JP7542467B2 - Carbon dioxide electrolysis device and method for operating the carbon dioxide electrolysis device - Google Patents

Description

The invention of this embodiment relates to a carbon dioxide electrolysis device.

In recent years, from the perspective of both energy and environmental issues, there is a demand not only for converting renewable energy such as solar power generation into electrical energy for use, but also for converting it into a form that can be stored and transported. In response to this demand, research and development is being conducted into artificial photosynthesis technology that uses sunlight to produce chemical substances, like photosynthesis by plants. This technology may make it possible to store renewable energy as storable fuel, and is also expected to create value by producing chemical substances that can be used as industrial raw materials.

As an apparatus for producing chemical substances using renewable energy such as solar power generation, an electrochemical reaction device is known that includes a cathode that reduces carbon dioxide (CO ₂ ) generated, for example, from a power plant or a waste treatment plant, and an anode that oxidizes water (H ₂ O). At the cathode, for example, carbon dioxide is reduced to produce carbon compounds such as carbon monoxide (CO). When such an electrochemical reaction device is realized in a cell form (also called an electrolysis cell), it is considered effective to realize it in a form similar to a fuel cell such as a Polymer Electric Fuel Cell (PEFC). By directly supplying carbon dioxide to the catalyst layer of the cathode, it is possible to rapidly proceed with the reduction reaction of carbon dioxide.

However, this type of cell configuration creates problems similar to those faced by PEFCs. That is, to realize a durable electrolysis cell that is less prone to breakdowns and to improve the efficiency of carbon compound production, it is necessary to steadily supply carbon dioxide to the cathode catalyst layer.

U.S. Patent No. 7,659,024 U.S. Patent No. 7,087,337

The problem that this invention aims to solve is to suppress the decrease in electrolysis efficiency of a carbon dioxide electrolysis device.

The carbon dioxide electrolysis device of the embodiment includes a cathode for reducing carbon dioxide to produce a carbon compound, an anode for oxidizing water to produce oxygen, a cathode gas flow path facing the cathode and for supplying a gas containing carbon dioxide, an anode solution flow path facing the anode and for supplying an electrolytic solution containing water, and a separator provided between the anode and the cathode. The aspect ratio of the cathode gas flow path defined by the ratio of the average depth h of the cathode gas flow path to the average width of the cathode gas flow path is greater than 1 and not greater than 3. The average fluid depth M of the cathode gas flow path defined by the ratio of the perimeter of the cathode gas flow path to the cross-sectional area of the cathode gas flow path and the average depth h of the cathode gas flow path satisfy the formula: h/8≦M<h/4, and M is 0.33 or more .

FIG. 1 is a schematic diagram for explaining a configuration example of a carbon dioxide electrolysis device. 4 is a schematic plan view showing an example of the structure of a portion of a flow path plate. FIG. 4 is a schematic cross-sectional view showing an example of the structure of a portion of a flow path plate. FIG. 11 is a schematic plan view showing another example of the structure of the flow path plate. FIG. 13 is a schematic cross-sectional view showing another example of the structure of a portion of the flow path plate. FIG. 13 is a schematic cross-sectional view showing another example of the structure of a portion of the flow path plate. FIG. 13 is a schematic cross-sectional view showing another example of the structure of a portion of the flow path plate. FIG. FIG. 13 is a schematic diagram showing another configuration example of the carbon dioxide electrolysis device. 1 is a flowchart illustrating an example of a method for operating a carbon dioxide electrolysis device. 11 is a flowchart for explaining an example of an operation of a refresh operation process. FIG. 1 is a graph showing the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode. FIG. 1 is a graph showing the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode.

The following describes the embodiments with reference to the drawings. Note that the drawings are schematic, and for example, the dimensions of each component, such as the thickness and width, may differ from the dimensions of the actual components. In addition, in the embodiments, substantially identical components may be given the same reference numerals, and descriptions thereof may be omitted.

In this specification, "connect" includes not only direct connection but also indirect connection, unless otherwise specified.

Figure 1 is a schematic diagram for explaining an example of the configuration of a carbon dioxide electrolysis device. Figure 1 shows a carbon dioxide electrolysis device 1 equipped with an electrolysis cell 10.

The electrolysis cell 10 includes an anode section 11, a cathode section 12, and a separator 13 that separates the anode section 11 and the cathode section 12. The electrolysis cell 10 is, for example, sandwiched between a pair of support plates and further fastened with bolts or the like.

The anode section 11 includes an anode 111, an anode solution flow path 112a provided in a flow path plate 112, and an anode current collector 113.

The cathode section 12 includes a cathode 121, a cathode gas flow path 122a provided in a flow path plate 122, and a cathode current collector 123.

The anode 111 is an electrode (oxidation electrode) that promotes the oxidation reaction of water (H ₂ O) in the anode solution to produce oxygen (O ₂ ) and hydrogen ions (H ⁺ ), or promotes the oxidation reaction of hydroxide ions (OH ⁻ ) generated in the cathode section 12 to produce oxygen and water.

The anode 111 is disposed between the separator 13 and the flow path plate 112 so as to be in contact with them. A first surface of the anode 111 is in contact with the separator 13. A second surface of the anode 111 is provided on the opposite side of the first surface of the anode 111 and faces the anode solution flow path 112a.

The compounds produced by the oxidation reaction of the anode 111 differ depending on the type of oxidation catalyst, etc. When an electrolyte is used as the anode solution, the anode 111 is preferably mainly composed of a catalyst material (anode catalyst material) capable of oxidizing water (H ₂ O) to produce oxygen and hydrogen ions, or oxidizing hydroxide ions (OH ⁻ ) to produce water and oxygen, and capable of reducing the overvoltage of such reactions. Examples of such catalytic materials include metals such as platinum (Pt), palladium (Pd), and nickel (Ni), alloys and intermetallic compounds containing these metals, binary metal oxides such as manganese oxide (Mn—O), iridium oxide (Ir—O), nickel oxide (Ni—O), cobalt oxide (Co—O), iron oxide (Fe—O), tin oxide (Sn—O), indium oxide (In—O), ruthenium oxide (Ru—O), lithium oxide (Li—O), and lanthanum oxide (La—O), ternary metal oxides such as Ni—Co—O, Ni—Fe—O, La—Co—O, Ni—La—O, and Sr—Fe—O, quaternary metal oxides such as Pb—Ru—Ir—O, and La—Sr—Co—O, and metal complexes such as Ru complexes and Fe complexes.

The anode 111 preferably has a structure capable of moving the anode solution or ions between the separator 13 and the anode solution flow path 112a, such as a substrate (support) having a porous structure, such as a mesh material, a punching material, or a porous body. Substrates having a porous structure include those with relatively large voids, such as metal fiber sintered bodies. The substrate may be made of a metal material such as titanium (Ti), nickel (Ni), iron (Fe), or an alloy containing at least one of these metals (e.g., SUS), or may be made of the above-mentioned anode catalyst material. When an oxide is used as the anode catalyst material, it is preferable to form a catalyst layer by attaching or laminating the anode catalyst material to the surface of a substrate made of the above-mentioned metal material. The anode catalyst material preferably has a shape such as nanoparticles, nanostructures, nanowires, etc., in order to enhance the oxidation reaction. A nanostructure is a structure in which nanoscale unevenness is formed on the surface of a catalyst material. In addition, it is not necessary to provide an oxidation catalyst on the oxidation electrode. An oxidation catalyst layer provided on a part other than the oxidation electrode may be electrically connected to the oxidation electrode.

The cathode 121 is an electrode (reduction electrode) for generating a carbon compound by causing a reduction reaction of carbon dioxide or a reduction reaction of a reduction product. Examples of carbon compounds include carbon monoxide (CO), formic acid (HCOOH), methane (CH ₄ ), ethane (C ₂ H ₆ ), ethylene (C ₂ H ₄ ), methanol (CH ₃ OH), acetic acid (CH ₃ COOH), ethanol (C ₂ H ₅ OH), formaldehyde (HCHO), propanol (C ₃ H ₇ OH), and ethylene glycol (C ₂ H ₆ O ₂ ). The reduction reaction at the cathode 121 may include a side reaction of generating hydrogen (H ₂ ) by causing a reduction reaction of water in addition to the reduction reaction of carbon dioxide.

The cathode 121 is preferably composed of an ion-conductive material in addition to the electrode substrate and the metal catalyst supported on the carbon material. The ion-conductive material acts to transfer ions between the metal catalysts contained in the layer, and is therefore effective in improving the activity of the electrode. As the ion-conductive material, a cation exchange resin or an anion exchange resin is preferably used.

The carrier for the metal catalyst preferably has a porous structure. In addition to the above-mentioned materials, applicable materials include carbon black such as Ketjen Black and Vulcan XC-72, activated carbon, and carbon nanotubes. By having a porous structure, the area of the active surface that contributes to the redox reaction can be increased, thereby increasing the conversion efficiency.

It is preferable that not only the carrier but also the catalyst layer itself formed on the substrate has a porous structure and has many relatively large pores. Specifically, it is preferable that the distribution frequency of pores is maximum in the diameter range of 5 μm to 200 μm in the pore size distribution of the catalyst layer measured by mercury intrusion porosimetry. In this case, gas diffuses quickly throughout the catalyst layer, and the reduction products are also easily discharged outside the catalyst layer via this route, resulting in an efficient electrode.

In order to efficiently supply carbon dioxide to the catalyst layer, it is preferable for the electrode substrate supporting the catalyst layer to have a gas diffusion layer. The gas diffusion layer is formed from a conductive porous body. If the gas diffusion layer is formed from a water-repellent porous body, the amount of water generated by the reduction reaction and the amount of water that has moved from the oxidation side can be reduced, and the water can be discharged through the reduction flow path, thereby increasing the proportion of carbon dioxide gas in the porous body, which is preferable.

If the thickness of the gas diffusion layer is extremely small, it is undesirable because it impairs uniformity on the cell surface. On the other hand, if the thickness is extremely large, it is undesirable because it increases material costs and reduces efficiency due to increased gas diffusion resistance. To further improve diffusion, it is more preferable to provide a denser diffusion layer (mesoporous layer (MPL)) between the gas diffusion layer and catalyst layer, as this changes the water repellency and porosity, promoting gas diffusion and the discharge of liquid components.

Examples of the metal catalyst supported on the carrier include materials that reduce the activation energy for reducing hydrogen ions and carbon dioxide. In other words, examples of the metal catalyst include metal materials that reduce the overvoltage when carbon compounds are produced by the reduction reaction of carbon dioxide. For example, it is preferable to use at least one metal and metal oxide selected from the group consisting of gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), nickel (Ni), (Co), iron (Fe), manganese (Mn), titanium (Ti), cadmium (Cd), zinc (Zn), indium (In), gallium (Ga), lead (Pb), and tin (Sn), or an alloy containing the metal. For example, it is preferable to use at least one of copper, gold, and silver. However, without being limited thereto, a metal complex such as a ruthenium (Ru) complex or a rhenium (Re) complex can also be used as the reduction catalyst. In addition, multiple materials may be mixed. Various shapes such as a plate, mesh, wire, particle, porous, thin film, and island shape can be applied to the metal catalyst.

When metal nanoparticles are used for the metal catalyst, the average diameter is preferably 1 nm or more and 15 nm or less, more preferably 1 nm or more and 10 nm or less, and even more preferably 1 nm or more and 5 nm or less. If this condition is met, the surface area of the metal per catalyst weight becomes large, and high activity is exhibited with a small amount of metal, which is preferable.

The anode 111 and the cathode 121 can be connected to a power source 20. The power source 20 applies a voltage between the anode 111 and the cathode 121. Examples of the power source 20 are not limited to a normal system power source or a battery, and may include a power source that supplies power generated by renewable energy such as a solar cell or wind power generation. The power source 20 may further include a power controller that adjusts the output of the power source to control the voltage between the anode 111 and the cathode 121. The power source 20 may be provided outside the carbon dioxide electrolysis device 1.

The anode solution flow path 112a has the function of supplying the anode solution to the anode 111. The anode solution flow path 112a is composed of pits (grooves/recesses) provided in the flow path plate 112. The flow path plate 112 has an inlet and an outlet (neither shown) connected to the anode solution flow path 112a, and the anode solution is introduced and discharged by a pump (not shown) via the inlet and outlet. The anode solution flows through the anode solution flow path 112a so as to come into contact with the anode.

As the anode solution, an aqueous solution (electrolytic solution) containing metal ions can be used. By using an electrolytic solution containing metal ions, the electrolysis efficiency can be increased. Examples of the aqueous solution include aqueous solutions containing phosphate ions (PO ₄ ^2- ), borate ions (BO ₃ ^3- ), sodium ions (Na ⁺ ), potassium ions (K ⁺ ), calcium ions (Ca ²⁺ ), lithium ions (Li ⁺ ), cesium ions (Cs ⁺ ), magnesium ions (Mg ²⁺ ), chloride ions (Cl ^- ), bicarbonate ions (HCO ₃ ^- ), carbonate ions (CO ₃ ^2- ), and the like. In addition, aqueous solutions containing LiHCO ₃ , NaHCO ₃ , KHCO ₃ , CsHCO ₃ , phosphoric acid, boric acid, and the like may be used.

The cathode gas flow path 122a faces the first surface of the cathode 121. The cathode gas flow path 122a has a function of supplying gas containing carbon dioxide to the cathode 121. The cathode gas flow path 122a can be connected to, for example, a carbon dioxide supply source that supplies gas containing carbon dioxide. Examples of the carbon dioxide supply source include facilities such as power plants and waste treatment plants. The cathode gas flow path 122a is composed of pits (grooves/recesses) provided in the flow path plate 122. The flow path plate 122 has an inlet and an outlet (neither shown) connected to the cathode gas flow path 122a, and the above gas is introduced and discharged through these inlet and outlet by a pump (not shown).

It is preferable that the flow path plate 112 and the flow path plate 122 are made of a material that has low chemical reactivity and high conductivity. Examples of such materials include metal materials such as Ti and SUS, and carbon. Although not shown, the flow path plate 112 and the flow path plate 122 have inlets and outlets for each flow path, as well as screw holes for tightening. Also, gaskets (not shown) are sandwiched in front of and behind each flow path plate as necessary. Also, the flow path plate 112 and the flow path plate 122 are mainly formed from a single member, but they may be formed from different members and stacked together. Furthermore, a surface treatment may be applied to a part or the entire surface to impart hydrophilic and water-repellent functions.

The flow path plate 122 may have a land that contacts the cathode 121 for electrical connection with the cathode 121. The shape of the cathode gas flow path 122a may be a shape adjacent to a cylindrical land or a serpentine shape formed by bending a long and thin flow path, but is not particularly limited as long as it has a cavity. It is preferable to configure the cathode gas flow path 122a with multiple flow paths or serpentine flow paths connected in parallel or a combination thereof, since this can increase the uniformity of the gas supplied to the cathode 121 and increase the uniformity of the electrolysis reaction.

Figure 2 is a schematic plan view showing an example of the structure of a portion of the flow path plate 122. Figure 2 shows the X-Y plane of the flow path plate 122, which includes the X-axis and the Y-axis perpendicular to the X-axis. In Figure 2, only the overlapping portion of the flow path plate 122 and the cathode 121 is shown. Figure 3 is a schematic cross-sectional view showing an example of the structure of a portion of the flow path plate 122. Figure 3 shows the Y-Z plane of the flow path plate 122, which includes the Y-axis and the Z-axis perpendicular to the Y-axis and the X-axis. The Z-axis direction is the thickness direction of the flow path plate 122.

The flow path plate 122 has a surface 241, a surface 242, and a cathode gas flow path 122a. The surface 241 contacts the cathode 121. The surface 242 is provided on the opposite side of the surface 241 and contacts the cathode current collector 123. The flow path plate 122 shown in Figures 2 and 3 has a rectangular parallelepiped shape. The three-dimensional shape of the flow path plate 122 is not limited to a rectangular parallelepiped shape.

The cathode gas flow channel 122a faces the gas diffusion layer of the cathode 121. The cathode gas flow channel 122a is connected to an inlet and an outlet. The inlet is provided for introducing a gas containing carbon dioxide into the cathode gas flow channel 122a. The outlet is provided for discharging the gas containing carbon dioxide from the cathode gas flow channel 122a and for discharging the product of the reduction reaction from the cathode gas flow channel 122a.

2 extends in a serpentine shape along the surface 241. Without being limited thereto, the cathode gas flow passage 122a may extend in a comb-tooth or spiral shape along the surface 241. The cathode gas flow passage 122a includes a space formed by, for example, a groove or an opening provided in the flow passage plate 122.

The carbon dioxide gas may be supplied in a dry state. The carbon dioxide concentration in the gas supplied to the cathode gas flow path 122a does not have to be 100%. In this case, the efficiency will decrease, but it is also possible to reduce gas containing carbon dioxide discharged from various facilities.

It is preferable that the flow path plate 112 and the flow path plate 122 have the same shape. This can increase the uniformity of the reaction. Note that the flow path plate 112 and the flow path plate 122 may have different shapes.

The anode current collector 113 contacts the surface of the flow path plate 112 opposite to the surface that contacts the anode 111. The anode current collector 113 is electrically connected to the anode 111. The anode current collector 113 preferably contains a material that has low chemical reactivity and high conductivity. Such materials include metal materials such as Ti and SUS, and carbon.

The cathode current collector 123 contacts the surface of the flow path plate 122 opposite to the surface that contacts the cathode 121. The cathode current collector 123 is electrically connected to the cathode 121. The cathode current collector 123 preferably contains a material that has low chemical reactivity and high conductivity. Such materials include metal materials such as Ti and SUS, and carbon.

The separator 13 is provided between the anode 111 and the cathode 121. The separator 13 is composed of an ion exchange membrane or the like that can move ions between the anode and the cathode and can separate the anode part and the cathode part. As the ion exchange membrane, for example, a cation exchange membrane such as Nafion or Flemion, or an anion exchange membrane such as Neocepta, Selemion, or Sustenion can be used. When an alkaline solution is used as the electrolyte and it is assumed that hydroxide ions (OH ⁻ ) mainly move, it is preferable that the separator is composed of an anion exchange membrane. In addition, the ion exchange membrane may be composed of a membrane having a basic skeleton of a hydrocarbon or a membrane having an amine group. However, other than the ion exchange membrane, a salt bridge, a glass filter, a porous polymer membrane, a porous insulating material, or the like may be applied to the separator as long as it is a material that can move ions between the anode and the cathode. However, if gas flows between the cathode part and the anode part, a circulation reaction due to reoxidation of the reduction product may occur. For this reason, it is preferable to minimize the gas exchange between the cathode and anode parts, so care must be taken when using a porous thin film as a separator.

Next, an operation example of the carbon dioxide electrolysis device of the embodiment will be described. Here, a case where the carbon dioxide electrolysis device 1 shown in FIG. 1 produces carbon monoxide as a carbon compound will be mainly described, but the carbon compound as a reduction product of carbon dioxide is not limited to carbon monoxide. In addition, the reduction product carbon monoxide may be further reduced to produce the above-mentioned organic compounds. In the case of producing a carbon compound in a solution state, it is preferable to use the electrolysis cell 10. In addition, the reaction process by the electrolysis cell 10 may be a case where hydrogen ions (H ⁺ ) are mainly produced, or a case where hydroxide ions (OH ⁻ ) are mainly produced, but is not limited to either of these reaction processes.

The reaction process when water (H ₂ O) is oxidized to generate hydrogen ions (H ⁺ ) will be mainly described. When a current is supplied from the power source 20 between the anode 111 and the cathode 121, an oxidation reaction of water (H ₂ O) occurs at the anode 111 in contact with the anode solution. Specifically, as shown in the following formula (1), H ₂ O contained in the anode solution is oxidized to generate oxygen (O ₂ ) and hydrogen ions (H ⁺ ).
2H ₂ O → 4H ⁺ +O ₂ +4e ^- (1)

The H ⁺ generated at the anode 111 moves through the electrolyte and separator 13 present in the anode 111 and reaches the vicinity of the cathode 121. A reduction reaction of carbon dioxide (CO ₂ ) occurs due to electrons (e ^- ) based on the current supplied from the power source 20 to the cathode 121 and the H ⁺ that has moved to the vicinity of the cathode 121. Specifically, as shown in the following formula (2), carbon dioxide supplied from the cathode gas flow channel 122a to the cathode 121 is reduced to generate carbon monoxide. Furthermore, hydrogen is generated by hydrogen ions receiving electrons as shown in the following formula (3). At this time, hydrogen may be generated simultaneously with carbon monoxide.
CO ₂ +2H ⁺ +2e ^- → CO+H ₂ O...(2)
2H ⁺ +2e ^- → H ₂ ...(3)

Next, a reaction process in which carbon dioxide (CO ₂ ) is reduced to generate hydroxide ions (OH ⁻ ) will be described. When a current is supplied from the power source 20 between the anode 111 and the cathode 121, water (H ₂ O) and carbon dioxide (CO ₂ ) are reduced near the cathode 121 to generate carbon monoxide (CO) and hydroxide ions (OH ⁻ ), as shown in the following formula (4). Furthermore, hydrogen is generated by water receiving electrons, as shown in the following formula (5). At this time, hydrogen may be generated simultaneously with carbon monoxide. The hydroxide ions (OH ⁻ ) generated by these reactions diffuse near the anode 111, and as shown in the following formula (6), the hydroxide ions (OH ⁻ ) are oxidized to generate oxygen (O ₂ ).
2CO ₂ +2H ₂ O+4e ^- → 2CO+4OH ^-... (4)
2H ₂ O+2e ^- → H ₂ +2OH ^-... (5)
4OH ^- → 2H ₂ O+O ₂ +4e ^-... (6)

In the electrolytic cell 10 shown in FIG. 1, the anode solution and ions are supplied from the separator 13, and carbon dioxide gas is supplied from the cathode gas flow path 122a.

The carbon dioxide electrolysis device 1 is not limited to being specialized for the reduction of carbon dioxide, but can also produce carbon dioxide reduction products and hydrogen in any ratio, such as producing carbon monoxide and hydrogen in a 1:2 ratio, followed by a chemical reaction to produce methanol.

Hydrogen is a cheap and easily available raw material from water electrolysis and fossil fuels, so the ratio of hydrogen does not need to be high. From these perspectives, it is economically and environmentally preferable for the ratio of carbon monoxide to hydrogen to be at least 1, and preferably 1.5 or more.

The shallower the cathode gas flow channel 122a, the better from the viewpoint of supplying carbon dioxide to the gas diffusion layer. On the other hand, if the cathode gas flow channel 122a is narrow, the pressure loss in the cathode gas flow channel 122a increases, which is undesirable from the viewpoint of energy loss in gas supply. Furthermore, when salt precipitates due to a reaction between metal ions in the anode solution and carbon dioxide gas, and the salt solidifies at the boundary between the cathode gas flow channel 122a and the gas diffusion layer, if the flow channel is shallow, the flow channel will be closed and carbon dioxide gas will not reach the entire surface of the electrode, which may cause a breakdown and affect durability.

In one example of a conventional fuel cell, a groove is formed on the inner bottom surface of the flow channel to store foreign matter (water droplets) in order to prevent the flow channel from being blocked by foreign matter (water droplets). However, in the case of a carbon dioxide electrolysis device, the precipitated salt solidifies near the opposing surface between the cathode 121 and the cathode gas flow channel 122a, so forming a groove on the inner bottom surface does not have much effect in preventing blockage.

In contrast, in the carbon dioxide electrolysis device of this embodiment, the cross-sectional shape of the cathode gas flow channel 122a is controlled to suppress clogging of the flow channel. The aspect ratio of the cathode gas flow channel 122a is preferably greater than 1 and equal to or less than 3. The aspect ratio of the cathode gas flow channel 122a is defined as the ratio of the depth h of the cathode gas flow channel 122a to the width W of the cathode gas flow channel 122a in the X-axis or Y-axis direction.

If the aspect ratio is less than 1, the flow path may be blocked due to salt precipitation. If the aspect ratio exceeds 3, the flow path plate 122 must be thickened, which increases material costs and processing costs. It is more preferable that the aspect ratio be 2 or more and 3 or less.

It is preferable that the average fluid depth M of the cathode gas channel 122a and the depth h of the cathode gas channel 122a satisfy the following formula (A).
Formula: h/8≦M<h/4 (A)

The average fluid depth M of the cathode gas flow channel 122a is defined by the cross-sectional area Ac of the cathode gas flow channel 122a relative to the perimeter S of the cathode gas flow channel 122a. The perimeter S may be calculated by (width W x 2) + (depth h x 2). Even if the aspect ratio of the cathode gas flow channel 122a is large, if the average fluid depth M of the cathode gas flow channel 122a is small, salt may precipitate in the cathode gas flow channel 122a, causing the cathode gas flow channel 122a to be easily clogged.

If the average fluid depth M is less than h/8, the flow path may become clogged due to salt precipitation. If the average fluid depth M is h/4 or more, the utilization rate of carbon dioxide may decrease. It is more preferable that the average fluid depth M is h/7.9 or more and h/6 or less.

The depth h, width W, perimeter S, and average fluid depth M can be measured by the following method. A cross section of the flow path plate 122 is cut at any position in a direction (X-axis direction in FIG. 2) perpendicular to the long direction of the cathode gas flow path 122a (Y-axis direction in FIG. 2), and the cross section is observed, for example, with a microscope to measure each parameter. As a non-destructive inspection method, for example, a method of visualizing the inside of the flow path plate using neutron radiography may be used. It is preferable to calculate these values by averaging values from multiple locations.

By forming the cathode gas flow passage 122a deep enough to satisfy the above conditions, a space is provided in the depth direction of the cathode gas flow passage 122a through which gas can be diverted, which is preferable from the viewpoint of eliminating gas supply when salt precipitates. As a result, even if salt precipitates in part of the cathode gas flow passage 122a, carbon dioxide gas can be easily supplied to the entire surface of the cathode 121, which is also preferable from the viewpoint of durability and resistance to breakdowns. Therefore, a carbon dioxide electrolysis device that suppresses a decrease in electrolysis efficiency and allows for high-efficiency and long-term operation can be provided.

The shape of the cathode gas flow passage 122a is not limited to the shape shown in Figures 2 and 3. Other examples of the shape of the cathode gas flow passage 122a are described below.

Figure 4 is a schematic plan view showing another structural example of the flow path plate 122. Figure 4 shows the XY plane of the flow path plate 122. The flow path plate 122 shown in Figure 4 differs from the flow path plate 122 shown in Figure 2 in that it has multiple flow path sections 244 in which the cathode gas flow paths 122a are connected in parallel in the XY plane. Note that the other parts are the same as the flow path plate 122 shown in Figure 2, so the above description can be used as appropriate.

The multiple flow path sections 244 extend along the long direction of the cathode gas flow path 122a (the Y-axis direction in FIG. 4). FIG. 4 shows an example in which two flow path sections 244 are connected in parallel each time the cathode gas flow path 122a turns around, but the number of flow path sections 244 is not limited to the number shown in FIG. 4. The width W of the cathode gas flow path 122a shown in FIG. 4 is defined by the width of one flow path section 244.

Figure 5 is a schematic cross-sectional view showing another structural example of a portion of the flow path plate 122. Figure 5 shows the Y-Z plane of the flow path plate 122. The flow path plate 122 shown in Figure 5 differs from the flow path plate 122 shown in Figure 3 in that the cathode gas flow path 122a has regions 122a1 and 122a2 in the X-Z cross section. Note that other parts are the same as the flow path plate 122 shown in Figure 3, so the above description can be used as appropriate.

Region 122a1 faces cathode 121 and has an inner wall surface 246. The cross-sectional shape of region 122a1 shown in FIG. 5 is rectangular, but the shape of region 122a1 is not limited to that shown in FIG. 5.

The region 122a2 is provided between the region 122a1 and the inner bottom surface 245 of the cathode gas flow channel 122a, and has an inner wall surface 247. The cross-sectional shape of the region 122a2 shown in FIG. 5 is rectangular, but the shape of the region 122a2 is not limited to that shown in FIG. 5.

The width W2 of the region 122a2 in the X-axis direction is wider than the width W1 of the region 122a1 in the X-axis direction. In the flow path plate 122 shown in FIG. 5, by making the width W2 wider than the width W1, the bypass space for carbon dioxide gas can be increased, and blockage of the cathode gas flow path 122a due to salt precipitation can be suppressed. The width W of the cathode gas flow path 122a shown in FIG. 5 is defined by the width W1. In addition, the average fluid depth M is defined by the perimeter of the cathode gas flow path 122a having the shape shown in FIG. 5, taking into account both the width W1 and the width W2.

Figure 6 is a schematic cross-sectional view showing another structural example of a portion of the flow path plate 122. Figure 6 shows the Y-Z plane of the flow path plate 122. The flow path plate 122 shown in Figure 6 differs from the flow path plate 122 shown in Figure 5 in the shape of the region 122a2 in the X-Z cross section. Note that other parts are the same as the flow path plate 122 shown in Figure 5, so the above description can be used as appropriate.

The cross-sectional shape of region 122a2 shown in FIG. 6 is a square, but the shape of region 122a2 is not limited to that shown in FIG. 6. In FIG. 6, the cross-sectional area of region 122a2 is larger than the cross-sectional area of region 122a1. This allows the bypass space for carbon dioxide gas to be increased, and prevents the cathode gas flow channel 122a from being blocked by salt precipitation. The width W of the cathode gas flow channel 122a shown in FIG. 6 is defined by the width W1. In addition, the average fluid depth M is defined by the perimeter of the cathode gas flow channel 122a having the shape shown in FIG. 6, taking into account both the width W1 and the width W2.

Figure 7 is a schematic cross-sectional view showing another structural example of a portion of the flow path plate 122. Figure 7 shows the Y-Z plane of the flow path plate 122. The flow path plate 122 shown in Figure 7 differs from the flow path plate 122 shown in Figure 3 in that, in the X-Z cross section, the cathode gas flow path 122a has regions 122a1 and 122a2, the inner wall surface 246 of region 122a1 is hydrophilic, and the inner wall surface 247 and inner bottom surface 245 of region 122a2 are water-repellent. Note that the other parts are the same as the flow path plate 122 shown in Figure 3, so the above description can be used as appropriate.

The contact angle of the hydrophilic inner wall surface 246 with water is, for example, greater than 0 degrees and less than or equal to 90 degrees. The hydrophilic inner wall surface 246 can be formed, for example, by using a flow path layer containing a hydrophilic material. The hydrophilic inner wall surface 246 may also be formed by subjecting a flow path layer containing a material applicable to the flow path plate 122 to a hydrophilic treatment.

The contact angle of the water-repellent inner wall surface 247 with water is, for example, greater than or equal to 100 degrees and less than 180 degrees. The water-repellent inner wall surface 247 can be formed, for example, by using a flow path layer containing a water-repellent material. The water-repellent inner wall surface 247 may also be formed by applying a water-repellent treatment to a flow path layer containing a material applicable to the flow path plate 122.

The thickness (length in the Z-axis direction) of region 122a1 is not particularly limited, but is preferably at least half the depth h of cathode gas flow channel 122a, for example.

In the cathode gas flow path 122a shown in FIG. 7, by forming a hydrophilic inner wall surface 246 and a water-repellent inner wall surface 247, for example, when metal ions in the anode solution flow into the cathode gas flow path 122a, the anode solution tends to flow into the region 122a1. Therefore, salt precipitation can be suppressed in the region 122a2, and blockage of the cathode gas flow path 122a due to salt precipitation can be suppressed. The structure shown in FIG. 7 may be appropriately combined with the structure shown in FIG. 5 or FIG. 6.

Second Embodiment
Fig. 8 is a schematic diagram showing another configuration example of a carbon dioxide electrolysis device. The carbon dioxide electrolysis device 1 shown in Fig. 8 includes an electrolysis cell 10, an anode solution supply system 100 that supplies an anode solution to the electrolysis cell 10, a gas supply system 300 that supplies carbon dioxide (CO ₂ ) gas to the electrolysis cell 10, a product collection system 400 that collects products generated by a reduction reaction in the electrolysis cell 10, a control system 500 that detects the type and amount of the collected products and controls the products and the refresh operation, a waste liquid collection system 600 that collects waste liquid of the anode solution, and a refresh material supply unit 700 that restores the anode, cathode, etc. of the electrolysis cell 10. Note that components necessary for the refresh operation are not necessarily provided.

The electrolytic cell 10 corresponds to the electrolytic cell 10 shown in FIG. 1. The explanation of each component of the electrolytic cell 10 can be appropriately referred to the explanation of the first embodiment.

In FIG. 8, a power supply 20 is provided to pass a current through the anode 111 and the cathode 121. The power supply 20 is connected to the anode current collector 113 and the cathode current collector 123 via a current introduction member. The power supply 20 is not limited to a normal system power supply or a battery, and may have a power source that supplies power generated by renewable energy such as solar cells or wind power generation. The power supply 20 may have the above power source and a power controller that adjusts the output of the above power source to control the voltage between the anode 111 and the cathode 121.

The anode solution is supplied as an electrolytic solution from the anode solution supply system 100 to the anode solution flow path 112a of the anode unit 11. The anode solution supply system 100 circulates the anode solution so that the anode solution flows through the anode solution flow path 112a. The anode solution supply system 100 has a pressure control unit 101, an anode solution tank 102, a flow rate control unit (pump) 103, a reference electrode 104, and a pressure gauge 105, and is configured so that the anode solution circulates through the anode solution flow path 112a. The anode solution tank 102 is connected to a gas component collector (not shown) that collects gas components such as oxygen (O ₂ ) contained in the circulating anode solution. The anode solution is introduced into the anode solution flow path 112a with the flow rate and pressure controlled by the pressure control unit 101 and the flow rate control unit 103.

The cathode gas flow passage 122a is supplied with _CO2 gas from a gas supply system 300. The gas supply system 300 has a _CO2 gas cylinder 301, a flow control unit 302, a pressure gauge 303, and a pressure control unit 304. The flow rate and pressure of the _CO2 gas are controlled by the flow control unit 302 and the pressure control unit 304, and the CO2 gas is introduced into the cathode gas flow passage 122a. The gas supply system 300 is connected to a product collection system 400 that collects products in the gas that has flowed through the cathode gas flow passage 122a. The product collection system 400 has a gas-liquid separation unit 401 and a product collection unit 402. Reduction products such as CO and _H2 contained in the gas that has flowed through the cathode gas flow passage 122a are accumulated in the product collection unit 402 via the gas-liquid separation unit 401.

As described above, the anode solution circulates through the anode solution flow path 112a during the electrolytic reaction operation. During the refresh operation of the electrolytic cell 10 described below, the anode solution is discharged into the waste liquid collection system 600 so that the anode 111 and the anode solution flow path 112a are exposed from the anode solution.

The waste liquid collection system 600 has a waste liquid collection tank 601 connected to the anode solution flow path 112a. Waste anode solution is collected in the waste liquid collection tank 601 by opening and closing a valve (not shown). The opening and closing of the valves is collectively controlled by the control system 500. The waste liquid collection tank 601 also functions as a collection unit for the rinse liquid supplied from the refreshing material supply unit 700. Furthermore, the gaseous material supplied from the refreshing material supply unit 700 and containing some liquid material is also collected in the waste liquid collection tank 601 as necessary.

The refreshment material supply unit 700 includes a gaseous substance supply system 710 and a rinse liquid supply system 720. The rinse liquid supply system 720 may be omitted in some cases. The gaseous substance supply system 710 includes a gas tank 711 that is a supply source of gaseous substances such as air, carbon dioxide, oxygen, nitrogen, and argon, and a pressure control unit 712 that controls the supply pressure of the gaseous substance. The rinse liquid supply system 720 includes a rinse liquid tank 721 that is a supply source of rinse liquid such as water, and a flow rate control unit (pump) 722 that controls the supply flow rate of the rinse liquid. The gaseous substance supply system 710 and the rinse liquid supply system 720 are connected to the anode solution flow path 112a and the cathode gas flow path 122a via piping. The gaseous substance and the rinse liquid are supplied to the anode solution flow path 112a and the cathode gas flow path 122a by opening and closing valves (not shown). The opening and closing of the valves is all controlled by the control system 500.

A portion of the reduction products accumulated in the product collection unit 402 is sent to a reduction performance detection unit 501 of the control system 500. The reduction performance detection unit 501 detects the production amount and ratio of each product, such as CO and _H2, in the reduction products. The detected production amount and ratio of each product are input to a data collection and control unit 502 of the control system 500. Furthermore, the data collection and control unit 502 collects electrical data such as the cell voltage, cell current, cathode potential, and anode potential, as well as data such as the internal pressure and pressure loss of the anode solution flow path 112a and the cathode gas flow path 122a, as part of the cell performance of the electrolysis cell 10, and sends the collected data to a refresh control unit 503.

The data collection and control unit 502 is electrically connected to the power source 20, the pressure control unit 101 and the flow control unit 103 of the anode solution supply system 100, the flow control unit 302 and the pressure control unit 304 of the gas supply system 300, and the pressure control unit 712 and the flow control unit 722 of the refreshment material supply unit 700, in addition to the reduction performance detection unit 501, via bidirectional signal lines, some of which are not shown, and these are controlled collectively. Each pipe is provided with a valve (not shown), and the opening and closing operation of the valve is controlled by a signal from the data collection and control unit 502. The data collection and control unit 502 may control the operation of the above components, for example, during electrolysis.

The refresh control unit 503 is electrically connected to the power source 20, the flow control unit 103 of the anode solution supply system 100, the flow control unit 302 of the gas supply system 300, and the pressure control unit 712 and flow control unit 722 of the refresh material supply unit 700 via two-way signal lines, some of which are not shown, and these are controlled collectively. Each pipe is provided with a valve (not shown), and the opening and closing operation of the valve is controlled by a signal from the refresh control unit 503. The refresh control unit 503 may control the operation of the above components, for example, during electrolysis. The refresh control unit 503 and the data collection and control unit 502 may also be configured as a single control unit.

The operation of the carbon dioxide electrolysis device 1 of the embodiment will be described. FIG. 9 is a flow chart for explaining an example of a method for operating the carbon dioxide electrolysis device 1. First, as shown in FIG. 9, a start-up step S101 of the carbon dioxide electrolysis device 1 is performed. In the start-up step S101 of the carbon dioxide electrolysis device 1, the following operations are performed. In the anode solution supply system 100, the pressure control unit 101 and the flow rate control unit 103 control the flow rate and pressure to introduce the anode solution into the anode solution flow path 112a. In the gas supply system 300, the flow rate control unit 302 and the pressure control unit 304 control the flow rate and pressure to introduce _CO2 gas into the cathode gas flow path 122a.

Next, the _CO2 electrolysis operation step S102 is performed. In the _CO2 electrolysis operation step S102, the power source 20 of the electrolysis device 1 in which the start-up step S101 has been performed starts applying an electrolysis voltage, and a voltage is applied between the anode 111 and the cathode 121 to supply a current. When a current is passed between the anode 111 and the cathode 121, an oxidation reaction occurs near the anode 111 and a reduction reaction occurs near the cathode 121 as shown below. The explanation of the oxidation reaction and reduction reaction can be appropriately cited from the explanation of the first embodiment.

The electrolysis operation may cause salt to precipitate in the cathode gas flow path 122a, resulting in a decrease in cell performance. This is because ions move between the anode 111 and the cathode 121 through the separator 30 and the ion exchange membrane, and the ions react with the gas components. For example, when a potassium hydroxide solution is used as the anode solution and carbon dioxide gas is used as the cathode gas, potassium ions move from the anode 111 to the cathode 121, and the ions react with carbon dioxide to produce salts such as potassium bicarbonate and potassium carbonate. When the salt is below its solubility in the cathode gas flow path 122a, the salt precipitates in the cathode gas flow path 122a. The salt precipitates the cell performance by preventing uniform gas flow throughout the cell. In particular, when multiple cathode gas flow paths 122a are provided, the decrease in cell performance is significant. In some cases, the performance of the cell itself may improve due to the gas flow rate being partially increased. This is because an increase in gas pressure increases the amount of gas components supplied to the catalyst, or gas diffusibility increases, improving cell performance. In order to detect such a decrease in cell performance, step S103 is carried out to determine whether the cell performance meets the required standards.

As described above, the data collection and control unit 502 periodically or continuously collects cell performance such as the amount and ratio of each product, the cell voltage of the electrolysis cell 10, the cell current, the cathode potential, the anode potential, the pressure inside the anode solution flow path 112a, and the pressure inside the cathode gas flow path 122a. Furthermore, the data collection and control unit 502 has a cell performance requirement set in advance, and determines whether the collected data meets the set requirement. If the collected data meets the set requirement, the electrolysis of CO ₂ is continued without stopping the electrolysis of CO ₂ (S104). If the collected data does not meet the set requirement, a refresh operation step S105 is performed.

The cell performance collected by the data collection and control unit 502 is defined by parameters such as the upper limit of the cell voltage when a constant current is applied to the electrolytic cell 10, the lower limit of the cell current when a constant voltage is applied to the electrolytic cell 10, and the Faraday efficiency of the carbon compound generated by the reduction reaction of CO _2. Here, the Faraday efficiency is defined as the ratio of the current that contributed to the generation of the target carbon compound to the total current flowing through the electrolytic cell 10. In order to maintain the electrolytic efficiency, it is preferable to perform the refresh operation step S105 when the upper limit of the cell voltage when a constant current is applied reaches 150% or more, preferably 120% or more of the set value. In addition, it is preferable to perform the refresh operation step S105 when the lower limit of the cell current when a constant voltage is applied reaches 50% or less, preferably 80% or less of the set value. In order to maintain the production amount of reduction products such as carbon compounds, it is preferable to perform the refresh operation step S105 when the Faraday efficiency of the carbon compound becomes 50% or less, preferably 80% or less than the set value.

The cell performance is judged to not satisfy the required standard when at least one of the parameters of the cell voltage, cell current, Faraday efficiency of the carbon compound, pressure inside the anode solution flow path 112a, and pressure inside the cathode gas flow path 122a does not satisfy the required standard, and the refresh operation step S105 is performed. The required standard of the cell performance may be set by combining two or more of the above parameters. For example, when both the cell voltage and the Faraday efficiency of the carbon compound do not satisfy the required standard, the refresh operation step S105 may be performed. The refresh operation step S105 is performed when at least one of the cell performance does not satisfy the required standard. In order to stably perform the _CO2 electrolysis operation step S102, it is preferable to perform the refresh operation step S105 at an interval of, for example, one hour or more.

For example, if the electrolysis cell 10 mainly produces CO, it can be determined that the required cell performance standards are not met if the hydrogen content rises to at least twice, and preferably 1.5 times, the normal level. For example, if the CO content falls to at least 0.8 times, and preferably 0.9 times, the normal level, it can be determined that the required cell performance standards are not met.

If salt is detected, the salt is discharged using a rinse solution, but if the amount of mass transfer does not change even after the salt is discharged, it may be determined that a leak has occurred in the electrolytic cell 10. Leaks in the electrolytic cell 10 are not limited to gas leaks between the anode 111 and the cathode 121, but also include, for example, gas leaks from between the cathode 121 and the cathode gas flow path 122a. This gas leak is likely to occur, for example, when an electrolytic cell 10 in which salt has precipitated is operated for a long period of time under conditions where the pressure in the cathode gas flow path 122a is high.

10 is a flow chart for explaining an example of the operation of the refresh operation step S105. First, the application of the electrolytic voltage by the power source 20 is stopped to stop the reduction reaction of _CO2 (S201). At this time, it is not necessary to stop the application of the electrolytic voltage. Next, the supply of gas to the cathode gas flow path 122a is stopped, the supply of the anode solution to the anode solution flow path 112a is stopped, and the anode solution is discharged from the anode solution flow path 112a (S202). Next, a rinse solution is supplied to the anode solution flow path 112a and the cathode gas flow path 122a (S203) to perform cleaning.

While the rinse solution is being supplied, a refresh voltage may be applied between the anode 111 and the cathode 121. This allows the removal of ions and impurities attached to the cathode catalyst layer. If a refresh voltage is applied so as to mainly cause an oxidation process, impurities such as ions and organic matter attached to the catalyst surface are oxidized and removed. In addition, by carrying out this process in the rinse solution, not only can the catalyst be refreshed, but also ions substituted in the ion exchange resin can be removed when an ion exchange membrane is used as the separator 30.

The refresh voltage is preferably, for example, -2.5V or more and 2.5V or less. Because the refresh operation uses energy, it is preferable that the range of the refresh voltage is as narrow as possible, and more preferably, for example, -1.5V or more and 1.5V or less. The refresh voltage may be applied cyclically so that oxidation and reduction processes of ions and impurities are performed alternately. This can accelerate the regeneration of the ion exchange resin and the regeneration of the catalyst. Furthermore, the refresh operation may be performed by applying a voltage equivalent to the electrolysis voltage during the electrolysis operation as the refresh voltage. In this case, the configuration of the power supply 20 can be simplified.

Next, gas is supplied to the anode solution flow path 112a and the cathode gas flow path 122a (S204) to dry the cathode 121 and the anode 111. When the rinsing liquid is supplied to the anode solution flow path 112a and the cathode gas flow path 122a, the saturation of water in the gas diffusion layer increases, and the output decreases due to the diffusibility of the gas. Supplying gas reduces the saturation of water, recovering the cell performance and enhancing the refresh effect. It is preferable to supply gas immediately after the rinsing liquid is circulated, and it is preferable to supply gas at least within 5 minutes after the end of the supply of the rinsing liquid. This is because the output decrease due to the increase in the saturation of water is large. For example, if the refresh operation is performed every hour, the output during the 5-minute refresh operation is 0 V or significantly low, so 5/60 of the output may be lost.

After the above refresh operation is completed, the anode solution is introduced into the anode solution flow path 112a and _CO2 gas is introduced into the cathode gas flow path 122a (S205). Then, the application of the electrolysis voltage between the anode 111 and the cathode 121 by the power source 20 is resumed to resume the _CO2 electrolysis operation (S206). Note that if the application of the electrolysis voltage is not stopped in S201, the above restart operation is not performed. A gas or a rinse liquid may be used to discharge the anode solution from the anode solution flow path 112a.

The supply and flow of the rinse solution (S203) is performed to prevent precipitation of the electrolyte contained in the anode solution and to clean the cathode 121, the anode 111, the anode solution flow path 112a, and the cathode gas flow path 122a. Therefore, the rinse solution is preferably water, more preferably water with an electrical conductivity of 1 mS/m or less, and even more preferably water with an electrical conductivity of 0.1 mS/m or less. In order to remove electrolyte and other precipitates in the cathode 121, the anode 111, etc., an acidic rinse solution such as low-concentration sulfuric acid, nitric acid, or hydrochloric acid may be supplied, thereby dissolving the electrolyte. When a low-concentration acidic rinse solution is used, a process of supplying a water rinse solution is performed in the subsequent process. It is preferable to perform a water rinse solution supply process immediately before the gas supply process in order to prevent additives contained in the rinse solution from remaining. FIG. 8 shows a rinse liquid supply system 720 having one rinse liquid tank 721, but if multiple rinse liquids are used, such as water and an acidic rinse liquid, multiple rinse liquid tanks 721 are used accordingly.

In particular, for refreshing the ion exchange resin, an acid or alkaline rinse solution is preferred, which has the effect of discharging the cations and anions that have been substituted for the protons and ^OH- in the ion exchange resin. For this reason, it is preferred to alternately pass the acid and alkaline rinse solutions, combine them with water having an electrical conductivity of 1 mS/m or less, and supply gas between the supply of multiple rinse solutions to prevent the rinse solutions from mixing.

The gas used in the gas supply and flow process S204 preferably contains at least one of air, carbon dioxide, oxygen, nitrogen, and argon. Furthermore, it is preferable to use a gas with low chemical reactivity. From this point of view, air, nitrogen, and argon are preferably used, and nitrogen and argon are more preferable. The supply of the rinse liquid and gas for refreshing is not limited to only the anode solution flow path 112a and the cathode gas flow path 122a, but the rinse liquid and gas may be supplied to the cathode gas flow path 122a to clean the surface of the cathode 121 that contacts the cathode gas flow path 122a. It is effective to supply gas to the cathode gas flow path 122a in order to dry the cathode 121 from the surface side that contacts the cathode gas flow path 122a as well.

The above describes the case where the refreshing rinse liquid and gas are supplied to both the anode section 11 and the cathode section 12, but the refreshing rinse liquid and gas may be supplied only to the cathode section 12.

As described above, whether to continue the CO ₂ electrolysis operation step S102 or to perform the refresh operation step S105 is determined based on whether the cell performance of the electrolysis cell 10 satisfies the required standard. By supplying a rinse liquid or gas for refreshing in the refresh operation step S105, the uneven distribution of ions and remaining gas near the anode 111 and the cathode 121, and the precipitation of electrolytes in the cathode 121, the anode 111, the anode solution flow path 112a, and the cathode gas flow path 122a, which are factors that cause a decrease in cell performance, are removed. Therefore, by resuming the CO ₂ electrolysis operation step S102 after the refresh operation step S105, the cell performance of the electrolysis cell 10 can be restored. By repeating such CO ₂ electrolysis operation step S102 and the refresh operation step S105 based on the required standard of cell performance, it is possible to maintain the CO ₂ electrolysis performance of the electrolysis device 1 for a long period of time.

As described above, in the carbon dioxide electrolysis device of this embodiment, when salt precipitates, clogging of the flow path can be suppressed by temporarily flowing a rinse liquid through the flow path to refresh the electrolysis cell. This makes it possible to suppress a decrease in the electrolysis efficiency of the carbon dioxide electrolysis device.

When performing the refresh operation, as shown in FIG. 7, by forming an area 122a1 having a hydrophilic inner wall surface 246 and an area 122a2 having a water-repellent inner wall surface 247 in the cathode gas flow path 122a, even if salt precipitates, the rinsing liquid bypasses the salt and flows easily through the area 122a2 near the salt because the inner wall surface 246 is hydrophilic near the salt, and the salt is easily dissolved. Furthermore, until the salt is dissolved, the rinsing liquid flows through the area 122a2, and the rinsing liquid can be supplied to the entire surface of the cathode 121, so the salt can be removed efficiently.

Example 1
A carbon dioxide electrolysis device was prepared as follows. Iridium oxide was formed as an oxidation catalyst on the surface of a titanium mesh. Carbon with 10.2 mass% gold was sprayed onto carbon paper with MPL to prepare carbon paper with a catalyst layer. This carbon paper and the titanium mesh with iridium oxide were sandwiched between ion exchange membranes to prepare a membrane electrode composite (catalyst area 4 cm square).

The cathode gas flow path and the anode solution flow path were formed of titanium and had a serpentine shape including two flow path sections connected in parallel, with a land width of 0.8 mm, a flow path width W of 1 mm, and a flow path depth h of 3 mm. The aspect ratio was 3, and the average fluid depth M was 0.38. The membrane electrode composite was sandwiched between the anode solution flow path and the cathode gas flow path to assemble the electrolysis cell.

A 0.1 M potassium bicarbonate solution was supplied to the anode solution flow path as an electrolyte at 10 mL/min. Carbon dioxide gas was supplied to the cathode gas flow path at a flow rate of 320 ccm. A current was passed between the anode and cathode while increasing the current value in stages, and the gas generated from the cathode side was collected and its flow rate and the carbon dioxide conversion efficiency were measured. The generated gas was sampled and identified and quantified by gas chromatography.

The current value at this time was measured with an ammeter. From the conversion efficiency of carbon dioxide to carbon monoxide, the partial current density of carbon monoxide (CO), which is an index of the proportion of the total current density used to generate carbon monoxide, was calculated. Furthermore, from the conversion efficiency of carbon dioxide to carbon monoxide and the flow rate of gas generated from the cathode side, the utilization rate of carbon dioxide at the cathode was calculated. From these, the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide at the cathode was evaluated.

(Comparative Example 1)
In the carbon dioxide electrolysis device of Example 1, an electrolysis cell was assembled in the same manner as in Example 1, except that the cathode gas flow channel had a land width of 0.8 mm, a flow channel width W of 1 mm, and a flow channel depth h of 0.5 mm. The cathode gas flow channel had an aspect ratio of 0.5 and a mean fluid depth M of 0.17. As in Example 1, the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode was evaluated.

(Comparative Example 2)
In the carbon dioxide electrolysis device of Example 1, an electrolysis cell was assembled in the same manner as in Example 1, except that the cathode gas flow channel had a land width of 0.8 mm, a flow channel width W of 1 mm, and a flow channel depth h of 1 mm. The cathode gas flow channel had an aspect ratio of 1 and an average fluid depth of 0.25. As in Example 1, the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode was evaluated.

Example 2
In the carbon dioxide electrolysis device of Example 1, an electrolysis cell was assembled in the same manner as in Example 1, except that the cathode gas flow channel had a land width of 0.8 mm, a flow channel width W of 1 mm, and a flow channel depth h of 2 mm. The cathode gas flow channel had an aspect ratio of 2 and an average fluid depth of 0.33. As in Example 1, the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode was evaluated.

( Comparative Example 3 )
In the carbon dioxide electrolysis device of Example 1, an electrolysis cell was assembled in the same manner as in Example 1, except that the cathode gas flow channel had a land width of 0.49 mm, a flow channel width W of 0.49 mm, and a flow channel depth h of 1 mm. The cathode gas flow channel had an aspect ratio of 2 and an average fluid depth of 0.16. As in Example 1, the relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode was evaluated.

The relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode in Example 1, Comparative Example 1, Comparative Example 2, and Example 2 is shown in FIG.

The relationship between the partial current density of carbon monoxide and the utilization rate of carbon dioxide in the cathode in Example 2 and Comparative Example 3 is shown in FIG.

11 shows that when the aspect ratio of the cathode gas flow channel is in the range of more than 1 and not more than 3, and the average flow channel depth M and depth h of the cathode gas flow channel satisfy the formula: h/8≦M<h/4, a high CO ₂ utilization rate of 30% or more can be realized at a high CO partial current density of 400 mA/cm ² or more. Also, FIG. 12 shows that even if the aspect ratio is the same, a larger average fluid depth M can achieve a higher CO ₂ utilization rate at a high CO partial current density.

The above embodiment is presented as an example and is not intended to limit the scope of the invention. The above embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The above embodiment and its variations are included in the scope and gist of the invention, as well as in the scope of the invention and its equivalents described in the claims.

10...electrolysis cell, 11...anode section, 12...cathode section, 13...separator, 20...power supply, 30...separator, 100...anode solution supply system, 101...pressure control section, 102...anode solution tank, 103...flow rate control section, 104...reference electrode, 105...pressure gauge, 111...anode, 112...flow path plate, 112a...anode solution flow path, 113...anode current collector, 121...cathode, 122...flow path plate, 122a...cathode gas flow path, 122a1...region, 122a2...region, 123...cathode current collector, 241...surface, 242...surface, 244...flow path section, 245...inner bottom surface, 246...inner wall surface, 247...inner wall surface, 300...gas supply system, 301...CO ₂ gas cylinder, 302...flow rate control unit, 303...pressure gauge, 304...pressure control unit, 400...product collection system, 401...gas-liquid separation unit, 402...product collection unit, 500...control system, 501...reduction performance detection unit, 502...data collection/control unit, 503...refreshment control unit, 600...waste liquid collection system, 601...waste liquid collection tank, 700...refreshing material supply unit, 710...gaseous substance supply system, 711...gas tank, 712...pressure control unit, 720...rinsing liquid supply system, 721...rinsing liquid tank, 722...flow rate control unit.

Claims (7)

a cathode for reducing carbon dioxide to produce carbon compounds;
an anode for oxidizing water to produce oxygen;
a cathode gas flow channel facing the cathode and for supplying a gas containing carbon dioxide;
an anode solution flow path facing the anode for supplying an electrolytic solution containing water;
a separator disposed between the anode and the cathode;
Equipped with
an aspect ratio of the cathode gas flow channel, defined as a ratio of an average depth h of the cathode gas flow channel to an average width of the cathode gas flow channel, is greater than 1 and less than or equal to 3;
In a cross section of the cathode gas flow channel along a direction perpendicular to a surface between the cathode and the cathode gas flow channel, a mean fluid depth M of the cathode gas flow channel is defined by a ratio of a circumferential length of the cathode gas flow channel to a cross-sectional area of the cathode gas flow channel, and an average value h of the depth of the cathode gas flow channel is expressed as follows:
Formula: h/8≦M<h/4
and M is 0.33 or more. The cathode gas flow path is
a first region facing the cathode;
a second region provided between the first region and an inner bottom surface of the cathode gas flow channel;
having
The device of claim 1 , wherein the second region has a width greater than a width of the first region. The cathode gas flow path is
a first region facing the cathode and having a hydrophilic first inner wall surface;
a second region provided between the first region and an inner bottom surface of the cathode gas flow channel, the second region having a water-repellent second inner wall surface;
The apparatus of claim 1 , further comprising: The device according to any one of claims 1 to 3, wherein the electrolytic solution contains metal ions. The device according to any one of claims 1 to 4, wherein the cathode includes at least one catalyst selected from the group consisting of copper, gold, and silver. an electrolysis cell including the cathode, the anode, the cathode gas flow path, the anode solution flow path, and the separator;
a gas supply unit that supplies the gas to the cathode gas flow channel;
a solution supply unit for supplying the electrolytic solution to the anode solution flow path;
a power source that applies a voltage between the anode and the cathode;
a refreshing agent supply unit including a liquid supply unit that supplies a rinsing liquid to the cathode gas flow path;
a control unit that controls an operation of stopping the supply of the gas by the gas supply unit, stopping the supply of the electrolytic solution by the solution supply unit, and supplying a rinse solution to the cathode by the refresh material supply unit based on a required standard of performance of the electrolytic cell;
The apparatus of claim 1 , further comprising: 1. A method for operating a carbon dioxide electrolysis device, comprising:
The carbon dioxide electrolysis device comprises an electrolysis cell,
The electrolysis cell comprises:
a cathode for reducing carbon dioxide to produce carbon compounds;
an anode for oxidizing water to produce oxygen;
a cathode gas flow channel facing the cathode and for supplying a gas containing carbon dioxide;
an anode solution flow path facing the anode for supplying an electrolytic solution containing water;
a separator disposed between the anode and the cathode;
Equipped with
an aspect ratio of the cathode gas flow channel, defined as a ratio of an average depth h of the cathode gas flow channel to an average width of the cathode gas flow channel, is greater than 1 and less than or equal to 3;
In a cross section of the cathode gas flow channel along a direction perpendicular to a surface between the cathode and the cathode gas flow channel, a mean fluid depth M of the cathode gas flow channel is defined by a ratio of a circumferential length of the cathode gas flow channel to a cross-sectional area of the cathode gas flow channel, and an average value h of the depth of the cathode gas flow channel is expressed as follows:
Formula: h/8≦M<h/4
and M is 0.33 or more;
The method comprises:
supplying a gas containing carbon dioxide to the cathode gas flow path and an electrolyte to the anode solution flow path;
applying a voltage between the anode and the cathode to reduce carbon dioxide near the cathode of the electrolysis cell to produce carbon compounds and oxidize water or hydroxide ions near the anode to produce oxygen;
stopping the supply of the gas and the electrolytic solution and supplying a rinse liquid to the cathode gas flow path based on a performance requirement of the electrolytic cell;
A method for operating a carbon dioxide electrolysis device comprising:

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