KR100841458B1 - Solid electrolyte for fuel cells and method for preparing the same - Google Patents

Abstract

A solid electrolyte for a fuel cell, and a method for preparing the solid electrolyte are provided to increase mechanical strength and to reduce the difference of thermal expansion coefficient between a negative electrode and an electrolyte. A solid electrolyte for a fuel cell comprises a gadolinia doped ceria-magnesium oxide composite which comprises gadolinia doped ceria(GDC) containing silicon dioxide(SiO2), and 0.3-20 mol% of magnesium oxide(MgO). The solid electrolyte is prepared by preparing gadolinia doped ceria containing silicon dioxide; mixing it with 0.3-20 mol% of magnesium oxide to form a mixture; and molding and sintering the obtained mixture.

Description

Solid electrolyte for fuel cell and manufacturing method thereof {Solid electrolyte for fuel cells and method for preparing the same}

1A to 1F show the complex impedance measurement results of specimens according to Examples 1 to 4 and Comparative Examples 1 and 2. FIG.

2A to 2F show SEM images of specimens according to Examples 1 to 4 and Comparative Examples 1 and 2. FIG.

3A to 3F illustrate changes in intragranular resistance, grain boundary resistance, average particle diameter, resistance per unit grain area, and SiO ₂ removal efficiency according to Examples 1 to 4 and Comparative Examples 1 to 3.

4A shows a TEM image of the GDC according to Example 2, and FIGS. 4B to 4F show the results of electron energy loss spectroscopy (EELS) analysis in the secondary phase, the grain boundary, the triple point, and the mouth, respectively.

FIG. 5 shows the change of lattice parameter according to Examples 1 to 4 and Comparative Examples 1 to 5 through XRD analysis.

6a and 6b show the change in R _gbs value when the concentration of MgO and CaO is added to GDC, respectively.

The present invention relates to a solid electrolyte for fuel cells and a method for manufacturing the same, and more particularly, to magnesium oxide (MgO) added to gadolinic-containing ceria (GDC) to increase grain boundary conductivity even at low temperatures and to provide excellent mechanical strength. It relates to an electrolyte and a method for preparing the same.

Many countries and companies around the world are doing their best to develop alternative energy due to concern about environmental pollution and depletion of petroleum energy. Among them, a solid oxide fuel cell (SOFC) is attracting attention because of its high energy conversion efficiency of 60% and the use of various fuel gases such as hydrogen and methane. The solid oxide fuel cell is hydrogen, and the negative electrode the oxidation of hydrocarbon or the like occurs, the oxygen gas O ^{2 -} made of a solid electrolyte ionic ^{conduction-anode} is reduced by ions, O ^2. Oxide solid electrolytes include stabilized zirconia, ceria, and the like.

To increase the price competitiveness of SOFCs, it is important to lower the operating temperature of the SOFCs. Currently, the most commonly used solid electrolyte is YSZ (Yttria-Stabilized Zirconia), and when the electrolyte support structure is adopted, the operating temperature reaches 900 ° C. After preparing a porous Ni-YSZ porous cathode and introducing a cathode support type having an YSZ electrolyte membrane having a thickness of about 10 μm, the operating temperature can be lowered to 700 ° C. The operating temperature can be lowered up to 500 ° C by changing the solid electrolyte used to Gadolinia doped Ceria (GDC). GDC also plays an important role in single-chamber fuel cells used at 500 ℃ ~ 600 ℃.

If the operation temperature is lowered while maintaining high ion conductivity and high conversion efficiency, economical gas sealant and connecting material can be used. At temperatures as low as 500 ° C, it is important to increase the conductivity of the grain boundary because the resistance of the grain boundary is about 100 to 1000 times larger than the resistance in the mouth. When impurities containing SiO ₂ are present in YSZ and GDC, the grain boundary resistance is known to increase by about 50 to 100 times because the impurities containing SiO ₂ are present in the grain boundary phase of high resistance. These high resistances increase the operating temperature of the SOFC of the GDC, and further worsen the energy conversion efficiency of the SOFC operating at low and medium temperatures. The inclusion of only 50 to 100 ppm of SiO ₂ -related impurities increases the resistance of the grain boundaries tens of times, which can be easily incorporated during ceramic processing, mixing, sintering, and SOFC operation. In particular, considering that SiO ₂ is the most easily incorporated impurities in nature, it is very difficult to prevent the incorporation of SiO ₂ . In addition, a problem of reducing the characteristics of the cathode when using a GDC containing SiO ₂ as a solid electrolyte has been reported.

At low temperatures of 400 to 600 ° C, the grain boundary resistance in the GDC electrolyte is about 100 to 1000 times higher than in the mouth. Reasons for increasing the grain boundary resistance at the grain boundary include an intrinic effect and an extrinsic effect. The intrinsic effect is a phenomenon in which ion conduction of oxygen ions becomes difficult due to the decrease of oxygen vacancies concentration at the bottom of the grain boundary due to the formation of a space charge layer at the grain boundary. The external effect is a phenomenon in which ion conductivity at the grain boundary becomes difficult due to the presence of high resistance grain boundaries.

Representative materials on grain boundaries are SiO ₂ . Even when only a few hundred ppm of SiO ₂ is added, it is known that the grain boundary resistance of GDC is increased by about 100 times. Since SiO ₂ is easily inhaled during the ceramic process, sintering, and SOFC operation, and GDC powder without SiO ₂ is expensive, the SiO ₂ phase must be removed for economical SOFC design.

The removal of high resistance intergranular phases containing SiO ₂ has a great effect on the efficient and stable operation of SOFC. Since continuous high-resistance grain boundaries containing SiO ₂ interfere with ion conduction at the grain boundaries, it is necessary to discontinuously convert high-resistance grain shapes or chemically react with other materials in order to reduce the grain boundaries. To remove them.

A method of reacting Si phase with alumina by adding Al ₂ O ₃ to YSZ, a method of de-weighting the grain boundary liquid by crystallization of grain boundary liquid, and US Pat. No. 6,838,119 adds CaO or SrO to GDC. It is reported that the ionic conductivity of the grain boundary is improved.

However, even with the above method, there are problems such as not only satisfactory ionic conductivity of grain boundaries but also weakness of mechanical properties and weakness of water.

In order to solve the above problems, the present invention provides a solid electrolyte for fuel cells having excellent ionic conductivity at grain boundaries and improved mechanical properties and the like.

In order to solve the above problems, the present invention provides a method for producing a solid electrolyte for a fuel cell with excellent ion conductivity of grain boundaries, improved mechanical properties and the like.

In order to achieve the above object, the present invention

Gadolinia doped ceria (GDC) containing silicon dioxide (SiO ₂ ) Gadolinia doped ceria (GDC) -MgO complex containing 0.3-20 mol% of magnesium oxide (MgO) It provides a solid electrolyte for a fuel cell containing.

In order to achieve the above another object, the present invention

Adding silicon dioxide (SiO ₂ ) to Gadolinia Doped Ceria (GDC);

Mixing 0.3-20 mol% of magnesium oxide (MgO) with the gadolinian-containing ceria containing silicon dioxide to form a mixture; And

Forming and firing the mixture to form a gadolinian-added ceria (GDC) -magnesium oxide (MgO) complex provides a method for producing a solid electrolyte for a fuel cell, including improving the ionic conductivity.

The MgO addition method in the present invention has a mechanism for removing grain boundary secondary phase containing SiO ₂ while MgO exists as a secondary phase, thereby improving grain boundary ion conductivity even with a small amount of addition, increasing mechanical strength, and increasing the negative electrode and electrolyte. The difference in thermal expansion coefficient between and is reduced.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The present invention provides a gadolinia-doped ceria (GDC) -magnesium oxide (MgO) complex containing 0.3-20 mol% of magnesium oxide (MgO) in a gadolinia-doped ceria (GDC) including silicon dioxide. Provided is a solid electrolyte for a fuel cell.

The present invention relates to a method of reducing grain boundary resistance of GDC containing SiO ₂ by adding MgO. In particular, the addition of CaO and SrO has a mechanism that changes the structure of the grain boundary into a coherent faceted structure, whereas MgO removes SiO ₂ and the coefficient of thermal expansion of the solid electrolyte / cathode. Reduce the difference and increase the mechanical strength of the solid electrolyte.

The content of MgO added to the gadolinian-containing ceria is preferably 0.3 mol% to 20 mol%. If the content of MgO is less than 0.3 mol%, it is not preferable because the resistance of the grain boundary is so high that the conductivity of the grain boundary is not improved.If the content of MgO is more than 0.3 mol%, most SiO ₂ reacts with MgO and MgO Since it is removed in the form of ₂ SiO ₄ , the resistance of the grain boundary is very low, thereby improving the grain boundary conductivity. However, when MgO is added 20 mol% or more, the fraction of MgO secondary phase increases, so that the conductivity in the mouth slightly decreases, and the grain boundary conductivity slightly decreases, which is not preferable.

When silicon dioxide is added in an amount of 0.01 to 1 mol% compared to gadolinic-containing ceria (GDC), the content of magnesium oxide (MgO) is more than twice the molar ratio with respect to the content of silicon dioxide, and to the gadolinian-containing ceria (GDC). It is preferable that it is 20 mol% or less with respect to.

Assuming that the content of Si added to the gadolinian-added ceria is 500 ppm, the weight ratio is 0.144 mol% when the molar percentage is changed. MgO is present in a second phase, and the SiO ₂ are removed MgO reacts with SiO ₂ to form a secondary phase of Mg ₂ SiO _4. Therefore, the minimum MgO content required to form the secondary phase of Mg ₂ SiO ₄ may be 0.288 mol%, which is almost in agreement with the minimum concentration of 0.3 mol% of the present invention. Therefore, when the content of MgO is less than 2.0 times the silicon dioxide content, the resistance of the grain boundary is very high, so the conductivity of the grain boundary is not improved, which is not preferable.

On the other hand, the content of magnesium oxide (MgO) is more than twice the molar ratio with respect to the content of silicon dioxide and the maximum content of MgO may be present up to 150 times depending on the content of silicon dioxide. Another condition related to the MgO content is that the maximum content of magnesium oxide is 20 mol% with respect to gadolinic-added ceria. This means that even if magnesium oxide is present at more than twice the amount of silicon dioxide, it cannot be increased without considering the content of gadolinian-containing ceria. That is, the minimum addition amount of MgO varies with the content of SiO ₂ , but the upper limit of addition of MgO is determined by how much MgO exists in GDC.

The larger the mechanical strength of the solid electrolyte is, the more preferable. In the present invention, the flexural strength of the gadolinian-added ceria-magnesium oxide (GDC-MgO) composite is preferably 150 MPa or more, more preferably 150 to 300 MPa. By adding MgO, mechanical properties are improved. In case of GDC containing 500 ppm of SiO ₂ , the flexural strength is 127 MPa to 147 MPa, whereas in the case of GDC-MgO composite with 2 mol% MgO, the flexural strength is improved to 150 MPa to 180 MPa, 20 mol When% MgO was added, the flexural strength was improved to 300 MPa. This is because MgO forms a secondary phase, and the formed secondary phase forms a composite to enhance strength.

In general, the grain boundary structure tends to have a random defaceted structure at a high temperature, and generally exhibits a faceted structure arranged at a low temperature. When CaO is added to gadolinian-added ceria (GDC), the structure of the grain boundary changes into a faceted structure as CaO enters the lattice. In the case of 500 ppm SiO ₂ doped GDC without CaO added, all grain boundaries exhibit random non-angular structures, whereas for CaO-added specimens, 70% of the grain boundaries exhibited angular faces. This means that the grain boundary structure of each face is large in the cohesiveness of the grain boundary. Therefore, when CaO is added, the structure of the grain boundary is changed into a angular shape without forming a secondary phase, and thus SiO ₂ existing at the grain boundary is changed. It contains a discontinuous shape, such that the containing secondary phase is pushed out near the triple point. Therefore, it can be seen that the addition of MgO according to the present invention differs from the addition of CaO in the grain boundary conduction enhancement mechanism.

When 10 mol% of SrO was added, a trace amount of SrCeO ₃ phase was observed according to the XRD pattern, and the substance is known as a proton conductor which is sensitive to moisture. In addition, even in case of CaO, it is known that the stability against moisture. However, in the case of MgO addition according to the present invention, the moisture resistance is superior to that of CaO and SrO addition.

In general, to form a solid oxide fuel cell (SOFC) in the mid-low temperature region, a cathode-supported structure is used. In this case, the cathode of Ni-GDC has an increased coefficient of thermal expansion compared to GDC due to the metal Ni portion. Therefore, there is a problem that the thermal shock resistance of the cell worsens due to the difference in thermal expansion with pure GDC which is an electrolyte.

The coefficient of thermal expansion of the GDC-MgO composite according to the present invention is preferably 12.5 × 10 ^-6 / ℃ to 13.5 × 10 ^-6 / ℃. The thermal expansion coefficients of the GDC-MgO composite show values of 12.5 × 10 ⁻⁶ / ° C. and 13.5 × 10 ⁻⁶ / ° C., which range from 12.5 × 10 ⁻⁶ / ° C. to 13.0, which is the thermal expansion coefficient of the cathode (Ni-GDC). Similar to x10 ^-6 / ° C, the formation of the MgO secondary phase can improve the mechanical strength of the solid electrolyte and the thermal shock resistance of the solid oxide fuel cell (SOFC).

According to another embodiment of the present invention, forming a gadolinia doped ceria (GDC) containing silicon dioxide; Mixing 0.3-20 mol% of magnesium oxide (MgO) with the gadolinian-containing ceria containing silicon dioxide to form a mixture; Forming and firing the mixture to form a gadolinian-added ceria (GDC) -magnesium oxide (MgO) complex provides a method for producing a solid electrolyte for a fuel cell comprising a;

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are provided by way of example to assist in the understanding of the present invention, and the scope of the present invention is not limited to the following examples.

Example

Example 1

After diluting the SiO ₂ sol to a concentration of 1/50, a pipette was used to place an amount corresponding to 500 ppm SiO ₂ in a container containing GDC, ethanol. Thereafter, ball milling and drying for 12 hours using a zirconia ball to prepare a fine powder of GDC containing 500 ppm of SiO ₂ . GDC powder containing 500 ppm SiO ₂ and 0.3 mol% MgO were mixed by a ball mill. The mixed fine powder was filled into a cylindrical mold, and cold isostatic pressed at a pressure of 150 MPa. Thereafter, the molded body was fired at a temperature of 1500 ° C. for 4 hours. After surface-molding the sintered compact, the Pt paste was prepared by screen printing, followed by heat treatment at 1000 ° C. for 1 hour to prepare a specimen.

Example 2

The same procedure as in Example 1 was carried out except that a GDC powder containing 500 ppm of SiO ₂ and 2 mol% of MgO were mixed by a ball mill.

Example 3

The same procedure as in Example 1 was carried out except that the GDC powder containing 500 ppm of SiO ₂ and 5 mol% of MgO were mixed by a ball mill.

Example 4

The same process as in Example 1 was carried out except that a GDC powder containing 500 ppm of SiO ₂ and 10 mol% of MgO were mixed by a ball mill.

Comparative Example 1

After diluting the SiO ₂ sol to a concentration of 1/50, a pipette was used to place an amount corresponding to 500 ppm SiO ₂ in a container containing GDC, ethanol. Thereafter, ball milling and drying for 12 hours using a zirconia ball to prepare a fine powder of GDC containing 500 ppm of SiO ₂ . GDC powder containing 500 ppm of SiO ₂ was filled into a cylindrical mold, and cold isostatic pressed at a pressure of 150 MPa. Thereafter, the molded body was fired at a temperature of 1500 ° C. for 4 hours. After surface-molding the sintered compact, the Pt paste was prepared by screen printing, followed by heat treatment at 1000 ° C. for 1 hour to prepare a specimen.

Comparative Example 2

A GDC powder containing 500 ppm SiO ₂ and 0.05 mol% MgO were mixed in the same manner as in Comparative Example 1 except that a ball mill was mixed.

Comparative Example 3

A GDC powder containing 500 ppm of SiO ₂ and 0.1 mol% of MgO were mixed in the same manner as in Comparative Example 1 except that a ball mill was mixed.

Comparative Example 4

After diluting the SiO ₂ sol to a concentration of 1/50, a pipette was used to place an amount corresponding to 500 ppm SiO ₂ in a container containing GDC, ethanol. Thereafter, ball milling and drying for 12 hours using a zirconia ball to prepare a fine powder of GDC containing 500 ppm of SiO ₂ . The GDC powder containing 500 ppm of SiO ₂ and the CaO content were mixed by a ball mill while changing the content of CaO to 0.05, 0.3, 1, 2, 5, 10 mol%. The mixed fine powder was filled into a cylindrical mold, and cold isostatic pressed at a pressure of 150 MPa. Thereafter, the molded body was fired at a temperature of 1500 ° C. for 4 hours. After surface-molding the sintered compact, the Pt paste was prepared by screen printing, followed by heat treatment at 1000 ° C. for 1 hour to prepare a specimen.

Comparative Example 5

GDC powder containing 500 ppm SiO ₂ and the content of SrO was changed to 0.05, 0.3, 1, 2, 5, 10 mol% and was carried out in the same manner as in Comparative Example 4 except for mixing by a ball mill.

Complex  Measurement of impedance

Complex impedances of the specimens according to Examples 1 to 4 and Comparative Examples 1 and 2 were measured at 450 ° C., and the results are shown in FIGS. 1A to 1F.

1A and 1B show the results according to Comparative Example 1 and Comparative Example 2, respectively, and FIGS. 1C to 1F show the complex impedances of Examples 1 to 4, respectively. Three impedance components appear from the low frequency region, and the low to three components correspond to the resistance due to electrode polarization, the grain boundary resistance (ρ _gb ), and the grain resistance (ρ _gi ).

Referring to FIG. 1A, SiO ₂ In the presence of 500 ppm, the grain boundary resistance of the specimen was 10 kΩ · cm. This is because a high resistance grain boundary phase containing SiO ₂ interferes with ion conduction at the grain boundary. Referring to FIG. 1B, when 0.05 mol% of MgO was added, the grain boundary resistance decreased to 5.6 kΩ · cm. Referring to Figure 1c, it can be seen that when the concentration of the added MgO is 0.3 mol% or more, the grain boundary resistance rapidly decreases to about 0.2 kΩ · cm. It means that the grain boundary resistance was reduced to about 1/50 by the addition of 0.3 mol% or more of MgO. 1D to 1F, even when MgO was added in an amount of 2 to 10 mol%, the grain boundary resistance was reduced to about 0.2 to 0.25 kΩ · cm.

Secondary Presence

SEM photographs of the specimens according to Examples 1 to 4 and Comparative Examples 1 and 2 were taken and are shown in FIGS. 2A to 2F. This is to calculate the particle size and to observe the presence of secondary phase.

Referring to FIG. 2A, the microstructure of the GDC specimen (Comparative Example 1) added with 500 ppm of SiO ₂ was uniform and had an average particle diameter of about 1.8 μm. 2B and 2C, when 0.05 mol% and 0.1 mol% of MgO were added (Comparative Example 2 and Comparative Example 3) in the microstructure, respectively, it was difficult to find a secondary phase and the microstructure was uniform. However, referring to FIG. 2D (Example 1), FIG. 2E (Example 2), and FIG. 2F (Example 3), it can be seen that a secondary phase appears when 0.3 mol% or more of MgO is added.

Change in resistance

Intragranular resistance (FIG. 3A), grain boundary resistance (FIG. 3B), average particle diameter (FIG. 3C), resistance per unit grain area (FIG. 3D), and SiO ₂ removal according to Examples 1 to 4 and Comparative Examples 1 to 3 The change in efficiency (Fig. 3e) is shown in Figs. 3a to 3f. Referring to FIG. 3A, it can be seen that the intragranular resistance is almost unchanged by the addition of MgO. Referring to FIG. 3B, it can be seen that when MgO is added at least 0.3 mol%, the grain boundary resistance decreases rapidly.

When the grain growth of GDC is promoted by the addition of MgO, the grain density per unit length may be reduced and thus the resistance of grain boundaries may be reduced. Therefore, in order to investigate the effect of MgO on the grain boundary resistance, it is necessary to calculate the resistance per unit grain area (R _gbs = ρ _gb / D = ρ _gb · d _g ) in which the grain boundary resistance is normalized to the grain boundary density. Where D is the grain boundary density and corresponds to the inverse of the particle diameter (d _g ). The resistance per unit grain area is shown in FIG. 3D. Referring to FIG. 3D, it can be seen that the resistance per unit grain area also decreases rapidly when MgO is added more than 0.3 mol%, and the reduction is about 1 / 40-1 / 50. Judgment of these results with respect to the presence of the secondary phase means that the precipitation of the secondary phase plays a decisive role in reducing the grain boundary resistance.

Electronic energy With loss spectroscopy (EELS)  Analysis results

The TEM image of the GDC according to Example 2 is shown in FIG. 4A, and the electron energy loss spectroscopy (EELS) analysis results in secondary phase, grain boundary, triple point, and mouth are shown in FIGS. 4B to 4E. That is to consider the mechanism to be the grain boundary phase is removed which includes the resistance of the SiO _2.

Referring to FIG. 4A, M1, M2, M3, M4, and M5 were shown as secondary phases rather than GDCs. Referring to FIGS. 4B to 4E, Mg and Si were detected together as a result of analyzing the second phase by using an Electro Energy Loss Spectrometry (EELS). Mg ₂ SiO ₄ was detected in all secondary phases, but MgO was also frequently found in other parts of TEM and EELS analysis. This means that a portion of the secondary phase present as MgO reacts with SiO ₂ to form Mg ₂ SiO ₄ . In the quantitative analysis, Mg: Si was found to be about 1: 0.6 by molar ratio. This means that MgO does not enter the lattice in the mouth and exists as a secondary phase, and forms a phase such as Mg ₂ SiO ₄ to remove the grain boundary phase including SiO ₂ having high resistance. On the other hand, SiO ₂ was not detected in all parts of the mouth (GI1, GI2, GI3, GI4, GI5), grain boundaries (GB1, GB2, GB3, GB4, GB5, GB6) and triple points (TPB1, TPB2). This means that the reaction of MgO secondary phase with SiO ₂ takes place very actively.

Change of lattice constant

The effects of addition of CaO and SrO were also investigated to confirm the difference between MgO added to GDC containing SiO ₂ and existing addition of CaO and SrO.

5 is a graph illustrating changes in lattice parameters according to Examples 1 to 4 and Comparative Examples 1 to 5 through XRD analysis. Referring to FIG. 5, in the case of Comparative Example 4 and Comparative Example 5 to which CaO and SrO were added, it can be seen that the lattice constant gradually increased according to the amounts of CaO and SrO added. The reason for this is the coordination number of Ca ²⁺ ion radius of 1.12Å when eight days, Sr ^{2 +} is 1.25Å, and the radius of the two ion Gd ^{3 +} ion (1.06 Å) and ionic radius of Ce ^{4 +} (0.97Å) Because of its larger size, the lattice constant was increased and absorbed into the mouth. Mg ^{2 +} is ion radius does not exist in the total electrostatic energy is large, stable lattice of 0.89Å so small that ions of the crystal than in the tetrahedral gaps spot size GDC precipitated second phase when the coordination number of 8.

6A and 6B show changes in resistance (R _gbs ) values per unit grain area when a concentration of MgO and CaO is added to a GDC containing 500 ppm SiO ₂ . 6A and 6B, the resistance of grain boundaries was lowered to 1/40 even when only 0.3 mol% of MgO was added, whereas the same effect was obtained only when 2 mol% of CaO was added. You can check it. In this case, it means that MgO exhibits a high removal effect even when a small amount is added, and it can be seen that the mechanism for improving grain boundary conduction by the two materials is completely different.

According to the present invention, the following effects can be obtained.

First, the method of adding magnesium oxide (MgO) to gadolinic-added ceria (GDC) can increase the grain boundary conductivity by the formation of a secondary phase.

Second, mechanical strength can be improved by forming a composite of gadolinian-added ceria-magnesium oxide (GDC-MgO) by MgO secondary phase generation.

Third, as the secondary phase fraction of MgO in gadolinic-added ceria (GDC) increases, the difference in coefficient of thermal expansion between the cathode and the electrolyte can be reduced.

Fourth, while conventional CaO and SrO are weak in water, MgO is more advantageous for use as a solid electrolyte for fuel cells because MgO is more resistant to water.

Claims (8)

Gadolinia doped ceria (GDC) containing silicon dioxide (SiO ₂ ) Gadolinia doped ceria (GDC) -MgO complex containing 0.3-20 mol% of magnesium oxide (MgO) Solid electrolyte for fuel cells containing. The method of claim 1, When the silicon dioxide is added 0.01 ~ 1 mol% compared to the GDC, the content of magnesium oxide (MgO) is more than twice the molar ratio with respect to the content of silicon dioxide, and 20 mol% or less with respect to gadolinian-added ceria (GDC) A solid electrolyte for a fuel cell, characterized in that. The method of claim 1, The thermal expansion coefficient of the GDC-MgO composite is a solid electrolyte for a fuel cell, characterized in that 12.5 × 10 ^-6 / ℃ to 13.5 × 10 ^-6 / ℃. The solid electrolyte of a fuel cell of claim 1, wherein the flexural strength of the GDC-MgO composite is 150 MPa to 300 MPa. Preparing Gadolinia Doped Ceria (GDC) containing silicon dioxide (SiO ₂ ); Mixing 0.3-20 mol% of magnesium oxide (MgO) with the gadolinian-containing ceria containing silicon dioxide to form a mixture; And Forming and firing the mixture to form a gadolinian-added ceria (GDC) -magnesium oxide (MgO) complex; a method for producing a solid electrolyte for a fuel cell comprising a. The method of claim 5, When the silicon dioxide is added 0.01 ~ 1 mol% compared to the GDC, the content of magnesium oxide (MgO) is more than twice the molar ratio with respect to the content of silicon dioxide, and 20 mol% or less with respect to gadolinian-added ceria (GDC) A method for producing a solid electrolyte for a fuel cell, characterized in that. The method of claim 5, The coefficient of thermal expansion of the GDC-MgO composite is 12.0 × 10 ^-6 / ℃ to 13.5 × 10 ^-6 / ℃ manufacturing method of a solid electrolyte for a fuel cell. The method of claim 5, Flexural strength of the GDC-MgO composite is a method of producing a solid electrolyte for a fuel cell, characterized in that 150 MPa to 300 MPa.

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