JP6754249B2 - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Description

The techniques disclosed herein relate to electrochemical reaction single cells.

A solid oxide fuel cell (hereinafter referred to as "SOFC") is known as one of the fuel cells that generate electricity by utilizing an electrochemical reaction between hydrogen and oxygen. The fuel cell single cell (hereinafter, simply referred to as “single cell”), which is a constituent unit of SOFC, has an electrolyte layer containing a solid oxide and a predetermined direction (hereinafter, referred to as “first direction”) with the electrolyte layer interposed therebetween. Includes air and fuel electrodes facing each other. The air electrode includes, for example, a perovskite-type oxide. Further, the fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics (for example, yttria-stabilized zirconia (hereinafter referred to as “YSZ”)) (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2015-84281

Generally, during the operation of SOFC, the partial pressure of water vapor is divided in the region on the downstream side of the functional layer of the fuel electrode in the flow direction orthogonal to the first direction of the gas (gas containing hydrogen) supplied to the fuel electrode side. (Ratio of water vapor in fuel gas) becomes high. This is because the water (water vapor) generated on the fuel electrode side due to 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 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 deterioration in the performance of the single cell. The conventional single-cell configuration has a problem that performance deterioration due to such operation is likely to occur.

It should be noted that such a problem is also common to the electrolytic single cell, which is a constituent unit of a solid oxide fuel cell (hereinafter referred to as “SOEC”) that generates hydrogen by utilizing the electrolysis reaction of water. Is. During the operation of the SOEC, water vapor as a gas supplied to the fuel electrode side is subjected to the reaction in a single cell while advancing in the gas flow direction, so that the region on the upstream side in the gas flow direction in the functional layer of the fuel electrode. The partial pressure of water vapor becomes high. Therefore, in SOEC as well, as in SOFC, the microstructural change of Ni contained in the functional layer is promoted by increasing the partial pressure of water vapor in a specific region of the functional layer, and the performance of a single cell is likely to deteriorate. There are challenges. In this specification, the fuel cell single cell and the electrolytic single cell are collectively referred to as an electrochemical reaction single cell.

This specification discloses a technique capable of solving the above-mentioned problems.

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

(1) The electrochemical reaction single cell disclosed in the present specification is electrochemically provided with 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. In the reaction single cell, the fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics, and is orthogonal to the first direction of the gas supplied to the fuel electrode side in the functional layer. The Ni content Cf2 (wt%) in the region on one side of 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 this electrochemical reaction single cell, the Ni content Cf2 (wt%) in the region on one side of the gas flow direction supplied to the fuel electrode side in the functional layer is the region on the other side in the gas flow direction. Since the Ni content is lower than Cf1 (wt%), by configuring this region to be the region on the side where the partial pressure of water vapor tends to increase during operation, the amount of Ni that accompanies the increase in the partial pressure of water vapor The amount of structural change generated can be reduced, and the deterioration of the performance of the electrochemical reaction single cell can be suppressed. Further, according to this electrochemical reaction single cell, the Ni content Cf2 (wt%) in the region on the other side of 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 the region on the side where the partial pressure of water vapor is unlikely to increase, the Ni content of the functional layer as a whole can be secured to some extent, and the deterioration of the initial performance of the electrochemical reaction single cell is suppressed. can do. Therefore, according to the present electrochemical reaction single cell, it is possible to suppress the deterioration of the performance due to the operation while suppressing the deterioration of the initial performance.

(2) In the electrochemical reaction single cell, 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 larger than 1. The configuration may be 1.851 or less. According to this electrochemical reaction single cell, the Ni content of the functional layer as a whole can be secured above a certain level, and the deterioration of the initial performance can be effectively suppressed while the performance deterioration due to the operation can be suppressed. it can.

(3) In the electrochemical reaction single cell, the fuel electrode is further arranged on the opposite side of the functional layer from the electrolyte layer, and has a substrate layer containing Ni and oxide ion conductive ceramics. In the substrate layer, the Ni content Cb2 (wt%) of the region on one side in the gas flow direction is higher than the Ni content Cb1 (wt%) in the region on the other side in the gas flow direction. It may be a configuration characterized by this. According to this electrochemical reaction single cell, in the substrate layer in which the partial pressure of water vapor is less likely to be higher than that of the functional layer, the microstructural change of Ni is performed by increasing the Ni content in the region on one side of the gas flow direction. It is possible to reduce the difference between the Ni content in the region on one side of the fuel electrode and the Ni content in the region on the other side of the fuel electrode while suppressing performance deterioration due to the above, which causes current concentration. Electrochemical reaction It is possible to suppress damage to a single cell.

The technique disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction single cell (fuel cell single cell or an electrolytic single cell), and 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) provided, a method for producing them, and the like.

It is a perspective view which shows the appearance structure of the fuel cell stack 100 in this embodiment. It is explanatory drawing which shows the XZ cross-sectional structure of the fuel cell stack 100 at the position of II-II of FIG. It is explanatory drawing which shows the YZ cross-sectional structure of the fuel cell stack 100 at the position of III-III of FIG. It is explanatory drawing which shows the XZ cross section configuration of two power generation units 102 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 configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the XY cross-sectional structure of the power generation unit 102 at the position of VI-VI of FIG. 4 and FIG. It is explanatory drawing which shows the XY cross-sectional structure of the power generation unit 102 at the position of VII-VII of FIG. 4 and FIG. It is a YZ cross-sectional view which shows typically the detailed structure of the fuel electrode 116. It is explanatory drawing which shows the performance evaluation result.

A. Embodiment:
A-1. Device configuration:
(Structure of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of the fuel cell stack 100 in the present embodiment, and FIG. 2 is an explanatory view showing an XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II of FIG. FIG. 3 is an explanatory view showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position III-III of FIG. Each figure shows XYZ axes that are orthogonal to each other to identify the direction. In the present specification, for convenience, the Z-axis positive direction is referred to as an upward direction, and the Z-axis negative direction is referred to as a downward direction, but the fuel cell stack 100 is actually in a direction different from such an orientation. It may be installed. The same applies to FIGS. 4 and later.

The fuel cell stack 100 includes a plurality of (seven in this embodiment) fuel cell power generation units (hereinafter, simply referred to as “power generation units”) 102, and a pair of end plates 104 and 106. The seven power generation units 102 are arranged side by side in a predetermined arrangement direction (vertical direction in this embodiment). The pair of end plates 104 and 106 are arranged so as to sandwich an aggregate composed of seven power generation units 102 from above and below. The arrangement direction (vertical direction) corresponds to the first direction in the claims.

A plurality of holes (eight in this embodiment) penetrating in the vertical direction are formed on the peripheral edge of each layer (power generation unit 102, end plates 104, 106) constituting the fuel cell stack 100 in the vertical direction. , 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.

A bolt 22 extending in the vertical direction is inserted into each communication hole 108, and the fuel cell stack 100 is fastened by the bolt 22 and the nuts 24 fitted on both sides of the bolt 22. As shown in FIGS. 2 and 3, between the nut 24 fitted on one side (upper side) of the bolt 22 and the upper surface of the end plate 104 forming 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 the 22 and the lower surface of the end plate 106 forming the lower end of the fuel cell stack 100. However, in the place where the gas passage member 27 described later is provided, the insulating sheets arranged on the upper side and the lower side of the gas passage member 27 and the gas passage member 27 between the nut 24 and the surface of the end plate 106, respectively. 26 is intervening. The insulating sheet 26 is made of, for example, a mica sheet, a ceramic fiber sheet, a ceramic dust 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 position is near the midpoint of one side (the side on the positive side of the X axis among the two sides parallel to the Y axis) on the outer circumference of the fuel cell stack 100 around the Z direction. In the space formed by the bolt 22 (bolt 22A) and the communication hole 108 through which the bolt 22A is inserted, the oxidant gas OG is introduced from the outside of the fuel cell stack 100, and the oxidant gas OG is generated for each power generation. It functions as an oxidizer gas introduction manifold 161 that is a gas flow path supplied to the unit 102, and is the midpoint of the side opposite to the side (the side on the negative side of the X axis among the two sides parallel to the Y axis). The space formed by the bolt 22 (bolt 22B) located in the vicinity and the communication hole 108 through which the bolt 22B is inserted provides the oxidant off-gas OOG, which is the gas discharged from the air chamber 166 of each power generation unit 102. It functions as an oxidizer gas discharge manifold 162 that discharges to the outside of the fuel cell stack 100. In this 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 positive direction of the Y axis among the two sides parallel to the X axis) on the outer circumference of the fuel cell stack 100 around the Z direction. In the space formed by the bolt 22 (bolt 22D) located in the above and the communication hole 108 through which the bolt 22D is inserted, the fuel gas FG is introduced from the outside of the fuel cell stack 100, and the fuel gas FG is generated by each power generation. A bolt 22 that functions as a fuel gas introduction manifold 171 to be supplied to the unit 102 and is located near the midpoint of the side opposite to the side (the side on the negative side of the Y axis of the two sides parallel to the X axis). The space formed by (bolt 22E) and the communication hole 108 through which the bolt 22E is inserted sends the fuel off-gas FOG, which is the gas discharged from the fuel chamber 176 of each power generation unit 102, to the outside of the fuel cell stack 100. It functions as a fuel gas discharge manifold 172 to be discharged. In the present embodiment, for example, a hydrogen-rich gas obtained by reforming city gas is used as the fuel gas FG.

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

(Structure of end plates 104 and 106)
The pair of end plates 104 and 106 are substantially rectangular flat plate-shaped conductive members, and are made of, for example, stainless steel. One end plate 104 is arranged above the power generation unit 102 located at the top, and the other end plate 106 is arranged below the power generation unit 102 located at the bottom. 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.

(Structure of power generation unit 102)
FIG. 4 is an explanatory view 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 an explanatory view showing an XZ cross-sectional configuration at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-sectional structure of two power generation units 102. Further, FIG. 6 is an explanatory view showing an XY cross-sectional configuration of the power generation unit 102 at the position of VI-VI of FIGS. 4 and 5, and FIG. 7 is a power generation unit at the position of VII-VII of FIGS. 4 and 5. It is explanatory drawing which shows the XY cross-sectional structure of 102.

As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air pole side frame 130, an air pole side current collector 134, a fuel pole side frame 140, and a fuel pole side. It includes a current collector 144 and a pair of interconnectors 150 that form the uppermost layer and the lowermost layer of the power generation unit 102. Holes corresponding to the communication holes 108 through which the above-mentioned bolts 22 are inserted are formed on the peripheral edges of the separator 120, the air pole side frame 130, the fuel pole side frame 140, and the interconnector 150 in the Z direction.

The interconnector 150 is a substantially rectangular flat plate-shaped conductive member, and is made of, for example, ferritic stainless steel. The interconnector 150 ensures electrical continuity between the power generation units 102 and prevents mixing of reaction gases between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by two adjacent power generation units 102. That is, the upper interconnector 150 in a certain power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Further, since the fuel cell stack 100 includes a pair of end plates 104 and 106, the power generation unit 102 located at the top of the fuel cell stack 100 does not have 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 single cell 110 includes an electrolyte layer 112, an air electrode (cathode) 114 and a fuel electrode (anode) 116 facing each other in the vertical direction (arrangement direction in which the power generation units 102 are arranged) with the electrolyte layer 112 in between. The single cell 110 of the present embodiment is a fuel pole support type single cell in which the fuel pole 116 supports the electrolyte layer 112 and the air pole 114.

The electrolyte layer 112 is a flat plate-shaped member that is substantially rectangular in the Z direction, and is a dense layer. The electrolyte layer 112 is formed of, for example, a solid oxide such as YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), and perovskite-type oxide. There is. The air electrode 114 is a substantially rectangular flat plate-shaped member smaller than the electrolyte layer 112 in the Z direction, and is a porous layer. The air electrode 114 is formed of, for example, a perovskite type oxide (for example, LSCF (lanternstrontium cobalt iron oxide), LSM (lanternstrontium manganese oxide), LNF (lantern nickel iron)). The fuel electrode 116 is a substantially rectangular flat plate-shaped member having substantially the same size as the electrolyte layer 112 in the Z direction, and is a porous layer. The fuel electrode 116 is formed of, for example, a cermet composed of Ni and oxide ion conductive ceramic particles (for example, YSZ). The configuration of the fuel electrode 116 will be described in detail later. As described above, 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-shaped member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed near the center, and is made of metal, for example. The peripheral portion of the hole 121 in the separator 120 faces the peripheral edge of the surface of the electrolyte layer 112 on the side of the air electrode 114. 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 wax) arranged at the opposite portion thereof. The separator 120 partitions the air chamber 166 facing the air pole 114 and the fuel chamber 176 facing the fuel pole 116, and a gas leak from one electrode side to the other electrode side at the peripheral edge of the single cell 110. It is suppressed.

As shown in FIG. 6, the air electrode side frame 130 is a frame-shaped member in which a substantially rectangular hole 131 penetrating in the vertical direction is formed near the center, and is formed of, for example, an insulator such as mica. .. The hole 131 of the air electrode side frame 130 constitutes an air chamber 166 facing the air electrode 114. The air electrode side frame 130 is in contact with the peripheral edge of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge of the surface of the interconnector 150 facing the air electrode 114. .. Further, the air electrode side frame 130 electrically insulates between the pair of interconnectors 150 included in the power generation unit 102. Further, in the air electrode side frame 130, the oxidant gas supply communication hole 132 that communicates the oxidant gas introduction manifold 161 and the air chamber 166, and the oxidant gas that communicates 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-shaped member in which a substantially rectangular hole 141 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. Hole 141 of the fuel electrode side frame 140 constitutes a fuel chamber 176 facing the fuel electrode 116. The fuel electrode side frame 140 is in contact with the peripheral edge of the surface of the separator 120 facing the electrolyte layer 112 and the peripheral edge of the surface of the interconnector 150 facing the fuel electrode 116. Further, in the fuel electrode side frame 140, a fuel gas supply communication hole 142 that communicates the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that communicates the fuel chamber 176 and the fuel gas discharge manifold 172. And are formed.

As shown in FIG. 6, the air electrode side current collector 134 is arranged in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of substantially square columnar current collector elements 135, 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 on the side facing the air electrode 114. However, as described above, since the power generation unit 102 located at the top of the fuel cell stack 100 does not have the upper interconnector 150, the air electrode side current collector 134 in the power generation unit 102 has an upper end plate. It is in contact with 104. 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, the flat plate-shaped portion of the integral member that is orthogonal to the vertical direction (Z-axis direction) functions as the interconnector 150, and is formed so as to project from the flat plate-shaped portion toward the air electrode 114. The current collector element 135, which is a plurality of convex portions, functions as the air electrode side current collector 134. Further, the integral member of the air electrode side current collector 134 and the interconnector 150 may be covered with a conductive coat, and both are placed 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 arranged 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 connecting the electrode facing portion 145 and the interconnector facing portion 146. For example, nickel or nickel alloy. , Stainless steel, etc. The electrode facing portion 145 is in contact with the surface of the fuel pole 116 opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is on the surface of the interconnector 150 facing the fuel pole 116. Are in contact. However, as described above, since the power generation unit 102 located at the bottom of the fuel cell stack 100 does not have the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 is the lower end plate. It is in contact with 106. Since the fuel pole side current collector 144 has such a configuration, the fuel pole 116 and the interconnector 150 (or the end plate 106) are electrically connected to each other. A spacer 149 formed of, for example, mica is arranged 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 follow. Good electrical connection with is maintained.

A-2. Operation of fuel cell stack 100:
As shown in FIGS. 2, 4 and 6, the oxidant gas is passed through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas introduction manifold 161. When the OG is supplied, the oxidant gas OG is supplied to the oxidant gas introduction manifold 161 through the holes of the branch portion 29 and the main body portion 28 of the gas passage member 27, and each power generation unit is supplied from the oxidizer gas introduction manifold 161. It is supplied to the air chamber 166 through the oxidant gas supply communication hole 132 of 102. Further, as shown in FIGS. 3, 5 and 7, the fuel gas is passed 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 holes of the branch portion 29 and the main body portion 28 of the gas passage member 27, and the fuel of each power generation unit 102 is supplied from the fuel gas introduction manifold 171. It is supplied to the fuel chamber 176 via 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 are supplied. Power is generated by an electrochemical reaction with. This power generation reaction is an exothermic reaction. In each power generation unit 102, the air pole 114 of the single cell 110 is electrically connected to one of the interconnectors 150 via the air pole side current collector 134, and the fuel pole 116 is via the fuel pole side current collector 144. It is electrically connected to the other interconnector 150. Further, the plurality of power generation units 102 included in the fuel cell stack 100 are electrically connected in series. Therefore, the electric energy generated in each power generation unit 102 is taken out from the end plates 104 and 106 that function as the output terminals of the fuel cell stack 100. Since the SOFC generates electricity at a relatively high temperature (for example, 700 ° C. to 1000 ° C.), the fuel cell stack 100 is a heater (for example, after the start-up, until the high temperature can be maintained by the heat generated by the power generation. (Not shown) may be heated.

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. 2, 4 and 6. Further, the fuel is passed through the holes of the main body 28 and the branch 29 of the gas passage member 27 provided at the position of the oxidant gas discharge manifold 162, and through the gas pipe (not shown) connected to the branch 29. It is discharged to the outside of 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 through the fuel gas discharge communication hole 143 as shown in FIGS. 3, 5 and 7. Further, the fuel cell stack 100 is passed through the holes of the main body 28 and the branch 29 of the gas passage member 27 provided at the position of the fuel gas discharge manifold 172, and through a gas pipe (not shown) connected to the branch 29. It is discharged to the outside of.

A-3. Detailed configuration of fuel pole 116:
FIG. 8 is a YZ cross-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 arranged on the side opposite to the electrolyte layer 112 side of the functional layer 350. In the present embodiment, the functional layer 350 is arranged adjacent to the electrolyte layer 112, and the substrate layer 360 is arranged adjacent to the functional layer 350. Both the functional layer 350 and the substrate layer 360 are formed of a cermet containing Ni and YSZ (yttria-stabilized zirconia) which is an oxide ion conductive ceramic.

The functional layer 350 is a layer that mainly exerts a function of reacting oxide ions supplied from the electrolyte layer 112 with hydrogen contained in the fuel gas FG to generate electrons and water vapor. Further, the substrate layer 360 is a layer that mainly exerts 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 thicker than the thickness of the functional layer 350 in the Z direction. Further, in order to enhance the gas diffusivity 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 from the fuel gas supply communication hole 142 formed in the fuel electrode side frame 140 toward the fuel gas discharge communication hole 143 (upper in the example of FIG. 7). From to the bottom). In the following description, the region of the fuel electrode 116 on the upstream side (the side where the gas is supplied) in the flow direction of the fuel gas FG is referred to as the fuel electrode upstream side region R1 and is the downstream side (the side in which the gas FG flows). The region on the gas discharge side) is referred to as the fuel extreme downstream region R2. As shown in FIG. 8 (and FIG. 7), the fuel pole upstream side region R1 is a region including at least the most upstream side region when the fuel pole 116 is divided into four equal parts along the flow direction of the fuel gas FG. The fuel pole downstream region R2 is a region including at least the most downstream region when the fuel pole 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 divided into four equal parts along the flow direction of the fuel gas FG, and the fuel electrode downstream region R2 is the fuel. It is preferable that the pole 116 is the most downstream region when the pole 116 is divided into four equal parts along the flow direction of the fuel gas FG.

Further, in the following description, in the functional layer 350 of the fuel electrode 116, the region on the upstream side in the flow direction of the fuel gas FG is referred to as the functional layer upstream region Rf1, and the region on the downstream side in the flow direction of the fuel gas FG is functional. It is called the layer downstream side region Rf2. Further, in the substrate layer 360 of the fuel electrode 116, the region on the upstream side in the flow direction of the fuel gas FG is referred to as the substrate layer upstream side region Rb1, and the region on the downstream side in the flow direction of the fuel gas FG is referred to as the substrate layer downstream region Rb2. That is. The functional layer upstream side region Rf1 and the substrate layer upstream side region Rb1 constitute the fuel electrode upstream side region R1, and the functional layer downstream side region Rf2 and the substrate layer downstream side region Rb2 constitute the fuel pole downstream side region R2.

In the single cell 110 of the present embodiment, a difference is provided in the Ni content of the fuel electrode 116 along the flow direction of the fuel gas FG in the plane direction (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. There is. Further, in the substrate layer 360 of the fuel electrode 116, contrary to the functional layer 350 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. It is higher than Cb1 (wt%). The Ni content of the fuel electrode 116 is the ratio of the Ni content to the total content of Ni and the oxide ion conductive ceramics (YSZ) expressed in wt%.

A-4. Manufacturing method of fuel cell stack 100:
An example of the method for manufacturing 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 which are pore-forming materials, butyral resin, dioctylphthalate (DOP) which is a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added. , Mix with a ball mill to prepare the slurry. At this time, two types of slurries 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 60 parts by weight of NiO powder and 40 parts by weight of YSZ powder, and a mixed powder of 50 parts by weight of NiO powder and 50 parts by weight of YSZ powder is used. To prepare the second slurry for the substrate layer. A threshold plate is provided in the center of the slurry dam 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 provided on the other side. Supply. A green sheet for a fuel electrode substrate layer is produced by applying both of the obtained two types of slurries at the same time. Among the produced green sheets for the fuel electrode substrate layer, the region obtained by applying the first slurry for the substrate layer (slurry having a relatively high content of NiO powder) is the above-mentioned downstream region Rb2 of the substrate layer. The region to be obtained by coating the second slurry for the substrate layer (slurry having a relatively low content of NiO powder) is the region to be the above-mentioned upstream region Rb1 of the substrate layer.

(Preparation of green sheet for fuel electrode functional layer)
To the mixed powder of NiO powder and YSZ powder, organic beads which are pore-forming materials, butyral resin, DOP which is a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added, and a ball mill is used. Mix to prepare the slurry. At this time, two types of slurries 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 prepare the second slurry for the functional layer. A threshold plate is provided in the center of the slurry dam in a direction parallel to the traveling direction of the carrier film, the first slurry for the functional layer is supplied to one side of the threshold plate, and the second slurry for the functional layer is provided on the other side. Supply. A green sheet for the fuel electrode functional layer is produced by applying both of the obtained two types of slurries at the same time. Among the produced green sheets for the functional layer of the fuel electrode, the region obtained by applying the first slurry for the functional layer (slurry having a relatively low content of NiO powder) is the region on the downstream side of the functional layer Rf2 described above. The region obtained by applying the second slurry for the functional layer (slurry having a relatively high content of NiO powder) is the region to be the above-mentioned upstream region Rf1 of the functional layer.

(Preparation of green sheet for electrolyte layer)
A butyral resin, a plasticizer DOP, a dispersant, and a mixed solvent of toluene and ethanol are added to YSZ powder (100 parts by weight) and mixed with a ball mill to prepare a slurry. The obtained slurry is thinned by the doctor blade method to prepare 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, for example, about 280 ° C. Further, for example, firing is performed at about 1350 ° C. to obtain a laminate of the electrolyte layer 112 and the fuel electrode 116 (functional layer 350 and substrate layer 360).

(Formation of air pole 114)
For example, a mixed solution of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder and isopropyl alcohol is prepared. The prepared mixed solution is spray-coated on the surface of the above-mentioned laminate of the electrolyte layer 112 and the fuel electrode 116 on the side of the electrolyte layer 112, and fired at, for example, about 1100 ° C. to form the air electrode 114.

Through the above steps, the single cell 110 having the above-described configuration is manufactured. In the manufactured single 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 higher 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%) of the substrate layer downstream region Rb2 is higher than the Ni content Cb1 (wt%) of the substrate layer upstream region Rb1. There is. After the plurality of single cells 110 are manufactured, the fuel cell stack 100 described above is manufactured by assembling the plurality of single cells 110 and other parts and fastening them with bolts 22.

A-5. Effect 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 a 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 fuel gas FG in the plane direction of the flow direction, specifically, the downstream region (region Rf2 on the downstream side of the functional layer) is the gas flow direction. The Ni content is lower than the Ni content Cf1 (wt%) in the other side, specifically, the upstream side region (functional layer upstream side region Rf1). Here, in the SOFC single cell 110, the partial pressure of water vapor increases in the region Rf2 on the downstream side of the functional layer during power generation operation. This is because the water (water vapor) generated on the fuel electrode 116 side due to the power generation reaction in the single cell 110 is carried to the downstream side by the flow of the fuel gas FG. When the partial pressure of water vapor increases in the region Rf2 on the downstream side of the functional layer, the microstructural change (aggregation) of Ni contained in the region Rf2 on the downstream side of the functional layer is promoted. The microstructure change of Ni contained in the functional layer 350 causes a decrease in the three-phase interface and causes a deterioration in the performance of the single cell 110. However, in the single cell 110 of the present embodiment, since the Ni content Cf2 (wt%) in the functional layer downstream region Rf2 is relatively low, Ni is accompanied by an increase in the water vapor partial pressure in the functional layer downstream region Rf2. The amount of microstructural change generated can be reduced, and the performance deterioration of the single cell 110 can be suppressed. Further, in the single cell 110 of the present embodiment, the Ni content Cf1 (wt%) is relatively high in the region Rf1 on the upstream side of the functional layer where the partial pressure of water vapor is unlikely to be high. Therefore, the Ni content of the functional layer 350 as a whole can be secured to some extent, and the 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 due to the operation while suppressing the deterioration of 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 arranged on the side opposite to the electrolyte layer 112 side of the functional layer 350, and Ni and oxide ion conductive ceramics are arranged. A substrate layer 360 containing the substrate layer is provided. In the substrate layer 360, the Ni content Cb2 (wt%) in the above-mentioned one side, specifically, the downstream side region (the substrate layer downstream side region Rb2) in the plane direction of the fuel gas is the gas flow direction. The Ni content is higher than the Ni content Cb1 (wt%) in the other side, specifically, the upstream side region (the substrate layer upstream side region Rb1). In general, in the substrate layer 360, unlike the functional layer 350 in which the power generation reaction is performed, the power generation reaction is hardly performed. Therefore, the substrate layer 360 is not easily affected by the water vapor generated by the power generation reaction, and the partial pressure of water vapor is maintained at a relatively lower state 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 microstructure changes contained in the substrate layer downstream region Rb2 is small, and the performance of the single cell 110 is high. Does not deteriorate significantly. Further, by relatively increasing the Ni content Cb2 (wt%) in the substrate layer downstream region Rb2, the fuel electrode downstream region R2 of the fuel electrode 116 (functional layer downstream region Rf2 and substrate layer downstream region Rb2). The difference between the Ni content in the fuel electrode upstream side region R1 (the functional layer upstream side region Rf1 and the substrate layer upstream side region Rb1) can be reduced. As a result, it is possible to suppress the occurrence of current concentration in the region on the upstream side of the fuel gas FG in the flow direction of the fuel electrode 116, and it is possible to suppress damage to the single cell 110 due to the current concentration. 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 due to the operation while suppressing the deterioration of the initial performance of the single cell 110, which further causes the current concentration. Damage to the single cell 110 can be suppressed.

A-6. Performance evaluation:
The performance evaluation performed using the samples of the plurality of fuel cell stacks 100 will be described below. FIG. 9 is an explanatory diagram showing the performance evaluation result. As shown in FIG. 9, the samples S1 to S12 have different fuel poles 116 from each single cell 110 constituting the fuel cell stack 100. More specifically, in each single cell 110 constituting the fuel cell stack 100, each sample has a Ni content Cf1 (wt%) of the functional layer upstream region Rf1 and a Ni content of the substrate layer upstream region Rb1. The combination 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 is 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 10.

(Evaluation items and evaluation methods)
In this performance evaluation, two items, the initial average output and the deterioration rate, were evaluated. The initial average output is the average value of the outputs (V) of each single cell 110 constituting the fuel cell stack 100 in the initial state. When the initial average output was higher than 0.8 (V), it was judged to be acceptable. The deterioration rate is the ratio of the amount of output drop after 1000 h operation (difference between the initial average output and the average output after 1000 h operation) to the initial average output as a percentage. When the deterioration rate was lower than 1.0 (%), it was judged to be acceptable.

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

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

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

On the other hand, in the samples S2 to S8, the initial average output was higher than 0.8 (V) and the deterioration rate was lower than 1.0 (%), so that the samples were judged to be acceptable (◯ or ⊚). In the 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 the samples S2 to S8, the Ni content Cf1 (wt%) in the functional layer upstream region Rf1 is relatively high to suppress the deterioration of the initial performance of the single cell 110, and the functional layer downstream region Rf2. It is considered that the performance deterioration of the single cell 110 due to the power generation operation could be suppressed by making the Ni content Cf2 (wt%) relatively low. Further, in the 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. There is. Therefore, in the 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 region Rb1 on the upstream side of the substrate layer) could be reduced, and the damage of the single cell 110 due to the current concentration could be suppressed.

In sample S8, the initial average output was 0.81 (V) or less, so it was only judged as passing (〇), but in samples S2 to S7, the initial average output was 0.81 (V). Since it was higher, it was judged 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 of the Ni content Cf1 of the functional layer upstream region Rf1 to the Ni content Cf2 of Rf2 (Cf1 / Cf2) is relatively large at 2.200. Therefore, although it is possible to suppress the deterioration of the performance of the single cell 110, it is considered that the deterioration of the initial performance is not as good as that of the samples S2 to S7. In the 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, it is considered that in the samples S2 to S7, the deterioration of the performance of the single cell 110 due to the operation can be suppressed while effectively suppressing the deterioration of 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 due to 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 deterioration of the performance of the single cell 110 due to the operation can be suppressed while effectively suppressing the deterioration of the performance.

Further, from the result of the above performance evaluation, if the Ni content Cb2 (wt%) in the substrate layer downstream region Rb2 is made higher than the Ni content Cb1 (wt%) in the substrate layer upstream region Rb1 in the single cell 110, It was confirmed that the damage of the single cell 110 caused by the current concentration can be suppressed.

A-7. Analysis method of fuel pole 116:
A method for analyzing the Ni content in the fuel electrode 116 of the single cell 110 will be described below.

(Acquisition method of analytical image)
First, an analysis image used for the analysis of the fuel electrode 116 is acquired by the following method. That is, a cross section of the single cell 110 substantially parallel to the vertical direction (Z direction), including a cross section including the fuel pole upstream side region R1 of the fuel pole 116 and a cross section including the fuel pole downstream side region R2 of the fuel pole 116. Is set arbitrarily. An image in which the entire functional layer 350 of the fuel electrode 116 can be confirmed in the vertical direction at three different positions in each of the two set cross sections is acquired as an analysis image. More specifically, the portion presumed to be the boundary B1 (see FIG. 8) between the functional layer 350 and the electrolyte layer 112 of the fuel electrode 116 is 10 divided regions obtained by dividing the image vertically into 10 equal parts. The portion located in the uppermost divided region of the fuel electrode 116 and presumed to be 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 region. The image is taken with, for example, a scanning electron microscope (SEM) and acquired as an analytical image. The analysis image may be a binarized image after binarizing the image taken by the SEM. However, if the particles in the binarized image are significantly different from the actual form, the contrast of the image before the binarization process taken by SEM is adjusted, and the image after the adjustment is binarized. It may be. Further, the analysis image may be the image itself before the binarization process taken by SEM.

(Specification of each boundary)
The boundary B1 between the functional layer 350 and the electrolyte layer 112 of the fuel electrode 116 can be specified in each of the above analytical images based on the difference in the constituent substances between the functional layer 350 and the electrolyte layer 112, visual recognition, and the like. Further, the boundary B2 between the functional layer 350 and the substrate layer 360 can be specified in each of the above analysis images based on the difference in porosity between the functional layer 350 and the substrate layer 360 and the like.

(Specification of Ni content)
For the Ni content (wt%) in each region, SEM-EDS is used to identify Ni and YSZ in each region in each of the above analytical images, and the ratio of the Ni content to the total content of Ni and YSZ is calculated. It can be specified by calculating in wt%. Regarding the Ni content Cf2 in the functional layer downstream region Rf2 and the Ni content Cf1 in the functional layer upstream region Rf1, the functional layer 350 was divided into three in the vertical direction (Z direction) in each of the above analysis images. The Ni content is calculated for the portion located on the uppermost side (electrolyte layer 112 side), and the average value of the Ni content calculated in each analytical image is taken as the final Ni content. 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 of the above analysis images, each of the above analysis images is divided into 10 equal parts in the vertical direction. The Ni content of the portion of the substrate layer 360 in the lowermost divided region among the obtained 10 divided regions was calculated, and the average value of the Ni contents calculated in each analysis image was finally obtained. Ni content.

B. Modification example:
The technique disclosed in the present specification is not limited to the above-described embodiment, and can be transformed into various forms without departing from the gist thereof. For example, the following modifications are also possible. For example, the techniques disclosed herein can also be applied to known structures of fuel cells such as cylindrical and cylindrical flat plates.

Further, in the above embodiment, the SOFC that generates power by utilizing the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidizing agent gas is targeted, but the present invention comprises an electrolysis reaction of water. It is also applicable to an electrolytic single cell, which is a constituent unit of a solid oxide fuel cell (SOEC) that uses it to generate hydrogen, and an electrolytic cell stack including a plurality of electrolytic single cells. The configuration of the electrolytic cell stack is not described in detail here because it is known as described in, for example, International Publication No. 2012/165409, but is generally the same as the fuel cell stack 100 in the above-described embodiment. It is the composition of. 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, during the operation of the electrolytic cell stack, a voltage is applied between both electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), and the voltage is applied through the communication hole 108. Water vapor as a raw material gas is supplied to the fuel chamber 176. As a result, an electrolysis reaction of water occurs in each electrolytic cell, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out of the electrolytic cell stack through the communication hole 108.

Here, during the operation of the SOEC, water vapor as a gas supplied to the fuel electrode 116 side is subjected to a reaction in the electrolytic single cell while advancing in the gas flow direction, so that the gas in the functional layer 350 of the fuel electrode 116 The partial pressure of water vapor increases in the region on the upstream side in the flow direction. Therefore, even in SOEC, there is a problem that the microstructural change of Ni contained in the functional layer 350 is promoted by increasing the partial pressure of water vapor in a specific region of the functional layer 350, and the performance of the electrolytic single cell is likely to deteriorate. is there. Therefore, even 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%) in the region on one side of the direction, specifically the upstream side, is lower than the Ni content (wt%) in the region on the other side in the gas flow direction, specifically the downstream side. If the configuration is adopted, it is possible to suppress the deterioration of the performance of the electrolytic single cell due to the operation while suppressing the deterioration of the performance of the electrolytic single cell. Further, also in the electrolytic single cell, the fuel electrode 116 is arranged on the side opposite to the electrolyte layer 112 side of the functional layer 350, has a substrate layer 360 containing Ni and oxide ion conductive ceramics, and has a substrate layer. In 360, the Ni content (wt%) of the above-mentioned one side in the gas flow direction, specifically, the upstream side region is the Ni content in the above-mentioned other side in the gas flow direction, specifically, the downstream side region. If a configuration higher than the rate (wt%) is adopted, damage to the electrolytic single cell due to current concentration can be suppressed.

Further, the configuration of the fuel electrode 116 (relationship of Ni content, etc.) described in the above embodiment includes all the single cells 110 (or electrolytic single cells) included in the fuel cell stack 100 (or the electrolytic cell stack, the same applies hereinafter). It may be adopted in (the same applies hereinafter), or it may be adopted in only a part of the single cell 110 included in the fuel cell stack 100.

In addition, the techniques disclosed in the present specification can also be realized as the following application examples.
[Application example 1]
In a fuel cell single cell provided with 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, and has a functional layer.
In the functional layer, the Ni content Cf2 (wt%) of the region on the downstream side in the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is on the upstream side in the gas flow direction. A fuel cell single cell characterized in that the Ni content in the region is lower than Cf1 (wt%).
[Application example 2]
In the fuel cell single cell described in Application Example 1,
The ratio (Cf1 / Cf2) of the Ni content Cf1 of the upstream region to the Ni content Cf2 of the downstream region in the functional layer is larger 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 is further arranged on the opposite side of the functional layer from the electrolyte layer, and has a substrate layer containing Ni and oxide ion conductive ceramics.
In the substrate layer, the Ni content Cb2 (wt%) in the region on the downstream side in the gas flow direction is higher than the Ni content Cb1 (wt%) in the region on the upstream side in the gas flow direction. Fuel cell single cell.
[Application example 4]
In a fuel cell stack including 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 Example 1 to Application Example 3.
[Application example 5]
In an electrolytic single cell provided with 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, and has a functional layer.
In the functional layer, the Ni content Cf2 (wt%) of the region on the upstream side in the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is on the downstream side in the gas flow direction. An electrolytic single cell characterized in that the Ni content of the region is lower than Cf1 (wt%).
[Application example 6]
In the electrolytic single cell according to Application Example 5,
The ratio (Cf1 / Cf2) of the Ni content Cf1 of the downstream region to the Ni content Cf2 of the upstream region in the functional layer is larger than 1 and 1.851 or less. Electrolytic single cell.
[Application 7]
In the electrolytic single cell according to Application Example 5 or Application Example 6,
The fuel electrode is further arranged on the opposite side of the functional layer from the electrolyte layer, and has a substrate layer 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 including 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 Example 5 to Application Example 7.

22: Bolt 24: Nut 26: Insulation sheet 27: Gas passage member 28: Main body 29: Branch 40: Current collector 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 pole 116: Fuel pole 120: Separator 121: Hole 124: Joint 130: Air pole side frame 131: Hole 132: Oxidizing agent gas supply communication hole 133: Oxidizing agent gas discharge communication hole 134: Air pole side current collector 135: Current collector element 140: Fuel pole 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 part 146: Interconnector facing part 147: Connecting part 149: Spacer 150: Interconnector 161: Oxidant Gas introduction manifold 162: Oxidizing agent 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 (5)

An electrolyte layer containing a solid oxide, and the air electrode and the fuel electrode facing each other in a first direction across the electrolyte layer, the electrochemical reaction unit cells of the fuel cell single cell with a
The fuel electrode has a functional layer containing Ni and oxide ion conductive ceramics, and has a functional layer.
In the functional layer, the Ni content Cf2 (wt%) of the region on one side downstream of the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the gas flow. rather low from the direction of the Ni content of the other side region on the upstream side Cf1 (wt%),
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 larger than 1 and 1.851 or less. , Electrochemical reaction single cell. In an electrochemical reaction single cell as a fuel cell single cell 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, and has a functional layer.
In the functional layer, the Ni content Cf2 (wt%) of the region on one side downstream of the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the gas flow. The Ni content is lower than Cf1 (wt%) in the region on the other side upstream of the direction.
The fuel electrode is further arranged on the opposite side of the functional layer from the electrolyte layer, and has a substrate layer containing Ni and oxide ion conductive ceramics.
In the substrate layer, the Ni content Cb2 (wt%) of the region on one side in the gas flow direction is higher than the Ni content Cb1 (wt%) in the region on the other side in the gas flow direction. Characterized by an electrochemical reaction single cell. In an electrochemical reaction single cell as an electrolytic single cell 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, and has a functional layer.
In the functional layer, the Ni content Cf2 (wt%) of the region on one side upstream of the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the gas flow. The Ni content is lower than the Ni content Cf1 (wt%) in the region on the other side, which is the downstream side in the direction.
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 larger than 1 and 1.851 or less. , Electrochemical reaction single cell. In an electrochemical reaction single cell as an electrolytic single cell 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, and has a functional layer.
In the functional layer, the Ni content Cf2 (wt%) of the region on one side upstream of the gas flow direction orthogonal to the first direction of the gas supplied to the fuel electrode side is the gas flow. The Ni content is lower than the Ni content Cf1 (wt%) in the region on the other side, which is the downstream side in the direction.
The fuel electrode is further arranged on the opposite side of the functional layer from the electrolyte layer, and has a substrate layer containing Ni and oxide ion conductive ceramics.
In the substrate layer, the Ni content Cb2 (wt%) of the region on one side in the gas flow direction is higher than the Ni content Cb1 (wt%) in the region on the other side in the gas flow direction. Characterized by an electrochemical reaction single cell. In an electrochemical reaction cell stack including a plurality of electrochemical reaction single cells arranged side by side in the first direction.
The electrochemical reaction cell stack according to any one of claims 1 to 4 , wherein at least one of the plurality of electrochemical reaction single cells is the electrochemical reaction single cell.

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