of the catalyst, thereby improving the catalytic activity. As can be seen from FIG. 1, according to the XRD test results, the molybdenum nitride obtained by the method only contains Mo2N phase exists, and MoN and Mo do not exist5N6And the like. As can be seen from FIG. 3, the SEM test results show that the Mo synthesized2N/NC has a pronounced lamellar structure.
Example 2
This example provides a Mo2The preparation method of the N/NC composite material comprises the following steps:
(1) taking 100mL of 1mg/mL graphene oxide aqueous solution, adding 150mg of ammonium molybdate tetrahydrate into the graphene oxide aqueous solution, and ultrasonically stirring for 20min until the ammonium molybdate is completely dissolved to obtain a first mixed solution;
(2) adding 20mL of hydrazine hydrate into the solution obtained in the step (1), stirring for 30min, standing and aging for 24h to obtain a second mixed solution;
(3) freezing the second mixed solution in a freezer cabinet of a refrigerator at-30 ℃ for 24h, and then placing the frozen product in a vacuum freeze dryer with the vacuum degree of 0.1Pa and the freeze drying temperature of-45 ℃ for freeze drying for 72h to obtain dried precursor solid powder;
(4) placing the dried precursor solid powder in a nitrogen atmosphere for calcination treatment, wherein the temperature rise rate of calcination is 5 ℃/min, raising the temperature to 800 ℃, calcining at the constant temperature of 800 ℃ for 3h, and then naturally cooling to obtain Mo2N/NC product.
The specific surface area of example 2 was 254.8m according to the conventional BET test2 g-1The obtained product has rich micropore and mesoporous structures and higher specific surface area, and is beneficial to increasing the active sites of the catalyst, thereby improving the catalytic activity. XRD test results show that the molybdenum nitride obtained by the method only contains Mo2N phase exists, and MoN and Mo do not exist5N6And the like. The SEM appearance characterization result shows that the synthesized Mo2N/NC has a pronounced lamellar structure.
Example 3
This example provides a Mo2The preparation method of the N/NC composite material comprises the following steps:
(1) taking 100mL of 1mg/mL graphene oxide aqueous solution, adding 50mg of ammonium molybdate tetrahydrate into the graphene oxide aqueous solution, and ultrasonically stirring for 20min until the ammonium molybdate is completely dissolved to obtain a first mixed solution;
(2) adding 10mL of hydrazine hydrate into the solution obtained in the step (1), stirring for 30min, standing and aging for 24h to obtain a second mixed solution;
(3) freezing the second mixed solution in a freezer cabinet of a refrigerator at-30 ℃ for 24h, and then placing the frozen product in a vacuum freeze dryer with the vacuum degree of 0.1Pa and the freeze drying temperature of-45 ℃ for freeze drying for 72h to obtain dried precursor solid powder;
(4) drying the forebodyCalcining the solid powder in nitrogen atmosphere at a temperature rise rate of 5 ℃/min to 800 ℃ for 3h at the constant temperature of 800 ℃, and naturally cooling to obtain Mo2N/NC product.
The specific surface area of example 3 was 359.1m according to the conventional BET test2 g-1The obtained product has rich micropore and mesoporous structures and higher specific surface area, and is beneficial to increasing the active sites of the catalyst, thereby improving the catalytic activity. According to XRD test results, the molybdenum nitride obtained by the method only contains Mo2N phase exists, and MoN and Mo do not exist5N6And the like. SEM test results show that the Mo synthesized2N/NC has a pronounced lamellar structure.
Comparative example 1
The comparative example provides a method of preparing a composite material, comprising the steps of:
(1) 100mg of ammonium molybdate tetrahydrate is dissolved in 100mL of graphene oxide aqueous solution (the concentration of graphene oxide is 1mg mL)-1) Performing ultrasonic stirring for 20min until the mixture is completely dissolved to obtain a mixed solution;
(2) freezing the mixed solution in a freezer cabinet of a refrigerator at-30 ℃ for 24h, then placing the frozen product in a vacuum freeze dryer with the vacuum degree of 0.1Pa and the freeze drying temperature of-45 ℃ for freeze drying for 72h to obtain dry precursor solid powder, and grinding for 10 min;
(3) and placing the dried precursor solid powder in a nitrogen atmosphere for one-step pyrolysis calcination treatment, wherein the temperature rise rate of the calcination is 5 ℃/min, the temperature is raised to 800 ℃, the precursor solid powder is calcined at the constant temperature of 800 ℃ for 3h, and then the precursor solid powder is naturally cooled to obtain the target product.
Comparative example 1 has a specific surface area of 174.7m according to the conventional BET test2 g-1The specific surface area of the product obtained without adding hydrazine hydrate is reduced. The hydrazine hydrate releases a large amount of ammonia gas in the sample preparation process, and can play a role in improving the porosity. As can be seen from FIG. 2, according to the XRD test results, no hydrazine hydrate was added during the synthesis, and the obtained product was Mo2C/C composite material, Mo could not be obtained2N/NC composite material. SEM characterization results show that the sample obtained by the method has obvious sheet-shaped structure, which indicates that hydrazine hydrate does not influence the generation of the sheet-shaped structure, but influences the phase formation of the product.
Comparative example 2
This comparative example provides a Mo2The preparation method of the N/NC composite material comprises the following steps:
(1) taking 100mL of 1mg/mL graphene oxide aqueous solution, adding 150mg of ammonium molybdate tetrahydrate into the graphene oxide aqueous solution, and ultrasonically stirring for 20min until the ammonium molybdate is completely dissolved to obtain a first mixed solution;
(2) adding 10mL of hydrazine hydrate into the solution obtained in the step (1), stirring for 30min, standing and aging for 24h to obtain a second mixed solution;
(3) putting the second mixed solution into a forced air drying oven for drying for 72 hours to obtain dry precursor solid powder;
(4) placing the dried precursor solid powder in a nitrogen atmosphere for calcination treatment, wherein the temperature rise rate of calcination is 5 ℃/min, raising the temperature to 800 ℃, calcining at the constant temperature of 800 ℃ for 3h, and then naturally cooling to obtain Mo2N/NC product.
Comparative example 2 has a specific surface area of 58.6m according to the conventional BET test2 g-1. Compared with a freeze drying mode, the sample dried by adopting the blast heat drying method for the solution has obviously reduced specific surface area. According to XRD results, the phase of the product consisted of Mo2N and MoN, and SEM characterization results show that the product is composed of a large number of particles with serious agglomeration and has no two-dimensional sheet structure. Indicating that the drying mode has a large influence on the structure and phase of the product.
Comparative example 3
This comparative example provides a Mo2The preparation method of the N/NC composite material comprises the following steps:
(1) taking 100mL of 1mg/mL graphene oxide aqueous solution, adding 150mg of ammonium molybdate tetrahydrate into the graphene oxide aqueous solution, and ultrasonically stirring for 20min until the ammonium molybdate is completely dissolved to obtain a first mixed solution;
(2) adding 10mL of hydrazine hydrate into the solution obtained in the step (1), and stirring for 2h to obtain a second mixed solution;
(3) freezing the second mixed solution in a freezer cabinet of a refrigerator at-30 ℃ for 24h, and then placing the frozen product in a vacuum freeze dryer with the vacuum degree of 0.1Pa and the freeze drying temperature of-45 ℃ for freeze drying for 72h to obtain dried precursor solid powder;
(4) placing the dried precursor solid powder in a nitrogen atmosphere for calcination treatment, wherein the temperature rise rate of calcination is 5 ℃/min, raising the temperature to 800 ℃, calcining at the constant temperature of 800 ℃ for 3h, and then naturally cooling to obtain Mo2N/NC product.
Comparative example 3 has a specific surface area of 281.5m according to the conventional BET test2 g-1. According to the XRD results, the sample of comparative example 3 consisted of Mo2C and Mo2N two phase composition, which shows that single Mo can not be obtained without aging process2An N phase.
Specific surface areas of the composite materials prepared in the above examples and comparative examples are shown in table 1.
TABLE 1 specific surface area of composites prepared in examples and comparative examples
Figure BDA0003306268500000101
Performance testing
The following comparative performance comparisons, including XRD and electrochemical hydrogen evolution performance tests, were performed on the final products obtained in example 1 and comparative example 1.
(I) XRD test
The products of example 1 and comparative example 1 were tested according to the standard of conventional XRD test, and the test results are shown in fig. 1 and fig. 2, respectively.
As can be seen from FIG. 1, Mo2As can be seen from comparison of the N standard diffraction peak pattern PDF #24-0771, the XRD diffraction peak of the product synthesized in example 1 of the invention can be compared with that of Mo2The N standard spectrum corresponds to that of the Mo in the final product obtained in example 1 of the invention, which is proved to be of high purity2N/NC material.
From FIG. 2As can be seen, the XRD diffraction pattern and Mo of comparative example 12The standard diffraction peak pattern of C corresponds to PDF #79-0744, and in comparative example 1, no hydrazine hydrate is added in the synthesis process, so that Mo cannot be generated2N/NC composite illustrating the preparation of Mo from hydrazine hydrate feedstock2Is indispensable in the N/NC process.
(II) the materials obtained in example 1 and comparative example 1 were used for hydrogen evolution reaction according to the conventional method, and the polarization curves thereof were tested, and the specific test results are shown in FIG. 4.
As can be seen from FIG. 4, when the current density was 10mA cm-2In this case, the overpotential of example 1 was only 0.126V, and the porous flaky Mo obtained in example 1 of the present invention was explained2The hydrogen evolution performance of the N/NC composite material exceeds that of the existing non-noble metal hydrogen evolution reaction catalyst, and the N/NC composite material shows the catalytic performance similar to that of a noble metal catalyst.
As is apparent from the above experimental results of examples and comparative examples, it is possible to prepare high-purity two-dimensional porous flaky Mo only under the experimental conditions of the present invention2N/NC composite material, the product obtained in the absence of hydrazine hydrate being Mo2C/C composite material, Mo could not be obtained2N/NC composite material; the morphology and the phase of the final product can be influenced when the reaction conditions are changed, such as the drying mode is changed, the standing aging step is omitted, and the like, so that the high-purity two-dimensional porous flaky Mo cannot be obtained2N/NC composite material, and the Mo2The N/NC composite exhibits catalytic performance similar to that of noble metal catalysts.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

Claims (10)

1. Mo2N/NC composite material, characterized in that the Mo2The N/NC composite material is in a porous sheet structure; the specific surface area is 200-450m2 g-1。
2. Mo according to claim 12N/NC composite material, characterized in that the Mo2The mass fraction of N in the composite material is 5-60%; the Mo2The particle size of N is 1-20 nm.
3. Mo according to claim 1 or 22The preparation method of the N/NC composite material is characterized by comprising the following steps:
adding a molybdenum source into a graphene oxide solution to obtain a first mixed solution;
adding hydrazine hydrate into the first mixed solution, stirring, standing and aging to obtain a second mixed solution;
carrying out freeze drying treatment on the second mixed solution to obtain precursor powder;
calcining the precursor powder in an inert atmosphere to obtain Mo2N/NC composite material.
4. Mo according to claim 32The preparation method of the N/NC composite material is characterized in that the hydrazine hydrate is added into the first mixed solution and stirred for 0.3-24 hours; standing and aging for 1-48 h.
5. Mo according to claim 32The preparation method of the N/NC composite material is characterized in that the freeze drying treatment step comprises the following steps: freezing the second mixed solution at-20 to-50 ℃ for 20 to 28 hours; then, carrying out vacuum freeze drying on the frozen product for 64-80 h; the vacuum degree of the vacuum freeze drying is 0.1-1 Pa, and the temperature is-30 to-60 ℃.
6. Mo according to claim 32The preparation method of the N/NC composite material is characterized in that the calcination treatment is one-step pyrolysis calcination; the temperature of the calcination treatment is 700-1000 ℃; the heating rate is 1-10 ℃/min; the treatment time is 1-5 h;the inert atmosphere is one or more of nitrogen, argon and helium, or one or more of mixed atmosphere containing 5% hydrogen/95% nitrogen, 5% hydrogen/95% argon and 5% hydrogen/95% helium by volume concentration.
7. Mo according to claim 32The preparation method of the N/NC composite material is characterized in that the concentration of the graphene oxide solution is 0.5-10 mg/mL; the molybdenum source is at least one of ammonium tetramolybdate, ammonium heptamolybdate, ammonium phosphomolybdate and molybdic acid.
8. Mo according to any one of claims 3 to 72The preparation method of the N/NC composite material is characterized in that the mass ratio of the molybdenum source to the graphene oxide is 1: 0.2 to 10; the mass ratio of the volume of the hydrazine hydrate to the graphene oxide is 1 mL: 5-15 mg.
9. Mo according to claim 1 or 22The application of the N/NC composite material in the field of catalysts.
10. A catalyst, characterized in that the catalyst comprises Mo according to claim 1 or 22N/NC composite material.
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