Method for producing co from solid oxide electrolytic cell (SOEC) while removing deposited carbon through power control

Abstract

According to the present invention, a step for cutting off power supply to a cathode is added in order to solve a carbon deposition phenomenon that occurs in conventional SOECs for producing CO from CO2. As a result, a novel method using CO2 is provided, wherein the method not only can simultaneously convert deposited carbon into CO while removing the deposited carbon by inducing the reverse Boudouard reaction, but does not require previously attempted means of suppressing carbon deposition, such as metal coating of the cathode or a change in electrolyte thickness, thus having the remarkable effect of making it possible to reduce CO2 in an eco-friendly manner through simple and easy manipulation of SOEC operating conditions.

Description

A method for producing CO by removing deposited carbon through power interruption in a solid oxide electrolytic cell (SOEC).

[0001] The present invention relates to a method for producing CO by decomposing CO2 in a solid oxide electrolytic cell (SOEC), and more particularly, to a method for producing CO while removing the deposited carbon by simply and easily manipulating the operating conditions of a SOEC in an environment where carbon is deposited by CO generated from an electrolytic reaction (Boudouard reaction) at a reduction electrode in an SOEC to which a CO2-containing gas is supplied.

[0002] Rising ocean temperatures and global warming are leading to accelerated melting of ice and other climate-related problems worldwide. Excessive emissions of the fossil fuel-derived greenhouse gas CO2 are identified as a contributing factor. To reduce excessive CO2 emissions, specific measures are being developed and implemented globally to achieve a carbon-neutral society. One example of these measures is CO2 utilization.

[0003] CO2 utilization, along with CO2 storage and capture, is a means of reducing greenhouse gases. For example, technologies are being researched and developed to convert CO2, which contains a single carbon atom, into fuels, chemical raw materials, and other materials. Useful substances obtained from CO2 include carbon monoxide (CO), which can be used as a reducing agent in metal refining processes or as a raw material for chemical reactions to produce methane, methanol, and other hydrocarbons, making it highly valuable industrially.

[0004] A solid oxide electrolysis cell (SOEC) can be utilized as a means of converting the above CO2 into CO. In the SOEC, CO2 is supplied to the reduction electrode, and CO is generated from CO2 through the CO2 electrolysis reaction of Equation 1 below, and ionized oxygen (O 2- ) moves to the cathode through the electrolyte, after which oxygen (O2) is generated and released.

[0005] (Formula 1)

[0006] Reduction electrode: CO2+ 2e - → CO + O 2-

[0007] Air electrode: O 2- → 1 / 2O2+ 2e -

[0008] However, in a power-supplied reduction electrode environment, the CO electrolysis reaction of Equation 2 below may progress further, generating carbon from CO and depositing it within the SOEC, including the reduction electrode. The deposited carbon reduces the specific surface area of ​​the electrode, which has the problem of deteriorating the performance and lifespan of the battery.

[0009] Reduction electrode: CO + 2e - → C + O 2- (Formula 2)

[0010] European Patent Publication No. 2940773 (published on April 11, 2015) discloses a method of injecting H2S to solve the above-mentioned carbon deposition problem in the CO2 decomposition reaction in the SOEC, Japanese Patent Publication No. 6192669 (registered on August 18, 2017) and Korean Patent Publication No. 10-2019-0018484 (published on February 22, 2019) disclose a method of suppressing carbon deposition by coating a reduction electrode with a specific metal or changing the thickness of an electrolyte, and other known technologies disclose a method of producing CO and H2 through a co-electrolysis reaction in which steam is injected together with carbon dioxide, and a method of producing CO and H2 by reacting carbon deposited due to excessive power supply with steam through the reaction of Equation 3 below.

[0011] (Formula 3)

[0012] Reduction electrode: CO2+ 2e - → CO + O 2-

[0013] H2O + 2e - → H2+ O 2-

[0014] Air electrode: 2O 2- → O2+ 4e -

[0015] However, the metals used as reduction electrode coating materials disclosed in the aforementioned prior art are generally expensive, and to uniformly coat the electrode surface, separate metal coating technology and optimized conditions are required, which can cause environmental pollution during the process. Furthermore, utilizing the co-electrolysis reaction within the SOEC requires a separate thermal energy source to generate steam from water, making it somewhat unsuitable for achieving the goal of CO2 reduction through CO2 utilization.

[0016] Therefore, the method of producing CO from CO2 through SOEC is suitable for achieving the goal of CO2 reduction and carbon neutrality by applying a reaction of electrolyzing single-molecule CO2, but research and development of simple and easy means and methods for removing precipitated carbon are needed.

[0017] (Prior art literature)

[0018] (Patent Document 1) European Patent Publication No. 2940773 (published on April 11, 2015)

[0019] (Patent Document 2) Japanese Patent Publication No. 6192669 (registered on August 18, 2017)

[0020] (Patent Document 3) Korean Patent Publication No. 10-2019-0018484 (Published on February 22, 2019)

[0021] The present invention provides a method for producing CO from CO2 in an SOEC, which can solve the problem of carbon deposition by supplying a CO2-containing gas as a reactant in the SOEC, but converting the reactant CO2 and the deposited carbon into CO through a reverse Boudard reaction without suppressing the carbon deposition phenomenon that occurs through the electrolysis reaction of the gas.

[0022] In order to solve the above problem, the present invention provides a method for producing CO while removing deposited carbon in a solid oxide electrolysis cell (SOEC) in which a CO2-containing gas is supplied to a reduction electrode, the method comprising: (a) a step of supplying power to an operating reduction electrode (cathode) to decompose CO2 in a CO2-containing gas through an electrolytic reaction; (b) a step of removing the deposited carbon through a reverse Boudouard reaction by cutting off the power supplied to the reduction electrode; and (c) a step of repeating steps (a) and (b).

[0023] The supplied CO2-containing gas may further include one or more selected from CO, H2O, H2, and an inert gas, and the CO2 may be 10 to 100 v / v% in the supplied gas.

[0024] As one embodiment of the present invention, the temperature of the reduction electrode operating at high temperature in step (a) may be 700 to 1,000°C.

[0025] The power supplied to the reduction electrode in the above step (a) may be a current of 10 mA or more.

[0026] In addition, the present invention provides an SOEC system for generating CO from CO2, which comprises a reduction electrode section including a reduction electrode and a CO2-containing gas inlet and a reaction product gas outlet; an oxidation electrode section including an oxidation electrode and a reaction product gas outlet; an electrolyte section; and a power supply device for supplying current to the electrode, and further including an electric interruption device capable of interrupting the current to the electrode.

[0027] In the above system, the reduction electrode may include a catalyst that promotes the reverse Boudard reaction on at least a portion of the electrode.

[0028] According to the present invention, in order to solve the carbon deposition phenomenon that occurs in the conventional SOEC that produces CO from CO2, adding a step of cutting off the power supply to the reduction electrode not only removes the deposited carbon by inducing a reverse Budard reaction and simultaneously converts it into CO, but also is a novel concept of CO2 utilization method that does not require means such as metal coating or changing the electrolyte thickness on the reduction electrode that were attempted to suppress the carbon deposition phenomenon in the past, and has a remarkable effect of reducing CO2 in an environmentally friendly manner only by simply and easily manipulating the SOEC operating conditions.

[0029] Figure 1 shows an operating diagram of a solid oxide electrolytic cell (SOEC) that electrolyzes CO2 to produce CO according to the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0031] Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0032] Hereinafter, a method for producing CO while removing deposited carbon through power interruption in the SOEC of the present invention will be described in detail.

[0033] Looking at the principles of preventing carbon deposition in SOECs in prior literature, the means for preventing carbon deposition disclosed in Patent Documents 2 and 3 correspond to methods for reducing the amount of carbon deposition derived from CO by coating the reduction electrode with a specific metal or changing the thickness of the electrolyte. While this has the advantage of reducing the carbon deposition phenomenon itself, as mentioned above, it requires metal coating technology on the electrode surface, and there is the problem that the coating solution containing the metal may pollute the environment.

[0034] In addition, the means for preventing carbon deposition disclosed in the above-mentioned background art patent document 1 and the publicly known technology are methods of injecting H2S or H2O (steam), and there is a problem in that a separate gas component to be injected and a supply device for the same must be provided.

[0035] However, according to the present invention, a method of removing carbon through a reverse Boudard reaction induced by cutting off the power supply during the operating conditions of a SOEC is proposed as a novel means capable of continuously removing carbon generated through an electrolysis reaction without requiring a separate supply gas and equipment for preventing carbon deposition disclosed in the above-mentioned prior art document and without reducing or preventing carbon deposition from the source.

[0036] As described in Equation 4 below, the reverse Boudard reaction is a reaction that converts supplied CO2 into CO by reacting with deposited carbon, and the technical feature of the present invention is that it is performed while the power supply for the CO2 electrolysis reaction is cut off.

[0037] CO2+ C ↔ 2CO (Equation 4)

[0038] The above-mentioned reverse Boudard reaction, which is an endothermic reaction, is performed at a cathode operating at high temperature, and the deposited carbon is converted to CO in the presence of CO2, so that CO can be produced while removing the deposited carbon even when the power supply is cut off.

[0039] Accordingly, the applicant of the present invention has conceived a technical idea that can fundamentally solve the problem of conventional carbon deposition phenomenon through simple and easy operation condition manipulation of periodic power supply interruption in SOEC, and has completed the present invention.

[0040] The present invention is characterized by comprising a method for producing CO from CO2, comprising: (a) a step of supplying power to a high-temperature operating cathode to decompose CO2 in a CO2-containing gas through an electrolytic reaction; (b) a step of removing deposited carbon through a reverse Boudouard reaction by cutting off the power supplied to the cathode; and (c) a step of repeating steps (a) and (b).

[0041] Figure 1 shows an operating diagram of a solid oxide electrolytic cell (SOEC) that electrolyzes CO2 to produce CO according to the present invention.

[0042] Referring to the above drawing 1, the SOEC may include, as an example, a reduction electrode unit, an oxidation electrode unit, and an electrolyte unit, and the reduction electrode unit may include a reduction electrode and a CO2-containing gas inlet and a reaction product gas outlet, and the oxidation electrode unit may include an oxidation electrode and a reaction product gas outlet.

[0043] The above reduction electrode may include a reaction catalyst that promotes a chemical reaction in at least a portion of the electrode, and the reaction catalyst included in the reduction electrode may be any known catalyst that reduces CO2 to produce CO and / or a reverse Butard reaction catalyst that produces CO from C and CO2, without limitation. The catalyst that reduces CO2 to produce CO is not limited thereto, but is a catalyst in which a metal or alloy is supported on a metal oxide support, and the support may be yttria-stabilized zirconia, gadolinium-doped ceria, scandia-stabilized zirconia, etc., and the catalyst for the reverse Butard reaction is not limited thereto, but may include a metal carbonate salt catalyst, a metal oxide catalyst, FeNi3, etc.

[0044] Hereinafter, a method for producing CO from CO2 in a solid oxide electrolysis cell (SOEC) in which a CO2-containing gas is supplied to a reduction electrode of the present invention will be described in detail step by step.

[0045] The above step (a) is a step of injecting CO2-containing gas through a gas inlet to the reduction electrode side, bringing the reactant CO2 into contact with the reduction electrode, and converting it into CO through the CO2 electrolysis reaction of Equation 1 below.

[0046] Reduction electrode: CO2+ 2e - → CO + O 2- (Formula 1)

[0047] Accordingly, as a condition for the electrolytic reaction of the above formula 1, the supplied CO2-containing gas includes CO2, CO, H2O and H2, and the CO2 may be 10 to 100 v / v% in the supplied gas.

[0048] In addition, the temperature of the high-temperature operating reduction electrode in the above step (a) may be 700 to 1,000°C. If the temperature of the reduction electrode is less than 700°C, the decomposition reaction of CO2 into CO is insufficient, and if the temperature of the reduction electrode exceeds 1,000°C, there is a risk of electrode damage.

[0049] The power supplied to the reduction electrode may be a current of 10 mA or more. The power may have a current density of 10 mA / cm. 2 If it is less than 3 A / cm, the CO2 electrolysis reaction progresses slowly, which causes a problem in that the power supply cycle becomes longer, and the power supply has a current density of 3 A / cm. 2 If exceeded, there is a risk of SOEC damage due to overvoltage and thermal shock.

[0050] In the reduction process of CO2 in the above step (a), CO may be over-reduced and deposited as carbon (C) on the electrode surface. The above step (b) is a step for removing the carbon deposited on the electrode surface, and is a step for removing the carbon deposited on the electrode surface through a reverse reaction by cutting off the power supplied to the reduction electrode.

[0051] In order to remove carbon through the reverse Budard reaction in the above step (b), the current supply must be stopped. This is because in a reduction electrode environment where power is supplied, CO, a product of the electrolytic reaction, can be deposited in the SOEC including the reduction electrode by generating carbon through the electrolytic reaction of Equation 2 below.

[0052] CO + 2e - → C + O 2- (Formula 2)

[0053] In order to remove carbon deposited in the reduction electrode, the supplied power is cut off to stop the electrolytic reaction of CO2 and CO, and a step of inducing a reverse Boudard reaction of Equation 4 below using the deposited carbon and the supplied CO2 as reactants is added to the SOEC electrolytic reaction process, which is a technical feature of the present invention.

[0054] CO2+ C ↔ 2 CO (Equation 4)

[0055] The SOEC, which blocks the power supplied to the reduction electrode, can induce the reverse Boudard reaction of the above equation 4, which is an endothermic reaction, under the operating temperature conditions described above, thereby removing carbon deposited in the reduction electrode and producing CO continuously, which has a remarkable effect.

[0056] There have been numerous prior art documents describing approaches to SOEC manufacturing technology for preventing carbon deposition, such as methods of metal-coating the electrodes that make up the SOEC or changing the thickness and pores of the electrolyte. However, an approach like the present invention, which intentionally deposits carbon in the environment of the reduction electrode during the operating conditions of the SOEC and artificially changes the power supplied to the reduction electrode to induce a chemical reaction that reduces the deposited carbon, has not been disclosed to date. However, in the present invention, a simple operation of simply interrupting the current can sufficiently convert the deposited carbon into CO again, and thus, there is no need to perform various operations to suppress carbon deposition in the CO2 reduction reaction.

[0057] The reduction electrode on which the reverse-Buddard reaction of the above step (b) is performed may include a reverse-Buddard reaction catalyst on the surface, and the reverse-Buddard reaction catalyst may include at least one active metal selected from the group consisting of a non-metal, a metal, and an alloy. In order to improve the catalytic performance, the active metal may be used in the form of a supported catalyst supported on at least one oxide of a metal or a non-metal, or a catalyst complex formed through a coordination bond between the active metal and a ligand. However, the present invention is not limited thereto, and any reverse-Buddard reaction catalyst known in the art of producing CO from CO2 may be used without limitation. For example, the reverse-Buddard reaction catalyst may include a metal carbonate salt catalyst, a metal oxide catalyst, FeNi3, etc.

[0058] The above step (c) is a step in which steps (a) and (b) are performed consecutively again after removing at least a portion of the carbon deposited by step (b) of the power supply. The generated CO can be discharged through the reaction product gas exhaust port.

[0059] In addition, the present invention provides an SOEC system for generating CO from CO2, which comprises a reduction electrode section including a reduction electrode and a CO2-containing gas inlet and a reaction product gas outlet; an oxidation electrode section including an oxidation electrode and a reaction product gas outlet; an electrolyte section; and a power supply device for supplying current to the electrode, and further including an electric interruption device capable of interrupting the current to the electrode.

[0060] In the above system, the reduction electrode may include a catalyst that promotes the reverse Boudard reaction on at least a portion of the electrode.

[0061] While the present invention has been described through one embodiment, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent embodiments are possible. Accordingly, the technical protection scope of the present invention should be defined by the following claims.

[0062] The present invention relates to a SOEC capable of reducing CO2 in an environmentally friendly manner, and does not require means such as metal coating on a reduction electrode or changing the thickness of an electrolyte, which have been attempted in the past to suppress carbon deposition, and can remove deposited carbon by inducing a reverse Boudouard reaction only by simply manipulating SOEC operating conditions, so that industrial applicability is recognized.

Claims

1. A method for producing CO in a solid oxide electrolytic cell (SOEC) in which a CO2-containing gas is supplied to a reduction electrode, (a) A step of supplying power to a high-temperature operating cathode to decompose CO2 in a CO2-containing gas through an electrolytic reaction; (b) a step of removing the deposited carbon through a reverse Boudouard reaction by cutting off the power supplied to the reduction electrode; and (c) A method for producing CO from CO2 in a SOEC, characterized in that it comprises a step of repeating steps (a) and (b).

2. In paragraph 1, A method for producing CO from CO2 in SOEC, wherein the supplied CO2-containing gas further comprises at least one selected from CO, H2O, H2, and an inert gas, and the CO2 is 10 to 100 v / v% in the supplied gas.

3. In paragraph 1, A method for producing CO from CO2 in a SOEC, characterized in that the temperature of the high-temperature operating reduction electrode in the above step (a) is 700 to 1,000°C.

4. In paragraph 1, A method for producing CO from CO2 in a SOEC, characterized in that the power supplied to the reduction electrode in the above step (a) is a current of 10 mA or more.

5. In the SOEC system that generates CO from CO2, It has a reduction electrode section including a reduction electrode and a CO2-containing gas inlet and a reaction product gas outlet; an oxidation electrode section including an oxidation electrode and a reaction product gas outlet; an electrolyte section; and a power supply device that supplies current to the electrodes. An SOEC system for generating CO from CO2, characterized in that it further includes an electrical interrupter capable of interrupting the current to the electrode.

6. In paragraph 5, An SOEC system for producing CO from CO2, wherein the reduction electrode comprises a catalyst that promotes a reverse Boudard reaction in at least a portion of the electrode.

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