A highly dispersed nickel-based carbon-nitrogen catalyst, preparation method and application thereof

Abstract

The present invention relates to a highly dispersed nickel-based carbon-nitrogen catalyst, a preparation method and an application thereof. The preparation method comprises the following steps: step 1: synthesizing a hydrotalcite precursor; step 2: preparing a calcined precursor; and step 3: preparing a highly dispersed nickel-based carbon-nitrogen catalyst. The preparation method of the highly dispersed nickel-based carbon-nitrogen catalyst of the present invention is simple, the raw materials are cheap, and it is suitable for large-scale production. The nickel in the highly dispersed nickel-based carbon-nitrogen catalyst of the present invention is highly dispersed, and has excellent electrocatalytic activity and selectivity; the carbon-nitrogen carrier has the functions of stabilizing the structure and regulating electrons, which is conducive to electron transfer and intermediate adsorption. The highly dispersed nickel-based carbon-nitrogen catalyst has high catalytic activity and high stability. After 30 hours of continuous electrolysis, its CO Faraday efficiency does not show obvious attenuation, and it has good stability and industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis, and in particular relates to a highly dispersed nickel-based carbon-nitrogen catalyst, a preparation method and applications thereof. Background Art

[0002] With the increasing severity of global climate change, carbon dioxide emissions have become a key factor affecting environmental sustainability. The electrocatalytic reduction of carbon dioxide (CO₂RR) to convert it into valuable carbon-based chemicals such as carbon monoxide, formic acid, and methanol not only facilitates carbon recycling but also provides a new pathway for the efficient storage and utilization of renewable energy. Currently, noble metal (e.g., Au, Ag)-based electrocatalysts exhibit excellent activity and selectivity in CO₂RR, but their high cost limits their large-scale application. In comparison, nickel-based catalysts have become a representative non-noble metal electrocatalyst due to their abundant reserves, excellent CO₂ adsorption activity, and low preparation cost. However, conventional nickel nanocatalysts face challenges such as agglomeration and low utilization of metal active sites, limiting their further application in CO₂RR.

[0003] In recent years, single-atom catalysts (SACs) have demonstrated outstanding performance in heterogeneous catalytic reactions such as CO₂RR due to their maximum atomic utilization and unique electronic structure control capabilities. However, existing methods for preparing highly dispersed nickel-based catalysts often suffer from complex precursor design, difficult ligand synthesis, the need for template-assisted or costly multi-step heat treatments, hindering large-scale synthesis and industrial application. Patent document CN118925768A utilizes a high internal phase emulsion template method to synthesize nitrogen-doped porous carbon. Highly dispersed nickel is then loaded onto the nitrogen-doped porous carbon via an impregnation method. After high-temperature calcination, a highly dispersed nickel-based catalyst is obtained. Patent document CN118910651A utilizes methanol as a solvent to prepare a PVP@ZIF-8 composite material with room temperature stirring. This MOF material is then used as a precursor and subjected to high-temperature carbonization and pyrolysis. The product is then acid-washed and dried to obtain a porous nitrogen-doped carbon material. This is then subjected to impregnation and pyrolysis to obtain a nickel-based single-atom catalyst. The methods for synthesizing highly dispersed nickel-based catalysts in the above two patents require template assistance or multi-step processing, which is not conducive to large-scale synthesis and industrial application.

[0004] To address the above issues, researchers have gradually focused on using inexpensive metal sources such as layered double hydroxides (LDHs), as well as structurally simple ligands and conductive carbon supports to construct highly dispersed catalysts. Although there have been attempts to use NiAl-LDH as a precursor for pyrolysis to prepare Ni-based catalytic materials, patent document CN115074750A synthesizes hydrotalcite by a hydrothermal method, and then co-pyrolyzes the hydrotalcite and a nitrogen source to prepare a highly dispersed nickel-based / AlN co-embedded carbon nanotube electrocatalyst. However, the hydrothermal method for preparing hydrotalcite is also relatively complex, which is not conducive to subsequent industrialization. Therefore, how to control the dispersion state of Ni, how to simply prepare catalytic materials and give them the ability to highly selectively electroreducing CO2 remain challenging.

[0005] Therefore, there is an urgent need to develop a catalyst preparation method with simple process, cheap raw materials, controllable highly dispersed structure, and suitable for efficient electrocatalytic CO2 reduction, so as to promote the industrial transformation and application of this technology, which is of great significance in the fields of catalysis, energy, etc. Summary of the Invention

[0006] The technical problem solved by the present invention is that the existing nickel-based electrocatalysts in the CO2 reduction reaction have problems such as complex preparation process, low utilization rate of active centers, and unstable catalytic performance.

[0007] In view of the technical problems existing in the prior art, the present invention designs a highly dispersed nickel-based carbon-nitrogen catalyst, a preparation method and an application thereof.

[0008] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "consisting of..." etc. and similar meanings.

[0009] In order to solve the above-mentioned technical problems, the present invention adopts the following solutions:

[0010] A method for preparing a highly dispersed nickel-based carbon-nitrogen catalyst comprises the following steps:

[0011] Step 1: Synthesis of hydrotalcite precursor;

[0012] Nickel nitrate hexahydrate and aluminum nitrate nonahydrate were weighed and dissolved in deionized water (referred to as solution A), and sodium hydroxide solution B was prepared. A hydrotalcite precursor, namely NiAl-LDH precursor, was synthesized by colloid grinding.

[0013] Step 2: preparing a calcined precursor;

[0014] The NiAl-LDH precursor, 1,10-phenanthroline and carbon black are dispersed uniformly in an ethanol solution, vacuum dried and then ground to obtain a calcined precursor.

[0015] Step 3: preparing a highly dispersed nickel-based carbon-nitrogen catalyst;

[0016] The calcined precursor obtained in step 2 is heat-treated under a nitrogen atmosphere to obtain a highly dispersed nickel-based carbon-nitrogen catalyst, namely, a Ni-NC catalyst;

[0017] In step 1, the molar ratio of nickel nitrate hexahydrate to aluminum nitrate nonahydrate in solution A is 2:1-4:1;

[0018] The total concentration of the nitrate solution A is 0.05-1.0 mol / L;

[0019] The concentration of the sodium hydroxide solution B is 1 mol / L-4 mol / L;

[0020] In step 2, the mass ratio of NiAl-LDH precursor to (1,10-phenanthroline + carbon black) is 0.01 to 0.5. The mass percentage of carbon black in the mixture of 1,10-phenanthroline and carbon black is 10-90%.

[0021] Furthermore, the synthesis of the hydrotalcite precursor by colloid milling is specifically as follows: while the colloid mill is rotating at a speed of 1500-9000 rpm, salt solution A and sodium hydroxide solution B are poured into the colloid mill at the same speed for 1-120 minutes, the mixture is taken out, washed to neutrality, dried by rotary evaporation at 40-80°C, and ground into powder.

[0022] Furthermore, in step 3, the heat treatment temperature is 550°C-950°C, the heating rate is 0.5-10°C / min, the nitrogen flow rate is 20-200 mL / min, and the heat treatment time is 1-5 h.

[0023] The invention also discloses a highly dispersed nickel-based carbon-nitrogen catalyst, which is prepared according to the above preparation method.

[0024] Furthermore, the highly dispersed nickel-based carbon-nitrogen catalyst has the following characteristics:

[0025] (1) Using carbon and nitrogen as carriers, nickel active sites are evenly distributed on the surface;

[0026] (2) Contains three types of doped nitrogen: graphitic N, pyridinic N, and pyrrolic N;

[0027] (3) Nickel exists in the form of Ni-Ni.

[0028] Furthermore, the mass fraction of Ni in the highly dispersed nickel-based carbon-nitrogen catalyst is 0.5-5wt%, and Ni is dispersed in the form of extremely small clusters.

[0029] Furthermore, the total mass fraction of nitrogen doping in the highly dispersed nickel-based carbon-nitrogen catalyst is 1-15wt%, of which graphite N accounts for 0-40%, pyridine N accounts for 20-80%, and pyrrole N accounts for 10-40%.

[0030] The present invention also discloses an application of the highly dispersed nickel-based carbon-nitrogen catalyst in an electrocatalytic reaction for selectively reducing CO2 to carbon monoxide.

[0031] In the application of the present invention, it is necessary to prepare a working electrode;

[0032] In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at a constant potential under the condition of continuous CO2 flow. The Faradaic efficiency of the CO2 reduction product at different potentials was calculated.

[0033] The potential in the constant potential reduction process was controlled at -1.4 V to -1.8 V. When preparing the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL was taken out and evenly dropped on a 1 cm 2 On carbon paper, dry under infrared lamp before use.

[0034] The highly dispersed nickel-based carbon-nitrogen catalyst of the present invention is applied to the aqueous CO2 electroreduction reaction, and the CO selectivity (Faradaic efficiency) is greater than 90% in the potential window of -1.4 V to -1.8 V (vs. Ag / AgCl).

[0035] In the present invention, the uniform dispersion in step 2 is achieved by dispersing the mixture under ultrasound for 20-40 minutes. Generally, there is no special requirement for the ultrasound power, as long as the uniform dispersion effect can be achieved.

[0036] In the present invention, the vacuum drying in step 2 is generally performed in a vacuum drying oven at 60-80°C.

[0037] In the prepared Ni-NC catalyst of the present invention, nickel active sites are uniformly distributed in the carbon-nitrogen matrix.

[0038] In the present invention, 1,10-phenanthroline acts as a nitrogen source and participates in the construction of the carbon skeleton during the pyrolysis process, forming a carbon-nitrogen skeleton rich in nitrogen functional groups; carbon black provides a high specific surface area and an excellent conductive network, effectively promoting electron transport; the nickel released during the pyrolysis of NiAl-LDH is nano-confined and anchored in the carbon-nitrogen structure, significantly inhibiting metal agglomeration and obtaining highly dispersed nickel active sites, thereby improving catalytic performance and structural stability.

[0039] In the present invention, a synergistic combination of nickel-containing layered double hydroxide (NiAl-LDH), high specific surface area carbon black and nitrogen source 1,10-phenanthroline is used in the catalyst preparation process. After pre-uniform dispersion and single-step pyrolysis, it is significantly superior to the existing multi-step impregnation-roasting or simple physical mixing methods. The essence of this technology is to utilize the staged decomposition characteristics of NiAl-LDH during high-temperature cracking, so that nickel is gradually precipitated in the carbon skeleton at a relatively slow rate. The interlayer "nano-confinement" effect can inhibit Ni from precipitating in the early and middle stages of pyrolysis. 2+ The rapid migration and disordered agglomeration cause it to preferentially deposit on the carbon black surface or defective areas. At the same time, the intermediate carbon and nitrogen fragments generated in the initial pyrolysis of 1,10-phenanthroline can react with the released Ni 2+ The formation of transient coordination complexes guides Ni to enrich in nitrogen sites at the molecular scale, reducing the risk of forming large metal agglomerates under high temperature conditions. In the late pyrolysis stage, these nitrogen sources evolve into various active nitrogen sites such as graphitic N, pyridinic N, and pyrrolic N during the carbonization and graphitization process, and gradually reduce to Ni 0 The nickel clusters form Ni at the interface of the support x –N x -C cooperative structure or nickel-rich electron interface, further regulates d orbital electron filling, and improves the adsorption and activation efficiency of CO2 molecules on the catalyst surface. Carbon black not only provides a porous conductive network, significantly improving the electron migration rate, but also can capture some Ni species due to its rich surface defects and dislocations, thereby strengthening the metal-carbon coupling interface. Through such a strategy of pre-molecular-level uniform mixing and simultaneous realization of metal confinement, nitrogen cooperative doping and directional regulation of carbon skeleton structure in a single-step pyrolysis, the present invention successfully solves the problems of metal agglomeration, uneven nitrogen doping, and chaotic interface charge distribution that are easily caused by the traditional method of first loading and then carbonization, so that nickel species are embedded in the carbon-nitrogen skeleton with higher dispersion, more reasonable electronic structure and more stable interface morphology, thereby effectively improving the electrocatalytic CO2 reduction performance and long-term stability.

[0040] In the present invention, the metal source in the catalyst preparation method can be other nickel-based hydrotalcites, such as one or more of NiCo-LDH, NiFe-LDH, etc.;

[0041] The nitrogen source may also be one or more other organic substances or ligands containing nitrogen;

[0042] The carbon source can also be other carbon-containing inorganic substances besides carbon black, such as carbon nanotubes, C 60 One or more of the above.

[0043] In the present invention, there is no need to soak the product with dilute acid (such as 0.1M HCl) (to remove possible residual metal particles), which also highlights the simplicity of the catalyst preparation method of the present invention.

[0044] The present invention provides a highly dispersed nickel-based carbon-nitrogen catalyst, a preparation method and its application, which have the following beneficial effects:

[0045] 1. The preparation method of the highly dispersed nickel-based carbon-nitrogen catalyst of the present invention is simple, the raw materials are cheap, and it is suitable for large-scale production.

[0046] 2. The nickel in the highly dispersed nickel-based carbon-nitrogen catalyst of the present invention is highly dispersed, and has excellent electrocatalytic activity and selectivity (FE CO -97%), that is, the Faradaic efficiency of carbon monoxide is about 97%; the carbon-nitrogen carrier has the functions of stabilizing the structure and regulating electrons, which is conducive to electron transfer and intermediate adsorption.

[0047] 3. The highly dispersed nickel-based carbon-nitrogen catalyst in the present invention has high catalytic activity and high stability. After 30 hours of continuous electrolysis, its CO Faradaic efficiency does not show obvious attenuation, and it has good stability and industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 : is a flow chart for preparing a highly dispersed nickel-based carbon-nitrogen catalyst of the present invention;

[0049] Figure 2 : Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 of the present invention;

[0050] Figure 3 : X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) patterns of the highly dispersed nickel-based carbon-nitrogen catalysts prepared in Examples 1-3 of the present invention, including a high-resolution N 1s pattern showing the N type distribution;

[0051] Figure 4 : Ni K-edge EXAFS spectrum and Fourier transform spectrum of the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 of the present invention;

[0052] Figure 5 : Faradaic efficiency (FE) curves of CO2 electroreduction reaction of different materials at different potentials in Examples 1-3 and Comparative Examples 1-5, and current (LSV) curves of Examples 1-3;

[0053] Figure 6 : This is the stability test curve of the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0055] Example 1 Preparation of Ni-NC-750

[0056] Ni-NC-750 is a highly dispersed nickel-based doped carbon-nitrogen catalytic material prepared by co-pyrolysis of nickel-aluminum hydrotalcite, 1,10-phenanthroline (phen) and carbon black at 750°C.

[0057] Nickel nitrate hexahydrate (13.96 g) and aluminum nitrate nonahydrate (3.34 g) were weighed and dissolved in 80 mL of deionized water (referred to as solution A), and sodium hydroxide (8.96 g) was weighed and dissolved in 80 mL of deionized water (referred to as solution B). The hydrotalcite precursor, i.e., NiAl-LDH precursor, was synthesized by colloidal grinding.

[0058] Among them, at this moment, the total concentration of nitrate solution A is 0.8 mol / L; the concentration of sodium hydroxide solution B is 2 mol / L;

[0059] The hydrotalcite precursor was synthesized by colloid milling as follows: salt solution A and sodium hydroxide solution B were poured into the colloid mill at a speed of 6000 rpm at the same time, and the speed was maintained for 60 minutes after pouring. The mixture was taken out, washed to neutrality, dried by rotary evaporation at 60°C, and ground into powder.

[0060] 6 mg of NiAl-LDH powder (Ni:Al molar ratio of 3:1), 100 mg of 1,10-phenanthroline (phen), and 100 mg of carbon black (Vulcan XC-72) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The mass ratio of NiAl-LDH precursor to (1,10-phenanthroline + carbon black) was 0.03, with the mass percentage of carbon black in the mixture of 1,10-phenanthroline and carbon black being 50%.

[0061] The slurry was dried (60° C., vacuum drying oven) and then ground to obtain a precursor mixture.

[0062] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 750°C (heating rate 5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni-NC-750.

[0063] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 The samples were placed on carbon paper and dried under an infrared lamp before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0064] Example 2: Preparation of Ni-NC-550

[0065] Ni-NC-550 is a highly dispersed nickel-based doped carbon-nitrogen catalytic material prepared by co-pyrolysis of nickel-aluminum hydrotalcite, 1,10-phenanthroline (phen) and carbon black at 550°C.

[0066] Nickel nitrate hexahydrate (0.78 g) and aluminum nitrate nonahydrate (0.28 g) were weighed and dissolved in 80 mL of deionized water (referred to as solution A), and sodium hydroxide (4.48 g) was weighed and dissolved in 80 mL of deionized water (referred to as solution B). The hydrotalcite precursor, i.e., NiAl-LDH precursor, was synthesized by colloidal grinding.

[0067] Among them, at this moment, the total concentration of nitrate solution A is 0.05 mol / L; the concentration of sodium hydroxide solution B is 1 mol / L;

[0068] The specific steps for synthesizing the hydrotalcite precursor using a colloid mill are as follows: salt solution A and sodium hydroxide solution B are poured into the colloid mill at a speed of 1500 rpm, the speed is maintained at this speed for 120 minutes, the mixture is taken out, washed to neutrality, dried by rotary evaporation at 40°C, and ground into powder.

[0069] 2 mg of NiAl-LDH powder (Ni:Al molar ratio of 2:1), 180 mg of 1,10-phenanthroline (phen), and 20 mg of carbon black (Vulcan XC-72) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The mass ratio of NiAl-LDH precursor to (1,10-phenanthroline + carbon black) was 0.01, with the mass percentage of carbon black in the mixture of 1,10-phenanthroline and carbon black being 10%.

[0070] The slurry was dried (70° C., vacuum drying oven) and then ground to obtain a precursor mixture.

[0071] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 550°C (heating rate 0.5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 1 hour and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni-NC-550.

[0072] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 The samples were dried under an infrared lamp on carbon paper before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0073] Example 3: Preparation of Ni-NC-950

[0074] Ni-NC-950 is a highly dispersed nickel-based doped carbon-nitrogen catalytic material prepared by co-pyrolysis of nickel-aluminum hydrotalcite, 1,10-phenanthroline (phen) and carbon black at 950°C.

[0075] Nickel nitrate hexahydrate (18.61 g) and aluminum nitrate nonahydrate (3.34 g) were weighed and dissolved in 80 mL of deionized water (referred to as solution A), and sodium hydroxide (17.92 g) was weighed and dissolved in 80 mL of deionized water (referred to as solution B). The hydrotalcite precursor, i.e., NiAl-LDH precursor, was synthesized by colloidal grinding.

[0076] Among them, at this moment, the total concentration of nitrate solution A is 1.0 mol / L; the concentration of sodium hydroxide solution B is 4 mol / L;

[0077] The hydrotalcite precursor was synthesized by colloid milling as follows: salt solution A and sodium hydroxide solution B were poured into the colloid mill at a speed of 9000 rpm, the speed was maintained at this speed for 1 minute, the mixture was taken out, washed to neutrality, dried by rotary evaporation at 80°C, and ground into powder.

[0078] 100 mg of NiAl-LDH powder (Ni:Al molar ratio of 4:1), 20 mg of 1,10-phenanthroline (phen), and 180 mg of carbon black (Vulcan XC-72) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The mass ratio of NiAl-LDH precursor to (1,10-phenanthroline + carbon black) was 0.5, with the mass percentage of carbon black in the mixture of 1,10-phenanthroline and carbon black being 90%.

[0079] The slurry was dried (80° C., vacuum drying oven) and then ground to obtain a precursor mixture.

[0080] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 950°C (heating rate 10°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 5 hours and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni-NC-950.

[0081] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 The samples were placed on carbon paper and dried under an infrared lamp before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0082] Comparative Example 1 Preparation of Ni-N-750

[0083] Ni-N-750 is a highly dispersed nickel-based doped carbon-nitrogen catalytic material prepared by co-pyrolysis of nickel-aluminum hydrotalcite and 1,10-phenanthroline (phen) at 750°C.

[0084] Nickel nitrate hexahydrate (13.96 g) and aluminum nitrate nonahydrate (3.34 g) were weighed and dissolved in 80 mL of deionized water (referred to as solution A), and sodium hydroxide (8.96 g) was weighed and dissolved in 80 mL of deionized water (referred to as solution B). The hydrotalcite precursor, i.e., NiAl-LDH precursor, was synthesized by colloidal grinding.

[0085] Among them, at this moment, the total concentration of nitrate solution A is 0.8 mol / L; the concentration of sodium hydroxide solution B is 2 mol / L;

[0086] The hydrotalcite precursor was synthesized by colloid milling as follows: salt solution A and sodium hydroxide solution B were poured into the colloid mill at a speed of 6000 rpm at the same time, and the speed was maintained for 60 minutes after pouring. The mixture was taken out, washed to neutrality, dried by rotary evaporation at 60°C, and ground into powder.

[0087] 6 mg of NiAl-LDH powder (Ni:Al molar ratio of 3:1) and 100 mg of 1,10-phenanthroline (phen) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The slurry was dried (60°C in a vacuum drying oven) and then ground to prepare a precursor mixture.

[0088] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 750°C (heating rate 5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni-N-750.

[0089] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 The samples were placed on carbon paper and dried under an infrared lamp before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0090] Comparative Example 2 Preparation of Ni-C-750

[0091] Ni-C-750 is a highly dispersed nickel-based doped carbon-nitrogen catalytic material prepared by co-pyrolysis of nickel-aluminum hydrotalcite and carbon black at 750°C.

[0092] Nickel nitrate hexahydrate (13.96 g) and aluminum nitrate nonahydrate (3.34 g) were weighed and dissolved in 80 mL of deionized water (referred to as solution A), and sodium hydroxide (8.96 g) was weighed and dissolved in 80 mL of deionized water (referred to as solution B). The hydrotalcite precursor, i.e., NiAl-LDH precursor, was synthesized by colloidal grinding.

[0093] Among them, at this moment, the total concentration of nitrate solution A is 0.8 mol / L; the concentration of sodium hydroxide solution B is 2 mol / L;

[0094] The hydrotalcite precursor was synthesized by colloid milling as follows: salt solution A and sodium hydroxide solution B were poured into the colloid mill at a speed of 6000 rpm at the same time, and the speed was maintained for 60 minutes after pouring. The mixture was taken out, washed to neutrality, dried by rotary evaporation at 60°C, and ground into powder.

[0095] 6 mg of NiAl-LDH powder (Ni:Al molar ratio 3:1) and 100 mg of carbon black (Vulcan XC-72) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The slurry was dried (60-80°C in a vacuum drying oven) and then ground to prepare a precursor mixture.

[0096] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 750°C (heating rate 5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni-C-750.

[0097] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2The samples were placed on carbon paper and dried under an infrared lamp before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0098] Comparative Example 3 Preparation of NC-750

[0099] NC-750 is a highly dispersed nickel-doped carbon-nitrogen catalytic material prepared by co-pyrolysis of 1,10-phenanthroline (phen) and carbon black at 750°C.

[0100] Take 100 mg of 1,10-phenanthroline (phen) and 100 mg of carbon black (Vulcan XC-72). Add these two components to an appropriate amount of anhydrous ethanol and ultrasonically disperse them for 30 minutes to obtain a uniform mixed slurry. Dry the slurry (60°C in a vacuum drying oven) and grind it to prepare the precursor mixture.

[0101] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 750°C (heating rate 5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni-C-750.

[0102] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 The samples were placed on carbon paper and dried under an infrared lamp before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0103] Comparative Example 4 Preparation of Ni(OH)2-NC-750

[0104] Ni(OH)2-NC-750 is a highly dispersed nickel-based doped carbon-nitrogen catalytic material prepared by co-pyrolysis of nickel hydroxide, 1,10-phenanthroline (phen) and carbon black at 750°C.

[0105] 6 mg of Ni(OH)2 powder, 100 mg of 1,10-phenanthroline (phen), and 100 mg of carbon black (Vulcan XC-72) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The slurry was dried (60°C in a vacuum drying oven) and then ground to prepare a precursor mixture.

[0106] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 750°C (heating rate 5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a black powder, which was the catalyst Ni(OH)2-NC-750.

[0107] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 The samples were placed on carbon paper and dried under an infrared lamp before use. In an H-type electrolytic cell separated by a Nafion 117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0108] Comparative Example 5 Preparation of Al(OH)3-NC-750

[0109] Al(OH)3-NC-750 is a carbon-nitrogen catalytic material prepared by co-pyrolysis of aluminum hydroxide, 1,10-phenanthroline (phen) and carbon black at 750°C.

[0110] 6 mg of Al(OH)3 powder, 100 mg of 1,10-phenanthroline (phen), and 100 mg of carbon black (Vulcan XC-72) were added to an appropriate amount of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform mixed slurry. The slurry was dried (60°C in a vacuum drying oven) and then ground to prepare a precursor mixture.

[0111] The precursor mixture was placed in a quartz boat, placed in a tube furnace, and heated to 750°C (heating rate 5°C / min) under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then naturally cooled to room temperature to obtain a black powder, which is the catalyst Al(OH)3-NC-750, or simply Al-NC-750.

[0112] To prepare the working electrode, 5 mg of the catalyst was dispersed in 1 mL of ethanol solution, and 20 μL of Nafion membrane solution was added. Ultrasonication was performed for 30 min to form a uniform ink. 200 μL of the ink was then evenly dropped onto a 1 cm 2 On carbon paper, dried under infrared light before use. In an H-type electrolytic cell separated by a Nafion117 proton exchange membrane (PEM) into an anode tank and a cathode tank, a platinum sheet was used as the counter electrode, and Ag / AgCl (3.5 M saturated KCl solution) was used as the reference electrode. The catalyst loading was 1 mg / cm 2 The hydrophobic carbon paper was used as the working electrode, and 20 mL of 0.5 M KHCO3 solution was loaded into the electrolytic cell. Before the test, 20 mL / min of CO2 was bubbled into the electrolyte for 30 minutes until saturation. Then, CO2 was reduced at the cathode at a constant potential under the condition of continuous CO2 flow. The Faraday efficiency of the CO2 reduction products (CO, H2) at different potentials was calculated.

[0113] Comparative Example 1 lacks carbon black, which acts as a conductive support material, improving the catalyst's electron transport properties. Its spherical skeleton structure serves as a structural template, controlling the morphology of the final material (spherical particles). Its structural stability during pyrolysis effectively anchors active sites and prevents sintering. Therefore, Example 1 outperforms the Ni-N-750 catalyst in Comparative Example 1.

[0114] Comparative Example 2 lacks 1,10-phenanthroline. This nitrogen source, used in the material preparation, can be pyrolyzed at high temperatures to generate pyridinic N, pyrrolic N, and graphitic N, helping to regulate the electronic structure of the N / C skeleton and improving the selectivity and activity of CO2 reduction. Therefore, Example 1 outperforms the Ni-C-750 in Comparative Example 2.

[0115] Comparative Example 3 lacks NiAl-LDH, which provides a highly dispersed Ni precursor that converts into active Ni sites during pyrolysis. Its layered structure facilitates uniform mixing with ligands and carbon sources, facilitating structural control. Furthermore, pyrolysis releases gases, forming a certain degree of pore structure (aiding pore formation). Therefore, Example 1 outperforms NC-750 in Comparative Example 3.

[0116] In Comparative Example 4, Ni(OH)2 was selected. Compared with Ni(OH)2, the interlayer water and anions (such as CO3 2- ) will decompose and release gas during pyrolysis, promoting the formation of a porous structure; more importantly, Al 3+ It is non-reducible and does not participate in the formation of metal particles, which can inhibit the agglomeration and sintering of Ni. Therefore, the performance of Example 1 is better than that of Ni(OH)2-NC-750 in Comparative Example 4.

[0117] Comparative Example 5 uses Al(OH)3, which lacks the active metal Ni and cannot form active sites. When heated to temperatures above 300°C, Al(OH)3 dehydrates to form Al2O3 (aluminum oxide), an insulating material with no electrocatalytic activity and even hinders electron conduction. Therefore, Example 1 outperforms the Al(OH)3-NC-750 in Comparative Example 5.

[0118] Figure 1 This is a flow chart for preparing the highly dispersed nickel-based carbon-nitrogen catalyst of the present invention;

[0119] from Figure 1 It can be seen that the preparation method of the present invention is simple and easy to operate.

[0120] Figure 2 Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 of the present invention;

[0121] from Figure 2 It can be seen that the SEM and TEM images jointly reveal that the material presents a uniform spherical particle structure, and its morphology is dominated by carbon black as a template; at the same time, no obvious metal Ni nanoparticles or agglomeration phenomena are observed, indicating that Ni is highly dispersed in the carbon-nitrogen skeleton and the carbon skeleton exists in an amorphous state, which helps to improve electronic conductivity and reaction interface uniformity.

[0122] Figure 3 X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) patterns of the highly dispersed nickel-based carbon-nitrogen catalysts prepared in Examples 1-3 of the present invention, including a high-resolution N 1s pattern showing the N type distribution;

[0123] from Figure 3It can be seen that XRD can observe obvious carbon peaks and weak diffraction peaks of the Ni nanoparticle (111) crystal plane, indicating that Ni is highly dispersed in the sample or the nanoparticle size is very small; XPS can be observed that the existence form of N in the highly dispersed nickel-based carbon-nitrogen catalysts prepared in Examples 1-3 is mainly pyridinic nitrogen and pyrrolic nitrogen.

[0124] Figure 4 Ni K-edge EXAFS spectrum and Fourier transform spectrum of the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 of the present invention;

[0125] from Figure 4 It can be seen that the Ni in the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 exists in the form of Ni-Ni bonds. It can be inferred that the Ni exists in the form of highly dispersed nanoclusters.

[0126] Figure 5 The Faraday efficiency (FE) curves of the CO2 electroreduction reaction of different materials at different potentials for Examples 1-3 and Comparative Examples 1-5, and the current (LSV) curves of Examples 1-3;

[0127] from Figure 5 It can be seen that Ni-NC-750 shows better CO2RR performance than Ni-NC-550 and Ni-NC-950, with the highest FE CO It can reach 97.5%, indicating that the catalyst has a significant inhibitory effect on the side reaction HER. It has a highly selective active center structure, that is, excellent COOH* adsorption and CO desorption equilibrium ability; and Ni-NC-750 shows a higher current density and a smaller starting potential than Ni-NC-550 and Ni-NC-950.

[0128] Figure 6 This is a stability test curve of the highly dispersed nickel-based carbon-nitrogen catalyst prepared in Example 1 of the present invention;

[0129] from Figure 6 As can be seen in the flow cell, the catalytic material in Example 1 can be 2 The electrolysis was carried out at a current density of 100 nm for 30 h, and the FE remained at around 90%. This demonstrates its good stability and good industrial application potential, showing the good application prospects of the material in future industrial CO2 electroconversion.

[0130] The highly dispersed nickel-based carbon-nitrogen catalyst prepared in the present invention has highly dispersed nickel and excellent electrocatalytic activity and selectivity; the carbon-nitrogen carrier has the functions of stabilizing the structure and regulating electrons, which is beneficial to electron transfer and intermediate adsorption.

[0131] The present invention has been described above by way of example in conjunction with the embodiments and accompanying drawings. It is obvious that the implementation of the present invention is not limited to the above-mentioned methods. As long as various improvements are made using the method concepts and technical solutions of the present invention, or the concepts and technical solutions of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a highly dispersed nickel-based carbon-nitrogen catalyst, characterized in that: The following steps are included: Step 1: Synthesis of a hydrotalcite precursor; nickel nitrate hexahydrate and aluminum nitrate nonahydrate were weighed and dissolved in deionized water, referred to as solution A, and sodium hydroxide solution B was prepared, and a hydrotalcite precursor, i.e., NiAl-LDH precursor, was synthesized by colloid milling; Step 2: preparing a calcined precursor; dispersing the NiAl-LDH precursor, 1,10-phenanthroline and carbon black in an ethanol solution, uniformly dispersing the mixture, vacuum drying and then grinding to obtain a calcined precursor; Step 3: preparing a highly dispersed nickel-based carbon-nitrogen catalyst; heat-treating the calcined precursor obtained in step 2 under a nitrogen atmosphere to obtain a highly dispersed nickel-based carbon-nitrogen catalyst, i.e., a Ni-NC catalyst; In step 1, the molar ratio of nickel nitrate hexahydrate to aluminum nitrate nonahydrate in solution A is 2:1-4:1; The total concentration of the nitrate solution A is 0.05-1.0 mol / L; The concentration of the sodium hydroxide solution B is 1 mol / L-4 mol / L; In step 2, the mass ratio of NiAl-LDH precursor to (1,10-phenanthroline + carbon black) is 0.01 to 0.5; wherein, in the mixture of 1,10-phenanthroline and carbon black, the mass percentage of carbon black is 10-90%; The mass fraction of Ni in the highly dispersed nickel-based carbon-nitrogen catalyst is 0.5-5wt%, and Ni is dispersed in the form of extremely small clusters; the nickel exists in the form of Ni-Ni.

2. The method for preparing a highly dispersed nickel-based carbon-nitrogen catalyst according to claim 1, wherein: The specific operation of synthesizing the hydrotalcite precursor by colloid mill is as follows: pouring salt solution A and sodium hydroxide solution B into the colloid mill at a speed of 1500-9000 rpm, maintaining the speed for 1-120 minutes, taking out, washing to neutrality, drying by rotary evaporation at 40-80°C, and grinding.

3. The method for preparing a highly dispersed nickel-based carbon-nitrogen catalyst according to claim 1, wherein: In the step 3, the heat treatment temperature is 550°C-950°C, the heating rate is 0.5-10°C / min, the nitrogen flow rate is 20-200 mL / min, and the heat treatment time is 1-5 h.

4. A highly dispersed nickel-based carbon-nitrogen catalyst, characterized in that: The compound is prepared according to the preparation method according to any one of claims 1 to 3.

5. The highly dispersed nickel-based carbon-nitrogen catalyst according to claim 4, characterized in that The highly dispersed nickel-based carbon-nitrogen catalyst has the following characteristics: (1) carbon-nitrogen is used as a carrier, and nickel active sites are evenly distributed on the surface; (2) it contains three types of doped nitrogen: graphitic N, pyridinic N, and pyrrolic N.

6. The highly dispersed nickel-based carbon-nitrogen catalyst according to claim 4, characterized in that: The total mass fraction of nitrogen doping in the highly dispersed nickel-based carbon-nitrogen catalyst is 1-15wt%, of which graphite N accounts for 0-40%, pyridine N accounts for 20-80%, and pyrrole N accounts for 10-40%.

7. Use of the highly dispersed nickel-based carbon-nitrogen catalyst according to any one of claims 4 to 6 in an electrocatalytic reaction for selectively reducing CO2 to carbon monoxide.

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