JP2018014309A - Method for manufacturing electrochemical reaction cell stack, and electrochemical reaction cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the change in the electrochemical reaction characteristic of an electrochemical reaction cell stack owing to the progress of Ni agglomeration during operation.SOLUTION: A method for manufacturing an electrochemical reaction cell stack including a plurality of electrochemical reaction single cells, each including a solid oxide-containing electrolyte layer, an air electrode disposed on one face of the electrolyte layer, and a fuel electrode disposed on the other face of the electrolyte layer with an active layer containing Ni and an oxygen ion-conducting substance comprises first and second reduction steps. In the first reduction step, the fuel electrode included in at least one electrochemical reaction single cell before the first reduction step and the second reduction step is reduced at a temperature lower than an operation temperature of the electrochemical reaction cell stack. In the second reduction step, the fuel electrode subjected to reduction in the first reduction step is reduced at a temperature higher than the operation temperature.SELECTED DRAWING: Figure 7

Description

  The technology disclosed herein relates to a method for manufacturing an electrochemical reaction cell stack.

  One type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen is a solid oxide fuel cell (hereinafter referred to as “SOFC”) having an electrolyte layer containing a solid oxide. It has been. The SOFC is generally used in the form of a fuel cell stack including a plurality of single cells. The single cell includes an electrolyte layer, an air electrode disposed on one surface side of the electrolyte layer, a fuel electrode disposed on the other surface side of the electrolyte layer, and containing Ni (nickel) and an oxygen ion conductive material. Is included.

  Thus, in a fuel cell stack including a single cell including a fuel electrode containing Ni, Ni aggregates during operation (power generation) of the fuel cell stack, so that power generation characteristics, temperature characteristics, etc. of the fuel cell stack Characteristics may change. For example, when Ni aggregates, the size (particle diameter) of Ni particles increases, and accordingly, the specific surface area of Ni particles decreases. When the specific surface area of the Ni particles is reduced, the catalytic effect of Ni is reduced, so that the power generation efficiency is reduced. Further, when Ni is agglomerated, the internal resistance of the fuel electrode is increased, and accordingly, Joule heat is increased, and the temperature of the fuel cell stack is increased. Thus, if the characteristics of the fuel cell stack change during operation, for example, there is a possibility that power generation control and temperature control of the fuel cell stack cannot be performed properly.

  Therefore, a technique is known in which Ni is aggregated by reducing the fuel electrode of the fuel cell stack at a temperature higher than the operating temperature of the fuel cell stack before starting operation (see Patent Document 1).

JP 2014-6978 A

  In the above-described technique in which the fuel electrode of the fuel cell stack is reduced at a temperature higher than the operating temperature before the operation starts, Ni is not sufficiently agglomerated, so that the change in characteristics of the fuel cell stack during the operation cannot be sufficiently suppressed. Problems arise.

  Such a problem occurs when an electrolytic cell stack, which is a form of a solid oxide electrolytic cell (hereinafter referred to as “SOEC”), which generates hydrogen using an electrolysis reaction of water, is manufactured. Is a common issue. In this specification, the fuel cell stack and the electrolytic cell stack are collectively referred to as an electrochemical reaction cell stack.

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

  The technology disclosed in this specification can be implemented as the following forms.

(1) An electrochemical reaction cell stack manufacturing method disclosed in the present specification includes an electrolyte layer containing a solid oxide, an air electrode disposed on one surface side of the electrolyte layer, and the other of the electrolyte layer. And a method for producing an electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells including a fuel electrode having an active layer containing Ni (nickel) and an oxygen ion conductive material, The first reduction step of reducing the fuel electrode contained in the electrochemical reaction unit cell before one first reduction step and the second reduction step at a temperature lower than the operating temperature of the electrochemical reaction cell stack; And the second reduction step of reducing the fuel electrode reduced in the first reduction step at a temperature higher than the operating temperature. According to the method for manufacturing an electrochemical reaction cell stack, for example, before starting operation, the fuel electrode is reduced at a temperature lower than the operating temperature of the electrochemical reaction cell stack in the first reduction step, thereby reducing the size of the Ni particles. Can be small. The small size of the Ni particles means that the specific surface area of Ni is large. The larger the specific surface area of Ni, the more easily Ni is aggregated in the second reduction step. Thereby, according to the manufacturing method of this electrochemical reaction cell stack, compared with the case where the fuel electrode is reduced at a temperature higher than the operating temperature without performing the first reduction step before the operation, the fuel electrode is reduced. Aggregation of Ni in (especially the active layer of the fuel electrode) can be promoted. Therefore, it is possible to suppress changes in the electrochemical reaction characteristics of the electrochemical reaction cell stack due to the progress of Ni aggregation during operation.

(2) In the method for manufacturing an electrochemical reaction cell stack, in the second reduction step, the fuel electrode may be reduced under a condition that a dew point of the reducing gas is −12 ° C. or lower. According to the method for producing an electrochemical reaction cell stack, in the second reduction step, by reducing the fuel electrode under a dry atmosphere condition in which the dew point of the reducing gas is −12 ° C. or less, Since the Ni agglomeration at the fuel electrode is further promoted, the electrochemical reaction characteristics of the electrochemical reaction cell stack can be more effectively suppressed during operation due to the progress of the Ni agglomeration. Can do.

(3) In the method for manufacturing an electrochemical reaction cell stack, at least one of the electrolyte layer and the fuel electrode contains Zr (zirconium) and is reduced in the first reduction step in the second reduction step. The fuel electrode may be reduced under a condition that the water vapor concentration of the reducing gas is 0.0003% or more and less than 3%. According to the manufacturing method of the electrochemical reaction cell stack, since the water vapor concentration of the reducing gas is 0.0003% or more, the fuel in the reduction process is compared with the case where the water vapor concentration of the reducing gas is less than 0.0003%. Reduction contraction of the pole can be suppressed. In addition, since the water vapor concentration of the reducing gas is less than 3%, the time required for the phase transition of the Zr crystal system from cubic to tetragonal as compared with the case where the water vapor concentration of the reducing gas is 3% or more is reduced. Prolongation can be suppressed. Thereby, an electrochemical reaction cell stack in which fluctuations in performance during operation are suppressed can be manufactured.

(4) The electrochemical reaction cell stack disclosed in this specification includes an electrolyte layer containing a solid oxide, an air electrode disposed on one surface side of the electrolyte layer, and the other surface side of the electrolyte layer. And an electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells including a fuel electrode having an active layer containing Ni (nickel) and an oxygen ion conductive material, wherein at least one electrochemical reaction is performed For an arbitrary cross section of the fuel electrode included in a single cell, a Ni dispersion index obtained by dividing the number of particles of Ni per unit area by the number of particles of the oxygen ion conductive material per unit area is 0.56 or more, And it is 0.84 or less. According to this electrochemical reaction cell stack, the initial voltage of the electrochemical reaction cell stack is suppressed while suppressing the change in the electrochemical reaction characteristics of the electrochemical reaction cell stack due to the progress of Ni aggregation during operation. Can be suppressed.

(5) In the electrochemical reaction cell stack, the Ni dispersion index may be 0.58 or more and 0.84 or less. According to this electrochemical reaction cell stack, the initial voltage of the electrochemical reaction cell stack is suppressed while suppressing the change in the electrochemical reaction characteristics of the electrochemical reaction cell stack due to the progress of Ni aggregation during operation. Can be suppressed.

  The technology disclosed in the present specification can be realized in various forms. For example, an electrochemical reaction unit cell (a fuel cell unit cell or an electrolysis cell), an electrochemical reaction unit (a fuel cell power generation unit) ), An electrochemical reaction cell stack (fuel cell stack or electrolytic cell stack) including a plurality of electrochemical reaction single cells, 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. 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. 3 is an explanatory diagram showing an XZ cross-sectional configuration of a part (electrolyte layer 112, fuel electrode 116) of a single cell 110. 4 is a flowchart showing a method for manufacturing the fuel cell stack 100. FIG. 6 is an explanatory diagram showing the results of performance evaluation 1 of a fuel electrode 116. It is explanatory drawing which shows the result of the performance evaluation 2 of the fuel electrode. It is explanatory drawing which shows the relationship between a phase transition peak intensity ratio and reduction time. It is explanatory drawing which shows the relationship between the amount of phase transition progress per 3 hours, and water vapor | steam density | concentration. It is explanatory drawing which shows the relationship between the poisoning amount of boron, and temperature. It is explanatory drawing which shows the relationship between the deterioration rate of the fuel cell stack 100, and the poisoning amount of boron.

A. Embodiment:
A-1. Constitution:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of a fuel cell stack 100 in the present embodiment, and FIG. 2 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 100 at a position II-II in FIG. FIG. 3 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position of III-III in FIG. 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 Z-axis direction is referred to as “upward”, and the negative Z-axis direction is referred to as “downward”. It may be installed in different orientations. The same applies to FIG. The fuel cell stack corresponds to the electrochemical reaction cell stack in the claims.

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

  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 are also referred to as “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 into 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 into which the bolts 22B are inserted has an oxidant off-gas OOG that is a 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) located at the position and the communication hole 108 into 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 for 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 into 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.

  As shown in FIGS. 4 and 5, the power generation unit 102 that is the minimum unit of power generation includes a single cell 110, a separator 120, an air electrode side frame 130, an air electrode side current collector 134, and a fuel electrode side frame. 140, a fuel electrode side current collector 144, and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer of the power generation unit 102. A hole corresponding to the above-described communication hole 108 into which the bolt 22 is inserted is formed in the peripheral portion around the Z direction in the separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150. The single cell 110 corresponds to a fuel cell single cell or an electrochemical reaction single cell in the claims.

  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, and an air electrode (cathode) 114 and a fuel electrode (anode) 116 that face each other in the vertical direction (the arrangement direction in which the power generation units 102 are arranged) with the electrolyte layer 112 interposed therebetween. The single cell 110 of the present embodiment is a fuel electrode-supported single cell that supports the electrolyte layer 112 and the air electrode 114 with the fuel electrode 116.

  The electrolyte layer 112 is a substantially rectangular flat plate-shaped member, for example, YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), CaSZ (calcia stabilized zirconia), SDC (samarium doped ceria), GDC (gadolinium). Doped ceria) and a solid oxide such as a perovskite oxide. The air electrode 114 is a substantially rectangular flat plate-shaped member, and is formed of, for example, a perovskite oxide (for example, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide), LNF (lanthanum nickel iron)). Has been. Thus, since the single cell 110 (power generation unit 102) of this embodiment contains a solid oxide as an electrolyte, the fuel cell of this embodiment is a solid oxide fuel cell (SOFC).

  The fuel electrode 116 is a substantially rectangular flat plate member. FIG. 6 shows an XZ sectional configuration of a part of the single cell 110 (the electrolyte layer 112 and the fuel electrode 116). As shown in FIG. 6, the fuel electrode 116 includes an active layer 350 adjacent to the electrolyte layer 112 and a substrate layer 360 adjacent to the surface of the active layer 350 opposite to the electrolyte layer 112. The active layer 350 and the substrate layer 360 are both formed of, for example, a cermet made of Ni (nickel) and ceramic particles, a Ni-based alloy, or the like. The ceramic particles have oxygen ion conductivity, and are, for example, the above-described materials (YSZ or the like) that form the electrolyte layer 112. The ceramic particles correspond to the oxygen ion conductive material in the claims.

  The active layer 350 mainly exhibits a function of reacting oxygen ions supplied from the electrolyte layer 112 with hydrogen or the like contained in the fuel gas FG to generate electrons and water vapor, and the substrate layer 360 mainly includes The function of supporting the active layer 350, the electrolyte layer 112, and the air electrode 114 is exhibited. For any cross section of the active layer 350 of the fuel electrode 116, the Ni dispersion index can be 0.56 or more and 0.84 or less, and can be 0.56 or more and 0.84 or less. it can. The Ni dispersion index is a value obtained by dividing the number of Ni particles per unit area by the number of ceramic particles (oxygen ion conductive material) per unit area, and is one of parameters indicating the degree of aggregation of Ni. . It means that the smaller the Ni dispersion index, the higher the aggregation degree of Ni, that is, the larger the size (particle size) of Ni particles. In order to increase the activity of the active layer 350, the Ni content (mol%) in the active layer 350 is preferably higher than the Ni content in the substrate layer 360. In order to increase the strength of the substrate layer 360, it is preferable that the thickness of the substrate layer 360 in the vertical direction is larger than the thickness of the active layer 350 in the vertical direction. In order to increase the gas diffusibility of the substrate layer 360, the porosity of the substrate layer 360 is preferably higher than the porosity of the active layer 350.

  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. The single cell 110 to which the separator 120 is bonded is referred to as “single cell with separator”.

  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. 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.

  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 made 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.

  The fuel electrode side current collector 144 is disposed in the fuel chamber 176. The fuel electrode side current collector 144 includes an interconnector facing portion 146, an electrode facing portion 145, and a connecting portion 147 that connects the electrode facing portion 145 and the interconnector facing portion 146. For example, nickel or a nickel alloy It is made of stainless steel or the like. The electrode facing portion 145 is in contact with the surface of the fuel electrode 116 on the side opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is on the surface of the interconnector 150 on the side facing the fuel electrode 116. In contact. 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 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. The air electrode side current collector 134 and the interconnector 150 may be formed as an integral member.

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 one interconnector 150 via the air electrode side current collector 134, and the fuel electrode 116 is connected via the fuel electrode side current collector 144. The other interconnector 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 startup until the high temperature can be maintained by heat generated by 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 via 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. Manufacturing method of fuel cell stack 100:
FIG. 7 is a flowchart showing a method for manufacturing the fuel cell stack 100 in the present embodiment. First, the single cell 110 is produced (S110). Specifically, it is as follows.
(Preparation of green sheet for fuel electrode substrate layer)
With respect to the mixed powder (100 parts by weight) of the NiO powder (50 parts by weight) and the YSZ powder (50 parts by weight), organic beads (15% by weight with respect to the mixed powder) as a pore former, butyral resin, Then, DOP which is a plasticizer, a dispersant, and a toluene + ethanol mixed solvent are added and mixed by a ball mill to prepare a slurry. The organic beads are, for example, spherical particles formed of a polymer such as polymethyl methacrylate or polystyrene. The obtained slurry is made into a thin film by a doctor blade method to produce a fuel electrode substrate layer green sheet having a thickness of 250 μm. Note that the ratio of the NiO powder and the YSZ powder in the green sheet for the fuel electrode substrate layer can be appropriately changed as long as the performance is satisfied. For example, the NiO powder: YSZ powder may be 60:40 or 40:60. I do not care. That is, the NiO powder can be appropriately changed between 40 to 60 parts by weight so that the mixed powder of the NiO powder and the YSZ powder becomes 100 parts by weight, and the rest can be changed to the YSZ powder.

(Preparation of green sheet for fuel electrode active layer)
For a mixed powder (100 parts by weight) of NiO powder (60 parts by weight) and YSZ powder (40 parts by weight), butyral resin, DOP as a plasticizer, dispersant, and toluene + ethanol mixed solvent. In addition, the slurry is prepared by mixing with a ball mill. For example, by adjusting the particle diameter of the NiO powder, the average particle diameter of Ni in the single cell 110 after reduction described later can be adjusted. Further, by adding organic beads (3.9% by weight with respect to the mixed powder) as a pore former to the above mixed powder, mixing with a ball mill, and adjusting the slurry, the porosity can be reduced to fuel. It is possible to produce a fuel electrode active layer green sheet that is higher than the electrode substrate layer green sheet. The obtained slurry is thinned by a doctor blade method to produce a green sheet for a fuel electrode active layer having a thickness of 6 μm to 36 μm. In addition, the ratio of the NiO powder and the YSZ powder of the green sheet for the fuel electrode active layer can be appropriately changed as long as the performance is satisfied. For example, even if the NiO powder: YSZ powder is 50:50 or 40:60 I do not care. That is, the NiO powder can be appropriately changed between 40 to 60 parts by weight so that the mixed powder of the NiO powder and the YSZ powder becomes 100 parts by weight, and the rest can be changed to the YSZ powder.

(Preparation of electrolyte sheet green sheet)
To the YSZ powder (100 parts by weight), a butyral resin, DOP as a plasticizer, a dispersant, and a toluene + ethanol mixed solvent are added and mixed in a ball mill to prepare a slurry. The obtained slurry is made into a thin film by a doctor blade method to produce a green sheet for an electrolyte layer having a thickness of 10 μm.

(Lamination of electrolyte layer 112 and fuel electrode 116)
The green sheet for the fuel electrode substrate layer, the green sheet for the fuel electrode active layer, and the green sheet for the electrolyte layer are attached and degreased at about 280 ° C. Further, firing is performed at about 1350 ° C. to obtain a laminate of the electrolyte layer 112 and the fuel electrode 116.

(Formation of air electrode 114)
A mixed solution composed of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder and isopropyl alcohol is prepared. By spray-coating the prepared liquid mixture on the surface of the electrolyte layer 112 in the laminate and firing at 1100 ° C., the air electrode 114 is formed to obtain a fired body (unit cell 110 before reduction). it can.

  Thereafter, the remaining assembly process (for example, joining of the air electrode 114 and the air electrode side current collector 134 and fastening of the fuel cell stack 100 by the bolt 22) is performed, and before the active layer 350 of the fuel electrode 116 is reduced. The assembly of the fuel cell stack 100 is completed (S120). The fuel electrode 116 included in the fuel cell stack 100 immediately after assembly in S120 corresponds to the fuel electrode included in the electrochemical reaction single cell before the first reduction process and the second reduction process in the claims.

(Reduction process)
The assembled fuel cell stack 100 is exposed to a hydrogen atmosphere at a first temperature lower than the operating temperature (eg, 700 ° C.) for a first reduction time, whereby the active layer 350 is reduced (NiO is reduced to Ni) (S130). ). This step is an example of a first reduction step. The operating temperature is a temperature having an activity of conducting oxygen ions of the electrolyte layer 112. The reducing gas used for the reduction is not limited to hydrogen. Methane gas or the like may be used. The first temperature can be 425 ° C to 600 ° C, can be 425 ° C to 550 ° C, and can be 425 ° C to 525 ° C. Further, the first temperature can be set to (425 ° C. (lower temperature at which reduction reaction is possible) + ((operation temperature −425 ° C.) / 2)) or less. The first reduction time is a time of 1 hour or more. The first temperature does not include the temperature of the fuel cell stack 100 during the temperature rising / falling process, and is, for example, the temperature of the fuel cell stack 100 that is maintained for one hour or more. In addition, “lower than the operating temperature” means that when the operating temperature during steady operation has a predetermined temperature range, it is lower than the lower limit temperature of the temperature range. Note that the fuel electrode 116 included in the fuel cell stack 100 in S130 corresponds to the fuel electrode reduced in the first reduction step in the claims.

  Next, the active layer 350 is reduced by exposing the fuel cell stack 100 after the first reduction step to a hydrogen atmosphere at a second temperature higher than the operating temperature for a second reduction time (S140). This step is an example of a second reduction step. The reducing gas used for the reduction is not limited to hydrogen, but may be methane gas or the like. The second temperature can be set at, for example, 770 ° C. to 1000 ° C. The second reduction time is a time of 1 hour or more. Note that the second temperature does not include the temperature of the fuel cell stack 100 in the process of temperature increase / decrease, and is, for example, the temperature of the fuel cell stack 100 maintained for one hour or more. Further, “higher than the operating temperature” means that when the operating temperature during the steady operation has a predetermined temperature range, it is higher than the upper limit temperature of the temperature range.

A-4. Analysis method of the active layer 350 of the fuel electrode 116:
The analysis method of the active layer 350 of the fuel electrode 116 of each unit cell 110 in the fuel cell stack 100 after the first reduction step and the second reduction step is as follows.

  Cross sections of the power generation unit 102 that are orthogonal to the oxidant gas flow direction are set at three positions along the oxidant gas flow direction (X-axis direction in the present embodiment as shown in FIG. 2). The SEM images (for example, 5000 times) in the FIB-SEM (acceleration voltage 1.5 kV) in which the active layer 350 is reflected are obtained at these three locations. That is, nine SEM images are obtained. Each SEM image is, for example, an image in which the whole of the active layer 350 in the vertical direction can be confirmed, and a portion estimated as a boundary B1 (see FIG. 6) between the electrolyte layer 112 and the fuel electrode 116 is vertically It is estimated that the boundary B2 (see FIG. 6) between the active layer 350 and the substrate layer 360 is located in the uppermost divided area among the 10 divided areas obtained by dividing into 10 equal parts in the direction. This is an image in which the portion or the lower end of the fuel electrode 116 (substrate layer 360) is located in the lowest divided region.

  The active layer 350 can be a layer from the interface B1 between the electrolyte layer 112 and the fuel electrode 116 to a position of 5 μm to 30 μm in the negative Z-axis direction. The boundary B1 between the electrolyte layer 112 (active layer 350) and the electrolyte layer 112 can be specified based on the difference in the constituent materials between the active layer 350 and the electrolyte layer 112, visual recognition, or the like in the SEM image. In addition, the boundary B2 between the active layer 350 and the substrate layer 360 may be specified based on the Ni content, the average Ni particle diameter, the difference in porosity, and the like in the SEM image. it can.

  The number of Ni particles and the number of oxygen ion conductive materials per unit area of the active layer 350 can be specified by the following method. The Ni particles and the ceramic particles (YSZ particles) in the active layer 350 can be identified using, for example, the light / dark difference in each SEM image. Specifically, by analyzing each SEM image, each SEM image can be classified into three regions according to lightness. SEM-EDS may be used as a method for discriminating Ni particles and ceramic particles from the three regions according to the brightness. Since elements can be identified by SEM-EDS, the number of Ni particles and ceramic particles per unit area can be identified from the SEM image acquired above.

A-5. Performance evaluation of fuel electrode 116:
A-5-1. Performance evaluation 1 (samples 1-6)
FIG. 8 is an explanatory diagram showing the results of performance evaluation 1 of the fuel electrode 116. As shown in FIG. 8, the performance evaluation 1 includes the combination of the presence / absence of the first reduction step, the first temperature and the first reduction time, and the second temperature, the second reduction time and the reducing atmosphere in the second reduction step. Six types of samples manufactured by different manufacturing methods were used. In FIG. 8, the initial voltage means an initial output voltage of the fuel cell stack 100 when the fuel cell stack 100 after the second reduction step is started to operate at an operating temperature of 700 ° C. “◎” in the determination of the initial characteristics means that the initial voltage is 0.95 V or more, “◯” means that the initial voltage is less than 0.95 V and 0.928 V or more, and “Δ "Means that the initial voltage is less than 0.928 V and 0.921 V or more, and" x "means that the initial voltage is less than 0.921. The IR deterioration rate is a ratio of a difference between the initial voltage and the post-test voltage with respect to the initial voltage when the output voltage when the rated power generation operation of the fuel cell stack 100 is performed for 1000 hours from the initial stage is set as the post-test voltage. is there. The lower the IR deterioration rate, the higher the durability of the fuel cell stack 100. “◎” in the durability judgment means that the IR deterioration rate is 0.64% or less, and “◯” means that the IR deterioration rate is larger than 0.64% and 0.89% or less. "X" means that the IR deterioration rate is larger than 0.89%.

  Sample 1 is a second sample in which the first reduction step is not performed, the second temperature is 710 ° C., which is higher than the operating temperature, the second reduction time is 3 hours, and the atmosphere is 80% hydrogen—20% water vapor. It is the sample manufactured by implementing a reduction process. For this sample 1, the initial characteristic is determined to be “◎”. On the other hand, regarding sample 1, since the Ni dispersion index is relatively large and the IR deterioration rate is also relatively high, the durability is determined as “x”. Only by performing the second reduction step, the degree of Ni aggregation before the start of operation cannot be made sufficiently high. For this reason, Sample 1 has a high IR deterioration rate due to the progress of Ni aggregation during operation. ing.

  On the other hand, in the sample 2, the first reduction step in which the first temperature is 690 ° C. lower than the operating temperature and the first reduction time is 3 hours, and the second reduction time is 770 ° C. in which the second temperature is higher than the operating temperature. Is a sample manufactured by carrying out the second reduction step in which the atmosphere is 500% and the atmosphere is 80% hydrogen and 20% water vapor. For Sample 2, the initial characteristic is determined to be “◯”. On the other hand, the Ni dispersion index of sample 2 is smaller than the Ni dispersion index of sample 1, and the IR deterioration rate of sample 2 is lower than the IR deterioration rate of sample 1, so the durability is determined as “◯”. Has been. By carrying out the first reduction step, the Ni particles become smaller than the size before the first reduction step and the specific surface area increases, so that Ni is likely to aggregate. As described above, the second reduction step is performed after the Ni is easily aggregated, so that the sample 2 has a higher degree of Ni aggregation before the start of operation than the sample 1. . This means that the aggregation of Ni in the fuel electrode 116 can be further promoted before the start of operation. This suppresses an increase in the IR deterioration rate due to the progress of Ni aggregation.

  Sample 3 has a first reduction step in which the first temperature is 500 ° C. lower than the operating temperature and the first reduction time is 16 hours, and 770 ° C. in which the second temperature is higher than the operating temperature and the second reduction time is 140 hours. And it is the sample manufactured by implementing the 2nd reduction process whose atmosphere is 80% of hydrogen-20% of water vapor | steam. With respect to Sample 3, both the initial characteristics and the durability are determined as “◯”. Furthermore, the Ni dispersion index of sample 3 is smaller than the Ni dispersion index of sample 2, and the IR deterioration rate of sample 3 is lower than the IR deterioration rate of sample 2. In sample 3, compared to sample 2, the first temperature is lower and the first reduction time is longer. For this reason, in sample 3, Ni is more likely to aggregate in the second reduction step by the amount that Ni particles can be made smaller than sample 2 in the first reduction step. As a result, even when the second reduction time is short, the degree of aggregation of Ni before the start of operation is high. Therefore, in sample 3, the total time of the first reduction time and the second reduction time can be made shorter than in sample 2. That is, in a reduction process (first reduction process and second reduction process) shorter than that of sample 2, sample 3 having a lower IR deterioration rate than sample 2 can be obtained.

  Sample 4 differs from sample 3 only in the atmosphere of the second reduction step. That is, in sample 4, the atmosphere of the second reduction time is 100% hydrogen, and the second reduction process is performed in a dry atmosphere as compared to sample 3. For sample 4, the initial characteristic is determined to be “Δ”, but the durability is determined to be “◯”. Further, the Ni dispersion index of sample 4 is smaller than the Ni dispersion index of sample 3, and the IR deterioration rate of sample 4 is lower than the IR deterioration rate of sample 3. This means that the aggregation degree of Ni before the start of operation can be further increased by performing the second reduction step in a dry atmosphere with a low moisture content (dew point of hydrogen gas is −12 ° C. or lower).

  Sample 5 has a first reduction step in which the first temperature is 690 ° C. lower than the operating temperature and the first reduction time is 3 hours, and 770 ° C. in which the second temperature is higher than the operating temperature and the second reduction time is 153 hours. And it is the sample manufactured by implementing the 2nd reduction process whose atmosphere is 80% of hydrogen-20% of water vapor | steam. With respect to this sample 5, both initial characteristics and durability are determined as “◯”. In Sample 5, the conditions of the first reduction step are substantially the same as those of Sample 2, the conditions of the second reduction step are substantially the same as those of Sample 3, and the Ni dispersion index of Sample 5 is the Ni dispersion index of Samples 2 and 3. It is larger than the dispersion index, and the IR deterioration rate of Sample 5 is higher than that of Samples 2 and 3. The comparison result between sample 5 and sample 2 means that the longer the second reduction time, the higher the degree of Ni aggregation before the start of operation. The comparison result between sample 5 and sample 3 means that the lower the first temperature and the longer the first reduction time, the higher the degree of Ni aggregation before the start of operation.

  Sample 6 has a first reduction step in which the first temperature is 500 ° C. lower than the operating temperature and the first reduction time is 16 hours, and the second temperature is 1000 ° C. higher than the operating temperature and the second reduction time is 1 hour. And it is the sample manufactured by implementing the 2nd reduction process whose atmosphere is 80% of hydrogen-20% of water vapor | steam. The durability of Sample 6 is determined as “判定”. On the other hand, the Ni dispersion index of Sample 6 is smaller than that of Samples 2 to 5, but the initial characteristic is determined to be “x”. This is because if the second temperature is too high, the size of the Ni particles becomes too large and the catalytic effect of Ni decreases, so the initial voltage increases.

A-5-2. Performance evaluation 2 (samples 11-17)
FIG. 9 is an explanatory diagram showing the results of performance evaluation 2 of the fuel electrode 116. The initial voltage and IR deterioration rate in FIG. 9 have the same meaning as the initial voltage and IR deterioration rate in FIG. As shown in FIG. 9, in the performance evaluation 2, the first temperature and the first reduction time in the first reduction step are the same, but the second temperature, the second reduction time, and the reducing atmosphere in the second reduction step are Seven types of samples (11 to 17) manufactured by different manufacturing methods were used. The first temperature in the first reduction step is 500 ° C., and the first reduction time is 16 hours.

Moreover, the electrolyte layer 112 in each sample of the performance evaluation 2 contains at least Zr (zirconium), and is formed of a solid oxide such as YSZ, ScSZ, or CaSZ, for example. In the present embodiment, Zr is contained in the electrolyte layer 112 in the form of partially stabilized zirconia (ZrO ₂ ). The crystal system of partially stabilized zirconia has high oxygen ion conductivity when heat treatment (including heat treatment due to heat generated during operation of the fuel cell stack 100) is performed for a predetermined time or longer, which is lower than the phase transition temperature of partially stabilized zirconia. Phase transition from cubic (cubic) to tetragonal (tetra) with low oxygen ion conductivity. In general, the phase transition temperature of partially stabilized zirconia is higher than the operating temperature of the fuel cell stack 100. For example, according to "Masatomo Yashima", two others, Solid State lonics, (Netherlands), Elsevier BV, 1996, volume 86-88, p. 1131, an 8YSZ solid electrolyte layer The phase transition temperature of the partially stabilized zirconia contained is 1200 (° C.).

The second reduction time in each sample (excluding sample 16) is the reference value (1. In the present embodiment, the phase transition peak intensity ratio of partially stabilized zirconia from the start of the second reduction step in the second reduction step). 2) It means the time required to become. The phase transition peak intensity ratio is, for example, “Taro Shimonosono”, five others, Solid State lonics, (Netherlands), Elsevier BV, 2012, volume 225, p. 69-72. As measured by Raman spectroscopy. The phase transition peak intensity ratio is such that the crystal system of partially stabilized zirconia contained in the electrolyte layer 112 belongs to cubic crystals (600 to 650 cm ⁻¹ ), and the crystal system of partially stabilized zirconia is cubic to tetragonal. It is the ratio of the intensity peak (250-300 cm < ^-1 >) at the time of phase transition. Therefore, the larger the phase transition peak intensity ratio, the higher the proportion of partially stabilized zirconia in which the crystal system has undergone phase transition from cubic to tetragonal.

  Each of Samples 11 to 13 is a sample manufactured by performing the second reduction step in which the water vapor concentration in the atmosphere (reducing gas) of the fuel chamber 176 is 0.0003% or more and less than 3%. Specifically, after the sample 11 has been subjected to the first reduction step, the second temperature is 780 ° C., which is higher than the operating temperature, and the atmosphere is 98% hydrogen—2% water vapor. It is a manufactured sample. The second reduction time in Sample 11 was 120 hours, the initial voltage was 0.838 V, and the IR deterioration rate was 0.980%.

  Sample 12 is subjected to the first reduction step, and then the second temperature is 800 ° C., which is higher than the second temperature in sample 11, and the atmosphere is the same as the atmosphere in sample 11. It is a manufactured sample. The second reduction time in sample 12 was 56 hours, shorter than the second reduction time in sample 11, and the initial voltage and IR deterioration rate were the same as the initial voltage and IR deterioration rate in sample 11. According to the performance evaluation results of sample 11 and sample 12, when the atmosphere is the same, the second reduction time, that is, the partial stability is maintained while maintaining the initial voltage and the IR deterioration rate by increasing the second temperature. It can be said that the time required for the phase transition peak intensity ratio of zirconia fluoride to reach the above-mentioned reference value (hereinafter referred to as “time required for phase transition prefetching”) can be shortened.

  After performing the first reduction step, the sample 13 has the same second temperature as the second temperature in the sample 12, and the atmosphere is 99.5% hydrogen-0.5% water vapor. It is the sample manufactured by implementing a different 2nd reduction process. The second reduction time in sample 13 was 16 hours, shorter than the second reduction time in sample 12, and the initial voltage and IR deterioration rate were the same as the initial voltage and IR deterioration rate in sample 12. According to the performance evaluation results of the sample 12 and the sample 13, when the second temperature is the same, it is necessary for the phase transition prefetching while maintaining the initial voltage and the IR deterioration rate by reducing the water vapor concentration in the reducing gas. It can be said that time can be shortened.

  Sample 14 has a second temperature that is the same as the second temperature in sample 11 after the first reduction step, but the atmosphere is 80% hydrogen—20% water vapor, and is different from the atmosphere in samples 11-13. It is the sample manufactured by implementing a reduction process. The second reduction time in sample 14 was 184 hours, which was longer than the second reduction time in samples 11-13, but the initial voltage and IR deterioration rate were the same as the initial voltage and IR deterioration rate in sample 12. According to the performance evaluation results of the sample 14 and the samples 11 to 13, when the water vapor concentration in the reducing gas is higher than the predetermined concentration, the initial voltage and the IR deterioration rate can be maintained, but the time required for the phase transition preemption becomes extremely long. I can say that.

  Here, FIG. 10 is an explanatory diagram showing the relationship between the phase transition peak intensity ratio and the reduction time. FIG. 10 shows the phase transition peak intensity ratio of partially stabilized zirconia with the passage of the reduction time for each of four atmospheres having different water vapor concentrations (water vapor concentrations of 0%, 4%, 20%, and 40%). Changes (increase trend) are shown. For example, for each of four atmospheres having different water vapor concentrations, the change in the phase transition peak intensity ratio of partially stabilized zirconia with the passage of the reduction time is measured, and the result of FIG. 10 is obtained based on the measurement result. can do. According to the result of FIG. 10, it can be said that the time required for the phase transition prefetching can be shortened as the water vapor concentration is lower. Note that this main factor is considered to be that the phase transfer of YSZ in which NiO is dissolved dissolves in a reducing atmosphere.

  Moreover, FIG. 11 is explanatory drawing which shows the relationship between the amount of phase transition progress per 3 hours, and water vapor | steam density | concentration. The amount of phase transition progress per 3 hours (hereinafter simply referred to as “phase transition progress amount”) is the ratio of the phase transition peak intensity of partially stabilized zirconia at the start of reduction and the phase transition peak intensity after 3 hours from the start of reduction. It means the absolute value of the difference from the ratio. FIG. 11 shows the amount of progress of the phase transition for each of the four atmospheres. According to the result of FIG. 11, it can be said that when the water vapor concentration becomes larger than the value corresponding to the dotted line in FIG. Thus, according to the results of FIG. 10 and FIG. 11, if the water vapor concentration of the reducing gas is less than 3%, the time required for the phase transition preemption can be reduced compared to the case where the water vapor concentration of the reducing gas is 3% or more. Prolongation can be suppressed.

  Sample 15 has the same atmosphere as Samples 11 and 12 after performing the first reduction process, but the second temperature is 870 ° C. and the second reduction process is higher than the second temperature in Samples 11-13. It is the sample manufactured by carrying out. The second reduction time in sample 15 is 4 hours, which is shorter than the second reduction time in samples 11 to 13, but the initial voltage is 0.813 V, which is lower than the initial voltage in samples 11 to 13, and the IR deterioration rate is 1 011%, which is higher than the IR deterioration rate in Samples 11-13. According to the performance evaluation results of Sample 15 and Samples 11 to 13, even if the water vapor concentration in the reducing gas is the same, if the second temperature is higher than the predetermined temperature, the initial voltage may decrease and the IR deterioration rate may increase. It can be said.

  Here, a phenomenon in which a pollutant (for example, silica, chromium, sulfur, boron, or the like) contained in the reaction gas adheres to the surfaces of particles constituting the air electrode 114 or the fuel electrode 116 and the reaction field decreases (the air electrode 114). Or, poisoning of the fuel electrode 116 may occur, and the performance of the fuel cell stack 100 may be deteriorated. FIG. 12 is an explanatory diagram showing the relationship between the amount of boron poisoning and the temperature. As can be seen from FIG. 12, when the temperature of the fuel cell stack 100 exceeds the temperature corresponding to the dotted line in FIG. 12 (about 820 ° C.), the poisoning amount of boron increases extremely. FIG. 13 is an explanatory diagram showing the relationship between the deterioration rate of the fuel cell stack 100 and the amount of boron poisoning. The deterioration rate of the fuel cell stack 100 is the ratio of the post-test voltage to the initial voltage when the output voltage when the fuel cell stack 100 is subjected to the rated power generation operation for 1000 hours from the initial stage is the post-test voltage. A lower deterioration rate of the fuel cell stack 100 means that the deterioration of the fuel cell stack 100 is progressing. As can be seen from FIG. 13, when the poisoning amount of boron exceeds 20 ppm, the deterioration rate of the fuel cell stack 100 greatly decreases. According to FIGS. 12 and 13, it can be said that when the temperature of the fuel cell stack 100 exceeds 820 ° C., the poisoning amount of boron exceeds 20 ppm, and accordingly, the progress of deterioration of the fuel cell stack 100 increases. Therefore, the second temperature in the second reduction step is preferably not less than the operating temperature and not more than 820 ° C.

  After the first reduction step, the sample 16 has a second temperature of 700 ° C., which is lower than the second temperature in the samples 11 to 13, the atmosphere is 80% hydrogen—20% water vapor, and the atmosphere in the samples 11 to 13 It is the sample manufactured by implementing a different 2nd reduction process. The second reduction time in sample 16 is 3 hours, and is the time before the phase transition peak intensity ratio of partially stabilized zirconia reaches the reference value. The initial voltage in sample 16 is 0.840 V, which is higher than the initial voltage in samples 11-13, but the IR deterioration rate is 1.243%, which is higher than the IR deterioration rate in samples 11-15. According to the performance evaluation results of the sample 16 and the samples 11 to 13, if the second temperature is lower than the predetermined temperature, the water vapor concentration is higher than the predetermined concentration, and the second reduction time is short, before the fuel cell stack 100 starts operating. , Fuel cell stack that could not fully perform the phase transition from cubic to tetragonal crystal system (preemption of phase transition), and as a result, the fluctuation of performance during operation was suppressed 100 cannot be manufactured.

  For sample 17, after the first reduction step, the second temperature is the same as the second temperature in sample 11, but the atmosphere is 100% hydrogen and the second reduction step is different from the atmosphere in samples 11-13. It is a manufactured sample. The second reduction time in sample 17 was 27 hours, which was shorter than the second reduction time in samples 11 and 12, but the initial voltage and IR deterioration rate could not be measured. This is because when the water vapor concentration in the reducing gas is extremely low, NiO contained in the fuel electrode 116 is reduced to Ni, so that the fuel electrode 116 contracts, so-called reduction contraction occurs rapidly. For example, it is assumed that the single cell 110 of the fuel cell stack 100 is damaged.

A-6. Effects of this embodiment:
In the method for manufacturing the fuel cell stack 100 of the present embodiment, the size of the Ni particles can be reduced by reducing the fuel electrode 116 at a temperature lower than the operating temperature of the fuel cell stack 100 in the first reduction step. The small size of the Ni particles means that the specific surface area of Ni is large. The larger the specific surface area of Ni, the more easily Ni is aggregated in the second reduction step. Thereby, aggregation of Ni in the fuel electrode 116 can be promoted as compared with a case where the fuel electrode is reduced at a temperature higher than the operation temperature without performing the first reduction step before the operation. Accordingly, it is possible to suppress the change in the characteristics of the fuel cell stack 100 due to the progress of the aggregation of Ni during operation (suppress the IR deterioration rate).

  Further, in the second reduction step, by reducing the fuel electrode 116 under a dry atmosphere condition where the dew point of the reducing gas is −12 ° C. or less, the aggregation of Ni in the fuel electrode 116 is further increased. Therefore, it is possible to more effectively suppress the change in the power generation characteristics of the fuel cell stack 100 due to the progress of Ni aggregation during operation.

  According to the manufacturing method of the fuel cell stack 100 of the present embodiment, since the water vapor concentration of the reducing gas is 0.0003% or more, the reducing step is compared with the case where the water vapor concentration of the reducing gas is less than 0.0003%. The reduction contraction of the fuel electrode can be suppressed. Further, since the water vapor concentration of the reducing gas is less than 3%, the partially stabilized zirconia crystal system is phase-transformed from cubic to tetragonal as compared with the case where the water vapor concentration of the reducing gas is 3% or more. Prolonged time required can be suppressed. Thereby, an electrochemical reaction cell stack in which fluctuations in performance during operation are suppressed can be manufactured.

B. Variations:
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.

  In the said embodiment, although the single cell 110 provided with the electrolyte layer 112 containing a partially stabilized zirconia was illustrated as an electrochemical reaction single cell, an electrochemical reaction single cell is not limited to this, A partially stabilized zirconia is included. A single cell having a fuel electrode may be used. Specifically, the fuel electrode may be formed of a solid oxide such as YSZ, ScSZ, or CaSZ. Further, neither the electrolyte layer 112 nor the fuel electrode 116 may contain partially stabilized zirconia.

  The manufacturing method of the electrochemical reaction cell stack may include another reduction step in addition to the first reduction step and the second reduction step. For example, a reduction process in which the reduction temperature is a temperature between the first temperature and the second temperature may be provided between the first reduction process and the second reduction process.

  In the above embodiment, in the second reduction step, the fuel electrode 116 may be reduced under a condition where the dew point of the reducing gas is higher than −12 ° C. Further, in the second reduction step, the fuel electrode 116 contained in the single cell 110 reduced in the first reduction step is reduced under the condition that the water vapor concentration of the reducing gas is less than 0.0003% or 3% or more. You may do that.

  In the above embodiment, the number of power generation units 102 included in the fuel cell stack 100 is merely an example, and the number of power generation units 102 is appropriately determined according to the output voltage required for the fuel cell stack 100 or the like.

  In the above embodiment, the nuts 24 are fitted on both sides of the bolt 22, but the bolt 22 has a head, and the nut 24 is fitted only on the opposite side of the head of the bolt 22. Also good.

  In the above embodiment, the end plates 104 and 106 function as output terminals. However, instead of the end plates 104 and 106, separate members (for example, the end plate 104) connected to the end plates 104 and 106, respectively. , 106 and the power generation unit 102) may function as output terminals.

  Moreover, in the said embodiment, although the space between the outer peripheral surface of the axial part of each bolt 22 and the inner peripheral surface of each communicating hole 108 is utilized as each manifold, it replaces with this and the axis | shaft of each bolt 22 is used. An axial hole may be formed in the part, and the hole may be used as each manifold. Further, each manifold may be provided separately from each communication hole 108 into which each bolt 22 is inserted.

  In the above 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. Two power generation units 102 may be provided with respective interconnectors 150. In the above embodiment, the upper interconnector 150 of the uppermost power generation unit 102 in the fuel cell stack 100 and the lower interconnector 150 of the lowermost power generation unit 102 are omitted. These interconnectors 150 may be provided without being omitted.

  Further, in the above embodiment, the fuel electrode side current collector 144 may have the same configuration as the air electrode side current collector 134, and the fuel electrode side current collector 144 and the adjacent interconnector 150 are an integral member. It may be. Further, the fuel electrode side frame 140 instead of the air electrode side frame 130 may be an insulator. The air electrode side frame 130 and the fuel electrode side frame 140 may have a multilayer structure.

  Moreover, the material which forms each member in the said embodiment is an illustration to the last, and each member may be formed with another material.

  In the above embodiment, the city gas is reformed to obtain the hydrogen-rich fuel gas FG, but the fuel gas FG may be obtained from other raw materials such as LP gas, kerosene, methanol, gasoline, Pure hydrogen may be used as the fuel gas FG.

  In the present specification, the fact that the member B and the member C are opposed to each other across the member (or a part having the member, the same applies hereinafter) A is not limited to the form in which the member A and the member B or the member C are adjacent to each other. It includes a form in which another component is interposed between member A and member B or member C. For example, even in a configuration in which another layer is provided between the electrolyte layer 112 and the air electrode 114, it can be said that the air electrode 114 and the fuel electrode 116 face each other with the electrolyte layer 112 interposed therebetween.

  In the above-described embodiment (or a modified example, the same applies hereinafter), all the power generation units 102 included in the fuel cell stack 100 are configured to be manufactured by the above-described manufacturing method, but are included in the fuel cell stack 100. With such a configuration for at least one power generation unit 102, there is an effect of suppressing changes in the characteristics of the fuel cell stack 100 due to the progress of Ni aggregation during operation.

  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 minimum 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, and the power generation unit 102 may be read as an electrolytic cell unit. 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 electrolysis cell unit and electrolysis cell stack having such a configuration, the configuration of suppressing the change in the characteristics of the fuel cell stack 100 due to the progress of the aggregation of Ni during operation, as in the above embodiment. Is employed, it is possible to suppress the change in the characteristics of the fuel cell stack 100 due to the progress of the aggregation of Ni during operation.

22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Body portion 29: Branch portion 100: Fuel cell stack 102: Power generation unit 104, 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 Body 135: Current collector element 140: Fuel electrode side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode side current collector 145: Electrode facing portion 146: Interconnector facing portion 147 : Connection part 149: Spacer 150: Interconnector 161: Oxidizing agent 162: Oxidant gas discharge manifold 166: Air chamber 171: Fuel gas introduction manifold 172: Fuel gas discharge manifold 176: Fuel chamber 250: Thickness 350: Active layer 360: Substrate layer FG: Fuel gas FMG: Fuel intermediate Gas FOG: Fuel off gas OG: Oxidant gas OOG: Oxidant off gas

Claims (6)

An electrolyte layer containing a solid oxide, an air electrode disposed on one surface side of the electrolyte layer, disposed on the other surface side of the electrolyte layer, and containing Ni (nickel) and an oxygen ion conductive material A method of manufacturing an electrochemical reaction cell stack including a plurality of electrochemical reaction single cells including a fuel electrode,
The first reduction step of reducing the fuel electrode contained in the electrochemical reaction unit cell before at least one of the first reduction step and the second reduction step at a temperature lower than the operating temperature of the electrochemical reaction cell stack;
A method for producing an electrochemical reaction cell stack, comprising: the second reduction step of reducing the fuel electrode reduced in the first reduction step at a temperature higher than the operating temperature. In the manufacturing method of the electrochemical reaction cell stack according to claim 1,
In the second reduction step, the fuel electrode is reduced under a condition that the dew point of the reducing gas is -12 ° C. or lower. In the manufacturing method of the electrochemical reaction cell stack according to claim 1 or claim 2,
At least one of the electrolyte layer and the fuel electrode contains Zr (zirconium),
In the second reduction step, the fuel electrode reduced in the first reduction step is reduced under a condition that the water vapor concentration of the reducing gas is 0.0003% or more and less than 3%. The manufacturing method of an electrochemical reaction cell stack. An electrolyte layer containing a solid oxide, an air electrode disposed on one surface side of the electrolyte layer, disposed on the other surface side of the electrolyte layer, and containing Ni (nickel) and an oxygen ion conductive material An electrochemical reaction cell stack comprising a plurality of electrochemical reaction single cells including a fuel electrode,
For any cross section of the fuel electrode contained in at least one electrochemical reaction unit cell,
The Ni dispersion index obtained by dividing the number of particles of Ni per unit area by the number of particles of the oxygen ion conductive material per unit area is 0.56 or more and 0.84 or less, Electrochemical reaction cell stack. The electrochemical reaction cell stack according to claim 4,
The electrochemical reaction cell stack, wherein the Ni dispersion index is 0.58 or more and 0.84 or less. The electrochemical reaction cell stack according to claim 4 or 5,
The electrochemical reaction cell stack, wherein the plurality of electrochemical reaction single cells are fuel cell single cells.

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