Nickel monatomic electrocatalyst with surface cavity structure and preparation method and application thereof

Abstract

The application belongs to the field of catalysts, and particularly relates to a nickel monatomic electrocatalyst with a surface hollow structure and a preparation method and application thereof. The preparation method comprises the following steps: 1) preparing a metal organic framework Mn@ZIF-8; 2) preparing a metal organic framework Ni / Mn@ZIF-8; and 3) calcining to obtain the nickel monatomic electrocatalyst with a surface hollow structure. The application adopts a double-solvent impregnation method to load Ni on Mn@ZIF-8, and by means of the effect of intensifying the Kirkendall effect of trace Mn in a pyrolysis process, uneven mutual diffusion between Zn 2+ , Ni 2+ and Mn 2+ occurs, Zn 2+ inside ZIF-8 continuously diffuses outward and volatilizes, Ni 2+ in the body is gradually captured by adjacent nitrogen-deficient defects, and a nickel monatomic catalyst with a surface hollow structure and high loading capacity is formed.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to a nickel single-atom electrocatalyst with a surface void structure, its preparation method, and its application. Background Technology

[0002] The use of fossil fuels underpins the global economy, but it also causes massive carbon dioxide emissions, disrupting the natural carbon balance and triggering a series of energy and environmental problems. Electrocatalytic carbon dioxide reduction technology uses electricity to convert carbon dioxide into chemical feedstocks and fuels, effectively replacing some traditional fossil fuels. This not only helps optimize the energy structure but also reduces environmental pollution, providing a new approach to the development of a low-carbon economy.

[0003] Among the many products, the conversion of CO2 to CO exhibits high selectivity (approaching 100%), low power and separation costs, and high technical and economic feasibility, thus being considered the closest pathway to large-scale industrialization. To date, numerous electrocatalysts for CO production have been extensively explored, including those based on noble metals, alloys, and metal oxides. However, they still suffer from problems such as high cost, low bias current density, severe hydrogen evolution reaction, and poor stability. Therefore, it is necessary to develop electrocatalysts with superior overall performance.

[0004] Among numerous materials, atomically dispersed transition metal and nitrogen-doped carbon materials (MNCs) exhibit impressive activity in catalysis due to their low cost, tunable coordination environment, and maximized atom utilization. Metal-organic frameworks (MOFs), as unique crystals constructed from metal nodes and organic ligands, possess tunable structures and compositions, and are considered ideal sacrificial templates for constructing atomically dispersed carbon-based materials. In particular, ZIF-8-based MOFs serve as common precursors for constructing MNC materials. During pyrolysis, the organic imidazole ligands are converted into nitrogen-doped graphitic carbon to anchor the metal atoms, while the low-boiling-point zinc nodes can be evaporated and removed.

[0005] However, MNC materials still have certain shortcomings. On the one hand, the intrinsic activity of single-metal active sites synthesized by simple pyrolysis methods cannot be fully activated. To improve the intrinsic activity of active sites, numerous strategies have been developed to modify the electronic microenvironment of the active metal center, such as introducing a second metal element to prepare diatomic catalysts or introducing a second non-metal element to regulate the activity of metal active sites. On the other hand, traditional pyrolysis strategies for synthesizing MNC materials mainly result in micropores, with most metal active sites deeply buried in the carbon substrate and unable to be exposed. This severely limits the accessibility of reactants to active sites, as well as mass transport and electron transfer. To address this issue, many researchers have employed various soft and hard template methods and molten salt methods to prepare layered porous carbon-supported single-atom catalysts. While these strategies effectively improve the electrocatalytic activity of MNC catalysts, introducing heteroatoms requires selecting appropriate methods and strictly controlling their loading, while the pore-forming process involves tedious and delicate synthetic steps. These strategies undoubtedly increase the difficulty and workload of synthesis. Therefore, developing a simple synthetic strategy that can both enhance the intrinsic activity of metal sites and increase the exposure rate of active sites, thus achieving the dual benefits, is worthy of attention. Summary of the Invention

[0006] The purpose of this invention is to provide a nickel single-atom electrocatalyst with a surface void structure, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a nickel single-atom electrocatalyst with a surface void structure includes the following steps: 1) preparing a metal-organic framework Mn@ZIF-8; 2) preparing a metal-organic framework Ni / Mn@ZIF-8; 3) calcining to obtain a nickel single-atom electrocatalyst with a surface void structure.

[0008] The specific steps of step 1) are as follows: a mixture of soluble Zn salt and soluble Mn salt is added to the ligand solution and then dried to obtain the product; Preferably, the molar ratio of the soluble Zn salt, the soluble Mn salt, and the ligand is 1:(0.04-0.16):(2-8); more preferably, it is 1:0.04:4.

[0009] The soluble Zn salt is zinc nitrate hexahydrate; the soluble Mn salt is manganese acetate tetrahydrate; the ligand is 2-methylimidazolium; preferably, the solvent for the mixture of the soluble Zn salt and the soluble Mn salt and the ligand solution is methanol.

[0010] The specific steps of step 2) are as follows: disperse the Mn@ZIF-8 obtained in step 1) in an organic solvent, add soluble Ni salt, and then dry. Preferably, the mass ratio of Mn@ZIF-8 to soluble Ni salt is 50:(0.5-2); more preferably, it is 50:1.5.

[0011] The soluble Ni salt is a nickel nitrate hexahydrate solution; the organic solvent is n-hexane.

[0012] The specific steps of step 3) are as follows: The Ni / Mn@ZIF-8 sample is calcined in a tube furnace at 810℃~1010℃ under high temperature argon gas for 1~2h, the heating rate is 1~5℃ / min, and the argon gas flow rate is 150mL / min.

[0013] The present invention also includes a nickel single-atom electrocatalyst with a surface void structure obtained by the preparation method described above.

[0014] The particle size distribution is 200–400 nm.

[0015] The present invention also includes the application of the aforementioned nickel single-atom electrocatalyst with a surface void structure, specifically for the electrocatalytic reduction of carbon dioxide.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a dual-solvent impregnation method to load Ni onto ZIF-8, utilizing the Zn during pyrolysis. 2+ with Ni 2+ The Kirkendall effect that occurs between them, and the Zn inside ZIF-8 2+ Ni continuously diffuses and volatilizes outwards within the body. 2+ Gradually captured by nearby nitrogen-rich defects, it forms a highly loaded nickel single-atom catalyst.

[0017] This invention uses Ni-loaded 2+ Previously, a host-guest strategy was used to encapsulate manganese acetate tetrahydrate molecules in a cage-like structure of ZIF-8. During pyrolysis, due to the presence of a small amount of larger-radius Mn in the framework... 2+ The existence of Zn 2+ Mn 2+ and Ni 2+ The presence of an uneven interdiffusion interface among the three elements exacerbates the Kirkendall effect. The solid polyhedral structure is gradually hollowed out through this uneven interdiffusion, forming a Ni material with a porous and wrinkled surface, abundant mesopores, high specific surface area, and high electrochemical active area. Mn -NC nickel single-atom catalyst, with particle size mainly distributed in the range of 200-400nm.

[0018] The process of this invention is simple and easy to operate. A high-load single-atom catalyst is directly generated by one-step pyrolysis without further acid washing. Only a small amount of Mn is added during the synthesis process to achieve the effect of amplifying the Kirkendall effect, which is suitable for large-scale industrial production. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the metal-organic framework nanoparticles Mn@ZIF-8 obtained in Example 1; Figure 2 Ni obtained in Example 1 Mn - Scanning electron microscope image of NC material; Figure 3 Here is a scanning electron microscope image of the Ni-NC material obtained in Comparative Example 1; Figure 4 NC obtained in Comparative Example 2 Mn Scanning electron microscope image of the material; Figure 5 Here is a scanning electron microscope image of the NC material obtained in Comparative Example 3; Figure 6 Ni obtained in Example 1 Mn - Transmission electron microscope image of NC material; Figure 7 The image shows a transmission electron microscope (TEM) image of the Ni-NC material obtained in Comparative Example 1. Figure 8 NC obtained in Comparative Example 2 Mn Transmission electron microscope image of the material; Figure 9 The image shows a transmission electron microscope (TEM) image of the NC material obtained in Comparative Example 3. Figure 10 The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn XRD crystal diffraction pattern of NC material; Figure 11 The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn N2 adsorption-desorption curves (a) and corresponding pore size distribution curves (b) of NC materials; Figure 12 The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn Linear sweep voltammetry curves of NC materials in a carbon dioxide-saturated 0.5 M KHCO3 solution; Figure 13The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn Double-layer capacitance diagram of NC materials; Figure 14 The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn The CO Faraday efficiency of NC materials at different potentials; Figure 15 The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn The bias current density curve of NC material; Figure 16 Ni with different amounts of Mn Ac- - Electrocatalytic carbon dioxide reduction activity test diagram of NC material; (a) CO Faraday efficiency diagram; (b) LSV curve diagram; (c) CO bias current density diagram; Figure 17 The Ni obtained in Examples 1, 5 and Comparative Example 1 Mn -NC, Ni Ac Electrocatalytic carbon dioxide reduction activity test diagrams for samples of -NC, Ni-NC, and; (a) CO Faradaic efficiency diagram; (b) LSV curve diagram; (c) CO bias current density diagram. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0021] Example 1: A method for preparing a nickel single-atom electrocatalyst with a surface void structure, comprising the following steps:

[0022] 1) 2.94 g of zinc nitrate hexahydrate and 0.098 g of manganese acetate tetrahydrate were uniformly dispersed in 80 mL of methanol solution and stirred for 20 min to obtain a mixture of soluble Zn and Mn salts; 3.24 g of 2-methylimidazole was uniformly dispersed in 80 mL of methanol solution and stirred for 20 min to obtain a ligand solution; the mixture of soluble Zn and Mn salts was added to the ligand solution and stirred continuously for 5 h. After centrifugation, the mixture was dried in a vacuum drying oven at 60 °C to obtain the metal-organic framework Mn@ZIF-8. (See [link to relevant documentation]). Figure 1 The scanning electron microscope (SEM) image of the obtained metallic framework nanoparticles shows their monodisperse dodecahedral structure. (See also...) Figure 6The transmission electron microscope (TEM) images of the obtained metal framework nanoparticles show a rhombic dodecahedral structure with numerous voids and collapses on the surface, and no metal nanoparticles are visible in the field of view.

[0023] 2) Disperse 0.25g of the metal-organic framework Mn@ZIF-8 in 30mL of n-hexane solution, sonicate for 20min at room temperature, and add 300μL of 25mg / mL solution. -1 The nickel nitrate hexahydrate solution was stirred for 1 hour, centrifuged, and dried in a vacuum drying oven at 60°C to obtain the metal-organic framework Ni / Mn@ZIF-8.

[0024] 3) The sample from Ni / Mn@ZIF-8 was collected and transferred to a ceramic boat, and then calcined in a tube furnace at 910℃ under argon atmosphere for 2 hours. The heating rate was 5℃ / min, and the argon flow rate was 150 mL / min. After the reaction, a nickel single-atom electrocatalyst with a surface void structure was obtained, denoted as 0.4-Ni. Mn -NC single-atom catalyst. Figure 2 The 0.4-Ni obtained in Example 1 Mn -The scanning electron microscope image of the NC material shows that it collapses on the basis of the original rhombic dodecahedral morphology, producing more wrinkles; Figure 6 The 0.4-Ni obtained in Example 1 Mn The transmission electron microscope image of the -NC material shows a rhombic dodecahedral structure with numerous voids and collapses on the surface, and no metal nanoparticles are visible in the field of view.

[0025] Example 2: The difference between Example 2 and Example 1 is that the amount of manganese acetate tetrahydrate added in step 1) is changed to 0.196g (0.8mmol), while the rest remains the same, denoted as 0.8-Ni. Mn -NC single-atom catalyst.

[0026] Example 3: The difference between Example 3 and Example 1 is that the amount of manganese acetate tetrahydrate added in step 1) is changed to 0.294 g (1.2 mmol), while the rest remains the same, denoted as 1.2-Ni. Mn -NC single-atom catalyst.

[0027] Example 4: The difference between Example 4 and Example 1 is that the amount of manganese acetate tetrahydrate added in step 1) is changed to 0.392 g (1.6 mmol), while the rest remains the same, denoted as 1.6-Ni. Mn -NC single-atom catalyst.

[0028] To verify the universality of improving electrocatalytic activity by forming surface-void nickel single-atom catalysts after Mn addition, we synthesized several X-Ni catalysts with different amounts of manganese addition. Mn-NC materials (X=0.4, 0.8, 1.2, 1.6 mmol).

[0029] We tested the electrocatalytic carbon dioxide reduction activity of this series of samples with different Mn addition amounts, see reference. Figure 16 The results showed that X-Ni with different amounts of Mn added... Mn -NC materials exhibit similar CO selectivity at different sites, but X-Ni with added Mn shows... Mn -NC showed a significant increase in CO bias current density at all potentials compared to the control without Mn.

[0030] Example 5: The preparation process follows the steps of Example 1, except that in step 1), manganese acetate tetrahydrate is replaced with the same molar amount of zinc acetate dihydrate, while the rest remains unchanged. This is denoted as Ni. AC- -NC single-atom catalyst.

[0031] To further demonstrate the role of Mn, a host-guest strategy and a dual-solvent method were combined with a one-step thermal decomposition to synthesize Ni. AC- Using a single-atom catalyst (NC), eliminating the influence of acetate ions in the reagents used, and identifying the role of Mn, we employed the same method, replacing manganese acetate tetrahydrate with the same molar amount of zinc acetate dihydrate, to synthesize Ni. Ac- -NC material, and then we tested its electrocatalytic carbon dioxide reduction activity, see reference. Figure 17 The results show that Ni Ac- The LSV curves of -NC and Ni-NC almost overlap, while Ni Ac- The bias current density of CO in -NC is also similar to that in Ni-NC, and significantly smaller than that in Ni. Mn -NC indicates that the catalyst performance was not improved after replacing manganese acetate tetrahydrate with zinc acetate dihydrate, thus ruling out the influence of acetate ions and proving to some extent the role of the introduction of Mn element in improving catalyst performance.

[0032] Comparative Example 1: A Ni-NC catalyst was obtained by a dual-solvent impregnation method followed by one-step pyrolysis. The preparation process followed the steps of Example 1, except that manganese acetate tetrahydrate was not added in step 1. See [link to example]. Figure 3 The scanning electron microscope (SEM) images of the obtained Ni-NC material reveal a contracted, sharply defined rhombic dodecahedral structure. (See also...) Figure 7 As can be seen from the transmission electron microscope image of the Ni-NC material obtained in this embodiment, the shrinking, angular, solid rhombic dodecahedral structure can be observed, and the pores remaining on the carbon substrate after Zn volatilization can also be seen.

[0033] Comparative Example 2: Obtaining NC using a one-step pyrolysis method MnThe catalyst was prepared according to the steps of Example 1, but step 2) of adding nickel nitrate was omitted; that is, the metal-organic framework Mn@ZIF-8 was directly added to a tube furnace for calcination. (See also...) Figure 4 The obtained N Mn Scanning electron microscope (SEM) images of the -C material reveal a uniform rhombic dodecahedral structure. (See also: [reference needed]) Figure 8 The NC obtained in this embodiment Mn Transmission electron microscopy (TEM) images of the materials show that all samples exhibit a uniform, dodecahedral rhombic structure, consistent with scanning electron microscopy. Comparison reveals that the formation of the surface void structure requires the simultaneous presence of both Ni and Mn elements; the addition of Mn exacerbates the Kirkendall effect.

[0034] Comparative Example 3: NC catalyst was obtained using a one-step pyrolysis method. The preparation process followed the steps of Example 1, but manganese acetate tetrahydrate was not added in step 1), and the nickel nitrate step in step 2) was omitted. See [link to example]. Figure 4 The obtained scanning electron microscope (SEM) images of the NC material show its monodisperse dodecahedral structure. (See also...) Figure 9 As can be seen from the transmission electron microscope image of the NC material obtained in this embodiment, a solid rhombic dodecahedral structure can be observed, which is consistent with the scanning electron microscope image.

[0035] Figure 10 The Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn The XRD crystal diffraction patterns of the NC materials showed that the pyrolysis samples all exhibited two distinct broad diffraction peaks near 24° and 44°, which are attributed to the (002) and (101) crystal planes of the low-crystallinity graphitic carbon, respectively. Furthermore, no peaks of metallic phases or metal compounds were found in these catalysts, indicating that the doped metals can be highly dispersed at the atomic level.

[0036] Figure 11 Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn Ni2 adsorption / desorption curves (a) and corresponding pore size distribution curves (b) of NC materials. Mn -NC has a specific surface area of ​​800 m² 2 g -1 It is significantly larger than the specific surface area of ​​Ni-NC (689 m²). 2 g -1 Furthermore, compared to Ni-NC, Ni... MnThe pore size distribution of -NC highlights the presence of mesopores. The results indicate that the Kirkendall effect, exacerbated by the addition of a small amount of Mn, plays a crucial role in the high specific surface area and the formation of mesopores.

[0037] Figure 12 Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn Linear scan voltammetry curves of NC materials in a carbon dioxide-saturated 0.5M KHCO3 solution are shown. The scan potential window is 0 to -1.12V (vs. RHE), and the scan rate is 10mV / s. The figure shows that for Ni... Mn The cathode current density of the NC sample in a carbon dioxide-saturated electrolyte is much higher than that in an argon-saturated electrolyte, indicating that the cathode current mainly originates from the electrocatalytic reduction of carbon dioxide. Furthermore, a comparison of these four materials reveals that Ni... Mn -NC has a higher carbon dioxide response and higher intrinsic activity.

[0038] Figure 13 Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn The double-layer capacitance diagram of NC material shows that Ni Mn -NC has the largest double-layer capacitance value, which also represents the largest electrochemical active area, which to some extent proves that the addition of Mn enhances the exposure of electrochemical active sites.

[0039] Figure 14 Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC Mn The CO Faraday efficiency of the NC material at different potentials was investigated. The results showed that the introduction of Ni significantly improved the selectivity of the catalyst for CO, indicating that Ni is the main active site for CO2RR. Ni... Mn -NC exhibits superior CO selectivity in the -0.62 to -1.02 V vs. RHE range, with FECO above 90%, and a maximum FECO of 98.49% at -0.72 V vs. RHE. Compared to Ni-NC, Ni... Mn -NC shows improved Faraday efficiency at low potentials, possibly due to the introduction of Mn altering the chemical state of the material and thus lowering the reaction energy barrier.

[0040] Figure 15 Ni obtained in Example 1 and Comparative Examples 1-3 Mn -NC, Ni-NC, NC MnThe bias current density curves of NC materials show that: Ni Mn -NC has the largest Jco over the entire potential range (-0.52 to -1.12 V vs. RHE), reaching a maximum of 21.91 mA cm⁻¹ at -1.02 V vs. RHE. -2 It is Ni-NC (12.56 mA cm) -2 1.74 times that of Ni with surface voids formed after the introduction of trace amounts of Mn. Mn -NC materials J CO This greatly improves efficiency, enabling more efficient CO2 conversion per unit of time.

[0041] In summary, this invention employs a dual-solvent impregnation method to load Ni onto ZIF-8, utilizing the Zn during pyrolysis. 2+ with Ni 2+ The Kirkendall effect that occurs between them, and the Zn inside ZIF-8 2+ Ni continuously diffuses and volatilizes outwards within the body. 2+ Gradually captured by nearby nitrogen-rich defects, it forms a highly loaded nickel single-atom catalyst.

[0042] This invention uses Ni-loaded 2+ Previously, a host-guest strategy was used to encapsulate manganese acetate tetrahydrate molecules in a cage-like structure of ZIF-8. During pyrolysis, due to the presence of a small amount of larger-radius Mn in the framework... 2+ The existence of Zn 2+ Mn 2+ and Ni 2+ The presence of an uneven interdiffusion interface among the three elements exacerbates the Kirkendall effect. The solid polyhedral structure is gradually hollowed out through this uneven interdiffusion, forming a Ni material with a porous and wrinkled surface, abundant mesopores, high specific surface area, and high electrochemical active area. Mn -NC nickel single-atom catalyst, with particle size mainly distributed in the range of 200-400nm.

[0043] The process of this invention is simple and easy to operate. A high-load single-atom catalyst is directly generated by one-step pyrolysis without further acid washing. Only a small amount of Mn is added during the synthesis process to achieve the effect of amplifying the Kirkendall effect, which is suitable for large-scale industrial production.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel single-atom electrocatalyst with a surface void structure, characterized in that, The process includes the following steps: 1) Preparing a metal-organic framework Mn@ZIF-8; adding a mixture of soluble Zn salt and soluble Mn salt to a ligand solution and then drying to obtain the ligand; the molar ratio of the soluble Zn salt, soluble Mn salt and ligand is 1:(0.04-0.16):(2-8); 2) Preparation of metal-organic framework Ni / Mn@ZIF-8; The Mn@ZIF-8 obtained in step 1) is dispersed in an organic solvent, and a soluble Ni salt is added and then dried; The mass ratio of Mn@ZIF-8 to soluble Ni salt is 50:(0.5-2); 3) Calcination yields a nickel single-atom electrocatalyst with a surface void structure.

2. The method for preparing a nickel single-atom electrocatalyst with a surface void structure according to claim 1, characterized in that, The molar ratio of the soluble Zn salt, the soluble Mn salt, and the ligand is 1:0.04:

4.

3. The method for preparing a nickel single-atom electrocatalyst with a surface void structure according to claim 2, characterized in that, The soluble Zn salt is zinc nitrate hexahydrate; the soluble Mn salt is manganese acetate tetrahydrate; the ligand is 2-methylimidazolium; and the solvent for the mixture of the soluble Zn salt and the soluble Mn salt, as well as the ligand solution, is methanol.

4. The method for preparing the nickel single-atom electrocatalyst with a surface void structure according to claim 1, wherein the mass ratio of Mn@ZIF-8 to soluble Ni salt is 50:1.

5.

5. The method for preparing a nickel single-atom electrocatalyst with a surface void structure according to claim 4, wherein the soluble Ni salt is a nickel nitrate hexahydrate solution; and the organic solvent is n-hexane.

6. The preparation method of the nickel single-atom electrocatalyst with surface void structure according to claim 1, the specific steps of step 3) are as follows: the Ni / Mn@ZIF-8 sample is calcined in a tube furnace at 810℃~1010℃ under high temperature argon gas for 1~2h, the heating rate is 1~5℃ / min, and the argon gas flow rate is 150mL / min.

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