Transition metal catalyst as well as preparation method and application thereof

Abstract

The invention discloses a transition metal catalyst as well as a preparation method and application thereof. The method comprises the following steps: S1, mechanically mixing a carbon source and transition metal salt to obtain a precursor; and S2, carrying out heat treatment on the precursor, and grinding, transition metal in the transition metal salt is selected from at least one of vanadium, tungsten or molybdenum; the carbon source comprises a nitrogen element; and the temperature of heat treatment is 700-1100 DEG C. The preparation method comprises the following steps: firstly, mechanically mixing a carbon source and a transition metal salt, and then carrying out heat treatment at a specific temperature, so that the prepared transition metal catalyst has high HER / OER electro-catalytic performance under acidic or alkaline conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a transition metal catalyst and a preparation method and application thereof. Background Art

[0002] With the rapid development of industrialization, there is an urgent need to develop new catalytic materials for environmental pollution control and clean energy production technology. Among them, photocatalysis and electrocatalysis are considered to be ideal reactions for the development of clean energy, but the conversion efficiency of such reactions is poor and they are highly dependent on precious metal catalysts. In order to meet the future global demand for hydrogen, low-cost, highly active multifunctional electrocatalysts are needed.

[0003] Therefore, it is necessary to develop a method for preparing bifunctional catalysts with higher HER / OER electrocatalytic performance. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the first aspect of the present invention provides a method for preparing a transition metal catalyst, wherein the transition metal catalyst prepared by the method has high HER / OER electrocatalytic performance.

[0005] The second aspect of the present invention also provides a transition metal catalyst.

[0006] The third aspect of the present invention also provides an application of a transition metal catalyst.

[0007] According to the first aspect of the present invention, a method for preparing a transition metal catalyst is provided; comprising the following steps:

[0008] S1, mechanically mixing a carbon source and a transition metal salt to obtain a precursor;

[0009] S2, heat-treating the precursor and grinding it;

[0010] The transition metal in the transition metal salt is selected from at least one of vanadium, tungsten or molybdenum;

[0011] The carbon source includes nitrogen element; the temperature of the heat treatment is 700°C to 1100°C.

[0012] The preparation method according to the embodiment of the present invention has at least the following beneficial effects:

[0013] The present invention first mechanically mixes the carbon source and the transition metal salt, and then performs heat treatment at a specific temperature, and the prepared transition metal catalyst has high HER / OER electrocatalytic performance under acidic or alkaline conditions. This is because the catalyst prepared by the preparation method of the present invention forms a heterojunction structure, which can further improve the HER / OER electrocatalytic performance.

[0014] Furthermore, the present invention can form nano-particulate transition metal carbides in the carbon layer through mechanical mixing, and the active sites thereof are greatly increased due to the small size, thereby improving the catalytic performance.

[0015] According to some embodiments of the present invention, the temperature of the heat treatment is 700-850°C. Therefore, the temperature includes any numerical value and sub-range between 700°C and 850°C, such as 700°C, 720°C, 750°C, 760°C, 780°C, 800°C, 820°C, 850°C and a range consisting of any two numerical values. Further, when the temperature of the heat treatment is at the above temperature, a monodisperse pure phase crystal face heterojunction catalyst can be prepared, and the generation of crystal face heterojunction will further improve its catalytic performance. The main reason is that different crystal faces have different adsorption capacities for reactants or intermediates, which have a synergistic effect, reduce the barriers to the catalytic reaction, and thus further improve the performance.

[0016] According to some embodiments of the present invention, the mechanical mixing includes ball milling. Therefore, the ball milling method is more likely to achieve uniform mixing, and after the transition metal is subjected to high-temperature pyrolysis treatment, uniform dispersion can be effectively achieved.

[0017] According to some embodiments of the present invention, too low a rotation speed results in a long time for uniform dispersion of the experimental precursor, and the particle size of the ball-milled precursor is large, and the subsequent heat treatment effect is not good; although a higher rotation speed can achieve a better dispersion effect, the improvement in performance is no longer obvious. Therefore, the rotation speed of the ball mill is 400-600rpm.

[0018] According to some embodiments of the present invention, the ball milling time is too short, resulting in uneven dispersion of the carbon source and the metal source, and the ball milled precursor has a large particle size, and the subsequent heat treatment effect is not good. Therefore, the ball milling time is 6 to 8 hours.

[0019] According to some embodiments of the present invention, the heat treatment is carried out for a holding time of 0.5 to 4 hours.

[0020] According to some embodiments of the present invention, the carbon source is selected from at least one of melamine, glycine, urea or polyaniline.

[0021] According to some embodiments of the present invention, the transition metal salt is selected from at least one of ammonium metavanadate, ammonium metatungstate, ammonium tungstate, ammonium molybdate, ammonium molybdate tetrahydrate or sodium molybdate.

[0022] According to some embodiments of the present invention, the molar ratio of the metal to the carbon element is 1:(6-12) calculated based on the metal in the transition metal salt and the carbon element in the carbon source.

[0023] According to some embodiments of the present invention, in step S2, the heat treatment is performed under an inert atmosphere.

[0024] According to some embodiments of the present invention, the gas used for the inert atmosphere is argon or nitrogen.

[0025] According to some embodiments of the present invention, the flow rate of the gas is 2-40 mL / min.

[0026] According to some embodiments of the present invention, in step S2, the heating rate during the heat treatment is 0.5-20°C / min.

[0027] According to some embodiments of the present invention, in step S2, the cooling rate during the heat treatment process is 1-10°C / min.

[0028] A transition metal catalyst provided in an embodiment according to the second aspect of the present invention is prepared by the method for preparing the transition metal catalyst described in the first aspect of the present invention.

[0029] Therefore, the transition metal catalyst of the present invention has high HER / OER electrocatalytic performance.

[0030] The third aspect of the present invention provides a transition metal catalyst as described above; or the method for preparing the transition metal catalyst as described in the first aspect of the present invention, and use of the transition metal catalyst prepared in electrocatalytic hydrogen production.

[0031] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0033] Figure 1 is the XRD pattern of the transition metal catalyst prepared in Example 1 of the present invention;

[0034] Figure 2 is a TEM image of the transition metal catalyst prepared in Example 2 of the present invention;

[0035] Figure 3 is the XRD pattern of the transition metal catalyst prepared in Example 3 of the present invention;

[0036] Figure 4 is a graph of the electrocatalytic performance of the transition metal catalyst prepared in Example 1 of the present invention;

[0037] Figure 5 is a graph of the electrocatalytic performance of the transition metal catalyst prepared in Example 2 of the present invention;

[0038] Figure 6 is a graph of the electrocatalytic performance of the transition metal catalyst prepared in Example 3 of the present invention;

[0039] Figure 7 is a graph of the electrocatalytic performance of the transition metal catalyst prepared in Example 4 of the present invention;

[0040] Figure 8 is a graph showing the electrocatalytic performance of the transition metal catalyst prepared in Example 5 of the present invention;

[0041] Fig. 9 is a graph of the electrocatalytic performance of the transition metal catalyst prepared in Example 6 of the present invention;

[0042] Fig.10 is the XRD pattern of the transition metal catalyst prepared in Comparative Example 1;

[0043] Fig.11 is the XRD pattern of the transition metal catalyst prepared in Comparative Example 2;

[0044] Fig.12 This is a graph of the electrocatalytic performance of the transition metal catalyst prepared in Comparative Example 2. DETAILED DESCRIPTION

[0045] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0046] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0047] Example 1

[0048] This example provides a transition metal catalyst, and its preparation method is as follows:

[0049] S1. Mix 0.8g melamine and 0.5g sodium molybdate, and pour the mixture into a ball mill; weigh ball mill beads of different diameters according to the number ratio (8mm:10mm:15mm=12:6:1), and pour them into one ball mill; the placement operation of another ball mill is the same as above; screw the screws on the top of the two ball mills; place two ball mills of equal mass in symmetrical positions on the planetary ball mill, set the ball milling speed to 400rpm and perform ball milling for 6h to obtain a carbide precursor;

[0050] S2, spreading the precursor powder in step S1 on a porcelain boat, placing it in a quartz tube, and performing heat treatment in an inert gas atmosphere;

[0051] In this embodiment, the inert gas atmosphere introduced is argon gas with a flow rate of 40 mL / min; the heat treatment temperature is 700° C., the holding time is 1 h, the heating rate is 5° C. / min; and the cooling rate is 4° C. / min.

[0052] S3. The product is cooled to room temperature and then ground. It is then washed and centrifuged several times with ultrapure water and anhydrous ethanol respectively, and then dried and ground to obtain a transition metal catalyst, which is recorded as sample 1. In this embodiment, the water washing conditions are as follows: the material in step S2 is placed in a 50% ultrapure water solution, placed in an ultrasonic cleaner for 3 minutes to disperse it, and then placed in a centrifuge at 8000 rpm for 2 times, and then washed twice with anhydrous ethanol by centrifugation at 8000 rpm, and dried at 80°C.

[0053] The sample prepared in Example 1 of the present invention was subjected to XRD detection, and the results were as follows: Figure 1 As shown in the figure, it can be seen that the diffraction characteristic peaks of sample 1 at 34.3°, 37.9°, 39.4°, 52.1°, 61.5° and 74.6° correspond to the (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0) and (1 1 2) crystal planes of Mo2C (PDF#35-0787); this indicates that the pure phase Mo2C material is obtained by the preparation method of the present invention without the aid of a template.

[0054] Example 2

[0055] This example provides a transition metal catalyst, and its preparation method is as follows:

[0056] S1. Mix 0.8g of melamine and 0.5g of ammonium tungstate to obtain a mixture; pour the mixture into a ball mill; weigh ball mill beads of different diameters in proportion to the number and pour them into one ball mill; the placement operation of another ball mill is consistent with the above; screw the screws on the top of the two ball mills; place two ball mills of equal mass in symmetrical positions on the planetary ball mill, set the ball milling speed to 400rpm and perform ball milling for 6h to obtain a carbide precursor;

[0057] S2, spreading the precursor powder on a porcelain boat, placing it in a quartz tube, and performing heat treatment in an inert gas atmosphere;

[0058] In this embodiment, the inert gas atmosphere introduced is argon gas with a flow rate of 20 mL / min; the heat treatment temperature is 800° C., the holding time is 1 h, the heating rate is 5° C. / min; and the cooling rate is 4° C. / min.

[0059] S3. After the product is cooled to room temperature, it is ground, and then washed and centrifuged several times with ultrapure water and anhydrous ethanol respectively, and then dried and ground to obtain a bifunctional transition metal carbide heterojunction catalyst, which is recorded as sample 2; wherein, in this embodiment, the water washing conditions are: the material in step S2 is placed in 50 mL of ultrapure water solution, placed in an ultrasonic cleaner for 3 minutes to disperse it, and then placed in a centrifuge at 8000 rpm for 2 times, and then washed twice with anhydrous ethanol by centrifugation at 8000 rpm, and dried at 80°C.

[0060] Figure 2 This is the TEM image of sample 2 prepared in this embodiment. It can be seen from the image that there are ultra-small nanoparticles on the carbon layer in the prepared composite material, and the corresponding crystal plane spacing and the interface between the crystal planes can be clearly seen.

[0061] Example 3

[0062] This example provides a transition metal catalyst, and its preparation method is as follows:

[0063] S1. Mix 0.8g of melamine and 0.5g of ammonium tungstate to obtain a mixture; pour the mixture into a ball mill; weigh ball mill beads of different diameters in proportion to the number and pour them into one ball mill; the placement operation of another ball mill is consistent with the above; screw the screws on the two ball mills; place two ball mills of equal mass at symmetrical positions on the planetary ball mill, set the ball milling speed to 400rpm and perform ball milling for 6h to obtain a carbide precursor;

[0064] S2, spreading the precursor powder on a porcelain boat, placing it in a quartz tube, and performing heat treatment in an inert gas atmosphere;

[0065] In this embodiment, the inert gas atmosphere introduced is argon gas with a flow rate of 40 mL / min; the heat treatment temperature is 700° C., the holding time is 1 h, the heating rate is 5° C. / min; and the cooling rate is 4° C. / min.

[0066] S3. After the product is cooled to room temperature, it is ground, and then washed and centrifuged several times with ultrapure water and anhydrous ethanol respectively, and then dried and ground to obtain a bifunctional transition metal carbide heterojunction catalyst, which is recorded as sample three; wherein, in this embodiment, the water washing conditions are: the material in step S2 is placed in 50 mL of ultrapure water solution, placed in an ultrasonic cleaner for 3 minutes to disperse it, and then placed in a centrifuge at 8000 rpm for 2 times, and then washed twice with anhydrous ethanol by centrifugation at 8000 rpm, and dried at 80°C.

[0067] Figure 3This is the XRD pattern of sample 3 prepared in this example. It can be seen from the figure that the diffraction characteristic peaks of sample 3 at 34.52°, 38.02°, 39.56°, 52.29°, 61.85°, 69.76°, 72.83°, 74.97° and 75.98° correspond to (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0), (1 1 2) and (2 0 3) of W2C (PDF#35-0776). 1) crystal plane; the diffraction characteristic peaks at 31.51°, 35.64°, 48.29°, 64.01°, 65.78°, 73.10°, 75.47° and 77.12° correspond to the (0 0 1), (1 0 0), (1 0 1), (1 1 0), (0 0 2), (1 1 1), (2 0 0) and (1 0 2) crystal planes of WC (PDF#73-0471); this indicates that the material in which W2C and WC coexist can be obtained by the preparation method of the present invention without the aid of a template.

[0068] Example 4

[0069] This example provides a transition metal catalyst, the preparation method and dosage of which are basically the same as those in Example 1, except that the heat treatment temperature is 780°C.

[0070] Example 5

[0071] This example provides a transition metal catalyst, the preparation method and dosage of which are basically the same as those in Example 1, except that the heat treatment temperature is 850°C.

[0072] Example 6

[0073] This example provides a transition metal catalyst, the preparation method and dosage of which are basically the same as those in Example 1, except that the heat treatment temperature is 950°C.

[0074] Comparative Example 1

[0075] This example provides a transition metal catalyst, the preparation method and dosage of which are basically the same as those in Example 1, except that the heat treatment temperature is 600°C.

[0076] Its XRD pattern is as follows Fig.10 As shown, it can be seen from the XRD diagram that there are no other phases and the carbonization temperature of Mo has not been reached. At this time, the catalytic activity is the worst, which may be the oxidation state of MO. At this time, the conductivity is poor and the overpotential cannot be measured.

[0077] Comparative Example 2

[0078] This example provides a transition metal catalyst, the preparation method and dosage of which are basically the same as those in Example 1, except that the heat treatment temperature is 1150°C.

[0079] Its XRD pattern is as follows Fig.11 As shown, the material is pure MO2C phase, but the XRD diffraction peak of the material is strong at this time, proving that the material has agglomerated at a temperature far above the carbonization temperature. At this temperature, the catalyst size is large, the dispersion of the prepared slurry is poor, and its catalytic activity and stability are reduced.

[0080] Electrocatalytic performance test

[0081] Sample 1 was tested for HER and OER, and the results are as follows: Figure 4 As shown, Figure 4 (a) Figure 4 (b) is the LSV curve of hydrogen evolution (HER) of sample 1 prepared in this example in 1M KOH and 0.5M H2SO4 solution. It can be seen from the figure that the composite material has a high efficiency at 10mAcm -2 The current density required for the overpotential is 199mV and 338mV respectively. Figure 4 (c) Figure 4 (d) is the LSV curve of oxygen evolution (OER) of sample 1 prepared in this example in 1M KOH and 0.5M H2SO4 solution. It can be seen from the figure that the composite material has a high -2 The overpotentials required for the current density of 940 mV and 860 mV, respectively, indicating that the material exhibits good bifunctional electrocatalytic activity under both acidic and alkaline conditions.

[0082] The sample 2 prepared in this example was subjected to HER test, and the results were as follows: Figure 5 As shown, Figure 5 (a) Figure 5 (b) is the LSV curve of hydrogen evolution (HER) of sample 2 prepared in this example in 1M KOH and 0.5M H2SO4 solution. It can be seen from the figure that the composite material has a high efficiency at 10mAcm -2 The current density required for the overpotential is 133mV and 261mV respectively.

[0083] The sample 3 prepared in Example 3 of the present invention was subjected to HER test, and the results are as follows: Figure 6 As shown, Figure 6 (a) Figure 6 (b) is the LSV curve of hydrogen evolution (HER) of sample 3 prepared in this example in 1M KOH and 0.5M H2SO4 solution. It can be seen from the figure that the composite material has a high efficiency at 10mAcm -2The overpotentials required for the current density are 193 mV and 264 mV, respectively, indicating that the material exhibits good hydrogen evolution electrocatalytic activity under both acidic and alkaline conditions.

[0084] The catalyst prepared in Example 4 of the present invention was subjected to HER test, and the results are as follows: Figure 7 As shown in the figure, the LSV curve of hydrogen evolution (HER) in 1M KOH solution shows that the composite material has a -2 The current density required for the overpotential is 191mV.

[0085] The catalyst prepared in Example 5 of the present invention was subjected to HER test, and the results are as follows: Figure 8 As shown in the figure, the LSV curve of hydrogen evolution (HER) in 1M KOH solution shows that the composite material has a -2 The current density required for the overpotential is 180mV respectively.

[0086] The catalyst prepared in Example 6 of the present invention was subjected to HER test, and the results are as follows: Fig. 9 As shown in the figure, the LSV curve of hydrogen evolution (HER) in 1M KOH solution shows that the composite material has a -2 The current density required for the overpotential is 265mV.

[0087] The catalyst prepared in Comparative Example 2 was subjected to HER test, and the results were as follows: Fig.12 As shown in the figure, the LSV curve of hydrogen evolution (HER) in 1M KOH solution shows that the composite material has a -2 The current density required for the overpotential is 375mV.

[0088] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for preparing a transition metal catalyst, characterized in that: The steps include: S1, mechanically mixing a carbon source and a transition metal salt to obtain a precursor; S2, heat-treating the precursor and grinding it; The transition metal in the transition metal salt is selected from at least one of vanadium, tungsten or molybdenum; The carbon source includes nitrogen element; the temperature of the heat treatment is 700°C to 1100°C.

2. The method for preparing a transition metal catalyst according to claim 1, characterized in that: The temperature of the heat treatment is 700-850°C.

3. The method for preparing a transition metal catalyst according to claim 1 or 2, characterized in that: The mechanical mixing includes ball milling.

4. The method for preparing a transition metal catalyst according to claim 3, characterized in that: The rotation speed of the ball mill is 400-600 rpm.

5. The method for preparing a transition metal catalyst according to claim 3, characterized in that: The ball milling time is 6 to 8 hours.

6. The method for preparing a transition metal catalyst according to claim 1 or 2, characterized in that: The heat treatment holding time is 0.5 to 4 hours.

7. The method for preparing a transition metal catalyst according to claim 1 or 2, characterized in that: The carbon source is selected from at least one of melamine, glycine, urea or polyaniline.

8. The method for preparing a transition metal catalyst according to claim 1, characterized in that: The transition metal salt is selected from at least one of ammonium metavanadate, ammonium metatungstate, ammonium tungstate, ammonium molybdate or sodium molybdate.

9. A transition metal catalyst, characterized in that The catalyst is prepared by the method for preparing the transition metal catalyst according to any one of claims 1 to 8.

10. Use of the transition metal catalyst according to claim 9; or the method for preparing the transition metal catalyst according to any one of claims 1 to 8 in electrocatalytic hydrogen production.

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