AN ELECTROCHEMICAL CELL FOR CONVERSION OF CARBON DIOXIDE AND A STACK INCLUDING THE SAME

Abstract

 Provided is an electrochemical cell for converting carbon dioxide, featuring an electrode-solid electrolyte assembly with a solid electrolyte layer made of a cation exchange solid electrolyte. The anode and cathode are integrated on opposite surfaces of the electrolyte layer, each comprising a catalyst and cation exchange binder. The cell includes porous transport layers for both electrodes and an interfacial layer with an anion exchange polymer between the cathode and its transport layer. Water is supplied to the anode for oxidation, while carbon dioxide is supplied to the cathode for reduction, producing formic acid, ethylene, propylene, and alcohols. The cell also includes reinforcement and antioxidant layers in the solid electrolyte and protective structures on its edges. Bipolar plates and gaskets ensure efficient fluid distribution. The design supports scalability with a laminate structure for multiple cells, making it suitable for large-scale applications.

Description

BACKGROUND

Technical Field

[0001] The present disclosure relates to electrochemical cells, specifically to the field of electrochemical conversion of carbon dioxide into useful chemical products. This disclosure pertains to the design and fabrication of electrode assemblies, solid electrolytes, and associated components used in the reduction of carbon dioxide, with applications in sustainable energy systems, chemical manufacturing, and environmental remediation. The disclosure addresses the integration of catalysts, porous transport layers, and bipolar plates to enhance the efficiency and scalability of carbon dioxide reduction processes.

Background

[0002] Increased emissions of greenhouse gases, i.e., carbon dioxide (CO₂), have accelerated global warming, resulting in climate change all over the world over the past few decades. Solving this problem has emerged as an important issue.

[0003] Accordingly, there has recently been a significant increase in interest in methods for converting either carbon dioxide captured from flue gas discharged through flues of industrial manufacturing plants or carbon dioxide captured directly from the atmosphere into high value-added compounds. Such a method includes a CO₂ conversion reaction, i.e., CO₂ reduction reaction (CO₂RR) or the like which converts carbon dioxide into other compounds through an electrochemical reduction reaction.

[0004] This method has advantages of removing carbon dioxide by consuming it as a reactant in electrochemical reactions, and at the same time, storing electricity based on renewable energy such as wind, solar, and hydropower, which is produced in excess and discarded before being used, in the form of high value-added compounds.

[0005] The carbon dioxide conversion reaction or carbon dioxide reduction reaction yields a wide variety of products depending on the cell structure constituting the conversion device, the type of electrolyte/electrode-catalyst, the characteristics of the parts or materials constituting the cell, and the operating conditions. Gaseous products include carbon monoxide (CO) containing single carbon, ethylene (C₂H₄) and propylene (C₃H₆) containing multi-carbon (C₂₊) and the like. In addition, liquid products include formic acid (HCOOH)/formate containing a single carbon, and alcohols such as methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH) and the like.

[0006] The carbon dioxide reduction reaction is greatly affected by the structure of the cell. Conventional methods include a liquid batch cell called "H-type cell", as shown in FIG. 1.

[0007] The liquid batch cell includes an anode as a counter electrode (CE), a cathode as a working electrode (WE), and a reference electrode (RE). An anolyte, which is an electrolyte of an anode compartment where an electrochemical oxidation reaction occurs, and a catholyte, which is an electrolyte of a cathode compartment where an electrochemical reduction reaction occurs, generally use a liquid, i.e., an aqueous solution. The anolyte and catholyte are separated by a solid electrolyte located in the middle of the cell. This solid electrolyte is usually an ionomer-based, neat or non-reinforced ion exchange solid electrolyte (IESE).

[0008] At the anode of the liquid batch cell, a reaction in which oxygen is generated (OER: oxygen evolution reaction) occurs through water electrolysis, and at the cathode, a reaction in which carbon dioxide gas dissolved in the catholyte is reduced (CO₂RR) occurs.

[0009] The liquid batch cell is widely used in catalyst analysis research because it has a simple structure and allows rapid and economical evaluation of catalytic activity. However, since the solubility of carbon dioxide in the liquid electrolyte is very low, 34 mM at room temperature of about 25°C, disadvantageously, the mass transport resistance or loss is large, operation is possible only at very low current densities, i.e., less than 100 mA/cm², and as a result, productivity is reduced. Eventually, the production speed of the product is greatly reduced, making large-scale manufacturing very difficult. Also, the liquid electrolyte has batch cell disadvantage of having low durability corresponding to only several tens of hours due to unstable cell structure and operation.

[0010] In an attempt to solve the problems of the liquid batch cell, a liquid flow cell as shown in FIG. 2 was developed.

[0011] The liquid flow cell has a configuration in which an anolyte is located between the solid electrolyte and the anode, and a catholyte is located between the solid electrolyte and the cathode. The anolyte and the catholyte generally use liquids and are isolated from each other through a solid electrolyte located in the middle of the cell. The solid electrolyte is usually an ionomer-based neat or non-reinforced ion exchange solid electrolyte. In addition, the liquid flow cell has an electrode-integrated porous transport layer (EIPTL) structure in which the anode and the cathode are attached to the anode porous transport layer (PTL) and the cathode porous transport layer, respectively. In this case, unlike the conventional liquid batch cell, carbon dioxide gas is directly supplied to the catalyst in the cathode through the cathode porous transport layer. As a result, the carbon dioxide reduction reaction rate can increase and thus the cell current density can be increased to more than 100 mA/cm² resulting in an increase in the product yield rate.

[0012] However, the liquid flow cell has problems in which the ohmic resistance between the solid electrolyte and the electrodes increases due to the presence of anolyte and catholyte, and flooding in which the pores inside the electrode-integrated porous transport layer are blocked by the liquid occurs. Flooding of the liquid flow cell makes sufficient supply of the reactant required for electrochemical reaction to the catalyst within the electrode impossible, resulting in an increased mass transport resistance or loss. Also, carbon dioxide reacts with hydroxide ions (OH^-) at the cathode to form a salt as a byproduct, resulting in unnecessary loss of carbon dioxide. Further, the salt may accumulate inside the cell. As a result, disadvantageously, the reaction rate and current density of the cell may decrease and performance and continuous operability of the cell may decrease.

[0013] In an attempt to solve the problems of liquid flow cells, solid electrolyte-based flow cells with electrode-integrated porous transport layers (EIPTLs), as shown in FIG. 3, were developed. The solid electrolyte-based flow cells with EIPTLs have neither anolyte nor catholyte in the internal structure thereof. In other words, there are no liquid electrolytes between the solid electrolyte and the electrodes, and the solid electrolyte and the electrodes are in direct contact, thus forming a zero-gap cell structure. As a result, the ohmic resistance of the cell decreases and cell performance increases. The solid electrolyte-based flow cells with EIPTLs have solved many of the problems of conventional liquid flow cells, but still has the problem of flooding of the EIPTL due to liquid products or water as the current density of the cell increases, because it adopts the EIPTL structure. That is, when the EIPTL is formed by directly applying an electrode slurry or catalyst ink, which is a mixture of a catalyst, a catalyst support, a binder, and solvents, onto the porous transport layer, the electrode slurry penetrates not only the surface of the porous transport layer but also the inside of the porous transport layer through the pores, resulting in excessive use of the electrode slurry compared to the required amount. In addition, excessively applied electrode slurry blocks the pores of the porous transport layer, thus reducing the mass transport capability of the porous transport layer.

[0014] In addition, the EIPTL structure has a configuration in which the electrode is attached to the porous transport layer, thus making close contact between the solid electrolyte and the electrode impossible, which results in increased contact resistance and reduced cell performance and durability.

[0015] In addition, solid electrolyte-based flow cells with EIPTLs have a configuration in which the solid electrolyte separates the anode and the cathode from each other, and the solid electrolyte is typically an ionomer-based non-reinforced ion exchange solid electrolyte. For this reason, the durability of the solid electrolyte is not sufficient, which may disadvantageously make the solid electrolyte thin due to degradation of the solid electrolyte during operation for a long period of time, leading to an increased formation of pinholes. As a result, the long-term durability and stability of the solid electrolyte are deteriorated. Therefore, the solid electrolyte-based flow cells with EIPTLs have beneficial effects of reducing the internal resistance of the cell and partially increasing the current density compared to conventional liquid bulk cells and liquid flow cells, but are still not suitable for large-scale manufacturing due to the problems such as low cell performance, low long-term durability and stability, flooding inside the cell, and difficulty in operating at high current densities.

[0016] The above information disclosed in this Background section is provided only for enhancement of understanding of the background of the invention, and therefore it may include information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE DISCLOSURE

[0017] The present disclosure has been made in an effort to solve the above-described problems associated with the prior art.

[0018] It is one object of the present disclosure to provide an electrochemical cell for conversion of carbon dioxide suitable for mass production.

[0019] It is another object of the present disclosure to provide an electrochemical cell for conversion of carbon dioxide that exhibits maximized performance due to low cell resistance.

[0020] It is another object of the present disclosure to provide an electrochemical cell for conversion of carbon dioxide that minimizes the problem of flooding.

[0021] It is another object of the present disclosure to provide an electrochemical cell for conversion of carbon dioxide that has high operational current density.

[0022] It is another object of the present disclosure to provide an electrochemical cell for conversion of carbon dioxide that is highly durable and thus has a long lifetime and is highly stable.

[0023] The objects of the present disclosure are not limited to those described above. The objects of the present disclosure will be clearly understood from the following description, and are capable of being implemented by means defined in the claims and combinations thereof. In one aspect, the present disclosure provides an electrochemical cell for conversion of carbon dioxide including an electrode-solid electrolyte assembly including a solid electrolyte layer containing a cation exchange solid electrolyte (CESE), an anode coated on one surface of the solid electrolyte layer and being integrated with the solid electrolyte layer, wherein the anode contains an anode catalyst and a first cation exchange binder, and a cathode coated on the other surface of the solid electrolyte layer and being integrated with the solid electrolyte layer, wherein the cathode contains a cathode catalyst and a second cation exchange binder, an anode porous transport layer disposed on the anode and having porosity, a cathode porous transport layer disposed on the cathode and having porosity, and an interfacial layer interposed between the cathode and the cathode porous transport layer and containing an anion exchange polymer, wherein water is supplied to the anode through the anode porous transport layer and an oxidation reaction of water occurs at the anode, and carbon dioxide is supplied to the cathode through the cathode porous transport layer and a reduction reaction of carbon dioxide occurs at the cathode.

[0024] As discussed, the method and system suitably include use of a controller or processer.

[0025] Other aspects and preferred embodiments of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

FIG. 1 shows a liquid batch cell according to the prior art;

FIG. 2 shows a liquid flow cell according to the prior art;

FIG. 3 shows a solid electrolyte-based flow cell with an electrode-integrated porous transport layer (EIPTL);

FIG. 4 shows a cell for conversion of carbon dioxide according to the present disclosure;

FIG. 5 shows a first embodiment of an electrode-solid electrolyte assembly according to the present disclosure;

FIG. 6 is a cross-sectional view taken along line A-A' of FIG. 5;

FIG. 7 shows a second embodiment of the electrode-solid electrolyte assembly according to the present disclosure;

FIG. 8 is a cross-sectional view taken along line B-B' of FIG. 7;

FIG. 9 shows a first embodiment of a solid electrolyte layer according to the present disclosure;

FIG. 10 shows a second embodiment of the solid electrolyte layer according to the present disclosure;

FIG. 11A shows an embodiment of an anode porous transport layer according to the present disclosure;

FIGS. 11B to 11D show modified embodiments of the anode porous transport layer of FIG. 11A;

FIG. 11E shows another embodiment of the anode porous transport layer according to the present disclosure;

FIGS. 11F to 11H show modified embodiments of the anode porous transport layer of FIG. 11E;

FIG. 12 shows a cathode porous transport layer according to the present disclosure;

FIG. 13 shows a reference diagram illustrating the cathode porous transport layer according to the present disclosure;

FIG. 14 shows an anode bipolar plate according to the present disclosure;

FIG. 15 shows a cross-sectional view illustrating the anode bipolar plate according to the present disclosure;

FIG. 16 shows an anode gasket according to the present disclosure;

FIG. 17 shows a combination of the anode gasket according to the present disclosure and the anode bipolar plate;

FIG. 18 shows a cathode bipolar plate according to the present disclosure;

FIG. 19 shows a cross-sectional view illustrating the cathode bipolar plate according to the present disclosure;

FIG. 20 shows a cathode gasket according to the present disclosure;

FIG. 21 shows a combination of the cathode gasket according to the present disclosure and the cathode bipolar plate;

FIG. 22 shows a stack according to the present disclosure;

FIG. 23 shows an end plate according to the present disclosure; and

FIG. 24 shows a cross-sectional view taken along line C-C' of FIG. 23.

DETAILED DESCRIPTION OF EMBODIMENTS

[0027] The objects described above, and other objects, features and advantages, will be clearly understood from the following preferred embodiments with reference to the annexed drawings. However, the present disclosure is not limited to the embodiments, and will be embodied in different forms. The embodiments are suggested only to offer thorough and complete understanding of the disclosed contents and to sufficiently inform those skilled in the art of the technical concept of the present disclosure.

[0028] Like reference numbers refer to like elements throughout the description of the figures. In the drawings, the sizes of structures are exaggerated for clarity. It will be understood that, although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be construed as being limited by these terms, and are used only to distinguish one element from another. For example, within the scope defined by the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. Singular forms are intended to include plural forms as well, unless the context clearly indicates otherwise.

[0029] It will be further understood that the terms "comprises", "has" and the like, when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, components or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof. In addition, it will be understood that, when an element such as a layer, film, region or substrate is referred to as being "on" another element, it can be directly on the other element, or an intervening element may also be present. It will also be understood that, when an element such as a layer, film, region or substrate is referred to as being "under" another element, it can be directly under the other element, or an intervening element may also be present.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. These terms are merely intended to distinguish one component from another component, and the terms do not limit the nature, sequence or order of the constituent components. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. In addition, the terms "unit", "-er", "-or", and "module" described in the specification mean units for processing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof.

[0031] Although exemplary embodiment is described as using a plurality of units to perform the exemplary process, it is understood that the exemplary processes may also be performed by one or plurality of modules. Additionally, it is understood that the term controller/control unit refers to a hardware device that includes a memory and a processor and is specifically programmed to execute the processes described herein. The memory is configured to store the modules and the processor is specifically configured to execute said modules to perform one or more processes which are described further below.

[0032] Further, the control logic of the present disclosure may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN).

[0033] Unless specifically stated or obvious from context, as used herein, the term "about" is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. "About" can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term "about".

[0034] Unless the context clearly indicates otherwise, all numbers, figures and/or expressions that represent ingredients, reaction conditions, polymer compositions and amounts of mixtures used in the specification are approximations that reflect various uncertainties of measurement occurring inherently in obtaining these figures, among other things. For this reason, it should be understood that, in all cases, the term "about" should be understood to modify all numbers, figures and/or expressions. In addition, when numeric ranges are disclosed in the description, these ranges are continuous and include all numbers from the minimum to the maximum including the maximum within the ranges unless otherwise defined. Furthermore, when a range refers to integers, it includes all integers from the minimum to the maximum including the maximum within the range, unless otherwise defined.

[0035] In conventional liquid electrolyte-based cells shown in FIGS. 1 and 2, alkaline solutions such as potassium hydroxide (KOH), neutral solutions, or acidic solutions such as sulfuric acid (H₂SO₄) may be used as anolytes and catholytes.

[0036] When the alkaline solution is used, carbon dioxide, which is a cathode reactant, is consumed before participating in a carbon dioxide reduction reaction due to hydroxide ions (OH^-), or the like to form a salt as a by-product, which causes deterioration in efficiency and stability of the cell. In addition, as the cost of alkaline and neutral solutions and equipment maintenance cost are added, the overall cost of the cell increases and the operating device within the system becomes complicated. Using an acidic solution can minimize the problem of salt formation, but still has problems of the additional cost of the acidic solution and equipment maintenance, and complicated operating equipment within the system.

[0037] Therefore, in order to solve the problems, the present disclosure provides a method in which a solid electrolyte is used rather than a liquid electrolyte in the cell internal structure and at the same time, deionized water is used as an anode reactant and humidified CO₂ gas is used as a cathode reactant.

[0038] FIG. 4 shows a cell for conversion of carbon dioxide 10 according to the present disclosure. The cell for conversion of carbon dioxide 10 may include an electrode-solid electrolyte assembly 100 including a solid electrolyte layer 110, an anode 120, and a cathode 130, an anode porous transport layer (PTL) 200 disposed on one surface of the electrode-solid electrolyte assembly 100, a cathode porous transport layer (PTL) 300 disposed on the other surface of the electrode-solid electrolyte assembly 100, an interfacial layer 800 interposed between the cathode 130 and the cathode porous transport layer 300, an anode bipolar plate 400 disposed on the anode porous transport layer 200, an anode gasket 500 mounted on the anode bipolar plate 400 outside of the anode porous transport layer 200, a cathode bipolar plate 600 disposed on the cathode porous transport layer 300, and a cathode gasket 700 mounted on the cathode bipolar plate plate 600 outside the cathode porous transport layer 300.

[0039] The electrochemical reaction proceeds in the electrochemical cell 10 as follows. Water is supplied to the anode 120 through the anode flow channel 430 and the anode porous transport layer 200 and an oxidation reaction of water occurs at the anode 120. Humidified carbon dioxide is supplied to the cathode 130 through the cathode flow channel 630 and the cathode porous transport layer 300 and a reduction reaction of carbon dioxide occurs at the cathode 130.

[0040] As a result of the reduction reaction of carbon dioxide, at least one product selected from the group consisting of formic acid, ethylene, propylene, alcohol, and combinations thereof can be obtained. This will be described later.

[0041] The electrode-solid electrolyte assembly 100 may include a solid electrolyte layer 110, an anode 120 that is coated on one surface of the solid electrolyte layer 110 and is integrated with the solid electrolyte layer 110, and a cathode 130 that is coated on the other surface of the solid electrolyte layer 110 and is integrated with the solid electrolyte layer 110.

[0042] As used herein, the term "integrated" refers to a state in which respective elements are strongly bound by directly applying the raw materials of the anode 120 and/or cathode 130 to the solid electrolyte layer 110, transferring the anode 120 and/or cathode 130 to the solid electrolyte layer 110, or attaching the anode 120 and/or cathode 130 to the solid electrolyte layer 110 and then pressurizing the resulting product with high pressure. The bonding force or peeling strength between respective elements of the electrode-solid electrolyte assembly 100 may be stronger than the bonding force or the peel strength between the electrode-solid electrolyte assembly 100 and the anode porous transport layer 200 and/or the cathode porous transport layer 300. The solid electrolyte-based flow cell with EIPTLs of FIG. 3 described above includes a five-layer laminate based on the EIPTL structure in which the electrode and the porous transport layer, rather than the electrode and the solid electrolyte, which play an important role in electrochemical reactions, are directly integrated, thus causing problems such as deterioration in the electrochemical reactivity and durability of the cell, and flooding of liquid products and/or water as the current density of the cell increases. The present disclosure is characterized by using a three-layer assembly in which the anode 120 and the cathode 130 are integrated into the solid electrolyte layer 110 rather than the porous transport layer. By directly assembling the anode 120 and the cathode 130 on the solid electrolyte layer 110, the contact resistance therebetween can be greatly reduced and the electrochemical reaction rate can be increased. In addition, durability and stability against a repetitive contraction-expansion degradation mode of the solid electrolyte layer 110 due to temperature/relative humidity (RH) changes and a freeze/thaw degradation mode due to seasonal changes can be improved during cell operation. Meanwhile, unlike the conventional solid electrolyte-based EIPTL-type flow cell structure, the electrode slurry is applied directly to the solid electrolyte layer 110 and thus can solve the problem in which the electrode slurry blocks the pores of the porous transport layer, thus lowering mass transport performances.

[0043] FIG. 5 shows a first embodiment of an electrode-solid electrolyte assembly 100 according to the present disclosure. FIG. 6 is a cross-sectional view taken along line A-A' of FIG. 5. The solid electrolyte layer 110 may include a central portion in contact with the anode 120 and the cathode 130, and an edge portion excluding the central portion. The electrode-solid electrolyte assembly 100 may include a protective member 140 located in the edge portion. Specifically, an anode protective member 141 may be mounted in the area defined by one surface of the edge portion and the side surface of the anode 120. The cathode protective member 142 may be mounted in the area defined by another surface of the edge portion and the side surface of the cathode 140.

[0044] The protective member 140 can improve the durability of the solid electrolyte layer 110 by delaying the deterioration of the solid electrolyte layer 110 during cell operation and can improve the durability of the cell by delaying the deterioration of the anode 120 and the cathode 130 caused by the deterioration of the solid electrolyte layer 110. In addition, a conventional structure not including the protective member 140 has problems in which when handling components during cell and stack manufacturing, the solid electrolyte layer, which is less rigid and is flexible, is directly touched and is thus contaminated, thus causing a problem of deteriorated handling properties. On the other hand, when the protective member 140 is used as in the present disclosure, contamination can be fundamentally prevented when handling the solid electrolyte layer 110, or the like and handling performance can be improved due to high rigidity thereof.

[0045] The protective member 140 may contain a material with excellent thermal resistance and chemical resistance. Specifically, the protective member 140 has a flexural modulus of 1 GPa or more, preferably 1.5 GPa or more, under the measurement conditions of ISO 178 (measurement speed: 2 mm/min) established by ISO (International Standardization Organization). The protective member 140 may have a heat deflection (or distortion) temperature of 60°C or higher, preferably 80°C or higher, under ISO 75 (measurement pressure: 1.8 MPa) measurement conditions. The protective member 140 that satisfies these characteristics may include at least one selected from the group consisting of polyimide (PI), poly(ether imide) (PEI), poly(phenylene oxide) (PPO), poly(phenylene ether) (PPE), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(trimethylene terephthalate) (PTT), poly(ethylene naphthalate) (PEN), poly(ether ether ketone) (PEEK), and combinations thereof. The protective member 140 should have a uniform surface to ensure airtightness of the cell and thus is preferably made exclusively of a polymer, rather than a mixture thereof with an inorganic substance such as a filler, if possible.

[0046] The electrode-solid electrolyte assembly 100 may include an adhesive member 150 interposed between the protective member 140 and the solid electrolyte layer 110 to attach the protective member 140 to the solid electrolyte layer 110.

[0047] The adhesive member 150 may be prepared by applying an adhesive to the surface of the protective member 140, followed by drying. The adhesive member 150 may include a polar adhesive such as silicone, epoxy or acryl, a non-polar adhesive such as polyethylene (PE), polypropylene (PP), poly(ethylene-co-propylene) or ethylene-propylene rubber (EPR), a modified adhesive in which a polar group is introduced into a non-polar adhesive, such as poly(ethylene-g-maleic anhydride), poly(propylene-g-maleic anhydride), chlorinated polyethylene, or chlorinated polypropylene, or a combination thereof.

[0048] The protective member 140 provided with the adhesive member 150 is mounted on the edge of the solid electrolyte layer 110 and then is attached thereto by compression-molding at a predetermined pressure and at about 70°C to 240°C, or 100°C to 200°C. When the temperature is less than 70°C, the protective member 140 may not be well bonded, and when the temperature exceeds 240°C, the materials contained in the solid electrolyte layer 110, the anode 120, the cathode 130 and the like may deteriorate.

[0049] FIG. 7 shows a second embodiment of an electrode-solid electrolyte assembly 100' according to the present disclosure. FIG. 8 shows a cross-sectional view taken along line B-B' of FIG. 7. In the second embodiment, the protective member 140' is located in an area defined by one surface of the solid electrolyte layer 110 and the side surface of the anode 120 and an area defined by the other surface of the solid electrolyte layer 110 and the side surface of the cathode 130, and covers the side surface of the solid electrolyte layer 110.

[0050] The protective member 140' may contain at least one selected from the group consisting of polyimide (PI), poly(ether imide) (PEI), poly(phenylene oxide) (PPO), poly(phenylene ether) (PPE), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(trimethylene terephthalate)) (PTT), poly(ethylene naphthalate) (PEN), poly(ether ether ketone) (PEEK), polyethylene (PE), polypropylene (PP), poly(ethylene-co-propylene)), ethylene-propylene rubber (EPR), poly(ethylene-g-maleic anhydride), poly(propylene-g-maleic anhydride), chlorinated polyethylene, chlorinated polypropylene, and combinations thereof. Meanwhile, the protective member 140' may further contain a filler such as glass fiber and carbon fiber to reinforce physical properties. The content of the filler is not specifically limited and may be 5% by weight to 50% by weight, or 10% by weight to 35% by weight, based on the total weight of the protective member 140'. When the content of the filler is less than 5% by weight, the effect of reinforcing physical properties may be insufficient and when the content exceeds 50% by weight, the properties of the polymer may decrease and melt processability may decrease.

[0051] The protective member 140' may be prepared on the outer portion of the assembly of the solid electrolyte layer 110, the anode 120, and the cathode 130 by injection molding. In addition, an adhesive member 150' may be applied to the surface of the protective member 140'. The adhesive member 150' may be used to bond the electrode-solid electrolyte assembly 100 to the anode porous transport layer 200 and the cathode porous transport layer 300. The type of the adhesive member 150' is the same as described above.

[0052] The solid electrolyte layer 110 may contain a cation exchange solid electrolyte (CESE). Examples of the solid electrolyte generally used in electrochemical cells may include an anion exchange solid electrolyte (AESE), a cation exchange solid electrolyte, a bipolar solid electrolyte (BPSE) and the like.

[0053] The anion exchange solid electrolyte may exchange anions such as hydroxide ions (OH^-). The backbone of the anion exchange solid electrolyte generally contains hydrocarbon rather than a fluorinated material. Representative anion exchange solid electrolytes may include Sustainion^™ based on polystyrene tetramethyl imidazolium chloride containing polystyrene (PS) as a main chain and an imidazolium group, a benzimidazolium-based solid electrolyte represented by Formula 1 below, a poly(aryl piperidinium)-based solid electrolyte represented by Formula 2 below, and the like. Alternatively, the anion exchange solid electrolyte may include commercially available Sustainion^™, Aemion^™, PiperION^™, and the like.

wherein n may be 10 to 1,000.

wherein x may be 10 to 1,000 and y may be 10 to 1,000.

[0054] Anion exchange solid electrolytes have been widely used because they are suitable for carbon dioxide reduction reactions at the cathode of conventional electrochemical cells for conversion of carbon dioxide. However, carbon dioxide, which is a reactant of the cathode, reacts with hydroxide ions and is consumed, thus disadvantageously causing formation and precipitation of salts as by-products at the cathode and deterioration of cell performance and durability. The by-products crossover from the cathode to the anode through the anion exchange solid electrolyte, thus causing a problem of reducing carbon dioxide (CO₂) utilization. In addition, the anion exchange solid electrolyte has a problem of oxidative degradation due to the low durability when an oxygen evolution reaction (OER) occurs at the anode. Due to these conventional problems, most anion exchange solid electrolytes have the disadvantages of low durability and very low suitability for large-scale manufacturing. For example, Sustainion^™ has poor handling properties because it should be stored in a state of being immersed in potassium hydroxide (KOH) before use and is less efficient to mass produce due to complicated sample treatment process.

[0055] To solve these problems, interest in cation exchange solid electrolytes, which have been used for decades in industries such as chlor-alkali electrolysis, and mass production and durability of which have been proven, has recently increased remarkably.

[0056] In general, cation exchange solid electrolytes have a great advantage in increasing the conversion rate of carbon dioxide because they have high durability and stability under various electrochemical operating conditions and inhibit the crossover of reactants or products from the cathode to the anode. In addition, by using the solid electrolyte layer 110 containing a cation exchange solid electrolyte according to the present disclosure and simultaneously using deionized water as an anode reactant, advantages of inhibiting accumulation of undesired impurities or by-products at the cathode and increased single pass conversion (SPC) efficiency can be obtained.

[0057] The cation exchange solid electrolyte may include a fluorinated solid electrolyte and/or a hydrocarbon solid electrolyte.

[0058] The fluorinated solid electrolyte may contain a per-fluorinated sulfonic acid (PFSA) compound. The PFSA compound has advantages such as high proton conductivity, excellent mechanical properties, chemical resistance, durability and handling properties, and extensive mass production. The PFSA-based compound is broadly classified into Nafion^™ having a long side chain, Dynyon^™ having a medium side chain, and Aquivion^™ having a short side chain, depending on the side chain structure thereof. In addition, the PFSA-based compound may include sulfonic acid, carboxylic acid or the like as a functional group at the end of the side chain.

[0059] The equivalent weight (EW) of the functional group of the PFSA compound may be about 600 g/mol to 1,000 g/mol, or about 700 g/mol to 950 g/mol. When the equivalent weight of the functional group is less than 600 g/mol, the solid electrolyte layer 110 may be excessively swollen in water and mechanical properties may be lowered due to excessively high content of the functional group. When the equivalent weight of the functional group is higher than 1,000 g/mol, the ion exchange capacity of the solid electrolyte layer 110 may deteriorate due to excessively low content of the functional group.

[0060] Compared to fluorinated solid electrolytes, hydrocarbon solid electrolytes may be based on compounds that are easier to polymerize or copolymerize various molecular structures. The hydrocarbon solid electrolyte includes sulfonated polyethylene, sulfonated polypropylene, sulfonated polystyrene, sulfonated polysulfone, sulfonated polybenzimidazole, sulfonated poly(phenylene oxide), sulfonated poly(phenylene ether), sulfonated poly(arylene ether ketone), sulfonated polyether ether ketone, sulfonated poly(ether ketone), sulfonated polyimide, sulfonated poly(ether imide), sulfonated poly(styrene-b-ethylene-r-butadiene-b-styrene) triblock copolymer or the like which contains a sulfonic acid group.

[0061] FIG. 9 shows a first embodiment of a solid electrolyte layer 110 according of the present disclosure. FIG. 10 shows a second embodiment of a solid electrolyte layer according to the present disclosure. Referring to FIGs. 9 and 10, the solid electrolyte layer 110 includes at least one reinforced layer 111 that contains pores filled with a first cation exchange solid electrolyte and an ion exchange layer 112 that is disposed on at least one surface of the reinforcement layer 111 and contains a second cation exchange solid electrolyte. The first cation exchange solid electrolyte and the second cation exchange solid electrolyte may be the same as or different from each other.

[0062] The present disclosure is characterized by increasing physical durability by introducing the reinforcement layer 111 into the solid electrolyte layer 110.

[0063] The reinforcement layer 111 may include one to four layers, or one or two layers. Without the reinforcement layer 111, the effect of strengthening the solid electrolyte cannot be obtained and, when the reinforcement layer 111 includes more than four layers, the process of manufacturing the solid electrolyte layer 110 may become complicated.

[0064] When the first cation exchange solid electrolyte is a fluorinated solid electrolyte, the reinforcement layer 111 may contain porous expanded poly(tetrafluoroethylene) (porous e-PTFE).

[0065] When the first cation exchange solid electrolyte is a hydrocarbon solid electrolyte, the reinforcement layer 111 may include a porous film made of polyimide (PI), poly(ether imide) (PEI), polyether ether ketone (PEEK), poly(ethylene naphthalate) (PEN), or poly(ether sulfone) (PES) or a combination thereof.

[0066] The porosity of the reinforcement layer 111 may be about 20% to 90% or about 40% to 80%. When the porosity is less than 20%, it is difficult to sufficiently impregnate the reinforced layer 111 with the first cation exchange solid electrolyte and bind the same to each other, and when the porosity exceeds 80%, the mechanical properties of the reinforced layer 111 are greatly reduced and the effect of introduction thereof cannot be obtained.

[0067] For example, the solid electrolyte layer 110 may be implemented by adding a filler such as a polymer fiber or glass fiber to the cation exchange solid electrolyte without the reinforcement layer 111, but is not limited thereto.

[0068] The thickness of the solid electrolyte layer 110 may be about 5 µm to 100 µm or about 8 µm to 70 µm. When the thickness is less than 5 µm, there is a problem that the mechanical properties are greatly reduced and the crossover of reactants/products of the cell is greatly increased. On the other hand, when the thickness exceeds 100 µm, the ohmic resistance of the solid electrolyte layer 110 may increase and cell performance may decrease as overpotential increases.

[0069] The volume of the reinforcement layer 111 may be about 10 vol% to 70 vol%, or about 20 vol% to 50 vol%, based on the total volume of the solid electrolyte layer 110. When the volume of the reinforcement layer 111 is less than 10% by volume, the effect of strengthening the solid electrolyte layer 110 may be insufficient, whereas when the volume exceeds 70% by volume, the content of the cation exchange solid electrolyte in the solid electrolyte layer 110 may decreases and the ion exchange capacity of the solid electrolyte layer 110 may be greatly reduced.

[0070] Hydrogen peroxide (HOOH) may be produced according to the structure and operating conditions of the electrochemical cell 10. In general, hydrogen peroxide produces highly reactive oxygen-containing radicals such as hydroxyl radicals (·OH) and hydroperoxyl radicals (·OOH). The radical attacks the cation exchange solid electrolyte in the solid electrolyte layer 110, a first cation exchange binder in the anode 120, and a second cation exchange binder in the cathode 130, thus causing chemical degradation of the electrode-solid electrolyte assembly 100 and deterioration in the long-term durability of the electrochemical cell 10 for conversion of carbon dioxide.

[0071] The present disclosure is characterized by adding an antioxidant to the solid electrolyte layer 110 to alleviate or suppress chemical degradation. Specifically, the antioxidant may be dispersed in the ion exchange layer 112.

[0072] The antioxidant may include a primary antioxidant that acts as a radical scavenger or quencher, and a secondary antioxidant that acts as a hydrogen peroxide decomposer.

[0073] When a fluorinated solid electrolyte is used as the cation exchange solid electrolyte, a cerium antioxidant may be used as the primary antioxidant. The cerium antioxidant may include cerium oxide (or ceria: CeO_x), modified cerium oxide, cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O), or the like. The modified cerium oxide may include cerium-zirconium oxide (CeZrO_x), cerium-manganese oxide (CeMnO_x), gadolinium (Gd)- or samarium (Sm)-doped cerium oxide, or the like.

[0074] The cerium antioxidant may be introduced in the form of a particle or powder (nanoparticle or nanopowder) having a crystallite size of several nm or tens of nm. However, cerium oxide and modified cerium oxide should be dispersed well in advance before addition to the fluorinated solid electrolyte because they are generally stored in an agglomerate state after production. In order to improve the degree of dispersion and/or distribution, a surfactant may be introduced along with the cerium antioxidant, which may reduce the activity of the cerium antioxidant. Therefore, in order to increase the dispersibility and activity of the cerium antioxidant, the cerium antioxidant may be introduced in the form of being supported on a support. The support may include titanium dioxide (TiO₂), silicon dioxide (silica, SiO₂), carbon powder, carbon nanotubes (CNTs) or the like. The content of the cerium antioxidant supported on the support may be about 2% to 70% by weight, or about 10% to 50% by weight, based on the total weight of the support and the cerium antioxidant. When the content of the cerium antioxidant is less than 2% by weight, the antioxidant performance may be deteriorated due to the excessively high content of the support compared to the cerium antioxidant. When the content exceeds 70% by weight, the cerium antioxidant is distributed excessively densely on the support, thus making efficient support and use of the cerium antioxidant difficult.

[0075] The content of the cerium antioxidant based on the total weight of the cation exchange solid electrolyte and the antioxidant in the solid electrolyte layer 110 may be about 200 ppm to 50,000 ppm, or about 1,000 ppm to 10,000 ppm. When the content of the cerium antioxidant is less than 200 ppm, antioxidant performances are greatly reduced, whereas when the content exceeds 50,000 ppm, it is difficult to uniformly disperse the cerium antioxidant in the solid electrolyte layer 110, ionic conductivity and other physical properties of the solid electrolyte layer 110 decrease, and costs may also increase.

[0076] Among the cerium antioxidants, cerium oxide and modified cerium oxide may have a crystallite size measured by X-ray of about 2 nm to 100 nm, or about 10 nm to 50 nm. When the crystallite size is less than 2 nm, the cerium antioxidant particles may agglomerate during cell operation, the activity over time and the long-term durability of the cerium antioxidant may be reduced. On the other hand, when the crystallite size exceeds 100 nm, the initial activity of the cerium antioxidant may be excessively low.

[0077] When the fluorinated solid electrolyte is used as the cation exchange solid electrolyte, the secondary antioxidant may be a manganese antioxidant such as manganese oxide, a non-manganese transition metal antioxidant such as platinum (Pt), gold (Au), or palladium (Pd), or a combination thereof.

[0078] To increase the dispersibility and activity of the secondary antioxidant, the secondary antioxidant may be supported on the support. The support is as described above. Here, the content of the secondary antioxidant supported on the support, and the content of the secondary antioxidant based on the total weight of the cation exchange solid electrolyte and the antioxidant in the solid electrolyte layer 110 are as described with reference to the cerium antioxidant.

[0079] When a hydrocarbon solid electrolyte is used as the cation exchange solid electrolyte, a sterically-hindered phenolic antioxidant may be used as the primary antioxidant. Specifically, the sterically-hindered phenolic antioxidant may include Irganox 1010^™ containing pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 1076^™ containing octadecyl-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 245^™ containing ethylene bis(oxyethylene) bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate) or the like.

[0080] The content of the sterically-hindered phenolic antioxidant based on the total weight of the cation exchange solid electrolyte and the antioxidant in the solid electrolyte layer 110 may be about 200 ppm to 50,000 ppm, or about 1,000 to 10,000 ppm. When the content of the sterically-hindered phenolic antioxidant is less than 200 ppm, antioxidant performances are greatly reduced, whereas when the content of sterically-hindered phenolic antioxidant exceeds 50,000 ppm, it is difficult to uniformly disperse the phenolic antioxidant, and the ionic conductivity and overall physical properties of the solid electrolyte layer 110 are reduced and costs may also rise.

[0081] When a hydrocarbon solid electrolyte is used as the cation exchange solid electrolyte, a phosphite antioxidant may be used as a secondary antioxidant. The phosphite antioxidant may include Irgafos 168^™ containing tris(2,4-ditert-butylphenyl) phosphite. Here, the content of the phosphite antioxidant based on the total weight of the cation exchange solid electrolyte and the antioxidant in the solid electrolyte layer 110 is as described with reference to the phenolic antioxidant.

[0082] The anode 120 may use water (H₂O) as a reactant and induce an oxidation reaction of the water as shown in Reaction Scheme 1 below, thus generating oxygen (O₂).

        [Reaction Formula 1]     H₂O → ½O₂ + 2H⁺+ 2e^-

[0083] The water supplied to the anode 120 may be deionized water having a specific resistance of 18 MΩ·cm or more. When the specific resistance of the deionized water falls within the range defined above, the purity of the deionized water can be maintained.

[0084] The anode 120 may contain an anode catalyst, a first cation exchange binder, an anode antioxidant, or the like.

[0085] The anode catalyst can increase the rate of oxygen evolution reaction (OER). The anode catalyst may include at least one selected from the group consisting of iridium oxide (IrOx), ruthenium oxide (RuOx), and combinations thereof.

[0086] The loading of platinum group metal (PGM) in the anode catalyst may be about 2.0 mg-PGM/cm² or less, or about 0.5 mg-PGM/cm² or less. When the loading exceeds 2.0 mg-PGM/cm², the cost greatly increases, the process of producing the uniform anode from the anode catalyst ink is difficult, and uniform dispersion of the anode catalyst within the anode is difficult.

[0087] In order to increase the dispersibility of the anode catalyst, the anode catalyst may be supported on a support. The support is preferably a non-carbon material that can be used under high potential conditions of 2V or more and examples thereof include tin (IV) oxide (SnO₂), titanium (Ti)-doped tin oxide (Ti-doped SnO₂), antimony (Sb)-doped tin oxide (Sb-doped SnO₂), nano-structured thin films (NSTFs), titanium dioxide (TiO₂), silicon dioxide (silica: SiO₂), or the like. The support ratio of the anode catalyst may be about 10% by weight to 70% by weight, or about 20% by weight to 50% by weight, based on the total content of the anode catalyst and the support. When the support ratio is less than 10% by weight, the support effect may be insufficient, whereas when the support ratio exceeds 70% by weight, the anode catalyst may be distributed excessively densely on the support, which may reduce the efficiency of the oxygen evolution reaction of the anode.

[0088] The first cation exchange binder may include a fluorinated solid electrolyte and/or a hydrocarbon solid electrolyte.

[0089] The fluorinated solid electrolyte may contain a per-fluorinated sulfonic acid (PFSA) compound. The PFSA compound has advantages such as high proton conductivity, excellent mechanical properties, chemical resistance, durability and handling properties, and extensive mass production. The PFSA-based compound is broadly classified into Nafion^™ having a long side chain, Dynyon^™ having a medium side chain, and Aquivion^™ having a short side chain, depending on the side chain structure thereof. In addition, the PFSA-based compound may include sulfonic acid, carboxylic acid or the like as a functional group at the end of the side chain.

[0090] The equivalent weight (EW) of the functional group of the PFSA compound may be about 600 g/mol to 1,100 g/mol, or about 700 g/mol to 950 g/mol. When the equivalent weight of the functional group is less than 600 g/mol, the anode 120 may be excessively swollen in water and mechanical properties may be lowered due to excessively high content of the functional group. On the other hand, when the equivalent weight of the functional group is higher than 1,100 g/mol, the ion exchange capacity of the anode 120 may deteriorate due to excessively low content of the functional group.

[0091] Compared to fluorinated solid electrolytes, hydrocarbon solid electrolytes may be based on compounds that are easier to polymerize or copolymerize various molecular structures. The hydrocarbon solid electrolyte includes sulfonated polyethylene, sulfonated polypropylene, sulfonated polystyrene, sulfonated polysulfone, sulfonated polybenzimidazole, sulfonated poly(phenylene oxide), sulfonated poly(phenylene ether), sulfonated poly(arylene ether ketone), sulfonated polyether ether ketone, sulfonated poly(ether ketone), sulfonated polyimide, sulfonated poly(ether imide), sulfonated poly(styrene-b-ethylene-r-butadiene-b-styrene) triblock copolymer or the like which contains a sulfonic acid group.

[0092] The first cation exchange binder may be the same as or different from the cation exchange solid electrolyte contained in the solid electrolyte layer 110 and is preferably the same as the cation exchange solid electrolyte.

[0093] The anode antioxidant is contained in the first cation exchange binder to alleviate or suppress chemical degradation of the anode 120 and may include a primary antioxidant and/or a secondary antioxidant.

[0094] When a fluorinated solid electrolyte is used as the first cation exchange binder, the anode antioxidant may be a cerium antioxidant, which is a primary antioxidant. The cerium antioxidant may include cerium oxide (or ceria: CeO_x), modified cerium oxide, or cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O), or the like. The modified cerium oxide may include cerium-zirconium oxide (CeZrO_x), cerium-manganese oxide (CeMnO_x), gadolinium (Gd)- or samarium (Sm)-doped cerium oxide) or the like.

[0095] The cerium antioxidant may be introduced in the form of a particle or powder (nanoparticle or nanopowder) having a crystallite size of several nm or tens of nm. However, cerium oxide and modified cerium oxide should be dispersed well in advance before addition to the fluorinated solid electrolyte because they are generally stored in an agglomerate state after production. In order to improve the degree of dispersion and/or distribution, a surfactant may be introduced along with the cerium antioxidant, which may reduce the activity of the cerium antioxidant. Therefore, in order to increase the dispersibility and activity of the cerium antioxidant, the cerium antioxidant may be introduced in the form of being supported on a support. The support may include titanium dioxide (TiO₂), silicon dioxide (silica, SiO₂), carbon powder, carbon nanotubes (CNTs) or the like. The content of the cerium antioxidant supported on the support may be about 2% to 70% by weight, or about 10% to 50% by weight, based on the total weight of the support and the cerium antioxidant. When the content of the cerium antioxidant is less than 2% by weight, the antioxidant performance thereof may be deteriorated due to the excessively high content of the support compared to the cerium antioxidant. On the other hand, when the content exceeds 70% by weight, the cerium antioxidant is distributed excessively densely on the support, thus making efficient support and use of the cerium antioxidant difficult.

[0096] The content of the cerium antioxidant based on the total weight of the first cation exchange binder and the antioxidant in the anode 120 may be about 200 ppm to 50,000 ppm, or about 1,000 ppm to 10,000 ppm. When the content of the cerium antioxidant is less than 200 ppm, antioxidant performances are greatly reduced, whereas when the content exceeds 50,000 ppm, it is difficult to uniformly disperse the cerium antioxidant in the anode 120, ionic conductivity and other physical properties of the anode 120 decrease, and costs may also increase.

[0097] Among the cerium antioxidants, cerium oxide and modified cerium oxide may have a crystallite size measured by X-ray of about 2 nm to 100 nm, or about 10 nm to 50 nm. When the crystallite size is less than 2 nm, the cerium antioxidant particles may agglomerate during cell operation, the activity over time and the long-term durability of the cerium antioxidant may be reduced. On the other hand, when the crystallite size exceeds 100 nm, the initial activity of the cerium antioxidant may be excessively low.

[0098] When the fluorinated solid electrolyte is used as the first cation exchange binder, the anode antioxidant may be, as a secondary antioxidant, a manganese antioxidant such as manganese oxide, a non-manganese transition metal antioxidant such as platinum (Pt), gold (Au), or palladium (Pd), or a combination thereof.

[0099] To increase the dispersibility and activity of the secondary antioxidant, the secondary antioxidant may be supported on the support. The support is as described above. Here, the content of the secondary antioxidant supported on the support and the content of the secondary antioxidant based on the total weight of the first cation exchange binder and the antioxidant in the anode 120 are as described with reference to the cerium antioxidant.

[0100] When a hydrocarbon solid electrolyte is used as the first cation exchange binder, the anode antioxidant may be, as the primary antioxidant, a sterically-hindered phenolic antioxidant. Specifically, the sterically-hindered phenolic antioxidant may include Irganox 1010^™ containing pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 1076^™ containing octadecyl-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 245^™ containing ethylene bis(oxyethylene) bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate) or the like.

[0101] The content of the sterically-hindered phenolic antioxidant based on the total weight of the first cation exchange binder and the antioxidant in the anode 120 may be about 200 ppm to 50,000 ppm, or about 1,000 to 10,000 ppm. When the content of the sterically-hindered phenolic antioxidant is less than 200 ppm, antioxidant performances are greatly reduced, whereas when the content of sterically-hindered phenolic antioxidant exceeds 50,000 ppm, it is difficult to uniformly disperse the phenolic antioxidant, and the ionic conductivity and overall physical properties of the anode 120 are reduced and costs may also rise.

[0102] When a hydrocarbon solid electrolyte is used as the first cation exchange binder, the anode antioxidant may be a phosphite antioxidant as the secondary antioxidant. The phosphite antioxidant may include Irgafos 168^™ containing tris(2,4-ditert-butylphenyl) phosphite. Here, the content of the phosphite antioxidant based on the total weight of the fist cation exchange binder and the antioxidant in the anode 120 is the same as those with reference to the phenolic antioxidant.

[0103] The content of the first cation exchange binder may be about 10% to 70% by weight, or about 20% to 50% by weight, based on the total weight of the anode 120. When the content of the first cation exchange binder is less than 10% by weight, binding of the anode catalysts is insufficient, the anode 120 is delaminated and the performance to efficiently transport the cations generated in the anode 120 to the solid electrolyte layer 110 may be deteriorated. On the other hand, when the content exceeds 70% by weight, the electrical resistance within the anode 120 increases, the pores become excessively small and thus the mass transport resistance within the anode 120 may increase.

[0104] The thickness of the anode 120 may be about 1 µm to 30 µm, or about 2 µm to 20 µm. When the thickness of the anode 120 is less than 1 µm, it may be difficult to uniformly apply the anode 120 on the solid electrolyte layer 110 due to the excessively small thickness thereof, whereas when the anode 120 exceeds 30 µm, cell resistance may increase and performance may deteriorate due to the excessively great thickness thereof.

[0105] The cathode 130 may use carbon dioxide as a reactant and induce at least one reduction reaction of carbon dioxide as depicted in Reaction Schemes 2 to 7 below, thus yielding a product.

        [Reaction Scheme 2]     CO₂ + 2H⁺ + 2e^- → CO(g) + H₂O

        [Reaction Scheme 3]     CO₂ + 2H⁺ + 2e^- → HCOOH(l)

        [Reaction Scheme 4]     CO₂ + 6H⁺+ 6e^- → CH₃OH(l) + H₂O

        [Reaction Scheme 5]     2CO₂ + 12H⁺ + 12e^- → C₂H₄(g) + 4H₂O

        [Reaction Scheme 6]     2CO₂ + 12H⁺ + 12e^- → C₂H₅OH(l) + 3H₂O

        [Reaction Scheme 7]     3CO₂ + 18H⁺ + 18e^- → C₃H₇OH(l) + 5H₂O

[0106] However, the reduction reaction of carbon dioxide is not limited to Reaction Schemes 2 to 7 above and other reactions may occur depending on the type of cathode catalyst, operating conditions, and the like.

[0107] The carbon dioxide may be humidified carbon dioxide with a relative humidity of about 10% to 90%, or about 30% to 70%. When the relative humidity of carbon dioxide is less than 10%, dehydration of the electrode-solid electrolyte assembly 100 may be severe, resulting in increased ohmic resistance and decreased cell performance. On the other hand, when the relative humidity of the carbon dioxide exceeds 90%, the water vapor is condensed into liquid water due to easy oversaturation and thus the water blocks the pores of the cathode 130 and the pores of the cathode porous transport layer 300, thus causing water flooding.

[0108] The cathode 130 may contain a cathode catalyst, a second cation exchange binder, a cathode antioxidant, or the like.

[0109] The cathode catalyst may include at least one selected from the group consisting of copper (Cu), cadmium (Cd), indium (In), tin (Sn), mercury (Hg), thallium (Tl), lead (Pb), bismuth (Bi), metal organic frameworks (MOFs), and combinations thereof.

[0110] The type of the cathode catalyst may vary depending on the type of product obtained by the reduction reaction of carbon dioxide.

[0111] When the desired product is carbon monoxide, the cathode catalyst may include a catalyst based on gold (Au), silver (Ag), or zinc (Zn).

[0112] When the desired product is ethylene (C₂H₄), a multi-carbon (C₂₊) gas, the cathode catalyst may include a copper (Cu)-based catalyst.

[0113] When the desired product is formic acid (HCOOH) or formate, the cathode catalyst may include a catalyst based on cadmium (Cd), indium (In), tin (Sn), mercury (Hg), thallium (Tl), lead (Pb), bismuth (Bi), or metal organic framework (MOF).

[0114] The indium-based catalyst may contain indium oxide. The tin-based catalyst may be tin (Sn), tin oxide (SnO_x), a tin alloy, a mixture thereof, or an alloy thereof. The bismuth-based catalyst may be bismuth nanoflakes, bismuth nanowires, bismuth nanosheets, bismuth nanoparticles fixed in nitrogen-doped porous carbon, a mixture thereof, or an alloy thereof.

[0115] When the desired product is an alcohol such as methanol (CH₃OH), ethanol (C₂H₅OH), or propanol (C₃H₇OH), the cathode catalyst may include a copper (Cu)-based catalyst.

[0116] The loading of the cathode catalyst may be about 5.0 mg/cm² or less, or about 2.0 mg/cm² or less. When the loading of the cathode catalyst exceeds 5.0 mg/cm², the cost greatly increases, the process of producing the uniform cathode from the cathode catalyst ink is difficult, and uniform dispersion of the cathode catalyst within the cathode is difficult.

[0117] In order to increase the dispersibility of the cathode catalyst, the cathode catalyst may be supported on a support. The support ratio of the cathode catalyst may be about 10% by weight to 70% by weight, or about 20% by weight to 50% by weight, based on the total content of the cathode catalyst and the support. When the support ratio is less than 10% by weight, the support effect may be insufficient, whereas when the support ratio exceeds 70% by weight, the cathode catalyst may be distributed excessively densely on the support, which may reduce the efficiency of the reduction reaction of carbon dioxide.

[0118] The second cation exchange binder may include a fluorinated solid electrolyte and/or a hydrocarbon solid electrolyte.

[0119] The fluorinated solid electrolyte may contain a per-fluorinated sulfonic acid (PFSA) compound. The PFSA compound has advantages such as high proton conductivity, excellent mechanical properties, chemical resistance, durability and handling properties, and extensive mass production. The PFSA-based compound is broadly classified into Nafion^™ having a long side chain, Dynyon^™ having a medium side chain, and Aquivion^™ having a short side chain, depending on the side chain structure thereof. In addition, the PFSA-based compound may include sulfonic acid, carboxylic acid or the like as a functional group at the end of the side chain.

[0120] The equivalent weight (EW) of the functional group of the PFSA compound may be about 600 g/mol to 1,100 g/mol, or about 700 g/mol to 950 g/mol. When the equivalent weight of the functional group is less than 600 g/mol, the cathode 130 may be excessively swollen in water and mechanical properties may be lowered due to excessively high content of the functional group. On the other hand, when the equivalent weight of the functional group is higher than 1,100 g/mol, the ion exchange capacity of the cathode 130 may deteriorate due to excessively low content of the functional group.

[0121] Compared to fluorinated solid electrolytes, hydrocarbon solid electrolytes may be based on compounds that are easier to polymerize or copolymerize various molecular structures. The hydrocarbon solid electrolyte includes sulfonated polyethylene, sulfonated polypropylene, sulfonated polystyrene, sulfonated polysulfone, sulfonated polybenzimidazole, sulfonated poly(phenylene oxide), sulfonated poly(phenylene ether), sulfonated poly(arylene ether ketone), sulfonated polyether ether ketone, sulfonated poly(ether ketone), sulfonated polyimide, sulfonated poly(ether imide), sulfonated poly(styrene-b-ethylene-r-butadiene-b-styrene) triblock copolymer or the like which contains a sulfonic acid group.

[0122] The second cation exchange binder may be the same as or different from the cation exchange solid electrolyte contained in the solid electrolyte layer 110 and the first cation exchange binder contained in the anode 120 and is preferably the same as the cation exchange solid electrolyte and the first cation exchange binder.

[0123] The cathode 130 may further contain an anion exchange binder. The main products of the carbon dioxide reduction reaction that occurs at the cathode 130 are carbon monoxide (CO), ethylene (C₂H₄), propylene (C₃H₆), formic acid (HCOOH)/formate, methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH), and the like and most of the by-products are hydrogen (H₂). The hydrogen may be used as a high value-added feedstock in conventional petroleum refining, fertilizer, metal production and food industries and thus the utilization value thereof may be high depending on market conditions only when it can be separated and stored efficiently after the carbon dioxide reduction reaction. In order to efficiently store the hydrogen, a high-pressure hydrogen gas storage system that can withstand a pressure in the range of about 1 MPa to 7 MPa (or 10 bar to 70 bar) should be provided outside the electrochemical cell 10.

[0124] The anion exchange binder includes polystyrene tetramethyl imidazolium chloride containing polystyrene (PS) as a main chain and an imidazolium group, a benzimidazolium-based binder represented by Formula 3 below, a poly(aryl piperidinium)-based binder represented by Formula 4 below, or the like. Alternatively, the anion exchange binder may include commercially available Sustainion^™, Aemion^™, PiperION^™, and the like.

wherein n may be 10 to 1,000.

wherein x may be 10 to 1,000 and y may be 10 to 1,000.

[0125] Meanwhile, the operating conditions of the electrochemical cell 10 for conversion of carbon dioxide may greatly affect the selectivity of the product. An acidic atmosphere with low pH promotes the production of formic acid and hydrogen, while an alkaline atmosphere with a high pH promotes the production of formate while inhibiting the production of hydrogen. Therefore, when an acidic atmosphere is desired, the second cation exchange binder may be used singly or the content of the second cation exchange binder in the blend of the second cation exchange binder and the anion exchange binder may be increased. On the other hand, when an alkaline atmosphere is desired, the content of the anion exchange binder in the blend of the second cation exchange binder and the anion exchange binder may be increased. The blending ratio of the second cation exchange binder and the anion exchange binder is not specifically limited and the second cation exchange binder and the anion exchange binder may be mixed at a ratio of, for example, about 95:5 to 50:50, or about 90:10 to 75:25. When the ratio of the anion exchange binder is less than 5, the blending effect is insufficient and blending the two materials is meaningless, whereas when the ratio of the anion exchange binder exceeds 50, phase separation between the two materials becomes severe, making it difficult to obtain a homogeneous mixture.

[0126] The cathode antioxidant is contained in the second cation exchange binder to alleviate or suppress chemical degradation of the cathode 130 and may include a primary antioxidant and/or a secondary antioxidant.

[0127] When a fluorinated solid electrolyte is used as the second cation exchange binder, the cathode antioxidant may be a cerium antioxidant, which is a primary antioxidant. The cerium antioxidant may include cerium oxide (or ceria: CeO_x), modified cerium oxide, cerium (III) nitrate hexahydrate: Ce(NO₃)₃·6H₂O), or the like. The modified cerium oxide may include cerium-zirconium oxide (CeZrO_x), cerium-manganese oxide (CeMnO_x), gadolinium (Gd)- or samarium (Sm)-doped cerium oxide or the like.

[0128] The cerium antioxidant may be introduced in the form of a particle or powder (nanoparticle or nanopowder) having a crystallite size of several nm or tens of nm. However, cerium oxide and modified cerium oxide should be dispersed well in advance before addition to the fluorinated solid electrolyte because they are generally stored in an agglomerate state after production. In order to improve the degree of dispersion and/or distribution, a surfactant may be introduced along with the cerium antioxidant, which may reduce the activity of the cerium antioxidant. Therefore, in order to increase the dispersibility and activity of the cerium antioxidant, the cerium antioxidant may be introduced in the form of being supported on a support. The support may include titanium dioxide (TiO₂), silicon dioxide (silica, SiO₂), carbon powder, carbon nanotubes (CNTs) or the like. The content of the cerium antioxidant supported on the support may be about 2% to 70% by weight, or about 10% to 50% by weight, based on the total weight of the support and the cerium antioxidant. When the content of the cerium antioxidant is less than 2% by weight, the antioxidant performance may be deteriorated due to the excessively high content of the support compared to the cerium antioxidant. On the other hand, when the content exceeds 70% by weight, the cerium antioxidant is distributed excessively densely on the support, thus making efficient support and use of the cerium antioxidant difficult.

[0129] The content of the cerium antioxidant based on the total weight of the second cation exchange binder and the antioxidant in the cathode 130 may be about 200 ppm to 50,000 ppm, or about 1,000 ppm to 10,000 ppm. When the content of the cerium antioxidant is less than 200 ppm, antioxidant performances are greatly reduced, whereas when the content exceeds 50,000 ppm, it is difficult to uniformly disperse the cerium antioxidant in the cathode 130, ionic conductivity and other physical properties of the cathode 130 decrease, and costs may also increase.

[0130] Among the cerium antioxidants, cerium oxide and modified cerium oxide may have a crystallite size measured by X-ray of about 2 nm to 100 nm, or about 10 nm to 50 nm. When the crystallite size is less than 2 nm, the cerium antioxidant particles may agglomerate during cell operation, and the activity over time and long-term durability of the cerium antioxidant may be reduced. On the other hand, when the crystallite size exceeds 100 nm, the initial activity of the cerium antioxidant may be excessively low.

[0131] When the fluorinated solid electrolyte is used as the second cation exchange binder, the cathode antioxidant may be, as a secondary antioxidant, a manganese antioxidant such as manganese oxide, a non-manganese transition metal antioxidant such as platinum (Pt), gold (Au), or palladium (Pd), or a combination thereof.

[0132] To increase the dispersibility and activity of the secondary antioxidant, the secondary antioxidant may be supported on the support. The support is as described above. Here, the content of the secondary antioxidant supported on the support and the content of the secondary antioxidant based on the total weight of the second cation exchange binder and the antioxidant in the cathode 130 are as described with reference to the cerium antioxidant.

[0133] When a hydrocarbon solid electrolyte is used as the second cation exchange binder, the cathode antioxidant may be, as the primary antioxidant, a sterically-hindered phenolic antioxidant. Specifically, the sterically-hindered phenolic antioxidant may include Irganox 1010^™ containing pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 1076^™ containing octadecyl-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 245^™ containing ethylene bis(oxyethylene) bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate) or the like.

[0134] The content of the sterically-hindered phenolic antioxidant based on the total weight of the second cation exchange binder and the antioxidant in the cathode 130 may be about 200 ppm to 50,000 ppm, or about 1,000 to 10,000 ppm. When the content of the sterically-hindered phenolic antioxidant is less than 200 ppm, antioxidant performances are greatly reduced, whereas when the content of sterically-hindered phenolic antioxidant exceeds 50,000 ppm, it is difficult to uniformly disperse the phenolic antioxidant, the ionic conductivity and overall physical properties of the cathode 130 are reduced, and costs may also rise.

[0135] When a hydrocarbon solid electrolyte is used as the second cation exchange binder, the cathode antioxidant may be a phosphite antioxidant as the secondary antioxidant. The phosphite antioxidant may include Irgafos 168^™ containing tris(2,4-ditert-butylphenyl) phosphite. Here, the content of the phosphite antioxidant based on the total weight of the second cation exchange binder and the antioxidant in the cathode 130 is as described with reference to the phenolic antioxidant.

[0136] The content of the second cation exchange binder may be about 10% to 70% by weight, or about 20% to 50% by weight, based on the total weight of the cathode 130. When the content of the second cation exchange binder is less than 10% by weight, binding the cathode catalysts is insufficient, the cathode 130 is delaminated, and the performance to efficiently transport the cations received from the solid electrolyte layer 110 to the cathode catalysts may be deteriorated. On the other hand, when the content exceeds 70% by weight, the electrical resistance within the cathode 130 increases, the pores become excessively small and thus the mass transport resistance within the cathode 130 may increase.

[0137] The thickness of the cathode 130 may be about 2 µm to 50 µm, or about 3 µm to 30 µm. When the thickness of the cathode 130 is less than 2 µm, it may be difficult to uniformly apply the cathode 130 onto the solid electrolyte layer 110 due to the excessively small thickness thereof, whereas when the thickness of the cathode 130 exceeds 50 µm, cell resistance may increase and performance may deteriorate due to the excessively great thickness thereof.

[0138] The method of manufacturing the electrode-solid electrolyte assembly 100 is not specifically limited. For example, the electrode-solid electrolyte assembly 100 may be produced using a decal transfer method, a direct coating method, a spraying method, or the like. In terms of mass production and quality stability, it may be preferable to manufacture the electrode-solid electrolyte assembly 100 using a decal transfer method.

[0139] Hereinafter, the decal transfer method will be described in brief. An electrode slurry or catalyst ink containing a catalyst, a catalyst support, a binder, a mixed solvent such as water and/or alcohol, or the like is applied onto a decal transfer film and dried at less than about 90°C. High temperature annealing is performed at about 90°C to 240°C, or about 100°C to 130°C to stabilize the structure of the dried electrode on the decal transfer film and increase hydrophobicity. When the heat treatment temperature is less than 90°C, the effect of the heat treatment may be insufficient, and when the heat treatment temperature exceeds 240°C, the binder in the electrode may undergo thermal degradation. After completing the high-temperature heat treatment, the electrode is pressed on the solid electrolyte layer 110 at about 110°C to 240°C, or about 130°C to 180°C using a hot-pressing method to transfer the anode 120 and/or the cathode 130 onto the solid electrolyte layer 110. When high-temperature pressing is performed at a temperature below 110°C, decal transfer may not be sufficient, and when high-temperature pressing is performed at a temperature above 240°C, the solid electrolyte layer 110 and the binder in the electrode may undergo thermal degradation.

[0140] The electrochemical cell 10 for conversion of carbon dioxide according to the present disclosure may include an anode porous transport layer 200 and a cathode porous transport layer 300 as independent elements.

[0141] As shown in FIG. 4, the anode porous transport layer 200 and the cathode porous transport layer 300 come into physical contact with the outer surfaces of the anode 120 and the cathode 130, respectively. The anode porous transport layer 200 supplies deionized water, which is an anode reactant, to the anode 120, and delivers and discharges both unreacted deionized water and a byproduct oxygen at anode 120 to the outside of the cell. The cathode porous transport layer 300 supplies humidified carbon dioxide, which is a cathode reactant, to the cathode 130, and transfers and discharges both unreacted carbon dioxide and the product of the cathode 130 to the outside of the cell.

[0142] The anode porous transport layer 200 and the cathode porous transport layer 300 have different required structures and characteristics depending on the operating conditions of each electrode. The anode porous transport layer 200 is made of an incompressible metal material due to the high potential operating conditions of the anode 120, whereas the cathode porous transport layer 300 is made of a compressible carbon material due to the relatively low potential operating conditions of the cathode 130.

[0143] FIG. 11A shows an embodiment of the anode porous transport layer 200 according to the present disclosure. Here, deionized water may be used as an anode reactant and an anode porous transport layer 200 made of titanium (Ti), or the like, which has excellent corrosion resistance, may be used because it can be operated at a high potential of 2V or more.

[0144] The anode porous transport layer 200 may include an anode macroporous substrate 210 including pores with a diameter of about 1 µm to 300 µm. The diameter may be measured using a mercury intrusion porosimetry method. When the pore size of the anode macroporous substrate 210 is less than 1 µm, it may be difficult to obtain performance of macropores, whereas when the pore size exceeds 300 µm, it may be difficult for the anode macroporous substrate 210 to serve as a support.

[0145] The anode macroporous substrate 210 may include at least one selected from the group consisting of titanium fiber felt, titanium fiber paper, titanium fiber cloth, titanium mesh, titanium foil, and combinations thereof.

[0146] In order to impart higher corrosion resistance to the anode macroporous substrate 210, a corrosion-resistant coating layer 230 may be formed on at least one surface of the anode macroporous substrate 210 as shown in FIGs. 11B to 11D. The corrosion-resistant coating layer 230 may be formed by coating the anode macroporous substrate 210 with at least one of titanium (Ti), iridium (Ir), platinum (Pt), and gold (Au) using sputtering or the like.

[0147] FIG. 11E shows another embodiment of the anode porous transport layer 200 according to the present disclosure. In order to lower the contact resistance between the anode porous transport layer 200 and the anode 120, and to facilitate mass transport of deionized water and oxygen, the anode microporous layer 220 is introduced on the anode macroporous substrate 210. The anode porous transport layer 200 may be laminated on the anode 120 such that the anode microporous layer 220 faces the anode 120.

[0148] The anode microporous layer 220 may include pores with a diameter of less than about 0.2 µm. The diameter may be measured using mercury intrusion porosimetry. When the pore size of the anode microporous layer 220 is 0.2 µm or more, it may be difficult to uniformly deliver deionized water to the anode 120.

[0149] The anode microporous layer 220 may include at least one selected from the group consisting of titanium (Ti), iridium (Ir), platinum (Pt), gold (Au), and combinations thereof.

[0150] The thickness of the anode microporous layer 220 may be about 5 µm to 200 µm, or about 10 µm to 50 µm. When the thickness is less than 5 µm, mass transport performances may be reduced and the effect of reducing contact resistance may be insufficient. On the other hand, when the thickness exceeds 200 µm, the mass transport path may become excessively long.

[0151] Meanwhile, as shown in FIGs. 11F to 11H, the corrosion-resistant coating layer 230 may be formed on at least one surface of the anode porous transport layer 200.

[0152] The thickness of the anode porous transport layer 200 may be about 50 µm to 1,000 µm, or about 100 µm to 600 µm. When the thickness is less than 50 µm, mechanical stiffness may decrease and the anode porous transport layer 200 may be damaged when the cell is operated for a long time. On the other hand, when the thickness exceeds 1,000 µm, the mass transport path may become excessively long.

[0153] The thickness of the corrosion-resistant coating layer 230 may be about 10 nm to 400 nm, or about 30 nm to 200 nm. When the thickness is less than 10 nm, the corrosion resistance effect may be insufficient, whereas when the thickness exceeds 400 nm, the ohmic resistance of the cell may increase and manufacturing costs may increase.

[0154] The porosity of the anode porous transport layer 200 may be about 20% to 90%, or about 40% to 70%. When the porosity is less than 20%, the mass transport performance of the anode porous transport layer 200 may be greatly reduced, whereas when the porosity exceeds 90%, the mechanical rigidity of the anode porous transport layer 200 may be excessively low and the anode porous transport layer 200 may be damaged when the cell is operated for a long time.

[0155] FIG. 12 shows the cathode porous transport layer 300 according to the present disclosure.

[0156] Considering the characteristic that the reduction reaction of the cathode 130 occurs at a low operation voltage of 0.4 V or less, and the electrical conductivity, cost, and material supply and demand of the cathode porous transport layer 300, the cathode porous transport layer 300 is preferably a compressible carbon material rather than a metal material, unlike the anode porous transport layer 200.

[0157] Since the cathode porous transport layer 300 greatly affects the mass transport performances of the cathode 130, it greatly affects the high current density operation associated with cell productivity and the selectivity of the type of product of the carbon dioxide reduction reaction. In addition, since the cathode porous transport layer 300 greatly affects the occurrence of problems such as salt precipitation depending on the mass transport performances, it may greatly affect the performance, durability and operational stability of the electrochemical cell 10. Compared to conventional saline electrolysis cells, chlor-alkali cells, fuel cells, and water electrolysis cells, the electrochemical cell 10 according to the present disclosure has remarkably different reaction conditions and operating conditions, and the cathode 130 has several differences including the presence of humidified carbon dioxide. Therefore, the present disclosure is characterized by optimizing and designing the structure of the cathode porous transport layer 300 to suit the unique characteristics.

[0158] The cathode porous transport layer 300 may include a cathode macroporous substrate 310 including pores having a diameter of about 1 µm to 300 µm and a microporous layer 320 disposed on the cathode macroporous substrate 310 and including pores having a diameter of less than about 0.2 µm. The cathode porous transport layer 300 may be laminated on the cathode 130 such that the cathode microporous layer 320 faces the cathode 130. By interposing the cathode microporous layer 320 between the cathode macroporous substrate 310 and the cathode 130, the problem in which the carbon fibers of the cathode macroporous substrate 310 puncture the cathode 130 and the solid electrolyte layer 110 can be solved and humidified carbon dioxide and products can be delivered more efficiently.

[0159] When the pore size of the cathode macroporous substrate 310 is less than 1 µm, it may be difficult to obtain performance of macropores, whereas when the pore size of the cathode macroporous substrate 310 exceeds 300 µm, it may be difficult for the cathode macroporous substrate 310 to serve as a support. When the pore size of the cathode microporous layer 320 is 0.2 µm or more, humidified carbon dioxide may not be uniformly delivered to the cathode 130. The pore size may be measured using a mercury intrusion porosimetry method.

[0160] The cathode macroporous substrate 310 may include at least one selected from the group consisting of carbon fiber felt, carbon fiber paper, carbon fiber cloth, and combinations thereof. In addition, the cathode macroporous substrate 310 may further contain a hydrophobic agent.

[0161] The cathode microporous layer 320 may include at least one selected from the group consisting of carbon blacks such as acetylene black carbon, black pearl carbon, Ketjen black carbon, Vulcan XC-72 carbon, graphene nanoplatelet, carbon nano-tube, carbon nano-fiber, and combinations thereof. In addition, the cathode microporous layer 320 may further contain a hydrophobic agent.

[0162] The hydrophobic agent may function to impart hydrophobicity or water repellency.

[0163] The hydrophobic agent may be a fluorinated homopolymer such as poly(tetrafluoroethylene) (PTFE), a fluorinated copolymer such as FKM/FFKM, a fluorinated ethylene-propylene copolymer (FEP) or a combination thereof.

[0164] The content of the hydrophobic agent in the cathode macroporous substrate 310 may be about 2% to 50% by weight, or about 5% to 30% by weight. When the content of the hydrophobic agent in the cathode macroporous substrate 310 is less than 2% by weight, hydrophobicity may be insufficient, whereas when the content exceeds 50% by weight, electrical resistance may greatly increase, porosity may decrease and thus cell performance may deteriorate. In addition, in order to further increase the hydrophobicity of the cathode macroporous substrate 310, the cathode macroporous substrate 310 may be plasma-modified to increase surface roughness.

[0165] The content of the hydrophobic agent in the cathode microporous layer 320 may be 10% by weight to 60% by weight, or 15% by weight to 40% by weight. When the content of the hydrophobic agent in the cathode microporous layer 320 is less than 10% by weight, hydrophobicity may be insufficient, whereas when the content exceeds 60% by weight, electrical resistance may greatly increase, porosity may decrease, and thus cell performance may deteriorate. In addition, in order to further increase the hydrophobicity of the cathode microporous layer 320, the cathode microporous layer 320 may be plasma-modified to increase surface roughness.

[0166] Considering the efficient discharge of water from the electrochemical cell 10, the content of the hydrophobic agent in the cathode microporous layer 320 facing the cathode 130 is higher than and more preferably at least two-fold higher than that of the hydrophobic agent in the cathode macroporous substrate 310.

[0167] The total thickness of the cathode porous transport layer 300 may be about 50 µm to 1,000 µm, or about 100 µm to 600 µm. When the thickness is less than 50 µm, mechanical rigidity may be excessively low, whereas when the thickness exceeds 1,000 µm, the mass transport path may be excessively long.

[0168] The porosity of the cathode porous transport layer 300 may be about 50% to 95%, or about 60% to 85%. When the porosity is less than 50%, the mass transport performance of the cathode porous transport layer 300 is greatly reduced, whereas when the porosity exceeds 95%, the cathode porous transport layer 300 may be damaged when the cell including the same is operated for a long time due to excessively low mechanical rigidity of the cathode porous transport layer 300.

[0169] The cathode porous transport layer 300 is compressible when pressure is applied thereto and the degree of compressibility is calculated as follows:

wherein ti is the thickness of the cathode porous transport layer 300 measured when a compression pressure of 50 kPa is applied thereto, and t₂ is the thickness of the cathode porous transport layer 300 measured when a compression pressure of 1 MPa is applied thereto. The degree of compressibility of the cathode porous transport layer 300 may be about 2% to 50%, or about 5% to 35%. When the degree of compressibility is less than 2%, the cathode porous transport layer 300 exhibits substantially incompressible behavior and becomes excessively stiff, and thus handling property is reduced when the cell is assembled by compression, whereas when the degree of compressibility exceeds 50%, the cathode porous transport layer 300 is excessively flexible (soft), thus worsening the problems in which the long-term durability of the cathode porous transport layer 300 decreases when the cell is assembled by compression, and the cathode porous transport layer 300 may intrude into the flow channel of the cathode bipolar plate 600.

[0170] The electrical resistance of the cathode porous transport layer 300 may be about 20 mΩ·cm² or less, or about 10 mΩ·cm² or less when a compression pressure of 1 MPa is applied thereto. This is because when the electrical resistance exceeds 20 mΩ·cm², the performance loss of the cell may greatly increase.

[0171] When the product of the cathode 130 is a low-pressure gas of less than 1 MPa (10 bar) or liquid, the cathode porous transport layer 300 is preferably a rolled product that is highly suitable for mass production and has excellent handling properties. When the product is high pressure gas higher than 1 MPa (10 bar), the cathode porous transport layer 300 may be a rolled or a sheet product.

[0172] When the bending stiffness of the cathode porous transport layer 300 is insufficient, the cathode porous transport layer 300 may be damaged when the cell including the same is operated for a long time. Therefore, the cathode porous transport layer 300 needs to exhibit sufficiently high bending stiffness.

[0173] The bending stiffness of the cathode porous transport layer 300 may be quantified by measuring Taber bending stiffness (TBS) or 3-point flexural modulus. For example, the Taber bending stiffness measured using a Taber bending stiffness tester of the cathode porous transport layer 300 may be about 2 g_f·cm or more, and more preferably about 4 g_f·cm or more.

[0174] The cathode macroporous substrate 310 may include carbon fibers and thus in-plane mechanical rigidity thereof may be anisotropic depending on manufacturing method thereof. In particular, in the rolled product, the mechanical rigidity in the machine direction (MD), which is a rolling direction in which the cathode porous transport layer 300 is wound on the roll, is typically greater than the mechanical rigidity of the cross-machine direction or transverse direction (CMD or TD). The degree of anisotropy of Taber bending stiffness indicating the difference between the bending stiffness in the high bending stiffness direction (HBSD) and the bending stiffness in the low bending stiffness direction (LBSD) of the cathode porous transport layer 300 is calculated as follows:

The degree of anisotropy of Taber bending stiffness = [(TBS₁ - TBS₂)/TBS₁] × 100 [%]

wherein TBS₁ is the Taber bending stiffness of the cathode porous transport layer 300 in the high bending stiffness direction, and TBS₂ is the Taber bending stiffness of the cathode porous transport layer 300 in the low bending stiffness direction.

[0175] When the degree of anisotropy of bending stiffness of the cathode porous transport layer 300 is 30% or more, the direction of one cathode flow channel which has the largest total length (major flow channel) among the cathode flow channels 630 and the high bending stiffness direction of the cathode porous transport layer 300 are arranged in a non-parallel mode, for example, perpendicular to each other at 90° in order to inhibit the problem in which the cathode porous transport layer 300 intrudes into the cathode flow channel 630 of the cathode bipolar plate 600, as shown in FIG. 13. When the degree of anisotropy of bending stiffness of the cathode porous transport layer 300 is less than 30%, the effect of inhibiting the intrusion problem by the structure in which the high bending rigidity direction of the cathode porous transport layer 300 and the major flow channel direction of the cathode flow channel 630 are arranged so as not to be parallel to each other may be insufficient. In FIG. 13, the direction of one cathode flow channel having a smaller total length than the direction of another cathode flow channel which has the largest total length (major flow channel) among the cathode flow channels 630 is shown as a minor flow channel direction.

[0176] The cathode porous transport layer 300 has high water repellency or hydrophobicity and thus has high mass transport performances. The cathode porous transport layer 300 has a large contact angle (CA) of water droplets on the surface thereof, a small sliding angle (SA), and a small contact angle hysteresis (CAH) measured by sessile droplet test. The contact angle hysteresis is calculated as follows.

Contact Angle Hysteresis = Advancing Contact Angle (ACA) - Receding Contact Angle (RCA)

[0177] The contact angle of the cathode macroporous substrate 310 is about 120° or more, more preferably about 130° or more, the sliding angle is about 60° or less, more preferably about 30° or less and the contact angle hysteresis is about 30° or less, more preferably about 20° or less.

[0178] The thickness of the cathode microporous layer 320 may be about 5 µm to 250 µm, or about 10 µm to 70 µm. When the thickness is less than 5 µm, the effects of increasing mass transport and reducing contact resistance are insufficient, whereas when the thickness exceeds 250 µm, the mass transport path may become longer.

[0179] The contact angle of the cathode microporous layer 320 is about 130° or more, more preferably about 140° or more, the slip angle is about 50° or less, more preferably about 25° or less, and the contact angle hysteresis is about 25° or less, more preferably about 15° or less.

[0180] In order to increase water repellency based on increased capillary force, the cathode microporous layer 320 may have a gradient of pore size such that the part of the cathode microporous layer 320 in contact with the cathode has the smallest pore size and the pore size gradually increases towards the part of the cathode microporous layer 320 in contact with the macroporous substrate.

[0181] Depending on the operating conditions of the cell and the water content inside the cell, cracks present on one surface of the cathode 130 of the cathode microporous layer 320 may affect cell performance and durability. When the solid electrolyte layer 110 is wet due to deionized water used as the anode reactant and humidified carbon dioxide gas used as the cathode reactant, as the reduction reaction of carbon dioxide proceeds at the cathode 130 for a long period of time, residual water increases in the cathode 130, thus causing the problem of flooding. When macro-cracks with a predetermined size or more exist on one surface of the cathode microporous layer 320, delay or interruption in the supply of carbon dioxide due to water flooding can be minimized. The microcracks present on one surface of the cathode microporous layer 320 may have a length of about 100 µm or more, or about 300 µm or more, based on a surface area of 5 mm × 5 mm. When the macro-crack length is less than 100 µm, the effect of water discharge may be insufficient. In addition, there may be at least 10 large cracks based on the surface area of 5 mm × 5 mm and the length defined above. When there are less than 10 large cracks, the effect of water discharge may be insufficient.

[0182] The present disclosure is characterized in that an interfacial layer 800 containing an anion exchange polymer is integrated with the surface of the cathode porous transport layer 300 to suppress the evolution of hydrogen, a side reaction product, at the cathode 130.

[0183] Since the interfacial layer 800 contains an anion exchange polymer, the cathode catalyst in the cathode 130 disposed on the cathode porous transport layer 300 can remain alkaline and thus suppresses hydrogen evolution reaction from occurring at the cathode 130.

[0184] The anion exchange polymer includes polystyrene tetramethyl imidazolium chloride containing polystyrene (PS) as a main chain and an imidazolium group, a benzimidazolium-based polymer represented by Formula 5 below, a poly(aryl piperidinium)-based polymer represented by Formula 6 below, and the like. Alternatively, the anion exchange polymer may include commercially available Sustainion^™, Aemion^™, PiperION^™, or the like.

wherein n may be 10 to 1,000.

wherein x may be 10 to 1,000 and y may be 10 to 1,000.

[0185] The interfacial layer 800 may be integrated with the cathode porous transport layer 300. The method of integrating the interfacial layer 800 is not specifically limited. For example, the interfacial layer 800 may be integrated into the cathode porous transport layer 300 by directly coating, spray-coating, or spin-coating the cathode porous transport layer 300 with a dispersion prepared by dissolving an anion exchange polymer in a solvent.

[0186] The interfacial layer 800 may have a thickness of about 20 nm to 3 µm, or about 100 nm to 1 µm. When the thickness of the interfacial layer 800 is less than 20 nm, it may be difficult to impart alkalinity to the cathode catalyst contacting the interfacial layer 800. On the other hand, when the thickness of the interfacial layer 800 exceeds 3 µm, the electrical resistance of the cathode porous transport layer 300 increases, the pores of the cathode microporous layer 320 may be clogged, and mass transport performances may be deteriorated.

[0187] A preferred example of the electrochemical cell 10 according to the present disclosure is that the cathode 130 contains a second cation exchange binder and an anion exchange binder, and the interfacial layer 800 containing the anion exchange polymer integrated with the cathode porous transport layer 300 may contact the cathode 130. The electrochemical cell 10 can effectively suppress hydrogen evolution reaction from occurring at the cathode 130.

[0188] FIG. 14 shows an anode bipolar plate 400 according to the present disclosure. The anode bipolar plate 400 may include a first anode manifold 410 penetrating therethrough at a predetermined position, a second anode manifold 420 penetrating therethrough at a position spaced apart from the first anode manifold 410 by a predetermined distance, and an anode flow channel 430 recessing into the anode bipolar plate 400 from one surface of the anode porous transport layer 200 and thereby connect the first anode manifold 410 to the second anode manifold 420.

[0189] When tens to hundreds of cells are assembled into a stack, manifolds are required to efficiently supply, recirculate and discharge each of reactants and products, as shown in FIG. 14. One pair of reactant manifolds and one pair of product manifolds are required for each anode bipolar plate 400 and the presence or absence of one pair of coolant manifolds may be determined depending on the target performance of the cell and system configuration. For example, when a multi-cell stack that has a large active area of 200 cm² or more for electrochemical reaction and has a high power of 50 kW or more should be sufficiently cooled, a coolant manifold to supply and recirculate the coolant may be used. FIG. 14 shows an example in which one pair of manifolds for reactants, one pair of manifolds for products, and one pair of manifolds for coolants exist for each bipolar plate.

[0190] The anode flow channel 430 may have a serpentine, parallel, interdigitated, mesh, or foam structure. FIG. 14 shows a serpentine structure of the anode flow channel 430. The anode flow channel 430 may include a major flow channel 431 having the largest total length and a minor flow channel 432 having a smaller total length.

[0191] FIG. 15 is a cross-sectional view illustrating the anode bipolar plate 400 according to the present disclosure. Since deionized water is used as an anode reactant and the cell is operated at a high voltage of 2 V or more, the anode bipolar plate 400 may have a dual layer structure including an anode bipolar plate base 440 made of a metal with excellent corrosion resistance such as titanium (Ti) or stainless steel (SS), and an anode bipolar plate coating layer 450 disposed on the surface thereof to increase corrosion resistance and reduce contact resistance.

[0192] The stainless steel constituting the anode bipolar plate base 440 exhibits excellent corrosion resistance due to the high chromium (Cr) content thereof and may include 446 as ferritic SS, 304, 316, or 316L as austenitic SS, or 410 or 440A as martensitic SS. The ferritic SS may have a Cr content of about 20% by weight to 40% by weight. When the Cr content is less than 20% by weight, corrosion resistance deteriorates, whereas when the Cr content exceeds 40% by weight, it may be difficult to maintain a balance between all physical properties.

[0193] The anode bipolar plate coating layer 450 may be formed as a single layer or double layers. A single anode bipolar plate coating layer 450, as shown in FIG. 15, may be formed by coating with titanium (Ti), iridium (Ir), platinum (Pt), gold (Au), niobium (Nb), tantalum (Ta) or a combination thereof. The single anode bipolar plate coating layer 450 may be formed using magnetron sputtering physical vapor deposition or the like. The thickness of the single anode bipolar plate coating layer 450 may be about 0.1 µm to 20 µm, or about 0.5 µm to 5 µm under high potential operating conditions of the anode 120. This is because, when the thickness is less than 0.1 µm, the effects of increasing corrosion resistance and reducing contact resistance may be insufficient, whereas when the thickness exceeds 20 µm, the cost of manufacturing the coating layer greatly increases.

[0194] Meanwhile, when the anode bipolar plate coating layer 450 is formed as a double layer structure, one surface of the anode bipolar plate base 440 is first coated with titanium (Ti) to form a first coating layer and then is further coated with Ti, Ir, Pt, Au, Nb, Ta, or a combination thereof to form a second coating layer in order to further increase corrosion resistance and reduce contact resistance. At this time, the Ti coating layer, as the first coating layer, may be formed using thermal spraying and another coating layer containing Ti, Ir, Pt, Au, Nb, Ta, or the like as the second coating layer may be formed using magnetron sputtering, physical vapor deposition, or the like. The thickness of the double-layer anode bipolar plate coating layer 450 may be about 0.1 µm to 20 µm, or about 0.5 µm to 5 µm. When the thickness is less than 0.1 µm, the effects of increasing corrosion resistance and reducing contact resistance may be insufficient, whereas when the thickness exceeds 20 µm, the cost of manufacturing the coating layer greatly increases.

[0195] FIG. 16 shows an anode gasket 500 according to the present disclosure. FIG. 17 shows a combination of the anode gasket 500 according to the present disclosure and the anode bipolar plate 400. The anode gasket 500 will be described later.

[0196] FIG. 18 shows a cathode bipolar plate 600 according to the present disclosure. The cathode bipolar plate 600 may include a first cathode manifold 610 penetrating therethrough at a predetermined position, a second cathode manifold 620 penetrating therethrough at a position spaced apart from the first cathode manifold 610 by a predetermined distance, and a cathode flow channel 630 recessing into the cathode bipolar plate 600 from one surface of the anode porous transport layer 200 and thereby connect the first cathode manifold 610 to the second cathode manifold 620.

[0197] When tens to hundreds of cells are assembled into a stack, manifolds are required to efficiently supply, recirculate and discharge each of reactants and products, as shown in FIG. 18. One pair of reactant manifolds and one pair of product manifolds are required for each cathode bipolar plate 600 and the presence or absence of one pair of coolant manifolds may be determined depending on the target performance of the cell and system configuration. For example, when a multi-cell stack that has a large active area of 200 cm² or more for electrochemical reaction and has a high power of 50 kW or more should be sufficiently cooled, a coolant manifold to supply and recirculate the coolant may be used. FIG. 18 shows an example in which one pair of manifolds for reactants, one pair of manifolds for products, and one pair of manifolds for coolants exist for each bipolar plate.

[0198] The cathode flow channel 630 may have a serpentine, parallel, interdigitated, mesh, or foam structure. FIG. 18 shows a serpentine structure of the cathode flow channel 630. The cathode flow channel 630 may include a major flow channel 631 having the largest total length and a minor flow channel 632 having a smaller total length.

[0199] FIG. 19 shows a cross-sectional view illustrating the cathode bipolar plate 600 according to the present disclosure.

[0200] The cathode bipolar plate 600 may have a dual layer structure including a cathode bipolar plate base 640 and a cathode bipolar plate coating layer 650.

[0201] The cathode bipolar plate base 640 may contain a metal material such as titanium or stainless steel having superior electrical conductivity, material supply and demand, excellent corrosion resistance and formability and low price compared to conventional carbon materials in order to eliminate the risk of damage to the cathode bipolar plate 600 due to external pressure upon mass forming and stack assembly. Stainless steel exhibits excellent corrosion resistance due to the high chromium (Cr) content thereof and may include 446 as ferritic SS, 304, 316, or 316L as austenitic SS, or 410 or 440A as martensitic SS. The ferritic SS may have a Cr content of 20% by weight to 40% by weight. When the Cr content is less than 20% by weight, corrosion resistance deteriorates, whereas when the Cr content exceeds 40% by weight, it may be difficult to maintain a balance between all physical properties.

[0202] The cathode bipolar plate coating layer 650 may be provided on the surface of the cathode bipolar plate base 640 to further increase corrosion resistance and reduce contact resistance. The cathode bipolar plate coating layer 650 may be formed by coating with titanium (Ti), iridium (Ir), platinum (Pt), gold (Au), niobium (Nb), tantalum (Ta) or a combination thereof. In addition, the cathode bipolar plate coating layer 650 may be formed by coating with a carbon or ceramic material or a combination thereof.

[0203] The thickness of the cathode bipolar plate coating layer 650 may be about 10 nm to 700 nm, or about 50 nm to 200 nm under low potential operating conditions of the cathode 130. When the thickness is less than 10 nm, the effects of increasing corrosion resistance and reducing contact resistance may be insufficient, whereas when the thickness exceeds 700 nm, the manufacturing cost of the cathode bipolar plate coating layer 650 increases greatly.

[0204] FIG. 20 shows a cathode gasket 700 according to the present disclosure. FIG. 21 shows a combination of the cathode gasket 700 according to the present disclosure and the cathode bipolar plate 600.

[0205] Gaskets with proper compressibility and high elasticity are generally required for each cell in order to maintain sealing of the reactants and products of the electrochemical cell and/or stack for conversion of carbon dioxide. When the size of the gasket is smaller than the size of the porous transport layer, the surface of the gasket is disposed on the surface of the porous transport layer and sealing of the cell cannot be maintained. Therefore, the size of the gasket should be greater than the size of the porous transport layer.

[0206] The anode gasket 500 and the cathode gasket 700 are made of polymer elastomers as base materials and are prepared by adding additives such as a crosslinking agent, a co-crosslinking agent or crosslinking accelerator, a filler, or the like to the polymer elastomers to prepare compounds and then crosslinking the compounds using heat.

[0207] In the related art, a stand-alone structure (free-standing structure), in which the gasket was separately manufactured and further combined with a bipolar plate, or an integrated structure in which the gasket was combined with a solid electrolyte was used. In particular, in order to efficiently mass-produce a stack with a high power of 50 kW or more based on large active area cells with an active area of 200 cm² or more, the components of each cell and stack must be assembled and laminated quickly. However, the conventional stand-alone structure is not suitable in terms of handling property of cell components required for manufacturing such a stack. In addition, an integrated structure in which the gasket is bonded to the solid electrolyte is also not suitable in terms of the thermal resistance required during high-temperature crosslinking of the gasket.

[0208] Therefore, in order to solve these conventional problems, the present disclosure provides an integrated structure in which an anode gasket 500 and a cathode gasket 700 are over-molded respectively on the anode bipolar plate 400 and the cathode bipolar plate 600 with excellent heat resistance by injection-molding, as shown in FIGs. 17 and 21.

[0209] The performance and long-term durability of the anode gasket 500 and cathode gasket 700 are closely related to various physical properties such as degree of compressibility, hardness, and compression set. In addition, high processability or flowability of the compound is required for efficient injection molding of the anode gasket 500 and the cathode gasket 700.

[0210] In the present disclosure, the compound is injection-molded on the anode bipolar plate 400 and the cathode bipolar plate 600 in an injection molding machine, followed by primary crosslinking to form an integrated structure and then the integrated structure is removed from the mold in the injection molding machine. Then, the structure is sufficiently subjected to secondary crosslinking or post-crosslinking (post-curing) in a dedicated crosslinking chamber. In particular, when the crosslinking speed is excessively high during the primary crosslinking, pre-curing or scorch problems may occur, thus making formation of the anode gasket 500 and the cathode gasket 700 impossible. On the other hand, when the crosslinking speed is excessively low, disadvantageously, the gasket production cycle time increases and productivity decreases. Therefore, it is important to precisely control the composition of the compound, injection molding time, and temperature in order to ensure an appropriate crosslinking speed.

[0211] The anode gasket 500 and the cathode gasket 700 should be compressible within an appropriate range when external pressure is applied thereto and the degree of compressibility is calculated as follows:

wherein ti is the thickness of the anode gasket 500 or the cathode gasket 700 measured when a compression pressure of 50 kPa is applied thereto, and t₂ is the thickness of the anode gasket 500 or the cathode gasket 700 measured when a compression pressure of 1 MPa is applied thereto. The degree of compressibility of the anode gasket 500 or the cathode gasket 700 may be about 2% to 40%, or about 5% to 25%. When the degree of compressibility is less than 2%, the anode gasket 500 or the cathode gasket 700 becomes excessively stiff and thus it becomes difficult to obtain intimate contact and sealing of cells within a stack when tens to hundreds of cells are assembled into the stack, whereas when the degree of compressibility exceeds 40%, the anode gasket 500 or the cathode gasket 700 is excessively flexible (soft), thus causing deterioration in long-term sealing and durability due to excessive compression of the anode gasket 500 or the cathode gasket 700 when the cell is compressed.

[0212] The hardness of the anode gasket 500 and the cathode gasket 700 should be maintained within an appropriate range because they are closely related to compressibility, elasticity, mechanical properties, crosslinking density, and chemical resistance. The anode gasket 500 and the cathode gasket 700 may have a Shore A hardness of about 30 to 90, or about 50 to 85, as measured under ASTM (American Society for Testing and Materials) D2240. When the Shore A hardness is less than 30, the anode gasket 500 and the cathode gasket 700 may be excessively compressed while the cells are pressurized, which may reduce long-term sealing and durability, whereas when the Shore A hardness exceeds 90, it may be difficult to obtain close contact and sealing of the cells in the stack.

[0213] The compression set of the anode gasket 500 and the cathode gasket 700 is closely related to elasticity and crosslink density. As the compression set decreases, the elasticity of the anode gasket 500 and the cathode gasket 700 increases. The compression set of the anode gasket 500 and the cathode gasket 700 may be about 15% or less, or about 10% or less when measured under ASTM D395 (method B, 25% deflection, 100°C/72 hours) conditions.

[0214] The Mooney Viscosity of the compound is an indicator of the moldability and fluidity of the anode gasket 500 and the cathode gasket 700, is inversely proportional to injection moldability and is preferably maintained within a predetermined range. The Mooney viscosity of the compound may be about 5 to 40, or about 10 to 30, when measured under ISO 289-1 (2005) (ML (1+4)/125°C) conditions. When the Mooney viscosity is less than 5, the overall physical properties of the anode gasket 500 and the cathode gasket 700, such as elasticity, mechanical properties, and handling properties, may be greatly reduced, whereas the Mooney viscosity exceeds 40, the injection moldability may decrease and productivity may decrease.

[0215] It is important to select materials for the anode gasket 500 and the cathode gasket 700 because the anode gasket 500 and the cathode gasket 700 require various physical properties and requirements such as compressibility, elasticity, mechanical properties, chemical resistance, long-term durability, formability, and cost.

[0216] A fluoroelastomer, a hydrocarbon elastomer, or a silicone elastomer may be used alone or in combination thereof for the anode gasket 500 and the cathode gasket 700.

[0217] The fluoroelastomer has excellent elasticity, chemical resistance, heat resistance, and the like. The fluoroelastomer exhibits unique properties due to low polarizability and strong electronegativity of fluorine atoms. Fluoroelastomers having a high fluorine content have excellent thermal stability, chemical stability, anti-aging, weather resistance, and chemical resistance. In addition, fluoroelastomers exhibit characteristics such as low dielectric constant, low flammability, low surface energy, and moisture absorption. The C-F bond of fluoroelastomers greatly contributes to high resistance to oxidation and resistance to hydrolysis. Fluoroelastomers may be broadly classified into FKM, FFKM, and the like in accordance with ASTM. The fluoroelastomer include a fluoroelastomer synthesized by copolymerization of monomers such as vinylidene fluoride (VDF), tetrafluoroethylene (TFE), hexafluoropropene (HFP), and perfluoroalkyl vinyl ether (PAVE), or a combination thereof.

[0218] The hydrocarbon elastomer has advantages such as low cost, excellent low temperature flexibility, and high chemical resistance. The hydrocarbon elastomer may include a copolymerized hydrocarbon elastomer such as EPDM (ethylene-propylene diene monomers) or EPR (ethylene-propylene rubber), or a combination thereof. As a termonomer, EPDM includes ethylidene norbornene (ENB), dicyclopentadiene (DCPD), and 1,4-hexadiene (HD), in addition to ethylene and propylene, and preferably includes ethylidene norbornene.

[0219] The silicone elastomer has low resistance to acid, but has high precision injection moldability and excellent physical properties for the gasket. The silicone elastomer may include a general-purpose silicone elastomer such as poly(dimethylsiloxane) (PDMS) or a modified silicone elastomer such as fluorosilicone with increased acid resistance or a combination thereof. Solid silicone elastomers may be used and liquid silicone rubber is preferably used for precise injection molding.

[0220] FIG. 22 shows a stack 1000 according to the present disclosure. The stack 1000 may include a laminate in which a plurality of electrochemical cells 10 are laminated and end plates 20 disposed on both surfaces of the laminate.

[0221] FIG. 23 shows an end plate 20 according to the present disclosure. FIG. 24 shows a cross-sectional view taken along line C-C' of FIG. 23.

[0222] The end plate 20 may be a penetrating type or a non-penetrating type. The penetrating-type end plate has a structure in which manifolds for reactants, products, and coolant is formed on a non-penetrating type end plate, and performs mass transport of the reactants, products, and coolant through the manifolds 21.

[0223] The end plate 20 supports each component within the stack 1000 and maintains uniform compression pressure to suppress an increase in contact resistance within the stack 1000 while fastening the stack 1000. To this end, the end plate 20 should have various functionalities such as high mechanical strength, chemical resistance, hydrolysis resistance, lightness, insulation, flame retardance, and mass productivity. Despite the importance of end plates, machined heavy metal materials that lack physical properties such as corrosion resistance, or exclusive polymer plastic materials that have very low mechanical properties compared to metal materials were generally used in the art. Therefore, the present disclosure provides novel multi-functional end plates to solve these problems of the prior art.

[0224] Conventional end plates are often formed only using a machined metal material such as stainless steel. In this case, the end plate may be corroded by reactants, products, and coolant used in the electrochemical reaction. In addition, metal corrosion products such as various metallic cations are generated and eluted, thus causing poisoning and contamination of internal components such as solid electrolytes of the cell and the binder in the electrode. In addition, metal materials may cause problems of increased weight of the end plate, decreased production speed due to machining, and increased manufacturing costs.

[0225] Alternatively, conventional end plates are formed using a polymer material alone. End plates made of polymer materials are lightweight, have excellent insulation properties, and are suitable for mass-production using injection molding. However, end plates made of polymer materials have disadvantages of very low mechanical strength, high strain rate and nonuniform compression pressure applied to the cells in the stack compared to end plates having the same structure and made of metal materials.

[0226] The end plate 20 according to the present disclosure may include a core 23 containing a metal and a shell 24 surrounding the core 23 and containing a composite material of a polymer and a glass fiber. By coating the outer surface of the core 23 with the shell 24 by injection molding, deformation can be minimized through the excellent mechanical strength of the core 23, while maintaining the excellent insulation, chemical resistance, hydrolysis resistance, lightness, and mass productivity of the shell 23.

[0227] The core 23 may contain at least one selected from stainless steel, aluminum (Al), and an aluminum alloy.

[0228] The shell 24 contains about 50% to 90% by weight of a thermoplastic polymer and about 10% to 50% by weight of a glass fiber, or about 60% to 80% by weight of a thermoplastic polymer and about 20% to 40% by weight of a glass fiber. When the content of the glass fiber is less than 10% by weight, the effect of reinforcing the physical properties by the addition of the glass fiber is insufficient, whereas when the content of the glass fiber exceeds 50% by weight, the content of the glass fiber becomes excessively large, reducing the injection moldability of the shell 24.

[0229] The thermoplastic polymer may include at least one selected from polyamide (PA), poly(phenylene sulfide) (PPS), polyimide (PI), poly(ether imide) (PEI), polycarbonate (PC), poly(phenylene oxide) (PPO), poly(phenylene ether) (PPE), polyethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(ether ketone) (PEK), poly(ether ether ketone) (PEEK), poly(ether ether ketone ketone) (PEEKK), polyethylene (PE), and polypropylene (PP) which are polymers applicable to injection molding. The thermoplastic polymer may include a homopolymer or a random, graft, block, or alternating copolymer, or a blend of the polymer with another thermoplastic polymer, thermosetting polymer, rubber, or the like. In addition, an organic additive and/or inorganic additive may be mixed with the thermoplastic polymer.

[0230] The polyamide may include at least one of aliphatic, aromatic, and semi-aromatic polyamides, and preferably includes a semi-aromatic polyamide which has excellent heat resistance and injection moldability.

[0231] The end plate 20 may be manufactured by injection-molding the shell 24 on the outer surface of the core 23. For example, when the core 23 containing austenitic SS 304 among stainless steels is covered with a composite of a semi-aromatic polyamide and a glass fiber, injection molding may be performed at a processing temperature of 310°C to 370°C in an injection molding machine, and at a temperature of 60°C to 170°C in an injection mold for 1 minute to 60 minutes.

[0232] The shell 24 may further contain a flame retardant. The shell 24 may be produced by adding an appropriate flame retardant along with the thermoplastic polymer, glass fiber and the like. The flame retardant may be in the form of a powder or masterbatch pellet. The flame retardant is preferably a masterbatch pellet in order to homogeneously mix the flame retardant with the thermoplastic polymer and/or glass fiber.

[0233] The flame retardant may include an environmentally friendly non-halogen (halogen-free) flame retardant. The halogen flame retardants have problems such as emission of toxic gases that are harmful to the human body in the event of a fire.

[0234] The non-halogen flame retardant includes aluminum hydroxide, magnesium hydroxide, calcium hydroxide, ammonium phosphate, ammonium phenyl phosphate, diammonium phosphate, ammonium dimethyl phosphate, ammonium ethyl phosphate, melamine phosphate, melamine diphenyl phosphate, melamine pyrophosphate, urea phosphate, expanded graphite, nano clay or a mixture thereof.

[0235] The content of the flame retardant may be about 1% to 40% by weight, or about 5% to 30% by weight, based on the total weight of the shell 24. When the content of the flame retardant is less than 1% by weight, the effect of flame retardant is insufficient, whereas when the content of the flame retardant exceeds 40% by weight, the dispersibility of the flame retardant decreases and various inherent physical properties of the shell 24 may also decrease due to excessively high flame retardant content.

[0236] As is apparent from the foregoing, according to the present disclosure, it is possible to obtain an electrochemical cell for conversion of carbon dioxide suitable for mass production.

[0237] According to the present disclosure, it is possible to obtain an electrochemical cell for conversion of carbon dioxide that exhibits maximized performance due to low cell resistance.

[0238] According to the present disclosure, it is possible to obtain an electrochemical cell for conversion of carbon dioxide that minimizes the problem of flooding.

[0239] According to the present disclosure, it is possible to obtain an electrochemical cell for conversion of carbon dioxide that has high operational current density.

[0240] According to the present disclosure, it is possible to obtain an electrochemical cell for conversion of carbon dioxide that is highly durable and thus has a long lifetime and is highly stable.

[0241] The effects of the present disclosure are not limited to those mentioned above. It should be understood that the effects of the present disclosure include all effects that can be inferred from the foregoing description of the present disclosure.

[0242] The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. An electrochemical cell for conversion of carbon dioxide comprising:
an electrode-solid electrolyte assembly comprising:

a solid electrolyte layer comprising a cation exchange solid electrolyte;

an anode coated on one surface of the solid electrolyte layer and being integrated with the solid electrolyte layer, wherein the anode comprises an anode catalyst and a first cation exchange binder; and

a cathode coated on the other surface of the solid electrolyte layer and being integrated with the solid electrolyte layer, wherein the cathode comprises a cathode catalyst and a second cation exchange binder;

an anode porous transport layer disposed on the anode;

a cathode porous transport layer disposed on the cathode; and

an interfacial layer interposed between the cathode and the cathode porous transport layer and containing an anion exchange polymer,

wherein water is supplied to the anode through the anode porous transport layer, where an oxidation reaction of water occurs at the anode, and

wherein carbon dioxide is supplied to the cathode through the cathode porous transport layer, where a reduction reaction of carbon dioxide occurs at the cathode.

2. The electrochemical cell according to claim 1, wherein at least one product selected from the group consisting of formic acid, ethylene, propylene, alcohol, and combinations thereof is obtained through the reduction reaction of carbon dioxide at the cathode.

3. The electrochemical cell according to claim 1, wherein the solid electrolyte layer comprises:

a central portion in contact with the anode and the cathode; and

an edge portion excluding the central portion,

the electrochemical cell further comprises a protective member disposed on the edge portion, and

the protective member is mounted in each of an area defined by one surface of the edge portion and one side surface of the anode and an area defined by another surface of the edge portion and one side surface of the cathode.

4. The electrochemical cell according to claim 1, wherein the solid electrolyte layer comprises:

at least one reinforcement layer having a plurality of pores filled with a first cation exchange solid electrolyte; and

an ion exchange layer disposed on at least one surface of the reinforcement layer and comprising a second cation exchange solid electrolyte.

5. The electrochemical cell according to claim 1, wherein at least one of the solid electrolyte layer, the anode and the cathode further comprises an antioxidant, and
wherein the antioxidant comprises at least one selected from the group consisting of cerium antioxidants, manganese antioxidants, non-manganese transition metal antioxidants, phenolic antioxidants, phosphite antioxidants, and combinations thereof.

6. The electrochemical cell according to claim 1, wherein the water supplied to the anode comprises deionized water having a specific resistance of about 18 MΩ·cm or more, and
wherein the carbon dioxide supplied to the cathode comprises humidified carbon dioxide having a relative humidity of about 10% to 90%.

7. The electrochemical cell according to claim 1, wherein the cathode further comprises an anion exchange binder.

8. The electrochemical cell according to claim 1, wherein the anode porous transport layer comprises an anode macroporous substrate comprising pores having a diameter of 1 µm to 300 µm, and
the anode macroporous substrate comprises at least one selected from the group consisting of titanium fiber felt, titanium fiber paper, titanium fiber cloth, titanium mesh, titanium foil, and combinations thereof.

9. The electrochemical cell according to claim 8, wherein the anode porous transport layer further comprises an anode microporous layer disposed on the anode macroporous substrate and comprising pores having a diameter of less than about 0.2 µm,

the anode microporous layer comprises at least one selected from the group consisting of titanium (Ti), iridium (Ir), platinum (Pt), gold (Au), and combinations thereof, and

the anode porous transport layer is laminated on the anode such that the anode microporous layer faces the anode.

10. The electrochemical cell according to claim 1, wherein the anode porous transport layer comprises a corrosion-resistant coating layer disposed on at least one surface of the anode porous transport layer and comprising at least one selected from the group consisting of titanium (Ti), iridium (Ir), platinum (Pt), gold (Au), and combinations thereof.

11. The electrochemical cell according to claim 1, wherein the cathode porous transport layer comprises a cathode macroporous substrate comprising pores having a diameter of about 1 µm to 300 µm, and
the cathode macroporous substrate comprises at least one selected from the group consisting of carbon fiber felt, carbon fiber paper, carbon fiber cloth, and combinations thereof.

12. The electrochemical cell according to claim 11, wherein the cathode porous transport layer further comprises a cathode microporous layer disposed on the cathode macroporous substrate and comprising pores having a diameter of less than about 0.2 µm,

the cathode microporous layer comprises at least one selected from the group consisting of carbon black, graphene nanoplate, carbon nanotube, carbon nanofiber and combinations thereof, and

the cathode porous transport layer is laminated on the cathode such that the cathode microporous layer faces the cathode.

13. The electrochemical cell according to claim 1, wherein the interfacial layer is integrated with the cathode porous transport layer.

14. The electrochemical cell according to claim 1, wherein the interfacial layer has a thickness of 20 nm to 3 µm.

15. The electrochemical cell according to claim 1, further comprising:

an anode bipolar plate disposed on the anode porous transport layer;

an anode gasket interposed between the electrode-solid electrolyte assembly and the anode bipolar plate;

a cathode bipolar plate disposed on the cathode porous transport layer; and

a cathode gasket interposed between the electrode-solid electrolyte assembly and the cathode bipolar plate,

wherein the anode bipolar plate comprises:

a first anode manifold penetrating therethrough at a predetermined position;

a second anode manifold penetrating therethrough at a position spaced apart from the first anode manifold by a predetermined distance; and

an anode flow channel recessing into the anode bipolar plate from one surface of the anode porous transport layer and thereby connect the first anode manifold to the second anode manifold, and

wherein water supplied through the first anode manifold flows through the anode flow channel and is supplied to the anode porous transport layer,

wherein the cathode bipolar plate comprises:

a first cathode manifold penetrating therethrough at a predetermined position;

a second cathode manifold penetrating therethrough at a position spaced apart from the first cathode manifold by a predetermined distance; and

a cathode flow channel recessing into the anode bipolar plate from one surface of the cathode porous transport layer and thereby connect the first anode manifold to the second cathode manifold, and

wherein carbon dioxide supplied through the first cathode manifold flows through the cathode flow channel and is supplied to the cathode porous transport layer.

Drawing