Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
  • C25B13/08—Diaphragms; Spacing elements characterised by the material based on organic materials
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/01—Products
  • C25B3/03—Acyclic or carbocyclic hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/25—Reduction
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
  • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/60—Constructional parts of cells
  • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections

Definitions

• 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.
• protons move from the first fluid to the second fluid, and hydrogen is added to the substance to be hydrided.
• 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.
• 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. 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.
• the above-mentioned side reaction is likely to occur in areas of 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.
• the electrochemical cells of the present disclosure can improve faradaic efficiency.
• 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.
• 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.
• 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 in the direction in which the anode section, electrolyte membrane, and cathode section are stacked.
• 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.
• an insulating member is disposed 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.
• the at least one flow field may include a conductive plate facing the electrolyte membrane and a porous diffusion layer disposed 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 extending 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.
• 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 formed by the grooves improves the flowability of the second fluid in the second flow field.
• the second fluid is more likely to come into contact with the second catalyst layer in the second flow field, which tends to improve the Faraday efficiency of the electrochemical cell.
• 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
• the second flow path may include a plurality of second grooves arranged in parallel
• at least some of the plurality of first grooves and at least some of the plurality of second grooves may be arranged alternately in a plan view.
• a first flow path having the above structure makes it easy to 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 makes it easy to quickly recover the hydride from the second flow field. As a result, the Faraday efficiency of the electrochemical cell is easily improved.
• the first flow path may include a first connecting groove, and the multiple first grooves may extend so as to branch off from the first connecting groove; the second flow path may include a second connecting groove, and the multiple second grooves may extend so as to branch off from the second connecting groove.
• the conductive plate may include 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.
• the sheet-shaped insulating member can be easily positioned at a desired position in the second flow field.
• the non-conductive region described above can be easily formed by sandwiching the sheet-shaped insulating member between the electrolyte membrane and the diffusion layer.
• the non-conductive region described above can also be easily formed by sandwiching the sheet-shaped insulating member between the diffusion layer and the conductive plate.
• the sheet-shaped insulating member may be positioned at a desired position in the first flow field.
• the sheet-like insulating material is integrated with the conductive plate, there is no need to align the insulating material with the conductive plate, improving the ease of assembly of the electrochemical cell.
• the insulating member may be a resin material integrated with the diffusion layer.
• an insulating member made of a resin material is integrated into the diffusion layer, there is no need to align the insulating member with the diffusion layer, 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 fluid or second fluid flows. This reduces pressure loss.
• the insulating member may be a resin material integrated with the conductive plate.
• 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.
• the substance to be hydrogenated may be toluene.
• MCH methylcyclohexane
• the first fluid may be mainly composed of 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.
• ⁇ 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.
• 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 pressurizes 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.
• aromatic compounds include benzene, naphthalene, anthracene, diphenylethane, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, and N-alkyldibenzopyrrole.
• one to four hydrogen atoms in the aromatic ring may be substituted with an alkyl group.
• alkyl refers to a linear or branched alkyl group having one to six carbon atoms.
• alkylbenzenes include toluene and ethylbenzene.
• dialkylbenzenes include xylene and diethylbenzene.
• trialkylbenzenes include mesitylene.
• alkylnaphthalenes include methylnaphthalene.
• 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
• 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 made of 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 ⁇ m or more and 300 ⁇ m or less.
• An electrolyte membrane 2 with a thickness of 5 ⁇ m or more easily separates the first fluid 101 and the second fluid 102.
• An electrolyte membrane 2 with a thickness of 300 ⁇ m or less easily allows protons to pass through.
• the thickness of the electrolyte membrane 2 may be 10 ⁇ m or more and 150 ⁇ m or less, or may be 20 ⁇ m or more and 100 ⁇ m or less.
• the first flow field 5 is the space in the anode section 3 through which the first fluid 101 flows. As shown in FIG. 1, 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. 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 that faces 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 sandwiched 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 difficult to react 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 made of a material with high oxidation resistance, such as platinum.
• the metal plate is made 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).
• the first diffusion layer 32 functions to diffuse the first fluid 101 supplied to the anode section 3 throughout the entire first flow field 5.
• the first diffusion layer 32 is a porous layer formed from 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 made up of multiple mesh plates with different mesh sizes stacked on top of each other, or multiple mesh plates with different mesh shapes stacked on top of each other.
• 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 sufficiently large first flow field 5 is formed within the anode portion 3, and the first fluid 101 can easily diffuse throughout the entire first flow field 5.
• 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, which contains oxygen produced by the electrolysis of water, can easily be discharged from the first flow field 5 quickly.
• the average thickness of the first diffusion layer 32 may be 0.2 mm to 2.5 mm, or 0.25 mm to 2.0 mm.
• 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 mainly 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 according to the sizes of the first conductive plate 31 and the first diffusion layer 32.
• 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 from an electrically insulating material that is resistant to the first fluid 101.
• Specific electrical insulating materials include, for example, epoxy resin, phenolic 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.
• 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 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 to the first surface 21.
• the cathode section 4 in this example comprises a second conductive plate 41, a second diffusion layer 42, a frame seal section 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 sandwiched 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 explained in a separate section later.
• 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 made of 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 made of 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 also be, for example, a metal plate.
• the metal plate may be made of, for example, titanium or a titanium alloy, or stainless steel.
• An electrode plate (not shown) is arranged 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 entire 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, resulting in the carbon fibers being entangled with each other.
• the entanglement process can be performed using, for example, needle punching or a water jet.
• the second diffusion layer 42 formed from a nonwoven fabric, has high elastic deformability.
• the second diffusion layer 42 which has high elastic deformability, is sandwiched between the electrolyte membrane 2 and the second conductive plate 41 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.
• 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 above average length is three or more, including a measurement at the center position of the electrolyte membrane 2 when viewed in a plan view.
• 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 portion 4, and the second fluid 102 is likely to diffuse throughout the entire second flow field 6.
• 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 does not become too large. In other words, because 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 easily 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 will be 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 from the outer periphery of the second diffusion layer 42. Therefore, in this example, the second flow field 6 is mainly formed from 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.
• 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 close to the second surface 22 of the electrolyte membrane 2.
• the second catalyst layer 40 promotes the reaction between the substance to be hydrided contained in the second fluid 102 and protons and electrons, resulting in the production of hydrides.
• the second catalyst layer 40 is formed integrally with the second surface 22 of the electrolyte membrane 2.
• the second catalyst layer 40 may also be formed integrally with at least the 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.
• 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.
• 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.
• the first conductive plate 31 and the second conductive plate 41, rather than bipolar plates, are disposed, respectively.
• the first flow path 61 has an inlet end 61A (first inlet end) that is directly connected to the inlet 6A ( Figure 1) of the second flow field 6, and an outlet end 61B (first outlet end) that is not directly connected to the outlet 6B ( Figure 1) of the second flow field 6.
• the inlet 6A is directly connected to the end of the second supply pipe 102A shown in Figure 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 entire 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.
• the outlet end 61B of the first flow path 61 is not directly connected to the outlet 6B of the second flow field 6, so the second fluid 102 flowing within 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, 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 the production of hydrides.
• the second flow path 62 is directly connected to the outlet 6B of the second flow field 6.
• 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 coming into contact with 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 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 so as to branch off from the first connecting groove 61b.
• the supply groove 61f extends so as to branch off from the first connecting groove 61b in the opposite direction to the extension of the first groove 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.
• the second fluid 102 flows easily at the outlet end 62B connected to the outlet 6B.
• the end 62e of the second groove 62d which is 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, which is made up of the closed end 62e. Because the opening of the second flow channel 62, which is made up of a groove with the above structure, faces the second diffusion layer 42, the second fluid 102 containing hydrides is quickly recovered into the second flow channel 62 from near the second catalyst layer 40. Water that has passed through the electrolyte membrane 2 is also quickly recovered into the second flow channel 62 from near the second catalyst layer 40.
• each of the multiple second grooves 62d may be directly connected to the manifold 4B.
• the second connecting groove 62b and the discharge groove 62f are not formed in the second conductive plate 41.
• the second flow path 62 may be configured so 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.
• 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.
• 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 become 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 grooves 61d and the second grooves 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 of the first grooves 61d and the second grooves 62d are measured at the start, end, and middle positions along their length. The average depth d is the average of all the 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 grooves 61d and the second grooves 62d may be uniform or may vary along their lengths.
• the first flow field 5 may include a flow path 50 that facilitates the flow of the first fluid 101.
• the flow path 50 is a groove formed in the first conductive plate 31.
• 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.
• 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.
• 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.
• 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.
• 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. If 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.
• the sheet-shaped insulating member 8 is arranged 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 arranged in this position insulates a portion of the second conductive plate 41.
• the insulating member 8 only needs to be arranged 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.
• the insulating member 8 is fixed to the second conductive plate 41 with an adhesive or the like. In this case, there is no need to align the insulating member 8 with the second conductive plate 41, 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, there is also no need to align the insulating member 8 with the second conductive plate 41, 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 of 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 it to or impregnating it into 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 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.
• 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.
• 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 ⁇ m, the thickness may change by up to approximately 40 ⁇ m. 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.
• 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.
• 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.
• the compressive strain in this example is, for example, the value obtained by dividing the amount of reduction in thickness ⁇ of the second diffusion layer 42 compressed by a surface pressure of 0.5 MPa or more and 0.8 MPa or less by the initial thickness t0 of the second diffusion layer 42 before compression.
• the reduction amount ⁇ 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.
• 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 can be 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 has excellent elastic deformability.
• a second diffusion layer 42 having a compressive strain of 0.3 to 0.8 deforms so that the thickness of the second diffusion layer 42 becomes smaller than the initial thickness t0 when a predetermined surface pressure is applied.
• a second diffusion layer 42 having such elastic deformability deforms again to approach or become equal to the initial thickness t0 when the surface pressure is reduced or removed.
• the compression strain may be 0.4 or more, 0.5 or more, 0.6 or more, or 0.7 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 released, 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.
• the second diffusion layer 42 that satisfies the above compressive strain is, for example, a nonwoven fabric containing carbon fiber.
• 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.
• the second diffusion layer 42 may also be a woven fabric containing carbon fiber.
• a woven fabric is made by alternately weaving warp and weft threads of carbon fiber.
• a 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.
• a binder that holds the carbon fibers in place.
• the deformation of the paper thickness is less than 20 ⁇ m, or even around 10 ⁇ m.
• a surface pressure of 0.5 MPa is applied, such paper has a compressive strain of less than 0.2, and is virtually undeformed.
• the average diameter of the carbon fibers forming the nonwoven fabric is, for example, 5 ⁇ m or more and 100 ⁇ m or less. Carbon fibers with an average diameter of 5 ⁇ m or more and 100 ⁇ m 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.
• the average diameter is 5 ⁇ m or more and 100 ⁇ m 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 ⁇ m or more and 80 ⁇ m or less, 5 ⁇ m or more and 50 ⁇ m or less, or 7 ⁇ m or more and 30 ⁇ m 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 multiple 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 multiple carbon fibers.
• the cross-section of the second diffusion layer 42 is 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-section is, for example, 500x or more and 3000x or less.
• 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 the above 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 are flow paths for the second fluid 102. Therefore, if the porosity is 40% or more, the second fluid 102 easily passes 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. If the porosity is 98% or less, the strength of the second diffusion layer 42 is likely to be maintained.
• 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.
• 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.
• the basis weight is 50 g/m 2 or more, the conductivity of the second diffusion layer 42 easily becomes high.
• 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.
• 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 ⁇ m or more and 50 ⁇ m 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.
• 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.
• the electrolyte membrane 2 was a proton-conductive thin film and had a thickness of 180 ⁇ m (micrometers).
• 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
• 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.
• 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.
• 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.
• 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 the total amount of charge minus the amount of charge used to produce hydrogen.
• 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.
• 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.
• 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.
• 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 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 in the second flow field 6 of 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.
• “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.
• 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.
• 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 .
• 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 ⁇ 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 .
• the initial thickness t0 of the carbon nonwoven fabric is measured using a commercially available thickness measurement device that conforms to Method A of JIS L 1096:2010, such as the constant pressure thickness measurement device PG-16J (measuring probe diameter: ⁇ 25.2 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.
• FIG 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, such as a micro strength evaluation tester MST-I type HR manufactured by Shimadzu Corporation.
• 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.
• the thickness of the carbon nonwoven fabric changes significantly with compression.
• Carbon nonwoven fabric has excellent elastic deformability.
• the 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.
• the second diffusion layer 42 adheres closely to the electrolyte membrane 2 and the second conductive plate 41, and almost no localized gaps are formed at the boundaries 1A and 1B.
• the almost complete absence of localized gaps at the boundaries 1A and 1B allows the second fluid 102 to easily circulate throughout the entire second flow field 6.
• the Faraday efficiency of the electrochemical cell 1 is expected to improve.
• the compressive strain of the carbon cloth when pressed with a surface pressure of 0.5 MPa 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.
• 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 boundaries 1A and 1B.
• 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.
• 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 very little due to the pressure.
• 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 boundaries 1A and 1B.
• electrochemical cell 1 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 above 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, and it is thought that these gaps are likely to cause a decrease in Faraday efficiency.
• the second diffusion layer 42 made of carbon nonwoven fabric maintains 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 the long term.
• Electrochemical cell 1 equipped with a second diffusion layer 42 made of carbon nonwoven fabric is designated electrochemical cell A
• electrochemical cell 1 equipped with a second diffusion layer 42 made of carbon paper is designated electrochemical cell B
• the two are compared. If, for electrochemical cell B, the same pump X as for 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 will increase the pressure loss within electrochemical cell B before electrolysis. Electrolysis makes it easier for hydrogen to be generated, further increasing the pressure loss, which could lead to liquid leakage from electrochemical cell B. For these reasons, electrochemical cell A, which uses carbon nonwoven fabric, has a wider range of operational conditions for obtaining a high Faraday efficiency than electrochemical cell B, which uses carbon paper.
• the porosity, basis weight and fiber diameter of the carbon nonwoven fabric X were 89.5%, 71 g/m 2 and 10 ⁇ m, respectively.
• the porosity, basis weight and fiber diameter of the carbon nonwoven fabric Y were 84.0%, 108 g/m 2 and 10 ⁇ m, respectively.
• the porosity, basis weight and fiber diameter of the carbon nonwoven fabric Z were 81.2%, 127 g/m 2 and 10 ⁇ m, 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 ⁇ m to 20 ⁇ m.
• 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.

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