Cathode gas diffusion layer for carbon dioxide reduction electrode, carbon dioxide reduction electrode, and carbon dioxide electrolysis cell

Abstract

To provide a cathode gas diffusion layer for a carbon dioxide reduction electrode capable of improving methane selectivity of the carbon dioxide reduction electrode, and a carbon dioxide reduction electrode and a carbon dioxide electrolysis cell comprising the cathode gas diffusion layer for a carbon dioxide reduction electrode.SOLUTION: A cathode gas diffusion layer for a carbon dioxide reduction electrode comprises a conductive fiber layer and a microporous layer which is provided on the conductive fiber layer and which is a porous body formed of conductive particles, and an application thereof.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a cathode gas diffusion layer for a carbon dioxide reduction electrode, a carbon dioxide reduction electrode, and a carbon dioxide electrolysis cell. [Background technology]

[0002] Methane (CH4) can be synthesized by applying electricity to carbon dioxide (CO2) and water (H2O) and causing the reduction of carbon dioxide over a catalyst. Various techniques for synthesizing methane by reducing carbon dioxide have been reported.

[0003] For example, Patent Document 1 discloses a technology using a carbon dioxide reduction electrode that includes a conductive support made of a porous conductive material and an electrode layer that is provided on the conductive support and contains a conductive material on which a nitrogen-containing metal complex is supported. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-63037 Summary of the Invention [Problem to be solved by the invention]

[0005] A typical cathode gas diffusion layer used in a carbon dioxide reduction electrode has a woven carbon fiber structure. The carbon dioxide reduction reaction requires contact between the CO2 gas, catalyst, and electrolyte. However, a cathode gas diffusion layer made of sintered woven carbon fiber, for example, has few contact points between the CO2 gas, catalyst, and electrolyte. This results in poor methane production efficiency. Therefore, there is a need to develop a cathode gas diffusion layer that can improve the methane selectivity of a carbon dioxide reduction electrode.

[0006] The present disclosure has been made in consideration of the above circumstances. An object of one embodiment of the present disclosure is to provide a cathode gas diffusion layer for a carbon dioxide reduction electrode that can improve the methane selectivity of the carbon dioxide reduction electrode. Another problem to be solved by another embodiment of the present disclosure is to provide a carbon dioxide reduction electrode and a carbon dioxide electrolysis cell including the above-mentioned cathode gas diffusion layer for a carbon dioxide reduction electrode. [Means for solving the problem]

[0007] Specific means for solving the problems include the following aspects. <1> A conductive fiber layer; a microporous layer provided on the conductive fiber layer and being a porous body formed of conductive particles; A cathode gas diffusion layer for a carbon dioxide reduction electrode comprising: <2> The material of the conductive fiber layer is carbon fiber. <1> 2. A cathode gas diffusion layer for a carbon dioxide reduction electrode according to claim 1. <3> The conductive particles are carbon particles. <1> or <2> 2. A cathode gas diffusion layer for a carbon dioxide reduction electrode according to claim 1. <4> <1> ~ <3> a cathode gas diffusion layer for a carbon dioxide reduction electrode according to any one of the above items; a cathode catalyst layer provided on the surface of the cathode gas diffusion layer for the carbon dioxide reduction electrode facing the microporous layer; A carbon dioxide reduction electrode having <5> <4> A carbon dioxide electrolysis cell comprising the carbon dioxide reduction electrode according to claim 1, an electrolyte, and an anode electrode. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, there is provided a cathode gas diffusion layer for a carbon dioxide reduction electrode that can improve the methane selectivity of the carbon dioxide reduction electrode. According to another embodiment of the present disclosure, there is provided a carbon dioxide reduction electrode and a carbon dioxide electrolysis cell comprising the above-described cathode gas diffusion layer for a carbon dioxide reduction electrode. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a partial cross-sectional SEM image (magnification: 300 times) of the cathode gas diffusion layer of the carbon dioxide reduction electrode of Example 1. [Figure 2] FIG. 2 is a schematic diagram of a gas diffusion half-cell incorporating a carbon dioxide reduction electrode, which was used in the selectivity evaluation test in the Examples. [Figure 3] FIG. 3 is a graph showing the results of the selectivity evaluation test in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and can be implemented by making appropriate modifications within the scope of the object of the present disclosure. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

[0011] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] In the numerical ranges described in stages in the present disclosure, the upper limit value described in one numerical range may be replaced with the upper limit value of another numerical range described in stages, and the lower limit value described in one numerical range may be replaced with the lower limit value of another numerical range described in stages. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with a value shown in the examples.

[0013] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0014] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0015] [Cathode gas diffusion layer for carbon dioxide reduction electrode] The cathode gas diffusion layer for a carbon dioxide reduction electrode according to the present disclosure (hereinafter also simply referred to as the "cathode gas diffusion layer") comprises a conductive fiber layer and a microporous layer that is provided on the conductive fiber layer and is a porous body formed from conductive particles. The cathode gas diffusion layer of the present disclosure can improve the methane selectivity of a carbon dioxide reduction electrode. Although the reason why the cathode gas diffusion layer of the present disclosure can exhibit such an effect is unclear, the inventors speculate as follows: However, the following speculation is not intended to limit the cathode gas diffusion layer of the present disclosure, but is described as an example.

[0016] The cathode gas diffusion layer of the present disclosure has a microporous layer, which is a porous body formed of conductive particles, on a conductive fiber layer, and therefore can increase the number of contact points between the CO2 gas, catalyst, and electrolyte required for the carbon dioxide reduction reaction compared to conventional cathode gas diffusion layers that have only a conductive fiber layer. This increase in contact points is presumably responsible for the improved methane selectivity of the carbon dioxide reduction electrode. On the other hand, the carbon dioxide reduction electrode described in Patent Document 1 uses carbon paper (CP) made of sintered graphite fiber as the cathode gas diffusion layer, and does not have a microporous layer, so it is thought that its methane selectivity is low.

[0017] In addition, the cathode gas diffusion layer of the present disclosure can also improve the selectivity of a carbon dioxide reduction electrode to C-based products other than methane, such as carbon monoxide (CO) selectivity and ethylene (C2H4) selectivity.

[0018] <Conductive fiber layer> The cathode gas diffusion layer of the present disclosure has a conductive fiber layer. The conductive fiber layer is a layer formed from conductive fibers, and is a layer through which fluid (for example, gas and liquid; the same applies hereinafter) can pass.

[0019] The material of the conductive fiber layer is not particularly limited. Specific examples of materials for the conductive fiber layer include carbon fiber and titanium fiber. The carbon fiber and titanium fiber may both be sintered. The material of the conductive fiber layer is preferably carbon fiber. As the carbon fiber, graphite fiber is preferred.

[0020] The density of the conductive fiber layer is not particularly limited, but is, for example, 0.10 g / cm 3 ~1.00g / cm 3 and preferably 0.30 g / cm 3 ~0.50g / cm 3 It is more preferable that:

[0021] The "density of the conductive fiber layer" in the present disclosure is a value calculated from the mass per unit area and the thickness.

[0022] The porosity of the conductive fiber layer is not particularly limited, but is preferably, for example, 70% to 90%, and more preferably 80% to 85%.

[0023] The thickness of the conductive fiber layer is not particularly limited, but is preferably 250 μm or less, more preferably 100 μm to 250 μm, and even more preferably 100 μm to 200 μm.

[0024] In the present disclosure, the "thickness of the conductive fiber layer" means the average thickness of the conductive fiber layer. The average thickness of the conductive fiber layer is a value determined by the following method. The cross section of the conductive fiber layer is observed using a scanning electron microscope (SEM). The thickness of the conductive fiber layer is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and the obtained value is the average thickness of the conductive fiber layer.

[0025] <Microporous layer> The cathode gas diffusion layer of the present disclosure has a microporous layer (MPL) that is a porous body formed from conductive particles. The MPL is provided on the conductive fibrous layer, and is preferably provided on one side of the conductive fibrous layer.

[0026] The conductive particles are not particularly limited as long as they contain a material having conductivity. Examples of conductive particles include carbon particles and conductive metal particles. Examples of conductive metal particles include titanium particles, copper particles, silver particles, and platinum particles. The conductive particles are preferably carbon particles. As the carbon particles, graphite particles are preferred.

[0027] The shape of the conductive particles is not particularly limited. The shape of the conductive particles may be, for example, spherical (eg, perfect sphere or oval sphere), plate-like, or irregular.

[0028] The size of the conductive particles is not particularly limited. The particle diameter of the conductive particles is preferably 50 nm or more, and more preferably 50 nm to 200 nm, from the viewpoint of forming pores of a size that allows good fluid flow, for example.

[0029] In the present disclosure, the "particle diameter of the conductive particles" refers to the average primary particle diameter of the conductive particles. The average primary particle size of the conductive particles is a value determined by the following method. The surface of the MPL is observed using a scanning electron microscope (SEM). Ten conductive particles are randomly selected from three randomly selected 1 μm square fields of view in the SEM image, and the circle-equivalent diameter of the primary particles is measured. The arithmetic mean of the measured values ​​is calculated, and this value is used as the average primary particle diameter of the conductive particles.

[0030] The shape of the pores in the porous MPL is not particularly limited. The shape of the holes may be, for example, circular (for example, perfect circle or ellipse), rectangular, or irregular.

[0031] The size of the pores in the porous MPL (hereinafter also referred to as "pore diameter of MPL") is not particularly limited as long as it allows fluid to pass through. The pore size of the MPL is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and, for example, preferably 3.0 μm or less, more preferably 1.0 μm or less. In one embodiment, the pore size of the MPL may be 0.01 μm to 3.0 μm, or may be 0.1 μm to 1.0 μm.

[0032] In this disclosure, "pore size of the MPL" refers to the average pore size of the MPL. The average pore size of MPL is a value determined by the following method. The cross section of the MPL in the thickness direction is observed using a scanning electron microscope (SEM). Ten pores are randomly selected from three randomly selected SEM images of 2 μm square and 50 μm square, and the equivalent circle diameters of these pores are measured. The arithmetic mean of the measured values ​​is calculated, and this value is used as the average pore diameter of the MPL.

[0033] The pore size of the MPL can be controlled, for example, by the size of the conductive particles.

[0034] The thickness of the MPL is not particularly limited, but is preferably 150 μm or less, more preferably 50 μm to 150 μm, and even more preferably 50 μm to 100 μm.

[0035] "MPL thickness" in this disclosure refers to the average thickness of the MPL. The average thickness of the MPL is a value determined by the following method. The cross section of the MPL is observed using a scanning electron microscope (SEM). The thickness of the MPL is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and this value is taken as the average thickness of the MPL.

[0036] [Carbon dioxide reduction electrode] The carbon dioxide reduction electrode of the present disclosure includes a cathode gas diffusion layer of the present disclosure and a cathode catalyst layer provided on the MPL side of the cathode gas diffusion layer of the present disclosure. That is, the carbon dioxide reduction electrode of the present disclosure has a layer structure of conductive fiber layer / MPL / cathode catalyst layer. With this layer structure, the carbon dioxide reduction electrode of the present disclosure exhibits high selectivity for methane. The carbon dioxide reduction electrode of the present disclosure also tends to exhibit high selectivity for carbon monoxide (CO) and ethylene (C2H4), which are C-based products other than methane. The carbon dioxide reduction electrode will be described in detail below. Note that the details of the cathode gas diffusion layer of the present disclosure have been described above, and therefore will not be described here.

[0037] <Cathode catalyst layer> The carbon dioxide reduction electrode of the present disclosure has a cathode catalyst layer. The cathode catalyst layer is provided on the MPL side of the cathode gas diffusion layer. When the cathode catalyst layer is provided on the MPL side of the cathode gas diffusion layer, CO2 gas comes into contact with the cathode catalyst in the cathode catalyst layer more easily, which tends to allow the carbon dioxide reduction reaction to proceed efficiently and produce methane selectively and efficiently.

[0038] The cathode catalyst layer is a layer containing a cathode catalyst. The cathode catalyst promotes the reduction reaction of carbon dioxide. The type of cathode catalyst is not particularly limited as long as it can promote the reduction reaction of carbon dioxide. Examples of the cathode catalyst include metals such as Cu, Ag, Zn, Sn, and Al, or alloys thereof. The cathode catalyst is preferably particles of these metals or alloys. The cathode catalyst layer is preferably a layer containing Cu particles, for example, from the viewpoint of methane production efficiency. In the present disclosure, a layer containing Cu particles is also referred to as a "Cu particle layer." The Cu particle layer is preferably a layer made of Cu particles.

[0039] When the cathode catalyst is Cu particles, the particle size of the Cu particles is not particularly limited, but is preferably 10 nm or less, and more preferably 5 nm to 10 nm. The smaller the particle size of the Cu particles, the more likely the efficiency of methane production will improve.

[0040] In the present disclosure, the "particle size of Cu particles" refers to the average primary particle size of Cu particles. The average primary particle size of the Cu particles is a value determined by the following method. The surface of the cathode catalyst layer is observed using a scanning transmission electron microscope (STEM), and the primary particle diameters of all Cu particles present in five 200 nm square fields are measured. The arithmetic mean of the measured values ​​is calculated, and this value is taken as the average primary particle diameter of the Cu particles.

[0041] The thickness of the cathode catalyst layer is not particularly limited, but is preferably, for example, 200 nm to 350 nm.

[0042] In the present disclosure, the "thickness of the cathode catalyst layer" means the average thickness of the cathode catalyst layer. The average thickness of the cathode catalyst layer is a value determined by the following method. The cross section of the cathode catalyst layer is observed using a scanning electron microscope (SEM). The thickness of the cathode catalyst layer is measured at six randomly selected locations in the thickness direction. The arithmetic mean of the measured values ​​is calculated, and this value is used as the average thickness of the cathode catalyst layer.

[0043] [Method of manufacturing carbon dioxide reduction electrode] The method for producing the carbon dioxide reduction electrode of the present disclosure is not particularly limited. The carbon dioxide reduction electrode of the present disclosure can be produced by a known method. A preferred method for producing a carbon dioxide reduction electrode according to the present disclosure (hereinafter also referred to as "production method X") will be described below, taking as an example a case in which the cathode catalyst layer is a layer containing Cu particles as the cathode catalyst. In the description of production method X, matters common to those described in the sections on the cathode gas diffusion layer and the carbon dioxide reduction electrode according to the present disclosure will be omitted.

[0044] Manufacturing method X includes a step of preparing a cathode gas diffusion layer of the present disclosure (hereinafter also referred to as a "cathode gas diffusion layer preparation step"), and a step of forming a cathode catalyst layer by adhering Cu particles to the MPL side surface of the prepared cathode gas diffusion layer of the present disclosure by an arc plasma method (hereinafter also referred to as a "cathode catalyst layer formation step"). The manufacturing method X may include steps other than the cathode gas diffusion layer preparation step and the cathode catalyst layer formation step (so-called other steps), such as washing the electrode with distilled water.

[0045] - Cathode gas diffusion layer preparation process - The manufacturing method X includes a step of preparing the cathode gas diffusion layer of the present disclosure (ie, a cathode gas diffusion layer preparation step). "Preparing a cathode gas diffusion layer of the present disclosure" means making a cathode gas diffusion layer of the present disclosure usable, and includes fabricating a cathode gas diffusion layer of the present disclosure unless otherwise specified. That is, the cathode gas diffusion layer preparation step may be a step of preparing a pre-fabricated cathode gas diffusion layer of the present disclosure, or a step of fabricating a cathode gas diffusion layer of the present disclosure.

[0046] The method for producing the cathode gas diffusion layer of the present disclosure is not particularly limited. The cathode gas diffusion layer of the present disclosure can be produced by a known method. The conductive fiber layer may be made of commercially available carbon paper.

[0047] -Cathode catalyst layer formation process- Manufacturing method X includes a step of forming a cathode catalyst layer by adhering Cu particles by an arc plasma method to the MPL side surface of the cathode gas diffusion layer of the present disclosure prepared in the cathode gas diffusion layer preparation step (cathode catalyst layer formation step). According to the cathode catalyst layer forming step, a cathode catalyst layer that is a Cu particle layer is formed. Forming a Cu particle layer using the arc plasma method tends to produce a carbon dioxide reduction electrode that can produce methane more efficiently. The arc plasma method is a gas-phase method that generates metal nanoparticles by vaporizing a metal through a high-temperature arc discharge between two electrodes. In the arc plasma method, the metal is evaporated by the plasma generated between the two electrodes, and the generated metal vapor grows into nano-sized particles as it cools while reacting with the ambient gas. Therefore, the arc plasma method can form a Cu particle layer with nano-sized Cu particles attached to the MPL side of the cathode gas diffusion layer of the present disclosure. It is believed that the smaller the particle diameter of the Cu particles that form the Cu particle layer, the larger the contact area with carbon dioxide, which effectively functions as a catalyst, resulting in more efficient methane production.

[0048] The arc plasma conditions are not particularly limited. The applied voltage is preferably, for example, 80V to 150V, and more preferably 110V to 120V. The number of discharges is preferably, for example, 50 to 1000 times. The capacitance of the capacitor is preferably, for example, 300 μF to 1500 μF. The pulse frequency is preferably, for example, 0.2 Hz to 10 Hz. A preferred example of the arc plasma conditions is an applied voltage of 120 V, a discharge count of 500, a capacitor capacity of 1080 μF, and a pulse frequency of 1 Hz. As the arc plasma device, an arc plasma method nanoparticle formation device (model: APD-1S-C) manufactured by Advance Riko Co., Ltd. can be suitably used. However, the arc plasma device in the present disclosure is not limited to this.

[0049] [Carbon dioxide electrolysis cell] The carbon dioxide electrolysis cell of the present disclosure comprises the carbon dioxide reduction electrode (so-called cathode electrode) of the present disclosure, an electrolyte, and an anode electrode. The carbon dioxide reduction electrode of the present disclosure has been described above, and therefore, a description thereof will be omitted here.

[0050] <Electrolyte> The carbon dioxide electrolysis cell of the present disclosure comprises an electrolyte. The electrolyte can be selected from known ion-exchange membrane-type electrolytes used in carbon dioxide electrolysis cells. The ion-exchange membrane-type electrolyte may have the property of selectively permeating cations or anions. The electrolyte may be, for example, a polymer electrolyte membrane (PEM). The electrolyte may be, for example, a fluorine-based polymer electrolyte membrane or a hydrocarbon-based polymer electrolyte membrane.

[0051] As the electrolyte, commercially available products can be used. Examples of commercially available electrolytes include "Nafion" (registered trademark) (manufactured by Chemours Corporation), "Flemion" (registered trademark) (manufactured by AGC Corporation), "Neosepta" (registered trademark) (manufactured by Atoms Corporation), "Selemion" (registered trademark) (manufactured by AGC Corporation), and "Sustainion" (registered trademark) (manufactured by Dioxide Materials Corporation).

[0052] <Anode electrode> The carbon dioxide electrolysis cell of the present disclosure has an anode electrode. The anode electrode is not particularly limited as long as it is made of a material that can oxidize water to produce oxygen and hydrogen ions, and can be selected from, for example, known anode electrodes used in carbon dioxide electrolysis cells.

[0053] Examples of materials for the anode electrode include metals such as iridium, platinum, palladium, and nickel; alloys containing these metals; intermetallic compounds containing these metals; binary metal oxides such as iridium oxide, manganese oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, and ruthenium oxide; ternary metal oxides such as Ni-Co-O, Ni-Fe-O, La-Co-O, Ni-La-O, and Sr-Fe-O; quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O; and metal complexes such as Ru complexes and Fe complexes. The anode electrode may be, for example, a composite electrode in which these materials are laminated on a substrate. The anode electrode may have various shapes such as mesh, wire, particle, porous, thin film, and island shapes. [Example]

[0054] The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited to the following examples. The matters shown in the following examples may be appropriately changed without departing from the spirit of the present disclosure.

[0055] [Preparation of carbon dioxide reduction electrode] Example 1 Carbon paper (CP) (product name: SIGRACET (registered trademark) 28BC, manufactured by SGL CARBON) was cut into a 2 cm square and used as a cathode gas diffusion layer. When the cross section of the cut CP in the thickness direction was observed using a scanning electron microscope (SEM) [trade name: GeminiSEM 460, manufactured by Carl Zeiss], it was confirmed that the CP had a structure in which a microporous layer (MPL), which is a porous body formed from conductive graphite particles, was provided on a layer made of a sintered body of conductive carbon fiber (i.e., a conductive fiber layer). Figure 1 shows an SEM image (magnification: 300x) of a cross section of the CP in the thickness direction.

[0056] The thickness of the conductive fiber layer was measured by the method described above and was found to be 116 μm. The thickness of the MPL was measured by the method described above and was found to be 72 μm. The pore size of the MPL was measured by the previously described method and was found to be 0.5 μm.

[0057] Next, using an arc plasma device (product name: Arc Plasma Nanoparticle Formation Device, model: APD-1S-C, manufactured by Advance Riko Co., Ltd.), Cu particles were deposited by arc plasma deposition on the MPL side of the cut CP. Specifically, the cut CP was placed in the arc plasma device using imide tape so that the MPL side was exposed, and then Cu was evaporated in a vacuum to generate Cu particles, which were then attached to the MPL side of the CP. The arc plasma conditions were set to a voltage of 120 V, a capacitor capacitance of 1080 μF, and 500 discharges. In this manner, a carbon dioxide reduction electrode of Example 1 was produced, which had a layer structure of cathode gas diffusion layer (conductive fiber layer / MPL) / cathode catalyst layer (Cu particle layer).

[0058] <Comparative Example 1> Carbon paper (CP) (product name: Toray Paper TGP-H-060, thickness: 190 μm, manufactured by Toray Industries, Inc.) was cut into 2 cm square pieces and used as the cathode gas diffusion layer. This cut CP was made of a sintered body of conductive carbon fiber, and corresponds to the so-called conductive fiber layer.

[0059] Next, using an arc plasma device (product name: Arc Plasma Nanoparticle Formation Device, model: APD-1S-C, manufactured by Advance Riko Co., Ltd.), Cu particles were vapor-deposited onto one side of the cut CP by arc plasma deposition. Specifically, the cut CP was placed in the arc plasma device using imide tape, and Cu was evaporated in a vacuum to generate Cu particles, which were then attached to one side of the CP. The arc plasma conditions were set to a voltage of 120 V, a capacitor capacitance of 1080 μF, and 500 discharge cycles. In this way, a carbon dioxide reduction electrode of Comparative Example 1 was prepared, having a layer structure of a cathode gas diffusion layer (conductive fiber layer) / cathode catalyst layer (Cu particle layer).

[0060] [Preparation of electrode body] An electrode assembly was fabricated using a carbon dioxide reduction electrode and an electrolyte. First, the electrolyte was subjected to the following pretreatment. An electrolyte (trade name: Sustainion (registered trademark) X37-50 Grade 60 Membrane, an anion exchange membrane, thickness: 50 μm, manufactured by Dioxide Materials) was immersed in an electrolytic solution (1 M KOH aqueous solution, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) for 24 hours. The electrolyte was removed from the electrolytic solution, and the surface of the electrolyte was washed with pure water.

[0061] (1) Production Example 1 (Carbon Dioxide Reduction Electrode: Example 1) The pretreated electrolyte and the carbon dioxide reduction electrode of Example 1 were overlapped so that the electrolyte was in contact with the surface of the cathode catalyst layer of the carbon dioxide reduction electrode of Example 1 facing the Cu particle layer, and then the resultant was press-molded at room temperature (25°C) using a press (product name: small heat press, model: H300-05, manufactured by AS ONE Corporation; the same applies hereinafter) to produce an electrode assembly of Production Example 1 having a layer structure of a carbon dioxide reduction electrode [cathode gas diffusion layer (conductive fiber layer / MPL) / cathode catalyst layer (Cu particle layer)] / electrolyte.

[0062] The pressing conditions were a pressure of 5 MPa and a pressing time of 5 minutes. To keep the electrolyte moist, Kimwipes (registered trademark) moistened with pure water was placed in contact with the surface of the electrolyte that was not overlapped with the carbon dioxide reduction electrode during press molding. The following Production Example 2 was also subjected to similar press molding under the same pressing conditions.

[0063] (2) Production Example 2 (Carbon Dioxide Reduction Electrode: Comparative Example 1) The pretreated electrolyte and the carbon dioxide reduction electrode of Comparative Example 1 were overlapped so that the electrolyte was in contact with the surface of the cathode catalyst layer of the carbon dioxide reduction electrode of Comparative Example 1 facing the Cu particle layer. The resulting mixture was then press-molded using a press at room temperature (25°C) to produce an electrode body of Production Example 2 having a layer structure of carbon dioxide reduction electrode [cathode gas diffusion layer (conductive fiber layer) / cathode catalyst layer (Cu particle layer)] / electrolyte.

[0064] [Evaluation: Selectivity] The selectivity of the cathode gas diffusion layer was evaluated using the electrode assembly of Production Example 1 equipped with the carbon dioxide reduction electrode of Example 1, and the electrode assembly of Production Example 2 equipped with the carbon dioxide reduction electrode of Comparative Example 1. The selectivity of the cathode gas diffusion layer was evaluated using the faradaic efficiency as an index. The faradaic efficiency indicates the proportion of the current used in the reaction to the product of the current that has been reacted. First, the electrode assembly was incorporated into a gas diffusion half-cell (see Figure 2). As shown in Figure 2, the half-cell has a structure in which the electrolyte is stored on one side of the electrode assembly (the electrolyte side) and CO2 gas can be supplied to the other side of the electrode assembly (the cathode gas diffusion layer side of the carbon dioxide reduction electrode). A Cu electrode was used as the working electrode (WE), an Ag / AgCl electrode as the reference electrode (RE), and a carbon rod as the counter electrode (CE). A 1 M KHCO3 aqueous solution was used as the electrolyte. The KHCO3 aqueous solution was bubbled with CO2 gas (purity: 99.99%) and then adjusted to a pH of 7.9 before use. Next, at room temperature (25°C), CO2 gas (purity: 99.99%) was flowed at a flow rate of 5 cc / min to the cathode gas diffusion layer side of the carbon dioxide reduction electrode to replace the gas in the line with CO2 gas. Next, a voltage was applied to the cathode gas diffusion layer side of the carbon dioxide reduction electrode so that the potential between the working electrode and the reference electrode was -1.4 V, -2.0 V, or -2.5 V, based on an Ag / AgCl reference electrode. After starting the voltage application and confirming that current was flowing, the flow rate of the generated gas was measured for 1.5 to 2 minutes using a flow meter (trade name: Defender® 530+, manufactured by Mesa Labs) connected to the exhaust line of a gas chromatograph (trade name: Nexis® GC-2030, manufactured by Shimadzu Corporation). After measuring the flow rate of the generated gas, the composition of the generated gas was analyzed using the gas chromatograph on the flow path. The generated gas was constantly circulated through the gas chromatograph flow path, and the flow path was switched at specified intervals to introduce the generated gas into a column (trade name: MICROPACKED-ST, manufactured by Shinwa Chemical Industry Co., Ltd.) and perform analysis. From the measurement results of the product gas flow rate and the analysis results of the product gas composition, the production amounts of hydrogen (H2), carbon monoxide (CO), methane (CH4), and ethylene (C2H4) were calculated and converted into electric charge. From the ratio of the converted electric charge to the actual current value, the production efficiency of hydrogen, carbon monoxide, methane, and ethylene (so-called Faraday efficiency) was calculated, and the selectivity of the cathode gas diffusion layer was evaluated. The composition of the produced gas and the Faraday efficiency of each component are shown in Table 1 and FIG. The Faraday efficiencies shown in Table 1 are values ​​after correcting the total to 100.0%. A component with a higher faradaic efficiency (unit: %) is more likely to produce a carbon dioxide reduction electrode, that is, a component with a higher selectivity for a carbon dioxide reduction electrode.

[0065] [Table 1]

[0066] 3, the carbon dioxide reduction electrode of Example 1 exhibited higher methane selectivity than the carbon dioxide reduction electrode of Comparative Example 1. Furthermore, the carbon dioxide reduction electrode of Example 1 exhibited higher selectivity than the carbon dioxide reduction electrode of Comparative Example 1 for carbon monoxide and ethylene, which are C-based products other than methane. The above results demonstrate that a cathode gas diffusion layer having an MPL, which is a porous body formed of conductive particles on a conductive fiber layer, can improve the methane selectivity, carbon monoxide selectivity, and ethylene selectivity of a carbon dioxide reduction electrode.

Claims

1. A conductive fiber layer; a microporous layer provided on the conductive fiber layer and being a porous body formed from conductive particles; A cathode gas diffusion layer for a carbon dioxide reduction electrode comprising:

2. 2. The cathode gas diffusion layer for a carbon dioxide reduction electrode according to claim 1, wherein the material of the conductive fiber layer is carbon fiber.

3. 2. The cathode gas diffusion layer for a carbon dioxide reduction electrode according to claim 1, wherein the conductive particles are carbon particles.

4. A cathode gas diffusion layer for a carbon dioxide reduction electrode according to any one of claims 1 to 3; a cathode catalyst layer provided on the surface of the cathode gas diffusion layer for the carbon dioxide reduction electrode facing the microporous layer; A carbon dioxide reduction electrode having

5. A carbon dioxide electrolysis cell comprising the carbon dioxide reduction electrode according to claim 4, an electrolyte, and an anode electrode.

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