Nickel oxide-stabilized zirconia composite oxide, process for production thereof, and anode for solid oxide type fuel cell comprising the composite oxide

Abstract

The present invention relates to a nickel oxide-stabilized zirconia composite in which nickel oxide is dispersed uniformly, a process for readily producing the composite oxide, and an anode for a solid oxide fuel cell having excellent output characteristics.More specifically, the present invention provides a nickel oxide-stabilized zirconia composite that is produced by sintering a mixture of nickel hydroxide and / or nickel carbonate and a hydroxide of stabilized zirconium.

Description

TECHNICAL FIELD[0001]The present invention relates to a nickel oxide-stabilized zirconia composite oxide, a process for producing the same, and an anode for a solid oxide fuel cell comprising the same.BACKGROUND ART[0002]Conventionally, nickel oxide, and stabilized zirconia, whose crystal structure is stabilized, are used as the anode materials for solid oxide fuel cells. These materials are mixed in a process for forming an anode. In that case, the properties of the obtained anode largely depend on the properties of the material after being mixed.[0003]For example, a nickel oxide in an anode is reduced from the nickel oxide state to a nickel metal by hydrogen gas, i.e., fuel, thereby to act as a conductor that efficiently conducts electrons produced in power generation, and as a decomposition catalyst for hydrogen gas. In this case, micronizing nickel and uniformalizing the distribution state thereof in the anode, namely, improving the nickel dispersibility, increases the specific ...

AI Technical Summary

Benefits of technology

[0068]The content of the composite oxide in the anode is not limited, however, about 80 to 100 wt % is preferable. The anode may contain known additives other than the composite oxide as long as they do not hamper the effects of the invention.

[0069]The method for producing the anode is not particularly limited, and a method that is similar to a known method can be employed except that the composite oxide described above is used. For example, after dispersing the composite oxide on the surface of the solid electrolyte plate by screen-printing, the dispersion is sintered thereon. The content of the composite oxide in the dispersion is not particularly limited, and may be suitably adjusted depending on the size and the like of the fuel cell. There is no particular limitation to the sintering conditions, and sintering may be suitably adjusted depending on the size and the like of the fuel electrode based on a known method so as to desirably obtain an anode.Advantageous Effects of Invention

[0070]In the present invention, by using nickel hydroxide and / or nickel carbonate as well as a hydroxide of stabilized zirconium to produce a composite oxide, it is possible to prevent or suppress the aggregation of the particles of a single type of compound, and a sedimentation phenomenon that occurs when the nickel hydroxide is mixed. As a result, it is possible to improve nickel dispersibility in the composite oxide.

[0071]By sintering nickel hydroxide and / or nickel carbonate simultaneously with a hydroxide of stabilized zirconium, dispersibility of the nickel in the composite oxide can be remarkably improved. In this case, the dispersibility of the nickel is probably further improved by thermal diffusion during the sintering.

[0072]When the weight ratio of the nickel to the stabilized zirconium, i.e., nickel oxide / stabilized zirconia, in the composite oxide of the present invention on an oxide basis is 1 / 9 to 9 / 1, the dispersibility of the nickel in the composite oxide is remarkably improved.

[0073]Furthermore, the method for producing the composite oxide of the present invention allows the composite oxide to be readily produced while preventing the generation of acidic gas.

Problems solved by technology

However, in the anode material obtained by this technique, an impairment of nickel dispersibility may be observed due to the difference in specific gravity between the nickel oxide and the stabilized zirconia, and due to electrostatic aggregation of the particles.

For example, particles having a submicron size of less than 1 μm cause a problem of remarkable electrostatic aggregation.

In the case of particles having a particle diameter of about several microns, the sedimentation rate of the particles increase, and the nickel oxide and stabilized zirconia are separated from each other due to the difference in specific gravity, resulting in significant deterioration in the nickel dispersibility.

However, the hydroxyl groups tend to be present on the particle surfaces in a non-uniform manner.

Therefore, when particle bombardment due to thermal motion is repeated, particles easily aggregate due to the non-uniform presence of hydroxyl groups.

Thus, in addition to aggregation between the nickel oxide and stabilized zirconia, electrostatic aggregation occurs among particles of the same material (nickel oxide particles, or stabilized zirconia particles), leading to insufficient nickel dispersibility in the obtained composite oxide.

In addition, since the particle size is enlarged due to electrostatic aggregation, the separation becomes more significant, leading to insufficient nickel dispersibility in the obtained composite oxide.

However, in this technique, there is a significant difference in the precipitation rate between the nickel salt and the zirconium salt resulting from the difference in their solubility in the solvent.

This causes a problem in that the nickel oxide is not dispersed uniformly in the composite oxide.

In addition, depending on the types of water-soluble nickel salt and water-soluble zirconium salt, a large amount of acid gas is generated upon thermal decomposition, which makes it difficult to manufacture the composite oxide.