Electrochemical reaction single cell and electrochemical reaction cell stack

Abstract

To suppress an occurrence of aggregation of electronically conductive materials in a fuel electrode.SOLUTION: An electrochemical reaction single cell includes: an electrolyte layer; an air electrode disposed on one side of the electrolyte layer in a first direction; and a fuel electrode disposed on the other side of the electrolyte layer in the first direction, the fuel electrode including ionically conductive materials and electronically conductive materials. In at least one cross section, of the fuel electrode, parallel to the first direction, a specific area from an interface between the electrolyte layer and the fuel electrode up to 5 μm to the other side in the first direction satisfies a first condition that an interparticle distance of the ionically conductive materials is 1.4 μm or less.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an electrochemical reaction unit cell and an electrochemical reaction cell stack. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs") are known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. A fuel cell unit (hereinafter simply referred to as a "unit cell"), which is a constituent unit of an SOFC, comprises an electrolyte layer, an air electrode disposed on one side of the electrolyte layer in a predetermined direction (hereinafter referred to as the "first direction"), and an anode electrode disposed on the other side of the electrolyte layer in the first direction. The anode electrode contains an ionically conductive material and an electronically conductive material.

[0003] Conventionally, a single cell designed to suppress the reaction resistance of the fuel electrode has been known. In this conventional single cell, in the region of the fuel electrode near the electrolyte layer, the particle diameter of Ni, which is an electronic conductive material, the particle diameter of the ion conductive material, and the pore diameter of the fuel electrode are each within a predetermined range (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5090575 Summary of the Invention [Problem to be solved by the invention]

[0005] Operation of a single cell causes particles of electronically conductive material to aggregate at the fuel electrode. The aggregation of particles of electronically conductive material can lead to a decrease in the performance of the single cell. For example, the aggregated particles of electronically conductive material may cover the surfaces of particles of ionically conductive material, reducing the reaction field (three-phase interface). The aggregated particles of electronically conductive material may fill the gaps between particles of ionically conductive material, hindering the diffusion of fuel gas. In the above-mentioned conventional single cells, the aggregation of particles of electronically conductive material has not been considered, leaving room for improvement.

[0006] These issues are also common to electrolysis cells, which are constituent units of solid oxide electrolysis cells (hereinafter referred to as "SOECs") that generate hydrogen using the electrolysis reaction of water. In this specification, fuel cell units and electrolysis cells are collectively referred to as electrochemical reaction units. These issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction units.

[0007] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0008] The technology disclosed in this specification can be realized, for example, in the following forms.

[0009] (1) The electrochemical reaction unit cell disclosed in this specification includes an electrolyte layer, an air electrode disposed on one side of the electrolyte layer in a first direction, and an anode disposed on the other side of the electrolyte layer in the first direction, the anode containing an ionically conductive material and an electronically conductive material. In at least one cross section of the anode parallel to the first direction, a specific region extending from the interface between the electrolyte layer and the anode to 5 μm on the other side in the first direction satisfies a first condition that the interparticle distance of the ionically conductive material is 1.4 μm or less. This configuration can suppress aggregation of the electronically conductive material in the anode, compared to a configuration in which the specific region does not satisfy the first condition.

[0010] (2) In the electrochemical reaction unit cell, the specific region may be configured to further satisfy a second condition that the interparticle distance of the ion conductive material is 0.3 μm or more. This configuration can suppress agglomeration of the electron conductive material in the fuel electrode and suppress deterioration of the initial characteristics of the electrochemical reaction unit cell, compared to a configuration in which the specific region does not satisfy the second condition.

[0011] (3) In the electrochemical reaction unit cell, the specific region may be configured to further satisfy a third condition that the particle diameter of the ion conductive material is 0.4 μm or more and 0.8 μm or less. This configuration can effectively suppress a decrease in the initial characteristics of the electrochemical reaction unit cell while suppressing aggregation of the electron conductive material in the fuel electrode, compared to a configuration in which the specific region does not satisfy the third condition.

[0012] (4) In the above electrochemical reaction unit cell, the specific region may be configured to further satisfy a fourth condition that the volume fraction of the ion-conductive material is 0.4 or more and 0.6 or less. This configuration makes it possible to effectively suppress a decrease in the initial characteristics of the electrochemical reaction unit cell while suppressing aggregation of the electron-conductive material in the fuel electrode, compared to a configuration in which the specific region does not satisfy the fourth condition.

[0013] (5) In the electrochemical reaction cell stack described above, in the electrochemical reaction cell stack including a plurality of electrochemical reaction unit cells arranged in the first direction, at least one of the plurality of electrochemical reaction unit cells may be the electrochemical reaction unit cell described above. With this configuration, aggregation of the electronic conductive material at the fuel electrode can be suppressed. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack according to a first embodiment; [Figure 2] FIG. 2 is a cross-sectional view showing the fuel cell stack of the first embodiment taken along line II-II in FIG. 1. [Figure 3]FIG. 3 is a cross-sectional view showing the fuel cell stack of the first embodiment taken along line III-III in FIG. 1. [Figure 4] 2 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, taken along the same line as line II-II in FIG. 1; [Figure 5] FIG. 3 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, taken along the same line as line III-III in FIG. 1; [Figure 6] Enlarged view of box F in Figure 5 [Figure 7] Explanatory diagram showing performance evaluation results DETAILED DESCRIPTION OF THE INVENTION

[0015] A. Implementation: A-1. Configuration of fuel cell stack 10: The first embodiment 1 will be described with reference to Figures 1 to 7. A fuel cell stack 10 (an example of an electrochemical reaction cell stack) of this embodiment is used in a solid oxide fuel cell having an electrolyte layer 112 containing a solid oxide.

[0016] (Overall configuration of fuel cell stack 10) 1 to 3, the fuel cell stack 10 includes a power generation block 100, an end separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating section 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating section 220, the end separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have rectangular outer shapes of approximately the same size and are arranged in this order, stacked in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0017] As shown in Figures 2 and 3, the power generation block 100 is composed of multiple (seven in this embodiment) electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction units 100U") arranged in a predetermined arrangement direction (vertical direction in Figure 2).

[0018] As shown in Fig. 1, the fuel cell stack 10 has bolt holes BH near each of the four corners, penetrating from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. A nut N is screwed onto both ends of each bolt B. These bolts B and nuts N fasten the members from the first end plate 210 to the second end plate 270 together. As shown in Figs. 2 and 3, the first plate 232 is supported by the terminal separator 230, and the four gas passage members 280 are connected to the second end plate 270.

[0019] (Overall configuration of 100U electrochemical reaction units) 4 and 5, the electrochemical reaction unit 100U includes a single cell 110, a single cell separator 120, an air electrode frame 130, an anode frame 140, an anode current collecting member 144, two interconnectors 190, and two IC separators 180. One IC separator 180 (an example of another member), the air electrode frame 130, the single cell separator 120, the anode frame 140, and the other IC separator 180 are stacked in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are supported by the two IC separators 180, and the anode current collecting member 144 is disposed between the single cell 110 and the interconnectors 190.

[0020] 4 and 5, the IC separator 180 and the interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Fig. 2, the reaction unit 100U located at one end (the lower end in Fig. 2) of the multiple reaction units 100U does not have the IC separator 180 and the interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 overlaps the fuel electrode frame 140.

[0021] (single cell 110) The unit cell 110 includes an electrolyte layer 112, a cathode 114, and an anode 116. As shown in Figures 4 and 5, the cathode 114, the electrolyte layer 112, and the anode 116 are stacked in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the cathode 114. The unit cell 110 of this embodiment is an anode-supported unit cell in which the anode 116 supports the other layers (electrolyte layer 112, cathode 114, and reaction prevention layer 118) that make up the unit cell 110.

[0022] The electrolyte layer 112 is a rectangular, flat member having one surface (upper surface in FIGS. 4 and 5) on which the air electrode 114 is disposed and another surface (lower surface in FIGS. 4 and 5) parallel to the first surface on which the fuel electrode 116 is disposed. The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular outer shape smaller than the electrolyte layer 112 and containing, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)).

[0023] The anode 116 is a substantially rectangular, flat-plate-shaped member having substantially the same size as the electrolyte layer 112, and is a porous layer (having a higher porosity than the electrolyte layer 112). The anode 116 includes a support layer that forms the lower surface of the anode 116, and an active layer that is disposed between the support layer and the electrolyte layer 112. In this embodiment, the active layer is adjacent to the electrolyte layer 112, and the support layer is adjacent to the active layer.

[0024] The active layer mainly functions to react oxygen ions supplied from the electrolyte layer 112 with hydrogen and the like contained in the fuel gas FG to generate electrons and water vapor. The active layer contains an ion-conductive material (in this embodiment, YSZ, which is a ceramic) and an electron-conductive material (in this embodiment, Ni, which is a transition metal). The thickness of the active layer is, for example, 10 μm to 40 μm. The support layer mainly functions to support the active layer, the electrolyte layer 112, and the air electrode 114. The thickness of the support layer is, for example, 200 μm to 1000 μm. In this embodiment, the support layer also contains an ion-conductive material (YSZ) and an electron-conductive material (Ni).

[0025] The reaction prevention layer 118 is a layer having a rectangular outer shape and approximately the same size as the air electrode 114, and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of an element (for example, Sr) diffused from the air electrode 114 with an element (for example, Zr) contained in the electrolyte layer 112, thereby preventing the generation of a highly resistive substance (for example, SrZrO3).

[0026] (Single cell separator 120) As shown in Figures 4 and 5, the single cell separator 120 is a rectangular frame-like member having a substantially rectangular through-hole 121 near the center, and is made of, for example, metal. The plate thickness of the single cell separator 120 is relatively thin, for example, not less than 0.05 mm and not more than 0.2 mm. The peripheral portion of the through-hole 121 in the single cell separator 120 is joined to the peripheral portion of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is disposed: the upper surface in Figures 4 and 5) with a sealant 124. The sealant 124 is made of, for example, a brazing material (Ag brazing).

[0027] (Air electrode frame 130) 4 and 5, the cathode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made of, for example, insulating ceramics (mica, etc.). The thickness of the cathode frame 130 is preferably 0.5 mm or more and 5 mm or less.

[0028] (fuel electrode frame 140) As shown in FIG. 5, the fuel electrode frame 140 is a rectangular frame-like member having a substantially rectangular through-hole 141 near the center, and is made of, for example, metal.

[0029] (IC separator 180) As shown in FIGS. 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center, and is made of metal.

[0030] (Interconnector 190 and anode current collecting member 144) 4 and 5, the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-like air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are electrically conductive and made of a metal (e.g., ferritic stainless steel). The coating layer 193 is electrically conductive and is disposed so as to cover the surface of the air electrode current collector 192 and the surface of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0031] The anode current collecting member 144 is a member that connects the interconnector 190 and the anode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 4 and 5, the anode current collecting member 144 has an interconnector facing portion 146, an electrode facing portion 145 that is parallel to the interconnector facing portion 146, and a connecting portion 147 that connects the electrode facing portion 145 and the interconnector facing portion 146, and has an overall U-shape. The electrode facing portion 145 is in contact with the anode 116, and the interconnector facing portion 146 is in contact with a flat portion 191 of the interconnector 190.

[0032] As described above, the interconnector 190 is shared by two adjacent reaction units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collecting part 192 is joined to the air electrode 114 of the unit cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, and is thereby electrically connected to the air electrode 114. The flat plate part 191 is electrically connected to the anode 116 of the unit cell 110 provided in the other of the two adjacent reaction units 100U via an anode current collecting member 144. This ensures electrical continuity between the two adjacent reaction units 100U.

[0033] However, as described above, the reaction unit 100U located at one end (the lower end in FIG. 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 included in this reaction unit 100U is connected to the second terminal plate 250 via the fuel electrode current collecting member 144.

[0034] A spacer 149 made of, for example, mica is disposed between the electrode facing portion 145 and the interconnector facing portion 146. This allows the anode current collecting member 144 to follow deformation of the reaction unit 100U due to temperature cycles and fluctuations in reactant gas pressure, and good electrical connection between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144 is maintained.

[0035] (Air chamber 313 and fuel chamber 323) 4 and 5, the space partitioned by the single cell separator 120, single cell 110, air electrode frame 130, IC separator 180, and interconnector 190 faces the air electrode 114 and serves as an air chamber 313 through which oxidant gas OG flows. The air electrode frame 130 partitions the entire periphery of the air chamber 313 from the external space and seals the gap between the single cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 to the external space.

[0036] The space partitioned by the single cell separator 120, the single cell 110, the fuel electrode frame 140, the IC separator 180, and the interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the entire periphery of the fuel chamber 323 from the external space, and seals the gap between the single cell separator 120 and the IC separator 180, thereby preventing gas from leaking from the fuel chamber 323 to the external space.

[0037] The single cell separator 120 separates the air chamber 313 and the fuel chamber 323, thereby preventing gas leakage (cross leakage) from the air electrode 114 side to the fuel electrode 116 side or from the fuel electrode 116 side to the air electrode 114 side around the single cell 110. In addition, the IC separator 180 and the interconnector 190 prevent gas leakage between adjacent reaction units 100U.

[0038] (First end plate 210) The first end plate 210 is a member formed by pressing (bending) a single plate-like member. The first end plate 210 is formed of a metal such as stainless steel. As shown in FIGS. 1 to 3 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is formed around the entire outer periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is formed around the entire inner periphery of the flat portion 211.

[0039] (insulating part 220) Insulating portion 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of an insulating material such as crystallized glass or insulating ceramics such as mica or forsterite. As shown in Fig. 2, insulating portion 220 is sandwiched between first end plate 210 and terminal separator 230, thereby ensuring insulation between first end plate 210 and terminal separator 230.

[0040] (Terminal separator 230) As shown in FIGS. 2 and 3, the terminal separator 230 is a rectangular frame-shaped member having a through-hole 231 near the center, and is made of, for example, metal.

[0041] (First Plate 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined by welding, for example, to the periphery of the through-hole 231 in the terminal separator 230. The terminal separator 230 and the first plate 232 separate the power generating block 100 from the external space of the fuel cell stack 10.

[0042] The first plate 232 is connected to an interconnector 190 (described later) provided in a reaction unit 100U arranged at one end (the upper end in Figure 2) of the multiple reaction units 100U that make up the power generation block 100, via a connecting member having the same structure as the anode current collecting member 144 (described later), thereby electrically connecting this reaction unit 100U and the first plate 232.

[0043] (First terminal plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through-hole 241 near the center, and is made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. The first terminal plate 240 is electrically connected to the reaction unit 100U arranged at one end (the upper end in FIG. 2) of the multiple reaction units 100U that make up the power generation block 100 via a first plate 232 and a terminal separator 230. One end (the right end in FIG. 2) of the first terminal plate 240 protrudes laterally from the power generation block 100, and this protruding portion functions as a positive output terminal for the fuel cell stack 10.

[0044] (2nd terminal plate 250) The second terminal plate 250 is a rectangular plate-shaped member made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. The second terminal plate 250 is electrically connected to the reaction unit 100U that is arranged at the other end (the lower end in FIG. 2) of the multiple reaction units 100U that make up the power generation block 100. One end (the right end in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0045] (Second plate 260) Second plate 260 is a rectangular, flat member made of, for example, an insulating material. The peripheral edge of second plate 260 is sandwiched between second terminal plate 250 and second end plate 270, thereby ensuring insulation between second terminal plate 250 and second end plate 270.

[0046] (Second end plate 270) The second end plate 270 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel. The second end plate 270 has a rectangular, frame-like flat portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the flat portion 271 in the direction opposite to the second terminal plate 250 (downward in FIG. 2). The flat portion 271 has holes that form the bolt holes BH described above. The outer convex portion 273 protrudes from the outer periphery of the flat portion 271. The outer convex portion 273 is formed around the entire outer periphery of the flat portion 271. The inner convex portion 274 protrudes from the inner periphery of the flat portion 271. The inner convex portion 274 is formed around the entire inner periphery of the flat portion 271.

[0047] (Manifolds 311, 312, 321, 322) 1, 2, and 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are an oxidant gas supply manifold 311, an oxidant gas discharge manifold 312, a fuel gas supply manifold 321, and a fuel gas discharge manifold 322, respectively.

[0048] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies an oxidant gas OG introduced from outside the fuel cell stack 10 to an air chamber 313 (described later) of each reaction unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges an oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the outside of the fuel cell stack 10. As the oxidant gas OG, for example, air is used.

[0049] 3, the fuel gas supply manifold 321 is a gas flow path that supplies fuel gas FG introduced from outside the fuel cell stack 10 to a fuel chamber 323 (described later) of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, a hydrogen-rich gas obtained by reforming city gas is used.

[0050] (Gas passage member 280) As shown in FIGS. 1 to 3 , each of the four gas passage members 280 includes a main body portion 281 and a flange portion 282. The main body portion 281 has a gas through hole 283 that penetrates in the vertical direction. The flange portion 282 is provided so as to protrude outward from the other end (the lower end in FIG. 2 ) of the main body portion 281. The flange portion 282 has a plurality of bolt holes 284. A bolt (not shown) for connecting the fuel cell stack 10 to an external device is inserted into each bolt hole 284. One end (the upper end in FIGS. 2 and 3 ) of the main body portion 281 included in each of the four gas passage members 280 is joined to the second end plate 270 by, for example, welding, and the gas through hole 283 communicates with the manifolds 311, 312, 321, and 322, respectively. A gas pipe (not shown) for supplying or discharging gas is connected to each of the main body portions 281.

[0051] A-2. Operation of fuel cell stack 10: 2, the oxidizing gas OG is supplied to the air chamber 313 through the gas passage member 280 and the oxidizing gas supply manifold 311. Also, as shown in FIG. 3, the fuel gas FG is supplied to the fuel chamber 323 through the gas passage member 280 and the fuel gas supply manifold 321.

[0052] When an oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and the fuel gas FG. This power generation reaction is exothermic. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures electrical continuity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, a second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end in FIG. 2 ) of the multiple reaction units 100U, and a first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end in FIG. 2 ). As a result, electrical energy generated in each reaction unit 100U is extracted from the terminal plates 240, 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (e.g., 700°C to 1000°C), after startup, the fuel cell stack 10 may be heated by a heater (not shown) until the high temperature can be maintained using the heat generated by power generation.

[0053] 2, the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidant gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in FIG. 3, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0054] A-3. Detailed configuration of fuel electrode 116: The detailed configuration of the fuel electrode 116 is as follows: Fig. 6 shows an enlarged XZ cross-sectional configuration of a portion (frame F in Fig. 5) of the fuel electrode 116 (active layer).

[0055] As described above, the anode 116 contains an ion-conductive material (in this embodiment, YSZ, which is a ceramic) and an electron-conductive material (in this embodiment, Ni, which is a transition metal). Fig. 6 schematically shows YSZ particles Py as particles of the ion-conductive material contained in the active layer, Ni particles Pn as particles of the electron-conductive material, and pores Po.

[0056] The meanings of the terms used in the following description are as follows: "Specific cross section of unit cell 110": any cross section parallel to the vertical direction of unit cell 110 (including at least the active layer of electrolyte layer 112 and fuel electrode 116; for example, the XZ cross section shown in FIG. 6). By cutting unit cell 110 (a button cell described later) and photographing the cut surface including electrolyte layer 112 and fuel electrode 116 with an FIB-SEM (acceleration voltage 15 kV), an SEM image (for example, 5000x magnification) of the specific cross section can be obtained. The "specific region T" is a region in the anode 116 after reduction treatment. The specific region T is a region extending 5 μm downward (opposite the electrolyte layer 112) from the interface M between the electrolyte layer 112 and the anode 116. The specific region T can be identified from the SEM image of the specific cross section. The specific region T is located mainly within the active layer of the anode 116. The "interface M" is defined as the position of the bottom end of a relatively large YSZ particle Py contained in the electrolyte layer 112 in the SEM image of the specific cross section (see FIG. 6).

[0057] In a specific cross section of the unit cell 110, a specific region T in the fuel electrode 116 satisfies the following first condition. <First condition> The interparticle distance of the ion-conductive material (YSZ particles Py) is 1.4 μm or less. The interparticle distance of the ion-conductive material is the distance between two adjacent particles of the ion-conductive material.

[0058] The interparticle distance of the ion-conductive material is determined as follows. As shown in FIG. 6, five imaginary lines L1 to L5 are drawn downward from the interface M at 1 μm intervals in a specific region T in an SEM image of a specific cross section. All five imaginary lines L1 to L5 are parallel to the interface M. For each of the five imaginary lines L1 to L5, all line segments (hereinafter referred to as "first line segments") located between two adjacent particles of the ion-conductive material are extracted. For example, line segment D1 of imaginary line L5 in FIG. 6 is a first line segment. The average length of all the first line segments extracted from the five imaginary lines L1 to L5 is determined to be the interparticle distance of the ion-conductive material.

[0059] Note that temperature variations may occur along the flow direction of the fuel gas FG in the fuel chamber 323 of the unit cell 110, which may result in differences in the degree of progress of aggregation of the electron conductive material in the fuel electrode 116. For this reason, the interparticle distances of the ion conductive material in the specific regions T may be calculated for each of three locations on the fuel electrode 116, namely, the upstream side, downstream side, and center side of the fuel gas FG, and the average value of these values ​​may be used as the interparticle distance of the ion conductive material.

[0060] In a specific cross section of the unit cell 110, the specific region T in the fuel electrode 116 preferably satisfies the following second condition. <Second condition> The distance between particles of the ion-conductive material is 0.3 μm or more.

[0061] In a specific cross section of the unit cell 110, the specific region T in the fuel electrode 116 preferably satisfies the following third condition. <Third condition> The particle diameter of the ion-conductive material is 0.4 μm or more and 0.8 μm or less. The particle diameter of the ion-conductive material is determined as follows. As shown in FIG. 6, in an SEM image of a specific cross section, for each of five virtual lines L1 to L5, all line segments (hereinafter referred to as "second line segments") that overlap with particles of the ion-conductive material are extracted. For example, line segment D2 of virtual line L5 is a second line segment. The average length of all the second line segments extracted from the five virtual lines L1 to L5 is determined to be the particle diameter of the ion-conductive material.

[0062] In a specific cross section of the unit cell 110, the specific region T in the fuel electrode 116 preferably satisfies the following fourth condition. <Fourth condition> The volume fraction of the ion-conductive material is 0.4 or more and 0.6 or less. The volume fraction of the ion-conductive material means the ratio of the volume of the ion-conductive material within a specific region. The volume fraction of the ion-conductive material is determined as follows: In an SEM image of a specific cross section, second line segments are extracted for each of five virtual lines L1 to L5, and the total length of one or more extracted second line segments (hereinafter simply referred to as the "total value of second line segments") is calculated. The ratio of the total value of the second line segments to the total length of each virtual line in the specific region T (= (total value of second line segments) / (total length of each virtual line) hereinafter referred to as the "second line segment ratio") is calculated. The average value of the five second line segment ratios calculated for each of the five virtual lines L1 to L5 is determined to be the volume fraction of the ion-conductive material.

[0063] A-4. Manufacturing method of the unit cell 110: An example of a method for manufacturing the unit cell 110 in this embodiment is as follows.

[0064] (Preparation of Green Sheet for Electrolyte Layer 112) Butyral resin, a plasticizer (DOP, dioctyl phthalate), a dispersant, and a mixed solvent of toluene and ethanol are added to the YSZ powder and mixed in a ball mill to prepare a slurry. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for the electrolyte layer 112 with a predetermined thickness (for example, about 10 μm).

[0065] (Preparation of Green Sheet for Support Layer of Fuel Electrode 116) A mixture of NiO powder and YSZ powder is mixed with organic beads (a pore former), butyral resin, DOP (a plasticizer), a dispersant, and a mixed solvent of toluene and ethanol in a ball mill to prepare a slurry. The organic beads are spherical particles formed from a polymer such as polymethyl methacrylate or polystyrene. The resulting slurry is thinned using a doctor blade method to prepare a green sheet for a support layer with a predetermined thickness (e.g., approximately 200 μm). The mixing ratio of the NiO powder and the YSZ powder when preparing the green sheet for the support layer may be appropriately set as long as the performance is satisfied. The mixed powder used to prepare the slurry contains, for example, 50 parts by weight of NiO powder and 50 parts by weight of YSZ powder per 100 parts by weight of the mixed powder. The amount of organic beads added to the mixed powder is, for example, 15 parts by weight per 100 parts by weight of the mixed powder.

[0066] (Preparation of green sheet for active layer of fuel electrode 116) A butyral resin, DOP (a plasticizer), a dispersant, and a mixed solvent of toluene and ethanol are added to a mixed powder of NiO powder and YSZ powder, and the mixture is mixed in a ball mill to prepare a slurry. As with the method for preparing the green sheet for the support layer described above, organic beads may be added as a pore-forming material when preparing the slurry. The resulting slurry is thinned using a doctor blade method to prepare a green sheet for the active layer having a predetermined thickness (e.g., approximately 20 μm). The mixing ratio of the NiO powder and the YSZ powder when preparing the green sheet for the active layer may be appropriately set as long as the performance is satisfied. For example, the mixed powder used to prepare the slurry contains 50 parts by weight of NiO powder and 50 parts by weight of YSZ powder per 100 parts by weight of the mixed powder. In this embodiment, no organic beads are added to the mixed powder.

[0067] Here, the interparticle distance of the YSZ particles Py in the fuel electrode 116 after the reduction treatment can be adjusted, for example, by the following method. In the above manufacturing stage, if the particle diameter (e.g., median diameter (D50)) of the YSZ powder is increased without changing the amount (wt %) of YSZ powder mixed in the mixed powder, the interparticle distance of the YSZ particles Py will be shortened. If the amount (wt %) of YSZ powder mixed in the mixed powder is increased without changing the particle diameter (e.g., median diameter) of the YSZ powder, the interparticle distance of the YSZ particles Py will be shortened. The volume fraction of the YSZ particles Py in the fuel electrode 116 after the reduction treatment can be adjusted by changing the amount (wt %) of YSZ powder mixed.

[0068] (Fabrication of a laminate of the electrolyte layer 112 and the fuel electrode 116) A green sheet laminate is fabricated by bonding together the green sheet for the support layer, the green sheet for the active layer, and the green sheet for the electrolyte layer 112. At this time, the green sheet for the active layer is positioned between the green sheet for the electrolyte layer 112 and the green sheet for the support layer. By fabricating the green sheet laminate in the above manner, the green sheet laminate is prepared.

[0069] Next, the green sheet laminate is degreased at a predetermined temperature (e.g., about 280°C). Furthermore, the degreased green sheet laminate is fired at a predetermined temperature (e.g., about 1350°C) for a predetermined time (e.g., about 1 hour). This produces a sintered body including an electrolyte layer 112 formed from the green sheets for the electrolyte layer 112, an active layer formed from the green sheets for the active layer, and a support layer formed from the green sheets for the support layer. In other words, a laminate of the electrolyte layer 112 and the fuel electrode 116 is produced.

[0070] (Formation of reaction prevention layer 118) Polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent are added to and mixed with GDC powder, and the viscosity is adjusted to prepare an intermediate layer paste. The adjusted intermediate layer paste is applied by screen printing, for example, to the surface of the electrolyte layer 112 side of the laminate of the electrolyte layer 112 and the fuel electrode 116, and then fired at, for example, 1200°C. This forms the reaction prevention layer 118.

[0071] (Formation of the air electrode 114) An air electrode paste is prepared by mixing LSCF powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent, and adjusting the viscosity. The prepared air electrode paste is applied to the surface of the reaction prevention layer 118 of the laminate by, for example, screen printing and dried. The laminate with the applied air electrode paste is then fired at a predetermined firing temperature (e.g., approximately 1100°C). This forms the air electrode 114. After the formation of the air electrode 114, a reduction treatment is performed in a reducing gas atmosphere (e.g., a hydrogen gas atmosphere) at a predetermined temperature (e.g., 700°C) to reduce NiO to Ni, resulting in the production of a single cell 110 including the fuel electrode 116, electrolyte layer 112, and air electrode 114.

[0072] A-5. Advantages of this embodiment: As described above, the unit cell 110 of this embodiment includes the anode 116, the electrolyte layer 112, and the cathode 114. The anode 116 includes an ion-conductive material (in this embodiment, YSZ, which is a ceramic) and an electron-conductive material (in this embodiment, Ni, which is a transition metal). In a specific cross section parallel to the vertical direction, in a specific region T of the anode 116, the interparticle distance of the ion-conductive material (YSZ particles Py) is 1.4 μm or less (first condition).

[0073] This configuration can suppress aggregation of the electronically conductive material in the anode 116, compared to a configuration in which the specific region T does not satisfy the first condition. That is, in this configuration, the distance between particles of the ionically conductive material is relatively narrow, and therefore there are few particles of the electronically conductive material adjacent to each other. Therefore, during long-term operation of the unit cell 110, the electronically conductive material is less likely to enter between particles of the ionically conductive material, and aggregation of the electronically conductive material is less likely to progress.

[0074] In this configuration, it is further preferable that, in the specific cross section, the interparticle distance of the ion-conductive material in the specific region T of the anode 116 is 0.3 μm or more (second condition). With this configuration, it is possible to suppress the aggregation of the electron-conductive material in the anode 116 while suppressing the deterioration of the initial characteristics of the unit cell 110, compared to a configuration in which the specific region T does not satisfy the second condition. That is, if the interparticle distance of the ion-conductive material is too narrow, the movement of electrons by the electron-conductive material in the anode 116 may be inhibited. In contrast, in this configuration, the interparticle distance of the ion-conductive material is 0.3 μm or more, and a reaction field is secured in the anode 116. This suppresses the inhibition of electron movement, thereby suppressing the deterioration of the initial characteristics of the unit cell 110.

[0075] A-6. Performance evaluation: Next, performance evaluation of this embodiment will be described. A plurality of single cell 110 samples (button cells, which will be described in detail later) having fuel electrodes 116 with different interparticle distances of the ion-conductive material (YSZ particles Py) were fabricated, and performance evaluation was performed using the samples.

[0076] (Performance evaluation method for single cell 110) In this performance evaluation, instead of the single cell 110, multiple button cells having the same basic configuration (materials, etc.) as the single cell 110 were used. Each sample (button cell) had a cathode 114 that was circular when viewed from above formed on a laminate including a fuel electrode 116 and an electrolyte layer 112 that were rectangular when viewed from above.

[0077] First, the initial performance of each sample (i.e., the output voltage before the durability test described below) was evaluated. For each sample, a reduction treatment was performed by supplying fuel gas FG (hydrogen) to the fuel electrode 116 at approximately 850°C for 3 hours. Thereafter, for each sample, an oxidant gas OG was supplied to the air electrode 114 and a fuel gas FG (hydrogen) was supplied to the fuel electrode 116 at approximately 850°C, and a current density of 0.55 A / cm was applied. 2 The output voltage of the single cell 110 was measured at this time. The output voltage value at this time was taken as the initial voltage V I Then, the initial voltage V I However, samples that were 0.9V or higher were classified as "particularly good (A)", samples that were less than 0.9V and greater than 0.8V were classified as "good (B)", and samples that were 0.8V or lower were classified as "fail (C)".

[0078] The initial voltage V of each sample I After the measurement, a durability test was performed on each sample by continuously operating it at 850°C for 600 hours. At that time, an oxidant gas OG was supplied to the air electrode 114, a fuel gas FG was supplied to the fuel electrode 116, and a current density was 0.55 A / cm. 2 After that, the output voltage of the samples after the durability test was measured under the same conditions as the initial performance evaluation, and the initial voltage V I The voltage drop rate (%) was calculated, which indicates the degree of drop in output voltage relative to the voltage V after use. E When (V I -V E ) / V I × 100%. Samples with a voltage drop rate of 5% or less were rated as "particularly good (A)", samples with a voltage drop rate of more than 5% but less than 10% were rated as "good (B)", and samples with a voltage drop rate of 10% or more were rated as "fail (C)".

[0079] (Performance evaluation results for single cell 110) Fig. 7 is an explanatory diagram showing the performance evaluation results. Samples S1 to S8 shown in Fig. 7 are different from one another in at least one of the interparticle distance of the ion-conductive material ("YSZ interparticle distance" in Fig. 7), the particle size of the ion-conductive material ("YSZ particle size" in Fig. 7), and the volume fraction of the ion-conductive material ("YSZ volume fraction" in Fig. 7).

[0080] As described above, the inter-YSZ distance can be adjusted by changing at least one of the particle diameter of the YSZ powder during the button cell manufacturing process ("Slurry D50" in FIG. 7) and the amount of YSZ powder mixed with respect to the mixed powder ("YSZ weight" in FIG. 7). For example, samples S1 to S3 have the same YSZ weight and approximately the same slurry D50, and therefore approximately the same inter-YSZ distance. Samples S4 and S7 have the same YSZ weight but different slurry D50. The inter-YSZ distance of sample S4, which has a large slurry D50, is shorter than that of sample S7, which has a small slurry D50. Samples S4 and S6 have the same slurry D50 but different YSZ weights. The inter-YSZ distance of sample S6, which has a large YSZ weight, is shorter than that of sample S4, which has a small YSZ weight.

[0081] The YSZ volume fraction can be adjusted by changing the weight of YSZ. For example, in samples S3 to S6, the greater the YSZ weight, the higher the YSZ volume fraction.

[0082] In the evaluation of the voltage drop rate, samples S1 to S6 were rated "particularly good (A)" or "good (B)," while samples S7 and S8 were rated "fail (C)." These evaluation results show that if the YSZ distance is 1.4 μm or less (first condition), Ni agglomeration during button cell operation is suppressed, and voltage drop (performance degradation) of the button cell can be suppressed. Furthermore, samples S1 to S3, S5, and S6 were rated "particularly good (A)," while sample S4 was rated "good (B)." These evaluation results show that if the YSZ distance is 1.1 μm or less, voltage drop (performance degradation) of the button cell can be more effectively suppressed.

[0083] Initial voltage V I In the evaluation, among samples S1 to S6, samples S1 to S5 were evaluated as "particularly good (A)" or "good (B)", and sample S6 was evaluated as "fail (C)". From this evaluation result, it can be seen that if the YSZ distance is 0.3 μm or more (second condition), a reaction field is secured in the fuel electrode 116, and the initial voltage V of the button cell is I It can be seen that the deterioration of the (initial characteristics) can be suppressed.

[0084] Initial voltage V I In the evaluation, samples S1 to S5 and S7 were evaluated as "particularly good (A)" or "good (B)", while samples S6 and S8 were evaluated as "fail (C)". From this evaluation result, it can be seen that if the YSZ particle diameter is 0.4 μm or more and 0.8 μm or less (third condition), a reaction field is secured in the fuel electrode 116, and the initial voltage V of the button cell is I It can be seen that the decrease in voltage (initial characteristics) can be suppressed. In addition, samples S1 to S3 were rated as "particularly good (A)," and samples S4, S5, and S7 were rated as "good (B)." These evaluation results show that if the YSZ particle diameter is 0.47 μm or more and 0.73 μm or less, the voltage drop (performance decrease) of the button cell can be more effectively suppressed.

[0085] Initial voltage V IIn the evaluation, samples S1 to S5 and S7 were evaluated as "particularly good (A)" or "good (B)", while samples S6 and S8 were evaluated as "fail (C)". From this evaluation result, it can be seen that if the YSZ volume fraction is 0.4 or more and 0.6 or less (fourth condition), the reaction field in the fuel electrode 116 is secured, and the initial voltage V of the button cell is I It can be seen that the decrease in voltage (initial characteristics) can be suppressed. In addition, samples S1 to S3 were evaluated as "particularly good (A)," and samples S4, S5, and S7 were evaluated as "good (B)." These evaluation results show that if the YSZ volume fraction is 0.45 or more and 0.55 or less, the voltage decrease (performance decrease) of the button cell can be more effectively suppressed.

[0086] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit thereof, for example, the following modifications are also possible.

[0087] In the above embodiment, the specific region T satisfies the first condition in any specific cross section of the anode 116. However, the specific region T may also satisfy the first condition in at least one cross section parallel to the vertical direction of the anode 116. In addition, in the above embodiment, the specific region T does not have to satisfy at least one of the second to fourth conditions. The second condition in the above embodiment may be that the YSZ distance is 0.5 μm or more.

[0088] In the above embodiment, the fuel cell stack 10 is configured to include a plurality of flat-plate type unit cells 110, but the electrochemical reaction cell stack may also include other types of unit cells (for example, cylindrical, flat cylindrical).

[0089] In the above embodiment, the electrochemical reaction cell stack is a cell stack used in a solid oxide fuel cell (SOFC). However, the above configuration is also applicable to cell stacks used in other types of fuel cells such as a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), and a molten carbonate fuel cell (MCFC), or to an electrolysis cell stack having, as a single cell, an electrolysis cell unit, which is a constituent unit of a solid oxide electrolysis cell (SOEC). [Explanation of symbols]

[0090] 10: Fuel cell stack 100: Power generation block 100U: Reaction unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Anode 118: Reaction prevention layer 120: Single cell separator 124: Sealing material 130: Air electrode frame 140: Anode frame 144: Anode current collecting member 145: Electrode opposing portion 146: Interconnector opposing portion 147: Connection portion 149: Spacer 180: IC separator 190: Interconnector 191: Flat plate portion 192: Air electrode current collecting portion 193: Coating layer 196: Conductive bonding material 210: First end plate 220: Insulating portion 230: Terminal separator 232: First plate 240, 250: Terminal plate 240: First terminal plate 250: Second terminal plate 260: Second plate 270: Second end plate 280: Gas passage member 281: Main body portion 282: Flange portion 283: Gas through hole 311: Oxidant gas supply manifold 312: Oxidant gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber B: Bolt M: Interface N: Nut Pn: Ni particles Po: Pores Py: YSZ particles T: Specific region

Claims

1. an electrolyte layer; a cathode disposed on one side of the electrolyte layer in a first direction; an anode disposed on the other side of the electrolyte layer in the first direction, the anode including an ion-conductive material and an electron-conductive material; In an electrochemical reaction unit cell comprising: an electrochemical reaction unit cell, characterized in that, in at least one cross section of the anode parallel to the first direction, a specific region extending from an interface between the electrolyte layer and the anode to a distance of 5 μm on the other side in the first direction satisfies a first condition that an interparticle distance of the ion conductive material is 1.4 μm or less.

2. 2. The electrochemical reaction unit cell according to claim 1, The electrochemical reaction unit cell is characterized in that the specific region further satisfies a second condition that the interparticle distance of the ion conductive material is 0.3 μm or more.

3. 3. The electrochemical reaction unit cell according to claim 1 or 2, The electrochemical reaction unit cell is characterized in that the specific region further satisfies a third condition that the particle diameter of the ion-conductive material is 0.4 μm or more and 0.8 μm or less.

4. 3. The electrochemical reaction unit cell according to claim 1 or 2, The electrochemical reaction unit cell is characterized in that the specific region further satisfies a fourth condition that the volume ratio of the ion-conductive material is 0.4 or more and 0.6 or less.

5. In an electrochemical reaction cell stack including a plurality of electrochemical reaction unit cells arranged side by side in the first direction, 3. An electrochemical reaction cell stack, wherein at least one of the plurality of electrochemical reaction unit cells is the electrochemical reaction unit cell according to claim 1 or 2.

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