KR100765115B1 - Novel metal composite oxides comprising strontium and ionic conductors using the same - Google Patents

Abstract

The present invention provides an ion conductor characterized by including oxygen defects and metal defects in the Cryolite lattice and an electrochemical device having the ion conductor.

Since the metal complex oxide of the present invention has improved ion conductivity due to a space secured by a defect of metal ion sites present in the lattice, the metal complex oxide may be usefully used in an electrochemical device requiring an ion conductor or ion conductivity. .

Strontium, Niobium, Tantalum, Oxides, Crystal Structure, Defects, Ionic Conductivity, Ionic Conductors

Description

New Strontium-Containing Metal Composite Oxides and Ion Conductors Using the Same

1 is a Rietveld profile comparing the X-ray diffraction pattern of the strontium-tantalum-containing composite oxide (Sr ₁₁ Ta ₄ O ₂₁ ) prepared in Example 1 with a theoretical pattern of a structural model.

FIG. 2 is a crystal structure diagram of the strontium-tantalum-containing composite oxide (Sr ₁₁ Ta ₄ O ₂₁ ) prepared in Example 1 in an ab plane (001 plane).

3 is Sr ₁₁ B ₄ O ₂₁ prepared in Examples 1 and 2 Is a diagram showing an ion conductivity according to the temperature of the known Sr ₁₂ Ta ₄ O _22, and (B = Ta, Nb).

The present invention relates to a novel metal composite oxide exhibiting ion conductivity, and more particularly, a novel metal composite oxide, which is easily ion-transferred due to an open space secured by a defect of a metal ion site in a lattice, the metal composite An ion conductor comprising an oxide and an electrochemical device having the ion conductor are provided.

Ionic conductors, in particular oxygen ion conductors, are generally solid materials that are being actively studied as electrolytes for electrochemical devices such as gas sensors, fuel cells and the like.

Current solid-electrolyte fuel cell (solid oxide fuel cell: SOFC) applications, the yttrium stabilized zirconium (Yttrium Stabilized Zirconia, hereinafter YSZ) the high temperature SOFC electrolyte is known as the most suitable material, 600 ^o C low temperature SOFC for the following Doped Ceria-type is known to be more suitable. In addition, in the case of high-temperature SOFC using a material other than YSZ (doped Ceria or La _0.8 Sr _0.2 GaO _3-δ ) as electrolyte, a material such as La _0.9 Sr _0.1 AlO _3-δ or Gd ₂ Zr ₂ O ₇ It can be used as a protective layer material of the cathode. In addition, the ion conductor membrane (membrane) used in the oxygen pump (Oxygen pump) must be present with both electrical conductivity and ion conductivity, it is possible to apply a material such as doped Ceria than YSZ which has little electrical conductivity.

As such, these materials all have potential, but each has advantages and disadvantages depending on the application of the materials. This is because the ion conductivity and physicochemical properties of the materials vary depending on the intrinsic properties such as crystal structure and ion defect structure of each material. Therefore, by developing a new type of material having a variety of ion conductivity required according to the application, it is intended to provide a foundation that can be radically advanced in the technical field that conventional ion conductor is required.

The inventors have found that a novel metal composite oxide synthesized by mixing strontium (Sr) and niobium (Nb) or strontium (Sr) and tantalum (Ta) in a specific ratio has a specific metal ion defect that is not known in the past. Rather, it was found that the ionic conductivity is improved due to the clearance in the lattice caused by the defect of the metal ions.

Accordingly, an object of the present invention is to provide a novel metal composite oxide exhibiting ion conductivity, an ionic conductor including the metal composite oxide, and an electrochemical device having the ion conductor.

The present invention provides an ion conductor characterized by including oxygen defects and metal defects in the Cryolite lattice and an electrochemical device having the ion conductor.

In addition, the present invention provides a novel strontium-containing composite oxide that can be represented by the following formula (1).

Sr _{12 - x} B ₄ O _{21 ± δ} C _z (I)

Where

B is Ta, Nb or a combination of Ta and Nb;

C is at least one anion or H ⁺ cation selected from the group consisting of S and a halogen element;

X is a prime number between 0.8 and 1.2 (0.8 ≦ x ≦ 1.2);

δ is a decimal number between 0 and 3 (0 ≦ x ≦ 3);

Z is a prime number between 0 and 7 (0 ≦ x ≦ 7).

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is characterized by providing a novel metal composite oxide having improved ion conductivity due to the defect presence of unique metal ions in the lattice.

Among the compounds having a cryolite structure, which is a conventional perovskite related structure, compounds having defects of oxygen ions in the lattice structure are already known. In contrast, the novel metal composite oxide of the present invention has a structural feature in which a defect of metal ions is added to the structure having the above-described oxygen defect.

The defects of the metal ions allow to secure additional open spaces in the lattice structure, and such open spaces can provide more improved ion conductivity by facilitating the movement of the ions. Therefore, the novel metal composite oxides of the present invention can faithfully serve as ionic conductors that exhibit conductivity according to future ion migration. In fact, it was confirmed through the experimental example of the present invention that the novel metal composite oxides represented by the general formula (1) of the present invention not only have defects of specific metal ions, but also have high oxygen ion conductivity (see FIG. 3).

The metal composite oxide according to the present invention has a cryolite structure and is not particularly limited as long as there are defects of metal ions together with oxygen defects. Preferably it may be represented by the formula (1).

The metal composite oxides represented by Formula 1 are not only the novel strontium-containing composite oxides that have been known in the related art but also have a cryolite structure and a structure in which additional metal ion defects exist in addition to oxygen defects in the lattice. Therefore, as described above, the open space in the lattice due to the metal defect can be secured to exhibit excellent ion conductivity.

In fact, the metal composite oxide of Formula 1 preferably satisfies crystallographic coordinates and site occupancy as shown in Table 1 (space group No. 225, Fm3m). At this time, the position indication in the grid is shown in space group No. P. 689 of International tables for crystallography (Vol. A, 5 ^th ed. Kluwer Academic Publishers, 2002). Based on 225. In particular, the smaller the fraction, the less the factor blocking the ion conducting channel can be exhibited excellent ion conductivity, the smaller the fraction is preferable if the above-described crystal structure is maintained.

Position of cation (X, Y, Z) Fraction (O) 8c (1/4, 1/4, 1/4) 0 <O ≤ 1 4b (1/2, 1/2, 1/2) 0 <O ≤ 1 4a (0, 0, 0) 0 <O ≤ 1 24e (x, 0, 0), 0.20 ≤ x ≤ 0.30 0 <O ≤ 1

Among the metal composite oxides represented by Formula 1, C is preferably H ⁺ cation. This is because hydrogen ions (H ⁺ , protons), which are present in the lattice by absorption of moisture (H ₂ O) in a moist atmosphere, are easily moved through the open space secured by the above-described metal ion defects. This is because it can be used as an ion conductor.

Indeed, many perovskite-related oxides having conventional oxygen ion conductivity are generally known to simultaneously have hydrogen ion conductivity under an atmosphere containing moisture (T. Norby, Solid State Ionics, 125 (1999) 1-11; I. Animitsa, T. Norby, S. Marion, R. Glockner, A. Neiman, Solid State Ionics, 145, (2001) 357-364). Therefore, as described above, specific metal ion defects in the metal composite oxide exist, and the metal complex oxides of the present invention, which exhibit oxygen ion conductivity through the space secured by the metal defect, move hydrogen protons through the aforementioned space. Also, since it will be easily determined, it can be predicted that not only oxygen ion conductivity but also hydrogen ion conductivity can be simultaneously exhibited.

The crystal system of the metal composite oxide represented by Chemical Formula 1 may be cubic, its lattice constant may be 8.327 ± 0.5 Å, and the space group may be fm-3m (No. 225). Further, non-limiting examples of the metal composite oxide represented by Chemical Formula 1 include Sr ₁₁ Ta ₄ O ₂₁ or Sr ₁₁ Nb ₄ O ₂₁ .

In addition to the above-described compounds of formula (1) or derivatives thereof, compounds which possess the above-mentioned structural characteristics and can exhibit ion conductivity are also within the scope of the present invention.

The novel metal composite oxide of the present invention can be prepared according to conventional methods known in the art. For one preferred embodiment thereof, precursor compounds containing only one or more of the elements (e.g., (a) Sr; (b) Nb, Ta, or a combination thereof, etc.) described in Chemical Formula 1 are mixed in appropriate molar ratios, respectively. It may then be prepared by firing at a temperature of 700 to 1700 ° C. and then cooling.

As the precursor compound of Formula 1 Sr; And all types of salts including Nb and / or Ta alone or one or more. In addition, the precursor compounds containing each element may be mixed in various molar ratios depending on the final product, and are not particularly limited.

The mixed mixture is calcined at a temperature of 700 ° C. or higher, wherein the firing temperature and firing time are preferably 700 to 1700 ° C. and 5 to 72 hours. However, it is not limited thereto.

The baking method of this invention can use the baking method conventional in the art, and the following two methods are mentioned as an example. The first is to fire the mixture into pellets, and the second is to fire the mixture itself. The two firing methods are based on the convenience of synthesis, and there is no particular limitation according to the kind of firing method.

The calcined compound can be cooled to room temperature to obtain a novel single phase metal complex oxide, such as a strontium-containing complex oxide of Formula 1 or a derivative thereof. At this time, the cooling may proceed at room temperature, and may also be cooled in a short time using liquid nitrogen or water at room temperature.

The present invention provides an ionic conductor, preferably an oxygen or proton, which is selective to a metal complex oxide having the above-described novel crystal structure.

Here, the ion conductor is a material exhibiting conductivity according to the movement and transfer of ions, and most of them are used in the form of a membrane including a separation factor that selectively permeates one component.

The ion conductors of the present invention can be prepared by conventional methods known in the art and, for example, by preferred coatings on conductive electrodes for application of an electric field. In this case, the metal composite oxide of the present invention may be used alone as an ion conductor, or may be mixed with other conventional materials known in the art depending on the purpose of use.

In addition, the present invention provides an electrochemical device comprising the aforementioned novel metal composite oxide as an ion conductor.

The electrochemical device includes all devices that undergo an electrochemical reaction, and non-limiting examples thereof include an oxygen probe, a fuel cell, a chemical membrane reactor, and an oxygen separation membrane. ), Oxygen pump, hydrogen separation membrane, hydrogen pump, hydrogen gas sensor, steam sensor, hydrocarbon sensor, hydrogen extraction ( hydrogen extraction, hydrogen pressure controller, isotope enrichment, tritium technology, steam electrolysis, H ₂ S electrolysis, HCl electrolysis, hydrogenation of hydrocarbon, dehydrognation, NH ₃ formation, electrochemical cell, electrochromic Electrochromic devices, gas sensors or No _x traps.

The novel metal composite oxides of the present invention, such as strontium-niobium (tantalum) oxides and derivatives thereof, contained in the electrochemical device serve as oxygen or proton ion conductors, for example, porous filters. Electrochemical filtration by, electrochemical treatment of gaseous effluents or heterogeneous catalysis, etc. It may also be incorporated into chemical membrane reactions or oxygen separation membranes in reactors for controlling oxidation of hydrocarbons, or may be used as electrolytes in fuel cells fueled with hydrogen.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

Example 1

Strontium carbonate (SrCO ₃ ) and tantalum oxide (Ta ₂ O ₅ ) compounds were weighed and mixed in a metal molar ratio of 11: 4, respectively, and then heated at a temperature of 1000 ° C. for 48 hours. After cooling and remixed to room temperature to form a powder or pellets were heated for 48 hours at a temperature of 1150 ℃ in air. After cooling, the synthesis of Sr ₁₁ Ta ₄ O ₂₁ compound was completed.

Example 2

A Sr ₁₁ Nb ₄ O ₂₁ compound was prepared in the same manner as in Example 1, except that a niobium oxide (Nb ₂ O ₅ ) compound was used instead of tantalum oxide (Ta ₂ O ₅ ).

Comparative Example 1

Sr ₁₂ Nb ₄ O was carried out in the same manner as in Example 1, except that the metal molar ratio of the strontium carbonate (SrCO ₃ ) and tantalum oxide (Ta ₂ O ₅ ) compounds was changed to 12: 4 instead of 11: 4. ₂₂ compound was prepared.

Experimental Example 1. Analysis of chemical composition of metal composite oxide (ICP-AES)

Inductively Coupled Plasma Atomic Emission Spectroscope (ICP-AES) was performed to analyze the chemical composition of the metal composite oxide according to the present invention.

As the sample, the strontium-tantalum-containing oxide prepared in Example 1 and the strontium-niobium-containing oxide prepared in Example 2 were used. Each sample was ground, put into a glass vial and dissolved using concentrated nitric acid, and the sample was completely decomposed with hydrogen peroxide. Dilutions were carried out in three different volumes and elemental analysis was performed using standard ICP-AES (GDC Integra XMP).

As a result of performing ICP element analysis, it was found that the molar ratio of strontium and tantalum in the metal composite oxide of Example 1 was 11.00: 4.00 (± 0.02), and oxygen was 21 calculated from the oxidation number of the metal and the above ratio. This confirmed that the chemical formula of the strontium-tantalum oxide of Example 1 is Sr ₁₁ Ta ₄ O ₂₁ . Similarly, in the metal composite oxide of Example 2, it was confirmed that strontium, niobium and oxygen also have the same molar ratio.

Experimental Example 2 Analysis of Crystal Structure of Metal Complex Oxide

In order to analyze the crystallographic structure of the metal composite oxide of the present invention, the following experiment was conducted.

2-1. Crystal structure analysis using X-ray diffraction pattern (XRDP)

As a sample of the diffraction analysis, the strontium-tantalum-containing composite oxide (Sr ₁₁ Ta ₄ O ₂₁ ) prepared in Example 1 was used. Each sample was pulverized well and filled into a sample holder for X-ray powder diffraction, and Bruker D8-Advance XRD was used. The X-ray was 0.02 with CuKα ₁ (λ = 1.5405 kV), an applied voltage of 40 KV and an applied current of 50 mV. It measured by scanning in ° steps.

The X-ray diffraction patterns (XRDP) of the strontium-tantalum-containing composite oxide (Sr ₁₁ Ta ₄ O ₂₁ ) prepared in Example 1 were examined, and found to be 8.327 ± 0.5 Hz from the peak positions of the XRDP. The lattice constant of was obtained, and the space group Fm-3m (no. 225) was determined by indexing all peaks and examining the extinction rule (see Table 2 and FIG. 1). In addition, all peaks of the XRDP phase were indexed, and it was confirmed that the strontium-tantalum oxide of Example 1 was a pure single phase without impurities.

Chemical formula Space Lattice constant Example 1 Sr ₁₁ Ta ₄ O ₂₁ Fm-3m a = 8.327 (5) Example 2 Sr ₁₁ Nb ₄ O ₂₁ Fm-3m a = 8.338 (5)

2-2. Structural model setup and Rietveld refinement analysis

In order to find out the crystal structure of the metal composite oxide according to the present invention, the peaks carried out in Experimental Example 2-1 were measured using GSAS (AC Larson and RB Von Dreele, "General Structure Analysis System," Report no. LAUR086-748, Los. Alamos National Laboratory, Los Alamos, NM 87545.) program. The initial Cryolite crystal structure was used as the initial model, and the Rietveld refinement of the XRD pattern was performed with the x coordinate of oxygen ion, the cation fraction, and the temperature factors as variables. As a result, the reliability of the structural model set by the present inventors represented R _w = 8.0%, and the finally analyzed crystallographic data is shown in Table 3 below.

In addition, Figure 1 shows a Rietveld profile, it was confirmed that the agreement in all ranges. In other words, the difference peak under the Bragg position of the Rietveld profile indicates that the measured peak and the simulation peak of the structural model coincide over the entire measurement interval. Not only is the crystal structure analysis correct, but the metal composite oxides of the present invention, such as strontium-tantalum containing composite oxides, prove that they are single phase.

In this case, the fraction of Sr1 and Sr2 sites in Sr ₁₂ Ta ₄ O ₂₂ (= Sr ₆ Ta ₂ O ₁₁ ), which is a strontium-tantalum-containing complex oxide known as a cryolite structure, is 1, respectively, and only the fraction of oxygen 1 or less (Soild State Ionics, 156 (2003) 95-102), the strontium-tantanium-containing composite oxide (Sr ₁₁ Ta ₄ O ₂₁ ) prepared in the present invention is not only oxygen, but also as described in Table 3 below The site fractions of Sr1 and Sr2 were both less than 1. In particular, the site fraction of Sr2 showed a smaller value (see Table 3). For reference, since an occupancy of less than 1 means that there is a defect of metal ions, the metal complex oxide of the present invention shows that there is a defect of metal ions in the lattice structure. there was.

Atom Site X y z Occup. U _iso ^a Sr1 8c 0.25 0.25 0.25 0.965 (4) 0.0475 (7) Sr2 4b 0.5 0.5 0.5 0.820 (7) 0.0475 (7) Ta 4a 0 0 0 One 0.0475 (7) O 24e 0.2693 (29) 0 0 0.875 0.0475 (7)

On the other hand, Figure 2 shows the ab-plane (001 plane) in the lattice structure of Sr ₁₁ Ta ₄ O ₂₁ prepared in Example 1, Sr (1), Sr (2), TaO ₆ octahedron of the lattice structure The location was detailed. At this time, Sr (1) is a site having 12 coordination of oxygen, and Sr (2) is a site having 6 coordination of oxygen. It can be seen that the metal composite oxide according to the present invention has a structural feature in which metal defects are present at Sr (1) and Sr (2) sites and oxygen ion defects are located at oxygen sites.

Experimental Example 3. Evaluation of Oxygen Ionic Conductivity

In order to evaluate the ionic conductivity of the metal composite oxide prepared according to the present invention, the following experiment was performed.

As a sample, the strontium-tantalum-containing composite oxide (Sr ₁₁ Ta ₄ O ₂₁ ) prepared in Example 1 and the strontium-niobium-containing composite oxide (Sr ₁₁ Nb ₄ O ₂₁ ) of Example 2 were used. The strontium-tantalum containing complex oxide (Sr ₁₂ Ta ₄ O ₂₂ ) of Comparative Example 1 was used, respectively.

The ion conductivity of the samples was measured by complex impedance spectroscopy in the 0.1 Hz to 32 MHz frequency range. At this time, the thermal stabilization was performed for about 1 hour at a potential of about 100 mV under air from which moisture was removed.

As a result, it was confirmed that the metal composite oxide according to the present invention had better ionic conductivity with temperature than strontium-tantalum (Sr ₁₂ Ta ₄ O ₂₂ ), which is a control group known to be free of metal defects. 3). It is interpreted that the ion conductivity is increased due to the lattice internal space secured by the metal ion defect in the crystal structure. Accordingly, it could be predicted that the metal complex oxide of the present invention may be usefully used as an ion conductor in the future.

The metal complex oxide of the present invention can be usefully used in electrochemical devices requiring ion conductors or ion conductivity by improving ion conductivity due to the space in the lattice, which is facilitated by defects of metal ion sites in the lattice. have.

Claims (11)

An ion conductor comprising both oxygen defects and metal defects in a cryolite lattice, wherein the ion conductors have crystallographic coordinates and site occupancy in Table 1 (space group No. 225, Fm3m). Ion conductors characterized by the fact that the position within the lattice is based on the space group No. 225 shown in P. 689 of International tables for crystallography (Vol. A, 5 ^th ed. Kluwer Academic Publishers, 2002). . TABLE 1 Position of cation (X, Y, Z) Fraction (O) 8c (1/4, 1/4, 1/4) 0 <O ≤ 1 4b (1/2, 1/2, 1/2) 0 <O ≤ 1 4a (0, 0, 0) 0 <O ≤ 1 24e (x, 0, 0), 0.20 ≤ x ≤ 0.30 0 <O ≤ 1 The ion conductor of claim 1, wherein the ion conductor is configured to move and transfer ions through a lattice internal space secured by a metal defect. delete The ion conductor according to claim 1, wherein the ion conductor is represented by the following Chemical Formula 1: [Formula 1] Sr _12-x B ₄ O _{21 ± δ} C _z (I) Where B is Ta, Nb or a combination of Ta and Nb; C is an anion or H ⁺ cation selected from the group consisting of S and a halogen element; X is a prime number between 0.8 and 1.2 (0.8 ≦ x ≦ 1.2); δ is a decimal number between 0 and 3 (0 ≦ x ≦ 3); Z is a prime number between 0 and 7 (0 ≦ x ≦ 7). The ion conductor of claim 1, wherein the ion conductor is selective to oxygen or proton (H ⁺ ). The electrochemical apparatus provided with the ion conductor of any one of Claims 1-2. The method of claim 6, wherein the electrochemical device is an oxygen probe, a fuel cell, a chemical membrane reactor, an oxygen separation membrane, an oxygen pump, a hydrogen separation membrane. (hydrogen separation membrane), hydrogen pump, hydrogen gas sensor, steam sensor, hydrocarbon sensor, hydrogen extraction, hydrogen pressure controller ), isotope enrichment, tritium technology, steam electrolysis, H ₂ S electrolysis, HCl electrolysis, hydrogenation of hydrocarbon, dehydrognation, NH ₃ formation, electrochemical cell, electrochromic device, gas sensor or No _x Trap-in device. A metal composite oxide represented by Formula 1 below: [Formula 1] Sr _12-x B ₄ O _{21 ± δ} C _z (I) Where B is Ta, Nb or a combination of Ta and Nb; C is an anion or H ⁺ cation selected from the group consisting of S and a halogen element; X is a prime number between 0.8 and 1.2 (0.8 ≦ x ≦ 1.2); δ is a decimal number between 0 and 3 (0 ≦ x ≦ 3); Z is a prime number between 0 and 7 (0 ≦ x ≦ 7). The oxide of claim 8, wherein the crystal system of the metal composite oxide is cubic. The oxide of claim 8, wherein a space group of the metal composite oxide is fm-3m (No. 225), and a lattice constant is 8.327 ± 0.5 μs. The oxide of claim 8, wherein the metal complex oxide is Sr ₁₁ Ta ₄ O ₂₁ or Sr ₁₁ Nb ₄ O ₂₁ .

Images