Electrode catalyst, cathode and electrochemical unit

Abstract

The present invention relates to an electrode catalyst comprising carbon black, and more particularly, to an electrode catalyst having sufficient pores in the electrode catalyst and having improved hydrophobicity by adjusting the specific surface area and content of carbon black, and a cathode and an electrochemical unit comprising the same.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0091260, filed with the Korean Intellectual Property Office on July 13, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to electrode catalysts and cathodes and electrochemical units comprising the same. Background Technology

[0004] Carbon dioxide is a greenhouse gas that contributes to global warming and therefore should be reduced. Methods for reducing carbon dioxide, such as capture, chemical conversion, or electrochemical conversion, are known. Among these methods, electrochemical conversion allows for precise control of components to produce other syngas, making it more economically advantageous than simply removing carbon dioxide. Furthermore, carbon dioxide can be electrolyzed with water to obtain carbon monoxide, ethylene, methane, formic acid, formate, various hydrocarbons, and organic substances such as aldehydes or alcohols.

[0005] The electrochemical decomposition and conversion of carbon dioxide using an electrochemical unit is as follows. When an electric current is applied while water is supplied to the anode, water decomposes into hydrogen ions and electrons, simultaneously producing oxygen. Electrons are transferred to the cathode via an external wire, and hydrogen ions are transferred to the cathode via an ion-selective membrane. Carbon dioxide and water vapor supplied to the cathode react with the transferred electrons and are decomposed into carbon monoxide and hydroxide ions (OH-). - ), and the generated hydroxide ions react with hydrogen ions (H+) at the anode. + The reaction produces water, thus achieving an electrically neutral state. Through the above process, the electrochemical decomposition reaction of carbon dioxide is completed.

[0006] Simultaneously, to commercialize the aforementioned electrochemical conversion technology of carbon dioxide, a high current is required to flow into the target product, thus increasing the voltage applied to the electrode. However, if a high voltage is applied to the cathode, the overvoltage creates a strong reducing environment within the cathode, which may enhance the electrowetting effect and reduce the cathode's hydrophobicity, potentially leading to cathode immersion in water. The phenomenon of interfering gases diffusing into the electrode and thus degrading electrode performance due to cathode immersion is called overflow. Specifically, overflow promotes the hydrogen evolution reaction (HER), thus significantly reducing not only the Faradaic efficiency of carbon monoxide production but also the long-term stability of the electrode catalyst. Therefore, there is a need to develop electrode catalysts capable of maintaining the performance of the electrochemical carbon dioxide conversion reaction over extended periods. Summary of the Invention

[0007] Technical issues

[0008] The present invention was designed to solve the aforementioned problems, and one object of the present invention is to ensure long-term stability in the electrolysis of carbon dioxide with high current using an electrochemical unit.

[0009] That is, in the electrode catalyst containing carbon black, the specific surface area and content of carbon black are adjusted by the present invention to fully form pores in the electrode catalyst, thereby allowing carbon dioxide to flow smoothly into the electrode catalyst layer containing the electrode catalyst, thus reducing the overvoltage of the electrode under high current. In addition, the carbon black increases the hydrophobicity of the electrode catalyst, which can also prevent the reduction of electrode efficiency caused by overflow phenomenon under high current.

[0010] Furthermore, another object of the present invention is to provide a cathode and an electrochemical unit comprising an electrode catalyst.

[0011] Technical solution

[0012] To achieve the above objectives, the present invention provides an electrode catalyst, as well as a cathode and an electrochemical unit comprising the catalyst.

[0013] (1) The present invention provides an electrode catalyst comprising metal nanoparticles and carbon black, wherein the specific surface area of ​​the carbon black is 100 m². 2 / g to 750 m 2 / g, and based on 100 parts by weight of metal nanoparticles, the carbon black content is 35 parts by weight to 350 parts by weight.

[0014] (2) In (1) above, the present invention provides an electrode catalyst wherein the resistivity of the carbon black is 1.5 Ω·cm or less.

[0015] (3) In (1) or (2) above, the present invention provides an electrode catalyst wherein the average diameter of the metal nanoparticles is 100 nm or less.

[0016] (4) In (1) to (3) above, the present invention provides an electrode catalyst, wherein the metal nanoparticles comprise one or more elements selected from the following: Ag, Au, Zn, In, Cu, Ni, Pt, Pd, Ti, Fe, Ga and Sn.

[0017] (5) In any of (1) to (4) above, the present invention provides an electrode catalyst, wherein the electrode catalyst comprises a cationic ionomer or an anionic ionomer.

[0018] (6) In any of (1) to (5) above, the present invention provides an electrode catalyst, wherein the content of cationic or anionic ionomer is from 0.1 to 20 parts by weight based on 100 parts by weight of metal nanoparticles.

[0019] (7) The present invention provides a cathode comprising an electrode catalyst layer and a gas diffusion layer, wherein the electrode catalyst layer comprises any one of the electrode catalysts of (1) to (6) above, and the electrode catalyst layer is stacked on at least one surface of the gas diffusion layer.

[0020] (8) In (7) above, the present invention provides a cathode in which the content of metal nanoparticles per unit area in the electrode catalyst layer is 0.5 mg / cm². 2 Up to 1.5 mg / cm 2 .

[0021] (9) The present invention provides a method for preparing a cathode, the method comprising (S1) preparing an electrode catalyst composition by mixing metal nanoparticles, carbon black and a solvent, and (S2) coating the electrode catalyst composition prepared in step (S1) onto a gas diffusion layer, wherein in step (S1), the specific surface area of ​​the carbon black is 100 m². 2 / g to 750 m 2 / g, and in step (S1), the carbon black content is 35 to 350 parts by weight based on 100 parts by weight of metal nanoparticles.

[0022] (10) The present invention provides an electrochemical unit comprising: a cathode of (7) or (8) above; an anode; and a separator disposed between the cathode and the anode.

[0023] Beneficial effects

[0024] If the electrode catalyst of the present invention is applied to the cathode and the electrochemical unit, the overvoltage of the cathode is reduced and the overflow phenomenon is mitigated under high current due to the formation of sufficient pores and high hydrophobicity in the electrode catalyst. Therefore, an electrochemical unit that can maintain low overvoltage and high carbon monoxide Faraday efficiency for a long time can be provided. Detailed Implementation

[0025] The invention will be described in more detail below to facilitate understanding of the invention.

[0026] It should be understood that the words or terms used herein should not be construed as having the meanings defined in commonly used dictionaries. It will be further understood that, based on the inventor's ability to appropriately define the meaning of a word or term in order to best illustrate the principles of the invention, the word or term should be interpreted as having a meaning consistent with its meaning in the context of the relevant field and technical concept of the invention.

[0027] The terminology used herein is for describing preferred embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0028] In this specification, it should be understood that the terms “comprising,” “including,” or “having” are intended to specify the presence of the said feature, quantity, step, element, or combination thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0029] In this specification, "content per unit area" is measured by dividing the weight difference between a substrate with electrode catalyst coated on its surface and a substrate before electrode catalyst coating by the area of ​​a surface.

[0030] In this specification, the "average diameter" is measured using a particle size analyzer by light scattering.

[0031] In this specification, "electrode catalyst" refers to a catalyst for an electrochemical reaction that is used in electrochemical devices such as carbon dioxide electrolysis and water electrolysis, or in fuel cells, as a catalyst for an oxidation or reduction reaction. In addition to metal nanoparticles, electrode catalysts may also contain additives, such as binders, and may include both a solution form obtained by dispersing metal nanoparticles in a solvent and a powder form obtained after solvent evaporation.

[0032] In this specification, "cathode" refers to the electrode in which the reduction reaction of reactants occurs in an electrochemical device such as carbon dioxide electrolysis and water electrolysis or a fuel cell, and may include an electrode catalyst layer.

[0033] In this specification, "electrochemical unit" refers to a device that includes a cathode, an anode, and a separator disposed between the cathode and the anode. Electrochemical units can be applied to electrochemical conversion devices capable of producing useful chemical substances through electrochemical conversion, such as electrochemical devices for carbon dioxide electrolysis and water electrolysis, fuel cells, etc.

[0034] Electrode catalyst

[0035] This invention provides an electrode catalyst.

[0036] According to one embodiment of the present invention, the electrode catalyst comprises metal nanoparticles and carbon black, wherein the specific surface area of ​​the carbon black can be 100 m². 2 / g to 750 m 2 / g, and based on 100 parts by weight of metal nanoparticles, the carbon black content can be from 35 parts by weight to 350 parts by weight.

[0037] The electrode catalyst of the present invention is characterized by containing carbon black to overcome the problems of electrode performance degradation caused by overflow phenomena occurring when the electrochemical unit is driven with high current and by hydrogen generation reactions due to overvoltage. The electrode catalyst can comprise both a solution form obtained by dispersing metal nanoparticles in a solvent and a powder form obtained after solvent evaporation. The electrode catalyst in solution form can be applied to a substrate such as a gas diffusion layer or separator and then dried to form an electrode catalyst layer. However, typical electrode catalysts composed of metal nanoparticles and binders exist in a state where the metal particles are aggregated by attraction between the metal particles, resulting in insufficient pores for carbon dioxide to move between the aggregated metal particles. Therefore, the problem with electrode catalyst layers containing typical electrode catalysts is that carbon dioxide gas cannot flow smoothly into the surface of the metal particles, leading to increased overvoltage at high currents. Furthermore, typical electrode catalysts also suffer from low dispersibility due to the aggregation phenomenon caused by attraction between metal nanoparticles in the electrode catalyst. Therefore, if a cathode is fabricated by coating an electrode catalyst onto one surface of a gas diffusion layer, the electrode catalyst layer will not be uniformly stacked on that surface. Furthermore, the gas diffusion layer, which is not adequately coated with the electrode catalyst, is easily submerged under high current, leading to deterioration of the electrode's performance. Therefore, to address these problems, the electrode catalyst of the present invention is characterized by comprising metal nanoparticles and a specific surface area of ​​100 m². 2 / g to 750 m 2 / g or less of carbon black, wherein the carbon black is included in an amount of 35 to 350 parts by weight based on 100 parts by weight of metal nanoparticles. Specifically, in the electrode catalyst, the metal nanoparticles exist in a form mixed between the carbon black, and unlike the form of supported catalysts in which the metal nanoparticles are attached to the surface of a typical carbon black support, in the electrode catalyst of the present invention, the metal nanoparticles and carbon black are not attached to each other. The carbon black can form sufficient pores in the electrode catalyst to facilitate the inflow of carbon dioxide into the electrode catalyst layer containing the electrode catalyst, thus reducing overvoltage under high current. Furthermore, the carbon particles of the carbon black in the electrode catalyst can interact with the metal nanoparticles, thus mitigating aggregation due to attraction between the metal nanoparticles, and as a result, improving the dispersibility of the electrode catalyst. Therefore, the electrode catalyst with improved dispersibility can be uniformly coated on one surface of the gas diffusion layer and then dried, thereby uniformly stacking on one surface of the gas diffusion layer in the form of an electrode catalyst layer, thus preventing the gas diffusion layer from being submerged. In addition, the carbon particles of carbon black are hydrophobic, which reduces overflow caused by immersion in the cathode containing the electrode catalyst.

[0038] Meanwhile, the specific surface area of ​​carbon black can be 100 m². 2 / g to 750 m 2 / g, and specifically, the specific surface area of ​​carbon black can be 100 m². 2 / g or greater, 125 m 2 / g or greater, 150 m 2 / g or greater, 175 m 2 / g or greater, 200 m 2 / g or greater, 225 m 2 / g or greater, or 250 m 2 / g or greater, and can also be 750 m 2 / g or less, 725 m 2 / g or less, 700 m 2 / g or less, 675 m 2 / g or less, 650 m 2 / g or less, 625 m 2 / g or less, 600 m 2 / g or less, 575 m 2 / g or less, 550 m 2 / g or less, 525 m 2 / g or less, 500 m 2 / g or less, 475 m 2 / g or less, 450m 2 / g or less, 425 m 2 / g or less, 400 m 2 / g or less, 375 m 2 / g or less, 350 m 2 / g or less, 325 m 2 / g or less, 300 m 2 / g or less, 275 m 2 / g or less, or 250 m 2 / g or less. If the specific surface area of ​​carbon black meets the above range, the carbon particles of carbon black can interact sufficiently with the metal nanoparticles in the electrode catalyst, thereby improving the dispersibility of the electrode catalyst. On the other hand, if the specific surface area of ​​carbon black is higher than the above range, the density of the electrode catalyst layer containing the electrode catalyst may decrease due to the high specific surface area of ​​carbon black, which may increase the resistance of the electrode. Therefore, there may be a problem of a significant increase in overvoltage when driving the electrochemical unit. In addition, as the specific surface area increases, the aggregation between carbon particles of carbon black increases, which may also reduce the dispersibility of the electrode catalyst. If the specific surface area is lower than the above range, the density of the electrode catalyst layer containing the electrode catalyst increases, resulting in a reduction in pores in the electrode catalyst layer. Therefore, it is not conducive to the inflow of carbon dioxide, which may lead to a significant increase in overvoltage and a decrease in carbon dioxide conversion rate when driving the electrochemical unit.

[0039] Meanwhile, based on 100 parts by weight of metal nanoparticles, the carbon black content can be from 35 parts by weight to 350 parts by weight. Specifically, based on 100 parts by weight of metal nanoparticles, the carbon black content can be 35 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, 55 parts by weight or more, 65 parts by weight or more, 75 parts by weight or more, 85 parts by weight or more, or 95 parts by weight or more, and can also be 350 parts by weight or less, 340 parts by weight or less, 330 parts by weight or less, 320 parts by weight or less, 310 parts by weight or less, or 300 parts by weight. Or less, 290 parts by weight or less, 280 parts by weight or less, 270 parts by weight or less, 260 parts by weight or less, 250 parts by weight or less, 240 parts by weight or less, 230 parts by weight or less, 220 parts by weight or less, 210 parts by weight or less, 200 parts by weight or less, 190 parts by weight or less, 180 parts by weight or less, 170 parts by weight or less, 160 parts by weight or less, 150 parts by weight or less, 140 parts by weight or less, 130 parts by weight or less, 120 parts by weight or less, 110 parts by weight or less, or 100 parts by weight or less. If the carbon black content in the electrode catalyst meets the above ranges, sufficient pores are formed in the electrode catalyst layer containing the electrode catalyst, which can promote the inflow of carbon dioxide and thus improve the carbon dioxide conversion performance. Furthermore, the carbon particles of carbon black can interact sufficiently with the metal nanoparticles in the electrode catalyst, thereby improving the dispersion of the electrode catalyst and increasing its hydrophobicity. This can mitigate the degradation of electrode performance caused by overflow. On the other hand, if the carbon black content is higher than the above range, the content per unit area of ​​the metal nanoparticles that act as catalysts in the carbon dioxide reduction reaction is relatively reduced, resulting in a decrease in the carbon dioxide reduction reaction in the cathode containing the electrode catalyst. Therefore, a decrease in carbon dioxide conversion rate may occur. If the carbon black content is lower than the above range, the interaction between carbon black and the aforementioned metal nanoparticles may not occur sufficiently in the electrode catalyst. This may reduce the dispersion of the electrode catalyst and also reduce its hydrophobicity, potentially leading to a degradation of electrode performance caused by overflow.

[0040] According to one embodiment of the invention, the resistivity of the carbon black can be 1.5 Ω·cm or less, and specifically, the resistivity of the carbon black can be 1.5 Ω·cm or less, 1.4 Ω·cm or less, 1.3 Ω·cm or less, 1.2 Ω·cm or less, 1.1 Ω·cm or less, 1.0 Ω·cm or less, or 0.9 Ω·cm or less, and can also be 0.1 Ω·cm or greater, 0.2 Ω·cm or greater, 0.3 Ω·cm or greater, 0.4 Ω·cm or greater, or 0.5 Ω·cm or greater. If the resistivity of the carbon black meets the above ranges, the resistance of the cathode containing the electrode catalyst is reduced due to the low resistivity of the carbon black, making it possible to obtain a cathode with excellent conductivity and low overvoltage even under high current.

[0041] According to one embodiment of the present invention, the average diameter of the metal nanoparticles can be 100 nm or less, and specifically, the average diameter of the metal nanoparticles can be 100 nm or less, 90 nm or less, or 80 nm or less, and can also be 5 nm or more, 10 nm or more, 20 nm or more, or 30 nm or more. If the average diameter of the metal nanoparticles meets the above ranges, the high specific surface area of ​​the metal nanoparticles can further promote the carbon dioxide reduction reaction in the cathode containing the electrode catalyst, thereby improving the carbon dioxide conversion rate.

[0042] According to one embodiment of the present invention, the metal nanoparticles may be metal nanoparticles comprising one or more elements selected from the following: Ag, Au, Zn, In, Cu, Ni, Pt, Pd, Ti, Fe, Ga, and Sn. Specifically, the metal nanoparticles may be silver nanoparticles comprising Ag, and the silver nanoparticles may be included in the catalyst layer of the cathode to act as a catalyst for the reduction reaction, thereby lowering the activation energy of the carbon dioxide reduction reaction. The metal elements listed above may be included in the metal nanoparticles and, like silver nanoparticles, may be used as catalysts for the carbon dioxide reduction reaction in the cathode.

[0043] According to one embodiment of the invention, the electrode catalyst may comprise a cationic ionomer or anionic ionomer. The cationic ionomer is an ion-conducting polymer containing cations, such as hydroxide ions (OH-). - Anions can pass through cations, and anionic ionomers are ion-conducting polymers containing anions, such as hydrogen ions (H+). +The cations of the ion can pass through the anions. Specifically, Nafion, manufactured by DuPont et al., can be used as an anionic ionomer. The cationic or anionic ionomer can be added to and mixed with an electrode catalyst in the form of a solution containing solvent, metal nanoparticles, and carbon black. The carbon particles of the metal nanoparticles and carbon black can be more strongly bound to the gas diffusion layer through the cationic or anionic ionomer, thus preventing deintercalation. Furthermore, ions that migrate to the electrode catalyst layer through the electrolyte solution can move more smoothly within the electrode catalyst layer, thereby reducing the interfacial resistance of the electrode catalyst and further promoting the carbon dioxide reduction reaction.

[0044] According to one embodiment of the invention, based on 100 parts by weight of metal nanoparticles, the content of cationic or anionic ionomer can be from 0.1 parts by weight to 20 parts by weight, and specifically, the content of ionomer can be 0.1 parts by weight or more, 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, or 10 parts by weight or more, and can also be 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, 17 parts by weight or less, 16 parts by weight or less, 15 parts by weight or less, 14 parts by weight or less, 13 parts by weight or less, 12 parts by weight or less, 11 parts by weight or less, or 10 parts by weight or less. If the content of ionomer meets the above ranges, the adhesion between the electrode catalyst and the gas diffusion layer increases, which can reduce the interfacial resistance of the cathode caused by the deintercalation and intercalation of the electrode catalyst layer. On the other hand, if the content of ionomers is too high, the ionomers may cover the metal nanoparticles in the electrode catalyst layer, which may reduce the carbon dioxide conversion performance.

[0045] cathode

[0046] The present invention provides a cathode comprising the above-described electrode catalyst.

[0047] According to one embodiment of the present invention, the cathode may include an electrode catalyst layer and a gas diffusion layer, wherein the electrode catalyst layer may contain an electrode catalyst, and the electrode catalyst layer may be stacked on at least one surface of the gas diffusion layer. The cathode of the present invention has the form in which the electrode catalyst layer is stacked on one surface of the gas diffusion layer, and in particular, the electrode catalyst layer may contain the electrode catalyst described above.

[0048] Simultaneously, the gas diffusion layer serves to diffuse carbon dioxide into the electrode catalyst layer. The gas diffusion layer can be a porous body made of carbon materials (e.g., carbon fiber cloth, carbon fiber felt, or carbon fiber paper), or a porous metal body made of a thin metal plate with a mesh structure (e.g., porous metal, mesh metal, etc.). Specifically, Sigrette 39BB manufactured by SGLCaron or JNT30-A6P manufactured by JNTG can be used as the gas diffusion layer to diffuse carbon dioxide supplied to the cathode into the electrode catalyst layer.

[0049] The cathode can be in the form of an electrode catalyst in solution applied to either surface of the gas diffusion layer, then dried to stack as an electrode catalyst layer on one surface of the gas diffusion layer, and in which the carbon dioxide reduction reaction can take place.

[0050] According to one embodiment of the present invention, the thickness of the electrode catalyst layer can be from 0.1 μm to 100 μm. The thickness of the electrode catalyst layer can vary depending on the content of metal nanoparticles and carbon black, the specific surface area of ​​carbon black, and the coating amount of electrode catalyst. If the thickness of the electrode catalyst layer is within the above range, the mechanical strength of the electrode catalyst layer can be high, and the increase in resistance caused by the catalyst layer can be low.

[0051] According to one embodiment of the present invention, the content of metal nanoparticles per unit area in the electrode catalyst layer can be 0.5 mg / cm². 2 Up to 1.5 mg / cm 2 Specifically, the content of metal nanoparticles per unit area can be 0.5 mg / cm². 2 or larger, 0.6 mg / cm 2 Or larger, 0.7 mg / cm 2 or larger, 0.8 mg / cm 2 Or larger, or 0.9 mg / cm 2 Or 1.0 mg / cm 2 Or larger, and could be as high as 1.5 mg / cm³. 2 Or smaller, 1.4 mg / cm 2 Or smaller, 1.3 mg / cm 2 Or smaller, 1.2 mg / cm 2 or smaller, 1.1 mg / cm 2 Or smaller, or 1.0 mg / cm 2 Or smaller.

[0052] If the content of metal nanoparticles per unit area in the electrode catalyst layer meets the above-mentioned range, the carbon dioxide conversion rate of the cathode including the electrode catalyst layer can be improved, and a low overvoltage can be maintained even under high current. Furthermore, the improvement in carbon dioxide conversion rate is significant compared to the cost of metal nanoparticles introduced within the above-mentioned range, making it economical.

[0053] Cathode preparation method

[0054] This invention provides a method for preparing a cathode.

[0055] According to one embodiment of the present invention, a method for preparing a cathode includes (S1) preparing an electrode catalyst composition by mixing metal nanoparticles, carbon black, and a solvent, and (S2) coating the electrode catalyst composition prepared in step (S1) onto a gas diffusion layer, wherein the specific surface area of ​​the carbon black mixed in step (S1) can be 100 m². 2 / g to 750 m 2 / g, and based on 100 parts by weight of metal nanoparticles, the content of carbon black mixed in step (S1) can be from 35 parts by weight to 350 parts by weight.

[0056] Specifically, step (S1) involves mixing metal nanoparticles, a solvent, and carbon black, and then stirring and dispersing the mixture to prepare an electrode catalyst composition, wherein the electrode catalyst composition refers to the aforementioned electrode catalyst in solution form. Furthermore, when preparing the electrode catalyst composition, step (S1) can be performed by further adding the aforementioned cationic or anionic ionomer.

[0057] In typical methods for preparing electrode catalyst compositions using carbon black and metal nanoparticles, metal nanoparticles are supported on a carbon black support to prepare supported catalyst particles, which are then mixed with a solvent to prepare the electrode catalyst composition. This results in an electrode catalyst composition in which the metal nanoparticles are attached to the surface of the carbon black support. However, a problem with cathodes using supported catalysts is the high overvoltage at high currents and the high hydrogen generation reaction rate. In contrast, the present invention is characterized by mixing carbon black with metal nanoparticles and a solvent to prepare the electrode catalyst composition. Therefore, in the electrode catalyst composition, the metal nanoparticles are present in a form mixed between the carbon black particles, and unlike typical supported catalysts, an electrode catalyst composition in which the metal nanoparticles and carbon black are not attached to each other can be prepared.

[0058] Furthermore, step (S1) may involve mixing the solvent and metal nanoparticles, and then adding to the mixture an amount of 35 to 350 parts by weight of metal nanoparticles with a specific surface area of ​​100 m² based on 100 parts by weight.2 / g to 750 m 2 The step involves mixing / g of carbon black to prepare the electrode catalyst composition. As described above, in the electrode catalyst layer of the cathode coated with the electrode catalyst composition, the carbon black promotes the inflow of carbon dioxide, thus enabling the cathode to have a low overvoltage at high current and a high carbon dioxide conversion rate. Furthermore, the dispersibility of the electrode catalyst composition can be improved, allowing it to be uniformly coated on one surface of the gas diffusion layer, and the hydrophobicity of the electrode catalyst composition can also be increased due to the carbon black, thereby mitigating overflow caused by immersion in the cathode coated with the electrode catalyst composition.

[0059] Step (S2) is the step of coating the electrode catalyst composition onto one surface of the gas diffusion layer. Specifically, this can be a step of coating the electrode catalyst composition onto one surface of the gas diffusion layer, followed by drying to remove the solvent from the electrode catalyst composition, and allowing the electrode catalyst layer to be uniformly stacked on one surface of the gas diffusion layer. Simultaneously, the coating can be performed by any method selected from doctor blade, die casting, comma coating, screen printing, spraying, electrospinning, roller coating, and brush coating. Specifically, this can be a step of coating by spraying the catalyst composition onto one surface of the gas diffusion layer, followed by drying to remove the solvent from the catalyst composition, and allowing the electrode catalyst layer to be stacked on one surface of the gas diffusion layer to a thickness of 0.1 μm to 100 μm.

[0060] In step (S2), the electrode catalyst composition can be coated such that the content of metal nanoparticles per unit area on any surface of the gas diffusion layer satisfies 0.5 mg / cm². 2 Up to 1.5 mg / cm 2 If the electrode catalyst composition is coated such that the content of metal nanoparticles per unit area on any surface of the gas diffusion layer meets the above-mentioned range, a cathode with excellent carbon dioxide conversion efficiency and low overvoltage can be manufactured even when a high current is applied. Furthermore, the improvement in carbon dioxide conversion efficiency is significant compared to the cost of metal nanoparticles introduced within the above-mentioned range, making it economical.

[0061] Electrochemical Unit

[0062] The present invention provides an electrochemical unit including a cathode.

[0063] According to one embodiment of the present invention, the electrochemical unit may include a cathode, an anode, and a separator disposed between the cathode and the anode.

[0064] According to one embodiment of the present invention, the electrochemical unit can be a unit for electrolyzing carbon dioxide and water vapor, thereby converting carbon dioxide and water vapor into carbon monoxide and hydroxide ions. Furthermore, besides carbon dioxide electrolysis devices, the electrochemical unit can also be used in all electrochemical conversion devices capable of generating useful chemicals through electrochemical conversion, such as fuel cells and water electrolysis devices. Meanwhile, electrolysis refers to the decomposition of materials by applying a direct current voltage to a redox reaction instead of a non-spontaneous decomposition reaction, and the electrolysis of carbon dioxide by the electrochemical unit of the present invention is carried out through the following process.

[0065] The anode of the electrochemical unit of the present invention is an oxidation electrode that oxidizes water to produce oxygen, and hydrogen ions are generated at the same time. The hydrogen ions generated in the anode can be transferred to the cathode through a separator, and the cathode is a reduction electrode, wherein carbon dioxide and water vapor introduced into the cathode can react with electrons transferred from the anode to produce carbon monoxide and hydrogen.

[0066] The anode and cathode of the electrochemical unit of the present invention may each include an electrode catalyst layer. The electrode catalyst layer of the cathode may contain an electrode catalyst that is active in the carbon dioxide reduction reaction, and in particular, since the carbon dioxide reduction reaction occurring in the cathode competes with the hydrogen generation reaction, an electrode catalyst that is active in the carbon dioxide reduction reaction and simultaneously has the high voltage required for the hydrogen generation reaction may be included. Specifically, the electrode catalyst may be the electrode catalyst of the present invention.

[0067] Meanwhile, the electrode catalyst layer of the anode may contain an electrode catalyst that is active in the oxidation reaction of water, and the electrode catalyst of the anode may include one or more of the following: Pt, Au, Pd, Ir, Ag, Rh, Ru, Ni, Al, Mo, Cr, Cu, Ti, W, Ta, their alloys or mixed metal oxides, such as Ta2O5, IrO2, etc., and specifically, the anode may be a titanium mesh substrate coated with iridium oxide (IrO2).

[0068] Simultaneously, the cathode may include a gas diffusion layer to uniformly supply wetted carbon dioxide to the electrode catalyst layer. Specifically, the gas diffusion layer may be the aforementioned gas diffusion layer, and the electrode catalyst layer may be stacked on one surface of the gas diffusion layer. If the cathode includes a gas diffusion layer, the supplied carbon dioxide can diffuse, distribute, and be supplied smoothly to the cathode's electrode catalyst layer, and the gas diffusion layer effectively prevents moisture condensation, thereby allowing a continuous and uniform supply of carbon dioxide to the electrode catalyst layer while allowing the electrolysis reaction to proceed smoothly.

[0069] Simultaneously, a separator can be placed between the anode and the cathode. The separator itself can be made of an inert material that does not participate in the electrochemical reaction, but it provides a path for ions to transfer between the anode and the cathode and can be used to isolate the physical contact between the anode and the cathode. Specifically, a porous separator can be used as the separator.

[0070] According to one embodiment of the invention, the electrochemical unit can be used in all electrochemical conversion devices, and can be used in devices for electrolyzing carbon dioxide to produce one or more of carbon monoxide, ethylene, methane, formic acid, hydrocarbons, aldehydes, and alcohols. Specifically, the electrochemical unit can electrolyze carbon dioxide to produce carbon monoxide.

[0071] Since the electrochemical unit of the present invention includes the cathode of the present invention described above, the electrode catalyst layer of the cathode comprises metal nanoparticles and has a specific surface area of ​​100 m². 2 / g to 750 m 2 / g of carbon black, wherein the carbon black content can be from 35 parts by weight to 350 parts by weight based on 100 parts by weight of metal nanoparticles. Therefore, as described above, the electrochemical unit of the present invention includes a cathode having an electrode catalyst layer in which sufficient pores are formed, thereby promoting the inflow of carbon dioxide, resulting in a high carbon dioxide conversion rate and a low overvoltage at high current.

[0072] The invention will be described in more detail below with reference to embodiments and experimental examples, but the invention is not limited to these embodiments and examples. Embodiments of the invention can be modified into various other forms, and the scope of the invention should not be construed as limited to the embodiments described below. Embodiments of the invention are provided to provide a more complete description of the invention to those skilled in the art.

[0073] Examples and Comparative Examples

[0074] Example 1

[0075] 1,000 mg of silver nanoparticles (Ag NP) were mixed with 100 mL of a solvent in which isopropanol and water were mixed in a 9:1 volume ratio to prepare a solution with a concentration of 10 mg / mL. Subsequently, 1,000 mg of a solution with a specific surface area of ​​250 m² was added to the solution. 2 A mixture of Vulcan XC-72 with a resistivity of 0.2 Ω cm to 1.0 Ω cm was prepared, and 100 mg of Nafion (DuPont) was added. The mixture was then stirred using a homogenizer and dispersed using an ultrasonic generator to prepare the electrode catalyst. The Vulcan XC-72 content of the electrode catalyst was 100 parts by weight based on 100 parts by weight of silver nanoparticles.

[0076] Example 2

[0077] The electrode catalyst was prepared in the same manner as in Example 1, except that 500 mg of Vulcan XC-72 was added. Based on 100 parts by weight of silver nanoparticles, the Vulcan XC-72 content of the electrode catalyst was 50 parts by weight.

[0078] Example 3

[0079] The electrode catalyst was prepared in the same manner as in Example 1, except that 3,000 mg of Vulcan XC-72 was added. Based on 100 parts by weight of silver nanoparticles, the Vulcan XC-72 content of the electrode catalyst was 300 parts by weight.

[0080] Example 4

[0081] The electrode catalyst was prepared in the same manner as in Example 1, except that 350 mg of Vulcan XC-72 was added. Based on 100 parts by weight of silver nanoparticles, the Vulcan XC-72 content of the electrode catalyst was 35 parts by weight.

[0082] Comparative Example 1

[0083] The electrode catalyst was prepared in the same manner as in Example 1, except that Vulcan XC-72 was not added.

[0084] Comparative Example 2

[0085] The electrode catalyst was prepared in the same manner as in Example 1, except that 5 mg of a catalyst with a specific surface area of ​​1,270 m² was added. 2 Ketjen Black EC600JD with a resistivity of 0.005 Ω·cm to 0.01 Ω·cm was used instead of Vulcan XC-72. The electrode catalyst contained 0.5 parts by weight of Ketjen Black EC600JD based on 100 parts by weight of silver nanoparticles.

[0086] Comparative Example 3

[0087] The electrode catalyst was prepared in the same manner as in Example 1, except that 1,000 mg of Ketjenblack EC600JD was added instead of Vulcan XC-72. The Ketjenblack EC600JD content of the electrode catalyst was 100 parts by weight based on 100 parts by weight of silver nanoparticles.

[0088] Comparative Example 4

[0089] The electrode catalyst was prepared in the same manner as in Example 1, except that 1,000 mg of a catalyst with a specific surface area of ​​800 m² was added. 2Ketjen Black EC300J, with a resistivity of 0.01 Ω·cm to 0.1 Ω·cm, was used instead of Vulcan XC-72. The electrode catalyst contained 100 parts by weight of Ketjen Black EC300J based on 100 parts by weight of silver nanoparticles.

[0090] Comparative Example 5

[0091] The electrode catalyst was prepared in the same manner as in Example 1, except that 200 mg of Vulcan XC-72 was added. Based on 100 parts by weight of silver nanoparticles, the Vulcan XC-72 content of the electrode catalyst was 20 parts by weight.

[0092] Comparative Example 6

[0093] The electrode catalyst was prepared in the same manner as in Example 1, except that 4,000 mg of Vulcan XC-72 was added. Based on 100 parts by weight of silver nanoparticles, the Vulcan XC-72 content of the electrode catalyst was 400 parts by weight.

[0094] Experimental Example

[0095] (1) Manufacturing of electrochemical units

[0096] The electrode catalysts of the various embodiments and comparative examples were coated onto a 25 cm² area using an ultrasonic sprayer at 120°C. 2 A cathode was fabricated on one surface of a gas diffusion layer (JNT30-A6P (JNTG Co.)). At this time, the silver nanoparticle content per unit area in the electrode catalyst layer stacked on one surface of the gas diffusion layer was uniform, at 1.0 mg / cm². 2 The thickness of the electrode catalyst layer was 30 μm for Example 1, 15 μm for Example 2, and 90 μm for Example 3.

[0097] Furthermore, a Ti mesh coated with IrO2 was used as the anode, and the area of ​​the Ti mesh was 25 cm². 2 0.25 MCs2CO3 was used as the anolyte. A porous separator was used as the separator, and the cathode and anode were stacked on both sides of the separator to complete the electrochemical unit.

[0098] (2) Evaluate electrochemical performance based on current density

[0099] The reaction was carried out for 30 minutes using an electrochemical unit, with an application rate of 100 mA / cm² applied using a VSP potentiostat (BioLogic Co.). 2 200 mA / cm 2 300 mA / cm 2400 mA / cm 2 and 500 mA / cm 2 The current density was maintained for 30 minutes at each time, and a reaction voltage ranging from 1 V to 4 V was applied to measure the carbon dioxide conversion rate, Faraday efficiency, and overvoltage of the products. Electrolyte solution was supplied to the anode at a rate of 25 mL / min, and humidified carbon dioxide at 40°C was supplied to the cathode at a rate of 200 ccm. The carbon dioxide conversion rate was calculated as the ratio of carbon monoxide produced to the amount of carbon dioxide gas introduced per hour, and the Faraday efficiency was measured by analyzing the gas composition at the exhaust line using gas chromatography (GC). Furthermore, the Faraday efficiency was calculated using the following equation.

[0100] [Equation 1]

[0101]

[0102] In Equation 1 above, Q is the flow rate at the discharge line, F is the Faraday constant, p is the pressure, T is the measured temperature, and R is the ideal gas constant. Total current i 总计 It is the value of the total current applied over time, and the current i for the product. 产物 The gas volume V measured by GC analysis 产物 The calculated values ​​are shown in Tables 1 to 3 below, based on the carbon dioxide conversion rate and the Faraday efficiency of each product at various current densities.

[0103] Overvoltage measurements were performed using a VSP potentiostat (BioLogic Co.). An 80 A boost converter was installed to apply a current corresponding to a large area. The voltage was measured at 100 mA / cm². 2 200 mA / cm 2 300 mA / cm 2 400 mA / cm 2 and 500 mA / cm 2 A holding current was applied for a predetermined time, and the voltage was recorded after 15 minutes. Gas chromatography (GC) analysis was also performed simultaneously, and the overvoltage values ​​are shown in Tables 1 to 3.

[0104] [Table 1]

[0105]

[0106] [Table 2]

[0107]

[0108] [Table 3]

[0109]

[0110] Referring to Tables 1 to 3 above, it can be seen that, compared with Comparative Example 1 without added carbon black, the electrochemical units using the electrode catalysts of each of Examples 1 to 4 exhibit low overvoltages, particularly at 500 mA / cm². 2 The low overvoltage at high current densities indicates that the electrode catalyst of the present invention comprises carbon black, thereby having sufficient pores formed in the electrode catalyst layer. This allows carbon dioxide to move smoothly within the electrode catalyst layer, thus reducing the overvoltage at high currents. Furthermore, it can be determined that in the case of Example 1, the hydrophobicity of the carbon black also mitigates overflow phenomena occurring at high currents, thereby suppressing the hydrogen generation reaction and thus reducing the hydrogen Faraday efficiency.

[0111] Meanwhile, compared with Examples 1 to 3, carbon black was added, but the specific surface area of ​​the carbon black was greater than 750 m². 2 In Comparative Examples 2 to 4, with a carbon black content of / g, the carbon dioxide conversion rate and carbon monoxide Faradaic efficiency were low at most current densities, while the hydrogen Faradaic efficiency and overvoltage were high. Furthermore, compared to Comparative Example 1 without added carbon black, Comparative Examples 2 to 4 showed lower carbon dioxide conversion rate and carbon monoxide Faradaic efficiency, while exhibiting higher hydrogen Faradaic efficiency and overvoltage. In particular, the performance of the electrochemical unit using the electrode catalysts of Comparative Examples 3 and 4 deteriorated to the point where it was impossible to achieve a current density of 500 mA / cm². 2 The highest current density drives the electrochemical unit to an excessively high overvoltage, making it impossible to measure carbon dioxide conversion and Faraday efficiency due to power supply limitations. From the above, it is determined that adding carbon black with a large specific surface area reduces the density of the electrode catalyst layer, thereby increasing resistance. Consequently, the overvoltage increases significantly, excessively promoting the hydrogen generation reaction, which may significantly degrade electrode performance.

[0112] Furthermore, it has been determined that in Comparative Example 1 and therein, a specific surface area of ​​100 m² was used. 2 / g to 750 m 2 In Comparative Example 5, where the carbon black content is less than the scope of the present invention, overflow phenomenon increases due to the low hydrophobicity of the electrode catalyst. Therefore, electrode performance is poor, with lower carbon dioxide conversion at high current, higher overvoltage, and higher Faraday efficiency for hydrogen compared to Example 1. Furthermore, in Comparative Example 6, where the carbon black content is greater than the scope of the present invention, it can be determined that the silver nanoparticle content per unit area of ​​the catalyst for the carbon dioxide reduction reaction is relatively lower, resulting in a lower carbon dioxide conversion rate compared to Example 1.

[0113] Based on the above results, it is determined that in the electrode catalyst of the present invention, carbon dioxide gas can move smoothly through the pores formed by carbon black in the electrode catalyst layer, and the overflow phenomenon is also reduced due to the hydrophobicity of carbon black. This allows for the improvement of carbon dioxide conversion rate and carbon monoxide Faraday efficiency in the electrochemical unit containing the electrode catalyst, and the reduction of hydrogen Faraday efficiency and overvoltage.

Claims

1. An electrode catalyst comprising: metal nanoparticles; and carbon black, in: The specific surface area of ​​the carbon black is 100 m². 2 / g to 750 m 2 / g; and Based on 100 parts by weight of the metal nanoparticles, the carbon black content is from 35 parts by weight to 350 parts by weight.

2. The electrode catalyst according to claim 1, wherein the resistivity of the carbon black is 1.5 Ω·cm or less.

3. The electrode catalyst according to claim 1, wherein the average diameter of the metal nanoparticles is 100 nm or less.

4. The electrode catalyst according to claim 1, wherein the metal nanoparticles comprise one or more elements selected from the following: Ag, Au, Zn, In, Cu, Ni, Pt, Pd, Ti, Fe, Ga, and Sn.

5. The electrode catalyst according to claim 1, wherein the electrode catalyst comprises a cationic ionomer or anionic ionomer.

6. The electrode catalyst according to claim 5, wherein the content of the cationic ionomer or the anionic ionomer is from 0.1 parts by weight to 20 parts by weight, based on 100 parts by weight of the metal nanoparticles.

7. A cathode, comprising: Electrode catalyst layer; and gas diffusion layer, in: The electrode catalyst layer comprises the electrode catalyst according to claim 1; as well as The electrode catalyst layer is stacked on at least one surface of the gas diffusion layer.

8. The cathode according to claim 7, wherein the content of the metal nanoparticles in the electrode catalyst layer is 0.5 mg / cm². 2 Up to 1.5 mg / cm 2 .

9. A method for preparing a cathode, the method comprising: (S1) An electrode catalyst composition is prepared by mixing metal nanoparticles, carbon black and solvent; as well as (S2) The electrode catalyst composition prepared in step (S1) is coated onto the gas diffusion layer. in: The carbon black in step (S1) has a specific surface area of ​​100 m². 2 / g to 750 m 2 / g; as well as Based on 100 parts by weight of the metal nanoparticles, the carbon black content in step (S1) is 35 to 350 parts by weight.

10. An electrochemical unit comprising a cathode according to claim 7; an anode; and a separator disposed between the cathode and the anode.

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