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
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
  • C25B11/032—Gas diffusion electrodes
• • 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
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
  • H01M8/0245—Composites in the form of layered or coated products
• • 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
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • 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
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/23—Carbon monoxide or syngas
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
  • H01M2008/1293—Fuel cells with solid oxide electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present invention relates to an electrochemical cell.
• Patent Document 1 discloses an electrochemical cell (electrolysis cell, fuel cell, etc.) that includes a cell body disposed on a metal support.
• the metal support has a plurality of communication holes formed on its main surface.
• the cell body includes a gas diffusion layer formed on the main surface of the metal support, a first electrode layer and a second electrode layer disposed on the gas diffusion layer, and an electrolyte layer disposed between the first and second electrode layers.
• Patent Document 1 describes forming through-holes in the gas diffusion layer that connect to the communication holes in the metal support to ensure smooth gas supply and discharge between the first electrode layer and the communication holes in the metal support.
• the objective of the present invention is to provide an electrochemical cell that can suppress damage to the gas diffusion layer.
• the electrochemical cell according to a first aspect of the present invention comprises a metal support having a plurality of through holes formed in a main surface, and a cell main body portion disposed on the main surface.
• the cell main body portion has a gas diffusion layer disposed on the main surface, a first electrode layer disposed on the gas diffusion layer, a second electrode layer, and an electrolyte layer disposed between the first electrode layer and the second electrode layer.
• the gas diffusion layer has through holes communicating with the through holes.
• the through holes have a gap space that penetrates into the gap between the main surface and the first electrode layer.
• the electrochemical cell according to a second aspect of the present invention is the electrochemical cell according to the first aspect, wherein the gap space is tapered toward the deepest part of the gap space in a plane direction perpendicular to the thickness direction of the gas diffusion layer.
• the electrochemical cell according to a third aspect of the present invention is related to the second aspect, and the gas diffusion layer has an exposed surface exposed to the gap space, and the exposed surface is curved.
• the electrochemical cell according to a fourth aspect of the present invention relates to any one of the first to third aspects, and the gas diffusion layer has a first extension portion sandwiched between the gap space and the first electrode layer in the thickness direction.
• the electrochemical cell according to a fifth aspect of the present invention relates to any one of the first to fourth aspects, wherein the gas diffusion layer has a second extension portion sandwiched between the gap space and the metal support in the thickness direction.
• the electrochemical cell according to a sixth aspect of the present invention relates to any one of the first to third aspects, wherein the width of the gap space in the planar direction is greater than the thickness of the gas diffusion layer in the thickness direction.
• the electrochemical cell according to a seventh aspect of the present invention relates to any one of the first to sixth aspects, wherein the width of the gap space in the planar direction is 10 ⁇ m or more.
• An electrochemical cell according to an eighth aspect of the present invention relates to any one of the first to ninth aspects, wherein the metal support has a substrate and an oxide film covering the surface of the substrate, and the thickness of a first portion of the oxide film exposed to the communication hole is greater than the thickness of a second portion of the oxide film facing the first electrode layer.
• the electrochemical cell according to a ninth aspect of the present invention relates to any one of the first to eighth aspects, wherein the average pore diameter of the plurality of first pores in the gas diffusion layer is smaller than the average pore diameter of the plurality of second pores in the first electrode layer.
• the electrochemical cell according to a tenth aspect of the present invention is the electrochemical cell according to the ninth aspect, wherein the porosity of the gas diffusion layer is greater than the porosity of the first electrode layer.
• the present invention provides an electrochemical cell that can suppress damage to the gas diffusion layer.
• FIG. 1 is a plan view of an electrolysis cell according to an embodiment.
• FIG. 2 is a cross-sectional view taken along line AA in FIG.
• FIG. 3 is a partially enlarged view of FIG. 2.
• FIG. 1 is a plan view of an electrolysis cell 1 according to an embodiment, and Fig. 2 is a cross-sectional view taken along line AA in Fig. 1.
• Electrolytic cell 1 is an example of an "electrochemical cell” according to the present invention. Electrolytic cell 1 is a so-called metal-supported electrolytic cell.
• the electrolytic cell 1 is formed in the shape of a plate extending in the X-axis and Y-axis directions.
• the electrolytic cell 1 is formed in the shape of a rectangle extending in the Y-axis direction when viewed in a plan view from the Z-axis direction, which is perpendicular to the X-axis and Y-axis directions.
• the planar shape of the electrolytic cell 1 is not particularly limited, and may be polygonal, elliptical, circular, or other shapes other than a rectangle.
• the electrolysis cell 1 comprises a metal support 10, a cell main body 20, and a flow path member 30.
• the metal support 10 supports the cell main body 20.
• the metal support 10 is formed in a plate shape.
• the metal support 10 may be in the shape of a flat plate or a curved plate.
• the metal support 10 only needs to be able to support the cell main body 20, and its thickness is not particularly limited, but can be, for example, between 0.1 mm and 2.0 mm.
• the metal support 10 has a plurality of communicating holes 11, a first main surface 12, and a second main surface 13.
• Each communication hole 11 penetrates the metal support 10 in the Z-axis direction from the first main surface 12 to the second main surface 13. Each communication hole 11 opens to both the first main surface 12 and the second main surface 13. In this embodiment, the opening of each communication hole 11 on the first main surface 12 side is covered by the cell main body 20 (specifically, the hydrogen electrode layer 6 described below). The opening of each communication hole 11 on the second main surface 13 side is connected to the flow path 30a described below.
• Each communication hole 11 can be formed by mechanical processing (e.g., punching), laser processing, or chemical processing (e.g., etching).
• each communication hole 11 is formed linearly along the Z-axis direction.
• each communication hole 11 may be inclined with respect to the Z-axis direction, or may not be linear.
• the communication holes 11 may be connected to each other.
• the first main surface 12 is provided on the opposite side of the second main surface 13.
• the cell main body 20 is disposed on the first main surface 12.
• the flow path member 30 is bonded to the second main surface 13.
• the metal support 10 is made of a metal material.
• the metal support 10 is made of an alloy material containing Cr (chromium).
• Examples of such metal materials include Fe-Cr alloy steel (stainless steel, etc.) and Ni-Cr alloy steel.
• Cr content in the metal support 10 can be between 4% and 30% by mass.
• the metal support 10 may contain Ti (titanium) or Zr (zirconium).
• the Ti content in the metal support 10 is not particularly limited, but may be 0.01 mol % or more and 1.0 mol % or less.
• the Zr content in the metal support 10 is not particularly limited, but may be 0.01 mol % or more and 0.4 mol % or less.
• the metal support 10 may contain Ti as TiO 2 (titania) or Zr as ZrO 2 (zirconia).
• the cell body 20 is disposed on the metal support 10.
• the cell body 20 is supported by the metal support 10.
• the cell body 20 has a gas diffusion layer 5, a hydrogen electrode layer 6 (cathode), an electrolyte layer 7, a reaction prevention layer 8, and an oxygen electrode layer 9 (anode).
• the gas diffusion layer 5, hydrogen electrode layer 6, electrolyte layer 7, reaction prevention layer 8, and oxygen electrode layer 9 are stacked in this order in the Z-axis direction from the metal support 10 side.
• the gas diffusion layer 5, hydrogen electrode layer 6, electrolyte layer 7, and oxygen electrode layer 9 are required components, while the reaction prevention layer 8 is optional.
• the gas diffusion layer 5 is disposed on the first main surface 12 of the metal support 10.
• the gas diffusion layer 5 is interposed between the metal support 10 and the hydrogen electrode layer 6.
• the gas diffusion layer 5 is in direct contact with both the metal support 10 and the hydrogen electrode layer 6.
• the gas diffusion layer 5 has a plurality of through holes 51, a first connection surface 52, and a second connection surface 53.
• Each through hole 51 penetrates the gas diffusion layer 5 in the Z-axis direction from the first connection surface 52 to the second connection surface 53.
• Each through hole 51 opens to the first connection surface 52 and the second connection surface 53.
• the opening of each through hole 51 on the first connection surface 52 side is covered by the hydrogen electrode layer 6.
• the opening of each through hole 51 on the second connection surface 53 side is connected to each communication hole 11 in the metal support 10. Therefore, the gas diffusion layer 5 does not cover each communication hole 11 in the metal support 10.
• the first connection surface 52 is connected to the first main surface 12 of the metal support 10.
• the first connection surface 52 is provided on the opposite side of the second connection surface 53.
• the second connection surface 53 is connected to the hydrogen electrode layer 6.
• the gas diffusion layer 5 is a porous body having electrical conductivity.
• the gas diffusion layer 5 electrically connects the metal support 10 and the hydrogen electrode layer 6.
• the gas diffusion layer 5 also supplies and exhausts gas between each of the communication holes 11 and the hydrogen electrode layer 6. Specifically, the gas diffusion layer 5 supplies the raw material gas supplied from each of the communication holes 11 to the hydrogen electrode layer 6, and exhausts the product gas generated in the hydrogen electrode layer 6 to each of the communication holes 11.
• the gas diffusion layer 5 includes a conductive material.
• the gas diffusion layer 5 may include a substrate for supporting the conductive material.
• the conductive material include metal materials such as Ni (nickel) and Fe (iron), and conductive ceramic materials.
• the substrate include YSZ, CSZ, ScSZ, GDC, SDC, (La, Sr) (Cr, Mn) O 3 , (La, Sr) TiO 3 , Sr 2 (Fe, Mo) 2 O 6 , (La, Sr) VO 3 , (La, Sr) FeO 3 , LDC (lanthanum-doped ceria), LSGM (lanthanum gallate), and a mixed material of two or more of these.
• the substrate may be insulating.
• the method for forming the gas diffusion layer 5 is not particularly limited, and methods such as firing, spray coating (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), PVD (sputtering, pulsed laser deposition, etc.), and CVD can be used.
• the hydrogen electrode layer 6 is an example of a "first electrode layer” according to the present invention.
• the hydrogen electrode layer 6 is disposed on the gas diffusion layer 5.
• the hydrogen electrode layer 6 is sandwiched between the gas diffusion layer 5 and the electrolyte layer 7.
• a source gas is supplied to the hydrogen electrode layer 6 through the communication holes 11 and the through holes 51.
• the source gas contains at least H2O .
• the hydrogen electrode layer 6 When the source gas contains only H 2 O, the hydrogen electrode layer 6 generates H 2 from the source gas in accordance with the electrochemical reaction of water electrolysis shown in the following formula (1).
• Hydrogen electrode layer 6 H 2 O+2e ⁇ ⁇ H 2 +O 2 ⁇ (1)
• the hydrogen electrode layer 6 produces H 2 , CO, and O 2 ⁇ from the source gas in accordance with the co-electrolytic electrochemical reactions shown in the following formulas (2), (3), and (4).
• ⁇ Hydrogen electrode layer 6 CO 2 +H 2 O+4e - ⁇ CO+H 2 +2O 2 -...(2) Electrochemical reaction of H 2 O: H 2 O + 2e ⁇ ⁇ H 2 + O 2 ⁇ (3) Electrochemical reaction of CO 2 : CO 2 + 2e ⁇ ⁇ CO + O 2 ⁇ (4)
• the hydrogen electrode layer 6 is a porous material with electrical conductivity.
• the hydrogen electrode layer 6 has gas diffusibility.
• the source gas is supplied to the hydrogen electrode layer 6 from the gas diffusion layer 5.
• the product gas generated in the hydrogen electrode layer 6 is discharged to the flow path 30a via each communication hole 11 and each through-hole 51.
• the hydrogen electrode layer 6 contains a conductive material.
• the conductive material include metal materials such as Ni (nickel) and Fe (iron), and conductive ceramic materials.
• Ni nickel
• Fe iron
• conductive ceramic materials In the case of co-electrolysis, Ni also functions as a thermal catalyst that promotes the thermal reaction between the generated H 2 and CO 2 contained in the feed gas, thereby maintaining an appropriate gas composition for methanation, reverse water-gas shift reaction, and the like.
• the conductive material When the conductive material is made of a metal material, the conductive material exists in an oxide state (e.g., NiO) in an oxidizing atmosphere and in a metallic state (e.g., Ni) in a reducing atmosphere.
• the hydrogen electrode layer 6 undergoes dimensional changes due to oxidation and reduction.
• the hydrogen electrode layer 6 includes an oxide ion conductive material.
• the oxide ion conductive material is an example of the "ion conductive material" according to the present invention.
• Examples of the oxide ion conductive material include YSZ, CSZ, ScSZ, GDC, SDC, (La,Sr)(Cr,Mn) O3 , (La,Sr) TiO3 , Sr2 (Fe,Mo) 2O6 , ( La,Sr) VO3 , (La,Sr) FeO3 , LDC, LSGM, and a mixed material of two or more of these.
• the hydrogen electrode layer 6 has a single-layer structure made of a single composition, but it may also have a multi-layer structure made of different compositions.
• the thickness of the hydrogen electrode layer 6 is not particularly limited, but can be, for example, 1 ⁇ m or more and 500 ⁇ m or less.
• thickness refers to the size in the thickness direction.
• the thickness direction is the direction perpendicular to the plane direction parallel to the hydrogen electrode layer side surface 71 of the electrolyte layer 7.
• the plane direction is the direction parallel to the approximation line of the hydrogen electrode layer side surface 71 obtained by the least squares method in the cross section of the electrolyte layer 7.
• the thickness direction may coincide with the Z-axis direction shown in Figures 1 and 2.
• the electrolyte layer 7 is disposed between the hydrogen electrode layer 6 and the oxygen electrode layer 9.
• the reaction prevention layer 8 is disposed between the electrolyte layer 7 and the oxygen electrode layer 9, so that the electrolyte layer 7 is sandwiched between the hydrogen electrode layer 6 and the reaction prevention layer 8.
• the electrolyte layer 7 has a hydrogen electrode layer side surface 71 that is connected to the hydrogen electrode layer 6.
• the electrolyte layer 7 covers the hydrogen electrode layer 6 and also covers the area of the first main surface 12 of the metal support 10 that is exposed from the gas diffusion layer 5.
• the electrolyte layer 7 transfers O 2 ⁇ generated in the hydrogen electrode layer 6 to the oxygen electrode layer 9.
• the electrolyte layer 7 is made of a dense material with oxide ion conductivity.
• the electrolyte layer 7 can be made of, for example, YSZ (yttria-stabilized zirconia, e.g., 8YSZ), GDC (gadolinium-doped ceria), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), or LSGM (lanthanum gallate).
• the porosity of the electrolyte layer 7 is not particularly limited, but can be, for example, 0.1% or more and 7% or less.
• the thickness of the electrolyte layer 7 is not particularly limited, but can be, for example, 1 ⁇ m or more and 100 ⁇ m or less.
• the method for forming the electrolyte layer 7 is not particularly limited, and methods such as firing, spray coating, PVD, and CVD can be used.
• reaction prevention layer 8 The reaction prevention layer 8 is disposed between the electrolyte layer 7 and the oxygen electrode layer 9. The reaction prevention layer 8 is disposed on the opposite side of the electrolyte layer 7 from the hydrogen electrode layer 6. The reaction prevention layer 8 prevents the constituent elements of the electrolyte layer 7 from reacting with the constituent elements of the oxygen electrode layer 9 to form a layer with high electrical resistance.
• the reaction prevention layer 8 is made of an oxide ion conductive material.
• the reaction prevention layer 8 can be made of GDC, SDC, etc.
• the porosity of the reaction prevention layer 8 is not particularly limited, but can be, for example, 0.1% to 50%.
• the thickness of the reaction prevention layer 8 is not particularly limited, but can be, for example, 1 ⁇ m to 50 ⁇ m.
• reaction prevention layer 8 There are no particular restrictions on the method for forming the reaction prevention layer 8, and methods such as baking, spray coating, PVD, and CVD can be used.
• the oxygen electrode layer 9 is an example of a "second electrode layer” according to the present invention.
• the oxygen electrode layer 9 is disposed on the opposite side of the hydrogen electrode layer 6 with respect to the electrolyte layer 7.
• the reaction prevention layer 8 is disposed between the electrolyte layer 7 and the oxygen electrode layer 9, and therefore the oxygen electrode layer 9 is connected to the reaction prevention layer 8. If the reaction prevention layer 8 is not disposed between the electrolyte layer 7 and the oxygen electrode layer 9, the oxygen electrode layer 9 is connected to the electrolyte layer 7.
• the oxygen electrode layer 9 generates O 2 from O 2 ⁇ transferred from the hydrogen electrode layer 6 via the electrolyte layer 7 in accordance with the chemical reaction of the following formula (5).
• Oxygen electrode layer 9 2O 2 ⁇ ⁇ O 2 + 4e ⁇ (5)
• the oxygen electrode layer 9 is a porous body having oxide ion conductivity and electrical conductivity, and can be made of a composite material of one or more of (La,Sr)(Co,Fe) O3 , (La,Sr) FeO3 , La(Ni,Fe) O3 , (La,Sr) CoO3 , and (Sm,Sr) CoO3 and an oxide ion conductive material (such as GDC).
• the porosity of the oxygen electrode layer 9 is not particularly limited, but can be, for example, 20% or more and 60% or less.
• the thickness of the oxygen electrode layer 9 is not particularly limited, but can be, for example, 1 ⁇ m or more and 100 ⁇ m or less.
• the method for forming the oxygen electrode layer 9 is not particularly limited, and methods such as firing, spray coating, PVD, and CVD can be used.
• the flow path member 30 is bonded to the second main surface 13 of the metal support 10.
• a flow path 30a is formed between the flow path member 30 and the metal support 10.
• a source gas is supplied to the flow path 30a.
• the source gas supplied to the flow path 30a is supplied to the hydrogen electrode layer 6 of the cell main body 20 via each communication hole 11 of the metal support 10.
• the flow path member 30 can be made of, for example, an alloy material.
• the flow path member 30 may also be made of the same material as the metal support 10. In this case, the flow path member 30 may be substantially integrated with the metal support 10.
• the flow path member 30 has a frame 31 and an interconnector 32.
• the frame 31 is an annular member that surrounds the side of the flow path 30a.
• the frame 31 is joined to the second main surface 13 of the metal support 10.
• the interconnector 32 is a plate-shaped member for electrically connecting an external power source or another electrolysis cell in series with the electrolysis cell 1.
• the interconnector 32 is joined to the frame 31.
• the frame body 31 and the interconnector 32 are separate components, but the frame body 31 and the interconnector 32 may also be an integrated component.
• Fig. 3 is a partially enlarged view of Fig. 2.
• the through-holes 51 in the gas diffusion layer 5 have gap spaces 51a that penetrate between the first main surface 12 of the metal support 10 and the hydrogen electrode layer 6. This provides flexibility to the metal support 10, thereby preventing stress from concentrating on the gas diffusion layer 5 when the hydrogen electrode layer 6 undergoes dimensional changes due to oxidation and reduction. This prevents damage to the gas diffusion layer 5 (peeling from the metal support 10 and hydrogen electrode layer 6, and cracks within the gas diffusion layer 5). Furthermore, the through-holes 51 have gap spaces 51a, which allows for smooth gas supply and exhaust between the through-holes 51 and the hydrogen electrode layer 6.
• the gap space 51a is preferably formed in a ring shape. That is, in Figure 3, the pair of gap spaces 51a formed on both sides of the through hole 51 in the planar direction are preferably connected together. This further prevents stress from concentrating on the gas diffusion layer 5, thereby further preventing damage to the gas diffusion layer 5.
• the gap space 51a is preferably tapered in the surface direction toward the deepest part P1 of the gap space 51a. This increases the area of the exposed surface 54 of the hydrogen electrode layer 6 that is exposed in the gap space 51a, allowing for smoother gas supply and discharge between the through hole 51 and the gas diffusion layer 5.
• the deepest part P1 is the tip of the gap space 51a in the surface direction, and indicates the position that penetrates deepest into the gas diffusion layer 5 in the surface direction.
• the exposed surface 54 of the hydrogen electrode layer 6 is preferably curved. This allows the curved exposed surface 54 to absorb the stress acting on the gas diffusion layer 5, further reducing damage to the gas diffusion layer 5.
• the gas diffusion layer 5 preferably has a first extension portion 5a sandwiched between the gap space 51a and the hydrogen electrode layer 6 in the thickness direction. This increases the contact area between the gas diffusion layer 5 and the hydrogen electrode layer 6, thereby improving the bonding between the gas diffusion layer 5 and the hydrogen electrode layer 6.
• the first extension portion 5a be tapered in the planar direction away from the deepest portion P1 of the gap space 51a. This can prevent cracks from occurring in the gas diffusion layer 5 that originate from the tip of the first extension portion 5a.
• the gas diffusion layer 5 preferably has a second extension portion 5b sandwiched between the gap space 51a and the metal support 10 in the thickness direction. This increases the contact area between the gas diffusion layer 5 and the metal support 10, thereby improving the bonding between the gas diffusion layer 5 and the metal support 10.
• the second extension portion 5b is preferably tapered in the planar direction away from the deepest portion P1 of the gap space 51a. This prevents cracks from occurring in the gas diffusion layer 5 that originate from the tip of the second extension portion 5b.
• the width W of the gap space 51a in the surface direction be greater than the thickness T of the gas diffusion layer 5 in the thickness direction. This further prevents stress from concentrating on the gas diffusion layer 5, thereby further preventing damage to the gas diffusion layer 5. From this perspective, it is particularly preferable that the width W of the gap space 51a be 10 ⁇ m or greater.
• the width W of the gap space 51a is the distance in the planar direction between the deepest part P1 of the gap space 51a and the inner end Q1 of the metal support 10.
• the inner circumferential surface 14 is defined as the area of the metal support 10 facing each other across the communication hole 11 in a cross section along the thickness direction, the inner end Q1 of the metal support 10 is the position on the inner circumferential surface 14 closest to the hydrogen electrode layer 6.
• the thickness T of the gas diffusion layer 5 is calculated using the following method. First, a cross section of the gas diffusion layer 5 along the thickness direction is exposed. Next, a backscattered electron image of the cross section is obtained at 3000x magnification using an SEM device (FE-SEM JSM-7900F, manufactured by JEOL Ltd.). Next, the thickness of the gas diffusion layer 5 is measured at three locations on the backscattered electron image that divide the area of the gas diffusion layer 5 where no interstitial spaces 51a exist into four equal parts in the surface direction. The thickness T of the gas diffusion layer 5 is then calculated by arithmetically averaging the three measured values. The thickness T of the gas diffusion layer 5 can be, for example, 1 ⁇ m or more and 50 ⁇ m or less.
• the metal support 10 may have a base material 10a and an oxide coating 10b.
• the substrate 10a is made of the above-mentioned metal material (such as Fe-Cr alloy steel or Ni-Cr alloy steel).
• Oxide film 10b covers the surface of substrate 10a.
• Oxide film 10b can be composed of oxides of the constituent elements of substrate 10a. Chromium oxide is a typical example of such an oxide.
• the thickness of the first portion b1 of the oxide film 10b exposed in the through-hole 11 of the metal support 10 is preferably thicker than the thickness of the second portion b2 of the oxide film 10b facing the hydrogen electrode layer 6. This improves the strength of the area of the metal support 10 surrounding the through-hole 11, thereby preventing distortion of the through-hole 11.
• the thickness of the first portion b1 is determined by taking the arithmetic mean of the thicknesses of the first portion b1 measured at three locations that divide the first portion b1 into four equal parts in the thickness direction on a backscattered electron image at 3000x magnification.
• the thickness of the second portion b2 is determined by taking the arithmetic mean of the thicknesses of the second portion b2 measured at three locations that divide the second portion b2 into four equal parts in the surface direction on a backscattered electron image at 3000x magnification.
• the gas diffusion layer 5 and the hydrogen electrode layer 6 each have a plurality of pores therein.
• the average pore diameter of the pores in the gas diffusion layer 5 is preferably smaller than the average pore diameter of the pores in the hydrogen electrode layer 6.
• the gas diffusion layer 5 preferably contains more small-diameter pores than the hydrogen electrode layer 6. This improves the gas diffusion properties of the gas diffusion layer 5, thereby enabling smoother gas supply and discharge between the through-holes 51 and the hydrogen electrode layer 6 via the gas diffusion layer 5.
• the porosity of the gas diffusion layer 5 is preferably greater than the porosity of the hydrogen electrode layer 6.
• the volume ratio of the gas flow paths in the gas diffusion layer 5 is preferably greater than the volume ratio of the gas flow paths in the hydrogen electrode layer 6. This further improves the gas diffusibility of the gas diffusion layer 5, thereby enabling even smoother gas supply and discharge between the through-holes 51 and the hydrogen electrode layer 6 via the gas diffusion layer 5.
• the average pore size and porosity in the gas diffusion layer 5 can be obtained as follows. First, the electrolytic cell 1 is heated to 750°C and hydrogen is supplied to the gas diffusion layer 5 and the hydrogen electrode layer 6, thereby reducing the gas diffusion layer 5 and the hydrogen electrode layer 6. Next, the electrolytic cell 1 is cooled while still in a reducing atmosphere, and the electrolytic cell 1 is cut along its thickness to expose the cross-sections of the gas diffusion layer 5 and the hydrogen electrode layer 6. Next, the cross-sections are precision-machined and then subjected to ion milling processing using an IM4000 from Hitachi High-Technologies Corporation.
• an FE-SEM Field Emission Scanning Electron Microscope
• an in-lens secondary electron detector is used to obtain SEM images at a magnification large enough to confirm the pores (e.g., 5,000 to 30,000 times).
• image analysis is performed using HALCON image analysis software manufactured by MVTec (Germany), to obtain an analysis image in which the black areas (corresponding to pores) on the SEM image are highlighted.
• the average pore diameter in the gas diffusion layer 5 is then calculated by arithmetically averaging the equivalent circle diameters of each pore (the diameter of a circle having the same area as the pore).
• the porosity of the gas diffusion layer 5 is calculated by dividing the total area of the pores (gas phase) by the area of the entire analysis image (solid phase).
• the average pore diameter and porosity of the hydrogen electrode layer 6 can be calculated in the same way as for the gas diffusion layer 5.
• the gas diffusion layer 5 can be formed as follows. First, the base material 10a of the metal support 10 is prepared, and a paste containing the desired oxide is applied to the surface of the base material 10a. In this case, the thickness of the applied paste may be thicker in the areas of the surface of the base material 10a exposed to the through-holes 11. Next, a pore-forming material of the desired shape and size is placed on the first main surface 12 of the metal support 10 so as to surround the openings of the through-holes 11. Next, a paste containing the constituent materials of the gas diffusion layer 5 is applied to the areas of the first main surface 12 of the metal support 10 where the pore-forming material is not placed, thereby forming a compact of the gas diffusion layer 5. Next, the hydrogen electrode layer 6 is placed on the compact of the gas diffusion layer 5, and the resulting product is fired (800 to 1500°C, 1 to 5 hours) to form a gas diffusion layer 5 having through-holes 51 including interstitial spaces 51a.
• electrolysis cell 1 was described as an example of an electrochemical cell, but electrochemical cells are not limited to electrolysis cells.
• An electrochemical cell is a general term for an element in which a pair of electrodes are arranged so that an electromotive force is generated from an overall oxidation-reduction reaction in order to convert electrical energy into chemical energy, and an element for converting chemical energy into electrical energy. Therefore, electrochemical cells include, for example, fuel cells that use oxide ions or protons as carriers.
• Electrolysis cell 10 Metal support 11 Communication hole 12 First main surface 13 Second main surface 20 Cell body 5 Gas diffusion layer 51 Through hole 51a Interstitial space 52 First connection surface 53 Second connection surface 54 Exposed surface 6 Hydrogen electrode layer 7 Electrolyte layer 8 Reaction prevention layer 9 Oxygen electrode layer 30 Flow path member 30a Flow path

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