Current collecting structure for electrochemical reaction cell stack and electrochemical reaction cell stack

Abstract

To suppress an increase in resistance of an electrochemical reaction cell stack.SOLUTION: A current collecting structure for an electrochemical reaction cell stack includes a Cr-containing member formed from an alloy containing Cr, and a Ni member formed from Ni and joined to the Cr-containing member. The Ni member contains 0.0001 mass% or more of a specific element selected from Ti, Al, Mn, Si, and Mg.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a current collecting structure for an electrochemical reaction cell stack and an electrochemical reaction cell stack. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs") are known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack. A fuel cell stack includes a single cell and a current collecting structure for a fuel cell stack (hereinafter simply referred to as a "current collecting structure"). The current collecting structure is electrically connected to the single cell and collects the electricity generated by the single cell.

[0003] Conventionally, a current collecting structure has been disclosed that includes an interconnector (Cr-containing member) formed from ferritic stainless steel, which is an alloy containing Cr, and a fuel electrode side current collector (Ni member) formed from Ni and joined to the interconnector (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6773472 Summary of the Invention [Problem to be solved by the invention]

[0005] During operation of the electrochemical reaction cell stack, Cr diffusing from the Cr-containing component reacts with oxygen dissociated from H2O contained in the gas in the electrochemical reaction cell stack, causing an internal oxidation layer (e.g., a layer containing Cr2O3) to grow inside the Ni component. The growth of the internal oxidation layer may block the conduction path in the current collecting structure, causing an increase in the resistance value of the electrochemical reaction cell stack.

[0006] Note that such issues are also common to current collecting structures used in electrolysis cell stacks, which are a type of electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen by electrolysis of water. In this specification, a single fuel cell cell and a single electrolysis cell are collectively referred to as a single electrochemical reaction cell, and a fuel cell stack and an electrolysis cell stack are collectively referred to as an electrochemical reaction cell stack. Furthermore, such 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 current collecting structure for an electrochemical reaction cell stack disclosed herein includes a Cr-containing member formed from an alloy containing Cr and a Ni member formed from Ni and joined to the Cr-containing member. The Ni member contains 0.0001 mass% or more of a specific element selected from the group consisting of Ti, Al, Mn, Si, and Mg. According to this current collecting structure for an electrochemical reaction cell stack, during the manufacturing process or operation of the electrochemical reaction cell stack, oxidation of the specific element within the Ni member occurs preferentially over oxidation of Cr diffusing from the Cr-containing member, resulting in the formation of an oxide containing the specific element. This prevents further penetration of oxygen into the Ni member and the growth of an internal oxidation layer in the Ni member. This prevents the current collecting structure for an electrochemical reaction cell stack from disrupting the conductive path, thereby preventing an increase in the resistance of the electrochemical reaction cell stack.

[0010] (2) In the current collecting structure for an electrochemical reaction cell stack, the Ni member may contain 1 mass % or less of the specific element. This current collecting structure for an electrochemical reaction cell stack can prevent continuous formation of oxides containing the specific element inside the Ni member. This can more effectively prevent the conductive path in the current collecting structure for an electrochemical reaction cell stack from being interrupted, and ultimately more effectively prevent an increase in the resistance value of the electrochemical reaction cell stack.

[0011] (3) In the current collecting structure for an electrochemical reaction cell stack, the Ni member may contain an oxide containing the specific element, and the oxide may be contained in a larger amount at the grain boundaries of Ni crystal grains than within the grains. According to this current collecting structure for an electrochemical reaction cell stack, the Ni member contains a large amount of the oxide containing the specific element at the grain boundaries between Ni crystal grains, where oxygen diffuses relatively quickly, thereby effectively suppressing further penetration of oxygen into the Ni member.

[0012] (4) In the current collecting structure for an electrochemical reaction cell stack, the Ni member may contain an oxide containing the specific element in a surface layer including the surface not bonded to the Cr-containing member. Generally, oxygen penetration into the interior of a Ni member is likely to occur at the surface of the Ni member not bonded to the Cr-containing member. According to this current collecting structure for an electrochemical reaction cell stack, the Ni member contains an oxide containing the specific element in a surface layer including the surface not bonded to the Cr-containing member, thereby effectively suppressing further penetration of oxygen into the interior of the Ni member.

[0013] (5) In the current collecting structure for an electrochemical reaction cell stack, the surface layer may contain an oxide containing the specific element at a ratio of 10% or more. Generally, oxygen penetration into the interior of a Ni component is likely to occur on the surface of the Ni component that is not joined to the Cr-containing component. According to this current collecting structure for an electrochemical reaction cell stack, the surface layer contains an oxide containing the specific element at a ratio of 10% or more, thereby effectively suppressing further penetration of oxygen into the interior of the Ni component.

[0014] (6) The electrochemical reaction cell stack disclosed in this specification includes the current collecting structure for an electrochemical reaction cell stack according to any one of (1) to (5) above, and a single cell electrically connected to the current collecting structure for an electrochemical reaction cell stack. According to this electrochemical reaction cell stack, the current collecting structure for an electrochemical reaction cell stack prevents further penetration of oxygen into the Ni components, thereby suppressing the growth of an internal oxidation layer in the Ni components. This prevents the current collecting structure for an electrochemical reaction cell stack from interrupting the conductive path, thereby preventing an increase in the resistance of the electrochemical reaction cell stack.

[0015] The technology disclosed in this specification can be realized in various forms, such as a current collecting structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a method for manufacturing a current collecting structure for an electrochemical reaction cell stack. [Brief explanation of the drawings]

[0016] [Figure 1] A perspective view showing the appearance of a fuel cell stack. [Figure 2] FIG. 2 is an explanatory diagram showing an XZ cross section of the fuel cell stack taken along the line II-II in FIG. 1; [Figure 3] FIG. 2 is an explanatory diagram showing an XZ cross section of the fuel cell stack taken along the line III-III in FIG. 1; [Figure 4] An explanatory diagram showing an XZ cross section of two adjacent power generating units at the same position as the cross section shown in Figure 2. [Figure 5] FIG. 4 is an explanatory diagram showing an XZ cross section of two adjacent power generating units at the same position as the cross section shown in FIG. 3. [Figure 6] 1 is a cross-sectional view showing details of a current collecting structure according to an embodiment; [Figure 7] 1 is a cross-sectional view showing details of a current collecting structure according to an embodiment; [Figure 8] Flowchart showing the method of manufacturing a current collecting structure [Figure 9] 10 is a cross-sectional view showing details of a current collecting structure according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] A. Implementation: (Configuration of fuel cell stack 10) FIG. 1 is a perspective view showing the appearance of a fuel cell stack 10. FIG. 2 is an explanatory diagram showing an XZ cross section of the fuel cell stack 10 taken along line II-II in FIG. 1 . FIG. 3 is an explanatory diagram showing an XZ cross section of the fuel cell stack 10 taken along line III-III in FIG. 1 . Each figure shows mutually orthogonal X, Y, and Z axes for identifying directions. For convenience, the Z-axis direction is 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 a direction different from these directions. Furthermore, unless otherwise specified, the "thickness" of each component in this specification refers to the vertical length of each component. The fuel cell stack 10 is an example of an electrochemical reaction cell stack.

[0018] 1 to 3, the fuel cell stack 10 includes a power generation block 100, an end separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating section 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating section 220, the end separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have rectangular outer shapes of approximately the same size and are arranged in a stacked manner in this order in a predetermined arrangement direction (vertical direction).

[0019] As shown in FIG. 1, the fuel cell stack 10 has bolt holes BH near each of the four corners, penetrating from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. A nut N is screwed onto both ends of each bolt B. These bolts B and nuts N fasten the members from the first end plate 210 to the second end plate 270 together. As shown in FIGS. 2 and 3, the first plate 232 is supported by the terminal separator 230. Four gas passage members 280 are connected to the second end plate 270.

[0020] As shown in FIGS. 2 and 3, 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] The first end plate 210 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel. As shown in FIGS. 1 to 3 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is formed around the entire outer periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is formed around the entire inner periphery of the flat portion 211.

[0022] Insulating section 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of, for example, an insulating material. As shown in Figures 2 and 3, insulating section 220 is sandwiched between first end plate 210 and end separator 230, thereby ensuring insulation between first end plate 210 and end separator 230.

[0023] As shown in FIGS. 2 and 3, the terminal separator 230 is a rectangular frame-shaped member having a through-hole 231 near the center, and is made of, for example, metal.

[0024] The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined by welding, for example, to the periphery of the through-hole 231 in the terminal separator 230. The terminal separator 230 and the first plate 232 separate the power generating block 100 from the external space of the fuel cell stack 10.

[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] 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] 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 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] 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] 1 to 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] 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 formed therethrough in the vertical direction. The flange portion 282 is provided so as to protrude outward from the other end (the lower end in FIGS. 2 and 3 ) 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 is connected to 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] Fig. 4 is an explanatory diagram showing an XZ cross section of two adjacent power generating units 100U at the same position as the cross section shown in Fig. 2. Fig. 5 is an explanatory diagram showing an XZ cross section of two adjacent power generating units 100U at the same position as the cross section shown in Fig. 3. As shown in Figs. 4 and 5, the power generating unit 100U includes a single cell 110, a single cell separator 120, an air electrode frame 130, an anode frame 140, a current collecting structure 160, 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.

[0035] The unit cell 110 includes an electrolyte layer 112, an air electrode 114, an anode 116, and a reaction prevention layer 118. As shown in Figures 4 and 5, the air electrode 114, the reaction prevention layer 118, the electrolyte layer 112, and the anode 116 are arranged 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, air electrode 114, and reaction prevention layer 118) that make up the unit cell 110. The unit cell 110 is supported by a unit cell separator 120.

[0036] The electrolyte layer 112 is a rectangular, flat member having one surface (the upper surface in FIGS. 4 and 5 ) on which the air electrode 114 is disposed and another surface (the lower surface in FIGS. 4 and 5 ) 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).

[0037] 4 and 5, the single cell separator 120 is a rectangular frame-like member having a substantially rectangular through-hole 121 near the center, and is made of, for example, metal. The peripheral edge of the through-hole 121 in the single cell separator 120 is joined to the peripheral edge of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is disposed: the upper surface in FIGS. 4 and 5) by a joint 124. The joint 124 is made of, for example, a brazing material (Ag brazing).

[0038] 4 and 5, 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. As shown in Fig. 4, 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.

[0039] 4 and 5, 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. 5, 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.

[0040] As shown in FIGS. 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center, and is made of, for example, metal.

[0041] The current collecting structure 160 is electrically connected to the unit cell 110 and collects the power generated in the unit cell 110. The current collecting structure 160 includes an interconnector 190 and an anode current collecting member 144. The current collecting structure 160 is an example of a current collecting structure for an electrochemical reaction cell stack. The interconnector 190 is an example of a Cr-containing member. The anode current collecting member 144 is an example of a Ni member.

[0042] As shown in FIGS. 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 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 formed from an alloy containing Fe and Cr (e.g., ferritic stainless steel) and are electrically conductive. 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. The interconnector 190 is supported by the IC separator 180.

[0043] The anode current collecting member 144 is a member that connects the interconnector 190 and the anode 116 and is made of Ni. In this specification, the anode current collecting member 144 is "made of Ni" means that Ni accounts for 90 wt % or more of the material of the anode current collecting member 144. The anode current collecting member 144 is a foil made of Ni. As shown in FIGS. 4 and 5 , the anode current collecting member 144 has an interconnector facing portion 146, an electrode facing portion 145 parallel to the interconnector facing portion 146, and a connecting portion 147 connecting the electrode facing portion 145 and the interconnector facing portion 146, and is U-shaped overall. The electrode facing portion 145 is joined to the anode 116, and the interconnector facing portion 146 is joined to a flat portion 191 of the interconnector 190. The anode current collecting member 144 is disposed between the unit cell 110 and the interconnector 190.

[0044] 4 and 5, the interconnector 190 is shared by two adjacent power generating units 100U. More specifically, as shown in FIGS. 4 and 5, 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.

[0045] However, as shown in Figure 2, the power generating unit 100U located at the other end (the lower end in Figure 2) of the multiple power generating units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 included in this power generating unit 100U is connected to the second terminal plate 250 via the fuel electrode current collecting member 144.

[0046] 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.

[0047] 4 and 5, the space partitioned by the single cell separator 120, single cell 110, air electrode frame 130, IC separator 180, and interconnector 190 faces the air electrode 114 and serves as an air chamber 313 through which oxidant gas OG flows. The air electrode frame 130 partitions the entire periphery of the air chamber 313 from the external space and seals the gap between the single cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 to the external space.

[0048] 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.

[0049] 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.

[0050] (Operation of fuel cell stack 10) As shown in Figures 2 and 4, 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.

[0051] As shown in FIGS. 3 and 5, 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.

[0052] 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.

[0053] 2 and 4, 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 5, 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.

[0054] (Details of current collecting structure 160) 6 and 7 are cross-sectional views showing details of the current collecting structure 160 of the embodiment. FIG. 6 shows an enlarged view of the X1 portion of FIG. 5. FIG. 7 shows an enlarged view of the X2 portion of FIG. 6. FIGS. 6 and 7 show a joint CP, which is a joint between the interconnector 190 and the anode current collecting member 144. The joint CP refers to a portion where the interconnector 190 and the anode current collecting member 144 are in physical contact. Specifically, when a cross section perpendicular to the XY plane is observed at 1000 times magnification using an SEM (e.g., a VE-9800 manufactured by Keyence Corporation; the same applies hereinafter), the joint CP refers to a portion where there is no gap of 1 μm or more between the interconnector 190 and the anode current collecting member 144. The anode current collecting member 144 also has a surface S1 that is not in contact with the interconnector 190 and a surface S2 that is in contact with the interconnector 190.

[0055] In addition to Ni, the anode current collecting member 144 contains 0.0001 mass % or more of a specific element selected from the group consisting of Ti, Al, Mn, Si, and Mg. The anode current collecting member 144 preferably contains 0.001 mass % or more of the specific element. The anode current collecting member 144 also preferably contains 1 mass % or less of the specific element. The anode current collecting member 144 may contain two or more of the specific elements.

[0056] The anode current collecting member 144 of this embodiment contains the specific element in the form of an oxide containing the specific element. An "oxide containing the specific element" is a compound containing at least the specific element and oxygen atoms, and may or may not contain other elements. The oxide contained in the anode current collecting member 144 can be identified as follows. Specifically, element mapping is performed using an EPMA on a cross section of the anode current collecting member 144 perpendicular to the XY plane. If oxygen atoms account for 50 mol % or more of the total elements excluding Ni in each measurement range, the compound contained in that measurement range can be identified as an oxide.

[0057] Oxides containing such specific elements are found more abundantly at the grain boundaries of Ni crystal grains contained in the anode current collecting member 144 than within the grains. In this specification, "grain boundaries" refers to the grain boundaries between Ni crystal grains and the area within 10 nm of the grain boundaries. The grain boundaries of Ni crystal grains can be identified as follows. First, the anode current collecting member 144 is processed using a focused ion beam (FIB), and the cross section of the anode current collecting member 144 is observed using a scanning electron microscope (SEM). Next, electron backscatter diffraction (EBSD) analysis is performed. In the crystal orientation map obtained by EBSD analysis, points where the crystal angles of adjacent measurement points differ by 10° or more can be identified as the grain boundaries of Ni crystal grains.

[0058] Furthermore, the oxide containing the specific element is present in a surface layer of the anode current collecting member 144, including the surface facing the fuel chamber 323. That is, the anode current collecting member 144 of this embodiment contains an oxide containing the specific element in a surface layer SL1, including the surface S1, which is the surface not bonded to the interconnector 190. The portion of the anode current collecting member 144 included in the surface layer SL1 can be identified as follows. First, a virtual perpendicular line is obtained starting from an arbitrary position on the surface S1. FIG. 7 shows a virtual perpendicular line PL1 as an example of a virtual perpendicular line. The virtual perpendicular line is an imaginary line whose starting point P1 is a point located on the surface S1 not bonded to the interconnector 190, passes through the interior of the anode current collecting member 144, and whose ending point P2 is a point located on the surface of the anode current collecting member 144 that is different from the starting point P1. Next, the virtual perpendicular line is divided into three equal parts. The portion of the anode current collecting member 144 located on the imaginary perpendicular line that is closest to the surface S1 among the three equal-divided imaginary perpendicular lines can be identified as the portion included in the surface layer SL1. When the anode current collecting member 144 is formed of foil as in this embodiment, a layer including the surface S1 when the anode current collecting member 144 is virtually divided into three equal parts in the thickness direction can be identified as the portion of the anode current collecting member 144 that is included in the surface layer SL1.

[0059] Furthermore, the surface layer SL1 contains an oxide containing the specific element at a ratio of 10% or more. The ratio of the specific element in the surface layer SL1 can be determined as follows. First, an SEM image of a cross section of the anode current collecting member 144 perpendicular to the XY plane is obtained at a magnification of 1000 times. Next, a line segment is drawn on the surface layer SL1 of the anode current collecting member 144 in the SEM image, connecting one end to the other end in a direction perpendicular to the thickness direction of the SEM image. Next, the length of the line segment (e.g., length Y) is determined. Next, the length of the portion of the line segment located on the oxide containing the specific element (e.g., length X) is determined. Next, the ratio of length X to length Y is calculated, thereby determining the ratio of the specific element in the surface layer SL1.

[0060] (Method of manufacturing current collecting structure 160) 8 is a flowchart showing a method for manufacturing the current collecting structure 160. The method for manufacturing the current collecting structure 160 is, for example, as follows.

[0061] First, the interconnector 190 and the anode current collecting member 144 are prepared (S11). The interconnector 190 and the anode current collecting member 144 can be formed by a known method. In this case, the anode current collecting member 144 is formed by mixing Ni and a specific element.

[0062] Next, the interconnector 190 and the anode current collecting member 144 are bonded (S12). Specifically, the interconnector 190 and the anode current collecting member 144 are bonded by, for example, maintaining them at a temperature of 850°C for 3 hours under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO. The oxygen partial pressure at which Ni is oxidized to NiO can be determined, for example, from an Ellingham diagram. The type of gas is not particularly limited as long as the oxygen partial pressure is equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO.

[0063] Next, the interconnector 190 and the anode current collecting member 144 are heated in a hydrogen gas atmosphere (S13). Specifically, the temperature is maintained at a predetermined temperature for three hours while hydrogen gas is circulated through the fuel chamber 323. As a result, the NiO oxidized in the step of S12 is reduced to Ni.

[0064] (Effects of this embodiment) As described above, the current collecting structure 160 of this embodiment includes the interconnector 190 made of an alloy containing Cr and the anode current collecting member 144 made of Ni and joined to the interconnector 190. The anode current collecting member 144 contains 0.0001 mass % or more of a specific element selected from the group consisting of Ti, Al, Mn, Si, and Mg. According to the current collecting structure 160 of this embodiment, during the manufacturing process or operation of the fuel cell stack 10, oxidation of the specific element occurs preferentially within the anode current collecting member 144 over oxidation of Cr diffusing from the interconnector 190, producing an oxide containing the specific element. This prevents further penetration of oxygen into the anode current collecting member 144 and inhibits the growth of an internal oxidation layer in the anode current collecting member 144. This prevents the current collecting structure 160 from disrupting the conductive path, thereby preventing an increase in the resistance of the fuel cell stack 10.

[0065] In the current collecting structure 160 of this embodiment, the anode current collecting member 144 contains 1 mass % or less of the specific element. The current collecting structure 160 of this embodiment can prevent continuous formation of oxides containing the specific element inside the anode current collecting member 144. This can more effectively prevent the conductive path in the current collecting structure 160 from being interrupted, and more effectively prevent an increase in the resistance value of the fuel cell stack 10.

[0066] In the current collecting structure 160 of this embodiment, the anode current collecting member 144 contains an oxide containing the specific element, and the oxide is contained in greater amounts at the grain boundaries of Ni crystal grains than within the grains. According to the current collecting structure 160 of this embodiment, the anode current collecting member 144 contains a large amount of the oxide containing the specific element at the grain boundaries between Ni crystal grains, where oxygen diffuses relatively quickly, and therefore, further penetration of oxygen into the anode current collecting member 144 can be effectively suppressed.

[0067] In the current collecting structure 160 of this embodiment, the anode current collecting member 144 contains an oxide containing a specific element in a surface layer SL1 that includes the surface S1 that is not joined to the interconnector 190. Generally, oxygen is likely to penetrate into the interior of the anode current collecting member 144 at the surface S1 of the anode current collecting member 144 that is not joined to the interconnector 190. According to the current collecting structure 160 of this embodiment, the anode current collecting member 144 contains an oxide containing a specific element in the surface layer SL1 that includes the surface S1 that is not joined to the interconnector 190, thereby effectively suppressing further penetration of oxygen into the interior of the anode current collecting member 144.

[0068] In the current collecting structure 160 of this embodiment, the oxide containing the specific element is present in a proportion of 10% or more in the surface layer SL1. Generally, oxygen is likely to penetrate into the interior of the anode current collecting member 144 at the surface S1 of the anode current collecting member 144 that is not joined to the interconnector 190. In the current collecting structure 160 of this embodiment, the oxide containing the specific element is present in a proportion of 10% or more in the surface layer SL1, so that further penetration of oxygen into the interior of the anode current collecting member 144 can be effectively suppressed.

[0069] The fuel cell stack 10 of this embodiment includes a current collecting structure 160 and a unit cell 110 electrically connected to the current collecting structure 160. According to the fuel cell stack 10 of this embodiment, the current collecting structure 160 prevents further intrusion of oxygen into the anode current collecting member 144, thereby suppressing the growth of an internal oxidation layer in the anode current collecting member 144. This prevents the current collecting structure 160 from interrupting the conductive path, thereby preventing an increase in the resistance value of the fuel cell stack 10.

[0070] (Performance evaluation) Next, performance evaluation of this embodiment will be described. Several samples (SA1 to SA15) of fuel cell stacks each having a current collecting structure with a different composition of the anode current collecting member were fabricated, and performance evaluation was carried out using these several samples. Table 1 shows the performance evaluation results.

[0071] First, the preparation of the evaluation sample will be described. A current collecting structure was prepared by the method described in the above-mentioned "Method for manufacturing current collecting structure 160." Specifically, an interconnector and an anode current collecting member were first prepared in step S11. Next, the components to be provided in the fuel cell stack were stacked, and the components from the first end plate to the second end plate were fastened together with bolts and nuts, and steps S12 and S13 were then carried out.

[0072] The fuel cell stack fabricated by the above method was subjected to a composition analysis of elements contained in the anode current collector. First, the anode current collector fabricated by the above method was dissolved in nitric acid. Next, the solution dissolved with nitric acid was subjected to inductively coupled plasma (ICP) emission spectroscopy to quantify Ti, Al, Mn, Si, Mg, Fe, and Ni.

[0073] The degradation rate of the fuel cell stack produced by the above method due to continuous operation was determined. First, the operation was started at 700°C, and the potential V I Next, the temperature was kept at 700°C and the operation was continued for 10,000 hours. E The deterioration rate of each sample of the fuel cell stack due to continuous operation was calculated using the following formula: Deterioration rate (%)=100×(V I -V E ) / V I

[0074] Table 1 shows the performance evaluation results. [Table 1]

[0075] The composition (mass %) of each element (Ti, Al, Mn, Si, Mg, Fe, and Ni) contained in the anode current collecting member of each sample and the deterioration rate of each sample are shown in Table 1. Of the elements contained in the anode current collecting member, Ti, Al, Mn, Si, and Mg are elements that fall under the aforementioned specific elements.

[0076] Among samples SA1 to SA15, the anode current collecting member of sample SA1 did not contain the specific element, while the anode current collecting members of samples SA2 to SA15 contained 0.0001 mass% or more of the specific element. Furthermore, the deterioration rates of samples SA2 to SA15 were lower than that of sample SA1. This confirmed that the deterioration rate of a fuel cell stack was reduced (i.e., durability was increased) when the anode current collecting member contained 0.0001% or more of the specific element.

[0077] The above results suggest the following. Specifically, since the specific element is more easily oxidized than Cr diffusing from the interconnector, oxidation of the specific element proceeds preferentially over oxidation of Cr during the manufacturing process or operation of the fuel cell stack, resulting in the formation of an oxide containing the specific element. This is thought to have suppressed further penetration of oxygen into the interior of the anode current collecting member and the growth of an internal oxidation layer in the anode current collecting member, thereby suppressing the interruption of the conductive path in the current collecting structure and suppressing an increase in the resistivity of the fuel cell stack.

[0078] Furthermore, among samples SA2 to SA15, the anode current collecting members of samples SA2 to SA13 contained 1 mass% or less of the specific element, while the anode current collecting members of samples SA14 and SA15 contained more than 1 mass% of the specific element. Furthermore, the deterioration rates of samples SA2 to SA13 were lower than those of samples SA14 and SA15. This confirmed that the deterioration rate of a fuel cell stack is lower (i.e., durability is increased) when the anode current collecting member contains 1 mass% or less of the specific element.

[0079] The above results suggest the following. Specifically, since the specific element is more easily oxidized than Cr diffusing from the interconnector, oxidation of the specific element proceeds preferentially over oxidation of Cr during the manufacturing process or operation of the fuel cell stack, resulting in the formation of an oxide containing the specific element. The oxide containing the specific element can suppress the oxidation of Cr, but if the content of the specific element is above a certain level, it is believed that the continuous formation of the oxide containing the specific element results in the interruption of the conductive path in the current collecting structure. It is believed that in samples in which the specific element contained 1 mass % or less of the specific element in the anode current collecting member, the continuous formation of the oxide containing the specific element was suppressed, thereby suppressing the interruption of the conductive path in the current collecting structure.

[0080] Among samples SA2 to SA15, the anode current collecting members of samples SA2, SA3, and SA9 to SA13 contained 0.001 mass% or more of the specific element, while the anode current collecting members of samples SA4 to SA8 contained less than 0.001 mass% of the specific element. Furthermore, the deterioration rates of samples SA2, SA3, and SA9 to SA13 were lower than those of samples SA4 to SA8. This confirmed that it is more preferable for the anode current collecting member to contain 0.001 mass% or more of the specific element (i.e., to have higher durability).

[0081] 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.

[0082] The configurations of the fuel cell stack 10 and the power generating unit 100U in the above embodiment are merely examples, and various modifications are possible.

[0083] 9 is a cross-sectional view showing details of the current collecting structure 160a of the modified example. In the following, parts of the fuel cell stack 10 of the modified example that are common to the fuel cell stack 10 of the above-described embodiment are denoted by the same reference numerals and descriptions thereof will be omitted as appropriate.

[0084] The current collecting structure 160a of the modified example differs from the current collecting structure 160 of the embodiment in the configuration of the anode current collecting member. Specifically, in the current collecting structure 160a of the modified example, the anode current collecting member 144a is formed of a mesh. The anode current collecting member 144a is formed of multiple wires made of Ni, and wires extending in the X-axis direction and wires extending in the Y-axis direction form a mesh structure. Each wire included in the mesh has a thickness T1.

[0085] As with the current collecting structure 160a of the modified example, the shape of the Ni member is not limited. In the anode current collecting member 144a of such a current collecting structure 160a, the portion of the anode current collecting member 144a included in the surface layer SL1a can be identified as follows. First, as with the anode current collecting member 144 of the embodiment, an imaginary perpendicular line is obtained starting from any position on the surface not joined to the interconnector 190. Next, the imaginary perpendicular line is divided into thirds. The portion of the anode current collecting member 144 located on the imaginary perpendicular line closest to the surface not joined to the interconnector 190 and at least one-third of the thickness T1 away from the surface of the interconnector 190 can be identified as the portion included in the surface layer SL1a. In other words, when the anode current collecting member 144a is formed of a mesh as in the present embodiment, the portion of the anode current collecting member 144 excluding the inner portion IP and the joining surface layer CS can be identified as the portion of the anode current collecting member 144a included in the surface layer SL1a. More specifically, the inner portion IP is a portion of the anode current collecting member 144a that is not located on any of the three equally divided imaginary perpendicular lines that is closest to the surface that is not joined to the interconnector 190. The joining surface layer CS is a surface layer of the anode current collecting member 144 in the vicinity of the joining portion CP with the interconnector 190. More specifically, the joining surface layer CS is a portion of the anode current collecting member 144 that is not more than one-third of the thickness T1 away from the surface of the interconnector 190.

[0086] The Ni member may contain 1 mass % or more of a specific element.

[0087] The Ni member does not necessarily have to contain the specific element in the form of an oxide. The oxide containing the specific element may be contained more in the Ni crystal grains than in the grain boundaries.

[0088] The Ni member does not necessarily have to contain an oxide containing the specific element in the surface layer, including the surface not joined to the Cr-containing member, and the proportion of the oxide containing the specific element in the surface layer may be less than 10%.

[0089] The number of unit cells 110 (number of power generating units 100U) included in the fuel cell stack 10 in the above embodiment is merely an example, and the number of unit cells is determined appropriately depending on the output voltage required for the fuel cell stack.

[0090] The materials of the components in the above embodiment are merely examples, and the components may be made of other materials.

[0091] The method for manufacturing the current collecting structure is not limited to the above embodiment.

[0092] 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.

[0093] 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.

[0094] In the current collecting structure 160 of the above embodiment, the interconnector 190 is an example of a Cr-containing member, but the Cr-containing member is not limited thereto. For example, if the first plate 232 in the above embodiment contains Cr, the first plate 232 can also be an example of a Cr-containing member, and if the metal support in a metal-supported unit cell contains Cr, the metal support can also be an example of a Cr-containing member. Similarly, in the current collecting structure 160 of the above embodiment, the anode current collecting member 144 is an example of a Ni member, but the Ni member is not limited thereto.

[0095] In the above embodiment, the fuel cell stack 10 is configured to have a plurality of flat-type unit cells 110, but the technology disclosed in this specification is equally applicable to fuel cell stacks having a plurality of unit cells of other types (e.g., cylindrical, flat cylindrical, etc.).

[0096] 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]

[0097] 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 130: air electrode frame 132: oxidant gas supply communication channel 133: oxidant gas discharge communication channel 140: fuel electrode frame 142: fuel gas supply communication channel 143: fuel gas discharge communication channel 144, 144a: fuel electrode current collecting member 149: spacer 160, 160a: current collecting structure 180: IC separator 190: interconnector 191: flat plate portion 192: air electrode current collecting portion 193: coating layer 196: conductive bonding material 210: first end plate 220: insulating portion 230: terminal separator 232: First plate 240: First terminal plate 250: Second terminal plate 260: Second plate 270: Second end plate 280: Gas passage member 311: Oxidizer gas supply manifold 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge 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 CP: Joint S1: Surface S2: Surface SL1, SL1a: Surface layer

Claims

1. a Cr-containing member formed from an alloy containing Cr; a Ni member formed from Ni and joined to the Cr-containing member; A current collecting structure for an electrochemical reaction cell stack, comprising: The Ni member contains 0.0001 mass % or more of a specific element selected from the group consisting of Ti, Al, Mn, Si, and Mg. A current collecting structure for an electrochemical reaction cell stack, comprising:

2. The current collecting structure for an electrochemical reaction cell stack according to claim 1, The Ni member contains the specific element in an amount of 1 mass% or less. A current collecting structure for an electrochemical reaction cell stack, comprising:

3. The current collecting structure for an electrochemical reaction cell stack according to claim 1, the Ni member contains an oxide containing the specific element, The oxide is contained more in the grain boundaries than in the grain interiors of Ni crystal grains. A current collecting structure for an electrochemical reaction cell stack, comprising:

4. The current collecting structure for an electrochemical reaction cell stack according to claim 1, The Ni member contains an oxide containing the specific element in a surface layer including a surface not joined to the Cr-containing member. A current collecting structure for an electrochemical reaction cell stack, comprising:

5. The current collecting structure for an electrochemical reaction cell stack according to claim 4, The surface layer contains an oxide containing the specific element at a ratio of 10% or more. A current collecting structure for an electrochemical reaction cell stack, comprising:

6. A current collecting structure for an electrochemical reaction cell stack according to any one of claims 1 to 5; a single cell electrically connected to the current collecting structure for the electrochemical reaction cell stack, An electrochemical reaction cell stack comprising:

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