Electrolysis apparatus 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 priority under Korean Patent Application No. 10-2022-0128363 dated October 7, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

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

[0003] Carbon dioxide is a greenhouse gas that causes global warming and must be reduced. Methods for reducing carbon dioxide include capture, chemical conversion, and electrochemical conversion. Of these, electrochemical conversion allows for precise control of the composition to produce other synthesis gases, yielding more economic benefits than simply removing carbon dioxide. Furthermore, carbon dioxide can be electrolyzed with water to obtain carbon monoxide, ethylene, methane, formic acid, formate salts, various hydrocarbons, and organic substances such as aldehydes or alcohols.

[0004] The electrochemical decomposition of carbon dioxide is similar to the electrolysis of water, but a strongly basic atmosphere improves the activity of the electrochemical reaction, so generally, a KOH aqueous solution of a predetermined concentration is used as the electrolyte. When an electric current is applied while water is supplied to the anode, the water is decomposed into hydrogen ions and electrons along with the generation of oxygen gas. The electrons move to the cathode via an external wire, and the hydrogen ions move to the cathode via an ion-selective separation membrane. Here, the moved electrons react with the carbon dioxide and water supplied to the cathode to form carbon monoxide and hydroxide ions (OH). - It is decomposed into ), and the resulting hydroxide ions are hydrogen ions (H) at the anode. +) reacts with it to generate water, thereby achieving an electrically neutral state. Through the above process, the electrochemical decomposition reaction of carbon dioxide is completed. Here, the water supplied together with carbon dioxide reacts with the electrons that have moved separately from the carbon monoxide generation reaction, undergoes electrolysis to generate hydrogen gas, and generates hydroxide ions. It can be said that such a reaction between water and electrons is in a competitive reaction relationship with the carbon monoxide generation reaction. Since the above reaction is an electrochemical reaction, by adjusting the voltage, the generation amount of carbon monoxide and the hydrogen / carbon dioxide ratio can be easily adjusted.

[0005] In the process of electrolyzing carbon dioxide using an electrolysis device, in order to improve the conversion rate of carbon dioxide, conventionally, a method of increasing the flow rate and velocity of the supplied carbon dioxide has been used. In this case, since the amount of supplied carbon dioxide increases, the conversion rate of carbon dioxide within a predetermined operating time can be improved. However, the unreacted carbon dioxide that is not electrolyzed inside the electrolysis device, escapes outside, and circulates in the electrolysis device increases. This ultimately leads to a situation of applying excessive current and voltage, and as a result, there is a limit in terms of the efficiency of the usage ratio of carbon dioxide.

[0006] Also, as the active area of the cell or stack included in the electrolysis device increases, gas and liquid penetrate through the separation membrane and mix, and in this case, there are problems such as a decrease in electrolysis efficiency, such as the generation of salts.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The problem that this invention aims to solve is to provide an electrolysis apparatus that can prevent the electrolyte from moving from the anode to the cathode by applying back pressure inside the cathode discharge section of the electrolysis apparatus, thereby maintaining electrolysis efficiency at an excellent level.

[0009] The problem that the present invention aims to solve is to provide an operating method for an electrolysis apparatus that can improve the utilization ratio of supplied carbon dioxide by reducing the flow rate of discharged products and unreacted carbon dioxide through the application of back pressure inside the cathode discharge section of the electrolysis apparatus. [Means for solving the problem]

[0010] The present invention provides an electrolysis apparatus and a method for operating the same.

[0011] (1) The present invention provides an electrolysis apparatus comprising an electrolysis stack in which one or more electrolysis cells, each containing an anode, a cathode, a separation membrane, and an electrolyte, are stacked; an anode inlet connected to the anode for transporting the electrolyte; and a cathode outlet connected to the cathode for discharging 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 an electrolysis apparatus in which the back pressure is 10 kPa or more and 50 kPa or less, as described in (1) above.

[0013] (3) The present invention provides an electrolysis apparatus in which the cathode discharge section includes a pressure control valve, in the case of (1) or (2) above.

[0014] (4) In any one of (1) to (3) above, the present invention provides that the electrolysis stack is 500 to 5,000 cm 2 The present invention provides an electrolysis apparatus having an electrode area of ​​[specified area].

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

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

[0017] (7) The present invention provides an electrolysis apparatus for electrolyzing carbon dioxide in any one of (1) to (6) above.

[0018] (8) The present invention provides an electrolysis apparatus in which, in any one of (1) to (7) above, the electrolysis apparatus produces one or more 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 electrolysis apparatus comprising the steps of: (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 comprising an anode, a cathode, a separation membrane and an electrolyte are stacked; (S2) carrying out an electrolysis reaction on the reactant in the electrolysis stack; and (S3) discharging the product and unreacted reactant generated by the electrolysis reaction in step (S2) to the outside of the electrolysis stack through a cathode discharge section, wherein step (S3) applies a back pressure of 10 kPa or more and 50 kPa or less to the product and unreacted reactant discharged through the cathode discharge section.

[0020] (10) The present invention provides a method for operating an electrolysis apparatus in which, in step (S3) above, the back pressure is 20 kPa or more and 40 kPa or less.

[0021] (11) The present invention provides a method for operating an electrolytic apparatus in which, in step (9) or (10), the flow rate of the reactants is kept constant while the electrolytic reaction is carried out.

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

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

[0024] According to the electrolysis apparatus of the present invention, when back pressure is applied to the cathode inlet, the phenomenon of electrolyte moving from the anode to the cathode during the electrochemical reaction can be prevented, thereby maintaining electrolysis efficiency and overvoltage at excellent levels.

[0025] According to the operating method of the electrolysis apparatus of the present invention, even when the same amount of carbon dioxide is supplied, the amount of carbon dioxide used in the electrochemical reaction can be increased, the conversion rate of carbon dioxide and the Faraday efficiency of carbon monoxide can be improved, and the power consumption for recirculating unreacted carbon dioxide can be reduced. [Brief explanation of the drawing]

[0026] [Figure 1] This is a graph of voltage and current data from the long-term performance evaluation of Example 5. [Figure 2] This graph shows the Faraday efficiency data for carbon dioxide and hydrogen from the long-term performance evaluation of Example 5. [Figure 3] This is a graph of voltage and current data from the long-term performance evaluation of Comparative Example 5. [Modes for carrying out the invention]

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

[0028] Herein, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0029] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0030] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more different features, figures, steps, components, or combinations thereof.

[0031] How to operate an electrolysis device The method of operating the electrolysis apparatus of the present invention includes the steps of: (S1) supplying electrolyte to an electrolysis stack, which is made up of one or more stacked electrolysis cells including an anode, a cathode, a separation membrane, and an electrolyte, via an anode supply unit and supplying reactants via a cathode supply unit; (S2) carrying out an electrolysis reaction on the reactants in the electrolysis stack; and (S3) discharging the products and unreacted reactants generated by the electrolysis reaction in step (S2) to the outside of the electrolysis 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 electrolysis apparatus of the present invention may include an electrolysis cell or 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 separation membrane disposed between the anode and the cathode, and an electrolyte, as described below. Furthermore, in order to increase the driving voltage and current efficiency, the electrolysis cell may form a membrane electrode assembly with a zero-gap structure in which a gas diffusion layer, a cathode, a separation membrane, and an anode with an electrolyte flow channel are stacked in order, and in this case, separation plates may be arranged on both sides of the membrane electrode assembly to form a single cell.

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

[0034] On the other hand, conventional methods for electrolyzing carbon dioxide have employed a method of operating the electrolysis apparatus under atmospheric pressure and increasing the flow rate and velocity of carbon dioxide, the reactant, to supply it to the electrolysis cell in order to obtain a high conversion rate. In this case, while the conversion rate can be increased by increasing the amount of carbon dioxide input, a large amount of unreacted carbon dioxide is discharged inside the electrolysis cell, and this must be recycled and supplied back into the electrolysis cell, resulting in a considerable consumption of current and electricity used to circulate the carbon dioxide. Furthermore, the greater the amount of unreacted carbon dioxide, the greater the cost and time consumed in the process of separating it from the products discharged along with it.

[0035] Furthermore, in conventional methods of electrolyzing carbon dioxide, the active area of ​​the electrolysis cell or stack is 1000 cm². 2 If the levels increase beyond a certain point, problems can arise where gas or liquid penetrates and mixes through the pores of the separation membrane. Specifically, unreacted carbon dioxide gas supplied from the cathode may move to the anode, and the cathode may experience problems where salts are formed due to the movement of electrolyte from the anode, reducing the electrolysis efficiency and making continuous operation impossible.

[0036] The operating method of the electrolysis apparatus of the present invention maintains a constant flow rate and flow velocity of supplied carbon dioxide during the electrolysis reaction, and reduces the flow rate of products and unreacted carbon dioxide discharged from the cathode discharge section, thereby allowing more carbon dioxide to react sufficiently inside the electrolysis cell. In other words, the operating method of the electrolysis apparatus of the present invention can increase the amount of carbon dioxide that reacts by increasing the pressure inside the electrolysis cell and / or stack by pressurizing the inside of the cathode discharge section, thereby improving the carbon dioxide utilization ratio and the Faraday efficiency of carbon monoxide. 2Even in the case of electrolysis cells or stacks having the above-mentioned active area, by applying back pressure inside the cathode discharge section and adjusting the ratio of internal pressure between the cathode discharge section and the anode supply section, it is possible to prevent the electrolyte from penetrating the separation membrane and moving salts or unreacted carbon dioxide gas.

[0037] According to one embodiment of the present invention, the method of operating the electrolysis apparatus of the present invention can be carried out by the steps of supplying carbon dioxide to the electrolysis apparatus (S1), electrolyzing the carbon dioxide (S2), and discharging the products and unreacted carbon dioxide produced by the electrolysis of carbon dioxide (S3), wherein the step of discharging the products and unreacted carbon dioxide in step (S3) can be carried out by applying back pressure to the discharged products and unreacted reactants.

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

[0039] According to an embodiment of the present invention, in the step (S3), a back pressure of 10 kPa or more and 50 kPa or less can be applied to the products and unreacted reactants discharged through the cathode discharge section. Specifically, the back pressure can 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, 30 kPa or less. When deviating from the lower limit of the pressure numerical range of the back pressure, the pressure applied to the discharged products and unreacted reactants is small, and the reduction amount of the flow rate of the discharged products and unreacted reactants is small, making it difficult to expect an improvement in the usage ratio of carbon dioxide and the Faraday efficiency of carbon monoxide. Also, when deviating from the upper limit of the pressure numerical range, the pressure applied to the discharged products and unreacted reactants is high, the discharge amount of the products reacted inside the electrolysis cell decreases, the conversion rate of carbon dioxide decreases, and the overvoltage may increase.

[0040] Also, according to an embodiment of the present invention, the internal pressure of the cathode discharge section and the internal pressure of the anode inflow section can 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 discharge section, P anode_in is the internal pressure of the anode inflow section.

[0043] Specifically, if the internal pressure of the cathode discharge section is equal to or greater than the internal pressure of the anode inlet section, electrolyte loss is reduced to a level of 0.1 L / day or less, allowing continuous operation of the electrolysis apparatus without a decrease in electrolysis efficiency. However, if the internal pressure of the cathode discharge section is lower than the internal pressure of the anode inlet section, the electrolyte will penetrate the separation membrane and move to the cathode discharge section, resulting in electrolyte loss at a level of 0.5 L / h, making continuous operation of the electrolysis apparatus difficult.

[0044] According to one embodiment of the present invention, the electrolyte can have a loss flow rate of 0.1 L / day or less. For example, the loss flow rate of the electrolyte can 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. On the other hand, in the case of a conventional electrolysis apparatus that does not apply back pressure to the cathode discharge section, the level falls to 0.5 L / h or more, in which case the electrolyte penetrates the separation membrane and moves to the cathode, increasing the amount of salt produced, making continuous electroconversion reactions impossible.

[0045] Here, the electrolyte loss flow rate is measured by comparing the amount of electrolyte lost over time with the initial amount of electrolyte filling the electrolysis cell.

[0046] According to one embodiment of the present invention, in step (S1), the supply flow rate of the reactants can be kept constant while the electrolysis reaction is carried out. The operating method of the electrolysis apparatus of the present invention can increase the carbon dioxide utilization ratio by maintaining a constant supply flow rate and flow rate of carbon dioxide supplied to the electrolysis cell, and by adjusting the discharge flow rate of the discharged product and unreacted carbon dioxide. The operating method of the electrolysis apparatus of the present invention can solve the problem that can occur when the conventional supply flow rate and flow rate are increased, which is that the carbon dioxide utilization ratio decreases and the amount of unreacted carbon dioxide that is recycled back into the electrolysis cell increases.

[0047] According to one embodiment of the present invention, the unreacted reactants discharged in step (S3) can also be circulated inside the electrolysis cell. The operating method of the electrolysis apparatus of the present invention can reduce the amount of electricity used to circulate the reactants inside the electrolysis cell by increasing the ratio of carbon dioxide used and reducing the amount of unreacted carbon dioxide. Furthermore, the operating method of the electrolysis apparatus of the present invention can reduce the amount of drive current applied to the electrolysis apparatus by increasing the Faraday 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 electrolysis apparatus of the present invention may include a pressure control valve, and the pressure inside the cathode discharge section can be controlled by opening or closing the pressure control valve. By closing the pressure control valve, the pressure inside the cathode discharge section can be increased, thereby 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, and in particular, a porous separation membrane having hydrophilic properties. 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. Furthermore, by including a hydrophilic porous substrate in the porous separation membrane, a constant amount of water content can be maintained. In addition, by including a porous substrate containing pores having an average particle size of 10 nm to 750 nm in the porous separation membrane, passages can be provided that allow various molecules, including ions and water molecules, to move smoothly by an aqueous electrolyte, thereby increasing the carbon dioxide conversion rate and reducing overvoltage when the electrolysis apparatus is in operation.

[0050] 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 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 contained in the porous separation membrane contained in the electrolytic cell of the present invention may include cellulose acetate.

[0051] In particular, the cellulose acetate has hydrophilic properties and high dimensional stability, meaning its dimensions and shape do not change under conditions such as temperature or humidity. Therefore, it has high mechanical and chemical strength and a uniform porous structure. On the other hand, in porous separation membranes used in electrolytic cells for carbon dioxide conversion, an aqueous electrolyte is impregnated into the pores formed in the porous separation membrane, and HCO3 is released through these pores. - CO3 2- , OH - Ions such as can move. As a result, when cellulose acetate, which has hydrophilic properties, high mechanical strength, and a uniform pore size, is used as a separation membrane in a carbon dioxide electrolytic cell using an aqueous electrolyte, it can exhibit a high carbon dioxide conversion rate, a high carbon monoxide Faraday efficiency, and low overpotential characteristics.

[0052] Furthermore, the operating method of the electrolysis apparatus of the present invention is a 100 cm³ device including the porous separation membrane described above. 2 By using the large-area electrolytic unit cells described above, the technology can be applied to high-performance unit batteries or stacks of multiple unit cells.

[0053] Electrolysis apparatus The electrolysis apparatus of the present invention includes an electrolysis stack in which one or more electrolysis cells, each containing an anode, a cathode, a separation membrane, and an electrolyte, are stacked; an anode inlet connected to the anode for transporting the electrolyte; and a cathode outlet connected to the cathode for discharging the product and unreacted reactants from the cathode, wherein the cathode outlet applies back pressure to the product and unreacted reactants discharged through the cathode outlet. Specifically, the electrolysis apparatus of the present invention may include an electrolysis cell or an electrolysis stack in which two or more electrolysis cells are stacked; a cathode supply unit; a cathode outlet unit; an anode supply unit; and an anode outlet unit. Furthermore, the electrolysis cell may include an anode, a cathode, a separation membrane disposed between the anode and the cathode, and an electrolyte. To improve the driving voltage and current efficiency, the electrolysis cell may form a membrane electrode assembly with a zero-gap structure in which a gas diffusion layer, a cathode, a separation membrane, and an anode with an electrolyte channel are stacked in sequence. In this case, separation plates can be arranged on both sides of the membrane electrode assembly to form a single cell. Otherwise, the electrolysis apparatus of the present invention is as described in the operating method of the electrolysis apparatus described herein.

[0054] The aforementioned back pressure is between 10 kPa and 50 kPa, as described in the operating method of the electrolysis apparatus in this specification. Furthermore, when the aforementioned back pressure range is met and the internal pressure of the cathode discharge section is equal to or greater than the internal pressure of the anode inlet section, the loss of anode moving from the anode to the cathode is reduced, enabling the operation of a highly efficient and continuous electrolysis apparatus.

[0055] The internal pressure of the cathode discharge section of the electrolysis apparatus can be between 10 kPa and 300 kPa, and the internal pressure of the anode discharge section can be between 5 kPa and 60 kPa. For example, the internal pressure of the cathode discharge section of the electrolysis apparatus can be between 10 kPa and 30 kPa, 50 kPa and 60 kPa, 70 kPa and 90 kPa and 100 kPa and 110 kPa and 120 kPa and 130 kPa and 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, and 140 kPa or less. Furthermore, as an example, the internal pressure of the anode discharge section can be 5kPa or more, 7kPa or more, 9kPa or more, 10kPa or more, 12kPa or more, 15kPa or more, 20kPa or more, 22kPa or more, 25kPa or more, 27kPa or more, 30kPa or more, 60kPa or less, 57kPa or less, 55kPa or less, 53kPa or less, 50kPa or less, 48kPa or less, 45kPa or less, 42kPa or less, 40kPa or less, 39kPa or less, 37kPa or less, or 35kPa or less.

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

[0057] Furthermore, according to one embodiment of the present invention, the internal pressure of the cathode discharge section and the internal pressure of the anode inlet section can be controlled to satisfy the following equation 1.

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

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

[0060] Specifically, if the internal pressure of the cathode discharge section is equal to or greater than the internal pressure of the anode inlet section, electrolyte loss is reduced to a level of 0.1 L / day or less, allowing for continuous operation of the electrolysis apparatus without a decrease in electrolysis efficiency. However, if the internal pressure of the cathode discharge section is lower than the internal pressure of the anode inlet section, the electrolyte will penetrate the separation membrane and move to the cathode discharge section, resulting in electrolyte loss at a level of 0.5 L / h, making it difficult to operate the electrolysis apparatus continuously.

[0061] According to one embodiment of the present invention, the electrolyte can have a loss flow rate of 0.1 L / day or less. For example, the loss flow rate of the electrolyte can 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. On the other hand, in the case of a conventional electrolysis apparatus that does not apply back pressure to the cathode discharge section, the level is 0.5 L / h or more, and in this case, the amount of electrolyte that penetrates the separation membrane and moves to the cathode to produce salt increases, making a continuous electroconversion reaction impossible.

[0062] Here, the loss flow rate of the electrolyte is measured by comparing the amount of electrolyte lost over time with the initial amount of electrolyte filling the electrolysis cell.

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

[0064] Referring to Figures 1 and 2, when a back pressure of 0.3 bar (approximately 30 kPa) is applied to the cathode discharge section, salt formation is suppressed, allowing for long-term operation, and the overvoltage actually decreases to 200 mA / cm². 2The reaction current density is maintained. Furthermore, the Faraday efficiency of carbon dioxide can be maintained at a high level, and the Faraday efficiency of hydrogen does not increase. In contrast, referring to Figure 3, if no back pressure is applied to the cathode discharge section, the electrolyte passes through the separation membrane and moves to the cathode side, causing salt formation. As a result, after about 12 hours of operation, the overvoltage increases, the reaction current is not maintained, and a decrease occurs.

[0065] On the other hand, in the case of fuel cells, considering the specifications for actual use, it is difficult to form large-area electrochemical cells or stacks. However, in the case of cells or stacks included in electrolysis devices, they can be formed over a large area in order to increase the amount of carbon dioxide or water converted per unit time. Here, in the case of electrolysis cells or stacks, it is important to maintain a large area over a long period of time, as well as physical / chemical durability and high electrolysis efficiency. However, as the electrode area of ​​the cell or stack becomes larger, the area of ​​the separation membrane applied also becomes larger, and the supply flow rate of the reaction gas also increases. When a large amount of reaction gas is supplied inside the cell or stack, the internal pressure also increases, and as a result, a pressure gradient is created between the anode and cathode with respect to the separation membrane, and the substances of both electrodes penetrate the separation membrane and mix with each other. Therefore, the electrolysis device of the present invention has been developed to maintain long-term durability without substance mixing between the two electrodes and to have high electrolysis efficiency, even under the conditions of such large-scale cells or stacks, by controlling the pressure relationship between the cathode discharge section and the anode inlet section at a predetermined ratio.

[0066] According to one embodiment of the present invention, the electrolysis stack is 500 to 5,000 cm². 2 It can have an electrode area of ​​500 to 5,000 cm². The electrode area of ​​an electrolysis stack refers to the area where the electrolysis reaction is activated, and such an electrolysis stack has an electrode area of ​​500 to 5,000 cm². 2 It can be. For example, the electrolysis stack is 500 cm³. 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 as follows, specifically 1,000 cm² 2 More than 4,000cm 2 The following electrode areas can be provided. In the case of the electrolysis apparatus of the present invention, by including a cell or stack that satisfies the range of the above electrode areas, high electrolysis efficiency per unit time and high physical / chemical durability can be maintained for a long period of time.

[0067] According to other embodiments of the present invention, the electrolysis apparatus can be used in all fields of electrochemical conversion, and the electrolysis apparatus can be a device capable of producing useful chemical substances by electrochemical conversion such as fuel cells and water electrolysis, and a device capable of reducing and converting carbon dioxide and NOx. Specifically, the electrolysis apparatus 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 electrolysis apparatus may include a cell or stack into which carbon dioxide is introduced and converted into carbon monoxide, and the cell or stack may include an anode, a cathode, an electrolyte, and a separation membrane. The cell may also be a membrane electrode assembly (MEA) with a zero-gap structure in which a gas diffusion layer, a cathode, a separation membrane, and an anode with an electrolyte channel are stacked in order.

[0069] The electrolysis described above means decomposing a substance by oxidation-reduction reactions by applying a DC voltage to a decomposition reaction that does not occur spontaneously. The anode acts as an oxidation electrode, oxidizing water to produce oxygen, where hydrogen ions are generated. The hydrogen ions generated from the anode are transferred to the cathode by the electrolyte, and the cathode acts as a reduction electrode, where reactants introduced into the cathode react with electrons and hydrogen ions that have moved from the anode to produce products. The separation membrane can be placed between the anode and the cathode. The separation membrane can be made of an inert material that does not participate in the electrochemical reaction itself, but it can provide a pathway for ions to move between the anode and the cathode and can serve to separate the physical contact between the anode and the cathode.

[0070] Furthermore, the anode and cathode of the electrolysis apparatus of the present invention may each include a catalyst layer. In addition, water vapor supplied together with carbon dioxide in the cathode region generates reduction products by an electro-reduction reaction on the surface of the cathode. 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 water condensation, thereby ensuring a continuous and uniform supply of carbon dioxide and allowing the electrolysis reaction to proceed smoothly. Furthermore, the catalyst layer may have a surface such as a porous structure so that its gas permeability characteristics are well exhibited.

[0071] According to one embodiment of the present invention, the anode may contain a catalyst active in the electrolysis of water, and the catalyst layer of the anode may contain 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., for the oxygen evolution reaction. Specifically, the anode in the carbon dioxide electrolysis apparatus of the present invention may contain titanium (Ti) coated with iridium oxide (IrO2).

[0072] Furthermore, since the reduction reaction of carbon dioxide generated in the cathode competes with the hydrogen evolution reaction, the catalyst may include one that requires a high voltage for the hydrogen evolution reaction and is active in the reduction reaction of carbon dioxide. The catalyst layer of the cathode may include one or more 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 evolution reaction. Specifically, the cathode in the carbon dioxide electrolysis apparatus of the present invention may include silver (Ag).

[0073] Furthermore, the separation membrane may include a cation exchange membrane (CEM) or an anion exchange membrane (AEM). Specifically, in the case of a cation exchange membrane, it can act as a degassing membrane to prevent oxidation by moving the reducing substance generated at the cathode through catalytic action to the anode, thereby suppressing the permeation of anions and hydrogen ions (H + A separation image can be obtained in which cations such as ) can pass through. In addition, water can be oxidized at the anode to obtain hydrogen ions (H + This can lead to the generation of OH, where an excess of hydrogen ions moves to the cathode, saturating the active site of the catalyst that converts carbon dioxide and reducing 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, - , HCO3 - CO3 2- This can mean a separated image in which anions can pass through.

[0074] Furthermore, the electrolytes include 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 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 aqueous solutions containing mixtures thereof can be used. Specifically, the electrolyte of the carbon dioxide electrolysis apparatus of the present invention may 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] Furthermore, the gas diffusion layer can be made of a porous material made of carbon, such as carbon fiber cloth, carbon fiber felt, or carbon fiber paper, or a porous metal made of a thin metal plate with a mesh structure, such as expanded metal or metal mesh. In the carbon dioxide electrolysis apparatus of the present invention, the gas diffusion layer can be made of carbon fiber cloth.

[0076] According to one embodiment of the present invention, the electrolysis apparatus can be used in all fields requiring electrochemical conversion, and in particular, it can electrochemically decompose carbon dioxide to obtain desired products. Specifically, the electrolysis apparatus can electrolyze carbon dioxide to produce one or more substances selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

[0077] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention may be realized in various different forms and is not limited to the embodiments described herein.

[0078] Example 1 A carbon dioxide electrolysis apparatus was operated under the following operating conditions. The apparatus was operated by applying a pressure of 0.4 bar (=40 kPa) to the cathode discharge port.

[0079] Reaction current density: 300 mA / cm² 2 (Constant current operation) Reaction voltage: 1~4V Reaction temperature: 40℃ Reaction pressure: 1 atm (atmospheric pressure) Anode catalyst: IrO2on 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: Humidified CO2 gas at 40°C 40℃ Humidified CO2 gas supply flow rate: 800 ml / min

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

[0081] Example 3 The reaction current density is 200 mA / cm². 2 The procedure was carried out in the same manner as in Example 1, except that the application was performed using [a specific method / tool].

[0082] Example 4 The reaction current density is 200 mA / cm². 2 , electrode area is 1,000 cm² 2 The procedure was carried out in the same manner as in Example 1, except that the 40°C Humidified CO2 gas supply flow rate was 6,000 ml / min and the anode electrolyte flow rate was 2 L / min.

[0083] Example 5 The reaction current density is 200 mA / cm². 2 A pressure of 0.50 bar (= 50 kPa) is applied to the cathode discharge section, and the electrode area is 1000 cm². 2 The procedure was carried out in the same manner as in Example 1, except that the 40°C Humidified CO2 gas supply flow rate was 18,000 ml / min and the anode electrolyte flow rate was 3 L / min.

[0084] Example 6 A pressure of 0.50 bar (= 50 kPa) is applied to the cathode discharge section, and the electrode area is 1000 cm². 2 The procedure was carried out in the same manner as in Example 1, except that the 40°C Humidified CO2 gas supply flow rate was 18,000 ml / min and the anode electrolyte flow rate was 3 L / min.

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

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

[0087] Comparative Example 3 Without applying pressure to the cathode discharge section, the reaction current density was set to 200 mA / cm². 2 The procedure was carried out in the same manner as in Example 1, except that the application was performed using [a specific method / tool].

[0088] Comparative Example 4 The reaction current density is 200 mA / cm². 2 , electrode area is 1,000 cm² 2 Therefore, 40℃ Humidified CO 2 The procedure was carried out in the same manner as in Example 1, 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 discharge port.

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

[0090] <Example of experiment> The carbon dioxide electrolysis apparatus was operated using the driving methods described in Examples 1-6 and Comparative Examples 1-4. Electrolysis was performed using the carbon dioxide electrolysis apparatus, and the carbon monoxide conversion rate (%), carbon monoxide Faraday efficiency (CO2 Faraday efficiency, %), and voltage were measured. The measured values ​​are shown in Table 1. In addition, long-term performance evaluations were conducted for Example 5 and Comparative Example 5, and the evaluation results are shown in Figures 1-3.

[0091] *Measurement method (1) Carbon monoxide conversion rate (%) The conversion rate (%) is calculated by the amount of carbon dioxide (CO2) added per hour. 2 The calculation was based on the ratio of carbon monoxide (CO) produced to the amount of gas.

[0092] (2) Faraday efficiency of carbon monoxide (%) The gas composition at the cathode outlet was measured by gas chromatography (GC) analysis. 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 discharge section, F is the Faraday constant, p is the pressure, T is the measured temperature, and R is the ideal gas constant. Total current (i total ) is the value of the total current applied over time, and the current (i) applied to the product product ) is the volume of gas (V) measured by GC analysis. product This is a value calculated from ).

[0095] (3) Voltage (V) Current application and voltage measurement were performed using a BioLogic VSP potentiostat. An 80A booster was installed, and a current corresponding to a large area was applied. The applied current was 200mA / cm². 2 and 300mA / cm 2 For each stage, the voltage was recorded after maintaining the specified time for 20 minutes. Gas-chromatography (GC) analysis was also performed simultaneously.

[0096] (4) Long-term performance evaluation The carbon dioxide electrolysis apparatuses of Example 5 and Comparative Example 5 were operated for more than 200 hours, and the carbon monoxide conversion rate, Faraday efficiency of carbon monoxide, Faraday efficiency of hydrogen, reaction current density, and overpotential of Example 5, as well as the reaction current density and overpotential of Comparative Example 5, were measured in the same manner as described above.

[0097] [Table 1]

[0098] Referring to Table 1, Examples 1-4 had the appropriate pressure applied to the cathode discharge section, Comparative Examples 1, 3, and 4 did not have pressure applied to the cathode discharge section, and Comparative Example 2 had a pressure applied to the cathode discharge section that deviated from the appropriate pressure range according to the operating method of the electrolysis apparatus of the present invention. Comparing Examples 1 and 2 with Comparative Examples 1 and 2, which applied the same current density, it can be confirmed that Examples 1 and 2, which applied the appropriate pressure to the cathode discharge section, had higher Faraday efficiency and carbon dioxide conversion rate, and lower overpotential compared to Comparative Examples 1 and 2, confirming that the electrolysis efficiency of Examples 1 and 2 is even better. In the case of Comparative Example 1, it showed the same Faraday efficiency and carbon dioxide conversion rate as Example 1, but the overpotential was high, and it can be confirmed that the electrolysis efficiency was lower compared to Example 1. Also, Examples 3 and Comparative Example 3 had a current density of 200 mA / cm². 2 Although a current is applied, in this case as well, it can be confirmed that the electrolysis efficiency of Example 3, in which appropriate pressure is applied to the cathode discharge section, is even better than that of Comparative Example 4, in which no pressure is applied. Furthermore, in Example 4 and Comparative Example 4, the electrode area and the flow rate of the cathode inlet section are similarly increased, but in this case as well, it can be confirmed that the electrolysis efficiency of Example 4, in which appropriate pressure is applied to the cathode discharge section, is superior to that of Comparative Example 4, in which no pressure is applied.

[0099] Furthermore, referring to Figures 1 and 2, the carbon dioxide electrolysis apparatus of Example 5 was subjected to a reaction current density of 200 mA / cm² for more than 200 hours. 2Under these conditions, the Faraday efficiency of carbon monoxide remained between 88% and 97%. The Faraday efficiency of hydrogen remained between 0% and 4%. Furthermore, the overvoltage was maintained within the range of -3.0V to -3.3V for over 200 hours. In Figure 1, ● represents voltage and ◆ represents current. In Figure 2, ● represents the Faraday efficiency of carbon dioxide and ◆ represents the Faraday efficiency of hydrogen.

[0100] Furthermore, an intermediate on-off evaluation was conducted for 200 hours, and it was confirmed that the system recovered to the initial high level of electrolysis efficiency. In other words, by applying a predetermined back pressure to the cathode discharge section and maintaining the pressure ratio between the anode inlet and cathode discharge section within the scope of the present invention, it was confirmed that salt generation is suppressed and the device can be operated for a long period of time.

[0101] On the other hand, referring to Figure 3, in the case of the carbon dioxide electrolysis apparatus of Comparative Example 5, it can be confirmed that the reaction current density decreases sharply after 12 hours and the overvoltage increases. This confirms that if back pressure is not applied to the cathode discharge section, salt is generated, and the salt makes long-term operation impossible. In Figure 3, ● represents voltage and ◆ represents current.

Claims

1. An electrolysis stack comprising one or more electrolysis cells, each containing an anode, cathode, separation membrane, and electrolyte, The anode inlet is connected to the anode and transports the electrolyte, an anode discharge section that discharges the used electrolyte to the outside, The cathode inlet for supplying the reactants, It includes a cathode discharge section connected to the cathode for discharging the product and unreacted reactants from the cathode, The cathode discharge section is subjected to a back pressure of 20 kPa or more and 40 kPa or less applied to the product and unreacted reactants discharged through the cathode discharge section in a carbon dioxide electrolysis apparatus.

2. The carbon dioxide electrolysis apparatus according to claim 1, wherein the cathode discharge section includes a pressure control valve.

3. The electrolysis stack described above has a range of 500 to 5,000 cm³. ２ The carbon dioxide electrolysis apparatus according to claim 1, having an electrode area of ​​the specified area.

4. The carbon dioxide electrolysis apparatus according to claim 1, 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 on which an electrolyte channel is formed are stacked in order.

5. The electrolysis apparatus is a carbon dioxide electrolysis apparatus according to claim 1, wherein the electrolysis apparatus electrolyzes carbon dioxide.

6. The electrolysis apparatus according to any one of claims 1 to 5, wherein the electrolysis apparatus produces one or more selected from the group consisting of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols.

7. Step (S1) involves supplying electrolyte to an electrolysis stack, which consists of one or more electrolysis cells stacked, each containing an anode, cathode, separation membrane, and electrolyte, via an anode inlet and a cathode inlet, and supplying reactants via a cathode inlet. Step (S2) of carrying out an electrolysis reaction with respect to the reactants in the electrolysis stack, The step (S3) includes discharging the product and unreacted reactants generated by the electrolysis reaction in step (S2) to the outside of the electrolysis stack via a cathode discharge section. Step (S3) is a method for operating a carbon dioxide electrolysis apparatus, wherein a back pressure of 20 kPa or more and 40 kPa or less is applied to the product and unreacted reactants discharged through the cathode discharge section.

8. In step (S1), the flow rate of the reactant is kept constant while the electrolysis reaction is carried out, the method of operating a carbon dioxide electrolysis apparatus according to claim 7.

9. The method for operating a carbon dioxide electrolysis apparatus according to claim 7, wherein the back pressure is controlled by opening and closing a pressure control valve located at the cathode discharge section.

10. The method of operating a carbon dioxide electrolysis apparatus according to any one of claims 7 to 9, wherein the unreacted reactants discharged in step (S3) are also circulated inside the electrolysis stack.

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