A nickel bimetallic carbon dioxide reduction catalyst with a wide voltage window and a method of making the same

Abstract

The application discloses a nickel bimetallic carbon dioxide electro-reduction catalyst with a wide voltage window and a preparation method thereof, and mainly comprises the following steps: (1) pyrolytic annealing of foam nickel and dicyandiamide in a tube furnace, in-situ growth of carbon nanotubes with Ni bimetallic active sites and uncoordinated nitrogen doped structures on the nickel substrate by using a precursor gas phase transfer method; and (2) acid etching, cleaning and drying of the product at a certain temperature to obtain the electro-catalyst. The catalyst has low cost, simple preparation method and controllable process, and when applied to the electro-catalytic CO2 reduction reaction, the carbon dioxide electro-reduction exhibits high CO selectivity of 92.78% at a low voltage of-0.25 V (vs. RHE), has high carbon dioxide electro-reduction activity and high CO selectivity in a wide voltage window of about 1.2 V, can reach an industrial-grade current density, and has good stability.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window and its preparation method. Background Technology

[0002] CO2 electrochemical reduction (CO2RR) is an effective way to convert CO2 into high-value chemicals such as CO and CH4. Its main advantage is its compatibility with sustainable energy conversion technologies (e.g., solar cells), allowing the generated electricity to be stored chemically within these high-value chemicals. However, in practical applications, variations in temperature and light intensity cause fluctuations in the output voltage of solar cells, and highly selective CO2RR can only be achieved within a narrow potential range, significantly limiting its practical application. Therefore, developing highly selective and efficient catalysts over a wide potential range is of great importance.

[0003] Studies have shown that MN x C (M represents metal) configurations, such as FeN4C, NiN4C, and CuN4C, are favorable for the electrocatalytic conversion of CO2 to CO. Considering the specific energy barriers for *COOH formation and CO desorption, single-atom Ni has attracted much attention due to its high selectivity. Furthermore, due to the synergistic effect between adjacent active sites, constructing diatomic metal sites can exhibit highly efficient catalytic performance. Simultaneously, by regulating its coordination structure, its catalytic activity at low potentials and its selectivity at high potentials can be further improved. Therefore, by designing atomically dispersed Ni active sites and their coordination structures, it is hoped that highly efficient and selective CO2 electrochemical reduction catalysts with wide voltage windows can be developed. Summary of the Invention

[0004] The purpose of this invention is to provide a nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window and its preparation method.

[0005] This invention proposes a nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window, prepared via an efficient precursor gas diffusion strategy. By introducing an appropriate amount of uncoordinated N-doped structure, a method for preparing a Ni diatomic catalyst is developed. When applied to CO2RR, this method achieves high intrinsic activity while suppressing the hydrogen evolution reaction, thus realizing high activity and high CO selectivity over a wide potential window. At a reduction voltage as low as -0.25 V (vs. RHE), FE... CO It achieves a current density of up to 92.78%, maintains high CO selectivity over an ultra-wide voltage window of approximately 1.2 V, and reaches industrial-grade current densities (100 mA / cm²). 2 Furthermore, this electrocatalyst exhibits good catalytic stability; during a continuous 10-hour constant voltage test, the product FE...CO It has remained above 97%.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution, specifically according to the following steps:

[0007] Step 1: Cut a piece of nickel foam (Ni) to a certain size, soak it in anhydrous ethanol and clean it with ultrasonic cleaning, then rinse it with deionized water and dry it in an oven for later use.

[0008] Step 2: Place a certain amount of dicyandiamide (DCD) upstream of the tubular furnace and nickel foam downstream of the tubular furnace.

[0009] Step 3: Using argon (Ar) as a protective gas, the tube furnace is heated to a certain temperature at an appropriate heating rate and held at this growth temperature for 0.2~3 h, and then naturally cooled to room temperature.

[0010] Step 4: Collect the reaction product, grind it thoroughly, and then etch the nickel foam by soaking it in HCl.

[0011] Step 5: After etching is complete, remove the product and wash it thoroughly with deionized water. Centrifuge at high speed and collect the Ni diatomic catalyst after it is completely dried.

[0012] The technical solution of the present invention also has the following characteristics:

[0013] In step 1, the chemical purity of the nickel foam is 98%~99.999%, and the cutting size can be determined according to the diameter of the tubular furnace.

[0014] In step 2, the dicyandiamide has a purity of 98% to 99.999%.

[0015] In step 3, the argon gas flow rate is 30~300 sccm. The heating rate of the tube furnace is 5~20 ℃ / min.

[0016] In step 4, the growth temperature is 600℃~1000℃, and the holding time is 0.2~3 h.

[0017] In step 5, the acid etching uses 1-5 mol / L hydrochloric acid, the acid etching temperature is 60-80℃, and the acid etching time is 48-100 h.

[0018] The morphology of the catalyst was characterized using scanning electron microscopy (SEM) in this invention, such as... Figure 1 As shown, the hollow carbon nanotube structure can be observed. Subsequently, high-angle annular dark-field scanning transmission electron microscopy was used to further characterize the catalyst's microstructure, such as... Figure 2It exhibits a typical bamboo-like structure of N-doped carbon nanotubes and a hollow tubular structure without Ni particles. For example... Figure 3 As shown, a large number of Ni atoms are dispersed on the carbon support, and diatomic Ni sites marked by red boxes can be observed, proving that the catalyst has a diatomic structure. EDS analysis shows that the distribution of C, N, and Ni elements is uniform (e.g., ...). Figure 4 No obvious particle accumulation was observed, further proving that the method of this invention can successfully prepare Ni diatomic catalysts. Furthermore, the phase composition of the catalyst was analyzed by XRD, such as... Figure 5 As shown, distinct characteristic peaks of graphite and metallic nickel appeared in D-Ni-700, and the intensity of the characteristic peak of nickel metal in D-Ni-700-H decreased significantly after acid etching. Figure 6 As shown in the Raman spectrum, the sample exhibits two characteristic graphite peaks, I D / I G The value of 1.09 indicates that the carbon six-membered ring of the catalyst support carbon nanotube contains a large number of defect structures. Further XPS characterization of the material, such as... Figure 7 As shown, fine structural analysis of the N 1s orbital reveals that its N doping types include five forms: pyridinic (398.4 eV), Ni-N (399.1 eV), pyrrolic (400.5 eV), graphitic (401.3 eV), and oxynitride (403.1 eV). This can be further illustrated by the Ni 2p orbital spectrum (as shown in the image). Figure 8 Comparison of Ni 0 (853.5 eV) and Ni 2+ (856 eV), Ni 2p of the catalyst 3 / 2 The binding energy lies within this range, indicating that the valence state of Ni atoms in each sample is between 0 and +2, consistent with the characteristics of atomic-level dispersion. Subsequently, XAS was used to further resolve the coordination structure of the Ni diatomic structure, and K-edge X-ray near-edge structure absorption (XANES) spectroscopy analysis was performed. Figure 9 This demonstrates that the near-edge absorption position of D-Ni-700-H lies between the nickel foil (Ni Foil) and nickel oxide (NiO), and is closer to nickel phthalocyanine (NiPc) with a NiN4 coordination structure. This indicates that the valence state of Ni atoms in D-Ni-700-H is between 0 and +2, which is consistent with the Ni 2p orbital analysis results in XPS. Subsequently, Fourier transform of the extended X-ray absorption fine structure (EXAFS) was performed to obtain the R-space data spectrum, as shown below. Figure 10As shown, comparing the Ni-Ni and Ni-N characteristic peaks with those in nickel foil and nickel phthalocyanine, it can be seen that Ni-Ni and Ni-N coordination environments exist in D-Ni-700-H. To more intuitively observe the composition of the active centers, we performed wavelet transform on the EXAFS data, from... Figure 11 It can be directly observed in the low-frequency region (5 Å) -1 There are signals of Ni-N and Ni-C, in the high-frequency region (9 Å). -1 The catalyst exhibited Ni-Ni characteristics, and by fitting the coordinate bonds and coordination number, it was proven that the obtained catalyst had a Ni2N4C2 coordination structure.

[0019] The Ni diatom electrocatalyst prepared in this invention generates CO in the CO2 reduction reaction. Using carbon paper supported on the Ni diatom electrocatalyst as the working electrode, a saturated silver / silver chloride electrode as the reference electrode, a platinum wire as the counter electrode, and a 0.5-2 mol / L potassium hydroxide solution as the electrolyte, the electroreduction of CO2 is carried out in a flow cell using a three-electrode system. Figure 12 As shown, at a low voltage of -0.25 V (vs. RHE), the catalyst can catalyze the reduction of CO2 to CO, and the product CO Faradaic efficiency (FE) is high. CO It can be as high as 92.78% (e.g.) Figure 13 It maintains over 92.78% CO selectivity over an ultra-wide voltage window of -0.25 V (vs. RHE) to -1.4 V (vs. RHE), and at -1.0 V (vs. RHE), FE CO Up to 99.2%, with a CO partial current density as high as 123.32 mA / cm². 2 It achieved an industrial-grade current density (100 mA / cm²). 2 )(like Figure 12 , 14 Furthermore, this electrocatalyst also exhibits good catalytic stability, such as... Figure 15 During a continuous 10-hour constant voltage test, the product FE... CO It has remained above 97%.

[0020] The beneficial effects of this invention are as follows: 1. The Ni diatomic electrocatalyst prepared by the method described in this invention uses inexpensive and readily available raw materials, and the preparation process is simple, economical, and reproducible, making it easy to mass-produce and showing good prospects for industrial application. 2. By adjusting the raw material composition, reaction temperature, and time, a Ni2N4C2 coordination structure catalyst can be obtained from the Ni diatomic electrocatalyst prepared by the method described in this invention. 3. The Ni diatomic electrocatalyst prepared by the method described in this invention can achieve highly selective electrocatalytic reduction of CO2 to CO at room temperature and pressure. At a low voltage of -0.25 V (vs. RHE), the catalyst can catalyze the reduction of CO2 to CO, and the product CO Faradaic efficiency (FE) is high. CO The CO selectivity can reach up to 92.78%, and it maintains over 92.78% CO selectivity over an ultra-wide voltage window of -0.25 V (vs. RHE) to -1.4 V (vs. RHE). At a reduction voltage of -1.0 V (vs. RHE), FE... CO Up to 99.2%, with a CO partial current density as high as 123.32 mA / cm². 2 It achieved an industrial-grade current density (100 mA / cm²). 2 Furthermore, this electrocatalyst exhibits good catalytic stability; during a continuous 10-hour constant voltage test, the product FE... CO It has remained above 97%. Attached Figure Description

[0021] Figure 1 Scanning electron microscope image of the catalyst prepared in Example 1 of this invention.

[0022] Figure 2 A high-angle annular dark-field scanning transmission electron microscope image of the catalyst prepared in Example 1 of this invention.

[0023] Figure 3 Aberration-corrected transmission electron microscope image of the catalyst prepared in Example 1 of this invention.

[0024] Figure 4 Elemental distribution diagram of the catalyst prepared in Example 1 of this invention.

[0025] Figure 5 X-ray diffraction pattern of the catalyst prepared in Example 1 of this invention.

[0026] Figure 6 Raman spectrum of the catalyst prepared in Example 1 of this invention.

[0027] Figure 7 The N1s orbital diagram of the X-ray photoelectron spectroscopy of the catalyst prepared in Example 1 of this invention.

[0028] Figure 8The Ni2p orbital diagram of the catalyst prepared in Example 1 of this invention.

[0029] Figure 9 The K-edge X-ray absorption spectrum of the catalyst prepared in Example 1 of this invention.

[0030] Figure 10 Extended X-ray absorption fine structure R-space Fourier transform spectrum of the catalyst prepared in Example 1 of the invention.

[0031] Figure 11 X-ray absorption spectrum wavelet transform spectrum of the catalyst prepared in Example 1 of this invention.

[0032] Figure 12 LSV curve of the CO2 electroreduction catalyst prepared in Example 1 of this invention.

[0033] Figure 13 The CO Faraday efficiency bar chart of the CO2 electroreduction catalyst prepared in Example 1 of this invention at different voltages.

[0034] Figure 14 The CO fractional current density curve of the CO2 electroreduction catalyst prepared in Example 1 of this invention.

[0035] Figure 15 The constant voltage stability test diagram of the CO2 electroreduction catalyst prepared in Example 1 of this invention. Detailed Implementation

[0036] The present invention is further illustrated below by way of examples, but is not limited to the examples described.

[0037] Example 1

[0038] A 2 cm × 2 cm piece of nickel foam (Ni) was immersed in anhydrous ethanol and ultrasonically cleaned, then rinsed with deionized water and dried in an oven. 2 g of dicyandiamide (DCD) was weighed using an electronic balance and placed in a ceramic boat. The ceramic boat containing DCD was placed upstream of a tube furnace, and the nickel foam was removed and placed in another ceramic boat downstream of the tube furnace. During the heating process in the tube furnace, 50 sccm of argon (Ar) was used as the protective gas, with a heating rate of 10 °C / min, reaching 700 °C and holding for 1 h, followed by natural cooling to room temperature. The product was collected and labeled D-Ni-700. After thorough grinding, the nickel foam was immersed in 5 mol / L (M) HCl for 80 h to etch it. It was then thoroughly washed with deionized water, centrifuged at high speed, and completely dried to obtain the Ni diatomic catalyst, labeled D-Ni-700-H. The catalyst was loaded onto carbon paper as the working electrode, with a saturated silver / silver chloride electrode as the reference electrode, a platinum wire as the counter electrode, and a 1 mol / L potassium hydroxide solution as the electrolyte. The electroreduction of CO2 was carried out in a flow cell using a three-electrode system.

[0039] Example 2

[0040] A 1 cm × 1 cm piece of nickel foam (Ni) was immersed in anhydrous ethanol, ultrasonically cleaned, rinsed with deionized water, and then dried in an oven. 3 g of dicyandiamide (DCD) was weighed using an electronic balance and placed in a ceramic boat. The ceramic boat containing DCD was placed upstream of a tube furnace, and the nickel foam was removed and placed in another ceramic boat downstream of the furnace. During the heating process in the tube furnace, 100 sccm of argon (Ar) was used as the protective gas, with a heating rate of 5 °C / min, reaching 750 °C and holding for 0.5 h, followed by natural cooling to room temperature. The reaction product was collected, thoroughly ground, and then immersed in 3 mol / L (M) HCl for 60 h to etch the nickel foam. It was then thoroughly washed with deionized water, centrifuged at high speed, and completely dried to obtain the Ni diatomic catalyst, labeled D-Ni-750-H. The catalyst was loaded onto carbon paper as the working electrode, with a saturated silver / silver chloride electrode as the reference electrode, a platinum wire as the counter electrode, and a 0.5 mol / L potassium hydroxide solution as the electrolyte. The electroreduction of CO2 was carried out in a flow cell using a three-electrode system.

[0041] Example 3

[0042] A 1.5 cm × 1.5 cm piece of nickel foam was ultrasonically cleaned by immersion in anhydrous ethanol, then rinsed with deionized water and dried in an oven. 1 g of dicyandiamide (DCD) was weighed using an electronic balance and placed in a ceramic boat. The ceramic boat containing DCD was placed upstream of a tube furnace, and the nickel foam was removed and placed in another ceramic boat downstream of the furnace. During the heating process in the tube furnace, argon (Ar) at 200 sccm was used as the protective gas, with a heating rate of 5 °C / min, reaching 800 °C and holding for 2 h, followed by natural cooling to room temperature. The reaction product was collected, thoroughly ground, and then immersed in 3 mol / L (M) HCl for 48 h to etch the nickel foam. It was then thoroughly washed with deionized water, centrifuged at high speed, and completely dried to obtain the Ni diatomic catalyst, labeled D-Ni-800-H. The catalyst was loaded onto carbon paper as the working electrode, with a saturated silver / silver chloride electrode as the reference electrode, a platinum wire as the counter electrode, and a 2 mol / L potassium hydroxide solution as the electrolyte. The electroreduction of CO2 was carried out in a flow cell using a three-electrode system.

Claims

1. A nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window, characterized in that, The catalyst is prepared by in-situ growth of carbon nanotubes with Ni dual-atom active sites and uncoordinated nitrogen-doped structures on a nickel substrate using a precursor vapor-phase transfer method at a certain temperature. The specific preparation steps of the catalyst include: (1) Cut a certain size of foamed nickel (Ni), soak it in anhydrous ethanol and ultrasonically clean it, then rinse it with deionized water and dry it in an oven for later use; (2) Place a certain amount of dicyandiamide (DCD) upstream of the tubular furnace and place the nickel foam downstream of the tubular furnace; (3) Using argon (Ar) as the protective gas, the tube furnace is heated to a certain temperature at an appropriate heating rate and held at the growth temperature for 0.2~3 h, and then naturally cooled to room temperature; (4) Collect the reaction product, grind it thoroughly, and then etch the nickel foam by soaking it in HCl; (5) After etching is complete, the product is taken out and washed thoroughly with deionized water, centrifuged at high speed, and collected after being completely dried.

2. The nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window according to claim 1, characterized in that, During the preparation process, the purity of the nickel foam is 98%~99.999%.

3. The nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window according to claim 1, characterized in that, During the preparation process, the purity of the dicyandiamide is 98%~99.999%.

4. The nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window according to claim 1, characterized in that, During the preparation process, the argon gas flow rate is 30~300 sccm, and the heating rate of the tube furnace is 5~20 ℃ / min.

5. The nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window according to claim 1, characterized in that, During the preparation process, the annealing temperature is 600~1000 ℃ and the holding time is 0.2~3 h.

6. The nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window according to claim 1, characterized in that, During the preparation process, the concentration of hydrochloric acid used for acid etching is 1~5 mol / L, the acid etching temperature is 60~80 ℃, and the acid etching time is 48~100 h.

7. The application of the nickel diatomic carbon dioxide electroreduction catalyst with a wide voltage window according to claim 1 in the electroreduction of CO2 to CO, characterized in that: Using carbon paper loaded with the aforementioned Ni diatomic electrocatalyst as the working electrode, a saturated silver / silver chloride electrode as the reference electrode, a platinum wire as the counter electrode, and a 0.5–2 mol / L potassium hydroxide solution as the electrolyte, an electroreduction reaction of CO2 was carried out in a flow cell using a three-electrode system. The catalytic reduction of CO2 to CO was achieved at a low voltage of -0.25 V (vs. RHE). The product CO Faradaic efficiency (FE) was [not specified]. CO It achieves a CO selectivity of up to 92.78% and maintains over 92.78% within an ultra-wide voltage window of -0.25 V (vs. RHE) to -1.4 V (vs. RHE). At a reduction voltage of -1.0 V (vs. RHE), FE... CO With a success rate as high as 99.2%, the CO partial current density reaches 123.32 mA / cm². 2 It reached 100 mA / cm 2 Industrial-grade current density.

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