KR20210088516A - Method and device for preparing reduction product of carbon dioxide - Google Patents

Abstract

The present invention relates to a carbon dioxide electroreduction method and an electrochemical battery. The carbon dioxide electroreduction method comprises the steps of: a) supplying water or electrolyte to an anode region; b) providing vaporized carbon dioxide to a carbonic anhydrase (CA) immobilized on a porous carbon support, and a composite cathode region including any one or two or more catalyst particles selected from a group consisting of indium (In), tin (Sn), lead (Pb), mercury (Hg), palladium (Pd), bismuth (Bi), antimony (Sb), nickel (Ni), thallium (Tl), and a metal oxide thereof to supply the humidified carbon dioxide gas under the condition that the relative humidity exceeds 100%; and c) applying a voltage between the anode region and the composite cathode region to form hydrogen ions (H^+) in the anode region, and generating a reduction product of carbon dioxide by electric reduction of carbon dioxide gas by moving the hydrogen ions (H^+) through an electrolyte membrane to the complex reduction electrode region. The gas phase electrical reduction reaction of carbon dioxide is carried out in the composite cathode region. The porous carbon support comprises carbon nanotubes, and the carbonic anhydrase is immobilized on a surface of the carbon nanotubes. The carbon nanotubes to which carbonic anhydrase is immobilized exist in the form of a complex complexed with catalyst particles. The present invention relates to a method for producing a reduction product of carbon dioxide at a high reaction rate by energy efficient electric reduction of carbon dioxide.

Description

Method and apparatus for preparing a reduction product from carbon dioxide {Method and device for preparing reduction product of carbon dioxide}

The present invention relates to a method and apparatus for producing a reduction product from carbon dioxide.

The rapid increase in the concentration of carbon dioxide due to the use of fossil fuels is causing various environmental problems due to global warming, and the treatment and reduction of carbon dioxide is an urgent situation in the country. Therefore, it is important to invent and develop improved methods to reduce the amount of carbon dioxide emissions into the atmosphere.

Currently, research on a carbon dioxide reduction method according to a photochemical, biochemical, or electrochemical method is being actively conducted, and among them, an effort to utilize carbon dioxide through an electrochemical reduction has been continued for a long time. The reduction of carbon dioxide through the electrochemical method has a simpler device structure than other methods because electricity is supplied from the outside. Therefore, if only electricity is connected, it is easy to configure the device through modularization, so it has the advantage of receiving less spatial and climatic restrictions than other methods.

In general, in the case of the liquid phase reduction reaction of carbon dioxide, the Faraday efficiency is 80% or more, which is higher than the gas phase reduction reaction, but since the product is mixed with the liquid electrolyte, the concentration of the reduction product is very low, at a level of several ppm, so the value as a product is low. It is very low and requires a separate separation and concentration process. In addition, the liquid-based reduction reaction has a very low solubility of carbon dioxide, and overcoming it is the biggest issue. On the other hand, the gas phase reduction reaction of carbon dioxide has a Faraday efficiency of 10% as reported so far, and requires a lot of energy due to involuntary reaction.

Accordingly, research to promote the reduction reaction of carbon dioxide using various metal catalysts is also being conducted, but there is a problem that the reaction rate is still very slow because it undergoes the _{CO 2} ^{− production reaction, which is the rate-limiting step of the carbon dioxide conversion reaction.}

Therefore, there is a need to develop a method for reducing carbon dioxide that can overcome the problem of low solubility of carbon dioxide and has high Faraday efficiency and excellent reaction efficiency.

KR 10-2013-0112037 A (2013.10.11)

An object of the present invention is to provide a method and apparatus for preparing a reduction product of carbon dioxide at a high reaction rate by energy-efficiently electric reduction of carbon dioxide without limiting the concentration of reactants due to the low solubility of carbon dioxide.

Another object of the present invention is to provide a method and apparatus for producing a reduction product of carbon dioxide at a high concentration with high Faraday efficiency by electroreduction of carbon dioxide.

The present invention provides a method for the electrical reduction of carbon dioxide,

a) supplying water or electrolyte to the anode region;

b) carbonic anhydrase (CA) immobilized on a porous carbon support, and indium (In), tin (Sn), lead (Pb), mercury (Hg), palladium (Pd), bismuth (Bi), Antimony (Sb), nickel (Ni), thallium (Tl), and by supplying humidified carbon dioxide gas to the composite cathode (Cathode) region containing any one or two or more catalyst particles selected from the group consisting of metal oxides thereof supplying the humidified carbon dioxide gas under the condition that the relative humidity exceeds 100%; and

c) By applying a voltage between the anode region and the composite cathode region, hydrogen ions (H ⁺ ) are formed in the anode region, and the hydrogen ions (H ⁺ ) pass through the electrolyte membrane and move to the complex cathode region to produce carbon dioxide Including; generating a reduction product of carbon dioxide by electroreducing the gas;

Gas-phase electrical reduction reaction of carbon dioxide is characterized in that the composite reduction electrode is carried out,

The porous carbon support includes carbon nanotubes,

The carbonic anhydrase is immobilized on the surface of the carbon nanotube,

The carbon nanotubes to which carbonic anhydrase is immobilized exist in the form of a complex complexed with catalyst particles.

In one embodiment according to the present invention, the weight ratio of the porous carbon support and the catalyst particles may be 1:0.01 to 1:1.

In one embodiment according to the present invention, the immobilization is,

oxidizing the porous carbon support;

reforming the oxidized porous carbon support with a —NH ₂ substituent; and

It may include immobilizing carbonic anhydrase on the modified porous carbon support.

In one embodiment according to the present invention, the immobilization may be immobilized by a covalent bond between a substituent on a porous carbon support and carbonic anhydrase.

In one embodiment according to the present invention, the temperature (T1) of the humidified carbon dioxide gas may be higher than the temperature (T2) of the composite cathode region.

In one embodiment according to the present invention, the T1 may be 10 to 100 ℃, the T2 may be 10 to 40 ℃.

In one embodiment according to the present invention, the relative humidity may be 150% to 200%.

In an embodiment according to the present invention, the reduction product of carbon dioxide may be generated with a Faradaic efficiency of 80% or more.

In one embodiment according to the present invention, the reduction product of carbon dioxide is formic acid, formaldehyde, formate, acetaldehyde, acetate, acetic acid, acetone, 1-butanol, 2-butanol, 2-butanone, ethanol, isopropanol, It may include any one or two or more selected from the group consisting of lactate, lactic acid, methanol, 1-propanal, 1-propanol, propionic acid, carbon monoxide, methane, ethylene, ethane, and mixtures thereof.

In one embodiment according to the present invention, the electrolyte is KHCO ₃ , K ₂ CO ₃ , KOH, KCl, KClO ₄ , K ₂ SiO ₃ , Na ₂ SO ₄ , NaNO ₃ , NaCl, NaF, NaClO ₄ , CaCl ₂ , guanidinium cation, H ⁺ cation, alkali metal cation, ammonium cation, alkylammonium cation, halide ion, alkyl amine, borate, carbonate, guanidinium derivative, nitrite, nitrate, phosphate, polyphosphate, perchlorate, It may be an aqueous solution containing any one or two or more selected from the group consisting of silicates, sulfates, tetraalkyl ammonium salts, and mixtures thereof.

The present invention also provides an electrochemical cell,

anode;

a cathode positioned opposite to the anode;

an electrolyte membrane positioned between the anode and the cathode;

a gas injection unit supplying humidified carbon dioxide to the cathode region; and

Including; a liquid injection unit for supplying water or electrolyte to the anode region;

The cathode includes a composite cathode according to an embodiment of the present invention.

In one embodiment according to the present invention, the composite reduction electrode may further include a catalyst metal layer.

In one embodiment according to the present invention, the composite cathode may further include a gas diffusion layer.

The carbon dioxide electroreduction method according to the present invention has the advantage of being able to overcome the problem of low carbon dioxide solubility caused by the liquid phase reduction reaction and also energy-efficiently producing the carbon dioxide reduction product with high reaction rate and efficiency.

The carbon dioxide electroreduction method according to the present invention also has the advantage of being able to produce a high concentration of carbon dioxide reduction product with a Faraday efficiency of 80% or more.

Even if the effects are not explicitly mentioned in the present invention, the effects described in the specification expected by the technical features of the present invention and the inherent effects thereof are treated as described in the specification of the present invention.

1 is a schematic diagram showing a method for producing a reduced product by the carbon dioxide electroreduction method according to the present invention.
2 is a view showing the structure of a membrane-electrode assembly according to an embodiment of the present invention.
3 is a view showing the Faraday efficiency and current density measurement results of the formic acid generation process according to an embodiment of the present invention.
4 is a view showing the Faraday efficiency and current density measurement results of the formic acid generation process according to an embodiment and a comparative example of the present invention.

Unless otherwise defined in technical terms and scientific terms used in this specification, those of ordinary skill in the art to which this invention belongs have the meanings commonly understood, and in the following description and accompanying drawings, the subject matter of the present invention Descriptions of known functions and configurations that may unnecessarily obscure will be omitted.

Also, the singular form used herein may be intended to include the plural form as well, unless the context specifically dictates otherwise.

In addition, in the present specification, the unit used without special mention is based on the weight, for example, the unit of % or ratio means weight % or weight ratio, and unless otherwise defined, the weight % is any one component of the entire composition. It means % by weight in the composition.

In addition, the numerical range used herein includes the lower limit and upper limit and all values within the range, increments logically derived from the form and width of the defined range, all values defined therein, and the upper limit of the numerical range defined in different forms. and all possible combinations of lower limits. Unless otherwise defined in the specification of the present invention, values outside the numerical range that may occur due to experimental errors or rounding of values are also included in the defined numerical range.

As used herein, the term 'comprising' is an open-ended description having an equivalent meaning to expressions such as 'comprising', 'containing', 'having' or 'characterized', and elements not listed further; Materials or processes are not excluded.

In addition, as used herein, the term 'substantially' means that other elements, materials, or processes not listed together with the specified element, material or process are unacceptable for at least one basic and novel technical idea of the invention. It means that it can be present in an amount or degree that does not significantly affect it.

The present invention comprises the steps of: a) supplying water or electrolyte to an anode region; b) carbonic anhydrase (CA) immobilized on a porous carbon support, and indium (In), tin (Sn), lead (Pb), mercury (Hg), palladium (Pd), bismuth (Bi), Antimony (Sb), nickel (Ni), thallium (Tl), and by supplying humidified carbon dioxide gas to the composite cathode (Cathode) region containing any one or two or more catalyst particles selected from the group consisting of metal oxides thereof supplying the humidified carbon dioxide gas under the condition that the relative humidity exceeds 100%; and c) applying a voltage between the anode region and the complex cathode region ^{to form hydrogen ions (H +} ) in the anode region, and the hydrogen ions (H ⁺ ) pass through the electrolyte membrane to move to the complex cathode region It provides an electroreduction method of carbon dioxide comprising; generating a reduction product of carbon dioxide by electroreduction of carbon dioxide gas.

As described above, in the case of a liquid-phase-based reduction reaction of carbon dioxide, as the reaction proceeds due to the low solubility of carbon dioxide as a reactant, the concentration of the reactant in the aqueous solution is lowered, so that productivity is lowered, and there are problems such as a low concentration of the reduction product, and the gas phase In the case of the reduction reaction, there is a problem that Faraday efficiency is low and a lot of energy is required. However, as described above, the electroreduction method of carbon dioxide according to the present invention does not have any restrictions due to the low solubility of carbon dioxide, and even though carbon dioxide is gaseous, it is possible to energy-efficiently produce a carbon dioxide reduction product with high reaction rate and efficiency. there are advantages to

As shown in FIG. 1, the present invention supplies water or electrolyte to the anode region, and supplies humidified carbon dioxide gas to the complex cathode region, so that the anode region and the complex under the condition that the relative humidity exceeds 100%. A reduction reaction of carbon dioxide gas may be caused by applying a voltage between the cathode regions. Specifically, the present invention uses a composite anode comprising carbonic anhydrase and catalyst particles immobilized on a porous carbon support in step b), and supplies humidified carbon dioxide gas to the complex cathode area. . Here, carbonic anhydrase refers to an enzyme that catalyzes the hydration reaction of carbon dioxide as a metal enzyme containing zinc therein. Specifically, the carbonic anhydrase hydrates 10 ⁵ to 10 ⁶ carbon dioxide per second in the complex reduction electrode and supplies it as a reactant to a metal and metal oxide catalyst, thereby further improving the reaction rate in addition to the advantages of the gas phase reaction. have. The method for electric reduction of carbon dioxide according to the present invention includes the above two features at the same time, so that carbon dioxide dissolved in a water film formed by condensing on the surface of the composite cathode can be used as a reactant, thereby maximizing the contact area between the carbon dioxide and the composite cathode. In addition, carbon dioxide as a reactant can be used as efficiently as possible through a high contact rate with carbonic anhydrase and catalyst particles included in the composite reduction electrode, thereby solving the problems of the existing carbon dioxide liquid- or gaseous-phase-based reduction reaction. can do. Furthermore, due to the high contact rate with carbonic anhydrase and catalyst particles, the reaction rate and efficiency can also be significantly increased.

Specifically, as shown in FIG. 1 , the porous carbon support includes macropores, the carbonic anhydrase is immobilized inside the macropores of the porous carbon support, and the catalyst particles are included in the porous carbon support. can The porous carbon support may be a macroporous carbon support having an average pore size of 50 nm or more, preferably 100 nm to 1 μm, and specific examples include carbon paper, carbon cloth, and carbon felt. (Carbon felt) can be selected from the group consisting of, but is not limited thereto.

As another specific example, the porous carbon support may include carbon nanotubes. Specifically, when the porous carbon support is carbon nanonubs, the carbonic anhydrase is immobilized on the surface of the carbon nanotube, and the carbon nanotube to which the carbonic anhydrase is immobilized may exist in a complexed state with the catalyst particles. have. That is, by using the porous carbon support containing carbonic anhydrase and catalyst particles in the above two forms as a composite reduction electrode, the supplied electric energy can be used for the reduction reaction of carbon dioxide, not for side reactions such as hydrogen production reaction, so that the reaction efficiency In addition to significantly increasing the , it is possible to prepare a high concentration carbon dioxide reduction product of 10,000 ppm to 100,000 ppm.

The carbonic anhydrase may be immobilized with respect to 100 parts by weight of the porous carbon support, 20 to 5000 IU, preferably 100 to 5000 IU, more preferably 500 to 5000 IU. Here, IU refers to the amount of enzyme carbonic anhydrase required to reduce 1 μmol of carbon dioxide per minute at 30°C. By immobilizing carbonic anhydrase on the porous carbon support in the above range, the activity of the enzyme can be maximized, and while acting simultaneously with the catalyst particles, it is possible to efficiently produce a carbon dioxide reduction product at a high concentration, as well as an excess of the enzyme It can also prevent the problem of reaction degradation caused by Further, the rate determining step of the reduction reaction of the carbon dioxide CO ₂ ^- because the reduced product without going through the resulting reaction can be generated, it is possible to significantly increase the reaction rate and efficiency.

In general, the reduction reaction of carbon dioxide reacts according to the following reaction formula, and undergoes _{a rate-limiting step, CO 2} ^{− production reaction according to Reaction Formula (1).} The CO ₂ ^-. Because the generating step forward reaction constant of only ^{6.2 Ⅹ10 -2 s -1 (25 ℃} , there are the production rate is very slow, the problem of discrete ring carbon reduction product, however, and the carbon anhydrase as described above By immobilizing on the porous carbon support, the rate-limiting step can be omitted, and the carbon dioxide product can be formed at a faster rate, and further, by simultaneously binding with the catalyst particles, a synergistic effect can be shown in terms of reaction rate and reaction efficiency .

(1) CO ₂ + e ^- →CO ₂ ^-

(2) CO ₂ ^- + H ⁺ + e ^- →HCOO ^-

(3) HCOO ^- + H ⁺ →HCOOH

The immobilization of carbonic anhydrase according to the present invention comprises the steps of oxidizing a porous carbon support; reforming the oxidized porous carbon support with a —NH ₂ substituent; and immobilizing carbonic anhydrase on the modified porous carbon support. The oxidation step may be performed using an oxidizing agent such as potassium permanganate, or any one or more acids selected from phosphoric acid, sulfuric acid and nitric acid, but is not limited thereto. After the oxidized porous carbon support is _{modified with a -NH 2} substituent, an immobilization step of carbonic anhydrase is performed, and a known amination step may be used without limitation. For example, RL-NH2 (R is NH2-, NCO-, SH- or OH-, and L is a divalent linking group of C1-C20 alkylene or arylene) can be coupled to a porous carbon support. And, the surface of the oxidized porous carbon support and the compound may be bonded through an ester bond, a urethane bond, an amide bond, or a urea bond. A coupling agent such as N,N'-dicyclohexylcarbodiimide (N,N'-dicyclohexylcarbodiimide; DCC) may be used for the coupling reaction, but is not limited thereto.

Finally, by mixing the modified porous carbon support with carbonic anhydrase, the carbonic anhydrase can be immobilized on the surface of the porous carbon support or inside the macropores. At this time, it can be carried out by stirring at 20 to 25° C. for 1 to 10 hours, preferably 1 to 6 hours, and the resulting carbonic anhydrase-immobilized porous carbon support is separated using a filtration device and washed with distilled water. and drying at room temperature may be further performed. According to the immobilization step, the substituent on the porous carbon support can be fixed by a covalent bond with carbonic anhydrase, and there is almost no leakage of carbonic anhydrase due to strong binding force, and the rigidity of the enzyme by multiple bonds As this increases, stability can be improved.

In addition, the weight ratio of the porous carbon support and the catalyst particles may be 1: 0.01 to 1:1, preferably 1: 0.2 to 1: 0.5, more preferably 1: 0.3 to 1: 0.5. By including the catalyst particles in the above range, it is possible not only to significantly lower the activation energy required for the reduction of carbon dioxide, but also to prevent the loss of the immobilized carbonic anhydrase, so that both the catalyst particles and carbonic anhydrase are on the surface of the composite reduction electrode. can participate effectively in the reaction.

The temperature (T1) of the humidified carbon dioxide gas may be higher than the temperature (T2) of the composite cathode region, specifically, the T1 is 10 to 150 ℃ preferably 25 to 130 ℃ 35 to 100 ℃ more preferably The T2 may be 10 to 100 ℃, preferably 10 to 80 ℃, more preferably 10 to 40 ℃. In the above range, the relative humidity of the composite cathode region may exceed 100%, and specifically, by representing 150% to 200%, moisture in which carbon dioxide is dissolved is condensed on the surface of the composite cathode to form a water film, , it is possible to cause a reduction reaction with carbon dioxide dissolved therein as a reactant to cause a reduction reaction of carbon dioxide with excellent Faraday efficiency in an environment substantially similar to a liquid-phase-based reduction reaction.

Specifically, the reduction product of carbon dioxide according to the electroreduction method of carbon dioxide of the present invention can be produced with a Faraday efficiency of 80% or more, preferably 82% to 90%. Here, the Faraday efficiency may refer to the efficiency at which charges are transferred in a system performing an electrochemical reaction, and is generally referred to as a Faradaic yield, a Coulombic efficiency, or a current efficiency. The Faraday efficiency can be obtained by comparing the stoichiometric amount of the starting material to the product by the applied current with the actually measured amount of the product, and in the present invention, the Faraday efficiency is the amount of carbon dioxide converted into a carbon dioxide reduction product due to the applied current. It can mean efficiency. That is, despite the fact that the carbon dioxide supplied in the present invention is in a gaseous phase, it shows the advantage of being able to exhibit a Faraday efficiency of 80% or more, which was possible only in the liquid carbon dioxide reduction reaction.

The reduction product of carbon dioxide may be produced in various ways depending on the number of electrons and hydrogen ions participating in the reaction, and specifically, formic acid, formaldehyde, formate, acetaldehyde, acetate, acetic acid, acetone, 1-butanol, 2- It may include any one or two or more selected from the group consisting of butanol, 2-butanone, ethanol, isopropanol, lactate, lactic acid, methanol, 1-propanal, 1-propanol, propionic acid, and mixtures thereof.

In addition, the electrolyte supplied to the anode region is KHCO ₃ , K ₂ CO ₃ , KOH, KCl, KClO ₄ , K ₂ SiO ₃ , Na ₂ SO ₄ , NaNO ₃ , NaCl, NaF, NaClO ₄ , CaCl ₂ , guanidinium cation, H ⁺ cation, alkali metal cation, ammonium cation, alkylammonium cation, halide ion, alkyl amine, borate, carbonate, guanidinium derivative, nitrite, nitrate, phosphate, polyphosphate, perchlorate, It may be an aqueous solution containing any one or two or more selected from the group consisting of silicates, sulfates, tetraalkyl ammonium salts, and mixtures thereof. Specifically, the electrolyte may have a concentration of 0.1 to 2 M, preferably 0.1 to 1 M, and more preferably 0.2 to 0.8 M, forming an equilibrium of the oxidation-reduction reaction of the anode region and the composite cathode region in the above range. can do.

The present invention also relates to an anode; a cathode positioned opposite to the anode; an electrolyte membrane positioned between the anode and the cathode; a gas injection unit supplying humidified carbon dioxide to the cathode region; and a liquid injection unit for supplying water or electrolyte to the anode region, wherein the cathode provides an electrochemical battery comprising a composite cathode according to an embodiment of the present invention.

Specifically, as shown in FIG. 2, the electrochemical cell includes a membrane-electrode assembly including an anode and a composite cathode positioned opposite to each other, and an electrolyte membrane positioned between the anode and the composite cathode. . In the anode, water is oxidized to generate oxygen, hydrogen ions and electrons, and the generated hydrogen ions move electrons through the electrolyte membrane to the composite cathode along an external circuit. In the composite anode, electrons and hydrogen ions moved from the anode meet with carbon dioxide to cause a reduction reaction, and various reduction products are generated depending on the number of electrons and hydrogen ions participating in the reaction. Specifically, the reduction product is formic acid, formaldehyde, formate, acetaldehyde, acetate, acetic acid, acetone, 1-butanol, 2-butanol, 2-butanone, ethanol, isopropanol, lactate, lactic acid, methanol, 1-propane It may include any one or two or more selected from the group consisting of al, 1-propanol, propionic acid, and mixtures thereof.

The anode may be used without limitation as long as it is typically used as a cathode material of an electrochemical reduction device, and preferably, it may be durable to oxide, specifically platinum (Pt), stainless steel, nickel (Ni) , gold (Au) and silver (Ag) may be at least one selected from the group consisting of, but is not limited thereto.

In addition, the electrolyte membrane may use a cation exchange membrane or an anion exchange membrane, and specifically, a cation exchange membrane such as Nafion 115 or Nafion 117 may be used, but is not limited thereto.

The composite cathode may further include a catalyst metal layer, and specifically, Sn, Sn alloy, Al, Au, Ag, C, Cd, Co, Cr, Cu, Cu alloy, Ga, Hg, In, Mo, Nb , Ni, NiCo2O4, Ni alloy, Ni-Fe alloy, Pb, Rh, Ti, V, W, Zn, elgiloy, nichrome, austenitic steel, duplex steel, ferritic steel, martensitic steel, stainless steel , modified doped p-Si, modified doped p-Si:As, modified doped p-Si:B, modified doped n-Si, modified doped n-Si:As, and modified doped n-Si: Any one or more selected from the group consisting of B and mixtures thereof can be used, and by further including the catalyst metal layer, the reduction process of carbon dioxide can be further activated while suppressing side reactions such as generation of hydrogen generated in the carbon dioxide reduction process. .

The composite cathode may further include a gas diffusion layer. The gas diffusion layer may serve as a passage through which the humidified carbon dioxide supplied from the gas injection unit can be uniformly supplied to the composite cathode region, and an electrically conductive carbon material may be used. Specifically, carbon paper (Carbon paper), carbon cloth (Carbon cloth), carbon felt (Carbon felt), etc. may be used, but is not limited thereto.

The electrochemical cell according to the present invention includes: a liquid chamber connected to a liquid injection unit for supplying water or an electrolyte to the anode region of the above-described membrane-electrode assembly, in which oxidation reaction occurs; and a humidifier or atomizer connected to the gas injection unit for supplying humidified carbon dioxide to the composite anode area and supplying humidified carbon dioxide to the complex cathode area. In addition, it is combined with the anode and the composite cathode, may further include an energy source capable of applying a voltage, the voltage is 1.2 V to 4 V, preferably a voltage of 1.3 to 3.5 V can be applied .

Hereinafter, the present invention will be described in detail by way of Examples, but these are for describing the present invention in more detail, and the scope of the present invention is not limited by the Examples below.

1. Preparation of composite cathode

A carbon nanotube was used as a porous carbon support, and 200 ml of a mixture of sulfuric acid and phosphoric acid in a 9:1 volume ratio was added to 10 g of the carbon nanotube, and 30 g of potassium permanganate as an oxidizing agent was added, and then at 4°C. The reaction was carried out for 24 hours. After completion of the reaction, the surface-oxidized carbon nanotubes were washed with water and dried at 80° C. for 5 hours.

After adding 60 ml of 3-aminopropyl-triethoxysilane (3-APTES) to the surface-oxidized carbon nanotube, it was completely sealed and reacted at 50° C. for 24 hours. After the reaction type, - The carbon nanotubes modified with the NH ₂ substituent were washed with water and dried at 80° C. for 5 hours.

The carbon nanotubes modified with the -NH ₂ substituent were dispersed in 100 mM sodium phosphate buffer solution (pH 7), carbonic anhydrase was added at a concentration of 3 mg/ml, and then stirred at 25° C. for 2 hours or more. Carbon nanotubes immobilized on the surface of carbonic anhydrase were prepared.

Based on 100 parts by weight of the carbon nanotube to which the carbonic anhydrase is immobilized and the carbon nanotube to which the carbonic anhydrase is immobilized, 40 parts by weight of tin nanoparticles are dispersed in distilled water with ultrasonic waves to thereby immobilize the carbon nanotube to which carbonic anhydrase is immobilized. A composite having a structure in which a tube and tin nanoparticles were complexed was prepared.

Next, tin nanoparticles were spray-coated on the surface of the cathode side of Nafion 115 (DuPont) having a size of 2Xcm ^{at 1.8 mg per cm 2 ,} and then the prepared complex was coated thereon to produce carbonic anhydrase 0.01 mg/cm ² and A composite cathode into which tin (Sn) 0.2 mg/cm ^{2 was introduced was prepared.}

2. Preparation of membrane-electrode assembly

2Xcm Ni mesh (100 mesh, Alfa Aesar) was used as an anode on the opposite side of the composite cathode prepared on the cathode side of Nafion 115, and platinum (Pt) powder was mixed with Nafion ionomer in alcohol as an anode catalyst. A catalyst solution was prepared by dispersing, and 0.5 mg/cm ^{2 was} spray-coated on the surface of the anode side of Nafion 115. Next, a membrane-electrode assembly having a size of 2Xcm was prepared on the composite cathode by using carbon paper with a thickness of 0.3 mm as a gas diffusion layer.

3. Preparation of formic acid

The anode region and the cathode region were separated using the prepared membrane-electrode assembly, and an aqueous solution containing 1 M KOH (Sigma-Aldrich 99.0 %) was filled in the chamber of the anode region, and the cathode region was humidified. Carbon dioxide was supplied at 30° C. at a relative humidity of 180% and a flow rate of 50 sccm. In order to maintain the relative humidity of the carbon dioxide, water vapor ^{was continuously supplied at 15 mg/cm 2} ·min and a voltage of 2.5 V was applied to electrically reduce carbon dioxide to prepare formic acid.

In Example 1, carbonic anhydrase was replaced with 0.01 instead of 0.002 mg/cm ^{2 The} same procedure was performed except that a composite reduction electrode introduced was used.

In Example 1, instead of 0.01 carbonic anhydrase, 0.02 mg/cm ^{2 The} same procedure was performed except that a composite reduction electrode introduced was used.

(Comparative Example 1)

The cathode in Example 1 was performed in the same manner except that tin (Sn) was used instead of the composite cathode.

(Comparative Example 2)

When manufacturing the membrane-electrode junction in Example 1, without using a gas diffusion layer, 1 M KOH (Sigma-Aldrich 99.0 %) aqueous solution was filled in the cathode region instead of humidified carbon dioxide, and carbon dioxide was continuously supplied to saturate the formic acid. The same procedure was performed except for the preparation.

Experimental Example: Faraday Efficiency and Current Density Measurement:

The performance of producing formic acid by electrochemical reduction of carbon dioxide according to Examples 1 to 3 and Comparative Examples 1 to 2 was evaluated, and the results are shown in FIGS. 3 and 4 .

Figure 3 (a) is a Faraday efficiency measurement result of the formic acid production process according to Examples 1 to 3, (b) is a view showing the current density measurement result. As can be seen in Fig. 3 (a), it can be confirmed that the formic acid prepared by the electroreduction method according to the present invention exhibits a Faraday efficiency of 80% or more in a wide voltage range even though the reactant is a gas phase. In addition, as can be seen in Fig. 3 (b), it can be seen that the formic acid prepared by the electric reduction method according to the present invention also increases the current density as the voltage increases, which indicates a fast reaction rate of formic acid production.

4 (a) is a Faraday efficiency measurement result of the formic acid production process according to Example 1 and Comparative Examples 1 and 2, (b) is a view showing the current density measurement result. As can be seen in Figure 4 (a), Example 1 shows a Faraday efficiency of 80% or more in a much wider voltage range compared to Comparative Examples 1 and 2, and shows a Faraday efficiency of up to 91.5%, whereas Comparative Example 1 has a narrow voltage range showed a maximum Faraday efficiency of 80.6%, and it can be seen that Comparative Example 2 exhibited a maximum Faraday efficiency of 66% in a narrower voltage range than Comparative Example 1.

Also, as can be seen in Figure 4 (b), at the voltage showing the maximum Faraday efficiency, Example 1 shows ^{a current density of 64.6 mA / cm 2} Comparative Example 1 16.3 mA / cm ² , Comparative Example 2 is 9.8 on the other hand showed a mA / cm ^2, more than 80% of the example 1 in the Faraday efficiency condition showing a maximum current density of 116.7 mA / cm ^2, Comparative examples 1 and 2 are respectively 16.3 mA / cm ² and 9.8 mA / cm was only ^2. That is, in fact, it can be seen that Example 1 can exhibit a reaction rate that is at least 7 times faster than Comparative Examples 1 and 2 under 80% or more Faraday efficiency conditions.

Claims (13)

a) supplying water or electrolyte to the anode region;
b) carbonic anhydrase (CA) immobilized on a porous carbon support, and indium (In), tin (Sn), lead (Pb), mercury (Hg), palladium (Pd), bismuth (Bi), Antimony (Sb), nickel (Ni), thallium (Tl), and by supplying humidified carbon dioxide gas to the composite cathode (Cathode) region containing any one or two or more catalyst particles selected from the group consisting of metal oxides thereof supplying the humidified carbon dioxide gas under the condition that the relative humidity exceeds 100%; and
c) By applying a voltage between the anode region and the composite cathode region, hydrogen ions (H ⁺ ) are formed in the anode region, and the hydrogen ions (H ⁺ ) pass through the electrolyte membrane and move to the complex cathode region to produce carbon dioxide Including; generating a reduction product of carbon dioxide by electroreducing the gas;
Gas-phase electrical reduction reaction of carbon dioxide is characterized in that the composite reduction electrode is carried out,
The porous carbon support includes carbon nanotubes,
The carbonic anhydrase is immobilized on the surface of the carbon nanotube,
The carbon nanotube to which carbonic anhydrase is immobilized is present in the form of a complex complexed with catalyst particles, the method for electroreduction of carbon dioxide According to claim 1,
The weight ratio of the porous carbon support and the catalyst particles is 1:0.01 to 1:1, the electroreduction method of carbon dioxide. According to claim 1,
The immobilization is
oxidizing the porous carbon support;
reforming the oxidized porous carbon support with a —NH ₂ substituent; and
An electroreduction method of carbon dioxide, comprising the step of immobilizing carbonic anhydrase on the modified porous carbon support. 4. The method of claim 3,
Wherein the immobilization is fixed by a covalent bond between a substituent on a porous carbon support and carbonic anhydrase. According to claim 1,
The temperature (T1) of the humidified carbon dioxide gas is higher than the temperature (T2) of the composite cathode region, the method of electrical reduction of carbon dioxide. 6. The method of claim 5,
The T1 is 10 to 100 ℃, the T2 is 10 to 40 ℃, the electroreduction method of carbon dioxide. According to claim 1,
The relative humidity is 150% to 200%, the electric reduction method of carbon dioxide. According to claim 1,
The reduction product of carbon dioxide is produced with a Faradaic efficiency of 80% or more, the method for the electric reduction of carbon dioxide. According to claim 1,
The reduction product of carbon dioxide is formic acid, formaldehyde, formate, acetaldehyde, acetate, acetic acid, acetone, 1-butanol, 2-butanol, 2-butanone, ethanol, isopropanol, lactate, lactic acid, methanol, 1-propane Al, 1-propanol, propionic acid, carbon monoxide, methane, ethylene, ethane and any one or two or more selected from the group consisting of mixtures thereof, the method for the electroreduction of carbon dioxide. According to claim 1,
The electrolyte is KHCO ₃ , K ₂ CO ₃ , KOH, KCl, KClO ₄ , K ₂ SiO ₃ , Na ₂ SO ₄ , NaNO ₃ , NaCl, NaF, NaClO ₄ , CaCl ₂ , guanidinium cation, H ⁺ cation, Alkali metal cations, ammonium cations, alkylammonium cations, halide ions, alkyl amines, borates, carbonates, guanidinium derivatives, nitrites, nitrates, phosphates, polyphosphates, perchlorates, silicates, sulfates, tetraalkyl ammonium salts and their salts An aqueous solution comprising any one or two or more selected from the group consisting of a mixture, an electroreduction method of carbon dioxide. anode;
a cathode positioned opposite to the anode;
an electrolyte membrane positioned between the anode and the cathode;
a gas injection unit supplying humidified carbon dioxide to the cathode region; and
Including; a liquid injection unit for supplying water or electrolyte to the anode region;
The cathode is an electrochemical cell comprising the compound cathode of any one of claims 1 to 4. 12. The method of claim 11,
The composite cathode further comprises a catalyst metal layer, electrochemical cell. 12. The method of claim 11,
The composite cathode further comprises a gas diffusion layer, electrochemical cell.

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