JP5699911B2 - Electrolyte membrane and method for producing the same - Google Patents

Description

  The present invention relates to an electrolyte membrane and a manufacturing method thereof.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of the environment and can realize high energy efficiency, it has been widely developed as a future energy supply system.

  A solid oxide fuel cell (SOFC) has a structure in which a solid oxide electrolyte is sandwiched between a fuel electrode and an oxygen electrode. Here, the ceria-based electrolyte is known to have high oxygen ion conductivity. However, the ceria-based electrolyte has electronic conductivity in a reducing atmosphere. Therefore, Patent Document 1 includes a reduction preventing layer having a density higher than that of the fuel electrode layer between the solid electrolyte layer containing the ceria-based electrolyte and the fuel electrode layer, and uses yttria-stabilized zirconia as the reduction preventing layer. The technology is disclosed.

JP 2006-185698 A

  However, when the two-layer electrolyte of yttria-stabilized zirconia and ceria-based electrolyte is produced by sintering using the technique of Patent Document 1, yttria-stabilized zirconia and ceria-based electrolyte are dissolved in each other. As a result, a low ion conductive layer may be formed. In this case, the conductivity of the electrolyte membrane decreases.

  An object of this invention is to suppress the electrical conductivity fall in the electrolyte membrane provided with a zirconia type electrolyte and a ceria type electrolyte.

The method for producing an electrolyte membrane according to the present invention includes oxidizing a dopant element commonly added to the ceria-based electrolyte and the zirconia-based electrolyte between the ceria-based electrolyte green layer and the zirconia-based electrolyte green layer. In the manufacturing method of an electrolyte membrane including a preparation step of preparing a laminate in which a physical layer is disposed and a firing step of firing the laminate , the dopant element is a trivalent rare earth element, To do. According to the method for manufacturing an electrolyte membrane according to the present invention, a decrease in conductivity can be suppressed in an electrolyte membrane including a zirconia-based electrolyte and a ceria-based electrolyte.

Oxide layer before Symbol dopant element may be a yttria. In the preparation step, a green layer made of ceria is disposed between the oxide layer of the dopant element and the ceria-based electrolyte green layer, and between the oxide layer of the dopant element and the zirconia-based electrolyte green layer. A green layer made of zirconia may be disposed.

The electrolyte membrane according to the present invention is a ceria-based electrolyte layer, a zirconia-based electrolyte layer, a solid solution layer formed at an interface between the ceria-based electrolyte layer and the zirconia-based electrolyte layer, and the ceria-based electrolyte A solid solution layer in which the zirconia-based electrolyte is solid-solved with each other, wherein the dopant element of the ceria-based electrolyte layer is the same as the dopant element of the zirconia-based electrolyte layer , and the dopant element is 3 It is characterized by being a rare earth element . In the electrolyte membrane according to the present invention, a decrease in conductivity can be suppressed . Before Symbol dopant element may be a yttrium. At the interface between the ceria-based electrolyte layer and the solid solution layer and at the interface between the zirconia-based electrolyte layer and the solid solution layer , the ceria-based electrolyte layer is Ce _(1-x) M _x O ₂ (M = Y, x = 0.1 to 0.2, y = 0.06 to 0.12), and the zirconia-based electrolyte is Zr _(1-y) M _y O ₂ (M = Y, y = 0.06 to It may have the composition of 0.12).

  ADVANTAGE OF THE INVENTION According to this invention, electrical conductivity fall can be suppressed in the electrolyte membrane provided with a zirconia type electrolyte and a ceria type electrolyte.

1 is a schematic cross-sectional view of a solid oxide fuel cell. It is a schematic diagram for demonstrating the manufacturing method of the electrolyte membrane which concerns on 1st Embodiment. It is a schematic diagram for demonstrating the manufacturing method of the electrolyte membrane which concerns on 2nd Embodiment.

  Hereinafter, modes for carrying out the present invention will be described. First, a configuration of a fuel cell that is a target in each of the following embodiments will be described, and then a manufacturing method according to each embodiment will be described.

(Configuration of fuel cell)
FIG. 1 is a schematic cross-sectional view of a solid oxide fuel cell 100 targeted in the following embodiment. The fuel cell 100 has a structure in which the support 10, one electrode, the electrolyte membrane 30, and the other electrode are stacked in this order. In this embodiment, as an example, the fuel cell 100 has a structure in which the support 10, the anode 20, the electrolyte membrane 30, and the cathode 40 are laminated in this order.

  As the support 10, a member having gas permeability and capable of supporting the electrolyte membrane 30 can be used. In this embodiment, a porous substrate is used as an example of the support 10. As an example of the porous substrate, a porous metal plate having a plurality of holes 11 communicating with the upper surface and the lower surface is used. The material of the porous metal plate is not particularly limited. For example, a material (such as stainless steel) containing a component that forms an insulating oxide film on the surface by oxidation is used.

The material of the anode 20 is not particularly limited as long as it has electrode activity as an anode. For example, an electrode constituent material containing a solid oxide such as NiO / ZrO ₂ , NiO / CeO ₂ , NiO / BaZrO ₃ Can be used. The material of the cathode 40 is not particularly limited as long as it has electrode activity as a cathode. For example, an electrode constituent material containing a solid oxide such as LaMnO ₃ , LaCoO ₃ , La ₂ NiO ₄ , or SmCoO ₃ Can be used.

The electrolyte membrane 30 is a solid oxide electrolyte having oxygen ion conductivity. Specifically, the electrolyte membrane 30 includes a ceria-based electrolyte and a zirconia-based electrolyte. As the ceria-based electrolyte, Ce _1-x M _x O ₂ (0 ≦ x <1, M = Y (yttrium), Yb (ytterbium), Sm (samarium), Sc (scandium), etc.) is used. be able to. As the zirconia-based electrolyte, Zr _1-x M _x O ₂ (0 ≦ x <1, M = Y (yttrium), Yb (ytterbium), Sm (samarium), Sc (scandium), etc.) is used. be able to. The dopant added to the ceria-based electrolyte and the dopant added to the zirconia-based electrolyte are the same.

Note that the anode 20 preferably includes a component included in the electrolyte membrane 30. In this case, the thermal expansion coefficient of the anode 20 becomes close to the thermal expansion coefficient of the electrolyte membrane 30, and the separation between the anode 20 and the electrolyte membrane 30 can be further suppressed. For example, therefore, the material of the anode 20 is preferably NiO / ZrO ₂ or NiO / CeO ₂ .

The fuel cell 100 generates power by the following action. First, hydrogen (H ₂ ) is supplied to the support 10, and oxygen (O ₂ ) is supplied to the cathode 40. In the cathode 40, oxygen supplied to the cathode 40 and electrons supplied from the external electric circuit react to form oxygen ions. The oxygen ions are transferred to the anode 20 side through the electrolyte membrane 30.

On the other hand, the hydrogen supplied to the support 10 passes through the holes 11 of the support 10 and reaches the anode 20. The hydrogen that has reached the anode 20 emits electrons at the anode 20 and reacts with oxygen ions conducted through the electrolyte membrane 30 from the cathode 40 side to become water (H ₂ O). The emitted electrons are taken out by an external electric circuit. The electrons extracted outside are supplied to the cathode 40 after performing electrical work. Power generation is performed by the above operation.

  The ceria-based electrolyte has high oxygen ion conductivity in the middle temperature range (around 600 ° C.). Since the ceria-based electrolyte also has electronic conductivity in the middle temperature range, it also causes a decrease in power generation efficiency due to an increase in leakage current when the fuel cell 100 generates power. However, since the electrolyte membrane 30 includes a zirconia-based electrolyte having almost no electron conductivity, the electron conduction in the electrolyte membrane 30 is suppressed. Therefore, the electrolyte membrane 30 can increase the power generation efficiency of the fuel cell 100. However, when the ceria-based electrolyte and the zirconia-based electrolyte are fired at a high temperature, the ceria-based electrolyte and the zirconia-based electrolyte are dissolved in each other, thereby forming a low ion conductive layer. In this case, the conductivity of the electrolyte membrane 30 may be reduced. In the following embodiments, a method for manufacturing the electrolyte membrane 30 that can suppress a decrease in conductivity will be described.

(First embodiment)
FIG. 2A to FIG. 2C are schematic views for explaining the manufacturing method of the electrolyte membrane 30 according to the first embodiment. In the present embodiment, an example in which Y (yttrium) is added as the same dopant to the ceria-based electrolyte and the zirconia-based electrolyte will be described. As shown in FIG. 2A, an yttria green layer 32 made of Y ₂ O ₃ is laminated on a YDC green layer 31 made of ceria to which yttria is added (hereinafter referred to as YDC). A YSZ green layer 33 made of yttria stabilized zirconia (hereinafter referred to as YSZ) is laminated thereon. The YDC green layer 31, the yttria green layer 32, and the YSZ green layer 33 are, for example, powder layers.

  Next, as shown in FIG.2 (b), a baking process is implemented with respect to the laminated body of Fig.2 (a). Specifically, the laminate of FIG. 2A is heated to about 1300 ° C. By performing the firing treatment, each electrolyte powder is sintered and densified. FIG. 2C is a diagram showing the configuration of the electrolyte membrane 30 obtained by the firing process. As shown in FIG. 2C, the YDC green layer 31 is sintered, and a part of the yttria green layer 32 diffuses into the sintered body, whereby the YDC electrolyte layer 41 is formed. Further, the YSZ green layer 33 is sintered, and a part of the yttria green layer 32 is diffused into the sintered body, whereby the YSZ electrolyte layer 42 is formed. In addition, since mutual diffusion occurs between YDC and YSZ during the firing process, a solid solution layer 43 in which YDC and YSZ are dissolved together is formed between the YDC electrolyte layer 41 and the YSZ electrolyte layer 42. The

  By the way, according to the defect equilibrium theory, the dopant exhibits the maximum effect when completely dispersed freely. When both different types of dopants A and B are introduced, aggregate AB is formed in the solid solution, and complete free dispersion is inhibited. Therefore, by introducing a plurality of types of dopants at the same time, the conductivity is lowered as compared with the linear prediction. In this embodiment, since the dopant for the ceria-based electrolyte and the dopant for the zirconia-based electrolyte are the same, even if the solid solution layer 43 is formed, a decrease in the conductivity of the electrolyte membrane 30 is suppressed. Therefore, according to the manufacturing method according to the present embodiment, a decrease in conductivity can be suppressed in the electrolyte membrane 30 including the zirconia-based electrolyte and the ceria-based electrolyte.

  In the electrolyte membrane 30, the YDC electrolyte layer 41 has high oxygen ion conductivity, and the YSZ electrolyte layer 42 suppresses electron conduction in the electrolyte membrane 30. Furthermore, since the yttria green layer 32 is disposed between the YDC green layer 31 and the YSZ green layer 33, the formation of the solid solution layer 43 can be suppressed during the firing process. From the above, the electrolyte membrane 30 can achieve both high ionic conductivity and low electronic conductivity.

(Second Embodiment)
FIG. 3A to FIG. 3C are schematic views for explaining a manufacturing method of the electrolyte membrane 30 according to the second embodiment. Also in this embodiment, an example in which Y (yttrium) is added as the same dopant to the ceria-based electrolyte and the zirconia-based electrolyte will be described. As shown in FIG. 3A, a ceria green layer 34 made of CeO ₂ is laminated on the YDC green layer 31. On the ceria green layer 34, the yttria green layer 32 is laminated. On the yttria green layer 32, a zirconia green layer 35 made of ZrO ₂ is laminated. A YSZ green layer 33 is stacked on the zirconia green layer 35. Each layer is a powder layer as an example.

  Next, as shown in FIG.3 (b), a baking process is implemented with respect to the laminated body of Fig.3 (a). By performing the firing treatment, each electrolyte powder is sintered and densified. FIG. 3C is a diagram showing the configuration of the electrolyte membrane 30 obtained by the firing process. As shown in FIG. 3C, a YDC electrolyte layer 41 is formed by sintering the YDC green layer 31, and a YSZ electrolyte layer 42 is formed by sintering the YSZ green layer 33.

In addition, since Y ₂ O ₃ of the yttria green layer 32 is doped into CeO ₂ of the ceria green layer 34, the ceria green layer 34 constitutes a part of the YDC electrolyte layer 41 by a firing process. Further, since Y ₂ O ₃ of the yttria green layer 32 is doped into ZrO ₂ of the zirconia green layer 35, the zirconia green layer 35 constitutes a part of the YSZ electrolyte layer 42 by the firing treatment. However, since mutual diffusion occurs between YDC and YSZ, a solid solution layer 43 in which YDC and YSZ are dissolved together is formed between the YDC electrolyte layer 41 and the YSZ electrolyte layer 42.

  Also in this embodiment, since the dopant for the ceria-based electrolyte and the dopant for the zirconia-based electrolyte are the same, even if the solid solution layer 43 is formed, a decrease in the conductivity of the electrolyte membrane 30 is suppressed. Therefore, according to the manufacturing method according to the present embodiment, a decrease in conductivity can be suppressed in the electrolyte membrane 30 including the zirconia-based electrolyte and the ceria-based electrolyte. In the electrolyte membrane 30, the YDC electrolyte layer 41 has a high oxygen content. It has ion conductivity, and the YSZ electrolyte layer 42 suppresses electronic conduction in the electrolyte membrane 30. Furthermore, since the yttria green layer 32 is disposed between the YDC green layer 31 and the YSZ green layer 33, the formation of the solid solution layer 43 can be suppressed during the firing process. From the above, the electrolyte membrane 30 can achieve both high ionic conductivity and low electronic conductivity.

(Other examples)
Both the zirconia-based electrolyte and the ceria-based electrolyte vary greatly in conductivity depending on the dopant element type. In general, a dopant element that satisfies the following conditions exhibits high conductivity.
(1) The valence is one less than the parent element (+3 for Zr, Ce).
(2) The ion radius is close to the base ions (Zr ⁴⁺ , Ce ⁴⁺ ).
Examples of elements that satisfy the above conditions include Y (yttrium), Yb (ytterbium), Sm (samarium), Sc (scandium), and the like.

  Further, since the conductivity of the zirconia-based electrolyte is smaller than the conductivity of the ceria-based electrolyte, the total resistance of the zirconia / ceria-based composite film depends greatly on the zirconia-based resistance. For this reason, it is preferable to select a dopant that increases the conductivity of the zirconia-based electrolyte. From the above viewpoint, it is particularly preferable to use Y (yttrium).

Note that, at the interface between the ceria-based electrolyte film and the zirconia-based electrolyte film obtained by firing, the ceria-based electrolyte is Ce _(1-x) M _x O ₂ (M = Y, x = 0.1 to 0.2, y = has a composition of 0.06 to 0.12), zirconia electrolytes had a composition of _{Zr (1-y) M y} O 2 (M = Y, y = 0.06~0.12) Preferably it is. This is because in this composition range, the ceria-based electrolyte and the zirconia-based electrolyte exhibit high conductivity.

In order to suppress the diffusion of Y (yttrium), it is preferable that the dopant concentrations in the YDC green layer 31 and the YSZ green layer 33 match as much as possible. Therefore, when YSZ is (ZrO ₂ ) _(1-x) (Y ₂ O ₃ ) x and YDC is Ce _(1-x) Y _x O _2-δ , x = 0.03 to 0.12. It is preferable that x = 0.06 to 0.10.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible.

DESCRIPTION OF SYMBOLS 10 Support body 20 Anode 30 Electrolyte membrane 31 YDC green layer 32 Yttria green layer 33 YSZ green layer 34 Ceria green layer 35 Zirconia green layer 41 YDC electrolyte layer 42 YSZ electrolyte layer 43 Solid solution layer 100 Fuel cell

Claims (6)

A laminate is prepared in which an oxide layer of a dopant element added in common to the ceria-based electrolyte and the zirconia-based electrolyte is disposed between the ceria-based electrolyte green layer and the zirconia-based electrolyte green layer. A preparation process;
A method for producing an electrolyte membrane, comprising: a firing step of firing the laminate , wherein the dopant element is a trivalent rare earth element . 2. The method for producing an electrolyte membrane according to claim 1 , wherein the oxide layer of the dopant element is yttria. In the preparation step, a green layer made of ceria is disposed between the oxide layer of the dopant element and the ceria-based electrolyte green layer, and between the oxide layer of the dopant element and the zirconia-based electrolyte green layer. The method for producing an electrolyte membrane according to claim 1 , wherein a green layer made of zirconia is disposed. A ceria-based electrolyte layer;
A zirconia-based electrolyte layer;
A solid solution layer formed at an interface between the ceria-based electrolyte layer and the zirconia-based electrolyte layer, wherein the ceria-based electrolyte and the zirconia-based electrolyte are in solid solution with each other, and
In the electrolyte membrane in which the dopant element of the ceria-based electrolyte layer is the same as the dopant element of the zirconia-based electrolyte layer , the dopant element is a trivalent rare earth element . The electrolyte membrane according to claim 4 , wherein the dopant element is yttrium. At the interface between the ceria-based electrolyte layer and the solid solution layer and at the interface between the zirconia-based electrolyte layer and the solid solution layer , the ceria-based electrolyte layer is Ce _(1-x) M _x O ₂ (M = Y, x = 0.1 to 0.2, y = 0.06 to 0.12), and the zirconia-based electrolyte is Zr _(1-y) M _y O ₂ (M = Y, y = 0.06 to The electrolyte membrane according to claim 5, which has a composition of 0.12).

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