JP7152142B2 - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Description

The technology disclosed by this specification relates to an electrochemical reaction single cell.

A solid oxide fuel cell (hereinafter referred to as "SOFC") is known as one type of fuel cell that generates power using an electrochemical reaction between hydrogen and oxygen. A fuel cell single cell (hereinafter simply referred to as "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 an anode arranged on one side of the electrolyte layer and an anode arranged on the other side in the first direction with respect to the electrolyte layer.

A fuel electrode including a plurality of layers is sometimes used as a fuel electrode that constitutes a single cell. Specifically, as the fuel electrode, a first fuel electrode layer (hereinafter referred to as a "support layer") that constitutes the surface of the fuel electrode on the other side in the first direction, and a gap between the support layer and the electrolyte layer. A second fuel electrode layer (hereinafter referred to as "active layer") containing an ion-conductive material (e.g., YSZ (yttria-stabilized zirconia)) and an electronically-conductive material (e.g., Ni (nickel)) A fuel electrode containing and may be used.

When a fuel electrode including a support layer and an active layer is used as the fuel electrode constituting the single cell, by setting the bonding length between the ion-conductive substance and the electronically-conductive substance in the active layer to a predetermined range, A technique for improving the performance of a single cell is known (see Patent Document 1, for example).

JP 2014-26720 A

As in the prior art described above, the performance of a single cell can be stably improved only by setting the junction length between the ion-conductive material and the electronically-conductive material in the active layer that constitutes the fuel electrode of the single cell to a predetermined range. The problem is that it cannot be done.

Such problems are also common to electrolytic single cells, which are structural units of solid oxide type electrolytic cells (hereinafter also referred to as "SOEC") that generate hydrogen using the electrolysis reaction of water. It is an issue. In this specification, the fuel cell single cell and the electrolysis single cell are collectively referred to as an electrochemical reaction single cell. Moreover, such a problem is not limited to SOFCs and SOECs, but is common to other types of electrochemical reaction single cells.

This specification discloses a technology capable of solving the above-described problems.

The technology disclosed in this specification can be implemented, for example, in the following forms.

(1) The electrochemical reaction unit cell disclosed in the present specification includes an electrolyte layer, an air electrode arranged on one side in a first direction with respect to the electrolyte layer, and the first electrode with respect to the electrolyte layer. a fuel electrode arranged on the other side in one direction, the first fuel electrode layer forming a surface of the fuel electrode on the other side in the first direction; and a second fuel electrode layer that is arranged between the electrolyte layer and contains an ion-conductive material and an electronically-conductive material. The porosity of the anode layer is lower than the porosity of the first anode layer, and particles of the ion-conductive material are present in at least one section of the second anode layer parallel to the first direction. and the particles of the electronically conductive substance, the total length of the interfaces between the particles of the ionically conductive substance and the pores, the total length of the interfaces between the particles of the electronically conductive substance and the pores, There is a first region having a total interfacial length of 2.5 μm/μm ² or more. The inventors of the present application have found that when a first region having a total interface length of 2.5 μm/μm ² or more exists in at least one cross section of the second fuel electrode layer parallel to the first direction, the electrochemical reaction unit We have newly found that the performance of the cell can be stably improved. Although the reason why the above effect is obtained by the above configuration is not necessarily clear, it is presumed as follows. If the total interfacial length of the second fuel electrode layer is relatively long, the second fuel electrode layer will have a fine structure, and the reaction field in the second fuel electrode layer will be relatively large, resulting in an electrochemical reaction. It is considered that the performance of the single cell is improved. Further, if we focus only on the interface length between the particles of the ion-conducting substance and the particles of the electron-conducting substance, even if this interface length is relatively long, the length of the interface between the particles of the ion-conducting substance and the pores, If the interfacial length between the particles of the electronically conductive substance and the pores is short, it is considered that the performance of the electrochemical reaction single cell is not sufficiently improved. In addition to the total interface length between the particles of the ion-conductive substance and the particles of the electronically-conductive substance, the inventors of the present application have found that the total length of the interface between the particles of the ion-conductive substance and the pores, Focusing on the total interface length, which is an index that considers the total length of the interface with pores, and adopting a configuration with a relatively long total interface length, the performance of the electrochemical reaction single cell can be stably improved. I discovered something new. Even if the total interfacial length of the second fuel electrode layer is relatively long, the second fuel electrode layer must have a lower porosity than the first fuel electrode layer. In some cases, the contact area between the fuel electrode layer and the electrolyte layer is reduced, or the diffusion of gas to the second fuel electrode layer is suppressed, so that the performance of the electrochemical reaction single cell is not sufficiently improved. This electrochemical reaction unit cell satisfies the requirement that the porosity of the second fuel electrode layer is lower than the porosity of the first fuel electrode layer in addition to the requirements regarding the total interfacial length described above. performance can be stably improved.

(2) In the above electrochemical reaction single cell, the number of particles of the electron conductive material located within the second region in at least one cross section of the second fuel electrode layer parallel to the first direction. The electron conductive substance cohesion index, which is the ratio of the area of the second region to the second region, may be 1.5 μm ² /piece or more and less than 2.5 μm ² /piece. In the present electrochemical reaction single cell, the electron conductive substance cohesion index is not excessively small as 1.5 μm ² /piece or more, so the number of isolated particles of the electronic conductive substance is relatively small. A sufficient electron conduction path can be secured in the electrode layer, and the performance of the electrochemical reaction single cell can be effectively improved. In addition, in the present electrochemical reaction single cell, the aggregation index of the electronic conductive substance is not excessively large at less than 2.5 μm ² /piece, so the degree of aggregation of the particles of the electronic conductive substance is not excessively high. Since it is possible to suppress the reduction of the three-phase interface, the local reduction of the pore diameter, and the clogging of the pores due to excessive aggregation of the conductive substance particles, it is possible to improve the dispersibility of the pores, thereby improving the gas diffusion. Therefore, the performance of the electrochemical reaction single cell can be effectively improved.

(3) In the above electrochemical reaction single cell, the first region may have a total interface length of 3.0 μm/μm ² or more. According to the present electrochemical reaction single cell, since the total interfacial length of the first region is longer in the present electrochemical reaction single cell, the reaction field in the second fuel electrode layer is further increased, and the electrochemical reaction single cell performance can be further effectively improved.

(4) In the electrochemical reaction single cell, the first region may have a total interface length of 4.5 μm/μm ² or less. If the total interfacial length of the second fuel electrode layer is excessively long, it is thought that the microstructure is too fine, resulting in increased bending of the pores, reduced gas diffusivity, and reduced performance of the electrochemical reaction single cell. . In this electrochemical reaction single cell, the total interfacial length of the first region is 4.5 μm/μm ² or less, which is not excessively long. can effectively improve the performance of

(5) In the above electrochemical reaction single cell, the electrochemical reaction single cell may be a fuel cell single cell. According to this electrochemical reaction single cell, the power generation performance of the fuel cell single cell can be stably improved.

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

1 is a perspective view showing an external configuration of a fuel cell stack 100 according to this embodiment; FIG. FIG. 2 is an explanatory view showing the XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II in FIG. 1; FIG. 2 is an explanatory view showing the 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 the 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. 6 is an explanatory diagram showing an enlarged YZ cross-sectional configuration of a portion (X1 section in FIG. 5) of the single cell 110; 3 is an explanatory diagram showing the detailed configuration of an active layer 320 of the fuel electrode 116; FIG. FIG. 5 is an explanatory diagram showing performance evaluation results; 3 is an explanatory diagram showing the relationship between the reciprocal of the total interfacial length Lo in the active layer 320 and the polarization resistance in the active layer 320; FIG. FIG. 10 is an explanatory diagram showing the relationship between the reciprocal of the YSZ—Ni interface length La in the active layer 320 and the polarization resistance in the active layer 320. As shown in FIG.

A. Embodiment:
A-1. Constitution:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing the external configuration of the fuel cell stack 100 in this embodiment, and FIG. 2 is an explanatory diagram showing the XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II in FIG. FIG. 3 is an explanatory diagram showing the 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 the sake of convenience, the positive Z-axis direction is referred to as the upward direction, and the negative Z-axis direction is referred to as the downward direction. may be installed. The same applies to FIG. 4 and subsequent figures.

The fuel cell stack 100 includes a plurality of (seven in this embodiment) power generation units 102 and a pair of end plates 104 and 106 . The seven power generation units 102 are arranged side by side in a predetermined arrangement direction (vertical direction in this embodiment). A 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 scope of claims.

A plurality of holes (eight in this embodiment) penetrating in the vertical direction are formed in the peripheral edge portion around the Z direction of each layer (the power generating unit 102, the end plates 104 and 106) constituting the fuel cell stack 100. Corresponding holes formed in each layer vertically communicate with each other to form communicating holes 108 extending vertically 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 the communication holes 108 .

A bolt 22 extending in the vertical direction is inserted through 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 . 2 and 3, between the nut 24 fitted on one side (upper side) of the bolt 22 and the upper surface of the end plate 104 constituting the upper end of the fuel cell stack 100, and between the bolt An insulating sheet 26 is interposed between the nut 24 fitted to the other side (lower side) of the fuel cell stack 22 and the lower surface of the end plate 106 forming the lower end of the fuel cell stack 100 . However, at a location where a gas passage member 27, which will be described later, is provided, between the nut 24 and the surface of the end plate 106, the insulating sheets disposed above and below the gas passage member 27 and the gas passage member 27, respectively. 26 intervenes. The insulating sheet 26 is composed 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 secured between the outer peripheral surface of the shaft portion of each bolt 22 and the inner peripheral surface of each communication hole 108 . As shown in FIGS. 1 and 2, the fuel cell stack 100 is located near the midpoint of one side (the 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 in the Z-direction. The space formed by the bolt 22 (bolt 22A) and the communication hole 108 through which the bolt 22A is inserted is supplied with the oxidant gas OG from the outside of the fuel cell stack 100, and the oxidant gas OG is used for each power generation. Functioning as an oxidant gas introduction manifold 161, which is a gas flow path for supplying to the unit 102, and 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) A space formed by the bolt 22 (bolt 22B) located nearby and the communication hole 108 through which the bolt 22B is inserted is the oxidant offgas OOG, which is the gas discharged from the air chamber 166 of each power generation unit 102. It functions as an oxidant 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.

Also, as shown in FIGS. 1 and 3, near the midpoint of one side (the side on the Y-axis positive side of the two sides parallel to the X-axis) on the outer circumference of the fuel cell stack 100 around the Z-direction The space formed by the bolt 22 (bolt 22D) positioned at the bottom and the communication hole 108 through which the bolt 22D is inserted is filled with the fuel gas FG from the outside of the fuel cell stack 100, and the fuel gas FG is used for each power generation. A bolt 22 that functions as a fuel gas introduction manifold 171 that supplies the unit 102 and is located near the midpoint of the side opposite to the side (the side on the Y-axis negative direction side 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 allows the fuel offgas FOG, which is the gas discharged from the fuel chamber 176 of each power generation unit 102, to flow outside the fuel cell stack 100. It functions as a fuel gas discharge manifold 172 that discharges the In this embodiment, hydrogen-rich gas obtained by reforming city gas, for example, is used as the fuel gas FG.

Four gas passage members 27 are provided in the fuel cell stack 100 . Each gas passage member 27 has a hollow tubular body portion 28 and a hollow tubular branch portion 29 branched from a side surface of the main body portion 28 . A hole in the branch portion 29 communicates with a 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 of the body portion 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. A hole in the body portion 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 body portion 28 of the gas passage member 27 arranged at the position of the bolt 22D forming the fuel gas introduction manifold 171 communicates with the fuel gas introduction manifold 171, and the fuel gas A hole in the body portion 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 .

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

(Configuration of power generation unit 102)
4 is an explanatory diagram showing the 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. FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of two power generation units 102;

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, an anode side frame 140, an anode side It has a current collector 144 and a pair of interconnectors 150 forming the top layer and the bottom layer of the power generation unit 102 . The separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150 are provided with holes corresponding to the communication holes 108 through which the bolts 22 are inserted.

The interconnector 150 is a substantially rectangular plate-shaped conductive member, and is made of, for example, ferritic stainless steel. The interconnector 150 ensures electrical continuity between the power generating units 102 and prevents mixing of reaction gases between the power generating units 102 . 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 . In addition, since the fuel cell stack 100 has a pair of end plates 104 and 106, the power generation unit 102 located at the top in the fuel cell stack 100 does not have the upper interconnector 150, and is located at the bottom. The generating unit 102 does not have a lower interconnector 150 (see Figures 2 and 3).

The single cell 110 includes an electrolyte layer 112 , an air electrode (cathode) 114 located above the electrolyte layer 112 , and a fuel electrode (anode) 116 located below the electrolyte layer 112 . The upper side corresponds to one side of the first direction in the claims, and the lower side corresponds to the other side of the first direction in the claims. In this embodiment, the thickness (size in the vertical direction) 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 constituting the unit cell 110 . That is, the single cell 110 of this embodiment is a fuel electrode-supported single cell.

The electrolyte layer 112 is a substantially rectangular plate-shaped member when viewed in the Z direction, and is a dense (low porosity) layer. The electrolyte layer 112 is made of solid oxide such as YSZ (yttria-stabilized zirconia). Thus, the single cell 110 of this embodiment is a solid oxide fuel cell (SOFC) using 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 direction, and is a porous layer (having a higher porosity than the electrolyte layer 112). The air electrode 114 is made of, for example, a perovskite oxide (eg, 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 direction, and is a porous layer (having a higher porosity than the electrolyte layer 112). FIG. 6 is an explanatory view showing an enlarged YZ cross-sectional configuration of a portion (X1 portion in FIG. 5) of the single cell 110. As shown in FIG. As shown in FIG. 6, the anode 116 includes a support layer 310 forming the lower surface of the anode 116 and an active layer 320 disposed between the support layer 310 and the electrolyte layer 112 . In this embodiment, the active layer 320 is adjacent to the electrolyte layer 112 and the support layer 310 is adjacent to the active layer 320 .

The active layer 320 mainly functions to react oxygen ions supplied from the electrolyte layer 112 with hydrogen or the like contained in the fuel gas FG to generate electrons and water vapor. The active layer 320 includes an oxygen ion conductive material (YSZ, which is ceramic in this embodiment) and an electron conductive material (Ni, which is a transition metal in this embodiment). 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 an oxygen ion conductive material (YSZ) and an electronic conductive material (Ni). The support layer 310 corresponds to the first fuel electrode layer in the claims, and the active layer 320 corresponds to the second fuel electrode layer in the claims.

As shown in FIGS. 4 and 5, the separator 120 is a frame-like member having a substantially rectangular hole 121 vertically penetrating near the center thereof, and is made of metal, for example. The peripheral portion of the separator 120 around the hole 121 faces the peripheral portion of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is joined to the electrolyte layer 112 (single cell 110) by a joining portion 124 formed of brazing material (for example, Ag brazing) arranged at the opposing portion. The air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116 are separated by the separator 120 to prevent gas leakage from one electrode side to the other electrode side in the peripheral portion of the unit cell 110 . Suppressed.

The air electrode side frame 130 is a frame-shaped member having a substantially rectangular hole 131 penetrating vertically in the vicinity of the center thereof, and is made of an insulator such as mica, for example. A hole 131 in the cathode-side frame 130 constitutes an air chamber 166 facing the cathode 114 . The air electrode-side frame 130 is in contact with the peripheral edge portion of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge portion of the surface of the interconnector 150 facing the air electrode 114 . . Also, the pair of interconnectors 150 included in the power generation unit 102 are electrically insulated by the air electrode side frame 130 . Further, the air electrode side frame 130 has an oxidizing gas supply communication hole 132 that communicates the oxidizing gas introduction manifold 161 and the air chamber 166, and an oxidizing gas supply communication hole 132 that communicates 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 having a substantially rectangular hole 141 vertically penetrating near the center thereof, and is made of metal, for example. A hole 141 in the anode-side frame 140 constitutes a fuel chamber 176 facing the anode 116 . The fuel electrode-side frame 140 is in contact with the periphery of the surface of the separator 120 facing the electrolyte layer 112 and the periphery of the surface of the interconnector 150 facing the fuel electrode 116 . The fuel electrode side frame 140 also has 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.

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 that connects the electrode-facing portion 145 and the interconnector-facing portion 146. For example, nickel or a nickel alloy is used. , stainless steel or the like. The electrode facing portion 145 is in contact with the surface of the fuel electrode 116 opposite to the side facing the electrolyte layer 112 , and the interconnector facing portion 146 is in contact with the surface of the interconnector 150 facing the fuel electrode 116 . in contact. However, as described above, since the lowest power generation unit 102 in the fuel cell stack 100 does not have the lower interconnector 150, the interconnector facing portion 146 of the power generation unit 102 is the lower end plate. 106 is in contact. Fuel electrode-side current collector 144 having such a configuration electrically connects fuel electrode 116 and interconnector 150 (or end plate 106). A spacer 149 made of mica, for example, 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 temperature cycles and reaction gas pressure fluctuations, and the fuel electrode 116 and the interconnector 150 (or the end plate 106) through the fuel electrode side current collector 144. good electrical connection with

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 quadrangular prism-shaped current collector elements 135, and is made of, for example, ferritic stainless steel. The air electrode-side current collector 134 is in contact with the surface of the air electrode 114 opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 facing the air electrode 114 . However, as described above, the uppermost power generation unit 102 in the fuel cell stack 100 does not have the upper interconnector 150, so the air electrode side current collector 134 in the power generation unit 102 is 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). The cathode-side current collector 134 and the interconnector 150 may be configured as an integral member. In addition, the air electrode side current collector 134 may be covered with a conductive coating, and a conductive bonding layer is interposed between the air electrode 114 and the air electrode side current collector 134 to bond the two. You may have

A-2. Operation of fuel cell stack 100:
As shown in FIGS. 2 and 4, the oxidant gas OG is supplied through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas introduction manifold 161. Then, the 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 portion 28 , and the oxidizing gas OG is supplied from the oxidizing gas introduction manifold 161 to each power generation unit 102 . The agent gas is supplied to the air chamber 166 through the agent gas supply communication hole 132 . 3 and 5, the fuel gas FG is supplied through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the fuel gas introduction manifold 171. Then, the fuel gas FG is supplied to the fuel gas introduction manifold 171 via the branch portion 29 of the gas passage member 27 and the hole of the main body portion 28, and the fuel gas supply communication of each power generation unit 102 from the fuel gas introduction manifold 171. It is supplied to fuel chamber 176 through 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, electric power is generated in the single cell 110 by the electrochemical reaction of the oxidant gas OG and the fuel gas FG. will be 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 through the air electrode side current collector 134, and the fuel electrode 116 is electrically connected through the fuel electrode side current collector 144. It is electrically connected to the other interconnector 150 . Also, 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 taken out from the end plates 104 and 106 that function as output terminals of the fuel cell stack 100 . Since the SOFC generates power at a relatively high temperature (for example, 700° C. to 1000° C.), the fuel cell stack 100 is heated by the heater ( (not shown).

As shown in FIGS. 2 and 4, the oxidant offgas 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 supplied to the fuel cell stack 100 via a gas pipe (not shown) connected to the branch portion 29 through the holes of the main body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the agent gas discharge manifold 162 . is discharged to the outside of the Further, as shown in FIGS. 3 and 5, the fuel offgas 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. Through the holes in the body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the exhaust manifold 172, the gas is supplied to the outside of the fuel cell stack 100 via a gas pipe (not shown) connected to the branch portion 29. Ejected.

A-3. Detailed configuration of the active layer 320 of the 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. As shown in FIG. FIG. 7 shows an enlarged view of the YZ cross-sectional configuration of a portion of the active layer 320 (the X2 portion in FIG. 6).

As described above, the active layer 320 of the fuel electrode 116 includes an oxygen ion conductive material (YSZ, which is ceramics in this embodiment) and an electron conductive material (Ni, which is a transition metal in this embodiment). I'm in. FIG. 7 schematically shows YSZ particles Py as oxygen ion conductive material particles, Ni particles Pn as electron conductive material particles, and pores PO contained in the active layer 320 .

In the fuel electrode 116 of this embodiment, the porosity of the active layer 320 is lower than that of the support layer 310 . The porosity of the active layer 320 is preferably 10 vol % or more and 30 vol % or less, more preferably 13 vol % or more and 20 vol % or less. The average pore diameter of the active layer 320 is preferably 0.3 μm or more. Moreover, the porosity of the support layer 310 is preferably 20 vol % or more and 45 vol % or less, and more preferably 33 vol % or more and 37 vol % or less. The average pore diameter of the support layer 310 is preferably 0.5 μm or more.

In addition, in the active layer 320 of the fuel electrode 116 in this embodiment, the total interfacial length Lo is 2.5 μm/μm ² or more in a cross section parallel to the vertical direction (for example, the YZ cross section shown in FIG. 7). Here, the total interface length Lo is the length of the interface Ba between the particles of the ion-conducting material (YSZ particles Py in this embodiment) and the particles of the electron-conducting material (Ni particles Pn in this embodiment). total (hereinafter referred to as "YSZ-Ni interface length La") and the total length of the interface Bb between the particles of the ion conductive material (YSZ particles Py) and the pores PO (hereinafter referred to as "YSZ-pore interface length Lb" ) and the total length of the interfaces Bc between the electron conductive material particles (Ni particles Pn) and the pores PO (hereinafter referred to as “Ni-pore interface length Lc”). That is, the total interfacial length Lo is the total length of each interface in the active layer 320 . In this embodiment, the total interfacial length Lo of such active layer 320 is relatively long, 2.5 μm/μm ² or more. The total interface length Lo of the active layer 320 is more preferably 3.0 μm/μm ² or more. Further, the total interfacial length Lo of the active layer 320 is more preferably 4.5 μm/μm ² or less.

Each of the interface lengths (YSZ-Ni interface length La, YSZ-pore interface length Lb, Ni-pore interface length Lc) constituting the total interface length Lo of the active layer 320 is 10% or more of the total interface length Lo. , preferably 55% or less.

In addition, in the active layer 320 of the fuel electrode 116 according to the present embodiment, the electron conductive substance cohesion index Ic is 1.5 μm ² /piece or more, 2 0.5 μm ² / piece. Here, the electron conductive substance cohesion index Ic is the ratio of the area of a given region to the number of electron conductive substance particles (Ni particles Pn) located in the region. That is, the electron conductive substance cohesion index Ic is an index indicating the degree of aggregation of electron conductive substance particles (Ni particles Pn). In the present embodiment, the electron conductive substance cohesion index Ic of the active layer 320 is neither too small nor too large, such as 1.5 μm ² /piece or more and less than 2.5 μm ² /piece.

The average particle size of the YSZ particles Py in the active layer 320 is preferably, for example, 0.4 μm or more and 0.8 μm or less. Also, the average particle size of the Ni particles Pn in the active layer 320 is preferably, for example, 0.3 μm or more and 0.8 μm or less. The content ratio of the YSZ particles Py and the Ni particles Pn in the active layer 320 is preferably 65:35 to 40:60.

A-4. Manufacturing method of fuel cell stack 100:
A method for manufacturing the fuel cell stack 100 according to the present 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 are added to a mixed powder of NiO powder and YSZ powder, and the mixture is placed in a ball mill. and mix to prepare a slurry. Organic beads are, for example, spherical particles made of polymers such as polymethyl methacrylate and polystyrene. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for fuel electrode supporting layer having a predetermined thickness (for example, 200 μm to 300 μm). The mixing ratio of the NiO powder and the 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 anode active layer)
A butyral resin, a plasticizer DOP, 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 slurry. It should be noted that organic beads as a pore-forming material may be added at the time of preparing the slurry in the same manner as in the method for producing the green sheet for the fuel electrode support layer described above. The obtained slurry is made into a thin film by a doctor blade method to prepare a green sheet for fuel electrode active layer having a predetermined thickness (for example, 10 μm to 40 μm). The mixing ratio of the NiO powder and the 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, a plasticizer DOP, 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 resulting slurry is thinned by a doctor blade method to produce a green sheet for electrolyte layer having a predetermined thickness (for example, 10 μm).

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

(Formation of air electrode 114)
LSCF powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent are mixed to adjust the viscosity to prepare an air electrode paste. The prepared air electrode paste is applied to the surface of the electrolyte layer 112 in the above-described laminate of the electrolyte layer 112 and the fuel electrode 116 by, for example, screen printing, and dried to obtain a laminate coated with the air electrode paste. is fired at a predetermined firing temperature (for example, 1100° C.). Thus, the air electrode 114 is formed, and the unit cell 110 including the fuel electrode 116, the electrolyte layer 112, and the air electrode 114 is produced.

After manufacturing a plurality of single cells 110 according to the above-described method, an assembly process (for example, a process of attaching other members such as separators 120 to each single cell 110, a process of stacking a plurality of single cells 110, and fastening with bolts 22) is performed. process, etc.). The manufacturing of the fuel cell stack 100 is thus completed. After that, in order to make the fuel cell stack 100 ready for power generation operation, a reduction step of reducing the active layer 320 of the fuel electrode 116 (that is, reducing NiO contained in the active layer 320 to Ni) is performed. . The reduction process is realized, for example, by exposing the fuel electrode 116 to a hydrogen atmosphere at a predetermined temperature for a predetermined period of time. The reducing gas used in the reduction step is not limited to hydrogen, and may be other gas such as methane gas. Thus, the production of the fuel cell stack 100 ready for power generation operation is completed.

A-5. Method for adjusting each characteristic of the fuel electrode 116:
When manufacturing the fuel cell stack 100 according to the method described above, each characteristic of the fuel electrode 116 constituting the fuel cell stack 100 can be adjusted, for example, as follows. A method for specifying each characteristic of the fuel electrode 116 will be described later in "A-7. Method for specifying each characteristic of the fuel electrode 116".

(Porosity of fuel electrode 116)
The adjustment of the porosity in each layer (the active layer 320 and the support layer 310) constituting the fuel electrode 116 is performed, for example, by preparing a slurry for producing a green sheet (the green sheet for the fuel electrode active layer or the green sheet for the fuel electrode support layer). can be realized by adjusting the amount of the pore-forming material added when preparing the . Specifically, when preparing a slurry for producing a green sheet for a certain layer, the more the amount of the pore former added, the higher the porosity of the layer.

(Total interfacial length Lo in active layer 320 of fuel electrode 116)
The adjustment of the total interfacial length Lo in the active layer 320 of the fuel electrode 116 is performed, for example, by using an electronic conductive material (Ni) or an ion conductive material (YSZ ), adjusting the size of the pore-forming material, or adjusting the firing conditions when firing the green sheet for the anode active layer. Specifically, the smaller the particle size of the raw materials of the electronically conductive material (Ni) and the ionically conductive material (YSZ), the longer the total interfacial length Lo in the active layer 320 . Also, the smaller the size of the pore-forming material, the longer the total interfacial length Lo in the active layer 320 . Also, the lower the baking temperature and the shorter the baking time, the longer the total interface length Lo in the active layer 320 .

(Electron-conductive substance cohesion index Ic in active layer 320 of fuel electrode 116)
The adjustment of the electron conductive substance cohesion index Ic in the active layer 320 of the fuel electrode 116 is performed, for example, by adjusting the particle size of the raw material of the electron conductive substance (Ni) when preparing the slurry for producing the green sheet for the fuel electrode active layer. It can be realized by adjusting the diameter, adjusting the dispersion performance by selecting the dispersant and setting the amount to be added, and adjusting the firing conditions when firing the green sheet for the anode active layer. . Specifically, the smaller the particle size of the raw material of the electronically conductive material (Ni), the smaller the electronically conductive material cohesion index Ic in the active layer 320 . In addition, as the dispersing ability of the dispersant increases, the electronic conductive substance cohesion index Ic in the active layer 320 decreases. Also, the lower the baking temperature and the shorter the baking time, the smaller the electronic conductive substance cohesion index Ic in the active layer 320 .

A-6. Performance evaluation:
A plurality of samples of the unit cells 110 having different characteristics described above were produced, and performance evaluation was performed using the samples. FIG. 8 is an explanatory diagram showing performance evaluation results.

A-6-1. For each sample:
As shown in FIG. 8, eight samples (samples S1 to S8) of the single cell 110 were used for this performance evaluation. Each sample was manufactured according to the method for manufacturing the single cell 110 described above. For each sample, the porosity (vol%) of the fuel electrode 116 (active layer 320 and support layer 310), the total interfacial length Lo (μm/μm ² ) of the active layer 320, and the YSZ-Ni interfacial length La (μm/ μm ² ) and the electronic conductive substance cohesion index Ic (μm ² /piece) are different from each other.

A-6-2. Evaluation items and evaluation methods:
In this performance evaluation, the power generation characteristics were evaluated. Specifically, for the fuel cell stack 100 using the single cell 110 of each sample, the air electrode 114 was supplied with the oxidant gas OG and the fuel electrode 116 with the fuel gas FG at about 700° C., and the current density was The output voltage of the single cell 110 at 0.55 A/cm ² was measured, and the measured voltage was evaluated in five stages from "A" to "E" as follows ("A" is the most excellent evaluation, and "E" is the most inferior evaluation).
・Evaluation: “A” Voltage: 0.920 V or more ・Evaluation: “B” Voltage: 0.915 V or more and less than 0.920 V ・Evaluation: “C” Voltage: 0.910 V or more , less than 0.915 V Evaluation: "D" Voltage: 0.900 V or more and less than 0.910 V Evaluation: "E" Voltage: less than 0.900 V

A-6-3. Evaluation results:
As shown in FIG. 8, sample S1 was the lowest "E" in the evaluation result of the power generation characteristics. The reason why the evaluation result of the sample S1 was low is not necessarily clear, but is presumed as follows. That is, in sample S1, the total interfacial length Lo in the active layer 320 was relatively short, at 2.28 μm/μm ² , and the reaction field in the active layer 320 was relatively small, so the power generation performance was degraded. be done.

On the other hand, in samples S2 to S7, the evaluation results of power generation characteristics were "D" or higher. The reason why the evaluation results of samples S2 to S7 were higher than the evaluation result of sample S1 is not necessarily clear, but is presumed as follows. That is, in the samples S2 to S7, the total interfacial length Lo in the active layer 320 is relatively long at 2.5 μm/μm ² or more, and the active layer 320 has a fine structure. It is thought that the power generation performance improved because of the relatively large amount of

However, in sample S8, although the total interfacial length Lo in the active layer 320 was 2.5 μm/μm ² or more, the evaluation result of the power generation characteristics was the lowest “E” evaluation. In sample S8, the porosity of active layer 320 is higher than that of support layer 310, unlike samples S2 to S7. Therefore, in sample S8, although the total interfacial length Lo in the active layer 320 is relatively long, the porosity of the support layer 310 is relatively high. It is considered that the gas diffusion to the active layer 320 was suppressed and the power generation performance was not sufficiently improved.

From the above results, in order to improve the power generation performance of the single cell 110, the porosity of the active layer 320 must be lower than the porosity of the support layer 310, and the total interfacial length Lo in the active layer 320 must be 2.5 μm/μm. It can be said that it is preferably ² or more.

Of the interface lengths (YSZ-Ni interface length La, YSZ-pore interface length Lb, Ni-pore interface length Lc) that make up the total interface length Lo in the active layer 320, attention is focused only on the YSZ-Ni interface length La. As a result, the YSZ-Ni interface length La of the sample S1, which was evaluated as "E", was longer than those of the samples S2 to S5, which were evaluated as "D" or higher. Therefore, in sample S1, although the YSZ-Ni interface length La is relatively long, the other interface lengths (YSZ-pore interface length Lb and Ni-pore interface length Lc) are relatively short, so that the power generation performance is sufficiently improved. presumably did not.

FIG. 9 is an explanatory diagram showing the relationship between the reciprocal of the total interfacial length Lo in the active layer 320 and the activation polarization in the active layer 320. As shown in FIG. FIG. 10 is an explanatory diagram showing the relationship between the reciprocal of the YSZ-Ni interface length La in the active layer 320 and the activation polarization in the active layer 320. As shown in FIG. FIG. 9 and FIG. 10 show a plurality of points indicating respective measured values for a plurality of samples and an approximate straight line calculated based on the plurality of points. However, in FIG. 9, the point of the sample with the smallest reciprocal of the total interface length Lo (shown in parentheses in FIG. 9) is not referred to when calculating the approximate straight line.

As shown in FIG. 9, the smaller the reciprocal of the total interface length Lo in the active layer 320 (that is, the longer the total interface length Lo), the smaller the polarization resistance in the active layer 320 (that is, the higher the power generation performance). There is a tendency. Note that when the reciprocal of the total interface length Lo becomes very small (that is, when the total interface length Lo becomes very long), the polarization resistance approaches zero. Similarly, as shown in FIG. 10, the smaller the reciprocal of the YSZ-Ni interface length La in the active layer 320 (that is, the longer the YSZ-Ni interface length La), the smaller the polarization resistance in the active layer 320 tends to be. be. However, as is clear from a comparison of FIGS. 9 and 10, the correlation between the YSZ—Ni interface length La in the active layer 320 and the polarization resistance is relatively low, whereas the total interface length Lo in the active layer 320 and the polarization resistance The correlation with resistance is remarkably high. Even if the YSZ-Ni interface length La in the active layer 320 is relatively long, if the other interface lengths (YSZ-pore interface length Lb and Ni-pore interface length Lc) are relatively short, the polarization in the active layer 320 This is because the resistance can be large. Therefore, even if only the YSZ-Ni interface length La in the active layer 320 is focused, it is difficult to improve the power generation performance of the single cell 110 without variation. It can be said that the power generation performance of the single cell 110 can be stably improved only by increasing the length Lo.

In addition, among the samples S2 to S7 in which the evaluation results of the power generation characteristics were “D” or higher, the evaluation results of the samples S2 and S3 were “D”, while the samples S4 to S7 were evaluated “C”. "It was more than rated. Sample S2 has an electronic conductive substance cohesion index Ic of less than 1.5 μm ² /piece, and sample S3 has an electronic conductive substance cohesion index Ic of 2.5 μm ² /piece or more. , the electron conductive substance cohesion index Ic is 1.5 μm ² /piece or more and less than 2.5 μm ² /piece. When the electron conductive substance cohesion index Ic is excessively small, as in sample S2, the number of isolated Ni particles Pn is relatively large, and an electron conduction path in the active layer 320 cannot be sufficiently secured, resulting in power generation performance. is considered to decrease. On the other hand, when the electron conductive substance cohesion index Ic is excessively large as in sample S3, the Ni particles Pn are excessively cohesive, not only reducing the three-phase interface but also impairing the homogeneity of the microstructure. , the dispersibility of the pores PO in the active layer 320 is reduced, the diameter of the pores PO is locally reduced, gas diffusibility is reduced, and the power generation performance is also reduced. On the other hand, in the samples S4 to S7, the electronic conductive substance cohesion index Ic was 1.5 μm ² /piece or more and less than 2.5 μm ² /piece, which is neither excessively small nor excessively large, so that the isolated By reducing the number of Ni particles Pn, it is possible to sufficiently secure an electron conduction path in the active layer 320, and suppress a decrease in gas diffusivity caused by a decrease in dispersibility of pores PO due to excessive aggregation of Ni particles Pn. It is considered that the power generation performance could be effectively improved.

In addition, among the samples S4 to S7 for which the evaluation result of the power generation characteristics was “C” or higher, the evaluation result was “C” for the samples S4 and S5, while the evaluation result was “B” for the samples S6 and S7. "It was more than rated. In samples S4 and S5, the total interfacial length Lo in the active layer 320 is less ^than 3.0 μm/μm2, while in samples S6 and S7, the total interfacial length Lo in the active layer 320 is 3.0 μm/μm2 or ^more . . Thus, in samples S6 and S7, since the total interfacial length Lo in the active layer 320 is longer, the active layer 320 has a finer structure, and the reaction field in the active layer 320 is further increased, resulting in improved power generation performance. It is considered that the improvement is more effective.

In addition, among the samples S6 and S7 whose evaluation results of the power generation characteristics were rated “B” or higher, the sample S6 was rated “B”, while the sample S7 was rated “A”. there were. In sample S6, the total interfacial length Lo in the active layer 320 is longer than 4.5 μm/μm ² , while in sample S7, the total interfacial length Lo in the active layer 320 is 4.5 μm/μm ² or less. In sample S6, since the total interfacial length Lo in the active layer 320 is excessively long, the structure of the active layer 320 is too fine and the bending of the pores PO becomes large. It is considered that On the other hand, in sample S7, since the total interface length Lo in the active layer 320 is not excessively long, it is possible to suppress the decrease in gas diffusivity due to the bending of the pores PO, and the power generation performance is extremely effective. Considered to be an improvement.

According to the above performance evaluation results, in order to improve the power generation characteristics of the single cell 110, the porosity of the active layer 320 should be lower than the porosity of the support layer 310 and the total interfacial length Lo of the active layer 320 should be 2.5. It is preferably 5 μm/μm ² or more, more preferably the electronic conductive substance cohesion index Ic is 1.5 μm ² / piece or more and less than 2.5 μm ² / piece, and the total interface length Lo in the active layer 320 is More preferably, the ^{total interface length Lo in the active layer 320 is 4.5 μm/μm 2 or} less.

A-7. Method for identifying each characteristic of the fuel electrode 116:
A method of specifying each characteristic of the fuel electrode 116 (electron-conductive substance cohesion index Ic of the active layer 320, total interfacial length Lo of the active layer 320, porosity of the active layer 320 and the support layer 310) is as follows. First, a cross section parallel to the vertical direction in the single cell 110 (a cross section including the fuel electrode 116 (active layer 320)) is arbitrarily set, and an FIB-SEM ( An SEM image (for example, 5000 times) is obtained at an accelerating voltage of 1.5 kV). This SEM image is, for example, an image in which the entirety of the active layer 320 can be confirmed in the vertical direction, and a portion presumed to be the boundary B1 (see FIG. 6) between the electrolyte layer 112 and the active layer 320 is the vertical direction of the image. It is assumed to be the boundary B2 (see FIG. 6) between the active layer 320 and the support layer 310, located in the uppermost divided region among the ten divided regions obtained by dividing into ten equal parts in the direction. The part is the image located in the bottommost subregion.

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

In the above SEM image, the particles of the electronically conductive material (Ni particles Pn in this embodiment) and the particles of the ionically conductive material (YSZ particles Py in this embodiment) can be distinguished, for example, by using the difference in brightness in the SEM image. 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 technique for distinguishing between the Ni particle Pn area and the YSZ particle Py area from the three areas corresponding to the brightness. Since the elements can be specified by SEM-EDS, it is possible to distinguish between the Ni particle Pn area and the YSZ particle Py area from the SEM image. Also, the remaining area of the three areas according to the brightness can be identified as the area of pores PO.

In the SEM image, the area of a specific region in the active layer 320 is identified, the number of Ni particles Pn present in the region is counted, and the area is divided by the number of electrons in the active layer 320. A conductive material cohesion index Ic can be determined.

Further, by analyzing the SEM image using image analysis software (for example, "HALCON" manufactured by Links Co., Ltd.), each interface length in the active layer 320 (YSZ-Ni interface length La, YSZ-pore interface length Lb, The Ni-pore interface length Lc) can be specified. The total interface length Lo in the active layer 320 can be specified by calculating the sum of the specified interface lengths La, Lb, and Lc. In addition, it is preferable to specify the total interface length Lo for the entire active layer 320 .

In addition, in the SEM image, the area of the specific region in the active layer 320 is specified, the area occupied by the pores PO is specified, and the ratio of the area occupied by the pores PO to the area of the specific region in the active layer 320 is calculated. Thus, the porosity of the active layer 320 is specified.

Similarly, an SEM image showing the support layer 310 is obtained, the area of a specific region in the support layer 310 is specified, the area occupied by the pores PO is specified, and the area of the specific region in the support layer 310 The porosity of the support layer 310 is specified by calculating the ratio of the area occupied by the pores PO. The magnification of the SEM image of the support layer 310 used at this time is the same as or lower than the magnification of the SEM image of the active layer 320 described above.

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

The configuration of the single cell 110 or the fuel cell stack 100 in the above embodiment is merely an example, and various modifications are possible. For example, in the above embodiment, the fuel electrode 116 has a two-layer structure of the active layer 320 and the support layer 310, but the fuel electrode 116 includes layers other than the active layer 320 and the support layer 310. good too.

In the above embodiment, the total interface length Lo is 2.5 μm/μm ² or more in any region of any cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116 . If at least one cross section parallel to the vertical direction of the active layer 320 has a region with a total interface length Lo of 2.5 μm/μm ² or more, the reaction field is relatively large at least in this region. The power generation performance of the cell 110 can be improved. The region preferably exists within a range of 10 μm or less from the boundary B1 between the active layer 320 and the electrolyte layer 112 . This area corresponds to the first area in the claims.

Similarly, in the above embodiment, in any region of any cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116, the electron conductive substance cohesion index Ic is 1.5 μm ² /piece or more, 2.5 μm ² However, at least one cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116 has an electron conductive substance aggregation index Ic of 1.5 μm ² /piece or more, 2.5 μm ² /piece If there is a region with less than 100, at least in this region, by reducing the number of isolated Ni particles Pn, it is possible to sufficiently secure an electron conduction path in this region, and at the same time, pores due to excessive aggregation of Ni particles Pn can be secured in this region. Since a decrease in gas diffusivity due to a decrease in PO dispersibility can be suppressed, the power generation performance of the single cell 110 can be improved. The region preferably exists within a range of 10 μm or less from the boundary B1 between the active layer 320 and the electrolyte layer 112 . This area corresponds to the second area in the claims. The first area may be the same area as the second area, or may be a different area.

Further, the materials forming each member in the above-described embodiment are merely examples, and each member may be formed of other materials. For example, in the above embodiment, Ni is used as the electronically conductive material contained in the active layer 320 of the fuel electrode 116, but other electronically conductive materials such as Mn, Fe, Co, and Cu can be used. be. However, since Ni has a high affinity with hydrogen, it is preferable to employ Ni as the electron conductive material contained in the active layer 320 of the fuel electrode 116 . In addition, in the above embodiment, YSZ is used as the ion conductive material contained in the active layer 320 of the fuel electrode 116, but other ion conductive materials such as ScSZ (scandia-stabilized zirconia) can be used. be. In addition, the active layer 320 of the fuel electrode 116 contains a material having both electronic conductivity and ionic conductivity (for example, GDC (gadolinium-doped ceria)), and the material is an electronically conductive material and an ionic conductor. It may function as both a conductive material. In this case, the total interfacial length Lo means the interfacial length between the substance and the pores PO.

Further, in the above embodiment, the support layer 310 of the fuel electrode 116 is made of YSZ and Ni, but the support layer 310 may be made of other materials (eg, metal).

In the above embodiment, the number of single cells 110 included in the fuel cell stack 100 is merely an example, and the number of single cells 110 is appropriately determined according to the required output voltage of the fuel cell stack 100 and the like. In the above-described embodiment, for all the single cells 110 included in the fuel cell stack 100, at least one cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116 has a total interfacial length Lo of 2.5 μm/μm. It is not necessary to satisfy conditions such as the presence of a region having a value of ² or more, and if at least one unit cell 110 included in the fuel cell stack 100 satisfies the condition, the power generation performance of the unit cell 110 can be improved. It can be said that

In the above embodiment, the fuel cell stack 100 has a configuration in which a plurality of flat unit cells 110 are stacked, but the present invention has other configurations, such as those described in International Publication No. 2012/165409. Similarly, a configuration in which a plurality of substantially cylindrical single fuel cells are connected in series can also be applied.

Further, in the above embodiments, SOFCs that generate electricity by utilizing the electrochemical reaction between the hydrogen contained in the fuel gas and the oxygen contained in the oxidant gas are used. It is also applicable to an electrolytic single cell, which is a structural unit of a solid oxide electrolysis cell (SOEC) that utilizes hydrogen to generate hydrogen, and an electrolytic cell stack comprising a plurality of electrolytic single cells. The configuration of the electrolysis cell stack is known, for example, as described in Japanese Patent Application Laid-Open No. 2016-81813, so it will not be described in detail here, but it is roughly the same as the fuel cell stack 100 in the above-described embodiment. is the configuration. That is, the fuel cell stack 100 in the above-described embodiment can be read as an electrolytic cell stack, the power generation unit 102 can be read as an electrolytic cell unit, and the single cell 110 can be read as an electrolytic single cell. However, during the operation of the electrolysis cell stack, a voltage is applied between the two electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode). Water vapor is supplied as a source gas. As a result, an electrolysis reaction of water occurs in each electrolytic single cell, hydrogen gas is generated in the fuel chamber 176, and the hydrogen is taken out of the electrolytic cell stack through the communication hole . Even in the electrolytic single cell having such a configuration, at least one cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116 has a region having a total interface length Lo of 2.5 μm/μm ² or more. is satisfied, the performance of the single cell 110 can be improved.

Also, in the above embodiments, a solid oxide fuel cell (SOFC) was described as an example, but the present invention is also applicable to other types of fuel cells (or electrolysis cells) such as a molten carbonate fuel cell (MCFC). Applicable.

22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Body portion 29: Branch portion 100: Fuel cell stack 102: Power generation unit 104: End plate 106: End plate 108: Communication hole 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 120: Separator 121: Hole 124: Joint 130: Air electrode side frame 131: Hole 132: Oxidant gas supply passage 133: Oxidant gas discharge passage 134: Air electrode side Current collector 135: Current collector element 140: Fuel electrode side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode side current collector 145: Electrode facing portion 146: Interconnector facing Part 147: Connection Part 149: Spacer 150: Interconnector 161: Oxidant Gas Introduction Manifold 162: Oxidant Gas Discharge Manifold 166: Air Chamber 171: Fuel Gas Introduction Manifold 172: Fuel Gas Discharge Manifold 176: Fuel Chamber 310: Support Layer 320: Active layer

Claims (5)

an electrolyte layer;
an air electrode disposed on one side in a first direction with respect to the electrolyte layer;
a first fuel electrode layer disposed on the other side in the first direction with respect to the electrolyte layer, the first fuel electrode layer constituting a surface of the fuel electrode on the other side in the first direction; a second anode layer disposed between the first anode layer and the electrolyte layer and including an ionically conductive material and an electronically conductive material;
In an electrochemical reaction single cell comprising
The thickness of the second fuel electrode layer is 10 μm to 40 μm,
The porosity of the second fuel electrode layer is lower than the porosity of the first fuel electrode layer,
In at least one cross section parallel to the first direction of the second fuel electrode layer, the total interface length between the particles of the ion-conductive material and the particles of the electronically-conductive material and the ion-conductive material The total interface length, which is the sum of the total interface length between the particles and pores of the electron conductive substance and the total interface length between the particles and pores of the electron conductive substance, is 2.5 μm/μm ² or more. exists and
A ratio of the area of the second region to the number of particles of the electronically conductive material located in the second region in at least one cross section of the second anode layer parallel to the first direction and the second region having an electronic conductive substance cohesion index of 1.5 μm ² / piece or more and less than 2.5 μm ² / piece,
Each of the first region and the second region is an SEM image obtained by FIB-SEM (acceleration voltage 1.5 kV) in a cross section of the electrochemical reaction single cell parallel to the first direction. is an image in which the entirety of the second fuel electrode layer in the first direction can be confirmed, and a portion presumed to be a boundary between the electrolyte layer and the second fuel electrode layer is the image in the first direction. Among the ten divided regions obtained by dividing into ten equal parts in one direction, the second fuel electrode layer and the second In the image in which the portion presumed to be the boundary with the first fuel electrode layer is located in the divided region on the other side in the first direction, the entire region representing the second fuel electrode layer An electrochemical reaction single cell, characterized by: In the electrochemical reaction single cell according to claim 1,
The electrochemical reaction single cell, wherein the first region is a region having a total interface length of 3.0 μm/μm ² or more. In the electrochemical reaction single cell according to claim 1 or claim 2,
The electrochemical reaction single cell, wherein the first region has a total interface length of 4.5 μm/μm ² or less. In the electrochemical reaction single cell according to any one of claims 1 to 3,
An electrochemical reaction single cell, wherein the electrochemical reaction single cell is a fuel cell single cell. In an electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells arranged side by side in the first direction,
An electrochemical reaction cell stack, wherein at least one of the plurality of electrochemical reaction single cells is the electrochemical reaction single cell according to any one of claims 1 to 4.

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