JP6841663B2 - How to manufacture an electrochemical reaction cell stack - Google Patents

Description

The techniques disclosed herein relate to methods of making electrochemical reaction cell stacks.

A solid oxide fuel cell (hereinafter referred to as "SOFC") having an electrolyte layer containing a solid oxide is known as one of the types of fuel cells that generate electricity by utilizing an electrochemical reaction between hydrogen and oxygen. Has been done. SOFCs are commonly used in the form of fuel cell stacks with multiple single cells. The single cell includes an electrolyte layer, an air electrode arranged on one surface side of the electrolyte layer, and a fuel electrode arranged on the other surface side of the electrolyte layer and containing Ni (nickel) and an oxygen ion conductive substance. Includes.

In a fuel cell stack including a single cell containing a fuel electrode containing Ni in this way, Ni aggregates during operation (power generation) of the fuel cell stack, so that the power generation characteristics and temperature characteristics of the fuel cell stack, etc. Characteristics may change. For example, when Ni aggregates, the size (particle size) of the Ni particles increases, and the specific surface area of the Ni particles decreases accordingly. When the specific surface area of Ni particles becomes small, the catalytic effect of Ni decreases, so that the power generation efficiency decreases. Further, when Ni aggregates, the internal resistance of the fuel electrode rises, and the Joule heat rises accordingly, and the temperature of the fuel cell stack rises. As described above, if the characteristics of the fuel cell stack change during operation, for example, it may not be possible to properly control the power generation and temperature of the fuel cell stack.

Therefore, there is known a technique for agglomerating Ni by reducing the fuel electrode of a fuel cell stack with pure hydrogen as a reducing gas before starting operation (see Patent Document 1). Further, a technique is known in which the fuel electrode of a fuel cell stack is reduced by hydrogen gas as a reducing gas and water vapor before the start of operation to suppress the destruction of the air electrode film by the hydrogen gas (Patent Documents). 2).

Japanese Unexamined Patent Publication No. 2014-6978 Japanese Unexamined Patent Publication No. 2006-236702

In the first conventional technique of reducing the fuel electrode with pure hydrogen, the water vapor concentration in the reducing gas is extremely low. Therefore, NiO (nickel oxide) contained in the fuel electrode is reduced to Ni, which causes the fuel electrode to shrink, so-called reduction shrinkage, which may cause damage to a single cell, for example. ..

Further, when at least one of the electrolyte layer and the fuel electrode contains Zr (zinc), the crystal system of Zr changes from cubic crystal having high oxygen ion conductivity to low oxygen ion conductivity during SOFC operation. The phase transition to the tetragonal crystal (tetra) causes a problem that the power generation performance of a single cell fluctuates greatly during operation. Therefore, it is preferable to perform a phase transition of the Zr crystal system from cubic to tetragonal before starting the operation. However, in the second conventional technique of reducing the fuel electrode by hydrogen gas and water vapor, the water vapor concentration in the reduced gas is extremely high. Therefore, the time required for the phase transition of the Zr crystal system from cubic to tetragonal is long, so that, for example, the production efficiency of the fuel cell stack may decrease.

It should be noted that such a problem is encountered in the production of an electrolytic cell stack, which is a form of a solid oxide type electrolytic cell (hereinafter referred to as “SOEC”) that generates hydrogen by utilizing an electrolysis reaction of water. Is also 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.

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

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

(1) The method for producing an electrochemical reaction cell stack disclosed in the present specification is an electrolyte layer containing a solid oxide, an air electrode arranged on one surface side of the electrolyte layer, and the other of the electrolyte layer. A method for producing an electrochemical reaction cell stack, which comprises a plurality of electrochemical reaction single cells including Ni (nickel) and a fuel electrode containing an oxygen ion conductive substance, which is arranged on the surface side of the above. At least one of the fuel electrodes contains Zr (zirconium), and the preparatory step of preparing the electrochemical reaction cell stack before the reduction step and at least one of the electrochemical reactions included in the electrochemical reaction cell stack before the reduction step. The reaction electrode comprises the reduction step of reducing the fuel electrode contained in the single cell under the conditions that the water vapor concentration of the reducing gas is 0.005% or more and less than 3%. According to the method for producing the electrochemical reaction cell stack, since the water vapor concentration of the reducing gas is 0.005% or more, the fuel in the reduction step is compared with the case where the water vapor concentration of the reducing gas is less than 0.005%. It is possible to suppress the reduction contraction of the pole. Further, 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 the cubic crystal to the tetragonal crystal is longer than that in the case where the water vapor concentration of the reducing gas is 3% or more. Prolongation can be suppressed. As a result, it is possible to manufacture an electrochemical reaction cell stack in which fluctuations in performance during operation are suppressed.

(2) In the method for manufacturing an electrochemical reaction cell stack, the electrochemical reaction cell stacks are further arranged side by side in the first direction to form a fuel gas flow path extending in the first direction and to be conductive. Is arranged in the space between the plurality of conductive members having the above and at least one pair of the conductive members adjacent to each other in the first direction among the plurality of conductive members, and the at least one pair of the conductive members. It may be configured to include a glass sealing material in contact with the sex member. According to the method for producing the electrochemical reaction cell stack, the water vapor concentration of the reducing gas is 0.005% or more, so that the conductive member can be used as compared with the case where the water vapor concentration of the reducing gas is less than 0.005%. When the oxide film is sufficiently formed, it is possible to suppress a decrease in the bonding strength between the glass seal and the conductive member.

(3) In the method for producing an electrochemical reaction cell stack, the reduction step may be characterized in that the fuel electrode is reduced at a temperature of 820 ° C. or lower. For example, a phenomenon in which pollutants contained in the reaction gas (for example, silica, chromium, sulfur, boron, etc.) adhere to the surface of particles constituting the fuel electrode and the reaction field is reduced (poisoning of the fuel electrode or the fuel electrode). Poisoning) may occur and performance may deteriorate. According to the method for producing this electrochemical reaction cell stack, since the reduction temperature is 820 ° C. or lower, the poisoning of the fuel electrode is reduced as compared with the case where the reduction temperature is higher than 820 ° C. Therefore, it is possible to manufacture an electrochemical reaction cell stack in which performance deterioration is suppressed.

The techniques disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction single cell (fuel cell single cell or electrolytic cell), an electrochemical reaction unit (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 method for producing the same, 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 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 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 XZ cross-sectional structure of a part (electrolyte layer 112, fuel electrode 116) of a single cell 110. It is a flowchart which shows the manufacturing method of the fuel cell stack 100. It is explanatory drawing which shows the result of the performance evaluation of a fuel electrode 116. 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 phase transition progress amount and water vapor concentration per 3 hours. 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 a fuel cell stack 100 and the poisoning amount of boron.

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 present embodiment, and FIG. 2 is an explanatory view showing an XZ cross-sectional configuration of the fuel cell stack 100 at the position II-II of FIG. FIG. 3 is an explanatory view showing a YZ cross-sectional configuration of the fuel cell stack 100 at the position III-III of FIG. 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 "upward" and the Z-axis negative direction is referred to as "downward", but the fuel cell stack 100 actually has such an orientation. It may be installed in a different orientation. The same applies to FIGS. 4 and later. The fuel cell stack corresponds to an electrochemical reaction cell stack within the scope of claims.

The fuel cell stack 100 includes a plurality of power generation units 102 (seven in this embodiment) 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 aggregate composed of seven power generation units 102 from above and below.

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 in the vertical 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 are also 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 forming 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 forming 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 located near the midpoint of one side (the side on the positive side of the X axis among the two sides parallel to the Y axis) on the outer circumference of the fuel cell stack 100 around the Z direction. In the space formed by the bolt 22 (bolt 22A) and the communication hole 108 into 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 oxidizer 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 direction of the X axis among 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 into which the bolt 22B is inserted provides the oxidizer 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. A fuel gas FG is introduced from the outside of the fuel cell stack 100 into the space formed by the bolt 22 (bolt 22D) located in the above and the communication hole 108 into which the bolt 22D is inserted, and the fuel gas FG is generated by 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 of the two sides parallel to the X axis). The space formed by (bolt 22E) and the communication hole 108 into which the bolt 22E is inserted sends 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 the present embodiment, for example, a hydrogen-rich gas obtained by reforming city gas is used as the fuel gas FG.

The fuel cell stack 100 is provided with four gas passage members 27. Each gas passage member 27 has a hollow tubular main body 28 and a hollow tubular branch 29 branched from the side surface of the main body 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 arranged above the power generation unit 102 located at the top, and the other end plate 106 is arranged 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 view 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 an XZ cross-sectional configuration 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.

As shown in FIGS. 4 and 5, the power generation unit 102, which is the minimum unit of power generation, includes a single cell 110, a separator 120, an air pole side frame 130, an air pole side current collector 134, and a fuel pole side frame. It includes 140, a current collector 144 on the fuel electrode side, and a pair of interconnectors 150 that form the uppermost layer and the lowermost layer of the power generation unit 102. Holes corresponding to the communication holes 108 into which the bolts 22 described above are inserted are formed in the peripheral edges 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 single cell 110 corresponds to a fuel cell single cell and an electrochemical reaction single cell within the scope of claims.

The interconnector 150 is a substantially rectangular flat plate-shaped conductive member, and is formed on a base material 156 made of a metal containing Cr (chromium) such as ferritic stainless steel, and on the air electrode 114 side of the base material 156. It is arranged and includes a coat 136 that constitutes a first surface 151 on the air electrode 114 side of the interconnector 150. The interconnector 150 ensures electrical continuity between the power generation units 102 and prevents mixing of reaction gases between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by two adjacent power generation units 102. That is, the upper interconnector 150 in a certain power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Further, since 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 includes an electrolyte layer 112, an air electrode (cathode) 114 and a fuel electrode (anode) 116 facing each other in the vertical direction (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 pole support type single cell in which the fuel pole 116 supports the electrolyte layer 112 and the air pole 114.

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 (gadrinium). It is formed of solid oxides such as dope ceria) and perovskite-type oxides. The air electrode 114 is a substantially rectangular flat plate-shaped member, and is formed of, for example, a perovskite-type oxide (for example, LSCF (lanternstrontium cobalt iron oxide), LSM (lanternstrontium manganese oxide), LNF (lantern nickel iron)). Has been done. As described above, since the single cell 110 (power generation unit 102) of the present embodiment contains a solid oxide as an electrolyte, the fuel cell of the present embodiment is a solid oxide fuel cell (SOFC).

The fuel pole 116 is a substantially rectangular flat plate-shaped member. FIG. 6 shows the XZ cross-sectional configuration of a part of the single cell 110 (electrolyte layer 112, 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. Both the active layer 350 and the substrate layer 360 are formed of, for example, a cermet composed 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-mentioned materials (YSZ or the like) that form the electrolyte layer 112. Ceramic particles correspond to oxygen ion conductive substances in the claims.

The active layer 350 mainly exerts 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 exhibits a function of generating electrons and water vapor. It exerts a function of supporting the active layer 350, the electrolyte layer 112, and the air electrode 114. 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, 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 particles of ceramic particles (oxygen ion conductive substance) per unit area, and is one of the parameters indicating the degree of aggregation of Ni. .. The smaller the Ni dispersion index, the higher the degree of cohesion of Ni, that is, the larger the size (particle size) of the 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. Further, 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 enhance the gas diffusivity 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-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 opposite portion 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 a gas leak from one electrode side to the other electrode side at the peripheral edge of the single cell 110. It is suppressed. The single cell 110 to which the separator 120 is joined is referred to as a "single cell with a separator".

The air electrode side frame 130 is a frame-shaped member in which a substantially rectangular hole 131 penetrating in the vertical direction is formed near the center, and is formed of, for example, an insulator such as mica. The hole 131 of the air electrode side frame 130 constitutes an air chamber 166 facing the air electrode 114. The air electrode side frame 130 is in contact with the peripheral 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.

The fuel electrode 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. 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.

The fuel electrode side current collector 144 is arranged in the fuel chamber 176. The fuel electrode side current collector 144 includes an interconnector facing portion 146, an electrode facing portion 145, and a connecting portion 147 connecting the electrode facing portion 145 and the interconnector facing portion 146, for example, nickel or nickel alloy. , Stainless steel, etc. The electrode facing portion 145 is in contact with the surface of the fuel pole 116 opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is on the surface of the interconnector 150 facing the fuel pole 116. Are in contact. 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 fuel pole side current collector 144 has such a configuration, the fuel pole 116 and the interconnector 150 (or the end plate 106) are electrically connected to each other. A spacer 149 formed of, for example, 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 air pole 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 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 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 oxidizer 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 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 one of the interconnectors 150 via the air pole side current collector 134, and the fuel pole 116 is via the fuel pole side current collector 144. It is electrically connected to the other interconnector 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, after the start-up, until the high temperature can be maintained by the heat generated by the power generation. 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. Through the holes of the main body 28 and the branch 29 of the gas passage member 27 provided at the position of the discharge manifold 172, and through a gas pipe (not shown) connected to the branch 29, to the outside of the fuel cell stack 100. It is discharged.

A-3. Gas seal in fuel cell stack 100:
When the fuel gas FG (or fuel off-gas FOG) leaks from each fuel gas flow path (fuel gas introduction manifold 171 and fuel gas discharge manifold 172) to the air chamber 166 in the fuel cell stack 100, the fuel cell stack 100 It is not preferable because it reduces efficiency. Therefore, the fuel cell stack 100 is required to have high gas sealability. Hereinafter, the gas seal in the fuel cell stack 100 will be described.

As shown in FIG. 5, between the separator 120 and the interconnector 150 facing the separator 120 with the air electrode side frame 130 interposed therebetween, around each of the fuel gas introduction manifold 171 and the fuel gas discharge manifold 172. An annular glass seal 240 is provided so as to surround it. The glass seal 240 is a fuel gas FG (or fuel off-gas FOG) from each fuel gas flow path through the interface between the air electrode side frame 130 and the separator 120 and the interface between the air electrode side frame 130 and the interconnector 150. Suppress leaks. Further, since the glass seal 240 is an insulator, the provision of the glass seal 240 does not hinder the electrical insulation between the pair of interconnectors 150 included in the power generation unit 102. Further, in the present embodiment, the glass seal 240 is not provided around the oxidant gas introduction manifold 161 and the oxidant gas discharge manifold 162. The separator 120, the fuel electrode side frame 140, the interconnector 150, and the end plates 104 and 106 correspond to a plurality of conductive members within the scope of the claims. Further, the glass seal 240 corresponds to a glass seal material within the scope of claims.

A-4. Coat 136 constituting the first surface 151 of the interconnector 150:
The entire surface of the base material 156 on the air electrode 114 side is covered with the coat 136. The coat 136 is a film of chromium oxide (chromia film). For example, by heat-treating the interconnector 150 (in the present embodiment, the reduction step), Cr precipitated from the base material 156 of the interconnector 150 coats the surface of the base material 156 on the air electrode 114 side. 136 (chromia film) can be formed.

A-5. Manufacturing method of fuel cell stack 100:
FIG. 7 is a flowchart showing a method of manufacturing the fuel cell stack 100 according to the present embodiment. First, a 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 NiO powder (50 parts by weight) and YSZ powder (50 parts by weight), organic beads (15% by weight with respect to the mixed powder) which are pore-forming materials, and butyral resin , DOP, which is a plasticizer, a dispersant, and a mixed solvent of toluene + ethanol are added and mixed with a ball mill to prepare a slurry. Organic beads are, for example, spherical particles formed of a polymer such as polymethyl methacrylate or polystyrene. The obtained slurry is thinned by the doctor blade method to prepare a green sheet for a fuel electrode substrate layer having a thickness of 250 μm. The ratio of NiO powder and 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, even if the NiO powder: YSZ powder is 60:40 or 40:60. I do not care. That is, the NiO powder can be appropriately changed between 40 and 60 parts by weight so that the mixed powder of the NiO powder and the YSZ powder is 100 parts by weight, and the rest can be the YSZ powder.

(Preparation of green sheet for fuel polar active layer)
A butyral resin, a plasticizer DOP, a dispersant, and a toluene + ethanol mixed solvent are added to a mixed powder (100 parts by weight) of NiO powder (60 parts by weight) and YSZ powder (40 parts by weight). In addition, the mixture is prepared by mixing with a ball mill. By adjusting the particle size of the NiO powder, for example, the average particle size of Ni in the reduced single cell 110, which will be described later, can be adjusted. Further, organic beads (3.9% by weight with respect to the mixed powder) as a pore-forming material are further added to the mixed powder and mixed with a ball mill to adjust the slurry, whereby the porosity is fueled. It is possible to produce a green sheet for a fuel polar active layer, which is higher than the green sheet for a polar substrate layer. The obtained slurry is thinned by the doctor blade method to prepare a green sheet for a fuel polar active layer having a thickness of 6 μm to 36 μm. The ratio of NiO powder and YSZ powder in the green sheet for the fuel polar 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 and 60 parts by weight so that the mixed powder of the NiO powder and the YSZ powder is 100 parts by weight, and the rest can be the YSZ powder.

(Preparation of green sheet for electrolyte layer)
Butyral resin, plasticizer DOP, dispersant, and toluene + ethanol mixed solvent are added to YSZ powder (100 parts by weight) and mixed with a ball mill to prepare a slurry. The obtained slurry is thinned by the doctor blade method to prepare 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 pole 114)
A _{mixed solution of La 0.6} Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder and isopropyl alcohol is prepared. The prepared mixed solution can be spray-coated on the surface of the electrolyte layer 112 in the laminate and fired at 1100 ° C. to form an air electrode 114 to obtain a fired body (single cell 110 before reduction). it can.

After that, the remaining assembly steps (for example, joining the air electrode 114 and the air electrode side current collector 134 and fastening the fuel cell stack 100 with the bolt 22) are performed, and before the active layer 350 of the fuel electrode 116 is reduced. 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 reduction step in the claims.

(Reduction process)
The active layer 350 is reduced (NiO is reduced to Ni) by exposing the assembled fuel cell stack 100 to a hydrogen atmosphere having a temperature equal to or higher than the operating temperature (for example, 700 ° C.) for a reduction time (S130). This step corresponds to the reduction step in the claims. The operating temperature is a temperature having an activity of conducting oxygen ions in the electrolyte layer 112. The reducing gas used for reduction is not limited to hydrogen. It may be methane gas or the like. The reduction temperature can be 700 ° C. or higher, 1000 ° C. or lower, 820 ° C. or lower, and 800 ° C. or lower. The reduction time is one hour or more. The reduction temperature does not include the temperature of the fuel cell stack 100 in the process of raising and lowering the temperature, and is, for example, the temperature of the fuel cell stack 100 maintained for 1 hour or more.

A-6. Analytical method of active layer 350 of fuel electrode 116:
The method of analyzing the active layer 350 of the fuel electrode 116 of each single cell 110 in the fuel cell stack 100 after the reduction step is as follows.

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

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

The number of Ni particles and the number of particles of the oxygen ion conductive substance per unit area of the active layer 350 can be specified by the following methods. The distinction between Ni particles and ceramic particles (YSZ particles) in the active layer 350 can be performed, for example, by using the difference in brightness in each SEM image. Specifically, by analyzing each SEM image, each SEM image can be classified into three regions according to the brightness. It is preferable to use SEM-EDS as a method for distinguishing Ni particles and ceramic particles from three regions according to the brightness. Since the elements can be specified by SEM-EDS, the number of Ni particles and ceramic particles per unit area can be specified from the SEM image obtained above.

A-7. Performance evaluation of fuel pole 116:
FIG. 8 is an explanatory diagram showing the result of performance evaluation of the fuel electrode 116. In FIG. 8, the initial voltage means the initial output voltage of the fuel cell stack 100 when the operation of the fuel cell stack 100 after the reduction step is started at an operating temperature of 700 ° C. The IR deterioration rate is the ratio of the difference between the initial voltage and the post-test voltage with respect to the initial voltage, where the post-test voltage is the output voltage of the fuel cell stack 100 when the rated power generation operation is performed for 1000 hours from the initial stage. is there. The lower the IR deterioration rate, the higher the durability of the fuel cell stack 100. As shown in FIG. 8, seven types of samples (1 to 7) produced by production methods in which the combinations of the reduction temperature, the reduction time, and the reduction atmosphere in the reduction step are different from each other were used for the performance evaluation.

Further, the electrolyte layer 112 in each sample for performance evaluation contains at least Zr (zirconium), and is formed of, for example, a solid oxide such as YSZ, ScSZ, or CaSZ. In this embodiment, Zr is contained in the electrolyte layer 112 in the form of partially stabilized zirconia (ZrO _2). The partially stabilized zirconia crystal system has high oxygen ion conductivity by performing heat treatment below the phase transition temperature of partially stabilized zirconia (including heat treatment due to heat generation during operation of the fuel cell stack 100) for a predetermined time or longer. Phase transition from cubic to tetragonal with low oxygen ion conductivity. Generally, 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, 2 outsiders, Solid State lonics, (Netherlands), Elsevier BV, 1996, volume86-88, p.1131", the 8YSZ solid electrolyte layer The phase transition temperature of the partially stabilized zirconia contained is 1200 ° C. In addition, "higher than the operating temperature" means that when the operating temperature during steady operation has a predetermined temperature range, it is higher than the upper limit temperature of the temperature range.

The reduction time in each sample (excluding sample 6) is from the start of the reduction step to the phase transition peak intensity ratio of the partially stabilized zirconia reaching the reference value (1.2 in this embodiment) in the reduction step. It means the time required. The phase transition peak intensity ratio is, for example, "Taro Shimonosono, 5 outsiders, Solid State lonics, (Netherlands), Elsevier BV, 2012, volume225, p.69-72". It was measured according to Raman spectroscopy as shown in. The phase transition peak intensity ratio is such that the partially stabilized zirconia crystal system is cubic to tetragonal with respect to the intensity peak in which the partially stabilized zirconia crystal system ^{contained in the electrolyte layer 112 belongs to cubic crystals (600 to 650 cm -1).} It is the ratio of the intensity peak (250 to 300 cm ^{-1) at the time of phase transition to yttria.} Therefore, the larger the phase transition peak intensity ratio, the higher the proportion of partially stabilized zirconia in which the crystal system undergoes a phase transition from cubic to tetragonal.

Samples 1 to 3 are all samples produced by carrying out a reduction step in which the water vapor concentration in the atmosphere (reducing gas) of the fuel chamber 176 is 0.005% or more and less than 3%. Specifically, Sample 1 is a sample produced by carrying out a reduction step in which the reduction temperature is 780 ° C., which is higher than the operating temperature, and the atmosphere is 98% hydrogen − 2% steam. The reduction time in sample 1 was 120 hours, the initial voltage was 0.838V, and the IR deterioration rate was 0.980%.

Sample 2 is a sample produced by carrying out a reduction step in which the reduction temperature is 800 ° C., which is higher than the reduction temperature in sample 1 and the atmosphere is the same as the atmosphere in sample 1. The reduction time in sample 2 was 56 hours, which was shorter than the reduction time in sample 1, and the initial voltage and IR deterioration rate were the same as the initial voltage and IR deterioration rate in sample 1. According to the performance evaluation results of Sample 1 and Sample 2, when the atmosphere is the same, the reduction time, that is, the partially stabilized zirconia, is maintained while maintaining the initial voltage and IR deterioration rate by increasing the reduction temperature. It can be said that the time required for the phase transition peak intensity ratio to reach the above reference value (hereinafter, referred to as “time required for phase transition preemption”) can be shortened.

Sample 3 is a sample produced by performing a reduction step different from the atmosphere in Sample 2 in that the reduction temperature is the same as the reduction temperature in Sample 2 and the atmosphere is 99.5% hydrogen-0.5% water vapor. Is. The reduction time in sample 3 was 16 hours, which was shorter than the reduction time in sample 2, and the initial voltage and IR deterioration rate were the same as the initial voltage and IR deterioration rate in sample 2. According to the performance evaluation results of Sample 2 and Sample 3, when the reduction temperature is the same, the time required for phase transition preemption while maintaining the initial voltage and IR deterioration rate by lowering the water vapor concentration in the reduction gas. Can be said to be shortened.

Sample 4 is a sample produced by performing a reduction step different from the atmosphere in Samples 1 to 3 because the reduction temperature is the same as the reduction temperature in Sample 1, but the atmosphere is 80% hydrogen-20% water vapor. The reduction time in sample 4 was 184 hours, which was longer than the reduction time in samples 1 to 3, but the initial voltage and IR deterioration rate were the same as the initial voltage and IR deterioration rate in sample 2. According to the performance evaluation results of Sample 4 and Samples 1 to 3, when the water vapor concentration in the reducing gas becomes higher than the predetermined concentration, the initial voltage and IR deterioration rate can be maintained, but the time required for phase transition preemption becomes extremely long. I can say.

Here, FIG. 9 is an explanatory diagram showing the relationship between the phase transition peak intensity ratio and the reduction time. FIG. 9 shows the phase transition peak intensity ratios of partially stabilized zirconia with the passage of reduction time for each of the four atmospheres (water vapor concentrations 0%, 4%, 20%, 40%) having different water vapor concentrations. Changes (increasing trends) are shown. For example, for each of the four atmospheres having different water vapor concentrations, the change in the phase transition peak intensity ratio of the partially stabilized zirconia with the passage of the reduction time was measured, and the result of FIG. 9 was obtained based on the measurement result. can do. According to the results of FIG. 9, it can be said that the lower the water vapor concentration, the shorter the time required for preempting the phase transition. It is considered that the main factor is that the phase transition of YSZ in which NiO is dissolved proceeds in a reducing atmosphere.

Further, FIG. 10 is an explanatory diagram showing the relationship between the amount of phase transition progress and the water vapor concentration per 3 hours. The amount of phase transition progress per 3 hours (hereinafter, simply referred to as "phase transition progress amount") is the phase transition peak intensity ratio of partially stabilized zirconia at the start of reduction and the phase transition peak intensity 3 hours after the start of reduction. It means the absolute value of the difference from the ratio. FIG. 10 shows the amount of phase transition progress for each of the above four atmospheres. According to the result of FIG. 10, it can be said that when the water vapor concentration becomes larger than the value corresponding to the dotted line of FIG. 10 (about 3%), the amount of phase transition progress becomes extremely small. As described above, according to the results of FIGS. 9 and 10, when the water vapor concentration of the reducing gas is less than 3%, the time required for preempting the phase transition is longer than that when the water vapor concentration of the reducing gas is 3% or more. Prolongation can be suppressed.

Sample 5 is a sample produced by carrying out a reduction step in which the atmosphere is the same as that in Samples 1 and 2, but the reduction temperature is 870 ° C., which is higher than the reduction temperature in Samples 1 to 3. The reduction time in sample 5 is 4 hours, which is shorter than the reduction time in samples 1 to 3, but the initial voltage is 0.813 V, which is lower than the initial voltage in samples 1 to 3, and the IR deterioration rate is 1.011%. Yes Higher than the IR deterioration rate in Samples 1 to 3. According to the performance evaluation results of Sample 5 and Samples 1 to 3, even if the water vapor concentration in the reducing gas is the same, if the reduction temperature is higher than the predetermined temperature, the initial voltage may decrease and the IR deterioration rate may increase. I can say.

Here, a phenomenon in which pollutants (for example, silica, chromium, sulfur, boron, etc.) contained in the reaction gas adhere to the surfaces of the particles constituting the air electrode 114 and the fuel electrode 116, and the reaction field is reduced (air electrode 114). Alternatively, poisoning of the fuel electrode 116) may occur, and the performance of the fuel cell stack 100 may deteriorate. FIG. 11 is an explanatory diagram showing the relationship between the amount of boron poisoned and the temperature. According to FIG. 11, it can be seen that when the temperature of the fuel cell stack 100 exceeds the temperature corresponding to the dotted line in FIG. 11 (about 820 ° C.), the amount of boron poisoned increases extremely. FIG. 12 is an explanatory diagram showing the relationship between the deterioration rate of the fuel cell stack 100 and the amount of boron poisoned. The deterioration rate of the fuel cell stack 100 is the ratio of the post-test voltage to the initial voltage, where the post-test voltage is the output voltage of the fuel cell stack 100 when the rated power generation operation is performed for 1000 hours from the initial stage. The lower the deterioration rate of the fuel cell stack 100, the more the deterioration of the fuel cell stack 100 is progressing. According to FIG. 12, it can be seen that when the amount of boron poisoned exceeds 20 ppm, the deterioration rate of the fuel cell stack 100 is significantly reduced. According to FIGS. 11 and 12, when the temperature of the fuel cell stack 100 exceeds 820 ° C., the amount of boron poisoned exceeds 20 ppm, and it can be said that the degree of deterioration of the fuel cell stack 100 increases accordingly. Therefore, the reduction temperature in the reduction step is preferably the operating temperature or higher and 820 ° C. or lower.

Sample 6 has a reduction temperature of 700 ° C., which is lower than the reduction temperature in Samples 1 to 3, and has an atmosphere of 80% hydrogen-20% water vapor, and is a sample produced by performing a reduction step different from the atmosphere in Samples 1 to 3. Is. The reduction time in sample 6 is 3 hours, which is the time before the phase transition peak intensity ratio of partially stabilized zirconia becomes a reference value. The initial voltage in Sample 6 is 0.840 V, which is higher than the initial voltage in Samples 1 to 3, but the IR deterioration rate is 1.243%, which is higher than the IR deterioration rate in Samples 1 to 5. According to the performance evaluation results of Sample 6 and Samples 1 to 3, if the reduction temperature is lower than the predetermined temperature, the water vapor concentration is higher than the predetermined concentration, and the reduction time is short, the fuel cell stack 100 is partially stabilized before the start of operation. It was not possible to sufficiently perform the phase transition of the zirconia crystal system from cubic to tetragonal (preemption of the phase transition), and as a result, a fuel cell stack 100 in which fluctuations in performance during operation were suppressed was manufactured. You will not be able to.

Sample 7 is a sample produced by performing a reduction step different from the atmosphere in Samples 1 to 3 because the reduction temperature is the same as the reduction temperature in Sample 1, but the atmosphere is 100% hydrogen. The reduction time in sample 7 was 27 hours, which was shorter than the reduction time in samples 1 and 2, but the initial voltage and IR deterioration rate could not be measured. The reason for this is that when the water vapor concentration in the reducing gas is extremely low, the fuel electrode 116 contracts due to the reduction of NiO contained in the fuel electrode 116 to Ni, that is, so-called reduction contraction occurs rapidly. It is assumed that the strength of the fuel electrode 116 is reduced due to the porosity, and for example, the single cell 110 of the fuel cell stack 100 is damaged.

A-8. Effect of this embodiment:
In the method for producing the fuel cell stack 100 of the present embodiment, since the water vapor concentration of the reducing gas is 0.005% or more, the fuel in the reduction step is compared with the case where the water vapor concentration of the reducing gas is less than 0.005%. The reduction shrinkage of the pole 116 can be suppressed. Further, 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 the cubic crystal to the tetragonal crystal is longer than that in the case where the water vapor concentration of the reducing gas is 3% or more. Prolongation can be suppressed. As a result, it is possible to manufacture the fuel cell stack 100 in which fluctuations in performance during operation are suppressed.

Further, according to the present embodiment, since the water vapor concentration of the reducing gas is 0.005% or more, the oxide film (chromia) is formed on the interconnector 150 as compared with the case where the water vapor concentration of the reducing gas is less than 0.005%. When the film) is sufficiently formed, it is possible to suppress a decrease in the bonding strength between the interconnector 150 and the glass seal 240. Hereinafter, a specific description will be given. As described above, the interconnector 150 includes a base material 156 formed of metal and a coat 136 constituting the first surface 151 of the base material 156, and the coat 136 is compared with the metal. It is a dense oxide film (chromia film). Therefore, the bonding strength between the interconnector 150 and the glass seal 240 is higher when the glass seal 240 is bonded to the base material 156 via the chromia film (coat 136) than when the glass seal 240 is directly bonded to the base material 156. can do. Further, as described above, in the present embodiment, by performing heat treatment on the interconnector 150 in the reduction step, Cr precipitated from the base material 156 of the interconnector 150 causes the air electrode 114 side of the base material 156 to be separated. A chromia film (coat 136) is formed on the surface. Here, if the water vapor concentration of the reducing gas in the reduction step is too low, the chromium film (coat 136) may not be sufficiently formed on the surface of the base material 156 on the air electrode 114 side.

On the other hand, since the water vapor concentration of the reducing gas is 0.005% or more, the chromaia film (coat 136) is sufficient for the interconnector 150 as compared with the case where the water vapor concentration of the reducing gas is less than 0.005%. It is possible to suppress a decrease in the bonding strength between the glass seal 240 and the interconnector 150. As a result, the fuel gas FG (or fuel off-gas FOG) leaks from each fuel gas flow path through the interface between the air electrode side frame 130 and the separator 120 and the interface between the air electrode side frame 130 and the interconnector 150. , Can be suppressed more reliably. According to a known Ellingham diagram (a graph plotting the standard Gibbs energy generated at each temperature for oxides), the water vapor concentration required to form a chromami film is the temperature at which boron poisoning occurs (820). ℃), it is assumed to be 0.005%. For example, in the Elingham diagram, the intersection of the hanging straight line at 800 ° C. and the graph of Cr is specified, and a straight line connecting the intersection and the point targeted for H (hydrogen) is drawn, and the straight line and H ₂ / H _{2 are drawn.} Approximately 0.005% can be specified from the intersection with the O ratio line. The water vapor concentration of hydrogen gas having a grade of hydrogen gas purity of first grade (dew point of -70 ° C or higher) defined by JIS standard (JIS K 0512: 1995) is 0.0004%, and hydrogen gas. The water vapor concentration of hydrogen gas having a purity grade (general grade applied to hydrogen bombs, etc.) of grade 2 (dew point of -60 ° C or higher) is 0.0017%, and the hydrogen gas purity grade is 3. The water vapor concentration of hydrogen gas of the class (dew point of −50 ° C. or higher) is 0.0059%. Therefore, for example, it is more desirable for the reduction step of the present invention to use a hydrogen gas of the grade (3rd grade) of hydrogen gas purity defined by this JIS standard as the reduction gas.

Further, according to the present embodiment, since the reduction temperature in the reduction step is 820 ° C. or lower, the air electrode 114 and the fuel electrode 116 are poisoned as compared with the case where the reduction temperature is higher than 820 ° C. By reducing the fuel cell stack 100, it is possible to manufacture the fuel cell stack 100 in which the deterioration in performance is suppressed.

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.

In the above embodiment, the single cell 110 including the electrolyte layer 112 containing the partially stabilized zirconia is exemplified as the electrochemical reaction single cell, but the electrochemical reaction single cell is not limited to this and includes the partially stabilized zirconia. It may be a single cell provided with a fuel electrode. Specifically, the fuel electrode may be formed of a solid oxide such as YSZ, ScSZ, CaSZ or the like.

Further, in the above embodiment, the glass seal 240 arranged between the interconnector 150 and the separator 120 is exemplified as the glass seal material, but the present invention is not limited to this, and for example, between the separator 120 and the interconnector 150. It may be a glass sealing material or the like arranged in.

Further, in the above embodiment, the reduction temperature may be higher than 820 ° C. in the reduction step. Further, the fuel cell stack 100 may not be provided with the glass seal 240.

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

Further, in the above embodiment, it is assumed that the nuts 24 are fitted on both sides of the bolt 22, but it is assumed that the bolt 22 has a head and the nut 24 is fitted only on the opposite side of the head of the bolt 22. May be good.

Further, in the above embodiment, the end plates 104 and 106 function as output terminals, but instead of the end plates 104 and 106, another member connected to each of the end plates 104 and 106 (for example, the end plate 104). , 106, and the conductive plate arranged between the power generation unit 102) may function as an output terminal.

Further, in the above embodiment, the space between the outer peripheral surface of the shaft portion of each bolt 22 and the inner peripheral surface of each communication hole 108 is used as each manifold, but instead of this, the shaft of each bolt 22 is used. Axial holes may be formed in the portion, and the holes 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.

Further, 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, but even in such a case. The two power generation units 102 may include their respective interconnectors 150. Further, in the above embodiment, the upper interconnector 150 of the power generation unit 102 located at the top of the fuel cell stack 100 and the lower interconnector 150 of the power generation unit 102 located at the bottom are omitted. These interconnectors 150 may be provided without omission.

Further, in the above embodiment, the fuel pole side current collector 144 may have the same configuration as the air pole side current collector 134, and the fuel pole side current collector 144 and the adjacent interconnector 150 are integrated members. It may be. Further, the fuel pole side frame 140 may be an insulator instead of the air pole side frame 130. Further, the air pole side frame 130 and the fuel pole side frame 140 may have a multi-layer structure.

Further, the material forming each member in the above embodiment is merely an example, and each member may be formed of another material.

Further, in the above embodiment, the city gas is reformed to obtain a hydrogen-rich fuel gas FG, but the fuel gas FG may be obtained from other raw materials such as LP gas, kerosene, methanol, and 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 face each other with the member (or a portion having the member, the same applies hereinafter) A sandwiching the member 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 the member A and the member B or the member C. For example, even if 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.

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 comprises an electrolysis reaction of water. It is also applicable to an electrolytic cell unit, which is the smallest unit of a solid oxide fuel cell (SOEC) that generates hydrogen by utilizing it, 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 as described in, for example, Japanese Patent Application Laid-Open No. 2016-81813, but is generally 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, and the power generation unit 102 may be read as an electrolytic cell unit. 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. Water vapor 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. By applying the present invention to an electrolytic cell stack having such a configuration, it is possible to manufacture an electrolytic cell stack in which fluctuations in performance during operation are suppressed, as in the above embodiment.

22: Bolt 24: Nut 26: Insulation sheet 27: Gas passage member 28: Main body 29: Branch 100: Fuel cell stack 102: Power generation unit 104, 106: End plate 108: Communication hole 110: Single cell 112: Electrolyte layer 114: Air pole 116: Fuel pole 120: Separator 121: Hole 124: Joint 130: Air pole side frame 131: Hole 132: Oxidizing agent gas supply communication hole 133: Oxidizing agent gas discharge communication hole 134: Air pole side current collection Body 135: Current collector element 136: Coat 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 Opposing part 147: Connecting part 149: Spacer 150: Interconnector 151: Surface 156: Base material 161: Oxidizing 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 240: Glass seal 350: Active layer 360: Substrate layer 700: Operating temperature B1: Boundary B2: Boundary FG: Fuel gas FOG: Fuel off gas OG: Oxidizing agent gas OOG: Oxidating agent off gas

Claims (3)

An electrolyte layer containing a solid oxide, an air electrode arranged on one surface side of the electrolyte layer, and Ni (nickel) and an oxygen ion conductive substance arranged on the other surface side of the electrolyte layer. A method for manufacturing an electrochemical reaction cell stack including a plurality of electrochemical reaction single cells including a fuel electrode.
At least one of the electrolyte layer and the fuel electrode contains Zr (zirconium) and
A preparatory step for preparing the electrochemical reaction cell stack before the reduction step, and
Wherein the fuel electrode is included in at least one of the electrochemical reaction unit cells included in the reduction step prior to the electrochemical reaction cell stack, water vapor concentration of the reducing gas is 0.005% or more, and state, and are less than 3%, and a temperature of 700 ° C. or higher, characterized in that it comprises, and the reducing step of reducing under conditions Ru der 870 ° C. a method for fabricating an electrochemical reaction cell stack. In the method for producing an electrochemical reaction cell stack according to claim 1.
The electrochemical reaction cell stack further
A plurality of conductive members arranged side by side in the first direction, forming a fuel gas flow path extending in the first direction, and having conductivity,
Among the plurality of conductive members, a glass sealing material arranged in a space between at least one pair of the conductive members adjacent to each other in the first direction and in contact with the at least one pair of the conductive members. A method for producing an electrochemical reaction cell stack, which comprises the above. In the method for producing an electrochemical reaction cell stack according to claim 1 or 2.
A method for producing an electrochemical reaction cell stack, which comprises reducing the fuel electrode at a temperature of 820 ° C. or lower in the reduction step.

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