A copper-based catalyst for the electroreduction of nitrate to ammonia and a method for preparing the same

Abstract

The application discloses a copper-based catalyst for local high-pH nitrate electro-reduction to prepare ammonia, which can realize high Faraday efficiency and high ammonia yield under near-neutral conditions. The copper-based catalyst comprises a carrier and an active component, the carrier is a carbon-based nanocage, and the active component is a copper-based nanoparticle filled into the inner cavity of the carbon-based nanocage. The confined copper-based catalyst prepared by the application is used for electro-catalysis of nitrate to prepare ammonia, and high ammonia yield and high Faraday efficiency can be obtained in a green, environment-friendly and inexpensive neutral electrolyte, thereby avoiding the use of an alkaline electrolyte which is high in cost, high in corrosion and difficult to store.

Description

TECHNICAL FIELD

[0001] The present application relates to a nitrate electro-reduction ammonia catalyst, in particular a copper-based catalyst for electro-reduction of nitrate to ammonia and a preparation method thereof. BACKGROUND

[0002] Ammonia is one of the most important basic raw materials in the world, widely used in chemical and fertilizer industries, and is also a promising hydrogen energy carrier. The traditional Haber-Bosch process for ammonia synthesis is energy-intensive (about 1-2% of the world's total energy consumption), capital-intensive chemical process, and has poor compatibility with distributed agriculture. The electrocatalytic nitrogen reduction reaction driven by renewable electricity to produce ammonia has the advantages of mild operating conditions, distributed production, ubiquitous resources, and high sustainability, which is a potential alternative to the Haber-Bosch process. However, the activation of the N≡N triple bond requires extremely high energy and is accompanied by a competitive hydrogen evolution reaction, resulting in poor ammonia production activity and selectivity. Although significant progress has been made in lithium-mediated electrocatalytic nitrogen reduction to ammonia, the use of organic electrolytes and expensive lithium salts that are harmful to the human body is not conducive to practical application. In contrast, the electrocatalytic reduction of nitrate to ammonia reaction has similar advantages to electrocatalytic nitrogen reduction, and is more thermodynamically and kinetically favorable, with higher ammonia yield and faradaic efficiency in aqueous electrolytes than electrocatalytic nitrogen reduction. In addition, nitrate is abundant in water bodies and soil, and redundant nitrate is even considered a source of pollution. Therefore, the electrocatalytic reduction of nitrate to ammonia reaction provides a win-win opportunity for distributed fertilizer synthesis and pollution control.

[0003] In alkaline electrolytes, electrocatalytic nitrate reduction has higher reaction kinetics, and the competitive hydrogen evolution reaction is suppressed. Therefore, the electrocatalytic reduction of nitrate to ammonia in alkaline electrolytes has higher ammonia yield and faradaic efficiency than in neutral conditions. However, a large amount of water containing nitrate in nature (such as groundwater) is close to neutral, and some nitrate-containing wastewater is even weakly acidic. The method of directly adding alkali to the electrolyte to meet the reaction conditions of electrocatalytic nitrate reduction to ammonia indeed improves ammonia yield and faradaic efficiency, but at the same time is accompanied by many disadvantages that are not conducive to practical application, such as side reactions between alkaline electrolytes and carbon dioxide in the air, high corrosiveness to equipment, high cost, etc. Therefore, it is crucial to develop a technology route for efficient electrocatalytic reduction of nitrate to ammonia in near-neutral electrolytes without the need for added alkali, and the most important thing is to develop an electrocatalyst that fits it.

[0004] Catalytic performance depends on the local chemical environment of the catalyst. The electrocatalytic reduction of nitrate to ammonia reaction formula (NO3 - + H2O + e - → NH3+ OH -It is known that the reaction is accompanied by the formation of hydroxyl ions, therefore, in principle, if these hydroxyl ions can be localized near the catalyst, the local pH value around the catalyst can be increased, thereby improving the catalytic activity and inhibiting the competitive hydrogen evolution reaction. However, usually these hydroxyl ions will quickly diffuse into the bulk electrolyte after being generated, resulting in a slow increase in the local pH value around the catalyst, which is difficult to meet the high pH value required for efficient electro-reduction of nitrate. Therefore, how to restrict these hydroxyl ions near the catalytic site to increase the local pH value is a challenging problem.

[0005] In recent years, our research group has developed carbon nanocages with high electrical conductivity, large specific surface area and three-dimensional hierarchical pore structure rich in micropores-mesopores-macropores, which can greatly promote the coordinated transport of substances and charges, and thus become carriers for advanced energy conversion and storage (CN 101284663 A; Adv. Mater. 2012, 24, 5593). Carbon nanocages have a large inner cavity and rich microporous channels through the cage wall, providing an ideal structure for encapsulating catalysts for electrocatalytic nitrate reduction to ammonia (e.g., copper-based compounds) and preventing the escape of in-situ generated hydroxyl ions, making it an ideal nano-reactor. The present application uses this strategy to encapsulate copper-based nanoparticles in hierarchical structure carbon nanocages, forming a local high pH value in the inner cavity of the carbon nanocage. This carbon nanocage-confined copper-based catalyst exhibits excellent electrocatalytic nitrate reduction to ammonia performance in near-neutral electrolyte. SUMMARY

[0006] The present application provides a copper-based catalyst for local high-pH nitrate electro-reduction to ammonia, which can achieve high faradic efficiency and high ammonia yield under the condition that the pH of the electrolyte is 7-12.

[0007] The copper-based catalyst described in the present application comprises a carrier and an active component, the carrier is a carbon-based nanocage, and the active component is a copper-based nanoparticle; the copper-based nanoparticle is filled into the inner cavity of the carbon-based nanocage;

[0008] The carbon-based nanocage is one of pure carbon nanocage and nitrogen, sulfur, phosphorus, boron, oxygen heteroatom doped or co-doped carbon nanocage;

[0009] The copper-based nanoparticle loading is 10-70wt% of the mass percentage of the catalyst;

[0010] The copper-based nanoparticles are one of Cu, Cu2O, CuO or a mixture of multiple thereof; the copper-based nanoparticles can also be a mixture of one of Cu, Cu2O, CuO and one of oxides, sulfides, phosphides of iron, cobalt, nickel, tin, antimony, ruthenium, rhodium, iridium, silver, palladium, platinum, gold; the copper-based nanoparticles can also be a mixture of one or more of Cu, Cu2O, CuO and one or more of iron, cobalt, nickel, tin, antimony, ruthenium, rhodium, iridium, silver, palladium, platinum, gold; the copper-based nanoparticles can also be an alloy of Cu and one or more of iron, cobalt, nickel, tin, antimony, ruthenium, rhodium, iridium, silver, palladium, platinum, gold.

[0011] The copper-based nanoparticles are filled into the inner cavity of the carbon-based nanocage, and the hydroxyl generated in the reaction process is localized in the inner cavity of the nanocage by the confinement effect of the carbon nanocage, so that the pH around the copper-based nanoparticles in the cage is improved.

[0012] The copper-based catalyst is used for the electrocatalytic reduction of nitrate to ammonia, and when the electrolyte is near neutral, the ammonia yield can reach 3 mol h -1 g -1 , and the Faraday efficiency is more than 90%.

[0013] The specific surface area of the carbon-based nanocage is preferably 500-2500 m 2 / g, and more preferably 1000-1500 m 2 / g. The rich micropore channels on the wall of the carbon-based nanocage can be used for the filling and preparation of the catalyst, and the diffusion of the hydroxyl generated in the reaction process from the inside to the outside of the cavity is inhibited, so that a high pH value is formed in the cavity. Too high specific surface area will lead to unstable structure and reduced conductivity; too low specific surface area will lead to difficult filling and preparation and difficult exchange of internal and external substances during the reaction process.

[0014] The source of the carbon-based nanocage is not particularly limited in the present application, and in the examples of the present application, the carbon nanocage and the nitrogen-doped carbon nanocage are preferably prepared by the methods disclosed in Chinese patents CN101284663A and CN102530922A. The sulfur-nitrogen co-doped carbon nanocage is preferably prepared by the method disclosed in Adv. Mater. 2020, 32, 2004632, and other co-doped carbon nanocage preparation methods are similar.

[0015] In the present application, the nitrogen-doped, oxygen-nitrogen co-doped, boron-nitrogen co-doped, sulfur-nitrogen co-doped, phosphorus-nitrogen co-doped carbon nanocage includes nitrogen, boron, oxygen, sulfur, phosphorus elements; the nitrogen, boron, oxygen, sulfur, phosphorus element doping amount in the nitrogen, sulfur, phosphorus, boron, oxygen heteroatom doped or co-doped carbon nanocage accounts for 0.1-15wt% of the mass percentage of the copper-based catalyst, more preferably 4-8wt%. The copper-based nanoparticle loading in the copper-based catalyst accounts for 10-70wt.% of the mass percentage of the copper-based catalyst, more preferably 15-45%.

[0016] The present application also provides a preparation method of the copper-based catalyst described in the above technical solution, which comprises the following steps:

[0017] (1) preparing a metal salt aqueous solution with a concentration of 0.1-1mol / L;

[0018] (2) placing the carbon-based nanocage into a two-necked flask and vacuumizing;

[0019] (3) quickly injecting the metal salt aqueous solution into the two-necked flask, stirring, and preparing a mixed solution;

[0020] (4) naturally filtering the above mixed solution with filter paper, drying by filtration, and freeze-drying;

[0021] (5) after the freeze-drying is completed, washing with water, naturally filtering with filter paper, drying by filtration, and freeze-drying;

[0022] (6) after the drying is completed, calcining in a tube furnace, and preparing a carbon-based nanocage filled with copper-based nanoparticles;

[0023] (7) to obtain catalysts with different carbon-based carriers, only different carbon-based nanocages need to be used.

[0024] (8) to obtain different copper-based nanoparticles, only the type of metal salt, calcination temperature or atmosphere, and other post-processing conditions need to be changed.

[0025] The preparation method is characterized in that the concentration of the metal salt filling solution is preferably 0.1-1.0mol / L. The calcination temperature is preferably 150-350℃, the heating rate is preferably 2-10℃, and the calcination time is preferably 0.5-6 hours. The atmosphere is oxygen, argon, hydrogen-argon mixed gas, and the flow rate is preferably 20-200mL / min. The carbon-based nanocage is a carbon nanocage and a nitrogen-doped, oxygen-nitrogen co-doped, sulfur-nitrogen co-doped, phosphorus-nitrogen co-doped carbon nanocage.

[0026] The metal salt is a water-soluble salt of copper, iron, cobalt, nickel, tin, antimony, ruthenium, rhodium, iridium, silver, palladium, platinum, and gold, including oxo acids and oxo acid salts, copper nitrate, iron nitrate, cobalt nitrate, nickel nitrate, tin chloride, antimony nitrate, ruthenium chloride, rhodium chloride, chloroiridic acid, silver nitrate, palladium chloride, chloroplatinic acid, and chloroauric acid.

[0027] In the present application, the vacuumizing operation in the preparation process aims to keep the inside of the carbon-based nanocage vacuumized so as to fill in the aqueous solution of metal salt such as copper nitrate, and the vacuum degree is preferably 0.1-100 Pa. The rapid injection of the aqueous solution of metal salt such as copper nitrate aims to make the aqueous solution of metal salt such as copper nitrate quickly enter the inner cavity of the carbon-based nanocage. The natural filtration of the filter paper aims to keep the aqueous solution of metal salt such as copper nitrate in the carbon-based nanocage from flowing out.

[0028] Beneficial effects:

[0029] The confined copper-based catalyst prepared by the present application is used for electrocatalytic reduction of nitrate to ammonia, and in green, environment-friendly and inexpensive neutral / near-neutral electrolyte, high ammonia yield and high Faraday efficiency can be obtained, and the use of high-corrosive, high-cost and difficult-to-store alkaline electrolyte is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Typical electron microscope photos of the confined Cu@hNCNC catalyst. (a, b) Scanning electron microscope photos. (c) Schematic diagram of Cu@hNCNC. (d) Transmission electron microscope photo.

[0031] As shown in the figure, the whole Cu@hNCNC is spherical, composed of staggered sheet structures, which are composed of interconnected nanocages; Cu-based nanoparticles are filled in the nanocages.

[0032] Figure 2 Yield (a) and Faraday efficiency (b) of confined Cu@hNCNC and supported Cu / hNCNC catalysts for electrocatalytic reduction of nitrate to ammonia in electrolyte with different pH values (pH=7-13). Electrolyte: mixture of 0.5 mol / L Na2SO4 and 0.05 mol / L NaNO3; working voltage: -1.5 V (vs Ag / AgCl).

[0033] It can be seen that in neutral / near-neutral electrolyte (pH=7 or 9), the Cu@hNCNC catalyst has obviously higher ammonia yield and Faraday efficiency than the Cu / hNCNC catalyst, and the ammonia yield and Faraday efficiency are similar to those of the Cu / hNCNC catalyst in strong alkaline electrolyte (pH=12). Thus it is proved that the Cu@hNCNC catalyst can obtain high ammonia yield performance under neutral or weak alkaline conditions.

[0034] Figure 3 Real-time change diagram of hydroxyl ion concentration on the surface of confined Cu@hNCNC and supported Cu / hNCNC electrodes under the conditions of no stirring (a) and stirring (b). The initial pH of the electrolyte is 7, the voltage is -1.5 V, and the electrolysis time is 30 minutes.

[0035] It can be seen that without stirring ( Figure 3 a) The hydroxide concentration [OH] on the Cu@hNCNC electrode surface compared to the Cu / hNCNC electrode surface during the reaction process. - The concentration of hydroxide ions initially low (in the first 15 minutes) and then high (after 15 minutes) is due to the following reasons: Compared to the Cu / hNCNC catalyst, the carbon-based nanocages of the Cu@hNCNC catalyst confine the hydroxide ions generated on the surface of the copper nanoparticles within the reaction chamber, inhibiting or delaying their diffusion outward. Therefore, the hydroxide concentration detected on the electrode surface is relatively low in the first 15 minutes. Furthermore, the confinement of the hydroxide ions generated within the chamber by the carbon-based nanocages creates a locally high pH environment, resulting in a higher ammonia production efficiency for Cu@hNCNC than for Cu / hNCNC, thus generating more hydroxide ions. Therefore, after 15 minutes, the concentration of hydroxide ions diffused from the Cu@hNCNC catalyst chamber in the bulk electrolyte exceeds the concentration of hydroxide ions generated by the Cu / hNCNC catalyst.

[0036] After stirring ( Figure 3 (b) The accelerated material transport reduces the difference in hydroxide concentration on the electrode surfaces of Cu@hNCNC and Cu / hNCNC catalysts in the initial stage of the reaction (up to the first 8 minutes). However, the confinement effect of the carbon-based nanocages on the hydroxide generated within the cavity still exists. Therefore, after about 8 minutes, the difference in hydroxide concentration between the Cu@hNCNC and Cu / hNCNC electrode surfaces becomes increasingly larger.

[0037] Figure 4 Model diagrams of Cu@hNCNC(4a) and Cu / hNCNC(4b) catalysts simulated theoretically, and a diagram of hydroxide concentration at a distance of 0-9 nm from the copper surface when the reaction reaches equilibrium (4c).

[0038] The simulation results show that the pH inside the Cu@hNCNC cage is significantly higher than that outside the cage, and also higher than that of Cu / hNCNC at the same location. This indicates that hNCNC does indeed block hydroxide ions, thus causing a local increase in pH inside the cage. This allows Cu@hNCNC to exhibit high catalytic performance in neutral / near-neutral electrolytes. In contrast, the hydroxide ions generated by the supported Cu / hNCNC catalyst rapidly diffuse into the bulk electrolyte, failing to form a local high pH environment and therefore failing to exhibit high performance. Detailed Implementation

[0039] The technical solutions in the present application will be described clearly and completely in combination with the examples in the present application. In the following cases, hCNC, hNCNC and hSNCNC are carbon nanocage, nitrogen-doped carbon nanocage and sulfur-nitrogen co-doped carbon nanocage respectively, and Cu, Cu-Cu2O, Cu2O and CuO are copper nanoparticles, copper / copper oxide composite nanoparticles, copper oxide nanoparticles and copper oxide nanoparticles respectively. Cu-Pd is copper-palladium alloy nanoparticles. Cu-Ni is copper-nickel alloy nanoparticles. Cu-Sn is copper-tin alloy nanoparticles. Cu-Sb is copper-antimony alloy nanoparticles. Cu-Ru is copper-ruthenium alloy nanoparticles. Cu-Rh is copper-rhodium alloy nanoparticles. Cu-Ir is copper-iridium alloy nanoparticles. Cu-Ag is copper-silver alloy nanoparticles. Cu-Pt is copper-platinum alloy nanoparticles. Cu-Au is copper-gold alloy nanoparticles. Cu / Co3O4 is copper and cobalt oxide mixture nanoparticles. Cu / CoP is copper and cobalt phosphide mixed nanoparticles. Cu / CoS is copper and cobalt sulfide mixed nanoparticles. Cu / Fe2O3 is copper and iron oxide mixture nanoparticles.The copper catalyst filled with carbon nanocages is marked as "Cu@hCNC"; the copper catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu@hNCNC"; the copper catalyst filled with sulfur-nitrogen co-doped carbon nanocages is marked as "Cu@hSNCNC"; the copper / copper oxide composite catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Cu2O@hNCNC"; the copper / palladium alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Pd@hNCNC"; the copper / nickel alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Ni@hNCNC"; the copper / tin alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Sn@hNCNC"; the copper / antimony alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Sb@hNCNC"; the copper / ruthenium alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Ru@hNCNC"; the copper / rhodium alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Rh@hNCNC"; the copper / iridium alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Ir@hNCNC"; the copper / silver alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Ag@hNCNC"; the copper / platinum alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Pt@hNCNC"; the copper / gold alloy nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu-Au@hNCNC"; the copper and cobalt tetroxide mixture nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu / Co3O4@hNCNC"; the copper and cobalt phosphide mixture nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu / CoP@hNCNC"; the copper and cobalt sulfide mixture nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu / CoS@hNCNC"; the copper and iron trioxide mixture nanoparticle catalyst filled with nitrogen-doped carbon nanocages is marked as "Cu / Fe2O3@hNCNC". The performance of the catalysts in electrocatalytic reduction of nitrate to ammonia is determined by an electrochemical workstation, the ammonia yield rate and the Faraday efficiency are determined by the indophenol blue spectrophotometry, and the specific evaluation indexes are the ammonia yield rate (NH3 yield rate) and the Faraday efficiency (FE). NH3 .

[0040] The examples described below are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all the other examples obtained by those skilled in the art without making creative efforts belong to the scope of protection of the present application.

[0041] Example 1

[0042] Cu@hNCNC:

[0043] A 0.4 mol / L copper nitrate filling solution was prepared. 50 mg of hNCNC was placed in two flasks and vacuumed to 1 Pa. 30 mL of the copper nitrate filling solution was quickly injected and stirred for 1 hour under vacuum. The mixed solution was naturally filtered with filter paper, dried, and then freeze-dried for 24 hours. After completion, the copper ions on the outer surface were washed away with water, naturally filtered with filter paper, dried, and then freeze-dried for 24 hours. After completion, the sample was transferred to a tube furnace, heated to 280-350°C at a rate of 5°C / min under a hydrogen-argon mixed gas atmosphere of 100 mL / min, and then kept for 2 hours. After the sample was cooled to room temperature, the Cu@hNCNC was obtained. Under the condition of no vacuum, the copper-based nanoparticle catalyst loaded on the outer surface of the hNCNC was prepared and denoted as Cu / hNCNC.

[0044] 5 mg of Cu@hNCNC, 200 μL of ethanol, 800 μL of deionized water, and 150 μL of a 5% perfluorosulfonic acid polymer solution were mixed to prepare a slurry by ultrasonic stirring. 3 μL of the slurry was uniformly coated on a glassy carbon electrode with a diameter of 3 mm as a working electrode; the working electrode was placed in an H-type three-electrode electrolytic cell, and 10 mL of a mixed electrolyte of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 with pH 9 was placed on both sides of the electrolytic cell, separated by a proton exchange membrane; an Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet were used as a reference electrode and a counter electrode, respectively. Under normal temperature and pressure, 20 mL / min of argon gas was introduced for 10 minutes to remove part of the dissolved O2 and CO2 in the solution, and then cyclic voltammetry scanning was performed for 200 cycles to activate the catalyst and discharge the absorbed gas. Then the catalyst was catalyzed at each potential for 30 minutes, and the electrolyte was collected for ammonia detection. Under the above reaction conditions, Cu@hNCNC can exhibit a high ammonia yield of 3.0 mol h -1 g -1 and a maximum FE NH3 of 90.0% at a lower potential (-1.5 V vs Ag / AgCl). While in the electrolyte with pH=9, Cu / hNCNC can only obtain an ammonia yield of 2.2 mol h -1 g -1 and a maximum FE NH3 of 80.0%; only when the pH of the electrolyte is increased to 12, Cu / hNCNC can obtain an ammonia yield and Faraday efficiency similar to Cu@hNCNC.

[0045] Example 2

[0046] Cu@hCNC:

[0047] A 0.4 mol / L copper nitrate filling solution was prepared and kept ready for use. 50 mg of hCNC was weighed into two flasks and vacuumed to 1 Pa. 30 mL of the copper nitrate filling solution was quickly injected and stirred for 1 hour under vacuum. The above mixed solution was naturally filtered with filter paper, and after filtration, it was freeze-dried for 24 hours. After completion, the copper ions on the outer surface were washed away with water, and naturally filtered with filter paper. After filtration, it was freeze-dried for 24 hours. After completion, it was transferred to a tube furnace, and heated to 280-350℃ at a rate of 5℃ / min under a hydrogen-argon mixed gas atmosphere of 100 mL / min, and then kept for 2 hours. After the sample was cooled to room temperature, the Cu@hCNC was obtained by taking out the sample.

[0048] 5 mg of Cu@hCNC, 200 μL of ethanol, 800 μL of deionized water, and 150 μL of 5% perfluorosulfonic acid polymer solution were mixed to prepare a slurry. 3 μL of the slurry was uniformly coated on a glassy carbon electrode with a diameter of 3 mm as a working electrode; the working electrode was placed in a H-type three-electrode electrolytic cell, and each side of the electrolytic cell had 10 mL of a mixed electrolyte of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 with a pH of 12, separated by a proton exchange membrane; an Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet were used as a reference electrode and a counter electrode, respectively. Under normal temperature and pressure conditions, 20 mL / min of argon gas was introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning was performed for 200 cycles to activate the catalyst and discharge the absorbed gas. Then the catalyst was catalyzed at each potential for 30 minutes, and the electrolyte was collected for ammonia detection; under the above reaction conditions, Cu@hCNC can exhibit an ammonia yield of 1.9 mol h -1 g -1 and a maximum FE NH3 of 71.9% at a lower potential (-1.5 V vs Ag / AgCl).

[0049] Example 3

[0050] Cu-Cu2O@hNCNC:

[0051] A 0.4 mol / L copper nitrate filling solution was prepared and kept ready for use. 50 mg of hNCNC was weighed into two flasks and vacuumed to 1 Pa. 30 mL of the copper nitrate filling solution was quickly injected and stirred for 1 hour under vacuum. The above mixed solution was naturally filtered with filter paper, and after filtration, it was freeze-dried for 24 hours. After completion, the copper ions on the outer surface were washed away with water, and naturally filtered with filter paper. After filtration, it was freeze-dried for 24 hours. After completion, it was transferred to a tube furnace, and heated to 180-280℃ at a rate of 5℃ / min under a hydrogen-argon mixed gas atmosphere of 100 mL / min, and then kept for 2 hours. After the sample was cooled to room temperature, the Cu-Cu2O@hNCNC was obtained by taking out the sample.

[0052] Take 5 mg Cu-Cu2O@hNCNC, 200 μL ethanol, 800 μL deionized water, 150 μL 5% perfluorosulfonic acid polymer solution, mix and ultrasonic stirring to make slurry. Take 3 μL slurry evenly coated on a glassy carbon electrode with a diameter of 3 mm as the working electrode; the working electrode is placed in a H-type three-electrode electrolytic cell, each side of the electrolytic cell has 10 mL of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 mixed electrolyte with pH 9, separated by a proton exchange membrane; Ag / AgCl electrode (3 mol / L KCl) and platinum sheet are used as reference electrode and counter electrode respectively. Under the conditions of normal temperature and pressure, 20 mL / min of argon gas flow is introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning is carried out for 200 cycles to activate the catalyst and discharge the absorbed gas. Then catalyze for 30 minutes at each potential, collect the electrolyte to detect ammonia; under the above reaction conditions, Cu-Cu2O@hNCNC shows 2.7 mol h -1 g -1 of ammonia yield and 91.0% of maximum FE NH3 .

[0053] Example 4

[0054] Cu2O@hNCNC:

[0055] Prepare 0.4 mol / L copper nitrate filling solution for use. Take 50 mg hNCNC into two flasks and vacuum to 1 Pa. Inject 30 mL of copper nitrate filling solution quickly and keep vacuum state for 1 hour. Filter the above mixed solution with filter paper naturally, dry the filter, and freeze-dry for 24 hours. After completion, wash off the copper ions on the outer surface with water, and filter naturally with filter paper, dry the filter, and freeze-dry for 24 hours. After completion, transfer to a tube furnace, under the atmosphere of 100 mL / min of argon gas, heat to 100-180℃ at a rate of 5℃ / min, and keep for 2 hours. After the sample is cooled to room temperature, the Cu2O@hNCNC is prepared.

[0056] Mix 5 mg Cu2O@hNCNC, 200 μL ethanol, 800 μL deionized water, and 150 μL of 5% perfluorosulfonic acid polymer solution, and ultrasonically stir to prepare a slurry. Apply 3 μL of the slurry evenly to a 3 mm diameter glassy carbon electrode as the working electrode. Place the working electrode in an H-type three-electrode electrolytic cell. Each side of the cell contains 10 mL of a mixed electrolyte solution of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 (pH 9), separated by a proton exchange membrane. An Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet are used as the reference and counter electrodes, respectively. Under normal temperature and pressure, argon gas is passed through at a flow rate of 20 mL / min for 10 minutes to remove dissolved O2 and CO2 gases from the solution. Then, perform 200 cyclic voltammetry scans to activate the catalyst and simultaneously expel the absorbed gases. Then, catalysis was performed at various potentials for 30 minutes, and the electrolyte was collected for ammonia detection. Under the above reaction conditions, Cu2O@hNCNC exhibited a yield of 2.0 mol / h at lower potentials (-1.5V vs Ag / AgCl). -1 g -1 Ammonia yield and maximum FE of 85.0% NH3 .

[0057] Example 5

[0058] CuO@hNCNC:

[0059] Prepare a 0.4 mol / L copper nitrate filling solution. Weigh 50 mg of hNCNC into a two-necked flask and evacuate to 1 Pa. Quickly pour in 30 mL of the copper nitrate filling solution and stir under vacuum for 1 hour. Filter the mixture naturally with filter paper, and freeze-dry for 24 hours after filtration. After completion, wash away copper ions from the outer surface with water, filter naturally with filter paper, and freeze-dry for 24 hours after filtration. Transfer to a tube furnace and heat to 200-350 °C at a rate of 5 °C / min in air atmosphere, then hold at that temperature for 2 hours. After cooling the sample to room temperature, remove the sample to obtain CuO@hNCNC.

[0060] Take 5 mg CuO@hNCNC, 200 μL ethanol, 800 μL deionized water, 150 μL 5% perfluorosulfonic acid polymer solution, mix and ultrasonic stirring to make slurry. Take 3 μL slurry evenly coated on a glassy carbon electrode with a diameter of 3 mm as the working electrode; the working electrode is placed in a H-type three-electrode electrolytic cell, each side of the electrolytic cell has 10 mL of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 mixed electrolyte with pH 9, separated by a proton exchange membrane; Ag / AgCl electrode (3 mol / L KCl) and platinum sheet are used as reference electrode and counter electrode respectively. Under the conditions of normal temperature and pressure, 20 mL / min of argon gas flow is introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning is carried out for 200 circles to activate the catalyst and discharge the absorbed gas. Then catalyze for 30 minutes at each potential, collect the electrolyte to detect ammonia; under the above reaction conditions, CuO@hNCNC shows 0.7 mol h -1 g -1 of ammonia yield and 65.0% of maximum FE NH3 .

[0061] Example 6

[0062] Cu@hSNCNC:

[0063] Prepare 0.4 mol / L copper nitrate filling solution for use. Weigh 50 mg of hSNCNC into two flasks and vacuum to 1 Pa. Quickly inject 30 mL of copper nitrate filling solution and keep vacuum state for 1 hour. Filter the above mixed solution with filter paper naturally, dry the filter, and freeze-dry for 24 hours. After completion, wash off the copper ions on the surface with water, and filter naturally with filter paper, dry the filter, and freeze-dry for 24 hours. After completion, transfer to a tube furnace, under the atmosphere of 100 mL / min of hydrogen and argon mixture, heat to 280-350℃ at a rate of 5℃ / min, and keep for 2 hours. After the sample is cooled to room temperature, the Cu@hSNCNC is prepared.

[0064] Take 5 mg of Cu@hSNCNC, 200 μL of ethanol, 800 μL of deionized water, and 150 μL of a 5% perfluorosulfonic acid polymer solution, mix them together, and ultrasonically stir to prepare a slurry. Take 3 μL of the slurry and evenly apply it to a glassy carbon electrode with a diameter of 3 mm as a working electrode; place the working electrode in a H-type three-electrode electrolytic cell, and on both sides of the electrolytic cell, there are 10 mL of a mixed electrolyte of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 with a pH of 12, which are separated by a proton exchange membrane; an Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet are used as a reference electrode and a counter electrode, respectively. Under normal temperature and pressure conditions, a flow of 20 mL / min of argon gas is introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning is performed for 200 cycles to activate the catalyst and discharge the absorbed gas. Then, catalysis is performed at each potential for 30 minutes, and the electrolyte is collected for ammonia detection; under the above reaction conditions, Cu@hSNCNC exhibits an ammonia yield of 1.8 mol h -1 g -1 and a maximum FE NH3 of 82.2% at a lower potential (-1.5 V vs Ag / AgCl).

[0065] Example 7

[0066] Cu-Pd@hNCNC:

[0067] A mixed filling solution of copper nitrate (0.4 mol / L) and palladium chloride (0.05 mol / L) is prepared and used as needed. Weigh 50 mg of hNCNC into two flasks and vacuumize to 1 Pa. Rapidly inject 30 mL of the mixed filling solution and keep the vacuum state for 1 hour of stirring. Filter the above mixed solution naturally with filter paper, dry the filter cake, and freeze-dry for 24 hours. After completion, wash off the metal ions on the surface with water, filter naturally with filter paper, dry the filter cake, and freeze-dry for 24 hours. After completion, transfer to a tube furnace, heat to 280-350°C at a rate of 5°C / min under a hydrogen-argon mixed gas atmosphere of 100 mL / min, and keep the temperature for 2 hours. After the sample cools to room temperature, the Cu-Pd@hNCNC is obtained.

[0068] Take 5 mg of Cu-Pd@hNCNC, 200 μL of ethanol, 800 μL of deionized water, and 150 μL of 5% perfluorosulfonic acid polymer solution, mix them together, and ultrasonically stir to prepare a slurry. Take 3 μL of the slurry and evenly apply it to a glassy carbon electrode with a diameter of 3 mm as the working electrode; place the working electrode in a H-type three-electrode electrolytic cell, and on both sides of the electrolytic cell, there are 10 mL of a mixed electrolyte of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 with a pH of 9, separated by a proton exchange membrane in the middle; an Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet are used as the reference electrode and the counter electrode, respectively. Under normal temperature and pressure conditions, a flow of 20 mL / min of argon gas is introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning is performed for 200 cycles to activate the catalyst and discharge the absorbed gas. Then, catalysis is performed at each potential for 30 minutes, and the electrolyte is collected for ammonia detection; under the above reaction conditions, Cu-Pd@hNCNC exhibits an ammonia yield of 3.3 mol h -1 g -1 NH3 .

[0069] Example 8

[0070] Cu / Co3O4@hNCNC:

[0071] A mixed filling solution of copper nitrate (0.4 mol / L) and cobalt nitrate (0.2 mol / L) is prepared and used as needed. Take 50 mg of hNCNC and place it in two flasks, and vacuumize to 1 Pa. Quickly inject 30 mL of the mixed filling solution, and keep the vacuum state and stir for 1 hour. Filter the above mixed solution naturally with filter paper, dry the filter cake, and freeze-dry for 24 hours. After completion, wash off the metal ions on the outer surface with water, and filter naturally with filter paper, dry the filter cake, and freeze-dry for 24 hours. After completion, transfer it to a tube furnace, and under the atmosphere of 100 mL / min of hydrogen-argon mixed gas, heat it to 280-350°C at a rate of 5°C / min, and keep it for 2 hours. After the sample cools to room temperature, take it out to prepare Cu / Co3O4@hNCNC.

[0072] ​Take 5 mg Cu / Co3O4@hNCNC, 200 μL ethanol, 800 μL deionized water, 150 μL 5% perfluorosulfonic acid type polymer solution, mix and ultrasonic stirring to prepare slurry. Take 3 μL slurry and evenly coat on a glassy carbon electrode with a diameter of 3 mm as the working electrode; the working electrode is placed in a H-type three-electrode electrolytic cell, each side of the electrolytic cell has 10 mL of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 mixed electrolyte with pH of 9, separated by a proton exchange membrane; Ag / AgCl electrode (3 mol / L KCl) and platinum sheet are used as the reference electrode and the counter electrode respectively. Under the conditions of normal temperature and pressure, 20 mL / min of argon gas flow is introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning is carried out for 200 cycles to activate the catalyst and discharge the absorbed gas. Then catalyze for 30 minutes at each potential, collect the electrolyte to detect ammonia; under the above reaction conditions, Cu / Co3O4@hNCNC shows 2.8 mol h -1 g -1 of ammonia yield and 85.0% of maximum FE NH3 .

[0073] Example 9

[0074] Cu / CoP@hNCNC:

[0075] Prepare 0.4 mol / L copper nitrate, 0.2 mol / L cobalt nitrate mixed filling solution for later use. Weigh 50 mg of hNCNC into two flasks and vacuum to 1 Pa. Rapidly inject 30 mL of mixed filling solution and keep vacuum state for 1 hour. Filter the above mixed solution with filter paper naturally, and after filtration, freeze-dry for 24 hours. After completion, wash off the metal ions on the outer surface with water, and filter naturally with filter paper, and after filtration, freeze-dry for 24 hours. After completion, mix with 100 mg of sodium dihydrogen phosphate, transfer to a tube furnace, under the atmosphere of 100 mL / min of argon gas, heat to 280-350℃ at a rate of 5℃ / min, and then keep for 2 hours. After the sample is cooled to room temperature, the sample is taken out to prepare Cu / CoP@hNCNC.

[0076] Take 5 mg Cu / CoP@hNCNC, 200 μL ethanol, 800 μL deionized water, 150 μL 5% perfluorosulfonic acid type polymer solution, mix and ultrasonic stirring to make slurry. Take 3 μL slurry and evenly coat on a glassy carbon electrode with a diameter of 3 mm as the working electrode; put the working electrode into a H-type three-electrode electrolytic cell, each side of the electrolytic cell has 10 mL of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 mixed electrolyte with pH of 9, separated by proton exchange membrane in the middle; Ag / AgCl electrode (3 mol / L KCl) and platinum sheet are used as reference electrode and counter electrode respectively. Under the conditions of normal temperature and pressure, 20 mL / min of argon gas flow is introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning is carried out for 200 circles to activate the catalyst and discharge the absorbed gas. Then catalyze for 30 minutes at each potential, collect the electrolyte to detect ammonia. Under the above reaction conditions, Cu / CoP@hNCNC shows high ammonia yield of 2.1 mol h -1 g -1 NH3 .

[0077] Example 10

[0078] Cu / CoS@hNCNC:

[0079] Prepare 0.4 mol / L copper nitrate, 0.2 mol / L cobalt nitrate mixed filling solution for standby. Take 50 mg hNCNC and put it into two flasks, and vacuum to 1 Pa. Inject 30 mL of mixed filling solution quickly, and keep vacuum state stirring for 1 hour. Filter the above mixed solution with filter paper naturally, and dry after filtration, then freeze-dry for 24 hours. After completion, wash off the metal ions on the outer surface with water, and filter naturally with filter paper, dry after filtration, then freeze-dry for 24 hours. After completion, mix with 100 mg of sulfur powder, transfer to a tube furnace, under the atmosphere of 100 mL / min of argon gas, heat to 150℃ at a rate of 5℃ / min, then keep for 2 hours, then heat to 220-350℃ at a rate of 5℃ / min, then keep for 2 hours. After the sample is cooled to room temperature, take out the sample to prepare Cu / CoS@hNCNC.

[0080] ​5 mg Cu / CoS@hNCNC, 200 μL ethanol, 800 μL deionized water, 150 μL 5% perfluorosulfonic acid type polymer solution were mixed to prepare a slurry by ultrasonic stirring. 3 μL of the slurry was uniformly coated on a glassy carbon electrode with a diameter of 3 mm as a working electrode; the working electrode was placed in a H-type three-electrode electrolytic cell, each side of the electrolytic cell had 10 mL of a mixed electrolyte of 0.5 mol / L Na2SO4 and 0.05 mmol / L NaNO3 with pH 9, separated by a proton exchange membrane in the middle; an Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet were used as a reference electrode and a counter electrode, respectively. Under the conditions of normal temperature and pressure, 20 mL / min of argon gas flow was introduced for 10 minutes to remove part of the dissolved O2 and CO2 and other gases in the solution, and then cyclic voltammetry scanning was performed for 200 cycles to activate the catalyst and discharge the absorbed gas. Then the catalyst was catalyzed at each potential for 30 minutes, and the electrolyte was collected for ammonia detection. Under the above reaction conditions, Cu / CoS@hNCNC showed a high ammonia yield of 2.0 mol h -1 g -1 NH3 .

[0081] Table 1 is a summary table of ammonia yield and Faraday efficiency data of each sample. As can be seen from the table, the Cu-Pd@hNCNC catalyst has the highest ammonia yield and Faraday efficiency, and the best ammonia production effect.

[0082] Table 1

[0083] Sample Ammonia yield (mol H2O / mol H2) -1 g -1 )]]> Faraday efficiency (%) Cu@hNCNC 3.0 90.0 Cu@hCNC 1.9 71.9 Cu-Cu20@hNCNC 2.7 91.0 [Cu2O@hNCNC] 2.0 85.0 CuO@hNCNC 0.7 65.0 Cu@hSNCNC 1.8 82.0 Cu@hNPCNC 2.4 78.9％ Cu / Co304@hNCNC 2.8 85.0 Cu / CoP@hNCNC 2.1 76.4％ Cu / CoS@hNCNC 2.0 78.2％ Cu / Fe203@hNCNC 2.5 86.7％ Cu-Pd@hNCNC 3.3 95.2 Cu-Ni@hNCNC 3.1 91.4％ Cu-Sn@hNCNC 2.3 90.1％ Cu-Sb@hNCNC 2.1 90.5％ Cu-Ru@hNCNC 2.8 91.7％ Cu-Rh@hNCNC 2.1 86.1％ Cu-Ir@hNCNC 1.8 75.1％ Cu-Ag@hNCNC 3.2 90.4％ Cu-Pt@hNCNC 0.5 60.4％ Cu-Au@hNCNC 2.2 81.2％

[0084] The preferred embodiments of the present application are described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and changes to the present application without creative labor based on the concept of the present application. Therefore, any technical solutions obtained by logical analysis, reasoning or limited experiments by those of ordinary skill in the art based on the concept of the present application in the prior art should be within the protection scope defined by the claims.​

Claims

1. The application of a copper-based catalyst in the electrocatalytic reduction of nitrate to ammonia in a neutral / near-neutral electrolyte, characterized in that, The copper-based catalyst is composed of a support and an active component; The carrier is a nitrogen-doped carbon nanocage, the active component is copper-based nanoparticles, and the copper-based nanoparticles fill the inner cavity of the carrier. The copper-based nanoparticles are Cu nanoparticles, or alloy nanoparticles formed by Cu and at least one of nickel, palladium, and silver. The electrolyte has a pH of 7-9, and the operating voltage for the electrocatalytic reaction is -1.5V relative to the Ag / AgCl reference electrode.

2. The application as described in claim 1, characterized in that, In the copper-based catalyst, the loading of copper-based nanoparticles is 15~45 wt%.

3. The application as described in claim 1, characterized in that, The specific surface area of ​​nitrogen-doped carbon nanocages is 1000~1500 m². 2 / g.

4. The application as described in claim 1, characterized in that, The nitrogen doping amount in the nitrogen-doped carbon nanocage is 4~8 wt%.

5. The application as described in claim 1, characterized in that, The preparation method of the copper-based catalyst includes the following steps: Step (1): Place the nitrogen-doped carbon nanocages in a vacuum environment, add a copper salt solution, or add a mixed salt solution of at least one of copper salt solution and palladium salt solution, nickel salt solution, and silver salt solution, and stir until the nitrogen-doped carbon nanocages are uniformly dispersed in the solution to form a mixed system. Step (2): The mixed system obtained in step (1) is filtered by filter paper, then freeze-dried, washed with water, and naturally filtered by filter paper. After that, it is freeze-dried again. The dried solid is calcined in a hydrogen-argon mixed atmosphere to obtain the final product of copper-based catalyst.

6. The application as described in claim 5, characterized in that, The concentration of copper salt in the copper salt solution is 0.1~1 mol / L; the concentration of palladium salt, nickel salt and silver salt in the palladium salt solution, nickel salt and silver salt solution is 0.05 mol / L.

7. The application as described in claim 5, characterized in that, The calcination temperature is 280~350℃, and the calcination time is 0.5~6 h.

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