KR101756695B1 - Method of preparing Ni/YSZ core-shell structures by using surfactant and ultrasonication - Google Patents

Abstract

The present invention relates to a method for preparing a nickel / yttria stabilized zirconia core-cell composite for the production of a solid oxide fuel cell anode using a surfactant and ultrasonic dispersion. According to an embodiment of the present invention, there is provided a method for preparing nickel particles, comprising: mixing distilled water with spherical nickel and a cationic surfactant having a size of 0.5 to 1 um together, dispersing the nickel particles dispersed by ultrasonic dispersion, and coating a nickel surface with a cationic surfactant; Dispersing yttria-stabilized zirconia by mixing ultrasonic dispersion of distilled water with zirconia in an amount of 50-100 nm and an anionic surfactant, and coating the surface of the yttria-stabilized zirconia with an anionic surfactant; Stabilized zirconia coated with a cationic surfactant-coated nickel and an anionic surfactant is stirred in a solvent having a pH ranging from 7 to 8, nickel is made into core by the difference in surface charge of the two particles, Preparing a core-cell composite with zirconia as a shell; And a high-temperature sintering step of producing the core-cell composite powder from the rod-shaped pellets and the high-temperature sintering. The present invention also provides a method for producing a nickel / stabilized zirconia core-cell composite for a solid oxide fuel cell anode. When the core-cell composite is used as a solid oxide fuel cell anode, the components of the core and the cell are uniformly distributed, and the crystal grains are nano-structured, and the microstructure becomes dense, thereby improving the electrical conductivity.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-yttria stabilized zirconia core-shell composite for solid oxide fuel cells using a surfactant and ultrasonic dispersion,

The present invention relates to a method of preparing a nickel / yttria-stabilized zirconia core-cell composite for preparing a solid oxide fuel cell anode using a surfactant and ultrasonic dispersion, and more particularly, By uniformly dispersing nickel and yttria-stabilized zirconia and coating positive surface charge on nickel (Ni) and negative surface charge on yttria-stabilized zirconia using different surfactants, To a technique for producing a core-cell composite.

With the recent depletion of fossil raw materials, there is a growing demand for new energy sources. Solid Oxide Fuel Cells, which convert chemical energy directly into electrical energy, have high energy conversion efficiency, can use various fuels by their own internal reforming, And is attracting attention as a next-generation energy source.

Solid oxide fuel cells utilize the high oxygen ion conductivity of the oxide electrolyte and have an anode connected in series. Spatial separation of hydrogen and oxygen is required to utilize the transfer of electrons. And a current is generated by inducing electrons to move to another electrode by chemical bonding. Solid oxide fuel cells operate at high temperatures (700-1000 ° C) compared to other fuel cells, which have high energy efficiency. Hydrogen, methanol, ethanol and natural gas can be used as the fuel of the fuel cell, and the fossil fuel can be used as the fuel through the additional gasification process. Here, oxygen or air is used together as an oxidizing agent.

In general, a solid oxide fuel cell has a structure in which an air electrode, a solid electrolyte and a fuel electrode are sequentially stacked, and a functional layer is interposed between the layers to reduce resistance and increase activity at each interface. Yttria-stabilized zirconia (YSZ) stabilized by adding nickel or nickel oxide and yttria is used as a fuel electrode of a solid oxide fuel cell which is commonly used at present. Nickel is a good electron conductor in the high-temperature reducing atmosphere, and serves as electron transfer path. Yttria-stabilized zirconia prevents the coarsening of the skeleton and nickel particles that maintain the microstructure and adjusts the thermal expansion coefficient to be similar to the constituent material , And forms an oxygen ion path, thereby acting as an excellent ion conductor.

In the method of manufacturing a high-strength anode support for a high-temperature fuel cell, a zirconia stabilized by 10% of yttria at a molar ratio of 45 to 65 vol% is prepared in a conventional Korean Patent Publication No. 2005-0004996 "Method for manufacturing a high strength anode support for a solid oxide fuel cell" Adding carbon powder of activated carbon or carbon black as a pore-forming agent in an amount of 30 to 45 vol% to a mixed powder to which 35 to 55 vol% of nickel oxide powder is added, and adding 1 to 15 wt% A step of molding into a flat plate or a cylindrical shape by pressure molding, extrusion molding, or tapping with 5 wt% of a dispersant, 1 to 10 wt% of a plasticizer, and 1 to 3 wt% of a release agent, and a step of sintering A method for manufacturing a high-strength cathode support for a solid oxide fuel cell, comprising the steps of:

A mixture of nickel or nickel oxide and yttria-stabilized zirconia (8 mol% Y ₂ O ₃ , 92 mol% ZrO ₂ ) can be easily mixed by a dry or wet method, but due to the large specific gravity difference between the powders, One particle distribution structure. In addition, when the nano-size is used, the powders are different from each other, so that the two powders can not be dispersed at the same dispersion condition and aggregation of powders occurs. Particularly, nonuniform particle distribution causes microstructure nonuniformity of the anode after sintering, so that the grain size becomes large and the pore distribution is not uniform, so that the reaction point at the three phase interface is reduced.

The unevenness of the crystal grains and the pore distribution due to the geometry, size, cohesion, etc. of the microstructure of the raw material constituting the fuel electrode adversely affects the electrical conductivity, fuel permeability, nickel coarsening and three phase interfacial activity, . The thermal cycling and long - term operation at the anode and the oxidation and reduction reactions reduce the electrochemical activity because they reduce the reaction area of the nickel interface, the stabilized zirconia and the pore. There is a problem that the output of the unit cell is lowered.

In order to solve such problems, the present inventors prepared a core-cell by adding a nano-sized spherical nickel metal powder, a stabilized zirconia powder and a surfactant synthesized by the hydrazine reduction precipitation method into an ultrasonic dispersing machine.

The present invention relates to a method for producing a nickel / yttria-stabilized zirconia core-cell composite in which nickel and yttria-stabilized zirconia are distributed uniformly and have a dense microstructure to improve the electrochemical reaction and long-term performance of the anode for a solid oxide fuel cell The purpose is to provide.

Another object of the present invention is to provide a nickel / yttria stabilized zirconia core-cell composite produced by the above production method.

In order to achieve the above object, according to the present invention, there is provided a method for producing a nickel-based electrochemical cell, comprising the steps of (A) mixing spherical nickel and a cationic surfactant having a size of 0.5 .mu.m to 1 .mu.m together with distilled water and dispersing the nickel particles by ultrasonic dispersion, ;

(B) dispersing yttria-stabilized zirconia in distilled water by mixing the zirconia stabilized zirconia with an anionic surfactant in an amount of 50 to 100 nm and dispersing the yttria-stabilized zirconia, and coating an anionic surfactant on the yttria-stabilized zirconia surface;

(C) stirring the yttria-stabilized zirconia coated with the cationic surfactant-coated nickel and the anionic surfactant in a solvent in the range of pH 7 to 8 to make nickel as a core by the surface charge difference of the two particles, Preparing a core-cell composite in which yttria-stabilized zirconia is used as a shell; And

(D) preparing a core-shell composite powder as a rod-shaped pellet followed by high-temperature sintering; and (d) preparing a core / shell composite powder for a solid oxide fuel cell anode anode / stabilized zirconia core-cell composite.

As the cationic surfactant, it is preferable to use cetyltrimethyl ammonium bromide (CTAB) having an amount not exceeding the critical micelle concentration (CMC). As the anionic surfactant, sodium dodecyl sulfate (SDS) having an amount not exceeding a critical micelle concentration (CMC) is preferably used.

The ultrasonic dispersion in the steps (A) and (B) is preferably performed for 10 to 30 minutes with a pulse of 1 to 5 seconds and a space of 1 to 5 seconds.

The nano-spherical nickel are nickel chloride using (Nickel chloride, NiCl ₂ and 6H ₂ O), uses hydrazine hydrate (N ₂ H ₄ and H ₂ O) as a reducing agent, sodium hydroxide (NaOH) as a precipitating agent as a starting material Which is produced by reacting at a molar ratio of 1: 2 to 10: 2 to 10, is preferable.

The yttria-stabilized zirconia in the sol state is preferably prepared by a solvent thermal method using zirconium hydroxide (Zr (OH) ₄ ) and yttrium nitrate (Y (NO ₃ ) ₃ ) Do.

In the step (D), the high-temperature sintering is performed by raising the temperature by 5 ° C per minute to 1400 ° C using H ₂ 5% and Ar 95% gas, and maintaining the heat treatment for 2 hours.

According to another aspect of the present invention, there is provided a nickel / stabilized zirconia core-cell composite for a solid oxide fuel cell anode, which is produced by the above production method.

The nickel / stabilized zirconia core-cell composite prepared according to the manufacturing method of the present invention has improved particle connectivity of nickel particles due to uniform particle arrangement and uniform distribution when used as an SOFC anode, , Sintering ability and strength enhancement, so that the deterioration of the cathode performance is reduced, the output of the single cell and the long-term stability are improved, and the single slurry is easily dispersed. It is easy to utilize in the process.

1 is a schematic view showing the principle of forming a core-shell structure of nickel / stabilized zirconia (YSZ) using the characteristics of a surfactant and ultrasonic dispersion.
2 is a scanning electron microscope (SEM) photographic view of a nickel / stabilized zirconia (YSZ) core-cell composite made using a surfactant in accordance with an embodiment of the present invention.
FIG. 3 is a view illustrating a sintered body obtained by molding a sintered body into a rod-shaped pellet by using a nickel / stabilized zirconia (YSZ) core-cell composite made by using a surfactant and ultrasonic dispersion according to an embodiment of the present invention, As shown in FIG.

Hereinafter, the present invention will be described in detail.

According to the present invention, there is provided a method for preparing an aqueous coating composition, comprising the steps of: (A) mixing spherical nickel and a cationic surfactant having a size of 0.5 .mu.m to 1 .mu.m together with distilled water, dispersing the nickel particles dispersed by ultrasonic dispersion, and coating the surface of the nickel with a cationic surfactant; (B) dispersing yttria-stabilized zirconia in distilled water by mixing the zirconia stabilized zirconia with an anionic surfactant in an amount of 50 to 100 nm and dispersing the yttria-stabilized zirconia, and coating an anionic surfactant on the yttria-stabilized zirconia surface; (C) stirring the yttria-stabilized zirconia coated with the cationic surfactant-coated nickel and the anionic surfactant in a solvent in the range of pH 7 to 8 to make nickel as a core by the surface charge difference of the two particles, Preparing a core-cell composite in which yttria-stabilized zirconia is used as a shell; And (D) high-temperature sintering the core-shell composite powder in the form of a rod-shaped pellet. The method for producing a nickel / stabilized zirconia core-cell composite for a solid oxide fuel cell anode is provided.

The spherical nickel can be prepared by the hydrazine reduction precipitation method. As an example, nickel chloride (NiCl ₂ ) is used as a starting material, and it is put into a molten metal together with distilled water. Adjust the initial temperature and pH of the mixture and add hydrazine (N ₂ H ₄ ) at a constant rate. Then, sodium hydroxide (NaOH) is added to precipitate nickel. At this time, the nickel chloride starting materials participating in the reaction (Nickel chloride, NiCl ₂ and 6H ₂ O), hydrazine hydrate (N ₂ H ₄ and H ₂ O) as a reducing agent and sodium hydroxide (NaOH) as a precipitating agent is 1: 2 or It is preferable to carry out the reaction at a molar ratio of 10: 2 to 10. This is washed with deionized water several times and dried.

The thus prepared nickel is mixed with a cationic surfactant and distilled water to perform ultrasonic dispersion. In this case, the cationic surfactant should be a mole which does not exceed the critical micelle concentration (CMC). Preferably, the cationic surfactant may be cetyltrimethyl ammonium bromide (CTAB) of 0.3 to 0.8 mM. In this process, the nickel surface is coated with a cationic surfactant to have (+) surface charge.

The yttria-stabilized zirconia in the sol state can be prepared by a solvent thermo-synthetic method. Zirconium hydroxide (Zr (OH) ₄ ), yttrium nitrate Y (NO ₃ ) ₃ · 6H ₂ O and distilled water are mixed and melted to prepare zirconia stabilized zirconia which is synthesized by solvent thermal process (Hydrothermal) . The mixture is mixed with an anionic surfactant and subjected to ultrasonic dispersion. The anionic surfactant should be a mole not exceeding the critical micelle concentration (CMC). Preferably, 0.3 to 0.8 mM of sodium dodecyl sulfate (SDS) may be used as the anionic surfactant. Thus, yttria-stabilized zirconia is coated with an anionic surfactant to produce yttria-stabilized zirconia having (-) surface charge.

As described above, in the present invention, ultrasonic dispersion is used to reduce the cohesion force of nano-sized particles and to increase the dispersing power, and surfactants having different charge are used in order to coat different surface charges thereon.

The nickel adsorbed on the cationic surfactant and the yttria-stabilized zirconia adsorbed on the anionic surfactant are stirred using a stirrer. It is more preferable that the agitation is performed using a solvent having a pH of 7 in order to increase the surface charge difference of the material. Here, nickel with positive surface charge and yttria stabilized zirconia with negative surface charge are adsorbed due to surface charge difference. After stirring for a period of time, the core is placed in the core and the core-cell complex is placed where the yttria-stabilized zirconia is located in the cell.

When a fuel electrode is manufactured using the nickel / stabilized zirconia core-cell composite for an anode electrode manufactured as described above, the core and the cell components are uniformly distributed, and the crystal grains are nano-structured and the microstructure becomes dense, .

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples.

However, the following examples are illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

Preparation Example 1: Preparation of nickel having (+) surface charge

In the present invention, an ultrasonic disperser is used to reduce the agglomeration phenomenon of nanospherical nickel particles and uniformly coat the surface of the nickel particles with the cationic surfactant. NiCl ₂ as a starting material, spherical nickel powder prepared with 5 mole of hydrazine reducing agent, 8 mole of sodium hydroxide precipitant, and 0.8 mM of Cetyltrimethyl ammonium bromide were mixed in distilled water and mixed. This was run for 20 minutes using an ultrasonic disperser with a pulse of 1 to 5 seconds and a blank of 1 to 5 seconds. Then, the mixture was stirred in a stirrer for about 120 minutes.

Production Example 2: Preparation of yttria-stabilized zirconia having (-) surface charge

In the present invention, an ultrasonic disperser is used to uniformly coat an anionic surfactant on nano-sized zirconia stabilized zirconia particles. Zirconia stabilized zirconia was synthesized by solvent thermo - synthesis using 92 mole% zirconium hydroxide and 8 mole% yttrium nitrate as starting materials. Synthesized yttria stabilized zirconia and 0.4 mM anionic surfactant (Sodium Dodecyl Sulfate) were added to distilled water and mixed. This was put into an ultrasonic dispersing machine and operated for 20 minutes with 1 to 5 seconds pulse and 1 to 5 seconds blank. Then, the mixture was stirred in a stirrer for about 120 minutes.

Example 1: Preparation of Ni-YSZ core-cell composite powder

Nickel adsorbed by the cationic surfactant and yttria stabilized zirconia adsorbed on the anionic surfactant are mixed in a distilled water solvent. At this time, the solvent used was a pH 7 range in which the surface charge difference of the two particles was the largest. The mixture was agitated at room temperature for 120 minutes to form a core-cell. After stirring, the particles were collected and dried in a hot air dryer for 24 hours to synthesize a composite having nickel and stabilized zirconia core-shell structure.

Example 2: Sintering of Ni-YSZ core-cell composite powder

The Ni-YSZ core-cell composite prepared in Example 1 was formed into rod-shaped pellets by a high-pressure uniaxial shrinking machine using a rod-shaped mold, followed by reduction sintering. As the reducing sintering condition, 5% H ₂ and 95% Ar were used to raise the temperature to 1400 ° C at a rate of 5 ° C per minute, followed by heat treatment for 2 hours.

Comparative Example 1: Preparation of Ni-YSZ mixed powder sample

To compare the electrical conductivity with the Ni-YSZ core-cell composite prepared in Example 1, a specimen was prepared from a mechanically mixed Ni-YSZ mixed powder rather than a core-shell structure. Mixed with a commercially available yttria stabilized zirconia having a pore size of 1 μm and a 100 nm size in a 6: 4 ratio. The rod-shaped mold was used to produce rod-shaped pellets by a high-pressure uniaxial shrinking machine, followed by reduction sintering. As the reducing sintering condition, 5% H ₂ and 95% Ar were used to raise the temperature to 1400 ° C at a rate of 5 ° C per minute, followed by heat treatment for 2 hours.

Test Example 1: Confirmation of formation of core-shell structure of composite

Cells of nickel and stabilized zirconia prepared by the above examples were analyzed by a scanning electron microscope (SEM) in order to confirm whether the core-shell structure was well formed. The results are shown in FIG. 2 . As can be seen in FIG. 2, it was found that the nickel surrounds the core-shell structure in which yttria-stabilized zirconia is adsorbed and encapsulated.

Test Example 2: Confirmation of formation of core-shell structure of composite

In order to examine the effect of forming the core-cell structure of the nickel-stabilized zirconia composite prepared by the above example on the electric conductivity after sintering, the specimens formed by the pelletization of the membrane pellets were subjected to the reduction and sintering, And the results are shown in FIG. As a result, it was confirmed that the electrical conductivity of the specimen prepared using the core-cell composite prepared according to the above-mentioned example was higher than that of the general mechanically mixed specimen according to the comparative example 1.

Claims (8)

(A) Sodium nickel of 0.5 ~ 1um in size and distilled water were mixed together with cetyltrimethyl ammonium bromide (CTAB) in an amount not exceeding the critical micelle concentration (CMC) as a cationic surfactant and ultrasonically dispersed to obtain aggregated nickel Dispersing the particles and coating a nickel surface with a cationic surfactant;
(B) Sodium dodecyl sulfate (SDS) in an amount of 50-100 nm in the amount of 50-100 nm in the amount of triallyl stabilized zirconia and an anionic surfactant not exceeding the critical micelle concentration (CMC) Dispersing the yttria-stabilized zirconia and coating the surface of the yttria-stabilized zirconia with an anionic surfactant;
(C) stirring the yttria-stabilized zirconia coated with the cationic surfactant-coated nickel and the anionic surfactant in a solvent of pH 7, making the nickel core a difference in surface charge difference between the two particles, Preparing a core-cell composite having zirconia as a shell; And
(D) a high-temperature sintering step in which the core-cell composite powder is formed into a rod-shaped pellet, and then heated to 1400 ° C at a temperature of 5 ° C per minute using H ₂ O 5 and Ar 95% Method for manufacturing a nickel / stabilized zirconia core - cell composite for an anode fuel cell. delete delete The method according to claim 1, wherein the ultrasonic dispersion in steps (A) and (B) is carried out for 10 to 30 minutes with 1 to 5 seconds of pulse and 1 to 5 seconds of space. Method for manufacturing a nickel / stabilized zirconia core - cell composite for an anode fuel cell. The method of claim 1, wherein the nano-spherical nickel metal powder starting material, nickel chloride (Nickel chloride, NiCl ₂ and 6H ₂ O), hydrazine hydrate as a reducing agent (N ₂ H ₄ and H ₂ O) and sodium hydroxide as a precipitating agent ( NaOH) in a molar ratio of 1: 2 to 10: 2 to 10, based on the total weight of the nickel / stabilized zirconia core-cell composite. The method according to claim 1,
Wherein the zirconia stabilized zirconia in the sol state is produced by a solvothermal method using zirconium hydroxide (Zr (OH) ₄ ) and yttrium nitrate (Y (NO ₃ ) ₃ ) as a starting material. Method for manufacturing nickel / stabilized zirconia core - cell composite for fuel cell anode. delete A nickel / stabilized zirconia core-cell composite for an anode anode prepared according to claim 1.

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