Ni-Co double-monatomic catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electro-catalysis carbon dioxide reduction reaction, and particularly discloses a Ni-Co double-monatomic catalyst and a preparation method and application thereof.The catalyst comprises a carbon carrier and atomic-scale dispersed Ni monatomic atoms anchored to the carbon carrier in a Ni-N4 configuration; atomically dispersed Co monatomic atoms are anchored to a carbon carrier in a Co-N4 configuration, and no metal-metal bond exists in the catalyst. According to the Ni-Co double-monatomic catalyst as well as the preparation method and the application thereof, CO2-to-CO conversion and hydrogen evolution reaction (HER) are independently regulated and controlled through Ni-N4 and Co-N4 double active sites respectively, so that a CO / H2 ratio is accurately adjustable in a range of 0.3: 1-2.5: 1; ni monatomic sites are used for regulating and controlling the rigidity of an interface water-hydrogen bond network, the activation kinetics of CO2 and H2O is balanced, and side reactions under the industrial-grade current density are inhibited.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrocatalytic carbon dioxide reduction reaction, in particular to a Ni-Co double-atomic catalyst and a preparation method and application thereof. BACKGROUND

[0002] The electrochemical carbon dioxide reduction reaction (ECO2RR) is a sustainable CO2 resource utilization technology, which can produce high-value-added chemicals and fuels. Synthesis gas (a mixture of CO and H2) is one of the important products of ECO2RR, which is widely used in industrial processes such as Fischer-Tropsch synthesis, hydroformylation reaction and methanol synthesis. However, the existing ECO2RR catalysts have the following defects: 1. The traditional catalysts are difficult to simultaneously control the activities of CO2 reduction and hydrogen evolution reaction (HER), resulting in uncontrollable CO / H2 ratio in the product.

[0003] 2. Although the single-atomic catalyst (SAC) has high activity, the single metal site cannot independently control the competitive reactions of CO2RR and HER.

[0004] 3. The existing bimetallic catalysts are mostly alloys or core-shell structures, and the interaction mechanism between the metal sites is not clear, and the agglomeration and deactivation are prone to occur.

[0005] 4. Under the industrial current density (≥250 mA / cm 2 ), the stability of the catalyst is insufficient, and the product selectivity is significantly reduced.

[0006] In view of the defects of the prior art, the application provides a Ni-Co double-atomic catalyst to solve the above technical problems. SUMMARY

[0007] The purpose of the application is to provide a Ni-Co double-atomic catalyst and a preparation method and application thereof, which can independently control the CO2-to-CO conversion and hydrogen evolution reaction (HER) through the Ni-N4 and Co-N4 double active sites, realize the accurate adjustment of the CO / H2 ratio in the range of 0.3:1-2.5:1, regulate the interface water hydrogen bond network rigidity through the Ni single-atomic site, balance the activation kinetics of CO2 and H2O, and inhibit the side reactions under the industrial current density; the catalyst can be stably operated in an acid proton exchange membrane (PEM) electrolyzer for more than 120 hours, and meets the industrial application requirements.

[0008] To achieve the above purpose, the application provides a Ni-Co double-atomic catalyst, which comprises a carbon carrier, atomically dispersed Ni single atoms anchored to the carbon carrier in a Ni-N4 configuration, and atomically dispersed Co single atoms anchored to the carbon carrier in a Co-N4 configuration, and no metal-metal bond exists in the catalyst.

[0009] Preferably, the molar ratio of Ni and Co is 1:1-1:3.

[0010] Preferably, the carbon carrier is nitrogen-doped porous carbon, with a specific surface area ≥800m 2 / g and a pore size distribution of 2-5nm.

[0011] The application also provides a preparation method of the Ni-Co double-atomic catalyst, comprising the following steps: Step 1: mixing Ni salt and Co salt with polyacrylamide gel and cyanuric acid, and freeze-drying to obtain a precursor; Step 2: pyrolyzing under an inert atmosphere at a temperature of 800-1000℃, and obtaining the catalyst after acid washing.

[0012] Preferably, in step 1, the Ni salt is Ni(NO3)2 and the Co salt is Co(NO3)2.

[0013] Preferably, in step 2, the inert atmosphere is a nitrogen atmosphere, the heating rate is 2-10℃ / min, and the holding time is 1-3h.

[0014] The application also provides an application of the Ni-Co double-atomic catalyst, which is applied to a reaction of synthesizing CO and H2 mixed gas by catalyzing electrochemical carbon dioxide reduction reaction, so as to regulate the rigidity of the interface water hydrogen bond network, balance the activation kinetics of CO2 and H2O, and inhibit the side reaction under an industrial current density.

[0015] The application also provides a preparation method of synthesizing CO and H2 mixed gas by electrochemical carbon dioxide reduction reaction, which uses the above-mentioned catalyst as a cathode, the anode electrolyte is 0.05MK2SO4, pH=1, humidified CO2 gas is introduced into the cathode, and when the full-cell voltage is ≤3.5V in an acid proton exchange membrane electrolyzer, the current density is 50-400mA / cm 2 , CO2 and H2O are converted into synthesis gas with adjustable CO / H2 ratio.

[0016] Preferably, the CO / H2 ratio is regulated by the current density, when the current density is 250mA / cm 2 , CO / H2=1:1, when the current density is 350mA / cm 2 , CO / H2=0.5:1.

[0017] The advantages and beneficial effects of the above-mentioned Ni-Co double-atomic catalyst, the preparation method and the application thereof are as follows: 1. The catalyst of the present application can precisely adjust the CO / H2 ratio in the range of 0.3:1-2.5:1 by independently regulating the CO2-to-CO conversion and hydrogen evolution reaction (HER) through the Ni-N4 and Co-N4 active sites, respectively; the rigidity of the interface water hydrogen bond network is regulated by the Ni single-atom site to balance the activation kinetics of CO2 and H2O, and to inhibit side reactions at industrial current density; the catalyst can be stably operated in an acidic proton exchange membrane (PEM) electrolyzer for more than 120 hours, meeting the requirements of industrial applications.

[0018] 2. Under the industrial current density (350mA / cm 2 ), the CO faradaic efficiency (FE_CO) reaches 65%, the H2 faradaic efficiency (FE_H2) reaches 35%, and the CO / H2 ratio is 0.5:1, meeting the requirements of Fischer-Tropsch synthesis; the stability test shows that the CO / H2 ratio fluctuates by less than 5% within 120 hours; the catalyst can achieve a current density of ≥300mA / cm 2 when the loading is ≤0.5mg / cm 2 ; the defect structure of the carbon carrier (I_D / I_G=1.2) inhibits metal aggregation, and the activity is retained by more than 90% after 1000 cycles.

[0019] The technical solutions of the present application will be further described in detail below through the accompanying drawings and examples. DETAILED DESCRIPTION

[0020] Figure 1 Fig. 1 is the HAADF-STEM image and EDS element distribution map of the Ni1Co1NC of the present application; wherein A is a low-resolution HAADF-STEM image, and B is the corresponding EDS map display; Figure 2 Fig. 2 is the curve of the CO / H2 ratio in the PEM electrolyzer of the present application changing with current density; Figure 3 Fig. 3 is the long-term stability test of the Ni1Co1NC at -0.5V vs. RHE; Figure 4 Fig. 4 is the performance evaluation of the acid ECO2R conversion to syngas of the Ni1Co1NC in the MEA electrolyzer of the present application, wherein a is the overall schematic diagram of the MEA electrolyzer, and b is the disassembly schematic diagram of the MEA electrolyzer; Figure 5 Fig. 5 is the long-term stability of the Ni1Co1NC in the acid feed MEA at 100mAcm -2 ; Figure 6 Fig. 6 is the performance comparison of the Ni1Co1NC and the electrocatalyst for long-term syngas production of the present application. DETAILED DESCRIPTION

[0021] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0022] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meaning understood by a person with ordinary skills in the art to which the present application belongs.

[0023] The following examples are not intended to limit the present application, but only serve to illustrate the present application. Unless otherwise specified, the experimental methods used in the following examples are generally carried out according to conventional conditions. Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial channels.

[0024] Example 1 The Ni-Co bimetallic monatomic catalyst comprises a carbon carrier, atomically dispersed Ni monatomic atoms anchored to the carbon carrier in a Ni-N4 configuration, and atomically dispersed Co monatomic atoms anchored to the carbon carrier in a Co-N4 configuration. The molar ratio of Ni to Co is 1:1-1:3, and no metal-metal bond is confirmed by extended X-ray absorption fine structure (EXAFS) analysis. The carbon carrier is nitrogen-doped porous carbon with a specific surface area ≥800 m 2 / g and a pore size distribution of 2-5 nm.

[0025] The preparation method of the Ni-Co bimetallic monatomic catalyst comprises the following steps: Step 1: Dissolve Ni salt (Ni(NO3)2) and Co salt (Co(NO3)2) solution with polyacrylamide (PAM) gel as carbon source and cyanuric acid as nitrogen source; form Ni / Co-PAM aerogel by freeze-drying.

[0026] Step 2: Heat to 800-1000℃ at 5℃ / min under N2 atmosphere, keep for 1-3 hours, and remove unstable metal particles by acid washing to obtain Ni1Co1NC catalyst.

[0027] The density of bimetallic monatomic sites is controlled by adjusting the molar ratio of Ni / Co (1:1-1:3), and the metal-nitrogen coordination structure is optimized.

[0028] The Ni-Co bimetallic monatomic catalyst is applied to the reaction of catalytic electrochemical reduction of carbon dioxide to synthesize CO and H2 mixed gas, to regulate the rigidity of the interface water hydrogen bond network, to balance the activation kinetics of CO2 and H2O, and to inhibit the side reactions under industrial current density.

[0029] A preparation method of an electrochemical carbon dioxide reduction reaction for synthesizing a CO and H2 mixed gas, using the above-mentioned catalyst as a cathode, an anode electrolyte being 0.05M K2SO4, pH=1, and a cathode being supplied with humidified CO2 gas, in an acidic proton exchange membrane electrolyzer, a full cell voltage being ≤3.5V, and a current density being 50-400mA / cm 2 The CO2 and H2O are converted into a synthesis gas with an adjustable CO / H2 ratio.

[0030] The CO / H2 ratio is regulated by the current density, and when the current density is 250mA / cm 2 , the CO / H2=1:1, and when the current density is 350mA / cm 2 , the CO / H2=0.5:1.

[0031] Example 2 A preparation method of a Ni-Co double-atomic catalyst, comprising the following steps: Step 1, dissolving a Ni salt (Ni(NO3)2) and a Co salt (Co(NO3)2) solution with polyacrylamide (PAM) gel as a carbon source and cyanuric acid as a nitrogen source, and forming a Ni / Co-PAM aerogel through freeze-drying.

[0032] Step 2, heating to 900℃ at 5℃ / min under N2 atmosphere, keeping for 1 hour, and removing unstable metal particles through acid washing to obtain a Ni1Co1NC catalyst.

[0033] The double-atomic site density is controlled by adjusting the Ni / Co molar ratio (1:1), and the metal-nitrogen coordination structure is optimized.

[0034] The catalyst prepared in Example 2 is subjected to performance testing, and the test results show that in a PEM electrolyzer, when the current density is 250mA / cm 2 , the CO / H2=1:1, the cell voltage is 2.8V, and the continuous operation lasts for 120 hours without attenuation.

[0035] Example 3 A preparation method of a Ni-Co double-atomic catalyst, comprising the following steps: Step 1, dissolving a Ni salt (Ni(NO3)2) and a Co salt (Co(NO3)2) solution with polyacrylamide (PAM) gel as a carbon source and cyanuric acid as a nitrogen source, and forming a Ni / Co-PAM aerogel through freeze-drying.

[0036] Step 2, heating to 950℃ at 8℃ / min under N2 atmosphere, keeping for 2 hours, and removing unstable metal particles through acid washing to obtain a Ni1Co1NC catalyst.

[0037] The density of double-atomic sites was controlled by adjusting the molar ratio of Ni / Co (1:2), and the metal-nitrogen coordination structure was optimized.

[0038] The catalyst prepared in Example 3 was tested for performance, and the test results were as follows: current density 350 mA / cm 2 at CO / H2=0.5:1, FE_CO=62%, FE_H2=38%.

[0039] Example 4 The preparation method of the Ni-Co double-atomic catalyst comprises the following steps: Step 1: Dissolve Ni salt (Ni(NO3)2) and Co salt (Co(NO3)2) solution with polyacrylamide (PAM) gel as a carbon source and cyanuric acid as a nitrogen source; and form a Ni / Co-PAM aerogel by freeze-drying.

[0040] Step 2: Heat to 1000℃ at 3℃ / min under N2 atmosphere, and keep for 3 hours; and remove unstable metal particles by acid washing to obtain a Ni1Co1NC catalyst.

[0041] The density of double-atomic sites was controlled by adjusting the molar ratio of Ni / Co (1:3), and the metal-nitrogen coordination structure was optimized.

[0042] The catalyst prepared in Example 4 was tested for performance, and the test results were as follows: current density 400 mA / cm 2 at CO / H2=0.3:1, which meets the requirement of methanol synthesis, and the cell voltage is 3.2V.

[0043] Figure 1 HAADF-STEM image and EDS element distribution map of Ni1Co1NC; Figure 1 A is a low-resolution HAADF-STEM image, Figure 1 B is a corresponding EDS spectrum, and C, Cl, Ni and Co elements are uniformly distributed.

[0044] Figure 2The figure shows the CO / H2 ratio as a function of current density in the PEM electrolyzer. Notably, the HER activity of the Co-N4 group in Ni1Co1NC is significantly lower than that in Co1NC, as evidenced by the significant difference in their jH2 values ​​at different potentials. However, both Ni1Co1NC and Co1NC exhibit similar jCO values ​​within the potential window of -0.4 to -0.7 V vs. RHE, indicating that the Ni-N4 group in Ni1Co1NC and Co1NC has roughly the same activity for CO2 to CO conversion. Compared to Co1NC, the HER activity of the single-atom Co site in Ni1Co1NC is reduced, thus optimizing the CO / H2 ratio of the syngas generated on Ni1Co1NC, resulting in CO / H2 ratios of 0.5:1, 1:1, and 1.5:1 for the syngas generated at -0.4, -0.5, and -0.7 V vs. RHE, respectively.

[0045] Figure 3 Long-term stability tests were performed on Ni1Co1NC at -0.5V vs. RHE. Figure 3 The long-term stability test verified the stability of Ni1Co1NC in continuously producing syngas with a CO / H2 ratio of approximately 1:1.

[0046] Figure 4 Performance evaluation of the conversion of acidic ECO2R from Ni1Co1NC to syngas in a MEA electrolyzer. Figure 4 In the diagram, 'a' represents the overall schematic diagram of the MEA electrolyzer. Figure 4 Figure b is a disassembly diagram of the MEA electrolyzer. Figure 5 100mAcm -2 Long-term stability of Ni1Co1NC in the acid feed MEA. Figure 6 This is a performance comparison of Ni1Co1NC with electrocatalysts used in long-term syngas production.

[0047] Evaluation of the potential of Ni1Co1NC in producing industrial-grade syngas in an acidified MEA electrolyzer ( Figure 4 a, Figure 4 (b) In this method, 0.05M K₂SO₄ (pH=1, adjusted with concentrated sulfuric acid) was selected as the anode electrolyte, and humidified CO₂ was used as the feedstock for syngas production. Industrial-grade current densities of 250 and 350 mA / cm⁻¹ were used. -2 At this temperature, the CO / H2 ratio in the syngas reaches 1:1 and 0.5:1, respectively, meeting the requirements for industrial production of aldehydes, alcohols, and Fischer-Tropsch synthetic liquid fuels. At 100 mA / cm²... -2 After 120 hours of continuous electrolysis, the CO / H2 ratio in the generated syngas remained consistently around 2.5:1, further confirming the long-term stability of Ni1Co1NC in the electrosynthesis of syngas with the target CO / H2 ratio. Figure 5 ).Figure 6 A performance comparison of Ni1Co1NC with other reported electrocatalysts for syngas production shows that Ni1Co1NC exhibits good stability during long-term electrolysis in H-type cells and MEA electrolyzers.

[0048] Therefore, this invention employs the aforementioned Ni-Co dual single-atom catalyst, its preparation method, and its application. The catalyst independently regulates the CO2-to-CO conversion and hydrogen evolution reaction (HER) through the dual active sites of Ni-N4 and Co-N4, achieving a precisely adjustable CO / H2 ratio within the range of 0.3:1 to 2.5:1. The catalyst operates stably for over 120 hours in an acidic proton exchange membrane (PEM) electrolyzer, meeting the requirements for industrial applications. It operates at an industrial-grade current density (350 mA / cm²). 2 Under these conditions, the CO Faradaic efficiency (FE_CO) reaches 65%, the H2 Faradaic efficiency (FE_H2) reaches 35%, and the CO / H2 ratio is 0.5:1, meeting the requirements for Fischer-Tropsch synthesis. Stability tests show that the CO / H2 ratio fluctuates by less than 5% over 120 hours. The defective structure of the carbon support inhibits metal aggregation, and the activity retention is >90% after 1000 cycles.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A Ni-Co dual single-atom catalyst, characterized in that: The catalyst comprises a carbon support, atomically dispersed Ni single atoms anchored to the carbon support in a Ni-N4 configuration, and atomically dispersed Co single atoms anchored to the carbon support in a Co-N4 configuration. There are no metal-metal bonds in the catalyst.

2. The Ni-Co dual single-atom catalyst according to claim 1, characterized in that: The molar ratio of Ni to Co is 1:1 to 1:

3.

3. The Ni-Co dual single-atom catalyst according to claim 1, characterized in that: The carbon support is nitrogen-doped porous carbon with a specific surface area ≥800 m². 2 / g, pore size distribution 2-5nm.

4. The method for preparing the Ni-Co dual single-atom catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Mix Ni salt and Co salt with polyacrylamide gel and cyanuric acid, and freeze-dry to obtain the precursor; Step 2: Pyrolysis is performed under an inert atmosphere at a temperature of 800-1000℃, followed by acid washing to obtain the catalyst.

5. The method for preparing the Ni-Co dual single-atom catalyst according to claim 4, characterized in that: In step 1, the Ni salt is Ni(NO3)2 and the Co salt is Co(NO3)2.

6. The method for preparing the Ni-Co dual single-atom catalyst according to claim 4, characterized in that: In step 2, the inert atmosphere is nitrogen, the heating rate is 2-10℃ / min, and the holding time is 1-3h.

7. The application of the Ni-Co dual single-atom catalyst according to any one of claims 1-3, characterized in that: It is applied to the catalytic electrochemical carbon dioxide reduction reaction to synthesize a mixture of CO and H2 gas, thereby regulating the rigidity of the interfacial water hydrogen bond network, balancing the activation kinetics of CO2 and H2O, and suppressing side reactions at industrial-grade current densities.

8. A method for preparing a mixture of CO and H2 gas by electrochemical carbon dioxide reduction reaction, characterized in that: Using the catalyst as described in any one of claims 1-3 as the cathode, the anolyte is 0.05M K2SO4 with pH=1, and humidified CO2 gas is introduced through the cathode, in an acidic proton exchange membrane electrolyzer, when the full cell voltage is ≤3.5V, the current density is 50-400 mA / cm². 2 The process converts CO2 and H2O into syngas with an adjustable CO / H2 ratio.

9. The method for preparing a mixture of CO and H2 gas by electrochemical carbon dioxide reduction reaction according to claim 8, characterized in that: The CO / H2 ratio is controlled by the current density, which is 250 mA / cm². 2 At that time, CO / H2 = 1:1, and the current density is 350 mA / cm². 2 At that time, CO / H2 = 0.5:1.

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