KR20210058062A - Electrode comprising composite metal oxide catalyst for water electrolysis, method for preparing same and water electrolysis comprising same - Google Patents

Abstract

The present invention provides a water electrolysis electrode having a low overvoltage and excellent catalytic activity, a method for manufacturing the same, and a water electrolysis device including the same. The water electrolysis electrode of the present invention includes a catalyst layer including a composite metal oxide and having a three-dimensional nanosheet structure, and an electrode substrate. The method for manufacturing a water electrolysis electrode of the present invention includes the steps of: immersing the electrode substrate in an electrolyte containing a metal oxide precursor; applying a voltage to electrodeposit a composite metal hydroxide; and annealing to form a composite metal oxide. The water electrolysis device of the present invention includes the water electrolysis electrode according to the present invention as a positive electrode.

Description

A water electrolytic electrode comprising a composite metal oxide catalyst, a method of manufacturing the same, and a water electrolysis device including the same TECHNICAL FIELD [ELECTRODE COMPRISING COMPOSITE METAL OXIDE CATALYST FOR WATER ELECTROLYSIS, METHOD FOR PREPARING SAME AND WATER ELECTROLYSIS COMPRISING SAME}

The present invention relates to a water electrolytic electrode comprising a composite metal oxide catalyst, a method of manufacturing the same, and a water electrolysis apparatus including the same. Specifically, it relates to a water electrolytic electrode comprising a composite metal oxide catalyst having excellent water electrolysis performance and excellent electrical conductivity, a method of manufacturing the same, and a water electrolysis device including the same.

The electrochemical process is described by an intensive parameter and an extensive parameter. Intensity parameters such as standard rate constant (k ^o ) and transfer coefficient (α) are determined by the properties of the reaction defined by the reactants and products. The size parameters depend on the size of the system, such as the electrode area and the amount of reactants. An electrochemical catalytic process is an electrochemical process in which the kinetics are accelerated by a catalyst. The k ^o becomes larger due to the reduced activation energy (Ea) by the catalyst, thereby improving the overall reaction rate. The kinetics improvement of the intensity variable is determined by the chemical and crystallographic identity of the electrochemical catalyst. For example, Ru and Ir have the greatest electrochemical catalytic activity in the oxygen reduction reaction (OER) among metal catalysts, while tungsten and gold are much worse than ruthenium. It is difficult to overcome the OER electroactivity of Ru/IR using different materials in terms of intensity activity (eg activity of a single active site). The only way to bring the overall reaction rate of the low activity catalyst close to that of the high activity catalyst is to increase the number of active sites in a defined apparent area. However, the amount of the active site cannot be infinitely increased because the access of the reactant to the active site is limited under high loads. Therefore, it is overwhelmingly important to design and construct catalyst particles to ensure efficient mass and electron transfer.

An electrochemical catalyst is needed at the anode to speed up the slow kinetics of the OER. Noble metal catalysts such as Pt, Pd, Ir, Ru, Au, etc., are not suitable for electrolytic devices due to their high cost and environmental issues.

Oxide catalysts based on less expensive transition metals have _{been considered as OER catalysts, including M x} Co _3-x O ₄ (M = Mn, Ni, Cu and Zn) having a spinel structure.

On the other hand, a practical electrode structure is based on coating a mixture of a catalyst, a conducting agent, and a binder on a flat plate current collector. Catalysts grown directly on porous current collectors have demonstrated successful electrocatalytic performance. The single component architecture on this current collector is considered to be energy density efficient and cost effective since no binders and additional conductive agents are used. In addition, direct growth enhances the electrical integration of the active material and the substrate (the current collector), ensuring fast electron transfer through the interface between the directly grown active material and the substrate. Architectures based on direct growth have been used in lithium-ion batteries, lithium-air batteries, and supercapacitors. However, it has not yet been applied to the anion exchange membrane water electrolysis system.

The technical problem to be achieved by the present invention is to provide a water electrolytic electrode containing a composite metal oxide catalyst grown directly on a support, a method of manufacturing the same, and a water electrolysis device including the same.

According to an aspect of the present invention, a foam (foam) shape support; And

As a water electrolytic electrode comprising a catalyst layer located on the foam-shaped support,

The catalyst layer is a Cu-Co oxide; And, it provides a water-electrolytic electrode comprising a composite metal oxide of at least one of Cu oxide and Co oxide, and having a hierarchical chestnut structure.

According to another aspect of the present invention, forming a mixed metal oxide precursor aqueous solution comprising a Cu oxide precursor, a Co oxide precursor, and a reducing agent;

Adding a foam-shaped support to the mixed metal oxide precursor aqueous solution and then performing hydrothermal treatment to obtain a composite metal hydroxide formed on the foam-shaped support; And

Annealing the composite metal hydroxide;

It provides a method of manufacturing a water electrolytic electrode according to the present invention comprising a.

According to another aspect of the present invention, there is provided a water electrolysis device including the electrolytic electrode according to the present invention as an anode.

In the water-receiving electrode according to an embodiment of the present invention, mass transfer paths for reactants and products are secured in micro-scale and nano-scale, and direct growth of the catalytically active material on the support improves adhesion and electrical conductivity.

In addition, when the water electrolytic electrode according to an embodiment of the present invention is introduced into the water electrolysis device, the water electrolysis efficiency can be increased.

1 is a view showing a hierarchical chestnut-shaped structure of a catalyst layer according to an embodiment of the present invention.
2 is a diagram schematically showing a manufacturing method according to an embodiment of the present invention step by step.
3 is a SEM photograph (FIGS. 3A to 3D) of the surface of an electrode sample including a composite metal oxide catalyst prepared in Example 1 of the present invention and a diagram showing EDS element mapping of Co, Cu, and O of the catalyst layer material ( 3e to 3g).
4 is a diagram showing an X-ray analysis result of an electrode sample including a composite metal oxide catalyst prepared in Example 1 of the present invention.
5 is a diagram showing the result of energy dispersive spectroscopy of an electrode sample including a composite metal oxide catalyst prepared in Example 1 of the present invention.
6 is a diagram showing an X-ray photoelectron spectrum of an electrode sample containing a composite metal oxide catalyst prepared in Example 1. FIG.
7 is a graph measuring the electrocatalytic activity of an electrode sample including a composite metal oxide catalyst of Example 1 in a three-electrode system.
8 is a graph showing a change in potential over time in a three-electrode system of an electrode sample including a composite metal oxide catalyst prepared in Example 1. FIG.
9 shows a polarization curve after cell activation using the electrode of Example 1 and IrO _{2 as the anode electrode.}
10 is a graph showing overvoltage over time of a cell including an electrode of Example 1. FIG.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

A water electrolytic electrode according to an embodiment of the present invention includes a foam-shaped support; And a catalyst layer positioned on the foam-shaped support, wherein the catalyst layer comprises: Cu-Co oxide; And, at least one of Cu oxide and Co oxide; and a composite metal oxide, and has a hierarchical chestnut-shaped structure.

According to one embodiment of the present invention, the catalyst layer is formed directly on the support without a conductive agent and a binder, so that the electrical conductivity is high and a mass transfer path for reactants and products can be secured in micro-scale and nano-scale.

The presence of the catalyst layer on the foam-shaped support means that it is placed on the surface of the support and/or on the surface of the foam structure inside the support.

In the foam-shaped support, the foam shape is not particularly limited as long as it has a porous structure, and the foam-shaped support may serve as a current collector. By using the foam-shaped support, the specific surface area is large, water is easily supplied, and the generated hydrogen or oxygen can easily escape, thereby reducing the material diffusion resistance.

According to one embodiment of the present invention, the foam-shaped support may include at least one of Ni, SUS, Ti, Au, Cu, ITO, and FTO, and preferably may be Ni.

According to an embodiment of the present invention, the hierarchical chestnut-shaped structure is 1 or more and 8 or less, 1 or more and 5 or less, 1 or more and 4 or less, for example, 2 or more and 4 or less threads. ) May be a collection of thorns. By having the number of threads within the above range, the catalytically active surface area can be increased.

The thread may have an average length of 600 nm to 1000 nm. By having a length in the above range, the active site of the catalyst can be increased.

According to one embodiment of the present invention, the thread may be a plurality of nano-beads having an average diameter of 8 nm to 12 nm, for example, 8 nm to 10 nm, arranged in succession. Since the nanobead has an average diameter in the above range, the reactive active surface area increases, and the thread has bulk characteristics, high durability can be expected. In addition, the plurality of nano-beads constituting the thread may include nano-pores between the nano-beads.

According to an exemplary embodiment of the present invention, a hierarchical structure may be formed at a micro-scale between thorns or between threads forming thorns and a nano-scale between nano-beads, thereby increasing catalytically active sites.

1 is a view showing a hierarchical chestnut-shaped structure of a catalyst layer according to an embodiment of the present invention.

As shown in FIG. 1, it is believed that the kinetic gain of the catalyst layer of the electrode according to an embodiment of the present invention originates from the hierarchical chestnut-type nanostructure. In other words, the mass transfer paths for reactants and products are secured on two different scales: a micro-scale path between the visible and a nano-scale path between the nano beads. In addition, more active sites exposed to the electrolyte are ensured by the hierarchical structure of chestnuts. Depending on the micro- and nano-scale routes, the reactants can meet the active sites of the catalyst.

According to one embodiment of the present invention, the catalyst layer may have a thickness of 400 nm to 3000 nm, 500 nm to 3000 nm, or 1000 nm to 3000 nm.

According to an embodiment of the present invention, the Cu-Co oxide is Cu _x Co _y O _z , the x and y satisfy x+y=3, and the z may be 4.

According to another aspect of the present invention, the water electrolytic electrode comprises: forming a mixed metal oxide precursor aqueous solution including a Cu oxide precursor, a Co oxide precursor, and a reducing agent; Adding a foam-shaped support to the mixed metal oxide precursor aqueous solution and then performing hydrothermal treatment to obtain a composite metal hydroxide formed on the foam-shaped support; And annealing the composite metal hydroxide.

Hereinafter, a method of manufacturing the electrolytic electrode will be described in detail for each step.

2 is a diagram schematically showing a manufacturing method according to an embodiment of the present invention step by step.

First, a Cu oxide precursor; A mixed metal oxide precursor aqueous solution containing a Co oxide precursor and a reducing agent is formed. Specifically, a Cu oxide precursor, a Co oxide precursor, and a reducing agent such as urea may be added to water and stirred to form a mixed metal oxide precursor aqueous solution.

Here, a Cu oxide precursor or a Co oxide precursor means a material capable of forming a Cu oxide, a Co oxide, or a Cu-Co oxide, respectively, after hydrothermal treatment and annealing.

According to an embodiment of the present invention, the Cu oxide precursor and the Co oxide precursor may each independently be a nitric oxide, a sulfur oxide, a chloride, or an acetate thereof.

The Cu oxide precursor may be included in an amount of 20 to 50 parts by weight based on 100 parts by weight of the Co oxide precursor. If it falls within the above content range, the hierarchical chestnut-shaped structure of the catalyst layer may be well maintained and the catalytic activity may not be impaired.

According to one embodiment of the present invention, a foam-shaped support is put in the mixed metal oxide precursor aqueous solution and then subjected to hydrothermal treatment to form a composite metal hydroxide, that is, a composite metal hydride oxide (FIG. 1(a)).

In this case, the foam-shaped support can be used by etching in advance to remove the oxide on the surface.

The hydrothermal treatment method is not particularly limited, and may be heated in an aqueous solution state. For example, it may be performed at a temperature of 80° C. to 100° C. for 8 to 10 hours. Alternatively, it may be heated for 9 hours at a temperature of 95°C.

Then, through the step of annealing the formed composite metal hydroxide, an electrode according to an embodiment of the present invention is obtained (Fig. 1(c)).

In the annealing step, the composite metal hydroxide becomes a composite metal oxide, and a hierarchical chestnut-shaped structure is formed at this time. In addition, gas is generated when the organic matter is decomposed in the annealing step, so that nano voids or nano pores may be formed between the nano beads constituting the thread.

According to an embodiment of the present invention, the annealing may be performed at a temperature of 250° C. to 350° C. for 4 to 7 hours. Alternatively, it may be performed at a temperature of 300° C. for 6 hours. When it is performed within the above temperature range and the above time range, the composite metal hydroxide is well converted into the composite metal oxide, so that catalytic activity may be imparted.

A water electrolysis device according to another embodiment of the present invention may include a water electrolysis electrode according to the present invention as an anode. That is, the water electrolytic electrode may be included as an oxygen generating electrode.

In the water electrolysis device according to an embodiment of the present invention, the cathode and the electrolyte are not particularly limited, and may be appropriately selected and used according to the type of the water electrolysis device.

By including the electrode according to an embodiment of the present invention as an anode, a water electrolysis device having excellent water electrolysis efficiency can be obtained.

Hereinafter, in order to describe the present invention in detail, it will be described in detail with reference to embodiments. However, embodiments according to the present invention may be modified in various forms, and the scope of the present invention is not construed as being limited to the embodiments described below. Embodiments of the present specification are provided to more completely describe the present invention to those of ordinary skill in the art.

Example

All reagents were purchased from Sigma-Aldrich and used as received unless otherwise noted.

Example 1

A 100 ml aqueous solution of a cobalt precursor and a nickel precursor was prepared in the presence of a reducing agent (urea) and a surfactant (hexadecyltrimethylammonium bromide, CTAB). The concentration was adjusted with 0.2M cobalt (II) nitrate hexahydrate, 0.1M copper (II) nitrate hexahydrate, 0.5M urea and 0.1M CTAB. As a result of stirring the mixed precursor aqueous solution at 40° C. at 300 rpm for 6 hours, the solution turned dark pink.

Ni foam (4 mm thick, Toyobo) was punched into a 25 mm diameter circle. To etch the oxidized Ni surface, it was immersed in 5M HCl for 30 minutes. A piece of Ni foam whose surface was etched was immersed in an 80 mL vial containing 50 mL of an aqueous mixed precursor solution prepared in advance. It was heated at 95 °C for 9 hours for hydrothermal synthesis. The Ni foam was covered with a blue-green precipitate.

Then, the sample was annealed for 8 hours at a temperature of 300 °C in a muffle furnace at a temperature increase rate of 3 °C /min to obtain an electrode sample containing a composite metal oxide catalyst.

3 is a SEM photograph of the surface of an electrode sample including a composite metal oxide catalyst prepared according to Example 1 of the present invention (FIGS. 3A to 3D) and a diagram showing EDS element mapping of Co, Cu, and O of the catalyst layer material. (FIGS. 3E to 3G).

3A and 3B, it can be seen that the composite metal oxide particles were successfully synthesized by hydrothermal treatment and annealing in the presence of a fine fibrous network of Ni foam.

3A and 3B, a chestnut-shaped structure of the composite metal oxide particles around the Ni foam was confirmed. That is, chestnuts having an average diameter of 4 μm were grown on the Ni foam.

At this time, the thorns of the chestnut are composed of 1 or more and 5 or less threads (FIG. 3C). Each thread has an average diameter of less than 10 nm nano-beads are successively arranged (Fig. 3d). Meanwhile, nanopores thought to be caused by gas generated due to decomposition of an organic component derived from a mixed metal oxide precursor during annealing were found between the nano beads (FIG. 3D). The hierarchical chestnut-like structure can provide a mass transfer path to the OER at the micro scale and the nanopores of the thread at the nano scale. In addition, the reactant can more efficiently reach the active site of the nanobead of the composite metal oxide.

On the other hand, through EDS mapping, it was confirmed that Cu, Co, and O, which are elements constituting the composite metal oxide, were evenly present in the visible (thread) of the chestnut (FIGS. 3E to 3G ).

An X-ray diffraction analysis of the electrode sample including the composite metal oxide catalyst prepared in Example 1 was performed, and the results are shown in FIG. 4.

As shown in FIG. 4A, _{an X-ray diffraction pattern (JCPDS: 37-0878) of a spinel structure of CuCo 2} O ₄ was obtained from a composite metal oxide catalyst having a hierarchical chestnut structure grown on a nickel foam. No impurity peaks were observed at 35.6°, 38.6°, 48.7° and 61.5° except for the copper oxide related peaks. In addition, each visible nanobead showed clear streaks with a layer spacing of 0.28 nm corresponding to the lattice spacing of the (220) plane _{of CuCo 2} O _{4 having a spinel structure (FIG. 4B).}

Meanwhile, the electrode sample prepared in Example 1 was analyzed by energy dispersive spectroscopy, and the results are shown in FIG. 5. The molar ratio of Co to Cu was estimated to be about 2. The elemental composition of the composite metal oxide catalyst was further supported by the X-ray photoelectron spectrum. 6 is a diagram showing an X-ray photoelectron spectrum of an electrode sample containing a composite metal oxide catalyst prepared in Example 1. FIG.

As shown in FIG. 6A, the peak area corresponding to each element was estimated to be Cu:Co:O = 10.1%: 21.0%: 48.1%.

6B and 6C are X-ray photoelectron spectra of _{CuCo 2} O _{4 having a spinel structure.}

In the X-ray photoelectron spectrum, the binding energy of the peaks assigned to Cu 2p and Co 2p of the composite metal oxide catalyst of Example 1 was consistent with _{the binding energy of the spinel structure of CuCo 2} O _4. On the other hand, as can be seen in FIG. 6D, the high-resolution XPS O1s spectrum of the composite metal oxide of Example 1 is deconvoluted into several peaks. The main peak of 529.4 eV in the O1s spectrum is due to the MOM binding energy (O _L ), which is a typical metal-oxygen bond because there is a large amount of oxygen in the lattice, and the peak of 529.9 eV (O _OH ) is a hydroxyl group or surface adsorbed. Regarding oxygen, the peak at 531.0 eV (O _V ) is due to oxygen defects due to the low oxygen coordination. In addition, the peak at 531.8 eV is related to the surface adsorbed water molecules.

Alkaline anion exchange membrane water electrolysis device (AEMWE) test

AEMWE of having an active area of 4.9cm ² of electrode performance evaluation test at a constant current at a current density of 500mA / cm ² at 1.3 at a scan rate of 5mV / s to 1.9V _cell range and CV 1 M KOH at 45 ℃ I did. The designed cell included an anion exchange membrane (AEM, X37-50 Grade T, Dioxide Materials) separating the cathode and the anode. AEM was stored in a 1.0 M KOH solution for 24 hours to exchange the bromide anion of the ionomer with a hydroxide ion, and then washed with distilled water to remove excess KOH solution. The diameters of the cathode and anode electrodes were 25 mm and 30 mm, respectively. The composite metal oxide catalyst of Example 1 grown directly on the nickel foam was used as an anode electrode. The cathode electrode was prepared by a catalyst coated substrate (CCS) method. Pt/C (40% by weight, HISPEC 4000, Johnson Matthey) was used as a cathode electrode for the hydrogen evolution reaction (HER), and 1 mg/cm ² of Pt was loaded on a carbon cloth with a microporous layer. The gas diffusion layer (GDL) was prepared by pressing Ni foam. The tightening pressure of the AEMWE cell was 20 N/m at each of the 8 bolts. A 1M KOH solution was circulated through the cell at a rate of 48 ml/min at 60°C, and the cell activation was performed with a cycling CV in the range of _{1.6 to 1.9 V cell at a scan rate of 5 mV/s when the cell temperature was about 45°C.} Performed. Cell performance after cell stabilization was measured by CV and chronopotentiometry. For comparison, the same test was performed using an _{IrO 2} electrode instead of the electrode including the composite metal oxide catalyst of Example 1.

The experiment was carried out in a three-electrode system to measure the activity of the composite metal oxide catalyst on the Ni foam prepared in Example 1. 7 is a graph measuring electrocatalytic activity in a three-electrode system including the electrode of Example 1.

As shown in FIG. 7, the OER activity of the electrode including the composite metal oxide catalyst prepared in Example 1 was superior to that of _{IrO 2 in the same alkaline medium.} This _{is surprising when you consider IrO 2} to be one of the best OER catalysts.

On the other hand, in order to measure the OER stability, the potential was measured for 20 hours at a constant current ^{of 100 mV s -1.}

8 is a graph showing a change in potential over time in a three-electrode system including an electrode prepared in Example 1. FIG.

As shown in Fig. 8, the potential of the electrode prepared in Example 1 did not change significantly after 20 hours. On the other hand, the commercial IrO ₂ electrode showed a rapid change in potential after the durability test. During the durability test, it was confirmed that stable oxygen bubbles were continuously generated (see inset drawing). The morphological advantage of the composite metal oxide catalyst of Example 1 is that the oxygen generating activity is _{superior to the reported CuCo 2} O ₄ (CCO) spinel structure value. For example, the electrode including the catalyst of Example 1 exhibits 1.609 V (RHE) at an oxygen generation polarization voltage of 100 mA/cm ^{2, whereas the CCO microflower structure 1.72 V (RHE), CCO nanosheet structure} Shows the values of 1.62 V (RHE) and 1.633 V (RHE) in the case of the CCO nanowire structure.

A fuel cell test was performed to confirm the possibility of using an electrode including a composite metal oxide catalyst according to an embodiment of the present invention in an actual water electrolysis system. The electrode of Example 1 was used as an anode electrode.

9 shows a polarization curve after cell activation using the electrode of Example 1 and IrO _{2 as the anode electrode.}

The IrO ₂ electrode showed a current density of about 0.87Acm ^{-2 at 1.8V.} This performance is similar to the results of a recent study using _{IrO 2 as the anode.} When the electrode of Example 1 was used as the anode electrode, it had an onset potential similar _{to that of IrO 2 at 1.55V.} As a result, it showed a higher current density in the high potential region.

As such, it is believed that an electrode comprising a composite metal oxide catalyst having a hierarchical chestnut structure is effective in reducing mass transfer loss in a high potential region where oxygen bubbles are generated. A current of 1.4A/cm ² was measured at 1.9V, which is the highest performance among the electrocatalysts used in the currently reported AEM among AEMWE cells using a non-precious metal as the anode electrode.

For the durability test of AEMWE, a high current density ^{of 500 mA/cm 2 was applied to a single cell for 12 hours.} 10 is a graph showing overvoltage over time of a cell including an electrode of Example 1. FIG.

As shown in FIG. 10, the water electrolysis device including the electrode of Example 1 exhibited excellent durability. As the stability test progressed, the initial overvoltage of AEMWE was 1.696V and gradually increased to 1.718V. This means that AEMWE maintained about 98.7% of its initial value.

Claims (13)

A foam-shaped support; And
As a water electrolytic electrode comprising a catalyst layer located on the foam-shaped support,
The catalyst layer is a Cu-Co oxide; And, at least one of Cu oxide and Co oxide; A water electrolytic electrode comprising a composite metal oxide of, and having a hierarchical chestnut structure.
The method of claim 1.
The foam-shaped support is a water electrolytic electrode comprising at least one of Ni, SUS, Ti, Au, Cu, ITO, and FTO.
The method of claim 1,
The hierarchical chestnut-shaped structure is a water electrolytic electrode that is an aggregate of thorns formed of 1 or more and 8 or less threads.
The method of claim 3,
The thread is a water electrolytic electrode in which a plurality of nano-beads having an average diameter of 8 nm to 12 nm are successively arranged.
The method of claim 4,
The plurality of nano-beads is a water electrolytic electrode in which nano-pores are present therebetween.
The method of claim 1,
The Cu-Co oxide is Cu _x Co _y O _z , the x and y satisfy x+y=3, and the z is 4.
Forming a mixed metal oxide precursor aqueous solution containing a Cu oxide precursor, a Co oxide precursor, and a reducing agent;
Adding a foam-shaped support to the mixed metal oxide precursor aqueous solution and then performing hydrothermal treatment to obtain a composite metal hydroxide formed on the foam-shaped support; And
Annealing the composite metal hydroxide;
A method of manufacturing a water-electrolytic electrode according to claim 1 comprising a.
The method of claim 7,
The Cu oxide precursor and the Co oxide precursor are each independently a nitride oxide, a sulfur oxide, a chloride, or an acetate of Cu and Co.
The method of claim 7,
The method of manufacturing a water electrolytic electrode, wherein the Cu oxide precursor is included in an amount of 10 to 30 parts by weight based on 100 parts by weight of the Co oxide precursor.
The method of claim 7,
The method of manufacturing a water electrolytic electrode wherein the reducing agent is urea.
The method of claim 7,
The hydrothermal treatment is a method of manufacturing a water electrolytic electrode that is performed for 8 to 10 hours at a temperature of 80 ℃ to 100 ℃.
The method of claim 7,
The annealing step is a method of manufacturing a water electrolytic electrode that is carried out for 4 to 7 hours at a temperature of 250 ℃ to 350 ℃.
A water electrolysis device comprising the water electrolysis electrode according to any one of claims 1 to 6 as an anode.

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