Ni-Mg bimetallic catalyst, preparation method thereof and application of Ni-Mg bimetallic catalyst in electrocatalytic reduction of carbon dioxide under high current density

Abstract

The invention belongs to the technical field of electro-catalysis carbon dioxide reduction, and provides a Ni-Mg bimetallic catalyst and a fused salt preparation method thereof, which are used for preparing carbon monoxide through high-selectivity electro-catalysis carbon dioxide reduction under high current density. The method comprises the following steps: grinding and mixing a nickel source, a magnesium source, a molten salt medium and a nitrogen-containing precursor, and carrying out high-temperature calcination. In the calcining process, a liquid phase environment generated by the molten salt and a space confinement effect jointly promote atomic-scale dispersion of Ni and Mg metals on the carrier, so that the high-performance catalyst is formed. The method has the advantages that the prepared catalyst is high in metal utilization rate, low in cost and simple in process. The selectivity of the product can be effectively regulated and controlled by regulating and controlling the molar ratio of Ni to Mg. Experiments show that when the molar ratio of Ni to Mg is 1: 2, the catalyst shows excellent electro-catalytic performance in a 1M KOH electrolyte, the Faraday efficiency of CO is as high as 94.1% under the potential of-0.6 V (vs. RHE), and the maximum bias current density within the potential interval of-0.8 V can reach 120.1 mA cm <-2 >.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrocatalytic CO2 reduction, and particularly relates to a Ni-Mg bimetallic catalyst, a preparation method thereof and application of the catalyst in electrocatalytic reduction of carbon dioxide at a large current density. BACKGROUND

[0002] Carbon dioxide (CO2) is one of the main greenhouse gases causing global climate change, and its excessive emission has triggered a series of environmental and energy crises. Converting CO2 into high-value-added chemicals is one of the effective strategies to achieve carbon cycle, relieve environmental pressure and solve energy problems. Among numerous conversion technologies, electrocatalytic CO2 reduction (CO2RR) has attracted much attention due to its mild reaction conditions and the ability to utilize renewable energy. However, the electrocatalytic CO2 reduction process still faces multiple challenges: CO2 molecules have stable structures, and their activation requires a high overpotential; the reaction pathway is complex and involves a multi-electron / proton transfer process, making it difficult to control the product selectivity; in aqueous electrolyte, the competitive hydrogen evolution reaction (HER) often dominates, further reducing the efficiency and selectivity of CO2 reduction.

[0003] In recent years, graphite phase carbon nitride (g-C3N4) has been widely used as an ideal support for metal catalysts due to its abundant nitrogen sites, tunable electronic structure and good chemical stability. Among them, atomically dispersed bimetallic catalysts can precisely regulate the electronic structure of active sites through strong metal-support interactions and synergistic effects of bimetallic sites, thereby significantly improving the catalytic performance. Currently, traditional methods such as impregnation and chemical reduction are commonly used to prepare such catalysts, but they generally have problems such as uneven metal dispersion, easy agglomeration and insufficient exposure of active sites, which limit their practical application.

[0004] Therefore, the present application proposes a Ni-Mg bimetallic catalyst preparation strategy based on a molten salt method. This method utilizes the liquid phase environment and spatial confinement effect of molten salt at high temperatures to promote the atomic-level uniform dispersion of Ni and Mg metal atoms on the g-C3N4 support and form stable Ni-N and Mg-N bond structures, effectively inhibiting metal agglomeration and enhancing metal-support interactions, ultimately obtaining a CO2RR electrocatalyst with high activity, high selectivity and excellent large current density tolerance. SUMMARY

[0005] To solve the problems of poor metal dispersion, easy agglomeration of active sites, low product selectivity and high reaction overpotential in existing electrocatalytic CO2 reduction technologies, the present application provides a Ni-Mg bimetallic atomic catalyst prepared by a molten salt method and its application in electrocatalytic CO2 reduction. The prepared catalyst has high activity, high selectivity and excellent large current density tolerance, and the process is simple, low-cost and has good application prospects.

[0006] A method for preparing a Ni-Mg bimetallic catalyst for electrocatalytic carbon dioxide reduction at high current density (200-400 mA cm⁻²) is characterized by being a molten salt method, comprising the following steps: mixing and grinding a nickel source, a magnesium source, a molten salt medium, and a nitrogen-containing precursor to obtain a precursor powder; calcining the precursor powder at 500-900 °C for 1-4 hours in a muffle furnace; after cooling, removing the molten salt medium, and drying to obtain a Ni-Mg bimetallic catalyst supported on a graphitic carbon nitride support; wherein the molar ratio of Ni element in the nickel source to Mg element in the magnesium source is 1:3 to 3:1; and the molten salt medium is a mixture of potassium chloride and lithium chloride.

[0007] The nickel source is nickel chloride hexahydrate, the magnesium source is magnesium chloride hexahydrate, and the nitrogen-containing precursor is melamine.

[0008] Includes the following steps: 1) Mix and grind 0.1-3 mmol (preferred range: 0.2-1.5 mmol, more preferably 0.4-1 mmol) of nickel chloride hexahydrate (NiCl2·6H2O), 0.2-3 mmol (preferred range: 0.3-1.5 mmol, more preferably 0.5-1 mmol) of magnesium chloride hexahydrate (MgCl2·6H2O), 1-20 mmol (preferred range: 5-18 mmol, more preferably 10-15 mmol) of potassium chloride (KCl), and 10-30 mmol (preferred range: 15-28 mmol, more preferably 20-26 mmol) of anhydrous lithium chloride (LiCl) until homogeneous; 2) Add 20-50 mmol of melamine (C3H6N6) (preferred range: 25-45 mmol, more preferred range: 35-40 mmol) to the mixture obtained in step (1), and continue grinding until the mixture is uniform to obtain the precursor powder; 3) The precursor powder is calcined at 300-900 ℃ (preferred range: 400-800 ℃, more preferred range: 500-700 ℃) for 3-10 hours (preferred range: 4-9 h, more preferred range: 5-8 h); 4) Cool the calcined product to 20-60 ℃ (preferred range: 25-50 ℃, more preferably range: 30-40 ℃), wash with deionized water and anhydrous ethanol, and dry to obtain the Ni-Mg bimetallic catalyst.

[0009] The Ni-Mg bimetallic catalyst prepared by the method described above is characterized in that the molar ratio of Ni to Mg in the catalyst is 1:3 to 3:1, and the Ni and Mg are atomically dispersed on a carbon nitride support.

[0010] The molar ratio of Ni to Mg is 1:2.

[0011] Application of the Ni-Mg bimetallic catalyst in the electrocatalytic carbon dioxide reduction reaction.

[0012] The specific process of the application is as follows: the Ni-Mg bimetallic catalyst is loaded onto carbon paper to form a working electrode. In a flow cell with 1 M KOH solution as the electrolyte, CO2 gas is introduced into the system. Then, a constant potential electrolysis is performed by applying a potential of -0.5 to -0.9 V (relative to the reversible hydrogen electrode) to achieve CO2 reduction.

[0013] The concentration of the KOH solution is 0.1-5 mol / L (preferred range: 0.1-3 mol / L, more preferred range: 0.5-2 mol / L); the flow rate of the CO2 gas is 10-100 mL / min (preferred range: 20-80 mL / min, more preferred range: 40-60 mL / min), and the duration is 20-50 min (preferred range: 25-45 min, more preferred range: 30-40 min).

[0014] This invention first provides a method for preparing molten salt of Ni-Mg bimetallic catalyst. As a preferred embodiment, the specific steps are as follows: (1) Grind 0.4 mmol nickel chloride hexahydrate (NiCl2·6H2O), 0.8 mmol magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol potassium chloride (KCl), and 21.176 mmol anhydrous lithium chloride (LiCl) evenly.

[0015] (2) 39.64 mmol of melamine (C3H6N6) was added to the powder in step 1) above and ground evenly.

[0016] (3) Place the powder from step 2) into a crucible, heat it to 600 ℃ in a muffle furnace at 2.3 ℃ / min, keep it at that temperature for 4 h, cool it down, wash it and centrifuge it to obtain the final product.

[0017] The present invention also provides the application of the Ni-Mg bimetallic catalyst prepared by the above method in electrocatalytic CO2 reduction, specifically, the catalyst is made into a working electrode and used as the cathode in a flow cell system for CO2 reduction reaction.

[0018] The working electrode is prepared by dispersing 5 mg of catalyst powder in a mixed solvent consisting of 735 μL of anhydrous ethanol, 235 μL of deionized water and 20 μL of Nafion solution, and ultrasonically treating it for 1 hour to prepare a uniform ink; then taking 500 μL of ink and quantitatively drop-coating it onto carbon paper, controlling the loading amount to be 1 mg / cm², and drying it at 60 °C.

[0019] The CO2 reduction reaction was carried out in a flow cell electrolyzer under the following conditions: 50 mL of 1 mol / L KOH solution was used as the electrolyte, and CO2 gas was continuously introduced (flow rate 48 mL / min) to remove air and achieve gas-liquid equilibrium; a three-electrode system was used, with the electrode prepared above as the working electrode, the Hg / HgO electrode as the reference electrode, and a platinum sheet as the counter electrode; the cathode chamber and the anode chamber were separated by an anion exchange membrane; and constant potential electrolysis was performed using a CHI 760e electrochemical workstation within a potential range of -0.5 to -0.9 V (vs. RHE).

[0020] Compared with the prior art, the beneficial effects of the present invention are: Excellent catalytic performance: The catalyst prepared by this invention exhibits optimal performance when the molar ratio of Ni to Mg is 1:2. At a potential of -0.6V (vs. RHE), the Faradaic efficiency of CO products reaches as high as 94.1%; at a potential of -0.8V, its CO partial current density can reach 120.1 mA cm⁻², demonstrating excellent selectivity and high current density operation capability.

[0021] The preparation method is unique: it employs a molten salt method, utilizing the liquid phase environment and spatial confinement effect generated by the molten salt to effectively promote the atomic-level dispersion of Ni and Mg metal atoms on the support and form stable MN bonds, fundamentally preventing metal agglomeration. This method is simple, the salt medium is recyclable, and it has the potential for large-scale production.

[0022] Significant synergistic effect: There is a strong electronic interaction between Ni-Mg bimetal and g-C3N4 support. The bimetallic synergy not only improves the dispersion of the metal, but also optimizes the electronic structure of the active site, jointly enhancing the intrinsic activity and selectivity of CO2 reduction.

[0023] Cost and environmental advantages: The non-precious metal raw materials used in this invention are inexpensive and the preparation process is green and safe, providing a competitive material solution for the industrial application of electrocatalytic CO2 reduction technology. Attached Figure Description

[0024] Figure 1 The images are XRD patterns of Embodiment 1 and Comparative Examples 1 and 2 of the present invention.

[0025] Figure 2The images shown are SEM spectra of Embodiment 1 and Comparative Examples 1 and 2 of the present invention.

[0026] Figure 3 The images shown are TEM and EDX mapping spectra from Embodiment 1 of the present invention.

[0027] Figure 4 These are the FT-IR images of Embodiment 1 and Comparative Examples 1 and 2 of the present invention.

[0028] Figure 5 This is an XPS image of Embodiment 1 of the present invention.

[0029] Figure 6 CO Faraday efficiency diagrams for Embodiment 1 and Comparative Examples 4 and 5 of this invention.

[0030] Figure 7 The results show the comprehensive performance test results of the NiMg-C3N4 catalyst in the electrocatalytic carbon dioxide reduction process.

[0031] Figure 7 a represents the linear cyclic voltammetry (LSV) curves for Example 1 and Comparative Examples 1 and 2. Figure 7 b. CO Faraday efficiency diagrams of Embodiment 1 and Comparative Examples 1 and 2 of the present invention; Figure 7 c. H2 Faraday efficiency diagrams of Embodiment 1 of the present invention and Comparative Examples 1 and 2; Figure 7 d represents the partial current density of CO in Example 1 and Comparative Examples 1 and 2. j CO ); Figure 7 e is the active specific surface area diagram of Example 1 and Comparative Examples 1 and 2; Figure 7 f represents the electrochemical impedance spectroscopy (EIS) curves of Example 1 and Comparative Examples 1 and 2; Figure 7 g represents the stability of Example 1 at a voltage of -0.6 V (vs. RHE); Figure 8 This is the in-situ Fourier transform infrared spectrum of Embodiment 1 of the present invention. Detailed Implementation

[0032] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0033] Example 1: The preparation method of the metallic nickel-magnesium catalyst material in this embodiment includes the following steps: Preparation of a Ni:Mg bimetallic catalyst electrode material with a molar ratio of 1:2: First, 0.4 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 0.8 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at a rate of 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain a NiMg-C3N4 material with a molar ratio of 1:2. Characterization results by XRD and FT-IR confirmed it to be NiMg-C3N4 material, with a theoretical C3N4 content of 63%.

[0034] Preparation of the working electrode: First, prepare an ink solution by mixing 735 μL of anhydrous ethanol, 235 μL of deionized water, and 20 μL of Nafion solution. Then, disperse 5 mg of NiMg-C3N4 powder (molar ratio 1:2) into the solution and ultrasonically disperse for 1 h to obtain a uniformly dispersed ink solution. Take 500 μL of the uniformly dispersed solution and drop it onto carbon paper with a loading of 1 mg / cm³. 2 After drying in an oven at 60 ℃, the working electrode is obtained.

[0035] The performance of electrocatalytic CO2 reduction was tested in a closed flow cell using an anion exchange membrane. A CHI 760e electrochemical workstation (Shanghai Chenhua Co., Ltd.) was used, employing a three-electrode system. A Pt sheet (2×3cm) was used as the counter electrode, an Hg / HgO electrode as the reference electrode, and carbon paper loaded with the catalyst as the working electrode. The electrolyte was a 1 mol / L KOH solution. Before testing, CO2 was introduced into the cathode chamber at a rate of 48 mL / min for at least 10 min, while a liquid circulation pump was activated to achieve gas-liquid equilibrium. CO2 was then continuously introduced during the electrocatalytic CO2 reduction process. All voltages used were converted to the reversible hydrogen electrode potential, as shown in the following formula: E(vs. RHE)=E(vs Hg / HgO)+0.0591×pH+0.098 V Cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy: Cyclic voltammetry was performed within the voltage range of 0 to -2 V vs Hg / HgO. Next, linear sweep voltammetry was performed within the same voltage range of 0 to -2 V vs Hg / HgO at a scan rate of 5 mV / s, repeated three times to ensure the curves largely overlapped. Furthermore, impedance spectroscopy was performed at a certain overpotential where CO2 reduction occurs, with a frequency range of 10...5 The frequency reaches 0.1 Hz, with an amplitude of 5 mV.

[0036] Catalytic product analysis: The electrocatalytic CO2 reduction performance was tested using the chronopotential method (it). Electrolysis was performed continuously for more than 20 minutes at different voltages, and the resulting gaseous products were analyzed online by gas chromatography. The Faradaic efficiency (FE) of the gaseous products was calculated based on the quantitative analysis of the gaseous products by chromatography, using the following formula: FE=

[0037] in, Carbon dioxide gas flow rate, mL / min; : Product concentration, ppm; n: Number of electrons transferred in the product; P: Atmospheric pressure, Pa; T: Temperature, K; I: Current at steady state, A.

[0038] J CO = J tatal FE CO in, J tatal Total cathode current (mA / cm) 2 ), FE CO The Faraday efficiency of CO (%) J CO The partial current density of CO (mA / cm) 2 ).

[0039] The processes and conditions of Examples 2-5 are the same as those of Example 1, with the differences described in the examples below.

[0040] Example 2:

[0041] Preparation of a Ni:Mg bimetallic catalyst electrode material with a molar ratio of 1:1: First, 0.6 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 0.6 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain a NiMg bimetallic catalyst material with a molar ratio of 1:1. Characterization results by XRD and FT-IR confirmed it to be a NiMg-C3N4 material, with a theoretical C3N4 content of 63.1%.

[0042] Example 3: Preparation of a Ni:Mg bimetallic catalyst electrode material with a molar ratio of 1:3: 0.3 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 0.9 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were first ground uniformly. 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at a rate of 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain a NiMg bimetallic catalyst material with a molar ratio of 1:3. Characterization results by XRD and FT-IR confirmed it to be a NiMg-C3N4 material, with a theoretical C3N4 content of 63.2%.

[0043] Example 4:

[0044] Preparation of a Ni:Mg bimetallic catalyst electrode material with a molar ratio of 3:1: First, 0.9 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 0.3 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at a rate of 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain a NiMg bimetallic catalyst material with a molar ratio of 3:1. Characterization results by XRD and FT-IR confirmed it to be a NiMg-C3N4 material, with a theoretical C3N4 content of 62.9%.

[0045] Example 5:

[0046] Preparation of a Ni:Mg bimetallic catalyst electrode material with a molar ratio of 2:1: First, 0.8 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 0.4 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at a rate of 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain a NiMg bimetallic catalyst material with a molar ratio of 2:1. Characterization results by XRD and FT-IR confirmed it to be a NiMg-C3N4 material, with a theoretical C3N4 content of 63.0%.

[0047] Comparative Example 1: The preparation method of Ni-C3N4 in this embodiment includes the following steps: Preparation of Ni-C3N4 catalyst electrode material: First, 1.2 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. Then, 39.64 mmol of melamine (C3H6N6) was added to the powder from the above steps and ground uniformly. The ground powder was placed in a crucible and heated to 600 ℃ in a muffle furnace at 2.3 ℃ / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain the Ni-C3N4 catalyst material. Characterization results by XRD and FT-IR confirmed it to be Ni-C3N4 material, with a theoretical C3N4 content of 62.8%.

[0048] Comparative Example 2: The preparation method of Mg-C3N4 in this embodiment includes the following steps: Preparation of Mg-C3N4 catalyst electrode material: First, 1.2 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. Then, 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain the Mg-C3N4 catalyst material. Characterization results by XRD and FT-IR confirmed it to be Mg-C3N4 material, with a theoretical C3N4 content of 63.3%.

[0049] Comparative Example 3: The preparation method of C3N4 in this embodiment includes the following steps: Preparation of C3N4 catalyst electrode material: First, 14.76 mmol of potassium chloride (KCl) and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. Then, 39.64 mmol of melamine (C3H6N6) was added to the powder from the above step and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain g-C3N4 catalyst material. Characterization results by XRD and FT-IR confirmed it to be C3N4 material, with a theoretical C3N4 content of 64.6%.

[0050] Comparative Example 4: The vacuum freeze-drying method for preparing NiMg-C3N4 in this embodiment includes the following steps: Preparation of NiMg-C3N4 material: 0.06 g of C3N4 was first dispersed in 30 mL of deionized water and sonicated for 1 h. A mixed solution of 0.1 mol / L nickel chloride hexahydrate (NiCl2·6H2O) and 0.1 mol / L magnesium chloride hexahydrate (MgCl2·6H2O) was then added dropwise to the above mixed solution, and the mixture was stirred for 2 h. Finally, the mixture was rapidly frozen in liquid nitrogen, then freeze-dried under vacuum, and ground uniformly to obtain NiMg-C3N4 powder catalyst. Characterization results by XRD and FT-IR confirmed it to be NiMg-C3N4 material, with a theoretical C3N4 content of 21.8%.

[0051] Comparative Example 5: The preparation method of FeMg-C3N4 in this embodiment includes the following steps: Preparation of FeMg-C3N4 electrode material: First, 0.4 mmol of ferric chloride hexahydrate (FeCl2·6H2O), 0.8 mmol of magnesium chloride hexahydrate (MgCl2·6H2O), 14.76 mmol of potassium chloride (KCl), and 21.176 mmol of anhydrous lithium chloride (LiCl) were ground uniformly. Then, 39.64 mmol of melamine (C3H6N6) was added to the powder from the above steps and ground uniformly. The ground powder was placed in a crucible and heated to 600 °C in a muffle furnace at 2.3 °C / min, held at that temperature for 4 h, cooled, washed, and centrifuged to obtain the FeMg-C3N4 catalyst material. Characterization results by XRD and FT-IR confirmed it to be FeMg-C3N4 material, with a theoretical C3N4 content of 63%.

[0052] The processes and conditions of Comparative Examples 1-5 are the same as those of Example 1, with the differences being described in the examples above. The catalyst prepared above underwent some structural and performance tests.

[0053] Figure 1 The images show the X-ray diffraction (XRD) patterns of the NiMg bimetallic catalyst materials from Examples 1 and Comparative Examples 1-2. Figure 1 Clear diffraction peaks were observed in all prepared catalyst samples. The diffraction peak angles of 12.8° and 27.5° matched the (100) and (002) crystal planes of the standard card for graphite C3N4; 18.8°, 38.4°, and 51.4° matched the Ni-C3N4 standard card (PDF#01-076-4326); and 18.95°, 32.3°, and 56.6° matched the Mg-C3N4 standard card (PDF#051-0540). Because Ni and Mg have similar crystal structures, the diffraction peak positions may overlap, and Ni... 2+ Ionic radius and Mg 2+ Similar. Characteristic peaks of C3N4 were observed in both samples. Figure 2 and Figure 3 Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization of the catalyst confirmed the successful preparation of the composite material.

[0054] Figure 2 Scanning electron microscopy (SEM) of Examples 1 and Comparative Examples 1-2 shows that the carrier exhibits an aggregated sheet-like structure.

[0055] Figure 3 TEM image and energy-dispersive X-ray elemental distribution image (EDX Mapping) of the NiMg-C3N4 bimetallic catalyst material in Example 1. From the low-magnification TEM image (... Figure 3 a) As can be seen, the material exhibits a sheet-like structure overall. High-resolution TEM image ( Figure 3 (b, 3c) shows that no Ni or Mg nanoparticles were observed throughout the field of view; simultaneously, only 0.69 nm and 0.34 nm lattice fringes were observed in the images, corresponding to the (100) and (002) crystal planes of g-C3N4, respectively. This proves that Ni and Mg elements do not form independent crystal phases, but are highly dispersed in the support at the atomic level. In addition, the EDX elemental surface scan results ( Figure 3 d) Further, it is shown that the four elements C, N, Ni and Mg are all highly uniformly distributed in the nanosheet region, which confirms the successful doping and uniform dispersion of Ni and Mg atoms in the g-C3N4 support.

[0056] Figure 4Fourier transform infrared (FTIR) spectra of Example 1 and Comparative Examples 1-2 are shown. The functional groups of the samples and the interactions between the catalysts were analyzed. Stretching vibrations attributable to -NH bonds or terminal -NH2 are observed at 3000–3600 cm⁻¹, and at 2140 cm⁻¹. -1 These are stretching and deformation vibrations of NCN, bending and stretching vibrations of C=N double bonds and CN single bonds of heterocyclic rings between 1000 and 1700 cm⁻¹, and the typical breathing vibration mode of triazine unit appears at 808 cm⁻¹. All of these indicate that the C3N4 support was successfully synthesized and that the metal atoms were loaded on it without damaging the C3N4 framework.

[0057] Figure 5 X-ray photoelectron spectroscopy (XPS) analyses of the catalysts in Example 1 and Comparative Examples 1-2 were presented to investigate their elemental composition and chemical state. Full-spectrum scans confirmed the presence of Ni, Mg, C, N, and O elements, indicating the successful synthesis of the NiMg-C3N4 catalyst. Notably, compared to the comparative examples, the binding energies of the characteristic peaks for Ni 2p, Mg 1s, and N 1s in Example 1 showed significant shifts. This reveals a significant electronic interaction between the Ni-Mg bimetal and the C3N4 support, optimizing the electronic structure of the active sites.

[0058] Figure 6 The CO Faradaic efficiency of the catalysts in Example 1 and Comparative Examples 4-5 was compared. The results showed that the NiMg-C3N4 catalyst prepared by the molten salt method exhibited significantly higher CO Faradaic efficiency than the same-component catalyst prepared by the freeze-drying method (Comparative Example 4) and the FeMg-C3N4 catalyst prepared by the molten salt method (Comparative Example 5). This performance advantage can be attributed to two aspects: First, the high-temperature melting environment created by the molten salt method helps to regulate the phase structure of the catalyst, increase the exposure of active sites, and improve electronic conductivity, thereby enhancing the selectivity for the CO pathway; second, there is a better synergistic effect between the NiMg bimetallic component and the C3N4 support, which better meets the catalytic requirements for the reduction of CO2 to CO.

[0059] Figure 7 These are the comprehensive performance test results of the NiMg-C3N4 catalyst in the electrocatalytic carbon dioxide reduction process.

[0060] In Figure 7a, the linear sweep voltammetry (LSV) curves of Example 1 and Comparative Examples 1-2 are shown. The tests were conducted in a 1 mol / L KOH electrolyte at a scan rate of 5 mV / s. The results showed that the onset potential of all catalysts under a CO2 atmosphere was significantly more positive than that under an Ar atmosphere, indicating that the CO2 reduction reaction is more likely to occur than the hydrogen evolution reaction, thus demonstrating the intrinsic catalytic activity of this series of catalysts for CO2 reduction.

[0061] Figure 7 bc represents the Faradaic efficiency of the gaseous products of Example 1 and Comparative Examples 1-2 at different potentials. When the molar ratio of Ni to Mg is 1:2 (Example 1), the catalyst exhibits the highest Faradaic efficiency for CO at -0.6 V (vs. RHE), reaching 94.1%, which is significantly higher than that of the comparative examples with other ratios, demonstrating its excellent selective control ability for CO products.

[0062] Figure 7 d represents the CO partial current density (j) of each catalyst. CO In comparison, it is through j 总 Multiply by FE CO Calculations show that, at all test potentials, j in Example 1... CO All were significantly higher than those of comparative examples 1-2, demonstrating that they have higher intrinsic catalytic activity.

[0063] The number of active sites on the catalyst was assessed using the electrochemical active area (ECSA). Example 1 exhibited the largest ECSA, indicating a more abundant exposure of active sites, which is beneficial for reactant mass transfer and electron transfer.

[0064] Figure 7 Electrochemical impedance spectroscopy (EIS) of f showed that Example 1 had the smallest charge transfer resistance, indicating that it had the fastest interfacial electron transport rate and a significant kinetic advantage.

[0065] Figure 7 g represents the stability test results of Example 1 at -0.6 V (vs. RHE). During the continuous 6-hour electrolysis process, the CO Faraday efficiency remained above 85%, demonstrating that the catalyst has good structural stability and catalytic durability.

[0066] Figure 8 The reduction pathway of CO2 on the surface of the NiMg-C3N4 catalyst was investigated using in-situ Fourier transform infrared spectroscopy (FTIR). After applying a cathode potential, characteristic absorption peaks for the COOH intermediate and CO2⁻ were observed at 1012 cm⁻¹ and 1234 cm⁻¹, respectively. This indicates that CO2 molecules can be efficiently activated and protonated to COOH at the NiMg dual site, and then rapidly converted to the final product CO. This result confirms at the molecular level that the synergistic effect between Ni and Mg effectively promotes the formation and transformation of key reaction intermediates, which is the root cause of its high selectivity.

[0067] The molten salt method employed in this invention can prepare NiMg-C3N4 catalysts with atomically dispersed metal centers, exhibiting a much higher degree of active site exposure than traditional nanoparticle catalysts. This catalyst demonstrates high selectivity, high activity, rapid reaction kinetics, and excellent stability in the electrocatalytic reduction of CO2 to CO reaction, showing broad prospects for industrial applications.

[0068] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and the above-described figures.

Claims

1. A method for preparing a Ni-Mg bimetallic catalyst for high current density electrocatalytic carbon dioxide reduction, characterized in that, The method is a molten salt method, comprising the following steps: mixing and grinding a nickel source, a magnesium source, a molten salt medium, and a nitrogen-containing precursor to obtain a precursor powder; calcining the precursor powder in a muffle furnace at 500-900 °C for 1-4 hours; after cooling, removing the molten salt medium, and drying to obtain a Ni-Mg bimetallic catalyst supported on a graphitic carbon nitride support; wherein the molar ratio of Ni element in the nickel source to Mg element in the magnesium source is 1:3 to 3:1; and the molten salt medium is a mixture of potassium chloride and lithium chloride.

2. The preparation method according to claim 1, characterized in that... The nickel source is nickel chloride hexahydrate, the magnesium source is magnesium chloride hexahydrate, and the nitrogen-containing precursor is melamine.

3. The preparation method according to claim 1, characterized in that, Includes the following steps: 1) Mix and grind 0.1-3 mmol (preferred range: 0.2-1.5 mmol, more preferably 0.4-1 mmol) of nickel chloride hexahydrate (NiCl2·6H2O), 0.2-3 mmol (preferred range: 0.3-1.5 mmol, more preferably 0.5-1 mmol) of magnesium chloride hexahydrate (MgCl2·6H2O), 1-20 mmol (preferred range: 5-18 mmol, more preferably 10-15 mmol) of potassium chloride (KCl), and 10-30 mmol (preferred range: 15-28 mmol, more preferably 20-26 mmol) of anhydrous lithium chloride (LiCl) until homogeneous; 2) Add 20-50 mmol of melamine (C3H6N6) (preferred range: 25-45 mmol, more preferred range: 35-40 mmol) to the mixture obtained in step (1), and continue grinding until the mixture is homogeneous to obtain the precursor powder; 3) The precursor powder is calcined at 300-900 ℃ (preferred range: 400-800 ℃, more preferred range: 500-700 ℃) for 3-10 hours (preferred range: 4-9 h, more preferred range: 5-8 h); 4) Cool the calcined product to 20-60 ℃ (preferred range: 25-50 ℃, more preferably range: 30-40 ℃), wash with deionized water and anhydrous ethanol, and dry to obtain the Ni-Mg bimetallic catalyst.

4. The Ni-Mg bimetallic catalyst prepared according to any one of claims 1-3, characterized in that, The catalyst has a Ni to Mg molar ratio of 1:3 to 3:1, and the Ni and Mg are atomically dispersed on a carbon nitride support.

5. The Ni-Mg bimetallic catalyst according to claim 4, characterized in that, The molar ratio of Ni to Mg is 1:

2.

6. The application of the Ni-Mg bimetallic catalyst according to claim 4 or 5 in the electrocatalytic carbon dioxide reduction reaction.

7. The application according to claim 6, characterized in that: The specific process of the application is as follows: the Ni-Mg bimetallic catalyst is loaded onto carbon paper to form a working electrode. In a flow cell with 1M KOH solution as electrolyte, CO2 gas is introduced into the system. Then, a potential of -0.5 to -0.9 V (relative to the reversible hydrogen electrode) is applied to perform constant potential electrolysis to achieve CO2 reduction.

8. The application according to claim 7, characterized in that: The concentration of the KOH solution is 0.1-5 mol / L (preferred range: 0.1-3 mol / L, more preferably 0.5-2 mol / L; the flow rate of CO2 gas is 10-100 mL / min (preferred range: 20-80 mL / min, more preferably 40-60 mL / min), and the duration is 20-50 min (preferred range: 25-45 min, more preferably 30-40 min).

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