electrolyzer

Abstract

The present invention relates to an electrolysis device comprising: an electrolysis cell including a gas diffusion layer, a cathode, a cation separator, an anode, and an electrolyte; and a storage tank connected to an outlet flow path outside the electrolysis cell that discharges a product from the cathode, wherein the acidic solution contained in the storage tank and the electrolyte contained in the electrolysis cell are the same type of solution.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0077537, filed on June 16, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an electrolyzer that electrochemically reduces carbon dioxide. [Background technology]

[0003] Carbon dioxide is a greenhouse gas that contributes to global warming and must be reduced. Methods for reducing carbon dioxide emissions include capture, chemical conversion, and electrochemical conversion. Electrochemical conversion, among others, allows for precise control of the components to produce other synthetic gases, which offers greater economic benefits than simply removing carbon dioxide. Carbon dioxide can also be electrolyzed with water to produce carbon monoxide, ethylene, methane, formic acid, formate salts, various hydrocarbons, and organic compounds such as aldehydes or alcohols.

[0004] The process of electrochemically decomposing carbon dioxide is similar to that of water electrolysis, but since the activity of the electrochemical reaction increases in a strongly alkaline atmosphere, a certain concentration of KOH aqueous solution is generally used as the electrolyte. When water is supplied to the anode and an electric current is applied, the water is decomposed into hydrogen ions and electrons, generating oxygen gas. The electrons move to the cathode via an external conductor, and the hydrogen ions move to the cathode via an ion-selective separator. At this time, the transferred electrons react with the carbon dioxide and water supplied to the cathode to produce carbon monoxide and hydroxide ions (OH - ) and the hydroxide ions generated are transported to the anode via hydrogen ions (H +) to produce water, resulting in an electrically neutral state. Through the above process, the electrochemical decomposition reaction of carbon dioxide is completed. At this time, the water supplied along with carbon dioxide reacts with the electrons transferred separately from the carbon monoxide production reaction, and is electrolyzed to produce hydrogen gas and hydroxide ions at the same time. This reaction between water and electrons can be said to be in a competitive relationship with the carbon monoxide production reaction. Because the reaction is an electrochemical reaction, the amount of carbon monoxide produced and the hydrogen / carbon dioxide ratio can be easily adjusted by adjusting the voltage.

[0005] On the other hand, conventional electrolyzers produce OH at the cathode as a side reaction during the electrolysis of carbon dioxide. - is generated, and the OH - reacts further with the supplied carbon dioxide to form carbonate (HCO3 - Therefore, conventional electrolyzers have a problem in that the supplied carbon dioxide is not converted into the desired product but instead produces carbonates, resulting in a loss of carbon dioxide. Furthermore, conventional electrolyzers have a problem in that the carbonates pass through the anion exchange membrane and diffuse to the anode, where they are oxidized to produce carbon dioxide, thereby reducing the efficiency of the electrolysis. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] KR10-2018-0133688A Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide an electrolyzer that can prevent the loss of carbon dioxide converted into carbonate by further separating carbon dioxide from carbonate generated by a side reaction during the electrolysis of carbon dioxide, thereby improving the yield of the product, and that can operate for a long period of time by adjusting the overall ion balance of the electrolyzer. [Means for solving the problem]

[0008] The present invention provides an electrolysis device.

[0009] (1) The present invention provides an electrolysis device comprising: an electrolysis cell including a gas diffusion layer, a cathode, a cation separator, an anode, and an electrolyte; and a storage tank connected to an outlet flow path outside the electrolysis cell that discharges a product from the cathode, wherein the acidic solution contained in the storage tank and the electrolyte contained in the electrolysis cell are the same type of solution.

[0010] (2) The present invention provides an electrolysis apparatus according to (1) above, wherein the acidic solution comprises an aqueous solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, acetic acid, citric acid, and oxalic acid; and a salt containing one or more selected from the group consisting of cesium, potassium, and sodium.

[0011] (3) The present invention provides the electrolysis apparatus according to (2) above, wherein the salt comprises one or more selected from the group consisting of Cs2CO3, CsHCO3, Cs2SO4, CsCl, CsNO3, K2CO3, KHCO3, K2SO4, K3PO4, KCl, KNO3, Na2CO3, NaHCO3, Na2SO4, Na3PO4, NaCl, and NaNO3.

[0012] (4) The present invention provides an electrolysis device according to any one of (1) to (3), wherein the storage tank includes an acidic solution storage section and an electrolyte storage section connected thereto, and the electrolyte storage section is connected to the anode by a solution exchange flow path.

[0013] (5) The present invention provides the electrolysis device according to (4), wherein the solution exchange flow path includes a first solution exchange flow path that transports an acidic solution from the electrolyte storage section to the anode, and a second solution exchange flow path that transports the electrolyte from the anode to the electrolyte storage section.

[0014] (6) The present invention provides the electrolyzer according to any one of (1) to (5), wherein the electrolytic cell is a zero-gap membrane electrode assembly cell in which the gas diffusion layer, the cathode, the separator, and an anode having an anode fluid flow path formed therein are stacked in this order.

[0015] (7) The present invention provides an electrolysis device according to any one of (1) to (6), wherein a product produced by the electrolysis reaction at the cathode is transferred to the storage tank via the discharge flow path, and the product includes carbon monoxide, water vapor, and salt.

[0016] (8) The present invention provides the electrolysis device according to (7) above, wherein carbon dioxide produced from the salt in the storage tank is supplied to the electrolysis cell.

[0017] (9) The present invention provides the electrolyzer according to (7) or (8) above, wherein the salt is a carbonate.

[0018] (10) The present invention provides the electrolyzer according to any one of (1) to (9), wherein the electrolyzer electrolyzes carbon dioxide.

[0019] (11) The present invention provides the electrolyzer according to (10) above, wherein the carbon dioxide is supplied to the electrolytic cell in a state containing water vapor.

[0020] (12) The present invention provides the electrolyzer according to any one of (1) to (11), wherein the electrolyzer electrolyzes carbon dioxide to produce one or more compounds selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols. [Effects of the Invention]

[0021] The electrolysis device of the present invention can prevent the loss of carbon dioxide by connecting a storage tank containing an acidic solution to an electrolysis cell and separating carbon dioxide from salts produced by side reactions.

[0022] Furthermore, the electrolyzer of the present invention can improve the efficiency of carbon dioxide electrolysis by reducing the loss of carbon dioxide, thereby increasing the yield of the product.

[0023] Furthermore, the electrolysis device of the present invention uses the same solution for the electrolyte in the electrolysis cell and the acidic solution in the storage tank, and transfers or circulates the solutions between them via a flow path connecting the electrolysis cell and the storage tank. This prevents pH changes in the storage tank and the electrolyte, and continuously replenishes cations to the electrolyte, maintaining ion balance and enabling the electrolysis device to operate for a long period of time. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram of a carbon dioxide electrolysis device according to the present invention. [Figure 2] 1 is a schematic diagram of a conventional carbon dioxide electrolysis device. [Figure 3] Graph (a) shows the change in pH of the electrolyte over time for Example 1, Comparative Example 1, and Comparative Example 3, and graph (b) shows the change in pH of the electrolyte over time for Example 2, Comparative Example 2, and Comparative Example 4. [Figure 4] Graph (a) shows the change in ionic conductivity of the electrolyte over time for Example 1, Comparative Example 1, and Comparative Example 3, and graph (b) shows the change in ionic conductivity of the electrolyte over time for Example 2, Comparative Example 2, and Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be described in more detail below for better understanding of the present invention. In this regard, the terms and words used in the specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical concept of the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0026] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0027] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0028] The present invention provides an electrolysis device comprising an electrolysis cell including a gas diffusion layer, a cathode 13, a cation separator 15, an anode 11, and an electrolyte; and a storage tank 2 connected to the outside of the electrolysis cell and to a discharge flow path 30 for discharging a product from the cathode, wherein the acidic solution contained in the storage tank 2 and the electrolyte are the same type of solution.

[0029] According to one embodiment of the present invention, the electrolyzer can be used in any electrochemical conversion field, and the electrolyzer can be a device capable of producing useful chemicals through electrochemical conversion, such as carbon dioxide electrolysis or water electrolysis, and a device capable of reducing and converting carbon dioxide and NOx. Specifically, the electrolyzer can be an electrochemical conversion device that converts carbon dioxide into carbon monoxide and ethylene.

[0030] In the conventional electrolysis cell having a structure in which an electrolyte flows in front of a cathode, as explained in the background art above, OH generated by a side reaction during the reduction process of carbon dioxide is - reacts further with carbon dioxide to form carbonate (HCO3 - ), resulting in a loss of carbon dioxide. While this problem could be solved by passing an acidic electrolyte over the front of the cathode, this solution introduced an additional problem: the acidic electrolyte increased resistance, causing an increase in voltage during operation of the conventional electrolysis cell. Furthermore, an anion exchange membrane was typically used as the separator in conventional electrolysis cells. While anion exchange membranes offer fast ion transfer and excellent carbon dioxide conversion efficiency, they have very low mechanical strength. Furthermore, the carbonates diffuse through the anion exchange membrane to the anode, where they are oxidized to produce carbon dioxide, reducing the efficiency of the electrolysis. Therefore, the inventors of the present invention developed an electrolysis device that can reduce the loss of supplied carbon dioxide by separating carbon dioxide from the carbonates without diffusing the produced carbonates to the anode.

[0031] According to one embodiment of the present invention, the electrolyzer according to the present invention includes an electrolytic cell and a storage tank 2 connected to an outlet flow path 30 outside the electrolytic cell. The electrolytic cell includes a cathode 13 and an anode 11, a gas diffusion layer disposed in close contact with the cathode 13, and a separator 15 and an electrolyte disposed between the cathode 13 and the anode 11. The separator 15 is a cation exchange membrane, and when the separator 15 is a cation exchange membrane, the generated carbonate can be prevented from being transported to the anode 11.

[0032] According to one embodiment of the present invention, the cathode 13 is connected to a supply channel through which a reactant is supplied and a discharge channel 30 through which a product generated after electrolysis is discharged. The reactant may be carbon dioxide. The carbon dioxide is in a gaseous state and may contain water vapor at about 40 to 60°C. The product is generated by electrolyzing the carbon dioxide and may be one or more selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols. Unreacted carbon dioxide, the water vapor, and carbonates generated by side reactions may also be discharged from the discharge channel 30 along with the product.

[0033] The storage tank 2 may be disposed outside the electrolysis cell and connected to the discharge channel 30. The storage tank 2 may contain an acidic solution. The acidic solution may include an aqueous solution containing at least one selected from the group consisting of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, acetic acid, citric acid, and oxalic acid; and a salt containing at least one selected from the group consisting of cesium, potassium, and sodium. For example, the acidic solution may be a mixed solution containing sulfuric acid (H2SO4) and cesium sulfate (Cs2SO4). The salt may include at least one selected from the group consisting of Cs2CO3, CsHCO3, Cs2SO4, CsCl, CsNO3, K2CO3, KHCO3, K2SO4, K3PO4, KCl, KNO3, Na2CO3, NaHCO3, Na2SO4, Na3PO4, NaCl, and NaNO3. The acidic solution filled in the storage tank 2 may further separate carbon dioxide from the carbonate. That is, the acidic solution reacts with the produced carbonate to produce carbon dioxide, and specifically, hydrogen ions (H + ) and carbonate (HCO3 - ) can react to produce water and carbon dioxide.

[0034] According to one embodiment of the present invention, the acidic solution may be the same type of solution as the electrolyte, and in this case, the acidic solution and the electrolyte may be a mixed solution containing, for example, sulfuric acid (HSO) and cesium sulfate (CsSO).

[0035] FIG. 2 is a schematic diagram of a conventional carbon dioxide electrolyzer. Referring to FIG. 2, the conventional carbon dioxide electrolyzer connects a discharge channel 30-1 of a cathode 13-1 to an acidic solution storage tank 20-1. While water and carbon dioxide can be separated from the carbonate using the acidic solution in the acidic solution storage tank 20-1, the acidic solution is continuously consumed, making it difficult for the reaction between the carbonate and hydrogen ions in the acidic solution to proceed over a long period of time. As a result, it is difficult to continuously operate the electrolysis while maintaining high electrolysis efficiency. Therefore, in the present invention, the acidic solution and the electrolyte are the same type of solution, and a structure is formed in which the solutions circulate between each other, allowing the supply of acidic solution from the electrolyte to continuously carry out the carbonate reaction in the acidic solution storage tank.

[0036] According to one embodiment of the present invention, the storage tank 2 includes the acid solution storage unit 20 and an electrolyte storage unit 22 connected thereto. The electrolyte storage unit 22 may be connected to the anode 11 via a solution exchange flow path. The electrolyte storage unit 22 may be spaced apart from the acid solution storage unit 20 and connected thereto via a connection unit 21. Gas-phase products, such as carbon monoxide and ethylene, transferred from the cathode may be mixed with the acid solution in the storage tank 2 and may not be completely discharged to the outside, resulting in a reduced product yield. To prevent this, the electrolyzer of the present invention divides the storage tank 2 into an acid solution storage unit 20 and an electrolyte storage unit 22. The acid solution can move between the acid solution storage unit 20 and the electrolyte storage unit 22 via the connection unit 21, thereby achieving a desired product yield and allowing the acid solution to be smoothly transferred to the anode via the solution exchange flow path. The solution contained in the electrolyte solution reservoir 22 may be the same solution as the acid solution and the electrolyte solution contained in the acid solution reservoir 20 .

[0037] FIG. 1 is a schematic diagram of a carbon dioxide electrolysis device according to the present invention. Referring to FIG. 1, the acidic solution storage unit 20 is connected to the cathode 13 via a discharge flow path 30. The acidic solution storage unit 20 may be connected to and spaced from the electrolyte storage unit 22 via a connection unit 21. The electrolyte storage unit 22 may be connected to the anode 11 via a solution exchange flow path. In the acidic solution storage unit 20, carbonate transferred from the cathode 13 via the discharge flow path 30 reacts with hydrogen ions in the acidic solution. The separated carbon dioxide and unreacted carbon dioxide can then flow into the electrolysis cell via the supply flow path of the cathode 13. The product transferred from the cathode 13 to the acidic solution storage unit 20 via the discharge flow path 30 is discharged from the acidic solution storage unit 20 to the outside of the electrolysis device via a product discharge unit. At this time, the separated carbon dioxide, unreacted carbon dioxide, and products are gaseous substances that may be mixed with the acidic solution and flow into the electrolyte storage unit 22 without being discharged to the outside of the storage tank 2. To prevent this, the product discharge unit, through which the products are discharged to the outside, is set higher than the connecting unit 21, and the acidic solution is filled up to the upper side of the connecting unit 21, thereby efficiently discharging the gaseous substances to the outside. The product discharge unit serves to discharge the gaseous substances in the acidic solution storage unit 20 to the outside, and the connecting unit 21 serves to connect the acidic solution storage unit 20 and the electrolytic cell storage unit 22 and transfer the acidic solution. For example, as shown in FIG. 1, the acidic solution storage unit 20, the connecting unit 21, and the electrolyte storage unit 22 may be arranged in an "H" shape.

[0038] In addition, according to one embodiment of the present invention, the solution exchange flow path may include a first solution exchange flow path 40 that transports the acidic solution from the electrolyte storage portion 22 to the anode 11, and a second solution exchange flow path 50 that transports the electrolyte from the anode 11 to the electrolyte storage portion 22.

[0039] The acidic solution contained in the electrolytic cell reservoir 22 can be transferred to the anode 11 via the first solution exchange flow path 40. In conventional electrolyzers, as the electrolysis reaction progresses, one or more cations selected from the group consisting of cesium, potassium, and sodium contained in the electrolyte migrate to the cathode due to the voltage applied to the electrolytic cell, resulting in continuous consumption of the cations in the electrolyte. Furthermore, the concentration of hydrogen ions increases relative to the cations in the electrolyte, lowering the pH of the electrolyte. This increases the hydrogen production reaction, which competes with the carbon dioxide production reaction, and reduces the efficiency of carbon dioxide production, potentially preventing the electrolyzer from operating for a long period of time. In the electrolyzer of the present invention, the acidic solution and the electrolyte are the same type of solution, so the cations are supplied to the anode 11 via the first solution exchange flow path 40, maintaining the pH and ionic conductivity of the electrolyte at levels similar to those at the initial stage of operation, thereby enabling continuous operation of the electrolyzer.

[0040] The electrolyte may be transferred from the anode 11 to the electrolyte storage unit 22 via the second solution exchange flow path 50. As described above, the acidic solution in the acidic solution storage tank reacts with carbonate to separate carbon dioxide, which causes the acidic solution to be continuously consumed, gradually increasing the pH in the acidic solution storage tank. As a result, the acidic solution storage tank ceases to function after a certain operating time. Because the acidic solution and the electrolyte are the same type of solution, the electrolyzer of the present invention supplies the electrolyte from the anode to the electrolyte storage unit 22 via the second solution exchange flow path 50 and transfers the electrolyte from the electrolyte storage unit to the acidic solution storage unit 22, thereby maintaining the pH of the acidic solution in the storage tank 2 and enabling continuous operation. In this case, since the material transferred from the anode 11 via the second solution exchange flow path may contain not only the electrolyte but also oxygen gas generated by an oxidation reaction, the second solution exchange flow path 50 may further include a gas-liquid separator 60. The gas-liquid separator separates gaseous substances and transfers only the electrolyte.

[0041] In other words, the electrolyzer of the present invention uses the same type of solution for the electrolyte in the electrolytic cell and the acidic solution in the acidic solution storage tank, and is configured so that the solutions are transferred or circulated between them via the solution exchange flow path. This makes it possible to maintain the overall ion balance of the electrolyzer at the same level as at the beginning of operation, and to operate the electrolyzer for a long period of time without a decrease in electrolysis efficiency.

[0042] According to one embodiment of the present invention, the electrolyte contains one or more cations selected from the group consisting of cesium, potassium, and sodium (Na + , K. + , Cs + ) may be an aqueous solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, acetic acid, citric acid, and oxalic acid; and one or more selected from the group consisting of Cs2CO3, CsHCO3, Cs2SO4, CsCl, CsNO3, K2CO3, KHCO3, K2SO4, K3PO4, KCl, KNO3, Na2CO3, NaHCO3, Na2SO4, Na3PO4, NaCl, and NaNO3. Also, as described above, the electrolyte and the acid solution in the acid solution storage tank 20 may be the same type of solution.

[0043] According to an embodiment of the present invention, the separator 15 may be a cation exchange membrane, specifically, a Nafion separator 15. The cation separator 15 may serve to prevent the carbonate generated at the cathode 13 from diffusing toward the anode 11. On the other hand, if the separator 15 is an anion exchange membrane, the carbonate may diffuse toward the anode, which may impede the transport of the carbonate to the acid solution storage tank, resulting in a decrease in overall electrolysis efficiency and an increase in loss of supplied carbon dioxide.

[0044] According to one embodiment of the present invention, the electrolysis cell may be a zero-gap membrane electrode assembly cell in which the gas diffusion layer, the cathode 13, the separator 15, and the anode 11 having a liquid flow path formed therein are sequentially stacked. Specifically, the zero-gap membrane electrode assembly may be formed in the form of a very thin membrane plate in order to increase driving voltage and current efficiency.

[0045] While conventional electrolytic cells have a gap structure in which the electrodes and separator are spaced apart by several millimeters, the zero-gap electrolytic cell is a sandwich-type electrolytic cell in which the cathode and anode are in contact with each other across the separator, eliminating the gap between the electrodes and the separator. The zero-gap electrolytic cell reduces the solution ionic resistance due to the presence of electrolyte and can reduce the increase in mass transfer resistance due to generated gases when large-area electrodes are implemented.

[0046] Specifically, the electrolyte flowing toward the cathode 13 is called the cathode 13 solution, and the electrolyte flowing toward the anode 11 is called the anode 11 solution. However, the zero-gap membrane electrode assembly does not contain the cathode 13 solution, but can contain only the anode 11 solution. An electrolysis cell having the zero-gap membrane electrode assembly structure has a structure in which the electrolyte does not flow in front of the cathode 13, but flows only in front of the anode 11. This minimizes the gap between the cathode 13, anode 11, and separator 15, thereby accelerating ion transport and increasing current efficiency. This also solves the additional problem of voltage buildup during the electrolysis reaction, thereby reducing overvoltage. Furthermore, in this case, separators can be disposed on both sides of the zero-gap membrane electrode assembly to form a single cell.

[0047] According to one embodiment of the present invention, products generated by the electrolysis reaction at the cathode 13 can be transferred to the storage tank 2 via the discharge flow path 30. The products can include carbon monoxide, water vapor, and salt. The salt can be carbonate. The carbon dioxide regenerated by separating carbon dioxide from the carbonate in the acid solution storage tank 20 can be resupplied to the cathode 13 via the supply flow path. The electrolysis device of the present invention can reduce carbon dioxide loss and improve electrolysis efficiency by separating carbon dioxide from carbonate in the storage tank 2 and circulating the carbon dioxide to the electrolysis cell. Furthermore, by using the same type of solution for the acid solution and the electrolyte, supplying the electrolyte to the storage tank 2, and supplying cations from the storage tank 2 to the electrolyte, the device can be operated for a long period of time and maintain high electrolysis efficiency.

[0048] The decomposition principle of the electrolyzer and each component of the electrolyzer will be described below.

[0049] Electrolysis refers to the decomposition of a substance through an oxidation-reduction reaction by applying a direct current voltage, which is a non-spontaneous decomposition reaction. The anode is an oxidation electrode that oxidizes water to generate oxygen, generating hydrogen ions. The hydrogen ions generated at the anode are transferred to the cathode via the electrolyte. The cathode is a reduction electrode, and reactants input to the cathode can react with electrons and hydrogen ions transferred from the anode to generate products. The separator can also be disposed between the anode and cathode. The separator is made of an inert material that does not participate in the electrochemical reaction itself, but it can provide a path for ions to move between the anode and cathode and separate the anode and cathode from physical contact.

[0050] In addition, the anode and the cathode of the electrolyzer of the present invention may each include a catalyst layer. Furthermore, water vapor supplied together with carbon dioxide in the cathode region undergoes an electroreduction reaction on the surface of the cathode to generate a reduction product. Therefore, the cathode may include a gas diffusion layer to uniformly supply humidified carbon dioxide gas to the cathode region. When the cathode includes a hydrophobic gas diffusion layer, the supplied carbon dioxide can be smoothly diffused, distributed, and supplied to the catalyst layer of the cathode. Furthermore, the hydrophobic gas diffusion layer effectively prevents water condensation, thereby ensuring a continuous and uniform supply of carbon dioxide and facilitating the electrolysis reaction. Furthermore, the catalyst layer may have a porous surface to effectively exhibit gas permeability.

[0051] According to one embodiment of the present invention, the anode may include a catalyst active in water electrolysis, and the catalytic layer of the anode may include, for the oxygen evolution reaction, one or more selected from the group consisting of Pt, Au, Pd, Ir, Ag, Rh, Ru, Ni, Al, Mo, Cr, Cu, Ti, W, alloys thereof, or mixed metal oxides such as Ta2O5, IrO2, etc. Specifically, the anode in the electrolyzer of the present invention may include titanium (Ti) coated with iridium oxide (IrO2).

[0052] Furthermore, since the carbon dioxide reduction reaction occurring at the cathode competes with the hydrogen generation reaction, a high voltage is required for the hydrogen generation reaction, and a catalyst active in the carbon dioxide reduction reaction may be included. The catalytic layer of the cathode may contain one or more elements selected from the group consisting of 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, and mixtures thereof for the hydrogen generation reaction. Specifically, the cathode in the electrolyzer of the present invention may contain silver (Ag).

[0053] The separator may include a cation exchange membrane (CEM), as described above, and may be a Nafion exchange membrane. The CEM acts as a barrier to prevent the reduced substances generated at the cathode by catalytic action from moving to the anode and being oxidized, and it also suppresses the permeation of anions and allows hydrogen ions (H + ) can be a separate phase permeable to cations.

[0054] The electrolyte solution may be the electrolyte solution according to the present invention as described above, specifically an acidic electrolyte solution, more specifically an aqueous solution containing cesium sulfate. The electrolyte solution composition may contain the electrolyte solution at a concentration of 0.1 to 15.0 M, preferably 0.25 to 10.0 M. The concentration of the electrolyte solution is related to the product generation efficiency (the generation efficiency of the target product relative to the applied current density) and voltage. The higher the concentration of the electrolyte solution, the lower the generated voltage, required voltage, or overvoltage. However, the above conditions are preferred to minimize increased production costs and the generation of adducts due to side reactions.

[0055] The gas diffusion layer may be a porous body made of a carbon material such as carbon fiber cloth, carbon fiber felt, or carbon fiber paper, or a porous metal body made of a thin metal plate with a mesh structure such as expanded metal or metal mesh. In the electrolysis device of the present invention, a carbon fiber cloth may be used as the gas diffusion layer.

[0056] According to one embodiment of the present invention, the electrolyzer can be used in all fields requiring electrochemical conversion, particularly for electrochemically decomposing carbon dioxide to obtain desired products. Specifically, the electrolyzer can electrolyze carbon dioxide to produce one or more products selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

[0057] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0058] Example 1 The carbon dioxide electrolyzer shown in the schematic diagram of Figure 1 was operated under the operating conditions described below. The electrolyzer included a membrane electrode assembly with a zero-gap structure, in which an anode, a cation separator (type: Nafion® 212), a cathode, and a gas diffusion layer were stacked in this order. The electrolyzer included an acidic solution storage tank connected to the outside of the cathode and the membrane electrode assembly and filled with an acidic solution (0.5M Cs2SO4, pH adjusted to 2-3 by H2SO4). First and second solution exchange flow paths were provided to circulate the acidic solution and electrolyte. Reaction current density: 100mA / cm 2 (Constant current operation) Reaction voltage: 1 to 4 V Reaction temperature: 40℃ Reaction pressure: 1 atm (normal pressure) Anode catalyst: IrO2 on Ti mesh Cathode catalyst: Ag powder Electrode area: 25cm 2 Gas diffusion layer: Sigracet 39BB Anodic electrolyte: 0.5M Cs2SO4, pH adjusted to 2-3 by H2SO4 (25ml / min) Cathode reactant: 40°C humidified CO2 gas (200 ccm) 40℃ Humidified CO2 gas supply flow rate: 200ml / min

[0059] Example 2 Reaction current density: 200mA / cm 2 The carbon dioxide electrolyzer was operated under the same conditions as in Example 1, except that the operation was carried out as follows.

[0060] Comparative Example 1 The carbon dioxide electrolyzer was operated under the same conditions as in Example 1, except that the acid solution storage tank was not included (see Table 1).

[0061] Comparative Example 2 The carbon dioxide electrolyzer was operated under the same conditions as in Example 2, except that the acid solution storage tank was not included (see Table 1).

[0062] Comparative Example 3 The carbon dioxide electrolyzer was operated under the same conditions as in Example 1, except that the carbon dioxide electrolyzer shown in the schematic diagram of FIG. 2 was used instead of the carbon dioxide electrolyzer shown in the schematic diagram of FIG. 1, and the conditions were changed to those listed in Table 1.

[0063] Comparative Example 4 The carbon dioxide electrolyzer was operated under the same conditions as in Example 2, except that the carbon dioxide electrolyzer shown in the schematic diagram of FIG. 2 was used instead of the carbon dioxide electrolyzer shown in the schematic diagram of FIG. 1, and the conditions were changed to those listed in Table 1.

[0064] The conditions for the examples and comparative examples are shown in Table 1 below.

[0065] [Table 1]

[0066] Experimental Example 1: Measurement of pH change in electrolyte The carbon dioxide electrolyzers according to the examples and comparative examples were operated for 8 hours, and the pH was measured over time from before operation of the electrolyzer until 8 hours after operation, and the values ​​are shown in Table 2. Table 2 also shows the change in pH from the initial pH value to the pH value after 8 hours.

[0067] Experimental Example 2: Measurement of ionic conductivity of electrolyte The carbon dioxide electrolyzers according to the examples and comparative examples were operated for 8 hours, and the ionic conductivity of the electrolyte was measured over time from before operation of the electrolyzer until 8 hours after operation. The measured values ​​are shown in Table 3. The change in ionic conductivity between the initial value and after 8 hours is also shown in Table 3.

[0068] [Table 2]

[0069] [Table 3]

[0070] 3 and 4, it can be seen that Examples 1 and 2, which were operated according to the electrolysis device of the present invention, showed significantly smaller changes in the pH and ionic conductivity of the electrolyte than the Comparative Example. That is, it can be seen that in Examples 1 and 2, the same type of solution was used for the solution contained in the acid solution storage tank and the electrolyte, and the solution was circulated, thereby maintaining the overall ion balance within the electrolysis device at a constant level.

[0071] Cesium ions contained in the electrolyte migrate to the cathode, leaving relatively more hydrogen ions behind. Over time, the pH of the electrolyte decreases, and the ionic conductivity of the electrolyte also increases due to hydrogen ions, which have higher ionic conductivity than cesium ions. However, if the pH of the electrolyte decreases and the balance between cesium ions and hydrogen ions is disrupted, the hydrogen generation reaction, which competes with the carbon dioxide generation reaction, becomes more active, reducing the carbon dioxide generation efficiency and making long-term operation impossible. Compared to Example 1, which is operated at the same current density, Comparative Examples 1 and 3 show a rapid decrease in pH after 8 hours and a significant change in the ionic conductivity of the electrolyte. Furthermore, Comparative Examples 2 and 4 also show a significant change in pH and ionic conductivity after 8 hours compared to Example 2. In other words, Comparative Examples 1 to 4 show a significant change in the pH and ionic conductivity of the electrolyte, resulting in a disruption of the ionic balance, which in turn leads to a more active hydrogen generation reaction and makes long-term operation difficult. [Explanation of symbols]

[0072] 2. Storage tank 11 Anode 13 Cathode 15 Separator 20 Acid solution storage section 21 Connecting part 22 Electrolyte storage unit 30 Discharge flow path 40 Solution exchange first flow path 50 Second solution exchange channel 60 Gas-liquid separator 11-1 Anode of conventional device 13-1 Cathode of conventional device 15-1 Separator of conventional equipment 20-1 Acid solution storage tank of conventional equipment 30-1 Exhaust flow path of conventional device 60-1 Conventional gas-liquid separator

Claims

1. an electrolysis cell including a gas diffusion layer, a cathode, a cation separator, an anode, and an electrolyte; a storage tank connected to a discharge flow path that discharges a product from the cathode, the storage tank being located outside the electrolysis cell; An electrolysis apparatus, wherein the acidic solution contained in the storage tank and the electrolyte contained in the electrolysis cell are the same type of solution.

2. 2. The electrolysis apparatus of claim 1, wherein the acidic solution comprises an aqueous solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, acetic acid, citric acid, and oxalic acid; and a salt containing one or more selected from the group consisting of cesium, potassium, and sodium.

3. The salt is Cs ２ CO ３ , CsHCO ３ , Cs ２ SO ４ , CsCl, CsNO ３ , K. ２ CO ３ , KHCO ３ , K. ２ SO ４ , K. ３ P.O. ４ , KCl, KNO ３ , Na ２ CO ３ , NaHCO ３ , Na ２ SO ４ , Na ３ P.O. ４ , NaCl, and NaNO ３ 3. The electrolysis device of claim 2, comprising one or more selected from the group consisting of:

4. The storage tank includes an acid solution storage unit and an electrolyte storage unit connected thereto, The electrolyzer according to claim 1 , wherein the electrolyte reservoir is connected to the anode through a solution exchange channel.

5. The solution exchange flow path includes a first solution exchange flow path that transfers an acidic solution from the electrolyte storage portion to the anode; 5. The electrolysis apparatus according to claim 4, further comprising: a second solution exchange flow path that transfers the electrolyte from the anode to the electrolyte storage section.

6. 2. The electrolysis device according to claim 1, wherein the electrolysis cell is a zero-gap membrane electrode assembly cell in which the gas diffusion layer, the cathode, the separator, and an anode having an anolyte flow path formed therein are stacked in this order.

7. A product produced by the electrolysis reaction at the cathode is transferred to the storage tank via the discharge channel; 10. The electrolysis apparatus of claim 1, wherein the products include carbon monoxide, water vapor, and salts.

8. 8. The electrolysis apparatus of claim 7, wherein carbon dioxide produced from the salt in the storage tank is supplied to the electrolysis cell.

9. 8. The electrolysis apparatus of claim 7, wherein the salt is a carbonate.

10. 2. The electrolysis device according to claim 1, which electrolyzes carbon dioxide.

11. The electrolysis apparatus according to claim 10, wherein the carbon dioxide is supplied to the electrolysis cell in a state containing water vapor.

12. 2. The electrolysis device according to claim 1, wherein carbon dioxide is electrolyzed to produce one or more selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

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