JP2019091584A - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Abstract

To stably enhance a performance of an electrochemical reaction single cell.SOLUTION: An electrochemical reaction single cell comprises an electrolyte layer, an air electrode and a fuel electrode. The fuel electrode includes: a first fuel electrode layer; and a second fuel electrode layer disposed between the first fuel electrode layer and the electrolyte layer and including an ion-conducting substance and an electron-conducting substance. The second fuel electrode layer has a porosity lower than that of the first fuel electrode layer. In at least one section of the second fuel electrode layer, there is a first region such that a gross interface length which is the sum total of a total interface length of particles of the ion-conducting substance and particles of the electron-conducting substance, a total interface length of particles of the ion-conducting substance and pores, and a total interface length of particles of the electron-conducting substance and pores is 2.5 μm/μmor larger.SELECTED DRAWING: Figure 7

Description

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

  A solid oxide fuel cell (hereinafter referred to as "SOFC") is known as one of the types of fuel cells that generate electricity using the electrochemical reaction of hydrogen and oxygen. The fuel cell single cell (hereinafter simply referred to as "single cell"), which is a constituent unit of SOFC, has a solid oxide-containing electrolyte layer and a predetermined direction (hereinafter referred to as "first direction") with respect to the electrolyte layer. And an anode disposed on the other side of the electrolyte layer in the first direction.

  A fuel electrode including a plurality of layers may be used as a fuel electrode constituting a single cell. Specifically, as a fuel electrode, a first fuel electrode layer (hereinafter, referred to as “support layer”) constituting the surface on the other side in the first direction of the fuel electrode, and a support layer and an electrolyte layer And a second fuel electrode layer (hereinafter referred to as "active layer") including an ion conductive material (eg, YSZ (yttria stabilized zirconia)) and an electron conductive material (eg, Ni (nickel)) And a fuel electrode containing the

  In the case of using a fuel electrode including a support layer and an active layer as a fuel electrode constituting a single cell, by setting the bonding length of the ion conductive material and the electron conductive material in the active layer to a predetermined range, A technique for improving the performance of a single cell is known (see, for example, Patent Document 1).

JP, 2014-26720, A

  As in the prior art described above, the performance of a single cell can be stably improved simply by setting the bonding length between the ion conductive material and the electron conductive material in the active layer constituting the fuel electrode of a single cell within a predetermined range. There is a problem that you can not

  In addition, such a subject is common to the electrolysis single cell which is a structural unit of a solid oxide type electrolysis cell (hereinafter, also referred to as “SOEC”) which generates hydrogen by utilizing the electrolysis reaction of water. It is a task. In the present specification, a fuel cell unit cell and an electrolysis unit cell are collectively referred to as an electrochemical reaction unit cell. Moreover, such a subject is a subject common to other types of electrochemical reaction single cells as well as SOFC and SOEC.

  The present specification discloses a technology that can solve the above-described problems.

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

(1) In the electrochemical reaction single cell disclosed in the present specification, an electrolyte layer, an air electrode disposed on one side in a first direction with respect to the electrolyte layer, and the first electrode relative to the electrolyte layer A first fuel electrode layer disposed on the other side of the first direction, the first fuel electrode layer constituting a surface of the other side of the first direction of the fuel electrode, and the first fuel electrode layer; A second fuel electrode layer disposed between the electrolyte layer and the second fuel electrode layer containing an ion conductive material and an electron conductive material; The porosity of the fuel electrode layer is lower than the porosity of the first fuel electrode layer, and at least one cross section of the second fuel electrode layer parallel to the first direction contains particles of the ion conductive material. The total length of the interface between the particle and the particle of the electron conductive material, and the particle and gas of the ion conductive material And the sum of the interface length between the total and the total surface length is the sum of the interface length between the particles and the pores of the electron conductive material is present the first region is 2.5 [mu] m / [mu] m ² or more. The inventor of the present invention has found that, in at least one cross section parallel to the first direction of the second fuel electrode layer, when there is a first region having a total interface length of 2.5 μm / μm ² or more, an electrochemical reaction unit is obtained. It has been newly found that the performance of the cell can be stably improved. The reason why the above effect is obtained by the above configuration is assumed to be as follows, though it is not necessarily clear. When the total interface length of the second fuel electrode layer is relatively long, the second fuel electrode layer has a fine structure, and the reaction field in the second fuel electrode layer is relatively large. It is considered that the performance of a single cell is improved. Also, if focusing only on the interface length between the particle of the ion conductive material and the particle of the electron conductive material, the interface length between the particle of the ion conductive material and the pores, or even if the interface length is relatively long, If the interface length between the particles of the electron conductive material and the pores is short, it is considered that the performance of the electrochemical reaction single cell is not sufficiently improved. The inventor of the present application has found that in addition to the total of the interface length between the particle of the ion conductive material and the particle of the electron conductive material, the total of the interface length between the particle of the ion conductive material and the pores and the particle of the electron conductive material Focus on the total interface length, which is an index that takes into consideration the total length of the surface and the interface with pores, and if the configuration with a relatively long total interface length is adopted, stably improve the performance of the electrochemical reaction single cell Found new things to do. Note that even if the total interface length of the second fuel electrode layer is relatively long, the second fuel cell is not satisfied with the requirement that the porosity of the second fuel electrode layer is lower than the porosity of the first fuel electrode layer. The contact area between the fuel electrode layer and the electrolyte layer may be reduced, or the diffusion of gas to the second fuel electrode layer may be suppressed, and the performance of the electrochemical reaction unit cell may not be sufficiently improved. The electrochemical reaction single 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 for the total interface length described above. Performance can be stably improved.

(2) In the electrochemical reaction unit cell, the number of particles of the electron conductive material located in the second region in at least one cross section of the second fuel electrode layer parallel to the first direction The second region may have a ratio of an area of the second region to an electron conductive material aggregation index of 1.5 μm ² / or more and less than 2.5 μm ² /. In this single electrochemical reaction cell, since the electron conductive substance aggregation index is not excessively small at 1.5 μm ² / piece or more, the number of isolated particles of the electron conductive substance is relatively small, so the second fuel An electron conduction path can be sufficiently secured in the electrode layer, and the performance of the electrochemical reaction single cell can be effectively improved. Further, in the present electrochemical reaction single cell, since the electron conductive substance aggregation index is not excessively large such as less than 2.5 μm ² / piece, the degree of aggregation of the particles of the electron conductive substance is not excessively high, and the electron Since the reduction of the three-phase interface due to excessive aggregation of the conductive material particles and the local reduction of pore diameter and pore blockage can be suppressed, the gas diffusion is enhanced by improving the pore dispersibility. The properties can be improved, and the performance of the electrochemical reaction unit cell can be effectively improved.

(3) In the electrochemical reaction unit cell, the first region may be a region having a total interface length of 3.0 μm / μm ² or more. According to the present electrochemical reaction unit cell, in the present electrochemical reaction unit cell, the total interface length in the first region is longer, so that the reaction field in the second fuel electrode layer is further increased. Performance can be further effectively improved.

(4) In the electrochemical reaction unit cell, the first region may be a region having a total interface length of 4.5 μm / μm ² or less. If the total interface length of the second fuel electrode layer is excessively long, it is considered that the structure is too small, the bending of the pores becomes large, the gas diffusibility decreases, and the performance of the electrochemical reaction single cell decreases. . In this single electrochemical reaction cell, since the total interface length in the first region is not excessively long such as 4.5 μm / μm ² or less, the decrease in gas diffusivity can be suppressed. Performance can be effectively improved.

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

  Note that the technology disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction single cell (fuel cell single cell or electrolysis single cell), a plurality of electrochemical reaction single cells It is possible to realize in the form of an electrochemical reaction cell stack (a fuel cell stack or an electrolysis cell stack), a method of manufacturing them, and the like.

It is a perspective view showing the appearance composition of fuel cell stack 100 in this embodiment. It is explanatory drawing which shows the XZ cross-section structure of the fuel cell stack 100 in the position of II-II of FIG. It is explanatory drawing which shows YZ cross-section structure of the fuel cell stack 100 in the position of III-III of FIG. It is explanatory drawing which shows the XZ cross-section structure of the two adjacent electric power generation units 102 in the same position as the cross section shown in FIG. It is explanatory drawing which shows YZ cross-section structure of the two adjacent electric power generation units 102 in the same position as the cross section shown in FIG. It is explanatory drawing which expands and shows YZ cross-section structure of a part (X1 part of FIG. 5) of the single cell 110. FIG. It is an explanatory view showing a detailed configuration of the active layer 320 of the fuel electrode 116. It is explanatory drawing which shows a performance evaluation result. FIG. 7 is an explanatory view showing a relationship between an inverse number of total interface length Lo in the active layer 320 and polarization resistance in the active layer 320. FIG. 10 is an explanatory view 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. In FIG.

A. Embodiment:
A-1. Constitution:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing an appearance configuration of a fuel cell stack 100 in the present embodiment, and FIG. 2 is an explanatory view showing an XZ cross-sectional configuration of the fuel cell stack 100 at a position II-II in FIG. FIG. 3 is an explanatory view showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position of III-III in FIG. In each figure, mutually orthogonal XYZ axes for specifying the direction are shown. In this specification, for convenience, the Z-axis positive direction is referred to as the upward direction, and the Z-axis negative direction is referred to as the downward direction. However, the fuel cell stack 100 actually has an orientation different from such an orientation. It may be installed. The same applies to FIG.

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

  A plurality of (eight in the present embodiment) holes are formed in the peripheral portion around the Z direction of each layer (power generation unit 102, end plates 104 and 106) constituting the fuel cell stack 100. The holes formed in each layer and corresponding to each other communicate with each other in the vertical direction, and form communication holes 108 extending in the vertical direction from one end plate 104 to the other end plate 106. In the following description, 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 vertically extending bolt 22 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 constituting the upper end of the fuel cell stack 100, and the bolt An insulating sheet 26 is interposed between the nut 24 fitted on the other side (lower side) of the electrode 22 and the lower surface of the end plate 106 constituting the lower end of the fuel cell stack 100. However, at the places where the gas passage members 27 described later are provided, insulating sheets disposed on the upper and lower sides of the gas passage members 27 and the gas passage members 27 between the nut 24 and the surface of the end plate 106, respectively. 26 and so on. The insulating sheet 26 is made of, for example, a mica sheet, a ceramic fiber sheet, a ceramic dust sheet, a glass sheet, a glass ceramic composite agent, or the like.

  The outer diameter of the shaft portion of each bolt 22 is smaller than the inner diameter of each communication hole 108. Therefore, a space is secured between the outer peripheral surface of the shaft portion of each bolt 22 and the inner peripheral surface of each communication hole 108. As shown in FIGS. 1 and 2, it is located near the midpoint of one side (the side on the X-axis positive direction side of the two sides parallel to the Y-axis) on the outer periphery of the fuel cell stack 100 around the Z direction. The oxidant gas OG is introduced from the outside of the fuel cell stack 100 into the space formed by the bolt 22 (bolt 22A) and the communication hole 108 through which the bolt 22A is inserted. It functions as an oxidant gas introduction manifold 161, which is a gas flow path for supplying to the unit 102, and is the middle point of the opposite side of this side (the side of the two sides parallel to the Y axis in the negative X axis direction). A space formed by the bolt 22 (bolt 22B) located in the vicinity and the communication hole 108 through which the bolt 22B is inserted is an oxidant off gas OOG which is a gas discharged from the air chamber 166 of each power generation unit 102. Burn Functions as the oxidizing gas discharging manifold 162 for discharging to the outside of the cell stack 100. In the present embodiment, for example, air is used as the oxidant gas OG.

  Further, as shown in FIGS. 1 and 3, the vicinity of the middle point of one side (the side on the Y-axis positive direction side of the two sides parallel to the X-axis) on the outer periphery of the fuel cell stack 100 around the Z direction. The fuel gas FG is introduced from the outside of the fuel cell stack 100 in the space formed by the bolt 22 (bolt 22D) located in the space and the communication hole 108 through which the bolt 22D is inserted. A bolt 22 functioning as a fuel gas introduction manifold 171 supplying to the unit 102 and located near the middle point of the opposite side of the side (the side of the two sides parallel to the X-axis in the negative Y-axis direction) A space formed by (the bolt 22E) and the communication hole 108 through which the bolt 22E is inserted is a fuel off gas FOG which is a gas discharged from the fuel chamber 176 of each power generation unit 102 as the fuel cell stack 1 Functions as a fuel gas exhaust manifold 172 for discharging to the outside of the 0. In the present embodiment, 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 portion 28 and a hollow cylindrical branch portion 29 branched from the side surface of the main body portion 28. The hole of the branch portion 29 communicates with the hole of the main body portion 28. A gas pipe (not shown) is connected to the branch portion 29 of each gas passage member 27. Further, as shown in FIG. 2, the holes of the main body portion 28 of the gas passage member 27 disposed at the position of the bolts 22A forming the oxidant gas introduction manifold 161 are in communication with the oxidant gas introduction manifold 161, The hole of the main body 28 of the gas passage member 27 disposed at the position of the bolt 22 B forming the oxidant gas discharge manifold 162 is in communication with the oxidant gas discharge manifold 162. Further, as shown in FIG. 3, the hole of the main body 28 of the gas passage member 27 disposed at the position of the bolt 22 D forming the fuel gas introduction manifold 171 is in communication with the fuel gas introduction manifold 171. The hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22E which forms the discharge manifold 172 is in communication with the fuel gas discharge manifold 172.

(Configuration of end plates 104 and 106)
The pair of end plates 104 and 106 is a substantially rectangular flat conductive member and is made of, for example, stainless steel. One end plate 104 is disposed on the upper side of the uppermost power generation unit 102, and the other end plate 106 is disposed on the lower side of the lowermost power generation unit 102. The plurality of power generation units 102 are held in a pressed state by the pair of end plates 104 and 106. The upper end plate 104 functions as a positive output terminal of the fuel cell stack 100, and the lower end plate 106 functions as a negative output terminal of the fuel cell stack 100.

(Configuration of power generation unit 102)
4 is an explanatory view showing the XZ cross-sectional configuration of two adjacent power generation units 102 at the same position as the cross section shown in FIG. 2, and FIG. 5 is adjacent to each other at the same position as the cross section shown in FIG. FIG. 6 is an explanatory view 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 the unit cell 110, the separator 120, the air electrode side frame 130, the air electrode side current collector 134, the fuel electrode side frame 140, and the fuel electrode side. A current collector 144 and a pair of interconnectors 150 constituting the top layer and the bottom layer of the power generation unit 102 are provided. In the peripheral portion around the Z direction in the separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150, holes corresponding to the communication holes 108 through which the above-described bolts 22 are inserted are formed.

  The interconnector 150 is a substantially rectangular flat 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 the mixing of reaction gases between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by 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. Further, since fuel cell stack 100 is provided with a pair of end plates 104 and 106, power generation unit 102 located at the top of fuel cell stack 100 does not have upper interconnector 150 and is located at the bottom. The power generation unit 102 does not have the lower interconnector 150 (see FIGS. 2 and 3).

  The unit cell 110 includes an electrolyte layer 112, an air electrode (cathode) 114 disposed on the upper side of the electrolyte layer 112, and a fuel electrode (anode) 116 disposed on the lower side of the electrolyte layer 112. 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 the present embodiment, the thickness (the size in the vertical direction) of the fuel electrode 116 is thicker than the thicknesses of the air electrode 114 and the electrolyte layer 112, and the fuel electrode 116 supports other layers constituting the unit cell 110. That is, the unit cell 110 of this embodiment is a unit cell of a fuel electrode support type.

  The electrolyte layer 112 is a flat plate-shaped member that is substantially rectangular in a Z direction view, and is a dense (low porosity) layer. The electrolyte layer 112 is formed of, for example, a solid oxide such as YSZ (yttria stabilized zirconia). Thus, the unit cell 110 of the present embodiment is a solid oxide fuel cell (SOFC) using a solid oxide as an electrolyte.

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

  The fuel electrode 116 is a substantially rectangular flat plate-like member having substantially the same size as the electrolyte layer 112 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 the YZ cross-sectional configuration of a part (X1 part in FIG. 5) of the single cell 110 in an enlarged manner. As shown in FIG. 6, the fuel electrode 116 includes a support layer 310 constituting 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 the present 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 and the like contained in the fuel gas FG to generate electrons and water vapor. The active layer 320 contains an oxygen ion conductive substance (in the present embodiment, YSZ which is a ceramic) and an electron conductive substance (in the present embodiment, Ni which is a transition metal). 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 the present embodiment, the support layer 310 also contains an oxygen ion conductive material (YSZ) and an electron 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-shaped member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed in the vicinity of the center, and is formed of, for example, metal. The peripheral portion of the hole 121 in the separator 120 faces the peripheral portion of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is bonded to the electrolyte layer 112 (unit cell 110) by a bonding portion 124 formed of a brazing material (for example, Ag wax) disposed in the facing 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, and the gas leaks from the one electrode side to the other electrode side in the peripheral portion of the unit cell 110. Be suppressed.

  The air electrode side frame 130 is a frame-shaped member in which a substantially rectangular hole 131 penetrating in the vertical direction is formed in the vicinity of the center, and is formed of, for example, an insulator such as mica. The hole 131 of the air electrode side frame 130 constitutes an air chamber 166 facing the air electrode 114. The air electrode side frame 130 is in contact with the peripheral portion of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral portion of the surface of the interconnector 150 facing the air electrode 114. . Further, the air electrode side frame 130 electrically insulates between the pair of interconnectors 150 included in the power generation unit 102. Further, an oxidant gas supply passage 132 communicating the oxidant gas introduction manifold 161 with the air chamber 166, and an oxidant gas communicating the air chamber 166 with the oxidant gas discharge manifold 162 in the air electrode side frame 130. A discharge communication hole 133 is formed.

  The fuel electrode side frame 140 is a frame-like member in which a substantially rectangular hole 141 penetrating in the vertical direction is formed in the vicinity of the center, and is made of, for example, metal. 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 portion of the surface of the separator 120 facing the electrolyte layer 112 and the peripheral portion of the surface of the interconnector 150 facing the fuel electrode 116. Further, in the fuel electrode side frame 140, a fuel gas supply passage 142 communicating the fuel gas introduction manifold 171 with the fuel chamber 176, and a fuel gas discharge passage 143 communicating the fuel chamber 176 with the fuel gas discharge manifold 172. And are formed.

  The fuel electrode side current collector 144 is disposed in the fuel chamber 176. The fuel electrode side current collector 144 is provided with an interconnector facing portion 146, an electrode facing portion 145, and a connecting portion 147 connecting the electrode facing portion 145 and the interconnector facing portion 146, for example, nickel or nickel alloy , Stainless steel or the like. The electrode facing portion 145 is in contact with the surface of the fuel electrode 116 opposite to the surface facing the electrolyte layer 112, and the interconnector facing portion 146 is on the surface of the interconnector 150 facing the fuel electrode 116. It is in contact. However, as described above, since the lowermost power generation unit 102 in the fuel cell stack 100 does not have the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 is the lower end plate Contact 106. The fuel electrode side current collector 144 electrically connects the fuel electrode 116 and the interconnector 150 (or the end plate 106) because of such a configuration. A spacer 149 made of mica, for example, is disposed between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to the temperature cycle and reaction gas pressure fluctuation, and the fuel electrode 116 and the interconnector 150 (or end plate 106) via the fuel electrode side current collector 144 The electrical connection with is well maintained.

  The air electrode side current collector 134 is disposed in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of substantially square pole 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 opposite to the air electrode 114. However, as described above, since the power generation unit 102 positioned at the top in the fuel cell stack 100 does not have the upper interconnector 150, the air electrode side current collector 134 in the power generation unit 102 is the upper end plate It is in contact with 104. Because of such a configuration, the air electrode side current collector 134 electrically connects the air electrode 114 and the interconnector 150 (or the end plate 104). The air electrode 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 by a conductive coat, and a conductive bonding layer for bonding the both is interposed between the air electrode 114 and the air electrode side current collector 134. It may be done.

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 oxidant gas OG is supplied to the oxidant gas introduction manifold 161 through the holes of the branch part 29 and the main body part 28 of the gas passage member 27, and the oxidant gas introduction manifold 161 oxidizes each power generation unit 102. The air is supplied to the air chamber 166 through the agent gas supply passage 132. Further, as shown in FIGS. 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 through 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. The fuel is supplied to the fuel chamber 176 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, the single cell 110 performs power generation by the electrochemical reaction of the oxidant gas OG and the fuel gas FG. It will be. This power generation reaction is an exothermic reaction. In each power generation unit 102, the air electrode 114 of the unit cell 110 is electrically connected to one of the interconnectors 150 through the air electrode side current collector 134, and the fuel electrode 116 is through the fuel electrode side current collector 144. The other interconnector 150 is electrically connected. 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 functioning as the output terminals of the fuel cell stack 100. Since the SOFC generates power at a relatively high temperature (eg, 700 ° C. to 1000 ° C.), the fuel cell stack 100 is heated (after start-up, until the heat can be maintained by the heat generated by the power generation). (Not shown).

  The oxidant off gas OOG discharged from the air chamber 166 of each power generation unit 102 is discharged to the oxidant gas discharge manifold 162 through the oxidant gas discharge communication hole 133 and further oxidized as shown in FIGS. 2 and 4. The fuel cell stack 100 is provided through the holes of the main body portion 28 of the gas passage member 27 and the branch portion 29 provided at the position of the agent gas discharge manifold 162 and the gas pipe (not shown) connected to the branch portion 29. Discharged to the outside of the Further, as shown in FIGS. 3 and 5, the fuel off gas FOG discharged from the fuel chamber 176 of each power generation unit 102 is discharged to the fuel gas discharge manifold 172 through the fuel gas discharge communication hole 143, and further the fuel gas To the outside of the fuel cell stack 100 through a gas pipe (not shown) connected to the branch portion 29 through the holes of the main body portion 28 of the gas passage member 27 and the branch portion 29 provided at the position of the discharge manifold 172 Exhausted.

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 view showing the detailed structure of the active layer 320 of the fuel electrode 116. As shown in FIG. FIG. 7 is an enlarged view of the YZ cross-sectional configuration of a part of the active layer 320 (X2 part in FIG. 6).

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

  In the fuel electrode 116 in the present embodiment, the porosity of the active layer 320 is lower than the porosity of the support layer 310. The porosity of the active layer 320 is preferably 10 vol% or more and 30 vol% or less, and 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. 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.

Further, in the active layer 320 of the fuel electrode 116 in the present embodiment, the total interface 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 particle of the ion conductive material (in the present embodiment, the YSZ particles Py) and the particle of the electron conductive material (in the present embodiment, the Ni particles Pn). Sum (hereinafter referred to as “YSZ-Ni interface length La”) and total length of interface Bb between ion conductive substance particles (YSZ particles Py) and pores PO (hereinafter referred to as “YSZ-pore interface length Lb” And the sum of the length of the interface Bc between the particle of the electron conductive material (Ni particle Pn) and the pore PO (hereinafter referred to as “Ni-pore interface length Lc”). That is, the total interface length Lo is a total of the lengths of the interfaces in the active layer 320. In the present embodiment, the total interface length Lo of the active layer 320 is relatively long at 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. The total interface 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 And 55% or less.

Further, in the active layer 320 of the fuel electrode 116 in the present embodiment, the electron conductive substance aggregation index Ic is 1.5 μm ² / piece or more, 2 in the cross section parallel to the vertical direction (for example, the YZ cross section shown in FIG. 7). It is less than .5 μm ² /. Here, the electron conductive substance aggregation index Ic is the ratio of the area of the area to the number of particles (Ni particles Pn) of the electron conductive substance located in a certain area. That is, the electron conductive substance aggregation index Ic is an index indicating the degree of aggregation of particles (Ni particles Pn) of the electron conductive substance. In the present embodiment, the electron conductive substance aggregation index Ic of the active layer 320 is not excessively small nor excessively large such as 1.5 μm ² / or more and less than 2.5 μm ² / /.

  The average particle diameter 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. The average particle diameter 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 YSZ particles Py to Ni particles Pn in the active layer 320 is preferably 65:35 to 40:60.

A-4. Method of Manufacturing Fuel Cell Stack 100:
The method of manufacturing the fuel cell stack 100 in the present embodiment is, for example, as follows.

(Preparation of green sheet for fuel electrode support layer)
To mixed powder of NiO powder and YSZ powder, add organic beads as pore former, butyral resin, DOP as plasticizer, mixed solvent of dispersant and toluene and ethanol, and add to ball mill Mix and prepare a slurry. The organic beads are, for example, spherical particles formed of a polymer such as polymethyl methacrylate or polystyrene. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for a 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 in producing the green sheet for the fuel electrode support layer may be appropriately set as long as the performance is satisfied.

(Production of green sheet for fuel electrode active layer)
To a mixed powder of NiO powder and YSZ powder, butyral resin, DOP as a plasticizer, a dispersant, and a mixed solvent of toluene and ethanol are added and mixed in a ball mill to prepare a slurry. In addition, you may add the organic bead as a pore making material in the case of adjustment of a slurry similarly to the preparation method of the green sheet for fuel electrode support layers mentioned above. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for a 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 in 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 mixed solvent of butyral resin, DOP which is a plasticizer, a dispersant, and toluene and ethanol is added to YSZ powder, and mixed in a ball mill to prepare a slurry. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for electrolyte layer having a predetermined thickness (for example, 10 μm).

(Production of a laminate of the electrolyte layer 112 and the 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 laminate of the green sheet 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)
An LSCF powder, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent are mixed, the viscosity is adjusted, and a paste for air electrode is prepared. A laminate in which the prepared paste for air electrode is applied by screen printing, for example, on the surface of the electrolyte layer 112 in the laminate of the electrolyte layer 112 and the fuel electrode 116 described above and dried, and the paste for air electrode is applied Are fired at a predetermined firing temperature (eg, 1100.degree. 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 manufactured.

  After producing a plurality of unit cells 110 according to the method described above, assembling steps (for example, attaching other members such as separator 120 to each unit cell 110, laminating the plurality of unit cells 110, fastening with bolts 22 Process). Thus, the manufacture of the fuel cell stack 100 is 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 step is realized, for example, by exposing the fuel electrode 116 to a hydrogen atmosphere at a predetermined temperature for a predetermined time. The reducing gas used in the reducing step is not limited to hydrogen, and may be another gas such as methane gas. As described above, the manufacturing of the fuel cell stack 100 in the power generation operable state is completed.

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

(Porosity of the fuel electrode 116)
The porosity of each layer (the active layer 320 and the support layer 310) constituting the fuel electrode 116 is adjusted, for example, by a slurry for producing a green sheet (a green sheet for the fuel electrode active layer or a green sheet for the fuel electrode support layer). This can be realized by adjusting the addition amount of the pore forming material when preparing. Specifically, when preparing a slurry for producing a green sheet for a certain layer, the porosity of the layer becomes higher as the addition amount of the pore forming material is increased.

(Total interface length Lo in the active layer 320 of the fuel electrode 116)
The adjustment of the total interface length Lo in the active layer 320 of the fuel electrode 116 can be achieved, for example, by using an electron conductive material (Ni) or an ion conductive material (YSZ) when preparing a slurry for producing a green sheet for the fuel electrode active layer. This can be achieved by adjusting the particle diameter of the raw material of (1), adjusting the size of the pore forming material, or adjusting the firing conditions at the time of firing the green sheet for the fuel electrode active layer. Specifically, as the particle diameter of the raw material of the electron conductive material (Ni) or the ion conductive material (YSZ) is reduced, the total interface length Lo in the active layer 320 becomes longer. In addition, as the size of the pore forming material is reduced, the total interface length Lo in the active layer 320 becomes longer. In addition, the lower the firing temperature and the shorter the firing time, the longer the total interface length Lo in the active layer 320.

(Electron conductive substance aggregation index Ic in the active layer 320 of the fuel electrode 116)
The adjustment of the electron conductive material aggregation index Ic in the active layer 320 of the fuel electrode 116 can be achieved, for example, by using particles of the raw material of the electron conductive material (Ni) in preparing a slurry for producing a green sheet for the fuel electrode active layer. This can be achieved by adjusting the diameter, adjusting the dispersion performance by selecting the dispersant and setting the addition amount, and adjusting the firing conditions at the time of firing the green sheet for the fuel electrode active layer. . Specifically, the electron conductive substance aggregation index Ic in the active layer 320 decreases as the particle diameter of the raw material of the electron conductive substance (Ni) decreases. Also, as the dispersing ability of the dispersant is increased, the electron conductive material aggregation index Ic in the active layer 320 decreases. In addition, as the firing temperature is lowered and the firing time is shortened, the electron conductive material aggregation index Ic in the active layer 320 is decreased.

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

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 manufacturing method of the single cell 110 mentioned above. Each sample has the porosity (vol%) of the fuel electrode 116 (the active layer 320 and the support layer 310), the total interface length Lo (μm / μm ² ) of the active layer 320, and the YSZ-Ni interface length La (μm / μm / μm ² ) and the electron conductive substance aggregation 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 unit cells 110 of each sample, the oxidant gas OG is supplied to the air electrode 114 at about 700 ° C., the fuel gas FG is supplied to the fuel electrode 116, and the current density is The output voltage of the unit cell 110 at 0.55 A / cm ² was measured, and it was evaluated in five steps of “A” to “E” as follows according to the value of the measured voltage (“A” Is the most excellent rating, and "E" is the most inferior rating).
Evaluation: "A": voltage: 0.920 V or more Evaluation: "B": voltage: 0.915 V or more, less than 0.920 V Evaluation: "C": voltage: 0.910 V or more Less than 0.915V Evaluation: "D": voltage: 0.900 V or more, less than 0.910 V Evaluation: "E": voltage: less than 0.900 V

A-6-3. Evaluation results:
As shown in FIG. 8, in the sample S1, the evaluation result of the power generation characteristics was the lowest "E" evaluation. The reason why the evaluation result of the sample S1 is lowered is assumed to be as follows, though it is not necessarily clear. That is, in the sample S1, the total interface length Lo in the active layer 320 is relatively short, 2.28 μm / μm ^2, and it is considered that the power generation performance is degraded because the reaction site in the active layer 320 is relatively small. Be

On the other hand, in the samples S2 to S7, the evaluation results of the power generation characteristics were “D” or more. The reason why the evaluation results of the samples S2 to S7 are higher than the evaluation result of the sample S1 is assumed as follows, although it is not necessarily clear. That is, in the samples S2 to S7, the total interface length Lo in the active layer 320 is relatively long as 2.5 μm / μm ² or more, and the active layer 320 has a fine structure, and the reaction site in the active layer 320 It is considered that the power generation performance is improved because

However, in the sample S8, although the total interface 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 the sample S8, unlike the samples S2 to S7, the porosity of the active layer 320 is higher than the porosity of the support layer 310. Therefore, in the sample S8, although the total interface length Lo in the active layer 320 is relatively long, the porosity of the support layer 310 is relatively high, and as a result, the contact area between the active layer 320 and the electrolyte layer 112 decreases. It is considered that the power generation performance is not sufficiently improved because the diffusion of the gas to the active layer 320 is suppressed.

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

  Among the interface lengths (YSZ-Ni interface length La, YSZ-pore interface length Lb, Ni-pore interface length Lc) constituting the total interface length Lo in the active layer 320, only the YSZ-Ni interface length La is noted. Then, YSZ-Ni interface length La is longer in sample S1 which was "E" evaluation compared with samples S2-S5 which were "D" evaluation or more. Therefore, in the sample S1, although YSZ-Ni interface length La is relatively long, other interface lengths (YSZ-pore interface length Lb and Ni-pore interface length Lc) are relatively short, so the power generation performance is sufficiently improved. It is thought that it did not do.

  FIG. 9 is an explanatory view showing the relationship between the reciprocal of the total interface length Lo in the active layer 320 and the activation polarization in the active layer 320. In FIG. FIG. 10 is an explanatory view 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. FIGS. 9 and 10 show a plurality of points indicating measurement values for a plurality of samples and approximate straight lines calculated based on the plurality of points. However, in FIG. 9, the point of the sample with the smallest inverse number of the total interface length Lo (shown in parentheses in FIG. 9) is not referred to in the calculation of 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 (ie, the higher the power generation performance). There is a tendency. 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, the smaller the polarization resistance in the active layer 320, the smaller the inverse of the YSZ-Ni interface length La. is there. However, as apparent from the comparison between FIG. 9 and FIG. 10, the correlation between the YSZ-Ni interface length La in the active layer 320 and the polarization resistance is relatively low, while the total interface length Lo in the active layer 320 is polarized. The correlation with resistance is extremely high. This is because, even if the YSZ-Ni interface length La in the active layer 320 is relatively long, the polarization in the active layer 320 is possible if the other interface lengths (YSZ-pore interface length Lb and Ni-pore interface length Lc) are relatively short. This is because the resistance can be large. Therefore, it is difficult to improve the power generation performance of the single cell 110 without variation even when focusing only on the YSZ-Ni interface length La in the active layer 320, focusing on the total interface length Lo in the active layer 320. It can be said that the power generation performance of the single cell 110 can be stably improved only by lengthening the length Lo.

Further, among samples S2 to S7 in which the evaluation result of the power generation characteristic is “D” or more, in the samples S2 and S3, the evaluation result is “D” evaluation, while in the samples S4 to S7, the evaluation result is “C It was more than evaluation. In the sample S2, the electron conductive substance aggregation index Ic is less than 1.5 μm ² / piece, and in the sample S3, the electron conductive substance aggregation index Ic is 2.5 μm ² / piece or more, while in the samples S4 to S7 And the electron conductive substance aggregation index Ic is 1.5 μm ² / or more and less than 2.5 μm ² /. As in the case of sample S2, when the electron conductive substance aggregation index Ic is excessively small, the isolated Ni particles Pn become relatively large, and the electron conduction path in the active layer 320 can not be sufficiently secured. Is considered to decrease. On the other hand, when the electron conductive substance aggregation index Ic is excessively large as in the sample S3, the Ni particles Pn are excessively aggregated to reduce not only the three-phase interface but also the homogeneity of the fine structure. It is considered that the dispersibility of the pores PO in the active layer 320 is reduced, the diameter of the pores PO is locally reduced, the gas diffusivity is reduced, and the power generation performance is also reduced. On the other hand, in the samples S4 to S7, the electron conductive substance aggregation index Ic is not less than 1.5 μm ² / piece and not more than 2.5 μm ² / piece, and it is isolated because it is neither excessively small nor excessively large. By reducing the Ni particles Pn, an electron conduction path can be sufficiently secured in the active layer 320, and excessive aggregation of the Ni particles Pn suppresses a decrease in gas diffusivity due to a decrease in the dispersibility of the pores PO. It is considered that the power generation performance could be effectively improved.

Further, among samples S4 to S7 in which the evaluation result of the power generation characteristic is "C" or higher, in the samples S4 and S5, the evaluation result is "C" evaluation, while in the samples S6 and S7, the evaluation result is "B It was more than evaluation. In the samples S4 and S5, the total interface length Lo in the active layer 320 is less than 3.0 μm / μm ² , while in the samples S6 and S7, the total interface length Lo in the active layer 320 is 3.0 μm / μm ² or more . As described above, in samples S6 and S7, since the total interface length Lo in the active layer 320 is longer, the active layer 320 has a finer structure, and the number of reaction sites in the active layer 320 is further increased. It is considered that the improvement has been made more effectively.

Further, among the samples S6 and S7 in which the evaluation result of the power generation characteristic is “B” or more, the evaluation result is “B” evaluation in the sample S6, while the evaluation result is “A” evaluation in the sample S7. there were. In the sample S6, while the total interface length Lo in the active layer 320 is longer than 4.5 μm / μm ² , in the sample S7, the total interface length Lo in the active layer 320 is 4.5 μm / μm ² or less. In sample S6, since the total interface length Lo in the active layer 320 is excessively long, the structure of the active layer 320 is too fine, whereby the bending of the pores PO becomes large, and as a result, the gas diffusivity decreases and the power generation performance decreases. It is considered to be On the other hand, in the 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 caused by the bending of the pores PO, and the power generation performance is extremely effective. It is considered to have improved.

According to the above performance evaluation results, in order to improve the power generation characteristics of the unit cell 110, the porosity of the active layer 320 is lower than the porosity of the support layer 310, and the total interface length Lo in the active layer 320 is 2. The electron conductive substance aggregation index Ic is preferably 5 μm / μm ² or more, more preferably 1.5 μm ² / or more and 2.5 μm ² / or less, and the total interface length Lo in the active layer 320 is It is more preferable that the thickness be 3.0 μm / μm ² or more, and it is extremely preferable that the total interface length Lo in the active layer 320 be 4.5 μm / μm ² or less.

A-7. How to identify each characteristic of anode 116:
The specification method of each characteristic (electron conductive substance aggregation index Ic of active layer 320, total interface length Lo of active layer 320, porosity of active layer 320 and support layer 310) of fuel electrode 116 is as follows. First, a cross section parallel to the vertical direction in the single cell 110 (however, a cross section including the fuel electrode 116 (the active layer 320)) is arbitrarily set, and an FIB-SEM (copy of the active layer 320 is shown at any position in the cross section). An SEM image (eg 5000 ×) at an accelerating voltage of 1.5 kV) is obtained. The SEM image is, for example, an image in which the whole in the vertical direction of the active layer 320 can be confirmed, and a portion presumed to be a boundary B1 (see FIG. 6) between the electrolyte layer 112 and the active layer 320 Of the 10 divided areas obtained by dividing into 10 equal parts in the direction, it is located in the uppermost divided area, and is presumed to be the boundary B2 between the active layer 320 and the support layer 310 (see FIG. 6) The part is an image located in the lowermost divided area.

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

  In the above-mentioned SEM image, discrimination between particles of electron conductive material (Ni particles Pn in the present embodiment) and particles of ion conductive material (YSZ particles Py in the present embodiment) uses, for example, contrast difference in the SEM image Can be realized. Specifically, by analyzing the SEM image, the SEM image can be classified into three regions according to the lightness. As a method of identifying the region of the Ni particles Pn and the region of the YSZ particles Py from the three regions according to the lightness, it is preferable to use SEM-EDS. Since the element can be identified by the SEM-EDS, the region of the Ni particles Pn and the region of the YSZ particles Py can be identified from the SEM image. In addition, the remaining area among the three areas according to the lightness can be identified as the area of the pore PO.

  In the SEM image, the area of a specific region in the active layer 320 is specified, and the number of Ni particles Pn present in the region is counted, and the area is divided by the number to obtain electrons in the active layer 320. The conductive substance aggregation index Ic can be identified.

  In addition, each of the interface lengths (YSZ-Ni interface length La, YSZ-pore interface length Lb in the active layer 320 is analyzed by analyzing the SEM image using image analysis software (for example, “HALCON” manufactured by Lynx Corporation). 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. Preferably, the total interface length Lo is specified for the entire active layer 320.

  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, the SEM image including the support layer 310 is acquired, the area of the specific area in the support layer 310 is specified, the area occupied by the pores PO is specified, and the area of the specific area in the support layer 310 is specified. 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. Modification:
The technology disclosed in the present specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the scope of the present invention. For example, the following modifications are also possible.

  The configuration of the unit 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 is a two-layer structure of the active layer 320 and the support layer 310, but the fuel electrode 116 includes other layers other than the active layer 320 and the support layer 310. It is also good.

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 there is a region having a total interface length Lo of 2.5 μm / μm ² or more in at least one cross section parallel to the vertical direction of the active layer 320, the reaction field is relatively large at least in the region. The power generation performance of the cell 110 can be improved. It is preferable that the distance from the boundary B1 between the active layer 320 and the electrolyte layer 112 be 10 μm or less. The area corresponds to the first area in the claims.

Similarly, in the above embodiment, the electron conductive substance aggregation index Ic is 1.5 μm ² / piece or more, 2.5 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 However, the electron conductive substance aggregation index Ic is not less than 1.5 μm ² / piece and not less than 2.5 μm ² / piece in at least one cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116. If there is a region that is less than, at least in the region, electron conduction paths can be sufficiently secured in the region by reducing isolated Ni particles Pn, and pores due to excessive aggregation of Ni particles Pn Since a decrease in gas diffusivity caused by a decrease in the dispersibility of PO can be suppressed, the power generation performance of the single cell 110 can be improved. It is preferable that the distance from the boundary B1 between the active layer 320 and the electrolyte layer 112 be 10 μm or less. The area corresponds to a second area in the claims. The first area may be the same as the second area or may be another area.

  Moreover, the material which forms each member in the said embodiment is an illustration to the last, and each member may be formed with another material. For example, in the above embodiment, Ni is employed as the electron conductive material contained in the active layer 320 of the fuel electrode 116, but other electron conductive materials such as Mn, Fe, Co, Cu, etc. can be used. is there. However, since Ni has a high affinity to hydrogen, it is preferable to use Ni as the electron conductive material contained in the active layer 320 of the fuel electrode 116. In the above embodiment, YSZ is employed as the ion conductive substance contained in the active layer 320 of the fuel electrode 116, but other ion conductive substances such as ScSZ (scandia stabilized zirconia) can be used. is there. Further, the active layer 320 of the fuel electrode 116 contains a substance having both electron conductivity and ion conductivity (for example, GDC (gadolinium-doped ceria)), which is an electron conductive substance and an ion. It may function as both a conductive material. In this case, the total interface length Lo means the interface length between the substance and the pore 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 another material (for example, metal).

Further, in the above embodiment, the number of unit cells 110 included in the fuel cell stack 100 is merely an example, and the number of unit cells 110 is appropriately determined according to the output voltage and the like required of the fuel cell stack 100. In the above embodiment, the total interface length Lo is 2.5 μm / μm in at least one cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116 for all the unit cells 110 included in the fuel cell stack 100. ^It is not necessary to satisfy the condition that there is a region of ^two or more, etc., and if the condition is satisfied for at least one single cell 110 included in the fuel cell stack 100, improve the power generation performance for the single cell 110. It can be said that

  Further, in the above embodiment, the fuel cell stack 100 has a configuration in which a plurality of flat single cells 110 are stacked, but the present invention is described in other configurations, for example, in WO 2012/165409. Thus, the present invention is similarly applicable to a configuration in which a plurality of substantially cylindrical fuel cell single cells are connected in series.

Further, in the above embodiment, SOFCs that generate electric power using electrochemical reaction between hydrogen contained in fuel gas and oxygen contained in oxidant gas are targeted, but the present invention relates to the electrolysis reaction of water The present invention is similarly applicable to an electrolytic single cell which is a constituent unit of a solid oxide electrolytic cell (SOEC) that uses hydrogen to generate hydrogen, and an electrolytic cell stack including a plurality of electrolytic single cells. The configuration of the electrolytic cell stack is not described in detail here because it is known as described in, for example, JP-A-2016-81813, but it is roughly the same as the fuel cell stack 100 in the embodiment described above. Configuration. That is, the fuel cell stack 100 in the embodiment described above may be read as an electrolysis cell stack, the power generation unit 102 may be read as an electrolysis cell unit, and the single cell 110 may be read as an electrolysis single cell. However, during operation of the electrolytic 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), and through the communication hole 108 Water vapor as a source gas is supplied. As a result, an electrolysis reaction of water occurs in each electrolysis single cell, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out to the outside of the electrolysis cell stack through the communication hole 108. Also in such an electrolytic single cell, a region having a total interface length Lo of 2.5 μm / μm ² or more exists in at least one cross section parallel to the vertical direction of the active layer 320 of the fuel electrode 116 described above If the following condition is satisfied, the performance of the single cell 110 can be improved.

  In the above embodiment, the solid oxide fuel cell (SOFC) has been described as an example, but the present invention is also applicable to other types of fuel cells (or electrolytic cells) such as a molten carbonate fuel cell (MCFC). It is 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 portion 130: air electrode side frame 131: hole 132: oxidant gas supply communication hole 133: oxidant gas discharge communication hole 134: air electrode side Current collector 135: Current collector element 140: Fuel electrode side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode current collector 145: Electrode facing portion 146: Interconnect facing Part 147: Joint part 149: Spacer 150: Interconnector 161: oxidant gas inlet manifold 162: oxidant gas outlet manifold 166: air chamber 171: fuel gas inlet manifold 172: fuel gas outlet manifold 176: fuel chamber 310: support layer 320: active layer

Claims (6)

An electrolyte layer,
An air electrode disposed on one side of the electrolyte layer in a first direction;
A fuel electrode disposed on the other side in the first direction with respect to the electrolyte layer, the first fuel electrode layer constituting a surface on the other side in the first direction in the fuel electrode; The fuel electrode including a second fuel electrode layer disposed between the first fuel electrode layer and the electrolyte layer and including an ion conductive material and an electron conductive material;
In the electrochemical reaction unit cell provided with
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 sum of the interface lengths of the particles of the ion conductive material and the particles of the electron conductive material, and the ion conductive material A first region having a total interface length of 2.5 μm / μm ² or more which is the sum of the total of the interface length between the particle and the pore and the interface length between the particle and the pore of the electron conductive material An electrochemical reaction unit cell characterized by the presence of In the electrochemical reaction single cell according to claim 1,
The ratio of the area of the second region to the number of particles of the electron conductive material located in the second region in at least one cross section of the second fuel electrode layer parallel to the first direction An electrochemically conductive single cell characterized in that the second region having an electron conductive substance aggregation index of 1.5 μm ² / or more and less than 2.5 μm ² / is present. In the electrochemical reaction unit cell according to claim 1 or 2,
The electrochemical reaction single cell, wherein the first region is a region where the total interface length is 3.0 μm / μm ² or more. The electrochemical reaction unit cell according to any one of claims 1 to 3.
The electrochemical reaction single cell, wherein the first region is a region where the total interface length is 4.5 μm / μm ² or less. In the electrochemical reaction single cell according to any one of claims 1 to 4,
The 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 in the first direction,
An electrochemical reaction cell stack, wherein at least one of the plurality of electrochemical reaction unit cells is the electrochemical reaction unit cell according to any one of claims 1 to 5.

Images