Electrolysis device and method of operation thereof

Abstract

The present invention relates to an electrolysis device including an electrolysis stack in which one or more electrolysis cells, each including an anode, a cathode, a separator, and an electrolyte, are stacked; an anode inlet connected to the anode to transport the electrolyte; and a cathode outlet connected to the cathode to discharge products and unreacted reactants from the cathode, wherein the cathode outlet applies back pressure to the products and unreacted reactants discharged through the cathode outlet.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0128363, filed October 7, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an electrolysis device for electrolyzing carbon dioxide and a method for operating the same. [Background technology]

[0003] Carbon dioxide is a greenhouse gas that contributes to global warming and must be reduced. Known methods for reducing carbon dioxide include capture, chemical conversion, and electrochemical conversion. Among these, electrochemical conversion allows precise control of the components to produce other synthetic gases, and is more economically advantageous than simply removing carbon dioxide. Carbon dioxide can also be electrolyzed with water to produce carbon monoxide, ethylene, methane, formic acid, formates, various hydrocarbons, and organic compounds such as aldehydes or alcohols.

[0004] The process of electrochemically decomposing carbon dioxide is similar to that of electrolysis of water, but because the activity of the electrochemical reaction improves in a strongly basic atmosphere, a KOH solution of a certain concentration is generally used as the electrolyte. When a current is applied while water is supplied to the anode, 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 separation membrane. Here, 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. This process completes the electrochemical decomposition reaction of carbon dioxide. Here, the water supplied together with carbon dioxide reacts with the electrons that have moved separately from the carbon monoxide production reaction, and is electrolyzed to produce hydrogen gas and hydroxide ions. This reaction of water and electrons can be said to be in a competitive relationship with the carbon monoxide production reaction. Because this 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] In the process of electrolyzing carbon dioxide using an electrolyzer, conventionally, the method of increasing the flow rate and speed of the supplied carbon dioxide has been used to improve the carbon dioxide conversion rate. In this case, the amount of supplied carbon dioxide increases, and the carbon dioxide conversion rate for a given operating time improves, but the amount of unreacted carbon dioxide that is not electrolyzed inside the electrolyzer and escapes to the outside or circulates to the electrolyzer increases. This ultimately leads to a situation where excessive current and voltage are applied, resulting in an inefficient use of carbon dioxide.

[0006] In addition, as the active area of ​​the cells or stacks included in the electrolysis device increases, gas and liquid may penetrate through the separation membrane and become mixed in, which may result in the generation of salt and other problems that reduce the efficiency of electrolysis. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-042280 Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide an electrolyzer that can maintain an excellent level of electrolysis efficiency by applying back pressure to the inside of the cathode discharge part of the electrolyzer to prevent the phenomenon of electrolyte moving from the anode to the cathode.

[0009] The problem to be solved by the present invention is to provide a method for operating an electrolyzer that can increase the utilization rate of supplied carbon dioxide by applying back pressure inside the cathode discharge part of the electrolyzer to reduce the flow rate of the discharged product and unreacted carbon dioxide. [Means for solving the problem]

[0010] The present invention provides an electrolysis apparatus and method of operation thereof.

[0011] (1) The present invention provides an electrolysis device including an electrolysis stack in which one or more electrolysis cells, each including an anode, a cathode, a separator, and an electrolyte, are stacked; an anode inlet connected to the anode to transport the electrolyte; and a cathode outlet connected to the cathode to discharge products and unreacted reactants from the cathode, wherein the cathode outlet applies back pressure to the products and unreacted reactants discharged through the cathode outlet.

[0012] (2) The present invention provides the electrolyzer according to (1) above, wherein the back pressure is 10 kPa or more and 50 kPa or less.

[0013] (3) The present invention provides the electrolyzer according to (1) or (2), wherein the cathode discharge section includes a pressure control valve.

[0014] (4) In any one of the above (1) to (3), the present invention is characterized in that the electrolysis stack has a flow rate of 500 to 5,000 cm 2 The present invention provides an electrolysis device having an electrode area of

[0015] (5) The present invention provides an electrolyzer according to any one of (1) to (4) above, wherein the electrolyte has a flow rate loss of 0.1 L / day or less.

[0016] (6) The present invention provides an electrolyzer according to any one of (1) to (5) above, wherein the electrolysis cell is a membrane electrode assembly (MEA) with a zero-gap structure in which a gas diffusion layer, a cathode, a separation membrane, and an anode having an electrolyte flow path formed therein are stacked in this order.

[0017] (7) The present invention provides, in any one of the above (1) to (6), an electrolyzer that electrolyzes carbon dioxide.

[0018] (8) The present invention provides an electrolyzer according to any one of (1) to (7) above, wherein the electrolyzer produces one or more compounds selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

[0019] (9) The present invention provides a method for operating an electrolyzer, comprising the steps of: (S1) supplying an electrolyte through an anode inlet and supplying reactants through a cathode inlet to an electrolytic stack having one or more stacked electrolytic cells, each of which includes an anode, a cathode, a separator, and an electrolyte; (S2) performing an electrolytic reaction on the reactants in the electrolytic stack; and (S3) discharging products and unreacted reactants produced by the electrolytic reaction in step (S2) to the outside of the electrolytic stack through a cathode outlet, wherein step (S3) applies a back pressure of 10 kPa or more and 50 kPa or less to the products and unreacted reactants discharged through the cathode outlet.

[0020] (10) The present invention provides the method for operating an electrolyzer according to (9), wherein the back pressure in the step (S3) is 20 kPa or more and 40 kPa or less.

[0021] (11) The present invention provides a method for operating an electrolyzer according to (9) or (10), wherein in step (S1), the supply flow rate of the reactants is maintained constant while the electrolysis reaction is carried out.

[0022] (12) The present invention provides the method for operating an electrolyzer according to any one of (9) to (11) above, wherein the back pressure is controlled by opening and closing a pressure control valve disposed in the cathode discharge part.

[0023] (13) The present invention provides a method for operating an electrolyzer according to any one of (9) to (12), wherein the unreacted reactants discharged in step (S3) are also circulated inside the electrolysis stack. [Effects of the Invention]

[0024] According to the electrolysis device of the present invention, back pressure is applied to the cathode inlet, which prevents the electrolyte from migrating from the anode to the cathode during an electrochemical reaction, thereby maintaining excellent electrolysis efficiency and overvoltage.

[0025] According to the method for operating an electrolyzer of the present invention, even if the same amount of carbon dioxide is supplied, the amount of carbon dioxide used in the electrochemical reaction can be increased, the carbon dioxide conversion rate and the faradaic efficiency of carbon monoxide can be increased, and the power consumption for recycling unreacted carbon dioxide can be reduced. [Brief explanation of the drawings]

[0026] [Figure 1] 10 is a graph of voltage and current data from a long-term performance evaluation of Example 5. [Figure 2] 10 is a graph of carbon dioxide and hydrogen faradaic efficiency data for the long term performance evaluation of Example 5. [Figure 3] 10 is a graph of voltage and current data for a long-term performance evaluation of Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0028] Here, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0029] 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.

[0030] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0031] Method of operating an electrolyzer The method for operating an electrolyzer of the present invention includes the steps of: (S1) supplying an electrolyte via an anode supply unit and supplying reactants via a cathode supply unit to an electrolytic stack having one or more stacked electrolytic cells, each of which includes an anode, a cathode, a separator, and an electrolyte; (S2) performing an electrolytic reaction on the reactants in the electrolytic stack; and (S3) discharging products and unreacted reactants produced by the electrolytic reaction in step (S2) to the outside of the electrolytic stack via a cathode discharge unit, wherein step (S3) applies a back pressure of 10 kPa or more and 50 kPa or less to the products and unreacted reactants discharged via the cathode discharge unit.

[0032] The electrolyzer of the present invention may include an electrolytic cell or an electrolytic stack in which two or more electrolytic cells are stacked, a cathode supply part, a cathode discharge part, an anode supply part, and an anode discharge part. As described below, the electrolytic cell may include an anode, a cathode, a separator membrane disposed between the anode and the cathode, and an electrolyte. Furthermore, to increase driving voltage and current efficiency, the electrolytic cell may have a zero-gap membrane electrode assembly in which a gas diffusion layer, a cathode, a separator membrane, and an anode having an electrolyte flow path formed therein are sequentially stacked. In this case, separators may be disposed on both sides of the membrane electrode assembly to form a single cell.

[0033] The cathode supply unit may supply reactants to the electrolytic cell and may be disposed adjacent to the cathode. The cathode discharge unit may discharge products generated by an electrochemical reaction and unreacted reactants from the electrolytic cell to the outside and may be disposed adjacent to the cathode. The anode supply unit may supply an electrolyte to the inside of the electrolytic cell or stack, and the anode discharge unit may discharge the used electrolyte after the electrolytic reaction to the outside.

[0034] Meanwhile, in conventional methods for electrolyzing carbon dioxide, in order to achieve a high conversion rate, an electrolyzer has been operated under atmospheric pressure conditions, and the flow rate and flow velocity of the reactant carbon dioxide has been increased and supplied to the electrolysis cell. In this case, the conversion rate can be increased by increasing the amount of carbon dioxide input, but a large amount of carbon dioxide remains unreacted inside the electrolysis cell and is discharged. This must be circulated and fed back to the electrolysis cell, which consumes a considerable amount of current and power to circulate the carbon dioxide. Furthermore, the larger the amount of unreacted carbon dioxide, the greater the cost and time required to separate it from the discharged products.

[0035] In addition, in conventional methods for electrolyzing carbon dioxide, the active area of ​​the electrolysis cell or stack is 1000 cm 2 If the concentration increases beyond this level, problems may occur in which gas or liquid penetrates through the pores of the separator and gets mixed in. Specifically, unreacted carbon dioxide gas supplied from the cathode moves to the anode, and the electrolyte moves from the anode to the cathode, producing salt, which reduces electrolysis efficiency and makes continuous operation impossible.

[0036] In the method for operating an electrolyzer of the present invention, the flow rate and flow velocity of the supplied carbon dioxide are maintained constant during the electrolysis reaction, and the flow rates of the product and unreacted carbon dioxide discharged from the cathode discharge port are reduced, allowing more carbon dioxide to react sufficiently inside the electrolysis cell. That is, in the method for operating an electrolyzer of the present invention, the pressure inside the cathode discharge port is increased, thereby increasing the pressure inside the electrolysis cell and / or stack and increasing the amount of carbon dioxide reacted, thereby improving the carbon dioxide usage rate and the carbon monoxide faradaic efficiency. In addition, the method for operating an electrolyzer of the present invention, which is capable of increasing the pressure inside the cathode discharge port, increases the amount of carbon dioxide reacted, thereby improving the carbon dioxide usage rate and the carbon monoxide faradaic efficiency. 2Even in the case of an electrolysis cell or stack having the above active area, by applying back pressure to the inside of the cathode discharge port and adjusting the ratio of the internal pressures of the cathode discharge port and the anode supply port, it is possible to prevent the electrolyte from penetrating the separator and transferring salt or unreacted carbon dioxide gas.

[0037] According to one embodiment of the present invention, a method for operating an electrolyzer of the present invention can be carried out by the steps of (S1) supplying carbon dioxide to the electrolyzer, (S2) electrolyzing the carbon dioxide, and (S3) discharging a product produced by electrolyzing the carbon dioxide and unreacted carbon dioxide, and the step of discharging the product and unreacted carbon dioxide in (S3) can be carried out by applying back pressure to the discharged product and unreacted reactant.

[0038] The back pressure refers to a resistance pressure acting in the opposite direction to the flow direction of a fluid when the fluid is discharged through a pipe. The cathode discharge port of the present invention may include a pressure control valve described below, and the back pressure can be controlled by changing the width of the cathode discharge port by opening or closing the pressure control valve. This can apply pressure in the opposite direction to the direction in which products and unreacted reactants are discharged through the cathode discharge port.

[0039] According to one embodiment of the present invention, step (S3) may apply a back pressure of 10 kPa to 50 kPa to the products and unreacted reactants discharged through the cathode discharge port. Specifically, the back pressure may be 10 kPa or more, 13 kPa or more, 15 kPa or more, 17 kPa or more, 20 kPa or more, 22 kPa or more, 25 kPa or more, 27 kPa or more, 32 kPa or more, 50 kPa or less, 47 kPa or less, 45 kPa or less, 42 kPa or less, 40 kPa or less, 37 kPa or less, 35 kPa or less, 32 kPa or less, or 30 kPa or less. If the back pressure deviates from the lower limit of the pressure range, the pressure applied to the discharged products and unreacted reactants is small, and the reduction in the flow rate of the discharged products and unreacted reactants is small, making it difficult to expect improvements in the carbon dioxide usage rate and the carbon monoxide faradaic efficiency. Furthermore, if the pressure deviates from the upper limit of the above range, the pressure applied to the discharged products and unreacted reactants may be high, reducing the discharge of products reacted inside the electrolysis cell, decreasing the carbon dioxide conversion rate, and increasing the overvoltage.

[0040] According to an 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:

[0041] [Formula 1] P cathode_out / P anode_in ≧1

[0042] In the formula 1, P cathode_out is the internal pressure of the cathode exhaust section, P anode_in is the internal pressure of the anode inlet.

[0043] Specifically, when the internal pressure of the cathode outlet is equal to or greater than the internal pressure of the anode inlet, the loss of electrolyte is reduced to 0.1 L / day or less, allowing continuous operation of the electrolyzer without a decrease in electrolysis efficiency. However, when the internal pressure of the cathode outlet is lower than the internal pressure of the anode inlet, the electrolyte passes through the separator and moves to the cathode outlet, resulting in a loss of electrolyte of 0.5 L / h, making continuous operation of the electrolyzer difficult.

[0044] According to one embodiment of the present invention, the electrolyte may have a loss flow rate of 0.1 L / day or less. Exemplarily, the loss flow rate of the electrolyte may be 0.1 L / day or less, 0.09 L / day or less, 0.08 L / day or less, 0.07 L / day or less, 0.06 L / day or less, 0.05 L / day or less, 0.04 L / day or less, 0.03 L / day or less, 0.02 L / day or less, or 0.01 L / day or less. Meanwhile, in a conventional electrolyzer that does not apply back pressure to the cathode discharge port, this corresponds to a level of 0.5 L / h or more. In this case, the electrolyte moves through the separator to the cathode, increasing the amount of salt produced, making continuous electroconversion reactions impossible.

[0045] Here, the loss flow rate of the electrolyte is a measurement of the amount of electrolyte lost over time relative to the initial amount of electrolyte filled inside the electrolytic cell.

[0046] According to one embodiment of the present invention, in step (S1), the supply flow rate of the reactants may be maintained constant during the electrolysis reaction. The method for operating an electrolyzer of the present invention maintains the supply flow rate and flow velocity of carbon dioxide supplied to the electrolysis cell constant, and adjusts the discharge flow rates of the discharged product and unreacted carbon dioxide, thereby increasing the carbon dioxide usage ratio. The method for operating an electrolyzer of the present invention solves the problem that can arise when the supply flow rate and flow velocity are increased in the conventional method, which is a decrease in the carbon dioxide usage ratio and an increase in the amount of unreacted carbon dioxide recycled to the electrolysis cell.

[0047] According to one embodiment of the present invention, the unreacted reactants discharged in step (S3) can be circulated back into the electrolytic cell. The method for operating an electrolyzer of the present invention can reduce the amount of unreacted carbon dioxide by increasing the carbon dioxide usage ratio, thereby reducing the amount of power used for circulating the reactants back into the electrolytic cell. Furthermore, the method for operating an electrolyzer of the present invention can reduce the consumption of driving current applied to the electrolyzer by increasing the faradaic efficiency of carbon monoxide.

[0048] According to one embodiment of the present invention, the cathode discharge section includes a pressure control valve, and the pressure of the product and unreacted reactants can be controlled by opening and closing the pressure control valve. Specifically, the cathode discharge section of the electrolyzer of the present invention can include a pressure control valve, and the pressure inside the cathode discharge section can be controlled by opening or closing the pressure control valve. Closing the pressure control valve can increase the pressure inside the cathode discharge section, applying pressure to the product and unreacted carbon dioxide and reducing the flow rate.

[0049] According to one embodiment of the present invention, the electrolysis cell includes a cathode, an anode, and a separation membrane. The separation membrane may be a porous separation membrane, particularly a hydrophilic porous separation membrane. Specifically, the porous separation membrane may be an ion-selective exchange membrane, and the porous separation membrane may include an anion exchange membrane, a cation exchange membrane, or an amphoteric ion exchange membrane. The porous separation membrane may include a hydrophilic porous substrate, thereby maintaining a constant water content. The porous separation membrane may include a porous substrate having pores with an average diameter of 10 nm to 750 nm, thereby providing passages for the smooth movement of various molecules, including ions and water molecules, through an aqueous electrolyte solution. This may increase the carbon dioxide conversion rate and reduce overvoltage during operation of the electrolysis device.

[0050] The hydrophilic porous substrate may be a cellulose-based resin. Specifically, the cellulose-based resin may be at least one selected from the group consisting of cellulose acetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetyl propionate, 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 include cellulose acetate.

[0051] In particular, cellulose acetate has hydrophilic properties and high dimensional stability, meaning that its dimensions and shape do not change under conditions such as temperature or humidity, and therefore has high mechanical and chemical strength and a uniform pore structure. Meanwhile, the porous separator used in the electrolytic cell for converting carbon dioxide is impregnated with an aqueous electrolyte solution formed in the porous separator, and HCO3 - , CO3 2- , O.H. - Thus, when cellulose acetate, which has the hydrophilic properties, high mechanical strength, and uniform pore size, is used as a separation membrane in a carbon dioxide electrolytic cell that uses an aqueous electrolyte, it can exhibit a high carbon dioxide conversion rate, a high carbon monoxide faradaic efficiency, and low overvoltage characteristics.

[0052] The method for operating the electrolyzer of the present invention also includes the step of: 2 By using the above-described large-area electrolysis unit cell, it is possible to apply it to a high-performance unit battery or a stack in which a plurality of unit cells are stacked.

[0053] electrolyzer The electrolyzer of the present invention includes an electrolysis stack in which one or more electrolysis cells, each including an anode, a cathode, a separator, and an electrolyte, are stacked, an anode inlet connected to the anode to transport the electrolyte, and a cathode outlet connected to the cathode to discharge products and unreacted reactants from the cathode, wherein the cathode outlet applies back pressure to the products and unreacted reactants discharged through the cathode outlet. Specifically, the electrolysis device of the present invention includes an electrolysis stack in which two or more electrolysis cells are stacked, a cathode supply unit, a cathode discharge unit, an anode supply unit, and an anode discharge unit. The electrolysis cell may include an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte. The electrolysis cell may have a zero-gap membrane electrode assembly in which a gas diffusion layer, a cathode, a separator, and an anode having an electrolyte flow path formed therein are sequentially stacked to increase driving voltage and current efficiency. In this case, separators may be disposed on both sides of the membrane electrode assembly to form a single cell. The electrolysis device of the present invention is otherwise the same as that described in the method for operating the electrolysis device of this specification.

[0054] The back pressure is 10 kPa or more and 50 kPa or less, as described in the method for operating an electrolyzer in this specification. Furthermore, if the back pressure range is satisfied and the internal pressure of the cathode outlet is equal to or greater than the internal pressure of the anode inlet, the loss of anode energy moving from the anode to the cathode is reduced, allowing for continuous operation of the electrolyzer with high efficiency.

[0055] The internal pressure of the cathode discharge part of the electrolyzer can be 10 kPa or more and 300 kPa or less, and the internal pressure of the anode discharge part can be 5 kPa or more and 60 kPa or less. Exemplarily, the internal pressure of the cathode discharge part of the electrolyzer can be 10 kPa or more, 30 kPa or more, 50 kPa or more, 60 kPa or more, 70 kPa or more, 90 kPa or more, 100 kPa or more, 110 kPa or more, 120 kPa or more, 130 kPa or more, 300 kPa or less, 270 kPa or less, 230 kPa or less, 220 kPa or less, 210 kPa or less, 200 kPa or less, 190 kPa or less, 170 kPa or less, 160 kPa or less, 150 kPa or less, or 140 kPa or less. Furthermore, for example, the internal pressure of the anode discharge part may be 5 kPa or more, 7 kPa or more, 9 kPa or more, 10 kPa or more, 12 kPa or more, 15 kPa or more, 20 kPa or more, 22 kPa or more, 25 kPa or more, 27 kPa or more, 30 kPa or more, 60 kPa or less, 57 kPa or less, 55 kPa or less, 53 kPa or less, 50 kPa or less, 48 ​​kPa or less, 45 kPa or less, 42 kPa or less, 40 kPa or less, 39 kPa or less, 37 kPa or less, or 35 kPa or less.

[0056] The cathode discharge portion may include a pressure control valve, and the back pressure may be controlled via the pressure control valve. Details regarding the pressure control valve and back pressure control are as described in the method for operating an electrolysis apparatus of this specification.

[0057] According to an 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:

[0058] [Formula 1] P cathode_out / P anode_in ≧1

[0059] In the formula 1, P cathode_out is the internal pressure of the cathode exhaust section, P anode_in is the internal pressure of the anode inlet.

[0060] Specifically, when the internal pressure of the cathode outlet is equal to or greater than the internal pressure of the anode inlet, the loss of electrolyte is reduced to 0.1 L / day or less, allowing continuous operation of the electrolyzer without a decrease in electrolysis efficiency. However, when the internal pressure of the cathode outlet is lower than the internal pressure of the anode inlet, the electrolyte passes through the separator and moves to the cathode outlet, resulting in a loss of electrolyte of 0.5 L / h, making continuous operation of the electrolyzer difficult.

[0061] According to one embodiment of the present invention, the electrolyte may have a loss flow rate of 0.1 L / day or less. Exemplarily, the loss flow rate of the electrolyte may be 0.1 L / day or less, 0.09 L / day or less, 0.08 L / day or less, 0.07 L / day or less, 0.06 L / day or less, 0.05 L / day or less, 0.04 L / day or less, 0.03 L / day or less, 0.02 L / day or less, or 0.01 L / day or less. Meanwhile, in a conventional electrolyzer that does not apply back pressure to the cathode discharge port, this corresponds to a level of 0.5 L / h or more. In this case, the amount of electrolyte that permeates the separator and moves to the cathode, generating an increased amount of salt, making continuous electroconversion reactions impossible.

[0062] Here, the loss flow rate of the electrolyte is measured by measuring the amount of electrolyte lost over time relative to the initial amount of electrolyte filled inside the electrolytic cell.

[0063] FIG. 1 is a graph of voltage and current data for the long-term performance evaluation of Example 5, FIG. 2 is a graph of carbon dioxide and hydrogen faradaic efficiency data for the long-term performance evaluation of Example 5, and FIG. 3 is a graph of voltage and current data for the long-term performance evaluation of Comparative Example 5.

[0064] Referring to FIGS. 1 and 2, when a back pressure of 0.3 bar (approximately 30 kPa) is applied to the cathode discharge section, salt generation is suppressed, allowing for long-term operation, and the overvoltage is reduced to 200 mA / cm. 2The reaction current density is maintained. In addition, the faradaic efficiency of carbon dioxide is maintained at a high level, while the faradaic efficiency of hydrogen does not increase. In contrast, referring to FIG. 3, when no back pressure is applied to the cathode outlet, the electrolyte passes through the separator and moves to the cathode side, generating salt. As a result, after about 12 hours of operation, the overvoltage increases and the reaction current is not maintained but decreases.

[0065] While fuel cells are difficult to fabricate into large-area electrochemical cells or stacks due to their practical specifications, cells or stacks used in electrolyzers can be fabricated with large areas to increase the amount of carbon dioxide or water converted per unit time. It is important for electrolytic cells or stacks to maintain a large area over a long period of time while also maintaining physical and chemical durability and high electrolysis efficiency. However, as the electrode area of ​​a cell or stack increases, the area of ​​the separator membrane used also increases, resulting in a higher reactant gas supply flow rate. When a large amount of reactant gas is supplied to the cell or stack, the internal pressure also increases. This ultimately creates a pressure gradient between the anode and cathode relative to the separator, leading to the phenomenon of materials at the two electrodes penetrating the separator and mixing with each other. Therefore, the electrolyzer of the present invention has been developed to maintain long-term durability and high electrolysis efficiency without material mixing between the electrodes, even under such large-scale cell or stack conditions, by controlling the pressure relationship between the cathode outlet and anode inlet at a predetermined ratio.

[0066] According to one embodiment of the present invention, the electrolysis stack has a flow rate of 500 to 5,000 cm 2 The electrode area of ​​the electrolysis stack means the area where the electrolysis reaction is activated, and the electrode area of ​​such an electrolysis stack is 500 to 5,000 cm. 2 Illustratively, the electrolysis stack can be 500 cm 2 More than 600cm 2 More than 700cm 2More than 800cm 2 Over 1,000cm 2 Over 1,200cm 2 Over 1,500cm 2 Over 2,000cm 2 Over 2,500cm 2 Over 5,000cm 2 Below, 4,500cm 2 Below, 4,300cm 2 Below, 4,100cm 2 Below 4,000cm 2 Below, 3,800cm 2 Below 3,500cm 2 Below, 3,300cm 2 Below, 3,100cm 2 Below 3,000cm 2 The electrode area can be less than 1,000 cm. 2 More than 4,000cm 2 The electrolysis device of the present invention can have the following electrode areas: By including a cell or stack that satisfies the above-mentioned electrode area range, it is possible to maintain high electrolysis efficiency per unit time and high physical / chemical durability for a long period of time.

[0067] According to another embodiment of the present invention, the electrolyzer can be used in any field of electrochemical conversion, and the electrolyzer can be a device capable of producing useful chemicals through electrochemical conversion, such as a fuel cell or water electrolysis, or 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.

[0068] According to one embodiment of the present invention, the electrolyzer may include a cell or stack that converts carbon dioxide into carbon monoxide, and the cell or stack may include an anode, a cathode, an electrolyte, and a separator. The cell may be a membrane electrode assembly (MEA) with a zero-gap structure in which a gas diffusion layer, a cathode, a separator, and an anode having an electrolyte flow path formed therein are sequentially stacked.

[0069] Electrolysis refers to the decomposition of a substance through an oxidation-reduction reaction by applying a direct current voltage to a decomposition reaction that does not occur spontaneously. The anode, as an oxidation electrode, oxidizes water to generate oxygen, generating hydrogen ions. The hydrogen ions generated from the anode are transferred to the cathode via the electrolyte, and the cathode, as a reduction electrode, reactants input to the cathode can react with electrons and hydrogen ions transferred from the anode to generate products. The separator can be disposed between the anode and the cathode. The separator can be 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 the cathode and serve to separate the anode and the cathode from physical contact.

[0070] 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 ensuring a smooth electrolysis reaction. Furthermore, the catalyst layer may have a porous surface to enhance gas permeability.

[0071] 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 carbon dioxide electrolyzer of the present invention may include titanium (Ti) coated with iridium oxide (IrO2).

[0072] Furthermore, since the reduction reaction of carbon dioxide generated at the cathode competes with the hydrogen generation reaction, a catalyst that requires a large voltage for the hydrogen generation reaction and is 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 alloys, Al, Au, Ag, C, Cd, Co, Cr, Cu, Cu alloys, Ga, Hg, In, Mo, Nb, Ni, NiCo2O4, Ni alloys, Ni-Fe alloys, Pb, Rh, Ti, V, W, Zn, and mixtures thereof for the hydrogen generation reaction. Specifically, the cathode in the carbon dioxide electrolyzer of the present invention may contain silver (Ag).

[0073] The separation membrane can include a cation exchange membrane (CEM) or an anion exchange membrane (AEM). Specifically, the cation exchange membrane can act as a degassing membrane that prevents the reduced substances generated at the cathode by catalytic action from moving to the anode and being oxidized, and it can suppress the permeation of anions and allow hydrogen ions (H + ) can be permeable to positive ions such as hydrogen ions (H + ) occurs, and an excessive amount of hydrogen ions move to the cathode, saturating the active sites of the catalyst where carbon dioxide is converted, which can result in a problem of a decrease in the carbon dioxide conversion rate. Here, the anion exchange membrane can reduce the amount of hydrogen ions that move to the cathode. The anion exchange membrane can prevent the carbon dioxide conversion performance of the cathode from being inhibited by blocking the movement of hydrogen ions, and OH - , HCO3 - , CO3 2- It can refer to a separation image that is permeable to anions such as:

[0074] The electrolyte may be KHCO3, K2CO3, KOH, KCl, KClO4, K2SiO3, Na2SO4, NaNO3, NaCl, NaF, NaClO4, CaCl2, Cs2CO3, H3PO4, KHPO4, guanidinium cation, H + One or more electrolytes selected from the group consisting of aqueous solutions containing cations, alkali metal cations, ammonium cations, alkylammonium cations, halide ions, alkylamines, borates, carbonates, guanidinium derivatives, nitrites, nitrates, phosphates, polyphosphates, perchlorates, silicates, sulfates, tetraalkylammonium salts, or mixtures thereof can be used. Specifically, the electrolyte of the carbon dioxide electrolyzer of the present invention can include an aqueous solution containing one or more selected from the group consisting of KOH, KHCO3, Cs2CO3, H3PO4, or a mixture of H3PO4 and KHPO4.

[0075] 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 metal porous body made of a thin metal plate with a mesh structure such as expanded metal or metal mesh. In the carbon dioxide electrolysis device of the present invention, the gas diffusion layer may be made of carbon fiber cloth.

[0076] According to one embodiment of the present invention, the electrolyzer can be used in all fields requiring electrochemical conversion, and in particular, can electrochemically decompose 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.

[0077] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0078] Example 1 The carbon dioxide electrolyzer was operated under the following operating conditions: The carbon dioxide electrolyzer was operated with a pressure of 0.4 bar (=40 kPa) applied to the cathode outlet.

[0079] Reaction current density: 300mA / 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: 100cm 2 Gas diffusion layer: Sigracet 39BB Anode electrolyte: 0.5 M KHCO3 (200 ml / min) Cathode reactant: 40°C humidified CO2 gas 40℃ Humidified CO2 gas supply flow rate: 800ml / min

[0080] Example 2 The same procedure as in Example 1 was carried out, except that a pressure of 0.20 bar (=20 kPa) was applied to the cathode discharge portion.

[0081] Example 3 Reaction current density: 200mA / cm 2 The same procedure as in Example 1 was carried out except that the voltage was applied at 100 V.

[0082] Example 4 Reaction current density is 200mA / cm 2 , electrode area is 1,000 cm 2 The same procedure as in Example 1 was carried out, except that the temperature was 40° C., the flow rate of the humidified CO2 gas supply was 6,000 ml / min, and the flow rate of the anode electrolyte was 2 L / min.

[0083] Example 5 Reaction current density: 200mA / cm 2 A pressure of 0.50 bar (=50 kPa) was applied to the cathode discharge section, and the electrode area was 1000 cm 2 The same procedure as in Example 1 was carried out, except that the temperature was 40° C., the flow rate of the humidified CO2 gas supply was 18,000 ml / min, and the flow rate of the anode electrolyte was 3 L / min.

[0084] Example 6 A pressure of 0.50 bar (=50 kPa) was applied to the cathode discharge section, and the electrode area was 1000 cm 2 The same procedure as in Example 1 was carried out, except that the temperature was 40° C., the flow rate of the humidified CO2 gas supply was 18,000 ml / min, and the flow rate of the anode electrolyte was 3 L / min.

[0085] Comparative Example 1 The same procedure as in Example 1 was carried out, except that no pressure was applied to the cathode discharge part.

[0086] Comparative Example 2 The same procedure as in Example 1 was carried out, except that a pressure of 0.60 bar (=60 kPa) was applied to the cathode discharge portion.

[0087] Comparative Example 3 No pressure was applied to the cathode outlet, and the reaction current density was set to 200 mA / cm 2 The same procedure as in Example 1 was carried out except that the voltage was applied at 100 V.

[0088] Comparative Example 4 Reaction current density is 200mA / cm 2 , electrode area is 1,000 cm 2 40℃ Humidified CO 2 The same procedure as in Example 1 was carried out, except that the gas supply flow rate was 6,000 ml / min, the anode electrolyte flow rate was 2 L / min, and no pressure was applied to the cathode outlet.

[0089] Comparative Example 5 The same procedure as in Example 5 was carried out, except that no pressure was applied to the cathode discharge part.

[0090] <Experimental Example> A carbon dioxide electrolyzer was operated using the driving methods of Examples 1 to 6 and Comparative Examples 1 to 4. Electrolysis was performed using the carbon dioxide electrolyzer, and the carbon monoxide conversion rate (%), carbon monoxide Faraday efficiency (CO Faraday efficiency, %), and voltage were measured. The measured results are shown in Table 1. In addition, a long-term performance evaluation was performed on Example 5 and Comparative Example 5, and the evaluation results are shown in Figures 1 to 3.

[0091] *Measurement method (1) Carbon monoxide conversion rate (%) The conversion rate (%) is the ratio of carbon dioxide (CO ) input per unit time. 2 ) It was calculated as the ratio of carbon monoxide (CO) produced to the amount of gas.

[0092] (2) Faraday efficiency of carbon monoxide (%) The composition of the gas at the cathode outlet was measured by GC (Gas Chromatography) analysis, and the Faraday efficiency was calculated using the following formula:

[0093] [Mathematical formula 1]

number

[0094] In the above mathematical formula 1, Q is the flow rate at the cathode outlet, F is the Faraday constant, p is the pressure, T is the measured temperature, and R is the ideal gas constant. total ) is the value of the total current applied over time, and the current to the product (i product ) is the volume of gas measured by GC analysis (V product ) is the value calculated from

[0095] (3) Voltage (V) The application of current and the measurement of voltage were carried out using a VSP potentiostat manufactured by BioLogic. An 80 A booster was attached, and a current corresponding to a large area was applied. The current application was 200 mA / cm. 2 and 300mA / cm 2 After maintaining each step for a predetermined time, the voltage was recorded after 20 minutes, and GC (Gas Chromatography) analysis was also performed at the same time.

[0096] (4) Long-term performance evaluation The carbon dioxide electrolysis devices of Example 5 and Comparative Example 5 were operated for 200 hours or more, and the carbon monoxide conversion rate, carbon monoxide faradaic efficiency, hydrogen faradaic efficiency, 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 described above.

[0097] [Table 1]

[0098] Referring to Table 1, Examples 1 to 4 apply an appropriate pressure to the cathode discharge section, Comparative Examples 1, 3, and 4 do not apply pressure to the cathode discharge section, and Comparative Example 2 applies a pressure to the cathode discharge section that deviates from the appropriate pressure range for the method of operating an electrolyzer of the present invention. Comparing Examples 1 and 2 with Comparative Examples 1 and 2, which apply the same current density, it can be seen that Examples 1 and 2, which apply an appropriate pressure to the cathode discharge section, have higher faradaic efficiency and carbon dioxide conversion rate and lower overvoltage than Comparative Examples 1 and 2, confirming that the electrolysis efficiency of Examples 1 and 2 is even better. Comparative Example 1 shows the same faradaic efficiency and carbon dioxide conversion rate as Example 1, but it can be seen that the overvoltage is higher and the electrolysis efficiency is lower than Example 1. Furthermore, Example 3 and Comparative Example 3 are both tested at a current density of 200 mA / cm. 2 In this case, it can be seen that the electrolysis efficiency of Example 3, in which an appropriate pressure was applied to the cathode outlet, was superior to that of Comparative Example 4, in which no pressure was applied. In addition, in both Example 4 and Comparative Example 4, the electrode area and the flow rate at the cathode inlet were similarly increased, and it can be seen that the electrolysis efficiency of Example 4, in which an appropriate pressure was applied to the cathode outlet, was superior to that of Comparative Example 4, in which no pressure was applied.

[0099] 1 and 2, the carbon dioxide electrolysis device of Example 5 was operated for 200 hours or more at a reaction current density of 200 mA / cm 2When operated under these conditions, the faradaic efficiency for carbon monoxide remained between 88% and 97%. The faradaic efficiency for hydrogen remained between 0% and 4%. The overvoltage remained within the range of -3.0V to -3.3V for more than 200 hours. In Figure 1, ● indicates voltage and ◆ indicates current. In Figure 2, ● indicates the faradaic efficiency for carbon dioxide and ◆ indicates the faradaic efficiency for hydrogen.

[0100] In addition, a 200-hour intermediate on-off evaluation was conducted, and it was confirmed that the initial high level of electrolysis efficiency was restored in this case as well. That is, it was confirmed that salt generation was suppressed and the device could be operated for a long period of time when a predetermined back pressure was applied to the cathode outlet and the pressure ratio between the anode inlet and the cathode outlet was maintained within the range of the present invention.

[0101] 3, in the case of the carbon dioxide electrolysis device of Comparative Example 5, it can be seen that the reaction current density drops sharply and the overvoltage increases after 12 hours, confirming that if back pressure is not applied to the cathode outlet, salt is generated and the device cannot be operated for a long period of time due to the salt. In FIG. 3, ● indicates voltage and ◆ indicates current.

Claims

1. an electrolysis stack including one or more stacked electrolysis cells each including an anode, a cathode, a separation membrane, and an electrolyte; an anode inlet connected to the anode and transporting an electrolyte; a cathode discharge part connected to the cathode and discharging products and unreacted reactants from the cathode; The electrolysis device, wherein the cathode discharge portion applies back pressure to the products and unreacted reactants discharged through the cathode discharge portion.

2. 2. The electrolysis apparatus according to claim 1, wherein the back pressure is 10 kPa or more and 50 kPa or less.

3. 10. The electrolysis apparatus of claim 1, wherein the cathode exhaust includes a pressure control valve.

4. The electrolysis stack has a thickness of 500 to 5,000 cm ２ 2. The electrolysis device of claim 1, having an electrode area of

5. 2. The electrolysis device according to claim 1, wherein the electrolyte has a flow rate loss of 0.1 L / day or less.

6. 2. The electrolysis device according to claim 1, wherein the electrolysis cell 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 formed therein are sequentially stacked.

7. The electrolyzer of claim 1 , wherein the electrolyzer electrolyzes carbon dioxide.

8. 8. The electrolyzer of claim 1, wherein the electrolyzer produces one or more selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

9. (S1) supplying an electrolyte through an anode inlet and a reactant through a cathode inlet to an electrolysis stack in which one or more electrolysis cells each including an anode, a cathode, a separator, and an electrolyte are stacked; performing an electrolysis reaction on the reactants in the electrolysis stack (S2); and (S3) discharging the product and unreacted reactants produced by the electrolysis reaction in the (S2) step to the outside of the electrolysis stack through a cathode discharge part, The method for operating an electrolyzer includes applying a back pressure of 10 kPa or more and 50 kPa or less to the product and unreacted reactants discharged through the cathode discharge port in the step (S3).

10. The method for operating an electrolyzer according to claim 9, wherein the back pressure in step (S3) is 20 kPa or more and 40 kPa or less.

11. 10. The method for operating an electrolyzer according to claim 9, wherein in step (S1), the supply flow rate of the reactants is maintained constant while the electrolysis reaction is carried out.

12. 10. The method for operating an electrolyzer according to claim 9, wherein the back pressure is controlled by opening and closing a pressure control valve disposed in the cathode discharge section.

13. The method for operating an electrolysis apparatus according to any one of claims 9 to 12, wherein the unreacted reactants discharged in step (S3) are also circulated inside the electrolysis stack.

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