JP7825792B2 - electrochemical cell - Google Patents

Description

The present disclosure relates to electrochemical cells.
This application claims priority based on Japanese Patent Application No. 2024-051441 filed on March 27, 2024, the entire contents of which are incorporated herein by reference.

In recent years, hydrogen has been attracting attention as a clean energy source. To ensure stable storage of hydrogen, studies have been conducted on adding hydrogen to materials to be hydrogenated. The hydrogen added to the materials to be hydrogenated is extracted through a dehydrogenation reaction at the point of demand. Materials to be hydrogenated are, for example, organic materials such as toluene. Patent Document 1 discloses an electrochemical reduction device, which is an organic hydride production device that adds hydrogen to materials to be hydrogenated.

The electrochemical reduction device comprises an electrolytic cell. The electrolytic cell comprises an anode section and a cathode section separated by an electrolyte membrane. A first fluid containing water is supplied to the anode section, and a second fluid containing the substance to be hydrided is supplied to the cathode section. When a direct current is applied to the electrolytic cell, protons move from the first fluid to the second fluid, and hydrogen is added to the substance to be hydrided. In this specification, the electrolytic cell is referred to as an electrochemical cell. An electrochemical cell in which the substance to be hydrided is hydrogenated by the conduction of protons from the anode section to the cathode section is a proton-conducting electrochemical cell.

International Publication No. 2013/111586

The electrochemical cell disclosed herein comprises an anode section through which a first fluid containing water flows, a cathode section through which a second fluid containing a substance to be hydrided flows, and an electrolyte membrane disposed between the anode section and the cathode section. The anode section comprises a first flow field that forms a space through which the first fluid flows so as to contact a first surface of the electrolyte membrane, and a first catalyst layer disposed in the first flow field. The cathode section comprises a second flow field that forms a space through which the second fluid flows so as to contact a second surface of the electrolyte membrane, and a second catalyst layer disposed in the second flow field. The cell further comprises an insulating member disposed in at least one of the first and second flow fields.

FIG. 1 is a diagram illustrating the operating principle of an electrochemical cell according to an embodiment. FIG. 2 is an exploded perspective view of an electrochemical cell according to an embodiment. FIG. 3 is a schematic diagram of a first conductive plate included in an electrochemical cell according to an embodiment. FIG. 4 is a schematic diagram of a second conductive plate included in an electrochemical cell according to an embodiment. FIG. 5 is a partial cross-sectional view of an electrochemical cell according to an embodiment. FIG. 6 is an explanatory diagram for explaining the first ridge region and the second ridge region of the second conductive plate described in the embodiment. FIG. 7 is an explanatory diagram of the arrangement position of an insulating member in an electrochemical cell described in the embodiment. FIG. 8 is an explanatory diagram of the arrangement of the second diffusion layer in the electrochemical cell described in the embodiment. FIG. 9 is a graph showing the results of Test Example 1. FIG. 10 is a graph showing the results of Test Example 1-2. FIG. 11 is a schematic diagram of the test device of Test Example 4. FIG. 12 is a graph showing the results of Test Example 4.

[Problem to be solved by the present disclosure]
In proton-conducting electrochemical cells, a side reaction occurs in which protons that have migrated to the cathode combine with each other to generate hydrogen. This side reaction can reduce the faradaic efficiency of the electrochemical cell. The faradaic efficiency in this specification is the percentage of the charge that contributed to hydrogenation when the total charge input to the electrochemical cell is taken as 100%.

The above-mentioned side reaction is likely to occur in areas in the cathode where the second fluid flows relatively slowly. Therefore, it is desirable to reduce the above-mentioned side reaction in areas where the second fluid flows relatively slowly.

One of the objectives of this disclosure is to provide an electrochemical cell that can improve the faradaic efficiency of the electrochemical cell.

[Effects of the present disclosure]
The electrochemical cells of the present disclosure can improve faradaic efficiency.

Description of the embodiments of the present disclosure
First, embodiments of the present disclosure will be listed and described.

<1> The proton-conducting electrochemical cell disclosed herein is an electrochemical cell comprising an anode section through which a first fluid containing water flows, a cathode section through which a second fluid containing a substance to be hydrided flows, and an electrolyte membrane disposed between the anode section and the cathode section. The anode section comprises a first flow field that forms a space through which the first fluid flows so as to contact a first surface of the electrolyte membrane, and a first catalyst layer disposed in the first flow field. The cathode section comprises a second flow field that forms a space through which the second fluid flows so as to contact a second surface of the electrolyte membrane, and a second catalyst layer disposed in the second flow field. The cell further comprises an insulating member disposed in at least one of the first flow field and the second flow field.

In the second flow field, a side reaction may occur in which protons are converted into hydrogen gas. This side reaction may reduce the Faraday efficiency of the electrochemical cell. In the electrochemical cell described in <1> above, the region in at least one of the first and second flow fields where the insulating member is located is a region in which no current flows along the stacking direction of the anode section, electrolyte membrane, and cathode section. By having such a non-current-carrying region in the electrochemical cell, the frequency of side reactions occurring can be reduced. As a result, the Faraday efficiency of the electrochemical cell can be improved.

A region in the second flow field where it is relatively difficult for the second fluid to flow may occur. Regions where it is relatively difficult for the second fluid to flow include, for example, a region in the second flow field that is distant from the inlet for the second fluid and a region that is distant from the outlet for the second fluid, specifically the first ridge region and second ridge region described below. In particular, if an insulating member is placed in a region where it is relatively difficult for the fluid to flow, the above-mentioned side reactions in that region can be reduced, effectively improving the Faraday efficiency.

<2> In the electrochemical cell described in <1> above, the at least one flow field comprises a conductive plate facing the electrolyte membrane and a porous diffusion layer arranged between the conductive plate and the electrolyte membrane, and the insulating member may overlap at least a portion of the conductive plate when viewed from a first direction perpendicular to the first surface and from the first surface toward the second surface.

Insulating members that overlap the conductive plate when viewed from the first direction are likely to form the non-conductive areas described above.

<3> In the electrochemical cell described in <2> above, the conductive plate in the second flow field may have a flow path consisting of a groove, and the flow path may be formed on the surface of the conductive plate facing the diffusion layer.

The flow path consisting of the groove improves the flowability of the second fluid in the second flow field. As a result, the second fluid can more easily come into contact with the second catalyst layer in the second flow field, which can improve the Faraday efficiency of the electrochemical cell.

<4> In the electrochemical cell described in <3> above, the flow path may include a first flow path and a second flow path, the first flow path may include a plurality of first grooves arranged in parallel, and the second flow path may include a plurality of second grooves arranged in parallel, and at least a portion of the plurality of first grooves and at least a portion of the plurality of second grooves may be arranged alternately in a planar view.

A first flow path having the above structure can easily quickly diffuse the second fluid containing the substance to be hydrided throughout the entire second flow field. A second flow path having the above structure can easily quickly recover the hydride from the second flow field. This can easily improve the Faraday efficiency of the electrochemical cell.

<5> In the electrochemical cell described in <4> above, the first flow path may have a first connecting groove, and the multiple first grooves may extend so as to branch off from the first connecting groove, and the second flow path may have a second connecting groove, and the multiple second grooves may extend so as to branch off from the second connecting groove. In this case, the conductive plate may have a strip-shaped first ridge region along the first connecting groove and a strip-shaped second ridge region along the second connecting groove. The first ridge region extends from the first connecting groove to the end of the second groove. The second ridge region extends from the second connecting groove to the end of the first groove. The insulating member overlaps at least a portion of the first ridge region and at least a portion of the second ridge region when viewed from the first direction.

By overlapping the insulating member in the portions of the diffusion layer corresponding to the first and second ridge regions, side reactions in the second flow field can be effectively reduced. As a result, the Faraday efficiency of the electrochemical cell is likely to be improved. Details of the first and second ridge regions will be described in detail in the embodiments.

<6> In the electrochemical cell described in <5> above, the insulating member may overlap the entire first ridge region and the entire second ridge region when viewed from the first direction.

By overlapping the insulating material over the entire first and second ridge regions, side reactions can be more effectively reduced.

<7> In the electrochemical cell described in any of <2> to <6> above, the insulating member may be a sheet arranged between the electrolyte membrane and the diffusion layer, or between the diffusion layer and the conductive plate.

The sheet-shaped insulating member can be easily positioned at a desired position in the second flow field. For example, the above-mentioned non-conductive region can be easily formed by sandwiching the sheet-shaped insulating member between the electrolyte membrane and the diffusion layer. The above-mentioned non-conductive region can also be easily formed by sandwiching the sheet-shaped insulating member between the diffusion layer and the conductive plate. Unlike the configuration of <7> above, the sheet-shaped insulating member may be positioned at a desired position in the first flow field.

<8> In the electrochemical cell described in <7> above, the sheet may be integrated with the conductive plate.

If the sheet-shaped insulating member is integrated with the conductive plate, there is no need to align the insulating member with the conductive plate, improving the ease of assembly of the electrochemical cell.

<9> In the electrochemical cell described in any of <2> to <6> above, the insulating member may be a resin material integrated with the diffusion layer.

If an insulating member made of a resin material is integrated into the diffusion layer, alignment between the insulating member and the diffusion layer is not required, improving the assembly of the electrochemical cell. In this configuration, the pores in the diffusion layer are blocked by the resin material, reducing the areas in the diffusion layer through which the first or second fluid flows. This reduces pressure loss.

<10> In the electrochemical cell described in any of <2> to <6> above, the insulating member may be a resin material integrated with the conductive plate.

If the insulating member made of a resin material is integrated with the conductive plate, there is no need to align the insulating member with the conductive plate, improving the ease of assembly of the electrochemical cell.

<11> In the electrochemical cell described in any of <1> to <10> above, the substance to be hydrogenated may be toluene.

Toluene is converted into methylcyclohexane (MCH) through hydrogenation. MCH can store six hydrogen atoms. MCH is a liquid at room temperature and pressure, allowing it to store large amounts of hydrogen relatively safely.

<12> In the electrochemical cell described in any of <1> to <11> above, the first fluid may be mainly water.

The water-based first fluid is pure water or an aqueous solution with pure water as the solvent. Water-based first fluids are inexpensive and easily available.

[Details of the embodiment of the present disclosure]
Specific examples of electrochemical cells according to the present disclosure will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. The dimensions of the components shown in the drawings are expressed for the purpose of clarity and do not necessarily represent actual dimensions. The present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included.

<Embodiment 1>
<Outline of organic hydride manufacturing equipment>
1 is a principle diagram of an organic hydride manufacturing apparatus 100 equipped with a proton-conducting electrochemical cell 1. The organic hydride manufacturing apparatus 100 supplies a first fluid 101 stored in a first tank 101T and a second fluid 102 stored in a second tank 102T to the electrochemical cell 1. The electrochemical cell 1 is equipped with an anode section 3 and a cathode section 4 separated by an electrolyte membrane 2. A DC power supply (not shown) is connected to the anode section 3 and the cathode section 4. The anode section 3 is connected to the positive electrode of the DC power supply, and the cathode section 4 is connected to the negative electrode of the DC power supply.

A first fluid 101 is supplied to the anode section 3 through a first supply pipe 101A. A first pump 101P that pumps the first fluid 101 to the anode section 3 is disposed in the first supply pipe 101A. A first catalyst layer 30 is disposed in the anode section 3. Protons (H ⁺ ), oxygen (O ₂ ), and electrons (e ⁻ ) are generated from water (H ₂ O) contained in the first fluid 101 by an electrochemical reaction. The protons move through the electrolyte membrane 2 to the cathode section 4. Electrons generated at the anode flow to the cathode via a DC power supply. The first fluid 101 in the anode section 3 is discharged to a first tank 101T through a first discharge pipe 101B.

The first fluid 101 containing water may be a fluid mainly composed of water. For example, the first fluid 101 is pure water or an aqueous solution. Commercially available pure water can be used. The pure water may contain ions due to circulation to the electrochemical cell 1. The ions may originate, for example, from some of the constituent materials of the first tank 101T. The first fluid 101 may also be water vapor.

The second fluid 102 is supplied to the cathode section 4 through the second supply pipe 102A. A second pump 102P is disposed in the second supply pipe 102A, which pumps the second fluid 102 to the cathode section 4. A second catalyst layer 40 is disposed in the cathode section 4. The substances to be hydrided contained in the second fluid 102 are hydrogenated by an electrochemical reaction in the second catalyst layer 40 by combining protons that have permeated the electrolyte membrane 2 with electrons supplied from the DC power source, producing hydrides. The second fluid 102 containing the hydrides is discharged from the cathode section 4 to the second tank 102T through the second discharge pipe 102B.

The substance to be hydrogenated contained in the second fluid 102 is, for example, an aromatic hydrocarbon compound containing one or more aromatic rings, or a nitrogen-containing heterocyclic aromatic compound. Specific examples of the aromatic compounds include benzene, naphthalene, anthracene, diphenylethane, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, and N-alkyldibenzopyrrole. In the aromatic hydrocarbon compound or the nitrogen-containing heterocyclic aromatic compound, one to four hydrogen atoms in the aromatic ring may be substituted with an alkyl group. The "alkyl" mentioned above refers to a linear or branched alkyl group having one to six carbon atoms. Examples of alkylbenzenes include toluene and ethylbenzene. Examples of dialkylbenzenes include xylene and diethylbenzene. Examples of trialkylbenzenes include mesitylene. Examples of alkylnaphthalenes include methylnaphthalene. In this example, the substance to be hydrogenated is toluene (denoted as TOL in the figure). The hydride produced by hydrogenating toluene is methylcyclohexane (hereinafter denoted as MCH). The electrochemical cell 1 in this example is also called an MCH electrosynthesis cell, and the reactions in the anode section 3 and the cathode section 4 are as follows:
・3H ₂ O → 1.5O ₂ +6H ⁺ +6e ^-
Toluene + 6H ⁺ + 6e ^- → methylcyclohexane

<Basic structure of an electrochemical cell>
As shown in FIG. 2, the electrochemical cell 1 includes an electrolyte membrane 2, a first flow field 5, a second flow field 6, a first catalyst layer 30, and a second catalyst layer 40.

The electrolyte membrane 2 is formed from a material that selectively allows protons to pass through. The electrolyte membrane 2 separates the first fluid 101 and the second fluid 102 within the electrochemical cell 1. The thickness of the electrolyte membrane 2 is, for example, 5 μm or more and 300 μm or less. An electrolyte membrane 2 having a thickness of 5 μm or more easily separates the first fluid 101 and the second fluid 102. An electrolyte membrane 2 having a thickness of 300 μm or less easily allows protons to pass through. The thickness of the electrolyte membrane 2 may be 10 μm or more and 150 μm or less, or may be 20 μm or more and 100 μm or less.

The first flow field 5 is a space in the anode section 3 through which the first fluid 101 flows. The inlet 5A and outlet 5B of the first flow field 5 are connected to the first supply pipe 101A and the first discharge pipe 101B, respectively, as shown in FIG. 1. The first flow field 5 allows the first fluid 101 to flow so as to contact the first surface 21 of the electrolyte membrane 2. The anode section 3 in this example includes a first conductive plate 31, a first diffusion layer 32, and a frame seal section 33. The first conductive plate 31 is a conductive plate material facing the first surface 21 of the electrolyte membrane 2. The first diffusion layer 32 is a conductive porous layer disposed between the first conductive plate 31 and the first surface 21. The first flow field 5 in this example is formed in the space between the first conductive plate 31 and the first surface 21. The first flow field 5 includes pores in the first diffusion layer 32.

The first conductive plate 31 has the function of applying a voltage to the electrochemical cell 1. The first conductive plate 31 also has the function of containing the first fluid 101 within the electrochemical cell 1. The first conductive plate 31 is required to be made of a material that is not easily reactive with the substances contained in the first fluid 101. The first conductive plate 31 is, for example, a plate made of a composite material of a conductive material and a resin. The conductive material is, for example, a carbon-based material such as graphite or carbon black. The resin is, for example, an epoxy resin, a phenol resin, a polyamide resin such as PA6 or PA66, a polyoxymethylene resin, a fluororesin such as polytetrafluoroethylene resin, or a polyphenylene sulfide resin. Composite materials are lightweight and inexpensive, and can be easily formed by molding. The first conductive plate 31 may be, for example, a metal plate with a coating layer. The coating layer is formed of a material with high oxidation resistance, such as platinum. The metal plate is formed of, for example, titanium or a titanium alloy. An electrode plate (not shown) is disposed on the surface of the first conductive plate 31 opposite the first diffusion layer 32. The electrode plate is connected to the anode of a DC power supply (not shown).

In the electrochemical cell 1, the first diffusion layer 32 functions to diffuse the first fluid 101 supplied to the anode section 3 throughout the first flow field 5. The first diffusion layer 32 is a porous layer formed of a metal material. The first diffusion layer 32 has, for example, a porous body with a three-dimensional mesh structure made of titanium or a titanium alloy, and a precious metal coating formed on the surface of the porous body. The precious metal is, for example, platinum. The porous body includes a porous layer such as a nonwoven fabric, or a mesh plate. The porous body may be a stack of multiple mesh plates with different mesh sizes, or a stack of multiple mesh plates with different mesh shapes.

The first diffusion layer 32 is sandwiched between the electrolyte membrane 2 and the first conductive plate 31. The first diffusion layer 32 is pressed between the electrolyte membrane 2 and the first conductive plate 31. Depending on the material of the first diffusion layer 32, the first diffusion layer 32 may be compressed by the pressure. A first diffusion layer 32 formed from a metal material has multiple pores but is resistant to deformation. The average thickness of the first diffusion layer 32 sandwiched between the electrolyte membrane 2 and the first conductive plate 31 in the electrochemical cell 1 is, for example, 0.15 mm to 3.0 mm. If the first diffusion layer 32 is formed from a metal material that is resistant to deformation by the pressure, for example, the average thickness of the first diffusion layer 32 when not sandwiched between the electrolyte membrane 2 and the first conductive plate 31 is substantially equal to the average thickness of the first diffusion layer 32 sandwiched between the electrolyte membrane 2 and the first conductive plate 31. The average thickness of the first diffusion layer 32 is the average of thicknesses at three or more different points. If the average thickness of the first diffusion layer 32 is 0.15 mm or more, the gap between the first conductive plate 31 and the electrolyte membrane 2 is sufficiently large. In other words, a first flow field 5 of sufficient size is formed in the anode portion 3, and the first fluid 101 can easily diffuse throughout the entire first flow field 5. If the average thickness of the first diffusion layer 32 is 3.0 mm or less, the gap between the first conductive plate 31 and the electrolyte membrane 2 is not too large. In other words, the first flow field 5 is not too large, and the first fluid 101 containing oxygen generated by the electrolysis of water can easily be discharged from the first flow field 5. The average thickness of the first diffusion layer 32 may be 0.2 mm or more and 2.5 mm or less, or 0.25 mm or more and 2.0 mm or less.

The porosity of the first diffusion layer 32 within the electrochemical cell 1 is, for example, 60% or more and 90% or less. Because the first diffusion layer 32 formed from a metal material has low elastic deformability, the porosity of the first diffusion layer 32 removed from the electrochemical cell 1 can be considered to be the porosity of the first diffusion layer 32 within the electrochemical cell 1. If the porosity is 60% or more, the first fluid 101 is likely to diffuse throughout the entire first flow field 5. If the porosity is 90% or less, the strength of the first diffusion layer 32 is likely to be obtained. The porosity of the first diffusion layer 32 may be, for example, 65% or more and 85% or less, or 68% or more and 80% or less.

The frame seal portion 33 surrounds the outer periphery of the first diffusion layer 32. The frame seal portion 33 prevents the first fluid 101 from leaking out beyond the outer periphery of the first diffusion layer 32. Therefore, in this example, the first flow field 5 is primarily formed by the space between the first surface 21 of the electrolyte membrane 2 and the first conductive plate 31, surrounded by the frame seal portion 33. By disposing the first diffusion layer 32 in this space, the first fluid 101 can use the pores in the first diffusion layer 32 as a flow path. The size of the frame seal portion 33 can be selected based on the sizes of the first conductive plate 31 and the first diffusion layer 32. In this example, the size of the window portion of the frame seal portion 33 roughly corresponds to the size of the first diffusion layer 32, and the size of the outer edge of the frame seal portion 33 roughly corresponds to the size of the first conductive plate 31. The frame seal portion 33 is formed of an electrically insulating material that is resistant to the first fluid 101. Specific examples of the electrical insulating material include epoxy resin, phenol resin, polyamide resin such as PA6 or PA66, polyoxymethylene resin, fluororesin, and polyphenylene sulfide resin.

The first catalyst layer 30 disposed in the first flow field 5 is in contact with or adjacent to the first surface 21 of the electrolyte membrane 2. The first catalyst layer 30 promotes the electrolysis of water contained in the first fluid 101, generating protons, oxygen, and electrons. In this example, the first catalyst layer 30 is integrally formed on the first surface 21 of the electrolyte membrane 2. The first catalyst layer 30 may also be integrally formed on at least a portion of the first diffusion layer 32 that contacts the electrolyte membrane 2. The first catalyst layer 30 may be a component independent of the electrolyte membrane 2 and the first diffusion layer 32. In this case, the first catalyst layer 30 is disposed between the electrolyte membrane 2 and the first diffusion layer 32. The first catalyst layer 30 includes a catalyst. The catalyst is, for example, a noble metal oxide-based catalyst such as _RuO2 or _IrO2 . This catalyst may have a structure in which the noble metal oxide is dispersed and supported on a substrate made of a metal wire or metal mesh, or a structure in which the noble metal oxide is coated on the substrate. The first catalyst layer 30 may include an ionomer that adheres the catalyst to the substrate. The metal constituting the substrate is, for example, one metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W, or an alloy containing the above metal as a main component. When _IrO2 is used as a catalyst, a structure in which the substrate is coated with a thin film made of _IrO2 reduces the amount of expensive precious metal used, thereby reducing production costs.

The second flow field 6 is a space in the cathode section 4 through which the second fluid 102 flows. The inlet 6A and outlet 6B of the second flow field 6 are connected to the second supply pipe 102A and the second discharge pipe 102B, respectively, as shown in FIG. 1. The second flow field 6 allows the second fluid 102 to flow so as to contact the second surface 22 of the electrolyte membrane 2. The second surface 22 is the surface of the electrolyte membrane 2 opposite the first surface 21. The cathode section 4 in this example includes a second conductive plate 41, a second diffusion layer 42, a frame seal portion 43, and an insulating member 8. The second conductive plate 41 is a conductive plate material facing the second surface 22 of the electrolyte membrane 2. The second diffusion layer 42 is a conductive porous layer disposed between the second conductive plate 41 and the second surface 22. The second flow field 6 in this example is formed in the space between the second conductive plate 41 and the second surface 22. The second flow field 6 includes pores in the second diffusion layer 42. The insulating member 8 will be described later in a separate section.

The second conductive plate 41 has the function of applying a voltage to the electrochemical cell 1. The second conductive plate 41 also has the function of containing the second fluid 102 within the electrochemical cell 1. The second conductive plate 41 is required to be formed from a material that is unlikely to react with substances contained in the second fluid 102. The second conductive plate 41 is, for example, a plate formed from a composite material of a conductive material, such as the carbon-based material described above, and a resin. Composite materials are lightweight and inexpensive, and can be easily formed by molding. The second conductive plate 41 may be, for example, a metal plate. The metal plate may be formed from, for example, titanium or a titanium alloy, or stainless steel. An electrode plate (not shown) is disposed on the surface of the second conductive plate 41 opposite the second diffusion layer 42. The electrode plate is connected to the cathode of a DC power supply (not shown).

The second diffusion layer 42 has the function of diffusing the second fluid 102 supplied to the cathode section 4 throughout the second flow field 6. The second diffusion layer 42 is a porous layer formed from a conductive material. The second diffusion layer 42 is, for example, a nonwoven fabric containing carbon fibers. The nonwoven fabric containing carbon fibers is formed by subjecting multiple carbon fibers to an entanglement process, thereby entangling the carbon fibers with each other. The entanglement process can be performed, for example, by needle punching or water flow.

The second diffusion layer 42, formed from a nonwoven fabric, has high elastic deformability. When the second diffusion layer 42, which has high elastic deformability, is sandwiched between the electrolyte membrane 2 and the second conductive plate 41 within the electrochemical cell 1 and pressed against them, the second diffusion layer 42 is compressed. This compression reduces the average thickness of the second diffusion layer 42. The average thickness of the second diffusion layer 42 sandwiched between the electrolyte membrane 2 and the second conductive plate 41 within the electrochemical cell 1 is, for example, 0.15 mm or more and 3.0 mm or less. In this specification, the average length between the electrolyte membrane 2 and the second conductive plate 41 in the electrochemical cell 1 is considered to be the average thickness of the second diffusion layer 42. The number of measurements required to determine the average length is three or more, including a measurement at the center of the electrolyte membrane 2 when viewed in plan.

If the average thickness of the second diffusion layer 42 in the compressed state is 0.15 mm or more, the amount of elastic deformation of the second diffusion layer 42 within the electrochemical cell 1 is likely to be large. As a result, the second diffusion layer 42 is likely to adhere closely to the electrolyte membrane 2 and the second conductive plate 41. Furthermore, if the average thickness of the second diffusion layer 42 is 0.15 mm or more, the gap between the second conductive plate 41 and the electrolyte membrane 2 is sufficiently large. In other words, a sufficiently large second flow field 6 is formed within the cathode section 4, and the second fluid 102 is likely to diffuse throughout the entire second flow field 6. If the average thickness of the second diffusion layer 42 in the compressed state is 3.0 mm or less, increases in the electrical resistance of the second diffusion layer 42 and the cell resistance of the electrochemical cell 1 are likely to be reduced. Furthermore, if the average thickness of the second diffusion layer 42 is 3.0 mm or less, the gap between the second conductive plate 41 and the electrolyte membrane 2 is not too large. In other words, since the second flow field 6 does not become too large, the second fluid 102 containing the hydride produced in the second catalyst layer 40 is likely to be quickly discharged from the second flow field 6. The average thickness of the second diffusion layer 42 may be 0.15 mm or more and less than 3.0 mm, or may be 0.2 mm or more and 2.5 mm or less, or may be 0.25 mm or more and 2.0 mm or less.

The porosity of the second diffusion layer 42 in the electrochemical cell 1 is, for example, 40% or more and 98% or less. Because the second diffusion layer 42 formed from nonwoven fabric deforms when compressed, the porosity of the second diffusion layer 42 in the electrochemical cell 1 can be determined based on the porosity measurement results of the second diffusion layer 42 removed from the electrochemical cell 1. An example of how to determine the porosity is explained in the section "Configuration of the Second Diffusion Layer" below. If the porosity is 40% or more, the second fluid 102 is likely to diffuse throughout the entire second flow field 6. If the porosity is 98% or less, the strength of the second diffusion layer 42 is likely to be obtained. The porosity of the second diffusion layer 42 may be, for example, 45% or more and 97% or less, or 50% or more and 96% or less.

The frame seal portion 43 surrounds the outer periphery of the second diffusion layer 42. The frame seal portion 43 prevents the second fluid 102 from leaking out beyond the outer periphery of the second diffusion layer 42. Therefore, in this example, the second flow field 6 is primarily formed by the space between the second surface 22 of the electrolyte membrane 2 and the second conductive plate 41, surrounded by the frame seal portion 43. By disposing the second diffusion layer 42 in this space, the second fluid 102 can use the pores of the second diffusion layer 42 as a flow path. For specifications such as the constituent materials and size of the frame seal portion 43 of the cathode portion 4, please refer to the explanation of the constituent materials, size, and other specifications of the frame seal portion 33 of the anode portion 3.

The second catalyst layer 40, located in the second flow field 6, is in contact with or adjacent to the second surface 22 of the electrolyte membrane 2. The second catalyst layer 40 promotes the reaction of the hydride contained in the second fluid 102 with protons and electrons, resulting in the production of hydrides. In this example, the second catalyst layer 40 is integrally formed on the second surface 22 of the electrolyte membrane 2. The second catalyst layer 40 may be integrally formed on at least a portion of the second diffusion layer 42 that contacts the electrolyte membrane 2. The second catalyst layer 40 may be a component independent of the electrolyte membrane 2 and the second diffusion layer 42. In this case, the second catalyst layer 40 is disposed between the electrolyte membrane 2 and the second diffusion layer 42. The second catalyst layer 40 includes a catalyst. The catalyst is, for example, a composition including a first catalytic metal and a second catalytic metal. The first catalytic metal includes at least one of the precious metals Pt and Pd. The second catalyst metal is one or more metals selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn, W, Re, Pb, and Bi. The catalyst may be a carbon support on which the above metal or metal oxide is supported. The second catalyst layer 40 may contain an ionomer that adheres the catalyst to the support. Other known catalysts may also be used.

The organic hydride manufacturing apparatus 100 of FIG. 1 typically includes a stack of multiple electrochemical cells 1. In the stack, of two adjacent electrochemical cells 1, the first conductive plate 31 of one electrochemical cell 1 and the second conductive plate 41 of the remaining electrochemical cell 1 form a bipolar plate. In the bipolar plate, the first surface of the bipolar plate functions as the first conductive plate 31, and the second surface opposite the first surface functions as the second conductive plate 41. Therefore, a first diffusion layer 32 is disposed on the first surface of the bipolar plate, and a second diffusion layer 42 is disposed on the second surface of the bipolar plate. At the first and second ends of the stack, the first conductive plate 31 and the second conductive plate 41, rather than bipolar plates, are disposed, respectively.

In electrochemical cell 1, it is desirable that the charge input to electrochemical cell 1 be used to hydrogenate the substance to be hydrogenated with high efficiency, i.e., that the Faraday efficiency be improved. Below, we will explain the configuration for improving the Faraday efficiency of electrochemical cell 1.

<Configuration of flow path in second flow field>
The second flow field 6 includes a first flow path 61 and a second flow path 62. In this example, the first flow path 61 and the second flow path 62 are not directly connected to each other and are independent of each other. Furthermore, the cathode section 4 has a region in which a part of the first flow path 61 and a part of the second flow path 62 are parallel to each other. For the explanation of the first flow path 61 and the second flow path 62, please refer mainly to FIG. 4. In FIG. 4, the approximate flow of the second fluid 102 is indicated by thick arrows.

The first flow path 61 has an inlet end 61A (first inlet end) that is directly connected to the inlet 6A (FIG. 1) of the second flow field 6, and an outlet end 61B (first outlet end) that is not directly connected to the outlet 6B (FIG. 1) of the second flow field 6. The inlet 6A is directly connected to the end of the second supply pipe 102A shown in FIG. 1. Therefore, the second fluid 102 easily flows into the first flow path 61 through the inlet end 61A. The first flow path 61 quickly diffuses the second fluid 102 throughout the second flow field 6, increasing the opportunity for the hydrogenated substance contained in the second fluid 102 to come into contact with the second catalyst layer 40. On the other hand, because the outlet end 61B of the first flow path 61 is not directly connected to the outlet 6B of the second flow field 6, the second fluid 102 flowing through the first flow path 61 is not directly discharged to the outlet 6B. The first flow path 61 having such a configuration allows the second fluid 102 that has diffused throughout the second flow field 6 to remain in the second flow field 6 to a certain extent, thereby promoting the production of hydrides.

The second flow path 62 has an inlet end 62A (second inlet end) that is not directly connected to the inlet 6A of the second flow field 6, and an outlet end 62B (second outlet end) that is directly connected to the outlet 6B of the second flow field 6. The second flow path 62, which is not directly connected to the inlet 6A of the second flow field 6, takes in the second fluid 102 from within the second flow field 6 without taking in the second fluid 102 directly from the inlet 6A of the second flow field 6. This reduces the amount of hydride to be discharged to the outside of the electrochemical cell 1 without contacting the second catalyst layer 40, promoting hydride production. Meanwhile, the second flow path 62 is directly connected to the outlet 6B of the second flow field 6. The outlet 6B is directly connected to the end of the second discharge pipe 102B shown in FIG. 1. This allows the second fluid 102 to be easily discharged from the second flow path 62 through the outlet end 62B. This second flow path 62 configuration allows the hydride-containing second fluid 102 to be quickly discharged to the outside of the electrochemical cell 1.

In the region where part of the first flow path 61 and part of the second flow path 62 are parallel, the second fluid 102 moves from the first flow path 61 to the second diffusion layer 42, and then moves within the second diffusion layer 42 toward the second flow path 62 while contacting the second catalyst layer 40. The second fluid 102 that has moved to the second flow path 62 is quickly discharged from the second flow field 6. Therefore, the material to be hydrogenated is smoothly supplied to the second catalyst layer 40, and the hydrogenated material is smoothly discharged from the second catalyst layer 40.

The first flow path 61 and the second flow path 62 in the second flow field 6 improve the flowability of the second fluid 102 in the second flow field 6 and reduce pressure loss in the second flow field 6. This allows for a larger supply amount of the second fluid 102 to the electrochemical cell 1. Increasing the supply amount of the second fluid 102 makes it easier for the substance to be hydrided to be supplied to the second catalyst layer 40 and for the hydride to be removed from the vicinity of the second catalyst layer 40. Furthermore, increasing the supply amount of the second fluid 102 makes it easier for water to be removed from the vicinity of the second catalyst layer 40. Water migrates from the first fluid 101 through the electrolyte membrane 2 to the second fluid 102, and inhibits the hydrogenation of the substance to be hydrided in the second catalyst layer 40. The rapid supply of the substance to be hydrided and the rapid removal of the hydride and water increase the faradaic efficiency of the electrochemical cell 1.

In this example, the first flow path 61 and the second flow path 62 are grooves formed in the second conductive plate 41. The openings of the grooves face the second diffusion layer 42. In other words, the openings of the grooves are positioned so as to connect to the pores in the second diffusion layer 42. Unlike this example, the first flow path 61 and the second flow path 62 may also be grooves formed in the second diffusion layer 42.

The first flow path 61 formed by the grooves formed in the second conductive plate 41 quickly diffuses the second fluid 102 over the entire surface of the second conductive plate 41. The second fluid 102 diffused over the entire surface of the second conductive plate 41 is likely to come into contact with the second catalyst layer 40. The second fluid 102 containing hydrides passes through the second diffusion layer 42 and is discharged to the second flow path 62. The second flow path 62 formed by the grooves formed in the second conductive plate 41 quickly discharges the second fluid 102 containing hydrides to the outside of the electrochemical cell 1. As a result, the Faraday efficiency of the electrochemical cell 1 is increased.

The shapes of the grooves forming the first flow path 61 and the second flow path 62 are not particularly limited. In this example, the first flow path 61 and the second flow path 62 are grooves with structures independent of each other. Specifically, the first flow path 61 includes a plurality of first grooves 61d, and the second flow path 62 includes a plurality of second grooves 62d. In a plan view, at least some of the plurality of first grooves 61d and at least some of the plurality of second grooves 62d are alternately arranged in parallel in a direction perpendicular to the extension direction of the first grooves 61d and the second grooves 62d. In this example, the first grooves 61d and the second grooves 62d are vertical grooves extending in a direction from the lower end to the upper end of the second conductive plate 41. The region where the first grooves 61d and the second grooves 62d are alternately arranged corresponds to the region where a portion of the first flow path 61 and a portion of the second flow path 62 are arranged in parallel.

In this example, the first flow path 61 further includes a first connecting groove 61b connecting the lower ends of the multiple first grooves 61d, and a supply groove 61f connecting the first connecting groove 61b and the manifold 4A. The multiple first grooves 61d extend branching off from the first connecting groove 61b. The supply groove 61f extends branching off from the first connecting groove 61b in the opposite direction to the extension of the first grooves 61d. The supply groove 61f is the inlet end 61A of the first flow path 61. The manifold 4A is directly connected to the end of the second supply pipe 102A shown in FIG. 1. That is, the supply groove 61f is directly connected to the inlet 6A of the second flow field 6 shown in FIG. 1 via the manifold 4A. The second fluid 102 flows easily through the inlet end 61A connected to the inlet 6A. On the other hand, the end 61e of the first groove 61d is closed. The end 61e is the outlet end 61B of the first flow path 61. The second fluid 102 does not easily flow through the outflow end 61B consisting of the closed end 61e. Since the opening of the first flow path 61 consisting of the groove with the above structure faces the second diffusion layer 42, the second fluid 102 is quickly diffused from the first flow path 61 throughout the second diffusion layer 42. As a result, the substance to be hydrogenated contained in the second fluid 102 is efficiently supplied to the second catalyst layer 40.

Unlike this example, each of the multiple first grooves 61d may be directly connected to the manifold 4A. In this case, the first connecting groove 61b and the supply groove 61f are not formed in the second conductive plate 41. Alternatively, the first flow path 61 may be configured such that some of the multiple first grooves 61d are connected to the first connecting groove 61b, and the remaining grooves are each directly connected to the manifold 4A.

In this example, the second flow path 62 further includes a second connecting groove 62b connecting the upper ends of the multiple second grooves 62d, and a discharge groove 62f connecting the second connecting groove 62b to the manifold 4B. The multiple second grooves 62d extend branching off from the second connecting groove 62b. The discharge groove 62f extends branching off from the second connecting groove 62b in the opposite direction to the extension of the second grooves 62d. The discharge groove 62f is the outlet end 62B of the second flow path 62. The manifold 4B is directly connected to the end of the second discharge pipe 102B shown in FIG. 1. That is, the discharge groove 62f is directly connected to the outlet 6B of the second flow field 6 shown in FIG. 1 via the manifold 4B. The second fluid 102 flows easily through the outlet end 62B connected to the outlet 6B. Meanwhile, the end 62e of the second groove 62d, which serves as the inlet for the second fluid 102 into the second flow path 62, is closed. The end 62e is the inlet end 62A of the second flow channel 62. The second fluid 102 does not flow easily through the inlet end 62A that is the closed end 62e. The opening of the second flow channel 62 that is the groove of the above structure faces the second diffusion layer 42, so the second fluid 102 containing the hydride is quickly recovered from near the second catalyst layer 40 into the second flow channel 62. Water that has passed through the electrolyte membrane 2 is also quickly recovered from near the second catalyst layer 40 into the second flow channel 62.

Unlike this example, each of the multiple second grooves 62d may be directly connected to the manifold 4B. In this case, the second connecting groove 62b and the discharge groove 62f are not formed in the second conductive plate 41. Alternatively, the second flow path 62 may be configured such that some of the multiple second grooves 62d are connected to the second connecting groove 62b, and the remaining grooves are directly connected to the manifold 4B. Here, the configuration of the groove connected to the manifold 4A and the configuration of the groove connected to the manifold 4B may be the same or different.

Figure 5 is a partial cross-sectional view of the electrochemical cell 1 of Figure 1 taken in a direction perpendicular to the first groove 61d and second groove 62d in Figure 4. In Figure 5, the thick arrows indicate the approximate flow of the second fluid 102 in the second diffusion layer 42. Furthermore, in Figure 5, the thick arrows indicate the approximate flow of the first fluid 101 in the first diffusion layer 32. As shown in Figure 5, a ridge 63 is formed between the first groove 61d of the first flow path 61 and the second groove 62d of the second flow path 62. The openings and ridges 63 of the first groove 61d and the second groove 62d are covered by the second diffusion layer 42. A portion of the second fluid 102 flowing through the first groove 61d passes through the second diffusion layer 42, which covers the ridges 63, and flows into the second groove 62d. At this time, the substance to be hydrogenated contained in the second fluid 102 is hydrogenated in the second catalyst layer 40, producing a hydride. Here, when the supply amount of the second fluid 102 increases, the flow rate of the second fluid 102 passing through the ridge portion 63 increases, and the material to be hydrogenated is quickly supplied to the second catalytic layer 40, and the hydrogenated material is quickly recovered from the second catalytic layer 40.

The flow velocity of the second fluid 102 passing through the rib portion 63 tends to increase depending on the width of the rib portion 63. The larger the average width W1 of the rib portion 63 is compared to the average width W2 of the first groove 61d and the second groove 62d, the greater the flow velocity of the second fluid 102 passing through the rib portion 63. The average width W1 can be calculated, for example, as follows: Measure the widths at the start position S1, the end position E1, and the middle position M1 along the length of each rib portion 63 shown in Figure 4. The average width W1 is calculated by averaging all the measured widths. The average width W2 can be calculated, for example, as follows: Measure the widths at the start position S2, the end position E2, and the middle position M2 along the length of each first groove 61d and second groove 62d. The average width W2 is calculated by averaging all the measured widths.

The ratio W1/W2 of the average width W1 to the average width W2 is, for example, greater than 1 and less than 50. As the ratio W1/W2 increases, the flow rate of the second fluid 102 increases, but the pressure loss in the second flow field 6 also increases, creating a trade-off. Specifically, as the ratio W1/W2 increases, the number of first grooves 61d and second grooves 62d in the second flow field 6 decreases. A decrease in the number of first grooves 61d and second grooves 62d increases the pressure loss in the second flow field 6. In other words, the upper limit of the amount of second fluid 102 supplied to the electrochemical cell 1 decreases. However, an increase in the average width W1 of the ridge portions 63 due to a decrease in the number of first grooves 61d and second grooves 62d increases the flow rate of the second fluid 102 in the ridge portions 63. An increase in the flow rate of the second fluid 102 in the ridge portions 63 is more likely to increase the Faraday efficiency than an increase in the amount of second fluid 102 supplied to the electrochemical cell 1. If the ratio W1/W2 is 50 or less, the number of first grooves 61d and second grooves 62d is not reduced too much. If the ratio W1/W2 is 50 or less, the effect of reducing an increase in flow velocity and an increase in pressure loss can be satisfactorily obtained. The ratio W1/W2 may be, for example, 2 or more and 45 or less, or 5 or more and 35 or less.

Here, even when the current density during operation of the electrochemical cell 1 is high, it is desirable for the electrochemical cell 1 to have a high faradic efficiency of 90% or more, or even 95% or more. High faradic efficiency can be obtained by increasing the ratio W1/W2 according to the magnitude of the current density during operation. For example, when the current density during operation is less than 1 A/cm ² , high faradic efficiency can be obtained when the ratio W1/W2 is greater than 1, or even greater than 3, or even greater than 5. For example, when the current density during operation is a higher current density of 1 A/cm ² or more, high faradic efficiency can be obtained when the ratio W1/W2 is greater than 5 and less than 40, or even greater than 8 and less than 38, or greater than 10 and less than 35.

The average width W1 of the ridge portion 63 is, for example, 1 mm or more and 50 mm or less. If the average width W1 is 1 mm or more, the flow velocity of the second fluid 102 in the ridge portion 63 is likely to be sufficiently high. If the average width W1 is 50 mm or less, the number of first grooves 61d and second grooves 62d in the second flow field 6 is sufficiently large, making it difficult for the pressure loss in the second flow field 6 to be high. The average width W1 may be, for example, 2 mm or more and 45 mm or less, or 3 mm or more and 40 mm or less.

The average width W2 of the first groove 61d and the second groove 62d is, for example, 0.5 mm or more and 5 mm or less. If the average width W2 is 0.5 mm or more, the second fluid 102 is more likely to diffuse from the first flow path 61 throughout the second flow field 6, and the diffused second fluid 102 is more likely to be recovered in the second flow path 62. If the average width W2 is 5 mm or less, the amount of second fluid 102 discharged from the second flow field 6 without coming into contact with the second catalyst layer 40 is reduced. The average width W2 may be, for example, 0.6 mm or more and 3 mm or less, or 0.8 mm or more and 2 mm or less.

The average depth d of the first groove 61d and the second groove 62d is, for example, 0.5 mm or more and 5 mm or less. The average depth d can be determined, for example, as follows: The depths of each first groove 61d and second groove 62d are measured at the start, end, and middle positions along their length. The average depth d is the average of all measured depths. If the average depth d is 0.5 mm or more, the pressure loss in the second flow field 6 is likely to be reduced. If the average depth d is 5 mm or less, the thickness of the second conductive plate 41 can be reduced while maintaining the strength of the second conductive plate 41. A thinner second conductive plate 41 allows for a more compact electrochemical cell 1. The average depth d may be, for example, 0.6 mm or more and 3 mm or less, or 0.8 mm or more and 2 mm or less. The depths of the first groove 61d and the second groove 62d may be uniform or may vary along their lengths.

In a configuration different from that described above, the end 61e of the first groove 61d of the first flow path 61 in FIG. 4 may be connected to the second connecting groove 62b of the second flow path 62 by a groove thinner than the first groove 61d. Even in this case, the first flow path 61 has a structure in which the second fluid 102 flows more slowly at the outlet end 61B than at the inlet end 61A. Furthermore, the end 62e of the second groove 62d of the second flow path 62 and the first connecting groove 61b of the first flow path 61 may be connected by a groove thinner than the second groove 62d. Even in this case, the second flow path 62 has a structure in which the second fluid 102 flows more slowly at the inlet end 62A than at the outlet end 62B.

<Configuration of flow path in first flow field>
As shown in FIG. 3 , the first flow field 5 may include a flow path 50 that facilitates the flow of the first fluid 101. In this example, the flow path 50 is a groove formed in the first conductive plate 31. In this example, the flow path 50 includes a supply groove 51, a first base groove 52, a plurality of branch grooves 53, a second base groove 54, and a discharge groove 55. The supply groove 51 is connected to a manifold 3A that penetrates the first conductive plate 31. The manifold 3A is directly connected to the end of the first supply pipe 101A shown in FIG. 1 . That is, the supply groove 51 is directly connected to the inlet 5A of the first flow field 5 shown in FIG. 1 via the manifold 3A. The first base groove 52 is located at the bottom of the first conductive plate 31 and extends parallel to the installation surface of the electrochemical cell 1. The second base groove 54 is located at the top of the first conductive plate 31 and extends parallel to the first base groove 52. The lower and upper ends of the branch groove 53 are connected to the first base groove 52 and the second base groove 54, respectively. The branch groove 53 extends upward from the first base groove 52.

The discharge groove 55 is connected to a manifold 3B that penetrates the first conductive plate 31. The manifold 3B is directly connected to the end of the first discharge pipe 101B shown in FIG. 1. That is, the discharge groove 55 is directly connected to the outlet 5B of the first flow field 5 by the manifold 3B. The flow path 50 having the above configuration is a straight flow path that is completely connected from the supply groove 51 to the discharge groove 55. The flow path 50 allows water contained in the first fluid 101 to be quickly diffused throughout the entire first flow field 5. The flow path 50 also allows oxygen generated in the first catalyst layer 30 to be quickly discharged to the outside of the electrochemical cell 1. Unlike this example, the flow path 50 may be formed in the first diffusion layer 32.

As shown by the thick arrows in Figure 5, in a straight flow path, a flow of the first fluid 101 from the branch groove 53 toward the first diffusion layer 32 and a flow of the first fluid 101 from the first diffusion layer 32 toward the branch groove 53 are likely to be formed.

Unlike this example, the flow path 50 of the first flow field 5 may be a groove having a structure similar to the first flow path 61 and the second flow path 62 of the second flow field 6.

<Formation of non-conductive areas>
In the second flow field 6 of the electrochemical cell 1 shown in FIG. 1 , a side reaction in which protons are converted into hydrogen gas may occur. This side reaction reduces the faradaic efficiency of the electrochemical cell 1. The frequency of the side reaction can be reduced by forming a non-current-carrying region in the electrochemical cell 1 where no current flows along the stacking direction of the anode section 3, the electrolyte membrane 2, and the cathode section 4. As shown in FIG. 2 , the non-current-carrying region is formed by an insulating member 8 disposed in at least one of the first flow field 5 and the second flow field 6. The reduced frequency of the side reaction improves the faradaic efficiency of the electrochemical cell 1.

For example, when the electrochemical cell 1 is viewed perpendicular to the first surface 21 and from a first direction from the first surface 21 toward the second surface 22, the insulating member 8 overlaps at least one of the first conductive plate 31 and the second conductive plate 41. The number of insulating members 8 may be one or more. In this example, one insulating member 8 overlaps the second conductive plate 41 in the second flow field 6.

In this example, the insulating member 8 is a rectangular frame-shaped sheet. This insulating member 8 overlaps at least a portion of the first ridge region 65 shown in FIG. 6. The first ridge region 65 is the region indicated by dashed-dotted lines. The first ridge region 65 is a strip-shaped region along the first connecting groove 61b of the first flow path 61. The first ridge region 65 extends from the edge of the first connecting groove 61b of the first flow path 61 to the end 62e of the second groove 62d of the second flow path 62. In this example, as shown in FIG. 7, the insulating member 8 is arranged so that the lower frame portion of the insulating member 8 covers the entire first ridge region 65. Also, in this example, the insulating member 8 extends into the first connecting groove 61b. Unlike this example, the insulating member 8 may extend to a portion of the second groove 62d near the end 62e. The insulating member 8 may have a cutout in the portion corresponding to the first groove 61d.

The insulating member 8 further overlaps at least a portion of the second ridge region 66 shown in FIG. 6. The second ridge region 66 is the region indicated by dashed-dotted lines. The second ridge region 66 is a strip-shaped region along the second connecting groove 62b of the second flow path 62. The second ridge region 66 extends from the groove edge of the second connecting groove 62b of the second flow path 62 to the end 61e of the first groove 61d of the first flow path 61. In this example, as shown in FIG. 7, the insulating member 8 is arranged so that the upper frame portion of the insulating member 8 covers the entire second ridge region 66. Also, in this example, the insulating member 8 extends into the second connecting groove 62b. Unlike this example, the insulating member 8 may extend to a portion of the first groove 61d near the end 61e. The insulating member 8 may have a cutout in the portion corresponding to the second groove 62d.

As shown in FIG. 7 , the portion of the second conductive plate 41 exposed through the window of the insulating member 8 is the current-carrying region 7 in which current flows in the first direction in the electrochemical cell 1. In the second flow field 6 of this example, the first ridge region 65 and the second ridge region 66 are regions in which the second fluid 102 has difficulty flowing compared to the region in which the first grooves 61d and the second grooves 62d are alternately arranged. When current flows in the first direction in this region in which the second fluid 102 has difficulty flowing, hydrogen is likely to be generated by a side reaction. In this example, the frame-shaped insulating member 8 covers the first ridge region 65 and the second ridge region 66, preventing current from flowing in the first direction in the first ridge region 65 and the second ridge region 66, thereby reducing the generation of hydrogen due to a side reaction. As a result, the high Faraday efficiency of the electrochemical cell 1 is maintained. Unlike this example, the first ridge region 65 and the second ridge region 66 may each be covered by an independent insulating member 8.

The insulating member 8 is formed of an electrically insulating material that is resistant to fluids. The resistivity of the insulating member 8 is, for example, ¹⁰ Ω·cm or more. The resistivity may be 10 ^Ω ·cm or more, or may be 10 ^Ω ·cm or more. Materials that satisfy this resistivity include, for example, epoxy resin, phenolic resin, polyamide resin such as PA6 or PA66, polyoxymethylene resin, fluororesin, polyphenylene sulfide resin, glass fiber, insulating rubber, and insulating varnish. The fluororesin is, for example, polytetrafluoroethylene resin or a copolymer of tetrafluoroethylene and perfluoroethylene.

The sheet-shaped insulating member 8 is disposed between the electrolyte membrane 2 and the second diffusion layer 42, or between the second diffusion layer 42 and the second conductive plate 41. The insulating member 8 disposed in this position insulates a portion of the second conductive plate 41. Unlike this example, when the sheet-shaped insulating member 8 is disposed in the first flow field 5, the insulating member 8 only needs to be disposed between the electrolyte membrane 2 and the first diffusion layer 32, or between the first diffusion layer 32 and the first conductive plate 31.

The insulating member 8 may be integrated with the second conductive plate 41. For example, the insulating member 8 is fixed to the second conductive plate 41 with an adhesive or the like. In this case, alignment between the insulating member 8 and the second conductive plate 41 is not required, improving the ease of assembly of the electrochemical cell 1. The insulating member 8 may be a resin material integrated with the second conductive plate 41. The resin material is applied to the second conductive plate 41, for example. In this case, alignment between the insulating member 8 and the second conductive plate 41 is also not required, improving the ease of assembly of the electrochemical cell 1.

The insulating member 8 may be a resin material integrated with the second diffusion layer 42. In this case, alignment between the insulating member 8 and the second diffusion layer 42 is not required, improving the ease of assembly of the electrochemical cell 1. The resin material may be integrated with the second diffusion layer 42 by applying or impregnating the second diffusion layer 42. In this case, the pores in the second diffusion layer 42 are blocked by the resin material. As a result, the second fluid 102 does not flow through the areas of the second diffusion layer 42 filled with the resin material, reducing pressure loss in the cathode section 4. This configuration may also be used in combination with a sheet-like insulating member 8.

<Configuration of the second diffusion layer>
The second diffusion layer 42 is a porous layer formed of a conductive material. As described above, the second diffusion layer 42 is compressed between the electrolyte membrane 2 and the second conductive plate 41. FIG. 8 is a schematic diagram showing the laminated state of a portion of the electrochemical cell 1. If local gaps exist at the boundary 1A between the second diffusion layer 42 and the electrolyte membrane 2 and at the boundary 1B between the second diffusion layer 42 and the second conductive plate 41, the second fluid 102 will not be uniformly distributed over the entire surface of the second catalyst layer 40. Furthermore, if the internal pressure of the second flow field 6 changes during operation of the electrochemical cell 1, these local gaps may be formed. If the compressed second diffusion layer 42 presses the electrolyte membrane 2 and the second conductive plate 41 with a surface pressure equal to or greater than a predetermined value, these local gaps are unlikely to be formed at the boundaries 1A and 1B. Furthermore, the thickness of the electrolyte membrane 2 may change by up to approximately 20% due to changes in temperature or moisture content. For example, if the thickness of the electrolyte membrane 2 is 200 μm, the thickness may change by up to approximately 40 μm. Because the temperature and the state of water flow within the electrochemical cell 1 differ between when the electrochemical cell 1 is operating and when it is stopped, the change in the thickness of the electrolyte membrane 2 may result in the formation of a gap of up to approximately 20% of the thickness of the electrolyte membrane 2. As described above, if the second diffusion layer 42 presses the electrolyte membrane 2 and the second conductive plate 41 with a surface pressure equal to or greater than a predetermined value, it can follow the change in the thickness of the electrolyte membrane 2. Therefore, even in this case, localized gaps are unlikely to form at the boundaries 1A and 1B.

The compressive strain of the second diffusion layer 42 when compressed within the cathode portion 4 of the electrochemical cell 1 is 0.3 or more and 0.8 or less. The surface pressure acting on the compressed second diffusion layer 42 within the electrochemical cell 1 is, for example, 0.5 MPa or more. The upper limit of the surface pressure is, for example, 0.8 MPa. As shown in Figure 12 of Test Example 4 described below, the greater the surface pressure, the greater the compressive strain. Therefore, if the compressive strain of the second diffusion layer 42 at a surface pressure of 0.5 MPa is 0.3 or more, the compressive strain of the second diffusion layer 42 within the cathode portion 4 subjected to a surface pressure of 0.5 MPa or more is also 0.3 or more. In this example, the compressive strain is, for example, the reduction in thickness λ of the second diffusion layer 42 compressed by a surface pressure of 0.5 MPa or more and 0.8 MPa or less, divided by the initial thickness t0 of the second diffusion layer 42 before compression. In other words, the reduction amount λ is expressed as t0 - t1, where t0 is the initial thickness of the second diffusion layer 42 and t1 is the thickness of the second diffusion layer 42 compressed with a surface pressure of 0.5 MPa or more and 0.8 MPa or less. Therefore, the compressive strain can be calculated by (t0 - t1)/t0. For example, when a second diffusion layer 42 having an initial thickness t0 of 1 mm is compressed with a surface pressure of 0.5 MPa, if the thickness t1 of the second diffusion layer 42 is 0.7 mm, the reduction amount λ is 0.3 mm. Since compressive strain = λ/t0, the compressive strain in this case is 0.3.

The thicknesses t0 and t1 of the second diffusion layer 42 are measured in accordance with Method A of JIS L 1096:2010. Specifically, the thickness of the second diffusion layer 42 is measured for a fixed time and under a fixed surface pressure using a commercially available thickness measuring device. The time is 10 seconds. The surface pressure used to measure the initial thickness t0 is 0.7 kPa. The initial thickness t0 is the average value of thicknesses measured at five or more points. The thickness t1 is measured in the same manner as the initial thickness t0 by changing the surface pressure to, for example, 0.5 MPa. The thicknesses t0 and t1 are measured for the second diffusion layer 42 when it is not assembled into the electrochemical cell 1. The initial thickness t0 of the second diffusion layer 42 is, for example, 0.3 mm or more and 3.5 mm or less.

A second diffusion layer 42 having a compressive strain of 0.3 to 0.8 inclusive has excellent elastic deformability. In other words, a second diffusion layer 42 having a compressive strain of 0.3 to 0.8 inclusive deforms so that its thickness becomes smaller than its initial thickness t0 when a predetermined surface pressure is applied. A second diffusion layer 42 having such elastic deformability re-deforms to approach or become equal to its initial thickness t0 when the surface pressure is reduced or removed. When compressed between the electrolyte membrane 2 and the second conductive plate 41, the second diffusion layer 42 attempts to return to its pre-compression thickness, pressing against the electrolyte membrane 2 and the second conductive plate 41 that sandwich the second diffusion layer 42 within the cathode section 4. Therefore, the second diffusion layer 42 is likely to come into surface contact with the electrolyte membrane 2 and the second conductive plate 41. This reduces the reduction in Faraday efficiency caused by local gaps at the boundaries 1A and 1B. The compressive strain may be 0.4 or more, 0.5 or more, 0.6 or more, or 0.7 or more.

The second diffusion layer 42, which is a porous layer, may satisfy the following elastic deformation characteristics, for example.
Elastic deformation characteristics: The thickness of the second diffusion layer 42 when subjected to a pressure of 0.5 MPa is tA, and the thickness of the second diffusion layer 42 when subjected to a surface pressure of 0.7 kPa after the load is removed is tB, and the thickness difference tB - tA is 40 μm or more.

The details of the method for measuring the thickness difference are as follows: A load of 0.5 MPa is applied to a 5 cm x 5 cm test piece. The holding time is 1 minute. After 1 minute has passed, the thickness tA is measured under this load. After the load is removed, 1 minute has passed and the thickness tB is measured under a surface pressure of 0.7 kPa. The method for measuring thickness tB is the same as the method for measuring the initial thickness t0 described above.

A second diffusion layer 42 with a thickness difference tB - tA of 40 μm or more has a high ability to return to the thickness it had before being subjected to a predetermined pressure, i.e., has excellent elastic deformation ability. The larger the thickness difference, the better the elastic deformation ability. The thickness difference depends on the initial thickness t0 and the surface pressure, but may be 50 μm or more, or 60 μm or more. The upper limit of the thickness difference is, for example, the initial thickness t0 x 0.9 μm. A second diffusion layer 42 with a compressive strain of 0.6 or more typically satisfies the above elastic deformation characteristics.

For example, when a second catalyst layer 40 is provided on the second surface 22 of the electrolyte membrane 2, the surface of the second catalyst layer 40 may be uneven. If the elastic deformation of the second diffusion layer 42 is small, the unevenness may cause small gaps of, for example, 100 μm or less to form locally between the second catalyst layer 40 and the second diffusion layer 42. These gaps can become through-holes for the fluid. If the second diffusion layer 42 has excellent elastic deformability, such as a compressive strain of 0.3 or more, preferably 0.5 or more, and particularly 0.6 or more, the second diffusion layer 42 can elastically deform to fill these gaps. The second diffusion layer 42 elastically deforms to conform to the small unevenness on the surface of the second catalyst layer 40, making it less likely that gaps that could become through-holes will form.

The second diffusion layer 42 that satisfies the above compressive strain is, for example, a nonwoven fabric containing carbon fiber. As described above, a nonwoven fabric containing carbon fiber is made by entangling multiple independent carbon fibers and does not have any bonding parts such as binders that hold the carbon fibers together. Nonwoven fabrics that do not have the above bonding parts have high elastic deformability. As long as the second diffusion layer 42 satisfies the above compressive strain, it may be a woven fabric containing carbon fiber. The woven fabric is made by alternately weaving warp and weft threads of carbon fiber. Woven fabric containing carbon fiber is also called carbon cloth. Paper containing carbon fiber is not considered to satisfy the above compressive strain. The paper contains multiple carbon fibers and a binder that holds the carbon fibers in place. For example, depending on the thickness of the paper before compression, even when a large surface pressure of 1 MPa is applied, the deformation of the paper thickness is less than 20 μm, or even approximately 10 μm. For example, such paper has a compressive strain of less than 0.2 when subjected to a surface pressure of 0.5 MPa, and is hardly deformed.

The second diffusion layer 42 may contain a component with a compressive strain of less than 0.3, as long as the overall compressive strain is 0.3 or greater. For example, the second diffusion layer 42 may be configured by laminating multiple nonwoven fabrics with different compressive strains, by laminating a nonwoven fabric and a woven fabric, by laminating a nonwoven fabric and paper, or by laminating a nonwoven fabric, a woven fabric, and paper.

The average diameter of the carbon fibers forming the nonwoven fabric is, for example, 5 μm or more and 100 μm or less. Carbon fibers with an average diameter of 5 μm or more and 100 μm or less are neither too thin nor too thick. A second diffusion layer 42 formed from carbon fibers that are neither too thin nor too thick has excellent elastic deformability. Therefore, the second diffusion layer 42 compressed between the electrolyte membrane 2 and the second conductive plate 41 easily adheres to the electrolyte membrane 2 and the second conductive plate 41. When the average diameter is 5 μm or more and 100 μm or less and the basis weight of the second diffusion layer 42 satisfies the range described below, the second diffusion layer 42 has higher elastic deformability. The average diameter of the carbon fibers may be, for example, 5 μm or more and 80 μm or less, 5 μm or more and 50 μm or less, or 7 μm or more and 30 μm or less.

The average diameter of carbon fibers is calculated by averaging the diameter of a circle having an area equal to the cross-sectional area of each of the carbon fibers. The average diameter of carbon fibers is calculated as follows: The second diffusion layer 42 is cut in a direction along the thickness of the second diffusion layer 42. This cutting exposes the cross-sections of the carbon fibers. The cross-sections of the second diffusion layer 42 are observed using a microscope, and five or more observation fields are taken. The microscope is, for example, a scanning electron microscope. The magnification for observing the cross-sections is, for example, 500x or more and 3000x or less. For three or more carbon fibers per observation field, the diameter of a circle having an area equal to the cross-sectional area of each carbon fiber is calculated. The diameters of the circles calculated for all five or more observation fields are averaged. The calculated average value is the average diameter of the carbon fibers.

The porosity of the second diffusion layer 42 when compressed within the electrochemical cell 1 is, for example, 40% or more and 98% or less. If the porosity of the second diffusion layer 42 is within this range, the density of the second diffusion layer 42 is neither too low nor too high, and the second diffusion layer 42 has excellent elastic deformability. The pores in the second diffusion layer 42 serve as flow paths for the second fluid 102. Therefore, a porosity of 40% or more facilitates permeation of the second fluid 102 through the second diffusion layer 42. Furthermore, the flow rate of the second fluid 102 passing through the second diffusion layer 42 is likely to be high. A porosity of 98% or less facilitates the maintenance of the strength of the second diffusion layer 42. The porosity may be, for example, 45% or more and 97% or less, or 50% or more and 96% or less. The porosity can be determined from a cross-sectional photograph of the cross section of the second diffusion layer 42. The cross-sectional photograph is binarized to determine the areas of the solid portion and the pore portion. The porosity is the ratio of the area of the pores to the total area of the solid and pores. If the amount of reduction in thickness of the second diffusion layer 42 in the electrochemical cell 1 is known, the porosity of the second diffusion layer 42 in the compressed state can be calculated.

The basis weight of the second diffusion layer 42 is, for example, 50 g/m ² (grams per square meter) or more and 400 g/m ² or less. When the basis weight of the second diffusion layer 42 is 50 g/m ² or more, the density of the second diffusion layer 42 does not become too low. Such a second diffusion layer 42 has excellent elastic deformability. Therefore, the second diffusion layer 42 compressed between the electrolyte membrane 2 and the second conductive plate 41 easily adheres to the electrolyte membrane 2 and the second conductive plate 41. Furthermore, when the basis weight is 50 g/m ² or more, the conductivity of the second diffusion layer 42 easily becomes high. When the basis weight of the second diffusion layer 42 is 400 g/m ² or less, the density of the second diffusion layer 42 does not become too high. Such a second diffusion layer 42 has excellent elastic deformability. Therefore, the second diffusion layer 42 compressed between the electrolyte membrane 2 and the second conductive plate 41 easily adheres to the electrolyte membrane 2 and the second conductive plate 41. Furthermore, if the basis weight is 400 g/ ^m2 or less, pores sufficient for flow are likely to be formed in the second diffusion layer 42. The basis weight may be, for example, 55 g/ ^m2 or more and 395 g/ ^m2 or less, or 60 g/ ^m2 or more and 390 g/ ^m2 or less. The basis weight may be, for example, 55 g/ ^m2 or more and 200 g/ ^m2 or less, or 60 g/ ^m2 or more and 150 g/ ^m2 or less. The basis weight is the mass of the second diffusion layer 42 per square meter. The basis weight can be calculated by dividing the mass of the second diffusion layer 42 by the area of the second diffusion layer 42 in a plan view.

When the second diffusion layer 42 is a nonwoven fabric containing carbon fibers, has a basis weight of 50 g/ ^m2 or more and 200 g/ ^m2 or less, and has an average diameter of the carbon fibers of 5 μm or more and 50 μm or less, the second diffusion layer 42 is likely to have high elastic deformability and adheres closely to the electrolyte membrane 2 and the second conductive plate 41. The adherence of the second diffusion layer 42 to the electrolyte membrane 2 and the second conductive plate 41 can improve the Faraday efficiency of the electrochemical cell 1. This effect will be specifically explained in the test examples described later.

<Configuration of the first diffusion layer>
The compressive strain of the first diffusion layer 32, which is made of a metal material, is smaller than the compressive strain of the second diffusion layer 42. That is, the first diffusion layer 32 is relatively less likely to deform than the second diffusion layer 42. If the second diffusion layer 42 has elastic deformability, the second diffusion layer 42 may strongly press against the electrolyte membrane 2 when the internal pressure of the cathode section 4 becomes higher than the internal pressure of the anode section 3. If the electrolyte membrane 2 is deformed by the second diffusion layer 42, the electrolyte membrane 2 may be damaged. Furthermore, gaps may be formed at the boundary 1A between the electrolyte membrane 2 and the second diffusion layer 42 and at the boundary 1B between the second diffusion layer 42 and the second conductive plate 41. In this example, the first diffusion layer 32, which is relatively less likely to deform than the second diffusion layer 42, prevents deformation of the electrolyte membrane 2. The less deformable first diffusion layer 32 supports the first surface 21 of the electrolyte membrane 2 and prevents excessive deformation of the electrolyte membrane 2.

<Test Example 1>
In Test Example 1, the influence of the first flow path 61 and the second flow path 62 formed in the second flow field 6 of the electrochemical cell 1 on the Faraday efficiency of the electrochemical cell 1 was investigated.

<Electrochemical cell configuration>
The electrolyte membrane 2, anode part 3, and cathode part 4 forming the electrochemical cell 1 were configured as follows.

・Electrolyte membrane 2
The electrolyte membrane 2 was a proton-conductive thin film and had a thickness of 180 μm (micrometers).

Anode part 3
The first catalyst layer 30 is formed on the first surface 21 of the electrolyte membrane 2. The catalyst contained in the first catalyst layer 30 is iridium oxide. The amount of iridium oxide in the first catalyst layer 30 is 1.0 mg (milligram)/ ^cm2 .
The first conductive plate 31 is formed from a composite material of a carbon-based material and a resin. A flow path 50 formed by a groove is formed on the surface of the first conductive plate 31 facing the first surface 21. The flow path 50 is a straight flow path that directly connects to the inlet 5A and outlet 5B of the first flow field 5. The branch grooves 53 that form the flow path 50 had an average width of 1 mm (millimeter) and an average depth of 1.5 mm. The average width of the ridges formed between adjacent branch grooves 53 was 1 mm.
The first diffusion layer 32 was made of a porous titanium body. The surface of the porous titanium body was coated with platinum. The thickness of the first diffusion layer 32 was 0.3 mm.

Cathode part 4
The second catalyst layer 40 is formed on the second surface 22 of the electrolyte membrane 2. The catalyst contained in the second catalyst layer 40 is carbon supported with platinum and ruthenium. The amount of catalyst in the second catalyst layer 40 is 1.0 mg/ ^cm2 .
The second conductive plate 41 is formed from a composite material of a carbon-based material and a resin. The surface of the second conductive plate 41 facing the second surface 22 is formed with a first flow path 61 and a second flow path 62, which are formed by grooves. The first grooves 61d and the second grooves 62d of the first flow path 61 and the second flow path 62 have an average width W2 of 1.0 mm and an average depth d of 1.0 mm. The ridge portions 63 formed between the first grooves 61d and the second grooves 62d have an average width W1 of 25 mm. The ratio W1/W2 was 25.
The second diffusion layer 42 was made of a carbon nonwoven fabric. The carbon nonwoven fabric was formed by randomly entangling multiple carbon fibers through the entanglement process described above. The initial thickness t0 of the second diffusion layer 42 was 1 mm, and the thickness of the second diffusion layer 42 after assembly into the electrochemical cell 1 was 0.3 mm.

<Test conditions>
Anode part 3
The first fluid 101 was pure water. A heater was disposed in the first supply pipe 101A, and the first fluid 101 was heated before being supplied to the first flow field 5. The temperature of the first fluid 101 at the inlet 5A of the first flow field 5 was 50°C or higher. The temperature increase by the heater was adjusted so that the temperature of the first fluid 101 at the outlet 5B of the first flow field 5 was 70°C or lower. The current density during the test was 1.0 A/ ^cm2 (amperes per square centimeter) or 1.5 A/ ^cm2 . The flow rate of the first fluid 101 under the 1.5 A/ ^cm2 condition was higher than the flow rate of the first fluid 101 under the 1.0 A/ ^cm2 condition. The current density is the current flowing between the first conductive plate 31 and the second conductive plate 41 divided by the current-carrying area to which the voltage is applied. The flow rate is the amount of the first fluid 101 flowing in each branch groove 53 per minute. Since the amount of the first fluid 101 supplied to the anode section 3 is known, the flow rate in the branch groove 53 can be found by calculation.

Cathode part 4
The second fluid 102 contains toluene as a substance to be hydrogenated. The toluene is converted into MCH by hydrogenation. A heater is disposed in the second supply pipe 102A, and the second fluid 102 is heated before being supplied to the second flow field 6. The temperature of the second fluid 102 at the inlet 6A of the second flow field 6 was 50°C or higher. The temperature increase by the heater was adjusted so that the temperature of the second fluid 102 at the outlet 6B of the second flow field 6 was 70°C or lower. The flow rate of the second fluid 102 under the condition of 1.5 A/ ^cm2 was greater than the flow rate of the second fluid 102 under the condition of 1.0 A/ ^cm2 .

Evaluation Method
Electricity was applied to the electrochemical cell 1, and the second fluid 102 was sampled from the second tank 102T at predetermined time intervals. The sampled second fluid 102 was analyzed by gas chromatography, and the toluene concentration contained in the second fluid 102 was calculated. The toluene concentration is expressed as a percentage of the number of toluene molecules when the total number of toluene and MCH molecules contained in the second fluid 102 is taken as 100% (percent).

The faradaic efficiency in the cathode section 4 was determined. In the cathode section 4, hydrogen is produced by a side reaction in which protons not consumed in the hydrogenation of toluene combine. The only side reaction in the cathode section 4 is the hydrogen production reaction. Therefore, by measuring the volume of hydrogen produced by the side reaction, it is possible to calculate the amount of charge not used to produce MCH out of the total amount of charge input to the electrochemical cell 1. The amount of charge used to produce MCH is determined by subtracting the amount of charge used to produce hydrogen from the total amount of charge. The faradaic efficiency is the amount of charge used to produce MCH when the total amount of charge is 100%. The unit of faradaic efficiency is %.

The relationship between the toluene concentration and the Faraday efficiency at each predetermined time interval is shown in the graph of FIG. 9 . The horizontal axis of the graph represents the toluene concentration (mol %), and the vertical axis represents the Faraday efficiency (%). The black circles represent the measurement results at a current density of 1.0 A/cm ^2. The diamonds represent the measurement results at a current density of 1.5 A/cm ^2. The toluene concentration in the second fluid 102 decreases with the passage of time from the start of current application. Therefore, the plots on the left side of the graph represent the measurement results of the second fluid 102 sampled after a longer time has passed since the start of current application.

<Evaluation Results>
In this test, the flow rate of the second fluid 102 in the cathode section 4 was significantly greater than the flow rate of the first fluid 101 in the anode section 3. However, no malfunctions due to internal pressure occurred in the electrochemical cell 1 in this test. It is presumed that the reason no malfunctions occurred in the electrochemical cell 1 is because the first flow path 61 and the second flow path 62 arranged in the second flow field 6 of the cathode section 4 reduced the pressure loss in the second flow field 6.

9 , it was revealed that, at a current density of 1.0 A/ ^cm2 , even when the toluene concentration in the second fluid 102 was 10%, the Faraday efficiency was approximately 99% or higher, and maintained at 95% or higher, and even at 98% or higher. It was also revealed that, at a current density of 1.5 A/ ^cm2 , even when the toluene concentration in the second fluid 102 was 10%, the Faraday efficiency was maintained at 90% or higher. An electrochemical cell 1 with a high flow rate of the second fluid 102 and high Faraday efficiency can produce a large amount of MCH in a short period of time.

<Test Example 1-2>
A second electrochemical cell 1 and a third electrochemical cell 1 were prepared, each having a different value of the ratio W1/W2 from that of the electrochemical cell of Test Example 1, and the Faraday efficiencies of the second electrochemical cell 1 and the third electrochemical cell 1 were examined. The ratio W1/W2 of the second electrochemical cell 1 was 5, and the ratio W1/W2 of the third electrochemical cell 1 was 45. The test conditions for Test Example 1-2 were the same as those for Test Example 1, where the current density was 1.0 A/ ^cm2 .

The measurement results for electrochemical cell 1 of Test Example 1 and the measurement results for second electrochemical cell 1 are shown in the graph in Figure 10. The way to read Figure 10 is the same as Figure 9. The black circle plots are the measurement results for electrochemical cell 1 of Test Example 1. The triangle plots are the measurement results for second electrochemical cell 1. The square plots are the measurement results for third electrochemical cell 1.

As shown in Figure 10, the faradaic efficiency of the second electrochemical cell 1 with a W1/W2 ratio of 5 was nearly 90%, even when the toluene concentration was 10%, demonstrating high faradaic efficiency. Furthermore, under the same toluene concentration conditions, the faradaic efficiency of the third electrochemical cell 1 with a W1/W2 ratio of 45 was nearly the same as that of the first electrochemical cell 1 with a W1/W2 ratio of 25, reaching nearly 99% or higher and maintaining a value of 98% or higher. It was found that at a relatively high current density of 1 A/ ^cm² , the greater the value of the W1/W2 ratio, the less likely the faradaic efficiency to decrease with decreasing toluene concentration. Note that under these test conditions, the pressure loss was extremely large for electrochemical cells 1 with a W1/W2 ratio of more than 50, making it impossible to evaluate the faradaic efficiency of those electrochemical cells 1.

<Test Example 2>
In Test Example 2, the influence of the average width W1 of the ridges 63 in the second flow field 6 on the pressure loss and Faraday efficiency in the second flow field 6 was investigated.

In Test Example 2, multiple electrochemical cells 1 were prepared with different average widths W1 of the ridge portions 63. The average width W1 was one of three values selected from the range of greater than 1 mm and less than or equal to 30 mm. Other than the average width W1, the configuration was the same as Test Example 1. A first fluid 101 and a second fluid 102 were passed through each electrochemical cell 1, and the pressure loss of the second flow field 6 in each electrochemical cell 1 and the Faraday efficiency of each electrochemical cell 1 were measured. The supply rate of the first fluid 101 was the flow rate of the first fluid 101 at the inlet 5A of the first flow field 5. The supply rate of the second fluid 102 was 0.5, 1, 2, or 5 times the supply rate of the first fluid 101. The supply rate of the second fluid 102 was the flow rate of the second fluid 102 at the inlet 6A of the second flow field 6. Table 1 shows the measurement results for the pressure loss of the second flow field 6, and Table 2 shows the measurement results for the Faraday efficiency of the electrochemical cell 1.

In Tables 1 and 2, "100% TOL * 0.4 A/cm ² * 0.5 h" indicates that the toluene concentration in the second fluid 102 before applying current to the electrochemical cell 1 was 100%, and that current was applied at a current density of 0.4 A/cm ² for 30 minutes. "10% TOL * 0.2 A/cm ² * 0.5 h" and "5% TOL * 0.2 A/cm ² * 0.5 h" also indicate the toluene concentration before applying current, the current density during application, and the application time. The value shown in the "Supply rate of second fluid" column is a multiplier relative to the supply rate of the first fluid 101. For example, "1x" means that the supply rate of the second fluid 102 is the same as the supply rate of the first fluid 101. The value shown in the "Average width W1 of ridge portion" column is a ratio with the smallest value being "1". The cells in Table 1 show the pressure loss value in the second flow field 6. The pressure loss of the second flow field 6 is the difference between the pressure of the second fluid 102 at the outlet 6B of the second flow field 6 and the pressure of the second fluid 102 at the inlet 6A of the second flow field 6. The unit of the pressure loss is kPa (kilopascal). The faradaic efficiency of the electrochemical cell 1 is shown in the cells of Table 2. The unit of the faradaic efficiency is %. Cells corresponding to conditions where no measurement was performed are marked with diagonal lines.

As shown in Table 1, the larger the average width W1 of the ridge portion 63, the greater the pressure loss in the second flow field 6. This is because, as the average width W1 of the ridge portion 63 increases, the number of first grooves 61d and second grooves 62d decreases, making it more difficult for the second fluid 102 to flow in the second flow field 6. Furthermore, the greater the supply amount of the second fluid 102, the greater the pressure loss in the second flow field 6.

As shown in Table 2, the larger the average width W1 of the ridge portion 63, the higher the Faraday efficiency of the electrochemical cell 1. Furthermore, the larger the flow rate of the second fluid 102 to the electrochemical cell 1, the higher the Faraday efficiency of the electrochemical cell 1. The results in Tables 1 and 2 reveal that MCH can be produced efficiently by increasing the average width W1 of the ridge portion 63 and the supply amount of the second fluid 102 within a range that reduces the increase in pressure loss.

Comparative Example
As a comparative example, we considered the pressure loss of an electrochemical cell in which neither the first nor second flow field had grooves. This electrochemical cell is called a comparative cell. In the comparative cell, the first flow field is formed solely by the pores in the first diffusion layer in the anode section, and the second flow field is formed solely by the pores in the second diffusion layer in the cathode section.

From the results in Table 1, when the toluene concentration is 100% and the supply amount of the second fluid is '1x', the pump pressure when the average ridge width W1 is '5' is more than three times the pump pressure when the average ridge width W1 is '1'. When the supply amount of the second fluid is '5x', the pump pressure when the average ridge width W1 is '5' is more than six times the pump pressure when the average ridge width W1 is '1'. In other words, the larger the ridges, the higher the pump pressure.

From these results, it is expected that in electrochemical cells with straight flow paths in the first flow field and no grooves in the second flow field, the pressure loss in the second flow field will be large. In comparative cells with no grooves in either the first or second flow field, the pressure loss will be extremely large.

<Test Example 3>
In Test Example 3, the influence of the placement of the insulating member 8 inside the electrochemical cell 1 on the faradic efficiency of the electrochemical cell 1 was investigated.

In Test Example 3, two electrochemical cells 1 without an insulating member 8 were prepared, and the Faraday efficiency of each electrochemical cell 1 was examined. The only difference between the two electrochemical cells 1 was the material of the second diffusion layer 42. The second diffusion layer 42 was a carbon nonwoven fabric or carbon paper. The average width W1 of the ridge portion 63 in the second conductive plate 41 was a value selected from the range of more than 1 and not more than 5. The area of the current-carrying region 7 of these electrochemical cells 1 was 25 ^cm2 . The toluene concentration of the second fluid 102 before current application was 100%, and the current density of the current-carrying region 7 was 0.4 A/ ^cm2 .

In Test Example 3, two electrochemical cells 1 each having an insulating member 8 disposed therein were prepared, and the Faraday efficiency of each electrochemical cell 1 was examined. The only difference between the two electrochemical cells 1 was the material of the second diffusion layer 42. The second diffusion layer 42 was a carbon nonwoven fabric or carbon paper. The average width W1 of the ridge portion 63 in the second conductive plate 41 was a value selected from the range of greater than 1 and less than or equal to 5. The insulating member 8 disposed in each electrochemical cell 1 was a rectangular frame-shaped sheet formed of polytetrafluoroethylene resin. The resistivity of the insulating member 8 was 10 ¹⁸ Ω·cm or greater. The sheet was disposed between the electrolyte membrane 2 and the second diffusion layer 42. The sheet covered the first ridge region 65 and the second ridge region 66, shown hatched in FIG. 6 . The area of the current-carrying region 7 of each electrochemical cell 1 was 17 cm ^2. The toluene concentration before energization was 100%, and the current density in the current-carrying region 7 was 0.4 A/cm ² .

As shown in Table 3, it was found that insulating the first ridge region 65 and the second ridge region 66 with the insulating member 8 increases the Faraday efficiency of the electrochemical cell 1. It was also found that forming the second diffusion layer 42 from a carbon nonwoven fabric increases the Faraday efficiency of the electrochemical cell 1. In particular, the electrochemical cell 1 equipped with the insulating member 8 and having the second diffusion layer 42 formed from a carbon nonwoven fabric had a Faraday efficiency of 99% or more.

<Test Example 4>
The compressive strain of the second diffusion layer 42 in the electrochemical cells 1 of Test Examples 1 to 3 was measured. The second diffusion layer 42 was formed of a carbon nonwoven fabric. The diameter of the carbon fibers forming the carbon nonwoven fabric was 10 μm. Before compression, the carbon nonwoven fabric had a thickness of 1000 μm, a basis weight of 90 g/cm ² , and a porosity of 95.6%. When this carbon nonwoven fabric was compressed to a thickness of 300 μm, the basis weight of the carbon nonwoven fabric was 90 g/cm ² and the porosity was 86.7%. The compressive strain was calculated by dividing the reduction in thickness λ (= t0 - t1) of the compressed second diffusion layer 42 by the initial thickness t0 of the second diffusion layer 42 before compression.

The initial thickness t0 of the carbon nonwoven fabric is measured using a commercially available thickness measurement device conforming to Method A of JIS L 1096:2010, such as the constant pressure thickness measurement device PG-16J (measuring probe diameter: Φ25.2 mm) manufactured by Teclock Corporation. The initial thickness t0 was measured by applying a surface pressure of 0.7 kPa to the carbon nonwoven fabric for 10 seconds.

Figure 11 is a schematic diagram of a compression device 9 for measuring the compressive strain of the second diffusion layer 42. The compression device 9 comprises a lower pedestal 90 and an upper pedestal 91. The upper pedestal 91 is configured to be movable downward. The compression device 9 applies a surface pressure to a member sandwiched between the lower pedestal 90 and the upper pedestal 91. The compression device 9 can automatically measure the surface pressure acting between the lower pedestal 90 and the upper pedestal 91, and the distance between the lower pedestal 90 and the upper pedestal 91. The compression device 9 is a commercially available strength evaluation device, for example, a micro strength evaluation tester MST-I type HR manufactured by Shimadzu Corporation.

When measuring the compressive strain of the carbon nonwoven fabric, a lower protective plate 92, second conductive plate 41, second diffusion layer 42, first conductive plate 31, and upper protective plate 93 were stacked in this order on top of the lower base 90. The lower protective plate 92 and upper protective plate 93 protect the second conductive plate 41 and first conductive plate 31 from damage and apply uniform surface pressure to the second diffusion layer 42. The lower protective plate 92 and upper protective plate 93 are made of stainless steel. Of the multiple components sandwiched between the lower base 90 and upper base 91, only the second diffusion layer 42 changes thickness. The lower protective plate 92, second conductive plate 41, first conductive plate 31, and upper protective plate 93 are rigid bodies, and their thicknesses do not substantially change.

The compression device 9 is operated to apply surface pressure to the second diffusion layer 42. The surface pressure applied to the second diffusion layer 42 is gradually increased while measuring the distance the upper base 91 moves in response to the magnitude of the surface pressure. The movement distance can be said to be equal to the reduction in thickness λ of the second diffusion layer 42. The compressive strain of the second diffusion layer 42 was calculated from the initial thickness t0 and the movement distance. Specifically, λ/t0 = compressive strain. Compressive strain is unitless. The relationship between compressive strain and surface pressure is shown in the graph in Figure 12. The horizontal axis of the graph represents compressive strain, and the vertical axis represents surface pressure.

In Test Example 4, the compressive strain was also measured for carbon cloth and carbon paper. Specifically, instead of carbon nonwoven fabric, the compressive strain of carbon cloth and carbon paper was measured in the same manner as for carbon nonwoven fabric. The results are also shown in the graph in Figure 12.

As shown in Figure 12, the compressive strain of the carbon nonwoven fabric when compressed at a surface pressure of 0.5 MPa was 0.3 to 0.8, more specifically, 0.6 to 0.8. Thus, the thickness of the carbon nonwoven fabric changes significantly with compression. Carbon nonwoven fabric has excellent elastic deformability. When a second diffusion layer 42 made of such a carbon nonwoven fabric is compressed between the electrolyte membrane 2 and the second conductive plate 41 as shown in Figure 8, the second diffusion layer 42 presses the electrolyte membrane 2 and the second conductive plate 41 with a surface pressure equal to the compressive force. As a result, the second diffusion layer 42 adheres closely to the electrolyte membrane 2 and the second conductive plate 41, resulting in almost no localized gaps at the boundaries 1A and 1B. The almost complete absence of localized gaps at the boundaries 1A and 1B facilitates the second fluid 102 to permeate the entire second flow field 6. As a result, the Faraday efficiency of the electrochemical cell 1 is expected to improve.

When pressed with a surface pressure of 0.5 MPa, the compressive strain of the carbon cloth was 0.3 or more, more specifically, 0.4 or more. In other words, the thickness of the carbon cloth changes to some extent depending on the pressure. When a second diffusion layer 42 made of such carbon cloth is placed between the electrolyte membrane 2 and the second conductive plate 41 as shown in Figure 8, gaps are unlikely to form at the boundaries 1A and 1B.

As mentioned above, with carbon cloth and carbon nonwoven fabric, the compressive strain is 0.3 or greater even when the surface pressure is relatively small, at around 0.1 MPa, and even when the surface pressure is greater, the compressive strain remains 0.3 or greater. Because the surface pressure within electrochemical cell 1 is greater than 0.1 MPa, it can be said that the compressive strain of the carbon cloth and carbon nonwoven fabric in electrochemical cell 1 is 0.3 or greater.

When pressed with a surface pressure of 0.5 MPa, the compressive strain of the carbon paper was less than 0.2, more specifically, 0.18 or less. In other words, the thickness of the carbon paper changed little due to the pressure. When a second diffusion layer 42 made of such carbon paper is placed between the electrolyte membrane 2 and the second conductive plate 41 as shown in Figure 8, gaps are likely to form at the boundaries 1A and 1B.

When the electrochemical cell 1 is enlarged or the number of electrochemical cells 1 stacked is increased, variations can occur in the dimensions of the components that make up the electrochemical cell and in the clamping pressure used to clamp multiple electrochemical cells 1 together. Furthermore, dimensional variations can also occur due to deformation of the components over time. In electrochemical cells 1 that include a second diffusion layer 42 made of carbon paper, which is resistant to elastic deformation, these variations are likely to cause gaps at boundaries 1A and 1B in Figure 8, which are thought to be prone to reducing the Faraday efficiency due to these gaps.

On the other hand, even if the above-mentioned variations exist, the second diffusion layer 42 made of carbon nonwoven fabric maintains a state of close contact with the electrolyte membrane 2 and the second conductive plate 41 due to elastic deformation. As a result, localized gaps are less likely to occur at the boundaries 1A and 1B in Figure 8. Therefore, it is believed that an electrochemical cell 1 equipped with a second diffusion layer 42 made of carbon nonwoven fabric can maintain high Faraday efficiency over a long period of time.

Electrochemical cell 1 with a second diffusion layer 42 made of carbon nonwoven fabric is designated electrochemical cell A, and electrochemical cell 1 with a second diffusion layer 42 made of carbon paper is designated electrochemical cell B. If, for electrochemical cell B, the same pump X as electrochemical cell A is used to obtain the same toluene flow rate as electrochemical cell A, the output of pump X will fall below the lower limit, making it impossible to maintain an appropriate flow rate. Increasing the output of pump X increases the pressure loss within electrochemical cell B before electrolysis. Hydrogen is more likely to be generated during electrolysis, further increasing the pressure loss, potentially leading to leakage from electrochemical cell B. For these reasons, electrochemical cell A, which uses carbon nonwoven fabric, offers a wider range of operational conditions for achieving a high Faraday efficiency than electrochemical cell B, which uses carbon paper.

<Test Example 4-2>
A plurality of carbon nonwoven fabrics X, Y, and Z having different porosities and basis weights from those of Test Example 4 were prepared, and the compressive strain of each of the carbon nonwoven fabrics X, Y, and Z was measured under the same conditions as those of Test Example 4.

The porosity, basis weight and fiber diameter of the carbon nonwoven fabric X were 89.5%, 71 g/m ² and 10 μm, respectively.
The porosity, basis weight and fiber diameter of the carbon nonwoven fabric Y were 84.0%, 108 g/m ² and 10 μm, respectively.
The porosity, basis weight and fiber diameter of the carbon nonwoven fabric Z were 81.2%, 127 g/m ² and 10 μm, respectively.
The porosity is the value when a carbon nonwoven fabric having a thickness of 1.0 mm is compressed to 0.3 mm.

The compressive strain of carbon nonwoven fabrics X, Y, and Z was in the range of 0.6 to 0.8. This test showed that a nonwoven fabric with a compressive strain of 0.6 to 0.8 can be constructed if the porosity in the compressed state is 80% to 90%, the basis weight is 70 g/ ^m2 to 130 g/ ^m2 , and the fiber diameter is 5 μm to 20 μm. These carbon nonwoven fabrics X, Y, and Z have excellent elastic deformability, and therefore, when used in the second diffusion layer 42 of the electrochemical cell 1, they can contribute to achieving high Faraday efficiency as shown in Test Examples 1 to 3.

1 Electrochemical cell 1A, 1B Boundary 2 Electrolyte membrane 21 First surface, 22 Second surface 3 Anode portion 3A, 3B Manifold 30 First catalyst layer, 31 First conductive plate, 32 First diffusion layer, 33 Frame seal portion 4 Cathode portion 4A, 4B Manifold 40 Second catalyst layer, 41 Second conductive plate, 42 Second diffusion layer, 43 Frame seal portion 5 First flow field 5A Inlet, 5B Outlet 50 Flow path, 51 Supply groove, 52 First base groove, 53 Branch groove 54 Second base groove, 55 Discharge groove 6 Second flow field 6A Inlet, 6B Outlet 61 First flow path, 61A Inlet end, 61B Outlet end 61b First connecting groove, 61d First groove, 61e End, 61f Supply groove 62 Second flow path, 62A Inlet end, 62B Outlet end 62b Second connecting groove, 62d Second groove, 62e End, 62f Discharge groove 63 Ridge portion 65 First ridge region 66 Second ridge region 7 Current-carrying region 8 Insulating member 9 Compression device 90 Lower base 91 Upper base 92 Lower protective plate 93 Upper protective plate 100 Organic hydride manufacturing apparatus 101 First fluid 101A First supply pipe 101B First discharge pipe 101P First pump 101T First tank 102 Second fluid 102A Second supply pipe 102B Second discharge pipe 102P Second pump 102T Second tank E1, E2 End positions S1, S2 Start position M1, M2 Middle position W1 Average width W2 Average width d Average depth

Claims (8)

An electrochemical cell comprising: an anode section through which a first fluid containing water flows; a cathode section through which a second fluid containing a substance to be hydrided flows; and an electrolyte membrane disposed between the anode section and the cathode section,
The anode section is
a first flow field that forms a space through which the first fluid flows so as to contact a first surface of the electrolyte membrane;
a first catalyst layer disposed in the first flow field;
The cathode section is
a second flow field that forms a space through which the second fluid flows so as to contact a second surface of the electrolyte membrane;
a second catalyst layer disposed in the second flow field;
moreover,
an insulating member disposed in at least one of the first flow field and the second flow field ;
the at least one flow field comprises a conductive plate facing the electrolyte membrane and a porous diffusion layer disposed between the conductive plate and the electrolyte membrane;
the conductive plate in the second flow field has a flow path formed by a groove;
the flow path includes a first flow path and a second flow path formed on a surface of the conductive plate facing the diffusion layer,
the first flow path includes a first connecting groove and a plurality of first grooves extending so as to branch off from the first connecting groove;
the second flow path includes a second connecting groove and a plurality of second grooves extending so as to branch off from the second connecting groove;
the plurality of first grooves are arranged in parallel with one another, the plurality of second grooves are arranged in parallel with one another, and at least some of the plurality of first grooves and at least some of the plurality of second grooves are arranged alternately in a plan view,
the conductive plate includes a first strip-shaped ridge region along the first connecting groove and a second strip-shaped ridge region along the second connecting groove;
the first ridge region includes an area from the first connecting groove to an end of the second groove,
the second ridge region includes from the second connecting groove to an end of the first groove,
When viewed from a first direction perpendicular to the first surface and from the first surface toward the second surface, the insulating member overlaps at least a portion of the first ridge region and at least a portion of the second ridge region.
Electrochemical cell. The electrochemical cell of claim 1 , wherein the insulating member overlaps the entire first ridge region and the entire second ridge region when viewed from the first direction. 3. The electrochemical cell according to claim 1 , wherein the insulating member is a sheet disposed between the electrolyte membrane and the diffusion layer, or between the diffusion layer and the conductive plate. 4. The electrochemical cell of claim 3 , wherein the sheet is integral with the conductive plate. 3. The electrochemical cell according to claim 1 , wherein the insulating member is a resin material integrated with the diffusion layer. 3. The electrochemical cell according to claim 1 , wherein the insulating member is a resin material integrated with the conductive plate. An electrochemical cell as described in claim 1 or claim 2, wherein the substance to be hydrided is toluene. An electrochemical cell as described in claim 1 or claim 2, wherein the first fluid is primarily water.