JP2023092600A - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Abstract

To suppress the occurrence of cracks in an electrolyte layer.SOLUTION: An electrochemical reaction single cell includes an electrolyte layer including a solid oxide, and an air electrode and a fuel electrode facing each other in the first direction with the electrolyte layer interposed therebetween, and a spinel-type oxide represented by a composition formula M3O4 (M includes at least one of Mn and Fe) is deposited inside the electrolyte layer. The spinel-type oxide deposited inside the electrolyte layer is reduced and expands in volume during operation of the electrochemical reaction single cell.SELECTED DRAWING: Figure 6

Description

The technology disclosed in this specification relates to an electrochemical reaction single cell.

A solid oxide fuel cell (hereinafter referred to as "SOFC") having an electrolyte layer containing a solid oxide is known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. It is SOFCs are generally used in the form of a fuel cell stack comprising a plurality of fuel cell single cells (hereinafter simply referred to as "single cells") arranged in a predetermined direction (hereinafter referred to as "first direction"). . BACKGROUND ART Conventionally, there has been known a single cell in which, for example, titanium oxide is dissolved in a solid electrolyte (see, for example, Patent Document 1).

JP-A-6-103993

In conventional single cells, cracks may occur in the electrolyte layer that makes up the single cell due to stress caused by the difference in thermal expansion between each member and stress due to pressure from surrounding members (e.g. interconnectors). There is Cracking in the electrolyte layer, for example, adversely affects single cell performance.

It should be noted that such a problem is solved by electrolysis having a plurality of electrolytic cell units, which are structural units of a solid oxide type electrolytic cell (hereinafter referred to as "SOEC") that generates hydrogen using the electrolysis reaction of water. This is also a common problem with cell stacks. Moreover, such a problem is not limited to SOFCs and SOECs, but is common to other types of electrochemical reaction cell stacks. In this specification, the fuel cell single cell and the electrolytic single cell are collectively referred to as the electrochemical reaction single cell, the power generation unit and the electrolytic cell unit are collectively referred to as the electrochemical reaction unit, and the fuel cell stack and the electrolytic cell are collectively referred to as the electrochemical reaction unit. The stack is collectively called an electrochemical reaction cell stack.

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

(1) The electrochemical reaction single cell disclosed in the present specification is an electric cell comprising an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in a first direction with the electrolyte layer interposed therebetween. In the chemical reaction single cell, a spinel-type oxide represented by a composition formula of M ₃ O ₄ (M includes at least one of Mn and Fe) is deposited inside the electrolyte layer. In this electrochemical reaction single cell, the spinel-type oxide deposited inside the electrolyte layer is reduced and volumetrically expanded during operation of the electrochemical reaction single cell, thereby increasing the compressive stress of the electrolyte layer. When the compressive stress in the electrolyte layer increases due to the volume expansion of the spinel-type oxide, the tensile stress generated in the electrolyte layer increases under the same tensile conditions as compared to the structure in which the spinel-type oxide does not exist inside the electrolyte layer. The tensile stress that causes cracks in the layer is far below the limit value, and the tensile stress that occurs in the electrolyte layer does not easily reach the limit value that causes cracks in the electrolyte layer even after reduction. Therefore, according to the present electrochemical reaction single cell, it is possible to suppress the occurrence of cracks in the electrolyte layer.

(2) In the electrochemical reaction unit cell, the electrolyte layer further contains a solid solution in which at least one of divalent Mn and divalent Fe dissolves in the electrolyte material constituting the electrolyte layer. It is good also as a structure which carries out. In the present electrochemical reaction single cell, the solid solution existing inside the electrolyte layer is oxidized, for example, when the electrochemical reaction single cell stops operating, and precipitates as a spinel-type oxide, further increasing the compressive stress of the electrolyte layer. Therefore, according to the present electrochemical reaction single cell, it is possible to more effectively suppress the occurrence of cracks in the electrolyte layer.

(3) In the electrochemical reaction single cell, the total concentration of divalent Mn and divalent Fe present as the solid solution in the region closer to the fuel electrode than the center in the first direction in the electrolyte layer (mass%) is higher than the total concentration of divalent Mn and divalent Fe present as the solid solution in the region closer to the air electrode than the center in the first direction in the electrolyte layer. good too. According to this electrochemical reaction single cell, on the fuel electrode side, where the amount of deformation during operation of the electrochemical reaction single cell is particularly large, the occurrence of cracks in the electrolyte layer is further suppressed by the volume expansion based on the solid solution in addition to the spinel oxide. can be effectively suppressed.

(4) In the above electrochemical reaction single cell, the total concentration of the elements contained as M in the electrolyte layer may be 3 mass % or less. According to the present electrochemical reaction single cell, it is possible to suppress an excessive decrease in the ionic conductivity of the electrolyte layer due to the element contained as M present in the electrolyte layer.

(5) In the above electrochemical reaction single cell, the electrolyte layer may contain a fluorite-type oxide. According to this electrochemical reaction single cell, the adhesion between the spinel-type oxide and the portion other than the spinel-type oxide in the electrolyte layer is high compared to the structure in which the electrolyte layer does not contain a fluorite-type oxide. It can improve the strength of the layer.

(6) In the above electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells arranged side by side in the first direction, at least one of the plurality of electrochemical reaction single cells is , any one of the above (1) to (5) may be an electrochemical reaction single cell. According to this electrochemical reaction cell stack, it is possible to suppress the occurrence of cracks in the electrolyte layer.

The technology disclosed in this specification can be implemented in various forms. For example, an electrochemical reaction cell stack (fuel cell stack or electrolysis cell stack) It can be realized in the form of a reaction system (a fuel cell system or an electrolytic cell system), a manufacturing method thereof, or the like.

1 is a perspective view showing an external configuration of a fuel cell stack 100 according to an embodiment; FIG. FIG. 2 is an explanatory view showing the XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II in FIG. 1; FIG. 2 is an explanatory view showing the YZ cross-sectional configuration of the fuel cell stack 100 at the position III-III in FIG. 1; FIG. 3 is an explanatory diagram showing the XZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 2 ; FIG. 4 is an explanatory diagram showing the YZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 3 ; 4 is an explanatory diagram schematically showing an example of the internal configuration of an electrolyte layer 112; FIG. 4 is an explanatory diagram schematically showing an example of the internal configuration of an electrolyte layer 112; FIG. FIG. 5 is an explanatory diagram showing performance evaluation results; 4 is an explanatory diagram showing Raman shift of an electrolyte layer 112; FIG. FIG. 4 is an explanatory diagram showing the measurement result of the absorption spectrum of the K absorption edge of Mn in the electrolyte layer 112; FIG. 4 is an explanatory diagram schematically showing an example of a mapping image of an electrolyte layer 112;

A. Embodiment:
A-1. composition:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing the external configuration of the fuel cell stack 100 in this embodiment, and FIG. 2 is an explanatory diagram showing the XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II in FIG. FIG. 3 is an explanatory diagram showing the YZ cross-sectional configuration of the fuel cell stack 100 at the position III-III in FIG. Each figure shows mutually orthogonal XYZ axes for specifying directions. In this specification, for the sake of convenience, the positive Z-axis direction is referred to as the "upward direction" and the negative Z-axis direction is referred to as the "downward direction." It may be installed in different orientations. The same applies to FIG. 4 and subsequent figures. The vertical direction (Z-axis direction) is an example of a first direction in the scope of claims. The fuel cell stack 100 is an example of an electrochemical reaction cell stack in the claims.

The fuel cell stack 100 includes a plurality of (seven in this embodiment) 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 (vertical direction in this embodiment). A pair of end plates 104 and 106 are arranged so as to sandwich an aggregate composed of seven power generation units 102 from above and below.

A plurality of holes (eight in the present embodiment) penetrating in the vertical direction are formed in the peripheral edge portion around the Z-axis direction of each layer (the power generation unit 102, the end plates 104 and 106) constituting the fuel cell stack 100. Corresponding holes formed in each layer vertically communicate with each other to form communicating holes 108 extending vertically 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 holes 108 are also referred to as "communication holes 108".

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 . 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 bolt An insulating sheet 26 is interposed between the nut 24 fitted to the other side (lower side) of the fuel cell stack 22 and the lower surface of the end plate 106 forming the lower end of the fuel cell stack 100 . However, at a location where a gas passage member 27, which will be described later, is provided, between the nut 24 and the surface of the end plate 106, the insulating sheets disposed above and below the gas passage member 27 and the gas passage member 27, respectively. 26 intervenes. The insulating sheet 26 is composed of, for example, a mica sheet, a ceramic fiber sheet, a ceramic powder sheet, a glass sheet, a glass-ceramic composite, or the like.

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, one side of the outer circumference of the fuel cell stack 100 around the Z-axis direction (the side on the positive side of the X-axis among the two sides parallel to the Y-axis) is near the midpoint. The space formed by the positioned bolt 22 (bolt 22A) and the communication hole 108 into which the bolt 22A is inserted receives the oxidant gas OG from the outside of the fuel cell stack 100, and the oxidant gas OG is introduced into each space. Functioning as an oxidant gas supply manifold 161, which is a gas flow path for supplying to the power generation unit 102, the side opposite to the side (the side on the negative side of the X axis among the two sides parallel to the Y axis) The space formed by the bolt 22 (bolt 22B) positioned near the point and the communication hole 108 into which the bolt 22B is inserted is the oxidant offgas 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 as an oxidizing gas discharge manifold 162 . In this embodiment, for example, air is used as the oxidant gas OG.

In addition, as shown in FIGS. 1 and 3, the midpoint of one side (the side on the Y-axis positive side of the two sides parallel to the X-axis) on the outer circumference of the fuel cell stack 100 around the Z-axis direction Fuel gas FG is introduced from the outside of the fuel cell stack 100 into the space formed by the bolt 22 (bolt 22D) located nearby and the communication hole 108 into which the bolt 22D is inserted. A bolt that functions as the fuel gas supply manifold 171 that supplies the power generation unit 102 and is positioned near the midpoint of the side opposite to the side (the side on the Y-axis negative direction side of the two sides parallel to the X-axis) 22 (bolt 22E) and the communication hole 108 into which the bolt 22E is inserted allows the fuel offgas FOG, which is the gas discharged from the fuel chamber 176 of each power generation unit 102, to flow outside the fuel cell stack 100. It functions as a fuel gas discharge manifold 172 that discharges to the In this embodiment, hydrogen-rich gas obtained by reforming city gas, for example, is used as the fuel gas FG.

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

(Configuration of end plates 104, 106)
The pair of end plates 104 and 106 are substantially rectangular plate-shaped conductive members, and are made of, for example, stainless steel. One end plate 104 is arranged above the uppermost power generating unit 102 and the other end plate 106 is arranged below the lowermost power generating unit 102 . A pair of end plates 104 and 106 hold a plurality of power generation units 102 in a pressed state. The upper end plate 104 functions as the positive side output terminal of the fuel cell stack 100 , and the lower end plate 106 functions as the negative side output terminal of the fuel cell stack 100 .

(Configuration of power generation unit 102)
4 is an explanatory diagram showing the XZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 2, and FIG. FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of two power generation units 102;

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, an anode side frame 140, an anode side It has current collectors 144 , spacers 149 , and a pair of interconnectors 150 forming the top layer and the bottom layer of the power generation unit 102 . The separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150 are provided with holes corresponding to the communication holes 108 through which the bolts 22 are inserted. The single cell 110 is an example of an electrochemical reaction single cell in the claims.

The interconnector 150 is a substantially rectangular plate-shaped conductive member, and is made of a metal material (for example, ferritic stainless steel) containing Mn (manganese), Cr (chromium), or the like. The interconnector 150 ensures electrical continuity between the power generating units 102 and prevents mixing of reaction gases between the power generating units 102 . In this embodiment, when two power generation units 102 are arranged adjacently, 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 the power generation unit 102 . In addition, since the fuel cell stack 100 has a pair of end plates 104 and 106, the power generation unit 102 located at the top in the fuel cell stack 100 does not have the upper interconnector 150, and is located at the bottom. The generating unit 102 does not have a lower interconnector 150 (see Figures 2 and 3).

The single cell 110 includes an electrolyte layer 112, and an air electrode (cathode) 114 and a fuel electrode (anode) 116 facing each other in the vertical direction (the direction in which the power generating units 102 are arranged) with the electrolyte layer 112 interposed therebetween. That is, the air electrode 114 and the fuel electrode 116 face each other in the vertical direction with the electrolyte layer 112 interposed therebetween. The single cell 110 of this embodiment is a fuel electrode supporting type single cell in which the electrolyte layer 112 and the air electrode 114 are supported by the fuel electrode 116 .

The electrolyte layer 112 is a substantially rectangular plate-shaped member when viewed from the top and bottom, and is a dense (low porosity) layer. The term “vertical view” as used herein means “when viewed from a direction parallel to the vertical direction” (the same applies to “vertical view” below). The electrolyte layer 112 is formed of a solid oxide such as YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), perovskite-type oxide, or the like. there is The air electrode 114 is a substantially rectangular plate-shaped member smaller than the electrolyte layer 112 when viewed from the top and bottom, and is a porous layer (having a higher porosity than the electrolyte layer 112). The air electrode 114 may be formed of, for example, a perovskite-type oxide that does not contain Mn (eg, LSCF (lanthanum strontium cobalt iron oxide), LNF (lanthanum nickel iron oxide)), or LSM containing Mn (lanthanum strontium manganese oxide). The fuel electrode 116 is a substantially rectangular plate-shaped member having substantially the same size as the electrolyte layer 112 when viewed from above, and is a porous layer (having a higher porosity than the electrolyte layer 112). The thickness of the fuel electrode 116 is, for example, 200 μm or more and 1000 μm or less. The average porosity of the portion of the fuel electrode 116 near the fuel electrode side current collector 144 is, for example, 25 vol% or more and 60 vol% or less, and the average pore diameter of the portion is, for example, 0.5 μm or more and 4 μm or less. . The single cell 110 (power generation unit 102) of this embodiment having such a configuration is a solid oxide fuel cell (SOFC) using a solid oxide as an electrolyte.

The separator 120 is a frame-like member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed near the center, and is made of metal, for example. The peripheral portion of the separator 120 around the hole 121 faces the peripheral portion of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is joined to the electrolyte layer 112 (single cell 110) by a joint portion 124 formed of a brazing material (for example, Ag brazing material) arranged at the opposing portion. The air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116 are separated by the separator 120 to prevent gas leakage from one electrode side to the other electrode side in the peripheral portion of the unit cell 110 . Suppressed.

The air electrode side frame 130 is a frame-shaped member having a substantially rectangular hole 131 penetrating vertically in the vicinity of the center thereof, and is made of an insulator such as mica, for example. A hole 131 in the cathode-side frame 130 constitutes an air chamber 166 facing the cathode 114 . The air electrode-side frame 130 is in contact with the peripheral edge portion of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge portion of the surface of the interconnector 150 facing the air electrode 114 . . Also, the pair of interconnectors 150 included in the power generation unit 102 are electrically insulated by the air electrode side frame 130 . The air electrode side frame 130 also has an oxidizing gas supply communication hole 132 that communicates the oxidizing gas supply manifold 161 and the air chamber 166, and an oxidizing gas supply communication hole 132 that communicates the air chamber 166 and the oxidizing gas discharge manifold 162. A discharge communication hole 133 is formed.

The fuel electrode-side frame 140 is a frame-shaped member having a substantially rectangular hole 141 penetrating vertically in the vicinity of the center thereof, and is made of metal, for example. A hole 141 in the anode-side frame 140 constitutes a fuel chamber 176 facing the anode 116 . The fuel electrode-side frame 140 is in contact with the periphery of the surface of the separator 120 facing the electrolyte layer 112 and the periphery of the surface of the interconnector 150 facing the fuel electrode 116 . Further, the fuel electrode side frame 140 has a fuel gas supply communication hole 142 that communicates the fuel gas supply 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. and are formed.

The air electrode side current collector 134 is arranged 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 made of, for example, ferritic stainless steel. The air electrode-side current collector 134 is in contact with the surface of the air electrode 114 opposite to the electrolyte layer 112 and the surface of the interconnector 150 facing the air electrode 114 . However, as described above, the uppermost power generation unit 102 in the fuel cell stack 100 does not have the upper interconnector 150, so the air electrode side current collector 134 in the power generation unit 102 is the upper end plate 104 is in contact. 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). In addition, in this embodiment, the air electrode side current collector 134 and the interconnector 150 are formed as an integral member. That is, a flat plate-shaped portion of the integrated member that is perpendicular to the vertical direction (Z-axis direction) functions as an interconnector 150, and is formed to protrude from the flat plate-shaped portion toward the air electrode 114. A current collector element, which is a plurality of protrusions, functions as the air electrode side current collector 134 . In addition, the surface of the air electrode 114 side of the integrated member of the air electrode side current collector 134 and the interconnector 150 may be covered with a conductive coating, and the air electrode 114 and the air electrode side current collector 134 may be covered with a conductive coating. A conductive bonding layer may be interposed between them to bond them together.

The fuel electrode side current collector 144 is arranged in the fuel chamber 176 . The fuel electrode-side current collector 144 includes an interconnector connecting portion 146, an electrode connecting portion 145, and a connecting portion 147 that connects the positive X-axis side of the electrode connecting portion 145 and the positive X-axis side of the interconnector connecting portion 146. and The electrode connecting portion 145 is electrically connected to the surface of the fuel electrode 116 opposite to the side facing the electrolyte layer 112 . In this specification, "the A member and the B member are electrically connected" is not limited to the configuration in which the A member and the B member are in direct contact with each other, and between the A member and the B member Also includes a configuration in which another conductive member is interposed. In this embodiment, the electrode connection portion 145 is in contact with the surface of the fuel electrode 116 . The interconnector connecting portion 146 is electrically connected to the surface of the interconnector 150 facing the fuel electrode 116 . That is, the interconnector connection portion 146 is provided on the surface of the interconnector 150 arranged on the lower side (one side in the vertical direction) of the single cell 110 among the pair of interconnectors 150 provided in the power generation unit 102. electrically connected. However, as described above, since the lowest power generation unit 102 in the fuel cell stack 100 does not have the lower interconnector 150, the interconnector connecting portion 146 of the power generation unit 102 is connected to the lower end plate. 106 is electrically connected.

In this embodiment, the fuel electrode-side current collector 144 is formed of a metal foil (for example, with a thickness of 10 μm or more and 800 μm or less) made of nickel, nickel alloy, cobalt, cobalt alloy, or the like. The anode-side current collector 144 is manufactured by bending a substantially rectangular metal foil.

Fuel electrode-side current collector 144 having such a configuration electrically connects fuel electrode 116 and interconnector 150 (or end plate 106). In this embodiment, the interconnector connecting portion 146, the electrode connecting portion 145, and the connecting portion 147 of the fuel electrode side current collector 144 are configured as an integral member.

A spacer 149 made of, for example, mica is arranged between the electrode connection portion 145 and the interconnector connection portion 146 . Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to temperature cycles and reaction gas pressure fluctuations, and the fuel electrode 116 and the interconnector 150 (or the end plate 106) through the fuel electrode side current collector 144. good electrical connection with The plate thickness of the spacer 149 is, for example, 0.5 mm or more and 3 mm or less.

A-2. Operation of fuel cell stack 100:
As shown in FIGS. 2 and 4, 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 supply manifold 161. Then, the oxidizing gas OG is supplied to the oxidizing gas supply manifold 161 via the branch portion 29 of the gas passage member 27 and the hole of the main body portion 28, and the oxidizing gas OG is supplied from the oxidizing gas supply manifold 161 to each power generation unit 102. The agent gas is supplied to the air chamber 166 through the agent gas supply communication hole 132 . 3 and 5, 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 supply manifold 171. Then, the fuel gas FG is supplied to the fuel gas supply manifold 171 via the branch portion 29 of the gas passage member 27 and the hole of the main body portion 28, and the fuel gas supply communication of each power generation unit 102 from the fuel gas supply manifold 171. It is supplied to fuel chamber 176 through hole 142 .

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, the oxygen contained in the oxidant gas OG and the hydrogen contained in the fuel gas FG in the single cell 110 Electricity is generated by an electrochemical reaction with 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 one interconnector 150 through the air electrode side current collector 134, and the fuel electrode 116 is electrically connected through the fuel electrode side current collector 144. It is electrically connected to the other interconnector 150 . Also, 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 output terminals of the fuel cell stack 100 . Since the SOFC generates power at a relatively high temperature (for example, 700° C. or higher and 1000° C. or lower), the fuel cell stack 100 heats up until a high temperature can be maintained by the heat generated by the power generation after startup. It may be heated by a vessel (not shown).

As shown in FIGS. 2 and 4, the oxidant offgas OOG discharged from the air chamber 166 of each power generation unit 102 is discharged to the oxidant gas discharge manifold 162 through the oxidant gas discharge communication hole 133 and further oxidized. The fuel cell stack 100 is supplied to the fuel cell stack 100 via a gas pipe (not shown) connected to the branch portion 29 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 agent gas discharge manifold 162 . is discharged to the outside of the Further, as shown in FIGS. 3 and 5, the fuel offgas FOG discharged from the fuel chamber 176 of each power generation unit 102 is discharged to the fuel gas discharge manifold 172 through the fuel gas discharge communication hole 143. Through the holes in the body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the exhaust manifold 172, the gas is supplied to the outside of the fuel cell stack 100 via a gas pipe (not shown) connected to the branch portion 29. Ejected.

A-3. Internal configuration of the electrolyte layer 112 in the single cell 110:
FIG. 6 is an explanatory diagram schematically showing an example of the internal configuration of the electrolyte layer 112. As shown in FIG. FIG. 6 shows an XZ cross-sectional configuration of the unit cell 110 in a region (region X1 in FIG. 4) including part of the air electrode 114 and part of the fuel electrode 116 with the electrolyte layer 112 interposed therebetween. FIG. 6A shows the internal structure of the electrolyte layer 112 before operation of the fuel cell stack 100 (for example, at the time of fabrication or shipment of the single cell 110), and FIG. The internal configuration of electrolyte layer 112 is shown during operation of stack 100 . In this specification, the inside of the electrolyte layer 112 is a portion of the electrolyte layer 112 that is vertically spaced apart from the other layers (the air electrode 114 and the fuel electrode 116) adjacent to the electrolyte layer 112. It does not include the boundaries between layer 112 and other layers.

As shown in FIG. 6, electrolyte layer 112 satisfies the following first condition.
<First condition>:
A spinel-type oxide SP represented by a composition formula of M ₃ O ₄ (M includes at least one of Mn and Fe) is deposited inside the electrolyte layer 112 .
Both Mn and Fe are elements whose valences change and whose volume expands upon reduction. Mn or Fe in the spinel-type oxide SP deposited inside the electrolyte layer 112 is, for example, 2.67-valent Mn or 2.67-valent Fe. Examples of _this spinel-type oxide SP are _{Mn3O4 , Fe3O4} , _{MnFe2O4 , FeMn2O4 ,} (Co _, Mn) _{3O4 ,} (Fe, _Ni ) _3O4 . Note that M (A site, B site) in the composition formula of these spinel-type oxides SP may contain an element other than the main elements (Mn, Fe, Co, Ni) at an impurity level. For example, the proportion of the main element in M may be 70% or more, preferably 90% or more, of the entire spinel-type oxide SP.

FIG. 7 is an explanatory diagram schematically showing an example of the internal configuration of the electrolyte layer 112. As shown in FIG. FIG. 7 shows an XZ cross-sectional configuration of the unit cell 110 in a region (region X1 in FIG. 4) including part of the air electrode 114 and part of the fuel electrode 116 with the electrolyte layer 112 interposed therebetween. FIG. 7A shows the internal structure of the electrolyte layer 112 before operation of the fuel cell stack 100 (for example, at the time of fabrication or shipment of the unit cells 110), and FIG. The internal configuration of electrolyte layer 112 is shown during operation of stack 100 .

As shown in FIG. 7, the electrolyte layer 112 preferably also satisfies the following second condition.
<Second condition>:
Inside the electrolyte layer 112 , there is also a solid solution SS in which at least one of divalent Mn and divalent Fe is dissolved in the electrolyte material forming the electrolyte layer 112 .
The electrolyte material forming the electrolyte layer 112 is, for example, a fluorite-type oxide (a Ce (cerium)-based oxide or a Zr (zirconium)-based oxide), which will be described later. Examples of solid solution SS include a composition in which at least one of divalent Mn and divalent Fe enters the Ce site of a Ce-based oxide, and a composition in which at least one of divalent Mn and divalent Fe enters the Zr site of a Zr-based oxide, and divalent Mn and 2 It is a composition in which at least one of valence Fe and Fe is incorporated.

The electrolyte layer 112 preferably also satisfies the following third condition.
<Third condition>:
The total concentration (mass%) of divalent Mn and divalent Fe present as a solid solution SS in a region closer to the fuel electrode 116 than the center of the electrolyte layer 112 in the vertical direction (Z-axis direction) is is higher than the total concentration of divalent Mn and divalent Fe present as a solid solution SS in the region closer to the air electrode 114 than the center in the vertical direction.

The electrolyte layer 112 preferably also satisfies the following fourth condition.
<Fourth condition>:
The total concentration of the elements contained as M in the electrolyte layer 112 is 3 mass % or less.

The electrolyte layer 112 preferably also satisfies the following fifth condition.
<Fifth condition>:
Electrolyte layer 112 contains a fluorite-type oxide.
Examples of fluorite-type oxides are Ce (cerium)-based oxides (eg, SDC, GDC) and Zr (zirconium)-based oxides (YSZ, ScSZ).

Furthermore, the vertical thickness of the region of the electrolyte layer 112 where the spinel-type oxide SP exists (the region vertically separated from both the electrolyte layer 112 and the fuel electrode 116) is equal to the thickness of the electrolyte layer 112. is preferably 10% or more and 90% or less, more preferably 30% or more and 60% or less. This can suppress the occurrence of separation between the electrolyte layer 112 and the air electrode 114 or the fuel electrode 116 due to volume expansion of the spinel-type oxide SP. In addition, it is preferable that a large amount of spinel-type oxide SP is present in the central portion of the electrolyte layer 112, particularly when viewed in the vertical direction. This is because the central portion of the electrolyte layer 112 becomes particularly hot during operation of the fuel cell stack 100 and cracks are likely to occur.

A-4. Performance evaluation:
Performance evaluation performed using a plurality of single cell 110 samples will be described below. FIG. 8 is an explanatory diagram showing performance evaluation results. In this evaluation, M in the electrolyte layer 112 shall be Mn. As shown in FIG. 8, each of the samples (S1 to S5) has a different Mn concentration (mass %) in the electrolyte layer 112 from each other.

A-4-1. Manufacturing method of single cell 110:
Each sample of the single cell 110 was manufactured according to the following manufacturing method.

(Formation of laminate of electrolyte layer 112 and fuel electrode 116)
A butyral resin, a plasticizer dioctyl phthalate (DOP), a dispersant, and a mixed solvent of toluene and ethanol are added to the YSZ powder and mixed in a ball mill to prepare a slurry. At this time, for the samples S1 to S4 of the single cell 110, Mn ₃ O ₄ as a spinel oxide is added to the YSZ powder and mixed to prepare a slurry. The resulting slurry is thinned by a doctor blade method to obtain a green sheet for an electrolyte layer having a thickness of, for example, about 10 μm. Further, NiO powder is weighed so as to be 55 parts by mass in terms of Ni weight, and mixed with 45 parts by mass of YSZ powder to obtain a mixed powder. A butyral resin, a plasticizer DOP, a dispersant, and a mixed solvent of toluene and ethanol are added to this mixed powder, and mixed in a ball mill to prepare a slurry. The resulting slurry is thinned by a doctor blade method to obtain, for example, a 270 μm-thick fuel electrode green sheet. The electrolyte layer green sheet and the fuel electrode green sheet are attached and dried. After that, by firing at, for example, 1400° C., a laminate of the electrolyte layer 112 and the fuel electrode 116 is obtained. When manufacturing the electrolyte layer 112 that satisfies the third condition, for example _{, two electrolyte layer green sheets having different amounts of Mn 3 O 4 to be} added are prepared _. An electrolyte layer green sheet containing a relatively small amount of Mn 3 O 4 may be arranged on the air electrode 114 side, and an electrolyte layer green sheet containing a relatively large amount of Mn ₃ O ₄ may be arranged on the fuel electrode 116 side.

(Formation of air electrode 114)
LSCF powder, GDC powder, alumina powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent are mixed and the viscosity is adjusted to prepare an air electrode active layer paste. The obtained air electrode active layer paste is applied to the surface of the electrolyte layer 112 in the laminate of the electrolyte layer 112 and the fuel electrode 116 by screen printing and dried. Also, LSCF powder, alumina powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent are mixed and the viscosity is adjusted to prepare an air electrode current collecting layer paste. The obtained air electrode current collecting layer paste is applied onto the air electrode active layer paste by screen printing, dried, and then fired at, for example, 1100°C to 1200°C. The firing forms an electrolyte layer 112 in which the spinel-type oxide SP is deposited (see FIG. 6). Through the steps described above, the single cell 110 having the configuration described above is manufactured. For example, when the amount of Mn ₃ O ₄ added to the green sheet for the electrolyte layer is a predetermined value or more, the electrolyte layer 112 in which the spinel-type oxide SP is deposited and the solid solution SS is present is formed. (see Figure 7).

A-4-2. Various performance evaluations:
<Confirmation of Presence or Absence of Precipitation of Spinel-Type Oxide (Mn ₃ O ₄ )>
Presence or absence of deposition of spinel-type oxide (Mn ₃ O ₄ ) in the electrolyte layer 112 was checked for each sample of the single cell 110 . Specifically, each sample of the single cell 110 is cut to a predetermined length, embedded in epoxy resin and solidified, and then a cross section (including the entire XZ cross section of the electrolyte layer 112) substantially parallel to the stacking direction of each layer. was cut so as to be observable, and polished to a mirror surface. After that, the polished surface (observation surface) of the sample was measured by microscopic laser Raman spectroscopy to confirm whether or not a peak of spinel oxide (Mn ₃ O ₄ ) in the electrolyte layer 112 was detected. For the measurement, for example, HR-800 manufactured by HORIBA, Ltd. is used, the wavelength of the laser light irradiated to the measurement sample is 514.53 nm, the laser light output is 100 mW, the analysis diameter is 1 μm, and the wave number is 100 to 680 cm. ^-1 range is measured. Each sample of the single cell 110 to be analyzed may be either pre-reduced or post-reduced.

FIG. 9 is an explanatory diagram showing the Raman shift of the electrolyte layer 112. FIG. Peaks attributed to the spinel oxide (Mn ₃ O ₄ ) were observed at 660 to 670 cm ⁻¹ , ₃₇₀ to 380 cm ⁻¹ , and 320 to 330 cm ^{−1 ,} respectively _. ) is present in the electrolyte layer 112 .

<Valence of Mn>
The valence of Mn present in the electrolyte layer 112 of each sample of the single cell 110 was measured, and from the measurement results, the spinel-type oxide (Mn ₃ O ₄ ) and the solid solution (Mn ²⁺ ) inside the electrolyte layer 112 Checked for existence. Specifically, for each sample of the single cell 110 after reduction, the air electrode 114 was scraped off to expose the surface of the electrolyte layer 112 on the air electrode 114 side. Then, XAFS (X-ray Absorption Fine Structure) of Mn in the electrolyte layer 112 was measured. That is, the absorption spectrum of the K absorption edge was measured for Mn on the exposed surface of the electrolyte layer 112 by the fluorescence collection method. By changing the incident angle of the X-rays on the surface of the electrolyte layer 112, the absorption spectrum of the K absorption edge of Mn at each position in the thickness direction (vertical direction) of the electrolyte layer 112 can be measured.

FIG. 10 is an explanatory diagram showing the measurement result of the absorption spectrum of the K absorption edge of Mn in the electrolyte layer 112. As shown in FIG. Graph G1 in FIG. 10 is reference data showing the absorption spectrum of the K absorption edge of divalent Mn (MnO), and graph G2 is the K absorption edge of 2.67 valent Mn (Mn ₃ O ₄ ). It is reference data showing the absorption spectrum of Graph H1 is measurement data showing the absorption spectrum of the K absorption edge of Mn when X-rays are incident on the surface of the electrolyte layer 112 on the air electrode 114 side at an incident angle of 45 degrees for the sample S1. 112 shows the average Mn valence over all. A comparison of graph H1, graph G1, and graph G2 reveals that both divalent Mn and 2.67-valent Mn are present in the entire electrolyte layer 112 . Graph H2 is measurement data showing the absorption spectrum of the K absorption edge of Mn when X-rays are incident on the surface of the electrolyte layer 112 on the fuel electrode 116 side at an incident angle of 10 degrees for the sample S1. shows the average Mn valence of the electrolyte layer 112 present in the region closer to the air electrode 114 than the center in the direction of . From a comparison between graph H2, graph G1, and graph G2, both divalent Mn and 2.67-valent Mn are present in the electrolyte layer 112 existing in the region closer to the air electrode 114 than the center in the first direction. However, it can be seen that the proportion of divalent Mn is lower than in graph H1. From these measurement data, in sample S1, spinel-type oxide SP containing 2.67 valent It can be seen that there exists a solid solution SS in which Mn is dissolved in the electrolyte material (Zr-based oxide or Ce-based oxide). Furthermore, divalent Mn is particularly abundant on the fuel electrode 116 side inside the electrolyte layer 112 . Similarly, for samples S2 to S4, it was confirmed that the spinel-type oxide SP was deposited and the solid solution SS was present inside the electrolyte layer 112 on both the air electrode 114 side and the fuel electrode 116 side. As for the sample S5, the existence of the spinel-type oxide SP and the solid solution SS inside the electrolyte layer 112 could not be confirmed.

<Mn Concentration in Electrolyte Layer 112>
For each sample of the single cell 110, the Mn concentration (mass%) in the electrolyte layer 112 was measured. Specifically, each sample of the single cell 110 is cut to a predetermined length, embedded in epoxy resin and solidified, and then a cross section (including the entire XZ cross section of the electrolyte layer 112) substantially parallel to the stacking direction of each layer. was cut so as to be observable, and polished to a mirror surface. After that, carbon deposition is performed on the polished surface (observation surface), and an EPMA (Electron Probe Micro Analyzer) is used to obtain an image of the electrolyte layer 112 and conduct an elemental mapping analysis of Mn to determine the Mn concentration in the electrolyte layer 112 ( Mn concentration) was calculated. For the measurement, for example, FE-EPMA JXA-8500F manufactured by JEOL is used, the electron beam irradiated to the measurement sample is accelerated at 15 kV, the irradiation current is 20 nA, the mapping area is 20 μm, and the conditions are 256 pixels × 256 pixels. Measure. The measurement time of X-rays at a pixel is assumed to be 30 milliseconds. PETH is used as an analyzing crystal for X-ray spectroscopy of Mn. Each sample of the single cell 110 to be analyzed may be either pre-reduced or post-reduced.

FIG. 11 is an explanatory diagram schematically showing an example of a mapping image of the electrolyte layer 112 of the sample S1. FIG. 11 shows an image obtained by binarizing the mapping image of Mn. The dark part in the image is Mn. As can be seen from this mapping image, it can be seen that a plurality of Mn elements are scattered at intervals so as to extend in directions (X direction and Y direction) perpendicular to the vertical direction. As a result, for example, it is possible to suppress the decrease in oxygen ion conductivity due to the presence of the Mn element, compared to a configuration in which many Mn elements are clustered and unevenly distributed in specific locations of the electrolyte layer 112. .

As shown in FIG. 8, in samples S1 to S4, the Mn concentration was higher than 0 mass%, in samples S1 to S3, the Mn concentration was 3 mass% or less, and in sample S4, the Mn concentration was higher than 3 mass%. In sample S5, the Mn concentration was 0 mass%.

<IR resistance>
As an initial evaluation of each sample of single cell 110, IR resistance (Ω·cm ² ) was measured. Specifically, for each sample of the single cell 110 produced, the IR resistance was measured at a current density of 0.55 A/cm ₂ under conditions of temperature: 700°C, atmosphere: hydrogen 320 ml, dew point temperature 30°C. A lower IR resistance means a higher oxygen ion conductivity of the electrolyte layer 112 .

According to FIG. 8, samples S1 to S3 with a Mn concentration of 3 mass % or less had IR resistance at the same level as sample S5 with a Mn concentration of 0 mass %. On the other hand, in sample S4 with a Mn concentration higher than 3 mass%, the IR resistance was higher than in sample S5 with a Mn concentration of 0 mass%. This means that the Mn concentration in the electrolyte layer 112 should be 3 mass % or less in order to suppress a significant decrease in the oxygen ion conductivity of the electrolyte layer 112 due to the presence of Mn inside the electrolyte layer 112. is preferred.

<Redox resistance>
Each sample of the single cell 110 was measured for redox resistance (durability against oxidation and reduction). Specifically, each sample of the single cell 110 after the initial evaluation was electrochemically oxidized by alternately applying a voltage of 1.0 V and a voltage of −0.1 V at intervals of 10 seconds. and reduction are repeated. In this process, applying a voltage of 1.0 V and a voltage of -0.1 V as one set, while counting the number of times one set is performed, the IR resistance of the single cell 110 is periodically measured, and the measurement result However, the test was terminated when the value exceeded three times the value of the IR resistance at the time of initial evaluation, and the number of times the test was performed was recorded. It means that the higher the number of times of execution, the higher the redox resistance of the single cell 110 . In this redox resistance test, it is assumed that cracks occurring in the electrolyte layer 112 are the main cause of the increase in the IR resistance of the single cell 110 .

It can be seen from FIG. 8 that the redox resistance of samples S1 to S4 in which Mn exists inside the electrolyte layer 112 is higher than the redox resistance of sample S5 in which Mn does not exist inside the electrolyte layer 112 . This means that in the samples S1 to S4, the presence of the spinel-type oxide SP inside the electrolyte layer 112 suppressed the occurrence of cracks in the electrolyte layer 112 . Further, in samples S1 to S4, it can be seen that the redox resistance of the single cell 110 is improved as the Mn concentration of Mn constituting the spinel-type oxide SP and the solid solution SS is increased. In recent years, the fuel cell stack 100 has been required to start and stop quickly and to change its load quickly, and it has become an issue to improve its resistance to redox. In the present embodiment, the single cell 110 can be realized that is less prone to cracking without lowering the ionic conductivity of the electrolyte layer 112 and has excellent redox resistance.

As described above, the thickness of the region of the electrolyte layer 112 where the spinel-type oxide SP is present in each sample is 10% or more and 90% or less of the thickness of the electrolyte layer 112. is preferably 30% or more and more preferably 60% or less.

Here, the method of determining the thickness D1 of the electrolyte layer 112 and the thickness D2 of the region where the spinel-type oxide SP exists is as follows. After each sample of the single cell 110 was cut to a predetermined length and embedded in epoxy resin and solidified, a cross section (including the entire XZ cross section of the electrolyte layer 112, see FIG. 11) substantially parallel to the stacking direction of each layer was observed. I cut it as much as possible and polished it to a mirror surface. Thereafter, carbon deposition was performed on the polished surface (observation surface), and then image acquisition of the electrolyte layer 112 and elemental mapping analysis of Mn were performed by EPMA. In this measurement, for example, FE-EPMA JXA-8500F manufactured by JEOL is used, the electron beam irradiated to the measurement sample is accelerated at 15 kV, and the irradiation current is 20 nA. It was measured. The measurement time of X-rays at a pixel is assumed to be 30 milliseconds. PETH is used as an analyzing crystal for X-ray spectroscopy of Mn. Each sample of the single cell 110 to be analyzed may be either pre-reduced or post-reduced.

The thickness D1 of the electrolyte layer 112 was determined by arbitrarily selecting three points from the image acquired in this way, measuring the thickness of the electrolyte layer 112, and averaging the measured thicknesses. Further, as shown in FIG. 11, the elemental mapping data of Mn in the electrolyte layer 112 is divided in units of 1 μm substantially parallel to the stacking direction of each layer, and the thickness of the divided region where Mn is present is measured. A thickness D2 of the region where the oxide SP exists was determined.

A-5. Effect of this embodiment:
As described above, in the fuel cell stack 100 according to the present embodiment, the electrolyte layer 112 contains spinel represented by the composition formula M ₃ O ₄ (M includes at least one of Mn and Fe). type oxide SP is deposited (first condition, see FIG. 6A). The spinel-type oxide SP deposited inside the electrolyte layer 112 is reduced during operation of the single cell 110 and expands in volume (see spinel-type oxide SP1 in FIG. 6B), thereby forming the electrolyte layer 112 ( The compressive stress of the electrolyte material part) increases. When the compressive stress in the electrolyte layer 112 increases due to the volume expansion of the spinel-type oxide SP, it occurs in the electrolyte layer 112 under the same tensile conditions as compared to the configuration in which the spinel-type oxide SP is not present inside the electrolyte layer 112. The tensile stress is much lower than the limit value TH of the tensile stress at which cracks occur in the electrolyte layer 112, and the tensile stress generated in the electrolyte layer 112 is less likely to reach the limit value TH even after reduction. Therefore, according to the present embodiment, the occurrence of cracks in the electrolyte layer 112 can be suppressed.

Specifically, in the single cell 110 , the thermal expansion coefficient of the electrolyte layer 112 is lower than the thermal expansion coefficients of the air electrode 114 and the fuel electrode 116 . Therefore, when the temperature rises due to the start of operation of the unit cell 110, a tensile stress is applied to the electrolyte layer 112 in a direction orthogonal to the vertical direction due to the difference in thermal expansion between the electrolyte layer 112 and the air electrode 114 or fuel electrode 116. is applied to increase the tensile stress generated in the electrolyte layer 112 . Furthermore, for example, when the fuel electrode 116 is oxidized and expands when the fuel cell stack 100 is stopped, the tensile stress generated in the electrolyte layer 112 increases and reaches the threshold value TH, causing cracks in the electrolyte layer 112. Here, as indicated by L2 in FIG. 6B, for example, in a comparative example in which the spinel-type oxide SP is not present inside the electrolyte layer 112, the tensile stress generated in the electrolyte layer 112 when the operation of the unit cell 110 is stopped is Assume that it increases from σ3 to σ4 and exceeds the limit value TH. On the other hand, as shown by L1 in FIG. 6B, in the present embodiment in which the spinel oxide SP exists inside the electrolyte layer 112, the spinel oxide SP is reduced when the unit cell 110 starts operating. As a result, the compressive stress of the electrolyte layer 112 increases. Therefore, in the present embodiment, when a tensile stress equivalent to that of the comparative example is applied, the tensile stress generated in the electrolyte layer 112 increases from σ1 to σ2, which is smaller than that of the comparative example, making it difficult to reach the limit value TH. .

In particular, in recent years, in order to further improve the performance of the single cell 110, efforts have been made to make the electrolyte layer 112 thinner to reduce the resistance. As the electrolyte layer 112 becomes thinner, the strength of the electrolyte layer 112 decreases. Tensile stress is applied and cracks are likely to occur. In the present embodiment, even in such a thin electrolyte layer 112, the generation of cracks can be effectively suppressed by allowing the spinel-type oxide SP, which expands in volume by reduction, to exist inside the electrolyte layer 112. can be done.

In the present embodiment, the electrolyte layer 112 further contains a solid solution SS in which at least one of divalent Mn and divalent Fe dissolves in the electrolyte material constituting the electrolyte layer 112 (second Condition 2 (Fig. 7(A) and Fig. 10). For example, tensile stress is applied to the electrolyte layer 112 when the fuel electrode 116 is oxidized and expands when the single cell 110 is stopped. However, as the fuel electrode 116 is oxidized, the solid solution SS existing in the electrolyte layer 112, particularly on the fuel electrode 116 side, is oxidized in an oxidizing atmosphere and precipitated as a spinel oxide SP2 (see FIG. 7(B)). The compressive stress of electrolyte layer 112 is further increased. Therefore, according to the present embodiment, it is possible to more effectively suppress the occurrence of cracks in the electrolyte layer 112 . Also, the redox resistance of the single cell 110 is further improved.

In the present embodiment, the total concentration (mass%) of divalent Mn and divalent Fe present as a solid solution SS in the region of the electrolyte layer 112 on the fuel electrode 116 side is It is higher than the total concentration of divalent Mn and divalent Fe present as a solid solution SS in the region (third condition). According to the present embodiment, on the side of the fuel electrode 116 where the amount of deformation during the operation of the single cell 110 is particularly large, the volume expansion based on the solid solution SS in addition to the spinel-type oxide SP effectively prevents cracks from occurring in the electrolyte layer 112. can be effectively suppressed.

In this embodiment, the total concentration of elements contained as M in the electrolyte layer 112 is 3 mass % or less (fourth condition). According to the present embodiment, it is possible to suppress an excessive decrease in the oxygen ion conductivity of the electrolyte layer 112 due to the element (Mn) contained as M present inside the electrolyte layer 112 .

In this embodiment, the electrolyte layer 112 contains a fluorite-type oxide (fifth condition). According to the present embodiment, the adhesion between the electrolyte material portion other than the spinel-type oxide SP in the electrolyte layer 112 and the spinel-type oxide SP is higher than in the case where the electrolyte layer 112 does not contain a fluorite-type oxide. Therefore, the strength of the electrolyte layer 112 can be improved. In addition, since the electrolyte layer 112 contains a fluorite-type oxide, the oxygen ion conductivity of the electrolyte layer 112 can be improved.

B. Variant:
The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the scope of the invention. For example, the following modifications are possible.

In the above-described embodiment, the electrolyte layer 112 satisfies the first condition for all the single cells 110 included in the fuel cell stack 100. However, for at least one unit cell 110 satisfying the condition, the electrolyte layer 112 is the first condition. If the configuration satisfies the condition of (1), cracking of the single cell 110, which is one of the conditions, is suppressed, so deterioration of the performance of the fuel cell stack 100 can be suppressed. In the above embodiment, the electrolyte layer 112 does not have to satisfy at least one of the second to fifth conditions.

The materials constituting each member in the above embodiment are merely examples, and each member may be made of another material.

In the above embodiments, SOFCs that generate electricity by utilizing the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas are targeted, but the present invention utilizes the electrolysis reaction of water. The present invention can also be applied to an electrolytic cell unit, which is the minimum unit of a solid oxide type electrolytic cell (SOEC) that generates hydrogen by squeezing, and an electrolytic cell stack including a plurality of electrolytic cell units. The configuration of the electrolysis cell stack is known, for example, as described in Japanese Patent Laid-Open No. 2016-81813. Configuration. That is, the fuel cell stack 100 in the above-described embodiment should be read as an electrolysis cell stack, and the power generation unit 102 should be read as an electrolysis cell unit.

The present invention can also be applied to composites and electrochemical reaction cell stacks having metal-supported single cells. A metal-supported single cell has a metal support disposed on the side opposite to the electrolyte layer with respect to one of the anode and the air electrode, and the metal support separates the other parts of the single cell (cathode, solid electrolyte, anode, etc.). An application example of a metal-supported single cell has a configuration similar to that of the fuel cell stack 100 in the above-described embodiment. That is, the interconnector 150 in the above-described embodiment should be read as a metal support.

24: Nut 26: Insulating sheet 27: Gas passage member 28: Body portion 29: Branch portion 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 124: Joint 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 passage 143: Fuel gas discharge passage 144: Fuel electrode side current collector 145: Electrode connection portion 146: Interconnector connection portion 147: Connection portion 149: Spacer 150: Interconnector 161: Oxidant gas supply manifold 162 : Oxidant gas discharge manifold 166: Air chamber 171: Fuel gas supply manifold 172: Fuel gas discharge manifold 176: Fuel chamber FG: Fuel gas FOG: Fuel offgas OG: Oxidant gas OOG: Oxidant offgas SP, SP1, SP2: Spinel type oxide SS: solid solution

Claims (6)

An electrochemical reaction single cell comprising an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in a first direction with the electrolyte layer interposed therebetween,
A spinel-type oxide represented by a composition formula of M ₃ O ₄ (M includes at least one of Mn and Fe) is deposited inside the electrolyte layer. Reaction single cell. In the electrochemical reaction single cell according to claim 1,
The electrochemical reaction unit is characterized in that a solid solution in which at least one of divalent Mn and divalent Fe is dissolved in the electrolyte material constituting the electrolyte layer is further present inside the electrolyte layer. cell. In the electrochemical reaction single cell according to claim 2,
The total concentration (mass%) of the divalent Mn and the divalent Fe present as the solid solution in the region on the fuel electrode side of the center in the first direction in the electrolyte layer is An electrochemical reaction unit cell, wherein the concentration is higher than the total concentration of divalent Mn and divalent Fe present as the solid solution in the region closer to the air electrode than the center in the first direction. In the electrochemical reaction single cell according to any one of claims 1 to 3,
The electrochemical reaction single cell, wherein the total concentration of the elements contained as M in the electrolyte layer is 3 mass % or less. In the electrochemical reaction single cell according to any one of claims 1 to 4,
The electrochemical reaction single cell, wherein the electrolyte layer contains a fluorite-type oxide. In an electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells arranged side by side in the first direction,
An electrochemical reaction cell stack, wherein at least one of the plurality of electrochemical reaction single cells is the electrochemical reaction single cell according to any one of claims 1 to 5.

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