JP2017123240A - Electrochemical reaction single cell, interconnector-electrochemical reaction single cell composite body, and electrochemical reaction cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the worsening of a performance owing to the extension of cracking in the surface of an electrochemical reaction single cell through a first layer of an electrode to a second layer closer to an electrolyte layer.SOLUTION: In an electrochemical reaction single cell, at least one of an air electrode and a fuel electrode includes a first layer and a second layer located on an electrolyte layer side; and a region which satisfies the relations S and T described below is present in a cross section in parallel with a first direction of the first layer. Relation S: R(1)≥20% (where R(1) is a rate of the number of first particles to the total number of particles in a predetermined range, and the first particles are particles of which the ratio of a particle length D2 in a second direction to a particle length D1 in the first direction is 2 or more). Relation T: aD2(A)<aD2(1) (where aD2(A) is an average value of the particle length D2 of all the particles in the predetermined range, and aD2(1) is an average value of the particle length D2 of the first particles in the predetermined range).SELECTED DRAWING: Figure 8

Description

  The technology disclosed by the present specification relates to an electrochemical reaction unit cell.

  One type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen is a solid oxide fuel cell (hereinafter referred to as “SOFC”) having an electrolyte layer containing a solid oxide. It has been. A fuel cell single cell (hereinafter simply referred to as “single cell”), which is the smallest structural unit of SOFC, faces each other in a predetermined direction (hereinafter referred to as “first direction”) across the electrolyte layer. An air electrode and a fuel electrode are included (see, for example, Patent Document 1).

JP 2014-49321 A

  In the single cell, at least one of the air electrode and the fuel electrode includes a first layer (also referred to as a “current collecting layer”) and an electrolyte layer side of the first layer in the first direction (that is, the first layer). It may be configured to include a second layer (also referred to as an “active layer”) located closer to the electrolyte layer. In a single cell having such a configuration, a crack may occur on the surface of the single cell due to stress caused by thermal expansion of each member, stress due to pressing force from another member (for example, an interconnector), or the like. In the configuration of the conventional single cell, the crack generated on the surface of the single cell may extend through the first layer of the electrode to the second layer closer to the electrolyte layer, thereby reducing the performance of the single cell. .

 Such a problem is also common to the electrolytic cell which is the minimum constituent unit of a solid oxide electrolytic cell (hereinafter referred to as “SOEC”) that generates hydrogen by utilizing an electrolysis reaction of water. It is. In the present specification, the fuel cell unit cell and the electrolysis cell are collectively referred to as an electrochemical reaction unit cell. Such a problem is not limited to SOFC and SOEC, but is common to other types of electrochemical reaction single cells.

  In this specification, the technique which can solve the subject mentioned above is disclosed.

  The technology disclosed in the present specification can be realized as, for example, the following forms.

(1) An electrochemical reaction unit cell disclosed in the present specification is an electrochemical reaction unit cell including an electrolyte layer, and an air electrode and a fuel electrode facing each other in a first direction with the electrolyte layer interposed therebetween. And at least one of the air electrode and the fuel electrode includes a first layer and a second layer located on the electrolyte layer side of the first layer in the first direction, A region satisfying the following relationships S and T exists in at least one cross section parallel to the first direction of one layer.
Relationship S: R (1) ≧ 20% (where R (1) is the ratio of the number of first type particles to the total number of particles in a predetermined range, and the first type particles are in the first direction) The aspect ratio (D2 / D1), which is the ratio of the grain length D2 in the second direction orthogonal to the first direction to the grain length D1 in FIG.
Relationship T: aD2 (A) <aD2 (1) (where aD2 (A) is an average value of the grain lengths D2 of all the particles in the predetermined range, and aD2 (1) is the value in the predetermined range. (It is the average value of the grain length D2 of the first kind particles.)
The first type particles having a relatively long grain length D2 and a shape that is long in a direction orthogonal to the first direction stop the extension of cracks generated on the surface of the electrochemical reaction single cell in the first direction. When functioning as a stopper, according to the present electrochemical reaction single cell, the composition ratio R (1) of the first kind particles in the first layer of the electrode is relatively large, and the grain length D2 of the first kind particles is Since the average value aD2 (1) is larger than the average value aD2 (A) of the particle length D2 of all particles, cracks generated on the surface of the electrochemical reaction single cell extend in the first direction in the first layer. It can suppress reaching to the 2nd layer in a position nearer to an electrolyte layer, and can suppress the performance fall of an electrochemical reaction single cell.

(2) In the electrochemical reaction single cell, the region may be a region that satisfies the following relationship U.
Relationship U: E ≦ 0.68 (μm) (where E is an absolute value of deviation of the grain length D2 of each particle in the predetermined range)
According to this electrochemical reaction single cell, since the variation in the grain length D2 in the second direction in the first layer of the electrode is relatively small, the number of contact points between the particles increases, and a conductive path is ensured above a certain level. It can suppress that the initial performance of an electrochemical reaction single cell falls.

(3) In the electrochemical reaction single cell, the region may be a region that satisfies the following relationship V.
Relationship V: R (2) ≧ 23% (where R (2) is the ratio of the number of second type particles to the total number of particles in the predetermined range, and the second type particles have an aspect ratio (D2). / D1) is a particle having 1 or less.)
The second type particles that are long in the first direction are advantageous in terms of ensuring conductivity in the first direction. According to this electrochemical reaction unit cell, the second type particles in the first layer of the electrode Since the composition ratio R (2) of the seed particles is relatively large, it is possible to suppress a decrease in the conductivity of the electrode.

(4) In the electrochemical reaction single cell, three cross sections of the first layer parallel to the first direction, and the air electrode is equally divided into four in the longitudinal direction as viewed in the first direction. It is good also as a structure where the said area | region exists in three cross sections. According to this electrochemical reaction single cell, since the composition ratio R (1) of the first type particles in the first layer of the electrode is relatively large in the second direction, the performance degradation of the electrochemical reaction single cell is reduced. It can be effectively suppressed.

(5) Moreover, the interconnector-electrochemical reaction single cell complex disclosed in the present specification includes at least the electrochemical reaction single cell, the air electrode and the fuel electrode of the electrochemical reaction single cell. And an interconnector having a convex portion disposed on one side and projecting to the at least one side of the air electrode and the fuel electrode. According to this interconnector-electrochemical reaction single cell composite, even if a crack is generated on the surface of the electrochemical reaction single cell due to the stress caused by the pressing force from the convex portion of the interconnector, the crack is in the first layer. Can be prevented from extending in the first direction to reach the second layer closer to the electrolyte layer, and the performance degradation of the electrochemical reaction single cell can be suppressed.

(6) In the electrochemical reaction single cell, the electrolyte layer may include a solid oxide or a carbonate. According to this electrochemical reaction unit cell, even if a crack occurs on the surface of the electrochemical reaction unit cell due to the stress due to thermal expansion of each member in the electrochemical reaction unit cell operated at a relatively high temperature, Can be prevented from extending in the first direction in the first layer and reaching the second layer at a position closer to the electrolyte layer, and the performance degradation of the electrochemical reaction single cell can be suppressed. .

  The technology disclosed in the present specification can be realized in various forms. For example, an electrochemical reaction single cell (fuel cell single cell or electrolytic cell), an electrochemical reaction single cell, an interconnector, Interconnector-electrochemical reaction single cell composite (interconnector-fuel cell single cell composite or interconnector-electrolytic cell composite), electrochemical reaction cell stack (fuel cell stack) including a plurality of electrochemical reaction single cells Alternatively, it can be realized in the form of an electrolytic cell stack) or a manufacturing method thereof.

1 is a perspective view showing an external configuration of a fuel cell stack 100 in the present embodiment. It is explanatory drawing which shows the XZ cross-section structure of the fuel cell stack 100 in the position of II-II of FIG. FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of a fuel cell stack 100 at a position of III-III in FIG. 1. It is explanatory drawing which shows XZ cross-section structure of the two electric power generation units 102 adjacent to each other in the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-section structure of the two electric power generation units 102 adjacent to each other in the same position as the cross section shown in FIG. It is explanatory drawing which shows the result of 1st performance evaluation. It is explanatory drawing which shows typically the XZ cross-section structure of the current collection layer 410 of the air electrode 114 in the sample 1 (comparative example). It is explanatory drawing which shows typically the XZ cross-sectional structure of the current collection layer 410 of the air electrode 114 in the sample 2 (Example). It is explanatory drawing which shows the result of 2nd performance evaluation.

A. Embodiment:
A-1. Constitution:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of a fuel cell stack 100 in the present embodiment, and FIG. 2 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 100 at a position II-II in FIG. FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position of III-III in FIG. In each figure, XYZ axes orthogonal to each other for specifying the direction are shown. In this specification, for the sake of 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. It may be installed. The same applies to FIG.

  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 the present embodiment). The pair of end plates 104 and 106 are arranged so as to sandwich an assembly composed of seven power generation units 102 from above and below. The arrangement direction (vertical direction) corresponds to the first direction in the claims.

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

  Bolts 22 extending in the vertical direction are inserted into the communication holes 108, and the fuel cell stack 100 is fastened by the bolts 22 and nuts 24 fitted on both sides of the bolts 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 the bolt An insulating sheet 26 is interposed between the nut 24 fitted on the other side (lower side) of 22 and the lower surface of the end plate 106 constituting the lower end of the fuel cell stack 100. However, in a place where a gas passage member 27 described later is provided, an insulating sheet disposed between the nut 24 and the surface of the end plate 106 on the upper and lower sides of the gas passage member 27 and the gas passage member 27, respectively. 26 is interposed. The insulating sheet 26 is made of, for example, a mica sheet, a ceramic fiber sheet, a ceramic powder sheet, a glass sheet, a glass ceramic composite agent, 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, the fuel cell stack 100 is located near the midpoint of one side (the X-axis positive direction side of two sides parallel to the Y-axis) on the outer periphery around the Z-direction. The space formed by the bolt 22 (bolt 22A) and the communication hole 108 through which the bolt 22A is inserted is introduced with the oxidant gas OG from the outside of the fuel cell stack 100, and the oxidant gas OG is generated by each power generation. It functions as an oxidant gas introduction manifold 161 that is a gas flow path to be supplied to the unit 102, and is the midpoint of the side opposite to the side (X-axis negative direction side of two sides parallel to the Y-axis) The space formed by the bolts 22 (bolts 22B) located in the vicinity and the communication holes 108 through which the bolts 22B are inserted contains the oxidant off-gas OOG that is the gas discharged from the air chamber 166 of each power generation unit 102. Burning Functions as the oxidizing gas discharging manifold 162 for discharging to the outside of the cell stack 100. In the present embodiment, for example, air is used as the oxidant gas OG.

  Further, as shown in FIGS. 1 and 3, the vicinity of the midpoint of one side (the side on the Y axis positive direction side of two sides parallel to the X axis) on the outer periphery of the fuel cell stack 100 around the Z direction The space formed by the bolt 22 (bolt 22D) positioned at the position and the communication hole 108 through which the bolt 22D is inserted is introduced with the fuel gas FG from the outside of the fuel cell stack 100, and the fuel gas FG is generated by each power generation. Bolt 22 that functions as a fuel gas introduction manifold 171 to be supplied to the unit 102 and is located in the vicinity of the midpoint of the opposite side (the side on the Y axis negative direction side of the two sides parallel to the X axis). The space formed by the (bolt 22E) and the communication hole 108 through which the bolt 22E is inserted is a fuel cell stack 1 that uses the fuel off-gas FOG that is a gas discharged from the fuel chamber 176 of each power generation unit 102 as the fuel cell stack 1 Functions as a fuel gas exhaust manifold 172 for discharging to the outside of the 0. In the present embodiment, as the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used.

  The fuel cell stack 100 is provided with four gas passage members 27. 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 part 29 communicates with the hole of the main body part 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 main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22 </ b> A forming the oxidant gas introduction manifold 161 communicates with the oxidant gas introduction manifold 161. The hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22 </ b> B that forms 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 fuel gas The hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22 </ b> E forming the discharge manifold 172 communicates with the fuel gas discharge manifold 172.

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

(Configuration of power generation unit 102)
4 is an explanatory diagram showing an 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. 5 is adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-section structure of the two electric power generation units.

  As shown in FIGS. 4 and 5, the power generation unit 102 that is the minimum unit of power generation includes a single cell 110, a separator 120, an air electrode side frame 130, an air electrode side current collector 134, and a fuel electrode side frame. 140, a fuel electrode side current collector 144, and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer of the power generation unit 102. The separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the periphery of the interconnector 150 around the Z direction are formed with holes corresponding to the communication holes 108 through which the bolts 22 are inserted.

  The interconnector 150 is a substantially rectangular flat plate-shaped conductive member, and is formed of, for example, ferritic stainless steel. The interconnector 150 ensures electrical continuity between the power generation units 102 and prevents reaction gas from being mixed 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 two adjacent power generation units 102. That is, the upper interconnector 150 in a 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. Further, since the fuel cell stack 100 includes the pair of end plates 104 and 106, the power generation unit 102 located at the top in the fuel cell stack 100 does not include the upper interconnector 150 and is located at the bottom. The power generation unit 102 does not include the lower interconnector 150 (see FIGS. 2 and 3).

  The unit cell 110 includes an electrolyte layer 112, and an air electrode (cathode) 114 and a fuel electrode (anode) 116 that face each other in the vertical direction (the arrangement direction in which the power generation units 102 are arranged) with the electrolyte layer 112 interposed therebetween. The single cell 110 of the present embodiment is a fuel electrode-supported single cell that supports the electrolyte layer 112 and the air electrode 114 with the fuel electrode 116.

  The electrolyte layer 112 is a substantially rectangular flat plate-shaped member. For example, YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samarium doped ceria), GDC (gadolinium doped ceria), perovskite oxide It is formed with solid oxides such as. The air electrode 114 is a substantially rectangular flat plate-shaped member, and is formed of, for example, a perovskite oxide (for example, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide), LNF (lanthanum nickel iron)). Has been. The configuration of the air electrode 114 will be described in detail later. The fuel electrode 116 is a substantially rectangular flat plate-like member, and is formed of, for example, Ni (nickel), cermet made of Ni and ceramic particles, Ni-based alloy, or the like. Thus, 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.

  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, for example, metal. The peripheral part of the hole 121 in the separator 120 is opposed to the peripheral part of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is bonded to the electrolyte layer 112 (single cell 110) by a bonding portion 124 formed of a brazing material (for example, Ag brazing) disposed in the facing portion. The separator 120 divides the air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116, and gas leaks from one electrode side to the other electrode side in the peripheral portion of the single cell 110. It is suppressed. The single cell 110 to which the separator 120 is bonded is also referred to as a single cell with a separator.

 The air electrode side frame 130 is a frame-like member in which a substantially rectangular hole 131 penetrating in the vertical direction 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 forms an air chamber 166 that faces the air electrode 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. . The pair of interconnectors 150 included in the power generation unit 102 is electrically insulated by the air electrode side frame 130. The air electrode side frame 130 has an oxidant gas supply communication hole 132 communicating the oxidant gas introduction manifold 161 and the air chamber 166, and an oxidant gas communicating the air chamber 166 and the oxidant gas discharge manifold 162. A discharge communication hole 133 is formed.

  The fuel electrode side frame 140 is a frame-like member in which a substantially rectangular hole 141 penetrating in the vertical direction is formed near the center, and is made of, for example, metal. The hole 141 of the fuel electrode side frame 140 forms a fuel chamber 176 that faces the fuel electrode 116. The fuel electrode side frame 140 is in contact with the peripheral portion of the surface of the separator 120 facing the electrolyte layer 112 and the peripheral portion 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 connects the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that connects the fuel chamber 176 and the fuel gas discharge manifold 172. And are formed.

  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. For example, nickel or a nickel alloy It is made of 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 on the surface of the interconnector 150 on the side facing the fuel electrode 116. In contact. However, as described above, since the lowermost power generation unit 102 in the fuel cell stack 100 does not include the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 has a lower end plate. 106 is in contact. 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. Note that a spacer 149 made 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 the temperature cycle and the reaction gas pressure fluctuation, and the fuel electrode 116 and the interconnector 150 (or the end plate 106) via the fuel electrode side current collector 144. The electrical connection with is maintained well.

  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 current collector elements 135 having a substantially quadrangular prism shape, and is formed 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 side facing the electrolyte layer 112 and the surface of the interconnector 150 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 includes the upper end plate. 104 is in contact. Since the air electrode side current collector 134 has such a configuration, the air electrode 114 and the interconnector 150 (or the end plate 104) are electrically connected. In the present embodiment, the air electrode side current collector 134 and the interconnector 150 are formed as an integral member. That is, a flat plate portion perpendicular to the vertical direction (Z-axis direction) of the integrated member functions as the interconnector 150 and is formed so as to protrude from the flat plate portion toward the air electrode 114. The current collector element 135 that is a plurality of convex portions functions as the air electrode side current collector 134. Moreover, the integral member of the air electrode side current collector 134 and the interconnector 150 may be covered with a conductive coat, and between the air electrode 114 and the air electrode side current collector 134, A conductive bonding layer to be bonded may be interposed. An integral member of the air electrode side current collector 134 and the interconnector 150 may be simply referred to as an interconnector.

  In this specification, as shown in FIGS. 4 and 5, a structure obtained by removing the air electrode side frame 130 and the air electrode side frame 130 side interconnector 150 from each power generation unit 102, that is, a single cell 110. A structure including the separator 120, the fuel electrode side frame 140, and the interconnector 150 on the fuel electrode side frame 140 side is also referred to as an interconnector-fuel cell single cell complex 107. As described above, the fuel cell stack 100 includes a plurality of power generation units 102 arranged in the vertical direction. In other words, the fuel cell stack 100 includes a plurality of fuel cell stacks 100 arranged with the air electrode side frame 130 interposed therebetween. It can be said that the interconnector-fuel cell single cell composite 107 is provided. The interconnector-fuel cell single cell complex 107 is an example of an interconnector-electrochemical reaction single cell complex.

A-2. Operation of the 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 introduction manifold 161. Then, 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 hole of the main body portion 28, and the oxidant gas introduction manifold 161 oxidizes each power generation unit 102. It is supplied to the air chamber 166 through the agent gas supply communication hole 132. Further, as shown in FIGS. 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 introduction manifold 171. Then, 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 hole of the main body portion 28, and the fuel gas supply communication of each power generation unit 102 from the fuel gas introduction manifold 171. The fuel chamber 176 is supplied through the 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, power is generated by an electrochemical reaction between the oxidant gas OG and the fuel gas FG in the single cell 110. Is called. 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 via the air electrode side current collector 134, and the fuel electrode 116 is connected via the fuel electrode side current collector 144. The other interconnector 150 is electrically connected. The plurality of power generation units 102 included in the fuel cell stack 100 are electrically connected in series. Therefore, 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 SOFC generates power at a relatively high temperature (for example, 700 ° C. to 1000 ° C.), the fuel cell stack 100 is heated by a heater (after the start-up until the high temperature can be maintained by the heat generated by the power generation. (Not shown).

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

A-3. Detailed configuration of the air electrode 114:
As shown in FIG. 5, the air electrode 114 includes an active layer 420 and a current collecting layer 410. The active layer 420 is located in the Z direction on the electrolyte layer 112 side of the current collection layer 410, that is, on the side closer to the electrolyte layer 112 than the current collection layer 410.

  The active layer 420 of the air electrode 114 is a layer that mainly functions as an ionization reaction field for oxygen contained in the oxidant gas OG. In the present embodiment, the active layer 420 includes a perovskite oxide and GDC (gadolinium-doped ceria) as an activating substance. The current collecting layer 410 of the air electrode 114 is a layer mainly functioning as a field for collecting the electricity obtained by the power generation reaction while diffusing the oxidant gas OG supplied from the air chamber 166. The current collecting layer 410 includes a perovskite oxide but does not include GDC. Note that the active layer 420 has a smaller overall particle size and is dense (that is, has a lower porosity) than the current collecting layer 410. The active layer 420 corresponds to the second layer in the claims, and the current collecting layer 410 corresponds to the first layer in the claims.

A-4. Performance evaluation:
The fuel cell stack 100 of this embodiment is characterized by the configuration of the current collecting layer 410 of the air electrode 114. Hereinafter, various performance evaluations performed using a plurality of samples having different configurations of the current collecting layer 410 of the air electrode 114 will be described.

(Performance evaluation of power generation deterioration rate)
As the first performance evaluation, the power generation deterioration rate was measured using samples (sample 1 and sample 2) of a plurality of single cells 110 having different configurations of the current collecting layer 410 of the air electrode 114. FIG. 6 is an explanatory diagram showing the results of the first performance evaluation. FIG. 7 is an explanatory diagram schematically showing an XZ cross-sectional configuration of the current collecting layer 410 (410 (1)) of the air electrode 114 in Sample 1 (Comparative Example), and FIG. 8 shows Sample 2 (Example). 3 is an explanatory diagram schematically showing the XZ cross-sectional configuration of the current collecting layer 410 (410 (2)) of the air electrode 114 in FIG.

  As shown in FIGS. 7 and 8, in the first performance evaluation, each particle included in the current collecting layer 410 of the air electrode 114 is placed in a direction orthogonal to the Z direction with respect to the grain length D1 in the Z direction (for example, in the X direction). The aspect ratio (D2 / D1), which is the ratio of the grain length D2 (hereinafter referred to as “plane direction”), is divided into three types of first seed particles P1, second seed particles P2, and third seed particles P3. Classified. The first type particles P1 are particles having an aspect ratio (D2 / D1) of 2 or more, and are particles having a shape that is long in the plane direction. The second type particles P2 are particles having an aspect ratio (D2 / D1) of 1 or less, and are particles having a long shape in the Z direction (vertical direction). The third type particles P3 are particles other than the first type particles P1 and the second type particles P2.

As shown in FIG. 6, in the current collecting layer 410 of Sample 1, the composition ratio R (n) of various particles in a cross section parallel to the Z direction (for example, XZ cross section) was as follows. The composition ratio R (n) is the ratio of the number of the n-th type particles Pn to the total number of particles in a predetermined range of the cross section (where n = 1, 2, 3).
-Composition ratio R (1) of the first kind particles P1 = 10 (%)
-Composition ratio R (2) of the second kind particles P2 = 23 (%)
-Composition ratio R (3) of the third kind particles P3 = 67 (%)

On the other hand, in the current collecting layer 410 of Sample 2, the constituent ratio R (n) of various particles in a cross section (for example, XZ cross section) parallel to the Z direction was as follows.
-Composition ratio R (1) of the first kind particles P1 = 20 (%)
-Composition ratio R (2) of the second kind particles P2 = 23 (%)
-Composition ratio R (3) of the third kind particles P3 = 57 (%)

  Thus, in the current collection layer 410 (see FIG. 7) of the sample 1, the composition ratio R (1) of the first type particles P1 is relatively small, and in the current collection layer 410 (see FIG. 8) of the sample 2, The composition ratio R (1) of the first kind particles P1 is relatively large. In addition, the constituent ratio R (2) of the second kind particles P2 included in the current collecting layer 410 is the same between the sample 1 and the sample 2.

Moreover, as shown in FIG. 6, in the current collection layer 410 of Sample 1, the average grain length D2 in the plane direction in the cross section was as follows. Note that the total particle average particle length aD2 (A) is the average value of the particle lengths D2 of all the particles in the predetermined range of the cross section, and the first type particle average particle length aD2 (1) is the above value of the cross section. It is an average value of the grain length D2 of the first kind particles P1 in a predetermined range.
・ All grains average grain length aD2 (A) = 1.37 (μm)
First type particle average grain length aD2 (1) = 1.99 (μm)

On the other hand, in the current collecting layer 410 of Sample 2, the average grain length D2 in the plane direction in the cross section was as follows.
・ All grains average grain length aD2 (A) = 1.2 (μm)
First type particle average grain length aD2 (1) = 1.56 (μm)

  Thus, in both sample 1 and sample 2, the relationship of total particle average particle length aD2 (A) <first type particle average particle length aD2 (1) was established. That is, in both sample 1 and sample 2, it can be said that the grain length D2 in the surface direction of the first kind particles P1 is larger than that of other kinds of particles.

  In the first performance evaluation, power generation deterioration is performed by a test that repeats the operation of stopping the operation from the steady operation and the operation of restarting the operation from the stopped state using the samples (sample 1 and sample 2) of the two single cells 110 described above. The rate was measured. More specifically, by repeating the combination of the operation to stop operation from steady operation and the operation to resume operation from a stopped state, the sample temperature is changed from high temperature to low temperature, and thermal shock is applied to the sample multiple times. It was. The voltage after the above operation combination was repeated about 20 times (post-test voltage) was measured, and the ratio of the difference between the initial voltage and the post-test voltage relative to the initial voltage was calculated as the power generation deterioration rate (%).

  As shown in FIG. 6, in the sample 1 (comparative example), the power generation deterioration rate was relatively high, and it was determined as rejected (x). On the other hand, in sample 2 (Example), the power generation deterioration rate was extremely low, and it was determined to be acceptable (◯). The following can be considered as this factor. That is, the stress caused by the thermal expansion of each member constituting the single cell 110, the stress due to the pressing force from the other member (for example, the air electrode side current collector 134 as the convex portion of the interconnector), etc. Cracks may occur on the surface of the cell 110, for example, the surface of the current collecting layer 410 of the air electrode 114. When cracks generated on the surface of the current collecting layer 410 of the air electrode 114 extend through the current collecting layer 410 to the active layer 420 located closer to the electrolyte layer 112, the power generation performance of the single cell 110 is degraded. Here, among the particles contained in the current collecting layer 410, the first type particles P1 having a relatively large grain length D2 and a long shape in the plane direction are stoppers that stop such cracks from extending in the Z direction. Function as. In Sample 1, since the composition ratio R (1) of the first type particles P1 in the current collecting layer 410 is relatively small, cracks generated on the surface of the single cell 110 extend in the current collecting layer 410 in the Z direction and are active. It is considered that reaching the layer 420 was not suppressed, and the performance degradation of the single cell 110 was not suppressed. On the other hand, in sample 2, the composition ratio R (1) of the first type particles P1 in the current collecting layer 410 is relatively large, and the first type particle average particle length aD2 (1) is the total particle average particle length aD2 (A Therefore, it is considered that cracks generated on the surface of the single cell 110 are prevented from extending in the Z direction in the current collecting layer 410 to reach the active layer 420, and the performance degradation of the single cell 110 is suppressed. It is done.

Thus, from the result of the first performance evaluation, there is a region where the current collecting layer 410 of the air electrode 114 satisfies the following relations S and T in at least one cross section (for example, XZ cross section) parallel to the Z direction. If configured so, cracks generated on the surface of the single cell 110 can be prevented from extending through the current collecting layer 410 to the active layer 420, and the performance of the single cell 110 can be reduced. I can say that.
Relationship S: Composition ratio R (1) ≧ 20% of the first kind particles P1
Relationship T: All particles average particle length aD2 (A) <First type particle average particle length aD2 (1)

  In addition, in the current collecting layer 410 of the air electrode 114, when the constituent ratio R (1) of the first type particles P1 is uniformly high in the plane direction, the generation occurs regardless of the crack generation position on the surface of the single cell 110. It can be said that the cracks are more preferable because the cracks in the current collecting layer 410 are prevented from extending in the Z direction and reaching the active layer 420. Therefore, for example, there are three cross sections parallel to the Z direction of the current collecting layer 410, and there are regions that satisfy the above relationships S and T in three cross sections that divide the air electrode 114 into four in the longitudinal direction when viewed in the Z direction. Thus, it can be said that the current collecting layer 410 of the air electrode 114 is more preferable.

In addition, the first type particle P1 is disadvantageous in terms of securing conductivity in the Z direction (vertical direction) as compared with the second type particle P2. In addition, it is preferable that the second type particles P <b> 2 exist in the current collection layer 410 at a certain composition ratio. Therefore, referring to the result of the first performance evaluation, it is more preferable that the region satisfying the relations S and T is a region satisfying the following relationship V, which can suppress a decrease in conductivity of the air electrode 114. It can be said.
Relationship V: Composition ratio R (2) ≧ 23% of the second kind particles P2

(Performance evaluation for initial voltage)
As a second performance evaluation, the initial voltage was measured using Sample 1 and Sample 2. FIG. 9 is an explanatory diagram showing the result of the second performance evaluation.

  Sample 1 and sample 2 are different from each other in the degree of deviation (difference from the average value) of the grain length D2 in the plane direction of each grain in a predetermined range of a certain section (for example, XZ section) parallel to the Z direction. Specifically, in sample 1, the maximum absolute value of the deviation (hereinafter referred to as “grain length maximum deviation E”) is relatively large at 0.97 (μm), and in sample 2, the maximum grain length deviation E is obtained. Is relatively small, 0.68 (μm). That is, sample 1 has a relatively large variation in grain length D2 in the plane direction, and sample 2 has a relatively small variation in grain length D2 in the plane direction.

In the second performance evaluation, the initial voltage (V) at 0.3 (A / cm ² ) was measured using the sample of the two single cells 110. As shown in FIG. 9, in sample 1, the initial voltage was relatively low, and it was determined to be rejected (x). On the other hand, in sample 2, the initial voltage was relatively high and determined to be good (◯). This is because the sample 2 has a relatively small variation in the grain length D2 in the surface direction in the current collecting layer 410, so that the number of contact points between the particles increases, a certain number of conductive paths are ensured, and the initial power generation performance. It is considered that the decrease in the temperature was suppressed.

As described above, from the result of the second performance evaluation, a region in which the current collecting layer 410 of the air electrode 114 satisfies the above relationships S and T in at least one cross section (for example, XZ cross section) parallel to the Z direction is as follows. It can be said that when the region satisfies the relationship U, the initial power generation performance can be prevented from decreasing.
Relationship U: Maximum grain length deviation E ≦ 0.68 (μm)

A-5. Manufacturing method of the single cell 110:
An example of the manufacturing method of the single cell 110 in this embodiment is as follows.

(Formation of laminated body of electrolyte layer 112 and fuel electrode 116)
For example, a butyral resin, dioctyl phthalate (DOP) as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added to a YSZ powder having a specific surface area of 5 to 7 m ² / g by the BET method. Then, a slurry is prepared by mixing with a ball mill. The obtained slurry is thinned by a doctor blade method to obtain a green sheet for an electrolyte layer having a thickness of about 10 μm, for example. Also, the NiO powder is the specific surface area, for example, 3 to 4 m ² / g by BET method, in terms of Ni by weight were weighed so as to be 55 parts by weight, 5 to 7 m is a BET specific surface area of for example ² / The mixed powder is obtained by mixing with 45 parts by mass of YSZ powder as g. To this mixed powder, a butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added and mixed in a ball mill to prepare a slurry. The obtained slurry is thinned by a doctor blade method to obtain a fuel electrode green sheet having a thickness of, for example, 270 μm. An electrolyte layer green sheet and a fuel electrode green sheet are attached and dried. Thereafter, firing is performed at 1400 ° C., for example, to obtain a laminate of the electrolyte layer 112 and the fuel electrode 116.

(Formation of air electrode 114)
Next, LSCF powder, GDC powder, alumina powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent are mixed as materials for the active layer 420 of the air electrode 114 to adjust the viscosity. To prepare an active layer paste. The prepared paste for active layer is applied to the surface on the electrolyte layer 112 side in the laminate of the electrolyte layer 112 and the fuel electrode 116 by screen printing and dried.

  Further, as the material of the current collecting layer 410 of the air electrode 114, 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 collect the current. A layer paste is prepared. The adjusted current collecting layer paste is applied onto the above-mentioned active layer paste by screen printing and dried. In addition, as a method for applying the paste for each layer of the air electrode 114, other methods such as spray application can be employed.

  Thereafter, for example, by firing at 1100 ° C., the air electrode 114 composed of the active layer 420 and the current collecting layer 410 is formed on the surface on the electrolyte layer 112 side in the laminate of the electrolyte layer 112 and the fuel electrode 116. It is formed.

  The constituent ratio R (n) of various particles in the current collecting layer 410 of the air electrode 114 can be adjusted by, for example, the following method. That is, when it is desired to increase the constituent ratio R (1) of the first type particles P1, the time for the pulverization process for producing the LSCF powder as the material of the current collecting layer 410 of the air electrode 114 should be made relatively short. Makes the particle shape relatively non-uniform. In this way, an LSCF powder material containing a large number of relatively long and narrow LSCF particles can be obtained. In addition, after applying and drying the adjusted current collecting layer paste, by applying a compressive force in the Z direction to the current collecting layer paste, at least the elongated LSCF particles contained in the current collecting layer paste A part of the first type particles P1 changes its posture so that its longitudinal direction approaches the plane direction, and the aspect ratio (ratio of the grain length D2 in the plane direction to the grain length D1 in the Z direction) is 2 or more. . Therefore, the composition ratio R (1) of the first kind particles P1 in the current collecting layer 410 can be increased by such a method. Further, when it is desired to increase the constituent ratio R (2) of the second seed particles P2, as in the case where the constituent ratio R (1) of the first seed particles P1 is to be increased, a pulverization process for producing the LSCF powder is performed. The particle shape is made relatively non-uniform by shortening the time of the above. However, when it is desired to increase the constituent ratio R (2) of the second type particles P2, a compressive force is not applied after the current collecting layer paste is applied and dried, or the size of the compressive force is reduced. The compression time is shortened, and the posture change of the elongated LSCF particles is not promoted. Thereby, the composition ratio R (2) of the second type particles P2 in the current collecting layer 410 can be increased. In addition, when it is desired to increase the constituent ratio R (3) of the third type particles P3 in the current collecting layer 410, the time for the pulverization process for preparing the LSCF powder may be made relatively long.

  Through the above steps, the unit cell 110 having the above-described configuration is manufactured. In addition, after the single cell 110 is manufactured, for example, an assembly process such as joining of the air electrode 114 and the air electrode side current collector 134 and fastening of the fuel cell stack 100 by the bolt 22 is performed. The fuel cell stack 100 is manufactured.

A-6. Analysis method of the air electrode 114:
(Acquisition method of analysis image M1)
A method for analyzing the air electrode 114 with respect to the grain length and the like will be described. First, the analysis image M1 used for the analysis of the air electrode 114 is acquired by the following method. In the single cell 110, one cross section (however, the cross section including the air electrode 114) parallel to the vertical direction (Z-axis direction) is arbitrarily set, and an image in which the entire vertical direction of the air electrode 114 can be confirmed in the cross section, Obtained as an analysis image M1. More specifically, the upper surface of the air electrode 114 (the surface in contact with the air electrode side current collector 134) is the uppermost of the ten divided regions obtained by dividing the image vertically into 10 equal parts. An image in which the boundary between the air electrode 114 and the electrolyte layer 112 is located in the lowest divided region is taken by, for example, a scanning electron microscope (SEM), and the analysis image M1 is located in the divided region. Get as. The analysis image M1 may be a binarized image obtained by binarizing an image photographed by the SEM. However, in the case where particles or the like in the binarized image are significantly different from the actual form, an image obtained by adjusting the contrast of the image taken by the SEM before the binarization process and binarizing the image after the adjustment But you can. In addition, the analysis image M1 may be an image before binarization processing that is taken by an SEM. The magnification of the SEM image is set to such a value that the whole of the air electrode 114 in the vertical direction fits in the analysis image M1 as described above, and can be set to 200 to 20,000 times, for example, but is not limited thereto. However, it can be changed as appropriate. The measurement range of the analysis image M1 corresponds to a predetermined range in the claims.

(Determination method of boundary between active layer 420 and current collecting layer 410)
The boundary between the active layer 420 and the current collecting layer 410 constituting the air electrode 114 is specified by the following method using the feature that the porosity of the active layer 420 is lower than the porosity of the current collecting layer 410. First, a plurality of virtual lines K perpendicular to the vertical direction (Z-axis direction) are drawn in order from the upper surface of the air electrode 114 at intervals of 0.3 μm with respect to the analysis image M1, and virtual lines K1, K2, K3,..., Km,..., K (m + 9), K (m + 10),. And the length of the part which overlaps with a pore in each virtual line K is measured, the sum total of the length of the part which overlaps with a pore is calculated, and the total length of the part which overlaps with the pore with respect to the full length of each virtual line K Is the ratio of the pores existing on the virtual line K (porosity Ks). Next, among the porosity Ks1, Ks2, Ks3,..., Ksm,..., Ks (m + 9), Ks (m + 10),. Each data group having the porosity Ks of each virtual line K is set, and the average value (Ave) of the 10 porosity Ks of each data group and the standard deviation (σ) of the porosity Ks of each data group are calculated. To do.

In order from the top, the data group G1 is composed of Ks1, Ks2,..., Ks10, the data group G2 is composed of Ks2, Ks3,..., Ks11, and the data group Gm is composed of Ksm, Ks (m + 1). ), Ks (m + 2),..., Ks (m + 9), and the data group G (m + 1) includes Ks (m + 1), Ks (m + 2),. That is, the data group G (m + 1) means nine porosity (Ks (m + 1),..., Ks) obtained by removing the porosity Ksm of the first virtual line Km of the data group Gm from the data group Gm. (M + 9)) is added to the porosity Ks (m + 10) of the virtual line K (m + 10) next to the last virtual line K (m + 9) of the data group, which means one group consisting of 10 porosity Ks. . The “average value of the porosity Ks of G (m + 1)” is a value obtained by adding a value twice the standard deviation (σ) of 10 porosity Ks of Gm to the average value of the porosity Ks of Gm. Or the average value of the porosity Ks of G (m + 1) is 2 of the standard deviation (σ) of 10 porosity Ks of Gm from the average value of the porosity Ks of Gm. The virtual line K (m + 10) corresponding to the tenth porosity Ks (m + 10) of the data group G (m + 1) when the value is lower than the value obtained by subtracting the double value for the first time is represented by the active layer 420 and the current collecting layer. Bound to 410. That is, when the average value of the porosity Ks of the data group Gm is Gmave, the average value of the porosity Ks of the data group G (m + 1) is G (m + 1) Ave, and the standard deviation of the porosity Ks of the data group Gm is σm. The virtual line K (m + 10) corresponding to the tenth porosity Ks (m + 10) of the first data group G (m + 1) satisfying the following formula (1) is defined as the boundary between the active layer 420 and the current collecting layer 410. To do. If this boundary is determined, the active layer 420 and the current collecting layer 410 can be distinguished on the analysis image M1.
| (G (m + 1) Ave) − (GmAve) |> 2σm (1)

(Measuring method of grain length)
The particle length of the current collector layer 410 of the air electrode 114 is “Miya Satoshi, Yoshiharu Ozaki, Toshio Kimura, Satoshi Yamaguchi,“ Ceramic Processing ”, published by Gihodo Publishing Co., Ltd., March 25, 1985, page 192 195 "". Specifically, in the analysis image M1, a straight line perpendicular to the vertical direction (Z-axis direction) is formed on the current collecting layer 410 at a predetermined interval ( For example, the length of the portion corresponding to each particle on each straight line is measured as the grain length, and the length of all the particles on one or more straight lines located in the target member or region is measured. And the average value of the grain length and the like are calculated using the measured values.

B. Variations:
The technology disclosed in the present 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 possible.

  In the above embodiment (or a modified example, the same applies hereinafter), the current collection layer 410 of the air electrode 114 is configured to satisfy the above relationships S to V. However, the current collection layer 410 is at least the above relationships S to V. If it is configured to satisfy T, it is possible to prevent cracks generated on the surface of the single cell 110 on the air electrode 114 side from extending in the current collecting layer 410 of the air electrode 114 in the Z direction and reaching the active layer 420. Thus, the performance degradation of the single cell 110 can be suppressed.

  Further, in the above embodiment, the air electrode 114 has a two-layer configuration of the active layer 420 and the current collecting layer 410, but the air electrode 114 is composed of layers other than the active layer 420 and the current collecting layer 410. It may be included.

  In the above-described embodiment, all the single cells 110 included in the fuel cell stack 100 are configured to satisfy the relationships S to V. However, at least one single cell 110 included in the fuel cell stack 100 is used. In such a single cell 110, cracks generated on the surface of the single cell 110 on the air electrode 114 side extend in the current collecting layer 410 of the air electrode 114 in the Z direction and become active. Reaching the layer 420 is suppressed, and the performance deterioration of the single cell 110 can be suppressed, and the conductivity decrease of the air electrode 114 can be suppressed.

  In the above embodiment, the number of unit cells 110 included in the fuel cell stack 100 is merely an example, and the number of unit cells 110 is appropriately determined according to the output voltage required for the fuel cell stack 100 or the like. Moreover, the material which forms each member in the said embodiment is an illustration to the last, and each member may be formed with another material.

  In the present specification, the fact that the member B and the member C are opposed to each other across the member (or a part having the member, the same applies hereinafter) A is not limited to the form in which the member A and the member B or the member C are adjacent to each other. It includes a form in which another component is interposed between member A and member B or member C. For example, another layer may be provided between the electrolyte layer 112 and the air electrode 114. Even with such a configuration, it can be said that the air electrode 114 and the fuel electrode 116 face each other with the electrolyte layer 112 interposed therebetween.

  Further, in the above embodiment, the fuel cell stack 100 has a configuration in which a plurality of flat-plate power generation units 102 are stacked. However, the present invention is described in other configurations, for example, Japanese Patent Application Laid-Open No. 2008-59797. In addition, the present invention can be similarly applied to a configuration in which a plurality of substantially cylindrical fuel cell single cells are connected in series.

  In the above embodiment, the SOFC that generates electricity using the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas is targeted. The present invention can be similarly applied to an electrolytic cell which is a minimum unit of a solid oxide electrolytic cell (SOEC) that generates hydrogen by using hydrogen, and an electrolytic cell stack including a plurality of electrolytic cells. The configuration of the electrolytic cell stack is well known as described in, for example, Japanese Patent Application Laid-Open No. 2014-207120, and thus will not be described in detail here. It is a configuration. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolytic cell stack, the power generation unit 102 may be read as an electrolytic cell unit, and the single cell 110 may be read as an electrolytic cell. However, when the electrolysis cell stack is operated, a voltage is applied between the two electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode). Water vapor as a source gas is supplied. 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. Also in the electrolysis cell and electrolysis cell stack having such a configuration, as in the case of the above-described embodiment, if the above-described relationships S to V are satisfied, they are generated on the surface of the single cell 110 on the air electrode 114 side. It is possible to prevent cracks from extending in the Z direction in the current collecting layer 410 of the air electrode 114 to reach the active layer 420, thereby suppressing the performance degradation of the single cell 110 and reducing the conductivity of the air electrode 114. Can be suppressed.

  In the above embodiment, the air electrode 114 includes the active layer 420 and the current collecting layer 410. However, the fuel electrode 116 is replaced with the air electrode 114 or together with the air electrode 114. Similarly to the configuration of the air electrode 114, the configuration may include an active layer and a current collecting layer. At this time, the current collecting layer of the fuel electrode 116 may be configured to satisfy the above relationships S to V, similarly to the current collecting layer 410 of the air electrode 114 described above. In this way, cracks generated on the surface of the unit cell 110 on the fuel electrode 116 side are prevented from extending in the Z direction in the current collecting layer of the fuel electrode 116 and reaching the active layer, and the performance of the unit cell 110 is improved. A decrease in conductivity can be suppressed, and a decrease in conductivity of the fuel electrode 116 can be suppressed.

 In the above embodiment, the solid oxide fuel cell (SOFC) has been described as an example. However, the present invention is applicable to other types of fuel cells (or electrolytic cells) such as a molten carbonate fuel cell (MCFC). Applicable. The present invention is more suitable for a fuel cell of a type in which gas temperature such as SOFC or MCFC becomes relatively high and cell cracking or delamination tends to be a problem.

22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Body portion 29: Branch portion 100: Fuel cell stack 102: Power generation unit 104: End plate 106: End plate 107: Interconnector-fuel cell single cell composite Body 108: Communication hole 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 120: Separator 121: Hole 124: Joint part 130: Air electrode side frame 131: Hole 132: Oxidant gas supply communication hole 133: Oxidant gas discharge communication hole 134: Air electrode side current collector 135: Current collector element 140: Fuel electrode side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode side current collection Body 145: Electrode facing portion 146: Interconnector facing portion 147: Connection 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 410: Current collecting layer 420: Active layer

Claims (7)

In an electrochemical reaction single cell comprising an electrolyte layer, and an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer,
At least one of the air electrode and the fuel electrode is
A first layer;
A second layer located on the electrolyte layer side of the first layer in the first direction;
Including
An electrochemical reaction unit cell characterized in that a region satisfying the following relationships S and T exists in at least one cross section parallel to the first direction of the first layer.
Relationship S: R (1) ≧ 20%
(Where R (1) is the ratio of the number of first type particles to the total number of particles in a predetermined range, and the first type particles are in the first direction relative to the grain length D1 in the first direction. (The aspect ratio (D2 / D1), which is the ratio of the grain length D2 in the second direction orthogonal to, is a particle having a ratio of 2 or more.)
Relationship T: aD2 (A) <aD2 (1)
(However, aD2 (A) is the average value of the particle length D2 of all particles in the predetermined range, and aD2 (1) is the average value of the particle length D2 of the first type particles in the predetermined range. is there.) The electrochemical reaction single cell according to claim 1,
The electrochemical reaction unit cell, wherein the region is a region satisfying the following relationship U:
Relation U: E ≦ 0.68 (μm)
(However, E is the absolute value of the deviation of the grain length D2 of each particle in the predetermined range.) The electrochemical reaction single cell according to claim 1 or 2,
The electrochemical reaction unit cell, wherein the region is a region satisfying the following relationship V:
Relationship V: R (2) ≧ 23%
(However, R (2) is the ratio of the number of second type particles to the total number of particles in the predetermined range, and the second type particles are particles whose aspect ratio (D2 / D1) is 1 or less. is there.) In the electrochemical reaction single cell as described in any one of Claim 1- Claim 3,
The region exists in three cross sections of the first layer that are parallel to the first direction and that divides the air electrode into four in the longitudinal direction when viewed in the first direction. An electrochemical reaction single cell characterized by In the interconnector-electrochemical reaction single cell complex,
The electrochemical reaction unit cell according to any one of claims 1 to 4,
An interconnector disposed on the at least one side of the air electrode and the fuel electrode of the electrochemical reaction unit cell, and having a protrusion protruding to the at least one side of the air electrode and the fuel electrode;
An interconnector-electrochemical reaction single cell composite comprising: In the electrochemical reaction single cell according to any one of claims 1 to 4,
The electrochemical reaction unit cell, wherein the electrolyte layer includes a solid oxide or a carbonate. 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 electrochemical reaction single cells is the electrochemical reaction single cell according to any one of claims 1 to 4.

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