Layered double hydroxide complex and method for preparing thereof

Abstract

The present invention relates to a layered double hydroxide composite and a method for manufacturing the same, characterized by comprising a hollow mesoporous metal nanostructure; and a layered double hydroxide formed on the surface of the hollow mesoporous metal nanostructure.

Description

Technology Field

[0001] The present invention relates to a layered double hydroxide composite and a method for manufacturing the same. Background Technology

[0002] Recently, as the increasing use of fossil fuels is a major cause of environmental pollution leading to global warming and abnormal climate conditions, research on the use of hydrogen energy as an alternative energy source is actively underway.

[0003] Hydrogen can be used as fuel for electrochemical eco-friendly energy production facilities such as fuel cells, and has the advantage of producing only water and heat as reaction byproducts.

[0004] Although methods for generating high-purity hydrogen through the electrolysis of water have been studied, the oxygen evolution reaction (OER) has a problem in that the reaction rate is slow because two water molecules give up four electrons to become one oxygen molecule, and a high overpotential is required to increase the reaction rate. To solve this problem, the use of a catalyst that promotes the efficiency of water electrolysis is required.

[0005] Meanwhile, layered double hydroxides (LDHs) are classified as excellent catalysts due to their relatively large surface area and anion exchange capacity. However, layered double hydroxides have the disadvantage of low electrical conductivity and weak structural stability due to the anions and water molecules present between the layers.

[0006] To overcome these drawbacks, research has been conducted to improve electrical conductivity through the hierarchical growth of layered double hydroxide structures using precious metals with excellent electrical conductivity. For example, the direct growth of layered double hydroxides on transition metal-based substrates, which are widely used as electrode materials, was achieved through a galvanic etching process. Several studies have reported that layered double hydroxide structures grown on metal substrates with a zero oxidation state, such as nickel or iron substrates, are highly effective as catalysts in water electrolysis.

[0007] However, the formation of layered double hydroxides on a substrate of such a metal electrode has the disadvantage that the reaction time is long and the active site of the electrode catalytic reaction is limited to the cross-sectional area of ​​the substrate.

[0008] To address these disadvantages, Patent Document 1 discloses a layered nanohybrid comprising a superlattice structure in which transition metal dichalcogenide nanosheets having opposite surface charges and layered double hydroxide nanosheets are alternately stacked, a method for manufacturing said layered nanohybrid, and an electrocatalyst comprising said layered nanohybrid. Prior art literature

[0009] Korean Registered Patent 10-2001443 The problem to be solved

[0010] The present invention aims to provide a layered double hydroxide composite having high stability and durability during an oxygen evolution reaction and excellent catalytic activity, and a method for manufacturing the same. means of solving the problem

[0011] One embodiment of the present invention for achieving the above-described purpose relates to a layered double hydroxide composite comprising: a hollow metal mesosphere; and a layered double hydroxide formed on the surface of the hollow metal mesosphere.

[0012] The metal of the hollow mesoporous metal nanostructure above may be any one selected from the group consisting of Ni, Cu, Mg, Fe, and Co.

[0013] The above layered double hydroxide may be represented by the following chemical formula 1.

[0014] [Chemical Formula 1]

[0015] [M 2+ (1-x) M' 2+ x (OH - )2][(A n- ) x / n ·yH2O] x- ;

[0016] [In the above formula,

[0017] M 2+ Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It is one type selected from among,

[0018] M' 2+ Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It is one type selected from among,

[0019] The above M 2+ and M' 2+ They are different species, and

[0020] 0 < x < 1, and

[0021] A n- CO 3- , OH - , F - , Cl - , Br - , I - , SO4 2- , NO3 - and PO43- It is one type selected from among,

[0022] n is an integer from 1 to 3, and

[0023] y is a number from 0.1 to 15.

[0024] The above M 2+ is Ni 2+ and, the above M' 2+ is Fe 2+ It could be.

[0025] The above hollow mesoporous metal nanostructure may be acid-treated with acid.

[0026] The above acid may be HCl.

[0027] The above hollow mesoporous metal nanostructure may be in the form of a nanochain.

[0028] Another embodiment of the present invention relates to a method for preparing a layered double hydroxide composite, comprising the steps of: synthesizing a hollow mesoporous metal nanostructure; and forming a layered double hydroxide on the surface of the hollow mesoporous metal nanostructure.

[0029] The metal of the hollow mesoporous metal nanostructure above may be any one selected from the group consisting of Ni, Cu, Mg, Fe, and Co.

[0030] The above layered double hydroxide may be represented by the following chemical formula 1.

[0031] [Chemical Formula 1]

[0032] [M 2+ (1-x) M' 2+ x (OH - )2][(A n- ) x / n ·yH2O] x- ;

[0033] [In the above formula,

[0034] M 2+ Zn 2+ , Mg2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It is one type selected from among,

[0035] M' 2+ Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It is one type selected from among,

[0036] The above M 2+ and M' 2+ They are different species, and

[0037] 0 < x < 1, and

[0038] A n- CO 3- , OH - , F - , Cl - , Br - , I - , SO4 2- , NO3 - and PO4 3- It is one type selected from among,

[0039] n is an integer from 1 to 3, and

[0040] y is a number from 0.1 to 15.

[0041] The above M 2+ is Ni 2+ and, the above M' 2+ is Fe 2+ It could be.

[0042] The method for manufacturing the above-described layered double hydroxide composite may further include the step of acid-treating the hollow mesoporous metal nanostructure synthesized from the step of synthesizing the hollow mesoporous metal nanostructure with an acid.

[0043] The above acid may be HCl.

[0044] The above hollow mesoporous metal nanostructure may be in the form of a nanochain. Effects of the invention

[0045] The layered double hydroxide composite of the present invention has a low overpotential and a Tafel gradient as an electrolytic catalyst, and exhibits excellent activity in the oxygen evolution reaction. In addition, it has high stability and durability during the oxygen evolution reaction, and exhibits excellent catalytic activity due to a wide active site and reduced resistance to charge transfer.

[0046] In addition, according to the method for manufacturing a layered double hydroxide composite of the present invention, the growth of the layered double hydroxide can be promoted by removing the oxide layer on the hollow mesoporous metal nanostructure, and since the hollow mesoporous metal nanostructure can be synthesized by a simple method, the composite can be manufactured efficiently and the cost can be reduced. Brief explanation of the drawing

[0047] Figure 1 is a schematic diagram showing the manufacturing method of an example. FIG. 2 is a graph showing the XRD patterns of the products prepared in Comparative Example 1 in case (a), Comparative Example 2 in case (b), and Example in case (c), respectively. Figure 3 is a Scanning Electron Microscope (SEM) image of hollow mesoporous nickel nanostructures prepared in Comparative Example 1 in case (a) and Example in case (b), respectively. Figure 4 shows the XPS (X-ray Photoelectron Spectroscopy) spectra of hollow mesoporous nickel nanostructures prepared in Comparative Example 1 for cases (a) and (c), and Examples for cases (b) and (d). Figure 5 is a Scanning Electron Microscope (SEM) image of the product prepared in Comparative Example 2 in case (a) and Example in case (b), respectively, and Transmission Electron Microscope (TEM) low-resolution and high-resolution images of the product prepared in Example in cases (c) and (d), respectively. Figure 6 is an SEM image comparing the layered double hydroxide growth of Experimental Example 4, with 0 M HCl for (a) and (b), 0.004 M HCl for (c) and (d), 0.04 M HCl for (e) and (f), 0.4 M HCl for (g) and (h), and 4 M HCl for (i) and (j). Figure 7 is an SEM image comparing the layered double hydroxide growth of Experimental Example 5, with NaCl 0M for (a) and (b), NaCl 0.005M for (c) and (d), NaCl 0.05M for (e) and (f), and NaCl 0.5M for (g) and (h). Figure 8 shows the XPS spectra of the composites prepared in Comparative Example 2 for (a), (c), and (e), and in Examples for (b), (d), and (f). Figure 9 shows a current density of 10 mA cm⁻¹ -2 This is a graph comparing the initial and after 10,000 CV scan overpotentials measured using the catalysts of Example and Comparative Example 4. Figure 10 is a graph showing the O2 generated at the RRDE-ring electrode under an applied voltage of 1.5 V (vs. RHE) when the catalysts of Example and Comparative Example 4 are used, expressed as an electrocatalytic RRDE-ring voltammogram. Figure 11 is a graph of Electrochemical Impedance Spectroscopy (EIS) analysis for the catalysts of Examples and Comparative Examples 1 to 4. Specific details for implementing the invention

[0048] Before describing the preferred embodiments of the present invention in detail below, it should be noted that the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0049] The present invention will be described in detail with reference to the embodiments and drawings. These embodiments are presented merely as examples to explain the invention more specifically, and it will be obvious to those skilled in the art that the scope of the invention is not limited by these embodiments.

[0050] Hereinafter, embodiments of the present invention are examined. However, the scope of the present invention is not limited to the following preferred embodiments, and those skilled in the art may implement various modified forms of the contents described herein within the scope of the present invention.

[0051] [Complex]

[0052] The layered double hydroxide composite of the present invention comprises a hollow metal mesosphere and a layered double hydroxide formed on the surface of the hollow metal mesosphere.

[0053] The metal of the hollow mesoporous metal nanostructure above is selected from the group consisting of Ni, Cu, Mg, Fe, and Co, and preferably may be Ni.

[0054] That is, the hollow mesoporous metal nanostructure may include hollow mesoporous nickel nanostructures, hollow mesoporous copper nanostructures, hollow mesoporous magnesium nanostructures, hollow mesoporous iron nanostructures, or hollow mesoporous cobalt nanostructures, each comprising Ni 2+ , Cu2+ , Mg 2+ , Fe 2+ or Co 2+ This applies to cases where it is formed from.

[0055] The above hollow mesoporous metal nanostructures may be acid-treated with acid. When using acid-treated hollow mesoporous metal nanostructures, layered double hydroxide composites can be synthesized in a cost-effective and simple manner, and layered double hydroxides can be efficiently formed due to the large surface area.

[0056] In addition, the hollow mesoporous metal nanostructure has a nanostructure form, more specifically, a nanochain form.

[0057] The above layered double hydroxide may include that represented by the following chemical formula 1.

[0058] [Chemical Formula 1]

[0059] [M 2+ (1-x) M' 2+ x (OH - )2][(A n- ) x / n ·yH2O] x- ;

[0060] In the above formula,

[0061] M 2+ As a divalent metal cation, Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It may be one type selected from among them.

[0062] M' 2+ As a divalent metal cation, Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It may be one type selected from among them.

[0063] The above M 2+ and M' 2+ are different species, and preferably, the above M 2+ is Ni 2+ and, the above M' 2+ is Fe 2+ It could be.

[0064] 0 < x < 1.

[0065] A n- is an anion, and n is the charge of the phase of the anion A, CO 3- , OH - , F - , Cl - , Br - , I - , SO4 2- , NO3 - and PO4 3- It may be one type selected from among, and OH - It is desirable that it is.

[0066] n is an integer from 1 to 3, and

[0067] y is a number from 0.1 to 15.

[0068] The layered double hydroxide can be formed by growing on the surface of the hollow mesoporous metal nanostructure. The growth of such layered double hydroxide may include a three-dimensional hierarchical growth form.

[0069] Since the above layered double hydroxide may be affected by the dissolution of oxides formed on the surface of the hollow mesoporous metal nanostructure during the synthesis process of the hollow mesoporous metal nanostructure (for example, in the case of a hollow mesoporous nickel nanostructure, it may be nickel oxide species such as NiO, Ni2O, Ni(OH)2, etc.), the above layered double hydroxide can be synthesized and formed more stably and effectively by removing such oxide layers through an acid treatment step with an acid described below and inducing a change in the charge state of the surface of the hollow mesoporous metal nanostructure.

[0070] [Method for manufacturing a composite]

[0071] Another embodiment of the present invention relates to a method for manufacturing a layered double hydroxide composite, comprising the steps of: synthesizing a hollow mesoporous metal nanostructure; and forming a layered double hydroxide on the surface of the hollow mesoporous metal nanostructure.

[0072] The metal of the hollow mesoporous metal nanostructure above is selected from the group consisting of Ni, Cu, Mg, Fe, and Co, and preferably may be Ni.

[0073] That is, the hollow mesoporous metal nanostructure may include hollow mesoporous nickel nanostructures, hollow mesoporous copper nanostructures, hollow mesoporous magnesium nanostructures, hollow mesoporous iron nanostructures, or hollow mesoporous cobalt nanostructures, each comprising Ni 2+ , Cu 2+ , Mg 2+ , Fe 2+ or Co 2+ This applies to cases where it is formed from.

[0074] The step of synthesizing the hollow mesoporous metal nanostructures described above may utilize a method using a template, such as silica or polymer beads, a seed-mediated method, or a template-free reflux method. When synthesizing hollow mesoporous metal nanostructures using a template method or a seed-mediated method, there are disadvantages such as complex processes and high time consumption, including substrate preparation and removal. Therefore, from the perspective of cost efficiency and large-scale synthesis, the template-free reflux method is more preferable as it is simpler in process and applicable to various metals.

[0075] FIG. 1 shows that the hollow mesoporous metal nanostructure is Ni 2+A schematic diagram of a method for manufacturing hollow mesoporous nickel nanostructures formed from is shown. Specifically, as shown in reaction scheme (1) below, the synthesis process begins with the formation of a complex between Ni(II) and hydrazine, followed by the formation of individual hollow mesoporous metal nanostructures. The formation of hollow mesoporous nickel nanostructures occurs through the process in reaction scheme (2) below, through which the gas generated during the reaction surrounds the hollow mesoporous nickel nanostructures outside the bubbles. At this time, the magnetism of Ni can promote the continuous formation of individual mesoporous metal nanostructures and their assembly into nanostructures.

[0076] Ni 2+ + 3N2H4→ [Ni(N2H4)3] 2+ (1)

[0077] [Ni(N2H4)3] 2+ + N2H4→ Ni↓ + 4NH3↑ + N2↑ + H2↑+ 2H + (2)

[0078] The above hollow mesoporous metal nanostructure has a nanostructure form, more specifically, a nanochain form.

[0079] The above-described synthesized hollow mesoporous metal nanostructure may further include a step of acid treatment with acid.

[0080] In the step of synthesizing the hollow mesoporous metal nanostructures described above, an oxide (for example, in the case of hollow mesoporous nickel nanostructures, it may be a nickel oxide species such as NiO, Ni2O, Ni(OH)2, etc.) may be formed on the surface of the hollow mesoporous metal nanostructures, and The above These oxides can be removed through an acid treatment step using acid.

[0081] Specifically, the growth of the layered double hydroxide described below may be affected by the dissolution of oxides formed on the surface of the hollow mesoporous metal nanostructure during the synthesis process of the hollow mesoporous metal nanostructure (for example, in the case of hollow mesoporous nickel nanostructures, these may be nickel oxide species such as NiO, Ni2O, Ni(OH)2, etc.). These oxides can be removed during the acid treatment process, and specifically, the process of removing nickel oxide species formed on the surface of the hollow mesoporous nickel nanostructure can be verified through the following reaction schemes (3) and (4). Removing the oxide layer from the surface of the hollow mesoporous metal nanostructure facilitates ionization according to the reaction mechanism of chlorine corrosion, thereby promoting the growth of the layered double hydroxide. The formation of the layered double hydroxide is obtained only when the oxide layer on the surface of the hollow mesoporous metal nanostructure is removed.

[0082] Ni(s)-NiO + 2H + → Ni(s) + Ni 2+ + H2O (3)

[0083] Ni(s)-NiO2+ 4H + + 2e - → Ni(s) + Ni 2+ + 2H2O (4)

[0084] In this way, when the above oxides are removed, the spontaneous growth of layered double hydroxide is promoted.

[0085] The above acid may be one selected from HCl, HNO3, H2SO4, HBr, and HI, and preferably may be HCl.

[0086] When the above acid is HCl, the concentration of HCl may be 3.0 M to 5.0 M, and preferably 3.5 M to 4.5 M. By satisfying the above concentration of HCl, the growth of layered double hydroxide is promoted.

[0087] When the above acid is HCl, the acid treatment time may be 5 to 20 seconds, and preferably 9 to 11 seconds. If the acid treatment time exceeds 20 seconds, there is a concern that the structure of the matrix may collapse and the formation of layered double hydroxide may not be sufficient.

[0088] The step of forming a layered double hydroxide on the surface of the hollow mesoporous metal nanostructure can be efficiently synthesized and formed if performed after the step of acid treatment with the acid.

[0089] Specifically, the process of synthesizing and forming layered double hydroxide on the surface of hollow mesoporous nickel nanostructures is as shown in the following reaction scheme (5), where the presence of Fe(II) and acid-treated hollow mesoporous nickel nanostructures promotes the spontaneous growth of layered double hydroxide.

[0090] Ni(s) + Fe 2+ + xOH - → NiFe(OH) x (5)

[0091] Furthermore, the growth of the layered double hydroxide described later may be influenced by the concentration of the electrolyte. Specifically, the thermodynamic equilibrium of the subsequent reaction depending on the degree of oxide layer removal is Cl2(aq) / 2Cl - It can be affected by the presence of (+1.396 V vs. RHE), which promotes the formation of layered double hydroxides.

[0092] The above electrolyte may contain chloride ions, and preferably may be NaCl.

[0093] When the above electrolyte is NaCl, the concentration of NaCl may be 0.3M to 0.7M, and preferably 0.4M to 0.6M. By satisfying the above concentration of NaCl, the growth of layered double hydroxide is promoted.

[0094] The above layered double hydroxide may include that represented by the following chemical formula 1.

[0095] [Chemical Formula 1]

[0096] [M 2+ (1-x) M' 2+ x (OH - )2][(A n- ) x / n ·yH2O] x- ;

[0097] In the above formula,

[0098] M 2+ As a divalent metal cation, Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It may be one type selected from among them.

[0099] M' 2+ As a divalent metal cation, Zn 2+ , Mg 2+ , Co 2+ , Cu 2+ , Ni 2+ and Fe 2+ It may be one type selected from among them.

[0100] The above M 2+ and M' 2+ are different species, and preferably, the above M 2+ is Ni 2+ and, the above M' 2+ is Fe 2+ It could be.

[0101] 0 < x < 1.

[0102] A n- is an anion, and n is the charge of the phase of the anion A, CO 3- , OH - , F - , Cl - , Br - , I - , SO4 2- , NO3- and PO4 3- It may be one type selected from among, and OH - It is desirable that it is.

[0103] n is an integer from 1 to 3, and

[0104] y is a number from 0.1 to 15.

[0105] In addition, in the process of forming a layered double hydroxide on the surface of the hollow mesoporous metal nanostructure using the layered double hydroxide represented by Chemical Formula 1, M during the reaction process 2+ -> M 3+ + e - or M' 2+ -> M' 3+ + e - Oxidation of the furnace may occur, which can increase the rate of formation of layered double hydroxide.

[0106] The layered double hydroxide composite of the present invention can be applied as an electrochemical catalyst in the oxygen evolution reaction of water electrolysis.

[0107] The present application will be described in more detail below through embodiments according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the embodiments presented below.

[0108] [Example]

[0109] (Synthesis of hollow mesoporous nickel nanostructures)

[0110] In a 3-neck flask, 1.2g NiCl2·6H2O and 1.671g PVP were dissolved in 100mL of ethylene glycol, then 5mL of 5.0M NaOH and hydrazine were added and stirred for 10 minutes. Afterward, a reflux condenser was connected and heated to 197°C for 4 hours, then washed repeatedly with ethanol, centrifuged, and freeze-dried to obtain hollow mesoporous nickel nanostructures (hNi).

[0111] (Synthesis of acid-treated hollow mesoporous nickel nanostructures)

[0112] Subsequently, 20 mg of the synthesized hollow mesoporous nickel nanostructures were treated with a 4.0 M HCl solution for 10 seconds. After acid treatment, the hollow mesoporous nickel nanostructures (hNiH) were obtained by repeatedly washing with ethanol until the pH became neutral.

[0113] (hNiH@NiFe-OH synthesis)

[0114] 20 mg of hNiH, 10 mL of NaCl (1.0 M), 3 mL of FeCl2·4H2O (20 mM), and 7 mL of distilled water were stirred at room temperature for 6 hours, then washed with distilled water, centrifuged, and freeze-dried to obtain the final product hNiH@NiFe-OH complex.

[0115] (XRD pattern analysis for structural information analysis)

[0116] Figure 2 shows the results of analyzing the XRD pattern of the fabricated composite. Referring to Figure 2(c), distinct peaks were observed at 44.5°, 51.8°, and 76.3°, which correspond to the (111) plane, (200) plane, and (220) plane of the hollow mesoporous nickel nanostructure, respectively, and represent a face-centered cubic (fcc) structure (#00-004-0850).

[0117] In addition, weak intensity was observed only at 21.7°, 34.2°, 39.3°, 46.8°, 60.3°, and 61.2°, corresponding to the planes (006), (012), (015), (018), (110), and (113), respectively, which was consistent with a typical layered double hydroxide (#00-049-0188).

[0118] [Comparative Example 1]

[0119] (Synthesis of hollow mesoporous nickel nanostructures)

[0120] Hollow mesoporous nickel nanostructures (hNi) were obtained in the same manner as in the example, except that no acid treatment was performed.

[0121] (XRD pattern analysis for structural information analysis)

[0122] Figure 2 shows the results of analyzing the XRD pattern of the fabricated hollow mesoporous nickel nanostructures. Referring to Figure 2(a), distinct peaks were observed at 44.5°, 51.8°, and 76.3°, which correspond to the (111) plane, (200) plane, and (220) plane of the hollow mesoporous nickel nanostructures, respectively, and represent a face-centered cubic (fcc) structure (#00-004-0850).

[0123] [Comparative Example 2]

[0124] (hNi@NiFe synthesis)

[0125] Layered double hydroxides were grown using hollow mesoporous nickel nanostructures (hNi) prepared in Comparative Example 1. Specifically, 20 mg of hNi, 10 mL of NaCl (1.0 M), 3 mL of FeCl2·4H2O (20 mM), and 7 mL of distilled water were stirred at room temperature for 6 hours, then washed with distilled water, centrifuged, and freeze-dried to obtain the final product hNi@NiFe composite.

[0126] (XRD pattern analysis for structural information analysis)

[0127] The results of analyzing the XRD pattern of the product are shown in FIG. 2. Referring to FIG. 2(b), distinct peaks were observed at 44.5°, 51.8°, and 76.3°, which correspond to the (111) plane, (200) plane, and (220) plane of the hollow mesoporous nickel nanostructure, respectively, and represent a face-centered cubic (fcc) structure (#00-004-0850).

[0128] In addition, weak signals were observed at 26.7°, 35.2°, 39.2°, and 56.0°, which closely match the pattern obtained from akaganeite (#00-042-1315).

[0129] [Comparative Example 3]

[0130] (FeN synthesis)

[0131] In a three-necked flask, 1.2g FeCl2·4H2O and 1.671g PVP were dissolved in 100mL of ethylene glycol, then 5mL of 5.0M NaOH and hydrazine were added and stirred for 10 minutes. Afterward, a reflux condenser was connected and heated to 197°C for 4 hours, followed by repeated washing with ethanol, centrifugation, and freeze-drying to obtain FeN (iron nanowires).

[0132] [Comparative Example 4]

[0133] Instead of the synthesized hNiH@NiFe-OH composite of the example, a commercial Ir / C catalyst (Premetek) embedded in Vulcan XC-72 at 20 wt% was used.

[0134] [Experimental Example 1 - Comparison of SEM Images of Hollow Mesoporous Nickel Nanostructures with and without Acid Treatment]

[0135] SEM images were compared for the acid-treated hollow mesoporous nickel nanostructure of Example 1 and the acid-untreated hollow mesoporous nickel nanostructure of Comparative Example 1.

[0136] Referring to FIG. 3, the diameter of the hollow mesoporous nickel nanostructure nanochains of the acid-treated example is 100 to 500 nm, and the diameter is reduced by about 40 nm compared to the hollow mesoporous nickel nanostructure of Comparative Example 1 that was not acid-treated. It can be seen that this reduction is due to the etching of the outer surface of the catalyst. In particular, the length of the acid-treated hollow mesoporous nickel nanostructure of the example remained the same as the length of the original hollow mesoporous nickel nanostructure sample before acid treatment.

[0137] [Experimental Example 2 - XPS Analysis for Confirmation of Oxide Layer Removal on Surface of Hollow Mesoporous Nickel Nanostructures]

[0138] To evaluate whether the oxide layer generated during the acid treatment process was removed, XPS analysis was performed on the acid-treated hollow mesoporous nickel nanostructures of the example and the acid-untreated hollow mesoporous nickel nanostructures of Comparative Example 1.

[0139] Referring to Fig. 4, the main O 1s signals of the Example and Comparative Example 1, respectively, maintained a constant binding energy position of 531.3 eV, whereas the MO peak at 529.2 eV corresponding to the oxidized metal was significantly reduced in the Example compared to Comparative Example 1.

[0140] The binding energies of Ni 2p1 / 2 and Ni 2p3 / 2 for Example and Comparative Example 1 were observed at 873.2 eV and 855.6 eV, respectively. In the example, the intensity of the peak at 853.6 eV attributed to NiO was significantly reduced.

[0141] From the O 1s and Ni 2p characteristics described above, it was found that in the case of the hollow mesoporous nickel nanostructure of the example, the oxide layer on the surface of the hollow mesoporous nickel nanostructure was significantly removed through the acid treatment process.

[0142] [Experimental Example 3 - Comparison of Layered Double Hydroxide Growth with and without Acid Treatment]

[0143] For the example and comparative example 2, SEM and TEM images showing layered double hydroxide growth depending on acid treatment were compared.

[0144] Referring to Fig. 5, Comparative Example 2 showed a thickness increase of about 1.6 times compared to the hollow mesoporous nickel nanostructure structure, but grew into a nonporous solid plane on the surface of the hollow mesoporous nickel nanostructure. This indicates that the nucleation process on the oxide-covered surface can hinder the formation of layered double hydroxides.

[0145] On the other hand, in the case of the example, typical 3D layered growth characteristics of the layered double hydroxide structure were exhibited, which indicates that a clean metal surface without an oxide film exhibits high surface energy, thereby promoting effective nucleation and growth of the layered double hydroxide nanostructure.

[0146] [Experimental Example 4 - Comparison of Layered Double Hydroxide Growth According to HCl Concentration]

[0147] For the acid-untreated hollow mesoporous nickel nanostructures of the example, acid treatment was performed using HCl, and SEM images showing the growth of layered double hydroxides according to HCl concentration were compared. In the step of forming layered double hydroxides, the concentrations of NaCl and FeCl2 were 0.5 M and 3 mM, respectively.

[0148] Referring to Figure 6, when the HCl concentration was less than 4.0 M, the growth of the layered double hydroxide did not proceed well, whereas when the HCl concentration was 4.0 M, the typical 3D layered growth characteristics of the layered double hydroxide structure were exhibited.

[0149] [Experimental Example 5 - Comparison of Layered Double Hydroxide Growth According to NaCl Concentration]

[0150] For the acid-treated hollow mesoporous nickel nanostructures of the example, SEM images showing layered double hydroxide growth according to NaCl concentration were compared. In the step of forming layered double hydroxide, the concentration of FeCl2 was 3 mM.

[0151] Referring to Figure 7, when the NaCl concentration was less than 0.5M, the growth of the layered double hydroxide did not proceed well, whereas when the NaCl concentration was 0.5M, the typical 3D layered growth characteristics of the layered double hydroxide structure were exhibited.

[0152] From the above experimental results, it was found that the formation of layered double hydroxide is affected by the concentration of NaCl.

[0153] [Experimental Example 6 - XPS Analysis for Evaluation of OER Catalyst Activity According to Change in Charge Density of NiFe Due to Oxide Layer Removal]

[0154] To investigate the effect of changes in local charge density of NiFe after oxide layer removal on OER catalytic activity, XPS spectra of the Fe 2p, Ni 2p, and O 1s regions for the hNiH@NiFe-OH composite of Example 1 and the hNi@NiFe composite of Comparative Example 2 were compared.

[0155] Referring to FIG. 8, the peaks at 712.5 eV and 726.1 eV in the Fe 2p region correspond to Fe 2p3 / 2 and Fe 2p1 / 2, respectively, indicating the presence of Fe(III) in both Example and Comparative Example 2. Simulation results Fe 2+ Although observed adjacent to the main peak, the satellite peaks at 717.5 eV and 732.2 eV clearly showed the dominance of Fe(III) in both samples. Compared to the satellite peak of Comparative Example 2, the peak of the Example is relatively broad, and the pre-peak observed at 706.3 eV also showed high intensity, which is expected to be the result of etching during the acid treatment process.

[0156] The Ni 2p spectrum showed peaks at 855.1 eV and 872.8 eV for Ni 2p3 / 2 and Ni 2p1 / 2, respectively, indicating the dominant presence of Ni(II) in both Example and Comparative Example 2. Peaks at 856.4 eV and 874.1 eV were accompanied by two shake-up satellites, indicating the coexistence of Ni(II) and Ni(III).

[0157] On the other hand, the peak at 529.3 eV, corresponding to the O 1s of the metal oxide, was significantly reduced in the example compared to Comparative Example 2, clearly indicating a change in the oxidation state of the composite surface.

[0158] From the characteristics of Fe 2p, Ni 2p, and O 1s as described above, it was found that in the case of the hNiH@NiFe-OH composite of the example, the charge density on the surface of the hollow mesoporous nickel nanostructure changed due to the removal of the oxide layer, thereby promoting the formation of layered double hydroxides and exhibiting excellent OER catalytic activity.

[0159] [Experimental Example 7 - Evaluation of Electrochemical Performance of the Complex]

[0160] (Evaluation Method)

[0161] All electrochemical measurements were performed using graphite rods, and Hg / HgO (NaOH, 1.0 M) electrodes were used as the counter and reference electrodes, respectively. The glass electrodes used were polished with 0.05 mm aluminum powder and a micro-cloth pad (ALLIED), and then ultrasonically treated in distilled water for 3 minutes to remove residual aluminum. All potentials were converted to Reversible Hydrogen Electrode (RHE) units using the Nernst equation. For Rotating Ring-Disk Electrode (RRDE) measurements, RRDE-3A (ALS Inc.) and CHI705E (CH Instruments) biopotentiostats were used. For OER measurements, 15 μL of catalyst suspension (50% Vulcan XC-72) (2 mg / mL) was used. -1 ) was placed on the working electrode. RDE / RRDE measurements were recorded at various electrode rotation speeds of 400, 900, 1600, 2500, and 3600 rpm. Electrochemical results were normalized by the geometric surface area of ​​the working electrode.

[0162] (result)

[0163] The overpotential (η), Tafel slope value, and catalytic activity regarding the electrochemical OER performance of Examples and Comparative Examples 1 to 4 were measured. 10 mA cm⁻¹ -2 Linear sweep voltammetry (LSV) was used to compare the overpotential (η). The results are shown in Table 1.

[0164] As can be seen from Table 1, the hNiH@NiFe-OH composite, such as the example, exhibits excellent catalytic activity by displaying low overpotential and low Tafel slope values. Meanwhile, Comparative Examples 1 and 3, which are single metal catalysts, showed relatively low catalytic activity compared to other catalysts.

[0165] η(mV) (at 10 mA cm -2 ) Table slope(mV dec -1 ) j (mA cm -2 (at η=400mV) Examples 288 37 72.9 Comparative Example 1 448 96 3.12 Comparative Example 2 357 61 25.4 Comparative Example 3 439 37 2.58 Comparative Example 4 340 56 56

[0166] In addition, as can be seen in Fig. 9, the hNiH@NiFe-OH composite of the example exhibits high stability and durability along with excellent catalytic activity during the OER process. 10 mA cm⁻¹ -2 The △η after 10,000 cycles of CV scan in the example was 29 mV, showing a relatively small change compared to 63 mV in Comparative Example 4. These results indicate that the hNiH@NiFe-OH composite of the example has high catalytic activity and excellent stability in OER even after long-term cycling.

[0167] In addition, as can be seen in Fig. 10, O2 generated from the RRDE-disk electrode was collected from the RRDE-ring electrodes of the Example and Comparative Example 4 under an applied voltage of 1.5 V (vs. RHE) to evaluate the OER efficiency. To ensure the reliability of the measurement, this evaluation process was repeated 10 times. The measured oxygen reduction reaction (ORR) current was higher in the Example than in Comparative Example 4, consistent with the trends observed in the overpotential and Tafel slope. As a result of calculating the collection efficiency of each catalyst converting from OER to ORR, the Example and Comparative Example 4 showed collection efficiencies of 55.2% and 51.3%, respectively. These results provide further evidence of the superior catalytic activity and stability of the Example compared to Comparative Example 4.

[0168] [Experimental Example 8 - EIS Analysis for Determination of Charge Transfer Rate]

[0169] EIS analysis was performed to determine the different charge transfer rates of each catalyst during OER at η = 320 mV. Referring to Fig. 11, the relatively higher charge transfer resistance (R) in Comparative Examples 1 to 3 ct ) was observed, indicating that the catalyst's potential barrier and reaction kinetics increased.

[0170] Meanwhile, the example provides a lower R along with reduced resistance to charge transfer. ct It represented a curve.

[0171] Therefore, it can be confirmed that the hNiH@NiFe-OH composite of the example exhibits enhanced OER activity due to reduced resistance to charge transfer.

[0172] [Experimental Example 9 - Comparison of Double-Layer Capacitance and Electrochemical Surface Area]

[0173] Double-layer capacitance (C) of Examples and Comparative Examples 1 and 2 dl The electrochemical surface area (ECSA), including the BET specific surface area, was evaluated. The results are shown in Table 2.

[0174] As can be seen from Table 2, the composite of the example has the highest double-layer capacitance (3.85 mF cm⁻¹) compared to Comparative Examples 1 and 2. -2 ) and BET specific surface area (47.0 m² 2 g -1 It represented ).

[0175] Therefore, it can be seen that the composite of the example enhances OER activity by providing a high density of active sites and a specific surface area for the adsorption and desorption of water molecules and gases.

[0176] C dl (mF cm -2 ) BET surface area(m 2 g -1 ) Examples 3.85 47.0 Comparative Example 1 2.34 5.1 Comparative Example 2 3.08 46.5

Claims

Claim 1 A layered double hydroxide composite comprising a hollow mesoporous metal nanostructure; and a layered double hydroxide formed on the surface of the hollow mesoporous metal nanostructure, wherein the metal of the hollow mesoporous metal nanostructure is Ni, and the layered double hydroxide is represented by the following chemical formula 1, [Chemical Formula 1][M 2+ (1-x) M' 2+ x (OH - )2][(A n- ) x / n ·yH2O] x- ;[In the above formula, M 2+ 은 Ni 2+ And, M' 2+ Silver Fe 2+ and, 0 < x < 1 and, A n- CO 3- , OH - , F - , Cl - , Br - , I - , SO4 2- , NO3 - and PO4 3- [One type selected from among, n is an integer from 1 to 3, and y is a number from 0.1 to 15.] The above hollow mesoporous metal nanostructure is a layered double hydroxide composite characterized by being acid-treated with HCl. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 In claim 1, the hollow mesoporous metal nanostructure is a layered double hydroxide composite in the form of a nanochain. Claim 8 A method for preparing a layered double hydroxide composite comprising the steps of: synthesizing a hollow mesoporous metal nanostructure; and forming a layered double hydroxide on the surface of the hollow mesoporous metal nanostructure, wherein the metal of the hollow mesoporous metal nanostructure is Ni, and the layered double hydroxide is represented by the following chemical formula 1, [Chemical Formula 1][M 2+ (1-x) M' 2+ x (OH - )2][(A n- ) x / n ·yH2O] x- ;[In the above formula, M 2+ 은 Ni 2+ And, M' 2+ Silver Fe 2+ and, 0 < x < 1 and, A n- CO 3- , OH - , F - , Cl - , Br - , I - , SO4 2- , NO3 - and PO4 3- [One type selected from among, n is an integer from 1 to 3, and y is a number from 0.1 to 15.] A method for manufacturing a layered double hydroxide composite characterized in that the hollow mesoporous metal nanostructure is acid-treated with HCl. Claim 9 delete Claim 10 delete Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 In claim 8, the above hollow mesoporous metal nanostructure is a method for manufacturing a layered double hydroxide composite in the form of a nanochain.

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