JP7075368B2 - Anode for solid oxide fuel cell - Google Patents

Description

The present invention relates to an anode for a solid oxide fuel cell, and _more particularly, a solid having a current collecting layer containing a composite oxide _{( YCZ} ) of Y2O3, _CeO2 and ZrO2 as a solid oxide electrolyte. Regarding the anode for oxide fuel cells.

Fuel cells are one of the powerful means for solving environmental and energy problems. In particular, solid oxide fuel cells (SOFCs) have a wide range of adaptability, from (1) high power generation efficiency, (2) compatible with a variety of fuels, and (3) small distributed power sources to large-scale thermal power alternative systems. It has advantages such as (4) no need for a Pt catalyst.
However, lowering the operating temperature (current operating temperature: 750 ° C.) is the key to the spread of SOFC. By lowering the temperature (for example, 600 ° C), (1) improvement of cell durability (chemical stability), (2) use of inexpensive housing (cheap stainless steel), and (3) shortening of start / stop time can be achieved. It will be possible.

Conventional SOFCs operate at 750 ° C and use yttria-stabilized zirconia (YSZ) as the electrolyte. Further, as the anode of the conventional SOFC, a composite of Ni as an electrode catalyst and YSZ as a solid oxide electrolyte (so-called “Ni—YSZ cermet”) is used. The crystal structure of YSZ is a fluorite structure, which is a crystal structure with high symmetry. Therefore, the oxygen ions in YSZ move due to the diffusion of pores in the three-dimensional direction.

YSZ has high ionic conductivity at high temperatures. Therefore, YSZ is exclusively used as the SOFC electrolyte and the solid electrolyte for the SOFC anode, and there are few examples in which other solid electrolytes are used. For example, Non-Patent Document 1 discloses an SOFC fuel electrode composed of Ni (56 wt%) -Ce _0.5 Zr _0.5 O _2-δ .

Non-Patent Document 2 describes Ni (5 wt%) -Ce _{0 to 1} Zr _{1 to 0} O _2-δ as a catalyst for steam reforming glycerol and producing a synthetic gas, although it is not an anode of SOFC. It has been disclosed. The document describes that Ce _0.5 Zr _0.5 O _2-δ is the most preferable point.
Further, Non-Patent Document 3 describes Ni (15 wt%) -MgO (10 wt%) -Ce _{0 to 1} Zr _{1 to 0} O as a catalyst for reforming methane together with carbon dioxide, although it is not an anode of SOFC. _2-δ is disclosed. This document describes the most preferable points of Ni-MgO-Ce _0.8 Zr _0.2 O _2-δ .

SOFC generally has a structure (stack structure) in which a single cell in which electrodes are bonded to both sides of an electrolyte is laminated. A current collector (also called a separator, an interconnector, etc.) having a gas flow path is arranged between each single cell.

In an SOFC having such a structure, when a fuel gas containing H ₂ is supplied to the anode flow path and air is supplied to the cathode flow path, O ^2- diffuses from the cathode through the electrolyte to the surface of the anode. As a result, O ^2- and H ₂ react on the surface of the anode to generate H ₂ O. Since H ₂ O is also an oxidizing agent, it causes oxidation of the electrode catalyst (Ni) contained in the anode. When Ni contained in the anode and existing near the contact surface with the current collector is oxidized, the contact resistance increases, which causes the battery performance to deteriorate. However, there has been no conventional example in which an anode capable of suppressing an increase in contact resistance due to oxidation of the surface of the anode on the current collector side has been proposed.

"Performance evaluation of CeO2-ZrO2-based SOFC fuel poles when directly supplying biogas", Denki Kagakkai 2017 (Spring) "Catalytic features of Ni supported on CeO2-ZrO2 solid solution in the steam reforming of glycerol for syngas production," RSC Adv., 2014, 4, 31142 "Key properties of Ni-MgO-CeO2, Ni-MgO-ZrO2, Ni-MgO-Ce1-xZrxO2 catalysts for the reforming of methane with carbon dioxid," Green Chem., 2018, 20, 1621

An object to be solved by the present invention is to provide a novel anode for a solid oxide fuel cell capable of suppressing an increase in contact resistance due to oxidation of the anode surface.

The anode for a solid oxide fuel cell according to the present invention in order to solve the above problems has the following configurations.
(1) The anode for a solid oxide fuel cell is
With the diffusion layer,
The current collector layer formed on the current collector side surface of the diffusion layer and
It includes an active layer formed on the electrolyte side surface of the diffusion layer.
(2) The diffusion layer is
Ni particles (A) and
It is composed of a cermet (A) containing an electrolyte particle (A) composed of yttria-stabilized zirconia.
(3) The current collector layer is
Ni particles (B) and
It is composed of a cermet (B) containing an electrolyte particle (B) composed of a composite oxide (YCZ) of Y ₂ O ₃ , CeO ₂ and ZrO ₂ .
(4) The active layer is
Ni particles (C) and
It is composed of a cermet (C) containing an electrolyte particle (C) composed of a solid oxide.

YCZ has oxygen storage / release ability in addition to its function as an oxide ion conductor. Therefore, when YCZ is applied to the current collector layer of the anode of SOFC, YCZ traps oxygen ions in the water vapor even if a large amount of water vapor is generated by power generation under high output. As a result, it is possible to suppress the oxidation of Ni in the vicinity of the surface of the anode on the current collector side and the increase in contact resistance between the anode and the current collector due to this.

It is a schematic diagram of the solid oxide fuel cell which used YCZ for the current collector layer of an anode. It is a schematic diagram of the conventional anode using Ni-YSZ cermet. It is a conceptual diagram of oxygen ion fixation by YCZ. FIG. 4A is an SEM image of the anode (Example 3). FIG. 4B is a Ce mapping result (EPMA analysis) of the anode (Example 3).

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Anode for solid oxide fuel cell]
The anode for a solid oxide fuel cell according to the present invention is
With the diffusion layer,
The current collector layer formed on the current collector side surface of the diffusion layer and
It includes an active layer formed on the electrolyte side surface of the diffusion layer.

[1.1. Diffusion layer]
In the present invention, the diffusion layer is composed of a cermet (A) containing Ni particles (A) and electrolyte particles (A) composed of yttria-stabilized zirconia. The diffusion layer is for supporting the active layer. In the anode containing the laminate of the diffusion layer and the active layer, the electrode reaction occurs mainly in the active layer. Therefore, the diffusion layer does not necessarily have to have high ionic conductivity.

That is, the diffusion layer is at least
(A) A function for supporting the active layer formed on the surface on the electrolyte side,
(B) The function of diffusing the fuel gas to the active layer,
(C) The function of transporting the electrons emitted in the active layer by the electrode reaction to the current collector, and
(D) It is necessary to have a function of discharging the water vapor generated in the active layer by the electrode reaction to the outside of the anode.
The composition of the diffusion layer is not particularly limited as long as it performs such a function.

[1.1.1. Ni particles (A)]
The content of the Ni particles (A) is not particularly limited as long as it functions as a diffusion layer. Generally, if the content of the Ni particles (A) is too small, the conductivity of the diffusion layer is lowered. Therefore, the content of Ni particles (A) is preferably 30 wt% or more. The content is preferably 40 wt% or more.
On the other hand, when the content of the Ni particles (A) becomes excessive, the content of the electrolyte particles (A) decreases, and the mechanical strength decreases. Therefore, the content of Ni particles (A) is preferably 70 wt% or less. The content is preferably 60 wt% or less.

[1.1.2. Electrolyte particles (A)]
In the present invention, the electrolyte particles (A) are composed of yttria-stabilized zirconia (YSZ). The composition of the electrolyte particles (A) is not particularly limited as long as it functions as a diffusion layer. That is, the electrolyte particles (A) may have the same composition as the electrolyte particles (C) contained in the active layer, or may have a different composition.

The Y ₂ O ₃ content of the electrolyte particles (A) is preferably 3 to 15 mol% in consideration of mechanical strength, a difference in thermal expansion coefficient from the electrolyte particles (C) used for the active layer, and the like.

[1.1.3. Porosity]
The porosity of the diffusion layer affects the gas diffusivity, strength, electron conductivity, etc. of the anode. Generally, if the porosity of the diffusion layer is too small, the gas diffusivity decreases. Therefore, the porosity of the diffusion layer is preferably 40% or more. The porosity is preferably 45% or more, more preferably 50% or more.
On the other hand, if the porosity of the diffusion layer becomes too large, the strength and electron conductivity will decrease. Therefore, the porosity of the diffusion layer is preferably 60% or less. The porosity is preferably 58% or less, more preferably 55% or less.

[1.2. Current collector layer]
The current collector layer is formed on the surface of the diffusion layer on the current collector side. In the present invention, the current collector layer is composed of a cermet (B) containing Ni particles (B) and electrolyte particles (B) composed of a composite oxide (YCZ) of Y ₂ O ₃ , CeO ₂ and ZrO ₂ . The current collector layer may further contain CZ particles made of CeO ₂ -ZrO ₂ solid solution (CZ).
The current collector layer is for transporting electrons from the diffusion layer to the current collector. Therefore, the current collector layer does not necessarily have to have high ionic conductivity. However, in order to suppress the increase in contact resistance due to the oxidation of the Ni particles (B), the material of the current collector layer needs to be a material having excellent oxidation resistance.

[1.2.1. Ni particles (B)]
The content of the Ni particles (B) is not particularly limited as long as it functions as a current collector layer. Generally, if the content of Ni particles (B) is too small, the conductivity of the current collector layer is lowered. Therefore, the content of Ni particles (B) is preferably 30 wt% or more. The content is preferably 40 wt% or more.
On the other hand, when the content of the Ni particles (B) becomes excessive, the content of the electrolyte particles (B) decreases, and the mechanical strength decreases. Therefore, the content of Ni particles (B) is preferably 70 wt% or less. The content is preferably 60 wt% or less.

[1.2.2. Electrolyte particles (B)]
[A. Oxygen storage / release capacity]
The electrolyte particles (B) are composed of a composite oxide (YCZ) of Y ₂ O ₃ , CeO ₂ and ZrO ₂ . CeO ₂ has the effect of imparting oxygen storage / release ability to ZrO ₂ . On the other hand, Y ₂ O ₃ introduces oxygen ion vacancies in ZrO ₂ or in a CeO ₂ -ZrO ₂ solid solution (hereinafter, also referred to as “CZ”) to improve the ionic conductivity of ZrO ₂ or CZ. It works. Therefore, when YCZ containing an appropriate amount of Y ₂ O ₃ and Ce O ₂ is used as the electrolyte particles (B), a current collector layer having both high power generation performance and high durability can be obtained.

The following formula (1) shows the reaction formula of the oxygen storage / release reaction of CZ. In formula (1), the reaction that proceeds to the right side represents an oxidation reaction, and the reaction that proceeds to the left side represents a reduction reaction.
CeO _2-x- ZrO ₂ + (x / 2) O ₂ ⇔ CeO ₂ -ZrO ₂ ... (1)
Ce ions dissolved in ZrO ₂ reversibly take a trivalent state (reduced state) and a tetravalent state (oxidized state) according to the oxygen partial pressure in the surrounding atmosphere. Can be done. Therefore, when the CZ is exposed to an oxidizing atmosphere, the CZ takes up oxygen ions in the atmosphere into the crystal lattice (see FIG. 3). On the other hand, when the CZ is exposed to the reducing atmosphere, the CZ releases the oxygen ions in the crystal lattice into the atmosphere. This point is the same for YCZ.

[B. composition]
The electrolyte particles (B) are particularly preferably those having a composition represented by the following formula (2).
Y _x Cey Zr _{1-xy O 2-δ} … (2)
however,
0 <x≤0.30,
0 <y ≦ 0.20,
δ is a value that maintains electrical neutrality.

[B. 1. 1. x]
In the formula (2), x represents the ratio of the number of moles of Y to the total number of moles of Y, Ce and Zr contained in the electrolyte particles (B). x is not particularly limited and may be more than 0.
However, if x becomes too large, the difference in thermal expansion coefficient from the electrolyte particles (A) contained in the diffusion layer becomes large, and the mechanical strength may decrease. Therefore, x is preferably 0.30 or less. x is preferably 0.20 or less.

[B. 2. 2. y]
In the formula (2), y represents the ratio of the number of moles of Ce to the total number of moles of Y, Ce and Zr contained in the electrolyte particles (B). As described above, Ce has an action of imparting oxygen storage / release ability to ZrO ₂ . Therefore, if y becomes too small, the oxidation resistance of the current collector layer decreases. Therefore, y is preferably more than 0. y is preferably 0.001 or more, more preferably 0.02 or more.

On the other hand, when y becomes too large, the activation energy of oxygen diffusion becomes large, and on the contrary, it becomes difficult for oxygen to diffuse (see Reference 1). Further, if y becomes too large, the sinterability is lowered and the mechanical properties of the current collector layer are lowered. Therefore, y is preferably 0.20 or less. y is preferably 0.1 or less, more preferably 0.08 or less.
[Reference 1] J. Phys. Chem. B 1997, 101, 1750-1753

[B. 3. 3. δ]
δ represents a value at which electrical neutrality is maintained. Zr is tetravalent, whereas Y is trivalent. In addition, Ce takes a tetravalent or trivalent value in ZrO ₂ . Therefore, when Y and Ce are dissolved in ZrO ₂ , a predetermined amount of oxygen vacancies are introduced so that the electrical neutrality is maintained.

[C. Ce / Zr ratio]
The "Ce / Zr ratio" means the ratio of the average molar concentration of Ce to the average molar concentration of Zr contained in the electrolyte particles (B).
The larger the Ce / Zr ratio, the better the durability of the current collector layer. In order to obtain such an effect, the Ce / Zr ratio is preferably 0.001 or more.

On the other hand, if the Ce / Zr ratio becomes too large, the ionic conductivity is rather lowered or the sinterability is lowered. Therefore, the Ce / Zr ratio is preferably 0.20 or less.

[12.3. Porosity]
The porosity of the current collector layer affects the gas diffusivity, strength, electron conductivity, etc. of the anode. In general, if the porosity of the current collector layer is too small, the gas diffusibility decreases. Therefore, the porosity of the current collector layer is preferably 40% or more. The porosity is preferably 45% or more, more preferably 50% or more.
On the other hand, if the porosity of the current collector layer becomes too large, the strength and electron conductivity will decrease. Therefore, the porosity of the current collector layer is preferably 60% or less. The porosity is preferably 58% or less, more preferably 55% or less.

[12.4. CZ particles]
CZ particles refer to particles made of CeO ₂ -ZrO ₂ solid solution. There are various methods for manufacturing a current collector layer containing YCZ. For example, when the surface of a diffusion layer made of Ni—YSZ cermet is impregnated with a slurry containing CZ particles and fired at a predetermined temperature, YSZ and CZ in the vicinity of the surface react with each other to generate YCZ. At this time, unreacted CZ particles may remain. The current collector layer may contain such unreacted CZ particles.

[1.3. Active layer]
The active layer is formed on the electrolyte side surface of the diffusion layer. In the present invention, the active layer is composed of a cermet (C) containing Ni particles (C) and electrolyte particles (C) made of a solid oxide. The active layer is a portion that serves as a reaction field for the electrode reaction. Therefore, the active layer needs to be excellent in electron conductivity and ion conductivity. Further, in order to obtain high durability, it is preferable that the active layer has excellent oxidation resistance.

[1.3.1. Ni particles (C)]
The Ni particles (C) function as an electrode catalyst and an electron conductor in the active layer. Therefore, if the content of Ni particles (C) is too small, the total resistance of the cell increases and the power generation output also decreases. Therefore, the content of Ni particles (C) is preferably 30 wt% or more.

On the other hand, when the content of the Ni particles (C) becomes excessive, the ratio of the electrolyte particles (C) in the active layer decreases, so that the total cell resistance increases and the power generation output also decreases. Therefore, the content of Ni particles (C) is preferably 70.0 wt% or less. The content of the Ni particles (C) is preferably 65.0 wt% or less, more preferably 60 wt% or less.

[1.3.2. Electrolyte particles (C)]
The composition of the electrolyte particles (C) is not particularly limited as long as it functions as an active layer. The electrolyte particles (C) may have the same composition as the electrolyte particles (A) and / or the electrolyte particles (B), or may have different compositions.

Examples of the electrolyte particles (C) include, for example.
(A) Yttria-stabilized zirconia containing Y ₂ O ₃ of 3 mol% or more and 15 mol% or less.
(B) YCZ, which satisfies the following equation (3),
and so on.
Y _{x'Cey '} Zr _1-x'-y' O _2-δ' … (3)
however,
0 <x'≤ 0.30,
0 <y'≤ 0.20,
δ'is a value that maintains electrical neutrality.

In particular, YCZ represented by the formula (3) has excellent oxidation resistance and is therefore suitable as the electrolyte particles (C) constituting the active layer. When the electrolyte particles (C) are made of YCZ, x'and y'preferably satisfy the following conditions.

[A. x']
In the formula (3), x'represents the ratio of the number of moles of Y to the total number of moles of Y, Ce and Zr contained in the electrolyte particles (C). As described above, Y has an effect of improving the ionic conductivity of ZrO ₂ . Therefore, if x'is too small, the ionic conductivity of the active layer will decrease. Therefore, x'preferably more than 0. x'is preferably 0.03 or more, preferably 0.05 or more, and more preferably 0.07 or more.

On the other hand, if x'becomes too large, the ionic conductivity will rather decrease. Therefore, x is preferably 0.30 or less. x is preferably 0.20 or less.

[B. y']
In the formula (3), y'represents the ratio of the number of moles of Ce to the total number of moles of Y, Ce and Zr contained in the electrolyte particles (C). As described above, Ce has an action of imparting oxygen storage / release ability to ZrO ₂ . Therefore, if y'is too small, the oxidation resistance of the active layer is lowered. Therefore, y'preferably more than 0. y'is preferably 0.001 or more.

On the other hand, when y'is too large, the activation energy of oxygen diffusion becomes large, and on the contrary, it becomes difficult for oxygen to diffuse (see Reference 1). On the other hand, if y'is too large, the sinterability is lowered and the mechanical properties of the active layer are lowered. Therefore, y'is preferably 0.20 or less.

[C. δ']
δ'represents a value at which electrical neutrality is maintained. Zr is tetravalent, whereas Y is trivalent. In addition, Ce takes a tetravalent or trivalent value in ZrO ₂ . Therefore, when Y and Ce are dissolved in ZrO ₂ , a predetermined amount of oxygen vacancies are introduced so that the electrical neutrality is maintained.

[D. Ce / Zr ratio]
The "Ce / Zr ratio" means the ratio of the average molar concentration of Ce to the average molar concentration of Zr contained in the electrolyte particles (C).
The larger the Ce / Zr ratio, the better the durability of the active layer. In order to obtain such an effect, the Ce / Zr ratio is preferably 0.001 or more. The Ce / Zr ratio is preferably 0.002 or more.

On the other hand, if the Ce / Zr ratio becomes too large, the ionic conductivity is rather lowered or the sinterability is lowered. Therefore, the Ce / Zr ratio is preferably 0.20 or less.

[1.3.3. Porosity]
The porosity of the active layer affects the power generation characteristics. If the porosity of the active layer is too small, the discharge characteristics of water vapor, which is a reaction product, deteriorate. Therefore, the porosity of the active layer is preferably 20% or more. The porosity is preferably 22% or more, more preferably 25% or more.
On the other hand, if the porosity of the active layer becomes too large, the three-phase interface becomes relatively small, and the power generation characteristics deteriorate. Therefore, the porosity of the active layer is preferably 40% or less. The porosity is preferably 35% or less, more preferably 30% or less.

[1.4. Characteristic]
[1.4.1. Ohmic resistance]
"Ohmic resistance" refers to the resistance component of the constituent material among the internal resistance of the fuel cell. By using YCZ for the current collector layer, it exhibits an oxygen storage effect and also improves oxygen diffusivity. Due to the oxygen storage action, the resistance to Ni oxidation is improved, and the decrease in the electron conductivity of the current collector layer is suppressed. As a result, the ohmic resistance is reduced.
Specifically, when the composition of the anode is optimized, the ohmic resistance becomes 0.12 Ω · cm or less. If the composition of the anode is further optimized, the ohmic resistance becomes 0.11 Ω · cm or less.

[1.4.2. Reaction resistance]
The "reaction resistance" refers to a resistance component due to the speed limit of a chemical reaction (electrode reaction) among the internal resistances of a fuel cell. When YCZ is used for the current collector layer, not only the ohmic resistance but also the reaction resistance is lowered.
Specifically, when the composition of the anode is optimized, the reaction resistance becomes 0.12 Ω · cm or less. If the composition of the anode is further optimized, the reaction resistance becomes 0.1 Ω · cm or less.

[2. Manufacturing Method of Anode for Solid Oxide Fuel Cell (1)]
The method for manufacturing an anode for a solid oxide fuel cell according to the first embodiment of the present invention is as follows.
(A) A diffusion layer molded body manufacturing step of manufacturing a diffusion layer molded body using a raw material mixture (A) containing the raw materials of Ni particles (A) and the electrolyte particles (A).
(B) A step of forming an active layer molded body using a raw material mixture (C) containing Ni particles (C) and raw materials of electrolyte particles (C) on the surface of the diffused layer molded body. ,
(C) A sintering step for sintering the obtained laminate, and
(D) YCZ is obtained by impregnating a surface of a sintered body composed of a diffusion layer / active layer on which an active layer is not formed with a slurry containing CZ particles and causing YSZ and CZ contained in the diffusion layer to undergo a solid phase reaction. And the current collector layer forming process to generate
(E) A reduction step of reducing the obtained sintered body and
It is equipped with.

[2.1. Diffusion layer molded body manufacturing process]
First, a diffusion layer molded body is produced using a raw material mixture (A) containing the raw materials of Ni particles (A) and the electrolyte particles (A) (diffusion layer molded body manufacturing step).

The type of the raw material of the electrolyte particles (A) is not particularly limited, and the optimum raw material can be selected according to the purpose.
For example, as a raw material for the electrolyte particles (A),
(A) YSZ powder having the desired composition,
(B) There is a mixture of ZrO ₂ powder and Y ₂ O ₃ powder blended so as to have a desired composition.
Examples of the raw material of the Ni particles (A) include NiO powder and the like.

Further, the raw material mixture (A) may contain a pore-forming material (for example, carbon powder). When NiO powder is added to the raw material mixture (A), it is reduced after the sintered body is produced. At that time, volume shrinkage occurs and pores are introduced into the sintered body. Therefore, the pore-forming material is not always necessary. However, when the pore-forming material is added to the raw material mixture (A), the degree of freedom in controlling the porosity is increased.

The method for producing the diffusion layer molded product is not particularly limited, and the optimum method can be selected according to the purpose. As a method for producing the diffusion layer molded body, for example,
(A) A method in which a slurry containing a raw material mixture (A) is tape-molded, a plurality of obtained green sheets are laminated, and the laminated body is pressure-bonded by hydrostatic pressure pressing.
(B) A method of press-molding the raw material mixture (A) with a die,
and so on.

[2.2. Active layer molded product manufacturing process]
Next, an active layer molded body is formed on the surface of the diffusion layer molded body using a raw material mixture (C) containing the raw materials of Ni particles (C) and the electrolyte particles (C) (active layer molded body manufacturing step). ).

The type of the raw material of the electrolyte particles (C) is not particularly limited, and the optimum raw material can be selected according to the purpose. As a raw material for the electrolyte particles (C),
(A) YSZ powder or YCZ powder having the desired composition,
(B) Mixture of YSZ powder blended to the desired composition and CeO ₂ powder and / or CZ powder (c) ZrO ₂ powder and Y ₂ O blended to the desired composition There is a mixture of ₃ powders, or a mixture of ZrO ₂ powder, Y ₂ O ₃ powder and CeO ₂ powder.
Since the details of the raw material of the Ni particles (C) are the same as those of the raw material of the Ni particles (A), the description thereof will be omitted.

Further, for the same reason as the raw material mixture (A), the raw material mixture (C) may contain a pore-forming material (for example, carbon powder).

The method for producing the active layer molded product is not particularly limited, and the optimum method can be selected according to the purpose. As a method for producing the active layer molded product, for example,
(A) A method in which a slurry containing a raw material mixture (C) is tape-molded, the obtained green sheet is laminated on a diffusion layer molded body, and the laminated body is pressure-bonded by hydrostatic pressure pressing.
(B) A method of preparing a slurry containing the raw material mixture (C) and screen-printing the slurry on the surface of the diffusion layer molded product.
and so on.

[2.3. Sintering process]
Next, the obtained laminate is sintered (sintering step). As for the sintering conditions, it is preferable to select the optimum conditions according to the raw material composition. Sintering is usually preferably carried out at 1000 ° C. to 1500 ° C. for 1 hour to 5 hours in an air atmosphere.
When two or more kinds of oxides are contained in the raw material mixture, a solid phase reaction proceeds during sintering to form a solid solution having a predetermined composition. Further, when the pore-forming material is contained in the raw material mixture, the pore-forming material disappears at the time of sintering, and pores are formed in the sintered body.

[2.4. Current collector layer formation process]
Next, the surface of the sintered body composed of the diffusion layer / the active layer on which the active layer is not formed is impregnated with the slurry containing the CZ particles. Then, this is heated to a predetermined temperature. As a result, YSZ and CZ contained in the diffusion layer undergo a solid phase reaction to generate YCZ. As the conditions for the solid phase reaction, it is preferable to select the optimum conditions according to the raw material composition. The solid phase reaction is usually preferably carried out at 500 ° C. to 1000 ° C. for 1 hour to 10 hours in an air atmosphere.

[2.5. Reduction process]
Next, the obtained sintered body is reduced (reducing step). As a result, the anode according to the present invention is obtained. The reduction treatment is performed to reduce the NiO particles contained in the sintered body to Ni particles. The reduction conditions are not particularly limited, and it is preferable to select the optimum conditions according to the composition of the anode, the electrolyte, and the cathode.
As will be described later, the solid oxide fuel cell is composed of an anode / electrolyte / reaction prevention layer / cathode junction. The reduction of the anode is usually done after joining the layers.

[3. Manufacturing Method of Anode for Solid Oxide Fuel Cell (2)]
The method for manufacturing an anode for a solid oxide fuel cell according to the second embodiment of the present invention is as follows.
(A) A diffusion layer molded body manufacturing step of manufacturing a diffusion layer molded body using a raw material mixture (A) containing the raw materials of Ni particles (A) and the electrolyte particles (A).
(B) Fabrication of an active layer molded body form in which an active layer molded body is formed by using a raw material mixture (C) containing Ni particles (C) and raw materials of electrolyte particles (C) on one surface of the diffusion layer molded body. Process and
(C) A current collector layer molding that forms a current collector layer molded body on the other surface of the diffusion layer molded body by using a raw material mixture (B) containing the raw materials of Ni particles (B) and the electrolyte particles (B). Body shape making process and
(D) A sintering step for sintering the obtained laminate, and
(E) A reduction step of reducing the obtained sintered body and
It is equipped with.

In the method according to the present embodiment, a laminated body composed of an active layer molded body / a diffusion layer molded body / a current collector layer molded body is produced, and the laminated body is integrally sintered. This point is different from the first embodiment. The method for forming the current collector layer molded body is the same as the method for forming the active layer molded body. Since other points are the same as those of the first embodiment, the description thereof will be omitted.

[4. Solid oxide fuel cell]
FIG. 1 shows a schematic diagram of a solid oxide fuel cell using YCZ for the current collector layer of the anode.
In FIG. 1, the solid oxide fuel cell (SOFC) 10 is
Electrolyte 12 and
The anode 14 bonded to one surface of the electrolyte 12 and
A cathode 16 bonded to the other surface of the electrolyte 12 and
The reaction prevention layer 18 inserted between the electrolyte 12 and the cathode 16 is provided.

The anode 14 includes a diffusion layer 14a, a current collector layer 14b formed on the surface of the diffusion layer 14a on the current collector side, and an active layer 14c formed on the surface of the diffusion layer 14a on the electrolyte 12 side. The details of the diffusion layer 14a, the current collector layer 14b, and the active layer 14c are as described above, and thus the description thereof will be omitted.

The materials of the electrolyte 12, the cathode 16, and the reaction prevention layer 18 are not particularly limited, and the optimum material can be selected according to the intended purpose.
For example, YSZ or the like can be used for the electrolyte 12. Further, (La, Sr) CoO ₃ (LSC), (La, Sr) (Co, Fe) O ₃ (LSCF) and the like can be used for the cathode 16.
The reaction prevention layer 18 is a layer for preventing a reaction caused by direct contact between the electrolyte 12 and the cathode 16, and is inserted as necessary. For example, when the electrolyte 12 is YSZ and the cathode 16 is LSC, it is preferable to use Gd-added CeO ₂ (GDC) for the reaction prevention layer 18.

[4. Action]
FIG. 2 shows a schematic diagram of a conventional anode using a Ni—YSZ cermet. In an SOFC whose anode is a Ni-YSZ cermet, when H ₂ gas is supplied to the anode and air is supplied to the cathode, O ^2- diffuses from the cathode side toward the anode side. As a result, the reaction of the following formula (4) proceeds on the surface of the anode.
H ₂ + O ^2- → H ₂ O + 2e-... ⁽ 4)

In order to reduce the cost and downsizing of SOFC, it is effective to increase the output per cell and reduce the number of cells in the stack. However, in power generation under high output, a large amount of water vapor is generated, and the water vapor oxidizes Ni in the anode. As a result, the electrode activity decreases. Further, when Ni is oxidized to NiO, the volume expands about 1.6 times, so that the anode may be peeled off or the cell may be destroyed.

On the other hand, YCZ has oxygen storage / release ability in addition to the function as an oxide ion conductor (see FIG. 3). Therefore, when YCZ is applied to the current collector layer of the anode of SOFC, YCZ traps oxygen ions in the water vapor even if a large amount of water vapor is generated by power generation under high output. As a result, it is possible to suppress the oxidation of Ni in the vicinity of the anode surface and the increase in contact resistance between the anode and the current collector due to this.

(Examples 1 to 4, Comparative Example 1)
[1. Cell production]
[1.1. Examples 1 to 4]
[1.1.1. Fabrication of SOFC cell]
Using a known method, SOFC cells in which the diffusion layer of the anode was made of Ni—YSZ cermet were prepared.

[1.1.2. Preparation of current collector layer containing YCZ]
A CZ slurry in which CZ particles having a concentration of 10 wt% were dispersed in ethanol was prepared. Next, the surface of the diffusion layer of the anode of the SOFC cell was impregnated with the CZ slurry. Further, the SOFC cell was dried at 100 ° C. and then calcined in the air at 800 ° C.

For CZ particles,
(A) 5 mol% CeO ₂ -ZrO ₂ particles (CZ0595) (Example 1),
(B) 9 mol% CeO ₂ -ZrO ₂ particles (CZ0991) (Example 2),
(C) 25 mol% CeO ₂ -ZrO ₂ particles (CZ2575) (Example 3), or
(D) 50 mol% CeO ₂ -ZrO ₂ particles (CZ5050) (Example 4),
Was used.

[1.2. Comparative Example 1]
The SOFC cell (without CZ slurry added) obtained in Example 1 was used as it was for the test.

[2. Test method]
[2.1. EPMA analysis]
An EPMA analysis of the cross section of the anode was performed.
[2.2. Ohmic resistance and reaction resistance]
The impedance of the SOFC cell was measured under the conditions of impedance amplitude: 100 mV and frequency range: 0.3 MHz to 0.1 Hz. From the obtained impedance, the total cell resistance (Ω · cm) was calculated. Further, the ohmic resistance (Ω · cm) and the reaction resistance (Ω · cm) were calculated from the total cell resistance (Ω · cm).

[2.3. Power generation output]
Fuel and oxidant were supplied to the anode and cathode of the SOFC cell, respectively, to generate electricity. 100% hydrogen was used as the fuel, and the hydrogen flow rate was 200 cc / min. Air was used as the oxidizing agent, and the air flow rate was set to 500 cc / min. The cell temperature was 700 ° C. The power generation output was calculated from the current value when the cell voltage was 0.8 V.

[3. result]
[3.1. EPMA analysis]
FIG. 4A shows an SEM image of the anode (Example 3). FIG. 4B shows the Ce mapping result (EPMA analysis) of the anode (Example 3). From FIG. 4, it was found that a current collector layer having a maximum length of 10 μm was formed in the diffusion layer by the above method.

[3.2. Cell resistance, power generation output]
Table 1 shows the power generation output, reaction resistance, and ohmic resistance. From Table 1, the following can be seen.
(1) The power generation output of Examples 1 to 4 was improved by 1.2 times or more as compared with Comparative Example 1.
(2) Both the reaction resistance and the ohmic resistance during power generation were reduced by adding CZ.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The anode for a solid oxide fuel cell according to the present invention can be used as an anode for a solid oxide fuel cell used in a household cogeneration system, an independent distributed power source, or the like.

Claims (9)

Anode for solid oxide fuel cells with the following configurations.
(1) The anode for a solid oxide fuel cell is
With the diffusion layer,
The current collector layer formed on the current collector side surface of the diffusion layer and
It includes an active layer formed on the electrolyte side surface of the diffusion layer.
(2) The diffusion layer is
Ni particles (A) and
It is composed of a cermet (A) containing an electrolyte particle (A) composed of yttria-stabilized zirconia.
(3) The current collector layer is
Ni particles (B) and
It is composed of a cermet (B) containing an electrolyte particle (B) composed of a composite oxide (YCZ) of Y ₂ O ₃ , CeO ₂ and ZrO ₂ .
(4) The active layer is
Ni particles (C) and
It is composed of a cermet (C) containing an electrolyte particle (C) composed of a solid oxide. The anode for a solid oxide fuel cell according to claim 1, wherein the electrolyte particles (B) have a composition represented by the following formula (2).
Y _x Cey Zr _{1-xy O 2-δ} … (2)
however,
0 <x≤0.30,
0 <y ≦ 0.20,
δ is a value that maintains electrical neutrality. The solid oxide fuel cell according to claim 1 or 2, wherein the electrolyte particles (B) have an average molar concentration ratio (Ce / Zr ratio) of Ce to Zr inside the particles of 0.001 or more and 0.2 or less. For anode. The anode for a solid oxide fuel cell according to any one of claims 1 to 3, wherein the current collecting layer further contains CZ particles composed of a CeO ₂ -ZrO ₂ solid solution (CZ). The anode for a solid oxide fuel cell according to any one of claims 1 to 4, wherein the current collector layer has a Ni particle (B) content of 30 wt% or more and 70 wt% or less. The anode for a solid oxide fuel cell according to any one of claims 1 to 5, wherein the ohmic resistance is less than 0.12 Ω · cm. The anode for a solid oxide fuel cell according to any one of claims 1 to 6, wherein the reaction resistance is less than 0.12 Ω · cm. The electrolyte particles (A) consist of yttria-stabilized zirconia containing Y ₂ O ₃ of 3 mol% or more and 15 mol% or less.
The anode for a solid oxide fuel cell according to any one of claims 1 to 7, wherein the content of the Ni particles (A) contained in the diffusion layer is 30 wt% or more and 70 wt% or less. The electrolyte particles (C) are
(A) Yttria-stabilized zirconia containing Y ₂ O ₃ of 3 mol% or more and 15 mol% or less, or
(B) It consists of YCZ that satisfies the following equation (3).
The anode for a solid oxide fuel cell according to any one of claims 1 to 8, wherein the content of the Ni particles (C) contained in the active layer is 30 wt% or more and 70 wt% or less.
Y _{x'Cey '} Zr _1-x'-y' O _2-δ' … (3)
however,
0 <x'≤ 0.30,
0 <y'≤ 0.20,
δ'is a value that maintains electrical neutrality.

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