JP7082456B2 - Electrochemical reaction single cell and electrochemical reaction cell stack - Google Patents

Description

The techniques disclosed herein relate to electrochemical reaction single cells.

A solid oxide fuel cell (hereinafter referred to as "SOFC") is known as one of the types of fuel cells that generate power by utilizing an electrochemical reaction between hydrogen and oxygen. A fuel cell single cell (hereinafter, simply referred to as “single cell”), which is a constituent unit of SOFC, has an electrolyte layer containing a solid oxide and an air electrode and a fuel electrode facing each other in a predetermined direction with the electrolyte layer interposed therebetween. Be prepared.

Japanese Unexamined Patent Publication No. 2016-170939

In addition to the resistance of each layer constituting the single cell and the IR resistance (resistance polarization) which is the resistance value of each interface, the polarization component as the resistance that lowers the voltage of the single cell includes each electrode (fuel electrode and air electrode). There are activation polarization, which is the resistance value of the gas ionization reaction in, and gas diffusion polarization, which is the resistance value of gas diffusion at each electrode. Conventionally, it has not been considered to reduce the total of each of these polarization components, and there is room for improvement in the output characteristics of a single cell.

It should be noted that such a problem is also common to the electrolytic single cell, which is a constituent unit of a solid oxide type electrolytic cell (hereinafter, also referred to as “SOEC”) that generates hydrogen by utilizing the electrolysis reaction of water. It is an issue. In the present specification, the fuel cell single cell and the electrolytic single cell are collectively referred to as an electrochemical reaction single cell. Further, such a problem is not limited to SOFC and SOEC, but is a problem common to other types of electrochemical reaction single cells.

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

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

(1) The electrochemical reaction single cell disclosed in the present specification is an electrochemical reaction single cell including an electrolyte layer and an air electrode and a fuel electrode facing each other in a first direction with the electrolyte layer interposed therebetween. By equivalent circuit analysis, the polarization component of the electrochemical reaction single cell is determined by the activation polarization of the fuel electrode, which is the resistance value of the gas ionization reaction at the fuel electrode, and the resistance value of the gas ionization reaction at the air electrode. 3 of activation polarization of a certain air electrode and gas diffusion polarization which is a resistance value of gas diffusion in a specific electrode having a thicker thickness in the first direction among the fuel electrode and the air electrode. The ratio (Pd / Pa) of the gas diffusion polarization Pd to the activation polarization Pa of the specific electrode when divided into two resistance components is 1.0 or more and 4.0 or less. According to this electrochemical reaction single cell, the η resistance of the electrochemical reaction single cell is reduced by achieving a good balance between the reduction of the activation polarization Pa of the specific electrode and the reduction of the gas diffusion polarization Pd, which are in a trade-off relationship. It is possible to improve the output characteristics of the electrochemical reaction single cell.

(2) In the electrochemical reaction single cell, the specific electrode is the fuel electrode, and the fuel electrode is located between the first fuel electrode layer, the first fuel electrode layer, and the electrolyte layer. The second fuel electrode layer, which is arranged and contains a transition metal, has an average pore diameter of 0.55 μm or more in the second fuel electrode layer, and the transition metal in the second fuel electrode layer has an average pore diameter of 0.55 μm or more. The average particle size may be 1.10 μm or less. According to this electrochemical reaction single cell, the gas flow path (diffusion path) in the second fuel electrode layer can be widened in a well-balanced manner, and the three-layer interface as a reaction field in the second fuel electrode layer. In a well-balanced manner, it is possible to reduce the η resistance of the electrochemical reaction single cell by achieving a good balance between the reduction of the activated polarization Pa of the fuel electrode and the reduction of the gas diffusion polarization Pd of the fuel electrode. It is possible to improve the output characteristics of the electrochemical reaction single cell.

(3) In the electrochemical reaction single cell, the ratio (Pd / Pa) of the gas diffusion polarization Pd to the activation polarization Pa of the specific electrode may be 1.7 or more and 2.5 or less. .. According to this electrochemical reaction single cell, the η resistance of the electrochemical reaction single cell is further effectively reduced by further reducing the activation polarization Pa of the specific electrode and the gas diffusion polarization Pd in a well-balanced manner. Therefore, the output characteristics of the electrochemical reaction single cell can be further effectively improved.

The technique disclosed in the present specification can be realized in various forms, for example, an electrochemical reaction single cell (fuel cell single cell or an electrolytic single cell), and a plurality of electrochemical reaction single cells. It can be realized in the form of an electrochemical reaction cell stack (fuel cell stack or electrolytic cell stack) provided, a method for manufacturing them, and the like.

It is a perspective view which shows the appearance structure of the fuel cell stack 100 in this embodiment. It is explanatory drawing which shows the XZ cross-sectional structure of the fuel cell stack 100 at the position of II-II of FIG. It is explanatory drawing which shows the YZ cross-sectional structure of the fuel cell stack 100 at the position of III-III of FIG. It is explanatory drawing which shows the XZ cross section composition of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross section configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which magnified and shows the XZ cross-sectional structure of a part of a single cell 110 (a part of an electrolyte layer 112 and a part of a fuel electrode 116). It is a flowchart which shows an example of the manufacturing method of the fuel cell stack 100 in this embodiment. It is explanatory drawing which shows the performance evaluation result. It is explanatory drawing which shows the relationship between the polarization ratio Pd (a) / Pa (a) and η resistance in the performance evaluation result. It is explanatory drawing which conceptually shows the relationship between the structure of the active layer 350 of a fuel electrode 116, and each characteristic. It is explanatory drawing which shows the equivalent circuit of a single cell 110.

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 in FIG. FIG. 3 is an explanatory diagram 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 an upward direction, and the Z-axis negative direction is referred to as a downward direction, but the fuel cell stack 100 is actually in a direction different from such an orientation. It may be installed. The same applies to FIGS. 4 and later.

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

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

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

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

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

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

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

(Structure of power generation unit 102)
FIG. 4 is an explanatory diagram showing an XZ cross-sectional configuration of two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. 2, and FIG. 5 is an explanatory view showing the XZ cross-sectional configuration of the two power generation units 102 adjacent to each other at the same position as the cross section shown in FIG. It is explanatory drawing which shows the YZ cross-sectional structure of two power generation units 102.

As shown in FIGS. 4 and 5, the power generation unit 102 includes a single cell 110, a separator 120, an air pole side frame 130, an air pole side current collector 134, a fuel pole side frame 140, and a fuel pole side. It includes a current collector 144 and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer of the power generation unit 102. A hole corresponding to the communication hole 108 through which the bolt 22 described above is inserted is formed in the peripheral portion of the separator 120, the air pole side frame 130, the fuel pole side frame 140, and the interconnector 150 in the Z direction.

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

The single cell 110 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. In this embodiment, the thickness of the fuel electrode 116 (the size in the vertical direction) is thicker than the thickness of the air electrode 114 and the electrolyte layer 112, and the fuel electrode 116 supports other layers constituting the single cell 110. That is, the single cell 110 of the present embodiment is a fuel electrode support type single cell. The fuel electrode 116 corresponds to a specific electrode in the claims.

The electrolyte layer 112 is a flat plate-shaped member having a substantially rectangular shape in the Z direction, and is a dense layer (with a low porosity). The electrolyte layer 112 is formed of, for example, a solid oxide such as YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), and perovskite-type oxide. There is. As described above, the single cell 110 of the present embodiment is a solid oxide fuel cell (SOFC) using a solid oxide as an electrolyte.

The air electrode 114 is a substantially rectangular flat plate-shaped member smaller than the electrolyte layer 112 in the Z direction, and is a porous layer (having a higher porosity than the electrolyte layer 112). The air electrode 114 is formed of, for example, a perovskite-type oxide (for example, LSCF (lanternstrontium cobalt iron oxide), LSM (lanternstrontium manganese oxide), LNF (lantern nickel iron)).

The fuel electrode 116 is a substantially rectangular flat plate-shaped member having substantially the same size as the electrolyte layer 112 in the Z direction, and is a porous layer (having a higher porosity than the electrolyte layer 112). FIG. 6 is an explanatory view showing an enlarged XZ cross-sectional configuration of a part of the single cell 110 (a part of the electrolyte layer 112 and a part of the fuel electrode 116). As shown in FIG. 6, the fuel electrode 116 includes a support layer 360 and an active layer 350 arranged between the support layer 360 and the electrolyte layer 112. In this embodiment, the active layer 350 is adjacent to the electrolyte layer 112, and the support layer 360 is adjacent to the active layer 350. The active layer 350 and the support layer 360 are formed of, for example, a transition metal Ni (nickel), a cermet composed of Ni and ceramic particles, a Ni-based alloy, or the like. The ceramic particles are materials having oxygen ion conductivity, and are, for example, the above-mentioned materials (YSZ or the like) forming the electrolyte layer 112.

The active layer 350 of the fuel electrode 116 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. Further, the support layer 360 of the fuel electrode 116 mainly exerts a function of supporting the active layer 350, the electrolyte layer 112, and the air electrode 114. In order to increase the strength of the support layer 360, the thickness of the support layer 360 is preferably thicker than that of the active layer 350. Further, in order to enhance the gas diffusivity of the support layer 360, it is preferable that the porosity of the support layer 360 is higher than the porosity of the active layer 350. The support layer 360 corresponds to the first fuel electrode layer in the claims, and the active layer 350 corresponds to the second fuel electrode layer 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 near the center, and is formed of, for example, metal. The peripheral portion of the hole 121 in the separator 120 faces the peripheral edge of the surface of the electrolyte layer 112 on the side of the air electrode 114. The separator 120 is bonded to the electrolyte layer 112 (single cell 110) by a bonding portion 124 formed of a brazing material (for example, Ag wax) arranged at the facing portions thereof. The separator 120 partitions the air chamber 166 facing the air electrode 114 and the fuel chamber 176 facing the fuel electrode 116, and 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 air pole side frame 130 is a frame-shaped member in which a substantially rectangular hole 131 penetrating in the vertical direction is formed near the center, and is formed of, for example, an insulator such as mica. The hole 131 of the air pole side frame 130 constitutes an air chamber 166 facing the air pole 114. The air electrode side frame 130 is in contact with the peripheral edge of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge of the surface of the interconnector 150 facing the air electrode 114. .. Further, the air electrode side frame 130 electrically insulates between the pair of interconnectors 150 included in the power generation unit 102. Further, in the air electrode side frame 130, the oxidant gas supply communication hole 132 that communicates the oxidant gas introduction manifold 161 and the air chamber 166, and the oxidant gas that communicates the air chamber 166 and the oxidant gas discharge manifold 162. A discharge communication hole 133 is formed.

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

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 electrode 116 opposite to the side facing the electrolyte layer 112, and the interconnector facing portion 146 is on the surface of the interconnector 150 on the side facing the fuel 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 current collector 144 on the fuel electrode side has such a configuration, the fuel electrode 116 and the interconnector 150 (or the end plate 106) are electrically connected to each other. A spacer 149 formed of, for example, a mica is arranged between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel electrode side current collector 144 follows the deformation of the power generation unit 102 due to the temperature cycle and the reaction gas pressure fluctuation, and the fuel electrode 116 and the interconnector 150 (or the end plate 106) via the fuel electrode side current collector 144 follow. Good electrical connection with is maintained.

The 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 current collector 134 on the air electrode side has such a configuration, the air electrode 114 and the interconnector 150 (or the end plate 104) are electrically connected to each other. The air electrode side current collector 134 and the interconnector 150 may be configured as an integral member. Further, the air electrode side current collector 134 may be covered with a conductive coat, and a conductive bonding layer for bonding the two is interposed between the air electrode 114 and the air electrode side current collector 134. You may be doing it.

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

When the oxidant gas OG is supplied to the air chamber 166 of each power generation unit 102 and the fuel gas FG is supplied to the fuel chamber 176, power is generated by the electrochemical reaction of the oxidant gas OG and the fuel gas FG in the single cell 110. Will be. This power generation reaction is an exothermic reaction. In each power generation unit 102, the air pole 114 of the single cell 110 is electrically connected to 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, until the high temperature can be maintained by the heat generated by the power generation after the start-up. It may be heated by (not shown).

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

A-3. Manufacturing method of fuel cell stack 100:
FIG. 7 is a flowchart showing an example of a method for manufacturing the fuel cell stack 100 according to the present embodiment. First, a single cell 110 is manufactured (S110). The method for producing the single cell 110 is, for example, as follows.

(Preparation of green sheet for fuel electrode support layer)
For a mixed powder (100 parts by weight) of NiO powder (50 parts by weight) and YSZ powder (50 parts by weight), organic beads as a pore-forming material, butyral resin, DOP as a plasticizer, and 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 a doctor blade method to prepare a green sheet for a fuel electrode support layer having a predetermined thickness (for example, 200 μm to 300 μm). The ratio of NiO powder and YSZ powder in the green sheet for the fuel electrode support 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. good. That is, the NiO powder can be appropriately changed between, for example, 40 to 60 parts by weight so that the mixed powder of NiO powder and YSZ powder is 100 parts by weight, and the rest can be 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, mix in a ball mill to prepare a slurry. As in the method for producing the green sheet for the fuel electrode support layer described above, organic beads as a pore-forming material may be added when preparing the slurry. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for a fuel polar active layer having a predetermined thickness (for example, 10 μm to 40 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. good. That is, the NiO powder can be appropriately changed between, for example, 40 to 60 parts by weight so that the mixed powder of NiO powder and YSZ powder is 100 parts by weight, and the rest can be 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 a doctor blade method to prepare a green sheet for an electrolyte layer having a predetermined thickness (for example, 10 μm).

(Preparation of a laminate of the electrolyte layer 112 and the fuel electrode 116)
The green sheet for the fuel electrode support layer, the green sheet for the fuel electrode active layer, and the green sheet for the electrolyte layer are attached and degreased at a predetermined temperature (for example, about 280 ° C.). Further, the laminated body of the green sheet after degreasing is fired at a predetermined temperature (for example, about 1350 ° C.). As a result, a laminate of the electrolyte layer 112 and the fuel electrode 116 (active layer 350 and support layer 360) is obtained.

(Formation of air electrode 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 liquid is spray-coated on the surface of the electrolyte layer 112 in the above-mentioned laminate of the electrolyte layer 112 and the fuel electrode 116, and fired at a predetermined temperature (for example, 1100 ° C.). As a result, an air electrode 114 is formed on the surface of the electrolyte layer 112, and as a result, a single cell 110 including a fuel electrode 116, an electrolyte layer 112, and an air electrode 114 is obtained.

After producing a plurality of single cells 110 according to the method described above, an assembly step (for example, a step of attaching another member such as a separator 120 to each single cell 110, a step of laminating a plurality of single cells 110, and fastening with bolts 22). Steps, etc.) (S120). As described above, the assembly of the fuel cell stack 100 before the active layer 350 of the fuel electrode 116 is reduced is completed.

(Reduction process)
After that, in order to bring the fuel cell stack 100 into a state in which power generation operation is possible, a reduction step of reducing the active layer 350 of the fuel electrode 116 (that is, reducing NiO contained in the active layer 350 to Ni) is performed (S130). The reduction step is realized, for example, by exposing the fuel electrode 116 to a hydrogen atmosphere at a predetermined temperature for a predetermined time. The reducing gas used in the reduction step is not limited to hydrogen, and may be another gas such as methane gas. As described above, the production of the fuel cell stack 100 in a state in which power generation operation is possible is completed.

A-4. How to adjust each characteristic of single cell 110:
When the fuel cell stack 100 is manufactured by the manufacturing method described above, each characteristic of the single cell 110 constituting the fuel cell stack 100 can be adjusted as follows, for example. The method for specifying each characteristic of the single cell 110 will be described in "A-6. Analytical method for the single cell 110" described later.

(Average pore diameter in the active layer 350 of the fuel electrode 116)
When preparing a slurry for a green sheet for a fuel electrode active layer, the smaller the solid content ratio of the slurry (ratio of the volume of solid content (NiO powder, YSZ powder) to the total volume), the more the active layer of the fuel electrode 116 is prepared. The average pore diameter at 350 can be increased. Further, when firing for producing a laminate of the electrolyte layer 112 and the fuel electrode 116, the higher the firing temperature and the longer the firing time, the more the average pore diameter of the fuel electrode 116 in the active layer 350 becomes larger. Can be made larger.

(Average porosity in the active layer 350 of the fuel electrode 116)
When preparing a slurry for a green sheet for a fuel electrode active layer, the larger the amount of the pore-forming material added, the higher the average porosity of the fuel electrode 116 in the active layer 350.

(Average particle size of Ni in the active layer 350 of the fuel electrode 116)
When preparing a slurry for a green sheet for a fuel electrode active layer, the smaller the particle size of the NiO powder, the smaller the average particle size of Ni in the active layer 350 of the fuel electrode 116. Further, when firing for producing a laminate of the electrolyte layer 112 and the fuel electrode 116, the lower the firing temperature and the shorter the firing time, the more the average grain size of Ni in the active layer 350 of the fuel electrode 116. The diameter can be reduced.

(Relationship with reduction process)
The relationship between the reduction step (S130 in FIG. 7) in the method for manufacturing the fuel cell stack 100 described above and each of the above characteristics is as follows. For example, as a reduction step, a first method of exposing the fuel cell stack 100 to a hydrogen atmosphere at a predetermined temperature (for example, 425 ° C. to 600 ° C.) lower than the operating temperature (for example, 700 ° C.) for a predetermined time (for example, 1 to 2 hours). After performing the reduction step, a two-step reduction is performed by performing a second reduction step of exposing the hydrogen atmosphere to a hydrogen atmosphere at a predetermined temperature (for example, 770 ° C. to 1000 ° C.) higher than the above operating temperature for a predetermined time (for example, 1 to 2 hours). The process can be adopted. In this case, the size of the Ni particles contained in the active layer 350 of the fuel electrode 116 is reduced by the first reduction step, and as a result, the specific surface area of Ni is increased and Ni is likely to aggregate. In the subsequent second reduction step, the aggregation of Ni particles sufficiently proceeds. Therefore, the average particle size of Ni in the active layer 350 after the reduction step is relatively large. In the case of performing the two-step reduction step, the lower the temperature in the first reduction step, the larger the average particle size of Ni in the active layer 350 after the reduction step. In the active layer 350 of the fuel electrode 116, the pore diameter tends to increase as the aggregation of Ni progresses. Therefore, when the above two-step reduction step is adopted, the average pore diameter in the active layer 350 is relatively large. growing.

On the other hand, when only the second reduction step is carried out without carrying out the first reduction step described above as the reduction step, the aggregation of Ni particles does not sufficiently proceed in the second reduction step. Therefore, the average particle size of Ni in the active layer 350 after the reduction step is relatively small, and the pore diameter in the active layer 350 is relatively small.

A-5. Performance evaluation:
Samples of a plurality of single cells 110 having different characteristics from each other were prepared, and performance evaluation was performed using the samples. FIG. 8 is an explanatory diagram showing the performance evaluation result.

A-5-1. For each sample:
As shown in FIG. 8, each sample (samples S1 to S11) has the above-mentioned characteristics (average pore diameter, average porosity, average Ni particle diameter in the active layer 350 of the fuel electrode 116) different from each other. Further, in each sample, the value of each polarization component of the single cell 110 is different from each other according to the difference in their characteristics. Here, the polarization component of the single cell 110 includes the IR resistance (resistance polarization) which is the resistance value of each layer constituting the single cell 110 and the resistance value of each interface, as well as the ionization reaction of the fuel gas FG at the fuel electrode 116. The fuel electrode activation polarization Pa (a), which is the resistance value of, the air electrode activation polarization Pa (c), which is the resistance value of the ionization reaction of the oxidizing agent gas OG at the air electrode 114, and the fuel gas FG at the fuel electrode 116. There are a fuel electrode gas diffusion polarization Pd (a) which is a resistance value of diffusion of the fuel electrode, and an air electrode gas diffusion polarization Pd (c) which is a resistance value of diffusion of an oxidant gas OG at the air electrode 114. As described above, since the single cell 110 of the present embodiment is a fuel electrode support type and the air electrode 114 is relatively thin, the air electrode gas diffusion polarization Pd (c) is negligibly small. A method for specifying the value of each polarization component in the single cell 110 will be described in "A-6. Analytical method for the single cell 110" described later.

In this performance evaluation, the evaluation was performed focusing on the ratio of the fuel electrode gas diffusion polarization Pd (a) to the fuel electrode activation polarization Pa (a) (hereinafter referred to as “polarization ratio”). In general, the larger the average pore diameter in the active layer 350 of the fuel electrode 116 and the higher the average porosity, the better the diffusivity of the fuel gas FG, and therefore the lower the fuel electrode gas diffusion polarization Pd (a). Therefore, the value of the polarization ratio Pd (a) / Pa (a) becomes smaller. Further, as the average Ni particle size of the active layer 350 of the fuel electrode 116 becomes smaller, the specific surface area of Ni increases, so that the three-layer interface which is the reaction field increases, and the fuel electrode activation polarization Pa (a) becomes smaller and polarized. The value of the ratio Pd (a) / Pa (a) becomes large.

A-5-2. Evaluation items and evaluation methods:
In this performance evaluation, the initial voltage and η resistance of the single cell 110 were measured, and the performance was evaluated based on the value of the η resistance. Specifically, power generation operation was performed at a temperature of 700 ° C. and a current density of 0.55 A / cm ² , and the initial voltage of the single cell 110 was measured. Further, under the above power generation operation conditions, the η resistance of the single cell 110 was measured by the current interruption method. As shown in FIG. 8, the lower the η resistance of the single cell 110, the higher the initial voltage of the single cell 110 tends to be. In this performance evaluation, if the η resistance of the single cell 110 is less than 0.2 Ωcm ² , it is judged as acceptable (〇), and if the η resistance of the single cell 110 is 0.2 Ωcm ² or more, it is judged as rejected (×). did. Further, when the η resistance of the single cell 110 was less than 0.14 Ωcm ² , it was judged to be good (⊚).

A-5-3. Performance evaluation result:
As shown in FIG. 8, in the samples S1, S2, S10, and S11, since the η resistance was 0.2 Ωcm ² or more, it was determined to be rejected (x). On the other hand, in the samples S3, S4, S8, and S9, the η resistance was less than 0.2 Ωcm ² , so it was judged to be acceptable (◯). Further, in the samples S5 to S7, the η resistance was less than 0.14 Ωcm ² , so it was judged to be good (⊚).

FIG. 9 is an explanatory diagram showing the relationship between the polarization ratio Pd (a) / Pa (a) and the η resistance in the performance evaluation result. As shown in FIGS. 8 and 9, the samples S1 and S2 determined to be rejected are samples in which the values of the polarization ratios Pd (a) / Pa (a) are relatively small (less than 1.0). The samples S10 and S11, which are also determined to be unacceptable, are samples having a relatively large (greater than 4.0) polarization ratio Pd (a) / Pa (a). On the other hand, the samples S3 to S9 judged to be acceptable or good are samples in which the value of the polarization ratio Pd (a) / Pa (a) is in the range of 1.0 or more and 4.0 or less. As described above, if the value of the polarization ratio Pd (a) / Pa (a) is too small or too large, the η resistance becomes high, and the value of the polarization ratio Pd (a) / Pa (a) is medium (1). It was confirmed that the η resistance was low when it was in the range of 0.0 or more and 4.0 or less). Further, it was confirmed that the η resistance was further lowered when the value of the polarization ratio Pd (a) / Pa (a) was in the range of 1.7 or more and 2.5 or less as in the samples S5 to S7. rice field.

Further, in the samples S3 to S9 judged to be acceptable or good, the average pore diameter in the active layer 350 of the fuel electrode 116 is 0.55 μm or more, and the average Ni particle size in the active layer 350 is 1.10 μm or less. there were.

FIG. 10 is an explanatory diagram conceptually showing the relationship between the configuration of the active layer 350 of the fuel electrode 116 and each characteristic. As shown in the left column of FIG. 10, the single cell 110 having a relatively small polarization ratio Pd (a) / Pa (a) like the samples S1 and S2 determined to be rejected has the fuel electrode 116. It is considered that the active layer 350 has a structure in which the degree of progress of Ni aggregation is large. That is, in such a single cell 110, in the active layer 350, the average Ni particle size is relatively large, the average pore diameter is relatively large, and the average porosity is relatively high. Therefore, in the single cell 110 having such a configuration, the fuel electrode gas diffusion polarization Pd (a) is relatively low due to the wide gas flow path in the active layer 350 of the fuel electrode 116, but the reaction field in the active layer 350. Since there are few three-layer interfaces, the fuel electrode activation polarization Pa (a) becomes extremely high. Therefore, in the single cell 110 having a configuration in which the reduction of the fuel electrode gas diffusion polarization Pd (a) is prioritized, the total of the fuel electrode gas diffusion polarization Pd (a) and the fuel electrode activation polarization Pa (a) is calculated. On the contrary, it gets bigger.

Further, as shown in the right column of FIG. 10, the single cell 110 having a relatively large value of the polarization ratio Pd (a) / Pa (a), such as the samples S10 and S11 determined to be unacceptable, has a fuel electrode. It is considered that the degree of progress of Ni aggregation in the active layer 350 of 116 is small. That is, in such a single cell 110, in the active layer 350, the average Ni particle size is relatively small, the average pore diameter is relatively small, and the average porosity is relatively low. Therefore, in the single cell 110 having such a configuration, the fuel electrode activation polarization Pa (a) is relatively low because there are many three-layer interfaces as reaction fields in the active layer 350 of the fuel electrode 116, but the fuel electrode 116 Since the gas flow path in the active layer 350 is narrow, the fuel electrode gas diffusion polarization Pd (a) becomes extremely high. Therefore, in the single cell 110 having a configuration in which the reduction of the fuel electrode activation polarization Pa (a) is prioritized, the total of the fuel electrode gas diffusion polarization Pd (a) and the fuel electrode activation polarization Pa (a) is calculated. On the contrary, it gets bigger.

On the other hand, as in the samples S3 to S9 judged to be acceptable or good, the value of the polarization ratio Pd (a) / Pa (a) is medium (within the range of 1.0 or more and 4.0 or less). As shown in the central column of FIG. 10, a single cell 110 is considered to have a structure in which the degree of progress of Ni aggregation in the active layer 350 of the fuel electrode 116 is moderate. That is, in such a single cell 110, in the active layer 350, the average Ni particle size is neither extremely large nor small, the average pore diameter is neither extremely large nor small, and the average porosity is extremely high or low. do not have. Therefore, in the single cell 110 having such a configuration, the fuel electrode gas diffusion polarization Pd (a) does not become extremely high because the gas flow path in the active layer 350 of the fuel electrode 116 is wide to some extent, and the active layer 350. Since there are a certain number of three-layer interfaces as reaction fields in the fuel electrode activation polarization Pa (a), the fuel electrode activation polarization Pa (a) does not become extremely high. That is, in the single cell 110 having a well-balanced configuration of the fuel electrode gas diffusion polarization Pd (a) and the fuel electrode activation polarization Pa (a), the fuel electrode gas diffusion polarization Pd (a) and the fuel electrode activation are activated. The sum with the polarization Pa (a) becomes smaller.

According to the above performance evaluation results, in the single cell 110 in which the value of the polarization ratio Pd (a) / Pa (a) is 1.0 or more and 4.0 or less, the fuel electrode activation polarization has a trade-off relationship. By achieving a good balance between the reduction of Pa (a) and the reduction of the fuel electrode gas diffusion polarization Pd (a), the η resistance of the single cell 110 can be reduced, and the output characteristics of the single cell 110 can be improved. It can be said that it can be done.

Further, in the single cell 110 in which the polarization ratio Pd (a) / Pa (a) is 1.7 or more and 2.5 or less, the fuel electrode activation polarization Pa (a) is reduced and the fuel electrode gas diffusion polarization Pd. It can be said that the η resistance of the single cell 110 can be further effectively reduced and the output characteristics of the single cell 110 can be further effectively improved by realizing the reduction of (a) in a more balanced manner.

Further, in the single cell 110 in which the average pore diameter in the active layer 350 of the fuel electrode 116 is 0.55 μm or more and the average Ni particle size in the active layer 350 is 1.10 μm or less, the gas flow in the active layer 350. Since the path (diffusion path) can be widened in a well-balanced manner and the three-layer interface as a reaction field in the active layer 350 can be increased in a well-balanced manner, the fuel electrode activation polarization Pa (a) can be reduced and the fuel can be increased. By achieving the reduction of the polar gas diffusion polarization Pd (a) in a well-balanced manner, the η resistance of the single cell 110 can be reduced, and the output characteristics of the single cell 110 can be improved.

A-6. Analysis method of single cell 110:
A-6-1. Method for identifying each polarization component of the single cell 110:
The method for specifying each polarization component of the single cell 110 (fuel electrode activated polarization Pa (a), air electrode activated polarization Pa (c), fuel electrode gas diffusion polarization Pd (a)) is, for example, as follows. As described above, since the single cell 110 of the present embodiment is a fuel electrode support type, the air electrode gas diffusion polarization Pd (c) is so small that it can be ignored.

First, a part of the single cell 110 is cut out, and a sample for performance evaluation and analysis is prepared. For this sample, AC impedance measurement was performed under the following conditions using a potentiometer / galvanostat and an impedance analyzer to obtain an impedance spectrum.
・ Power generation operating temperature: 700 ℃
・ Open circuit voltage (OCV) standard ・ Measurement frequency band: 0.1Hz-100,000Hz (0.1MHz)
・ AC amplitude: 10 mV
-Gas temperature: (air electrode side) A mixed gas of 20 vol% oxygen and 80 vol% nitrogen
(Fuel electrode side) A mixed gas of 96 vol% hydrogen and 4 vol% water vapor

Next, by matching the obtained impedance spectrum with the equivalent circuit shown in FIG. 11, the resistance values (R1, R2, R3) of each polarization component are obtained in addition to the IR resistance (R0). The method of matching the impedance spectrum to the equivalent circuit and specifying each polarization component in this way is called equivalent circuit analysis. L1 in the equivalent circuit of FIG. 11 is the inductance generated by the electrical connection between the measuring device and the sample. Further, R0 is a resistance value possessed by each layer (electrolyte layer 112, fuel electrode 116, air electrode 114) constituting the single cell 110, and an interfacial resistance value between the layers. Further, R1 is the fuel electrode activated polarization Pa (a), R2 is the air electrode activated polarization Pa (c), and R3 is the fuel electrode gas diffusion polarization Pd (a). Note that C1, C2, and C3 are capacitive components corresponding to the fuel electrode activated polarization Pa (a), the air electrode activated polarization Pa (c), and the fuel electrode gas diffusion polarization Pd (a), respectively.

In the equivalent circuit analysis, the vertex frequency f of the arc represented by f = 1 / (2πRC) is
(1) The resistance value when the voltage is lower than 21 Hz is defined as the fuel electrode gas diffusion polarization Pd (a).
(2) The resistance value at 21 Hz or higher and lower than 510 Hz is defined as the air electrode activation polarization Pa (c).
(3) The resistance value at 510 Hz or higher is defined as the fuel electrode activation polarization Pa (a).

A-6-2. Method for identifying each characteristic of the active layer 350 of the fuel electrode 116:
(Method of specifying active layer 350)
The method for specifying the active layer 350 in the fuel electrode 116 is, for example, as follows. Flow direction of reaction gas (oxidizer gas OG or fuel gas FG) (As shown in FIG. 2, in the present embodiment, the flow direction of the oxidant gas OG is the X-axis direction, and the flow direction of the fuel gas FG is the Y-axis direction. A cross section (fuel electrode 116, electrolyte layer 112, and air electrode 114) substantially orthogonal to the flow direction of the reaction gas (oxidant gas OG or fuel gas FG) is laminated at any three positions arranged along the line. As shown in FIG. 4, a cross section parallel to the Z-axis direction) is set, and the active layer 350 of the fuel electrode 116 is shown at any three points of each cross section. An SEM image (for example, 5000 times) in FIB-SEM (acceleration voltage 1.5 kV) is obtained. 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. Of the 10 divided regions obtained by dividing into 10 equal parts in the direction, the portion located in the uppermost divided region and presumed to be the boundary B2 (see FIG. 6) between the active layer 350 and the support layer 360. Or, it is an image in which the lower end of the fuel electrode 116 is located in the lowermost divided region.

The boundary B1 between the electrolyte layer 112 and the fuel electrode 116 can be specified in each of the above SEM images based on the difference in the constituent substances between the electrolyte layer 112 and the fuel electrode 116, visual recognition, and the like. Further, the boundary B2 between the active layer 350 and the support layer 360 in the fuel electrode 116 has a difference in the Ni content, the average Ni particle size, the porosity, etc. between the active layer 350 and the support layer 360 in each of the above SEM images. Can be specified based on. By specifying the boundary B1 and the boundary B2, the active layer 350 of the fuel electrode 116 can be specified.

(Method of specifying the average Ni particle size in the active layer 350 of the fuel electrode 116)
The method for specifying the average Ni particle size in the active layer 350 of the fuel electrode 116 is, for example, as follows. When specifying the average Ni particle size, it is preferable to use the reduced active layer 350. In each of the above SEM images, a plurality of straight lines orthogonal to the vertical direction are drawn at predetermined intervals (for example, 1 μm to 5 μm intervals). Here, the distinction between Ni particles, YSZ particles, and pores 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. The length of each part corresponding to Ni on each straight line is measured, and the average value of the lengths of each part corresponding to Ni is multiplied by a predetermined coefficient (specifically, "Ceramic Processing" by Satoshi Mizutani (Gihodo Publishing)). With reference to the description on p.192-195 of the above, Ni is considered to be spherical, and the average value multiplied by a coefficient of 1.5) is defined as the particle size of Ni on the line. The average value of the Ni particle diameters in the plurality of straight lines drawn on the active layer 350 is taken as the average Ni particle size in the active layer 350.

(Method of specifying the average pore diameter in the active layer 350 of the fuel electrode 116)
The method for specifying the average pore diameter in the active layer 350 of the fuel electrode 116 is, for example, as follows. Similar to the above-mentioned method for specifying the average Ni particle size, in each of the above SEM images, a plurality of straight lines orthogonal to the vertical direction are drawn at predetermined intervals (for example, at intervals of 1 μm to 5 μm), and each portion corresponding to the pores on each straight line is drawn. A value obtained by measuring the length and multiplying the average value of the lengths of the parts corresponding to the pores by a predetermined coefficient (specifically, as in the case of the above Ni particle diameter, the pores are considered to be spherical and the average value is multiplied by a coefficient 1. The value obtained by multiplying by 5) is taken as the pore diameter on the line. The average value of the pore diameters in the plurality of straight lines drawn on the active layer 350 is taken as the average pore diameter in the active layer 350.

(Method of specifying the average porosity in the active layer 350 of the fuel electrode 116)
The method for specifying the average porosity in the active layer 350 of the fuel electrode 116 is as follows, for example. Similar to the above-mentioned method for specifying the average particle size of Ni, in each of the above SEM images, a plurality of straight lines orthogonal to the vertical direction are drawn at predetermined intervals (for example, at intervals of 1 μm to 5 μm), and each portion corresponding to the pores on each straight line. The ratio of the total length of each portion corresponding to the pores to the total length of the straight line is taken as the porosity on the line. The average value of the porosity in the plurality of straight lines drawn by the active layer 350 is taken as the average porosity in the active layer 350.

B. Modification example:
The technique disclosed in the present specification is not limited to the above-described embodiment, and can be transformed into various forms without departing from the gist thereof, and for example, the following modifications are also possible.

The configuration of the single cell 110 or the fuel cell stack 100 in the above embodiment is merely an example and can be variously modified. For example, in the above embodiment, the fuel pole 116 has a two-layer structure of the active layer 350 and the support layer 360, but the fuel pole 116 includes layers other than the active layer 350 and the support layer 360. It may be a single layer structure. The fuel electrode 116 means an assembly of a portion having the activity of the anode reaction of the fuel cell and a portion in contact with the portion and through which the fuel gas FG passes through the inside. Further, the air electrode 114 means an assembly of a portion having the activity of the cathode reaction of the fuel cell and a portion in contact with the portion and through which the oxidant gas OG passes through the inside.

Further, in the above embodiment, a reaction prevention layer containing, for example, ceria may be provided between the electrolyte layer 112 and the air electrode 114. In the case of such a configuration, the IR resistance component described above includes the resistance value of the reaction prevention layer and the interfacial resistance value between the reaction prevention layer and another layer.

Further, in the above embodiment, the number of single cells 110 included in the fuel cell stack 100 is only an example, and the number of single cells 110 is appropriately determined according to the output voltage and the like required for the fuel cell stack 100. In the above embodiment, the values of the polarization ratios Pd (a) / Pa (a) are always in the range of 1.0 or more and 4.0 or less for all the single cells 110 included in the fuel cell stack 100. Etc. are not required, and if the conditions are satisfied for at least one single cell 110 included in the fuel cell stack 100, the η resistance can be reduced and the output characteristics of the single cell 110 can be improved. It can be said that it can be done.

Further, the material forming each member in the above embodiment is merely an example, and each member may be formed of another material. For example, in the above embodiment, Ni is adopted as the transition element contained in the fuel electrode 116, but other transition elements such as Mn, Fe, Co, and Cu can be used. However, since Ni is relatively inexpensive and has a high affinity for hydrogen, it is preferable to use Ni as the transition element contained in the fuel electrode 116. Further, the fuel electrode 116 does not necessarily have to contain a transition element.

Further, in the above embodiment, the fuel electrode 116 is thicker than the air electrode 114 and the electrolyte layer 112, and the fuel electrode 116 supports the other layers constituting the single cell 110. The fuel electrode support type single cell 110 However, the present invention has an air electrode support type in which the thickness of the air electrode 114 is thicker than the thickness of the fuel electrode 116 and the electrolyte layer 112, and the air electrode 114 supports other layers constituting the single cell 110. It is also applicable to the single cell 110 of. In this case, pay attention to the ratio (polarization ratio) of the air electrode gas diffusion polarization Pd (c) to the air electrode activation polarization Pa (c), and the value of the polarization ratio Pd (c) / Pa (c) is 1. Within the range of 0.0 or more and 4.0 or less, the single cell 110 can be achieved by achieving a good balance between the reduction of the air electrode activation polarization Pa (c) and the reduction of the air electrode gas diffusion polarization Pd (c). The η resistance can be reduced and the output characteristics of the single cell 110 can be improved. In this case, the air electrode 114 corresponds to the specific electrode in the claims.

Further, in the above embodiment, the fuel cell stack 100 has a configuration in which a plurality of flat plate-shaped single cells 110 are laminated, but the present invention is described in another configuration, for example, International Publication No. 2012/165409. As described above, it is similarly applicable to a configuration in which a plurality of substantially cylindrical fuel cell single cells are connected in series.

Further, in the above embodiment, the SOFC that generates power by utilizing the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidizing agent gas is targeted, but the present invention relates to an electrolysis reaction of water. It is also applicable to an electrolytic single cell, which is a constituent unit of a solid oxide type electrolytic cell (SOEC) that uses it 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, for example, as described in Japanese Patent Application Laid-Open No. 2016-81813, but is schematically the same as the fuel cell stack 100 in the above-described embodiment. It is the composition of. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolytic cell stack, the power generation unit 102 may be read as an electrolytic cell unit, and the single cell 110 may be read as an electrolytic cell. However, during the operation of the electrolytic cell stack, a voltage is applied between both electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode), and the voltage is applied through the communication hole 108. Steam as a raw material gas is supplied. As a result, an electrolysis reaction of water occurs in each electrolytic cell, hydrogen gas is generated in the fuel chamber 176, and hydrogen is taken out to the outside of the electrolytic cell stack through the communication hole 108. Even in the electrolytic single cell having such a configuration, if the above-mentioned conditions such as the value of the polarization ratio Pd (a) / Pa (a) being in the range of 1.0 or more and 4.0 or less are satisfied, η The resistance can be reduced and the output characteristics can be improved.

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

22: Bolt 24: Nut 26: Insulation sheet 27: Gas passage member 28: Main body 29: Branch 100: Fuel cell stack 102: Power generation unit 104: End plate 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 Collector 135: Collector element 140: Fuel pole side frame 141: Hole 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 144: Fuel pole side current collector 145: Electrode facing part 146: Interconnector facing Part 147: Connecting part 149: Spacer 150: Interconnector 161: Oxidizing 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 350: Active layer 360: Support layer

Claims (4)

In an electrochemical reaction single cell comprising an electrolyte layer and an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer.
Before the start of operation, the polarization component of the electrochemical reaction single cell is measured based on the open circuit voltage, measurement frequency band: 0.1 Hz to 0.1 MHz, AC amplitude: 10 mV , temperature: 700 ° C., gas used: said air electrode. Ionization of gas at the fuel electrode by equivalent circuit analysis based on the result of AC impedance measurement under the condition that the mixed gas of oxygen 20 vol% and nitrogen 80 vol% on the side and the mixed gas of hydrogen 96 vol% and water vapor 4 vol% on the fuel electrode side . The activation polarization (Ω) of the fuel electrode, which is the resistance value of the reaction, the activation polarization (Ω) of the air electrode, which is the resistance value of the gas ionization reaction at the air electrode, and the fuel electrode and the air electrode. The activation of the specific electrode when divided into three resistance components, gas diffusion polarization (Ω), which is the resistance value of gas diffusion in the specific electrode having the thicker thickness in the first direction. The ratio (Pd / Pa) of the gas diffusion polarization Pd to the polarization Pa is 1.0 or more and 4.0 or less.
The specific electrode is a fuel electrode and
The fuel electrode includes a first fuel electrode layer and a second fuel electrode layer disposed between the first fuel electrode layer and the electrolyte layer.
The fuel electrode is composed of Ni and YSZ.
An electrochemical reaction single cell characterized in that the porosity of the first fuel electrode layer is higher than the porosity of the second fuel electrode layer. In the electrochemical reaction single cell according to claim 1,
The second fuel electrode layer contains a transition metal and contains
The average pore diameter in the second fuel electrode layer is 0.55 μm or more, and is
An electrochemical reaction single cell characterized in that the average particle size of the transition metal in the second fuel electrode layer is 1.10 μm or less. In the electrochemical reaction single cell according to claim 1 or 2.
An electrochemical reaction single cell, wherein the ratio (Pd / Pa) of the gas diffusion polarization Pd to the activation polarization Pa of the specific electrode is 1.7 or more and 2.5 or less. In the electrochemical reaction cell stack including a plurality of electrochemical reaction single cells arranged side by side in the first direction.
The electrochemical reaction cell stack according to any one of claims 1 to 3, wherein at least one of the plurality of electrochemical reaction single cells is the electrochemical reaction single cell.

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