KR20210034348A - 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 cell. The carbon dioxide electroreduction method comprises the following steps of: a) supplying water or electrolyte to an anode area; b) supplying humidified carbon dioxide gas under the condition that relative humidity is greater than 100% by supplying humidified carbon dioxide gas to a composite cathode area containing any one or two or more catalyst particles selected from the group consisting of carbonic anhydrase (CA) immobilized on a porous carbon support, indium (In), tin (Sn), lead (Pb), mercury (Hg), palladium (Pd), bismuth (Bi), antimony (Sb), nickel (Ni), thallium (Tl), and metal oxides thereof; and c) forming hydrogen ion (H+) in the anode area by applying voltage between the anode area and the composite cathode area, and generating reduction product of carbon dioxide by electroreduction of carbon dioxide gas by allowing the hydrogen ion (H+) to pass through an electrolyte membrane and move to the composite cathode area.

Description

[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 has caused various environmental problems due to global warming, and the treatment and reduction of carbon dioxide is in a national urgent situation. Therefore, it is important to invent and develop improved methods of reducing the amount of carbon dioxide released into the atmosphere.

Currently, researches on carbon dioxide reduction methods according to photochemical, biochemical, or electrochemical methods are being actively conducted, and among them, efforts to utilize carbon dioxide through electrochemical reduction have been continued for a long time. Since the reduction of carbon dioxide through the electrochemical method receives electricity from the outside, the device structure is simpler than other methods. Therefore, if only electricity is connected, it is easy to configure the device through modularization, so it has the advantage that it is less subject to spatial and climatic constraints than other methods.

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

Thus, although FIG going research to promote the reduction reaction of carbon dioxide using a variety of metal catalysts, the rate limiting step of CO ₂ in the CO shift reaction ^- There is the reaction rate is still too slow because of the problem goes through the resulting reaction.

Accordingly, there is a need to develop a method for reducing carbon dioxide having high Faraday efficiency and excellent reaction efficiency while being able to overcome the problem of low solubility of carbon dioxide.

KR 10-2013-0112037 A (2013.10.11)

It is an object of the present invention to provide a method and apparatus for producing a reduction product of carbon dioxide at a high reaction rate by energy-efficient electro-reduction of carbon dioxide without limitation of reactant concentration due to low solubility of carbon dioxide.

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

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

a) supplying water or an 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), By supplying a humidified carbon dioxide gas to a composite cathode region containing one or two or more catalyst particles selected from the group consisting of antimony (Sb), nickel (Ni), thallium (Tl), and metal oxides thereof. Supplying the humidified carbon dioxide gas under conditions in which the relative humidity exceeds 100%; And

c) A voltage is applied between the anode area and the complex cathode area ^{to form hydrogen ions (H +} ) in the anode area, and the hydrogen ions (H ⁺ ) pass through the electrolyte membrane and move to the complex cathode area to generate carbon dioxide. It includes; electro-reducing the gas to produce a reduction product of carbon dioxide.

In an embodiment according to the present invention, the porous carbon support may include carbon nanotubes.

In an embodiment according to the present invention, the porous carbon support includes macropores, the carbonic anhydrase is immobilized inside the macropores of the porous carbon support, and the catalyst particles are contained within the porous carbon support. Can be.

In one embodiment according to the present invention, the carbonic anhydrase may be immobilized from 20 to 5000 IU based on 100 parts by weight of the porous carbon support.

In an 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 an embodiment according to the present invention, the immobilization is performed by oxidizing the porous carbon support; Modifying the oxidized porous carbon support with an -NH ₂ substituent; And immobilizing carbonic anhydrase on the modified porous carbon support.

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

In an 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 an embodiment according to the present invention, T1 may be 10 to 100°C, and T2 may be 10 to 40°C.

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

In one 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 contain 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 an 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, alkyl ammonium 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,

An anode;

A cathode disposed 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 an electrolyte solution to the anode region,

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

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

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

The carbon dioxide electro-reduction method according to the present invention has the advantage of being able to overcome the problem of low carbon dioxide solubility caused by a liquid-phase reduction reaction and to efficiently produce a carbon dioxide reduction product at a 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 products 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 of producing a reduced product by the carbon dioxide electro-reduction method according to the present invention.
2 is a diagram showing the structure of a membrane-electrode assembly according to an embodiment of the present invention.
3 is a diagram showing a result of measuring Faraday efficiency and current density in a formic acid generation process according to an embodiment of the present invention.
4 is a diagram showing a result of measuring Faraday efficiency and current density in a process of generating formic acid according to an embodiment and a comparative example of the present invention.

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

In addition, the singular form used in the present specification may be intended to include the plural form unless otherwise indicated in the context.

In addition, the units used in the present specification are based on weight, for example, the unit of% or ratio means weight% or weight ratio, and the weight% means any one component of the total composition unless otherwise defined. It means the weight percent occupied in the composition.

In addition, the numerical range used in the present specification is the lower limit and the upper limit and all values within the range, increments that are logically derived from the shape and width of the defined range, all of the limited values, and the upper limit of the numerical range limited to 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.

In the present specification, the term'include' is an open type description having a meaning equivalent to expressions such as'include','include','have' or'as a feature', and elements not listed further, It does not exclude materials or processes.

In addition, the term'substantially' in this specification means that other elements, materials, or processes that are 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 is meant to be present in an amount or degree that does not have a significant effect.

The present invention comprises the steps of: a) supplying water or an 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), By supplying a humidified carbon dioxide gas to a composite cathode region containing one or two or more catalyst particles selected from the group consisting of antimony (Sb), nickel (Ni), thallium (Tl), and metal oxides thereof. Supplying the humidified carbon dioxide gas under conditions in which the relative humidity exceeds 100%; And c) applying a voltage between the anode area and the composite cathode area ^{to form hydrogen ions (H +} ) in the anode area, and the hydrogen ions (H ⁺ ) pass through the electrolyte membrane and move to the complex cathode area. It provides a method for electro-reduction of carbon dioxide comprising; generating a reduction product of carbon dioxide by electro-reducing 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 decreases, resulting in a decrease in productivity, as well as problems such as a low concentration of the reduction product. In the case of a reduction reaction, there is a problem that the Faraday efficiency is low and requires a lot of energy. However, as described above, the electro-reduction method of carbon dioxide according to the present invention has no constraints due to the low solubility of carbon dioxide, and energy-efficient carbon dioxide reduction products can be produced with high reaction speed and efficiency even though carbon dioxide is in the gaseous phase. There is an advantage.

In the present invention, as shown in FIG. 1, water or an electrolyte is supplied to the anode area, and humidified carbon dioxide gas is supplied to the complex cathode area, and the compound is combined with the anode area under the condition that the relative humidity exceeds 100%. A voltage is applied between the cathode regions to cause a reduction reaction of carbon dioxide gas. Specifically, the present invention is characterized by using a composite cathode comprising carbonic anhydrase and catalyst particles immobilized on a porous carbon support in step b), and supplying humidified carbon dioxide gas to the composite cathode region. . Here, carbonic anhydrase refers to an enzyme that catalyzes the hydration reaction of carbon dioxide as a metal enzyme containing zinc inside. Specifically, the carbonic anhydrase can hydrate 10 ⁵ to 10 ⁶ carbon dioxide per second in the composite cathode and supply it as a reactant to the metal and metal oxide catalysts, thereby further improving the reaction speed in addition to the advantages of the gas phase reaction. have. The electric reduction method of carbon dioxide according to the present invention includes the above two characteristics at the same time, so that carbon dioxide dissolved in the water film formed by condensation 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, it is possible to use carbon dioxide as a reactant as efficiently as possible through a high contact rate with carbonic anhydrase and catalyst particles included in the composite cathode, thereby solving the problems of the existing carbon dioxide liquid phase or gas phase-based reduction reaction. can do. Furthermore, due to the high contact rate with carbonic anhydrase and the catalyst particles, the reaction rate and efficiency can also be remarkably increased.

Specifically, the porous carbon support includes macropores, as shown in FIG. 1, the carbonic anhydrase is immobilized inside the macropores of the porous carbon support, and the catalyst particles are included in the porous carbon support. I 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 One or more can be selected from the group consisting of (Carbon felt), but is not limited thereto.

As another specific example, the porous carbon support may include carbon nanotubes. Specifically, when the porous carbon support is a carbon nanonub, the carbonic anhydrase is immobilized on the surface of the carbon nanotubes, and the carbon nanotubes to which the carbonic anhydrase is immobilized may exist in a complex state with the catalyst particles. have. In other words, by using a porous carbon support including 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 rather than side reactions such as hydrogen generation reaction. In addition to significantly increasing the concentration, it is possible to prepare a carbon dioxide reduction product having a high concentration of 10,000 ppm to 100,000 ppm.

The carbonic anhydrase may be immobilized from 20 to 5000 IU, preferably from 100 to 5000 IU, more preferably from 500 to 5000 IU, based on 100 parts by weight of the porous carbon support. Here, IU refers to the amount of enzyme needed for carbonic anhydrase to reduce 1 μmol of carbon dioxide per minute at 30°C. By immobilizing carbonic anhydrase in the above range on a porous carbon support, the activity of the enzyme can be exhibited as much as possible, while simultaneously acting 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 enzymes. 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 and the reaction according to the following reaction scheme, the rate limiting step of CO ₂ according to reaction ⁽¹⁾ goes through the resulting reaction. In the CO ₂ ^- generation step, since the forward ^{reaction constant is only 6.2 X 10 -2} s ^-1 (25°C), there is a problem in that the rate of generation of the reduced carbon dioxide product is very slow. However, as described above, by immobilizing carbonic anhydrase on a porous carbon support, the rate controlling step can be omitted, thereby forming a carbon dioxide product at a faster rate, and furthermore, by simultaneously binding with the catalyst particles, the reaction rate And it can exhibit a synergistic effect in terms of reaction efficiency.

^{_{(1) CO 2 + e -}} → CO 2 -

^{_{(2) CO 2 - + H}} + + e - → HCOO -

^{(3) HCOO - + H +} → HCOOH

Immobilization of carbonic anhydrase according to the present invention comprises the steps of oxidizing the porous carbon support; Modifying the oxidized porous carbon support with an -NH ₂ substituent; And immobilizing carbonic anhydrase on the modified porous carbon support. The oxidation step may be oxidized 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. The oxidized porous carbon support _{undergoes a step of modifying with an -NH 2} substituent, and then performs a step of immobilizing carbonic anhydrase, 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 C1-C20 alkylene or a divalent linking group of arylene) can be coupled to a porous carbon support. In addition, 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. For the coupling reaction, a coupling agent such as N,N'-dicyclohexylcarbodiimide (N,N'-dicyclohexylcarbodiimide; DCC) may be used, but is not limited thereto.

Finally, by mixing the modified porous carbon support with carbonic anhydrase, the carbonic anhydrase may 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 then washed with distilled water. And drying at room temperature may be further performed. Depending on the immobilization step, the substituents on the porous carbon support may be fixed by covalent bonds with carbonic anhydrase, and due to strong binding force, there is little outflow of carbonic anhydrase, and the rigidity of the enzyme due to multiple bonds This increases, so 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, the activation energy required for the reduction of carbon dioxide can be significantly lowered, as well as the loss of the immobilized carbonic anhydrase can be prevented. You will be able to participate in the reaction efficiently.

The temperature (T1) of the humidified carbon dioxide gas may be higher than the temperature (T2) of the composite cathode region, and specifically, the T1 is 10 to 150°C, preferably 25 to 130°C, more preferably 35 to 100°C. The T2 may be 10 to 100°C, preferably 10 to 80°C, and more preferably 10 to 40°C. In the above range, the relative humidity of the composite cathode region may exceed 100%, and specifically indicates 150% to 200%, so that water in which carbon dioxide is dissolved is condensed on the surface of the composite cathode to form a water film. As a result, the dissolved carbon dioxide is used as a reactant to cause a reduction reaction, so that a reduction reaction of carbon dioxide can be caused with excellent Faraday efficiency in an environment substantially similar to that of a liquid phase reduction reaction.

Specifically, the reduction product of carbon dioxide according to the method for reducing carbon dioxide of the present invention may be generated with a Faraday efficiency of 80% or more, preferably 82% to 90%. Here, the Faraday efficiency may mean the efficiency at which charges are transferred in the system performing the electrochemical reaction, and is generally referred to as Faradaic yield, Coulombic efficiency, or Current efficiency. The Faraday efficiency can be obtained by comparing the stoichiometric amount of the starting material converted into a product by the applied current with the actual measured product amount. In the present invention, the Faraday efficiency is the conversion of carbon dioxide to the carbon dioxide reduction product due to the applied current. It can mean efficiency. That is, even though the carbon dioxide supplied in the present invention is in the gaseous phase, it shows an advantage of exhibiting a Faraday efficiency of 80% or more, which was only possible in a 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- 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, alkyl ammonium cation, halide ion, alkyl amine, borate, carbonate, guanidinium derivative, nitrite, nitrate, phosphate, polyphosphate, perchlorate, It may be an aqueous solution containing 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, more preferably 0.2 to 0.8 M, and in the above range, the oxidation-reduction reaction of the anode region and the composite cathode region is formed. can do.

The present invention also includes an anode; A cathode disposed 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 supplying water or an electrolyte to the anode region, wherein the cathode includes a composite cathode according to an embodiment of the present invention.

Specifically, the electrochemical cell includes a membrane-electrode assembly including an anode and a composite cathode disposed opposite to each other, and an electrolyte membrane disposed between the anode and the composite cathode, as shown in FIG. 2. . In the anode, water is oxidized to generate oxygen, hydrogen ions, and electrons, and the generated hydrogen ions move electrons through an electrolyte membrane to the composite cathode through an external circuit. In the composite cathode, electrons and hydrogen ions moving 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 Al, 1-propanol, propionic acid, and may include any one or two or more selected from the group consisting of a mixture thereof.

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

In addition, the electrolyte membrane may be a cation exchange membrane or an anion exchange membrane, and specifically, a cation exchange membrane generally used 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, 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, ferrite steel, martensite 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 a mixture thereof may be used, and by further including the catalyst metal layer, side reactions such as hydrogen generation occurring in the carbon dioxide reduction process can be suppressed, while the reduction process of carbon dioxide can be further activated. .

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 a carbon material having electrical conductivity may be used. Specifically, carbon paper, carbon cloth, carbon felt, etc. may be used, but the present invention is not limited thereto.

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

Hereinafter, the present invention will be described in detail through examples, but these are for explaining the present invention in more detail, and the scope of the present invention is not limited by the following examples.

1. Fabrication of composite cathode

Carbon nanotubes were used as a porous carbon support, 200 ml of a mixture of sulfuric acid and phosphoric acid in a volume ratio of 9:1 was added to 10 g of the carbon nanotubes, and 30 g of potassium permanganate as an oxidizing agent was added, and then at 4°C. It was reacted 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 NH ₂ substituents were washed with water and dried at 80° C. for 5 hours.

After dispersing the carbon nanotubes modified with the -NH ₂ substituent 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 were prepared with carbonic anhydrase immobilized on the surface.

Carbon nanotubes immobilized with carbonic anhydrase by ultrasonically dispersing 40 parts by weight of tin nanoparticles based on 100 parts by weight of carbon nanotubes immobilized with carbonic anhydrase in distilled water and carbonic anhydrase-immobilized carbon nanotubes A composite structure was prepared in which a tube and tin nanoparticles were combined.

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

2. Preparation of membrane-electrode assembly

2x2 cm 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 the Nafion 115, and platinum (Pt) powder was added to alcohol together with Nafion ionomer 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, on the composite cathode, a membrane-electrode assembly having a size of 2×2 cm was prepared by using a carbon paper having a thickness of 0.3 mm as a gas diffusion layer.

3. Preparation of formic acid

The prepared membrane-electrode assembly was used to separate the anode area and the cathode area, and the chamber of the anode area was filled with an aqueous solution containing 1 M KOH (Sigma-Aldrich 99.0%), and the cathode area was humidified. Carbon dioxide was supplied at 30° C. at 180% relative humidity 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 was applied at 2.5 V to electroreduce carbon dioxide to prepare formic acid.

In Example 1, the carbonic anhydrase was carried out in the same manner as in the case of using a composite cathode electrode ^{, in which 0.002 mg/cm 2 was introduced instead of 0.01.}

In Example 1, the carbonic anhydrase was carried out in the same manner as in the case of using a composite cathode electrode in which ^{0.02 mg/cm 2 was introduced instead of 0.01.}

(Comparative Example 1)

In Example 1, the cathode was carried out in the same manner, except that tin (Sn) was used instead of the composite cathode.

(Comparative Example 2)

In the manufacturing of the membrane-electrode junction in Example 1, a gas diffusion layer was not used, and a 1 M KOH (Sigma-Aldrich 99.0%) aqueous solution was added to the cathode area instead of humidified carbon dioxide, and carbon dioxide was continuously supplied to saturate the formic acid. It was carried out in the same manner except for the one prepared.

Experimental example : Faraday Efficiency and current density measurement:

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

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

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

In addition, as can be seen in Figure 4 (b), at the voltage showing the maximum Faraday efficiency, Example 1 showed ^{a current density of 64.6 mA / cm 2} , Comparative Example 1 16.3 mA / cm ² , Comparative Example 2 9.8 mA/cm ^{2 was shown, and the maximum current density was 116.7 mA/cm 2} under the Faraday efficiency condition of 80% or more of Example 1, whereas Comparative Example 1 and Comparative Example 2 were 16.3 mA/cm ² and 9.8 mA/cm, respectively. ^It was only 2. That is, in practice, it can be seen that Example 1 may 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 (16)

a) supplying water or an 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), By supplying a humidified carbon dioxide gas to a composite cathode region containing one or two or more catalyst particles selected from the group consisting of antimony (Sb), nickel (Ni), thallium (Tl), and metal oxides thereof. Supplying the humidified carbon dioxide gas under conditions in which the relative humidity exceeds 100%; And
c) A voltage is applied between the anode area and the complex cathode area ^{to form hydrogen ions (H +} ) in the anode area, and the hydrogen ions (H ⁺ ) pass through the electrolyte membrane and move to the complex cathode area to generate carbon dioxide. Electroreduction of carbon dioxide comprising a; step of generating a reduction product of carbon dioxide by electro-reducing gas. The method of claim 1,
The method of electroreduction of carbon dioxide, wherein the porous carbon support includes carbon nanotubes. The method of claim 1,
The porous carbon support includes macropores, the carbonic anhydrase is immobilized in the macropores of the porous carbon support, and the catalyst particles are contained within the porous carbon support. The method of claim 1,
The carbonic anhydrase is an electro-reduction method of carbon dioxide immobilized from 20 to 5000 IU based on 100 parts by weight of the porous carbon support. The method of claim 1,
The weight ratio of the porous carbon support and the catalyst particles is 1:0.01 to 1:1, the carbon dioxide electroreduction method. The method of claim 1,
The immobilization is
Oxidizing the porous carbon support;
Modifying the oxidized porous carbon support with an -NH ₂ substituent; And
Electroreduction method of carbon dioxide comprising the step of immobilizing carbonic anhydrase on the modified porous carbon support. The method of claim 6,
The immobilization method of carbon dioxide is immobilized by a covalent bond between a substituent on a porous carbon support and a carbonic anhydrase. The method of 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 claim 1,
The T1 is 10 to 100 ℃, the T2 is 10 to 40 ℃ carbon dioxide electro-reduction method. The method of claim 1,
The relative humidity is 150% to 200% carbon dioxide electric reduction method. The method of claim 1,
The reduction product of carbon dioxide is a carbon dioxide electro-reduction method that is generated with a Faradaic efficiency of 80% or more. The method of 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 carbon dioxide electroreduction method comprising any one or two or more selected from the group consisting of a mixture thereof. The method of 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, alkyl ammonium cations, halide ions, alkyl amines, borates, carbonates, guanidinium derivatives, nitrites, nitrates, phosphates, polyphosphates, perchlorates, silicates, sulfates, tetraalkyl ammonium salts and these Carbon dioxide electro-reduction method that is an aqueous solution containing any one or two or more selected from the group consisting of a mixture. An anode;
A cathode disposed 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 an electrolyte solution to the anode region,
The electrochemical cell comprising the composite cathode of any one of claims 1 to 7, wherein the cathode is selected from claim 1 to claim 7. The method of claim 11,
The electrochemical cell of the composite cathode further comprises a catalyst metal layer. The method of claim 11,
The electrochemical cell of the composite cathode further comprises a gas diffusion layer.

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