CN113652709B - Nitrogen-doped carbon nanotube-coated nickel iron/molybdenum carbide and preparation method and application thereof - Google Patents
Nitrogen-doped carbon nanotube-coated nickel iron/molybdenum carbide and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of nano material preparation, and particularly relates to nickel iron/molybdenum carbide wrapped by nitrogen-doped carbon nano tubes and a preparation method and application thereof. The method comprises the following steps: mixing a nickel source and an iron source for reaction, then mixing a product with a molybdenum source, dicyandiamide or melamine, adding a proper amount of water, and heating in a water bath; drying the solution after the reaction is finished, and grinding to obtain a uniformly mixed trimetal precursor; and finally, taking the trimetal precursor, and calcining the trimetal precursor in two steps under the protection of gas to obtain the carbon-coated nickel iron/molybdenum carbide loaded composite of the carbon nano tube. The invention mixes NiFe and Mo 2 Encapsulation of C into N-doped CNTs can not only inhibit agglomeration of the active nanoparticles, but also facilitate rapid charge transfer. The nitrogen-doped carbon nanotube wrapped ferronickel/molybdenum carbide prepared by the method shows excellent hydrogen evolution and oxygen evolution performances under the dual functions of water electrolysis, and has better stability under high current.
Description
Technical Field
The invention belongs to the technical field of nano material preparation, and particularly relates to a nitrogen-doped carbon nanotube coated ferronickel/molybdenum carbide and a preparation method and application thereof.
Background
Hydrogen gas has a high gravimetric energy density (33.3 kWh kg) -1 ) Combustion with zero carbon emissions has become an important energy carrier that can alleviate energy related problems. In essence, renewable energy driven electrolytic water technology stores renewable intermittent energy in the form of hydrogen for on-demand use, and is extremely attractive from a sustainable and eco-friendly perspective. However, the high energy consumption of the current electrolyzed water greatly limits the development thereof, and the reasonable design of a stable and active bifunctional catalyst to promote the reaction kinetics and minimize the required energy input has great significance for the development of the electrolyzed water technology. Although Pt and IrO 2 Are highly efficient electrocatalysts for HER and OER, respectively, but are not suitable for large-scale hydrogen production due to their scarcity and extremely high cost. The method needs to search a bifunctional catalyst with hydrogen evolution and oxygen evolution to replace Pt and IrO 2 Currently, a large number of non-noble metal materials have been investigated for use in HER and OER, and despite recent positive advances in monofunctional electrocatalysts for HER or OER, since HER and OER require different reactive sites, respectively, it remains challenging to develop bifunctional electrocatalysts to achieve effective electrocatalytic decomposition of water.
Disclosure of Invention
In order to solve the defects and shortcomings of the prior art, the invention mainly aims to provide a preparation method of nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide. In the process, C is formed in the first step by two high temperature calcinations 3 N 4 Secondly, forming carbon nano tubes and molybdenum carbide, wherein the catalytic nano particles encapsulated in the carbon material can obtain enhanced catalytic activity and high electrocatalytic stability; and by reasonably designing a two-phase structure, a heterogeneous structure is constructed to enrich active sites and promote electron transfer, thereby improving the electrocatalytic activity.
The carbon nano tube is a nano material consisting of two-dimensional hexagonal crystals of carbon atoms, is bent towards one direction and combined to form a hollow cylinder, can wrap active substances in the carbon nano tube, can protect and stabilize an active center, and can fully contact the active material and electrolyte. The dicyandiamide or the melamine can be catalyzed by iron and nickel to generate a carbon nano tube carrier in a high-temperature environment, and the OER active centers of the iron and the nickel can be well protected, so that the excellent OER performance of the dicyandiamide or the melamine is reflected. Molybdenum carbide, on the other hand, has Pt-like properties and is therefore considered to be an excellent hydrogen evolution catalyst. The carbon nano tube is one of allotropes of carbon, and the electronic interaction between the iron family and the carbon is beneficial to improving the electronic transmission capability of the material. Therefore, the performance optimization of the bifunctional catalyst can be realized by optimizing the proportion of the carbon nano tube and the active component, controlling the shape of the material, introducing the carbon nano tube to coat the trimetal and electronically modulating the active component.
Another object of the present invention is to provide a method for preparing a nitrogen-doped carbon nanotube coated nickel iron/molybdenum carbide.
The invention further aims to provide application of the nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide.
The purpose of the invention is realized by the following technical scheme:
a preparation method of nickel iron/molybdenum carbide wrapped by nitrogen-doped carbon nanotubes comprises the following steps:
(1) Mixing a nickel source and an iron source to obtain a reactant, and marking as NiFe;
(2) Mixing the reactant obtained in the step (1) and a molybdenum source with dicyandiamide or melamine; adding a proper amount of water into the mixture, heating the mixture in a water bath, and stirring the mixture until the raw materials are uniformly stirred to obtain a solution; wherein the mass ratio of the total mass of the nickel source and the iron source to the molybdenum source is 15-6;
(3) Drying the solution prepared in the step (2) to remove the solvent, and grinding to obtain a uniformly mixed trimetal precursor, which is recorded as NiFeMo;
(4) Taking a proper amount of trimetal precursor, and obtaining a carbon-coated nickel iron/molybdenum carbide loaded composite, namely NiFe/Mo, on a carbon nano tube by two-step calcination under the protection of gas 2 C @ NCNT; the two-step calcination is carried out, wherein the heat preservation temperature of the first step of calcination is 400-600 ℃, and the heat preservation temperature of the second step of calcination is 800-1000 ℃.
The nickel source in the step (1) is at least one of nickel acetylacetonate, nickel formate, nickel acetate and nickelocene, and the iron source is at least one of ferrocene, ferrocenecarboxylic acid, acetylferrocene and iron acetate; the mass ratio of the nickel source to the iron source is 3:1 and mixing.
In the step (2), the concentration of the nickel source in the solution is 4.5-22.5 g/L, and the concentration of the iron source in the solution is 1.5-7.5 g/L; the concentration of dicyandiamide in the solution is 10-30 g/L, and the concentration of melamine in the solution is 10-20 g/L.
The molybdenum source in the step (2) is ammonium molybdate.
The concentration of the molybdenum source in the solution in the step (2) is 0.4-5 g/L.
The water bath heating temperature in the step (2) is 60-100 ℃, and the stirring time is 1-8 h.
The drying temperature in the step (3) is 70-100 ℃; the grinding time is 0.5-2 h.
The two-step calcination in the step (4) has the temperature rise rate of 1-5 ℃/min and the heat preservation time of 1-6 h.
Preferably, in the step (2), the mass ratio of the total mass of the nickel source and the iron source to the molybdenum source is 10.
Preferably, the two-step calcination is performed in the step (4), wherein the calcination heat preservation temperature in the first step is 550 ℃, and the calcination heat preservation temperature in the second step is 850 ℃.
The nitrogen-doped carbon nanotube prepared by the method wraps the nickel iron/molybdenum carbide. The carbon nano tube is used as a carrier, and the carbon-coated nickel iron/molybdenum carbide hybrid nano particles are loaded at the top end of the carbon nano tube to form a carbon-coated nickel iron/molybdenum carbide loaded carbon nano tube compound with a heterostructure.
The nitrogen-doped carbon nanotube is used for wrapping the nickel iron/molybdenum carbide and is applied to a bifunctional catalyst (namely a hydrogen evolution and oxygen evolution catalyst) for electrolyzing water.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. NiFe/Mo prepared by the invention 2 The C @ NCNT shows excellent difunctional hydrogen and oxygen evolution performances of the electrolyzed water and has better stability under high current.
2. The invention mixes NiFe and Mo 2 Encapsulation of C into N-doped CNTs can not only inhibit agglomeration of the active nanoparticles, but also facilitate rapid charge transfer.
3. The preparation method is simple, and the nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide composite can be prepared on a large scale.
Drawings
FIG. 1 shows NiFe/Mo obtained in example 1 2 Scheme for the synthesis of C @ NCNT.
FIG. 2 shows NiFe/Mo obtained in example 1 2 SEM image (a), TEM (b-c), HRTEM (d-f) and mapping image (g) of C @ NCNT.
FIG. 3 shows NiFe/Mo values obtained in example 1 2 XRD spectrum (a) and Raman spectrum (b) of C @ NCNT.
FIG. 4 shows NiFe/Mo obtained in example 1 2 Hydrogen evolution stability Curve (a) and analysis of C @ NCNTOxygen stability curve (b).
FIG. 5 is a hydrogen evolution LSV of the Ni-Fe/Mo-carbide wrapped nitrogen doped carbon nanotubes obtained in examples 1-4 (a); tafel (b) and EIS curves (c), indicated by arrows in the figure, curves 3, 4, 2, 1 are NiFe/Mo, respectively 2 C@NCNT、NiFe/Mo 2 C@NCNT-4、NiFe/Mo 2 C@NCNT-2、NiFe/Mo 2 Test results for C @ NCNT-1.
FIG. 6 is a graph (a) of oxygen evolution LSV of Ni-Fe/Mo-carbide wrapped nitrogen-doped carbon nanotubes obtained in examples 1-4; tafel (b) and EIS curves (c), indicated by arrows in the figure, curves 3, 4, 2, 1 are NiFe/Mo, respectively 2 C@NCNT、NiFe/Mo 2 C@NCNT-4、NiFe/Mo 2 C@NCNT-2、NiFe/Mo 2 Test results for C @ NCNT-1.
FIG. 7 shows NiFe/Mo values obtained in example 1 2 Polarization curve (a) for the full water splitting test of C @ NCNT; the time current curve (b) of the material for full water splitting at 1.56V, and the comparison (c) of theoretical and actual hydrogen production and oxygen production.
FIG. 8 shows NiFe/Mo values obtained in example 1 2 C @ NCNT, niFe @ NCNT obtained in comparative example 1, and Mo obtained in comparative example 2 2 Hydrogen evolution LSV polarization curves (a) for C @ NCNT and Pt/C (20 w%); EIS curves (b), in which the curves 4, 3, 2, 1 are NiFe @ NCNT, mo, respectively, as indicated by the arrows 2 C@NCNT、NiFe/Mo 2 C @ NCNT, 20% Pt/C.
FIG. 9 shows NiFe/Mo values obtained in example 1 2 C @ NCNT, niFe @ NCNT obtained in comparative example 1, and Mo obtained in comparative example 2 2 C @ NCNT and RuO 2 The oxygen evolution LSV polarization curve (a); EIS curve (b), in the figure, indicated with reference to the arrow, curves 4, 3, 2, 1 are Mo respectively 2 C@NCNT、NiFe@NCNT、NiFe/Mo 2 C@NCNT、RuO 2 The test results of (1).
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. The raw materials related to the invention can be directly purchased from the market. For process parameters not specifically noted, reference may be made to conventional techniques.
Example 1
A preparation method of nickel iron/molybdenum carbide wrapped by nitrogen-doped carbon nanotubes comprises the following steps:
(1) Mixing 750mg of nickel acetate and 250mg of iron acetate, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 100mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24h at 70 ℃, grinding for 1h to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Calcining at 550 ℃ and 850 ℃ for 2h respectively in the atmosphere, and obtaining a black powder product recorded as NiFe/Mo when the heating rate is 2 ℃/min 2 C@NCNT。
Example 2
A preparation method of nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide comprises the following steps:
(1) Mixing 225mg of nickel acetate and 75mg of iron acetate, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 20mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24h at 70 ℃, grinding for 1h to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Calcining at 550 ℃ and 850 ℃ for 2h in the atmosphere respectively, and obtaining a black powder product when the heating rate is 2 ℃/min, and recording as NiFe/Mo 2 C@NCNT-1。
Example 3
A preparation method of nickel iron/molybdenum carbide wrapped by nitrogen-doped carbon nanotubes comprises the following steps:
(1) Mixing 360mg of nickel acetate and 120mg of iron acetate, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 40mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24 hours at 70 ℃, and grinding for 1 hour to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Calcining at 550 ℃ and 850 ℃ for 2h in the atmosphere respectively, and obtaining a black powder product when the heating rate is 2 ℃/min, and recording as NiFe/Mo 2 C@NCNT-2。
Example 4
A preparation method of nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide comprises the following steps:
(1) 1125mg of nickel acetate and 375mg of iron acetate are mixed, stirred and ground to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 250mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24 hours at 70 ℃, and grinding for 1 hour to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and carrying out Ar reaction 2 Calcining at 550 ℃ and 850 ℃ for 2h respectively in the atmosphere, and obtaining a black powder product recorded as NiFe/Mo when the heating rate is 2 ℃/min 2 C@NCNT-4。
Example 5
A preparation method of nickel iron/molybdenum carbide wrapped by nitrogen-doped carbon nanotubes comprises the following steps:
(1) Mixing 750mg of nickel acetate and 250mg of ferrocene, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 100mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24 hours at 70 ℃, and grinding for 1 hour to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Calcining at 550 ℃ and 850 ℃ for 2h in the atmosphere respectively, and obtaining a black powder product when the heating rate is 2 ℃/min, and recording as NiFe/Mo 2 C@NCNT-5。
Example 6
A preparation method of nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide comprises the following steps:
(1) Mixing 750mg of nickel cyclopentadienyl and 250mg of ferric acetate, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 100mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24 hours at 70 ℃, and grinding for 1 hour to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and carrying out Ar reaction 2 Calcining at 550 ℃ and 850 ℃ for 2h respectively in the atmosphere, and obtaining a black powder product recorded as NiFe/Mo when the heating rate is 2 ℃/min 2 C@NCNT-6。
Example 7
A preparation method of nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide comprises the following steps:
(1) Mixing 750mg of nickelocene and 250mg of ferrocene, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 100mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24 hours at 70 ℃, and grinding for 1 hour to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Calcining at 550 ℃ and 850 ℃ for 2h respectively in the atmosphere, and obtaining a black powder product recorded as NiFe/Mo when the heating rate is 2 ℃/min 2 C@NCNT-7。
Example 8
The catalyst for wrapping nickel iron/molybdenum carbide by nitrogen-doped carbon nanotubes is prepared in the embodiment, and the difference from the embodiment 1 is that (2) 2g of melamine is added into a beaker, 50ml of deionized water is added into the beaker, and then the mixture is heated and stirred for 120min in a water bath at 60 ℃ to obtain a solution.
Example 9
The catalyst for wrapping nickel iron/molybdenum carbide by nitrogen-doped carbon nanotubes is prepared in the embodiment, and is different from the embodiment 1 in that 1g of melamine is added into a beaker in the step (2), 50ml of deionized water is added into the beaker, and then the mixture is heated and stirred for 120min in a water bath at 60 ℃ to obtain a solution.
Example 10
The catalyst prepared in the embodiment is a nitrogen-doped carbon nanotube wrapped nickel iron/molybdenum carbide catalyst, and is different from the catalyst prepared in the embodiment 1 in that 1.5g of melamine is added into a beaker in the step (2), 50ml of deionized water is added into the beaker, and then the beaker is heated and stirred for 120min in a water bath at 60 ℃ to obtain a solution.
Example 11
The catalyst for wrapping nickel iron/molybdenum carbide by nitrogen-doped carbon nanotubes is prepared in the embodiment, and the difference from the embodiment 1 is that (2) 2.5g of dicyandiamide is added into a beaker, 50ml of deionized water is added into the beaker, and then the beaker is heated and stirred for 120min in a water bath at 60 ℃ to obtain a solution.
Example 12
The difference between the catalyst prepared in the embodiment and the embodiment 1 is that (2) 3g of dicyandiamide is added into a beaker, 50ml of deionized water is added into the beaker, and then the beaker is heated and stirred for 120min in a water bath at 60 ℃ to obtain a solution.
Comparative example 1
A preparation method of nickel iron wrapped by nitrogen-doped carbon nanotubes comprises the following steps:
(1) Mixing 750mg of nickel acetate and 250mg of iron acetate, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1) and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) putting the solution obtained in the step (2) into an oven, drying for 24 hours at 70 ℃, and grinding for 1 hour to obtain a reaction product, wherein the reaction product is a uniformly mixed bimetallic precursor and is marked as NiFe.
(4) Putting the reaction product of the bimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Calcining at 550 ℃ and 850 ℃ for 2h in the atmosphere respectively, and obtaining a black powder product when the heating rate is 2 ℃/min, and recording as NiFe @ NCNT.
Comparative example 2
A preparation method of nitrogen-doped carbon nanotube coated molybdenum carbide comprises the following steps:
(1) Mixing 750mg of nickel acetate and 250mg of iron acetate, stirring, and grinding to obtain a reactant;
(2) Adding the reactant obtained in the step (1), 100mg of ammonium molybdate and 2g of dicyandiamide into a beaker, adding 50ml of deionized water into the beaker, and then heating and stirring the mixture for 120min in a water bath at 60 ℃ to obtain a solution.
(3) And (3) placing the solution obtained in the step (2) in an oven, drying for 24h at 70 ℃, grinding for 1h to obtain a reaction product, wherein the reaction product is a uniformly mixed trimetal precursor and is marked as NiFeMo.
(4) Putting the reaction product trimetal precursor into a clean porcelain boat, putting the porcelain boat into a tube furnace, and putting the porcelain boat into Ar 2 Respectively at 55 deg.C under gas atmosphereCalcining at 0 ℃ and 850 ℃ for 2h respectively, and obtaining a black powder product when the heating rate is 2 ℃/min, and recording as NiFe/Mo 2 C@NCNT。
(5) The product NiFe/Mo 2 C @ NCNT added with H with concentration of 1mol/L 2 SO 4 Stirring for 24h, dissolving the alloy therein, centrifuging, washing and drying after the reaction is finished to obtain a reaction product, which is marked as Mo 2 C@NCNT。
With respect to example 1:
FIG. 1 shows NiFe/Mo 2 Synthesis scheme of C @ NCNT.
FIG. 2 uses SEM and TEM to study NiFe/Mo 2 Structure and morphology of C @ NCNT. As is apparent from the SEM image of (a) in FIG. 2, niFe/Mo 2 The C @ NCNT material has a large number of carbon nanotube structures, the surface is smooth, and it is clear from the macroscopic TEM image (fig. 2 (b) and (c)) that the tips of the smooth carbon nanotubes are wrapped with nanoparticles. In NiFe/Mo 2 In the high-resolution TEM of C @ NCNT ((d) in FIG. 2), niFe/Mo is observed 2 The C is wrapped by the multilayer carbon layer, the NCNT serves as a conductive carrier, and the nanoparticles are encapsulated in the NCNT to protect dispersed particles in a complex environment, prevent the particles from aggregating and effectively avoid the particles from being corroded in a severe environment. The synergistic effect of NCNT and confined nanoparticles can generate extremely high active sites for electrochemical hydrogen and oxygen evolution, contributing to the improvement of the electrocatalytic properties of the material. NiFe/Mo 2 High-power TEM image of C @ NCNT ((e) in FIG. 2 and (f) in FIG. 2) measured lattice spacings of 0.21nm and 0.23nm, corresponding to NiFe and Mo, respectively 2 Two substances C, in addition NiFe/Mo 2 NiFe and Mo in C @ NCNT material 2 C are in intimate contact, providing a rich heterogeneous interface. NiFe/Mo 2 The element profile ((g) in FIG. 2) of C @ NCNT also shows the presence and uniform dispersion of Ni, fe, mo, N and C.
Fig. 3 (a) shows a diffraction peak of the high-temperature-derived graphitic carbon corresponding to a position of about 26 °. NiFe/Mo 2 The diffraction peaks of the Ni-Fe alloy in C @ NCNT are 44.2 degrees, 51.5 degrees and 75.8 degrees, and the peaks are combined with Ni from face-centered cubic 3 Fe (JCPDS standard card number 65-3244) is matched, and the higher intensity of the diffraction peak indicates the better junction of the materialAnd (4) crystallinity. NiFe/Mo 2 The diffraction peaks of molybdenum carbide in C @ NCNT are at 34.4 deg., 38.0 deg., 39.4 deg., 52.1 deg., 61.6 deg., 9.6 deg., 75.4 deg., corresponding to Mo 2 Crystal face of C (JCPDS standard card number 71-0242). And no obvious impurity peak, indicating the successful preparation of the material. NiFe/Mo 2 The Raman spectrum of C @ NCNT is shown in FIG. 3 (b), and the material after calcination in a tube furnace is 1343cm -1 And 1586cm -1 Shows distinct characteristic peaks, namely D band peak and G band peak, niFe/Mo 2 I of C @ NCNT D /I G The ratio is 1.08, which indicates that NiFe/Mo 2 The carbons in C @ NCNT have a large number of defective or disordered sites.
FIG. 4 (a) shows NiFe/Mo prepared in example 1 2 After 24-hour continuous test, the material maintains the original current density value of 92.5%, which indicates that the metal active center has excellent corrosion resistance under the wrapping of the N-doped carbon nano tube, and proves that NiFe/Mo 2 The stability of the C @ NCNT material for good hydrogen evolution, and the stability test result of (b) in FIG. 4 also shows that NiFe/Mo 2 The good stability of the C heterojunction material, its current density did not decay significantly after 40 hours and maintained 92.3% of the original current density value.
As can be seen from (a) in FIG. 7, pt/C and RuO 2 Still exhibit excellent properties, and the NiFe/Mo prepared 2 C @ NCNT also shows lower HER and OER overpotentials, and the fact that the two are better in bifunctional activity is verified again, the full-hydrolysis test under the alkaline condition shows low driving voltage, and an LSV curve shows that only 1.554V is needed to reach 10mA cm -2 Current density of very close to Pt/C and RuO 2 A catalyst. NiFe/Mo 2 The constant voltage of 1.56V test (figure 7 (b)) of full water electrolysis of the electrolytic cell assembled by the C @ NCNT electrode material maintains 90.3 percent of the original current after 30h, and keeps good stability.
With respect to examples 1 to 4
We synthesized NiFe/Mo 2 C @ NCNT-X material and hydrogen evolution electrochemical tests were performed separately on it (FIG. 5). As in FIG. 5 (a) compared to NiFe/Mo 2 C@NCNT-1(206mV)，NiFe/Mo 2 C @ NCNT-2 (183 mV) and NiFe/Mo 2 C@NCNT-4 (171 mV), niFe/Mo prepared in example 1 2 The C @ NCNT can reach 10mA cm by only applying 156mV voltage -2 The current density of (1). At different ratios of NiFe/Mo 2 NiFe/Mo obtained in example 1 of C @ NCNT-X Material 2 C @ NCNT possesses the fastest reaction rate (80 mV dec) -1 ) (fig. 5 (b)) and the optimum charge transfer rate (R) ct =25.9 Ω) (fig. 5 (c)), the catalyst activity showed a tendency of increasing and then decreasing as the Mo content increases, indicating NiFe/Mo 2 C @ NCNT is the most preferred catalyst.
We synthesized nitrogen-doped carbon nanotube-wrapped nickel iron/molybdenum carbide material and individually oxygen evolution electrochemical tests were performed on it (fig. 6). (a) in the polarization graph 6 shows, in comparison with NiFe/Mo 2 C@NCNT-1(η 10 ＝329mV)，NiFe/Mo 2 C@NCNT-2(η 10 =311 mV) and NiFe/Mo 2 C@NCNT-4(η 10 =293 mV), niFe/Mo prepared in example 1 2 Overpotential (. Eta.) of C @ NCNT 10 =284 mV) lower, closest to RuO 2 . From the Tafel plot ((b) of FIG. 6), the electrochemical impedance curve ((c) of FIG. 6), it can also be found that NiFe/Mo prepared in example 1 2 C @ NCNT possesses the fastest reaction rate (53 mV dec) -1 ) Optimum charge transfer rate (R) ct =15.8 Ω), so the test results indicate that NiFe/Mo prepared in example 1 is 2 C @ NCNT is an optimum proportion of OER catalyst.
With respect to example 1 and comparative examples 1-2:
to evaluate the NiFe/Mo prepared in example 1 2 HER performance of c @ ncnt we used a three electrode system to electrochemically test the material in 1M KOH solution. For comparison, niFe @ NCNT, mo 2 C @ NCNT and 20wt% Pt/C were also tested under the same conditions. As shown in FIG. 8 (a), pt/C activity was optimized in all materials, while NiFe/Mo synthesized in example 1 2 C @ NCNT of 1 and 10mA cm -2 The current density of the current is only 79mV and 156mV, which are obviously less than NiFe @ NCNT (174mV @1mA cm) -2 ，305mV@10mA cm -2 ) And Mo 2 C@NCNT(109mV@1mA cm -2 ，194mV@10mA cm -2 ). As shown in (b) of fig. 8, the magnitude of the charge transfer resistance RctThe sequence is Pt/C < NiFe/Mo 2 C@NCNT＜Mo 2 NiFe/Mo prepared in example 1, C @ NCNT < NiFe @ NCNT 2 The Rct value of C @ NCNT is only higher than Pt/C, indicating a fast charge transfer rate.
In addition to HER activity, we also tested the NiFe/Mo prepared in example 1 2 OER performance of C @ NCNT in alkaline solution. FIG. 9 (a) is NiFe/Mo 2 C@NCNT、NiFe@NCNT、Mo 2 C @ NCNT and RuO 2 Polarization curves in 1M KOH solution, respectively, with NiFe @NCNTand Mo 2 Comparison of C @ NCNT with NiFe/Mo prepared in example 1 2 Polarization curves for C @ NCNT exhibit a closer approximation to RuO 2 The OER activity of (2) can be increased to 10mA cm at an overpotential of 284mV -2 With a current density of oxygen evolution of NiFe @ NCNT and Mo 2 C @ NCNT requires 317mV and 602mV, respectively. The test of (b) in FIG. 9 shows that NiFe/Mo prepared in example 1 2 R of C @ NCNT ct 15.8 omega, which is much lower than NiFe @ NCNT (103.8 omega) and Mo 2 C @ NCNT (403 Ω), closer to the noble metal RuO 2 。
For examples 1,5 to 7:
TABLE 1 NiFe/Mo obtained in example 1 2 C @ NCNT and NiFe/Mo obtained in examples 5-7 2 Data of C @ NCNT-X (5-7)
As shown in Table 1, niFe/Mo can be seen 2 C @ NCNT material and NiFe/Mo 2 Comparison of data for HER, OER, total hydrolysis and stability with C @ NCNT-X (5-7) shows no significant difference in data results, and further confirms that the performance of examples 5-7 is substantially the same as that of example 1.
The electrochemical test of the sample prepared by the invention is completed on a Yingsi 4030 electrochemical workstation of Guangzhou Yingsi sensing technology Co. The test adopts a three-electrode system, and comprises an electrode made of synthetic materials as a working electrode, a graphite rod as a counter electrode, a saturated calomel electrode as a reference electrode, and a conversion relation between the reference electrode and a standard hydrogen electrode as follows: e RHE ＝E Hg/HgCl2 +0.059pH +0.241V, and the electrolyte used in the experiment is 1.0M KOH. The sweep rate of the linear sweep voltammogram was 5mV s -1 。
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (9)
1. A preparation method of nickel iron/molybdenum carbide wrapped by nitrogen-doped carbon nanotubes is characterized by comprising the following steps:
(1) Mixing a nickel source and an iron source to obtain a reactant;
(2) Mixing the reactant obtained in the step (1), a molybdenum source and dicyandiamide or melamine; adding a proper amount of water into the mixture, heating the mixture in a water bath, and stirring the mixture until the raw materials are uniformly stirred to obtain a solution; wherein the mass ratio of the total mass of the nickel source and the iron source to the molybdenum source is 15-6;
(3) Drying the solution prepared in the step (2), and grinding to obtain a uniformly mixed trimetal precursor;
(4) Taking a trimetal precursor, and calcining the trimetal precursor in two steps under the protection of gas to obtain a carbon-coated nickel iron/molybdenum carbide loaded composite on a carbon nano tube; the two-step calcination is carried out, wherein the first-step calcination heat preservation temperature is 400-600 ℃, and the second-step calcination heat preservation temperature is 800-1000 ℃;
the nickel source in the step (1) is at least one of nickel acetylacetonate, nickel formate, nickel acetate and nickelocene, and the iron source is at least one of ferrocene, ferrocenecarboxylic acid, acetylferrocene and iron acetate; the molybdenum source in the step (2) is ammonium molybdate; the mass ratio of the nickel source to the iron source is 3:1 and mixing.
2. The method for preparing nitrogen-doped carbon nanotube-coated ferronickel/molybdenum carbide according to claim 1, wherein in the step (2), the concentration of the iron source in the solution is 1.5 to 7.5g/L, and the concentration of the nickel source in the solution is 4.5 to 22.5g/L; the concentration of the molybdenum source in the solution is 0.4-5 g/L; the concentration of dicyandiamide in the solution is 10-30 g/L, and the concentration of melamine in the solution is 10-20 g/L.
3. The method for preparing nitrogen-doped carbon nanotube-wrapped nickel iron/molybdenum carbide according to claim 1, wherein the water bath heating temperature in the step (2) is 60-100 ℃, and the stirring time is 1-8 h.
4. The method for preparing nitrogen-doped carbon nanotube-wrapped nickel iron/molybdenum carbide according to claim 1, wherein in the step (2), the mass ratio of the total mass of the nickel source and the iron source to the molybdenum source is 10.
5. The method for preparing nitrogen-doped carbon nanotube-coated nickel iron/molybdenum carbide according to claim 1, wherein the drying temperature in the step (3) is 70-100 ℃; the grinding time is 0.5-2 h.
6. The method for preparing nitrogen-doped carbon nanotube-coated ferronickel/molybdenum carbide according to claim 1, wherein the two-step calcination in the step (4) is performed at a heating rate of 1-5 ℃/min and a holding time of 1-6 h.
7. The method for preparing nitrogen-doped carbon nanotube-coated ferronickel/molybdenum carbide according to claim 1, wherein the calcination is performed in two steps in the step (4), wherein the calcination temperature in the first step is 550 ℃ and the calcination temperature in the second step is 850 ℃.
8. A nitrogen doped carbon nanotube coated nickel iron/molybdenum carbide prepared by the method of any one of claims 1-7.
9. The use of the nitrogen doped carbon nanotubes coated nickel iron/molybdenum carbide as catalyst in hydrogen evolution from hydrogen evolution by electrolysis.
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