Electrolysis device and method for operating same

Abstract

The present disclosure relates to an electrolysis device including an electrolysis stack in which one or more electrolysis cells including an anode, a cathode, a separator, and an electrolyte solution are stacked, an anode inlet connected to the anode to transfer the electrolyte solution, and a cathode outlet connected to the cathode to discharge products and unreacted reactants from the cathode, wherein in the cathode outlet, a back pressure is applied to the product discharged from the cathode outlet and the unreacted reactant.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2022-0128363 filed on October 7, 2022, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The invention relates to an electrolysis device for electrolyzing carbon dioxide and a method for operating the device. Background Art

[0005] Carbon dioxide is a greenhouse gas that causes global warming, so it should be reduced. As a method for reducing carbon dioxide, known methods such as capture, chemical conversion or electrochemical conversion are used. In the above method, the electrochemical conversion method allows accurate control of components to produce other synthetic gases, which is more economically advantageous than simply removing carbon dioxide. In addition, carbon dioxide can be electrolyzed with water to obtain carbon monoxide, ethylene, methane, formic acid, formates, various hydrocarbons and organic substances such as aldehydes or alcohols.

[0006] The process of electrochemical decomposition of carbon dioxide is similar to the technology of electrolysis of water. However, since the activity of the electrochemical reaction increases in a strong alkaline atmosphere, a certain concentration of KOH aqueous solution is usually used as the electrolyte solution. When an electric current is applied while water is supplied to the anode, the water is decomposed into hydrogen ions and electrons, and oxygen is produced at the same time. The electrons are transmitted to the cathode through an external wire, and the hydrogen ions are transmitted to the cathode through an ion selective separator. At this time, the transmitted electrons react with the carbon dioxide and water supplied to the cathode, and then are decomposed into carbon monoxide and hydroxide ions (OH - ), the generated hydroxide ions react with the hydrogen ions (H + ) reacts to produce water, thereby being in an electrically neutral state. Through the above process, the electrochemical decomposition reaction of carbon dioxide is completed. At this time, the water supplied together with carbon dioxide reacts with the transport electrons separated from the carbon monoxide production reaction and is electrolyzed, thereby producing hydrogen and hydroxide ions. It can be said that such a reaction of water and electrons is in a competitive relationship with the carbon monoxide production reaction. Since the reaction is an electrochemical reaction, the amount of carbon monoxide produced and the ratio of hydrogen / carbon dioxide can be easily controlled by controlling the voltage.

[0007] In the process of electrolyzing carbon dioxide using an electrolyzer, in order to improve the conversion rate of carbon dioxide, a method for increasing the flow rate and flow rate of supplied carbon dioxide is generally used. In this case, since the amount of supplied carbon dioxide increases, the conversion rate of carbon dioxide can be improved within a predetermined operating time. However, the amount of unreacted carbon dioxide that is not electrolyzed in the electrolyzer and escapes to the outside and then circulates back to the electrolyzer increases, which ultimately causes the situation of applying excessive current and voltage, and therefore, there is an inefficient limitation in terms of the utilization rate of carbon dioxide.

[0008] Furthermore, as the active area of ​​a unit or stack included in an electrolysis device increases, there are cases where gas and liquid permeate through a separator and mix, in which case salt or the like is generated, which reduces electrolysis efficiency.

[0009] (Patent Document 001) JP 2022-042280 A Summary of the invention

[0010] Technical issues

[0011] One aspect of the present invention provides an electrolysis device in which back pressure is applied to the inside of a cathode outlet of the electrolysis device to prevent a phenomenon in which an electrolyte solution flows from an anode to a cathode and to maintain electrolysis efficiency at an excellent level.

[0012] Another aspect of the present invention provides a method for operating an electrolyzer, wherein back pressure is applied to the interior of a cathode outlet of the electrolyzer to reduce the flow of products and unreacted carbon dioxide to be discharged, thereby increasing the utilization rate of supplied carbon dioxide.

[0013] Technical Solution

[0014] The invention provides an electrolysis device and an operation method thereof.

[0015] (1) The present invention provides an electrolysis device comprising an electrolysis stack in which one or more electrolysis units including an anode, a cathode, a separator and an electrolyte solution are stacked, an anode inlet connected to the anode for transmitting the electrolyte solution, and a cathode outlet connected to the cathode for discharging products and unreacted reactants from the cathode, wherein in the cathode outlet, back pressure is applied to the products and unreacted reactants discharged from the cathode outlet.

[0016] (2) In (1) above, the present invention provides an electrolysis apparatus wherein the back pressure is about 10 kPa to about 50 kPa.

[0017] (3) In (1) or (2) above, the present invention provides an electrolysis device wherein the cathode outlet includes a pressure control valve.

[0018] (4) In any of the above (1) to (3), the present invention provides an electrolysis device, wherein the electrode area of ​​the electrolysis stack is about 500 cm 2 To about 5,000cm 2 .

[0019] (5) In any one of (1) to (4) above, the present invention provides an electrolysis device wherein a loss flow rate of the electrolyte solution is about 0.1 L / day or less.

[0020] (6) In any one of (1) to (5) above, the present invention provides an electrolysis device, wherein the electrolysis unit is a membrane electrode assembly (MEA) having a zero-gap structure in which a gas diffusion layer, a cathode, a separator, and an anode having an electrolyte flow path are sequentially stacked.

[0021] (7) In any one of (1) to (6) above, the present invention provides an electrolysis device, wherein the electrolysis device electrolyzes carbon dioxide.

[0022] (8) In any one of (1) to (7) above, the present invention provides an electrolysis device, wherein the electrolysis device produces at least one selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

[0023] (9) The present invention provides a method for operating an electrolysis device, wherein the method comprises S1: supplying an electrolyte solution to an electrolysis stack in which one or more electrolysis units including an anode, a cathode, a separator and an electrolyte solution are stacked through an anode inlet, and supplying reactants through a cathode inlet; S2: subjecting the reactants to an electrolysis reaction in the electrolysis stack; and S3: discharging the products and unreacted reactants generated by the electrolysis reaction of step S2 to the outside of the electrolysis stack through a cathode outlet, wherein in step S3, a back pressure of about 10 kPa to about 50 kPa is applied to the products and unreacted reactants discharged through the cathode outlet.

[0024] (10) In (9) above, the present invention provides a method for operating an electrolysis device, wherein the back pressure in step S3 is about 20 kPa to about 40 kPa.

[0025] (11) In (9) or (10) above, the present invention provides a method for operating an electrolysis apparatus, wherein in step S1, the supply flow rate of the reactant is kept constant while the electrolysis reaction is being carried out.

[0026] (12) In any one of (9) to (11) above, the present invention provides a method for operating an electrolysis device, wherein the back pressure is controlled by opening and closing a pressure control valve provided in a cathode outlet.

[0027] (13) In any of the above (9) to (12), the present invention provides a method for operating an electrolysis apparatus, wherein the unreacted reactants discharged in step S3 are circulated back into the electrolysis stack.

[0028] Beneficial Effects

[0029] According to the electrolysis device of the present invention, back pressure is applied to the cathode outlet to prevent the electrolyte solution from flowing from the anode to the cathode when the electrochemical reaction is performed, and therefore, the electrolysis efficiency and overvoltage can be maintained at excellent levels.

[0030] According to the method for operating an electrolysis device of the present invention, even if the same carbon dioxide is supplied, the amount of carbon dioxide used in the electrochemical reaction can be increased, so that the conversion rate of carbon dioxide and the Faraday efficiency of carbon monoxide can be improved, and the power consumption for recycling unreacted carbon dioxide can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a graph of voltage and current data for the long term performance evaluation of Example 5.

[0032] Figure 2 is a graph of carbon dioxide and hydrogen Faradaic efficiency data for the long term performance evaluation of Example 5.

[0033] Figure 3 is a graph of voltage and current data for the long term performance evaluation of Comparative Example 5. DETAILED DESCRIPTION

[0034] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. In this case, it will be understood that the words or terms used in the specification and claims should not be interpreted as having the meanings defined in the commonly used dictionaries. It will be further understood that based on the inventors can appropriately define the meanings of the words or terms to best illustrate the principles of the present invention, the words or terms should be interpreted as having the meanings consistent with their meanings in the context of the relevant fields and technical concepts of the present invention.

[0035] The terms used herein are only used to describe exemplary embodiments and are not intended to limit the present invention. Terms in the singular form may include plural forms unless the context clearly indicates otherwise.

[0036] In this specification, it should be understood that the terms "include", "comprises" or "has" are intended to illustrate the existence of stated features, numbers, steps, elements, or combinations thereof, but do not exclude the existence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0037] Method for operating an electrolysis device

[0038] The method for operating an electrolysis device of the present invention includes S1: supplying an electrolyte solution to an electrolysis stack in which one or more electrolysis units including an anode, a cathode, a separator and an electrolyte solution are stacked through an anode inlet, and supplying reactants through a cathode inlet; S2: performing an electrolysis reaction on the reactants in the electrolysis stack; and S3: discharging the products and unreacted reactants generated by the electrolysis reaction of step S2 to the outside of the electrolysis stack through a cathode outlet, wherein in step S3, a back pressure of about 10 kPa to about 50 kPa is applied to the products and unreacted reactants discharged through the cathode outlet.

[0039] The electrolysis device of the present invention may include an electrolysis unit or an electrolysis stack in which two or more electrolysis units are stacked, a cathode inlet, a cathode outlet, an anode inlet and an anode outlet. As will be described later, the electrolysis unit may include an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte solution. In addition, in order to improve the driving voltage and current efficiency, the electrolysis unit may form a membrane electrode assembly having a zero gap structure in which a gas diffusion layer, a cathode, a separator and an anode having an electrolyte flow path are sequentially stacked, in which case a separator may be provided on both sides of the membrane electrode assembly to form a unit.

[0040] The cathode inlet can be used to supply reactants to the electrolysis unit and can be arranged adjacent to the cathode. In addition, the cathode outlet can be used to discharge the products and unreacted reactants produced by the electrochemical reaction from the electrolysis unit to the outside, and can be arranged adjacent to the cathode. In addition, the anode inlet can be used to supply the electrolyte solution to the electrolysis unit or the stack, and the anode outlet can be used to discharge the used electrolyte solution to the outside after the electrolysis reaction.

[0041] Meanwhile, in a typical method for electrolyzing carbon dioxide, in order to obtain a high conversion rate, a method of supplying carbon dioxide as a reactant to an electrolysis unit is used as follows: the flow rate and flow rate of carbon dioxide are increased while the electrolysis device is operated under atmospheric pressure conditions. In this case, although the conversion rate can be improved by increasing the amount of carbon dioxide introduced, the amount of carbon dioxide that is unreacted and re-discharged in the electrolysis unit increases, and the unreacted carbon dioxide needs to be recycled and introduced into the electrolysis unit, so that the consumption of current and power for circulating carbon dioxide is significant. In addition, the greater the amount of unreacted carbon dioxide, the greater the cost and time consumed in the process of classifying the unreacted carbon dioxide and the products discharged therewith.

[0042] Furthermore, in a typical process for electrolysis of carbon dioxide, if the active area of ​​the electrolysis unit or stack is increased to 1000 cm 2If the electrolyte is molten or larger, there may be a problem of gas or liquid permeating through the pores of the separator and mixing. Specifically, unreacted carbon dioxide gas supplied from the cathode flows to the anode, and the electrolyte solution flows from the anode to the cathode, so that salt is generated, which may cause a problem of reduced electrolysis efficiency and impossibility of continuous operation.

[0043] The method for operating an electrolysis device of the present invention maintains the flow rate and flow velocity of the supplied carbon dioxide constant during the electrolysis reaction, but reduces the flow rate of the product and unreacted carbon dioxide discharged from the cathode outlet, thereby allowing a sufficient amount of carbon dioxide to react within the electrolysis unit. That is, the method for operating an electrolysis device of the present invention can pressurize the interior of the cathode outlet to increase the pressure inside the electrolysis unit and / or the stack, thereby increasing the amount of reacted carbon dioxide, and thus can improve the utilization rate of carbon dioxide and the Faraday efficiency of carbon monoxide. In addition, even if the electrolysis unit or stack has a pressure of about 1000 cm 2 In the case of an active area of ​​1000 Nm or larger, by applying back pressure to the inside of the cathode outlet and controlling the internal pressure ratio between the cathode outlet and the anode inlet, it is possible to prevent the electrolyte solution from transmitting salt through the separator or unreacted carbon dioxide gas from flowing out.

[0044] According to one embodiment of the present invention, the method for operating an electrolysis device of the present invention can be carried out as follows: S1 supplies carbon dioxide to the electrolysis device; S2 electrolyzes carbon dioxide; and S3 discharges the product produced by the electrolysis of carbon dioxide and unreacted carbon dioxide, wherein the discharge of the product and unreacted carbon dioxide of step S3 can be carried out by applying back pressure to the product to be discharged and the unreacted reactant.

[0045] Back pressure refers to the resistance pressure acting in the direction opposite to the direction of fluid flow when the fluid is discharged through the tube. The cathode outlet of the present invention may include a pressure control valve to be described below, wherein the back pressure can be controlled by changing the width of the cathode outlet by opening and closing the pressure control valve, and pressure can be applied in the direction opposite to the direction in which the product to be discharged through the cathode outlet and the unreacted reactant are discharged.

[0046] According to one embodiment of the present invention, in step S3, a back pressure of about 10 kPa to about 50 kPa may be applied to the product and unreacted reactant discharged through the cathode outlet. Specifically, the back pressure may be about 10 kPa or greater, about 13 kPa or greater, about 15 kPa or greater, about 17 kPa or greater, about 20 kPa or greater, about 22 kPa or greater, about 25 kPa or greater, about 27 kPa or greater, about 32 kPa or greater, about 50 kPa or less, about 47 kPa or less, about 45 kPa or less, about 42 kPa or less, about 40 kPa or less, about 37 kPa or less, about 35 kPa or less, about 32 kPa or less, or about 30 kPa or less. If the back pressure exceeds the lower limit of the above pressure value range, the pressure applied to the products to be discharged and the unreacted reactants is low, causing a small decrease in the flow rate of the products to be discharged and the unreacted reactants, making it difficult to expect the utilization rate of carbon dioxide and the improvement of the Faraday efficiency of carbon monoxide. In addition, if the back pressure exceeds the upper limit of the above pressure value range, the pressure applied to the products to be discharged and the unreacted reactants is high, so that the amount of the product of the reaction in the electrolysis unit is reduced, the conversion rate of carbon dioxide may be reduced, and the overvoltage may be increased.

[0047] In addition, according to one embodiment of the present invention, the internal pressure of the cathode outlet and the internal pressure of the anode inlet may be controlled to satisfy the following Formula 1.

[0048] [Formula 1]

[0049] P 阴极出口 / P 阳极入口 ≥1

[0050] In the above formula 1,

[0051] P 阴极出口 is the internal pressure at the cathode outlet, and

[0052] P 阳极入口 is the internal pressure at the anode inlet.

[0053] Specifically, if the internal pressure of the cathode outlet is equal to or higher than the internal pressure of the anode inlet, the loss of the electrolyte solution is reduced to about 0.1 L / day or less, and the electrolysis device can be continuously operated without reducing the electrolysis efficiency. However, if the internal pressure of the cathode outlet is less than the internal pressure of the anode inlet, the electrolyte solution permeates the separator and is transmitted to the cathode outlet, and the loss of the electrolyte solution corresponds to a level of about 0.5 L / hour, making it difficult to continuously drive the electrolysis device.

[0054] According to one embodiment of the present invention, the loss flow of the electrolyte solution can be about 0.1L / day or less. For example, the loss flow of the electrolyte solution can be about 0.1L / day or less, about 0.09L / day or less, about 0.08L / day or less, about 0.07L / day or less, about 0.06L / day or less, about 0.05L / day or less, about 0.04L / day or less, about 0.03L / day or less, about 0.02L / day or less, or about 0.01L / day or less. On the other hand, in the case of a typical electrolysis device without applying back pressure to the cathode outlet, the loss flow corresponds to a level of about 0.5L / hour or more, in which case the amount of salt produced by the electrolytic solution flowing to the cathode through the separator increases, making it impossible to carry out a continuous electroconversion reaction.

[0055] Here, the loss flow of the electrolyte solution is measured by the amount of electrolyte solution lost over time relative to the initial amount of electrolyte solution contained in the electrolysis cell.

[0056] According to one embodiment of the present invention, in step S1, the supply flow rate of the reactant can be kept constant during the electrolysis reaction. The method for operating an electrolysis device of the present invention keeps the supply flow rate and flow rate of carbon dioxide supplied to the electrolysis unit constant, but controls the discharge flow rate of the discharged product and unreacted carbon dioxide, so that the utilization rate of carbon dioxide can be increased. The method for operating an electrolysis device of the present invention can solve the limitation that the utilization rate of carbon dioxide is reduced and the amount of unreacted carbon dioxide recycled to the electrolysis unit is increased, which may occur when the supply flow rate and flow rate are generally increased.

[0057] According to one embodiment of the present invention, the unreacted reactants discharged in step S3 can be circulated back to the electrolysis unit. The method for operating an electrolysis device of the present invention can reduce the amount of unreacted carbon dioxide by increasing the utilization rate of carbon dioxide, thereby reducing the power consumption that may be used to circulate unreacted carbon dioxide back to the electrolysis unit. In addition, the method for operating an electrolysis device of the present invention can increase the Faraday efficiency of carbon monoxide to reduce the consumption of the driving current applied to the electrolysis device.

[0058] According to one embodiment of the present invention, the cathode outlet includes a pressure control valve, and the pressure on the product and the unreacted reactant can be controlled by opening and closing the pressure control valve. Specifically, the cathode outlet of the electrolysis device of the present invention may include a pressure control valve, and the pressure inside the cathode outlet can be controlled by opening or closing the pressure control valve. The pressure inside the cathode outlet can be increased by closing the pressure control valve, and the flow rate can be reduced by applying pressure to the product and the unreacted carbon dioxide.

[0059] According to one embodiment of the present invention, the electrolysis unit includes a cathode, an anode and a separator, wherein the separator can be a porous separator, in particular, a porous separator with hydrophilic properties. Specifically, the porous separator can be an ion selective exchange membrane, and the porous separator can include an anion exchange membrane, a cation exchange membrane or an amphoteric ion exchange membrane. In addition, the porous separator can include a hydrophilic porous substrate, so it is possible to allow the moisture content to remain at a certain level. In addition, the porous separator includes a porous substrate, and the porous substrate includes holes with an average particle size of about 10nm to about 750nm, therefore, it is possible to provide a path that allows various molecules including ions and water molecules to be smoothly transmitted through an electrolyte based on an aqueous solution, therefore, during the operation of the electrolysis device, the carbon dioxide conversion rate can be improved, and the overvoltage can be reduced.

[0060] The hydrophilic porous substrate may be a cellulose-based resin. Specifically, the hydrophilic porous substrate may be a cellulose-based resin, and the cellulose-based resin may be one or more selected from the following: cellulose acetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose levulinate, cellulose diacetate, cellulose dibutyrate, cellulose tributyrate, and cellulose nitrate. More specifically, the porous substrate included in the porous separator included in the electrolytic cell of the present invention may contain cellulose acetate.

[0061] In particular, cellulose acetate has hydrophilic properties, has high mechanical and chemical strength due to high dimensional restrictions that do not allow size and shape to change under conditions such as temperature or humidity, and has a uniform pore structure. Meanwhile, in a porous separator used in an electrolytic cell for converting carbon dioxide, pores formed in the porous separator are impregnated with an aqueous solution-based electrolyte solution, and ions such as HCO3 - 、CO3 2- and OH - It can be transported through the pores. Therefore, when cellulose acetate having hydrophilic properties, high mechanical strength and uniform pore size is used as a separator of a carbon dioxide electrolysis unit using an aqueous solution-based electrolyte solution, it can exhibit the characteristics of high carbon dioxide conversion rate, high carbon monoxide Faraday efficiency and low overvoltage.

[0062] Furthermore, the method for operating an electrolysis device of the present invention uses an electrolytic device of about 100 cm including the above-mentioned porous separator. 2 or larger large-area electrolytic unit cells, and thus can be applied to high-performance unit cells or stacked bodies in which a plurality of unit cells are stacked.

[0063] Electrolysis device

[0064] The electrolysis device of the present invention includes an electrolysis stack in which one or more electrolysis units including an anode, a cathode, a separator and an electrolyte solution are stacked, an anode inlet connected to the anode to transmit the electrolyte solution, and a cathode outlet connected to the cathode to discharge products and unreacted reactants from the cathode, wherein in the cathode outlet, back pressure is applied to the products discharged from the cathode outlet and the unreacted reactants. Specifically, the electrolysis device of the present invention may include an electrolysis unit or an electrolysis stack in which two or more electrolysis units are stacked, a cathode inlet, a cathode outlet, an anode inlet and an anode outlet. In addition, the electrolysis unit may include an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte solution, and in order to improve the driving voltage and current efficiency, the electrolysis unit may form a membrane electrode assembly having a zero gap structure in which a gas diffusion layer, a cathode, a separator and an anode having an electrolyte flow path are sequentially stacked, in which case a separator may be provided on both sides of the membrane electrode assembly to form a unit. In addition, the electrolysis device of the present invention is the same as described in the method for operating the electrolysis device of this specification.

[0065] The back pressure is about 10 kPa to about 50 kPa, and is the same as described in the method for operating the electrolysis device of the present specification. In addition, if the above back pressure range is met, and the internal pressure of the cathode outlet is equal to or higher than the internal pressure of the anode inlet, the loss of the anode transmitted from the anode to the cathode is reduced, and the electrolysis device can be continuously operated at high efficiency.

[0066] The internal pressure of the cathode outlet of the electrolyzer may be about 10 kPa to about 300 kPa, and the internal pressure of the anode outlet may be about 5 kPa to about 60 kPa. For example, the internal pressure of the cathode outlet of the electrolyzer may be about 10 kPa or more, about 30 kPa or more, about 50 kPa or more, about 60 kPa or more, about 70 kPa or more, about 90 kPa or more, about 100 kPa or more, about 110 kPa or more, about 120 kPa or more, about 130 kPa or more, about 300 kPa or less, about 270 kPa or less, about 230 kPa or less, about 220 kPa or less, about 210 kPa or less, about 200 kPa or less, about 190 kPa or less, about 170 kPa or less, about 160 kPa or less, about 150 kPa or less, or about 140 kPa or less. In addition, for example, the internal pressure at the anode outlet can be about 5 kPa or greater, about 7 kPa or greater, about 9 kPa or greater, about 10 kPa or greater, about 12 kPa or greater, about 15 kPa or greater, about 20 kPa or greater, about 22 kPa or greater, about 25 kPa or greater, about 27 kPa or greater, about 30 kPa or greater, about 60 kPa or less, about 57 kPa or less, about 55 kPa or less, about 53 kPa or less, about 50 kPa or less, about 48 kPa or less, about 45 kPa or less, about 42 kPa or less, about 40 kPa or less, about 39 kPa or less, about 37 kPa or less, or about 35 kPa or less.

[0067] The cathode outlet may include a pressure control valve, wherein the back pressure may be controlled by the pressure control valve, and the contents related to the pressure control valve and the back pressure control are the same as those described in the method for operating the electrolysis device of the present specification.

[0068] Furthermore, according to one embodiment of the present invention, the internal pressure of the cathode outlet and the internal pressure of the anode inlet may be controlled to satisfy the following Formula 1.

[0069] [Formula 1]

[0070] P 阴极出口 / P 阳极入口 ≥1

[0071] In the above formula 1,

[0072] P 阴极出口 is the internal pressure at the cathode outlet, and

[0073] P 阳极入口 is the internal pressure at the anode inlet.

[0074] Specifically, if the internal pressure of the cathode outlet is equal to or higher than the internal pressure of the anode inlet, the loss of the electrolyte solution is reduced to about 0.1 L / day or less, and the electrolysis device can be continuously operated without reducing the electrolysis efficiency. However, if the internal pressure of the cathode outlet is less than the internal pressure of the anode inlet, the electrolyte solution permeates the separator and is transmitted to the cathode outlet, and the loss of the electrolyte solution corresponds to a level of about 0.5 L / hour, making it difficult to continuously drive the electrolysis device.

[0075] According to one embodiment of the present invention, the loss flow of the electrolyte solution can be about 0.1L / day or less. For example, the loss flow of the electrolyte solution can be about 0.1L / day or less, about 0.09L / day or less, about 0.08L / day or less, about 0.07L / day or less, about 0.06L / day or less, about 0.05L / day or less, about 0.04L / day or less, about 0.03L / day or less, about 0.02L / day or less, or about 0.01L / day or less. On the other hand, in the case of a typical electrolysis device without applying back pressure to the cathode outlet, the loss flow corresponds to a level of about 0.5L / hour or more, in which case the amount of salt produced by the electrolytic solution flowing to the cathode through the separator increases, making it impossible to carry out a continuous electroconversion reaction.

[0076] Here, the loss flow of the electrolyte solution is measured by the amount of electrolyte solution lost over time relative to the initial amount of electrolyte solution contained in the electrolysis cell.

[0077] Figure 1 is a graph of voltage and current data for the long term performance evaluation of Example 5, Figure 2 is a graph of carbon dioxide and hydrogen Faradaic efficiency data for the long term performance evaluation of Example 5, Figure 3 is a graph of voltage and current data for the long term performance evaluation of Comparative Example 5.

[0078] Reference Figure 1 and Figure 2 When a back pressure of about 0.3 bar (about 30 kPa) is applied to the cathode outlet, salt generation is suppressed, allowing long-term operation, with a greatly reduced overvoltage and maintaining about 200 mA / cm 2 In addition, the Faraday efficiency of carbon dioxide can be maintained at a high level, and the Faraday efficiency of hydrogen may not increase. On the other hand, Figure 3 , if back pressure is not applied to the cathode outlet, the electrolyte solution flows to the cathode side through the separator, thereby generating salt, and therefore, the overvoltage increases after about 12 hours of operation, and the reaction current is not maintained and decreases.

[0079] Meanwhile, in the case of a fuel cell, considering the specifications of the electrochemical unit or stack when it is actually used, there are difficulties in forming it into a large-area electrochemical unit or stack, but in the case of a unit or stack included in an electrolysis device, the unit or stack can be formed into a large area to increase the amount of carbon dioxide or water converted per unit time. At this time, in the case of an electrolysis unit or stack, it is important to maintain a large area for a long period of time while maintaining physical / chemical durability and high electrolysis efficiency. However, as the electrode area of ​​the unit or stack increases on a large scale, the area of ​​the separator applied also increases, so the supply flow of the reaction gas also increases, and when a large amount of reaction gas is supplied to the unit or stack, its internal pressure also increases, so that a pressure gradient is generated between the anode and the cathode based on the separator, causing the materials of the two electrodes to mix with each other through the separator. Therefore, in the electrolysis device of the present invention, even under the conditions of such a large-scale unit or stack, the pressure relationship between the cathode outlet and the anode inlet is also controlled at a certain ratio, so that such an electrolysis device is developed: it maintains long-term durability and has a high electrolysis efficiency when the materials of the two electrodes are not mixed.

[0080] According to one embodiment of the present invention, the electrode area of ​​the electrolytic stack may be about 500 cm 2 To about 5,000cm 2 The electrode area of ​​the electrolysis stack refers to the area in which the electrolysis reaction is activated. The electrode area of ​​such an electrolysis stack may be about 500 cm 2 To about 5,000cm 2 For example, the electrode area of ​​the electrolysis stack may be about 500 cm 2 Or larger, about 600cm 2 or larger, about 700cm 2 or larger, about 800cm 2 or larger, about 1,000cm 2 or larger, about 1,200cm 2 or larger, about 1,500cm 2 or larger, about 2,000cm 2 or larger, about 2,500cm 2 or larger, about 5,000cm 2 or smaller, about 4,500cm 2 or smaller, about 4,300cm 2 or less, about 4,100 or less, about 4,000cm 2 or smaller, about 3,800cm 2 or smaller, about 3,500cm 2 or smaller, about 3,300cm 2 or smaller, about 3,100cm2 or smaller, about 3,000cm 2 or less, specifically, about 1,000 cm 2 To about 4,000cm 2 The electrolysis device of the present invention includes a unit or a stack satisfying the above-mentioned electrode area range, and thus can maintain high electrolysis efficiency per unit time and high physical / chemical durability for a long period of time.

[0081] According to another embodiment of the present invention, the electrolysis device can be used in all fields of electrochemical conversion. The electrolysis device can be a fuel cell, a device capable of producing useful chemicals by electrochemical conversion (such as water electrolysis), or can be used to reduce and convert carbon dioxide and NO. x Specifically, the electrolysis device can be an electrochemical conversion device that converts carbon dioxide into carbon monoxide and ethylene.

[0082] According to one embodiment of the present invention, the electrolysis device may include a unit or stack for converting introduced carbon dioxide into carbon monoxide, and the unit or stack may include an anode, a cathode, an electrolyte and a separator. In addition, the unit may be a membrane electrode assembly (MEA) having a zero-gap structure in which a gas diffusion layer, a cathode, a separator and an anode having an electrolyte flow path are sequentially stacked.

[0083] Electrolysis refers to the decomposition of materials by redox reactions that do not occur spontaneously through the application of a direct current voltage. The anode is an oxidizing electrode that oxidizes water to produce oxygen while producing hydrogen ions. The hydrogen ions produced in the anode are transported to the cathode through an electrolyte, and the cathode is a reducing electrode where reactants introduced into the cathode can react with hydrogen ions and electrons transmitted from the anode and produce products. In addition, a separator can be disposed between the anode and the cathode. The separator itself can be composed of an inert material that does not participate in the electrochemical reaction, but provides a path that allows ions to be transported between the anode and the cathode, and can be used to separate the physical contact of the anode and the cathode.

[0084] In addition, the anode and cathode of the electrolysis device of the present invention may each include a catalyst layer. In addition, in the cathode region, water vapor supplied with carbon dioxide produces a reduction product by an electroreduction reaction on the cathode surface. Therefore, the cathode may include a gas diffusion layer to uniformly supply humidified carbon dioxide gas to the cathode region. If 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. In addition, the hydrophobic gas diffusion layer effectively prevents moisture condensation, thereby allowing a continuous and uniform supply of carbon dioxide, while allowing the electrolysis reaction to proceed smoothly. In addition, the catalyst layer may have a surface with a porous structure, etc. to play a good role in gas permeability characteristics on the surface.

[0085] According to one embodiment of the present invention, the anode may include a catalyst active in the electrolysis of water, and the catalyst layer of the anode may include one or more selected from the following to perform an oxygen generation reaction: Pt, Au, Pd, Ir, Ag, Rh, Ru, Ni, Al, Mo, Cr, Cu, Ti, W, alloys thereof, or mixed metal oxides (e.g., Ta2O5, IrO2, etc.). Specifically, in the carbon dioxide electrolysis device of the present invention, the anode may include titanium (Ti) coated with iridium oxide (IrO2).

[0086] In addition, since the carbon dioxide reduction reaction occurring in the cathode competes with the hydrogen generation reaction, the voltage required for the hydrogen generation reaction is high, and a catalyst active in the carbon dioxide reduction reaction may be included. The catalyst layer of the cathode may include one or more selected from the following: 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. Specifically, in the carbon dioxide electrolysis device of the present invention, the cathode may include silver (Ag).

[0087] In addition, as a separator, a cation exchange membrane (CEM) or an anion exchange membrane (AEM) may be included. Specifically, the cation exchange membrane may be used as a membrane that prevents the reduced material generated in the cathode by catalysis from being transferred to the anode and oxidized, and may be a membrane that inhibits the transfer of anions and allows cations such as hydrogen ions (H + ) transported. In addition, hydrogen ions (H + ), excessive hydrogen ions flow to the cathode to saturate the active part of the catalyst that converts carbon dioxide, which may cause the problem of reduced carbon dioxide conversion rate. At this time, the anion exchange membrane can reduce the amount of hydrogen ions flowing to the cathode. The anion exchange membrane blocks the transmission of hydrogen ions, thereby preventing the carbon dioxide conversion performance of the cathode from decreasing, and can refer to allowing anions such as OH to - 、HCO3 - and CO3 2- The transmission separation phase.

[0088] In addition, as the electrolyte, one or more electrolytes selected from the group consisting of KHCO3, K2CO3, KOH, KCl, KClO4, K2SiO3, Na2SO4, NaNO3, NaCl, NaF, NaClO4, CaCl2, Cs2CO3, H3PO4, KHPO4, guanidine cation, H+ Cations, alkali metal cations, ammonium cations, alkylammonium cations, halide ions, alkylamines, borates, carbonates, guanidine derivatives, nitrites, nitrates, phosphates, polyphosphates, perchlorates, silicates, sulfates, tetraalkylammonium salts, or aqueous solutions containing mixtures thereof. Specifically, the electrolyte of the carbon dioxide electrolysis device of the present invention may include an aqueous solution containing one or more selected from the following: KOH, KHCO3, Cs2CO3, H3PO4, or a mixture of H3PO4 and KHPO4.

[0089] In addition, the gas diffusion layer can use a porous body using carbon materials such as carbon fiber cloth, carbon fiber felt, carbon fiber paper, etc., or a metal porous body made of a thin metal plate with a mesh structure such as expanded metal, metal mesh, etc. In the carbon dioxide electrolysis device of the present invention, the gas diffusion layer can use carbon fiber cloth.

[0090] According to one embodiment of the present invention, the electrolysis device can be used in all fields requiring electrochemical conversion, in particular, allowing the desired products to be obtained by electrochemical decomposition of carbon dioxide. Specifically, the electrolysis device can electrolyze carbon dioxide to produce one or more selected from the following: carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes and alcohols.

[0091] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments set forth herein.

[0092] Example 1

[0093] The carbon dioxide electrolysis device was operated under the operating conditions described below: A pressure of about 0.4 bar (= 40 kPa) was applied to the cathode outlet to operate the carbon dioxide electrolysis device.

[0094] Reaction current density: 300mA / cm 2 (Constant current operation)

[0095] Reaction voltage: 1V to 4V

[0096] Reaction temperature: 40℃

[0097] Reaction pressure: 1atm (atmospheric pressure)

[0098] Anode catalyst: IrO2 on Ti mesh

[0099] Cathode catalyst: Ag powder

[0100] Electrode area: 100cm 2

[0101] Gas diffusion layer: Sigracet 39BB

[0102] Anodic electrolyte: 0.5M KHCO3 (200ml / min)

[0103] Cathode reactant: humidified CO2 gas at 40°C

[0104] 40℃ humidified CO2 gas supply flow rate: 800ml / min

[0105] Example 2

[0106] The same process as in Example 1 was performed except that a pressure of about 0.20 bar (= 20 kPa) was applied to the cathode outlet.

[0107] Example 3

[0108] The same process as in Example 1 was performed except that about 200 mA / cm 2 The reaction current density.

[0109] Example 4

[0110] The same process as in Example 1 was carried out, except that the reaction current density was about 200 mA / cm 2 , the electrode area is about 1,000 cm 2 The supply flow rate of humidified CO2 gas at 40°C was about 6,000 ml / min, and the flow rate of the anode electrolyte was about 2 L / min.

[0111] Example 5

[0112] The same process as in Example 1 was carried out, except that the reaction current density was about 200 mA / cm 2 , a pressure of about 0.50 bar (=50 kPa) is applied to the cathode outlet, and the electrode area is about 1000 cm 2 The supply flow rate of humidified CO2 gas at 40°C was about 18000 ml / min, and the flow rate of the anode electrolyte was about 3 L / min.

[0113] Example 6

[0114] The same process as in Example 1 was carried out, except that a pressure of about 0.50 bar (=50 kPa) was applied to the cathode outlet and the electrode area was about 1000 cm 2 The supply flow rate of humidified CO2 gas at 40°C was about 18000 ml / min, and the flow rate of the anode electrolyte was about 3 L / min.

[0115] Comparative Example 1

[0116] The same process as in Example 1 was performed except that no pressure was applied to the cathode outlet.

[0117] Comparative Example 2

[0118] The same process as in Example 1 was performed except that a pressure of about 0.60 bar (= 60 kPa) was applied to the cathode outlet.

[0119] Comparative Example 3

[0120] The same process as in Example 1 was performed except that no pressure was applied to the cathode outlet and about 200 mA / cm 2 The reaction current density.

[0121] Comparative Example 4

[0122] The same process as in Example 1 was carried out, except that the reaction current density was about 200 mA / cm 2 , the electrode area is about 1,000 cm 2 , the supply flow rate of humidified CO2 gas at 40°C was about 6,000 ml / min, the flow rate of the anode electrolyte was about 2 L / min, and no pressure was applied to the cathode outlet.

[0123] Comparative Example 5

[0124] The same process as in Example 5 was performed except that no pressure was applied to the cathode outlet.

[0125] <Experimental example>

[0126] The carbon dioxide electrolysis device was operated using the operation method according to Examples 1 to 6 and Comparative Examples 1 to 4. Electrolysis was performed using the carbon dioxide electrolysis device, and the conversion rate (%) of carbon monoxide, the CO Faraday efficiency (%) of carbon monoxide, and the voltage were measured at this time. The measurement result values ​​are shown in Table 1. In addition, long-term performance evaluation was performed on Example 5 and Comparative Example 5, and the evaluation results are shown in Table 1. Figures 1 to 3 middle.

[0127] Measurement method

[0128] (1) Conversion rate of carbon monoxide (%)

[0129] The conversion rate (%) was calculated as the ratio of carbon monoxide (CO) produced relative to the amount of carbon dioxide (CO2) gas introduced per hour.

[0130] (2) Faradaic efficiency of carbon monoxide (%)

[0131] The gas composition at the cathode outlet was measured by gas chromatography (GC) analysis. In addition, the Faraday efficiency was calculated by the following formula.

[0132] [Formula 1]

[0133]

[0134] In the above formula 1, Q is the flow rate at the cathode outlet, F is the Faraday constant, p is the pressure, T is the measurement temperature, and R is the ideal gas constant. 总计 is the value of the total current applied over time, and the current i associated with the product 产物 is the gas volume V measured by GC analysis 产物 The calculated value.

[0135] (3) Voltage (V)

[0136] The application of current and the measurement of voltage were performed by a VSP potentiostat from BioLogic Co. An 80A intensifier was installed to apply current corresponding to a large area. The current was applied at 200 mA / cm 2 and 300mA / cm 2 The voltage was recorded at 20 minutes after the predetermined period of time. At this time, gas chromatography (GC) analysis was performed simultaneously.

[0137] (4) Long-term performance evaluation

[0138] The carbon dioxide electrolysis devices of Example 5 and Comparative Example 5 were operated for at least 200 hours, and the carbon monoxide conversion rate, the Faraday efficiency of carbon monoxide, the Faraday efficiency of hydrogen, the reaction current density and overvoltage of Example 5 and the reaction current density and overvoltage of Comparative Example 5 were measured in the same manner as in the above-mentioned measurement method.

[0139] [Table 1]

[0140]

[0141] Referring to Table 1, in Examples 1 to 4, a suitable pressure was applied to the cathode outlet, in Comparative Examples 1, 3 and 4, no pressure was applied to the cathode outlet, and in Comparative Example 2, a pressure outside the suitable pressure range of the method for operating an electrolysis device according to the present invention was applied to the cathode outlet. When Examples 1 to 2 in which the same current density was applied were compared with Comparative Examples 1 to 2, Examples 1 to 2 in which a suitable pressure was applied to the cathode outlet exhibited higher Faraday efficiency and carbon dioxide conversion rate and lower overvoltage than Comparative Examples 1 and 2, so it can be determined that the electrolysis efficiency of Examples 1 and 2 is better than that of Comparative Examples 1 and 2. Comparative Example 1 exhibits the same Faraday efficiency and carbon dioxide conversion rate as those of Example 1, but has a higher overvoltage, so it can be seen that the electrolysis efficiency of Comparative Example 1 is lower than that of Example 1. In addition, in Example 3 and Comparative Example 3, a current density of 200 mA / cm 2 Even in this case, it can be seen that the electrolysis efficiency of Example 3 in which a suitable pressure is applied to the cathode outlet is better than the electrolysis efficiency of Comparative Example 4 in which no pressure is applied. In addition, Example 4 and Comparative Example 4 have the same increase in electrode area and cathode inlet flow rate, and even in this case, it can be seen that the electrolysis efficiency of Example 4 in which a suitable pressure is applied to the cathode outlet is better than the electrolysis efficiency of Comparative Example 4 in which no pressure is applied.

[0142] In addition, refer to Figure 1 and Figure 2 When the carbon dioxide electrolysis device of Example 5 is operated at 200 mA / cm 2 When operated under the reaction current density conditions of , the Faraday efficiency of carbon monoxide remains constant at a value of about 88% to about 97% for at least 200 hours. In addition, the Faraday efficiency of hydrogen remains constant at a value of about 0% to about 4%. In addition, the overvoltage is maintained in the range of about -3.3V to about -3.0V for at least 200 hours. Figure 1 In the equation, ● represents voltage and ◆ represents current. Figure 2 In the figure, ● represents the Faraday efficiency of carbon dioxide, and ◆ represents the Faraday efficiency of hydrogen.

[0143] In addition, a 200-hour interim on-off evaluation was performed, and even in this case, it can be seen that the initial high electrolysis efficiency level was restored. That is, if a predetermined back pressure is applied to the cathode outlet to maintain the pressure ratio between the anode inlet and the cathode outlet within the range of the present invention, it can be determined that the device can be operated for a long period of time due to the suppression of salt generation.

[0144] On the other hand, refer to Figure 3In the case of the carbon dioxide electrolysis device of Comparative Example 5, it can be confirmed that the reaction current density decreases rapidly and the overvoltage increases after 12 hours, thereby confirming that the salt prevents long-term operation when back pressure is not applied to the cathode outlet. Figure 3 In the table, ● represents voltage and ◆ represents current.

Claims

1. An electrolysis device comprising: Where stacking an electrolytic stack having one or more electrolytic cells including an anode, a cathode, a separator, and an electrolyte solution; an anode inlet connected to the anode for delivering the electrolyte solution; as well as a cathode outlet connected to the cathode for discharging products and unreacted reactants from the cathode, In the cathode outlet, a back pressure is applied to the product and the unreacted reactant discharged from the cathode outlet.

2. The electrolysis device of claim 1, wherein the back pressure is about 10 kPa to about 50 kPa.

3. The electrolysis device according to claim 1, wherein the cathode outlet comprises a pressure control valve.

4. The electrolysis device according to claim 1, wherein the electrode area of ​​the electrolysis stack is about 500 cm 2 To about 5,000cm 2 . 5 . The electrolysis device according to claim 1 , wherein a loss flow rate of the electrolyte solution is about 0.1 L / day or less. 6 . The electrolysis device according to claim 1 , wherein the electrolysis unit is a membrane electrode assembly (MEA) having a zero-gap structure in which a gas diffusion layer, a cathode, a separator, and an anode having an electrolyte flow path are sequentially stacked.

7. The electrolysis device according to claim 1, wherein the electrolysis device electrolyzes carbon dioxide.

8. The electrolysis device of claim 1, wherein the electrolysis device produces at least one selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

9. A method for operating an electrolysis device, the method comprising: S1: supplying an electrolyte solution to an electrolysis stack in which one or more electrolysis units including an anode, a cathode, a separator and an electrolyte solution are stacked through an anode inlet, and supplying a reactant through a cathode inlet; S2: performing an electrolytic reaction on the reactants in the electrolytic stack; as well as S3: discharging the product and unreacted reactants produced by the electrolysis reaction in step S2 to the outside of the electrolysis stack through the cathode outlet, In step S3, a back pressure of about 10 kPa to about 50 kPa is applied to the product and the unreacted reactant discharged through the cathode outlet. 10 . The method according to claim 9 , wherein the back pressure in step S3 is about 20 kPa to about 40 kPa.

11. The method according to claim 9, wherein in step S1, the supply flow rate of the reactant is kept constant when the electrolysis reaction is performed. 12 . The method of claim 9 , wherein the back pressure is controlled by opening and closing a pressure control valve provided in the cathode outlet.

13. The method according to claim 9, wherein the unreacted reactants discharged in step S3 are circulated back into the electrolysis stack.

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