Application of nitrogen / halogen co-coordinated monatomic catalyst in water electrolysis oxygen evolution, nitrogen / halogen co-coordinated monatomic catalyst and preparation method of nitrogen / halogen co-coordinated monatomic catalyst

Abstract

The invention discloses application of a nitrogen / halogen co-coordinated monatomic catalyst in water electrolysis oxygen evolution, the nitrogen / halogen co-coordinated monatomic catalyst and a preparation method of the nitrogen / halogen co-coordinated monatomic catalyst, and belongs to the field of water electrolysis oxygen evolution. According to the technical scheme, the nitrogen / halogen co-coordinated monatomic catalyst is of a two-dimensional structure, and the molecular formula is M-N4X1; m is selected from metal elements, and X is selected from halogen elements. The preparation method is applied to the aspect of electrolyzed water oxygen evolution, solves the technical problem that an existing atom catalyst preparation method is uncontrollable and complex in process, so that the application of the atom catalyst as a catalyst is limited, and has the characteristics of high catalytic activity and controllable and adjustable loading capacity.

Description

Technical Field

[0001] The invention belongs to the field of oxygen evolution by water electrolysis, and in particular relates to an application of a nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis, a nitrogen / halogen co-coordinated single atom catalyst and a preparation method thereof. Background Art

[0002] In the context of the increasingly urgent fossil energy crisis, it is urgent to develop economical, efficient and environmentally friendly green energy technologies. Hydrogen energy is considered to be one of the next generation of green energy due to its high energy density and clean and pollution-free characteristics, but it also faces many challenges. As an important way to produce hydrogen energy, water electrolysis is composed of two half reactions: oxygen evolution reaction and hydrogen evolution reaction. Among them, the oxygen evolution reaction on the anode side involves a complex four-electron-proton coupling process, and its slow reaction kinetics seriously restrict the efficiency of hydrogen production by electrolysis. It is urgent to develop efficient catalysts to achieve low-barrier conversion of oxygen evolution reaction.

[0003] As one of the most promising research frontiers in the field of catalysis, single-atom catalysts (SACs) have attracted much attention due to their unique catalytic performance, ultra-high atom efficiency, and interesting structure-activity relationships. Metal single atoms (M) have extremely high surface energy, are easy to migrate and agglomerate, and usually have poor thermodynamic stability. In most cases, the central metal atom of a single-atom catalyst is firmly attached to the support material by coordinating with four N atoms to construct an M-N4 configuration to improve stability. However, the high electronic / structural symmetry of the M-N4 site is not conducive to charge transfer during the oxygen evolution reaction in water electrolysis, hindering the further performance optimization of MNC single-atom catalysts. Recently, many studies have been devoted to the incorporation of non-nitrogen (O, P, S, Cl, etc.) atoms to improve the catalytic activity of M-N4 for various chemical and electrochemical reactions. Due to the different electronegativity and atomic radius of N atoms, the introduction of heteroatoms can effectively regulate the electronic and geometric structures of the central metal atom, thereby affecting its adsorption behavior and catalytic performance. For example, Huang Minghua's team prepared a Co single-atom catalyst containing a Co-N3P1 active site through a two-step method, which achieved unprecedented catalytic activity in the electrolytic water oxygen evolution reaction [Adv.Mater.2022,34,2204021]. However, the introduction of P atoms inevitably changes the properties of the carrier, and because it involves a high-temperature pyrolysis process, the metal single atoms are very easy to agglomerate and the loading amount is usually very low, which is not conducive to the improvement of catalytic activity. Patent CN115491713A discloses a method for preparing a Cl-doped Ni-NC single-atom material, which exhibits excellent electrocatalytic performance in a CO2 reduction test. This strategy uses expensive metal-organic complexes and cannot controllably establish direct bonding between metal and chlorine, which is not conducive to the development of low-cost single-atom catalysts with controllable coordination environments. Patent CN117380274A discloses a single-atom iron nanozyme with axial coordination of chlorine atoms and a preparation method thereof, wherein the introduction of chlorine atoms significantly improves the catalytic activity of the Fe enzyme center. The above research demonstrates the advanced nature of optimizing single-atom catalytic activity through halogen atoms, but there is still a lack of low-cost, simple, controllable and universal preparation processes.

[0004] Here, we provide a nitrogen coordination-programmed temperature control strategy that can efficiently and controllably prepare nitrogen-halogen co-coordinated single-atom materials with adjustable metal loading, and provide applications of this material in the field of electrocatalytic water desorption and oxygen extraction. Summary of the invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to alleviate the technical problem that the existing atomic catalyst preparation method is uncontrollable and the process is complicated, thereby limiting its application as a catalyst. A nitrogen / halogen co-coordinated single atom catalyst with high catalytic activity and controllable loading is proposed for use in oxygen evolution by electrolysis of water, a nitrogen / halogen co-coordinated single atom catalyst and a preparation method thereof.

[0006] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0007] On one hand, the present invention discloses an application of a nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis. The nitrogen / halogen co-coordinated single atom catalyst has a two-dimensional structure and a molecular formula of M-N4X1; the M is selected from metal elements, and the X is selected from halogen elements.

[0008] Another aspect of the present invention discloses a nitrogen / halogen co-coordinated single atom catalyst, which is used for the application of the nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis.

[0009] The present invention also discloses a method for preparing the nitrogen / halogen co-coordinated single atom catalyst, comprising a nitrogen-containing metal single atom carrier preparation step, a second carrier preparation step, and a nitrogen / halogen co-coordinated single atom catalyst preparation step;

[0010] The preparation step of the nitrogen metal single atom carrier comprises: mixing a carbon source, a nitrogen source and a metal molten salt uniformly and then calcining under a protective atmosphere to obtain the nitrogen metal single atom carrier; the carbon source is selected from at least one of polyacrylonitrile, petroleum asphalt, FCC slurry oil, vacuum residue oil and formaldehyde resin;

[0011] The preparation steps of the nitrogen / halogen co-coordinated single atom catalyst include: calcining the second carrier in a protective atmosphere, the calcination temperature is 200-600°C, the calcination time is 3-12h, and the heating rate during calcination is 0.5-5°C / min.

[0012] Preferably, the second carrier preparation step comprises: mixing the nitrogen metal single atom carrier, metal halide and solvent, and separating them to obtain the second carrier.

[0013] Preferably, the molten metal salt is selected from any one of potassium chloride, sodium chloride, magnesium chloride, and calcium chloride, or a combination of at least two of them; the metal halide is selected from any one of chromium halide, manganese halide, iron halide, nickel halide, copper halide, zinc halide, ruthenium halide, and palladium halide.

[0014] Preferably, the metal molten salt is selected from potassium chloride and sodium chloride; the metal halide is selected from nickel halide; and the nitrogen source is selected from urea.

[0015] Preferably, the mass ratio of the carbon source, the nitrogen source and the metal molten salt is (0.1-1):(0.1-4):(0.1-30).

[0016] Preferably, the mass ratio of the nitrogen metal single atom carrier, the metal halide and the solvent is (0.1-1):(0.1-1):(10-100).

[0017] Preferably, in the step of preparing the nitrogen metal single atom carrier, the calcination conditions for uniformly mixing the carbon source, the nitrogen source and the metal molten salt and then calcining under a protective atmosphere are: calcination temperature is 600-1200°C, calcination time is 1-6h, and the heating rate during calcination is 2-15°C / min.

[0018] Preferably, in the second carrier preparation step, the solvent includes any one or a combination of at least two of deionized water, methanol, ethanol, propanol, toluene, acetone, n-hexane, cyclohexane and N,N-dimethylformamide; the mixing temperature is selected from 10-100°C, and the mixing time is selected from 2-24h.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention discloses an application of a nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis. By limiting the structure and composition of the nitrogen / halogen co-coordinated single atom catalyst, the application of the nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis is achieved while ensuring the catalytic activity.

[0021] The invention discloses a method for preparing a nitrogen / halogen co-coordinated single-atom catalyst. A nitrogen-containing metal single-atom carrier is first synthesized, and the nitrogen content is adjustable within the range of 0-30%. The abundant nitrogen element in the carrier can ensure the formation of metal-nitrogen coordination. At the same time, the metal molten salt used can significantly increase the specific surface area of ​​the carrier, so that the nitrogen anchoring points can be fully exposed, which is beneficial to increasing the metal single-atom loading amount. In addition, by controlling the heating rate and the insulation time, part of the metal-halogen bonds in the metal halide are selectively broken and anchored by the nitrogen element in the carrier. This method can ensure the synthesis of nitrogen / halogen co-coordinated metal single atoms, and the metal single-atom loading amount can be adjusted within the range of 0-20%. Importantly, this method does not require the subsequent step of pickling to remove metal agglomerates, and has the characteristics of high controllability, simple process and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The X-ray diffraction pattern of the nitrogen-chlorine co-coordinated single atom catalyst provided in Example 1-2 of the present invention;

[0023] Figure 2X-ray diffraction patterns of the nitrogen-halogen co-coordinated single-atom catalysts provided in Examples 1 and 4-6 of the present invention;

[0024] Figure 3 A high-angle annular dark field image-scanning transmission electron microscope image of the nitrogen-chlorine co-coordinated metal single atom catalyst provided in Example 7 of the present invention;

[0025] Figure 4 A high-angle annular dark field image-scanning transmission electron microscope image of the nitrogen-chlorine co-coordinated metal single atom catalyst provided in Example 8 of the present invention;

[0026] Figure 5 A high-angle annular dark field image-scanning transmission electron microscope image of the nitrogen-chlorine co-coordinated metal single atom catalyst provided in Example 10 of the present invention;

[0027] Figure 6 A high-angle annular dark field image-scanning transmission electron microscope image of the nitrogen-chlorine co-coordinated metal single atom catalyst provided in Example 11 of the present invention;

[0028] Figure 7 The X-ray photoelectron spectrum of the nitrogen-chlorine co-coordinated metal single atom catalyst provided in Example 8 of the present invention;

[0029] Figure 8 A scanning electron microscope image of the nitrogen-chlorine co-coordinated metal single atom catalyst provided in Example 9 of the present invention;

[0030] Fig. 9 X-ray photoelectron spectrum of the metal single atom catalyst provided in Comparative Example 2 of the present invention;

[0031] Fig.10 This is a high-angle annular dark field image-scanning transmission electron microscope image of the metal single-atom catalyst provided in Comparative Example 2 of the present invention;

[0032] Fig.11 The performance diagram of the metal single atom catalyst obtained in Examples 1, 4, 5, and 6 for electrocatalytic water decomposition of oxygen;

[0033] Fig.12 The performance diagram of the metal single-atom catalyst obtained in Examples 1, 7, and 8 for electrocatalytic water decomposition of oxygen;

[0034] Fig.13 This is a performance diagram of the metal single-atom catalyst obtained in Example 1 and Comparative Example 3 for electrocatalytic water decomposition of oxygen. DETAILED DESCRIPTION

[0035] The technical scheme in the specific embodiment of the present invention is described in detail and completely below. Obviously, the described embodiment is only a part of the specific implementation of the overall technical scheme of the present invention, rather than all the implementations. Based on the overall concept of the present invention, all other embodiments obtained by ordinary technicians in this field fall within the scope of protection of the present invention.

[0036] On the one hand, the present invention discloses an application of a nitrogen / halogen co-coordinated single atom catalyst in electrolysis of water for oxygen evolution, wherein the nitrogen / halogen co-coordinated single atom catalyst is a two-dimensional structure with a molecular formula of M-N4X1; the M is selected from a metal element, and the X is selected from a halogen element. By limiting the structure and composition of the nitrogen / halogen co-coordinated single atom catalyst, the application of the nitrogen / halogen co-coordinated single atom catalyst in electrolysis of water for oxygen evolution is achieved, while ensuring the catalytic activity. Preferably, M is selected from nickel (using nickel as a metal element can further improve the catalytic activity of the catalyst in electrochemical oxygen production), and X is selected from chlorine.

[0037] Another aspect of the present invention discloses a nitrogen / halogen co-coordinated single atom catalyst, which is used for the application of the nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis.

[0038] The present invention also discloses a method for preparing the nitrogen / halogen co-coordinated single atom catalyst, comprising a nitrogen-containing metal single atom carrier preparation step, a second carrier preparation step, and a nitrogen / halogen co-coordinated single atom catalyst preparation step;

[0039] The preparation step of the nitrogen metal single atom carrier comprises: mixing a carbon source, a nitrogen source and a metal molten salt uniformly and then calcining under a protective atmosphere to obtain the nitrogen metal single atom carrier; the carbon source is selected from at least one of polyacrylonitrile, petroleum asphalt, FCC slurry oil, vacuum residue oil and formaldehyde resin;

[0040] The preparation steps of the nitrogen / halogen co-coordinated single atom catalyst include: calcining the second carrier in a protective atmosphere, the calcination temperature is 200-600°C, the calcination time is 3-12h, and the heating rate during calcination is 0.5-5°C / min.

[0041] The above method first synthesizes a nitrogen-containing metal single atom carrier, and the nitrogen content is adjustable in the range of 0-30%. The rich nitrogen element in the carrier can ensure the formation of metal-nitrogen coordination. At the same time, the metal molten salt used can significantly increase the specific surface area of ​​the carrier, so that the nitrogen anchoring site can be fully exposed, which is conducive to increasing the metal single atom loading; in addition, by controlling the heating rate and the insulation time, some metal-halogen bonds in the metal halide are selectively broken and anchored by the nitrogen element in the carrier. This method can ensure the synthesis of nitrogen / halogen co-coordinated metal single atoms, and the metal single atom loading can be adjusted in the range of 0-20%. Importantly, this method does not require the subsequent acid washing step to remove metal agglomerates, and has the characteristics of high controllability, simple process and good stability. This method optimizes its catalytic activity by precisely controlling the electronic structure of the single atom site with halogen atoms of different electronegativity. This preparation method is applicable to a variety of transition metal single atoms, and its loading can be controllably adjusted to alleviate the uncontrollable and complex technical problems of the existing preparation method.

[0042] In the above preparation process, the preparation step of the nitrogen metal single atom carrier specifically includes: mixing the carbon source, nitrogen source and metal molten salt, grinding them evenly and then calcining them under a protective atmosphere (preferably an argon atmosphere or a nitrogen atmosphere), washing the obtained calcined material to remove the metal molten salt, and obtaining a nitrogen metal single atom carrier with a high specific surface area and adjustable nitrogen content; the carbon source is preferably petroleum asphalt. This process specifically limits the type of carbon source, because the carbon source with a viscous coating ability can obtain a two-dimensional structure under the template effect of the metal molten salt. The characteristics of the two-dimensional structure lead to the full exposure of the active sites, and the material transfer is faster during the electrocatalytic reaction. The reason why glucose cannot be used as a carbon source in this scheme is that the abundant hydroxyl groups in glucose make it extremely easy to chelate during its carbonization process to obtain a three-dimensional carbon structure, and the three-dimensional carbon is not conducive to the full exposure of the active sites and the rapid transfer of materials in the electrocatalytic reaction, resulting in poor catalytic activity.

[0043] The preparation step of the nitrogen / halogen co-coordinated single atom catalyst specifically includes: calcining the second carrier under a protective atmosphere, the calcination temperature is 200-600°C, the calcination time is 3-12h, and the heating rate during calcination is 0.5-5°C / min. This process slowly breaks part of the metal-halogen bonds in the metal halide by programmed temperature increase, so that the single atoms still carrying part of the metal-halogen bonds are anchored by the second atom, and a nitrogen / halogen co-coordinated metal single atom catalyst is obtained. This step specifically limits the use of a single calcination method and the calcination conditions at the same time. The reason is that the number of calcinations, the calcination temperature and the rate of heating have a crucial influence. If the calcination temperature is too high, the metal single atoms are easy to agglomerate to form metal nanoparticles. If the calcination temperature is too low, the metal single atoms are difficult to load onto the carrier. In addition, too fast a heating rate will also cause the metal single atoms to agglomerate. It can be understood that the calcination temperature can also be 300°C, 400°C, 500°C and any point value within the range, the calcination time can also be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h and any point value within the range, and the heating rate during calcination can also be 1°C / min, 2°C / min, 3°C / min, 4°C / min and any point value within the range.

[0044] In a preferred embodiment, the second carrier preparation step comprises: mixing the nitrogen metal single atom carrier, metal halide and solvent, and separating them to obtain the second carrier. The solvent comprises any one or a combination of at least two of deionized water, methanol, ethanol, propanol, toluene, acetone, n-hexane, cyclohexane and N,N-dimethylformamide; the mixing temperature is selected from 10-100°C, and the mixing time is selected from 2-24h.

[0045] In a preferred embodiment, the metal molten salt is selected from any one of potassium chloride, sodium chloride, magnesium chloride, and calcium chloride, or a combination of at least two thereof; the metal halide is selected from any one of chromium halide, manganese halide, iron halide, nickel halide, copper halide, zinc halide, ruthenium halide, and palladium halide. Further, the metal molten salt is selected from potassium chloride and sodium chloride; the metal halide is selected from nickel halide; and the nitrogen source is selected from urea. The technical solution specifically defines the types of metal molten salts, metal halides and nitrogen sources. The reason is that the choice of carbon source has a greater impact on the microscopic morphology of the catalyst (one-dimensional, two-dimensional or three-dimensional), the number of nitrogen sources has a greater impact on the loading of metal single atoms, and significantly affects the degree of defect (conductivity) of the catalyst. The choice of metal molten salt has a greater impact on the specific surface area and pore size distribution of the catalyst. The larger the specific surface area, the more fully the nitrogen sites of the anchored metal single atoms are exposed, which is conducive to increasing the loading of single atoms and improving catalytic activity. In the process of loading metal single atoms, different nitrogen-halogen co-coordinated metal single atom catalysts can be obtained by adjusting the selection of metal halides. By limiting the types of metal molten salts, metal molten salts can provide a molten environment for carbon sources and nitrogen sources to grow controllably into a two-dimensional structure, and its etching effect is conducive to improving the specific surface area of ​​the material. At the same time, the metal molten salts used in the present invention also have the characteristics of low toxicity and easy recovery. Further, using urea as a nitrogen source also has the characteristics of low cost and low toxicity.

[0046] In a preferred embodiment, the mass ratio of the carbon source, the nitrogen source and the metal molten salt is (0.1-1): (0.1-4): (0.1-30). In a preferred embodiment, the mass ratio of the nitrogen metal single atom carrier, the metal halide and the solvent is (0.1-1): (0.1-1): (10-100). This technical solution specifically defines the dosage relationship of each component, among which the amount of nitrogen source has a greater influence on the loading amount of metal single atoms and significantly affects the defect degree (conductivity) of the catalyst.

[0047] In a preferred embodiment, in the step of preparing the nitrogen metal single atom carrier, the calcination conditions of calcining under a protective atmosphere after the carbon source, nitrogen source and metal molten salt are uniformly mixed are as follows: the calcination temperature is 600-1200°C, the calcination time is 1-6h, and the heating rate during calcination is 2-15°C / min. It can be understood that the calcination temperature can also be 800°C, 1000°C, 1100°C and any point value within the range, the calcination time can also be 2h, 3h, 4h, 5h and any point value within the range, and the heating rate during calcination can also be 4°C / min, 6°C / min, 8°C / min, 10°C / min, 12°C / min and any point value within the range.

[0048] In order to more clearly and in detail introduce the application of the nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by electrolysis of water, the nitrogen / halogen co-coordinated single atom catalyst and its preparation method provided by the embodiments of the present invention, the following will be described in conjunction with specific embodiments.

[0049] Example 1

[0050] A method for preparing a nitrogen / chlorine co-coordinated Ni single-atom catalyst comprises the following steps:

[0051] (a) 1g of petroleum asphalt (the main components of petroleum asphalt include 18.63wt.% saturated fraction, 30.13wt.% aromatic fraction, 37.21wt.% colloid and 7.40wt.% asphaltenes) is dispersed in 30mL of toluene, 4g of urea, 3g of potassium chloride and 7g of sodium chloride are added, and ultrasonic dispersion is performed for 1h, and then the toluene is evaporated and recovered by a vacuum distillation device at 90°C to obtain a uniformly mixed precursor; then the precursor is subjected to programmed temperature calcination in a nitrogen atmosphere. The programmed heating rate is 5°C / min, the starting temperature is room temperature, the temperature is maintained at 800°C, and the insulation time is 3h. The obtained calcined material is placed in 1M hydrochloric acid and washed for 12h to remove the metal molten salt in the calcined material to obtain a nitrogen-doped carbon carrier A with a high specific surface area;

[0052] (b) 0.1 g of nitrogen-doped carbon carrier A was added to 50 mL of anhydrous ethanol and stirred evenly, which was marked as solution A; 0.1 g of nickel chloride (NiCl2) was added to 50 mL of anhydrous ethanol and stirred evenly, which was marked as solution B; solution A was stirred on a magnetic stirrer, and solution B was slowly added dropwise to solution A and stirred continuously for 12 hours, and the sample was collected by centrifugation to obtain carrier B loaded with nickel chloride;

[0053] (c) Carrier B was placed in an argon atmosphere for programmed temperature calcination. The programmed temperature rate was 5°C / min, the starting temperature was room temperature, the temperature was maintained at 300°C, and the holding time was 5h. The calcined material was ultrasonically washed three times in anhydrous ethanol to remove the metal single atoms that were not firmly anchored, and a nitrogen / chlorine co-coordinated Ni single atom catalyst (Ni1-N / Cl-C) was obtained.

[0054] Example 2

[0055] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Ni single-atom catalyst (Ni1-N / Cl-C). Except for replacing the petroleum asphalt in Example 1 with glucose, the remaining steps and process parameters are the same as those in Example 1.

[0056] Example 3

[0057] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Ni single-atom catalyst (Ni1-N / Cl-C). Except for replacing 4g of urea in Example 1 with 1g of urea, the remaining steps and process parameters are the same as those in Example 1.

[0058] Example 4

[0059] This embodiment provides a method for preparing a nitrogen / fluorine co-coordinated Ni single-atom catalyst (Ni1-N / FC). Except for replacing the nickel chloride (NiCl2) in Example 1 with nickel fluoride (NiF2), the remaining steps and process parameters are the same as those in Example 1.

[0060] Example 5

[0061] This embodiment provides a method for preparing a nitrogen / bromine co-coordinated Ni single-atom catalyst (Ni1-N / Br-C). Except for replacing the nickel chloride (NiCl2) in Example 1 with nickel bromide (NiBr2), the remaining steps and process parameters are the same as those in Example 1.

[0062] Example 6

[0063] This embodiment provides a method for preparing a nitrogen / iodine co-coordinated Ni single-atom catalyst (Ni1-N / IC). Except for replacing the nickel chloride (NiCl2) in Example 1 with nickel iodide (NiI2), the remaining steps and process parameters are the same as those in Example 1.

[0064] Example 7

[0065] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Fe single atom catalyst (Fe1-N / Cl-C). Except for replacing the nickel chloride (NiCl2) in Example 1 with ferric chloride (FeCl3), the remaining steps and process parameters are the same as those in Example 1.

[0066] Example 8

[0067] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Co single-atom catalyst (Co1-N / Cl-C). Except for replacing the nickel chloride (NiCl2) in Example 1 with cobalt chloride (CoCl2), the remaining steps and process parameters are the same as those in Example 1.

[0068] Example 9

[0069] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Ni single-atom catalyst (Ni1-N / Cl-C). Except for removing the metal molten salt (potassium chloride and sodium chloride) in Example 1, the remaining steps and process parameters are the same as those in Example 1.

[0070] Example 10

[0071] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Ni single-atom catalyst (Ni1-N / Cl-C). Except for replacing 0.1 g of nickel chloride in Example 1 with 0.02 g of nickel chloride, the remaining steps and process parameters are the same as those in Example 1.

[0072] Embodiment 11

[0073] This embodiment provides a method for preparing a nitrogen / chlorine co-coordinated Ni single-atom catalyst (Ni1-N / Cl-C). Except for replacing 0.1 g of nickel chloride in Example 1 with 0.3 g of nickel chloride, the remaining steps and process parameters are the same as those in Example 1.

[0074] Comparative Example 1

[0075] This comparative example provides a method for preparing a Co single-atom catalyst (Co1-N / Cl-C3) having a Co-N3Cl1 coordination configuration, comprising the following steps:

[0076] (a) 1g of petroleum asphalt (the main components of petroleum asphalt include 18.63wt.% saturated fraction, 30.13wt.% aromatic fraction, 37.21wt.% colloid and 7.40wt.% asphaltenes) is dispersed in 30mL of toluene, 4g of urea, 3g of potassium chloride and 7g of sodium chloride are added, and ultrasonic dispersion is performed for 1h, and then the toluene is evaporated and recovered by a vacuum distillation device at 90°C to obtain a uniformly mixed precursor; then the precursor is subjected to programmed temperature calcination in a nitrogen atmosphere. The programmed heating rate is 5°C / min, the starting temperature is room temperature, the temperature is maintained at 800°C, and the insulation time is 3h. The obtained calcined material is placed in 1M hydrochloric acid and washed for 12h to remove the metal molten salt in the calcined material to obtain a nitrogen-doped carbon carrier A with a high specific surface area;

[0077] (b) 0.1 g of nitrogen-doped carbon carrier A was added to 50 mL of anhydrous ethanol and stirred evenly, which was marked as solution A; 0.1 g of cobalt chloride (CoCl2) was added to 50 mL of anhydrous ethanol and stirred evenly, which was marked as solution B; solution A was stirred on a magnetic stirrer, and solution B was slowly added dropwise to solution A and stirred continuously for 12 hours, and the sample was collected by centrifugation to obtain carrier B loaded with nickel chloride;

[0078] (c) Carrier B was placed in an argon atmosphere for programmed temperature calcination. The programmed temperature rate was 5°C / min, the starting temperature was room temperature, the holding temperature was 450°C, and the holding time was 5h. The calcined material was ultrasonically washed three times in anhydrous ethanol to remove the metal atoms that were not firmly anchored, and a Co single atom catalyst (Co1-N / Cl-C) with a Co-N4Cl1 coordination configuration was obtained.

[0079] (d) 0.1 g of Co1-N / Cl-C was placed in an argon atmosphere for programmed temperature calcination. The programmed temperature rate was 2°C / min, the starting temperature was room temperature, the holding temperature was 500°C, and the holding time was 5h. The coordination number of N was adjusted by secondary high-temperature heat treatment to obtain a Co single-atom catalyst (Co1-N / Cl-C3) with a Co-N3Cl1 coordination configuration.

[0080] Comparative Example 2

[0081] This comparative example provides a method for preparing a Co single-atom catalyst (Co1-NC) having a Co-N4 coordination configuration. Except that the maintaining temperature of 450°C in step (c) of comparative example 1 is replaced with 300°C, the remaining steps and process parameters are the same as those of comparative example 1.

[0082] Comparative Example 3

[0083] This comparative example provides a method for preparing a Ni single-atom catalyst (Ni1-NC) having a Ni-N3-Cl1 coordination configuration, and the rest is the same as comparative example 1.

[0084] Performance Testing

[0085] In order to verify the technical effects of the embodiments and comparative examples, the following experiments were conducted.

[0086] Experimental Example 1

[0087] The catalysts provided in Examples 1-2 were characterized by scanning electron microscopy, and the specific results are as follows: Figure 1 shown.

[0088] from Figure 1 It can be seen that using glucose with chelating properties as a carbon source tends to obtain a three-dimensional porous nitrogen-doped carbon carrier, while using petroleum asphalt with a sticky coating property as a carbon source tends to obtain a two-dimensional porous nitrogen-doped carbon carrier. Therefore, the technical solution proposed in the present invention has the advantage of adjusting the catalyst morphology by adjusting the type of carbon source.

[0089] Experimental Example 2

[0090] The catalysts provided in Examples 4-6 were characterized by X-ray diffraction. The specific results are as follows: Figure 2 shown.

[0091] from Figure 2 It can be seen that the X-ray diffraction pattern of the prepared nitrogen / halogen co-coordinated Ni single atom catalyst has two diffraction peaks at around 25.3° and 43.1°, corresponding to the (002) and (100) crystal plane diffraction peaks of carbon, respectively; apart from these, there are no diffraction peaks of Ni and its compounds, indicating that Ni may be uniformly dispersed in the nitrogen-doped carbon support in the form of single atoms, and can serve as an active center for efficient electrocatalytic water decomposition and oxygen production.

[0092] Experimental Example 3

[0093] The catalysts provided in Examples 7-8 and 10-11 were characterized by high-angle annular dark field imaging-scanning transmission electron microscopy. The specific results are as follows: Figure 3-Figure 6 shown.

[0094] from Figure 3-Figure 4 It can be seen that the metal elements are monodispersed in the catalyst without obvious aggregation, indicating that the synthesis of metal single-atom catalysts through this technical solution has a certain universality and can synthesize a variety of nitrogen-halogen co-coordinated metal single-atom catalysts. Figure 5-Figure 6 It can be seen that there are obvious differences in the number of metal single atoms, indicating that by adjusting the amount of metal halide added, the loading amount of metal single atoms can be significantly adjusted, and the single-atom electrochemical oxygen evolution activity can be further regulated.

[0095] Experimental Example 4

[0096] The catalyst provided in Example 8 was characterized by X-ray photoelectron spectroscopy. The specific results are as follows: Figure 7 shown.

[0097] from Figure 7 The presence of cobalt-nitrogen and cobalt-chlorine bonds can be clearly observed, indicating the successful synthesis of nitrogen / chlorine co-coordinated cobalt single-atom catalysts.

[0098] Experimental Example 5

[0099] The catalyst provided in Example 9 was characterized by scanning electron microscopy, and the specific results are as follows: Figure 8 shown.

[0100] from Figure 8 It can be seen that after the metal molten salt (potassium chloride and sodium chloride) in the carrier synthesis process is taken out, the morphology of the nitrogen-doped carbon carrier is a block structure with a smooth surface, indicating that the presence of the metal molten salt is conducive to the formation of a two-dimensional morphology with a high specific surface area. The two-dimensional carbon carrier can fully expose the anchoring sites, thereby increasing the loading amount of metal nitrogen atoms. At the same time, its rapid material transfer can obtain excellent electrocatalytic activity.

[0101] Experimental Example 6

[0102] The catalyst provided in Comparative Example 2 was characterized by X-ray photoelectron spectroscopy and high-angle annular dark field imaging-scanning transmission electron microscopy. The specific results are as follows: Figure 9-10 shown.

[0103] from Fig. 9 and Fig.10It can be seen that the cobalt single-atom catalyst obtained in Comparative Example 2 is only coordinated with the nitrogen element, and is evenly dispersed in the carrier in the form of single atoms, indicating that the coordinated chlorine element can be removed by secondary high-temperature treatment, highlighting the excellent controllability of the technical solution of the present invention.

[0104] Experimental Example 7

[0105] The electrochemical oxygen evolution performance test was carried out on the catalysts provided in Examples 4-8 and Comparative Examples 1-3. The specific results are as follows: Figure 11-13 shown.

[0106] The electrolysis oxygen evolution performance of the catalysts provided in Examples 4-8 and Comparative Examples 1-3 was tested using a three-electrode system: the test was carried out in a 1.0 M sodium hydroxide solution, and the polarization curves obtained were as follows: Figure 11-13 shown.

[0107] from Fig.11 It can be seen that the obtained nitrogen / halogen co-coordinated Ni single atom catalyst has a lower hydrogen evolution overpotential and a higher limiting current density than the pure nitrogen coordinated Ni single atom catalyst. Among them, the nitrogen and chlorine co-coordinated Ni single atom catalyst can achieve excellent water electrolysis oxygen evolution performance at only 1.58V, which has excellent industrial application prospects. Fig.12 It can be seen that the obtained nitrogen-chlorine co-coordinated metal single atom catalysts all have excellent catalytic activity, indicating the excellent universality of this technical solution. Fig.13 It can be seen that the Ni single-atom catalyst with Ni-N4Cl1 coordination configuration has better electrocatalytic water desorption and oxygen performance than that with Ni-N3Cl1 configuration.

Claims

1. Application of a nitrogen / halogen co-coordinated single atom catalyst in oxygen evolution by water electrolysis, characterized in that: The nitrogen / halogen co-coordinated single atom catalyst is a two-dimensional structure with a molecular formula of M-N4X1; the M is selected from metal elements, and the X is selected from halogen elements.

2. A nitrogen / halogen co-coordinated single atom catalyst, characterized in that: Use of the nitrogen / halogen co-coordinated single atom catalyst as claimed in claim 1 in oxygen evolution by water electrolysis.

3. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 2, characterized in that: The method comprises the steps of preparing a nitrogen-containing metal single atom carrier, preparing a second carrier, and preparing a nitrogen / halogen co-coordinated single atom catalyst; The preparation step of the nitrogen metal single atom carrier comprises: mixing a carbon source, a nitrogen source and a metal molten salt uniformly and then calcining under a protective atmosphere to obtain the nitrogen metal single atom carrier; the carbon source is selected from at least one of polyacrylonitrile, petroleum asphalt, FCC slurry oil, vacuum residue oil and formaldehyde resin; The preparation steps of the nitrogen / halogen co-coordinated single atom catalyst include: calcining the second carrier in a protective atmosphere, the calcination temperature is 200-600°C, the calcination time is 3-12h, and the heating rate during calcination is 0.5-5°C / min.

4. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 3, characterized in that: The second carrier preparation step includes: mixing the nitrogen metal single atom carrier, metal halide and solvent, and separating them to obtain the second carrier.

5. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 4, characterized in that: The molten metal salt is selected from any one of potassium chloride, sodium chloride, magnesium chloride, and calcium chloride, or a combination of at least two thereof; the metal halide is selected from any one of chromium halide, manganese halide, iron halide, nickel halide, copper halide, zinc halide, ruthenium halide, and palladium halide.

6. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 5, characterized in that: The metal molten salt is selected from potassium chloride and sodium chloride; the metal halide is selected from nickel halide; and the nitrogen source is selected from urea.

7. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 3, characterized in that: The mass ratio of the carbon source, the nitrogen source and the metal molten salt is (0.1-1):(0.1-4):(0.1-30).

8. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 4, characterized in that: The mass ratio of the nitrogen metal single atom carrier, the metal halide and the solvent is (0.1-1):(0.1-1):(10-100).

9. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 3, characterized in that: In the step of preparing the nitrogen metal single atom carrier, the carbon source, the nitrogen source and the metal molten salt are mixed evenly and then calcined under a protective atmosphere under the following calcination conditions: calcination temperature is 600-1200°C, calcination time is 1-6h, and heating rate during calcination is 2-15°C / min.

10. The method for preparing the nitrogen / halogen co-coordinated single atom catalyst according to claim 3, characterized in that: In the second carrier preparation step, the solvent includes any one of deionized water, methanol, ethanol, propanol, toluene, acetone, n-hexane, cyclohexane and N,N-dimethylformamide, or a combination of at least two thereof; the mixing temperature is selected from 10-100°C, and the mixing time is selected from 2-24h.

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