Method for electrolyzing carbon dioxide in solid oxide electrolytic tank

Abstract

The invention relates to the field of carbon dioxide electrolysis, and discloses a method for electrolyzing carbon dioxide by a solid oxide electrolytic cell, which comprises the following steps: when the solid oxide electrolytic cell is assembled and pressure is applied, introducing inert gas and carbon dioxide into a fuel electrode of the solid oxide electrolytic cell; and electrolyzing the carbon dioxide at the fuel electrode to generate carbon monoxide. When carbon dioxide is electrolyzed, gas introduced into the fuel electrode of the solid oxide electrolytic tank is carbon dioxide and inert gas, the inert gas does not participate in electrode reaction, the inert gas can help the carbon dioxide to be better diffused to a reaction interface, and meanwhile, the fuel electrode can be prevented from being oxidized by the carbon dioxide with weak oxidizing property; the effects of protecting the fuel electrode and prolonging the service life of the solid oxide electrolytic tank are achieved to a certain extent. And moreover, the inert gas can also play a role in diluting carbon monoxide, so that the carbon deposition phenomenon caused by local overhigh concentration of the carbon monoxide is avoided, and the damage to the fuel electrode structure is relieved to a certain extent.

Description

Technical Field

[0001] The present application relates to the field of carbon dioxide electrolysis, and in particular to a method for electrolyzing carbon dioxide in a solid oxide electrolysis cell. Background Art

[0002] Carbon dioxide (CO2) is a weak oxidizing gas. When using a solid oxide electrolysis cell (SOEC) to electrolyze CO2, a certain amount of reducing gas is usually introduced into the nickel-based fuel electrode as a protective gas to prevent oxidation of active nickel.

[0003] The commonly used reducing gases are hydrogen (H2) and carbon monoxide (CO). When hydrogen is used, the H2 / CO2 fuel electrode atmosphere seems to be beneficial to improve the durability and conversion rate of SOEC, but due to the presence of reverse water-gas reaction (H2+CO2=H2O+CO) and CO2 electrolysis reaction, the water generated by the reverse water-gas reaction may increase the humidity of the fuel electrode and thus lead to Ni agglomeration and percolation loss in the fuel electrode. The unreacted H2 consumed by the reverse water-gas reaction will be discharged from the gas outlet of the fuel electrode along with the product CO. It is difficult to separate H2 from CO, which will result in the product being unable to be directly purified and utilized. When CO / CO2 is used as the fuel electrode atmosphere, since the nickel electrode has a good catalytic effect on the CO disproportionation reaction at high temperature, the introduction of CO leads to an increase in the CO concentration in the fuel electrode, which may increase the risk of carbon deposition and thus affect the battery performance and durability.

[0004] Therefore, how to solve the above technical problems should be the focus of technical personnel in this field. Summary of the invention

[0005] The purpose of the present application is to provide a method for electrolyzing carbon dioxide in a solid oxide electrolysis cell to avoid carbon deposition, while protecting the electrodes of the solid oxide electrolysis cell and extending the service life of the solid oxide electrolysis cell.

[0006] In order to solve the above technical problems, the present application provides a method for electrolyzing carbon dioxide in a solid oxide electrolysis cell, comprising:

[0007] When the solid oxide electrolytic cell is assembled and pressure is applied, an inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolytic cell;

[0008] The carbon dioxide is electrolyzed at the fuel electrode to generate carbon monoxide.

[0009] Optionally, before the inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolysis cell, the process further comprises:

[0010] The inert gas is used to purge the air at the fuel pole.

[0011] Optionally, when electrolyzing the carbon dioxide, the voltage is less than or equal to the thermal neutral voltage of the solid oxide electrolysis cell.

[0012] Optionally, the voltage ranges from 1.1V to 1.3V, including endpoint values.

[0013] Optionally, the inert gas is nitrogen.

[0014] Optionally, the inlet flow rate range of the inert gas is 0.2 liters / minute to 0.4 liters / minute; the inlet flow rate range of the carbon dioxide is 0.2 liters / minute to 0.4 liters / minute.

[0015] Optionally, electrolyzing the carbon dioxide at the fuel electrode includes:

[0016] The carbon dioxide is electrolyzed at the fuel electrode using renewable energy.

[0017] Optionally, also include:

[0018] Separate part of the tail gas at the fuel electrode, compress and store the carbon monoxide in the tail gas; and pass part of the tail gas into the fuel electrode to maintain a reducing atmosphere at the fuel electrode.

[0019] Optionally, also include:

[0020] The oxygen ions undergo an oxidation reaction at the air electrode to generate oxygen; the oxygen ions are generated when the carbon dioxide is electrolyzed;

[0021] The oxygen is collected.

[0022] Optionally, before the inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolysis cell, the process further comprises:

[0023] Place a nickel mesh on the fuel electrode cover and apply nickel paste.

[0024] Placing the solid oxide electrolytic cell on a fuel electrode cover plate having the nickel mesh;

[0025] Applying pressure to the solid oxide electrolysis cell through bolts located on a cover plate, the cover plate being located at both ends of the fuel electrode, and the bolts being perpendicular to the solid oxide electrolysis cell;

[0026] The air electrode cover plate is covered, and pressure is applied to the solid oxide electrolysis cell on the air electrode cover plate.

[0027] The present application provides a method for electrolyzing carbon dioxide in a solid oxide electrolysis cell, comprising: when the solid oxide electrolysis cell is assembled and pressure is applied, introducing inert gas and carbon dioxide into a fuel electrode of the solid oxide electrolysis cell; and electrolyzing the carbon dioxide at the fuel electrode to generate carbon monoxide.

[0028] It can be seen that in the present application, when electrolyzing carbon dioxide, the gas introduced into the fuel pole of the solid oxide electrolyzer is carbon dioxide and inert gas, and the inert gas does not participate in the electrode reaction. The inert gas can help carbon dioxide to diffuse better to the reaction interface, and can prevent the weakly oxidizing carbon dioxide from oxidizing the fuel pole, which plays a role in protecting the fuel pole and extending the life of the solid oxide electrolyzer to a certain extent. In addition, the inert gas can also play a role in diluting carbon monoxide, avoiding the carbon deposition phenomenon caused by the local excessive concentration of carbon monoxide, and alleviating the destruction of the fuel pole structure to a certain extent. At the same time, inert gas is used in the present application, and there is no hydrogen on one side of the fuel pole, which is more conducive to the utilization of subsequent tail gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 A process for electrolyzing carbon dioxide in a solid oxide electrolytic cell provided in an embodiment of the present application Figure 1 ;

[0031] Figure 2 A process for electrolyzing carbon dioxide in a solid oxide electrolytic cell provided in an embodiment of the present application Figure 2 ;

[0032] Figure 3 A schematic diagram of the assembly of a solid oxide electrolytic cell provided in an embodiment of the present application;

[0033] Figure 4 A schematic diagram of a process for electrolyzing carbon dioxide provided in an embodiment of the present application;

[0034] Figure 5 This is a schematic diagram of the structure of the solid oxide electrolytic cell used for electrolysis in the embodiment of the present application;

[0035] Figure 6 This is a graph showing the electrolysis current of a solid oxide electrolytic cell according to an embodiment of the present application changing with time;

[0036] Figure 7The comparison of instantaneous discharge performance before and after long-term constant potential electrolysis of CO2 in the embodiment of the present application is shown in FIG.

[0037] Figure 8 The figure shows a comparison of the instantaneous charging performance before and after long-term constant potential electrolysis of CO2 in the embodiment of the present application. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0039] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0040] As mentioned in the background technology section, the commonly used reducing gases are hydrogen (H2) and carbon monoxide (CO). When H2 is used, the unreacted H2 will be discharged from the fuel electrode outlet along with the product CO. It is difficult to separate H2 from CO, which will result in the product being unable to be directly purified and utilized. When CO is used, the risk of carbon deposition may increase, thereby affecting battery performance and durability.

[0041] In view of this, the present application provides a method for electrolyzing carbon dioxide in a solid oxide electrolysis cell, please refer to Figure 1 ,include:

[0042] Step S101: When the solid oxide electrolysis cell is assembled and pressure is applied, an inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolysis cell.

[0043] The inert gas includes, but is not limited to, any one or any combination of nitrogen, helium, neon, argon, krypton, xenon, and radon.

[0044] In order to reduce the cost of electrolysis of carbon dioxide, in one embodiment of the present application, the inert gas is nitrogen.

[0045] A pressure device is used to apply pressure to the solid oxide electrolytic cell, and the applied pressure ranges from 80 kg to 120 kg. For example, the applied pressure can be 80 kg, 100 kg, 110 kg, 120 kg, etc.

[0046] The inert gas flow rate range is 0.2 liters per minute (standard litre per minute, SLM) to 0.4 liters per minute; the carbon dioxide flow rate range is 0.2 liters per minute to 0.4 liters per minute.

[0047] Step S102: electrolyzing the carbon dioxide at the fuel electrode to generate carbon monoxide.

[0048] The fuel electrode of the solid oxide electrolysis cell is a nickel-based fuel electrode. Carbon dioxide is electrolyzed on the fuel electrode to produce carbon monoxide and oxygen ions. The specific reaction equation at the fuel electrode is:

[0049] CO2+2e — →CO+O 2— .

[0050] The electrolysis of carbon dioxide is carried out at a certain voltage. As an implementable method, when electrolyzing the carbon dioxide, the voltage is less than or equal to the thermal neutral voltage of the solid oxide electrolytic cell to avoid polarization of the solid oxide electrolytic cell and reduced stability.

[0051] Optionally, the voltage during electrolysis of carbon dioxide ranges from 1.1V to 1.3V, including endpoint values. For example, the voltage during electrolysis may be 1.1V, 1.2V, 1.3V, etc.

[0052] As an implementation method, electrolyzing the carbon dioxide at the fuel electrode includes:

[0053] The carbon dioxide is electrolyzed at the fuel electrode using renewable energy.

[0054] Using renewable energy to provide electricity for carbon dioxide electrolysis can reduce the cost of carbon dioxide electrolysis. Renewable energy can be wind energy, solar energy, etc., all of which are within the scope of protection of this application.

[0055] In the present embodiment, when electrolyzing carbon dioxide, the gas introduced into the fuel pole of the solid oxide electrolyzer is carbon dioxide and an inert gas. The inert gas does not participate in the electrode reaction. The inert gas can help carbon dioxide diffuse better to the reaction interface, and can prevent the weakly oxidizing carbon dioxide from oxidizing the fuel pole, which plays a role in protecting the fuel pole and extending the life of the solid oxide electrolyzer to a certain extent. In addition, the inert gas can also play a role in diluting carbon monoxide, avoiding the carbon deposition phenomenon caused by the local excessive concentration of carbon monoxide, and alleviating the damage of the fuel pole structure to a certain extent. At the same time, inert gas is used in this application, and there is no hydrogen on one side of the fuel pole, which is more conducive to the subsequent use of tail gas.

[0056] Based on the above embodiments, in one embodiment of the present application, please refer to Figure 2, the method for electrolyzing carbon dioxide in a solid oxide electrolysis cell comprises:

[0057] Step S201: When the solid oxide electrolytic cell is assembled and pressure is applied, the air at the fuel electrode is purged cleanly using the inert gas.

[0058] Step S202: introducing inert gas and carbon dioxide into the fuel electrode of the solid oxide electrolysis cell.

[0059] Step S203: electrolyzing the carbon dioxide at the fuel electrode to generate carbon monoxide.

[0060] Step S204: separating part of the tail gas at the fuel electrode, compressing and storing the carbon monoxide in the tail gas; and passing part of the tail gas into the fuel electrode to maintain a reducing atmosphere at the fuel electrode.

[0061] The tail gas includes carbon monoxide and unreacted carbon dioxide, and the unreacted carbon dioxide can be directly discharged into the atmosphere. The separation method of carbon monoxide and carbon dioxide can be chemical adsorption method, membrane separation method, etc.

[0062] Step S205: Oxygen ions undergo an oxidation reaction at the air electrode to generate oxygen; the oxygen ions are generated when the carbon dioxide is electrolyzed.

[0063] Carbon dioxide is electrolyzed at the fuel electrode to produce oxygen ions. The oxygen ions are transferred from the fuel electrode side to the air electrode side through the electrolyte, and lose electrons on the air electrode side to produce oxygen. The specific reaction equation at the air electrode is:

[0064] O 2— →2e — +1 / 2O2,

[0065] The overall reaction equation is:

[0066] CO2→CO+1 / 2O2.

[0067] Step S206: collecting the oxygen.

[0068] The collected oxygen is pressurized and stored.

[0069] Based on any of the above embodiments, in one embodiment of the present application, before the inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolysis cell, the process further includes:

[0070] Place a nickel mesh on the fuel electrode cover and apply nickel paste.

[0071] Placing the solid oxide electrolytic cell on a fuel electrode cover plate having the nickel mesh;

[0072] Applying pressure to the solid oxide electrolytic cell through bolts located on a cover plate, the cover plate being located at both ends of the fuel electrode, and the bolts being perpendicular to the upper surface of the solid oxide electrolytic cell;

[0073] The air electrode cover plate is covered, and pressure is applied to the solid oxide electrolysis cell on the air electrode cover plate.

[0074] The two ends of the fuel electrode and the surrounding area of ​​the fuel electrode are sealed with glass sealing materials.

[0075] In the related art, when assembling the solid oxide electrolytic cell, when applying pressure through the bolts on the cover plates at both ends of the fuel electrode, the bolts are parallel to the upper surface of the solid oxide electrolytic cell (that is, the bolts are parallel to the upper surfaces of the cover plates at both ends of the fuel electrode), which easily causes the solid oxide electrolytic cell to crack from the middle. In this embodiment, when assembling the solid oxide electrolytic cell, the bolts are perpendicular to the upper surface of the solid oxide electrolytic cell, which improves the problem of stress on the upper surface of the solid oxide electrolytic cell. In addition, in this embodiment, pressure is applied to the solid oxide electrolytic cell on the upper side of the air electrode cover plate, which can better improve the sealing performance of the battery.

[0076] It should be pointed out that before covering the air electrode cover, the following steps are also included:

[0077] A silver mesh is placed between the air electrode and the air electrode cover, and silver paste is applied.

[0078] The method for electrolyzing carbon dioxide in a solid oxide electrolysis cell of the present application is introduced below using a specific case.

[0079] Step 1: The battery is assembled in a fixture made of SUS430 stainless steel: Please refer to Figure 3 First, the solid oxide electrolytic cell 11 is placed on the fuel electrode stainless steel cover plate 8, a nickel mesh is placed between the fuel electrode stainless steel cover plate 8 and the solid oxide electrolytic cell 11, and nickel slurry is applied, a silver mesh is placed between the air electrode and the air electrode cover plate 10, and silver slurry is applied, the two ends of the fuel electrode and the surrounding of the fuel electrode are sealed with glass sealing materials, the cover plates 9 at both ends of the fuel electrode are fixed with bolts 12 perpendicular to the upper surface of the cover plates 9, and then the gap is filled with sealing materials, and finally the air electrode cover plate 10 is covered, and the air pipe and the conductive column are screwed on;

[0080] Step 2: After the solid oxide electrolytic cell is assembled, a pressurizing device is used to pressurize the air electrode cover plate 10 to increase the pressure to 80-120 kg;

[0081] Step 3: Use 0.2-0.4SLM nitrogen to purge the air in the SOEC fuel electrode. After the purge is completed, introduce 0.2-0.4SLM carbon dioxide feed gas. When the open circuit voltage is stable, start the performance test;

[0082] Step 4: Set a constant voltage of 1.1 to 1.3 V to start electrolysis. The set voltage value is usually less than or equal to the thermal neutral voltage. The electricity required for electrolysis of carbon dioxide can come from renewable energy sources such as wind energy and solar energy.

[0083] Step 5: During the long-term constant-pressure electrolysis process, the tail gas on the fuel electrode is separated, and the unreacted carbon dioxide is directly discharged into the atmosphere, and the carbon monoxide is compressed and stored, and part of it is returned to the feed gas to maintain the reducing atmosphere of the fuel electrode of the electrolytic cell; the process diagram of the electrolysis of carbon dioxide is as follows Figure 4 As shown, nitrogen (N2) and carbon dioxide (CO2) are introduced into the fuel electrode, and air (air) is introduced into the air electrode. The flow rates of nitrogen, carbon dioxide and air are controlled by a gas mass flow controller, and carbon dioxide is electrolyzed under the voltage provided by a power supply to output fuel and air.

[0084] Step 6: Collect oxygen from the air electrode outlet and store it after pressurization.

[0085] In order to evaluate the long-term durability of the solid oxide electrolysis cell for constant potential electrolysis of carbon dioxide, a flat tube solid oxide cell was used as an example to conduct constant potential electrolysis of carbon dioxide in the laboratory. The test lasted for more than 100 hours. Figure 5 As shown, it includes an air electrode 1, a barrier layer 2, an electrolyte 3, a fuel electrode 4, a fuel channel 5, a support layer 6, and a current collecting layer 7. The experimental temperature is 750 degrees Celsius, the high temperature pressurization pressure is about 120kg, the fuel electrode intake atmosphere is 50% N2-50% CO2, and the electrolysis voltage is 1.1V.

[0086] During long-term operation, the electrolysis current of the solid oxide electrolysis cell changes with time as follows Figure 6 As shown, the horizontal axis is the test time, the vertical axis is the voltage, the flow rate of N2 is 0.3SLM, the flow rate of CO2 is 0.3SLM, and the electrolysis current attenuation rate is about 3.57%, which basically maintains stable operation, illustrating the feasibility of the experimental method in this application.

[0087] Comparison of instantaneous discharge performance before and after long-term constant potential electrolysis of CO2 Figure 7 As shown, the nitrogen flow rate is 0.6SLM, the air flow rate is 2SLM, Figure 7 The middle horizontal axis is current density, the left vertical axis is voltage, and the right vertical axis is power; the instantaneous charging performance before and after long-term constant potential electrolysis of CO2 is compared. Figure 8 As shown, the nitrogen flow rate is 0.15SLM, the carbon dioxide flow rate is 0.45SLM, and the air flow rate is 3SLM. Figure 8 The horizontal axis is the current density, and the vertical axis is the voltage. Figure 7 and Figure 8It can be seen that after the long-term electrolysis test, the battery discharge IV polarization curve has obvious attenuation, while the charge IV polarization curve has less attenuation.

[0088] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0089] The above is a detailed introduction to the method for electrolyzing carbon dioxide in a solid oxide electrolysis cell provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A method for electrolyzing carbon dioxide in a solid oxide electrolysis cell, characterized in that: include: When the solid oxide electrolytic cell is assembled and pressure is applied, an inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolytic cell; The carbon dioxide is electrolyzed at the fuel electrode to generate carbon monoxide.

2. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: Before the inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolysis cell, the method further comprises: The inert gas is used to purge the air at the fuel pole.

3. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: When electrolyzing the carbon dioxide, the voltage is less than or equal to the thermal neutral voltage of the solid oxide electrolysis cell.

4. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 3, characterized in that: The voltage ranges from 1.1V to 1.3V, including endpoint values.

5. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: The inert gas is nitrogen.

6. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: The inert gas flow rate range is 0.2 liters / minute to 0.4 liters / minute; the carbon dioxide flow rate range is 0.2 liters / minute to 0.4 liters / minute.

7. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: Electrolyzing the carbon dioxide at the fuel electrode comprises: The carbon dioxide is electrolyzed at the fuel electrode using renewable energy.

8. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: Also includes: Separating part of the tail gas at the fuel pole, compressing and storing the carbon monoxide in the tail gas; Part of the tail gas is introduced into the fuel electrode to maintain a reducing atmosphere at the fuel electrode.

9. The method for electrolyzing carbon dioxide in a solid oxide electrolytic cell according to claim 1, characterized in that: Also includes: Oxygen ions undergo oxidation reaction at the air pole to generate oxygen; The oxygen ions are generated when the carbon dioxide is electrolyzed; The oxygen is collected.

10. The method for electrolyzing carbon dioxide using a solid oxide electrolysis cell according to any one of claims 1 to 9, characterized in that: Before the inert gas and carbon dioxide are introduced into the fuel electrode of the solid oxide electrolysis cell, the method further comprises: Place a nickel mesh on the fuel electrode cover and apply nickel paste. Placing the solid oxide electrolytic cell on a fuel electrode cover plate having the nickel mesh; Applying pressure to the solid oxide electrolysis cell through bolts located on a cover plate, the cover plate being located at both ends of the fuel electrode, and the bolts being perpendicular to the solid oxide electrolysis cell; The air electrode cover plate is covered, and pressure is applied to the solid oxide electrolysis cell on the air electrode cover plate.

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