JPH05174836A - Forming method for fuel electrode of solid electrolytic fuel cell - Google Patents

Abstract

PURPOSE:To maintain conductive performance even if nickel quantity considerably decreases compared to ceramics quantity by facilitating the production of a green sheet without separating nickel from ceramics caused by a difference in specific gravity, and by totally uniforming the compositions of a formed electrode, and by readily fusing and joining nickel-coated ceramics particulates, themselves, with nickel. itself, having features of mutual contact and high surface solubility in forming an electrode. CONSTITUTION:A fuel electrode is formed by laminating a green sheet for forming a solid electrolyte and a nickel-coated ceramics particulates-containing green sheet for forming an electrode and by burning the resulting laminated compact and by then applying monoblock sintering to the laminated compact. In this lamination, a green sheet for forming an air electrode may be laminated, if necessary. This integrates the fuel electrode with a solid electrolytic plate and simply and efficiently incorporates the fuel electrode into a fuel cell. In this case, there is no development of damage or destruction due to thermal stress caused by other materials. In addition, conductivity is improved and superior gas permeability, electrochemical reaction, and conductivity are available.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a fuel electrode for a solid oxide fuel cell, and more specifically, it has improved conductivity, excellent breathability and electrochemical reactivity, and
The present invention relates to a method for integrally manufacturing a fuel electrode that is not damaged or destroyed by thermal stress with other members and is integrally sintered with a solid electrolyte layer.

[0002]

2. Description of the Related Art When a sintered body of a conductive metal such as nickel is used as a fuel electrode (anode) material of a solid electrolyte fuel cell in order to enhance an electrochemical reaction and conductivity, the solid electrolyte and a separator are Due to incompatibility of thermal expansion characteristics with other current collectors, it is easy for the battery to be damaged or destroyed due to strain due to thermal stress. It is easy to cause the output of the battery to decrease due to the decrease in battery charge and the increase in contact resistance.

Further, in order to bring the thermal expansion characteristics closer to those of a solid electrolyte, a porous sintered body of metal and ceramics, especially a fuel electrode of nickel zirconia cermet has been proposed and well studied, but it is non-conductive. There is a limit to the mixing ratio of a certain zirconia, and a decrease in conductivity is inevitable compared to metals. Further, when the nickel zirconia cermet is formed on the electrolyte plate from a green sheet or slurry containing nickel particles and zirconia particles, there is also a problem that the composition in the thickness direction tends to be non-uniform due to the difference in specific gravity between the particles.

In order to solve these problems, a fuel electrode for a solid electrolyte fuel cell has recently been proposed, which is formed into a plate shape by using ceramic particles coated with nickel particles on the surface and is fired (see Japanese Patent Laid-Open No. Hei 10 (1999) -264242). 3-49156 publication).

[0005]

However, this electrode is obtained by forming the particles into a shaped plate and then firing the obtained shaped plate to obtain a porous sintered plate. In order to form a solid electrolyte fuel cell by using it, in order to form a dense and homogeneous electrolyte membrane on a porous electrode plate, complicated and advanced treatment such as EVD process and plasma spraying is required, resulting in high cost. I cannot escape.

Under the circumstances, the present invention has improved conductivity, excellent breathability and electrochemical reactivity, and
It is an object of the present invention to provide a method for easily and efficiently forming a fuel electrode for a solid electrolyte fuel cell, which is not damaged or destroyed by thermal stress with other members.

[0007]

The inventors of the present invention have conducted various studies to develop a method for forming a fuel electrode for a solid electrolyte fuel cell having the above-mentioned preferable characteristics, and as a result, have unbaked raw solid electrolyte. A plate-forming green sheet, an electrode-forming green sheet containing ceramic particles whose surfaces are coated with nickel, and an air electrode (cathode) -forming green sheet arranged on the other surface of the electrolyte as needed are laminated. Then, the solid electrolyte and the electrode can be compositely integrated with each other by forming the electrode independently by firing and sintering together, and the above-mentioned desirable characteristics can be imparted to the electrode itself. They have found that they can be achieved, and have completed the present invention based on this finding.

That is, according to the present invention, after a solid electrolyte forming green sheet and an electrode forming green sheet containing particles whose ceramic particles are coated with nickel (hereinafter referred to as nickel coated ceramic particles) are laminated, The present invention provides a method for forming a fuel electrode for a solid electrolyte fuel cell, which comprises firing and then integrally sintering.

In the present invention, each green sheet is formed by molding a slurry, paste or clay-like material obtained by mixing each battery member material with an organic binder, a plasticizer, a solvent and the like into a thin plate shape by a doctor blade method or a calendar method. Made by.

The ceramic particles used in the present invention are not particularly limited, but may be those which are used for ordinary solid electrolyte materials, such as zirconia, ceria, yttria-stabilized zirconia, and partially-stabilized zirconia. It may be ceramic particles such as alumina or silicon carbide having a small coefficient of thermal expansion such as expansion coefficient.

The particle size of the ceramic particles is usually 5
To 70 μm, preferably 10 to 50 μm. If the particle size is less than 5 μm, the porosity of the formed fuel electrode layer is lowered, and if it exceeds 70 μm, the surface area of nickel involved in the electrochemical reaction is reduced, which is not preferable.

The use ratio of the ceramic particles and nickel is usually 95: 5 to 10:90, preferably 70:30 to 30:70 by weight. If this ratio is less than 10:90, the matching of the thermal expansion characteristics between the electrode and other fuel cell members will be insufficient, and if it exceeds 95: 5, the nickel coating will not be complete or the coating will be insufficient. Since it becomes extremely thin, the conductivity decreases, which is not preferable.

An organic binder, a plasticizer, a solvent, etc. are advantageously used for preparing a paste or slurry for preparing the green sheet of the above-mentioned nickel-coated ceramic particles, and other optional additives such as a dispersant are added. Ingredients may be added.

Examples of the organic binder include polyvinyl butyral, polyvinyl alcohol, methyl cellulose, ethyl cellulose, polyacrylic acid ester, polyethylene oxide and the like. The proportion of the binder used is usually 3 to 30% by weight, preferably 5 to 20% by weight, based on the nickel-coated ceramic particles.

Examples of the plasticizer include butyl phthalate, polyethylene glycol, glycerin and polyol.

Examples of the solvent include terpineol, trichloroethylene, ethyl alcohol, propyl alcohol, toluene, xylene, ethyl acetate, acetone, and mixed solvents thereof.

In the present invention, it is preferable to use the nickel-coated ceramic particles alone. However, nickel-coated ceramic particles to which a small amount of nickel particles are added may be used, or a small amount of nickel-coated ceramic particles may be coated. You may use the thing which added the ceramic particle which is not. However, the addition ratio of these is preferably 20% or less.

The solid electrolyte-forming material is not particularly limited as long as it has oxygen ion conductivity, and for example, stabilized zirconia such as yttria-stabilized zirconia (YSZ) and calcia-stabilized zirconia (CSZ), It is a known solid electrolyte material such as those obtained by adding a metal oxide such as alumina to these stabilized zirconia.

A preferable example of the laminated molded body of each of these green sheets is a two-layer laminated structure comprising a solid electrolyte forming green sheet and an anode forming green sheet containing nickel-coated ceramic particles, or the two layers. A three-layer laminated structure in which a cathode forming green sheet containing a cathode material such as lanthanum manganate stabilized with an alkaline earth metal is laminated on the opposite side of the laminated structure with an electrolyte layer between them Be done.

In the method of the present invention, an electrode forming green sheet containing nickel-coated ceramic particles is laminated on the solid electrolyte forming green sheet, and another cathode (air electrode) forming green sheet is laminated as the case may be. In some cases, it may be molded, fired, and then integrally sintered at a higher temperature. In this way, the required electrode is easily formed and the electrode is integrated with the solid electrolyte plate.

Further, in the method of the present invention, it is preferable that the green sheets are alternately accumulated with the current collector and then fired. By doing so, a solid oxide fuel cell can be easily manufactured. In the case where the electrolyte and both electrodes are integrally sintered, the current collector is alternately laminated, and in the case where two layers of the fuel electrode and the electrolyte are integrally sintered, the cathode material is applied and then the current collector is applied. The batteries may be assembled in alternating layers with the body. In the latter case, the solvent, binder, etc. are removed during the process of raising the temperature.

The method for producing the solid oxide fuel cell will be described below. The current collector of this battery member usually comprises a separator and a terminal plate.

The separator is 1 from the number of solid electrolyte plates.
It is a small number of dense conductive plates with no gas permeability, and both sides are usually provided with grooves so as to intersect with each other to form gas flow paths for fuel gas and oxidant gas, respectively. In addition, the terminal plate is two dense conductive plates that are not gas permeable, and usually has a plurality of parallel grooves formed on one surface thereof, and has a gas flow path for an oxidant gas and a gas flow path for a fuel gas, respectively. Are formed.

As described above, the separator electrically connects the electrodes of the adjacent single cells, and has grooves on both sides which serve as flow passages for the fuel gas and the oxidant gas, and each flow passage has its own cathode. The gas passages on the side of the anode and the side of the anode. A plurality of grooves to be the respective gas passages are arranged in parallel, and the groove on one surface and the groove on the other surface are arranged in a direction intersecting with each other, preferably in a right angle direction. If you place it like this,
After the cells are integrated, the inlet and outlet of the fuel gas and the inlet and the outlet of the oxidant gas can be arranged on the same side end face, respectively, and the configuration of the gas supply / exhaust system as an integrated cell can be made simple and easy. it can.

As the conductive plate used for the separator and the terminal plate, a metal such as nickel or cobalt, a heat-resistant alloy containing nickel, chromium, cobalt, iron or the like, or various sintered bodies are usually used. Examples of the sintered body include lanthanum chromite complex oxide doped with an alkaline earth metal and Co, Ni, Fe, Zn and other metals, conductive ceramics such as silicon carbide, molybdenum silicide, and chromium silicide, and conductive Examples thereof include a sintered body obtained by firing a metal material and a heat-resistant inorganic compound in a non-oxidizing atmosphere, for example, in a reducing atmosphere or in a vacuum. The conductive metal material, for example, nickel metal, nickel-based alloy,
Cobalt metal, cobalt-based alloys, iron metals, iron-based alloys, etc. may be mentioned, and nickel-based alloys include Ni-Cr.
System alloy, Ni-Cr-Fe system alloy, Ni-Cr-Mo system alloy, Ni-Cr-Mo-Co system alloy, Ni-Cr-M
o-Fe alloys and the like, and cobalt-based alloys,
Co-Cr type alloy, Co-Cr-Fe type alloy, Co-C
r-W series alloys, Co-Cr-Ni-W series alloys, and iron-based alloys include Fe-Ni-Cr series alloys and Fe-
Examples include Cr-Ni based alloys and Fe-Cr-Ni-Co based alloys. Further, examples of the heat-resistant inorganic compound include alumina, silica, titania, indium oxide, stannic oxide, silicon carbide, silicon nitride, lanthanum chromite-based composite oxide, and yttrium chromite-based composite oxide.

A solid oxide fuel cell is preferably manufactured as follows using the above members.

First, unit cells composed of the fuel electrode formed of the green sheet and the electrolyte and the air electrode (cathode) are laminated with a separator interposed therebetween to form a multi-stage series structure of single cells, and the single cells are laminated. By appropriately adjusting the number and providing terminal plates at both ends, a battery including a series-type stacked multi-stage cell including a large number of single cells is assembled.
At that time, a sealing material is interposed between each unit cell and the separator or between the unit cell and the terminal plate at the edge of the separator or the terminal plate along the groove direction to seal the unit so as not to leak gas.

A fuel cell is completed by attaching a manifold including an exhaust pipe for supplying an oxidant gas such as fuel gas and air to the thus assembled battery, that is, a multi-layered cell. As an example of this manifold, its inner surface,
There is a structure in which four chambers partitioned by the inner surface of the cell inscribed therein serve as supply and discharge spaces for the fuel gas and the oxidant gas and serve as a member for forming a gas passage and also as an outer wall.

[0029]

EFFECTS OF THE INVENTION According to the method of the present invention, there are problems of the conventional method, for example, mere nickel /
When using a zirconia mixture, nickel and zirconia are easily separated from each other because of a large difference in specific gravity between the components,
The composition of the formed electrode is not uniform throughout,
When the proportion of nickel in the mixture is less than 30% by weight, it becomes difficult to sinter the nickel particles together,
It is possible to easily eliminate disadvantages such as decrease in conductivity. Especially, in nickel-coated ceramic particles, since ceramics such as zirconia are covered with nickel, the difference in specific gravity between nickel and ceramics It is easy to produce a green sheet without separating with each other, and the composition of the formed electrode is uniform throughout, and the nickel-coated ceramic particles are in contact with each other because the nickel particles are easily melted. There is a remarkable effect that they are easily joined by fusion or the like, and the conductive performance can be maintained even if the amount of nickel is considerably smaller than the amount of ceramics.

The fuel electrode formed by the method of the present invention is
Since it is integrated with the solid electrolyte plate, it can be easily and efficiently incorporated into the fuel cell, in which case it does not cause damage or destruction due to thermal stress with other members,
It has the advantages of improved conductivity and excellent breathability and electrochemical reactivity.

[0031]

The present invention will be described in more detail with reference to Examples.

Example An integral sintered body composed of a fuel electrode, an air electrode and a solid electrolyte was prepared as follows. Partially stabilized zirconia containing 3 mol% yttria (hereinafter referred to as stabilized zirconia)
50 parts by weight of a terpineol solution containing 6% by weight of polyvinyl butyral was added to 100 parts by weight of the powder (average particle size: 6μ), and the mixture was mixed well by a ball mill to form a paste, and a solid of 50 × 50 × 0.4 mm was formed by a doctor blade method. An electrolyte-forming green sheet was prepared.

Separately from this, lanthanum manganate-based La ₀ . ₉ Sr ₀ . ₁ MnO ₃ powder (average particle size 5 μm)
Is mixed with the same binder solution as above to form a paste, and 50 × 50 × 0.
A 3 mm air electrode forming green sheet was prepared.

On the other hand, stabilized zirconia particles coated with Ni on the surface (average particle size 50 μm, stabilized zirconia / Ni weight ratio = 70/30) were mixed with the same binder solution as above to prepare a paste, which was prepared by the doctor blade method. By 50
A green sheet for forming a fuel electrode having a size of x50x0.3 mm was prepared.

A fuel electrode and an air electrode were laminated on each of these green sheets with an electrolyte layer sandwiched therebetween to produce a laminate having a 50 × 50 mm square three-layer structure.

Next, using an electric furnace, the temperature was raised by heating in an air atmosphere to remove the solvent, the binder was burned off, and the temperature was raised to 1500 ° C. by subsequent heating to obtain a three-layer composite sintered body. Obtained.

Next, a three-stage series cell solid electrolyte fuel cell was assembled as follows. As the current collectors of the separator and the terminal plate, a 50 × 50 × 5 mm square flat plate made of a Ni-based heat-resistant alloy provided with a gas passage having a groove width of 2 mm and a groove depth of 1 mm was used.

The above three-layer composite sintered body and the current collector are combined into a single cell.
The layers were laminated in layers, and a glass paste having a softening point of about 800 ° C. was interposed between the sintered body and the current collector for gas sealing. This glass paste softens at the operating temperature of the battery and seals the gas.

A cylindrical alumina manifold was attached to the battery thus integrated. The contact portion between the manifold and the battery was sealed with a glass paste for gas sealing.
A platinum lead wire was welded to and electrically connected to the terminal, which is an electrical outlet.

The fuel cell thus manufactured was heated. That is, heating from room temperature to 150 ° C. was performed at 1 ° C./min, and from 150 ° C. to 300 ° C. was raised at 5 ° C./min to remove the solvent of the glass paste. At a temperature of 300 ° C. or higher, in order to prevent the oxidation of the anode on the hydrogen passage side, nitrogen gas was flown to raise the temperature to 1000 ° C. at 5 ° C./min.

100% of the fuel cell thus obtained was used.
The temperature was maintained at 0 ° C., hydrogen was flown on the anode side and air was flown on the cathode side to start power generation. Open voltage is 1.28V, ohmic resistance is 38mΩ, gas cross leak is 0.1 of hydrogen.
% Or less.

Table 1 shows the current-voltage characteristics (discharge characteristics) of this battery.

[0043]

[Table 1]

Comparative Example In place of the nickel-coated particles of the anode raw material of the example, a mixture was used in which Ni powder having an average particle size of 5 μm and stabilized zirconia powder having an average particle size of 50 μm were mixed at a weight ratio of 55:45. A fuel cell was produced in the same manner as in Example except for the above. This battery was heated and then generated as in the example. Open voltage is 1.28V, ohmic resistance is 58m
Ω, gas cross leak was 0.1% or less of hydrogen.

Table 2 shows the current-voltage characteristics (discharge characteristics) of this battery.

[0046]

[Table 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Yoshida 1-3-1 Nishitsurugaoka, Oi-cho, Iruma-gun, Saitama Tonen Research Institute

Claims (1)

[Claims] 1. A solid electrolyte forming green sheet and an electrode forming green sheet containing particles having ceramic particles whose surfaces are coated with nickel are laminated, fired and then integrally sintered. A method for forming a fuel electrode for a solid oxide fuel cell.