CN116445955A - Cobalt phosphide electrolytic water catalyst and preparation method thereof - Google Patents
Cobalt phosphide electrolytic water catalyst and preparation method thereof Download PDFInfo
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- CN116445955A CN116445955A CN202310448905.4A CN202310448905A CN116445955A CN 116445955 A CN116445955 A CN 116445955A CN 202310448905 A CN202310448905 A CN 202310448905A CN 116445955 A CN116445955 A CN 116445955A
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- 239000003054 catalyst Substances 0.000 title claims abstract description 81
- 239000010941 cobalt Substances 0.000 title claims abstract description 62
- 229910017052 cobalt Inorganic materials 0.000 title claims abstract description 62
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 title claims abstract description 62
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 50
- 238000002360 preparation method Methods 0.000 title claims abstract description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 172
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 88
- 239000000243 solution Substances 0.000 claims abstract description 63
- 238000006243 chemical reaction Methods 0.000 claims abstract description 50
- 239000001267 polyvinylpyrrolidone Substances 0.000 claims abstract description 50
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 claims abstract description 50
- 229920000036 polyvinylpyrrolidone Polymers 0.000 claims abstract description 50
- 239000006260 foam Substances 0.000 claims abstract description 43
- 239000000463 material Substances 0.000 claims abstract description 41
- 239000012621 metal-organic framework Substances 0.000 claims abstract description 40
- QGUAJWGNOXCYJF-UHFFFAOYSA-N cobalt dinitrate hexahydrate Chemical compound O.O.O.O.O.O.[Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O QGUAJWGNOXCYJF-UHFFFAOYSA-N 0.000 claims abstract description 25
- LXBGSDVWAMZHDD-UHFFFAOYSA-N 2-methyl-1h-imidazole Chemical compound CC1=NC=CN1 LXBGSDVWAMZHDD-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000011259 mixed solution Substances 0.000 claims abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 17
- 239000007789 gas Substances 0.000 claims abstract description 9
- 239000012299 nitrogen atmosphere Substances 0.000 claims abstract description 7
- 238000002156 mixing Methods 0.000 claims abstract description 6
- 238000002791 soaking Methods 0.000 claims abstract description 6
- 238000000926 separation method Methods 0.000 claims abstract description 5
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 36
- 238000010438 heat treatment Methods 0.000 claims description 34
- 150000003839 salts Chemical class 0.000 claims description 26
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims description 16
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 16
- KWSLGOVYXMQPPX-UHFFFAOYSA-N 5-[3-(trifluoromethyl)phenyl]-2h-tetrazole Chemical compound FC(F)(F)C1=CC=CC(C2=NNN=N2)=C1 KWSLGOVYXMQPPX-UHFFFAOYSA-N 0.000 claims description 14
- 229910001379 sodium hypophosphite Inorganic materials 0.000 claims description 14
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 12
- 239000001103 potassium chloride Substances 0.000 claims description 8
- 235000011164 potassium chloride Nutrition 0.000 claims description 8
- 230000000630 rising effect Effects 0.000 claims description 6
- 239000002904 solvent Substances 0.000 claims description 6
- 238000002604 ultrasonography Methods 0.000 claims description 4
- 239000003795 chemical substances by application Substances 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 230000035484 reaction time Effects 0.000 claims description 3
- 230000002349 favourable effect Effects 0.000 abstract description 5
- 238000006555 catalytic reaction Methods 0.000 abstract 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 19
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 15
- 238000001035 drying Methods 0.000 description 15
- 239000001257 hydrogen Substances 0.000 description 15
- 229910052739 hydrogen Inorganic materials 0.000 description 15
- 239000010453 quartz Substances 0.000 description 15
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 15
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 14
- 239000001301 oxygen Substances 0.000 description 14
- 229910052760 oxygen Inorganic materials 0.000 description 14
- 239000008367 deionised water Substances 0.000 description 13
- 229910021641 deionized water Inorganic materials 0.000 description 13
- 230000003197 catalytic effect Effects 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 11
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 10
- 238000005406 washing Methods 0.000 description 10
- 229910052757 nitrogen Inorganic materials 0.000 description 9
- 239000012018 catalyst precursor Substances 0.000 description 8
- 230000000694 effects Effects 0.000 description 8
- 229910021607 Silver chloride Inorganic materials 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 7
- 229910052723 transition metal Inorganic materials 0.000 description 7
- 150000003624 transition metals Chemical class 0.000 description 7
- 238000011010 flushing procedure Methods 0.000 description 6
- 238000001000 micrograph Methods 0.000 description 6
- 238000011144 upstream manufacturing Methods 0.000 description 6
- 238000001816 cooling Methods 0.000 description 5
- 239000003792 electrolyte Substances 0.000 description 5
- 150000002815 nickel Chemical class 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
- 239000010411 electrocatalyst Substances 0.000 description 3
- 239000007795 chemical reaction product Substances 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000005868 electrolysis reaction Methods 0.000 description 2
- 239000006261 foam material Substances 0.000 description 2
- 230000001788 irregular Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 230000027756 respiratory electron transport chain Effects 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 108010020056 Hydrogenase Proteins 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 229910000365 copper sulfate Inorganic materials 0.000 description 1
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 description 1
- 238000002484 cyclic voltammetry Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000000840 electrochemical analysis Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 239000008235 industrial water Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- -1 oxides Chemical class 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 125000004437 phosphorous atom Chemical group 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 230000007096 poisonous effect Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
Classifications
-
- 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
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
- C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
-
- 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
-
- 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
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
- C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
- C25B11/031—Porous electrodes
-
- 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
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
- C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
- C25B11/061—Metal or alloy
-
- 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
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Catalysts (AREA)
Abstract
The invention provides a cobalt phosphide electrolytic water catalyst and a preparation method thereof, wherein the preparation method comprises the following steps: (1) Soaking the foam nickel in polyvinylpyrrolidone solution, and reacting to obtain modified foam nickel; (2) Mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, adding the modified foam nickel into the mixed solution, and reacting to obtain a metal organic framework ZIF-67@foam nickel material; (3) And (3) under the nitrogen atmosphere, performing a separation type gas phosphating reaction on the metal organic framework ZIF-67@foamed nickel material to obtain the cobalt phosphide electrolytic water catalyst. The cobalt phosphide catalyst prepared by the method has higher specific surface area and porosity, is favorable for exposing active sites, and has excellent electrolytic water catalysis performance.
Description
Technical Field
The invention relates to the technical field of catalysts, in particular to a cobalt phosphide electrolytic water catalyst and a preparation method thereof.
Background
The water electrolysis catalyst can accelerate reaction kinetics, reduce energy barrier of water decomposition and save energy consumption; the electrolyzed water catalyst comprises a noble metal-based electrocatalyst and a non-noble transition metal-based electrocatalyst, the noble metal-based electrocatalyst has excellent electrolyzed water catalytic performance, however, the raw materials are rare and expensive, so that the method cannot be widely applied to industrial water electrolysis hydrogen production; in recent years, materials such as non-noble transition metal phosphides, carbides, nitrides, oxides, and hydroxides exhibit excellent electrocatalytic properties.
The transition metal phosphide has a structure similar to that of hydrogenase, and the P atom with negative charge in the catalyst can capture proton and serve as H 2 The dissociated sites are also active sites for reducing oxygen molecules into hydroxyl groups, however, the transition metal phosphide prepared by the prior art has irregular morphology, and the surface active sites are exposed less, so that the catalytic performance of the transition metal phosphide cannot be fully exerted, and therefore, based on the problems, a transition metal phosphide catalyst with better catalytic performance needs to be studied.
Disclosure of Invention
The cobalt phosphide catalyst prepared by the method has higher specific surface area and porosity, is favorable for exposing active sites and has excellent electrolyzed water catalytic performance.
In a first aspect, the invention provides a method for preparing a cobalt phosphide electrolytic water catalyst, which comprises the following steps:
(1) Soaking the foam nickel in polyvinylpyrrolidone solution, and reacting to obtain modified foam nickel;
(2) Mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, adding the modified foam nickel into the mixed solution, and reacting to obtain a metal organic framework ZIF-67@foam nickel material;
(3) And (3) under the nitrogen atmosphere, performing a separation type gas phosphating reaction on the metal organic framework ZIF-67@foamed nickel material to obtain the cobalt phosphide electrolytic water catalyst.
Preferably, in step (1), the solvent of the polyvinylpyrrolidone solution is hydrochloric acid; the mass concentration of the polyvinylpyrrolidone solution is 1-30%.
Preferably, in the polyvinylpyrrolidone solution, the relative molecular mass of polyvinylpyrrolidone is 0.8-130 ten thousand; preferably, the polyvinylpyrrolidone has a relative molecular mass of 0.8 to 22 ten thousand.
Preferably, in the step (1), the temperature of the reaction is 25-30 ℃ and the time is 25-35 min; the reaction is preferably carried out under ultrasound conditions.
Preferably, in step (2), the solvents of the cobalt nitrate hexahydrate solution and the 2-methylimidazole solution are both anhydrous methanol;
the molar ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1: (1-10).
Preferably, in the step (2), the temperature of the reaction is 25-30 ℃ and the time is 25-35 min; the reaction is preferably carried out under ultrasonic conditions of 20 to 40 kHz.
Preferably, in step (3), the phosphating agent used in the split gas phosphating reaction is sodium hypophosphite;
the reaction temperature is 300-500 ℃ and the reaction time is 1.5-2.5 h; the temperature rising rate is 8-12 ℃/min.
Preferably, before the step (3), the method further comprises the step of placing the metal organic framework ZIF-67@foamed nickel material in a molten salt medium for heating reaction under a nitrogen atmosphere.
Preferably, the molten salt medium comprises potassium chloride and lithium chloride, wherein the molar ratio of the potassium chloride to the lithium chloride is (1-10): (10-1).
Preferably, the temperature of the heating reaction is 500-800 ℃ and the time is 1.5-2.5 h; the temperature rising rate is 2-10 ℃/min.
In a second aspect, the present invention provides a cobalt phosphide electrolytic water catalyst as described in any one of the first aspects above.
Compared with the prior art, the invention has at least the following beneficial effects:
(1) Firstly, polyvinylpyrrolidone is adopted to modify foam nickel, then the modified foam nickel is compounded with a metal organic frame, so that a metal organic frame ZIF-67 grows on the surface of the modified foam nickel, and finally, the modified foam nickel is subjected to phosphating treatment to prepare a cobalt phosphide catalyst, so that the modified foam nickel is beneficial to the activity expression of the catalyst, the diffusion and electron transfer of electrolyte are facilitated, and the catalytic performance of the prepared cobalt phosphide catalyst is more excellent; meanwhile, the cobalt phosphide catalyst well maintains the polyhedral shape of the metal organic framework template, has higher specific surface area and porosity, and is favorable for exposing the active site of the cobalt phosphide catalyst, so that the cobalt phosphide catalyst has excellent electrocatalytic hydrogen evolution and electrocatalytic oxygen evolution performances.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an electron scanning electron microscope image of a metal organic framework ZIF-67@foam nickel material provided in example 1 of the present invention;
FIG. 2 is an electron scanning electron microscope image of the metal organic framework ZIF-67@foam nickel material provided in example 2 of the present invention;
FIG. 3 is an electron scanning electron microscope image of the metal organic framework ZIF-67@foam nickel material provided in example 3 of the present invention;
FIG. 4 is an electron scanning electron microscope image of the metal organic framework ZIF-67@foam nickel material provided in example 4 of the present invention;
FIG. 5 is an electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material provided in the embodiment 7 of the invention after molten salt heat treatment;
FIG. 6 is an electron scanning electron microscope image of a metal organic framework ZIF-67@foamed nickel material provided in example 10 of the present invention after heat treatment;
FIG. 7 is an AC impedance plot of a cobalt phosphide electrolyzed water catalyst provided in examples 1 to 4 of the present invention;
FIG. 8 is a graph of capacitance current density versus scan rate for a cobalt phosphide water-splitting catalyst according to examples 1-4 of the present invention having an overpotential of 0.25V;
FIG. 9 is a graph showing oxygen evolution activity of a cobalt phosphide electrolytic water catalyst provided in examples 1 to 4 and comparative examples 2 to 3 of the present invention in a KOH solution at 1 mol/L;
FIG. 10 is a Tafel slope plot of a cobalt phosphide electrolyzed water catalyst provided in examples 1 to 4 and comparative examples 2 to 3 of the present invention;
FIG. 11 is a graph showing hydrogen evolution activity of a cobalt phosphide electrolytic water catalyst according to examples 7 to 9 of the present invention;
FIG. 12 is a graph showing the slope of Tafel hydrogen evolution for a cobalt phosphide electrolyzed water catalyst according to examples 7 to 9 of the present invention;
FIG. 13 is a graph showing oxygen evolution activity of a cobalt phosphide electrolytic water catalyst according to examples 7 to 9 of the present invention;
fig. 14 is a graph showing the slope of oxygen evolution Tafel of a cobalt phosphide electrolyzed water catalyst according to examples 7 to 9 of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments, and all other embodiments obtained by those skilled in the art without making any inventive effort based on the embodiments of the present invention are within the scope of protection of the present invention.
The transition metal phosphide catalyst prepared in the prior art has larger particle size and irregular morphology, so that the surface active sites of the catalyst are fewer, and the catalyst prepared by the catalyst has poorer catalytic performance, therefore, the embodiment of the invention provides a preparation method of the cobalt phosphide electrolytic water catalyst, which comprises the following steps:
(1) Soaking the foam nickel in polyvinylpyrrolidone solution, and reacting to obtain modified foam nickel;
(2) Mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, adding the modified foam nickel into the mixed solution, and reacting to obtain a metal organic framework ZIF-67@foam nickel material;
(3) And (3) under the nitrogen atmosphere, performing a separation type gas phosphating reaction on the metal organic framework ZIF-67@foamed nickel material to obtain the cobalt phosphide electrolytic water catalyst.
According to the invention, firstly, foamed nickel is soaked in a polyvinylpyrrolidone solution, the surface of the foamed nickel can be modified by the polyvinylpyrrolidone, then, the modified foamed nickel is soaked in a mixed solution containing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution, and a metal organic framework ZIF-67 grows on the surface of the foamed nickel, so that a metal organic framework ZIF-67@foamed nickel material is obtained, and finally, the metal organic framework ZIF-67@foamed nickel material is subjected to phosphating treatment, so that the cobalt phosphide electrolytic water catalyst is prepared.
According to some preferred embodiments, in step (1), the solvent of the polyvinylpyrrolidone solution is hydrochloric acid; the polyvinylpyrrolidone solution has a mass concentration of 1-30% (e.g., may be 1%, 5%, 10%, 15%, 20%, 25% or 30%);
in the polyvinylpyrrolidone solution, the relative molecular mass of polyvinylpyrrolidone is 0.8-130 ten thousand (for example, 0.8 ten thousand, 1 ten thousand, 5 ten thousand, 5.8 ten thousand, 8 ten thousand, 10 ten thousand, 15 ten thousand, 22 ten thousand, 40 ten thousand, 80 ten thousand, 100 ten thousand or 130 ten thousand; preferably, the polyvinylpyrrolidone has a relative molecular mass of 0.8 to 22 ten thousand (e.g., may be 0.8 ten thousand, 1 ten thousand, 5 ten thousand, 10 ten thousand, 15 ten thousand, 20 ten thousand, or 22 ten thousand).
In the invention, the polyvinylpyrrolidone with the relative molecular mass is adopted to modify and modify the foam nickel, the polyvinylpyrrolidone can be attached to the surface of the foam nickel, and the size of a metal organic framework ZIF-67 grown on the surface of the foam nickel can be controlled by controlling the relative molecular mass of the polyvinylpyrrolidone attached to the surface of the foam nickel, so that the prepared cobalt phosphide catalyst has larger electrochemical active area and excellent catalytic activity; experiments prove that when the relative molecular weight of the polyvinylpyrrolidone is in the range, the electrocatalytic performance of the catalyst is more favorable to be improved, and if the relative molecular weight of the polyvinylpyrrolidone is higher than the range, the viscosity is relatively higher, so that the dispersion of ZIF-67 and active sites on the surface of the nickel foam is unfavorable, and the catalytic performance of the catalyst is further reduced; meanwhile, because the small-size nano material is superior to the active expression of the catalyst, the relative molecular mass of polyvinylpyrrolidone is preferably 0.8-22 ten thousand in the invention, which is more beneficial to preparing the cobalt phosphide catalyst with better catalytic performance.
According to some preferred embodiments, in step (1), the temperature of the reaction is 25-30 ℃ (e.g., may be 25 ℃, 26 ℃, 27 ℃, 28 ℃, 29 ℃ or 30 ℃), for 25-35 min (e.g., may be 25min, 28min, 30min, 32min or 35 min); the reaction is preferably carried out under ultrasound conditions.
In the invention, when preparing modified nickel foam, a certain mass of polyvinylpyrrolidone is firstly dissolved in 2mol/L hydrochloric acid to prepare a polyvinylpyrrolidone solution with a mass concentration of 1-30%, then the nickel foam is cut into slices with a specification of 1cm multiplied by 2cm and a thickness of 0.3-2 mm, the cut nickel foam is immersed in the polyvinylpyrrolidone solution, and then ultrasonic reaction is carried out at room temperature, so that the successful adhesion of polyvinylpyrrolidone on the surface of the nickel foam can be ensured, and the nickel foam is modified.
In the invention, after modification of the foamed nickel by using the polyvinylpyrrolidone solution, the method further comprises the steps of taking the modified foamed nickel out of the polyvinylpyrrolidone solution and washing and drying, wherein deionized water can be used for repeatedly washing the foamed nickel, for example, the washing can be carried out for 2-3 times, and the foamed nickel can be washed cleanly and placed in a vacuum oven at 60 ℃ for drying, so that the modified foamed nickel material can be obtained.
According to some preferred embodiments, in step (2), the solvent of the cobalt nitrate hexahydrate solution and the 2-methylimidazole solution are both anhydrous methanol;
the molar ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1: (1-10) (e.g., may be 1:1, 1:2, 1:4, 1:5, 1:6, 1:8, or 1:10).
According to some preferred embodiments, in step (2), the temperature of the reaction is 25-30 ℃ (e.g., may be 25 ℃, 27 ℃, 28 ℃, 29 ℃ or 30 ℃) for 25-35 min (e.g., may be 25min, 28min, 30min, 32min or 35 min); the reaction is preferably carried out under ultrasound conditions.
In the invention, when preparing a metal organic framework ZIF-67@foamed nickel material, cobalt nitrate hexahydrate and 2-methylimidazole can be respectively dissolved in absolute methanol to prepare a cobalt nitrate hexahydrate solution with the concentration of 0.1mol/L and a 2-methylimidazole solution with the concentration of 0.4mol/L, then the 2-methylimidazole solution is slowly poured into the cobalt nitrate hexahydrate solution, the cobalt nitrate hexahydrate solution is mixed to obtain a mixed solution, the modified foamed nickel is placed in the mixed solution for ultrasonic reaction, the mixed solution is placed for 24 hours after the ultrasonic reaction, the reacted foamed nickel material is taken out from the solution, and is washed for 3-4 times by adopting methanol, and finally the mixed solution is placed in a vacuum oven at 60 ℃ for drying for 12 hours to obtain the metal organic framework ZIF-67@foamed nickel material, which can also be called ZIF-67/NF material or ZIF-67@NF material for short.
According to some preferred embodiments, in step (3), the phosphating agent used in the split gas phosphating reaction is sodium hypophosphite; the temperature of the phosphating reaction is 300-500 ℃ (for example, 300 ℃, 350 ℃, 400 ℃, 450 ℃ or 500 ℃) and the time is 1.5-2.5 h (for example, 1.5h, 1.8h, 2h or 2.5 h); the temperature rise rate is 8 to 12 ℃/min (for example, 8 ℃/min, 9 ℃/min, 10 ℃/min or 12 ℃/min).
In the invention, after the metal organic framework ZIF-67@foamed nickel material is prepared, sodium hypophosphite powder is adopted to carry out phosphating treatment, and at the moment, the metal cobalt and the metal nickel in the ZIF-67@NF material can be heated and decomposed by sodium hypophosphite to form PH 3 The phosphating is cobalt phosphide, so as to obtain cobalt phosphide catalyst, in the invention, the too low or too high temperature of the phosphating reaction is unfavorable for the sufficient occurrence of the phosphating reaction, if the temperature of the phosphating reaction is too low, naH 2 PO 2 Thermal decomposition to produce pH 3 Too slowly, if the temperature of the phosphating reaction is too high, the pH 3 Is easy to run off. Meanwhile, since sodium hypophosphite is easily oxidized and the pH generated after decomposition thereof 3 As poisonous gas, when separating phosphating reaction is carried out, a quartz boat filled with sodium hypophosphite can be arranged at the upstream of a tube furnace, ZIF-67@NF material is arranged at the downstream of the tube furnace, firstly inert gas is introduced into the quartz boat, then the quartz boat is heated to a target temperature, after the reaction, the quartz boat is naturally cooled, deionized water and absolute ethyl alcohol are used for washing 2 to 3 times, and finally the quartz boat is placed at 60 ℃ in vacuumAnd drying in an oven to obtain the cobalt phosphide electrolytic water catalyst. In the present invention, the pH generated by the pyrolysis of sodium hypophosphite can be absorbed by a copper sulfate solution 3 The part of the gas which does not participate in the reaction.
According to some preferred embodiments, before step (3), the method further comprises the step of placing the metal organic framework ZIF-67@foamed nickel material in a molten salt medium under nitrogen atmosphere for heating reaction.
In the invention, before the phosphating reaction, the metal organic framework ZIF-67@foamed nickel material is placed in a fused salt medium for heat treatment, and the fused salt medium can permeate into the interior of the metal organic framework ZIF-67, so that the pore structure of the surface of the metal organic framework ZIF-67 is further richer, the exposure of the surface active sites of the cobalt phosphide catalyst is facilitated, the catalytic performance of the cobalt phosphide catalyst is fully exerted, and the catalytic performance of the cobalt phosphide catalyst is further enhanced.
According to some preferred embodiments, in step (3), the molten salt medium comprises potassium chloride and lithium chloride, wherein the molar ratio of potassium chloride to lithium chloride is (1-10): (10-1) (e.g., may be 1:10, 0.5:2, 1:1, 1:2, 1:5, 2:3, 2:2, 3:2, 4:2, 4:5, 8:2, 9:1, 10:6, or 10:1), more preferably, the molar ratio of the potassium chloride to the lithium chloride is (0.5-2): 5.
according to the invention, firstly, the prepared metal organic framework ZIF-67@foamed nickel material is placed in a fused salt medium for heat treatment, and due to the template effect of the fused salt medium, a special liquid environment can be provided in the fused salt heat treatment process so as to permeate into the ZIF-67, after washing, the fused salt on the surface of the ZIF-67 is removed, so that the surface of the ZIF-67 maintains a rich pore structure, the specific surface area of the prepared catalyst is increased, the exposure quantity of active sites is increased, and the diffusion and electron transfer of electrolyte on the surface of the catalyst are facilitated, so that the cobalt phosphide catalyst has excellent hydrogen evolution and oxygen evolution performances. Meanwhile, in the invention, the template effect on cobalt phosphide can be further enhanced by controlling the molar ratio of the molten salt medium, so that more active sites are exposed.
According to some preferred embodiments, the heating reaction is carried out at a temperature of 500-800 ℃ (e.g., may be 500 ℃,600 ℃, 700 ℃, or 800 ℃) for a time of 1.5-2.5 hours (e.g., may be 1.5 hours, 1.8 hours, 2 hours, or 2.5 hours); in the invention, the molten salt heat treatment is preferably carried out in the temperature range, so that the ZIF-67@foamed nickel material of the metal organic framework is more favorable for exposing more internal sites under the strong polarization effect of molten salt medium, when the temperature is lower than the range, the fluidity of molten salt is poor, the molten salt is difficult to enter the interior of the ZIF-67@foamed nickel material, and a rich cavity structure cannot be formed to expose more active sites, and when the temperature is too high, the framework structure of the ZIF-67@foamed nickel material is collapsed.
The temperature rising rate of the reaction is 2-10 ℃/min (for example, the temperature rising rate can be 2 ℃/min, 5 ℃/min, 8 ℃/min or 10 ℃/min), and the temperature lowering rate is 3-5 ℃/min (3 ℃/min, 4 ℃/min or 5 ℃/min).
In the invention, when the metal organic framework ZIF-67@foamed nickel material is subjected to molten salt heat treatment, a molten salt medium with a certain molar ratio is firstly mixed and then ground, the metal organic framework ZIF-67@foamed nickel material is firstly placed in a quartz boat, the ground molten salt medium is then added into the quartz boat, the quartz boat is placed in a tube furnace and is heated according to a certain heating rate, and in the invention, the temperature is preferably raised and lowered in a stage manner, so that the framework structure of the ZIF-67@foamed nickel material is better protected, the temperature is raised at a speed of 6-10 ℃/min when the temperature is lower than 500 ℃, the temperature is raised at a speed of 2-5 ℃/min when the temperature is higher than 500 ℃, and the constant temperature reaction is kept after the temperature is raised to a target temperature; after the reaction is finished, the temperature is reduced at a speed of 3-5 ℃/min at a temperature higher than 500 ℃, the temperature is naturally cooled at a temperature lower than 500 ℃, and then the product is placed in a vacuum drying oven at 60 ℃ for storage for standby.
Before the phosphating reaction and the molten salt heat treatment are carried out, nitrogen can be firstly introduced into the reactor, oxygen is discharged, and the time for introducing the nitrogen is 25-35 min, so that the ZIF-67@foamed nickel material can be prevented from being oxidized.
The invention also provides a cobalt phosphide electrolytic water catalyst which is prepared by adopting the preparation method of any one of the above.
In order to more clearly illustrate the technical scheme and advantages of the invention, a cobalt phosphide electrolytic water catalyst and a preparation method thereof are described in detail below through several examples.
Example 1:
(1) Adding polyvinylpyrrolidone with relative molecular mass of 0.8 ten thousand into 40mL of 2mol/L hydrochloric acid to prepare polyvinylpyrrolidone solution with mass concentration of 1%, soaking foam nickel with mass concentration of 1 multiplied by 2cm into the polyvinylpyrrolidone solution, carrying out ultrasonic reaction at 25 ℃ for 30min, taking out the foam nickel from the polyvinylpyrrolidone solution, washing with deionized water for 3 times, and drying in a vacuum oven at 60 ℃ for 6h to obtain modified foam nickel;
(2) Dissolving 5.8206g of cobalt nitrate hexahydrate in 200mL of absolute methanol to obtain a cobalt nitrate hexahydrate solution, dissolving 6.5683g of 2-methylimidazole in 200mL of absolute methanol to obtain a 2-methylimidazole solution, slowly pouring the 2-methylimidazole solution into the cobalt nitrate hexahydrate solution, carrying out ultrasonic reaction at 25 ℃ for 30min, standing for 24h to obtain a mixed solution, taking out the modified nickel foam from the mixed solution, washing 3 times with methanol, and drying in a vacuum oven at 60 ℃ for 12h to obtain a metal organic framework ZIF-67@nickel foam material; wherein, the mol ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1:4;
(3) And (3) placing a quartz boat filled with 1g of sodium hypophosphite powder on the upstream of a tube furnace, placing a metal organic framework ZIF-67@foamed nickel material on the downstream of the tube furnace, introducing nitrogen for 30min, heating the tube furnace to 300 ℃ according to the heating rate of 10 ℃/min, reacting at constant temperature for 2h, naturally cooling to room temperature of 25 ℃, flushing with deionized water and absolute ethyl alcohol for 3 times respectively, and drying in a vacuum oven at 60 ℃ for 12h to obtain the cobalt phosphide electrolytic water catalyst which is recorded as ZIF-67/NF-1-300 x 1P.
Example 2:
example 2 is substantially the same as example 1 except that in step (1), the relative molecular mass of polyvinylpyrrolidone at the time of preparing the modified nickel foam is 5.8 ten thousand; is denoted as ZIF-67/NF-2-300 x 1P.
Example 3:
example 3 is essentially the same as example 1 except that in step (1) a modified nickel foam is prepared, the polyvinylpyrrolidone has a relative molecular mass of 22 ten thousand, denoted as ZIF-67/NF-3-300 x 1p.
Example 4:
example 4 is essentially the same as example 1 except that in step (1) a modified nickel foam is prepared, the polyvinylpyrrolidone has a relative molecular mass of 130 ten thousand, denoted as ZIF-67/NF-4-300 x 1p.
FIGS. 1 to 4 show surface morphology graphs of the metal-organic frameworks ZIF-67@foamed nickel prepared in examples 1 to 4, respectively, and it can be seen from the graphs that ZIF-67 grown on the foamed nickel treated with polyvinylpyrrolidone of different relative molecular masses in examples 1 to 4 are dodecahedrons with distinct edges and corners, and the sizes of the dodecahedrons are respectively distributed between 500-800, 700-1000 and 800-1200 nm; it is clear that the ZIF-67 size of the surface of the nickel foam treated with polyvinylpyrrolidone having a relatively large molecular weight is also increased.
As can be seen from fig. 7, the charge transfer resistances of the cobalt phosphide catalyst surfaces in examples 1 to 4 are 5.970 Ω, 43.298 Ω, 63.454 Ω and 100.095 Ω, respectively, and as the relative molecular mass of polyvinylpyrrolidone decreases, the charge transfer resistance of the cobalt phosphide catalyst surfaces decreases and the hydrogen evolution performance improves; as can be seen from FIG. 8, the electric double layer capacitance values of the cobalt phosphide catalysts in examples 1 to 4 were estimated by cyclic voltammograms in the non-Faraday region of 0.2 to 0.3V vs. RHE, and the electric double layer capacitance values in examples 1 to 4 were 21.11 mF.cm, respectively -2 、3.94mF·cm -2 、3.14mF·cm -2 And 2.88 mF.cm -2 Along with the reduction of the relative molecular mass of polyvinylpyrrolidone, the electric double layer capacitance value of the cobalt phosphide catalyst is increased, and the hydrogen evolution performance is improved; the cobalt phosphide catalysts prepared in examples 1 to 4 have better alkaline hydrogen evolution performance.
As can be seen from FIG. 9, the cobalt phosphide catalysts in examples 1 to 4 reached 10 mA.cm -2 Is of (a)The overpotential of the flow densities were 384mV,393mV, 383 mV and 401mV, respectively, which revealed that the cobalt phosphide catalysts prepared in examples 1 to 4 of the present invention had good oxygen evolution activity.
Example 5:
example 5 is essentially the same as example 1 except that in step (3), sodium hypophosphite powder is 0.5g, noted ZIF-67/NF-1-300 x 0.5p.
Hydrogen evolution performance: the cobalt phosphide catalyst prepared in example 5 had a current density of 10 mA.cm -2 At the same time, the overpotential in example 5 was 146mV, and the current density was 100 mA.cm -2 At an overpotential of 440mV, tafel slope value of 130.1 mV.dec -1 The method comprises the steps of carrying out a first treatment on the surface of the Oxygen evolution performance: the cobalt phosphide catalyst prepared in example 5 had a current density of 10 mA.cm -2 The overpotential in example 5 was 398mV and the current density was 100mA cm -2 At the time of overpotential is 319 mV, tafel slope value is 63.3 mV.dec -1 。
Example 6:
example 6 was substantially the same as example 1, except that in step (3), a quartz boat containing 1g of sodium hypophosphite powder was placed upstream of a tube furnace, a catalyst precursor was placed downstream of the tube furnace, after introducing nitrogen gas for 35 minutes, the tube furnace was warmed to 500 ℃ at a warming rate of 10 ℃/min, reacted at constant temperature for 2 hours, naturally cooled to room temperature of 25 ℃, rinsed 3 times with deionized water and absolute ethyl alcohol, respectively, and dried in a vacuum oven at 60 ℃ for 12 hours to obtain a cobalt phosphide electrolyzed water catalyst, denoted as ZIF-67/NF-1-500 x 1p.
Hydrogen evolution performance: the cobalt phosphide catalyst prepared in example 6 had a current density of 10 mA.cm -2 At the time, the overpotential in example 6 was 270mV, and the current density was 100 mA.cm -2 At the time of overpotential being 624mV, tafel slope value 188.9 mV.dec -1 The method comprises the steps of carrying out a first treatment on the surface of the Oxygen evolution performance: the cobalt phosphide catalyst prepared in example 6 had a current density of 10 mA.cm -2 At the time, the overpotential in example 6 was 380mV, and the current density was 100 mA.cm -2 At an overpotential of 603mV, tafel slope value of 62.0 mV.dec -1 。
Example 7:
(1) Adding polyvinylpyrrolidone with relative molecular mass of 0.8 ten thousand into 40mL of 2mol/L hydrochloric acid to prepare polyvinylpyrrolidone solution with mass concentration of 1%, soaking foam nickel with mass concentration of 1 multiplied by 2cm into the polyvinylpyrrolidone solution, carrying out ultrasonic reaction at 25 ℃ for 30min, taking out the foam nickel from the polyvinylpyrrolidone solution, washing with deionized water for 3 times, and drying in a vacuum oven at 60 ℃ for 6h to obtain modified foam nickel;
(2) Mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, adding modified foam nickel into the mixed solution, carrying out ultrasonic reaction for 30min at 25 ℃, standing for 24h, taking out the modified foam nickel from the mixed solution, washing 3 times with methanol, and drying in a vacuum oven at 60 ℃ for 12h to obtain a metal organic framework ZIF-67@foam nickel material; wherein, the mol ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1:4;
(3) Mixing and grinding 1.6191g of potassium chloride and 1.3809g of lithium chloride to obtain a molten salt medium, placing a metal organic framework ZIF-67@foamed nickel material into a quartz boat, adding the molten salt medium, placing the quartz boat into the middle section of a tubular furnace, introducing nitrogen for 30min, heating the tubular furnace to 400 ℃ at a heating rate of 10 ℃/min, reacting at a constant temperature for 2h, cooling to the room temperature of 25 ℃ at a heating rate of 5 ℃/min, flushing with deionized water and absolute ethyl alcohol for 3 times respectively, and drying in a vacuum oven at 60 ℃ for 12h to obtain a catalyst precursor;
(4) And (3) placing a quartz boat filled with 1g of sodium hypophosphite powder on the upstream of a tube furnace, placing a catalyst precursor on the downstream of the tube furnace, introducing nitrogen for 30min, heating the tube furnace to 300 ℃ according to the heating rate of 10 ℃/min, reacting at constant temperature for 2h, naturally cooling to room temperature of 25 ℃, respectively flushing with deionized water and absolute ethyl alcohol for 3 times, and drying in a vacuum oven at 60 ℃ for 12h to obtain the cobalt phosphide electrolyzed water catalyst which is recorded as ZIF-67/NF-1-400s-300 x 1P.
Example 8:
example 8 is substantially the same as example 7, except that in step (3), when preparing the catalyst precursor, the tube furnace is heated to 500 ℃ at a heating rate of 10 ℃/min, then the tube furnace is heated to 600 ℃ at a heating rate of 2 ℃/min, the reaction is carried out at a constant temperature of 600 ℃ for 2 hours, firstly, the temperature is reduced to 500 ℃ at a rate of 5 ℃/min, then the reaction product is naturally cooled to room temperature of 25 ℃, the reaction product is respectively rinsed 3 times with deionized water and absolute ethyl alcohol, and dried in a vacuum oven at 60 ℃ for 12 hours, thus obtaining the catalyst precursor, which is denoted as ZIF-67/NF-1-600s-300 x 1p.
Example 9:
example 9 is substantially the same as example 7, except that in step (3), when preparing the catalyst precursor, the tube furnace is heated to 500 ℃ at a heating rate of 8 ℃/min, then heated to 800 ℃ at a heating rate of 4 ℃/min, reacted at a constant temperature of 800 ℃ for 2 hours, cooled to 500 ℃ at a heating rate of 5 ℃/min, naturally cooled to room temperature of 25 ℃, rinsed 3 times with deionized water and absolute ethyl alcohol respectively, and dried in a vacuum oven at 60 ℃ for 12 hours to obtain the catalyst precursor, which is denoted as ZIF-67/NF-1-800s-300 x 1p.
FIGS. 11 to 14 show graphs of hydrogen evolution performance and oxygen evolution performance of the cobalt phosphide catalysts prepared in examples 7 to 9, respectively, as can be seen from FIGS. 11 to 12, at a current density of 10 mA.cm -2 The overpotential in examples 7 to 9 was 211, 205, 181mV,100mA cm, respectively -2 The required overpotential is 516, 492, 463 mV, tafel slopes 155.5, 142.3 and 132.8mV dec, respectively -1 The hydrogen evolution performance of the prepared catalyst is gradually improved along with the increase of the heat treatment temperature of the molten salt; as can be seen from FIGS. 13 to 14, the temperature was set at 10 mA.cm -2 The overpotential for the catalysts of examples 7 to 9 were 437, 433 and 437mV, respectively, and the corresponding Tafel slopes were 70.8, 76.4 and 71.4 mV.dec, respectively -1 With the increase of the molten salt heat treatment temperature, the oxygen evolution performance of the prepared catalyst is gradually improved.
Example 10:
example 10 is substantially the same as example 7, except that in step (3), a metal organic framework ZIF-67@nickel foam material is placed in the middle section of a tube furnace, nitrogen is introduced into the tube furnace for 30min, the tube furnace is heated to 800 ℃ according to a heating rate of 10 ℃/min, the temperature is kept constant for 2h, the temperature is reduced to room temperature of 25 ℃ at a rate of 5 ℃/min, deionized water and absolute ethyl alcohol are respectively used for flushing 3 times, and the catalyst precursor is obtained after drying in a vacuum oven at 60 ℃ for 12h, and is recorded as ZIF-67/NF-1-800-300 x 1P.
Hydrogen evolution performance: the cobalt phosphide catalyst prepared in example 10 had a current density of 10 mA.cm -2 At the time, the overpotential in example 10 was 259mV, and the current density was 100 mA.cm -2 At an overpotential of 750 mV, tafel slope value of 164.1 mV.dec -1 The method comprises the steps of carrying out a first treatment on the surface of the Oxygen evolution performance: the cobalt phosphide catalyst prepared in example 10 had a current density of 10 mA.cm -2 At this point, the overpotential in example 10 was 481mV and the Tafel slope value was 74.4 mV.dec -1 。
Comparative example 1:
(1) Dissolving 5.8206g of cobalt nitrate hexahydrate in 200mL of absolute methanol to obtain a cobalt nitrate hexahydrate solution, dissolving 6.5683g of 2-methylimidazole in 200mL of absolute methanol to obtain a 2-methylimidazole solution, slowly pouring the 2-methylimidazole solution into the cobalt nitrate hexahydrate solution, carrying out ultrasonic reaction at 25 ℃ for 30min, standing for 24h, carrying out centrifugal separation at 6000r/min for 5min, washing 3 times with methanol, and drying in a vacuum oven at 60 ℃ for 12h to obtain a metal organic framework ZIF-67; wherein, the mol ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1:4;
(2) And (3) placing a quartz boat filled with 1g of sodium hypophosphite powder on the upstream of a tube furnace, placing a metal organic framework ZIF-67 on the downstream of the tube furnace, introducing nitrogen for 30min, heating the tube furnace to 300 ℃ according to the heating rate of 10 ℃/min, carrying out constant-temperature reaction for 2h, naturally cooling to room temperature of 25 ℃, respectively flushing with deionized water and absolute ethyl alcohol for 3 times, and drying in a vacuum oven at 60 ℃ for 12h to obtain the cobalt phosphide electrolytic water catalyst, wherein the cobalt phosphide electrolytic water catalyst is recorded as ZIF-67-300 x 1P.
Hydrogen evolution performance: the cobalt phosphide catalyst prepared in comparative example 1 had a current density of 10 mA.cm -2 At the time, the overpotential in comparative example 1 was made to be 351mV, and the Tafel slope value was 203.9 mV.dec -1 . Comparative example 2:
comparative example 2 is essentially the same as example 7 except that in step (2) the nickel foam used was nickel foam not modified with polyvinylpyrrolidone and was denoted as ZIF-67/NF-300 x 1p.
Comparative example 3:
placing a quartz boat filled with 1g of sodium hypophosphite powder on the upstream of a tube furnace, placing 1X 2cm of foam nickel on the downstream of the tube furnace, introducing nitrogen for 30min, heating the tube furnace to 300 ℃ according to the heating rate of 10 ℃/min, reacting for 2h at constant temperature, naturally cooling to room temperature of 25 ℃, respectively flushing with deionized water and absolute ethyl alcohol for 3 times, drying in a vacuum oven at 60 ℃ for 12h, and obtaining an electrolyzed water catalyst which is marked as NF-300 x 1P.
As can be seen from FIG. 9, the catalysts prepared in comparative example 2 and comparative example 3 reached 10mA cm -2 The overpotential of the current density of (a) was 349mV and 343mV, respectively.
The catalysts of examples 1 to 10 and comparative examples 1 to 4 were subjected to electrochemical performance tests, and the test results are shown in table 1.
The test method comprises the following steps: the electrochemical test adopts a Chenhua electrochemical workstation CHI660E, and the test temperature is room temperature. To avoid the influence of oxygen in the electrolyte on the electrode performance test result, the test is carried out at 10 mL.min before the test -1 Nitrogen was introduced into the electrolyte at a rate of 30min. The catalytic performance characterization of both HER and OER of the catalyst was tested on a standard three electrode system; the fully decomposed water adopts a two-electrode system. In a three-electrode system, the reference electrode is Ag/AgCl (E Ag/AgCl =0.223V vs NHE), the counter electrode is a Pt sheet. Respectively in alkaline (1M KOH) and acidic (0.5. 0.5M H) 2 SO 4 ) The test was performed in an electrolyte solution. The potential measured at the electrochemical workstation (vs Ag/AgCl) was converted to an electrode potential relative to the Reversible Hydrogen Electrode (RHE) using the following equation.
E vs RHE ＝E apply -rE Ag/AgCl (vs NHE)+0.0592×pH
Wherein E is vs RHE is the electrode potential after switching relative to RHE, E apply Potential value applied to electrochemical workstation relative to Ag/AgCl, E Ag/AgCl (vs NHE) is the electrode potential of the Ag/AgCl reference electrode relative to the NHE, and the pH is the pH value of the electrolyte.
TABLE 1
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The preparation method of the cobalt phosphide electrolytic water catalyst is characterized by comprising the following steps:
(1) Soaking the foam nickel in polyvinylpyrrolidone solution, and reacting to obtain modified foam nickel;
(2) Mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, adding the modified foam nickel into the mixed solution, and reacting to obtain a metal organic framework ZIF-67@foam nickel material;
(3) And (3) under the nitrogen atmosphere, performing a separation type gas phosphating reaction on the metal organic framework ZIF-67@foamed nickel material to obtain the cobalt phosphide electrolytic water catalyst.
2. The method of claim 1, wherein in step (1):
the solvent of the polyvinylpyrrolidone solution is hydrochloric acid; the mass concentration of the polyvinylpyrrolidone solution is 1-30%; and/or
In the polyvinylpyrrolidone solution, the relative molecular mass of polyvinylpyrrolidone is 0.8-130 ten thousand; preferably, the polyvinylpyrrolidone has a relative molecular mass of 0.8 to 22 ten thousand.
3. The method of claim 1, wherein in step (1):
the reaction temperature is 25-30 ℃ and the reaction time is 25-35 min; the reaction is preferably carried out under ultrasonic conditions of 20 to 40 kHz.
4. The method of claim 1, wherein in step (2):
the cobalt nitrate hexahydrate solution and the 2-methylimidazole solution are both anhydrous methanol as solvents;
the molar ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1: (1-10).
5. The method of claim 1, wherein in step (2):
the reaction temperature is 25-30 ℃ and the reaction time is 25-35 min; the reaction is preferably carried out under ultrasound conditions.
6. The method of claim 1, wherein in step (3):
the phosphating agent used in the separated gas phosphating reaction is sodium hypophosphite; and/or
The temperature of the phosphating reaction is 300-500 ℃, the time is 1.5-2.5 h, and the temperature rising rate is 8-12 ℃/min.
7. The method of claim 1, further comprising the step of heating the metal organic framework ZIF-67@ foam nickel material in a molten salt medium under nitrogen atmosphere prior to step (3).
8. The method of manufacturing according to claim 7, wherein:
the molten salt medium comprises potassium chloride and lithium chloride, wherein the molar ratio of the potassium chloride to the lithium chloride is (1-10): (10-1).
9. The method of manufacturing according to claim 7, wherein:
the temperature of the heating reaction is 500-800 ℃ and the time is 1.5-2.5 h; the temperature rising rate is 2-10 ℃/min.
10. A cobalt phosphide electrolytic water catalyst, characterized in that it is prepared by the preparation method according to any one of claims 1 to 9.
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