JP2020149803A - Method for manufacturing fuel electrode-solid electrolyte layer composite - Google Patents

Abstract

To provide a fuel electrode-solid electrolyte layer composite excellent in ion conductivity and ion transport number.SOLUTION: A method for manufacturing a fuel electrode-solid electrolyte layer composite includes: a first step of obtaining a precursor in which a porous first solid electrolyte layer and a second solid electrolyte layer having a smaller porosity than the first solid electrolyte layer are integrated; and a second step of imparting catalyst particles into pores of the first solid electrolyte layer of the precursor. The second step includes firing the precursor at temperatures of 200-1,100°C, after a dispersion including the catalyst particles dispersed therein has been contained in the pores.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for producing a fuel electrode-solid electrolyte layer composite used in a fuel cell and / or a steam electrolysis cell.

A fuel cell is a device that generates electricity by an electrochemical reaction between a fuel gas such as hydrogen and air (oxygen), and can directly convert chemical energy into electricity, so that the power generation efficiency is high. Among them, solid oxide fuel cells (hereinafter referred to as SOFC) having an operating temperature of 700 ° C. or higher, particularly 800 ° C. to 1000 ° C., have a high reaction rate, and all the components of the cell structure are solid. Therefore, it is easy to handle. On the other hand, since the operating temperature is extremely high, it is mainly used for large-scale stationary power generation equipment or household power generation. At present, where energy saving is required, there is a demand for expanding the applications of SOFCs, which have high power generation efficiency, low noise, low emission of environmentally hazardous substances, and a simple cell structure.

As the solid electrolyte, a metal oxide having oxygen ion conductivity, for example, yttria-stabilized Zirconia (YSZ) is used. The operating temperature of SOFCs using oxygen ion conductive YSZ as an electrolyte is as high as 750 ° C to 1000 ° C. From the viewpoint of reducing the energy consumption required for heating and the selectivity of materials with high temperature resistance, the development of SOFCs that operate in the medium temperature range of 400 ° C to 600 ° C, which can use inexpensive general-purpose stainless steel, is underway. ..

The operating temperature of SOFC is high because oxide ions are transferred in a solid electrolyte made of a ceramic material. Therefore, PCFC (Protonic Ceramic Fuel Cell), a proton conductive oxide fuel cell, which uses hydrogen ions (protons) that can move even in a medium temperature range (for example, 400 ° C. to 600 ° C.) instead of oxide ions as charge carriers. ) Is being studied.

As solid electrolyte materials applicable to PCFC, Patent Document 1 and Patent Document 2 are metal oxides having a perovskite-type structure of ABO ₃ , which contain Ba at the A site and Zr at the B site and a trivalent substitution element. Discloses metal oxides including.

For example, perovskite oxides such as BaCe _0.8 Y _0.2 O _2.9 (BCY) and BaZr _0.8 Y _0.2 O _2.9 (BZY) exhibit high proton conductivity in the mid-temperature range. , Is expected as a solid electrolyte for medium temperature fuel cells.

Japanese Unexamined Patent Publication No. 2001-307546 JP-A-2007-197315

In order to improve the power generation characteristics of SOFC, it is preferable that the solid electrolyte layer is as thin as possible. Therefore, an electrolyte layer-electrode composite (bonded body) in which a solid electrolyte is formed on a cathode or an anode having increased mechanical strength may be used. Such a composite (bonded body) is called a cathode-supported solid electrolyte layer or an anode-supported solid electrolyte layer.

The anode-supported solid electrolyte layer generally forms a coating film containing the solid electrolyte on the surface of a molded product of a mixture of a nickel component (for example, NiO) serving as a hydrogen dissociation catalyst and the solid electrolyte, and is fired (cosintered). ) Is produced. The anode thus produced is initially dense. However, when used as an SOFC, NiO is reduced to Ni by hydrogen supplied to the anode as fuel, and changes to porous due to volume shrinkage that occurs at the same time as this reduction.

However, during co-sintering, Ni in the anode can diffuse to the solid electrolyte layer side. When the metal oxide is used for the solid electrolyte layer, Ni in the anode may diffuse into the metal oxide and the ionic conductivity may decrease. In addition, Ni diffused in the metal oxide also lowers the ion transport number, so that the leakage current can increase. Therefore, when the electrolyte layer-electrode composite is used in the steam electrolysis cell, the electrolysis efficiency tends to decrease.

In particular, when a proton conductive metal oxide having a perovskite-type structure doped with yttrium, such as BCY and BZY described above, is used for the solid electrolyte layer, it is usually at a high temperature of 1400 ° C. or higher in consideration of low sinterability. Co-sintering is performed. Therefore, Ni tends to diffuse into the solid electrolyte layer, and the proton conductivity tends to decrease.

One aspect of the present invention is a first step of obtaining a precursor in which a porous first solid electrolyte layer and a second solid electrolyte layer having a porosity smaller than that of the first solid electrolyte layer are integrated. A second step of imparting catalyst particles into the pores of the first solid electrolyte layer of the precursor is provided, and the second step comprises disperse the dispersion of the catalyst particles in the pores. The present invention relates to a method for producing a fuel electrode-solid electrolyte layer composite, which comprises firing at 200 ° C. to 1100 ° C. after being contained in.

By applying the method for producing a fuel electrode-solid electrolyte layer composite according to the present invention to the production of a fuel cell and / or a steam electrolytic cell, high ionic conductivity and high ion transport number can be obtained, and current efficiency is improved. ..

It is sectional drawing which shows typically the fuel cell manufactured by the manufacturing method which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the cell structure contained in the fuel cell of FIG. It is a photograph which shows the cross section in the thickness direction of the fuel electrode-solid electrolyte layer composite in the Example of this invention. FIG. 3 is an enlarged photograph of a part of the fuel electrode. FIG. 3 is an enlarged photograph of a part of the fuel electrode. It is a photograph which shows the cross section in the thickness direction of the fuel electrode-solid electrolyte layer composite in the comparative example. FIG. 5 is an enlarged photograph of a part of the fuel electrode.

[Explanation of Embodiments of the Invention]
First, the contents of the embodiments of the present invention will be listed and described.
(1) One embodiment of the present invention obtains a precursor in which a porous first solid electrolyte layer and a second solid electrolyte layer having a porosity smaller than that of the first solid electrolyte layer are integrated. It has one step and a second step of imparting catalyst particles into the pores of the first solid electrolyte layer of the precursor, and the second step contains a dispersion in which the catalyst particles are dispersed in the pores. The present invention relates to a method for producing a fuel electrode-solid electrolyte layer composite, which comprises firing at 200 ° C to 1100 ° C.

The fuel electrode is also called a hydrogen electrode and corresponds to an anode in a fuel cell. On the other hand, the cathode in a fuel cell is also called an air electrode or an oxygen electrode. The fuel electrode-solid electrolyte layer composite is also called a fuel electrode-solid electrolyte layer conjugate, an anode-solid electrolyte layer conjugate, or an anode-supported solid electrolyte layer.

The first solid electrolyte layer constitutes the fuel electrode in the fuel electrode-solid electrolyte layer composite. The second solid electrolyte layer constitutes the solid electrolyte layer in the fuel electrode-solid electrolyte layer composite. The fuel electrode-solid electrolyte layer composite is, for example, integrated with the first solid electrolyte layer and the second solid electrolyte layer by co-sintering in the first step, and then in the second step, the first solid electrolyte layer. It is manufactured by supporting catalyst particles on the inner side wall of the pores of the above.

According to the above embodiment of the present embodiment, the step of applying the catalyst particles (second step) can be performed at a relatively low temperature of 1100 ° C. or lower. Therefore, the components of the catalyst particles are suppressed from diffusing into the first solid electrolyte layer and the second solid electrolyte layer. Therefore, high ionic conductivity and ion transport number can be maintained, and when a fuel cell and / or a steam electrolysis cell is configured, a fuel cell and a steam electrolysis cell having excellent current efficiency can be realized.

The first solid electrolyte layer is formed porous in the first step, for example, by firing a mixture in which a pore-forming agent described later is added to the raw material of the first solid electrolyte layer. In this case, the pore diameter of the first solid electrolyte layer formed porously is determined by the particle diameter of the pore-forming agent. Further, the porosity of the first solid electrolyte layer can be controlled by the blending ratio of the pore-forming agent in the mixture.

The second solid electrolyte layer has a smaller porosity than the first solid electrolyte layer and is densely formed. A slight gap may be present in the second solid electrolyte layer, but it is preferably substantially non-porous.

The porosity of the first and second solid electrolyte layers is determined based on the cross-sectional image of the fuel electrode-solid electrolyte layer composite as well as the particle size of the catalyst particles. In the cross-sectional image, the ratio of the area of the region where the first solid electrolyte layer does not exist to the total area of the formed region of the first solid electrolyte layer is defined as the porosity of the first solid electrolyte layer. Similarly, the ratio of the area of the region where the second solid electrolyte layer does not exist to the total area of the formation region of the second solid electrolyte layer is defined as the porosity of the second solid electrolyte layer. Usually, the porosity of the first solid electrolyte layer and the porosity of the second solid electrolyte layer are significantly different, and the difference can be clearly confirmed by visually recognizing the cross-sectional image. For example, the porosity of the first solid electrolyte layer may be, for example, 30% or more and 80% or less, and may be 50% or more and 70% or less. On the other hand, the porosity of the second solid electrolyte layer is, for example, 10% or less, or 5% or less.

In the second step, the catalyst particles are imparted into the pores of the first solid electrolyte layer formed porously. The application of the catalyst particles can be performed by impregnating the precursor with a dispersion in which the catalyst particles are dispersed. The dispersion may include a dispersion medium, catalyst particles and, if necessary, a dispersant. Then, by heat-treating the precursor containing the dispersion, the catalyst particles are supported on the inner side wall of the pores of the first solid electrolyte layer.

The dispersion is, for example, a metal nanoink in which a colloid of metal nanoparticles, which is a catalyst particle, is dispersed in a dispersion medium. By adding the dispersant, the aggregation of the metal nanoparticles can be suppressed and the colloidal state can be stabilized. As the dispersant, for example, a compound having a polar functional group capable of coordinating with the metal particles and an organic group having a low affinity for the metal nanoparticles (for example, a hydrophobic organic group) can be used. Examples of the polar functional group include an amino group, a mercapto group, a hydroxyl group (including a phenolic hydroxyl group), a carbonyl group, an ester group, an oxygen-containing group such as a carboxyl group, and the like.

Water or an organic solvent can be used as the dispersion medium. Examples of the organic solvent include, but are not limited to, alcohols, ethers, esters, ketones, hydrocarbons (alicyclic hydrocarbons, aromatic hydrocarbons, etc.) and the like. As the metal nanoparticles, those formed by evaporating a metal material may be used, or those prepared by utilizing a chemical reaction in a liquid phase or a gas phase may be used.

When the temperature of the heat treatment is 1100 ° C. or lower, the components of the catalyst particles hardly diffuse into the first solid electrolyte layer and the second solid electrolyte layer, and the decrease in ion conductivity and ion transport number is suppressed. The impregnation of the dispersion and the heat treatment may be repeated a plurality of times.

The temperature of the heat treatment may be, for example, 200 ° C. to 1000 ° C., 400 ° C. to 1000 ° C., or 400 ° C. to 700 ° C. The heat treatment time may be 5 minutes or more and 4 hours or less, or 10 minutes or more and 2 hours or less.

The method for producing a fuel electrode-solid electrolyte layer composite of the present embodiment can be suitably used in the production of a fuel cell (SOFC) or a steam electrolytic cell operating in a medium temperature range of 400 ° C. to 600 ° C. The fuel cell contains, for example, a fuel electrode-solid electrolyte layer composite and an air electrode, and is oxidized to a cell structure or an air electrode in which a second solid electrolyte layer is interposed between the first solid electrolyte layer and the air electrode. It includes an oxidant flow path for supplying the agent and a fuel flow path for supplying fuel to the fuel electrode.

(2) The particle size of the catalyst particles contained in the dispersion is 10 nm to 500 nm, and the pore size of the first solid electrolyte layer may be 5 μm or more. In this case, the particle size of the catalyst particles is sufficiently smaller than the pore size of the first solid electrolyte layer.

Since the particle size of the catalyst particles is sufficiently smaller than the pore size of the first solid electrolyte layer, the catalyst particles can penetrate deep into the pores of the first solid electrolyte layer. Further, the catalyst particles can be formed in the first solid electrolyte layer so as to cover almost the entire inner wall surface of the pores. As a result, the surface area of the catalyst particles in contact with the fuel gas becomes very large, and high catalytic reaction efficiency can be obtained.

The particle size of the catalyst particles contained in the dispersion may be 50 nm to 100 nm.

Here, the pore diameter of the first solid electrolyte layer is determined by image analysis of an electron micrograph of a cross section of the fuel electrode-solid electrolyte layer composite. The pore diameters (diameters of circles having the same area as the cross-sectional area of the pores) at multiple positions (for example, 20 or more) of the first solid electrolyte layer were obtained from the cross-sectional photograph, and 5 of them were obtained in order from the one having the largest pore diameter. , And 5 in order from the one with the smallest pore diameter, for a total of 10 are removed, and the average value of the pore diameters at the remaining positions is calculated. The calculated average value is used as the pore diameter of the first solid electrolyte layer.
Similarly, for the particle size of the catalyst particles, a plurality of (for example, 20 or more) catalyst particles are extracted from the cross-sectional photograph, and each particle size (diameter of a circle having the same area as the cross-sectional area of the particles) is obtained. It is calculated as the remaining average value obtained by removing 5 particles in order from the one having the largest particle diameter and 5 particles in order from the one having the smallest particle diameter. With the use of fuel cells or steam electrolysis cells, the particle size of the catalyst particles can increase. However, the particle size of the catalyst particles at the time of production is at least equal to or less than the particle size of the catalyst particles calculated based on the cross-sectional photograph.

(3) The catalyst particles preferably contain nickel particles. For example, the catalyst particles may be metal Ni nanoparticles. The catalyst particles may be nickel oxide (NiO) nanoparticles.
When NiO nanoparticles are used, a reduction step for converting NiO into metallic Ni is required separately. Since the reduction step can be performed at a relatively low temperature of about 600 ° C. to 700 ° C., diffusion of the nickel component into the first solid electrolyte layer and the second solid electrolyte layer during the reduction step is suppressed. Therefore, high ionic conductivity and ionic transport number are maintained even after the reduction step.

The catalyst particles may contain a catalyst metal other than nickel. Examples of the catalyst metal other than nickel include copper (Cu), platinum (Pt), palladium (Pd), and an alloy of nickel and iron (Ni—Fe). The catalyst particles may be nanoparticles such as copper (Cu), platinum (Pt), palladium (Pd), and an alloy of nickel and iron (Ni—Fe).

(4) The first step includes a first precursor layer containing a raw material for the first solid electrolyte layer and a pore-forming material, and a second precursor layer containing a raw material for the second solid electrolyte layer and not containing the pore-forming material. , And may have a step of obtaining a laminated body in which, and a step of removing at least a part of a pore-forming agent. By removing the pore-forming agent from the first precursor layer, a porous first solid electrolyte layer is formed. On the other hand, since the second solid electrolyte layer is formed from the second precursor layer that does not contain a pore-forming agent, the porosity is smaller than that of the first solid electrolyte layer, and the layer is densely formed.

The pore-forming material is not particularly limited as long as it is a material that can be easily decomposed at a temperature equal to or lower than the sintering temperature, and a known material used in SOFC can be used. Examples of the pore-forming material include carbonaceous pore-forming materials and organic pore-forming materials. The shape of the pore-forming material is not particularly limited, and particulate or fibrous materials may be used.

The particle size of the pore-forming material defines the pore size of the porous first solid electrolyte layer. When a particulate pore-forming material is used, the average particle diameter is, for example, 1 μm to 200 μm, and may be 5 μm to 100 μm. The average particle size means the median diameter D50 in the volume-based particle size distribution. In addition to the particulate pore-forming agent, a fibrous pore-forming material may be included in the first precursor layer.

Examples of the carbonaceous pore-forming material include carbon particles such as graphite and carbon black, and carbon fibers such as carbon nanofibers. Examples of the organic pore-forming material include organic polymer particles and fibers. Examples of the organic polymer include synthetic resins such as acrylic resins, as well as natural polymers such as starch such as cornstarch. As the pore-forming material, one type may be used alone or two or more types may be used in combination.

(5) In the above (4), the first precursor layer is formed from the coating film of the first paste containing the raw material of the first solid electrolyte layer and the pore-forming material, and / or the second precursor layer is formed. , It may be formed from a coating film of a second paste containing the raw material of the second solid electrolyte layer and not containing the pore-forming material.

For example, by firing the laminate formed from the coating films of the first and second pastes, the pore-forming agent can be removed and a porous first solid electrolyte layer can be formed. The firing temperature may be 400 ° C. to 1000 ° C. or 400 ° C. to 800 ° C.

The first paste is obtained by dispersing the raw material of the first solid electrolyte layer and the pore-forming material in a dispersion medium such as water or an organic solvent. The second paste is obtained by dispersing the raw material of the second solid electrolyte layer in a dispersion medium, and it is not necessary to add a pore-forming agent. The first paste and / or the second paste may optionally contain additives such as binders, surfactants, and / or glutinates.

(6) In the above (4), at least one of the first precursor layer and the second precursor layer may be formed by pressure molding. For example, a pellet-shaped first precursor may be obtained by filling a mold with a powder obtained by mixing the raw material of the first solid electrolyte layer and the pore-forming material and pressurizing the powder, and the powder of the raw material of the second solid electrolyte layer may be obtained. A pellet-shaped second precursor may be obtained by filling the mold and pressurizing. More preferably, the powder obtained by mixing the raw material of the first solid electrolyte layer and the pore-forming material is packed in a mold to form the first precursor layer, and then the powder of the raw material of the second solid electrolyte layer is packed in the same mold. Alternatively, a laminated body may be obtained by forming a second precursor layer on the first precursor layer and simultaneously pressurizing the first precursor layer and the second precursor layer.

The fired product of the laminate can then be fired (co-fired) in an oxygen atmosphere at a high temperature of, for example, about 1500 to 1650 ° C. (preferably 1550 to 1650 ° C.). By this firing, it is possible to obtain a sintered body in which two layers of a porous first solid electrolyte layer and a dense second solid electrolyte layer are integrated.

(7) In the above (6), the first precursor layer and the second precursor layer may be pressure-molded in a state of being overlapped to obtain a laminated body. As a result, both the first precursor layer and the second precursor layer are pressure-molded at the same time to obtain a laminated body.

In the above (5) to (7), one of the first precursor layer and the second precursor layer may be formed by applying a paste, and the other may be formed by pressure molding. For example, in order to form a fuel electrode, a first precursor layer which is usually thickly formed may be formed by pressure molding, and a second precursor layer may be formed by applying a paste on the first precursor layer. ..

(8) Before the second step, the laminate may be fired at 1500 ° C. or higher. By firing, the first solid electrolyte layer and the second solid electrolyte layer can be integrated in a strongly bonded state. Since the firing is performed before the addition of the catalyst particles, the catalyst particles are not exposed to a high temperature of 1500 ° C. or higher, and the components of the catalyst particles diffuse into the first solid electrolyte layer (and the second solid electrolyte layer). The problem of doing is avoided. Therefore, the decrease in ionic conductivity and ionic transport number in the solid electrolyte layer is suppressed.

The upper limit of the firing temperature of the laminated body is not particularly limited, but may be 1800 ° C. or lower.

(9) The first solid electrolyte layer and the second solid electrolyte layer have a perovskite-type structure and contain a metal oxide represented by the following formula (1): A _x B _{1- y My} O _3-δ. It may include. Here, the element A is at least one selected from the group consisting of Ba, Ca and Sr. Element B is at least one selected from the group consisting of Ce and Zr. The element M is at least one selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In and Sc. δ is the amount of oxygen deficiency, which satisfies 0.95 ≦ x ≦ 1, 0 <y ≦ 0.5.

A metal oxide satisfying the above conditions has high proton conductivity even in a temperature range of 400 ° C. to 600 ° C. Therefore, by using this metal oxide in the first solid electrolyte layer and the second solid electrolyte layer, high proton conductivity and high ion transport number can be ensured. Therefore, high current efficiency can be exhibited when a fuel cell and / or a steam electrolysis cell is configured.

The ion transport number of the metal oxide may be 0.8 or more in a humidified oxygen atmosphere at 600 ° C. When the ion transport number is in such a range, higher current efficiency can be exhibited when the fuel electrode-solid electrolyte layer composite is applied to the steam electrolysis cell and / or the fuel cell. Here, the humidified oxygen atmosphere may be a mixed gas atmosphere of water vapor and oxygen, and the partial pressure of water vapor is 0.05 atm (5.0 × 10 ³ Pa) and the partial pressure of oxygen is 0.95 atm (9.5 × 10 ⁴ Pa). ) Atmosphere is sufficient.

The ion transport number is the ratio of the amount of electricity carried by anions and cations to the total amount of electricity carried by electrons, holes, cations, and anions when an electric current is passed through the electrolyte. The ion transport number is 1 when the total amount of electricity carried is equal to the amount of electricity carried by the anions and cations. For example, in the case of BZY, since protons, oxide ions and holes exist as carriers, the ion transport number indicates what percentage of the total electricity flows by the protons and oxide ions.

The element A may contain Ba, the element B may contain Zr, and the element M may contain Y. This makes it possible to improve the durability of the fuel electrode-solid electrolyte layer composite.

As described above, according to the method for producing the fuel electrode-solid electrolyte layer composite of the present embodiment, the diffusion of the catalyst component (for example, Ni) into the solid electrolyte layer is suppressed by the heat treatment at a high temperature during the production. , High ion conductivity and high ion transport number can be maintained. In particular, when a proton-conducting metal oxide is used as the solid electrolyte layer, the decrease in proton conductivity due to the diffusion of the catalyst component into the metal oxide is remarkably suppressed, and the fuel cell and steam electrolytic cell having excellent current efficiency Can be realized. However, the production method of the present embodiment is not limited to the case where the proton conductive solid electrolyte layer is used, and is also effective when the oxide ion conductive solid electrolyte layer is used. For example, an oxide ion conductive metal oxide containing lanthanum such as a lanthanum gallate-based oxide or a lanthanum silicate-based oxide has oxide ion conductivity due to the diffusion of Ni, which is a catalyst component, into the metal oxide. Is known to decrease. By applying the production method of the present embodiment, even when the above-mentioned lanthanum-based metal oxide is used as the first solid electrolyte layer and / or the second solid electrolyte layer, the oxide ion conductivity during production is reduced. It is possible to realize a fuel cell and a steam electrolytic cell that are suppressed and have excellent current efficiency.

[Details of Embodiments of the Invention]
Specific examples of the embodiments of the present invention will be described below with reference to the drawings as appropriate. It should be noted that the present invention is not limited to these examples, and is indicated by the appended claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. ..

(Fuel cell)
FIG. 1 shows a specific example of a fuel cell manufactured by using the method for manufacturing a fuel electrode-solid electrolyte layer composite of the present embodiment. FIG. 1 is a schematic view showing a cross-sectional structure of a fuel cell (solid oxide fuel cell).

The fuel cell 10 includes a cell structure 1. An example of the cross-sectional structure of the cell structure is schematically shown in FIG. As shown in FIG. 2, the cell structure 1 includes an air electrode (cathode) 2, a fuel electrode (anode) 3, and a solid electrolyte layer 4 interposed between them. The fuel electrode 3 and the solid electrolyte layer 4 are integrated to form a fuel electrode-solid electrolyte layer composite 5.

The fuel electrode 3 includes a porous first solid electrolyte layer. The solid electrolyte layer 4 contains a densely formed second solid electrolyte layer having a smaller porosity than the first solid electrolyte layer. The first solid electrolyte layer and the second solid electrolyte layer are integrated to form a complex.

In addition to the cell structure 1, the fuel cell 10 has an oxidant flow path 23 for supplying an oxidant to the air electrode 2 and a fuel flow for supplying fuel to the fuel electrode 3, as shown in FIG. A road 53 is provided. In the example shown in FIG. 2, the oxidant flow path 23 is formed by the air pole side separator 22, the fuel flow path 53 is formed by the fuel pole side separator 52, and the cell structure 1 is formed by the air pole side separator 22. , It is sandwiched between the fuel electrode side separator 52 and the fuel electrode side separator 52. The oxidant flow path 23 of the air pole side separator 22 is arranged so as to face the air pole 2 of the cell structure 1, and the fuel flow path 53 of the fuel pole side separator 52 is arranged so as to face the fuel pole 3. Will be done.

(1st solid electrolyte layer)
The first solid electrolyte layer constitutes at least a part of the fuel electrode 3. In the first solid electrolyte layer, a reaction (fuel oxidation reaction) of oxidizing a fuel gas (for example, hydrogen gas) introduced from a fuel flow path and releasing protons and electrons proceeds.

For the first solid electrolyte layer, a metal oxide having a perovskite-type structure (ABO ₃ phase) and having a composition represented by the above formula (1) can be used. Element A is contained in the A site of the perovskite type structure, and element B (which does not indicate boron) is contained in the B site. A part of the B site is replaced with the element M from the viewpoint of ensuring high proton conductivity.

The ratio x of element A to the total of element B and element M is preferably 0.95 ≦ x ≦ 1 from the viewpoint of ensuring high proton conductivity and ion transport number, and 0.98 ≦ x ≦ 1. More preferably. Further, when x does not exceed 1, the precipitation of the element A is suppressed, and the corrosion of the proton conductor due to the action of water can be suppressed. From the viewpoint of ensuring proton conductivity, y is preferably 0 <y ≦ 0.5, more preferably 0.1 <y ≦ 0.3.

The element A is at least one selected from the group consisting of Ba (barium), Ca (calcium) and Sr (strontium). Among them, the element A preferably contains Ba in that excellent proton conductivity can be obtained. The ratio of Ba to the element A is preferably 50 atomic% or more, and more preferably 80 atomic% or more. It is more preferable that the element A is composed only of Ba.

Element B is at least one selected from the group consisting of Ce (cerium) and Zr (zirconium). Among them, the element B preferably contains Zr from the viewpoint of durability. The ratio of Zr to the element B is preferably 50 atomic% or more, and more preferably 80 atomic% or more. It is more preferable that the element B is composed only of Zr.

The element M is selected from the group consisting of Y (yttrium), Yb (ytterbium), Er (erbium), Ho (holmium), Tm (thulium), Gd (gadrinium), In (indium) and Sc (scandium). At least one kind. The element M is a dopant, which causes oxygen defects, and the metal oxide having a perovskite-type structure exhibits proton conductivity.

In the formula (1), the oxygen deficiency amount δ can be determined according to the amount of the element M, for example, 0 ≦ δ ≦ 0.15. The ratio of each element in the metal oxide can be determined using, for example, wavelength dispersive X-ray analysis (Wavelength Dispersive X-ray Spectroscopy, hereinafter referred to as WDX) using an electron probe microanalyzer.

Specific examples of the metal oxide include yttrium-doped barium zirconate [Ba _x Zr _1-y Y _y O _3-δ (hereinafter referred to as BZY)] and yttrium-doped barium cerium [Ba _x]. Ce _1-y Y _y O _3-δ (BCY)], a mixed oxide of yttrium-doped barium zirconate / barium cerium [Ba _x Zr _1-y-z Ce _z Y _y O _3-δ (BZCY) )] And so on. As a specific example of BZY, BaZr _0.8 Y _0.2 O _2.9 (x = 1, y = 0.2, δ = 0.1) may be used. As a specific example of BCY, BaCe _0.8 Y _0.2 O _2.9 (x = 1, y = 0.2, δ = 0.1) may be used. BCY and BZY show high proton conductivity in the medium temperature range of 400 ° C to 600 ° C.

The first solid electrolyte layer can be formed by mixing the raw material of the metal oxide and a pore-forming agent (for example, carbon) and sintering them. At the time of sintering, the pore-forming agent is removed to obtain a porous first solid electrolyte layer.

Catalyst particles are supported on the inner side walls of the pores of the porous first solid electrolyte layer. A catalyst that promotes the hydrogen dissociation reaction is arranged on at least the surface of the catalyst particles. The particle size of the catalyst particles is, for example, 500 nm or less, 10 nm to 500 nm, and more preferably 50 nm to 200 nm. The catalyst particles are nanoparticles of, for example, Ni, Cu, Pt, Pd, an alloy containing these, and a catalyst metal such as a Ni—Fe alloy. The catalyst particles can be supported in the pores of the first solid electrolyte layer by impregnating the first solid electrolyte layer with nanoparticles in which nanoparticles of the catalyst metal are dispersed together with a dispersant in a dispersion medium.

The catalyst particles may be supported in the pores of the first solid electrolyte layer by impregnating the first solid electrolyte layer with a solution containing nickel (for example, an aqueous nickel nitrate solution). However, the method of impregnating the first solid electrolyte with a dispersion in which nanoparticles of the catalyst metal are dispersed can support a large amount of catalyst particles with a single impregnation, as compared with the method of impregnating with a nickel solution. preferable.

The thickness of the first solid electrolyte layer can be appropriately determined from, for example, 10 μm to 2 mm, and may be 10 μm to 100 μm.

(Second solid electrolyte layer)
The second solid electrolyte layer constitutes at least a part of the solid electrolyte layer 4. When the second solid electrolyte layer has proton conductivity, the second solid electrolyte layer moves the protons generated in the fuel electrode 3 (first solid electrolyte layer) to the air electrode 2.

As the second solid electrolyte layer, the proton conductive metal oxide having the above-mentioned perovskite type structure in the first solid electrolyte layer can be used. The composition of the metal oxide of the first solid electrolyte layer and the metal oxide of the second solid electrolyte layer may be the same or different. The second solid electrolyte layer can be formed, for example, by sintering the raw material of the metal oxide.

The thickness of the second solid electrolyte layer is, for example, 1 μm to 50 μm, preferably 3 μm to 20 μm. When the thickness of the second solid electrolyte layer is in such a range, the resistance of the solid electrolyte layer 4 can be suppressed low.
Binders and the like may be added to the first and second solid electrolyte layers together with the raw materials, if necessary.

(Air pole)
The air electrode 2 has a porous structure. When the second solid electrolyte layer (solid electrolyte layer 4) has proton conductivity, in the air electrode 2, the reaction between the protons conducted through the second solid electrolyte layer and the oxide ions (oxygen reduction reaction). Progresses. Oxide ions are generated by the dissociation of the oxidant (oxygen) introduced from the oxidant flow path.

As the material of the air electrode, a known material can be used. As the material of the air electrode, for example, a compound containing lanthanum and having a perovskite structure (ferrite, manganite, and / or cobaltite, etc.) is preferable, and among these compounds, those further containing strontium are more preferable. Specifically, lanthanum strontium cobalt ferrite _{(LSCF, La 1-x1 Sr} x1 Fe 1-y1 Co y1 O 3-δ1, 0 <x1 <1,0 <y1 <1, δ1 is the oxygen deficiency amount), Lantern Strontium Manganite (LSM, La _1-x2 Sr _x2 MnO _3-δ1 , 0 <x2 <1, δ1 are oxygen deficient amounts), Lantern Strontium Cobaltite (LSC, La _1-x3 Sr _x3 CoO _3-δ1) , 0 <x3 ≦ 1, δ1 is the amount of oxygen deficiency) and the like. From the viewpoint of promoting the reaction between the proton and the oxide ion, the air electrode may contain a catalyst such as Pt. When a catalyst is included, the air electrode can be formed by mixing the catalyst and the above materials and sintering them.

The air electrode can be formed, for example, by sintering the raw materials of the above materials. If necessary, a binder, an additive, and / or a dispersion medium may be used together with the raw material.
The thickness of the air electrode is not particularly limited, but can be appropriately determined from, for example, 5 μm to 2 mm, and may be about 5 μm to 40 μm.

In FIGS. 1 and 2, the thickness of the first solid electrolyte layer constituting the fuel electrode 3 is thicker than the thickness of the air electrode 2, and the fuel electrode 3 (first solid electrolyte layer) is the solid electrolyte layer 4 (third). 2 Solid electrolyte layer) As a result, it functions as a support for supporting the cell structure 1. The thickness of the fuel electrode 3 does not necessarily have to be thicker than that of the air electrode 2. For example, the thickness of the fuel electrode 3 may be about the same as the thickness of the air electrode 2.

(Oxidizing agent flow path and fuel flow path)
The oxidant flow path 23 has an oxidant inlet into which the oxidant flows and an oxidant discharge port for discharging water generated by the reaction, an unused oxidant, and the like (neither is shown). Examples of the oxidizing agent include a gas containing oxygen. The fuel flow path 53 has a fuel gas inlet into which a fuel gas containing water vapor and a hydrocarbon gas flows in, and a fuel gas discharge port for discharging unused fuel, H ₂ O, N ₂ , CO _2, etc. generated by the reaction. Has (neither is shown).

(Separator)
When a plurality of cell structures are laminated to form a fuel cell, for example, the cell structure 1, the air electrode side separator 22, and the fuel electrode side separator 52 can be laminated as one unit. The plurality of cell structures 1 may be connected in series by, for example, a separator having gas flow paths (oxidizer flow path and fuel flow path) on both sides.

Examples of the material of the separator include heat-resistant alloys such as stainless steel, nickel-based alloys, and chromium-based alloys in terms of electrical conductivity and heat resistance. Of these, stainless steel is preferable because it is inexpensive. In a proton conductive solid oxide fuel cell (PCFC: Protomic Ceramic Fuel Cell), since the operating temperature is about 400 ° C. to 600 ° C., stainless steel can be used as a material for the separator.

(Current collector)
The fuel cell 10 may include a fuel pole side current collector 51 that is arranged between the fuel pole 3 and the fuel pole side separator 52 and is in contact with the fuel pole 3. In addition to the current collecting function, the fuel electrode side current collector 51 fulfills a function of diffusing and supplying the fuel gas introduced from the fuel flow path 53 to the fuel electrode 3. The fuel cell 10 may also include an air electrode side current collector 21 that is arranged between the air electrode 2 and the air electrode side separator 22 and is in contact with the air electrode 2. In addition to the current collecting function, the air electrode side current collector 21 functions to diffuse and supply the oxidant gas introduced from the oxidant flow path 23 to the air electrode 2.
That is, the air pole side current collector 21 forms at least a part of the oxidant flow path 23, and the fuel pole side current collector 51 forms at least a part of the fuel flow path 53. Therefore, it is preferable that each current collector has a structure having sufficient air permeability.

Examples of the structure used for the air pole side current collector and the fuel pole side current collector include a metal porous body containing silver, a silver alloy, nickel, a nickel alloy and the like, a metal mesh, a punching metal, an expanded metal and the like. Be done. Of these, a metal porous body is preferable in terms of light weight and breathability. In particular, a metal porous body having a three-dimensional network-like structure is preferable. The three-dimensional network-like structure refers to a structure in which rod-shaped or fibrous metals constituting a metal porous body are three-dimensionally connected to each other to form a network. For example, a sponge-like structure or a non-woven fabric-like structure can be mentioned.

The metal porous body can be formed, for example, by coating a resin porous body having continuous voids with the metal as described above. When the resin inside is removed after the metal coating treatment, a cavity is formed inside the skeleton of the porous metal body, and the cavity becomes hollow. As a commercially available metal porous body having such a structure, nickel "Celmet" manufactured by Sumitomo Electric Industries, Ltd. or the like can be used.

The fuel cell can be manufactured by a known method except that the above cell structure is used.

When the fuel cell 10 contains a proton-conducting solid electrolyte (first solid electrolyte layer and second solid electrolyte layer), it can be operated in a medium temperature range of less than 700 ° C., preferably about 400 ° C. to 600 ° C. Is. In this case, the catalyst particles in the first solid electrolyte layer are not exposed to a high temperature (for example, exceeding 800 ° C.) even when the fuel cell is operated, so that the catalyst component diffuses into the first solid electrolyte layer. The decrease in proton conductivity and ion transport number due to this is also suppressed. Therefore, the performance deterioration due to the use of the fuel cell 10 is suppressed.

Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1]
(1) Preparation of fuel electrode-solid electrolyte layer composite BZY (BaZr _0.8 Y _0.2 O _2.9 ) powder containing 30% by volume and spherical carbon (average particle size 50 μm) containing 70% by volume. Binder (Polyvinyl Butyral manufactured by Wako Pure Chemical Industries, Ltd.), Dispersant (Nichiyu Co., Ltd., Marialim AKM-0531), Plasticizer (Nacalai Tesque Co., Ltd., Di-n-butyl phthalate), Ethanol, and toluene are mixed well. The slurry was dried at 60 ° C. and then pulverized using a pulverizing propeller or the like rotating at high speed to obtain a powder for the first solid electrolyte layer.
Further, BZY (BaZr _0.8 Y _0.2 O _2.9 ) and a binder (NCB-166, manufactured by DIC Corporation) are mixed at a mass ratio of 7: 1, and then a sieve having an opening of 150 μm is used. Sieve was performed to obtain a powder for the second solid electrolyte layer.

The powder for the first solid electrolyte layer was packed in a mold having an inner diameter of 19 mm and a depth of about 3 mm and lightly compacted. The powder for the second solid electrolyte layer was spread in a gap of several tens to several hundreds of μm formed by compaction, pressed at about 220 MPa, and uniaxially molded into a cylindrical pellet. The molded product was heated to 750 ° C. at a rate of 0.3 ° C./min and held for 2 hours to remove spherical carbon and binder. Then, it was sintered in an oxygen atmosphere at 1600 ° C. to obtain a precursor in which the first solid electrolyte layer and the second solid electrolyte layer were integrated.

A Ni nanoparticle dispersion liquid in which Ni nanoparticles (average particle diameter 100 nm) were dispersed in butyl carbitol (dispersion medium) was prepared. The first solid electrolyte layer of the precursor was impregnated with the Ni nanoparticle dispersion liquid. The precursor impregnated with the Ni nanoparticle dispersion liquid in the first solid electrolyte layer was heat-treated at 600 ° C. for 1 hour in an argon atmosphere. The impregnation and heat treatment were repeated three times to prepare a fuel electrode-solid electrolyte layer composite X.

(2) Preparation of fuel cell Next, on the surface of the second solid electrolyte layer, a powder of LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ ), which is a material for the air electrode. The LSCF paste, which is a mixture of and an organic solvent (butyl carbitol acetate), was screen-printed and dried at 120 ° C. to form an air electrode. As a result, a cell structure was obtained.
The thickness of the air electrode was 10 μm.

A stainless steel fuel electrode side separator having a gas flow path is laminated on the surface of the fuel electrode (first solid electrolyte layer) of the cell structure obtained above, and the gas flow path is provided on the surface of the air electrode. A stainless steel cathode-side separator was laminated to prepare a fuel cell having the configuration shown in FIG.
One end of the lead wire was joined to each of the anode side separator and the cathode side separator. The other end of each lead was pulled out of the fuel cell and connected to a measuring instrument so that the current and voltage values between each lead could be measured.

[Comparative Example 1]
(1) Preparation of fuel electrode-solid electrolyte layer composite NiO and BZY (BaZr _0.8 Y _0.2 O _2.9 ) powder are mixed with a binder (polyvinyl alcohol) and a surfactant (polycarboxylic acid type interface). The activator) and an appropriate amount of ethanol were mixed with a ball mill and granulated. At this time, NiO and BZY were mixed at a volume ratio of 70:30. The amounts of the binder and the surfactant were 10 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the total amount of NiO and BZY. The obtained granulated product was uniaxially molded to obtain a molded product having a first precursor layer (diameter 16 mm, thickness 0.7 mm).

By mixing BZY (BaZr _0.8 Y _0.2 O _2.9 ), binder (ethyl cellulose), surfactant (polycarboxylic acid type surfactant), and an appropriate amount of butyl carbitol acetate. A paste of two solid electrolyte layers was prepared. The amounts of the binder and the surfactant were 6 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the second proton conductor. The paste of the second solid electrolyte layer was applied to one surface of the molded product by screen printing.

The molded product after forming the coating film was heated at 750 ° C. for 10 hours to perform a binder removal treatment. Next, the molded product was calcined at 1600 ° C. for 10 hours in an air atmosphere to prepare a fuel electrode-solid electrolyte layer composite Y.
Other than this, a fuel cell was prepared and evaluated in the same manner as in Example 1. The manufactured fuel cell was incorporated into an evaluation device, and hydrogen gas was passed through the fuel electrode to convert NiO into Ni.

FIG. 3 is a reflected electron image of SEM, and shows a cross-sectional photograph of the fuel electrode-solid electrolyte layer composite X in the thickness direction in Example 1. In FIG. 3, a black (or dark gray), substantially circular portion in the fuel electrode 3 (first solid electrolyte layer) is a cross section of a pore, and a white portion indicates a BZY layer or catalyst particles. ..

FIG. 4A is an enlarged view in which the vicinity of a certain pore is enlarged 2000 times in FIG. 3, and FIG. 4B is a cross-sectional view in which a part of FIG. 4A is further enlarged and enlarged 10000 times with respect to FIG. is there. It can be seen that the inner side wall of the pore is covered with Ni particles. As shown in FIG. 4B, Ni particles are deposited on the inner side wall in the state of nanoparticles to form a layer of nanoparticles. There are gaps between the nanoparticles.

The fuel cell using the above-mentioned fuel electrode-solid electrolyte layer composite X showed a good OCV (open circuit voltage) of about 1.05 V and a high current density even under operating conditions of 600 ° C.

On the other hand, FIG. 5 is a reflected electron image of SEM, which is a cross-sectional photograph in the thickness direction of the fuel electrode-solid electrolyte layer composite Y obtained by disassembling the evaluated fuel cell in Comparative Example 1. .. FIG. 5 is an enlarged view enlarged 1000 times, and FIG. 6 is an enlarged view obtained by magnifying the vicinity of a certain pore by 5000 times. In FIGS. 5 and 6, the black portion indicates the void, the gray portion indicates the nickel metal, and the white (lighter gray) portion indicates the BZY layer.

The surface of the Ni particles is exposed in a part of the inner wall surface of the pores. However, the particle size of the Ni particles is large, and the reaction area of the catalyst is small even though Ni occupies a considerable amount of the first solid electrolyte layer. Further, in the production of the composite Y, a part of Ni is diffused into the first and second solid electrolyte layers due to the high temperature of 1600 ° C. during sintering, and the proton conductivity is lowered.

The OCV of the fuel cell using the fuel electrode-solid electrolyte layer composite Y was 0.93 to 1.02 V under the operating conditions of 600 ° C. The variation in OCV is considered to be due to the difference in the density of the second solid electrolyte layer.

The fuel electrode-solid electrolyte layer composite according to the embodiment of the present invention is suitable for use in a solid electrolyte fuel cell (SOFC), and is particularly suitable for SOFC operating in a medium temperature range of 400 ° C. to 600 ° C.

1: Cell structure 2: Air electrode 3: Fuel electrode 4: Solid electrolyte layer 5: Fuel electrode-solid electrolyte layer composite 10: Fuel cell 21, 51: Current collector 22, 52: Separator 23: Oxidizing agent flow path 53: Fuel flow path

Claims (9)

A first step of obtaining a precursor in which a porous first solid electrolyte layer and a second solid electrolyte layer having a porosity smaller than that of the first solid electrolyte layer are integrated.
It has a second step of imparting catalyst particles into the pores of the first solid electrolyte layer of the precursor.
A method for producing a fuel electrode-solid electrolyte layer composite, wherein the second step comprises containing a dispersion in which the catalyst particles are dispersed in the pores and then firing at 200 ° C to 1100 ° C. The particle size of the catalyst particles contained in the dispersion is 10 nm to 500 nm.
The method for producing a fuel electrode-solid electrolyte layer composite according to claim 1, wherein the pore diameter of the first solid electrolyte layer is 5 μm or more. The method for producing a fuel electrode-solid electrolyte layer composite according to claim 1 or 2, wherein the catalyst particles contain nickel particles. The first step includes a first precursor layer containing the raw material of the first solid electrolyte layer and a pore-forming material, and a second precursor containing the raw material of the second solid electrolyte layer and not containing the pore-forming material. The process of obtaining a laminated body in which layers are laminated,
The method for producing a fuel electrode-solid electrolyte layer composite according to any one of claims 1 to 3, further comprising a step of removing at least a part of the pore-forming material. The first precursor layer is formed from a coating film of a first paste containing the raw material of the first solid electrolyte layer and the pore-forming material, and / or the second precursor layer is formed of the second solid. The method for producing a fuel electrode-solid electrolyte layer composite according to claim 4, which is formed from a coating film of a second paste containing a raw material for an electrolyte layer and not containing the pore-forming material. The method for producing a fuel electrode-solid electrolyte layer composite according to claim 4, wherein at least one of the first precursor layer and the second precursor layer is formed by pressure molding. The fuel electrode-solid electrolyte layer composite according to claim 6, wherein in the first step, the first precursor layer and the second precursor layer are pressure-molded in a state of being overlapped to obtain the laminated body. Manufacturing method. The method for producing a fuel electrode-solid electrolyte layer composite according to any one of claims 4 to 7, wherein the laminate is fired at 1500 ° C. or higher before the second step. The first solid electrolyte layer and the second solid electrolyte layer have a perovskite-type structure, and the following formula (1):
A _x B _{1- y My} O _3-δ
Contains metal oxides represented by
Element A is at least one selected from the group consisting of Ba, Ca and Sr.
Element B is at least one selected from the group consisting of Ce and Zr.
The element M is at least one selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In and Sc.
δ is the amount of oxygen deficient, and the fuel electrode-solid electrolyte layer composite according to any one of claims 1 to 8, which satisfies 0.95 ≦ x ≦ 1 and 0 <y ≦ 0.5. Production method.