JP7349847B2 - Electrochemical cell, electrochemical reaction cell stack - Google Patents

Description

TECHNICAL FIELD The technology disclosed herein relates to electrochemical cells.

Solid oxide fuel cells (hereinafter referred to as "SOFC") are known as one type of fuel cells that generate electricity using an electrochemical reaction between hydrogen and oxygen. A fuel cell single cell (hereinafter simply referred to as a "single cell"), which is a structural unit of SOFC, has an electrolyte layer containing a solid oxide and a predetermined direction (hereinafter referred to as "first direction") with respect to the electrolyte layer. ), and a fuel electrode is provided on the other side of the electrolyte layer in the first direction.

As a fuel electrode constituting a single cell, a fuel electrode having a porous layer (hereinafter referred to as "active layer") containing an electronically conductive substance and an ionically conductive oxide is sometimes used. Specifically, a metal containing Ni (nickel) is used as the electron conductive substance, and as the ion conductive oxide, for example, YSZ (yttria stabilized zirconia), which is an ion conductive oxide having oxygen ion conductivity, is used. ) is sometimes used. The active layer mainly generates electrons and water vapor by reacting oxygen ions supplied to the active layer from the electrolyte layer with hydrogen, etc. contained in the fuel gas supplied to the fuel chamber facing the fuel electrode. Demonstrate function.

Furthermore, the above-mentioned SOFC can be used as a solid oxide electrolytic cell (hereinafter referred to as "SOEC") by energizing in the opposite direction, which eliminates surplus, which is an issue in the process of introducing renewable energy. It is also known to be used as an energy storage technology that converts water vapor into hydrogen using electricity. In this case, the active layer mainly reacts water vapor contained in the fuel gas supplied to the fuel chamber facing the fuel electrode to generate oxygen ions and hydrogen that are supplied from the active layer to the electrolyte layer. Demonstrate function.

JP2019-091584A

In the SOFC having the above configuration, the metal (metal containing Ni, hereinafter simply referred to as "metal") present in the fuel electrode may aggregate, which may deteriorate the performance of the electrochemical cell.

The ion conductive oxide present in the fuel electrode functions as an obstacle that suppresses the movement of metal (metal containing Ni) present in the fuel electrode. The larger the cross-sectional area of the ion-conducting oxide, the more effectively the ion-conducting oxide inhibits metal migration. By the ion-conducting oxide functioning as an obstacle in this manner, metal aggregation is suppressed and, as a result, deterioration in the performance of the single cell is suppressed. Therefore, in the SOFC having the above configuration, the larger the total cross-sectional area of each ion-conductive oxide present in the fuel electrode in the cross section parallel to the first direction, the more the metal aggregation is suppressed, and thereby Performance deterioration of the single cell can be suppressed.

However, there is a problem in that simply increasing the total cross-sectional area of each ion-conductive oxide present in the fuel electrode cannot sufficiently suppress performance deterioration of the single cell.

It is known that Ni agglomeration progresses more easily under conditions of higher oxygen partial pressure, but in the electrolytic single cell that is the structural unit of SOEC, water vapor is supplied to the fuel electrode side As a result, the oxygen partial pressure tends to be high and Ni agglomeration tends to proceed, which becomes a bigger problem. Note that in this specification, a single fuel cell cell and a single electrolytic cell are collectively referred to as an electrochemical cell.

This specification discloses a technique that can solve the above-mentioned problems.

The technology disclosed in this specification can be realized, for example, as the following form.

(1) The electrochemical cell disclosed herein includes an electrolyte layer containing a solid oxide, an air electrode disposed on one side in a first direction of the electrolyte layer, and an air electrode disposed on one side in a first direction of the electrolyte layer. An electrochemical cell comprising: a fuel electrode disposed on the other side, the fuel electrode containing a metal containing Ni (hereinafter simply referred to as "metal") and an ion-conductive oxide; In at least one cross section parallel to direction 1, for a specific region where the distance from the interface with the electrolyte layer in the fuel electrode is up to 10 μm, the total area of each ion conductive oxide relative to the area of the specific region. The area ratio, which is a ratio, is Sa%, the pore area ratio, which is the ratio of the total area of each pore existing in a specific area to the area of the specific area, is Sb%, and the number of pores per unit area in the specific area is N. pieces/μm ² , formula (1): Sa≧30 and formula (2): Sb/N≦54 are satisfied. The inventors of the present application have newly discovered that when the above formulas (1) and (2) are satisfied, deterioration in the performance of the electrochemical cell can be suppressed. Although the reason why the above effect is obtained by the above structure is not necessarily clear, it is presumed as follows.

In an electrochemical cell that does not satisfy the above formula (1) or formula (2), the above metal (hereinafter simply referred to as "metal") present in the fuel electrode aggregates, which reduces the performance of the electrochemical cell. There are things to do.

The ion-conducting oxide functions as an obstacle that suppresses the movement of metal. The larger the cross-sectional area of the ion-conducting oxide, the more effectively the ion-conducting oxide inhibits metal migration. By the ion-conducting oxide functioning as an obstacle in this way, metal aggregation is suppressed and, as a result, deterioration in the performance of the electrochemical cell is suppressed. Therefore, the larger Sa (ratio of the total area of each ion-conducting oxide to the area of the specific region) is, the more the aggregation of metal is suppressed, and the deterioration of the performance of the electrochemical cell is suppressed.

Moreover, the smaller the total cross-sectional area of the pores of the fuel electrode, the more suppressed is the aggregation of metal, and the more suppressed is the deterioration of the performance of the electrochemical cell. Therefore, the smaller the value of Sb (pore area ratio, which is the ratio of the total area of each pore existing in a specific region to the area of the specific region), the more the aggregation of metal is suppressed, and the lower the performance of the electrochemical cell. suppressed. Further, the smaller the value of N (the number of pores per unit area in a specific region of the fuel electrode), the higher the probability that the cross-sectional area of the pores (particularly the width in the direction perpendicular to the gas flow direction) is large. The larger the cross-sectional area of the pores, the easier the movement of metal, and therefore the more likely metal aggregation will occur. Therefore, the performance of the electrochemical cell is likely to deteriorate. Therefore, the larger the value of N, the more agglomeration of metal is suppressed, and the deterioration of the performance of the electrochemical cell is more likely to be suppressed.

In addition to Sb, the inventor of the present application focused on the index Sb/N, which takes N into consideration, and found that if a configuration in which the value of Sa is relatively large and the value of Sb/N is relatively small is adopted, the electrochemical cell can be improved. They have newly discovered that it is possible to suppress the decline in performance.

(2) In the electrochemical cell, the average diameter D of the pores in the specific region may be 0.50 μm or less. According to this electrochemical cell, since the average diameter D of the pores in the specific region is sufficiently small, metal aggregation can be more effectively suppressed, and deterioration in the performance of the electrochemical cell can be more effectively suppressed. be able to.

(3) In the above electrochemical cell, when the number of three-phase interfaces where the metal, the ion conductive oxide, and the pores intersect per unit area in a specific region is n pieces/μm ² , formula (3): A configuration may be adopted that satisfies n/N≦2.8. According to this electrochemical cell, (3): n/N≦2.8 is satisfied. The inventors of the present application have newly discovered that when the above formula (3): n/N≦2.8 is satisfied, deterioration in the performance of the electrochemical cell can be more effectively suppressed. Although the reason why the above effect is obtained by the above structure is not necessarily clear, it is presumed as follows.

The larger the average diameter of the metal, the fewer the number of the three-phase interfaces that function as electrode reaction fields, and the smaller the surface area of the metal (metal particles), the smaller the area of the metal exposed to the gas phase. Since surface diffusion of metal is less likely to occur, aggregation of metal is suppressed, and deterioration in the performance of the electrochemical cell is easily suppressed. Therefore, the smaller the value of n (the number of three-phase interfaces per unit area in a specific region), the more agglomeration of metals is suppressed, and the deterioration of the performance of the electrochemical cell is more likely to be suppressed. Furthermore, as described above, the larger the N (the number of pores per unit area in a specific region), the more likely metal aggregation will occur, and therefore the performance of the electrochemical cell will tend to deteriorate. In addition to n, the inventors of the present application focused on an index n/N that takes N into consideration, and found that if a configuration in which the value of n/N is relatively small is adopted, deterioration in the performance of the electrochemical cell can be more effectively suppressed. We have discovered that it is possible to suppress this phenomenon.

Note that the technology disclosed in this specification can be realized in various forms, such as an electrochemical cell (a fuel cell single cell or an electrolytic single cell), an electrochemical reaction system including a plurality of electrochemical cells, etc. It can be realized in the form of a cell stack (fuel cell stack or electrolytic cell stack), a manufacturing method thereof, and the like.

FIG. 1 is a perspective view showing the external configuration of a fuel cell stack 100 in this embodiment. 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. 1. FIG. FIG. 2 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position III-III in FIG. 1. FIG. 3 is an explanatory diagram showing 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. FIG. 4 is an explanatory diagram showing a YZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 3. FIG. FIG. 5 is an explanatory diagram showing an enlarged YZ cross-sectional configuration of a portion of the single cell 110 (X1 section in FIG. 5). FIG. 7 is an explanatory diagram showing an enlarged detailed structure of the active layer 320 of the fuel electrode 116 (the YZ cross-sectional structure of the X2 section in FIG. 6). FIG. 2 is an explanatory diagram showing an XZ cross-sectional configuration of an electrolytic cell stack 100A having a configuration similar to that of the fuel cell stack 100 of the present embodiment. 9 is an explanatory diagram showing a YZ cross-sectional configuration of the electrolytic cell stack 100A shown in FIG. 8. FIG. 9 is an explanatory diagram showing an XZ cross-sectional configuration of two mutually adjacent electrolytic cell units 102A at the same position as the cross section shown in FIG. 8. FIG. 10 is an explanatory diagram showing a YZ cross-sectional structure of two electrolytic cell units 102A adjacent to each other at the same position as the cross section shown in FIG. 9. FIG. It is an explanatory diagram showing a performance evaluation result.

A. Embodiment:
A-1. composition:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of a fuel cell stack 100 in this 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 III-III in FIG. Each figure shows mutually orthogonal XYZ axes for specifying directions. In this specification, for convenience, the positive Z-axis direction will be referred to as the upward direction, and the negative Z-axis direction will be referred to as the downward direction, but the fuel cell stack 100 is actually oriented in a different direction. may be installed. The same applies to FIG. 4 and subsequent figures.

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

A plurality of holes (eight in this embodiment) that penetrate in the vertical direction are formed in the peripheral edge of each layer (power generation unit 102, end plates 104, 106) that constitutes the fuel cell stack 100 around the Z-axis direction. The corresponding holes formed in each layer 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 constitute the communication holes 108 may also be referred to as the communication holes 108.

A bolt 22 extending in the vertical direction is inserted into each communication hole 108, and the fuel cell stack 100 is fastened by the bolt 22 and nuts 24 fitted on both sides of the bolt 22. 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 that constitutes the upper end of the fuel cell stack 100, An insulating sheet 26 is interposed between the nut 24 fitted on the other side (lower side) of the nut 22 and the lower surface of the end plate 106 that constitutes the lower end of the fuel cell stack 100. However, at a location where a gas passage member 27 (described later) is provided, an insulating sheet is placed between the nut 24 and the surface of the end plate 106, and 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, 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 ensured between the outer circumferential surface of the shaft portion of each bolt 22 and the inner circumferential surface of each communication hole 108. As shown in FIGS. 1 and 2, near the midpoint of one side (the side in the positive X-axis direction of the two sides parallel to the Y-axis) on the outer periphery of the fuel cell stack 100 around the Z-axis direction. The space formed by the located bolt 22 (bolt 22A) and the communication hole 108 into which the bolt 22A is inserted is a space into which oxidizing gas OG is introduced from outside the fuel cell stack 100, and the oxidizing gas OG is It functions as an oxidizing gas introduction manifold 161 that is a gas flow path for supplying the power generation unit 102, and inside the side opposite to this side (the side on the negative side of the X-axis of the two sides parallel to the Y-axis). The space formed by the bolt 22 (bolt 22B) located near the point and the communication hole 108 through which the bolt 22B is inserted contains oxidant off-gas OOG, which is gas discharged from the air chamber 166 of each power generation unit 102. It functions as an oxidizing gas exhaust manifold 162 that exhausts the oxidant gas to the outside of the fuel cell stack 100. Note that in this embodiment, air, for example, is used as the oxidant gas OG.

Further, as shown in FIGS. 1 and 3, the midpoint of one side (the side in the positive Y-axis direction of the two sides parallel to the X-axis) on the outer periphery of the fuel cell stack 100 around the Z-axis direction The space formed by the bolt 22 (bolt 22D) located nearby and the communication hole 108 into which the bolt 22D is inserted allows fuel gas FG to be introduced from outside the fuel cell stack 100, and the fuel gas FG to be passed through the space. A bolt that functions as a fuel gas introduction manifold 171 for supplying to the power generation unit 102 and is located near the midpoint of the side opposite to this side (the side on the negative side of the Y-axis of the two sides parallel to the X-axis) 22 (bolts 22E) and the communication holes 108 into which the bolts 22E are inserted, the space is configured to transport fuel off-gas FOG, which is 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 exhaust manifold 172 that discharges fuel gas to. In this embodiment, a hydrogen-rich gas obtained by reforming city gas, for example, 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 cylindrical main body 28 and a hollow cylindrical branch 29 branching from a side surface of the main body 28 . The hole in the branch portion 29 communicates with the hole in the main body portion 28 . A gas pipe (not shown) is connected to the branch portion 29 of each gas passage member 27. Further, as shown in FIG. 2, the hole in the main body 28 of the gas passage member 27 located at the position of the bolt 22A forming the oxidant gas introduction manifold 161 communicates with the oxidant gas introduction manifold 161, A hole in the main body portion 28 of the gas passage member 27 located 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 holes in the main body 28 of the gas passage member 27 disposed at the positions of the bolts 22D forming the fuel gas introduction manifold 171 communicate with the fuel gas introduction manifold 171, and A hole in the main body portion 28 of the gas passage member 27 located at the position of the bolt 22E forming the exhaust manifold 172 communicates with the fuel gas exhaust manifold 172.

(Configuration of end plates 104, 106)
The pair of end plates 104 and 106 are substantially rectangular flat plate-shaped conductive members, and are made of stainless steel, for example. One end plate 104 is arranged above the uppermost power generation unit 102, and the other end plate 106 is arranged below the lowermost power generation unit 102. 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)
FIG. 4 is an explanatory diagram showing the XZ cross-sectional structure of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 2, and FIG. FIG. 2 is an explanatory diagram showing a YZ cross-sectional configuration of two power generation units 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 frame 130. It includes a current collector 144 and a pair of interconnectors 150 forming the uppermost layer and the lowermost layer of the power generation unit 102. Holes corresponding to the communication holes 108 into which the bolts 22 described above are inserted are formed in the peripheral edges of the separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150 around the Z-axis 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 reaction gases from mixing between the power generation units 102 . In addition, in this embodiment, when two power generation units 102 are arranged adjacently, one interconnector 150 is shared by the two adjacent power generation units 102. That is, the upper interconnector 150 in a certain power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Furthermore, since the fuel cell stack 100 includes a pair of end plates 104 and 106, the uppermost power generation unit 102 in the fuel cell stack 100 does not include the upper interconnector 150, and the lowermost power generation unit 102 does not include the upper interconnector 150. The power generation unit 102 does not include a lower interconnector 150 (see FIGS. 2 and 3).

The single cell 110 includes an electrolyte layer 112, an air electrode (cathode) 114 disposed above the electrolyte layer 112, a fuel electrode (anode) 116 disposed below the electrolyte layer 112, and an air electrode (cathode) 114 disposed above the electrolyte layer 112. and an intermediate layer 180 disposed between the pole 114 and the intermediate layer 180 . Note that the upper side corresponds to one side in the first direction in the claims, and the lower side corresponds to the other side in the first direction in the claims. In this embodiment, the thickness (vertical size) of the fuel electrode 116 is thicker than the thickness of the air electrode 114 and the electrolyte layer 112, and the fuel electrode 116 supports the other layers that constitute the unit cell 110. That is, the single cell 110 of this embodiment is a fuel electrode supporting type single cell.

The electrolyte layer 112 is a substantially rectangular flat plate-shaped member when viewed in the Z-axis direction, and is a dense layer (low porosity). The electrolyte layer 112 contains, for example, a solid oxide such as YSZ (yttria stabilized zirconia). In this way, the single cell 110 of this embodiment is a solid oxide fuel cell (SOFC) that uses a solid oxide as an electrolyte.

The air electrode 114 is a substantially rectangular plate-shaped member smaller than the electrolyte layer 112 when viewed in the Z-axis direction, and is a porous layer (having a higher porosity than the electrolyte layer 112). The air electrode 114 is formed of, for example, a perovskite oxide (for example, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide), LNF (lanthanum nickel iron)).

The fuel electrode 116 is a substantially rectangular flat member having substantially the same size as the electrolyte layer 112 when viewed in the Z-axis direction, and is a porous layer (having a higher porosity than the electrolyte layer 112). FIG. 6 is an explanatory diagram showing an enlarged YZ cross-sectional configuration of a portion of the single cell 110 (X1 section in FIG. 5). As shown in FIG. 6, the fuel electrode 116 includes a support layer 310 forming the lower surface of the fuel electrode 116, and an active layer 320 disposed between the support layer 310 and the electrolyte layer 112. In this embodiment, active layer 320 is adjacent to electrolyte layer 112 and support layer 310 is adjacent to active layer 320.

The active layer 320 mainly functions to generate electrons and water vapor by causing oxygen ions supplied from the electrolyte layer 112 to react with hydrogen or the like contained in the fuel gas FG. The active layer 320 includes Ni, which is an electron conductive material, and an ion conductive oxide (eg, YSZ), which is a material having oxygen ion conductivity. The thickness of the active layer 320 is, for example, 10 μm to 40 μm. The support layer 310 mainly functions to support the active layer 320, the electrolyte layer 112, and the air electrode 114. The thickness of the support layer 310 is, for example, 200 μm to 1000 μm. In this embodiment, the support layer 310 also includes Ni, which is an electron conductive material, and an ion conductive oxide (eg, YSZ), which is a material having oxygen ion conductivity.

The intermediate layer 180 is a substantially rectangular plate-shaped member, and is formed of a solid oxide having ion conductivity, such as SDC, GDC, LDC (lanthanum-doped ceria), and YDC (yttrium-doped ceria). The intermediate layer 180 is formed into a high-resistance layer by the reaction between Sr contained in the air electrode 114 and the transition element (for example, Zr) contained in the electrolyte layer 112 under high-temperature conditions such as during operation of the fuel cell stack 100. (For example, SrZrO ₃ ) functions as a reaction prevention layer that suppresses formation. Note that, since the intermediate layer 180 has ionic conductivity, it also has a function of moving oxide ions generated by an ionization reaction of oxygen molecules contained in the oxidant gas OG at the air electrode 114 to the electrolyte layer 112.

As shown in FIGS. 4 and 5, the separator 120 is a frame-shaped member in which a substantially rectangular hole 121 is formed near the center and penetrates in the vertical direction, and is made of, for example, metal. The surrounding portion of the hole 121 in the separator 120 faces the peripheral edge 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 at opposing portions. The separator 120 separates an air chamber 166 facing the air electrode 114 and a fuel chamber 176 facing the fuel electrode 116, thereby preventing gas from leaking from one electrode side to the other electrode side at the periphery of the single cell 110. suppressed.

The air electrode side frame 130 is a frame-like member in which a substantially rectangular hole 131 is formed near the center and penetrates in the vertical direction, and is made of an insulator such as mica, for example. 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 on the side opposite to the side facing the electrolyte layer 112 and the peripheral edge of the surface of the interconnector 150 on the side opposite to the air electrode 114. . Further, the pair of interconnectors 150 included in the power generation unit 102 are electrically insulated by the air electrode side frame 130. The air electrode side frame 130 also includes an oxidizing gas supply communication hole 132 that communicates between the oxidizing gas introduction manifold 161 and the air chamber 166, and an oxidizing gas supply communication hole 132 that communicates between the air chamber 166 and the oxidizing gas discharge manifold 162. A discharge communication hole 133 is formed.

The fuel electrode side frame 140 is a frame-shaped member in which a substantially rectangular hole 141 that vertically penetrates is formed near the center, and is made of metal, for example. The 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 . The fuel electrode side frame 140 also includes a fuel gas supply communication hole 142 that communicates between the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that communicates between the fuel chamber 176 and the fuel gas discharge manifold 172. is formed.

The fuel electrode side current collector 144 is arranged within the fuel chamber 176. The fuel electrode side current collector 144 includes an interconnector facing part 146, an electrode facing part 145, and a connecting part 147 connecting the electrode facing part 145 and the interconnector facing part 146, and is made of, for example, nickel or nickel alloy. , stainless steel, etc. 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 in contact with the surface of the interconnector 150 on the side opposite to the fuel electrode 116. are in contact. However, as described above, since the lowest 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 is located on the lower end plate. 106 is in contact. Since the fuel electrode side current collector 144 has such a configuration, it electrically connects the fuel electrode 116 and the interconnector 150 (or the end plate 106). Note that a spacer 149 made of mica, for example, is arranged between the electrode facing part 145 and the interconnector facing part 146. Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to temperature cycles and reaction gas pressure fluctuations, and connects the fuel electrode 116 and the interconnector 150 (or end plate 106) via the fuel electrode side current collector 144. Good electrical connection is maintained.

The air electrode side current collector 134 is arranged within the air chamber 166. The air electrode side current collector 134 is composed of a plurality of substantially square columnar current collector elements, and is made of, for example, ferritic stainless steel. The air electrode side current collector 134 is in contact with the surface of the air electrode 114 on the side opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 on the side opposite to the air electrode 114. However, as described above, since the uppermost power generation unit 102 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 is connected to the upper end plate. 104 is in contact. Since the air electrode side current collector 134 has such a configuration, it electrically connects the air electrode 114 and the interconnector 150 (or the end plate 104). Note that the air electrode side current collector 134 and the interconnector 150 may be configured as an integral member. Further, the air electrode side current collector 134 may be covered with a conductive coat, and a conductive bonding layer is interposed between the air electrode 114 and the air electrode side current collector 134 to bond them together. You may do so.

A-2. Operation of fuel cell stack 100:
As shown in FIGS. 2 and 4, the oxidizing gas OG is supplied through a gas pipe (not shown) connected to the branch part 29 of the gas passage member 27 provided at the position of the oxidizing gas introduction manifold 161. Then, the oxidizing gas OG is supplied to the oxidizing gas introduction manifold 161 through the branch portion 29 of the gas passage member 27 and the hole of the main body 28, and is supplied to the oxidizing gas introduction manifold 161 from the oxidizing gas introduction manifold 161 to the oxidizing gas OG of each power generation unit 102. The agent gas is supplied to the air chamber 166 via the agent gas supply communication hole 132. Further, as shown in FIGS. 3 and 5, fuel gas FG is supplied via a gas pipe (not shown) connected to a branch part 29 of the gas passage member 27 provided at the position of the fuel gas introduction manifold 171. Then, the fuel gas FG is supplied to the fuel gas introduction manifold 171 via the branch part 29 of the gas passage member 27 and the hole of the main body part 28, and is connected to the fuel gas supply communication of each power generation unit 102 from the fuel gas introduction manifold 171. The fuel chamber 176 is supplied through the hole 142 .

When the oxidant gas OG is supplied to the air chamber 166 of each power generation unit 102 and the fuel gas FG is supplied to the fuel chamber 176, power generation is performed in the single cell 110 by an electrochemical reaction between the oxidant gas OG and the fuel gas FG. be exposed. 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 electrically connected via the fuel electrode 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 electrical energy generated in each power generation unit 102 is extracted from the end plates 104 and 106 that function as output terminals of the fuel cell stack 100. Note that SOFC generates power at a relatively high temperature (for example, 700°C to 1000°C), so after startup, the fuel cell stack 100 is not connected to the heater ( (not shown).

As shown in FIGS. 2 and 4, 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, and further oxidized. The fuel cell stack 100 is passed through the main body portion 28 of the gas passage member 27 provided at the position of the agent gas discharge manifold 162 and the hole in the branch portion 29, and through a gas pipe (not shown) connected to the branch portion 29. is discharged to the outside. 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. Externally through the main body 28 and branch section 29 of the gas passage member 27 provided at the exhaust manifold 172, and through a gas pipe (not shown) connected to the branch section 29, be discharged.

A-3. Detailed configuration of active layer 320 of fuel electrode 116:
Next, the configuration of the active layer 320 of the fuel electrode 116 will be described in more detail. FIG. 7 is an explanatory diagram showing the detailed configuration of the active layer 320 of the fuel electrode 116. FIG. 7 shows an enlarged YZ cross-sectional configuration of a portion of the active layer 320 (X2 section in FIG. 6).

As described above, the active layer 320 of the fuel electrode 116 includes Ni, which is an electron conductive material, and YSZ, which is an ion conductive oxide having oxygen ion conductivity. FIG. 7 shows Ni particles Pn as particles of an electron conductive substance contained in the active layer 320, YSZ particles Py as particles of an oxygen ion conductive substance, pores PO, Ni particles Pn and YSZ particles Py. A three-phase interface I intersecting with the pore PO is schematically shown. FIG. 6 shows a position Ba at a distance of 10 μm from the interface with the electrolyte layer 112 in the fuel electrode 116.

In the fuel cell stack 100 of this embodiment, in the cross section shown in FIG. 7 (or FIG. 5, or FIG. 6), the specific area SA is an area where the distance from the interface with the electrolyte layer 112 in the fuel electrode 116 is up to 10 μm. , the area ratio, which is the ratio of the total area of each ion conductive oxide (YSZ particles Py in this embodiment) to the area of the specific area SA, is Sa (hereinafter simply referred to as "the area ratio of the ion conductive oxide in the specific area SA"). The ratio of the total area of each pore existing in the specific area SA to the area of the specific area SA (hereinafter also referred to as the ``pore area ratio of the specific area SA'') is Sb%. When the number of pores per unit area in the specific area SA is N/μm ² , formula (1): Sa≧30 and formula (2): Sb/N≦54 are satisfied. In this embodiment, the cross section shown in FIG. 7 (or FIG. 5, or FIG. 6) corresponds to "at least one cross section parallel to the first direction" in the claims.

In the fuel cell stack 100 of this embodiment, the average diameter D of the pores in the specific area SA is 0.50 μm or less.

In the fuel cell stack 100 of this embodiment, the number of three-phase interfaces (three-phase interfaces where Ni particles Pn, YSZ particles Py, and pores PO intersect) I per unit area in the specific area SA is n pieces/μm ² Then, formula (3): n/N≦2.8 is satisfied.

A-4. Method for manufacturing fuel cell stack 100:
The method for manufacturing the fuel cell stack 100 in this embodiment is, for example, as follows.

(Preparation of green sheet for fuel electrode support layer)
Organic beads as a pore-forming material, butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol were added to a mixed powder of NiO powder and YSZ powder, and the mixture was placed in a ball mill. Mix to prepare slurry. Organic beads are, for example, spherical particles formed from polymers such as polymethyl methacrylate and polystyrene. The obtained slurry is made into a thin film by a doctor blade method to prepare a green sheet for a fuel electrode support layer having a predetermined thickness (for example, 200 μm to 300 μm). Note that the mixing ratio of NiO powder and YSZ powder when producing the green sheet for the fuel electrode support layer may be appropriately set as long as the performance is satisfied.

(Preparation of green sheet for fuel electrode active layer)
Butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added to a mixed powder of NiO powder and YSZ powder, and mixed in a ball mill to prepare a slurry. Note that, similar to the above-described method for producing a green sheet for a fuel electrode support layer, organic beads as a pore-forming material may be added when preparing the slurry. The obtained slurry is made into a thin film by a doctor blade method to produce a green sheet for a fuel electrode active layer having a predetermined thickness (for example, 10 μm to 40 μm). Note that the mixing ratio of NiO powder and YSZ powder when producing the green sheet for the fuel electrode active layer may be appropriately set as long as the performance is satisfied.

(Preparation of green sheet for electrolyte layer)
A butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added to the YSZ powder and mixed in a ball mill to prepare a slurry. The obtained slurry is made into a thin film by a doctor blade method to produce a green sheet for an electrolyte layer having a predetermined thickness (for example, 10 μm).

(Preparation of laminate of electrolyte layer 112 and fuel electrode 116)
The green sheet for the fuel electrode support layer, the green sheet for the fuel electrode active layer, and the green sheet for the electrolyte layer are attached and degreased at a predetermined temperature (for example, about 280° C.). Furthermore, the degreased green sheet laminate is fired at a predetermined temperature (for example, about 1350° C.). Thereby, a laminate of the electrolyte layer 112 and the fuel electrode 116 (active layer 320 and support layer 310) is obtained.

(Formation of intermediate layer 180)
Polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent are added and mixed to the GDC powder, and the viscosity is adjusted to prepare a paste for the intermediate layer. The adjusted intermediate layer paste is applied to the surface of the electrolyte layer 112 side of the above-mentioned laminate of the electrolyte layer 112 and the fuel electrode 116 by, for example, screen printing, and is fired at, for example, 1200°C. As a result, an intermediate layer 180 is formed.

(Formation of air electrode 114)
An air electrode paste is prepared by mixing LSCF powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent, and adjusting the viscosity. The prepared air electrode paste is applied to the surface of the intermediate layer 180 in the above-described laminate of the intermediate layer 180, electrolyte layer 112, and fuel electrode 116 by screen printing, and dried to apply the air electrode paste. The resulting laminate is fired at a predetermined firing temperature (for example, 1100°C). As a result, the air electrode 114 is formed, and the single cell 110 including the fuel electrode 116, the electrolyte layer 112, and the air electrode 114 is manufactured.

After producing a plurality of unit cells 110 according to the method described above, an assembly process (for example, a process of attaching other members such as a separator 120 to each unit cell 110, a process of stacking a plurality of unit cells 110, and a process of fastening with bolts 22) process, etc.). Through the above steps, manufacturing of the fuel cell stack 100 is completed. Note that after that, in order to put the fuel cell stack 100 into a state where power generation operation is possible, a reduction step is performed to reduce the active layer 320 of the fuel electrode 116 (that is, reduce NiO contained in the active layer 320 to Ni). . The reduction process is realized, for example, by exposing the fuel electrode 116 to a hydrogen atmosphere at a predetermined temperature for a predetermined time. Note that the reducing gas used in the reduction step is not limited to hydrogen, and may be other gas such as methane gas. Through the above steps, the manufacturing of the fuel cell stack 100 that is ready for power generation operation is completed.

A-5. How to adjust each characteristic of specific area SA:
When manufacturing the fuel cell stack 100 according to the method described above, the specific area SA of the fuel electrode 116 constituting the fuel cell stack 100 (in the cross section shown in FIG. 7, the distance from the interface with the electrolyte layer 112 in the fuel electrode 116 is For example, each characteristic of the area (up to 10 μm) can be adjusted as follows. Note that the method for specifying each characteristic of the specific area SA will be explained in "A-7. Method for specifying each characteristic of the specific area SA" below.

(Area ratio Sa of ion conductive oxide in specific area SA)
The area ratio (ratio of the total area of each ion conductive oxide to the area of the specific area SA) Sa of the ion conductive oxide (in this embodiment, YSZ particles Py) in the specific area SA is adjusted, for example, by This can be achieved by adjusting the amount of YSZ particles Py added when preparing the slurry for producing the green sheet for the extremely active layer. Specifically, when preparing the slurry for producing the green sheet for the fuel electrode active layer, the larger the amount of YSZ particles Py added, the larger the area ratio Sa of the ion conductive oxide in the specific area SA. Become.
(Pore area ratio Sb of specific area SA)
The pore area ratio (the ratio of the total area of each pore existing in the specific area SA to the area of the specific area SA) Sb in the specific area SA of the fuel electrode 116 can be adjusted by adjusting the amount of the YSZ particles Py added. This can be achieved by adjusting the amount of pore-forming material added as an additional parameter, for example, when preparing a slurry for producing a green sheet for an anode active layer, although it may be increased or decreased. Specifically, when preparing a slurry for producing a green sheet for an anode active layer, the greater the amount of pore-forming material added, the higher the pore area ratio S of the specific area SA becomes.

(Number of pores per unit area in specific area SA N)
Adjustment of the number N of pores per unit area in the specific area SA increases or decreases depending on the amount of YSZ particles Py added and the amount of pore-forming material added, but as further parameters, for example, the green sheet for the fuel electrode active layer This can be achieved by adjusting the particle size of the pore-forming material when preparing the slurry for producing the pore-forming material. Specifically, when preparing the slurry for producing the green sheet for the fuel electrode active layer, the smaller the particle size of the pore-forming material, the greater the number N of pores per unit area in the specific area SA. .

(Average diameter D of pores in specific area SA)
Adjustment of the average diameter D of the pores in the specific area SA increases or decreases depending on the amount of the YSZ particles Py added, the amount of the pore-forming material added, and the particle size. This can be achieved by adjusting the mixing ratio of Ni particles Pn and YSZ particles Py when preparing a slurry for producing. Specifically, when preparing a slurry for producing a green sheet for an anode active layer, the larger the abundance ratio of Ni particles Pn to the abundance ratio of YSZ particles Py, the greater the average diameter of pores in the specific area SA. D becomes larger.

The number n of three-phase interfaces (three-phase interfaces where Ni particles Pn, YSZ particles Py, and pores PO intersect) I per unit area in the specific area SA can be adjusted by adjusting the amount of the YSZ particles Py added and the pore-forming material. It increases or decreases depending on the amount added, the particle size, and the abundance ratio of Ni particles Pn and YSZ particles Py, but as an additional parameter, for example, when preparing a slurry for producing a green sheet for the fuel electrode active layer, Ni particles Pn This can be achieved by adjusting the particle size of. Specifically, when preparing a slurry for producing a green sheet for an anode active layer, the smaller the particle size of the Ni particles Pn, the smaller the three-phase interface I per unit area in the specific area SA. The number n increases.

A-6. Application to SOEC:
In the above, an application example (fuel cell stack 100 ), the invention related to the fuel cell stack 100 described above includes an electrolytic single cell that is a constituent unit of a SOEC (solid oxide electrolytic cell) that generates hydrogen using the electrolysis reaction of water, It is similarly applicable to an electrolytic cell stack comprising a plurality of electrolytic single cells. An example (electrolytic cell stack 100A) in which the invention is applied to SOEC will be described below.

A-6-1. Configuration of electrolytic cell stack 100A:
First, the configuration of the electrolytic cell stack 100A will be explained. FIG. 8 is an explanatory diagram showing an XZ cross-sectional configuration of an electrolytic cell stack 100A having a configuration similar to that of the fuel cell stack 100 described above. FIG. 9 is an explanatory diagram showing a YZ cross-sectional configuration of the electrolytic cell stack 100A shown in FIG. 8. FIG. 10 is an explanatory diagram showing an XZ cross-sectional structure of two mutually adjacent electrolytic cell units 102A at the same position as the cross-section shown in FIG. FIG. 11 is an explanatory diagram showing a YZ cross-sectional structure of two mutually adjacent electrolytic cell units 102A at the same position as the cross-section shown in FIG.

The configuration of the electrolytic cell stack 100A is generally the same as that of the fuel cell stack 100 described above. Further, the basic configuration of the electrolytic cell stack is known, for example, as described in Japanese Patent Application Laid-Open No. 2016-81813. Therefore, basically, the "fuel cell stack 100" of this embodiment described above should be read as "electrolytic cell stack 100A", the "power generation unit 102" should be read as "electrolytic cell unit 102A", and the "single cell 110" should be read as "electrolytic cell stack 100A". It may be read as "electrolytic single cell 110A". Furthermore, "oxidant gas supply communication hole 132" is read as "oxygen discharge communication hole 132", "fuel gas supply communication hole 142" is read as "hydrogen discharge communication hole 142", and "fuel gas discharge communication hole 143" is read as "oxygen discharge communication hole 132". "steam supply communication hole 143", "oxidant gas introduction manifold 161", "oxygen discharge manifold 161", "fuel gas introduction manifold 171", "hydrogen discharge manifold 171", "fuel gas discharge manifold" 172" may be read as "steam introduction manifold 172."

However, when the electrolytic cell stack 100A is operated, a voltage is applied between the two electrodes so that the air electrode 114 is positive (anode) and the fuel electrode (hydrogen electrode) 116 is negative (cathode), and the two electrodes are connected. The operation of the electrolytic cell stack 100A is partially different from the operation of the fuel cell stack 100, such as that water vapor WV is supplied as a raw material gas through the hole 108. The points in which the operation of the electrolytic cell stack 100A differs from the operation of the fuel cell stack 100 will be described later. In the following, the same components as those of the fuel cell stack 100 described above will be given the same reference numerals and the description thereof will be omitted as appropriate.

The electrolytic single cell 110A described above has the same configuration as the fuel cell stack 100 as described below. That is, the electrolytic single cell 110A includes an electrolyte layer 112 containing a solid oxide, an air electrode 114 disposed above the electrolyte layer 112 (one side in the vertical direction), and an air electrode 114 disposed below the electrolyte layer 112 (on the other side in the vertical direction). The fuel electrode 116 includes a fuel electrode 116 disposed on the side) and containing Ni and an ion-conductive oxide. The electrolytic single cell 110A has a specific region SA that is a region within a distance of 10 μm from the interface with the electrolyte layer 112 in the fuel electrode 116 in at least one cross section parallel to the vertical direction, and each ion with respect to the area of the specific region SA. The area ratio, which is the ratio of the total area of the conductive oxide (YSZ particles Py in this embodiment), is Sa%, and it is the ratio of the total area of each pore existing in the specific area SA to the area of the specific area SA. When a certain pore area ratio is Sb% and the number of pores per unit area in the specific area SA is N pieces/μm2, formula ( ¹ ): Sa≧30 and formula (2): Sb/N≦54 It meets the following.

Furthermore, in the electrolytic single cell 110A, the average diameter D of pores in the specific area SA is 0.50 μm or less.

Furthermore, in the electrolytic single cell 110A, when the number of three-phase interfaces where Ni, ion conductive oxide, and pores intersect per unit area in the specific area SA is n pieces/μm ² , equation (3): n /N≦2.8 is satisfied.

A-6-2. Operation of electrolytic cell stack 100A:
As shown in FIGS. 9 and 11, when water vapor WV is supplied through a gas pipe (not shown) connected to the branch part 29 of the gas passage member 27 provided at the position of the water vapor introduction manifold 172, The water vapor WV is supplied to the water vapor introduction manifold 172 through the branch part 29 of the gas passage member 27 and the hole in the main body part 28, and is supplied to the water vapor introduction manifold 172 from the water vapor introduction manifold 172 through the water vapor supply communication hole 143 of each electrolytic cell unit 102A. chamber 176.

When water vapor WV is supplied to the fuel chamber 176 of each electrolytic cell unit 102A and a voltage is applied between both electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), the electrolytic cell Electrolysis is performed in the cell 110A by an electrochemical reaction of water vapor WV. This electrolytic reaction is an endothermic reaction. Through this electrolytic reaction, water vapor WV is decomposed into hydrogen H and oxide ions. Hydrogen H is discharged from the hydrogen discharge communication hole 142 to the outside of the fuel chamber 176, and the oxide ions move to the air electrode 114 through the electrolyte layer 112, and electrons are separated from the oxide ions at the air electrode 114. It becomes oxygen O. Oxygen O passes through the air electrode 114 and the air chamber 166, and is discharged to the outside of the air chamber 166 from the oxygen discharge communication hole 132.

Hydrogen H discharged from the fuel chamber 176 of each electrolytic cell unit 102A is discharged to the hydrogen discharge manifold 171 via the hydrogen discharge communication hole 142, as shown in FIGS. The gas is discharged to the outside of the electrolytic cell stack 100A through the main body portion 28 of the gas passage member 27 and the hole in the branch portion 29 provided in the gas passage member 27, and through a gas pipe (not shown) connected to the branch portion 29. Thereby, hydrogen H generated in each electrolytic cell unit 102A is taken out. Further, as shown in FIGS. 8 and 10, oxygen O discharged from the air chamber 166 of each electrolytic cell unit 102A is discharged to the oxygen discharge manifold 161 through the oxygen discharge communication hole 132, and further to the oxygen discharge manifold 161. The gas is discharged to the outside of the electrolytic cell stack 100A through the main body 28 of the gas passage member 27 provided at the position and the hole in the branch 29, and through a gas pipe (not shown) connected to the branch 29. .

In addition, in the electrolytic cell stack 100A described above, air AR may be supplied into the electrolytic cell stack 100A in order to control the temperature of the electrolytic cell stack 100A. Hereinafter, the "oxidant gas discharge communication hole 133" of this embodiment described above will be read as "air supply communication hole 133", and the "oxidant gas discharge manifold 162" will be read as "air introduction manifold 162", and the air AR Explain the flow. As shown in FIGS. 8 and 10, when air AR is supplied through a gas pipe (not shown) connected to the branch part 29 of the gas passage member 27 provided at the position of the air introduction manifold 162, Air AR is supplied to the air introduction manifold 162 through the branch part 29 of the gas passage member 27 and the hole in the main body part 28, and from the air introduction manifold 162 through the air supply communication hole 133 of each electrolytic cell unit 102A. is supplied to chamber 166. The air AR supplied to the air chamber 166 is discharged to the outside of the electrolytic cell stack 100A through the oxygen discharge communication hole 132, the oxygen discharge manifold 161, etc. together with the oxygen O generated at the air electrode 114. The air AR supplied to the air chamber 166 in this manner controls the temperature of the electrolytic cell stack 100A.

A-7. Performance evaluation:
Next, performance evaluation of this embodiment will be explained. The results of the performance evaluation of this embodiment show roughly the same tendency for SOFC and SOEC, but SOEC has better performance due to gas diffusivity within the fuel electrode 116 (performance related to electrode reaction). Since the change in fuel cell stack 100 tends to appear more conspicuously, below, performance evaluation of an electrolytic cell stack 100A, which is an example in which a configuration similar to that of the fuel cell stack 100 described above is applied to an SOEC, will be described.

Samples of a plurality of electrolytic single cells 110A having different characteristics as described above were prepared, and performance evaluation was performed using the samples. FIG. 12 is an explanatory diagram showing the performance evaluation results.
A-7-1. For each sample:

As shown in FIG. 12, 11 samples (samples S1 to S11) of the electrolytic single cell 110A were used in this performance evaluation. Each sample was manufactured according to the method for manufacturing the electrolytic single cell 110A described above. In the electrolytic cell stack 100A used for this performance evaluation, voltage terminals are formed in each layer so that the voltage of each sample can be drawn out individually. In addition, each sample has a specific area SA of the fuel electrode 116 (an area where the distance from the interface with the electrolyte layer 112 in the fuel electrode 116 is up to 10 μm in the cross section shown in FIG. 7). Area ratio Sa (%), pore area ratio Sb (%), number of pores per unit area N (pcs/μm ² ), and number of three-phase interfaces I per unit area n (pcs/μm ² ) , the value of S/N, the average diameter D (μm) of pores, and the value of n/N are different. As described above, the "area ratio of ion conductive oxides" is the ratio of the total area of each ion conductive oxide present in the specific area SA to the area of the specific area SA. In addition, as described above, the "pore area ratio Sb" is the ratio of the total area of each pore existing in the specific area SA to the area of the specific area SA, and the "three-phase interface I" is It is a three-phase interface where YSZ (ion conductive oxide), YSZ (ion conductive oxide), and pores intersect.

A-7-2. Evaluation items and evaluation method:
In this performance evaluation, the rate of performance deterioration during operation of the electrolytic cell stack 100A was evaluated. Specifically, in order to generate a predetermined amount of hydrogen for an electrolytic cell stack 100A using an electrolytic single cell 110A of each sample, water vapor WV is supplied to the fuel electrode (hydrogen electrode) 116 at about 700°C, and the current is Measure the voltage drop when a voltage is continuously applied between the air electrode 114 and the fuel electrode 116 for 1000 hours at a density of 1.2 A/cm ² , and based on the measured voltage drop value. (The lower the value of the voltage drop, the slower the rate of performance deterioration, and therefore the evaluation is excellent).

A-7-3. Evaluation results:
As shown in FIG. 12, in sample S10, the measured voltage drop value was the largest at 223 (mV/kh (1000 hours)), and the durability obtained from the evaluation results was the lowest. The reason why the durability obtained from the evaluation results of sample S10 was low is not necessarily clear, but it is presumed as follows. In other words, it is thought that the higher the area ratio Sa of the ion conductive oxide in the specific area SA, the less likely Ni aggregation will occur (the reason will be explained later), and the higher the area ratio Sa of the ion conductive oxide in the specific area SA It is relatively low at "29 (%)", and Ni tends to aggregate easily, which is considered to be the reason why the performance of the electrolytic cell stack 100A deteriorated. In addition, in sample S11, the measured voltage drop value was "145 (mV/kh (1000 hours))", which was the second highest after sample S10, and the durability obtained from the evaluation results was the second lowest after sample S10. The reason why the durability obtained from the evaluation results of sample S11 was low is not necessarily clear, but it is presumed as follows. In other words, it is thought that the lower the Sb/N value is, the less Ni agglomeration occurs (the reason will be explained later), and the Sb/N value is relatively high at 57.38, making it difficult for Ni aggregation to occur. tends to occur, which is considered to be the reason why the performance of the electrolytic cell stack 100A deteriorates.

On the other hand, in samples S1 to S9, the measured voltage drop values were relatively low, and the durability obtained from the evaluation results was relatively high. The reason why the durability obtained from the evaluation results of samples S1 to S9 was higher than the evaluation results of samples S10 and S11 is not necessarily clear, but it is assumed as follows. That is, when the area ratio Sa of the ion conductive oxide in the specific area SA is relatively high, such as 30% or more, as in samples S1 to S9, Ni tends to be less likely to aggregate, and therefore, the electrolytic cell stack 100A is It is thought that the durability has improved. Furthermore, when the Sb/N value is relatively low, such as 54 or less, as in samples S1 to S9, Ni tends to be less likely to aggregate, which is thought to improve the durability of the electrolytic cell stack 100A. .

The reason why Ni aggregation becomes less likely to occur as the area ratio Sa of the ion conductive oxide in the specific region SA becomes higher is not necessarily clear, but it is assumed as follows. The ion conductive oxide functions as an obstacle that suppresses the movement of Ni. The larger the cross-sectional area of the ion-conducting oxide, the more effectively the ion-conducting oxide suppresses the movement of Ni. By the ion-conducting oxide functioning as an obstacle in this way, aggregation of Ni is suppressed. Therefore, the larger Sa (ratio of the total area of each ion conductive oxide to the area of the specific region) is, the more the aggregation of Ni is suppressed.

The reason why Ni aggregation becomes less likely to occur as the Sb/N value decreases is not necessarily clear, but it is assumed as follows. The smaller the total cross-sectional area of the pores of the fuel electrode 116, the more suppressed is the aggregation of Ni. Therefore, the smaller the value of Sb (pore area ratio, which is the ratio of the total area of each pore existing in the specific area SA to the area of the specific area SA), the more suppressed is the aggregation of Ni. Further, the smaller the value of N (the number of pores per unit area in the specific area SA), the higher the probability that the cross-sectional area of the pores (particularly the width in the direction perpendicular to the gas flow direction) is large. The larger the cross-sectional area of the pores, the easier Ni moves, and therefore the more likely Ni agglomeration occurs. Therefore, the larger the value of N, the more likely Ni aggregation is suppressed.

From the above results, in order to improve the durability of the electrolytic single cell 110A, the area ratio Sa of the ion conductive oxide in the specific area SA must be 30% or more, and the value of Sb/N must be 54 or less. It can be said that it is preferable.

In addition, among samples S1 to S9 in which the area ratio Sa of the ion conductive oxide in the specific area SA was 30% or more and the value of Sb/N was 54 or less, samples S2 and S3 showed that the evaluation results While the obtained durability was evaluated as relatively low, samples S1 and S4 to 9 had relatively high durability obtained from the evaluation results. In sample S3, the average diameter D of pores is larger than 0.50 μm, while in samples S1 and S4 to S9, the average diameter D of pores is 0.50 μm or less. When the average diameter D of the pores is excessively large, as in sample S3, Ni tends to aggregate, which is considered to be the reason for the decrease in the durability of the electrolytic single cell 110A. Further, in sample S2, the value of n/N is greater than 2.8, while in samples S1 and S4 to 9, the value of n/N is less than or equal to 2.8. The larger the value of n/N, the more likely Ni agglomeration occurs (the reason will be explained later), and as in sample S7, when the value of n/N is large, Ni agglomeration tends to occur more easily. , it is considered that the durability of the electrolytic cell stack 100A decreases. On the other hand, when the average diameter D of the pores is sufficiently small, such as 0.50 μm or less, as in S1 and S4 to S9, agglomeration of Ni can be suppressed, thereby improving the durability of the electrolytic single cell 110A. It is thought that it is possible to do so. Furthermore, when the value of n/N is sufficiently small, such as 2.8 or less, as in samples S1 and S4 to S9, agglomeration of Ni can be suppressed and the durability of the electrolytic unit cell 110A can be improved. It is considered possible.

The reason why Ni agglomeration is more likely to occur as the value of n/N is larger is not necessarily clear, but it is presumed as follows. The larger the average diameter D of Ni, the smaller the number of three-phase interfaces I and the smaller the surface area of Ni (Ni particles), which reduces the area of Ni exposed to the gas phase and increases the surface diffusion of Ni. Since this makes it difficult for Ni to occur, aggregation of Ni is likely to be suppressed. Therefore, the smaller the value of n (the number of three-phase interfaces I per unit area in the specific area SA), the more easily Ni aggregation is suppressed. Further, as described above, the larger N (the number of pores per unit area in the specific area SA), the more likely Ni aggregation occurs.

From the above results, it can be said that in order to improve the durability of the electrolytic single cell 110A, it is preferable that the average diameter D of the pores is 0.50 μm or less, and that the value of n/N is 2.8 or less. It can also be said that it is desirable.

A-8. How to identify each characteristic of specific area SA:
Method for specifying each characteristic (Sa, Sb/N, average diameter of pores D, n/N) of specific area SA of fuel electrode 116 (area where the distance from the interface with electrolyte layer 112 in fuel electrode 116 is up to 10 μm) is as follows. First, a vertically parallel cross section of the single cell 110 (a cross section including the fuel electrode 116 (active layer 320)) is arbitrarily set, and an arbitrary position in the cross section (a position including a specific area SA of the fuel electrode 116) is set. ), an FIB-SEM (acceleration voltage: 1.5 kV) SEM image (for example, 5000 times magnification) in which the active layer 320 is captured is obtained.

In the above SEM image, the boundary B1 between the electrolyte layer 112 and the active layer 320 can be identified based on the difference in constituent materials between the electrolyte layer 112 and the active layer 320, visual recognition, and the like. In addition, in the above SEM image, the boundary B2 between the active layer 320 and the support layer 310 can be specified based on the difference in Ni content, average particle size of Ni, porosity, etc. between the active layer 320 and the support layer 310. I can do it.

In the above SEM image, the particles of the electron conductive material (Ni particles Pn in this embodiment) and the particles of the ion conductive material (YSZ particles Py in this embodiment) can be distinguished using, for example, the difference in brightness in the SEM image. It can be realized by Specifically, by analyzing the SEM image, the SEM image can be classified into three regions according to brightness. SEM-EDS may be used as a method for identifying the Ni particle Pn region and the YSZ particle Py region from the three regions depending on the brightness. Since the elements can be identified by SEM-EDS, the Ni particle Pn region and the YSZ particle Py region can be identified from the SEM image. Further, the remaining region among the three regions according to the brightness can be identified as a region of pores PO.

In the above SEM image, the area of the specific area SA (the area where the distance from the interface with the electrolyte layer 112 in the fuel electrode 116 is up to 10 μm) is specified, and the area of each YSZ particle Py existing in the specific area SA is specified. , by calculating the ratio of the total area of each ion conductive oxide (YSZ particles Py in this embodiment) to the area of the specific area SA, the area ratio of the ion conductive oxide in the specific area SA (specific area Specify Sa (the ratio of the total area of each ion conductive oxide to the area of SA). In addition, by specifying the area of each pore PO existing in the specific area SA and calculating the ratio of the total area of each pore PO to the area of the specific area SA, the pore area ratio of the specific area SA (the area of the specific area SA The ratio (ratio of the total area of each pore PO existing in the specific area SA to the area) Sb is specified. In the above SEM image, N (the number of pores per unit area in the specific area SA) can be determined by counting the total number of pores using image analysis software and dividing the area of the specific area SA by the number. . At this time, it is desirable from the viewpoint of data reliability to set the range of the specific area SA so that N is 100 or more. By dividing Sb by N, the value of Sb/N can be determined.

The average diameter D of pores can be calculated using an intercept method. In the above SEM image, assuming that each pore PO is approximately spherical, by multiplying by 1.5 the average length of the line drawn on the specific area SA in the SEM image across each pore PO, By calculating the average diameter D of each pore PO, the average diameter D can be specified.

In the above SEM image, by counting the number of three-phase interfaces I using image analysis software, n (the number of three-phase interfaces I per unit area in the specific area SA) can be specified. At this time, it is desirable from the viewpoint of data reliability to set the range of the specific area SA so that n is 100 or more.

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

The configuration of the single cell 110 (or electrolytic single cell 110A, hereinafter the same) or fuel cell stack 100 (or electrolytic cell stack 100A, the same hereinafter) in the above embodiment is just an example, and can be modified in various ways. . For example, in the above embodiment, the solid oxide contained in the electrolyte layer 112 is YSZ, but instead of YSZ, a substance other than YSZ (for example, ScSZ (scandium stabilized zirconia), LSGM (LaSrGaMgO ₃ -based perovskite oxide) is used). (object)) may be used.

Further, in the above embodiment, the fuel electrode 116 has a two-layer structure including the active layer 320 and the support layer 310, but it is assumed that the fuel electrode 116 includes layers other than the active layer 320 and the support layer 310. Good too. Further, the fuel electrode 116 does not need to include the support layer 310.

In the above embodiment, the electron conductive material contained in the active layer 320 of the fuel electrode 116 is Ni, but instead of Ni, a metal containing Ni and a metal other than Ni (for example, a metal containing Ni and Co) is used. alloy, etc.). Further, in the above embodiment, the ion conductive oxide contained in the active layer 320 of the fuel electrode 116 is YSZ, which is a substance having oxygen ion conductivity. It may be a substance that has The ion-conductive oxide contained in the active layer 320 of the fuel electrode 116 may be a substance having conductivity for ions other than oxygen ions (for example, protons).

The fuel cell stack 100 has a cross section of the electrolyte layer 112 other than the cross section shown in FIG. 1): Sa≧30 and formula (2): Sb/N≦54 may be satisfied. Also in this configuration, by satisfying formula (1): Sa≧30 and formula (2): Sb/N≦54, agglomeration of Ni can be suppressed for the same reason as described above. Thereby, the performance of the fuel cell stack 100 can be improved. Furthermore, in another cross section, the average diameter D of the pores in the specific area SA may be 0.50 μm or less. Also in this configuration, since the average diameter D is 0.50 μm or less, agglomeration of Ni can be suppressed for the same reason as described above, thereby improving the performance of the fuel cell stack 100. I can do it. Furthermore, in another cross section, a configuration may be adopted that satisfies the above formula (3): n/N≦2.8. Also in this configuration, by satisfying n/N≦2.8, agglomeration of Ni can be suppressed for the same reason as described above, and the performance of the fuel cell stack 100 can be improved. In these configurations, another cross section corresponds to "at least one cross section parallel to the first direction" in the claims.

In the above embodiment, the fuel cell stack 100 satisfies formula (1): Sa≧30 and formula (2): Sb/N≦54. Considering durability and the like, the value of Sa is more preferably 37 or more. Further, at the same time, considering ensuring the durability of the single cell 110, the value of Sa is preferably 50 or less. Considering durability and the like, the value of Sb/N is more preferably 40 or less. Further, at the same time, considering ensuring the durability of the single cell 110, etc., the value of Sb/N is preferably 5 or more.

In the embodiment described above, in the fuel cell stack 100, the average diameter D of the pores in the specific area SA is 0.50 μm or less. Considering durability and the like, the average diameter D is more preferably 0.45 μm or less. Moreover, at the same time, considering ensuring the durability of the single cell 110, the average diameter D is preferably 0.2 μm or more.

In the above embodiment, the fuel cell stack 100 satisfies the above formula (3): n/N≦2.8. Considering durability and the like, the value of n/N is more preferably 2.4 or less. Furthermore, in consideration of securing the durability of the single cell 110, etc., the value of n/N is preferably 1.5 or more.

In the above embodiment, the intermediate layer 180 may not be disposed between the electrolyte layer 112 and the air electrode 114, and the electrolyte layer 112 and the air electrode 114 may be directly connected.

Further, in the above embodiment, the number of single cells 110 included in the fuel cell stack 100 is just an example, and the number of single cells 110 is determined as appropriate depending on the output voltage required of the fuel cell stack 100 and the like. In the above embodiment, all the single cells 110 included in the fuel cell stack 100 do not necessarily have to satisfy the above formula (1): Sa≧30 and formula (2): Sb/N≦54. It can be said that if the condition is satisfied for at least one single cell 110 included in the fuel cell stack 100, metal aggregation can be suppressed, and thereby the performance of the fuel cell stack 100 can be improved. .

Further, in the above embodiment, the fuel cell stack 100 has a structure in which a plurality of flat plate-shaped unit cells 110 are stacked, but the present invention is applicable to other structures, such as those described in International Publication No. 2012/165409. As such, the present invention is similarly applicable to a configuration in which a plurality of substantially cylindrical single fuel cells are connected in series.

22: Bolt 22A: Bolt 22B: Bolt 22D: Bolt 22E: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 100: Fuel cell stack 100A: Electrolytic cell stack 102: Power generation unit 102A: Electrolytic cell unit 104: End plate 106: End plate 108: Communication hole 110: Single cell 110A: Electrolytic single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 120: Separator 130: Air electrode side frame 132: Oxidizing gas supply communication hole 133: Oxidizing agent Gas discharge communication hole 134: Air electrode side current collector 140: Fuel electrode side frame 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode side current collector 149: Spacer 150: Interconnector 161: Oxidation Agent gas introduction manifold 162: Oxidizing gas discharge manifold 166: Air chamber 171: Fuel gas introduction manifold 172: Fuel gas discharge manifold 176: Fuel chamber 180: Intermediate layer

Claims (4)

an electrolyte layer containing a solid oxide;
an air electrode disposed on one side of the electrolyte layer in the first direction;
An electrochemical cell comprising: a fuel electrode disposed on the other side of the electrolyte layer in the first direction, the fuel electrode containing a metal containing Ni and an ion-conductive oxide;
In at least one cross section parallel to the first direction, each of the ion-conducting oxides with respect to the area of the specific region has a distance of up to 10 μm from the interface with the electrolyte layer in the fuel electrode. The area ratio, which is the ratio of the total area of the object, is Sa%, and the pore area ratio, which is the ratio of the total area of each pore existing in the specific area to the area of the specific area, is Sb%. When the number of pores per unit area is N pores/ ^μm2 , formula (1): Sa≧30 and formula (2): 5≦ Sb/N≦54 are satisfied ,
The average diameter D of the pores in the specific region is 0.2 μm or more and 0.50 μm or less,
The average diameter D of the pores is determined by acquiring a SEM image of the cross section in the electrochemical cell, assuming that each pore has a substantially spherical shape, and a line drawn on the specific area of the SEM image representing each of the pores. Calculated by multiplying the average length across the pores by 1.5,
An electrochemical cell characterized by: an electrolyte layer containing a solid oxide;
an air electrode disposed on one side of the electrolyte layer in the first direction;
An electrochemical cell comprising: a fuel electrode disposed on the other side of the electrolyte layer in the first direction, the fuel electrode containing a metal containing Ni and an ion-conductive oxide;
In at least one cross section parallel to the first direction, each of the ion-conducting oxides with respect to the area of the specific region has a distance of up to 10 μm from the interface with the electrolyte layer in the fuel electrode. The area ratio, which is the ratio of the total area of the object, is Sa%, and the pore area ratio, which is the ratio of the total area of each pore existing in the specific area to the area of the specific area, is Sb%. When the number of pores per unit area is N pores/μm2 ^, formula (1): Sa≧30 and formula (2): 5≦Sb/N≦54 are satisfied,
When the number of three-phase interfaces where the metal, the ion conductive oxide, and the pores intersect per unit area in the specific region is n pieces/μm2, formula (3): 1.5≦n/N ^≦ 2.8 is satisfied.
An electrochemical cell characterized by: The electrochemical cell according to claim 1,
When the number of three-phase interfaces where the metal, the ion-conductive oxide, and the pores intersect per unit area in the specific region is n pieces/ ^μm2 , formula (3): 1.5≦ n/N≦ 2.8 is satisfied.
An electrochemical cell characterized by: In an electrochemical reaction cell stack comprising a plurality of electrochemical cells,
An electrochemical reaction cell stack, wherein at least one of the plurality of electrochemical cells is the electrochemical cell according to any one of claims 1 to 3.

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