JP7096643B2 - Electrochemical reaction unit and electrochemical reaction cell stack - Google Patents

Description

The techniques disclosed herein relate to electrochemical reaction units.

A solid oxide fuel cell (hereinafter referred to as "SOFC") is known as one of the fuel cells that generate power by utilizing an electrochemical reaction between hydrogen and oxygen. The fuel cell power generation unit (hereinafter referred to as “power generation unit”), which is a constituent unit of the SOFC, includes a fuel cell single cell (hereinafter referred to as “single cell”). The single cell has an electrolyte layer, an air electrode arranged on one side in a predetermined direction (hereinafter referred to as "first direction") with respect to the electrolyte layer, and the other side in the first direction with respect to the electrolyte layer. Includes fuel poles located in.

Further, the power generation unit includes a conductive current collector arranged on the other side of the fuel electrode in the first direction. The current collector is a member for extracting electric power generated by a power generation reaction in a single cell. The current collector has a plurality of current collectors conducting on the other side surface of the fuel electrode in the first direction. During power generation operation, electrons are exchanged between the fuel electrode and the current collector at a portion where the surface of the fuel electrode and each current collector of the current collector conduct with each other. 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 does not face each current collector portion of the current collector (not covered by each current collector portion). It flows into the pole.

Conventionally, in order to improve the performance of a 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 Unexamined Patent Publication No. 9-190824

However, it is not possible to sufficiently improve the performance of the power generation unit only by considering the preferable range of the thickness of the fuel electrode as in the conventional case, and there is room for further performance improvement.

It should be noted that such a problem is also common to the electrolytic cell unit, which is a constituent unit of a solid oxide type electrolytic cell (hereinafter referred to as “SOEC”) that generates hydrogen by utilizing the electrolysis reaction of water. Is. In this specification, the fuel cell power generation unit and the electrolytic cell unit are collectively referred to as an electrochemical reaction unit.

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

The techniques disclosed herein can be realized, for example, in the following forms.

(1) The electrochemical reaction unit disclosed in the present specification includes an electrolyte layer, an air electrode arranged on one side in the first direction with respect to the electrolyte layer, and the first with respect to the electrolyte layer. An electrochemical reaction single cell comprising a fuel electrode arranged on the other side of the direction of the fuel electrode, and the first direction of the fuel electrode arranged on the other side of the first direction with respect to the fuel electrode. In an electrochemical reaction unit comprising a conductive current collector having a plurality of current collectors conducting on the other side surface of the fuel electrode, the pore ratio of the collector-side portion of the fuel electrode is 35% or more. The specific current collector, which is at least one of the plurality of collectors, is next to the specific collector and the specific collector in the second direction orthogonal to the first direction. The first ratio (β / α), which is the ratio of the thickness β of the fuel electrode in the first direction to the shortest distance α between the positioned current collector, is 0.20 or more. In this electrochemical reaction unit, since the porosity of the part on the collector side of the fuel electrode is 35% or more, the gas can be satisfactorily penetrated into the fuel electrode, and the increase in gas diffusion polarization can be suppressed. can. Further, since the electrochemical reaction unit has a structure in which the thickness β of the fuel electrode 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, the fuel is used. When the electrons generated in the reaction field at the pole (the part on the electrolyte layer side) move along a direction in which the inclination with respect to the first direction is within a certain range, the electrons generated there are collected in the reaction field at the fuel pole. It is possible to reduce the region where it is difficult to reach the current collecting part of the electric body, and it is possible to improve the performance of the electrochemical reaction unit by suppressing the increase in the activation polarization. Therefore, according to the present electrochemical reaction unit, the performance of the electrochemical reaction unit can be improved.

(2) In the electrochemical reaction unit, for the specific current collector, the fuel electrode in the first direction with respect to the width γ of the portion of the specific current collector facing the fuel electrode in the second direction. The second ratio (β / γ), which is the ratio of the thickness β of, may be 0.06 or more. Since the present electrochemical reaction unit has a structure in which the thickness β of the fuel electrode is thick to some extent and / or the width γ of the current collecting portion of the current collector is narrow to some extent, the fuel gas flowing into the fuel electrode is the first. When the inclination with respect to the direction of the fuel flows along a certain range of directions, the region of the reaction field at the fuel electrode where the fuel gas is difficult to reach can be reduced, and the increase in gas diffusion polarization can be suppressed. Therefore, according to the present electrochemical reaction unit, the performance of the electrochemical reaction unit can be improved.

(3) In the electrochemical reaction unit, the first ratio (β / α) of the specific current collector may be 0.40 or more. According to this electrochemical reaction unit, the thickness β of the fuel electrode can be made thicker, and / or the shortest distance α between the current collectors of the current collector can be made shorter. By further effectively reducing the region of the reaction field at the fuel electrode where the electrons generated there are difficult to reach the current collector of the current collector, and by further effectively suppressing the increase in activated polarization. The performance of the electrochemical reaction unit can be further effectively improved. Therefore, according to the present electrochemical reaction unit, the performance of the electrochemical reaction unit can be further effectively improved.

(4) In the electrochemical reaction unit, the second ratio (β / γ) of the specific current collector may be 0.50 or less. According to this electrochemical reaction unit, it is possible to suppress that the thickness β of the fuel electrode becomes excessively thick, and / or it is possible to suppress that the width γ of the current collecting portion of the current collector becomes excessively narrow. The performance of the electrochemical reaction unit can be effectively improved by suppressing the increase in gas diffusion polarization and the damage of the fuel electrode due to stress concentration.

(5) In the electrochemical reaction unit, the first ratio (β / α) of the specific current collector may be 0.60 or less. According to this electrochemical reaction unit, it is possible to prevent the thickness β of the fuel electrode from becoming excessively thick, and / or the shortest distance α between the current collectors of the current collector is excessive. It can suppress shortening. By suppressing the thickness β of the first fuel electrode layer from becoming excessively thick, it is possible to suppress an increase in gas diffusion polarization. Further, by suppressing the shortest distance α between the current collector and the current collector of the current collector from becoming excessively short, the increase in gas pressure loss due to the narrowing of the flow path is suppressed, and the cell is suppressed. The gas is evenly distributed in the plane. From the 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 may be configured. According to this electrochemical reaction unit, it is possible to suppress an increase in gas diffusion polarization while ensuring a reaction field (three-phase interface length).

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

The technique disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction unit (fuel cell power generation unit or electrolytic cell unit), and electricity having 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 method for manufacturing them, and the like.

It is a perspective view which shows the appearance structure of the fuel cell stack 100 in embodiment. It is explanatory drawing which shows the XZ cross-sectional structure of the fuel cell stack 100 at the position of II-II of FIG. It is explanatory drawing which shows the YZ cross-sectional structure of the fuel cell stack 100 at the position of III-III of FIG. It is explanatory drawing which shows the XZ cross section composition of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross section configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the XY cross-sectional structure of the power generation unit 102 at the position of VI-VI of FIG. It is explanatory drawing which shows the XY cross-sectional structure of the power generation unit 102 at the position of VII-VII of FIG. It is explanatory drawing which shows the cross section SE1 used for specifying the current collector width γ and the shortest distance α between current collectors. It is explanatory drawing which shows the cross section SE1 used for specifying the current collector width γ and the shortest distance α between current collectors. It is explanatory drawing which shows the performance evaluation result. It is explanatory drawing which conceptually shows the relationship between the 1st ratio R1 (= β / α), and the power generation performance. It is explanatory drawing which conceptually shows the relationship between the 1st ratio R1 (= β / α), and the power generation performance. It is explanatory drawing which conceptually shows the relationship between the 1st ratio R1 (= β / α), and the power generation performance. It is explanatory drawing which conceptually shows the relationship between the 2nd ratio R2 (= β / γ) and power generation performance. It is explanatory drawing which conceptually shows the relationship between the 2nd ratio R2 (= β / γ) and power generation performance. It is explanatory drawing which conceptually shows the relationship between the 2nd ratio R2 (= β / γ) and power generation performance. It is explanatory drawing which shows the method of specifying the porosity of a fuel electrode 116.

A. Embodiment:
A-1. Constitution:
(Structure 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 the position II-II in FIG. 1 (and FIGS. 6 and 7 described later). It is explanatory drawing which shows the structure, and FIG. 3 is an explanatory view which shows the YZ cross section structure of the fuel cell stack 100 at the position of III-III of FIG. 1 (and FIGS. 6 and 7 which will be described later). Each figure shows XYZ axes that are orthogonal to each other to identify the direction. In the present specification, for convenience, the Z-axis positive direction is referred to as an upward direction, and the Z-axis negative direction is referred to as a downward direction, but the fuel cell stack 100 is actually in a direction different from such an orientation. It may be installed. The same applies to FIGS. 4 and later.

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

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

A bolt 22 extending in the vertical direction is inserted into each communication hole 108, and the fuel cell stack 100 is fastened by the bolt 22 and the nuts 24 fitted on both sides of the bolt 22. As shown in FIGS. 2 and 3, between the nut 24 fitted on one side (upper side) of the bolt 22 and the upper surface of the end plate 104 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 22 and the lower surface of the end plate 106 constituting the lower end of the fuel cell stack 100. However, in the place where the gas passage member 27 described later is provided, the insulating sheets arranged on the upper side and the lower side of the gas passage member 27 and the gas passage member 27 between the nut 24 and the surface of the end plate 106, respectively. 26 is intervening. The insulating sheet 26 is made of, for example, a mica sheet, a ceramic fiber sheet, a ceramic dust sheet, a glass sheet, a glass-ceramic composite agent, or the like.

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

Further, as shown in FIGS. 1 and 3, the vicinity of the midpoint of one side (the side on the positive side of the Y axis among the two sides parallel to the X axis) on the outer circumference of the fuel cell stack 100 around the Z direction. In the space formed by the bolt 22 (bolt 22D) located at the center and the communication hole 108 through which the bolt 22D is inserted, the fuel gas FG is introduced from the outside of the fuel cell stack 100, and the fuel gas FG is generated for each power generation. A bolt 22 that functions as a fuel gas introduction manifold 171 to be supplied to the unit 102 and is located near the midpoint of the opposite side (the side on the negative side of the Y axis among the two sides parallel to the X axis). The space formed by (bolt 22E) and the communication hole 108 through which the bolt 22E is inserted causes the fuel off-gas FOG, which is the gas discharged from the fuel chamber 176 of each power generation unit 102, to the outside of the fuel cell stack 100. It functions as a fuel gas discharge manifold 172 to be discharged. In this embodiment, as the fuel gas FG, for example, a 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 portion 29 communicates with the hole of the main body portion 28. A gas pipe (not shown) is connected to the branch portion 29 of each gas passage member 27. Further, as shown in FIG. 2, the hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22A forming the oxidant gas introduction manifold 161 communicates with the oxidant gas introduction manifold 161. The hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22B forming the oxidant gas discharge manifold 162 communicates with the oxidant gas discharge manifold 162. Further, as shown in FIG. 3, the hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22D forming the fuel gas introduction manifold 171 communicates with the fuel gas introduction manifold 171 and fuel gas. The hole of the main body 28 of the gas passage member 27 arranged at the position of the bolt 22E forming the discharge manifold 172 communicates with the fuel gas discharge manifold 172.

(Structure of end plates 104 and 106)
The pair of end plates 104 and 106 are substantially rectangular flat plate-shaped conductive members, and are made of, for example, stainless steel. One end plate 104 is located above the power generation unit 102 located at the top, and the other end plate 106 is located below the power generation unit 102 located at the bottom. A plurality of power generation units 102 are sandwiched by a pair of end plates 104 and 106 in a pressed state. The upper end plate 104 functions as a positive output terminal of the fuel cell stack 100, and the lower end plate 106 functions as a negative output terminal of the fuel cell stack 100.

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

As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air pole side frame 130, an air pole side current collector 134, a fuel pole side frame 140, and a fuel pole side. The 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. A hole corresponding to the communication hole 108 through which the bolt 22 described above is inserted is formed in the peripheral portion of the separator 120, the air pole side frame 130, the fuel pole side frame 140, and the interconnector 150 in the Z direction.

The interconnector 150 is a substantially rectangular flat plate-shaped conductive member, and is made of, for example, ferritic stainless steel. The interconnector 150 ensures electrical conduction between the power generation units 102 and prevents mixing of the reaction gas between the power generation units 102. In this 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 one power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Further, since the fuel cell stack 100 includes a pair of end plates 104 and 106, the power generation unit 102 located at the top of the fuel cell stack 100 does not have the upper interconnector 150 and is located at the bottom. The power generation unit 102 does not include the lower interconnector 150 (see FIGS. 2 and 3).

The single cell 110 has an electrolyte layer 112, an air electrode (cathode) 114 arranged on one side (upper side) of the electrolyte layer 112 in the vertical direction (first direction), and the other side in the vertical direction of the electrolyte layer 112 (upper side). It includes a fuel electrode (anode) 116 arranged on the lower side) and an intermediate layer 180 arranged between the electrolyte layer 112 and the air electrode 114. The single cell 110 of the present embodiment is a fuel pole support type single cell that supports other layers (electrolyte layer 112, air pole 114, intermediate layer 180) constituting the single cell 110 with the fuel pole 116.

The electrolyte layer 112 is a flat plate-shaped member having a substantially rectangular shape in the Z direction, and is a dense layer. The electrolyte layer 112 is formed of, for example, a solid oxide such as YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), and perovskite-type oxide. There is. 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 in the Z direction, and is a porous layer. The air electrode 114 is formed so as to contain a perovskite-type oxide such as LSCF (lanthanum strontium cobalt iron oxide).

The fuel electrode 116 is a substantially rectangular flat plate-shaped member having substantially the same size as the electrolyte layer 112 in the Z direction, and is a porous layer. The fuel electrode 116 is formed of, for example, a cermet composed of Ni and oxide ion conductive ceramic particles (for example, YSZ). In the present embodiment, the porosity of the fuel electrode 116 is substantially uniform in the direction parallel to the Z-axis direction, but may differ in the Z-axis direction. For example, the porosity of the lower part (the side away from the electrolyte layer 112) of the fuel pole 116 (the porosity RO1 of the collector side part of the fuel pole 116 described later) is set to the upper side (the electrolyte layer 112) of the fuel pole 116. It is higher than the porosity of the portion (closer side) (porosity RO2 of the part on the electrolyte layer side in the fuel electrode 116 described later). With such a configuration, it is possible to suppress an increase in gas diffusion polarization while ensuring a reaction field (three-phase interface length). The porosity (porosity RO1) of the lower portion of the fuel electrode 116 is preferably high to some extent in order to secure gas diffusivity. Specifically, the porosity (porosity RO1) of the lower portion of the fuel electrode 116 is preferably 35% or more, and preferably 55% or less. Further, the porosity (porosity RO2) of the upper portion of the fuel electrode 116 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). In the intermediate layer 180, 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 highly resistant substance (for example, SrZrO ₃ ). Suppress.

The separator 120 is a frame-shaped member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. The peripheral portion of the hole 121 in the separator 120 faces the peripheral edge of the surface of the electrolyte layer 112 on the side of the air electrode 114. The separator 120 is bonded to the electrolyte layer 112 (single cell 110) by a bonding portion 124 formed of a brazing material (for example, Ag wax) arranged at the facing portions thereof. The separator 120 partitions 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 at the peripheral edge of the single cell 110. It is suppressed.

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

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

As shown in FIGS. 4, 5 and 7, the fuel pole side current collector 144 is arranged in the fuel chamber 176 (more specifically, below the fuel pole 116). The fuel electrode side current collector 144 is a member having conductivity and not gas permeability, and is formed of, for example, nickel, 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 connecting each electrode facing portion 145 and the interconnector facing portion 146. As shown in the partially enlarged view in FIG. 7, the fuel electrode side current collector 144 is manufactured by making a cut in a substantially rectangular flat plate member (for example, nickel foil) and processing the plurality of rectangular portions so as to bend them up. Ru. Each bent rectangular portion becomes an electrode facing portion 145, and a flat plate portion having a hole OP other than the bent portion becomes an interconnector facing portion 146, and the electrode facing portion 145 and the interconnector facing portion 146 are formed. The connecting portion becomes the connecting portion 147. In the partially enlarged view in FIG. 7, in order to show the manufacturing method of the fuel electrode side current collector 144, a state of a part of the rectangular portion before the bending raising process is completed is shown.

Each electrode facing portion 145 is in contact with the surface of the fuel electrode 116 on the side opposite to the side facing the electrolyte layer 112. That is, each electrode facing portion 145 is conductive to the lower surface 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 power generation unit 102 located at the bottom of the fuel cell stack 100 does not have the lower interconnector 150, the interconnector facing portion 146 in the power generation unit 102 is the lower end plate. It is in contact with 106. Since the current collector 144 on the fuel electrode side has such a configuration, the fuel electrode 116 and the interconnector 150 (or the end plate 106) are electrically connected to each other. A spacer 149 formed of, for example, a mica is arranged between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to the temperature cycle and the reaction gas pressure fluctuation, and the fuel electrode 116 and the interconnector 150 (or the end plate 106) via the fuel electrode side current collector 144 follow. Good electrical connection with is maintained. The fuel electrode side current collector 144 corresponds to a current collector in the claims, and the plurality of electrode facing portions 145 correspond to a plurality of current collectors in the claims.

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

Further, 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 formed of, for example, a spinel-type oxide. In the following description, unless otherwise specified, the air electrode side current collector 134 (current collector element 135) means "air electrode side current collector 134 covered with coat 136 (current collector element 135)". Note that FIG. 6 omits the illustration of the coat 136. Further, 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 by a conductive bonding layer 138. The bonding layer 138 is formed of, for example, a spinel-type oxide. The bonding layer 138 electrically connects the air electrode 114 and the air electrode side current collector 134. It was explained earlier that the current collector 134 on the air electrode side is in contact with the surface of the air electrode 114, but to be precise, a bonding layer 138 is provided between the current collector 134 on the air electrode side and the air electrode 114. It is intervening.

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

As shown in FIGS. 2 and 4, the oxidant off-gas OOG discharged from the air chamber 166 of each power generation unit 102 is discharged to the oxidant gas discharge manifold 162 through the oxidant gas discharge communication hole 133, and further oxidized. The fuel cell stack 100 is passed through the holes of the main body 28 and the branch 29 of the gas passage member 27 provided at the position of the agent gas discharge manifold 162, and the gas pipe (not shown) connected to the branch 29. It is discharged to the outside of. 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 via a gas pipe (not shown) connected to the branch portion 29 through the holes of the main body portion 28 and the branch portion 29 of the gas passage member 27 provided at the position of the discharge manifold 172. It is 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 fuel electrode 116 in the Z-axis direction is referred to as “fuel electrode thickness β”. When the thickness of the fuel electrode 116 is not uniform, the fuel electrode thickness β is the thinnest in the fuel electrode 116 (however, the portion of the current collector 144 on the fuel electrode side facing the electrode facing portion 145). The thickness of the part.

Further, the width (the size in the direction orthogonal to the Z-axis direction) of the portion facing the fuel pole 116 (the portion in contact with the fuel pole 116) in each electrode facing portion 145 of the fuel pole side current collector 144 is set to "collection". It is called "electric part width γ".

As shown in FIGS. 8 and 9, four points (P1) are specified on the outer peripheral 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) In the cross section SE1 (YZ cross section in the examples of FIGS. 8 and 9) including the minor axis Am of the virtual ellipse VE and parallel to the Z axis direction when the inscribed virtual ellipse VE is set. Assumed to be performed.

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

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

Further, the ratio (β / α) of the fuel extreme 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 portions 145 is narrow), and / or the fuel thickness β Means that the value of is large. Further, the ratio (β / γ) of the fuel extreme thickness β to the current collector width γ is referred to as a “second ratio R2”. The high value of the second ratio R2 means that 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 maximum thickness β is large. Means.

(For each sample)
FIG. 10 is an explanatory diagram showing a performance evaluation result. As shown in FIG. 10, each sample (S1 to S14) of the power generation unit 102 used for the performance evaluation has the above-mentioned shortest distance α between the current collectors, the fuel maximum thickness β, and the current collector width γ. The values 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, each sample has a porosity RO1 of a portion of the fuel pole 116 near the fuel electrode side current collector 144 (hereinafter referred to as “collector side portion”) and a side close to the electrolyte layer 112 of the fuel pole 116. The values of the porosity RO2 of the portion (hereinafter referred to as “electrolyte layer side portion”) are different from each other. As shown in FIG. 10, in all the samples used for the performance evaluation, the porosity RO1 of the collector side portion of the fuel electrode 116 is higher than the porosity RO2 of the electrolyte layer side portion of the fuel electrode 116. The method for specifying the porosity RO1 and the porosity RO2 will be described later.

In preparing each sample, the fuel electrode 116 was formed of a cermet composed of Ni and YSZ. Further, the porosity RO1 of the collector side portion of the fuel electrode 116 and the porosity RO2 of the electrolyte layer side portion were adjusted by adjusting the particle size of the raw material and 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 the current collectors and the width γ of the current collectors were made different from each other by making the shapes and arrangements of the electrode facing portions 145 and the like different from each other.

(About evaluation method)
In this performance evaluation, the power generation performance was evaluated. Specifically, for each sample of the produced power generation unit 102, the 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, " It was evaluated on a scale of 7 from "A" to "G"("A" is the best evaluation and "G" is the worst).
・ Evaluation: “A” ・ ・ ・ Initial voltage: 0.92V or more ・ Evaluation: “B” ・ ・ ・ Initial voltage: 0.915V or more, less than 0.92V ・ Evaluation: “C” ・ ・ ・ Initial voltage: 0 .91V or more and less than 0.915V ・ Evaluation: “D” ・ ・ ・ Initial voltage: 0.905V or more and less than 0.91V ・ Evaluation: “E” ・ ・ ・ Initial voltage: 0.9V or more and less than 0.905V・ Evaluation: “F” ・ ・ ・ Initial voltage: 0.8V or more, less than 0.9V ・ Evaluation: “G” ・ ・ ・ Initial voltage: Less than 0.8V

(About the evaluation result)
(About sample S1)
As shown in FIG. 10, the evaluation result of sample S1 was the lowest "G" evaluation. In sample S1, the porosity RO1 of the current collector side portion of the fuel electrode 116 is 20%, which is lower than that of the other samples (in each case, the porosity RO1 of the current collector side portion is 35% or more). ing. Therefore, in the sample S1, the fuel gas FG supplied to the fuel chamber 176 does not enter the fuel electrode 116 well, and the fuel gas FG is insufficient in the reaction field (the portion on the electrolyte layer 112 side) in the fuel electrode 116. It is probable that the gas diffusion polarization became extremely large, and as a result, the initial voltage became extremely low. From this result, it can be said that the porosity RO1 of the current collector side portion 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 deterioration of the power generation performance).

(About sample S2)
The evaluation result of sample S2 was the second lowest "F" evaluation. In the sample S2, although the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.19, and the samples S3 to S14 (both are the first). The ratio R1 of 1 is 0.20 or more), which is a lower value. Therefore, it is considered that the initial voltage of the sample S2 is lower than that of the 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 part 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 of the configuration of the power generation unit 102 shown in FIG. 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 of the configuration of the power generation unit 102 shown in FIG. Further, in the configuration of the power generation unit 102 shown in FIG. 12, the value of the fuel maximum thickness β is smaller than that of 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 of the configuration of the power generation unit 102 shown in FIG.

Here, the electrons generated by the electrode reaction in the reaction field Ax0 (the portion of the fuel electrode 116 on the electrolyte layer 112 side) pass through the fuel electrode 116 and enter the fuel electrode side current collector 144. However, the exchange of electrons (e ⁻ ) between the fuel electrode 116 and the fuel electrode side current collector 144 does not face the electrode facing portion 145 of the fuel electrode side current collector 144 in the surface of the fuel electrode 116. It is not performed in the (non-contacting) portion (that is, the portion corresponding to the shortest distance α between the current collecting portions), and the portion facing (contacting) the electrode facing portion 145 of the fuel electrode side current collector 144 (that is, the width of the current collecting portion). It is done in the part corresponding to γ). Further, the electrons generated in the reaction field Ax0 at the fuel electrode 116 flow toward the fuel electrode side current collector 144 along a direction in which the inclination with respect to the Z-axis direction is generally within a predetermined value θ1. Therefore, as shown in FIG. 11, the value of the shortest distance α between the current collectors is relatively large, and as shown in FIG. 12, the value of the fuel maximum thickness β is relatively small (that is, the first ratio R1). In the configuration where the value is relatively small), the electrons generated in a part of the region Ax1 in the reaction field Ax0 are less likely to reach the electrode facing portion 145 of the fuel electrode side current collector 144, so that the activation polarization becomes large. As a result, the initial voltage of the power generation unit 102 becomes low.

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. 12 Compared with the configuration of, the value of the fuel extra-thickness β is large. 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 of the configuration of the power generation unit 102 shown in FIGS. 11 and 12. 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 reaction field Ax0 of the fuel electrode 116 are the electrodes of the fuel electrode side current collector 144. It is possible to reduce the area of the region that is difficult to reach the facing portion 145. Further, in the configuration of the power generation unit 102 shown in FIG. 13, since the value of the fuel electrode thickness β is relatively large, the moving distance of the electrons generated in the reaction field Ax0 of the fuel electrode 116 in the direction orthogonal to the Z-axis direction. Can be relatively long. Therefore, as shown in FIG. 13, in the configuration in which the value of the first ratio R1 is relatively large, the electrons generated in the reaction field Ax0 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 the activation polarization.

As described above, the evaluation result of the sample S2 in which the first ratio R1 (= β / α) is less than 0.20 is based on the evaluation result of the samples S3 to S14 in which the first ratio R1 is 0.20 or more. Considering the inferiority, it can be said that the first ratio R1 is preferably 0.20 or more in order to improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance).

(About samples S3 and S4)
The evaluation results of the samples S3 and S4 were the third lowest "E" evaluations. In the samples S3 and S4, the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% or more, and the first ratio R1 (= β / α) is 0.20 or more, but the second one. The ratio R2 (= β / γ) is less than 0.06, which is lower than that of the samples S5 to S14 (in each case, the second ratio R2 is 0.06 or more). Therefore, it is considered that the initial voltage of the samples S3 and S4 is lower than that of the samples S5 to S14 as described below.

14 to 16 are explanatory views 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 part 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 of the configuration of the power generation unit 102 shown in FIG. 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 of 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 maximum thickness β is smaller than that of 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 of 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 fuel electrode 116 facing (contacting) the electrode facing portion 145 of the fuel electrode side current collector 144 (that is, the width of the current collecting portion). The fuel electrode does not flow in from the portion corresponding to γ) and does not face (contact) the electrode facing portion 145 of the fuel electrode side current collector 144 (that is, the portion corresponding to the shortest distance α between the current collectors). It flows into 116. Further, the fuel gas FG flowing into the fuel electrode 116 has a reaction field Ax0 at the fuel electrode 116 (on the side of the electrolyte layer 112 at the fuel electrode 116) along a direction in which the inclination with respect to the Z-axis direction is generally within a predetermined value θ2. Flow toward the part). Therefore, as shown in FIG. 14, the value of the collector width γ is relatively large, and as shown in FIG. 15, the value of the fuel maximum thickness β is relatively small (that is, the value of the second ratio R2 is In a relatively small configuration), the fuel gas FG becomes difficult to reach a part of the region Ax2 in the reaction field Ax0 of the fuel electrode 116, so that the gas diffusion polarization becomes large, and as a result, the initial voltage of the power generation unit 102 becomes high. It gets lower.

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. 15 Compared with, the value of the fuel extra-thickness β is large. 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 of the configuration of the power generation unit 102 shown in FIGS. 14 and 15. 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, it is possible to reduce the area of the reaction field Ax0 of the fuel electrode 116 in the region where the fuel gas FG is difficult to reach. Further, in the configuration of the power generation unit 102 shown in FIG. 16, since the value of the fuel electrode thickness β is relatively large, the moving distance of the fuel gas FG that has entered the fuel electrode 116 in the direction orthogonal to the Z-axis direction ( The diffusion distance) 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, it is possible to reduce the region of the reaction field Ax0 of the fuel electrode 116 where the fuel gas FG is difficult to reach, and the gas diffusion polarization can be achieved. The decrease in the initial voltage can be suppressed by suppressing the increase in the fuel.

As described above, the evaluation results of the samples S3 and S4 having the second ratio R2 (= β / γ) of less than 0.06 are the evaluations of the samples S5 to S14 having the second ratio R2 of 0.06 or more. Considering that it is inferior to the result, it can be said that the second ratio R2 is preferably 0.06 or more in order to further improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance).

(About samples S5 to S7)
The evaluation results of the samples S5 to S7 were the 4th lowest (that is, the 4th highest) "D" evaluation. In the samples S5 to S7, the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.20 or more, and the second ratio. Although R2 (= β / γ) is 0.06 or more, the first ratio R1 is less than 0.40, and the samples S8 to S14 (in each case, the first ratio R1 is 0.40 or more). The value is lower than that. As described above, the larger the value of the first ratio R1, the more difficult it is for the electrons generated in the reaction field Ax0 of the fuel electrode 116 to reach the electrode facing portion 145 of the fuel electrode side current collector 144. It is possible to improve the power generation performance (suppress the decrease in the power generation performance) by suppressing the increase in the activation polarization. The evaluation result of the samples S5 to S7 having the first ratio R1 (= β / γ) of less than 0.40 is inferior to the evaluation result of the samples S8 to S14 having the first ratio R1 of 0.40 or more. Considering this, it can be said that the first ratio R1 is preferably 0.40 or more in order to further improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance).

(About sample S8)
The evaluation result of sample S8 was the 5th lowest (that is, the 3rd highest) "C" rating. In sample S8, the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.40 or more, and the second ratio R2 ( = Β / γ) is 0.06 or more, but the second ratio R2 exceeds 0.50, which is compared with the samples S9 to S14 (in each case, the second ratio R2 is 0.50 or less). It is an excessively high value. An excessively high value of the second ratio R2 means that the value of the fuel thickness β is excessively large and / or the value of the current collector width γ is excessively small. If the value of the fuel electrode thickness β is excessively large, the diffusion path of the fuel gas FG from the surface of the fuel electrode 116 to the reaction field Ax0 becomes excessively long, so that the gas diffusion polarization becomes large, and as a result, the initial voltage becomes high. In addition to being lower, it causes an increase in the amount of material used to form the fuel electrode 116 and an increase in the possibility of interface separation between the fuel electrode 116 and other layers. Further, if the value of the current collector width γ is excessively small, the contact area between the fuel electrode 116 and the fuel electrode side current collector 144 becomes excessively small, so that stress concentrates and causes damage to the fuel electrode 116. As a result, the initial voltage becomes low. It is considered that the initial voltage was lowered in the sample S8 for at least one of these reasons. Considering that the evaluation result of the sample S8 in which the second ratio R2 (= β / γ) exceeds 0.50 is inferior to the evaluation result of the samples S9 to S14 in which the second ratio R2 is 0.50 or less. In order to further improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance), it can be said that the second ratio R2 is preferably 0.50 or less.

(About sample S9)
The evaluation result of sample S9 was the 6th lowest (that is, the 2nd highest) "B" rating. In sample S9, the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% or more, the first ratio R1 (= β / α) is 0.40 or more, and the second ratio R2 ( = Β / γ) is 0.06 or more and 0.50 or less, but the first ratio R1 exceeds 0.60, and the samples S10 to S14 (in each case, the first ratio R1 is 0.60 or less). It is an excessively high value compared to). When the first ratio R1 is excessively high, it means that the value of the fuel thickness β is excessively large and / or the value of the shortest distance α between the current collectors is excessively small. If the value of the fuel electrode thickness β is excessively large, the diffusion path of the fuel gas FG from the surface of the fuel electrode 116 to the reaction field Ax0 becomes excessively long, so that the gas diffusion polarization becomes large, and as a result, the initial voltage becomes high. In addition to being lower, it causes an increase in the amount of material used to form the fuel electrode 116 and an increase in the possibility of interface separation between the fuel electrode 116 and other layers. Further, if the value of the shortest distance α between the current collectors is excessively small, the area of the portion of the fuel electrode 116 not covered by the electrode facing portion 145 of the fuel electrode side current collector 144 becomes excessively small, so that the fuel chamber The fuel gas FG supplied to the 176 does not enter the fuel electrode 116 well, the gas diffusion polarization becomes large, and as a result, the initial voltage becomes low. Further, if the value of the shortest distance α between the current collectors is excessively small, the gas flow path becomes excessively narrow, which increases the pressure loss of the gas and makes it difficult to uniformly distribute the gas in the cell surface, resulting in this. , The initial voltage becomes low. It is considered that the initial voltage was lowered in the sample S9 for at least one of these reasons. Considering that the evaluation result of the sample S9 in which the first ratio R1 (= β / α) exceeds 0.60 is inferior to the evaluation result of the samples S10 to S14 in which the first ratio R1 is 0.60 or less. In order to further improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance), it can be said that the first ratio R1 is preferably 0.60 or less.

(Summary of performance evaluation results)
With reference to the performance evaluation results described above, in order to improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance), the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% or more, and the porosity RO1 is 35% or more. The first ratio R1 (ratio of the fuel thickness β to the shortest distance α between the current collectors (β / α)) is preferably 0.20 or more, and the second ratio R2 (with respect to the collector width γ). The ratio of the fuel thickness β (β / γ)) is more preferably 0.06 or more, the first ratio R1 is more preferably 0.40 or more, and the second ratio R2 is 0. It is more preferably 50 or less, and it can be said that the first ratio R1 is most preferably 0.60 or less.

A-4. How to identify the porosity of the fuel electrode 116:
The above-mentioned specification of the porosity RO1 of the current collector side portion of the fuel electrode 116 is described in p. The following method was followed with reference to the description of 193-195 (see FIG. 17). First, in the power generation unit 102 (single cell 110), the fuel gas FG is arranged at arbitrary three positions along the flow direction of the fuel gas FG (Y-axis direction in this embodiment as shown in FIGS. 5 and 7). A cross section (XZ cross section in this embodiment) substantially orthogonal to the flow direction of the fuel pole 116 is set, and a portion including the surface of the fuel pole side current collector 144 side of the fuel pole 116 is shown at any three points of each cross section. -Obtain an SEM image (5000 times) at SEM (acceleration voltage 1.5 kV). That is, nine SEM images are obtained. In each of the above SEM images, five virtual straight lines VL (VL11 to VL15) orthogonal to the Z-axis direction are set at 1 μm intervals near the surface of the fuel pole side current collector 144 side of the fuel pole 116. In each of the five virtual straight lines VL, the length of each part corresponding to the pores is measured, and the ratio of the total length of each part corresponding to the pores to the total length of the virtual straight line VL is defined as 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 RO1 of the collector side portion of the fuel electrode 116.

Similarly, the porosity RO2 of the electrolyte layer side portion of the fuel electrode 116 was specified according to the following method (see FIG. 17). First, in the power generation unit 102 (single cell 110), a cross section substantially orthogonal to the flow direction of the fuel gas FG at any three positions arranged along the flow direction of the fuel gas FG (Y-axis direction in the present embodiment). In this embodiment, an XZ cross section is set, and an SEM image (acceleration voltage 1.5 kV) in the FIB-SEM (acceleration voltage 1.5 kV) showing a portion of the fuel electrode 116 including the surface on the electrolyte layer 112 side at any three points in each cross section (acceleration voltage 1.5 kV). 5000 times) is obtained. That is, nine SEM images are obtained. In each of the above SEM images, 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 fuel electrode 116 on the electrolyte layer 112 side. The surface of the fuel electrode 116 on the electrolyte layer 112 side can be specified in each of the above SEM images based on the difference in the constituent substances between the fuel electrode 116 and the electrolyte layer 112. In each of the five virtual straight lines VL, the length of each part corresponding to the pores is measured, and the ratio of the total length of each part corresponding to the pores to the total length of the virtual straight line VL is defined as 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 electrolyte layer side portion of the fuel electrode 116.

B. Modification example:
The technique disclosed in the present specification is not limited to the above-described embodiment, and can be transformed into various forms without departing from the gist thereof, and for example, the following modifications are also 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 can be variously modified. For example, in the above embodiment, the fuel pole 116 has a single-layer configuration, but the fuel pole 116 may be composed of a plurality of layers having different configurations. Even when the fuel pole 116 is composed of a plurality of layers, the thickness β of the fuel pole 116 in the vertical direction (first direction) means the thickness of the entire fuel pole 116 (total thickness of each layer). do.

For example, the fuel electrode 116 has two, a first fuel electrode layer (substrate layer) located on the fuel electrode side current collector 144 side and a second fuel electrode layer (active layer) located on the electrolyte layer 112 side. It may have a layered structure. In such a configuration, the thickness β of the fuel electrode 116 in the vertical direction (first direction) is the thickness of the first fuel electrode layer (board layer) and the thickness of the second fuel electrode layer (active layer). Means the sum of. Even in such a configuration, the porosity of the first fuel electrode layer (substrate layer) in the fuel electrode 116 (porosity RO1 of the collector side portion in the fuel electrode 116) is the second fuel electrode in the fuel electrode 116. It is preferably higher than the porosity of the layer (active layer) (porosity RO2 of the portion on the electrolyte layer side in the fuel electrode 116). For example, the porosity of the first fuel electrode layer (board layer) in the fuel electrode 116 (porosity RO1 of the current collector side portion in the fuel electrode 116) is preferably 35% or more, preferably 55% or less. Is preferable. Further, the porosity of the second fuel electrode layer (active layer) in the fuel electrode 116 (porosity RO2 of the portion on the electrolyte layer side in the fuel electrode 116) is preferably 10% or more, preferably 30% or less. Is preferable.

Further, in the above embodiment, the fuel pole side current collector 144 is composed of the electrode facing portion 145, the interconnector facing portion 146, and the connecting portion 147, but the fuel pole side current collector 144 is the fuel pole 116. As long as it has a plurality of current collectors conducting on the surface of the above, other configurations may be used. For example, the fuel pole side current collector 144 may be composed of a plurality of substantially square columnar current collector elements, similarly to the air pole side current collector 134. In such a configuration, the plurality of current collector elements function as a plurality of current collectors. Further, in the above embodiment, the spacer 149 is arranged between the electrode facing portion 145 and the interconnector facing portion 146, but the spacer 149 can be omitted.

Further, in the above embodiment, on the surface of the fuel electrode 116 on the fuel electrode side current collector 144 side, a conductive material having gas permeability (for example, a fine pitch formed of Ni (from the arrangement pitch of the electrode facing portion 145). A mesh material (of fine pitch) is arranged, and the surface of the fuel electrode 116 is conducted to the electrode facing portion 145 of the fuel electrode side current collector 144 via the conductive material having the gas permeability. You may be there. In such a configuration, the fuel electrode 116 corresponds to the fuel electrode in the claims, the fuel electrode side current collector 144 corresponds to the current collector in the claims, and the conductive material having the gas permeability. Does not correspond to a fuel electrode or a current collector within the scope of the claims.

Further, in the above embodiment, the fuel electrode side current collector 144 may be covered with a conductive coat. In such a configuration, if 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 fuel electrode or the current collector in the claims.

The shortest distance α between the current collectors, the fuel thickness β, and the current collector width γ are preferably in the following ranges, respectively.
・ 1000 μm ≤ shortest distance between current collectors α ≤ 3000 μm
210 μm ≤ fuel thickness β ≤ 1210 μm
・ 500 μm ≤ current collector width γ ≤ 9000 μm

Further, in the above embodiment, the single cell 110 includes the intermediate layer 180, but the single cell 110 does not necessarily have to include the intermediate layer 180. Further, 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. Further, 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. Further, in the above embodiment, the air electrode side current collector 134 is in contact with the air electrode 114 via the bonding layer 138, but the air electrode side current collector 134 is in contact with the air electrode 114 without passing through the bonding layer 138. It may be.

Further, in the above embodiment, the number of single cells 110 (power generation unit 102) included in the fuel cell stack 100 is only an example, and the number of single cells 110 (power generation unit 102) is required for the fuel cell stack 100. It is appropriately determined according to the output voltage and the like. Further, the material constituting each member in the above embodiment is merely an example, and each member may be composed of another material.

Further, the constituent requirements for improving the power generation performance (suppressing the deterioration of the power generation performance) of the power generation unit 102 described in the above embodiment (for example, the pore ratio RO1 of the collector side portion of the fuel electrode 116 is 35% or more, and , The first ratio R1 (= β / α) is 0.20 or more, etc.) does not necessarily have to be satisfied in all of the plurality of power generation units 102 constituting the fuel cell stack 100, and the fuel cell. It suffices if it is satisfied in at least one of the plurality of power generation units 102 constituting the stack 100. Further, when focusing on one power generation unit 102, the constituent requirements do not necessarily have to be satisfied in all of the plurality of electrode facing portions 145 included in the fuel pole side current collector 144, and the fuel pole side current collector is not required. It suffices if it is filled in at least one of the plurality of electrode facing portions 145 included in the body 144. In addition, in order to effectively improve the power generation performance of the power generation unit 102 (suppress the deterioration of the power generation performance), among all the electrode facing portions 145 provided in the fuel electrode side current collector 144, 30% or more of the electrode facing portions 145 are described above. It is preferable that the constituent requirements are satisfied, it is more preferable that the above-mentioned constituent requirements are satisfied in 50% or more of the electrode facing portions 145, and the above-mentioned constituent requirements are satisfied in 70% or more of the electrode facing portions 145. It is more preferable that 90% or more of the electrode facing portions 145 satisfy the above-mentioned constituent requirements, and most preferably 100% of the electrode facing portions 145 satisfy the above-mentioned constituent requirements. The electrode facing portion 145 satisfying the constituent requirements corresponds to a specific current collecting portion within the scope of the claims.

Further, in the above embodiment, the SOFC that generates power by utilizing the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidizing agent gas is targeted, but the present invention relates to an electrolysis reaction of water. It is also applicable to an electrolytic cell unit, which is a constituent unit of a solid oxide type electrolytic cell (SOEC) that uses it to generate hydrogen, and an electrolytic cell stack having a plurality of electrolytic cell units. The configuration of the electrolytic cell stack is not described in detail here because it is known, for example, as described in Japanese Patent Application Laid-Open No. 2016-81813, but is schematically the same as the fuel cell stack 100 in the above-described embodiment. It is the composition of. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolytic cell stack, the power generation unit 102 may be read as an electrolytic cell unit, and the single cell 110 may be read as an electrolytic cell. However, during the operation of the electrolytic cell stack, a voltage is applied between both electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), and the voltage is applied through the communication hole 108. Steam as a raw material gas is supplied. As a result, an electrolysis reaction of water occurs in each electrolytic cell unit, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out to the outside of the electrolytic cell stack through the communication hole 108. Even in the electrolytic cell unit and the electrolytic cell stack having such a configuration, in order to improve the performance (suppress the performance deterioration), the porosity RO1 of the collector side portion of the fuel electrode 116 is 35% as in the above embodiment. It is preferable that the first ratio R1 (= β / α) is 0.20 or more, and the second ratio R2 (= β / γ) is 0.06 or more. , The first ratio R1 is more preferably 0.40 or more, the second ratio R2 is more preferably 0.50 or less, and the first ratio R1 is most preferably 0.60 or less. preferable.

Further, in the above embodiment, the solid oxide fuel cell (SOFC) has been described as an example, but the present invention can also be applied to other types of fuel cells (or electrolytic cells) such as a molten carbonate fuel cell (MCFC). Applicable.

22: Bolt 24: Nut 26: Insulation sheet 27: Gas passage member 28: Main body 29: Branch 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 130: Air electrode side frame 131: Hole 132: Oxidating agent gas supply communication hole 133: Oxidating agent gas discharge communication hole 134: Air Polar side current collector 135: Current collector element 136: Coat 138: Bonding layer 140: Fuel pole side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel pole side current collector 145 : Electrode facing part 146: Interconnector facing part 147: Connecting part 149: Spacer 150: Interconnector 161: Oxidizing agent gas introduction manifold 162: Oxidizing agent gas discharge manifold 166: Air chamber 171: Fuel gas introduction manifold 172: Fuel gas discharge Manifold 176: Fuel chamber 180: Intermediate layer

Claims (8)

Electricity comprising an electrolyte layer, an air electrode arranged on one side of the electrolyte layer in the first direction, and a fuel electrode arranged on the other side of the first direction with respect to the electrolyte layer. Chemical reaction single cell and
A conductive current collector arranged on the other side of the fuel electrode in the first direction and having a plurality of current collectors conducting to the surface of the other side of the fuel electrode in the first direction. When,
In an electrochemical reaction unit comprising
The porosity of the portion of the fuel electrode on the current collector side is 35% or more and 55% or less.
The current collector further connects an interconnector facing portion arranged on the other side of the first direction with respect to the plurality of current collecting portions, the interconnector facing portion, and each of the current collectors. With multiple connectors,
The plurality of current collectors have the same shape as each other, and are along a second direction orthogonal to both the first direction and the gas flow direction in the fuel chamber facing the fuel electrode, and the like. They are arranged at intervals and at equal intervals along the gas flow direction in the fuel chamber.
With respect to the specific current collector, which is at least one of the plurality of current collectors, the specific current collector and the current collector located next to the specific current collector in the second direction. The first ratio (β / α), which is the ratio of the thickness β of the fuel electrode in the first direction to the shortest distance α in the second direction between them, is 0.20 or more. An electrochemical reaction unit. In the electrochemical reaction unit according to claim 1,
A second ratio of the thickness β of the fuel electrode in the first direction to the width γ of the portion of the specific current collector facing the fuel electrode in the second direction. The ratio (β / γ) of is 0.06 or more, which is an electrochemical reaction unit. In the electrochemical reaction unit according to claim 2,
The electrochemical reaction unit, wherein the first ratio (β / α) of the specific current collector is 0.40 or more. In the electrochemical reaction unit according to claim 3,
An electrochemical reaction unit characterized in that the second ratio (β / γ) of the specific current collector is 0.50 or less. In the electrochemical reaction unit according to claim 4,
The electrochemical reaction unit, wherein the first ratio (β / α) of the specific current collector is 0.60 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 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. .. In the electrochemical reaction unit according to any one of claims 1 to 6.
The electrochemical reaction single cell is an electrochemical reaction unit, characterized in that it is a fuel cell single cell. In the electrochemical reaction cell stack having a plurality of electrochemical reaction units arranged side by side in the first direction.
The electrochemical reaction cell stack according to any one of claims 1 to 7, wherein at least one of the plurality of electrochemical reaction units is the electrochemical reaction unit.

Images