JPH0584031B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a molten carbonate type fuel cell, etc.
In particular, the present invention relates to an electrode improved to prevent plastic deformation and creep deformation of the electrode and elution of electrode material, a manufacturing method thereof, and a fuel cell.

[Conventional technology]

For example, in a molten carbonate type fuel cell, electrodes are arranged on both sides of an electrolyte plate, and a spallator is arranged outside the electrodes to form a unit cell. As electrodes used in such fuel cells, electrodes in which nickel powder is impregnated with nickel wire mesh or stainless steel wire mesh have been proposed (Japanese Patent Laid-Open No. 57-3466, JP-A No. 52-136336, JP-A No. 52-136336, Publication No. 57-40866).

[Problem to be solved by the invention]

In the conventional electrodes mentioned above, plastic deformation and creep deformation occurs over time during battery operation, especially at the anode, and sintering progresses after short-term use, resulting in a decrease in specific surface area and a decrease in electrode pore volume. There was a problem that this led to a decrease in the performance of the fuel cell. On the other hand, in the cathode, there was a problem in that the electrode material eluted over time, and battery performance deteriorated accordingly.

In order to solve such problems, conventional methods have been proposed in which ceramic materials are mixed with nickel electrodes (Japanese Patent Application Laid-Open No. 61-271749, Japanese Patent Application Laid-open No. 62-271,
Publication No. 2455, JP-A-61-267267, JP-A-62
5566) and a method of coating ceramic powder with an electrode material (Japanese Patent Application Laid-open No. 107543/1983).

However, electrodes containing ceramic materials have problems in that contact resistance increases and electrode activity decreases due to coexistence of inert substances, making it impossible to exhibit sufficient battery performance. Further, electrodes made of ceramic powder coated with an electrode material have poor sinterability, and there is a problem in that cracks and warpage occur during the electrode manufacturing process.

The purpose of the present invention is to stabilize the electrodes of fuel cells,
In order to prevent plastic deformation and creep deformation of the electrode during battery operation, to have low contact resistance between the electrode and current collector plate, to exhibit stable battery performance over a long period of time, and to prevent elution of electrode materials. An object of the present invention is to provide an electrode, a method for manufacturing the same, and a fuel cell using the electrode.

[Means to solve the problem]

In order to achieve the above object, a fuel cell electrode according to the present invention is a fuel cell electrode formed by sintering metal particles, in which the electrode is formed porous and the surface of the particle is A solid solution layer of metal composite oxide is formed.

The present invention also provides an electrode for a fuel cell formed by sintering metal particles, in which the electrode is porous and solid solution particles of a metal composite oxide are dispersed between the particles. It is something that exists. Here, the particle size of the metal is preferably larger than the particle size of the solid solution particles.

The metal composite oxide includes Mg, Ca, Ta, Ti,
It contains one or more components selected from Mo, Nb, Al, Li, and La, and one or more components selected from Ni, Co, and Cu.

In the electrode, the metal composite oxide solid solution may be a metal composite oxide consisting of AxB _1-x Oy (where A and B are metal atoms). Here, metal atoms A are Mg, Al, Li, La, Ca,
Examples include at least one of Ta, Ti, Mo, and Nb, and the metal atom B is one or more components selected from Ni, Co, and Cu. In the metal composite oxide solid solution AxB _1-x Oy, the value of x is preferably in the range of 0.01 to 0.8 in terms of atomic ratio, and the value of y is preferably in the range of 1 to 3. The ionic radius of metal atoms A and B is preferably 0.6 to 0.7 Å. Further, the metal composite oxide solid solution is preferably a substitutional metal oxide solid solution. The ionic radii of various metal atoms are shown below.

As metal atom A, Mg ²⁺ (6)0.66, Ca ³⁺ (6)0.62,
Ta ⁵⁺ (6)0.68, Ti ⁴⁺ (6)0.68, Mo ⁶⁺ (6)0.62, Nb ³⁺
0.69, Li ⁺ (6)0.68, Al ³⁺ (6)0.51, La ³⁺ (8)1.18Å, and the metal atoms B are Ni ²⁺ (4)0.65, Co ²⁺ (4)0.68,
Cu ²⁺ (4) is 0.68 Å. Here, ( ) indicates the predicted configuration. A metal composite oxide solid solution is likely to be formed in a combination in which the difference in ionic radius between the metal atoms A and the metal atoms B is within 0.1 Å.

The fuel cell electrode manufacturing method according to the present invention includes the steps of forming and firing metal particles as a raw material slurry to form a porous electrode, and immersing this electrode in a metal composite oxide solid solution raw material solution to form a porous electrode. The process includes a step of impregnating the inside of the porous electrode, and a step of drying the electrode and then oxidizing and baking it in an oxidizing atmosphere to form a metal composite oxide solid solution layer on the particle surface of the porous electrode.

When the porous electrode is made of Ni, Co, or Cu, Mg, Ca, Ta, Ti, Mo, Nb, Al, Li, La
A substitution type composite oxide solid solution is formed by impregnating the pores with a solution containing one or more components selected from the above, drying, and then oxidizing and firing. In addition, when the porous electrode is made of materials other than Ni, Co, and Cu, one or more components selected from the above-mentioned Mg, Ca, Al, etc., and nickel (Ni), cobalt (Co), and copper (Cu) are used. It is also possible to form a metal composite oxide solid solution layer on the electrode surface by preparing a mixed solution using a porous electrode, drying it, and oxidizing it.

Further, the electrode manufacturing method according to the present invention includes a step of forming a metal composite oxide solid solution layer on the surface of metal particles in advance, and a step of forming and firing a porous electrode after this step.

Further, the electrode manufacturing method according to the present invention includes a step of coating particles of a metal composite oxide solid solution with metal particles, and a step of forming and firing after this step to form a porous electrode. This makes it possible to easily manufacture electrodes with low contact resistance.

The fuel cell according to the present invention is formed of a unit cell including an electrolyte body, a cathode and an anode disposed on both sides of the electrolyte body, and a separator disposed outside the cathode and anode. In the fuel cell, the cathode and/or anode are formed of any of the electrodes described above.

[Effect]

A metal composite oxide solid solution layer formed on the particle surface of a porous electrode formed by partially sintering metal particles or a metal composite oxide solid solution particle dispersed between the metal particles is heated in a reducing atmosphere. It is also extremely stable, and even when used as an anode in a hydrogen atmosphere, it prevents sintering, plastic deformation, and creep deformation of the porous electrode, and maintains high electrode activity with little increase in electrical resistance. On the other hand, when used as a cathode, the metal composite oxide solid solution layer suppresses elution of the electrode material. This is thought to be due to the fact that the coexistence of magnesium (Mg) and lithium (Li) increases the basicity of the electrode, or that the alkali resistance improves due to the formation of metal composite oxides. .

〔Example〕

The electrode according to the present invention will be explained below with reference to FIG. The porous electrode was created by the following steps. First, in a metal slurry manufacturing process 10, a metal powder 11 is used as a starting material, mixed with an organic binder 12 and stirred 13, and then degassed under reduced pressure 14 and viscosity adjusted 15 to obtain a predetermined raw material slurry 16.

Next, this raw material slurry 16 is attached to a wire mesh 20 made of nickel or the like in a molding/firing step 30, and the thickness is approximately
After molding 32 to 1.0 mm, it was dried 33 at room temperature and reduced and calcined 34 at 750° C. for 1 hour in a hydrogen atmosphere.
As a result, a porous electrode 35 was obtained.

Next, in a metal composite oxide solid solution layer forming step 40, this porous electrode 35 is immersed in a metal composite oxide solid solution raw material solution 41 to impregnate the inside of the pores of the porous electrode for 5 to 50 minutes at 50 to 150°C. Dry for 20 hours 43.

Next, in an oxidizing atmosphere at a temperature of 400 to 1000℃,
After oxidation firing 44 for 10 hours, reduction firing is performed for 1 to 10 hours at a temperature of 600 to 900°C to obtain a fuel cell electrode. If the oxidation firing temperature is below 400°C, the metal oxide solid solution layer will not be sufficiently formed. On the other hand, if the temperature exceeds 1000°C, the electrode pore volume will decrease significantly, which is not preferable. Further, if the reduction firing temperature is 600°C or lower, sufficient activity cannot be obtained. Moreover, at temperatures above 900° C., sintering of the electrode occurs and the specific surface area of the electrode decreases, which is not preferable.

A metal composite oxide solid solution layer is formed on the particle surface of the porous electrode, and the thickness of the solid solution layer is 0.01~
1μm is good. If the thickness is less than 0.01 μm, plastic deformation and creep deformation of the electrode during battery operation cannot be suppressed. On the other hand, if the thickness is 1 μm or more, the contact resistance between the electrode and the current collector plate increases, causing a problem that the battery performance deteriorates. Further, when an electrode including a metal composite oxide solid solution layer is applied to the cathode, elution of the electrode material can be suppressed if the thickness of the layer is 0.01 μm or more. Further, the solid solution raw material solution 41
The solid solution particles of the metal composite oxide are dispersed between the particles by appropriately changing the concentration of , the conditions of oxidation calcination and reduction calcination, and the like.

In addition, apart from the manufacturing process shown in Figure 1, a similar electrode can also be manufactured by forming a metal composite oxide solid solution layer on the surface of metal particles in advance, and then forming and firing to form a porous electrode. . Alternatively, a porous electrode may be formed by coating particles of a metal composite oxide solid solution with metal particles, followed by molding and firing.

Metal composite oxide solid solutions include Mg, Ca, Ta,
The A component selected from Ti, Mo, Nb, Al, Li, or La and one or more B components selected from Ni, Co, and Cu have a composition ratio of AxB _1-x Oy, and the X atoms The ratio is
It is preferable that a substitution type complex oxide solid solution is formed in the range of 0.01 to 0.8, and y is in the range of 1 to 3. FIG. 2 is a diagram showing the relationship between the Mg/Ni composition ratio and the peak change of the (200) plane. Here, the term "substitution type" refers to one in which Ni at the lattice points of the crystal lattice is partially replaced with Mg. If the value of x is less than 0.01, it is insufficient to suppress plastic deformation and creep deformation of the electrode, and the electrode thickness and pore volume decrease over time, leading to a decrease in battery performance. . On the other hand, when the value of x is 0.8 or more, electrical resistance increases and electrode activity decreases, which is not preferable.

When the starting material for the porous electrode is Ni, Co, or Cu, Mg, Ta, Ti, Mo, Nb, Li, Al,
After impregnating with a La-containing solution, it is dried, oxidized and fired,
Next, a desired fuel electrode can be obtained by reduction firing.

On the other hand, when the starting material of the porous electrode is made of components other than Ni, Co, and Cu, one or more selected from Mg, Ta, Ti, Mo, Nb, Li, Al, and La and Ni , Co and Cu selected from
After creating a mixed solution of three or more and impregnating the porous electrode with this, the metal composite oxide solid solution layer can be created according to the metal composite oxide solid solution layer forming step 40.

Example 1 Nickel powder (average particle size
A 0.2% carboxymethyl cellulose (CMC) solution was added thereto and mixed with stirring, followed by deaeration under reduced pressure and the slurry viscosity was adjusted to about 120 poise. This was applied as a raw material slurry to a nickel metal (20 mesh) to a thickness of 1 mm, and after drying at room temperature for about 20 hours, 70% hydrogen-30
% nitrogen mixed gas at 750° C. for 1 hour to prepare a porous electrode. The thickness of the obtained porous electrode is
It had a porosity of 0.8 mm, a porosity of 72 Vol%, and a specific surface area of 0.9 m ² /g. This porous electrode was made of magnesium nitrate {Mg
(NO ₃ ) ₂ ·6H ₂ O}492 g was immersed in a magnesium solution prepared by dissolving 1 part of distilled water to impregnate the pores of the porous electrode with magnesium. This was dried at 120°C for about 10 hours and then oxidized and calcined at 600°C for 7 hours in an air atmosphere. Next, in a 70% hydrogen-30% room atmosphere
Reduction firing was performed at 800° C. for 1 hour to obtain a fuel cell electrode according to the present invention.

The X-ray diffraction pattern of the obtained electrode is shown in FIG. It was confirmed from the X-ray diffraction peak that a magnesium-nickel composite oxide solid solution was formed. Lattice constant determined from diffraction peak value (200 planes)
was 4.204 Å, and when the X value of MgxNi _ix O was calculated from this, it was found that X = 0.7. From this result, the crystal structure formula of the composite oxide solid solution formed on the electrode surface is Mg ₀

Claims (1)

[Claims] 1. In a fuel cell electrode formed by sintering metal particles, the electrode is formed porous, and the surface of the metal particles contains Mg, Ca, Ta,
A solid solution layer of metal composite oxide is formed consisting of one or more components selected from Ti, Mo, Nb, Al, Li, and La and one or more components selected from Ni, Co, and Cu. A fuel cell electrode characterized by: 2. In a fuel cell electrode formed by sintering metal particles, the electrode is formed porous, and between the metal particles, Mg, Ca, Ta,
Solid solution particles of a metal composite oxide consisting of one or more components selected from Ti, Mo, Nb, Al, Li, and La and one or more components selected from Ni, Co, and Cu are dispersed. A fuel cell electrode characterized by: 3. The fuel cell electrode according to claim 2, wherein the particle size of the metal is larger than the particle size of the solid solution particles. 4. In a fuel cell electrode formed by sintering metal particles, the electrode is formed porous, and Mg, Ca, Ta,
A solid solution layer of a metal composite oxide consisting of one or more components selected from Ti, Mo, Nb, Al, Li, and La and one or more components selected from Ni, Co, and Cu is 0.01
A fuel cell electrode characterized by being formed with a thickness of ~1 μm. 5. In claim 1, 2 or 4, the solid solution of metal composite oxide consists of A _x B _1-x O _y (where A and B are metal atoms), and metal atom A is Mg, Ca, Ta, Ti. ，
One or more components selected from Mo, Nb, Al, Li, and La, metal atom B is one or more components selected from Ni, Co, and Cu, and the value of x is an atomic ratio.
A fuel cell electrode in the range of 0.01 to 0.8, with the value of y in the range of 1 to 3. 6. The fuel cell electrode according to claim 5, wherein the metal atoms A and B have an ionic radius of 0.6 to 0.7 Å. 7. The fuel cell electrode according to claim 5, wherein the metal composite oxide solid solution is a substitutional metal oxide solid solution. 8 The process of forming and firing metal particles as a raw material slurry to form a porous electrode, and the process of forming this electrode.
Metal composite oxide solid solution raw material consisting of one or more components selected from Mg, Ca, Ta, Ti, Mo, Nb, Al, Li, La and one or more components selected from Ni, Co, Cu a step of immersing the electrode in a solution to impregnate it inside the pores; a step of drying the electrode and then oxidizing it in an oxidizing atmosphere to form a metal composite oxide solid solution layer on the surface of the metal particles of the porous electrode; A fuel cell electrode manufacturing method including: 9 Mg, Ca, Ta, Ti,
A step of forming a metal composite oxide solid solution layer consisting of one or more components selected from Mo, Nb, Al, Li, and La and one or more components selected from Ni, Co, and Cu; and this step. A method for producing an electrode for a fuel cell, including a step of subsequently forming and firing a porous electrode. 10 Mg, Ca, Ta, Ti, Mo, Nb, Al, Li,
One or more components selected from La and Ni, Co, Cu
A process of coating metal particles on particles of a metal composite oxide solid solution consisting of one or more components selected from the above, and a process of forming and firing after this process to form a porous electrode. Electrode manufacturing method. 11. A fuel cell configured by stacking unit cells each including an electrolyte body, a cathode and an anode disposed on both sides of the electrolyte body, and a separator disposed outside the cathode and anode, 5. A fuel cell, wherein the cathode and/or anode are comprised of the electrodes according to claim 1, 2, or 4.