KR20240082133A - Solid oxide cell and composition for air electrode thereof - Google Patents

Abstract

One embodiment of the present invention includes a fuel electrode, an air electrode, and an electrolyte disposed between the fuel electrode and the air electrode, wherein the air electrode includes an ion-electron conductor and an ion conductor, and the ion-electron conductor has the formula ABO ₃ Expressed, where A includes La, and B includes at least one of Fe, Mn, Co, and Sc, providing a solid oxide cell.

Description

Solid oxide cell and composition for air electrode of solid oxide cell {SOLID OXIDE CELL AND COMPOSITION FOR AIR ELECTRODE THEREOF}

The present invention relates to a solid oxide cell and a composition for an air electrode of the solid oxide cell.

A solid oxide fuel cell (SOFC) and a solid oxide electrolysis cell (SOEC) include a cell composed of an air electrode, a fuel electrode, and a solid electrolyte with ion conductivity, where the cell contains solid oxide. It can be called a cell. Solid oxide cells produce electrical energy through an electrochemical reaction or produce hydrogen by electrolyzing water through the reverse reaction of a solid oxide fuel cell. Solid oxide cells are compared to other types of fuel cells or water electrolytic cells, such as phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), polymer electrolyte fuel cells (PEMFC), and direct methanol fuel cells (DMFC). Based on low activation polarization, overvoltage is low and irreversible loss is low, so efficiency is high. In addition, it can be used as a carbon or hydrocarbon-based fuel in addition to hydrogen, giving a wide range of fuel choices, and has the advantage of not requiring expensive precious metals as an electrode catalyst because the reaction rate at the electrode is high.

The electrode layer of a solid oxide cell may contain a conductive material for ions and electrons, and in order to improve the performance of the solid oxide cell, it is necessary to increase the overall conductivity of the electrode layer.

One of the purposes of the present invention is to implement a solid oxide cell with improved performance by including an electrode layer with high ion conductivity. Additionally, another object of the present invention is to provide a composition for a cathode of a high-efficiency solid oxide cell that functions as an ion-electron conductor.

As a method for solving the above-described problems, the present invention seeks to propose a novel structure of a solid oxide cell through an example, specifically comprising a fuel electrode, an air electrode, and an electrolyte disposed between the fuel electrode and the air electrode, The air electrode includes an ion-electron conductor and an ion conductor, and the ion-electron conductor is expressed by the formula ABO ₃ , where A includes La, and B includes at least one of Fe, Mn, Co, and Sc. Includes.

In one embodiment, A may further include at least one of Sr and Ca.

In one embodiment, the content of at least one of Sr and Ca may be 40 mol or less compared to 100 mol of the total content of A.

In one embodiment, the content of Sc may be less than 10 moles based on 100 moles of the total content of B.

In one embodiment, the content of Sc may be 5 mol or more compared to 100 mol of the total content of B.

In one embodiment, the ion conductor is Scandia stabilized zirconia (SSZ), yttria stabilized zirconia (YSZ), Scandia ceria stabilized zirconia (SCSZ), Scandia ceria yttria stabilized zirconia (SCYSZ), and Scandia ceria ytterbia stabilized zirconia (SCYbSZ). ) may include at least one of

In one embodiment, the weight ratio of the ion-electron conductor to the ion conductor in the air electrode may be 30:70 to 70:30.

Meanwhile, another aspect of the present invention is,

It includes a fuel electrode, an air electrode, and an electrolyte disposed between the fuel electrode and the air electrode, wherein the air electrode includes an ion-electron conductor, and the ion-electron conductor is expressed by the formula ABO ₃ , where A includes La. In addition, the B includes at least one of Fe, Mn, and Co and Sc, and the content of the Sc is less than 10 moles based on the total content of 100 moles of the B. It provides a solid oxide cell.

In one embodiment, the content of Sc may be 5 mol or more compared to 100 mol of the total content of B.

Another aspect of the present invention is,

ABO ₃ is expressed in the formula, where A includes La, B includes at least one of Fe, Mn, and Co and Sc, and the content of Sc is less than 10 moles relative to 100 moles of the total content of B. A composition for an air electrode of a solid oxide cell is provided.

In one embodiment, the content of Sc may be 5 mol or more compared to 100 mol of the total content of B.

When a solid oxide cell is implemented using the composition for the air electrode of the solid oxide cell according to an example of the present invention, the ionic conductivity of the air electrode can be improved. Performance can be improved when these solid oxide cells are used as fuel cells or water electrolysis cells.

1 is a cross-sectional view schematically showing a solid oxide cell according to an embodiment of the present invention.
Figure 2 is a cross-sectional view schematically showing a solid oxide cell according to another embodiment of the present invention.
Figure 3 shows an enlarged view of one area (area A) of the anode.
Figure 4 shows an enlarged view of one area (area B) of the air electrode.
Figure 5 is a graph showing the results of measuring the change in electrical conductivity according to temperature in air electrodes obtained from compositions with different amounts of Sc added.
Figure 6 is a graph measuring the polarization resistance to oxygen reduction reaction in air electrodes obtained from compositions with different amounts of Sc added.
Figure 7 shows the results of H ₂ -TPR (Temperature Programmed Reduction) analysis.
Figure 8 shows the relationship between current density and voltage and the resulting power density in a solid oxide cell including an air electrode obtained from compositions with different amounts of Sc added.
Figure 9 shows the relationship between current density and voltage, and the resulting power density, in an air electrode formed from a composite of LSFSc05 (Sc: 5 mol%) and an ion conductor (YSZ).

Hereinafter, embodiments of the present invention will be described with reference to specific embodiments and attached drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Additionally, embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation, and elements indicated by the same symbol in the drawings are the same element.

In order to clearly explain the present invention in the drawings, parts that are not relevant to the description are omitted, and the thickness is enlarged to clearly express various layers and regions, and components with the same function within the scope of the same idea are referred to by the same reference. Explain using symbols. Furthermore, throughout the specification, when a part is said to “include” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

1 is a cross-sectional view schematically showing a solid oxide cell according to an embodiment of the present invention. Figure 2 is a cross-sectional view schematically showing a solid oxide cell according to another embodiment of the present invention. Figure 3 shows an enlarged view of one area (area A) of the anode, and Figure 4 shows an enlarged view of one area (area B) of the air electrode.

Referring to FIGS. 1 to 4, the solid oxide cell 100 according to an embodiment of the present invention includes a fuel electrode 110, an air electrode 120, and an electrolyte 130 disposed between them as main components. Here, the air electrode 120 includes an ion-electron conductor 121 and an ion conductor 122. And the ion-electron conductor 121 is expressed by the formula ABO ₃ , where A includes La, and B includes at least one of Fe, Mn, Co, and Sc. In the case of this embodiment, the air electrode 120 includes an ion-electron conductor 121 with high ionic conductivity, so that the reactivity in the air electrode 120 can be improved, thereby improving the performance of the solid oxide cell 100. It can be. Hereinafter, the components of the solid oxide cell 100 will be described in detail, and the case where the solid oxide cell 100 is used as a fuel cell will mainly be described. However, the solid oxide cell 100 can also be used as a water electrolysis cell, and in this case, a reaction opposite to that in the case of a fuel cell will occur at the anode 110 and the air electrode 120 of the solid oxide cell 120.

The anode 110 and the air electrode 120 correspond to electrode layers where major reactions occur in the solid oxide cell 100. Specifically, when the solid oxide cell 100 is a fuel cell, for example, water production or an oxidation reaction of a carbon compound may occur due to oxidation of hydrogen in the anode 110, and oxygen may occur due to decomposition of oxygen in the air electrode 120. An ion generating reaction may occur. In the case of a water electrolysis cell, the opposite reaction may occur. For example, hydrogen gas may be generated in the anode 110 due to a reduction reaction of water, and oxygen may be generated in the air electrode 120. As another example, in the case of a fuel cell, a reaction of hydrogen decomposition (generating hydrogen ions) occurs in the anode 110, and oxygen and hydrogen ions combine to generate water in the air electrode 120. In the case of a water electrolysis cell, , a reaction of water decomposition (generating hydrogen and oxygen ions) occurs in the anode 110, and oxygen may be generated in the air electrode 120.

Meanwhile, in the case of the solid oxide cell 100 of FIG. 1, the anode 110 and the air electrode 120 may correspond to the so-called electrolyte 130-supported solid oxide cell 100 supported by the electrolyte 130. In this case, the width of the electrolyte 130 may be the widest. In such an electrolyte 130-supported solid oxide cell 100, reliability may be excellent, but the electrolyte 130 may be formed relatively thick to perform the support function. However, in addition to the electrolyte 130-supported structure, other structures may also be employed. For example, as in the embodiment of FIG. 2, it may be implemented as a support type for the anode 110, and in this case, the anode 110 may be the thickest.

As shown in FIG. 3, the fuel electrode 110 may include an electronic conductor 111 and an ion conductor 112, which may be sintered bodies of particles. The electronic conductor 111 may perform electrical conduction functions and catalytic functions, and may include, for example, Ni-based or lanthanum chromite-based (La _1-x Sr _x CrO ₃ , where 0≤x<1) materials. You can. And the ion conductor 111 may include yttria-stabilized zirconia-based (YSZ), ceria-based (CeO ₂ ), bismuth oxide-based (Bi ₂ O ₃ ), and lanthanum gallate-based (LaGaO ₃ ) materials. Additionally, the anode 110 may be a porous body including pores H1, and gases, fluids, etc. may pass in and out through the pores H1.

The electrolyte 130 is disposed between the fuel electrode 110 and the air electrode 120, and ions can move to the fuel electrode 110 or the air electrode 120. As an example of the material constituting the electrolyte 130, the material constituting the ion conductors 112 and 122 of the anode 110 and the air electrode 120 can be used. As a representative example, electrolyte 130 may include stabilized zirconia. Specifically, the electrolyte 130 includes Scandia stabilized zirconia (SSZ), yttria stabilized zirconia (YSZ), Scandia ceria stabilized zirconia (SCSZ), Scandia ceria yttria stabilized zirconia (SCYSZ), and Scandia ceria ytterbia stabilized zirconia (SCYbSZ). It may include etc.

As shown in Figure 4, the air electrode 120 includes an ion-electron conductor 121 and an ion conductor 122, which may be sintered bodies of particles. The air electrode 120 may be a porous body including pores H2, and gases, fluids, etc. may pass in and out through the pores H2. As described above, the ion-electron conductor 121 is expressed by the formula ABO ₃ , where A contains La, and B is obtained from a composition for an air electrode containing at least one of Fe, Mn, Co and Sc. This can be obtained, and as a result, the ionic conductivity of the air electrode 120 can be increased. Additionally, by using a composite material of the ion-electron conductor 121 compared to using only the electronic conductor, the interface between the ion conductor and the electronic conductor can be increased, and thus the effective reaction area within the air electrode 120 can be increased. In the case of La-based oxide, such as La _0.8 Sr _0.2 MnO ₃ , which is conventionally used as a material for the air electrode 120, it is close to an electronic conductor with low ionic conductivity, and when used, the reaction area is at the interface between the air electrode 120 and the electrolyte 130. However, it may be limited to the interface between the electronic conductor and the ion conductor within the air electrode 120. In this embodiment, the reactivity of the cathode 120 can be increased by using the ion-electron conductor 121 with a composition in which Sc is partially substituted at the B site.

Meanwhile, the ion conductor 122 is made of Scandia stabilized zirconia (SSZ), Yttria stabilized zirconia (YSZ), Scandia ceria stabilized zirconia (SCSZ), Scandia ceria yttria stabilized zirconia (SCYSZ), and Scandia ceria ytterbia stabilized zirconia (SCYbSZ). It may include at least one of: By including the ion conductor 122, ion conductivity within the air electrode 120 can be further increased and the reaction area can be increased. The weight ratio of the ion-electron conductor 121 and the ion conductor 122 in the air electrode 120 may be 30:70 to 70:30. If the relative proportion of the ion-electron conductor 121 within the air electrode 120 is reduced to less than 30%, an electron conduction path may not be sufficiently secured. Additionally, if the relative proportion of the ion conductor 122 is reduced to less than 30%, a three-phase interface that can serve as a reaction region within the air electrode 120 may not be sufficiently secured.

However, when using the ion-electron conductor 121 in which the B site is partially replaced by Sc as in this embodiment, the air electrode 120 may have high ionic conductivity, and in this case, the air electrode 120 has the ion conductor 122. ) may not be included.

Describing the composition of the ion-electron conductor 121 in detail, the ion-electron conductor 121 basically has a perovskite structure expressed by the formula ABO ₃ , where A is a lanthanide oxide containing La. am. In this case, A may further include at least one of Sr and Ca. That is, at least one of Sr and Ca may be added to the composition of the ion-electron conductor 121, so that a portion of La in the A site may be replaced with at least one of Sr and Ca. In this case, the content of at least one of Sr and Ca may be 40 mol (40 mol%) or less compared to 100 mol of the total content of A.

The B includes at least one of Fe, Mn, Co, and Sc. That is, in the composition of the ion-electron conductor 121, Sc is added, that is, doped, in addition to polyoxidation elements such as Fe, Mn, and Co, and some of the polyoxidation elements are replaced with Sc. Sc has a fixed oxidation number (+3), and it is understood that oxygen vacancies can be induced by substituting part of polyoxidation number elements such as Fe, Mn, and Co, thereby increasing ionic conductivity. In this case, the Sc content can be set to a more appropriate range by considering all characteristics such as electrical conductivity and ionic conductivity. Specifically, the content of Sc in the ion-electron conductor 121 may be less than 10 mol (10 mol%) compared to 100 moles of the total content of B, and more specifically, the content of Sc in the ion-electron conductor 121 The content may be more than 5 moles (5 mol%) based on 100 moles of the total content of B.

The present inventors manufactured the air electrode 121 using a composition having the above-mentioned composition conditions, measured various characteristics, and compared it with a comparative example (without Sc added). In addition, the characteristics were examined in two cases: when the Sc-added ion-electron conductor (121) was used alone and when the ion conductor (122) was used together.

First, Figure 5 is a graph showing the results of measuring the change in electrical conductivity according to temperature in air electrodes obtained from compositions with different amounts of Sc added. Here, LSF (Sc: 0 mol%) is La _0.6 Sr _0.4 FeO ₃ , LSFSc05 (Sc: 5 mol%) is La _0.6 Sr _0.4 Fe _0.95 Sc _0.05 O ₃ , and LSFSc10 (Sc: 10 mol%) is La _0.6 Sr. _0.4 Fe _0.9 Sc _0.1 O ₃ , LSFSc20 (Sc: 20 mol%) represents La _0.6 Sr _0.4 Fe _0.8 Sc _0.2 O ₃ . Referring to the experimental results in FIG. 5, it can be seen that when Sc is added, the electrical conductivity decreases compared to the LSF composition, and as the amount of Sc added increases, the electrical conductivity decreases. This is understood to mean that when Sc, which has a fixed oxidation number, is added to the B site, the electrical conductivity is reduced by the Zener Double-Exchange Mechanism. However, according to the present inventors' research, even though the electrical conductivity was slightly lowered due to the addition of Sc, there was no problem in functioning as the air electrode 120. In contrast, as will be described later, it was confirmed that the performance improvement effect due to the increase in ionic conductivity was significant. .

Next, Figure 6 is a graph measuring the polarization resistance against the oxygen reduction reaction in the air electrode obtained from compositions with different amounts of Sc added. In the graph of FIG. 6, the horizontal axis represents the real part of the impedance, the vertical axis represents the imaginary part of the impedance, and half the distance between the two X-intercepts in each curve corresponds to the polarization resistance. Referring to the experimental results, it can be seen that when Sc other than LSFSc20 (Sc: 20 mol%) is added, polarization resistance tends to decrease compared to the LSF composition. Although the electrical conductivity decreased due to the addition of Sc, it is understood that the reason why the polarization resistance of the electrode decreased was because the concentration of oxygen vacancies in the material increased, thereby improving the overall oxygen ion conductivity. Looking at this through the H ₂ -TPR (Temperature Programmed Reduction) analysis results in FIG. 7, it can be seen that Fe ³⁺ ions are formed at a low temperature according to the addition of Sc, and through this, it can be predicted that oxygen vacancies are formed more easily. . In addition, when measuring the polarization resistance of an electrode according to oxygen partial pressure, it can be inferred that the reaction determining step of the electrode is. The closer the reaction rate determining value (m value) is to 1, the gas diffusion step is known as the reaction rate determining step. there is. Table 1 below measures the reaction rate determination value (m value) according to the amount of Sc added and temperature. It can be seen that as the amount of Sc added increases, the m value (calcination at 1050°C) increases. In addition, the m value increased rapidly in the composite electrode mixed with 50 wt% of YSZ, a pure ion conductor, and this confirms that the effect of adding Sc is substantially the same as the effect of mixing ion conductors.

800℃ 700℃ 600℃ LSF 0.1179 0.0825 0.1021 LSFSc05 0.1656 0.1891 0.2291 LSFSc10 0.3355 0.3299 0.3306 LSFSc20 0.4307 0.3701 0.3958 LSFSc20+ YSZ (50wt%) 0.6076 0.4888 0.4206

Next, Figure 8 shows the relationship between current density and voltage in a solid oxide cell including an air electrode obtained from a composition with different amounts of Sc added, and the resulting power density (Power Density). As shown in the graph of FIG. 8, among the multiple lines, substantially straight lines represent voltage (left vertical axis), and parabolic lines represent power density (right vertical axis), where power density is the product of current density and voltage. corresponds to Referring to the experimental results, it can be confirmed that the power density is the highest in the air electrode containing an ion-electron conductor with a composition in which Sc is added at a level of 5 mol%.

Next, Figure 9 shows the relationship between current density and voltage in an air electrode formed of a composite of LSFSc05 (Sc: 5 mol%) and an ion conductor (YSZ), and the resulting power density. Here, the weight ratio of the ion-electron conductor and the ion conductor included in the composite is each 50%. As can be seen from the experimental results in FIG. 9, it can be seen that the output increases by more than 30% when an ion conductor is added in addition to the ion-electron conductor. In addition, as explained in the experimental results in Table 1, it can be confirmed that when an ion conductor such as YSZ is added, a rapid improvement in the reaction order can be obtained, similar to the addition of Sc.

The present invention is not limited by the above-described embodiments and attached drawings, but is limited by the attached claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and change are possible without departing from the technical spirit of the present invention as set forth in the claims, and this is also subject to the appended claims. It may be said to belong to the technical idea described in .

100: solid oxide cell
110: fuel electrode
120: electrolyte
130: air electrode

Claims (11)

fuel electrode;
air pole; and
It includes an electrolyte disposed between the fuel electrode and the air electrode,
The air electrode includes an ion-electron conductor and an ion conductor,
The ion-electron conductor is expressed by the formula ABO ₃ , where A includes La, and B includes at least one of Fe, Mn, Co, and Sc. A solid oxide cell.
According to paragraph 1,
The A is a solid oxide cell further containing at least one of Sr and Ca.
According to paragraph 2,
A solid oxide cell in which the content of at least one of Sr and Ca is 40 mol or less based on 100 mol of the total content of A.
According to paragraph 1,
A solid oxide cell in which the content of Sc is less than 10 moles compared to 100 moles of the total content of B.
According to clause 4,
A solid oxide cell in which the content of Sc is 5 mol or more compared to the total content of 100 mol of B.
According to paragraph 1,
The ion conductor is at least one of Scandia stabilized zirconia (SSZ), yttria stabilized zirconia (YSZ), Scandia ceria stabilized zirconia (SCSZ), Scandia ceria yttria stabilized zirconia (SCYSZ), and Scandia ceria ytterbia stabilized zirconia (SCYbSZ). A solid oxide cell containing.
According to paragraph 1,
A solid oxide cell wherein the weight ratio of the ion-electron conductor to the ion conductor in the air electrode is 30:70 to 70:30.
fuel electrode;
air pole; and
It includes an electrolyte disposed between the fuel electrode and the air electrode,
The air electrode includes an ion-electron conductor,
The ion-electron conductor is expressed by the formula ABO ₃ , wherein A includes La, and B includes at least one of Fe, Mn, Co and Sc,
A solid oxide cell in which the content of Sc is less than 10 moles compared to 100 moles of the total content of B.
According to clause 8,
A solid oxide cell in which the content of Sc is 5 mol or more compared to the total content of 100 mol of B.
ABO ₃ is expressed in the formula, where A includes La, and B includes at least one of Fe, Mn, Co and Sc,
A composition for an air electrode of a solid oxide cell wherein the content of Sc is less than 10 moles based on 100 moles of the total content of B.
According to clause 10,
A composition for an air electrode of a solid oxide cell wherein the content of Sc is 5 mol or more compared to 100 mol of the total content of B.