KR20180001484A - Porous composite and catalyst for oxygen evolution reaction including the same - Google Patents

Abstract

The present invention relates to a porous composite which includes a metal layered double hydroxide (LDH) nanosheet having surface positive charge and a conductive metal oxide sheet having surface negative charge, wherein the metal LDH nanosheet and the conductive metal oxide sheet are uniformly mixed and re-precipitated; and also relates to a catalyst for the oxygen generation reaction including the porous composite.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous composite and a catalyst for oxygen generating reaction including the porous composite,

The present invention relates to a porous composite comprising a metal double layer hydroxide nanosheet and a conductive metal oxide sheet, and to a catalyst for oxygen generating reaction comprising the porous composite.

Research on alternative energy is actively being carried out due to problems such as depletion of fossil fuels currently used and environmental pollution. In this regard, the water decomposition reaction is a reaction that is utilized in alternative energy sources such as metal cells, solar cells, and fuel cells. During the water decomposition reaction, the oxygen generation reaction occurring in the cathode slows the reaction and generates an overvoltage because the four electrons and hydrogen move and form an oxygen-oxygen double bond. Therefore, it is important to develop a catalyst for oxygen generation reaction that lowers overvoltage.

As reported previously, metal double layer hydroxides are known to exhibit oxygen generating catalytic reactions [Fang Song; Xile Hu; The peeled metal double layer hydroxide contains metal materials having excellent electrical activity and has a porous structure and can be utilized as a good oxygen generating reaction catalyst. However, it has a low conductivity, There is a problem in that it exhibits a phenomenon of agglomeration between particles because it contains many hydroxyl groups. In addition, nanocomposites using graphene, carbon nanotubes, carbon quantum dots, and the like synthesized based on carbon as an additive to metal double layer hydroxides have been disclosed. However, the proportion of the carbonaceous materials in the total nanocomposites is 20 % To 30% by weight of the additive. Therefore, it is required to develop a catalyst for oxygen generating reaction which shows a stable and low overvoltage even when a very small amount of additive is added.

The present invention relates to a metal double layer hydroxide nanosheet having surface positive charge; And a conductive metal oxide sheet having a surface negative charge, the porous composite having the metal double layer hydroxide nanosheet and the conductive metal oxide sheet uniformly mixed and reprecipitated, and a catalyst for oxygen generation reaction comprising the porous composite, .

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

The first aspect of the present invention relates to a metal double layer hydroxide (LDH) nanosheet having a surface positive charge; And a conductive metal oxide sheet having a surface negative charge, wherein the metal double layer hydroxide nanosheets and the conductive metal oxide sheet are uniformly mixed and reprecipitated.

A second aspect of the present invention is a catalyst for oxygen generating reaction comprising a porous composite according to the first aspect of the present invention, wherein the porous composite comprises a metal double layer hydroxide having a surface positive charge and a conductive metal oxide sheet having a surface negative charge And the metal double layer hydroxide nanosheets and the conductive metal oxide sheet are uniformly mixed and reprecipitated.

According to one embodiment of the present invention, it is possible to provide a porous composite material comprising a metal double layer hydroxide nanosheet and a conductive metal oxide sheet, which exhibits a low overvoltage while adding only a small amount of the conductive metal oxide sheet, Can be applied.

According to one embodiment of the present invention, the separated metal double-layer hydroxide nanosheets are positively charged and the peeled conductive metal oxide sheet is negatively charged, so that a stable re-precipitate is formed by electrostatic attraction without any additive, .

Figure 1 compares the powder X-ray diffraction patterns of porous composites according to the amount of each different ruthenium dioxide sheet in one embodiment of the present invention.
2A is an electron micrograph (SEM) image of a metal double layer hydroxide nanosheet without an addition of a ruthenium dioxide sheet in one embodiment of the invention, and Figs. 2B-2D illustrate, in one embodiment, Scanning electron microscope (SEM) image of a porous composite in which ruthenium sheets are added in different ratios, respectively.
Figures 3A-3C are energy-dispersive EDS elemental mapping of porous composites according to the amount of each different ruthenium dioxide sheet in one embodiment of the present invention.
FIGS. 4A and 4B are transmission electron microscope (TEM) images of a ruthenium dioxide sheet and a NiCo LDH nanosheet, respectively, in one embodiment of the invention, and FIGS. 4C-4E illustrate, in one embodiment, (TEM) image of a porous composite according to the relative amounts of different ruthenium dioxide sheets; and Figure 4f is a high resolution-transmission electron microscope (HR-TEM) image of a porous composite according to one embodiment of the present invention.
Figure 5 compares the linear scan voltage-current (LSV) curves of porous composites according to the amounts of ruthenium dioxide sheet, NiCo LDH nanosheet, and different ruthenium dioxide sheets, respectively, in one embodiment of the present invention.
6 is a graph comparing the linear scan voltage-current curve (LSV) of a physical mixture of a NiCo LDH nanosheet and a ruthenium dioxide sheet, a NiCo LDH nanosheet, and a NiCo LDH-ruthenium dioxide porous composite in one embodiment of the present invention It is.
FIG. 7 compares the Tafel Plots of porous composites according to the amounts of ruthenium dioxide sheet, NiCo LDH nanosheet, and different ruthenium dioxide sheets, respectively, in one embodiment of the present invention.
Figure 8 compares the impedance analysis of a porous composite according to the amount of ruthenium dioxide sheet, NiCo LDH nanosheet, and ruthenium dioxide sheet, each different, in one embodiment of the present invention.
Figure 9 compares the curve of the time complexion of iridium carbon with the time course of the porous composite according to the addition of NiCo LDH and 1 wt% ruthenium dioxide sheet in one embodiment of the present invention.
10 compares the linear scan voltage-current (LSV) curve of the porous nanocomposite according to the amount of the ruthenium dioxide sheet added to the NiFe LDH nanosheet in one embodiment of the present invention.

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is "on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

As used herein, the terms "about," " substantially, "and the like are used herein to refer to or approximate the numerical value of manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to prevent unauthorized exploitation by unauthorized intruders of the mentioned disclosure.

The term " step " or " step of ~ " as used throughout the specification does not imply " step for.

Throughout this specification, the term "combination (s) thereof " included in the expression of the machine form means a mixture or combination of one or more elements selected from the group consisting of the constituents described in the expression of the form of a marker, Quot; means at least one selected from the group consisting of the above-mentioned elements.

Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these embodiments and examples and drawings.

The first aspect of the present invention relates to a metal double layer hydroxide (LDH) nanosheet having a surface positive charge; And a conductive metal oxide sheet having a surface negative charge, wherein the metal double layer hydroxide nanosheets and the conductive metal oxide sheet are uniformly mixed and reprecipitated.

The porous composite according to one embodiment of the present invention comprises metal double layer hydroxide nanosheets having surface positive charge. In addition, the metal double layer hydroxide nanosheet includes a separated metal double layer hydroxide nanosheet, and may be in the form of a two-dimensional nanosheet, having hydrophilicity.

In one embodiment of the present invention, the metal double layer hydroxide nanosheet may include, but is not limited to, those represented by the following chemical formula 1:

[Chemical Formula 1]

[M ¹ _(1-x) M ² _x (OH) ₂ ] [A ^n- ] _{x / n} .zH ₂ O;

In the above formula, M ¹ is a +2 valent metal cations, e.g., Ca ^{+ 2,} Mg ^{+ 2,} Zn ^{+ 2,} Ni ^2+, Mn ^{+ 2,} Co ^{+ 2,} Fe ^{+ 2,} Cu ^{+ 2} , And combinations thereof, and M ² is a metal cation of +3 valence, for example Fe ^{3 +} , Al ^{3 +} , Cr ^{3 +} , Mn ^{3 +} , Ga ^{3 +} , Co ^{3 +} , Ni ^{3 +} , and combinations thereof, and A ^n- may be a hydroxide cation (OH ^- ), a nitrate ion (NO ₃ ^- ), PO ₄ ^3- , HPO ₄ ^{2 -} , H ₂ PO ₄ ^- , and combinations thereof, 0 <x <1, n is an integer of 1 to 3, and z is an anion selected from the group consisting of 0.1 to 15.

For example, the metal double layer hydroxide nanosheet may include, but is not limited to, nickel-cobalt double layer hydroxide (NiCo LDH) or nickel-iron hydroxide (NiFe LDH).

In one embodiment of the present invention, the metal double layer hydroxide nanosheet may include, but is not limited to, a two-dimensional nanosheet having a size ranging from about 50 nm to about 200 nm. For example, the size of the metal double layer hydroxide nanosheets may range from about 50 nm to about 200 nm, from about 50 nm to about 180 nm, from about 50 nm to about 160 nm, from about 50 nm to about 140 nm, 120 nm, about 50 nm to about 100 nm, about 50 nm to about 80 nm, about 70 nm to about 200 nm, about 100 nm to about 200 nm, about 130 nm to about 200 nm, about 150 nm to about 200 nm , Or from about 170 nm to about 200 nm, but is not limited thereto.

A conductive metal oxide sheet having a surface negative charge as an additive is added to the metal double layer hydroxide nanosheet to be uniformly mixed. The conductive metal oxide sheet includes a peeled conductive metal oxide sheet, and may be in the form of a two-dimensional sheet, having hydrophilicity. In addition, the metal double layer hydroxide nanosheets and the conductive metal oxide sheets both have hydrophilicity and can be mixed uniformly. Since the two materials have a two-dimensional nanosheet shape, a stable porous structure can be maintained, The two materials can attract opposite surface charges to form stable reprecipitates without additional additives due to electrostatic attraction. The exfoliated metal double layer hydroxide contains metal materials having excellent electrical activity and has a porous structure and can be utilized as an excellent oxygen generating reaction catalyst. However, it exhibits a low conductivity and a large number of hydroxyl groups, There is a problem. However, the problem of low conductivity of the metal double-layered hydroxide nanosheets can be solved by adding the metal oxide sheet having excellent conductivity to the peeled metal double layer hydroxide.

In one embodiment of the invention, the conductive metal oxide sheet may comprise an oxide or a composite oxide of a metal selected from the group consisting of ruthenium, manganese, nickel, cobalt, iron, and combinations thereof. For example, the conductive metal oxide sheets are _{RuO 2, CoO 2, [Ni} 1/3 Co 1/3 Mn 1/3] O 2, iron oxides, and conductive metal oxides selected from the group consisting of a combination of . &Lt; / RTI &gt;

In one embodiment of the invention, the conductive metal oxide sheet may comprise, but is not limited to, a two-dimensional nanosheet having a size ranging from about 1 [mu] m to about 5 [mu] m. For example, the size of the conductive metal oxide sheet may range from about 1 [mu] m to about 5 [mu] m, from about 1 [mu] m to about 4 [ but may be, but is not limited to, from about 1 μm to about 1.2 μm, from about 1.2 μm to about 5 μm, from about 1.5 μm to about 4 μm, or from about 2 μm to about 3 μm.

The porous composite according to one embodiment of the present invention can exhibit excellent performance even when containing only a small amount of the conductive metal oxide sheet, and the conductive metal oxide sheet is preferably larger in size than the metal double layer hydroxide nanosheet can do.

In one embodiment of the present invention, the weight ratio of the conductive metal oxide sheet to the weight of the metal double layer hydroxide nanosheets may comprise from about 0.5 wt% to about 1.5 wt%, preferably about 1.0 wt% But is not limited thereto. For example, the weight ratio of the conductive metal oxide sheet may be from about 0.5 wt% to about 1.5 wt%, from about 0.5 wt% to about 1.3 wt%, from about 0.5 wt% to about 1.0 wt%, from about 0.5 wt% to about 0.7 about 0.7 wt% to about 1.5 wt%, about 1.0 wt% to about 1.5 wt%, about 1.3 wt% to about 1.5 wt%, about 0.6 wt% to about 1.4 wt%, about 0.7 wt% about 0.8 wt% to about 1.2 wt%, about 0.9 wt% to about 1.1 wt%, about 0.8 wt% to about 1.4 wt%, about 0.8 wt% to about 1.3 wt%, about 0.8 wt% wt%, or from about 0.8 wt% to about 1.1 wt%.

The porous composite comprising: preparing a conductive metal oxide sheet colloid; Preparing a metal double layer hydroxide nanosheet colloid; And synthesizing the porous composite by adding the conductive metal oxide sheet colloid to the metal double layer hydroxide nanosheet colloid and reacting it. Also, the metal double layer hydroxide nanosheet may have a surface positive charge, the conductive metal oxide sheet may have a surface negative charge, and the metal double layer hydroxide nanosheet and the conductive metal oxide sheet may be uniformly mixed and reprecipitated.

In one embodiment of the present invention, the step of preparing the conductive metal oxide sheet colloid may include, but is not limited to, stripping the conductive layered metal oxide sheet.

In one embodiment of the present invention, the step of preparing the metal double layer hydroxide nanosheet colloid may include peeling the metal double layer hydroxide nanosheet, but the present invention is not limited thereto. The metal double layer hydroxide nanosheets may be peeled to have a porous structure.

A second aspect of the present invention is a catalyst for oxygen generating reaction comprising a porous composite according to the first aspect of the present invention, wherein the porous composite comprises a metal double layer hydroxide having a surface positive charge and a conductive metal oxide sheet having a surface negative charge And the metal double layer hydroxide nanosheets and the conductive metal oxide sheet are uniformly mixed and reprecipitated.

The catalyst for the oxygen generating reaction according to the second aspect of the present invention can be applied to all of the porous composites according to the first aspect of the present invention and detailed descriptions of the overlapping parts are omitted, The same can be applied.

In one embodiment of the present invention, the oxygen generating reaction catalyst may be, but not limited to, an electrode catalyst that oxidizes oxygen anions in electrochemical decomposition of water to generate oxygen.

In one embodiment of the present invention, the catalyst for oxygen generating reaction may be one which acts as a photocatalyst for oxidizing oxygen anions in the photolysis of water to generate oxygen, but the present invention is not limited thereto.

In one embodiment of the present invention, the metal double layer hydroxide nanosheet may include, but is not limited to, those represented by the following chemical formula 1:

[Chemical Formula 1]

[M ¹ _(1-x) M ² _x (OH) ₂ ] [A ^n- ] _{x / n} .zH ₂ O;

In the above formula, M ¹ is a +2 valent metal cations, e.g., Ca ^{+ 2,} Mg ^{+ 2,} Zn ^2+, Ni ^{+ 2,} Mn ^{+ 2,} Co ^{+ 2,} Fe ^{+ 2,} Cu ^{+ 2} , And combinations thereof, and M ² is a metal cation of +3 valence, for example Fe ^{3 +} , Al ^{3 +} , Cr ^{3 +} , Mn ^{3 +,} Ga ^{+ 3,} Co ^{+ 3,} Ni ^{+ 3,} and may be one containing a metal cation selected from the group consisting of a combination thereof, a ^n- is a hydroxyl ion (OH ^-), nitrate ion (NO ₃ ^- ), PO ₄ ^3- , HPO ₄ ^{2 -} , H ₂ PO ₄ ^- , and combinations thereof, 0 <x <1, n is an integer of 1 to 3, and z Is in the range of 0.1 to 15.

For example, the metal double layer hydroxide nanosheet may include, but is not limited to, nickel-cobalt double layer hydroxide (NiCo LDH) or nickel-iron hydroxide (NiFe LDH).

In one embodiment of the present invention, the metal double layer hydroxide nanosheet may include, but is not limited to, a two-dimensional nanosheet having a size ranging from about 50 nm to about 200 nm. For example, the size of the metal double layer hydroxide nanosheets may range from about 50 nm to about 200 nm, from about 50 nm to about 180 nm, from about 50 nm to about 160 nm, from about 50 nm to about 140 nm, 120 nm, about 50 nm to about 100 nm, about 50 nm to about 80 nm, about 70 nm to about 200 nm, about 100 nm to about 200 nm, about 130 nm to about 200 nm, about 150 nm to about 200 nm , Or from about 170 nm to about 200 nm, but is not limited thereto.

In one embodiment of the invention, the conductive metal oxide sheet may comprise an oxide or a composite oxide of a metal selected from the group consisting of ruthenium, manganese, nickel, cobalt, iron, and combinations thereof. For example, the conductive metal oxide sheets are _{RuO 2, CoO 2, [Ni} 1/3 Co 1/3 Mn 1/3] O 2, iron oxides, and conductive metal oxides selected from the group consisting of a combination of . &Lt; / RTI &gt;

In one embodiment of the invention, the conductive metal oxide sheet may comprise, but is not limited to, a two-dimensional nanosheet having a size ranging from about 1 [mu] m to about 5 [mu] m. For example, the size of the conductive metal oxide sheet may range from about 1 [mu] m to about 5 [mu] m, from about 1 [mu] m to about 4 [ but may be, but is not limited to, from about 1 μm to about 1.2 μm, from about 1.2 μm to about 5 μm, from about 1.5 μm to about 4 μm, or from about 2 μm to about 3 μm.

In one embodiment of the present invention, the weight ratio of the conductive metal oxide sheet to the weight of the metal double layer hydroxide nanosheets may comprise from about 0.5 wt% to about 1.5 wt%, preferably about 1.0 wt% But is not limited thereto. For example, the weight ratio of the conductive metal oxide sheet may be from about 0.5 wt% to about 1.5 wt%, from about 0.5 wt% to about 1.3 wt%, from about 0.5 wt% to about 1.0 wt%, from about 0.5 wt% to about 0.7 about 0.7 wt% to about 1.5 wt%, about 1.0 wt% to about 1.5 wt%, about 1.3 wt% to about 1.5 wt%, about 0.6 wt% to about 1.4 wt%, about 0.7 wt% about 0.8 wt% to about 1.2 wt%, about 0.9 wt% to about 1.1 wt%, about 0.8 wt% to about 1.4 wt%, about 0.8 wt% to about 1.3 wt%, about 0.8 wt% wt%, or from about 0.8 wt% to about 1.1 wt%. When the weight ratio of the conductive metal oxide sheet added to the oxygen generating reaction catalyst is about 1.0 wt%, the lowest overvoltage may be exhibited, but the present invention is not limited thereto.

The exfoliated metal double layer hydroxide contains metal materials having excellent electrical activity and has a porous structure and can be utilized as an excellent oxygen generating reaction catalyst. However, it exhibits a low conductivity and a large number of hydroxyl groups, There is a problem. However, by adding a metal oxide sheet having excellent conductivity to the peeled metal double layer hydroxide, it is possible to solve the problem of low conductivity of the metal double layer hydroxide nanosheet and to produce a catalyst for oxygen generation reaction exhibiting low overvoltage.

In one embodiment of the present invention, the oxygen generating reaction catalyst exhibits a low overvoltage and thus exhibits excellent catalytic activity. In the catalyst for oxygen generating reaction according to an embodiment of the present invention, an overvoltage at a current density of 10 mA cm ^-2 But is not limited to, less than about 340 mV. For example, the over-voltage for the oxygen evolution catalyst is current 10 mA cm ^-2 in less than about 340 mV, about 330 mV or less, about 320 mV or less, about 310 mV or less, about 300 mV or less, about 290 mV or less, About 260 mV to about 340 mV, about 260 mV to about 320 mV, about 260 mV to about 300 mV, or about 260 mV to about 280 mV, for example, about 280 mV or less, about 270 mV or less, about 260 mV or less , But is not limited thereto. In the oxygen generating reaction catalyst, the current of 10 mA cm &lt; ² &gt; is the same current density as the point at which the oxygen generation is ended in the actual solar fuel cell, and the lower the overvoltage at this time, the better the catalyst efficiency.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

[ Example ]

Example  1: Preparation of Porous Composite 1

1. Ruthenium dioxide sheet synthesis

Ruthenium dioxide sheet was obtained by peeling off the screen layer H _{0. 2} RuO _2, first, for the production of a layered H _{0. 2} RuO _2, to thereby prepare a precursor NaRuO ₂ of H _{0. 2} RuO _2. H _{0 .} The _precursor of RuO ₂ NaRuO ₂ is Na ₂ CO ₃ (Sigma Aldrich), Ru (Alfa Aesar), RuO 2 (Sigma Aldrich) at a molar ratio of 2: 1: 3 and then heated at 900 ° C for 12 hours while flowing argon gas. Then, the reaction was conducted with Na ₂ S ₂ O ₈ aqueous solution for 3 days to obtain Na _{0 . 2} RuO ₂ was obtained, which was reacted with an aqueous solution of 1 M HCl for 3 days while changing the acid solution to obtain H _0.2 RuO ₂ .

After each of the above processes, the resultant was washed with sufficient distilled water and dried to confirm its structure. The synthesis of H _{0. 2} RuO ₂ tetrabutylammonium hydroxide (TBA · OH, tetrabuthylammonium hydroxide; Sigma Aldrich) aqueous solution and then stirred for 10 days, the supernatant was taken and centrifuged for 30 min at 2,000 rpm ruthenium dioxide (RuO ₂ ) sheet colloid.

2. Peeled  Nickel cobalt Double layer  Hydroxide synthesis

The peeled nickel cobalt double layer hydroxide was obtained by stirring the nickel cobalt double layer hydroxide obtained through hydrothermal synthesis with formamide (JUNSEI). The nickel cobalt hydroxide double layer was prepared by dissolving Ni (NO ₃ ) ₂ .6H ₂ O (Sigma Aldrich) and Co (NO ₃ ) ₂ .6H ₂ O (Sigma Aldrich) in a molar ratio of 3: 2 in 60 mL of methyl alcohol ) And 12 mL of carbon dioxide-free distilled water, and hydrothermal synthesis was carried out at 180 ° C for 24 hours by adding brominated settimoronium (CTAB; Sigma Aldrich). It was washed with ethanol (SAMCHUN) and distilled water from which carbon dioxide had been removed, and dried in a vacuum oven at 50 ° C. 50 mg of the synthesized nickel cobalt double layer hydroxide was added to 100 mL of formamide in which nitrogen gas was sufficiently flowed. The mixture was stirred for 24 hours while flowing nitrogen gas, and then peeled NiCo LDH (hereinafter referred to as RuO ₂ Is referred to as NCRO) was obtained as a NiCo LDH.

3. Peeled  Nickel cobalt Double layer  Synthesis of hydroxide-ruthenium dioxide sheet composite

To the synthesized peeled nickel cobalt double layer hydroxide were added 0.5 wt%, 1 wt%, and 1.5 wt% ruthenium dioxide sheet, respectively, based on the weight of the nickel cobalt hydroxide double layer, and reacted for 24 hours to remove the peeled nickel cobalt double layer hydroxide- Ruthenium sheet complex (NiCo LDH-RuO ₂ ) was synthesized (hereinafter, the synthesized complexes were referred to as NCR05, NCR10, and NCR15, respectively). The previously reacted NCR samples were washed with formamide and ethyl alcohol and then dried in a vacuum oven at 50 ° C.

Example  2: Preparation of Porous Composite 2

One. Peeled  Nickel iron Double layer  Hydroxide synthesis

The exfoliated nickel iron double layer hydroxide was obtained by stirring the nickel iron double layer hydroxide prepared by coprecipitation with formamide (JUNSEI). Ni (NO ₃ ) ₂ .6H ₂ O (Sigma Aldrich) and Fe (NO ₃ ) ₃ .9H ₂ O (Sigma Aldrich) were added to distilled water at a molar ratio of 2: 1 while flowing nitrogen gas And the mixture was adjusted to pH 8 by adding 1 M solution of NaOH (Sigma Aldrich), followed by stirring for 1 hour. This was washed with distilled water from which carbon dioxide had been removed and dried in a vacuum oven at 50 ° C. 50 mg of the synthesized nickel iron double-layer hydroxide was added to 100 mL of formamide in which nitrogen gas was sufficiently flowed, stirred for 24 hours while flowing nitrogen gas, and then peeled nickel iron double layer hydroxide (NiFe LDH; hereinafter referred to as RuO ₂ Is referred to as &quot; NFRO &quot;).

2. Peeled  Nickel iron Double layer  Synthesis of hydroxide-ruthenium dioxide sheet composite

In this embodiment, the ruthenium dioxide sheet used was the same ruthenium dioxide sheet as that prepared in Example 1 above. In addition, mixing ratios showing the best performance in the samples of the nickel-cobalt double-layer hydroxide-ruthenium dioxide sheet composite (NiCo LDH-RuO ₂ ) of Example 1 were introduced into the nickel-iron double- A ruthenium dioxide sheet of 1 wt% based on weight was added and reacted for 24 hours to synthesize a peeled nickel iron double layer hydroxide-ruthenium dioxide sheet composite (NiFe LDH-RuO ₂ ) (hereinafter, box). The previously reacted NFR 10 sample was washed with formamide and ethyl alcohol and then dried in a vacuum oven at 50 ° C.

Example  3: Preparation of catalyst for oxygen generating reaction and catalyst test

The catalyst ink for the oxygen generating reaction was added to an aqueous solution consisting of 4 mL of tertiary distilled water, 1 mL of iso-propyl alcohol (SAMCHUN), and 25 μL of 5 wt% Nafion (Sigma Aldrich) mg of the synthesized sample and 3 mg of Vulcan Carbon (Premetek Co.) were added, and the mixture was dispersed for 30 minutes or more using a sonicator.

The activity of the prepared catalyst ink was measured by rotating disc electrode test method. 10 [mu] L catalyst ink was applied on a glass carbon electrode having a diameter of 3 mm and dried. The activity was measured in a three electrode environment. A glass carbon electrode coated with a sample was used as the working electrode, a saturated calomel electrode (SCE) was used as the reference electrode, and a platinum wire was used as the counter electrode. In addition, a 1 M potassium hydroxide solution was used as an electrolyte, and oxygen gas was supplied for 30 minutes or more to saturate the oxygen. The voltage range was 0.1 V to 0.7 V based on the saturated calomel electrode and the scan rate was measured at 5 mV / s. In addition, the impedance measurement was performed in the frequency range of 0.1 Hz to 10,000 Hz under the condition of applying a voltage of 0.55 V (vs saturated calomel electrode) after the occurrence of the oxygen generating reaction. In the time zone potential method, the current density was measured while maintaining a current density of 10 mA cm ^-2 for 10,000 seconds. All potentials in this embodiment are expressed in terms of potentials converted to reversible hydrogen electrode potentials.

Characteristic analysis of the porous composite and catalyst test result

1. Powder X-ray diffraction analysis of porous composite

FIG. 1 shows powder X-ray diffraction (XRD; Rigaku, D / Max-2000 / PC) patterns for NCR samples synthesized according to the addition ratios of different ruthenium dioxide sheets. 1 (a) to (d) show NCR0, NCR05, NCR10, and NCR15, respectively. Compared with NCRO (NiCo LDH), even when a ruthenium dioxide sheet was added to a metal double layer hydroxide, the aspect of the peak did not change significantly, and the ruthenium dioxide sheet aggregated to form an impurity peak. As a result, it was confirmed that the nickel cobalt double layer hydroxide nanosheet and the ruthenium dioxide sheet were uniformly re-precipitated to form a nanocomposite.

2. Porous composite SEM  analysis

2A to 2D are electron micrograph (FE-SEM; JEOL, JSM-6700-F) images of NCR0, NCR05, NCR10 and NCR15 samples, respectively. NCR0 looks like a thick, broad plate, but in NCR05, NCR10, and NCR15, nickel cobalt bilayer hydroxides became smaller and thinner with exfoliation and reprecipitation. In the re-precipitated NCR05, NCR10, and NCR15, it was confirmed that the sheets were disorderly re-precipitated.

3. EDS element of porous composite Mapping  analysis

Figures 3A-3C are energy-dispersive EDS elemental mapping of NCR05, NCR10, and NCR15 samples, respectively. In Figs. 2B to 2D, it is difficult to distinguish the sheets. In Figs. 3A to 3C, X-rays generated by the nickel, cobalt, and ruthenium elements are detected in the overall portion of the sample and are indicated by dots. It was confirmed that the cobalt double-layered hydroxide nanosheets were uniformly mixed and reprecipitated instead of being aggregated.

4. Porous composite TEM  analysis

4A-4E are TEM (JEOL, FEM-2100F) images of ruthenium dioxide nanosheets and NCR samples, respectively. As shown in FIG. 4A, the ruthenium dioxide sheet was confirmed to be a sheet having a size of about 1 μm to about 1.5 μm, and as shown in FIG. 4B, the nickel cobalt double layer hydroxide had a size of 100 nm to 200 nm Of the total amount of water. Further, as shown in Figs. 4C to 4E, it was confirmed that the porous composite in which the two sheets were reprecipitated had a shape in which nickel cobalt double layer hydroxide adhered on the surface of a wide ruthenium dioxide sheet. Since the two sheets have different electrostatic potentials, small nickel cobalt double layer hydroxide nanosheets adhered to such a wide range of ruthenium dioxide sheet and reprecipitated. In particular, FIG. 4F shows an enlarged view of NCR10. As shown in FIG. 4F, the (10-2) plane represented by nickel cobalt double layer hydroxide and the (018) plane represented by ruthenium dioxide can be respectively identified. And it was confirmed that it forms a hybrid body.

5. Activity analysis of catalyst for oxygen generating reaction

5 is a graph showing a linear sweep voltammetry (LSV) curve. As a result, it was confirmed that the NCR samples to which various ruthenium dioxide (RuO ₂ ) . The results showed that NCR05, NCR10, and NCR15 appeared at a lower potential than that of NCR0 (NiCo LDH) without addition of carbon dioxide ruthenium.

As Comparative Example 1, nickel cobalt double layer hydroxide (NCRO) in which RuO ₂ sheet as an additive was not added and Comparative Examples 2 and 3 were added in an amount of less than 0.5 wt% and an amount of ruthenium dioxide in an amount exceeding 1.5 wt% , Porous composites each having addition amounts of ruthenium dioxide sheet of 0.1 wt% and 2.5 wt% were prepared and their performance was measured (hereinafter, the synthesized complexes were referred to as NCR01 and NCR25, respectively). Also, in addition to the NCR sample, the activity of iridium / carbon (Ir / C), which is usually used as a catalyst as Comparative Example 4, and ruthenium dioxide sheet added as an additive as Comparative Example 5 were measured. In addition, the peak formed at 1.3 V to 1.4 V is a peak generated by oxidation of nickel and cobalt, which means that the wider the area, the wider the active area.

In Table 1, the voltage at a current density of 10 mA cm ^-2 is calculated as an overvoltage in the linear scan voltage-current curve of FIG. As can be seen from the following Table 1, ruthenium dioxide sheet added as an additive exhibited the largest overvoltage, and consequently, it was concluded that the activity was poor when the ruthenium dioxide sheet alone was used as a catalyst for oxygen generating reaction. On the other hand, in the case of NCR10 in which the ruthenium dioxide sheet as an additive was added in an amount of 1 wt% based on the weight of the nickel cobalt double layer hydroxide, the overvoltage was much lower than that of the other samples. It was confirmed that the overvoltage of NCR10 is lower than that of the commonly used iridium / carbon. NCR05 and NCR15 also showed lower overvoltage values than NCR0, and it was confirmed that the overvoltage of NCR0 was less than 0.5 wt% or more than 1.5 wt%

[Table 1]

Figure 6 is a linear scan voltage-current curve of a mixture of physically mixed nickel cobalt bilayer hydroxide and ruthenium dioxide sheet. The mixing ratio of the mixture was the same as that of the NCR10 which was the most excellent in the present embodiment, and was merely a physically mixed mixture rather than an electrostatic attraction, and showed similar performance to that of NCR0. However, The value of the dislocation was larger. These results indicate that the mixing of nano-units rather than the performance of ruthenium dioxide sheet itself contributed greatly to the performance improvement.

7 is a Tafel plot showing the reaction rate in the oxygen generating reaction. In FIG. 7, NCR0 showed 92.4 mV dec- ¹ , while the best performance of the previous NCR10 was 79.4 mV dec- ¹ , NCR05 and NCR15 were 85.1 and 86.7 mV dec- ¹ , respectively. When the ruthenium dioxide sheet was added, it was confirmed that the reaction rate at the time of oxygen generation was increased, and a low overvoltage occurred during the oxygen generation reaction.

FIG. 8 shows an impedance spectroscopy (EIS) graph showing that the diameters of the semicircles represented by the materials to which ruthenium dioxide sheet was added were smaller than those of NCRO. The smaller the diameter of the semicircle is, the smaller the resistance of the charge behavior. This result means that the ruthenium dioxide sheet increases the charge transfer reaction. The above results also show that the ruthenium dioxide sheet has the effect of lowering the overvoltage during the oxygen generating reaction.

FIG. 9 shows the curve of the time zone potential method (chronopotentiometry), comparing iridium carbon (Ir / C), which is a catalyst usually used for oxygen generation, with NCR0 and NCR10. In the case of iridium carbon, the initial electric potential was low, but the electric potential increased with time, and it was confirmed that the nickel cobalt double layer hydroxide based material exhibited a stable electric potential. In particular, the ruthenium dioxide doped NCR10 according to the present example exhibited a remarkably stable curve even at a low potential.

10 shows the activity of NFR0 (NiFe LDH) and NFR10 prepared in Example 2 as an oxygen generating reaction catalyst, as a linear sweep voltammetry (LSV) curve. The peak formed at 1.4 V is the peak produced by oxidation of nickel and iron. It was confirmed that when a small amount of the ruthenium dioxide sheet was added, the voltage at 10 mA cm ^-2 was reduced. As a result, it was confirmed that ruthenium dioxide sheet can be applied as an additive to NiCo LDH as well as other nanosheets.

The nickel cobalt double layer hydroxide used in this embodiment is composed of nickel and cobalt having good electrical activity and has a porous structure, so that it can be utilized as an excellent oxygen generating reaction catalyst. However, the material has a low conductivity and contains a large number of hydroxyl groups, and thus the particles are aggregated. Therefore, in order to compensate for this, ruthenium dioxide sheet was added to the exfoliated nickel-cobalt bilayer hydroxide, and the re-precipitated nickel cobalt bilayer hydroxide-ruthenium dioxide nanocomposite was synthesized. The ruthenium dioxide sheet has high conductivity, which can solve the low conductivity problem of the nickel cobalt hydroxide double layer. In addition, the ruthenium dioxide sheet can be uniformly mixed with the peeled nickel cobalt double layer hydroxide having the same properties as the hydrophilic material, and both materials maintain a porous structure in that they are two-dimensional nanosheets, I could. In addition, the exfoliated metal double layer hydroxide nanosheet was positively charged, and the ruthenium dioxide sheet was negatively charged, so that a stable re-precipitate could be formed without any additional additives.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (9)

Layered double hydroxide (LDH) nanosheet with surface positive charge; And
Conductive metal oxide sheet having surface negative charge
A porous composite,
Wherein the metal double layer hydroxide nanosheets and the conductive metal oxide sheet are uniformly mixed and reprecipitated.
Porous composites.
The method according to claim 1,
Wherein the metal double layer hydroxide nanosheets comprise those represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]
[M ¹ _(1-x) M ² _x (OH) ₂ ] [A ^n- ] _{x / n} .zH ₂ O;
In the above formula,
M ¹ is a group consisting of a +2 valent metal ^{cations, Ca 2 +, Mg 2 +} , Zn 2 +, Ni 2 +, Mn 2 +, Co 2 +, Fe 2 +, Cu 2+, and combinations thereof Lt; RTI ID = 0.0 &gt; a &lt; / RTI &gt; metal cation,
M ² is a divalent metal cation in +3, Fe ^{+ 3,} Al ^{+ 3,} Cr ^{+ 3,} Mn ^{+ 3,} Ga ^{+ 3,} Co ^{+ 3,} Ni ^{+ 3,} and a metal selected from the group consisting of a combination of A cation,
A ^n- is an anion selected from the group consisting of hydroxide ions (OH ^- ), nitrate ions (NO ₃ ^- ), PO ₄ ^3- , HPO ₄ ^{2 -} , H ₂ PO ₄ ^-
0 &lt; x &lt; 1,
n is an integer of 1 to 3,
z is a number of from 0.1 to 15;
The method according to claim 1,
Wherein the metal double layer hydroxide nanosheet comprises a two-dimensional nanosheet having a size in the range of 50 nm to 200 nm.
The method according to claim 1,
Wherein the conductive metal oxide sheet comprises an oxide or composite oxide of a metal selected from the group consisting of ruthenium, manganese, nickel, cobalt, iron, and combinations thereof.
The method according to claim 1,
Wherein the conductive metal oxide sheet comprises a two-dimensional sheet having a size ranging from 1 [mu] m to 5 [mu] m.
The method according to claim 1,
Wherein the metal double layer hydroxide nanosheet and the conductive metal oxide sheet each have independently hydrophilic properties.
The method according to claim 1,
Wherein the weight ratio of the conductive metal oxide sheet to the weight of the metal double layer hydroxide nanosheets is 0.5 wt% to 1.5 wt%.
A catalyst for oxygen generating reaction, comprising the porous composite according to any one of claims 1 to 7,
Wherein the porous composite comprises a metal double layer hydroxide having a surface positive charge and a conductive metal oxide sheet having a surface negative charge, wherein the metal double layer hydroxide nanosheet and the conductive metal oxide sheet are uniformly mixed and reprecipitated.
Catalyst for oxygen generating reaction.
9. The method of claim 8,
Wherein the catalyst for oxygen generating reaction acts as an electrode catalyst or a photocatalyst for generating oxygen by oxidizing oxygen anions in electrochemical decomposition of water or photodecomposition of water.

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