Electrochemical reaction cell component and electrochemical reaction cell stack

Abstract

To prevent a coating layer from peeling off from a substrate.SOLUTION: An electrochemical reaction cell member is electrically connected to an electrochemical reaction cell. The electrochemical reaction cell member includes a metal substrate, a coating layer covering at least a portion of the surface of the substrate, and an oxide film located between the substrate and the coating layer. The oxide film has a plurality of large protrusions. After a current treatment equivalent to 3000 hours at 900°C, the plurality of protrusions are embedded in the coating layer and have a greater height difference than the surface of the substrate.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The technology disclosed by this specification relates to a member for an electrochemical reaction cell.

Background Art

[0002] As one of fuel cells that generate electricity by utilizing the electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") is known. A fuel cell power generation unit (hereinafter referred to as "power generation unit"), which is a constituent unit of an SOFC, includes a fuel cell single cell (hereinafter referred to as "single cell") and an interconnector member. The single cell includes an electrolyte layer, and an air electrode and a fuel electrode that face each other in a predetermined direction (hereinafter referred to as "first direction") with the electrolyte layer interposed therebetween. The interconnector member is electrically connected to the air electrode or the fuel electrode that constitutes the single cell.

[0003] The interconnector member includes a metal base material, a coating layer that covers the surface of the base material, and an oxide film located between the base material and the coating layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a conventional interconnector member, for example, due to aging deterioration or the like, the thickness of the oxide film formed on the surface of the base material increases. As the thickness of the oxide film increases, stress caused by the thermal expansion difference between the base material and the coating layer during a thermal cycle accumulates, and the coating layer is likely to peel off from the base material.

[0006] Such problems are not limited to interconnector members, but are common problems also for members for an electrochemical reaction cell that are electrically connected to an electrochemical reaction cell, such as separators and current collectors, and for members for an electrochemical reaction cell that are electrically connected to an electrolysis cell unit which is a constituent unit of a solid oxide type electrolysis cell (hereinafter also referred to as "SOEC") that generates hydrogen by utilizing an electrolysis reaction of water. In this specification, a fuel cell power generation unit and an electrolysis cell unit are collectively referred to as an electrochemical reaction unit. Further, such problems are common problems not limited to SOFCs and SOECs, but also for other types of electrochemical reaction units.

[0007] This specification discloses a technology capable of solving the above-described problems.

Means for Solving the Problems

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

[0009] (1) The member for an electrochemical reaction cell disclosed in this specification is electrically connected to an electrochemical reaction cell. The member for an electrochemical reaction cell includes a metal base material, a coating layer covering at least a part of the surface of the base material, and an oxide film positioned between the base material and the coating layer. The oxide film has a plurality of convex portions that bite into the coating layer after energization treatment equivalent to 3000 hours at 900°C, and the plurality of convex portions have a greater height difference than the surface of the base material.

[0010] A member for an electrochemical reaction cell that is electrically connected to the electrochemical reaction cell has, for example, due to aging deterioration or the like, an increase in the thickness of the oxide film formed on the surface of the base material. As the thickness of the oxide film increases, stress caused by the thermal expansion difference between the base material and the coating layer during thermal cycling accumulates, making the coating layer more likely to peel off from the base material. According to this member for an electrochemical reaction cell, after energization treatment equivalent to 3000 hours at 900 °C, the oxide film has a plurality of convex portions that bite into the coating layer and have a greater height difference than the surface of the base material. Therefore, the peeling of the coating layer from the base material can be suppressed by the anchor effect of the plurality of convex portions.

[0011] (2) In the member for an electrochemical reaction cell, the metal base material may contain chromium, and the main component of the oxide film may be chromium oxide. According to this member for an electrochemical reaction cell, since the main component of the oxide film is chromium oxide with high chemical stability, the peeling of the coating layer from the base material can be effectively suppressed.

[0012] (3) In the member for an electrochemical reaction cell, the plurality of convex portions may include a first convex portion and a second convex portion adjacent to each other, and the height difference of the first convex portion may be equal to or greater than the maximum separation distance between the first convex portion and the second convex portion. According to this member for an electrochemical reaction cell, since the anchor effect is further enhanced, the peeling of the coating layer from the base material can be effectively suppressed.

[0013] Note that the technology disclosed in this specification can be realized in various forms. For example, a member for an electrochemical reaction cell (interconnector member, separator, current collector, etc.) that is electrically connected to an electrochemical reaction cell, an electrochemical reaction unit (fuel cell power generation unit or electrolysis cell unit) including a member for an electrochemical reaction cell and an electrochemical reaction single cell (fuel cell single cell or electrolysis single cell), an electrochemical reaction cell stack (fuel cell stack or electrolysis cell stack) including a plurality of electrochemical reaction units, and their manufacturing methods and other forms.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0015] A. Embodiment: A-1. Configuration of the fuel cell stack 100: (Configuration of the fuel cell stack 100) FIG. 1 is a perspective view showing the external configuration of the fuel cell stack 100 in the present embodiment, FIG. 2 is an explanatory view showing the XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II of FIG. 1 (and FIGS. 6 and 7 described later), and FIG. 3 is an explanatory view showing the YZ cross-sectional configuration of the fuel cell stack 100 at the position III-III of FIG. 1 (and FIGS. 6 and 7 described later). In each figure, XYZ axes orthogonal to each other for specifying directions are shown. In this specification, for convenience, the positive direction of the Z axis is referred to as the upward direction, and the negative direction of the Z axis is referred to as the downward direction. However, the fuel cell stack 100 may actually be installed in a direction different from such a direction. The same applies to FIGS. 4 and later.

[0016] The fuel cell stack 100 includes a plurality of (seven in the present embodiment) fuel cell power generation units (hereinafter simply referred to as "power generation units") 102 and a pair of end plates 104 and 106. The seven power generation units 102 are arranged side by side in a predetermined arrangement direction (the vertical direction in the present embodiment). The pair of end plates 104 and 106 are arranged so as to sandwich the assembly composed of the seven power generation units 102 from above and below.

[0017] A plurality of (eight in the present embodiment) holes penetrating in the vertical direction are formed at the peripheral portions of each layer (power generation unit 102, end plates 104 and 106) constituting the fuel cell stack 100 in the circumferential direction around the Z axis. The holes formed in each layer and corresponding to each other communicate with each other in the vertical direction to constitute a communication hole 108 extending in the vertical direction from one end plate 104 to the other end plate 106. In the following description, the holes formed in each layer of the fuel cell stack 100 to constitute the communication hole 108 may also be referred to as the communication hole 108.

[0018] A bolt 22 extending in the vertical direction is inserted into each communication hole 108, and the fuel cell stack 100 is fastened by the bolt 22 and nuts 24 fitted on both sides of the bolt 22. As shown in FIGS. 2 and 3, between the nut 24 fitted on one side (upper side) of the bolt 22 and the upper surface of the end plate 104 constituting the upper end of the fuel cell stack 100, and between the nut 24 fitted on the other side (lower side) of the bolt 22 and the lower surface of the end plate 106 constituting the lower end of the fuel cell stack 100, an insulating sheet 26 is interposed. However, at the location where the gas passage member 27 described later is provided, between the nut 24 and the surface of the end plate 106, the gas passage member 27 and the insulating sheets 26 arranged on the upper and lower sides of the gas passage member 27 are interposed. The insulating sheet 26 is composed of, for example, a mica sheet, a ceramic fiber sheet, a ceramic compacted powder sheet, a glass sheet, a glass-ceramic composite, etc.

[0019] The outer diameter of the shaft portion of each bolt 22 is smaller than the inner diameter of each communication hole 108. Therefore, a space is secured between the outer peripheral surface of the shaft portion of each bolt 22 and the inner peripheral surface of each communication hole 108. As shown in FIGS. 1 and 2, a bolt 22 (bolt 22A) located near the midpoint of one side (the side on the positive X-axis side of the two sides parallel to the Y-axis) on the outer periphery of the fuel cell stack 100 around the Z-axis direction, and the space formed by the communication hole 108 through which the bolt 22A is inserted functions as an oxidant gas introduction manifold 161, which is a gas flow path for introducing the oxidant gas OG from the outside of the fuel cell stack 100 and supplying the oxidant gas OG to each power generation unit 102. A bolt 22 (bolt 22B) located near the midpoint of the opposite side (the side on the negative X-axis side of the two sides parallel to the Y-axis) of the side functions as an oxidant gas discharge manifold 162 for discharging the oxidant off-gas OOG, which is the gas discharged from the air chamber 166 of each power generation unit 102, to the outside of the fuel cell stack 100. In this embodiment, for example, air is used as the oxidant gas OG.

[0020] Also, as shown in FIGS. 1 and 3, a space formed by a bolt 22 (bolt 22D) located near the midpoint of one side (the side on the positive Y-axis side of the two sides parallel to the X-axis) on the outer periphery of the fuel cell stack 100 around the Z-axis, and a communication hole 108 through which the bolt 22D is inserted functions as a fuel gas introduction manifold 171 for introducing fuel gas FG from outside the fuel cell stack 100 and supplying the fuel gas FG to each power generation unit 102. A space formed by a bolt 22 (bolt 22E) located near the midpoint of the opposite side (the side on the negative Y-axis side of the two sides parallel to the X-axis) of the side, and a communication hole 108 through which the bolt 22E is inserted functions as a fuel gas discharge manifold 172 for discharging fuel off-gas FOG, which is the gas discharged from the fuel chamber 176 of each power generation unit 102, to the outside of the fuel cell stack 100. In this embodiment, as the fuel gas FG, for example, a hydrogen-rich gas obtained by reforming city gas is used.

[0021] Four gas passage members 27 are provided in the fuel cell stack 100. Each gas passage member 27 has a hollow cylindrical main body portion 28 and a hollow cylindrical branch portion 29 branched from the side surface of the main body portion 28. The hole of the branch portion 29 communicates with the hole of the main body portion 28. A gas pipe (not shown) is connected to the branch portion 29 of each gas passage member 27. Also, as shown in FIG. 2, the hole of the main body portion 28 of the gas passage member 27 arranged at the position of the bolt 22A forming the oxidant gas introduction manifold 161 communicates with the oxidant gas introduction manifold 161, and the hole of the main body portion 28 of the gas passage member 27 arranged at the position of the bolt 22B forming the oxidant gas discharge manifold 162 communicates with the oxidant gas discharge manifold 162. Further, as shown in FIG. 3, the hole of the main body portion 28 of the gas passage member 27 arranged at the position of the bolt 22D forming the fuel gas introduction manifold 171 communicates with the fuel gas introduction manifold 171, and the hole of the main body portion 28 of the gas passage member 27 arranged at the position of the bolt 22E forming the fuel gas discharge manifold 172 communicates with the fuel gas discharge manifold 172.

[0022] (Configuration of End Plates 104 and 106) The pair of end plates 104 and 106 are conductive members in a substantially rectangular flat plate shape, and are formed of, for example, stainless steel. One end plate 104 is disposed above the uppermost power generation unit 102, and the other end plate 106 is disposed below the lowermost power generation unit 102. The plurality of power generation units 102 are sandwiched between the pair of end plates 104 and 106 in a pressed state. The upper end plate 104 functions as the positive output terminal of the fuel cell stack 100, and the lower end plate 106 functions as the negative output terminal of the fuel cell stack 100.

[0023] (Configuration of the power generation unit 102) FIG. 4 is an explanatory view showing the XZ cross-sectional configuration of two adjacent power generation units 102 at the same position as the cross section shown in FIG. 2, and FIG. 5 is an explanatory view showing the YZ cross-sectional configuration of two adjacent power generation units 102 at the same position as the cross section shown in FIG. 3. At the upper part of FIG. 5, the YZ cross-sectional configuration of a part of the power generation unit 102 is shown enlarged. Further, FIG. 6 is an explanatory view showing the XY cross-sectional configuration of the power generation unit 102 at the position of VI-VI in FIG. 4, and FIG. 7 is an explanatory view showing the XY cross-sectional configuration of the power generation unit 102 at the position of VII-VII in FIG. 4.

[0024] As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air electrode side frame 130, an air electrode side current collector 134, a fuel electrode side frame 140, a fuel electrode side current collector 144, and a pair of interconnects 150 that constitute the uppermost layer and the lowermost layer of the power generation unit 102. Holes corresponding to the through holes 108 through which the above-described bolts 22 are inserted are formed at the peripheral portions of the separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnect 150 around the Z-axis direction.

[0025] The interconnector 150 is a substantially rectangular flat plate-shaped conductive member, and is formed of, for example, a ferrite-based stainless steel. The interconnector 150 ensures electrical conductivity between the power generation units 102 and prevents mixing of the reaction gases between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by the two adjacent power generation units 102. That is, the upper interconnector 150 in a certain power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of that power generation unit 102. Further, since the fuel cell stack 100 includes a pair of end plates 104 and 106, the power generation unit 102 located at the uppermost position in the fuel cell stack 100 does not include the upper interconnector 150, and the power generation unit 102 located at the lowermost position does not include the lower interconnector 150 (see FIGS. 2 and 3).

[0026] The single cell 110 includes an electrolyte layer 112, a fuel electrode (anode) 116 disposed on one side (lower side) in the vertical direction (first direction) of the electrolyte layer 112, an air electrode (cathode) 114 disposed on the other side (upper side) in the vertical direction of the electrolyte layer 112, and an intermediate layer 180 disposed between the electrolyte layer 112 and the air electrode 114. The single cell 110 of the present embodiment is a fuel electrode support type single cell that supports the other layers (electrolyte layer 112, air electrode 114, intermediate layer 180) constituting the single cell 110 with the fuel electrode 116.

[0027] The electrolyte layer 112 is a substantially rectangular flat plate-shaped member when viewed in the Z-axis direction and is a dense layer. The electrolyte layer 112 is formed of, for example, a solid oxide such as YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), or a perovskite-type oxide. That is, the single cell 110 (power generation unit 102) of the present embodiment is a solid oxide fuel cell (SOFC) that uses a solid oxide as an electrolyte.

[0028] The air electrode 114 is a substantially rectangular flat plate-shaped member that is smaller than the electrolyte layer 112 when viewed in the Z-axis direction, and is a porous layer. The air electrode 114 is formed of, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganate), LNF (lanthanum nickel iron oxide)).

[0029] The fuel electrode 116 is a substantially rectangular flat plate-shaped member that is substantially the same size as the electrolyte layer 112 when viewed in the Z-axis direction, and is a porous layer. The fuel electrode 116 is formed of, for example, a cermet composed of Ni and oxide ion-conductive ceramic particles (e.g., YSZ).

[0030] The intermediate layer 180 is a substantially rectangular flat plate-shaped member and is formed to contain GDC (gadolinium-doped ceria). The intermediate layer 180 suppresses 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 generate a high-resistance substance (e.g., SrZrO3).

[0031] The separator 120 is a frame-shaped member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. The peripheral portion of the hole 121 in the separator 120 faces the peripheral edge of the surface on the air electrode 114 side in the electrolyte layer 112. The separator 120 is joined to the electrolyte layer 112 (single cell 110) by a joint portion 124 formed by a brazing material (e.g., Ag brazing) disposed at the facing portion. The separator 120 partitions the air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116, and suppresses gas leakage from one electrode side to the other electrode side at the peripheral edge of the single cell 110.

[0032] As shown in FIGS. 4 to 6, the air electrode side frame 130 is a frame-shaped member in which a substantially rectangular hole 131 penetrating vertically is formed near the center, and is formed of an insulator such as mica, for example. The hole 131 of the air electrode side frame 130 constitutes an air chamber 166 facing the air electrode 114. The air electrode side frame 130 is in contact with the peripheral edge of the surface of the separator 120 on the side opposite to the side facing the electrolyte layer 112, and the peripheral edge of the surface of the interconnector 150 on the side facing the air electrode 114. Further, the air electrode side frame 130 electrically insulates between a pair of interconnectors 150 included in the power generation unit 102. Further, the air electrode side frame 130 is formed with an oxidant gas supply communication hole 132 that communicates the oxidant gas introduction manifold 161 and the air chamber 166, and an oxidant gas discharge communication hole 133 that communicates the air chamber 166 and the oxidant gas discharge manifold 162.

[0033] As shown in FIGS. 4, 5, and 7, the fuel electrode side frame 140 is a frame-shaped member in which a substantially rectangular hole 141 penetrating vertically is formed near the center, and is formed of metal, for example. The hole 141 of the fuel electrode side frame 140 constitutes a fuel chamber 176 facing the fuel electrode 116. The fuel electrode side frame 140 is in contact with the peripheral edge of the surface of the separator 120 on the side facing the electrolyte layer 112, and the peripheral edge of the surface of the interconnector 150 on the side facing the fuel electrode 116. Further, the fuel electrode side frame 140 is formed with a fuel gas supply communication hole 142 that communicates the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that communicates the fuel chamber 176 and the fuel gas discharge manifold 172.

[0034] As shown in FIGS. 4, 5, and 7, the fuel electrode side current collector 144 is disposed in the fuel chamber 176. The fuel electrode side current collector 144 includes an interconnector facing portion 146, an electrode facing portion 145, and a connecting portion 147 that connects the electrode facing portion 145 and the interconnector facing portion 146, and is formed of, for example, nickel, a nickel alloy, stainless steel, or the like. The electrode facing portion 145 is in contact with the surface of the fuel electrode 116 on the side opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is in contact with the surface of the interconnector 150 on the side facing the fuel electrode 116. However, as described above, since the power generation unit 102 located at the bottom in the fuel cell stack 100 does not include the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 is in contact with the lower end plate 106. Since the fuel electrode side current collector 144 has such a configuration, the fuel electrode 116 and the interconnector 150 (or the end plate 106) are electrically connected. A spacer 149 formed of, for example, mica is disposed between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to temperature cycles or reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnector 150 (or the end plate 106) through the fuel electrode side current collector 144 is maintained well.

[0035] As shown in FIGS. 4 to 6, the air electrode side current collector 134 is disposed in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of substantially quadrangular prism-shaped current collector elements, and is formed of, for example, a ferrite-based stainless steel. The air electrode side current collector 134 is formed in a convex shape that protrudes from the interconnector 150 in the negative Z-axis direction (the above-mentioned one side in the Z-axis direction (the side of the air electrode 114)). The air electrode side current collector 134 is connected to (in contact with) the surface of the air electrode 114 on the side opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 on the side facing the air electrode 114. However, as described above, since the power generation unit 102 located at the top in the fuel cell stack 100 does not include the upper interconnector 150, the air electrode side current collector 134 in the power generation unit 102 is in contact with the upper end plate 104. Since the air electrode side current collector 134 has such a configuration, it electrically connects the air electrode 114 and the interconnector 150 (or the end plate 104).

[0036] In addition, as shown in FIGS. 4 and 5, in the present embodiment, the air electrode side current collector 134 and the interconnector 150 are formed as an integral member. That is, among the integral members (hereinafter referred to as "metal member 190"), a flat plate-shaped portion orthogonal to the vertical direction (Z-axis direction) functions as the interconnector 150, and a plurality of current collector elements formed so as to protrude from the flat plate-shaped portion toward the air electrode 114 function as the air electrode side current collector 134. The metal member 190 is an example of a base material in the claims.

[0037] As shown in FIG. 5, an oxide film layer 194 containing Cr oxide (for example, Cr2O3 (chromia)) is formed on the surface of the metal member 190. Further, as shown in FIGS. 4 and 5, the surface of the metal member 190 (more specifically, the surface of the oxide film layer 194 disposed on the surface of the metal member 190 opposite to the metal member 190) is covered with a conductive Mn-Co coating layer 196. The oxide film layer 194 is an example of an oxide film in the claims, and the Mn-Co coating layer 196 is an example of a coating layer in the claims.

[0038] As shown in FIGS. 4 and 5, the air electrode 114 and the air electrode side current collector 134 are joined by a conductive joint 138. The joint 138 is made of, for example, an oxide having a spinel crystal structure (e.g., Mn 1.5 Co 1.5 O4, MnCo2O4, ZnCo2O4, ZnMn2O4, ZnMnCoO4, CuMn2O4). The joint 138 electrically connects the air electrode 114 and the air electrode side current collector 134. As described above, the air electrode side current collector 134 is connected to (in contact with) the surface of the air electrode 114. However, precisely speaking, a joint 138 is interposed between the air electrode side current collector 134 and the air electrode 114.

[0039] In the following description, the metal member 190 (an integral member of the interconnector 150 and the air electrode side current collector 134), the oxide film layer 194 formed on the surface of the metal member 190, and the Mn-Co film layer 196 formed on the surface of the oxide film layer 194 opposite to the surface facing the metal member 190 are collectively referred to as the interconnector composite 200. The interconnector composite 200 is electrically connected to the air electrode 114 via the joint 138 and is also electrically connected to the fuel electrode 116 via the fuel electrode side current collector 144. The configuration of the interconnector composite 200 will be described in detail later. Note that the interconnector composite 200 is an example of a member for an electrochemical reaction cell in the claims.

[0040] A-2. Operation of the fuel cell stack 100: As shown in FIGS. 2 and 4, when the oxidant gas OG is supplied through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas introduction manifold 161, the oxidant gas OG is supplied to the oxidant gas introduction manifold 161 through the branch portion 29 of the gas passage member 27 and the holes in the main body portion 28, and is supplied from the oxidant gas introduction manifold 161 to the air chamber 166 through the oxidant gas supply communication holes 132 of each power generation unit 102. Further, as shown in FIGS. 3 and 5, when the fuel gas FG is supplied through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the fuel gas introduction manifold 171, the fuel gas FG is supplied to the fuel gas introduction manifold 171 through the branch portion 29 of the gas passage member 27 and the holes in the main body portion 28, and is supplied from the fuel gas introduction manifold 171 to the fuel chamber 176 through the fuel gas supply communication holes 142 of each power generation unit 102.

[0041] When the oxidant gas OG is supplied to the air chamber 166 of each power generation unit 102 and the fuel gas FG is supplied to the fuel chamber 176, power generation by the electrochemical reaction of the oxidant gas OG and the fuel gas FG is performed in the single cell 110. This power generation reaction is an exothermic reaction. In each power generation unit 102, the air electrode 114 of the single cell 110 is electrically connected to the interconnector complex 200 (an aggregate of the metal member 190, the oxide film layer 194, and the Mn-Co film layer 196) through the joint portion 138, and the fuel electrode 116 is electrically connected to the interconnector complex 200 through the fuel electrode side current collector 144. That is, the plurality of power generation units 102 included in the fuel cell stack 100 are electrically connected in series. Therefore, the electrical energy generated in each power generation unit 102 is taken out from the end plates 104 and 106 that function as the output terminals of the fuel cell stack 100. Since the SOFC generates power at a relatively high temperature (for example, 700°C to 1000°C), after startup, the fuel cell stack 100 may be heated by a heater (not shown) until it reaches a state where the high temperature can be maintained by the heat generated by power generation.

[0042] The oxidant off-gas OOG discharged from the air chamber 166 of each power generation unit 102 is discharged into the oxidant gas discharge manifold 162 through the oxidant gas discharge communication hole 133 as shown in FIGS. 2 and 4, and further passes through the holes of the main body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas discharge manifold 162, and is discharged to the outside of the fuel cell stack 100 through a gas pipe (not shown) connected to the branch portion 29. Further, the fuel off-gas FOG discharged from the fuel chamber 176 of each power generation unit 102 is discharged into the fuel gas discharge manifold 172 through the fuel gas discharge communication hole 143 as shown in FIGS. 3 and 5, and further passes through the holes of the main body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the fuel gas discharge manifold 172, and is discharged to the outside of the fuel cell stack 100 through a gas pipe (not shown) connected to the branch portion 29.

[0043] A-3. Detailed configuration of the interconnector composite 200: FIG. 8 is an explanatory diagram showing the detailed configuration of the interconnector composite 200 in the present embodiment. FIG. 8 is a schematic diagram of the mapping result of the Cr element by EPMA (Electron Probe Micro Analyzer) mapping. In FIG. 8, the cross-sectional configuration of the X1 portion in FIG. 5 is shown enlarged. As described above, the interconnector composite 200 includes a metal member 190 (an integral member of the air electrode side current collector 134 and the interconnector 150), an oxide film layer 194 disposed on the surface of the metal member 190, and an Mn-Co film layer 196 disposed on the surface of the oxide film layer 194 opposite to the metal member 190.

[0044] The metal member 190 contains Fe as a main component and also contains Cr. In this specification, the main component means the component with the highest concentration (mass%). In the present embodiment, the metal member 190 may further contain other elements.

[0045] The oxide film layer 194 contains Cr oxide (for example, Cr2O3 (chromia)). The Cr concentration (mass %) of the oxide film layer 194 is higher than that of the metal member 190. The thickness of the oxide film layer 194 is preferably, for example, 0.5 μm or more. Since the oxide film layer 194 has low oxygen permeability, it suppresses the oxidation of Fe, which is less preferable for the metal member 190. That is, the oxide film layer 194 functions as an oxidation-resistant film. On the other hand, since the oxide film layer 194 has a relatively high electrical resistance, it is not preferable for the oxide film layer 194 to grow further, for example, with the use of the fuel cell stack 100.

[0046] The Mn-Co film layer 196 is a conductive layer having a spinel-type crystal structure and containing a spinel-type oxide (for example, MnCo2O4) containing Mn and Co. In this embodiment, the Mn-Co film layer 196 further contains Ni. Since the Mn-Co film layer 196 suppresses the permeation of oxygen, it can suppress the growth of the oxide film layer 194 having a high electrical resistance. As a result, an increase in the electrical resistance of the interconnector composite 200 (and thus a decrease in the performance of the power generation unit 102) can be suppressed. In addition, since the Mn-Co film layer 196 suppresses the evaporation of Cr from the metal member 190, it can suppress the occurrence of Cr poisoning of the electrode (for example, the air electrode 114) of the single cell 110. As a result, a decrease in the performance of the power generation unit 102 can be suppressed. From the viewpoints of ensuring the coating function and reducing the electrical resistance of the Mn-Co film layer 196, the thickness of the Mn-Co film layer 196 is preferably, for example, 2 μm or more and 30 μm or less, and the porosity of the Mn-Co film layer 196 is preferably 10% or more and 30% or less.

[0047] The ratio of the concentration of Mn (atm%) to the concentration of Co (atm%) in the Mn-Co coating layer 196 is 1:1 to 2. The reason why the ratio of the concentration of Mn to the concentration of Co in the Mn-Co coating layer 196 is set to such a value is that in a configuration where the ratio deviates from such a value, the difference in the coefficient of thermal expansion from the metal member 190 and the oxide coating layer 194 becomes large, and as a result, the Mn-Co coating layer 196 is likely to peel off (from the oxide coating layer 194).

[0048] In the present embodiment, after energization equivalent to 3000 hours at 900 °C, the oxide coating layer 194 has a plurality of oxide film protrusions T1. Each oxide film protrusion T1 protrudes so as to bite into the Mn-Co coating layer 196. Further, the height difference (the longest length from the base) of the plurality of oxide film protrusions T1 is larger than the height difference of the metal protrusions T2 on the surface of the metal member 190. For example, as shown in FIG. 8, within a region having the same lateral width (for example, within 10 μm) in the same visual field, the average value of the height differences (see H1 to H3 in FIG. 8) of the plurality of oxide film protrusions T1 is larger than the average value of the height differences (see J1 to J3 in FIG. 8) of the metal protrusions T2. The height difference of each oxide film protrusion T1 is preferably 5 μm or more and 20 μm or less.

[0049] As shown in FIG. 8, for example, the height difference (maximum height difference) H1 of the first oxide film protrusion T1 (hereinafter referred to as "the first oxide film protrusion T1") from the left is larger than the maximum separation distance D1 between the first oxide film protrusion T1 and the second oxide film protrusion T1 (hereinafter referred to as "the second oxide film protrusion T1") from the left. The same relationship also holds for the third oxide film protrusion T1 and the fourth oxide film protrusion T1 from the left.

[0050] A-4. Method for manufacturing the interconnector composite 200: Next, a method for manufacturing the interconnector composite 200 will be described.

[0051] First, prepare a metal member 190. Next, apply a coating paste to the metal member 190 (S120). The coating paste is obtained, for example, by mixing a powder of Mn2CoO4 having a spinel crystal structure as a conductive powder, a solvent, and a binder. This coating paste is applied to the metal member 190 by spray coating or printing.

[0052] Next, by firing the metal member 190 coated with the coating paste, an oxide film layer 194 and an Mn - Co coating layer 196 containing Co oxide (for example, MnCo2O4) are formed on the metal member 190.

[0053] FIG. 9 is an explanatory diagram showing the detailed configuration of the interconnector composite 200 in the reference example. FIG. 9 is a schematic diagram of the mapping result of the Cr element by EPMA mapping. In this reference example, the detailed configuration of the interconnector composite 200 when the metal member 190 is subjected to energization treatment equivalent to 1500 hours at 900°C is shown. As shown in FIG. 9, the height difference of each oxide film convex portion T1 is relatively small. On the other hand, when the metal member 190 is subjected to energization treatment equivalent to 3000 hours at 900°C, as shown in FIG. 8, there will be oxide film convex portions T1 with a larger height difference than the height difference on the surface of the metal member 190 (the height difference of the metal convex portions T2). The energization treatment equivalent to 3000 hours may be, for example, an energization treatment by an acceleration test in which energization is performed at a relatively high voltage for a time shorter than 3000 hours. Also, before the above-mentioned energization treatment, it is preferable that the Mn - Co coating layer 196 has a plurality of oxidation - promoting portions scattered by controlling the variations in thickness (for example, 2 μm or more and 30 μm or less) and porosity (for example, 10% or more and 30% or less). By the manufacturing method described above, the interconnector composite 200 having the above-described configuration is manufactured. Regarding the measurement of the thickness and the height difference of the oxide film layer 194, etc., it can be evaluated by observation using a scanning electron microscope (SEM).

[0054] A - 5. Effects of this embodiment: As described above, the interconnector composite 200 in the present embodiment includes a metal member 190 containing Fe and Cr, a oxide film layer 194 containing Cr oxide and disposed on the negative Z-axis side (one side in the Z-axis direction) of the metal member 190, and a Mn-Co coating layer 196 containing a spinel-type oxide containing Mn and Co and disposed on the negative Z-axis side of the oxide film layer 194. The oxide film layer 194 has a plurality of oxide film protrusions T1 after energization equivalent to 3000 hours at 900°C. Each oxide film protrusion T1 protrudes so as to bite into the Mn-Co coating layer 196. Also, the height difference (the longest length from the base) of the plurality of oxide film protrusions T1 is larger than the height difference of the metal protrusions T2 on the surface of the metal member 190.

[0055] Here, in the interconnector composite 200, for example, due to aging deterioration or the like, the thickness of the oxide film layer 194 formed on the surface of the metal member 190 increases. As the thickness of the oxide film layer 194 increases, stress caused by the thermal expansion difference between the metal member 190 and the Mn-Co coating layer 196 during thermal cycling accumulates, and the Mn-Co coating layer 196 becomes more likely to peel off from the metal member 190. On the other hand, according to the present embodiment, after energization treatment equivalent to 3000 hr at 900°C, the oxide film layer 194 has a plurality of oxide film protrusions T1 that bite into the Mn-Co coating layer 196. The oxide film protrusions T1 have a larger height difference than the surface of the metal member 190. Therefore, due to the anchor effect of the plurality of oxide film protrusions T1, peeling of the Mn-Co coating layer 196 from the metal member 190 can be suppressed.

[0056] In the present embodiment, the metal member 190 contains Fe as a main component and also contains Cr. Thereby, since the main component of the oxide film layer 194 is chromium oxide with high chemical stability, peeling of the Mn-Co coating layer 196 from the metal member 190 can be effectively suppressed.

[0057] In this embodiment, for example, the height difference H1 of the first oxide film protrusion T1 is greater than the maximum separation distance D1 between the first oxide film protrusion T1 and the second oxide film protrusion T1. Thereby, since the anchor effect is further strengthened, peeling of the Mn-Co coating layer 196 from the metal member 190 can be effectively suppressed.

[0058] B. Modification example: The technology disclosed in this specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the gist thereof. For example, the following modifications are also possible.

[0059] The configuration of the single cell 110, the power generation unit 102, or the fuel cell stack 100 in the above embodiment is merely an example, and various modifications are possible.

[0060] Further, in the above embodiment, in the step of S130, a ketone solvent is used as the solvent for immersing the metal member 190, but other solvents (for example, a solvent obtained by adding hydrochloric acid to ethanol) may be used.

[0061] Also, in the above embodiment, the interconnector 150 and the air electrode side current collector 134 are assumed to be an integral member (metal member 190), but the interconnector 150 and the air electrode side current collector 134 may be separate members. In that case, the present invention is also applicable to an interconnector member composed of the interconnector 150 or the air electrode side current collector 134, the oxide film layer 194, and the Mn-Co film layer 196. In the above embodiment, the Mn-Co film layer 196 is exemplified as the coating layer, but the present invention is not limited to this. Examples of the material for forming the coating layer include spinel-type oxides and perovskite-type oxides containing at least one element selected from the group consisting of Mn, Co, Cu, and Zn, and ZnO. Spinel-type oxides are metal oxides having a spinel-type crystal structure, and examples thereof include CuMn2O4, MnCo2O4, CoMn2O4, MnFe2O4, ZnMn2O4, CuFe2O4, NiMn2O4, and CoCr2O4. Note that spinel-type oxides are oxides represented by the composition formula AB2O4, but the ratio of the elements in the two sites where the cations called the A site and the B site are arranged in the crystal may deviate as long as it is a spinel-type oxide.

[0062] Also, in the above embodiment, the air electrode side current collector 134 is in contact with the air electrode 114 via the joint portion 138, but the air electrode side current collector 134 may be in contact with the air electrode 114 without passing through the joint portion 138.

[0063] In the above-described embodiment, the SOFC that generates power by utilizing the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas is targeted. However, the present invention is similarly applicable to an electrolysis cell unit that is a constituent unit of a solid oxide electrolysis cell (SOEC) that generates hydrogen by utilizing the electrolysis reaction of water, and an electrolysis cell stack including a plurality of electrolysis cell units. Note that the configuration of the electrolysis cell stack is known as described in, for example, Japanese Unexamined Patent Application Publication No. 2016-81813, and thus will not be described in detail here. Generally, it has the same configuration as the fuel cell stack 100 in the above-described embodiment. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolysis cell stack, the power generation unit 102 may be read as an electrolysis cell unit, and the single cell 110 may be read as an electrolysis single cell. However, during the operation of the electrolysis cell stack, a voltage is applied between the two electrodes such that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), and water vapor as a raw material gas is supplied through the communication hole 108. As a result, an electrolysis reaction of water occurs in each electrolysis cell unit, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out of the electrolysis cell stack through the communication hole 108. Also in the electrolysis cell unit and the electrolysis cell stack having such a configuration, by adopting the interconnector composite 200 having the above-described configuration, peeling of the coating layer (Mn-Co coating layer 196) from the base material (metal member 190) can be suppressed. Further, in the above-described embodiment, the interconnector composite 200 is exemplified as a member for an electrochemical reaction cell. However, the present invention is not limited thereto, and any member for an electrochemical reaction cell that is electrically connected to the electrochemical reaction cell, such as a separator 120 or a fuel electrode side current collector 144, may be used. In the above-described embodiment, the metal member 190 containing Cr is exemplified as the base material, but a metal base material not containing Cr may also be used.

[0064] Further, in the above-described embodiment, the solid oxide fuel cell (SOFC) has been described as an example. However, the present invention is also applicable to other types of fuel cells (or electrolysis cells) such as molten carbonate fuel cells (MCFC).

Explanation of Reference Numerals

[0065] 22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Main body part 29: Branch part 100: Fuel cell stack 102: Power generation unit 104, 106: End plate 108: Communication hole 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 120: Separator 130: Air electrode side frame 132: Oxidant gas supply communication hole 133: Oxidant gas discharge communication hole 134: Air electrode side current collector 140: Fuel electrode side frame 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode side current collector 145: Electrode facing part 146: Interconnector facing part 147: Connection part 149: Spacer 150: Interconnector 161: Oxidant gas introduction manifold 162: Oxidant gas discharge manifold 166: Air chamber 171: Fuel gas introduction manifold 172: Fuel gas discharge manifold 176: Fuel chamber 180: Intermediate layer 190: Metal member 194: Oxide film layer 196: Mn - Co film layer 200: Interconnector composite D1: Maximum separation distance T1: Oxide film convex part T2: Metal convex part

Claims

1. A member for an electrochemical reaction cell that is electrically connected to an electrochemical reaction cell, comprising a metal base material, a coating layer covering at least a part of the surface of the base material, and an oxide film located between the base material and the coating layer, wherein the oxide film has a plurality of convex portions that penetrate into the coating layer after an energization treatment equivalent to 3000 hours at 900°C, and the plurality of convex portions have a greater height difference than the surface of the base material, The member for an electrochemical reaction cell is characterized by this.

2. The member for an electrochemical reaction cell according to Claim 1, wherein the metal base material contains chromium, and the main component of the oxide film is chromium oxide, The member for an electrochemical reaction cell is characterized by this.

3. The member for an electrochemical reaction cell according to Claim 1 or Claim 2, wherein the plurality of convex portions include a first convex portion and a second convex portion adjacent to each other, and the height difference of the first convex portion is equal to or greater than the maximum separation distance between the first convex portion and the second convex portion, The member for an electrochemical reaction cell is characterized by this.

4. In an electrochemical reaction cell stack including a plurality of electrochemical reaction single cells, the member for an electrochemical reaction cell that is electrically connected to at least one of the plurality of electrochemical reaction single cells is the member for an electrochemical reaction cell according to Claim 1 or Claim 2, The electrochemical reaction cell stack is characterized by this.

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