CN109126844B - Molybdenum carbide nanosheet and preparation method and application thereof - Google Patents

Molybdenum carbide nanosheet and preparation method and application thereof Download PDF

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CN109126844B
CN109126844B CN201811009185.7A CN201811009185A CN109126844B CN 109126844 B CN109126844 B CN 109126844B CN 201811009185 A CN201811009185 A CN 201811009185A CN 109126844 B CN109126844 B CN 109126844B
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molybdenum
molybdenum carbide
heating
glycine
ammonium nitrate
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CN109126844A (en
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古思勇
张厚安
陈伟斌
周洪涛
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Xiamen University of Technology
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Abstract

The invention relates to a molybdenum carbide nanosheet and a preparation method and application thereof, wherein the method comprises the steps of uniformly mixing a molybdenum source, ammonium nitrate and glycine, heating to 160-180 ℃ to obtain a mixture 1, adding glucose, heating to 230-280 ℃ to obtain a fluffy solid, placing the fluffy solid in a hydrogen atmosphere, heating to 450-550 ℃, and cooling to obtain the molybdenum carbide nanosheet. The preparation method of the molybdenum carbide nanosheet is low in heating temperature and convenient to operate and popularize, and the prepared molybdenum carbide is not agglomerated, is irregular and flaky, is large in specific surface area and has excellent catalytic performance in application to electrocatalytic hydrogen production.

Description

Molybdenum carbide nanosheet and preparation method and application thereof
Technical Field
The invention relates to a preparation method of molybdenum carbide, in particular to a molybdenum carbide nanosheet and a preparation method and application thereof.
Background
The utilization of hydrogen energy is the best alternative green energy of the traditional fossil energy, and the utilization of the hydrogen energy depends on the development of hydrogen production technology. The water electrolysis hydrogen production technology is known as the most ideal industrial hydrogen production method in the industry, and the most core problem of the technology is the development of preparing the electrocatalyst with high efficiency, stability and good quality. Currently, platinum-based catalysts are the most effective electrocatalysts, but their high cost and low storage volume severely restrict the widespread use of such catalysts.
Molybdenum carbide (Mo)2C) Due to the advantages of noble metal-like property, roasting resistance, sulfur resistance, nitrogen resistance, high melting point and the like, the catalyst has attracted wide attention in the field of catalysis, and becomes one of the most potential catalytic materials for replacing noble metals Pt and Pd. At present, the preparation methods of molybdenum carbide mainly comprise a chemical vapor deposition method, a temperature programmed reduction method and a carbon-heat hydrogen reduction method. The chemical vapor deposition method can prepare the film Mo with high specific surface and high quality2C catalyst, but the deposition efficiency of the process is low. Nanometer Mo can be prepared by temperature programmed reduction method2C catalyst, while having a high activity, but the process requires complexity and rigorThe synthesis conditions of (2) and the controllability are poor. The carbothermic hydrogen reduction method can synthesize high-performance Mo with high specific surface area and controllable grain size by controlling active components and temperature2And C, a catalyst. In terms of raw materials, the carbon source is synthesized high-performance Mo2One key of C, different carbon sources can synthesize Mo with different crystal structures2And C, a catalyst. At present, the carbon sources mainly used are gases such as ethane, methane, n-heptane and n-butane, and the carbon sources usually need to be mixed with hydrogen to realize carbonization to obtain Mo2And C, the synthesis process is complex. At the same time, Mo is present2C is synthesized by heating at a relatively high temperature, e.g. at 20% CH4~80%H2The mixed gas is a carbon source, the reaction temperature needs to be 700-900 ℃, and incomplete carbonization can be caused when the reaction temperature is low. Higher synthesis temperature can inevitably cause Mo2The sintering and agglomeration of C cause the reduction of the specific surface area of the catalyst, and seriously affect the exertion of the activity of the catalyst.
Disclosure of Invention
The invention aims to solve the problems of high synthesis temperature and product agglomeration of the existing molybdenum carbide, and provides a molybdenum carbide nanosheet and a preparation method and application thereof.
The specific scheme is as follows:
a preparation method of molybdenum carbide nanosheets comprises the following steps:
step 1: uniformly mixing a molybdenum source, ammonium nitrate and glycine, and then heating to 160-180 ℃ to obtain a mixture 1;
step 2: adding glucose into the mixture 1 obtained in the step 1, and then heating to 230-280 ℃ to obtain fluffy solid;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a hydrogen atmosphere, heating to 450-550 ℃, and cooling to obtain the molybdenum carbide nanosheet.
Further, in the step 1, the molybdenum source is at least one of ammonium paramolybdate, ammonium tetramolybdate or ammonium dimolybdate;
optionally, the molar amount of molybdenum in the molybdenum source in step 1: the molar amount of the ammonium nitrate and the molar amount of the glycine are 0.5-1.0: 2.2-3.2;
optionally, the mass of ammonium nitrate in step 1: the mass of the glycine is 0.8-3.2.
Further, step 1 comprises: 1a, mixing a molybdenum source, ammonium nitrate and glycine, adding deionized water, and stirring until the molybdenum source, the ammonium nitrate and the glycine are dissolved; 1b, heating the solution to 165-175 ℃, and preserving the heat for 3-6 minutes to obtain a mixture 1.
Further, the mass ratio of the glucose to the molybdenum in the molybdenum source in the step 2 is 0.8-1.0: 1.6-2.8;
optionally, glucose is prepared into an aqueous glucose solution with the concentration of 0.1-0.3 g/mL in the step 2, and 10-50 mL of the aqueous glucose solution is added into the mixture 1 obtained in the step 1.
Further, the heating temperature in the step 2 is 240-270 ℃, and the heat preservation time is 10-20 minutes.
Further, H in the hydrogen atmosphere in step 32The flow rate of (A) is 100 to 500 mL/min.
Further, in the step 3, the heating temperature is 460-500 ℃, and the heat preservation time is 1-3 hours.
The invention also provides the molybdenum carbide nanosheet prepared by the preparation method of the molybdenum carbide nanosheet.
Furthermore, the molybdenum carbide nanosheet has a crystalline structure, is irregular and flaky and has a thickness of 10-30 nm.
The invention also protects the application of the molybdenum carbide nanosheet in electrocatalytic hydrogen production.
Has the advantages that:
in the invention, the molybdenum carbide nanosheet adopts glucose as a carbon source, and in the reaction process, the glucose is dispersed and heated to form an amorphous carbon nanosheet which is used as a structural template formed by molybdenum carbide and is one of the keys for determining that the molybdenum carbide has a flaky nano structure.
In addition, the invention utilizes ammonium nitrate and glycine as reaction auxiliary agents, thereby not only effectively reducing the temperature in the process of generating molybdenum carbide and realizing the synthesis of molybdenum carbide nanosheets by hydrocarbon reduction at medium temperature (450-550 ℃), but also forming a precursor containing amorphous molybdenum oxide and amorphous carbon nanosheets by virtue of a large amount of reducing gas released in the reaction process of ammonium nitrate and glycine.
In a word, the preparation method of the molybdenum carbide nanosheet is low in heating temperature and convenient to operate and popularize, and the prepared molybdenum carbide is not agglomerated, is irregular and flaky, has a large specific surface area and has excellent catalytic performance in application to electrocatalytic hydrogen production.
Drawings
In order to illustrate the technical solution of the present invention more clearly, the drawings will be briefly described below, and it is apparent that the drawings in the following description relate only to some embodiments of the present invention and are not intended to limit the present invention.
FIG. 1 is an XRD diffraction spectrum of a precursor provided in example 1 of the present invention;
FIG. 2 is a scanning electron micrograph of a precursor provided in example 1 of the present invention;
fig. 3 is an XRD diffraction spectrum of molybdenum carbide nanosheets provided in example 1 of the present invention;
fig. 4 is a scanning electron microscope photograph of molybdenum carbide nanosheets provided in example 1 of the present invention;
FIG. 5 is an XRD diffraction spectrum of a dense solid provided by comparative example 1 of the present invention;
FIG. 6 is an XRD diffraction spectrum of comparative example 1 provided by comparative example 1 of the present invention;
FIG. 7 is a scanning electron micrograph of comparative example 1 provided in comparative example 1 of the present invention;
FIG. 8 is an XRD diffraction spectrum of a fluffy solid provided by comparative example 2 of the present invention;
FIG. 9 is a scanning electron micrograph of a fluffy solid provided in comparative example 2 of the present invention;
FIG. 10 is an XRD diffraction spectrum of comparative example 2 provided by comparative example 2 of the present invention;
FIG. 11 is a scanning electron micrograph of comparative example 2 provided in comparative example 2 of the present invention.
Detailed Description
The definitions of terms used in the present invention have definitions and meanings well known in the art.
In the preparation method of the molybdenum carbide nanosheet, the molybdenum source is preferably ammonium paramolybdate, and the molybdenum source is mixed with deionized water to form a solution, so that the solution is uniformly dispersed, the subsequent reaction speed can be controlled, and a product with uniform thickness can be formed.
In the preparation method of the molybdenum carbide nanosheet provided by the invention, the molar amount of molybdenum in the molybdenum source is as follows: (the molar amount of the ammonium nitrate and the molar amount of the glycine) is 0.5-1.0: 2.2-3.2, preferably 0.7: 2.5-2.9, for example 0.7:2.7, which is less than the ratio (0.5-1.0: 2.2-3.2), the ammonium nitrate and the glycine are too much and react violently, the generated temperature is too high, the generated precursor is easy to form a sintering adhesion state, an amorphous structure and a nano sheet structure cannot be completely formed, and meanwhile, the yield of the product is low compared with that of a molybdenum source. Above this ratio, too little ammonium nitrate + glycine would decompose the molybdenum source to the oxide. Wherein the mass of ammonium nitrate is: the mass of the glycine is 0.8-3.2, preferably 1.3-2.5: more preferably 1.8 to 2.3, for example 2.2, in a stoichiometric ratio, below or above which the temperature required for the decomposition of the molybdenum source is not reached, and in which the amount of gas released by the reaction is not sufficient to form the nanosheet structure. Ammonium nitrate and glycine are subjected to oxidation-reduction reaction, the reaction releases heat, a large amount of reducing gas is generated, the reducing gas not only acts on the reduction process of glucose, but also promotes a molybdenum source to form a precursor containing amorphous molybdenum oxide. The mass ratio of the glucose to the molybdenum in the molybdenum source is 0.8-1.0: 1.6-2.8, if the glucose is excessive, excessive amorphous carbon nano-sheets can be formed, and the amorphous carbon nano-sheets can not be completely reacted and eliminated in the process of carbon-hydrogen reduction, so that the product Mo can be generated2More carbon remained in C.
In the preparation method of the molybdenum carbide nanosheet, the step 1 is heated to 160-180 ℃ to obtain a mixture 1, preferably 165-175 ℃, the temperature is kept for 3-6 minutes, more preferably 170 ℃, the temperature is kept for 5 minutes, and a molybdenum source is heated to form a precursor containing amorphous molybdenum oxide.
In the preparation method of the molybdenum carbide nanosheet, the step 2 is heated to 230-280 ℃ to obtain a fluffy solid, preferably 240-270 ℃, the heat preservation time is 10-20 minutes, more preferably 250 ℃, and the heat preservation time is 15 minutes, the fluffy solid is a mixture of amorphous molybdenum oxide and amorphous carbon nanosheets, and the XRD diffraction spectrum shows that the fluffy solid forms an obvious amorphous diffraction peak at a diffraction angle of 23 degrees, which indicates that the fluffy solid consists of amorphous substances.
In the preparation method of the molybdenum carbide nanosheet, the step 3 is heated to 450-550 ℃, preferably 480-530 ℃, the heat preservation time is 1-3 hours, more preferably 500 ℃, the heat preservation time is 2 hours, the reaction needs to be carried out in a hydrogen atmosphere with the flow rate of 100-500 mL/min to ensure the progress of the hydrocarbon reaction, the flow rate is too low, the hydrocarbon reaction is insufficient, and Mo cannot be completely formed2C, the flow is large, which causes waste. The hydrogen atmosphere may be pure hydrogen, or hydrogen and other gases may be mixed, for example, hydrogen and nitrogen, or hydrogen and inert gas, and in principle, any gas containing hydrogen may be used, which has no influence on the temperature, but has an influence on the hydrogen flow rate, for example, hydrogen/nitrogen mixed gas, and the gas flow rate must be large enough to ensure sufficient hydrogen, and preferably pure hydrogen is used, and the flow rate is 100 to 500 mL/min.
The molybdenum carbide nanosheet prepared by the method can be used as a catalyst instead of noble metals Pt and Pd, and is particularly used in electrocatalytic hydrogen production. The analysis on the components and the morphology of the product shows that the prepared molybdenum carbide nanosheet is free from agglomeration, is irregular and flaky, has a large specific surface area and a good structural advantage, and can exert good catalytic performance.
In the present invention, the source of each raw material is not particularly limited, and the raw material may be obtained commercially or may be prepared by various conventional methods, and is preferably an analytically pure grade. In addition, in the present invention, the heating may be carried out in any manner as long as the reaction system can be maintained in a stable temperature range. For example, muffle furnaces, tube furnaces. In addition, the maintaining system may be a mixture of hydrogen and other inert gases, such as hydrogen and nitrogen, which are known to those skilled in the art and will not be described herein.
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available. In the following examples, "%" denotes% by weight and degrees denote C, unless otherwise specified.
The test methods used below included:
XRD test: the phase of the product was determined by X-ray diffractometry (Rigaku D/max-RB12, XRD) under the test conditions of Cu target, Ka (λ 0.1541nm)
Scanning electron microscope: the product was subjected to microscopic morphology observation using a field emission scanning electron microscope (FEI Quanta FEG 450).
Example 1
Preparing molybdenum carbide nanosheets according to the following steps:
step 1: simultaneously placing 18.5 g of ammonium paramolybdate, 20 g of ammonium nitrate and 12 g of glycine into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium paramolybdate, the ammonium nitrate and the glycine are completely dissolved to form a mixed solution, placing the beaker containing the mixed solution into a muffle furnace, heating for 5 minutes at 160 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: adding glucose into ionized water to prepare a glucose solution with the concentration of 0.2g/mL, adding 30mL of glucose solution into the solution after the heating in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 240 ℃, heating for 12 minutes, and obtaining fluffy solid after the heating is finished;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a tubular furnace, reducing the fluffy solid for 1.5 hours by using hydrocarbon at 500 ℃ under flowing hydrogen with the hydrogen flow rate of 200mL/min, keeping the flowing hydrogen state after the reduction of the hydrocarbon is finished, and taking out the powder after the furnace temperature is reduced to the room temperature to obtain the molybdenum carbide nanosheet.
XRD test and electron microscope test are respectively carried out on the fluffy solid prepared in the step 2 and the molybdenum carbide nanosheet prepared in the step 3, and the results are shown in figures 1-4.
As can be seen from fig. 1, the fluffy solid forms a distinct amorphous diffraction peak at a diffraction angle of 23 °, indicating that the fluffy solid is composed of amorphous material, which is a mixture of amorphous molybdenum oxide and amorphous nanocarbon flakes. Fig. 2 is a scanning electron micrograph of a fluffy solid, and from fig. 2, the fluffy solid is in a nano-sheet structure, and no distinct crystalline phase is found, which is consistent with the results of XRD.
Fig. 3 is an XRD diffraction spectrum of the molybdenum carbide nanosheet, and as can be seen from fig. 3, the molybdenum carbide nanosheet is in a crystalline structure, and fig. 4 is a scanning electron microscope photograph of molybdenum carbide, which shows that the molybdenum carbide nanosheet is in an irregular sheet shape, has a thickness of about 15nm, and has a large specific surface area.
Example 2
Step 1: putting 11.2 g of ammonium tetramolybdate, 18 g of ammonium nitrate and 9 g of glycine into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium tetramolybdate, the ammonium nitrate and the glycine are completely dissolved to form a mixed solution, putting the beaker containing the mixed solution into a muffle furnace, heating for 4 minutes at 170 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: adding glucose into ionized water to prepare a glucose solution with the concentration of 0.2g/mL, adding 20mL of glucose solution into the solution after the heating in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 250 ℃, heating for 10 minutes, and obtaining a fluffy solid after the heating is finished;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a tubular furnace, reducing the carbon hydrogen at 450 ℃ for 2 hours under flowing hydrogen with the hydrogen flow rate of 150mL/min, keeping the flowing hydrogen state after the carbon hydrogen reduction is finished, and taking out the powder after the furnace temperature is reduced to room temperature to obtain the molybdenum carbide nanosheet. The film is irregular flake-shaped and has a thickness dimension of about 20nm when tested by a scanning electron microscope.
Example 3
Step 1: simultaneously placing 23.6 g of ammonium dimolybdate, 22 g of ammonium nitrate and 13 g of glycine into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium dimolybdate, the ammonium nitrate and the glycine are completely dissolved to form a mixed solution, placing the beaker containing the mixed solution into a muffle furnace, heating for 5 minutes at 165 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: adding glucose into ionized water to prepare a glucose solution with the concentration of 0.2g/mL, adding 20mL of glucose solution into the solution after the heating in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 230 ℃, heating for 15 minutes, and obtaining a fluffy solid after the heating is finished;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a tubular furnace, reducing the hydrocarbon at 550 ℃ for 1 hour under flowing hydrogen with the hydrogen flow rate of 150mL/min, keeping the flowing hydrogen state after the reduction of the hydrocarbon is finished, and taking out the powder after the furnace temperature is reduced to room temperature to obtain the molybdenum carbide nanosheet. The film is irregular flake-shaped and has a thickness dimension of about 25nm when tested by a scanning electron microscope.
Example 4
Step 1: simultaneously placing 19.3 g of ammonium paramolybdate, 20 g of ammonium nitrate and 25 g of glycine into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium paramolybdate, the ammonium nitrate and the glycine are completely dissolved to form a mixed solution, placing the beaker containing the mixed solution into a muffle furnace, heating for 3 minutes at 180 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: adding glucose into ionized water to prepare a glucose solution with the concentration of 0.2g/mL, adding 23mL of glucose solution into the solution after the heating in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 240 ℃, heating for 10 minutes, and obtaining a fluffy solid after the heating is finished;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a tubular furnace, reducing by using hydrocarbon at 460 ℃ for 3 hours under flowing hydrogen with the hydrogen flow rate of 500mL/min, keeping the flowing hydrogen state after the reduction of the hydrocarbon is finished, and taking out the powder after the furnace temperature is reduced to room temperature to obtain the molybdenum carbide nanosheet.
Example 5
Step 1: putting 26.3 g of ammonium paramolybdate, 20 g of ammonium nitrate and 6.3 g of glycine into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium paramolybdate, the ammonium nitrate and the glycine are completely dissolved to form a mixed solution, putting the beaker containing the mixed solution into a muffle furnace, heating for 6 minutes at 170 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: adding glucose into ionized water to prepare a glucose solution with the concentration of 0.2g/mL, adding 26mL of glucose solution into the solution after the heating in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 270 ℃, heating for 10 minutes, and obtaining a fluffy solid after the heating is finished;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a tubular furnace, reducing the fluffy solid for 1 hour by using hydrocarbon at 500 ℃ under flowing hydrogen with the hydrogen flow rate of 100mL/min, keeping the flowing hydrogen state after the reduction of the hydrocarbon is finished, and taking out the powder after the furnace temperature is reduced to room temperature to obtain the molybdenum carbide nanosheet.
Comparative example 1
Step 1: putting 18.5 g of ammonium paramolybdate into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium paramolybdate is completely dissolved to form a solution, putting the beaker containing the solution into a muffle furnace, heating for 5 minutes at 160 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: adding glucose into ionized water to prepare a glucose solution with the concentration of 0.2g/mL, adding 30mL of glucose solution into the solution after the heating in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 240 ℃, heating for 12 minutes, and obtaining dense solid instead of fluffy powder after the heating is finished;
and step 3: and (3) putting the compact solid obtained in the step (2) into a tubular furnace, reducing the compact solid with hydrocarbon at 500 ℃ for 1.5 hours under flowing hydrogen with the hydrogen flow rate of 200mL/min, keeping the flowing hydrogen state after the reduction of the hydrocarbon is finished, and taking out the powder after the furnace temperature is reduced to room temperature to obtain a comparative sample 1.
XRD test and electron microscope test are respectively carried out on the compact solid prepared in the step 2 and the comparative sample prepared in the step 3, and the results are shown in figures 5-7.
As can be seen from fig. 5, the dense solid still forms a distinct amorphous diffraction peak, but a diffraction peak of molybdenum oxide (molybdenum dioxide, molybdenum trioxide) appears at the same time, indicating that the molybdenum oxide has changed into a crystalline phase and cannot form amorphous molybdenum oxide, which leads to the failure of smooth synthesis of molybdenum carbide in the subsequent hydrocarbon reduction step.
FIG. 6 is an XRD diffraction spectrum of comparative sample 1 obtained in step 3. from FIG. 6, comparative sample 1 is composed of a main phase of molybdenum dioxide and a small amount of molybdenum carbide, indicating that the molybdenum carbide phase could not be synthesized successfully. Fig. 7 is a scanning electron microscope photograph of comparative sample 1, which shows that the morphology is large-sized particles, and a nanosheet-shaped morphology structure cannot be formed.
Comparative example 2
Step 1: simultaneously placing 18.5 g of ammonium paramolybdate, 20 g of ammonium nitrate and 12 g of glycine into a 1000ml beaker, adding 100ml of deionized water, stirring until the ammonium paramolybdate, the ammonium nitrate and the glycine are completely dissolved to form a mixed solution, placing the beaker containing the mixed solution into a muffle furnace, heating for 5 minutes at 160 ℃, and keeping full contact with air in the heating process while fully stirring;
step 2: preparing citric acid into a citric acid solution with the concentration of 0.2g/mL, adding 30mL of the citric acid solution into the solution heated in the step 1, stirring to form a mixed solution, putting the mixed solution into a heating furnace with the temperature of 240 ℃, heating for 12 minutes, and obtaining fluffy solid powder after heating;
and step 3: and (3) putting the fluffy solid powder obtained in the step (2) into a tubular furnace, reducing the carbon hydrogen for 1.5 hours at 500 ℃ under the flowing hydrogen with the hydrogen flow rate of 200mL/min, keeping the flowing hydrogen state after the carbon hydrogen reduction is finished, and taking out the powder after the furnace temperature is reduced to room temperature to obtain a comparative sample 2.
XRD test and electron microscope test are respectively carried out on the compact solid prepared in the step 2 and the comparative sample prepared in the step 3, and the results are shown in figures 8-11.
As can be seen from fig. 8, the fluffy solid powder forms a distinct amorphous diffraction peak, indicating that the fluffy solid is composed of an amorphous material, which is a mixture of amorphous molybdenum oxide and amorphous nanocarbon flakes. Fig. 9 is a scanning electron microscope photograph of the fluffy solid powder, and it can be seen from fig. 9 that the fluffy solid powder has a porous sheet structure, and the thickness is about 2 to 4 micrometers, so that a nano sheet structure cannot be formed, which is obviously different from fig. 2.
Fig. 10 is an XRD diffraction spectrum of comparative sample 2, and as can be seen from fig. 10, comparative sample 2 is composed of a major phase molybdenum carbide and a minor phase molybdenum dioxide, indicating that the molybdenum carbide phase cannot be completely synthesized. Fig. 11 is a scanning electron microscope photograph of comparative example 2, and it can be seen from fig. 11 that comparative example 2 still maintains the morphology before the reduction of hydrocarbon, i.e. porous sheet structure, and cannot form nano sheet structure, which is clearly different from fig. 4.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims (10)

1. A preparation method of molybdenum carbide nanosheets is characterized by comprising the following steps: the method comprises the following steps:
step 1: uniformly mixing a molybdenum source, ammonium nitrate and glycine, wherein the mass of the ammonium nitrate is as follows: the mass = 0.8-3.2 of the glycine, and then heating to 160-180 ℃ to obtain a mixture 1;
step 2: adding glucose into the mixture 1 obtained in the step 1, wherein the mass ratio of the glucose to molybdenum in the molybdenum source is 0.8-1.0: 1.6-2.8, and then heating to 230-280 ℃ to obtain fluffy solid, wherein the fluffy solid is a mixture of amorphous molybdenum oxide and amorphous carbon nano-sheets;
and step 3: and (3) putting the fluffy solid obtained in the step (2) into a hydrogen atmosphere, heating to 450-550 ℃, and cooling to obtain the molybdenum carbide nanosheet.
2. A method of producing molybdenum carbide nanoplates as claimed in claim 1, characterised in that: in the step 1, the molybdenum source is at least one of ammonium paramolybdate, ammonium tetramolybdate or ammonium dimolybdate;
optionally, the molar amount of molybdenum in the molybdenum source in step 1: (the molar amount of ammonium nitrate + the molar amount of glycine) =0.5 to 1.0:2.2 to 3.2.
3. A method of producing molybdenum carbide nanoplates as claimed in claim 2, characterised in that: the step 1 comprises the following steps: 1a, mixing a molybdenum source, ammonium nitrate and glycine, adding deionized water, and stirring until the molybdenum source, the ammonium nitrate and the glycine are dissolved; 1b, heating the solution to 165-175 ℃, and preserving the heat for 3-6 minutes to obtain a mixture 1.
4. A method of producing molybdenum carbide nanoplates as claimed in claim 1, characterised in that: and (3) preparing glucose into a glucose aqueous solution with the concentration of 0.1-0.3 g/mL in the step (2), and adding 10-50 mL of the glucose aqueous solution into the mixture 1 obtained in the step (1).
5. A method of producing molybdenum carbide nanoplates as claimed in claim 1, characterised in that: in the step 2, the heating temperature is 240-270 ℃, and the heat preservation time is 10-20 minutes.
6. A method of producing molybdenum carbide nanoplates as claimed in claim 1, characterised in that: h in the hydrogen atmosphere in step 32The flow rate of (A) is 100 to 500 mL/min.
7. A method of producing molybdenum carbide nanoplates as claimed in claim 1, characterised in that: in the step 3, the heating temperature is 460-500 ℃, and the heat preservation time is 1-3 hours.
8. The molybdenum carbide nanosheet prepared by the method for preparing the molybdenum carbide nanosheet according to any one of claims 1 to 7.
9. Molybdenum carbide nanoplatelets according to claim 8 wherein: the molybdenum carbide nanosheet has a crystalline structure, is irregular and flaky and has a thickness of 10-30 nm.
10. Use of molybdenum carbide nanoplates as defined in claim 8 or 9 in the electrocatalytic production of hydrogen.
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