KR102226103B1 - Method for Enhancing SOFC cathode performance by solution infiltration using ultrasonic machine - Google Patents

Abstract

The present invention relates to a method of improving the activity and stability of a cathode by infiltrating SSC into the surface of a porous cathode using an ultrasonic device, and more particularly, using an ultrasonic spray technique on the surface of a porous cathode, SSC (Sm _{1- x} Sr _x CoO _3-δ , where 0.1≦x≦0.8, 0≦δ≦0.1) is infiltrated to coat the SSC thin film, thereby improving the performance and stability of the cathode. The present invention can be usefully applied to a large-area cell to significantly improve an electrode of a fuel cell at a low cost.

Description

Method for enhancing SOFC cathode performance by solution infiltration using ultrasonic machine}

The present invention relates to a method for improving the performance of a solid oxide fuel cell, and more particularly, to a method for improving the activity and stability of a cathode by infiltrating SSC having excellent electrocatalytic activity into the surface of a porous cathode using an ultrasonic device. will be.

Solid oxide fuel cell (SOFC) uses solid oxygen ion conductive ceramic as an electrolyte, and produces electricity by electrochemical reaction between fuel and air (oxygen) at a high temperature of 700℃ to 900℃. It is a clean power generation device that generates furnace water. High-temperature solid state electrochemical devices based on ceramic membranes such as solid oxide fuel cells (SOFCs) and solid oxide electrolytic cells (SOECs) represent next-generation energy technologies for clean power production and large-scale energy storage (LJ Miara, et al. ., J. Electrochem. Soc. 159 (2012) F419-F425).

SOFC uses an electrolyte in a chemical reaction in which hydrogen (H2) and oxygen (O2) meet to generate water (H2O), and has the characteristic of generating electricity continuously as long as fuel is supplied. SOFC is composed of an electrolyte having oxygen ion conductivity, an anode and a cathode on both sides (S.P.S. Badwal and K. Foger, Ceramics International, 22, (1996), 257-265). The principle of SOFC is that when fuel is supplied to the anode, the fuel is oxidized and electrons are released through the external circuit. When oxygen is supplied to the cathode, electrons are received from the external circuit and are reduced to oxygen ions, and the reduced oxygen ions are transferred to the anode through the electrolyte. It moves to and reacts with the oxidized hydrogen ions to generate water, and at this time, electricity is produced by the flow of electrons from the anode to the cathode. The fuel electrode, the air electrode, and the electrolyte, which are the core components of SOFC, require various conditions depending on their role.

The anode must have a porous microstructure, high electron conductivity and ionic conductivity in order to facilitate diffusion and oxidation reactions of fuel. In addition, for the mechanical stability of a multi-layered fuel cell, it must have a thermal expansion coefficient similar to that of the surrounding components and secure chemical and phase stability in oxidation and reduction atmospheres (S. Zha, et al., Solid State Ionics, 166 , (2004), 241-250). If the difference in the coefficient of thermal expansion is large, it may cause serious problems such as microcracks and delamination during the manufacturing process or during operation. For the anode, a material having excellent catalytic properties must be used to increase electrochemical activity, and must have excellent activity for reforming reactions for smooth use of fuel. And it must have excellent resistance to impurity contamination due to the reforming reaction (W.Z. Zhu and S.C. Deevi, A362, (2003), 228-239). In addition, a sufficient amount of triple phase boundary (TPB) must be present in order to facilitate the electrochemical reaction of the fuel, and the porosity must be controlled to maintain the mechanical properties of the anode and the smooth discharge of reaction products.

The main function of the electrolyte is to transfer ions between the cathode and the anode and separate the fuel from oxygen. Therefore, the electrolyte must be composed of a dense membrane to prevent the oxidizing agent from directly reacting with the fuel, stability of chemical and phase, etc. must be ensured in the oxidation and reduction atmosphere, the reaction gas must not be permeated, and high ionic conductivity under operating conditions. Should have. Because SOFC operates at high temperatures, the electrolyte must be chemically and thermally stable with surrounding components from room temperature to operating temperature and even at higher temperatures at which fuel cells are manufactured (HJ Hwang, et al., Journal of the Korean Ceramic Society, 42, 0(2005), 787-792 and BCH Steele, et al., Journal of Materials Science, 36, (2001), 1053-1068). The thermal expansion of the electrolyte should be similar to the surrounding components to prevent cracking and delamination during manufacturing and thermal cycle operation. In addition, the thermal expansion coefficient of the electrolyte must remain unchanged despite changes in the oxygen partial pressures of the anode and the cathode during operation, and the electrolyte must be selected as the basic material, and other battery materials must be selected in consideration of the thermal expansion characteristics.

The cathode should have a porous microstructure in order to facilitate diffusion of oxygen, and should have high electronic conductivity and ion conductivity in order to minimize a decrease in power due to resistance existing in the electrode material itself. In addition, the polarization resistance against the reduction reaction of oxygen should be small, and the stability of chemical and phase should be excellent in oxidation and reduction atmospheres. And the cathode material must be able to maintain a continuous single phase in the range of room temperature and operating temperature. At SOFC operating temperature, the cathode should have no interfacial reaction with the electrolyte. When an interfacial reaction with an electrolyte occurs, a compound having a low oxygen ion conductivity is formed, so the interfacial reaction has a fatal effect on the long-term stability of the operating performance of a solid oxide fuel cell (EI Tif, et al., Journal of the European Ceramic Society, 21, (2001), 1805-1811). The unit cell constituting the SOFC is composed of a combination of an electrolyte, an electrode, and a connector, and must have a thermal expansion coefficient similar to that of the surrounding components during heat treatment in the process of bonding with each other or in the process of reaching operating conditions.

SOFC's broad market penetration requires innovation to improve fuel cell efficiency, extend life and reduce cost. Based on the technical problems identified by previous studies, it can be seen that the cathode is a major constituent urea that determines the performance and reliability of the battery (S. Zhen, et al., J. Power Sources 315 (2016) 140- 144). Recently, the cathode materials are making great efforts to study new materials and structures due to the slow oxygen exchange rate and high activation energy (Y. Zhang, et al., ACS Appl. Mater. Interfaces 8 (2016) 3003-3011). . Although alternatives (KT Lee, et al., MRS Bull. 39 (2014) 783-791 and J. Li, et al., Electrochim. Acta 187 (2016) 179-185) or nanostructures (J. Hwang, et al. al., J. Electrochem. Soc. 159 (2012) F639-F643 and JM Vohs, et al., Adv. Mater. 21 (2009) 943-956) have been used to improve electrode function, but there have been significant achievements in improving electrode function, but practical Implementing new electrodes in cells has mostly failed because they inevitably brought high functionality at the expense of chemical and structural stability.

One of the most promising methods to overcome this barrier is a nanoscale technique based on a solution infiltration process. In the infiltration process, a precursor solution of the active ingredient is injected into a pre-fabricated porous support, and a desired phase is formed by subsequent heat treatment. This unique procedure offers several advantages over conventional electrode manufacturing processes. Specifically, calcination for phase formation generally requires strong bonding to occur at the interface, and heat treatment at a lower temperature than the electrode sintering process alleviates chemical compatibility problems such as harmful chemical reactions and interdiffusion.

Accordingly, the present inventors have endeavored to develop a new method for improving the performance of the cathode using a nano-size technique based on the permeation process. As a result, by infiltrating the highly active SSC into the surface of the porous LSCF cathode using ultrasonic equipment, the size of the SSC nanocatalyst It was confirmed that an ideal electrode structure with excellent performance and long-term stability can be implemented based on morphology, and furthermore, by confirming that performance improvement of at least 30% to maximum 100% can be achieved depending on the number of penetrations of SSC, the present invention Completed.

_{An object of the present invention is to infiltrate SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.1) into the cathode surface of a unit cell of a solid oxide fuel cell using ultrasonic equipment. It is to provide a method of improving the performance and long-term durability of the cathode by coating the SSC thin film as a technique.

Another object of the present invention is a cathode manufactured by the method according to the present invention, with improved performance and stability, a solid oxide fuel cell comprising the cathode, and a solid oxide fuel cell comprising the solid oxide fuel cell cell It provides a stack.

_{In order to achieve the above object, the present invention penetrates SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.1) using an ultrasonic spray technique on the surface of the porous cathode ( Infiltration) to provide a method for improving the performance of a cathode for a solid oxide fuel cell (SOFC) comprising the step of coating an SSC thin film.

_{In addition, the present invention is manufactured by infiltration of SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.3) using an ultrasonic spray technique on the surface of the porous cathode. , Provides a cathode for a solid oxide fuel cell with improved performance.

In addition, the present invention provides a solid oxide fuel cell including the cathode for a solid oxide fuel cell according to the present invention.

In addition, the present invention

i) preparing an SSC solution prepared by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water, and urea, followed by stirring;

ii) performing heat treatment after infiltration of the SSC solution prepared in step i) on the surface of the porous cathode using an ultrasonic spray technique; And

iii) manufacturing a solid oxide fuel cell including the cathode penetrated in step ii). It provides a method of manufacturing a solid oxide fuel cell with improved performance.

The present invention improves electrocatalytic activity and contributes to electrode stability at low cost by applying a thin film coating of SSC catalyst to the surface of the cathode of a unit cell of a solid oxide fuel cell using a wet infiltration method using ultrasonic equipment. I can.

In the present invention, the use of surfactants (urea, ethanol, distilled water) in the preparation of the SSC solution helps to form the SSC phase, and the improvement of wettability can broaden the range of a uniform catalyst in the porous electrode.

In the present invention, SSC penetration using the ultrasonic spray technique can improve the performance and stability of the air electrode through a post heat treatment process, and this effect can be significantly improved compared to the case of using a syringe, one of the existing wet penetration methods. .

In particular, the present invention compares the performance according to the number of SSC penetrations using the ultrasonic spray technique and establishes an optimal penetration condition, thereby improving performance of at least 30% to maximum 100%.

The present invention can be applied to a large-area cell and optimize the wet permeation method at a low cost, thereby remarkably improving the electrode of the fuel cell.

1 is a diagram showing a schematic diagram of a manufacturing process of a segmented flat tubular SOFC cell.
2 is a diagram showing a manufacturing process of a segmented flat tubular SOFC cell.
3 is a diagram showing a schematic diagram of a flat tubular SOFC unit cell to which a segmented cathode is applied.
4 is a diagram showing the configuration of an ultrasonic equipment: (a) an ultrasonic machine; (b) a controller; (c) ultrasonic nozzles; (d) a frequency controller; And (e) a syringe pump.
5 is a diagram showing the manufacturing process of the SSC (Sm _0.2 Sr _0.8 CoO _{3-δ) solution.}
6 is a diagram showing the reaction formula of the SSC nanophase formation process.
7 is a diagram showing conditions and processes of an SSC penetration process using an ultrasonic device.
8 is a diagram showing the result of EDS analysis of SSC penetration on the surface of an LSCF cathode.
9 is a diagram showing a scanning electron microscope (SEM) image of observing the microstructure of SSC nanoparticles penetrated into the porous LSCF cathode backbone using a syringe.
10 is a diagram showing a scanning electron microscope (SEM) image of observing the microstructure of SSC nanoparticles penetrated into the porous LSCF cathode backbone using an ultrasonic machine.
11 is a diagram showing a scanning electron microscope (SEM) image observing the microstructure of the cross section of the LSCF cathode according to the number of SSCs.
12 is a diagram showing the IV measurement results of a blank and SSC-permeated SOFC unit cell operated by supplying 2 L/min of air and 400/min of hydrogen at 700°C.
13 is a diagram showing the IV measurement results of blank and SSC-permeated SOFC unit cells operated by supplying 2 L/min of air and 400/min of hydrogen at 750°C.
14 is a diagram showing the impedance spectrum measurement results of blank and SSC-permeated SOFC unit cells in an open circuit condition of 700°C.
15 is a diagram showing the measurement result of impedance spectrum of a blank and SSC-permeated SOFC unit cell under an open circuit condition of 750°C.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described later in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance the possibility of the presence or addition.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in the present specification. Does not.

Hereinafter, the present invention will be described in detail.

The present invention coats the SSC thin film by infiltration of _{SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.1) using an ultrasonic spray technique on the surface of the porous cathode. It provides a method for improving the performance of a cathode for a solid oxide fuel cell (SOFC) comprising the step of.

The porous curved pole is preferably a multi-layered structure including a Lanthanum Strontium Cobalt Ferrite (LSCF)-Gadolinium Doped Ceria (GDC) layer and an LSCF layer.

The porous curved electrode has a multilayer structure in which LSCF is applied as a Co-containing perovskite mixed conductor and a GDC buffer layer is formed, and LSCF-GDC is used as a functional layer, and as a current collecting layer. It is preferable to use LSCo on the LSCF surface.

It is preferable to use ultrasonic equipment including a controller, an ultrasonic spray nozzle, a frequency controller, an air flow meter, and a syringe pump as the ultrasonic spray technique.

The ultrasonic spray technique is preferably ultrasonically sprayed under conditions of an ultrasonic driving frequency of 75 to 85 kHz, a syringe pump flow rate of 2 to 4 µl/min, and an air flow rate of 2 to 4 µl/min, but is not limited thereto.

The penetration is preferably carried out through a process of spraying an SSC solution prepared by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water, and urea and then stirring it using an ultrasonic device, and then drying it.

The SSC solution is preferably prepared by mixing distilled water and ethanol with urea and nitrate aqueous solution Sm(NO ₃ ) ₃ ·6H ₂ O, Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ ·6H ₂ O Here, urea forms a perovskite phase and acts as a composite agent to homogenize the composition of the precipitate, and ethanol is added to the aqueous solution to improve the wettability of the porous cathode.

Looking at the operational principle of the penetration, After completion of permeation of the SSC solution in the cathode surface of the cell of urea to drying and decomposition in the process of ammonia and carbon dioxide, ammonia and carbon dioxide is a hydroxyl group (OH ^-) and hydroxyl carbonyl carbonate ( It _{is decomposed into CO 3} ^2- ), and is homogeneously precipitated due to the hydroxy group and the hydroxycarbonate, and plays the role of forming the SSC nanophase in the calcination process.

In the permeation, the SSC solution is preferably sprayed at a concentration of 0.1 to 2 mol/L.

The penetration is preferably 1 to 7 times, more preferably 3 to 5 times.

It is preferable to calcinate for 2 to 3 hours at 800 to 900° C. after passing through the permeation process.

_{In addition, the present invention is manufactured by infiltration of SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.1) using an ultrasonic spray technique on the surface of the porous cathode. , Provides a cathode for a solid oxide fuel cell with improved performance.

The penetration is preferably 1 to 7 times, more preferably 3 to 5 times.

The penetration is preferably carried out through a process of drying and heat treatment after spraying through ultrasonic equipment.

In addition, the present invention provides a solid oxide fuel cell including the cathode for a solid oxide fuel cell according to the present invention.

The fuel cell may be configured with a conventional solid oxide fuel cell other than the SSC-infiltrated cathode.

In addition, the present invention

i) preparing an SSC solution prepared by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water, and urea, followed by stirring;

ii) performing heat treatment after infiltration of the SSC solution prepared in step i) on the surface of the porous cathode using an ultrasonic spray technique; And

iii) manufacturing a solid oxide fuel cell including the cathode penetrated in step ii). It provides a method of manufacturing a solid oxide fuel cell with improved performance.

In the above manufacturing method, the SSC solution in step i) is an aqueous solution of urea and nitrate in distilled water and ethanol Sm(NO ₃ ) ₃ ·6H ₂ O, Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ · It is preferable to prepare by mixing 6H _{2 O.}

In the above manufacturing method, the penetration in step ii) is preferably 1 to 7 times, and more preferably 3 to 5 times.

In the above manufacturing method, the drying in step ii) is preferably dried at room temperature, and the heat treatment is preferably heat treated at 800 to 900°C.

Hereinafter, the present invention will be described in detail by the following examples and experimental examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following Examples and Experimental Examples.

< Example 1> Fabrication of solid oxide fuel cell cell

<1-1> Anode Support type Unit cell making

Based on the method of manufacturing a solid oxide fuel cell, an anode support type segmented flat tubular cell was manufactured. To fabricate the anode support type unit cell, a pore-forming agent, Korea Carbon Black Co. KOREA, was mixed with NiO (Kojundo Chemical Co. KOREA) and 8 mol.% YSZ (TZ-8YSZ, Tosho Co.) powder. . Zirconia balls and ethanol were added to the mixed powder, ball milled for 3 days, uniformly dispersed, and dried at 80° C. for 24 hours. After drying, a mixed anode powder was prepared through sieving with a sieve plate having a size of 100 μm.

The mixed anode powder and YB-130D as a binder, distilled water as a solvent, DG as a plasticizer, and Cellosol as a lubricant were added and kneaded. After kneading the mixture was pressed and extruded using an extruder (Extruding machine), a flat tubular mold was mounted to extrude the flat tubular anode support.

The extruded flat tubular anode support was dried in a thermo-hygrostat maintaining constant temperature and humidity. The extruded support was dried in a thermo-hygrostat (temperature 80° C., humidity 90%) for 72 hours, and the support was turned over every 1 hour for the initial 24 hours to prevent the support from bending during drying.

After drying the thermo-hygrostat, a pre-sintering process was performed in order to impart the necessary strength to the coating process. In order to prevent bending of the support during pre-sintering and improve flatness, an alumina plate was placed between each support and a load was applied using a porous ceramic. Pre-sintering heat treatment is maintained for 5 hours after raising the temperature to 350℃ (0.58℃/min) in a sintering furnace, and maintained for 3 hours after raising the temperature to 750℃ (1.33℃/min), and maintained at 1100℃ (0.58℃/min). After heating, heat treatment was performed for 3 hours. Through the presintering heat treatment, the pore former, the binder, the distilled water, the plasticizer and the lubricant could be completely volatilized.

<1-2> Segment Flat tube Coating process

The anode functional layer (AFL) was coated on the support having completed pre-sintering by immersion method. The AFL slurry was immersed in Ni-ScSZ for 10 seconds, and then dried at room temperature for 30 minutes. After the AFL coating, the support was heated to 1000°C (1.67°C/min) in a sintering furnace and then sintered for 3 hours.

In order to coat the dense thin film electrolyte, vacuum slurry coating was performed using a vacuum pump. The electrolyte slurry was prepared at a concentration of 3 wt.% ScSZ. Before starting the ScSZ electrolyte slurry coating, ultrasonic treatment was performed for 30 minutes under 75% condition of Amplitude. When coating the electrolyte, tape masking was performed on the interconnect (I.C) part to prevent the electrolyte from being coated at the position where the connector of the anode is coated. A jig was manufactured according to the size of the anode-supported unit cell, and a vacuum state was created with a vacuum pump. Coating was applied for 30 seconds by immersing in the slurry while applying a vacuum of 600 mmHg to the inside of the support. After coating, it was dried at room temperature for 30 minutes and the masking tape was removed. After the ScSZ electrolyte coating, the support was heated to 1100°C (0.58°C/min) in a sintering furnace and sintered for 5 hours.

GDC as a buffer layer was coated in the same process as ScSZ electrolyte coating. The buffer layer slurry was prepared at a concentration of 3 wt.%. As with the electrolyte slurry coating, the connector portion of the anode was masked with tape, and then immersed in the GDC slurry and coated for 30 seconds. After coating the GDC buffer layer, the support was heated to 1400° C. (1.67° C./min) in a sintering furnace and co-sintered the anode support, the anode functional layer, the electrolyte, and the buffer layer for 5 hours.

The air electrode was coated on the sintered support using a screen printing method. In screen printing, five segments were formed by printing electrodes with a certain thickness and shape. As the cathode paste, LSCF-GDC (FCM Co.) and LSCF (FCM Co.) were used. A total of 4 times were performed by screen printing twice each using the paste. After screen printing of the cathode, the support was heated to 1150°C (2.4°C/min) in a sintering furnace and then sintered for 3 hours.

The connecting material was screen-printed in the same process as the air electrode. After preparing the Ag-glass, the binder paste was mixed for 5 minutes at 500 rpm, 1000 rpm, and 2000 rpm using a centrifugal mixer. The paste was screen-printed twice on the portion of the sintered support where the connector was masked with the tape of the anode, and the temperature was raised to 800°C (3.33°C/min) in a sintering furnace and then sintered for 30 minutes.

After cell fabrication was completed, a gas leak test was performed to determine the density of the electrolyte.

1 shows a schematic diagram of a manufacturing process of a segmented flat tubular SOFC cell, and FIG. 2 shows a state of the manufacturing process.

<1-3> Material selection between each component

Based on the SOFC manufacturing method, a segmented flat-tubular unit cell was fabricated. The unit cell is based on an anode support, an anode functional layer (AFL), an electrolyte, a buffer layer, a cathode functional layer (CFL), and a cathode current collecting layer ( It was composed of a multi-layered structure consisting of a cathode current collection layer (CCCL) and interconnect. The design components of the flat tubular SOFC unit cell to which the segmented cathode is applied and the experimental materials according to the design components are shown in Table 1 below.

Configuration material Anode support Ni-YSZ
(Yttria-stabilized zirconia) Anode functional layer Ni-ScSZ
(Ni/Sc ₂ O ₃ -stabilized ZrO ₂ ) Electrolyte ScSZ
(Sc ₂ O ₃ -stabilized ZrO ₂ ) Buffer layer GDC (Gd-doped CeO2) Air cathode functional layer _{LSCF (La 0 6 Sr 0 4} Co 0 2 Fe 0 8 O 3....) -
_{GDC (Gd 0. 1 Ce 0} . 9 O 3) Cathode current collector layer LSCF
(La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ) Connector Ag-glass

Ni and YSZ were used to fabricate the anode support. The mixture of NiO and electrolyte is reduced _{to Ni metal in a reducing atmosphere (H 2} , CO, etc.), thereby performing a catalyst heat reduction necessary for the oxidation reaction of the fuel, and increasing the porosity inside the anode to increase the fuel gas, electron conductor, and ion conductor. The fuel electrode functional layer serves to prevent holes or microcracks generated during the production process of the support, and the fuel oxidation reaction on the flat tubular anode support using Ni and ScSZ as the anode functional layer in the unit cell This was made to occur easily. ScSZ with an amount of scandia of 10 mol.% was used as the electrolyte of the unit cell. In the case of ScSZ, when the amount of scandia to be substituted is 10 mol.%, the ionic conductivity represents the maximum value.

_{A CeO 2} based solid electrolyte to prevent the reaction between the _{ZrO 2} solid electrolyte and LSCF that occurs during the heat treatment process of the cathode, and the LSCF is applied as a Co-containing perovskite mixed conductor with high electrical conductivity to be applied as the cathode. Was used in the form of a multi-layered structure formed as a buffer layer, and GDC in which the amount of gadolium was 10 mol.% was used as the buffer layer.

LSCF-GDC was used as the cathode functional layer, and the cathode was designed into 5 segments for experimental variables. Each electrode area was 2 cm ² , the spacing between each segment was 0.5 cm, and the total length was designed to be 7 cm. LSCo paste was used on the LSCF surface to reduce the contact resistance with the cathode current collecting layer.

The connecting material must electrically connect the anode of the flat tubular unit cell with the cathode of the next cell that will be stacked, and must play a role of preventing hydrogen and air from being mixed due to its high density. The connector was designed to screen-print an area of ^{22.5 cm 2} using a paste made of Ag and glass.

After cell fabrication was completed, a gas leak test was conducted, and a metal jig for fuel supply was sealed using a glass sealant (Mico), and the cathode and connector were used with Ag mesh, Ag wire, and Pt wire. Electric current was collected.

3 is a schematic diagram of a flat tubular SOFC unit cell to which a segmented cathode is applied.

< Example 2> Using ultrasonic equipment SSC Thin film deposition

<2-1> Preparation of ultrasonic machine

The ultrasonic equipment was constructed as shown in Lou, Xiaoyuan, et al., Solid State Ionics 180.23-25 (2009): 1285-1289. The ultrasonic wave of the equipment maintained the driving frequency range (79 ∼ 81 kHz) with a frequency of 80 kHz, and the width and narrowness of the sprayed pattern was controlled by controlling the flow rate with an air flow meter, and the flow rate change of the syringe pump. The amount of penetration was optimized by supplying the desired amount.

4 shows the configuration of an ultrasonic device.

<2-2> SSC ( Sm _{0 . 2} Sr _{0 . 8} CoO _{3 -δ} ) Preparation of solution

_{Figure 5 shows urea and nitrate aqueous solution Sm(NO 3} ) ₃ ·6H ₂ O, Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ ·6H ₂ O in 55 vol% of distilled water and 45 vol% of ethanol. And mixed together.

Urea was used as a composite agent to form the perovskite phase, and ethanol was added to the aqueous solution to improve the wettability of the porous LSCF cathode. The cation precipitation depends on the drying process, and composition heterogeneity occurs locally depending on the rate at which each is precipitated. Urea was added to homogenize the composition of the precipitate. After infiltrating the SSC solution into the cell, it is dried at 80°C, and urea is decomposed into ammonia and carbon dioxide during this process. Ammonia and carbon dioxide is a hydroxyl group (OH ^-) are decomposed into carbon and a hydroxyl carbonate (CO ₃ ^2-). Due to the hydroxy group and the hydroxycarbonate, it is homogeneously precipitated and plays a role in the formation of SSC nanophases in the calcination process.

6 shows the SSC nanophase formation reaction scheme.

<2-3> SSC ( Sm _{0 . 2} Sr _{0 . 8} CoO _{3 -δ} ) Thin film deposition

_{A catalytic Sm 0.2} Sr _0.8 CoO _3-δ (SSC) thin film was deposited on the surface of the porous LSCF cathode through ultrasonic equipment.

The concentration of the aqueous solution is fixed at 1 mol/L, and for accurate control, a syringe pump is used in 5 segments (Ref, SSC 1 time, SSC 2 times, SSC 3 times, SSC syringe) according to the number of times in the air electrode. And infiltrated through the ultrasonic equipment at a flow rate of 3 μl/min. An experiment was also prepared for comparison with the reference electrode (Ref) that did not go through the penetration process. After passing through the permeation process, it was calcined at 850° C. for 2 hours.

< Experimental example 1> EDS analysis

The SSC solution was infiltrated into a segmented flat tubular cell and calcined at 850° C. for 2 hours in a bulk state, followed by energy dispersive spectroscopy (EDS).

The incident electrons entered a depth of 3 µm and subjected to qualitative and quantitative analysis of the surface. Point A analyzed the part coated with SSC on the LSCF surface, and B analyzed the clean LSCF surface without SSC penetration.

As a result, the surface component results are shown in FIG. 8 and Table 2 below. Through this, it was confirmed that the SSC penetrated into the intact phase on the LSCF surface with the compositional ratio of each LSCF and SSC for each point.

Point A LA Sm Sr Co Fe Total amount 5.54 3.35 8.13 8.89 7.27 La _{0 . 6} Sr _{0 . 4} Co _{0 . 2} Fe _{0 . 8} O _{3 -δ} 5.54 0.00 3.69 1.81 7.27 Sm _{0 . 5} Sr _{0 . 5} CoO _{3 -δ} 0.00 3.35 4.44 7.08 0.00

< Experimental example 2> Microstructure observation

<2-1> Microstructure observation according to the wet penetration method

In the wet penetration method, the surface tension varies depending on the material of the cathode, so the selection of a surfactant plays an important role. Ethanol and distilled water were used as surfactants. In general, ethanol (22 dynes/cm) has a lower surface tension than distilled water (72 dynes/cm). Distilled water and ethanol were used together, which improved wettability by reducing the surface tension.

In order to compare with ultrasonic equipment using a syringe, which is one of the existing wet penetration methods, a cold type field-emission scanning electron microscope (SEM-4800) was analyzed according to the depth of the cathode layer.

As a result, the microstructures observed in FIGS. 9 and 10 are shown. In the wet penetration method using a syringe, it was observed that when the air electrode was viewed as a whole, it was observed that the air electrode was relatively largely distributed from the upper part to the lower part due to excessive penetration of the solution from the upper part. The wet permeation method using an ultrasonic device confirmed that a homogeneous solution was evenly distributed through droplet size refinement.

<2-2> SSC Microstructure observation according to the number of times

1 mol/L SSC solution was infiltrated into the three segmented cathodes once, twice, and three times, respectively. By controlling the amount of droplets with a syringe pump, intaglio masked as much as the air electrode area with an OHP film so that the sprayed pattern could evenly penetrate only the air electrode area.

As a result, as shown in FIG. 11, before infiltration, the surface of the LSCF cathode was clean and the particle interface was clearly visible. As the number of penetrations increased, the majority of particle surfaces were coated with SSC nanoparticles. The LSCF particle interface did not appear to be the formation of a discontinuous thin film of SSC. The average particle size was observed to be about 80 nm.

SSC had higher surface oxygen exchange rate and oxygen reduction than LSCF, so it could be confirmed that it was deposited on the surface of the cathode in a small amount, and nano-catalyst particles could be implemented by controlling the composition precision as the number of times increased.

< Experimental example 3> Segment Flat tube Fuel cell performance measurement

The current of the unit cell was adjusted by the constant current measurement method, and the current was measured for each segment accordingly. Performance measurement evaluation shows the I-V measurement results of SOFC unit cells by supplying 2 L/min of air and 500/min of hydrogen at 700° C. and 750° C. using a constant current method. The composition of each segment was designated as Ref (Blank), SSC 1 time, SSC 2 times, SSC 3 times, and SSC syringe, and the performance measurement was analyzed.

As a result, as shown in Fig. 12, each open circuit voltage (OCV: Open Circuit Voltage) was 1.12V, 1.12V, 1.10V, 1.10V, 1.09V in ^{an electrode effective area of 2 cm 2 at 700°C, respectively.} The maximum power density of 211 mW/cm ² , 356 mW/cm ² , 400 mW/cm ² , 416 mW/cm ² , and 223 mW/cm ² showed battery performance.

In addition, as shown in Fig. 13, each open circuit voltage was 1.10V, 1.10V, 1.09V, 1.09V, 1.07V in ^{the electrode effective area of 2 cm 2 at 750°C, and the maximum power density of each was 300 mW/} It was confirmed that the battery performance of ^{cm 2} , 546 mW/cm ² , 572 mW/cm ² , 600 mW/cm ² , and 310 mW/cm ^{2 was shown.}

As a result of the catalytic effect of SSC infiltration, it was confirmed that the performance increased by about 30% when the SSC was infiltrated once compared to the reference cell at 700°C and 750°C, respectively. The catalyst coating modified the surface of the LSCF cathode and improved the battery performance of the segmented flat tubular SOFC with high electrocatalytic activity and stability.

< Experimental example 4> Segment Flat tube Fuel cell impedance analysis

AC impedance was measured using SP-240 (Bio-logic Co. KOREA). The frequency ranged from 300 kHz to 0.1 Hz, and the magnitude of the AC voltage applied between the working electrode and the reference electrode was 14 mV. It was measured when the voltage was kept constant in the open circuit voltage state.

As a result, as shown in FIGS. 14 to 15, it was confirmed that the polarization resistance (Rp) represented by the width of the two arcs (Arc) significantly decreased with penetration. The electrode performance is improved due to urea, resulting in a smaller particle size and a uniform distribution. The impedance spectrum consists of two main arcs, and the high-frequency and low-frequency arcs carry oxygen ions to the surface and the interface, respectively. It can be seen that the low-frequency impedance is reduced, which is due to structural and chemical modifications to the electrode surface characteristics due to the widening of the high active area of the SSC electrochemically.

Ohmic resistance (ΩOhmic) and polarization resistance (Rp) for each segment are shown in Table 3 below.

Segment R _ohmic (Ω) R _p (Ω) Blank 0.429 0.860 SSC 1time 0.330 0.706 SSC 2times 0.367 0.650 SSC 3times 0.292 0.407 SSC syringe 0.352 0.616

Claims (12)

_{SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.1) is infiltrated on the surface of the porous LSCF (Lanthanum Strontium Cobalt Ferrite) cathode using ultrasonic spray technique. Including the step of coating the SSC thin film,
here,
The infiltration is carried out by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water and urea, and then spraying the SSC solution prepared by stirring and drying it,
The SSC solution is sprayed at a concentration of 0.1 to 2 mol/L,
The penetration is characterized in that to penetrate 1 to 7 times,
A method of improving the performance of cathodes for solid oxide fuel cells (SOFCs).
◈ Claim 2 was abandoned upon payment of the set registration fee. The method of claim 1,
The porous Lanthanum Strontium Cobalt Ferrite (LSCF) cathode has a multi-layered structure including a Lanthanum Strontium Cobalt Ferrite (LSCF)-GDC (Gadolinium Doped Ceria) layer and an LSCF layer.
◈ Claim 3 was abandoned upon payment of the set registration fee.◈ The method of claim 1,
The ultrasonic spray technique is a method of improving the performance of a cathode for a solid oxide fuel cell, characterized in that using ultrasonic equipment including a controller, an ultrasonic spray nozzle, a frequency controller, an air flow meter, and a syringe pump.
◈ Claim 4 was abandoned upon payment of the set registration fee. The method of claim 1,
The ultrasonic spray technique is a method for improving the performance of a cathode for a solid oxide fuel cell, characterized in that ultrasonic spraying is performed under conditions of an ultrasonic driving frequency of 75 to 85 kHz, a syringe pump flow rate of 2 to 4 µl/min, and an air flow rate of 2 to 4 ℓ/min. .
delete delete delete ◈ Claim 8 was abandoned upon payment of the set registration fee. The method of claim 1,
A method for improving the performance of a cathode for a solid oxide fuel cell, characterized in that calcining at 800 to 900° C. for 2 to 3 hours after passing through the permeation process.
_{SSC (Sm 1-x} Sr _x CoO _3-δ , where 0.1≤x≤0.8, 0≤δ≤0.1) is infiltrated on the surface of the porous LSCF (Lanthanum Strontium Cobalt Ferrite) cathode by using ultrasonic spray technique. As a cathode for a solid oxide fuel cell,
here,
The infiltration is to spray an SSC solution prepared by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water and urea and then stirring and drying the solution,
The SSC solution is sprayed at a concentration of 0.1 to 2 mol/L,
The penetration is characterized in that the penetration is 1 to 7 times,
Cathode for solid oxide fuel cells.
A solid oxide fuel cell comprising the cathode for a solid oxide fuel cell of claim 9.
i) preparing an SSC solution prepared by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water, and urea, followed by stirring;
ii) performing heat treatment after infiltration of the SSC solution prepared in step i) on the surface of a porous LSCF (Lanthanum Strontium Cobalt Ferrite) cathode using an ultrasonic spray technique; And
iii) manufacturing a solid oxide fuel cell including the cathode penetrated in step ii); including,
here,
The infiltration is carried out by mixing an aqueous nitrate solution of samarium, cerium, and cobalt with ethanol, distilled water and urea, and then spraying the SSC solution prepared by stirring and drying it,
The SSC solution is sprayed at a concentration of 0.1 to 2 mol/L,
The penetration is characterized in that to penetrate 1 to 7 times,
A method of manufacturing a solid oxide fuel cell with improved performance.
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