Manufacturing method for gas diffusion layer, cathode, ion exchange membrane-electrode joint and solid electrolyte type electrolytic apparatus

Abstract

To provide a manufacturing method for a gas diffusion layer with high electrolytic activity, a cathode comprising the gas diffusion layer, an ion exchange membrane-electrode joint, and a solid electrolyte type electrolytic apparatus.SOLUTION: There is provided a manufacturing method for a gas diffusion layer 10 having a carbon fiber layer 10a containing carbon fiber and a porous layer 10c containing a conductive substance and a binding resin, where a conductive substance P is applied from a surface 10b side of the carbon fiber layer 10a of a laminate having the carbon fiber layer 10a and the porous layer 10c by a spraying method or a gas phase method.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The technology disclosed herein relates to a method for producing a gas diffusion layer, a cathode, an ion exchange membrane-electrode assembly, and a solid electrolyte electrolysis device. [Background technology]

[0002] Carbon dioxide is emitted when energy is extracted from fossil fuels, etc. An increase in the concentration of carbon dioxide in the atmosphere is said to be one of the causes of global warming. Carbon dioxide is an extremely stable substance, so there have been few ways to utilize it in the past. However, in an era where global warming is becoming more serious, there is a demand for new technologies to convert carbon dioxide into other substances and reuse them as resources. For example, progress is being made in the development of carbon dioxide reduction devices that can directly reduce gaseous carbon dioxide.

[0003] Among carbon dioxide reduction devices, polymer electrolyte electrolysis devices that use polymer electrolytes have attracted attention because they can directly reduce carbon dioxide in the gas phase and can sufficiently reduce the resistance to ion migration by using a thin-film polymer electrolyte. A cathode for carbon dioxide reduction generally has a structure in which a catalyst layer containing a catalyst is laminated on a gas diffusion layer. For example, a gas diffusion layer generally uses a conductive porous material to send carbon dioxide to the catalyst layer, and various studies are being conducted on improving the conductivity, gas diffusion, etc.

[0004] For example, Patent Document 1 proposes a gas diffusion electrode containing carbon fiber, carbon powder, and a fluororesin containing a hydrophilic organic solvent as a binder. In this method, a doctor blade method is used to apply the mixture to the carbon fiber, and then the electrode is immersed in water to solidify the resin and form pores. Furthermore, Patent Document 2 discloses a method in which a mixture of carbon fibers, carbon powder, and a thermosetting resin is molded into a sheet and then thermally cured to form a gas diffusion layer. Furthermore, Patent Document 3 discloses a gas diffusion electrode for a fuel cell in which the conductivity is improved by forming a metal film on a conductive porous body such as carbon fiber by sputtering. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-31515 [Patent Document 2] JP 2010-15908 A [Patent Document 3] JP 2007-095586 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the doctor blade method disclosed in Patent Document 1, an excessive amount of the mixture is applied to the carbon fiber, so that the amount of the mixture applied cannot be controlled, and it is difficult to ensure the voids necessary for gas diffusion. In addition, there is a problem that the conductive material adheres to the surface of the gas diffusion layer on the side where the catalyst layer is laminated, and acts as an active site for an unintended reaction (side reaction), which is an adverse effect. In addition, it is difficult to prepare a uniform and large-area gas diffusion layer and electrode, and there are also problems that there are many post-processes after application, which tend to increase the manufacturing cost.

[0007] The method disclosed in Patent Document 2 has the problem that the thermosetting resin and the thermosetting process are relatively expensive, and it is difficult to control the structure of the product by thermosetting, making it difficult to control the physical properties. In addition, as with Patent Document 1, there is also the problem that it is difficult to obtain sufficient pores for gas diffusion.

[0008] In the invention disclosed in Patent Document 3, when a metal is sputtered only onto the gas diffusion layer, there is a risk that the metal particles will get around to the catalyst layer side and act as another catalyst, which may cause a reaction different from the CO2 reduction reaction (for example, an H2 production reaction due to water reduction), just like the problem in Patent Document 1, and there is a problem that it cannot be applied to an electrolysis cell for CO2 reduction.

[0009] The technology of the present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to solve the above problem by providing a method for producing a gas diffusion layer having high electrolytic activity, a cathode including the gas diffusion layer, an ion exchange membrane-electrode assembly, and a solid electrolyte electrolysis device. [Means for solving the problem]

[0010] <1> A method for producing a gas diffusion layer having a carbon fiber layer containing carbon fibers and a porous layer containing a conductive material 1 and a binder resin, the method comprising applying a conductive material 2 to a surface side of the carbon fiber layer of a laminate having the carbon fiber layer and the porous layer by a spray method or a vapor phase method.

[0011] <2> The porous layer has a porosity of 10 to 60% and an average pore size of 10 to 500 nm. <1> A method for producing the gas diffusion layer according to claim 1. <3> The conductive material 1 and the conductive material 2 are each independently one or more selected from the group consisting of carbon materials and metals. <1> or <2> A method for producing the gas diffusion layer according to claim 1.

[0012] <4> A mixed solution containing the conductive material 2 and a binder resin is sprayed onto the surface side of the carbon fiber layer. <1> ~ <3> 13. A method for producing the gas diffusion layer according to any one of claims 1 to 12. <5> The mixed solution has a total amount of the conductive material 2 and the binder resin in the mixed solution of 0.05 to 2 mg / cm 2 Spray so that <4> A method for producing the gas diffusion layer according to claim 1. <6> The conductive material 2 is applied to the surface side of the carbon fiber layer by vapor deposition or sputtering. <1> ~ <3> 13. A method for producing the gas diffusion layer according to any one of claims 1 to 12. <7> The amount of the conductive material 2 applied is 0.5 to 5 μg / cm 2 is <6> A method for producing the gas diffusion layer according to claim 1.

[0013] <8> <1> ~ <7> a gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to any one of the above items 1 to 5, the gas diffusion layer comprising: a carbon fiber layer containing a conductive material 2 and carbon fibers, the carbon fibers being partly coated with the conductive material 2; and a porous layer containing a conductive material 1 and a binder resin; and a cathode having a catalyst layer on the porous layer side.

[0014] <9> a gas diffusion layer comprising: a carbon fiber layer containing a conductive material 2 and carbon fibers, the carbon fibers being partially coated with the conductive material 2, and the conductive material 2 being present from the surface to a position of 60% or more in the depth direction; and a porous layer containing a conductive material 1 and a binder resin, having a porosity of 10 to 60% and an average pore size of 10 to 500 nm; and A catalyst layer on the porous layer side A cathode having

[0015] <10> The carbon fiber layer further contains a binder resin, and the amount of the conductive material 2 and the binder resin supported is 0.05 to 2 mg / cm 2 is <8> or <9> 2. The cathode according to claim 1 . <11> The conductive material 1 and the conductive material 2 are each independently one or more selected from the group consisting of carbon materials and metals. <8> ~ <10> 2. The cathode according to any one of claims 1 to 11.

[0016] <12> <8> ~ <11> 1. An ion exchange membrane-electrode assembly comprising the cathode according to any one of 1 to 8, a solid electrolyte, and an anode. <13> The solid electrolyte is an anion exchange membrane. <12> The ion exchange membrane-electrode assembly according to claim 1.

[0017] <14> <8> ~ <11> a cathode according to any one of the above items; an anode that constitutes a pair of electrodes together with the cathode; a solid electrolyte disposed between and in contact with the cathode and the anode; a voltage application unit that applies a voltage between the cathode and the anode; A solid electrolyte electrolysis device having the above structure. <15> The solid electrolyte is an anion exchange membrane. <14> The solid electrolyte electrolysis device according to claim 1. Effect of the Invention

[0018] According to the technique of the present disclosure, it is possible to provide a method for producing a gas diffusion layer having high electrolytic activity, a cathode including the gas diffusion layer, an ion exchange membrane-electrode assembly, and a solid electrolyte electrolysis device. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic diagram of an ion exchange membrane-electrode assembly preferably used in the present embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a laminate of a gas diffusion layer and a catalyst layer. [Diagram 3] 3A to 3C are schematic diagrams showing an example of a method for producing a gas diffusion layer preferably used in the present embodiment. [Figure 4] FIG. 1 is a schematic diagram of a solid electrolyte electrolysis device suitably used in the present embodiment. [Diagram 5] 2 is an electron microscope image of a cross section of the carbon fiber of the gas diffusion layer of Example 1. [Figure 6] 4 is an electron microscope image of a cross section of the carbon fiber of the gas diffusion layer of Example 2. [Figure 7] 1 is an electron microscope image of a cross section of carbon fibers in a gas diffusion layer of Comparative Example 2. [Figure 8] 1 shows the depth distribution of the ratio of detected fluorescent X-ray counts of Ag / C near the interface between the carbon fiber layer and the porous layer in the gas diffusion layer of Example 1. [Figure 9]13 shows the depth distribution of the ratio of the number of detected fluorescent X-rays of S / C near the interface between the carbon fiber layer and the porous layer in the gas diffusion layer of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present disclosure. In addition, unless otherwise specified, a numerical range of "lower limit value to upper limit value" described in this specification means not less than the lower limit value and not more than the upper limit value.

[0021] <Method of manufacturing gas diffusion layer> The method for producing a gas diffusion layer according to the present embodiment is a method for producing a gas diffusion layer having a carbon fiber layer containing carbon fibers and a porous layer containing a conductive material 1 and a binder resin, in which the conductive material 2 is applied by a spray method or a gas phase method to a surface side of the carbon fiber layer of a laminate having the carbon fiber layer and the porous layer. The gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to the present embodiment can be applied not only to a carbon dioxide reduction electrolysis device but also to a water electrolysis device, a fuel cell, a gas diffusion electrode for an air battery, and the like. However, in this specification, the method for manufacturing a gas diffusion layer in a carbon dioxide reduction electrolysis device will be mainly described.

[0022] First, the structure of the gas diffusion layer will be described. A schematic diagram of an ion exchange membrane-electrode assembly suitable for use in this embodiment is shown in Fig. 1. Fig. 1 shows an ion exchange membrane-electrode assembly 50 having a gas diffusion layer 10, a catalyst layer 20, a solid electrolyte 30, and an anode 40. Details of the ion exchange membrane-electrode assembly 50 will be described later. As shown in FIG. 1, the gas diffusion layer 10 is adjacent to the catalyst layer 20, and takes in carbon dioxide (CO 2 ) from the outside air and supplies it to the catalyst layer 20.

[0023] FIG. 2 is a schematic diagram of a laminate of a gas diffusion layer 10 and a catalyst layer 20. The gas diffusion layer 10 has a carbon fiber layer 10a and a porous layer 10c. The catalyst layer 20 contains a catalyst 24 and is adjacent to the gas diffusion layer 10, and more precisely, is adjacent to the porous layer 10c. In FIG. 2, the depth direction of the carbon fiber layer 10a as viewed from the surface 10b of the carbon fiber layer 10a is indicated by an arrow D1. The depth direction of the carbon fiber layer 10a can be referred to as the lamination direction of the gas diffusion layer 10 and the catalyst layer 20, or the thickness direction of the carbon fiber layer 10a.

[0024] Fig. 3 is a schematic diagram showing an example of a method for producing a gas diffusion layer preferably used in this embodiment. Fig. 3 shows a state in which a conductive material P (conductive material 2) is applied from a coating device C to a surface 10b of the carbon fiber layer 10a by a spray method or a gas phase method in a gas diffusion layer 10 of a laminate having a carbon fiber layer 10a and a porous layer 10c, and the conductive material P (conductive material 2) is attached to the carbon fiber layer 10a in a depth direction D1.

[0025] In the manufacturing method of the gas diffusion layer suitably used in this embodiment, "applying the conductive material 2 from the surface side of the carbon fiber layer by a spray method or a gas phase method" means applying the conductive material P (conductive material 2) from a coating device C toward the surface 10b of the carbon fiber layer 10a in Fig. 3, and means applying the conductive material P (conductive material 2) not only to the surface 10b of the carbon fiber layer 10a but also to the inside in the depth direction D1 of the carbon fiber layer 10a. Specifically, the conductive material 2 can be applied from the surface 10b in the depth direction D1 to a position that is 60% or more of the carbon fiber layer thickness. In FIG. 3, the application direction D2 of the conductive substance P (conductive substance 2) is shown perpendicular to the surface 10b of the carbon fiber layer 10a, but it does not necessarily have to be perpendicular, and the conductive substance P (conductive substance 2) may be applied at an acute or obtuse angle to the surface 10b.

[0026] Here, when the carbon fiber layer is, for example, a hexahedral flat plate, all six faces of the carbon fiber layer are the surface of the carbon fiber layer. However, in the manufacturing method of the gas diffusion layer suitably used in this embodiment, the carbon fiber layer 10a adjacent to the porous layer 10c is used, so that the conductive material P (conductive material 2) applied from the coating device C does not come into contact with the adjacent surface of the porous layer 10c among the surfaces of the carbon fiber layer 10a. Therefore, in this embodiment, the "surface of the carbon fiber layer" can be rephrased as the "exposed surface of the carbon fiber layer". Furthermore, among the surfaces of the carbon fiber layer, the surface having the larger area is particularly treated as the "surface of the carbon fiber layer" in the manufacturing method of the gas diffusion layer according to this embodiment. That is, in FIG. 3, the surface 10b of the carbon fiber layer 10a is mainly referred to as the "surface of the carbon fiber layer". However, this does not exclude the conductive material P (conductive material 2) applied from the coating device C penetrating into the side surface of the carbon fiber layer 10a and adhering to the side surface and inside of the carbon fiber layer 10a.

[0027] A carbon fiber layer is usually a porous layer with a structure in which carbon fibers that spread in a mesh-like manner in a planar direction are laminated in a direction perpendicular to the planar direction. Therefore, the carbon fiber layer has low electrical conductivity in the vertical direction (the same direction as the depth direction D1 in Figure 2 and the opposite direction), and electrical resistance is likely to be relatively large, which causes a decrease in electrolysis efficiency due to voltage drop during electrolysis. Since the potential drop due to resistance is proportional to the current density, this decrease in efficiency is particularly noticeable when a large current density is applied. This problem occurs not only in CO2 electrolysis but also in water electrolysis, fuel cells, and air batteries. Therefore, gas diffusion electrodes often use gas diffusion layers in which highly conductive carbon powder (amorphous carbon; carbon black) is mixed in addition to the carbon substrate. However, as described in Patent Documents 1 to 3, conventional methods of imparting conductivity have had problems such as difficulty in securing voids necessary for gas diffusion, and conductive materials adhere to the surface of the gas diffusion layer on which the catalyst layer is laminated, causing adverse effects such as acting as active sites for unintended reactions (side reactions).

[0028] This is believed to be because when the surface of the gas diffusion layer is solidly coated by the doctor blade method described in Patent Document 1 or the gas diffusion layer is immersed in a solution containing a conductive material, the surface of the carbon fiber is almost entirely coated with the conductive material, resulting in a large coating thickness. As a result, the gas diffusion layer obtained by the conventional method of imparting conductivity loses the hydrophobicity inherent to the carbon fiber, and the mesh of the carbon fiber is covered with a coating film with a large coating thickness, impairing the gas diffusibility.

[0029] In contrast, the method for manufacturing a gas diffusion layer according to the present embodiment makes it possible to manufacture a gas diffusion layer that has high electrical conductivity, hydrophobicity, and electrolytic activity in the depth direction. By applying the conductive substance 2 from the surface side of the carbon fiber layer by a spray method or a gas phase method, it is possible to adhere the conductive substance 2 to part of the surface of the carbon fiber, thereby maintaining the hydrophobicity of the carbon fiber and obtaining a highly hydrophobic gas diffusion layer. In addition, it is considered that the conductive substance 2 applied from the surface side of the carbon fiber layer reaches the surface of the carbon fibers deep inside the carbon fiber layer through the pores in the carbon fiber layer, and therefore a gas diffusion layer with high conductivity in the depth direction can be obtained.

[0030] Furthermore, it is believed that the coating thickness of the conductive material 2 on the carbon fiber surface can be reduced, making it possible to maintain gas diffusivity. In addition, since the gas diffusion layer has high hydrophobicity, when the gas diffusion layer is used in an electrolysis device containing an electrolyte, the electrolyte leaking through the catalyst layer can be prevented from being soaked by the gas diffusion layer, and the supply of CO2 to the catalyst layer is less likely to be impaired. Therefore, it is believed that the CO2 reduction reaction in the catalyst layer can be improved, thereby increasing the electrolytic activity. The method of applying the conductive substance 2 will be described in more detail below.

[0031] [Method of applying conductive material 2] In the method for producing a gas diffusion layer according to this embodiment, the conductive material 2 is applied from the surface side of the carbon fiber layer by a spray method or a vapor phase method. By applying the conductive material 2 by a spray method or a gas phase method, the electrical conductivity of the carbon fiber layer can be improved in a simple and efficient manner without adversely affecting the catalyst layer while maintaining the porous structure of the carbon fibers. By applying the conductive material 2 by a spray method or a gas phase method, fine conductive material particles of a μm scale or less can be successively deposited on the carbon fibers. Therefore, it is easy to control the amount of the conductive material 2 carried on the carbon fibers, and the μm scale pores of the carbon fibers are less likely to be blocked. In addition, since the same equipment as that used in the production process of the catalyst layer can be used, the production cost can also be reduced.

[0032] The components applied by the spray method or gas phase method need only contain the conductive substance 2, and may be a mixture containing the conductive substance 2, a binder resin, a solvent, etc., or may be the conductive substance 2 alone. Examples of methods for applying the conductive material 2 include a spray method (also called a spray method) in which the conductive material 2 is sprayed, and a vapor phase method such as a deposition / sputtering method in which the conductive material 2 is applied by deposition or sputtering.

[0033] (Conductive substance 2) The conductive material 2 may be, for example, a carbon material or a metal. Examples of the carbon material include carbon black (furnace black, acetylene black, ketjen black, medium thermal carbon black, etc.), activated carbon, graphite, carbon nanotubes, carbon nanofibers, carbon nanohorns, graphene nanoplatelets, nanoporous carbon, and the like. Among these, carbon black is preferred from the viewpoints of small primary particle diameter and low material costs. Examples of the metal include silver, copper, aluminum, nickel, iron, and indium, and silver is preferred from the viewpoints of high stability and electrical conductivity. The conductive material 2 may contain only one of the above components, or two or more of them.

[0034] From the viewpoint of more efficiently applying the conductive material 2 to the carbon fiber layer by spraying, the conductive material 2 is preferably in particulate form. The conductive material particles preferably have a primary particle diameter of 10 to 100 nm, more preferably 10 to 50 nm. The primary particle diameter of the conductive material particles can be measured by a transmission electron microscope. From the same viewpoint, it is preferable that the secondary particle size (particle size of the aggregate) of the conductive material particles is small.

[0035] (Binding resin) The binder resin is a component for attaching the conductive material 2 to the carbon fiber, and it is preferable to use an ionomer. In order not to impair the conductivity of the gas diffusion layer, the ionomer is preferably conductive, and is more preferably a polymer electrolyte. It is further preferable that the polymer electrolyte is an ion exchange resin. The ion exchange resin may be a cation exchange resin or an anion exchange resin, but is preferably an anion exchange resin. In particular, when an anion exchange resin is used, the anion exchange resin itself has the ability to adsorb carbon dioxide, and this, together with the ease of ion transfer of the ion exchange resin, makes it possible to greatly improve the efficiency of electrolysis of carbon dioxide.

[0036] Examples of the cation exchange resin include fluororesins having sulfonic groups and styrene-divinylbenzene copolymers having sulfonic groups. Commercially available products can also be used, such as Nafion (manufactured by Chemours), Aquivion (manufactured by Solvay Specialty Polymers), DIAION (manufactured by Mitsubishi Chemical), and Fumasep (manufactured by FUMATECH). Examples of anion exchange resins include resins having one or more ion exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. Commercially available products can also be used, such as Sustainion (manufactured by Dioxide Materials), Fumasep (manufactured by FUMATECH), PENTION (manufactured by Xergy), DURION (manufactured by Xergy), NEOSEPTA (manufactured by Astom), and TOYOPEARL (manufactured by Tosoh).

[0037] From the viewpoint of improving electrical conductivity, the anion exchange resin is required to have a basic site density of 2.0 to 5.0 mmol / cm in a dry state. 3 and preferably 2.5 mmol / cm 3 More than 4.5mmol / cm 3 More preferably, it is less than 2.9 mmol / cm 3 More than 4.5mmol / cm 3 It is even more preferable that it is less than 1000 .mu.m. The base site density of anion exchange resin is 1 It can be obtained from the signal integral value when performing H NMR measurement. Furthermore, with respect to an anion exchange resin, a dry state means that the anion exchange resin does not contain free water; for example, the anion exchange resin can be brought into a dry state by heating in a vacuum.

[0038] (solvent) The solvent is used as a dispersion medium for the conductive material, and it is preferable to use a solvent that does not react with the conductive material 2 and the binder resin. Specific examples include alcohol, water, toluene, dimethyl sulfoxide, etc., and among these, alcohol is preferable, and ethanol is more preferable. The solvent may be used alone or in combination of two or more.

[0039] In the mixed solution containing the conductive substance 2 and the binder resin, the ratio (a / r) of the mass (a) of the conductive substance 2 to the mass (r) of the binder resin is preferably 1 / 1 to 10 / 1, more preferably 2 / 1 to 8 / 1, and even more preferably 3 / 1 to 7 / 1.

[0040] When a metal is used as the conductive material 2, it is preferable to apply the conductive material 2 to the carbon fiber layer by vapor deposition or sputtering.

[0041] As described above, when the spraying method is adopted, it is preferable to spray a mixed solution containing the conductive material 2 and the binder resin from the surface side of the carbon fiber layer, and when the vapor deposition / sputtering method is adopted, it is preferable to apply the conductive material 2 from the surface side of the carbon fiber layer by vapor deposition or sputtering. Next, the spray method and the deposition / sputtering method will be explained.

[0042] (spray method) In the spraying method, for example, a mixed solution containing the conductive material 2 and a binder resin is sprayed from the surface side of the carbon fiber layer. Specifically, for example, a spraying device is used as the coating device C shown in Fig. 3, and the mixed solution is sprayed from the spraying device toward the surface of the carbon fiber layer. When spraying the mixed solution, it is preferable to heat the carbon fiber layer to 65 to 85°C and mix the mixed solution with pressurized air to form a mist. In addition, in order to prevent the conductive material 2 from getting around the catalyst layer side surface of the carbon fiber layer, it is preferable to provide a porous layer on the catalyst layer side surface of the carbon fiber layer. The mixed solution may be a solution containing the conductive material 2 and the binder resin in the amounts [ratio (a / r)] described above.

[0043] From the viewpoint of the balance of the electrical conductivity, hydrophobicity, and gas diffusivity of the carbon fiber layer, the total amount of the conductive material 2 and the binder resin in the mixed solution is 0.05 to 2 mg / cm 2 It is preferable to spray so that the concentration is 0.10 to 1.50 mg / cm. 2 It is more preferable to spray so that the concentration is 0.15 to 1.00 mg / cm.2 It is more preferable to spray the mixture so as to obtain the above-mentioned. By spraying the mixed solution in the above range, the amounts of the conductive material 2 and the binder resin carried in the carbon fiber layer are in the same range as the total amount of the conductive material 2 and the binder resin in the mixed solution.

[0044] (Evaporation / sputtering method) In the deposition / sputtering method, for example, a conductive material 2 (particularly, a metal) is applied from the surface side of the carbon fiber layer by deposition or sputtering. By depositing clusters or atoms of the conductive substance 2 on a portion of the carbon fiber, it is possible to impart conductivity in the depth direction while maintaining the hydrophobicity and gas diffusivity of the carbon fiber layer. Specifically, for example, a vapor deposition device or a sputtering device is used as the coating device C shown in Fig. 3, and the conductive material 2 is applied from the vapor deposition device or the sputtering device to the surface of the carbon fiber layer. When applying the conductive material 2, it is preferable to perform vapor deposition or sputtering while replacing the inside of the device with a dilute inert gas (for example, argon gas). The amount of the conductive material 2 applied is 0.5 to 5 μg / cm from the viewpoint of the balance of the conductivity, hydrophobicity, and gas diffusivity of the carbon fiber layer. 2 is preferably 0.7 to 4 μg / cm 2 More preferably, it is 1 to 3 μg / cm 2 It is more preferable that: By providing the conductive material 2 in the above range, the amount of the conductive material 2 supported in the carbon fiber layer will be in the same range as the provided amount.

[0045] [Gas diffusion layer] The gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to this embodiment has a carbon fiber layer and a porous layer.

[0046] (Carbon fiber layer) The carbon fiber layer used in the method for producing a gas diffusion layer according to this embodiment contains carbon fibers. The carbon fiber may be carbon paper or nonwoven fabric, for example, graphite carbon, glassy carbon, or the like. The carbon fiber layer may further include a metal mesh such as titanium or SUS steel, or may be made of carbon fiber. It is preferable that the carbon fiber layer does not contain a binder resin, that is, the content of the binder resin in the carbon fiber layer is 0 mass %.

[0047] (porous layer) The porous layer used in the manufacturing method of the gas diffusion layer according to this embodiment contains a conductive material 1 and a binder resin. The porous layer has a porous structure in which the conductive materials are laminated one on top of another with voids formed therebetween. By providing the gas diffusion layer with a porous layer in addition to the carbon fiber layer, it is possible to prevent the conductive material 2 from adhering to the surface of the gas diffusion layer adjacent to the catalyst layer without impairing the electrical conductivity and gas diffusibility of the gas diffusion layer. The porous layer is preferably located between the carbon fiber layer and the catalyst layer. The porous layer may be a single layer or two or more layers.

[0048] The porous layer preferably has a porosity of 10 to 60% and an average pore size of 10 to 500 nm. A porosity of 10% or more improves the gas diffusion rate, and a porosity of 60% or less improves the support efficiency of the catalyst layer. In addition, an average pore size of 10 μm or more improves the gas diffusion rate, and an average pore size of 500 μm or less improves the support efficiency of the catalyst layer. The porosity of the porous layer is more preferably from 10 to 50%, and further preferably from 12 to 40%. The average pore size of the porous layer is more preferably from 30 to 450 nm, and further preferably from 60 to 400 nm.

[0049] The porosity and average pore size of the porous layer can be measured by mercury intrusion porosimetry (JIS Z 8890:2017) or X-ray CT (Computed Tomography).

[0050] The conductive substance 1 and binder resin may be the same as the conductive substance 2 and binder material described as components of the mixed solution used when applying the conductive substance 2 to the carbon fiber layer by spraying. That is, the conductive substance 1 contained in the porous layer can be a carbon material or a metal, and can be any material that is gas permeable, conductive, and capable of capturing nanoparticles, and can be in the form of a sheet such as a graphene sheet, or in the form of a mesh such as titanium foam.

[0051] Of these, carbon black, activated carbon, graphite, carbon nanotubes, carbon nanofibers, nanoporous carbon, aluminum, and titanium are preferred, and carbon black and carbon nanotubes are more preferred, as the conductive substance 1. Only one type of conductive substance 1 may be used, or two or more types may be used.

[0052] The content of the conductive substance 1 in the porous layer is preferably 50 to 99.9% by mass, and more preferably 70 to 99% by mass, and the content of the binder resin in the porous layer is preferably 0.1 to 50% by mass, and more preferably 1 to 30% by mass. The porous layer may be a commercially available gas diffusion layer in which a carbon fiber layer and a porous layer are laminated.

[0053] The gas diffusion layer according to the present embodiment manufactured as described above has a carbon fiber layer containing a conductive material 2 and carbon fibers, with the carbon fibers being partly coated with the conductive material 2, and a porous layer containing a conductive material 1 and a binder resin.

[0054] The conductive material 2 in the carbon fiber layer is provided not only on the surface of the carbon fiber layer but also inside the carbon fiber layer in the depth direction by the manufacturing method of the gas diffusion layer preferably used in this embodiment. In other words, the conductive material 2 is present from the surface to a position that is 60% or more of the carbon fiber layer thickness in the depth direction. Here, the "surface of the carbon fiber layer" means the surface opposite to the surface adjacent to the porous layer, and refers to the surface 10b in Figs. 2 and 3. The location of the conductive material 2 from the surface of the carbon fiber layer in the depth direction is preferably 70% or more, more preferably 80% or more, and may be 100% of the thickness of the carbon fiber layer.

[0055] The depth from the surface of the carbon fiber layer to the location of the conductive material 2 can be confirmed by using a scanning electron microscope and a fluorescent X-ray analyzer. Specifically, an image is obtained with a scanning electron microscope to find the measurement location, and the sample is irradiated with an electron beam and the fluorescent X-rays emitted from the sample are dispersed with an X-ray analyzer. The depth distribution of the ratio of the detection number of the fluorescent X-rays of the conductive material 2 element / C or the binder resin / C near the interface between the carbon fiber layer and the porous layer in the gas diffusion layer can be measured. Here, "C" means carbon. For example, the magnification of the electron microscope is set to 100 to 500 times, and the count ratio is measured at each position near the interface between the carbon fiber layer and the porous layer. When the thickness of the carbon fiber layer is, for example, 315 μm, if it is confirmed that the conductive material exists from the interface to a position about 20 μm toward the carbon fiber layer, it can be said that the conductive material exists from the surface of the carbon fiber layer in the depth direction to a position that is 90% or more of the carbon fiber layer thickness.

[0056] For example, when Ag is applied as conductive material 2 to a carbon fiber layer by vapor deposition or sputtering, the depth distribution of the ratio of the detection counts of Ag / C fluorescent X-rays near the interface between the carbon fiber layer and the porous layer is measured. In addition, for example, when a mixed solution containing a conductive material 2 and a binder resin is sprayed onto a carbon fiber layer by a spray method using an ionomer having a sulfo group (S) as the binder resin, the depth direction distribution of the S / C fluorescent X-ray detection number ratio near the interface between the carbon fiber layer and the porous layer is measured. For example, by creating a graph with the count ratio of Ag / C or S / C on the vertical axis and the position of the detection target (Ag or S) on the horizontal axis, the position of the conductive material 2 present in the carbon fiber layer can be confirmed. A larger count ratio means that more conductive material 2 is present at each position in the carbon fiber layer.

[0057] The carbon fibers are partially coated with the conductive material 2, and the conductive material 2 is present even inside in the depth direction, so that the gas diffusion layer has high conductivity in the depth direction. It is sufficient that at least a part of the surface of the carbon fiber is coated with the conductive material 2, and the entire surface of the carbon fiber may be coated with the conductive material 2. The extent to which the carbon fiber is coated with the conductive material 2 can be confirmed by an electron microscope.

[0058] <Cathode> The cathode (negative electrode) according to this embodiment is manufactured by the manufacturing method of the gas diffusion layer according to this embodiment, and has a gas diffusion layer including a carbon fiber layer containing a conductive material 2 and carbon fibers, with the carbon fibers being partially coated with the conductive material 2, and a porous layer containing a conductive material 1 and a binder resin; and a catalyst layer on the porous layer side.

[0059] More specifically, the cathode (negative electrode) according to this embodiment has a gas diffusion layer including a carbon fiber layer containing a conductive material 2 and carbon fibers, the carbon fibers being partially coated with the conductive material 2, and the conductive material 2 being present from the surface to a position that is 60% or more in the depth direction, and a porous layer containing a conductive material 1 and a binder resin, and having a porosity of 10 to 60% and an average pore diameter of 10 to 500 nm; and a catalyst layer on the porous layer side.

[0060] The method for confirming the degree of coverage of the conductive material 2 on the carbon fibers and the location of the conductive material 2 in the carbon fiber layer is as described above. When the carbon fiber layer is produced by the spraying method in the method for producing a gas diffusion layer according to the present embodiment, the carbon fiber layer further contains a binder resin, and the amount of the conductive material 2 and the binder resin supported in the carbon fiber layer is 0.05 to 2 mg / cm from the viewpoint of the balance of the electrical conductivity, hydrophobicity, and gas diffusivity of the carbon fiber layer. 2 From the same viewpoint, the amount of the conductive material 2 and the binder resin carried in the carbon fiber layer produced by the spraying method is preferably 0.10 to 1.50 mg / cm. 2 More preferably, the concentration is 0.15 to 1.00 mg / cm. 2 It is more preferable that:

[0061] When the carbon fiber layer is produced by a vapor deposition / sputtering method in the method for producing a gas diffusion layer according to this embodiment, the amount of the conductive material 2 supported in the carbon fiber layer is 0.5 to 5 μg / cm from the viewpoint of the balance of the electrical conductivity, hydrophobicity, and gas diffusivity of the carbon fiber layer. 2 From the same viewpoint, the amount of the conductive material 2 carried in the carbon fiber layer produced by the vapor deposition / sputtering method is preferably 0.7 to 4 μg / cm 2 More preferably, it is 1 to 3 μg / cm 2 It is more preferable that:

[0062] As described above, the gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to the present embodiment can be applied not only to carbon dioxide reduction electrolysis devices, but also to water electrolysis devices, fuel cells, gas diffusion electrodes for air batteries, etc. Similarly, the catalyst layer can be used not only for carbon dioxide reduction but also for various batteries, electrodes, etc. When a carbon dioxide reduction catalyst layer is used as the catalyst layer, the cathode according to this embodiment is provided with a gas diffusion layer manufactured by the gas diffusion layer manufacturing method according to this embodiment, and therefore the supply of CO to the catalyst layer is not reduced, and the cathode has excellent electrolytic activity. The details of the gas diffusion layer are as described in the description of the manufacturing method of the gas diffusion layer. The catalyst layer will be described below.

[0063] [Catalyst layer] The catalyst layer according to this embodiment contains at least a catalyst, and may further contain an ionomer. The catalyst layer according to this embodiment is located on the porous layer side of the gas diffusion layer; in other words, in a laminate structure represented by carbon fiber layer / porous layer / catalyst layer, it is located on the porous layer surface opposite to the carbon fiber layer side.

[0064] (catalyst) The catalyst according to this embodiment preferably comprises a carrier containing carbon and carrying inorganic fine particles or a metal complex. In the catalyst in the technology of the present disclosure, the component exhibiting catalytic action is an inorganic fine particle or a metal complex supported on a carrier, and in the technology of the present disclosure, the inorganic fine particle and the metal complex are referred to as the "catalyst source," and the carrier on which the catalyst source is supported is referred to as the "catalyst."

[0065] [Inorganic particles, metal complexes] The support according to this embodiment supports inorganic fine particles or a metal complex as a catalyst source. The inorganic fine particles and metal complexes are not particularly limited as long as they are components that exhibit catalytic activity. In the technology of the present disclosure, the inorganic fine particles refer to metals and inorganic compounds having an average particle size of 1 to 100 nm as measured by photographic observation using a scanning electron microscope or the like.

[0066] For example, when the catalyst source is used in a catalyst layer for a fuel cell, platinum, gold, nickel, ruthenium, rhodium, etc. can be used as the inorganic fine particles, and nickel complexes, cobalt complexes, iron complexes, manganese complexes, zinc complexes, etc. can be used as the metal complexes.

[0067] Furthermore, for example, when the catalyst source is used in a catalyst layer for a secondary battery electrode, platinum, gold, nickel, iridium, metal oxides, etc. can be used as the inorganic fine particles, and nickel complexes, cobalt complexes, iron complexes, manganese complexes, zinc complexes, etc. can be used as the metal complexes.

[0068] When the catalyst layer is used as a catalyst layer for reducing carbon dioxide, it is preferable to use, as the inorganic fine particles and the metal complex, a catalyst source having an action of producing at least carbon monoxide by a reduction reaction. Specifically, the inorganic fine particles for carbon dioxide reduction are preferably fine particles selected from the group consisting of gold, silver, copper, nickel, iron, cobalt, zinc, chromium, palladium, tin, manganese, aluminum, indium, bismuth, molybdenum, and carbon nitride. Only one inorganic fine particle may be used, or two or more inorganic fine particles may be used in combination. Among the above, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the material of the inorganic fine particles is preferably silver, gold, zinc, tin, copper and bismuth, more preferably silver, gold, copper and tin, and even more preferably silver, gold and copper.

[0069] The average particle size of the inorganic fine particles as a catalyst source for carbon dioxide reduction is preferably 65 nm or less, more preferably 60 nm or less, more preferably 50 nm or less, more preferably 40 nm or less, and more preferably 30 nm or less, from the viewpoint of the reaction rate of the carbon dioxide reduction reaction. In addition, although there is no restriction on the lower limit of the average particle size, from the viewpoint of ease of production, it is preferably 1 nm or more, and more preferably 5 nm or more. The average particle size can be measured by photographic observation using a scanning electron microscope or the like.

[0070] The metal complex as a catalyst source for carbon dioxide reduction is a metal complex in which a ligand is coordinated to a metal or an ion of the metal, and the metal ion is preferably selected from the group consisting of copper, nickel, iron, cobalt, zinc, manganese, molybdenum, and aluminum. Among these, from the viewpoint of the reaction efficiency of the carbon dioxide reduction reaction, the metal is preferably nickel, cobalt, iron, copper, zinc, or manganese, more preferably nickel, cobalt, iron, or copper, and further preferably nickel, cobalt, or iron. The metal complex may contain only one type of metal or ion of the metal, or may contain two or more types of metals. The type of ligand is not particularly limited, and examples thereof include phthalocyanine complexes, porphyrin complexes, pyridine complexes, metal-supported covalent triazine structures, and metal organic structures. Among these, phthalocyanine complexes, porphyrin complexes, pyridine complexes, and metal-supported covalent triazine structures are preferred, phthalocyanine complexes, porphyrin complexes, and metal-supported covalent triazine structures are more preferred, and porphyrin complexes and metal-supported covalent triazine structures are even more preferred. The metal complex may contain only one type of ligand, or may contain two or more types.

[0071] The inorganic fine particles and the metal complex are supported on the carrier according to the present embodiment by carrying out a known method such as vapor deposition, deposition, adsorption, accumulation, adhesion, welding, physical mixing, spraying, or the like.

[0072] In addition, the catalyst in the technology of the present disclosure is preferably coated with an ionomer. By coating the catalyst with an ionomer, an ion-conducting channel between the coated catalyst and a solid electrolyte described later is easily formed, facilitating the movement of ions generated by the reaction, and making it possible to improve the efficiency of electrolysis.

[0073] [Ionomer] The catalyst layer may further include an ionomer. The ionomer functions as a binder resin in the catalyst layer and is a matrix resin (continuous phase) that can disperse and immobilize the additive and catalyst according to this embodiment. It also has a function of transmitting ions generated by electrolysis and improving the efficiency of CO electrolysis. The ionomer may be the binder material described as a component of the mixed solution used when applying a conductive material to the carbon fiber layer by spraying, and is preferably an anion exchange resin.

[0074] When the cathode (negative electrode) according to this embodiment is used in an ion exchange membrane-electrode assembly and a solid electrolyte electrolysis device described below, it is preferable to use the same resin as that of the solid electrolyte (ion exchange membrane) as the ionomer, from the viewpoint of improving electrical conductivity.

[0075] [Carrier] The support according to the present embodiment is not particularly limited, but preferably contains carbon from the viewpoint of imparting electrical conductivity. Carbon generally has electrical conductivity, and therefore a support containing carbon is an electrically conductive support. The carbon-containing carrier is not limited as long as it is a conductive material that can be used as a gas diffusion layer in an electrode provided in an apparatus for reducing carbon dioxide, and examples of the carbon-containing carrier include carbon black (furnace black, acetylene black, ketjen black, medium thermal carbon black, etc.), activated carbon, graphite, carbon nanotubes, carbon nanofibers, carbon nanohorns, graphene nanoplatelets, nanoporous carbon, and the like. Of these, carbon black is preferable from the viewpoint of improving the active site density.

[0076] From the viewpoint of increasing the active site density and increasing the current density, the primary particle diameter of the carbon black is preferably 5 to 200 nm, more preferably 10 to 100 nm, and even more preferably 10 to 50 nm. The primary particle diameter of the carbon black can be measured by a transmission electron microscope. The primary particle diameter can be measured by measuring the length in the longest direction of the particle revealed by the microscope, taking it as the major axis, and calculating the average value of the obtained major axes. From the same viewpoint, it is preferable that the secondary particle size (particle size of aggregates) of the carbon black is small, and it is preferable that the carbon black has a large amount of functional groups. The carbon black may be a commercially available product, and examples thereof include Vulcan (registered trademark) XC-72 (manufactured by Cabot Corporation) and BLACK PEARL 2000 (manufactured by Cabot Corporation). The carrier may be used alone or in combination of two or more kinds.

[0077] From the viewpoint of further improving the production efficiency of the CO-containing synthesis gas, the content of the catalyst according to this embodiment in the catalyst layer is preferably 5 to 90 mass%, more preferably 10 to 80 mass%, and further preferably 15 to 60 mass%.

[0078] <Ion exchange membrane-electrode assembly> The ion exchange membrane-electrode assembly according to this embodiment has the cathode according to the embodiment described above, a solid electrolyte, and an anode. The ion exchange membrane-electrode assembly according to this embodiment includes a cathode including a gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to the present disclosure, and therefore has high electrolytic activity and a high CO2 reduction reaction rate. 1, the ion exchange membrane-electrode assembly according to this embodiment has a PEM type structure in which a solid electrolyte 30 is sandwiched between a catalyst layer 20 and an anode 40, and the catalyst layer 20 contains a plurality of catalysts 24 according to this embodiment and an ionomer 22. In addition, a gas diffusion layer 10 is combined with the surface of the catalyst layer 20 opposite to the surface in contact with the solid electrolyte 30 to form a cathode (negative electrode) according to this embodiment. As shown in FIG. 1, carbon dioxide (CO2) is supplied to the catalyst layer 20 from the surface 10b side of the gas diffusion layer 10, and carbon monoxide (CO) is produced by a reduction reaction. In the following description, the reference numerals in FIG. 1 will be omitted.

[0079] [Solid electrolyte] The ion exchange membrane-electrode assembly according to this embodiment has a solid electrolyte. The solid electrolyte may be a polymer membrane. The polymer may be any of various ionomers, and may be either a cation exchange resin or an anion exchange resin, but is preferably an anion exchange resin. That is, the solid electrolyte is preferably an anion exchange membrane. It is more preferable to use the same anion exchange resin as the ionomer used in the catalyst layer. The solid electrolyte may be a commercially available product such as a cation exchange membrane or an anion exchange membrane. In addition, when an anion exchange membrane is used as the solid electrolyte, the base site density is 0.5 to 5.0 mmol / cm in a dry state. 3 and preferably 2.5 mmol / cm 3 More than 4.5mmol / cm 3 More preferably, it is less than 2.9 mmol / cm 3 More than 4.5mmol / cm 3 It is even more preferable that it is less than 1000 .mu.m.

[0080] Examples of the cation exchange membrane that can be used include strongly acidic cation exchange membranes having sulfonic groups introduced into a fluororesin matrix, such as Nafion117, Nafion115, Nafion212, and Nafion350 (manufactured by Chemours Corporation), and strongly acidic cation exchange membranes having sulfonic groups introduced into a styrene-divinylbenzene copolymer matrix, such as Neosepta CSE (manufactured by Astom Corporation). Examples of anion exchange membranes include anion exchange membranes having one or more ion exchange groups selected from the group consisting of quaternary ammonium groups, primary amino groups, secondary amino groups, and tertiary amino groups. Specific examples include Neocepta (registered trademark) ASE, AHA, ACS, and AFX (manufactured by Astom Corporation), and Selemion (registered trademark) AMVN, DSVN, AAV, ASVN, and AHO (manufactured by Asahi Glass Co., Ltd.).

[0081] The reduction reaction of carbon dioxide at the cathode (negative electrode) according to this embodiment differs depending on the type of solid electrolyte. When a cation exchange membrane is used as the solid electrolyte, the reduction reactions shown in the following reaction formulas (1) and (2) occur, and when an anion exchange membrane is used as the solid electrolyte, the reduction reactions shown in the following reaction formulas (3) and (4) occur.

[0082] CO2+2H + +2e - →CO+H2O (1) 2H + +2e - →H2(2) H2O+CO2+2e - →CO+2OH - (3) 2H2O+2e - →H2+2OH - (4)

[0083] 〔anode〕 The oxidation reaction at the anode varies depending on the type of solid electrolyte. When a cation exchange membrane is used as the solid electrolyte, the oxidation reaction shown in the following reaction formula (5) occurs, and when an anion exchange membrane is used as the solid electrolyte, the oxidation reaction shown in the following reaction formula (6) occurs.

[0084] 2H2O→O2+4H + +4e - (5) 4OH - →O2+2H2O+4e - (6)

[0085] The anode is a gas diffusion electrode that includes a gas diffusion layer. The gas diffusion layer includes, for example, a metal mesh. Examples of the electrode material of the anode include Ir, IrO2, Ru, RuO2, Co, CoOx, Cu, CuOx, Fe, FeOx, FeOOH, FeMn, Ni, NiOx, NiOOH, NiCo, NiCe, NiC, NiFe, NiCeCoCe, NiLa, NiMoFe, NiSn, NiZn, SUS, Au, and Pt.

[0086] <Solid electrolyte electrolyzer> The solid electrolyte electrolysis device according to this embodiment includes the cathode according to the embodiment described above, an anode that constitutes a pair of electrodes together with the cathode, a solid electrolyte that is interposed between the cathode and the anode in contact with each other, and a voltage application unit that applies a voltage between the cathode and the anode. The solid electrolyte electrolysis device according to this embodiment is equipped with a cathode (negative electrode) including a gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to the present disclosure, and therefore has high electrolytic activity and a high reduction reaction rate of CO2.

[0087] FIG. 4 is a schematic diagram of a solid electrolyte electrolysis device preferably used in this embodiment. FIG. 4 shows a solid electrolyte electrolysis device 800 having a cathode (negative electrode) 200 according to this embodiment, an anode (positive electrode) 400 which constitutes a pair of electrodes together with the cathode 200, a solid electrolyte 300 which is interposed between the cathode 200 and the anode 400 in contact with each other, and a voltage application unit 700 which applies a voltage between the cathode 200 and the anode 400. The solid electrolyte electrolysis device 800 shown in FIG. 4 further includes a cathode current collector 100, an anode current collector 500, and an electrolyte solution 600. The cathode according to the present embodiment described above is used as the cathode 200. The solid electrolyte 300 is the same as the solid electrolyte 30 in Fig. 1, and the solid electrolyte 300 is preferably an anion exchange membrane. The anode 400 is the same as the anode 40 in Fig. 1. The details of the cathode 200, the solid electrolyte 300, and the anode 400 are as described above. In the following description, the reference numerals of each element other than the cathode 200, the solid electrolyte 300, and the anode 400 will be omitted.

[0088] [Cathode current collector] Examples of the cathode current collector include metal materials such as copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, and brass, among which copper is preferred from the viewpoints of ease of processing and cost. When the cathode current collector is made of a metal material, examples of the shape of the cathode current collector include metal foil, metal plate, metal thin film, expanded metal, punched metal, and foamed metal.

[0089] The cathode current collector may be provided with a gas supply hole for supplying a raw material gas containing carbon dioxide to the cathode and a gas recovery hole for recovering a generated gas containing carbon monoxide. By providing the gas supply hole and the gas recovery hole, the raw material gas can be uniformly and efficiently fed to the cathode and the generated gas (including unreacted raw material gas) can be discharged. The gas supply hole and the gas recovery hole may be provided independently of each other, either alone or in pairs or more. The shape, location, size, etc. of the gas supply hole and the gas recovery hole are not limited and may be appropriately set. In addition, when the cathode current collector is permeable, the gas supply hole and the gas recovery hole are not necessarily required. When the cathode has a function of transferring electrons, the cathode current collector is not necessarily required.

[0090] [Anode current collector] The anode current collector preferably has electrical conductivity to receive electrons from the anode and has rigidity to support the anode. From this viewpoint, the anode current collector can be made of a metal material such as titanium (Ti), copper (Cu), nickel (Ni), stainless steel (SUS), nickel-plated steel, brass, etc.

[0091] The anode current collector may be provided with a gas flow path for feeding a raw material gas (such as HO) to the anode. By providing the gas flow path in the anode current collector, the raw material gas can be fed uniformly and efficiently to the anode. The number, shape, location, size, etc. of the gas flow path are not limited and may be set appropriately.

[0092] [Voltage application section] The voltage application unit applies a voltage between the cathode and the anode by applying a voltage to the cathode current collector and the anode current collector. Since both current collectors are conductors, they supply electrons to the cathode and receive electrons from the anode. In addition, a control unit (not shown) may be electrically connected to the voltage application unit to apply an appropriate voltage.

[0093] [Electrolyte] The electrolyte is preferably an aqueous solution having a pH of 5 or more. For example, carbonate aqueous solution, bicarbonate aqueous solution (e.g., KHCO3 aqueous solution), sulfate aqueous solution, borate aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium chloride aqueous solution, etc. can be mentioned.

[0094] (Reaction gas supply section) In the solid electrolyte electrolysis device according to this embodiment, a reaction gas supply unit (not shown) may be provided outside the solid electrolyte electrolysis device. That is, as long as the reaction gas CO2 is supplied to the catalyst layer of the cathode, the reaction gas may be supplied from the reaction gas supply unit to the gas supply hole via a pipe (not shown), or the reaction gas may be sprayed onto the surface of the cathode current collector opposite to the contact surface with the cathode. From an environmental point of view, it is preferable to use factory exhaust gas discharged from a factory as the reaction gas.

[0095] [CO generation method] Next, a method for producing CO using the solid electrolyte electrolysis device according to this embodiment will be described. First, CO2, which is a reactant gas serving as a raw material, is supplied in a gas phase to the solid electrolyte electrolysis device by a reactant gas supply unit (not shown). At this time, CO2 is supplied to the cathode, for example, through a gas supply hole provided in the cathode current collector. Next, the CO2 supplied to the cathode comes into contact with the catalyst layer of the cathode, and when a cation exchange membrane is used as the solid electrolyte, the reduction reactions of the above-mentioned reaction formulas (1) and (2) occur, or when an anion exchange membrane is used as the solid electrolyte, the reduction reactions of the above-mentioned reaction formulas (3) and (4) occur, thereby producing a synthesis gas containing at least CO and H2. Next, the synthesis gas containing the generated CO and H2 is sent to a gas recovery device (not shown), for example, through a gas recovery hole provided in the cathode current collector plate, and is recovered in predetermined gas fractions. EXAMPLES

[0096] The technology of the present disclosure will now be specifically described with reference to examples, but the technology of the present disclosure is not limited to these examples in any way.

[0097] <Manufacture of gas diffusion layer> Example 1 The gas diffusion layer of Example 1 was produced by a sputtering method, specifically as follows. Using a magnetron sputtering device, pure Ag (99.99 mass%) was sputtered at a concentration of 2 μg / cm 2 at a sputtering current of 20 mA toward the surface of the carbon fiber layer 1 having a porous layer opposite to the surface on which the porous layer was provided. 2 Thus, the gas diffusion of Example 1 was obtained. The magnetron sputtering device used was a JFC-1600 manufactured by JEOL Ltd., and sputtering was carried out with the inside replaced with diluted Ar. The carbon fiber layer 1 with a porous layer was made using a product with the product name "Sigracet (registered trademark) 39BB" manufactured by SGL Carbon Co., Ltd. The thickness of the carbon fiber layer portion of the carbon fiber layer 1 was 315 μm, and the porous layer had a porosity of 15 to 30% and an average pore size of 100 to 300 nm (catalog values).

[0098] Comparative Example 1 The gas diffusion layer of Comparative Example 1 was produced by sputtering, specifically as follows. Using a magnetron sputtering device (manufactured by JEOL Ltd., product name "JFC-1600"), with the inside replaced with dilute Ar, pure Ag (99.99 mass%) was sputtered at a concentration of 2 μg / cm 2 toward the surface of the carbon fiber layer 2 not having a porous layer at a sputtering current of 20 mA. 2 Thus, the gas diffusion of Reference Example 1 was obtained. The carbon fiber layer 2 not provided with a porous layer was manufactured by Toray Industries, Inc. and sold under the trade name "TGP-H-060."

[0099] Example 2 The gas diffusion layer of Example 2 was produced by a spray method, specifically as follows. Carbon black having a primary particle diameter of 30 nm (conductive substance 2 according to this embodiment) and binder resin 1 or binder resin 2 were mixed so that the ratio (a / r) of the mass of the conductive substance (a) to the mass of the binder resin (r) was 5 / 1, and the mixture was dispersed in ethanol to prepare mixed solution 1. With the carbon fiber layer 1 with the porous layer heated to 75°C, the mixed solution 1 was mixed with pressurized air and sprayed in a mist form from a spray device onto the surface of the carbon fiber layer 1 opposite to the surface adjacent to the porous layer. The mixed solution 1 was sprayed so that the amount of the conductive material and the binder resin carried was 0.2 mg / cm. 2 The gas diffusion layer of Example 2 was obtained. The binder resin 1 used was a product name "Nafion (registered trademark) D521" manufactured by Chemours, Inc. The spraying device used was an external mixing type two-fluid nozzle (manufactured by Apiross, Inc., product name "LPVN (registered trademark) 10").

[0100] Example 3 In the production of the gas diffusion layer of Example 2, the mixed solution 1 was sprayed so that the amount of the conductive material and the binder resin was 0.6 mg / cm 2 A gas diffusion layer of Example 3 was produced in the same manner, except that the process was stopped when

[0101] Example 4 The gas diffusion layer of Example 4 was produced by a spray method, specifically as follows. Carbon black having a primary particle diameter of 30 nm (conductive substance 2 according to this embodiment) and binder resin 2 were mixed so that the ratio (a / r) of the mass of the conductive substance (a) to the mass of the binder resin (r) was 5 / 1, and the mixture was dispersed in ethanol to prepare mixed solution 2. With the carbon fiber layer 1 with the porous layer heated to 75°C, the mixed solution 2 was mixed with pressurized air and sprayed in a mist form from a spray device onto the surface of the carbon fiber layer 1 opposite the surface on which the porous layer was provided. The mixed solution 2 was sprayed so that the amount of the conductive material and the binder resin carried was 0.4 mg / cm. 2 The gas diffusion layer of Example 4 was obtained. The binder resin 2 used was manufactured by Chemours under the product name "Teflon (registered trademark) PTFE DISP 30." The spraying device used was an externally mixed two-fluid nozzle (manufactured by Apiross under the product name "LPVN (registered trademark) 10").

[0102] Comparative Example 2 A carbon fiber layer 1 having a porous layer (manufactured by SGL Carbon, product name "Sigracet (registered trademark) 39BB") was used as a gas diffusion layer in Comparative Example 2.

[0103] Comparative Example 3 The gas diffusion layer of Comparative Example 3 was produced by the liquid phase method, specifically as follows. The carbon fiber layer 1 having a porous layer was immersed in the mixed solution 1 prepared in the production of the gas diffusion layer in Example 2, and the carbon fiber layer 1 was mixed with the mixed solution 1 to obtain a carbon fiber having a porous layer of 0.8 mg / cm 2 The mixture of the conductive material and the binder resin was supported on the carbon fiber layer 1 to obtain a gas diffusion layer of Comparative Example 3.

[0104] <Measurement of side reaction amount> An anion exchange membrane having a thickness of about 30 μm, a carbon anode (manufactured by DioxideMaterials) supporting iridium oxide as an anode, and the gas diffusion layer of Example 1 or Comparative Example 1 as a cathode (negative electrode) were bonded together to form a membrane-electrode assembly. The anion exchange membrane is made of a fluororesin (base density 2.1 mmol / cm) that has an aromatic ring in the main chain and quaternary ammonium groups bonded to the main chain as side chains. 3 The anode was in contact with the electrolyte tank. Using this device, pure CO2 was supplied to the cathode. Under conditions where the cell was heated to 80°C, the applied potential of the cathode was set to -2.6 V relative to the anode, and CO2 was electrolyzed to generate H2 from H2O as a by-reaction. The current density [mA / cm 2 The results are summarized in Table 1.

[0105] [Table 1]

[0106] As shown in Table 1, when a conductive material was applied to the carbon fiber layer with a porous layer (Example 1), the partial current density due to the side reaction of H2 generation increased significantly compared to when no porous layer was provided (Comparative Example 1), and it was found that the amount of CO generated decreased. In Comparative Example 1, the conductive material was introduced into the surface of the gas diffusion electrode and acted as an active site for the side reaction, whereas the formation of such active sites was significantly suppressed by providing the carbon fiber layer with a porous layer.

[0107] <Measurement of electrical resistance of gas diffusion electrode> Each gas diffusion layer (geometric area 2.25 cm) of Examples 1 to 4 and Comparative Examples 2 to 3 2 ) was sandwiched between two gold electrodes and subjected to a current of 100 mA / cm 2 The electrical resistance in the vertical direction of the electrodes was measured by measuring the voltage drop between the gold electrodes using the four-terminal method under the application of a direct current of 1000 kV. The results are summarized in Table 2.

[0108] [Table 2]

[0109] As shown in Table 2, when Ag was added to the carbon fiber layer having a porous layer by the gas phase method (Example 1) and when carbon black was added (Examples 2, 3, and 4), the electrical resistance was significantly lower than when no carbon black was added (Comparative Example 2). In the case where carbon black was applied to a carbon fiber layer having a porous layer by a liquid phase method (Comparative Example 3), although the electrical resistance was reduced, a conductive substance was attached to the surface of the porous layer. Therefore, when a catalyst layer is placed adjacent to the porous layer, there is a risk of adverse effects such as the carbon black acting as an active site for an unintended reaction (side reaction). In addition, by using the spraying method and the sputtering method to supply fine particles of the conductive material, the conductive material was able to reach the inside of the gas diffusion layer uniformly, and therefore it was found that the gas diffusion layers produced in Examples 1 to 4 had excellent conductivity in the depth direction.

[0110] <Evaluation of hydrophobicity of gas diffusion layer> Cross-sectional electron microscope images of the carbon fibers in the gas diffusion layers of Example 1, Example 2, and Comparative Example 2 are shown in Figures 5, 6, and 7, respectively. Note that Figure 5 (Example 1) is a backscattered electron image, and Figure 6 (Example 2) and Figure 7 (Comparative Example 2) are secondary electron images. As can be seen from Figures 5 to 7, in the gas diffusion layers of Example 1 (Figure 5) and Example 2 (Figure 6), a portion of the carbon fiber surface is coated with a conductive material without filling the voids inside the gas diffusion layer, and the porosity and hydrophobicity provided by the carbon fibers are maintained.

[0111] In addition, at the bottom of the photo in Figure 5, 1μm Test 2022 / 09 / 08 X 10,000 15.0kV COMPO SEM WD7.8mm 10:30:12 The length of the white line corresponds to 1 μm. At the bottom of the photo in Figure 6, 1μm Test 20 X 10,000 5.0kV SEI SEM WD7.2mm The length of the white line corresponds to 1 μm. At the bottom of the photo in Figure 7, 1μm Test 2022 / 09 / 08 X 10,000 5.0kV SEI SEM WD8.0mm 10:09:57 The length of the white line corresponds to 1 μm.

[0112] <Evaluation of the location of conductive material in carbon fiber layer> Under the following measurement conditions, the depth distribution of the fluorescence X-ray detection ratio of Ag / C near the interface between the carbon fiber layer and the porous layer was measured for the gas diffusion layer of Example 1; and the depth distribution of the fluorescence X-ray detection ratio of S / C near the interface between the carbon fiber layer and the porous layer was measured for the gas diffusion layer of Example 2. (Measurement conditions) Scanning electron microscope: Field emission scanning electron microscope (model number: JSM-7001F, manufactured by JEOL Ltd.) Energy dispersive X-ray fluorescence analyzer: UltraDry (Thermo Fisher Scientific Inc.) Accelerating voltage: 15kV

[0113] In the measurement of the gas diffusion layer of Example 1, the position of the conductive material present in the carbon fiber layer was confirmed by creating a graph with the Ag / C count ratio on the vertical axis and the position of the detection target (Ag) on ​​the horizontal axis. The created graph is shown in Figure 8. The magnification of the electron microscope was set to 500 times, and the count ratio was measured at each position near the interface between the carbon fiber layer and the porous layer. In Fig. 8, "Ag(L)" in the "Ag(L) / C(K) count ratio" on the vertical axis means the L line of Ag, and "C(K)" means the K line of carbon. The "position (μm)" on the horizontal axis indicates the distance in the depth direction from the interface between the carbon fiber layer and the porous layer, with the interface being 0 μm (the porous layer side is positive).

[0114] In the measurement of the gas diffusion layer of Example 2, the position of the conductive material present in the carbon fiber layer was confirmed by creating a graph with the S / C count ratio on the vertical axis and the position of the detection target (S) on the horizontal axis. The created graph is shown in Figure 9. The magnification of the electron microscope was set to 300 times, and the count ratio was measured at each position near the interface between the carbon fiber layer and the porous layer. In Fig. 9, "S(K)" in the "S(K) / C(K) count ratio" on the vertical axis means the K line of sulfur, and "C(K)" means the K line of carbon. The "position (μm)" on the horizontal axis indicates the distance in the depth direction from the interface between the carbon fiber layer and the porous layer, with the interface being 0 μm (the porous layer side is positive).

[0115] FIG. 8 shows the depth distribution of the detection ratio of Ag / C fluorescent X-rays near the interface between the carbon fiber layer and the porous layer in the gas diffusion layer of Example 1; FIG. 9 shows the depth distribution of the detection ratio of S / C fluorescent X-rays near the interface between the carbon fiber layer and the porous layer in the gas diffusion layer of Example 2. A larger count ratio means that a larger amount of the detection target is present at each position in the carbon fiber layer. In the measurement of the gas diffusion layer in Example 1, the conductive substance Ag was detected, and a larger count ratio in FIG. 8 indicates that more Ag was present at each position in the carbon fiber layer.

[0116] In the measurement of the gas diffusion layer of Example 2, the detection target was sulfo groups contained in binder resin 1 (manufactured by Chemours, product name "Nafion (registered trademark) D521") used as the binder resin, and the larger the count ratio in FIG. 9, the more sulfo groups are present at each position in the carbon fiber layer. The gas diffusion layer of Example 2 was manufactured by spraying a mixed solution 1 containing a conductive material and a binder resin onto the surface of the carbon fiber layer 1. Therefore, it is considered that the conductive material also reaches the inside of the carbon fiber layer in the depth direction together with the binder resin from the surface, and the conductive material is also present at the position where the sulfo group is detected.

[0117] As can be seen from FIG. 8, in the gas diffusion layer of Example 1, it was confirmed that a large amount of conductive material was present from the interface between the carbon fiber layer and the porous layer to a position approximately 20 μm toward the carbon fiber layer (a position that is 90% or more of the carbon fiber layer thickness in the depth direction from the surface). 9, it was confirmed that many sulfo groups were present in the gas diffusion layer of Example 2 from the interface between the carbon fiber layer and the porous layer to a position about 10 μm into the carbon fiber layer (a position at or above 90% of the carbon fiber layer thickness in the depth direction from the surface). Therefore, it can be said that many conductive substances are also present in a position about 100% deep from the surface. As described above, although there was some local variation in concentration, it was confirmed that the conductive material was present up to the vicinity of the interface between the carbon fiber layer and the porous layer.

[0118] <Catalyst Production> In a beaker, 0.4 g of carbon black support (support according to this embodiment) having a primary particle diameter of 30 nm was mixed with 1.1 mmol of pentaethylenehexamine and 0.7 mmol of nickel (II) chloride hexahydrate in 15 mL of ethanol to prepare an ethanol dispersion.

[0119] The obtained ethanol dispersion was irradiated with ultrasonic waves for 10 minutes, and then the ethanol dispersion was heated and dried to evaporate the ethanol, obtaining a mixture. The obtained mixture was heated in an inert gas furnace at 900°C for 10 seconds or more to be calcined. The product was then washed with an aqueous sulfuric acid solution, and the solid matter was collected using a suction filter and vacuum-dried overnight at 60°C to obtain a catalyst powder (intermediate) carrying a Ni complex.

[0120] Furthermore, 0.3 g of the obtained catalyst powder was placed in a pot together with 10 g of zirconia balls with a diameter of 0.5 mm and 10 mL of water, and ground for 20 minutes at a rotation speed of 800 rpm using a planetary ball mill to recover the catalyst slurry. The catalyst slurry was washed again with an aqueous sulfuric acid solution, and the solid matter was recovered using a suction filter. The recovered solid matter was vacuum-dried at 60°C overnight to obtain the final catalyst powder. The primary particle size of the carbon black was determined by laser diffraction particle size distribution measurement.

[0121] <Manufacture of solid electrolyte electrolysis devices> Example 5 22 mg of the obtained catalyst powder was dispersed in ethanol, and 2 mg of "Nafion (registered trademark)" (cation exchange resin) manufactured by Chemours was mixed as an ionomer into the dispersion liquid. After mixing, the dispersion liquid was irradiated with ultrasonic waves for 10 minutes, and exposed to a vacuum chamber in a reduced pressure environment of 10 kPa (absolute pressure) for 10 minutes. Then, a spray coater was used to apply a coating of 1 to 2 mg / cm2 on the porous layer side of the gas diffusion layer of Example 2. 2 The dispersion was applied to the cathode so as to form a cathode (negative electrode). The cathode had a coating film of the dispersion as a catalyst layer.

[0122] An ion exchange membrane A having a thickness of about 30 μm and a carbon anode carrying iridium oxide (manufactured by DioxideMaterials) were attached to the obtained cathode to form an ion exchange membrane-electrode assembly. The ion exchange membrane A is an anion exchange membrane with a thickness of about 30 μm, and is made of a fluororesin (base site density: 2.1 mmol / cm) that has an aromatic ring in the main chain and has quaternary ammonium groups bonded to the main chain as side chains. 3 ). The anode (positive electrode) was designed to be in contact with a tank of electrolyte (0.5 mol / L KHCO3 aqueous solution).

[0123] Example 6 A solid electrolyte electrolysis device of Example 6 was produced in the same manner as in the production of the solid electrolyte electrolysis device of Example 5, except that the gas diffusion layer of Example 4 was used instead of the gas diffusion layer of Example 2.

[0124] Example 7 A solid electrolyte electrolysis device of Example 7 was produced in the same manner as in Example 5, except that the gas diffusion layer of Example 1 was used instead of the gas diffusion layer of Example 2.

[0125] Example 8 A solid electrolyte electrolysis device of Example 8 was produced in the same manner as in the production of the solid electrolyte electrolysis device of Example 5, except that the ion exchange membrane B was used instead of the ion exchange membrane A. The ion exchange membrane B is manufactured by DioxideMaterials, Inc., has a product name of "X37-50 grade 60", and has a structure with polystyrene as the main chain and imidazolium-based ion exchange groups on the side chains.

[0126] Comparative Example 4 A solid electrolyte electrolysis device of Comparative Example 4 was produced in the same manner as in Example 5, except that the gas diffusion layer of Comparative Example 2 was used instead of the gas diffusion layer of Example 2.

[0127] Comparative Example 5 A solid electrolyte electrolysis device of Comparative Example 5 was produced in the same manner as in the production of the solid electrolyte electrolysis device of Comparative Example 4, except that the ion exchange membrane B was used instead of the ion exchange membrane A.

[0128] Comparative Example 6 A solid electrolyte electrolysis device of Comparative Example 6 was produced in the same manner as in Example 5, except that the gas diffusion layer of Comparative Example 3 was used instead of the gas diffusion layer of Example 2.

[0129] <Evaluation of solid electrolyte electrolysis devices> [Examples 5 to 8 and Comparative Examples 4 to 6] (current density) Using each of the solid electrolyte electrolysis devices of Examples 5 to 8 and Comparative Examples 4 to 6, pure CO2 was supplied to the cathode at a flow rate of 100 sccm. CO2 was electrolyzed under the conditions that the cell was heated to 80°C in the solid electrolyte electrolysis devices of Examples 5 to 7 and Comparative Examples 4 and 6 using ion exchange membrane A, and to 70°C in the solid electrolyte electrolysis devices of Example 8 and Comparative Example 5 using ion exchange membrane B, with the applied potential of the cathode set to -2.6 V relative to the anode. The CO generation current density [mA / cm 2 ] and CO selectivity [%] were measured, and the results are summarized in Table 3.

[0130] [Table 3]

[0131] As can be seen from Table 3, the reduction in electrical resistance confirmed an improvement in current density when a constant voltage was applied. The same improvement was confirmed when two types of ion exchange membranes, A and B, were used. [Industrial Applicability]

[0132] According to this embodiment, for example, CO2 gas discharged from a factory is used as a raw material for the solid electrolyte electrolysis device, and renewable energy such as a solar cell is used for the voltage application unit, thereby making it possible to generate a synthesis gas containing at least CO and H2 in a desired production ratio. The synthesis gas thus generated can be used to generate fuel base stocks, chemical raw materials, etc., by methods such as FT synthesis (Fischer-Tropsch synthesis) and methanation. [Explanation of symbols]

[0133] 10 Gas diffusion layer 20 Catalyst layer 22 Ionomer 24 Catalyst 30 Solid electrolyte (ion exchange membrane) 40 Anode 50 Ion exchange membrane-electrode assembly 100 Cathode current collector 200 Cathode 300 Solid electrolyte (ion exchange membrane) 400 Anode 500 Anode current collector 600 Electrolyte 700 Voltage application section 800 Solid electrolyte electrolyzer

Claims

1. A method for manufacturing a gas diffusion layer having a carbon fiber layer containing carbon fibers and a porous layer containing a conductive material 1 and a binder resin, A method for manufacturing a gas diffusion layer, comprising applying a conductive substance 2 to the surface side of the carbon fiber layer of a laminate having the carbon fiber layer and the porous layer by a spraying method or a gas phase method.

2. The method for manufacturing a gas diffusion layer according to claim 1, wherein the porous layer has a porosity of 10 to 60% and an average pore diameter of 10 to 500 nm.

3. A method for manufacturing a gas diffusion layer according to claim 1 or 2, wherein the conductive material 1 and the conductive material 2 are each independently selected from the group consisting of carbon materials and metals, one or more of these materials.

4. A method for producing a gas diffusion layer according to claim 1 or 2, wherein a mixed solution containing the conductive material 2 and the binder resin is sprayed from the surface side of the carbon fiber layer.

5. The mixed solution contains a total amount of the conductive substance 2 and the binder resin in the mixed solution of 0.05 to 2 mg / cm³. ２ A method for producing a gas diffusion layer according to claim 4, wherein the gas is sprayed in such a manner.

6. A method for manufacturing a gas diffusion layer according to claim 1 or 2, wherein the conductive material 2 is applied from the surface side of the carbon fiber layer by vapor deposition or sputtering.

7. The amount of conductive material 2 applied is 0.5 to 5 μg / cm³. ２ The method for producing a gas diffusion layer according to claim 6.

8. A gas diffusion layer manufactured by the method for manufacturing a gas diffusion layer according to claim 1 or 2, comprising a carbon fiber layer containing a conductive material 2 and carbon fibers, wherein a portion of the carbon fibers is coated with the conductive material 2, and a porous layer containing a conductive material 1 and a binder resin; and Catalyst layer on the porous layer side A cathode having

9. A gas diffusion layer comprising a carbon fiber layer containing conductive material 2 and carbon fibers, wherein a portion of the carbon fibers is coated with the conductive material 2 and the conductive material 2 extends to a depth of 60% or more from the surface; and a porous layer containing conductive material 1 and a binder resin, having a porosity of 10 to 60% and an average pore diameter of 10 to 500 nm; and Catalyst layer on the porous layer side A cathode having

10. The carbon fiber layer further contains a binder resin, and the amount of the conductive substance 2 and the binder resin supported is 0.05 to 2 mg / cm². ２ The cathode according to claim 9.

11. The cathode according to claim 9 or 10, wherein the conductive material 1 and the conductive material 2 are each independently selected from the group consisting of carbon materials and metals.

12. An ion exchange membrane-electrode assembly having a cathode according to claim 9 or 10, a solid electrolyte, and an anode.

13. The ion exchange membrane-electrode assembly according to claim 12, wherein the solid electrolyte is an anion exchange membrane.

14. A cathode according to claim 9 or 10, The cathode and the anode which constitute a pair of electrodes, A solid electrolyte interposed in contact between the cathode and the anode, A voltage application unit that applies a voltage between the cathode and the anode. A solid electrolyte type electrolytic device having the following features.

15. The solid electrolyte type electrolytic apparatus according to claim 14, wherein the solid electrolyte is an anion exchange membrane.

Images