Nitrogen-doped graphdiynyl copper-molybdenum alloy catalyst as well as preparation method and application thereof

Abstract

The invention provides a nitrogen-doped graphdiynyl copper-molybdenum alloy catalyst as well as a preparation method and application thereof. The nitrogen-doped graphdiynyl copper-molybdenum alloy catalyst comprises a carrier and an active component deposited on the carrier, the carrier is a nitrogen-doped graphdiynyl group; and the active component is a copper-molybdenum alloy. According to the invention, the characteristic that the graphdiyne material can grow in situ on any substrate is combined with an electro-deposition process of Cu and Mo active components, so that the catalyst can be directly prepared in situ on the surface of an electrode, and a traditional catalyst loading process is avoided. The nitrogen-doped graphdiynyl copper-molybdenum alloy catalyst is used as a catalytic electrode and can be directly used for synthesizing urea through electrocatalytic carbon dioxide / nitrogen / water reaction, and the urea electrocatalytic synthesis selectivity, activity and long-acting stability are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of photoelectric material chemistry and carbon capture, utilization and storage (CCUS), and relates to a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, a preparation method and an application thereof. Background Art

[0002] The rapid development of industrial society has led to massive carbon dioxide emissions, exacerbating the greenhouse effect and causing a series of adverse impacts on the climate and environment. Therefore, in today's context, the capture, utilization, and storage of carbon dioxide have become a topic of great concern.

[0003] Urea is an important agricultural fertilizer and industrial raw material, possessing significant value for human production and life. Electrochemical synthesis of urea by directly reacting carbon dioxide with water and nitrogen is a promising option for carbon dioxide resource recovery, yet current researchers have paid limited attention to this technology. The lack of highly selective, active, and stable electrode catalyst materials is a crucial factor limiting the electrocatalytic synthesis of urea.

[0004] Among numerous carbon materials, graphyne (GD) is a novel carbon allotrope composed of sp and sp2 hybridized carbon, exhibiting a two-dimensional planar network structure consisting of diacetylenic bonds conjugated to benzene rings. GD exhibits a rich carbon chemical bond structure, a continuous, large conjugated system, wide interplanar spacing, outstanding mechanical and chemical stability, and semiconductor properties comparable to silicon, demonstrating promising applications in catalysis. Therefore, GD can be used as a support for the electrocatalytic conversion of urea.

[0005] However, the disadvantage of competing with the hydrogen evolution reaction (HER) during urea electrocatalytic synthesis also hinders the output of urea. Therefore, to address the above problems, it is urgent to develop a new electrode catalyst material with high yield and high activity that can inhibit the progress of HER and achieve urea synthesis, which has important guiding significance and practical value for the electrocatalytic production of urea. Summary of the Invention

[0006] The purpose of the present invention is to provide a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, a preparation method and application thereof. The nitrogen-doped graphene-based copper-molybdenum alloy catalyst can be used as a catalytic electrode to directly electrocatalyze the carbon dioxide / nitrogen / water reaction to synthesize urea, greatly improving the selectivity, activity and long-term stability of the electrocatalytic synthesis of urea, and better meeting the needs of developing CCUS technology.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, wherein the nitrogen-doped graphene-based copper-molybdenum alloy catalyst comprises a carrier and an active component deposited on the carrier;

[0009] The carrier is a nitrogen-doped graphene base;

[0010] The active component is copper-molybdenum alloy.

[0011] The catalyst of the present invention can be directly used as a catalytic electrode and can be directly used in urea electrocatalytic synthesis, thereby greatly improving the selectivity, activity and long-term stability of urea electrocatalytic synthesis.

[0012] It is worth noting that the present invention designs active centers composed of Cu and Mo in the catalyst structure, and Cu and Mo respectively achieve efficient adsorption of carbon dioxide and free nitrogen, thereby suppressing the hydrogen evolution (HER) side reaction produced by water electrolysis, and greatly promoting the selectivity and yield of the catalytic reaction for urea products.

[0013] It is worth noting that the electronic structure of graphyne can be effectively regulated by utilizing the characteristics of graphyne materials such as rich carbon chemical bonds, continuous large conjugated system, wide interplanar spacing, and outstanding mechanical and chemical stability, combined with nitrogen atom doping, to produce better metal-support interaction, and further optimize the catalyst activity and stability through synergistic effect with active centers.

[0014] As a preferred technical solution of the present invention, the mass content of the copper-molybdenum alloy in the nitrogen-doped graphene-based copper-molybdenum alloy catalyst is 1-6wt%, for example, it can be 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt% or 5.5wt%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] Preferably, the particle size of the copper-molybdenum alloy is less than 30 nm, for example, it can be 28 nm, 25 nm, 23 nm, 20 nm, 18 nm, 15 nm, 12 nm, 10 nm, 8 nm, 6 nm, 5 nm, 3 nm or 2 nm, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 4-10 nm.

[0016] In the present invention, the copper-molybdenum alloy particles of the active component are smaller in size and more active, and efficient urea electrocatalytic synthesis can be achieved by depositing only a trace amount of the copper-molybdenum alloy.

[0017] Preferably, the nitrogen-doped graphyne in the nitrogen-doped graphyne base is in-situ grown on the surface of the substrate.

[0018] As a preferred technical solution of the present invention, the preparation method of the nitrogen-doped graphene group includes:

[0019] (1) mixing hexaethynylbenzene, cuprous iodide, and an organic solvent to obtain a mixed solution, then placing a substrate in the mixed solution, and then performing a thermal reaction to obtain a graphene group;

[0020] (2) Annealing the Graphyne group described in step (1) in an ammonia atmosphere to obtain a nitrogen-doped Graphyne group.

[0021] It is worth noting that due to the characteristic of graphyne materials that they can be grown in situ on any substrate, the catalyst can be prepared directly in situ on the electrode surface, avoiding the traditional catalyst loading process; in addition, annealing the graphyne base in an ammonia atmosphere and doping with nitrogen atoms can effectively regulate the graphyne electronic structure and produce a better metal-support interaction.

[0022] As a preferred technical solution of the present invention, the mass ratio of hexaethynylbenzene and cuprous iodide in step (1) is (2.5-40):1, for example, it can be 5:1, 7:1, 9:1, 10:1, 12:1, 15:1, 20:1, 25:1, 30:1 or 35:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the solid-to-liquid ratio of the hexaethynylbenzene and the organic solvent in step (1) is (0.25-4):1 mg / mL, for example, it can be 0.5:1 mg / mL, 0.7:1 mg / mL, 0.9:1 mg / mL, 1:1 mg / mL, 1.2:1 mg / mL, 1.5:1 mg / mL, 2:1 mg / mL, 2.5:1 mg / mL, 3:1 mg / mL or 3.5:1 mg / mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, the organic solvent in step (1) comprises pyridine.

[0025] Preferably, the substrate in step (1) comprises carbon cloth.

[0026] Preferably, the thermal reaction in step (1) is carried out in a light-proof and inert atmosphere.

[0027] In the present invention, the inert atmosphere includes nitrogen and / or argon.

[0028] Preferably, the temperature of the thermal reaction in step (1) is 60-130°C, for example, it can be 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or 125°C, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 80-110°C.

[0029] Preferably, the thermal reaction time in step (1) is 12-72 h, for example, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, 55 h, 60 h, 65 h or 70 h, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the graphyne in the graphyne base in step (1) is in situ grown on the surface of the substrate.

[0031] In the present invention, the thermal reaction further includes washing and drying.

[0032] As a preferred technical solution of the present invention, the flow rate of the ammonia gas in step (2) is 100-200 mL / min, for example, it can be 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min or 190 mL / min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the heating rate of the annealing in step (2) is 2-5°C / min, for example, it can be 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min or 4.5°C / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the annealing temperature in step (2) is 450-650°C, for example, 460°C, 470°C, 490°C, 500°C, 520°C, 540°C, 550°C, 560°C, 580°C, 600°C, 620°C or 640°C, etc., but is not limited to the values ​​listed, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the holding time for annealing in step (2) is 4-10 h, for example, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h or 9.5 h, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] In a second aspect, the present invention provides a method for preparing the nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to the first aspect, the preparation method comprising:

[0037] Copper and molybdenum are deposited on the nitrogen-doped graphene base by an electrodeposition method to obtain the nitrogen-doped graphene base copper-molybdenum alloy catalyst.

[0038] The present invention utilizes electrochemical reduction deposition of Cu and Mo on a support to produce a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, avoiding traditional catalyst loading processes. The preparation method is simple and convenient, the required raw materials are readily available, the preparation efficiency is high, and large-scale production is possible. The resulting catalyst exhibits significantly improved selectivity, activity, and long-term stability for urea electrocatalytic synthesis.

[0039] As a preferred technical solution of the present invention, the electrodeposition method specifically includes:

[0040] The nitrogen-doped graphene-based catalyst is used as a working electrode and a three-electrode system is adopted to carry out a first electrodeposition reaction in a copper-containing electrolyte to obtain a nitrogen-doped graphene-based copper catalyst. Then, the nitrogen-doped graphene-based catalyst is used as a working electrode and a three-electrode system is adopted to carry out a second electrodeposition reaction in a molybdenum-containing electrolyte.

[0041] In the present invention, both the first electrodeposition reaction and the second electrodeposition reaction are electrochemical reduction deposition at a constant current density.

[0042] After the first electrodeposition reaction of the present invention, each electrode and the electrolytic cell are cleaned, and the electrolyte is replaced with a molybdenum-containing electrolyte.

[0043] As a preferred technical solution of the present invention, the three-electrode system uses a graphite rod as a counter electrode and a saturated calomel electrode as a reference electrode.

[0044] Preferably, the copper-containing electrolyte comprises a mixed solution of a copper source and sulfuric acid.

[0045] Preferably, the concentration of the copper source in the copper-containing electrolyte is 20-100 mol / L, for example, 30 mol / L, 40 mol / L, 50 mol / L, 60 mol / L, 70 mol / L, 80 mol / L or 90 mol / L, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 30-80 mol / L.

[0046] Preferably, the concentration of sulfuric acid in the copper-containing electrolyte is 0.2-0.8 mol / L, for example, it can be 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.6 mol / L or 0.7 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the copper source comprises any one of copper chloride, copper sulfate, copper acetate or copper nitrate, or a combination of at least two thereof, wherein the combinations are typically but not limited to: a combination of copper chloride and copper sulfate, a combination of copper acetate and copper sulfate, or a combination of copper chloride and copper nitrate.

[0048] The copper source in the present invention can be selected from anhydrous raw materials and / or hydrate raw materials.

[0049] Preferably, the current density of the first electrodeposition reaction is 10-100 mA / cm 2 , for example, it can be 20mA / cm 2 、30mA / cm 2 , 40mA / cm 2 , 50mA / cm 2 、60mA / cm 2 , 70mA / cm 2 、80mA / cm 2 or 90mA / cm 2 etc., but not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 20-50 mA / cm 2 .

[0050] Preferably, the deposition time of the first electrodeposition reaction is 800-3600s, for example, it can be 900s, 1000s, 1200s, 1500s, 1800s, 2000s, 2200s, 2500s, 2800s, 3000s or 3500s, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 1000-2400s.

[0051] As a preferred technical solution of the present invention, the molybdenum-containing electrolyte includes a mixed solution of a molybdenum source and sulfuric acid.

[0052] Preferably, the concentration of the molybdenum source in the molybdenum-containing electrolyte is 5-50 mol / L, for example, it can be 10 mol / L, 15 mol / L, 20 mol / L, 25 mol / L, 30 mol / L, 35 mol / L, 40 mol / L or 45 mol / L, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 20-50 mol / L.

[0053] Preferably, the concentration of sulfuric acid in the molybdenum-containing electrolyte is 0.2-0.8 mol / L, for example, it can be 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.6 mol / L or 0.7 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] Preferably, the molybdenum source comprises sodium molybdate and / or ammonium molybdate.

[0055] The molybdenum source in the present invention can be an anhydrous raw material and / or a hydrate raw material.

[0056] Preferably, the current density of the second electrodeposition reaction is 1-30 mA / cm 2 , for example, it can be 2mA / cm 2 , 4mA / cm 2 , 5mA / cm 2 , 7mA / cm 2 , 10mA / cm 2 , 12mA / cm 2 , 15mA / cm 2 , 17mA / cm 2 , 20mA / cm 2 or 25mA / cm 2 etc., but not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 5-15 mA / cm 2 .

[0057] Preferably, the deposition time of the second electrodeposition reaction is 200-3600s, for example, it can be 400s, 600s, 900s, 1000s, 1200s, 1500s, 1800s, 2000s, 2200s, 2500s, 2800s, 3000s or 3500s, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 500-2400s.

[0058] Preferably, the second electrodeposition reaction further includes washing and drying in sequence.

[0059] In the present invention, the washing method can be selected as long as the solid matter is cleaned, and the method can be selected according to the actual production situation, and is not specifically limited here. The drying method can be selected as long as the washed solid matter is dried, and the method can be selected according to the actual production situation, and is not specifically limited here.

[0060] In a third aspect, a use of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst as described in the first aspect is provided, wherein the nitrogen-doped graphene-based copper-molybdenum alloy catalyst is used for electrocatalytic synthesis of urea.

[0061] Preferably, the application method comprises: using the nitrogen-doped graphene-based copper-molybdenum alloy catalyst as a working electrode, adopting a three-electrode system, and using carbon dioxide, nitrogen and water as raw materials to carry out an electrocatalytic reaction.

[0062] The three-electrode system of the present invention uses a graphite rod as a counter electrode and a saturated calomel electrode as a reference electrode.

[0063] In the present invention, in the electrocatalytic reaction, the electrolyte is a KHCO3 solution with a concentration of 0.1 mol / L, and is pre-saturated with a mixture of carbon dioxide and nitrogen in a volume ratio of 1:1; at the same time, during the electrocatalytic reaction, the mixture of carbon dioxide and nitrogen is introduced at a flow rate of 2-10 mL / min.

[0064] Preferably, the voltage of the working electrode (standard electrode potential) is 0.3-1.0 V, for example, 0.4 V, 0.5 V, 0.6 V, 0.7 V, 0.8 V or 0.9 V, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] In the present invention, the electrocatalytic reaction is carried out at a constant voltage.

[0066] Preferably, the working time of the working electrode is 1-20h, for example, it can be 2h, 3h, 4h, 5h, 7h, 9h, 10h, 12h, 15h, 17h or 19h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] (1) The catalyst provided by the present invention uses nitrogen-doped graphene as a carrier. The electronic structure of the graphene can be effectively regulated by nitrogen atom doping, resulting in a better metal-carrier effect. Further, through the synergistic effect with the active center, the catalyst activity and stability can be optimized. Copper-molybdenum alloy is used as the active component, and Cu and Mo respectively achieve efficient adsorption of carbon dioxide and free nitrogen, thereby suppressing the side reaction of hydrogen evolution in water electrolysis, and greatly promoting the selectivity and yield of the catalytic reaction for urea products.

[0070] (2) The catalyst provided by the present invention can be used as a catalytic electrode directly for urea electrocatalytic synthesis, significantly improving the selectivity, activity and long-term stability of urea electrocatalytic synthesis;

[0071] (2) The preparation method provided by the present invention combines the property of graphyne material that can be grown in situ on any substrate with the electrodeposition process of Cu and Mo active components, so that the catalyst can be prepared in situ directly on the electrode surface, avoiding the traditional catalyst loading process; the preparation method is simple and convenient, the required raw materials are easy to obtain, the preparation efficiency is high, and large-scale production can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 TEM image of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 1;

[0073] Figure 2 This is an SEM image of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 1;

[0074] Figure 3 Graphs showing the current density-time relationship of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 1 for electrocatalytic synthesis of urea at different constant potentials;

[0075] Figure 4 The UV-visible absorption spectra of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 1 after being treated with electrocatalytic synthesis product solutions at different constant potentials;

[0076] Figure 5 The urea yield results of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 1 at different constant potentials;

[0077] Figure 6 The urea Faraday efficiency results of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 1 at different constant potentials are shown;

[0078] Figure 7 TEM image of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 2;

[0079] Figure 8The urea yield results of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 2 at different constant potentials;

[0080] Figure 9 The urea Faraday efficiency results of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in Example 2 at different constant potentials;

[0081] Figure 10 The UV-visible absorption spectra of the commercial nickel foam in Comparative Example 1 after being treated with electrocatalytic synthesis product solution at different constant potentials. DETAILED DESCRIPTION

[0082] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0083] Example 1

[0084] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, the preparation method comprising:

[0085] (1) 80 mg of hexaethynylbenzene, 5 mg of cuprous iodide, and 200 mL of pyridine were mixed and magnetically stirred to obtain a mixed solution, and then carbon was placed in the mixed solution and stirring was stopped. Then, a thermal reaction was carried out at 110° C. in a dark environment and nitrogen atmosphere for 72 h, followed by washing and drying to obtain a graphene group;

[0086] The graphyne in the graphyne base is in situ grown on the surface of the carbon cloth;

[0087] (2) annealing the graphene alkyl group described in step (1) at a heating rate of 5°C / min to 500°C under an ammonia flow rate of 100 mL / min and keeping the temperature for 6 h to obtain a nitrogen-doped graphene alkyl group;

[0088] (3) A three-electrode system was used, with the nitrogen-doped graphene base described in step (2) as the cathode, the graphite rod as the counter electrode, and the saturated calomel electrode as the reference electrode. In a copper-containing electrolyte, at a constant cathode current density of 50 mA / cm 2 The first electrodeposition reaction was carried out for 1200 s, and then the electrodes and the electrolytic cell were cleaned to obtain a nitrogen-doped graphene-based copper catalyst;

[0089] The copper-containing electrolyte is a mixed solution of 50 mol / L copper chloride dihydrate and 0.5 mol / L sulfuric acid;

[0090] (4) A three-electrode system was used, with the nitrogen-doped graphene-based copper catalyst described in step (3) as the cathode, a graphite rod as the counter electrode, and a saturated calomel electrode as the reference electrode. In a molybdenum-containing electrolyte, at a constant cathode current density of 10 mA / cm 2 A second electrodeposition reaction is carried out for 2000s, followed by washing and drying in sequence to obtain the nitrogen-doped graphene-based copper-molybdenum alloy catalyst;

[0091] The molybdenum-containing electrolyte is a mixed solution of 20 mol / L sodium molybdate dihydrate and 0.5 mol / L sulfuric acid.

[0092] The nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in this example was characterized by inductively coupled plasma spectroscopy. The total content of Cu and Mo elements in the nitrogen-doped graphene-based copper-molybdenum alloy catalyst was 1.21% by mass.

[0093] Depend on Figure 1-2 It can be seen that the nitrogen-doped graphyne material in this embodiment grows uniformly in situ on the carbon cloth substrate, presenting a relatively regular nanomorphology. The copper-molybdenum nanoparticles in the nitrogen-doped graphyne-based copper-molybdenum alloy catalyst prepared in this embodiment have a particle size of about 5 nm, which can be clearly shown under a transmission electron microscope. The catalyst of this size has a greatly increased specific surface area and surface free energy, thereby significantly improving the catalytic activity; and the catalyst with a small particle size can interact more closely with the abundant acetylenic bonds in the graphyne structure, thereby achieving a more secure anchoring of the nanoparticles and improving the stability of the catalyst.

[0094] Depend on Figure 3 It can be seen that when the catalyst prepared in this example is used for electrocatalytic synthesis of urea at a constant cathode potential of 0.4-0.7 V, the current density gradually stabilizes within a reaction time of 2 h.

[0095] Depend on Figure 4 It can be seen that the absorption peak at 525 nm in the UV-visible absorption spectrum reflects the presence of urea, which shows that the catalyst provided in this embodiment can achieve urea electrosynthesis;

[0096] Depend on Figure 5-6 It can be seen that the catalyst prepared in this example exhibits the best electrocatalytic urea synthesis performance when the cathode potential is 0.6 V, and its maximum yield and Faraday efficiency are 152.6 μmol 尿素 g cat . -1 h -1 , 4.52%.

[0097] Example 2

[0098] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, the preparation method comprising:

[0099] (1) 100 mg of hexaethynylbenzene, 5 mg of cuprous iodide, and 200 mL of pyridine were mixed and magnetically stirred to obtain a mixed solution, and then carbon was arranged in the mixed solution and stirring was stopped. Then, a thermal reaction was carried out at 80°C in a dark environment and nitrogen atmosphere for 72 h, and then washed and dried in sequence to obtain a graphene group;

[0100] The graphyne in the graphyne base is in situ grown on the surface of the carbon cloth;

[0101] (2) heating the Graphene Oxide of step (1) to 450° C. at a heating rate of 5° C. / min under an ammonia flow rate of 100 mL / min and annealing the mixture for 8 h to obtain a nitrogen-doped Graphene Oxide;

[0102] (3) A three-electrode system was used, with the nitrogen-doped graphene base described in step (2) as the cathode, the graphite rod as the counter electrode, and the saturated calomel electrode as the reference electrode. In a copper-containing electrolyte, at a constant cathode current density of 60 mA / cm 2 The first electrodeposition reaction was carried out for 1800 s, and then the electrodes and the electrolytic cell were cleaned to obtain a nitrogen-doped graphene-based copper catalyst;

[0103] The copper-containing electrolyte is a mixed solution of 50 mol / L copper sulfate pentahydrate and 0.5 mol / L sulfuric acid;

[0104] (4) A three-electrode system was used, with the nitrogen-doped graphene-based copper catalyst described in step (3) as the cathode, the graphite rod as the counter electrode, and the saturated calomel electrode as the reference electrode. In a molybdenum-containing electrolyte, at a constant cathode current density of 20 mA / cm 2 A second electrodeposition reaction is carried out for 2000s, followed by washing and drying in sequence to obtain the nitrogen-doped graphene-based copper-molybdenum alloy catalyst;

[0105] The molybdenum-containing electrolyte is a mixed solution of 30 mol / L sodium molybdate dihydrate and 0.5 mol / L sulfuric acid.

[0106] The nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in this example was characterized by inductively coupled plasma spectroscopy. The total content of Cu and Mo elements in the nitrogen-doped graphene-based copper-molybdenum alloy catalyst was 3.67% by mass.

[0107] Depend on Figure 7 It can be seen that the particle size of the copper-molybdenum nanoparticles in the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared in this example is similar to that in Example 1, which is about 5 nm, but the metal alloy particles show a tendency to partially aggregate;

[0108] Depend on Figure 8-9It can be seen that the catalyst prepared in this example exhibits the best electrocatalytic urea synthesis performance when the cathode potential is 0.6 V, and its maximum yield and Faraday efficiency are 65.5 μmol 尿素 g cat . -1 h -1 , 1.97%.

[0109] Example 3

[0110] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, the preparation method comprising:

[0111] (1) 200 mg of hexaethynylbenzene, 10 mg of cuprous iodide, and 200 mL of pyridine were mixed and magnetically stirred to obtain a mixed solution, and then carbon was arranged in the mixed solution and stirring was stopped. Then, a thermal reaction was carried out at 95°C in a dark environment under nitrogen for 72 h, and then washed and dried in sequence to obtain a graphene group;

[0112] The graphyne in the graphyne base is in situ grown on the surface of the carbon cloth;

[0113] (2) heating the Graphene base described in step (1) to 650° C. at a heating rate of 3° C. / min under an ammonia flow rate of 150 mL / min, annealing the Graphene base and keeping the temperature for 4 h to obtain a nitrogen-doped Graphene base;

[0114] (3) A three-electrode system was used, with the nitrogen-doped graphene base described in step (2) as the cathode, the graphite rod as the counter electrode, and the saturated calomel electrode as the reference electrode. In a copper-containing electrolyte, at a constant cathode current density of 20 mA / cm 2 The first electrodeposition reaction was carried out for 2400 s, and then the electrodes and the electrolytic cell were cleaned to obtain a nitrogen-doped graphene-based copper catalyst;

[0115] The copper-containing electrolyte is a mixed solution of 50 mol / L copper sulfate pentahydrate and 0.5 mol / L sulfuric acid;

[0116] (4) A three-electrode system was used, with the nitrogen-doped graphene-based copper catalyst described in step (3) as the cathode, the graphite rod as the counter electrode, and the saturated calomel electrode as the reference electrode. In a molybdenum-containing electrolyte, at a constant cathode current density of 5 mA / cm 2 A second electrodeposition reaction is carried out for 2400s, followed by washing and drying in sequence to obtain the nitrogen-doped graphene-based copper-molybdenum alloy catalyst;

[0117] The molybdenum-containing electrolyte is a mixed solution of 40 mol / L sodium molybdate dihydrate and 0.5 mol / L sulfuric acid.

[0118] Example 4

[0119] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst. Except that the concentration of copper chloride dihydrate in step (3) is 10 mol / L, other conditions are the same as those in Example 1.

[0120] Example 5

[0121] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst. Except that the concentration of copper chloride dihydrate in step (3) is 120 mol / L, other conditions are the same as those in Example 1.

[0122] Example 6

[0123] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, except that the current density of the first electrodeposition reaction in step (3) is 5 mA / cm 2 Except for this, other conditions are the same as those in Example 1.

[0124] Example 7

[0125] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, except that the current density of the first electrodeposition reaction in step (3) is 120 mA / cm 2 Except for this, other conditions are the same as those in Example 1.

[0126] Example 8

[0127] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst. Except that the concentration of sodium molybdate dihydrate in step (4) is 2 mol / L, other conditions are the same as those in Example 1.

[0128] Example 9

[0129] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst. Except that the concentration of sodium molybdate dihydrate in step (4) is 60 mol / L, other conditions are the same as those in Example 1.

[0130] Example 10

[0131] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, except that the current density of the second electrodeposition reaction in step (4) is 1 mA / cm 2 Except for this, other conditions are the same as those in Example 1.

[0132] Example 11

[0133] This embodiment provides a method for preparing a nitrogen-doped graphene-based copper-molybdenum alloy catalyst, except that the current density of the second electrodeposition reaction in step (4) is 40 mA / cm2 Except for this, other conditions are the same as those in Example 1.

[0134] Comparative Example 1

[0135] In this comparative example, commercial nickel foam purchased from Wuzhou Sanhe New Material Technology Co., Ltd. was used as a catalyst.

[0136] In the electrolyte obtained by using commercial nickel foam as the catalytic electrode in this comparative example, no absorption peak reflecting the presence of urea was observed in the UV-visible absorption spectrum after treatment (such as Figure 10 As shown), it is shown that urea electrosynthesis cannot be achieved using the catalyst provided in this comparative example.

[0137] Comparative Example 2

[0138] In this comparative example, commercial foam copper purchased from Wuzhou Sanhe New Material Technology Co., Ltd. was used as a catalyst.

[0139] Comparative Example 3

[0140] This comparative example provides a method for preparing a graphene-based copper-molybdenum alloy catalyst. Except that ammonia is not introduced in step (2), other conditions are the same as those in Example 1.

[0141] Comparative Example 4

[0142] This comparative example provides a method for preparing a nitrogen-doped graphene-based molybdenum catalyst. Except that step (3) is not performed, other conditions are the same as those in Example 1.

[0143] Comparative Example 5

[0144] This comparative example provides a method for preparing a nitrogen-doped graphene-based copper catalyst. Except that step (4) is not performed, other conditions are the same as those in Example 1.

[0145] The catalysts prepared in the above examples and comparative examples were used for electrocatalytic synthesis of urea. The specific method was as follows: the catalysts prepared in the above examples and comparative examples were used as the working electrode (cathode), a graphite rod as the counter electrode, and a saturated calomel electrode as the reference electrode. A three-electrode system was used, with a 0.1 mol / L KHCO3 solution as the electrolyte, which was pre-saturated with a mixture of carbon dioxide and nitrogen in a volume ratio of 1:1. The electrocatalytic reaction was carried out at a constant cathode potential of 0.4-0.7 V (relative standard electrode potential) for 2 h. During the reaction, the mixed gas was always passed into the electrolyte at a flow rate of 5 mL / min. After the reaction, the electrolyte was recovered, and the urea yield and Faradaic efficiency were determined by UV-visible spectrophotometry according to the literature Clin. Chim. Acta, 1980, 107, 3–9. The results are shown in Table 1.

[0146] Table 1

[0147]

[0148]

[0149] From Table 1 we can see that:

[0150] (1) Using the preparation method provided in Examples 1-3, the nitrogen-doped graphene-based copper-molybdenum alloy catalyst prepared can efficiently realize the electrocatalytic synthesis of urea, and the yield of synthetic urea can reach 152.6 μmol 尿素 g cat. -1 h -1 , the Faraday efficiency can reach 4.52%;

[0151] (2) From the comparison between Example 1 and Examples 4-5, it can be seen that when the concentration of the copper source in the electrolyte is low, the metal loading after in-situ electrochemical reduction is low, resulting in insufficient catalyst activity; when the concentration of the copper source in the electrolyte is high, the metal loading after in-situ electrochemical reduction is too high, and the catalyst mainly undergoes the side reaction of hydrogen evolution in water electrolysis, and the catalytic activity and selectivity for urea synthesis are both low;

[0152] (3) From the comparison between Example 1 and Examples 6-7, it can be seen that when the current density of the first electrodeposition reaction is low, the metal loading after in-situ electrochemical reduction is low, resulting in insufficient catalyst activity; when the current density of the first electrodeposition reaction is high, the metal loading after in-situ electrochemical reduction is too high, and the catalyst mainly undergoes the side reaction of hydrogen evolution by electrolysis of water, resulting in low activity and selectivity of the catalyst for catalytic synthesis of urea;

[0153] (4) From the comparison between Example 1 and Examples 8-9, it can be seen that when the concentration of the molybdenum source in the electrolyte is low, the metal loading after in-situ electrochemical reduction is low, resulting in insufficient catalyst activity; when the concentration of the molybdenum source in the electrolyte is high, the metal loading after in-situ electrochemical reduction is too high, and the catalyst mainly undergoes the side reaction of hydrogen evolution by electrolysis of water, and the catalytic activity and selectivity for urea synthesis are both low;

[0154] (5) From the comparison between Example 1 and Examples 10-11, it can be seen that when the current density of the second electrodeposition reaction is low, the metal loading after in-situ electrochemical reduction is low, resulting in insufficient catalyst activity; when the current density of the second electrodeposition reaction is high, the metal loading after in-situ electrochemical reduction is too high, and the catalyst mainly undergoes the side reaction of hydrogen evolution by electrolysis of water, resulting in low activity and selectivity of the catalyst for catalytic synthesis of urea;

[0155] (6) From the comparison of Comparative Examples 1-2, it can be seen that urea electrosynthesis cannot be achieved using commercially available nickel foam or copper foam;

[0156] (7) From the comparison between Example 1 and Comparative Example 3, it can be seen that when the graphyne material is not modified by nitrogen atom doping, the electronic structure of graphyne cannot be effectively regulated, which leads to insufficient catalyst activity;

[0157] (8) From the comparison between Example 1 and Comparative Examples 4-5, it can be seen that when only a single active component, molybdenum or copper, is deposited, the catalytic intrinsic activity thereof is lower than that of bimetallic alloy nanoparticles due to the absence of synergistic effects between adjacent dissimilar metal atoms.

[0158] The applicant declares that the present invention is intended to illustrate the detailed structural features of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed structural features. This does not mean that the present invention must rely on the above-described detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific embodiments, etc., fall within the scope of protection and disclosure of the present invention.

[0159] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0160] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0161] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A nitrogen-doped graphene-based copper-molybdenum alloy catalyst, characterized in that: The nitrogen-doped graphene-based copper-molybdenum alloy catalyst includes a carrier and an active component deposited on the carrier; The carrier is a nitrogen-doped graphene base; The active component is copper-molybdenum alloy.

2. The nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to claim 1, characterized in that The mass content of the copper-molybdenum alloy in the nitrogen-doped graphene-based copper-molybdenum alloy catalyst is 1-6wt%; Preferably, the particle size of the copper-molybdenum alloy is less than 30 nm, preferably 4-10 nm; Preferably, the nitrogen-doped graphyne in the nitrogen-doped graphyne base is in-situ grown on the surface of the substrate.

3. The nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to claim 1 or 2, characterized in that: The preparation method of the nitrogen-doped graphene group comprises: (1) mixing hexaethynylbenzene, cuprous iodide, and an organic solvent to obtain a mixed solution, then placing a substrate in the mixed solution, and then performing a thermal reaction to obtain a graphene group; (2) Annealing the Graphyne group described in step (1) in an ammonia atmosphere to obtain a nitrogen-doped Graphyne group.

4. The nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to claim 3, characterized in that: The mass ratio of hexaethynylbenzene to cuprous iodide in step (1) is (2.5-40):1; Preferably, the solid-to-liquid ratio of hexaethynylbenzene and the organic solvent in step (1) is (0.25-4):1 mg / mL; Preferably, the organic solvent in step (1) comprises pyridine; Preferably, the substrate in step (1) comprises carbon cloth; Preferably, the thermal reaction in step (1) is carried out in a light-proof and inert atmosphere; Preferably, the temperature of the thermal reaction in step (1) is 60-130°C, preferably 80-110°C; Preferably, the thermal reaction time in step (1) is 12-72 hours; Preferably, the graphyne in the graphyne base in step (1) is in situ grown on the surface of the substrate.

5. The nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to claim 3 or 4, characterized in that: The flow rate of the ammonia gas in step (2) is 100-200 mL / min; Preferably, the heating rate of the annealing in step (2) is 2-5°C / min; Preferably, the annealing temperature in step (2) is 450-650°C; Preferably, the annealing holding time in step (2) is 4-10 hours.

6. A method for preparing the nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to any one of claims 1 to 5, characterized in that: The preparation method comprises: Copper and molybdenum are deposited on the nitrogen-doped graphene base by an electrodeposition method to obtain the nitrogen-doped graphene base copper-molybdenum alloy catalyst.

7. The preparation method according to claim 6, characterized in that The electrodeposition method specifically includes: The nitrogen-doped graphene-based catalyst is used as a working electrode and a three-electrode system is adopted to carry out a first electrodeposition reaction in a copper-containing electrolyte to obtain a nitrogen-doped graphene-based copper catalyst. Then, the nitrogen-doped graphene-based catalyst is used as a working electrode and a three-electrode system is adopted to carry out a second electrodeposition reaction in a molybdenum-containing electrolyte.

8. The preparation method according to claim 7, characterized in that The three-electrode system uses a graphite rod as the counter electrode and a saturated calomel electrode as the reference electrode; Preferably, the copper-containing electrolyte comprises a mixed solution of a copper source and sulfuric acid; Preferably, the concentration of the copper source in the copper-containing electrolyte is 20-100 mol / L, preferably 30-80 mol / L; Preferably, the concentration of sulfuric acid in the copper-containing electrolyte is 0.2-0.8 mol / L; Preferably, the copper source comprises any one of copper chloride, copper sulfate, copper acetate or copper nitrate, or a combination of at least two thereof; Preferably, the current density of the first electrodeposition reaction is 10-100 mA / cm 2 , preferably 20-50mA / cm 2 ; Preferably, the deposition time of the first electrodeposition reaction is 800-3600 s, preferably 1000-2400 s.

9. The preparation method according to claim 7 or 8, characterized in that The molybdenum-containing electrolyte comprises a mixed solution of a molybdenum source and sulfuric acid; Preferably, the concentration of the molybdenum source in the molybdenum-containing electrolyte is 5-50 mol / L, preferably 20-50 mol / L; Preferably, the concentration of sulfuric acid in the molybdenum-containing electrolyte is 0.2-0.8 mol / L; Preferably, the molybdenum source comprises sodium molybdate and / or ammonium molybdate; Preferably, the current density of the second electrodeposition reaction is 1-30 mA / cm 2 , preferably 5-15 mA / cm 2 ; Preferably, the deposition time of the second electrodeposition reaction is 200-3600 s, preferably 500-2400 s.

10. Use of the nitrogen-doped graphene-based copper-molybdenum alloy catalyst according to any one of claims 1 to 5, characterized in that: The nitrogen-doped graphene-based copper-molybdenum alloy catalyst is used for electrocatalytic synthesis of urea; Preferably, the application method comprises: using the nitrogen-doped graphene-based copper-molybdenum alloy catalyst as a working electrode, adopting a three-electrode system, and using carbon dioxide, nitrogen and water as raw materials to perform an electrocatalytic reaction; Preferably, the voltage of the working electrode is 0.3-1.0V; Preferably, the working time of the working electrode is 1-20 hours.

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