JP2013140737A - Method for manufacturing solid electrolyte fuel cell, and solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid electrolyte fuel cell that produces high output due to low contact resistance between a solid electrolyte membrane and an air electrode, and a solid electrolyte fuel cell.SOLUTION: A fuel electrode 13, a solid electrolyte membrane 14, and an interconnector 16 are formed on a substrate tube 11, and then sintered together. An air electrode intermediate layer 15a mainly composed of a ceria compound represented by SmCeO, where 0.8≤x≤0.9, is formed on the solid electrolyte membrane 14 and the interconnector 16 sintered together. An air electrode conductive layer 15b represented by LaSrCaMnO, where y>1, 0.4≤a≤0.8, 0.4≤b≤0.8, in which the ratio of the total number of moles of La, Sr, and Ca to the number of moles of Mn is higher than or equal to 0.92 and lower than or equal to 0.98, is formed on the air electrode intermediate layer 15a. Mn in the air electrode conductive layer 15b is diffused into the air electrode intermediate layer 15a by sintering the air electrode intermediate layer 15a and the air electrode conductive layer 15b.

Description

  The present invention relates to a method for manufacturing a solid oxide fuel cell in which a plurality of single elements are formed on a base tube.

  In a general configuration of a cylindrical solid oxide fuel cell (SOFC), a single element in which a fuel electrode, a solid electrolyte membrane, and an air electrode are laminated in order on a porous substrate tube along the longitudinal direction of the substrate tube. A plurality of adjacent single elements are connected by an interconnector. Although the electromotive force per single element is small, the voltage can be increased and a high output can be obtained by connecting a plurality of elements in series.

The fuel electrode is made of a material obtained by mixing nickel and a zirconia-based electrolyte material such as yttria-stabilized zirconia (YSZ). YSZ is mainly used for the solid electrolyte membrane.
The interconnector is made of a conductive perovskite oxide such as SrTiO ₃ . The interconnector is for electrically connecting single elements. When the electrical conductivity of the interconnector is low, less electric power can be taken out, and thus high electrical conductivity is required. The interconnector also serves to prevent fuel and air from mixing when fuel gas is supplied to the inside of the base tube. Therefore, high airtightness of the contact interface between the interconnector and the single element is also required.
The air electrode is composed of, for example, a conductive perovskite oxide made of LaMnO ₃ .

In the solid oxide fuel cell having the above configuration, a large contact resistance exists at the interface portion between the air electrode and the solid electrolyte membrane. In order to reduce the contact resistance and improve the electrode activity between the air electrode and the electrolyte, Patent Document 1 discloses an air electrode such as LaAMnO ₃ (A = Sr or Ca), YSZ or scandinavian stabilized zirconia ( It discloses that an electrode reaction layer having high oxygen ion conductivity is provided between an electrolyte such as SSZ). The electrode reaction layer of Patent Document 1 is a cerium oxide such as (CeO ₂ ) _0.8 (Sm ₂ O ₃ ) _0.1 or a mixture of cerium oxide and lanthanum manganite.

Patent Document 2 discloses a second electrolyte having a CeO ₂ oxide between a first electrolyte film having a ZrO ₂ oxide and an air electrode containing a LaCoO ₃ oxide or a LaMnO ₃ oxide. A solid oxide fuel cell having a membrane is disclosed.

Japanese Patent No. 3661676 (claims 1, 2, 14, paragraphs [0007] to [0008], [0053], [0073] to [0078], [0101] to [0104], [0160] to [0163] [0184] to [0187]) Japanese Patent No. 4592484 (Claims 1, 5, paragraphs [0033] to [0035])

  The present invention provides a method for manufacturing a solid oxide fuel cell that exhibits high output by reducing the contact resistance between the solid electrolyte membrane and the air electrode, and a solid electrolyte fuel cell manufactured by the manufacturing method. With the goal.

A method for manufacturing a solid oxide fuel cell according to the present invention includes a plurality of single elements including a fuel electrode, a solid electrolyte membrane, and an air electrode on a base tube, and an interconnector that electrically connects the adjacent single elements. A method of manufacturing a solid oxide fuel cell comprising: forming the fuel electrode and the solid electrolyte membrane on an outer peripheral surface of the base tube; and the fuel electrode between the plurality of single elements. And forming the interconnector on the solid electrolyte membrane; sintering the fuel electrode, the solid electrolyte membrane and the interconnector together with the base tube; and on the co-sintered solid electrolyte A slurry mainly composed of a ceria compound represented by Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9) is applied to form an air electrode intermediate layer as the air electrode. Process and the air electrode On the _{tier, La (a + b) /} 2 Sr (1-a) / 2 Ca (1-b) / 2 Mn y O 3 ( where, y> 1,0.4 ≦ a ≦ 0.8,0 . 4 ≦ b ≦ 0.8), and the main component is a perovskite oxide in which the ratio of the total number of moles of La, Sr, and Ca to the number of moles of Mn is 0.92 or more and 0.98 or less. Applying slurry to form an air electrode conductive layer as the air electrode, sintering the air electrode intermediate layer and the air electrode conductive layer, and converting Mn in the air electrode conductive layer to the air electrode intermediate layer And diffusing to.

The solid oxide fuel cell of the present invention includes a plurality of single elements each including a fuel electrode, a solid electrolyte membrane, and an air electrode on a base tube, and an interconnector that electrically connects the adjacent single elements. An air electrode intermediate layer mainly comprising a ceria compound represented by Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9) on the solid electrolyte membrane; La _{(a + b) / 2} Sr _{(1-a) / 2} Ca _{(1-b) / 2} Mn _y O ₃ (where y> 1, 0.4 ≦ a ≦ ₎ formed on the air electrode intermediate layer 0.8, 0.4 ≦ b ≦ 0.8), and the ratio of the total number of moles of La, Sr and Ca to the number of moles of Mn is 0.92 or more and 0.98 or less. An air electrode conductive layer mainly composed of an object is laminated.
In this case, it is preferable that the air electrode intermediate layer contains the Mn diffused from the air electrode conductive layer by heat treatment.

In the solid oxide fuel cell, La _{(a + b) / 2} Sr _{(1-a) / 2} Ca _(wherein the air electrode has a two-layer structure and the air electrode conductive layer has an excess Mn with respect to the stoichiometric composition. _{1-b) / 2} Mn _y O ₃ An air electrode intermediate layer mainly composed of Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9) and the air electrode on a base tube on which a fuel electrode, a solid electrolyte membrane, and an interconnector are formed. When the conductive layer is formed and sintered, excess Mn in the air electrode conductive layer diffuses into the air electrode intermediate layer. In particular, if the air electrode conductive layer is formed such that the ratio of the total number of La, Sr, and Ca to Mn moles is 0.92 or more and 0.98 or less, the stoichiometric composition of the air electrode conductive layer is obtained. Compared with the case where it forms, the solid oxide fuel cell which has high electric power generation performance can be obtained.

  The solid oxide fuel cell of the present invention in which excess Mn in the air electrode conductive layer diffuses into the air electrode intermediate layer has higher power generation performance than the case where the stoichiometric air electrode conductive layer is formed. It becomes a solid oxide fuel cell.

1 is a schematic cross-sectional view of a solid oxide fuel cell produced by the production method of the present invention. Different _{La 0.5 Sr 0.25 Ca 0.25 Mn y} O 3 with A / B ratio is a graph showing the relationship between the operating voltage and current density of the solid electrolyte fuel cell using the air electrode conductive layer. Different _{La 0.5 Sr 0.25 Ca 0.25 Mn y} O 3 with A / B ratio is a graph showing the relationship between the output density current density of the solid electrolyte fuel cell using the air electrode conductive layer.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a cylindrical solid oxide fuel cell 10 according to the present embodiment. On the outer peripheral surface of the base tube 11, a single element 12 in which a fuel electrode 13, a solid electrolyte membrane 14, and air electrodes 15 a and 15 b are stacked in this order from the base tube 11 side is formed. In the solid oxide fuel cell 10 of this embodiment, fuel (hydrogen gas or the like) flows in the direction of reference numeral 17 inside the base tube 11 and air flows in the direction of reference number 18 outside the base tube 11. is there.

  The single element 12 is formed in the circumferential direction of the base tube 11, and a plurality of single elements 12 are arranged in parallel in the longitudinal direction of the base tube 11. A part of the solid electrolyte membrane 14 contacts the base tube 11 at one end of the single element 12 in the longitudinal direction of the base tube 11. However, the solid electrolyte membrane 14 of the single element 12 is not in contact with the fuel electrode 13 of the adjacent single element 12. An interconnector 16 that connects adjacent single elements is formed between each of the plurality of single elements 12. The interconnector 16 is in contact with the base tube 11 between the solid electrolyte membrane 14 of the single element 12 and the fuel electrode 13 of the adjacent single element 12.

  In the present embodiment, the air electrode is composed of an air electrode intermediate layer 15a and an air electrode conductive layer 15b in order from the base tube 11 side. The air electrode intermediate layer 15 a is provided in contact with the solid electrolyte membrane 14 and the interconnector 16. The air electrode conductive layer 15b is provided in contact with the air electrode intermediate layer 15a.

In the present embodiment, the base tube 11 is made of a porous material mainly composed of calcia-stabilized zirconia (CSZ) or a mixture of CSZ and nickel oxide (NiO) (CSZ + NiO). The base tube 11 is porous, and hydrogen gas used as fuel can flow from the inside of the base tube 11 to the outside (the fuel electrode 13 side).
The fuel electrode 13 is composed of a composite material of nickel oxide (NiO) and a zirconia-based electrolyte material. As the composite material, for example, a mixture of NiO and yttria stabilized zirconia (YSZ) is used. The thickness of the fuel electrode 13 is 120 μm, for example.
The solid electrolyte membrane 14 is electronically insulative, and is required to have gas tightness that prevents gas from passing and high ion permeability at high temperatures. Therefore, the solid electrolyte is mainly composed of Y ₂ O ₃ stabilized ZrO ₂ (YSZ) or the like. It is said. The thickness of the solid electrolyte membrane 14 is, for example, 80 μm.
The interconnector 16 is a conductive perovskite represented by M _1-z L _z TiO ₃ such as strontium titanate (M is an alkaline earth metal element, L is a lanthanoid element, 0.05 ≦ z ≦ 0.2). It is composed of a type oxide. For example, the interconnector material is Sr _1-z La _z TiO ₃ (0.05 ≦ z ≦ 0.2). The interconnector 16 is a dense film so that fuel gas and air are not mixed.
In the present embodiment, the materials of the base tube 11, the fuel electrode 13, the solid electrolyte membrane 14, and the interconnector 16 are not limited to the above materials.

The air electrode conductive layer 15b is composed of La _{(a + b) / 2} Sr _{(1-a) / 2} Ca _{(1-b) / 2} Mn _y O ₃ (where y> 1, 0.4 ≦ a ≦ 0.8, The main component is a perovskite oxide represented by 0.4 ≦ b ≦ 0.8). That is, the perovskite oxide has an excess of Mn as a B site relative to La, Sr, and Ca as an A site. In the perovskite oxide, the A / B ratio before sintering (the ratio of the total number of moles of La, Sr, and Ca to the number of moles of Mn) is 0.92 or more and 0.98 or less.
The film thickness of the air electrode conductive layer 15b is in the range of 500 μm to 1500 μm.

The air electrode intermediate layer 15a is mainly composed of a ceria compound represented by Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9), and contains Mn diffused from the air electrode conductive layer 15b. Yes. The film thickness of the air electrode intermediate layer 15a is 10 to 20 μm.

A method for manufacturing the solid oxide fuel cell 10 of the present embodiment will be described below.
(Base tube forming)
For example, a base tube 11 made of calcium stabilized zirconia (CSZ) is formed by an extrusion method.

(Formation of fuel electrode and solid electrolyte membrane)
A mixed powder of Ni + YSZ and an aqueous vehicle (water added with a dispersant, a binder, and an antifoaming agent) are mixed to produce a fuel electrode slurry. The mixing ratio of Ni and YSZ is appropriately selected depending on the performance required for the fuel electrode 13. The mixing ratio of the mixed powder and the water-based vehicle is appropriately selected in consideration of the thickness of the fuel electrode 13, the state of the fuel electrode film after slurry application, and the like.

  A YSZ powder and an aqueous vehicle are mixed to produce a solid electrolyte membrane slurry. The mixing ratio is appropriately selected in consideration of the thickness of the solid electrolyte membrane 14, the state of the solid electrolyte membrane after slurry application, and the like.

  The fuel electrode slurry and the solid electrolyte membrane slurry are applied by screen printing in the circumferential direction on the outer peripheral surface of the base tube 11 to form the fuel electrode 13 and the solid electrolyte membrane 14. At this time, as shown in FIG. 1, the laminated film of the fuel electrode 13 and the solid electrolyte film 14 is divided into a plurality of areas corresponding to a single element.

(Formation of interconnector)
M _1-z L _z TiO ₃ (M is an alkaline earth metal element, L is a lanthanoid element, 0.05 ≦ z ≦ 0.2) powder and an aqueous vehicle are mixed to prepare an interconnector slurry. The composition of the powder is appropriately selected according to the performance required for the interconnector. The mixing ratio of the powder and the water-based vehicle is appropriately selected in consideration of the state of the interconnector after applying the slurry.

  As shown in FIG. 1, the interconnector is formed in the circumferential direction of the outer peripheral surface of the base tube 11 between the adjacent laminated films in the base tube 11 on which the fuel electrode 13 and the solid electrolyte membrane 14 are formed. The slurry is applied by screen printing to form the interconnector 16.

(Co-sintering)
The base tube 11 on which the fuel electrode 13, the solid electrolyte membrane 14, and the interconnector 16 are formed is co-sintered in the atmosphere. The sintering temperature is specifically 1350 ° C. to 1450 ° C.

(Formation of air electrode intermediate layer)
Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9) powder and an aqueous vehicle are mixed to prepare an air electrode intermediate layer slurry. The mixing ratio of the powder and the water-based vehicle is appropriately selected in consideration of the state of the air electrode intermediate layer after slurry application.

  As shown in FIG. 1, the air electrode intermediate layer slurry is applied to the solid electrolyte membrane 14 of the base tube 11 after co-sintering along the circumferential direction of the base tube 11, and the air electrode intermediate layer 15a is applied. Form. The air electrode intermediate layer is formed by brushing, film formation by a roller, film formation by a dispenser, or the like.

(Formation of air electrode conductive layer)
La _{(a + b) / 2} Sr _{(1-a) / 2} Ca _{(1-b) / 2} Mn _y O ₃ (y> 1, 0.4 ≦ a ≦ 0.8, 0.4 ≦ b ≦ 0.8 A / B ratio: 0.92 to 0.98) The powder and the water-based vehicle are mixed to prepare a slurry for the air electrode conductive layer. The mixing ratio of the powder and the water-based vehicle is appropriately selected in consideration of the state of the air electrode conductive layer after slurry application.

As shown in FIG. 1, the air electrode conductive layer slurry is applied onto the air electrode intermediate layer 15a by screen printing along the circumferential direction of the base tube 11 to form the air electrode conductive layer 15b.
(Sintering of air electrode intermediate layer and air electrode conductive layer)

The base tube 11 on which the air electrode intermediate layer 15a and the air electrode conductive layer 15b are formed is sintered in the atmosphere. The sintering temperature is specifically 1100 ° C. to 1250 ° C. The sintering temperature here is lower than the co-sintering temperature after the base tube 11 to the interconnector 16 are formed.
Through the above process, the solid oxide fuel cell 10 in which the single element 12 is formed on the base tube 11 is obtained.

  The air electrode conductive layer 15b of the present embodiment contains an excessive amount of Mn with respect to the stoichiometric composition of the perovskite structure. Before sintering, excess Mn exists as free Mn in the air electrode conductive layer 15b. At the time of sintering, part of the free Mn in the air electrode conductive layer 15b diffuses into the air electrode intermediate layer 15a. For this reason, the air electrode intermediate layer 15a of the present embodiment includes Mn derived from the air electrode conductive layer.

A power generation test was conducted on solid oxide fuel cells using La _0.5 Sr _0.25 Ca _0.25 Mn _y O ₃ having different A / B ratios as the air electrode conductive layer.
A solid oxide fuel cell was fabricated using the following materials.
Base tube: Calcium stabilized zirconia (Ca addition amount 15 mol%)
Fuel electrode: Ni: YSZ (Y addition amount 8 mol%) = 50:50 (mass ratio), film thickness 120 μm
Solid electrolyte membrane: YSZ (Y addition amount 8 mol%), film thickness 80 μm
Interconnector: Sr _0.9 La _0.1 TiO ₃
Air electrode intermediate layer: Sm _0.2 Ce _0.8 O ₂ , film thickness 15 μm
Air electrode conductive _{layer: La 0.5 Sr 0.25 Ca 0.25 Mn} y O 3, thickness 1000 .mu.m, A / B ratio = 0.92,0.95,0.98,1

The co-sintering conditions of the base tube to the interconnector were 1400 ° C. for 4 hours, and the sintering conditions for the air electrode intermediate layer and the air electrode conductive layer were 1150 ° C. for 2 hours.
The length of the base tube was 850 mm, and the number of single elements formed on the base tube was 22 elements.

A power generation test was conducted using H ₂ + N ₂ as a fuel. The power generation test condition was 900 ° C.

FIG. 2 is a graph showing the relationship between the current density obtained in the power generation test using the solid oxide fuel cell and the operating voltage. In the figure, the horizontal axis represents current density and the vertical axis represents operating voltage. FIG. 3 is a graph showing the relationship between the current density and the output density obtained in the power generation test using the solid oxide fuel cell. In the figure, the horizontal axis represents current density and the vertical axis represents output density.

  As shown in FIGS. 2 and 3, the solid oxide fuel cell in which the air electrode conductive layer of A / B = 0.92 to 0.98 is formed is a solid state in which the air electrode conductive layer of A / B = 1 is formed. Compared to the electrolyte fuel cell, the operating voltage and output density at each current density are increased. In particular, at A / B = 0.95, high operating voltage and power density are obtained at each current density.

  In the solid oxide fuel cell in which the air electrode conductive layer of A / B = 0.92 to 0.98 was formed, elemental analysis of the air electrode intermediate layer with EPMA confirmed the presence of Mn. In addition, the detection position of Sm and the detection position of Mn substantially coincide.

From this, the free Mn in the air electrode conductive layer diffuses into the air electrode intermediate layer during sintering to form SmMnO ₃ (samarium manganate). SmMnO ₃ is a material exhibiting high electronic conductivity. In the solid oxide fuel cell having air electrode conductivity of A / B = 0.92 to 0.98, the air electrode intermediate layer contains SmCeO ₂ having ion conductivity and SmMnO ₃ having electron conductivity. As a result, the power generation performance is improved.

2 and 3, the result that the power generation performance of A / B = 0.92 is lower than that of A / B = 0.95 is obtained. From this result, when an air electrode conductive layer having an A / B ratio lower than 0.92 is formed, the diffusion amount of Mn increases, and a large amount of SmMnO ₃ is generated, while CeO ₂ that does not exhibit ionic conductivity is formed. As a result, excellent power generation performance cannot be obtained.

  Diffusion of Mn from the air electrode conductive layer occurs even during the power generation test, but in the power generation test, the solid oxide fuel cell in which the air electrode conductive layer of A / B = 0.92 to 0.98 was formed Sufficient power generation performance can be maintained even after 10,000 hours.

DESCRIPTION OF SYMBOLS 10 Solid electrolyte type fuel cell 11 Base tube 12 Single element 13 Fuel electrode 14 Solid electrolyte membrane 15a Air electrode intermediate layer 15b Air electrode conductive layer 16 Interconnector

Claims (3)

A plurality of single elements including a fuel electrode, a solid electrolyte membrane, and an air electrode on the base tube, and an interconnector that electrically connects the adjacent single elements,
An air electrode intermediate layer mainly composed of a ceria compound represented by Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9) on the solid electrolyte membrane; La _{(a + b) / 2} Sr _{(1-a) / 2} Ca _{(1-b) / 2} Mn _y O ₃ (where y> 1, 0.4 ≦ a ≦ 0. 8, 0.4 ≦ b ≦ 0.8), and the ratio of the total number of moles of La, Sr and Ca to the number of moles of Mn is 0.92 or more and 0.98 or less. A solid oxide fuel cell in which an air electrode conductive layer as a main component is laminated.   The solid electrolyte fuel cell according to claim 1, wherein the air electrode intermediate layer contains the Mn diffused from the air electrode conductive layer by heat treatment. A method for manufacturing a solid oxide fuel cell, comprising: a plurality of single elements including a fuel electrode, a solid electrolyte membrane, and an air electrode on a substrate tube; and an interconnector that electrically connects the adjacent single elements. ,
Forming the fuel electrode and the solid electrolyte membrane on the outer peripheral surface of the base tube;
Forming the interconnector on the fuel electrode and the solid electrolyte membrane between the plurality of single elements;
Sintering the fuel electrode, the solid electrolyte membrane and the interconnector together with the base tube;
On the co-sintered solid electrolyte, a slurry mainly containing a ceria compound represented by Sm _1-x Ce _x O ₂ (0.8 ≦ x ≦ 0.9) is applied, Forming an air electrode intermediate layer as an air electrode;
La _{(a + b) / 2} Sr _{(1-a) / 2} Ca _{(1-b) / 2} Mn _y O ₃ (where y> 1, 0.4 ≦ a ≦ 0.8) 0.4 ≦ b ≦ 0.8), and the ratio of the total number of moles of La, Sr and Ca to the number of moles of Mn is 0.92 to 0.98. Applying a slurry as a component and forming an air electrode conductive layer as the air electrode;
A method of manufacturing a solid oxide fuel cell, comprising: sintering the air electrode intermediate layer and the air electrode conductive layer, and diffusing Mn in the air electrode conductive layer into the air electrode intermediate layer.

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