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
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
• • 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.
• An 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.
• At least one of the first and second flow fields comprises a first flow path having a first inlet end and a first outlet end, the first outlet end having a structure that makes it more difficult for the fluid to flow than the first inlet end, and a second flow path having a second inlet end and a second outlet end, the second inlet end having a structure that makes it more difficult for the fluid to flow than the second outlet end, and has an area in which a portion of the first flow path and a portion of the second flow path are juxtaposed.
• 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 faradaic efficiency in this specification is the ratio of the amount of charge contributed to hydrogenation when the total amount of charge input to the electrochemical cell is taken as 100%.
• Increasing the amount of fluid supplied to the electrochemical cell can be considered to improve the Faraday efficiency. However, increasing the amount of fluid supplied increases the pressure loss within the electrochemical cell. Therefore, there is an upper limit to the amount of fluid that can be supplied to the electrochemical cell.
• One of the objectives of this disclosure is to provide an electrochemical cell that can increase the amount of fluid supplied to the electrochemical cell while reducing pressure loss within the proton-conducting electrochemical cell.
• the electrochemical cell of the present disclosure can increase the amount of fluid supplied to the electrochemical cell while reducing pressure loss within the electrochemical cell.
• 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.
• At least one of the first and second flow fields comprises a first flow path having a first inlet end and a first outlet end, the first outlet end having a structure that makes it more difficult for the fluid to flow than the first inlet end, and a second flow path having a second inlet end and a second outlet end, the second inlet end having a structure that makes it more difficult for the fluid to flow than the second outlet end, and has a region in which a portion of the first flow path and a portion of the second flow path are juxtaposed.
• the fluid flowing through the first flow path first moves to the catalyst layer and then easily moves to the second flow path. This promotes chemical reactions in the catalyst layer.
• One example of a structure in which the first outflow end is more difficult for fluid to flow through than the first inflow end is provided with a groove whose outflow end is completely closed.
• Another example is provided with a groove whose outflow end has a smaller groove width than the inflow end.
• One example of a structure in which the second inflow end is more difficult for fluid to flow through than the second outflow end is provided with a groove whose inflow end is completely closed.
• Another example is provided with a groove whose inflow end has a smaller groove width than the outflow end.
• the first flow path of the second flow field quickly diffuses the second fluid throughout the entire second flow field, increasing the opportunity for the substances to be hydrided contained in the second fluid to come into contact with the second catalytic layer.
• the substances to be hydrided are hydrogenated in the second catalytic layer, producing hydrides.
• the second fluid has difficulty flowing out from the first outlet end of the first flow path, the second fluid that has diffused throughout the second flow field remains in the second flow field to a certain extent. This reduces the amount of substances to be hydrided that are discharged outside the electrochemical cell without coming into contact with the second catalytic layer, promoting the production of hydrides.
• the second flow path of the second flow field takes in the second fluid from within the second flow field.
• an electrochemical cell As protons move, a small amount of water passes through the electrolyte membrane from the first fluid in the anode section to the second fluid in the cathode section.
• the water in the cathode section inhibits the hydrogenation of the substance to be hydrogenated, reducing the faradaic efficiency of the electrochemical cell.
• the second flow path quickly drains water from the cathode section of the electrochemical cell, reducing the reduction in faradaic efficiency.
• the cathode section may include a conductive plate facing the second surface and a porous diffusion layer disposed between the conductive plate and the second surface, and the first flow path and the second flow path may be grooves formed on the surface of the conductive plate facing the diffusion layer.
• the first flow path formed by the grooves formed in the conductive plate quickly diffuses the second fluid over the entire surface of the conductive plate.
• the second fluid diffused over the entire surface of the conductive plate is likely to come into contact with the second catalyst layer.
• the second fluid containing the hydride passes through the diffusion layer and is discharged into the second flow path.
• the second flow path formed by the grooves formed in the conductive plate quickly discharges the second fluid containing the hydride to the outside of the electrochemical cell. As a result, the Faraday efficiency of the electrochemical cell described above in ⁇ 3> is increased.
• 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, and 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 planar view.
• the first flow path of the above structure makes it easy to quickly diffuse the second fluid containing the substance to be hydrided throughout the entire second flow field.
• the second flow path of the above structure makes it easy to quickly recover the second fluid containing the hydride from near the second catalyst layer.
• the first flow path and the second flow path may be grooves of the above structure that are independent of each other, or a portion of the groove of the above structure that forms the first flow path may be locally connected to a portion of the groove of the above structure that forms the second flow path.
• An example of a structure in which the first flow path and the second flow path are locally connected is a structure having a narrow groove that connects the end of the first groove of the first flow path to the second flow path, and a narrow groove that connects the end of the second groove of the second flow path to the first flow path.
• the width of this narrow groove is narrower than the widths of the first and second grooves. In a configuration having independent grooves of the above structure, the width of the narrow groove is zero.
• the first and second grooves are grooves with completely closed ends.
• the ratio W1/W2 of the average width W1 of the ridge portion formed between the adjacent first and second grooves to the average width W2 of the first and second grooves may be greater than 1 and less than or equal to 50.
• the flow rate of the second fluid flowing from the first groove of the first flow path through the ridges toward the second groove of the second flow path increases.
• the second fluid with a high flow rate quickly supplies the material to be hydrogenated to the second catalyst layer and quickly removes the material and water from the second catalyst layer.
• the number of first grooves and second grooves in the second flow field decreases.
• a decrease in the number of first grooves and second grooves increases the pressure loss in the second flow field.
• the upper limit of the amount of second fluid supplied to the electrochemical cell decreases.
• an increase in the average width W1 of the ridge portions due to a decrease in the number of first grooves and second grooves increases the flow rate of the second fluid in the ridge portions.
• An increase in the flow rate of the second fluid in the ridge portions is more likely to contribute to an increase in the Faraday efficiency than an increase in the amount of second fluid supplied to the electrochemical cell.
• the average width W1 may be 1 mm or more and 50 mm or less.
• the average width W1 of the ridge portion is 1 mm or more, the flow velocity of the second fluid in the ridge portion is likely to be sufficiently high. If the average width W1 of the ridge portion is 50 mm or less, the number of first grooves and second grooves in the second flow field will be sufficiently large, and the pressure loss in the second flow field will not easily become high.
• the average width W2 may be 0.5 mm or more and 5 mm or less.
• the second fluid is more likely to diffuse from the first flow path throughout the second flow field, and the diffused second fluid is more likely to be recovered in the second flow path. If the average width W2 of the first and second grooves is 5 mm or less, the amount of second fluid discharged from the second flow field without coming into contact with the second catalyst layer is reduced.
• the average depth d of the first groove and the second groove may be 0.5 mm or more and 5 mm or less.
• the pressure loss in the second flow field is likely to be reduced. If the average depth d of the first groove and the second groove is 5 mm or less, the amount of the second fluid discharged from the second flow field without coming into contact with the second catalyst layer is reduced.
• 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.
• the porosity of the diffusion layer may be 40% or more and 98% or less.
• the porosity of the diffusion layer when incorporated into an electrochemical cell is 40% or more, the fluid will easily diffuse throughout the entire flow field. If the porosity of the diffusion layer is 98% or less, the strength of the diffusion layer will be sufficiently high.
• the average thickness of the diffusion layer may be 0.1 mm or more and 3.0 mm or less.
• the gap between the conductive plate and the electrolyte membrane will be sufficiently large. This makes it easier for the fluid to diffuse throughout the entire flow field. If the average thickness of the diffusion layer is 3.0 mm or less, the gap between the conductive plate and the electrolyte membrane will not be too large. This makes it easier for the fluid flowing near the electrolyte membrane to be quickly collected in the grooves of the conductive plate.
• ⁇ 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.
• 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 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 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.
• 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 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 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.
• 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.
• the Faraday efficiency be improved.
• the second flow field 6 includes a first flow path 61 and a second flow path 62.
• the first flow path 61 and the second flow path 62 are not directly connected to each other and are independent of each other.
• 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.
• the first flow path 61 and the second flow path 62 please refer mainly to 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 ( 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 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.
• a second flow path 62 with this configuration allows the second fluid 102 containing hydrides to be quickly discharged to the outside of the electrochemical cell 1.
• 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 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.
• the substance to be hydrided is more easily supplied to the second catalyst layer 40, and the hydride is more easily removed from near the second catalyst layer 40.
• water is more easily removed from near 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.
• 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.
• the openings of the grooves are positioned so as to connect to the pores of the second diffusion layer 42.
• the first flow path 61 and the second flow path 62 may also be grooves formed in the second diffusion layer 42.
• the shapes of the grooves forming the first flow path 61 and the second flow path 62 are not particularly limited.
• the first flow path 61 and the second flow path 62 are grooves with structures independent of each other.
• the first flow path 61 has a plurality of first grooves 61d
• the second flow path 62 has a plurality of second grooves 62d.
• at least a portion of the plurality of first grooves 61d and at least a portion 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.
• 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, as described above.
• 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 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.
• 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 flow easily through the outflow end 61B, which is made up of the closed end 61e. Because the opening of the first flow path 61, which is made up of grooves 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.
• each of the multiple first grooves 61d may be directly connected to the manifold 4A.
• the first connecting groove 61b and the supply groove 61f are not formed in the second conductive plate 41.
• 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 portions are each directly connected to the manifold 4A.
• 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 and 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. In other words, the discharge groove 62f is directly connected to the outlet 6B of the second flow field 6 shown in FIG.
• 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.
• FIG. 5 is a partial cross-sectional view of the electrochemical cell 1 of FIG. 1 cut in a direction perpendicular to the first groove 61d and second groove 62d in FIG. 4.
• the approximate flow of the second fluid 102 in the second diffusion layer 42 is indicated by bold arrows.
• the approximate flow of the first fluid 101 in the first diffusion layer 32 is indicated by bold arrows.
• a ridge portion 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 ridge portion 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 covering the ridge portion 63 and flows into the second groove 62d.
• the substance to be hydrogenated contained in the second fluid 102 is hydrogenated in the second catalyst layer 40, producing a hydride.
• the supply rate of the second fluid 102 increases, the flow rate of the second fluid 102 passing through the ridges 63 increases, and the material to be hydrogenated is quickly supplied to the second catalyst layer 40, while the hydrogenated material is quickly recovered from the second catalyst layer 40.
• 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 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 flow path 50 of the first flow field 5 may be a groove having a structure similar to that of the first flow path 61 and the second flow path 62 of the second flow field 6.
• 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 that extends 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.
• the insulating member 8 is arranged so that its lower frame portion covers the entire first ridge region 65.
• 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 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 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.
• 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 ⁇ ⁇ cm or more.
• the resistivity may be 10 ⁇ ⁇ cm or more, or may be 10 ⁇ ⁇ 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 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 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 ⁇ m 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.
• a second diffusion layer 42 with a thickness difference tB - tA of 40 ⁇ m 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 thickness difference depends on the initial thickness t0 and the surface pressure, but may be 50 ⁇ m or more, or 60 ⁇ m or more.
• the upper limit of the thickness difference is, for example, the initial thickness t0 x 0.9 ⁇ m.
• a second diffusion layer 42 with a compressive strain of 0.6 or more typically satisfies the above elastic deformation characteristics.
• 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 ⁇ m 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. As the second diffusion layer 42 elastically deforms in accordance with the small unevenness on the surface of the second catalyst layer 40, gaps that could become through-holes are less likely to form.
• 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 second diffusion layer 42 may contain a member with a compressive strain of less than 0.3, as long as the overall compressive strain is 0.3 or greater.
• the second diffusion layer 42 may be configured by laminating multiple nonwoven fabrics with different compressive strains, or by laminating nonwoven fabric and woven fabric, or by laminating nonwoven fabric and paper, or by laminating nonwoven fabric, woven fabric and paper.
• 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 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 a compressed state can be calculated.
• 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).
• 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 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.
• 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.
• 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.
• the measurement results for the pressure loss in the second flow field 6 are shown in Table 1, and the measurement results for the Faraday efficiency of the electrochemical cell 1 are shown in 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 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 ⁇ m.
• the carbon nonwoven fabric had a thickness of 1000 ⁇ m, a basis weight of 90 g/cm 2 , and a porosity of 95.6%.
• the basis weight of the carbon nonwoven fabric was 90 g/cm 2 and the porosity was 86.7%.
• 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.
• 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, the only component whose thickness changes is the second diffusion layer 42.
• 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 the movement distance of the upper base 91 corresponding to the magnitude of the surface pressure is measured.
• the movement distance can be said to be equal to the reduction in thickness ⁇ of the second diffusion layer 42.
• 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.
• 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 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.
• 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.

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