KR20120132058A - Solid oxide fuel cell having the improved electrodes and its preparation - Google Patents

Abstract

PURPOSE: A solid oxide fuel cell is provided to improve performance by uniformly maintaining porosity and particles in a negative electrode layer small and to restrain the crack generation and porous structure change of the negative electrode layer. CONSTITUTION: A solid oxide fuel cell comprises a negative electrode support, a negative electrode layer selectively formed on the negative electrode support, an electrolyte layer formed on the negative electrode support or negative electrode layer, and a positive electrode layer formed on the electrolyte layer. The negative electrode support comprises NiO, one or more components selected from a group consisting of YSZ, ScSZ, SmSZ, GDC, and a heat-expansion-controllable oxide. The heat expansion ratio of the heat-expansion-controllable oxide is 7.0x10^(-6)/°C-10.0x10^(-6)/°C.

Description

Solid oxide fuel cell having improved electrode reaction layer and its manufacturing method

The present invention relates to the formation of a cathode support, a cathode layer and an electrolyte layer, and an anode layer of a solid oxide fuel cell, and in particular, to increase the performance by keeping the constituent particles and porosity of the cathode layer small and uniform, and during use of the fuel cell. The present invention relates to a method of fabricating a stable structured cell in which the pore structure of the cathode layer and cracking are suppressed even under repeated oxidation and reduction conditions.

The solid oxide fuel cell has a flat, tubular, flat tube type, and is generally used, and in most cases, NiO / YSZ as a cathode (fuel electrode) support, YSZ (Yttria-stabilized Zirconia) as an electrolyte, and GDC (Gadollium-doped Ceria) It is well known to operate at high temperature of 600 ~ 1,000 ℃ by combining (La, Sr) MnO ₃ or (La, Sr) (Co, Fe) O ₃ as anode (air cathode). .

The solid oxide fuel cell has good electrical performance per unit area at high temperatures (800 ~ 1,000 ℃), but has a problem that performance is remarkably degraded at high temperatures (600 ~ 750 ℃). There are many attempts, such as changes in development and production methods, but there are still few results.

If the solid oxide fuel cell exhibits high activity in the lower temperature range (600 to 700 ° C), the system design is easier because it is close to the operating temperature range of the fuel reformer, and the choice of using metal materials for stack and system fabrication is high. It can widen and induce cost reduction, and in particular, the power generation efficiency of the fuel is increased at a low temperature, thereby providing the advantage of maintaining high electrical energy efficiency.

For this reason, there is a method of reducing the electric potential by using GDC with high O ^- ion conductivity instead of YSZ as an electrolyte in a medium-temperature SOFC, but this method has a limitation in obtaining a dense sintering, so that a small amount of some sintering aid is added. And the like. However, when GDC is used as the material of the electrolyte layer, it is not suitable in the case where the support of NiO / YSZ and other thermal expansion coefficients is different so that oxidation / reduction or start / stop is repeated, or the operating condition (temperature) change is large. In addition, there is a disadvantage that GDC is not stable in the hydrogen (H ₂ ) atmosphere.

Alternatively, the use of ScSZ (Scandium-doped Zirconia) or SmSZ (Samarium-doped Zirconia) instead of YSZ has been suggested in the research data, but ScSZ and SmSZ, etc., are vulnerable under high temperature reducing conditions. Insufficient operational reliability, especially when hot spots are formed in part of a large area, causes cracks in the cell, which can lead to severe cell failure.

In general, crack generation in a cell is often caused by a large difference in coefficient of thermal expansion of adjacent interfaces or deformation (including pores) in the electrolyte. The anode of the solid oxide fuel cell is a site where fuel oxidation occurs. During the manufacturing process, the cathode is subjected to a high temperature oxidation atmosphere. During operation, the cathode material is reduced (NiO-> Ni) by maintaining a hydrogen (H ₂ ) atmosphere. Under the influence of Ni, the coefficient of thermal expansion of the cathode increases, stressing the cell in the event of a temperature change or start / stop.

In addition, the cathode substrate is upon re-exposure to the air, the volume expansion while the Ni metal in the pores of the cathode support oxidation back to the NiO may be induced around the crack, which is that is defective in the electrolyte oxygen (O ₂₎ directly The phenomenon of reaching the cathode (fuel electrode) layer may occur. In order to avoid this, there are various attempts such as making the electrolyte coating uniform and dense and sintering temperature of 1,400 ℃ or higher, but especially in large-area cells, it is necessary to coat the electrolyte several times in order to eliminate defects on the whole area. Work may be applied.

Usually, the cell uses NiO / YSZ (usually 55:45, weight ratio) as the negative electrode support, and YSZ is used as the electrolyte and sintered at a high temperature of about 1,400 ° C., where the fine structure of the negative electrode support and the negative electrode layer is used. Is deformed. In the anode layer, the sintering temperature is about 1,200 ℃, the cell performance is increased or decreased according to the shape of the microstructure generated during the sintering process. The microstructure region of the anode and the anode in contact with the electrolyte is called the reaction triple phase of boundary (TPB), and it is known that the fine and uniformity of the structure provides high cell performance by providing more reaction active points. have.

The basic requirements for the fabrication of SOFC cells include the formation of a stable electrolyte dense film at high temperatures, the formation of microstructures in the reaction three-phase interface, the well matched thermal expansion coefficients of the support and the electrolyte, and the porosity and electrical and electronics of the cathode support. Good conductivity is also known to be important.

Representatively applied negative electrode support (Ni / YSZ at the time of reduction) structure, Ni particles and Ni particles are connected to each other to express sufficient electrical conductivity of several hundred S / cm normally required in the negative electrode support, and NiO content is usually YSZ content Used more. However, this means that the influence of Nickel on the thermal expansion rate or oxidation / reduction of the negative electrode support is great, but in the general manufacturing process, it is limited to controlling the electrical conductivity and porosity for gas permeation after reduction in the negative electrode support. In other words, while many attempts have been made to change the amount or type of pore formers to increase porosity, few attempts have been made to increase the stability of the support or cell and to increase the active point (TPB) of the cathode layer.

That is, when the cell manufactured under the oxidizing condition is changed to the use condition, that is, the reducing condition, the thermal expansion coefficient of the negative electrode support may be largely different from the thermal expansion coefficient of the electrolyte. Problems such as thermal stress and delamination occur. In addition, when cells are exposed to air, they develop severe cracks, an example of which is shown in Solid State Ionics 176 (2005) 847-859.

In order to avoid this problem, thermal expansion characteristics and oxidation-reduction stability according to the material composition between the anode and the electrolyte in a solid oxide fuel cell have been proposed in US Pat. No. 7,351,487 B2 (2008). It shows little difference in thermal expansion rate, good electrical conductivity, no cracking and good cell performance. Instead of NiO / YSZ where cracks occur during redox, instead of YSZ, a single-earth rare-earth metal oxide composite is used, which may be a material constraint during mass production, No characteristics are given.

In addition, Japanese Patent Application Publication No. 10-2005-0004996 suggested a cell having increased mechanical strength by using 10YSZ (10mol% Y ₂ O ₃ substituted zirconia) instead of 8YSZ (8mol% substituted zirconia) in NiO / YSZ cathode support. No changes were made to conditions or cell performance.

In addition, Korean Patent Laid-Open Publication No. 10-2005-0036914 discloses a secondary skeleton such as LaCrO ₃ and SrTiO ₃ having electrical conductivity through pores formed in the primary skeleton, after forming the primary skeleton of the cathode support using the first ceramic of YSZ. By supporting a ceramic material and firing the same, a method of manufacturing a negative electrode support having electrical conductivity without using metallic components such as Ni, Co, and Cu is proposed. The purpose is to provide cell performance without excessive carbon deposition even in internal direct reforming in fuel cells, but the electrical conductivity is less than 1 S / cm and the performance of the manufactured cell is also not high.

Nitrogen-containing cermets, such as NiO / YSZ, are effective in providing electrical conductivity and high cell performance of the cathode support.In the ideal case, however, the mechanical framework of the cathode support in the NiO / YSZ thermite is YSZ and YSZ directly In the case where NiO is distributed around the YSZ-YSZ skeleton while forming the basic skeleton structure, the thermal expansion coefficient is the same regardless of the oxidation condition or the reduction condition because the YSZ of the electrolyte and the YSZ of the cathode support skeleton are the same materials. The degree of thermal expansion between the cathode support layer and the electrolyte layer is also the same for temperature changes up to and including 1,000 ° C, thus ensuring mechanical thermal stability between the electrode interfaces of the cells.

In practical cases, however, in the case of cathode support fabrication of planar type, especially flat tube or tubular solid oxide fuel cells, NiO is mixed with YSZ, binders, dispersants, water, etc. As for raising the extrudate (extrudate) to form a pyeonggwan, after drying, aging them in air to a temperature over the organic firing (calcining), and after this the electrolytes such as YSZ coating and firing the sintering them at 1,300? 1,500 ℃ In the process, the skeletal structure of the cathode support causes not only the bond between YSZ and YSZ but also NiO-NiO bond, which is a Ni-Ni bond at the time of reduction, which is a factor to rapidly increase the thermal expansion rate of the cathode support under operating conditions. .

Usually, the thermal expansion rate of YSZ is about 10.5x10 ^-6 / ℃, NiO is about 10.5x10 ^-6 / ℃, and Ni is known to be more than 14.5x10 ^-6 / ℃, which is Ni-Ni connection part of cathode support under reducing conditions Increasing the coefficient of thermal expansion may cause thermal stress with the electrolyte YSZ layer or intensify thermal stress due to frequent temperature changes in long-term operation or non-operational cycles.

In particular, the cell reoxidation is accompanied by exposure to air after operation under high temperature reduction conditions, and the effect on the cell crack can be increased by increasing the oxidation volume and reagglomeration of NiO. Related literature studies [Solid State Ionics 176 (2005) 847-859] show that when the pore structure of the cathode support is minute, a large crack is generated in the entire support during the redox process. It suggests that it should consist of large pore (coarse).

This phenomenon is difficult to achieve an ideal structure in which the NiO or Ni is connected and distributed around the YSZ skeleton while the mechanical skeleton structure is composed of YSZ particles and YSZ particles during the manufacturing process of the cathode support in the mixed state of NiO and YSZ particles. In case of NiO / YSZ in a typical anode support fuel cell, many cracks occur during and after use.

In another document [Journal of Power Sources 195 (2010) 1920-1925], a method of using a mixture of (Sr, Y) TiO ₃ system reduced at high temperature (about 1,400 ° C) as an electrical conductor and YSZ as an ion conductor is also used. Presented. Here, the thermal expansion rate of (Sr, Y) TiO ₃ is almost similar to that of YSZ, so that the support is stable to the redox cycle, but (Sr, Y) TiO ₃ is exposed to air during use. Once oxidized, although the rate of extinction is low, there is a disadvantage that the process of hydrogen reduction at about 1,200 ° C. or more is required in order to dissipate the electrical conductivity and generate the required electrical conductivity. Yes. In addition, when the cathode support is made by mixing with YSZ as an ion conductor, an interfacial reaction occurs at high temperature, and the overall electrical conductivity is reduced to several tens of S / cm. In particular, the electrochemical reaction property required for the fuel cell is very weak, so The process of additionally supporting the nickel component is necessary, but a complicated method is required in which the supported nickel solution must penetrate to the interface with the electrolyte (reaction interface, TPB) and be concentrated at the interface.

On the other hand, the manufacturing process of the solid oxide fuel cell is applied according to the size, type, or researchers of the fuel cell, but the sintering process and the temperature of the fabricated cell are virtually similar. For example, the production of the support is usually in the range of 1,000 to 1,300 ° C., the cathode layer is in the range of 900 to 1,300 ° C., the electrolyte is in the range of 1,300 to 1,500 ° C., and the anode layer is performed in the furnace under atmospheric conditions in the range of 1,000 to 1,300 ° C. do.

As mentioned above, the microstructure development of the three-phase interface (TPB, reaction interface) of the cathode and anode, which plays an important role in the electrochemical performance of the cell, can be significantly changed depending on the cell sintering process.

In the three-phase interface (reaction interface) of the cathode layer, Ni, which mainly has good H ₂ reaction activity, is basically used, and YSZ is commonly used as an O ^- transfer medium, but Ni and YSZ particle size control or fineness during high temperature sintering There is no known method for improving pore formation. However, there are examples in which some pore-forming agents, for example, activated carbon, etc., are added in advance to increase the porosity of the cathode functional layer.

As can be easily expected, the performance of the cathode layer is poor when Ni particles grow in the cathode layer (cathode function layer), YSZ particles grow, micro pores do not develop properly, or pore occlusion (closed pores). It can be expected to be significantly reduced. In particular, the grain growth of Ni and YSZ, the oxygen ions delivered by the electrolyte layer on the anode layer [O ^-] significantly reduced the number of contact points are Ni-YSZ reaction met with hydrogen (H ₂₎ in the negative electrode layer (anode layer) This leads to a drastic reduction in the O ^- transfer rate per unit area, or electron conductivity, resulting in a lower fuel cell reaction performance.

In addition, in the anode layer, a material that promotes O ₂ adsorption and activation, such as LSM or LSCF, and YSZ as an O ^- transfer medium are mixed and coated on the electrolyte and formed by high temperature sintering in air. Reaction proceeds between particles such as LSM or LSCF and YSZ particles to produce a non-conductive material such as La ₂ Zr ₂ O ₇ to increase electrical resistance, and to grow LSM, LSCF, or YSZ particles, Problems such as lowering the porosity too much result in a significant reduction in the electrochemical performance of the anode.

In order to avoid this, the direction of lowering the temperature may be preferred in the case of sintering the anode layer, but in this case, the bonding force between the constituent particles of the anode layer, for example, LSM, LSCF, and YSZ may be reduced, which may impede long-term performance. have.

In addition, the LSCF, which is suitable as a medium-temperature cathode material, has a smaller stability at high temperature, thereby increasing the above problems, and in order to suppress this, an intermediate layer made of GDC or the like is used to be mixed.

Due to the various problems of the above-described cell fabrication, in the case of a solid oxide fuel cell manufactured for the purpose of enlargement, when the operating temperature is substantially high, for example, at least 800 ° C or more, and partially 750 ° C or more. Its performance is limited, and in order to achieve proper performance at lower temperatures, it is difficult to select difficult materials and form complicated electrode structures.

Therefore, nickel element with excellent electrochemical reactivity required in fuel cell is used, but minimizes the difference of thermal expansion between anode support and electrolyte in oxidation state or reduction state simultaneously to suppress interfacial separation between electrolyte and support and There is a need to reduce the thermal stress between the interfaces, and at the same time, a method that does not generate cracks due to NiO regeneration even after exposure to reoxidation atmosphere is required.

In addition, the pore structure of the negative electrode support is well developed without occluding pores, and particles of Ni and YSZ are small and uniform at the reaction interface (TPB) of the negative electrode layer (cathode functional layer) and the electrolyte to maintain a high electron conductivity while simultaneously maintaining a high pore structure. It is necessary to maintain fine pores without occluded pores, and to suppress side reactions of LSM, LSCF, YSZ, etc. in the anode layer and to maintain the fine particles to provide a high reaction activity point, thereby increasing the overall electrochemical reaction activity.

In the case of electrolytes, YSZ is usually thinner (usually less than µm), but in the case of large cells, it is usually about twice as large as about 20 µm in order to avoid defects in the manufacturing process or work process and to reduce defects. Good to do. In this case, the type of electrolyte may be selected according to the thermal expansion coefficient of the support or the stability in a high temperature reducing atmosphere.

As is well known, in the case of coating an electrolyte on a cathode support (such as when a cathode functional layer is coated) or NiO / YSZ, a porous cathode support is dip into an electrolyte slurry solution (for example, an YSZ slurry solution). Coating (dip-coating) to coat the slurry and dry it, calcining (calcining) in the air at about 300 ~ 700 ℃ and densified sintering (sintering) at 1,300 ~ 1,500 ℃.

In this process, the skeletal structure of the NiO / YSZ anode support is also compacted and the pores are changed very small. This leads to a process that causes cracks in the cell as NiO volume increases and reaggregates in the micro pores during redox reduction. In addition, in the NiO / YSZ negative electrode support, the thermal expansion difference between the NiO / YSZ negative electrode support and the electrolyte at a high temperature condition is not different in the oxidizing condition, but has a disadvantage in that the reduction condition is large.

In order to improve this, the thermal expansion control material having a lower thermal expansion coefficient than that of the electrolyte (for example, YSZ) is partially used instead of the support YSZ, so that in the oxidation state, the average thermal expansion rate of the negative electrode support is slightly smaller than that of the electrolyte (YSZ). In this case, a method of bringing the thermal expansion degree closer to the electrolyte YSZ under oxidation and reduction conditions based on the electrolyte YSZ is required. In addition, in the case of using a material having a smaller thermal expansion coefficient with YSZ for the support, it is also necessary to maintain a certain amount of pores in the support in the range of 0.1 to 20 μm after sintering at 1,300 to 1,500 ° C.

The negative electrode support undergoes co-sintering at high temperature (1,300 ~ 1,500 ° C) together with the electrolyte YSZ layer coated on the negative electrode support (including the negative electrode functional layer coating). As the (YSZ) layer is densified, leak holes gradually disappear, electrolyte (YSZ) grains grow, and grain boundaries decrease.

However, in the case where the cathode support is coarse and the pores are large, the pore of the support may provide a more stable structure during reoxidation after lateral or cell operation, whereas leak holes in the layer of the coated electrolyte (YSZ, etc.) This may remain and a large amount of grain boundary may exist, which is a contradictory factor that significantly reduces the performance of the fabricated cell. In addition, when sintering characteristics of particles are delayed to delay volume shrinkage during sintering of the negative electrode support to maintain large pores, coating of electrolyte (YSZ) particles is uneven, and H ₂ or O ₂ passes through the electrolyte (YSZ) layer after sintering. It may exist as a leak hole or the electrolyte (YSZ) grain boundary may also remain, causing H ₂ or O ₂ leak during operation.

This phenomenon may be contrary to the fact that the coarse of the negative electrode support can make a cell stable to redox and that the densification of the electrolyte YSZ layer should be well done.

Accordingly, there is a need for a new method that simultaneously satisfies the thermal expansion coefficient of the negative electrode support, maintains the pore structure of the negative electrode support, and densifies the electrolyte. In particular, when thermal expansion control oxide is added, the sintering speed may be slower than that of the cermet of NiO / YSZ itself, which may help to form rough pores of the support, but it may be an obstacle to dense sintering of the anode functional layer or the electrolyte layer. May remain.

In order to induce densification of the anode functional layer or the electrolyte layer, which is coated even at a high temperature (1,300? 1,500 ° C) sintering with coarse pores, in order to induce densification, a solution dip of the anode functional layer or the electrolyte layer is provided on the anode support. After the coating, before the drying step, in a separate device, it is necessary to apply a vacuum to the inside of the negative electrode support to remove the solvent and to increase the density between the coating layer particles, followed by drying, firing and sintering.

The problem to be solved in the present invention in the background as described above is that the thermal expansion rate of the negative electrode support in the oxidation state is lower than the thermal expansion rate of the electrolyte layer, and at the same time the thermal expansion rate of the electrolyte layer in the reduced state, so that both high-temperature redox conditions To provide a method for the difference between the thermal expansion degree of the electrolyte and the thermal expansion degree of the negative electrode support is similar.

Another problem to be solved by the present invention is a stable anode functional layer and an electrolyte on a large pore support while preventing the crack of the cell under repeated redox conditions even under the coarse porosity of the negative electrode support with thermal expansion A method of forming a layer is provided.

Another problem to be solved by the present invention is to improve the electrochemical performance of the cell by controlling the microstructures of the anode functional layer and the anode functional layer small and uniform, to provide a cell manufacturing method showing a high performance even in the mid-temperature range will be.

Another problem to be solved by the present invention is to form an electrolyte layer without formation of defects in a large-area cell by forming the electrolyte in two layers, in the layer in contact with the cathode layer using a stable material in a high temperature reducing atmosphere, the anode ( Air cathode) by applying a material with high O ^- ion conductivity to provide a stable performance even in the high temperature generating part of the cell.

The problem solving means according to the present invention is to form a negative electrode support, a negative electrode (functional) layer, an electrolyte and an anode layer of a unit cell of a solid oxide fuel cell exhibiting electrochemical performance and high long-term operation stability even at high temperatures. i) Part of YSZ ScSZ, SmSZ, or GDC is used as NiO / YSZ or NiO / ScSZ, NiO / SmSZ, NiO / GDC as a thermal expansion control oxide having a smaller thermal expansion rate and stable under reducing conditions. ) YSZ, ScSZ, SmSZ, GDC or the like or a mixture thereof as an electrolyte material on the negative electrode support or the negative electrode (functional) layer to form an electrolyte membrane, iii) coating the negative electrode layer, the electrolyte layer and the positive electrode layer and removing the solvent, In drying, firing and sintering at a high temperature, the sintering is produced in a manner in which oxygen of 900 ° C. or higher proceeds in a thin air stream.

In the present invention, a negative electrode support may be used such as NiO / YSZ, NiO / SmSZ, NiO / GDC and the like, and it is preferable to use NiO / YSZ which is low in cost, stability and manufacturing problems. In the case of YSZ, a reducing atmosphere of a high temperature and hydrogen stable condition one, the oxygen ions of the YSZ (O ^-) conductivity is low and is mainly expressed in high performance high temperature, on the one hand, the support structure is easily destroyed in a repeated oxidation-reduction atmosphere in , YSZ ₂ O is lower than the thermal expansion coefficient of a portion CaAl it involves the (crack occurrence), the problem is _{4, MgAl 2 O 4, NiAl} 2 O 4, CuAl 2 O 4, CoAl 2 O 4 spinel and Y, such as ₂ Provided is a method of mixing with an oxide such as O ₃ , Yb ₂ O ₃ and the like, characterized in that the ratio of the additional oxide in the mixture with YSZ is 10 ~ 90%.

In the practice of the present invention, the coefficient of thermal expansion of the oxide for further thermal expansion adjustment is 7.0x10 ^-6 / 占? 10.0x10 ^-6 / ℃, the average particle is larger than YSZ, larger than the average 0.1㎛, preferably larger than 0.3㎛ and smaller than 10㎛. Typically, the thermal expansion coefficient of YSZ is 10.8 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of Y ₂ O ₃ is about 8.1 × 10 ⁻⁶ / ° C.

Although the present invention has been described using NiO / YSZ as an example, ScSZ, SmSZ, or other structure GDC having a similar structure to YSZ may also be used with YSZ, and the present description is not limited to NiO / YSZ. Do not.

In the present invention, when NiO / YSZ lacks stability for repeated exposure of redox, when YSZ is substituted with an oxide for thermal expansion alone, for example, when NiO / MgAl ₂ O ₄ , the stability of repeated exposure of redox is decreased. And the effect sought in the present invention cannot be expressed, because a large difference in thermal expansion with the electrolyte layer occurs in the process produced under oxidizing conditions or a large difference in coefficient of thermal expansion with the electrolyte layer in the reducing process. Accordingly, in the case of YSZ, mixed with other thermal expansion coefficient adjusting oxide, at least 10% or more can be used to increase the effect.

On the other hand, when the thermal expansion control oxide is mixed with YSZ or ScSZ or the like, GDC (Gadollium-doped Ceria) or reducing stability and electrical conductivity and thermal expansion rate of YSZ are almost similar to that of YSZ instead of YSZ or ScSZ. Perovskite oxides, such as TiO ₃ and (Y, Sr) CrO ₃ , can be used to further replace and mix some of YSZ or ScSZ.

In the present invention, in the manufacture of a solid oxide fuel cell, a cathode (functional) layer, an electrolyte layer, and an anode layer are formed on a cathode support, and then fired in air to remove the organic additives included in the manufacturing process, and then, at a higher temperature. In sintering, in order to control the microstructure of the pore and cathode layer of the support and the microstructure of the anode layer, it is carried out under an oxygen-lean gas stream such as nitrogen to increase the electrochemical performance at high temperatures and repeated exposure of redox It also provides a stable cell.

In the present invention, the formation of the electrode layer or the electrolyte layer of the cathode / anode of the cell is mainly described by dip-coating, but the present invention is not limited thereto. In this case, the anode support includes an oxide for controlling thermal expansion instead of YSZ. Oxides are used for mixing.

The negative electrode support mixes NiO about 50-70wt%, YSZ (or ScSZ, etc.) and the mixture of thermal expansion control oxide at a ratio of about 30-50 wt%. Can be adjusted. Usually, the thermal expansion control oxide has a low specific gravity, and in this case, the thermal expansion control oxide occupies a relatively large volume, so there is no significant difference in the overall volume composition even if NiO is increased. 1-10 wt% of activated carbon or carbon black is added as a pore control agent and ball milled for about 1 day or more in an ethanol solution to dry and volatilize the ethanol.

1 to 10 wt% binder, 1 to 5% dispersant, and the like are added to the homogeneously mixed powder mixture, and then kneaded for at least 5 hours, and then aged for 2 days, and then extruded in a flat or tubular extruder. Extruded molded products are dried and then burned and burned with organic materials at 1,000 ~ 1,300 ℃ in a kiln, and then fired and sintered. At this time, the temperature rise is kept below 5 ℃ / min.

In the present invention, it is possible to prevent hole generation in the electrolyte layer due to coarse pores of the negative electrode support, to increase the bonding force with the electrolyte layer, and to increase the reaction active point (TPB) in the cathode layer / electrolyte layer. The negative electrode layer (negative electrode functional layer) is coated. The cathode functional layer uses NiO / YSZ, NiO / ScSZ, NiO / SmSZ, NiO / GDC, etc., but the NiO ratio is about 50 wt% compared to the mixture with YSZ (or ScSZ, SmSZ, GDC). It provides a weight ratio of more than 45% but not more than 55%, and the NiO / ScSZ, NiO / SmSZ, or NiO / GDC or a mixture thereof is preferred to NiO / YSZ for high electrochemical performance at high temperature. do.

The negative electrode support is dipped in a slurry solution, dip-coated under atmospheric pressure, coated to a uniform thickness, and then taken out and vacuumed inside the support in a separate device to remove the solvent from the coating layer, while simultaneously coating the coating layer. It provides a way to (dense). This provides an effective method of increasing the connectivity between particles while suppressing particle separation of NiO or YSZ during drying or heating. In the present invention, the thickness of the final coating layer of the cathode layer is preferably 3 to 30 µm, preferably 3 to 25 µm.

The support coated with the negative electrode functional layer is calcined at about 900 to 1,300 ° C. The temperature is raised to about 500 to 700 ° C while raising the temperature, and at least 900 ° C or higher, and replaced with a gas such as nitrogen (N ₂ ). It provides a method of supplying, the kind of oxygen-lean gas is nitrogen (N ₂ ), argon (Ar), helium (He), carbon dioxide (CO ₂ ). Water vapor or the like can be used. At this time, the residual concentration of O ₂ , CO, H ₂ or hydrocarbon in nitrogen, etc. is preferably 5% by volume, preferably 0.1% by volume or less.

Normally, electrolyte coating is performed by dip-coating under atmospheric pressure. In particular, in the case of a large cell, dip coating is performed under normal pressure, and the electrolyte is coated with a uniform thickness throughout the support. In the present invention, the electrolyte forming operation is to prevent leak hole generation at least two times, at least the portion in contact with the cathode layer is YSZ, the portion in contact with the anode layer is characterized in that the ScSZ, SmSZ or GDC. Each coating thickness is about 5 ~ 20㎛ finally have a thickness of about 10 ~ 15㎛ used.

In the present invention, when the dip coating is carried out under normal pressure, the support is taken out and vacuumed inside the support in a separate device to remove the solvent on the surface and the inner surface of the support while simultaneously densifying the YSZ, ScSZ or GDC particles, thereby compacting It provides a way to increase the number of steps and prevent leak holes.

The first sintering of the anode support coated with electrolyte is carried out at 1,100 ~ 1,300 ° C, and the final sintering is carried out at 1,300 ~ 1,500 ° C, or the densified electrolyte by co-sintering the entire electrolyte layer at once. A film is obtained, in which the temperature rise is preferably less than 5 ° C / min, more preferably less than 2 ° C / min.

In particular, while increasing the temperature during the sintering of the electrolyte, it is carried out in the atmospheric atmosphere up to approximately 500 to 700 ℃, and at 900 ℃ or more provides a method of supplying by replacing with a gas such as nitrogen (N ₂ ) lean, oxygen thin gas Types of nitrogen (N ₂ ), argon (Ar), helium (He), carbon dioxide (CO ₂ ). Water vapor or the like can be used. At this time, the residual concentration of O ₂ , CO, H ₂ or hydrocarbon in nitrogen, etc. is preferably 5% by volume, preferably 0.1% by volume or less.

It is also possible to co-sinter the negative electrode functional layer and the electrolyte layer at once, and even in this case, it is required to proceed the sintering using a gas rarely oxygen at 900 ° C or higher.

The anode layer is usually LSM / YSZ, LSM / ScSZ, LSCF / GDC, etc. can be used and coated by screen printing or tape casting, etc., and then fired at about 1,000 ~ 1,200 ℃. In particular, while increasing the temperature during the sintering of the anode layer is carried out in the air to approximately 500 to 700 ℃, and at least 900 ℃ or more provides a method of supplying by substituting with a gas sparing oxygen such as nitrogen (N ₂ ), Types of gases include nitrogen (N ₂ ), argon (Ar), helium (He), and carbon dioxide (CO ₂ ). Water vapor or the like can be used. At this time, the residual concentration of O ₂ , CO, H ₂ or hydrocarbon in nitrogen, etc. is preferably 5% by volume, preferably 0.1% by volume or less.

In the present invention has been described on the basis of mainly manufacturing a cell for a solid oxide fuel cell by dip coating, the method of forming the support and the negative electrode, the electrolyte anode of the cell can also be produced by tape casting or printing method, in this case After forming the cell layer and calcining it, it proceeds in an air-lean stream of oxygen in the process of sintering it at a high temperature, the same as the effect described in the present invention. In addition, the composition ratio of the negative electrode support, the composition ratio of the negative electrode (functional) layer and the electrolyte layer, regardless of the form or manufacturing process of the solid oxide has the same effect as described in the present patent.

The present invention in another aspect, a) at least one component selected from the group consisting of NiO, Co ₂ O ₃ , CuO; b) at least one component selected from the group consisting of YSZ, ScSZ, SmSZ, GDC; And c) one or two from the group consisting of CaAl ₂ O ₄ , MgAl ₂ O ₄ , NiAl ₂ O ₄ , CuAl ₂ O ₄ , FeAl ₂ O ₄ , Y ₂ O ₃ , Yb ₂ O ₃ , Al ₂ O ₃ It comprises at least one selected thermal expansion control oxide, wherein a) is 50 to 70% by weight, b) + c) is 30 to 50% by weight, the weight ratio of b) and c) is 1: 9-9: Provided is a negative electrode support for a solid oxide fuel cell.

According to the present invention, there is provided a solid oxide fuel cell which is stable in a repetitive atmosphere of high temperature oxidation / reduction while providing high performance electrochemical performance that can be applied at a high temperature.

The electrolyte according to the present invention constitutes one or more layers, providing uniform and fine structure of the reaction layer of the cathode and anode by providing a method that does not contact the atmosphere in the sintering of the anode layer, the electrolyte layer and the anode layer at high temperature. Function to maintain it.

In addition, in the present invention, the oxygen ion in the negative electrode layer (O ^-) and the like conductivity is here as the production of a cell that exhibits high performance in the good ScSZ, used on using SmSZ etc. with Ni, those parts in contact with the cathode layer YSZ In addition, ScSZ, SmSZ, GDC, etc. are used in contact with the anode to provide a stable electrolyte structure under operating conditions and high-performance electrochemical performance at high temperatures.

In addition, in the present invention, the difference in high temperature heat deformation in the oxidizing and reducing atmosphere between the negative electrode support and the electrolyte does not cause thermal stress or interfacial separation between the negative electrode support and the electrolyte, and at the same time when Ni is converted to the oxidation atmosphere, It provides a method that crack does not occur in a cell including a cathode support by NiO volume expansion.

Hereinafter, the present invention will be described in detail through examples. The following examples are intended to illustrate the invention and should not be described to limit the scope of the invention.

Comparative Example 1

The negative electrode support was mixed with NiO at a rate of 55 wt% and YSZ 45 wt%, and 10 wt% of activated carbon was added thereto as a pore regulator to ball mill the ethanol solution for at least 1 day to uniformly mix and take out the ethanol to dry volatilize it.

5 wt% binder, 3 wt% dispersant and the like were added to the homogeneously mixed powder mixture as a molding aid, kneaded for at least 5 hours, aged for 2 days, and then extruded in a flat tube extruder.

The extruded molded product was dried and then burned off the organic material while heating at 3 ° C./min to 1,100 ° C. in a kiln to prepare a negative electrode support. At this time, the porosity was 45%.

Using the prepared negative electrode support, the negative electrode functional layer slurry solution prepared with NiO / YSZ 55:45 wt% solution was dip-coated under normal pressure, dried in air, then placed in a heating furnace, and heated to 3 ° C./min up to 1,200 ° C. Calcined. The thickness of the cathode functional layer after the fabrication of the cell was about 15㎛ and maintained almost the same shape as the cathode support.

The negative electrode support coated with the negative electrode functional layer was put in the YSZ electrolyte slurry solution, and was dip-coated with the electrolyte slurry solution under normal pressure. This was taken out and dried in air to remove the solvent. This was put into a heating furnace in the air state and was performed twice while heating at 3 ° C./min to 1,200 ° C., and the second sintering was performed at 1,400 ° C. After fabrication of the final cell, the thickness of the electrolyte was 27 μm. The average porosity of the support in the oxidized state was 20% and the average porosity was 0.6 μm.

In the state prepared as described above, a cathode slurry prepared by mixing (La, Sr) MnO ₃ and YSZ in a weight ratio of 60:40 was prepared, coated and dried, and again (La, Sr) (Co, Fe) O ₃ The slurry was coated and dried, and then fired by heating to 1,150 ° C. in a heating furnace to prepare an SOFC cell.

Attach the SOFC cell to the fuel cell test device, heat it down to 650 ℃ while flowing hydrogen (H ₂ ), reduce the open circuit voltage (OCV) to 1.0V, and raise it to 800 ℃ The performance was measured.

After the H ₂ supply was stopped (off) and after 5 hours, H ₂ supply was started again and the current voltage characteristics were measured. Then, the temperature was lowered and the crack state was observed in the cell. The results of these runs are shown in Table 1.

Example 1

The negative electrode support was mixed with 24 wt% of YSZ and 5 wt% of thermal expansion control oxide MgAl ₂ O ₄ and 11 wt% of Y ₂ O ₃ based on the total mixture, and a mixed powder containing NiO of about 60 wt% was added thereto. 10 wt% of carbon black was added thereto as a pore controlling agent, and ball milled for at least one day on an ethanol solution to uniformly mix, and the ethanol was dried and volatilized. The average particle size of the YSZ particles used 0.5㎛, MgAl ₂ O ₄ particles, and the mean 2㎛, in MgAl ₂ O ₄ Mg have a ratio of approximately 0.4 to 0.5 compared to Al.

5 wt% binder, 3 wt% dispersant, and the like were added to the homogeneously mixed powder mixture, and then kneaded for 5 hours or more, and aged at room temperature for 2 days, followed by extrusion in a flat tube extruder.

The extruded molded article was dried and then heated to 3,100 / min in a firing furnace to burn off the organic material to prepare a negative electrode support.

NiO / ScSZ was composed of 51:49 wt% to prepare a negative electrode functional layer, and a lower concentration slurry solution was prepared than the comparative example, and the prepared negative electrode support was dip coated on the negative electrode functional layer slurry solution. This was removed, and vacuum was applied to the inside of the support in a separate apparatus at about 50 torr to remove the solvent contained in the support and the solvent present in the outer coated layer. It is put into a heating furnace in the atmospheric state and calcined while heating at 1 ° C./min up to 500 ° C., followed by sintering while raising the temperature to 1,200 ° C. under nitrogen (90 ppm oxygen impurity in N ₂ ) flow and maintaining for 3 hours, followed by 2 ° C. The temperature was lowered to room temperature at / min. The thickness of the cathode functional layer after cell preparation was about 10 μm.

As described above, the electrolyte primary layer was coated using a cathode support coated with a cathode functional layer. It was put in YSZ electrolyte slurry solution of lower concentration than the comparative example and was dip-coated with electrolyte slurry solution under normal pressure. This was removed and vacuum was applied to the inside of the support in a separate apparatus at about 50 torr to remove the solvent contained in the support and the solvent present in the outer coated layer. After drying in the air, the mixture was put into a heating furnace and calcined while heating at 1 ° C./min up to 500 ° C., followed by sintering while raising the temperature to 1,200 ° C. under nitrogen (90 ppm oxygen impurity level in N ₂ ) and maintaining for 3 hours. The temperature was lowered to 2 ° C./min at room temperature.

Electrolytic coating was carried out twice and the second coating was coated using ScSZ solution and the concentration was equal to YSZ. The second electrolyte coating was calcined while heating at 1 ° C./min to 500 ° C., followed by sintering while heating at 1,350 ° C. for 3 hours under a nitrogen (90 ppm level of oxygen impurity in N ₂ ) flow, followed by 2 ° C./min. The temperature was lowered to room temperature. After fabrication of the final cell, the thickness of the electrolyte was 19 μm, and the average porosity of the support in oxidation state was 23% and the average porosity was 1.4 μm.

In the state prepared as described above, a cathode slurry (positive electrode primary) in which (La, Sr) MnO ₃ and YSZ were mixed 50:50 was prepared, coated and dried by a spray method, and again (La, Sr) MnO ₃ (Anode Secondary) was continuously coated by the spray method, dried, and calcined and sintered. The furnace was calcined while heating at 1 ° C./min up to 500 ° C., and then sintered while heating at 1,150 ° C. and maintained for 3 hours under a flow of nitrogen (oxygen impurity in N ₂ at 90 ppm), followed by 2 ° C./min. The temperature was lowered to room temperature.

For the anode layer, the tertiary was coated with a slurry composed of (La, Sr) (Co, Fe) O ₃ , and then dried and calcined. Likewise, the temperature of the furnace is calcined while heating at 1 ° C./min up to 500 ° C., followed by sintering while heating the temperature up to 1,050 ° C. under nitrogen (90 ppm of oxygen impurities in N ₂ ) and maintaining for 3 hours, followed by 2 ° C./min The temperature was lowered to room temperature.

The SOFC cell fabricated as described above was attached to the fuel cell test apparatus, heated to 650 ° C while flowing with hydrogen (H ₂ ), and reduced while the open circuit voltage (OCV) became 1.0 V and then increased to 700 ° C. Current-voltage performance was measured.

After the H ₂ supply was stopped (off) and after 3 hours, the H ₂ supply was started again and the current voltage characteristics were measured. Then, the temperature was lowered and the crack state was observed in the cell. The results of these runs are shown in Table 1.

Example 2

A cell was prepared as in Example 1 and the cell temperature was the same as that in Example 1 except that the temperature was 750 ° C. The results of such an implementation are shown in Table 1.

Example 3

The negative electrode support, the negative electrode functional layer, and the positive electrode were prepared as in Example 1, and the electrolyte primary layer was used as ScSZ instead of YSZ, and both the electrolyte primary and secondary layers consisted of ScSZ, measured at a temperature of 820 ° C. Except that was carried out as in Example 1. The results of these runs are shown in Table 1.

Example 4

Coating the negative electrode functional layer, the electrolyte, and the positive electrode as in Example 1, except that the firing process was all performed in the air. Using this, the cell performance was measured at a temperature of 800 ° C., and these results are shown in Table 1.

Example 5

As in Example 1, the negative electrode support was mixed with YSZ 24wt% and thermal expansion control oxide MgAl ₂ O ₄ at 5wt%, Y ₂ O ₃ 11wt% based on the total mixture, and NiO corresponding to about 60wt% was added thereto. A mixed powder was prepared, but the process was performed as in Example 1, except that argon (oxygen impurity about 10 ppm) was used in the sintering process, and was the same as in Example 1, and the results of the implementation are shown in Table 1.

Example 6

As in Example ₁ , except that 23 wt% of YSZ, 5 wt% of MgAl ₂ O ₄ , 12 wt% of Y ₂ O ₃ , 1 wt% of Co ₃ O ₄ and 59 wt% of NiO were used. The results of these runs are shown in Table 1.

Claims (18)

a) NiO; b) at least one component selected from the group consisting of YSZ, ScSZ, SmSZ, GDC; And c) forming an electrolyte layer and an anode layer on a fuel cell support including a thermal expansion control oxide, and optionally on a cathode support having a cathode layer formed on the surface thereof, and sintering under a sparse stream of oxygen of 900 ° C. or higher. Cell production method for an oxide fuel cell. The method of claim 1,
Oxygen-lean streams are characterized by supplying nitrogen (N ₂ ), argon (Ar), helium (He), carbon dioxide (CO ₂ ), water vapor (H ₂ O) or one or more combinations thereof. Cell manufacturing method for an oxide fuel cell. The method of claim 1,
The oxygen-lean stream of air is a solid oxide fuel cell manufacturing method, characterized in that the vacuum state of less than 0.01 torr. The method according to claim 1 or 2,
Oxygen (O ₂ ) concentration is 5.0 vol% or less cell manufacturing method for a solid oxide fuel cell. The method according to claim 1 or 2,
A method for manufacturing a cell for a solid oxide fuel cell, wherein the hydrogen (H ₂ ), carbon monoxide (CO), or hydrocarbons (hydrocarbons) are 5.0 vol% or less during sintering. The method of claim 1, wherein the sintering temperature is performed at 900 ° C. or higher and 1,600 ° C. or lower, and the sintering of the electrolyte is nitrogen (N ₂ ), argon (Ar), helium (He), A method of manufacturing a cell for a solid oxide fuel cell, characterized in that the water vapor (H ₂ O), carbon dioxide (CO ₂ ) or a mixture thereof or proceeds under an oxygen lean airflow under a vacuum. According to claim 1 or 2, wherein the electrolyte layer is subjected to a dip coating the negative electrode support coated with the negative electrode layer in the electrolyte slurry solution, and to take out the vacuum from the outside to the inside of the negative electrode support, the negative electrode support and the negative electrode function A layer and a method for manufacturing a cell for a solid oxide fuel cell, characterized in that dry firing after removing the solvent remaining in the electrolyte coating layer. The method of claim 1 or 2, wherein the electrolyte layer is formed of a multilayer including YSZ, ScSZ, SmSZ, GDC, or one or more thereof. The method for manufacturing a cell for a solid oxide fuel cell according to claim 8, wherein the electrolyte layer in contact with the cathode layer is made of YSZ or a composite of GDC, ScSZ, SmSZ. an anode support comprising a) NiO, b) at least one component selected from the group consisting of YSZ, ScSZ, SmSZ, GDC, and c) thermal expansion controlling oxides;
A cathode layer selectively formed on the cathode support;
An electrolyte layer formed on the negative electrode support or the negative electrode layer; And
Anode layer formed on the electrolyte layer
, ≪ / RTI >
The thermal expansion control oxide is a solid oxide fuel cell, it characterized in that the thermal expansion coefficient of 7.0x10 ^-6 /℃?10.0x10 ^-6 / ℃. The method of claim 10,
The thermal oxide is adjusted _{AB 2 O 4 (A / B} = 0.3-0.6) CaAl composite oxide in the form _{2 O 4, MgAl 2 O 4} , NiAl 2 O 4, CuAl 2 O 4, FeAl 2 O 4 and Y ₂ Solid oxide fuel cell, characterized in that at least one selected from the group consisting of O ₃ , Yb ₂ O ₃ , Al ₂ O ₃ . The method of claim 11,
The thermal expansion control oxide is a solid oxide fuel cell, characterized in that the average particle size of 0.3㎛ ~ 10㎛. The method of claim 11,
The cathode layer is made of NiO / YSZ, NiO / ScSZ, NiO / SmSZ or NiO / GDC or a mixture thereof, the NiO content is 45 ~ 53 wt%, the thickness of the cathode layer in the cell is 1 ~ 30㎛, Or 3 to 25 µm. The method of claim 11,
The negative electrode support is made of 50-70wt% NiO, YSZ, ScSZ, SmSZ, GDC and at least one component selected from the group consisting of 30-50 wt% of thermal expansion control oxide,
At least one component selected from the group consisting of YSZ, ScSZ, SmSZ, GDC and the thermal expansion control oxide is a solid oxide fuel cell, characterized in that the weight ratio of 1: 9-9: 1. The method according to any one of claims 10-14,
At least one of the negative electrode support, the negative electrode layer, the electrolyte layer, and the positive electrode layer is a solid oxide fuel cell, characterized in that the sintered layer sintered under a stream of oxygen lean 900 ℃ or more. a) at least one component selected from the group consisting of NiO, Co ₂ O ₃ , CuO;
b) at least one component selected from the group consisting of YSZ, ScSZ, SmSZ, GDC; And
c) 1 or 2 species from the group consisting of CaAl ₂ O ₄ , MgAl ₂ O ₄ , NiAl ₂ O ₄ , CuAl ₂ O ₄ , FeAl ₂ O ₄ , Y ₂ O ₃ , Yb ₂ O ₃ , Al ₂ O ₃ It is made of the above selected thermal expansion control oxide,
Here, a) 50 to 70% by weight, b) + c) 30 to 50% by weight, the weight ratio of b) and c) is 1: 9-9: 1
Cathode support for solid oxide fuel cell. 17. The method of claim 16,
The anode support is a cathode support for a solid oxide fuel cell further comprising a Perovskite oxide. 18. The method according to claim 16 or 17,
The cathode support is a solid oxide fuel cell, characterized in that the thermal expansion rate is less than the electrolyte layer in the oxidation state, and larger than the electrolyte layer in the reduced state.