Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia and preparation method and application thereof

Abstract

The application provides a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia and a preparation method and application thereof, and belongs to the technical field of intermetallic compounds. The Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia comprises a Co-based intermetallic compound and a carbon carrier; the general formula of the Co-based intermetallic compound is Co x M y wherein x is 1-7, y is 1-4; the metal M is one or two of metal germanium, tin, nickel and copper; and the Co-based intermetallic compound is uniformly loaded on the carbon carrier. The binary and ternary Co-based intermetallic compound / carbon composite material is prepared by a solid grinding method, which is simple in operation and can be produced in large scale and batches; and the prepared Co-based intermetallic compound / carbon composite material has excellent performance and outstanding durability in electrocatalytic reduction of nitrate to synthesize ammonia, and meets the development requirements in the field of electrocatalytic synthesis of ammonia.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of intermetallic compounds, and relates to a Co-based intermetallic compound / carbon composite for electrocatalytic synthesis of ammonia as well as a preparation method and application thereof, in particular to a binary and ternary Co-based intermetallic compound / carbon composite, a preparation method and application in electrocatalytic synthesis of ammonia. BACKGROUND

[0002] Groundwater is an important fresh water resource for human beings. However, in recent years, the nitrate content in groundwater has increased, which poses a threat to human health and reduces the quality of agricultural products. In addition, the demand for ammonia (NH3) is increasing in many fields such as fertilizer production and energy production, and the current industrial synthesis of NH3 mainly relies on the Haber-Bosch process with high energy consumption. To solve these problems, the electrocatalytic reduction of nitrate (NO3RR) at room temperature and atmospheric pressure has attracted widespread attention, which not only provides a sustainable way for the treatment of nitrate pollution in groundwater, but also promotes the preparation of renewable NH3. Previous studies have explored a variety of metal-based catalysts (such as Cu, Ru, Pd, Co, etc.) for NO3RR to NH3. - Among them, Co-based materials are considered as potential catalysts for NO3RR due to their excellent NH3 selectivity, which is mainly attributed to their unfilled d-orbital electrons that can efficiently activate NO3 - . However, the NO3RR mechanism involves a complex eight-electron / nine-proton transfer process, which is highly dependent on active hydrogen (*H) from water dissociation, while competing with the hydrogen evolution reaction (HER) on the catalyst-electrolyte interface. In theory, the improvement of NO3 - adsorption on the catalyst surface and the increase of *H supply can synergistically achieve high NH3 selectivity and yield. However, balancing the two on the active sites is still a key challenge for NO3RR.

[0003] To solve this problem, alloying the catalytic metal with promoting elements has been widely studied, but the random distribution of active sites in traditional solid solution alloys limits the precise control of the distribution of NO3 - / H + optimization. In contrast, intermetallic compounds (IMCs) with long-range atomic order can provide catalytic sites with uniform configuration, thereby promoting the synergistic optimization of NO3 - adsorption and *H delivery. In addition, IMCs can be precisely regulated by stoichiometric ratio adjustment guided by phase diagrams due to their active site configuration, and the formed structure has low formation enthalpy, thus exhibiting excellent structural and performance stability. Therefore, constructing IMCs by combining catalytic metals with promoting elements is an effective strategy to synergistically regulate NO3 - adsorption and *H supply, thereby improving the activity of NO3RR.

[0004] Therefore, it is of great significance to develop an intermetallic compound catalyst which can quickly and effectively convert nitrate into ammonia. SUMMARY

[0005] In order to solve the technical problems existing at present, the application provides a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia and a preparation method and application thereof.

[0006] The technical scheme of the application is as follows:

[0007] The Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia comprises a Co-based intermetallic compound and a carbon carrier; the general formula of the Co-based intermetallic compound is Co x M y wherein x is 1-7, y is 1-4; the metal M is one or two of metal germanium (Ge), tin (Sn), nickel (Ni) and copper (Cu); and the Co-based intermetallic compound is uniformly loaded on the carbon carrier.

[0008] According to the application, preferably, the metal M is germanium (Ge), tin (Sn), a combination of germanium (Ge) and nickel (Ni), a combination of nickel (Ni) and tin (Sn), or a combination of germanium (Ge) and copper (Cu).

[0009] According to the application, preferably, the Co-based intermetallic compound for electrocatalytic synthesis of ammonia is selected from one of the following compounds: Co2Ge, Co7Ge4, Co3Ge2, CoGe, Co 2.9 Sn2, CoNiGe, CoNiSn, Co2CuGe2.

[0010] According to the application, the preparation method of the Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia comprises the following steps:

[0011] (1) uniformly mixing a metal Co precursor, a metal M precursor, monocyannide and a carbon carrier by a solid grinding method to obtain a mixture;

[0012] (2) performing high-temperature heat treatment on the mixture obtained in step (1) in a reducing atmosphere to obtain the Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia.

[0013] According to the application, preferably, the metal Co precursor in step (1) is a water-soluble Co salt, and further preferably Co(NO3)2·6H2O.

[0014] According to the application, preferably, the metal M precursor in step (1) is a water-soluble metal M salt, and the metal M is one or two of germanium (Ge), tin (Sn), nickel (Ni), and copper (Cu); further preferably, the metal germanium precursor is (NH4)2GeF6, the metal tin precursor is SnCl2·2H2O, the metal nickel precursor is Ni(NO3)2·6H2O, and the metal copper precursor is Cu(NO3)2·3H2O.

[0015] According to the application, preferably, the mass of the monocyamine to the number of moles of the metal Co precursor in step (1) is 50-150 mg:0.1 mmol.

[0016] According to the application, preferably, the carbon carrier in step (1) is superconducting carbon kish black, carbon nanotubes, carbon black (Vulcan xc-72R), or carbon nanofibers (CNFs); and the mass of the carbon carrier to the number of moles of the metal Co precursor is 30-90 mg:0.1 mmol.

[0017] According to the application, preferably, in step (1), the solid grinding step is: mixing the metal Co precursor, the metal M precursor, and the monocyamine, grinding for 5-15 minutes, then adding the carbon carrier and continuing to grind for 20-30 minutes to obtain a mixture.

[0018] According to the application, preferably, the reducing atmosphere in step (2) is argon-hydrogen mixed gas, and the volume fraction of hydrogen in the mixed gas is 5-10%.

[0019] According to the application, preferably, the temperature of the high-temperature heat treatment in step (2) is 700-1000℃, the time of the high-temperature heat treatment is 3-12 h, and the heating rate of the high-temperature heat treatment process is 2-8℃ / min.

[0020] The application also provides a use of the Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia in electrocatalytic reduction of nitrate to synthesize ammonia.

[0021] The technical features and advantages of the application are as follows:

[0022] 1. The target Co-based intermetallic compound prepared by the simple solid grinding method of the application not only has the advantages of simple and fast operation, easy mass production, rich content, and low cost of the metal Co precursor and other metal precursors, but also has the advantages of large specific surface area, excellent catalytic activity, and excellent stability, and exhibits excellent catalytic activity and stability in electrocatalytic reduction of nitrate to synthesize ammonia, thereby meeting the requirements of application and development in related fields and having good application prospects.

[0023] 2. In the preparation of the Co-based intermetallic compound of the present invention, a specific metal is selected to form a binary or ternary alloy with Co, and is loaded on a specific carrier, thereby ensuring that the resulting composite material has excellent catalytic activity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 X-ray diffraction patterns (XRD) of the Co-based intermetallic compound / carbon composite materials prepared in Examples 1-4, wherein (a) Co2Ge / C; (b) Co7Ge4 / C; (c) Co3Ge2 / C; and (d) CoGe / C.

[0025] Figure 2 The X-ray diffraction patterns (XRD) of the Co-based intermetallic compound / carbon composite material prepared in Examples 5-8, wherein (a) Co 2.9 Sn2 / C; (b) CoNiGe / C; (c) CoNiSn / C; (d) Co2CuGe2 / C.

[0026] Figure 3 Scanning electron microscope (SEM) images of the Co-based intermetallic compound / carbon composite materials prepared in Examples 1-4, wherein (a) Co2Ge / C; (b) Co7Ge4 / C; (c) Co3Ge2 / C; and (d) CoGe / C.

[0027] Figure 4 These are low-magnification high-angle dark field scanning transmission electron microscopy (HAADF-STEM) images of the Co-based intermetallic compound / carbon composite materials prepared in Examples 1-4, where (a) Co2Ge / C; (b) Co7Ge4 / C; (c) Co3Ge2 / C; and (d) CoGe / C.

[0028] Figure 5 The Co-based intermetallic compound / carbon composite material prepared in Example 1-4 was placed in a 0.1 mol / L KOH solution with or without 500 ppm NO3 - Linear sweep voltammetry (LSV) curves at -N, where (a) Co2Ge / C; (b) Co7Ge4 / C; (c) Co3Ge2 / C; (d) CoGe / C.

[0029] Figure 6 The Co-based intermetallic compound / carbon composite material prepared in Example 1-4 was dissolved in 0.1 mol / L KOH solution and 500 ppm NO3 - Ammonia yield and Faradaic efficiency (FE) at -N, where (a) Co2Ge / C; (b) Co7Ge4 / C; (c) Co3Ge2 / C; (d) CoGe / C.

[0030] Figure 7 Co-based intermetallic compound / carbon composite prepared for Example 9 in 0.1 mol / L KOH solution, 500 ppm NO3 - - Ammonia production rate and Faraday efficiency (FE) at -N.

[0031] Figure 8 Co-based intermetallic compound / carbon composite prepared for Example 2 in 0.1 mol / L KOH solution, 500 ppm NO3 - - Ammonia production rate and Faraday efficiency (FE) after 15 cycles of stability test at -N.

[0032] Figure 9 Co-based intermetallic compound / carbon composite prepared for Example 2 in 0.1 mol / L KOH solution, 500 ppm NO3 - - X-ray diffraction pattern (XRD) of the sample after 15 cycles of stability test at -N.

[0033] Figure 10 Co-based intermetallic compound / carbon composite prepared for Example 2 in 0.1 mol / L KOH solution, 500 ppm NO3 - - Morphology characterization of the sample after 15 cycles of stability test at -N, wherein (a) scanning electron microscope (SEM) image; (b) low-magnification transmission electron microscope (TEM) image. DETAILED DESCRIPTION

[0034] In order to better understand the technical solutions of the present application, the present application includes but is not limited to the specific embodiments described below, and similar technologies and methods should be considered as falling within the scope of the present application. In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail with reference to the drawings and specific embodiments.

[0035] It should be clear that the embodiments described in the present application are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0036] Example 1

[0037] A preparation method of a Co-based intermetallic compound / carbon composite for electrocatalytic synthesis of ammonia, comprising the following steps:

[0038] 1) Preparation of mixture: 0.2 mmol Co(N03)2-6H20 and 0.1 mmol (NH4)2GeF6 metal precursors, 100 mg monocyane were ground in a mortar for 10 min, then 64 mg of superconducting carbon kish graphite was added and ground for 20 min to make them fully mixed and uniform, forming a mixture.

[0039] 2) Preparation of Co2Ge intermetallic compound / carbon composite material: The mixture obtained was heated to 900℃ at a heating rate of 5℃ / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas was 5%), and heat treated for 6 h, and naturally cooled to room temperature to obtain a Co2Ge intermetallic compound / carbon composite material, denoted as Co2Ge / C.

[0040] Example 2

[0041] A method for preparing a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0042] 1) Preparation of mixture: 0.175 mmol Co(N03)2-6H20 and 0.1 mmol (NH4)2GeF6 metal precursors, 100 mg monocyane were ground in a mortar for 10 min, then 64 mg of superconducting carbon kish graphite was added and ground for 20 min to make them fully mixed and uniform, forming a mixture.

[0043] 2) Preparation of Co7Ge4 intermetallic compound / carbon composite material: The mixture obtained was heated to 900℃ at a heating rate of 5℃ / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas was 5%), and heat treated for 6 h, and naturally cooled to room temperature to obtain a Co7Ge4 intermetallic compound / carbon composite material, denoted as Co7Ge4 / C.

[0044] Example 3

[0045] A method for preparing a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0046] 1) Preparation of mixture: 0.15 mmol Co(N03)2-6H20 and 0.1 mmol (NH4)2GeF6 metal precursors, 100 mg monocyane were ground in a mortar for 10 min, then 64 mg of superconducting carbon kish graphite was added and ground for 20 min to make them fully mixed and uniform, forming a mixture.

[0047] 2) Preparation of Co3Ge2 intermetallic compound / carbon composite material: the obtained mixture is heated to 900℃ at a heating rate of 5℃ / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas is 5%), heat treated for 6h, and naturally cooled to room temperature to obtain a Co3Ge2 intermetallic compound / carbon composite material, denoted as Co3Ge2 / C.

[0048] Example 4

[0049] A preparation method of a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0050] 1) Preparation of mixture: 0.1mmol Co(NO3)2·6H2O and 0.1mmol (NH4)2GeF6 metal precursors, 100mg monocyane are ground in a mortar for 10min, then 64mg of superconducting carbon kish graphite is added and ground for 20min to make them fully mixed and uniform, forming a mixture.

[0051] 2) Preparation of CoGe intermetallic compound / carbon composite material: the obtained mixture is heated to 900℃ at a heating rate of 5℃ / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas is 5%), heat treated for 6h, and naturally cooled to room temperature to obtain a CoGe intermetallic compound / carbon composite material, denoted as CoGe / C.

[0052] Example 5

[0053] A preparation method of a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0054] 1) Preparation of mixture: 0.12mmol Co(NO3)2·6H2O and 0.08mmol SnCl2·2H2O metal precursors, 100mg monocyane are ground in a mortar for 10min, then 64mg of superconducting carbon kish graphite is added and ground for 20min to make them fully mixed and uniform, forming a mixture.

[0055] 2) Preparation of Co 2.9 Sn2 intermetallic compound / carbon composite material: the obtained mixture is heated to 900℃ at a heating rate of 5℃ / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas is 5%), heat treated for 3h, and naturally cooled to room temperature to obtain a Co 2.9 Sn2 intermetallic compound / carbon composite material, denoted as Co 2.9 Sn2 / C.

[0056] Example 6

[0057] A preparation method of a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0058] 1) Preparation of a mixture: 0.1 mmol of Co(NO3)2·6H2O, 0.1 mmol of Ni(NO3)2·6H2O, and 0.1 mmol of (NH4)2GeF6 metal precursor, and 100 mg of monocyamine were ground in a mortar for 10 min, and then 64 mg of superconducting carbon Ketjen black was added and ground for 20 min to fully mix and uniformly form a mixture.

[0059] 2) Preparation of a CoNiGe intermetallic compound / carbon composite material: the mixture was heated to 900°C at a heating rate of 5°C / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas being 5%), and heat treated for 6 h, and then naturally cooled to room temperature to obtain a CoNiGe intermetallic compound / carbon composite material, denoted as CoNiGe / C.

[0060] Example 7

[0061] A preparation method of a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0062] 1) Preparation of a mixture: 0.1 mmol of Co(NO3)2·6H2O, 0.1 mmol of Ni(NO3)2·6H2O, and 0.1 mmol of SnCl2·2H2O metal precursor, and 100 mg of monocyamine were ground in a mortar for 10 min, and then 64 mg of superconducting carbon Ketjen black was added and ground for 20 min to fully mix and uniformly form a mixture.

[0063] 2) Preparation of a CoNiSn intermetallic compound / carbon composite material: the mixture was heated to 900°C at a heating rate of 5°C / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas being 5%), and heat treated for 6 h, and then naturally cooled to room temperature to obtain a CoNiSn intermetallic compound / carbon composite material, denoted as CoNiSn / C.

[0064] Example 8

[0065] A preparation method of a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, comprising the following steps:

[0066] 1) Preparation of the mixture: 0.2 mmol Co(NO3)2·6H2O, 0.1 mmol Cu(NO3)2·3H2O and 0.2 mmol (NH4)2GeF6metal precursors, 100 mg monocyanoamine were ground in a mortar for 10 min, then 64 mg of superconducting carbon kish graphite was added and ground for 20 min to make them fully mixed and uniform, forming a mixture.

[0067] 2) Preparation of Co2CuGe2 intermetallic compound / carbon composite material: the mixture was heated to 900℃ at a heating rate of 5℃ / min in a reducing atmosphere (argon-hydrogen mixed gas, the volume fraction of hydrogen in the mixed gas was 5%), and heat treated for 6 h, and then naturally cooled to room temperature to obtain a Co2CuGe2 intermetallic compound / carbon composite material, denoted as Co2CuGe2 / C.

[0068] Example 9

[0069] A method for preparing a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia was as described in Example 2, except that equal mass of carbon nanotubes was used instead of superconducting carbon kish graphite in step (1).

[0070] Comparative Example 1

[0071] A method for preparing a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia was as described in Example 2, except that no carbon carrier was added.

[0072] In this comparative example, no carbon carrier was added, and no Co-based intermetallic compound was obtained.

[0073] The comprehensive analysis is as follows:

[0074] 1. X-ray powder diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM)

[0075] The X-ray diffraction patterns (XRD) of the Co-based intermetallic compound / carbon composite materials prepared in Examples 1-8 are shown in Figures 1-2 respectively, and it can be seen from Figures 1-2 that the X-ray diffraction patterns of the obtained products correspond to the standard patterns of the corresponding Co-based intermetallic compounds, and a characteristic peak of carbon appears at about 24º.

[0076] Figures 3-4 The SEM and TEM images of the Co-based intermetallic compound / carbon composite materials prepared in Examples 1-4 are shown in Figures 3-4It can be seen that the Co-based intermetallic compounds prepared in Examples 1-4 have a rough porous structure, a large specific surface area, and the nanoparticles are uniformly distributed on the superconducting carbon coke, and the particle sizes of Co2Ge, Co7Ge4, Co3Ge2, and CoGe / C are about 27 nm, 23 nm, 24 nm, and 22 nm, respectively.

[0077] 2. Performance of Co-based intermetallic compounds in nitrate reduction (NO3RR)

[0078] (1) The performance of the Co-based intermetallic compounds / carbon composites prepared in Examples 1-4 as catalysts in nitrate reduction (NO3RR) was tested by linear sweep voltammetry, and the specific steps were as follows:

[0079] i. Preparation of working electrode: 5 mg of catalyst sample, 50 μL of 5wt% Nafion solution, and 950 μL of isopropyl alcohol were ultrasonically mixed for 1 hour to prepare a uniform black ink. Then 200 μL of the catalyst ink was uniformly coated on a 1 cm 2 carbon paper (CP), and naturally air-dried to obtain a working electrode, with a catalyst loading of 1 mg / cm 2 .

[0080] ii. The performance of the reduction reaction (NO3RR) was evaluated in a three-electrode system using a CHI 660E electrochemical workstation, with the electrode obtained in step i as the working electrode, a platinum sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte was a 0.1 mol / L KOH aqueous solution containing 500 ppm NO3 - -N (provided by KNO3), and the test was performed in an H-type electrolytic cell, with the anode and cathode chambers separated by a Nafion 211 membrane, which was pretreated as follows: first soaked in a 50°C 5wt% H2O2 aqueous solution for 1 hour, then treated in a 50°C 0.1 mol / L H2SO4 aqueous solution for 1 hour, and finally repeatedly washed with deionized water. All potentials were converted to the reversible hydrogen electrode (RHE) scale (E RHE =E Ag / AgC +0.059×pH+0.197V), and the test potential range was 0 to -0.85V (vs. RHE) with a scan rate of 10 mV s -1 . To investigate the effect of nitrate ions, tests were performed under conditions without NO3 - -N, and all data were not IR corrected.

[0081] The results are shown in Figure 5 , and Figure 5It can be seen that the current density of the Co-based intermetallic compound / carbon composite material prepared in Examples 1-4 with nitrate is much larger than that without nitrate, indicating that all Co-based intermetallic compounds have NO3RR catalytic performance.

[0082] (2) Select different voltages to test the yield of ammonia and Faraday efficiency

[0083] The specific test steps are as follows: a working potential of-0.4V to-0.8V (vs. RHE) is applied to the working electrode, and chronoamperometry test is carried out respectively and lasts for 1 hour, and the cumulative electric quantity in the electrolysis process is recorded. After electrolysis, the absorbance of NH4 + in the solution is determined by indophenol blue colorimetry, and the ammonia yield is calculated and the corresponding Faraday efficiency is evaluated.

[0084] The results are shown in Figure 6 , and it can be seen from Figure 6 that the yield of ammonia increases with the increase of voltage, and at-0.8V, Co2Ge / C, Co7Ge4 / C, Co3Ge2 / C and CoGe / C have the maximum ammonia yield, which are 6.95mg h -1 cm -2 , 7.56mgh -1 cm -2 , 7.15mg h -1 cm -2 , 5.79mg h -1 cm -2 . However, the Faraday efficiency of ammonia first increases and then decreases with the increase of voltage, and at-0.6V, it reaches the maximum value, which is 91.47%, 97.76%, 94.24% and 88.94% respectively, indicating that Co7Ge4 / C has the best NO3RR performance and the performance is better than most of the reported electrocatalysts. The ammonia yield and Faraday efficiency of the Co-based intermetallic compound / carbon composite material obtained by replacing the carbon carrier with carbon nanotubes in Example 9 are shown in Figure 7 , and it can be seen from Figure 7 that the maximum ammonia yield is 7.04mg h -1 cm -2 at-0.8V, and the maximum Faraday efficiency is 93.02% at-0.6V, which are lower than the composite material obtained by using superconducting carbon kish black as the carbon carrier.

[0085] (3) Stability test

[0086] Stability is another important indicator for evaluating the practical application of electrocatalysts, as Figure 8As shown, 15 cycles were carried out at-0.6 V, and it was found that the ammonia production rate and Faraday efficiency remained almost unchanged, proving that the Co-based intermetallic compound / carbon composite prepared in Example 2 has excellent stability. Subsequently, the sample after electrolysis was characterized by XRD, SEM and TEM, as shown in Figure 9 and Figure 10 As shown, it was found that the morphology and crystal phase did not change, further proving that the Co7Ge4 intermetallic compound has excellent stability.

[0087] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0088] In addition, those skilled in the art can understand that although some of the embodiments herein include certain features rather than others included in other embodiments, the combination of features of different embodiments means to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in the background section is only intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia, characterized in that: It includes a Co-based intermetallic compound and a carbon support; the general formula of the Co-based intermetallic compound is Co x M y , wherein x is 1-7, y is 1-4; the metal M is one or two of metal germanium, tin, nickel, and copper; the Co-based intermetallic compound is uniformly loaded on a carbon support; the carbon support is superconducting carbon Ketjen black, carbon nanotubes, carbon black, or carbon nanofibers; The Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia is prepared by the following method, which comprises the following steps: (1) uniformly mixing a metal Co precursor, a metal M precursor, monocyanamide and a carbon support by a solid grinding method to obtain a mixture; the metal Co precursor is a water-soluble Co salt; the metal M precursor is a water-soluble metal M salt; (2) The mixture obtained in step (1) is subjected to high-temperature heat treatment in a reducing atmosphere to obtain a Co-based intermetallic compound / carbon composite material for electrocatalytic synthesis of ammonia.

2. The Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to claim 1, characterized in that: The metal M is germanium, tin, a combination of germanium and nickel, a combination of nickel and tin, or a combination of germanium and copper.

3. The Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to claim 1, characterized in that: The Co-based intermetallic compound for electrocatalytic synthesis of ammonia is selected from one of the following compounds: Co2Ge, Co7Ge4, Co3Ge2, CoGe, Co 2.9 Sn2, CoNiGe, CoNiSn, Co2CuGe2.

4. The Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to claim 1, characterized in that: In step (1), the metal Co precursor is Co(NO3)2·6H2O; the metal germanium precursor is (NH4)2GeF6, the metal tin precursor is SnCl2·2H2O, the metal nickel precursor is Ni(NO3)2·6H2O, and the metal copper precursor is Cu(NO3)2·3H2O.

5. The Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to claim 1, characterized in that: The ratio of the mass of the monocyanamide to the molar number of the metal Co precursor in step (1) is 50-150 mg:0.1 mmol; The carbon carrier is superconducting carbon Ketjen black, carbon nanotubes, carbon black or carbon nanofibers; the ratio of the mass of the carbon carrier to the molar number of the metal Co precursor is 30-90 mg:0.1 mmol.

6. The Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to claim 1, characterized in that: In step (1), the solid grinding step is: mixing the metal Co precursor, the metal M precursor, and monocyanamide, grinding for 5-15 minutes, and then adding the carbon support and continuing to grind for 20-30 minutes to obtain a mixture.

7. The Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to claim 1, characterized in that: The reducing atmosphere in step (2) is an argon-hydrogen mixed gas, and the volume fraction of hydrogen in the mixed gas is 5-10%; the temperature of the high-temperature heat treatment is 700-1000°C, and the time of the high-temperature heat treatment is 3-12h; the heating rate of the high-temperature heat treatment process is 2-8°C / min.

8. Use of the Co-based intermetallic compound / carbon composite material for electrocatalytic ammonia synthesis according to any one of claims 1 to 7 in electrocatalytic nitrate reduction to synthesize ammonia.

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