Method of manufacturing anode core-shell complex for solid oxide fuel cell using hydrazine reducing agent and surfactant

Abstract

Provided is a method of manufacturing an anode core-shell complex for a solid oxide fuel cell, including (A) manufacturing a stabilized zirconia (YSZ) sol by using zirconium hydroxide (Zr(OH).sub.4) and yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O) as a starting material and distilled water as a solvent by a hydrothermal method, (B) agitating nickel chloride, stabilized zirconia in a sol state, and a surfactant, (C) adding sodium hydroxide (NaOH), (D) adjusting a pH to a range of 6 to 8, and (E) sintering the nickel-stabilized zirconia core-shell powder.

Claims

1. A method of manufacturing an anode core-shell complex for a solid oxide fuel cell, comprising: manufacturing a stabilized zirconia (YSZ) sol by using zirconium hydroxide (Zr(OH).sub.4) and yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O) as a starting material and distilled water as a solvent by a hydrothermal method; agitating nickel chloride, stabilized zirconia in a sol state, and a surfactant to uniformly mix nickel chloride, stabilized zirconia, and the surfactant, such that the surfactant having a polymer structure surrounds particles of a nickel precursor generated when hydrazine (N.sub.2H.sub.4) is added and stabilized zirconia due to electrostatic attractive force to prevent the particles from being agglomerated and uniformly disperse the particles; adding sodium hydroxide (NaOH) to chain-adsorb hydrophobic chain groups due to attractive force of the hydrophobic chain groups of the surfactant adsorbed on surfaces of the nickel precursor and stabilized zirconia and to attach nickel precipitated from the nickel precursor and uniformly distributed and stabilized zirconia; adjusting a pH to a range of 6 to 8 and performing agitation for 4 to 12 hours to reinforce an adsorption ability of the hydrophobic chain groups of the surfactant to manufacture a nickel/stabilized zirconia core-shell complex having a dense structure; and manufacturing a nickel-stabilized zirconia core-shell powder into pellets and then sintering the nickel-stabilized zirconia core-shell powder.

2. The method of claim 1, wherein cetyltrimethyl ammonium bromide (CTAB) is used as the surfactant of the agitating of nickel chloride, stabilized zirconia in the sol state, and the surfactant while being added at a concentration not exceeding a critical micelle concentration (CMC).

3. The method of claim 1, wherein in the agitating of nickel chloride, stabilized zirconia in the sol state, and the surfactant, and the adding of sodium hydroxide, a reaction time after sodium hydroxide (NaOH) is added and until a reaction is finished is adjusted to 1 to 180 minutes to perform the reaction.

4. The method of claim 1, wherein the stabilized zirconia sol is synthesized by using Zr(OH).sub.4 and Y(NO.sub.3).sub.3.6H.sub.2O as the starting material, setting a ratio to 92:08%, and using distilled water as the solvent by the hydrothermal method.

5. The method of claim 1, wherein in the agitating of nickel chloride, stabilized zirconia in the sol state, and the surfactant, and the adding of sodium hydroxide, a ratio of nickel chloride (NiCl.sub.2.6H.sub.2O), hydrazine hydrate (N.sub.2H.sub.4.H.sub.2O), and sodium hydroxide (NaOH) as the starting material involved in the reaction is a molar ratio of 1:2 to 10:2 to 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view showing a principle that nickel/stabilized zirconia (YSZ) form a core-shell structure by using a property of a surfactant.

(2) FIG. 2 is a scanning electron microscope (SEM) picture of a core-shell of nickel/stabilized zirconia (YSZ) manufactured by using a surfactant according to an exemplary embodiment of the present invention.

(3) FIG. 3 is a transmission electron microscope (TEM) picture of a core-shell particle of nickel/stabilized zirconia (YSZ) manufactured by using the surfactant according to the exemplary embodiment of the present invention.

DETAILED DESCRIPTION

(4) Hereinafter, the present invention will be described in detail.

(5) According to the present invention, there is provided a method of manufacturing a nickel/stabilized zirconia core-shell complex for a anode of a fuel cell, which includes (A) manufacturing stabilized zirconia (YSZ) in a state of a sol synthesized by a hydrothermal method by using zirconium hydroxide (Zr(OH).sub.4) and yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O) as a starting material and distilled water as a solvent, (B) agitating nickel chloride, stabilized zirconia in a sol state, and a surfactant to uniformly mix nickel chloride, stabilized zirconia, and the surfactant, such that the surfactant having a polymer structure surrounds particles of a nickel precursor generated when hydrazine (N.sub.2H.sub.4) is added and stabilized zirconia due to electrostatic attractive force to prevent the particles from being agglomerated and uniformly disperse the particles, in order to use a hydrazine synthesis method, (C) adding sodium hydroxide (NaOH) to chain-adsorb hydrophobic chain groups due to attractive force of the hydrophobic chain groups of the surfactant adsorbed on surfaces of the nickel precursor and stabilized zirconia and to attach nickel precipitated from the nickel precursor and uniformly distributed and stabilized zirconia, (D) adjusting a pH to a range of 6 to 8 and performing agitation for 4 to 12 hours to reinforce an adsorption ability of the hydrophobic chain groups of the surfactant to manufacture a nickel/stabilized zirconia core-shell complex having a dense structure, and (E) manufacturing a nickel-stabilized zirconia core-shell powder into pellets and then sintering the nickel-stabilized zirconia core-shell powder at high temperatures.

(6) According to an exemplary embodiment, first, zirconium hydroxide (Zr(OH).sub.4), yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O), and distilled water are mixed and then put into molten metal to manufacture stabilized zirconia in the state of the sol synthesized by the hydrothermal method. Next, the manufactured nickel chloride, stabilized zirconia sol, and surfactant are agitated. Subsequently, an initial temperature and a pH of the aforementioned mixture are adjusted, and hydrazine (N.sub.2H.sub.4) is put at a predetermined speed. In addition, sodium hydroxide (NaOH) is put to precipitate nickel. The pH is adjusted to about 6 to 8 by using a hydrochloric acid (HCl) diluted solution and agitation is performed for 4 to 12 hours to reinforce the adsorption ability of the surfactant. The synthesized solution agitated for a predetermined time is washed by water and dried. The manufactured nickel-stabilized zirconia core-shell powder is manufactured into the pellets, and then sintered at high temperatures to manufacture the complex where nickel/stabilized zirconia are uniformly and continuously linked.

(7) In the present invention, stabilized zirconia in the sot state manufactured by using the hydrothermal method is used to increase a dispersion ability of nano-sized particles to reduce agglomeration. More specifically, stabilized zirconia (YSZ) in the sol state is synthesized by using zirconium hydroxide (Zr(OH).sub.4) and yttrium nitrate (Y(NO.sub.3).sub.3.6H.sub.2O) as the starting material and distilled water as the solvent by the hydrothermal method. Stabilized zirconia (YSZ) is manufactured in the sol state to reduce agglomeration of the nano-sized particles.

(8) It is preferable that cetyltrimethyl ammonium bromide (CTAB) be used as the surfactant of step (B) in a predetermined amount not exceeding a critical micelle concentration (CMC). In this case, it is preferable to use a sonicator to physically disperse nickel chloride, stabilized zirconia, and the surfactant in step (B).

(9) The hydrazine synthesis method is a method of manufacturing nickel by using nickel chloride as the starting material. However, in the present invention, nickel chloride, the surfactant, and yttria stabilized zirconia are put together from the beginning to perform synthesis so that an area and a probability of reaction sites are increased by using a property of the surfactant to form a core-shell structure including nickel and stabilized zirconia. Herein, hydrazine hydrate is used as a reducing agent to form the nickel precursor by nickel chloride. Sodium hydroxide is used as a precipitator to precipitate nickel from nickel chloride. In steps (B) and (C), it is preferable that nickel chloride (NiCl.sub.2.6H.sub.2O) as the starting material involved in the reaction, hydrazine hydrate (N.sub.2H.sub.4.H.sub.2O) as the reducing agent, and sodium hydroxide (NaOH) as the precipitator be reacted at a molar ratio of 1:2 to 10:2 to 12

(10) It is preferable that a reaction time after sodium hydroxide (NaOH) is added and until a reaction is finished be adjusted to 5 to 180 minutes to perform the reaction.

(11) The surfactant having the polymer structure surrounds surfaces of the particles of the nickel precursor and stabilized zirconia, and thus the particles are not agglomerated but uniformly monodispersed. The hydrophobic chain groups are chain-adsorbed due to attractive force of the hydrophobic chain groups of the surfactant adsorbed on the surfaces of the nickel precursor and stabilized zirconia. Nickel precipitated from the nickel precursor and uniformly distributed and stabilized zirconia are attached to each other. Subsequently, the pH is adjusted to the range of 6 to 8 by using a buffer solution and agitation is performed for 4 hours or more to increase the adsorption ability of the chain groups of the surfactant. Accordingly, the nickel/stabilized zirconia core-shell complex for the fuel cell, in which stabilized zirconia is densely adsorbed to surround the circumference of nickel, is manufactured (FIG. 1).

(12) The manufactured complex powder having the core-shell structure of nickel and stabilized zirconia may be molded to manufacture the pellets, and then reduced and sintered to be applied to the anode of the fuel cell. Nickel/stabilized zirconia do not require a separate reducing process during sintering at high temperatures.

EXAMPLE

(13) A better understanding of the present invention may be obtained in light of the following Examples which are set forth to illustrate, but are not to be construed to limit the present invention.

Preparation Example 1

Manufacturing of the Yttria Stabilized Zirconia (YSZ) Sol

(14) In the present invention, stabilized zirconia (YSZ) in a sol state was manufactured by using the hydrothermal method to reduce agglomeration of the nano-sized particles. The hydrothermal method was used to synthesize stabilized zirconia in the sol state. Zirconium hydroxide (Zr(OH).sub.4), yttrium nitrate (Y(NO.sub.3).sub.3).6H.sub.2O), and distilled water were added, put into the autoclave, and reacted at 200 C. for 8 hours.

Example 1

Manufacturing of the NiYSZ Complex Powder

(15) 1 mole of nickel chloride hydrate and stabilized zirconia (YSZ) in the sol state manufactured in Preparation Example 1 were added at a predetermined ratio (NiCl.sub.2:YSZ=1:0.1 to 1), 0.01 to 0.5 mole of cetyltrimethyl ammonium bromide (CTAB) was mixed at a concentration not exceeding the critical micelle concentration, and dispersed by using the sonicator. The hydrazine hydrate was added as the reducing agent at a predetermined speed to precipitate nickel from nickel chloride in the dispersed mixture solution. Sodium hydroxide (NaOH) was used as the precipitator. In this case, the reaction molar ratio of NiCl.sub.2.6H.sub.2O:N.sub.2H.sub.4.H.sub.2O:NaOH was set to 1:2 to 10:2 to 12.

(16) The reaction time after sodium hydroxide (NaOH) used as the precipitator was added and until the reaction was finished was adjusted to 5 to 180 minutes.

Example 2

Manufacturing of the NiYSZ Complex Powder

(17) After synthesis was performed like Example 1, the pH was adjusted to 6 to 8 by using the hydrochloric acid (HCl) buffer solution and agitation was performed for about 4 to 12 hours to increase the hydrophobic adsorption ability of the chain group of the surfactant. After agitation, the particles were recovered and dried in the drier for 24 hours to synthesize the complex of nickel and stabilized zirconia having the core-shell structure.

Example 3

Sintering of the NiYSZ Complex Powder

(18) The NiYSZ complex manufactured in Example 1 was manufactured into pellets by the high-pressure uniaxial molder, reduced, and sintered. With respect to the reduction and sintering condition, gas of 5% of H.sub.2 and 95% of Ar was used to increase the temperature to 1400 C. at the rate of 5 C./min and maintain heat treatment for 2 hours.

Experimental Example 1

Confirming of Formation of the Core-Shell Structure of the Complex

(19) The analysis was performed by the scanning electron microscope (SEM) in order to confirm whether in the complex having the core-shell structure of nickel and stabilized zirconia manufactured by the aforementioned Examples, the core-shell structure is formed well. The results are shown in FIG. 2. From FIG. 2, it could be seen that the core-shell structure where stabilized zirconia is adsorbed to surround the circumference of nickel was formed.

Experimental Example 2

Confirming of Formation of the Core-Shell Structure of the Complex

(20) Formation of the core-shell structure of the complex of nickel and stabilized zirconia manufactured by the aforementioned Examples was confirmed by the transmission electron microscope (TEM). In FIG. 3, the core-shell particles were observed by using the transmission electron microscope (TEM), and it could be confirmed that surrounding polygonal small particles were attached to nickel particles at the center.