JP2018037330A - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical reaction single cell arranged so as to be able to suppress the degradation of a performance accompanying an operation while suppressing the worsening of an initial performance of the electrochemical reaction single cell.SOLUTION: An electrochemical reaction single cell 110 comprises: an electrolyte layer 112 including a solid oxide; and an air electrode and a fuel electrode 116 which are opposed to each other with an electrolyte layer located therebetween. In the electrochemical reaction single cell 110, the fuel electrode has a functional layer 350 including Ni, and an oxide ion-conducting ceramic. In the functional layer, a Ni content Cf2 (wt.%) in a region on one side of a direction of a flow of gas supplied to a fuel electrode side is lower than a Ni content Cf1 (wt.%) in a region on the other side of the gas flow direction.SELECTED DRAWING: Figure 8

Description

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

  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. A fuel cell single cell (hereinafter simply referred to as “single cell”), which is a constituent unit of SOFC, includes an electrolyte layer containing a solid oxide and a predetermined direction (hereinafter referred to as “first direction”) across the electrolyte layer. Includes an air electrode and a fuel electrode facing each other. 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”)) (for example, see Patent Document 1).

Japanese Patent Laying-Open No. 2015-84281

  In general, during the operation of SOFC, the partial pressure of water vapor in the downstream region of the flow direction orthogonal to the first direction of the gas (gas containing hydrogen) supplied to the fuel electrode side in the functional layer of the fuel electrode (Proportion of water vapor in fuel gas) increases. This is because water (water vapor) generated on the fuel electrode side by the reaction in the single cell is carried to the downstream region by the gas flow. When the partial pressure of water vapor increases in a certain region of the functional layer of the fuel electrode, the microstructural change (aggregation) of Ni contained in the region of 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 a deterioration in the performance of the single cell. In the configuration of the conventional single cell, there is a problem that the performance deterioration due to such operation is likely to occur.

 Such a problem is also common to electrolytic single cells that are constituent units of solid oxide electrolytic cells (hereinafter referred to as “SOEC”) that generate hydrogen using an electrolysis reaction of water. It is. During the operation of the SOEC, water vapor as gas supplied to the fuel electrode side is used for the reaction in the single cell while proceeding in the gas flow direction, so the region upstream of the gas flow direction in the functional layer of the fuel electrode The water vapor partial pressure increases. Therefore, in SOEC, as in SOFC, the partial pressure change of Ni contained in the functional layer is promoted by increasing the water vapor partial pressure in a specific region in the functional layer, and the performance deterioration of the single cell is likely to occur. There are challenges. In the present specification, the fuel cell unit cell and the electrolysis unit cell are collectively referred to as an electrochemical reaction unit cell.

  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 includes an electrolyte layer including a solid oxide, and an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer. In the reaction unit cell, the fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics, and the functional layer is orthogonal to the first direction of the gas supplied to the fuel electrode side. The Ni content Cf2 (wt%) in the region on one side in the gas flow direction is lower than the Ni content Cf1 (wt%) in the region on the other side in the gas flow direction. According to the present electrochemical reaction single cell, the Ni content Cf2 (wt%) in the region on one side in the flow direction of the gas supplied to the fuel electrode side in the functional layer is equal to the region in the other side in the gas flow direction. Since the Ni content is lower than Cf1 (wt%), by configuring this region to be a region on the side where the water vapor partial pressure tends to be high during operation, the fineness of Ni accompanying an increase in the water vapor partial pressure is obtained. The amount of structural changes can be reduced, and performance degradation of the electrochemical reaction single cell can be suppressed. Moreover, according to the present electrochemical reaction single cell, the Ni content Cf2 (wt%) in the region on the other side in the flow direction of the gas supplied to the fuel electrode side in the functional layer is relatively high. By configuring this region to be a region on the side where the water vapor partial pressure is unlikely to be high, it is possible to secure a certain amount of Ni content in the entire functional layer, and suppress deterioration in the initial performance of the electrochemical reaction single cell. can do. Therefore, according to the present electrochemical reaction single cell, it is possible to suppress deterioration in performance due to operation while suppressing a decrease in initial performance.

(2) In the electrochemical reaction unit cell, a ratio (Cf1 / Cf2) of the Ni content Cf1 of the other region to the Ni content Cf2 of the one region of the functional layer is greater than 1. , 1.851 or less. According to the present electrochemical reaction single cell, it is possible to ensure a certain level or more of the Ni content as a whole of the functional layer, and to effectively suppress the deterioration of the initial performance, and to suppress the performance deterioration accompanying the operation. it can.

(3) In the electrochemical reaction single cell, the fuel electrode further includes a substrate layer disposed on the opposite side of the functional layer from the electrolyte layer and containing Ni and oxide ion conductive ceramics. In the substrate layer, the Ni content Cb2 (wt%) of the one side region in the gas flow direction is higher than the Ni content Cb1 (wt%) of the other side region in the gas flow direction. It is good also as a structure characterized by this. According to this electrochemical reaction single cell, in the substrate layer in which the water vapor partial pressure is less likely to be higher than that of the functional layer, by increasing the Ni content in the region on the one side in the gas flow direction, the microstructure change of Ni While suppressing the performance deterioration due to the above, it is possible to reduce the difference between the Ni content in the one region of the fuel electrode and the Ni content in the other region of the fuel electrode, which causes current concentration. Damage to the electrochemical reaction single cell can be suppressed.

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

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. 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 XY cross-section structure of the electric power generation unit 102 in the position of VI-VI of FIG. 4 and FIG. FIG. 6 is an explanatory diagram showing an XY cross-sectional configuration of a power generation unit at a position VII-VII in FIGS. 4 and 5. 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. Device configuration:
(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. 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 (seven 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 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. 6 is an explanatory diagram showing an XY cross-sectional configuration of the power generation unit 102 at the position VI-VI in FIGS. 4 and 5, and FIG. 7 is a power generation unit at the position VII-VII in FIGS. 4 and 5. It is explanatory drawing which shows XY cross-section structure of 102. FIG.

  As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air electrode side frame 130, an air electrode side current collector 134, a fuel electrode side frame 140, and a fuel electrode side. A current collector 144 and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer of the power generation unit 102 are provided. 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 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 FIG. 6, 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.

  As shown in FIG. 7, 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.

  As shown in FIG. 6, the air electrode side current collector 134 is disposed in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of 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.

  As shown in FIG. 7, the fuel electrode side current collector 144 is disposed in the fuel chamber 176. The fuel electrode side current collector 144 includes an interconnector facing portion 146, an electrode facing portion 145, and a connecting portion 147 that connects the electrode facing portion 145 and the interconnector facing portion 146. 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.

A-2. Operation of the fuel cell stack 100:
As shown in FIGS. 2, 4, and 6, 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 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 each power generation unit is supplied from the oxidant gas introduction manifold 161. 102 is supplied to the air chamber 166 through the oxidant gas supply communication hole 132. Further, as shown in FIGS. 3, 5, and 7, the fuel gas is supplied via 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 the fuel of each power generation unit 102 is supplied from the fuel gas introduction manifold 171. The fuel is supplied to the fuel chamber 176 through the gas supply communication 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, oxygen contained in the oxidant gas OG and hydrogen contained in the fuel gas FG in the single cell 110. Power is generated by an electrochemical reaction. 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 startup until the high temperature can be maintained by heat generated by 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 through the oxidant gas discharge communication hole 133 as shown in FIGS. Further, the fuel passes through the holes of the main body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas discharge manifold 162 and is connected to the branch portion 29 through a gas pipe (not shown). It is discharged outside the battery stack 100. Further, 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 as shown in FIGS. 3, 5, and 7. Further, the fuel cell stack 100 is connected to a gas pipe member (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 fuel gas discharge manifold 172. Is discharged outside.

A-3. Detailed configuration of the fuel electrode 116:
FIG. 8 is a YZ sectional view schematically showing the detailed configuration of the fuel electrode 116. As shown in FIG. 8, the fuel electrode 116 includes a functional layer 350 and a substrate layer 360 disposed on the opposite side of the functional layer 350 from the electrolyte layer 112 side. 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 is a layer that 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. 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 FIG. 8, the flow direction of the fuel gas FG in the direction orthogonal to the Z direction (hereinafter referred to as “plane direction”) is a direction from right to left. As shown in FIG. 7, the flow direction of the fuel gas FG is a direction from the fuel gas supply communication hole 142 formed in the fuel electrode side frame 140 toward the fuel gas discharge communication hole 143 (in the example of FIG. Direction from the bottom to the bottom). In the following description, the region on the upstream side (the side where gas is supplied) in the fuel gas FG flow direction in the fuel electrode 116 is referred to as the fuel electrode upstream region R1, and the downstream side in the fuel gas FG flow direction ( The region on the gas discharge side) is referred to as the fuel electrode downstream region R2. As shown in FIG. 8 (and FIG. 7), the fuel electrode upstream region R1 is a region including at least the most upstream region when the fuel electrode 116 is equally divided into four along the flow direction of the fuel gas FG. The fuel electrode downstream region R2 is a region including at least the most downstream region when the fuel electrode 116 is divided into four equal parts along the flow direction of the fuel gas FG. More specifically, the fuel electrode upstream region R1 is the most upstream region when the fuel electrode 116 is equally divided into four along the flow direction of the fuel gas FG, and the fuel electrode downstream region R2 It is preferable that the most downstream region when the pole 116 is divided into four equal parts along the flow direction of the fuel gas FG.

  In the following description, in the functional layer 350 of the fuel electrode 116, the upstream region in the flow direction of the fuel gas FG is referred to as a functional layer upstream region Rf1, and the downstream region in the flow direction of the fuel gas FG is a function. This is referred to as a layer downstream region Rf2. Further, in the substrate layer 360 of the fuel electrode 116, the upstream region in the flow direction of the fuel gas FG is referred to as the substrate layer upstream region Rb1, and the downstream region in the flow direction of the fuel gas FG is the substrate layer downstream region Rb2. That's it. The functional layer upstream region Rf1 and the substrate layer upstream region Rb1 constitute a fuel electrode upstream region R1, and the functional layer downstream region Rf2 and the substrate layer downstream region Rb2 constitute a fuel electrode downstream region R2.

  In the unit cell 110 of the present embodiment, the difference in Ni content of the fuel electrode 116 is provided along the flow direction of the fuel gas FG in the plane direction (the direction from right to left in FIG. 8). Specifically, in the functional layer 350 of the fuel electrode 116, the Ni content Cf2 (wt%) of the functional layer downstream region Rf2 is lower than the Ni content Cf1 (wt%) of the functional layer upstream region Rf1. Yes. Further, in the substrate layer 360 of the fuel electrode 116, the Ni content Cb2 (wt%) of the substrate layer downstream region Rb2 is the Ni content of the substrate layer upstream region Rb1, contrary to the functional layer 350 of the fuel electrode 116. 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: 60 parts by weight and YSZ powder: 40 parts by weight, and a mixed powder of NiO powder: 50 parts by weight and YSZ powder: 50 parts by weight is used. To prepare the second slurry for the substrate layer. At the center of the slurry dam, a threshold plate is provided in a direction parallel to the traveling direction of the carrier film, the first slurry for the substrate layer is supplied to one side of the threshold plate, and the second slurry for the substrate layer is supplied to the other side. Supply. A green sheet for a fuel electrode substrate layer is prepared by performing coating simultaneously using both of the two types of slurries obtained. Of the produced fuel electrode substrate layer green sheets, the region obtained by applying the first slurry for substrate layer (slurry with a relatively high content of NiO powder) is the substrate layer downstream region Rb2 described above. The region obtained by coating the second slurry for substrate layer (slurry with a relatively low content of NiO powder) is the region to be the substrate layer upstream region Rb1 described above.

(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 NiO powder: 45 parts by weight and YSZ powder: 55 parts by weight, and a mixed powder of NiO powder: 55 parts by weight and YSZ powder: 45 parts by weight is used. To adjust the second slurry for the functional layer. At the center of the slurry dam, a threshold plate is provided in a direction parallel to the traveling direction of the carrier film, the first slurry for functional layer is supplied to one side of the threshold plate, and the second slurry for functional layer is supplied to the other side. Supply. A green sheet for a fuel electrode functional layer is prepared by performing coating simultaneously using both of the two types of slurries obtained. Of the produced green sheets for the fuel electrode functional layer, the region obtained by coating the first slurry for functional layer (slurry with a relatively low content of NiO powder) is the functional layer downstream region Rf2 described above. The region obtained by applying the second slurry for functional layer (slurry with a relatively high content of NiO powder) is the region to be the functional layer upstream region Rf1 described above.

(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 green sheet for the fuel electrode substrate layer, the green sheet for the fuel electrode functional layer, and the green sheet for the electrolyte layer are attached and degreased at about 280 ° C., for example. Further, for example, firing is performed at about 1350 ° C. to obtain a laminate of the electrolyte layer 112 and the fuel electrode 116 (the functional layer 350 and the substrate layer 360).

(Formation of air electrode 114)
For example, a mixed solution composed of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder and isopropyl alcohol is prepared. The air mixture 114 is formed by spray-coating the prepared mixed solution on the surface of the above-described laminate of the electrolyte layer 112 and the fuel electrode 116 on the side of the electrolyte layer 112 and firing at about 1100 ° C., for example.

  Through the above steps, the unit cell 110 having the above-described configuration is manufactured. In the manufactured unit cell 110, in the functional layer 350 of the fuel electrode 116, the Ni content Cf2 (wt%) of the functional layer downstream region Rf2 is greater than the Ni content Cf1 (wt%) of the functional layer upstream region Rf1. In the substrate layer 360 of the fuel electrode 116, the Ni content Cb2 (wt%) in the substrate layer downstream region Rb2 is higher than the Ni content Cb1 (wt%) in the substrate layer upstream region Rb1. Yes. After the plurality of unit cells 110 are manufactured, the plurality of unit cells 110 and other parts are assembled and fastened with the bolts 22 to manufacture the fuel cell stack 100 described above.

A-5. Effects of this embodiment:
As described above, in each single cell 110 constituting the fuel cell stack 100 of the present embodiment, the fuel electrode 116 includes the functional layer 350 containing Ni and oxide ion conductive ceramics. In the functional layer 350, the Ni content Cf2 (wt%) in one side of the flow direction in the surface direction of the fuel gas FG, specifically, the downstream region (functional layer downstream region Rf2) is It is lower than the Ni content Cf1 (wt%) in the other side, specifically, the upstream region (functional layer upstream region Rf1). Here, in the SOFC single cell 110, the water vapor partial pressure is increased in the functional layer downstream region Rf2 during the power generation operation. This is because water (water vapor) generated on the fuel electrode 116 side in response to the power generation reaction in the single cell 110 is carried downstream by the flow of the fuel gas FG. When the water vapor partial pressure increases in the functional layer downstream region Rf2, the microstructural change (aggregation) of Ni contained in the functional layer downstream region Rf2 is promoted. The change in the microstructure of Ni contained in the functional layer 350 causes a decrease in the three-phase interface and causes the performance of the single cell 110 to deteriorate. However, in the single cell 110 of the present embodiment, the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is relatively low, so that Ni accompanying the increase in the water vapor partial pressure in the functional layer downstream region Rf2 The amount of occurrence of microstructural changes can be reduced, and the performance degradation of the single cell 110 can be suppressed. In the single cell 110 of this embodiment, the Ni content Cf1 (wt%) is relatively high in the functional layer upstream region Rf1 where the water vapor partial pressure is difficult to increase. Therefore, the Ni content in the functional layer 350 as a whole can be ensured to some extent, and deterioration of the initial performance of the single cell 110 can be suppressed. Therefore, according to the single cell 110 of the present embodiment, it is possible to suppress the deterioration of the performance of the single cell 110 associated with the operation while suppressing a decrease in the initial performance of the single cell 110.

  Further, in each single cell 110 constituting the fuel cell stack 100 of the present embodiment, the fuel electrode 116 is disposed on the opposite side of the functional layer 350 from the electrolyte layer 112 side, and Ni and oxide ion conductive ceramics are disposed. A substrate layer 360 is provided. In the substrate layer 360, the Ni content Cb2 (wt%) in the one side of the flow direction in the surface direction of the fuel gas, specifically, the downstream region (substrate layer downstream region Rb2) is expressed in the gas flow direction. It is higher than the Ni content Cb1 (wt%) in the other side, specifically, the upstream region (substrate layer upstream region Rb1). In general, unlike the functional layer 350 in which a power generation reaction is performed, the power generation reaction is hardly performed in the substrate layer 360. 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 downstream region Rb2 is relatively high, the amount of Ni microstructural change contained in the substrate layer downstream region Rb2 is small, and the performance of the single cell 110 Will not deteriorate significantly. Further, by making the Ni content Cb2 (wt%) in the substrate layer downstream region Rb2 relatively high, the fuel electrode downstream region R2 of the fuel electrode 116 (functional layer downstream region Rf2 and substrate layer downstream region Rb2). And the Ni content in the fuel electrode upstream region R1 (the functional layer upstream region Rf1 and the substrate layer upstream region Rb1) can be reduced. As a result, the occurrence of current concentration in the upstream region of the fuel electrode 116 in the flow direction of the fuel gas FG can be suppressed, and damage to the single cell 110 caused by the current concentration can be suppressed. Therefore, according to the single cell 110 of the present embodiment, it is possible to suppress the deterioration of the performance of the single cell 110 accompanying the operation while suppressing the deterioration of the initial performance of the single cell 110, and further, due to current concentration. Damage to the single cell 110 can be suppressed.

A-6. Performance evaluation:
Performance evaluation performed using a plurality of fuel cell stack 100 samples will be described below. FIG. 9 is an explanatory diagram showing the performance evaluation results. As shown in FIG. 9, the samples S <b> 1 to S <b> 12 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 a Ni content Cf1 (wt%) of the functional layer upstream region Rf1 and a Ni content of the substrate layer upstream region Rb1 in each single cell 110 constituting the fuel cell stack 100. The combinations of Cb1 (wt%), the Ni content Cf2 (wt%) of the functional layer downstream region Rf2, and the Ni content Cb2 (wt%) of the substrate layer downstream region Rb2 are different from each other. In this performance evaluation, the number of single cells 110 included in the fuel cell stack 100 of each sample was set to ten.

(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 initial average output, when higher than 0.8 (V), 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 1.0 (%), it determined with a pass.

(Evaluation results)
In sample S1 and sample S11, since the deterioration rate was 1.0 (%) or more, it was determined to be rejected (x). In Sample S1 and Sample S11, regarding the configuration of the functional layer 350, the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is higher than the Ni content Cf1 (wt%) in the functional layer upstream region Rf1, It is the same value as Ni content rate Cf1 (wt%). Therefore, in sample S1 and sample S11, the microstructure of Ni contained in the functional layer downstream region Rf2 at a relatively high content rate as the water vapor partial pressure in the functional layer downstream region Rf2 increases during power generation operation. It is considered that the change is promoted and the performance of the single cell 110 is deteriorated.

  In samples S9 and S10, since the initial average output was 0.8 (V) or less, it was determined as rejected (x). In samples S9 and S10, the Ni average content is considerably low in both the functional layer upstream region Rf1 and the functional layer downstream region Rf2. Therefore, it is considered that the initial average output is low. In samples S9 and S10, the Ni content rate Cf2 (wt%) in the functional layer downstream region Rf2 was extremely low, so the deterioration rate was not rejected.

  Moreover, in sample S12, since the breakage of the single cell 110 occurred during the power generation operation for evaluating the deterioration rate, it was determined as rejected (x). In the sample S12, the Ni content in the fuel electrode downstream region R2 (the functional layer downstream region Rf2 and the substrate layer downstream region Rb2) is equal to the fuel electrode upstream region R1 (the functional layer upstream region Rf1 and the substrate layer upstream region). Since it is much lower than the Ni content in Rb1), it is considered that current concentration occurred in the fuel electrode upstream region R1 and the single cell 110 was damaged.

  On the other hand, in samples S2 to S8, since the initial average output was higher than 0.8 (V) and the deterioration rate was lower than 1.0 (%), it was determined as acceptable (◯ or ◎). In samples S2 to S8, regarding the configuration of the functional layer 350, the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is lower than the Ni content Cf1 (wt%) in the functional layer upstream region Rf1. Therefore, in samples S2 to S8, the Ni content Cf1 (wt%) in the functional layer upstream region Rf1 is relatively high, thereby suppressing the deterioration of the initial performance of the single cell 110, and in the functional layer downstream region Rf2. It is thought that the performance deterioration of the single cell 110 accompanying the power generation operation could be suppressed by relatively reducing the Ni content Cf2 (wt%). In Samples S2 to S8, regarding the configuration of the substrate layer 360, the Ni content Cb2 (wt%) in the substrate layer downstream region Rb2 is higher than the Ni content Cb1 (wt%) in the substrate layer upstream region Rb1. Yes. Therefore, in samples S2 to S8, the Ni content in the fuel electrode downstream region R2 (functional layer downstream region Rf2 and substrate layer downstream region Rb2) of the fuel electrode 116 and the fuel electrode upstream region R1 (functional layer upstream side). It is considered that the difference between the Ni content in the region Rf1 and the substrate layer upstream region Rb1) can be reduced, and the breakage of the single cell 110 due to current concentration can be suppressed.

  In sample S8, since the initial average output was 0.81 (V) or less, it was determined to be acceptable (◯), but in samples S2 to S7, the initial average output was 0.81 (V). Since it was higher, it was determined to be particularly good (◎). In sample S8, the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is significantly lower than the Ni content Cf1 (wt%) in the functional layer upstream region Rf1, that is, the functional layer downstream region The ratio (Cf1 / Cf2) of the Ni content Cf1 of the functional layer upstream region Rf1 to the Ni content Cf2 of Rf2 is relatively large at 2.200. Therefore, although it is possible to suppress the performance deterioration of the single cell 110, it is considered that it did not reach the samples S2 to S7 in terms of suppressing the initial performance deterioration. In samples S2 to S7, the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is lower than the Ni content Cf1 (wt%) in the functional layer upstream region Rf1, but Cf1 / Cf2 is suppressed to a low value. (Specifically, it is 1.851 or less). Therefore, in samples S2 to S7, it is considered that the performance deterioration of the single cell 110 accompanying the operation could be suppressed while effectively suppressing the decrease in the initial performance of the single cell 110.

  From the results of the performance evaluation described above, in the single cell 110, if the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is lower than the Ni content Cf1 (wt%) in the functional layer upstream region Rf1, It was confirmed that the deterioration of the performance of the single cell 110 accompanying the operation can be suppressed while suppressing the deterioration of the initial performance of the single cell 110. Further, if the ratio (Cf1 / Cf2) of the Ni content Cf1 in the functional layer upstream region Rf1 to the Ni content Cf2 in the functional layer downstream region Rf2 is larger than 1 and 1.851 or less, the initial stage of the single cell 110 It was confirmed that the performance deterioration of the single cell 110 accompanying operation can be suppressed while effectively suppressing the decrease in performance.

  Further, from the results of the performance evaluation, in the single cell 110, if the Ni content Cb2 (wt%) in the substrate layer downstream region Rb2 is higher than the Ni content Cb1 (wt%) in the substrate layer upstream region Rb1, It was confirmed that damage to the single cell 110 caused by current concentration can be 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 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, a cross section of the unit cell 110 substantially parallel to the vertical direction (Z direction), including a cross section including the fuel electrode upstream region R1 of the fuel electrode 116, and a cross section including the fuel electrode downstream region R2 of the fuel electrode 116. Is set arbitrarily. Images that can be confirmed in the vertical direction of the functional layer 350 of the fuel electrode 116 at three different positions in each of the two set cross sections are acquired as analysis images. More specifically, the portion estimated as the boundary B1 (see FIG. 8) between the functional layer 350 and the electrolyte layer 112 of the fuel electrode 116 is divided into 10 divided regions obtained by dividing the image vertically into 10 equal parts. Is located in the uppermost divided area, and the portion estimated as the boundary B2 (see FIG. 8) between the functional layer 350 and the substrate layer 360 of the fuel electrode 116 is located in the lowermost divided area. The captured image 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%. In addition, regarding the Ni content Cf2 in the functional layer downstream region Rf2 and the Ni content Cf1 in the functional layer upstream region Rf1, in each analysis image, the functional layer 350 is divided into three in the vertical direction (Z direction). The Ni content is calculated for the portion located on the uppermost side (electrolyte layer 112 side) at that time, and the average value of the Ni content calculated in each analysis image is the final Ni content. In addition, regarding the Ni content Cb2 in the substrate layer downstream region Rb2 and the Ni content Cb1 in the substrate layer upstream region Rb1, in each analysis image, each analysis image described above is divided into 10 equal parts in the vertical direction. The Ni content rate of the portion of the substrate layer 360 in the lowermost divided region of the obtained 10 divided regions is calculated, and the average value of the Ni content rate calculated in each analysis image is calculated as the final value. Ni content is determined.

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. For example, the technology disclosed in this specification can be applied to a known structure of a fuel cell such as a cylindrical type or a cylindrical flat plate type.

  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 single cell that is a constituent unit of a solid oxide electrolytic cell (SOEC) that generates hydrogen by using hydrogen, and an electrolytic cell stack including a plurality of electrolytic single cells. 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, during operation of the SOEC, water vapor as a gas supplied to the fuel electrode 116 side is used for the reaction in the electrolysis unit cell while proceeding in the gas flow direction. The water vapor partial pressure increases in the upstream region in the flow direction. Therefore, also in SOEC, the water vapor partial pressure is increased in a specific region in the functional layer 350, whereby the microstructure change of Ni contained in the functional layer 350 is promoted, and the performance deterioration of the electrolytic cell is likely to occur. is there. Therefore, also in the electrolytic single cell, the fuel electrode 116 has a functional layer 350 containing Ni and oxide ion conductive ceramics, and the flow of gas (water vapor) supplied to the fuel electrode 116 side in the functional layer 350. The Ni content (wt%) of one side in the direction, specifically the upstream region, is lower than the Ni content (wt%) of the other side in the gas flow direction, specifically the downstream region. If a structure is employ | adopted, the performance degradation of the electrolysis single cell accompanying a driving | operation can be suppressed, suppressing the performance fall of an electrolysis single cell. Also in the electrolytic unit cell, 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. In 360, the Ni content (wt%) of the one side in the gas flow direction, specifically the upstream region, is the Ni content in the other side, specifically the downstream region, in the gas flow direction. If a configuration higher than the rate (wt%) is adopted, it is possible to suppress damage to the electrolytic cell due to current concentration.

  In addition, the configuration of the fuel electrode 116 described in the above embodiment (the relationship of Ni content, etc.) is the same as all the single cells 110 (or electrolytic single cells) included in the fuel cell stack 100 (or electrolytic cell stack, the same applies hereinafter). The same applies hereinafter), or may be adopted in only a part of the 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 single cell comprising 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,
In the functional layer, the Ni content Cf2 (wt%) in the downstream region in the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the upstream side in the gas flow direction. A fuel cell single cell characterized by being lower than the Ni content Cf1 (wt%) of the region.
[Application Example 2]
In the fuel cell single cell described in Application Example 1,
The ratio (Cf1 / Cf2) of the Ni content Cf1 in the upstream region to the Ni content Cf2 in the downstream region in the functional layer is greater than 1 and 1.851 or less, Fuel cell single cell.
[Application Example 3]
In the fuel cell single cell 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,
In the substrate layer, the Ni content Cb2 (wt%) in the downstream region in the gas flow direction is higher than the Ni content Cb1 (wt%) in the upstream region in the gas flow direction. A single fuel cell.
[Application Example 4]
In a fuel cell stack comprising a plurality of fuel cell single cells arranged side by side in the first direction,
A fuel cell stack, wherein at least one of the plurality of fuel cell single cells is the fuel cell single cell according to any one of application examples 1 to 3.
[Application Example 5]
In an electrolytic unit cell comprising 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,
In the functional layer, the Ni content Cf2 (wt%) of the upstream region in the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the downstream of the gas flow direction. An electrolytic single cell characterized by being lower than the Ni content Cf1 (wt%) of the region.
[Application Example 6]
In the electrolytic single cell described in Application Example 5,
The ratio (Cf1 / Cf2) of the Ni content Cf1 in the downstream region to the Ni content Cf2 in the upstream region in the functional layer is greater than 1 and 1.851 or less, Electrolytic single cell.
[Application Example 7]
In the electrolytic cell described in Application Example 5 or Application Example 6,
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,
In the substrate layer, the Ni content Cb2 (wt%) in the upstream region in the gas flow direction is higher than the Ni content Cb1 (wt%) in the downstream region in the gas flow direction. Electrolytic single cell.
[Application Example 8]
In an electrolytic cell stack comprising a plurality of electrolytic single cells arranged side by side in the first direction,
An electrolytic cell stack, wherein at least one of the plurality of electrolytic single cells is the electrolytic single cell according to any one of application examples 5 to 7.

22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Main part 29: Branching part 40: Current collecting part 51: Electrode support 52: Fuel gas flow path 53: Interconnector 70: Storage container 73: Manifold 76: reformer 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: Junction 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 14 4: Fuel electrode side current collector 145: Electrode facing portion 146: Interconnector facing portion 147: Connection portion 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 350: Functional layer 360: Substrate layer

Claims (4)

In an electrochemical reaction unit cell comprising 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,
In the functional layer, the Ni content Cf2 (wt%) of the region on one side of the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the other in the gas flow direction. An electrochemical reaction single cell characterized by being lower than the Ni content Cf1 (wt%) in the side region. The electrochemical reaction single cell according to claim 1,
The ratio (Cf1 / Cf2) of the Ni content Cf1 of the other side region to the Ni content Cf2 of the one side region in the functional layer is greater than 1 and 1.851 or less. An electrochemical reaction single cell. The electrochemical reaction single cell 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,
In the substrate layer, the Ni content Cb2 (wt%) in the one side region in the gas flow direction is higher than the Ni content Cb1 (wt%) in the other side region in the gas flow direction. Characterized by an electrochemical reaction single cell. In an electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells arranged side by side in the first direction,
The electrochemical reaction cell stack according to claim 1, wherein at least one of the plurality of electrochemical reaction single cells is the electrochemical reaction single cell according to claim 1.

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