Preparation method, product and application of a catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions

Abstract

The present invention discloses a preparation method of a catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions. The preparation method includes: (1) mixing a conductive carbon material with a nitrogen-rich material, and subjecting the mixture to a first high-temperature carbonization under an inert atmosphere to obtain a carbonitride support; (2) dispersing the carbonitride support and a metal salt in an organic solvent, drying and collecting the product, and subjecting the product to a second high-temperature carbonization under an inert atmosphere to obtain a precursor of the catalyst material; (3) subjecting the precursor of the catalyst material to a third high-temperature carbonization under an inert atmosphere to obtain a catalyst for electroreduction of carbon dioxide. The present invention also discloses the catalyst obtained by the above preparation method and its application in electroreduction of carbon dioxide under acidic electrolyte conditions. The catalyst provided by the present invention can effectively increase the working current of the catalytic material under acidic electrolyte, and thus can be applied to electroreduction of carbon dioxide under acidic electrolyte conditions.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalytic chemistry, and particularly relates to a preparation method of a catalyst for highly efficient electroreduction of carbon dioxide under strongly acidic conditions, as well as its products and applications. Background Art

[0002] In recent years, the massive consumption of traditional fossil fuels has led to a continuous increase in the carbon dioxide content in the atmosphere. Converting carbon dioxide into chemicals and fuels through renewable energy is one of the effective ways, and more and more researchers have focused on the electrochemical reduction of carbon dioxide to solve the environmental problems brought by the "greenhouse effect". As one of the products of the above-mentioned carbon dioxide reduction, carbon monoxide is a gas under normal pressure and is more easily separated from the electrolyte solution. It is considered to be one of the most promising products for industrialization due to its high energy efficiency and high selectivity.

[0003] During the electroreduction of carbon dioxide, the solution is usually alkaline or neutral to increase the solubility of carbon dioxide. For example, Chinese Patent with publication number CN113122874A discloses the application of a cadmium sulfide catalyst in the electroreduction of carbon dioxide, and a KOH solution is used during the electroreduction of carbon dioxide; Chinese Patent with publication number CN111686780A discloses a metal-nitrogen-carbon catalyst for carbon dioxide electroreduction, and KHCO 3 solution is used during the electroreduction of carbon dioxide. However, this will form a strongly alkaline or locally strongly alkaline environment in the electrolytic cell, resulting in the reaction of carbon dioxide with hydroxide ions to form carbonates. The carbonate ions can permeate through the anion exchange membrane, leading to cross-contamination, and also dragging down the reaction efficiency and raw material utilization rate. Research shows that more than 50% of the energy is used to recover the carbon dioxide that forms carbonates during the electroreduction of carbon dioxide under alkaline conditions.

[0004] In contrast, if the electrochemical reduction of carbon dioxide can be carried out under acidic conditions, the conversion of carbon dioxide into carbonates can be inhibited, which is also beneficial to the separation of substances. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a catalyst for highly efficient electroreduction of carbon dioxide under strongly acidic conditions. The prepared catalyst can effectively increase the working current of the catalytic material in acidic electrolytes, so that it can be applied to the electroreduction of carbon dioxide under acidic electrolyte conditions.

[0006] The present invention provides the following technical solutions:

[0007] A preparation method of a catalyst for highly efficient electroreduction of carbon dioxide under strongly acidic conditions, the preparation method comprising:

[0008] (1) After mixing the conductive carbon material with the nitrogen-rich material, it is subjected to the first high-temperature carbonization under an inert atmosphere to obtain a carbonitride support;

[0009] (2) The carbonitride support and the metal salt are dispersed in an organic solvent, dried and the product is collected, and then subjected to the second high-temperature carbonization under an inert atmosphere to obtain a precursor of the catalyst material;

[0010] (3) The precursor of the catalyst material is subjected to the third high-temperature carbonization under an inert atmosphere to obtain a catalyst for electro-reducing carbon dioxide.

[0011] The present invention uses a multi-step high-temperature calcination method, replaces noble metals with transition metals, controls their step-by-step bonding with the nitrogen-doped support, increases the number of reaction sites, effectively increases the specific surface area of the catalyst material, improves its adsorption capacity for carbon dioxide, and significantly increases the working current. And a unique metal coordination environment is constructed through multi-step high-temperature calcination, which is the active site for carbon dioxide electro-reduction under acidic electrolyte catalytic conditions. The formed abundant mesopores improve the local pH of the reaction, enabling the catalyst to still have high activity under acidic conditions. The transition metal adopted in the present invention as the reaction site effectively reduces the catalyst synthesis cost, more efficiently utilizes carbon dioxide resources in a large-current electrolysis in an acidic electrolytic cell, solves problems such as carbonate deposition, and provides a new strategy for the industrial development of carbon dioxide electro-reduction.

[0012] The temperature of the first high-temperature carbonization and the second high-temperature carbonization is 500 - 1100 °C, and the temperature of the second high-temperature carbonization is 100 - 450 °C.

[0013] In the present invention, the purpose of the first high-temperature carbonization stage is to dope nitrogen elements into the carbon support. The purpose of the second low-temperature carbonization is to initially anchor the nickel salt on the nitrogen-doped support and remove a part of the ligand ions in the nickel salt. The purpose of the third high-temperature carbonization is to completely remove the ligand ions in the metal salt (when the metal salt is nickel salt, the ligand ions refer to the chloride ions in nickel chloride and the nitrate ions in nickel nitrate), so that the metal element is completely anchored on the nitrogen-doped carbon support, forming a structure with metal single atoms or metal particles anchored on the nitrogen-doped carbon support, and this structure is the active site under acidic electrolysis conditions.

[0014] The time for the first high-temperature carbonization, the second high-temperature carbonization, and the third high-temperature carbonization is 10 min - 100 h; the heating rate for the first high-temperature carbonization, the second high-temperature carbonization, and the third high-temperature carbonization is 1 - 10 °C / min. The present invention controls the form of nitrogen existence and the size of nickel particles in the catalyst by controlling the above carbonization time.

[0015] Preferably, the time for the first high-temperature carbonization and the third high-temperature carbonization is 1 h, and the time for the second high-temperature carbonization is 5 h. Preferably, the heating rate for the first high-temperature carbonization and the second high-temperature carbonization is 5 °C / min, and the heating rate for the third high-temperature carbonization is 2 °C / min.

[0016] The conductive carbon material is selected from one or more of carbon spheres, carbon nanocages, commercial acetylene black, carbon fibers, carbon nanotubes, X72 carbon powder, or Ketjenblack (Ketjenblack EC300J, Ketjenblack EC600JD, Carbon ECP, Carbon ECP600JD) prepared by the stober method; the nitrogen-rich material is selected from one or more of urea, dicyandiamide, or melamine.

[0017] In step (1), the mass ratio of the conductive carbon material to the nitrogen-rich material is 1:0.1 - 1:100. Preferably, the mass ratio of the conductive carbon material to the nitrogen-rich material is 1:10.

[0018] In step (2), the metal salt is a nickel salt, a cobalt salt, or an iron salt; the mass ratio of the carbonitride carrier to the metal salt is 1:0.1 - 1:100. The purpose of regulating the ratio of the metal salt to the nitrogen-rich carrier is to ensure that the metal salt is converted into active sites for the catalytic reaction to the maximum extent, and at the same time ensure that the composition of the active sites is beneficial to the electroreduction of carbon dioxide under acidic conditions.

[0019] Preferably, the mass ratio of the carbonitride carrier to the metal salt is 1:1.74.

[0020] Preferably, the metal salt is a nickel salt. As a transition metal, nickel has a selectivity for the product carbon monoxide of greater than 90%, and is an ideal substitute for noble metal catalysts such as gold and silver.

[0021] Preferably, in step (2), the precursor of the catalyst material is washed and dried in an ethanol aqueous solution. The volume concentration of the washing ethanol aqueous solution is 10% - 75%, and more preferably 50%.

[0022] Preferably, in step (3), the product after the third high-temperature carbonization is subjected to acid treatment in an acidic solution, and the catalyst for electroreducing carbon dioxide is obtained after washing and drying. The acidic solution is hydrochloric acid (HCl) with a mass concentration of 0.5 M - 10 M, nitric acid (HNO 3 ) with a mass concentration of 0.5 M - 10 M, sulfuric acid (H 2 SO 4 ) with a mass concentration of 0.5 M - 10 M, or perchloric acid (HClO 4) The treatment temperature is 40°C - 120°C, preferably 70°C; the treatment time is 1 - 100 h, preferably 6 h. The purpose of the acid treatment is to remove larger-sized metal particles in the catalyst, as larger-sized metal particles are unstable under strong acidic conditions.

[0023] Preferably, the preparation method further includes:

[0024] In step (2), the product is mixed with a nitrogen-rich material and then subjected to a second high-temperature carbonization under an inert atmosphere;

[0025] Or / and,

[0026] In step (3), the precursor is mixed with a nitrogen-rich material and then subjected to a third high-temperature carbonization under an inert atmosphere.

[0027] The existence form of nitrogen element in the catalyst and the coordination environment of nickel element are the keys affecting acid catalysis. By a multi-step (two-step or three-step) nitrogen doping method, the existence form of nitrogen element in the catalyst and the coordination environment of nickel element can be better regulated, thereby improving its acid catalysis effect. Preferably, nitrogen is doped in both steps (2) and (3).

[0028] The mass ratio of the product to the nitrogen-rich material is 1:0.1 - 1:100, and the mass ratio of the precursor to the nitrogen-rich material is 1:0.1 - 1:100. Preferably, the mass ratio of the product to the nitrogen-rich material is 1:10, and the mass ratio of the precursor to the nitrogen-rich material is 1:10.

[0029] In the present invention, the reactor for high-temperature carbonization in the preparation method is a tube furnace, and the inert atmosphere can be selected from nitrogen and argon; the drying is vacuum drying at 50 - 120°C (preferably 60°C).

[0030] The present invention also provides a catalyst for electro-reducing carbon dioxide obtained according to the above preparation method.

[0031] The present invention also provides an application of the above catalyst for electro-reducing carbon dioxide in electro-reducing carbon dioxide under acidic electrolyte conditions.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] Existing catalyst preparation methods often can only carry out the electrocatalytic reduction of carbon dioxide under alkaline or neutral electrolyte conditions. Problems such as the consumption of carbon dioxide in the electrolyte and the deposition of carbonates on the surface of the catalytic electrode affecting the reaction stability are the key technical barriers to be solved in the industrial development process of carbon dioxide. The structure of the catalyst provided by the present invention is a metal supported on a carbon nitride substrate, which is applied to acidic or alkaline carbon dioxide electrocatalysis. Especially when applied to acidic carbon dioxide electrocatalysis, it significantly increases the working current in the acidic electrochemical reduction process, solves the problem of carbon dioxide resource consumption in alkaline electrolytes, and inhibits the hydrogen evolution reaction.

[0034] The catalyst provided by the present invention realizes the large-current electroreduction of carbon dioxide under strong acidic (pH = 1) conditions. Optimally, when the selectivity of the product carbon monoxide remains at about 90%, the current density can still reach 500 A / cm 2 ².

[0035] The preparation method of the catalyst provided by the present invention is simple, and the materials used do not contain precious metals, showing low overpotential and high stability, which better meets the market demand. Description of the Drawings

[0036] Figure 1 XRD patterns of the catalysts prepared in Examples 1-5.

[0037] Figure 2 SEM images of the catalyst in Example 1, with scales of 1 μm and 100 nm respectively.

[0038] Figure 3 Faraday efficiency of the catalyst prepared in Example 1 at different currents.

[0039] Figure 4 Faraday efficiency of the catalyst prepared in Example 4 at different currents.

[0040] Figure 5 Faraday efficiency of the catalyst prepared in Example 5 at different currents.

[0041] Figure 6 Faraday efficiency of the catalyst prepared in Comparative Example 1 at different currents. Detailed Embodiments

[0042] In order to further understand the present invention, the preferred implementation embodiments of the present invention are described below in conjunction with specific embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention rather than limiting the patent requirements of the present invention.

[0043] In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0044] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or alternative embodiments that are mutually exclusive of other embodiments.

[0045] Example 1

[0046] Take 0.1 g of VXC72R carbon powder, reflux and stir it in concentrated nitric acid (9 M) at 60 °C for 3 h. Mix the carbon powder activated with concentrated nitric acid and urea in a mass ratio of 1:10, and grind them evenly. Place it in a tube furnace, anneal it at 800 °C for 1 h under a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0047] Mix the carbonitride after the first high-temperature carbonization and nickel chloride hexahydrate in a mass ratio of 100:174, place it in 20 ml of ethanol solution, ultrasonicate for 20 min, and collect the product by rotary evaporation after uniform dispersion.

[0048] Mix the rotary evaporation product and urea in a mass ratio of 1:10, grind them, place it in a tube furnace, and perform the second annealing at 300 °C for 5 h under a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0049] Wash the product after the second annealing in an ethanol aqueous solution with a volume concentration of 50%, and then collect the product by centrifugation. Dry it overnight at 60 °C in a vacuum drying oven.

[0050] Mix the product after vacuum drying and urea in a mass ratio of 1:10, grind them, place it in a tube furnace, and perform the third annealing at 800 °C for 1 h under a nitrogen atmosphere, and the heating rate is 2 °C / min.

[0051] Place the product after the third annealing in 1 M hydrochloric acid, heat it to 70 °C and stir for 6 h, collect the product by centrifugation, and dry it overnight at 60 °C in a vacuum drying oven. That is, the electroreduction carbon dioxide catalytic material is obtained.

[0052] Prepare the electrode paste. Take 700 μL of isopropanol, 250 μL of deionized water, and 50 μL of Nafion membrane solution, and mix them evenly. Add 10 mg of the above catalyst material and ultrasonicate for 30 min to disperse it evenly. Spray the electrode paste on the carbon paper of model 28BC, and the size of the carbon paper is 2.2 * 2.2 cm 2, a gas diffusion electrode is fabricated. The gas diffusion electrode is placed in a Flow-cell to act as the cathode for the electrocatalytic reduction of carbon dioxide reaction. The anode is an iridium-coated titanium sheet. The cathode electrolyte is a 0.25 M potassium sulfate solution with the pH adjusted to 1 using sulfuric acid, and the anode uses a 0.25 M potassium sulfate solution. The anode and cathode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are carbon monoxide and hydrogen.

[0053] Example 2

[0054] Take 0.1 g of VXC72R carbon powder, reflux and stir it in concentrated nitric acid (9 M) at 60 °C for 3 h. Mix the carbon powder activated by concentrated nitric acid with urea in a mass ratio of 1:10 and grind them evenly. Place them in a tube furnace, anneal at 800 °C for 1 h in a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0055] Mix the carbonitride after the first high-temperature carbonization with nickel chloride hexahydrate in a mass ratio of 100:119, place it in 20 ml of ethanol solution, ultrasonicate for 20 min, and collect the product by rotary evaporation after uniform dispersion.

[0056] Mix the rotary evaporation product with urea in a mass ratio of 1:10, grind them, place them in a tube furnace, and perform the second annealing at 300 °C for 5 h in a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0057] Wash the product after the second annealing in an ethanol aqueous solution with a volume concentration of 50%, and then collect the product by centrifugation. Dry it overnight at 60 °C in a vacuum drying oven.

[0058] Mix the dried product with urea in a mass ratio of 1:10, grind them, place them in a tube furnace, and perform the third annealing at 800 °C for 1 h in a nitrogen atmosphere, and the heating rate is 2 °C / min.

[0059] Place the product after the third annealing in 1 M hydrochloric acid, heat and stir at 70 °C for 6 h, collect the product by centrifugation, and dry it overnight at 60 °C in a vacuum drying oven. That is, the electroreduction of carbon dioxide catalytic material is obtained.

[0060] Prepare the electrode slurry. Take 700 μL of isopropanol, 250 μL of deionized water, and 50 μL of Nafion membrane solution, and mix them evenly. Add 10 mg of the above catalyst material and ultrasonicate for 30 min to disperse it evenly. Spray the electrode slurry on carbon paper of model 28BC, and the size of the carbon paper is 2.2 * 2.2 cm 2, a gas diffusion electrode is fabricated. The gas diffusion electrode is placed in a Flow-cell to act as the cathode for the electrocatalytic reduction of carbon dioxide reaction. The anode is an iridium-plated titanium sheet. The cathode electrolyte is a 0.25 M potassium sulfate solution with the pH adjusted to 1 using sulfuric acid, and the anode uses a 0.25 M potassium sulfate solution. The anode and cathode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are carbon monoxide and hydrogen.

[0061] Example 3

[0062] Take 0.1 g of VXC72R carbon powder, reflux and stir it in concentrated nitric acid (9 M) at 60 °C for 3 h. Mix the carbon powder activated with concentrated nitric acid with urea in a mass ratio of 1:10 and grind them evenly. Place them in a tube furnace, anneal at 800 °C for 1 h in a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0063] Mix the carbonitride after the first high-temperature carbonization with nickel chloride hexahydrate in a mass ratio of 100:237, place it in 20 ml of ethanol solution, ultrasonicate for 20 min, and collect the product by rotary evaporation after uniform dispersion.

[0064] Mix the rotary evaporation product with urea in a mass ratio of 1:10, grind them, place them in a tube furnace, and perform the second annealing at 300 °C for 5 h in a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0065] Wash the product after the second annealing in an ethanol aqueous solution with a volume concentration of 50%, then centrifuge to collect the product, and dry it overnight at 60 °C in a vacuum drying oven.

[0066] Mix the dried product with urea in a mass ratio of 1:10, grind them, place them in a tube furnace, and perform the third annealing at 800 °C for 1 h in a nitrogen atmosphere, and the heating rate is 2 °C / min.

[0067] Place the product after the third annealing in 1 M hydrochloric acid, heat and stir at 70 °C for 6 h, centrifuge to collect the product, and dry it overnight at 60 °C in a vacuum drying oven. That is, the electroreduction carbon dioxide catalytic material is obtained.

[0068] Prepare the electrode slurry. Take 700 μL of isopropanol, 250 μL of deionized water, and 50 μL of Nafion membrane solution, mix them evenly. Add 10 mg of the above catalyst material and ultrasonicate for 30 min to disperse evenly. Spray the electrode slurry on a carbon paper of model 28BC, and the size of the carbon paper is 2.2 * 2.2 cm 2, a gas diffusion electrode is fabricated. The gas diffusion electrode is placed in a Flow-cell to act as the cathode for the electrocatalytic reduction of carbon dioxide reaction. The anode uses an iridium-plated titanium sheet. The cathode electrolyte uses a 0.25M potassium sulfate solution, but the pH is adjusted to 1 with sulfuric acid. The anode uses a 0.25M potassium sulfate solution. The anode and cathode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are carbon monoxide and hydrogen.

[0069] Example 4

[0070] Take 0.1g of VXC72R carbon powder, reflux and stir it in concentrated nitric acid (9M) at 60°C for 3h. Mix the carbon powder activated by concentrated nitric acid with urea in a mass ratio of 1:10 and grind it evenly. Place it in a tube furnace and anneal it at 800°C for 1h in a nitrogen atmosphere, with a heating rate of 5°C / min.

[0071] Mix the carbonitride after the first high-temperature carbonization with nickel chloride hexahydrate in a mass ratio of 100:174, place it in 20ml of ethanol solution, ultrasonicate for 20min, and collect the product by rotary evaporation after uniform dispersion.

[0072] Place the rotary evaporation product in a tube furnace and anneal it at 300°C for 5h in a nitrogen atmosphere, with a heating rate of 5°C / min.

[0073] Wash the product after the second annealing in an ethanol aqueous solution with a volume concentration of 50%, then centrifuge to collect the product and dry it overnight at 60°C in a vacuum drying oven.

[0074] Mix the washed product with urea in a mass ratio of 1:10, grind it, place it in a tube furnace, and anneal it at 800°C for 1h in a nitrogen atmosphere, with a heating rate of 2°C / min.

[0075] Place the product after the third annealing in 1M hydrochloric acid, heat it to 70°C and stir for 6h, centrifuge to collect the product, and dry it overnight at 60°C in a vacuum drying oven. The electroreduction of carbon dioxide catalytic material is obtained.

[0076] Prepare the electrode slurry. Take 700μL of isopropanol, 250μL of deionized water, and 50μL of Nafion membrane solution, mix them evenly. Add 10mg of the above catalyst material and ultrasonicate for 30min to disperse it evenly. Spray the electrode slurry on carbon paper of model 28BC, and the size of the carbon paper is 2.2*2.2cm 2, a gas diffusion electrode was fabricated. The gas diffusion electrode was placed in a Flow-cell to act as the cathode for the electrocatalytic reduction of carbon dioxide reaction. The anode was a titanium sheet coated with iridium. The cathode electrolyte was a 0.25 M potassium sulfate solution with the pH adjusted to 1 using sulfuric acid, and the anode was a 0.25 M potassium sulfate solution. The anode and cathode electrode chambers were separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurred at the cathode, and the main products were carbon monoxide and hydrogen.

[0077] Example 5

[0078] Take 0.1 g of VXC72R carbon powder, reflux and stir it in concentrated nitric acid (9 M) at 60 °C for 3 h. Mix the carbon powder activated by concentrated nitric acid with urea at a mass ratio of 1:10 and grind them evenly. Place it in a tube furnace, anneal it at 800 °C for 1 h under a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0079] Mix the carbonitride after the first high-temperature carbonization with nickel chloride hexahydrate at a mass ratio of 100:174, place it in 20 ml of ethanol solution, ultrasonicate for 20 min, and collect the product by rotary evaporation after uniform dispersion.

[0080] Place the rotary evaporation product in a tube furnace, anneal it at 300 °C for 5 h under a nitrogen atmosphere, and the heating rate is 5 °C / min.

[0081] Wash the product after the second annealing in an ethanol aqueous solution with a volume concentration of 50%, then centrifuge to collect the product, and dry it overnight at 60 °C in a vacuum drying oven.

[0082] Place the dried product in a tube furnace, anneal it at 800 °C for 1 h under a nitrogen atmosphere, and the heating rate is 2 °C / min.

[0083] Place the product after the third annealing in 1 M hydrochloric acid, heat and stir at 70 °C for 6 h, centrifuge to collect the product, and dry it overnight at 60 °C in a vacuum drying oven. The electroreduction of carbon dioxide catalytic material is obtained.

[0084] Prepare the electrode paste. Take 700 μL of isopropanol, 250 μL of deionized water, and 50 μL of Nafion membrane solution, and mix them evenly. Add 10 mg of the above catalyst material and ultrasonicate for 30 min to disperse evenly. Spray the electrode paste onto carbon paper of model 28BC, and the size of the carbon paper is 2.2 * 2.2 cm 2 , a gas diffusion electrode was fabricated. The gas diffusion electrode was placed in a Flow-cell to act as the cathode for the electrocatalytic reduction of carbon dioxide reaction. The anode was a titanium sheet coated with iridium. The cathode electrolyte was a 0.25 M potassium sulfate solution with the pH adjusted to 1 using sulfuric acid, and the anode was a 0.25 M potassium sulfate solution. The anode and cathode electrode chambers were separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurred at the cathode, and the main products were carbon monoxide and hydrogen.

[0085] Example 6

[0086] Mix multi-walled carbon nanotubes and urea at a mass ratio of 1:10 and grind them evenly. Place them in a tube furnace and anneal at 800 °C for 1 h in a nitrogen atmosphere with a heating rate of 5 °C / min.

[0087] Mix the nitrogen-doped carbon nanotubes after the first high-temperature carbonization and nickel chloride hexahydrate at a mass ratio of 100:174, place them in 20 ml of ethanol solution, sonicate for 20 min, and collect the product by rotary evaporation after uniform dispersion.

[0088] Mix the rotary evaporation product and urea at a mass ratio of 1:10, grind them, place them in a tube furnace, and perform the second annealing at 300 °C for 5 h in a nitrogen atmosphere with a heating rate of 5 °C / min.

[0089] Wash the product after the second annealing in an ethanol aqueous solution with a volume concentration of 50%, then centrifuge to collect the product, and dry it overnight at 60 °C in a vacuum drying oven.

[0090] Mix the dried product and urea at a mass ratio of 1:10, grind them, place them in a tube furnace, and perform the third annealing at 800 °C for 1 h in a nitrogen atmosphere with a heating rate of 2 °C / min.

[0091] Place the product after the third annealing in 1 M hydrochloric acid, heat and stir at 70 °C for 6 h, centrifuge to collect the product, and dry it overnight at 60 °C in a vacuum drying oven. That is, the electrocatalytic material for carbon dioxide reduction is obtained.

[0092] Prepare the electrode paste. Take 700 μL of isopropanol, 250 μL of deionized water, and 50 μL of Nafion membrane solution, mix them evenly. Add 10 mg of the above catalyst material and sonicate for 30 min to disperse evenly. Spray the electrode paste on carbon paper of model 28BC with a size of 2.2 * 2.2 cm 2 , and make a gas diffusion electrode. Place the gas diffusion electrode in the Flow-cell to act as the cathode for the electrocatalytic reduction of carbon dioxide reaction. The anode uses an iridium-coated titanium sheet. The cathode electrolyte uses a 0.25 M potassium sulfate solution but adjusts the pH to 1 with sulfuric acid, and the anode uses a 0.25 M potassium sulfate solution. The anode and cathode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are carbon monoxide and hydrogen.

[0093] Comparative Example 1

[0094] Take 0.1 g of VXC72R carbon powder and reflux and stir it in concentrated nitric acid (9 M) at 60 °C for 3 h. Take 0.1 g of activated carbon powder, add it to 20 ml of deionized water, ultrasonicate for 30 min, and after uniform dispersion, place it on a magnetic stirrer for stirring. Prepare a dilute nickel chloride solution of 3 mg / ml, and drop 2 ml during the stirring process. After stirring overnight, centrifuge to collect the product, vacuum dry it overnight, and then incorporate it with urea in a mass ratio of 1:10 and place it in a tubular furnace at 800 °C for 1 h (heating rate 2 °C / min).

[0095] As Figure 1 shown, the X-ray diffraction (XRD) patterns of the catalysts prepared in Examples 1-5 are as follows. It can be seen from Figure 1 them that in one-step or two-step nitrogen doping, nickel particles are not obvious or the nickel particles are small. In the case of three-step nitrogen doping, nickel particles are obvious, indicating that the active sites under acidic catalysis are tiny nickel particles.

[0096] As Figure 2 shown, the overall morphology of the catalyst prepared in Example 1 is uniform particles, mainly nitrogen-doped carbon powder, in which there are some aggregated nickel particles.

[0097] As Figure 3 、 4 、5 shown, at a current of 700 mA, the nickel-loaded catalyst with three-step nitrogen doping (Example 1) still has a carbon monoxide selectivity of nearly 90%, while the carbon monoxide selectivity of the catalysts with one-step nitrogen doping and two-step nitrogen doping decreases, and only has a high carbon monoxide selectivity at a lower current, indicating that a more unique nickel-nitrogen coordination environment is formed in the three-step nitrogen doping, thus increasing the stable active sites for acidic catalysis.

[0098] As Figure 6 shown, the nickel-carbon-nitrogen catalyst prepared in Comparative Example 1 by the traditional one-step calcination method is mainly in the form of nickel single atoms supported on a nitrogen-doped carbon carrier, and its catalytic performance is not good under acidic conditions, which is in contrast to the performance of the catalyst prepared in the present invention.

Claims

1. Preparation method of catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions, characterized in that, the preparation method includes: (1) After mixing a conductive carbon material and a nitrogen-rich material, subjecting them to a first high-temperature carbonization under an inert atmosphere to obtain a carbonitride carrier; (2) Dispersing the carbonitride carrier and a metal salt in an organic solvent, drying and collecting the product, and subjecting it to a second high-temperature carbonization under an inert atmosphere to obtain a precursor of the catalyst material; (3) Subjecting the precursor of the catalyst material to a third high-temperature carbonization under an inert atmosphere to obtain a catalyst for electroreduction of carbon dioxide; the temperature of the first high-temperature carbonization and the third high-temperature carbonization is 500-1100 °C, and the temperature of the second high-temperature carbonization is 100-450 °C; The time for the first high-temperature carbonization, the second high-temperature carbonization, and the third high-temperature carbonization is 10 min-100 h; the heating rate for the first high-temperature carbonization, the second high-temperature carbonization, and the third high-temperature carbonization is 1-10 °C / min.

2. The preparation method of the catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions according to claim 1, characterized in that, the conductive carbon material is selected from one or more of carbon spheres, carbon nanocages, commercial acetylene black, carbon fibers, carbon nanotubes, X72 carbon powder or Ketjen black prepared by the stober method; the nitrogen-rich material is selected from one or more of urea, dicyandiamide or melamine.

3. The preparation method of the catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions according to claim 1, characterized in that, in step (1), the mass ratio of the conductive carbon material to the nitrogen-rich material is 1:0.1-1:

100.

4. The preparation method of the catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions according to claim 1, characterized in that, in step (2), the metal salt is a nickel salt, a cobalt salt or an iron salt; the mass ratio of the carbonitride carrier to the metal salt is 1:0.1-1:

100.

5. The preparation method of the catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions according to claim 1, characterized in that, the preparation method includes: in step (2), mixing the product with a nitrogen-rich material and then subjecting it to a second high-temperature carbonization under an inert atmosphere; or / and, in step (3), mixing the precursor with a nitrogen-rich material and then subjecting it to a third high-temperature carbonization under an inert atmosphere.

6. The preparation method of the catalyst for highly efficient electroreduction of carbon dioxide under strong acidic conditions according to claim 5, characterized in that, the mass ratio of the product to the nitrogen-rich material is 1:0.1-1:100, and the mass ratio of the precursor to the nitrogen-rich material is 1:0.1-1:

100.

7. A catalyst for electroreduction of carbon dioxide obtained by the preparation method according to any one of claims 1-6.

8. Application of the catalyst for electroreduction of carbon dioxide according to claim 7 in electroreduction of carbon dioxide under acidic electrolyte conditions.

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