KR20140032597A - Tubular solid oxide fuel unit cells, method of manufacturing the same, and for tubular solid oxide fuel cells comprising the same - Google Patents

Abstract

The present invention relates to a cylindrical solid oxide unit cell for a fuel cell, a production method of the same, and a cylindrical solid oxide fuel cell comprising the same, and more specifically, to: a cylindrical solid oxide unit cell for a fuel cell which is capable of reducing production costs by optimizing the production process of a cylindrical solid oxide fuel cell, and has a high electric density at medium and high temperatures (450-700°C); a production method of the same; and the cylindrical solid oxide fuel cell comprising the same.

Description

Cylindrical Solid Oxide Fuel Cells, Method of Manufacturing the Same, and for Tubular Solid Oxide Fuel Cells Comprising the Same

The present invention relates to a cylindrical unit cell for a solid oxide fuel cell, a method of manufacturing the same, and a cylindrical solid oxide fuel cell including the same. More specifically, it is excellent in economic efficiency through optimization of the manufacturing process, and low to medium temperature (450 to 700 ° C.) The present invention relates to a unit cell for a cylindrical solid oxide fuel cell having a high power density, a method for manufacturing the same, and a cylindrical solid oxide fuel cell including the same.

Solid Oxide Fuel Cells (SOFCs) produce electricity by electrochemical reaction of fuel (H ₂ , CO) and air (oxygen) at a high temperature of 600 ~ 1000 ℃ using solid ceramic as electrolyte. As a fuel cell, there is an advantage in generating power generation efficiency and excellent economic efficiency among the existing power generation technology.

SOFCs can be manufactured in various types of unit cells, such as flat and cylindrical, because the electrolyte and the electrode are in a solid state, and the anode support type, the cathode support type, and the electrolyte support type according to the fuel cell support. Are classified.

Plate-type SOFCs have high power density, high productivity, and thin electrolyte, but require a gas seal using a separate sealing material, and due to the use of a metal connecting material at high temperature, electrode efficiency is reduced due to chromium volatilization. However, it has a disadvantage of lacking reliability due to low resistance to thermal cycles. Moreover, because flat panel SOFCs are difficult to manufacture large-area cells and also difficult to manufacture large-capacity stacks, solving these problems becomes a key to practical use.

Cylindrical SOFCs do not require or be easily gas sealed, and the mechanical strength of the support has been proven to be reliable. Compared to flat-panel SOFCs, the current path has a long internal current resistance and low power density. However, it is the closest model to commercialization because of its stability against thermal cycle and easy large area.

Operation of cylindrical SOFCs at moderate temperatures (600-800 ° C) and low temperatures (450-600 ° C) allows the cells to operate reliably and the use of cost-effective gas seals and connectors.

The present inventors have intensively researched to lower the manufacturing cost and obtain high power density by optimizing the manufacturing process of the anode support of the cylindrical SOFCs described above, and as a result, the economical efficiency is excellent, and at low to low temperatures (450-700 ° C.) A cylindrical solid oxide fuel cell having a high power density, a manufacturing method thereof, and a cylindrical solid oxide fuel cell including the same have been developed.

The present invention, in consideration of the problems of the prior art, excellent economic efficiency through the optimization of the manufacturing process, a unit cell for a cylindrical solid oxide fuel cell having a high power density at low to low temperatures (450 ~ 700 ℃), a manufacturing method and the same It is an object to provide a cylindrical solid oxide comprising.

The present invention is to solve the above problems, an anode support including yttria stabilized zirconia (YSZ) and NiO; A NiO-functional layer comprising NiO formed on one side of the anode support; A NiO-GDC cathode layer including NiO and GDC (gadolinium-doped ceria) formed on the NiO-functional layer; A solid electrolyte layer including GDC (gadolinium-doped ceria) formed on the NiO-GDC cathode layer; And a first cathode layer including the LSCF-GDC formed on the surface of the solid electrolyte layer and a second cathode layer including the LSCF formed thereon.

The composition for forming the anode support may include the yttria stabilized zirconia (YSZ), the NiO, a pore former, a binder, and distilled water.

In the composition for forming the anode support, the volume ratio of the yttria stabilized zirconia (YSZ) powder and the NiO powder is preferably 50 to 70:30 to 50.

The thickness of the anode support is preferably about 1.0 to 1.4 mm.

The composition for forming the NiO-functional layer may further include the NiO, surfactant, pore former and binder.

The NiO-functional layer is formed by dip-coating, the thickness of the NiO-functional layer is preferably 13 to 15 ㎛.

The composition for forming the NiO-GDC cathode layer may further include the NiO, the gadolinium-doped ceria (GDC), a surfactant, a pore-forming agent and a binder.

The NiO-GDC cathode layer is formed by dip-coating, and the thickness of the NiO-GDC cathode layer is preferably 11 to 13 μm.

The composition for forming the solid electrolyte layer of the unit cell for a cylindrical solid oxide fuel cell of the present invention may further include a gadolinium-doped ceria (GDC), a dispersant, a surfactant, a plasticizer and a binder.

The solid electrolyte layer provides that formed by carbonate coprecipitation.

The carbonate coprecipitation method, the first step of dissolving the raw material in distilled water to form an aqueous solution; A second step of making a precipitate using a reverse strike method of slowly dropping the aqueous solution prepared in the first step into the (NH ₄ ) ₂ CO ₃ aqueous solution; A third step of washing and drying the precipitate made in the second step; And a fourth step of pulverizing the material dried in the third step. The raw material provides Ce (NO ₃ ) ₃ .6H ₂ O and Gd (NO ₃ ) ₃ .6H ₂ O. The thickness of the solid electrolyte layer is preferably 21 to 22㎛.

The first cathode layer of the cylindrical unit cell for a solid oxide fuel cell of the present invention may include La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ , GDC (gadolinium-doped ceria), dispersant, plasticizer, surfactant, and binder, The second cathode layer formed on the first cathode layer may further include La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ , a dispersant, a plasticizer, a surfactant, and a binder.

The first and second cathode layers of the cylindrical unit cell for a solid oxide fuel cell of the present invention may be formed using dip coating. The unit cell for a cylindrical solid oxide fuel cell of the present invention comprises a first step of sequentially stacking an anode support, a NiO-functional layer, a NiO-GDC cathode layer, a solid electrolyte layer, a first cathode and a second cathode layer to form a laminate; And a second step of sintering the laminate.

The present invention provides a cylindrical solid oxide fuel cell employing the cylindrical solid oxide fuel cell unit cell prepared above.

In the cylindrical solid oxide fuel cell of the present invention, a yttria stabilized zirconia (Ni-YSZ) composite is used for a cathode support, and a gadolinium-doped ceria (GDC) is used for a solid electrolyte layer, and the anode support and the solid electrolyte layer are generated between the anode support and the solid electrolyte layer. In order to prevent the interfacial reaction, the NiO-functional layer and the NiO-GDC cathode layer may be disposed to implement a fuel cell having high power density and excellent economic efficiency at low to low temperatures (450 to 700 ° C.).

1 is an X-ray diffraction pattern of a carbonate precursor prepared by carbonate coprecipitation.
2 is an SEM image of particles of the synthesized carbonate precursor.
3 is an apparent density graph of pellet pellets sintered by the Archimedes method.
4 is an image of a cell for a cylindrical solid oxide fuel cell.
5 is a premise image of a cell for a cylindrical solid oxide fuel cell.
6 is a pore image formed on the surface of the GDC electrolyte.
7 is an SEM image showing the cross section of the cell.
8 is a graph of IV and IP characteristics of cells measured at 450-600 ° C.
9 is a graph measuring the complex impedance of 450-600 ° C. in an open circuit state.
FIG. 10 is a graph illustrating the ohmic resistance Rb, the electrode resistance Re, and the total resistance Rt of the cell based on FIG. 8.
11 is an image of a cell at 450-600 ° C. by sintering an electrolyte layer.
12 sintered the electrolyte layer and measured the cell performance at 450-600 ° C.

Hereinafter, the present invention will be described in detail. In the following description of the present invention, detailed descriptions of related well-known configurations or functions may be omitted.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and should be construed in accordance with the technical meanings and concepts of the present invention.

The embodiments described in the present specification and the configurations shown in the drawings are preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention and thus various equivalents and modifications Can be.

When a portion of a layer, film, substrate, etc. is "on top" of another component, this includes not only being on another component, but also having another component in between. Conversely, when a part is "just above" another component, it means that there is no other component in the middle.

Solid oxide fuel cells (SOFCs) are devices that directly convert the chemical energy of hydrogen and hydrocarbon fuels into electrical energy, and have high energy conversion efficiency, low emission of pollutants and flexibility of fuel. This is high. SOFCs are largely divided into planar type and tubular type according to their shape. Cylindrical SOFCs do not require or facilitate gas sealing, provide good mechanical strength of the support, good stability against thermal cycles and easy large area. However, cylindrical SOFCs have a problem of low power density due to high internal resistance due to long current paths.

In the present invention, through the optimization of the manufacturing process of the cylindrical solid oxide fuel cell, a unit cell for a cylindrical solid oxide fuel cell having a high power density at a low to medium temperature (450 ~ 700 ℃) with excellent economics, a manufacturing method and a cylindrical solid comprising the same To provide an oxide.

The present invention provides an anode support including yttria stabilized zirconia (YSZ) and NiO; A NiO-functional layer comprising NiO formed on one side of the anode support; A NiO-GDC cathode layer including NiO and GDC (gadolinium-doped ceria) formed on the NiO-functional layer; A solid electrolyte layer including GDC (gadolinium-doped ceria) formed on the NiO-GDC cathode layer; And a first cathode layer including LSCF-GDC formed on the surface of the solid electrolyte layer and a second cathode layer including LSCF formed thereon.

First, the anode support supports the entire fuel cell in a tubular shape. The oxidation of hydrogen and carbon monoxide introduced into the fuel cell occurs.

The volume ratio of yttria stabilized zirconia (YSZ) and NiO for forming the anode support is preferably 50 to 70:30 to 50.

Ni has high electron conductivity and at the same time, adsorption of hydrogen and a hydrocarbon-based fuel occurs, thereby exhibiting high electrode catalyst activity. In addition, it is advantageous as an electrode material in that the value is lower than that of platinum. Yttria-stabilized zirconia (YSZ) is a ceramic material made by adding yttrium oxide (yttria) to zirconium oxide (zirconia) to make it stable at room temperature. It also has the advantage of good ion conductivity even at high temperatures.

The composition for forming the anode support may further include a pore-forming agent, a binder and distilled water. Here, the cathode support may be manufactured in a porous cylindrical form using activated carbon, carbon black, and poly (methyl methacrylate) (hereinafter referred to as PMMA) as a pore forming agent. Here, the binder may be used without limitation that is commonly known in the art to the present invention, for example, methyl cellulose (Methyl cellulose), hydroxypropyl methyl cellulose (Hydroxypropyl methyl cellulose) may be used as the binder. . The binder serves to bind the powdered composite and at the same time serves to form pores with the pore forming agent. Here, distilled water must be used in an appropriate amount so that the anode support can be easily extruded. However, it is not limited thereto.

The NiO-functional layer may be formed by dip-coating on the anode support, and the composition for forming the NiO-functional layer may further include a dispersant, a surfactant, a pore-forming agent, and a binder. have.

First, in order to prepare a coating liquid for coating a NiO-functional layer, it is preferable to add NiO powder, which is a coating material, and the pore-forming agent to mix and ball mill for 20 to 30 hours. Here, the pore-forming agent may use activated carbon, carbon black, PMMA, or the like. However, it is not limited thereto. After the addition of the plasticizer and the binder is preferably ball milling for another 20 to 30 hours to prepare a NiO coating solution. The anode support was immersed in the NiO coating solution for 10 to 15 seconds and then slowly lifted up and dried at room temperature. At this time, the settling speed and the tensile speed is preferably 100 to 120 mm / min and 10 to 15 mm / min, respectively.

The plasticizer and the binder may be used without limitation to those commonly known in the art, for example, the plasticizer is Di-n-butyl phthalate and the like, the binder is polyvinly butyral, methyl cellulose (Methyl cellulose) And hydroxypropyl methyl cellulose may be used. However, it is not limited thereto. After that, it is preferable to heat-treat the dried NiO-functional layer formed at 1000 to 1200 ° C. for 2 to 4 hours to obtain easy mechanical strength. It is preferable that the thickness of the said NiO-functional layer is 13-15 micrometers.

The NiO-GDC cathode layer may be formed by dip-coating on the NiO-functional layer, and the composition for forming the NiO-GDC cathode layer may include a dispersant, a surfactant, a pore-forming agent, and a binder. It may further include. First, it is preferable to add NiO powder and GDC (gadolinium-doped ceria, Gd _0.1 Ce _0.9 O _1.95 ) powder, which is a coating material, in a weight ratio of 1: 1 to prepare a coating liquid for coating the NiO-GDC cathode layer. The NiO-GDC anode layer may further include a plasticizer and a binder. The plasticizer and the binder can be used without limitation, those conventionally known in the art. The coating solution prepared here is coated on the NiO-GDC cathode layer, and then heat-treated at 1000 to 1200 ° C. for 2 to 4 hours to obtain a mechanical strength that is easy to handle the NiO-GDC cathode layer. It is preferable that the thickness of the said NiO-GDC cathode layer is 11-13 micrometers.

The solid electrolyte layer is formed on the NiO-GDC cathode layer. Since the solid electrolyte has a lower ionic conductivity than a liquid electrolyte such as an aqueous solution or a molten salt, the solid electrolyte has a low voltage drop due to resistance polarization. However, since the minute gaps, pores, or scratches are likely to occur, the electrolyte employed in the unit cell for a solid oxide fuel cell requires homogeneity, compactness, heat resistance, mechanical strength, and stability, and Ce (NO ₃₎ is a material for the solid electrolyte. ) ₃ · 6H ₂ O and Gd (NO ₃ ) ₃ · 6H ₂ O can be used.

The solid electrolyte layer may be formed by carbonate co-precipitation, and the composition for forming the solid electrolyte layer may further include a dispersant, a surfactant, a plasticizer and a binder.

The carbonate co-precipitation method, a first step of dissolving the raw material in distilled water to make an aqueous solution; a second step of making a precipitate using a reverse strike method of slowly dropping the aqueous solution prepared in the first step in (NH ₄ ) ₂ CO ₃ aqueous solution ; A third step of washing and drying the precipitate made in the second step; And a fourth step of obtaining a powdery product by grinding the material dried in the third step. The raw material may be made of Ce (NO ₃ ) ₃ · 6H ₂ O and Gd (NO ₃ ) ₃ · 6H ₂ O.

 In the solid electrolyte layer, unlike the NiO-functional layer or the NiO-GDC cathode layer, it is preferable not to add a pore-forming agent to obtain a dense layer. The powder form obtained in the carbonate coprecipitation method is preferably coated on the NiO-GDC cathode layer using the aforementioned immersion coating and then dried at about 300 to 500 ° C. in order to obtain easy mechanical strength. Thereafter, the heat treatment is repeated for 2 to 3 hours to form a GDC (gadolinium-doped ceria) solid electrolyte layer having an appropriate thickness. The thickness of the solid electrolyte layer is preferably 21 to 22 ㎛.

In addition, the solid electrolyte layer may include LSGM (strontium- and magnesium-doped lanthanium gallate). The thickness of the solid electrolyte layer is preferably thinned to 21 to 22 ㎛, which helps to lower the operating temperature of the unit cell to 700 to 850 ℃. In addition, since the GDC (gadolinium-doped ceria) and LSGM (strontium- and magnesium-doped lanthanium gallate) has high ion conductivity, the operating temperature of the unit cell can be further lowered to 600 ° C or less.

Then, first and second air cathode layers are formed on the solid electrolyte layer. The first and second cathode layers are made of perovskite oxide. In particular, the catalyst activity and electronic conductivity are both high lanthanum strontium manganite arsenide _{(La 0 .84 Sr 0 .16)} Mn0 3 may typically be used. Oxygen is converted to oxygen ions by the catalytic action of LaMnO ₃ . Perovskite-type oxides containing transition metals are suitable as materials for the first and second cathode layers because they have electron conductivity along with ion conductivity. However, any other suitable material besides the above-mentioned materials may be used for the first and second cathode layers. The first and second cathode layers may be formed using a dip coating method. Here, the immersion coating method is a method commonly known in the art to form the first and second air cathode layers, and can be used without limitation. However, it is not limited thereto.

For example, the first cathode layer is _{La 0 .6 Sr 0 .4 Co 0} .2 Fe 0 .8 O 3 -δ powder and Gd _{0 .1} Ce _{0 .9} O _{1 .95} powder mass ratio of 50: 50 LSCF-GDC coating solution was added to the coating solvent and mixed, and then, the mixture was prepared by adding LS-dispersant as a dispersant, Di-butyl phthalate as a plasticizer, Triton X-100 as a surfactant, and polyvinyl butyral as a binder.

In addition, the second cathode layer is _{La 0 .6 Sr 0 .4 Co 0} .2 Fe 0 .8 O 3 -δ can be prepared by adding the powder of the same organic material as above was added to a coating solvent. Herein, the coating solvent may be used without limitation what is commonly known in the art to which the present invention pertains, and the organic material refers to the words collectively referred to herein as a dispersant, a plasticizer, a surfactant, and a binder.

The cylindrical unit cell for a solid oxide fuel cell is formed by sequentially stacking a cathode support, a NiO-functional layer, a NiO-GDC cathode layer, a solid electrolyte layer, a first cathode layer, and a second cathode layer, and forming the laminate. It can be prepared by sintering.

The fuel cell according to the present invention is caused by the interdiffusion occurring at the interface between the anode support and the electrolyte layer during the high temperature sintering process during the manufacturing of the unit cell by disposing the electrolyte interfacial reaction prevention layer between the anode support and the solid electrolyte as described above. The problem of lowering the power density was solved by suppressing the secondary phase having high resistance. Meanwhile, in the above embodiment, a cylindrical fuel cell having a circular cross section is described, but the cylindrical shape may be implemented by being deformed into any shape having a tubular shape, that is, a square column, a triangular column, a hexagonal column, or a flat tube shape.

The present invention may also include a cylindrical solid oxide fuel cell employing the cylindrical solid oxide fuel cell unit cell.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for describing the present invention in more detail and that the scope of the present invention is not limited by these embodiments in accordance with the gist of the present invention .

Example 1 : Fabrication of unit cell for cylindrical solid oxide fuel cell.

1) Manufacture of Ni-YSZ anode support

8 YSZ (8 mol% yttria-stabilized zirconia) powder and NiO (J. T. Baker Co., USA) powder were mixed at a volume ratio of NiO: 8 YSZ = 40: 60 to form a mixed powder. The powder and the activated carbon to be used as a pore-forming agent were put into a ball mill for 14 days and dried. The paste was mixed evenly with the binder and 25 wt% distilled water. The paste is made of tubes by extrusion and then dried at 120 ℃ for 12 hours. The green body thus produced was sintered at 1100 ° C. to form a Ni-YSZ support.

2) NiO-functional layer and NiO-GDC cathode layer fabrication

The NiO-functional layer including NiO was coated on the porous Ni-YSZ anode support by dip-coating. NiO coated slurry was made by the following procedure. NiO powder, a coating material, and activated carbon, a pore-forming agent, were added to a mixed solvent of toluene and 2-propanal. After sorbitan trioleate and Triton X-100 were added as a dispersant and a surfactant, ball milling was performed for 24 hours. Di-n-butyl phthalate was added to the slurry as a plasticizer and polyvinly butyral was added to the slurry as a binder, followed by ball milling for 24 hours.

The Ni-YSZ cylindrical support was immersed in the NiO coating solution for 10 seconds and then slowly lifted up and dried at room temperature. Settling and pulling speeds are 110mm / min and 10.6mm / min, respectively. The NiO film formed after drying is heat treated at 1100 ° C. for 3 hours to obtain easy mechanical strength. NiO-GDC cathode layer containing Ni and GDC was obtained by immersion coating in Ni-GDC coating liquid. Was used as NiO and _{Gd 0 .1 Ce 0 .9 O 1} .95 with a coating material NiO and GDC powder was added in a weight ratio of 50:50. After coating the NiO-GDC cathode layer was also heat-treated for 3 hours at 1100 ℃.

3) Solid electrolyte layer production

The GDC powder used for the GDC solid electrolyte layer was a powder synthesized by carbonate coprecipitation. Unlike the NiO coating solution and the Ni-GDC coating solution, no pore-forming agent was added to obtain a dense layer. Dip coating, drying, and heat treatment at 400 ° C. for 2 hours were repeated twice to form a GDC layer. The produced cell was sintered at 1300-1400 ° C. for 5 hours. _{La 0 .6 Sr 0 .4 Co 0} .2 Fe 0 .8 O 3 -δ (LSCF, Fuelcellmaterials, USA) -Gd 0.1 Ce 0.9 O 1.95 (GDC, Anan Kasei Co., Japan) over a composite sintered electrolyte layer The layer and the LSCF layer were sequentially formed by immersion coating. After drying for a predetermined time and heat treatment at 1150 ℃ for 3 hours all the added organic material was burned out. The structure of the finished cell is as Ni-YSZ / NiO / Ni-GDC / GDC / LSCF-GDC / LSCF.

Experimental Example 1 : Solid electrolyte  Apparent density measurement after powder synthesis.

The specimen was prepared by synthesizing the solid electrolyte powder in the same manner as in Example 1, and after sintering the prepared specimen at 1050-1400 ° C. for 5 hours, the apparent density was measured using the Archimedes method.

Experimental Example 2 : Unit cell performance measurement for cylindrical solid oxide fuel cells.

Before measuring the cell performance, the cells were reduced at 600 ° C. for 3 hours while flowing 10 sccm of H 2 in a quartz tube. After NiO was completely reduced to Ni, nickel felt connected with Ni wire was fixed to the inside of the cell with a paste, and used as a negative electrode current collector. Ag wire was wound around the positive electrode and used as a positive electrode current collector. H2 was moisturized using water and flowed at 250 cc / min inside the cell, and air was flowed at 1.5 L / min outside the cell to measure cell performance.

Experimental Example 3 : Of unit cell for cylindrical solid oxide fuel cell Ni - YSZ  Characterization of Powders and Cells.

Phase and crystallinity of the Ni-YSZ powder were analyzed by X-ray diffraction analysis (Rigaku, DMAX-II A, Cu Kα). Scanning microscope (SEM) (FE-SEM, Hitachi S-4800) was used to observe the structure of the powder and the cell. IV characteristics were measured using a DC electronic load. The complex impedance analysis of the cell used an interface with a high frequency analyzer (Solartron-1260, Solartron Instruments, UK) in the frequency range 10-2-106Hz.

As a result of analyzing the X-ray diffraction pattern of the raw material of the solid electrolyte layer according to Example 1, it was as shown in FIG. 1. 1 (b) and 1 (c), after calcining at 700 ° C. and 900 ° C. for 2 hours, it can be seen that crystallized GDC powder having a fluorite phase is formed. The crystallite sizes of the GDC powders calcined at 700 ° C and 900 ° C calculated using the Scherrer equation are 31.0 ± 1.2 nm and 52.8 ± 1.5nm. This means that the higher the calcination temperature, the coarser the particles were.

FIG. 2 is an SEM image of raw material particles of the solid electrolyte layer synthesized according to Example 1. FIG. 2 (a) shows the synthesized raw material particles are secondary particles composed of very small primary particles (size: 95 ± 14 nm). FIG. 2 (b) shows that the size of the primary particles of the powder heat-treated at 700 ° C. was reduced to 66 ± 12 nm in the SEM analysis, which shows that the raw material was decomposed into oxide during the heat treatment. 2 (c) shows that when calcined at a higher 900 ° C., the particle size increases to 88 ± 16 nm, which is the same result as the X-ray diffraction analysis.

FIG. 3 is an apparent density graph of pellet samples obtained by calcining the calcined powder according to Experimental Example 1 at 1050-1400 ° C. for 5 hours by the Archimedes method. When the powder calcined at 900 ° C., the apparent density increases until the sintering temperature reaches 1200 ° C. and slightly saturates above that with a slight difference. On the other hand, if the calcination temperature is lowered to 700 ° C, densification increases significantly. The density of the sintering temperature is 1050 ℃ when GDC pellet is 6.9g / cm ^3, is 7.18g / cm ³ when the sintering temperature is increased to 1200 ℃. Considering that the theoretical density of GDC powder synthesized in this study is 7.214g / cm ³ , 8 it can be seen that the relative density is 95% at 1050 ℃.

Densification of ceramics is greatly affected by the state of the initial powder and the degree of densification of the green body. Until now, chemical methods such as solid phase reaction method, combustion process, sol-gel method, hydrothermal process, and carbonate coprecipitation method have been proposed to synthesize high purity GDC powder. In particular, the carbonate coprecipitation method is known as a method that can be fully densified at low sintering temperature. For example, Li et al. Report that fully densify the _{Gd 0 .2 Ce 0 .8 O 1} .9 at the sintering temperature of 1100 ℃. This study was further sintered at a low temperature of _{Gd 0 .1 Ce 0 .9 O 1} .95 densification, which is considered to be because it has the high reactivity of this powder made through a carbonate co-precipitation.

After immersing the GDC layer on the NiO-YSZ support / NiO / NiO-GDC and sintering at 1300-1400 ° C. for 5 hours. When the powder calcined at 700 ° C., the GDC layer was largely cracked or fell from the cathode layer. On the other hand, when using the powder calcined at 900 ℃ impermeable GDC layer was obtained. When two different layers of laminate structure are densified, if the final shrinkage and the shrinkage rate differ greatly during densification, the two layers split or fall apart. Considering that the densities of GDC pellet specimens sintered at 1300-1400 ° C were similar regardless of the calcination temperature (Fig. 3), the cracks and cracks found in cells fabricated using powder calcined at 700 ° C The floating between the layers is believed to be due to the difference in the amount of shrinkage that occurs during the densification process. Thus, a cylindrical SOFC cell was constructed using powder calcined at 900 ° C.

4 is an image of a cell for a cylindrical solid oxide fuel cell according to Example 1. FIG. As shown in FIG. 4 (a), a NiO-YSZ tube (length: ˜8 cm, outer diameter: 7.5 mm, inner diameter: 4.9 mm) was used as a support, and a NiO-GDC layer was used as a cathode. YSZ and _{Gd 0 .2 Ce 0 .8 O 1} .9 is high by mutual diffusion of Y, Zr, Gd, Ce at a temperature of at least 1200 ℃ secondary trader of resistance _{Ce 0.37 Zr 0.38 Gd 0.18 Y 0.70} O _1.87 which is formed It is known. Therefore, the NiO-functional layer was sandwiched between the anode support and the NiO-GDC cathode layer to prevent the formation of the secondary phase generated in the sintering process and the bonding strength between the support and the NiO-GDC cathode layer was improved. 4 (b) shows that after coating the NiO-functional layer and the NiO-GDC cathode layer, the GDC layer was immersed and heat-treated at 400 ° C. As shown in FIG. 4 (c), the NiO-YSZ / NiO / NiO-GDC / GDC tube had shrinkage of about 25% after sintering at 1400 ° C. FIG. In order to increase the triple phase boundary, a double layer of LSCF-GDC and LSCF was coated on the GDC to complete the cell. The finished cell was reduced in an H ₂ atmosphere at 600 ° C. to convert the NiO component, which is a ceramic, into Ni, which is a metal. The appearance of the entire cell for the measurement is shown in FIG. The actual activation area is 3.95 cm ² for cells sintered at 1350 ° C. and 3.77 cm ² for cells sintered at 1400 ° C. The cell thickness is similar to 1.20mm.

6 is a pore image formed on the surface of the GDC electrolyte according to Example 1. When the surface of the GDC electrolyte was observed in FIG. In Figure 6 (b) as the sintering temperature is increased to 1400 ℃ most of the pores that existed on the surface was removed.

An SEM image showing the cross section of the cell according to Example 1 is shown in FIG. 7. 7 (b) and 7 (d) show that the densification degree of the specimen sintered at 1350 ° C. is lower than that of the specimen sintered at 1400 ° C. through the photograph of the high magnification of the GDC electrolyte layer. As shown in FIG. 3, the additional densification of the electrolyte is not significant as the sintering temperature is increased from 1350 ° C. to 1400 ° C., and there are many pores on the surface of the cell sintered at 1350 ° C. during the co-sintering process of the electrolyte and the support. It is understood that the support does not shrink sufficiently so that the plastic shrinkage difference between the two layers occurs. All interfaces can be distinguished except the interface between LSCF-GDC and LSCF layer. The thicknesses of the layers are about 23, 21, 11, 13 μm in order from the anode to the Ni layer in the cell sintered at 1350 ° C., and 21, 22, 13, 15 μm in the cell sintered at 1400 ° C. It was measured to have and can be seen through Figure 7 (a) and 7 (c).

The results of IV and IP characteristic graphs of the cells measured at 450-600 ° C. according to Experimental Example 2 are shown in FIG. 8. The cell sintered at 1350 ℃ shows an open circuit voltage (OCV) of 1.0V at 450 ℃ and then slightly decreases to 0.87V as the temperature rises to 600 ℃. This value is lower than the theoretical value of 1.1V at 600 ° C. Maximum power densities are 72, 134, 233 and 350 mW / cm ² at 450, 500, 550 and 600 ° C. For cells sintered at 1400 ° C, the OCV drops from 0.94V to 0.84V when the measurement temperature increases from 450 ° C to 600 ° C. Maximum power densities are 141, 288, 445 and 594 mW / cm ² at 450, 500, 550 and 600 ° C, respectively. In general, the decrease in OCV that occurs when GDC electrolyte is used seems to be due to the increase in electrolyte conductivity at very low O2 partial pressure.

9 is a graph measuring the complex impedance of 450-600 ° C. in an open circuit state according to Experimental Example 2. FIG. The ohmic resistance (Rb), electrode resistance (Re), and total resistance (Rt) of the cell are calculated from the impedance graph and shown in FIG. 10.

FIG. 10 is a graph showing ohmic resistance (Rb), electrode resistance (Re), and total resistance (Rt) of a cell according to Experimental Example 3 based on FIG. 9. As can be seen from Figure 10 (a) Rb value of the cell prepared by sintering at 1350 ℃ was reduced from 1.72 to 0.87Ωcm ² as the operating temperature increases from 450 ℃ to 600 ~ C. On the other hand, Re value in Figure 10 (a) was greatly reduced from 5.34 to 0.09Ωcm ² due to the activation of the electrode reaction with temperature. On the other hand, FIG. 10 (b) shows that the Rb and Re values of the cells sintered at 400 ° C. were lower than those of the cells sintered at 1350 ° C., and the overall tendency of Rb and Re values according to operating temperatures was similar. Therefore, it can be seen that the total resistance of both cells depends on the electrode resistance at 450 ° C and ohmic resistance at 600 ° C.

The Re value of the cell sintered at 1350 ° C. is 1.6-2.2 times larger than the cell sintered at 1400 ° C. In general, at low measurement temperatures of 600 ° C for SOFCs, most of the electrode resistance is determined by the polarization resistance of the anode. Although the boundary between the LSCF and LSCF-GDC layers is unclear, the thickness of the LSCF-GDC layer cannot be accurately distinguished between the two cells.However, since a reproducible cell was fabricated through repeated experiments, there was a big difference in the thickness and composition of the anode. It is judged that there is no. Through this, Re value may be determined according to the state of the interface between LSCF-GDC and GDC. As can be seen from FIG. 6 (a) than the cell sintered at 1400 ° C. as shown in FIG. Due to the surface defects of, the anode layer was relatively unevenly coated on the electrolyte layer, resulting in a decrease in the length of the triple point.

As shown in FIG. 9, since the portion of the electrode resistance in the total resistance at 600 ° C. is very small, in order to increase the power density of the cell at 600 ° C., an electrolyte having high ion conductivity should be used, and the operating temperature is 500 ° C. Lowering below C requires the use of electrode materials with low resistance at low temperatures of 500 ° C.

In addition, the use of scandia-stabilized zirconia (ScSZ, Sc2O3-stabilzied ZrO2) with higher ionic conductivity than YSZ lowers the operating temperature and the maximum power density is reported to be 690 mW / cm2 at 700 ° C.

The maximum power density of the cell fabricated in the present invention was 594 mW / cm 2 at 600 ° C. This value is the highest among the maximum power density values that can be obtained if the operating temperature of SOFCs using Ni-YSZ as a support is lowered to 600 ° C. The maximum power density of a cell fabricated at 550 ° C is 445 mW / cm2, which is the maximum power density reported in a micro-cylindrical cell with Ni-GDC as the cathode and support, and the cell diameter is 0.8-1.8 mm. 350? 1,310 mW / cm2). Considering that the power density of the cells of cylindrical SOFCs is inversely proportional to the diameter of the tube, the power density of the cell of 6 mm diameter is high enough. The cell of the present invention using a Ni-YSZ anode support having a manageable size is commercialized at low and low temperatures due to the advantages of excellent mechanical strength of the anode support, stable operation of the cell, and the use of a cost-competitive Ni-YSZ material. Has an advantage.

11 is an image of a cell at 450-600 ° C. by sintering the solid electrolyte layer according to Experimental Example 3. FIG. Generally, the sintering of the GDC solid electrolyte layer of SOFCs requires a high temperature of 1400 ° C. In order to determine the possibility of a lower sintering process, the solid electrolyte layer was sintered at 1300 ° C. to measure the cell performance at 450-600 ° C. (see FIGS. 11 and 12). The thickness and composition of the cell is similar to the cell fabricated by sintering at 1350 ℃ and 1400 ℃. The activation area was 3.93 cm ² , and the thicknesses of the NiO-functional layer of the cell, the NiO-GDC cathode layer, the GDC solid electrolyte layer, and the anode layer of LSCF-GDC / LSCF were 13, 11, 21, and 13 μm in turn (Fig. 11 (b)). Almost the same thicknesses were made, except that the anode layer was slightly thinner than the cell fabricated earlier. Surface defects formed on the surface of the electrolyte (see FIG. 11 (a)) and pores inside the electrolyte (see FIG. 11 (b)) are caused by the difference in the degree of shrinkage between the electrolyte layer and the Ni-YSZ support. The OCV of the cell was 0.83 V at 600 ° C., and the maximum power density was 179 mW / cm ² (see FIG. 12). This suggests the possibility of lowering the sintering temperature of the cell to 1300 ° C.

In the present invention, a carbonate coprecipitation method was used to synthesize a GDC powder having a relative density of 97% even at 1200 ° C. However, due to the additional shrinkage of the NiO-YSZ anode support occurring above 1200 ° C, the shrinkage amount of NiO-YSZ and GDC occurred, resulting in surface defects and pores in the electrolyte of the cells sintered at 1300 ° C and 1350 ° C. . It is thought that the amount of shrinkage can be adjusted by adjusting the size of the Ni powder, the YSZ powder size, the additive, and the sintering temperature of the NiO-YSZ green body of the NiO-YSZ anode support. Since the powder calcined at 700 ° C. has a relative density of 95% or more at 1050 ° C., if the degree of shrinkage of the NiO-YSZ anode support is well controlled, the sintering temperature can be greatly reduced to 1050 ° C. The structure of the cell may be simplified by removing the NiO-functional layer, which is added to prevent the reaction between YSZ and GDC of NiO-YSZ occurring above 1200 ° C.

As described above, preferred embodiments of the present invention have been disclosed in the present specification and drawings, and although specific terms have been used, they have been used only in a general sense to easily describe the technical contents of the present invention and to facilitate understanding of the invention , And are not intended to limit the scope of the present invention.

It is to be understood by those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

Claims (21)

An anode support including yttria stabilized zirconia (YSZ) and NiO;
A NiO-functional layer comprising NiO formed on one side of the anode support;
A NiO-GDC cathode layer including NiO and GDC (gadolinium-doped ceria) formed on the NiO-functional layer;
A solid electrolyte layer including GDC (gadolinium-doped ceria) formed on the NiO-GDC cathode layer; And
And a first cathode layer comprising LSCF-GDC formed on the surface of the solid electrolyte layer and a second cathode layer comprising LSCF formed thereon.
The method of claim 1,
The composition for forming the anode support is a cylindrical solid oxide fuel cell unit cell comprising the yttria stabilized zirconia (YSZ), the NiO, pore-forming agent, a binder and distilled water.
The method of claim 1,
The volume ratio of the YSZ (yttria stabilized zirconia) and NiO in the composition for forming the anode support is a cylindrical solid oxide fuel cell unit cell, characterized in that 50 ~ 70:30 ~ 50.
The method of claim 1,
A unit cell for a cylindrical solid oxide fuel cell, characterized in that the thickness of the anode support is 1.0 to 1.4 mm.
The method of claim 1,
The composition for forming the NiO-functional layer is a unit cell for a cylindrical solid oxide fuel cell, characterized in that containing the NiO, a surfactant, a pore-forming agent and a binder.
The method of claim 1,
The unit cell for a cylindrical solid oxide fuel cell, wherein the NiO-functional layer is formed by dip-coating.
The method of claim 1,
The unit cell for a cylindrical solid oxide fuel cell, wherein the NiO-functional layer has a thickness of 13 to 15 μm.
The method of claim 1,
The composition for forming the NiO-GDC cathode layer is a cylindrical solid oxide fuel cell unit cell comprising the NiO, the GDC (gadolinium-doped ceria), a surfactant, a pore-forming agent and a binder.
The method of claim 1,
The NiO-GDC cathode layer is a cylindrical solid oxide fuel cell unit cell, characterized in that formed by dip-coating (dip-coating).
The method of claim 1,
The unit cell for a cylindrical solid oxide fuel cell, wherein the NiO-GDC cathode layer has a thickness of 11 to 13 μm.
The method of claim 1,
The composition for forming the solid electrolyte layer is a cylindrical solid oxide fuel cell unit cell comprising the GDC (gadolinium-doped ceria), dispersant, surfactant, plasticizer and binder.
The method of claim 1,
The solid electrolyte layer is a cylindrical solid oxide fuel cell unit cell, characterized in that formed by carbonate coprecipitation method.
The method of claim 12,
The carbonate coprecipitation method,
A first step of dissolving the raw material in distilled water to form an aqueous solution;
A second step of dropping the aqueous solution prepared in the first step into a (NH ₄ ) ₂ CO ₃ aqueous solution by using a reverse strike method;
A third step of washing and drying the precipitate made in the second step; And
And a fourth step of pulverizing the material dried in the third step.
14. The method of claim 13,
The raw material is a cylindrical unit cell for a solid oxide fuel cell, characterized in that consisting of Ce (NO ₃ ) ₃ · 6H ₂ O and Gd (NO ₃ ) ₃ · 6H ₂ O.
The method of claim 1,
The unit cell for a cylindrical solid oxide fuel cell, characterized in that the thickness of the solid electrolyte layer is 21 to 22 ㎛.
The method of claim 1,
The composition for forming the first cathode layer is a unit cell for a cylindrical solid oxide fuel cell, characterized in that the LSCF-GDC coating liquid, dispersant, plasticizer, surfactant and binder.
The method of claim 1,
The composition for forming the second cathode layer is a unit cell for a cylindrical solid oxide fuel cell, characterized in that the LSCF coating solution, dispersant, plasticizer, surfactant and binder.
The method of claim 1,
The first cathode layer and the second cathode layer is a cylindrical solid oxide fuel cell unit cell, characterized in that formed by immersion coating.
The method of claim 1,
The unit cell for a cylindrical solid oxide fuel cell, wherein the first cathode layer and the second cathode layer have a thickness of 13 to 23 μm.
A first step of sequentially stacking an anode support, a NiO-functional layer, a NiO-GDC cathode layer, a solid electrolyte layer, a first cathode layer, and a second cathode layer to form a laminate; And
A second step of sintering the laminate; Method for manufacturing a unit cell for a solid oxide fuel cell comprising a.
A cylindrical solid oxide fuel cell employing a cylindrical solid oxide fuel cell unit cell manufactured by the manufacturing method of claim 20.

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