ELECTROLYSIS DEVICE, ELECTROLYSIS SYSTEM, AND METHOD OF OPERATING ELECTROLYSIS DEVICE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2023-151655, filed on Sep. 19, 2023; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments relate to an electrolysis device and an electrolysis system.

BACKGROUND

In recent years, renewable energies should be exploited by not only being converted into electric energy as solar power generation but also being converted into storable and conveyable resources, in view of both an energy problem and an environment problem. This request has developed research and development of an artificial photosynthesis technology of generating a chemical substance using sunlight as in photosynthesis by plants. This technology may enable converting renewable energy into storable fuels, and may enable producing a chemical substance as an industrial raw material to create valuables.

Examples of an apparatus, which produces the chemical substance using the renewable energy of solar power generation, include an electrolysis device (electrochemical reaction device) such as a carbon dioxide electrolysis device having a cathode and a anode, the cathode reducing carbon dioxide (CO₂) generated from a power station or a waste treatment plant, and the anode oxidizing water (H₂O). The cathode can reduce carbon dioxide to produce a carbon compound such as carbon monoxide (CO), for example. When the electrolysis device is composed by forming a cell (also referred to as an electrolysis cell), it is considered effective to compose the electrolysis device by forming a cell similar to a cell of a fuel cell such as Polymer Electric Fuel Cell (PEFC), for example. The carbon dioxide electrolysis device can directly supply carbon dioxide to a catalyst layer of the cathode to speedily reduce the carbon dioxide. Further, the carbon dioxide electrolysis device can have a stack structure, which is formed by stacking electrolysis cells, to prevent an increase of the area of the carbon dioxide electrolysis device and to efficiently reduce the carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a configuration example of an electrolysis device in an embodiment.

FIG. 2 is a perspective schematic view illustrating an example structure of a cell structure 100.

FIG. 3 is a schematic view illustrating an example structure of a membrane electrode assembly MEA.

FIG. 4 is a schematic view illustrating an example structure of a cathode flow path plate 14.

FIG. 5 is a schematic view illustrating an example structure of an anode flow path plate 15.

FIG. 6 is a schematic view illustrating an example structure of a cathode current collector 16.

FIG. 7 is a schematic view illustrating an example structure of an anode current collector 17.

FIG. 8 is a schematic view illustrating an example structure of an insulating layer 18.

FIG. 9 is a schematic view for explaining the flow of a cathode fluid and the flow of an anode fluid in the cell structure 100.

FIG. 10 is a perspective schematic view illustrating an example structure of the cell structure 100.

FIG. 11 is a schematic view illustrating an appearance in which an impurity and a reducible material in the cathode fluid flow in series through electrolysis cells 10.

FIG. 12 is a chart illustrating examples of graphs indicating the relation among a current density flowing through the electrolysis cell 10, a cell voltage, and a Faraday efficiency.

FIG. 13 is a schematic view illustrating another example of the electrolysis device in the embodiment.

FIG. 14 is a schematic view illustrating another example of the electrolysis device in the embodiment.

FIG. 15 is a schematic view illustrating another example of the electrolysis device in the embodiment.

FIG. 16 is a schematic view illustrating another example of the electrolysis device in the embodiment.

DETAILED DESCRIPTION

An electrolysis device according to an embodiment includes: a first electrolysis cell configured to reduce a reducible material and to oxidize an oxidizable material; a second electrolysis cell configured to reduce the reducible material and to oxidize the oxidizable material; a first supply source configured to supply a first fluid to the first electrolysis cell and the second electrolysis cell, the first fluid containing a gas of the reducible material; a second supply source configured to supply a second fluid to the first electrolysis cell and the second electrolysis cell, the second fluid containing a liquid of the oxidizable material; and at least one power supply configured to supply a first power supply current to the first electrolysis cell and to supply a second power supply current to the second electrolysis cell. The at least one power supply is configured to set a value of the first power supply current and a value of the second power supply current so that a current density of current flowing through the second electrolysis cell when reducing the reducible material is higher than a current density of current flowing through the first electrolysis cell when reducing the reducible material.

Electrolysis devices in embodiments will be explained below with reference to the drawings. In the embodiments explained below, substantially the same components are denoted by the same reference signs and the explanation thereof will be partially omitted in some cases. The drawings are schematic, in which the relationship between the thickness and planar dimensions, a thickness ratio among the components, and so on may be different from actual ones.

In this specification, “connecting” includes not only directly connecting but also indirectly connecting unless otherwise specified. Further, in this specification, “connecting” includes not only physically connecting but also electrically connecting unless otherwise specified.

FIG. 1 is a schematic view illustrating a configuration example of an electrolysis device in an embodiment. FIG. 1 illustrates a configuration example of an electrolysis device 1. The electrolysis device 1 includes an electrolysis cell 10 which performs an electrolytic reaction, a cathode supply source 20 which supplies cathode a fluid, an anode supply source 30 which supplies an anode fluid, and a power supply 40 which feeds power to the electrolysis cell 10. FIG. 1 illustrates an X-axis, a Y-axis, and a Z-axis. The X-axis, the Y-axis, and the Z-axis vertically cross one another. The Z-axis is along a thickness direction of the electrolysis cell 10. FIG. 1 illustrates a part of an X-Z cross section including the X-axis and the Z-axis.

The electrolysis cell 10 has a cathode 11, an anode 12, a diaphragm (separator) 13, a cathode flow path plate 14 having a cathode flow path 140, an anode flow path plate 15 having an anode flow path 150, a cathode current collector 16, and an anode current collector 17. The cathode 11, the anode 12, and the diaphragm 13 may be stacked to form a membrane electrode assembly MEA. The order of stacking the components of the electrolysis cell 10 is not limited to that in FIG. 1, but they may be stacked, for example, in an order reverse to the order illustrated in FIG. 1.

The electrolysis device 1 has a plurality of the electrolysis cells 10. The electrolysis cells 10 are stacked, for example, with an insulating layer 18 intervening therebetween to form a cell structure 100 such as a cell stack. FIG. 2 is a perspective schematic view illustrating an example structure of the cell structure 100. The cell structure 100 further has an insulating layer 18 between two stacked electrolysis cells 10. The stacked electrolysis cells 10 may be sandwiched between a pair of supporting plates and further fastened with bolts or the like. FIG. 1 and FIG. 2 illustrate electrolysis cells 10_1, 10_2, 10_3 as the electrolysis cells 10, but the number of electrolysis cells 10 only needs to be two or more and is not limited to the number illustrated in FIG. 1 and FIG. 2.

The cathode 11 is an electrode (a reduction electrode) for causing, for example, a reduction reaction of at least one reducible material (at least one substance to be reduced) to produce a reduction product. The at least one reducible material includes, for example, carbon dioxide or nitrogen. The cathode 11 is in contact with the diaphragm 13. The cathode 11 is an electrode (a reduction electrode) for causing a reduction reaction of the reducible material to produce the reduction product. Examples of the reducible material include carbon dioxide, nitrogen, hydrogen, oxygen, reduction product, and so on. Examples of the reduction product include carbon compound, ammonia, and so on. Examples of the carbon compound include carbon monoxide (CO), methane (CH₄), ethane (C₂H₆), and so on. The reduction reaction at the cathode 11 may include a side reaction of causing a reduction reaction of water to produce hydrogen (H₂). Further, the reduction reaction at the cathode 11 may include a side reaction of causing a reduction reaction of carbon dioxide and a reduction reaction of oxygen to produce water (H₂O).

The cathode 11 is supplied with the anode fluid and ions from the diaphragm 13 and is supplied with the cathode fluid from the cathode flow path 140. The cathode 11 may have a gas diffusion layer and a cathode catalyst layer provided on the gas diffusion layer. The cathode 11 may further have a porous layer denser than the gas diffusion layer, between the gas diffusion layer and the cathode catalyst layer. The gas diffusion layer is arranged adjacent to the cathode flow path 140, and the cathode catalyst layer is arranged adjacent to the diaphragm 13. The cathode catalyst layer may extend into the gas diffusion layer. The cathode catalyst layer preferably has a catalyst nanoparticle, a catalyst nanostructure, or the like. The gas diffusion layer is composed of, for example, carbon paper, carbon cloth, or the like, and may have been subjected to a water repellent treatment. The porous layer is composed of a porous member smaller in pore size than the carbon paper or carbon cloth.

An appropriate water repellent treatment to the gas diffusion layer allows a carbon dioxide gas to reach the cathode catalyst layer mainly by gas diffusion. The reduction reaction of the carbon dioxide and the reduction reaction of a carbon compound produced thereby occur near the boundary between the gas diffusion layer and the cathode catalyst layer or near the cathode catalyst layer intruding into the gas diffusion layer.

The cathode catalyst layer preferably contains a catalyst material (cathode catalyst material) capable of decreasing an overvoltage of the reduction reaction. Examples of the material include metals such as gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), titanium (Ti), cadmium (Cd), zinc (Zn), indium (In), gallium (Ga), lead (Pb), and tin (Sn), metal materials such as alloys and intermetallic compounds containing at least one of the metals, carbon materials such as carbon (C), graphene, CNT (carbon nanotube), fullerene, and ketjen black, and metal complexes such as a Ru complex and a Re complex. To the cathode catalyst layer, various shapes such as a plate shape, a mesh shape, a wire shape, a particle shape, a porous shape, a thin film shape, or an island shape can be applied.

The cathode catalyst material constituting the cathode catalyst layer preferably has a nanoparticle of the above metal material, a nanostructure of the metal material, a nanowire of the metal material, or a composite in which the nanoparticle of the metal material is supported by a carbon material such as carbon particle, carbon nanotube, or graphene. The use of the catalyst nanoparticle, the catalyst nanostructure, a catalyst nanowire, a catalyst nanosupport structure, or the like, as the cathode catalyst material can enhance the reaction efficiency of the reduction reaction of carbon dioxide at the cathode 11.

The anode 12 is provided between the diaphragm 13 and the anode flow path 150 and is in contact with them. The anode 12 is an electrode (an oxidization electrode) for oxidizing water (H₂O) in an anode solution contained in the anode fluid to produce oxygen (O₂) and hydrogen ions (H) or an electrode for oxidizing hydroxide ions (OH) produced by the reduction reaction of carbon dioxide at the cathode 11 to produce oxygen and water.

The anode 12 preferably contains a catalyst material (a anode catalyst material) capable of decreasing an overvoltage of the oxidation reaction. Examples of the catalyst material include metals such as platinum (Pt), palladium (Pd), and nickel (Ni), alloys and intermetallic compounds containing those 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 a Ru complex and a Fe complex.

The anode 12 includes a base material having a structure capable of moving liquid and ions between the diaphragm 13 and the anode flow path 150, for example, a porous structure such as a mesh material, a punched material, a porous member, or a metal fiber sintered compact. The base material may be composed of a metal such as titanium (Ti), nickel (Ni), or iron (Fe) or a metal material such as an alloy (for example SUS) containing at least one of the metals, or may be composed of the aforementioned anode catalyst material. In the case of using an oxide as the anode catalyst material, it is preferable to bond or stack the anode catalyst material on the surface of the base material composed of the above metal material to form a catalyst layer. The anode catalyst material preferably has a nanoparticle, a nanostructure, a nanowire, or the like in order to enhance the oxidation reaction. The nanostructure is a structure obtained by forming nanoscale irregularities on the surface of the catalyst material. The oxidation catalyst does not always need to be provided at the anode 12. An oxidation catalyst layer provided other than the anode 12 may be electrically connected to the anode 12.

The diaphragm 13 is provided between the cathode 11 and the anode 12. The diaphragm 13 is arranged to separate the cathode 11 and the anode 12 from each other. The diaphragm 13 includes an ion exchange membrane capable of moving ions between the cathode 11 and the anode 12 and separating the cathode 11 and the anode 12 from each other. Examples of the usable ion exchange membrane include a cation exchange membrane such as Nafion or Flemion, or an anion exchange membrane such as Neosepta, Selemion, or Sustainion. In the case of assuming the movement of mainly OH by using an alkaline solution for the electrolytic solution, the diaphragm 13 is preferably composed of an anion exchange membrane. The ion exchange membrane may be composed using a film using hydrocarbon as a basic structure or a film 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, as long as it is a material capable of moving ions between the cathode 11 and the anode 12, may be applied to the diaphragm 13. However, if passage of gas occurs between the cathode 11 and the anode 12, a circular reaction due to reoxidation of the reduction product may occur. Therefore, it is preferable that there is less exchange of gas between the cathode 11 and the anode 12. Therefore, it is necessary to take care when using a thin film of a porous member as the diaphragm 13.

The cathode flow path plate 14 has the cathode flow path 140. The cathode flow path 140 faces on the cathode 11. The cathode flow path 140 allows the cathode fluid to be supplied to the cathode 11 and containing the reducible material to flow therethrough. The cathode fluid may contain water vapor by humidification. The reduction product is mainly discharged from the cathode flow path 140 while being contained in the cathode fluid. The reduction product is different depending on the type of the reduction catalyst or the like. Together with the gas products, vapor or moisture obtained by dew condensation of vapor contained in the humidified carbon dioxide gas is drained from the cathode flow path 140.

The reduction product is different also depending on the composition of the cathode fluid. In the case where the cathode fluid contains a carbon dioxide gas or a humidified carbon dioxide gas, a carbon monoxide gas and a reduction product such as hydrogen as a by-product are mainly produced. In the case where the cathode fluid contains a nitrogen gas, a reduction product such as ammonia is mainly produced. In the case where the cathode fluid contains an impurity gas such as oxygen, oxygen is reduced to produce water as a reduction product.

The cathode flow path 140 is provided on the surface of the cathode flow path plate 14. The cathode flow path plate 14 has a groove (recessed portion) which forms the cathode flow path 140 on the surface. The cathode flow path plate 14 is preferably formed using a material low in chemical reactivity and high in conductivity. Examples of the material include metal materials such as Ti and SUS, carbon, and the like. Examples of the material of the flow path plate include a material low in chemical reactivity and having no conductivity. Examples of the material include insulating resin materials such as an acrylic resin, polyether ether ketone (PEEK), and a fluorocarbon resin. The cathode flow path plate 14 has a not-illustrated screw hole for fastening. Further, before and after cathode flow path plates 14, not-illustrated packing may be sandwiched as necessary. The cathode flow path 140 may be provided in the cathode current collector 16.

The cathode flow path 140 has an inlet and an outlet, is supplied with the cathode fluid from the cathode supply source 20 through the inlet, and discharges an unreacted reducible material and the reduction product through the outlet. The cathode fluid flows through the inside of the cathode flow path 140 in a manner to be in contact with the cathode 11. The cathode fluid discharged from the cathode flow path 140 may contain the unreacted reducible material, the reduction product, and so on.

The cathode flow path 140 may have a land in contact with the cathode 11 for electrical connection with the cathode 11. The shape of the cathode flow path 140 is not particularly limited, and can be a serpentine structure obtained by folding an elongated flow path or the like. Thus, it is preferable that the cathode fluid uniformly flows on the surface of the cathode 11, thereby allowing a uniform reaction to be performed at the cathode 11.

The cathode fluid may be supplied in a dry state. In the case where the cathode fluid contains a carbon dioxide gas, a carbon dioxide concentration of the cathode fluid to be supplied from the cathode supply source 20 to the cathode flow path 140 does not have to be 100%. It is also possible to use fluid containing the carbon dioxide gas discharged from various facilities, as the cathode fluid. In this case, the cathode fluid may contain an impurity gas. Assuming that a first gas contained in the cathode fluid is the carbon dioxide gas, a second gas is a substance different from carbon dioxide, such as oxygen or nitrogen. The concentration of the second gas is preferably lower than the concentration of the first gas and is, for example, 1 ppm or higher and 100000 ppm or lower.

The cathode flow path plate 14 is mainly formed of one member, but may be formed of a plurality of different members and constructed by stacking them. Further, a surface treatment may be performed partially or entirely on the cathode flow path plate 14 to add a hydrophilic or water repellent function to the cathode flow path plate 14.

The anode flow path plate 15 has the anode flow path 150. The anode flow path 150 faces on the anode 12. The anode flow path 150 allows the anode fluid to be supplied to the anode 12 to flow therethrough. The anode fluid contains liquid such as the anode solution.

The anode solution preferably contains at least water (H₂O). For example, in the case where the reducible material is carbon dioxide, carbon dioxide is supplied from the cathode flow path 140, so that the anode solution may or may not contain carbon dioxide.

As the anode solution, an aqueous solution (electrolytic solution) containing metal ions can be used. Examples of the aqueous solution include aqueous solutions containing phosphate ion (PO₄²⁻), borate ion (BO₃³⁻), sodium ion (Na), potassium ion (K⁺), calcium ion (Ca²⁺), lithium ion (Li⁺), cesium ion (Cs⁺), magnesium ion (Mg²⁺), chloride ion (Cl), hydrogen carbonate ion (HCO₃⁻), and so on. In addition, aqueous solutions containing lithium hydrogen carbonate (LiHCO₃), sodium hydrogen carbonate (NaHCO₃), potassium hydrogen carbonate (KHCO₃), cesium hydrogen carbonate (CsHCO₃), phosphoric acid, boric acid, and so on may be used.

The anode flow path 150 is provided on the surface of the anode flow path plate 15. The anode flow path plate 15 is for supplying the anode fluid to the anode 12, and has a groove (recessed portion) which forms the anode flow path 150 on the surface. The anode flow path plate 15 is preferably formed using a material low in chemical reactivity and high in conductivity. Examples of the material include metal materials such as Ti and SUS, carbon, and so on. The anode flow path 150 may be provided at the anode current collector 17. Further, examples of the material of the anode flow path plate 15 include a material low in chemical reactivity and having no conductivity. Examples of the material include insulating resin materials such as an acrylic resin, polyether ether ketone (PEEK), and a fluorocarbon resin. The anode flow path plate 15 has a not-illustrated screw hole for fastening.

The anode flow path plate 15 is mainly formed of one member, but may be formed of a plurality of different members and constructed by stacking them. Further, a surface treatment may be performed partially or entirely on the anode flow path plate 15 to add a hydrophilic or water repellent function to the anode flow path plate 15.

The anode flow path 150 has an inlet and an outlet, is supplied with the anode fluid from the anode supply source 30 through the inlet, and discharges the anode fluid through the outlet. The anode fluid flows through the inside of the anode flow path 150 in a manner to be in contact with the anode 12. The anode fluid discharged from the anode flow path 150 may contain an unreacted oxidizable material, an oxidation product, and so on.

The anode flow path 150 may have a land in contact with the anode 12 for electrical connection with the anode 12. The shape of the anode flow path 150 is not particularly limited, and can be a serpentine structure obtained by folding an elongated flow path or the like. Thus, it is preferable that the anode fluid uniformly flows on the surface of the anode 12, thereby allowing a uniform reaction to be performed at the anode 12.

The cathode current collector 16 is electrically connected to the cathode 11. The cathode current collector 16 is in contact with a surface of the cathode flow path plate 14 across the cathode flow path plate 14 from the cathode flow path 140. The cathode current collector 16 preferably contains a material low in chemical reactivity and high in conductivity. Examples of the material include metal materials such as Ti and SUS, carbon, and so on.

The anode current collector 17 is electrically connected to the anode 12. The anode current collector 17 is in contact with a surface of the anode flow path plate 15 across the anode flow path plate 15 from the anode flow path 150. The anode current collector 17 preferably contains a material low in chemical reactivity and high in conductivity. Examples of the material include metal materials such as Ti and SUS, carbon, and so on.

The insulating layer 18 is provided between two electrolysis cells 10. The insulating layer 18 is formed using a material such as a material coated with a fluorocarbon resin such as silicone or polytetrafluoroethylene (PTFE), an insulating resin material such as an acrylic resin, polyether ether ketone (PEEK), or a fluorocarbon resin, or the like. The electrolysis device 1 may have a plurality of the insulating layers 18.

The cathode supply source 20 can supply the cathode fluid to, for example, the electrolysis cell 10. The cathode supply source 20 is connected to the cathode flow path 140 of the electrolysis cell 10_1 via, for example, a pipe.

The anode supply source 30 can supply the anode fluid to, for example, the electrolysis cell 10. The anode supply source 30 is connected to the anode flow path 150 of the electrolysis cell 10_1 via, for example, a pipe.

The power supply 40 can supply power supply currents to the electrolysis cells 10, for example. The power supply 40 is electrically connected to the cathode current collectors 16 of the electrolysis cells 10 via at least one wire. The cathode current collectors 16 may be electrically connected in parallel with one another. The power supply 40 is electrically connected to the anode current collectors 17 of the electrolysis cells 10 via at least one wire. The anode current collectors 17 may be electrically connected in parallel with one another.

Examples of the power supply 40 are not limited to a normal system power supply or battery, but examples of the power supply 40 may include a power supply which supplies power generated with renewable energy of a solar cell, wind power generation, or the like. The use of the renewable energy is preferable in terms of environment in addition to the effective utilization of the reducible material. The power supply 40 may further have a power controller that adjusts an output of the power supply 40 to control the voltage between the cathode 11 and the anode 12. The power supply 40 may be provided outside the electrolysis device 1. The power supply 40 controls the current or voltage to be supplied to each electrolysis cell 10 to enable optimally operating the electrolysis cell 10 and enhance the reaction efficiency of the reduction reaction of the reducible material at the cathode 11. Further, the power supply 40 can adjust the current or voltage to be supplied to each electrolysis cell 10 to enable optimally operating the electrolysis cell 10 and enhance the reaction efficiency of the reduction reaction of the reducible material at the cathode 11. The electrolysis device 1 may have an element for monitoring the current, the element being provided on connection between the power supply 40 and the electrolysis cell 10 or connection between the power supply 40 and the cell structure 100, and examples of the element including a resistor element. This can control the voltage to enable optimally operating the electrolysis cell 10 and enhance the reaction efficiency of the reduction reaction at the cathode 11.

The cathode fluid and the anode fluid can be supplied to flow in series or in parallel through the electrolysis cells 10. In the case of supplying the cathode fluid and the anode fluid to make them flow in series through the electrolysis cells 10, the electrolysis cells 10 may be configured such that the cathode flow paths 140 are connected in series and the anode flow paths 150 are connected in series. An example structure of the components of the electrolysis cell 10 in the case where the cathode flow paths 140 are connected in series and the anode flow paths 150 are connected in series, will be explained below.

FIG. 3 is a schematic view illustrating an example structure of the membrane electrode assembly MEA. FIG. 3 illustrates an X-Y plane view. The membrane electrode assembly MEA may be surrounded by a supporting plate 130. The supporting plate 130 has, for example, an opening 130a and an opening 131. The opening 130a is provided through the supporting plate 130 in a Z-axis direction, and is a space in which the membrane electrode assembly MEA is arranged. The opening 131 is provided through the supporting plate 130 in the Z-axis direction, and examples of the opening 131 include a through hole such as a via. The supporting plate 130 has a plurality of the openings 131. The openings 131 are provided around the opening 130a. One of the openings 131 allows the cathode fluid to flow therethrough. Another of the openings 131 allows the anode fluid to flow therethrough. FIG. 3 illustrates an opening 131_1 and an opening 131_2 as the openings 131, but the number of the openings 131 only needs to be two or more and is not limited to the number illustrated in FIG. 3. The opening 131_1 allows the cathode fluid to flow therethrough. The opening 131_2 allows the anode fluid to flow therethrough. The supporting plate 130 is preferably formed using an insulating material. The above configuration is one example, and the openings 131 may be provided in another member such as the cathode 11 or the anode 12 in place of the supporting plate 130 as long as the cathode fluid and the anode fluid can pass, without leakage, through a layer including the membrane electrode assembly MEA.

FIG. 4 is a schematic view illustrating an example structure of the cathode flow path plate 14. FIG. 4 illustrates an X-Y plane view. The cathode flow path plate 14 has, for example, the cathode flow path 140 and an opening 141. The cathode flow path 140 is provided adjacent to the membrane electrode assembly MEA of the cathode flow path plate 14, and may be formed in a serpentine shape along an X-Y plane as illustrated in FIG. 14 or may have another shape. The opening 141 is provided through the cathode flow path plate 14 in the Z-axis direction, and examples of the opening 141 include a through hole such as a via. The cathode flow path plate 14 has a plurality of the openings 141. One of the openings 141 allows the cathode fluid to flow therethrough. Another of the openings 141 allows the anode fluid to flow therethrough. FIG. 4 illustrates an opening 141_1, an opening 141_2, and an opening 141_3 as the openings 141, but the number of the openings 141 only needs to be two or more and is not limited to the number illustrated in FIG. 4. The cathode flow path 140 is connected to the opening 131_1. The opening 141_1 is provided on a surface of the cathode flow path plate 14, the surface being provided across the cathode flow path plate 14 from the formation surface of the cathode flow path 140. The opening 141_1 overlaps with one end of the cathode flow path 140. The opening 141_1 is connected to the cathode flow path 140. The opening 141_2 is connected, for example, to the opening 131_2. Another end of the cathode flow path 140 overlaps with, for example, the opening 131_1. The opening 141_1 allows the cathode fluid to flow therethrough. The opening 141_2 allows the anode fluid to flow therethrough.

FIG. 5 is a schematic view illustrating an example structure of the anode flow path plate 15. FIG. 5 illustrates an X-Y plane view. The anode flow path plate 15 has, for example, the anode flow path 150 and an opening 151. The anode flow path 150 may be formed in a serpentine shape along an X-Y plane as illustrated in FIG. 5 or may have another shape. The opening 151 is provided through the anode flow path plate 15 in the Z-axis direction, and examples of the opening 151 include a through hole such as a via. The anode flow path plate 15 has a plurality of the openings 151. One of the openings 151 allows the cathode fluid to flow therethrough. Another of the openings 151 allows the anode fluid to flow therethrough. FIG. 5 illustrates an opening 151_1 and an opening 151_2 as the openings 151, but the number of openings 151 only needs to be two or more and is not limited to the number illustrated in FIG. 5. The opening 151_1 is connected, for example, to the opening 131_1. The opening 151_2 is provided on a surface of the anode flow path plate 15, the surface being across the anode flow path plate 15 from the formation surface of the anode flow path 150. The opening 151_2 overlaps with one end of the anode flow path 150. The opening 151_2 is connected, for example, to the opening 131_2. The opening 151_1 allows the cathode fluid to flow therethrough. The opening 151_2 allows the anode fluid to flow therethrough.

FIG. 6 is a schematic view illustrating an example structure of the cathode current collector 16. FIG. 6 illustrates an X-Y plane view. The cathode current collector 16 has, for example, an opening 161. The opening 161 is provided through the cathode current collector 16 in the Z-axis direction, and examples of the opening 161 include a through hole such as a via. The cathode current collector 16 has a plurality of the openings 161. One of the openings 161 allows the cathode fluid to flow therethrough. Another of the openings 161 allows the anode fluid to flow therethrough. FIG. 6 illustrates an opening 161_1 and an opening 161_2 as the openings 161, but the number of the openings 161 only needs to be two or more and is not limited to the number illustrated in FIG. 6. The opening 161_1 is connected, for example, to the opening 161_1. The opening 161_2 is connected, for example, to the opening 141_2. The opening 161_1 allows the cathode fluid to flow therethrough. The opening 161_2 allows the anode fluid to flow therethrough.

FIG. 7 is a schematic view illustrating an example structure of the anode current collector 17. FIG. 7 illustrates an X-Y plane view. The anode current collector 17 has, for example, an opening 171. The opening 171 is provided through the anode current collector 17 in the Z-axis direction, and examples of the opening 171 include a through hole such as a via. The anode current collector 17 has a plurality of the openings 171. One of the openings 171 allows the cathode fluid to flow therethrough. Another of the openings 171 allows the anode fluid to flow therethrough. FIG. 7 illustrates an opening 171_1 and an opening 171_2 as the openings 171, but the number of the openings 171 only needs to be two or more and is not limited to the number illustrated in FIG. 7. The opening 171_1 is connected, for example, to the opening 151_1. The opening 171_2 is connected, for example, to the opening 151_2. The opening 171_1 allows the cathode fluid to flow therethrough. The opening 171_2 allows the anode fluid to flow therethrogh.

FIG. 8 is a schematic view illustrating an example structure of the insulating layer 18. FIG. 8 illustrates an X-Y plane view. The insulating layer 18 has, for example, an opening 181. The opening 181 is provided through the insulating layer 18 in the Z-axis direction, examples of the opening 18 include a through hole such as a via. The insulating layer 18 has a plurality of the openings 181. One of the openings 181 allows the cathode fluid to flow therethrough. Another of the openings 181 allows the anode fluid to flow therethorugh. FIG. 8 illustrates an opening 181_1 and an opening 181_2 as the openings 181, but the number of the openings 181 only needs to be two or more and is not limited to the number illustrated in FIG. 8. The opening 181_1 is connected, for example, to the opening 171_1. The opening 181_2 is connected, for example, to the opening 171_2. The opening 181_1 allows the cathode fluid to flow therethrough. The opening 181_2 allows the anode fluid to flow therethrough.

When the electrolysis cells 10 are stacked with the insulating layer 18 intervening therebetween, positions of the openings 131, the openings 141, the openings 151, the openings 161, the openings 171, and the openings 181 may be different between an electrolysis cell 10_2n-1 (n is a natural number) at an odd stage such as the electrolysis cell 10_1 and an electrolysis cell 10_2n (n is a natural number) at an even stage such as the electrolysis cell 10_2. For example, positions of the opening 131_1 and the opening 131_2, positions of the opening 141_1 and the opening 141_2, positions of the opening 151_1 and the opening 151_2, positions of the opening 161_1 and the opening 161_2, positions of the opening 171_1 and the opening 171_2, and positions of the opening 181_1 and the opening 181_2 each may have a symmetrical relationship between the electrolysis cell 10_2n-1 (n is a natural number) at the odd stage and the electrolysis cell 10_2n (n is a natural number) at the even stage. Further, depending on the shape of the flow path, positions of the opening 131_1 and the opening 131_2, positions of the opening 141_1 and the opening 141_2, positions of the opening 151_1 and the opening 151_2, positions of the opening 161_1 and the opening 161_2, positions of the opening 171_1 and the opening 171_2, and positions of the opening 181_1 and the opening 181_2 each may have an asymmetrical relationship between the electrolysis cell 10_2n-1 (n is a natural number) at the odd stage and the electrolysis cell 10_2n (n is a natural number) at the even stage. In the case where packing is provided, the packing may be provided with a plurality of openings, and through which the cathode fluid and the anode fluid may be allowed to pass.

The flow of the cathode fluid and the flow of the anode fluid in each electrolysis cell 10 in supplying the cathode fluid and the anode fluid so that they flow in series through the electrolysis cells 10 will be explained with reference to FIG. 9 and FIG. 10. FIG. 9 and FIG. 10 are schematic views for explaining the flow of the cathode fluid and the flow of the anode fluid in the electrolysis cells 10. Arrows of solid lines illustrated in FIG. 9 and FIG. 10 indicate the flow of the cathode fluid. Arrows of dotted lines in FIG. 9 and FIG. 10 indicate the flow of the anode fluid.

In the electrolysis cell 10_2n-1 at the odd stage such as the electrolysis cell 10_1 at a first stage, as illustrated in FIG. 9, the cathode fluid passes through the opening 161_1, passes through the opening 141_1, moves from one end to the other end of the cathode flow path 140, passes through the opening 131_1, passes through the opening 151_1, passes through the opening 171_1, and passes through the opening 181_1, and thereby can move to the electrolysis cell 10 at a next stage.

In the electrolysis cell 10_2n-1 at the odd stage, as illustrated in FIG. 9, the anode fluid passes through the opening 161_2, passes through the opening 141_2, passes through the opening 131_2, moves from one end to the other end of the anode flow path 150, passes through the opening 151_2, passes through the opening 171_2, and passes through the opening 181_2, and thereby can move to the electrolysis cell 10 at the next stage.

In the electrolysis cell 10_2n at the even stage such as the electrolysis cell 10_1 at a second stage, as illustrated in FIG. 10, the cathode fluid passes through the opening 161_1, passes through the opening 141_1, moves from one end to the other end of the cathode flow path 140, passes through the opening 131_1, passes through the opening 151_1, passes through the opening 171_1, and passes through the opening 181_1, and thereby can move to an electrolysis cell 10 at a next stage.

Next, an example method of operating the electrolysis device 1 will be explained. Here, the case of producing carbon monoxide as the carbon compound will be mainly explained, but the reduction product of carbon dioxide is not limited to the carbon compound.

First, a reaction process in the case of oxidizing mainly water (H₂O) to produce hydrogen ions (H⁺) will be explained. When the cathode fluid is supplied from the cathode supply source 20 to the cathode flow path 140, the anode fluid is supplied from the anode supply source 30 to the anode flow path 150, and current is supplied between the cathode 11 and the anode 12 from the power supply 40, an oxidation reaction of water (H₂O) occurs at the anode 12 in contact with the anode solution. Specifically, H₂O contained in the anode solution is oxidized to produce oxygen (O₂) and hydrogen ions (H⁺) as expressed in Formula (1) below.

2H₂O→4H⁺+O₂+4e⁻ (1)

H⁺ produced at the anode 12 moves through the electrolytic solution existing in the anode flow path 150 and the diaphragm 13 and reaches the vicinity of the cathode 11. Electrons (e⁻) based on the current supplied from the power supply 40 to the cathode 11 and H⁺ moved to the vicinity of the cathode 11 cause a reduction reaction of carbon dioxide. Specifically, carbon dioxide supplied from the cathode flow path 140 to the cathode 11 is reduced to produce carbon monoxide as expressed by Formula (2) below. Further, hydrogen ions receive electrons to produce hydrogen as in Formula (3) below. In this event, hydrogen may be produced at the same time with carbon monoxide.

CO₂+2H⁺+2e⁻→CO+H₂O (2)

2H⁺+2e⁻→H₂ (3)

Next, a reaction process in the case of reducing mainly carbon dioxide (CO₂) to produce hydroxide ions (OH⁻) will be explained. When current is supplied between the cathode 11 and the anode 12 from the power supply, water (H₂O) and carbon dioxide (CO₂) are reduced to produce carbon monoxide (CO) and hydroxide ions (OH⁻) near the cathode 11 as expressed by Formula (4) below. Further, water receives electrons as in Formula (5) below to produce hydrogen. In this event, hydrogen may be produced at the same time with carbon monoxide. The hydroxide ions (OH) produced by the reactions diffuse in the vicinity of the anode 12, whereby the hydroxide ions (OH⁻) are oxidized to produce oxygen (O₂) as in Formula (6) below.

2CO₂+2H₂O+4e⁻→2CO+4OH⁻ (4)

2H₂O+2e⁻→H₂+2OH⁻ (5)

4OH⁻→2H₂O+O₂+4e⁻ (6)

As above, the electrolysis cell 10 is not specialized only for the reduction of carbon dioxide, but can produce, for example, carbon monoxide and hydrogen at 1:2 and also manufacture a reduction product and hydrogen at an arbitrary ratio such as manufacturing methanol by a chemical reaction thereafter.

Since hydrogen is a raw material inexpensive and easily available from electrolysis of water or a fossil fuel, the percentage of hydrogen does not need to be large. In view of these facts, the percentage of carbon monoxide to hydrogen is at least 1 or more, and preferably 1.5 or more in terms of economy and environment.

Next, a reaction process in the case of reducing mainly oxygen (O₂) to produce water (H₂O) will be explained. When current is supplied between the cathode 11 and the anode 12 from the power supply, oxygen (O₂) is reduced to produce water (H₂O) in the vicinity of the cathode 11 as expressed in Formula (7) below. In this event, water may be produced at the same time with carbon monoxide and hydrogen, but it is considered that reduction of oxygen mainly proceeds because of the difference in reduction potential. Water in the electrolytic solution is oxidized to produce oxygen (O₂) and protons (H⁺) as expressed in Formula (8) below, and protons (H⁺) required for the reaction in Formula (7) below diffuse from the vicinity of the anode 12. Further, hydrogen peroxide (H₂O₂) may be produced as an intermediate product or a product. Conceivable oxygen reduction reactions are two-electron reduction and four-electron reduction, and can occur in any of acidic and alkaline environments.

O₂+4H⁺+4e⁻→2H₂O (7)

2H₂O→O₂+4H⁺+4e⁻ (8)

The electrolysis cell 10 is not specialized only for the reduction of carbon dioxide, but if impurity gases of oxygen and nitrogen are mixed, the electrolysis cell 10 can also reduce them.

In the case of a nitrogen electrolysis device, the cathode 11 can reduce nitrogen to produce ammonia. For the other configuration of the nitrogen electrolysis device, the configuration of the electrolysis device 1 can be appropriately used. In this case, the impurity gas of the cathode fluid is not nitrogen.

In the case where the cathode fluid contains gas of the reducible material such as carbon dioxide or nitrogen and gas of an impurity such as oxygen when the cathode fluid is supplied from the cathode supply source 20 to the cell structure 100 and the electrolysis cell 10 reduces the reducible material to produce the reduction product, current is consumed for the reduction of the impurity gas and therefore current is accordingly wastefully consumed. Further, the current for reducing the reducible material accordingly decreases, the amount of carbon dioxide to be reduced decreases, and the Faraday efficiency of the reduction product such as the carbon compound and ammonia may decrease. In the conventional electrolysis device, the cathode fluid, the anode fluid, and the power supply current are supplied to flow through the cell stack in series, and therefore it is difficult to control the current supply amount of the electrolysis cell at the first stage where the reduction of the impurity gas mainly occurs. Further, to achieve the high electrolysis efficiency of the electrolysis device, it is necessary to make the electrolysis device operable with low power consumption.

In contrast, the electrolysis device in the embodiment can supply a first power supply current to the electrolysis cells 10 in a first group including the electrolysis cell 10 at the first stage, and supply a second power supply current to the electrolysis cells 10 in a second group including at least one of the electrolysis cells 10 at the next and subsequent stages. In the electrolysis device 1 illustrated in FIG. 1, a plurality of the electrolysis cells 10 are connected in parallel to the power supply 40, and thereby current can be independently supplied to each of the electrolysis cells 10. Not limited to this configuration, the first power supply current may be supplied to the electrolysis cells 10 in the first group including the electrolysis cells 10 at the first stage to an X stage (X is a natural number of 2 or more), and the second power supply current may be supplied to the electrolysis cells 10 in the second group including at least one of the electrolysis cells 10 at an X+1 and subsequent stages.

FIG. 11 is a schematic view illustrating an appearance in which an impurity such as oxygen and a reducible material such as carbon dioxide in the cathode fluid flow in series through the electrolysis cells 10. FIG. 12 is a chart illustrating examples of graphs indicating the relation among a current density flowing through the electrolysis cell 10, a cell voltage, and a Faraday efficiency. A curve of a solid line illustrated in FIG. 12 indicates the relation between a cell voltage of the electrolysis cell 10 supplied with a mixed gas containing gas of carbon dioxide and gas of oxygen and a current density of current flowing through the electrolysis cell 10. A curve of a dotted line illustrated in FIG. 12 indicates the relation between a cell voltage of the electrolysis cell 10 supplied with a single gas of carbon dioxide and a current density of current flowing through the electrolysis cell 10. A curve of a one-dotted chain line illustrated in FIG. 12 indicates the relation between a Faraday efficiency of carbon monoxide of the electrolysis cell 10 supplied with a single gas of carbon dioxide and a current density of current flowing through the electrolysis cell 10. A curve of a two-dotted chain line illustrated in FIG. 12 indicates the relation between a Faraday efficiency of carbon monoxide of the electrolysis cell 10 supplied with a mixed gas containing a carbon dioxide gas and an oxygen gas and a current density of current flowing through the electrolysis cell 10.

In the case where the current density of current flowing through the electrolysis cell 10 is low, current is consumed mainly for producing water by the oxygen reduction, so that the production of carbon monoxide by the reduction of carbon dioxide does not proceed. On the other hand, in the case where the current density of current flowing through the electrolysis cell 10 is high, current is consumed mainly for production of carbon monoxide, and the production of carbon monoxide proceeds. This can be considered because oxygen is preferentially reduced in the vicinity of the inlet of the cathode flow path 140 of the electrolysis cell 10, the oxygen concentration decreases, and mainly carbon dioxide is reduced at the middle and subsequent stages in the cathode flow path 140, resulting in a preferable environment. As illustrated in FIG. 11 and FIG. 12, the reduction of oxygen is mainly and preferentially performed in a range (range A in FIG. 12) of a low current density of 100 mA/cm²or less, current is mainly consumed for the production of water or the like by the oxygen reduction, so that the production of carbon monoxide by the reduction of carbon dioxide does not proceed. Further, in a range (the range B in FIG. 12) of a high current density of 200 mA/cm²or more, the reduction of carbon dioxide is mainly and preferentially performed and current is mainly consumed for the production of carbon monoxide by the reduction of carbon dioxide.

Hence, the first power supply current is supplied so that the current flowing through the electrolysis cell 10 at the first stage (electrolysis cell 10_1) has a low current density. The current density at this time is, for example, 1 mA/cm²or more and 150 mA/cm²or less. This allows the reduction of oxygen to be preferentially performed in the electrolysis cell 10 at the first stage. As a result, almost all of the impurities in the cathode fluid are reduced in the electrolysis cell 10 at the first stage, so that the composition of the cathode fluid flowing through the electrolysis cells 10 at the next and subsequent stage is only gas of mainly the reducible material. Here, the area of the electrolysis cell 10 at the first stage and the area of the electrolysis cell 10 at the next or subsequent stage are the same, but the areas of the electrolysis cells 10 do not always need to be the same. The area of the electrolysis cell 10 includes, for example, the area of an overlapping portion of the cathode 11 and the cathode flow path 140, the area of an overlapping portion of the anode 12 and the anode flow path 150, and so on.

Further, the second power supply current is supplied so that the current flowing through the electrolysis cells 10 at the next and subsequent stages has a high current density. The current density at this time is, for example, 150 mA/cm²or more. The upper limit of the current density is not particularly limited but is, for example, 1000 mA/cm²or less. Thus, more reducible material can be reduced at the electrolysis cells 10 at the next and subsequent stages, and the composition of the cathode fluid to be supplied to the electrolysis cells 10 at the next and subsequent stages can be composed of almost only gas of the reducible material, so that the electrolysis cell 10 where the current is consumed for the reduction of impurities can be limited to the electrolysis cell 10 at the first stage, thereby making it possible to suppress the unnecessary current consumption in the electrolytic reaction such as the reduction reaction of impurities. Thus, it is possible to provide the electrolysis device operable with low power consumption. The impurity gas such as oxygen is sometimes supplied also to the electrolysis cells 10 at the second and subsequent stages. In this case, in the electrolysis device in the embodiment, the power supply current can be supplied from the power supply 40 so that the current density of the current flowing through each of the electrolysis cells 10 in the second group including at least one of the electrolysis cells 10 at the next and subsequent stages is higher than the current density of the current flowing through each of the electrolysis cells 10 in the first group including the electrolysis cell 10_1 at the first stage and at least one of the electrolysis cells 10 at the second and subsequent stages. Further, the reduction potential of a carbon dioxide gas is higher than the reduction potential of an oxygen gas as illustrated in FIG. 12.

FIG. 13 is a schematic view illustrating another example of the electrolysis device in the embodiment. FIG. 13 illustrates another configuration example of the electrolysis device 1. The electrolysis device 1 may share one cathode current collector 16 and one anode current collector 17 among a plurality of the stacked electrolysis cells 10 as illustrated in FIG. 13. FIG. 13 illustrates an example including an electrolysis cell 10_2 and an electrolysis cell 10_3 between the one cathode current collector 16 and the one anode current collector 17 in which the anode flow path plate 15 in the electrolysis cell 10_2 is electrically connected to the cathode flow path plate 14 in the electrolysis cell 10_3. The above configuration can decrease the numbers of the cathode current collectors 16 and the anode current collectors 17 and thereby can suppress the manufacturing cost and thickness of the cell structure 100.

FIG. 14 is a schematic view illustrating another example of the electrolysis device in the embodiment. FIG. 14 illustrates another configuration example of the electrolysis device 1. The electrolysis device 1 may have a power supply 41 and a power supply 42 as illustrated in FIG. 14.

The power supply 41 is electrically connected to the electrolysis cells 10 in the first group including the electrolysis cell 10 at the first stage. The power supply 41 can supply the first power supply current to the electrolysis cell 10 at the first stage. For the other explanation of the power supply 41, the explanation of the power supply 40 can be appropriately used.

The power supply 42 is electrically connected to the electrolysis cells 10 in the second group including at least one of the electrolysis cells 10 at stages next and subsequent to the electrolysis cells 10 in the first group. The power supply 42 can supply the second power supply current to the electrolysis cell 10 at the next and subsequent stages. For the other explanation of the power supply 42, the explanation of the power supply 40 can be appropriately used.

The values of the first power supply current and the second power supply current are adjusted by the power supply 41 and the power supply 42 so that when the area of the electrolysis cells 10 in the first group and the area of the electrolysis cells 10 in the second group are the same, the current density of the current flowing through the electrolysis cells 10 in the second group is higher than the current density of the current flowing through the electrolysis cells 10 in the first group. The above configuration can individually set the first power supply current and the second power supply current, for example, to have optimum current densities in accordance with the respective cell voltages of the electrolysis cells 10 in the first group and the electrolysis cells 10 in the second group, and supply them. In this event, if the prediction of the voltage is difficult, the optimum current densities can be adjusted by providing a resistor between the electrolysis cells 10 in the first group and the electrolysis cells 10 in the second group or connecting a current monitor to each of the electrolysis cells 10. The current may be supplied while controlling the cell voltage of each electrolysis cell 10. The reduction product may be selectively changed by controlling the voltage or current of the electrolysis cells 10 in the second group. Here, the area of the electrolysis cells 10 in the first group and the area of the electrolysis cells 10 in the second group are the same, but the areas of a plurality of electrolysis cells do always need to be the same. In this case, the values of the current density of the first power supply current and the current density of the second power supply current are adjusted by the power supply 41 and the power supply 42 so that the current density of current flowing through the electrolysis cells 10 in the second group is higher than the current density of current flowing through the electrolysis cells 10 in the first group.

FIG. 15 is a schematic view illustrating another example of the electrolysis device in the embodiment. FIG. 15 illustrates another configuration example of the electrolysis device 1. As illustrated in FIG. 15, the electrolysis device 1 may have a power supply 41, a power supply 42, a pipe 19a for separating the electrolysis cells 10 in the first group and the electrolysis cells 10 in the second group and supplying the cathode fluid from the electrolysis cells 10 in the first group to the electrolysis cells 10 in the second group, and a pipe 19b for supplying the anode fluid from the electrolysis cells 10 in the first group to the electrolysis cells 10 in the second group.

The pipe 19a connects the cathode flow path 140 of the electrolysis cell 10 at the final stage in the first group and the cathode flow path 140 of the electrolysis cell 10 at the initial stage in the second group. The pipe 19b connects the anode flow path 150 of the electrolysis cell 10 at the final stage in the first group and the anode flow path 150 of the electrolysis cell 10 at the initial stage in the second group. The pipe 19a and the pipe 19b can be formed using, for example, a metal material or an insulating material. The above configuration can keep a distance between the electrolysis cells 10 in the first group and the electrolysis cells 10 in the second group. This can efficiently utilize, for example, even a small installation space.

FIG. 16 is a schematic view illustrating another example of the electrolysis device in the embodiment. FIG. 16 illustrates another configuration example of the electrolysis device 1. As illustrated in FIG. 16, the electrolysis device 1 may have a power supply 41 and a power supply 42, supply the cathode fluid from the cathode supply source 20 to flow in parallel through the electrolysis cells 10, and supply the anode fluid from the anode supply source 30 to flow in parallel through the stacked electrolysis cells 10. The cathode flow paths 140 of the electrolysis cells 10 in the first group and the cathode flow paths 140 of the electrolysis cells 10 in the second group may be connected, for example, in parallel. The anode flow paths 150 of the electrolysis cells 10 in the first group and the anode flow paths 150 of the electrolysis cells 10 in the second group may be connected, for example, in parallel. The above configuration can individually set optimum current and gas composition and its gas flow rate in accordance with the respective cell voltages of the electrolysis cells 10 in the first group and the electrolysis cells 10 in the second group, and make them flow. In this event, in the case where the prediction of voltage is difficult, the optimum current density can be adjusted by providing a resistor between the electrolysis cells 10 in the first group and the electrolysis cells 10 in the second group or connecting a current monitor to each of the electrolysis cells 10. The current may be supplied while controlling the cell voltage of each electrolysis cell 10. The reduction product may be selectively changed by controlling the voltage or current of the electrolysis cells 10 in the second group.

When the cathode fluid contains a first gas of the reducible material and a second gas of an impurity and the second gas is nitrogen, the electrolysis cells 10 in the first group reduce nitrogen to produce ammonia, and the electrolysis cells 10 in the second group reduce the reducible material such as carbon dioxide to produce a reduction product such as a carbon compound.

The cathodes 11 in the electrolysis cells 10 in the first group may have a first catalyst and the cathodes 11 in the electrolysis cells 10 in the second group may have a second catalyst. The first catalyst is different from the second catalyst. Examples of the first catalyst include platinum and its alloy. Examples of the second catalyst include gold. The selection of an optimum catalyst according to a main product for each electrolysis cell 10 can improve the electrolysis efficiency of the electrolysis device.

The electrolysis device 1 may be employed, for example, for an electrolysis system. The electrolysis system may further include a control device. The control device can control, for example, the power supply voltages or the power supply currents from the power supply 40. Further, the control device can control, for example, the flow rate of the cathode fluid from the cathode supply source 20. Further, the control device can control, for example, the flow rate of the anode fluid from the anode supply source 30. The control device has, for example, hardware having an arithmetic unit such as a processor. Each operation may be held as an operating program on a computer-readable recording medium such as a memory and each operation may be executed by appropriately reading the operation program stored on the recording medium by the hardware.

The above configuration examples of the electrolysis device 1 can be arbitrarily combined.

The configurations of the above-described embodiments are applicable in combination. Further, parts thereof are replaceable. While certain embodiments of the present invention have been described above, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

The above embodiments can be summarized in the following clauses.

(Clause 1)

An electrolysis device comprising:

- a first electrolysis cell configured to reduce a reducible material and to oxidize an oxidizable material;
- a second electrolysis cell configured to reduce the reducible material and to oxidize the oxidizable material;
- a first supply source configured to supply a first fluid to the first electrolysis cell and the second electrolysis cell, the first fluid containing a gas of the reducible material;
- a second supply source configured to supply a second fluid to the first electrolysis cell and the second electrolysis cell, the second fluid containing a liquid of the oxidizable material; and
- at least one power supply configured to supply a first power supply current to the first electrolysis cell and to supply a second power supply current to the second electrolysis cell, wherein
- the at least one power supply is configured to set a value of the first power supply current and a value of the second power supply current so that a current density of current flowing through the second electrolysis cell when reducing the reducible material is higher than a current density of current flowing through the first electrolysis cell when reducing the reducible material.

(Clause 2)

The electrolysis device according to clause 1, wherein:

- the first electrolysis cell has:
  - a first membrane electrode assembly having a first cathode, a first anode, and a first diaphragm between the first cathode and the first anode;
  - a first cathode flow path plate having a first cathode flow path facing on the first cathode; and
  - a first anode flow path plate having a first anode flow path facing on the first anode;
- the second electrolysis cell has:
  - a second membrane electrode assembly having a second cathode, a second anode, and a second diaphragm between the second cathode and the second anode;
  - a second cathode flow path plate having a second cathode flow path facing on the second cathode; and
  - a second anode flow path plate having a second anode flow path facing on the second anode; and
- the device further comprises:
- a first cathode current collector electrically connected to the first cathode and the at least one power supply;
- a first anode current collector electrically connected to the first anode and the at least one power supply;
- a second cathode current collector electrically connected to the second cathode and the at least one power supply; and
- a second anode current collector electrically connected to the second anode and the at least one power supply.

(Clause 3)

The device according to clause 2, wherein

- the second cathode flow path is connected in series to the first cathode flow path.

(Clause 4)

The device according to clause 2, wherein

- the second cathode flow path is connected in parallel to the first cathode flow path.

(Clause 5)

The device according to any one of clause 2 to clause 4, wherein:

- the at least one power supply includes a power supply configured to supply the first power supply current to the first electrolysis cell via the first cathode current collector and the first anode current collector and supply the second power supply current to the second electrolysis cell via the second cathode current collector and the second anode current collector; and
- the first cathode current collector, the first anode current collector, the second cathode current collector, and the second anode current collector are electrically connected to the power supply.

(Clause 6)

The device according to any one of clause 2 to clause 4, wherein

- the at least one power supply includes:
- a first power supply configured to supply the first power supply current to the first electrolysis cell via the first cathode current collector and the first anode current collector; and
- a second power supply configured to supply the second power supply current to the second electrolysis cell via the second cathode current collector and the second anode current collector.

(Clause 7)

The device according to any one of clause 1 to clause 6, wherein:

- the first fluid contains a first gas and a second gas;
- the first gas is gas of carbon dioxide;
- the second gas is gas of a substance different from the carbon dioxide;
- the first electrolysis cell and the second electrolysis cell reduce the carbon dioxide and reduce the substance; and
- a reduction potential of the carbon dioxide is higher than a reduction potential of the substance.

(Clause 8)

The device according to clause 7, wherein

- the substance is oxygen.

(Clause 9)

The device according to clause 7, wherein

- the substance is nitrogen.

(Clause 10)

The device according to any of clause 7 to clause 9, wherein

- a concentration of the second gas of the first fluid is 1 ppm or higher and 100000 ppm or lower.

(Clause 11)

The device according to any one of clause 2 to clause 6, further comprising

- a third electrolysis cell between the second cathode current collector and the second anode current collector, wherein
- the third electrolysis cell having
  - a third cathode;
  - a third anode;
  - a third diaphragm between the third cathode and the third anode;
  - a third cathode flow path plate having a third cathode flow path facing on the third cathode; and
  - a fourth anode flow path plate having a third anode flow path facing on the third anode; and
- the third cathode is electrically connected to the second anode, or the third anode is electrically connected to the second cathode.

(Clause 12)

The device according to any one of clause 2 to clause 7, comprising:

- a first pipe configured to connect the first electrolysis cell and the second electrolysis cell, and supply the first fluid from the first cathode flow path to the second cathode flow path; and
- a second pipe configured to connect the first electrolysis cell and the second electrolysis cell, and supply the second fluid from the first anode flow path to the second anode flow path.

(Clause 13)

The device according to any one of clause 2 to clause 6 and clause 12, wherein

- the first cathode has a first catalyst;
- the second cathode has a second catalyst; and
- the first catalyst is different from the second catalyst.

(Clause 14)

The device according to any one of clause 2 to clause 6, clause 12, and clause 13, wherein:

- the first fluid contains gas of carbon dioxide;
- the first electrolysis cell is configured to reduce carbon dioxide by the first cathode to produce a carbon compound; and
- the second electrolysis cell is configured to reduce the carbon dioxide by the second cathode to produce the carbon compound.

(Clause 15)

The device according to any one of clause 2 to clause 6, clause 12, and clause 13, wherein

- the first fluid contains a gas of nitrogen;
- the first electrolysis cell is configured to reduce nitrogen by the first cathode to produce ammonia; and
- the second electrolysis cell is configured to reduce the nitrogen by the second cathode to produce the ammonia.

(Clause 16)

The device according to any one of clause 2 to clause 6 and clause 12 to clause 15, wherein

- the first electrolysis cell comprises:
  - a first membrane electrode assembly having the first cathode, the first anode, and the first diaphragm;
  - a first supporting plate surrounding the first membrane electrode assembly and having a first opening and a second opening;
  - a first cathode flow path plate having the first cathode flow path connected to the first opening, a third opening connected to the first cathode flow path, and a fourth opening connected to the second opening;
  - a first anode flow path plate having the first anode flow path connected to the second opening, a fifth opening connected to the first opening, and a sixth opening connected to the first anode flow path;
  - the first cathode current collector having a seventh opening connected to the third opening and an eighth opening connected to the fourth opening; and
  - the first anode current collector having a ninth opening connected to the fifth opening and a tenth opening connected to the sixth opening; and
- the second electrolysis cell comprises:
  - a second membrane electrode assembly having the second cathode, the second anode, and the second diaphragm;
  - a second supporting plate surrounding the second membrane electrode assembly and having an eleventh opening and a twelfth opening;
  - a second cathode flow path plate having the second cathode flow path connected to the eleventh opening, a thirteenth opening connected to the second cathode flow path, and a fourteenth opening connected to the twelfth opening;
  - a second anode flow path plate having the second anode flow path connected to the twelfth opening, a fifteenth opening connected to the eleventh opening, and a sixteenth opening connected to the second anode flow path;
  - the second cathode current collector having a seventeenth opening connected to the thirteenth opening and an eighteenth opening connected to the fourteenth opening; and
  - the second anode current collector having a nineteenth opening connected to the fifteenth opening and a twentieth opening connected to the sixteenth opening.

(Clause 17)

The device according to clause 16, further comprising

- an insulating layer provided between the first electrolysis cell and the second electrolysis cell and having a twenty-first opening connecting the ninth opening and the fourteenth opening, and a twenty-second opening connecting the tenth opening and the thirteenth opening.

(Clause 18)

An electrolysis system comprising the device according to any one of clause 1 to clause 17.

(Clause 19)

A method of operating an electrolysis device,

- the device comprising:
  - a first electrolysis cell configured to reduce a reducible material and to oxidize an oxidizable material;
  - a second electrolysis cell configured to reduce the reducible material and to oxidize the oxidizable material;
  - a first supply source configured to supply a first fluid to the first electrolysis cell and the second electrolysis cell, the first fluid containing a gas of the reducible material;
  - a second supply source configured to supply a second fluid to the first electrolysis cell and the second electrolysis cell, the second fluid containing a liquid of the oxidizable material; and
  - at least one power supply configured to supply a first power supply current to the first electrolysis cell and to supply a second power supply current to the second electrolysis cell,
- the method comprising:
- supplying the first fluid to the first electrolysis cell and the second electrolysis cell, and supplying the second fluid to the first electrolysis cell and the second electrolysis cell; and
- supplying the first power supply current to the first electrolysis cell to reduce the reducible material, and supplying the second power supply current to the second electrolysis cell to reduce the reducible material, wherein
- a current density of a current flowing through the second electrolysis cell when reducing the reducible material is higher than a current density of a current flowing through the first electrolysis cell when reducing the reducible material.

(Clause 20)

The method according to clause 19, wherein

- the first fluid contains a gas of carbon dioxide or a gas of nitrogen.

ELECTROLYSIS DEVICE, ELECTROLYSIS SYSTEM, AND METHOD OF OPERATING ELECTROLYSIS DEVICE

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