WO2013165079A1 - Cathode material for solid oxide fuel cell, composition for cathode containing thereof, cathode for solid oxide fuel cell, and solid oxide fuel cell - Google Patents

Abstract

A cathode material for a solid oxide fuel cell represented by chemical formula AA'_1-xCa_xB₂O_5+δ, and a fuel cell using the same are disclosed. In said chemical formula, A is a lanthanide element, A' is an alkaline earth metal element, B is a transition metal element, 0<x<1.0, and δ is a positive number of 1 or less, and thus the compound represented by chemical formula 1 is electrically neutral. It is possible to maintain electrical conductivity of a predetermined level or more while securing the stability of a cathode using the cathode material represented by said chemical formula.

Description

Cathode material for solid oxide fuel cell, composition for cathode comprising same, cathode for solid oxide fuel cell, and solid oxide fuel cell

The present invention relates to a solid oxide fuel cell. Specifically, the present invention relates to a solid oxide fuel cell having an oxide having a perovskite related structure as a cathode.

Solid oxide fuel cell (SOFC) is a high efficiency and environmentally friendly electrochemical power generation technology that directly converts the chemical energy of fuel gas into electrical energy. SOFCs are simpler in structure than other fuel cells because they are all solid, relatively inexpensive, and free from electrolyte loss and replenishment and corrosion. Solid oxide fuel cells can also use relatively high impurity fuels, and have many advantages, such as hybrid power generation capability and high efficiency. In addition, hydrocarbon-based fuels can be used directly without the need to reform the fuel into hydrogen, which can simplify fuel cell systems and reduce manufacturing costs.

SOFCs are anodes (anodes or anodes, cathodes) in which fuels such as hydrogen or hydrocarbons are oxidized, cathodes (cathodes or cathodes, anodes) in which oxygen gas is reduced to oxygen ions (O ^2- ), and oxygen ion conductivity in which oxygen ions are conducted. It contains a solid electrolyte and requires special physical properties depending on the type of material used.

Conventional SOFCs operate at high temperatures in the range of 800 to 1,000 ° C, the highest of all fuel cell types, so high temperature alloys or expensive ceramic materials must be used. There is a problem that the durability of the material during operation is reduced. In addition, there was a problem of rising overall costs, which is the biggest obstacle to commercialization. Accordingly, many studies have been conducted to develop a so-called medium-temperature solid oxide fuel cell (IT-SOFC) capable of generating electricity effectively even at an operating temperature of 800 ° C or lower, for example, about 400 to 800 ° C.

However, the reduction in operating temperature dramatically increases the electrical resistance of SOFC materials, which in turn serves as the main reason for reducing the power density of SOFCs. It is known that most of this electrical resistance, which is a problem in reducing the operating temperature, occurs at the cathode portion. Therefore, reducing the cathode resistance has become an important issue in lowering the operating temperature of SOFCs. Conventionally, Haile et al. Proposed Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode material in 2004. However, similar studies verifying the performance level proposed by Haile et al. Using this cathode material have not been published yet, and commercialization is not yet done.

The operation of SOFCs at these intermediate temperatures requires a novel combination of electrolytes and electrolyte materials that can quickly transport ions at the three-phase interface where oxygen reduction and fuel oxidation occur. It is not yet met.

In particular, the cathode material should have high oxygen reduction, high electron conductivity and high ion conductivity. When the electron conductivity is low, the electrons required for the anode reaction are not easily moved, and thus the efficiency of the electrochemical reaction is reduced. When the ion conductivity is low, the oxygen ion reaction generated through the cathode reaction is restricted and oxygen reduction reaction occurs. There is not enough active point.

On the other hand, the conventional cathode material is a phenomenon that the stability is sharply lowered as the use time increases. That is, the reduction of oxygen in the cathode does not occur smoothly, and as a result, a voltage drop occurs during operation of the SOFC system, which reduces the performance of the battery.

The technical problem of the present invention is to provide a novel cathode material and a method of manufacturing the same that can improve the stability of the cathode.

Another technical problem of the present invention is to provide a solid oxide fuel cell including the material.

In order to solve the above technical problem, in one aspect of the present invention, there is provided a cathode material for a solid oxide fuel cell, comprising a compound of formula RSQO _{5 + δ} , wherein R is one or more elements selected from the lanthanides, S is one or more elements selected from alkaline earth metal groups, Q is one or more elements selected from transition metals, O is oxygen, and δ is a positive number of 1 or less, and is represented by the formula RSQO _{5 + δ} It is the value which makes a compound electric neutral.

In order to solve the above technical problem, in one aspect of the present invention, there is provided a material for a solid oxide fuel cell cathode having a double-layer perovskite structure comprising a compound of formula (1).

<Formula 1>

AA ' _1-x Ca _x B ₂ O _{5 + δ}

In Formula 1, A is an element selected from lanthanides, A 'is an element selected from alkaline earth metal groups, and B is an element selected from transition metals, x is a number greater than 0 and less than 1.0, and δ is As a positive number of 1 or less, it is a value which makes the said compound of Formula 1 electrical neutral.

In one embodiment of the present invention, A may be any one of neodymium (Nd), praseodymium (Pr) or a mixture thereof. In addition, A 'is barium (Ba), B may be cobalt (Co).

In one embodiment of the invention, x is greater than 0 and less than or equal to 0.5.

In one embodiment of the present invention, Chemical Formula 1 is PrBa _1-x Ca _x Co ₂ O _{5 + δ} .

In order to solve the above technical problem, in one aspect of the present invention, there is provided a material for a solid oxide fuel cell cathode having a double-layer perovskite structure comprising a compound of formula (2).

<Formula 2>

AA ' _0.75 A'' _0.25 B _2-x B' _x O _{5 + δ}

In Chemical Formula 2, A is an element selected from lanthanides, A 'and A' 'are selected from alkaline earth metal groups, and B is an element selected from transition metals, wherein x is a number greater than 0 and less than 1.0. Is a positive number of 1 or less, and is a value that makes the compound of Formula 2 electrically neutral.

In one embodiment of the present invention, A is an element selected from the lanthanide group, among the elements selected from the alkaline earth metal group A 'is barium (Ba), A' 'is calcium (Ca), and B of the elements selected from the transition metal Cobalt (Co), B 'is iron (Fe), copper (Cu), manganese (Mn), nickel (Ni) and the like. X is a number greater than 0 and less than 1.0, and δ is a positive number of 1 or less, which is a value that makes the compound of Formula 2 electrically neutral.

In order to solve the above technical problem, in one aspect of the present invention, there is provided a material for a solid oxide fuel cell cathode comprising a compound of formula (3).

<Formula 3>

LnBa _a Sr _b Co _2-x Fe _x O _{5 + δ}

In Formula 3, Ln is samarium, neodymium, praseodymium, or a mixture thereof, wherein a and b are each greater than 0 and less than 1, and satisfies a + b = 1, and x is greater than 0 and less than 1.0 Is a positive number of 1 or less, and is a value that makes the compound of Formula 3 electrically neutral.

In one embodiment of the present invention, the a and the b may be 0.5. X may be 0.25 or more and 0.75 or less. X may be 0.25 or more and 0.50 or less.

In one embodiment of the present invention, the cathode material, PrBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} or NdBa _0.5 Sr _0.5 Co _{2 -x} Fe _x O _{5 + δ} It may be. X may be greater than 0 and less than or equal to 0.75. X may be 0.25 or more and 0.50 or less.

In another aspect of the present invention provides a cathode composition comprising the above-described cathode material for a solid oxide fuel cell, an oxygen ion conductive solid oxide and an organic binder. This composition may be in the form of a slurry. In one embodiment the oxygen ion conducting solid oxide is a group consisting of yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), samaria doped ceria (SDC), gadolinia doped ceria (GDC) and mixtures thereof You can choose from.

Another aspect of the present invention provides a cathode for a solid oxide fuel cell comprising the cathode material described above. This cathode may be a complex of an oxygen ion conducting solid oxide with a compound of formula 1, a compound of formula 2, or a compound of formula 3.

Another aspect of the present invention discloses a solid oxide fuel cell including the aforementioned cathode, an anode disposed facing the cathode, and an electrolyte that is an oxygen ion conducting solid oxide disposed between the cathode and the anode. The anode in this fuel cell is not particularly limited and a known anode can be used.

In yet another aspect of the invention, a method of making a cathode material is provided.

The manufacturing method includes dissolving metal oxide precursors in a solvent to obtain a precursor solution; Obtaining a solid from the precursor solution; Calcining the solid in air to obtain a calcined product; And polishing the calcined product, wherein the metal oxide precursors may be a mixture of Pr, Ba, Ca, and Co compounds in a stoichiometric ratio capable of producing a compound of Formula 4 below.

<Formula 4>

PrBa _1-x Ca _x Co ₂ O _{5 + δ}

In Formula 4, x is a number greater than 0 and less than 1.0.

The manufacturing method includes dissolving metal oxide precursors in a solvent to obtain a precursor solution; Obtaining a solid from the precursor solution; Calcining the solid in air to obtain a calcined product; And polishing the fired product, wherein the metal oxide precursors may be a mixture of Nd, Ba, Ca, Co and Fe compounds in a stoichiometric ratio capable of producing a compound of Formula 5 below.

<Formula 5>

NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ}

In Formula 5, x is a number greater than 0 and less than 1.0.

The manufacturing method includes dissolving metal oxide precursors in a solvent to obtain a precursor solution; Obtaining a solid from the precursor solution; Calcining the solid in air to obtain a calcined product; And polishing the calcined product, wherein the metal oxide precursors may be a mixture of Ln, Ba, Sr, Co, and Fe compounds in a stoichiometric ratio capable of producing a compound of Formula 6 below.

<Formula 6>

LnBa _a Sr _b Co _2-x Fe _x O _{5 + δ}

In Formula 6, x is a number greater than 0 and less than 1.0, and Ln is samarium, neodymium, praseodymium, or a mixture thereof.

According to one embodiment of the present invention, it is possible to provide a solid oxide fuel cell having improved oxygen reduction kinetics by reducing an area resistivity and increasing a three-phase interface in which a cathode reaction occurs.

According to one embodiment of the present invention, the stability of the cathode may be improved. In addition, the fuel cell can operate effectively even at low temperatures below 800 ° C.

1 is a diagram illustrating a double layer perovskite structure.

FIG. 2 is a lanthanide oxide of an aligned double perovskite crystal structure containing interstitial oxygen, showing a crystal structure of one oxide of praseodymium, barium and cobalt.

3 is a view showing an X-ray diffraction pattern according to the content of Ca in the embodiment of the present invention.

4 is a diagram illustrating an X-ray diffraction pattern of NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} according to the amount of Fe in the embodiment of the present invention.

Figure 5 is a graph showing the X-ray diffraction pattern of SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} by iron content in one embodiment of the present invention.

FIG. 6 is an Arrhenius graph illustrating the correlation between electrical conductivity and temperature for NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} .

7 is NdBaCo ₂ O _{5 + δ} and _{NdBa 0.75 Ca 0.25 Co 2-x} Fe x O 5 + δ (x = 0, 0.25) NdBa due to changes in partial pressure of oxygen gas in the operating temperature range with respect to _0.75 Ca _It is a graph which measured the ratio of the number of moles of oxygen with respect to _0.25 Co _2-x Fe _x O _{5 + δ} .

8 is NdBaCo ₂ O _{5 + δ} and _{NdBa 0.75 Ca 0.25 Co 2-x} Fe x O 5 + δ (x = 0, 0.25) NdBa due to changes in partial pressure of oxygen gas in the operating temperature range with respect to _0.75 Ca _It is a graph showing the change in electrical conductivity for _0.25 Co _2-x Fe _x O _{5 + δ} .

FIG. 9 shows the iron content of Area Specific Resistance obtained from the Nyquist plot showing the frequency spectrum of impedance at 600 ° C. for NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25). The graph shown by.

10 (a) to 10 (f) show the cross-sections of the cathode-electrolyte interface of the entire unit cell containing SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} cathode according to the iron content. The picture was taken using a microscope (FESEM).

FIG. 11 is a cross-sectional view of the cathode-electrolyte interface of a cathode-containing total unit cell of NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} having different iron contents using a field emission scanning electron microscope from Nova SEM. to be.

12 and 13 illustrate the results of measuring the stability of a fuel cell in one embodiment of the present invention.

FIG. 14 shows the results of measuring stability of a unit cell with respect to NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25) in the embodiment of the present invention. FIG.

FIG. 15 shows the results of measuring stability of a unit cell with respect to NdBaCo ₂ O _{5 + δ} (x = 0) in an embodiment of the present invention. FIG.

FIG. 16 is a diagram illustrating I-V polarization curves and maximum power densities of fuel cells according to Ca content in an embodiment of the present invention.

17 is a graph showing IV polarization curves for NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25).

FIG. 18 is a graph showing thermogravimetric analysis (TGA) results of iron content of NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ in which} oxygen content is generated according to temperature.

19 (a) and 19 (b) show the correlation between electrical conductivity and temperature for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. Areneus graph showing the relationship by iron content.

20 (a) and 20 (b) show the frequency spectra of impedances for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. Nyquist plot.

FIG. 21 is a Nyquist plot showing the frequency spectrum of impedance for NBSCF50 at 600 ° C. FIG.

22 (a) and 22 (b) are shown at 500 ° C. and 600 ° C. for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively, and FIG. 22 (c) shows SmBa _0.5 Sr _0.5 Co _2-x. The area specific resistance obtained from the Nyquist plot at 500 ° C. for Fe _× O _{5 + δ} is a graph showing the iron content.

23 (a) and 23 (b) show cathode polarization conductivity and temperature for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. Areneus graph showing correlations by iron content.

FIG. 24 shows the Arrhenius graph and activation energy of FIG. 23 (a).

25 shows the Arrhenius graph and activation energy of FIG. 23 (b).

FIG. 26 is a graph showing IV polarization curves for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} .

27 and 28 are graphs showing IV polarization curves for NdBa _0.5 Sr _0.5 Co ₂ O _{5 + δ} and NdBa _0.5 Sr _0.5 CoFeO _{5 + δ} , respectively.

29 is a graph showing the power density of a battery having an NBSCF-GDC cathode.

30 are graphs showing IV polarization curves for SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} .

FIG. 31 is a graph illustrating power density of the battery of FIG. 30.

32 (a) and 32 (b) are graphs showing power densities obtained from IV polarization curves according to iron content at 500 ° C. and 600 ° C. for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. .

The material for a solid oxide fuel cell cathode according to an embodiment of the present invention has the above-described double-layer perovskite crystal structure, and particularly, includes a compound in which a part of the element of A ′ is substituted with calcium. The compound may be represented by Formula 1 below.

[Formula 1]

AA ' _1-x Ca _x B ₂ O _{5 + δ}

In Formula 1, A is an element selected from lanthanides, A 'is an element selected from alkaline earth metal groups, and B is an element selected from transition metals, x is a number greater than 0 and less than 1.0, and δ is As a positive number of 1 or less, it is a value which makes the said compound of Formula 1 electrical neutral.

For example, in Formula 1, A may be one of neodymium (Nd), praseodymium (Pr), or a mixture thereof. In addition, A 'is barium (Ba), B may be cobalt (Co).

For example, in Formula 1, x is greater than 0 and less than or equal to 0.5.

For example, in Formula 1, it may be PrBa _1-x Ca _x Co ₂ O _{5 + δ} .

In the bilayer perovskite lanthanide compound of Chemical Formula 1, a lamination permutation of [BO ₂ ]-[AO]-[BO ₂ ]-[A'O] is basically repeated along the c-axis, and a part of A'O is It can be understood as a structure substituted with CaO.

Hereinafter, the present invention will be described in more detail. In interpreting the terms or words used in the present specification and claims below, the inventors must be conventional or not based on the principle that the inventors can appropriately define the concept of terms in order to best explain their invention. It should not be construed as being limited only to a dictionary meaning, but it should be understood that it should be interpreted as meanings and concepts corresponding to the technical spirit of the present invention as described herein.

In general, the electrochemical reaction of a solid oxide fuel cell is carried out through an anode reaction in which the oxygen gas O ₂ of the cathode is converted into an oxygen ion O ^2, as well as oxygen transferred through the fuel (H ₂ or hydrocarbon) and the electrolyte of the anode as shown in the following reaction formula. It consists of a cathode reaction in which ions react.

<Scheme>

Anode ^{_{reaction: 1/2 O 2 + 2e - -}} > O 2-

Cathode ^{_{reaction: H 2 + O 2- ->}} H 2 O + 2e -

In the cathode of the solid oxide fuel cell, oxygen adsorbed on the electrode surface is dissociated and diffused through the surface to the triple phase boundary where electrolyte, cathode, and pores meet to obtain electrons to become oxygen ions Since the ions move to the anode through the electrolyte, increasing the area of the three-phase interface in which the anode reaction occurs can improve the electrode reaction speed.

On the other hand, the simple perovskite structure represented by ABO ₃ has a large ion radius such as rare earth elements, alkaline rare earths, and alkaline elements at the A-site, which is the corner position of the cubic lattice. Is located, and has 12 coordination number (CN) by oxygen ion. In the B-site, which is the center of the cubic lattice, transition metals having a small atomic radius such as Co and Fe are located, and octahedral (6 coordination number) is formed by oxygen ions. Finally, oxygen ions are located at each core of the cubic lattice.

Such a simple perovskite structure generally has a structural displacement when another substance is substituted at the A-site, and its closest oxygen mainly around an element located at the B-site. Structural variation occurs in the octahedron of BO ₆ composed of six ions.

1 is a diagram illustrating a double-layer perovskite structure, a crystal lattice structure in which two or more elements are regularly arranged in an A-site, and may have a chemical formula of AA′B ₂ O _{5 + δ} . Such bilayer perovskite structures can impart improved ionic conductivity to the cathode by the presence of oxygen vacancies to facilitate the movement of ions.

In addition, the inventors have found that the use of novel lanthanide oxides in an ordered double perovskite structure with enhanced oxygen diffusivity and conductivity properties as cathode materials is suitable for medium temperature fuel cells. In the present specification, the aligned double perovskite refers to a crystal lattice structure in which A- or B-site ions are substituted with two or more elements in a general unaligned simple perovskite of ABO ₃ form.

FIG. 2 is a lanthanide oxide of an aligned double perovskite crystal structure containing interstitial oxygen, showing a crystal structure of one oxide of praseodymium, barium and cobalt.

As shown in Fig. 2, the aligned double perovskite has a structure in which A-site and B-site ions, in this case, praseodymium (Pr) and barium (Ba) are regularly arranged. Another example of an aligned double perovskite is NBSCo. In the perovskite of FIG. 2, NBSCo is replaced by neodymium (Nd) instead of praseodymium and strontium (Sr) instead of barium in place of A, and the Ba / Sr layer on the Nd layer due to the difference in atomic size of Nd and Ba / Sr. And again, Nd is regularly arranged thereon. However, in the case of unaligned perovskite, the atoms are disordered so that the layers do not separate regularly like aligned perovskite. For example, in the case of LaBaCo ₂ O _{5 + δ} , since La and Ba do not have much difference in atomic size, La and Ba may form layers in order to form an unaligned perovskite structure. However, this is exemplary and in the case of LaBaCo ₂ O _{5 + δ} according to the synthesis method, it is possible to form an aligned perovskite structure.

Solid oxide fuel cell cathode (cathode) material according to an embodiment of the present invention includes a compound of formula RSQO _{5 + δ} , wherein R is one or more elements selected from lanthanides, S is an alkaline earth metal group Is one or more elements selected from Q, Q is one or more elements selected from transition metals, O is oxygen, and δ is a positive number of 1 or less, which makes the compound of formula RSQO _{5 + δ} electrically neutral. Value.

The material for a solid oxide fuel cell cathode according to an embodiment of the present invention has the above-described double-layer perovskite crystal structure, and particularly, includes a compound in which a part of the element of A ′ is substituted with calcium. The compound may be represented by Formula 1 below.

[Formula 1]

AA ' _1-x Ca _x B ₂ O _{5 + δ}

In Formula 1, A is an element selected from lanthanides, A 'is an element selected from alkaline earth metal groups, and B is an element selected from transition metals, x is a number greater than 0 and less than 1.0, and δ is As a positive number of 1 or less, it is a value which makes the said compound of Formula 1 electrical neutral.

For example, in Formula 1, A may be one of neodymium (Nd), praseodymium (Pr), or a mixture thereof. In addition, A 'is barium (Ba), B may be cobalt (Co).

For example, in Formula 1, x is greater than 0 and less than or equal to 0.5.

For example, in Formula 1, it may be PrBa _1-x Ca _x Co ₂ O _{5 + δ} .

In the bilayer perovskite lanthanide compound of Chemical Formula 1, a lamination permutation of [BO ₂ ]-[AO]-[BO ₂ ]-[A'O] is basically repeated along the c-axis, and a part of A'O is It can be understood as a structure substituted with CaO.

While not intended to be bound by any particular theory regarding the principle of operation of the present invention, for illustrative purposes, the lamination permutations of [BO ₂ ]-[AO]-[BO ₂ ]-[A'O] are along the c-axis. Repeatedly, the oxygen bonding force in the [AO] layer is weakened, providing disordered vacancy, and as a result, the diffusion rate of oxygen ions in the cathode bulk when the cathode is formed is significantly improved, thus the oxygen of the molecular oxygen It is thought that the surface defect site | part which improves the reactivity to ions can be provided.

In Chemical Formula 1, when a part of A 'element is substituted with Ca, the performance and stability of the cathode is improved when the cathode is formed. As such, the performance of the cathode is improved because the electron conductivity is improved, and the stability is improved when the calcium is substituted (x = 0.25) than the calcium is not substituted as a result of the coulometric titration. This may be due to maintaining thermodynamic stability at lower oxygen partial pressures.

In Formula 1, A may be neodymium (Nd) or praseodymium (Pr) or a mixture thereof, and A ′ may be barium (Ba), strontium (Sr), or a mixture thereof. In addition, B may be cobalt (Co). As a specific example, Chemical Formula 1 may be PrBa _1-x Ca _x Co ₂ O _{5 + δ} . Hereinafter, for the convenience of description, the formula 1 is described as PrBa _1-x Ca _x Co ₂ O _{5 + δ} , but the present invention is not limited thereto, and may be a compound having various combinations of A, A ', and B described above. have.

The oxide of Formula 1 includes interstitial oxygen to improve conductivity of oxygen ions. In the oxide, δ represents an invasive oxygen and may have a value of 0 <δ ≦ 0.5, but is not limited thereto. The value of δ may be determined according to a specific crystal structure.

In the cathode material of Formula 1, the value of x, the stoichiometric coefficient of Ca, is greater than 0 and less than 1, specifically, greater than 0 and less than 0.5. When the x value of the cathode material is within the above range, the cathode material has excellent electrochemical characteristics, the development of secondary phases formed at the interface between the cathode and the electrolyte of the solid oxide fuel cell, and the thermal cycle effect ( Since the thermal cycling effect can be optimized, the performance and stability of the cathode can be improved.

The oxide of Formula 1 includes interstitial oxygen to improve conductivity of oxygen ions. In the oxide, δ represents an invasive oxygen and may have a value of 0 <δ ≦ 0.5, but is not limited thereto. The value of δ may be determined according to a specific crystal structure.

In the cathode material of Formula 1, the value of x, the stoichiometric coefficient of Ca, is greater than 0 and less than 1, specifically, greater than 0 and less than 0.5. When the x value of the cathode material is within the above range, the cathode material has excellent electrochemical characteristics, the development of secondary phases formed at the interface between the cathode and the electrolyte of the solid oxide fuel cell, and the thermal cycle effect ( Since the thermal cycling effect can be optimized, the performance and stability of the cathode can be improved.

Figure 3 shows the X-ray diffraction pattern according to the content of Ca in the embodiment of the present invention.

Referring to FIG. 3, when the stoichiometric coefficient x of Ca is 1.0, it can be seen that a heterogeneous substance having a peak that is completely different from when x has a value of 0, 0.25, or 0.5 is synthesized. This is inferred as a result of the structural interaction by the different ionic radii of each material.

On the other hand, in the case of the power density that has a significant effect on the electrical conductivity in the prior art was about 1.16 W / cm ² at 600 ℃, the highest level in the present invention, when some of Ba is replaced with Ca, the higher at the same 600 ℃ It has been found that maximum power density can be obtained. For example, when Ba is replaced with Ca so that x is about 0.25, it is possible to secure the stability of the cathode while having excellent electrical conductivity as compared with the prior art. Accordingly, the cathode material of the double layer perovskite structure of PrBa _1-x Ca _x Co ₂ O _{5 + δ} according to the present invention has the advantage of harmonizing excellent electrical conductivity and chemical stability due to proper substitution of calcium. .

In addition, the material for a solid oxide fuel cell cathode according to an embodiment of the present invention has the above-described double-layer perovskite crystal structure, and in particular, includes a compound in which a part of the element of A 'is substituted with calcium. . The compound may be represented by the following formula (2).

[Formula 2]

AA ' _0.75 A'' _0.25 B _2-x B' _x O _{5 + δ}

In Formula 2, A may be an element selected from lanthanides, A 'and A' 'may be different elements selected from alkaline earth metal groups, and B and B' are selected from transition metals. It may be another element. X may be a number greater than 0 and less than 1.0. Δ is a positive number of 1 or less, and may be a value that makes the compound of Formula 2 electrically neutral.

For example, in Formula 2, A may be any one of lanthanum (La), samarium (Sm), neodymium (Nd), praseodymium (Pr), gadolinium (Gd), or a mixture thereof.

For example, in Formula 2, A ′ may be barium (Ba), and A ″ may be calcium (Ca). Alternatively, in Formula 2, A ′ may be calcium (Ca) and A ″ may be barium (Ba).

For example, in Formula 2, B may be cobalt (Co), and B 'may be iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), or a mixture thereof.

In the bilayer perovskite lanthanide compound of Chemical Formula 2, the lamination permutation of [BO ₂ ]-[AO]-[BO ₂ ]-[A'O] is basically repeated along the c-axis, and a part of A'O is It can be understood as a structure substituted with CaO.

While not intended to be bound by any particular theory regarding the principle of operation of the present invention, for illustrative purposes, the lamination permutations of [BO ₂ ]-[AO]-[BO ₂ ]-[A'O] are along the c-axis. Repeatedly, the oxygen bonding force in the [AO] layer is weakened, providing disordered vacancy, and as a result, the diffusion rate of oxygen ions in the cathode bulk when the cathode is formed is significantly improved, thus the oxygen of the molecular oxygen It is thought that the surface defect site | part which improves the reactivity to ions can be provided.

In addition, in Chemical Formula 2, a part of A 'element is substituted with calcium (Ca), and due to the proper substitution of iron in place of B' element, it is possible to secure both sufficiently good electrical conductivity and stability of the cathode material. There is this.

In Formula 2, A may be lanthanum (La), samarium (Sm), neodymium (Nd), praseodymium (Pr), gadolinium (Gd), or a mixture thereof, and A 'may be barium (Ba), calcium (Ca) Or mixtures thereof. In addition, the B may be cobalt (Co), iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), or a mixture thereof. In addition, the B 'may be cobalt (Co), iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), or a mixture thereof. In addition, B may be cobalt (Co), and B 'may be iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), or a mixture thereof.

As a specific example, Chemical Formula 2 may be NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} . Hereinafter, for the convenience of description, Formula 2 is described as NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} , but the present invention is not limited thereto, and the compound having various combinations of A, A ', and B described above. Can be.

4 is a diagram illustrating an X-ray diffraction pattern of NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} according to the amount of Fe in the embodiment of the present invention.

The oxide of Formula 2 includes interstitial oxygen to improve conductivity of oxygen ions. In the oxide, δ represents an invasive oxygen and may have a value of 0 <δ ≦ 0.5, but is not limited thereto. The value of δ may be determined according to a specific crystal structure.

In the cathode material of Formula 2, the value of x, which is a stoichiometric coefficient of Fe, is greater than 0 and less than 1, specifically, 0 or more and 0.5 or less. When the x value of the cathode material is within the above range, the cathode material has excellent electrochemical characteristics, the expression of secondary phases formed at the interface between the cathode and the electrolyte of the solid oxide fuel cell and the thermal cycle effect (Thermal) Since the cycling effect can be optimized, the stability of the cathode can be improved.

When A 'includes Ba and includes A ″ in which a part of A' is substituted with Ca, excellent electrical conductivity can be ensured. In addition, in the case of including B 'in which a part of the B, which is a cobalt position that may be somewhat weak in terms of stability, is substituted with iron, stability may be increased. For example, it has been found that in this case a good performance of about 1.041 W / cm ² can be maintained at 600 ° C. even after 120 hours of stability experiments.

Therefore, the cathode material of the double layer perovskite structure of NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} according to the present invention can harmonize the excellent electrical conductivity and chemical stability due to the proper substitution of calcium and iron. There is an advantage to that.

In addition, the solid oxide fuel cell cathode (cathode) material according to an embodiment of the present invention has the above-described alignment double perovskite crystal structure, a solid oxide fuel cell comprising a lanthanide oxide of the formula (3) Providing materials for cathode

[Formula 3]

LnBa _a Sr _b Co _2-x Fe _x O _{5 + δ}

In Formula 3, Ln is samarium, neodymium, praseodymium, or mixtures thereof, wherein a and b are each greater than 0 and less than 1, and satisfies a + b = 1, and x is greater than 0 and less than 1.0 Δ is a positive number of 1 or less, and is a value that makes the compound of Formula 3 electrically neutral.

The alignment double perovskite lanthanide compound of Formula 3 is basically BaO / CoO ₂ / LnO _d / CoO ₂ in the ideal crystal structure in which the lamination permutation is repeated part of BaO is SrO, part of CoO ₂ is FeO ₂ It can be understood as a structure substituted with. Here, d is determined according to the specific crystal structure.

While not intending to be bound by any particular theory regarding the principle of operation of the present invention, for the sake of understanding, the ordered vacancy in the aligning double perovskite lanthanide oxides, when the cathode is formed, It is believed that the diffusion rate of oxygen ions in the cathode bulk can be significantly improved, and that the surface defect sites can be provided to improve the reactivity of molecular oxygen to oxygen ions.

The lanthanide oxide of Formula 3 includes interstitial oxygen to improve conductivity of oxygen ions. Δ corresponds to a value representing invasive oxygen in the oxide. For example, in one specific case, 0 <δ ≦ 0.5. The value of δ depends on the specific element type of Ln or the iron substitution ratio of cobalt (that is, the value of x).

In the cathode material of Formula 3, the value of x is greater than 0 and less than 1, specifically 0.25 or more and 0.75 or less, and more specifically 0.25 or more and 0.50 or less. When the x value of the cathode material is within the above range, the three-phase interface between the cathode, the electrolyte, and the oxygen of the solid oxide fuel cell is widened to increase oxygen ion conductivity and oxygen reduction kinetics of the material at medium temperature. The resistance of the cathode can be reduced. While not intended to be bound by any particular theory with regard to the working principle of the present invention, for the sake of understanding, it is impossible to form an aligned double perovskite structure when x is 0, and even when x is 1 or more, simple unaligned. It is believed that the advantage of the above-described alignment double perovskite structure cannot be obtained because of the change to the perovskite crystal structure.

The cathode material of the double-aligned perovskite structure of LnBa _a Sr _b Co _2-x Fe _x O _{5 + δ} according to the present invention has the advantage of harmonizing excellent electrical conductivity and chemical stability due to proper substitution of iron. have. In the case of the power density which has a large influence on the electrical conductivity, about 1.0 W / cm ² is the highest in the prior art at 600 degrees Celsius. However, the present invention has found that, for example, when Ln is neodymium, the maximum power density can be obtained at 600 degrees higher than that of a cathode material in which neodymium is equally employed but not substituted with Fe. In the cathode material of the present invention, when Ln is samarium or praseodymium, the maximum power density is similar to or better than that of the prior art.

In an embodiment of the present invention, an electric quantity titration experiment and an electrical conductivity experiment are simultaneously performed, and as the iron content in the cathode material is increased, the electrical conductivity is lowered, and the chemical stability of the cathode material is improved to an area where the oxygen partial pressure is lower. I found that. It has also been found that the cathode material of an unaligned simple perovskite structure with an iron stoichiometric coefficient x of 1.0 tends to be less chemically stable compared to the double perovskite structure. Thus, in at least some embodiments of the inventive cathode material, cobalt substitution with iron such that x is about 0.5 ensures chemical stability of the material while maintaining a certain level or more of electrical conductivity. Furthermore, in the cathode material of the present invention, by controlling the substitution ratio of strontium and barium, it is possible to compensate for the decrease in electrical conductivity which may occur due to iron substitution. In short, the cathode material of the present invention. In some embodiments, there may be some loss of electrical conductivity compared to conventional cathode materials with good conductivity, but because of the superior chemical stability, overall fuel cell performance may be improved.

In the cathode material of Chemical Formula 3, barium, strontium, and substitution rates a and b may be changed in a range where a + b = 1 and a and b satisfy a nonzero positive number. In one specific embodiment a = b = 0.5.

In one embodiment of the present invention, Ln is samarium and neodymium. When Ln is these elements, neodymium is advantageous in terms of high electrical conductivity and samarium in low coefficient of thermal expansion.

In one specific embodiment of the present invention, the cathode material of Chemical Formula 3 is PrBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} or NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and x is greater than 0 and less than 1. In a more specific embodiment, the cathode material of Formula 3 may include PrBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} or NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and x is greater than 0 and less than or equal to 0.75. In a more specific embodiment, the cathode material of Chemical Formula 3 is PrBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} or NdBa _0.5 Sr _0.5 Co _{2- x} Fe _x O _{5 + δ} , and x is 0.25 or more and 0.75 or less. In the most specific embodiment, the cathode material of Formula 3 may include PrBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} or NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , and x is 0.25 or more and 0.50 or less.

In one aspect of the present invention, a method of manufacturing the cathode material for a solid oxide fuel cell is disclosed. This manufacturing method comprises the steps of mixing (eg, wet using a solvent) with each metal precursor metered to the composition of Formula 1, Formula 2 or Formula 3, obtaining a solid from the (wet) mixture. And firing the solid in air to obtain a fired product and polishing the fired product.

The metal precursor is mixed in a stoichiometric ratio to obtain the compound of Formula 1 or Formula 2. Examples of the metal precursor may include, but are not limited to, nitrides, oxides, halides, etc. of Pr, Ba, Ca, and Co, which are each metal component constituting the cathode material of Formula 1 or Formula 2. Examples of the metal precursor may include, but are not limited to, nitrides, oxides, halides, etc. of Ln, Ba, Sr, Co, and Fe, which are each metal component constituting the cathode material of Formula 3.

For example, the metal oxide precursors may be a mixture of Pr, Ba, Ca, and Co compounds in stoichiometric ratios capable of producing a compound of Formula 4 below.

<Formula 4>

PrBa _1-x Ca _x Co ₂ O _{5 + δ}

In Formula 4, x is a number greater than 0 and less than 1.0.

For example, the metal oxide precursors may be a mixture of Nd, Ba, Ca, Co, and Fe compounds in a stoichiometric ratio capable of producing a compound of Formula 5 below.

<Formula 5>

NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ}

In Formula 5, x is a number greater than 0 and less than 1.0.

For example, the metal oxide precursors may be a mixture of Ln, Ba, Sr, Co, and Fe compounds in a stoichiometric ratio capable of producing a compound of Formula 6 below.

<Formula 6>

LnBa _a Sr _b Co _2-x Fe _x O _{5 + δ}

In Formula 6, x is a number greater than 0 and less than 1.0, and Ln is samarium, neodymium, praseodymium, or a mixture thereof.

Water may be used as the solvent used in the solvent mixing step, but is not limited thereto. Any metal that can dissolve the metal precursor can be used without limitation, for example, lower alcohol having a total carbon number of 5 or less such as methanol, ethanol, 1-propanol, 2-propanol, butanol and the like; Acidic solutions such as nitric acid, hydrochloric acid, sulfuric acid, citric acid; water; Organic solvents such as toluene, benzene, acetone, diethyl ether and ethylene glycol; Etc. may be used alone or in combination.

The mixing process is carried out at a temperature of about 100 to 200 ℃, it may be carried out for a predetermined time under stirring so that each component is sufficiently mixed.

The mixing process, the removal of the solvent and the addition of additives necessary for this are well known, for example, as the glycine nitrate process, and thus are not described herein.

After the mixing process, an ultrafine solid may be obtained by a spontaneous combustion process. The ultra-fine solids may then be heat treated (calcined, sintered) for about 1 hour to about 5 hours, for example at about 600 ° C. for about 4 hours in a temperature range of about 400 ° C. to about 950 ° C.

If necessary, a second heat treatment (calcination, sintering) may be performed after the firing. This second heat treatment step is a step of firing in air for about 1 hour to 12 hours at a temperature of about 800 to 1300 ° C., for example, about 12 hours at a temperature of about 1100 to 1150 ° C. to obtain a powdery product. do.

Subsequently, the fired product may be ground or pulverized to obtain a fine powder of a predetermined size. For example, milling and mixing by ball milling in acetone for about 24 hours. Next, the mixed powder is put into a metal mold and pressed, and the pressed pellet may be sintered in air to prepare a cathode material. Sintering may be performed in a temperature range of about 800 ° C. to about 1500 ° C. for about 5 hours to about 12 hours, for example, about 12 hours at a temperature of about 1100 to 1150 ° C., but is not limited thereto. The calcined product may be polished or pulverized to obtain a fine powder of a predetermined size.

Another aspect of the present invention provides a cathode composition further comprising the aforementioned cathode material for a solid oxide fuel cell and an oxygen ion conductive solid oxide and an organic binder. This composition may be in the form of a slurry. In one embodiment, the oxygen ion conductive solid oxide comprises yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), samaria doped ceria (SDC), gadolinia doped ceria (GDC), lanthanum strontium magnesium gallate ( LSGM) and mixtures thereof. The content of the cathode material and the oxygen ion conductive solid oxide in the cathode forming composition may be, for example, about 20 parts by weight to about 80 parts by weight based on 100 parts by weight of the cathode material.

A cathode may be prepared from the cathode composition. For example, the cathode composition may be coated on a substrate and then heat-treated to form a cathode.

The cathode thickness may typically range from about 1 μm to about 100 μm in a solid oxide fuel cell. For example, the thickness of the cathode may range from about 5 μm to about 50 μm.

Another aspect of the present invention discloses a solid oxide fuel cell including the aforementioned cathode, an anode disposed facing the cathode, and an electrolyte that is an oxygen ion conducting solid oxide disposed between the cathode and the anode. The anode in this fuel cell is not particularly limited and a known anode can be used.

The material constituting the solid oxide electrolyte is not particularly limited as long as it can be generally used in the art. For example, the following may be used as the solid oxide electrolyte. For example, the solid oxide electrolyte may be a stabilized zirconia system such as yttria stabilized zirconia (YSZ) and scandia stabilized zirconia (ScSZ); Ceria-based to which rare earth elements, such as Samaria doped ceria (SDC) and gadolinia doped ceria (GDC), are added; Other LSGM ((La, Sr) (Ga, Mg) O ₃ ) systems; Etc. can be used. In addition, as the solid oxide electrolyte, lanthanum gallate doped with strontium or magnesium may be used.

Since the solid oxide fuel cell may be manufactured using a conventional method known in various documents in the art, a detailed description thereof will be omitted herein. In addition, the solid oxide fuel cell may be applied to various structures, such as a cylindrical stack, a flat tubular stack, and a planar type stack.

The solid oxide fuel cell may be in the form of a stack of unit cells. For example, a unit cell (MEA, Membrane and Electrode Assembly) composed of the cathode, the anode and the solid oxide electrolyte is stacked in series and a separator is electrically connected between the unit cells. A stack of cells can be obtained.

EXAMPLE

Hereinafter, the present invention will be described in more detail with reference to Preparation Examples and Experimental Examples. The following examples are intended to illustrate the invention in detail and are not intended to limit the scope of the invention in any case.

Synthesis of Cathode Material: First Embodiment

Cathode PrBa _1-x Ca _x Co ₂ O _{5 + δ} having a stoichiometric coefficient x of Ca of 0, 0.25 or 0.50 was synthesized by a Pechini process.

In the stoichiometric ratio corresponding to PrBa _1-x Ca _x Co ₂ O _{5 + δ} according to each x, Pr (NO ₃ ) ₃ · 6H ₂ O (Aldrich, 99.9% based on metal), Ba (NO ₃ ) ₂ (Aldrich, 99% or more), Ca (NO ₃ ) ₂ 4H ₂ O (Alfa Aesar, 99.98% or more) and Co (NO ₃ ) ₃ .6H ₂ O (Aldrich, 98% or more) It was dissolved in distilled water together with ethylene glycol and citric acid.

After dissolution, the self-combustion process yields a very fine solid. The ultra-solid was heat-treated at 600 ° C. for 4 hours, then milled and mixed by ball milling in acetone for 24 hours, then dried, compressed into pellets at 5 MPa and 1100 ° C. in air for 24 hours. Sintered with.

Synthesis of Cathode Material: Second Example

Cathode NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} having a stoichiometric coefficient x of Fe of 0, 0.25 or 0.50 was synthesized by a Pechini process.

In the stoichiometric ratio corresponding to NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} according to each x, Nd (NO ₃ ) ₃ .6H ₂ O (Aldrich, 99.9% based on metal), Ba ( NO ₃ ) ₂ (Aldrich, 99% or more), Ca (NO ₃ ) ₂ 4H ₂ O (Alfa Aesar, 99.98% or more) and Co (NO ₃ ) ₃ · 6H ₂ O (Aldrich, 98% or more) ) Was dissolved in distilled water together with ethylene glycol and citric acid.

After dissolution, the self-combustion process yields a very fine solid. The ultra-solids were heat-treated at about 600 ° C. for about 4 hours, then milled and mixed in acetone for about 24 hours, then dried, compressed into pellets at about 5 MPa and in air Sintered at about 1150 ° C. for 12 hours.

Synthesis of Cathode Material: Third Example

SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} cathode material having a stoichiometric coefficient x of Fe of 0, 0.25, 0.50, 0.75 or 1.0 was synthesized by the glycine-nitrate process (GNP). .

The SmBa _0.5 Sr _0.5 (99.9% by Aldrich Corporation, metal _{basis) Co 2-x Fe x O} 5 + δ appropriate stoichiometric proportion to _{Sm (NO 3) 3 · H} 2 O , which in accordance with the respective x, Ba ( NO _{3) 2} (Aldrich Co., over _{99%), Sr (NO 3} ) 2 (Aldrich Co., over _{99%), Co (NO 3} ) 3 · H 2 O (Aldrich Co., 98%), and Fe (NO ₃ ) ₃ H ₂ O (Aldrich, 98%) was dissolved in distilled water together with glycine to obtain a solution.

The solution was heated to 350 ° C. in air and then subjected to a combustion reaction to form fine powder. The powder was calcined at 600 ° C. for 4 hours and then ground to obtain a primary powder. The primary powder was calcined again at 900 ° C. for 4 hours. For conductivity measurements and calorimetry titration, the calcined powder was compressed into pellets at 5 MPa and sintered at 1100 ° C. for 24 hours in air.

5 is an X-ray diffraction pattern of SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} prepared in Example 3. FIG. X-ray diffraction was measured by powder dispersion method of Cu Kα radiation using the diffractometer of Rigaku of Japan. In FIG. 5, x indicates the stoichiometric coefficient of iron of the formula SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ and} is 0, 0.25, 0.50, 0.75 or 1.

All SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} samples in FIG. 5 formed a single phase free of impurities after sintering at 1100 ° C. for 12 hours in air. X-ray diffraction results show a distinct doublet, which is characteristic of an aligned double perovskite structure at low iron content of 0.75 or less and clearly separated from each other. On the other hand, in the high iron content (x = 1) SBSCF, the X-ray diffraction spectrum does not overlap the single peak, which means that the crystal structure of x = 1 SBSCF is not an ordered double-aligned perovskite in order like the rest of SBSCF. It also shows that the degree may have been changed to an unaligned simple perovskite structure. Here, the aligned double perovskite structure where x is 0.75 or less is a space group Pmmm of a tetragonal system, and an unaligned simple perovskite crystal structure of poor order of x = 1 is a space group Pnma of a tetragonal system. Unit structure parameters and volume changes according to cobalt substitution of iron in the crystal lattice are summarized in Tables 1 and 2 below. As can be seen in Table 1 and Table 2, when x = 1.0, it is not easy to accurately determine whether the perovskite is aligned or unaligned perovskite. Table 1 and Table 2 show different volume values according to the interpretation of the spatial group of the SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} oxide.

Table 1

Structural Parameters of SmBa 0.5 Sr 0.5 Co 2-x Fe x O 5 + δ Oxide
x	Space	a (Å)	b (Å)	c (Å)	Volume
0	Pmmm	3.865	3.788	7.724	113.075
0.25	Pmmm	3.863	3.797	7.717	113.180
0.50	Pmmm	3.866	3.805	7.720	113.574
0.75	Pmmm	3.879	3.839	7.737	115.206
1.00 a	Pnma	5.476	5.457	7.689	229.767
a formula Sm 0.5 Ba 0.25 Sr 0.25 Co 0.5 Fe lattice parameter a volume basis in the 0.5 O 3 structure

TABLE 2

Structural Parameters of SmBa 0.5 Sr 0.5 Co 2-x Fe x O 5 + δ Oxide
x	Space	a (Å)	b (Å)	c (Å)	Volume
0	P4 / mmm	3.862	3.862	7.571	112.913
0.25	P4 / mmm	3.863	3.863	7.759	113.354
0.50	P4 / mmm	3.866	3.866	7.616	113.809
0.75	P4 / mmm	3.870	3.870	7.653	114.612
1.00	P4 / mmm	3.867	3.867	7.690	114.986

From the results in Table 1 and Table 2, the smaller the radius of Co ³⁺ (r = 0.545 Å) or Co ⁴⁺ (r = 0.530 Å) as the iron content in the crystal structure was increased, the larger the radius of Fe ³⁺ (r = 0.645 Å). ) Or Fe ⁴⁺ (r = 0.585 Å), the volume of the lattice increases. In the case of NBSCF cathode materials, the iron content was lower than 1, but the ordered double perovskite structure was shown, but the iron content of 1 was not the ordered double alignment perovskite like the rest of NBSCF, and the order was poorly aligned. It also shows that it may have been changed to a simple perovskite structure. As can be seen in Table 3 and Table 4, when x = 1.0, it is not easy to accurately determine whether the perovskite is aligned or unaligned perovskite. Tables 3 and 4 show different volume values depending on the interpretation of the spatial group of the NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} oxide.

TABLE 3

Structural Parameters of NdBa 0.5 Sr 0.5 Co 2-x Fe x O 5 + δ Oxide
x	Space	a (Å)	b (Å)	c (Å)	Volume
0	P4 / mmm	3.846	3.846	7.699	113.881
0.25	P4 / mmm	3.849	3.849	7.705	114.148
0.50	P4 / mmm	3.849	3.849	7.709	114.207
0.75	P4 / mmm	3.857	3.857	7.724	114.905
1.00 a	Pnma	5.485	5.466	7.702	230.925
a formula Nd 0.5 Ba 0.25 Sr 0.25 Co 0.5 Fe lattice parameter a volume basis in the 0.5 O 3 structure

Table 4

Structural Parameters of NdBa 0.5 Sr 0.5 Co 2-x Fe x O 5 + δ Oxide
x	Space	a (Å)	b (Å)	c (Å)	Volume
0	P4 / mmm	3.846	3.846	7.699	113.899
0.25	P4 / mmm	3.849	3.849	7.704	114.149
0.50	P4 / mmm	3.849	3.849	7.709	114.212
0.75	P4 / mmm	3.858	3.858	7.724	114.966
1.00	P4 / mmm	3.864	3.864	7.718	115.226

Synthesis of Cathode Material: Fourth Example

Cathode NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} having a stoichiometric coefficient x of Fe of 0, 0.25, 0.50, 0.75 or 1.0 was synthesized by the glycine-nitrate process (GNP). .

In the stoichiometric ratio corresponding to NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} according to each x, Nd (NO ₃ ) ₃ .6H ₂ O (Aldrich, 99.9% based on metal), Ba ( NO ₃ ) ₂ (Aldrich, 99% or more), Sr (NO ₃ ) ₂ (Aldrich, 99% or more), Co (NO ₃ ) ₃ · 6H ₂ O (Aldrich, 98% or more) and Fe (NO ₃ ) ₃ · 6H ₂ O (Aldrich, 98%) was dissolved in distilled water together with glycine to obtain a solution.

The solution was heated to 350 ° C. in air and then subjected to a combustion reaction to form fine powder. The powder was calcined at 600 ° C. for 4 hours and then ground to obtain a primary powder. The primary powder was calcined again at 900 ° C. for 4 hours. For conductivity measurements and calorimetry titration, the calcined powder was compressed into pellets at 5 MPa and sintered at 1100 ° C. for 24 hours in air.

Synthesis of Cathode Slurry

Cathode slurries were synthesized from the cathode materials of the first, second, third, and fourth embodiments using the following method, respectively.

After grinding the pellets of the cathode material of the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment, Ce _0.9 Gd _0.1 Gd _2-δ (hereinafter referred to as oxygen ion conductive oxide) Composite cathode) was prepared. The GDC was synthesized by the aforementioned glycine-nitrate method (GNP) using the metal nitrate and glycine. Specifically, the cathode material powder and the GDC powder were completely mixed in a weight ratio of 6: 4. All electrode powders were mixed with an organic binder (Heraeus V006) for slurry formation. The weight ratio of the cathode material powder, the GDC powder and the organic binder was mixed at 6: 4: 12.

Manufacture of Fuel Cells

For impedance measurement, a symmetric half cell of electrode / GDC / electrode structure was prepared. The GDC powder was compressed into pellets and sintered at 1350 ° C. for 4 hours in air to obtain a dense electrolyte. The cathode slurries corresponding to Example 1, Example 2, Example 3, and Example 4 were respectively applied so as to be symmetrical on both sides of this dense GDC electrolyte, and then sintered at 950 ° C. for 4 hours in air. It was.

The full single cell was manufactured by the co-press method. NiO powder, GDC powder and starch were mixed by ball milling in ethanol at a weight ratio of 6: 4: 1.5 for about 24 hours. The mixture was dried and compressed into pellets to form an anode. The anode surface of the Ni-GDC was then dispersed by air dispersion (co-press method) or by a drop coating method on the anode surface and sintered at about 1350 ° C. for about 5 hours in air. To form an electrolyte of GDC. Next, after screen printing the cathode slurries corresponding to Example 1, Example 2, Example 3, and Example 4 on the electrolyte, respectively, at about 1350 ° C. for about 4 hours in air or about Sintering was carried out at 950 ° C. to produce a fuel cell.

The formed cathode and electrolyte were each about 20 [mu] m thick and silver wire was attached to the cathode and anode using silver paste for current collection.

FIG. 6 is an Arennius graph illustrating the correlation between electrical conductivity and temperature for NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} of Example 2. FIG.

Electrical conductivity was measured by four terminal DC arrangement of the cathode of the corresponding cathode material in air. Silver wires were used as the probes of the four terminals. Current and voltage were measured using a potentiostat of BioLogic (Potentiaostat) at intervals of about 50 ° C. in the measurement interval of about 100 ° C. to about 900 ° C.

Referring to FIG. 6, it can be seen that as the iron content of the cathode material of Example 2 increases, and as the temperature increases, electrical conductivity decreases. Aligned double perovskite crystal systems exhibited a metallic behavior of decreasing electrical conductivity with increasing temperature above 300 ° C.

The cathode of a fuel cell is a porous composite structure that requires high ionic conductivity, large surface area for rapid reactivity, and a three phase boundary where gases, ions, and electrons can react together. All of these properties also change with the constituents of the material and with the catalytic material being a trace additive. Cathode is measured in the state exposed to air differently from anode, but the literature reports that the low partial pressure environment is created at the interface between the cathode material and the electrolyte.

7 is NdBaCo ₂ O _{5 + δ} and _{NdBa 0.75 Ca 0.25 Co 2-x} Fe x O 5 + δ (x = 0, 0.25) NdBa due to changes in partial pressure of oxygen gas in the operating temperature range with respect to _0.75 Ca _It is a graph which measured the ratio of the number of moles of oxygen with respect to _0.25 Co _2-x Fe _x O _{5 + δ} .

8 is NdBaCo ₂ O _{5 + δ} and _{NdBa 0.75 Ca 0.25 Co 2-x} Fe x O 5 + δ (x = 0, 0.25) NdBa due to changes in partial pressure of oxygen gas in the operating temperature range with respect to _0.75 Ca _It is a graph showing the change in electrical conductivity for _0.25 Co _2-x Fe _x O _{5 + δ} .

FIG. 9 shows the iron content of Area Specific Resistance obtained from the Nyquist plot showing the frequency spectrum of impedance at 600 ° C. for NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25). It is a graph shown according to.

NdBa of Example 2_0.75Ca_0.25Co_2-xFe_xO_{5 + δ}7 and 8 show the results of measuring the ratio of oxygen in the measurement cathode material to the number of moles of the cathode material according to the change in the partial pressure of oxygen gas using the cathode material. It was. NdBa with both calcium and iron substituted_0.75Ca_0.25Co_2-xFe_xO_{5 + δ}(x = 0.25) NdBa without calcium or iron substitution_0.75Ca_0.25Co₂O_{5 + δ}I NdBaCo₂O_{5 + δ}It can be seen that the ratio of oxygen in the cathode material can be maintained at a lower oxygen partial pressure. In addition, by measuring the electrical conductivity at each oxygen partial pressure, the change in electrical conductivity could also be compared and observed.

10 (a) to 10 (f) show the cathode-electrolyte interface of the entire unit cell including the cathode of SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} (SBSCF) of the third embodiment by iron content The cross section of the photo was taken using a field emission scanning electron microscope (FESEM) from Nova SEM.

10 (a) shows a cross section of the cathode and the GDC electrolyte, and the thickness of the cathode and the electrolyte is about 20 μm. 10 (b) to FIG. 10 (f) are SEM photographs showing the cross-section of the SBSCF-GDC composite according to the iron content, and the microstructure does not seem to have a large difference according to the iron content. The thickness of the cathode was about 20 μm and the thickness of the GDC electrolyte was about 20 μm. In addition, to improve the performance, the thickness of the GDC electrolyte was improved to 10 to 15 μm. It can be confirmed that the manufacturing of the unit cell manufactured from FIG. 10 was successful because there were no holes, voids, or cracks. All of these cells have similar microstructures, suggesting that iron content does not significantly affect the microstructures.

11 is a scanning electron micrograph of the cross-section of the entire unit cell including the NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} (NBSCF) cathode of the fourth embodiment by iron content.

In Figure 11, NBSCF25 in the formula x = 0.25, NBSCF50 in the formula x = 0.50, NBSCF75 in the formula x = 0.75, NBSCF10 indicates x = 1.0 in the formula. 11 (a) to 11 (e), the microstructure of the NBSCF-GDC composite also seems to have no significant difference in the microstructure according to the iron content as in the SBSCF-GDC composite.

Stability Measurement of Fuel Cell of Cathode Material of Example 1

The stability of the cathode material, the GDC electrolyte, and the NiO-GDC composite anode battery of Example 1 was evaluated.

12 and 13 illustrate the results of measuring the stability of a fuel cell in one embodiment of the present invention.

The fuel cell to be evaluated includes a cathode formed of a cathode material of PrBa _1-x Ca _x Co ₂ O _{5 + δ} (x = 0.25) and PrBa _1-x Ca _x Co ₂ O _{5 + δ} (x = 0.5), The result when x = 0.25 is shown in FIG. 12, and the result when x = 0.5 is shown in FIG.

Specifically, FIG. 12 is a result of measuring a change in voltage when a constant current of -400 mA is applied at 600 ° C. for 100 hours, and FIG. 13 is a case where a constant voltage of 700 mV is applied at 600 ° C. for 100 hours. This is the result of measuring the change of current.

As shown in Figs. 12 and 13, it can be seen that the response while driving is quite stable, and that no detectable voltage or current drop has occurred. Therefore, when the cathode is formed using the cathode material according to the present invention, it can be seen that the fuel cell including the same has excellent stability.

However, when cathodes were made of PrBa _1-x Ca _x Co ₂ O _{5 + δ} cathode material with _x 0.25, a total of 3.3% current loss occurred over 100 hours, whereas PrBa _1-x Ca with _x 0.5 _{When the} cathode was manufactured from a cathode material of _x Co ₂ O _{5 + δ} , a total voltage loss of 10% was observed under the same conditions. Hereinafter, as shown in FIG. 12, when x is 0.25, 0.5 is 0.5. It can be seen that it is superior in terms of stability than the case.

Stability Measurement of Fuel Cell of Cathode Material of Example 2

The stability of the cathode material of Example 2, the GDC electrolyte, and the entire NiO-GDC composite anode battery was evaluated.

FIG. 14 shows the results of measuring stability of a unit cell with respect to NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25) in the embodiment of the present invention. FIG. FIG. 15 shows the results of measuring stability of a unit cell with respect to NdBaCo ₂ O _{5 + δ} (x = 0) in an embodiment of the present invention. FIG.

The fuel cell to be evaluated includes a cathode formed of a cathode material of NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25), and the result of x = 0.25 is shown in FIG. , FIG. 15 shows the case where x = 0 and the result of NdBaCo ₂ O _{5 + δ} .

Specifically, FIG. 14 is a result of measuring a change in current when a constant voltage of about 700 mV is applied at about 600 ° C. for about 150 hours. 15 is a result of measuring the change in voltage when a constant current of about -400 mA is applied at about 550 ° C. for about 100 hours.

As shown in Figs. 14 and 15, it can be seen that the response while driving is quite stable, and that no detectable voltage or current drop has occurred. Therefore, when the cathode is formed using the cathode material according to the present invention, the fuel cell including the same can be expected to have excellent stability.

As shown in FIGS. 14 and 15, in the case of NdBaCo ₂ O _{5 + δ} without substitution of calcium and iron, voltage loss of about 50% or more occurred at about 600 ° C. for about 100 hours. In the case where the unit cell was made of a cathode material of NdBa _0.75 Ca _0.25 Co ₂ O _{5 + δ} in which x was 0, total voltage loss of 11.1% occurred under the same conditions. On the other hand, when the unit cell was made of a cathode material of NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} having x of 0.25, a total current loss of 2% occurred for about 150 hours at the same temperature. Therefore, as shown in FIG. 14 and FIG. 15, when calcium and iron are appropriately substituted, it can be seen that they are excellent in terms of both power density and stability.

Power Density of Fuel Cell of Cathode Material of Example 1

The electrochemical performance of the cathode material, the GDC electrolyte, and the NiO-GDC composite anode total battery of Example 1 was evaluated. The cathode material comprises a compound of PrBa _1-x Ca _x Co ₂ O _{5 + δ} .

FIG. 16 is a diagram illustrating I-V polarization curves and maximum power densities of fuel cells according to Ca content in an embodiment of the present invention.

FIG. 16 shows the I-V polarization curves when x is 0, 0.25 and 0.5, and the maximum power density according to the value of x at 600 ° C. On the other hand, I-V polarization curve was measured at 500 to 650 ℃ using a constant potential device of BioLogic. Specifically, the I-V polarization curve used humidified hydrogen gas (3% moisture) as a fuel and a stationary ambient air as an oxidant at 500 to 650 ° C.

Referring to FIG. 16, it can be seen that power density increases as x has a value of 0.25 or 0.5, compared to when x is 0. Specifically, the maximum power density when x is zero, at 600 ℃ is 1.161W / cm ^2, while being on, x is a maximum power density of 0.25 when il is the 1.484W / cm ^2, x has a maximum power density when 0.5 days 1.218 W / cm ² . This is judged to be superior to the prior art in which the power density was about 1.16 / cm ² at 600 ° C. at the highest level.

From the above examples, it was confirmed that the double-layered perovskite structure lanthanide oxide cathode material of the present invention makes it possible to manufacture a solid oxide fuel cell exhibiting excellent electrochemical performance at a medium temperature below 800 ° C.

Power Density of Fuel Cell of Cathode Material of Example 2

The electrochemical performance of the cathode material of Example 2, the GDC electrolyte, and the entire NiO-GDC composite anode battery was evaluated. The cathode material comprises a compound of PrBa _1-x Ca _x Co ₂ O _{5 + δ} .

17 is a graph showing IV polarization curves for NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} (x = 0, 0.25).

FIG. 17 shows I-V polarization curves and maximum power density when x is 0, 0.25. On the other hand, I-V polarization curve was measured in the range of about 500 ℃ to about 650 ℃ using a constant potential device of BioLogic. Specifically, the I-V polarization curve used humidified hydrogen gas (3% moisture) as the fuel and stationary ambient air as the oxidant in the range of about 500 ° C to about 650 ° C.

Referring to FIG. 17, it can be seen that power density improves as x has a value of 0.25 as compared with when x is 0. Specifically, the maximum power density when x is zero at about 600 ℃ is 1.263 W / cm ² being, x is a maximum power density of 0.25 days, while when the was 1.331 W / cm ^2. This is judged to be superior to the prior art in which the power density was about 1.16 W / cm ² at 600 ° C. at the highest level.

From the above examples, it was confirmed that the double-layered perovskite structure lanthanide oxide cathode material of the present invention enables the production of a solid oxide fuel cell exhibiting excellent electrochemical performance at a medium temperature of about 800 ° C. or less.

Thermal Stability of Cathode Materials of Example 3

FIG. 18 is a graph showing thermogravimetric analysis (TGA) results of iron content of NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ in which} oxygen content is generated according to temperature. The vertical axis represents the reduction in oxygen content in weight percent based on before heating, and the horizontal axis is the heating temperature.

Thermogravimetric analysis was measured in air over 100 ° C. to 900 ° C. at a heating / cooling rate of 2 ° C. per minute using a SDT-Q600 thermogravimetric analyzer from TA instruments, USA. The initial room temperature oxygen content was determined by indirect iodometric titration in air.

18, it can be seen that the thermal stability of the NBSCF cathode material according to one embodiment of the present invention, evaluated for the degree of maintenance of oxygen content, is a sufficient level for use at an operating temperature of 800 ° C or lower. Because of the loss of interstitial oxygen in the lattice, NBSCF samples began to lose oxygen from 200 ° C. From the relationship between the degree of loss of interstitial oxygen and the iron content, one can infer that oxygen binds more strongly with iron than cobalt in the lattice. This is consistent with the standard product free energy of Fe ₃ O ₄ (-1017.438 kJ / mol) being greater than the standard product free energy of Co ₃ O ₄ (-794.871 kJ / mol).

Electrical Conductivity of Cathode Materials of Examples 3 and 4

19 (a) and 19 (b) show the correlation between electrical conductivity and temperature for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. Areneus graph showing the relationship by iron content.

An arehenius graph showing the correlation between the electrical conductivity and temperature of the NBSCF and SBSCF cathode materials synthesized in Examples 3 and 4 is shown in FIGS. 19 (a) (NBSCF) and 19 (b) (SBSCF). .

Electrical conductivity was measured by four terminal DC arrangement of the cathode of the cathode material in air. Silver wires were used as the probes of the four terminals. Current and voltage were measured using a potentiostat of BioLogic at intervals of 50 ° C. at a measurement interval of 100 to 900 ° C.

19, it can be seen that the electrical conductivity decreases as the iron content of the cathode material increases and as the temperature increases. However, in the case of SBSCF, the electrical conductivity monotonously decreased as the iron content increased from 0 to 0.75 at the same temperature. However, when x = 1.0 which is determined to not maintain a stable alignment double perovskite structure, the electrical conductivity was It was located between the aligned double perovskite SBSCFs with x = 0 and x = 0.25. In the case of x = 1.0, at the temperature above 300 ° C, the electrical conductivity decreased as the temperature increased. On the other hand, when x = 1.0, the electrical conductivity increases as the temperature increases and then decreases as the temperature exceeds 350 ° C, which is a transition from the semiconductor to the metallic behavior.

Area resistivity of symmetric cathode half cells of Examples 3 and 4

20 (a) and 20 (b) show the frequency spectra of impedances for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. Nyquist plot.

The area specific resistance behaviors of the NBSCF-GDC and SBSCF-GDC composite cathode symmetric half-cells synthesized in Examples 3 and 4 at 600 ° C. are shown in FIG. 20 (a) (NBSCF) and FIG. 20 (b). (SBSCF). In the half cell for measuring the area resistivity, a silver wire was connected to both electrodes using silver paste as a current collector. This half cell was fixed to the alumina tube using a ceramic adhesive. Impedance spectroscopy measurements were made under open circuit voltage (OCV) over a frequency range of 500 kHz to 1 MHz with an AC perturbation of 14 mA in the range 500 ° C. to 650 ° C. using a constant potential device from BioLogic.

Area resistivity is an indicator covering all resistance elements associated with an electrode, i.e. resistance occurring at the gas-cathode interface, in the bulk of the cathode, or at the cathode-electrolyte interface. Area resistivity is defined as the impedance intercept value for the real axis of the Nyquist plot between high and low frequencies. The area resistivity of the NBSCF cathodes in Fig. 20 (a) is 0.105 Ωcm ² , 0.066 Ωcm ² , 0.087 Ωcm ² , 0.106 Ωcm ² and 0.179 Ω · in order of increasing iron content at 600 ° C., respectively. cm ² .

FIG. 21 is a Nyquist plot showing the frequency spectrum of impedance for NBSCF50 at 600 ° C. FIG.

Referring to FIG. 21, in the case of NBSCF50, when ASR was measured by blowing air, the result was 0.066 Ω · cm ² at 600 ° C., which is an improvement over the previous 0.087 Ω · cm ² .

NBSCF-GDC composite cathode had the lowest area resistivity at the measurement temperature when compared to the area resistivity measured at 500 ℃ and 550 ℃. At 500 ℃, 0.441 Ωcm ² , 600 ℃ Was 0.066 Ωcm ² . This is considered to be the lowest value of the area resistivity at 500 ° C of cathodes published to date.

22 is a graph showing the area resistivity of NBSCF measured at 500 ° C. and 600 ° C. and SBSCF measured at 500 ° C., based on iron content.

22 (a) and 22 (b) are shown at 500 ° C. and 600 ° C. for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively, and FIG. 22 (c) shows SmBa _0.5 Sr _0.5 Co _2-x. The area specific resistance obtained from the Nyquist plot at 500 ° C. for Fe _× O _{5 + δ} is a graph showing the iron content.

As the iron content increases at 500 ° C, the area resistivity decreases to 0.5 Ω · cm ² and then increases again. It can be seen that the aligned double perovskite structure is significantly lower than the case where the area resistivity of the positive cathode material (x ≠ 1) is x = 1.

In general, as the concentration of the mobile oxygen species increases, the rate of oxygen reduction reaction may increase. It is not intended to be bound by any particular theory regarding the working principle of the present invention, but for the sake of understanding, the oxygen reduction kinetics also increases as the iron content increases and the invasive oxygen concentration increases in the Ln-O layer. The cobalt: iron ratio is thought to be accelerated until it reaches 3: 1 (ie x = 0.5). However, higher iron content at this point changes the structure of the oxide with less orderly simple perovskite in the ordered double perovskite where the cations form an orderly arrangement.

It can be seen that the SBSCF-GDC cathode of FIG. 20 (b) also has an impedance behavior similar to that of the NBSCF-GDC cathode. In the case of SBSCF-GDC, the rate of oxygen reduction reaction seems to be the fastest when the Fe content x is about 0.50 and 0.75, unlike NBSCF-GDC. However, when iron is doped to x, the stability of the aligned double perovskite structure is deteriorated and the rate of oxygen reduction is slowed.

Cathode Polarization Conductivity of Examples 3 and 4

23 (a) and 23 (b) show cathode polarization conductivity and temperature for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} and SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. Areneus graph showing correlations by iron content.

Arrhenius graphs of NBSCF and SBSCF cathode polarization conductance are shown in FIGS. 23 (a) (NBSCF) and 23 (b) (SBSCF), respectively.

From the data in FIG. 23 (a), the apparent activation energy of NBSCF was 105.76 kJ / mol, 95.46 kJ / mol, 101.81 kJ / mol for iron content (x) 0, 0.25, 0.50, 0.75 and 1.0, respectively. , 104.98 kJ / mol and 126.46 kJ / mol. This apparent activation energy shows that the ordered aligned double perovskite structure has lower activation energy than the less ordered unaligned simple perovskite structure.

FIG. 24 shows the Arrhenius graph and activation energy of FIG. 23 (a).

Referring to FIG. 24, the activation energy of the NBSCF-GDC as measured as described above was supplied with air of 101.07 kJ / mol, 90.08 kJ / mol, and 107.55 kJ / for iron contents (x) of 0, 0.5, and 1.0. improved to mol

It can be seen that the SBSCF-GDC cathode of FIG. 23 (b) also has an activation energy similar to that of the NBSCF-GDC cathode. The activation energy of the SBSCF-GDC cathode was 125.28 kJ / mol, 116.88 kJ / mol, 104.59 kJ / mol, 112.15 kJ / mol and 119.93 kJ / mol, respectively. In other words, it shows that the activation energy is minimal near x = 0.5, and the activation energy appears somewhat larger in the case of the unaligned perovskite structure x = 1.0 and in the absence of iron (x = 0.0). have.

25 shows the Arrhenius graph and activation energy of FIG. 23 (b).

Referring to FIG. 25, the activation energy of SBSCF-GDC as measured as described above was supplied with 114.06 kJ / mol, 101.13 kJ / mol, and 112.23 kJ / for iron content (x) of 0, 0.5, and 1.0. improved to mol

Power Density of the Whole Cell of Examples 3 and 4

FIG. 26 is a graph showing IV polarization curves for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} .

The electrochemical performance of the composite cathode material of NBSCF and SBSCF, GDC electrolyte, and NiO-GDC composite anode cells obtained in Examples 3 and 4 was evaluated. IV polarization curves were measured at 500 to 650 ° C. using a constant potential device from BioLogic. Humidified hydrogen gas (3% moisture) was used as the fuel at 500 to 650 ° C, and stationary ambient air was used as the oxidant. 26 (a) to 26 (e) are graphs showing IV polarization curves and power densities measured for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} -GDC cathode containing cells in order of increasing x value to be. The maximum power densities of NdBa _0.5 Sr _0.5 Co ₂ O _{5 + δ} aligned double perovskite structure with x = 0 are 0.246, 0.482, 0.814 and 1.152 W / cm ² at 500 ° C, 550 ° C, 600 ° C and 650 ° C, respectively. It was. On the other hand, NdBa _0.5 Sr _0.5 CoFeO _{5 + δ} unaligned simple perovskite structures with x = 1 have power densities of 0.215, 0.451, 0.814 and 1.225 W / 500 at 500 ° C, 550 ° C, 600 ° C and 650 ° C, respectively. cm ² . This result indicates that the lower order NdBa _0.5 Sr _0.5 CoFeO _{5 + δ} maximum power density is relatively lower at higher temperatures than the highly ordered NdBa _0.5 Sr _0.5 Co ₂ O _{5 + δ} . If the thickness of the electrolyte is reduced to 10-15 um and the electrode manufacturing method is changed to the drop coating method, the performance is further improved.

27 and 28 are graphs showing IV polarization curves for NdBa _0.5 Sr _0.5 Co ₂ O _{5 + δ} -GDC and NdBa _0.5 Sr _0.5 CoFeO _{5 + δ} -GDC, respectively.

Referring to FIG. 27, the maximum power densities of the NdBa _0.5 Sr _0.5 Co ₂ O _{5 + δ} aligned double perovskite structure were 0.55, 1.06, 1.69 and 2.35 W / at 500 ° C, 550 ° C, 600 ° C and 650 ° C, respectively. cm ² .

Referring to FIG. 28, the maximum power density for NdBa _0.5 Sr _0.5 CoFeO _{5 + δ} is improved to 0.56, 1.01, 1.57 and 2.07 W / cm ² at 500 ° C., 550 ° C., 600 ° C. and 650 ° C., respectively.

It is also clear that at lower temperatures the electrochemical performance of the oxide cathodes of the unaligned simple perovskite structure is significantly lower than the aligned double perovskite cathodes. In the relationship between the iron content and the electrochemical performance, NBSCF increased the iron content and the electrochemical performance up to x = 0.25 based on the iron content, and then decreased again after 0.25. For example, a battery having an NBSCF-GDC cathode at 600 ° C. is considered to be the best among previously reported values with a power density of 1.104 W / cm ² .

29 is a graph showing the power density of a battery having an NBSCF-GDC cathode.

Referring to FIG. 29, when the manufacturing method is improved as described above, the power density becomes 1.95 W / cm ² . It was 0.63, 1.17, 2.52 W / cm <^2> at 500 degreeC, 550 degreeC, and 650 degreeC, respectively.

FIG. 30 is a graph showing IV polarization curves and power densities measured for SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ-} GDC cathode containing cells in order of increasing iron content (x).

SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} -GDC cathode showed the highest electrochemical performance with the maximum power density of 0.964 W / cm ² at 600 ° C when the Fe content was 0.50.

FIG. 31 is a graph illustrating power density of the battery of FIG. 30.

Referring to FIG. 31, when the manufacturing method is improved, the maximum power density is improved to 1.56 W / cm ² .

32 (a) and 32 (b) are graphs showing power densities obtained from IV polarization curves according to iron content at 500 ° C. and 600 ° C. for NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , respectively. .

As shown in FIGS. 32 (a) and 32 (b), the performance (x = 0.25, 0.50 and 0.70) of the NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ-} GDC cathode-containing battery was x = 0.5. It was the best exceeding 1 W / cm ² at 600 ℃ when, the higher the iron content was reduced the electrochemical performance.

From the above examples, it was confirmed that the aligning double perovskite structure lanthanide oxide cathode material of the present invention makes it possible to manufacture a solid oxide fuel cell exhibiting excellent electrochemical performance at a medium temperature below 800 ° C.

Although the present invention has been described with reference to specific contents and some embodiments as described above, it should be understood that this is only a description given as a specific example in order to help a more general understanding of the present invention. The present invention is not limited to the above-described embodiments, and those skilled in the art may make various modifications and variations to such embodiments, and such modifications and variations are also within the spirit of the present invention. Covered in

Accordingly, the embodiments described above and the appended claims, as well as all equivalents and equivalent modified embodiments of the claims, fall within the scope of the present invention.

Claims (25)

1. A cathode material for a solid oxide fuel cell, comprising a compound of formula RSQO _{5 + δ} :

   R is one or more elements selected from lanthanides, S is one or more elements selected from alkaline earth metal groups, Q is one or more elements selected from transition metals, O is oxygen,

   Δ is a positive number of 1 or less, and is a value that makes the compound of formula RSQO _{5 + δ} electrically neutral.
2. The method of claim 1,

   The compound of formula RSQO comprises a compound of formula 1, the cathode material for a solid oxide fuel cell:

   <Formula 1>

   AA ' _1-x Ca _x B ₂ O _{5 + δ}

   In Formula 1, A is an element selected from the lanthanide group, A 'is an element selected from the alkaline earth metal group, and B is an element selected from the transition metal,

   X is a number greater than 0 and less than 1.0,

   Δ is a positive number of 1 or less, and is a value that makes the compound of Formula 1 electrically neutral.
3. The method of claim 2,

   The A is any one of neodymium (Nd), praseodymium (Pr) or a mixture thereof, the cathode material for a solid oxide fuel cell.
4. The method of claim 2,

   A 'is barium (Ba), the cathode material for a solid oxide fuel cell.
5. The method of claim 2,

   B is cobalt (Co), the cathode material for a solid oxide fuel cell.
6. The method of claim 2,

   X is greater than 0 and less than or equal to 0.5, a cathode material for a solid oxide fuel cell.
7. The method of claim 2,

   Formula 1 is a PrBa _1-x Ca _x Co ₂ O _{5 + δ} , the cathode material for a solid oxide fuel cell.
8. The method of claim 1,

   The compound of Formula RSQO comprises a compound of Formula 2, the cathode material for a solid oxide fuel cell:

   <Formula 2>

   AA ' _0.75 A'' _0.25 B _2-x B' _x O _{5 + δ}

   In Formula 2, A is an element selected from the lanthanide group, A 'and A' 'are different elements selected from the alkaline earth metal group, and B and B' are different from each other selected from the transition metal. Elemental,

   X is a number greater than 0 and less than 1.0,

   Δ is a positive number of 1 or less, and is a value that makes the compound of Formula 2 electrically neutral.
9. The method of claim 8,

   The A is any one of lanthanum (La), samarium (Sm), neodymium (Nd), praseodymium (Pr), gadolinium (Gd) or a mixture thereof, the cathode material for a solid oxide fuel cell.
10. The method of claim 8,

    A ′ is barium (Ba), and A ″ is calcium (Ca), a cathode material for a solid oxide fuel cell.
11. The method of claim 8,

    B is cobalt (Co), and B 'is iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), or a mixture thereof, a cathode material for a solid oxide fuel cell.
12. The method of claim 8,

    X is greater than 0 and less than or equal to 0.5, a cathode material for a solid oxide fuel cell.
13. The method of claim 8,

    Formula 2 is NdBa _0.75 Ca _0.25 Co _2-x Fe _x O _{5 + δ} , the cathode material for a solid oxide fuel cell.
14. The method of claim 1,

    The compound of formula RSQO is a solid oxide fuel cell cathode material comprising the compound of formula

    <Formula 3>

    LnBa _a Sr _b Co _2-x Fe _x O _{5 + δ}

    In Formula 3, Ln is samarium, neodymium, praseodymium, or a mixture thereof, wherein a and b are each greater than 0 and less than 1, and satisfies a + b = 1, and x is greater than 0 and less than 1.0 Is a positive number of 1 or less, and is a value that makes the compound of Formula 3 electrically neutral.
15. The method of claim 14,

    And a and b are 0.5, the cathode material for a solid oxide fuel cell.
16. The method of claim 14,

    X is 0.25 or more and 0.75 or less, the cathode material for a solid oxide fuel cell.
17. The method of claim 16,

    X is 0.25 or more and 0.50 or less, the cathode material for a solid oxide fuel cell.
18. The method of claim 14,

    The cathode material is PrBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} , SmBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} or NdBa _0.5 Sr _0.5 Co _2-x Fe _x O _{5 + δ} X is greater than 0 and less than or equal to 0.75.
19. The method of claim 18,

    X is 0.25 or more and 0.50 or less, the cathode material for a solid oxide fuel cell.
20. 20. A composition for a cathode, further comprising a cathode material according to claim 1, an oxygen ion conducting solid oxide, and an organic binder.
21. The method of claim 20,

    The oxygen ion conducting solid oxides are yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), samaria doped ceria (SDC), gadolinia doped ceria (GDC), lanthanum strontium magnesium gallate (LSGM) and these The composition for a cathode selected from the group consisting of.
22. 20. A cathode for a solid oxide fuel cell comprising the cathode material of claim 1.
23. The method of claim 22,

    A cathode for a solid oxide fuel cell, wherein the cathode is a complex of an oxygen ion conductive solid oxide and the compound of Formula 1, the compound of Formula 2, or the compound of Formula 3. 3.
24. A cathode according to claim 23;

    An anode disposed facing the cathode; And

    A solid oxide fuel cell comprising an electrolyte that is an oxygen ion conducting solid oxide disposed between the cathode and the anode.
25. The method of claim 24,

    Solid oxide fuel cell, the operating temperature of the solid oxide fuel cell is 800 ℃ or less.

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