CN111841593B - Molybdenum carbide-based catalyst, preparation method and application - Google Patents
Molybdenum carbide-based catalyst, preparation method and application Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 81
- QIJNJJZPYXGIQM-UHFFFAOYSA-N 1lambda4,2lambda4-dimolybdacyclopropa-1,2,3-triene Chemical compound [Mo]=C=[Mo] QIJNJJZPYXGIQM-UHFFFAOYSA-N 0.000 title claims abstract description 70
- 229910039444 MoC Inorganic materials 0.000 title claims abstract description 70
- 238000002360 preparation method Methods 0.000 title abstract description 16
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 23
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 23
- 239000001257 hydrogen Substances 0.000 claims abstract description 23
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 23
- 239000000843 powder Substances 0.000 claims abstract description 23
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 21
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 claims abstract description 18
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 17
- MEFBJEMVZONFCJ-UHFFFAOYSA-N molybdate Chemical compound [O-][Mo]([O-])(=O)=O MEFBJEMVZONFCJ-UHFFFAOYSA-N 0.000 claims abstract description 17
- 238000000034 method Methods 0.000 claims abstract description 14
- 238000001027 hydrothermal synthesis Methods 0.000 claims abstract description 13
- 238000006243 chemical reaction Methods 0.000 claims abstract description 11
- 238000001035 drying Methods 0.000 claims abstract description 8
- 239000007789 gas Substances 0.000 claims abstract description 8
- 238000005406 washing Methods 0.000 claims abstract description 8
- 238000001354 calcination Methods 0.000 claims abstract description 6
- 238000001914 filtration Methods 0.000 claims abstract description 5
- DDFHBQSCUXNBSA-UHFFFAOYSA-N 5-(5-carboxythiophen-2-yl)thiophene-2-carboxylic acid Chemical compound S1C(C(=O)O)=CC=C1C1=CC=C(C(O)=O)S1 DDFHBQSCUXNBSA-UHFFFAOYSA-N 0.000 claims description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- APUPEJJSWDHEBO-UHFFFAOYSA-P ammonium molybdate Chemical compound [NH4+].[NH4+].[O-][Mo]([O-])(=O)=O APUPEJJSWDHEBO-UHFFFAOYSA-P 0.000 claims description 13
- 235000018660 ammonium molybdate Nutrition 0.000 claims description 13
- 239000011609 ammonium molybdate Substances 0.000 claims description 13
- 229940010552 ammonium molybdate Drugs 0.000 claims description 13
- XJHCXCQVJFPJIK-UHFFFAOYSA-M caesium fluoride Chemical compound [F-].[Cs+] XJHCXCQVJFPJIK-UHFFFAOYSA-M 0.000 claims description 6
- NROKBHXJSPEDAR-UHFFFAOYSA-M potassium fluoride Chemical compound [F-].[K+] NROKBHXJSPEDAR-UHFFFAOYSA-M 0.000 claims description 6
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 claims description 6
- 238000005868 electrolysis reaction Methods 0.000 claims description 4
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 3
- MODMKKOKHKJFHJ-UHFFFAOYSA-N magnesium;dioxido(dioxo)molybdenum Chemical compound [Mg+2].[O-][Mo]([O-])(=O)=O MODMKKOKHKJFHJ-UHFFFAOYSA-N 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 239000011591 potassium Substances 0.000 claims description 3
- 229910052700 potassium Inorganic materials 0.000 claims description 3
- 235000007686 potassium Nutrition 0.000 claims description 3
- 235000003270 potassium fluoride Nutrition 0.000 claims description 3
- 239000011698 potassium fluoride Substances 0.000 claims description 3
- 235000013024 sodium fluoride Nutrition 0.000 claims description 3
- 239000011775 sodium fluoride Substances 0.000 claims description 3
- 235000015393 sodium molybdate Nutrition 0.000 claims description 3
- 239000011684 sodium molybdate Substances 0.000 claims description 3
- TVXXNOYZHKPKGW-UHFFFAOYSA-N sodium molybdate (anhydrous) Chemical compound [Na+].[Na+].[O-][Mo]([O-])(=O)=O TVXXNOYZHKPKGW-UHFFFAOYSA-N 0.000 claims description 3
- 239000002073 nanorod Substances 0.000 abstract description 14
- 230000000694 effects Effects 0.000 abstract description 11
- 229910000476 molybdenum oxide Inorganic materials 0.000 abstract description 7
- PQQKPALAQIIWST-UHFFFAOYSA-N oxomolybdenum Chemical compound [Mo]=O PQQKPALAQIIWST-UHFFFAOYSA-N 0.000 abstract description 7
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 abstract description 4
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 abstract description 4
- 238000003763 carbonization Methods 0.000 abstract description 4
- 238000005530 etching Methods 0.000 abstract description 4
- 239000011737 fluorine Substances 0.000 abstract description 4
- 229910052731 fluorine Inorganic materials 0.000 abstract description 4
- 229910000040 hydrogen fluoride Inorganic materials 0.000 abstract description 4
- JKQOBWVOAYFWKG-UHFFFAOYSA-N molybdenum trioxide Inorganic materials O=[Mo](=O)=O JKQOBWVOAYFWKG-UHFFFAOYSA-N 0.000 abstract description 4
- 230000002195 synergetic effect Effects 0.000 abstract description 3
- QXYJCZRRLLQGCR-UHFFFAOYSA-N dioxomolybdenum Chemical compound O=[Mo]=O QXYJCZRRLLQGCR-UHFFFAOYSA-N 0.000 description 28
- 230000000052 comparative effect Effects 0.000 description 18
- 229910003178 Mo2C Inorganic materials 0.000 description 16
- 239000008367 deionised water Substances 0.000 description 6
- 229910021641 deionized water Inorganic materials 0.000 description 6
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 6
- 239000004810 polytetrafluoroethylene Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 238000003917 TEM image Methods 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 3
- 229910002804 graphite Inorganic materials 0.000 description 3
- 239000010439 graphite Substances 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- -1 polytetrafluoroethylene Polymers 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 238000000967 suction filtration Methods 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000007865 diluting Methods 0.000 description 2
- 238000002272 high-resolution X-ray photoelectron spectroscopy Methods 0.000 description 2
- 238000001453 impedance spectrum Methods 0.000 description 2
- 238000004502 linear sweep voltammetry Methods 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 150000002222 fluorine compounds Chemical group 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Images
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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
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
-
- B01J35/33—
-
- B01J35/40—
-
- B01J35/60—
-
- B01J35/61—
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention provides a molybdenum carbide-based catalyst and a preparation method and application thereof, wherein the preparation method comprises the following steps: adding molybdate and fluoride into a nitric acid solution, then carrying out hydrothermal reaction, and filtering, washing and drying after the reaction is finished to obtain white powder; and placing the white powder in a tubular furnace, and calcining the white powder in a mixed gas of hydrogen and methane to obtain the molybdenum carbide-based catalyst. The preparation method of the invention firstly prepares MoO3Nanorods which form a porous structure due to etching by fluoride and then are coated on CH4/H2The mixed gas is carbonized, fluorine and hydrogen are combined to form hydrogen fluoride in the carbonization process, the specific surface area of molybdenum carbide is successfully increased, a porous nanorod structure is formed, when the molybdenum carbide is exposed to air, the molybdenum carbide is partially oxidized to form a rich carbide and molybdenum oxide heterostructure, and due to the high specific surface area and the synergistic effect between the molybdenum carbide and the molybdenum oxide, the ultrahigh-alkaline hydrogen electro-evolution activity is realized.
Description
Technical Field
The invention relates to the technical field of electrolytic water catalysts, in particular to a molybdenum carbide-based catalyst and a preparation method and application thereof.
Background
Hydrogen production by water electrolysis is of great interest due to its efficient and environmentally friendly operation, however, one of the most serious problems with water electrolysis techniques under alkaline conditions is the relatively slow Hydrogen Evolution Reaction (HER), even with Pt as a catalyst.
Therefore, the development of basic HER catalysts with excellent activity, high stability and low price to replace expensive commercial Pt/C is one of the most urgent tasks in the field of hydrogen energy technology. Molybdenum carbide (Mo) in catalyst2C) It exhibits HER activity similar to Pt catalyst under alkaline conditions due to its platinum-like electronic configuration, good electronic conductivity and excellent catalytic activity for water dissociation.
For further improvement of Mo-based2C catalyst HER activity, the prior art discloses the doping of molybdenum carbide nanorods with phosphorus to optimize Mo2Hydrogen adsorption energy of C to achieve an overpotential of 89 mV. However, Mo2The synthesis of C usually requires a high temperature carbonization process, resulting in Mo2The C-based catalyst has a small specific surface area, and Mo is limited due to relatively few exposed active sites2HER activity of C-based catalysts.
Based on the shortcomings of the prior art, there is a need for improvements in existing molybdenum carbide based catalysts.
Disclosure of Invention
In view of the above, the invention provides a molybdenum carbide-based catalyst, and a preparation method and an application thereof, so as to solve the defects of the existing molybdenum carbide-based catalyst.
In a first aspect, the present invention provides a method for preparing a molybdenum carbide-based catalyst, comprising:
adding molybdate and fluoride into a nitric acid solution, then carrying out hydrothermal reaction, and filtering, washing and drying after the reaction is finished to obtain white powder;
and placing the white powder in a tubular furnace, and calcining the white powder in a mixed gas of hydrogen and methane to obtain the molybdenum carbide-based catalyst.
Optionally, the molybdate comprises one of ammonium molybdate, sodium molybdate, potassium molybdate and magnesium molybdate; the fluoride comprises one of ammonium fluoride, sodium fluoride, potassium fluoride and cesium fluoride.
Optionally, molybdate and fluoride are added into a nitric acid solution, and hydrothermal reaction is carried out for 18-24 hours at the temperature of 180-220 ℃.
Optionally, the calcination specifically comprises: and raising the temperature to 750-800 ℃ at the rate of 5 ℃ per minute, and preserving the heat for 3-6 hours to obtain the molybdenum carbide-based catalyst.
Optionally, the molar ratio of the fluoride to the molybdate is 0.1-0.8.
Optionally, the preparation method of the nitric acid solution comprises the following steps: dissolving 1 time volume of concentrated nitric acid in 4-8 times volume of water to obtain a nitric acid solution.
Optionally, molybdate and fluoride are added into a nitric acid solution, then hydrothermal reaction is carried out, after the reaction is finished, filtering, washing and drying at the temperature of 60-70 ℃ are carried out, so as to obtain white powder.
In a second aspect, the invention also provides a molybdenum carbide-based catalyst prepared by the preparation method.
In a third aspect, the invention also provides the application of the molybdenum carbide-based catalyst in the preparation of hydrogen by electrolyzing water.
Compared with the prior art, the preparation method of the molybdenum carbide-based catalyst provided by the invention has the following beneficial effects:
(1) the preparation method of the molybdenum carbide-based catalyst comprises the step of preparing MoO with the diameter of 300-500 nm by a hydrothermal method3Nanorods which form a porous structure due to etching by fluoride and then are coated on CH4/H2The combination of fluorine and hydrogen during the carbonization process forms hydrogen fluoride, successfully increases the specific surface area of molybdenum carbide, forms a porous nanorod structure, is partially oxidized to form a h-Mo2C/MoO2 catalyst rich in the heterogeneous structure of carbide and molybdenum oxide when exposed to air, and has the number of surface active sites and the solid content of each active site due to the higher specific surface area and the synergistic effect between molybdenum carbide and molybdenum oxideThe activity is greatly improved, so that the ultrahigh alkaline hydrogen electrolysis activity is realized, and the method has a good application prospect.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a process flow diagram of a method for preparing a molybdenum carbide-based catalyst according to the present invention;
FIG. 2 is an XRD spectrum of the catalysts prepared in example 1 and comparative examples 1-2 of the present invention;
FIG. 3 is a graph showing N2 adsorption isotherms of catalysts prepared in examples 1 to 3 and comparative example 2 of the present invention;
FIG. 4 is a transmission electron microscope image of the molybdenum carbide-based catalyst prepared in examples 1 to 3 of the present invention at a low magnification;
FIG. 5 is a transmission electron microscope image of the molybdenum carbide-based catalyst prepared in example 1 of the present invention at high resolution;
FIG. 6 is an XPS spectrum of catalysts prepared in example 1 and comparative examples 1-2 of the present invention;
FIG. 7 is a graph of Linear Sweep Voltammetry (LSV) in 1M KOH for catalysts prepared in examples 1-3 of the present invention and comparative example 2;
FIG. 8 is a Mo 3d HR-XPS plot of catalysts prepared in examples 1-3 of the present invention and comparative example 2;
FIG. 9 is a graph showing the electric double layer capacitance curves at different scanning speeds for catalysts prepared in example 1 and comparative example 2 of the present invention;
fig. 10 is an electrochemical impedance spectrum of the catalyst prepared in example 1 of the present invention and comparative example 2.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Example 1
As shown in fig. 1, a method for preparing a molybdenum carbide-based catalyst includes the steps of:
s1, adding molybdate and fluoride into a nitric acid solution, then carrying out hydrothermal reaction, and filtering, washing and drying after the reaction is finished to obtain white powder;
and S2, placing the white powder in a tubular furnace, and calcining the white powder in a mixed gas of hydrogen and methane to obtain the molybdenum carbide-based catalyst.
It should be noted that, in the embodiment of the present application, the molybdate includes one of ammonium molybdate, sodium molybdate, potassium molybdate, and magnesium molybdate; the fluoride comprises one of ammonium fluoride, sodium fluoride, potassium fluoride and cesium fluoride; specifically, ammonium molybdate is used as molybdate and ammonium fluoride is used as fluoride in the present application.
In the embodiment of the application, 8ml of concentrated nitric acid is diluted to 40ml by deionized water to obtain a nitric acid solution; dissolving ammonium molybdate and ammonium fluoride in a nitric acid solution, then putting the solution into a 50ml PTFE (polytetrafluoroethylene) reactor, carrying out hydrothermal reaction for 20h at 200 ℃, carrying out suction filtration after the reaction is finished, washing with deionized water, and drying at 65 ℃ to obtain white powder; the white powder is fluoride etched MoO3And (4) nanorods.
In the examples of the present application, the molar ratio of ammonium fluoride to ammonium molybdate was 0.5, and the specific mass of ammonium molybdate was 1.4 g.
In the embodiment of the application, the obtained white powder is placed in a tubular furnace, the temperature is raised to 750 ℃ at the rate of 5 ℃ per minute under the mixed gas of hydrogen and methane for 4 hours, and the molybdenum carbide-based catalyst h-Mo is obtained after the mixture is cooled to room temperature2C/MoO2. Wherein the volume ratio of the hydrogen to the methane is 4: 1.
According to the embodiment of the application, MoO with the diameter of 300-500 nm is prepared by a hydrothermal method3Nanorods which form a porous structure due to etching by fluoride and then are coated on CH4/H2The combination of fluorine and hydrogen during the carbonization process forms hydrogen fluoride, successfully improves the specific surface area of the molybdenum carbide, forms a porous nanorod structure, and is partially oxidized to form h-Mo rich in the heterostructure of carbide and molybdenum oxide when exposed to air2C/MoO2The catalyst has high specific surface area and synergistic effect of molybdenum carbide and molybdenum oxide, and the number of surface active sites and the inherent activity of each active site are greatly improved, so that the ultrahigh-alkalinity electrohydrogen evolution activity is realized, and the catalyst has a good application prospect.
Based on the same inventive concept, the embodiment of the application also provides a molybdenum carbide-based catalyst which is prepared by adopting the preparation method.
Based on the same inventive concept, the embodiment of the application also provides the application of the molybdenum carbide-based catalyst in preparing hydrogen by electrolyzing water.
Example 2
The same as example 1, except that the molar ratio of ammonium fluoride to ammonium molybdate was 0.2.
Example 3
The same as example 1, except that the molar ratio of ammonium fluoride to ammonium molybdate was 0.75.
Comparative example 1
MoO2The synthesis of (2): MoO (MoO)2The preparation method comprises the following steps:
diluting 8ml of concentrated nitric acid to 40ml by using deionized water to obtain a nitric acid solution; then adding 1.4g of ammonium molybdate into the nitric acid solution, then putting the ammonium molybdate into a 50ml PTFE (polytetrafluoroethylene) reactor, carrying out hydrothermal reaction for 20h at 200 ℃, carrying out suction filtration after the reaction is finished, washing with deionized water, and drying at 65 ℃ to obtain white powder; the white powder is MoO3And (4) nanorods.
The MoO to be obtained3Putting the nano-rods into a tube furnaceCalcining the mixture in argon-hydrogen mixed gas for 2 hours at the temperature of 600 ℃ to obtain brown MoO2And (3) powder.
Comparative example 2
Mo2C, synthesis: mo2The preparation method of C comprises the following steps:
diluting 8ml of concentrated nitric acid to 40ml by using deionized water to obtain a nitric acid solution; then adding 1.4g of ammonium molybdate into the nitric acid solution, then putting the ammonium molybdate into a 50ml PTFE (polytetrafluoroethylene) reactor, carrying out hydrothermal reaction for 20h at 200 ℃, carrying out suction filtration after the reaction is finished, washing with deionized water, and drying at 65 ℃ to obtain white powder; the white powder is MoO3And (4) nanorods.
The MoO to be obtained3Putting the nano-rods into a tube furnace, heating to 750 ℃ at the rate of 5 ℃ per minute under the mixed gas of hydrogen and methane, keeping for 4 hours, and cooling to room temperature to obtain black powder Mo2C。
Performance characterization
The molybdenum carbide-based catalysts h-Mo prepared in example 1 were tested separately2C/MoO2And MoO prepared in comparative examples 1 to 22、Mo2The XRD pattern result of C is shown in figure 2. As can be seen from FIG. 2, at diffraction angles of 35.35 °, 37.98 °, 39.39 °, 52.12 °, 61.53 °, 69.57 °, 74.65 ° correspond to the (100), (002), (101), (102), (110), (103), (112) crystal planes (PDF: 35-0787) of molybdenum carbide, respectively. In addition, in the fluorine-etched molybdenum carbide catalyst, in addition to the diffraction peaks of the above-mentioned molybdenum carbide, MoO is present at 26.08 °, 37.06 °, 41.95 °, and 53.66 ° positions2Was observed (PDF: 76-1807), confirming that not only molybdenum carbide but also molybdenum oxide was formed after the fluoride etching.
The molybdenum carbide-based catalysts h-Mo prepared in examples 1 to 3 were tested separately2C/MoO2And Mo obtained by preparation in comparative example 22The specific surface area of C, the results are shown in FIG. 3; specific surface area measured by using a Microactive (micromeritics Instrument corporation) N2 adsorption isotherm for ASAP 2460 Brunauer-Emmett-Teller (B)ET) method. In FIG. 3, h-Mo2C/MoO20.2 represents the molybdenum carbide-based catalyst prepared in example 2, h-Mo2C/MoO20.5 represents the molybdenum carbide-based catalyst prepared in example 1, h-Mo2C/MoO2-0.75 represents the molybdenum carbide-based catalyst prepared in example 3. As can be seen from fig. 3, the specific surface area is smallest without doping ammonium fluoride, and increases and then decreases as the molar ratio of ammonium fluoride increases from 0.2, 0.5 to 0.75, and reaches the maximum at a molar ratio of ammonium fluoride of 0.5.
Transmission electron micrographs of the molybdenum carbide-based catalysts prepared in examples 1 to 3 at low magnification were respectively measured, and the results are shown in fig. 4, where (a) in fig. 4 is a transmission electron micrograph of the molybdenum carbide-based catalyst prepared in example 2, (b) in fig. 4 is a transmission electron micrograph of the molybdenum carbide-based catalyst prepared in example 1, and (c) in fig. 4 is a transmission electron micrograph of the molybdenum carbide-based catalyst prepared in example 3. It can be seen from FIG. 4 that when the molar ratio of ammonium fluoride is between 0.2 and 0.5, the nanorod morphology remains intact, but when the molar ratio of ammonium fluoride is further increased to 0.75, the nanorod morphology collapses, which is the reason why the specific surface area is rather decreased when the molar ratio of ammonium fluoride is too high.
The molybdenum carbide-based catalyst prepared in example 1 was further tested in a transmission electron micrograph at high resolution, and the results are shown in fig. 5. As can be seen from fig. 5, the molybdenum carbide-based catalyst is densely distributed with a heterojunction structure of molybdenum carbide and molybdenum oxide, and it is due to such a high-density heterojunction structure that the catalyst has a high catalytic activity.
The molybdenum carbide-based catalysts h-Mo prepared in example 1 were tested separately2C/MoO2MoO prepared in comparative example 12MoO prepared in comparative example 22The XPS spectrum of (A) is shown in FIG. 6. From FIG. 6, it can be seen that the molybdenum carbide-based catalyst h-Mo in the present example2C/MoO2Consists of three elements of C, Mo and O, and is in the presence of molybdenum carbide-based catalyst h-Mo2C/MoO2No peak of F was found, and it was laterally confirmed that the formation of pores may be caused by hydrogen fluoride from fluorine and hydrogenIs carried away by the air flow. Meanwhile, the results of the surface atomic ratio of the different catalysts obtained from the XPS spectrum of FIG. 6 are shown in Table 1 below.
TABLE 1 atomic specific gravities of different catalysts
| Mo(at.％) | C(at.％) | O(at.％) | |
| Mo2C | 20.73 | 52.42 | 26.85 |
| h-Mo2C/MoO2 | 22.722 | 28.77 | 48.51 |
| MoO2 | 21.5 | 25.75 | 52.74 |
As can be seen from Table 1, the difference of the surface oxygen content among the three catalysts indicates the degree of oxidation of the catalysts, and compared with the case that ammonium fluoride is not added in comparative examples 1-2, the ammonium fluoride added in example 1 of the present application has a larger specific surface area and a higher degree of oxidation.
The molybdenum carbide-based catalysts h-Mo prepared in examples 1 to 3 were tested separately2C/MoO2And Mo in comparative example 22The Linear Sweep Voltammetry (LSV) profile of C in 1M KOH is shown in FIG. 7. Specifically, a three-electrode system was used, the working electrode was a GC electrode with a diameter of 3mm, the auxiliary electrode was a graphite rod, and the reference electrode was a Hg/HgO electrode, obtained at a scan rate of 5 mV/s.
In FIG. 7, h-Mo2C/MoO20.2 represents the molybdenum carbide-based catalyst prepared in example 2, h-Mo2C/MoO20.5 represents the molybdenum carbide-based catalyst prepared in example 1, h-Mo2C/MoO20.75 represents the molybdenum carbide-based catalyst prepared in example 3, and it can be seen from FIG. 7 that the hydrogen evolution activity shows a tendency of decreasing after increasing with increasing molar ratio of ammonium fluoride, and the activity is the best when the molar ratio of ammonium fluoride is 0.5, which is highly consistent with the BET test results, demonstrating the direct relationship between catalytic activity and specific surface area.
The molybdenum carbide-based catalysts h-Mo prepared in examples 1 to 3 were tested separately2C/MoO2And Mo in comparative example 22The Mo 3d HR-XPS plot of C is shown in FIG. 8. In FIG. 8, h-Mo2C/MoO20.2 represents the molybdenum carbide-based catalyst prepared in example 2, h-Mo2C/MoO20.5 represents the molybdenum carbide-based catalyst prepared in example 1, h-Mo2C/MoO2-0.75 represents the molybdenum carbide-based catalyst prepared in example 3, and as can be seen from fig. 8, the Mo 3d also exhibits a similar trend to the BET test, and the valence is the highest when the molar ratio of ammonium fluoride is 0.5, indicating a higher degree of oxidation, suggesting that the number of heterojunctions formed is the highest when the molar ratio of ammonium fluoride is 0.5.
Test of the molybdenum carbide-based catalyst h-Mo prepared in example 12C/MoO2And Mo obtained in comparative example 22C electric double layer capacitance curves obtained at different scanning speeds, the results are shown in fig. 9. Specifically, a three-electrode system is adopted, the electrolyte is 1M KOH, and a working electrode is adoptedFor GC, the auxiliary electrode was a graphite rod, the reference electrode was Hg/HgO, the potential window for the test was 0.16V to 0.26V relative to the reversible hydrogen electrode, and the sweep rate was from 10mV/s to 100 mV/s.
The electric double layer capacitance is used for evaluating the number of active sites of the catalyst reaction, and it can be seen from fig. 9 that after the ammonium fluoride is added to form a heterojunction, the number of the active sites is greatly increased, and the catalytic activity is better.
Test of the molybdenum carbide-based catalyst h-Mo prepared in example 12C/MoO2And Mo obtained in comparative example 22The electrochemical impedance spectrum of C is shown in FIG. 10.
Specifically, a three-electrode system is adopted, a working electrode is a GC electrode with the diameter of 3mm, an auxiliary electrode is a graphite rod, a reference electrode is a Hg/HgO electrode, the frequency range of an EIS test is from 10000Hz to 0.1Hz, and the potential is-0.092V relative to a reversible hydrogen electrode.
Electrochemical impedance was used to evaluate how fast charge was transported in the catalytic reaction, as can be seen from FIG. 10, in the example of the present application, the molybdenum carbide-based catalyst h-Mo2C/MoO2The impedance of (a) is reduced, indicating that charge transfer is faster in the heterojunction catalyst, which is more favorable for the catalytic reaction.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (5)
1. A method for preparing a molybdenum carbide-based catalyst, comprising:
adding molybdate and fluoride into a nitric acid solution, then carrying out hydrothermal reaction, and filtering, washing and drying after the reaction is finished to obtain white powder;
placing the white powder in a tubular furnace, and calcining the white powder in a mixed gas of hydrogen and methane to obtain a molybdenum carbide-based catalyst;
the molybdate comprises one of ammonium molybdate, sodium molybdate, potassium molybdate and magnesium molybdate; the fluoride comprises one of ammonium fluoride, sodium fluoride, potassium fluoride and cesium fluoride;
adding molybdate and fluoride into a nitric acid solution, and carrying out hydrothermal reaction at the temperature of 180-220 ℃ for 18-24 h;
the calcination is specifically as follows: raising the temperature to 750-800 ℃ at the rate of 5 ℃ per minute, and preserving the heat for 3-6 hours to obtain a molybdenum carbide-based catalyst;
the molar ratio of the fluoride to the molybdate is 0.1-0.8.
2. The method of preparing the molybdenum carbide-based catalyst according to claim 1, wherein the nitric acid solution is prepared by: dissolving 1 time volume of concentrated nitric acid in 4-8 times volume of water to obtain a nitric acid solution.
3. The method for preparing the molybdenum carbide-based catalyst according to claim 1, wherein the molybdate and the fluoride are added to a nitric acid solution, and then hydrothermal reaction is performed, and after the reaction is completed, the mixture is filtered, washed, and dried at a temperature of 60 to 70 ℃ to obtain white powder.
4. A molybdenum carbide-based catalyst, characterized by being produced by the production method according to any one of claims 1 to 3.
5. Use of the molybdenum carbide-based catalyst according to claim 4 for the production of hydrogen by electrolysis of water.
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