JP2014154537A - Method of producing fuel electrode of solid oxide fuel cell - Google Patents

Abstract

Solid oxide capable of improving electrode performance by using a fuel electrode material as a composite material in which the supported state between particles is uniform and the surface of one particle is reliably coated with the other particle A method for manufacturing a fuel electrode for a fuel cell and a solid oxide fuel cell including a fuel electrode manufactured by such a method are provided.
The surface of one particle (core powder) carries a charged polymer opposite to the other particle (coating material particle) and is brought into contact with the other particle by contacting the other particle (coating material particle). The surface of the particle is coated with the other particle.
[Selection] Figure 1

Description

  The present invention relates to a technology for manufacturing a solid oxide fuel cell, which can uniformly combine a plurality of electrode materials at a low temperature, prevent agglomeration of material powder, and achieve high performance even in long-term operation. The present invention relates to a method for producing a fuel electrode that can be maintained, and a solid oxide fuel cell using a fuel electrode produced by the production method.

  A solid oxide fuel cell (SOFC) has electrodes having gas permeability on both sides of an electrolyte made of a solid oxide such as yttria-stabilized zirconia (YSZ) having oxide ion conductivity. It is a fuel cell that has an arranged structure and operates at a high temperature close to 1000 ° C.

As a fuel electrode in such a solid oxide fuel cell, metals such as Ni (nickel), copper (Cu), platinum (Pt) and YSZ (yttria stabilized zirconia: Zr _1-x Y _x O ₂ ), A sintered body (cermet) with an oxide ion conductor such as SDC (Samaria doped ceria: Ce _1-x Sm _x O ₂ ), GDC (gadria doped ceria: Ce _1-x Gd _x O ₂ ), etc. Used.
In such a fuel cell electrode, the metal tends to aggregate during the firing process during power generation or during power generation, and when the metal aggregates, the electrode performance deteriorates as a result of the reduction of the three-phase interface serving as the electrode reaction field. It has been pointed out.

  From the viewpoint of suppressing performance degradation due to such metal aggregation, Patent Document 1 sprays a composite ceramic powder having composite particles in which one particle group is unevenly distributed on the surface of another type of particle group. It is disclosed to produce by a pyrolysis method. Further, it is described that the composite ceramic powder thus obtained is used as an electrode material for a solid oxide fuel cell.

  And in the column of the Example of the said patent document 1, the raw material liquid which disperse | distributed YSZ sol in the aqueous solution of nickel acetate is introduce | transduced into the atomization chamber 2 of the manufacturing apparatus 1, and is made into a mist state with an ultrasonic wave, It is pulverized by introducing it into a quartz tube 5 heated to 200 to 1000 ° C. with a carrier gas (air). The powder is collected by the electric dust collector 8, calcined at 1000 ° C. for 4 hours, recrystallized, and then gently unraveled, whereby the surface of the NiO particle group is covered with the YSZ particle group. Obtaining ceramic powder is described.

JP 09-309768 A

  However, in the method described in Patent Document 1, the contact state between the NiO particles and the YSZ particles depends on the probability, so that the supported state cannot be controlled. Therefore, the NiO particles are not necessarily covered with the YSZ particles, and the carrying state tends to be uneven. In addition, a large amount of heat energy is required for the composite of both particles, and since the firing is performed at a high temperature, the same kind of particles aggregate and enlarge, and as a result, when applied to a fuel cell, the three-phase interface decreases, There is a problem that electrode performance cannot be maintained over a long period of time.

  The present invention has been made in order to solve the above-mentioned problems related to the composite technology of different kinds of particles required for manufacturing a fuel electrode in a solid oxide fuel cell. And the purpose is that the electrode performance can be improved by using a fuel electrode material in which the support state between different kinds of particles is good and the surface of one particle is reliably coated with the other particle. An object of the present invention is to provide a method for producing a fuel electrode for a solid oxide fuel cell. It is another object of the present invention to provide a solid oxide fuel cell with improved durability by including a fuel electrode manufactured by such a method.

  As a result of intensive studies to achieve the above object, the present inventors have coated the other particle on the surface of one particle, and the other particle on the surface of one particle (that is, the core powder). The inventors have found that the above object can be achieved by previously supporting a polymer having a charge opposite to that of the coating material particles (that is, the coating material particles), and have completed the present invention.

  The present invention is based on the above knowledge, and the method for producing a fuel electrode of a solid oxide fuel cell according to the present invention comprises a polymer having a charge opposite to the coating material particles coated on the core powder on the surface of the core powder. A polymer carrying step for carrying the coating material, a coating step for coating the core material powder carrying the polymer with the coating material particles in a dispersion in which the coating material particles are dispersed, and a core material powder coated with the coating material particles A fuel electrode material comprising a core material powder and a coating material particle combined by a process including a firing process for firing is used.

  A solid oxide fuel cell according to the present invention includes a fuel electrode manufactured by the above method.

  According to the present invention, a polymer having a charge opposite to that of the coating material particles is supported on the surface of the core material powder, and then the coating material particles are coated on the polymer-supported core material powder in a dispersion in which the coating material particles are dispersed. Thus, the coating material particles can be reliably and uniformly coated on the surface of the core powder by the electrostatic attraction force. In addition, since the core powder surface is uniformly covered with the coating material particles, the fuel electrode is manufactured using such a composite material, thereby preventing aggregation of the core powder during the operation of the fuel cell. The three-phase interface can be secured and the durability of the fuel cell can be improved.

It is a TEM (transmission electron microscope) image of the fuel electrode material formed by coating the surface of nickel powder with YSZ particles by the production method of the present invention.

  Below, the manufacturing method of the fuel electrode of the solid oxide fuel cell of the present invention will be described in more detail and specifically. In the present specification, “%” represents mass percentage unless otherwise specified.

In the method for producing a fuel electrode for a solid oxide fuel cell according to the present invention, the fuel electrode material comprising the core material powder and the coating material particles used in the production of the fuel electrode is as described above.
(1) A polymer supporting step for supporting a polymer having a charge opposite to that of the coating material particles coated on the core material powder on the surface of the core material powder;
(2) A coating step of coating the coating material particles on the core powder having the polymer supported on the surface by the step (1) in a dispersion in which the coating material particles are dispersed;
(3) A firing step of firing the core material powder coated with the coating material particles by the step (2),
Are combined by a process including:

In the polymer loading step, the core material is loaded with a polymer having a charge opposite to that of the coating material, so that the surface of the core material is charged with the charge opposite to that of the coating material. It is the process processed so that coating | covering material particle may adhere easily.
Specifically, Step 1 of preparing a core material powder and a raw material liquid containing a polymer having a charge opposite to the coating material particles covering the core material powder, and stirring the raw material liquid containing the core material powder and the polymer Step 2 of forming a polymer-supported core material by supporting the polymer on the surface of the core material powder and step 3 of separating the polymer-supported core material powder from the raw material liquid containing the polymer-supported core material are performed in this order. Is done.

  That is, in Step 1, the core material powder is mixed into the polymer-containing solution to prepare a raw material liquid dispersed in the solution. Next, in step 2, the raw material liquid is stirred to obtain a polymer-supporting core material in the raw material liquid. In step 3, the polymer-supporting core material is separated from the raw material liquid as a powder. In other words, after leaving the raw material liquid in which the core powder carrying the polymer is dispersed, the supernatant liquid is removed, the precipitate is washed with distilled water (washing is repeated as necessary), and then dried. Thus, a polymer-supported core material powder in a powder state is obtained from the raw material liquid.

The coating step is a step of mixing the polymer-carrying core material powder obtained in the polymer-carrying step in a dispersion of the coating material particles in order to coat the core material powder with the coating material particles.
Specifically, the step 4 of mixing the polymer-supported core material powder obtained in the polymer-supporting step into the dispersion of the coating material particles, and the stirring of the mixed dispersion of the coating material particles and the polymer-supporting core material powder are performed. The step 5 of coating the surface of the polymer-supporting core material powder with the coating material particles and the step 6 of obtaining the polymer-supporting core material powder coated with the coating material particles from the mixed dispersion are performed in this order.

That is, in step 4, a dispersion of coating material particles is prepared, and the polymer-supported core material powder obtained in the polymer-supporting step is mixed therein. Next, in step 5, the surface of the polymer-supporting core material powder is coated with the coating material particles by stirring the mixed dispersion. In Step 6, the supernatant of the mixed dispersion that has been allowed to stand is removed, and the residue is dried, whereby a polymer-supported core material powder coated with the coating material particles is obtained.
In addition, as a dispersion medium of the covering material particle | grains in the process 4, nonpolar solvents, such as chloroform, hexane, benzene, toluene, are used, for example.

The firing step includes an organic substance contained in the polymer-supported core powder coated with the coating material particles obtained in the coating step, that is, the polymer and a surfactant used to promote dispersion of the coating material particles. This is a process for joining the core material and the covering material at the same time as the removal by the heat treatment.
Specifically, this is performed after the coating step, including the step 7 of heat-treating the polymer-supporting core material powder coated with the coating material particles and removing the organic components contained in the powder. In addition, as heat processing temperature at this time, it is normally performed at 500-800 degreeC in air | atmosphere.

In the fuel electrode manufacturing method of the present invention, after the above-described firing step, if necessary, the core material powder coated with the coating material particles obtained by the reduction treatment step, that is, the firing step, may be subjected to a reduction treatment. it can.
That is, it is performed when the core powder is an oxide and reduction is required in advance in the manufacturing process of the fuel electrode of the solid oxide fuel cell. On the other hand, when the oxide can be used in the process, it is reduced during power generation after being made into a cell, even if the core material powder is not subjected to a reduction treatment.

As the coating material particles used in the fuel electrode manufacturing method of the present invention, particles having a particle diameter of 1 nm to 10 nm can be suitably used.
That is, by using such nano-level particles, the high surface energy and specific surface area can be utilized, adhesion between the core material powder and the coating material particles is promoted, and the process can be performed at a low temperature.

Further, it is desirable that the surface of the coating material particles is previously coated with a component that promotes dispersion of the coating material particles in the dispersion medium when the coating material dispersion is prepared. Since the particles are dispersed in the dispersion medium without agglomeration, it is effective for uniformly covering the core material with the coating material particles and maintaining the nano particle size.
Examples of such a dispersion promoting component include oleate.

For example, by using particles synthesized by the oleic acid hydrothermal method as the coating material particles, the oleate remaining in the particles can be used as a component for promoting dispersion in the dispersion medium.
The oleic acid hydrothermal method is also effective for uniform synthesis of nano-level particles.

In the method for producing a fuel electrode of a solid oxide fuel cell according to the present invention, it is desirable to use a core powder made of an electronic conductor and a coating material particle made of an oxide ion conductor.
That is, by coating the electron conductive material with an oxide ion conductive material, it is possible to effectively form a three-phase interface and prevent aggregation of the electron conductive material as a fuel electrode of a solid oxide fuel cell.

Here, nickel (Ni) can be used as the electronic conductor constituting the core powder, and fibrous nickel is particularly desirable.
By making nickel into a fibrous form, the electron conduction path is linear compared to granular or spherical particles of the same volume, reducing the internal resistance of the battery, increasing the surface area, and increasing the three-phase interface. Can be achieved.

On the other hand, as the oxide ion conductor constituting the coating material particles, zirconium oxide doped with a rare earth element (zirconia: ZrO ₂ ) or cerium oxide doped with a rare earth element (ceria: CeO ₂ ) is used alone. Or it can mix and use.
Specific examples include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), gadolinium-doped ceria (GDC), and samarium-doped ceria (SDC).

In the fuel electrode manufacturing method of the present invention, as the polymer having the opposite charge to the coating material particles supported on the surface of the core material powder, the YSZ particles are anionic in the solution in order to coat the core material powder made of nickel with the YSZ particles. A cationic polymer is preferably used.
Such a cationic polymer is not particularly limited, and for example, polydiallyldimethylammonium chloride (PDDA), polyethyleneimine (PEI), polyallylamine hydrochloride (PAH) and the like can be used.

  In the composite material obtained by the above-described series of processes, the coating material particles are reliably and uniformly coated on the surface of the core material powder. By using such a material for the production of the fuel electrode, Aggregation of the core powders in can be prevented, a three-phase interface in the fuel electrode can be efficiently formed, and an electrode reaction field can be secured. Therefore, the performance and durability of the solid oxide fuel cell having the fuel electrode manufactured as described above are improved.

  The fuel electrode material in which the core material powder and the coating material particles are combined is mixed with a binder (for example, ethyl cellulose), a dispersant (for example, butyl acetate), and a pore-forming agent as necessary. After forming an electrode paste, it is applied onto an electrolyte made of YSZ, SSZ, GDC, SDC or the like, or a metal substrate such as high Cr steel or Ni steel, and then fired to form a fuel electrode.

On the other hand, as the air electrode of a solid oxide fuel _{cell, LSM (La 1-x Sr} x MnO 3), LSCF (La 1-x Sr x Co 1-y Fe y O 3), LSC (La 1-x Sr _x CoO ₃ ), SSC (Sm _x Sr _1-x CoO ₃ ), LSF (La _x Sr _1-x FeO ₃ ), BSCF (Ba _x Sr _1-x Co _y Fe _1-y O ₃ ), LNF ( _{LaNi 1-x Fe x O 3} ), SSC (Sm x Sr 1-x CoO 3) and perovskite compounds such _as, La ₂ NiO _4, perforated consisting (LaSr) 2 (CoFe) _O oxides such ₄ A quality material is used.
In addition, when YSZ is applied as an electrolyte, it is necessary to provide an intermediate layer between them in order to prevent reaction with the air electrode. For such an intermediate layer, a ceria-based material such as SDC, YDC, or GDC is used.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, it cannot be overemphasized that this invention is not limited at all by such an Example.
In this example, acicular nickel oxide (NiO) was used as a core powder, and this surface was coated with YSZ (coating material) particles by the following procedure.

[Polymer loading process]
(Step 1: Preparation of raw material liquid)
1 mmol of acicular nickel oxide (diameter: 25-600 nm, length: 2.5-10 mm) in 4.5 mL (pH = 9) of 1% aqueous solution of cationic polymer, poly (diallyldimethylammonium chloride) (PDDA) Was added as a core powder to obtain a raw material liquid.
Here, as said acicular nickel oxide, what was obtained by heat-processing nickel oxalate was used. In addition to this, an electrospinning method, a template method, or the like can be used, and the manufacturing method is not particularly limited.

(Step 2: Polymer loading)
PDDA was supported on the surface of the NiO core material by stirring the raw material liquid containing PDDA and NiO at room temperature with a glass rod about 10 to 20 times.

(Step 3: Preparation of polymer-supported core powder)
After the raw material liquid after stirring is allowed to stand at room temperature for 6 hours, the polymer-supporting core material in the raw material liquid is precipitated at the bottom of the container, and then the supernatant liquid is removed, and 4.5 mL of distilled water is added, The precipitated polymer-supported core material was washed.
Next, the supernatant liquid after washing is removed, and the precipitate (polymer-supporting core material) at the bottom of the container is dried for 10 minutes in a drier at 80 ° C. until it becomes a powder state to obtain a polymer-supporting core material powder. It was.

[Coating process]
(Step 4: Preparation and mixing of coating material dispersion)
3 mmol of YSZ particles (particle size: 4 to 10 nm) synthesized by the oleic acid hydrothermal method were dispersed in 4.5 mL of cyclohexane. Since the YSZ particles are synthesized by the oleic acid hydrothermal method, the surfaces of the particles are covered with the remaining oleate.
Next, the polymer-supported core material powder (NiO + PDDA) obtained in step 3 was mixed in this dispersion.

(Process 5: Coating of coating material)
The surface of the polymer-supported core material powder was coated with YSZ particles by stirring the mixed dispersion of the polymer-supported core material powder obtained in Step 4 and the YSZ particles with a glass rod at room temperature about 10 to 20 times. .

(Process 6: Sorting of composite material)
The polymer dispersion core powder coated with YSZ particles is allowed to settle in the dispersion by allowing the mixed dispersion after stirring to stand at room temperature for 6 hours, and then the supernatant is removed for about 3 minutes. By allowing to stand and evaporating cyclohexane as a dispersion medium, a YSZ-coated polymer-supported core material powder was obtained.

[Baking process]
(Step 7: Heat treatment)
The YSZ-coated polymer-supported core powder obtained in step 6 is baked in the atmosphere at 500 ° C. for 30 minutes, thereby decomposing and removing organic components such as cyclohexane, oleate, and PDDA remaining in the powder. As a result, a fuel electrode material composited in a state where the surface of the nickel oxide powder was coated with YSZ particles was obtained.

(Step 8: Reduction treatment)
The composite fuel electrode material obtained in step 7, ie, YSZ-coated NiO powder, is reduced in 800% 3% hydrogen atmosphere for 2 hours to reduce NiO of the core material, and the surface of the metallic nickel powder The fuel electrode material was coated with YSZ particles.
In addition, about reduction process conditions, if time is taken, it can further reduce in temperature, For example, the process conditions of 600 degreeC and 4 hours may be sufficient.

  FIG. 1 is a TEM (transmission electron microscope) image of the fuel electrode material thus compounded, and it is recognized that the surface of the nickel powder is uniformly and densely coated with YSZ particles.

The obtained fuel electrode material is used for manufacturing a fuel electrode, for example, as a fuel electrode paste mixed with ethyl cellulose (binder) and butyl acetate (dispersant).
Further, it is applied to the production of a fuel electrode of a fuel cell as a green sheet to which a water-soluble acrylic binder and polyethylene glycol (pore forming agent) are added.

  In the fuel electrode of the solid oxide fuel cell manufactured in this way, the surface of the nickel powder is uniformly covered with YSZ particles, so that the nickel powder may agglomerate during the firing process and power generation. In addition, the reduction of the three-phase interface is prevented, and excellent electrode performance is exhibited over a long period of time.

Claims (14)

A polymer carrying step of carrying on the surface of the core material powder a polymer having a charge opposite to that of the coating material particles coated on the core material powder;
In a dispersion in which the coating material particles are dispersed, a coating step of coating the coating material particles on the core material powder carrying the polymer;
A firing step of firing the core material powder coated with the coating material particles;
A fuel electrode manufacturing method for a solid oxide fuel cell, wherein a fuel electrode material combined by a process including The polymer supporting step is
Step 1 of preparing a core material powder and a raw material liquid containing a polymer having a charge opposite to that of the coating material particles covering the core material powder;
Step 2 is carried out after Step 1 above, and the raw material liquid containing the core material powder and the polymer is stirred to support the polymer on the surface of the core material powder to form a polymer-supported core material;
Step 3 is performed after Step 2, and the polymer-supported core material powder is separated from the raw material liquid containing the polymer-supported core material;
The fuel electrode manufacturing method according to claim 1, comprising: The coating step is
Step 4 is performed after the polymer supporting step, and the polymer supporting core material powder obtained in the polymer supporting step is mixed in the dispersion of the coating material particles.
Step 5 is carried out after Step 4 and agitating the mixed dispersion of the coating material particles and the polymer-supporting core material powder to coat the surface of the polymer-supporting core material powder with the coating material particles;
Step 6 which is performed after Step 5 and obtains a polymer-supported core material powder coated with coating material particles from the mixed dispersion;
The fuel electrode manufacturing method according to claim 1, wherein The firing step is
4. The method according to claim 1, further comprising a step 7 of heat-treating the polymer-supported core material powder coated with the coating material particles after the coating step and removing an organic component contained in the powder. The fuel electrode manufacturing method according to one of the items.   The method for producing a fuel electrode according to any one of claims 1 to 4, further comprising a step of reducing the core powder coated with the coating material particles after the firing step.   The fuel electrode manufacturing method according to any one of claims 1 to 5, wherein a particle diameter of the covering material particles is 1 to 10 nm.   The fuel electrode manufacturing method according to any one of claims 1 to 6, wherein a surface of the coating material particles is coated with a dispersion promoting component for a dispersion medium.   The fuel electrode manufacturing method according to claim 7, wherein the dispersion promoting component is oleate.   The fuel electrode manufacturing method according to any one of claims 1 to 8, wherein the core material powder is made of an electron conductor, and the coating material particles are made of an oxide ion conductor.   The method for producing a fuel electrode according to claim 9, wherein the electron conductor constituting the core powder is nickel.   The method for producing a fuel electrode according to claim 10, wherein the nickel is fibrous.   The anode production according to any one of claims 9 to 11, wherein the oxide ion conductor constituting the coating material particles is zirconium oxide and / or cerium oxide doped with a rare earth element. Method.   The method for producing a fuel electrode according to claim 12, wherein the polymer is a cationic polymer.   A solid oxide fuel cell comprising a fuel electrode manufactured by the method according to any one of claims 1 to 13.

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