JP2018174039A - Electrochemical reaction unit and electrochemical reaction cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the performance of an electrochemical reaction unit.SOLUTION: An electrochemical reaction unit comprises a single cell having an electrolyte layer, an air electrode disposed on one side of the electrolyte layer in a first direction, and a fuel electrode disposed on the other side of the electrolyte layer in the first direction. The fuel electrode includes: a 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 disposed between the first fuel electrode layer and the electrolyte layer. The electrochemical reaction unit further comprises a current collector having a plurality of current collecting parts put in electrical conduction with the surface of the first fuel electrode layer on the other side in the first direction. The first fuel electrode layer has a porosity of 35% or more. As to a particular current collecting part of the plurality of current collecting parts, the first ratio (β/α) which is a ratio of a thickness β of the first fuel electrode layer in the first direction to a shortest distance α between the particular current collecting part and the current collecting part adjacent thereto in a second direction orthogonal to the first direction is 0.18 or more.SELECTED DRAWING: Figure 13

Description

  The technology disclosed herein relates to electrochemical reaction units.

  A solid oxide fuel cell (hereinafter referred to as “SOFC”) is known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. A fuel cell power generation unit (hereinafter referred to as “power generation unit”), which is a constituent unit of SOFC, includes a fuel cell single cell (hereinafter referred to as “single cell”). The single cell includes an electrolyte layer, an air electrode disposed on one side in a predetermined direction with respect to the electrolyte layer (hereinafter referred to as “first direction”), and the other side in the first direction with respect to the electrolyte layer. And a fuel electrode disposed on the surface.

  The power generation unit includes a conductive current collector disposed on the other side in the first direction with respect to the fuel electrode. The current collector is a member for taking out the electric power generated by the power generation reaction in the single cell. The current collector has a plurality of current collectors that are electrically connected to the surface on the other side in the first direction of the fuel electrode. During the power generation operation, electrons are exchanged between the fuel electrode and the current collector at a portion where the surface of the fuel electrode is electrically connected to each current collector of the current collector. Further, the fuel gas supplied to the fuel chamber facing the fuel electrode is fueled from a portion of the surface of the fuel electrode that is not opposed to each current collector of the current collector (not covered by each current collector). It flows into the pole.

  Conventionally, in order to improve the performance of the power generation unit, a preferable range of the thickness of the fuel electrode (thickness in the first direction) has been proposed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-190824

  However, just considering the preferable range of the thickness of the fuel electrode as in the past, the performance of the power generation unit cannot be sufficiently improved, and there is room for further performance improvement.

 Such a problem is common to the electrolytic cell unit that is a constituent unit of a solid oxide electrolytic cell (hereinafter referred to as “SOEC”) that generates hydrogen using an electrolysis reaction of water. It is. In the present specification, the fuel cell power generation unit and the electrolysis cell unit are collectively referred to as an electrochemical reaction unit.

  In this specification, the technique which can solve the subject mentioned above is disclosed.

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

(1) The electrochemical reaction unit disclosed in the present specification includes an electrolyte layer, an air electrode disposed on one side in a first direction with respect to the electrolyte layer, and the first with respect to the electrolyte layer. A fuel electrode disposed on the other side of the fuel electrode, the first fuel electrode layer constituting the surface of the fuel electrode on the other side in the first direction, the first fuel electrode layer, and the fuel electrode An electrochemical reaction unit cell comprising: a fuel electrode comprising: a second fuel electrode layer disposed between the electrolyte layer; and the first fuel electrode layer in the first direction. A conductive current collector having a plurality of current collectors disposed on the other side and conducting to the surface of the first fuel electrode layer on the other side in the first direction. The porosity of the first fuel electrode layer is 35% or more, and is at least of the plurality of current collectors. For one specific current collector, the shortest distance α between the specific current collector in the second direction orthogonal to the first direction and the current collector adjacent to the specific current collector The first ratio (β / α), which is the ratio of the thickness β of the first fuel electrode layer in the first direction, is 0.18 or more. In this electrochemical reaction unit, since the porosity of the first fuel electrode layer constituting the surface of the other side in the first direction in the fuel electrode is 35% or more, gas is favorably contained in the first fuel electrode layer. The gas diffusion polarization can be suppressed from increasing. The electrochemical reaction unit has a configuration in which the thickness β of the first fuel electrode layer is thick to some extent and / or the shortest distance α between the current collector and the current collector of the current collector is short to some extent. Therefore, when electrons generated in the second fuel electrode layer functioning as a reaction field in the fuel electrode move along a direction in which the inclination with respect to the first direction is within a certain range, the inside of the second fuel electrode layer Thus, it is possible to reduce the region where the generated electrons do not easily reach the current collector of the current collector, and to improve the performance of the electrochemical reaction unit by suppressing the increase in activation polarization. Therefore, according to this electrochemical reaction unit, the performance of the electrochemical reaction unit can be improved.

(2) In the electrochemical reaction unit, with respect to the specific current collector, the first direction with respect to a width γ of a portion of the specific current collector facing the first fuel electrode layer in the second direction The second ratio (β / γ), which is the ratio of the thickness β of the first fuel electrode layer, may be 0.05 or more. This electrochemical reaction unit has a configuration in which the thickness β of the first fuel electrode layer is thick to some extent and / or the width γ of the current collector of the current collector is narrow to some extent. When the fuel gas that has flowed into the gas flows along a direction with a certain degree of inclination with respect to the first direction, a region in the second fuel electrode layer that functions as a reaction field in the fuel electrode is difficult to reach. This can be reduced, and an increase in gas diffusion polarization can be suppressed. Therefore, according to this electrochemical reaction unit, the performance of the electrochemical reaction unit can be improved.

(3) The said electrochemical reaction unit WHEREIN: About the said specific current collection part, it is good also as a structure whose said 1st ratio ((beta) / (alpha)) is 0.39 or more. According to this electrochemical reaction unit, the thickness β of the first fuel electrode layer is made thicker and / or the shortest distance α between the current collector and the current collector of the current collector is made shorter. Therefore, in the second fuel electrode layer functioning as a reaction field in the fuel electrode, it is possible to more effectively reduce the region where electrons generated there are difficult to reach the current collector of the current collector, The performance of the electrochemical reaction unit can be further effectively improved by more effectively suppressing the increase of the crystallization polarization. Therefore, according to this electrochemical reaction unit, the performance of the electrochemical reaction unit can be further effectively improved.

(4) In the electrochemical reaction unit, the second current ratio (β / γ) may be 0.49 or less for the specific current collector. According to this electrochemical reaction unit, the thickness β of the first fuel electrode layer can be suppressed from becoming excessively thick, and / or the width γ of the current collector of the current collector can be excessively narrowed. Therefore, it is possible to effectively improve the performance of the electrochemical reaction unit by suppressing an increase in gas diffusion polarization and damage to the fuel electrode due to stress concentration.

(5) In the electrochemical reaction unit, the first current ratio (β / α) may be 0.58 or less for the specific current collector. According to the present electrochemical reaction unit, it is possible to suppress the thickness β of the first fuel electrode layer from becoming excessively thick and / or the shortest distance between the current collector and the current collector of the current collector It can suppress that (alpha) becomes too short. By suppressing the thickness β of the first fuel electrode layer from becoming excessively thick, an increase in gas diffusion polarization can be suppressed. Further, by suppressing the shortest distance α between the current collector and the current collector of the current collector from becoming excessively short, an increase in gas pressure loss due to narrowing of the flow path is suppressed, and the cell Gas is evenly distributed in the plane. As described above, the performance of the electrochemical reaction unit can be further effectively improved.

(6) In the electrochemical reaction unit, the porosity of the other side portion of the fuel electrode in the first direction is higher than the porosity of the one side portion of the fuel electrode in the first direction. It is good also as a structure. According to this electrochemical reaction unit, an increase in gas diffusion polarization can be suppressed while ensuring a reaction field (three-phase interface length).

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

  Note that the technology disclosed in this specification can be realized in various forms, for example, an electrochemical reaction unit (a fuel cell power generation unit or an electrolysis cell unit), and an electricity provided with a plurality of electrochemical reaction units. It can be realized in the form of a chemical reaction cell stack (fuel cell stack or electrolytic cell stack), a manufacturing method thereof, and the like.

1 is a perspective view showing an external configuration of a fuel cell stack 100 in an embodiment. It is explanatory drawing which shows the XZ cross-section structure of the fuel cell stack 100 in the position of II-II of FIG. FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of a fuel cell stack 100 at a position of III-III in FIG. 1. It is explanatory drawing which shows XZ cross-section structure of the two electric power generation units 102 adjacent to each other in the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-section structure of the two electric power generation units 102 adjacent to each other in the same position as the cross section shown in FIG. FIG. 5 is an explanatory diagram showing an XY cross-sectional configuration of a power generation unit at a position of VI-VI in FIG. 4. It is explanatory drawing which shows XY cross-section structure of the electric power generation unit 102 in the position of VII-VII of FIG. It is explanatory drawing which shows cross-section SE1 used for specification of the current collection part width (gamma) and the shortest distance (alpha) between current collection parts. It is explanatory drawing which shows cross-section SE1 used for specification of the current collection part width (gamma) and the shortest distance (alpha) between current collection parts. It is explanatory drawing which shows a performance evaluation result. It is explanatory drawing which shows notionally the relationship between 1st ratio R1 (= (beta) / (alpha)) and electric power generation performance. It is explanatory drawing which shows notionally the relationship between 1st ratio R1 (= (beta) / (alpha)) and electric power generation performance. It is explanatory drawing which shows notionally the relationship between 1st ratio R1 (= (beta) / (alpha)) and electric power generation performance. It is explanatory drawing which shows notionally the relationship between 2nd ratio R2 (= (beta) / (gamma)) and electric power generation performance. It is explanatory drawing which shows notionally the relationship between 2nd ratio R2 (= (beta) / (gamma)) and electric power generation performance. It is explanatory drawing which shows notionally the relationship between 2nd ratio R2 (= (beta) / (gamma)) and electric power generation performance. 4 is an explanatory diagram showing a method for specifying the porosity of each layer of the fuel electrode 116. FIG.

A. Embodiment:
A-1. Constitution:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of the fuel cell stack 100 in the embodiment, and FIG. 2 is an XZ cross section of the fuel cell stack 100 at a position II-II in FIG. 1 (and FIGS. 6 and 7 described later). FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position of III-III in FIG. 1 (and FIGS. 6 and 7 described later). In each figure, XYZ axes orthogonal to each other for specifying the direction are shown. In this specification, for the sake of convenience, the positive direction of the Z axis is referred to as the upward direction, and the negative direction of the Z axis is referred to as the downward direction. However, the fuel cell stack 100 is actually different from such an orientation. It may be installed. The same applies to FIG.

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

  A plurality of (eight in the present embodiment) holes penetrating in the vertical direction are formed in the peripheral portion around the Z direction of each layer (power generation unit 102, end plates 104, 106) constituting the fuel cell stack 100. The holes formed in each layer and corresponding to each other communicate with each other in the vertical direction to form a communication hole 108 extending in the vertical direction from one end plate 104 to the other end plate 106. In the following description, the holes formed in each layer of the fuel cell stack 100 to form the communication holes 108 may also be referred to as the communication holes 108.

  Bolts 22 extending in the vertical direction are inserted into the communication holes 108, and the fuel cell stack 100 is fastened by the bolts 22 and nuts 24 fitted on both sides of the bolts 22. 2 and 3, between the nut 24 fitted on one side (upper side) of the bolt 22 and the upper surface of the end plate 104 constituting the upper end of the fuel cell stack 100, and the bolt An insulating sheet 26 is interposed between the nut 24 fitted on the other side (lower side) of 22 and the lower surface of the end plate 106 constituting the lower end of the fuel cell stack 100. However, in a place where a gas passage member 27 described later is provided, an insulating sheet disposed between the nut 24 and the surface of the end plate 106 on the upper and lower sides of the gas passage member 27 and the gas passage member 27, respectively. 26 is interposed. The insulating sheet 26 is made of, for example, a mica sheet, a ceramic fiber sheet, a ceramic powder sheet, a glass sheet, a glass ceramic composite agent, or the like.

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

  Further, as shown in FIGS. 1 and 3, the vicinity of the midpoint of one side (the side on the Y axis positive direction side of two sides parallel to the X axis) on the outer periphery of the fuel cell stack 100 around the Z direction The space formed by the bolt 22 (bolt 22D) positioned at the position and the communication hole 108 through which the bolt 22D is inserted is introduced with the fuel gas FG from the outside of the fuel cell stack 100, and the fuel gas FG is generated by each power generation. Bolt 22 that functions as a fuel gas introduction manifold 171 to be supplied to the unit 102 and is located in the vicinity of the midpoint of the opposite side (the side on the Y axis negative direction side of the two sides parallel to the X axis). The space formed by the (bolt 22E) and the communication hole 108 through which the bolt 22E is inserted is a fuel cell stack 1 that uses the fuel off-gas FOG that is a gas discharged from the fuel chamber 176 of each power generation unit 102 as the fuel cell stack 1 Functions as a fuel gas exhaust manifold 172 for discharging to the outside of the 0. In the present embodiment, as the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used.

  The fuel cell stack 100 is provided with four gas passage members 27. Each gas passage member 27 has a hollow cylindrical main body portion 28 and a hollow cylindrical branch portion 29 branched from the side surface of the main body portion 28. The hole of the branch part 29 communicates with the hole of the main body part 28. A gas pipe (not shown) is connected to the branch portion 29 of each gas passage member 27. Further, as shown in FIG. 2, the hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22 </ b> A forming the oxidant gas introduction manifold 161 communicates with the oxidant gas introduction manifold 161. The hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22 </ b> B that forms the oxidant gas discharge manifold 162 communicates with the oxidant gas discharge manifold 162. Further, as shown in FIG. 3, the hole of the main body portion 28 of the gas passage member 27 arranged at the position of the bolt 22D forming the fuel gas introduction manifold 171 communicates with the fuel gas introduction manifold 171 and the fuel gas The hole of the main body portion 28 of the gas passage member 27 disposed at the position of the bolt 22 </ b> E forming the discharge manifold 172 communicates with the fuel gas discharge manifold 172.

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

(Configuration of power generation unit 102)
4 is an explanatory diagram showing an XZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 2, and FIG. 5 is adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-section structure of the two electric power generation units. In the lower part of FIG. 4, an XZ sectional configuration of a part of the power generation unit 102 is shown enlarged. 6 is an explanatory diagram showing the XY cross-sectional configuration of the power generation unit 102 at the position VI-VI in FIG. 4, and FIG. 7 shows the XY cross-sectional configuration of the power generation unit 102 at the position VII-VII in FIG. It is explanatory drawing shown.

  As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air electrode side frame 130, an air electrode side current collector 134, a fuel electrode side frame 140, and a fuel electrode side. A current collector 144 and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer of the power generation unit 102 are provided. The separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the periphery of the interconnector 150 around the Z direction are formed with holes corresponding to the communication holes 108 through which the bolts 22 are inserted.

  The interconnector 150 is a substantially rectangular flat plate-shaped conductive member, and is formed of, for example, ferritic stainless steel. The interconnector 150 ensures electrical continuity between the power generation units 102 and prevents reaction gas from being mixed between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by two adjacent power generation units 102. That is, the upper interconnector 150 in a power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Further, since the fuel cell stack 100 includes the pair of end plates 104 and 106, the power generation unit 102 located at the top in the fuel cell stack 100 does not include the upper interconnector 150 and is located at the bottom. The power generation unit 102 does not include the lower interconnector 150 (see FIGS. 2 and 3).

  The unit cell 110 includes an electrolyte layer 112, an air electrode (cathode) 114 disposed on one side (upper side) of the electrolyte layer 112 in the up-down direction (first direction), and the other side of the electrolyte layer 112 in the up-down direction ( A fuel electrode (anode) 116 disposed on the lower side, and an intermediate layer 180 disposed between the electrolyte layer 112 and the air electrode 114 are provided. The single cell 110 of this embodiment is a fuel electrode-supported single cell that supports the other layers (the electrolyte layer 112, the air electrode 114, and the intermediate layer 180) constituting the single cell 110 with the fuel electrode 116.

  The electrolyte layer 112 is a substantially rectangular flat plate member as viewed in the Z direction, and is a dense layer. The electrolyte layer 112 is formed of a solid oxide such as YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samarium doped ceria), GDC (gadolinium doped ceria), perovskite oxide, and the like. Yes. That is, the single cell 110 (power generation unit 102) of the present embodiment is a solid oxide fuel cell (SOFC) that uses a solid oxide as an electrolyte.

  The air electrode 114 is a substantially rectangular flat plate-shaped member smaller than the electrolyte layer 112 when viewed in the Z direction, and is a porous layer. The air electrode 114 is formed so as to include a perovskite oxide such as LSCF (lanthanum strontium cobalt iron oxide).

  The fuel electrode 116 is a substantially rectangular flat plate member having substantially the same size as the electrolyte layer 112 when viewed in the Z direction, and is a porous layer. The fuel electrode 116 is formed of, for example, a cermet made of Ni and oxide ion conductive ceramic particles (for example, YSZ). As shown in FIG. 4, in the present embodiment, the fuel electrode 116 includes a substrate layer 210 that forms a lower surface of the fuel electrode 116 (a surface facing a fuel electrode side current collector 144 described later), The active layer 220 is disposed between the substrate layer 210 and the electrolyte layer 112. The active layer 220 is a layer that mainly functions as an electrode reaction in the fuel electrode 116 (reaction that generates electrons and water from oxide ions supplied from the electrolyte layer 112 and hydrogen contained in the fuel gas FG). is there. The substrate layer 210 mainly functions as a field for supporting each layer constituting the single cell 110, diffusing the fuel gas FG supplied from the fuel chamber 176, and moving electrons obtained by the electrode reaction. It is a layer to do. The substrate layer 210 corresponds to the first fuel electrode layer in the claims, and the active layer 220 corresponds to the second fuel electrode layer in the claims.

  In the present embodiment, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is higher than the porosity RO2 of the active layer 220. That is, the porosity of the lower part of the fuel electrode 116 is higher than the porosity of the upper part of the fuel electrode 116. Note that the porosity of the substrate layer 210 and the active layer 220 is substantially uniform in a direction parallel to the Z-axis direction. According to such a configuration, an increase in gas diffusion polarization can be suppressed while ensuring a reaction field (three-phase interface length). The porosity RO1 of the substrate layer 210 is preferably high to some extent in order to ensure gas diffusibility. Specifically, the porosity RO1 of the substrate layer 210 is preferably 35% or more, and preferably 55% or less. The porosity RO2 of the active layer 220 is preferably 10% or more, and preferably 30% or less.

The intermediate layer 180 is a substantially rectangular flat plate-shaped member, and is formed so as to include GDC (gadolinium-doped ceria). The intermediate layer 180 indicates that an element (for example, Sr) diffused from the air electrode 114 reacts with an element (for example, Zr) contained in the electrolyte layer 112 to generate a high-resistance material (for example, SrZrO ₃ ). Suppress.

  The separator 120 is a frame-like member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed near the center, and is made of, for example, metal. The peripheral part of the hole 121 in the separator 120 is opposed to the peripheral part of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is bonded to the electrolyte layer 112 (single cell 110) by a bonding portion 124 formed of a brazing material (for example, Ag brazing) disposed in the facing portion. The separator 120 divides the air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116, and gas leaks from one electrode side to the other electrode side in the peripheral portion of the single cell 110. It is suppressed.

 As shown in FIGS. 4 to 6, the air electrode side frame 130 is a frame-like member in which a substantially rectangular hole 131 penetrating in the vertical direction is formed near the center, and is formed of an insulator such as mica, for example. ing. The hole 131 of the air electrode side frame 130 forms an air chamber 166 that faces the air electrode 114. The air electrode side frame 130 is in contact with the peripheral edge portion of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge portion of the surface of the interconnector 150 facing the air electrode 114. . The pair of interconnectors 150 included in the power generation unit 102 is electrically insulated by the air electrode side frame 130. The air electrode side frame 130 has an oxidant gas supply communication hole 132 communicating the oxidant gas introduction manifold 161 and the air chamber 166, and an oxidant gas communicating the air chamber 166 and the oxidant gas discharge manifold 162. A discharge communication hole 133 is formed.

  As shown in FIGS. 4, 5, and 7, the fuel electrode side frame 140 is a frame-like member in which a substantially rectangular hole 141 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. . The hole 141 of the fuel electrode side frame 140 forms a fuel chamber 176 that faces the fuel electrode 116. The fuel electrode side frame 140 is in contact with the peripheral portion of the surface of the separator 120 facing the electrolyte layer 112 and the peripheral portion of the surface of the interconnector 150 facing the fuel electrode 116. Further, the fuel electrode side frame 140 has a fuel gas supply communication hole 142 that connects the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that connects the fuel chamber 176 and the fuel gas discharge manifold 172. And are formed.

  As shown in FIGS. 4, 5, and 7, the fuel electrode side current collector 144 is disposed in the fuel chamber 176 (more specifically, below the substrate layer 210 of the fuel electrode 116). The fuel electrode side current collector 144 is a member that has conductivity and does not have gas permeability, and is formed of, for example, nickel, a nickel alloy, stainless steel, or the like.

  The fuel electrode side current collector 144 includes an interconnector facing portion 146, a plurality of electrode facing portions 145, and a connecting portion 147 that connects each electrode facing portion 145 and the interconnector facing portion 146. As shown in the partial enlarged view of FIG. 7, the fuel electrode side current collector 144 is manufactured by cutting a substantially rectangular flat plate member (for example, nickel foil) and bending a plurality of rectangular portions. The Each rectangular portion bent up is an electrode facing portion 145, and a flat plate portion in which a hole OP other than the bent raised portion is opened becomes an interconnector facing portion 146, and the electrode facing portion 145 and the interconnector facing portion 146 are connected to each other. The connecting portion is a connecting portion 147. In addition, in the partial enlarged view in FIG. 7, in order to show the manufacturing method of the fuel electrode side collector 144, the state before a bending raising process is completed about a part of rectangular part is shown.

  Each electrode facing portion 145 is in contact with the surface of the fuel electrode 116 opposite to the side facing the electrolyte layer 112. That is, each electrode facing portion 145 is electrically connected to the lower surface of the substrate layer 210 of the fuel electrode 116. The interconnector facing portion 146 is in contact with the surface of the interconnector 150 on the side facing the fuel electrode 116. However, as described above, since the lowermost power generation unit 102 in the fuel cell stack 100 does not include the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 has a lower end plate. 106 is in contact. Since the fuel electrode side current collector 144 has such a configuration, the fuel electrode 116 and the interconnector 150 (or the end plate 106) are electrically connected. Note that a spacer 149 made of, for example, mica is disposed between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to the temperature cycle and the reaction gas pressure fluctuation, and the fuel electrode 116 and the interconnector 150 (or the end plate 106) via the fuel electrode side current collector 144. The electrical connection with is maintained well. The fuel electrode side current collector 144 corresponds to the current collector in the claims, and the plurality of electrode facing portions 145 correspond to the plurality of current collectors in the claims.

  As shown in FIGS. 4 to 6, the air electrode side current collector 134 is disposed in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of current collector elements 135 having a substantially quadrangular prism shape, and is formed of, for example, ferritic stainless steel. The air electrode side current collector 134 is in contact with the surface of the air electrode 114 opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 facing the air electrode 114. However, as described above, since the power generation unit 102 located at the top in the fuel cell stack 100 does not include the upper interconnector 150, the air electrode side current collector 134 in the power generation unit 102 includes the upper end plate. 104 is in contact. Since the air electrode side current collector 134 has such a configuration, the air electrode 114 and the interconnector 150 (or the end plate 104) are electrically connected. In the present embodiment, the air electrode side current collector 134 (current collector element 135) and the interconnector 150 are formed as an integral member. That is, a flat plate-shaped portion perpendicular to the vertical direction (Z-axis direction) of the integral member functions as the interconnector 150 and is formed so as to protrude toward the air electrode 114 from the flat plate-shaped portion. The plurality of current collector elements 135 function as the air electrode side current collector 134.

  As shown in FIGS. 4 and 5, the surface of the air electrode side current collector 134 (current collector element 135) is covered with a conductive coat 136. The coat 136 is made of, for example, a spinel oxide. In the following description, unless otherwise specified, the air electrode side current collector 134 (current collector element 135) means “the air electrode side current collector 134 (current collector element 135) covered with the coat 136”. In FIG. 6, the illustration of the coat 136 is omitted. As shown in FIGS. 4 and 5, the air electrode 114 and the air electrode side current collector 134 (current collector element 135) are bonded together by a conductive bonding layer 138. The bonding layer 138 is made of, for example, a spinel oxide. The air electrode 114 and the air electrode side current collector 134 are electrically connected by the bonding layer 138. Although it has been described above that the air electrode side current collector 134 is in contact with the surface of the air electrode 114, the bonding layer 138 is precisely between the air electrode side current collector 134 and the air electrode 114. Intervene.

A-2. Operation of the 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 branch portion 29 of the gas passage member 27 and the hole of the main body portion 28, and the oxidant gas introduction manifold 161 oxidizes each power generation unit 102. It is supplied to the air chamber 166 through the agent gas supply communication hole 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 chamber 176 is supplied through the hole 142.

  When the oxidant gas OG is supplied to the air chamber 166 of each power generation unit 102 and the fuel gas FG is supplied to the fuel chamber 176, power is generated by an electrochemical reaction between the oxidant gas OG and the fuel gas FG in the single cell 110. Is called. 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 the interconnector 150 via the air electrode side current collector 134, and the fuel electrode 116 is connected to the interconnector via the fuel electrode side current collector 144. 150 is electrically connected. The plurality of power generation units 102 included in the fuel cell stack 100 are electrically connected in series. Therefore, electrical energy generated in each power generation unit 102 is taken out from the end plates 104 and 106 that function as output terminals of the fuel cell stack 100. Since SOFC generates power at a relatively high temperature (for example, 700 ° C. to 1000 ° C.), the fuel cell stack 100 is heated by a heater (after the start-up until the high temperature 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 as shown in FIGS. The fuel cell stack 100 is connected to the branch portion 29 via a gas pipe (not shown) 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 outside. 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 via the fuel gas discharge communication hole 143, and further to the fuel gas. The gas passage member 27 provided at the position of the discharge manifold 172 passes through the body portion 28 and the branch portion 29 and passes through a gas pipe (not shown) connected to the branch portion 29 to the outside of the fuel cell stack 100. Discharged.

A-3. Performance evaluation:
Each power generation unit 102 constituting the fuel cell stack 100 of the present embodiment is characterized by the relationship between the fuel electrode 116 and the electrode facing portion 145 of the fuel electrode side current collector 144. Hereinafter, the performance evaluation performed regarding the relationship between the fuel electrode 116 and the electrode facing portion 145 of the fuel electrode side current collector 144 will be described.

(For each parameter)
As shown in FIG. 4, in this performance evaluation, the thickness of the substrate layer 210 of the fuel electrode 116 in the Z-axis direction is referred to as “fuel electrode substrate layer thickness β”. When the thickness of the substrate layer 210 of the fuel electrode 116 is not uniform, the fuel electrode substrate layer thickness β is equal to the substrate layer 210 of the fuel electrode 116 (however, the electrode facing the electrode of the fuel electrode side current collector 144). The thickness of the thinnest part in the part facing the part 145). The boundary between the substrate layer 210 and the active layer 220 in the fuel electrode 116 can be specified based on the difference in Ni content, Ni average particle diameter, porosity, etc. in the SEM image of the cross section of the fuel electrode 116. it can.

  In addition, the width (the size in the direction orthogonal to the Z-axis direction) of the portion of the electrode facing portion 145 of the fuel electrode-side current collector 144 that faces the substrate layer 210 of the fuel electrode 116 (the portion that contacts the substrate layer 210) Is referred to as “current collector width γ”.

  As shown in FIGS. 8 and 9, the current collector width γ is specified at four points (P1) on the outer circumferential line of the electrode facing portion 145 in the XY cross section of the electrode facing portion 145 of the fuel electrode side current collector 144. ~ P4) When a virtual ellipse VE inscribed above is set, in a cross section SE1 including the minor axis Am of the virtual ellipse VE and parallel to the Z-axis direction (YZ cross section in the examples of FIGS. 8 and 9) Assumed to be performed.

  Further, the measurement position of the current collector width γ in the cross section SE1 is the lowermost position of the thinnest part in the substrate layer 210 of the fuel electrode 116 (however, the part facing the electrode facing part 145 of the fuel electrode side current collector 144). And a position separated by a distance Lx (= 10 μm) downward. For example, as shown in FIG. 4, in the configuration in which the thickness of the substrate layer 210 of the fuel electrode 116 is substantially uniform, the current collector width γ is the fuel in the cross section SE1 (XZ cross section in the example of FIG. 4). The position is specified by a distance Lx (= 10 μm) below the lower surface of the substrate layer 210 of the pole 116 and on a virtual straight line VL1 orthogonal to the Z-axis direction.

  Further, the shortest distance between the one electrode facing portion 145 and the other electrode facing portion 145 located adjacent thereto (the shortest distance in the direction perpendicular to the Z-axis direction) is referred to as “the shortest distance α between current collectors”. . The shortest distance α between the current collectors is specified on the virtual straight line VL1 in the cross section SE1 similarly to the current collector width γ (see FIG. 4).

  The ratio (β / α) of the fuel electrode substrate layer thickness β to the shortest distance α between the current collectors is referred to as “first ratio R1”. The high value of the first ratio R1 means that the value of the shortest distance α between the current collectors is small (that is, the distance between the two electrode facing parts 145 is narrow) and / or the fuel electrode substrate layer thickness. This means that the value of β is large. The ratio (β / γ) of the fuel electrode substrate layer thickness β to the current collector width γ is referred to as a “second ratio R2”. When the value of the second ratio R2 is high, the value of the current collector width γ is small (that is, the width of the electrode facing portion 145 is narrow) and / or the value of the fuel electrode substrate layer thickness β is low. It means big.

(About each sample)
FIG. 10 is an explanatory diagram showing the performance evaluation results. As shown in FIG. 10, each sample (S1 to S14) of the power generation unit 102 used for performance evaluation is the shortest distance α between current collectors, the fuel electrode substrate layer thickness β, and the current collector width described above. The values of γ are different from each other, and as a result, the values of the first ratio R1 and the second ratio R2 are different from each other. Further, the samples have different values of the porosity RO1 of the substrate layer 210 of the fuel electrode 116 and the porosity RO2 of the active layer 220 of the fuel electrode 116. As shown in FIG. 10, in all samples used for performance evaluation, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is higher than the porosity RO2 of the active layer 220 of the fuel electrode 116. A method for specifying the porosity RO1 and the porosity RO2 will be described later.

  In producing each sample, the fuel electrode 116 (the substrate layer 210 and the active layer 220) was formed of cermet made of Ni and YSZ. Further, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 and the porosity RO2 of the active layer 220 were adjusted by adjusting the particle size of the raw material or adjusting the firing temperature. Further, the fuel electrode side current collector 144 (electrode facing portion 145, interconnector facing portion 146, connecting portion 147) was made of Ni foil, and the spacer 149 was made of mica. For each sample, the values of the shortest distance α between current collectors and the current collector width γ were varied by changing the shape and arrangement of the electrode facing portion 145 and the like.

(About evaluation method)
In this performance evaluation, the power generation performance was evaluated. Specifically, for each sample of the produced power generation unit 102, an initial voltage was measured under the conditions of temperature: 700 ° C. and current density: 0.55 A / cm ² , and according to the value of the initial voltage, “ Evaluation was made in 7 stages from “A” to “G” (“A” is the best evaluation, and “G” is the worst).
Evaluation: “A”: Initial voltage: 0.92 V or more Evaluation: “B”: Initial voltage: 0.915 V or more and less than 0.92 V Evaluation: “C”: Initial voltage: 0 .91 V or more and less than 0.915 V Evaluation: “D”: Initial voltage: 0.905 V or more, less than 0.91 V Evaluation: “E”: Initial voltage: 0.9 V or more, less than 0.905 V・ Evaluation: “F”: Initial voltage: 0.8 V or more and less than 0.9 V ・ Evaluation: “G”: Initial voltage: less than 0.8 V

(About evaluation results)
(About sample S1)
As shown in FIG. 10, the evaluation result of sample S1 was the lowest “G” evaluation. In the sample S1, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 20%, which is a lower value than the other samples (both have a porosity RO1 of the substrate layer 210 of 35% or more). . Therefore, in the sample S1, the fuel gas FG supplied to the fuel chamber 176 does not enter the substrate layer 210 of the fuel electrode 116 well, and the fuel gas FG is insufficient in the active layer 220 functioning as a reaction field in the fuel electrode 116. By doing so, the gas diffusion polarization becomes extremely large, and as a result, the initial voltage is considered to be extremely low. From this result, it can be said that the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is preferably 35% or more in order to improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance).

(About sample S2)
The evaluation result of sample S2 was the second lowest “F” evaluation. In the sample S2, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more, but the first ratio R1 (= β / α) is 0.17, and the samples S3 to S14 (both are the first ones). The ratio R1 is 0.18 or more). For this reason, it is considered that the initial voltage of sample S2 is lower than that of samples S3 to S14 as described below.

  11 to 13 are explanatory views conceptually showing the relationship between the first ratio R1 (= β / α) and the power generation performance. 11 to 13 show an XZ cross-sectional configuration of a part of the power generation unit 102 (X1 portion in FIG. 4). In the configuration of the power generation unit 102 shown in FIG. 11, the value of the shortest distance α between the current collectors is larger than that in the configuration of the power generation unit 102 shown in FIG. 13. Therefore, in the configuration of the power generation unit 102 shown in FIG. 11, the value of the first ratio R1 is smaller than that in the configuration of the power generation unit 102 shown in FIG. In addition, in the configuration of the power generation unit 102 shown in FIG. 12, the value of the fuel electrode substrate layer thickness β is smaller than that in the configuration of the power generation unit 102 shown in FIG. Therefore, in the configuration of the power generation unit 102 shown in FIG. 12, the value of the first ratio R1 is smaller than that in the configuration of the power generation unit 102 shown in FIG.

Here, the electrons generated by the electrode reaction in the active layer 220 of the fuel electrode 116 pass through the substrate layer 210 from the active layer 220 and enter the fuel electrode side current collector 144. The exchange of electrons (e ⁻ ) with the side current collector 144 is a portion of the surface of the substrate layer 210 that does not face (is not in contact with) the electrode facing portion 145 of the fuel electrode side current collector 144 (that is, the current collector). This is not performed at the portion corresponding to the shortest distance α between the electric parts), but at the portion facing (in contact with) the electrode facing portion 145 of the fuel electrode side current collector 144 (that is, the portion corresponding to the current collecting portion width γ). . Electrons generated in the active layer 220 flow toward the fuel electrode side current collector 144 along a direction in which the inclination with respect to the Z-axis direction is approximately within a predetermined value θ1. Therefore, a configuration in which the value of the shortest distance α between the current collectors is relatively large as shown in FIG. 11 or a configuration in which the value of the fuel electrode substrate layer thickness β is relatively small as shown in FIG. In the configuration in which the value of R1 is relatively small), the electrons generated in a part of the region Ax1 in the active layer 220 do not easily reach the electrode facing portion 145 of the fuel electrode side current collector 144, thereby activating polarization. As a result, the initial voltage of the power generation unit 102 decreases.

  On the other hand, in the configuration of the power generation unit 102 shown in FIG. 13, the value of the shortest distance α between the current collectors is smaller than that of the configuration of the power generation unit 102 shown in FIG. 11, and the power generation unit 102 shown in FIG. The value of the fuel electrode substrate layer thickness β is larger than that of the configuration. That is, in the configuration of the power generation unit 102 shown in FIG. 13, the value of the first ratio R1 is larger than that in the configuration of the power generation unit 102 shown in FIGS. In the configuration of the power generation unit 102 shown in FIG. 13, since the value of the shortest distance α between the current collectors is relatively small, the electrons generated in the active layer 220 of the fuel electrode 116 are the electrodes of the fuel electrode side current collector 144. The area of a region that is difficult to reach the facing portion 145 can be reduced. Further, in the configuration of the power generation unit 102 shown in FIG. 13, since the value of the fuel electrode substrate layer thickness β is relatively large, electrons generated in the active layer 220 of the fuel electrode 116 in the direction orthogonal to the Z-axis direction. The moving distance can be made relatively long. Therefore, as shown in FIG. 13, in the configuration in which the value of the first ratio R1 is relatively large, electrons generated in the active layer 220 of the fuel electrode 116 reach the electrode facing portion 145 of the fuel electrode side current collector 144. The difficult region can be reduced, and the decrease in the initial voltage can be suppressed by suppressing the increase in activation polarization.

  As described above, the evaluation result of the sample S2 in which the first ratio R1 (= β / α) is less than 0.18 is more than the evaluation result of the samples S3 to S14 in which the first ratio R1 is 0.18 or more. Considering the inferiority, it can be said that the first ratio R1 is preferably 0.18 or more in order to improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance).

(About samples S3 and S4)
The evaluation results of samples S3 and S4 were the third lowest “E” evaluation. In samples S3 and S4, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more and the first ratio R1 (= β / α) is 0.18 or more, but the second ratio R2 (= β / γ) is less than 0.05, which is a lower value than the samples S5 to S14 (all of which the second ratio R2 is 0.05 or more). Therefore, in samples S3 and S4, as described below, it is considered that the initial voltage is lower than in samples S5 to S14.

  14 to 16 are explanatory diagrams conceptually showing the relationship between the second ratio R2 (= β / γ) and the power generation performance. 14 to 16 show an XZ cross-sectional configuration of a part of the power generation unit 102 (X1 portion in FIG. 4). In the configuration of the power generation unit 102 shown in FIG. 14, the value of the current collector width γ is larger than that in the configuration of the power generation unit 102 shown in FIG. 16. Therefore, in the configuration of the power generation unit 102 shown in FIG. 14, the value of the second ratio R2 is smaller than that in the configuration of the power generation unit 102 shown in FIG. Further, in the configuration of the power generation unit 102 shown in FIG. 15, the value of the fuel electrode substrate layer thickness β is smaller than that in the configuration of the power generation unit 102 shown in FIG. Therefore, in the configuration of the power generation unit 102 shown in FIG. 15, the value of the second ratio R2 is smaller than that in the configuration of the power generation unit 102 shown in FIG.

  Here, the fuel gas FG supplied to the fuel chamber 176 is a portion of the surface of the substrate layer 210 of the fuel electrode 116 that faces (contacts) the electrode facing portion 145 of the fuel electrode side current collector 144 (that is, contact). The portion that does not flow in from the current collector width γ and does not face (not in contact with) the electrode facing portion 145 of the fuel electrode side collector 144 (that is, the portion that corresponds to the shortest distance α between the current collectors) ) Into the substrate layer 210 of the fuel electrode 116. The fuel gas FG that has flowed into the substrate layer 210 of the fuel electrode 116 enters the active layer 220 that functions as a reaction field in the fuel electrode 116 along a direction in which the inclination with respect to the Z-axis direction is approximately within a predetermined value θ2. It flows toward. Therefore, as shown in FIG. 14, the current collector width γ has a relatively large value, and as shown in FIG. 15, the fuel electrode substrate layer thickness β has a relatively small value (ie, the second ratio R2). In the configuration in which the value is relatively small), the gas diffusion polarization becomes large due to the fact that the fuel gas FG does not easily reach a part of the region Ax2 in the active layer 220 of the fuel electrode 116. The voltage is lowered.

  On the other hand, in the configuration of the power generation unit 102 shown in FIG. 16, the value of the current collector width γ is smaller than that of the configuration of the power generation unit 102 shown in FIG. 14, and the configuration of the power generation unit 102 shown in FIG. The value of the fuel electrode substrate layer thickness β is larger than That is, in the configuration of the power generation unit 102 shown in FIG. 16, the value of the second ratio R2 is larger than that in the configuration of the power generation unit 102 shown in FIGS. In the configuration of the power generation unit 102 shown in FIG. 16, since the value of the current collector width γ is relatively small, the area of the active layer 220 of the fuel electrode 116 where the fuel gas FG is difficult to reach can be reduced. In the configuration of the power generation unit 102 shown in FIG. 16, the value of the fuel electrode substrate layer thickness β is relatively large, so that the fuel gas FG that has entered the substrate layer 210 of the fuel electrode 116 is orthogonal to the Z-axis direction. The moving distance (diffusion distance) in the direction can be made relatively long. Therefore, as shown in FIG. 16, in the configuration in which the value of the second ratio R2 is relatively large, the region where the fuel gas FG is difficult to reach in the active layer 220 of the fuel electrode 116 can be reduced, and the gas diffusion polarization is performed. By suppressing the increase in the initial voltage, a decrease in the initial voltage can be suppressed.

  As described above, the evaluation results of the samples S3 and S4 with the second ratio R2 (= β / γ) being less than 0.05 are the evaluations of the samples S5 to S14 with the second ratio R2 being 0.05 or more. In consideration of being inferior to the results, it can be said that the second ratio R2 is preferably 0.05 or more in order to further improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance).

(About samples S5 and S6)
The evaluation results for samples S5 and S6 were the 4th lowest (ie 4th highest) “D” rating. In samples S5 and S6, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.18 or more, and the second ratio R2 Although (= β / γ) is 0.05 or more, the first ratio R1 is less than 0.39, which is compared with the samples S7 to S14 (all of which the first ratio R1 is 0.39 or more). The value is low. As described above, as the value of the first ratio R1 is larger, the region in which electrons generated in the active layer 220 of the fuel electrode 116 are less likely to reach the electrode facing portion 145 of the fuel electrode side current collector 144 can be reduced. By suppressing the increase in activation polarization, the power generation performance can be improved (decrease in power generation performance can be suppressed). The evaluation result of the samples S5 and S6 in which the first ratio R1 (= β / α) is less than 0.39 is inferior to the evaluation result of the samples S7 to S14 in which the first ratio R1 is 0.39 or more. Considering it, it can be said that the first ratio R1 is preferably 0.39 or more in order to further improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance).

(About samples S7 and S8)
The evaluation results of samples S7 and S8 were the fifth lowest (ie third highest) “C” rating. In samples S7 and S8, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.39 or more, and the second ratio R2 Although (= β / γ) is 0.05 or more, the second ratio R2 exceeds 0.49, and samples S9 to S14 (all of which the second ratio R2 is 0.49 or less) The value is excessively high. That the second ratio R2 is excessively high means that the value of the fuel electrode substrate layer thickness β is excessively large and / or the value of the current collector width γ is excessively small. When the value of the fuel electrode substrate layer thickness β is excessively large, the diffusion path of the fuel gas FG from the surface of the substrate layer 210 of the fuel electrode 116 to the active layer 220 as a reaction field becomes excessively long. As a result, the initial voltage is lowered, and the amount of material used to form the substrate layer 210 of the fuel electrode 116 can be increased, and interface separation between the substrate layer 210 of the fuel electrode 116 and other layers can be performed. Causes increased sex. Also, if the value of the current collector width γ is excessively small, the contact area between the substrate layer 210 of the fuel electrode 116 and the fuel electrode-side current collector 144 becomes excessively small. Causes damage, resulting in lower initial voltage. For at least one of these reasons, the samples S7 and S8 are considered to have a low initial voltage. Consider that the evaluation results of the samples S7 and S8 in which the second ratio R2 (= β / γ) exceeds 0.49 are inferior to the evaluation results of the samples S9 to S14 in which the second ratio R2 is 0.49 or less. Then, it can be said that the second ratio R2 is preferably 0.49 or less in order to further improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance).

(About sample S9)
The evaluation result for sample S9 was the sixth lowest (ie second highest) “B” rating. In the sample S9, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.39 or more, and the second ratio R2 (= β / γ) is 0.05 or more and 0.49 or less, but the first ratio R1 exceeds 0.58, and samples S10 to S14 (both of which the first ratio R1 is 0.58 or less) It is an excessively high value compared to (Yes). That the first ratio R1 is excessively high means that the value of the fuel electrode substrate layer thickness β is excessively large and / or the value of the shortest distance α between the current collectors is excessively small. When the value of the fuel electrode substrate layer thickness β is excessively large, the diffusion path of the fuel gas FG from the surface of the substrate layer 210 of the fuel electrode 116 to the active layer 220 as a reaction field becomes excessively long. As a result, the initial voltage is lowered, and the amount of material used to form the substrate layer 210 of the fuel electrode 116 can be increased, and interface separation between the substrate layer 210 of the fuel electrode 116 and other layers can be performed. Causes increased sex. If the value of the shortest distance α between the current collectors is excessively small, the area of the substrate layer 210 of the fuel electrode 116 that is not covered with the electrode facing portion 145 of the fuel electrode-side current collector 144 is excessively small. Therefore, the fuel gas FG supplied to the fuel chamber 176 does not enter the substrate layer 210 of the fuel electrode 116 well, and the gas diffusion polarization increases, and as a result, the initial voltage decreases. In addition, if the value of the shortest distance α between the current collectors is excessively small, the gas flow path is excessively narrowed to increase the pressure loss of the gas, which makes it difficult to distribute the gas uniformly in the cell plane. The initial voltage is lowered. For at least one of these reasons, the initial voltage is considered to be low in sample S9. Considering that the evaluation result of the sample S9 in which the first ratio R1 (= β / α) exceeds 0.58 is inferior to the evaluation result of the samples S10 to S14 in which the first ratio R1 is 0.58 or less, In order to further improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance), it can be said that the first ratio R1 is preferably 0.58 or less.

(Summary of performance evaluation results)
Referring to the performance evaluation results described above, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more for improving the power generation performance of the power generation unit 102 (suppressing power generation performance degradation), and 1 ratio R1 (ratio of fuel electrode substrate layer thickness β to current collector shortest distance α (β / α)) is preferably 0.18 or more, and second ratio R2 (current collector width γ) Is more preferably 0.05 or more, the first ratio R1 is more preferably 0.39 or more, and the second ratio R2 Is more preferably 0.49 or less, and the first ratio R1 is most preferably 0.58 or less.

A-4. Method for specifying the porosity of each layer of the fuel electrode 116:
The above-described porosity RO1 of the substrate layer 210 of the fuel electrode 116 can be specified by “Mr. Mizutani” “Ceramic Processing” (Gihodo Publishing) p. Referring to the description of 193-195, the following method was used (see FIG. 17). First, in the power generation unit 102 (single cell 110), the fuel gas FG is arranged at any three positions along the flow direction of the fuel gas FG (in this embodiment, the Y-axis direction as shown in FIGS. 5 and 7). A cross section (XZ cross section in the present embodiment) that is substantially orthogonal to the flow direction of the fuel electrode 116 is set, and a portion including the surface on the fuel electrode side current collector 144 side in the substrate layer 210 of the fuel electrode 116 at any three positions of each cross section SEM image (5000 times) in FIB-SEM (acceleration voltage 1.5 kV) in which is shown. That is, nine SEM images are obtained. In each SEM image, five virtual straight lines VL (VL11 to VL15) orthogonal to the Z-axis direction are set at 1 μm intervals near the surface on the fuel electrode side current collector 144 side of the substrate layer 210 of the fuel electrode 116. . In each of the five virtual straight lines VL, the length of each portion corresponding to the pore is measured, and the ratio of the total length of each portion corresponding to the pore to the entire length of the virtual straight line VL is the porosity on the virtual straight line VL. . The average value of the porosity on all the virtual straight lines VL set in all the SEM images is set as the porosity RO1 of the substrate layer 210 of the fuel electrode 116.

  Similarly, the porosity RO2 of the active layer 220 of the fuel electrode 116 was specified according to the following method (see FIG. 17). First, in the power generation unit 102 (unit cell 110), cross sections (substantially orthogonal to the flow direction of the fuel gas FG) at any three positions aligned along the flow direction of the fuel gas FG (in this embodiment, the Y-axis direction). In this embodiment, an XZ cross section) is set, and FIB-SEM (acceleration voltage 1.5 kV) in which portions including the surface on the electrolyte layer 112 side of the active layer 220 of the fuel electrode 116 are reflected at any three positions in each cross section. SEM image (5000 times) is obtained. That is, nine SEM images are obtained. In each SEM image, five virtual straight lines VL (VL21 to VL25) orthogonal to the Z-axis direction are set at 1 μm intervals near the surface of the active layer 220 of the fuel electrode 116 on the electrolyte layer 112 side. The surface on the electrolyte layer 112 side of the active layer 220 of the fuel electrode 116 can be specified based on the difference in constituent materials between the active layer 220 of the fuel electrode 116 and the electrolyte layer 112 in each of the SEM images. In each of the five virtual straight lines VL, the length of each portion corresponding to the pore is measured, and the ratio of the total length of each portion corresponding to the pore to the entire length of the virtual straight line VL is the porosity on the virtual straight line VL. . The average value of the porosity on all the virtual straight lines VL set in all the SEM images is defined as the porosity RO2 of the active layer 220 of the fuel electrode 116.

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

  The configuration of the single cell 110, the power generation unit 102, or the fuel cell stack 100 in the above embodiment is merely an example, and various modifications can be made. For example, in the above-described embodiment, the fuel electrode 116 has a two-layer configuration, but the fuel electrode 116 may include three or more layers having different configurations.

  In the above embodiment, the fuel electrode side current collector 144 includes the electrode facing portion 145, the interconnector facing portion 146, and the connecting portion 147, but the fuel electrode side current collector 144 is configured by the fuel electrode 116. Any other configuration may be used as long as it has a plurality of current collecting portions that are electrically connected to the surface of the substrate layer 210. For example, the fuel electrode side current collector 144 may be composed of a plurality of substantially square columnar current collector elements, like the air electrode side current collector 134. In such a configuration, a plurality of current collector elements function as a plurality of current collectors. Moreover, in the said embodiment, although the spacer 149 is arrange | positioned between the electrode opposing part 145 and the interconnector opposing part 146, the spacer 149 is omissible.

  Further, in the above embodiment, a conductive material having gas permeability (for example, a fine pitch (electrode facing portion 145 made of Ni) is formed on the surface of the substrate layer 210 of the fuel electrode 116 on the fuel electrode side current collector 144 side. The mesh material) having a pitch smaller than the arrangement pitch of the fuel electrode 116 is disposed, and the surface of the substrate layer 210 of the fuel electrode 116 is disposed on the fuel electrode side current collector 144 via the conductive material having gas permeability. It may be electrically connected to the electrode facing portion 145. In such a configuration, the substrate layer 210 of the fuel electrode 116 corresponds to the first fuel electrode layer in the claims, the fuel electrode side current collector 144 corresponds to the current collector in the claims, and The conductive material having gas permeability does not correspond to the first fuel electrode layer or the current collector in the claims.

  In the above embodiment, the fuel electrode side current collector 144 may be covered with a conductive coat. In such a configuration, when the coat does not have gas permeability, the fuel electrode side current collector 144 and the coat correspond to the current collector in the claims, and the coat has gas permeability. In this case, the fuel electrode side current collector 144 corresponds to the current collector in the claims, and the coat does not correspond to the first fuel electrode layer or the current collector in the claims.

In addition, the shortest distance α between the current collectors, the fuel electrode substrate layer thickness β, and the current collector width γ are preferably in the following ranges, respectively.
・ 1000μm ≦ shortest distance between current collectors α ≦ 3000μm
・ 200μm ≦ fuel electrode substrate layer thickness β ≦ 1200μm
・ 500μm ≦ Current collector width γ ≦ 9000μm

  In the above embodiment, the single cell 110 includes the intermediate layer 180, but the single cell 110 does not necessarily include the intermediate layer 180. In the above embodiment, the interconnector 150 and the air electrode side current collector 134 are integrated members, but the interconnector 150 and the air electrode side current collector 134 may be separate members. In the above embodiment, the air electrode side current collector 134 is covered with the coat 136, but the air electrode side current collector 134 may not be covered with the coat 136. In the above embodiment, the air electrode side current collector 134 is in contact with the air electrode 114 through the bonding layer 138, but the air electrode side current collector 134 is in contact with the air electrode 114 without through the bonding layer 138. It may be.

  In the above embodiment, the number of single cells 110 (power generation units 102) included in the fuel cell stack 100 is merely an example, and the number of single cells 110 (power generation units 102) is required for the fuel cell stack 100. It is determined appropriately according to the output voltage and the like. Moreover, the material which comprises each member in the said embodiment is an illustration to the last, and each member may be comprised with the other material.

  Moreover, the structural requirements for the power generation performance improvement (suppression of power generation performance degradation) of the power generation unit 102 described in the above embodiment (for example, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more, and The first ratio R1 (= β / α is 0.18 or more) is not necessarily satisfied in all of the plurality of power generation units 102 constituting the fuel cell stack 100, and the fuel cell stack It is sufficient that at least one of the plurality of power generation units 102 constituting 100 is satisfied. Further, when attention is paid to one power generation unit 102, the constituent element does not necessarily have to be satisfied in all of the plurality of electrode facing portions 145 included in the fuel electrode side current collector 144. It is sufficient that at least one of the plurality of electrode facing portions 145 included in the body 144 is satisfied. Note that, in order to effectively improve the power generation performance of the power generation unit 102 (suppress the reduction in power generation performance), 30% or more of the electrode facing portions 145 included in the fuel electrode side current collector 144 have the above-mentioned It is preferable that the structural requirements are satisfied, and it is more preferable that 50% or more of the electrode facing portions 145 satisfy the above structural requirements, and 70% or more of the electrode facing portions 145 satisfy the above structural requirements. It is more preferable that 90% or more of the electrode facing portions 145 satisfy the above-described configuration requirements, and 100% of the electrode facing portions 145 most preferably satisfy the above-described configuration requirements. The electrode facing portion 145 that satisfies the configuration requirements corresponds to the specific current collector in the claims.

  In the above embodiment, the SOFC that generates electricity using the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas is targeted. The present invention can be similarly applied to an electrolytic cell unit that is a constituent unit of a solid oxide electrolytic cell (SOEC) that generates hydrogen by using hydrogen, and an electrolytic cell stack including a plurality of electrolytic cell units. The configuration of the electrolysis cell stack is well known as described in, for example, Japanese Patent Application Laid-Open No. 2006-81813, and therefore will not be described in detail here, but is roughly the same as the fuel cell stack 100 in the above-described embodiment. It is the composition. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolytic cell stack, the power generation unit 102 may be read as an electrolytic cell unit, and the single cell 110 may be read as an electrolytic single cell. However, when the electrolysis cell stack is operated, a voltage is applied between the two electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode). Water vapor as a source gas is supplied. As a result, an electrolysis reaction of water occurs in each electrolysis cell unit, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out of the electrolysis cell stack through the communication hole. Also in the electrolytic cell unit and the electrolytic cell stack having such a configuration, the porosity RO1 of the substrate layer 210 of the fuel electrode 116 is 35% or more in order to improve performance (suppression of performance degradation) as in the above embodiment. And the first ratio R1 (= β / α) is preferably 0.18 or more, and the second ratio R2 (= β / γ) is more preferably 0.05 or more, The first ratio R1 is more preferably 0.39 or more, the second ratio R2 is more preferably 0.49 or less, and the first ratio R1 is most preferably 0.58 or less. .

 In the above embodiment, the solid oxide fuel cell (SOFC) has been described as an example. However, the present invention is applicable to other types of fuel cells (or electrolytic 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: Fuel cell power generation unit 104: End plate 106: End plate 108: Communication hole 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 120: Separator 121: Hole 124: Joint part 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 136: Coat 138: Bonding layer 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 portion 147: Connection portion 14 : 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 180: Intermediate layer 210: Substrate layer 220: Active layer

Claims (8)

An electrolyte layer, an air electrode disposed on one side in a first direction with respect to the electrolyte layer, and a fuel electrode disposed on the other side in the first direction with respect to the electrolyte layer, wherein A first fuel electrode layer constituting a surface of the other side of the fuel electrode in the first direction; a second fuel electrode layer disposed between the first fuel electrode layer and the electrolyte layer; An electrochemical reaction unit cell comprising: the fuel electrode comprising:
A plurality of current collectors disposed on the other side in the first direction with respect to the first fuel electrode layer and conducting to the surface on the other side in the first direction in the first fuel electrode layer A conductive current collector having
In an electrochemical reaction unit comprising:
The porosity of the first fuel electrode layer is 35% or more,
About the specific current collector that is at least one of the plurality of current collectors, the specific current collector in the second direction orthogonal to the first direction and the specific current collector located next to the specific current collector The first ratio (β / α) that is the ratio of the thickness β of the first fuel electrode layer in the first direction to the shortest distance α between the current collector and the current collector is 0.18 or more. An electrochemical reaction unit characterized by that. The electrochemical reaction unit according to claim 1,
For the specific current collector, the thickness of the first fuel electrode layer in the first direction with respect to the width γ of the portion of the specific current collector in the second direction facing the first fuel electrode layer The electrochemical reaction unit, wherein the second ratio (β / γ), which is a ratio of β, is 0.05 or more. The electrochemical reaction unit according to claim 2,
The electrochemical reaction unit, wherein the first current ratio (β / α) of the specific current collector is 0.39 or more. The electrochemical reaction unit according to claim 3,
The electrochemical reaction unit characterized in that the second ratio (β / γ) of the specific current collector is 0.49 or less. The electrochemical reaction unit according to claim 4,
The electrochemical reaction unit, wherein the first current ratio (β / α) of the specific current collector is 0.58 or less. In the electrochemical reaction unit according to any one of claims 1 to 5,
An electrochemical reaction unit characterized in that the porosity of the other side portion in the first direction of the fuel electrode is higher than the porosity of the one side portion of the fuel electrode in the first direction. . In the electrochemical reaction unit according to any one of claims 1 to 6,
The electrochemical reaction unit cell is a fuel cell unit cell, an electrochemical reaction unit. In an electrochemical reaction cell stack comprising a plurality of electrochemical reaction units arranged side by side in the first direction,
The electrochemical reaction cell stack according to claim 1, wherein at least one of the plurality of electrochemical reaction units is the electrochemical reaction unit according to claim 1.

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