JP2018037331A - Electrochemical reaction cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the worsening of an initial performance of an electrochemical reaction cell stack and to suppress the degradation of a performance accompanying an operation.SOLUTION: An electrochemical reaction cell stack comprises: a plurality of electrochemical reaction single cells each including an electrolyte layer including a solid oxide, and an air electrode and a fuel electrode which are opposed to each other with the electrolyte layer located therebetween. The fuel electrode has a functional layer including Ni, and an oxide ion-conducting ceramic. In the electrochemical reaction cell stack, a first fuel chamber facing the fuel electrode of the first electrochemical reaction single cell, a second fuel chamber facing the fuel electrode of the second electrochemical reaction single cell, and a gas passage in communication with the first and second fuel chambers are formed. In the functional layer of the fuel electrode of the second electrochemical reaction single cell, a Ni content Cf2 (wt.%) is lower than a Ni content Cf1 (wt.%) in the functional layer of the fuel electrode of the first electrochemical reaction single cell.SELECTED DRAWING: Figure 13

Description

  The technology disclosed herein relates to an electrochemical reaction cell stack.

  A solid oxide fuel cell (hereinafter referred to as “SOFC”) is known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. The SOFC is generally used in the form of a fuel cell stack including a plurality of fuel cell single cells (hereinafter simply referred to as “single cells”) arranged in a predetermined direction (hereinafter referred to as “array direction”). Each single cell constituting the fuel cell stack includes an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in the arrangement direction with the electrolyte layer interposed therebetween. The air electrode includes, for example, a perovskite oxide. The fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics (for example, yttria-stabilized zirconia (hereinafter referred to as “YSZ”)).

  As one form of the fuel cell stack, a first fuel chamber facing a fuel electrode of a first single cell (hereinafter referred to as “upstream single cell”) of a plurality of single cells, and a plurality of single cells The second fuel cell communicates with the second fuel chamber facing the fuel electrode of the second single cell (hereinafter referred to as the “downstream single cell”), and the gas discharged from the first fuel chamber is the second fuel. A so-called series-type or series-parallel type fuel cell stack in which a gas flow path leading to a chamber is formed is known (see, for example, Patent Document 1).

JP 2005-537625 A

  In general, when the above-described series-type or series-parallel type fuel cell stack is operated, the partial pressure of water vapor is higher in the functional layer of the fuel electrode of the downstream single cell than in the upstream single cell. This is because water (water vapor) generated on the fuel electrode side by the power generation reaction in the upstream single cell is carried to the downstream single cell by the gas flow. When the water vapor partial pressure in the functional layer of the fuel electrode of the downstream single cell increases, the microstructure change (aggregation) of Ni contained in the functional layer is promoted. The change in the microstructure of Ni contained in the functional layer causes a decrease in the three-phase interface and causes the performance deterioration of the downstream single cell. In the configuration of the conventional fuel cell stack, there is a problem that the performance deterioration due to such operation is likely to occur.

 Such a problem is an electrolytic cell including a plurality of electrolytic single cells that are constituent units of a solid oxide electrolytic cell (hereinafter referred to as “SOEC”) that generates hydrogen using an electrolysis reaction of water. This is a common issue for stacks. A serial type in which a gas flow path is formed to guide the gas discharged from the first fuel chamber facing the fuel electrode of the upstream electrolytic unit cell to the second fuel chamber facing the fuel electrode of the downstream electrolytic unit cell, or In a series-parallel type electrolysis cell stack, water vapor as gas supplied to the fuel electrode is consumed in the hydrogen generation reaction in each electrolysis unit cell during operation. The water vapor partial pressure in the functional layer of the fuel electrode of the electrolytic single cell is increased. Therefore, in the electrolytic cell stack, the water vapor partial pressure in the functional layer of the fuel electrode of the upstream electrolytic unit cell is increased to promote the change in the microstructure of Ni contained in the functional layer, and the performance deterioration of the upstream electrolytic unit cell. There is a problem that is likely to occur. In the present specification, the fuel cell unit cell and the electrolysis unit cell are collectively referred to as an electrochemical reaction unit cell, and the fuel cell stack and the electrolysis cell stack are collectively referred to as an electrochemical reaction cell stack.

  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 cell stack disclosed in the present specification includes an electrolyte layer containing a solid oxide, and an electric electrode and a fuel electrode facing each other in a first direction across the electrolyte layer. In an electrochemical reaction cell stack including a plurality of chemical reaction single cells, the fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics, and the electrochemical reaction cell stack includes the electrochemical reaction. A first fuel chamber that faces the fuel electrode of a first electrochemical reaction unit cell that is one of the single cells, and a second electrochemical reaction unit cell that is the other one of the electrochemical reaction unit cells A second fuel chamber facing the fuel electrode, and a gas flow path communicating with the first fuel chamber and the second fuel chamber, and the second electrochemical reaction unit. Ni content in the functional layer of the fuel electrode of the cell Cf2 (wt%) is being lower than the Ni content Cf1 (wt%) in the functional layer of the fuel electrode of the first electrochemical reaction unit cells. According to this electrochemical reaction cell stack, the Ni content Cf2 (wt%) in the functional layer of the fuel electrode of the second electrochemical reaction single cell is the functional layer of the fuel electrode of the first electrochemical reaction single cell. Since the Ni content Cf1 (wt%) is lower than that in the electrochemical reaction cell, the second electrochemical reaction single cell becomes an electrochemical reaction single cell on the side where the water vapor partial pressure tends to increase during operation. By forming the stack, it is possible to reduce the amount of Ni microstructural change caused by an increase in the partial pressure of water vapor in the functional layer of the fuel electrode of the second electrochemical reaction unit cell. The performance deterioration of the single cell can be suppressed. In addition, according to the electrochemical reaction cell stack, the Ni content Cf1 (wt%) is relatively high in the functional layer of the fuel electrode of the first electrochemical reaction single cell in which the water vapor partial pressure is difficult to increase. Therefore, Ni content in the functional layer as a whole of the electrochemical reaction cell stack can be secured to some extent, and deterioration of the initial performance of the electrochemical reaction cell stack can be suppressed. Therefore, according to the present electrochemical reaction cell stack, it is possible to suppress deterioration in performance due to operation while suppressing a decrease in initial performance of the electrochemical reaction cell stack.

(2) In the electrochemical reaction cell stack, the function of the fuel electrode of the first electrochemical reaction unit cell with respect to the Ni content Cf2 in the functional layer of the fuel electrode of the second electrochemical reaction unit cell. The ratio of the Ni content Cf1 in the layer (Cf1 / Cf2) may be greater than 1 and 1.231 or less. According to this electrochemical reaction cell stack, it is possible to suppress a decrease in the initial performance of the second electrochemical reaction unit cell, and it is possible to effectively suppress a decrease in the initial performance of the electrochemical reaction cell stack.

(3) In the electrochemical reaction cell stack, the fuel electrode further includes a substrate layer disposed on the side of the functional layer opposite to the electrolyte layer and containing Ni and oxide ion conductive ceramics. The Ni content Cb2 (wt%) in the substrate layer of the fuel electrode of the second electrochemical reaction single cell is the Ni content in the substrate layer of the fuel electrode of the first electrochemical reaction single cell. It is good also as a structure characterized by being higher than Cb1 (wt%). According to this electrochemical reaction cell stack, the Ni content Cb2 (wt%) in the substrate layer of the fuel electrode of the second electrochemical reaction single cell is determined for the substrate layer in which the water vapor partial pressure is less likely to be higher than that of the functional layer. By making it relatively high, it is possible to suppress the deterioration of the initial performance of the second electrochemical reaction single cell while suppressing the performance deterioration due to the change in the microstructure of Ni, and the deterioration of the initial performance of the electrochemical reaction cell stack. Can be effectively suppressed. Further, the Ni content in the fuel electrode (functional layer and substrate layer) of the second electrochemical reaction single cell and the Ni content in the fuel electrode (functional layer and substrate layer) of the first electrochemical reaction single cell. A difference can be made small and the dispersion | variation in the reaction amount in each electrochemical reaction single cell which comprises an electrochemical reaction cell stack can be suppressed. By suppressing the variation in reaction amount in each electrochemical reaction single cell, it is possible to perform a stable reaction in the entire stack, and to suppress the occurrence of uneven performance deterioration in each electrochemical reaction single cell. As a result, the electrochemical reaction cell stack has a long life.

  The technology disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction cell stack (fuel cell stack or electrolytic cell stack), a method for manufacturing an electrochemical reaction cell stack, and the like. It is possible to realize in the form.

1 is a perspective view showing an external configuration of a fuel cell stack 100 in the present embodiment. 3 is an explanatory diagram showing a planar configuration of the upper side of the fuel cell stack 100. FIG. 2 is an explanatory view showing a planar configuration of the lower side of the fuel cell stack 100. FIG. FIG. 4 is an explanatory diagram showing an XZ cross-sectional configuration of a fuel cell stack 100 at a position of IV-IV in FIGS. 1 to 3. FIG. 4 is an explanatory diagram showing a YZ cross-sectional configuration of a fuel cell stack 100 at a position of VV in FIGS. 1 to 3. FIG. 4 is an explanatory diagram showing a YZ cross-sectional configuration of a fuel cell stack 100 at a position of VI-VI in FIGS. 1 to 3. FIG. 5 is an explanatory diagram illustrating an XZ cross-sectional configuration of one downstream power generation unit 102D and one upstream power generation unit 102U that are adjacent to each other at the same position as the cross section illustrated in FIG. 4. It is explanatory drawing which shows the YZ cross-section structure of the two upstream power generation units 102U 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 downstream electric power generation units 102D in the same position as the cross section shown in FIG. It is explanatory drawing which shows XY cross-sectional structure of the upstream power generation unit 102U in the position of XX of FIG. It is explanatory drawing which shows XY cross-section structure of the upstream power generation unit 102U in the position of XI-XI of FIG. It is explanatory drawing which shows XY cross-section structure of downstream electric power generation unit 102D in the position of XII-XII of FIG. 2 is a YZ sectional view schematically showing a detailed configuration of a fuel electrode 116. FIG. 2 is a YZ sectional view schematically showing a detailed configuration of a fuel electrode 116. FIG. It is explanatory drawing which shows a performance evaluation result.

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 according to the present embodiment, FIG. 2 is an explanatory diagram showing an upper plan configuration of the fuel cell stack 100, and FIG. It is explanatory drawing which shows the planar structure of the lower side. 4 is an explanatory view showing the XZ cross-sectional configuration of the fuel cell stack 100 at the position IV-IV in FIGS. 1 to 3, and FIG. 5 is the fuel at the position VV in FIGS. FIG. 6 is an explanatory diagram showing a YZ cross-sectional configuration of the battery stack 100, and FIG. 6 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position VI-VI in FIGS. 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. However, the fuel cell stack 100 is actually different from such an orientation. It may be installed. The same applies to FIG.

  The fuel cell stack 100 includes a plurality (six in this embodiment) of fuel cell power generation units (hereinafter simply referred to as “power generation units”) 102 and a pair of end plates 104 and 106. The six power generation units 102 are arranged side by side in a predetermined arrangement direction (vertical direction in the present embodiment). Hereinafter, among the six power generation units 102, the three power generation units 102 from the top are also referred to as downstream power generation units 102D, and the remaining three power generation units 102, that is, the three power generation units 102 from the bottom are also referred to as upstream power generation units 102U. Say. The pair of end plates 104 and 106 are arranged so as to sandwich an assembly composed of six 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. 4 to 6, 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. 2 to 4, the fuel cell stack 100 is located near the center of one side (the side on the X-axis positive direction side of two sides parallel to the Y-axis) on the outer periphery around the Z direction. A space formed by the bolt 22 (bolt 22A) and the communication hole 108 into which the bolt 22A is inserted is an oxidant gas introduction that is a gas flow path into which the oxidant gas OG is introduced from the outside of the fuel cell stack 100. Bolts 22 that function as the manifold 161 and are located near the midpoint of one side (the side on the negative X-axis side of two sides parallel to the Y-axis) on the outer periphery of the fuel cell stack 100 around the Z-direction. The space formed by the bolts 22B) and the communication holes 108 into which the bolts 22B are inserted is used to supply the oxidant off-gas OOG, which is a gas discharged from the air chamber 166 of each power generation unit 102, to the fuel cell. Functions as the oxidizing gas discharging manifold 162 for discharging to the outside of the click 100. In the present embodiment, for example, air is used as the oxidant gas OG.

  Further, as shown in FIGS. 2, 3, and 5, the bolt 22 located near one vertex (vertex on the X-axis positive direction side and Y-axis negative direction side) on the outer periphery around the Z direction of the fuel cell stack 100. The space formed by the (bolt 22C) and the communication hole 108 into which the bolt 22C is inserted is introduced with the fuel gas FG from the outside of the fuel cell stack 100, and the fuel gas FG is supplied to each upstream power generation unit 102U. It functions as a fuel gas introduction manifold 171 to be supplied, near the midpoint of one side (the Y axis positive direction side of two sides parallel to the X axis) on the outer periphery around the Z direction of the fuel cell stack 100. A space formed by the positioned bolt 22 (bolt 22D) and the communication hole 108 into which the bolt 22D is inserted is discharged from the fuel chamber 176 of each upstream power generation unit 102U. Fuel intermediate gas FMG is a gas, and functions as a fuel gas relay manifold 172 is a gas flow path which carries toward the downstream of the power generation unit 102D. The fuel intermediate gas FMG contains hydrogen that has not been used for the power generation reaction in the fuel chamber 176 of each upstream power generation unit 102U. 2, 3, and 6, one side of the outer periphery of the fuel cell stack 100 around the Z direction (the side on the Y axis negative direction side of the two sides parallel to the X axis) The space formed by the bolt 22 (bolt 22E) located near the midpoint and the communication hole 108 into which the bolt 22E is inserted is fuel that is gas discharged from the fuel chamber 176 of each downstream power generation unit 102D. It functions as a fuel gas discharge manifold 173 that discharges the off-gas FOG to the outside of the fuel cell stack 100. In the present embodiment, as the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used.

  As shown in FIGS. 4 to 6, 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. 4, the hole of the main body portion 28 of the gas passage member 27 arranged 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. 5, the hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22C forming the fuel gas introduction manifold 171 communicates with the fuel gas introduction manifold 171. As shown, the hole of the main body portion 28 of the gas passage member 27 arranged at the position of the bolt 22 </ b> E forming the fuel gas discharge manifold 173 communicates with the fuel gas discharge manifold 173.

(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)
7 is an explanatory diagram showing an XZ cross-sectional configuration of one downstream power generation unit 102D and one upstream power generation unit 102U adjacent to each other at the same position as the cross section shown in FIG. 4, and FIG. FIG. 9 is an explanatory diagram showing a YZ cross-sectional configuration of two upstream power generation units 102U adjacent to each other at the same position as the cross section shown, and FIG. 9 shows two downstream power generations 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 unit 102D. 10 is an explanatory diagram showing an XY cross-sectional configuration of the upstream power generation unit 102U at the position XX in FIG. 7, and FIG. 11 shows the upstream power generation unit 102U at the position XI-XI in FIG. FIG. 12 is an explanatory diagram showing the XY cross-sectional configuration, and FIG. 12 is an explanatory diagram showing the XY cross-sectional configuration of the downstream power generation unit 102D at the position XII-XII in FIG.

  As shown in FIGS. 7 to 9, the power generation unit 102 which is a constituent unit of the fuel cell stack 100 includes a fuel cell single cell (hereinafter simply referred to as “single cell”) 110, a separator 120, and an air electrode side frame 130. An air electrode side current collector 134, a fuel electrode side frame 140, a fuel electrode side current collector 144, and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer of the power generation unit 102. A hole corresponding to the above-described communication hole 108 into which the bolt 22 is inserted is formed in the peripheral portion around the Z direction in the separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150.

  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. 4 to 6).

  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 unit cell 110 corresponds to the electrochemical reaction unit cell in the claims, and the unit cell 110 provided in the upstream power generation unit 102U (hereinafter also referred to as “upstream unit cell 110U”) is defined in the claims. The single cell 110 (hereinafter, also referred to as “downstream single cell 110D”) provided in the downstream power generation unit 102D corresponds to the first electrochemical reaction single cell in FIG. Corresponds to a single reaction cell.

  The electrolyte layer 112 is a substantially rectangular flat plate member as viewed in the Z direction, and is a dense layer. 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 oxide, and the like. Yes. The air electrode 114 is a substantially rectangular flat plate-shaped member smaller than the electrolyte layer 112 when viewed in the Z direction, and is a porous layer. The air electrode 114 is made of, for example, a perovskite oxide (for example, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide), LNF (lanthanum nickel iron)). The fuel electrode 116 is a substantially rectangular flat plate member having substantially the same size as the electrolyte layer 112 when viewed in the Z direction, and is a porous layer. The fuel electrode 116 is formed of, for example, a cermet made of Ni and oxide ion conductive ceramic particles (for example, YSZ). The configuration of the fuel electrode 116 will be described in detail later. 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.

  As shown in FIGS. 7 to 10, 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. Has been. 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 hole 131 of the air electrode side frame 130 forms an air chamber 166 that faces 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.

  As shown in FIGS. 7 to 9, 11 and 12, 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. It is formed by. 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. As shown in FIGS. 8 and 11, the fuel electrode side frame 140 of each upstream power generation unit 102 </ b> U has a fuel gas supply communication hole 142 </ b> U that connects the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel chamber 176. A fuel gas discharge communication hole 143U that communicates with the fuel gas relay manifold 172 is formed. Further, as shown in FIGS. 9 and 12, the fuel electrode side frame 140 of each downstream power generation unit 102D has a fuel gas supply communication hole 142D communicating the fuel gas relay manifold 172 and the fuel chamber 176, and a fuel chamber. A fuel gas discharge communication hole 143 </ b> D that connects 176 and the fuel gas discharge manifold 173 is formed.

  The air electrode side current collector 134 is disposed in the air chamber 166 as shown in FIGS. 7 to 10. The air electrode side current collector 134 is composed of a plurality of substantially quadrangular columnar conductive members arranged at predetermined intervals, 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 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. The air electrode side current collector 134 and the interconnector 150 may be formed as an integral member.

  The fuel electrode side current collector 144 is disposed in the fuel chamber 176 as shown in FIGS. 7 to 9, 11, and 12. The fuel electrode side current collector 144 includes an interconnector facing portion 146, a plurality of electrode facing portions 145, and a connecting portion 147 that connects each electrode facing portion 145 and the interconnector facing portion 146. Or nickel alloy, stainless steel or the like. Each electrode facing portion 145 is in contact with the surface of the fuel electrode 116 opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is a surface of the interconnector 150 on the side facing the fuel electrode 116. Touching. 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.

A-2. Operation of the fuel cell stack 100:
As shown in FIGS. 4, 7, and 10, the oxidant gas is connected via 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. When the OG is supplied, the oxidant gas OG is supplied to the oxidant gas introduction manifold 161 through the branch part 29 of the gas passage member 27 and the hole of the main body part 28, and from the oxidant gas introduction manifold 161 downstream and upstream. Are supplied to the air chamber 166 through the oxidant gas supply passage 132 of each of the power generation units 102D and 102U.

  Further, as shown in FIGS. 5, 8, and 11, the fuel gas is connected 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. When the FG is supplied, 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 each power generation unit 102U upstream from the fuel gas introduction manifold 171 is supplied. Is supplied to the fuel chamber 176 of each upstream power generation unit 102U through the fuel gas supply communication hole 142U. Since the fuel gas introduction manifold 171 does not communicate with the fuel chamber 176 of each downstream power generation unit 102D, the fuel gas FG is supplied from the fuel gas introduction manifold 171 to the fuel chamber 176 of each downstream power generation unit 102D. Never happen. The fuel intermediate gas FMG discharged from the fuel chamber 176 of each upstream power generation unit 102U is discharged to the fuel gas relay manifold 172 via the fuel gas discharge communication hole 143U. As shown in FIGS. 6, 9 and 12, in the fuel chamber 176 of each downstream power generation unit 102D, the fuel intermediate gas FMG discharged from each upstream power generation unit 102U is supplied with a fuel gas relay manifold 172, and The fuel gas is supplied through the fuel gas supply communication hole 142D of each downstream power generation unit 102D.

  When the oxidant gas OG is supplied to the air chamber 166 of each upstream power generation unit 102U and the fuel gas FG is supplied to the fuel chamber 176 of each upstream power generation unit 102U, in the single cell 110U of each upstream power generation unit 102U. Power generation is performed by an electrochemical reaction of the oxidant gas OG and the fuel gas FG. Further, when the oxidant gas OG is supplied to the air chamber 166 of each downstream power generation unit 102D and the fuel intermediate gas FMG is supplied to the fuel chamber 176 of each downstream power generation unit 102D, each downstream power generation unit 102D has a single unit. In the cell 110D, power generation is performed by an electrochemical reaction of the oxidant gas OG and the fuel intermediate gas FMG. These power generation reactions are exothermic reactions. 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 startup until the high temperature can be maintained by heat generated by power generation) (Not shown).

  As shown in FIGS. 4, 7, and 10, the oxidant discharged from the air chamber 166 of each of the downstream and upstream power generation units 102 </ b> U and 102 </ b> D to the oxidant gas discharge manifold 162 through the oxidant gas discharge communication hole 133. The off-gas OOG passes through 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 oxidant gas discharge manifold 162. And discharged to the outside of the fuel cell stack 100. As shown in FIGS. 6, 9 and 12, the fuel off-gas FOG discharged from the fuel chamber 176 of each downstream power generation unit 102D to the fuel gas discharge manifold 173 via the fuel gas discharge communication hole 143D The outside of the fuel cell stack 100 is passed through 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 gas discharge manifold 173. To be discharged.

  As described above, the flow path configuration of the fuel gas FG of the fuel cell stack 100 of the present embodiment is such that the fuel gas FG introduced from the outside is supplied in parallel to the plurality of upstream power generation units 102U, and each upstream power generation unit. This is a so-called series-parallel flow path configuration in which the fuel intermediate gas FMG discharged from 102U is supplied in parallel to a plurality of downstream power generation units 102D via the fuel gas relay manifold 172. The fuel chamber 176 of the upstream power generation unit 102U corresponds to the first fuel chamber in the claims, and the fuel chamber 176 of the downstream power generation unit 102D corresponds to the second fuel chamber in the claims, The fuel gas relay manifold 172 corresponds to a gas flow path in the claims.

A-3. Detailed configuration of the fuel electrode 116:
13 and 14 are YZ cross-sectional views schematically showing the detailed configuration of the fuel electrode 116. FIG. 13 schematically illustrates the configuration of the fuel electrode 116 included in the upstream single cell 110U, and FIG. 14 schematically illustrates the configuration of the fuel electrode 116 included in the downstream single cell 110D. Yes.

  As shown in FIGS. 13 and 14, the fuel electrode 116 is disposed on the opposite side of the functional layer 350 and the electrolyte layer 112 side of the functional layer 350 in both the upstream single cell 110U and the downstream single cell 110D. The substrate layer 360 is provided. In the present embodiment, the functional layer 350 is disposed adjacent to the electrolyte layer 112, and the substrate layer 360 is disposed adjacent to the functional layer 350. The functional layer 350 and the substrate layer 360 are both formed of cermet containing Ni and YSZ (yttria stabilized zirconia) which is an oxide ion conductive ceramic.

  The functional layer 350 mainly exhibits a function of generating electrons and water vapor by reacting oxide ions supplied from the electrolyte layer 112 with hydrogen contained in the fuel gas FG (or the fuel intermediate gas FMG). It is. The substrate layer 360 is a layer that mainly exhibits a function of supporting the functional layer 350, the electrolyte layer 112, and the air electrode 114. In order to increase the strength of the substrate layer 360, the thickness of the substrate layer 360 in the Z direction is preferably larger than the thickness of the functional layer 350 in the Z direction. In order to increase the gas diffusibility of the substrate layer 360, the porosity of the substrate layer 360 is preferably higher than the porosity of the functional layer 350.

  In the fuel cell stack 100 of the present embodiment, there is a difference in the Ni content of the fuel electrode 116 between the upstream single cell 110U and the downstream single cell 110D. Specifically, for the functional layer 350, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is equal to the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. The content is lower than Cf1 (wt%). On the contrary, for the substrate layer 360, the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D is the Ni content in the substrate layer 360 of the fuel electrode 116 of the upstream single cell 110U. It is higher than Cb1 (wt%). The Ni content of the fuel electrode 116 is expressed as wt% of the ratio of Ni content to the total content of Ni and oxide ion conductive ceramics (YSZ).

A-4. Manufacturing method of fuel cell stack 100:
An example of the manufacturing method of the fuel cell stack 100 in the present embodiment is as follows.

(Preparation of green sheet for fuel electrode substrate layer)
To the mixed powder of NiO powder and YSZ powder, organic beads as a pore former, butyral resin, dioctyl phthalate (DOP) as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added. Mix with a ball mill to prepare a slurry. At this time, two types of slurry are prepared using two types of mixed powders having different ratios of NiO powder and YSZ powder. For example, the first slurry for the substrate layer is prepared using a mixed powder of NiO powder: 50 parts by weight and YSZ powder: 50 parts by weight, and a mixed powder of NiO powder: 60 parts by weight and YSZ powder: 40 parts by weight is used. To prepare the second slurry for the substrate layer. One of the two types of slurries is coated with a first slurry for a substrate layer (a slurry having a relatively low content of NiO powder) to produce a green sheet for a fuel electrode substrate layer for the upstream unit cell 110U. To do. Further, a second electrode substrate layer slurry (a slurry having a relatively high content of NiO powder), which is the other of the two types of slurries, is applied, and a fuel electrode substrate layer green sheet for downstream single cell 110D is applied. Is made.

(Manufacture of green sheet for fuel electrode functional layer)
To the mixed powder of NiO powder and YSZ powder, add organic beads as a pore former, butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol. Mix to prepare slurry. At this time, two types of slurry are prepared using two types of mixed powders having different ratios of NiO powder and YSZ powder. For example, the first slurry for the functional layer is prepared using a mixed powder of 55 parts by weight of NiO powder and 45 parts by weight of YSZ powder, and a mixed powder of 45 parts by weight of NiO powder and 55 parts by weight of YSZ powder is used. To adjust the second slurry for the functional layer. A functional layer first slurry (a slurry having a relatively high NiO powder content), which is one of the two types of slurry, is applied to produce a fuel electrode functional layer green sheet for the upstream single cell 110U. To do. In addition, a second functional layer slurry (a slurry having a relatively low content of NiO powder), which is the other of the two types of slurries, is applied, and a green sheet for a fuel electrode functional layer for a downstream single cell 110D Is made.

(Preparation of electrolyte sheet green sheet)
To the YSZ powder (100 parts by weight), 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 produce a green sheet for an electrolyte layer.

(Preparation of a laminate of the electrolyte layer 112 and the fuel electrode 116)
The fuel cell substrate layer green sheet and the fuel electrode functional layer green sheet for the downstream single cell 110D and the electrolyte layer green sheet are attached and degreased at, for example, about 280 ° C., and then, for example, at about 1350 ° C. By firing, a laminated body (laminated body for the downstream single cell 110D) of the electrolyte layer 112 and the fuel electrode 116 (the functional layer 350 and the substrate layer 360) is obtained. Similarly, the green sheet for the fuel electrode substrate layer and the green sheet for the fuel electrode functional layer for the upstream single cell 110U and the green sheet for the electrolyte layer are attached and degreased at, for example, about 280 ° C., and then, for example, about 1350 By firing at 0 ° C., a laminate of the electrolyte layer 112 and the fuel electrode 116 (functional layer 350 and substrate layer 360) (a laminate for the upstream single cell 110U) is obtained.

(Formation of air electrode 114)
For example, a mixed liquid composed of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder and isopropyl alcohol is prepared, and the mixed liquid is used as a laminate for the downstream single cell 110D described above. The air electrode 114 is formed by spray-coating on the surface on the electrolyte layer 112 side of the substrate, and then baking at about 1100 ° C., for example. Thereby, the downstream single cell 110D is manufactured. Similarly, for example, a mixed liquid composed of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder and isopropyl alcohol is prepared, and the mixed liquid is used for the upstream single cell 110U described above. The air electrode 114 is formed by spray-coating on the surface on the electrolyte layer 112 side of the laminate, followed by firing at about 1100 ° C., for example. Thereby, the upstream single cell 110U is manufactured.

  For example, by manufacturing the downstream single cell 110D and the upstream single cell 110U in accordance with the above-described method, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D can be calculated using the upstream single cell. The Ni content Cf1 (wt%) in the functional layer 350 of the 110U fuel electrode 116 can be made lower, and the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D can be set upstream. The Ni content Cb1 (wt%) in the substrate layer 360 of the fuel electrode 116 of the single cell 110U can be made higher.

(Assembly of fuel cell stack 100)
After the plurality of unit cells 110 (the downstream unit cell 110D and the upstream unit cell 110U) are manufactured, the plurality of unit cells 110 and other parts are assembled and fastened with the bolts 22, whereby the fuel cell having the above-described configuration. The stack 100 is manufactured.

A-5. Effects of this embodiment:
As described above, in the fuel cell stack 100 according to the present embodiment, the fuel electrode 116 of each single cell 110 constituting the fuel cell stack 100 includes the functional layer 350 containing Ni and oxide ion conductive ceramics. . Further, in the fuel cell stack 100 of this embodiment, the fuel chamber 176 (first fuel chamber) facing the fuel electrode 116 of the upstream single cell 110U and the fuel facing the fuel electrode 116 of the downstream single cell 110D. The chamber 176 (second fuel chamber), the first fuel chamber, and the second fuel chamber communicate with each other (more specifically, the gas discharged from the first fuel chamber is the second fuel chamber). A fuel gas relay manifold 172 which is a gas flow path (which leads to the fuel chamber) is formed. Further, in the fuel cell stack 100 of the present embodiment, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is equal to that in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. The Ni content is lower than Cf1 (wt%). Here, in the fuel cell stack 100 of the present embodiment, during the power generation operation, the water vapor partial pressure (ratio of water vapor in the fuel gas) increases in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D. This is because water (water vapor) generated on the fuel electrode 116 side by the power generation reaction in the upstream single cell 110U is carried to the downstream single cell 110D by the gas flow. When the water vapor partial pressure increases in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D, the microstructure change (aggregation) of Ni contained in the functional layer 350 is promoted. The change in the microstructure of Ni contained in the functional layer 350 causes a decrease in the three-phase interface, which causes performance deterioration of the downstream single cell 110D. However, in the fuel cell stack 100 of the present embodiment, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is relatively low, and therefore the fuel of the downstream single cell 110D. It is possible to reduce the amount of Ni microstructural change that accompanies an increase in the water vapor partial pressure in the functional layer 350 of the electrode 116, and to suppress the performance deterioration of the downstream single cell 110D. Further, in the fuel cell stack 100 of the present embodiment, the Ni content Cf1 (wt%) is relatively high in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U where the water vapor partial pressure is difficult to increase. . Therefore, the Ni content in the functional layer 350 of the fuel cell stack 100 as a whole can be ensured to some extent, and deterioration of the initial performance of the fuel cell stack 100 can be suppressed. Therefore, according to the fuel cell stack 100 of the present embodiment, it is possible to suppress deterioration in performance due to operation while suppressing a decrease in the initial performance of the fuel cell stack 100.

  In the fuel cell stack 100 of the present embodiment, the fuel electrode 116 of each single cell 110 constituting the fuel cell stack 100 is disposed on the side opposite to the electrolyte layer 112 side of the functional layer 350, and Ni and oxide ions A substrate layer 360 containing conductive ceramics is provided. Further, in the fuel cell stack 100 of the present embodiment, the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D is equal to that of the substrate layer 360 of the fuel electrode 116 of the upstream single cell 110U. It is higher than Ni content Cb1 (wt%). In general, unlike the functional layer 350 in which the power generation reaction is performed, the power generation reaction is hardly performed in the substrate layer 360 of the fuel electrode 116. Therefore, the substrate layer 360 is hardly affected by water vapor generated by the power generation reaction, and is maintained in a state where the water vapor partial pressure is relatively lower than that of the functional layer 350 even during the power generation operation. Therefore, even if the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D is relatively high, the amount of Ni microstructural change contained in the substrate layer 360 is small, and the downstream The performance of the single cell 110D does not deteriorate significantly. Further, by making the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D relatively high, a decrease in the Ni content of the fuel electrode 116 as a whole is avoided and the downstream single cell 110D is avoided. The deterioration of the initial performance can be suppressed. Furthermore, the Ni content in the fuel electrode 116 (functional layer 350 and substrate layer 360) of the downstream single cell 110D and the Ni content in the fuel electrode 116 (functional layer 350 and substrate layer 360) of the upstream single cell 110U. A difference can be made small and the dispersion | variation in the electric power generation amount in each single cell 110 which comprises the fuel cell stack 100 can be suppressed. Therefore, according to the fuel cell stack 100 of the present embodiment, it is possible to suppress the deterioration of the performance of the fuel cell stack 100 while effectively suppressing the deterioration of the initial performance of the fuel cell stack 100. Variations in the amount of power generation can be suppressed. By suppressing the variation in power generation amount in each single cell 110, stable power generation in the entire fuel cell stack 100 is possible, and it is possible to suppress the occurrence of uneven power generation performance in each single cell 110. As a result, the fuel cell stack 100 has a long life.

A-6. Performance evaluation:
Performance evaluation performed using a plurality of fuel cell stack 100 samples will be described below. FIG. 15 is an explanatory diagram showing a performance evaluation result. As shown in FIG. 15, the samples S <b> 1 to S <b> 10 are different from each other in the configuration of the fuel electrode 116 of each single cell 110 constituting the fuel cell stack 100. More specifically, each sample includes the Ni content Cf1 (wt%) in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U and the Ni content in the substrate layer 360 of the fuel electrode 116 of the upstream single cell 110U. Rate Cb1 (wt%), the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D, and the Ni content Cb2 in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D. Combinations with (wt%) are different from each other. In this performance evaluation, the fuel cell stack 100 of each sample has 10 single cells 110, of which 6 are upstream single cells 110U and the remaining 4 are downstream single cells 110D. It is. The value of each Ni content shown in FIG. 15 is an average value of Ni contents in a plurality of upstream single cells 110U (or downstream single cells 110D) provided in the fuel cell stack 100.

(Evaluation items and evaluation methods)
In this performance evaluation, two items of initial average output and deterioration rate were evaluated. The initial average output is an average value of outputs (V) of the single cells 110 constituting the fuel cell stack 100 in the initial state. About an initial average output, when it was 0.8 (V) or more, it determined with a pass. Further, the deterioration rate is a percentage of the ratio of the output drop after 1000h operation (difference between the initial average output and the average output after 1000h operation) to the initial average output. About a deterioration rate, when it was lower than 1.5 (%), it determined with a pass.

(Evaluation results)
In sample S1 and sample S9, since the deterioration rate was 1.5 (%) or more, it was determined to be rejected (x). In sample S1 and sample S9, the Ni content Cf2 (wt%) of the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is equal to the Ni content Cf1 (wt%) of the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. wt%) or the same value as the Ni content Cf1 (wt%). Therefore, Sample S1 and Sample S9 are included in the functional layer 350 at a relatively high content rate as the water vapor partial pressure in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D increases during the power generation operation. It is considered that the change in the microstructure of Ni is promoted and the performance of the downstream single cell 110D is deteriorated.

  In samples S7, S8, and S10, since the initial average output was lower than 0.8 (V), it was determined as rejected (x). In samples S7, S8, and S10, the Ni content of the functional layer 350 of the fuel electrode 116 is considerably low in both the upstream single cell 110U and the downstream single cell 110D, and therefore the initial average output is low. Conceivable. In samples S7, S8, and S10, the Ni content rate Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D was extremely low, so the deterioration rate was not rejected.

  On the other hand, in samples S2 to S6, the initial average output was 0.8 (V) or more and the deterioration rate was lower than 1.5 (%), so it was determined to be acceptable (◯ or ◎). In samples S2 to S6, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is equal to the Ni content Cf1 (wt) in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. %) Is lower. Therefore, in samples S2 to S6, the Ni content Cf1 (wt%) in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U is made relatively high while suppressing deterioration in the initial performance of the fuel cell stack 100. The deterioration of the performance of the downstream single cell 110D associated with the power generation operation can be suppressed by relatively reducing the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D. it is conceivable that. In samples S2 to S6, the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D is the Ni content Cb1 in the substrate layer 360 of the fuel electrode 116 of the upstream single cell 110U. It is higher than (wt%). Therefore, in samples S2 to S6, it is considered that the initial performance of the downstream single cell 110D can be prevented from being lowered and the initial performance of the fuel cell stack 100 can be effectively prevented from being lowered.

  In sample S6, although the initial average output was 0.8 (V) or higher, it was determined to be acceptable (◯) because it was 0.81 (V) or lower, but in samples S2 to S5, Since the initial average output was higher than 0.81 (V), it was determined to be particularly good (◎). In the sample S6, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is the Ni content Cf1 (wt%) in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. The ratio of the Ni content Cf1 in the functional layer 350 of the fuel electrode 116 of the upstream unit cell 110U to the Ni content Cf2 in the functional layer 350 of the fuel electrode 116 of the downstream unit cell 110D ( Cf1 / Cf2) is relatively large at 1.361. Therefore, although it is possible to suppress the performance deterioration of the downstream single cell 110D, it is considered that the performance did not reach the samples S2 to S5 in terms of suppression of the initial performance deterioration of the downstream single cell 110D. In samples S2 to S5, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is equal to the Ni content Cf1 (wt) in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. %), Cf1 / Cf2 is suppressed to a low value (specifically, it is 1.231 or less). Therefore, in samples S2 to S5, it is considered that the deterioration of the initial performance of the fuel cell stack 100 could be effectively suppressed by suppressing the deterioration of the initial performance of the downstream single cell 110D.

  From the results of the performance evaluation described above, the Ni content Cf2 (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is determined as the Ni content in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U. It has been confirmed that if it is lower than Cf1 (wt%), it is possible to suppress deterioration in performance due to operation while suppressing a decrease in the initial performance of the fuel cell stack 100. Furthermore, the ratio (Cf1 / Cf2) of the Ni content Cf1 in the functional layer 350 of the fuel electrode 116 of the upstream single cell 110U to the Ni content Cf2 in the functional layer 350 of the fuel electrode 116 of the downstream single cell 110D is larger than 1. And if it was set to 1.231 or less, it was confirmed that the performance deterioration accompanying a driving | operation can be suppressed, suppressing the fall of the initial performance of the fuel cell stack 100 effectively.

  Further, from the result of the performance evaluation, the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D is determined as the Ni content in the substrate layer 360 of the fuel electrode 116 of the upstream single cell 110U. It has been confirmed that if it is higher than Cb1 (wt%), a decrease in the initial performance of the downstream single cell 110D can be suppressed, and a decrease in the initial performance of the fuel cell stack 100 can be effectively suppressed.

A-7. Analysis method of fuel electrode 116:
A method for analyzing the Ni content in the fuel electrode 116 of the single cell 110 (upstream single cell 110U or downstream single cell 110D) will be described below.

(Analysis image acquisition method)
First, an analysis image used for analyzing the fuel electrode 116 is acquired by the following method. That is, the cross section of the single cell 110 that is substantially parallel to the vertical direction (Z direction) is arbitrarily set. Images that can be confirmed in the vertical direction of the functional layer 350 of the fuel electrode 116 at three different positions in the set cross section are acquired as analysis images. More specifically, 10 portions obtained by dividing the image vertically into 10 equal parts are assumed to be the boundary B1 (see FIGS. 13 and 14) between the functional layer 350 and the electrolyte layer 112 of the fuel electrode 116. The portion that is located in the uppermost divided region of the divided regions and is assumed to be the boundary B2 (see FIGS. 13 and 14) between the functional layer 350 and the substrate layer 360 of the fuel electrode 116 is the lowest. An image located in the divided area is taken with, for example, a scanning electron microscope (SEM) and acquired as an analysis image. The analysis image 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. Further, the analysis image may be an image itself before binarization processing taken by SEM.

(Identification of each boundary)
The boundary B1 between the functional layer 350 and the electrolyte layer 112 of the fuel electrode 116 can be identified based on the difference in the constituent materials between the functional layer 350 and the electrolyte layer 112, visual recognition, and the like in each analysis image. In addition, the boundary B2 between the functional layer 350 and the substrate layer 360 can be specified based on the difference in porosity between the functional layer 350 and the substrate layer 360 in each analysis image.

(Specification of Ni content)
The Ni content (wt%) in each region is identified by using SEM-EDS to identify Ni and YSZ in each region in each analysis image, and the ratio of the Ni content to the total content of Ni and YSZ. It can be specified by calculating in wt%. The Ni content (Cf1 or Cf2) in the functional layer 350 is located on the uppermost side (electrolyte layer 112 side) when the functional layer 350 is divided into three in the vertical direction (Z direction) in each analysis image. The Ni content is calculated for the portion, and the average value of the Ni content calculated in each analysis image is set as the final Ni content. In addition, regarding the Ni content (Cb1 or Cb2) in the substrate layer 360, in each of the above analysis images, the lowest of the 10 divided regions obtained by dividing each analysis image described above into 10 equal parts. The Ni content of the portion of the substrate layer 360 in the divided region located on the side is calculated, and the average value of the Ni content calculated in each analysis image is used as the final Ni content.

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.

  The configuration of the fuel cell stack 100 in the above embodiment is merely an example, and various modifications can be made. For example, in the above embodiment, the fuel electrode 116 is configured by two layers of the functional layer 350 and the substrate layer 360. However, the fuel electrode 116 may be configured by only the functional layer 350, The fuel electrode 116 may include a layer other than the functional layer 350 and the substrate layer 360.

  In the above embodiment, regarding the configuration of the substrate layer 360, the Ni content Cb2 (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream single cell 110D is equal to the substrate layer of the fuel electrode 116 of the upstream single cell 110U. Although it is said that it is higher than the Ni content Cb1 (wt%) in 360, it is not always necessary to have such a relationship.

  In the above embodiment, a reaction preventing layer containing, for example, ceria may be provided between the electrolyte layer 112 and the air electrode 114. In the above embodiment, the number of unit cells 110 (upstream unit cell 110U and downstream unit cell 110D) included in the fuel cell stack 100 is merely an example, and the number of unit cells 110 is included in the fuel cell stack 100. It is determined appropriately according to the required output voltage.

  Moreover, in the said embodiment, although the electrolyte layer 112 is formed with the solid oxide, the electrolyte layer 112 may contain another substance other than a solid oxide. 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. For example, in the above-described embodiment, the functional layer 350 and the substrate layer 360 of the fuel electrode 116 include YSZ as oxide ion conductive ceramics. Other oxide ion conductive ceramics may be included.

  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 stack including a plurality of electrolytic single cells that are constituent units of a solid oxide electrolytic cell (SOEC) that generates hydrogen by using hydrogen. The configuration of the electrolytic cell stack is well known as described in, for example, International Publication No. 2012/165409, and thus will not be described in detail here. However, the configuration is generally the same as that of the fuel cell stack 100 in the above-described embodiment. It is the composition. 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 single 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 to the fuel chamber 176. As a result, an electrolysis reaction of water occurs in each electrolytic single cell, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out of the electrolytic cell stack through the communication hole.

  Here, when the SOEC is operated, water vapor as a gas supplied to the fuel electrode 116 is consumed in a hydrogen generation reaction in each electrolysis unit cell, and therefore, an upstream electrolysis unit cell as compared with a downstream electrolysis unit cell. The water vapor partial pressure in the functional layer 350 of the fuel electrode 116 becomes higher. Therefore, also in SOEC, the change in the microstructure of Ni contained in the functional layer 350 is promoted by increasing the water vapor partial pressure in the functional layer 350 of the fuel electrode 116 of the upstream electrolytic single cell, and the performance of the upstream electrolytic single cell. There is a problem that deterioration tends to occur. Therefore, also in the electrolytic cell stack, the fuel electrode 116 has a functional layer 350 containing Ni and oxide ion conductive ceramics, and the Ni content (wt) in the functional layer 350 of the fuel electrode 116 of the upstream electrolytic single cell. %) Is lower than the Ni content (wt%) in the functional layer 350 of the fuel electrode 116 of the downstream electrolytic unit cell, the performance deterioration due to operation is suppressed while suppressing the deterioration of the initial performance of the electrolytic cell stack. Can be suppressed. Also in the electrolytic cell stack, the fuel electrode 116 is disposed on the opposite side of the functional layer 350 from the electrolyte layer 112 side, and has a substrate layer 360 containing Ni and oxide ion conductive ceramics, and upstream. If the Ni content (wt%) in the substrate layer 360 of the fuel electrode 116 of the electrolytic cell is higher than the Ni content (wt%) in the substrate layer 360 of the fuel electrode 116 of the downstream electrolytic cell, While effectively suppressing the deterioration of the initial performance of the electrolytic cell stack, it is possible to suppress the performance deterioration due to the operation, and further, it is possible to suppress the variation of the reaction amount in each electrolytic single cell.

  In addition, the configuration of the fuel electrode 116 described in the above embodiment, specifically, the Ni content of the functional layer 350 (or the substrate layer 360) of the upstream single cell 110U and the functional layer 350 (or the downstream single cell 110D). The high / low relationship with the Ni content of the substrate layer 360) is adopted in all upstream and downstream single cells 110 (or electrolytic single cells, and so on) included in the fuel cell stack 100 (or electrolytic cell stacks and so on). Alternatively, it may be adopted only in some upstream and downstream single cells 110 included in the fuel cell stack 100.

The technology disclosed in this specification can also be realized as the following application examples.
[Application Example 1]
In a fuel cell stack comprising a plurality of fuel cell single cells each including 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,
The fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics,
The fuel cell stack includes
A first fuel chamber facing the fuel electrode of a first fuel cell unit cell that is one of the fuel cell unit cells;
A second fuel chamber facing the fuel electrode of a second fuel cell single cell which is another one of the fuel cell single cells;
A gas flow path that communicates with the first fuel chamber and the second fuel chamber and guides the gas discharged from the first fuel chamber to the second fuel chamber;
Is formed,
The Ni content Cf2 (wt%) in the functional layer of the fuel electrode of the second fuel cell single cell is the Ni content Cf1 (wt) in the functional layer of the fuel electrode of the first fuel cell single cell. %) Lower, fuel cell stack.
[Application Example 2]
In the fuel cell stack described in Application Example 1,
Ratio of Ni content Cf1 in the functional layer of the fuel electrode of the first fuel cell single cell (Cf1 / Cf2) to Ni content Cf2 in the functional layer of the fuel electrode of the second fuel cell single cell Is greater than 1 and less than or equal to 1.231.
[Application Example 3]
In the fuel cell stack according to Application Example 1 or Application Example 2,
The fuel electrode further includes a substrate layer disposed on the side of the functional layer opposite to the electrolyte layer and containing Ni and oxide ion conductive ceramics,
The Ni content Cb2 (wt%) in the substrate layer of the fuel electrode of the second fuel cell single cell is the Ni content Cb1 (wt) in the substrate layer of the fuel electrode of the first fuel cell single cell. %) Fuel cell stack, characterized by higher.
[Application Example 4]
In an electrolytic cell stack comprising a plurality of electrolytic single cells each including an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in the first direction across the electrolyte layer,
The fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics,
The electrolytic cell stack includes
A first fuel chamber facing the fuel electrode of a first electrolytic single cell that is one of the electrolytic single cells;
A second fuel chamber facing the fuel electrode of a second electrolysis unit cell that is another one of the electrolysis unit cells;
A gas flow path that communicates with the first fuel chamber and the second fuel chamber and guides the gas discharged from the second fuel chamber to the first fuel chamber;
Is formed,
The Ni content Cf2 (wt%) in the functional layer of the fuel electrode of the second electrolytic unit cell is the Ni content Cf1 (wt%) in the functional layer of the fuel electrode of the first electrolytic unit cell. Electrolytic cell stack, characterized by a lower.
[Application Example 5]
In the electrolytic cell stack described in Application Example 4,
The ratio (Cf1 / Cf2) of the Ni content Cf1 in the functional layer of the fuel electrode of the first electrolytic unit cell to the Ni content Cf2 in the functional layer of the fuel electrode of the second electrolytic unit cell is An electrolytic cell stack, wherein the electrolytic cell stack is greater than 1 and less than or equal to 1.231.
[Application Example 6]
In the electrolytic cell stack according to Application Example 4 or Application Example 5,
The fuel electrode further includes a substrate layer disposed on the side of the functional layer opposite to the electrolyte layer and containing Ni and oxide ion conductive ceramics,
The Ni content Cb2 (wt%) in the substrate layer of the fuel electrode of the second electrolytic single cell is the Ni content Cb1 (wt%) in the substrate layer of the fuel electrode of the first electrolytic single cell. Electrolytic cell stack, characterized by a higher.

22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Body portion 29: Branch portion 100: Fuel cell stack 102: Fuel cell power generation unit 104: End plate 106: End plate 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 140: Fuel electrode side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode side current collector 145: Electrode facing portion 146: Interconnector facing portion 147: Connection Part 149: Spacer 150: Interconnector 161: Acid Containing gas inlet manifold 162: oxidizing gas discharging manifold 166: an air chamber 171: fuel gas inlet manifold 172: fuel gas relay manifold 173: fuel gas discharging manifold 176: fuel chamber 350: functional layer 360: substrate layer

Claims (3)

In an electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells including an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer,
The fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics,
The electrochemical reaction cell stack includes
A first fuel chamber facing the fuel electrode of a first electrochemical reaction unit cell that is one of the electrochemical reaction unit cells;
A second fuel chamber facing the fuel electrode of a second electrochemical reaction unit cell, which is another one of the electrochemical reaction unit cells;
A gas flow path communicating with the first fuel chamber and the second fuel chamber;
Is formed,
The Ni content Cf2 (wt%) in the functional layer of the fuel electrode of the second electrochemical reaction single cell is the Ni content Cf1 in the functional layer of the fuel electrode of the first electrochemical reaction single cell. Electrochemical reaction cell stack, characterized in that it is lower than (wt%). The electrochemical reaction cell stack according to claim 1,
The ratio of the Ni content Cf1 in the functional layer of the fuel electrode of the first electrochemical reaction single cell to the Ni content Cf2 in the functional layer of the fuel electrode of the second electrochemical reaction single cell (Cf1 / Cf2) is an electrochemical reaction cell stack characterized by being greater than 1 and not greater than 1.231. The electrochemical reaction cell stack according to claim 1 or 2,
The fuel electrode further includes a substrate layer disposed on the side of the functional layer opposite to the electrolyte layer and containing Ni and oxide ion conductive ceramics,
The Ni content Cb2 (wt%) in the substrate layer of the fuel electrode of the second electrochemical reaction single cell is the Ni content Cb1 in the substrate layer of the fuel electrode of the first electrochemical reaction single cell. Electrochemical reaction cell stack, characterized in that it is higher than (wt%).

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