A copper monatomic catalyst with an asymmetric dinitrogen coordination structure, and a preparation method and use thereof
By regulating the local coordination environment of copper atoms, a copper single-atom catalyst with an asymmetric dinitrogen coordination structure was prepared, which solved the problem that the electroreduction of carbon dioxide mainly produces carbon monoxide in the existing technology. It achieved the effect of efficient methane production within a wide voltage window and has good application prospects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-21
- Publication Date
- 2026-03-24
AI Technical Summary
Existing single-atom catalysts cannot effectively generate the multi-electron product methane during the electroreduction of carbon dioxide, mainly due to insufficient adsorption capacity for the key intermediate CO, resulting in the generation of carbon monoxide as the primary product and limiting the generation of other multi-electron products.
By controlling the local coordination environment of copper atoms and using formamide as a carbon and nitrogen source, a copper single-atom catalyst with an asymmetric dinitrogen coordination structure was prepared. The inexpensive copper salt and a simple hydrothermal method were used to avoid calcination and acid washing steps, and copper atoms were uniformly dispersed on a nitrogen-doped carbon substrate.
It significantly improves the efficiency of carbon dioxide electroreduction to methane over a wide voltage window, exhibiting excellent electrocatalytic performance, low cost, and potential for industrial application.
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Figure CN119736659B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of electrocatalysis, and more particularly relates to a copper monatomic catalyst with an asymmetric dinitrogen coordination structure and a preparation method and use thereof. BACKGROUND
[0002] Ideally, carbon dioxide (CO2) is generated in various ways, while being consumed in equal amounts in various ways, and the entire system environment tends to be stable. However, due to the intensification of human industrial activities, this balance is gradually broken, resulting in more carbon dioxide generation and making global warming a pressing problem. On the other hand, with the acceleration of modernization and the higher requirements of the people for material life, more energy resources are being used in industrial production at a faster rate, and the main consumption is still fossil fuels such as coal and oil. However, they are non-renewable energy sources, and with the increasing consumption, this situation cannot continue for long. Considering the above two aspects, if the emitted carbon dioxide can be effectively converted into the above-mentioned fuels, it not only has an important influence on reducing the content of carbon dioxide, but also has great economic benefits, because 80% of our energy comes from fossil fuels.
[0003] Methane, as the simplest hydrocarbon, has high calorific value (55.5 MJ / kg), is easy to store, and is well compatible with existing natural gas-based facilities, and has good application prospects for preparing methane through carbon dioxide electroreduction. In this process, in order to inhibit unnecessary carbon-carbon coupling to generate multi-carbon byproducts, monatomic catalysts are a good platform to catalyze carbon dioxide electroreduction to a specific one-carbon product, and monatomic catalysts also have high atomic utilization rate, clear and adjustable structure, and many other advantages. However, the common monatomic catalysts used for carbon dioxide electroreduction can only obtain carbon monoxide in the gas phase product, because the adsorption energy of these monatomic catalysts for the key intermediate *CO is too weak, resulting in the desorption of the *CO intermediate to obtain a two-electron CO product when CO2 is reduced, greatly limiting the generation of other multi-electron products such as methane. By taking monatomic catalysts as a platform, regulating the local coordination structure of the central atom to optimize the adsorption of the key intermediate *CO, it is expected to obtain more chemically valuable multi-electron product methane. In view of the above, the present application is proposed. SUMMARY
[0004] The application optimizes the adsorption behavior of the key intermediate CO by regulating the local coordination environment of the central copper atom, aiming to solve the problem that the gaseous product is limited to the two-electron product CO when the conventional copper monatomic catalyst with symmetrical tetranitrogen coordination structure is used for the electroreduction of carbon dioxide. The preparation method uses formamide as the carbon source and nitrogen source, and copper chloride as the metal source, to obtain the copper monatomic catalyst with asymmetric nitrogen coordination structure by chelating the copper atom with the nitrogen-doped carbon obtained by the Schiff base reaction of formamide at high temperature. The catalyst shows good performance in the electroreduction of carbon dioxide to methane in a wide voltage window, and has good application prospect in the field of electrocatalytic reduction of carbon dioxide.
[0005] The first aspect of the application provides a copper monatomic catalyst with asymmetric nitrogen coordination structure, wherein the copper is uniformly dispersed in the nitrogen-doped carbon substrate in the form of a single atom, the single atom copper presents an asymmetric nitrogen coordination structure, and the loading of copper is 0.13-0.27 at%.
[0006] Preferably, the catalyst presents a rod-like morphology, and the diameter of the rod is 50-150 nm.
[0007] The second aspect of the application provides a preparation method of the copper monatomic catalyst with asymmetric nitrogen coordination structure according to the first aspect, characterized in that it comprises the following steps:
[0008] 1) dispersing a copper salt in a formamide solvent to form a precursor solution A; wherein the molar concentration of the copper salt is 2-4 mmol / L;
[0009] 2) ultrasonic treatment of the precursor solution A for 30-60 minutes to make the solution uniformly dispersed, to obtain a uniformly dispersed solution B;
[0010] 3) placing the solution B into a high-temperature and high-pressure reaction kettle to perform a hydrothermal reaction, to obtain a suspension C; the temperature of the hydrothermal reaction is 180-200 DEG C, and the time is 8-12 hours;
[0011] 4) after the suspension C is naturally cooled to room temperature, centrifuging the suspension C to collect the precipitate, and washing with water and centrifuging several times, then drying to obtain a black solid powder D, to obtain the copper monatomic catalyst with asymmetric nitrogen coordination structure.
[0012] Preferably, in step 1), the metal salt is copper chloride dihydrate.
[0013] Preferably, in step 4), the centrifugation is specifically at a speed of 9000-11000 r / min for 7-12 minutes.
[0014] Preferably, in step 4), the centrifugation is specifically at a speed of 9000-11000r / min for 7-12 minutes. In step 4), the drying is specifically at 50-70 degrees Celsius for 8-12 hours.
[0015] The third aspect of the present application provides an application of the asymmetrically two-nitrogen coordinated structure copper monatomic catalyst of the first aspect in electrocatalytic reduction of carbon dioxide to synthesize methane.
[0016] Preferably, the electrocatalytic process comprises: performing constant voltage electrolysis in 0.1-0.5M aqueous KHCO3 solution, and the voltage of the relative reference electrode used for the constant voltage electrolysis is-1.35V to-1.95V.
[0017] Preferably, the catalyst is prepared as a corresponding working electrode.
[0018] The application described above specifically comprises: dispersing the copper monatomic catalyst in a solvent, adding a Nafion solution as a binder, and ultrasonic treatment to obtain a uniform catalyst dispersion liquid; uniformly coating the catalyst dispersion liquid on a conductive carbon paper, drying at room temperature to obtain a working electrode; and performing constant voltage mode electrolytic reduction in a closed three-electrode system.
[0019] When applied, preferably, the conductive carbon paper is a gas diffusion electrode. The solvent is a volatile alcohol, and the concentration of the catalyst dispersion liquid is 2-4mg / mL. The alcohol includes ethanol, isopropyl alcohol, etc. The mass concentration of the Nafion solution is 4.5-5.4%, and the volume ratio of the Nafion solution to the electrode dispersion liquid is 1:100-200.
[0020] Further, the three-electrode system uses silver / silver chloride as a reference electrode, and nickel mesh or nickel foam as a counter electrode.
[0021] Compared with the prior art, the present application has the following beneficial effects:
[0022] 1) The present application uses inexpensive copper salt as a metal source, and inexpensive formamide as a nitrogen source and a carbon source at the same time, and a one-step hydrothermal method is used to prepare a copper monatomic catalyst with an asymmetric two-nitrogen coordinated structure. In the material, the active site single-atom copper presents a unique asymmetric two-nitrogen coordinated structure.
[0023] This special structure greatly improves the adsorption capacity of copper atoms for carbon monoxide molecules. Compared with the common symmetric four-nitrogen coordinated structure of copper monatomic catalyst, the copper monatomic catalyst described herein has a strong adsorption behavior for carbon monoxide molecules. CO is a key intermediate for obtaining multi-electron CH4 product by electrochemical reduction of CO2, and strengthening the adsorption capacity of CO is crucial for electrocatalytic reduction of carbon dioxide to synthesize CH4.
[0024] 2) The catalyst of the present application has excellent electrocatalytic performance for carbon dioxide reduction. The special coordination structure of the catalyst endows the copper atom with strong carbon monoxide molecule adsorption behavior, and high methane product selectivity (42-59%) is obtained in a wide potential window (-1.35 V to -1.95 V vs. RHE).
[0025] 3) The synthesis method of the catalyst is simple and easy to operate, and the cost is low. After the catalyst is hydrothermally synthesized, no subsequent treatment means such as calcination and pickling is needed, and the catalyst has the potential to be applied to industrial production, and can have good application prospect in the field of electrocatalytic reduction of carbon dioxide.
[0026] 4) In the prior art, the preparation scheme of the copper monatomic catalyst generally needs to add metal zinc and has subsequent calcination and sublimation of zinc to separate the copper atoms from the metal zinc to form the copper monatomic catalyst.
[0027] The preparation method of the present application is characterized in that the addition of metal zinc and the subsequent calcination operation are omitted, and the copper monatomic catalyst is still formed, and the catalyst has the characteristics of asymmetric dinitrogen coordination structure and high efficiency of electrocatalytic reduction of carbon dioxide to synthesize CH4, which is unexpected by the applicant.
[0028] 5) In particular, the present application finds that the molar concentration of the copper salt in the formamide solvent is crucial to the structure of the product. The structure of the product has a significant impact on the performance of the electrocatalytic reduction of carbon dioxide. By controlling the molar concentration of the copper salt in the formamide solvent to be 2-4 mmol / L, the copper monatomic catalyst with asymmetric dinitrogen coordination structure can be obtained, and the efficiency of electrocatalytic reduction of carbon dioxide to synthesize CH4 is improved.
[0029] If the molar concentration of the copper salt in the formamide solvent is not within the above range, the copper monatomic catalyst obtained has other coordination structures, for example, the coordination number is 3. BRIEF DESCRIPTION OF DRAWINGS
[0030] Figure 1 The transmission electron microscope image of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0031] Figure 2 The X-ray diffraction pattern of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0032] Figure 3 The X-ray photoelectron spectroscopy pattern of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0033] Figure 4Elemental mapping of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0034] Figure 5 High-angle annular dark field scanning transmission electron microscopy image of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%) with spherical aberration correction;
[0035] Figure 6 X-ray absorption near-edge spectrum of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0036] Figure 7 Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0037] Figure 8 First shell fitting result of the Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0038] Figure 9 In-situ diffuse reflectance Fourier-transform infrared spectrum of carbon monoxide adsorption of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0039] Figure 10 X-ray absorption near-edge spectrum of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.27 at%);
[0040] Figure 11 Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.27 at%);
[0041] Figure 12 First shell fitting result of the Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.27 at%);
[0042] Figure 13 X-ray absorption near-edge spectrum of the prepared copper monatomic catalyst with asymmetric trinitrogen coordination structure;
[0043] Figure 14 Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with asymmetric trinitrogen coordination structure;
[0044] Figure 15 First shell fitting result of the Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with asymmetric trinitrogen coordination structure;
[0045] Figure 16 Scanning electron microscopy and transmission electron microscopy images of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0046] Figure 17 X-ray diffraction spectrum of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0047] Figure 18 X-ray absorption near-edge spectrum of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0048] Figure 19 Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0049] Figure 20 First shell fitting results of the Fourier-transform X-ray absorption extended fine structure spectrum of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0050] Figure 21 In-situ diffuse reflectance Fourier-transform infrared spectrum of carbon monoxide absorption of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0051] Figure 22 Carbon dioxide electroreduction product distribution plot of the prepared copper monatomic catalyst with asymmetric dinitrogen coordination structure (0.13 at%);
[0052] Figure 23 Carbon dioxide electroreduction product distribution plot of the prepared copper monatomic catalyst with asymmetric trinitrogen coordination structure;
[0053] Figure 24 Carbon dioxide electroreduction product distribution plot of the prepared copper monatomic catalyst with symmetric tetranitrogen coordination structure;
[0054] Figure 25 X-ray diffraction spectrum of the material after high-temperature calcination of the copper monatomic catalyst with asymmetric dinitrogen coordination structure;
[0055] Figure 26 High-angle annular dark-field scanning transmission electron microscopy image of the material after high-temperature calcination of the copper monatomic catalyst with asymmetric dinitrogen coordination structure. DETAILED DESCRIPTION
[0056] The present application will be described below in connection with specific embodiments, but the embodiments of the present application are not limited thereto. The experimental methods not specified in the examples are generally performed according to the conventional conditions and the conditions described in the manuals, or using the general equipment, materials, reagents, etc. as suggested by the manufacturers, unless otherwise specified. The raw materials required in the following examples and comparative examples are commercially available.
[0057] Example 1
[0058] The preparation of the copper monatomic catalyst with asymmetric dinitrogen coordination structure includes the following steps:
[0059] Step 1, disperse a certain amount of copper chloride dihydrate in a formamide solvent to form a precursor solution A with a concentration of 2 mmol / L;
[0060] Step 2, ultrasonically treat the precursor solution A for 30 minutes to make the solution uniformly dispersed, obtaining a uniformly dispersed solution B;
[0061] Step 3, place the solution B into a high-temperature and high-pressure reaction kettle to perform a hydrothermal reaction, the temperature of the hydrothermal reaction is 180 degrees Celsius, and the time of the hydrothermal reaction is 8 hours, finally obtaining a suspension C;
[0062] Step 4, after the suspension C is naturally cooled to room temperature, centrifugally collect the precipitate of the suspension C, and then water-wash and centrifugally collect several times, then dry at 50 degrees Celsius for 8 hours to obtain a black solid powder D, obtaining the copper monatomic catalyst with asymmetric dinitrogen coordination structure (named as Cu-N2 / C-2). The centrifugation is specifically performed at a speed of 9000 r / min for 12 minutes. SA -N2 / C-2). The centrifugation is specifically performed at a speed of 9000 r / min for 12 minutes.
[0063] In this example, the transmission electron microscope and the spherical aberration electron microscope are used to perform microscopic morphology characterization and analysis on the catalyst. From the transmission electron micrograph of Figure 1 , it can be seen that the prepared catalyst macroscopically presents a rod-like morphology, the diameter of the rod is 50-150 nm, specifically about 100 nm. From the X-ray diffraction spectrum of Figure 2 , it can be seen that the prepared catalyst only has a carbon diffraction peak at about 27 degrees, and no diffraction signal of agglomerated large-size copper particles is found. From the X-ray photoelectron spectrum of Figure 3 , it can be seen that the prepared catalyst has a successful loading of copper, and the copper loading amount is 0.13 at%.
[0064] From the element distribution map of Figure 4 , it can be seen that the copper, nitrogen and carbon in the prepared catalyst are uniformly distributed, and there is no agglomeration between atoms. More deeply, from the high-resolution transmission electron micrograph of Figure 5The single-atom dispersion of copper atoms in the prepared catalyst can be proved by the high-angle annular dark-field scanning transmission electron microscopy image of the spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy image.
[0065] Further, the local coordination environment of the copper atoms in the prepared catalyst is analyzed in depth by using the synchrotron radiation X-ray absorption spectrum. From the X-ray absorption near-edge spectrum of the prepared catalyst, it can be seen that the oxidation state of the prepared copper atoms is between 1 and 2 valences, and the pre-edge signals A and B different from the absorption spectrum of copper phthalocyanine are observed, which preliminarily indicates that the prepared copper single-atom material has a coordination structure different from that of copper phthalocyanine (a copper single-atom catalyst with a symmetrical four-nitrogen coordination structure). Figure 6 Figure 7 From the Fourier transform X-ray absorption extended fine spectrum of the prepared catalyst, it can be seen that the prepared catalyst has a clear Cu-N coordination structure, but no Cu-Cu coordination signal, which further indicates that the prepared catalyst is a nitrogen-coordinated single-atom catalyst. To further confirm the coordination structure of the prepared catalyst, the Fourier transform X-ray absorption extended fine spectrum of the prepared catalyst is subjected to first-shell fitting, Figure 8 and the fitting results of Table 1 indicate that the coordination number of the copper atoms in the prepared catalyst is 2.
[0066] Figure 9 The in-situ diffuse reflectance Fourier transform infrared spectrum of the carbon monoxide absorption of the asymmetric two-nitrogen coordination structure copper single-atom catalyst prepared in Example 1 indicates that the prepared catalyst has a strong carbon monoxide molecule adsorption behavior. CO is a key intermediate for obtaining multi-electron CH4 products in the electro-reduction of CO2, and the adsorption capacity of CO is strengthened, which is crucial for the electro-catalytic reduction of carbon dioxide to synthesize CH4.
[0067] Example 2
[0068] The preparation of the asymmetric two-nitrogen coordination structure copper single-atom catalyst includes the following steps:
[0069] Step 1, a certain amount of copper chloride dihydrate is dispersed in a formamide solvent to form a precursor solution A with a concentration of 4 mmol / L;
[0070] Step 2, the precursor solution A is subjected to ultrasonic treatment for 60 minutes to make the solution uniformly dispersed, and a uniformly dispersed solution B is obtained;
[0071] Step 3, the solution B is placed into a high-temperature and high-pressure reaction kettle for hydrothermal reaction, the temperature of the hydrothermal reaction is 200 degrees Celsius, and the time of the hydrothermal reaction is 12 hours, and finally a suspension C is obtained;
[0072] Step 4: After the suspension C cools naturally to room temperature, centrifuge the suspension C to collect the precipitate, wash it with water, centrifuge it several times, and then dry it at 70 degrees Celsius for 12 hours to obtain a black solid powder D, which is a copper single-atom catalyst with an asymmetric dinitrogen coordination structure (named Cu). SA -N2 / C-4). The centrifugation was specifically carried out at a speed of 11000 r / min for 7 minutes.
[0073] In this embodiment, from Figure 10 The X-ray diffraction pattern shows that the prepared catalyst only exhibits a carbon diffraction peak at approximately 27 degrees, and no diffraction signals from agglomerated large copper particles were found. Furthermore, synchrotron X-ray absorption spectroscopy was used to analyze the local coordination environment of copper atoms in the prepared catalyst. Figure 11 The fine-scale Fourier transform X-ray absorption spectrum shows a clear Cu-N coordination structure, but no Cu-Cu coordination signal, further indicating that the prepared catalyst is a nitrogen-coordinated single-atom catalyst. To further confirm the coordination structure of the prepared catalyst, a first-shell fitting was performed on the fine-scale Fourier transform X-ray absorption spectrum. Figure 12 The fitting results in Table 1 indicate that the coordination number of copper atoms in the prepared catalyst is 2. X-ray photoelectron spectroscopy reveals a copper loading of 0.27 at%.
[0074] Comparative Example 1
[0075] The preparation of asymmetric trinitrogen coordination structure copper single-atom catalysts includes the following steps:
[0076] Step 1: Disperse a certain amount of copper chloride dihydrate in formamide solvent to form a precursor solution A with a concentration of 5 mmol / L;
[0077] Step 2: Ultrasonic treatment of precursor solution A for 30 minutes to make the solution uniformly dispersed, resulting in uniformly dispersed solution B.
[0078] Step 3: Place solution B into a high-temperature and high-pressure reactor for hydrothermal reaction. The hydrothermal reaction temperature is 180 degrees Celsius and the hydrothermal reaction time is 8 hours, finally obtaining suspension C.
[0079] Step 4: After the suspension C cools naturally to room temperature, centrifuge the suspension C to collect the precipitate, wash it with water, centrifuge it several times, and then dry it at 50 degrees Celsius for 8 hours to obtain a black solid powder D, thus obtaining a copper single-atom catalyst with an asymmetric trinitrogen coordination structure. Specifically, the centrifugation is performed at a speed of 9000 r / min for 12 minutes.
[0080] In this comparative example, from Figure 13The X-ray diffraction pattern shows that the prepared catalyst only exhibits a carbon diffraction peak at approximately 27 degrees, and no diffraction signals from agglomerated large copper particles were found. Furthermore, synchrotron X-ray absorption spectroscopy was used to analyze the local coordination environment of copper atoms in the prepared catalyst. Figure 14 The fine-scale Fourier transform X-ray absorption spectrum shows a clear Cu-N coordination structure, but no Cu-Cu coordination signal, further indicating that the prepared catalyst is a nitrogen-coordinated single-atom catalyst. To further confirm the coordination structure of the prepared catalyst, a first-shell fitting was performed on the fine-scale Fourier transform X-ray absorption spectrum. Figure 15 The fitting results in Table 1 indicate that the coordination number of copper atoms in the prepared catalyst is 3 (named Cu). SA -N3 / C).
[0081] Comparative Example 2
[0082] The synthesis of a copper single-atom catalyst with a symmetrical tetranitrogen coordination structure includes the following steps:
[0083] Step 1: Disperse a certain amount of copper chloride dihydrate and anhydrous zinc chloride in formamide solvent to form precursor solution A with a copper salt concentration of 2 mmol / L and a zinc salt concentration of 100 mmol.
[0084] Step 2: Ultrasonic treatment of precursor solution A for 30 minutes to make the solution uniformly dispersed, resulting in uniformly dispersed solution B.
[0085] Step 3: Place solution B into a high-temperature and high-pressure reactor for hydrothermal reaction. The hydrothermal reaction temperature is 180 degrees Celsius and the hydrothermal reaction time is 8 hours, finally obtaining suspension C.
[0086] Step 4: After the suspension C cools naturally to room temperature, centrifuge the suspension C to collect the precipitate, wash it with water, centrifuge several more times, and then dry it at 50 degrees Celsius for 8 hours to obtain a black solid powder D. Specifically, the centrifugation is performed at 9000 r / min for 12 minutes.
[0087] Step 5: Spread the above solid powder D evenly in a ceramic boat and place it in a tube furnace. Purge the air with argon gas for 30 minutes at a flow rate of 200 mL / min. Raise the temperature to a set temperature of 950 degrees Celsius using a programmed temperature control method, and calcine at this temperature for 2 hours at a heating rate of 5 degrees Celsius / min. After calcineation, allow it to cool naturally to room temperature to obtain a black powder, which is the copper single-atom catalyst with a symmetrical tetranitrogen coordination structure (named Cu). SA -N4 / C).
[0088] In this comparative example, the microstructure of the catalyst was characterized and analyzed using transmission electron microscopy and aberration-corrected electron microscopy. From... Figure 16 Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the prepared symmetrical tetranitrogen-coordinated copper single-atom catalyst exhibited an amorphous morphology, and no large metal particles were observed. From... Figure 17 The X-ray diffraction pattern shows that the prepared catalyst only has a carbon diffraction peak at around 27 degrees, and no diffraction signal of agglomerated large copper particles was found.
[0089] Furthermore, synchrotron X-ray absorption spectroscopy was used to analyze the local coordination environment of copper atoms in the prepared catalyst. From Figure 18 The near-edge X-ray absorption spectrum shows that the oxidation states of the prepared copper atoms are between monovalent and divalent. Figure 19 The fine-scale Fourier transform X-ray absorption spectrum shows a clear Cu-N coordination structure, but no Cu-Cu coordination signal, further indicating that the prepared catalyst is a nitrogen-coordinated single-atom catalyst. To further confirm the coordination structure of the prepared catalyst, a first-shell fitting was performed on the fine-scale Fourier transform X-ray absorption spectrum. Figure 20 The fitting results in Table 1 show that the coordination number of copper atoms in the prepared catalyst is 4.
[0090] Figure 21 The in-situ diffuse reflectance Fourier transform infrared spectrum of carbon monoxide absorption of the prepared copper single-atom catalyst with symmetrical tetranitrogen coordination structure shows that the prepared catalyst has almost no adsorption behavior of carbon monoxide molecules.
[0091] Application Example 1
[0092] Preparation of the working electrode for an asymmetric dinitrogen-coordinated copper single-atom catalyst in the electrocatalytic reduction of carbon dioxide:
[0093] A precise amount of the asymmetric dinitrogen-coordinated copper single-atom catalyst prepared in Example 1 was weighed and dispersed in anhydrous ethanol solvent to form a catalyst dispersion with a concentration of 2 mg / mL. Then, a certain amount of Nafion solution was added as a binder; the mass concentration of the Nafion solution was 5%, and the volume ratio of the Nafion solution to the electrode dispersion was 1:200. The catalyst dispersion was ultrasonically treated for 45 minutes to obtain a uniformly dispersed catalyst dispersion. The catalyst dispersion was then uniformly coated onto a gas diffusion electrode and dried at room temperature to obtain the working electrode.
[0094] Experiment on the electrolytic reduction of carbon dioxide with controlled potential:
[0095] The electro-catalytic process was carried out in a closed three-electrode system, and the electrochemical workstation was Koster CS2350H. The working electrode was the working electrode obtained in the above process, the reference electrode was silver / silver chloride, and the counter electrode was nickel foam. The electrolyte was 0.5M potassium bicarbonate aqueous solution saturated with carbon dioxide gas. Before electrolysis, carbon dioxide was introduced for 20 minutes, and then constant potential mode electrolysis was carried out to reduce carbon dioxide. The gaseous products were introduced into a gas chromatograph for analysis, in which CO, CH4, C2H4, and C2H6 products were quantitatively detected by an ion flame detector, and H2 was detected and quantified by a thermal conductivity detector. The liquid phase products were analyzed by nuclear magnetic resonance hydrogen spectrum, and the program used was water peak suppression 1 H spectrum, and the internal standard used was heavy water solution of dimethyl sulfoxide.
[0096] Product detection and quantification under different reduction potentials:
[0097] The effect of different reduction potentials on product selectivity was detected, in which the control potentials were -1.35V vs. RHE, -1.45V vs. RHE, -1.55V vs. RHE, -1.65V vs. RHE, -1.75V vs. RHE, -1.85V vs. RHE and -1.95V vs. RHE, respectively. The time of constant potential electrolysis reduction was 1 hour. The results are shown in Figure 22 It can be seen that the catalyst exhibits excellent performance in the production of multi-electron CH4 products in the electro-reduction of carbon dioxide in a wide voltage window (-1.35V to -1.95V vs. RHE), and the Faraday efficiency at control potentials of -1.35V vs. RHE, -1.45V vs. RHE, -1.55V vs. RHE, -1.65V vs. RHE, -1.75V vs. RHE, -1.85V vs. RHE and -1.95V vs. RHE, respectively, is 42.5%, 46.7%, 47.9%, 53.2%, 56.7%, 57.8% and 58.9%, respectively. It can be seen that the highest Faraday efficiency reaches 58.9%.
[0098] Comparative Example Application Example 1
[0099] Preparation of copper monatomic catalyst with asymmetric tri-nitrogen coordination structure as working electrode in electro-catalytic reduction of carbon dioxide:
[0100] A certain amount of the asymmetric tri-nitrogen coordination structure copper monatomic catalyst prepared in Comparative Example 1 was accurately weighed, and was dispersed in anhydrous ethanol solvent to form a catalyst dispersion liquid, and the concentration of the catalyst dispersion liquid was 2 mg / mL. Then a certain amount of Nafion solution was added as a binder, the mass concentration of the Nafion solution was 5%, and the volume ratio of the Nafion solution to the electrode dispersion liquid was 1:200. The catalyst dispersion liquid was treated by ultrasonic wave for 45 minutes to obtain a uniformly dispersed catalyst dispersion liquid. Then the catalyst dispersion liquid was uniformly coated on a gas diffusion electrode, and was dried at room temperature to obtain a working electrode.
[0101] Controlled potential electrolysis carbon dioxide reduction experiment:
[0102] A closed three-electrode system was used in the electrocatalysis process, and a Koster CS2350H electrochemical workstation was used. The working electrode was the working electrode obtained in the above process, the reference electrode was a silver / silver chloride electrode, and the counter electrode was a nickel foam. The electrolyte was a 0.5 M aqueous potassium bicarbonate solution saturated with carbon dioxide gas. Before electrolysis, carbon dioxide was introduced for 20 minutes, and then constant potential mode electrolysis reduction of carbon dioxide was carried out. The gaseous products were introduced into a gas chromatograph for analysis, in which CO, CH4, C2H4, and C2H6 products were quantitatively detected by an ion flame detector, and H2 was quantitatively detected by a thermal conductivity detector. The liquid phase products were analyzed by nuclear magnetic resonance hydrogen spectrum, and the program used was water peak suppression H spectrum, and the internal standard used was heavy water solution of dimethyl sulfoxide. 1
[0103] Product detection and quantification under different reduction potentials:
[0104] The influence of different reduction potentials on product selectivity was detected, in which the control potentials were -1.35 V vs. RHE, -1.45 V vs. RHE, -1.55 V vs. RHE, -1.65 V vs. RHE, and -1.75 V vs. RHE. The constant potential electrolysis reduction time was 1 hour. The results are shown in Figure 23 It can be seen that the catalyst exhibits good performance in the production of multi-electron CH4 product in the carbon dioxide electro-reduction under the voltage window (-1.35 V to -1.75 V vs. RHE), and the highest Faraday efficiency is 43.8%, which is lower than the Faraday efficiency of the asymmetric tri-nitrogen coordination structure copper monatomic catalyst of the present application.
[0105] Comparative Example 2
[0106] Preparation of a working electrode of a symmetric tetranitrogen coordination structure copper monatomic catalyst in electrocatalytic reduction of carbon dioxide and electrocatalytic carbon dioxide reduction performance:
[0107] A certain amount of copper single-atom catalyst with symmetrical tetranitrogen coordination structure prepared in Comparative Example 2 was accurately weighed and dispersed in anhydrous ethanol solvent to form a catalyst dispersion liquid, and the concentration of the catalyst dispersion liquid was 2 mg / mL. Then a certain amount of Nafion solution was added as a binder, the mass concentration of the Nafion solution was 5%, and the volume ratio of the Nafion solution to the electrode dispersion liquid was 1:200. The catalyst dispersion liquid was treated by ultrasonic wave for 45 minutes to obtain a uniformly dispersed catalyst dispersion liquid. Then the catalyst dispersion liquid was uniformly coated on the gas diffusion electrode, and dried at room temperature to obtain a working electrode.
[0108] A closed three-electrode system was used in the electrocatalytic process, and a Koster CS2350H electrochemical workstation was used. The working electrode was the working electrode obtained in the above process, the reference electrode was silver / silver chloride, and the counter electrode was nickel foam. The electrolyte was a 0.5M aqueous potassium bicarbonate solution saturated with carbon dioxide gas. Before electrolysis, carbon dioxide was introduced for 20 minutes, and then constant potential mode electrolysis was carried out at different electrolysis voltages to reduce carbon dioxide. The results are shown in Figure 24 It can be seen that the catalyst can only obtain a small amount of two-electron CO product in a relatively wide voltage window (-0.7V to -1.1V vs. RHE), and cannot obtain methane.
[0109] Comparative Example 3
[0110] The copper single-atom catalyst with asymmetrical dinitrogen coordination structure was subjected to high-temperature calcination treatment:
[0111] The copper single-atom solid powder with asymmetrical dinitrogen coordination structure obtained in Example 1 was laid flat in a porcelain boat and placed in a tube furnace. Argon was introduced for 30 minutes to purge the air therein, and the argon flow rate was 200 mL / min. The temperature was raised to a set temperature of 950 degrees Celsius by a programmed temperature control method, and calcination was carried out at this temperature for 2 hours, and the temperature rising rate was 5 degrees Celsius per minute. After calcination, it was naturally cooled to room temperature to obtain a black powder, which was named Cu SA -N2 / C-calcined.
[0112] The materials obtained in the above process were subjected to lattice diffraction analysis by X-ray diffraction pattern, and the micro-morphology of the materials was characterized by spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. From the X-ray diffraction pattern of Figure 25 It can be seen that only the diffraction peak of carbon at about 27 degrees exists, and there is no diffraction signal of agglomerated large-size copper particles. However, Figure 26The high-angle annular dark-field scanning transmission electron microscopy (STEM) image with more accurate spherical aberration correction for structural characterization analysis shows that the material has obvious atomic agglomeration phenomenon, and forms clusters with a size of about 2 nm. The results show that during the high-temperature calcination process of the copper monatomic catalyst with an asymmetric dinitrogen coordination structure, agglomeration occurs between copper atoms, and copper clusters with a size of about 2 nm are formed. It should be pointed out that in order to inhibit the generation of carbon-carbon coupling to form multi-carbon byproducts and maximize the selectivity of carbon monomer products, the formation of the cluster deviates from the single atom platform pursued in the catalyst design process here.
[0113] In summary: the present application uses cheap copper salt as metal source, and cheap formamide as nitrogen source and carbon source at the same time to chelate copper atoms through Schiff base reaction at high temperature, and a copper monatomic catalyst with asymmetric dinitrogen coordination structure is prepared by a simple one-step hydrothermal method. Compared with the common copper monatomic catalyst with symmetric tetranitrogen coordination structure, the special coordination structure of the copper monatomic catalyst with asymmetric dinitrogen coordination structure described herein endows the catalyst with a strong adsorption behavior for CO molecules. CO is a key intermediate for obtaining multi-electron CH4 product by electrochemical reduction of CO2, and strengthening the adsorption capacity of CO is crucial for electrocatalytic reduction of carbon dioxide to synthesize CH4. The synthesis method of the catalyst is simple and easy to operate, and the catalyst has excellent catalytic effect and low cost. After hydrothermal synthesis of the catalyst, no subsequent treatment such as calcination and acid washing is needed, and the catalyst has the potential to be applied in industrial production, and has good application prospect in the field of electrochemical reduction of carbon dioxide.
[0114] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.
[0115] Table 1
[0116]
Claims
1. A copper single-atom catalyst with an asymmetric dinitrogen coordination structure, characterized in that, In the catalyst, copper is uniformly dispersed in single-atom form on a nitrogen-doped carbon substrate. The single-atom copper exhibits an asymmetric dinitrogen coordination structure, and the copper loading is 0.13 at%-0.27 at%; The catalyst exhibits a rod-shaped morphology with a diameter of 50-150 nm.
2. A method for preparing a copper single-atom catalyst with an asymmetric dinitrogen coordination structure as described in claim 1, characterized in that, Includes the following steps: 1) A copper salt is dispersed in a formamide solvent to form a precursor solution A; wherein the molar concentration of the copper salt is 2-4 mmol / L; 2) Sonicate the precursor solution A for 30-60 minutes to make the solution uniformly dispersed, and obtain a uniformly dispersed solution B. 3) Place solution B into a high-temperature and high-pressure reactor for hydrothermal reaction to obtain suspension C; the temperature of the hydrothermal reaction is 180-200 degrees Celsius and the time is 8-12 hours. 4) After the suspension C cools naturally to room temperature, centrifuge the suspension C to collect the precipitate, wash it with water and centrifuge it several times, and then dry it to obtain black solid powder D, which is the copper single-atom catalyst with an asymmetric dinitrogen coordination structure.
3. The preparation method according to claim 2, characterized in that, In step 1), the metallic copper salt is copper chloride dihydrate.
4. The preparation method according to claim 2, characterized in that, In step 4), the centrifugation is specifically carried out at a speed of 9000-11000 r / min for 7-12 minutes.
5. The application of the copper single-atom catalyst with the asymmetric dinitrogen coordination structure as described in claim 1 in the electrocatalytic reduction of carbon dioxide to methane.
6. The application according to claim 5, characterized in that, The electrocatalytic process includes constant voltage electrolysis in a 0.1-0.5 M KHCO3 aqueous solution, with the voltage of the relative reference electrode being -1.35 V to -1.95 V.