KR20210061496A - Metal nano cluster catalysts, method of preparing metal nano cluster catalysts, method of synthesis of urea using metal nano cluster catalysts, and electrochemical system including metal nano cluster catalysts - Google Patents

Abstract

The present invention is to provide a metal nanocluster catalyst, a method for manufacturing the same, and a urea synthesis method using the metal nanocluster catalyst, which has improved chemical selectivity with respect to a reaction for generating urea by reducing carbon dioxide and nitrate together, and has high urea production efficiency at room temperature and atmospheric pressure conditions. According to an embodiment of the present invention, a method for manufacturing a metal nanocluster catalyst comprises the steps of: dispersing a carbon support, Nafion and a binder in a solvent to form a carbon support-binder structure; coating the carbon support-binder structure on a conductive substrate; and forming metal nanoclusters by coating a solution containing transition metal ions on the carbon support-binder structure.

Description

Metal nanocluster catalyst and its manufacturing method, urea synthesis method using metal nanocluster catalyst, and electrochemical system including metal nanocluster catalyst {METAL NANO CLUSTER CATALYSTS, METHOD OF SYNTHESIS OF UREA USING METAL NANO CLUSTER CATALYSTS, AND ELECTROCHEMICAL SYSTEM INCLUDING METAL NANO CLUSTER CATALYSTS}

The present invention relates to a metal nanocluster catalyst and a method of manufacturing the same, a method of synthesizing urea by co-reducing carbon dioxide and nitrate using as a metal nanocluster catalyst, and an electrochemical system including a metal nanocluster catalyst will be.

Urea (CO(NH ₂ ) ₂ ) is an essential nitrogen fertilizer used in agriculture, producing millions of tons per year, and is expected to increase continuously as the population grows. However, in order to produce urea by a generalized method, it is not economical because it requires high temperature and high pressure conditions, and it is not eco-friendly because a large amount of air pollutants is discharged during the production process. Accordingly, there is a need to develop a catalyst capable of minimizing the emission of air pollutants and converting the air pollutants into urea at room temperature and pressure conditions.

One of the technical problems to be achieved by the technical idea of the present invention is a metal nanocluster catalyst having improved chemical selectivity for a reaction that generates urea by reducing carbon dioxide and nitrate together, and having high urea generation efficiency under room temperature and pressure conditions, and It is to provide a manufacturing method and a method for synthesizing urea using a metal nanocluster catalyst.

In addition, one of the technical problems to be achieved by the technical idea of the present invention is to provide an electrochemical system including such a metal nanocluster catalyst.

Metal nanoclusters according to an embodiment of the present invention, graphene-formed porous carbon (GMC), a binder bonded by π-π interaction with the graphene-formed porous carbon, and the surface of the graphene-formed porous carbon by the binder It includes a copper nanocluster adsorbed on, and the binder includes an organic compound having a structure including at least 3 or more aromatic rings and at least 3 or more nitrogen atoms.

The method of manufacturing a metal nanocluster catalyst according to an embodiment of the present invention includes dispersing a carbon support, Nafion, and a binder in a solvent to form a carbon support-binder structure, and coating the carbon support-binder structure on a conductive substrate. And forming metal nanoclusters by coating a solution containing transition metal ions on the carbon support-binder structure.

The electrochemical system according to an embodiment of the present invention includes a reactor including an aqueous electrolyte solution in which at least one of carbon dioxide and nitrate is dissolved, first and second electrodes in which at least one portion of the electrolyte solution is immersed, and the surface of the first electrode. A metal nanocluster catalyst adsorbed on the surface of the coated carbon support, and a power supply for applying electrical signals to the first and second electrodes so that carbon dioxide and nitrate are co-reduced to generate urea. do.

A method of manufacturing a metal nanocluster catalyst that has improved chemical selectivity for urea generation and improves urea generation efficiency during co-reduction of carbon dioxide and nitrate, urea synthesis method using metal nanocluster catalyst, electrochemistry using metal nanocluster catalyst A system can be provided.

Various and beneficial advantages and effects of the present invention are not limited to the above description, and will be more easily understood in the course of describing specific embodiments of the present invention.

1 is a TEM, HAADF-STEM image of a metal nanocluster catalyst according to an embodiment of the present invention.
2A to 2C are diagrams showing the molecular structural formula of an organic compound used to prepare a metal nanocluster catalyst according to an embodiment of the present invention.
3 is a schematic diagram of a urea generating electrochemical system according to an embodiment of the present invention.
4 is a graph showing X-ray photoelectron spectroscopy (XPS) results of a metal nanocluster catalyst according to an embodiment of the present invention.
5A and 5B are graphs showing the results of nuclear magnetic resonance analysis of a product synthesized by a metal nanocluster catalyst prepared according to an embodiment of the present invention.
6A and 6B are graphs showing the Faraday efficiency of a product synthesized by a metal nanocluster catalyst prepared according to an embodiment of the present invention.
7A to 8 are graphs showing changes in current density according to potential in an electrode on which a metal nanocluster catalyst is formed according to an exemplary embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

The embodiments of the present invention may be modified in various different forms or may be combined with various embodiments, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for clearer explanation, and elements indicated by the same reference numerals in the drawings are the same elements.

Metal nanocluster catalyst and its manufacturing method

A method of manufacturing a metal nanocluster catalyst and a metal nanocluster catalyst will be described with reference to FIGS. 1 to 2C.

1 shows a metal nanocluster catalyst according to an embodiment of the present invention.

2A to 2C show molecular structural formulas of an organic compound used as a binder when preparing a metal nanocluster catalyst according to an embodiment of the present invention.

1A and 1B are TEM (Transmission Electron Microscopy) images of a metal nanocluster catalyst manufactured by a method of manufacturing a metal nanocluster catalyst according to an embodiment of the present invention. Referring to FIGS. 1A and 1B, metal nanoclusters 20 having various sizes are formed on the surface of the porous carbon support 10. The metal nanoclusters 20 appear relatively dark compared to the porous carbon support 10. Here, the metal nanoclusters 20 may be monodisperse particles having an average diameter of about 20 nm to about 100 nm formed by aggregation of copper atoms, for example. However, the technical idea of the present invention is not limited thereto, and the types of metals forming the metal nanoclusters 20 may vary, and may also have a form such as a nanotube, a nanofiber, or a nanowire other than a cluster form. . The metal nanocluster 20 can be stably formed on the surface of the carbon support by a binder to be described later, for example, NTB (tris(2-benzimidazolylmethyl) amine), and forms a plurality of active sites. can do.

1C is a HAADF-STEM (High-Angle Annular Dark Field Scanning Transmission Electron Microscopy) image of a metal nanocluster catalyst according to an embodiment of the present invention. Referring to (c) of FIG. 1, the form in which the metal nanoclusters 20 are distributed on the surface of the carbon support 10 is shown in more detail. In the HADDF-STEM image, the greater the difference in element number, the clearer the difference in contrast appears, and those shown in black correspond to carbon atoms, and those shown in white correspond to copper atoms. Copper atoms appear in the form of white spots, and a number of copper atoms aggregate to form nanoclusters and are adsorbed on the surface of the carbon support. These nanoclusters of copper atoms can be stably formed on the carbon support by NTB or the like used as a binder to be described later.

Next, a method of manufacturing the metal nanocluster catalyst of FIG. 1 will be described.

A method of preparing a metal nanocluster catalyst according to an embodiment of the present invention includes (1) dispersing a carbon support, Nafion, and a binder in a solvent to form a carbon support-binder structure, (2) a carbon support -Coating a binder structure on a conductive substrate, and (3) forming a metal nanocluster by coating a solution containing transition metal ions on the carbon support-binder structure. Hereinafter, each step will be described in detail.

(1) A carbon support, Nafion, and a binder are dispersed in a solvent to form a carbon support-binder structure.

(1-1) A first solution in which a carbon support is dispersed in a solvent with Nafion is prepared.

The carbon support may be provided as a support to increase the surface area participating in the reaction. For example, the carbon support is graphitized mesoporous carbon (GMC), carbon black, acetylene black, carbon nanotubes, graphite, graphene, graphite nanofibers It may include at least one of, and fullerene. In one embodiment, when the carbon support includes GMC, the carbon support has a high porosity and specific surface area, so that the exposure of the catalytic active site is maximized, and when used as a catalyst, an active dynamic reaction may be possible. In particular, when the carbon support includes GMC, a π-π interaction is possible, so that a binder to be described later can efficiently bond on the surface of the carbon support through a π-π interaction with a carbon atom. Here, "π-π interaction" may refer to an attractive force that interacts between a compound forming a resonance structure, for example, a compound including an aromatic ring. Grapheneized porous carbon delocalized by pi (π) bonds spanning several carbon atoms can form a resonance structure. Accordingly, graphene-formed porous carbon may interact with each other by π-π interaction with a binder including a compound having an aromatic ring.

Nafion can be used to prepare a catalyst ink by dispersing a carbon support in an organic solvent. Nafion can be mixed in an organic solvent with a carbon support.

The solvent may be an alcohol-based organic solvent. For example, the solvent may include at least one of methanol, ethanol, isopropyl alcohol, butyl alcohol, and isobutyl alcohol.

In the process of dispersing the carbon support in the organic solvent, stirring or sonication may be performed to uniformly disperse the carbon support in the organic solvent.

(1-2) A second solution is prepared by adding a binder solution to the first solution. The second solution includes a carbon support-binder structure formed by bonding a carbon support to a binder.

The binder may be an organic compound containing both an aromatic ring and an amine functional group. For example, referring to FIGS. 2A to 2C, the binder is tris(2-benzimidazolylmethyl ) amine), tris(2-pyridylmethyl) amine (TPA) of FIG. 2B, and tris(2-quinolylmethyl) amine (TQA) of FIG. 2C. However, the binder used in the manufacture of the metal nanocluster of the present invention is not limited to the organic compounds shown in FIGS. 2A to 2C. In an exemplary embodiment, the binder may be an organic compound having a structure including at least 3 or more aromatic rings and at least 3 or more nitrogen atoms (N). When the carbon support contains GMC and the binder contains NTB, several carbon atoms of GMC form a resonance structure with delocalized pi bonds, and can strongly interact with NTB containing aromatic rings due to π-π interaction have. NTB is adsorbed on the surface of the carbon support by the π-π interaction to form a carbon support-binder structure in a thermodynamic equilibrium state. In addition, since NTB contains amine functional groups capable of binding with transition metal ions, transition metal particles can be stabilized so that the transition metal can be uniformly adsorbed on the surface of the carbon support.

(2) A carbon support-binder structure can be coated on a conductive substrate.

(2-1) The second solution containing the carbon support-binder structure is centrifuged, washed with an alcohol-based organic solvent such as ethanol, and dried to collect the carbon support-binder structure. The carbon support-binder structure may be collected in the form of a powder.

(2-2) After dispersing the carbon support-binder structure again in a solvent to make ink, it is coated on a conductive substrate in the form of a catalyst ink.

The conductive substrate may include at least one of carbon paper, metal plate, and stainless steel. The conductive substrate may be a substrate for applying a catalyst to a surface, and may be used as an electrode in an electrochemical system.

The carbon support-binder structure may be dispersed in a solvent to make ink, and then coated on the surface of a conductive substrate in the form of a catalyst ink, and then dried.

In the process of dispersing the carbon support-binder structure again in the solvent, the carbon conductor may be additionally dispersed together. The carbon conductor may be a material added to prepare the carbon support-binder structure as an ink-type catalyst, and may include a material added to facilitate the transfer of electrons from the electrode of the electrochemical system to the catalyst. In an exemplary embodiment, the mass ratio of the carbon conductor and catalyst may be from about 0.1:1 to about 1:1.

(3) A solution containing transition metal ions is coated on the carbon support-binder structure to form metal nanoclusters.

A solution including transition metal ions may be coated on the surface of the carbon support-binder structure coated on the conductive substrate. The transition metal may be, for example, copper, and the solution including copper ions may be, for example, a solution including copper nitrate (Cu(N0 ₃ ) ₂ ). Copper atoms may be adsorbed on the surface of the carbon support-binder structure to form nanoclusters. The binder allows copper atoms to be uniformly and stably adsorbed on the surface of the carbon support-binder structure.

However, the method of manufacturing a metal nanocluster according to an embodiment of the present invention is not limited thereto, and unlike the above, a solution including a transition metal ion may be directly added to the second solution including the carbon support-binder structure. have. Even in this case, metal nanoclusters may be formed on the carbon support-binder structure to prepare a metal nanocluster catalyst.

Urea synthesis method and urea synthesis electrochemical system through co-reduction of carbon dioxide and nitrate

The method for synthesizing urea through conjugation of carbon dioxide and nitrate according to an embodiment of the present invention includes the steps of (1) dispersing a carbon support, Nafion, and a binder in a solvent to form a carbon support-binder structure, ( 2) coating a carbon support-binder structure on a conductive substrate, (3) coating a solution containing transition metal ions on the carbon support-binder structure to form metal nanoclusters, (4) the copper nanoclusters Coating a catalyst on the surface of the first electrode, (5) preparing a reactor for accommodating the first electrode, the second electrode, and an aqueous electrolyte solution in which carbon dioxide and nitrate are dissolved, and (6) electrical It may include the step of co-reducing carbon dioxide and nitrate dissolved in the aqueous electrolyte solution by applying a signal. Steps (1) to (3) are steps according to the method of manufacturing the metal nanocluster catalyst described above, and thus redundant descriptions will be omitted.

The step (4) is a step of coating the prepared metal nanocluster catalyst on the surface of an electrode for a urea generating electrochemical system. Specifically, the metal nanocluster catalyst may be collected in the form of a powder, dispersed in an alcohol-based solvent containing Nafion, and then coated on the electrode by, for example, a drop-casting method. The solvent may be a solvent for dispersing the metal nanocluster catalyst and fixing it to the electrode.

In the step (5), the first electrode coated with the metal nanocluster catalyst as described above is prepared in a reactor containing an aqueous electrolyte solution in which carbon dioxide and nitrate are dissolved together with the second electrode to construct an electrochemical system for urea generation. It is a step to do. The electrochemical system will be described in detail with reference to FIG. 3.

3 is a schematic diagram of an electrochemical system system according to an embodiment of the present invention.

Referring to FIG. 3, the electrochemical system 100 includes a reactor 110, an aqueous electrolyte solution 120, a first electrode 130, a second electrode 140, an exchange membrane 150, and A power supply unit 160 and a carbon dioxide supply unit 170 may be included. The first and second electrodes 130 and 140 may be connected by the power supply unit 160. In addition, according to embodiments, the electrochemical system 100 may further include a reference electrode connected to the power supply unit 160 and a product collection unit.

The electrochemical system 100 may be a system for generating a product including urea by co-reducing carbon dioxide and nitrate in the aqueous electrolyte solution 120. In addition to urea, the product may further contain hydrogen, oxygen, and ammonia. Confirmation of urea generation and urea conversion rate will be described again with reference to FIGS. 5A to 7B.

The reactor 110 may be made of a material capable of accommodating the aqueous electrolyte solution 120. The reactor 110 may be made of, for example, pyrex, acrylic, polyvinyl chloride (PVC), or the like. The reactor 110 may have a closed structure, and may control the gas atmosphere inside the electrochemical system 100 with argon (Ar) or carbon dioxide.

The aqueous electrolyte solution 120 is accommodated in the reactor 110 and may serve as a source of carbon dioxide and nitrate nitrate. The electrolyte aqueous solution 120 is a compound containing nitrate in distilled water in which carbon dioxide is dissolved, for example, potassium nitrate (KNO ₃ ), nitric acid (HNO ₃ ), sodium nitrate (NaNO ₃ ), and calcium nitrate (Ca (NO _It may be a solution further including at least one of 3) _2). Electrolyte solution 120 is NO ₃ ^- may include at least one ^{_{of, NH 2 OH -, NO 2}} . In addition, the electrolyte aqueous solution 120 may be a solution further including at least one of potassium chloride (KCl), potassium hydrogen carbonate (KHCO ₃ ), carbonic acid (H ₂ CO ₃ ), and sodium hydrogen carbonate (NaHCO _{3 ).} The electrolyte aqueous solution 120 may preferably be a solution containing _{potassium nitrate (KNO 3} ), potassium chloride (KCl), and potassium hydrogen carbonate (KHCO _{3 ).} The aqueous electrolyte solution 120 may be supplied by bubbling carbon dioxide by a carbon dioxide supply unit 170 to be described later, and the aqueous electrolyte solution 120 may be a solution maintaining a saturated state of carbon dioxide by the carbon dioxide supply unit 170. have.

Part or all of the first and second electrodes 130 and 140 may be immersed in the aqueous electrolyte solution 120. The first electrode 130 may be a working electrode, and the second electrode 140 may be a counter electrode. Each of the first and second electrodes 130 and 140 may be made of a semiconductor material or a conductive material. For example, the first and second electrodes 130 and 140 are aluminum (Al), gold (Au), silver (Ag), carbon (C), cadmium (Cd), cobalt (Co), chromium (Cr) , At least one of nickel (Ni), copper (Cu), mercury (Hg), platinum (Pt), tin (Sn), zinc (Zn), iron (Fe), and alloys thereof, or stainless steel It may include. The first electrode 130 may be a reduction electrode, and the second electrode 140 may be an oxidation electrode.

The first electrode 130 may be prepared by the process of steps (1) to (3) of the manufacturing method of the metal nanocluster catalyst described above. Accordingly, a catalyst layer 135 including a metal nanocluster of the present invention may be positioned on at least one surface of the first electrode 130. For example, in one embodiment, the first electrode 130 may be formed of a carbon plate, and the catalyst layer 135 may be a layer coated with a carbon support-binder structure in which copper (Cu) nanoclusters are adsorbed on the surface. In an exemplary embodiment, the carbon support may be GMC, and the binder may be NTB.

When a voltage is applied between the first and second electrodes 130 and 140 in the electrochemical system 100, a reaction in which urea is generated at the first electrode 130 and oxygen is generated at the second electrode 140 This will happen. The reaction in which urea is generated in the first electrode 130 is represented by the following reaction equations 1 to 3. That is, carbon dioxide and nitrate are reduced at the same time to _{generate intermediates of CO and NH 2} , respectively, and the intermediates react with each other to finally produce urea. The net reaction equation of the urea generation reaction is expressed as in Scheme 4.

[Reaction Scheme ^{_{1] CO 2 + 2H + +}} 2e - → CO ( intermediate) + H ₂ O

[Reaction Scheme _{^{2] NO 3 - + 8e -}} + 8H + → NH 2 ( intermediate) 3 + H ₂ O

[Scheme 3] CO (intermediate) + 2NH ₂ (intermediate) → NH ₂ CONH ₂

[Reaction Scheme ^{_{4] CO 2 + NO 3 -}} + 18e - + 18H + → NH 2 CONH 2 + 7H 2 O

When carbon dioxide is reduced in the reduction electrode, the types of hydrocarbons that can be produced may vary, and thus chemical selectivity for a target product may be low. In addition, when the electrochemical reduction is performed in an aqueous solution environment in the electrochemical system, the hydrogen generation reaction acts competitively, so that the production efficiency of the target product may decrease.

According to the technical idea of the present invention, by coating the catalyst layer 135 including the metal nanocluster catalyst on the first electrode 130, carbon dioxide and nitrate present in the aqueous electrolyte solution 120 are co-reduced to generate urea. Can catalyze. The catalyst layer 135 including the metal nanocluster catalyst may improve urea conversion efficiency so that the reduction reaction materials supplied from the aqueous electrolyte solution 120 can be converted to urea other than ammonia or hydrocarbon. The catalyst layer 135 may have a relatively low activity with respect to the hydrogen generation reaction, so that the hydrogen generation reaction may also be minimized. Accordingly, a catalyst having improved chemical selectivity for the urea generation reaction may be provided. Confirmation of the generation of urea and a description of the performance of the catalyst with improved chemical selectivity and urea generation efficiency for urea will be described again with reference to FIGS. 5A to 7B.

The exchange membrane 150 may be a membrane formed of an ion-permeable material by dividing the first and second electrodes 130 and 140. The exchange membrane 150 may be a cation exchange membrane or an anion exchange membrane, and the material used as the exchange membrane 150 is not particularly limited.

The power supply unit 160 may cause a co-reduction reaction of carbon dioxide and nitrate to occur by applying an electrical signal to the reactor 110. The power supply 160 may be connected to both the first and second electrodes 130 and 140, or may be connected to only a part of the first and second electrodes 130 and 140. The voltage applied by the power supply unit 160 may range from 0.2 V to 100 V, but is not limited thereto.

The reference electrode may be an electrode for measuring the electrode potential of the first and second electrodes 130 and 140, and there is no particular limitation, but may include at least one of silver chloride (AgCl), silver (Au), or an alloy thereof. have. The reference electrode may be positioned on either the cathode or the anode.

Examples of copper nanocluster catalysts and electrochemical systems including the same

An electrochemical system for producing a copper nanocluster catalyst and urea of an embodiment was prepared as follows.

About 4 mg of GMC was dispersed in about 1 mL of ethanol with Nafion solution (about 20 μL, 2.5 wt%). The ethanol solution in which GMC was dissolved was subjected to sonication for about 5 minutes so that GMC was uniformly dispersed in ethanol. Next, a solution in which about 2 mg of NTB was dissolved in about 0.5 mL of ethanol was prepared, and it was added to the ethanol solution in which GMC was dissolved. The mixed solution was stirred for about 6 hours so that NTB was adsorbed on the GMC surface to reach an equilibrium state. In this process, the NTB is uniformly adsorbed on the surface of the GMC particles due to the π-π interaction, and the GMC-NTB structure is formed. Next, the mixed solution containing the GMC-NTB structure was centrifuged, and unadsorbed NTB was removed using about 1 mL of ethanol, and dried at a temperature of about 60 °C for about 1 hour to obtain GMC-NTB powder. Got it. About 2 mg of GMC-NTB powder was re-dispersed in about 0.5 mL of ethanol to make ink. As an electrode, carbon paper was prepared, and GMC-NTB catalyst ink was drop-casted on the carbon paper and dried. The active area of the electrode is about 0.25 cm ² , and the coated amount of the GMC-NTB catalyst ink is about 60 μl. Next, after preparing a copper nitrate (Cu(NO ₃ )) aqueous solution, the copper nitrate aqueous solution was similarly drop-casted onto the GMC-NTB catalyst ink, and then dried. The concentration of the aqueous copper nitrate solution is about 10 mg per mL of the solution, and the amount coated with the aqueous copper nitrate solution is about 40 μl. In this process, the amine group of NTB causes copper ions to be stably adsorbed on the GMC surface to form nanoclusters. A GMC-NTB-Cu catalyst may be formed on carbon paper, where Cu may be a nanocluster in which copper atoms are formed in the form of monodisperse particles. Next, the carbon paper on which the catalyst was formed was immersed in water for about 30 seconds to remove copper nitrate not formed by the GMC-NTB-Cu catalyst. Accordingly, a carbon paper electrode coated with a GMC-NTB-Cu catalyst can be prepared.

Using the electrode coated with the GMC-NTB-Cu catalyst as a working electrode, a platinum plate as a counter electrode, an Ag/AgCl electrode as a reference electrode, and an aqueous electrolyte solution containing _{0.1 M KNO 3 saturated with carbon dioxide gas.} A three-electrode system was prepared. Using X-ray photoelectron spectroscopy, the metal nanoclusters were qualitatively analyzed. Using the cyclic current voltage method, it was repeated 10 times at a scan rate of 0.01 mV/s between 0 V and -1.5 V compared to the reference electrode. Current was measured over time at each fixed potential, and the generation of urea was confirmed using nuclear magnetic resonance analysis, and the product was quantified.

4 is a graph showing XPS results of a metal nanocluster catalyst as an embodiment of the present invention. The metal of the metal nanocluster catalyst may be copper.

Referring to FIG. 4, the oxidation state of copper in the copper nanocluster catalyst can be seen from two peaks of XPS for the 2p orbital of the copper element. The 2p _1/2 orbital peaked at 952.8 eV binding energy and the 2p _3/2 orbital peaked at 933.3 eV binding energy.As a result of the 2p _3/2 orbital peak, it was found that the oxidation number of copper in the copper nanocluster catalyst was zero. I can. That is, the copper atom of the copper nanocluster catalyst exists as a copper metal rather than an oxide form. As will be described later, it is understood that the improvement in performance of the copper nanocluster catalyst as a catalyst is because copper atoms present in the copper nanocluster catalyst exist as copper metal particles, not in the form of copper oxide.

5A and 5B show the results of nuclear magnetic resonance spectroscopy (NMR) analysis of a product produced in a reduction electrode coated with a metal nanocluster catalyst according to an embodiment of the present invention. This is a result of confirming whether or not urea is generated by the metal nanocluster catalyst of the present invention.

Referring to FIGS. 5A and 5B, it is confirmed that the product produced in the reduction electrode contains urea. 5A is a result of nuclear magnetic resonance spectroscopy using hydrogen, and FIG. 5B is a result of nuclear magnetic resonance spectroscopy using ^{N 13.} It can be understood that carbon dioxide and nitrate present in the aqueous electrolyte solution are co-reduced to synthesize urea. In this process, it can be interpreted that the copper nanoclusters coated on the surface of the reduction electrode acted as a catalyst.

6A and 6B are graphs showing Faraday efficiency of a product produced in a reduction electrode coated with a metal nanocluster catalyst according to an embodiment of the present invention.

6A shows a comparison of the Faradaic efficiency of a metal nanocluster catalyst according to an embodiment of the present invention and the Faraday efficiency of a commercially available copper substrate (Cu plate).

Referring to FIG. 6A, as a result of analyzing Faraday efficiency at various potentials, compared to comparison, in the case of the embodiment, copper than the copper substrate for all voltages from -0.3 potential (V vs RHE) to -1.1 potential (V vs RHE). In the case of the nanocluster catalyst, the Faraday efficiency was high. That is, in the case of the embodiment, it can be seen that the ratio of elements is relatively increased in all the measured potential regions. In particular, at a potential of -0.8 V to -0.7 V, the conversion rate of urea formed by co-reduction of carbon dioxide and nitrate using a copper nanocluster catalyst was found to be about 82.7%.

According to these results, it can be seen that in the case of using the metal nanocluster catalyst of the present invention, urea generation efficiency and chemical selectivity can be improved compared to simply producing urea using a copper substrate. This is due to the active points on the surface of the copper nanoclusters uniformly distributed in the form of monodisperse particles of the porous carbon support by the porous carbon support, the binder of NTB bound to the porous carbon support, and the binder in the above description with reference to FIG. 3 I can understand.

Referring to FIG. 6B, as a result of analyzing the Faraday efficiency at various potentials, it is possible to confirm the respective ratios of urea, ammonia, and hydrogen in the product. The Faraday efficiency of urea and ammonia is plotted for each potential based on 100%, and the Faraday efficiency of hydrogen is a value obtained by subtracting the sum of the Faraday efficiency of urea and ammonia from 100%. In particular, at a potential of -0.8 V to -0.7 V, it can be seen that the conversion rate of the urea formed by the co-reduction of carbon dioxide and nitrate using the copper nanocluster catalyst has a Faraday efficiency of approximately 85% as a maximum value.

According to these results, it can be seen that when the metal nanocluster catalyst of the present invention is used, urea generation efficiency and chemical selectivity can be improved. This is due to the active points on the surface of the copper nanoclusters uniformly distributed in the form of monodisperse particles of the porous carbon support by the porous carbon support, the binder of NTB bound to the porous carbon support, and the binder in the above description with reference to FIG. I can understand.

7A to 8 show results of a cyclic voltammetry performed to analyze an electrochemical reaction occurring in a reduction electrode having a metal nanocluster catalyst formed thereon according to an embodiment of the present invention.

7A shows the results of cyclic voltammetry when the metal nanocluster catalyst according to an embodiment of the present invention is coated on a reduction electrode and the inside of the reactor is controlled in a gas atmosphere of _{argon (Ar) or carbon dioxide (CO 2 ), respectively.} Show. NTB of Fig. 2A was used as a binder.

Referring to FIG. 7A, when a negative voltage is applied to the cathode at the same scan rate, a change in current density as the voltage increases can be confirmed. It can be seen that the magnitude of the current density relative to the same voltage, that is, the absolute value, increased when the reactor was controlled by a carbon dioxide gas atmosphere than when the inside of the reactor was controlled by a gas atmosphere of argon (Ar). That is, when the inside of the reactor is in a carbon dioxide gas atmosphere, it can be seen that carbon dioxide participated in the urea generation reaction as carbon dioxide, which is the reactant of Scheme 4, was supplied.

Figure 7b shows the results of the cyclic voltammetry when the metal nanocluster catalyst according to an embodiment of the present invention is coated on the reduction electrode and the inside of the reactor _{is controlled in a gas atmosphere of argon (Ar) or carbon dioxide (CO 2 ).} Show. TPA of Fig. 2b was used as a binder.

Referring to FIG. 7B, when a negative voltage is applied to the cathode at the same scan rate, a change in current density as the voltage increases can be confirmed. As described above with reference to FIG. 7A, it was found that the magnitude of the current density relative to the same voltage, that is, the absolute value, increased when the reactor was controlled by a carbon dioxide gas atmosphere than when the inside of the reactor was controlled by a gas atmosphere of argon (Ar). I can. On the other hand, compared with FIG. 7A, it can be seen that a relatively high voltage is required to generate the element. It seems that the degree of π-π interaction with the carbon support of the organic compound used as a binder and the number of amine functional groups influenced the formation of metal nanoclusters.

Figure 7c is a comparative example for the present invention, when Phen (Phenanthroline) is used as a binder, and the inside of the reactor _{is controlled in a gas atmosphere of argon (Ar) or carbon dioxide (CO 2} ), respectively, the results of cyclic voltammetry. Show.

Referring to FIG. 7C, unlike the description described above with reference to FIGS. 7A and 7B, it can be seen that the results of the cyclic voltammetry method are almost the same even when the gas atmosphere is changed. In view of this, when Phen is used as a binder, it can be understood that the urea synthesis reaction through the co-reduction of carbon dioxide and nitrate did not proceed. Therefore, it is interpreted that only some organic compounds as a binder play a role of stably forming metal nanoclusters on the surface of the carbon support.

8 shows the results of the cyclic voltammetry when the metal nanocluster catalyst according to an embodiment of the present invention is coated on a reduction electrode and the nitrate concentration of an aqueous electrolyte solution is changed.

Referring to FIG. 8, when a negative voltage is applied to the cathode, it can be seen that the magnitude of the current density, that is, the absolute value, increases as the concentration of nitrate increases. When nitrate is not included in the electrolyte solution and only carbon dioxide is saturated, the magnitude of the current density does not increase. On the other hand, it can be seen that the magnitude of the current density increases as the concentration of nitrate in the aqueous electrolyte solution increases from about 10 mM to about 500 mM. As the reactant of Scheme 4, carbon dioxide and nitrate were reduced together.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited by the appended claims. Therefore, various types of substitutions, modifications, and changes will be possible by those of ordinary skill in the art within the scope not departing from the technical spirit of the present invention described in the claims, and this also belongs to the scope of the present invention. something to do.

100: electrochemical system
110: reactor
120: aqueous electrolyte solution
130: first electrode
135: catalyst layer
140: second electrode
150: exchange membrane
160: power supply
170: carbon dioxide supply unit

Claims (10)

A reactor containing an aqueous electrolyte solution in which carbon dioxide and nitrate are dissolved;
First and second electrodes at least partially immersed in the aqueous electrolyte solution;
A catalyst comprising metal nanoclusters adsorbed on the surface of the carbon support coated on the surface of the first electrode; And
An electrochemical system comprising a power supply for applying electrical signals to the first and second electrodes so that carbon dioxide and nitrate are co-reduced to generate urea.
The method of claim 1,
The metal nanoclusters are adsorbed on the surface of the carbon support by a binder.
The method of claim 2,
The binder is an electrochemical system comprising an organic compound having a structure comprising at least three or more aromatic rings and at least three or more nitrogen atoms (N).
The method of claim 3,
The binder is an electrochemical system comprising at least one of tris(2-benzimidazolylmethyl) amine, tris(2-pyridylmethyl) amine, and tris(2-quinolylmethyl) amine.
The method of claim 1,
The carbon support includes graphitized porous carbon (GMC),
An electrochemical system in which the average diameter of the metal nanoclusters is in the range of 20 nm to 100 nm.
The method of claim 1,
Carbon dioxide is saturated in the aqueous electrolyte solution,
The electrolyte solution is _{^{NO 3 -, NO 2 -,}} NH 2 The electrochemical system includes at least one of OH.
Graphitized porous carbon (GMC);
A binder bonded to the graphene-formed porous carbon through π-π interaction; And
Including copper nanoclusters adsorbed on the surface of the graphene-formed porous carbon by the binder,
The binder is a metal nanocluster catalyst comprising an organic compound having a structure including at least 3 or more aromatic rings and at least 3 or more nitrogen atoms.
Dispersing a carbon support, Nafion, and a binder in a solvent to form a carbon support-binder structure;
Coating the carbon support-binder structure on a conductive substrate; And
A method for producing a metal nanocluster catalyst comprising the step of forming a metal nanocluster by coating a solution containing a transition metal ion on the carbon support-binder structure.
The method of claim 8,
The carbon support is graphene-formed porous carbon (GMC),
The transition metal is copper (Cu), a method of manufacturing a metal nanocluster catalyst.
The method of claim 8,
The binder is tris(2-benzimidazolylmethyl) amine, tris(2-pyridylmethyl) amine, and tris(2-quinolylmethyl) amine.

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