JP2018181683A - Electrochemical reaction unit cell and electrochemical reaction cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of cracking of a single cell while suppressing occurrence of peeling of an air electrode. An electrochemical reaction single cell is provided with an electrolyte layer, a fuel electrode arranged on one side of the electrolyte layer in a first direction, and a fuel electrode arranged on the other side of the electrolyte layer in the first direction, and a perovskite-type oxidation cell is formed. And an air electrode containing an object. The Vickers hardness on the surface of the other side of the air electrode in the first direction is 8 HV or more and 21 HV or less. [Selection diagram] Fig. 6

Description

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

  A solid oxide fuel cell (hereinafter referred to as "SOFC") equipped with an electrolyte layer containing solid oxide is known as one of the types of fuel cells that generate electricity using the electrochemical reaction of hydrogen and oxygen. It is done. The fuel cell single cell (hereinafter referred to as "single cell"), which is a constituent unit of SOFC, includes an electrolyte layer, a fuel electrode disposed on one side of the electrolyte layer, and an air electrode disposed on the other side of the electrolyte layer. Equipped with The air electrode contains, for example, a perovskite oxide such as lanthanum strontium cobalt iron oxide (hereinafter referred to as "LSCF") (see, for example, Patent Document 1).

JP, 2017-10709, A

  In the unit cell, if the hardness of the air electrode is excessively low (that is, if necking between particles constituting the air electrode is excessively weak), the air electrode may be peeled off. On the other hand, when the hardness of the air electrode is excessively high (that is, the necking between particles constituting the air electrode is excessively strong), the deformability is excessively lowered, and the single cell is cracked by the thermal stress at the time of temperature rise. It may occur. The conventional single cell has room for improvement in the point of coexistence with generation | occurrence | production suppression of peeling of an air electrode, and generation | occurrence | production suppression of the crack of a single cell.

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

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

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

(1) The electrochemical reaction single cell disclosed in the present specification includes an electrolyte layer, a fuel electrode disposed on one side of the first direction of the electrolyte layer, and the first direction of the electrolyte layer. In the electrochemical reaction unit cell comprising an air electrode disposed on the other side and containing a perovskite oxide, the Vickers hardness of the surface on the other side of the first direction of the air electrode is 8 HV or more and 21 HV or less It is. According to the present electrochemical reaction unit cell, it is possible to prevent the hardness of the air electrode from becoming excessively low or excessively high, so suppressing the occurrence of peeling of the air electrode and suppressing the occurrence of cracking of the single cell. And can be made compatible.

(2) In the electrochemical reaction unit cell, the Vickers hardness of the surface on the other side of the first direction of the air electrode may be 10 HV or more and 18 HV or less. According to the present electrochemical reaction unit cell, it is possible to more reliably prevent the hardness of the air electrode from becoming excessively low or excessively high. And the suppression of the occurrence of

(3) In the electrochemical reaction unit cell, the air electrode may include SO ₃ , CaO, and SiO ₂ . According to the present electrochemical reaction unit cell, it is possible to avoid that the hardness of the air electrode becomes excessively low or excessively high with respect to the air electrode containing SO ₃ , CaO and SiO _2. It is possible to simultaneously suppress the occurrence of peeling of the pole and the occurrence of cracking of the unit cell.

(4) In the electrochemical reaction unit cell, the content rate C1 (wt%) of SO _{3 in} the air electrode, the content rate C2 (wt%) of CaO, and the content rate C3 (wt%) of SiO ₂ ; The sum of (C1 + C2 + C3) may be 30 (wt%) or less. According to the present electrochemical reaction unit cell, it is possible to avoid that the content of the additive that causes the increase of the IR resistance in the air electrode becomes excessively high, so that the performance deterioration of the unit cell can be suppressed. .

(5) The electrochemical reaction single cell disclosed in the present specification includes an electrolyte layer, a fuel electrode disposed on one side of the first direction of the electrolyte layer, and the first direction of the electrolyte layer. In the electrochemical reaction unit cell comprising an air electrode disposed on the other side and containing a perovskite oxide, the air electrode contains SO ₃ , CaO and SiO _2, and the average particle in the air electrode The diameter is 0.2 μm or more and 0.7 μm or less, and the content rate C1 (wt%) of SO _{3 in} the air electrode, the content rate C ₂ (wt%) of CaO, and the content rate C3 SiO ₂ The index value Vh calculated by the following equation (1) using wt%) is 9.4 or more and 18.9 or less.
Vh = 118 × C1-1358 × C2 + 446 × C3 + 15.8 (1)

In the case where the average particle diameter of the air electrode is 0.2 μm or more and 0.7 μm or less, the inventor of the present invention has a content C1 (wt%) of SO _{3 and} a content C2 (wt%) of CaO in the air electrode. It has been found that the index value Vh calculated by the equation (1) using the content ratio C3 (wt%) of SiO ₂ and the Vickers hardness of the air electrode. Therefore, according to the present electrochemical reaction unit cell, it is possible to prevent the hardness of the air electrode from becoming excessively low or excessively high. It can be made compatible with the occurrence suppression.

(6) In the electrochemical reaction unit cell, the index value Vh may be 10.5 or more and 18.4 or less. According to the present electrochemical reaction unit cell, it is possible to more reliably prevent the hardness of the air electrode from becoming excessively low or excessively high. And the suppression of the occurrence of

(7) In the electrochemical reaction unit cell, the content rate C1 (wt%) of SO _{3 in} the air electrode, the content rate C2 (wt%) of CaO, and the content rate C3 (wt%) of SiO ₂ ; The sum of (C1 + C2 + C3) may be 30 (wt%) or less. According to the present electrochemical reaction unit cell, it is possible to avoid that the content of the additive that causes the increase of the IR resistance in the air electrode becomes excessively high, so that the performance deterioration of the unit cell can be suppressed. .

(8) In the electrochemical reaction unit cell, the electrochemical reaction unit cell may be a fuel cell unit cell. According to the present electrochemical reaction unit cell, it is possible to simultaneously suppress the occurrence of separation of the air electrode constituting the fuel cell unit cell and the occurrence suppression of the crack of the fuel cell unit cell.

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

It is a perspective view showing the appearance composition of fuel cell stack 100 in this embodiment. It is explanatory drawing which shows the XZ cross-section structure of the fuel cell stack 100 in the position of II-II of FIG. It is explanatory drawing which shows YZ cross-section structure of the fuel cell stack 100 in the position of III-III of FIG. It is explanatory drawing which shows the XZ cross-section structure of the two adjacent electric power generation units 102 in the same position as the cross section shown in FIG. It is explanatory drawing which shows YZ cross-section structure of the two adjacent electric power generation units 102 in the same position as the cross section shown in FIG. It is explanatory drawing which shows a performance evaluation result.

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

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

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

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

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

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

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

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

(Configuration of power generation unit 102)
4 is an explanatory view showing the XZ cross-sectional configuration of two adjacent power generation units 102 at the same position as the cross section shown in FIG. 2, and FIG. 5 is adjacent to each other at the same position as the cross section shown in FIG. FIG. 6 is an explanatory view showing a YZ cross-sectional configuration of two power generation units 102.

  As shown in FIGS. 4 and 5, the power generation unit 102 includes the unit cell 110, the separator 120, the air electrode side frame 130, the air electrode side current collector 134, the fuel electrode side frame 140, and the fuel electrode side. A current collector 144 and a pair of interconnectors 150 constituting the top layer and the bottom layer of the power generation unit 102 are provided. In the peripheral portion around the Z direction in the separator 120, the air electrode side frame 130, the fuel electrode side frame 140, and the interconnector 150, holes corresponding to the communication holes 108 through which the above-described bolts 22 are inserted are formed.

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

  The unit cell 110 includes an electrolyte layer 112, a fuel electrode 116 disposed on one side (lower side) of the electrolyte layer 112, and an air electrode 114 disposed on the other side (upper side) of the electrolyte layer 112. The unit cell 110 of this embodiment is a unit cell of the fuel electrode support type in which the electrolyte layer 112 and the air electrode 114 are supported by the fuel electrode 116.

  The electrolyte layer 112 is a substantially rectangular flat plate-shaped member, and for example, YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samarium doped ceria), GDC (gadolinium doped ceria), perovskite oxide And so on. Thus, the unit cell 110 (power generation unit 102) of the present embodiment is a solid oxide fuel cell (SOFC) using a solid oxide as an electrolyte. The fuel electrode 116 is a substantially rectangular flat plate-shaped member, and is made of, for example, Ni (nickel), a cermet composed of Ni and ceramic particles, a Ni-based alloy or the like.

The air electrode 114 is a substantially rectangular flat plate-shaped member, and includes a current collecting layer 410 and an active layer 420. The active layer 420 is located on the electrolyte layer 112 side of the air electrode 114, and functions mainly as a site for the ionization reaction of oxygen contained in the oxidant gas OG. The active layer 420 is a perovskite type oxide represented by the general formula ABO ₃ (A: rare earth and alkaline earth, B: transition metal) (eg, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide) And LNF (lanthanum nickel iron)) as the main components. In the present specification, the main component means a component having the highest content ratio (wt%). In the present embodiment, the active layer 420 further includes an activating substance (for example, GDC (gadolinium-doped ceria)) and predetermined additives (SO ₃ , CaO, SiO ₂ ).

Further, the current collection layer 410 is located on the opposite side of the air electrode 114 to the electrolyte layer 112 side, and mainly diffuses the oxidant gas OG supplied from the air chamber 166 and collects the electricity obtained by the power generation reaction. It functions as a place to call. The current collecting layer 410 contains a perovskite oxide as a main component. In the present embodiment, the current collecting layer 410 further contains predetermined additives (SO ₃ , CaO, SiO ₂ ). Since the air electrode 114 has such a configuration, the upper surface of the air electrode 114 (hereinafter, referred to as “first surface SU1”) is configured by the current collecting layer 410. The first surface SU1 of the air electrode 114 corresponds to the other surface of the first direction in the claims.

  The separator 120 is a frame-shaped member in which a substantially rectangular hole 121 penetrating in the vertical direction is formed in the vicinity of the center, and is formed of, for example, metal. The peripheral portion of the hole 121 in the separator 120 faces the peripheral portion of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is bonded to the electrolyte layer 112 (unit cell 110) by a bonding portion 124 formed of a brazing material (for example, Ag wax) disposed in the facing portion. The air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116 are separated by the separator 120, and the gas leaks from the one electrode side to the other electrode side in the peripheral portion of the unit cell 110. Be suppressed.

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

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

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

  The air electrode side current collector 134 is disposed in the air chamber 166. The air electrode side current collector 134 is composed of a plurality of substantially square pole shaped current collector elements 135, and is made of, for example, ferritic stainless steel. The air electrode side current collector 134 is in contact with the surface of the air electrode 114 opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 opposite to the air electrode 114. However, as described above, since the power generation unit 102 positioned at the top in the fuel cell stack 100 does not have the upper interconnector 150, the air electrode side current collector 134 in the power generation unit 102 is the upper end plate It is in contact with 104. Because of such a configuration, the air electrode side current collector 134 electrically connects the air electrode 114 and the interconnector 150 (or the end plate 104). In the present embodiment, the air electrode side current collector 134 and the interconnector 150 are formed as an integral member. That is, a flat plate-shaped portion of the integral member which is orthogonal to the vertical direction (Z-axis direction) functions as the interconnector 150 and is formed so as to project from the flat-plate portion toward the air electrode 114 The plurality of convex portions, ie, the current collector elements 135 function as the air electrode side current collector 134. In addition, the integral member of the air electrode side current collector 134 and the interconnector 150 may be covered with a conductive coat, and between the air electrode 114 and the air electrode side current collector 134 A conductive bonding layer to be bonded may be interposed.

A-2. Operation of Fuel Cell Stack 100:
As shown in FIGS. 2 and 4, the oxidant gas OG is supplied through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the oxidant gas introduction manifold 161. Then, the oxidant gas OG is supplied to the oxidant gas introduction manifold 161 through the holes of the branch part 29 and the main body part 28 of the gas passage member 27, and the oxidant gas introduction manifold 161 oxidizes each power generation unit 102. The air is supplied to the air chamber 166 through the agent gas supply passage 132. Further, as shown in FIGS. 3 and 5, the fuel gas FG is supplied through a gas pipe (not shown) connected to the branch portion 29 of the gas passage member 27 provided at the position of the fuel gas introduction manifold 171. Then, the fuel gas FG is supplied to the fuel gas introduction manifold 171 through the branch portion 29 of the gas passage member 27 and the hole of the main body portion 28, and the fuel gas supply communication of each power generation unit 102 from the fuel gas introduction manifold 171. The fuel is supplied to the fuel chamber 176 through the hole 142.

  When the oxidant gas OG is supplied to the air chamber 166 of each power generation unit 102 and the fuel gas FG is supplied to the fuel chamber 176, oxygen contained in the oxidant gas OG and hydrogen contained in the fuel gas FG in the single cell 110 Power generation is performed by electrochemical reaction with the This power generation reaction is an exothermic reaction. In each power generation unit 102, the air electrode 114 of the unit cell 110 is electrically connected to one of the interconnectors 150 through the air electrode side current collector 134, and the fuel electrode 116 is through the fuel electrode side current collector 144. The other interconnector 150 is electrically connected. Also, the plurality of power generation units 102 included in the fuel cell stack 100 are electrically connected in series. Therefore, the electrical energy generated in each power generation unit 102 is taken out from the end plates 104 and 106 functioning as the output terminals of the fuel cell stack 100. Since the SOFC generates power at a relatively high temperature (eg, 700 ° C. to 1000 ° C.), the fuel cell stack 100 is heated (after start-up, until the heat can be maintained by the heat generated by the power generation). (Not shown).

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

A-3. Performance evaluation of air electrode 114:
The fuel cell stack 100 of the present embodiment is characterized in the configuration of the air electrode 114 of each unit cell 110. Hereinafter, various performance evaluations (performance evaluations regarding peeling resistance and cell crack resistance) performed using a plurality of samples having different configurations of the air electrode 114 will be described. FIG. 6 is an explanatory view showing a result of performance evaluation.

(About the sample)
As shown in FIG. 6, ten single cell 110 samples (samples S1 to S10) were used for performance evaluation. The air electrode 114 in each sample contains LSCF which is a perovskite type oxide. Also, the air electrode 114 contains SO ₃ , CaO and SiO ₂ as additives. The average particle diameter of the air electrode 114 is 0.2 μm or more and 0.7 μm or less. In addition, the measuring method of the average particle diameter in the air electrode 114 is mentioned later.

The samples have different Vickers hardnesses on the first surface SU1 of the air electrode 114. In addition, the measuring method of Vickers hardness in 1st surface SU1 of the air electrode 114 is mentioned later. In this performance evaluation, the content of each additive in the air electrode 114 (content C1 of SO ₃ (wt%), content of CaO C2 (wt%), content of SiO ₂ C3 (wt) for each sample Vickers hardness is made to differ from each other by making%) different from each other. In addition, the content rate of each said additive in the air electrode 114 can be specified, for example by a fluorescent X ray elemental analysis method.

The mechanism by which the Vickers hardness at the first surface SU1 of the air electrode 114 is affected by the additive content is not necessarily clear, but is presumed as follows. That is, the Vickers hardness of the air electrode 114 becomes higher as the necking between the particles constituting the air electrode 114 becomes stronger. Since S (sulfur) has a function of extracting the element at the A site of the perovskite type oxide, the perovskite type oxide becomes rich at the B site when the SO ₃ content C1 (wt%) is high, and as a result, the sinterability It is thought that the Vickers hardness becomes high, and the necking between the particles constituting the air electrode 114 becomes strong. Further, since Ca is an alkaline earth metal, when the content ratio C2 (wt%) of CaO is high, the perovskite oxide becomes A site rich, and as a result, the sinterability decreases and the particles constituting the air electrode 114 become It is thought that the Vickers hardness becomes low. In addition, since Si functions as a sintering aid, if the content ratio C3 (wt%) of SiO ₂ is high, the sinterability is improved and the necking between particles constituting the air electrode 114 becomes strong, and the Vickers hardness is increased. Is considered to be high.

(Performance evaluation of peeling resistance)
Peeling of the air electrode 114 mainly occurs inside the air electrode 114 (inside the current collection layer 410). Therefore, the performance evaluation about peeling resistance was performed as follows. A commercially available cellophane tape cut to a size smaller than the first surface SU1 of the air electrode 114 is attached to the first surface SU1 of the air electrode 114 in the unit cell 110 of each sample (at this time, the cellophane tape is the air electrode). The edge of the 114 was not covered), and then the cellophane tape was peeled off. The ratio of the area of the air electrode 114 peeled off when the cellophane tape was peeled off to the area of the cellophane tape was calculated. When the ratio is lower than 30%, it is judged as good (〇), and when it is 30% or more and lower than 50%, it is judged as acceptable (△), and when it is 50% or more, it is unacceptable (×) It was judged.

  As shown in FIG. 6, the samples S1 and S2 were determined to be unacceptable (x). In samples S1 and S2, since the Vickers hardness at the first surface SU1 of air electrode 114 is 6.0 HV and 7.0 HV and is lower than samples S3 to S10 (both have Vickers hardness of 8 HV or more), the air electrode It is considered that the necking between the particles constituting 114 is very weak and large peeling has occurred.

  Further, the sample S3 was determined to be acceptable (Δ). In the sample S3, although the Vickers hardness of the first surface SU1 of the air electrode 114 is 8 HV or more, it is lower than the samples S4 to S10 (all have a Vickers hardness of 10 HV or more). Necking is somewhat weak and it is considered that some peeling occurred.

  On the other hand, samples S4 to S10 were determined to be good (o). In the samples S4 to S10, since the Vickers hardness on the first surface SU1 of the air electrode 114 is 10 HV or more, it is considered that the necking between the particles constituting the air electrode 114 is strong and no peeling occurs.

  According to the performance evaluation for the peeling resistance described above, in order to suppress the occurrence of peeling of the air electrode 114, the Vickers hardness of the first surface SU1 of the air electrode 114 is preferably 8 HV or more, and 10 HV It can be said that it is more preferable to be more than.

(Performance evaluation of cell crack resistance)
When the temperature of the unit cell 110 is raised, thermal stress is generated, and there is a possibility that a crack (cell crack) of the unit cell 110 may occur. Therefore, the performance evaluation about cell crack resistance was performed as follows. That is, a cell when the single cell 110 (120 mm × 120 mm rectangular shape) of each sample is sandwiched by two stainless steel plates (150 mm × 150 mm rectangular shape) and a compressive force is applied to the single cell 110 through the stainless steel plate. The presence or absence of a crack was visually confirmed. Even if compression at 20 kN does not cause cell cracking, it is judged as good (〇), and compression at 15 kN does not cause cell cracking, but it is possible when compression at 20 kN causes cell cracking (Δ) It was determined that the cell breakage occurred due to compression at 15 kN, and it was judged as not possible (x).

  As shown in FIG. 6, the samples S9 and S10 were determined to be unacceptable (x). In samples S9 and S10, since the Vickers hardness at the first surface SU1 of air electrode 114 is 23.0 HV and 25.0 HV and is higher than samples S1 to S8 (both have Vickers hardness of 21 HV or less), the air electrode It is considered that the necking between the particles constituting 114 is very strong, and as a result, the deformability is very low, and the cell crack is caused even by the relatively small compression force.

  In addition, it is determined that the sample S8 is acceptable (Δ). In the sample S8, although the Vickers hardness at the first surface SU1 of the air electrode 114 is 21 HV or less, it is higher than the samples S1 to S7 (all have a Vickers hardness of 18 HV or less). The necking was rather strong, and as a result, the deformability was slightly lowered, and it is considered that cell cracking occurred when a relatively large compressive force was applied.

  On the other hand, samples S1 to S7 were determined to be good (O). In the samples S1 to S7, since the Vickers hardness at the first surface SU1 of the air electrode 114 is 18 HV or less, the necking between the particles constituting the air electrode 114 is weak, and as a result, the deformability is increased. It is considered that cell breakage did not occur even when a large compression force was applied.

  According to the above-described performance evaluation for cell crack resistance, the Vickers hardness of the first surface SU1 of the air electrode 114 is preferably 21 HV or less in order to suppress the occurrence of the cracks in the unit cell 110. It is more preferable that it is 18 HV or less.

(Comprehensive judgment)
For two performance evaluations of exfoliation resistance and cell crack resistance, when it is determined that it is not possible (x) in any of the performance evaluations, it is comprehensively determined as not possible (x) and is not possible in any of the performance evaluations (x) However, if any of the performance evaluations are judged as acceptable (Δ), it is judged comprehensively as acceptable (Δ), and any performance evaluation is judged as good (〇). In the case where it was determined, it was comprehensively judged as good (o). As a result, samples S4 to S7 were determined to be good (〇), samples S3 and S8 were determined to be acceptable (Δ), and samples S1 and S2 and S9 and S10 were determined to be unacceptable (×). Therefore, in order to suppress the occurrence of cracking of the unit cell 110 while suppressing the occurrence of peeling of the air electrode 114, the Vickers hardness of the first surface SU1 of the air electrode 114 is 8 HV or more and 21 HV or less It is more preferable to be 10 HV or more and 18 HV or less.

In the case where the average particle diameter of the air electrode 114 is 0.2 μm or more and 0.7 μm or less, the inventor of the present application has determined that the index value Vh calculated by the following equation (1) is the first value of the air electrode 114. It was found to approximate Vickers hardness on the surface SU1. As described above, C1 is the SO ₃ content (wt%) in the air electrode 114, C 2 is the CaO content (wt%) in the air electrode 114, and C 3 is the air electrode 114. The content (wt%) of SiO ₂ in FIG. 6 shows the index value Vh calculated for each sample.
Vh = 118 × C1-1358 × C2 + 446 × C3 + 15.8 (1)

  In view of the above-described performance evaluation results, in order to suppress the occurrence of cracking of the unit cell 110 while suppressing the occurrence of peeling of the air electrode 114, the index value Vh is 9.4 or more and 18.9 or less. It may be said that it is preferable that the ratio is 10.5 or more and 18.4 or less.

Further, the above-mentioned additives (SO ₃ , CaO, SiO ₂ ) contained in the air electrode 114 cause an increase in IR resistance in the air electrode 114, so it is not preferable that the content is excessively high. Therefore, the sum (C1 + C2 + C3) of the SO ₃ content C1 (wt%), the CaO content C2 (wt%), and the SiO ₂ content C3 (wt%) in the air electrode 114 is 30 ( It is preferable that it is wt% or less. At this time, each of the content rates C1, C2, and C3 is more preferably 10 (wt%) or less. Moreover, it is more preferable that the sum total (C1 + C2 + C3) of the said content rate is 10 (wt%) or less. At this time, each of the content rates C1, C2, and C3 is more preferably 3.3 (wt%) or less. Moreover, it is most preferable that the sum total (C1 + C2 + C3) of the said content rate is 1 (wt%) or less. At this time, each of the content rates C1, C2, and C3 is more preferably 0.33 (wt%) or less.

A-4. Analysis method of cathode 114:
(Method of measuring Vickers hardness at the first surface SU1 of the air electrode 114)
The method of measuring the Vickers hardness at the first surface SU1 of the air electrode 114 is as follows. The measurement of Vickers hardness is performed by a method according to JIS 2244. That is, after pressing the quadrangular pyramidal indenter against the surface of the air electrode with a constant load (test force: F (N), 0.1 N / sec), the diagonal line in the indentation (dent) formed when the indenter is removed. Measure the average length d (mm) of The Vickers hardness is determined by substituting the test force F and the average length d of the diagonal line into the following equation. In addition, the load (test force) used by this test is 1N. The load (test force) is preferably 1 N, and Vickers hardness measured with a load of 1 N or less may be called micro Vickers hardness. Moreover, the measurement of the Vickers hardness of an air electrode shall be performed in the state of the single cell in which the fuel electrode, the solid electrolyte layer, and the air electrode were formed.
Vickers hardness = 0.1891 × F / d ²

(Method of measuring average particle size at air electrode 114)
The measuring method of the average particle diameter in the air electrode 114 is as follows. First, an analysis image M1 used for analysis of the air electrode 114 is acquired by the following method. In the unit cell 110, one cross section (a cross section including the air electrode 114) parallel to the vertical direction (Z axis direction) is arbitrarily set, and an image in which the entire air electrode 114 in the vertical direction can be confirmed in the cross section is Acquire as an analysis image M1. More specifically, the upper surface of the air electrode 114 (the surface in contact with the air electrode side current collector 134) is the uppermost of ten divided regions obtained by dividing the image into ten equal parts in the vertical direction. For example, a scanning electron microscope (SEM) is used to capture an image located in the divided area and in which the boundary between the air electrode 114 and the electrolyte layer 112 is positioned in the lowermost divided area, and the analysis image M1 Get as. The analysis image M1 may be a binarized image obtained by binarizing the image captured by the SEM. However, if the particles and the like in the binarized image are significantly different from the actual form, the contrast of the image before binarization processing taken by the SEM is adjusted, and the image after the adjustment is binarized. May be. Moreover, the analysis image M1 may be the image before the binarization processing itself taken by the SEM. The magnification of the image of the SEM is set to a value such that the whole in the vertical direction of the air electrode 114 falls within the analysis image M1 as described above, and can be, for example, 200 to 30,000 times, but is limited thereto It can be changed appropriately.

  The mean particle size of the air electrode 114 is as follows: "Mizutani, Y. Ozaki, Toshio Kimura, Toshio Yamaguchi," Ceramic processing ", published by Gikhodo Publishing Co., Ltd., March 25, 1985, pp. 192 to 195" Specifically, in the analysis image M1, a straight line in the vertical direction (Z-axis direction) and a straight line in the direction orthogonal to the vertical direction are specified in the analysis image M1. Draw multiple pieces at intervals (for example, 0.5 μm intervals) and measure the length of the part corresponding to the particle on each straight line as the particle diameter For all particles on one or more straight lines located in the target member or region The average particle size of the air electrode 114 is taken as the average particle size of the air electrode 114.

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

  The configuration of the unit cell 110, the power generation unit 102, or the fuel cell stack 100 in the above embodiment is merely an example, and various modifications are possible. For example, in the above embodiment, although the air electrode 114 has a two-layer structure of the active layer 420 and the current collecting layer 410, the air electrode 114 may have a single-layer structure, or the active layer 420 and The configuration may be three or more layers including other layers other than the current collection layer 410. Furthermore, in the above embodiment, another layer (for example, a reaction prevention layer) may be disposed between the air electrode 114 and the electrolyte layer 112.

Moreover, the material which forms each member in the said embodiment is an illustration to the last, and each member may be formed with another material. For example, the air electrode 114 may not contain at least one of SO ₃ , CaO, and SiO ₂ .

  Further, in the above embodiment, the number of unit cells 110 included in the fuel cell stack 100 is merely an example, and the number of unit cells 110 is appropriately determined according to the output voltage and the like required of the fuel cell stack 100. Further, in the above embodiment, the preferred range of the Vickers hardness (or the index value Vh) described above does not have to be satisfied in all the unit cells 110 included in the fuel cell stack 100, and is included in the fuel cell stack 100. When the preferable range of the Vickers hardness (or the index value Vh) described above is satisfied for at least one unit cell 110, the occurrence of peeling of the air electrode 114 is suppressed for the unit cell 110 while the cracking of the unit cell 110 is suppressed. Occurrence can be suppressed.

  Further, in the above embodiment, SOFCs that generate electric power using electrochemical reaction between hydrogen contained in fuel gas and oxygen contained in oxidant gas are targeted, but the present invention relates to the electrolysis reaction of water The present invention is similarly applicable to an electrolytic single cell which is a constituent unit of a solid oxide electrolytic cell (SOEC) that uses hydrogen to generate hydrogen, and an electrolytic cell stack including a plurality of electrolytic single cells. The configuration of the electrolytic cell stack is not described in detail here because it is known as described in, for example, JP-A-2016-81813, but it is roughly the same as the fuel cell stack 100 in the embodiment described above. Configuration. That is, the fuel cell stack 100 in the embodiment described above may be read as an electrolysis cell stack, the power generation unit 102 may be read as an electrolysis cell unit, and the single cell 110 may be read as an electrolysis single cell. However, during operation of the electrolytic cell stack, a voltage is applied between the two electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), and through the communication hole 108 Water vapor as a source gas is supplied. As a result, an electrolysis reaction of water occurs in each electrolysis cell unit, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out to the outside of the electrolysis cell stack through the communication hole 108. Also in the electrolytic cell and the electrolytic cell stack of such a configuration, as in the above embodiment, if the preferable range of the Vickers hardness (or index value Vh) at the first surface SU1 of the air electrode 114 is satisfied, It is possible to suppress the occurrence of cracking of the unit cell 110 while suppressing the occurrence of peeling of the pole 114.

 In the above embodiment, the solid oxide fuel cell (SOFC) has been described as an example, but the present invention is applicable to other types of fuel cells (or electrolytic single cells) such as a molten carbonate fuel cell (MCFC). Is also applicable.

22: Bolt 24: Nut 26: Insulating sheet 27: Gas passage member 28: Body portion 29: Branch portion 100: Fuel cell stack 102: Power generation unit 104: End plate 106: End plate 108: Communication hole 110: Single cell 112: Electrolyte layer 114: air electrode 116: fuel electrode 120: separator 121: hole 124: joint portion 130: air electrode side frame 131: hole 132: oxidant gas supply communication hole 133: oxidant gas discharge communication hole 134: air electrode side Current collector 135: Current collector element 140: Fuel electrode side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel electrode current collector 145: Electrode facing portion 146: Interconnect facing Part 147: Joint part 149: Spacer 150: Interconnector 161: oxidant gas inlet manifold 162: oxidant gas outlet manifold 166: air chamber 171: fuel gas inlet manifold 172: fuel gas outlet manifold 176: fuel chamber 410: current collecting layer 420: active layer

Claims (9)

An electrolyte layer, a fuel electrode disposed on one side of the electrolyte layer in the first direction, and an air electrode disposed on the other side of the electrolyte layer in the first direction and containing a perovskite oxide In the electrochemical reaction unit cell,
An electrochemical reaction single cell characterized in that a Vickers hardness of a surface on the other side in the first direction of the air electrode is 8 HV or more and 21 HV or less. In the electrochemical reaction single cell according to claim 1,
An electrochemical reaction single cell, wherein a Vickers hardness of a surface on the other side in the first direction of the air electrode is 10 HV or more and 18 HV or less. In the electrochemical reaction unit cell according to claim 1 or 2,
The electrochemical reaction single cell characterized in that the air electrode contains SO ₃ , CaO and SiO ₂ . In the electrochemical reaction unit cell according to claim 3,
The content C1 of the SO ₃ in the air electrode (wt%), and the content of CaO C2 (wt%), and SiO ₂ content ratio C3 (wt%), total (C1 + C2 + C3) is of, 30 (wt% 2.) An electrochemical reaction unit cell characterized by the following. An electrolyte layer, a fuel electrode disposed on one side of the electrolyte layer in the first direction, and an air electrode disposed on the other side of the electrolyte layer in the first direction and containing a perovskite oxide In the electrochemical reaction unit cell,
The air electrode includes SO ₃ , CaO and SiO ₂ ,
The average particle diameter at the air electrode is 0.2 μm or more and 0.7 μm or less,
Calculated by the following equation (1) using the content rate C1 (wt%) of SO _{3 in} the air electrode, the content rate C2 (wt%) of CaO, and the content rate C3 (wt%) of SiO ₂ The electrochemical reaction single cell characterized in that the index value Vh is 9.4 or more and 18.9 or less.
Vh = 118 × C1-1358 × C2 + 446 × C3 + 15.8 (1) In the electrochemical reaction unit cell according to claim 5,
The electrochemical reaction single cell characterized in that the index value Vh is 10.5 or more and 18.4 or less. In the electrochemical reaction unit cell according to claim 5 or 6,
The content C1 of the SO ₃ in the air electrode (wt%), and the content of CaO C2 (wt%), and SiO ₂ content ratio C3 (wt%), total (C1 + C2 + C3) is of, 30 (wt% 2.) An electrochemical reaction unit cell characterized by the following. In the electrochemical reaction single cell according to any one of claims 1 to 7,
The electrochemical reaction single cell, wherein the electrochemical reaction single cell is a fuel cell single cell. In an electrochemical reaction cell stack comprising a plurality of electrochemical reaction unit cells arranged in the first direction,
An electrochemical reaction cell stack characterized in that at least one of the plurality of electrochemical reaction unit cells is the electrochemical reaction unit cell according to any one of claims 1 to 8.

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