Axial sulfur-coordinated aluminum monatomic electrocatalytic material and preparation method and application thereof

Abstract

The present application relates to single-atom electrocatalytic material preparation and battery energy conversion technical field, disclose a kind of axial sulfur coordination aluminum single-atom electrocatalytic material and its preparation method and application, axial sulfur coordination aluminum single-atom electrocatalytic material is by S, N co-doped porous carbon carrier and aluminum single-atom atomically dispersed on the carrier composition;The aluminum single-atom exists in the form of positive electricity or partial positive electricity.This application can regulate the local electronic structure and spatial coordination configuration of aluminum single-atom site without introducing transition metal active center, weaken the overstrong adsorption of oxygen-containing intermediate on Al site, improve the intermediate conversion rate in ORR reaction process, and improve the structural stability and electrochemical durability of material in long-term operation process.

Description

Technical Field

[0001] This invention relates to the field of single-atom electrocatalytic material preparation and battery energy conversion technology, and in particular to an axial sulfur-coordinated aluminum single-atom electrocatalytic material, its preparation method and application. Background Technology

[0002] The large-scale application of green energy conversion and storage devices such as fuel cells and zinc-air batteries relies on efficient, low-cost, and long-term stable cathode oxygen reduction reaction (ORR) electrocatalysts. ORR involves a multi-step proton-electron coupling transfer process with slow reaction kinetics, which is often a significant factor limiting the energy conversion efficiency and output power of related electrochemical devices. Therefore, developing non-precious metal ORR catalytic materials that can replace precious metal platinum-based catalysts is an important research direction in the fields of electrocatalysis and new energy materials. Currently, commercial ORR catalysts mainly rely on Pt-based materials. Pt-based catalysts have high ORR activity, but they suffer from high cost, limited resource reserves, insufficient resistance to poisoning, and the need to improve long-term stability, limiting their widespread application in large-scale energy devices. Non-precious metal single-atom catalysts have advantages such as high metal utilization, well-defined active sites, and strong structural designability, and are considered an important technological route to replace Pt-based catalysts.

[0003] Single-atom catalysts (SACs) have shown promising application prospects in the fields of energy storage and energy conversion due to their high atomic utilization, well-defined metal active sites, and tunable metal-support interactions.

[0004] Currently, among non-noble metal single-atom catalysts, 3d transition metal single-atom catalysts, represented by Fe-NC and Co-NC, typically exhibit high initial activity in oxygen reduction reactions (ORRs). However, during actual electrochemical operation, these catalysts may induce Fenton-type side reactions (radical-related side reactions), generating highly oxidizing reactive oxygen radicals that attack the carbon substrate, electrode components, or polymer films, leading to catalyst activity decay and reduced device lifetime. This, in turn, causes degradation of the carbon support, ion-conducting membrane, or electrode structure, affecting the long-term durability of the catalyst and related devices. Compared to transition metal single-atom catalysts, main group metal single-atom catalysts, such as Mg, Al, Sn, and Sb, have potential advantages in reducing the risk of radical-related side reactions due to their valence electron structures differing from those of transition metal centers with partially occupied d orbitals. Therefore, main group metal single-atom catalysts are considered important candidate systems for constructing low-cost, highly stable non-noble metal ORR catalysts. However, existing main group metal single-atom catalysts still have significant activity limitations. The s / p electrons of main group metal single atoms have strong delocalization, and their electronic interaction with reaction intermediates differs from the adsorption regulation mechanism involving d orbitals of transition metals.

[0005] Among numerous main group metal candidate elements, aluminum possesses advantages such as high crustal abundance, low cost, and wide availability. Furthermore, the aluminum center does not rely on partially occupied d orbitals to participate in the ORR process, offering potential advantages in reducing the risk of Fenton-type side reactions, making it a promising candidate for constructing low-cost, highly stable cathode catalytic materials. However, in conventional planar Al-N4 coordination structures, the Al center typically corresponds to oxygen-containing intermediates in the ORR process, such as… O2, O、 OOH and The interactions between OH groups are strong, especially in the later stages of the reaction. OH intermediates exhibit strong adsorption, which easily leads to The difficulty in OH desorption and the occupation of active sites leading to catalytic inertness limit the ORR reaction kinetics. This problem makes it difficult for traditional planar Al-N4 single-atom sites to fully realize their potential catalytic activity. Therefore, how to improve the intrinsic ORR activity while maintaining the structural stability of aluminum single atoms and reducing the risk of free radical side reactions is a key issue currently facing aluminum-based main group single-atom catalysts. In addition, aluminum species are prone to migration, volatilization, or aggregation during high-temperature pyrolysis. It is difficult to stably construct aluminum single-atom active centers with well-defined axial coordination structures using conventional methods of directly mixing and calcining metal precursors with carbon / nitrogen matrices. In particular, existing methods are generally unable to further construct vertically asymmetric coordination microenvironments outside the two-dimensional carbon plane, and it is also difficult to simultaneously achieve highly dispersed aluminum single-atom anchoring, hierarchical porous structure construction, and intermediate adsorption energy modulation.

[0006] Currently, the pyrolysis synthesis of single-atom catalytic materials typically relies on the direct mixing and calcination of metal precursors with carbon / nitrogen matrices. For aluminum single-atom catalysts, this traditional one-step pyrolysis method suffers from the following main shortcomings.

[0007] First, existing methods have limited ability to control the coordination symmetry of Al atoms. The resulting products typically tend to form a thermodynamically stable planar Al-N4 configuration, making it difficult to introduce clearly defined axially coordinating atoms in the direction perpendicular to the carbon plane. Therefore, conventional Al-N4 sites are difficult to effectively eliminate. The reaction is limited by the excessive adsorption of oxygen-containing intermediates such as OH.

[0008] Second, the defect distribution and pore structure in traditional porous carbon substrates are often not controllable. Under high-temperature pyrolysis conditions, aluminum species are prone to migration, volatilization, or local agglomeration, making it difficult for them to be effectively captured and stably locked by coordination sites in the carbon substrate. This can lead to insufficient density of single-atom sites in the material, or the coexistence of multiple species such as single atoms, metal clusters, and metal particles, thereby reducing the uniformity and controllability of active sites.

[0009] Third, conventional carbon supports are mostly microporous structures with narrow pore distribution, resulting in limited mass transfer capacity. Under conditions of high current density discharge or long-term operation, oxygen diffusion, electrolyte wetting, ion migration, and transport of reaction intermediates may all be restricted, leading to actual catalytic efficiency lower than that achievable by the active sites themselves.

[0010] Fourth, existing technologies typically struggle to simultaneously achieve the following three objectives: first, to stably anchor aluminum single atoms under high-temperature conditions; second, to construct an axial coordination structure distinct from traditional planar Al-N4; and third, to obtain a porous carbon support possessing high specific surface area, a microporous-mesoporous cascade structure, and good electrical conductivity. Therefore, existing aluminum single-atom ORR catalysts still face the challenge of achieving a balance between activity, stability, and mass transfer performance.

[0011] Therefore, there is an urgent need for an axially sulfur-coordinated aluminum single-atom electrocatalytic material, its preparation method, and its application to solve the above-mentioned technical problems. Summary of the Invention

[0012] The purpose of this invention is to overcome the problems of insufficient regulation of the electronic structure of main group metals, easy blockage of active sites by oxygen-containing intermediates, and limited mass transfer capacity of microporous structures in existing planar aluminum single-atom catalysts. This invention provides an axial sulfur-coordinated aluminum single-atom electrocatalytic material, its preparation method, and its application.

[0013] To achieve the above objectives, the present invention is implemented according to the following technical solution: An axial sulfur-coordinated aluminum single-atom electrocatalytic material is provided, wherein the axial sulfur-coordinated aluminum single-atom electrocatalytic material is composed of an S and N co-doped porous carbon support and aluminum single atoms atomically dispersed on the support; the aluminum single atoms exist in a positively charged or partially positively charged form.

[0014] Preferably, the aluminum single atom is located at the center of a coordination environment composed of four in-plane N atoms, and forms a coordination relationship with an axial S atom above or below it, thereby forming an AlN4-S type five-coordinate local structure.

[0015] Preferably, the axially sulfur-coordinated aluminum single-atom electrocatalytic material has a hierarchical porous structure, including micropores of 0.6~0.8 nm and mesopores of 1~3 nm.

[0016] The axial sulfur-coordinated aluminum single-atom electrocatalytic material provided by this invention is denoted as AlSNC. This material consists of an S and N co-doped porous carbon support and aluminum single atoms atomically dispersed on that support. The aluminum single atoms exist in a positively charged or partially positively charged form and can be denoted as Al. δ+ .

[0017] In the preferred structure, the Al atom is located at the center of a coordination environment composed of four in-plane N atoms, and further coordinates with an axial S atom above or below it, thus forming an AlN4-S type five-coordinate localized structure. Synchrotron radiation X-ray absorption spectroscopy, including XANES, EXAFS, and wavelet transform analysis, shows that the Al atom does not exist solely in the traditional planar Al-N4 structure, but rather forms an asymmetric coordination structure with axial S coordination characteristics. EXAFS fitting reveals that the average Al-N bond length in the first coordination shell is approximately 1.98 Å, and the Al-S coordination bond length is approximately 2.36 Å. Compared to the approximately 1.90 Å Al-N bond length in the traditional planar Al-N4 configuration, the introduction of axial S coordination stretches the Al-N bonds to a certain extent, indicating an out-of-plane shift or distortion of the local geometry of the Al atom. This structure is beneficial for regulating the electron distribution at the Al center and altering its interaction with the oxygen-containing intermediate in the ORR.

[0018] The AlSNC material obtained by this invention has a hierarchical porous structure, including micropores of 0.6–0.8 nm and mesopores of 1–3 nm. This micropore-mesopore cascade structure facilitates the exposure of single-atom active sites and promotes the transport of oxygen, electrolyte ions, and reaction intermediates during the ORR process. In a preferred embodiment, the material's BET specific surface area can reach 1200 m². 2 g -1 The mass loading of Al can reach approximately 3.25 wt%. These structural features collectively endow AlSNC materials with high active site density, good mass transfer capability, and high structural stability.

[0019] This invention also includes a method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material, comprising the following steps: a) Preparation of ZIF-8 precursor: Zinc salt and 2-methylimidazole were dissolved separately in alcohol solvents. The two solutions were then mixed and stirred to react. After the reaction was completed, the mixture was centrifuged, washed and dried to obtain ZIF-8 nanocrystal particles. b) Precursor mixing and sulfur source introduction assisted by sulfur-containing salts: The ZIF-8 nanocrystal particles obtained in step a) are mixed with sulfur-containing salts to obtain a mixed powder; c) Preparation of crude S,N co-doped porous carbon support by molten salt-assisted pyrolysis: The mixed powder obtained in step b) was pyrolyzed under a flowing inert atmosphere to obtain a black crude product: S and N co-doped porous carbon support crude product. d) Acid etching and purification: The black crude product obtained in step c) was ground and added to the acid washing solution, followed by washing and drying to obtain an S and N co-doped porous carbon support, denoted as SNC; e) Vapor phase aluminum source migration and defect confinement trapping: An aluminum source was introduced into the SNC prepared in step d) to obtain an axially sulfur-coordinated aluminum single-atom electrocatalytic material. In step e), the aluminum source is introduced through a combination of primary pyrolysis, secondary pyrolysis after impregnation, or a combination of primary pyrolysis and post-impregnation pyrolysis.

[0020] Preferably, in step a), the zinc salt is a soluble zinc salt, the molar ratio of zinc salt to 2-methylimidazole is 1:(3-6); the stirring reaction time is 0.5-8 h; the drying temperature is 60-100 ℃, and the drying time is 6-16 h.

[0021] More preferably, in step a), the zinc salt is zinc nitrate hexahydrate, the alcohol solvent is anhydrous methanol, the molar ratio of zinc salt to 2-methylimidazole is 1:4.5; the stirring reaction time is 5 h; the drying temperature is 70 ℃; and the drying time is 12 h. More preferably, in step a), the average particle size of the obtained ZIF-8 nanocrystal particles is preferably 90-110 nm.

[0022] Specifically, step a includes the following processes: a) Preparation of ZIF-8 precursor: Soluble zinc salt and 2-methylimidazole were dissolved separately in alcohol solvents. The two solutions were then mixed and stirred at room temperature. After the reaction was completed, the mixture was centrifuged, washed and dried to obtain ZIF-8 nanocrystal particles. The zinc salt is preferably zinc nitrate hexahydrate; the alcohol solvent is preferably anhydrous methanol; the molar ratio of zinc salt to 2-methylimidazole is 1:(3-6), preferably about 1:4.5; the stirring reaction time is 0.5-8 h, preferably 5 h; the drying temperature is 60-100 ℃, preferably 70 ℃; the drying time is 6-16 h, preferably overnight drying. The average particle size of the obtained ZIF-8 nanocrystal particles is preferably about 100 nm.

[0023] Preferably, in step b), the sulfur-containing salt is a sulfur-containing salt that can provide a sulfur source and participate in etching reconstruction during pyrolysis; the mixing method is at least one of solution stirring and mechanical grinding; the mass ratio of the sulfur-containing salt to ZIF-8 is 1:(2-6).

[0024] Preferably, in step b), the sulfur-containing salt is potassium thiocyanate, and the mass ratio of potassium thiocyanate to ZIF-8 is 1:(2-6).

[0025] Further preferably, the mass ratio of potassium thiocyanate to ZIF-8 is 1:2.

[0026] More preferably, when the mixing method is mechanical grinding, the mechanical grinding time is 10-120 min; preferably 30 min.

[0027] More preferably, when the mixing method is solution mixing, the solvent used is anhydrous ethanol, and after mixing, it is dried at 60-90℃ for 2-6 h; preferably, it is dried at 70℃ for 3 h.

[0028] Specifically, step b) includes the following process: b) Precursor mixing and sulfur source introduction assisted by sulfur-containing salts: The ZIF-8 nanocrystal particles obtained in step a) are mixed with sulfur-containing salts to make the sulfur-containing salts uniformly distributed on the surface of ZIF-8 particles and near the pores, thus obtaining a mixed powder; the mixing method can be solution stirring, mechanical grinding or a combination of the two. The sulfur-containing salt is preferably potassium thiocyanate (KSCN), but other sulfur-containing salts that can provide a sulfur source and participate in etching and reconstruction during pyrolysis can also be selected; the mass ratio of KSCN to ZIF-8 can be 1:(2-6), preferably 1:2; if mechanical grinding is used for mixing, the mechanical grinding time can be 10-120 min, preferably 30 min; if solution mixing is used, the solvent is preferably anhydrous ethanol, and after mixing, it can be dried at 60-90 ℃ for 2-6 h, preferably at 70 ℃ for 3 h.

[0029] Preferably, in step c), the inert atmosphere is at least one of N2, Ar, or He; during the pyrolysis process, the heating rate is 1-5 °C / min. -1 The pyrolysis temperature is 800-1100 ℃, and the isothermal pyrolysis time at the pyrolysis temperature is 1-3 h.

[0030] More preferably, in step c), the inert atmosphere is high-purity Ar; during the pyrolysis process, the heating rate is 5°C / min. -1 The pyrolysis temperature is 900 ℃, and the constant temperature pyrolysis time is 2 h. After the pyrolysis is completed, the furnace is naturally cooled to room temperature.

[0031] Specifically, step c) includes the following processes: c) Preparation of crude S,N co-doped porous carbon support by molten salt-assisted pyrolysis: The mixed powder obtained in step b) is spread evenly in a high-temperature resistant boat and placed in the reaction zone of a tube furnace; under the protection of a flowing inert atmosphere, the ZIF-8 precursor is subjected to programmed temperature rise pyrolysis, which causes carbonization of the precursor, while the sulfur-containing salt undergoes melting, decomposition and doping, thereby obtaining a carbon-based material containing S and N heteroatoms and a porous structure: crude S and N co-doped porous carbon carrier. The inert atmosphere can be N2, Ar, or He, preferably high-purity Ar; the heating rate can be 1-5 °C / min. -1 Preferably 5 ℃ min -1 The pyrolysis temperature can be 800-1100 ℃, preferably 900 ℃; the isothermal pyrolysis time can be 1-3 h, preferably 2 h; after pyrolysis, the system is naturally cooled to room temperature with the furnace.

[0032] Preferably, in step d), the pickling solution is a hydrochloric acid solution or a sulfuric acid solution; the pickling time is 4-16 h, and the pickling temperature is 25-80 ℃; The drying temperature is 50-80 ℃, and the drying time is 6-16 h.

[0033] More preferably, the pickling time is 12 h, the pickling temperature is 80 ℃, the drying temperature is 60 ℃, and the drying time is 12 h.

[0034] A further preferred embodiment is that the hydrochloric acid solution used for pickling is prepared by adding 33 mL of concentrated hydrochloric acid with a mass fraction of 36%~36.8% to deionized water and diluting it to a final volume of 200 mL to prepare the pickling solution. The sulfuric acid solution used for pickling has a concentration of 0.5 mol / L. -1 .

[0035] More preferably, the total volume of the pickling solution is 100-250 mL, and more preferably 200 mL.

[0036] In a further preferred embodiment, after acid washing, the solid product is washed multiple times with deionized water and / or ethanol until the washing solution is neutral.

[0037] The obtained SNC carrier has a wrinkled lamellar morphology and a hierarchical porous structure.

[0038] Specifically, step d) includes the following processes: d) Acid etching and purification: The black crude product obtained in step c) is ground and added to the pickling solution. The residual zinc species and other ineffective inorganic components are removed by pickling. After washing and drying, S and N co-doped porous carbon support is obtained, denoted as SNC. The pickling solution can be hydrochloric acid or sulfuric acid; the total volume of the pickling solution can be 100-250 mL, preferably 200 mL; the pickling time can be 4-16 h, preferably 12 h; the pickling temperature can be room temperature to 80 ℃, preferably 80 ℃; after pickling, the solid product is washed multiple times with deionized water and / or ethanol until the washing solution is neutral; then it is dried at 50-80 ℃ for 6-16 h, preferably at 60 ℃ for 12 h, to obtain an SNC carrier with a wrinkled lamellar morphology and a hierarchical porous structure.

[0039] Preferably, in step e), the SNC, aluminum source and supplementary nitrogen source prepared in step d) are mixed and ground, and then pyrolyzed in a pyrolysis atmosphere. After pyrolysis, the mixture is naturally cooled to room temperature to obtain an axial sulfur-coordinated aluminum single-atom electrocatalytic material. The aluminum source is one or more of aluminum phthalocyanine chloride, aluminum acetylacetonate, and aluminum isopropoxide; the supplementary nitrogen source is dicyandiamide (DICY); the mass ratio of SNC, aluminum source, and dicyandiamide is 1:(0.5-1.5):(5-15); The grinding time is 10-60 min; the pyrolysis atmosphere is Ar, N2, He, or a mixture of H2 / Ar; during pyrolysis, the heating rate is 1-5 ℃ min. -1 The pyrolysis temperature is 800-1100 ℃, and the isothermal pyrolysis time at the pyrolysis temperature is 1-3 h.

[0040] Further preferably, the pyrolysis atmosphere is a 20% H2 / Ar reducing mixture; during pyrolysis, the heating rate is 5℃ / min. -1 The preferred pyrolysis temperature is 850 °C, and the preferred isothermal pyrolysis time at the pyrolysis temperature is 1 h.

[0041] More preferably, in step e), the aluminum source is aluminum phthalocyanine chloride (AlPcCl); the mass ratio of SNC, AlPcCl and DICY is 1:(0.5-1.5):(5-15); the preferred mass ratio of SNC, AlPcCl and DICY is 1:1:10; and the preferred grinding time is 30 min.

[0042] Preferably, in step e), the SNC, aluminum phthalocyanine chloride, and trimesic acid prepared in step d) are ground and mixed in a mass ratio of 1:(0.5-1.5):(0.1-0.3) to obtain a mixed powder; the mixed powder undergoes a two-stage pyrolysis treatment to obtain the pyrolysis product. The two-stage pyrolysis process is as follows: Under the protection of a pyrolysis atmosphere, the first stage is carried out at 1-5 ℃ min. -1The temperature is increased to 200-400 ℃ and held for 10-90 min at a heating rate for initial crosslinking and stabilization of the precursor; the second stage is carried out at 1-5 ℃ / min. -1 The heating rate is increased to 800-1100 ℃ and held for 1-3 h, which is used for the volatilization and migration of aluminum species, defect capture and the formation of axial coordination structures; After pyrolysis, the product was dispersed in anhydrous ethanol and stirred. Then, an aluminum source was added and stirred. After stirring, the anhydrous ethanol was evaporated and the solid product was pyrolyzed to obtain an axially sulfur-coordinated aluminum single-atom electrocatalytic material. The mass ratio of the product to the aluminum source after pyrolysis is (10-15):1; the aluminum source is one or more of aluminum chloride phthalocyanine, aluminum acetylacetonate, and aluminum isopropoxide. The solid product pyrolysis process is as follows: under a pyrolysis atmosphere, at 1-5 ℃ min -1 The temperature is increased to 800-1100 ℃ at a heating rate and held for 1-3 h.

[0043] Further preferably, the pyrolysis atmosphere is Ar, N2, He, or a mixture of H2 / Ar.

[0044] Specifically, step e) includes the following processes: e) Vapor phase aluminum source migration and defect confinement trapping: After mixing and grinding the SNC support, aluminum source, and supplementary nitrogen source prepared in step d), the mixture was placed in a tube furnace and pyrolyzed under an inert or reducing atmosphere. This allowed the aluminum species released from the aluminum source to migrate and be captured by the S / N defect sites in the SNC support, forming axially sulfur-coordinated aluminum single-atom active centers. After pyrolysis, the mixture was naturally cooled to room temperature, and the black solid powder was collected to finally obtain the axially sulfur-coordinated aluminum single-atom electrocatalytic material AlSNC. The preferred aluminum source is aluminum phthalocyanine chloride (AlPcCl). In other embodiments, the aluminum source can also be introduced by a combination of primary mixing pyrolysis, secondary pyrolysis after impregnation, or primary pyrolysis and subsequent impregnation pyrolysis. The aluminum source may include one or more of aluminum phthalocyanine chloride, aluminum acetylacetonate, and aluminum isopropoxide; the supplementary nitrogen source is preferably dicyandiamide (DICY); the mass ratio of SNC, AlPcCl and DICY may be 1:(0.5-1.5):(5-15), preferably 1:1:10; the grinding time may be 10-60 min, preferably 30 min; The pyrolysis atmosphere can be Ar, N2, He, or a H2 / Ar mixture, preferably a 20% H2 / Ar reducing mixture; the heating rate can be 1-5 °C / min. -1 Preferably 5 ℃ min -1The pyrolysis temperature can be 800-1100 ℃, preferably 850 ℃; the isothermal pyrolysis time can be 1-3 h, preferably 1 h; In some embodiments, step e) may also be a two-stage pyrolysis method: the first stage is held at 200-400 °C for 10-90 min for the initial cross-linking and stabilization of the precursor; the second stage is heated to 800-1100 °C and held for 1-3 h for the volatilization and migration of aluminum species, defect capture and the formation of axial coordination structures.

[0045] The preparation process of the AlSNC catalytic material of this invention includes two key stages: the first is the in-situ reconstruction of the ZIF-8 precursor assisted by sulfur salt and the formation of a porous carbon support co-doped with S and N; the second is the volatilization and migration of gaseous aluminum species and the capture of S / N defect sites.

[0046] First, ZIF-8 nanoparticles with high nitrogen content are mixed with low-melting-point sulfur-containing salts, such as potassium thiocyanate (KSCN, melting point approximately 173 °C), in an alcohol solvent. KSCN can be distributed on the surface of the ZIF-8 particles, in the interparticle spaces, and in some channels or pore regions. During the subsequent high-temperature pyrolysis, the sulfur-containing salt undergoes melting, decomposition, and etching, simultaneously providing a sulfur source, leading to structural reconstruction of the ZIF-8-derived carbon material. This process promotes the transformation of the three-dimensional ZIF-8 framework into a two-dimensional porous carbon sheet with a wrinkled morphology, introducing S and N heteroatoms and various coordination defect sites into the carbon skeleton, resulting in an S-N co-doped porous carbon support (SNC). This SNC support exhibits a high defect density, numerous edge sites, and a microporous-mesoporous coexistence structure. S and N atoms can serve as potential coordination sites, providing a localized chemical environment for the subsequent anchoring of aluminum single atoms and the formation of axial coordination structures. Simultaneously, the porous sheet structure helps increase the specific surface area, improve electrolyte wettability, and enhance reactant mass transfer.

[0047] Subsequently, in the second-stage pyrolysis process, aluminum phthalocyanine chloride (AlPcCl) was used as the aluminum source, and dicyandiamide (DICY) was used as the supplementary nitrogen source. The mixture was thoroughly mixed with the SNC support before pyrolysis. During heating, AlPcCl releases aluminum species, which migrate in the gas or quasi-gas phase and are captured by S / N defect sites on the surface of the SNC support. Driven by coordination interactions, the Al species can coordinate with in-plane N atoms and further form axial coordination with neighboring S atoms, thereby constructing AlN4-S type single-atom active centers. During pyrolysis, dicyandiamide decomposes and releases nitrogen-containing species, which helps to supplement or maintain the N coordination environment in the carbon support and, to some extent, inhibits excessive loss of carbon framework defects. Through the above-mentioned support reconstruction, defect introduction, aluminum source volatilization and migration, and coordination capture processes, this invention can obtain an AlSNC catalytic material with highly dispersed aluminum single-atom sites, an axial S coordination structure, and a hierarchical porous support. From a catalytic perspective, axial S coordination can regulate the local electronic structure of the Al center, reducing the dependence of the Al sites on some oxygen-containing intermediates, especially... The excessive adsorption of OH intermediates improves the adsorption, transformation, and desorption equilibrium of intermediates during the ORR reaction. This structural modulation helps to improve ORR reaction kinetics and enhance the stability of the material during long-term electrochemical operation.

[0048] The present invention also includes the application of the axial sulfur-coordinated aluminum single-atom electrocatalytic material described above or the axial sulfur-coordinated aluminum single-atom electrocatalytic material prepared by the preparation method described above in oxygen reduction reaction and metal-air battery.

[0049] This invention introduces a low-melting-point sulfur-containing salt as an in-situ molten etching agent and sulfur source to restructure and dope the ZIF-8 precursor, transforming the traditional three-dimensional ZIF-8 precursor into a two-dimensional porous carbon support, denoted as SNC, with edge defects, S / N coordination sites, and a hierarchical porous structure during high-temperature pyrolysis. Subsequently, by introducing a volatile aluminum source and supplementary nitrogen source, aluminum species sublimate, migrate, and are captured by the S / N defect sites in the SNC support during confined pyrolysis, thereby constructing AlN4-S single-atom active centers with axial sulfur coordination characteristics outside the carbon plane.

[0050] Through the above technical solution, the present invention can regulate the local electronic structure and spatial coordination configuration of aluminum single-atom sites without introducing transition metal active centers, reduce the excessive adsorption of oxygen-containing intermediates on Al sites, improve the intermediate conversion rate in the ORR reaction process, and improve the structural stability and electrochemical durability of the material during long-term operation.

[0051] Aluminum (Al), as a typical p-block main group metal, possesses [Ne]3s 2 3p 1Valence electron configuration. Addressing the shortcomings of traditional planar Al-N4 sites, such as insufficient electronic structure control, excessive adsorption of oxygen-containing intermediates, and insufficient high-temperature stability of aluminum species, this invention proposes a design strategy for aluminum single-atom electrocatalytic materials based on axial coordination regulation. Specifically, this invention utilizes a pyrolysis process combining precursor reconstruction and gas-phase volatilization-defect trapping to construct atomically dispersed axially sulfur-coordinated aluminum single-atom active centers, namely the AlN4-S coordination structure, within a two-dimensional porous carbon network co-doped with S and N. This axial sulfur coordination structure differs from the traditional planar Al-N4 configuration. By introducing axial S-coordinated atoms perpendicular to the carbon plane, the space charge distribution and local electronic structure around the Al center can be adjusted, thereby altering the interaction between the Al center and oxygen-containing intermediates. Theoretical calculations show that axial sulfur coordination enables the Al center to not occupy p-sites. z The band center shifts downward, for example, from -3.03 eV in a planar configuration to -4.00 eV in an axially coordinated configuration. This change in electronic structure weakens the Al-O bond strength and reduces... This invention mitigates the risk of active site blockage caused by excessive adsorption of OH intermediates and improves the adsorption, transformation, and desorption processes of key intermediates in the ORR process. Furthermore, this invention regulates Alp through the spatial competition between axial sulfur coordination and oxygen-containing adsorption intermediates. z The interaction between the orbitals and the adsorbate moderately weakens the Al-O covalent interaction. Theoretical calculations show that axial sulfur coordination can overcome the difficult-to-cross orbitals in traditional planar Al-N4 sites. The OH desorption step has been transformed into a more easily controlled process. The OOH formation step reduces the maximum reaction free energy change from approximately 2.54 eV to approximately 0.61 eV. Therefore, this invention, while leveraging the structural advantage of aluminum's low free radical side reaction tendency, significantly improves the dynamic transformation process of oxygen-containing intermediates, thereby enhancing the ORR catalytic activity and long-term operational stability of the material.

[0052] Beneficial effects: The axial sulfur-coordinated aluminum single-atom electrocatalytic material of this invention constitutes an AlN4-S type five-coordinate localized structure, which is beneficial for regulating the electron distribution of the Al center and changing its interaction with oxygen-containing intermediates in ORR. It has a high active site density, good mass transfer capacity and high structural stability. This invention can regulate the local electronic structure and spatial coordination configuration of aluminum single-atom sites without introducing transition metal active centers, weaken the excessive adsorption of oxygen-containing intermediates on Al sites, improve the intermediate conversion rate in the ORR reaction process, and improve the structural stability and electrochemical durability of the material during long-term operation. Attached Figure Description

[0053] Figure 1 This is a schematic diagram illustrating the synthesis process and mechanism of the axial sulfur-coordinated AlSNC single-atom catalytic material prepared in Example 1 of the present invention; Figure 2 Transmission electron microscope (TEM) and high-resolution TEM images of the AlSNC single-atom catalytic material prepared in Example 1 of this invention; Figure 3 The powder X-ray diffraction phase patterns of the materials prepared in Example 1 and Comparative Examples 1-2 of this invention; Figure 4 The Raman spectra of structural defects of the materials prepared in Example 1 and Comparative Examples 1-2 of this invention; Figure 5 The nitrogen adsorption-desorption isotherms and pore size distribution diagrams of the materials prepared in Example 1 and Comparative Examples 1-2 of this invention are shown. Figure 6 The images show aberration-corrected scanning transmission electron microscopy (STEM) image of a single atom bright spot and an EDS elemental mapping image of the AlSNC single-atom catalytic material prepared in Example 1 of this invention. Figure 7 The X-ray absorption near-edge structure spectrum, extended X-ray absorption fine structure Fourier transform spectrum, and fitting curve of Example 1 and each control sample of the present invention are shown. Figure 8 This is a comparison of the LSV polarization curves of oxygen reduction reaction in oxygen-saturated 0.1 M KOH electrolyte for Example 1 and Comparative Examples 1-3 of the present invention. Figure 9 This is a comparison diagram of Tafel slope and dynamic current density corresponding to Embodiment 1 and Comparative Examples 1-3 of the present invention; Figure 10 A comparison of LSV polarization curves of the AlSNC catalyst material prepared in Example 1 of this invention before and after 50,000 accelerated durability tests. Figure 11 This is a comparison chart of the chronocurrent stability test and methanol cross-interference resistance of the commercial Pt / C catalyst materials in Example 1 and Comparative Example 3 of the present invention. Figure 12 The images show the dynamic in-situ infrared absorption spectra of Example 1 and Comparative Example 1 during the ORR reaction process of this invention. Figure 13 This is an example of in-situ electrochemical impedance spectroscopy and relaxation time distribution decoupling spectrum of Embodiment 1 of the present invention under different bias working potentials; Figure 14 The open-circuit voltage, power density polarization curve, multi-current step discharge curve, and 1500-hour charge-discharge long cycle curve of the liquid zinc-air battery assembled using Example 1 of the present invention as the air cathode catalyst are shown.

[0054] Figure 15 The oxygen reduction free energy step diagram and the P of the central aluminum atom are calculated using the theories of Example 1 and Comparative Example 1 of this invention. z Orbital state density distribution; Figure 16 Powder X-ray diffraction phase patterns of the materials prepared in Examples 2-4 of this invention; Figure 17 The Raman spectra of structural defects in the materials prepared in Examples 2-4 of this invention are shown. Figure 18 The LSV polarization curves of oxygen reduction reaction in oxygen-saturated 0.1 M KOH electrolyte are for Examples 1-4 and Comparative Example 1 of this invention. Detailed Implementation

[0055] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0056] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0057] There are no particular restrictions on the purity of any of the raw materials used in this invention; however, it is preferred to use materials with conventional purity levels used in the field.

[0058] All processes in this invention are referred to by abbreviations that are common abbreviations in the field. Each abbreviation is clear and specific in its relevant application area, and those skilled in the art can understand its conventional process steps based on the abbreviation.

[0059] In the following examples, room temperature refers to 25°C.

[0060] Example 1: A method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material includes the following steps: 1) Preparation of two-dimensional porous S, N co-doped carbon support (SNC) First, 2.94 g of zinc nitrate hexahydrate and 3.24 g of 2-methylimidazole were completely dissolved in 100 mL of high-purity anhydrous methanol under stirring. The two solutions were then mixed and reacted with stirring at room temperature for 5 h. After the reaction was complete, the resulting suspension was centrifuged, the precipitate was collected, and washed three times with anhydrous methanol. The precipitate was then placed in a vacuum oven and dried overnight at 70 °C to obtain ZIF-8 nanocrystal particles with an average particle size of approximately 100 nm.

[0061] Next, 315 mg of potassium thiocyanate (KSCN) was weighed and completely dissolved in 20 mL of anhydrous ethanol to obtain a clear solution. Then, 630 mg of the ZIF-8 nanoparticles prepared above were added to this solution, and the mixture was stirred continuously for 10 min to ensure thorough mixing of KSCN and ZIF-8. After stirring, the resulting suspension was placed in an oven and dried at 70 °C under normal pressure for 3 h to obtain a white solid mixture.

[0062] The dried solid mixture was transferred to a quartz boat and placed in the central isothermal zone of a tube furnace. Before introducing high-purity argon, two evacuation-argon purging cycles were performed to remove residual air from the furnace tubes. Subsequently, under a high-purity Ar flowing protective atmosphere, the mixture was heated at 5 °C for 1 minute. -1 The temperature was increased to 900 °C at a rising rate, and then pyrolyzed at 900 °C for 2 h. After pyrolysis, the system was allowed to cool naturally to room temperature. The black crude product was then removed and ground.

[0063] To remove residual zinc species, 33 mL of concentrated hydrochloric acid (36%–36.8% by mass) was added to deionized water and diluted to a final volume of 200 mL to prepare an acid washing solution. The aforementioned black crude product was added to the acid washing solution and refluxed magnetically at 80 °C for 12 h. After acid washing, the solution was centrifuged, the solid product was collected, and washed repeatedly with ultrapure water and anhydrous ethanol until the pH of the washing solution was close to neutral. Finally, the washed solid sample was placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a two-dimensional porous S, N co-doped carbon support with a wrinkled, sheet-like morphology, denoted as SNC.

[0064] 2) Preparation of axial sulfur-coordinated aluminum single-atom electrocatalytic material (AlSNC) The SNC, aluminum phthalocyanine chloride (AlPcCl, 98% purity), and dicyandiamide (DICY) prepared in the above steps were mixed in a mass ratio of 1:1:10. Specifically, 100 mg of SNC, 100 mg of AlPcCl, and 1000 mg of DICY were weighed and placed together in an agate mortar, and continuously mechanically ground for 30 min to ensure that the components were thoroughly refined and uniformly mixed.

[0065] Subsequently, the obtained mixed powder was transferred to a high-temperature resistant corundum ceramic boat and evenly spread, then placed in the reaction center of a tube furnace. Under a continuously flowing reducing mixed atmosphere (20% H₂ / Ar) at a velocity of 80 sccm, the reaction was carried out at 5 °C for 1 minute. -1The temperature was increased to 850 °C at a heating rate, and then isothermal pyrolysis was performed at 850 °C for 1 h. During pyrolysis, aluminum species released from AlPcCl volatilized and migrated, and were synergistically captured by in-plane N sites and axial S sites in the SNC support, forming axial sulfur-coordinated aluminum single-atom sites. Nitrogen-containing species released from the decomposition of DICY help maintain or replenish the nitrogen coordination environment in the support.

[0066] After pyrolysis, the tube furnace was allowed to cool naturally to room temperature. The corundum boat was removed, and the black, loose solid powder inside was collected, yielding the axially sulfur-coordinated aluminum single-atom electrocatalytic material, denoted as AlSNC. The obtained product can be directly used for subsequent structural characterization and electrochemical testing.

[0067] Example 2 A method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material includes the following steps: 1) Preparation of two-dimensional porous S, N co-doped carbon support (SNC) First, ZIF-8 nanocrystal particles were synthesized according to the ZIF-8 preparation method in Example 1. 250 mg of KSCN was weighed and dissolved in 20 mL of anhydrous ethanol, followed by the addition of 625 mg of ZIF-8 nanoparticles, making the mass ratio of KSCN to ZIF-8 1:2.5. The mixture was continuously mechanically ground in an agate mortar for 20 min to form a homogeneous slurry. After grinding, the slurry was dried at 70 °C for 3 h.

[0068] The dried solid mixture was transferred to a quartz boat and spread evenly, then placed in the central region of a tube furnace. Under a high-purity helium atmosphere, it was heated at 1 °C for 1 min. -1 The temperature was increased to 800 °C at a rising rate and maintained at 800 °C for 3 h. After pyrolysis, the furnace was cooled to room temperature. The black crude product was removed and ground, and then added to 100 mL of 0.5 mol / L solution. -1 The SNC carrier was etched by continuous stirring in an H2SO4 solution at room temperature for 4 h. After etching, the carrier was washed with a large amount of deionized water until the washing solution was neutral and then dried to obtain the SNC carrier.

[0069] 2) Preparation of axial sulfur-coordinated aluminum single-atom electrocatalytic material (AlSNC) The SNC, AlPcCl, and trimesic acid prepared in the above steps were mixed at a mass ratio of 1:0.5:0.1 and ground for 30 min. The resulting powder was then transferred to a corundum ceramic boat and placed in the reaction center of a tube furnace. A two-stage annealing treatment was performed under high-purity helium protection. The first stage was annealed at 1 °C for 1 min. -1The temperature was increased to 200 °C at a heating rate and held at 200 °C for 90 min to complete the initial crosslinking and stabilization of the precursor; the second stage continued at a heating rate of 1 °C / min. -1 The temperature was increased to 800 °C at a heating rate and held at 800 °C for 3 h.

[0070] After the reaction system cooled naturally, the sample was removed. 90 mg of the obtained product powder was weighed and dispersed in anhydrous ethanol, and continuously sonicated or stirred for 30 min to form a homogeneous suspension. Then, 9 mg of aluminum acetylacetonate was added to the suspension, making the mass ratio of product to aluminum acetylacetonate 10:1, and the mixture was continuously stirred at room temperature for 12 h to ensure the aluminum source was fully impregnated in the support. After stirring, the anhydrous ethanol was evaporated in an oven at 80 °C to obtain the precursor mixture. Finally, the precursor mixture was placed in a quartz boat and, under the protection of flowing high-purity helium, incubated at 1 °C for 1 min. -1 The temperature was increased to 800 °C at a heating rate and maintained at pyrolysis for 2 h. After cooling, the product was collected to obtain the AlSNC catalyst sample.

[0071] Example 3 A method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material includes the following steps: 1) Preparation of two-dimensional porous S, N co-doped carbon support (SNC) First, ZIF-8 nanocrystal particles were synthesized according to the ZIF-8 preparation method in Example 1. 150 mg of KSCN was weighed and dissolved in anhydrous ethanol, followed by the addition of 900 mg of ZIF-8 nanoparticles, making the mass ratio of KSCN to ZIF-8 1:6. The mixture was thoroughly ground in an agate mortar for 120 min and dried at 70 °C under normal pressure for 3 h.

[0072] The dried mixture was transferred to a corundum boat and placed in the central region of a tube furnace. Under a high-purity Ar atmosphere, it was heated at 5 °C for [time missing]. -1 The temperature was increased to 1100 °C at a rising rate and maintained at 1100 °C for 1 h. After pyrolysis, the furnace was cooled to room temperature. The product was removed and ground, and then added to 250 mL of a 0.5 mol / L solution. -1 In dilute sulfuric acid, the substrate was continuously etched with stirring at room temperature for 16 h to remove residual metal species. After etching, the substrate was washed with a large amount of deionized water until the washing solution was neutral, and then dried in a vacuum oven at 60 °C to obtain an SNC carrier with a porous structure and defect sites.

[0073] 2) Preparation of axial sulfur-coordinated aluminum single-atom electrocatalytic material (AlSNC) The SNC, AlPcCl, and trimesic acid prepared in the above steps were added to an agate mortar at a mass ratio of 1:1.5:0.3 and ground continuously for 60 min to ensure thorough mixing. The mixed powder was then transferred to a corundum boat and placed in a tube furnace. A two-stage pyrolysis treatment was performed under a high-purity Ar atmosphere. The first stage was carried out at 5 °C for [time missing]. -1 The temperature was increased to 400 °C at a heating rate of 5 °C / min and held at 400 °C for 10 min; in the second stage, the temperature was increased to 400 °C at a heating rate of 5 °C / min. -1 The temperature was increased to 1100℃ at a heating rate and maintained at 1100℃ for 1 h for pyrolysis.

[0074] After the system cooled naturally, the crude product was removed. 90 mg of the product powder was weighed and placed in anhydrous ethanol and mechanically stirred for 30 min. Then, 6 mg of aluminum acetylacetonate was added, making the mass ratio of product to aluminum acetylacetonate 15:1. The mixture was continuously stirred at room temperature for 20 h to ensure complete impregnation of the aluminum source. After stirring, the anhydrous ethanol was evaporated to dryness at 100 °C. Finally, the resulting solid sample was placed in a tube furnace and heated at 5 °C for 1 min under pure Ar flow protection. -1 The temperature was increased to 1100 °C at a heating rate and maintained at pyrolysis for 1 h. After cooling in the furnace, the product was collected to obtain the AlSNC catalyst.

[0075] Example 4 A method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material includes the following steps: 1) Preparation of two-dimensional porous S, N co-doped carbon support (SNC) First, 2.94 g of zinc nitrate hexahydrate and 3.24 g of 2-methylimidazole were dissolved separately in 100 mL of anhydrous methanol, and the two solutions were mixed and stirred at room temperature for 30 min. After the reaction was completed, the solid was collected by centrifugation and dried in a vacuum oven to obtain ZIF-8 nanocrystal particles with relatively uniform particle size.

[0076] Next, 315 mg of KSCN was weighed and dissolved in anhydrous ethanol, followed by the addition of 630 mg of the aforementioned ZIF-8 nanoparticles, making the mass ratio of KSCN to ZIF-8 1:2. The mixture was continuously mechanically ground in an agate mortar for 30 min and dried at 70 °C for 3 h. The resulting powder mixture was then spread evenly in a porcelain boat and placed in the central region of a tube furnace. Under a high-purity N2 atmosphere, it was heated at 3 °C for 3 min. -1 The temperature was increased to 900 °C at a rising rate, and pyrolysis was maintained at 900 °C for 2 h. After the furnace cooled to room temperature, the product was removed, ground, and added to 200 mL of a 0.5 mol / L solution. -1The SNC carrier was etched in a sulfuric acid solution with continuous stirring at room temperature for 12 h. After etching, it was washed with deionized water until the washing solution was neutral and dried at 60 °C to obtain a porous SNC carrier.

[0077] 2) Preparation of axial sulfur-coordinated aluminum single-atom electrocatalytic material (AlSNC) The SNC, AlPcCl, and trimesic acid prepared in the above steps were added to a mortar in a mass ratio of 1:1:0.2 and ground continuously for 30 min to ensure thorough mixing. The mixture was then transferred to a tube furnace reaction center and subjected to a two-stage pyrolysis treatment under a high-purity N2 atmosphere. The first stage was carried out at 3 °C for [time missing] min. -1 The temperature was increased to 300 °C at a heating rate of 3 °C and held at 300 °C for 30 min; in the second stage, the temperature was increased to 3 °C per minute. -1 The temperature was increased to 1000 °C at a heating rate and maintained at 1000 °C for 1 h for pyrolysis.

[0078] After the furnace cooled, the obtained solid powder was removed. 90 mg of this solid powder was weighed and dispersed in anhydrous ethanol, and mechanically stirred for 30 min. Then, 6 mg of aluminum isopropoxide was added, and the mixture was continuously stirred at room temperature for 12 h to ensure complete impregnation of the aluminum source. After stirring, the anhydrous ethanol was evaporated to dryness at 80 °C. Finally, the resulting precursor mixture was placed in the isothermal zone of a tube furnace reaction, and under a flowing high-purity N2 atmosphere, the reaction was carried out at 3 °C for 1 min. -1 The temperature was increased to 950 °C at a rising rate, and pyrolysis was maintained at 950 °C for 2 h. After the system cooled to room temperature, the black powder was collected, which yielded the AlSNC catalyst sample.

[0079] Comparative Example 1: Traditional planar coordination AlNC catalytic materials lack axial S-coordination. 1) Preparation of two-dimensional porous carbon supports (NC) First, ZIF-8 nanocrystals with an average particle size of approximately 100 nm were synthesized according to the ZIF-8 preparation method in Example 1. 630 mg of ZIF-8 nanoparticles were weighed and, without the addition of KSCN or other sulfur-containing salts, were evenly spread in a quartz boat and placed in the center of a tube furnace reaction. Under a pure Ar flowing protective atmosphere, the reaction was carried out at 5 °C for [time missing]. -1 The temperature was increased to 900 °C at a rising rate and maintained at 900 °C for 2 h for pyrolysis. After pyrolysis, the system was cooled to room temperature along with the furnace.

[0080] The crude product was removed and ground, then added to an acid pickling solution diluted from 33 mL of concentrated hydrochloric acid to 200 mL. The solution was continuously stirred and refluxed at 80 °C for 12 h to remove residual metal species. After acid pickling, the solid product was washed until the filtrate was neutral and dried at 60 °C for 12 h to obtain a sulfur-free porous carbon support, denoted as NC.

[0081] 2) Preparation of planar coordinated aluminum single-atom catalytic materials (AlNC) The NC, AlPcCl, and DICY obtained in the above steps were mixed at a mass ratio of 1:1:10 and mechanically ground in an agate mortar for 30 min. The mixed powder was then transferred to a corundum porcelain boat and spread evenly, then placed in the center of a tube furnace. Under a continuous 20% H2 / Ar mixed atmosphere, the mixture was ground at 5 ℃ for 30 min. -1 The temperature was increased to 850 °C at a rising rate, and pyrolysis was maintained at 850 °C for 1 h. After the reaction was completed and naturally cooled to room temperature, the black solid powder was removed and collected, yielding a planar aluminum single-atom catalytic material without axial S coordination, denoted as AlNC. This comparative example is used to illustrate the effect of axial S coordination on the ORR catalytic performance of aluminum single atoms.

[0082] Comparative Example 2: SNC carrier The SNC support was prepared according to step 1 of Example 1. Specifically, ZIF-8 nanoparticles and KSCN were mixed at a mass ratio of 2:1, pyrolyzed at 900 °C for 2 h under high-purity Ar protection, followed by acid washing with dilute hydrochloric acid at 80 °C for 12 h, and then washed until neutral and vacuum dried to obtain a two-dimensional porous S, N co-doped carbon support, denoted as SNC. This sample did not undergo the second-stage aluminum single-atom introduction and gas-phase defect trapping treatment. This comparative example is used to illustrate the ORR performance of the porous carbon support with only S, N co-doped carbon and no aluminum single-atom active centers.

[0083] Comparative Example 3: Commercial Pt / C catalysts A commercial platinum-carbon electrocatalyst with a metal mass fraction of 20 wt% (20 wt% Pt / C, Alfa Aesar) was selected. Without additional chemical pretreatment, ORR (Objective Response Rate) was directly tested using conventional electrode preparation processes. This comparative example serves as a performance benchmark for commercial noble metal catalysts.

[0084] Electrochemical measurement of ORR: All electrochemical ORR catalytic activity tests on the synthesized materials were performed at room temperature. The testing was conducted using an electrochemical workstation equipped with a rotating disk electrode system. A three-electrode system was used for the electrochemical tests, with the working electrode being a glassy carbon rotating disk electrode loaded with catalyst ink. The glassy carbon disk had a diameter of 5 mm and a corresponding geometric area of ​​0.196 cm². 2 The reference electrode was a saturated calomel electrode (SCE); the counter electrode was a large-area platinum mesh or platinum wire electrode. All test potentials were converted to the reversible hydrogen electrode (RHE) scale and iR compensation was performed as needed for the test. The electrolyte was a 0.1 M KOH solution.

[0085] The catalyst ink was prepared as follows: 2 mg of the catalyst to be tested was weighed and placed in a clean centrifuge tube. 180 μL of anhydrous ethanol, 60 μL of ultrapure water, and 10 μL of 5 wt% Nafion solution were added sequentially. The mixture was then ultrasonically dispersed for at least 30 min until a homogeneous catalyst ink was formed. 10 μL of the catalyst ink was then dropped onto the polished and cleaned glassy carbon RDE surface using a micropipette, resulting in a catalyst loading of 0.4 mg / cm³. -2 After the drop coating is completed, allow the electrode to air dry naturally at room temperature.

[0086] Before cyclic voltammetry testing, high-purity N2 or O2 was bubbled into the electrolyte for at least 30 minutes to obtain a gas-saturated electrolyte. The CV test scan rate was 50 mV s. -1 LSV testing was performed in an O2-saturated 0.1 M KOH electrolyte, with a rotating disk electrode speed of 1600 rpm and a scan rate of 5 mV / s. -1 The half-wave potential, limiting current density, and kinetic current density were obtained from the LSV curve, and the ORR activity and stability of the material were evaluated by combining the Tafel curve, accelerated durability test, and chronoamperometry test.

[0087] The structural characterization and performance test results of Example 1 are as follows: like Figure 1 The diagram shown illustrates the synthesis process and mechanism of the axial sulfur-coordinated AlSNC single-atom catalytic material prepared in Example 1 of this invention. like Figure 2 The image shown is a transmission electron microscope (TEM) and a high-resolution TEM image of the AlSNC single-atom catalytic material prepared in Example 1 of this invention. Figure 2 a is a transmission electron microscope image. Figure 2 b is a high-resolution transmission electron microscope image; like Figure 3 The image shows the powder X-ray diffraction phase patterns of the materials prepared in Example 1 and Comparative Examples 1-2 of this invention. like Figure 4 The image shows the Raman spectral structural defect patterns of the materials prepared in Example 1 and Comparative Examples 1-2 of this invention. like Figure 5 The figure shows the nitrogen adsorption-desorption isotherms and pore size distribution of the materials prepared in Example 1 and Comparative Examples 1-2 of this invention. Figure 5 a represents the nitrogen adsorption-desorption isotherm. Figure 5 bd is the aperture distribution diagram; like Figure 6 The image shown is a single-atom bright spot image and an EDS elemental mapping image of the AlSNC single-atom catalytic material prepared in Example 1 of this invention, obtained by spherical aberration correction scanning transmission electron microscopy. Figure 6 a is a single-atom bright spot image obtained by scanning transmission electron microscopy with spherical aberration correction. Figure 6 b is the EDS element mapping graph; like Figure 7 The image shows the X-ray absorption near-edge structure spectrum, extended X-ray absorption fine structure Fourier transform spectrum, and fitting curve of Example 1 of the present invention and each control sample. Figure 7 a shows the X-ray absorption near-edge structure spectra of Example 1 and each control sample. Figure 7 b represents the extended X-ray absorption fine structure Fourier transform spectra of Example 1 and each control sample. Figure 7 c is the fitted curve of Comparative Example 1. Figure 7 d is the fitted curve of Example 1; Figure 1 The synthesis process of AlSNC is shown. TEM image ( Figure 2 The results show that the AlSNC material prepared in Example 1 inherits the ultrathin two-dimensional nanosheet morphology of the SNC carrier, and the surface of the sheets exhibits obvious wrinkled structures. (PXRD pattern) Figure 3 In the 10°-90° scanning range, broadened diffraction peaks corresponding to carbon materials were mainly observed. No obvious diffraction peaks belonging to elemental aluminum, aluminum chloride, or alumina crystal phases were observed, indicating that no detectable aluminum-based crystal particles were formed in the material. Raman spectroscopy ( Figure 4 The results show that the material exhibits distinct D-band and G-band characteristics, with an ID / IG ratio of approximately 0.93, indicating that the material possesses certain defect structures and a relatively good degree of carbon framework reconstruction. Nitrogen adsorption-desorption testing (…) Figure 5 This indicates that the AlSNC material has a high specific surface area, with a BET specific surface area of ​​1223.3 m². 2 g -1 It exhibits a pore structure characterized by the coexistence of micropores (0.6–0.8 nm) and mesopores (1–3 nm). ICP results indicate that the Al mass loading can reach approximately 3.25 wt%. Aberration-corrected HAADF-STEM images ( Figure 6The results showed numerous dispersed, high-contrast bright spots on the carbon support, which could be attributed to atomically dispersed Al sites; no obvious metal agglomeration was observed. EDS elemental mapping results showed that C, N, S, and Al elements were uniformly distributed throughout the material. Synchrotron radiation XAS (…) Figure 7 Characterization further confirmed the local coordination environment of Al. XANES results showed that the Al center was in a partially electron-deficient positive state. In the EXAFS fitting curve and WT wavelet transform plot, in addition to the Al-N scattering peak at approximately 1.55 Å attributed to the first shell, a characteristic shoulder peak related to Al-S scattering was observed at approximately 1.95 Å. The fitting results showed that the Al-N coordination number was approximately 4.1, the Al-S coordination number was approximately 1.2, and the Al-N and Al-S bond lengths were approximately 1.98 Å and 2.36 Å, respectively, indicating that Example 1 successfully constructed an AlN4-S single-atom structure with axial S coordination characteristics.

[0088] like Figure 8 The figure shown is a comparison of the LSV polarization curves of oxygen reduction reaction in oxygen-saturated 0.1 M KOH electrolyte of Example 1 and Comparative Examples 1-3 of the present invention. like Figure 9 The figure shown is a comparison of Tafel slope and dynamic current density corresponding to Embodiment 1 and Comparative Examples 1-3 of the present invention; Figure 9 a is the Tafel slope graph corresponding to Example 1 and Comparative Examples 1-3. Figure 9 b is a comparison diagram of the dynamic current density corresponding to Example 1 and Comparative Examples 1-3; like Figure 10 The figure shown is a comparison of the LSV polarization curves of the AlSNC catalyst material prepared in Example 1 of the present invention before and after 50,000 accelerated durability tests. like Figure 11 The figure shown is a comparison of the chronocurrent stability test and resistance to methanol cross-interference of the commercial Pt / C catalyst materials in Example 1 and Comparative Example 3 of this invention. like Figure 12 The image shows the dynamic in-situ infrared absorption spectra of Example 1 and Comparative Example 1 during the ORR reaction process of this invention. like Figure 13 The figure shows the in-situ electrochemical impedance spectroscopy and relaxation time distribution decoupling diagram of Embodiment 1 of the present invention under different bias working potentials. like Figure 14 The figure shows the open-circuit voltage, power density polarization curve, multi-current step discharge curve, and 1500-hour charge-discharge long cycle curve of the liquid zinc-air battery assembled using Example 1 of the present invention as the air cathode catalyst. Figure 14 'a' represents the open-circuit voltage. Figure 14 b is the power density polarization curve. Figure 14 c represents the multi-current step discharge curve. Figure 14 d represents the charge-discharge long-cycle curve after 1500 hours; like Figure 15 As shown, this is a step diagram of the oxygen reduction free energy and the P of the central aluminum atom calculated using the theories of Example 1 and Comparative Example 1 of this invention. z Orbital state density distribution diagram; Figure 15 a is the free energy step diagram. Figure 15 b is the orbital state density distribution diagram; Figure 16 Powder X-ray diffraction phase patterns of the materials prepared in Examples 2-4 of this invention; Figure 17 The Raman spectra of structural defects in the materials prepared in Examples 2-4 of this invention are shown. Figure 18 The graphs show the LSV polarization curves of the oxygen reduction reaction in oxygen-saturated 0.1 M KOH electrolyte for Examples 1-4 and Comparative Example 1 of the present invention; AlSNC in the graphs represents Example 1, and AlNC in the graphs represents Comparative Example 1.

[0089] ORR electrochemical tests were performed in an O2-saturated 0.1 M KOH electrolyte. The AlSNC prepared in Example 1 exhibited high ORR catalytic activity. Figure 8 The half-wave potential reaches 0.920 V vs. RHE. The Tafel slope is 42.8 mV dec. -1 kinetic current density J k 19.49 mA cm -2 Based on the test results, its intrinsic transition frequency (TOF) reaches 370 h. -1 Compared to planar AlNC, the contrast ratio is significantly improved ( Figure 9 ). Tested for 50,000 accelerated durability cycles ( Figure 10 After that, the half-wave potential of AlSNC only decayed by 16mV. Chronocurrent test ( Figure 11 The results showed that AlSNC maintained 94.3% of its initial current after 20 hours of continuous operation and exhibited good tolerance to methanol cross-interference. Furthermore, in-situ ATR-SEIRAS testing revealed that AlSNC and planar AlNC exhibited significantly different intermediate adsorption behaviors during the ORR process. Figure 12 Among them, AlNC exhibits stronger performance within the ORR operating potential range. The steady-state signal of OOH indicates that its intermediate is consumed slowly and accumulates to some extent; in contrast, AlSNC's... The significantly weakened OOH signal indicates that axial S coordination can moderately weaken the interaction between the Al site and the oxygen-containing intermediate, promoting... The continuous transformation of the key OOH intermediate reduces the risk of active site blockage. In-situ EIS combined with relaxation time distribution analysis further reveals the kinetic advantages of AlSNC. Figure 13 DRT results showed that AlSNC exhibited a faster charge transfer response and lower kinetic resistance within the ORR operating range; under deeper polarization conditions, its mass transfer-related response was enhanced, reflecting the concentration polarization characteristics caused by the rapid consumption of local O2 by highly active sites. These results indicate that axial S-coordination and the hierarchical porous carbon support synergistically promoted oxygen transport, electron transfer, and intermediate reaction processes. When the AlSNC prepared in Example 1 was used as an air cathode catalyst in the assembly of a liquid zinc-air battery, the device exhibited good performance for practical applications. Figure 14 This battery exhibits high open-circuit voltage and peak power density, and maintains stable discharge under different current densities. In rechargeable zinc-air battery tests, the AlSNC-based air cathode can operate stably for over 1500 hours, indicating that the material of this invention not only possesses excellent half-cell ORR activity but also good device applicability and long-term operational stability. Theoretical calculations show that the traditional planar Al-N4 sites are mainly limited by OH desorption, with a maximum reaction free energy change of approximately 2.54 eV. Figure 15 a) After the introduction of axial S coordination, the AlN4-S site transforms the limiting step into the OOH formation process and reduces the maximum reaction free energy change to approximately 0.61 eV, indicating that axial S coordination can alleviate the restriction. Site blockage caused by excessive OH adsorption. Furthermore, axial S coordination shifts the unoccupied pz-state center of Al from -3.03 eV to -4.00 eV. Figure 15 (b) Weakening Al-O interactions improves the adsorption, conversion, and desorption balance of oxygen-containing intermediates, thereby enhancing ORR catalytic activity and stability.

[0090] Explanation of the results of the examples and comparative examples: Examples 2-4 are a series of samples obtained in the AlSNC system by adjusting the proportion of sulfur-containing salts, pyrolysis atmosphere, heating rate, pyrolysis temperature, aluminum source introduction method, and secondary pyrolysis conditions. These samples are used to illustrate the applicability of the preparation method of the present invention under different process parameters and to further determine the preferred implementation conditions. PXRD results ( Figure 16 The results show that no diffraction peaks clearly belonging to the aluminum-based crystalline phase were observed in Examples 2-4 and the relevant comparative examples, indicating that no detectable large-sized aluminum-based crystal particles were formed in the obtained materials. Raman spectroscopy results ( Figure 17This indicates that different pyrolysis conditions affect the degree of defect and graphitization of the carbon support, thereby further affecting the formation of aluminum single-atom sites and its electrocatalytic performance. Electrochemical test results show that, compared with the AlNC comparison sample without axial S coordination and the SNC comparison sample without aluminum single atoms, the materials obtained in Examples 2-4 all exhibited improved ORR catalytic performance. Figure 18 This indicates that the construction of the sulfur-containing salt-induced S / N co-doped porous carbon support and the aluminum source defect trapping process have a positive effect on improving ORR activity. Specifically, the KSCN / ZIF-8 mass ratio, SNC support pyrolysis temperature, AlPcCl / DICY introduction method, and 850 ℃ secondary pyrolysis condition used in Example 1 are more conducive to the formation of a highly active axially sulfur-coordinated AlN4-S single-atom structure, resulting in superior performance of the obtained AlSNC material in terms of half-wave potential, Tafel slope, kinetic current density, and durability. Therefore, Example 1 can be considered a preferred embodiment of the present invention.

[0091] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. An axially sulfur-coordinated aluminum single-atom electrocatalytic material, characterized in that: The axial sulfur-coordinated aluminum single-atom electrocatalytic material is composed of an S and N co-doped porous carbon support and aluminum single atoms atomically dispersed on the support; the aluminum single atoms exist in a positively charged or partially positively charged form.

2. The axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 1, characterized in that: The aluminum single atom is located at the center of a coordination environment composed of four in-plane N atoms, and forms a coordination relationship with an axial S atom above or below it, thereby forming an AlN4-S type five-coordinate local structure.

3. A method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material, characterized in that, Includes the following steps: a) Preparation of ZIF-8 precursor: Zinc salt and 2-methylimidazole were dissolved separately in alcohol solvents. The two solutions were then mixed and stirred to react. After the reaction was completed, the mixture was centrifuged, washed and dried to obtain ZIF-8 nanocrystal particles. b) Precursor mixing and sulfur source introduction assisted by sulfur-containing salts: The ZIF-8 nanocrystal particles obtained in step a) are mixed with sulfur-containing salts to obtain a mixed powder; c) Preparation of crude S,N co-doped porous carbon support by molten salt-assisted pyrolysis: The mixed powder obtained in step b) was pyrolyzed under a flowing inert atmosphere to obtain a black crude product: S and N co-doped porous carbon support crude product. d) Acid etching and purification: The black crude product obtained in step c) was ground and added to the acid washing solution, followed by washing and drying to obtain an S and N co-doped porous carbon support, denoted as SNC; e) Vapor phase aluminum source migration and defect confinement trapping: An aluminum source was introduced into the SNC prepared in step d) to obtain an axially sulfur-coordinated aluminum single-atom electrocatalytic material. In step e), the aluminum source is introduced through a combination of primary pyrolysis, secondary pyrolysis after impregnation, or a combination of primary pyrolysis and post-impregnation pyrolysis.

4. The method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 3, characterized in that: In step a), the zinc salt is a soluble zinc salt, and the molar ratio of zinc salt to 2-methylimidazole is 1:(3-6); the stirring reaction time is 0.5-8 h; the drying temperature is 60-100 ℃, and the drying time is 6-16 h.

5. The method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 3, characterized in that: In step b), the sulfur-containing salt is a sulfur-containing salt that can provide a sulfur source and participate in etching reconstruction during the pyrolysis process; the mixing method is at least one of solution stirring and mechanical grinding; the mass ratio of the sulfur-containing salt to ZIF-8 is 1:(2-6).

6. The method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 3, characterized in that: In step c), the inert atmosphere is at least one of N2, Ar, or He; during the pyrolysis process, the heating rate is 1-5℃ / min. -1 The pyrolysis temperature is 800-1100 ℃, and the isothermal pyrolysis time at the pyrolysis temperature is 1-3 h.

7. The method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 3, characterized in that: In step d), the pickling solution is a hydrochloric acid solution or a sulfuric acid solution; the pickling time is 4-16 h, and the pickling temperature is 25-80℃. The drying temperature is 50-80 ℃, and the drying time is 6-16 h.

8. The method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 3, characterized in that: In step e), the SNC, aluminum source and supplementary nitrogen source prepared in step d) are mixed and ground, and then pyrolyzed in a pyrolysis atmosphere. After pyrolysis, the mixture is naturally cooled to room temperature to obtain an axial sulfur-coordinated aluminum single-atom electrocatalytic material. The aluminum source is one or more of aluminum phthalocyanine chloride, aluminum acetylacetonate, and aluminum isopropoxide; the supplementary nitrogen source is dicyandiamide; the mass ratio of SNC, aluminum source, and dicyandiamide is 1:(0.5-1.5):(5-15); The grinding time is 10-60 min; the pyrolysis atmosphere is Ar, N2, He, or a mixture of H2 / Ar; during pyrolysis, the heating rate is 1-5 ℃ min. -1 The pyrolysis temperature is 800-1100 ℃, and the isothermal pyrolysis time at the pyrolysis temperature is 1-3 h.

9. The method for preparing an axially sulfur-coordinated aluminum single-atom electrocatalytic material according to claim 3, characterized in that: In step e), the SNC, aluminum phthalocyanine chloride, and trimesic acid prepared in step d) are ground and mixed in a mass ratio of 1:(0.5-1.5):(0.1-0.3) to obtain a mixed powder; the mixed powder undergoes a two-stage pyrolysis treatment to obtain the pyrolysis product. The two-stage pyrolysis process is as follows: Under the protection of a pyrolysis atmosphere, the first stage is carried out at 1-5 ℃ min. -1 The temperature is increased to 200-400 ℃ and held for 10-90 min at a rising rate; the second stage is heated at 1-5 ℃ per minute. -1 The temperature is increased to 800-1100 ℃ at a heating rate and held for 1-3 hours; After pyrolysis, the product was dispersed in anhydrous ethanol and stirred. Then, an aluminum source was added and stirred. After stirring, the anhydrous ethanol was evaporated and the solid product was pyrolyzed to obtain an axially sulfur-coordinated aluminum single-atom electrocatalytic material. The mass ratio of the product to the aluminum source after pyrolysis is (10-15):1; the aluminum source is one or more of aluminum chloride phthalocyanine, aluminum acetylacetonate, and aluminum isopropoxide. The solid product pyrolysis process is as follows: under a pyrolysis atmosphere, at 1-5 ℃ min -1 The temperature is increased to 800-1100℃ at a certain rate and held for 1-3 hours.

10. The application of the axial sulfur-coordinated aluminum single-atom electrocatalytic material according to any one of claims 1-2 or the axial sulfur-coordinated aluminum single-atom electrocatalytic material prepared by the preparation method according to any one of claims 3-9 in oxygen reduction reaction and metal-air battery.

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