Iridium cluster / iron monatomic double-active-site oxygen electrocatalyst as well as preparation and application thereof

Abstract

The invention provides an iridium cluster / iron monatomic double-active-site oxygen electrocatalyst, a geometric regulation preparation method of the iridium cluster / iron monatomic double-active-site oxygen electrocatalyst and application of the iridium cluster / iron monatomic double-active-site oxygen electrocatalyst in a metal-air battery cathode, and relates to the field of electrocatalytic materials and new energy devices. According to the preparation method, in-situ polypyrrole coating is guided through a precious metal iridium doped ferroferric oxide porous sphere template, and the oxygen electrocatalyst with a multi-scale through pore channel structure is obtained through confinement pyrolysis. Wherein the spatial isolation effect of the porous ball template effectively inhibits high-temperature agglomeration of iridium clusters, and uniform dispersion of the iridium nanoclusters is realized; the integrity of the polypyrrole precursor is kept in the template structure evolution process, and a micropore-mesopore-macropore synergistic multistage mass transfer network is inherited and formed; the synergistic effect of iron monatomic sites and iridium clusters specifically improves oxygen reduction and oxygen evolution bifunctional reaction kinetics respectively. When the zinc-air battery cathode material is applied to a zinc-air battery cathode, high-power-density output and excellent cycle life stability can be realized, and the comprehensive performance of the zinc-air battery cathode material is far better than that of a commercial precious metal reference system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an iridium cluster / iron single-atom dual active site oxygen electrocatalyst, its preparation and application in metal-air batteries. BACKGROUND

[0002] Under the driving of global energy transformation and carbon neutralization strategy, developing efficient and sustainable energy storage technology has become the core issue of scientific research and industry. Metal-air batteries are considered as one of the most promising electrochemical systems due to their high theoretical energy density, good environmental compatibility and outstanding safety. However, their practical application is limited by the inherent kinetic lag of oxygen reduction reaction and oxygen evolution reaction in the air electrode, resulting in serious battery polarization, low energy efficiency and insufficient cycle life. As the core component for regulating the oxygen redox process, the performance of the cathode bifunctional electrocatalyst directly determines the commercialization process of the battery. Current technology faces multiple challenges, and high-performance catalytic systems are heavily dependent on noble metal materials, such as platinum-based oxygen reduction catalysts and iridium, ruthenium-based oxygen evolution catalysts. Although noble metals have excellent activity, their scarcity and cost restrict industrialization. More seriously, in order to make up for the poor oxygen evolution activity of traditional transition metal single-atom catalysts, a heterogenous noble metal with intrinsic reactivity is introduced as a synergistic component, but existing synthesis methods often lead to severe aggregation of noble metal atoms and require ultra-high loading, not only increasing the cost, but also reducing the atomic utilization rate due to the shielding of active sites. At the same time, the preparation of traditional transition metal single-atom catalysts is usually achieved by pyrolyzing metal-organic mixtures, which easily leads to overlapping of active sites and agglomeration of metal particles, hindering the effective exposure of sites. In terms of support structure, a multi-level porous carbon framework with micro-mesopore-macropore synergy can maximize the exposure of active sites and promote the transport of reactants, but existing construction techniques have significant defects. For example, metal-organic framework derived carbon materials can generate abundant micropores, but the size of the pores is too small to limit the diffusion of substances; salt template method can construct meso / macropores, but the pore collapse is easy to occur due to capillary force in the template removal process. These structural failure mechanisms and uncontrolled active sites problems are interwoven, which seriously restrict the performance breakthrough of bifunctional catalysts. Therefore, developing a cathode catalyst that can simultaneously achieve low noble metal loading, precise construction and isolation of active sites, and has a thermally stable multi-level pore structure, has become a technical barrier that needs to be overcome to promote the industrialization of metal-air batteries.

[0003] In view of this, the present application is proposed to solve at least one of the above technical problems. SUMMARY

[0004] The first purpose of the present application is to provide a preparation method of an iridium cluster / iron single-atom dual active site oxygen electrocatalyst to alleviate the problems of high noble metal loading, active site agglomeration and uncontrollable pore structure in the prior art

[0005] The second object of the present application is to provide an oxygen electrocatalyst prepared by the above preparation method.

[0006] The third object of the present application is to provide a cathode electrocatalyst.

[0007] The fourth object of the present application is to provide a cathode.

[0008] The fifth object of the present application is to provide a metal-air battery.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted:

[0010] The preparation method of the oxygen electrocatalyst provided by the present application comprises the following steps:

[0011] (a) providing a heterogeneous noble metal doped magnetite porous nanosphere;

[0012] A first solution is provided, which is formed by an organic polymer monomer, a soluble inorganic acid, a surfactant and a solvent; wherein the organic polymer monomer comprises a nitrogen-containing polymer monomer, and the soluble inorganic acid comprises a proton-containing acid;

[0013] (b) mixing the heterogeneous noble metal doped magnetite nanosphere with a porous structure with the first solution under ultrasonic, then centrifuging and solid-liquid separating and high-temperature drying to obtain a porous polymer intermediate product;

[0014] (c) pyrolyzing and carbonizing the polymer intermediate product under high temperature in an inert atmosphere to obtain a carbon nanosphere with a multi-scale through-hole structure.

[0015] Further, in the above technical solutions of the present application, in step (a), the preparation method of the heterogeneous noble metal doped magnetite porous nanosphere comprises the following steps:

[0016] The noble metal salt, the iron salt and the organic solvent containing a crystal morphology regulator are mixed according to a predetermined mass ratio, loaded into a high-temperature high-pressure reaction kettle, and subjected to a solvothermal reaction under specified temperature and time conditions. After the reaction is completed, the solid-liquid separation is performed by centrifugation, and the separated solid is subjected to high-temperature vacuum drying treatment to obtain the heterogeneous noble metal doped magnetite nanosphere with a porous structure.

[0017] Further, in the above technical solutions of the present application, in step (a), the heterogeneous noble metal salt further comprises any one of iridium salt, ruthenium salt, platinum salt or palladium salt;

[0018] Preferably, the iron salt further comprises any one of ferric chloride hexahydrate, ferrous chloride anhydrous or ferric nitrate nonahydrate;

[0019] Preferably, the crystal morphology regulator further includes any one of anhydrous sodium acetate, trisodium citrate dihydrate, polyvinyl alcohol or cetyltrimethylammonium bromide;

[0020] Preferably, the organic polyol solvent further includes any one of ethylene glycol, propylene glycol or triethylene glycol;

[0021] Preferably, the concentration of the noble metal salt is 0.1 g / L to 0.5 g / L;

[0022] Preferably, the concentration of the iron salt is 10 g / L to 50 g / L;

[0023] Preferably, the concentration of the crystal morphology regulator is 50 g / L to 150 g / L;

[0024] Preferably, the solvothermal reaction is carried out at a temperature of 100-200℃ for 5-24 hours under a pressure of 0.1-10.0 MPa;

[0025] Further, in the above technical solution of the present application, in step (a), the surfactant in the first solution further includes any one of cetyltrimethylammonium bromide, polyvinylpyrrolidone, dodecylamine or sodium dodecylbenzenesulfonate;

[0026] Preferably, the nitrogen-containing polymer monomer in the first solution further includes any one of pyrrole, aniline, acrylonitrile or pyrazole;

[0027] Preferably, the proton-containing acid in the first solution further includes any one of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid;

[0028] Further, in the above technical solution of the present application, in step (b), the preparation method includes the following steps:

[0029] First, the heterogeneous noble metal-doped magnetite nanospheres with a porous structure are dispersed in a solvent, then a certain concentration of surfactant is added to fully disperse the nanospheres, and then a nitrogen-containing polymer monomer and a proton-containing acid are sequentially added, wherein the proton destroys the structure of the heterogeneous noble metal-doped magnetite to release metal ions, the trivalent iron ions with high oxidation state oxidize the polymerized nitrogen-containing polymer monomer, and the metal ion agglomeration is confined and isolated, and finally a porous polymer intermediate product is obtained after high-temperature drying.

[0030] Further, in the above technical solution of the present application, in step (b), the solvent in the first solution includes water or ethanol;

[0031] Preferably, the concentration of the surfactant in the first solution is 5-50 g / L;

[0032] Preferably, the volume fraction concentration of the nitrogen-containing polymer monomer in the first solution is 0.5-5% (v / v);

[0033] Preferably, the volume fraction concentration of the proton acid in the first solution is 0.5-5% (v / v);

[0034] Further, on the basis of the technical scheme of the present application, in step (c), the inert atmosphere further comprises nitrogen or argon;

[0035] Preferably, the temperature of the high-temperature pyrolysis is 800-1000℃, the pyrolysis time is 2-4h, and the heating rate is 1-10℃ / min.

[0036] The present application also provides an iridium cluster / iron single-atom dual active site oxygen electrocatalyst prepared by the above preparation method.

[0037] The present application also provides a cathode electrocatalyst prepared by the above oxygen electrocatalyst.

[0038] The present application also provides a cathode comprising the above cathode electrocatalyst.

[0039] The present application also provides a metal-air battery comprising the above cathode.

[0040] The metal-air battery comprises any one of a zinc-air battery, a lithium-air battery, or an aluminum-air battery.

[0041] Compared with the prior art, the present application has the following beneficial effects:

[0042] (1) The present application provides a preparation method of an iridium cluster / iron single-atom dual active site oxygen electrocatalyst. By reacting noble metal salt, iron salt, and crystal morphology regulator under solvothermal conditions, a heterogeneous noble metal doped ferroferric oxide porous nanosphere is prepared, and its uniform porous structure provides a spatial basis for subsequent metal ion confinement; then, the metal ions are released by etching with a proton acid, and the in-situ oxidative polymerization of a nitrogen-containing polymer monomer in the mesoporous channel is simultaneously initiated, forming a polymer-coated structure. In this process, the polymer network effectively isolates the metal ions to prevent agglomeration, and the nitrogen atoms anchor the metal ions to the site. Finally, in the high-temperature pyrolysis stage, the polymer is carbonized into a nitrogen-doped carbon network, the iron ions migrate to the micropores to form atomically dispersed sites, and the noble metal ions are converted into metal clusters under the space limitation of the mesoporous structure, obtaining a nanosphere with a micropore-mesopore-macropore three-level structure. This method uses a porous oxide with precisely controllable structure as a template, and realizes the synergistic optimization of active sites and pore structure through solvothermal-polymerization-pyrolysis three steps, greatly reducing the dependence on noble metals. Moreover, the process parameters are clear and suitable for industrial scale-up production, providing a commercially viable solution for high-performance metal-air battery cathode materials.

[0043] (2) The application provides an oxygen electrocatalyst prepared by the preparation method. The oxygen electrocatalyst has a unique pore structure due to the advantages of the preparation method, can effectively promote electron transfer and mass transfer, can improve the specific surface area of the material, thereby exposing more catalytically active sites, and has higher catalytic performance.

[0044] (3) The application provides a cathode electrocatalyst prepared by the preparation method. The cathode electrocatalyst has similar or even more excellent electrocatalytic performance than existing noble metal cathode electrocatalysts due to the advantages of the iridium cluster / iron single-atom dual active site oxygen electrocatalyst, and has a lower noble metal loading, thereby greatly reducing the preparation cost of the cathode electrocatalyst and providing a new preparation method for the cathode electrocatalyst.

[0045] (4) The application provides a cathode comprising the cathode electrocatalyst. The cathode also has the same advantages due to the advantages of the cathode electrocatalyst.

[0046] (5) The application provides a metal-air battery comprising the cathode. The metal-air battery also has the same advantages due to the advantages of the cathode. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0048] Figure 1 It is a scanning electron microscope image of the intermediate in different processing stages in Example 1 of the application, wherein (a) is a noble metal iridium-doped ferroferric oxide nanosphere with a porous structure, (b) is a porous polypyrrole intermediate product, and (c) is an iridium cluster / iron single-atom dual active site oxygen electrocatalyst;

[0049] Figure 2 It is a chemical phase and electronic structure characterization of the bifunctional catalyst in Example 1 of the application, wherein (a) is an X-ray diffraction spectrum of the oxygen electrocatalyst, (b) is a synchrotron radiation X-ray absorption near-edge spectrum of the iron element in the oxygen electrocatalyst, (c) is a synchrotron radiation X-ray absorption fine structure spectrum of the iron element in the oxygen electrocatalyst, and (d) is a synchrotron radiation X-ray absorption fine structure spectrum of the iridium element in the oxygen electrocatalyst;

[0050] Figure 3 It is a spherical aberration-corrected transmission electron microscope image of the bifunctional catalyst in Example 1 of the application.

[0051] Figure 4 Specific surface area comparison chart of Example 1, Comparative Example 1 and Examples 3-4 of the present application;

[0052] Figure 5 Linear sweep voltammogram of oxygen reduction reaction of Example 5, Examples 7-8, Comparative Examples 5-7 of the present application and noble metal Pt / C;

[0053] Figure 6 Linear sweep voltammogram of oxygen evolution reaction of Example 5, Examples 7-8, Comparative Examples 5-7 of the present application and noble metal IrO2;

[0054] Figure 7 Charge-discharge cycle chart of zinc-air battery assembled with Example 5, Comparative Examples 5-6 and noble metal Pt / C+IrO2 of the present application;

[0055] Figure 8 Photo of zinc-air battery assembled with Example 5 of the present application lighting LED. DETAILED DESCRIPTION

[0056] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not noted in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not noted by the manufacturer are all conventional products that can be obtained by market purchase.

[0057] According to a first aspect of the present application, a preparation method of an oxygen electrocatalyst is provided, comprising the following steps:

[0058] (a) providing a heterogeneous noble metal doped magnetite porous nanosphere;

[0059] A first solution is provided by mixing an organic polymer monomer, a soluble inorganic acid, a surfactant and a solvent; wherein the organic polymer monomer comprises a nitrogen-containing polymer monomer, and the soluble inorganic acid comprises a proton-containing acid;

[0060] (b) mixing the heterogeneous noble metal doped magnetite nanosphere with a porous structure with the first solution under ultrasonic, then centrifuging to separate the solid and liquid and drying at high temperature to obtain a porous polymer intermediate product;

[0061] (c) pyrolyzing and carbonizing the polymer intermediate product at high temperature under inert atmosphere to obtain a carbon nanosphere with a multi-scale through-pore structure.

[0062] Specifically, in step (a), providing the heterogeneous noble metal-doped ferroferric oxide porous nanospheres refers to introducing or loading the heterogeneous noble metal elements in the form of atoms into the ferroferric oxide nanosphere matrix with a porous structure through a specific synthesis method. The reason for doping the heterogeneous noble metal elements is mainly to increase the specific catalytic active sites.

[0063] In step (b), the heterogeneous noble metal-doped ferroferric oxide nanospheres with a porous structure are mixed with the first solution under ultrasonic, and a certain concentration of surfactant is used to fully disperse the nanospheres, followed by sequentially adding the nitrogen-containing polymer monomer and the protonic acid. The proton destroys the structure of the heterogeneous noble metal-doped ferroferric oxide to release metal ions, the trivalent iron ions with high oxidation state oxidize the polymerized nitrogen-containing polymer monomer, and the metal ion agglomeration is confined and isolated, and then high-temperature drying is performed to obtain a porous polymer intermediate product.

[0064] In step (c), the intermediate product is pyrolyzed (high-temperature carbonization), the polymer is carbonized into a nitrogen-doped carbon skeleton, the iron ions migrate to the micropores to form atomically dispersed sites, and the noble metal ions are converted into metal clusters under the limitation of the mesoporous space to obtain nanospheres with a three-level structure of micropores-mesopores-macropores.

[0065] The preparation method of the oxygen electrocatalyst provided by the application is as follows: the noble metal salt, the iron salt, and the crystal morphology regulator are reacted under solvothermal conditions to prepare heterogeneous noble metal-doped ferroferric oxide porous nanospheres. The uniform porous structure of the nanospheres provides a spatial basis for the subsequent confinement of metal ions. Then, the metal ions are released by etching with a protonic acid, and the in-situ oxidative polymerization of the nitrogen-containing polymer monomer in the mesoporous channel is simultaneously initiated to form a polymer-coated structure. In this process, the polymer network effectively isolates the metal ions to prevent agglomeration, and the nitrogen atoms anchor the metal ions to the sites. Finally, in the high-temperature pyrolysis stage, the polymer is carbonized into a nitrogen-doped carbon network, the iron ions migrate to the micropores to form atomically dispersed sites, and the noble metal ions are converted into metal clusters under the limitation of the mesoporous space to obtain nanospheres with a three-level structure of micropores-mesopores-macropores. The spatial confinement effect of the template reduces the noble metal loading and breaks through the traditional size of the cluster particle diameter, significantly improving the utilization rate of noble metal atoms. The synergistic effect of the multi-level pores accelerates the diffusion of the electrolyte and reduces the oxygen transfer resistance. This method uses the porous oxide with controllable porosity as a template to realize the synergistic optimization of active sites and pore structure through the three steps of solvothermal-polymerization-pyrolysis, greatly reduces the dependence on noble metals, and has clear process parameters, which is suitable for industrial scale-up production. The method provides a solution with commercial prospects for high-performance metal-air battery cathode materials.

[0066] As an optional embodiment of the application, in step (a), the preparation method of the heterogeneous noble metal-doped ferroferric oxide porous nanospheres includes the following steps:

[0067] The heterogeneous noble metal doped porous magnetite nanospheres are synthesized by a solvothermal method. The noble metal salt, iron salt and organic polyol solvent containing a crystal morphology regulator are mixed according to a predetermined mass ratio, and are loaded into a high-temperature and high-pressure reaction kettle to perform a solvothermal reaction under a specified temperature and time condition. During the reaction, the polyol not only acts as a solvent, but also acts as a reducing agent. In the alkaline environment provided by the crystal morphology regulator, the polyol promotes the hydrolysis of the iron salt to generate a ferric hydroxide intermediate, and simultaneously reduces the noble metal ion in situ to an atomic state. Subsequently, the ferric hydroxide is partially reduced to form a magnetite crystal nucleus, and the newly born noble metal atom is doped by lattice embedding or surface anchoring. The crystal morphology regulator is selectively adsorbed on the high-energy crystal face of the magnetite to inhibit the growth rate thereof, break the anisotropy of the crystal growth, and drive the particle to evolve towards a spherical morphology which is more stable in thermodynamics. Meanwhile, with the particle dissolution and re-deposition and the volatilization of the solvent molecules at high temperature, a porous spherical structure with through pores is finally formed. After the reaction, the solid-liquid separation is performed by centrifugation, the residual solvent is removed gently, and the separated solid is placed in a high-temperature vacuum drying treatment to obtain the heterogeneous noble metal doped magnetite nanospheres with a porous structure.

[0068] The type of the noble metal salt is not specifically limited, and as an optional embodiment of the present application, any one of iridium trichloride trihydrate or ruthenium trichloride hydrate is included.

[0069] As an optional embodiment of the present application, the concentration of the noble metal salt in the solution containing the noble metal salt is 0.05-0.25 g / L.

[0070] The typical but non-limiting concentration of the noble metal salt in the solution containing the noble metal salt is 0.05 g / L, 0.075 g / L, 0.1 g / L, 0.125 g / L, 0.15 g / L, 0.175 g / L, 0.2 g / L, 0.225 g / L or 0.25 g / L.

[0071] The type of the iron salt is not specifically limited, and as an optional embodiment of the present application, any one of ferric chloride hexahydrate, ferrous chloride or ferric nitrate nonahydrate is included.

[0072] As an optional embodiment of the present application, the concentration of the iron salt in the solution containing the iron salt is 10-50 g / L.

[0073] The typical but non-limiting concentration of the iron salt in the solution containing the iron salt is 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L or 50 g / L.

[0074] The type of the crystal morphology regulator is not particularly limited, and as an optional embodiment of the present application, any one of anhydrous sodium acetate, sodium citrate or polyvinyl alcohol is included.

[0075] As an optional embodiment of the present application, the concentration of the crystal morphology regulator in the solution containing the crystal morphology regulator is 50-150 g / L.

[0076] The typical but non-limiting concentration of the iron salt in the solution containing the iron salt is 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L or 150 g / L.

[0077] The type of the organic polyhydric alcohol solvent is not particularly limited, and as an optional embodiment of the present application, any one of ethylene glycol, propylene glycol or triethylene glycol is included.

[0078] As an optional embodiment of the present application, the volume of the organic polyhydric alcohol solvent is 20-60 mL.

[0079] The typical but non-limiting volume of the organic polyhydric alcohol solvent is 20 mL, 30 mL, 40 mL, 50 mL or 60 mL.

[0080] As an optional embodiment of the present application, the temperature of the solvothermal reaction is 100-200℃, the reaction time is 5-24 h, and the pressure is 0.1-10.0 MPa.

[0081] The typical but non-limiting temperature of the solvothermal reaction is 100℃, 120℃, 140℃, 160℃, 180℃ or 200℃; the typical but non-limiting time of the solvothermal reaction is 5 h, 10 h, 15 h, 20 h or 24 h; and the typical but non-limiting pressure of the solvothermal reaction is 0.1 MPa, 0.5 MPa, 1 MPa, 2 MPa, 5 MPa, 6 MPa, 8 MPa or 10 MPa.

[0082] In the high-temperature and high-pressure reaction kettle, the reaction kinetics can be significantly improved, and the hydrolysis of the iron salt and the reduction of the noble metal and other thermodynamically unfavorable steps can be promoted, thereby ensuring the completeness of the doping reaction. At the same time, the high temperature and high pressure enhance the ion diffusion capacity, so that the noble metal atoms are embedded in the lattice or anchored on the surface at the stage of nucleation in the magnetite lattice, thereby avoiding the agglomeration problem caused by post-doping.

[0083] As an optional embodiment of the present application, in step (b), the preparation method of the porous polymer intermediate product comprises the following steps:

[0084] The heterogeneous noble metal-doped ferroferric oxide nanospheres with porous structure are mixed and dispersed with the first solution under ultrasonic action. Then a surfactant with a specific concentration is added. The amphiphilic molecules of the surfactant are adsorbed on the surface of the nanospheres through the hydrophobic chains, and the hydrophilic ends extend outward to form a steric hindrance layer, thereby inhibiting the re-agglomeration of the particles and obtaining a stable and uniform dispersion system. Then the nitrogen-containing polymer monomer and the proton acid solution are sequentially injected. The protons generated by the dissociation of the proton acid selectively attack the weak coordination sites of the Fe-O bond, and especially preferentially dissolve the lattice of the noble metal-doped region, so as to controllably release the trivalent iron ions and the noble metal ions. These high oxidation state metal ions play a dual role. On the one hand, they act as oxidizing agents to initiate the redox polymerization of the monomers; on the other hand, the noble metal ions are reduced to atomic state. In this process, the micelles of the surfactant and the porous structure of the nanospheres cooperatively form a confined microenvironment, which prevents the migration and agglomeration of the metal ions through the steric isolation effect, and ensures the high dispersion of the active sites. After high-temperature drying, a porous polymer intermediate product is obtained.

[0085] The type of the optional surfactant is not specifically limited, and as an optional embodiment of the present application, any one of cetyltrimethylammonium bromide, polyvinylpyrrolidone, dodecylamine or sodium dodecylbenzenesulfonate is included.

[0086] As an optional embodiment of the present application, the concentration of the surfactant in the solution containing the surfactant is 5-30 g / L.

[0087] The typical but non-limiting concentration of the surfactant in the solution containing the surfactant is 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L or 30 g / L.

[0088] Preferably, the nitrogen-containing polymer monomer in the first solution further includes any one of pyrrole, aniline, acrylonitrile or pyrazole;

[0089] Preferably, the proton acid in the first solution further includes any one of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid;

[0090] By further limiting the type of the nitrogen-containing polymer monomer and the proton acid, the chain orientation order of the conductive polymer is improved and the doping efficiency is optimized, and at the same time, the exposure mode of the metal active site is controlled through the steric template effect of the protons, which further promotes the improvement of the electrocatalytic performance.

[0091] As an optional embodiment of the present application, in step (c), the inert atmosphere includes any one of argon or nitrogen.

[0092] As an optional embodiment of the present application, in step (c), the pyrolysis temperature is 800-1000℃, the pyrolysis time is 0.5-2h, and the heating rate is 1-10℃ / min. The typical but non-limiting pyrolysis temperature is 800℃, 850℃, 900℃, 950℃ or 1000℃, the typical but non-limiting pyrolysis time is 0.5h, 1h, 1.5h or 2h, and the typical but non-limiting heating rate is 1℃ / min, 2℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min.

[0093] By further limiting the pyrolysis temperature, time and heating rate, the noble metal nanocluster forms a strong electronic coupling interface with the carbon matrix at a more suitable pyrolysis temperature, the porous carbon skeleton realizes directional graphitization and retains single-atom-level dispersed iron active sites, and the stability of the porous channel structure is significantly enhanced, so that the cathode electrocatalyst prepared by using the oxygen electrocatalyst exhibits excellent oxygen reduction and oxygen evolution performance in an alkaline electrolyte.

[0094] According to a second aspect of the present application, an iridium cluster / iron monatomic dual active site oxygen electrocatalyst is also provided, which is prepared by the above preparation method.

[0095] In view of the advantages of the above-mentioned preparation method of the oxygen electrocatalyst, by means of the precise control of the synthesis process, an atomic-level dispersed iridium-iron synergistic active center is constructed in the porous carbon matrix, so as to optimize the electronic structure, maximize the utilization rate of the active site and enhance the redox reaction activity.

[0096] According to a third aspect of the present application, a cathode electrocatalyst is also provided, which is prepared by using the above-mentioned oxygen electrocatalyst.

[0097] In view of the advantages of the above-mentioned oxygen electrocatalyst, the cathode electrocatalyst has similar or even more excellent electrocatalytic performance than the existing noble metal cathode electrocatalyst, and the preparation cost of the cathode electrocatalyst is greatly reduced by using the oxygen electrocatalyst as a raw material, thereby providing a new way for the preparation of the cathode electrocatalyst.

[0098] According to a fourth aspect of the present application, a cathode is provided, which comprises the above-mentioned cathode electrocatalyst. In view of the advantages of the above-mentioned cathode electrocatalyst, the cathode also has the same advantages.

[0099] According to a fifth aspect of the present application, a metal-air battery is provided, which comprises the above-mentioned cathode; the metal-air battery comprises any one of a zinc-air battery, a lithium-air battery or an aluminum-air battery.

[0100] In view of the advantages of the above-mentioned cathode, the air cell also has the same advantages.

[0101] The application will be further described below in conjunction with specific examples and comparative examples.

[0102] Example 1

[0103] The preparation method of the iridium cluster / iron single atom dual active site oxygen electrocatalyst provided in this embodiment comprises the following steps:

[0104] (a) providing hetero noble metal iridium doped ferroferric oxide porous nanospheres;

[0105] 2.7 g of iron chloride hexahydrate and 0.01 g of iridium chloride hexahydrate were dispersed in 80 mL of ethylene glycol solvent under magnetic stirring, then 7.2 g of anhydrous sodium acetate was added, and the stirring was continued for about 30 minutes. The uniform solution was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene. The autoclave was incubated at 200℃ for 8 hours, and then naturally cooled to room temperature. The obtained product was centrifuged, washed with anhydrous ethanol for six times, and then vacuum dried at 60℃ for 12 hours, to obtain the hetero noble metal iridium doped ferroferric oxide porous nanospheres;

[0106] A first solution formed by an organic polymer monomer, a soluble inorganic acid, a surfactant and a solvent was provided;

[0107] The organic polymer monomer comprises 2.0 mL of pyrrole monomer, the soluble inorganic acid comprises 20 mL of hydrochloric acid (6M), the surfactant comprises 1.0 g of cetyltrimethylammonium bromide, and the solvent comprises 30 mL of water;

[0108] (b) The hetero noble metal iridium doped ferroferric oxide nanospheres with a porous structure were mixed with the first solution under ultrasonic, then centrifuged for solid-liquid separation and high-temperature dried, to obtain a porous polymer intermediate product;

[0109] 0.3 g of iridium doped ferroferric oxide nanospheres were dispersed in 60 mL of deionized water and ultrasonically treated for 1 h. Then, 1.0 g of cetyltrimethylammonium bromide was dissolved in 10 mL of anhydrous ethanol and added to the above-mentioned solvent, and ultrasonically treated for 30 minutes. Subsequently, 2.0 mL of pyrrole monomer dissolved in 10 mL of anhydrous ethanol and 20 mL of hydrochloric acid solution (6M) were added in sequence. The ultrasonic treatment was continued for 80 minutes. The black product was centrifuged, and then dried at 80℃ for 12 hours, to obtain a porous polypyrrole intermediate product;

[0110] (c) Then, the porous polypyrrole intermediate product was placed in a tube furnace, heated to 950℃ under an inert atmosphere at a heating rate of 3℃ / min, and incubated for 1 hour, to perform pyrolysis, to obtain the iridium cluster / iron single atom dual active site oxygen electrocatalyst.

[0111] Example 2

[0112] The preparation method of the oxygen electrocatalyst provided in this example is the same as that in Example 1, except that the noble metal salt is replaced by 0.01 g of ruthenium trichloride trihydrate.

[0113] Example 3

[0114] The preparation method of the oxygen electrocatalyst provided in this example is the same as that in Example 1, except that the noble metal salt is replaced by 0.02 g of iridium trichloride trihydrate.

[0115] Example 4

[0116] The preparation method of the oxygen electrocatalyst provided in this example is the same as that in Example 1, except that the noble metal salt is replaced by 0.03 g of iridium trichloride trihydrate.

[0117] Examples 5-8

[0118] Examples 5-8 provide a cathode electrocatalyst, which is made of the oxygen electrocatalyst provided in Examples 1-4, respectively.

[0119] Comparative Example 1

[0120] The preparation method of the oxygen electrocatalyst provided in this example is the same as that in Example 1, except that no noble metal iridium salt is added.

[0121] Comparative Example 2

[0122] The preparation method of the oxygen electrocatalyst provided in this example comprises the following steps:

[0123] Dissolve 10.0 mg of iridium trichloride trihydrate and 8.4 g of ammonium persulfate in 80 mL of water in a round-bottom flask, and place it in an ice bath. Then, under strong magnetic stirring, add 2.0 mL of pyrrole monomer to the solution. Continue to vigorously stir the mixture in the ice bath for 5 hours to allow the pyrrole to fully polymerize. Then, centrifuge the black product and dry it in an oven at 80°C for 12 hours to obtain a porous polypyrrole intermediate product containing only iridium active material. Place the porous polypyrrole intermediate product in a tube furnace and pyrolyze it at 950°C at a heating rate of 3°C / min for 1 hour to obtain an iridium cluster catalyst.

[0124] Comparative Example 3

[0125] The preparation method of the oxygen electrocatalyst provided in this example is the same as that in Comparative Example 2, except that no noble metal iridium salt is added.

[0126] Comparative Example 4

[0127] The present comparative example provides a preparation method of an oxygen electrocatalyst, comprising the following steps:

[0128] (a) providing a porous magnetite nanosphere;

[0129] 2.7 g of iron chloride hexahydrate was dispersed in 80 mL of ethylene glycol solvent under magnetic stirring, and then 7.2 g of anhydrous sodium acetate was added, and the stirring was continued for about 30 minutes. The uniform solution was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene. The autoclave was incubated at 200°C for 8 hours, and then naturally cooled to room temperature. The resulting product was centrifuged, washed with anhydrous ethanol six times, and then vacuum dried at 60°C for 12 hours to obtain a porous magnetite nanosphere;

[0130] A first solution was provided by mixing an organic polymer monomer, a soluble inorganic acid, a surfactant and a solvent;

[0131] The organic polymer monomer includes 2.0 mL of pyrrole monomer, the soluble inorganic acid includes 20 mL of hydrochloric acid (6M), the surfactant includes 1.0 g of cetyltrimethylammonium bromide, and the solvent includes 30 mL of water;

[0132] (b) The porous magnetite nanosphere with a porous structure was mixed with the first solution under ultrasonic treatment, and then centrifuged to separate the solid and liquid and dried at high temperature to obtain a porous polymer intermediate product;

[0133] 0.3 g of the magnetite nanosphere was dispersed in 60 mL of deionized water and ultrasonically treated for 1 h. Then, 1.0 g of cetyltrimethylammonium bromide was dissolved in 10 mL of anhydrous ethanol and added to the above solvent, and ultrasonically treated for 30 minutes. Then, 2.0 mL of pyrrole monomer dissolved in 10 mL of anhydrous ethanol and 20 mL of hydrochloric acid solution (6M) were added in sequence. Ultrasonic treatment was continued for 80 minutes. The black product was centrifuged and then dried at 80°C for 12 hours to obtain a porous polypyrrole intermediate product;

[0134] (c) The porous polypyrrole intermediate product was then placed in a tube furnace and heated to 950°C under an inert atmosphere at a heating rate of 3°C / min, and incubated for 1 hour to perform pyrolysis, thereby obtaining a single-atom iron electrocatalyst.

[0135] Comparative Example 5-Comparative Example 8

[0136] Comparative Example 5-Comparative Example 8 provides a cathode electrocatalyst, which is prepared by using the oxygen electrocatalysts provided in Comparative Examples 1-4, respectively. The preparation method of the cathode electrocatalyst is the same as that of Examples 5-8.

[0137] To verify the technical effects of the examples and comparative examples, the following experiments were performed.

[0138] Experimental Example 1

[0139] Observe the morphology of the raw materials at different processing stages in Example 1, such as Figure 1 As shown. Among them, Figure 1 (a) is a porous noble metal iridium-doped iron tetroxide nanosphere, (b) is a porous polypyrrole intermediate, and (c) is an oxygen electrocatalyst with iridium cluster / iron single-atom dual active sites. Figure 1 As shown, the iridium-doped iron oxide nanospheres exhibit a regular spherical particle size and a uniformly distributed porous structure, providing a stable supporting framework for subsequent in-situ polymer coating. Furthermore, the interconnected channels within them create favorable conditions for mass transport and active site deposition. The porous polypyrrole intermediate retains the spherical shape and pore network of the template. The polypyrrole layer grows uniformly on the surface of the spheres and within the pores, without significant collapse or aggregation, indicating that the morphological characteristics of the template are well inherited during the polymerization process. The iridium cluster / iron single-atom dual-active-site oxygen electrocatalyst also retains the spherical hierarchical porous structure of the first two steps, and the internal micropore-mesopore-macropore pore system remains intact, achieving morphological integration from template to intermediate to final product. Overall, the high consistency of morphology at each stage not only demonstrates the effectiveness of the template but also provides a stable guarantee for the high exposure of active sites and efficient mass transfer of the catalyst.

[0140] Simultaneously, the chemical state and electronic structure of the iridium cluster / iron single-atom dual-active-site oxygen electrocatalyst were examined. For example... Figure 2 As shown in (a), X-ray diffraction testing revealed that the material's XRD pattern only exhibited broadened carbon crystal diffraction peaks, indicating that no iridium or iron crystal diffraction peaks were detected, and the support was a graphitized carbon structure. It is noteworthy that... Figure 3 Aberration-corrected transmission electron microscopy images show the coexistence of metal clusters and single atoms. Synchrotron radiation studies further provide fine structural information at the atomic scale. Figure 2 The K-edge X-ray absorption near-edge structure spectrum and R-space spectrum of iron indicate that iron atoms are in a typical M-N4-C planar coordination environment. The L-edge spectrum of iridium shows that the iridium in Experiment 1 is close to the characteristics of metallic iridium foil, indicating that the iridium cluster is predominantly in a metallic state. Combined with the aberration diagram, this confirms that iridium exists in a cluster form. These results collectively verify the cooperative configuration of iridium clusters and single iron atoms in a carbon matrix, laying the electronic structural foundation for bifunctional catalytic activity.

[0141] Experimental Example 2

[0142] Using Examples 1, 3-4, and Comparative Example 1 as examples, the specific surface area of ​​oxygen electrocatalysts was compared to demonstrate template inheritance. Specifically, as follows... Figure 4 As shown, the oxygen electrocatalyst of Example 1 has a specific surface area as high as 649.1 m². 2 / In Examples 3 and 4, the increased number of heterojunction iridium metals led to excessive atomic migration during pyrolysis, resulting in structural collapse. This demonstrates that with effective inheritance of the template structure and precise control of process parameters, the multi-level pores of the catalyst synergistically amplify the surface area advantage, significantly increasing the number of exposed active sites and reducing mass transfer resistance, thus providing an ideal structural basis for bifunctional oxygen catalytic reactions.

[0143] Experimental Example 3

[0144] The oxygen reduction reaction and oxygen evolution reaction of the cathode electrocatalysts provided in Examples 5-8 and Comparative Examples 5-8 were detected, and the specific results are shown in Table 1.

[0145] The specific detection method for the oxygen reduction reaction is as follows: 2 mg of catalyst is added to a mixed solution of water, isopropanol, and Nafion (v / v / v = 1:3:0.2) in 400 μL, and sonicated for 30 minutes. Then, 15 μL of the suspension is pipetted onto a polished rotating disc electrode (RDE, diameter: 4 mm) or a polished rotating ring electrode (RRDE, diameter: 4 mm), dried at room temperature, and used as the working electrode. A three-electrode system is used for testing, where the counter electrode is a platinum wire, and the Ag / AgCl (saturated KCl) electrode is the reference electrode. Linear scan voltammetry: the scan range is 0.2–1.1 V, the scan rate is 10 mV / s, and the rotation speed is 1600 rpm. The test is performed in 0.1 M KOH electrolyte solution at room temperature. The test voltage is calculated according to formula (E... RHE =E Ag / AgCl +0.059pH+0.197) is converted to a relative standard hydrogen electrode (VS). RHE Voltage. For comparison, commercial 20% Pt / C was prepared and its performance was tested.

[0146] For OER, catalyst-modified pretreated nickel foam, calomel (saturated KCl) electrode, and platinum sheet were used as the working electrode, reference electrode, and counter electrode, respectively. 2 mg of catalyst was added to a 200 μL mixed solution containing anhydrous ethanol and Nafion (v / v = 1:0.05), and then sonicated for 30 min. Then, 100 μL of the suspension was pipetted into the pretreated nickel foam (1 cm²). 2 The catalyst was then dried at room temperature and used as the working electrode. All OER measurements were performed in 1M KOH. Linear sweep voltammetry was used to track the catalyst performance at a scan rate of 10 mV / s, with a similar solution resistance correction (90%) applied in this case. The overpotential of the oxygen evolution reaction is given by η = E RHE -1.23V was calculated. For comparison, commercial IrO2 was prepared and its performance was tested.

[0147] Table 1

[0148]

[0149] As can be seen from the data in Table 1, the electrocatalytic performance of the cathode electrocatalyst provided by Example 1 is overall superior to that of the comparative examples.

[0150] Among them, represented by Example 5, Experimental Examples 7-8 and Comparative Examples 5-7, the oxygen reduction electrocatalytic performance and oxygen evolution electrocatalytic performance of the cathode electrocatalyst were detected, as shown in Figure 5 and Figure 6 As can be seen from Figure 5 , the oxygen reduction electrocatalytic performance of the cathode electrocatalyst prepared by Example 1 is significantly superior to that of other experimental examples and comparative examples, and its initial potential is close to that of commercial Pt / C, and the half-wave potential is superior to that of Pt / C. The excellent performance is mainly due to the electronic synergistic effect between the single-atom iron site and the hetero-iridium cluster, and the multi-scale pore channel structure through the micropore-mesopore-macropore, which significantly enhances the accessibility of active sites and accelerates the mass transfer speed of electrolyte and reactants.

[0151] As shown in Figure 6 , the oxygen evolution electrocatalytic performance of the cathode electrocatalyst prepared by Example 5 is significantly superior to that of other experimental examples and comparative examples, and its overpotential is comparable to that of commercial IrO2. The excellent performance is due to the strong electronic synergistic effect between the nitrogen-doped carbon substrate and the iridium nanocluster, and the hierarchical porous structure. The substrate-catalyst cluster synergistic effect can accelerate the kinetic process of the oxygen evolution reaction, and the multi-scale pore channel system provides a low-resistance channel for the transport of reactants and products. Therefore, the oxygen electrocatalyst constructed by iridium clusters and iron single-atom sites has high oxygen reduction and evolution reaction performance, and is a metal-air battery cathode material with great application potential.

[0152] Experimental Example 4

[0153] The cathode electrocatalysts provided by Example 5 and Comparative Examples 5-6 were used to prepare zinc-air batteries, and the specific method included: 6 mg of catalyst was dispersed in a mixture of 400 microliters of Nafion and 1600 microliters of anhydrous ethanol, and the mixture was ultrasonicated to obtain a uniform ink. It was dropped on a 2.5 cm x 2.5 cm hydrophobic carbon cloth (loading capacity of 1 mg / cm 2The zinc sheets were then dried in an oven at 80°C for 2 hours to prepare the air positive electrode for the zinc-air battery. The polished zinc sheets were immersed in acetone solution to remove the surface oxide layer, dried, and then used as the metal negative electrode for the zinc-air battery. The electrolyte was a mixed solution of 6M KOH and 0.2M zinc acetate. The zinc-air battery was assembled, and then two electrode sheets were assembled into a box-type battery using three different acrylic plates and screws, with electrolyte injected into the middle volume. A commercially available Pt / C+IrO2 (mass ratio 1:1) coated carbon cloth was used as the air positive electrode for comparison.

[0154] like Figure 7 As shown, the charge-discharge cycle performance of the zinc-air battery using the cathode electrocatalyst prepared in Example 5 is significantly better than that of Comparative Examples 5-6 and commercial noble metal-based catalysts. The cathode discharge plateau voltage based on the iridium cluster / iron single-atom dual-active-site oxygen electrocatalyst is significantly increased, while the charging plateau voltage is significantly decreased. Compared with zinc-air batteries with cathodes supported only on iridium clusters or only on iron single-atom oxygen catalysts, this improves discharge efficiency and reduces energy loss, respectively. In addition to having a relatively small voltage gap, the zinc-air battery with the iridium cluster / iron single-atom dual-active-site oxygen electrocatalyst cathode also exhibits good cycle stability, with almost no significant voltage decay after 460 charge-discharge cycles.

[0155] Figure 8 An LED photograph was demonstrated, illuminated sequentially by two connected zinc-air batteries based on Example 5; the batteries exhibited significant operational stability for over 12 hours under atmospheric conditions, which was verified by the lack of significant decrease in LED brightness.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an iridium cluster / iron monatomic dual active site oxygen electrocatalyst, characterized in that, The method comprises the following steps: (a) providing heterogeneous noble metal doped ferroferric oxide porous nanospheres; A first solution is provided, which is formed by an organic polymer monomer, a soluble inorganic acid, a surfactant and an organic polyhydric alcohol solvent; wherein the organic polymer monomer comprises a nitrogen-containing polymer monomer, and the soluble inorganic acid comprises a proton-containing acid; (b) mixing the heterogeneous noble metal doped ferroferric oxide nanospheres with a porous structure and the first solution under ultrasonic, then performing solid-liquid separation by centrifugation and high-temperature drying to obtain a porous polymer intermediate product; (c) pyrolyzing and carbonizing the polymer intermediate product under high temperature in an inert atmosphere to obtain carbon nanospheres with a multi-scale through-pore structure.

2. The method for preparing heterogeneous noble metal-doped iron(III) oxide porous nanospheres according to claim 1, characterized in that, In step (a), the preparation method comprises the following steps: The noble metal salt, the iron salt and the organic solvent containing a crystal morphology regulator are mixed according to a predetermined mass ratio, and are loaded into a high-temperature and high-pressure reaction kettle to perform a solvothermal reaction under a specified temperature and time condition. After the reaction is completed, solid-liquid separation is performed by centrifugation, and the separated solid is subjected to high-temperature vacuum drying treatment to obtain the heterogeneous noble metal doped ferroferric oxide nanospheres with a porous structure.

3. The preparation method according to claim 2, characterized in that, In step (a), the heterogeneous noble metal salt further comprises any one of iridium salt, ruthenium salt, platinum salt or palladium salt; Preferably, the iron salt further comprises any one of ferric chloride hexahydrate, ferrous chloride anhydrous or ferric nitrate nonahydrate; Preferably, the crystal morphology regulator further comprises any one of sodium acetate anhydrous, sodium citrate, polyvinyl alcohol or cetyltrimethylammonium bromide; Preferably, the organic polyhydric alcohol solvent further comprises any one of ethylene glycol, propylene glycol or triethylene glycol; Preferably, the concentration of the noble metal salt is 0.05 g / L-0.25 g / L; Preferably, the concentration of the iron salt is 10 g / L-50 g / L; Preferably, the concentration of the crystal morphology regulator is 50 g / L-150 g / L; Preferably, the temperature of the solvothermal reaction is 100-200 ℃, the reaction time is 5-24 h, and the pressure is 0.1-10.0 MPa.

4. The production method according to claim 2, characterized by, In step (a), preferably, the surfactant in the first solution further comprises any one of cetyltrimethylammonium bromide, polyvinylpyrrolidone, dodecylamine or sodium dodecylbenzenesulfonate; Preferably, the nitrogen-containing polymer monomer in the first solution further comprises any one of pyrrole, aniline, acrylonitrile or pyrazole; Preferably, the proton-containing acid in the first solution further comprises any one of hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid.

5. The method for preparing heterogeneous noble metal-doped iron oxide nanospheres according to any one of claims 1-4, characterized in that, In step (b), the preparation method comprises the following steps: First, the heterogeneous noble metal doped ferroferric oxide nanospheres with a porous structure are dispersed in a solvent, then a surfactant with a certain concentration is added to fully disperse the nanospheres, and then a nitrogen-containing polymer monomer and a proton-containing acid are sequentially added, wherein the proton destroys the structure of the heterogeneous noble metal doped ferroferric oxide to release metal ions, and the trivalent iron ions with high oxidation state oxidize the polymerization of the nitrogen-containing polymer monomer to limit and isolate the metal ion agglomeration, and finally high-temperature drying is performed to obtain the porous polymer intermediate product.

6. The production method according to claim 5, characterized by, In step (b), preferably, the solvent in the first solution comprises water or ethanol; Preferably, the concentration of the surfactant in the first solution is 5-20 g / L; Preferably, the volume fraction concentration of the nitrogen-containing polymer monomer in the first solution is 0.5-5% (v / v); Preferably, the volume fraction concentration of the protonic acid in the first solution is 0.5-5% (v / v).

7. The method of any one of claims 1-6, wherein, In step (c), preferably, the inert atmosphere further comprises nitrogen or argon; Preferably, the temperature of the high-temperature pyrolysis is 800-1000℃, the pyrolysis time is 2-4h, and the heating rate is 1-10℃ / min.

8. An iridium cluster / iron monatomic bi-active site oxygen electrocatalyst, characterized in that, The metal air battery is prepared by the preparation method of any one of claims 1-7.

9. A cathode characterized by, The cathode bifunctional electrocatalyst comprises the cathode of claim 8.

10. A metal-air battery, characterized by, The cathode comprises the cathode of claim 9. The metal air battery comprises any one of a zinc air battery, a lithium air battery, or an aluminum air battery.

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