JPH0813178A - Cathode for electrochemical cell - Google Patents

Abstract

PURPOSE:To obtain a cathode for an electrochemical cell with decreased cell resistance by coating Y2O3-stabilized ZrO2 with a porous electrode material comprising fine particles and coarse particles of transition metal oxide and Y2O3-stabilized ZrO2 or MgAl2O4. CONSTITUTION:A cathode material having a two-layer structure is formed on Y2O3-stabilized ZrO2 which is an oxygen ion conductive solid electrolyte. The first layer which is directly in contact with the solid electrolyte of the cathode material is a porous electrolyte material comprising oxide fine particles. The second layer on the first layer is a porous electrode material comprising an oxide coarse particle material having a larger particle size than the particles in the first layer. Further, both of the porous electrode materials above described are a mixture of transition metal oxides and Y2O3-stabilized ZrO2 or MgAl2O4. Thereby, a high-performance cathode for an electrochemical cell is obtd.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cathode of an electrochemical cell such as a high temperature steam electrolysis cell or a solid oxide fuel cell.

[0002]

2. Description of the Related Art The operation principle of a high temperature steam electrolysis cell as an example of an electrochemical cell will be described with reference to FIG. The oxygen-ion conductive solid electrolyte tube 1 provided with electrodes was heated from 900 ° C to 10
When the temperature is raised to 00 ° C., the solid electrolyte 1 is used as a partition wall, steam is supplied to the inside and air is supplied to the outside, and a voltage is applied between the electrodes so that the water vapor side electrode (cathode) 2 has a negative potential. The steam is electrolyzed to generate hydrogen gas and oxygen gas. Of the generated gas, oxygen gas is reduced by electrons to become oxygen ions and diffuses the solid electrolyte 1 to the air-side electrode (anode) 3, and at the anode 3, the oxygen ions release electrons to become oxygen gas. The hydrogen gas generated at the cathode 2 is used as product hydrogen. In order to efficiently obtain hydrogen using such a high temperature steam electrolysis cell, it is necessary to reduce the supplied electric energy as much as possible, but for that purpose, it is necessary to reduce the resistance of the unit cell. In addition, 4 in FIG. 3 is an oxide interconnector.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The characteristics are as described above, but the cell resistance has an electrical resistance.
There is an electrochemical resistance that is spent in
In order to reduce the resistance, it is necessary to lower both resistances. Electric
As a method of reducing air resistance, cell components with low specific resistance
To optimize the film thickness. for example
For example, the oxygen ion conductive solid electrolyte that is a solid electrolyte is Z
rO₂ZrO is used as the base oxide ₂To Y₂O₃
Or CaO is doped, and the resistivity is optimized by optimizing the amount.
A small oxygen ion conductive solid electrolyte with a small size is selected.
In the solid electrolyte, the current direction is the film thickness direction, so
It is necessary to reduce the film thickness of the degrading. Yin at the electrode
High electron conductivity because current flows laterally in both pole and anode
Need sex. In addition, the electrodes reduce water vapor and generate oxygen.
Low resistance to electrochemical reactions such as life
Is required. In view of the above requirements, the present invention provides an electrochemical cell
Provide high performance cathode material to reduce the cell resistance of
It is the one to try.

[0004]

The present invention meets the above-mentioned needs.
The present invention is based on the oxygen ion conductive solid electrolysis.
Quality is Y₂O₃Stabilized ZrO₂Cathode material in direct contact with
And a porous electrolyte material formed of an oxide fine particle material
And has a larger particle size than the above oxide fine particle material
Coated with porous electrode material formed of oxide grit material
Porous layer having a two-layer structure and formed of the oxide fine particle material
Porous electrode made of electrode material and oxide coarse particle material
Materials are transition metal oxide and oxygen ion conductive solid electrolysis.
Quality is Y ₂O₃Stabilized ZrO₂Or MgAl₂O
_FourElectrochemical cell shade characterized by being a mixture with
It is a pole.

The oxygen ion conductive solid electrolyte Y ₂ O ₃ stabilized ZrO ₂ used in the present invention is generally represented by xZrO _2. (1-x) Y ₂ O ₃ and x is 0.
06-1 Preferably x is 0.07-0.8. The coating thickness of the oxide fine particle material used in the present invention is generally 1 to 50 μm, preferably 5 to 30 μm.
The coating thickness of the oxide coarse particle material is generally 50 to 2
The thickness is 00 μm, preferably 50 to 100 μm.

A preferred material for the oxide fine particle material and the oxide coarse particle material used in the present invention is a mixture of a transition metal oxide and Y ₂ O ₃ -stabilized ZrO ₂ or MgAl ₂ O ₄ . The properties required for the cathode are high conductivity and linear expansion coefficient matching with other constituent materials (such as solid electrolyte materials). In order to improve the conductivity, it is necessary to increase the addition amount of the oxide of the transition metal, but since the linear expansion coefficient also increases with this, an optimum blending ratio is necessary, and generally, The weight ratio of the transition metal oxide is 20.
-80 wt% is preferable. The transition metals used as oxides of transition metals include Fe, Co, Ni, Cu and Z.
n, Mo and the like.

[0007]

Since the electrochemical cell of the present invention is constructed as described above, the resistance of the cell can be lowered.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the cathode structure of the present invention will be described with reference to FIG. On the surface of the oxygen ion conductive solid electrolyte (YSZ), NiO and 0.86ZrO ₂ −0.
A porous electrode made of a mixture of 14Y ₂ O ₃ fine particle materials is formed, and NiO and MgAl are formed as a second layer on the surface of the porous electrode.
A two-layer structure of a cathode is formed by forming a porous electrode composed of a mixture of coarse particle materials of ₂ O ₄ . NiO and 0.86Zr
The component weight ratio in the mixture of O ₂ -0.14Y ₂ O ₃ is Ni.
O is 80 wt%, 0.86ZrO ₂ -0.14Y ₂ O ₃
Is 20 wt%. The weight ratio of the components in the mixture of NiO and MgAl ₂ O ₄ is 60% by weight of NiO, MgAl ₂ O ₄
Is 40 wt%.

Ni on the surface of the oxygen ion conductive solid electrolyte
O and 0.86 ZrO₂-0.14Y ₂O₃From a mixture of
The porous electrode consisting of
Was. Nickel nitrate: 80 g dissolved in distilled water: 200 g
Then, the distilled water is evaporated at about 80 ° C. to obtain a dried product. this
Is baked at 1000 ° C. for 5 hours in air to obtain NiO.
You. Zirconium oxide: 86 g and yttrium oxide: 1
Mix 4g in a ball mill and mix at 1500 ° C for 5 hours
Zirconia-yttria solid solution
(YSZ) is obtained. NiO and YSZ in a weight ratio of 8: 2
Boiled 100g and distilled water: 100g in a ball mill
Apply the mixture for 10 hours on the surface of the solid electrolyte, and
Bake in air at 00 ° C for 2 hours to make a porous electrode for reaction.
I do. After baking, the average particle size of NiO particles in the electrode is about
The average particle diameter of the YSZ particles is 2 μm and is about 5 μm. This
NiO-MgAl formed on the surface of the electrode film of₂O_Fourelectrode
Was synthesized by the following method to form an electrode film. NiO synthesis is described above
It is the same as the method. MgAl₂O_FourIs magnesia
Um and aluminum oxide become Mg: Al = 1: 2
And mixed in air and calcined in air at 1650 ° C. for 20 hours. Grilled
Made MgAl₂O_Four40 g and NiO: 60 g, and
200g of distilled water mixed in a ball mill for 20 hours
Is applied to the surface of the NiO-YSZ electrode film and 1350 ° C.
It was baked for 5 hours. The electrode thickness of the first layer is about 50μ
The second layer has a thickness of about 60 μm. The electrode after baking is
NiO particles about 5μm, MgAl₂O_FourParticle is about 10μ
m. These particle sizes can be measured by water
NiO is reduced to Ni in an element and the cross section is observed with an optical microscope.
The particle size of each was measured. Such a two-layer electric
The overvoltage characteristic of the pole structure is the same as that of the conventional 80NiO-20YSZ.
FIG. 2 shows the result of comparison with the single-layer electrode. Has a two-layer electrode
The electrode of the present invention has a lower overvoltage than the one-layer electrode and
Effective in reducing cell resistance by using as an electrode for steam electrolysis
It turned out to work.

In this embodiment, the first layer is NiO and Y ₂ O ₃
Stabilized ZrO ₂ mixture, second layer is NiO and MgAl ₂
Although a mixture of O ₄ is used, the mixture used for the first layer has a function as a second layer if the particle size is increased, and similarly, the mixture used for the second layer also has a decreased particle size. First
Can be used as a layer. However, since the electrochemical reaction characteristics of the mixture of NiO and MgAl ₂ O ₄ used for the second layer are lower than that of the mixture of the first layer, NiO and MgAl 2
_{The 2} O ₄ mixture is preferably used primarily as a function of the second layer.

[0011]

As described above, according to the present invention, as the cathode of the electrochemical cell, the first layer is composed of the porous electrode formed of the fine particle material, and the porous electrode having a relatively large particle size is formed thereon. By using a cathode having a two-layer structure in which the electrodes are covered, it effectively acts to reduce the resistance of the electrochemical cell.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrode structure manufactured in an example of the present invention.

FIG. 2 is a chart showing an example of electrode overvoltage data manufactured in Examples of the present invention.

FIG. 3 is a schematic diagram showing the principle of general high temperature steam electrolysis.

Claims (1)

[Claims] 1. A Y ₂ which is an oxygen ion conductive solid electrolyte.
A cathode material that is in direct contact with O ₃ -stabilized ZrO ₂ is a porous electrolyte material formed of an oxide fine particle material, and a porous electrode formed of an oxide coarse particle material having a larger particle size than the oxide fine particle material Two-layer structure coated with material,
The porous electrode material formed of the oxide fine particle material and the porous electrode material formed of the oxide coarse particle material are Y ₂ O which is an oxide of a transition metal and an oxygen ion conductive solid electrolyte.
₃ Cathode for electrochemical cell, characterized in that it is a mixture with stabilized ZrO ₂ or MgAl ₂ O ₄ .