CN115110114B - Preparation method of molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia, product and application thereof - Google Patents

Preparation method of molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia, product and application thereof Download PDF

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CN115110114B
CN115110114B CN202210691176.0A CN202210691176A CN115110114B CN 115110114 B CN115110114 B CN 115110114B CN 202210691176 A CN202210691176 A CN 202210691176A CN 115110114 B CN115110114 B CN 115110114B
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composite material
ammonia
electrocatalytic
boron carbide
molybdenum
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CN115110114A (en
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傅杰
孙艺轩
林雯雯
王江浩
欧阳平凯
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Zhejiang University ZJU
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    • 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
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/90—Carbides
    • C01B32/914—Carbides of single elements
    • C01B32/949—Tungsten or molybdenum carbides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
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    • C01B32/914—Carbides of single elements
    • C01B32/991—Boron carbide
    • 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
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    • C01P2004/00—Particle morphology
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    • C01—INORGANIC CHEMISTRY
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
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    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
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    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Abstract

The invention discloses a preparation method of a molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia, which comprises the following steps: mo is added with 2 C and B 4 Calcining after ball milling treatment to obtain Mo 2 C‑B 4 C composite material. The invention also provides a molybdenum carbide-boron carbide composite material obtained by the preparation method and application thereof in electrocatalytic ammonia synthesis. Mo prepared by adopting the preparation method 2 C‑B 4 The C composite material has an interface structure and electrochemical performance superior to those of molybdenum carbide and boron carbide, and can effectively improve the yield and Faraday efficiency of electrocatalytic synthesis ammonia when being applied to electrocatalytic synthesis ammonia.

Description

Preparation method of molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia, product and application thereof
Technical Field
The invention relates to the field of electrocatalytic nitrogen reduction electrode materials, in particular to a preparation method of a molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia, a product and application thereof.
Background
Ammonia (NH) 3 ) Is one of the most widely used inorganic chemicals in industry, and is widely applied to fertilizer production, drug synthesis and many other industrial fields. Furthermore, ammonia has a high energy density (5.52 kW h kg) -1 ) And 17.6wt% hydrogen, so ammonia has application prospects as a hydrogen storage carrier and a "no-carbon fuel". Currently, the worldwide industrial synthesis of ammonia is almost entirely dependent on the traditional Haber-Bosch process, which is carried out at high temperatures (400-600 ℃) and pressures (20-30 MPa), consuming about 2% of fossil energy worldwide and emitting CO annually 2 About account for1.4% of global total emissions, which has a great impact on the environment. Thus, environmentally friendly NH was developed 3 The synthesis method is imperative. Electrochemical synthesis of ammonia (E-NRR) using electricity generated from renewable energy sources such as solar or wind energy, N being reacted by heterogeneous catalysts under ambient conditions 2 Electrochemical reduction to NH 3 . Thermodynamically, the mildly clean E-NRR is 20% more energy efficient than the Haber-Bosch process. Decentralized production of ammonia can also be achieved to reduce transportation costs and is therefore one of the most promising alternatives to conventional ammonia synthesis processes. Wherein, the high-performance E-NRR catalyst is designed to strengthen N 2 Is critical for adsorption and activation.
Document "Atheoretical evaluation of possible transition metal electro-catalysts for N 2 The reduction "shows by theoretical calculation that metallic Mo is an element located at the peak of the E-NRR activity volcanic plot.
The Chinese patent publication No. CN113058658A discloses a preparation method of a super-hydrophobic supported molybdenum catalyst, which utilizes phosphotungstic acid with rich oxygen coordination sites as a carrier and molybdenum chloride pentahydrate as a precursor of a modified species to develop a high-performance super-hydrophobic supported molybdenum species phosphotungstic acid electrocatalyst for electrocatalytic nitrogen fixation.
The Chinese patent publication No. CN113215598A discloses a Bi-MoS for electrocatalytic synthesis of ammonia 2 The nano composite material is prepared by compounding bismuth nanocrystals and molybdenum disulfide nanosheets by a hydrothermal reaction by taking molybdenum disulfide as a substrate. Is used for electrocatalytic synthesis of ammonia.
However, mo-based materials (e.g., mo 2 C) While also exhibiting excellent HER catalytic performance, which limits the use of molybdenum-based catalysts in the E-NRR catalytic field. Therefore, how to improve the catalytic performance is a technical problem to be solved in the current field.
Disclosure of Invention
The invention aims to provide a preparation method of a molybdenum carbide-boron carbide composite material for electrocatalytic ammonia synthesis, a product and application thereof, and Mo prepared by the preparation method 2 C-B 4 The C composite material has better boundary than molybdenum carbide and boron carbideThe surface structure and the electrochemical performance can be applied to the electrocatalytic synthesis of ammonia, so that the electrocatalytic synthesis of ammonia yield and Faraday efficiency can be effectively improved.
The invention provides the following technical scheme:
a preparation method of a molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia, which comprises the following steps: mo is added with 2 C and B 4 Calcining after ball milling treatment to obtain Mo 2 C-B 4 C composite material.
The Mo is 2 C and B 4 The mole ratio of Mo to B in C is 1:1-1:4.
Mo 2 C and B 4 The molar ratio of Mo to B in C affects the number of Mo-B bonds in the catalyst, which have a positive effect on the catalytic performance. Preferably, the Mo 2 C and B 4 The molar ratio of Mo to B in C is 1:2, where the most Mo-B bonds are formed.
The ball milling time is 1-16 h, the ball-material ratio is 20:1-30:1, and the rotating speed is 20-60Hz. The ball milling promotes the two-phase mixing, the particle size of the particles is changed, the ball milling time is too short, and the particles are larger; the ball milling time is too long, particles are not further reduced, and the catalyst structure is possibly changed, which is unfavorable for electrocatalysis.
Preferably, the ball milling time is 3 to 6 hours. Mo (Mo) 2 C-B 4 The C composite material has larger electrochemical active surface area and higher conductivity as a catalyst. Further preferably, the ball milling time is 4 hours, and the catalyst has the largest electrochemical active surface area and the highest conductivity under the condition of ball milling for 4 hours, so that the activity is optimal.
The calcination is performed under a non-oxygen atmosphere, such as a nitrogen atmosphere. The calcination temperature is 450-750 ℃, the temperature rising rate is 2-10 ℃/min, and the time is 1-10 h. The invention promotes Mo by calcining 2 C and B 4 The C two-phase chemical bonding ensures that the calcined composite material has higher electrochemical active surface area and high conductivity, and is beneficial to electrocatalytic synthesis of ammonia. Preferably, the atmosphere of the calcination is N 2 The calcining temperature is 450-550 ℃, the heating rate is 5 ℃/min, and the time is 4 hours.
Wherein, the preparation method further comprises the steps of washing and drying the calcined product: placing the mixture in 0.5mol/L dilute sulfuric acid, carrying out ultrasonic treatment for 1h, carrying out suction filtration and washing to be neutral, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible. The catalyst was dried in a vacuum oven at 40 ℃ for 10 hours, then ground to a powder, and stored in a sample bottle.
The invention also provides a molybdenum carbide-boron carbide composite material obtained by the preparation method.
B in the molybdenum carbide-boron carbide composite material 4 Part C is coated on Mo 2 C surface to Mo 2 The surface of C is modified, and Mo-B bonds are generated between two phases.
In the molybdenum carbide-boron carbide composite material provided by the invention, B 4 Part C is coated on Mo 2 C surface has abundant defect sites and can adsorb a large amount of N 2 The formation of a large number of Mo-B bonds in both phases effectively promotes the electrochemical process.
The invention also provides application of the molybdenum carbide-boron carbide composite material in electrocatalytic ammonia synthesis.
Mo rich in defects 2 C-B 4 The B-Mo double site exposed by the C composite material has stronger N compared with the single site 2 Adsorption and a stronger charge transfer capacity. Therefore, the synergistic effect of the molybdenum and the boron ensures that the composite material has excellent electrocatalytic ammonia synthesis performance.
Compared with the prior art, the method synthesizes the molybdenum carbide-boron carbide composite material by adopting ball milling and calcining methods, and has an interface structure and electrochemical performance superior to those of molybdenum carbide and boron carbide by controlling the technological process, so that the method can effectively improve the yield and Faraday efficiency of electrocatalytic synthesis ammonia and has good stability in 5-cycle test.
Mo provided by the invention 2 C-B 4 The C composite material is used for compositing boron and a molybdenum-based catalyst, so that the hydrogen evolution capacity of the Mo surface is weakened, and meanwhile, the effective E-NRR catalysis is realized by utilizing the synergistic catalysis of the molybdenum-based catalyst and the boron-based catalyst.
Mo provided by the invention 2 C-B 4 The ammonia yield of the C composite material can reach 8 mu g h -1 mg -1 cat. The faraday efficiency can reach 18% (0.1M HCl electrolyte at ph=1).
Drawings
FIG. 1 is Mo prepared in example 1 2 C-B 4 An X-ray diffraction spectrogram of the C composite material;
FIG. 2 is Mo prepared in example 1 2 C-B 4 C, a transmission electron microscope image of the composite material;
FIG. 3 is Mo prepared in example 1 2 C-B 4 X-ray photoelectron spectrum of the C composite material;
FIG. 4 is Mo prepared in example 1 2 C-B 4 A nitrogen adsorption and desorption curve of the composite material C;
FIG. 5 is Mo prepared in example 1 2 C-B 4 C composite material and Mo 2 C and B 4 C ammonia yield for electrocatalytic synthesis of ammonia;
FIG. 6 is Mo prepared in example 1 2 C-B 4 Ammonia yield and faraday efficiency plot for C composite;
FIG. 7 shows the Mo prepared in examples 1-3 2 C-B 4 NH for electrocatalytic nitrogen reduction of C composite material 3 Yield comparison plot;
FIG. 8 shows the Mo prepared in examples 1, 4, 5 and 6 2 C-B 4 NH for electrocatalytic nitrogen reduction of C composite material 3 Yield comparison plot;
FIG. 9 shows the Mo prepared in examples 1, 7, 8 and 9 2 C-B 4 NH for electrocatalytic nitrogen reduction of C composite material 3 Yield comparison plot;
FIG. 10 shows the Mo prepared in examples 1, 4, 5 and 6 2 C-B 4 The electrochemically active surface area of the C composite;
FIG. 11 shows the Mo prepared in examples 1, 4, 5 and 6 2 C-B 4 Electrochemical impedance of the C composite material;
FIG. 12 shows the Mo prepared in examples 1, 7, 8 and 9 2 C-B 4 C composite materialIs a metal oxide;
FIG. 13 shows the Mo prepared in examples 1, 7, 8 and 9 2 C-B 4 Electrochemical impedance of the C composite material;
FIG. 14 shows the Mo prepared in examples 1-3 2 C-B 4 The C composite material is subjected to XPS test to obtain different bond types of boron and B-Mo bond ratios.
Detailed Description
The following detailed description of embodiments of the invention is provided, but it should be noted that the scope of the invention is not limited by these embodiments, but is defined by the appended claims. In the following examples and comparative examples, the raw materials used are all commercially available unless otherwise specified.
All publications, patent applications, patents, and other references mentioned in this specification are herein incorporated by reference in their entirety. Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art. In case of conflict, the present specification, definitions, will control.
The present invention will be described in further detail with reference to examples, but the present invention is not limited to these examples.
Mo of the invention 2 C-B 4 The C composite material has excellent electrocatalytic ammonia synthesis performance, 5mg of catalyst sample is dispersed into 900 mu l of ethanol, 100 mu l of Nafion solution is added to form uniform slurry, ultrasonic treatment is carried out for 1h, then 40 mu l of mixed solution is dripped into pretreated carbon paper, and the loading concentration is 0.2mg cm -2 As a working electrode, an electrocatalytic ammonia synthesis test can be performed.
The i-t test of the invention was performed in 0.1M HCl electrolyte at ph=1 using CHI660E electrochemical workstation, with Ag/AgCl (3M KCl) as reference electrode, carbon rod as counter electrode, and the electrode prepared with the above catalyst as working electrode.
In the context of the present specification, including in the examples and comparative examples below, the catalytic performance of the electrocatalytic ammonia synthesis reaction was investigated by yield and faraday efficiency and stability.
Ammonia yield = measured concentration of ammonia in electrolyte x volume of electrolyte/mass of catalyst/reaction time.
Faraday efficiency = measured ammonia concentration in electrolyte x volume of electrolyte x 96485 x 3/charge x 100%.
Example 1
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 2
(1) 0.816g of molybdenum carbide and 0.110g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 3
(1) 0.816g of molybdenum carbide and 0.442g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 4
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 1 hour.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 5
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 8 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 6
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 16 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 7
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 Heating to 450 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 8
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 650 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Example 9
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 And heating to 750 ℃ at a heating rate of 5 ℃/min under the atmosphere, maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Comparative example 1
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and manually milled in a mortar for 30 minutes.
(2) Calcining the black powder obtained in step (1) in a porcelain boat, and adding the black powder into N 2 Heating to 550 ℃ at a heating rate of 5 ℃/min under the atmosphereAnd maintaining for 4 hours, and taking out the porcelain boat after the tube furnace is cooled to room temperature to obtain black solid powder.
(3) Placing the black powder obtained in the step (2) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(4) Placing the solid powder obtained in the step (3) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Comparative example 2
(1) 0.816g of molybdenum carbide and 0.221g of nano boron carbide were added to a ball milling pot and ball milled in a planetary ball mill at a rotational speed of 40Hz for 4 hours.
(2) Placing the black powder obtained in the step (1) in dilute sulfuric acid, carrying out ultrasonic treatment for 1 hour, carrying out suction filtration and washing to neutrality, so as to fully clean unreacted substances and remove ammonia pollution in the catalyst as far as possible.
(3) Placing the solid powder obtained in the step (2) in a vacuum drying oven, drying at 40 ℃ for 10 hours, and grinding to powder to obtain Mo 2 C-B 4 C。
Comparative example 3
Commercial molybdenum carbide.
Comparative example 4
Commercial nano boron carbide.
Test example 1
XRD test: mo obtained in example 1 2 C-B 4 The C composite samples were subjected to XRD testing as shown in figure 1. X-ray diffraction peak can be equal to Mo 2 C standard card corresponds to, and shows the same with B 4 C consistent weak diffraction peak, indicating Mo 2 C-B 4 Successful synthesis of C composite material, and wherein B 4 The crystallinity of the C phase is low.
Transmission electron microscope: mo obtained in example 1 2 C-B 4 The C composite was subjected to transmission electron microscopy as shown in fig. 2. High resolution TEM images show Mo 2 C and B 4 C tightly bonded, proving Mo synthesized according to the above experimental method 2 C-B 4 M in C composite materialo 2 C and B 4 C, successful compounding.
Test example 2
XPS test: mo obtained in example 1 2 C-B 4 The C composite samples were subjected to XPS testing as shown in fig. 3. And B is connected with 4 C and Mo 2 C-B 4 C (not calcined), mo 2 C-B 4 C (after calcination) the peak at the low binding energy of its B1s spectrum is clearly shifted to the left, indicating that there is a large amount of B-Mo bond formation during calcination. The formation of B-Mo bonds represents B 4 C and Mo 2 The C is not simply physically mixed, and coordination bonds are formed at the two-phase interface, so that electron transfer between the interfaces is facilitated.
N 2 TPD test: the samples of example 1 and comparative examples 2-4 were tested for nitrogen adsorption and desorption curves as shown in fig. 4. B (B) 4 C and Mo 2 C-B 4 C shows a certain nitrogen adsorption capacity, and Mo after calcination 2 C-B 4 The desorption peak of C is 415 ℃ which is obviously higher than 365 ℃ before calcination, and meanwhile, mo after calcination 2 C-B 4 C has a larger desorption peak area. Mo after calcination 2 C-B 4 The C composite material can more closely adsorb a large amount of N 2 The material has stronger N when exposing B-Mo double sites compared with single site 2 Adsorption.
Test example 3
Electrochemical performance test: mo obtained in example 1 2 C-B 4 And C, assembling the composite material into an electrode, and performing electrochemical performance test under a three-electrode system.
Dispersing 5mg of catalyst sample into 900. Mu.l of ethanol, adding 100. Mu.l of Nafion solution to form uniform slurry, carrying out ultrasonic treatment for 1h, and then dripping 40. Mu.l of mixed solution into pretreated carbon paper, wherein the load concentration is 0.2mg cm -2 As a working electrode; ag/AgCl (3M KCl) is used as a reference electrode, and a carbon rod is used as a counter electrode. The CHI660E electrochemical workstation was used in 0.1M HCl electrolyte at ph=1.
FIG. 5 is a graph of NH for electrocatalytic nitrogen reduction for test example 1 and comparative examples 3, 4 3 Yield. Example 1 has a much higher NH than comparative example 3/4 3 Yield, proof molybdenum,Synergistic catalysis by boron.
FIG. 6 shows the Mo obtained in example 1 2 C-B 4 NH of C composite material under different electric potentials 3 Yield and Faraday efficiency plot, wherein the curve is Faraday efficiency of ammonia synthesis and the histogram is NH 3 Yield. As can be seen from FIG. 6, mo in the present invention 2 C-B 4 The C composite material has good electrocatalytic activity and excellent selectivity for synthesizing ammonia.
FIG. 7 is a schematic representation of NH for electrocatalytic nitrogen reduction of examples 1-3 3 Yield the effect of Mo and B ratio on the electrocatalytic nitrogen reduction activity was examined. When Mo: b=1:1, too little B 4 C causes Mo 2 Excessive exposure of hydrogen adsorption sites on the surface of C leads to excessive hydrogen evolution competing reactions in the system, thus reducing the selectivity of electrocatalytic nitrogen reduction. When Mo: b=1:4, too much B 4 C is covered with Mo 2 The surface of C is favorable for inhibiting hydrogen evolution reaction, but the number of active sites of the junction of Mo and B on the surface is reduced, so that the electrocatalytic nitrogen reduction activity is inhibited.
FIG. 8 is an NH for use in electrocatalytic nitrogen reduction of examples 1, 4, 5, 6 3 Yield. The effect of ball milling time on electrochemical nitrogen reduction performance in the synthesis process was examined, wherein example 1 exhibited the best electrocatalytic nitrogen reduction activity.
FIG. 9 is an NH Point for use in examples 1, 7, 8, 9 for electrocatalytic nitrogen reduction 3 Yield. The effect of calcination temperature on electrochemical nitrogen reduction performance in the synthesis process was examined, wherein example 1 exhibited the best electrocatalytic nitrogen reduction activity.
FIG. 10 shows the Mo prepared in examples 1, 4, 5 and 6 2 C-B 4 Electrochemically active surface area of the C composite. Example 1 shows 3.07mF cm -2 Is higher than that of example 4 (1.75 mF cm) -2 ) Example 5 (2.13 mF cm) -2 ) And example 6 (2.42 mF cm) -2 ) It was revealed that example 1 has a large number of active sites to facilitate improvement of reactivity.
FIG. 11 is a diagram of the electrochemical impedance Nyquist for examples 1, 4, 5, 6, example 1 having a minimum radius of curvature compared to examples 4, 5, 6One step proves that Mo 2 C and B 4 The C two phases are fully mixed and the phase interface and the particle size are regulated, so that electron transfer in the electrochemical process is facilitated. Faster electron transfer to adsorbed N 2 The electrocatalytic nitrogen reduction process can be accelerated.
Fig. 12 shows the electrochemically active surface areas of examples 1, 7, 8, and 9. Examples 1 and 7, which were calcined at 450 ℃ and 550 ℃, had nearly the same electrochemically active surface area, and as the calcination temperature was increased to 650 ℃ and 750 ℃, examples 8 and 9 had electrochemically active surface areas decreased to 82% of example 1.
Fig. 13 shows the electrochemical impedance of examples 1, 7, 8, and 9. Examples 1 and 7, calcined at 450 ℃ and 550 ℃, had nearly identical conductivities, with the radius of curvature also increasing significantly in the Nyquist plot as the calcination temperature was increased to 650 ℃ and 750 ℃. Thus, too high a calcination temperature during synthesis is detrimental to the electrocatalytic nitrogen reduction performance of the catalyst.
FIG. 14 shows the different bond types and B-Mo bond ratios of boron obtained by XPS test of examples 1-3, wherein the B-Mo bond ratio of example 1 is 32.9% higher than that of example 2 and 24.9% of example 3, and the B-Mo active center greatly promotes the polarization and breaking of nonpolar N≡N bond due to the different electron accepting and feedback capacities of boron and molybdenum, thereby improving the electrocatalytic nitrogen reduction catalytic activity.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (7)

1. The preparation method of the molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia is characterized by comprising the following steps of: mo is added with 2 C and B 4 C ball milling treatment is carried outCalcining to obtain Mo 2 C-B 4 C composite material; the calcination is carried out in a non-oxygen atmosphere, the calcination temperature is 450-750 ℃, the temperature rising rate is 2-10 ℃/min, and the time is 1-10 h.
2. The method for producing molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia as set forth in claim 1, wherein the Mo 2 C and B 4 The mole ratio of Mo to B in C is 1:1-1:4.
3. The method for preparing the molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia according to claim 1, wherein the ball milling time is 1-16 h, the ball-to-material ratio is 20:1-30:1, and the rotating speed is 20-60Hz.
4. A method for preparing a molybdenum carbide-boron carbide composite material for electrocatalytic synthesis of ammonia as claimed in claim 3, wherein the calcined atmosphere is N 2 The calcining temperature is 450-550 ℃.
5. A molybdenum carbide-boron carbide composite material obtainable by the process of any one of claims 1 to 4.
6. The molybdenum carbide-boron carbide composite material of claim 5, wherein B in the molybdenum carbide-boron carbide composite material 4 Part C is coated on Mo 2 C surface to Mo 2 The surface of C is modified, and Mo-B bonds are generated between two phases.
7. Use of the molybdenum carbide-boron carbide composite material of claim 5 in electrocatalytic synthesis of ammonia.
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CN113058658A (en) * 2021-03-15 2021-07-02 福州大学 Super-hydrophobic molybdenum-loaded catalyst and preparation method and application thereof
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