JP3340526B2 - Reduction electrode for barium-cerium-based oxide solid electrolyte and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reducing electrode used for an electrochemical device or sensor such as a fuel cell using a barium-cerium-based oxide solid electrolyte and a method for producing the same.

[0002]

2. Description of the Related Art A barium-cerium-based oxide solid electrolyte is a perovskite oxide having high ionic conductivity at a high temperature, and is stably present in a reducing and oxidizing atmosphere. Currently, applications of various electrochemical devices using this type of oxide as a solid electrolyte are being studied, and applications to sensors and fuel cells in particular are expected to replace conventional zirconia-based solid electrolytes. . However, the solid electrolyte of this system has just begun to attract attention recently, and an optimum electrode material for this system and a production method thereof have not been established. At present, platinum and silver which are stable in a standard high temperature reducing / oxidizing atmosphere are used as electrodes.

On the other hand, as a reducing electrode of a zirconia fuel cell, a material mainly composed of nickel is used.
Cermet or the like mixed with zirconia powder is used in order to suppress oversintering of nickel, and the amount of mixed oxide causes poor electron conductivity or a problem with reactivity with an electrolyte. Further, a material mainly composed of nickel is used also in the reduction electrode of the molten carbonate fuel cell, but problems such as oversintering remain.

[0004]

As described above, no optimum reducing electrode has been found for a barium-cerium-based oxide solid electrolyte, and platinum and silver electrodes are costly and not suitable for practical use. It is desired to develop a highly electron conductive electrode material that does not react with a barium-cerium-based oxide solid electrolyte and can maximize the performance of the electrolyte. Also, a reduction electrode that can withstand long-time use at high temperatures is desired.

[0005]

The reduction electrode for the barium-cerium-based oxide solid electrolyte of the present invention comprises Mn, Fe, C
at least one selected from the group consisting of o, carbonyl nickel and Cu , and BaCe _0.8 Dy _0.2 O _3-x or
Other is characterized in that it comprises a _{BaCe 0.8 Gd 0.2 O 3-x} .

Further, the barium-cerium oxide solid electrolyte process for the preparation of the reduction electrode for the present invention, the surface of the barium-cerium oxide solid electrolyte, Mn, Fe, Co, carbo
At least one selected from the group consisting of nilnickel and Cu , and BaCe _0.8 Dy _0.2 O _3-x or BaC
a step of forming a layer containing e _0.8 Gd _0.2 O _3-x , a step of heating and baking the layer in air, and a step of heating and reducing in a reducing atmosphere.

Here, the layer containing the metal and ceria or barium-cerium-based oxide for producing the reduction electrode can be formed on the surface of the solid electrolyte by a PVD method such as plasma spraying or a sputtering method, or a CVD method. However, it is most convenient to apply a mixture of the metal powder and the ceria or barium-cerium-based oxide powder to the surface of the solid electrolyte using a suitable binder, in which case the particle size of these powders is , Preferably less than 5 microns.
The baking step is performed at 800 to 1000 ° C. for at least 1 hour, and the reducing step is performed at 800 ° C. in a hydrogen atmosphere.
It is preferred to take at least 1 hour at ~ 1000 ° C.

[0008]

In the electrode of the present invention, ceria or barium-cerium oxide prevents oversintering of metals such as Mn and Fe during operation of the electrode. And impair the electrode performance. Depending on the metal used, a suitable range for the oxide is 5 to 75% by weight of the mixture of metal and oxide.

According to the present invention, it is possible to maximize the performance of an electrolyte without reacting with a barium-cerium-based oxide solid electrolyte at a low cost, and furthermore, a long-life reduction capable of withstanding long-term use at a high temperature. You can get poles. Further, by the above manufacturing method, an electrode can be obtained in a simple process at low cost.

[0010]

The present invention will be described below with reference to examples. [Embodiment 1] In this embodiment, an electrode material is applied to a barium-cerium-based oxide solid electrolyte, which is baked and reduced, and the electrode performance is examined by impedance analysis. B as a barium-cerium oxide solid electrolyte
Using aCe _0.8 Dy _0.2 O _3-x , this oxide sintered body was cut into a disc having a diameter of 13 mm and a thickness of 0.50 mm, and after being polished, the size became 0.50 cm ² on one surface. A platinum powder is applied and baked to form an oxidized electrode, and a paste of a reduced electrode material having a size of 0.50
Apply to make cm ² .

The paste is prepared by adding 4% by weight of polyvinyl butyral as a binder to the raw material of the powder and mixing them in a mixed solvent of ethanol and toluene. A mixture of 95% by weight of Mn, Fe, Co, Ni or Cu and 5% by weight of the same oxide as the solid electrolyte is used as an electrode material. The particle sizes of these materials are prepared in four types: 2-3 microns, about 5 microns, about 10 microns, and 20 to 30 microns. The baking is performed in an air atmosphere at 1000 ° C. for 3 hours, and then a reduction treatment is performed in a hydrogen atmosphere at 1000 ° C. for 3 hours. Note that a Pt electrode is used as a comparative example.

For each of the reducing electrodes obtained as described above,
Table 1 shows the impedance measured at 600 ° C., 800 ° C., and 1000 ° C. at an applied voltage of 0.05 V and a frequency of 1 Hz to 1 MHz. However, the measured value is the value at the intersection (bulk resistance value) with the real axis as represented by the Cole-Cole plot, excluding the portion of the lead wire (platinum) of less than 2 m.

[0013]

[Table 1]

As can be seen from the table, Mn, Fe, Co,
The reduction electrode manufactured by using a powder material of Ni and Cu, particularly having a particle diameter of 5 μm or less, sufficiently brings out the performance of the electrolyte similarly to the conventional platinum electrode. Also, no direct reaction between these materials and the electrolyte was observed, suggesting that they can be used as electrode materials for a long time.

Example 2 A 0.50 mm thick oxide sintered body BaCe was used as a barium-cerium-based oxide solid electrolyte.
_{Using 0.8} Gd _0.2 O _3-x , a platinum electrode is baked on one surface as an oxidation electrode, and a paste of a reduction electrode material is applied to the other surface so as to have a size of 0.50 cm ² . This paste is obtained by adding 4% by weight of polyvinyl butyral as a binder to a mixture of 75% by weight of carbonyl nickel powder having a particle size of 2 to 3 μm and 25% by weight of ceria or the same barium cerium gadolinium oxide powder as the solid electrolyte. , Prepared by mixing in a mixed solvent of ethanol and toluene. Under the same conditions as in Example 1, baking and reduction treatment are performed to produce a reduction electrode.

The fuel cell device obtained as described above is
At 0 ° C., 200 ml / min air and 200 ml / min humidified hydrogen were supplied to the oxidation electrode and the reduction electrode, respectively.
FIG. 1 shows a voltage change when a continuous discharge is performed at 0 mA / cm ² . a is a battery using a reduction electrode made from a mixture of carbonyl nickel and barium-cerium-cadolinium oxide as a raw material; b is a battery using a reduction electrode made from a mixture of carbonyl nickel and ceria as a raw material; This shows the characteristics of the battery used for the pole.

Although it is considered that most of the voltage change is due to the electrode performance, the battery a using the reduction electrode according to the present invention,
b is substantially equal in performance to the battery c using the conventional platinum electrode, and the deterioration rate is reduced from the conventional 6% / 1000h to 2% to 3% / 1000h when any of the electrodes is used. are doing. It is clear that the electrode performance is clearly maintained over a long period of time. By using the material of the present invention, it is possible to obtain an electrode having lower cost and longer life than conventional electrodes.

In this embodiment, a mixture of Ni and ceria or barium-cerium-based oxide is used.
Not limited to i, for example, Ni 70% by weight, Co 10% by weight,
A mixture such as 10% by weight of ceria and 10% by weight of barium cerium gadolinium oxide may be used, and Mn, Fe, C
Any mixture may be used as long as at least one of o and Cu is mixed. Needless to say, the method of preparing and synthesizing the material may be mixing in a metal state or mixing in an oxide state, and any method of synthesizing an alloy or a composite oxide may be used.

[0019]

As described above, according to the present invention, it is possible to obtain a high-performance, long-life reducing electrode which does not react with a barium-cerium-based oxide solid electrolyte at low cost and can maximize the performance of the electrolyte. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram comparing continuous discharge characteristics of fuel cells using various types of reduction electrodes.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-1453 (JP, A) JP-A-2-262260 (JP, A) JP-A 4-169067 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 4/86 H01M 4/88

Claims (3)

(57) [Claims] 1. at least one selected from the group consisting of Mn, Fe, Co, carbonyl nickel, and Cu
And BaCe _0.8 Dy _0.2 O _3-x or BaCe _0.8 Gd
_0.2 O _3-x and the reduction electrode for a barium-cerium oxide solid electrolyte, which comprises a. 2. A barium-cerium-based oxide solid electrolyte having at least one selected from the group consisting of Mn, Fe, Co, carbonyl nickel, and Cu , and Ba
Ce _0.8 Dy _0.2 O _3-x or BaCe _0.8 Gd _0.2 O _3-x and forming a layer containing a <br/>, the layer of heated in step, and in a reducing atmosphere baked by heating in air A method for producing a reduction electrode for a barium-cerium-based oxide solid electrolyte, comprising: 3. The method according to claim 1, wherein the layer is Mn, Fe, Co, carbon
Selected from the group consisting of nickel and Cu
And one kind of powder , BaCe _0.8 Dy _0.2 O _3-x or B
3. The method for producing a reduced electrode for a barium-cerium-based oxide solid electrolyte according to claim 2 , comprising a mixture with aCe _0.8 Gd _0.2 O _3-x powder , wherein the powder has a particle size of 5 μm or less.