CN112751040B

CN112751040B - Composite structure Co-Nx/C monatomic catalyst, preparation method thereof and fuel cell

Info

Publication number: CN112751040B
Application number: CN202011440304.1A
Authority: CN
Inventors: 郑智平; 张新瑜; 李岩岩
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology
Priority date: 2020-12-11
Filing date: 2020-12-11
Publication date: 2022-04-19
Anticipated expiration: 2040-12-11
Also published as: CN112751040A

Abstract

The invention discloses a composite structure Co-N_xan/C monatomic catalyst, a preparation method thereof and a fuel cell. The composite structure Co-N_xThe catalyst comprises a catalyst shell, a catalyst core, a catalyst component, a catalyst component and a catalyst component, wherein the catalyst component is a hollow structure with double shell layers and comprises an inner shell layer and an outer shell layer coated on the inner shell layer, the inner shell layer is coated to form a cavity, and a gap is formed between the inner shell layer and the outer shell layer; the materials of the inner shell layer and the outer shell layer both contain Co-N_xA single atom active site. The composite structure can provide and expose a large amount of catalytic active sites, the utilization rate of the catalytic active sites is improved, the stability of the catalytic active sites is good, and the mass-charge transmission efficiency of the catalytic active sites is high. The preparation method has easily controlled process conditions and can ensure that Co-N is compatible_xThe structure and performance of the/C monatomic catalyst are stable, and the efficiency is high. The fuel cell comprises the composite structure Co-N_xthe/C monatomic catalyst has high electrochemical energy conversion efficiency.

Description

Composite structure Co-Nx/C monatomic catalyst, preparation method thereof and fuel cell

Technical Field

The invention belongs to the technical field of fuel cells, and particularly relates to Co-N with a composite structure_xan/C monatomic catalyst, a preparation method thereof and a fuel cell.

Background

Since the 21 st century, energy problems become one of the most important factors restricting the development of human beings, and the search for new energy to replace the traditional non-renewable energy is an important way for solving the energy problems. In the developed new energy technology, a proton exchange membrane fuel cell directly catalyzes fuel to react with oxygen through a catalyst to convert chemical energy into electric energy, the energy efficiency is as high as 70%, most of products are water, the environmental damage is extremely low, and the proton exchange membrane fuel cell is one of the most potential energy storage technologies.

In the proton exchange membrane fuel cell, the cathode electrocatalytic Oxygen Reduction Reaction (ORR) is taken as an important reaction in the proton exchange membrane fuel cell, which relates to the transfer of four electrons, and the kinetics is slower, so that the overpotential of the reaction is higher; the secondary electron transfer reaction of the reaction is serious, and the electrochemical energy conversion efficiency is influenced; in addition, the problems of mass transfer, internal ohmic resistance and the like exist in the reaction process, so that the output voltage of the fuel cell is far lower than the theoretical value, and the overall performance of the fuel cell is seriously influenced. Therefore, designing a synthetic efficient ORR catalyst is the key to improving fuel cell performance.

In order to synthesize a high-efficiency ORR catalyst, the researchers in the field have been continuously making diligent efforts, such as the nitrogen-doped carbon-supported cobalt-based monatomic catalyst (Co-N) which is publicly reported at present_xthe/C SACs) has good catalytic performance on ORR catalysis, and has wide research and development prospects. A large number of studies have shown that Co-N_xthe/C SACs have excellent catalytic activity on ORR reaction, can effectively reduce overpotential of the reaction, promote the generation of a four-electron transfer process, and integrally improve the ORR catalytic performance.

However, the currently reported Co-N is also found in practical application_xThere are also significant deficiencies with/C SACs: (1) the load of the monatomic Co is low, the catalytic reaction kinetics is poor, and the catalytic activity of the catalyst needs to be further improved; (2) the active sites are easy to fall off in the catalysis process, and the stability of the catalyst needs to be enhanced; (3) in the catalytic reaction, the charge and the substance transfer resistance between the active sites and reactants and products are large, and the reaction kinetics is poor. The reason for this is that the current research lacks effective regulation and control of catalytic active sites from the structural design, which results in the failure to effectively increase the density of active sites, increase the stability of active sites, and improve the mass transfer and load transfer efficiency, and is the bottleneck of this type of catalyst.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a composite structure Co-N_xa/C monatomic catalyst and a preparation method thereof, aiming at solving the problem of the prior Co-N_xThe catalyst/C SACs has the technical problems of low load of catalytic monatomic Co and unstable active sites, which cause unsatisfactory catalytic activity and low mass transfer and load transfer efficiency.

Another object of the present invention is to provide a fuel cell to solve the problem of the prior art containing Co-N_xThe fuel cell of the/C SACs catalyst has the technical problem of unsatisfactory electrochemical energy conversion efficiency.

To achieve the above object, in one aspect of the present invention,provides a composite structure Co-N_xa/C monatomic catalyst. The composite structure Co-N_xThe catalyst comprises a catalyst shell, a catalyst core, a catalyst component, a catalyst component and a catalyst component, wherein the catalyst component is a hollow structure with double shell layers and comprises an inner shell layer and an outer shell layer coated on the inner shell layer, the inner shell layer is coated to form a cavity, and a gap is formed between the inner shell layer and the outer shell layer; wherein the materials of the inner shell layer and the outer shell layer both contain Co-N_xA single atom catalyst of/C, and said Co-N_xthe/C monatomic catalyst contains Co-N_xA single atom active site.

In another aspect of the invention, a composite structure Co-N is provided_xA preparation method of/C monatomic catalyst. The composite structure Co-N_xThe preparation method of the/C monatomic catalyst comprises the following steps:

carrying out first mixing treatment on a first Co simple substance precursor solution containing zinc ions and a first organic ligand and carrying out first coordination reaction to generate a first bimetal ZnCo-MOF precursor;

carrying out second mixing treatment on the suspension containing the first bimetallic ZnCo-MOF precursor, a second Co simple substance precursor solution containing zinc ions and a second organic ligand, and carrying out second coordination reaction to generate a second bimetallic ZnCo-MOF precursor;

sintering the second bimetallic ZnCo-MOF precursor in nitrogen atmosphere to volatilize zinc and generate a composite structure Co-N with a double-shell hollow structure_xa/C monatomic catalyst.

In yet another aspect of the present invention, a fuel cell is provided. The fuel cell comprises a cathode, and the catalyst is the composite structure Co-N of the invention_xa/C single-atom catalyst or Co-N with a composite structure of the invention_xComposite structure Co-N prepared by preparation method of/C monatomic catalyst_xa/C monatomic catalyst.

Compared with the prior art, the invention has the following technical effects:

composite structure Co-N of the invention_xthe/C monatomic catalyst is of a hollow double-shell structure, and the inner wall and the outer wall of each shell can provide and expose a large number of catalytic active sitesHigh utilization rate of catalytic active sites, thereby remarkably improving the Co-N of the composite structure_xThe catalytic activity of the/C monatomic catalyst; meanwhile, the contained double-shell structure strengthens the protection effect between layers, can effectively resist the influence of various adverse factors such as external electrolyte, redox reaction, side reaction and the like on the stability of the catalytic active sites, and is favorable for improving the stability of materials. In addition, the composite structure Co-N_xThe hollow cavity contained in the/C monatomic catalyst and the gaps between the layers can ensure the full contact between the catalytic active sites and oxygen molecules and electrolyte, effectively accelerate charge and ion transmission, reduce the diffusion resistance of gas molecules, electrolyte and the like, are beneficial to the timely generation and conversion of intermediates, and promote the forward reaction.

Composite structure Co-N of the invention_xThe preparation method of the/C monatomic catalyst can ensure that the prepared composite structure Co-N_xthe/C monatomic catalyst material has excellent structural stability, large specific surface area and rich catalytic reaction active sites, and has the composite structure Co-N_xThe advantages described for the/C monatomic catalyst; on the other hand, the process conditions are easy to control, and the Co-N composite structure can be ensured_xThe structure and performance of the/C monatomic catalyst are stable, and the efficiency is high.

The fuel cell of the invention comprises the composite structure Co-N of the invention at the cathode_xthe/C monatomic catalyst, therefore, the electrochemical energy conversion efficiency of the fuel cell is obviously improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 shows a composite structure of Co-N according to an embodiment of the present invention_xA structural schematic diagram of a/C monatomic catalyst;

FIG. 2 shows a composite structure of Co-N according to an embodiment of the present invention_xA preparation design scheme of the/C monatomic catalyst;

FIG. 3 shows a composite structure of Co-N according to an embodiment of the present invention_xA process flow schematic diagram of a preparation method of the/C monatomic catalyst;

FIG. 4 shows a composite structure of Co-N in example 1 of the present invention_x/C SACs(DS·Co-N_xthe/C SACs) catalyst morphology characterization graph; wherein 4(a) is DS. Co-N_xSEM image of/C SACs catalyst, 4(b) TEM image, 4(C) HRTEM image, 4 (d-e) Cs-TEM image, and 4(f) EDS-Mapping image;

FIG. 5 shows a composite structure of Co-N in example 1 of the present invention_x/C SACs(DS·Co-N_x/C SACs) catalyst and SS. Co-N in comparative example 1_xStructural representation diagrams of/C SACs, Co simple substance and CoO; wherein FIG. 5(a) shows DS. Co-N in example 1_x/C SACs and SS. Co-N in comparative example 1_xXRD patterns of/C SACs, FIG. 5(b) is an XPS pattern of N1s, FIG. 5(C) is an XPS pattern of Co 2p, and FIG. 5(d) is DS. Co-N in example 1_xCo XANES diagram of/C SACs with Co simple substance, CoO, FIG. 5(e) is DS. Co-N in example 1_xFourier transform of Co K absorption edge of/C SACs and Co simple substance, FIG. 5(f) is N₂An adsorption-desorption isotherm graph, and FIG. 5(g) is a comparative graph of the content of Co measured by ICP-MS;

FIG. 6 shows a composite structure of Co-N in example 1 of the present invention_x/C(DS·Co-N_x/C SACs) and comparative examples 1 to 2 catalysts in alkaline medium; wherein FIG. 6(a) shows DS. Co-N in example 1_xThe linear polarization curves of the/C SACs, the catalysts of comparative example 1 to comparative example 2 at RDE test rotation speed of 1600rpm and sweep speed of 5mV/s, FIG. 6(b) is the Tafel plot fitted to FIG. 6(a), and FIG. 6(C) is the kinetic current density J at 0.80V for the three_kAnd a graph comparing half-wave potentials, FIG. 6(d) is DS. Co-N of example 1_x/C SACs and SS. Co-N of comparative example 1_xECSA of/C SACs, FIG. 6(e) is DS. Co-N of example 1_xLSV diagram of/C SACs at different rotation speeds, and the electron transfer numbers n and H of the three are shown in FIG. 6(f)₂O₂FIG. 6(g) is a schematic view showing the yield of DS. Co-N in example 1_xLSV patterns of/C SACs before and after 10000 CV scans, FIG. 6(h) is DS. Co-N of example 1_xMethanol tolerance test plots for/C SACs and Pt/C of comparative example 2;

FIG. 7 shows a composite structure of Co-N in example 1 of the present invention_x/C(DS·Co-N_x/C SACs) and comparative example 1 to comparative example 2 catalysts in an acidic medium; wherein FIG. 7(a) shows DS. Co-N in example 1_xLinear polarization curves of the/C SACs, comparative example 1 to comparative example 2 catalysts at RDE test speed of 1600rpm with sweep speed of 5mV/s, FIG. 7(b) is a Tafel plot fitted from FIG. 7(a), and FIG. 7(C) is the kinetic current density J at 0.70V for the three_kAnd a half-wave potential comparison chart, FIG. 7(d) is DS. Co-N of example 1_x/C SACs and SS. Co-N of comparative example 1_xECSA of/C SACs, FIG. 7(e) is DS. Co-N of example 1_xLSV diagram of/C SACs at different rotation speeds, and the electron transfer numbers n and H of the three are shown in FIG. 7(f)₂O₂FIG. 7(g) is a schematic view showing the yield of DS. Co-N in example 1_xLSV profiles of/C SACs before and after 10000 CV scans, FIG. 7(h) is DS. Co-N of example 1_xMethanol tolerance test plots for/C SACs and Pt/C of comparative example 2.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In this application, the term "and/or" describes an association relationship of associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present application may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present application as long as it is scaled up or down according to the description of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In one aspect, embodiments of the present invention provide a composite structure Co-N_xa/C monatomic catalyst.The composite structure is a hollow structure with double shell layers as shown in fig. 1, and comprises an inner shell layer 2 and an outer shell layer 4 coated on the inner shell layer 2, wherein the inner shell layer is coated to form a cavity 1, and a gap 3 is arranged between the inner shell layer 2 and the outer shell layer 4. Since the embodiment of the invention relates to Co-N_xa/C monatomic catalyst, so that the material of both the inner shell 2 and the outer shell 4 contains Co-N_xA single atom catalyst of/C, and Co-N_xthe/C monatomic catalyst contains Co-N_xA single atom site.

Thus, the composite structure Co-N_xThe inner wall and the outer wall of each shell layer contained in the/C monatomic catalyst can provide and expose a large number of catalytic active sites, so that the utilization rate of the catalytic active sites is improved, and the catalytic activity of the catalyst can be obviously improved; meanwhile, the contained double-shell structure strengthens the protection effect between the inner shell layer 2 and the outer shell layer 4, can effectively resist the influence of various adverse factors such as external electrolyte, redox reaction, side reaction and the like on the stability of the catalytic active sites, and is favorable for improving the stability of materials. In addition, the hollow cavity 1 and the gap 3 between the inner shell layer 2 and the outer shell layer 4 contained in the composite structure can ensure the full contact between the catalytic active site and oxygen molecules and electrolyte, effectively accelerate charge and ion transmission, reduce the diffusion resistance of gas molecules, electrolyte and the like, are favorable for the timely generation and conversion of intermediates, and promote the forward reaction.

Wherein, the composite structure Co-N_xThe inner shell layer 2 of the/C monatomic catalyst and the cavity 1 formed by coating the inner shell layer can also be regarded as the Co-N with the composite structure of the embodiment of the invention_xA core of a/C monatomic catalyst, and the core is a hollow core. In one embodiment, the thickness of the inner shell layer 2 is 20-50 nm; by controlling and optimizing the thickness of the inner shell layer 2, the active area of the material and the exposure degree of active sites can be effectively adjusted, and meanwhile, the mass-load transmission capability in the reaction process is adjusted, so that the improvement of the catalytic performance is facilitated.

In one embodiment, the diameter of the cavity 1 formed by the inner shell 2 is 250-300 nm. The size of the cavity 1 formed by coating the inner shell layer 2 is controlled and optimized, so that the Co-N of the composite structure can be further improved_xa/C monatomic catalyst, in particularThe catalytic active sites contained in the shell layer 2 are fully contacted with oxygen molecules and electrolyte, so that the charge and ion transmission is effectively accelerated, the diffusion resistance of gas molecules, electrolyte and the like is reduced, the timely generation and conversion of intermediates are facilitated, and the forward reaction is promoted.

In addition, the shape of the inner shell layer 2 is generally a sphere shape or an approximate sphere shape, and may be other three-dimensional shapes.

In one embodiment, the composite structure is Co-N_xThe shell layer 4 of the/C monatomic catalyst has a thickness of 10 to 20 nm. Through optimizing the thickness of outer shell 4, can effectively adjust the distance in clearance 3 between outer shell 4 and the inner shell 2 for the transmission ability of electric charge, ion reduces reaction process mass transfer resistance, promotes the reaction and goes on forward.

In another embodiment, the gap 3 between the outer shell layer 4 and the inner shell layer 2 is 20-50 nm. By optimizing the size of the gap 3, the synergistic effect between the gap 3 and the cavity 1 is improved, and the Co-N of the composite structure is further improved_xthe/C monatomic catalyst, particularly the catalytic active site contained in the inner shell layer 2, is fully contacted with oxygen molecules and electrolyte, so that the charge and ion transmission is effectively accelerated, the diffusion resistance of gas molecules, electrolyte and the like is reduced, the timely generation and conversion of an intermediate are facilitated, and the forward reaction is promoted.

In addition, the shape of the outer shell layer 4 is generally a rhomboid 12-sided body shape or an approximate sphere shape, but may be other three-dimensional shapes.

The composite structure Co-N is obtained by the above examples_xthe/C single-atom catalyst is subjected to shape characterization analysis such as TEM, SEM, EDX-Mapping, CS-TEM and the like to obtain the Co-N with the composite structure_xthe/C monatomic catalyst has the characteristics of a hollow double-shell structure, the outer layer is a nearly regular rhombic dodecahedron, and the inner layer is a nearly regular spherical shape, as shown in fig. 4(a) and 4(b) in fig. 4. The composite structure Co-N was confirmed by HRTEM and SAED shown in FIG. 4(c)_xthe/C single-atom catalyst is of a carbon structure and has no obvious crystallization. The Cs-TEM shown in FIGS. 4(d) and 4(e) confirmed the Co-N of the composite structure_xThe monoatomic Co in the/C monoatomic catalyst is uniformly dispersed in the inner and outer layer structures, and is not obviousAnd (4) agglomeration. Confirmation of composite Co-N by EDX-Mapping shown in FIG. 4(f)_xthe/C monatomic catalyst is composed of Co, N and C elements. And further measured that the composite structure Co-N in each of the above examples_xCo-N contained in/C monatomic catalyst_xX in the/C monatomic catalyst is 3.5-4.5.

The composite structure Co-N is obtained by the above examples_xThe structure characterization analysis of the/C monatomic catalyst such as XRD, XPS, XAFS, ICP-MS, BET and the like shows that the composite structure Co-N_xThe (002) and (101) crystal planes of the graphite carbon are 26 DEG and 44 DEG in the/C monatomic catalyst, and no obvious Co monoplasm peak is generated, as shown in figure 5(a) in figure 5. The confirmation of the composite structure Co-N by XPS as shown in FIGS. 5(b) to 5(c)_xThe content of the active species Co-N in the/C monatomic catalyst is higher than that in the single-layer structure, which indicates that the number of active sites in the structure is increased. And shows Co in XPS characterization²⁺The characteristic peak of (a), Co may be positively charged due to coordination of N, is shown in fig. 5 (c). Confirmation of composite Co-N Structure by XANES and XAFS shown in FIGS. 5(d) to 5(e)_xThe valence of Co in the/C monatomic catalyst is Co⁰-Co^IIExhibits a positive valence state, and has a coordination number of Co of about 4, and has a structure of Co-N₄The coordination environment of (2) and the absence of metallic Co-Co bonds, the synthesis of Co single atoms is confirmed.

The composite structure Co-N is obtained by BET test analysis_xThe specific surface area of the/C monatomic catalyst is 800-900m²G, rich porous structure, in particular BET test composite structure Co-N as shown in FIG. 5(f)_xThe specific surface area of the/C monatomic catalyst is as high as 815.84m²G, also higher than 729.49m of the monolayer structure in comparative example 1²(g) further illustrates the composite structure Co-N_xthe/C monatomic catalyst double-layer shell and the hollow structure can expose more active sites, which is also beneficial to the improvement of the catalytic performance. These results demonstrate that the hollow double shell structure has important effects on increasing the single atom loading and increasing the active sites.

Confirmation of composite Co-N by ICP-MS_xThe Co monoatomic ratio of the/C monoatomic catalyst was 2.5 to 3.0 wt%, and the ICP-MS shown in FIG. 5(g) confirmed that Co monoatomic in the materialThe loading of atoms was as high as 2.61 wt% which is higher than 1.50 wt% of the monolayer structure in comparative example 1.

It is due to the composite structure Co-N in the above examples_xthe/C monatomic catalyst has the above-described morphology and structural characteristics, and it has excellent catalytic activity (ORR catalytic activity). E.g. composite structure Co-N as in the previous examples_xORR catalytic efficiency tests of the/C monatomic catalyst under alkaline and acidic conditions show that the composite structure Co-N is in an acidic and alkaline environment_xThe ORR catalytic activity and the stability of the/C monatomic catalyst are far higher than those of a single-shell structure and commercial grade Pt/C catalyst, and the composite structure Co-N is shown_xthe/C monatomic catalyst shows excellent catalytic efficiency and catalytic stability in both basic media and acidic media, as shown in FIG. 6, FIG. 7, and tables 1 and 2.

Thus, the composite structure Co-N of the above examples_xThe inner wall and the outer wall of each shell layer of the/C monatomic catalyst can provide and expose a large number of catalytic active sites, so that the utilization rate of the catalytic active sites is improved; the protection among the layers can also resist the influence of the stability of the active sites caused by external adverse factors; the cavity 1 and the interlayer gap 3 formed by the coating of the inner shell layer 2 can also ensure the full contact between the catalytic active sites and oxygen molecules and electrolyte, improve the mass-charge transmission efficiency, so that the Co-N with a composite structure_xthe/C single-atom catalyst is a double-shell and hollow structure, is beneficial to timely generation and conversion of an intermediate, and promotes forward reaction, so that the catalyst has excellent ORR catalytic activity and stability. And a composite structure of Co-N_xThe structure stability and the specific surface area of the/C monatomic catalyst are large.

Correspondingly, the embodiment of the invention also provides the composite structure Co-N_xA preparation method of/C monatomic catalyst. The composite structure Co-N_xThe design route of the preparation of the/C monatomic catalyst is shown in figure 2, and according to the design route, the composite structure Co-N_xThe process flow of the preparation method of the/C monatomic catalyst is shown in figure 3, and is combined with figure 1, and the preparation method comprises the following steps:

step S01: carrying out first mixing treatment on a first Co simple substance precursor solution containing zinc ions and a first organic ligand and carrying out first coordination reaction to generate a first bimetal ZnCo-MOF precursor;

step S02: carrying out second mixing treatment on the suspension containing the first bimetallic ZnCo-MOF precursor, a second Co simple substance precursor solution containing zinc ions and a second organic ligand, and carrying out second coordination reaction to generate a second bimetallic ZnCo-MOF precursor;

step S03: sintering the second bimetallic ZnCo-MOF precursor in nitrogen atmosphere to volatilize zinc and generate a composite structure Co-N with a double-shell hollow structure_xa/C monatomic catalyst.

Thus, the composite structure Co-N_xThe preparation method of the/C monatomic catalyst firstly prepares a double-layer ZnCo-MOF precursor and then integrally sinters to form a process design, so that the prepared composite structure Co-N can be formed_xthe/C monatomic catalyst material has excellent structural stability, large specific surface area, abundant catalytic reaction active sites and a composite structure Co-N as shown in the embodiment of the invention_xThe advantages described for the/C monatomic catalyst; on the other hand, the process conditions are easy to control, and the Co-N composite structure can be ensured_xThe structure and performance of the/C monatomic catalyst are stable, and the efficiency is high.

In step S01, zinc ions are added to the first Co simple substance precursor solution, so that the first Co simple substance precursor solution and the Co ions react with the first organic ligand together to generate a first bimetallic ZnCo-MOF precursor containing Zn. Zn is additionally arranged on the first bimetal ZnCo-MOF precursor, so that Zn ions form similar grids in the first bimetal ZnCo-MOF precursor, Co ions are isolated, and the Co ions can be distributed at intervals.

In an embodiment, in the step of performing the first mixing treatment, a molar ratio of the zinc compound providing zinc ions, the first elemental Co precursor, and the first organic ligand is 1: 1: 4-1: 1: 8, i.e. 1: 1: (4-8), specifically 1.8: 1.8: 7.5. in the mixed solution formed by the first mixing treatment, the concentration of the first elemental Co precursor is preferably 0.05-0.1mol/L, and is preferably 0.0625 mol/L. By optimizing the mixing proportion of the Zn ions and the Co ions and the control and optimization of the solute concentration of the mixture, the Zn ions and the Co ions can fully perform ligand reaction with the first organic ligand, and meanwhile, the Zn ions are distributed in a grid form in the first bimetal ZnCo-MOF precursor, and the Co ions are enclosed in a single Zn grid, so that the Co ions are distributed in a dispersed manner to the maximum extent.

In particular embodiments, the zinc compound comprises Zn (NO)₃)₂. The first Co elemental precursor comprises Co (NO)₃)₂、CoCl₂At least one of (1). The first organic ligand comprises 2-methylimidazole. In the mixed solution formed by the first mixing treatment, the solvent of the mixed solution includes at least one of methanol, ethanol, and Dimethylformamide (DMF). By selecting and optimizing the metal salt, the organic ligand and the solvent, the dispersibility of the metal salt is improved, so that metal ions can effectively perform coordination reaction with the organic ligand, the generation efficiency of the first bimetal ZnCo-MOF precursor is improved, and the dispersibility of the Co ions is improved.

In step S02, zinc ions are added to the second Co simple substance precursor solution, and react with Co ions and second organic ligands, so that a Zn-containing bimetallic ZnCo-MOF precursor coating layer is generated in situ on the surface of the first bimetallic ZnCo-MOF precursor, and the first bimetallic ZnCo-MOF precursor is coated, thereby obtaining a Zn-containing second bimetallic ZnCo-MOF precursor. The zinc ions are added in the second Co simple substance precursor solution, the action of the zinc ions is the same as that of the zinc ions added in the first Co simple substance precursor solution, so that the Zn ions form similar grids in the double-metal ZnCo-MOF precursor coating layer, the Co ions are isolated, and the Co ions can be distributed at intervals. In this way, in the second bimetallic ZnCo-MOF precursor generated in step S02, in the first bimetallic ZnCo-MOF precursor particles and the bimetallic ZnCo-MOF precursor coating layer coating the first bimetallic ZnCo-MOF precursor particles, Zn ions are distributed in a grid form, and Co ions are enclosed in a single Zn grid, so that Co ions are distributed dispersedly to the maximum extent.

In an embodiment, in the step of performing the second mixing treatment, the molar ratio of the first bimetallic ZnCo-MOF precursor, the zinc compound providing zinc ions, the second elemental Co precursor, and the second organic ligand is 0.26: 0.03: 1.2-0.24: 0.06: 1.2 specifically comprises the following components: 0.26: 0.03: 1.2. in the mixed liquid formed by the second mixing treatment, the concentration of the second Co simple substance precursor is preferably 0.0007-0.0012mol/L, and preferably 0.001 mol/L. By optimizing the mixing proportion of the four components and the control and optimization of the solute concentration of the mixture, Zn ions and Co ions can fully perform ligand reaction with a second organic ligand, and meanwhile, the Zn ions are distributed in a grid shape in the bimetallic ZnCo-MOF precursor coating layer, and the Co ions are enclosed in a single Zn grid, so that the prepared Co ions are distributed in a dispersed manner to the maximum extent.

In particular embodiments, the zinc compound comprises Zn (NO)₃)₂It may be the same as or different from the zinc compound in step S01. The second Co elemental precursor comprises Co (NO)₃)₂、CoCl₂Which may be the same as or different from the first elemental Co precursor. The second organic ligand comprises 2-methylimidazole, which may be the same or different from the second organic ligand. In the mixed solution formed by the second mixing treatment, the solvent of the mixed solution includes at least one of methanol, ethanol, and Dimethylformamide (DMF), which may be the same as or different from the mixed solution solvent in step S01. By selecting and optimizing the metal salt, the organic ligand and the solvent, the dispersibility of the metal salt is improved, so that metal ions can effectively perform coordination reaction with the organic ligand, the generation efficiency of the bimetallic ZnCo-MOF precursor coating layer in the step S02 is improved, and the dispersibility of Co ions is improved.

In step S03, during the sintering treatment of the second bimetallic ZnCo-MOF precursor prepared in step S02 in the nitrogen atmosphere of S03, the second bimetallic ZnCo-MOF precursor undergoes a decomposition reaction, wherein both the first organic ligand and the second first organic ligand contained in the second bimetallic ZnCo-MOF precursor are carbonized to generate carbon; both Co and Zn contained in the second bimetallic ZnCo-MOF precursor can be generated into a single atomic state, but in the embodiment of the invention, a generated Zn single atom can be generated in the sintering processIs volatilized and removed. In this way, the first bimetallic ZnCo-MOF precursor contained in the second bimetallic ZnCo-MOF precursor is formed into the inner shell layer 2 and the cavity 1 formed by the coating of the inner shell layer 2 as shown in fig. 1, i.e. the first bimetallic ZnCo-MOF precursor forms a hollow core body structure during the sintering process. A bimetallic ZnCo-MOF precursor cladding layer contained in the second bimetallic ZnCo-MOF precursor forms an outer shell layer 4, and the generated outer shell layer 4 and an inner shell layer 2 form a gap 3 and a hollow cavity 1 due to organic ligand carbonization and the chemical reaction of a Zn compound and a Co precursor in the sintering process, so that the outer shell layer 4 and the inner shell layer 2 are endowed with rich porous structures, and the generated composite structure Co-N is endowed_xthe/C single-atom catalyst has large specific surface area. Meanwhile, in the sintering treatment process, generated Zn single atoms are volatilized, and independently distributed Co atoms are left, so that the Co atoms have good dispersibility.

In one embodiment, the temperature of the sintering process is 800-. Preferably 800 deg.c. Through the temperature optimization of the sintering treatment, the second double-metal ZnCo-MOF precursor component is subjected to the chemical reaction, and the zinc atom component is volatilized, so that the composite structure Co-N of the hollow structure with double shells in the embodiment of the invention shown in figure 1 is formed_xThe catalyst has improved structure stability and catalytic activity stability.

Thus, the above composite structure Co-N_xThe preparation method of the/C monatomic catalyst enables the prepared Co-N with the composite structure to be controlled and optimized through the design of a preparation process route and the control and optimization of each process step and condition_xthe/C monatomic catalyst material has a hollow structure with double shell layers, has excellent structural stability and large specific surface area, has rich catalytic reaction active sites, and has the composite structure Co-N of the invention_xThe advantages described for the/C monatomic catalyst; meanwhile, the process conditions are easy to control, and the Co-N composite structure can be ensured_xthe/C monatomic catalyst has stable structure and performance and high efficiency, and is suitable for industrial production and preparation.

On the other hand, Co-N based on the composite structure described above_xThe embodiment of the invention also provides a fuel cell cathode and a fuel cell comprising the fuel cell cathode. The cathode structure of the fuel cell can be the conventional structure of the cathode of the fuel cell, and the difference is that the catalyst contained in the cathode of the fuel cell is the composite structure Co-N of the embodiment of the invention_xa/C monatomic catalyst. Since the fuel cell cathode contains the above-described composite structure Co-N_xThe catalyst has high catalytic activity.

The fuel cell includes a cathode and, of course, other components necessary for the fuel cell. Wherein the cathode is the fuel cell cathode. Thus, the electrochemical energy conversion efficiency of the fuel cell is significantly improved.

The following examples illustrate the composite structure Co-N of the present invention_xa/C monatomic catalyst, a preparation method and application thereof and the like. Wherein, Co-N of each example_xX in the/C monatomic catalyst is 4 +/-0.5.

Example 1

The present example provides a composite Co-N structure_xa/C monatomic catalyst and a preparation method thereof. The composite structure Co-N_xThe structure of the/C monatomic catalyst is shown in figure 1, the catalyst is a hollow structure with double shell layers and comprises an inner shell layer 2 and an outer shell layer 4 coated on the inner shell layer 2, the inner shell layer 2 is coated to form a cavity 1, and a gap 3 is formed between the inner shell layer 2 and the outer shell layer 4; wherein the materials of the inner shell layer 2 and the outer shell layer 4 both contain Co-N_xa/C monatomic catalyst material. Based on the composite structure Co-N_xStructure of/C monatomic catalyst, composite structure Co-N of the present example_xThe catalyst/C is marked as DS Co-N_xa/C SACs catalyst.

DS·Co-N_xThe preparation method of the/C SACs catalyst comprises the following specific steps:

s1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂O1.8 mmol was dissolved in 15mL of methanol and stirred to form a clear and transparent solutionA; dissolving about 7.5mmol of 2-methylimidazole in 15mL of methanol to form a clear and transparent solution B;

s2: mixing the solution A and the solution B in the step S1, stirring for 12 hours at room temperature, and carrying out coordination reaction; after the reaction is finished, adding a certain amount of methanol in sequence, filtering, washing and drying to obtain a bimetallic ZnCo-MOF precursor; taking 50mg of ZnCo-MOF precursor, and dispersing the ZnCo-MOF precursor in 30mL of methanol to form ZnCo-MOF precursor suspension;

s3: mixing Co (NO)₃)₂·6H₂O 0.03mmol、Zn(NO₃)₂·6H₂Dissolving 0.26mmol of O in 10mL of methanol to form a clear and transparent solution C; dissolving about 0.0985g (1.2mmol) of 2-methylimidazole in 10mL of methanol to form a clear and transparent solution D, mixing the solution C and the solution D, adding the mixture into the ZnCo-MOF precursor suspension prepared in the step S2, stirring for 24h at room temperature, centrifuging, washing for 3 times by using methanol, and drying in vacuum to obtain the core-shell type bimetallic ZnCo-MOF precursor.

S4: putting the core-shell bimetallic ZnCo-MOF precursor prepared in the step S3 in N₂Sintering at 800 ℃ in atmosphere to obtain DS, Co-N_x/C SACs。

Example 2

S1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂Dissolving O1.8 mmol in 15mL of methanol, and stirring to form a clear and transparent solution A; dissolving about 10.8mmol of 2-methylimidazole in 15mL of methanol to form a clear and transparent solution B;

s3: mixing Co (NO)₃)₂·6H₂O 0.03mmol、Zn(NO₃)₂·6H₂Dissolving 0.26mmol of O in 10mL of methanol to form a clear and transparent solution C; 2-methylimidazole is mixed with 0.0985g (1.2mmol) is dissolved in 10mL of methanol to form a clear and transparent solution D, the solution C and the solution D are mixed, then added into the ZnCo-MOF precursor suspension prepared in the step S2, stirred for 24h at room temperature, centrifuged, washed for 3 times by methanol, and dried in vacuum to obtain the core-shell bimetallic ZnCo-MOF precursor.

Example 3

S1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂Dissolving O1.8 mmol in 15mL of methanol, and stirring to form a clear and transparent solution A; dissolving about 14.4mmol of 2-methylimidazole in 15mL of methanol to form a clear and transparent solution B;

Example 4

S1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂O Dissolving 1.8mmol of the compound in 15mL of methanol, and stirring to form a clear and transparent solution A; dissolving about 7.5mmol of 2-methylimidazole in 15mL of methanol to form a clear and transparent solution B;

s3: mixing Co (NO)₃)₂·6H₂O 0.06mmol、Zn(NO₃)₂·6H₂Dissolving 0.24mmol of O in 10mL of methanol to form a clear and transparent solution C; dissolving about 0.0985g (1.2mmol) of 2-methylimidazole in 10mL of methanol to form a clear and transparent solution D, mixing the solution C and the solution D, adding the mixture into the ZnCo-MOF precursor suspension prepared in the step S2, stirring for 24h at room temperature, centrifuging, washing for 3 times by using methanol, and drying in vacuum to obtain the core-shell type bimetallic ZnCo-MOF precursor.

Example 5

S1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂Dissolving O1.8 mmol in 15mL of methanol, and stirring to form a clear and transparent solution A; dissolving about 7.5mmol of 2-methylimidazole in 15mL of methanol to form a clear and transparent solution B;

s3: mixing Co (NO)₃)₂·6H₂O 0.045mmol、Zn(NO₃)₂·6H₂O0.255 mmol, dissolved in 10mL of methanolIn alcohol, a clear and transparent solution C is formed; dissolving about 0.0985g (1.2mmol) of 2-methylimidazole in 10mL of methanol to form a clear and transparent solution D, mixing the solution C and the solution D, adding the mixture into the ZnCo-MOF precursor suspension prepared in the step S2, stirring for 24h at room temperature, centrifuging, washing for 3 times by using methanol, and drying in vacuum to obtain the core-shell type bimetallic ZnCo-MOF precursor.

Example 6

S1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂Dissolving O1.8 mmol in 15mL ethanol, and stirring to form a clear and transparent solution A; dissolving about 7.5mmol of 2-methylimidazole in 15mL of ethanol to form a clear and transparent solution B;

s2: mixing the solution A and the solution B in the step S1, stirring for 12 hours at room temperature, and carrying out coordination reaction; after the reaction is finished, sequentially adding a certain amount of ethanol, filtering, washing and drying to obtain a bimetallic ZnCo-MOF precursor; taking 50mg of ZnCo-MOF precursor, and dispersing in 30mL of ethanol to form ZnCo-MOF precursor suspension;

s3: mixing Co (NO)₃)₂·6H₂O 0.03mmol、Zn(NO₃)₂·6H₂Dissolving 0.26mmol of O in 10mL of ethanol to form a clear and transparent solution C; dissolving about 0.0985g (1.2mmol) of 2-methylimidazole in 10mL of ethanol to form a clear and transparent solution D, mixing the solution C and the solution D, adding the mixture into the ZnCo-MOF precursor suspension prepared in the step S2, stirring for 24h at room temperature, centrifuging, washing for 3 times by using ethanol, and drying in vacuum to obtain the core-shell type bimetallic ZnCo-MOF precursor.

Example 7

S1: mixing Co (NO)₃)₂·6H₂O 1.8mmol、Zn(NO₃)₂·6H₂Dissolving O1.8 mmol in 15mL DMF, and stirring to form a clear and transparent solution A; dissolving about 7.5mmol of 2-methylimidazole in 15mL of DMF to form a clear and transparent solution B;

s2: mixing the solution A and the solution B in the step S1, stirring for 12 hours at room temperature, and carrying out coordination reaction; after the reaction is finished, sequentially adding a certain amount of DMF, filtering, washing and drying to obtain a bimetallic ZnCo-MOF precursor; taking 50mg of ZnCo-MOF precursor, and dispersing the ZnCo-MOF precursor in 30mL of DMF to form ZnCo-MOF precursor suspension;

s3: mixing Co (NO)₃)₂·6H₂O 0.03mmol、Zn(NO₃)₂·6H₂O0.26 mmol, dissolved in 10mL DMF to form clear and transparent solution C; dissolving about 0.0985g (1.2mmol) of 2-methylimidazole in 10mL of DMF to form a clear and transparent solution D, mixing the solution C and the solution D, adding the mixture into the ZnCo-MOF precursor suspension prepared in the step S2, stirring for 24h at room temperature, centrifuging, washing for 3 times by using DMF, and drying in vacuum to obtain the core-shell type bimetallic ZnCo-MOF precursor.

Example 8

S1: adding CoCl₂1.8 mmol、Zn(NO₃)₂·6H₂Dissolving O1.8 mmol in 15mL of methanol, and stirring to form a clear and transparent solution A; dissolving about 7.5mmol of 2-methylimidazole in 15mL of methanol to form a clear and transparent solution B;

s3: adding CoCl₂ 0.03mmol、Zn(NO₃)₂·6H₂O0.26 mmol, dissolved in 10mL of methanol to form a clear solutionClear solution C; dissolving about 0.0985g (1.2mmol) of 2-methylimidazole in 10mL of methanol to form a clear and transparent solution D, mixing the solution C and the solution D, adding the mixture into the ZnCo-MOF precursor suspension prepared in the step S2, stirring for 24h at room temperature, centrifuging, washing for 3 times by using methanol, and drying in vacuum to obtain the core-shell type bimetallic ZnCo-MOF precursor.

Comparative example 1

This comparative example provides a Co-N of a Single Shell_xa/C SACs catalyst. It is a single shell Co-N of example 1 without the shell 4_xa/C SACs catalyst, i.e. a single-shell hollow Co-N catalyst comprising only an inner shell layer 2 and a hollow cavity 1 formed by coating the inner shell layer 2_xCatalyst of/C SACs, denoted as SS. Co-N_x/C SACs。

SS·Co-N_xThe preparation method of the/C SACs catalyst comprises the following specific steps:

s1: refer to step S1 of example 1;

s2: mixing the solution A and the solution B in the step S1, stirring for 12 hours at room temperature, and carrying out coordination reaction; after the reaction is finished, adding a certain amount of methanol in sequence, filtering, washing and drying to obtain a bimetallic ZnCo-MOF precursor; taking 50mg of ZnCo-MOF precursor;

s3: the ZnCo-MOF precursor prepared in the step S2 is added into N₂Sintering at 800 ℃ in atmosphere to obtain SS. Co-N_x/C SACs。

Comparative example 2

Commercial Pt/C catalysts are provided.

Fuel cell embodiment

The DS Co-N provided in examples 1 to 8 above_xthe/C SACs catalysts and the catalysts provided in comparative examples 1 to 2 were prepared as air cathodes, respectively, as follows:

preparing a cathode: the DS Co-N provided in examples 1 to 8 were taken_xCatalyst for/C SACsAnd the catalyst provided in the comparative example, the catalyst, isopropanol, deionized water and 5%

The suspension was ultrasonically mixed in alcohol to make an electrode containing 35 wt% of the total

A slurry of content applied to a cathode electrode to a catalyst loading of-4.0 mg/cm²Thereby preparing the cathode of each fuel cell separately.

Anode: commercial Pt/C catalyst at a loading of about 0.1mg_Pt/cm²(Please give a method or material for the preparation of the anode)

Electrolyte solution:

212 proton membrane

Assembling the fuel cell: the proton membrane fuel cells were assembled into fuel cells of the respective examples.

Correlation characteristic test

1.DS·Co-N_xCharacterization and structural analysis of the/C SACs:

(1) DS Co-N provided in examples 1 to 8_xThe morphology characterization analysis of the/C SACs catalyst such as TEM, SEM, EDX-Mapping, CS-TEM and the like:

example 1 provides DS Co-N_xSEM images of/C SACs catalysts are shown in FIG. 4(a), TEM images are shown in FIG. 4(b), HRTEM images are shown in FIG. 4(C), and the inset image in FIG. 4(C) is a corresponding SAED image; Cs-TEM images are shown in FIGS. 4(d) to 4 (e); the HAADF-STEM Mapping diagram is shown in FIG. 4 (f).

As can be seen from FIG. 4, DS. Co-N_xthe/C SACs catalyst has the characteristics of a hollow double-shell structure, the outer layer is a nearly regular rhombic dodecahedron, and the inner layer is a nearly regular spherical shape, as shown in fig. 4(a) and 4 (b). DS Co-N_xthe/C SACs catalyst is a carbon structure with no significant crystallization, as shown in FIG. 4 (C). DS Co-N_xThe monoatomic Co in the/C SACs catalyst is uniformly dispersed in the inner and outer layer structures, and does not containSignificant agglomeration is seen in FIG. 4(d) and FIG. 4 (e). DS Co-N_xthe/C SACs catalyst is composed of Co, N, C elements, as shown in FIG. 4 (f).

(2) The DS Co-N provided in examples 1 to 8 above_xStructural characterization analysis of XRD, XPS, XAFS, ICP-MS, BET, etc. of the/C SACs catalysts and the catalysts provided in comparative examples 1 to 2:

among them, DS. Co-N provided in example 1_xXRD patterns of the/C SACs catalysts and comparative example 1 are shown in FIG. 5(a), XPS pattern of N1s is shown in FIG. 5(b), XPS pattern of Co 2p is shown in FIG. 5(C), and N is shown in FIG. 5(C)₂The adsorption-desorption isotherm graph is shown in FIG. 5(f), and the ICP-MS test Co content comparison graph is shown in FIG. 5 (g); example 1 provides DS Co-N_xThe Co XANES diagram of the/C SACs catalyst and Co simple substance, CoO is shown in FIG. 5 (d); example 1 provides DS Co-N_xThe Fourier transform plot of the Co K absorption edge of the/C SACs catalyst with Co simple substance is shown in FIG. 5 (e).

As can be seen from FIG. 5, DS. Co-N_xThe 26 ° and 44 ° in the/C SACs catalyst are (002) and (101) crystal planes of graphitic carbon, with no significant Co singlet peaks, as shown in fig. 5 (a). DS Co-N_xThe content of the active species Co-N in the/C SACs catalyst is higher than that in the single-layer structure in the comparative example 1, which shows that the active sites in the structure are increased, and the XPS characterization shows that Co is added²⁺The characteristic peaks of (a) and (b) are shown in fig. 5 to 5(c), in which Co is positively charged due to the coordination of N. DS Co-N_xCo-N in/C SACs catalyst₄The coordination environment of (a) is shown in FIGS. 5(d) to 5(e), in which no metal bond Co-Co bond exists. DS. Co-N in example 1_xThe specific surface area of the/C SACs catalyst is as high as 815.84m²G, also higher than 729.49m of the single-layer structure in comparative example 1²(ii)/g, as shown in FIG. 5(f), further illustrates DS. Co-N_xthe/C monatomic catalyst double-layer shell and the hollow structure can expose more active sites, which is also beneficial to the improvement of the catalytic performance. These results demonstrate that the hollow double shell structure has important effects on increasing the single atom loading and increasing the active sites. DS. Co-N in example 1_xThe load rate of Co single atom in the/C single atom catalyst is as high as 2.61 wt%, which is obviously higher than that of the single layer in the comparative example 11.50 wt% of the structure, as shown in FIG. 5 (g).

In addition, DS. Co-N provided in examples 2 to 8_xMorphology and Structure characterization results for/C SACs vs. DS. Co-N as provided in example 1 above_xThe appearance and structure characterization results of the/C SACs are approximate.

2.DS·Co-N_xORR catalytic performance analysis of/C SACs

(1) Analysis of ORR catalytic efficiency under alkaline conditions:

the DS Co-N provided in examples 1 to 8 above_xthe/C SACs catalysts and the catalysts provided in comparative examples 1 to 2 were subjected to ORR catalytic efficiency tests in the following alkaline medium, respectively:

in an alkaline medium (0.1M KOH), DS. Co-N_xThe results of ORR catalytic efficiency testing of the/C SACs and the catalysts of comparative examples 1 to 2 are shown in FIG. 6, in which DS. Co-N of example 1_xThe linear polarization curves (LSV) of the/C SACs, the catalysts of comparative example 1 to comparative example 2 at RDE test speed of 1600rpm and sweep speed of 5mV/s are shown in FIG. 6(a), the Tafel plot fitted from FIG. 6(a) is shown in FIG. 6(b), and the kinetic current density J of the three at 0.80V is shown_kAnd a half-wave potential comparison chart as shown in FIG. 6(c), DS. Co-N of example 1_x/C SACs and SS. Co-N of comparative example 1_xThe ECSA plot of the/C SACs is shown in FIG. 6 (d); DS. Co-N of example 1_xThe LSV graph of the/C SACs at different rotating speeds is shown in FIG. 6(e), and the interpolation graph of 6(e) is a K-L curve; electron transfer numbers n and H of the three₂O₂The yield scheme is shown in FIG. 6 (f); DS. Co-N of example 1_xLSV graphs of the/C SACs before and after 10000 CV scans are shown in FIG. 6(g), and an interpolation graph of 6(g) is a test graph of 100h i-t; DS. Co-N of example 1_xThe methanol tolerance test patterns for the/C SACs and Pt/C of comparative example 2 are shown in FIG. 6 (h);

as can be seen from FIG. 6, the DS. Co-N of example 1 was tested by rotating the disk (RDE) in 0.1M KOH solution_xThe initial potential of the/C SACs is 1.02V and the half-wave unit is 0.88V, as shown in FIG. 6 (a); furthermore, the Tafel slope value fitted by LSV was 64mV/dec (as shown in FIG. 6 (b)); the kinetic current density fitted by the K-L equation was 23.3mA/cm²As shown in fig. 6 (c); the electrochemical active area (ECSA) was 45mF/cm²As shown in FIG. 6 (d); the K-L curve shows good linearity () showing that the first order reaction kinetics of ORR is independent of the electron transfer rate of the potential and the electron transfer number is 3.88, H₂O₂The yields of (a) and (b) are 2% to 7% as shown in FIG. 6 (e-f). In addition, in terms of catalytic stability, as shown in FIG. 6(g), after 10000 cycles of CV, DS. Co-N_xBoth the initial potential and the half-wave potential of the/C SACs did not decay significantly, the current density remained 95% after 100h of current-time (i-t) testing at the limiting current density, and it was strongly resistant to methanol, as shown in FIG. 6 (h). The results are much higher than the single shell structure in comparative example 1 and the commercial grade Pt/C catalyst in comparative example 2, indicating DS. Co-N_xthe/C SACs exhibited excellent catalytic efficiency in alkaline media, as shown in table 1 below.

(2) Analysis of ORR catalytic efficiency under acidic conditions:

the DS Co-N provided in examples 1 to 8 above_xthe/C SACs catalysts and the catalysts provided in comparative examples 1 to 2 were subjected to ORR catalytic efficiency tests in the following acidic media, respectively:

in acidic medium (0.5M H)₂SO₄) Mixing DS, Co-N_xThe results of the ORR catalytic efficiency test of the/C SACs and the catalysts of comparative examples 1 to 2 are shown in FIG. 7, in which DS. Co-N of example 1_xThe linear polarization curves (LSV) of the/C SACs, the catalysts of comparative example 1 to comparative example 2 at RDE test speed of 1600rpm and sweep speed of 5mV/s are shown in FIG. 7(a), the Tafel plot fitted from FIG. 7(a) is shown in FIG. 7(b), and the kinetic current density J of the three at 0.70V is shown_kAnd a half-wave potential comparison chart shown in FIG. 7(c), DS. Co-N of example 1_x/C SACs and SS. Co-N of comparative example 1_xThe ECSA plot of the/C SACs is shown in FIG. 7 (d); DS. Co-N of example 1_xThe LSV graph of the/C SACs at different rotating speeds is shown in FIG. 7(e), and the interpolation graph of 7(e) is a K-L curve; electron transfer numbers n and H of the three₂O₂The yield scheme is shown in FIG. 7 (f); DS. Co-N of example 1_xLSV graphs of/C SACs before and after 10000 CV scans are shown in the figure7(g), the 7(g) interpolation graph is a 100h current-time (i-t) test graph. DS. Co-N of example 1_xThe methanol tolerance test patterns for the/C SACs and Pt/C of comparative example 2 are shown in FIG. 7 (h);

as can be seen from FIG. 7, the value is 0.5M H₂SO₄The DS Co-N of example 1 was tested in solution by Rotating Discs (RDE)_xThe initial potential of the/C SACs was 0.95V and the half-wave unit was 0.78V, as shown in FIG. 7 (a); furthermore, the Tafel slope value fitted by LSV was 77mV/dec (as shown in FIG. 7 (b)); the kinetic current density fitted by the K-L equation was 28.1mA/cm²As shown in FIG. 7 (c); the electrochemical active area (ECSA) was 54mF/cm²As shown in FIG. 7 (d); the K-L curve shows good linearity, showing that the first order reaction kinetics of ORR is independent of the electron transfer rate of the potential and the electron transfer number is 3.88, H₂O₂The yield of (a) was 8%, as shown in FIG. 7 (e-f). Further, in view of catalytic stability, as shown in FIG. 7(g), DS. Co-N was obtained after 10000 cycles of CV_xthe/C SACs have slight decay in half-wave potential, a current density of 91% after 100h of current-time (i-t) test, and strong methanol tolerance, as shown in FIG. 7 (h). The results are much higher than the single shell structure in comparative example 1 and the commercial grade Pt/C catalyst in comparative example 2, indicating DS. Co-N_xthe/C SACs exhibited excellent catalytic efficiency in alkaline media, as shown in table 1 below.

In addition, DS. Co-N provided in examples 2 to 8_xORR catalytic efficiency of/C SACs under alkaline and acidic conditions is comparable to DS. Co-N provided in example 1 above_xThe ORR catalytic efficiency of the/C SACs under alkaline and acidic conditions is similar.

TABLE 1 DS. CoN under basic and acidic conditions_xORR catalytic Performance comparison of/C SACs

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. Co-N with composite structure_xthe/C monatomic catalyst is characterized in that: the composite structure Co-N_xThe catalyst comprises a catalyst shell, a catalyst core, a catalyst component, a catalyst component and a catalyst component, wherein the catalyst component is a hollow structure with double shell layers and comprises an inner shell layer and an outer shell layer coated on the inner shell layer, the inner shell layer is coated to form a cavity, and a gap is formed between the inner shell layer and the outer shell layer; wherein the materials of the inner shell layer and the outer shell layer both contain Co-N_xA single atom catalyst of/C, and said Co-N_xthe/C monatomic catalyst contains Co-N_xA single atom site;

the diameter of the cavity in the inner shell layer is 250-300 nm;

the gap distance between the inner shell layer and the outer shell layer is 20-50 nm;

the composite structure Co-N_xThe specific surface area of the/C monatomic catalyst is 800-900m²/g。

2. Composite structure Co-N according to claim 1_xthe/C monatomic catalyst is characterized in that: the thickness of the inner shell layer is 20-50 nm; and/or

The thickness of the outer shell layer is 10-20 nm.

3. Composite structure Co-N according to claim 1 or 2_xthe/C monatomic catalyst is characterized in that: the composite structure Co-N_xThe load of Co single atom in the/C single atom catalyst is 2.5 wt% -3.0 wt%.

4. Composite structure Co-N according to any one of claims 1 to 3_xThe preparation method of the/C monatomic catalyst is characterized by comprising the following steps:

5. The method of claim 4, wherein: in the first mixing treatment step, a molar ratio of a zinc compound providing the zinc ions, the first elemental Co precursor and a first organic ligand is 1: 1: 4-1: 1: 8; and/or

And in the mixed solution formed by the first mixing treatment, the concentration of the first Co simple substance precursor is 0.05-0.1 mol/L.

6. The method of claim 5, wherein: the zinc compound comprises Zn (NO)₃)₂(ii) a And/or

The first Co elemental precursor comprises Co (NO)₃)₂、CoCl₂At least one of; and/or

The first organic ligand comprises 2-methylimidazole; and/or

In the mixed solution formed by the first mixing treatment, the solvent of the mixed solution includes at least one of methanol, ethanol, and dimethylformamide.

7. The production method according to any one of claims 4 to 6, characterized in that: in the second mixing treatment step, the molar ratio of the first bimetallic ZnCo-MOF precursor, the zinc compound providing the zinc ions, the second elemental Co precursor and the second organic ligand is: 0.26: 0.03: 1.2-0.24: 0.06: 1.2; and/or

And in the mixed solution formed by the second mixing treatment, the concentration of the second Co simple substance precursor is 0.0007-0.0012 mol/L.

8. The method of claim 7, wherein: the zinc compound in the mixed liquid formed by the second mixing treatment includes Zn (NO)₃)₂At least one of; and/or

The second Co elemental precursor comprises Co (NO)₃)₂、CoCl₂At least one of; and/or

The second organic ligand comprises 2-methylimidazole; and/or

In the mixed solution formed by the second mixing treatment, the solvent of the mixed solution includes at least one of methanol, ethanol and DMF.

9. The production method according to any one of claims 4 to 6 and 8, characterized in that: the temperature of the sintering treatment is 800-900 ℃.

10. A fuel cell comprising a cathode including a catalyst, characterized in that: the catalyst is the composite structure Co-N of any one of claims 1 to 3_x/C monatomic catalyst or composite structure Co-N prepared by the preparation method according to any one of claims 4 to 9_xa/C monatomic catalyst.