KR20000013388A - Method for improving capacity of solid oxide fuel cell cathode using yttria stabilized zirconia sol - Google Patents

Abstract

PURPOSE: A method for improving the capacity of a Solid Oxide Fuel Cell(SOFC) cathode is provided to improve the capacity of the cathode by coating the SOFC cathode with an Yttria Stabilized Zirconia(YSZ) sol, by fabricating a slurry by injecting a conventional SOFC cathode powder into the YSZ sol and coating the SOFC electrolyte with the slurry, by coating the surface of the conventional SOFC cathode powder with the YSZ using the YSZ sol and by using the cathode powder coated with the YSZ as the SOFC cathode material. CONSTITUTION: The capacity of a Solid Oxide Fuel Cell(SOFC) cathode is improved using an Yttria Stabilized Zirconia(YSZ) sol. The capacity of the SOFC cathode is improved by coating the SOFC cathode fabricated by a conventional material and method with an Yttria Stabilized Zirconia(YSZ) sol. The capacity of a Solid Oxide Fuel Cell(SOFC) cathode is improved by fabricating a slurry by injecting a conventional SOFC cathode powder into the YSZ sol and coating the SOFC electrolyte with the slurry. The capacity of a Solid Oxide Fuel Cell(SOFC) cathode is improved by coating the surface of the conventional SOFC cathode powder with the YSZ using the YSZ sol and by using the cathode powder coated with the YSZ as the SOFC cathode material.

Description

Method for Improving Performance of Solid Oxide Fuel Cell Electrode Using Yttria Stabilized Zirconia Sol

The present invention relates to a method for improving the performance of a cathode used in a solid oxide fuel cell (SOFC) using a yttria stabilized zirconia (YSZ) sol. will be. More specifically, the present invention provides a method for improving the performance of a cathode by coating an YSZ sol on an SOFC cathode prepared using conventional materials and methods, and 2) dispersing the conventional SOFC cathode powder on an YSZ sol to obtain a slurry. After the preparation, the slurry is coated on SOFC electrolyte to produce a cathode, and 3) a method of improving cathode performance, and 3) a cathode powder coated with YSZ on an existing SOFC cathode powder surface using an YSZ sol. The present invention relates to a method for improving the performance of an air electrode by using the as an SOFC cathode material.

As a cathode material of SOFC, La _1-x Sr _x MnO ₃ (x: 0.05 to 0.85, LSM), which is an electron conductive ceramic material, is generally used (MJL Ostergard and M. Mogensen, Electrochemica Acta. 38, 2015- 2020 (1993) and H. Kamata, A. Hosaka, Yuji Ikegami and J. Mizusaki, H. Tagawa, in first European Solid Oxide Fuel Cell Forum, eds.Ulf Bossel, Proceedings vol 2, 725-733 (1994). and also consideration of the thermal expansion characteristics of the electrolyte, use by the addition of substances, such as SOFC electrolyte material is YSZ or doped ceria (CeO ₂ doped, hereinafter DC) in LSM. These cathode materials are bonded to one surface of a dense electrolyte made of an ion conductive solid oxide such as YSZ or DC to form an SOFC.

In general SOFCs operating at 700 to 1000 ° C., the performance of the cathode is very low compared to that of the anode and it is necessary to improve its performance.

The performance of the SOFC cathode is largely determined by the electrode reaction resistance generated by the electrochemical reaction at the cathode and the interface resistance generated at the contact of the cathode and the electrolyte. By reducing this resistance value, the performance of the cathode can be improved. Particularly in the case of low temperature SOFC operated at 700 to 800 ° C., SOFC performance is greatly affected by the electrode reaction resistance and the electrode-electrolyte interface resistance in the air electrode (T. Tsai and SA Barnett, in Solid Oxide Fuel). Cells V, eds.U. Stimming, SC Singhal, H. Tagawa and W Lehnert, The Electrochemical Society Proceedings Series PV 97-40, 368-375 (1997) and M. Suzuki, H. Sasaki, S. Otoshi, A. Kajimura, N. Sugiura, and M. Ippommatsu, J. Electrochem.Soc. 141, 1928-1931 (1994)), in order to fabricate high-performance SOFCs, necessarily reduce the electrode reaction resistance at the cathode and the interface resistance between the cathode and the electrolyte. You have to.

However, the electrochemical reaction (1/2 O ₂ + 2e → O ^2- ) in SOFC cathode occurs at the triple phase boundary where the cathode, electrolyte and oxygen meet, and the three phase interface is in contact with the electrolyte and cathode. It is greatly affected.

Therefore, if the cathode-electrolyte interface is formed to increase the contact area between the electrolyte and the cathode while oxygen diffuses well, the interface resistance of the cathode-electrolyte is lowered, and the electrode reaction resistance is also reduced by increasing the area of the three-phase interface at which the reaction takes place. This improves the performance of the cathode as a whole.

The simplest way to improve the contact of the cathode-electrolyte interface is to control the junction temperature of the cathode-electrolyte. In a typical SOFC manufacturing process using YSZ as an electrolyte, the cathode material is coated on the surface of the electrolyte in order to bond the cathode with the electrolyte and then sintered at a temperature of 1100 to 1400 ° C.

However, when the cathode material containing LSM is sintered at a temperature of 1200 ° C. or higher and bonded to the YSZ electrolyte, a high resistance material, SrZrO ₃ or La ₂ Zr ₂ O _7, is formed at the electrode-electrolyte interface, thereby reducing SOFC performance. M. Mogensen and Steen Skaarup, Solid State Ionics 86-88, 1151-1160 (1996)). In addition, when the sintering temperature is set lower than 1200 ° C, the bonding between the cathode and the electrolyte interface is not easy, so the interface resistance of the cathode-electrolyte is considerably large, and thus the performance of the SOFC is low.

In order to improve the contact area of the cathode-electrolyte and the area of the three-phase interface, a technique of solid state mixing of LSM powder and YSZ powder as a cathode material is commonly used (T. Kenjo and M. Nishiya). , Solid State Ionics 57, 295-302 (1992). However, even in this case, it is necessary to control the junction temperature of the cathode-electrolyte well in order to manufacture a high-performance battery. That is, since the particle size of the YSZ powder used as an additive is generally relatively large, such as 0.2 μm or more, it is not easy to bond to the surface of the YSZ electrolyte at a temperature of 1200 ° C. or less. In addition, when the sintering temperature is increased to 1200 ° C. or more in order to facilitate bonding, SrZrO ₃ or La ₂ Zr ₂ O ₇ , which is a high resistance compound, is formed at the cathode-electrolyte interface, thereby acting as an important factor in reducing battery performance. .

In addition to controlling the junction temperature or adding YSZ powder when preparing the cathode to improve the characteristics of the cathode-electrolyte interface, a method of using electrochemical vapor deposition (EVD) has been proposed (Document M. Suzuki, H. Sasaki, S. Otoshi, A. Kajimura, N. Sugiura, and M. Ippommatsu, J. Electrochem.Soc. 141, 1928-1931 (1994). This method is a method for producing an YSZ electrolyte on the surface of the cathode by using the LSM cathode, and it is reported that some YSZ layers are also formed inside the cathode during the EVD process, thereby enlarging the three-phase interface and greatly reducing the electrode reaction resistance of the cathode. In particular, the EVD method is known that the bonding between the cathode and the electrolyte is possible even at a temperature of 1100 ° C. or lower, so that the interface product between the LSM electrode and the YSZ electrolyte is not formed, and thus the interface resistance of the cathode-electrolyte is low.

However, since the EVD method requires expensive materials and equipment, a method of manufacturing a high performance SOFC cathode more economically is required for practical use.

It is therefore an object of the present invention to provide a method of improving the performance of the cathode used in SOFC more economically using YSZ sol. More specifically, an object of the present invention is to 1) improve the performance of the cathode by coating the YSZ sol on the SOFC cathode prepared using conventional materials and methods, 2) by dispersing the existing SOFC cathode powder in the YSZ sol After the slurry is prepared, the slurry is coated on the SOFC electrolyte to prepare the cathode, thereby improving the performance of the cathode, and 3) YSZ is coated on the surface of the existing SOFC cathode powder using the YSZ sol, and the YSZ is coated. It is to provide a method of improving the performance of the cathode by using the cathode powder as the SOFC cathode material.

1a and 1b is a conceptual diagram showing the effect of improving the contact between the cathode and the electrolyte and the three-phase interface expansion effect when using the method according to the invention.

2 is a view showing the performance improvement effect of a solid oxide fuel cell when using the method according to the present invention.

3 shows the results of XRD analysis of the cathode-electrolyte interface with and without the method according to the invention.

According to the present invention 1) to improve the performance of the cathode by coating the YSZ sol on the SOFC cathode prepared using conventional materials and methods, 2) after dispersing the existing SOFC cathode powder in the YSZ sol to prepare a slurry To improve the performance of the cathode by coating the slurry on the SOFC electrolyte to manufacture the cathode, and 3) coating YSZ on the surface of the existing SOFC cathode powder using YSZ sol, and applying the cathode powder coated with YSZ to the SOFC cathode. By using it as a material, a method of improving the performance of an air electrode is provided.

In the present invention, a very fine YSZ sol having a particle size suitable for coating of several nm was prepared, and by using this, fine YSZ particles were formed around the cathode-electrolyte, thereby improving the contact between the cathode-electrolyte and the electrochemical reaction. The area increase effect of the interface was brought.

According to the present invention, the performance of the SOFC cathode can be improved by effectively controlling the microstructure of the SOFC cathode-electrolyte interface using an YSZ sol which can be synthesized in a simple process without using expensive equipment, starting materials, or a high temperature process. have.

1A and 1B are conceptual views showing the bonding effect between the electrolyte and the cathode interface when YSZ sol is used. Figure 1a is a conventional LSM powder when used as a cathode material, Figure 1b is a mixed powder (hereinafter referred to as LSM-YSZ) LYS-added to the LSM or Ld-doped ceria (Gd _0.2 Ce _0.8 O ₂ , GDC below) In the case of using a mixed powder (hereinafter referred to as LSM-GDC) added as a cathode material, the performance of the cathode is improved by using YSZ sol.

In general, the smaller the particle size of the ceramic powder, the higher the surface area of the powder and the higher the sintering property. Therefore, after preparing a sol in which fine YSZ particles are dispersed, forming a fine YSZ particle layer at the cathode-electrolyte interface by using the same, the bonding resistance of the cathode-electrolyte is improved due to the increase of sintering property, thereby reducing the interface resistance and the cathode. Also, the area of the three-phase interface where the electrolyte and the oxygen meet is enlarged, thereby improving the performance of the cathode.

In addition, when using the LSM-YSZ or LSM-GDC mixed powder as the cathode material as shown in Figure 1b, the fine YSZ particles prepared from the YSZ sol not only assists the bonding between the LSM and the electrolyte interface, but also the YSZ or Bonding with GDC powders can be provided to provide a larger area three phase interface. In particular, even when a material having high ionic conductivity but not easy to bond with an electrolyte is added to the LSM electrode, the cathode-electrolyte can be easily bonded by coating the YSZ sol on the cathode, thereby improving the performance of the SOFC cathode.

In the present invention, a method for synthesizing an YSZ sol suitable for improving SOFC cathode performance was devised, and a method for improving the performance of the cathode using the synthesized YSZ sol was developed.

First, in order to improve the performance of the cathode, as shown in FIG. 1, a fine YSZ particle layer should be formed at the cathode-electrolyte interface. Thus, YSZ sol was synthesized to be suitable for forming the cathode. At this time, YSZ sol was prepared by first synthesizing zirconia sol and then adding yttrium salt to zirconia sol, and synthesized into two types of polymeric sol and particulate sol. The specific manufacturing method of YSZ polymerization sol and particle sol is as follows.

YSZ polymerization sol is a mixed solution of zirconium alkoxide and alcohol as a starting material, to which acetic acid is added as a chelating agent, and then a catalyst solution containing nitric acid or hydrochloric acid as water, alcohol and catalyst is administered. After preparing a zirconia polymerization sol, it can manufacture by adding the solution which dissolved the yttrium salt in alcohol to this zirconia polymerization sol.

At this time, the molar ratio of zirconium alkoxide and alcohol in the starting material is 1:10 to 30, the complexing agent is added so that the molar ratio of alkoxide and acetic acid is 1: 0 to 3, and the catalyst solution is 1: molar ratio of alkoxide and water. 1-4, the molar ratio of alkoxide and alcohol is 1: 10-30, and it is manufactured so that the molar ratio of alkoxide, nitric acid, or hydrochloric acid may be 1: 0.5-1.5.

In addition, the yttrium salt is dissolved in alcohol so that the molar ratio of yttrium salt and alcohol is 1: 10-30, and the molar ratio of zirconium and yttrium (ZrO ₂ ) _0.90-0.97 (Y ₂ O ₃ ) in the final YSZ polymerization sol is _0.10 to _0.03 . Add as much as possible.

On the other hand, YSZ particle sol is prepared by using a mixed solution of zirconium alkoxide and alcohol as a starting material, and adding nitric acid or hydrochloric acid as water and catalyst thereto to prepare a zirconia particle sol, and then dissolving yttrium salt in water in the zirconia particle sol. It can be prepared by adding a solution.

At this time, the molar ratio of zirconium alkoxide and alcohol in the starting material is 1: 10-30, water is mixed so that the molar ratio of H ₂ O / Zr is 100-200, nitric acid or hydrochloric acid as a catalyst is H ⁺ / Zr It is added so that molar ratio may be 0.5-2.0.

Similarly, the yttrium salt is added so that the dissolved water in the molar ratio of zirconium and yttrium in the final sol particle YSZ _{(ZrO 2) 0.90~0.97 (Y 2} O 3) 0.10~0.03.

There are three ways to improve the performance of the cathode using the YSZ sol prepared as described above.

The first method is to improve the performance of the cathode by coating the YSZ sol on a SOFC cathode prepared using conventional materials and methods. Specifically, the LSM cathode, the LSM-YSZ cathode, and the ceria doped with CSM doped YSZ polymerized sol or particle sol prepared by the present invention to the SOFC electrolyte surface by the conventional method (hereinafter referred to as LSM-DC). Or La _x Sr _1-x Co _y Fe _1-y O ₃ (x: 0.05 to 0.85, y: 0.05 to 0.85) repeatedly dip coating on the cathode to form fine YSZ particles at the cathode-electrolyte interface. Way. As the doped ceria, ceria doped with up to 20 mol% of Y, Sm, Gd and the like can be used.

In this case, the contact area of the cathode-electrolyte is increased to reduce the interface resistance, and the area of the three-phase interface at which the electrochemical reaction occurs is also enlarged, thereby improving the performance of the cathode.

The second method is to improve the performance of the cathode by dispersing existing SOFC cathode powder in YSZ sol to prepare a slurry, and then coating the slurry on SOFC electrolyte to prepare cathode. Specifically, the conventional LSM powder, LSM-YSZ powder, LSM-DC powder or La _x Sr _1-x Co _y Fe _1-y O ₃ (x: 0.05 to 0.85, y: 0.05 to 0.85) to prepare a slurry by dispersing the powder, and the slurry is immersed in coating, screen printing, spray coating or tape casting on the surface of the prepared SOFC electrolyte. It is a method of forming fine YSZ particles at the cathode-electrolyte interface by coating by a method such as casting) and then sintering at 1000 to 1200 ° C. to prepare the cathode. Likewise, ceria doped with up to 20 mol% Y, Sm, Gd, etc. may be used as the doped ceria.

Even in this case, the interfacial resistance is reduced by the fine YSZ particles formed at the interface of the cathode-electrolyte, and the area of the three-phase interface is also expanded, thereby improving the performance of the cathode. In particular, in this case, the bonding between the electrolyte and the cathode can be performed at a relatively low temperature of 1200 ° C. or lower, so that the interface resistance caused by the interface product generated when the sintering temperature is increased to 1200 ° C. or higher can be prevented from increasing. have.

The third method is to improve the performance of the cathode by coating YSZ on the surface of the conventional SOFC cathode powder using the YSZ sol and using the cathode powder coated with YSZ as the SOFC cathode material. Specifically, the YSZ polymerization sol or particle sol prepared according to the present invention may be prepared using conventional LSM powder, LSM-YSZ powder, LSM-DC powder, or La _x Sr _1-x Co _y Fe _1-y O ₃ (x: 0.05 to 0.85, y: 0.05 to 0.85) It is a method of using a composite powder formed by mixing with powder to induce gelling and then drying and calcining as a cathode material. In addition, the doped ceria may be a ceria doped with up to 20 mol% Y, Sm, Gd and the like.

Even in this case, as mentioned above, the sinterability is increased by the fine YSZ formed on the surface of the cathode powder, so that the bonding between the electrolyte and the cathode can be easily performed even at a temperature of 1200 ° C. or lower, and due to the high surface area of the YSZ sol particles. A wider three-phase interface can be obtained and the cathode performance is improved.

The objects, features and advantages of the present invention will become more apparent by a review of the description of the preferred embodiments of the present invention provided in conjunction with the accompanying drawings.

<Example 1>

YSZ polymerization sol was synthesized in the following manner.

First, acetic acid was added as a complexing agent such that the molar ratio of alkoxide and acetic acid was 1: 2 to a solution having a molar ratio of zirconium n-butoxide and isopropanol 1:15, and then the molar ratio of alkoxide to water was 1: 2 and alkoxide. A zirconia polymerization sol was prepared by administering a catalyst solution such that the molar ratio of nitric acid was 1: 1.2 and the molar ratio of alkoxide and isopropanol was 1:15.

A solution in which yttrium nitrate was dissolved in isopropanol in a molar ratio of 1:30 was added to the zirconia polymerization sol to prepare a final YSZ polymerization sol having a ratio of zirconium to yttrium of (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 .

<Example 2>

YSZ particle sol was synthesized in the following manner.

First, distilled water is added to a solution having a molar ratio of zirconium isopropoxide and ethanol as a starting material of 1:15, and mixed so that the molar ratio of H ₂ O / Zr is 150.The hydrochloric acid is used as a catalyst with a molar ratio of H ⁺ / Zr of 1.5. After the addition, the mixture was stirred for about 3 hours to prepare a transparent zirconia particle sol.

The alcohol obtained as an adduct is then evaporated at about 90 ° C., and the molar ratio of zirconium and yttrium corresponds to (ZrO ₂ ) _0.92 (Y ₂ O ₃ ) _0.08 by adding a solution of yttrium chloride dissolved in distilled water to the zirconia particle sol. The final YSZ particle sol was prepared.

<Example 3>

The YSZ polymerization sol synthesized in Example 1 was coated on an SOFC cathode prepared using conventional materials and methods, and the effect of improving the performance of SOFC was determined.

The YSZ polymerized sol synthesized in Example 1 was immersed and coated on an air electrode manufactured using a conventional LSM powder (La _0.85 Sr _0.15 MnO ₃ ) to form fine YSZ particles around the electrolyte and the electrode.

At this time, the LSM cathode was prepared by mixing the existing LSM powder with water to prepare a slurry, and then coating the slurry on one side of the YSZ electrolyte disk having a diameter of 25 mm and a thickness of 1.3 mm by screen printing and sintering at 1100 ° C. Produced. Ni / YSZ cermet electrodes were prepared on the other side of the YSZ electrolyte disk prior to fabricating the cathode.

After immersion coating of the YSZ polymerization sol synthesized in Example 1 on the LSM air electrode thus prepared three times, the performance of SOFC was measured at 1000 ° C. At this time, hydrogen containing 3% water vapor was supplied at a rate of 100 cc / min to the anode, and air was supplied at a rate of 200 cc / min to the cathode.

2 shows the current-voltage characteristics of SOFC coated with YSZ polymerized sol on LSM cathode and SOFC not coated on cathode. In the case of coating the YSZ sol on the LSM cathode in Figure 2 it can be seen that the performance of the SOFC is significantly superior to the case of using the existing LSM cathode as it is. That is, the SOFC using the conventional LSM cathode exhibits the performance of 0.26 V at the current density of 200 mA / cm ² , while the SOFC manufactured by coating the YSZ sol on the LSM cathode has a much higher performance of 0.70 V at the same current density. It showed a performance of 0.2 V or more even at a load of 400 mA / cm ² . Therefore, when the YSZ polymer sol is coated on the cathode manufactured by the existing materials and methods, the performance of the cathode may be improved, and thus the output of the SOFC may be increased.

<Example 4>

The YSZ polymerized sol or particle sol synthesized in Example 1 or Example 2 was coated on an SOFC cathode prepared using existing materials and methods to determine the effect of improving the performance of the cathode.

The YSZ polymerized sol or particle sol synthesized in Example 1 or 2 was immersed in an air electrode prepared using a conventional LSM powder (La _0.85 Sr _0.15 MnO ₃ ) to form fine YSZ particles around the electrolyte and the electrode. It was.

At this time, the LSM cathode was manufactured by the method described in Example 3, and was manufactured in a symmetrical form on both sides of the YSZ electrolyte disk having a diameter of 25 mm and a thickness of 1.0 mm. The YSZ polymerized sol or particle sol was immersed and coated three times on LSM cathodes prepared on both sides of the YSZ electrolyte disk, and then impedance analysis was performed at 1000 ° C. and 800 ° C. to measure the resistance of the cathode. At this time, air was supplied to both surfaces of the symmetrical battery at a rate of 200 cc / min.

Table 1 summarizes the effect of improving the cathode performance by reducing the resistance of the cathode when the YSZ polymerized sol or particle sol synthesized in Example 1 or Example 2 is coated on a conventional LSM cathode. In Table 1, when the YSZ sol is coated on the LSM cathode, the resistance of the cathode is greatly reduced compared to the case where the conventional LSM cathode is used as it is, and thus the cathode performance is improved. That is, the resistance of the conventional LSM cathode is 2.2 and 32.6 Ω-cm ² at 1000 ℃ and 800 ℃, respectively, whereas when the YSZ polymer sol is coated on the LSM cathode, the cathode resistance is 0.03 and 0.5 at 1000 ℃ and 800 ℃, respectively. With Ω-cm ² , the resistance is reduced to 1/50 or less compared to the conventional LSM cathode, and even when YSZ particle sol is coated on the LSM cathode, the cathode resistance is reduced to 1/3 or less compared to the LSM cathode, resulting in improved cathode performance. Improved. Therefore, it can be seen that the performance of the cathode is improved when the YSZ polymerization sol or particle sol is coated on the cathode manufactured by the existing materials and methods.

YSZ sol coating reduces the resistance of LSM cathode Air cathode Resistance of air cathode (Ω-cm ² ) 1000 ℃ 800 ℃ Legacy LSM 2.2 32.6 LSM Coated YSZ Polymeric Sol 0.03 0.5 LSM Coated YSZ Particle Sol 0.73 9.6

Example 5

After dispersing the conventional SOFC cathode powder in the YSZ polymerization sol prepared in Example 1 to prepare a slurry, the slurry was coated on the surface of the SOFC electrolyte to prepare a cathode and to determine the effect of improving the performance of the cathode.

A slurry was prepared by dispersing a conventional LSM (La _0.85 Sr _0.15 MnO ₃ ) powder in the YSZ polymerization sol prepared in Example 1, and coating the slurry on both sides of the YSZ electrolyte disk mentioned in Example 4 by screen printing. After sintering at 1100 ℃ to produce a symmetrical battery.

When the resistance of the cathode was measured by impedance analysis at 1000 ° C., the resistance of the cathode of the conventional LSM was 2.2 Ω-cm ² , whereas the LSM powder was dispersed in an YSZ sol to prepare a slurry, and the slurry was coated on the SOFC electrolyte. The resistance of the cathode was reduced to 1/5 or less by using an YSZ sol having a cathode resistance of 0.4 Ω-cm ² .

Meanwhile, after the experiment, the battery was disassembled and the cathode-electrolyte interface was analyzed by XRD (X-ray diffraction) method to investigate the presence of the interface product. As a result, as shown in FIG. 3, the slurry was prepared by dispersing the LSM powder in the YSZ sol, and when the slurry was coated on the YSZ electrolyte to prepare the cathode, no interfacial compound was produced, whereas the existing LSM powder was mixed with the YSZ electrolyte. In the case of direct bonding, an interface compound La ₂ Zr ₂ O ₇ having a high resistance was necessarily generated at a temperature of 1200 to 1300 ° C. for easy bonding to reduce SOFC performance.

<Example 6>

The experiment was carried out in the same manner as in Example 5, but using the composite cathode powder (hereinafter referred to as LSM-YSZ) in which 40 vol% of YSZ was added to the LSM instead of the conventional LSM powder, the performance improvement effect of the cathode was determined.

The slurry was prepared by dispersing the LSM-YSZ powder in the YSZ sol, spraying the slurry on both sides of the YSZ electrolyte disk mentioned in Example 4 using a spray device, and then sintering at 1100 ° C. A symmetrical battery was fabricated and the performance improvement effect of the cathode was identified by the aforementioned method.

As a result, the resistance of the conventional LSM-YSZ cathode is 2.5 Ω-cm ² at 1000 ° C, while the resistance of the cathode is measured to 0.35 Ω-cm ² when the YSZ sol is coated on the LSM-YSZ cathode. As a result, the resistance of the cathode decreased to 1/7 or less.

<Example 7>

After coating YSZ on the surface of the conventional SOFC cathode powder using the YSZ particle sol prepared in Example 2, and manufacturing the SOFC cathode using the cathode powder coated with YSZ as the cathode material, grasp the effect of improving the performance of the cathode. It was.

The YSZ particle sol prepared in Example 2 was mixed with a conventional cathode powder (hereinafter referred to as LSM-GDC) in which 40 vol% of GDC (Gd _0.2 Ce _0.8 O ₂ ) was added to an existing LSM (La _0.85 Sr _0.15 MnO ₃ ). , The pH of the mixed solution was adjusted with ammonia water to cause gelling. The powder was dried in a 90 ° C. dryer, then dispersed in water and methylcellulose solution to prepare a slurry, and air cathodes were prepared on both sides of the YSZ disk by the method described in Example 5.

As a result of confirming the cathode resistance through impedance analysis at 1000 ℃, the resistance of the conventional LSM-GDC cathode is 1.9 Ω-cm ² , whereas when the YSZ sol is coated on the LSM-GDC cathode, the resistance of the cathode is 0.25 Ω-cm ^2. The resistance of the cathode was reduced to 1/7 or less by using YSZ sol.

According to the present invention, by coating an YSZ sol on an existing SOFC cathode, a fine YSZ particle layer is formed at the cathode-electrolyte interface, thereby greatly improving the performance of the SOFC cathode.

In addition, in the case of using the conventional cathode material LSM powder or mixed powder such as LSM-YSZ, LSM-GDC, the existing cathode powder is mixed with the YSZ sol to prepare a slurry, and the slurry is coated on the SOFC electrolyte to prepare the cathode. Alternatively, by using an YSZ sol coated on the surface of the existing cathode powder, a fine YSZ particle layer may be formed at the cathode-electrolyte interface, thereby greatly improving the performance of the SOFC cathode.

In particular, when YSZ sol is used together with the conventional cathode powder, the cathode-electrolyte can be bonded at a temperature of 1200 ° C or lower, thereby suppressing the formation of highly resistant interfacial compounds, thereby reducing the contact resistance, and also providing a fine YSZ particle layer. As a result, the area of the three-phase interface is increased to improve the performance of the air electrode.

Therefore, the present invention is a very effective method for improving the performance of the conventional SOFC cathode in a simple and economical way compared to the conventional method. In particular, using the method of improving the cathode performance proposed in the present invention, the performance of SOFC operating at low temperature of 700 to 800 ° C. is considered to be greatly improved.

Claims (15)

A method of improving the performance of a solid oxide fuel cell (SOFC) cathode using a Yttria Stabilized Zirconia (YSZ) sol. The method of claim 1, wherein the YSZ sol is coated on an SOFC cathode prepared using existing materials and methods to improve the performance of the cathode. The method of claim 1, wherein the slurry is prepared by dispersing existing SOFC cathode powder in an YSZ sol, and then coating the slurry on the SOFC electrolyte to prepare a cathode, thereby improving the performance of the cathode. The method of claim 1, wherein the YSZ sol is mixed with the existing SOFC cathode powder and then gelling occurs to coat YSZ on the cathode powder surface, and the SOFC cathode is manufactured from the cathode powder coated with YSZ. To improve performance. The YSZ sol according to claim 2, 3, or 4, wherein acetic acid is added as a chelating agent to a mixed solution of a zirconium alkoxide and an alcohol, and then water and alcohol. And an YSZ polymerization sol prepared by administering a catalyst solution containing nitric acid or hydrochloric acid as a catalyst to produce a zirconia polymerization sol, and then adding a solution in which yttrium salt is dissolved in alcohol to the zirconia polymerization sol. The molar ratio of zirconium alkoxide and alcohol is 1: 10-30, the complexing agent is added so that the molar ratio of alkoxide and acetic acid may be 1: 0-3, and the catalyst solution has a molar ratio of alkoxide and water of 1: 1. 4, the molar ratio of alkoxide to alcohol is 1:10 to 30, the molar ratio of alkoxide to nitric acid or hydrochloric acid is 1: 0.5 to 1.5, and the yttrium salt is such that the molar ratio of yttrium salt and alcohol is 1:10 to 30. Dissolving in alcohol and adding so that the molar ratio of zirconium and yttrium in the final YSZ polymerization sol is (ZrO ₂ ) _{0.90 to 0.97} (Y ₂ O ₃ ) _0.10 to _0.03 . The YSZ sol is prepared from a mixed solution of zirconium alkoxide and an alcohol as a starting material, and nitric acid or hydrochloric acid is added thereto to prepare a zirconia particle sol. A YSZ particle sol prepared by adding a solution in which yttrium salt is dissolved in water to a zirconia particle sol. The method of claim 7 wherein the molar ratio of the zirconium alkoxide and the alcohol is from 1: 10 to 30, and water, and mixed such that the molar ratio of 100 to 200 in H ₂ O / Zr, of nitric acid or hydrochloric acid as the catalyst is H ⁺ / Zr The molar ratio is added so as to be 0.5 to 2.0, and the yttrium salt is dissolved in water and added so that the molar ratio of zirconium and yttrium in the final YSZ particle sol is (ZrO ₂ ) _{0.90 to 0.97} (Y ₂ O ₃ ) _0.10 to _0.03 . Way. The method according to claim 2 or 3, wherein a dip coating method is used as the coating method. The method according to claim 3 or 4, wherein a screen printing method is used as the method of manufacturing the cathode. The method according to claim 3 or 4, wherein a spray coating method is used as the method of manufacturing the cathode. The method according to claim 2, 3 or 4, wherein La _1-x Sr _x MnO ₃ (x: 0.05 to 0.85, hereinafter LSM) is used as the SOFC cathode material. The method according to claim 2, 3 or 4, wherein a composite powder obtained by adding YSZ to the LSM is used as the SOFC cathode material. The method according to claim 2, 3 or 4, wherein as the SOFC cathode material, a composite powder obtained by adding up to 20 mol% of ceria (CeO ₂ ) doped with Y, Sm, Gd, etc. to LSM is used. The method according to claim 2, 3 or 4, wherein La _x Sr _1-x Co _y Fe _1-y O ₃ (x: 0.05 to 0.85, y: 0.05 to 0.85) is used as the SOFC cathode material. Way.