KR20120070665A - Double perovskite interconnect materials and their application methods for solid oxide fuel cells - Google Patents

Abstract

PURPOSE: A double perovskite based electroconnector material is provided to have excellent sintering performance at low temperatures lower than 1400 deg.C. and electro conductivity in an oxidation or reduction atmosphere at 800 deg. C., thereby capable of being used as an electroconnector of a dense and thin film coated on the positive electrode or negative electrode of a non-planer type SOFC. CONSTITUTION: A double perovskite based electroconnector material electrically connects the positive electrode and negative electrode of nearby unit cells, and comprises titanium. The double perovskite based electroconnector material has a structural formula of A_xA'_(1-x)TiB'O_6, wherein A is a rare earth element, A' is alkaline earth metal, and B' is a transition metal. The rare earth metal is La and/or Y, the alkaline earth metal is Ca and/or Sr, and the transition metal is one or more selected from Co, Cr, Fe, Mn, Mo, Nb, Ni, Ti, and V.

Description

Double Perovskite Interconnect Materials and Their Application Methods for Solid Oxide Fuel Cells}

The present invention relates to a ceramic connecting material for a solid oxide fuel cell, and more particularly, to a high-conductivity ceramic connecting material for a high temperature solid oxide fuel cell in which a positive electrode and a negative electrode of a solid oxide fuel cell unit cell are electrically connected to form a stack. .

Solid oxide fuel cells (SOFCs), which may be referred to as third generation fuel cells, have used zirconium oxide in which yttria is added as an electrolyte and stabilized in crystal structure. This material has the conductivity of oxygen ions, but it is characterized by the desired conductivity as a fuel cell in the high temperature range of 800 to 1000. For this reason, and the operating temperature of the SOFC is more than the normal 800, the electrode material is also this conductive material resistant to such high temperatures are used the cathode air is introduced by way of example are (LaSr) MnO _3, it is a fuel electrode in which hydrogen is introduced Ni-ZrO ₂ Mixtures are commonly used. In general, a fuel cell is electrically connected to the anode of one unit cell and the anode of a neighboring unit cell repeatedly to form a final stack. The interconnects used between the neighboring unit cells are used to manufacture the stack. This is very important in the case of not only serves to electrically connect the opposite electrodes between the two unit cells, but also to physically block the mixing of the fuel gas supplied to the cathode and the air supplied to the anode.

The requirements of materials for use as SOFC electrical connectors vary depending on the type and structural shape of the SOFC unit cell, the gas channel design method, or the unit cell connection method, but generally gas-tight dense film formation, structural stability, Some or all conditions such as high electrical conductivity (> 2 Scm ^-1 ), thermal expansion coefficient (10.5 ± 0.510 ^-6 / ° C) similar to electrode and electrolyte, thermal stability under oxidation / reduction atmosphere (> 50,000hr) and ease of processing Is required (US 5614127).

Specifically, the electrical connector used for the planar type SOFC is a conductive material that electrically connects the cathode and the anode of the upper and lower unit cells and stacks gas channels for introducing fuel and air to each electrode. Metal material is used. Therefore, in this case, a metal alloy, such as Ni-Cr or Fe-Cr, which has high electrical conductivity and low fabrication cost, is used, but it has disadvantages such as low corrosion resistance and difference in thermal expansion coefficient with the electrode. On the other hand, the ceramic connecting material has the advantages of high corrosion resistance and thermal expansion coefficient similar to that of the electrode, but has disadvantages such as low electrical conductivity due to thick thickness and difficulty in forming a dense film. In non-planar SOFCs, the electrical connector conditions are quite different from those of the flat type, for example in cylindrical or flat-type SOFCs, the electrical connectors are the opposite poles between neighboring unit cells, since air or fuel channels already exist inside the tubes. In addition to the role of electrically connecting between the air of the cathode and the fuel gas of the anode to serve as a barrier to block the mixing of each other at the same time and is usually covered with a thin film. Therefore, under these conditions, the electrical connector should be secured in the oxidation atmosphere and hydrogen reduction atmosphere due to the presence of oxygen under high temperature reaction conditions, while having sufficient electrical conductivity, forming a dense membrane to prevent mixing of air and fuel, surrounding electrodes and electrolyte. The physical property conditions such as the thermal expansion coefficient and high temperature firing and ease of processing must be satisfied.

Representative ceramic electrical connectors reported to date include LaCrO ₃ -based oxides of Perovskite structure (ABO ₃ ), but not only form volatile CrO ₃ at temperatures above 1400 ℃ and oxidation atmosphere but also sinterability under 1400 ℃ Not only does not have a problem that the dense film is not formed, as the volume is expanded from Cr (IV) to Cr (III) in the hydrogen reduction atmosphere of the cathode, the interface separation phenomenon with the electrode occurs. In addition, the coefficient of thermal expansion of LaCrO ₃ is 8.610 ^-6 / ℃ and needs to match the thermal expansion coefficient (10.810 ^-6 / ℃) of Ni-YSZ (Subhash C Singhal and Kevin Kendall, High Temperature Solid Oxide Fuel Cell) Fundamentals, Design & Applications, 2003 Elsevier). In order to make up for the shortcomings of LaCrO ₃ oxide, it is possible to obtain 95% or more theoretical density at 1400 ~ 1600 ℃ temperature and oxidation atmosphere by doping alkaline earth metal such as Ca, Sr, Mg or transition metal such as Zn, Cu (US 5185301, US 5286686), have not yet been reported to be satisfactory in terms of high temperature thermal stability and electrical conductivity in a hydrogen reducing atmosphere.

On the other hand, the doped titanium oxide-based perovskite material (for example, SrTiO ₃ or CaTiO ₃ ) has been reported to have electrical conductivity in a hydrogen reducing atmosphere, and has a high dense film formation even at 1400 ° C. or below. However (US 2009/0186249), in the oxidation atmosphere, there is a disadvantage in that the electrical conductivity is not expressed because there is no thermal stability, it is likewise impossible to use in an atmosphere of oxidation-reduction.

Accordingly, there is a need to solve the problems of the conventional SOFC ceramic coupling material and to develop a new coupling material that simultaneously exhibits electrical conductivity in an oxidation-reducing atmosphere.

The problem to be solved by the present invention is to provide a new ceramic electrical connector material that can solve the problem of low temperature sinterability that the dense film is not formed at a low temperature below 1400 ℃ as well as the conductivity simultaneously expressed in the oxidation-reduction atmosphere of the existing SOFC ceramic connector. It is.

Another problem to be solved by the present invention is to provide a new structure of electrical connection material that can solve the above problems.

In order to achieve the above object, the ceramic connecting material for SOFC according to the present invention is characterized in that the composite oxide having a double perovskite structure (Titanium).

In the present invention, a specific molecular formula of the double perovskite-based composite oxide is represented by A _x A ' _{1 - x} TiB'O ₆ and rare earth metals such as La and Y at A and Ca at A'. And alkaline earth metals such as Sr and transition metals such as Co, Cr, Fe, Mn, Mo, Nb, Ni, Zn, and V at the position of B '.

In another aspect, the present invention is characterized in that the SOFC uses a composite oxide having a double perovskite structure including Titanium as an electrical connector.

In an aspect of the present invention, the conductive ceramic has a structural formula of A _x A ' _{1 - x} TiB'O ₆ . A is a rare earth, A 'is an alkaline earth metal, B' is a transition metal, it is characterized by consisting of a double perovskite-based composite oxide.

The double perovskite-based conductive ceramic electrical connector having the structural formula A _x A ' _{1 - x} TiB'O ₆ for a solid oxide fuel cell according to the present invention is excellent in sintering at low sintering temperature of 1400 ° C and oxidation or reduction at 800 ° C. Due to the high electrical conductivity in the atmosphere, it is possible to use it as a surface coating material of a metal electrical connection material or a dense film electrical connection material coated on a cathode or an anode of a non-planar SOFC.

1 is a view showing the X-ray diffraction analysis of the double perop Sky teugye composite oxide _{(La 0 .1 Ca 0 .9 TiB'O} 6) in accordance with the present invention.
2 is a view showing a double perop Sky teugye composite oxide _{(La 0 .1 Ca 0 .9 TiB'O} 6) scanning electron microscopy (SEM) analysis of the resulting surface according to the invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.

Example 1

Ti-containing double perovskite-based composite oxide of the present invention is a starting material Ca (NO ₃ ) ₂ H ₂ O, Co (NO ₃ ) ₃ H ₂ O, Cr (NO ₃ ) ₃ H ₂ O, Fe (NO ₃ ) ₃ ? H ₂ O, La (NO ₃ ) ₃ ? H ₂ O, Mn (NO ₃ ) ₂ ? H ₂ O, Ni (NO ₃ ) ₂ ? H ₂ O, Y (NO ₃ ) ₃ ? It is prepared by mixing in equivalence ratio using transition metal nitrate such as H ₂ O and metal alkoxide such as Ti [OCH (CH ₃ ) ₂ ] _4, and then synthesizing by nano powder synthesis such as solid state synthesis or Pechini method. can do. For example, the nano-powder synthesis by Pechini method is a mixture of at least one 1M nitrate solution and metal alkoxide of the transition metal nitrate to citric acid and ethylene glycol solution at a temperature of 60 ~ 70 ℃ to make a uniform solution After stirring and heating to about 150 ~ 160 ℃ to remove the water until the gel (gel) state and then calcined at about 900 ℃ for more than 5 hours. The calcined powder was ground to a fine powder and calcined at about 1250 ° C. for at least 5 hours. The composite oxide powder was mixed with ethanol and ball milled for at least 3 days. The composite oxide slurry was dried at about 50 ° C. for more than 12 hours, and pellets were produced under a pressure of about 2 ton, and then sintered at about 4 hours at a low temperature of 1,400 ° C. or less.

The composite oxide powder was confirmed to have a single phase double perovskite structure through X-ray diffraction analysis as shown in FIG.

Example 2

After sintering the above double perovskite-based composite oxide pellets at 1400 ° C. for 8 hours, Au wires were fixed with Au paste at a certain distance on the pellets and then oxidized (air) or reduced (800%) at a temperature of 800 ° C. ₂ / N ₂ ) The electrical conductivity was measured after 2 hours under the atmosphere.

As shown in Table 1 below, the electrical conductivity of the Ti-based double perovskite composite oxide is 2 S / cm or more when B '= Co, Fe, Cr, Mn in an oxidizing atmosphere, in particular, B' = Cr, In the case of Fe and Mn, it satisfies the requirements as a ceramic electrical connection material for SOFC in oxidizing and reducing atmospheres.

Complex oxide
(La _x Ca _1-x TiBO ₆ ) Electrical Conductivity in Oxidation Atmosphere (Air, 800 ℃) (S / cm) Reducing atmosphere (Hydrogen, 800 ℃)
Conductivity at (S / cm) La _{0 .1} Ca _{0 .9} TiO ₃ negligible 2.9 La _0.1 Ca _0.9 TiCoO ₆ 2.2 negligible La _0.1 Ca _0.9 TiNiO ₆ 0.1 negligible La _0.1 Ca _0.9 TiCrO ₆ 0.4 0.1 La _0.1 Ca _0.9 TiFeO ₆ 2.2 1.2 La _{0 .1} Ca _{0 .9} TiMnO ₆ 5.0 3.4 Y _{0 .1} Ca _{0 .9} TiMnO ₆ 4.2 2.8

Electrical Conductivity of Double Perovskite Composite Oxides

Example 3

The double perovskite-based composite oxide pellets were sintered at 1400 ° C. for 8 hours, and then further reduced in a reducing atmosphere (10% H ₂ / N ₂ ) at 800 ° C. for 2 hours or more, and then subjected to scanning electron microscopy (SEM). ) Analysis was performed.

As shown in figure 2, La _{0 .1} Ca For _{0 .9} TiO ₃ is then sintered at a temperature of 1400 ℃ exists a large number of pores, however, the double perovskite teugye composite oxide (La _{0 .1 0} Ca _{In the case of} TiB'O ₆ , B '= Co, Cr or Mn), it was confirmed that a dense structure with almost no pores 10 was formed. The formation of this dense structure seems to be based on the liquid phase 20 present in the grain boundary as well as the improvement of sinterability due to the transition metal located at B '.

Claims (20)

An electrical connector for electrically connecting the positive electrode and the negative electrode of neighboring unit cells of an SOFC, the electrical connector comprising a double perovskite-based composite oxide containing titanium. The method of claim 1, wherein the double perovskite-based composite oxide has a structural formula of A _x A ' _{1 - x} TiB'O ₆ , wherein A is a rare earth, A' is an alkaline earth metal, B 'is a transition metal Electrical connection material. The method of claim 2, wherein the rare earth metal is at least one selected from La, Y, the alkaline earth metal is at least one selected from Ca, Sr, the transition metal is Co, Cr, Fe, Mn, Mo, Nb, Ni, Electrical connection material, characterized in that at least one selected from Ti, V. The method of claim 1, wherein the double perovskite-based composite oxide is LaxCa1-xTiCrO _{6 ,}
LaxCa1-xTiFeO _6, LaxCa1-xTiMnO _6, or YxCa1-xTiMnO ₆ , the electrical connector. The electrical connector of claim 4, wherein x is less than 0.5. The electrical connector of claim 1, wherein the double perovskite-based composite oxide has an electrical conductivity of 0.1 S / cm or more in an oxidizing and reducing atmosphere of 1000 ° C or less. The electrical connector of claim 1, wherein the double perovskite-based composite oxide has an electrical conductivity of 0.1 S / cm or more in an oxidizing and reducing atmosphere at a temperature of 850 ° C or lower. The electrical connector of claim 1, wherein the double perovskite-based composite oxide forms a dense structure having a relative density of 94% or more at a sintering temperature of 1600 ° C. or less. The electrical connector of claim 1, wherein the double perovskite-based composite oxide forms a dense structure having a relative density of 94% or more at a sintering temperature of 1400 ° C. or less. SOFC, characterized in that the ceramic electrical connector material is a composite oxide of double perovskite structure comprising titanium. The SOFC according to claim 10, wherein the electrical connector has an electrical conductivity of 0.1 S / cm or more in an oxidizing and reducing atmosphere. The SOFC according to claim 10 or 11, wherein the double perovskite-based composite oxide is coated on the surface of the metal electrical connector. The SOFC according to claim 10, wherein the double perovskite-based composite oxide is doped in a cathode or an anode. The method of claim 10, wherein the double perovskite-based composite oxide has a structural formula of A _x A ' _{1 - x} TiB'O ₆ , wherein A is a rare earth, A' is an alkaline earth metal, B 'is a transition metal SOFC. The method of claim 10, wherein the rare earth metal is at least one selected from La, Y, the alkali metal is at least one selected from Ca, Sr, the transition metal is Co, Cr, Fe, Mn, Mo, Nb, Ni, SOFC, characterized in that at least one selected from Ti, V. The SOFC according to claim 10, wherein the double perovskite-based composite oxide is LaxCa _{1 - x} TiCrO _{6 ,} LaxCa _1-x TiFeO _6, LaxCa _{1 - x} TiMnO _{6 ,} or YxCa _{1 - x} TiMnO ₆ . As a double perovskite-based composite oxide, it has a structural formula of A _x A ' _{1 - x} TiB'O ₆ . Wherein A is a rare earth, A 'is an alkaline earth metal, and B' is a transition metal. The method of claim 17, wherein the rare earth metal is at least one selected from La, Y, the alkali metal is at least one selected from Ca, Sr, the transition metal is Co, Cr, Fe, Mn, Mo, Nb, Ni, Conductive ceramic, characterized in that at least one selected from Ti, V. The method of claim 17, wherein the double perovskite-based composite oxide is LaxCa _{1 - x} TiCrO _{6 ,} LaxCa _1-x TiFeO _6, LaxCa _{1 - x} TiMnO _{6 ,} or YxCa _{1 - x} TiMnO ₆ , wherein x is less than 0.5. A conductive ceramic, characterized in that. 18. The conductive ceramic as claimed in claim 17, wherein the conductive ceramic has an electrical conductivity of 0.1 S / cm or more in an oxidizing atmosphere, a reducing atmosphere, or both.

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