Ultrafine Vacancy-Rich Co9S8-x / MnS-Decorated S, N-Doped Hollow Carbon Nanotube Derived via Cooperative In-Situ Sulfidation and Interface Tuning as a Bifunctional Oxygen Electrocatalyst for High-Performance Zinc-Air Batteries

Abstract

The present invention relates to a dual-function oxygen electrocatalyst for high-performance zinc-air batteries, comprising a superfine defect-rich Co9S8-x / MnS decorated on S, N-doped hollow carbon nanotubes induced through cooperative in-situ sulfidation and interface tuning, characterized by comprising: a hollow interior; and a porous structure containing a metal sulfide.

Description

Technology Field

[0001] The present invention relates to Co9S8-x / MnS, a superfine defect-rich material decorated on S, N-doped hollow carbon nanotubes induced through cooperative in-situ sulfidation and interface tuning, as a dual-function oxygen electrocatalyst for high-performance zinc-air batteries. Background Technology

[0002] Zinc-air batteries are attracting attention as next-generation energy storage devices due to their advantages, such as high energy density, relatively low material costs, and stability. These batteries operate by using oxygen from the air as the positive electrode reactant and metallic zinc as the negative electrode. This battery structure is characterized by the ability to theoretically provide a much higher energy density compared to traditional lithium-ion batteries.

[0003] However, currently commercialized zinc-air batteries have limitations in that they fail to fully realize theoretical performance during actual operation. This is primarily due to the slow reaction rates of the oxygen reduction (ORR) and oxygen evolution (OER) reactions occurring mainly at the air electrode, as well as the low reversibility between the two reactions. Furthermore, there is a problem where the electrode structure degrades easily during repeated charging and discharging, leading to a shortened lifespan.

[0004] Therefore, there is an urgent need for research on cleaning solution compositions capable of removing wafer fixing adhesive residues at a high cleaning rate without damaging the wafer's protective layer or semiconductor components.

[0005] To address these issues, various transition metal-based dual-functional catalysts have been studied as alternatives to precious metal catalysts. For example, sulfide catalysts utilizing metals such as cobalt (Co) or manganese (Mn), or composite materials in which these are dispersed within carbon structures, have been proposed. However, the problem of reduced catalytic efficiency—resulting from catalyst particle aggregation during high-temperature processes that decreases the active surface area and an imbalance in the adsorption and desorption reactions of oxygen intermediates—remains unresolved.

[0006] Therefore, research and development are required for the development of new electrode materials that can increase catalyst activity and improve stability. The problem to be solved

[0007] To solve the aforementioned problems, the present invention aims to provide a catalyst for a bifunctional metal-air battery having excellent electrochemical performance and long-term stability in both oxygen reduction and oxygen evolution reactions, and a method for manufacturing the same.

[0008] In addition, another objective of the present invention is to provide an air electrode containing the catalyst and exhibiting a low overvoltage, and a metal-air battery containing the same. means of solving the problem

[0009] In order to achieve the aforementioned objectives, the inventors continuously researched to manufacture a catalyst capable of increasing catalyst activity and improving stability. As a result, they discovered that when using a catalyst in which a catalyst containing a metal sulfide is dispersed on a doped carbon body having a porous structure, the reaction rate and reversibility of the oxygen electrochemical reaction can be simultaneously improved by precisely controlling the electron density of the metal center and the adsorption energy of the oxygen intermediate, thereby completing the present invention.

[0010] The present invention provides a catalyst for a metal-air battery comprising a hollow interior; and a porous structure containing a metal sulfide.

[0011] According to one embodiment, the structure may include a carbon structure doped with two or more heteroatoms.

[0012] According to one embodiment, the structure may include a carbon structure doped with nitrogen (N) and sulfur (S).

[0013] According to one embodiment, the carbon structure of the structure may be a heterointerface in contact with two or more metal sulfides.

[0014] According to one embodiment, the carbon structure of the structure may include micropores and mesopores.

[0015] According to one embodiment, the structure may have a BET specific surface area of ​​200 m² / g or more.

[0016] According to one embodiment, the metal sulfide may comprise one or more metals selected from the group consisting of cobalt (Co), zinc (Zn), iron (Fe), cadmium (Cd), nickel (Ni), manganese (Mn), and copper (Cu).

[0017] According to one embodiment, the metal sulfide may include cobalt (Co) sulfide and manganese (Mn) sulfide.

[0018] According to one embodiment, the metal sulfide may include particles having an average diameter of 1 to 15 nm.

[0019] According to one embodiment, the metal sulfide may include a structure in which some sulfur atoms within the crystal structure are defective (S-vacancy).

[0020] According to one embodiment, the surface contact angle of the catalyst may be 100° or more.

[0021] According to one embodiment, the structure may have a thickness of 10 to 100 nm.

[0022] According to one embodiment, the catalyst may be a nanotube structure having an inner diameter of 10 to 300 nm and an outer diameter of 30 to 500 nm.

[0023] According to one embodiment, the catalyst may be a bifunctional catalyst.

[0024] The present invention provides a catalyst precursor for a metal-air battery comprising: a heteroelement-containing template including nitrogen (N) and sulfur (S); a metal-organic framework layer formed on the surface of the template; and a polymer coating layer on the metal-organic framework layer.

[0025] According to one embodiment, the template may be a nanorod structure.

[0026] According to one embodiment, the metal-organic framework layer may include an organic ligand, a first metal, a second metal, and a third metal.

[0027] According to one embodiment, the polymer coating layer may include a conductive polymer.

[0028] The present invention can provide an air electrode comprising a coating layer including the aforementioned metal-air battery catalyst.

[0029] According to one embodiment, the coating layer may contain 30 to 99 weight percent of the catalyst for the metal-air battery.

[0030] The present invention can provide a metal-air battery comprising a cathode; an electrolyte; and the air electrode described above.

[0031] The present invention comprises the steps of: (A) forming a heteroelement-containing template comprising nitrogen (N) and sulfur (S);

[0032] (B) A step of forming a metal-organic framework layer on the above template;

[0033] (C) a step of forming a polymer coating layer on the metal-organic framework layer; and

[0034] (D) a heat treatment step; a method for manufacturing a catalyst for a metal-air battery is provided.

[0035] According to one embodiment, step (A) may be to prepare a template by self-assembling melamine and trithiocyanuric acid.

[0036] According to one embodiment, step (B) may include the step of forming a metal-organic framework comprising a first metal and a second metal; and the step of introducing a third metal into the metal-organic framework.

[0037] According to one embodiment, the step (D) may be performed at a temperature of 700°C or higher.

[0038] According to one embodiment, through step (D), a portion of the template may be vaporized to form a hollow structure.

[0039] According to one embodiment, through step (D), a heteroatom is doped into the polymer coating layer and the metal of the metal-organic framework layer is sulfidated to form a metal sulfide. Effects of the invention

[0040] A catalyst for a metal-air battery according to one embodiment of the present invention exhibits high electrochemical activity for both oxygen evolution (OER) and oxygen reduction (ORR), thereby improving the energy efficiency and output characteristics of the battery. In particular, the adsorption and desorption energies of intermediates *OH, *O, and *OOH, which are major active species in the electrochemical reaction, are precisely controlled, resulting in a lower overpotential of the reaction and an increased reaction rate. Accordingly, the catalyst of the present invention can simultaneously achieve a low overpotential and a high reduction potential, and can realize excellent reversibility in the bidirectional oxygen reaction.

[0041] Furthermore, the catalyst of the present invention maintains stable catalytic activity without structural collapse or degradation of activity even in environments of repeated charge-discharge over long periods, thereby significantly improving the long-term lifespan and output retention characteristics of metal-air batteries. This is a unique effect of the present invention realized by controlling the electron density and binding energy of the catalyst surface through doping and defect control, which enhances the chemical stability and electron transfer characteristics of the active site. Accordingly, the catalyst of the present invention can achieve battery performance such as high energy density, high output density, and long lifespan, and can be utilized as a practical and economically viable alternative to precious metal catalysts.

[0042] Furthermore, the method for manufacturing a catalyst for a metal-air battery according to the present invention has the advantage that most precursor synthesis proceeds at room temperature, and that hollow and porous structures can be simultaneously realized through the selective evaporation of Zn and organic materials in the final heat treatment step. This shortens electron and mass transfer pathways, thereby reducing internal resistance during battery operation and enabling high-speed reaction characteristics. As such, the manufacturing method of the present invention has the advantages of being simple, highly reproducible, and applicable to mass production processes. Brief explanation of the drawing

[0043] FIG. 1 is a schematic diagram briefly illustrating a method for manufacturing a catalyst according to one embodiment. FIG. 2 (a) is an SEM image of the catalyst according to Example 1, FIG. 2 (b) is a TEM image, FIG. 2 (c) and FIG. 2 (d) are HR-TEM images, and FIG. 2 (e) is a schematic diagram showing the molecular structure of the catalyst according to Example 1. Figure 3 is a graph of the pore size distribution obtained by BET and BJH analysis of the catalyst according to Example 1. FIG. 4 is a schematic diagram of a zinc-air battery using a catalyst according to one embodiment as an air electrode. Figure 5 shows the results of a lighting experiment using a battery with a catalyst according to Example 1. Figure 6 is a graph of the cycle life results of the battery of Example 1. Specific details for implementing the invention

[0044] Unless otherwise defined in this specification, all technical and scientific terms have the same meaning as generally understood by those skilled in the art to which the present invention pertains. The terms used in the description herein are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0045] The singular form used in this specification is intended to include the plural form unless specifically indicated otherwise in the context.

[0046] Additionally, numerical ranges used herein include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding are also included in the defined numerical range.

[0047] The term “comprising” in this specification is an open description having an equivalent meaning to expressions such as “comprising,” “containing,” “having,” or “characterizing,” and does not exclude elements, materials, or processes not additionally listed.

[0048] Hereinafter, a catalyst for a metal-air battery and a method for manufacturing the same according to one embodiment of the present invention will be described in more detail.

[0049] The present invention provides a catalyst for a metal-air battery comprising a hollow interior and a porous structure containing a metal sulfide. The catalyst may have a structure in which a hollow interior and a porous structure form the exterior in the form of a nanotube.

[0050] According to one embodiment, the structure may include a carbon structure doped with two or more heteroatoms, and the heteroatoms may be one or more selected from the group consisting of nitrogen, oxygen, silicon, sulfur, and phosphorus. Specifically, the structure may include a carbon structure doped with nitrogen (N) and sulfur (S). The nitrogen doping of the structure may be derived from one or more selected from the group consisting of melamine, trithiocyanurate, 2-methylimidazole, and polydopamine, a conductive polymer, described later, and the sulfur doping of the structure may be derived from one or more selected from the group consisting of trithiocyanurate and metal sulfides, described later.

[0051] According to one embodiment, the carbon structure of the structure may be a heterointerface in contact with two or more metal sulfides. The two or more metal sulfides may include two or more sulfides selected from the group consisting of manganese sulfide, cobalt sulfide, zinc sulfide, etc. Specifically, the two or more metal sulfides may include manganese sulfide and cobalt sulfide, and the carbon structure of the structure may be a heterointerface in contact with both manganese sulfide and cobalt sulfide simultaneously.

[0052] According to one embodiment, the carbon structure of the structure may be a porous structure including micropores and mesopores. The micropores refer to small pores with a diameter of 2 nm or less, and the mesopores refer to medium-sized pores with a diameter between 2 and 50 nm. Since the carbon structure of the structure includes micropores and mesopores simultaneously, the performance of a bifunctional catalyst for electrochemical oxygen reduction (ORR) and oxygen evolution (OER) can be significantly improved by increasing the number of active sites and promoting movement within the carbon structure.

[0053] According to one embodiment, the structure may have a BET specific surface area of ​​200 m² / g or more, 250 m² / g or more, 280 m² / g or more, 290 m² / g or more, or 800 m² / g or less. A catalyst comprising a structure satisfying the above range may provide exposure to multiple active sites and excellent reaction / transport pathways.

[0054] According to one embodiment, the metal sulfide may comprise one or more metals selected from the group consisting of cobalt (Co), zinc (Zn), iron (Fe), cadmium (Cd), nickel (Ni), manganese (Mn), and copper (Cu). Specifically, the metal sulfide may comprise cobalt (Co) and manganese (Mn) sulfides.

[0055] According to one embodiment, the metal sulfide may include a sulfide of cobalt and manganese, and the molar ratio (or weight ratio) of cobalt to manganese may be 1 to 10:1, 1 to 5:1, or 2 to 3:1.

[0056] According to one embodiment, the metal sulfide may include particles having an average diameter of 1 to 20 nm, 1 to 15 nm, 2 to 10 nm, or 3 to 7 nm.

[0057] According to one embodiment, the metal sulfide may include a structure in which some sulfur atoms within the crystal structure are defective (S-vacancy). Specifically, during the process in which a sulfidation reaction occurs through heat treatment in the manufacturing process described below, some of the sulfur may be formed by lattice deformation occurring at the interface with MnS due to Mn doping and thermodynamic instability. The sulfur defect (S-vacancy) can be confirmed by HAADF-STEM, EXAFS, XPS analysis, etc., described below. Due to the presence of the sulfur defect (S-vacancy), the performance of the catalyst can be significantly improved, such as an increase in active sites for OER / ORR reactions, improved energy efficiency, and enhanced durability.

[0058] According to one embodiment, the metal sulfide may include Co-S bonds with a bond length of 1.7 Å or more, 1.8 Å or more, 1.9 Å or more, or 2.0 Å or less, based on the results of extended X-ray absorption microstructure (EXAFS) analysis.

[0059] According to one embodiment, the surface contact angle of the catalyst may be 100° or more, 110° or more, or 115° or more, or 180° or less, or 150° or less.

[0060] According to one embodiment, the structure may have a thickness of 10 to 100 nm, 15 to 80 nm, or 20 to 60 nm. The thickness of the structure can be calculated as the value of outer diameter minus inner diameter.

[0061] According to one embodiment, the catalyst may be a nanotube structure having an inner diameter of 10 to 300 nm, 50 to 100 nm, or 70 to 90 nm, and an outer diameter of 30 to 500 nm, 60 to 300 nm, 100 to 200 nm, or 140 to 180 nm.

[0062] According to one embodiment, the catalyst may be a nanotube structure having a length of 0.01 μm to 10 μm, 0.1 μm to 5 μm, or 0.5 μm to 3 μm.

[0063] According to one embodiment, the catalyst may be a bifunctional catalyst capable of effectively promoting two or more electrochemical reactions, such as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).

[0064] The present invention provides a catalyst precursor for a metal-air battery comprising: a heteroelement-containing template including nitrogen (N) and sulfur (S); a metal-organic framework (MOF) layer on the template; and a polymer coating layer on the metal-organic framework layer. The catalyst precursor can be converted into the catalyst described above by undergoing carbonization and sulfidation processes in a heat treatment process described later.

[0065] According to one embodiment, the template may be a nanorod structure formed by self-assembly. The template may be a nanorod structure having a diameter of 10 to 500 nm, 20 to 300 nm, 30 to 200 nm, or 50 to 100 nm, and a length of 0.01 µm to 10 µm, 0.1 µm to 5 µm, or 0.5 µm to 3 µm. The template may serve as a template for a hollow carbon nanotube structure through a process such as heat treatment with the metal-organic framework (MOF).

[0066] According to one embodiment, the metal-organic framework layer may include an organic ligand, a first metal, a second metal, and a third metal.

[0067] The above organic ligand may include one or more selected from the group consisting of imidazole (2-methylimidazole), melamine, trithiocyanurate, and ethylenediamine.

[0068] The first metal, second metal, and third metal may be one or more metals selected independently from the group consisting of cobalt (Co), zinc (Zn), iron (Fe), cadmium (Cd), nickel (Ni), manganese (Mn), and copper (Cu), etc.

[0069] According to one embodiment, the polymer coating layer may include a conductive polymer. The conductive polymer may include one or more selected from polydopamine, polyaniline, polypyrrole, polyacetylene, poly(p-phenylene), poly(p-phenylene vinylene) (PPV), polythiophene, poly(3,4-ethylenediothiophene) (PEDOT), polyindole, and polyphenol. Specifically, the polymer coating layer may include polydopamine. The polymer coating layer may have a thickness of 1 to 100 nm, 1 to 50 nm, or 3 to 15 nm. The polymer coating layer is coated on a metal-organic framework formed on a nanorod temple-like surface to maintain the shape of the catalyst so as not to collapse during the sulfidation / carbonization process and to suppress the phenomenon of metal sulfide particles aggregating.

[0071] The present invention may provide an air electrode comprising a coating layer containing the aforementioned catalyst for a metal-air battery. The structure of the air electrode may use any structure or material known or commonly used in the industrial field without limitation, in addition to using a catalyst for a metal-air battery.

[0072] According to one embodiment, the coating layer may contain the metal-air battery catalyst in an amount of 30 to 99 weight%, 50 to 99 weight%, or 60 to 95 weight%.

[0073] According to one embodiment, the coating layer may further include a binder. The binder may be used to improve the adhesion of the catalyst, and any material used in the field may be used without limitation. Nafion or PTFE may be used without limitation, but is not limited thereto.

[0074] According to one embodiment, the coating layer may further include a conductive agent. The conductive agent may be carbon black, graphite, carbon nanotubes (CNT), graphene, silver, nickel, tin oxide, iron oxide, etc., but any material used in the field may be used without limitation.

[0075] According to one embodiment, the coating layer may be applied with a thickness of 0.1 to 50 μm or 1 to 30 μm. Additionally, the air electrode may have a catalyst loading amount per area of ​​0.01 to 50 mg / cm², 0.1 to 30 mg / cm², or 0.5 to 10 mg / cm².

[0076] The present invention may provide a metal-air battery comprising a negative electrode; an electrolyte; and the air electrode described above. The structure of the metal-air battery may use any structure or material known or commonly used in the industrial field without limitation, except that it uses an air electrode containing a catalyst for a metal-air battery.

[0077] According to one embodiment, the cathode may be a metal cathode, and the metal cathode may be zinc metal.

[0078] According to one embodiment, the electrolyte may be a basic aqueous electrolyte, and the electrolyte may include a hydroxide solution. The hydroxide solution may be one or more selected from the group consisting of NaOH, KOH, Mg(OH)2, Ca(OH)2, and Ba(OH)2.

[0079] The present invention comprises the steps of: (A) forming a heteroelement-containing template comprising nitrogen (N) and sulfur (S);

[0080] (B) A step of forming a metal-organic framework layer on the above template;

[0081] (C) a step of forming a polymer coating layer on the metal-organic framework layer; and

[0082] (D) a heat treatment step; a method for manufacturing a catalyst for a metal-air battery is provided.

[0083] According to one embodiment, the catalyst precursor described above can be prepared through steps (A), (B), and (C), and step (D) can be performed.

[0084] According to one embodiment, step (A) may be to prepare a template by self-assembling melamine and trithiocyanuric acid. The melamine and trithiocyanuric acid may satisfy a molar ratio of 1 to 9:1, a molar ratio of 1 to 5:1, or a molar ratio of 1 to 2:1.

[0085] According to one embodiment, step (B) may include: forming a metal-organic framework comprising a first metal and a second metal; and introducing a third metal into the metal-organic framework. The first metal and the second metal may independently be cobalt, zinc, or manganese, and the third metal may be cobalt or manganese. The metal-organic framework may be formed by reacting the metal with the organic ligand described above. Additionally, the molar ratio of the first metal : second metal : third metal may be 1 to 5 : 1 to 5 : 1 to 5 or 1 to 2 : 1 to 2 : 1 to 2.

[0086] According to one embodiment, step (D) may include carbonization and sulfidation processes. Step (D) may be performed under an inert gas atmosphere at a temperature of 700°C or higher, 800°C or higher, 880°C or higher, or 1500°C or lower for a time of 10 minutes or more, 30 minutes or more, 100 minutes or more, or 1000 minutes or less.

[0087] According to one embodiment, through step (D), a portion of the template may be vaporized to form a hollow structure. Specifically, through step (D), molecules such as organic ligands, polydopamine (PDA), and melamine of the template may be thermally decomposed and carbonized, and metals (especially Zn) may volatilize at high temperatures, thereby vaporizing the interior of the nanorod structure to form a nanotube shape having a hollow interior. Additionally, through step (D), heteroelements such as nitrogen and sulfur may be doped into the carbon structure during the decomposition process.

[0088] According to one embodiment, through step (D), heteroelements, specifically nitrogen and sulfur elements, may be doped into the polymer coating layer. The concentration of nitrogen doping for the entire catalyst analyzed by XPS analysis may be 1 to 20 atom%, 2 to 15 atom%, or 5 to 10 atom%, and the concentration of sulfur doping for the entire catalyst may be 1 to 10 atom%, 2 to 6 atom%, or 3 to 4 atom%. The metal of the metal-organic framework layer may be sulfidated to form a metal sulfide.

[0089] According to the above-described method, a catalyst comprising a nitrogen / sulfur-doped carbon structure forming a hollow structure through Zn volatilization can be manufactured. The catalyst is a bifunctional catalyst, and using the catalyst, a zinc-air battery with excellent durability and high output can be manufactured.

[0090] Embodiments of the present invention will be described in detail below with reference to the attached drawings. However, this is provided to enable those skilled in the art to easily implement the invention, and the present invention may be embodied in various different forms, and the concept of the present invention is not necessarily limited to these embodiments.

[0091] [Example 1]

[0092] 70 mL of deionized water in which melamine (1.94 g) was dissolved and 30 mL of deionized water in which trithiocyanuric acid (2.73 g) was dissolved were mixed and stirred for 20 minutes to allow the reaction to proceed. After the reaction was complete, the product was washed three times each with deionized water and ethanol, and then dried at 60°C for 12 hours to obtain an MTCA nanorod template.

[0093] 300 mg of the formed MTCA template was dispersed in 40 mL of a methanol-ethanol (1:1) mixed solvent, and 2-methylimidazole (16 mmol) was added. In a separate container, cobalt(II) nitrate containing the first metal (Co(NO3)2, 1 mmol) and zinc nitrate containing the second metal (Zn(NO3)2, 0.5 mmol) were completely dissolved in the same 40 mL solvent, then combined with the MTCA dispersion, stirred for 2 minutes, and reacted at room temperature for 12 hours. The resulting Co / Zn-MOF@MTCA precipitate was centrifuged and dried at 60°C for 12 hours.

[0094] Dry Co / Zn-MOF@MTCA powder was dispersed in 40 mL of ethanol, and a manganese salt containing a tertiary metal (Mn salt, dissolved in 5 mL of deionized water) was slowly added dropwise. After stirring the mixture for 24 hours, the product was washed three times each with deionized water and ethanol, and then dried in an oven overnight to prepare Mn-Co / Zn-MOF@MTCA.

[0095] 300 mg of the prepared Mn-Co / Zn-MOF@MTCA was placed in 30 mL of Tris buffer and sonicated for 10 minutes. Dopamine hydrochloride (35 mg) was added to this, and the mixture was stirred for 2 hours to form a polydopamine (PDA) coating layer on the surface. After the reaction was complete, the product was centrifuged, washed, and dried in an oven for 12 hours.

[0096] A CM@SNHCT catalyst was synthesized by heat-treating PDA-coated Mn-Co / Zn-MOF@MTCA powder at 900°C for 2 hours in an argon (Ar) atmosphere. Subsequently, the resulting powder was washed in a 0.1 M HCl solution (80°C) to remove unnecessary metals or unstable components, and finally, after washing with deionized water and drying, the catalyst for a metal-air battery according to Example 1 was obtained.

[0097] The catalyst for a metal-air battery according to Example 1 above was analyzed according to the following method.

[0098] [Comparative Example 1]

[0099] The catalyst (C@SNHCT) according to Comparative Example 1 was obtained by performing the same procedure as Example 1, except that manganese salt was not added in Example 1.

[0100] [Comparative Example 2]

[0101] The catalyst (M@SNHCT) according to Comparative Example 2 was obtained by performing the same procedure as Example 1, except that cobalt(II) nitrate was not added in Example 1 and instead manganese salt was added.

[0102] [Comparative Example 3]

[0103] The catalyst (CM) according to Comparative Example 3 was obtained by performing the same procedure as Example 1, except that a polydopamine coating layer was not formed in Example 1.

[0105] [Evaluation Example 1] Morphological and Structural Analysis

[0106] Scanning electron microscope (FE-SEM, JSM-IT800), transmission electron microscope (Talos F200X G2 TEM), and high-resolution transmission electron microscope (HR-TEM) analysis were performed on the MTCA nanorod template of Example 1 and the catalyst for a metal-air battery according to Example 1.

[0107] SEM, TEM, and HR-TEM images are shown in Fig. 2. Through the SEM image in Fig. 2 (a) and the TEM image in Fig. 2 (b), it was confirmed that the catalyst of Example 1 has a hollow nanotube structure with an outer diameter of approximately 165 nm and an inner diameter of approximately 80 nm. Additionally, through Fig. 2 (c), Co9S8 / MnS heterojunction nanoparticles with an average diameter of 5.27 nm are uniformly distributed inside the nanotube, and lattice spacings of 0.175 nm and 0.185 nm were confirmed on the (440) plane of Co9S8 and the (200) plane of MnS, respectively. Through Fig. 2 (d), a structure in which sulfur atoms are vacant due to the Jahn-Teller effect resulting from the introduction of MnS into the catalyst crystal structure was confirmed.

[0108] In addition, statistical analysis of the size distribution of metal sulfide nanoparticles present in the catalyst was performed by counting more than 200 HR-TEM images using ImageJ software, and the average diameter was found to be 5.27 nm and the standard deviation was approximately 0.65 nm. It was confirmed that the metal sulfide according to Example 1 has a very uniform particle distribution, and 5–6 nm particles account for more than 72% of the total, which is advantageous for efficient exposure of active sites.

[0110] [Evaluation Example 2] Analysis of composition and chemical state

[0111] Changes in the crystal phase and composition of the catalyst powder were evaluated using an X-ray diffraction analyzer (XRD, SmartLab, Rigaku). Measurements were performed under Cu-Kα radiation conditions (λ=1.54 Å), in the range of 2θ=10–80°, at a scan rate of 2° / min. As a result, in the CM@SNHCT sample, distinct peaks of the (002) and (101) planes of graphene carbon were observed around 25° and 44°. Additionally, peaks corresponding to the characteristic crystal planes of Co9S8 were detected at 15.5°, 29.8°, 31.3°, 39.6°, 47.6°, and 52.1°, while peaks corresponding to the crystal planes of MnS were detected at 34.5° and 39.6°, confirming the coexistence of the two sulfide phases. Since no peaks of the metal (Co, Mn) single phase were detected, it was also confirmed that all metals had been completely converted to the sulfide phase.

[0112] In addition, defects and the degree of grapheneization of the synthesized carbon structure were analyzed using a Raman spectrometer (ARAMIS, Horiba). Measurements using a 532 nm laser showed approximately 1590 cm⁻¹. -1 (G band) and 1350 cm -1 Characteristic peaks of graphene carbon and defect carbon appeared in the (D band), respectively, and the ID / IG ratio of CM@SNHCT was confirmed to be 1.01, indicating that the defect level was higher compared to Comparative Example 1 (C@SNHCT, ID / IG 0.95). This was predicted to be a structural defect introduced by S / N doping and metal-carbon interactions.

[0113] In addition, the elemental composition and chemical state of the catalyst surface were analyzed using XPS (X-ray Photoelectron Spectroscopy, Axis-Supra, Kratos). As a result of the analysis, characteristic peaks such as Co 2p, Mn 2p, S 2p, N 1s, and C 1s were evenly detected on the CM@SNHCT surface, and in the Co 2p spectrum, Co 2+ (780.6 eV), Co 3+(778.3 eV) It was found that two oxidation states coexist. In particular, a downward shift in the Co 2p binding energy was observed, with the introduction of Mn lowering it by 0.38 eV, indicating that electron transfer from Mn to Co occurred. Additionally, various bonding states such as Co-S (161.6 eV), Mn-S (162.8 eV), CSC (163.8 eV), and C=S (164.8 eV) were detected in the S 2p spectrum, confirming that sulfur doping of the carbon body and heterometal sulfide structures were well formed.

[0114] Furthermore, the oxidation states and bonding environments of Co and Mn were evaluated using X-ray absorption spectroscopy (XAFS, KIST XAFS system). In the Co K-edge XANES results, the oxidation state of Co was close to +2. In the Fourier-transform EXAFS spectrum, the Co-S bond length increased from 1.78 Å in C@SNHCT to 1.93 Å in CM@SNHCT, indicating that lattice distortion and changes in electronic structure occurred due to the introduction of Mn, confirming that this serves as evidence for S atomic defects. The Mn K-edge results were similar... 2+ It was confirmed to be in an oxidized state, and an increase in the electrochemical activity of Co was expected due to the electron redistribution effect.

[0115] In addition, the elemental composition and distribution within the catalyst were confirmed using TEM-EDS (TEM equipped with an energy-dispersive X-ray analyzer, Talos F200X G2). As a result, it was visually verified that all elements, including Co, Mn, S, N, and C, were uniformly distributed throughout the nanotube structure. Quantitative analysis of the TEM-EDS confirmed that the atomic ratio of the catalyst consisted of Co (18.31 at%), Mn (1.10 at%), S (12.79 at%), N (5.17 at%), and C (62.63 at%). Furthermore, the presence of Co and Mn in the same region visually confirmed that the interfacial structure of the heterometal sulfide was well formed.

[0116] Therefore, it was confirmed that the CM@SNHCT catalyst according to Example 1 above has a structure in which ultrafine Co9S8 / MnS heterojunction nanoparticles are evenly dispersed inside S, N-doped hollow nanotubes, and that a high-performance catalyst with maximized exposure of lattice defects and active sites was prepared.

[0118] [Evaluation Example 3] Analysis of physical properties and surface condition

[0119] To evaluate the specific surface area and pore structure of the catalyst, nitrogen adsorption-desorption (BET) analysis was performed using Micromeritics 3Flex. As a result of analyzing freeze-dried powder samples at a temperature of 77 K liquid nitrogen, the BET surface area of ​​CM@SNHCT in Example 1 was 300.12 m² / g, which was significantly increased compared to 176.45 m² / g of Comparative Example 1 (C@SNHCT). In addition, as shown in the pore size distribution graph in Fig. 3, the nitrogen adsorption-desorption curve of the catalyst in Example 1 exhibited a typical type IV isotherm and a distinct hysteresis loop through BJH (Barrett-Joyner-Halenda) analysis. It was confirmed that the carbon structure of Example 1 contained both mesopores of 4–24 nm and micropores of less than 2 nm, thereby confirming that a porous structure was well formed due to the evaporation of Zn and melamine. A dual pore structure in which mesopores capable of effectively accessing active sites as in Example 1 and highly reactive micropores coexist can achieve smooth diffusion of oxygen / ion / electrolyte and accelerated reaction rates.

[0120] In addition, the hydrophobicity of the catalyst surface was evaluated by measuring the contact angle (using a contact angle analyzer). Catalyst powders according to the examples and comparative examples were coated onto flat carbon paper, and a water drop (approx. 5 μL) was dropped onto each specimen to immediately measure the contact angle. As a result, the contact angle of CM@SNHCT in Example 1 was 121.31°, showing very high hydrophobicity. On the other hand, C@SNHCT without Mn showed a relatively low value of 90.98°. The high contact angle of Example 1 was predicted to be due to increased hydrophobicity caused by surface CSC bonds formed by S doping of the carbon body of the structure. This allows for suppressing excessive penetration of the electrolyte during subsequent battery manufacturing and facilitating gas (oxygen) diffusion at the electrode-electrolyte interface.

[0122] [Evaluation Example 4] Performance evaluation of oxygen electrocatalyst

[0123] To evaluate the electrochemical performance of the catalysts prepared according to the above examples and comparative examples, a three-electrode cell was prepared and cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses were performed.

[0124] First, 5 mg of catalyst powder prepared according to the examples and comparative examples was dispersed in 1 mL of ethanol and Nafion (5 wt%, 50 μL) to make a catalyst ink, which was then drop-cast onto a glass carbon rotating disc electrode (RDE, 3 mm) to coat and dry it to a thickness of 0.25 mg / cm² (ORR evaluation) or 1 mg / cm² (OER). Subsequently, a three-electrode cell was constructed using the RDE coated with the catalyst layer as the working electrode, Hg / HgO as the reference electrode, Pt line as the control electrode, and O2-saturated 0.1 M KOH as the electrolyte, and electrochemical oxygen reduction (ORR) and oxygen evolution (OER) performance evaluations were performed using a BioLogic VSP potentiostat-galvanos instrument.

[0125] Oxygen Reduction Reaction (ORR) performance was analyzed using LSV with a rotating ring-disk electrode (RDE) in a 0.1 M KOH solution. Measurements were taken at a scan rate of 5 mV / s and various rotation speeds, and Koutecky-Levich analysis was performed concurrently. As a result, an onset potential (E0) of 0.93 V and a half-wave potential (E) of 0.84 V were observed. 1 / 2 ...was shown. In addition, the diffusion-limiting current was found to be greater than that of Pt / C, confirming the excellent current responsiveness for oxygen reduction. Furthermore, the electron transfer number (n) derived from Koutecky-Levich analysis approached 4, confirming that the catalyst according to Example 1 performs ORR through a 4-electron reaction pathway. As a result of the chronoamperometric test, the catalyst of Example 1 maintained 96.5% of the initial current density even after 25 hours, whereas Pt / C decreased rapidly to 87.8% within 15 hours.

[0126] Oxygen Evolution Reaction (OER) performance was analyzed using LSV with 95% iR correction in a 1M KOH electrolyte. The results showed that an overpotential of 275 mV was required to achieve a current density of 10 mA / cm², and an overpotential of 332 mV was observed at 100 mA / cm². Additionally, the Tafel slope, which indicates the reaction rate of the OER, was measured at 64.4 mV / dec, representing the lowest value among the comparison group including commercial IrO2 catalysts. This confirmed that the catalyst of the present invention exhibits excellent reaction rate and a low energy barrier for OER.

[0127] In addition, the electrochemically active surface area (ECSA) was indirectly calculated by measuring the double-layer capacitance (Cdl) through CV. As a result of the measurement, the catalyst of Example 1 showed a significantly high Cdl value of 40.62 mF / cm², confirming that the catalyst of the present invention exposes more reactive active sites on its surface, thereby enabling it to exhibit excellent activity in electrochemical reactions.

[0128] Furthermore, in the cycling test, there was no loss of activity even after 5,000 cycles at 10 mA / cm², and the overpotential increased only slightly to 7 mV. Moreover, to evaluate the reversibility of the oxygen reaction, the half-wave potential of the oxygen reduction reaction (E 1 / 2 The potential difference (ΔE) between the ) and the overpotential at 10 mA / cm² in the oxygen evolution reaction was calculated. As a result, when the catalyst of Example 1 was used, ΔE = 0.68 V was observed, indicating that the catalyst of the present invention exhibits balanced bifunctional performance in both ORR and OER reactions and can realize excellent bidirectional reaction reversibility.

[0130] [Evaluation Example 5] Battery Performance Evaluation

[0131] A battery was manufactured using the catalyst of Example 1 as the air-cathode of an aqueous zinc-air battery and a zinc foil as the anode, as illustrated in Fig. 4.

[0132] Specifically, 5 mg of catalyst powder prepared according to Example 1 was dispersed in 1 mL of ethanol and Nafion (5 wt%, 50 μL) to create a catalyst ink, and an air electrode was prepared by drop-casting 1 mg / cm² of this ink onto the surface of carbon paper (1 cm²) and drying. For the cathode, high-purity zinc foil (Zn foil) was prepared by cutting it to an appropriate size, and an aqueous solution of 6 M KOH + 0.2 M Zn acetate was used as the electrolyte. The air electrode and the zinc cathode were placed parallel to each other, sufficient electrolyte was injected between them, and then assembled. A single cell was completed by fixing each component using a cell holder. Various electrochemical characteristics of the cell, such as open-circuit voltage (OCV), discharge / charge curve, maximum power density, energy density, and cycle life, were evaluated.

[0133] The open circuit voltage (OCV) of a zinc-air battery (ZAB) using the catalyst of Example 1 was measured, and a stable OCV of 1.45 V was observed for 10 hours, which was confirmed to be very similar to the OCV of a commercial Pt / C+IrO2-based ZAB, which is 1.46 V.

[0134] In addition, discharge / charge curves were obtained in galvanostatic mode at 10 mA / cm² for charging in the current density range of 5 to 100 mA / cm² for the zinc-air battery using the catalyst of Example 1. As a result of evaluating the discharge rate characteristics while varying the current density from 5 to 100 mA / cm², excellent stability was observed under all current density conditions, and excellent reversibility was confirmed as performance was fully recovered even when returned from 100 mA / cm² to 5 mA / cm². Furthermore, as the current density was increased, the maximum power density was calculated in real time by calculating the product of the voltage (V) and current (I) measured at each current value (P=VХI, mW / cm²). As a result, the battery of the above example showed a maximum power density of 185 mW / cm², which is a value exceeding 170 mW / cm² for Pt / C+IrO2.

[0135] In addition, as a result of measuring the specific capacity based on Zn consumption, the catalyst-based ZAB of Example 1 showed 808 mAh / g, which is higher performance than the Pt / C+IrO2-based system that showed approximately 737 mAh / g under the same conditions (10 mA / ㎠). Long-term stability was also evaluated through continuous constant current charge / discharge tests; while the catalyst-based ZAB showed only an extremely small voltage gap for 250 hours at 10 mA / ㎠, the Pt / C+IrO2-based ZAB showed significant performance degradation within just 25 hours, and the energy efficiency of the catalyst-based ZAB of Example 1 decreased only slightly from 67% to 59%, confirming that its durability and reversibility are excellent.

[0136] In addition, the calculated specific energy density of the battery of Example 1 (calculated as Wh / kg by combining the total discharge capacity (based on the consumption of the zinc anode, in mAh units) and average discharge voltage of the ZAB at a constant current discharge of 10 mA / ㎠ and dividing this value by the weight of zinc (kg)) is 993.84 Wh / kg, which is the highest level of ZAB performance currently available. These results confirm that the battery of the present invention surpasses commercial precious metal-based Pt / C+IrO2 systems and demonstrates superior performance compared to the latest high-performance ZAB technology. Figure 5 records an experiment in which a digital timer was driven and a green LED bulb was lit by connecting the batteries using the catalyst according to Example 1 in series.

[0137] In addition, the cycle life of the battery in Example 1 was evaluated by using a potentiostat program to automatically and repeatedly drive the ZAB for more than 250 hours (750 cycles) under conditions of 10 minutes of charge-10 minutes of discharge at 10 mA / ㎠, and continuously monitoring the maintenance of the charge-discharge voltage and performance degradation (voltage drop, capacity reduction, etc.) of each cycle, and the results are shown in FIG. 6.

[0138] The excellent durability and high efficiency of a battery using a catalyst according to one embodiment are a synergistic effect of continuous charge transfer characteristics promoted by a precise Co / Mn sulfide heterostructure having abundant vacancy defects and a heteroatom-doped graphene carbon substrate, and are unique effects realized as the components of the present invention are organically combined.

[0139] As described above, the present invention has been explained by limited embodiments, but this is provided merely to aid in a more comprehensive understanding of the invention. The present invention is not limited to the above embodiments, and those skilled in the art can make various modifications and variations from this description.

[0140] Accordingly, the scope of the present invention is not limited to the described embodiments, and all things equivalent to or having equivalent variations to the claims set forth below, as well as the claims set forth below, shall be considered to fall within the scope of the concept of the present invention.

Claims

Claim 1 A catalyst for a metal-air battery comprising: a hollow interior; and a porous structure containing a metal sulfide; wherein the metal sulfide comprises cobalt (Co) sulfide and manganese (Mn) sulfide, the structure comprises a carbon structure doped with two or more types of heteroatoms, the carbon structure of the structure is a heterointerface in contact with two or more types of metal sulfides, and the metal sulfide comprises a structure in which some sulfur atoms are bonded (S-vacancy) within the crystal structure. Claim 2 delete Claim 3 In claim 1, the structure is a catalyst for a metal-air battery comprising a carbon structure doped with nitrogen (N) and sulfur (S). Claim 4 delete Claim 5 In claim 3, the carbon structure of the above structure is a catalyst for a metal-air battery comprising micropores and mesopores. Claim 6 In claim 1, the structure is a catalyst for a metal-air battery having a BET specific surface area of ​​200 m² / g or more. Claim 7 delete Claim 8 delete Claim 9 In claim 1, the metal sulfide is a catalyst for a metal-air battery comprising particles having an average diameter of 1 to 15 nm. Claim 10 delete Claim 11 A catalyst for a metal-air battery having a contact angle of 100° or more in claim 1. Claim 12 In claim 1, the structure is a catalyst for a metal-air battery having a thickness of 10 to 100 nm. Claim 13 In claim 1, the catalyst is a catalyst for a metal-air battery having a nanotube structure with an inner diameter of 10 to 300 nm and an outer diameter of 30 to 500 nm. Claim 14 In claim 1, the catalyst is a metal-air battery catalyst that is a bifunctional catalyst. Claim 15 delete Claim 16 delete Claim 17 delete Claim 18 delete Claim 19 An air electrode comprising a coating layer including a catalyst for a metal-air battery selected from any one of claims 1, 3, 5, 6, 9 and 11 to 14. Claim 20 In claim 19, the coating layer comprises an air electrode containing 30 to 99 weight percent of the catalyst for the metal-air battery. Claim 21 A metal-air battery comprising a cathode; an electrolyte; and the air electrode of claim 19. Claim 22 A method for manufacturing a catalyst for a metal-air battery, comprising: (A) a step of forming a heteroelement-containing template including nitrogen (N) and sulfur (S); (B) a step of forming a metal-organic framework layer on the template; (C) a step of forming a polymer coating layer on the metal-organic framework layer; and (D) a heat treatment step; wherein step (B) comprises a step of forming a metal-organic framework including a first metal and a second metal; and a step of introducing a third metal into the metal-organic framework; wherein the first metal is cobalt (Co), the second metal is zinc (Zn), and the third metal is manganese (Mn); and in step (D), the first metal and the third metal are sulfidated to form a metal sulfide including cobalt sulfide and manganese sulfide, and the metal sulfide includes a structure in which some sulfur atoms are vacant (S-vacancy) within the crystal structure. Claim 23 A method for manufacturing a catalyst for a metal-air battery, wherein step (A) above involves self-assembling melamine and trithiocyanuric acid to produce a template. Claim 24 delete Claim 25 A method for manufacturing a catalyst for a metal-air battery, wherein, in claim 22, step (D) is performed at a temperature of 700°C or higher. Claim 26 A method for manufacturing a catalyst for a metal-air battery according to claim 22, wherein, through step (D) above, a portion of the template is vaporized to form a hollow structure. Claim 27 A method for manufacturing a catalyst for a metal-air battery according to claim 22, wherein, through step (D) above, a heteroatom is doped into the polymer coating layer and the metal of the metal-organic framework layer is sulfidated to form a metal sulfide.

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