CARBON DIOXIDE ELECTROLYSIS CELL AND CARBON DIOXIDE ELECTROLYSIS DEVICE

Description

CROSS-REFERENCE TO RELATED APPLICATION

Priority is claimed on Japanese Patent Application No. 2023-058261, filed Mar. 31, 2023, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a carbon dioxide electrolysis cell and a carbon dioxide electrolysis device.

Description of Related Art

A technology to obtain valuable resources by electrochemical reduction of exhaust gases and carbon dioxide in the atmosphere is a promising technology that has a possibility of achieving carbon neutrality, but the biggest issue is economic efficiency. In order to improve economic efficiency, it is important to reduce loss as much as possible and electrolyze carbon dioxide with high energy efficiency.

As the technique for electrochemically reducing carbon dioxide, a technique for electrochemical reduction by supplying a carbon dioxide gas to a cathode in which a catalyst layer is formed using a carbon dioxide reduction catalyst on the side of a gas diffusion layer in contact with an electrolyte from the side of the gas diffusion layer opposite to the catalyst layer is known (Patent Document 1).

In addition, as the technique for electrochemically reducing carbon dioxide, a carbon dioxide electrolysis device that includes a gas supply flow path for supplying carbon dioxide to a cathode, and supplies raw material carbon dioxide in a gaseous state and electrochemically reduces it is known (Patent Document 2).

Patent Documents

[Patent Document 1] PCT International Publication No. WO 2018/232515

[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2022-141239

SUMMARY OF THE INVENTION

As the technique for electrochemically reducing carbon dioxide, a raw material solution supply type carbon dioxide electrolysis cell that supplies an electrolyte containing carbon dioxide being a raw material in an ionic state (CO₂ ³⁻) to a cathode is conceivable. In a raw material solution supply type carbon dioxide electrolysis cell, a flow path structure through which an electrolyte flows greatly affects supply of the raw material to the reaction field. It is thought that, when the flow path structure has a low pressure loss, the raw material directly passes through the gas diffusion layer without being introduced thereinto and the unreacted raw material leaves the cell, and the reduction efficiency is not sufficiently high. In addition, in this case, there is a concern that carbon dioxide electrolysis is unlikely to occur because no raw material is supplied to the reaction field, and by-product generation becomes dominant.

An object of the present invention is to provide a carbon dioxide electrolysis cell and a carbon dioxide electrolysis device in which a raw material is forcibly introduced into a gas diffusion layer and the reduction efficiency is improved in the raw material solution supply type carbon dioxide electrolysis cell.

The present invention includes the following aspects.

Aspect 1 of the present invention is a raw material solution supply type carbon dioxide electrolysis cell, including a cathode section having a cathode-side solution flow path, an anode section having an anode-side solution flow path, and a diaphragm arranged between the cathode section and the anode section, wherein the cathode section includes a cathode including a gas diffusion layer and a cathode catalyst layer, and a cathode-side solution flow path forming member that forms a cathode-side solution flow path between itself and the cathode, wherein the anode section includes an anode and an anode-side solution flow path forming member that forms an anode-side solution flow path between itself and the anode, and wherein the cathode-side solution flow path forming member includes a flow blocking convex part that projects toward the cathode-side solution flow path so that it obstructs a flow of a cathode-side solution flowing through the cathode-side solution flow path and extends in a direction intersecting a flow direction of the cathode-side solution.

Aspect 2 of the present invention is the carbon dioxide electrolysis cell of Aspect 1, wherein the cathode-side solution flow path forming member includes a concave part that projects in a direction opposite to the projection direction on the upstream side before the flow blocking convex part.

Aspect 3 of the present invention is the carbon dioxide electrolysis cell of Aspect 1 or 2, wherein the anode includes a gas diffusion layer and an anode catalyst layer, and the anode-side solution flow path forming member includes a flow blocking convex part that projects toward the anode-side solution flow path so that it obstructs a flow of the anode-side solution flowing through the anode-side solution flow path and extends in a direction intersecting a flow direction of the anode-side solution.

Aspect 4 of the present invention is the carbon dioxide electrolysis cell of Aspect 3, wherein the anode-side solution flow path forming member includes a concave part that projects in a direction opposite to the projection direction on the upstream side before the flow blocking convex part.

Aspect 5 of the present invention is a carbon dioxide electrolysis device including the carbon dioxide electrolysis cell according to any one of Aspect 1 to Aspect 4, a first feed conductor, a second feed conductor, and a power source device.

Aspect 6 of the present invention is a carbon dioxide electrolysis device including the plurality of carbon dioxide electrolysis cells according to any one of Aspect 1 to Aspect 4, and further including a first feed conductor, a second feed conductor, and a power source device.

Aspect 7 of the present invention is the carbon dioxide electrolysis device of Aspect 3, wherein a cathode-side solution flow path forming member included in one carbon dioxide electrolysis cell among the plurality of carbon dioxide electrolysis cells, and an anode-side solution flow path forming member included in a carbon dioxide electrolysis cell adjacent to the one carbon dioxide electrolysis cell are common members, and a solution flow path is formed on the front side and the back side of the common members.

According to Aspect 1 to Aspect 7, it is possible to provide a carbon dioxide electrolysis cell and a carbon dioxide electrolysis device in which a raw material is forcibly introduced into a gas diffusion layer and the reduction efficiency is improved in the raw material solution supply type carbon dioxide electrolysis cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a carbon dioxide electrolysis cell according to an embodiment.

FIG. 2 is a schematic plan view of a cathode-side solution flow path forming member of the carbon dioxide electrolysis cell shown in FIG. 1 when viewed from the side of the cathode.

FIG. 3A is a conceptual diagram for illustrating an effect of a flow blocking convex part and a diagram of a cathode-side solution flow path forming member including a flow blocking convex part.

FIG. 3B is a conceptual diagram for illustrating an effect of a flow blocking convex part and a diagram of a cathode-side solution flow path forming member including no flow blocking convex part.

FIG. 4 is a diagram schematically showing a cross section of a part of the cathode-side solution flow path forming member shown in FIG. 2 taken along the line X-X′.

FIG. 5 is a schematic plan view of an anode-side solution flow path forming member of the carbon dioxide electrolysis cell shown in FIG. 1 when viewed from the side of the anode.

FIG. 6A is a schematic plan view of a wave flow path structure of a cathode-side solution flow path forming member to explain the cathode-side solution flow path forming member shown in FIG. 6B.

FIG. 6B is a schematic plan view of another example of the cathode-side solution flow path forming member, which a carbon dioxide electrolysis cell according to an embodiment comprises, having the wave flow path structure shown in FIG. 6A, with a flow blocking convex part.

FIG. 6C is a schematic cross-sectional view of a part of a single wave part of the wave flow path structure to explain the cathode-side solution flow path forming member shown in FIG. 6B.

FIG. 7 is a schematic cross-sectional view taken along a solution flow direction F in the vicinity of the flow blocking convex part and thickened concave part shown in FIG. 6B.

FIG. 8 is a schematic cross-sectional view of a carbon dioxide electrolysis device including a single carbon dioxide electrolysis cell according to an embodiment.

FIG. 9 is a schematic cross-sectional view of a carbon dioxide electrolysis device including a plurality of carbon dioxide electrolysis cells according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, dimensions and the like of exemplified drawings in the following description are only examples, and the present invention is not necessarily limited thereto, but can be appropriately changed and implemented within ranges in which the scope and spirit of the invention are not changed.

FIG. 1 is a schematic cross-sectional view of a carbon dioxide electrolysis cell according to an embodiment.

A carbon dioxide electrolysis cell 10 shown in FIG. 1 is a raw material solution supply type carbon dioxide electrolysis cell, and includes a cathode section 20 having a cathode-side solution flow path, an anode section 30 having an anode-side solution flow path, and a diaphragm 40 arranged between the cathode section 20 and the anode section 30.

The cathode section 20 includes a cathode 21, and a cathode-side solution flow path forming member 24 that forms a cathode-side solution flow path 22 between itself and the cathode 21.

The cathode 21 is an electrode (reduction electrode) that reduces carbon dioxide (CO₂) to produce a carbon compound and reduces water to produce hydrogen. Examples of carbon compounds produced according to a reduction reaction of carbon dioxide include carbon monoxide (CO), methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄), methanol (CH₃OH), ethanol (C₂H₅OH), and ethylene glycol (C₂H₆O₂).

For example, according to the following reaction, carbon monoxide and ethylene are produced as gaseous products. In the cathode 21, hydrogen is also produced according to the following reaction.

CO₂+H₂O→CO+2OH⁻

2CO+8H₂O→C₂H₄+8OH⁻+2H₂O

2H₂O→H₂+2OH⁻

The cathode 21 includes, for example, a gas diffusion layer 21A and a cathode catalyst layer 21B. A part of the cathode catalyst layer may enter the gas diffusion layer. A porous layer denser than the gas diffusion layer may be arranged between the gas diffusion layer and the cathode catalyst layer.

As a cathode catalyst for forming the cathode catalyst layer, a known catalyst that promotes reduction of carbon dioxide can be used. Specific examples of cathode catalysts include metals such as gold, silver, copper, platinum, palladium, nickel, cobalt, iron, manganese, titanium, cadmium, zinc, indium, gallium, lead, and tin, their alloys and intermetallic compounds, and metal complexes such as ruthenium complexes and rhenium complexes. Among these, copper and silver are preferable, and copper is more preferable in order to promote reduction of carbon dioxide. Cathode catalysts may be used alone or two or more thereof may be used in combination.

As the cathode catalyst, a supported catalyst in which metal particles are supported on a carbon material (carbon particles, carbon nanotubes, graphene, etc.) may be used.

The gas diffusion layer in the cathode 21 is not particularly limited, and for example, carbon paper and carbon cloth may be exemplified.

The method of producing the cathode 21 is not particularly limited, and for example, a method of applying a solution composition containing a cathode catalyst to the surface of the gas diffusion layer opposite to the cathode-side solution flow path forming member 24 and drying it may be exemplified.

The reduction reaction of CO₂ is thought to occur near the boundary between the gas diffusion layer and the cathode catalyst layer (or cathode catalyst) in the cathode 21.

The anode section 30 includes an anode 31 and an anode-side solution flow path forming member 34 that forms an anode-side solution flow path 32 between itself and the anode 31.

The anode 31 is an electrode for oxidizing hydroxide ions to produce oxygen. The anode 31 includes, for example, a gas diffusion layer and a cathode catalyst layer.

An anode catalyst for forming an anode catalyst layer is not particularly limited, and a known anode catalyst can be used. Specifically, for example, metals such as platinum, palladium, and nickel, their alloys and intermetallic compounds, metal oxides such as manganese oxide, iridium oxide, nickel oxide, cobalt oxide, iron oxide, tin oxide, indium oxide, ruthenium oxide, lithium oxide, and lanthanum oxide, and metal complexes such as ruthenium complexes and rhenium complexes may be exemplified. Anode catalysts may be used alone or two or more thereof may be used in combination.

As the gas diffusion layer in the anode 31, for example, carbon paper and carbon cloth may be exemplified. In addition, as the gas diffusion layer, a porous component such as a mesh material, a punching material, a porous material, and a metal fiber sintered component may be used. As the material of the porous component, for example, metals such as titanium, nickel, and iron, and their alloys (for example, SUS) may be exemplified.

As the diaphragm 40, a known separator that can move ions between the anode section and the cathode section and can separate the anode section and the cathode section can be used. Typical examples include ion exchange membranes such as an anion exchange membrane, a cation exchange membrane, a proton exchange membrane, and a bipolar membrane. In addition, in addition to ion exchange membranes, separators such as various porous membranes can be applied as long as they are made of materials that can move ions between the anode section and the cathode section.

The thickness of the diaphragm 40 is preferably 0.03 to 0.5 mm and more preferably 0.05 to 0.1 mm. If the thickness of the diaphragm 40 is equal to or more than the lower limit value of the above range, mechanical strength and durability can be obtained. If the thickness of the diaphragm 40 is equal to or less than the upper limit value of the above range, ion movement resistance is kept low.

FIG. 2 is a view of the cathode-side solution flow path forming member 24 of the carbon dioxide electrolysis cell 10 shown in FIG. 1 when viewed from the side of the cathode. As the cathode-side solution flow path forming member, a member that forms any known flow path structure pattern can be used. FIG. 2 is an example thereof, and is a cathode-side solution flow path forming member that can form a flow path structure in a parallel pattern in which flow paths are arranged in parallel. Other examples will be described below.

As shown in FIG. 2, six linear grooves 24a are formed in parallel with each other on the surface of the cathode-side solution flow path forming member 24 on the side of a cathode section 21. A part of each groove 24a surrounded by the cathode-side solution flow path forming member 24 and the cathode section 21 serves as the cathode-side solution flow path 22. On one side of each cathode-side solution flow path 22 in the length direction, an inlet side flow path 22a through which an electrolyte in which carbon dioxide flows in an ionic state (CO₂ ³⁻) is distributed to each cathode-side solution flow path 22 is formed. On the other side of each cathode-side solution flow path 22 in the length direction, an outlet side flow path 22b through which a product produced by a reduction reaction in the cathode section 21 is collected from each cathode-side solution flow path 22 and discharged is formed.

The number of cathode-side solution flow paths 22 that the carbon dioxide electrolysis cell 10 has is not limited to six, but can be appropriately set depending on dimensions and the like of the carbon dioxide electrolysis cell 10, and can be, for example, 5 to 1,000.

The cathode-side solution flow path forming member 24 shown in FIG. 2 includes a flow blocking convex part 24A that projects toward the cathode-side solution flow path 22 so that it obstructs (blocks) a flow of a cathode-side solution flowing through the cathode-side solution flow path 22 and extends in a direction intersecting a flow direction D1 of the cathode-side solution.

FIGS. 3A and 3B are a conceptual diagram for illustrating an effect of the flow blocking convex part 24A. FIG. 3A is a diagram conceptually showing a case in which a dead end (wall) that blocks a flow is provided in a flow path and FIG. 3B is a diagram conceptually showing a general flow path without a dead end (wall) that blocks a flow. FIG. 4 is a diagram schematically showing a cross section of a part of the cathode-side solution flow path forming member 24 shown in FIG. 2 taken along the line X-X′.

In the raw material solution supply type carbon dioxide electrolysis cell, the flow path structure is very important in that it affects supply of the raw material to the reaction field. When the flow path structure has a low pressure loss, there are concerns that the raw material will directly pass, the unreacted raw material will leave the electrolysis cell, the fluid will be retained after the reaction in the reaction field, and thus a desired reaction will be unlikely to occur, and by-product generation will become dominant (for example, see “H₂” in FIG. 3B). Therefore, in the carbon dioxide electrolysis cell according to the present embodiment, the flow path is made substantially a dead end to create a situation in which the raw material forcibly passes through the gas diffusion layer and comes into contact with a catalyst or a situation in which the raw material passes through the catalyst layer, and therefore the cathode-side solution flow path forming member 24 is set to have a structure including the flow blocking convex part 24A. This structure increases the selectivity of the carbon dioxide reduction reaction.

As shown in FIG. 3B, when there is no wall that blocks a flow of the electrolyte, the ionic carbon dioxide (carbonate ion) in the electrolyte easily flows without passing through the gas diffusion layer, as indicated by the arrow in FIG. 3B. On the other hand, as shown in FIG. 3A, when there is a wall W that blocks a flow of the electrolyte, since the flow of the electrolyte containing the ionic carbon dioxide (carbonate ion) is blocked by the wall, the electrolyte forcibly passes through the gas diffusion layer, and thus carbon dioxide is easily reduced.

FIG. 4 is a schematic cross-sectional view showing an example of a specific structure of the flow blocking convex part 24A shown in FIG. 2.

The flow blocking convex part 24A shown in FIG. 4 can be produced, for example, by metal press processing the cathode-side solution flow path forming member 24 made of a metal. In this case, a part that is not pressed by the metal press functions as a flow path. In this case, since the cathode-side solution flow path forming member including the flow blocking convex part can be produced by metal press processing, it is suitable for mass production.

In the cathode-side solution flow path 22 including the flow blocking convex part 24A shown in FIG. 4, the flow of the electrolyte (cathode-side solution) flowing in the arrow direction is blocked by the flow blocking convex part 24A that extends in a direction intersecting the flow direction. If the flow path is made substantially a dead end, the electrolyte passes through the gas diffusion layer of the cathode 21, and carbon dioxide is easily reduced.

While the example in which the flow blocking convex part 24A shown in FIG. 2 extends in a direction intersecting the flow direction is shown, the direction in which the flow blocking convex part 24A extends is not limited to the direction intersecting the flow direction, and may be a direction which intersects the flow direction and in which the pressure loss increases and the flow path is made substantially a dead end.

FIG. 5 is a diagram of the anode-side solution flow path forming member 34 of the carbon dioxide electrolysis cell 10 shown in FIG. 1 when viewed from the anode.

As shown in FIG. 5, on the surface of the anode-side solution flow path forming member 34 on the side of the anode 31, six linear grooves 34a are formed in parallel with each other. A part of each groove 34a surrounded by the anode-side solution flow path forming member 34 and the anode 31 serves as the anode-side solution flow path 32. On one side of each anode-side solution flow path 32 in the length direction, an inlet side flow path 32a through which a solution containing at least water (H₂O) is distributed to each anode-side solution flow path 32 is formed. On the other side of each anode-side solution flow path 32 in the length direction, an outlet side flow path 32b through which a product produced by an oxidation reaction in the anode 31 is collected from each anode-side solution flow path 32 and discharged is formed.

The number of anode-side solution flow paths 32 that the carbon dioxide electrolysis cell 10 has is not limited to six, but can be appropriately set depending on dimensions and the like of the carbon dioxide electrolysis cell 10, and can be, for example, 5 to 1,000.

As shown in FIG. 5, similar to the cathode-side solution flow path forming member 24, the anode-side solution flow path forming member 34 can include a flow blocking convex part 34A.

Another example of the cathode-side solution flow path forming member will be described with reference to FIG. 6A to FIG. 6C. In FIG. 6A to FIG. 6C, FIG. 6B is a diagram showing the cathode-side solution flow path forming member included in the carbon dioxide electrolysis cell according to the present embodiment, and FIG. 6A and FIG. 6C are diagrams for illustrating the cathode-side solution flow path forming member shown in FIG. 6B.

As described above, as the cathode-side solution flow path forming member, a member that can form any known flow path structure pattern can be used, but a member that can be produced by metal pressing is suitable for mass production and is desirable.

As the material of the cathode-side solution flow path forming member that can be produced by metal pressing, a thin metal plate, for example, a thin plate of stainless steel, titanium, a titanium alloy, or the like as a metal having corrosion resistance and conductivity can be used. For example, a thin metal plate that has been subjected to an anti-corrosion treatment such as gold plating can be used.

FIG. 6A is a schematic plan view of a part of the cathode-side solution flow path forming member.

The cathode-side solution flow path forming member shown in FIG. 6A is a member that can form a so-called wave flow path, and can be produced by metal pressing.

In a cathode-side solution flow path forming member 124 shown in FIG. 6A, when viewed from above (+Z), a convex part (peak part) 124a and a concave part (trough part) 124b are alternately formed, and a plurality of single wave parts (124-1, 124-2, 124-3, 124-4, . . . ) extending in the X direction are arranged in parallel, and the plurality of wave parts (124-1, 124-2, 124-3, 124-4, . . . ) are alternately inclined in the direction opposite to the direction F in which the solution flows.

FIG. 6C is a schematic cross-sectional view of a part of a single wave part.

As shown in FIG. 6C, in the cathode-side solution flow path forming member 124, the convex part 124a is a convex portion pressed during pressing, and the concave part 124b is a concave portion pressed during pressing, with respect to a flat part (reference surface) 124c that is not pressured during pressing.

FIG. 6B is a schematic plan view of a part of the cathode-side solution flow path forming member.

The cathode-side solution flow path forming member 24-1 shown in FIG. 6B includes the flow blocking convex part 24A, and further includes the thickened concave part 24B that projects in a direction opposite to the projection direction of the flow blocking convex part 24A on the upstream side before the flow blocking convex part 24A in the solution flow direction F. When the thickened concave part 24B is provided, an effect of forcibly passing the electrolyte through the gas diffusion layer becomes stronger.

FIG. 7 is a schematic cross-sectional view taken along a solution flow direction F in the vicinity of the flow blocking convex part 24A and the thickened concave part 24B.

The flow blocking convex part 24A and the thickened concave part 24B can have the same shapes that are symmetrical when rotated by 180°.

As will be described below, if the cathode-side solution flow path forming member has a structure including a flow blocking convex part and a thickened concave part, when a carbon dioxide electrolysis cell stack in which a plurality of carbon dioxide electrolysis cells according to the present embodiment are laminated is produced, the back side of the cathode-side solution flow path forming member of one carbon dioxide electrolysis cell can be used as the anode-side solution flow path forming member of the adjacent carbon dioxide electrolysis cell. That is, the front side and back side of one solution flow path forming member can be used as a cathode-side solution flow path forming member and an anode-side solution flow path forming member between adjacent carbon dioxide electrolysis cells.

FIG. 8 is a schematic cross-sectional view of a carbon dioxide electrolysis device 100 including a carbon dioxide electrolysis cell 10.

The carbon dioxide electrolysis device 100 shown FIG. 8 includes a carbon dioxide electrolysis cell 10, a first feed conductor 51, a second feed conductor 52, and a power source device 60, and is interposed between a pair of support plates (not shown), and additionally fastened with a bolt or the like.

Examples of materials of the first feed conductor 51 and the second feed conductor 52 include metals such as copper, gold, titanium, and SUS, and carbon. As the first feed conductor 51 and the second feed conductor 52, those obtained by performing a plating treatment such as gold plating on the surface of a copper substrate may be used.

The cathode-side solution flow path forming member 24 and the anode-side solution flow path forming member 34 are conductors, and a voltage is applied between the cathode 21 and the anode 31 from the power source device 60.

The power source 60 is not limited to a general grid power source, a battery and the like, but may be a power source that supplies power generated by renewable energy from solar cells, wind power generation, geothermal power generation or the like.

FIG. 9 is a schematic cross-sectional view of a carbon dioxide electrolysis device 200 including a plurality of carbon dioxide electrolysis cells 10.

The carbon dioxide electrolysis device 200 shown in FIG. 9 includes a plurality (N) of carbon dioxide electrolysis cells 10, a first feed conductor 151 and a second feed conductor 152 arranged to surround the plurality of carbon dioxide electrolysis cells 10, and the power source device 60.

The carbon dioxide electrolysis device 200 shown in FIG. 9 further includes support plates 81 and 82 on the outside of the first feed conductor 151 and the second feed conductor 152 with insulation plates 71 and 72 therebetween, which are fastened with a bolt (not shown) or the like.

In the example shown in FIG. 9, the cathode-side solution flow path forming member 24 and the anode-side solution flow path forming member 34 of the adjacent carbon dioxide electrolysis cells 10 are the front side and the back side of a common member.

The N carbon dioxide electrolysis cells 10 are the carbon dioxide electrolysis cell 10-1, the carbon dioxide electrolysis cell 10-2, . . . the carbon dioxide electrolysis cell 10-(N−1), and the carbon dioxide electrolysis cell 10-N in order from the side of the first feed conductor 151. The anode-side solution flow path forming member 34 included in the carbon dioxide electrolysis cell 10-1 and the cathode-side solution flow path forming member 24 included in the carbon dioxide electrolysis cell 10-2 form a solution flow path on the front side and the back side of a common member.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.

EXPLANATION OF REFERENCES

• • 10 Carbon dioxide electrolysis cell
  • 20 Cathode section
  • 21 Cathode
  • 22 Cathode-side solution flow path
  • 24, 24-1 Cathode-side solution flow path forming member
  • 24A Flow blocking convex part
  • 24B Thickened concave part
  • 30 Anode section
  • 31 Anode
  • 32 Anode-side solution flow path
  • 34 Anode-side solution flow path forming member
  • 34A Flow blocking convex part
  • 40 Diaphragm
  • 100, 200 Carbon dioxide electrolysis device