Polymetallic single atom catalysts, methods of making and using the same

Abstract

The application discloses a multi-metal single-atom catalyst and a preparation method and application thereof, relates to the technical field of catalysts, and discloses a multi-metal single-atom catalyst, which comprises nitrogen-doped graphene and M metal atoms loaded on the nitrogen-doped graphene, and the M metal atoms form a coordination structure with nitrogen; the M metal comprises iron, cobalt, nickel, copper and iridium. The technical scheme of the application is characterized in that five metal atoms of iron, cobalt, nickel, copper and iridium are loaded on nitrogen-doped graphene, and the M metal atoms form a coordination structure with nitrogen to be anchored on the nitrogen-doped graphene structure, which is beneficial to forming a more complex and adjustable electronic environment.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a multi-metal single-atom catalyst, its preparation method, and its application. Background Technology

[0002] Alkaline water electrolysis, due to its use of non-precious metal catalysts and strongly alkaline electrolytes, offers advantages such as low cost and good stability, making it one of the mainstream technologies for industrial hydrogen production. However, in an alkaline environment, the hydrogen evolution reaction (HER) typically suffers from slow kinetics, requiring a large overpotential to drive the reaction, which severely limits the improvement of electrolysis efficiency.

[0003] To enhance catalytic activity, single-atom catalysts have shown great potential in the HER field due to their maximized atom utilization and tunable coordination environment. However, existing single-atom catalysts still face the challenge of insufficient intrinsic activity. The fundamental reason is that the catalyst's adsorption / desorption capacity for H* is limited by an intrinsic scaling relationship, resulting in insufficient activity regulation and difficulty in simultaneously optimizing adsorption and desorption energies. Summary of the Invention

[0004] The main objective of this invention is to propose a multi-metal single-atom catalyst, its preparation method, and its application, aiming to improve the catalytic performance of the catalyst and thus solve the problems of slow kinetics and high overpotential in the hydrogen evolution reaction.

[0005] To achieve the above objectives, the present invention proposes a multi-metal single-atom catalyst, comprising nitrogen-doped graphene and M metal atoms supported on the nitrogen-doped graphene, wherein the M metal atoms form a coordination structure with nitrogen. The M metal includes iron, cobalt, nickel, copper, and iridium.

[0006] In one embodiment, the M metal atom accounts for 0.5 to 1.5 wt% of the multi-metal single-atom catalyst.

[0007] In one embodiment, iron atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, cobalt atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, nickel atoms constitute 0.1 to 0.3 wt% of the multimetallic single-atom catalyst; And / or, copper atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, iridium atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst.

[0008] In one embodiment, the M metal forms an M-N4 coordination structure with the nitrogen-doped graphene.

[0009] This invention further proposes a method for preparing the above-mentioned multi-metal single-atom catalyst, comprising the following steps: A. After mixing and stirring the graphene oxide, nitrogen source and M metal salt solution, freeze-drying is performed to obtain the precursor; B. The precursor is subjected to the first pyrolysis under an inert atmosphere; C. The precursor is subjected to a second pyrolysis under an inert atmosphere; In step B, the pyrolysis temperature of the first pyrolysis is 360–380°C, and the pyrolysis time is 2.5–3.5 h. In step C, the pyrolysis temperature of the first pyrolysis is 630-650℃, and the pyrolysis time is 2.5-3.5h.

[0010] In one embodiment, step D is further included, and step D is located between step B and step C, and / or step D is located after step C; D. The precursor is sequentially acid-washed and ethanol-washed; The acid concentration used for pickling is 0.01–0.1 mol / L.

[0011] In one embodiment, in step A, the stirring time is 25-27 hours, and the freeze-drying time is 72-73 hours.

[0012] In one embodiment, in step B, the inert atmosphere is an argon atmosphere, and the flow rate of the argon is 190-200 sccm. And / or, in step C, the inert atmosphere is an argon atmosphere, and the flow rate of the argon is 95-105 sccm.

[0013] In one embodiment, in step A, the graphene oxide is obtained by sequentially oxidizing and exfoliating expanded graphite and then heat-treating it, and the nitrogen source is acrylamide.

[0014] The present invention further proposes an application of the above-mentioned polymetallic single-atom catalyst in the hydrogen evolution reaction of alkaline electrolyte, wherein the additive is ammonia.

[0015] The technical solution of this invention loads five metal atoms—iron, cobalt, nickel, copper, and iridium—on nitrogen-doped graphene, and anchors them onto the nitrogen-doped graphene structure by forming a coordination structure between the M metal atoms and nitrogen. This facilitates the formation of a more complex and tunable electronic environment, producing a synergistic effect that cannot be achieved by existing single / bimetallic single-atom catalysts. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 A photograph of the precursor obtained in an embodiment of the present invention; Figure 2 A photograph of the FeCoNiCuIr-SAC prepared according to an embodiment of the present invention; Figure 3 The image shows a broad XPS spectrum of FeCoNiCuIr-SAC obtained in an embodiment of the present invention. Figure 4 This is a high-resolution XPS spectrum of the C1s peak in FeCoNiCuIr-SAC prepared according to an embodiment of the present invention. Figure 5 This is a high-resolution XPS spectrum of the N1s peak in FeCoNiCuIr-SAC obtained in an embodiment of the present invention. Figure 6 This is a high-resolution XPS spectrum of M metal atoms in FeCoNiCuIr-SAC prepared according to an embodiment of the present invention; Figure 7 The XRD pattern of FeCoNiCuIr-SAC obtained in an embodiment of the present invention; Figure 8 The linear sweep voltammetry polarization curves of Application Examples 1-1 and 1-2 of this invention are shown below. Figure 9 The Tafel diagrams for application embodiments 1-1 and 1-2 of the present invention.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] Existing single-atom catalysts contain only one type of metal atom with a fixed electronic structure. Limited by inherent scaling relationships, their activity regulation capabilities are insufficient, making it difficult to simultaneously optimize adsorption and desorption energies. Furthermore, although some technologies extend single-atom catalysts to bimetallic atoms, allowing the second metal atom to regulate the electronic structure of the active center through orbital coupling or long-range interactions, these techniques only partially overcome scaling relationships, and their improvement on the catalytic performance of single-atom catalysts remains limited.

[0023] Therefore, in order to effectively overcome the inherent scaling relationship, this application proposes a multi-metal single-atom catalyst, comprising nitrogen-doped graphene and M metal atoms supported on the nitrogen-doped graphene, wherein the M metal atoms form a coordination structure with nitrogen; the M metal includes iron, cobalt, nickel, copper, and iridium. By loading five metal atoms (iron, cobalt, nickel, copper, and iridium) onto the nitrogen-doped graphene and anchoring them to the nitrogen-doped graphene structure through the coordination structure between the M metal atoms and nitrogen, it is beneficial to form a more complex and tunable electronic environment, generating a synergistic effect that cannot be achieved by existing single / bimetallic single-atom catalysts.

[0024] Specifically, the electronic structure regulation dimension formed by the five metal atoms—iron, cobalt, nickel, copper, and iridium—is higher. When any one metal atom acts as an active site, the other metal atoms can act as corresponding sites. This structure effectively weakens the scaling limit because the other metal atoms acting as corresponding sites can act as in-plane modulation factors, regulating the electronic structure of the active site. Furthermore, the orbital coupling (bonding) and long-range (non-bonding) interactions among the five metal atoms—iron, cobalt, nickel, copper, and iridium—create a synergistic effect, which helps to bring the adsorption / desorption energy of H* closer to the optimal value. Moreover, when the multi-metal single-atom catalyst of this application is applied to electrochemical reactions, it can provide more coordinating sites, facilitating the regulation of the electronic structure during the reaction, which is more conducive to accelerating the kinetic process and reducing the overpotential.

[0025] To further clarify, the M metal atom accounts for 0.5 to 1.5 wt% of the multi-metal single-atom catalyst.

[0026] In a preferred embodiment of this technical solution, since single-atom catalysts in multi-metal systems are prone to agglomeration during the preparation process, forming metal clusters or nanoparticles, in order to ensure that metal atoms are kept at the atomic level in nitrogen-doped graphene, the overall metal atom loading in this application is controlled in a low range of 0.5 to 1.5 wt%.

[0027] Furthermore, iron atoms account for 0.1–0.3 wt% of the polymetallic single-atom catalyst; And / or, cobalt atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, nickel atoms constitute 0.1 to 0.3 wt% of the multimetallic single-atom catalyst; And / or, copper atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, iridium atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst.

[0028] In a preferred embodiment of this technical solution, the loading of each metal atom in the multi-metal system is also controlled, which is beneficial for: (1) ensuring atomic-level dispersion: when the content of any metal exceeds 0.3 wt%, agglomeration is more likely to occur during pyrolysis, especially in multi-metal systems. (2) maintaining multi-metal synergistic coordination: lower and similar metal contents are conducive to the uniform formation of stable coordination structures of the five metals, effectively avoiding competition for nitrogen sites. (3) avoiding iridium (Ir) agglomeration: Ir is more likely to form Ir–Ir bonds, and limiting its content to below 0.3 wt% can ensure that it remains in a single-atom state. (4) ensuring structural stability and repeatability: the above range can effectively avoid the generation of unstable metal species and ensure that the catalyst structure remains consistent between different batches.

[0029] Furthermore, the M metal and the nitrogen-doped graphene form an M-N4 coordination structure.

[0030] The M-N4 coordination structure facilitates the formation of a stable structure of M metal atoms in nitrogen-doped graphene, and effectively ensures the consistency and controllability of catalyst preparation. Furthermore, compared to the M-N2 and M-N3 coordination structures, the M-N4 coordination structure is less prone to metal migration and can provide near-optimal hydrogen adsorption energy, thus achieving better catalytic performance.

[0031] In the prior art, single-atom catalysts of three or more metals are rarely reported, mainly because: (1) high preparation difficulty: multi-metal systems are more prone to agglomeration during pyrolysis, forming metal clusters or nanoparticles. (2) competition for coordination sites: multiple metals compete for N coordination sites, making it difficult to maintain atomic-level dispersion at the same time. (3) thermodynamic instability: the formation energy of multi-metal systems is more complex, often tending to form alloys or oxides rather than stable single-atom structures. In addition, existing preparation methods for single / bimetallic single-atom catalysts are difficult to directly apply to multi-metal systems, and the agglomeration phenomenon has not been effectively improved. In this regard, this technical solution also proposes a preparation method for the above-mentioned multi-metal single-atom catalyst, including the following steps: A. After mixing and stirring the graphene oxide, nitrogen source and M metal salt solution, freeze-drying is performed to obtain the precursor; B. The precursor is subjected to the first pyrolysis under an inert atmosphere; C. The precursor is subjected to a second pyrolysis under an inert atmosphere; In step B, the pyrolysis temperature of the first pyrolysis is 360–380°C, and the pyrolysis time is 2.5–3.5 h. In step C, the pyrolysis temperature of the first pyrolysis is 630-650℃, and the pyrolysis time is 2.5-3.5h.

[0032] To ensure stable atomic-level dispersion of M metal atoms in nitrogen-doped graphene, this scheme reduces the energy required for the metal compound to form single atoms through a two-step pyrolysis method, thereby enhancing the dispersion of metal atoms on the nitrogen-doped graphene carrier and solving the problem of easier aggregation in multi-metal systems.

[0033] In the prior art, the preparation method of single / bimetallic single-atom catalysts usually adopts a one-step pyrolysis technique. Compared with the above methods, the two-step pyrolysis method of this scheme has the following advantages: (1) Avoiding metal agglomeration: The first step of low-temperature (360-380℃) pyrolysis only decomposes the organic precursor and forms a nitrogen-doped carbon framework, which will not cause the metal ions to be reduced in advance, thus avoiding early agglomeration. (2) Stabilizing the MN coordination structure: The second step of high-temperature (630-650℃) pyrolysis can strengthen the MN bond and improve the graphitization degree of the carbon support, thereby improving conductivity and structural stability. (3) When five metals are present at the same time, the competition for nitrogen sites is stronger. The two-step pyrolysis can ensure that each metal is uniformly anchored and avoid the formation of mixed metal clusters. In addition, in order to ensure the effective decomposition of the precursor and avoid the migration of metals, this scheme also optimizes the range of pyrolysis temperature.

[0034] Optionally, in step B, the pyrolysis temperature of the first pyrolysis is 370℃ and the pyrolysis time is 3h; in step C, the pyrolysis temperature of the first pyrolysis is 640℃ and the pyrolysis time is 3h.

[0035] To further explain, it also includes step D, which is located between step B and step C, and / or step D is located after step C; D. The precursor is sequentially acid-washed and ethanol-washed; The acid concentration used for pickling is 0.01–0.1 mol / L.

[0036] As a preferred embodiment of the above preparation method, this application further includes an acid washing and ethanol washing step between and / or after the two pyrolysis steps. This step can effectively remove weakly coordinated and / or unstable metal species formed during pyrolysis, retaining only strongly coordinated MN sites, which is more conducive to the formation of a stable and uniform coordination structure between M metal atoms and nitrogen in the catalyst.

[0037] In addition, this application also optimizes the acid concentration during the pickling process. When the acid concentration is not less than 0.01 mol / L, it is beneficial to ensure the washing effect of weakly coordinated and / or unstable metal species. When the acid concentration is not greater than 0.1 mol / L, it can avoid excessively high acid concentration from damaging stable MN sites.

[0038] It should be noted that the washing process in step D can be repeated 5 to 6 times as needed to further ensure the washing effect of weakly coordinated and / or unstable metal species.

[0039] Optionally, H2SO4 is used for pickling, and the acid concentration of the pickling is 0.05 mol / L.

[0040] To further explain, in step A, the stirring time is 25-27 hours, and the freeze-drying time is 72-73 hours.

[0041] In this way, thorough stirring can fully exfoliate and disperse the graphene oxide sheets, while simultaneously allowing the M metal salt and nitrogen source in the solution to uniformly penetrate between the graphene sheets. At the same time, stirring provides sufficient kinetic energy and time to ensure that the M metal ions and nitrogen source molecules are fully and uniformly dispersed and pre-anchored to the active sites of the graphene oxide, preventing the aggregation of metal atoms during subsequent pyrolysis. Freeze-drying is used to lock the M metal ions and nitrogen source molecules in situ within the ice crystals after freezing, avoiding the migration and aggregation phenomena that occur during conventional drying, thus laying the structural foundation for the subsequent generation of single-atom catalysts.

[0042] Optionally, in step A, the stirring time is 26 hours and the freeze-drying time is 72 hours.

[0043] To further clarify, in step B, the inert atmosphere is an argon atmosphere, and the flow rate of the argon is 190-200 sccm. And / or, in step C, the inert atmosphere is an argon atmosphere, and the flow rate of the argon is 95-105 sccm.

[0044] Thus, the flowing inert gas is more conducive to maintaining an inert environment during pyrolysis and preventing oxidation. It should be noted that sccm (standard cubic centimeters per minute) refers to standard milliliters per minute.

[0045] Optionally, in step B, the flow rate of the argon gas is 200 sccm; And / or, in step C, the flow rate of the argon gas is 100 sccm.

[0046] To further explain, in step A, the graphene oxide is obtained by sequentially oxidizing and exfoliating expanded graphite and then heat-treating it, and the nitrogen source is acrylamide.

[0047] This scheme also proposes an application of the above-mentioned multi-metal single-atom catalyst in the hydrogen evolution reaction of alkaline electrolyte, with ammonia as the additive.

[0048] In the hydrogen evolution reaction (HER) in an alkaline electrolyte with ammonia as an additive, the coordination of ammonia with metal atoms in a single-atom catalyst is a dynamic and crucial interfacial process. This process is not a simple physical adsorption but involves the formation and breaking of chemical bonds, profoundly affecting the mechanism of the catalytic reaction. In the aforementioned HER under alkaline conditions, ammonia, as a Lewis base, coordinates its lone pair electrons with the metal center. The metal atom, as a Lewis acid, accepts electrons. The coordination effect modulates the distribution of d-orbital electrons in the metal center, thereby altering the adsorption / desorption energy of H* and enhancing the kinetics of the HER reaction.

[0049] The present invention will be further illustrated below through specific embodiments: Example A. Weigh the raw materials, including graphene oxide, acrylamide, and Fe, each with a concentration of 0.05 mol / L. 3+ Co 2+ Ni 2+ Cu 2+ and Ir 4+ The solution was stirred for 26 hours after mixing, and then freeze-dried for 72 hours to obtain the precursor. A picture of the actual product is shown below. Figure 1 As shown; B. Under an argon atmosphere with a flow rate of 200 sccm, the precursor was subjected to a first pyrolysis at a temperature of 370℃ for 3 hours. D. The precursor was acid-washed with H2SO4 at a concentration of 0.05 mol / L, and then washed with ethanol; the above washing process was repeated 5 times. C. Under an argon atmosphere with a flow rate of 100 sccm, the precursor was subjected to a second pyrolysis at 640℃ for 3 hours to obtain FeCoNiCuIr-SAC. The iron, cobalt, nickel, copper, and iridium atoms accounted for 0.16 wt%, 0.17 wt%, 0.17 wt%, 0.20 wt%, and 0.29 wt% of the mass of FeCoNiCuIr-SAC, respectively. A photograph of the actual product is shown below. Figure 2 As shown.

[0050] Raw material description: 1. Graphene oxide: Based on the modified Hummers method, it is synthesized from expanded graphite through sequential oxidation exfoliation and heat treatment.

[0051] 2. Acrylamide: Purchased from Sigma-Aldrich, USA.

[0052] 3. Fe 3+ Solution: An aqueous solution of ferric chloride hexahydrate (FeCl3·6H2O), which was purchased from Sigma-Aldrich, USA.

[0053] 4. Co 2+Solution: An aqueous solution of cobalt chloride hexahydrate (CoCl2·6H2O), which was purchased from Sigma-Aldrich, USA.

[0054] 5. Ni 2+ Solution: An aqueous solution of nickel chloride hexahydrate (NiCl2·6H2O), which was purchased from Sigma-Aldrich, USA.

[0055] 6. Cu 2+ Solution: An aqueous solution of copper chloride dihydrate (CuCl2·2H2O), which was purchased from Sigma-Aldrich, USA.

[0056] 7. Ir 4+ Solution: An aqueous solution of chloroiridic acid (H2IrCl6·xH2O), which was purchased from Sigma-Aldrich, USA.

[0057] Characterization and Analysis: 1. The elemental bonding states and chemical structures of the FeCoNiCuIr-SAC prepared in the examples were characterized using a PHI 5000 VersaProbe III scanning X-ray photoelectron spectroscopy (XPS) instrument manufactured by ULVAC-PHI.

[0058] like Figure 3 The image shows a broad XPS spectrum of FeCoNiCuIr-SAC, indicating that the FeCoNiCuIr-SAC prepared in the examples has C1s, N1s, O1s, Fe2p, Co2p, Ni2p, Cu2p and Ir4f peaks.

[0059] like Figure 4 The figure shows the high-resolution XPS spectrum of the C1s peak in FeCoNiCuIr-SAC. As can be seen from the figure, the C1s energy level contains two visible C species, corresponding to the C-C bond (284.6 eV) and the CO bond (286.0 eV), respectively.

[0060] like Figure 5 The image shows the high-resolution XPS spectrum of the N1s peak in FeCoNiCuIr-SAC. As can be seen from the image, four visible nitrogen species exist in the N1s level: pyridine nitrogen (398.2 eV), methyl nitrogen (398.9 eV), pyrrole nitrogen (400.8 eV), and nitrogen oxides (407.0 eV). Additionally, M in the image represents five metallic elements: iron, cobalt, nickel, copper, and iridium.

[0061] like Figure 6 The figures shown are high-resolution XPS spectra of iron (a), cobalt (b), nickel (c), copper (d), and iridium (e). The figures show that iron, cobalt, nickel, and copper atoms have a 2p... 1 / 2and 2p 3 / 2 The valence state is different, while the iridium atom exhibits a 4f valence state and is also partially oxidized.

[0062] 2. The interlayer spacing of FeCoNiCuIr-SAC prepared in the examples was determined using a PANalytical XRD apparatus, and the crystallinity of FeCoNiCuIr-SAC was evaluated.

[0063] like Figure 7 The XRD pattern of FeCoNiCuIr-SAC is shown. A broad graphitic carbon peak (002 crystal plane) is observed at 2θ = 21.2°, and the interlayer spacing d = 4.2 Å is calculated according to Bragg's law. This broad graphitic carbon peak can be attributed to the polycrystalline structure characteristics. Due to the low loading of metal species, no other peaks associated with metal clusters or their oxide / nitride compounds were detected.

[0064] In summary, the FeCoNiCuIr-SAC prepared in the examples was characterized using XPS and XRD techniques, confirming its atomic dispersion and structural integrity, and confirming that no metal clusters or their oxides were detected.

[0065] Application Example 1-1 The hydrogen evolution reaction performance of FeCoNiCuIr-SAC prepared in the examples was tested using a rotating ring-disk electrode (RRDE) device (ALSCo RRDE-3A) in conjunction with a Gamry 5000E electrochemical workstation in a 0.1 mol / L potassium hydroxide solution without ammonia.

[0066] Application Examples 1-2 The hydrogen evolution reaction performance of FeCoNiCuIr-SAC prepared in the examples was tested using a rotating ring electrode (RRDE) device (ALSCo RRDE-3A) in conjunction with a Gamry 5000E electrochemical workstation in a 0.1 mol / L potassium hydroxide solution with ammonia as an additive.

[0067] like Figure 8 The figures shown are linear sweep voltammetry (LSV) polarization curves for Application Examples 1-1 and 1-2, achieving a current density of -10 mA / cm² in a 0.1 mol / L potassium hydroxide solution without ammonia. 2 The overpotential was 0.43V; in a 0.1 mol / L potassium hydroxide solution with ammonia as an additive, the current density reached was -10 mA / cm². 2The overpotential was 0.32 V. That is, regardless of the presence of ammonia, the FeCoNiCuIr-SAC prepared in this example exhibited a low overpotential in the hydrogen evolution reaction in 0.1 mol / L KOH solution, indicating high activity of FeCoNiCuIr-SAC. It is noteworthy that the activity of the hydrogen evolution reaction was effectively enhanced when ammonia was introduced into the reaction. This is attributed to the fact that ammonia, as an additive, coordinates with the single-atom active centers in FeCoNiCuIr-SAC, effectively regulating the adsorption / desorption energy of H*, thereby improving reaction kinetics.

[0068] like Figure 9 The diagram shows the Tafel plots for Application Examples 1-1 and 1-2. The Tafel slope of FeCoNiCuIr-SAC under ammonia-free conditions is 305.6 mV / dec, while the Tafel slope under ammonia-containing conditions is 129.9 mV / dec. Notably, the introduction of ammonia into the hydrogen evolution reaction effectively reduces the Tafel slope of FeCoNiCuIr-SAC, indicating that the coordination effect of ammonia improves the kinetics of the hydrogen evolution reaction.

[0069] In summary, this application loads five metal atoms—iron, cobalt, nickel, copper, and iridium—on nitrogen-doped graphene, and anchors them onto the nitrogen-doped graphene structure by forming a coordination structure between the M metal atoms and nitrogen. This facilitates the formation of a more complex and tunable electronic environment, effectively solving the problems of slow kinetics and high overpotential in the hydrogen evolution reaction.

[0070] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A multi-metal single-atom catalyst, characterized in that, It includes nitrogen-doped graphene and M metal atoms loaded on the nitrogen-doped graphene, wherein the M metal atoms form a coordination structure with nitrogen; The M metal includes iron, cobalt, nickel, copper, and iridium.

2. The multi-metal single-atom catalyst as described in claim 1, characterized in that, The M metal atoms account for 0.5 to 1.5 wt% of the multi-metal single-atom catalyst.

3. The multi-metal single-atom catalyst as described in claim 2, characterized in that, Iron atoms account for 0.1–0.3 wt% of the polymetallic single-atom catalyst; And / or, cobalt atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, nickel atoms constitute 0.1 to 0.3 wt% of the multimetallic single-atom catalyst; And / or, copper atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst; And / or, iridium atoms account for 0.1 to 0.3 wt% of the polymetallic single-atom catalyst.

4. The multi-metal single-atom catalyst as described in claim 1, characterized in that, The M metal forms an M-N4 coordination structure with the nitrogen-doped graphene.

5. A method for preparing a multi-metal single-atom catalyst as described in any one of claims 1 to 4, characterized in that, Includes the following steps: A. After mixing and stirring the graphene oxide, nitrogen source and M metal salt solution, freeze-drying is performed to obtain the precursor; B. The precursor is subjected to the first pyrolysis under an inert atmosphere; C. The precursor is subjected to a second pyrolysis under an inert atmosphere; In step B, the pyrolysis temperature of the first pyrolysis is 360–380°C, and the pyrolysis time is 2.5–3.5 h. In step C, the pyrolysis temperature of the first pyrolysis is 630-650℃, and the pyrolysis time is 2.5-3.5h.

6. The method for preparing the multi-metal single-atom catalyst as described in claim 5, characterized in that, It also includes step D, which is located between step B and step C, and / or step D is located after step C; D. The precursor is sequentially acid-washed and ethanol-washed; The acid concentration used for pickling is 0.01–0.1 mol / L.

7. The method for preparing the multi-metal single-atom catalyst as described in claim 5, characterized in that, In step A, the stirring time is 25-27 hours, and the freeze-drying time is 72-73 hours.

8. The method for preparing the multi-metal single-atom catalyst as described in claim 5, characterized in that, In step B, the inert atmosphere is an argon atmosphere, and the flow rate of the argon is 190-200 sccm. And / or, in step C, the inert atmosphere is an argon atmosphere, and the flow rate of the argon is 95-105 sccm.

9. The method for preparing the multi-metal single-atom catalyst as described in claim 5, characterized in that, In step A, the graphene oxide is obtained by sequentially oxidizing and exfoliating expanded graphite and then heat-treating it, and the nitrogen source is acrylamide.

10. The application of a multi-metal single-atom catalyst as described in any one of claims 1 to 4 in the hydrogen evolution reaction of an alkaline electrolyte, characterized in that, The additive is ammonia.

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