Composite catalyst structure, manufacturing method therefor, water electrolysis apparatus comprising same, and metal-air secondary battery

Abstract

A composite catalyst structure having catalytic activity for an oxygen evolution reaction (OER) or an oxygen reduction reaction (ORR) is disclosed. The composite catalyst structure may comprise: a porous metal support; a metal nitride nanosheet grown from the porous metal support; and a layered double hydroxide nanosheet disposed on the surface of the metal nitride nanosheet.

Description

Composite catalyst structure, method for producing the same, electrolysis device and metal-air secondary battery having the same

[0001] The present invention relates to a composite catalyst structure having catalytic activity for an oxygen evolution reaction or an oxygen reduction reaction, a method for producing the same, an electrolysis device having the same, and a metal-air secondary battery.

[0002] Due to problems such as the depletion of fossil fuels and environmental pollution, research is being actively conducted on environmentally friendly renewable energy devices that use hydrogen, such as fuel cells, and metal-air secondary batteries that store energy generated from renewable energy devices.

[0003] To produce the above hydrogen in an environmentally friendly manner, water electrolysis devices are widely used, and these water electrolysis devices can produce hydrogen and oxygen from water through an oxygen evolution reaction (OER) that occurs at the anode and a hydrogen evolution reaction (HER) that occurs at the cathode.

[0004] And metal-air secondary batteries can store electrical energy through the oxygen reduction reaction (ORR) that occurs at the air electrode and the metal oxidation reaction that occurs at the metal electrode.

[0005] In the case of water electrolysis devices and metal-air secondary batteries that are currently commercialized or mainly being studied, precious metal-based materials such as iridium and ruthenium have been mainly used as catalysts for the oxygen evolution reaction (OER) or the oxygen reduction reaction (ORR). However, due to the high price of the catalyst, not only has the economic feasibility decreased, but various studies are being conducted on non-precious metal-based catalyst materials to further improve stability.

[0006] Among the non-precious metal-based catalysts, layered metal double-layer hydroxide (LDH) catalysts are less expensive and more abundant than precious metals, and have recently attracted significant attention as OER or ORR catalysts. However, LDH catalysts have the disadvantage of low electrical conductivity, making it difficult to expect high catalytic activity.

[0007] One object of the present invention is to provide a composite catalyst structure having relatively high electrical conductivity and high catalytic activity for an OER reaction or an ORR reaction.

[0008] Another object of the present invention is to provide a method for producing the composite catalyst structure.

[0009] Another object of the present invention is to provide a water electrolysis device that uses the composite catalyst structure as a catalyst for an OER reaction.

[0010] Another object of the present invention is to provide a metal-air secondary battery using the composite catalyst structure as a catalyst for an ORR reaction.

[0011] A composite catalyst structure according to an embodiment of the present invention may include: a porous metal support; a metal nitride nanosheet grown from the porous metal support; and a layered metal double-layer hydroxide nanosheet disposed on a surface of the metal nitride nanosheet.

[0012] In one embodiment, the porous metal support may include a metal or an alloy thereof capable of forming a conductive metal nitride. For example, the porous metal support may be formed of one or more metals or alloys thereof selected from the group consisting of titanium (Ti), tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), rhenium (Re), aluminum (Al), indium (In), gallium (Ga), and germanium (Ge).

[0013] In one embodiment, the porous metal support may include a metal foam, a metal sponge, or a metal lattice structure.

[0014] In one embodiment, the metal nitride nanosheet is grown in a direction perpendicular or inclined to the surface of the porous metal support, and the layered metal bilayer hydroxide nanosheet may include a first LDH nanosheet and a second LDH nanosheet formed on each of both sides of the metal nitride nanosheet.

[0015] In one embodiment, a plurality of through holes spaced apart from each other are formed in the metal nitride nanosheet, and the first LDH nanosheet and the second LDH nanosheet can be connected to each other through the through holes. In one embodiment, the through holes can each have a size of 1 to 500 nm.

[0016] In one embodiment, the layered metal bilayer hydroxide nanosheet may include a material represented by the following chemical formula 1 or 2.

[0017] [Chemical Formula 1]

[0018] [M 1 1-x M 2 x (OH)2][A n- ] x / n ·cH2O

[0019] [Chemical Formula 2]

[0020] [M 1 1-(a+b) M 2 a Y 3+ b (OH)2][A n- ] (a+b) / n ·cH2O

[0021] In the above chemical formulas 1 and 2, M 1 is a first transition metal cation with an oxidation state of +2, and M2 is a second transition metal cation with an oxidation state of +3, A is an interlayer anion with an oxidation state of -n, and x is "0 <x<1"의 조건을 만족하는 실시이고, a, b는 각각 "0<a+b<1"의 조건을 만족하는 양의 실수이고, n은 1 이상 5 이하의 정수이며, c는 양의 실수이다.

[0022] In one embodiment, the first transition metal cation is Ca 2+ , Mg 2+ , Zn 2+ , Ni 2+ , Mn 2+ , Co 2+ , Fe 2+ and Cu 2+ comprising at least one selected from the group consisting of, wherein the second transition metal cation is Fe 3+ , Al 3+ , Cr 3+ , Mn 3+ , Ga 3+ , Co 3+ and Ni 3+ Contains at least one selected from the group consisting of, wherein the interlayer anion is OH - , NO3 - , PO4 3- , HPO4 2- and H2PO4 - It may include one or more selected from the group consisting of .

[0023] In one embodiment, the layered metal bilayer hydroxide nanosheet comprises a material represented by the following chemical formula 1 or 2, wherein the material of the chemical formula 2 is such that each of the first transition metal cations has six hydroxide ions (OH - ) formed by coordination of the first octahedral structure, each of the second transition metal cations having six hydroxide ions (OH - ) and the second octahedral structure formed by coordination with the yttrium ion and seven hydroxide ions (OH -) may include an icosahedral structure formed by coordination.

[0024] In one embodiment, in the chemical formula 2, a+b may be 0.2 or more and 0.5 or less, and the molar ratio (a / b) of the second transition metal cation to the yttrium ion may be 20 or more and 150 or less.

[0025] A method for manufacturing a composite catalyst structure according to an embodiment of the present invention may include a first step of forming a metal oxide nanosheet on the surface of a porous metal support using a hydrothermal synthesis method; a second step of converting the metal oxide nanosheet into a metal nitride nanosheet; and a third step of forming a layered metal double-layer hydroxide nanosheet on the surface of the metal nitride nanosheet using a hydrothermal synthesis method.

[0026] In one embodiment, the second step may be performed by heat-treating the metal oxide nanosheet in a nitrogen-containing atmosphere. For example, the second step may be performed by heat-treating the metal oxide nanosheet in an ammonia gas atmosphere at a temperature of about 600 to 1000°C for about 0.5 to 2 hours.

[0027] In one embodiment, the third step is performed by immersing the porous metal support on which the metal nitride nanosheets are formed in a mixed precursor solution for a layered metal bilayer hydroxide and heating the mixed precursor solution in an inert atmosphere at 120 to 180° C. for 20 to 28 hours, and during the third step, the layered metal bilayer hydroxide nanosheets can be formed on both sides of the metal nitride nanosheets.

[0028] In one embodiment, during the second step, a plurality of through holes having a size of about 1 to 500 nm are formed in the metal nitride nanosheet, and during the third step, the layered metal bilayer hydroxide nanosheet may be formed so as to be connected to each other through the through holes on both sides of the metal nitride nanosheet.

[0029] A water electrolysis device according to an embodiment of the present invention includes an ion exchange membrane and a first electrode and a second electrode facing each other with the ion exchange membrane interposed therebetween, wherein the first electrode, where an oxygen evolution reaction (OER) occurs, may include a composite catalyst structure comprising: a porous metal support; metal nitride nanosheets grown from the porous metal support; and layered metal double-layer hydroxide nanosheets arranged on a surface of the metal nitride nanosheets.

[0030] In one embodiment, a path for diffusing gas may be formed inside the porous metal support.

[0031] A metal-air secondary battery according to an embodiment of the present invention includes an air electrode and a metal electrode spaced apart from each other, and an electrolyte disposed between the air electrode and the metal electrode, wherein the air electrode may include a composite catalyst structure comprising: a porous metal support; metal nitride nanosheets grown from the porous metal support; and layered metal double-layer hydroxide nanosheets disposed on a surface of the metal nitride nanosheets.

[0032] In one embodiment, the metal electrode may include any one metal selected from the group consisting of zinc (Zn), lithium (Li), and aluminum (Al).

[0033] According to the composite catalyst structure of the present invention, the method for manufacturing the same, and the electrolysis device and metal-air secondary battery including the same, layered metal double-layer hydroxide nanosheets are formed on both surfaces of metal nitride nanosheets grown from the surface of a porous metal support, and the metal double-layer hydroxide nanosheets have a structure in which they are connected through through holes formed in the metal nitride nanosheets, so that the adhesive force or bonding force between the metal support and the metal nitride nanosheets and between the metal nitride nanosheets and the metal double-layer hydroxide nanosheets is significantly improved, so that the durability and lifespan of the composite catalyst structure can be significantly improved.

[0034] And since it has a structure in which the metal nitride nanosheet having relatively high conductivity is arranged between the metal double-layer hydroxide nanosheets, it can exhibit significantly improved catalytic performance for oxygen evolution reaction (OER) or oxygen reduction reaction (ORR) compared to the metal double-layer hydroxide nanosheet alone.

[0035] In addition, since the composite nanosheet having catalytic activity composed of the metal nitride nanosheet and the metal double-layer hydroxide nanosheet is fixed to the porous metal support, not only does a separate support not require, but gas can move inside the porous metal support, so it can be easily applied as an electrode where an oxygen evolution reaction occurs in a water electrolysis device or an air electrode of a metal-air secondary battery.

[0036] FIG. 1 is a flowchart illustrating a method for manufacturing a layered metal bilayer hydroxide catalyst according to an embodiment of the present invention.

[0037] Figure 2 is a drawing for explaining a water electrolysis device according to an embodiment of the present invention.

[0038] FIG. 3 is a drawing for explaining a metal-air secondary battery according to an embodiment of the present invention.

[0039] Figure 4 shows X-ray diffraction analysis data for Ti@TiN / LDH900.

[0040] Figure 5 shows field-effect electron microscope (FE-SEM) images of Ti foam, Ti@TiO2, Ti@TiN900, and Ti@TiN / LDH900.

[0041] Figure 6 is an electron scanning microscope elemental analysis image of Ti@TiN / LDH900.

[0042] Figure 7 shows XANES and EXAFS data of Ti@TiN / LDH700, 800, and 900.

[0043] Figure 8 is data showing the results of measuring the catalytic activity of Ti@TiN, Ti@LDH, Ti@TiN / LDH700, Ti@TiN / LDH800, and Ti@TiN / LDH900 for the oxygen evolution reaction (OER).

[0044] Figure 9 shows data showing the results of Raman analysis measured during the oxygen evolution reaction of Ti@LDH and Ti@TiN / LDH900.

[0045] Figure 10 shows XRD pattern data measured for materials synthesized according to Examples 2-1 to 2-3 and Comparative Example 2.

[0046] Figure 11 shows a TEM image (a), an elemental mapping image (b), and a STEM image (c) of a material synthesized according to Example 2-2.

[0047] Figure 12 shows XANES data of materials synthesized according to Example 2-2 and Comparative Example 2, respectively.

[0048] Figure 13 shows EXAFS data of materials synthesized according to Example 2-2 and Comparative Example 2, respectively.

[0049] Figure 14 shows data showing the results of electrochemical performance tests of catalysts synthesized according to Examples 2-1 to 2-3 and Comparative Example 2, respectively.

[0050] Figure 15 shows the results of in situ Raman analysis during an oxygen evolution reaction conducted to analyze the reaction mechanism of the catalysts synthesized according to Example 2-2 and Comparative Example 2.

[0051] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention may be modified in various ways and may take various forms. Therefore, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing each drawing, similar reference numerals are used to indicate similar components. In the attached drawings, the dimensions of structures are shown larger than actual size to ensure clarity of the present invention.

[0052] While terms like "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component."

[0053] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, step, operation, component, part, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, steps, operations, components, parts, or combinations thereof.

[0054] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0055]

[0056] <Composite catalyst structure>

[0057] A composite catalyst structure according to an embodiment of the present invention may include a porous metal support, a metal nitride nanosheet, and a layered metal double-layer hydroxide nanosheet, and may have catalytic activity that promotes an oxygen evolution reaction (OER) or an oxygen reduction reaction (ORR).

[0058] The porous metal support may include a metal or an alloy thereof capable of forming a conductive or semiconducting metal nitride.

[0059] In one embodiment, the porous metal support may be formed of one or more metals selected from titanium (Ti), tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), rhenium (Re), etc. or alloys thereof, or may be formed of one or more metals selected from aluminum (Al), indium (In), gallium (Ga), germanium (Ge), etc. or alloys thereof.

[0060] In one embodiment, the porous metal support may have a structure such as a metal foam, a metal sponge, or a metal lattice structure formed of the metal or alloy.

[0061] The above metal nitride nanosheet can be grown from the surface of the porous metal support and can be formed from the nitride of the metal contained in the metal support.

[0062] In one embodiment, the metal nitride nanosheet can be grown upward from the surface of the metal support through a hydrothermal method. For example, the metal nitride nanosheet can be grown upward in a direction perpendicular to or inclined with respect to the surface of the porous metal support. In one embodiment, the metal nitride nanosheet can be manufactured by growing a metal oxide nanosheet on the surface of the porous metal support through a hydrothermal method and then nitriding the same. For example, when the porous metal support is a titanium foam, the titanium nitride nanosheet can be formed on the titanium foam by growing a titanium oxide nanosheet on the surface of the titanium foam through a hydrothermal method and then nitriding the titanium oxide nanosheet.

[0063] In one embodiment, the metal nitride nanosheet may have a plurality of spaced apart through holes formed therein. In one embodiment, the through holes may be formed during nitriding of the metal oxide nanosheet. In one embodiment, the metal nitride nanosheet may have through holes having a size of about 1 to 500 nm formed therein. For example, the metal nitride nanosheet may have through holes having a size of about 5 to 200 nm or about 10 to 100 nm formed therein.

[0064] The above layered metal double layer hydroxide nanosheet can be formed on the surface of the above metal nitride nanosheet.

[0065] In one embodiment, the layered metal bilayer hydroxide nanosheets may be formed on both surfaces of the metal nitride nanosheet. Since the conductivity of the metal nitride nanosheet is higher than that of the layered metal bilayer hydroxide nanosheet, a nanosheet composite in which the layered metal bilayer hydroxide nanosheets are formed on the surface of the metal nitride nanosheet has higher conductivity than a single layered metal bilayer hydroxide nanosheet, and thus the nanosheet composite may have improved catalytic activity for oxygen evolution reaction (OER) or oxygen reduction reaction (ORR) than a single layered metal bilayer hydroxide nanosheet.

[0066] In one embodiment, when a plurality of through holes are formed in the metal nitride nanosheet, the layered metal bilayer hydroxide nanosheets formed on each side of the metal nitride nanosheet can be connected to each other through the through holes. In this case, the adhesive force between the metal nitride nanosheet and the layered metal bilayer hydroxide nanosheets is significantly enhanced, thereby significantly improving the durability or lifespan of the composite catalyst structure.

[0067] In one embodiment, the layered metal bilayer hydroxide nanosheet may include a material represented by the following chemical formula 1 or 2 and may have a layered metal bilayer structure.

[0068] [Chemical Formula 1]

[0069] [M 1 1-x M 2 x (OH)2][A n- ] x / n ·cH2O

[0070] [Chemical Formula 2]

[0071] [M 1 1-(a+b) M 2 a Y 3+ b (OH)2][A n- ] (a+b) / n ·cH2O

[0072] In the above chemical formulas 1 and 2, M 1 is a first transition metal cation with an oxidation state of +2, and M 2 is a second transition metal cation having an oxidation state of +3, and A may be an interlayer anion having an oxidation state of -n. And x, a, and b are each "0 <x<1", "0<a+b<1"의 조건을 만족하는 양의 실수이고, n은 1 이상 5 이하의 정수이며, c는 양의 실수일 수 있다.

[0073] In one embodiment, the first transition metal cation is Ca 2+ , Mg 2+ , Zn 2+ , Ni 2+ , Mn 2+ , Co 2+ , Fe 2+ , Cu 2+ It may include at least one selected from the group consisting of Fe, and the second transition metal cation is Fe 3+ , Al 3+ , Cr 3+ , Mn 3+ , Ga3+ , Co 3+ , Ni 3+ It may include one or more selected from the group consisting of, and the interlayer anion is OH - , NO3 - , PO4 3- , HPO4 2- , H2PO4 - It may include one or more selected from the group consisting of:

[0074] In one embodiment, the layered metal double layer hydroxide (LDH) nanosheet of the chemical formula 1 is such that each of the first transition metal cations has six hydroxide ions (OH - ) formed by coordination of the first octahedral structure, each of the second transition metal cations having six hydroxide ions (OH - ) may have a structure in which the interlayer anion is arranged between two-dimensional layered structures formed by covalently bonding the second octahedral structure formed by coordination. In one embodiment, in the chemical formula 1, x may be about 0.2 or more and 0.5 or less, for example, about 0.3 to 0.4.

[0075] In one embodiment, the layered metal double layer hydroxide (LDH) nanosheet of the above chemical formula 2 is such that each of the first transition metal cations has six hydroxide ions (OH - ) formed by coordination of the first octahedral structure, each of the second transition metal cations having six hydroxide ions (OH - ) and the second octahedral structure formed by coordination with the yttrium ion and seven hydroxide ions (OH -) may have a structure in which the interlayer anions are arranged between the two-dimensional layered structures formed by covalently linking the decahedral structures formed by coordination by yttrium ions. In one embodiment, each of the first and second transition metal cations may have an ionic radius smaller than that of the yttrium ion. Compared to the layered metal bilayer hydroxide of Chemical Formula 1, the layered metal bilayer hydroxide of Chemical Formula 2 has an enhanced ability to adsorb oxygen evolution reaction reactants due to the increased coordination number through yttrium (Y) substitution having a relatively large ionic radius, thereby more actively promoting the oxygen evolution reaction. In one embodiment, in Chemical Formula 2, a+b may be about 0.2 or more and 0.5 or less, for example, about 0.3 to 0.4. And the molar ratio (a / b) of the second transition metal cation to the yttrium ion may be about 20 or more and 150 or less. When the molar ratio (a / b) of the second transition metal cation to the yttrium ion is less than 33, the change in the average coordination number within the lattice due to yttrium ion substitution may be minimal, thereby reducing the effect on oxygen generation performance. When it exceeds 100, a problem may arise in which Y-related impurities such as Y(OH)3 appear together during the synthesis process. For example, the molar ratio (a / b) of the second transition metal cation to the yttrium ion may be about 33 or more and 105 or less, or about 40 or more and 75 or less.

[0076] In one embodiment, the layered metal bilayer hydroxide nanosheet of the above chemical formula 1 may include Ni-Fe LDH or Co-Fe LDH, and the layered metal bilayer hydroxide nanosheet of the above chemical formula 2 may include Ni-Fe:Y LDH or Co-Fe:Y LDH.

[0077] According to the composite catalyst structure of the present invention, layered metal bilayer hydroxide nanosheets are formed on both surfaces of metal nitride nanosheets grown from the surface of a porous metal support, and the metal bilayer hydroxide nanosheets have a structure in which they are connected through through holes formed in the metal nitride nanosheets, so that the adhesive force or bonding force between the metal support and the metal nitride nanosheets and between the metal nitride nanosheets and the metal bilayer hydroxide nanosheets is significantly improved, so that the durability and lifespan of the composite catalyst structure can be significantly improved.

[0078] And since it has a structure in which the metal nitride nanosheet having relatively high conductivity is arranged between the metal double-layer hydroxide nanosheets, it can exhibit significantly improved catalytic performance for oxygen evolution reaction (OER) or oxygen reduction reaction (ORR) compared to the metal double-layer hydroxide nanosheet alone.

[0079] In addition, since the composite nanosheet having catalytic activity composed of the metal nitride nanosheet and the metal double-layer hydroxide nanosheet is fixed to the porous metal support, not only does a separate support not require, but gas can move inside the porous metal support, so it can be easily applied as an electrode where an oxygen evolution reaction occurs in a water electrolysis device or an air electrode of a metal-air secondary battery.

[0080]

[0081] <Method for producing a composite catalyst>

[0082] Figure 1 is a flowchart for explaining a method for manufacturing a composite catalyst structure according to an embodiment of the present invention.

[0083] Referring to FIG. 1, a method for manufacturing a composite catalyst structure according to an embodiment of the present invention may include a first step (S110) of forming a metal oxide nanosheet on the surface of a porous metal support using a hydrothermal synthesis method; a second step (S120) of converting the metal oxide nanosheet into a metal nitride nanosheet; and a third step (S130) of forming a layered metal double-layer hydroxide nanosheet on the surface of the metal nitride nanosheet using a hydrothermal synthesis method.

[0084] In the first step (S110), the porous metal support may have a structure such as a metal foam, a metal sponge, or a metal lattice structure formed of a metal or an alloy thereof capable of forming a conductive metal nitride. Since this has been described in detail above, a detailed description thereof will be omitted below.

[0085] In one embodiment, the metal oxide nanosheet can be manufactured through a hydrothermal synthesis process in an alkaline aqueous solution. In one embodiment, when the porous metal support is titanium foam (Ti foam), the titanium oxide nanosheet is formed through a hydrothermal synthesis process in which the titanium foam is immersed in a sodium hydroxide (NaOH) aqueous solution and then heated at a temperature of about 160 to 230° C. for about 8 to 16 hours to form Na2Ti2O4(OH)2 nanosheets on the surface of the titanium foam; the titanium foam on which the Na2Ti2O4(OH)2 nanosheets are formed is immersed in an acidic aqueous solution, for example, a hydrochloric acid (HCl) aqueous solution, to form Na2Ti2O4(OH)2 nanosheets. + ions and H of the above hydrochloric acid solution +A step of converting the Na2Ti2O4(OH)2 nanosheet into a H2Ti2O4(OH)2 nanosheet by inducing an exchange reaction between ions; and a step of converting the H2Ti2O4(OH)2 nanosheet into a TiO2 nanosheet by heat-treating the H2Ti2O4(OH)2 nanosheet in air at a temperature of about 400 to 500°C for about 1 to 3 hours. In this case, the TiO2 nanosheet may be formed to protrude in a direction perpendicular to or inclined with respect to the surface of the titanium foam.

[0086] In the second step (S120), the metal oxide nanosheet can be converted into the metal nitride nanosheet by heat-treating the metal oxide nanosheet in a nitrogen-containing atmosphere.

[0087] In one embodiment, the metal nitride nanosheet can be formed by heat-treating the metal oxide nanosheet in an ammonia gas atmosphere at a temperature of about 600 to 1000° C. for about 0.5 to 2 hours, and a plurality of through holes having a size of about 1 to 500 nm can be formed in the metal nitride nanosheet formed by such nitrogen-containing atmosphere heat treatment.

[0088] In the third step (S130), the layered metal double-layer hydroxide nanosheet can be formed on the surface of the metal nitride nanosheet through a hydrothermal synthesis method.

[0089] In one embodiment, the layered metal bilayer hydroxide nanosheet can be formed on the surface of the metal nitride nanosheet through a hydrothermal synthesis method in which a porous metal support on which the metal nitride nanosheet is formed is immersed in a mixed precursor solution for the layered metal bilayer hydroxide nanosheet and the mixed precursor solution is heated at about 120 to 180° C. for about 20 to 28 hours in an inert atmosphere.

[0090] In one embodiment, when the layered metal bilayer hydroxide nanosheet is formed of a material of chemical formula 1, the mixed precursor solution is M 1 Precursor material and M 2 It can be prepared by mixing a first solution containing a precursor material dissolved therein with a second solution containing an interlayer anion together with an alkaline solution. In this case, the M 1 Precursor material and M 2 The precursor material is M 1 Metal salts and M 2 Each may contain metal salts.

[0091] In one embodiment, when the layered metal bilayer hydroxide nanosheet is formed of a material of chemical formula 2, the mixed precursor solution is M 1 Precursor material, M 2 It can be prepared by mixing a first solution containing a precursor material and a yttrium precursor material dissolved therein with a second solution containing an interlayer anion together with an alkaline solution. In this case, the M 1 Precursor material, M 2 Precursor materials and yttrium precursor materials are M 1 Metal salt, M 2 Each may include a metal salt and an yttrium salt.

[0092] In one embodiment, when a plurality of through holes are formed in the metal nitride nanosheet, the layered metal bilayer hydroxide nanosheets formed on each side of the metal nitride nanosheet can be connected to each other through the through holes.

[0093]

[0094] <Water electrolysis device>

[0095] Figure 2 is a drawing for explaining a water electrolysis device according to an embodiment of the present invention.

[0096] Referring to FIG. 2, a water electrolysis device (100) according to an embodiment of the present invention may include an ion exchange membrane (110), a first electrode (120), and a second electrode (130).

[0097] The ion exchange membrane (110) may be any ion exchange membrane applicable to a known water electrolysis device without limitation. For example, the ion exchange membrane (110) may include a cation exchange membrane or an anion exchange membrane.

[0098] The first electrode (120) and the second electrode (130) may be arranged to face each other with the ion exchange membrane (110) interposed therebetween.

[0099] An oxygen evolution reaction (OER) can occur at the first electrode (120), and a hydrogen evolution reaction (HER) can occur at the second electrode (130).

[0100] In one embodiment, the first electrode (120) may include a composite catalyst structure according to the embodiment of the present invention described above. In this case, among the composite catalyst structures, a nanosheet composite composed of the metal nitride nanosheet and the layered metal double-layer hydroxide nanosheet formed on the surface thereof may function as a first catalyst layer, and a porous metal support may function as a first gas diffusion layer.

[0101] The second electrode layer (130) may include a second catalyst layer (131) disposed to face the first catalyst layer (121) with the ion exchange membrane (110) interposed therebetween, and a second gas diffusion layer (132) disposed on the outer side of the second catalyst layer (131). As the second catalyst layer (131) and the second gas diffusion layer (132), a catalyst layer and a gas diffusion layer applied to a hydrogen generation electrode of a known water electrolysis device may be applied without limitation.

[0102]

[0103] Metal-air secondary battery

[0104] FIG. 3 is a drawing for explaining a metal-air secondary battery according to an embodiment of the present invention.

[0105] Referring to FIG. 3, a metal-air secondary battery (200) according to an embodiment of the present invention may include an air electrode (220), a metal electrode (230), and an electrolyte (210).

[0106] The air electrode (220) and the metal electrode (230) may be spaced apart from each other with the electrolyte (210) interposed therebetween.

[0107] The above-described air electrode (220) may have a porous structure and may include a catalyst for oxygen reduction reaction (ORR). For example, the above-described air electrode (220) may include a composite catalyst structure according to the embodiment of the present invention described above.

[0108] The above metal electrode (230) may include a metal such as zinc (Zn), lithium (Li), or aluminum (Al).

[0109] When the above metal-air secondary battery (200) is discharged, hydroxide ions (OH) are generated at the air electrode (220) by the oxygen reduction reaction (ORR). - ) can be generated, and at the metal electrode (230), metal hydroxide and electrons can be generated by the reaction of the metal forming the metal electrode (230) and the hydroxide ions. And, when charging the metal-air secondary battery (200), at the air electrode (220), the hydroxide ions (OH - ) can generate oxygen, water and electrons, and at the metal electrode (230), metal, water and hydroxide ions can be generated by the reaction of the metal hydroxide and electrons.

[0110]

[0111] Hereinafter, specific embodiments of the present invention will be described in detail. However, the following examples are merely some embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

[0112]

[0113] [Examples 1-1, 1-2, 1-3]

[0114] Step 1: Synthesis of TiO2 nanosheets

[0115] To clean the surface of the Ti metal foam, it was immersed in acetone, ethanol, and distilled water, respectively, and ultrasonicated for a certain period of time. Next, the Ti metal foam was cut into a certain size, immersed in a 5 M NaOH aqueous solution, and hydrothermal synthesis was performed at 180℃ for 12 hours (forming Na2Ti2O4(OH)2 nanosheets). Next, it was immersed in a 0.1 M HCl aqueous solution for 1 hour (forming H2Ti2O4(OH)2 nanosheets). Next, the surface was washed by flowing distilled water until the pH became neutral, and then dried in an oven. After drying, it was heat-treated at 450℃ in air for 2 hours (forming TiO2 nanosheets). Hereinafter, the hybrid synthesized in Step 1 is referred to as Ti@TiO2.

[0116]

[0117] Step 2: Synthesis of porous TiN nanosheets

[0118] The Ti@TiO2 synthesized in Step 1 was heat-treated together at 700°C, 800°C (Example 1-2), and 900°C (Example 1-3) for 1 hour under ammonia gas. At this time, the heating rate was controlled to 2°C / min. Hereinafter, the hybrids finally synthesized in Step 2 are named Ti@TiN700, Ti@TiN800, and Ti@TiN900, respectively.

[0119]

[0120] Step 3: Synthesis of LDH (Layered Double Hydroxide) Nanosheets

[0121] Ni(NO3)2·6H2O (0.532 mmol), Fe(NO3)3·9H2O (0.266 mmol), urea (1.5 mmol), and sodium citrate (0.1 mmol) were added to 50 mL of distilled water to prepare a mixed solution. Subsequently, Ti@TiN700, Ti@TiN800, and Ti@TiN900 synthesized in Step 2 were each immersed in the above mixed solution and heated at 150°C for 24 hours to perform a hydrothermal synthesis reaction. After the hydrothermal synthesis reaction was completed, the produced hybrids were washed with distilled water and dried in an oven. The hybrids synthesized in Step 3 are named Ti@TiN / LDH700 (Example 1-1), Ti@TiN / LDH800 (Example 1-2), and Ti@TiN / LDH900 (Example 1-3), respectively.

[0122]

[0123] [Experimental Example 1]

[0124] A three-electrode system was configured by applying Ti@TiN / LDH700 (Example 1-1), Ti@TiN / LDH800 (Example 1-2), and Ti@TiN / LDH900 (Example 1-3) to the working electrode, and the catalytic activity of Ti@TiN / LDH700, 800, and 900 for the oxygen evolution reaction was measured. Specifically, each of Ti@TiN / LDH700 (Example 1-1), Ti@TiN / LDH800 (Example 1-2), and Ti@TiN / LDH900 (Example 1-3) was used as a working electrode including 1x1 cm as an active site, a graphite rod was used as a counter electrode, an SCE electrode was used as a reference electrode, and a 1 M KOH aqueous solution was used as an electrolyte.

[0125] The catalytic activities of Ti@TiN / LDH700, 800, and 900 for the oxygen evolution reaction were measured using linear scanning voltammetry and Tafel plots. The data obtained from linear scanning voltammetry were subjected to voltage drop correction using the following equation 1.

[0126] [Formula 1]

[0127] Vf(Voltage after compensation) = Vi(Voltage before compensation) - I(Current)*Rs(Electrolyte resistance)

[0128] In Equation 1, Vf represents the voltage after compensation, Vi represents the voltage before compensation, I represents the current, and Rs represents the electrolyte resistance.

[0129]

[0130] Figure 4 is X-ray diffraction analysis data for Ti@TiN / LDH900 of Example 1-3.

[0131] Referring to Fig. 4, it can be seen through each peak that Ti@TiN / LDH900 exists in a hybridized form of Ti metal foam, TiN nanosheets, and NiFe-LDH nanosheets. In addition, it can be seen that NiFe-LDH nanosheets grow and are maintained in a crystalline form on the surface of the TiN nanosheets.

[0132] Figure 5 shows field-effect electron microscope (FE-SEM) images of Ti foam, Ti@TiO2, Ti@TiN900, and Ti@TiN / LDH900.

[0133] Referring to Fig. 5, it can be seen that Ti@TiO2 is in the form of a nanosheet, and Ti@TiN900 is in the form of a nanosheet with numerous through holes penetrating the sheet. In addition, in the case of Ti@TiN / LDH900, it can be seen that thin LDH nanosheets are formed on both surfaces of TiN.

[0134] Figure 6 is an electron scanning microscope elemental analysis image of Ti@TiN / LDH900.

[0135] Referring to Fig. 6, it can be seen that Ni and Fe are very evenly distributed on the TiN nanosheet, and from this, it can be seen that TiN and NiFe-LDH are hybridized.

[0136] Figure 7 shows XANES and EXAFS data of Ti@TiN / LDH700, 800, and 900.

[0137] Referring to XANES data of a and b in Fig. 7, it can be seen that Ni and Fe in Ti@TiN / LDH700, 800 and 900 have oxidation states of +2 and +3, respectively, through comparison with the metal oxide (NiO) measured together as a control group.

[0138] Referring to the EXAFS data of c and d in Fig. 7, Ni K-edge and Fe K-edge EXAFS analysis showed that the bond lengths of nickel-oxygen and iron-oxygen increased after hybridization of Ti@TiN and LDH, which indicates that LDH receives electrons when Ti@TiN and LDH are hybridized.

[0139] Figure 8 shows data showing the results of measuring the catalytic activity of Ti@TiN, Ti@LDH, Ti@TiN / LDH700, Ti@TiN / LDH800, and Ti@TiN / LDH900 for the oxygen evolution reaction (OER). At this time, the catalytic activity for the oxygen evolution reaction (OER) was measured in a 1 M KOH solution with the scan rate set to 1 mV / s.

[0140] Referring to Fig. 8a, which is data measuring the current density of the catalyst through linear scanning voltammetry, Ti@TiN / LDH700, 800, and 900 were found to have much higher current values ​​than Ti@LDH and Ti@TiN.

[0141] Referring to Fig. 8b, which is data measuring the overvoltage at 100 mV, it was found that Ti@TiN / LDH700, 800, and 900 showed much lower overvoltages than Ti@LDH and Ti@TiN, and this result is due to the hybridization of TiN and LDH.

[0142] Referring to Fig. 8c, which is a Tafel plot data that can confirm the electrochemical reaction rate through the change in current according to voltage, Ti@TiN / LDH700, 800, and 900 were found to have lower slopes than Ti@LDH and Ti@TiN, and from these results, it can be seen that the reaction rate was greatly improved by the hybridization of TiN and LDH.

[0143] Referring to Fig. 8d, which is data measuring electrochemically active sites, it was found that Ti@TiN / LDH700, 800, and 900 had larger active sites than Ti@LDH and Ti@TiN.

[0144] 100 mA·cm -2 Referring to Fig. 8e, which shows the results of stability evaluation at a current density of , TI@TiN / LDH900 was found to maintain the initial voltage for more than 100 hours, and from these results, it can be seen that Ti@TiN / LDH catalysts are very stable and have excellent durability and long lifespan.

[0145] Referring to Fig. 8f, which is the measurement result of electrochemical impedance spectroscopy, it was found that Ti@TiN / LDH700, 800, and 900 all had significantly lower charge transfer resistance than Ti@LDH and Ti@TiN, and from these results, it can be seen that Ti@TiN / LDH700, 800, and 900 have excellent charge transfer characteristics.

[0146] These improved oxygen evolution catalytic performance data confirm that the hybridization of TiN and LDH not only increases conductivity but also exhibits various synergistic effects.

[0147] Figure 9 shows data showing the results of Raman analysis measured during the oxygen evolution reaction of Ti@LDH and Ti@TiN / LDH900.

[0148] Referring to Fig. 9, in the case of Ti@LDH, it was confirmed that a peak corresponding to NiOOH, an oxygen evolution reaction intermediate, appeared when a voltage of about 1.55 V was applied, deviating from the existing structure. In contrast, in the case of Ti@TiN / LDH900, NiOOH was confirmed to appear when a voltage of about 1.45 V, which is lower than that of Ti@LDH, was applied. From these results, it can be seen that Ti@TiN / LDH900 can generate an oxygen evolution intermediate at a lower voltage than Ti@LDH, which means that the oxygen evolution reaction occurs more actively in Ti@TiN / LDH900 than in Ti@LDH, and thus it can be seen that Ti@TiN / LDH900 exhibits superior oxygen evolution catalytic performance.

[0149]

[0150] [Examples 2-1 to 2-3]: Synthesis of NiFeY-LDH.

[0151] A mixed solution was prepared by dissolving 6.6 mmol of Ni(NO3)26H2O, (3.3-x) mmol of Fe(NO3)36 H2O, and x mmol of Y(NO3)3·6H2O (Company: Sigma-Aldrich) in 40 ml of decarbonated distilled water, and a 1 M NaOH solution was prepared using the decarbonated distilled water, and 13.2 mmol of NaNO3 (Company: Thermo Fisher Scientific) was dissolved in 100 ml of decarbonated distilled water and stirred to prepare a NaNO3 solution.

[0152] Next, the above mixed solution and the above NaOH solution were added dropwise to the above NaNO3 solution and mixed, and then the pH was adjusted to 9. The mixture was stirred for 24 hours while flowing nitrogen gas to form NiFeY-LDH.

[0153] Next, the crystal-grown NiFeY-LDH was sufficiently washed with decarbonized distilled water and then freeze-dried for 12 hours to obtain the final NiFeY-LDH.

[0154] Here, the mole numbers of Y(NO3)3·6H2O were synthesized in three mole numbers, x= 0.033 (Example 2-1), 0.066 (Example 2-2), and 0.099 (Example 2-3), respectively, and the synthesized samples were named NiFe-LDH, NiFeY-LDH-1, NiFeY-LDH-2, and NiFeY-LDH-3.

[0155]

[0156] [Comparative Example 2]

[0157] NiFe-LDH was synthesized in the same manner as in Examples 2-1 to 2-3, except that Y(NO3)3·6H2O was not added as a control.

[0158]

[0159] [Experimental Example 2]

[0160] 7 mg of the materials synthesized according to Examples 2-1 to 2-3 and Comparative Example 2 and 3 mg of conductive carbon (Vulcan-XC72R) were added to 4 ml of tertiary distilled water and 1 ml of isopropanol solution, and then 40 ml of a 5 wt% Nafion solution was added thereto and dispersed for 1 hour using ultrasonic waves. 10 ml of the dispersed solution was applied to a Glassy Carbon (GC) electrode to manufacture a working electrode.

[0161] The oxygen evolution reaction (OER) performance was tested using a three-electrode system equipped with a working electrode manufactured by RRDE-3A Rotating Ring Disk Electrode Apparatus (ALS). The SCE standard was used as the reference electrode, a Pt wire as the counter electrode, and a 1 M KOH solution as the electrolyte.

[0162]

[0163] Figure 10 shows XRD pattern data measured for materials synthesized according to Examples 2-1 to 2-3 and Comparative Example 2.

[0164] Referring to Fig. 10, it can be confirmed that NiFe-LDH and Y-substituted NiFeY-LDH-1, NiFeY-LDH-2, and NiFeY-LDH-3 all have a typical NiFe-LDH crystal structure. In other words, it was confirmed that an impurity-free LDH structure can be realized even if Y is substituted.

[0165] Figure 11 shows a TEM image (a), an elemental mapping image (b), and a STEM image (c) of a material synthesized according to Example 2-2.

[0166] Referring to Fig. 11, NiFeY-LDH-2 was confirmed to have a nanosheet shape with a size of about 800 nm (see a), Y was confirmed to be uniformly distributed throughout NiFeY-LDH-2 (see b), and Y was confirmed to be substituted within the crystal lattice (see c).

[0167] Figure 12 shows XANES data of materials synthesized according to Example 2-2 and Comparative Example 2, respectively.

[0168] Referring to Fig. 12, it was confirmed through Ni K-edge, Fe K-edge, and Y K-edge XANES analysis that the crystal structure of LDH was maintained even after Y substitution, and through comparison with NiO, FeO, Fe2O3, and Y(OH)3 reference materials, nickel, iron, and yttrium in the NiFeY-LDH-2 material were Ni 2+ , Fe 3+ , Y 3+ It was confirmed that it has an oxidation state of .

[0169] Figure 13 shows EXAFS data of materials synthesized according to Example 2-2 and Comparative Example 2, respectively.

[0170] Referring to Fig. 13, Ni K-edge and Fe K-edge EXAFS analyses confirmed that the crystal structure was maintained even after Y substitution. In addition, Y K-edge EXAFS analysis confirmed that the metal-metal FT EXAFS peaks in NiFeY-LDH-2 were found at different positions compared to the Y(OH)3 data, and from this, it can be confirmed that Y(OH)3 phase was not additionally generated in NiFeY-LDH-2, but rather Y was substituted into the NiFe-LDH lattice.

[0171] Figure 14 shows data showing the electrochemical performance test results of catalysts synthesized according to Examples 2-1 to 2-3 and Comparative Example 2. All materials were measured in a 1 M KOH solution, and the scan rate was 5 mV / s.

[0172] As shown in Fig. 14a, the catalysts synthesized according to Examples 2-1 to 2-3 were found to have lower overvoltage and higher current than the catalyst synthesized according to Comparative Example 2, and it can be confirmed from this that the substitution of Y helps improve the electrochemical catalytic performance of LDH.

[0173] As shown in b, c, and d of FIG. 14, the catalysts synthesized according to Examples 2-1 to 2-3 were found to have smaller Tafel slopes, larger ECSA values, and smaller charge transfer resistances compared to the catalyst synthesized according to Comparative Example 2. Among the catalysts synthesized according to Examples 2-1 to 2-3, NiFeY-LDH-2 exhibited the best catalytic performance, which is much better than that of conventional commercialized Ir / C and RuO2 catalyst materials.

[0174] Figure 15 shows the results of in situ Raman analysis during an oxygen evolution reaction conducted to analyze the reaction mechanism of the catalysts synthesized according to Example 2-2 and Comparative Example 2.

[0175] Referring to Fig. 15, both NiFe-LDH and NiFeY-LDH-2 samples were found to maintain the original LDH structure at 1.5 V. However, in the case of the NiFeY-LDH-2 sample, a peak corresponding to NiOOH, an oxygen evolution reaction intermediate, appeared at 1.55 V, whereas in the case of NiFe-LDH, a NiOOH peak appeared at 1.6 V. These results indicate that the NiFeY-LDH-2 sample exhibits superior catalytic performance because the oxygen evolution reaction occurs at a lower voltage.

[0176] In addition, at 1.65 V, a peak corresponding to FeOOH, which does not appear in NiFe-LDH, appeared in NiFeY-LDH-2, indicating that Fe additionally contributes to the oxygen evolution reaction in the NiFeY-LDH-2 sample. That is, when Y element is substituted into NiFe-LDH according to Chemical Formula 2, it can exhibit better catalytic performance for the oxygen evolution reaction due to the relatively rapid formation of NiOOH intermediate during the oxygen evolution reaction and the additional formation of FeOOH intermediate that does not appear in the conventional NiFe-LDH.

[0177]

[0178] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims

1. Porous metal support; Metal nitride nanosheets grown from the above porous metal support; and A composite catalyst structure comprising a layered metal double-layer hydroxide nanosheet arranged on the surface of the metal nitride nanosheet.

2. In paragraph 1, A composite catalyst structure, characterized in that the porous metal support comprises a metal or an alloy thereof capable of forming a conductive or semiconducting metal nitride.

3. In paragraph 1, A composite catalyst structure characterized in that the porous metal support is formed of one or more metals or alloys thereof selected from the group consisting of titanium (Ti), tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), rhenium (Re), aluminum (Al), indium (In), gallium (Ga), and germanium (Ge).

4. In paragraph 2, A composite catalyst structure, characterized in that the porous metal support comprises a metal foam, a metal sponge or a metal lattice structure.

5. In paragraph 1, The above metal nitride nanosheets are grown in a direction perpendicular or inclined to the surface of the porous metal support, A composite catalyst structure, characterized in that the layered metal double-layer hydroxide nanosheet comprises a first LDH nanosheet and a second LDH nanosheet formed on each side of the metal nitride nanosheet.

6. In paragraph 5, In the above metal nitride nanosheet, a plurality of through holes spaced apart from each other are formed, A composite catalyst structure, characterized in that the first LDH nanosheet and the second LDH nanosheet are connected to each other through the through holes.

7. In paragraph 6, A composite catalyst structure, characterized in that each of the above through holes has a size of 1 to 500 nm.

8. In paragraph 6, The above layered metal double layer hydroxide nanosheet is a composite catalyst structure characterized by including a material represented by the following chemical formula 1 or 2: [Chemical Formula 1] [M 1 1-x M 2 x (OH)2][A n- ] x / n ·cH2O [Chemical Formula 2] [M 1 1-(a+b) M 2 a Y 3+ b (OH)2][A n- ] (a+b) / n ·cH2O In the above chemical formulas 1 and 2, M 1 is a first transition metal cation with an oxidation state of +2, and M 2 is a second transition metal cation with an oxidation state of +3, A is an interlayer anion with an oxidation state of -n, and x is "0 <x<1"의 조건을 만족하는 실시이고, a, b는 각각 "0<a+b<1"의 조건을 만족하는 양의 실수이고, n은 1 이상 5 이하의 정수이며, c는 양의 실수이다.

9. In paragraph 8, The first transition metal cation is Ca 2+ , Mg 2+ , Zn 2+ , Ni 2+ , Mn 2+ , Co 2+ , Fe 2+ and Cu 2+ Contains at least one selected from the group consisting of, The second transition metal cation is Fe 3+ , Al 3+ , Cr 3+ , Mn 3+ , Ga 3+ , Co 3+ and Ni 3+ Contains one or more selected from the group consisting of: The above interlayer anion is OH - , NO3 - , PO4 3- , HPO4 2- and H2PO4 - A composite catalyst structure characterized by comprising at least one selected from the group consisting of:

10. In paragraph 9, The above layered metal double layer hydroxide nanosheet comprises a material represented by the following chemical formula 2, The substance of the above chemical formula 2 is a compound in which each of the first transition metal cations has six hydroxide ions (OH - ) formed by coordination of the first octahedral structure, each of the second transition metal cations having six hydroxide ions (OH - ) and the second octahedral structure formed by coordination with the yttrium ion and seven hydroxide ions (OH - ) is characterized by including a decahedral structure formed by coordination.

11. In paragraph 10, A composite catalyst structure characterized in that in the above chemical formula 2, a+b is 0.2 or more and 0.5 or less, and the molar ratio (a / b) of the second transition metal cation to the yttrium ion is 20 or more and 150 or less.

12. A first step of forming a metal oxide nanosheet on the surface of a porous metal support using a hydrothermal synthesis method; A second step of converting the above metal oxide nanosheet into a metal nitride nanosheet; A method for producing a composite catalyst structure, comprising a third step of forming a layered metal double-layer hydroxide nanosheet on the surface of the metal nitride nanosheet using a hydrothermal synthesis method.

13. In paragraph 12, A method for manufacturing a composite catalyst structure, characterized in that the second step is performed by heat-treating the metal oxide nanosheet in a nitrogen-containing atmosphere.

14. In paragraph 13, A method for producing a composite catalyst structure, characterized in that the second step is performed by heat-treating the metal oxide nanosheet at a temperature of about 600 to 1000°C for about 0.5 to 2 hours in an ammonia gas atmosphere.

15. In paragraph 13, The third step is performed by immersing the porous metal support on which the metal nitride nanosheets are formed in a mixed precursor solution for a layered metal double layer hydroxide and heating the mixed precursor solution at 120 to 180° C. for 20 to 28 hours in an inert atmosphere. A method for manufacturing a composite catalyst structure, characterized in that the layered metal double-layer hydroxide nanosheets are formed on both sides of the metal nitride nanosheets during the third step.

16. In paragraph 15, During the second step, a plurality of through holes having a size of about 1 to 500 nm are formed in the metal nitride nanosheet, A method for manufacturing a composite catalyst structure, characterized in that the layered metal double-layer hydroxide nanosheets are formed on both sides of the metal nitride nanosheets so as to be connected to each other through the through-holes during the third step.

17. In a water electrolysis device including an ion exchange membrane and a first electrode and a second electrode facing each other with the ion exchange membrane interposed therebetween, A water electrolysis device characterized in that the first electrode, where an oxygen evolution reaction (OER) occurs, comprises a composite catalyst structure comprising: a porous metal support; metal nitride nanosheets grown from the porous metal support; and layered metal double-layer hydroxide nanosheets arranged on the surface of the metal nitride nanosheets.

18. In paragraph 17, A water electrolysis device characterized in that a path for diffusing gas is formed inside the porous metal support.

19. In a metal-air secondary battery including an air electrode and a metal electrode spaced apart from each other and an electrolyte disposed between the air electrode and the metal electrode, A metal-air secondary battery characterized in that the air electrode comprises a composite catalyst structure comprising: a porous metal support; metal nitride nanosheets grown from the porous metal support; and layered metal double-layer hydroxide nanosheets arranged on the surface of the metal nitride nanosheets.

20. In paragraph 19, A metal-air secondary battery, characterized in that the metal electrode comprises any one metal selected from the group consisting of zinc (Zn), lithium (Li), and aluminum (Al).

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