CN111408390B - Pure phase polygon W2C nano material and preparation method thereof - Google Patents
Pure phase polygon W2C nano material and preparation method thereof Download PDFInfo
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- IYDGMDWEHDFVQI-UHFFFAOYSA-N phosphoric acid;trioxotungsten Chemical compound O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.OP(O)(O)=O IYDGMDWEHDFVQI-UHFFFAOYSA-N 0.000 description 1
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- 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
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
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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
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
- B01J35/33—Electric or magnetic properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- 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
- B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
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Abstract
The invention provides a pure phase polygon W2C nanometer material and a preparation method thereof, wherein the preparation method comprises the following steps: 1)mixing and stirring a tungsten source and ethylene glycol uniformly to obtain a first solution; 2) mixing and stirring a carbon source, ethylene glycol and water uniformly to obtain a second solution; 3) mixing and stirring the first solution and the second solution uniformly to obtain a suspension, and separating out solids; 4) carrying out heat treatment on the solid obtained in the step 3) in a reducing atmosphere to obtain a pure-phase polygon W2And C, nano-materials. According to the method, pure-phase, high-surface-area and high-activity W can be prepared under the condition of adding no toxic, harmless and organic matters2And C, nano-materials.
Description
Technical Field
The invention belongs to the technical field of inorganic nano materials, and particularly relates to an environment-friendly method for preparing pure-phase polygonal W2C nanometer material.
Background
Tungsten carbide (WC and W)2C) The catalyst has the d-band electronic state density similar to that of Pt, is a powerful substitute of a platinum-based catalyst, and can be widely used for hydrogen evolution half reaction (HER) of electrolyzed water to improve the reaction efficiency. In recent years, in particular, a series of IVB-VIB transition metal carbides performance researches carried out by Wirth et al in 2012 under an acidic condition indicate that tungsten carbide has the best catalytic activity and is even better than commercial Mo applied to a commercial all-vanadium redox flow battery and a hydrogen evolution end of combined hydrogen production by electrolysis of waterxC, has important commercial value. And in a large number of subsequent studies, the Lee topic group was obtained by theoretical calculations, W2C has a higher catalytic activity than WC, and the results of this study are published on Nature Communication, which is phase-pure W2The application of the C nano material in the commercial electrolysis of water to produce hydrogen opens a door.
However, W2C is often a by-product of WC synthesis and is thermodynamically unstable at 1250 ℃ and is therefore phase-pure W2C synthesis is challenging and rarely reported. And W2The synthesis of C requires the use of high temperatures (C)>1000K) Is liable to cause W2The excessive growth of C crystal results in the reduction of the nano-crystallization degree of active center of the material, and influences the catalytic performance of the material. W with high specific surface area2The C nano material canExposing more catalytically active sites will also facilitate and promote the catalytic reaction. Therefore, the synthesis of pure phase W with high specific surface area is urgently needed in the field2And C, a preparation method of the nanometer material.
Disclosure of Invention
The invention aims to overcome the defects of small specific surface area, low activity and high activity W of the existing tungsten carbide material2C nanometer material is difficult to synthesize and the like, and provides a pure-phase polygon W with high HER activity2C nanometer material and a preparation method thereof.
In a first aspect, the present application provides a phase-pure polygon W with high HER activity2A method for preparing a C nanomaterial, the method comprising the steps of:
1) mixing and stirring a tungsten source and ethylene glycol uniformly to obtain a first solution;
2) mixing and stirring a carbon source, ethylene glycol and water uniformly to obtain a second solution;
3) mixing and stirring the first solution and the second solution uniformly to obtain a suspension, and separating out solids;
4) carrying out heat treatment on the solid obtained in the step 3) in a reducing atmosphere to obtain a pure-phase polygon W2And C, nano-materials.
In the preparation method, water is added into the precursor, so that the precursor can be subjected to spontaneous protonation and electrostatic crosslinking, and the spontaneous protonation and electrostatic crosslinking degree of the precursor can be controlled by controlling the water addition amount of the precursor, namely, in the first stirring step (namely, the steps 1 and 2), the precursor starts a spontaneous protonation process to form a chain structure in a high-temperature stirring process, and the spontaneous protonation degree of the material is controlled by adjusting the water addition amount; in the second step (i.e. the step 3), during the stirring process, the material surface is charged by different kinds due to spontaneous protonation, and the material is crosslinked under the electrostatic action, and is spontaneously arranged into a regular dodecahedral structure to form a 'invisible template', and is subjected to heat treatment to obtain pure phase W2And C, nano-materials. The growth of the nano particles can be controlled by changing the heat treatment temperature to obtain W with different sizes and appearances2And C, nano-particles. According to the above method, water is controlled only by not passing through the templateThe shape and the grain diameter of the material can be controlled (and the pure phase W of the regular dodecahedron shape is formed)2The C nano particle is never reported), the specific surface area can be improved by the regular dodecahedron with small and uniform particle size, certain catalytic activity crystal faces (such as (220) (111) crystal faces) of the material can be fully exposed by the morphology of the dodecahedron, and the intrinsic catalytic activity of the material can be improved to the maximum extent while the number of active sites is increased. In addition, the method has no organic material and no hazardous gas in the preparation process, is environment-friendly and easy to control, and can be used for batch production.
According to the method, pure-phase, high-surface-area and high-activity W can be prepared under the condition of adding no toxic, harmless and organic matters2And C, nano-materials.
Preferably, the tungsten source is ammonium tungstate, and the carbon source is melamine.
Preferably, in step 1), the ratio of the tungsten source to the ethylene glycol is: 0.1-10L of ethylene glycol is used per mole of tungsten source.
Preferably, in the step 2), the ratio of the carbon source to the ethylene glycol is: 0.1-10L of ethylene glycol is used per mole of carbon source.
Preferably, in the step 2), the volume of the water is 0.2 to 0.6 times of the volume of the ethylene glycol.
Preferably, the feeding molar ratio of the tungsten source to the carbon source is 1: 10-1: 2, preferably 5: 32.
preferably, in the step 1), the stirring temperature is controlled to be 50-100 ℃, preferably 60-80 ℃, and the stirring time is controlled to be 1-10 hours.
Preferably, in the step 2), the stirring temperature is controlled to be 50-100 ℃, preferably 60-80 ℃, and the stirring time is controlled to be 1-10 hours.
Preferably, in the step 3), the stirring temperature is controlled to be 20-80 ℃, preferably 20-40 ℃, and the stirring time is controlled to be 1-4 hours.
Preferably, in step 4), the reducing atmosphere is 95% H2+5％Ar。
Preferably, in the step 4), the heat treatment temperature is 800-1000 ℃ and the heat treatment time is 1-4 h.
In a second aspect, the present application provides a composition comprisingPure phase polygon W prepared by any one of the above preparation methods2C nano material, said phase-pure polygon W2The particle size of the C nano material is 100-2000 nm, preferably 100-500 nm, and the C nano material is of a dodecahedral structure.
Has the advantages that:
(1) the preparation method provided by the application can prepare pure-phase W2C, nano material;
(2) the method does not adopt a template, and controls the protonation degree of the precursor by controlling the added water quantity, thereby controlling W2C, exposing the edge; by controlling the heat treatment temperature, the growth of the nano particles is controlled, and pure phase W is formed2C, obtaining nano particles with different sizes and appearances;
(3) the method is simple and easy to implement, the precursor is free of organic matters, the method is environment-friendly, the preparation conditions are mild, and batch production can be realized.
Drawings
FIG. 1 shows the pure phase W prepared in examples 1, 2, 32XRD pattern of C nano material.
Fig. 2 shows XRD patterns of the materials prepared in comparative example 1 and example 4.
FIG. 3 shows pure phase W prepared in examples 1, 22FE-SEM photo of C nano-material.
FIG. 4 shows W prepared in example 42FE-SEM photo of C nano-material.
Fig. 5 shows the results of hydrogen evolution electrocatalytic activity tests of the materials obtained in the examples and comparative examples.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
One embodiment of the invention provides a template-free, substrate-free and environment-friendly pure phase W2C, preparing the nanometer material. The method adopts a two-step stirring method, and controls the spontaneous protonation and electrostatic crosslinking degree of a precursor by controlling the water addition amount of the precursor, namely, the precursor starts to generate spontaneous protons at high temperature in the first-step stirring processA chain structure is formed in the chemical process, and the spontaneous protonation degree of the material is controlled by adjusting the added water amount; in the second step of stirring, the material surface is charged with different charges due to spontaneous protonation, and generates electrostatic action to generate crosslinking, the material is spontaneously arranged into a regular dodecahedron structure to form an invisible template, the invisible template is subjected to heat treatment in a specific atmosphere, and the growth of nano particles is controlled by changing the heat treatment temperature to obtain W with different sizes and appearances2And C, nano-particles. The pure phase W thus obtained2The grain size of the C nano material is about 100-500 nm. The method has the advantages of simple preparation process, mild conditions, no addition of any organic matters, environmental friendliness, easy operation and suitability for large-scale commercial use. The method belongs to the field of inorganic nano material synthesis. The method is described in detail below.
Adding a tungsten source into a certain amount of glycol solution, and stirring for a certain time at a certain temperature to uniformly disperse the tungsten source to obtain a first solution.
The first solution is, for example, a white solution. The tungsten source may be selected from ammonium tungstate ((NH)4)10W12O41·xH2O), tungstic acid (H)2WO4) Phosphotungstic acid (H)3O40PW12) Among them, ammonium tungstate is preferable because a part of ammonia gas escapes during high-temperature stirring, so that ammonium tungstate is positively charged and cross-linked with a solvent ethylene glycol to form a precursor having a long-chain structure. The dosage ratio of the tungsten source to the ethylene glycol can be as follows: 0.1-10L of ethylene glycol is used per mole of tungsten source. At this ratio, the ethylene glycol is sufficiently protonated to form a chain structure with tungstate ions. The stirring temperature can be 50-100 ℃, preferably 60-80 ℃, and the protonation can be fully carried out by stirring at a higher temperature. The stirring time can be controlled within 1-10 h, preferably 5-10 h.
Adding a carbon source into a mixed aqueous solution containing a certain amount of glycol and a little water (preferably deionized water), and stirring for a certain time at a certain temperature to uniformly disperse the carbon source to obtain a second solution.
The second solution is, for example, a white solution. The carbon source may be selected from melamine (C)3N3(NH2)3) Sucrose (C)12H22O11) Glucose (C)6H12O6) Among them, melamine is preferable because melamine has three primary amino groups and is easily protonated to form positive ions. The molar ratio of the tungsten source to the carbon source can be controlled to be 1: 10-1: 2, preferably 5: 32, long chains formed at the molar ratio are connected to each other and pass through electrostatic interaction between ions (e.g., NH 4)+And OH-) So that they spontaneously arrange to form a certain structure. The dosage ratio of the carbon source to the ethylene glycol can be: 0.1-10L of ethylene glycol is used per mole of carbon source. At this ratio the carbon source can achieve sufficient protonation. The final W can be regulated and controlled by controlling the added water quantity2Exposed edges and morphology of the C nano material. Preferably, the amount of water added to the solution is 0.2 to 0.6 times the volume of the added glycol. Within this range, a dodecahedral structure, such as a nearly regular dodecahedral structure, can be obtained. Selecting different proportions in this range can obtain pure phase W with different particle sizes2And C, nano-materials. More preferably, the amount of water added to the solution is 0.2 to 0.4 times the volume of the ethylene glycol added. If the amount of water is too small, the protonation degree of the carbon source is small, and the subsequent substitution/polymerization reaction is difficult to occur; if the amount of water is too large, excess protonated and unprotonated groups may be present in the substituted chain, and subsequent substitution/polymerization reactions occur simultaneously and violently, making it difficult to control the extent of the reaction. The stirring temperature can be 50-100 ℃, preferably 60-80 ℃, and the protonation can be fully carried out by stirring at a higher temperature. The stirring time can be controlled within 1-10 h, preferably 5-10 h.
And mixing the first solution and the second solution, and stirring at a certain temperature for a certain time to uniformly mix the first solution and the second solution to obtain a suspension. The suspension is white, for example. In one example, the first solution is added dropwise to the second solution to mix the two. The stirring temperature can be controlled at 20-80 deg.C, preferably 20-40 deg.C to ensure substitution/polymerization (such as NH)4 +With OH-Reaction of (d) to occur mildly and orderly, thereby controlling the resulting pure phase W2Shape and size of C nanoparticles. The stirring time can be controlled within 1-4 h.
The reaction system takes ethylene glycol as a solvent, not only can realize a protonation process in the first solution, but also can ensure that the protonated ethylene glycol can be combined with a tungstate chain to form a long-chain structure, and can fully dissolve a carbon source in the second solution to ensure that the carbon source is subjected to the protonation process. When the first solution and the second solution are fully mixed, chemical reaction can not occur due to the consistent solvent, so that the occurrence of subsequent substitution/polymerization reaction is ensured.
The precipitate was collected from the suspension and dried in vacuo to give a solid. The precipitate is for example a white flocculent precipitate. The solid obtained is, for example, a white powder. The collection method may be centrifugation or the like. The drying temperature is controlled to be 50-100 ℃.
Heat treating the obtained solid to obtain W2And C, nano-materials. The heat treatment atmosphere may be a reducing atmosphere, for example, 95% H2A/5% Ar atmosphere in which the material formed is guaranteed to be W in a pure phase2C. W can be controlled by controlling the heat treatment temperature2The particle size of the C crystals. The heat treatment temperature may be 860 to 960 ℃, preferably 880 to 920 ℃. The heat treatment time can be 1-4 h.
The application provides a template-free and substrate-free preparation of pure phase W2The method for preparing the C nano material adopts the steps of controlling the added water amount, selecting a proper tungsten source, a proper carbon source and a proper solvent to ensure that a precursor is spontaneously protonated to form heterogeneous charges so as to form an invisible template through mutual crosslinking arrangement, specifically, preparing first and second solutions respectively, fully protonating the solutions in a high-temperature stirring process, mixing the solutions, and generating functional groups (such as NH 4) between the two solutions due to protonation+And OH-) Thereby performing substitution/polymerization reactions resulting in spontaneous alignment of the crystal structure. In the first solution, the solvent glycol is used for protonation (the glycol and ammonium tungstate act for protonation); in the second solution is the protonation of the carbon source (the carbon source is protonated by the action of water and ethylene glycol). The ethylene glycol is used as a solvent, so that a protonation process can be realized in the first solution, the protonated ethylene glycol can be combined with tungstate chains to form a long-chain structure, and a carbon source in the second solution can be fully dissolved to perform the protonation process. When the first solution and the second solution are fully mixed, the solvent is consistent and cannot be dischargedThe chemical reaction is carried out, thereby ensuring the occurrence of the subsequent substitution/polymerization reaction; then, heat treatment is carried out under reducing atmosphere to synthesize pure-phase polygon W with certain edge structure2The C nano material greatly improves the catalytic activity area of the material, which is not reported internationally. W prepared according to one embodiment of the present invention2The C nano material is pure W2The phase C is in a nearly regular dodecahedral structure and has a particle size of about 100-500 nm.
In one example, the phase-pure polygon W2The preparation method of the C nano material comprises the following steps:
(1) dissolving 5mmol ammonium tungstate in 20mL ethylene glycol solution, and stirring at 80 ℃ for 8 h;
(2) dissolving 32mmol of melamine in 20mL of glycol solution, adding deionized water with the volume 0.2-0.6 times that of the glycol solution, and stirring at 80 ℃ for 8 hours;
(3) dropwise adding the uniform solution obtained in the step (1) into the solution obtained in the step (2), and stirring for 1h at 25 ℃;
(4) centrifugally collecting the white flocculent precipitate obtained in the step (3), washing with ethanol for 3-5 times, and drying in vacuum for 12 hours;
(5) placing the white powder obtained in the step (4) in a tube furnace with 95% H2Carrying out heat treatment for 2h at 860-960 ℃ in 5% Ar atmosphere to obtain pure-phase polygon W2And C, nano-materials.
The preparation method provided by the application has the following advantages:
(1) the method adopts inorganic precursors, and controls W by controlling the amount of added water2C exposed edge, W is controlled by controlling heat treatment temperature2The grain diameter of C crystal realizes the generation of pure phase W2C, simultaneously controlling the appearance of the material;
(2) pure phase W prepared by the method2The C nano-particles have a nearly dodecahedral shape, and the particle size can be 100-500 nm;
(3) the method is simple and easy to implement, mild in preparation conditions, environment-friendly and capable of realizing industrial mass production.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
Firstly, 5mmol of ammonium tungstate (15.2129 g) is dissolved in 20mL of glycol solution, and the solution is stirred for 8 hours in a water bath kettle at the temperature of 80 ℃ to obtain a uniform white solution. Then 32mmol of melamine (i.e. 4.03584g) was dissolved in another 20mL of ethylene glycol solution, and deionized water with a volume 0.4 times that of the ethylene glycol solution was added, and the mixture was stirred in a water bath kettle at 80 ℃ for 8 hours to obtain a uniform white solution. Mixing the above two white solutions, and stirring at 25 deg.C for 1h to obtain white flocculent precipitate. Thereafter, the white precipitate was collected by centrifugation and washed 3 times with ethanol, and dried in a vacuum oven at 70 ℃ for 12 hours. Finally, the precipitate was collected in 95% H2Heating at 900 deg.C for 2h in 5% Ar atmosphere to obtain pure phase W2C nano material, as shown by W-2-900 spectral line in XRD spectrum of figure 1.
The prepared material has a particle size of about 200nm (table 1) and a shape of nearly dodecahedron, as shown in the SEM photographs of c and d in fig. 3.
Example 2
32mmol of melamine (4.03584 g) were dissolved in 20mL of ethylene glycol solution, and deionized water was added in an amount of 0.2 times the volume of the ethylene glycol solution under the same operating conditions as in example 1. The structure of the obtained material is pure phase W2And C, as shown by a W-1-900 line in an XRD pattern of figure 1, has the particle size of about 250nm (Table 1) and the shape of a nearly dodecahedron, as shown by SEM pictures of a and b in figure 3.
Example 3
32mmol of melamine (4.03584 g) were dissolved in 20mL of ethylene glycol solution, and deionized water was added in an amount of 0.6 times the volume of the ethylene glycol solution under the same operating conditions as in example 1. The structure of the obtained material is pure phase W2C, W-3-90 in XRD pattern as shown in figure 1The 0 line shows a particle size of about 500nm (Table 1) and a morphology variation, as shown in the SEM pictures of e, f in FIG. 3.
Example 4
The collected precipitate was subjected to 950 ℃ 95% H2Thermal treatment for 2h in 5% Ar atmosphere, otherwise as in example 1, to produce a material phase W2And C, as shown in a W-2-950 spectral line in an XRD spectrum of figure 2, part of grains are obviously grown (the grain diameter is 1-2 mu m) and are fully grown regular dodecahedral grains, as shown in SEM pictures of g and h in figure 3.
Comparative example 1
The collected precipitate was subjected to 95% H at 850 deg.C2Thermal treatment for 2h in 5% Ar atmosphere, otherwise as in example 1, the material phase prepared is WO2As shown by the W-2-850 line in the XRD pattern of fig. 2.
Comparative example 2
32mmol of melamine (i.e., 4.03584g) were dissolved in 20mL of ethylene glycol solution, and deionized water was added in a volume 0.1 times that of the ethylene glycol solution, and the other operating conditions were the same as in example 1. The obtained material is small nanoparticles which do not grow completely, the particle size is 1-20 nm, and the SEM photo in a in figure 4 shows.
Comparative example 3
32mmol of melamine (i.e., 4.03584g) were dissolved in 20mL of ethylene glycol solution, and deionized water was added in a volume 0.8 times that of the ethylene glycol solution, and the other operating conditions were the same as in example 1. The obtained material is a material with mutually cross-linked large and small particles, wherein the particle size of the small particles is 10-20 nm, the particle size of the large particles is about 1 μm, and the obtained material is in a polygonal structure, as shown in an SEM picture of b in figure 4.
TABLE 1 pure phase W prepared2Particle size of C nanomaterial
The materials obtained in the above examples and comparative examples were subjected to hydrogen evolution electrocatalytic activity test by the following methods: three-electrode method (using Shanghai Chenghua CHI 760E electrochemical workstation). The test results are shown in FIG. 5, when the water content is 0.4Multiple pure phase polygon W obtained at a heat treatment temperature of 900 DEG C2The best C performance is 0.5M H2SO4The overpotential in the solution was about 220 mV.
Claims (4)
1. Environment-friendly pure-phase polygon W2The preparation method of the C nano material is characterized by comprising the following steps:
1) mixing and stirring a tungsten source and ethylene glycol uniformly to obtain a first solution, wherein the stirring temperature is controlled to be 50-100 ℃, and the dosage ratio of the tungsten source to the ethylene glycol is as follows: 0.1-10L of ethylene glycol is used for each mole of tungsten source;
2) uniformly mixing and stirring a carbon source, ethylene glycol and water to obtain a second solution, wherein the stirring temperature is controlled to be 50-100 ℃, and the dosage ratio of the carbon source to the ethylene glycol is as follows: 0.1-10L of ethylene glycol is used for each mole of carbon source, the volume of water is 0.2-0.6 times of that of the ethylene glycol, and the feeding molar ratio of the tungsten source to the carbon source is 1: 10-1: 2;
3) mixing and stirring the first solution and the second solution uniformly to obtain a turbid liquid, and separating out solids, wherein the stirring temperature is controlled to be 20-80 ℃;
4) carrying out heat treatment on the solid obtained in the step 3) in a reducing atmosphere to obtain a pure-phase polygon W2C, the heat treatment temperature is 860-960 ℃, and the heat treatment time is 1-4 hours.
2. The method of claim 1, wherein the tungsten source is ammonium tungstate and the carbon source is melamine.
3. The preparation method according to claim 1, wherein in the step 1), the stirring temperature is controlled to be 60-80 ℃, and the stirring time is controlled to be 1-10 h; in the step 2), the stirring temperature is controlled to be 60-80 ℃, and the stirring time is controlled to be 1-10 h; in the step 3), the stirring temperature is controlled to be 20-40 ℃, and the stirring time is controlled to be 1-4 h.
4. The production method according to any one of claims 1 to 3,in step 4), the reducing atmosphere is 95% H2+5% Ar。
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