WO2019212273A1 - Sealing glass composition and solid oxide fuel cell using same - Google Patents

Abstract

The present invention relates to a glass composition available as a sealing material and a solid oxide fuel cell using same. A sealing glass composition according to the present invention comprises 5-30 wt% of SiO₂, 3-35 wt% of B₂O₃, 30-65 wt% of BaO, and 2-20 wt% of CaO and can be properly employed, unlike conventional sealing glass compositions, in a solid oxide fuel cell operating at low and moderate temperatures.

Description

Sealing Glass Composition and Solid Oxide Fuel Cell Using the Same

The present invention relates to a glass composition that can be used as a sealing material and a solid oxide fuel cell using the same.

Solid oxide fuel cells (SOFCs) are chemical cells that generate electricity by receiving oxidizing gases such as air and reducing fuel gases such as H ₂ , CO, and CH ₄ at high temperatures, respectively. SOFC has advantages such as high thermal efficiency and low dependence on expensive catalysts due to high operating temperature.

However, in SOFC, since the component material is exposed to high temperature, durability of the battery component material becomes a big problem. For this reason, basic research on the operating temperature, medium and low temperature materials, battery configuration, etc. is needed prior to practical use.

SOFC is composed of unit cell consisting of cathode, solid electrolyte, and anode, and planar design according to the type of interconnects that connect unit cells to each other. ), Tubular design, and plat tube design, and the development of sealing material is essential for flat SOFCs to prevent mixing between fuels and to join components within a unit cell.

Recently, a lot of research is in progress for the practical use of low-temperature SOFC. The low and medium temperature solid oxide fuel cell operating at 600 ℃ ~ 800 ℃ has a number of advantages over the existing high temperature solid oxide fuel cell operating at 800 ℃ ~ 1000 ℃. In the case of high temperature solid oxide fuel cell, it is necessary to use the connector as ceramic due to the problem of metal oxidation. However, when the operating temperature is lowered below 700 ℃, the manufacturing cost can be lowered because the metal connector can be used. In terms of design and material selection of the BOP (balance of plant), which accounts for about%, the choice of materials can be lowered and the manufacturing cost can be lowered. In addition, the lower the temperature, the easier it is to respond to thermal cycles such as start-up and shutdown, and increase durability.

In the case of the flat plate type, the short current path shows excellent characteristics in terms of efficiency and power density compared to the cylindrical shape, but since most of the materials constituting the ceramic composite are monolithic, there are technical problems due to the complicated manufacturing process. In particular, development of a sealing glass material is essential as a sealing material for bonding between component layers. If fuel gas and air gas are mixed at a high temperature, the SOFC stack structure may be damaged due to heat generation or explosion due to oxidation of fuel gas by air. In addition, when the partial pressure of each gas is lowered at the fuel electrode and the air electrode by mixing the two gases, the electromotive force is reduced and normal electricity production is not achieved.

Currently, many technologies have been developed for suitable sealing methods and sealing materials that can satisfy both the long-term sealing performance and reliability of materials required for flat panel SOFCs, but the technology to the extent that the SOFC can be commercialized and commercialized has not been developed. It is true.

In this regard, sealing glass compositions applied to solid oxide fuel cells operating at 800 ° C to 1000 ° C are widely known.

However, since the sealing material applied to the solid oxide fuel cell operating at 800 ℃ ~ 1000 ℃ is heat-treated at least 850 ℃ or more, there is a problem that is difficult to use in the low-temperature solid oxide fuel cell.

In addition, the existing sealing material contains a certain amount of components for improving the flowability of the glass, but does not have a suitable component and composition ratio that can match the thermal expansion coefficient with the base material, there is a problem such as cracking during long-term operation of SOFC. .

In addition, unlike conventional sealing materials, while the heat treatment is performed at 800 ℃ or less, the development of a sealing glass composition excellent in chemical durability and heat resistance under SOFC operating conditions of 600 ~ 700 ℃ is required.

It is an object of the present invention to provide a novel sealing glass composition suitable for use in solid oxide fuel cells operating at medium to low temperatures of 600 to 700 ° C.

In addition, an object of the present invention is to provide a new sealing glass composition having excellent durability while improving the high temperature fluidity of the glass and matching the coefficient of thermal expansion with the base material to prevent peeling or breakage.

Moreover, an object of this invention is to provide the new sealing glass composition excellent in chemical durability and heat resistance in SOFC operation conditions of 600-700 degreeC, even if heat processing is carried out at 800 degrees C or less.

In order to provide a sealing glass composition suitable for use in a solid oxide fuel cell operating at low and low temperatures, the sealing glass composition according to the present invention comprises 5 to 30% by weight of SiO ₂ , 3 to 35% by weight of B ₂ O ₃ , and BaO 30 to 65 wt% and CaO 2-20 wt%.

In addition, in order to improve the high temperature fluidity of the glass and to provide a new sealing glass composition in which the thermal expansion coefficient with the base material is matched so that no peeling or breakage occurs, the sealing glass composition according to the present invention has a content of SiO ₂ . It may be less than 1/2 of the content of BaO, and also the content of CaO may be less than the content of B ₂ O ₃ .

In addition, at least one of Al ₂ O ₃ , ZrO ₂ and La ₂ O ₃ to provide a new sealing glass composition excellent in chemical durability and heat resistance under SOFC operating conditions of 600 ~ 700 ℃ while the heat treatment is carried out at 800 ℃ or less. It may further include.

The sealing glass composition according to the present invention has a novel component system containing SiO ₂ , B ₂ O ₃ , BaO and CaO in a unique composition ratio of the present invention, which is suitable for a solid oxide fuel cell operating at low and low temperatures unlike a conventional sealing material glass composition. Can be used.

In addition, the sealing glass composition according to the present invention may have an optimum ratio of SiO ₂ and BaO, and may also have an optimum ratio of CaO and B ₂ O ₃ to improve the high temperature fluidity of the glass and to have a coefficient of thermal expansion with the base material. Is matched and there is an effect that peeling or breakage does not occur.

Furthermore, the sealing glass composition according to the present invention may further include at least one of Al ₂ O ₃ , ZrO ₂ and La ₂ O ₃ , which may be subjected to heat treatment at 800 ° C. or lower, and to chemical durability at SOFC operating conditions of 600 to 700 ° C. It is effective in excellent heat resistance.

1 is a cross-sectional view showing a schematic structure of a planar solid oxide fuel cell.

3 is a SEM image showing the sealing material according to Example 5 and the sealing material according to Comparative Example 1 compared with each other.

3 is a SEM image showing a state change of Example 5 according to the operating conditions.

The above objects, features, and advantages will be described in detail below, and thus, those skilled in the art may easily implement the technical idea of the present invention. In describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail.

The present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, only this embodiment to make the disclosure of the present invention complete and to those skilled in the art to fully understand the scope of the invention It is provided to inform you.

Hereinafter, the sealing glass composition and the solid oxide fuel cell using the same according to the present invention will be described in detail.

<Sealing glass composition>

There is a need for the development of a sealing glass composition suitable for application to a medium to low temperature solid oxide fuel cell driven at a temperature of about 600 ~ 700 ℃. Accordingly, the present inventors have completed a novel sealing glass composition which is particularly suitable for a heat treatment process (sealing process) at 800 ° C. or lower and excellent in durability even when applied to a medium-low temperature solid oxide fuel cell for a long time.

The sealing glass composition according to the present invention includes 5 to 30% by weight of SiO ₂ , 3 to 35% by weight of B ₂ O ₃ , 30 to 65% by weight of BaO and 2 to 20% by weight of CaO.

SiO ₂ is a component for improving the glass forming ability and forming the network structure of the glass. Sealing glass composition according to the present invention comprises the SiO ₂ in the range of 5 to 30% by weight. When the SiO ₂ is contained in less than 5% by weight crystallization of the glass is easily generated, there is a problem that the sealing itself is difficult, and when the SiO ₂ is contained in excess of 30% by weight, the fusion flow at a high temperature is sharply increased. Accordingly, there is a problem that sufficient sealing is not achieved between components.

B ₂ O _3, together with SiO ₂ , serves as a glass former to allow sufficient vitrification and corresponds to a component that lowers the melting temperature, softening temperature, and high temperature viscosity of the glass and reduces the amount of crystallization of the glass composition. The sealing glass composition according to the present invention contains 3 to 35% by weight of the B ₂ O ₃ . When the B ₂ O ₃ is included in less than 3% by weight, the softening point is increased to increase the viscosity at high temperatures may lower the airtightness. In addition, when the B ₂ O ₃ is included in excess of 35% by weight, the water resistance of the sealing material is weak, and above all, there is a problem that may cause material degradation during long-term operation of the low-temperature SOFC.

BaO is a component that can suppress the devitrification of the glass and improve the fluidity by lowering the high temperature viscosity. The sealing glass composition according to the present invention contains 30 to 65% by weight of BaO. If BaO is included in less than 30% by weight may cause a problem that the flowability of the glass is lowered. In addition, when BaO is included in excess of 65% by weight, the Ba component in the glass composition reacts with the Cr component derived from the base material (connecting material) formed of stainless steel, in particular, to generate BaCrO ₄ , thereby causing a large change in the coefficient of thermal expansion of the sealing material. There is a problem that cracks may occur in the base material and the sealing material during a long time operation of the SOFC.

CaO corresponds to a component capable of controlling the coefficient of thermal expansion of the sealing glass composition and improving the durability of the sealing material. The sealing glass composition according to the present invention contains 2 to 20% by weight of CaO. If the CaO is included in less than 2% by weight may not obtain the required coefficient of thermal expansion may cause a problem that the flowability of the glass is lowered. In addition, when the CaO is included in excess of 20% by weight, devitrification of the glass may occur, and there is a problem that high temperature fluidity may be lowered.

More preferably, in the sealing glass composition according to the present invention, the content of the SiO ₂ may be adjusted to 1/2 or less of the content of BaO. The BaO component corresponds to the component which improves the fluidity as mentioned above, and is preferably contained at least twice the content of SiO ₂ in order to impart proper fluidity in the component system of the sealing glass composition according to the present invention. On the contrary, if the content of SiO ₂ exceeds 1/2 of the content of BaO, there is a problem that the sealing of the glass is poor because the flowability of the glass is reduced.

In addition, the sealing glass composition according to the present invention may be adjusted so that the content of CaO is less than the content of B ₂ O ₃ in order to match the coefficient of thermal expansion with the base material. The sealing glass composition according to the present invention may be advantageous in matching the coefficient of thermal expansion with the base material while ensuring the flowability of the glass because CaO is contained in less than the content of B ₂ O ₃ .

Next, the sealing glass composition according to the present invention may further include at least one of Al ₂ O ₃ , ZrO ₂ and La ₂ O ₃ to improve the chemical durability and heat resistance of the sealing material, preferably 0.1 to 20 weight It can be included in the range of%. When at least one of Al ₂ O ₃ , ZrO ₂ and La ₂ O ₃ is included in less than 0.1% by weight, the effect of improving chemical durability and heat resistance may be insignificant. There is a problem that can occur.

In addition, the sealing glass composition according to the present invention may further include one or more of SrO, MgO and ZnO to maintain an appropriate high temperature viscosity, preferably may be included in the range of 0.1 to 12% by weight. When at least one of the SrO, MgO and ZnO is included in less than 0.1% by weight, the effect of improving chemical durability and heat resistance may be insignificant, and when it is included in more than 12% by weight, crystallization of the glass is easily generated, making it difficult to seal. there is a problem.

In addition, the sealing glass composition according to the present invention may preferably have a hemispherical temperature of 800 ° C. or less so as to be suitable for a heat treatment process (sealing process) of 800 ° C. or less. The hemispherical temperature may be measured by a microscopic method using a high temperature microscope, and means a temperature at which cylindrical test specimens fuse with each other to form a hemispherical mass. When the sealing glass composition which concerns on this invention has hemispherical temperature of 800 degrees C or less, sufficient airtightness can be ensured at the temperature of about 600-700 degreeC.

<Solid oxide fuel cell and sealing method thereof>

The present invention provides a solid oxide fuel cell including a sealing material formed of the aforementioned sealing glass composition. More preferably, the solid oxide fuel cell may be a low temperature solid oxide fuel cell operating in a temperature range of 600 ~ 700 ℃.

Referring to FIG. 1, a solid oxide fuel cell may include a cathode and an anode, an electrolyte, an interconnector, and a frame provided between the cathode and the anode, and the structure thereof is not particularly limited.

Solid oxide fuel cells are required to prevent gas mixing between the positive and negative electrodes and to provide a complete seal for electrical insulation at the edges of the electrodes, electrolytes and interconnectors of each cell.

To this end, the sealing material formed of the sealing glass composition according to the present invention may be applied to seal between each electrode and the interconnector, between the electrolyte and the interconnector, between the cell stack and the frame.

In addition, the sealing material formed of the sealing glass composition according to the present invention can be applied to various parts depending on the structure of the solid oxide fuel cell.

The sealing method of the solid oxide fuel cell according to the present invention is applied by applying the sealing glass composition according to the present invention to a portion in need of sealing, and performing heat treatment at a temperature of 800 ° C. or lower (sealing process). .

Hereinafter, specific embodiments of the present invention will be described with reference to Examples.

<Example>

<Production of Sealing Glass Composition>

A sealing glass composition having a composition ratio shown in Table 1 below was prepared. BaCO, CaO and SrO were used as raw materials of BaO ₃ , CaCO ₃ and SrCO ₃ , respectively, and the same ingredients as those listed in Table 1 were used. The prepared glass composition was melted in an electric furnace at a temperature range of 1200 to 1350 ° C. and then quenched dryly using a twin roll. The cullet obtained by quenching was pulverized with a dry mill and passed through a 230 mesh sieve to prepare a glass powder having a D ₅₀ particle size of 15 to 25 μm.

Ingredient (% by weight)	Example					Comparative example
	One	2	3	4	5	One	2
SiO 2	24.2	18.2	18.8	16.9	26.3	39.8	38.7
B 2 O 3	13.5	10.4	11.5	12.1	11.1	9.1	8.7
BaO	53.1	52.1	51.8	51.9	50.8	38.3	44.7
CaO	9.2	11	12.7	8.2	7.5	0.9	1.1
Al 2 O 3	-	6.4	-	7.9	2.5	4.9	3.7
ZrO 2	-	0.2	-	0.3	One	-	-
La 2 O 3	-	1.7	-	2	-	7.0	-
SrO	-	-	3.1	0.5	0.8	-	3.1
MgO	-	-	1.4	0.2	-	-	-
ZnO	-	-	0.7	-	-	-	-

Experimental Example

The coefficient of thermal expansion of the sealing glass compositions prepared in Examples and Comparative Examples was measured, and specimens were prepared to examine their reactivity with the base metal (stainless steel). Physical property measurement and reactivity results are summarized in Table 2 below.

1. Measurement of coefficient of thermal expansion (CTE (x10 ^-7 / ℃))

The powders prepared from the examples and the comparative examples were prepared into pellets, and then maintained at 750 ° C., and after the furnace cooling, the coefficient of thermal expansion was measured by using a TMA equipment (TMA-Q400 TA instrument).

2. Review of reactivity of sealing materials and base materials

Glass powders prepared according to Examples 1 to 5 were prepared as pellets and placed on stainless steel (SUS441), and then heat-treated at 750 ° C. for 5 hours. After the heat treatment, the exposure was carried out at 680 ° C. for 50 hours, and the change of the sealing material was examined.

	Example					Comparative example
	One	2	3	4	5	One	2
Coefficient of Thermal Expansion (CTE (x10 -7 / ℃))	104.2	103.1	105.5	107.7	103.6	87.14	93.1

As described in Table 2, Examples 1 to 5 according to the present invention fall within the range of 103 to 114 (x10 ⁻⁷ / ° C.). The bonding base material is stainless steel (SUS441), and its thermal expansion coefficient corresponds to about 115 (x10 ⁻⁷ / ° C.). Examples 1 to 5 show that the bonding base material and the thermal expansion coefficient match. However, in Comparative Examples 1 and 2, the thermal expansion coefficient was in the range of 85 to 95 (x10 ⁻⁷ / ° C.), and thus the bonding base material and the thermal expansion coefficient did not match.

Next, the sealing material prepared from Examples 1 to 5 and the sealing material prepared from the comparative example were placed on stainless steel (SUS441), and then heat-sealed at 750 ° C. for 5 hours to observe sealing properties.

Examples 1 to 5 all had good sealing characteristics such as gas tightness, but the sealing material according to the comparative example was found to have a problem in gas tightness because the high temperature fluidity under heat treatment conditions was too low. In particular, Figure 2 shows an SEM image of the sealing material according to Example 5 and Comparative Example 1. Referring to FIG. 2, the sealing material according to Example 5 has an appropriate high temperature viscosity (spreadability) in the maximum temperature range (700 ° C. to 800 ° C.) of the sealing process, thereby ensuring the airtightness of the SOFC. However, since the sealing material according to the comparative example has a high temperature viscosity, it is difficult to secure the airtightness and adhesive strength of the SOFC.

Next, the sealing material produced from Examples 1 to 5 was heat-treated at 750 ° C. for 5 hours and exposed at 680 ° C. for 50 hours, and then the change of the sealing material was examined. In addition, the change of the sealing material was examined after heat-sealing the sealing material produced from Examples 1-5 for 5 hours at 750 degreeC, and exposing for 150 hours at 680 degreeC.

The surface of the long-term exposed sealing material after fabrication and heat treatment from Examples 1 to 5 was observed by scanning electron microscopy (SEM). SEM image of Example 5 is shown in FIG. 3.

As a result, in Examples 1 to 5, no change such as crystallization or uniformity of the sealing material was observed in spite of prolonged exposure at 680 ° C.

Although the present invention has been described as described above, the present invention is not limited to the embodiments disclosed herein, and it is obvious that various modifications can be made by those skilled in the art within the scope of the technical idea of the present invention. In addition, even if the above described embodiments of the present invention while not explicitly described and described the effect of the effect of the configuration of the present invention, it is obvious that the effect predictable by the configuration is also to be recognized.

Claims (10)

1. SiO ₂ 5-30 wt%,

   B ₂ O ₃ 3-35 wt%,

   30-65 wt% BaO and

   CaO containing 2-20 wt%

   Sealing glass composition.
2. The method of claim 1,

   The content of SiO ₂ is a sealing glass composition, characterized in that less than 1/2 of the content of BaO.
3. The method of claim 1,

   The content of CaO is a sealing glass composition, characterized in that less than the content of B ₂ O ₃ .
4. The method of claim 1,

   Sealing glass composition, characterized in that it further comprises at least one of Al ₂ O ₃ , ZrO ₂ and La ₂ O ₃ .
5. The method of claim 4, wherein

   At least one of the Al ₂ O ₃ , ZrO ₂ and La ₂ O ₃

   Sealing glass composition, characterized in that included in the range of 0.1 to 20% by weight.
6. The method of claim 1,

   Sealing glass composition, characterized in that it further comprises at least one of SrO, MgO and ZnO.
7. The method of claim 6,

   At least one of the SrO, MgO and ZnO is

   Sealing glass composition, characterized in that included in the range of 0.1 to 12% by weight.
8. The method of claim 1,

   Hemispherical temperature is 800 degrees C or less, The sealing glass composition characterized by the above-mentioned.
9. The solid oxide fuel cell containing the sealing material formed from the sealing glass composition of any one of Claims 1-8.
10. The sealing method of the solid oxide fuel cell containing the process of heat-processing the sealing glass composition of any one of Claims 1-8 at 800 degrees C or less.

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