Electrochemical reaction cell stack

Abstract

To provide an electrochemical reaction cell stack capable of mitigating stress.SOLUTION: A fuel cell stack 10 includes: a single cell 110; a separator 120 for single cells and a separator 180 for ICs which are made of metal and which separate a fuel chamber 323 where fuel gas FG supplied to a fuel electrode 116 circulates and an air chamber 313 where oxidant gas OG supplied to an air electrode 114 circulates, the fuel chamber and the air chamber being connected to the single cell 110; and a fuel electrode frame 140 which is made of metal and supports the separator 120 for single cells and the separator 180 for ICs. When an average crystal grain diameter of metal constituting the separator 120 for single cells is ADspC, and an average crystal grain diameter of metal constituting the fuel electrode frame 140 is ADsu, ADspC>ADsu is satisfied. In addition, when an average crystal grain diameter of metal constituting the separator 180 for ICs is ADspI, and an average crystal grain diameter of metal constituting the fuel electrode frame 140 is ADsu, ADspI>ADsu is satisfied.SELECTED DRAWING: Figure 6

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"), which have an electrolyte layer containing solid oxide, are known as one type of fuel cell that generates electricity using the electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack, in which multiple structural units (electrochemical reaction units) are arranged in a predetermined direction (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6827091 Summary of the Invention [Problem to be solved by the invention]

[0004] During operation of a fuel cell stack, the inside of the stack becomes hot, and stress may occur in the cell stack due to differences in the thermal expansion coefficients of the members that make up the cell stack.

[0005] These issues are also common to electrolysis cell stacks that include multiple electrolysis cell units, which are constituent units of solid oxide electrolysis cells (hereinafter referred to as "SOECs") that generate hydrogen using the electrolysis reaction of water, and are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

[0006] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms. (1) The electrochemical reaction cell stack disclosed in this specification comprises a unit cell having an air electrode, an electrolyte layer, and an anode, a metal separator connected to the unit cell and separating a fuel gas flow space through which a fuel gas supplied to the anode flows and an oxidizer gas flow space through which an oxidizer gas supplied to the air electrode flows, and a metal support member supporting the separator, wherein when the average crystal grain size of the metal constituting the separator is defined as ADsp and the average crystal grain size of the metal constituting the support member is defined as ADsu, ADsp > ADsu is satisfied.

[0008] According to the above configuration, by making the average crystal grain size of the metal constituting the separator larger than the average crystal grain size of the metal constituting the support member, the separator can be made relatively more susceptible to plastic deformation, which can alleviate stress generated in the cell stack and reduce its impact on the unit cells.

[0009] (2) In the electrochemical reaction cell stack described in (1) above, the metal crystal grains constituting the support member may have a flat shape and be arranged in a position along the support surface of the support member facing the separator, and when the average length of the metal crystal grains constituting the support member in a direction perpendicular to the support surface is defined as ATsu and the average length of the metal crystal grains constituting the separator in a direction perpendicular to the support surface is defined as ATsp, ATsp > ATsu may be satisfied.

[0010] The load of the separator is applied to the support member in a direction perpendicular to the support surface. With the above configuration, the support member has a smaller tolerance for plastic deformation in the direction perpendicular to the support surface than in the direction along the support surface, so that the force with which the support member can withstand the load of the separator applied in the direction perpendicular to the support surface can be relatively increased.

[0011] (3) In the electrochemical reaction cell stack described in (1) or (2) above, the support member may have a first region adjacent to the support surface facing the separator and a second region farther from the support surface than the first region, and when the average crystal grain size of the crystal grains of the metal constituting the support member contained in the first region is ADsu1 and the average crystal grain size of the crystal grains contained in the second region is ADsu2, ADsu1>ADsu2 may be satisfied.

[0012] With this configuration, the first region of the support member adjacent to the support surface is relatively susceptible to plastic deformation and is therefore more likely to follow the plastic deformation of the separator, thereby reducing stress generated on the support surface.

[0013] The technology disclosed in this specification can be realized in various forms, for example, in the form of an electrochemical reaction cell stack and a manufacturing method thereof. [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 an embodiment; [Figure 2] FIG. 2 is a cross-sectional view of the fuel cell stack according to the embodiment taken along line II-II in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the fuel cell stack according to the 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 embodiment, cut at the same position as line II-II in FIG. 1. [Figure 5] 3 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, cut at the same position as line III-III in FIG. 1. [Figure 6] 1 is a diagram showing a schematic diagram of crystal grains constituting a single cell separator, a fuel electrode frame, and an IC separator according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0015] A. Implementation: A-1. Configuration of fuel cell stack 10: The embodiment will be described with reference to Figures 1 to 6. A fuel cell stack 10 (an example of an electrochemical reaction cell stack) of the present 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) As shown in Figures 1 to 3, the fuel cell stack 10 includes a power generation block 100, a first end plate 210, a second end plate 230, an end separator 220, and four gas passage members 280A, 280B. The power generation block 100 is composed of multiple (seven in this embodiment) electrochemical reaction units 100U (hereinafter, sometimes abbreviated as "reaction units 100U"). Each 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.

[0017] The first end plate 210, power generation block 100, terminal separator 220, and second end plate 230 have rectangular outer shapes of approximately the same size, and are stacked in this order in a predetermined arrangement direction (the 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 terminal separator 220. A bolt B is inserted into each bolt hole BH. The second end plate 230 has four screw holes (not shown) at positions corresponding to the four bolt holes BH. One end of each bolt B is screwed into the corresponding screw hole, and a nut N is screwed onto the other end of each bolt B. These bolts B and nuts N fasten the members from the first end plate 210 to the second end plate 230 together. As shown in FIGS. 2 and 3, the four gas passage members 280A, 280B are connected to the second end plate 230.

[0019] The multiple reaction units 100U that make up the power generation block 100 are arranged side by side in a predetermined arrangement direction (the vertical direction in FIG. 2). As shown in FIGS. 4 and 5, each reaction unit 100U is composed of one IC separator 180, an air electrode frame 130, a single cell separator 120 (an example of a separator), an anode frame 140 (an example of a support member), and another IC separator 180 (an example of a separator), stacked in this order. The single cell 110 is supported by the single cell separator 120, and two interconnectors 190 are supported by the two IC separators 180, respectively. The anode current collecting member 144 is disposed between the single cell 110 and the interconnector 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 terminal separator 220 overlaps the fuel electrode frame 140.

[0021] (single cell 110) The unit cell 110 includes an electrolyte layer 112, an air electrode 114, and an anode 116. As shown in Figures 3 and 4, the air electrode 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 air electrode 114. The unit cell 110 of this embodiment is an anode-supported unit cell in which the other layers (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) that constitute the unit cell 110 are supported by the anode 116.

[0022] The electrolyte layer 112 is a rectangular, flat-plate member and contains a solid oxide. The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite oxide (e.g., lanthanum strontium cobalt iron oxide (LSCF)). The fuel electrode 116 is a layer having a rectangular shape and approximately the same size as the electrolyte layer 112 and contains Ni (nickel). The reaction prevention layer 118 is a layer having a rectangular 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 (e.g., Sr) diffused from the air electrode 114 with an element (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO).

[0023] (Single cell separator 120) As shown in Figures 4 and 5, the single cell separator 120 is a rectangular frame-shaped member having a substantially rectangular through-hole 121 near the center, and is made of a metal such as ferritic stainless steel. 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 electrolyte layer 112 by a joint 124. The joint 124 is made of, for example, a brazing material (Ag brazing).

[0024] (Air electrode frame 130) As shown in FIGS. 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.).

[0025] (fuel electrode frame 140) As shown in FIGS. 4 and 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 a metal such as ferritic stainless steel.

[0026] (IC separator 180) As shown in FIGS. 4 and 5, IC separator 180 is a frame-like member having a substantially rectangular through-hole 181 near the center, and is made of a metal such as ferritic stainless steel.

[0027] (Interconnector 190 and anode current collecting member 144) As shown in Figures 4 and 5, the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from the flat plate portion 191 toward the air electrode 114, a coating layer 193, and an oxide coating 194. The flat plate portion 191 and the air electrode current collector 192 are electrically conductive and formed 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 side of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The oxide coating 194 is disposed so as to cover the side of the flat plate portion 191 opposite to the side on which the air electrode current collector 192 is disposed.

[0028] 4 and 5, the interconnector 190 has a rectangular outer shape that is slightly larger than the edge of the through-hole 181, and is placed on the IC separator 180 so as to close the through-hole 181. The flat plate portion 191 is placed on the peripheral portion of the through-hole 181 in the IC separator 180 via an oxide film 194, and is joined by welding.

[0029] 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 includes an interconnector facing portion 146, an electrode facing portion 145 that is parallel to the interconnector facing portion 146, and a connecting portion (not shown) that connects the electrode facing portion 145 and the interconnector facing portion 146. 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.

[0030] 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.

[0031] 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 terminal separator 220 via the fuel electrode current collecting member 144.

[0032] 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 terminal separator 220) via the anode current collecting member 144 is maintained.

[0033] (Air chamber 313 and fuel chamber 323) 4 and 5, the space partitioned by the single cell separator 120, the single cell 110, the air electrode frame 130, the IC separator 180, and the interconnector 190 faces the air electrode 114 and serves as an air chamber 313 (an example of an oxidant gas flow space) through which the oxidant gas OG flows. The air electrode frame 130 separates the air chamber 313 from the external space along the entire periphery, and also 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.

[0034] 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 serves as a fuel chamber 323 (an example of a fuel gas flow space) through which the fuel gas FG flows. The fuel electrode frame 140 separates 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.

[0035] 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.

[0036] A glass seal portion 125 containing glass is disposed near the edge of the through-hole 121 in the unit cell separator 120. The glass seal portion 125 covers the edge of the through-hole 121 and is disposed so as to be in contact with the surface of the unit cell 110 (electrolyte layer 112 in this embodiment), thereby sealing the gap between the edge of the through-hole 121 and the unit cell 110. The glass seal portion 125 effectively prevents gas 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.

[0037] (First end plate 210) The first end plate 210 is a rectangular frame-shaped member having a through-hole 211 near the center, and is made of a conductive material such as stainless steel. The first end plate 210 is electrically connected to the reaction unit 100U arranged at the other end (the upper end in FIG. 2) of the multiple reaction units 100U that make up the power generation block 100. The first end plate 210 functions as a positive output terminal of the fuel cell stack 10.

[0038] (Terminal separator 220) The terminal separator 220 is a rectangular flat plate member made of a conductive material such as metal.

[0039] (Second end plate 230) The second end plate 230 is a rectangular frame-shaped member having a through-hole 231 near the center and is made of a conductive material such as stainless steel. The peripheral edge of the terminal separator 220 is sandwiched between the power generation block 100 and the second end plate 230 and joined to the second end plate 230 by welding, for example, and is electrically connected to the second end plate 230. The second end plate 230 is connected to the anode 116 of the reaction unit 100U located at one end (the lower end in FIG. 2 ) of the multiple reaction units 100U via the anode current collecting member 144 and the terminal separator 220, thereby electrically connecting the reaction unit 100U to the second end plate 230. The second end plate 230 functions as the negative output terminal of the fuel cell stack 10.

[0040] (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 230. 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.

[0041] 2, the oxidant gas supply manifold 311 is a gas flow path for supplying the oxidant gas OG introduced from outside the fuel cell stack 10 to the air chamber 313 of each reaction unit 100U. The oxidant gas discharge manifold 312 is a gas flow path for discharging the 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.

[0042] 3, the fuel gas supply manifold 321 is a gas flow path for supplying fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chamber 323 of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path for discharging 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.

[0043] (Gas passage members 280A, 280B) Two of the four gas passage members 280A, 280B are gas passage members 280A connected to the oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312, respectively. As shown in FIG. 2, each gas passage member 280A has a substantially rectangular tubular main body 281A and a cylindrical branch portion 282A branching off from the side surface of the main body 281A. The internal space of the branch portion 282A is in communication with the internal space of the main body 281A. A gas pipe (not shown) is connected to the branch portion 282A. The two gas passage members 280A are each connected to the second end plate 230 via an insulating sheet S. The internal spaces of the two gas passage members 280A are in communication with the oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312, respectively.

[0044] The other two of the four gas passage members 280A, 280B are gas passage members 280B connected to the fuel gas supply manifold 321 and the fuel gas discharge manifold 322, respectively. As shown in FIG. 3, each gas passage member 280B has a cylindrical main body 281B and a cylindrical branch portion 282B branching off from the side surface of the main body 281B. The internal space of the branch portion 282B is in communication with the internal space of the main body 281B. A gas pipe (not shown) is connected to the branch portion 282B. The two gas passage members 280B are each connected to the second end plate 230 via an insulating sheet S. The internal spaces of the two gas passage members 280B are in communication with the fuel gas supply manifold 321 and the fuel gas discharge manifold 322, respectively.

[0045] A-2. Operation of fuel cell stack 10: 2 and 4, the oxidizing gas OG is supplied to the air chamber 313 through the gas passage member 280A and the oxidizing gas supply manifold 311. Also, as shown in FIGS. 3 and 5, the fuel gas FG is supplied to the fuel chamber 323 through the gas passage member 280B and the fuel gas supply manifold 321.

[0046] 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, the reaction unit 100U located at one end (the lower end in FIG. 2 ) of the multiple reaction units 100U is electrically connected to a second end plate 230, and the reaction unit 100U located at the other end (the upper end in FIG. 2 ) is electrically connected to a first end plate 210. As a result, electrical energy generated in each reaction unit 100U is extracted from the second end plate 230, which functions as an output terminal 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.

[0047] 2, the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidant gas discharge manifold 312 passes through the inside of the gas passage member 280A and is discharged to the outside of the fuel cell stack 10. 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 passes through the inside of the gas passage member 280B and is discharged to the outside of the fuel cell stack 10.

[0048] A-3. Detailed configuration of the single cell separator 120, the fuel electrode frame 140, and the IC separator 180: As described above, the unit cell separator 120, the fuel electrode frame 140, and the IC separator 180 are stacked in this order. The fuel electrode frame 140 has a first support surface 140F1 (an example of a support surface: the upper surface in FIG. 6) that contacts the unit cell separator 120, and a second support surface 140F2 (an example of a support surface: the lower surface in FIG. 6) that is the surface opposite to the first support surface 140F1 and that contacts the IC separator 180. In this embodiment, the second support surface 140F2 is a surface parallel to the first support surface 140F1.

[0049] The average crystal grain size of the metal constituting the fuel electrode frame 140 is smaller than the average crystal grain size of the metal constituting the single cell separator 120. When the average crystal grain size of the metal constituting the single cell separator 120 is ADspC (an example of the average crystal grain size ADsp) and the average crystal grain size of the metal constituting the fuel electrode frame 140 is ADsu, the values ​​of the average crystal grain sizes ADspC and ADsu satisfy the following formula (1).

[0050] ADspC>ADsu···(1)

[0051] The average crystal grain sizes ADspC and ADsu are calculated as follows.

[0052] A microscopic image of a cross section of the single cell separator 120 and the anode frame 140 cut perpendicular to the first support surface 140F1 is obtained. On the obtained microscopic image, multiple imaginary lines L1 parallel to the first support surface 140F1 and multiple imaginary lines L2 perpendicular to the first support surface 140F1 are drawn. From the obtained microscopic image, multiple crystal grains 120P included in the single cell separator 120 are randomly selected. To prevent bias in the tendency of the crystal grains 120P, 10 or more crystal grains 120P are selected while avoiding adjacent crystal grains 120P in a single image. Furthermore, crystal grains 120P are selected from at least two or more microscopic images. For each of the selected multiple crystal grains 120P, the length in the direction parallel to the first support surface 140F1 (parallel length WspC) and the length in the direction perpendicular to the first support surface 140F1 (perpendicular length TspC) are measured. FIG. 6 illustrates one of the multiple imaginary lines L1 and L2. As shown in FIG. 6, the parallel length WspC of a certain crystal grain 120P is determined by measuring the distance between two points where the contour line of the crystal grain 120P intersects with the imaginary line L1. The perpendicular length TspC of a certain crystal grain 120P is determined by measuring the distance between two points where the contour line of the crystal grain 120P intersects with the imaginary line L2. The average of the determined parallel length WspC and perpendicular length TspC is defined as the crystal grain diameter DspC of the crystal grain 120P. The average value of the crystal grain diameters DspC of the multiple crystal grains 120P is calculated and defined as the average crystal grain diameter ADspC of the single cell separator 120.

[0053] The average crystal grain size ADsu of the fuel electrode frame 140 is calculated in the same manner.

[0054] Furthermore, the average crystal grain size of the metal constituting the anode frame 140 is smaller than the average crystal grain size of the metal constituting the IC separator 180. When the average crystal grain size of the metal constituting the IC separator 180 is ADspI (an example of the average crystal grain size ADsp) and the average crystal grain size of the metal constituting the anode frame 140 is ADsu, the values ​​of the average crystal grain sizes ADspI and ADsu satisfy the following formula (2).

[0055] ADspI>ADsu···(2)

[0056] The average crystal grain sizes ADspI and ADsu are calculated in the same manner as the average crystal grain sizes ADspC and ADsu described above by drawing multiple imaginary lines parallel to the second support surface 140F2 and multiple imaginary lines perpendicular to the second support surface 140F2 on a microscopic image of a cross section of the IC separator 180 and the fuel electrode frame 140 cut perpendicular to the second support surface 140F2.

[0057] As described above, the power generation reaction occurring in the single cell 110 is an exothermic reaction, and therefore the temperature inside the fuel cell stack 10 rises during operation, which can cause stress due to differences in the thermal expansion coefficients of the components that make up the fuel cell stack 10.

[0058] Here, the anode frame 140 is required to support the unit cells 110 and the separators 120, 180. Generally, metal materials are more susceptible to plastic deformation when the crystal grain size is larger. Therefore, by making the average crystal grain size ADsu of the metal constituting the anode frame 140 smaller than the average crystal grain sizes ADspC, ADspI of the metal material constituting the separators 120, 180, the separators 120, 180 are more susceptible to plastic deformation relative to the anode frame 140. As a result, the generated stress is alleviated by the plastic deformation of the separators 120, 180, and adverse effects on the unit cells 110 are suppressed. Furthermore, a decrease in the force supporting the unit cells 110 and the separators 120, 180 due to plastic deformation of the anode frame 140 can be suppressed.

[0059] The metal crystal grains 140P that make up the fuel electrode frame 140 have a flat shape and are arranged in a position that follows the support surfaces 140F1 and 140F2.

[0060] When the average length of the metal crystal grains 140P constituting the fuel electrode frame 140 in the direction perpendicular to the first support surface 140F1 is ATsu, and the average length of the metal crystal grains 120P constituting the single cell separator 120 in the direction perpendicular to the first support surface 140F1 is ATspC (an example of the average length ATsp), the values ​​of the average lengths ATspC and ATsu satisfy the following formula (3).

[0061] ATspC>ATsu···(3)

[0062] The average lengths ATspC and ATsu are calculated as follows.

[0063] The perpendicular length TspC is determined for each of the selected crystal grains 120P in the same manner as in the calculation of the average crystal grain size ADspC described above. The average perpendicular length TspC of the crystal grains 120P is calculated and designated as the average length ATspC of the single cell separator 120. The average length ATsu of the fuel electrode frame 140 is calculated in the same manner.

[0064] Furthermore, when the average length of the metal crystal grains 140P constituting the fuel electrode frame 140 in the direction perpendicular to the second support surface 140F2 is defined as ATsu, and the average length of the metal crystal grains 180P constituting the IC separator 180 in the direction perpendicular to the second support surface 140F2 is defined as ATspI (an example of the average length ATsp), the values ​​of the average lengths ATspI and ATsu satisfy the following equation (4).

[0065] ATspI>ATsu···(4)

[0066] The average lengths ATspI and ATsu are calculated in the same manner as the above average lengths ATspC and ATsu by drawing multiple imaginary lines parallel to the second support surface 140F2 and multiple imaginary lines perpendicular to the second support surface 140F2 on a microscopic image of a cross section of the IC separator 180 and the fuel electrode frame 140 cut perpendicular to the second support surface 140F2.

[0067] A load is applied to the anode frame 140 in a direction perpendicular to the support surfaces 140F1 and 140F2 from other members overlapping the anode frame 140. Because the crystal grains 140P contained in the anode frame 140 have a flat shape and are arranged in a position along the support surfaces 140F1 and 140F2, the anode frame 140 has a smaller tolerance for plastic deformation in the direction perpendicular to the support surfaces 140F1 and 140F2 than in the direction along the support surfaces 140F1 and 140F2. Furthermore, because the average length ATsu of the crystal grains 140P included in the anode frame 140 is smaller than the average lengths ATspC and ATspI of the crystal grains 120P and 180P included in the separators 120 and 180, the tolerance of plastic deformation in the direction perpendicular to the support surfaces 140F1 and 140F2 of the anode frame 140 is smaller than the tolerance of plastic deformation in the direction perpendicular to the support surfaces 140F1 and 140F2 of the separators 120 and 180. This configuration allows the anode frame 140 to relatively increase its ability to withstand a load applied in the direction perpendicular to the support surfaces 140F1 and 140F2.

[0068] For example, by cold rolling the metal plate that is the material for the anode frame 140, the crystal grains 140P contained in the anode frame 140 can be made into a flat shape having a desired average length ATsu.

[0069] 6, the region of the anode frame 140 adjacent to the first support surface 140F1 and the region adjacent to the second support surface 140F2 are defined as the first region Ar1, and the region inside the first region Ar1, that is, the region farther from both the first support surface 140F1 and the second support surface 140F2 than the first region Ar1, is defined as the second region Ar2. When the average crystal grain size of the crystal grains 140P included in the first region Ar1 is defined as ADsu1 and the average crystal grain size of the crystal grains 140P included in the second region Ar2 is defined as ADsu2, the values ​​of the average crystal grain sizes ADsu1 and ADsu2 satisfy the following formula (5).

[0070] ADsu1>ADsu2···(5)

[0071] With this configuration, the first regions Ar1 of the fuel electrode frame 140 adjacent to the support surfaces 140F1 and 140F2 are relatively susceptible to plastic deformation and are more likely to follow the plastic deformation of the separators 120 and 180. This reduces the stress generated on the support surfaces 140F1 and 140F2.

[0072] For example, by heating the metal plate that will be used to make the anode frame 140 at a high temperature for a short time and then rapidly cooling it, the average crystal grain size ADsu1 of the crystal grains 140P contained in the first region Ar1 can be made larger than the average crystal grain size ADsu2 of the crystal grains 140P contained in the second region Ar2. Generally, by heating a metal material at a high temperature, crystal grains can be grown. Because it takes a certain amount of time for heat to penetrate to the inside of the material, shortening the time the material is held at the highest temperature when heated allows the crystal grains in the region near the surface of the material to grow relatively larger.

[0073] A-4. Advantages of this embodiment: As described above, the fuel cell stack 10 of this embodiment includes a single cell 110 including an air electrode 114, an electrolyte layer 112, and an anode 116; a metal single cell separator 120 and an IC separator 180 connected to the single cell 110, which separate a fuel chamber 323 through which fuel gas FG supplied to the anode 116 flows and an air chamber 313 through which oxidizer gas OG supplied to the air electrode 114 flows; and a metal anode frame 140 supporting the single cell separator 120 and the IC separator 180. When the average crystal grain size of the metal constituting the single cell separator 120 is ADspC and the average crystal grain size of the metal constituting the anode frame 140 is ADsu, the relationship ADspC > ADsu is satisfied. Furthermore, when the average crystal grain size of the metal constituting the IC separator 180 is ADspI and the average crystal grain size of the metal constituting the anode frame 140 is ADsu, the relationship ADspI > ADsu is satisfied.

[0074] The above configuration allows the unit cell separator 120 and the IC separator 180 to be relatively more susceptible to plastic deformation, thereby alleviating stress generated in the fuel cell stack 10 and reducing the impact on the unit cells 110.

[0075] Furthermore, metal crystal grains 140P that make up the fuel electrode frame 140 have a flat shape and are arranged in a position that follows support surfaces 140F1 and 140F2 of the fuel electrode frame 140 that face the unit cell separator 120 and the IC separator 180. When the average length of the metal crystal grains 140P that make up the fuel electrode frame 140 in the direction perpendicular to the first support surface 140F1 is ATsu and the average length of the metal crystal grains 120P that make up the unit cell separator 120 in the direction perpendicular to the first support surface 140F1 is ATspC, then ATspC > ATsu is satisfied. Furthermore, when the average length of the metal crystal grains 140P constituting the fuel electrode frame 140 in the direction perpendicular to the second support surface 140F2 is defined as ATsu, and the average length of the metal crystal grains 180P constituting the IC separator 180 in the direction perpendicular to the second support surface 140F2 is defined as ATspI, the relationship ATspI>ATsu is satisfied.

[0076] The load of the unit cell separator 120 and the IC separator 180 is applied to the fuel electrode frame 140 in a direction perpendicular to the support surfaces 140F1 and 140F2. According to the above configuration, the fuel electrode frame 140 has a smaller tolerance for plastic deformation in the direction perpendicular to the support surfaces 140F1 and 140F2 than in the direction along the support surfaces 140F1 and 140F2, so that the force withstanding the load of the unit cell separator 120 and the IC separator 180 applied from the direction perpendicular to the support surfaces 140F1 and 140F2 can be relatively increased.

[0077] The anode frame 140 has a first region Ar1 adjacent to the support surfaces 140F1 and 140F2 and a second region Ar2 that is farther from the support surfaces 140F1 and 140F2 than the first region Ar1. When the average crystal grain size of the metal crystal grains 140P that make up the anode frame 140 is defined as ADsu1 and the average crystal grain size of the metal crystal grains 140P that are included in the first region Ar1 is defined as ADsu2, ADsu1 > ADsu2 is satisfied.

[0078] With this configuration, the first region Ar1 of the fuel electrode frame 140 adjacent to the support surfaces 140F1 and 140F2 is relatively susceptible to plastic deformation and is more likely to follow the plastic deformation of the unit cell separator 120 and the IC separator 180. This reduces the stress generated on the support surfaces 140F1 and 140F2.

[0079] 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. (1) In the above embodiment, the support member is the fuel electrode frame 140, but the support member may be, for example, a metal air electrode frame. (2) In the above embodiment, the single cell separator 120 overlaps the first support surface 140F1 of the fuel electrode frame 140, and the IC separator 180 overlaps the second support surface 140F2. However, the separator may overlap only one surface of the support member. In this case, the region adjacent to one surface of the support member may be defined as the first region, and the region adjacent to the other surface opposite the one surface may be defined as the second region. (3) In the above embodiment, the average grain size of the crystal grains 140P included in the first region Ar1 of the anode frame 140 is set to ADsu1, and the average grain size of the crystal grains 140P included in the second region Ar2 is set to ADsu2. However, for example, the grain size of the crystal grains included in the support member may be uniform overall. Also, the average grain size of the crystal grains 140P included in the first region Ar1 may be set to ADsu1, and the average grain size of the crystal grains 140P included in the second region Ar2 may be set to smaller than ADsu2. (4) In the above embodiment, the crystal grains 140P contained in the fuel electrode frame 140 have a flat shape, but for example, the crystal grains contained in the support member may have a shape close to spherical. Also, the shape of the crystal grains contained in the separator may be arbitrary. (5) In the above embodiment, the single cell separator 120 and the IC separator 180 are in contact with the fuel electrode frame, but the support member does not have to be in contact with the separator. For example, the support member may be bonded to the separator via a bonding material. (6) In the above embodiment, ferritic stainless steel was used as an example of the material for the single cell separator 120, the IC separator 180, and the fuel electrode frame 140. However, the material for the support member and the separator may be a metal other than ferritic stainless steel. Furthermore, the material for the support member and the material for the separator may be different metals. Even when different metals are used, the larger the particle size, the easier it is to undergo plastic deformation. Therefore, the configuration disclosed in this specification can be applied. (7) The above configuration can also be applied to cell stacks used in other types of fuel cells, such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolysis cell stacks that include electrolysis cell units, which are the constituent elements of solid oxide electrolysis cells (SOECs), as single cells. [Explanation of symbols]

[0080] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Anode 118: Reaction prevention layer 120: Separator for single cell (separator) 120P: Crystal grains 121: Through hole 124: Joint portion 125: Glass seal portion 130: Air electrode frame 131: Through hole 140: Anode frame (support member) 140F1: First support surface (support surface) 140F2: Second support surface (support surface) 140P: Crystal grains 141: Through hole 144: Anode current collecting member 145: Electrode facing portion 146: Interconnector facing portion 149: Spacer 180: IC separator (separator) 180P: Crystal grains 181: Through hole 190: Interconnector 191: Flat plate portion 192: Air electrode current collecting portion 193: Coating layer 194: Oxide coating 196: Conductive bonding material 210: First end plate 211: Through hole 220: Terminal separator 230: Second end plate 231: Through hole 280A, 280B: Gas passage member 281A, 281B: Main body portion 282A, 282B: Branch portion 311: Oxidant gas supply manifold 312: Oxidant gas discharge manifold 313: Air chamber (oxidant gas flow space) 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber (fuel gas flow space) Ar1: First region Ar2: Second region B: Bolt BH: Bolt hole FG: Fuel gas FOG: Fuel off-gas L1, L2: Virtual lines N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas S: Insulation sheet TspC: Vertical length WspC: Parallel length

Claims

1. a single cell including an air electrode, an electrolyte layer, and an anode; a metallic separator connected to the single cell and separating a fuel gas flow space through which a fuel gas supplied to the fuel electrode flows and an oxidant gas flow space through which an oxidant gas supplied to the air electrode flows; a metal support member that supports the separator; Equipped with When the average crystal grain size of the metal constituting the separator is ADsp and the average crystal grain size of the metal constituting the support member is ADsu, ADsp>ADsu is satisfied; Electrochemical reaction cell stack.

2. the metal crystal grains constituting the support member have a flat shape and are arranged along a support surface of the support member that faces the separator, The average length of the metal crystal grains constituting the support member in the direction perpendicular to the support surface is denoted by ATsu, When the average length of the crystal grains of the metal constituting the separator in the direction perpendicular to the support surface is defined as ATsp, ATsp>ATsu is satisfied; The electrochemical reaction cell stack according to claim 1 .

3. The support member is a first region adjacent to the support surface facing the separator; a second region that is farther from the support surface than the first region, Among the crystal grains of the metal constituting the support member, The average grain size of the crystal grains contained in the first region is defined as ADsu1, When the average crystal grain size of the crystal grains contained in the second region is ADsu2, ADsu1>ADsu2 is satisfied; The electrochemical reaction cell stack according to claim 1 or 2.

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