KR20130052286A - Fabrication and structure of low- and intermediate-temperature-operating solid oxide fuel cell by spin coating and low-temperature sintering - Google Patents

Abstract

PURPOSE: A solid oxide fuel cell structure is provided to make a starting material or a high cost device unnecessary, to restrain defects on a tensile strength and interface reaction between an electrode and an electrolyte. CONSTITUTION: A solid oxide fuel cell comprises a fuel electrode support, a YSZ thin film electrolyte layer formed on the fuel electrode support, a GDC diffusion barrier layer formed on the YSZ thin film electrolyte; a GDC/LSCF composite layer formed on the GDC diffusion barrier layer, and an LSCF air electrode formed on the GDC/LSCF composite layer. AT least one of the YSZ thin film electrolyte layer, GDC diffusion barrier layer, GDC/LSCF compsite layer, and LSCF air electrode is formed by a spin process.

Description

Fabrication and structure of low- and intermediate-temperature-operating solid oxide fuel cell by spin coating and low-temperature sintering

The present invention relates to a structure and a manufacturing method of a solid oxide fuel cell (SOFC) operating in a medium-low temperature region using the formation of components by a solution coating-based spin coating process and its low temperature sintering.

SOFCs require the use of expensive separator materials due to the high operating temperatures of 750 ° C and above, and the range of sealing material selection is very limited. Therefore, this high operating temperature is a direct cause of threat to the durability of the SOFC and lowering the economic efficiency. In order to improve the durability and economic efficiency of SOFC, it is important to develop a medium temperature solid oxide fuel cell that operates in the range of 600-700 ℃ where the separator material is made of stainless steel and the sealing material can be applied to various materials other than glass. .

However, if the operating temperature is lowered, the resistance of the existing yttria-stabilized zirconia (YSZ) electrolyte, as well as the resistance of the lanthanum strontium manganite (LSM) -based air electrode, which has been generally used, increases the resistance, resulting in a rapid increase in resistance. Performance degradation is inevitable.

First, in terms of electrolytes, one way to address this degradation is to apply an alternative electrolyte with better ion conductivity than YSZ in the mid-temperature range, such as gadolinia-doped ceria (GDC). In order to reduce the resistance, the thickness of the existing YSZ electrolyte layer is reduced.

However, GDC applied as an alternative electrolyte has electronic conductivity at the low oxygen partial pressure, so when exposed to the reducing atmosphere of the anode, leakage current occurs and the open circuit voltage (OCV) of the cell is lowered. Performance is degraded. Other lanthanum gallate systems, such as (La, Sr) (Ga, Mg) O _{3 -x} (LSGM) electrolytes, are poor in high temperature structural stability and have very narrow tolerances in chemical compatibility with anode and cathode materials. As a result, it is expected that a very limited application as an electrolyte of a solid oxide fuel cell will be possible. Therefore, it is preferred to reduce the thickness of the YSZ electrolyte, which has already been found to be capable of large area of the unit cell, since YSZ is the most excellent structural and chemical stability material at the manufacturing process temperature and operating temperature. .

Various methods have been tried to reduce the thickness of the YSZ electrolyte, and some of the vacuum vapor deposition methods have secured the airtightness of the electrolyte.However, when more economical slurry or solution processes are applied, the airtightness of the YSZ electrolyte layer is lowered below a certain range. It decreases and eventually decreases the OCV of the unit cell. In order to overcome this problem, when the electrolyte thickness is increased, it is necessary to reach almost the same thickness as the thick film electrolyte layer by the conventional screen printing method to ensure airtightness, and thus the purpose of obtaining a decrease in resistance by reducing the electrolyte thickness is achieved. Cannot be achieved.

On the cathode side, the cathode material is also a high-performance material containing cobalt in the conventional LSM, La _{1 - x} Sr _x CoO _{3- d} (LSC), La _{1 - x} to prevent the increase in polarization resistance of the cathode due to the decrease in operating temperature. _{Sr x Co 1 - y Fe y} O 3 -d (LSCF), Sm 1 - and applying a mixed conducting oxide, such as _{x Sr x Co 1 O 3 -d} (SSC). Among them, the LSCF air electrode which has confirmed chemical stability at relatively high temperature is reported to be most suitable as a medium temperature type. However, when the LSCF cathode is formed in the YSZ electrolyte, the interfacial reaction occurs during the manufacturing process to form an insulating oxide such as SrZrO ₃ or La ₂ ZrO ₇ , thereby significantly increasing the interfacial resistance, thereby significantly reducing the performance of the unit cell.

The method of inserting the GDC diffusion barrier layer between the YSZ electrolyte layer and the LSCF cathode layer is mainly used to suppress the interfacial reaction in the formation of the cathode, but the GDC is already on top of the YSZ electrolyte layer without further plastic shrinkage through half cell firing. Forming a diffusion barrier layer economically without defects has emerged as an important technical challenge. Of course, it is possible to form a relatively ideal GDC diffusion barrier layer by the vacuum deposition method, but it requires a lot of expensive equipment construction, which leaves many questions about whether the large area of the unit cell is possible. Currently, GDC diffusion barrier layer using general screen printing method has problems of process defect and high residual porosity due to limited sintering by half-cell substrate formed by sintering up to YSZ electrolyte layer. It must be increased considerably, which is another cause of increase in internal resistance.

In particular, since the GDC diffusion barrier layer forming process using the conventional screen printing method requires a very high firing temperature of about 1300 ° C., the problem of increasing the interfacial resistance due to the formation of a solid solution with YSZ having the same crystal structure is highlighted. In order to secure the airtightness of the GDC diffusion barrier layer and to suppress the formation of a solid solution with YSZ, it is necessary to lower the formation temperature of the GDC diffusion barrier layer to 1200 ° C. or less, which can satisfy the required microstructure even in the confined state of the half-cell substrate.

Accordingly, an object of the present invention is to form a thin-film YSZ electrolyte having airtightness on the anode support through a spin process using a solution process method that does not require expensive equipment or starting materials, and the GDC diffusion barrier layer is 1200 ° C or less. It is to provide a low-temperature manufacturing process of a solid oxide fuel cell to form without defects at low temperatures, and to form an LSCF cathode at a temperature lower than the formation temperature of GDC thereon.

The object of the present invention as described above, in the YSZ electrolyte to reduce the grain size by low temperature sintering of the electrolyte in order to ensure the structural stability of the electrolyte to prepare an electrolyte having a thickness larger than the anode grain size, but proceeds under the constraint of the substrate In order to suppress structural defects occurring during the limited sintering process of the electrolyte, YSZ dispersion particles having internal binding force may be added to the YSZ solution to suppress the absolute influence of the substrate binding force.

The GDC diffusion barrier layer also uses a GDC solution in which GDC nanopowder particles are dispersed to form a local internal stress field that can cope with the absolute binding force of the substrate, thereby obtaining densification and suppressing the anisotropy of the microstructure. It is possible to prevent the formation of the anisotropic pores that have the greatest influence on the. In addition, by firing at a temperature lower than the firing temperature of the YSZ layer it is possible to fundamentally suppress the grain growth of the YSZ layer and minimize the grain size of the GDC.

Since the air cathode should not generate additional grain growth of YSZ and GDC during the formation process, it should be formed at a temperature lower than the formation temperature of GDC, but should have sufficient interfacial bonding force. Therefore, the LSCF / GDC intermediate layer is formed and low temperature sintering is performed by applying a solution process. Can be achieved.

Specifically, according to an aspect of the present invention, an anode support, an YSZ thin film electrolyte layer formed on the anode support, a GDC diffusion barrier layer formed on the YSZ thin film electrolyte, a GDC / LSCF composite layer formed on the GDC diffusion barrier layer, And an LSCF cathode formed on the GDC / LSCF composite layer. At least one of the YSZ thin film electrolyte layer, the GDC diffusion barrier layer, the GDC / LSCF composite layer, and the LSCF cathode is formed by a spin process; The maximum size of the YSZ crystal grains contained in the YSZ thin film electrolyte layer is smaller than the thickness of the YSZ thin film electrolyte layer, and the maximum size of the GDC crystal grains contained in the GDC diffusion barrier layer is smaller than the thickness of the GDC diffusion barrier layer. ; Disclosed is a solid oxide fuel cell, wherein the maximum reduction pore diameter of the anode support is smaller than the sum of the thicknesses of the YSZ thin film electrolyte layer and the GDC diffusion barrier layer.

According to another aspect of the invention, (a) forming a YSZ thin film electrolyte layer on the anode support, (b) forming a GDC diffusion barrier layer on the YSZ thin film electrolyte, (c) the GDC diffusion barrier layer A method of manufacturing a solid oxide fuel cell, comprising the steps of: forming a GDC / LSCF composite layer on (d) forming an LSCF cathode on the GDC / LSCF composite layer; Step (a) is performed by spin coating and sintering a solution containing yttrium salt, zirconium salt and YSZ nanopowder; Step (b) is carried out by spin coating and sintering a solution comprising gadolinium salt, cerium salt, and GDC nanopowder; Disclosed is a method for manufacturing a solid oxide fuel cell, wherein the average sintering temperature of the GDC diffusion barrier layer is lower than the average sintering temperature of the YSZ thin film electrolyte layer.

According to the present invention, an economical solution process is used for the thin film YSZ electrolyte which does not permeate the reaction gas, the GDC diffusion barrier layer having a dense structure capable of suppressing the reaction between the YSZ electrolyte and the LSCF cathode, and sufficient interfacial bonding force with the GDC. With the present invention, a method of forming LSCF, which does not inhibit the structural stability of YSZ and GDC, has been provided, thereby providing a solid oxide fuel cell expressing high performance in the mid-low temperature region.

In the present invention, the low-temperature process does not require expensive equipment or starting materials, is not restricted by the shape and size of the substrate, and can suppress defects caused by the tensile stress of the substrate and the interfacial reaction between the electrode and the electrolyte. Since the solid oxide fuel cell with enhanced interfacial strength can be manufactured, it is expected to contribute greatly to the yield improvement, large area, and practical use of SOFC.

1 is a schematic diagram of a defect that a thin film formed by a solution process under the limited sintering effect of a substrate without a local internal stress field.
2 is a schematic diagram of the principle that the defect is suppressed in the thin film formed by the solution process when the local internal stress field is formed by the dispersed particles.
3 is a scanning electron micrograph of the surface (FIG. 3A) and the cross section (FIG. 3B) of the YSZ electrolyte thin film prepared in Step 1 of Example 1 of the present invention.
4 is a scanning electron micrograph of the surface (FIG. 4A) and the cross section (FIG. 4B) of the GDC diffusion barrier layer prepared in Step 2 of Example 1 of the present invention.
5 is a scanning electron micrograph of the LSCF powder prepared in Step 4 of Example 1 of the present invention.
6 is an X-ray diffraction analysis result of the LSCF powder prepared in Step 4 of Example 1 of the present invention.
7 is a scanning micrograph of the air electrode formed of the LSCF powder dispersed LSCF solution prepared in step 4 of Example 1 of the present invention, Figure 7a is a low magnification photograph of the surface, Figure 7b is a high magnification photograph of the surface, Figure 7c is Photo of the cross section.
8 is a graph illustrating voltage-current-power measurements of a unit cell obtained by driving a solution process-based SOFC unit cell prepared in Example 1 of the present invention at 650-500 ° C.
FIG. 9 illustrates voltage-current-power measurements obtained by driving a single cell at 650 ° C. with or without an SSC impregnated into an LSCF cathode in a solution process-based SOFC unit prepared in Example 2 of the present invention. It is a graph.

According to an aspect of the present invention, an anode support, an YSZ thin film electrolyte layer formed on the anode support, a GDC diffusion barrier layer formed on the YSZ thin film electrolyte, a GDC / LSCF composite layer formed on the GDC diffusion barrier layer, and the A solid oxide fuel cell comprising an LSCF cathode formed on a GDC / LSCF composite layer; At least one of the YSZ thin film electrolyte layer, the GDC diffusion barrier layer, the GDC / LSCF composite layer, and the LSCF cathode is provided by a solid oxide fuel cell formed by a spin process of spin coating and sintering a precursor solution on a lower layer thereof. do.

Here, for the normal operation of the solid oxide fuel cell, the maximum size of the YSZ crystal grains contained in the YSZ thin film electrolyte layer is smaller than the thickness of the YSZ thin film electrolyte layer, and the maximum size of the GDC crystal grains contained in the GDC diffusion barrier layer. Should be less than the thickness of the GDC diffusion barrier layer. That is, the maximum size of the YSZ crystal grains contained in the YSZ thin film electrolyte layer needs to meet all the conditions of the spin process so as to be smaller than the thickness of the YSZ thin film electrolyte layer as mentioned above, and likewise inside the GDC diffusion barrier layer It is necessary to meet all the conditions of the spin process so that the maximum size of the GDC grains included is also smaller than the thickness of the GDC diffusion barrier layer as mentioned above.

In addition, a spin process may be performed by adjusting process conditions such that the maximum reduction pore diameter of the anode support is smaller than the sum of the thicknesses of the YSZ thin film electrolyte layer and the GDC diffusion barrier layer, wherein the reduction pore diameter of the anode support is typically Corresponding to the grain size of the anode functional layer, it is clear that a person skilled in the art can easily measure or determine the numerical value based on the disclosure of the present invention and common knowledge in the art.

Particularly, the thickness of the YSZ thin film electrolyte layer is 100 nm or more, and the thickness of the GDC diffusion barrier layer is preferably 100 nm or more. In this case, the maximum size of the YSZ grains and the GDC crystal grains is smaller than the thickness of each layer. The spin process should be performed by adjusting the process conditions. In this case, when the thickness of the YSZ thin film electrolyte layer is less than 100 nm and the thickness of the GDC diffusion barrier layer is less than 100 nm, anisotropic microstructural defects occur rapidly in the YSZ thin film electrolyte layer and the GDC diffusion barrier layer, respectively. It has been confirmed that the airtightness may collapse.

In addition, the sum of the thicknesses of the YSZ thin film electrolyte layer and the GDC diffusion barrier layer is preferably 500-1000 nm, and NiO reduction when the sum of the thicknesses of the YSZ thin film electrolyte layer and the GDC diffusion barrier layer is less than 500 nm. It is confirmed that the structural stability of each layer is rapidly collapsed due to the stress field caused by the formation of pores and the shrinkage of the anode, and when the thickness exceeds 1000 nm, the battery operation performance can be drastically decreased in the mid-temperature region by decreasing the resistance. .

In addition, the YSZ grain size contained in the YSZ thin film electrolyte layer is 10-95 nm, the GDC grain size contained in the GDC diffusion barrier layer is preferably 10-95 nm, the inside of the YSZ thin film electrolyte layer When the YSZ grain size contained in the GSS diffusion barrier layer exceeds 95 nm or the GDC grain size contained in the GDC diffusion barrier layer exceeds 95 nm, the anisotropic microstructural defects in the YSZ thin film electrolyte layer and the GDC diffusion barrier layer are respectively This occurred and confirmed that the interlayer airtightness could collapse.

According to another embodiment, the YSZ thin film electrolyte layer is formed by spin coating and sintering a solution containing yttrium salt, zirconium salt, and YSZ nanopowder; The GDC diffusion barrier layer is formed by spin coating and sintering a solution containing a gadolinium salt, a cerium salt, and a GDC nanopowder; The average sintering temperature of the GDC diffusion barrier layer is preferably lower than the average sintering temperature of the YSZ thin film electrolyte layer.

According to one embodiment, the GDC / LSCF composite layer comprises (i) a lanthanum salt, strontium salt, cobalt salt, iron salt, a first composite layer solution comprising GDC nanopowder or (ii) gadolinium salt, cerium salt, LSCF Provided is a solid oxide fuel cell formed by spin coating and sintering a second composite layer solution containing nanopowders. Through this, the internal stress field was formed, and the driving force was secured enough to form a sufficient solid-phase crosslinking at low temperature by the solution and the nanopowder.

According to another embodiment, the LSCF cathode is formed by spin coating and sintering a solution comprising a lanthanum salt, strontium salt, cobalt salt, iron salt, and LSCF nanopowder; The average sintering temperature of the LSCF cathode is preferably lower than the average sintering temperature of the GDC diffusion barrier layer.

According to another embodiment, the YSZ thin film electrolyte layer is formed by spin coating and sintering a solution containing yttrium salt, zirconium salt, and YSZ nanopowder; The GDC diffusion barrier layer is formed by spin coating and sintering a solution containing a gadolinium salt, a cerium salt, and a GDC nanopowder; The LSCF cathode is formed by spin coating and sintering a solution containing a lanthanum salt, a strontium salt, a cobalt salt, an iron salt, and an LSCF nanopowder; When the sintering treatment of the YSZ thin film electrolyte layer is performed by raising the temperature to the first YSZ sintering temperature and then lowering the temperature to the second YSZ sintering temperature; The sintering treatment of the GDC diffusion barrier layer is performed by raising the temperature to the first GDC sintering temperature and then lowering the temperature to the second GDC sintering temperature; The first GDC sintering temperature is lower than the first YSZ sintering temperature; The average sintering temperature of the LSCF cathode is lower than the first GDC sintering temperature is provided a solid oxide fuel cell.

According to one embodiment, the first YSZ sintering temperature and the second YSZ sintering temperature are in the range of 1050-1150 ° C. and 950-1050 ° C., respectively; The first and second GDC sintering temperatures are in the range of 1000-1100 ° C. and 950-1050 ° C., respectively; The sintering temperature of the LSCF cathode is provided in the solid oxide fuel cell, characterized in that in the range of 900-1000 ℃.

According to another embodiment, the LSCF cathode comprises a solution penetrating layer thereon; The solution permeation layer comprises (i) a solution comprising a lanthanum salt, a strontium salt, a cobalt salt, (ii) a solution comprising a samarium salt, a strontium salt, a cobalt salt, and (iii) a mixed solution thereof. Formed by spin coating and sintering the LSCF cathode; The sintering treatment is provided a solid oxide fuel cell, characterized in that performed at less than 900 ℃. It may include an LSC or SSC solution penetrating layer formed by spin coating and sintering the LSC or SSC solution on the LSCF cathode, whereby the low-temperature operating performance of the fuel cell is greatly improved, but the sintering temperature is 900 ℃ or more. It was confirmed that the grain growth in the LSCF air electrode or the lower layer thereof rapidly reduced the interlayer airtightness.

In the solid oxide fuel cell according to various embodiments of the present invention, the YSZ nanopowder, the GDC nanopowder, and the LSCF nanopowder have particle sizes of 10-30 nm, 10-20 nm, and 50-, respectively, according to BET measurement results. 100 nm; The surface areas according to the results of the BET measurement are 140-180 m ² / g, 80-120 m ² / g and 10-30 m ² / g, respectively; Based on the final volume of each layer is provided a solid oxide fuel cell, characterized in that the volume of the nanopowder is 2-8% by volume, 2-8% by volume, 92-98% by volume, respectively. Here, the volume content of the nanopowder refers to the volume content of the nanopowder based on the total volume of the solid powder remaining after the heat treatment in the salt solution, that is, in the case of YSZ and GDC, 2-8 volumes of the solid phase volume of the final membrane. The% is derived from the nanopowder and the remaining 92-98% by volume is derived from the salt solution, while for LSCF, 92-98% by volume of the solid phase volume of the final membrane is derived from the nanopowder and the remaining 2-8% by volume is the salt solution. It means that comes from.

According to another aspect of the invention, (a) forming a YSZ thin film electrolyte layer on the anode support, (b) forming a GDC diffusion barrier layer on the YSZ thin film electrolyte, (c) the GDC diffusion barrier layer A method of manufacturing a solid oxide fuel cell, comprising the steps of: forming a GDC / LSCF composite layer on (d) forming an LSCF cathode on the GDC / LSCF composite layer; Step (a) is performed by spin coating and sintering a solution containing yttrium salt, zirconium salt and YSZ nanopowder; Step (b) is carried out by spin coating and sintering a solution comprising gadolinium salt, cerium salt, and GDC nanopowder; The average sintering temperature of the GDC diffusion barrier layer is lower than the average sintering temperature of the YSZ thin film electrolyte layer is provided a method for producing a solid oxide fuel cell.

According to one embodiment, the YSZ thin film electrolyte layer and the GDC diffusion barrier layer is a thickness of the YSZ thin film electrolyte layer is 100 nm or more and the thickness of the GDC diffusion barrier layer is 100 nm or more and the YSZ thin film electrolyte layer and the GDC The sum of the thicknesses of the diffusion barrier layers is formed to be 500-1000 nm; It is preferable that the YSZ grain size included in the YSZ thin film electrolyte layer is 10-95 nm, and the GDC grain size contained in the GDC diffusion barrier layer is 10-95 nm.

According to another embodiment, step (c) comprises (i) a lanthanum salt, strontium salt, cobalt salt, iron salt, a first composite layer solution comprising GDC nanopowder and (ii) gadolinium salt, cerium salt, LSCF nano Provided is a method for manufacturing a solid oxide fuel cell, which is performed by spin coating and sintering a composite layer solution selected from a second composite layer solution including powder on the LSCF cathode.

According to another embodiment, the step (d) is carried out by spin coating and sintering a solution comprising a lanthanum salt, strontium salt, cobalt salt, iron salt, LSCF nanopowder; The average sintering temperature of the LSCF cathode is lower than the average sintering temperature of the GDC diffusion barrier layer is provided a solid oxide fuel cell manufacturing method.

According to one embodiment, the sintering of the YSZ thin film electrolyte layer in the step (a) is carried out by raising the temperature to the first YSZ sintering temperature and then lowering the temperature to the second YSZ sintering temperature; In step (b), the sintering treatment of the GDC diffusion barrier layer is performed by raising the temperature to the first GDC sintering temperature and then lowering the temperature to the second GDC sintering temperature; The first GDC sintering temperature is lower than the first YSZ sintering temperature; The average sintering temperature of the LSCF cathode is lower than the first GDC sintering temperature is provided.

According to another embodiment, the first YSZ sintering temperature and the second YSZ sintering temperature are in the range of 1050-1150 ° C. and 950-1050 ° C., respectively; The first and second GDC sintering temperatures are in the range of 1000-1100 ° C. and 950-1050 ° C., respectively; The sintering temperature of the LSCF cathode is provided in the solid oxide fuel cell manufacturing method, characterized in that in the range of 900-1000 ℃.

According to another embodiment, the solid oxide fuel cell manufacturing method further comprises the step of (e) forming a solution penetration layer on top of the LSCF cathode; Step (e) comprises the steps of (i) a solution comprising a lanthanum salt, a strontium salt, a cobalt salt, (ii) a solution comprising a samarium salt, a strontium salt, a cobalt salt, and (iii) a mixed solution thereof. By spin coating and sintering the LSCF air electrode; The sintering treatment is provided a solid oxide fuel cell manufacturing method characterized in that performed at less than 900 ℃.

In the method of manufacturing a solid oxide fuel cell according to various embodiments of the present invention, the YSZ nanopowder, the GDC nanopowder, and the LSCF nanopowder have a particle size of 10-30 nm, 10-20 nm, respectively, according to a BET measurement result. 50-100 nm; The surface areas according to the results of the BET measurement are 140-180 m ² / g, 80-120 m ² / g and 10-30 m ² / g, respectively; The volume content of the nanopowder is preferably 2-8% by volume, 2-8% by volume, and 92-98% by volume based on the final volume of each layer.

In the following, more specific description will be given with respect to the present invention. First, in order to apply a thin YSZ electrolyte to a medium temperature solid oxide fuel cell, two structural stability criteria must be satisfied.

First, for structural stability in the manufacturing process, the thickness of the electrolyte layer should always be larger than the grain size of the electrolyte. The grain size is a primary function of the firing temperature that dominates grain growth, and as the firing temperature increases for the same material, the grain size increases, so that the thickness of the electrolyte that secures the structural stability also increases. Therefore, it can be said that it is ideal to lower the firing temperature in order to satisfy the primary structural stability criteria. In other words, if the grain size is reduced by suppressing the grain growth of the electrolyte through low temperature sintering, the thickness of the electrolyte can be reduced accordingly. In this aspect, it is very advantageous to prepare the electrolyte layer by a solution process method that can significantly reduce the firing temperature compared to the conventional powder process.

When a solid oxide fuel cell is introduced into the operating environment with primary stability criteria that depend on the correlation between electrolyte thickness and grain size, the nickel oxide in the anode (usually a NiO-YSZ composite) is reduced to metallic nickel, forming pores. . Subsequently, the metal nickel is redistributed through sintering and grain growth, and the electrolyte layer existing on the nickel oxide grains is exposed to the pores. The electrolyte layer exposed to the pores by the formation of the reducing pores is in a state of being mechanically supported by the YSZ grains in the fuel electrode present around the pores. Since the sintering and grain growth of the metal nickel cause the volume shrinkage of the anode, the YSZ electrolyte layer is in a compressive stress state to the electrolyte surface, and the YSZ electrolyte layer exposed to the pores causes buckling to be convex upward under the compressive stress. do. At this time, since the interface between the YSZ electrolyte layer and the anode at the pore edge is in the tensile stress state up and down, mechanical damage may occur if the bonding force between the YSZ electrolyte and the YSZ grains of the anode is not sufficient, and may develop into a peeling defect. The second stability criterion to prevent such defects is that the thickness of the electrolyte should be larger than the size of the anode pores generated by the reduction.

As a result, reducing the grain size by the low temperature sintering of the electrolyte and preparing an electrolyte having a thickness larger than the pore size of the anode is the most effective method to secure and maintain the structural stability of the electrolyte in the manufacturing process and the operation process. However, as in the case of using the solution process method, it is very difficult to prepare the electrolyte layer, which is completed through the firing process, under the constraint of the substrate having the structure already completed. Since the already sintered substrate does not undergo any shrinkage during the firing process of the electrolyte layer, the electrolyte layer whose volume and shape are changed by the plastic shrinkage is under a tensile stress field due to the restraining force of the substrate. The brittle oxide layer has extremely limited plastic shrinkage in the direction parallel to the substrate surface under this tensile stress field, and only plastic shrinkage in the vertical direction is allowed. Thus, as in most thin films fired under substrate restraint, pores and grains tend to selectively develop in a direction perpendicular to the substrate. This process is shown schematically in FIG. 1. Since the electrolyte of the solid oxide fuel cell should play a role of preventing the mixing of the fuel gas of the anode and the air of the cathode, the pores vertically developed on the substrate inhibit the airtightness that can suppress gas mixing between the anode and the cathode. Becomes

As a result, suppressing structural defects occurring during the limited sintering process of the electrolyte that proceeds under the restraint force of the substrate is the most important factor in forming an airtight electrolyte layer. The core of the substrate restraint is the tensile stress field applied to the electrolyte layer in a direction parallel to the surface of the substrate, and the direction of the stress field determines the orientation of the sintered microstructure. Therefore, in order to suppress the influence of the tensile stress field formed in the electrolyte layer, it is necessary to change the stress distribution in the electrolyte layer. To this end, it is necessary to restrain the development of the microstructure in a selective direction by imparting an isotropic restraining force internally to suppress the substrate restraining force which has an absolute influence on the densification of the electrolyte layer and the development of the microstructure.

In the formation of the internal stress field, when the powder particles having low or no sinterability are dispersed between the constituent powder particles constituting the electrolyte layer, internal stress may be generated due to the difference in the sinterability of matrix particles in the matrix phase and the dispersed phase. This principle is shown in FIG. In general, since the magnitude of the internal stress is governed by the size and content of the dispersed particles, the size and content of the dispersed particles that can form a local internal stress field to suppress the absolute influence of the substrate binding force is required.

In particular, in the solution process, the formation of a local internal stress field that can suppress such substrate restraint plays a very important role. Precursor powder is formed after removing the organic material in the heat treatment process of the thin film formed by the solution process is very fine particles, the sintering driving force is very large, but because the organic content is very large, the volume shrinkage during the heat treatment process is large. The large volume shrinkage means that the filling density of the precursor powder is low, which means that the nonuniformity of the filling structure is likely to increase when non-uniform stress is applied. In addition, the high sintering driving force means that sintering shrinkage occurs in a narrow temperature range in a short time, so that the fine defects easily grow in the non-uniform packing structure, which means that there is a high possibility of growing into a critical size defect. Therefore, in order to produce an electrolyte membrane in a state without a critical defect through a solution process, it is necessary to add the dispersing particles having an internal restraining force as described above to suppress the absolute effect of the precursor powder on the substrate restraining force. The dispersed phase particles dispersed in the precursor powder are generally the same composition but must be larger than the ultrafine particles formed from the precursor to form an internal stress field. Considering that the size of the precursor powder synthesized in the solution process is in the range of several nanometers, the size of the dispersed particles may be small enough to form a small local stress field, even if only a few tens of nanometers, to suppress the anisotropic development of the microstructure, and to pursue the overall isotropy. You can switch. Actually, the size of the isotropic stress field caused by the dispersed particles is very small compared to the tensile stress field caused by the substrate restraint, but if the content is increased, the sum of the locally formed stress field suppresses the development of the anisotropic microstructure due to the absolute influence of the stress field caused by the substrate confinement. Done.

Indeed, the local stress field caused by the dispersed particles reduces the densification rate as a whole, but the effect greatly decreases the densification rate in the vertical direction of the substrate, whereas the densification rate of the state which is almost absent in the parallel direction of the substrate is meaningful. The effect is to increase to the level. In addition, considering that the precursor powder is formed while the organic material is removed at a temperature of 400 ° C. or lower, the local stress field caused by the dispersed phase particles suppresses the precursor powder particles from having an anisotropic filling structure while rearranging by the restraint force of the substrate. It serves to make the filling structure of the precursor powder particles uniform. In other words, since the removal of organic material at a low temperature is accompanied by a volume change, the stress field due to substrate confinement dominates the rearrangement of the precursor powder particles, and the rearrangement of the precursor powder particles also has anisotropy because of the anisotropy of the stress field. However, the isotropic internal stress field caused by the dispersed phase particles transforms the anisotropic stress field caused by the substrate into a stress field that tends to be fairly isotropic, whereby precursor particle rearrangements occur evenly throughout the electrolyte membrane and eventually fill the precursor powder particles. It is to make the structure even. As a result, it is possible to promote uniformity of the microstructure of the electrolyte thin film by dispersing dispersed phase particles having low sinterability, thereby suppressing anisotropic process defects caused by anisotropic sintering.

Once the solution process is applied using the nanopowder dispersion solution in the YSZ electrolyte formation step, it is possible to suppress the formation of anisotropic pores that threaten the airtightness, which is a basic characteristic of the electrolyte. When the anisotropic pores are suppressed, controlling the grain size becomes a variable that determines the thickness of the electrolyte membrane. After all, lowering the sintering temperature can minimize the thickness of the electrolyte membrane by reducing the grain size. Since the calcination temperature of the optimized YSZ electrolyte membrane is 1000-1100 ℃ and the grain size is about 10-95 nm, the thickness of the electrolyte membrane should be at least 100 nm. In the process conditions that can completely suppress the anisotropic microstructural defects, since only the grain size is a parameter that determines the minimum electrolyte membrane thickness, it is necessary to adjust the heat treatment temperature at which no further grain growth occurs in the subsequent process.

Although the electrolyte layer having a thickness larger than the grain size is formed, it is confirmed that when the unit cell is put into operation and reduction of the anode occurs, the electrolyte layer is affected by the pore size generated by the reduction of NiO and the stress field due to the shrinkage of the anode. Since the size of the reducing pores is almost the same as the grain size of the anode sintered body, it was confirmed that the thickness of the electrolyte layer should be 500 nm or more because the grain size of the anode functional layer was less than 500 nm. In fact, it was confirmed that when the thickness of the YSZ electrolyte layer was formed in the range of about 500-1000 nm, the excellent electrolyte hermeticity was obtained with an open circuit voltage of 1.1 V or more.

Once the formation of the gas-tight YSZ electrolyte layer to prevent the mixing of the gas is completed, it is necessary to form a GDC diffusion barrier layer to prevent chemical reaction with the LSCF cathode. The first GDC barrier layer also requires a close enough condition to prevent the diffusion of cations in the cathode material during the cathode formation process. As with the YSZ electrolyte layer, the binding force of the substrate acts as a factor that delays the sintering of the GDC layer, and the development of the anisotropic microstructure is the biggest factor of the airtightness inhibition. Thus, the GDC layer, like the YSZ layer, uses the GDC solution in which the GDC nanopowder particles are dispersed to form a local internal stress field that can cope with the absolute binding force of the substrate, thereby suppressing densification and anisotropy of the microstructure, thereby having the greatest influence on the airtightness. The impact can prevent the formation of anisotropic pores. In addition, by firing at a temperature lower than the firing temperature of the YSZ layer it is possible to fundamentally suppress the grain growth of the YSZ layer and minimize the grain size of the GDC. In practice, the firing temperature of the GDC layer can be adjusted in the range of about 1000-1050 ° C., and the grain size can be controlled to about 50-60 nm or less. Thus, if necessary, the thickness of the GDC diffusion barrier layer can be reduced to at least 50-100 nm. Since the firing temperature of GDC is in the range of 1000-1050 ° C, it is possible to control the thickness relatively freely while avoiding the formation of a solid solution with YSZ.

GDC, which is a diffusion barrier layer material formed on the YSZ electrolyte layer, has the same crystal structure as YSZ and has a high structural similarity to form a solid solution at a high temperature. In fact, when the GDC barrier layer is formed on the YSZ electrolyte layer, GDC and YSZ are formed. It was confirmed that the interface has an excellent interface coherency and forms an interface having excellent bonding strength. The strong interfacial bonding force due to the continuous interfacial structure is the driving force that the YSZ electrolyte and the GDC barrier layer are almost integrated, and the two-layered electrolyte layer is referred to in the present invention as a double-layered electrolyte. It was found that the structural stability of the MMZ was not dependent on the thickness of the YSZ monolayer but on the overall thickness of the bilayer electrolyte. That is, during the manufacturing process, the structural stability can be maintained when the grain size of each component layer is smaller than the thickness of the individual component layers. When the reduction pores occur, the structural stability of the electrolyte layer is determined by the total thickness of the double layer electrolyte. Therefore, in the YSZ single layer electrolyte, an YSZ layer of 500 nm or more, which is a reduction pore size corresponding to the grain size of the anode functional layer, must be formed. However, in the case of a double layer electrolyte, when the sum of the thicknesses of the two layers is 500 nm or more, even in the presence of reducing pores, It was confirmed that the structural stability of the electrolyte can be maintained. When the total thickness of the bilayer electrolyte having structural stability in consideration of the reduction pore diameter is determined to be 500 nm, it is possible to control the thickness of the bilayer electrolyte within 100 nm, which is the structural stability standard in the manufacturing process of the individual layer thicknesses of YSZ and GDC. It is possible to build a double layer electrolyte structure of a combination of thicknesses.

The formation of the cathode must satisfy the following conditions. First, even if a double layer electrolyte thin film having a thickness and microstructure satisfying the structural stability criteria in the process and operation processes is formed, additional structural growth of the cathode may not guarantee the structural stability of the individual components. . Therefore, it is necessary to develop a cathode manufacturing process capable of forming the cathode at a temperature lower than the GDC forming temperature of 1000-1050 ℃. Second, the structure of the LSCF cathode, which is a mixed conducting oxide, should have a pore structure in which air can be smoothly delivered along with a structure having as high a surface area as possible in order to maximize the surface reaction area. Although the specific surface area of various non-spherical particles has a higher surface area than spherical particles, single particles close to the spherical surface having a low specific surface area are structurally more stable than non-spherical particles in terms of high temperature structural stability. Therefore, assuming spherical particles having structural stability, it is necessary to obtain a suitable size of LSCF grain size that can maintain the geometric stability in the manufacturing process and operating temperature. Third, it is necessary to give sufficient bonding force between these constituent particles to ensure structural stability of the porous cathode in the stack to which external force is applied.

Finally, the LSCF cathode must have a strong interfacial bond with the GDC barrier layer to ensure structural stability and electrochemical performance. In order to secure interfacial bonding force with the GDC barrier layer, as much solid-solid crosslinking as possible should be formed. In other words, it is necessary to maximize the number of solid-state crosslinks connected to the same material of the GDC barrier layer and the cathode layer to maximize the interfacial bonding force. This means that inserting a GDC / LSCF composite layer between the GDC barrier layer and the LSCF cathode layer is a method of increasing the interfacial bonding force. This maximizes the solid-state crosslinking between the GDC barrier layer and the GDC grains in the composite layer, and the solid-state crosslinking between the LSCF in the composite layer and the LSCF grains in the cathode layer, thereby increasing the total number of solid-state crosslinks. It should be noted that all these conditions must be achieved at a sintering temperature of 1000-1050 ° C below the first condition to ensure structural stability of the bilayer electrolyte. In order to secure sufficient interfacial bonding force with the GDC barrier layer even through low temperature sintering, LSCF powder and a solution may be applied to the LSCF cathode layer in parallel with the insertion of the GDC / LSCF intermediate layer. When the low temperature sintering is applied by the solution process, the grain size can be minimized. If the grain size is reduced, the number of solid-state crosslinking can be increased in the same composition, thereby maximizing the interfacial bonding force. In addition, when the solution process is applied, heterogeneous sintering occurs due to the difference in the sintering speed of the LSCF powder and the precursor powder formed from the LSCF solution. It is possible to increase the structural stability of the cathode.

However, in this case, it is desirable to form a pore channel for securing gas permeability that can offset the decrease of the pore size when the size of the LSCF powder is maximized by reducing the size of the LSCF powder. It is possible to form a continuous pore structure of large pore diameter.

The LSCF cathode thus formed is infiltrated with a high-performance cathode material such as LSC or SSC having higher electrode activity than LSCF to further improve low temperature operating performance, and then heat treated at a temperature lower than the LSCF cathode formation temperature. Can be formed.

Hereinafter, the present invention will be described in detail through examples. However, the embodiments are only examples of the present invention, and the present invention is not limited thereto.

Example

Example  1. Manufactured by solution process YSZ  Thin film electrolyte, GDC  Diffusion barrier layer , GDC -LSCF Composite layer , LSCF To the air pole  Done Anode  Support type Unit cell  Manufacture and evaluation

(1) having structural stability YSZ  Electrolyte Manufacturing Method

First, ethanol as a solvent, DMF as a solvent and drying regulator, and acetylacetonate as a complexing agent are stirred at room temperature for 30 minutes, and then zirconium acetate and yttrium nitrate dissolved in water are added to the previously prepared dispersion solvent, and then at room temperature. Stir for at least 6 hours. The pH value of the YSZ solution thus prepared was maintained at about 4. The prepared YSZ solution was evaporated to a concentration of 2M on a 150 ° C. hotplate. This is called YSZ salt solution.

YSZ nanopowder (particle size: 10-30 nm, specific surface area: 160 m ² / g, fuelcellmaterials.com) and dispersant PVP were added to the prepared YSZ salt solution, respectively, and ultrasonically irradiated for 6 hours to apply YSZ solution. Prepare. The YSZ solution prepared by adding the YSZ nanopowders is called an YSZ dispersion solution. The compositions of the YSZ salt solution and the YSZ dispersion solution are shown in Table 1.

ingredient content Role Yttrium nitrate hexahydrate [Y (NO ₃ ) ₃ · 6H ₂ O] Y _{0 .15} Zr _{0 .85} O _{1 .93}
(8YSZ) = 2 M Precursor Zirconium acetate solution in dilute acetic acid Dimethylformamide [DMF, C ₃ H ₇ NO] 1.4 M menstruum Ethanol [EtOH, C ₂ H ₆ O] 0.62 M Solvent Aid Water [H ₂ O] 0.5 M menstruum Aceylacetonate [Acac, C ₅ H ₈ O ₂ ] 0.27 M Complexing agent Nano-YSZ powder (manufacturer: fuelcellmaterials) 5 vol% Nano powder Polyvinylpyrrolidone [PVP, (C ₆ H ₉ NO) _n ]
(Mn = 10,000) 25 wt% of the nano-powder Dispersant

On the other hand, NiO-YSZ substrate and NiO-YSZ functional layer to be coated with the YSZ solution was prepared as follows. NiO-YSZ granules made by liquid condensation method are hot pressed, and then NiO-YSZ functional layers are formed more densely by screen printing, followed by sintering (1400 ℃, 3 hours). NiO-YSZ substrate was made.

Each YSZ solution was coated on a NiO-YSZ substrate thus obtained with a spin coater. Coating was carried out at 2000 rpm twice with YSZ dispersion twice with YSZ salt solution twice with YSZ dispersion twice with 2000 rpm in each air atmosphere. The coated YSZ thin film was heated up to 1100 ℃ and then heated to 1000 ℃ without holding time for 12 hours to obtain a final YSZ electrolyte structure.

Scanning electron micrographs of the surface and cross section of the YSZ electrolyte thin film prepared according to the above method are shown in FIGS. 3A and 3B , respectively. As shown, the YSZ thin film was found to form a dense microstructure having a very uniform but little pin-hole despite the non-uniform surface of the substrate.

(2) having structural stability GDC Diffusion barrier layer  Manufacturing method

After ethanol as a solvent, DMF as a solvent and drying regulator, and acetylacetonate as a complexing agent were stirred for 30 minutes at room temperature, gadolinium nitrate and cerium nitrate dissolved in water were added to the previously prepared mixed solvent and stirred at room temperature for 1 hour. do. The pH value of the GDC solution thus prepared was maintained at about 4. The prepared GDC solution is aged for 3 hours on a 90 ℃ hot plate. Through this aging process, the microstructure of the crack shape due to the fast volatility of gadolinium ions can be reduced, and the thickness of the GDC thin film can be controlled through viscosity control.

GDC nanopowder (particle size: about 10 nm, specific surface area: 97 m ² / g) prepared by coprecipitation method and PVP, a dispersant, were added to the prepared GDC solution for 10 minutes of ultrasonic irradiation, and then glycerol, a drying regulator, was added. To prepare a GDC solution to be applied. The composition of the GDC solution is shown in Table 2.

ingredient content Role _{Gadolinium nitrate hexahydrate [Gd (NO 3} ) 3 · H 2 O] _{Gd 0 .2 Ce 0 .8 O 1} .9
(GDC) = 0.1 M Precursor _{Cerium nitrate hexahydrate [Ce (NO 3} ) 3 · H 2 O] Dimethylformamide [DMF, C ₃ H ₇ NO] 1.0719 M menstruum Ethanol [EtOH, C ₂ H ₆ O] 0.6274 M Solvent Aid Water [H ₂ O] 1 M menstruum Aceylacetonate [Acac, C ₅ H ₈ O ₂ ] 0.4428 M Complexing agent Acetic acid [AC, C ₂ H ₄ O ₂ ] 0.363 M Increased complexing and solubility Glycerol [C ₃ H ₅ (OH) ₃ ] 5 wt% Drying regulator Nano-GDC powder (manufactured by co-precipitation) 5 vol% Nano powder Polyvinylpyrrolidone [PVP, (C ₆ H ₉ NO) _n ]
(Mn = 10,000) 10 wt% of the nano-powder Dispersant

The GDC solution thus obtained was spin coated on the YSZ electrolyte obtained in step 1 at about 2000 rpm. After each coating step, drying was carried out at 300 ° C. using Rapid thermal processing (RTP), and the number of coatings was adjusted until the desired thickness of the GDC solution was approximately 80-100 nm. The coated GDC diffusion barrier layer was heated to 1050 ° C. in an air atmosphere, and then heated to 1000 ° C. without a holding time for 12 hours.

The method as shown by scanning electron micrographs of the surface and cross section of the prepared GDC diffusion barrier layer in each of Figures 4a and 4 b. As shown, the GDC diffusion barrier layer was found to form a very fine and dense microstructure without defects.

(3) GDC Of LSCF  To improve interfacial bonding GDC  Powder dispersion LSCF  Composition of the solution and application examples

After stirring the mixed solvent of ethanol, DMF, acetylacetonate and acetic acid for 30 minutes at room temperature, lanthanum nitrate, strontium nitrate, cobalt nitrate and iron nitrate dissolved in water were added to the previously prepared mixed solvent and 6 hours at room temperature. Stir to prepare LSCF solution. GDC nanopowder prepared by coprecipitation and PVP as a dispersant were added to the prepared LSCF solution, and then a GDC / LSCF solution prepared by ultrasonic irradiation for 10 minutes was prepared. The composition of the GDC / LSCF solution is shown in Table 3.

ingredient content Role _{Lanthanum nitrate hexahydrate [La (NO 3} ) 3 · H 2 O] _{La 0 .6 Sr 0 .4 Co 0} .2 Fe 0 .8 O 3
(LSCF) = 0.035 M Precursor Strontium nitrate [Sr (NO ₃ ) ₂ ] _{Cobalt nitrate hexahydrate [Co (NO 3} ) 2 · H 2 O] _{Iron Nitrate Nonahydrate [Fe (NO 3} ) 3 · H 2 O] Dimethylformamide [DMF, C ₃ H ₇ NO] 0.5588 M menstruum Ethanol [EtOH, C ₂ H ₆ O] 0.37 M Solvent Aid Water [H ₂ O] 0.6 M menstruum Aceylacetonate [Acac, C ₅ H ₈ O ₂ ] 0.1588 M Complexing agent Acetic acid [AC, C ₂ H ₄ O ₂ ] 0.2834 M Complexing agent and solubility increase Nano-GDC powder (manufactured by co-precipitation) 45 vol% Nano powder Polyvinylpyrrolidone [PVP, (C ₆ H ₉ NO) _n ]
(Mn = 10,000) 10 wt% of the nano-powder Dispersant

The GDC / LSCF solution thus obtained was spin coated twice at about 2000 rpm onto the GDC expansion barrier layer obtained in step 2. After each coating step, drying was performed at 600 ° C. using RTP, and the coating thickness was approximately 50 nm or less to improve the interfacial bonding force between the cathode and the GDC diffusion barrier layer without affecting the cathode performance deterioration.

(4) LSCF Air cathode Surface area Air permeability  To maximize LSCF  Powder dispersion LSCF  Composition of the solution and application examples

First, to prepare LSCF powder, ethylenediaminetetraacetic acid is added to 300 ml of ammonia water, and respective LSCF precursor salts are added, followed by stirring at room temperature for 30 minutes. Citric acid is added to the prepared solution, mixed for 3 hours, and then titrated with ammonia water until the pH reaches 10. The composition of the prepared LSCF powder is shown in Table 4.

ingredient content Role _{Lanthanum nitrate hexahydrate [La (NO 3} ) 3 · H 2 O] _{La 0 .6 Sr 0 .4 Co 0} .2 Fe 0 .8 O 3
(LSCF) = 0.4 M Precursor Strontium nitrate [Sr (NO ₃ ) ₂ ] _{Cobalt nitrate hexahydrate [Co (NO 3} ) 2 · H 2 O] _{Iron Nitrate Nonahydrate [Fe (NO 3} ) 3 · H 2 O] Etylenediaminetetraaecticacid [EDTA, (C ₁₀ H ₁₆ N ₂ O ₈ )] 0.4 M Complexing agent Citric aicd [CA, (C ₆ H ₈ O ₇ )] 0.6 M Complexing agent Ammonium hydroxide [NH ₄ OH] pH = 10 pH regulator

The prepared solution was stirred at 70 ° C. for 3 hours, and then aged at 100 ° C. for one night. The aged solution is dried while increasing the temperature to 250 ℃. The dry powder is sieved and then calcined at 700 ° C. for 3 hours. Microstructure photographs and XRD measurements of the powders prepared according to the above method are shown in FIGS. 5 and 6. The particle size and surface area of the LSCF powder measured by BET were 54 nm and 17 m ² / g, respectively. It can be observed in Figure 5 that the LSCF powder having a particle size of less than 100 nm was prepared, as shown in Figure 6, it was confirmed that the LSCF powder without the secondary phase was prepared.

Next, to prepare a coating solution for LSCF cathodes, a mixed solvent of propanediol, methoxyethanol, acetylacetonate and acetic acid was stirred at room temperature for 30 minutes, and then lanthanum nitrate, strontium nitrate, and cobalt nitrate dissolved in water. Iron nitrates are added to the previously prepared mixed solvent and stirred at room temperature for 6 hours. The LSCF nanopowder and the dispersant were added to the prepared LSCF solution, and ultrasonically irradiated for 30 minutes. Then, the surfactant and the binder were added and milled for one day. The pore former is added to the milled LSCF solution and then milled another day to prepare the LSCF solution to be applied. The composition of the LSCF solution is shown in Table 5.

ingredient content Role _{Lanthanum nitrate hexahydrate [La (NO 3} ) 3 · H 2 O] _{La 0 .6 Sr 0 .4 Co 0} .2 Fe 0 .8 O 3
(LSCF) = 0.2 M Precursor Strontium nitrate [Sr (NO ₃ ) ₂ ] _{Cobalt nitrate hexahydrate [Co (NO 3} ) 2 · H 2 O] _{Iron Nitrate Nonahydrate [Fe (NO 3} ) 3 · H 2 O] 1,3-Propanediol [C ₃ H ₈ O ₂ ] 2.3 M menstruum 2-Methoxyethanol [C ₃ H ₈ O ₂ ] 0.98 M Solvent Aid Water [H ₂ O] 0.34 M menstruum Aceylacetonate [Acac, C ₅ H ₈ O ₂ ] 0.35 M Complex Acetic acid [AC, C ₂ H ₄ O ₂ ] 0.53 M Increased complexing and solubility Nano-LSCF powder (manufactured by complex compounding method) 95.384 vol% Nano powder Polyvinylpyrrolidone [PVP, (C ₆ H ₉ NO) _n ]
(Mn = 10,000) 10 wt% of the nano-powder Dispersant Hydroxypropyl cellulose [HPC, M _w = 80,000] 2 wt% Pore former Polyvinyl butyral 79 [(C ₈ H ₁₄ O ₂ ) _n ] 5 wt% Binder Triton X-100 [C ₁₄ H ₂₂ O (C ₂ H ₄ O) _n (n = 9-10)] 2 wt% Surfactants

The prepared LSCF solution was spin-coated at about 2000 rpm on the GDC / LSCF coating layer obtained in step 3. After each coating step, drying was performed at 600 ° C. using RTP and the number of coatings was adjusted until the desired thickness. The coated LSCF cathode layer was sintered at 950 ° C. for 2 hours.

Scanning electron micrographs of the surface and cross section of the LSCF cathode layer prepared according to the above method are shown in FIGS . 7A, 7B and 7C , respectively. As shown, the LSCF cathode layer formed sufficient pores for gas to pass through, and a small particle size LSCF due to LSCF salt solution and a relatively large about 200 nm particle size LSCF due to LSCF powder were mixed. It was observed that a cathode layer with a thickness of about 5 μm was formed. This means that the specific surface area of the entire LSCF cathode layer to be in contact with the air gas is maximized, which means that it can operate as a cathode even at a relatively thin thickness compared to the LSCF cathode layer, which is typically manufactured to a thickness of about 20 μm.

(5) prepared by the solution process YSZ  Electrolyte, GDC Diffusion Barrier Layer , GDC Of LSCF  Floor and LSCF  Air cathode layer Unit cell  Performance evaluation

The NiO-YSZ anode support substrate was cut out according to the size of 2 × 2 cm, followed by spin coating five times according to the manufacturing method of the YSZ thin film structure described in Step 1, followed by sintering at 1100-1050 ° C. to an YSZ electrolyte having a thickness of about 400 nm. A membrane was obtained. A total of four coatings were carried out according to the method for preparing the GDC diffusion barrier layer described in Step 2, followed by sintering at 1050-1000 ° C. lower than the sintering temperature of the YSZ electrolyte to prepare a GDC diffusion barrier layer having a thickness of about 350 nm. In order to increase the interfacial bonding force with the LSCF cathode layer on the prepared GDC diffusion barrier layer, the GDC / LSCF layer was coated twice as described in Step 3 to prepare a GDC / LSCF interfacial bonding increasing layer of about 50 nm or less. After the eight-coating according to the LSCF cathode manufacturing method described in Step 4, sintering was performed at 950 ° C. for 2 hours at a sintering temperature lower than that of the YSZ electrolyte layer and the GDC diffusion barrier layer, and the LSCF cathode layer having a thickness of about 5 μm. Paper was prepared. The manufactured unit cell had a cathode area of about 1.5 × 1.5 cm, and the flow rate of hydrogen of the anode and air of the cathode was about 500-650 ° C. using a 1 × 1 cm current collector and a separator plate. Performance evaluation was performed. This result is shown in FIG. As shown in FIG . 8 , the OCV value of the YSZ thin film + 350 nm GDC barrier layer having a thickness of about 400 nm is 1.116 V at 650 ° C., which is about 10-15 μm thick, screen printed YSZ electrolyte generally produced. A lossless OCV value was obtained in comparison with. This value means that the YSZ electrolyte prepared by the solution process operates stably as the electrolyte. In addition, the performance of the unit cell prepared by the solution process was about 850 mW at 650 ℃, indicating that the GDC diffusion barrier layer well suppressed the interfacial diffusion reaction between the electrolyte and the cathode layer, the GDC / LSCF coating membrane LSCF cathode It is shown that the interfacial bonding force was improved to enable low-temperature sintering. Finally, despite the relatively thin thickness of 5 μm, the LSCF cathode also showed comparable performance to the 20 μm thick screen-printed LSCF cathode.

Example  2. Manufactured by solution process YSZ  Thin film electrolyte, GDC  Diffusion barrier layer , GDC -LSCF Compound layer SSC end Impregnated LSCF To the air pole  Done Anode  Support type Unit cell  Manufacture and evaluation

(1) at low temperature LSCF Air cathode  To improve performance SSC  Composition and Application Examples of Solution Infiltration

To prepare the SSC infiltration solution, samarium nitrate, strontium nitrate and cobalt nitrate were added to a mixed solvent of water and ethanol, respectively, stirred at room temperature for about 30 minutes, and then urea was added and mixed at room temperature for 3 hours. The composition of the prepared SSC solution is shown in Table 6.

ingredient content Role _{Samarium nitrate hexahydrate [Sa (NO 3} ) 3 · H 2 O] Sa _0.5 Sr _0.5 CoO ₃
(8YSZ) = 2 M Precursor Strontium nitrate [Sr (NO ₃ ) ₂ ] _{Cobalt nitrate hexahydrate [Co (NO 3} ) 2 · H 2 O] Ethanol [EtOH, C ₂ H ₆ O] 0.81 M menstruum Water [H ₂ O] 0.375 M Solvent Aid Urea [C ₂ H ₄ O ₂ ] 4 M Complex

The prepared SSC solution was infiltrated by spin coating four times at 1500 rpm on the LSCF cathode layer prepared in Step 4 of Example 1, and after each coating step, heat-treated at 600 ° C. using RTP.

(2) prepared by the solution process YSZ  Electrolyte, GDC Diffusion Barrier Layer , GDC Of LSCF  layer, LSCF  Air cathode layer and SSC  Infiltration Unit cell  Performance evaluation

In general, the prepared NiO-YSZ anode support substrate is cut out according to the size of 2 × 2 cm, and according to the manufacturing method of the YSZ thin film described in Step 1 of Example 1, the YSZ dispersion solution is spin coated once and then 1100-1050 ° C. Sintering yielded an YSZ electrolyte membrane having a thickness of less than about 100 nm. In total, the coating was performed four times according to the method for preparing the GDC diffusion barrier layer described in Step 2 of Example 1, and then sintered at 1050-1000 ° C. lower than the sintering temperature of the YSZ electrolyte to prepare a GDC diffusion barrier layer having a thickness of about 350 nm. . In order to increase the interfacial bonding force with the LSCF cathode layer on the prepared GDC diffusion barrier layer, the GDC / LSCF layer was coated twice as described in Step 3 of Example 1 to prepare a GDC / LSCF interfacial bonding increasing layer of about 50 nm or less. In addition, according to the LSCF cathode manufacturing method described in Step 4 of Example 1, after coating eight times, the sintering temperature was lowered at 950 ° C. for 2 hours, which was lower than that of the YSZ electrolyte layer and the GDC diffusion barrier layer, and the thickness was about 5 μm. LSCF cathode layers were prepared. According to the manufacturing method of the SSC infiltration solution described in step 1 of Example 2 on the prepared LSCF cathode layer, the SSC solution was infiltrated four times and heat-treated at 600 ° C. to prepare a solid oxide fuel cell unit cell based on the solution process. It was. In order to confirm the effect of SSC impregnation, a single cell without SSC impregnation was also prepared. The manufactured cells had a cathode area of about 1.5 × 1.5 cm, and the flow rates of hydrogen in the anode and air in the cathode were ranged from 200 sccm to 500-650 ° C. using a current collector and a separator of 1 × 1 cm size. Performance evaluation was performed. The performance results at 650 ° C. are shown in FIG. 9.

As shown in FIG . 9 , the OCV value of the about 100 nm YSZ thin film electrolyte + 350 nm GDC diffusion barrier layer is about 1V when SSC is not impregnated and 0.89V when it is impregnated at 650 ° C., and the total of the YSZ and GDC layers is Since the thickness does not reach 500 nm, it can be seen that OCV is lower than that of Example 1. However, at 650 ° C., the performance value is 1.2 W without SSC impregnation, which is higher than that of Example 1, which is presumably because the thickness of the YSZ electrolyte is about 1/4 thinner than that of Example 1. In particular, the SSC impregnation showed a high performance value of 1.72 W despite the lower OCV, which is evidence that SSC penetration has a positive effect on the cathode performance.

Claims (16)

An anode support, an YSZ thin film electrolyte layer formed on the anode support, a GDC diffusion barrier layer formed on the YSZ thin film electrolyte, a GDC / LSCF composite layer formed on the GDC diffusion barrier layer, and a GDC / LSCF composite layer formed on the anode support A solid oxide fuel cell comprising an LSCF cathode;
At least one of the YSZ thin film electrolyte layer, the GDC diffusion barrier layer, the GDC / LSCF composite layer, and the LSCF cathode is formed by a spin process;
The maximum size of the YSZ crystal grains contained in the YSZ thin film electrolyte layer is smaller than the thickness of the YSZ thin film electrolyte layer, and the maximum size of the GDC crystal grains contained in the GDC diffusion barrier layer is smaller than the thickness of the GDC diffusion barrier layer. ;
And the maximum reduction pore diameter of the anode support is smaller than the sum of the thicknesses of the YSZ thin film electrolyte layer and the GDC diffusion barrier layer. The method of claim 1, wherein the YSZ thin film electrolyte layer is formed by spin coating and sintering a solution containing yttrium salt, zirconium salt, and YSZ nanopowder;
The GDC diffusion barrier layer is formed by spin coating and sintering a solution containing a gadolinium salt, a cerium salt, and a GDC nanopowder;
The average sintering temperature of the GDC diffusion barrier layer is lower than the average sintering temperature of the YSZ thin film electrolyte layer. The composite layer of claim 1, wherein the GDC / LSCF composite layer comprises (i) a lanthanum salt, strontium salt, cobalt salt, iron salt, a first composite layer solution comprising GDC nanopowder, or (ii) a gadolinium salt, cerium salt, LSCF A solid oxide fuel cell, characterized in that formed by spin coating and sintering a second composite layer solution containing nanopowders. The method of claim 1, wherein the LSCF cathode is formed by spin coating and sintering a solution containing a lanthanum salt, strontium salt, cobalt salt, iron salt, LSCF nanopowder;
And the average sintering temperature of the LSCF cathode is lower than the average sintering temperature of the GDC diffusion barrier layer. The method of claim 1, wherein the YSZ thin film electrolyte layer is formed by spin coating and sintering a solution containing yttrium salt, zirconium salt, and YSZ nanopowder;
The GDC diffusion barrier layer is formed by spin coating and sintering a solution containing a gadolinium salt, a cerium salt, and a GDC nanopowder;
The LSCF cathode is formed by spin coating and sintering a solution containing a lanthanum salt, a strontium salt, a cobalt salt, an iron salt, and an LSCF nanopowder;
The sintering treatment of the YSZ thin film electrolyte layer is performed by raising the temperature to the first YSZ sintering temperature and then lowering the temperature to the second YSZ sintering temperature;
The sintering treatment of the GDC diffusion barrier layer is performed by raising the temperature to the first GDC sintering temperature and then lowering the temperature to the second GDC sintering temperature;
The first GDC sintering temperature is lower than the first YSZ sintering temperature;
And the average sintering temperature of the LSCF cathode is lower than the first GDC sintering temperature. The method of claim 5, wherein the first YSZ sintering temperature and the second YSZ sintering temperature are in the range of 1050-1150 ° C. and 950-1050 ° C., respectively;
The first and second GDC sintering temperatures are in the range of 1000-1100 ° C. and 950-1050 ° C., respectively;
Solid oxide fuel cell, characterized in that the sintering temperature of the LSCF cathode is in the range of 900-1000 ℃. 7. The method of claim 6, wherein the LSCF cathode comprises a solution permeation layer thereon;
The solution permeation layer may comprise (i) a solution comprising a lanthanum salt, a strontium salt, a cobalt salt, (ii) a solution comprising a samarium salt, a strontium salt, a cobalt salt, and (iii) a mixed solution thereof. Formed by spin coating and sintering the LSCF cathode;
The sintering treatment is a solid oxide fuel cell, characterized in that performed at less than 900 ℃. The particle size according to any one of claims 1 to 7, wherein the YSZ nanopowder, the GDC nanopowder, and the LSCF nanopowder have a particle size of 10-30 nm, 10-20 nm, and 50-100, respectively. nm; The surface areas according to the results of the BET measurement are 140-180 m ² / g, 80-120 m ² / g and 10-30 m ² / g, respectively; Based on the final volume of each layer, the volume content of the nanopowder is 2-8% by volume, 2-8% by volume, 92-98% by volume, characterized in that the solid oxide fuel cell. (a) forming an YSZ thin film electrolyte layer on the anode support,
(b) forming a GDC diffusion barrier layer on the YSZ thin film electrolyte,
(c) forming a GDC / LSCF composite layer on the GDC diffusion barrier layer,
(d) a method of manufacturing a solid oxide fuel cell comprising forming an LSCF cathode on the GDC / LSCF composite layer;
Step (a) is performed by spin coating and sintering a solution containing yttrium salt, zirconium salt and YSZ nanopowder;
Step (b) is carried out by spin coating and sintering a solution comprising gadolinium salt, cerium salt, and GDC nanopowder;
The average sintering temperature of the GDC diffusion barrier layer is lower than the average sintering temperature of the YSZ thin film electrolyte layer manufacturing method of a solid oxide fuel cell. The YSZ thin film electrolyte layer and the GDC diffusion barrier layer each have a thickness of 100 nm or more and a thickness of the GDC diffusion barrier layer 100 nm or more. The sum of the thicknesses of the diffusion barrier layers is formed to be 500-1000 nm;
The YSZ grain size contained in the YSZ thin film electrolyte layer is 10-95 nm, the GDC grain size contained in the GDC diffusion barrier layer is 10-95 nm characterized in that the manufacturing method. 10. The method of claim 9, wherein step (c) comprises: (i) a lanthanum salt, strontium salt, cobalt salt, iron salt, a first composite layer solution comprising GDC nanopowder, and (ii) gadolinium salt, cerium salt, LSCF nanoparticles. Method of manufacturing a solid oxide fuel cell, characterized in that the spin coating and sintering the composite layer solution selected from the second composite layer solution containing powder to the LSCF cathode. 12. The method of claim 11, wherein step (d) is performed by spin coating and sintering a solution comprising a lanthanum salt, a strontium salt, a cobalt salt, an iron salt, and an LSCF nanopowder;
And the average sintering temperature of the LSCF cathode is lower than the average sintering temperature of the GDC diffusion barrier layer. The method of claim 12, wherein in the step (a), the sintering treatment of the YSZ thin film electrolyte layer is performed by raising the temperature to the first YSZ sintering temperature and then lowering the temperature to the second YSZ sintering temperature;
In step (b), the sintering treatment of the GDC diffusion barrier layer is performed by raising the temperature to the first GDC sintering temperature and then lowering the temperature to the second GDC sintering temperature;
The first GDC sintering temperature is lower than the first YSZ sintering temperature;
And an average sintering temperature of the LSCF cathode is lower than the first GDC sintering temperature. The method of claim 13, wherein the first YSZ sintering temperature and the second YSZ sintering temperature are in the range of 1050-1150 ° C. and 950-1050 ° C., respectively;
The first and second GDC sintering temperatures are in the range of 1000-1100 ° C. and 950-1050 ° C., respectively;
The sintering temperature of the LSCF cathode is in the range of 900-1000 ℃ solid oxide fuel cell manufacturing method. 10. The method of claim 9, wherein the solid oxide fuel cell manufacturing method further comprises: (e) forming a solution penetration layer on top of the LSCF cathode;
Step (e) comprises the steps of (i) a solution comprising a lanthanum salt, a strontium salt, a cobalt salt, (ii) a solution comprising a samarium salt, a strontium salt, a cobalt salt, and (iii) a mixed solution thereof. By spin coating and sintering the LSCF air electrode;
The sintering treatment is a solid oxide fuel cell manufacturing method, characterized in that performed at less than 900 ℃. The particle size according to any one of claims 9 to 15, wherein the YSZ nanopowder, the GDC nanopowder, and the LSCF nanopowder are 10-30 nm, 10-20 nm, and 50-100, respectively, according to the BET measurement result. nm; The surface areas according to the results of the BET measurement are 140-180 m ² / g, 80-120 m ² / g and 10-30 m ² / g, respectively; Based on the final volume of each layer, the volume content of the nanopowder is 2-8% by volume, 2-8% by volume, 92-98% by volume manufacturing method of a solid oxide fuel cell, characterized in that.

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