Electrochemical reaction cell stack

Abstract

To suppress the occurrence of cracks around an oxide film in an electrochemical reaction cell stack.SOLUTION: An electrochemical reaction cell stack includes a single cell, a metal member, an oxide film formed on a surface of the metal member and containing Ti, and an insulating member disposed between the single cell or a conductive member electrically connected to the single cell and the oxide film. When a TiO2 voltage is applied between the metallic member and the single cell or an electrically conductive member electrically connected to the single cell at 700 °C for 200 hours, an absolute difference between a TiO2 abundance ratio after the voltage application and a TiO2 abundance ratio before the voltage application is 0.3 or less, where the 20V abundance ratio is a value obtained by dividing a TiO2 content in the oxide film by a total value of a TiO content and the TiO2 content.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to electrochemical reaction cell stacks. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs") are known as one type of fuel cell that generates electricity by utilizing an electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack. Conventionally, a cell stack has been known that includes a plurality of fuel cell units, a manifold made of an alloy material containing Cr, and a glass seal member that joins the fuel cell units and the manifold (see, for example, Patent Document 1).

[0003] As described above, a fuel cell stack includes a unit cell, a metal member, and an insulating member. The fuel cell stack may further include an oxide film containing Ti formed on the surface of the metal member. In such a fuel cell stack, the insulating member is disposed between the unit cell or a conductive member electrically connected to the unit cell and the oxide film formed on the surface of the metal member. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-107593 Summary of the Invention [Problem to be solved by the invention]

[0005] Because an insulating member is interposed between the oxide film and a single cell or a conductive member electrically connected to the single cell, a relatively large electric field is generated, for example, when a fuel cell stack generates electricity. If the current flowing through the single cell leaks through the insulating member to the oxide film containing Ti, the ratio of TiO to TiO2 in the oxide film may change due to a change in the valence of Ti. If the ratio of TiO to TiO2 changes, the volume of the oxide film changes, causing cracks in the oxide film or at the interface between the oxide film and other components, which may eventually lead to peeling between the oxide film and other components.

[0006] Note that these issues are also common to electrolysis cell stacks, which are a type of electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen using the electrolysis reaction of water. In this specification, a single fuel cell cell and a single electrolysis cell are collectively referred to as a single cell, and a fuel cell stack and an electrolysis cell stack are collectively referred to as an electrochemical reaction cell stack. Furthermore, these issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

[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 cell stack disclosed in this specification comprises a unit cell, a metal member, an oxide film containing Ti formed on the surface of the metal member, the unit cell or a conductive member electrically connected to the unit cell, and an insulating member disposed between the oxide film. When the TiO2 abundance ratio is defined as the value obtained by dividing the TiO2 content in the oxide film by the sum of the TiO2 content and the TiO2 content, when a voltage of 20 V is applied between the metal member and the unit cell or the conductive member electrically connected to the unit cell at 700°C for 200 hours, the absolute value of the difference between the TiO2 abundance ratio before and after voltage application is 0.3 or less.

[0010] With this electrochemical reaction cell stack, when a voltage of 20 V is applied for 200 hours at 700°C, the absolute value of the difference between the abundance ratio of TiO2 after the voltage application and the abundance ratio of TiO2 before the voltage application is 0.3 or less. In other words, by suppressing the conversion between TiO and TiO2, for example, it is possible to suppress changes in the volume of the oxide film that accompany changes in the ratio of TiO to TiO2 in the oxide film, and to suppress the occurrence of cracks in the oxide film or at the interface between the oxide film and other components.

[0011] (2) In the electrochemical reaction cell stack, the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application may be 0.1 or less. According to this configuration, the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application is 0.1 or less. In other words, for example, by suppressing conversion between TiO and TiO2, it is possible to suppress changes in the volume of the oxide film that accompany changes in the ratio of TiO to TiO2 in the oxide film, and more effectively suppress the occurrence of cracks in the oxide film or at the interface between the oxide film and other components.

[0012] (3) In the electrochemical reaction cell stack, the oxide film may contain at least one of Al and Cr. According to this configuration, when the metal member contains a metal such as Fe, the Al or Cr contained in the oxide film can suppress oxidation of the metal in the metal member, thereby suppressing oxidation of the metal member.

[0013] (4) In the electrochemical reaction cell stack, the metal member may contain 0.05 mass % or more of Ti. According to this configuration, when the metal member contains other metals such as Fe, Ti contained in the metal member and having a relatively high ionization tendency can suppress oxidation of the other metals in the metal member, and thus can suppress oxidation of the metal member itself.

[0014] (5) In the electrochemical reaction cell stack, the insulating member may be made of crystallized glass. With this configuration, since the insulating member is made of crystallized glass, it is possible to ensure both insulation between the oxide film and the single cell or a conductive member electrically connected to the single cell, and bonding between the insulating member and the oxide film.

[0015] The technology disclosed in this specification can be realized in various forms, for example, in the form of an electrochemical reaction cell stack, a manufacturing method thereof, or the like. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack 10 according to an embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram showing the XZ cross-sectional configuration of the fuel cell stack 10 taken along the line II-II in FIG. 1. [Figure 3] FIG. 3 is an explanatory diagram showing the XZ cross-sectional configuration of the fuel cell stack 10 taken along the line III-III in FIG. 1. [Figure 4] FIG. 4 is an explanatory diagram showing the YZ cross-sectional configuration of the fuel cell stack 10 taken along the line IV-IV in FIG. [Figure 5]FIG. 3 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generating units 100U at the same position as the cross-section shown in FIG. 2. [Figure 6] FIG. 4 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generating units 100U at the same position as the cross-section shown in FIG. 3. [Figure 7] FIG. 7 is an explanatory diagram showing an enlarged XZ cross-sectional configuration of the X1 portion of FIG. 6. [Figure 8] FIG. 4 is an explanatory diagram showing an enlarged XZ cross-sectional configuration of the X2 portion of FIG. 3. [Figure 9] Top view of the test piece [Figure 10] Cross-sectional view of the test piece at position XX in Figure 9 DETAILED DESCRIPTION OF THE INVENTION

[0017] A. Implementation: A-1. Configuration of fuel cell stack 10: FIG. 1 is a perspective view showing the external configuration of a fuel cell stack 10 according to this embodiment. FIG. 2 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 10 taken along line II-II in FIG. 1 . FIG. 3 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 10 taken along line III-III in FIG. 1 . FIG. 4 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 10 taken along line IV-IV in FIG. 1 . Each figure shows mutually orthogonal X, Y, and Z axes for identifying directions. For convenience, the Z-axis direction will be referred to as the up-down direction, the positive Z-axis direction as the up-down direction, and the negative Z-axis direction as the down-down direction in this specification. However, the fuel cell stack 10 may actually be installed in an orientation different from these orientations. The fuel cell stack 10 is an example of an electrochemical reaction cell stack as defined in the claims.

[0018] (Overall configuration of fuel cell stack 10) 1 to 4, 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 a stacked manner in this order in a predetermined arrangement direction (vertical direction).

[0019] As shown in FIGS. 1 and 4, 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 to 4, 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.

[0020] As shown in FIGS. 2 to 4, the power generation block 100 is made up of a plurality of (seven in this embodiment) power generation units 100U arranged side by side in a predetermined arrangement direction (vertical direction).

[0021] (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 and contains 0.05% or more by mass of Ti. As will be described in detail later, an oxide film OM2 is formed on the surface of the first end plate 210 (see FIG. 8). As shown in FIGS. 1 to 4, the first end plate 210 includes a rectangular, frame-shaped flat portion 211 having a through-hole 212 near the center, and outer and inner protrusions 213 and 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 protrusion 213 protrudes from the outer periphery of the flat portion 211. The outer protrusion 213 is formed around the entire periphery of the flat portion 211. The inner protrusion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is formed along the entire inner periphery of the flat portion 211. The first end plate 210 is an example of a metal member defined in the claims.

[0022] (insulating part 220) Insulating portion 220 is a rectangular frame-shaped member with a through-hole near the center, and is formed from 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. Insulating portion 220 is an example of an insulating member defined in the claims.

[0023] (Terminal separator 230) 2 to 4, 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. The terminal separator 230 is an example of a conductive member in the claims.

[0024] (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 to 4, the first plate 232 is joined, for example, by welding, to the peripheral portion of the through-hole 231 in the terminal separator 230. The terminal separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0025] The first plate 232 is connected to an interconnector 190 (described later) provided in a power generation unit 100U arranged at one end (the upper end in Figure 2) of the multiple power generation 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 the power generation unit 100U and the first plate 232.

[0026] (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 power generating unit 100U located at one end (the upper end in FIG. 2) of the multiple power generating units 100U that make up the power generating 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 generating block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0027] (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 has an alumina oxide coating on its surface. The second terminal plate 250 is electrically connected to the power generating unit 100U that is located at the other end (the lower end in FIG. 2) of the multiple power generating units 100U that make up the power generating block 100. One end (the right end in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generating block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0028] (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.

[0029] (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.

[0030] (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.

[0031] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies the oxidant gas OG introduced from outside the fuel cell stack 10 to an air chamber 313 (described later) of each power generating unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges the oxidant off-gas OOG discharged from the air chamber 313 of each power generating unit 100U to the outside of the fuel cell stack 10. For example, air is used as the oxidant gas OG. The oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312 are arranged on opposite sides of the air chamber 313.

[0032] As shown in Fig. 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 power generating 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 power generating unit 100U to the outside of the fuel cell stack 10. For example, hydrogen-rich gas obtained by reforming city gas is used as the fuel gas FG. The fuel gas supply manifold 321 and the fuel gas discharge manifold 322 are arranged on opposite sides of the fuel chamber 323.

[0033] (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.

[0034] (Overall configuration of 100U power generation unit) Fig. 5 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generating units 100U at the same position as the cross-section shown in Fig. 2. Fig. 6 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generating units 100U at the same position as the cross-section shown in Fig. 3. As shown in Figs. 5 and 6, the power generating unit 100U includes a single cell 110, a single cell separator 120, an air electrode frame 130, a glass seal portion 135, an anode frame 140, an anode current collecting member 144, two interconnectors 190, and two IC separators 180. One IC separator 180, the air electrode frame 130, the single cell separator 120, the anode frame 140, and the other IC separator 180 are arranged in this order, stacked one on top of the other. The unit cell 110 is supported by a unit cell separator 120 , the interconnector 190 is supported by an IC separator 180 , and the anode current collecting member 144 is disposed between the unit cell 110 and the interconnector 190 .

[0035] 5 and 6, the IC separator 180 and the interconnector 190 are shared by two adjacent power generating units 100U. However, as shown in Fig. 2, the power generating unit 100U located at the other end (the lower end in Fig. 2) of the multiple power generating 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.

[0036] (single cell 110) The unit cell 110 includes an electrolyte layer 112, a cathode 114, an anode 116, and a reaction prevention layer 118. As shown in Figures 5 and 6, the cathode 114, the reaction prevention layer 118, the electrolyte layer 112, and the anode 116 are stacked in this order. 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.

[0037] The electrolyte layer 112 is a rectangular, flat member having one surface (the upper surface in FIGS. 5 and 6 ) on which the air electrode 114 is disposed and another surface (the lower surface in FIGS. 5 and 6 ) parallel to the first surface on which the anode 116 is disposed. The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The cathode 114 is a layer having a rectangular shape smaller than that of the electrolyte layer 112 and containing, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)). The anode 116 is a layer having a rectangular shape and approximately the same size as the electrolyte layer 112 and containing, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, or the like. The reaction prevention layer 118 is a layer having a rectangular shape and approximately the same size as the air electrode 114 and containing, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of preventing elements (e.g., Sr) diffused from the air electrode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0038] (Single cell separator 120) As shown in FIGS. 5 and 6, 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, 0.05 mm or more and 0.2 mm or less. 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 FIGS. 5 and 6) by a joint 124. The joint 124 is made of, for example, brazing material (Ag brazing). The single cell separator 120 is an example of a conductive member within the scope of the claims.

[0039] (Air electrode frame 130) As shown in Figures 5 and 6, the air electrode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made of, for example, mica. The thickness of the air electrode frame 130 is preferably 0.5 mm or more and 5 mm or less. As shown in Figure 5, the air electrode frame 130 has an oxidant gas supply communicating channel 132 that connects the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communicating channel 133 that connects the air chamber 313 and the oxidant gas discharge manifold 312. The air electrode frame 130 is an example of an insulating member as defined in the claims.

[0040] (Glass seal part 135) The glass seal 135 is provided between the single cell separator 120 and the IC separator 180, which face each other in the vertical direction with the cathode frame 130 sandwiched between them. The glass seal 135 is made of crystallized glass. The glass seal 135 is annular and is disposed so as to surround the fuel gas supply manifold 321 and the fuel gas discharge manifold 322. The glass seal 135 prevents leakage of fuel gas (FG) or fuel off-gas (FOG) from the fuel gas supply manifold 321 and the fuel gas discharge manifold 322 through the interface between the cathode frame 130 and the single cell separator 120 or the interface between the cathode frame 130 and the IC separator 180. The glass seal 135 is an example of an insulating member as defined in the claims.

[0041] (fuel electrode frame 140) 5 and 6, the anode 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. As shown in Fig. 6, the anode frame 140 has a fuel gas supply communication channel 142 that connects the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication channel 143 that connects the fuel chamber 323 and the fuel gas discharge manifold 322.

[0042] (IC separator 180) As shown in Figures 5 and 6, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center. IC separator 180 is made of metal and contains 0.05 mass % or more of Ti. As will be described in detail later, an oxide film OM1 is formed on the surface of IC separator 180 (see Figure 7). IC separator 180 is an example of a metal member within the scope of the claims.

[0043] (Interconnector 190 and anode current collecting member 144) 5 and 6, 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.

[0044] 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 5 and 6, 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.

[0045] As described above, the interconnector 190 is shared by two adjacent power generating units 100U. More specifically, as shown in Figures 5 and 6, the air electrode current collecting portion 192 is joined to the air electrode 114 of the unit cell 110 provided in one of the two adjacent power generating units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, thereby being electrically connected to the air electrode 114. The flat plate portion 191 is electrically connected to the anode 116 of the unit cell 110 provided in the other of the two adjacent power generating units 100U via an anode current collecting member 144. This ensures electrical continuity between the two adjacent power generating units 100U.

[0046] However, as described above, the power generating unit 100U located at the other end (the lower end in FIG. 2) of the multiple power generating units 100U does not have an interconnector 190 on the side of the anode 116. The anode 116 included in this power generating unit 100U is connected to the second terminal plate 250 via the anode current collecting member 144.

[0047] 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 power generating unit 100U due to temperature cycles and reactant gas pressure fluctuations, and good electrical connection is maintained between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144.

[0048] (Air chamber 313 and fuel chamber 323) 5 and 6, 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.

[0049] 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.

[0050] 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 power generating units 100U.

[0051] A-2. Operation of fuel cell stack 10: As shown in Figures 2 and 5, the oxidizing gas OG is supplied to the oxidizing gas supply manifold 311 via a gas pipe (not shown) and a gas passage member 280, and is supplied to the air chamber 313 via the oxidizing gas supply communicating passage 132.

[0052] As shown in FIGS. 3 and 6, the fuel gas FG is supplied to the fuel gas supply manifold 321 via a gas pipe (not shown) and a gas passage member 280, and is supplied to the fuel chamber 323 via the fuel gas supply communication passage 142.

[0053] When an oxidant gas OG is supplied to the air chamber 313 of each power generating unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power is generated in the unit 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 power generating units 100U, and the interconnector 190 ensures electrical continuity between the two adjacent power generating units 100U. In other words, the multiple power generating 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 power generating unit 100U located at the other end (the lower end in FIG. 2 ) of the multiple power generating units 100U, and a first terminal plate 240 is electrically connected to the power generating unit 100U located at one end (the upper end in FIG. 2 ). As a result, electrical energy generated in each power generating 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.

[0054] 2 and 5, the oxidant off-gas OOG discharged from the air chamber 313 of each power generating unit 100U to the oxidant gas discharge manifold 312 via the oxidant gas discharge communicating passage 133 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in FIGS. 3 and 6, the fuel off-gas FOG discharged from the fuel chamber 323 of each power generating unit 100U to the fuel gas discharge manifold 322 via the fuel gas discharge communicating passage 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0055] A-3.Detailed structure of the oxide film OM surroundings: Fig. 7 is an explanatory diagram showing an enlarged XZ cross-sectional configuration of part X1 in Fig. 6. Fig. 7 shows a part of the single cell separator 120, a part of the cathode frame 130, a part of the glass seal part 135, and a part of the IC separator 180.

[0056] An oxide film OM1 is formed on the surface of the IC separator 180. The cathode frame 130 and the glass seal 135 are each disposed between the oxide film OM1 and the unit cell separator 120, which is electrically connected to the unit cell 110 via the joint 124. Due to this configuration, a relatively large electric field is generated around the oxide film OM1, for example, when the fuel cell stack 10 generates electricity. Note that, for example, in a configuration in which the fuel cell stack 10 does not include the unit cell separator 120 (specifically, a configuration in which part of the unit cell 110 extends to the outer edge of the power generation block 100), the cathode frame 130 and the glass seal 135 may each be directly connected to the unit cell 110 and disposed between the unit cell 110 and the oxide film OM1.

[0057] The oxide film OM1 contains, for example, 0.1 mass % or more (preferably 0.5 mass % or more) and 10 mass % or less of Ti. Specifically, the oxide film OM1 contains Ti oxides such as TiO and TiO2. Furthermore, the IC separator 180 of this embodiment contains at least one of Al and Cr in addition to Ti.

[0058] Fig. 8 is an explanatory diagram showing an enlarged XZ cross-sectional configuration of part X2 in Fig. 3. Fig. 7 shows a part of end separator 230, a part of insulating part 220, and a part of first end plate 210.

[0059] An oxide film OM2 is formed on the surface of the first end plate 210. The insulating portion 220 is disposed between the oxide film OM2 and a terminal separator 230 electrically connected to the unit cell 110 via the interconnector 190, the anode current collecting member 144, and the first plate 232. Due to this configuration, an electric field is generated around the oxide film OM2, for example, when the fuel cell stack 10 generates power.

[0060] The oxide film OM2 contains Ti. Specifically, the oxide film OM2 contains Ti oxides such as TiO and TiO. Furthermore, the first end plate 210 of this embodiment contains at least one of Al and Cr in addition to Ti.

[0061] In the fuel cell stack 10 of this embodiment, when a voltage of 20 V is applied to the fuel cell stack 10 at 700°C for 200 hours, the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application is 0.3 or less, preferably 0.1 or less, where the moles of TiO2 in each of the oxide films OM1 and OM2 (hereinafter collectively referred to as "oxide films OM") are divided by the sum of the moles of TiO2 and the moles of TiO2. Examples of means for achieving such a configuration include increasing the resistance of the insulating members, such as the glass seal portion 135, the cathode frame 130, and the insulating portion 220. More specifically, this can be achieved by increasing the thickness of the insulating members, using a material with high volume resistivity (e.g., alumina), or, when glass is used as the insulating member, adjusting the transition metal content of the glass or increasing the crystallinity of the glass.

[0062] A-4. Advantages of this embodiment: As described above, the fuel cell stack 10 of this embodiment includes a unit cell 110, metal members (IC separator 180, first end plate 210), a Ti-containing oxide film OM formed on the surface of the metal member, the unit cell 110 or conductive members electrically connected to the unit cell 110 (single cell separator 120, terminal separator 230), and insulating members (air electrode frame 130, glass seal member 135, insulating member 220) disposed between the unit cell 110 and the oxide film OM. When the TiO content in the oxide film OM is divided by the sum of the TiO content and the TiO content, when a voltage of 20 V is applied between the metal member and the unit cell 110 or the conductive member electrically connected to the unit cell 110 at 700°C for 200 hours, the absolute value of the difference between the TiO content before and after voltage application is 0.3 or less.

[0063] According to the fuel cell stack 10 of this embodiment, when a voltage of 20 V is applied for 200 hours at 700° C., the absolute value of the difference between the abundance ratio of TiO2 after the voltage application and the abundance ratio of TiO2 before the voltage application is 0.3 or less. That is, for example, by suppressing the conversion between TiO and TiO2, it is possible to suppress a change in the volume of the oxide film OM that accompanies a change in the ratio of TiO to TiO2 in the oxide film OM, and to suppress the occurrence of cracks in the oxide film OM or at the interface between the oxide film OM and other components.

[0064] Furthermore, in the fuel cell stack 10 of this embodiment, the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application is 0.1 or less. According to the fuel cell stack 10 of this embodiment, the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application is 0.1 or less. That is, for example, by suppressing conversion between TiO and TiO2, it is possible to suppress changes in the volume of the oxide film OM that occur in accordance with changes in the ratio of TiO to TiO2 in the oxide film OM, and it is possible to more effectively suppress the occurrence of cracks in the oxide film OM or at the interface between the oxide film OM and other components.

[0065] Furthermore, in the fuel cell stack 10 of this embodiment, the oxide film OM contains at least one of Al and Cr. According to the fuel cell stack 10 of this embodiment, when the metal member contains a metal such as Fe, Al or Cr contained in the oxide film OM can suppress oxidation of the metal in the metal member, and thus can suppress oxidation of the metal member.

[0066] Furthermore, in the fuel cell stack 10 of this embodiment, the metal members contain 0.05 mass % or more of Ti. According to the fuel cell stack 10 of this embodiment, when the metal members contain other metals such as Fe, Ti contained in the metal members and having a relatively high ionization tendency can suppress oxidation of the other metals in the metal members, and ultimately suppress oxidation of the metal members.

[0067] In the fuel cell stack 10 of this embodiment, the glass seal portion 135 is made of crystallized glass. According to the fuel cell stack 10 of this embodiment, since the glass seal portion 135 is made of crystallized glass, it is possible to ensure both insulation between the single cell 110 and the oxide film OM and bonding between the glass seal portion 135 and the oxide film OM.

[0068] A-5. Performance evaluation: Next, performance evaluation of this embodiment will be described. For example, by adjusting the resistance value of the insulating member, multiple fuel cell stack 10 samples were produced with different absolute values ​​of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application, and the crack resistance (resistance to cracks) was evaluated using these multiple samples. Table 1 shows the performance evaluation results.

[0069] (Measurement of the absolute value of the difference in the abundance ratio of TiO2 in each sample) The absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before and after voltage application was measured using a test piece simulating a fuel cell stack 10. FIG. 9 shows a top view of the test piece, and FIG. 10 shows a cross-sectional view of the test piece taken along the line XX in FIG. 9. The test piece is composed of two metal members ME, an insulating member IM, two metal plates PL, two insulators IN, a bolt B, and two nuts N. Each of the metal members ME, the insulating member IM, the metal plates PL, and the insulators IN has a through-hole formed near the center.

[0070] The method for preparing the test piece will be described below. First, a metal member ME containing Ti was heat-treated, for example, at 1000°C, to form an oxide film OM on the surface of the metal member ME. Next, one insulator IN, one metal plate PL, one metal member ME, an insulating member IM, the other metal member ME, the other metal plate PL, and the other insulator IN were stacked in this order so that their through holes were connected, and bolts B were inserted into the through holes and all the members were fastened together using nuts N to prepare the test piece.

[0071] The test piece fabricated by the above method was subjected to a voltage application test. The voltage application test was performed by placing the test piece in an electric furnace at 700°C and applying a voltage of 20 V for 200 hours. The voltage was applied by connecting cords connected to an external power source to each of the two metal plates PL. Note that one metal member ME corresponds to the terminal separator 230 and the single cell separator 120 in the fuel cell stack 10, while the other metal member ME corresponds to the first end plate 210 and the IC separator 180 in the fuel cell stack 10. The insulating member IM corresponds to the insulating section 220, the cathode frame 130, and the glass seal section 135 in the fuel cell stack 10. The insulator IN does not correspond to any of the components in the fuel cell stack 10, but is used to insulate the metal plate PL from the nut N.

[0072] To measure the TiO and TiO2 contents in the oxide film OM before voltage application, a portion of the test piece was cut out before the voltage application test to serve as a measurement sample. The measurement sample was then fractured within the oxide film OM layer of the test piece, and the fractured surface was subjected to XPS (X-ray photoelectron spectroscopy) measurement. To measure the TiO and TiO2 contents in the oxide film OM after voltage application, the test piece was fractured within the oxide film OM layer after the voltage application test, and the fractured surface was subjected to XPS measurement. The XPS measurement was performed with a beam diameter of 100 μm and within a binding energy range of 452 eV to 468 eV. TiO-derived Ti2p 3 / 2 , Ti2p 1 / 2 The peaks of TiO2 are at 455 eV and 461 eV, respectively. 3 / 2 , Ti2p 1 / 2 The peaks of Ti2p are at 458 eV and 464 eV, respectively. 3 / 2 Peak area and Ti2p 1 / 2 Since the peak area ratio is 2:1, the TiO content is expressed as Ti2p 3 / 2 Peak area and Ti2p 1 / 2 The area ratio of the peaks was fixed at 2:1 and fitting was performed. 3 / 2 and Ti2p 1 / 2 The total peak area of ​​the TiO2 was calculated using the same method. The TiO2 content was calculated using the obtained TiO content and TiO2 content, and the TiO2 abundance ratio was calculated using the following formula (1). TiO2 abundance ratio = TiO2 content ÷ (TiO content + TiO2 content) (1) For each test piece, the difference in absolute value between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application was calculated, and the characteristics of each test piece were evaluated. The abundance ratio of TiO2 in the oxide film provided in an actual product (e.g., fuel cell stack 10) can be measured by taking out members corresponding to one metal member ME, the other metal member ME, and the insulating member IM and using them in the same manner as the measurement method for the test piece.

[0073] (Crack resistance evaluation) Crack resistance was evaluated by using multiple fuel cell stacks 10 as samples, each with the same insulating material composition, insulating material thickness, and other conditions as the test pieces. The fuel cell stacks 10 were heated under certain conditions, and the presence or absence of cracks in the oxide film OM or at the interface between the oxide film OM and other materials was assessed. One heating cycle consisted of raising the temperature from 70°C to 700°C over two hours, holding it at 700°C for two hours, and then lowering the temperature from 700°C to 70°C over 12 hours. Each fuel cell stack 10 underwent 280 heating cycles, after which the presence or absence of cracks was checked. Fuel cell stacks 10 that showed no cracks after 280 cycles were subjected to an additional 120 heating cycles (400 cycles in total), and the presence or absence of cracks was then checked. The evaluation criteria were as follows: a sample that had cracks after 280 cycles was rated as "poor" (x); a sample that had no cracks after 280 cycles but had cracks after 400 cycles was rated as "passable" (△); and a sample that had no cracks after 400 cycles was rated as "good" (○). The presence or absence of cracks was determined by observation using a SEM (scanning electron microscope).

[0074] (Performance evaluation results) Table 1 shows the performance evaluation results. [Table 1]

[0075] The crack resistance evaluation of each sample is shown in Table 1. In the table, the "absolute value of the difference in the abundance ratio of TiO2 before and after voltage application" indicates the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application.

[0076] As shown in Table 1, the crack resistance evaluations of all samples (S1, S2) in which the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application was greater than 0.3 were poor (×). Furthermore, the crack resistance evaluations of all samples (S3 to S5) in which the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application was 0.3 or less but greater than 0.1 were fair (△). Furthermore, the crack resistance evaluations of all samples (S6 to S8) in which the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application was 0.1 or less were good (◯). These results confirmed that the occurrence of cracks can be suppressed in a fuel cell stack 10 in which the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application is 0.3 or less, preferably 0.1 or less.

[0077] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible.

[0078] The configurations of the fuel cell stack 10 and the power generating units 100U in the above embodiment are merely examples and can be modified in various ways. For example, the number of unit cells 110 included in the fuel cell stack 10 in the above embodiment (the number of power generating units 100U) is merely an example, and the number of unit cells 110 is determined appropriately depending on the output voltage required for the fuel cell stack 10.

[0079] The materials constituting each component in the above embodiment are merely examples, and each component may be made of other materials. For example, the glass seal portion 135 in the above embodiment is made of crystallized glass, but it may be made of other insulating materials such as mica or insulating ceramics, or may include multiple insulating materials.

[0080] In the above embodiment, no oxide film is formed on the conductive members (single cell separator 120 and terminal separator 230), but an oxide film may be formed on the conductive members.

[0081] In the above embodiment, the single cell separator 120 is an example of a conductive member and the IC separator 180 is an example of a metal member, but the single cell separator 120 may be an example of a metal member and the IC separator 180 may be an example of a conductive member.

[0082] In the above embodiment, the oxide film OM contains at least one of Al and Cr, but it does not necessarily have to contain at least one of Al and Cr.

[0083] In the above embodiment, the metal members (IC separator 180 and first end plate 210) contain 0.05 mass % or more of Ti, but they do not necessarily need to contain Ti.

[0084] The fuel cell stack 10 of the above embodiment is a co-flow type SOFC, but the technology disclosed in this specification is also applicable to counter-flow type SOFCs and cross-flow type SOFCs.

[0085] In the above embodiment, the unit cell 110 is an anode-supported unit cell, but it may be another type of unit cell such as an electrolyte-supported type or a metal-supported type.

[0086] In the above embodiment, the fuel cell stack 10 is configured to have a plurality of flat-type unit cells 110, but the present invention is equally applicable to fuel cell stacks that have a plurality of unit cells of other types (e.g., cylindrical, flat cylindrical, etc.).

[0087] 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]

[0088] 10: fuel cell stack 100: power generation block 100U: power generation unit 110: single cell 112: electrolyte layer 114: air electrode 116: fuel electrode 118: reaction prevention layer 120: single cell separator 121: through hole 124: joint portion 130: air electrode frame 131: through hole 132: oxidant gas supply communicating channel 133: oxidant gas discharge communicating channel 135: glass seal portion 140: fuel electrode frame 141: through hole 142: fuel gas supply communicating channel 143: fuel gas discharge communicating channel 144: fuel electrode current collecting member 145: electrode opposing portion 146: interconnector opposing portion 147: connecting portion 149: spacer 180: IC separator 181: through hole 190: interconnector 191: flat plate portion 192: Air electrode current collecting portion 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat portion 212: Through hole 213: Outer convex portion 214: Inner convex portion 220: Insulating portion 230: Terminal separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Flat portion 272: Through hole 273: Outer convex portion 274: Inner convex portion 280: Gas passage member 281: Main body portion 282: Flange portion 283: Gas through hole 284: Bolt hole 311: Oxidant gas supply manifold 312: Oxidant gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas exhaust manifold 323: Fuel chamber B: Bolt BH: Bolt hole N: Nut FG: Fuel gas FOG: Fuel off-gas OG: Oxidizer gas OOG: Oxidizer off-gas OM1: Oxide film OM2: Oxide film

Claims

1. A single cell and A metal member; an oxide film containing Ti formed on the surface of the metal member; an insulating member disposed between the unit cell or a conductive member electrically connected to the unit cell and the oxide film; An electrochemical reaction cell stack comprising: TiO in the oxide film ２ The content of TiO and TiO ２ The value obtained by dividing the value by the total content of TiO ２ When a voltage of 20 V is applied between the metal member and the single cell or a conductive member electrically connected to the single cell at 700° C. for 200 hours, the TiO ２ and the TiO before voltage application ２ The absolute value of the difference between the abundance ratio of An electrochemical reaction cell stack comprising:

2. The electrochemical reaction cell stack according to claim 1, The TiO after voltage application ２ and the TiO before voltage application ２ The absolute value of the difference between the abundance ratio of An electrochemical reaction cell stack comprising:

3. The electrochemical reaction cell stack according to claim 1, the oxide film contains at least one of Al and Cr; An electrochemical reaction cell stack comprising:

4. The electrochemical reaction cell stack according to claim 1, The metal member contains 0.05 mass% or more of Ti. An electrochemical reaction cell stack comprising:

5. The electrochemical reaction cell stack according to any one of claims 1 to 4, The insulating member is made of crystallized glass. An electrochemical reaction cell stack comprising:

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