JP5313726B2 - Solid oxide fuel cell and interconnector for the cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interconnector which contains no element that degrades battery performance and secures both low reduction expansion nature and high conductivity. <P>SOLUTION: The composition inclination type interconnector is configured so that a reduction expansion rate rises or drops stepwise from one to other facing surfaces of a cell. It is formed from perovskite oxide represented by a general formula Ln<SB>1-x</SB>Ae<SB>x</SB>MO<SB>3-&delta;</SB>(where, Ln is at least one selected from lanthanoid, Ae is one or more kinds selected from a group comprising Sr, Ba, and Ca, M is one or more kinds selected from a group comprising Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, Mn, Mg, Rh, Pd, Pt, and Au, and 0&le;x&le;1). The composition of perovskite oxide differs from each other for each portion of different reduction expansion rate in stepwise manner. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a composition gradient interconnector for a solid oxide fuel cell and a solid oxide fuel cell including the interconnector.

  A solid oxide fuel cell (hereinafter sometimes referred to simply as “SOFC”) is also called a third generation fuel cell, and has the following advantages over other fuel cells. There is. For example, in SOFC, since the operating temperature can be increased, a reaction accelerator (catalyst) is unnecessary, and the running cost is reduced. Further, by reusing the high-temperature exhaust gas (exhaust heat), the overall efficiency (total efficiency) can be increased. Furthermore, since the SOFC has a high output density, it can be miniaturized. From these facts, it is expected as a distributed power generation apparatus that replaces an internal combustion engine such as a steam turbine or a gas turbine.

  When the SOFC is actually used, it is typically operated in a state where a plurality of single cells are overlapped to form a multi-layer in order to obtain a high voltage. This multi-layered assembly of single cells is called a stack. In such a stack, an interconnector is used to connect single cells. The interconnector separates the oxidizing gas (typically air) from the reducing gas (typically a fuel gas such as hydrogen or methane) while physically and electrically connecting the single cells. It also serves as a separator.

As an interconnector as described above, it has high conductivity, high stability in a reducing atmosphere (that is, low reduction expansion coefficient), low reactivity with cell materials such as electrolyte materials and electrode materials, and heat similar to cell materials. It is preferably formed from a material having properties such as an expansion coefficient.
As such an interconnector material, a metal material or a ceramic material has been proposed. As ceramic materials, as shown in Patent Documents 1 to 8, various perovskite oxide materials have been proposed. For _{example, La 1-p A p CrO} 3 ( where, A is at least one selected from the group consisting from Mg, Ca, Sr, Ba, a 0 ≦ p <1.) Such as lanthanum chromite system Perovskite oxide, or a perovskite oxide in which the B site is partially substituted (doped) with another element (for example, Si, Ti, Co, Ni, or Zr), and MTiO ₃ (where M is Li, And titanate-based perovskite oxides such as Ca, Cu, Sr, Ba, La, Ce, Pb, and Bi.

JP-A-8-55629 JP-A-8-83620 JP-A-8-190922 JP-A-10-125340 Japanese Patent Laid-Open No. 11-3720 JP 2003-331874 A JP 2003-288919 A JP 2007-39279 A

  However, among the ceramic-based interconnector materials as described above, for example, in the case of a material containing chromium (Cr), when a solid oxide fuel cell including an interconnector made of the material is used, Cr is ( There is a risk that the battery performance will gradually deteriorate due to diffusion (typically to the air electrode) (this phenomenon is generally referred to as Cr poisoning).

  Further, since the interconnector material described above has a relatively high reduction expansion coefficient, for example, when forming a stack composed of a plurality of large single cells, the interconnector has a fuel electrode (reducing atmosphere) side and an air electrode (oxidized). There is a risk that the durability of the fuel cell (stack) may be reduced, such as a difference in expansion degree between the (atmosphere) side (that is, a stress difference between the two increases and a crack). Accordingly, an interconnector material having a low reduction expansion rate (low reduction expansion property) is desired. However, there are many such materials that can reduce conductivity when pursuing low reductive expansibility, so that low reductive expansivity is maintained while maintaining high conductivity sufficient for practical use as an interconnector. It was difficult to realize an interconnector provided.

  The present invention has been made in view of the above points, and its main object is to include a solid oxide including an interconnector that does not contain an element that decreases battery performance and can achieve both low reductive expansion and high conductivity. A fuel cell is provided. Another object is to provide such an interconnector.

In order to achieve the above object, an interconnector provided by the present invention comprises a solid oxide comprising a plurality of cells each composed of an air electrode as a positive electrode, a fuel electrode as a negative electrode, and a solid oxide electrolyte disposed between the two electrodes. In a physical fuel cell, a composition gradient type interconnector for a solid oxide fuel cell disposed between the cells to electrically connect the plurality of cells. And this interconnector is comprised so that a reduction | restoration expansion coefficient may rise or fall in steps toward the other cell opposing surface from one cell opposing surface of this interconnector. Here, the interconnector has the following general formula:
Ln _1-x Ae _x MO _3-δ
(1)
(Here, Ln is at least one element selected from lanthanoids, Ae is one or more elements selected from the group consisting of Sr, Ba and Ca, and M is Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, Mn, Mg, Rh, Pd, a two or more elements that will be selected from the group consisting of Pt and Au, 0 ≦ x ≦ 1, δ is a value determined so as to satisfy the charge neutrality condition.), and each portion of each portion of the interconnector having a different reductive expansion coefficient in the above-described step is formed. while increasing the reduction original inflatable perovskite oxide constituting, mode of the element M to lower the conductivity, while increasing the conductivity of the perovskite oxide, the element M that increases the reduction expansion coefficients Ratio is equal to or are different from each other.

The composition gradient type interconnector according to the present invention is composed of the perovskite oxide of the above general formula (1), and includes portions having different reduction expansion coefficients stepwise by changing the composition of the perovskite oxide. Since such a perovskite oxide does not contain Cr, the use of the interconnector according to the present invention prevents battery performance from being deteriorated due to Cr poisoning.
In addition, the interconnector is configured such that the reduction expansion coefficient increases or decreases stepwise from one cell facing surface of the interconnector to the other cell facing surface. Thus, for example, one cell facing surface having a relatively high reduction expansion coefficient (that is, having a high reduction expansion property) is one of two cells (single cells) that sandwich the interconnector from both sides. The other cell facing surface facing the air electrode of one cell and having a relatively low reduction expansion coefficient (that is, having a low reduction expansion property or a high reduction expansion resistance) is used as the fuel electrode of the other cell. By disposing the interconnector so as to face each other, the expansion of the interconnector facing the cell facing surface facing the fuel electrode is suppressed, and the interconnector's fuel electrode (reducing atmosphere) side and air electrode ( The difference in expansion that can occur between the oxidation atmosphere) side is reduced, and the occurrence of cracks and the like is prevented.
In addition, the perovskite oxide having a composition that provides high reductivity is typically provided with relatively high conductivity, while the perovskite oxide having a composition that provides low reductivity is low in conductivity. Become. As a result, the composition-graded interconnector according to the present invention has a low reduction as compared to an interconnector composed entirely of a perovskite oxide having a composition having a low reduction expansion property but low conductivity. Both expandability and high conductivity can be provided.
Therefore, according to the present invention, a composition gradient type interface for a solid oxide fuel cell (SOFC) suitable for a solid oxide fuel cell (SOFC) that does not contain an element that degrades the battery performance and realizes both high conductivity and reduction expansion resistance is realized. A connector can be provided. Further, by providing such an interconnector, it is possible to provide a preferable SOFC that can maintain high battery performance and durability over a long period of time.

In a preferred aspect of the composition gradient interconnector disclosed herein, the one cell facing surface having a relatively high reduction expansion coefficient is a surface facing the air electrode of one cell sandwiching the interconnector, and The other cell facing surface having a relatively low reduction expansion coefficient is disposed so as to be a surface facing the fuel electrode of the other cell sandwiching the interconnector.
By using the composition-gradient interconnector having such a configuration, the occurrence of cracks or the like due to a difference in expansion between the one cell facing surface side facing the air electrode and the other cell facing surface side facing the fuel electrode of the interconnector is further increased. It is possible to provide a more preferable SOFC that is more reliably prevented and has improved durability and also has high conductivity as the whole interconnector.

In a further preferred aspect of the composition gradient interconnector disclosed herein, the composition of the perovskite oxide is different from each other from the one cell-facing surface to the other cell-facing surface. A multilayer structure composed of a plurality of layers is formed so that the reduction expansion coefficient gradually decreases from the layer constituting one cell facing surface toward the layer constituting the other cell facing surface. In the multilayer structure, the layer constituting the one cell facing surface having a high reduction expansion coefficient is disposed on the air electrode side of the cell, and the layer constituting the other cell facing surface having a low reduction expansion coefficient. Is arranged on the fuel electrode side of the cell.
A structure (structure) in which the reduction expansion coefficient is increased or decreased stepwise from one cell facing surface of the interconnector to the other cell facing surface by using such a multilayered composition gradient type interconnector. It is possible to provide a preferable SOFC that can be easily realized and can maintain high battery performance and durability over a long period of time.

In another preferable aspect of the interconnector disclosed herein, the perovskite oxides having different compositions constituting the portions having different reduction expansion coefficients in stages are all represented by the following general formula:
La _1-x Sr _x M _1-y Fe _y O _3-δ (2)
(Here, M is one or two selected from the group consisting of Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, Mn, Mg, Rh, Pd, Pt, and Au. The above elements, 0 ≦ x ≦ 1, 0.5 ≦ y ≦ 0.9, and δ is a value determined so as to satisfy the charge neutrality condition.) It is included.
By applying such a perovskite oxide to an interconnector, the composition can be adjusted to easily form an interconnector composed of portions (typically a plurality of layers) having different reduction expansion coefficients in stages. Can be realized.

In a preferable aspect of the multilayered composition graded interconnector disclosed herein, a two-layer structure of a layer constituting one cell facing surface and a layer constituting the other cell facing surface having mutually different reduction expansion coefficients It is characterized by comprising.
By using the composition gradient type interconnector having such a configuration, the reduction expansion coefficient is gradually increased or decreased from the one cell facing surface to the other cell facing surface even in a simple configuration. It can be realized easily and effectively.

In a preferred aspect of the above-described composition gradient type interconnector having the two-layer structure, the reduction expansion coefficient of one layer of the two-layer structure is 0.15% or more, and the reduction expansion coefficient of the other layer is 0. Less than 15%.
By using a composition-gradient interconnector having such a reduction expansion coefficient, cracks are generated due to a difference in expansion between one cell facing surface side facing the air electrode of the interconnector and the other cell facing surface side facing the fuel electrode. Is effectively prevented, and the durability of the interconnector, and thus the SOFC, is improved. Note that the reduction expansion ratio in the present specification, E _R (%) thermal expansion coefficient under a reducing atmosphere (hydrogen gas), when the thermal expansion coefficient under an air atmosphere and E _A (%), the following (3 ).
Reduction expansion rate (%) = [{(1 + E _R / 100) − (1 + E _A / 100)} / (1 + E _A / 100)] × 100 (3)

Moreover, in another preferable aspect of the composition gradient type interconnector disclosed herein, the electrical conductivity is 50 S / cm or more over the entire interconnector.
By using an interconnector having such conductivity throughout, it is possible to provide an SOFC having conductivity that is excellent in practicality.

Further, the present invention, as another aspect, is a solid oxide fuel cell comprising a plurality of cells composed of an air electrode as a positive electrode, a fuel electrode as a negative electrode, and a solid oxide electrolyte disposed between the two electrodes,
It is possible to provide an SOFC characterized in that the composition gradient interconnector disclosed herein is disposed between the plurality of cells.

It is sectional drawing which shows typically the interconnector of the two-layer structure which concerns on one Embodiment of this invention. 1 is an exploded perspective view schematically showing a configuration of a flat plate type solid oxide fuel cell according to an embodiment of the present invention. It is the figure which showed typically the apparatus for exposing the perovskite type oxide which concerns on an Example to an air atmosphere and a reducing atmosphere, and measuring generation | occurrence | production of a leak.

  Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than matters specifically mentioned in the present specification (for example, constituent materials of interconnectors) and matters necessary for the implementation of the present invention (for example, configuration of solid oxide fuel cell (single cell)) And the construction method) can be grasped as a design matter of a person skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

As described above, the composition-graded interconnector provided by the present invention is excellent in practicality as a SOFC, prevention of Cr poisoning, suppression of deterioration due to expansion under a reducing atmosphere (low reductive expansion), and SOFC. For the purpose of realizing high conductivity, it is composed of a perovskite oxide represented by the above general formula (1). In addition, the interconnector according to the present invention is configured such that the reduction expansion coefficient decreases stepwise from the air electrode side of one cell sandwiching the interconnector toward the fuel electrode side of the other cell. It is the composition inclination type interconnector characterized by this, Comprising: It is not limited by the other component which does not characterize this invention. Therefore, as long as the above object can be achieved, there is no particular limitation on the content and composition of other subcomponents that can be included in the interconnector according to the present invention.
In addition, the composition gradient type interconnector according to the present invention is a solid oxide fuel cell having various structures (for example, a flat plate type, a cylindrical type, or a flat type in which a cylindrical side surface is crushed vertically. It can be preferably applied to a tubular type or the like, and the shape of the fuel cell is not particularly limited.

The interconnector disclosed herein is configured such that the reduction expansion coefficient increases or decreases stepwise from one cell facing surface of the interconnector to the other cell facing surface. The following general formula:
Ln _1-x Ae _x MO _3-δ
(1)
It is formed from the perovskite type oxide represented by these. Here, Ln is at least one element selected from lanthanoids, and preferably La (lanthanum). Ae is one or more elements selected from the group consisting of Sr (strontium), Ba (barium) and Ca (calcium), and is preferably Sr. M is titanium (Ti), zirconium (Zr), aluminum (Al), gallium (Ga), niobium (Nb), tantalum (Ta), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), manganese (Mn), magnesium (Mg), rhodium (Rh), palladium (Pd), platinum (Pt) and gold (Au) 2 or more elements that will be selected from the group consisting of. Further, “x” in the general formula (1) is a value indicating the ratio of Ln replaced by Ae in this perovskite structure. The possible range of x is 0 ≦ x ≦ 1 (preferably 0 ≦ x <1, for example, 0.4 ≦ x ≦ 0.6).
Note that δ is a value determined so as to satisfy the charge neutrality condition. The number of oxygen atoms in the general formula (1) varies depending on the type of atom that substitutes a part of the perovskite structure, the substitution ratio, and other conditions, so that it is difficult to display accurately. Therefore, it is appropriate to adopt a positive number δ (0 <δ <1) that does not exceed 1 as a value that is determined so as to satisfy the charge neutrality condition, and to display the number of oxygen atoms as 3-δ. However, in the following, it may be displayed as 3 for convenience. However, even if the number of oxygen atoms is represented as 3 for convenience, it does not represent a different compound.

The perovskite oxide is more preferably a perovskite oxide represented by the general formula (1):
La _1-x Sr _x M _1-y Fe _y O _3-δ (2)
The perovskite type oxide represented by the formula (1), containing Fe at the B site. M is one or more selected from the group consisting of Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, Mn, Mg, Rh, Pd, Pt and Au. An element, preferably Ti and / or Zr. That is, as a suitable example of such a perovskite oxide, a perovskite oxide represented by La _1-x Sr _x Ti _1-y Fe _y O _{3 -δ} (hereinafter referred to as “LSTF oxide”), or And a perovskite oxide (hereinafter referred to as “LSZF oxide”) represented by La _1-x Sr _x Zr _1-y Fe _y O _3-δ . Thus, the perovskite oxide containing Ti and / or Zr is preferable because the reduction expansion of the oxide is suppressed and a low reduction expansion coefficient (high reduction expansion resistance) can be exhibited.

  Zr and Fe are elements that can be included as a constituent material of a single cell in a general SOFC. That is, typical electrolyte materials include yttria stabilized zirconia (YSZ) or other stabilized zirconia (for example, scandia stabilized zirconia (ScSZ)). Examples of the air electrode (cathode) material include lanthanum strontium manganite (LSM) and lanthanum strontium cobaltite (LSC) perovskite oxides, or composites of these oxides with zirconia. It is used. Further, as a fuel electrode (anode) material, for example, a nickel-zirconia composite is used. Thus, Zr and Fe are contained as component elements of a typical single cell constituent material. Therefore, by applying a perovskite oxide powder containing Fe and Zr as a constituent material of the interconnector disclosed herein, Zr and Fe are used as single-cell electrodes (for example, from the interconnector for a long period of time). Even if there is a risk of diffusion to the air electrode side, the SOFC battery performance is unlikely to deteriorate (decrease).

However, the Ti and Zr give the perovskite oxide represented by the general formula (2) with reduction expansion resistance, but may reduce conductivity. On the other hand, while Fe imparts conductivity to the perovskite oxide, there is a risk of increasing the reduction expansion coefficient. Therefore, by changing the content (molar ratio) of Fe and Ti (and / or Zr) at the B site, the conductivity of the interconnector formed from the perovskite oxide represented by the general formula (2) The reduction expansion resistance can be adjusted in a well-balanced manner.
Thus, as a perovskite type oxide suitable as a component capable of providing both the reduction expansion resistance and conductivity, the molar ratio of M and Fe at the B site in the general formula (2) is (1-y). : If y, the possible range of y is 0 <y ≦ 1, preferably 0.4 ≦ y <1, and more preferably 0.5 ≦ y ≦ 0.9. Particularly preferably, 0.7 ≦ y ≦ 0.9.

  The composition gradient type interconnector disclosed here is electrically conductive to such an extent that a single cell is electrically connected (typically in series) via the interconnector, and a high output that is practical as a stack can be obtained. It is preferable to have the property over the entire interconnector. Such an interconnector has a conductivity of 50 S / cm or more (more preferably 55 S / cm or more, particularly preferably 75 S / cm or more) over the entire operating temperature range of SOFC (for example, 800 ° C. to 1000 ° C.). An interconnector formed from the perovskite oxide is preferable because it has a conductivity in the above range.

Moreover, the composition gradient type interconnector disclosed here is preferable because it can have a thermal expansion coefficient similar to the electrode material of SOFC by being formed from the perovskite oxide. The electrode material has a thermal expansion coefficient (typically an average value between room temperature (25 ° C.) and 1000 ° C. based on a general differential expansion method (TMA)) of 1 × 10 ⁻⁵ to 1. a 2 × ^{10 -5} / K, the above-mentioned general formula (1) and / or (2) of the perovskite oxide represented by, in particular LSTF oxides and LSZF oxides, its thermal expansion coefficient is within the above range Therefore, it is preferable. In such an interconnector, the difference in thermal expansion between adjacent electrodes when using the SOFC is reduced, so that distortion, cracks, and the like that may occur at the connection between the interconnector and the electrode can be effectively prevented. .

The composition gradient type interconnector disclosed here is configured to gradually reduce (or increase) the reduction expansion coefficient from one cell facing surface toward the other cell facing surface. In the structure in which the portions having different reduction expansion coefficients are arranged stepwise as described above, the portions formed from the perovskite oxides having different compositions from each other are arranged stepwise (that is, the perovskite type). The composition is preferably realized by a composition gradient structure in which the oxide composition is gradually graded. In addition, such a composition gradient structure is a stepwise process in which a plurality of layers having different compositions of the perovskite oxide are stepped from the layer constituting the one cell facing surface toward the layer constituting the other cell facing surface. It is preferably realized by a multilayer structure laminated so that the reduction expansion coefficient decreases.
The perovskite type oxide forming each layer constituting such a multilayer structure may be any perovskite type oxide represented by the general formula (1) and / or (2), but each layer is formed. The perovskite oxides having the same constituent elements are more preferably different in composition from each other due to the different contents (molar ratio) of the constituent elements. That is, for example, in a composition gradient interconnector in which layers formed of a perovskite oxide represented by the general formula (2) are stacked, preferably all the layers are La as constituent elements of the perovskite oxide. , Sr, Fe, and the same M, but the values of x and / or y are different in each layer. The composition graded interconnector having a multilayer structure formed from the perovskite oxide having such a composition increases the affinity between adjacent layers, and therefore, the occurrence of peeling or cracking at the interface (contact surface) of each layer This is preferable because the durability of the entire interconnector is improved.

  The simplest structure of the composition graded interconnector having the multilayer structure as described above includes a layer constituting one cell facing surface and a layer constituting the other cell facing surface having mutually different reduction expansion coefficients. This is an interconnector configured by a two-layer structure. In such a two-layer composition graded interconnector, one layer of the two-layer structure constitutes a layer having a relatively high reduction expansion coefficient, and the other layer comprises a layer having a relatively low reduction expansion coefficient. Since it is configured, even a simple structure of two layers can exhibit the same effect as a multilayer structure. Therefore, the composition gradient type interconnector having such a two-layer structure can be preferably used. Hereinafter, as an embodiment of the composition gradient type interconnector according to the present invention, a two-layer interconnector will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an interconnector 10 having such a two-layer structure, but the two layers 2 and 4 are not shown in cross section.

  As shown in FIG. 1, a composition gradient type interconnector 10 having a two-layer structure according to an embodiment of the present invention includes a layer 2 having a relatively low reduction expansion coefficient (hereinafter simply referred to as “low reduction expansion layer 2”). And a layer 4 having a relatively high reduction expansion coefficient but a high conductivity (hereinafter sometimes simply referred to as a “high conductivity layer 4”). When the interconnector 10 is disposed between the cells, the surface facing the low reduction expansion layer 2 facing one cell is the cell facing surface 12, and the surface facing the high conductivity layer 4 facing the other cell is the cell facing. Let it be surface 14. When the interconnector 10 is provided in the SOFC, the cell facing surface 12 faces the fuel electrode of one cell holding the interconnector 10, and the cell facing surface 14 contacts the air electrode of the other cell. Arranged so as to face each other.

Reduction expansion ratio in the composition graded interconnector 10 according bilayer structure, the thermal expansion coefficient in an air atmosphere (e.g., oxygen partial pressure of about 200 hPa (approximately 0.12Tm) and _{E A,} a reducing atmosphere (e.g. hydrogen _(H 2) 5 vol %, nitrogen _(N 2) a reducing atmosphere containing 95 vol%) thermal expansion coefficient as _{E R,} given by Eq. (3) shown.
Reduction expansion rate (%) = [{(1 + E _R / 100) − (1 + E _A / 100)} / (1 + E _A / 100)] × 100 (3)
Here, in the interconnector 10, it is preferable that the reduction expansion coefficient of the low reduction expansion layer 2 is less than 0.15% (more preferably 0.14% or less, and further preferably 0.10% or less). When the low reductive expansion layer 2 has a reductive expansion rate included in such a range, the interconnector 10 is arranged so that the cell facing surface 12 constituting the low reductive expansive layer 2 faces the fuel electrode of one cell. Even when the low reductive expansion layer 2 is exposed to a reducing atmosphere when it is disposed, it is preferable because reductive expansion of the exposed portion can be effectively prevented.
On the other hand, the highly conductive layer 4 has high conductivity, and its reduction expansion coefficient is higher than that of the low reduction expansion layer 2. Such a reduction expansion rate can typically be 0.15% or more (eg, 0.15% to 0.7%), or 0.2% or more (eg, 0.28% to 0.7%). For example, when the reductive expansion coefficient of the highly conductive layer 4 formed of LSZF oxide is not less than the above range, the conductivity of the layer at 1000 ° C. is approximately 80 S / cm or more. The composition gradient interconnector 10 including the highly conductive layer 4 having such conductivity is preferable because the interconnector as a whole can have high conductivity excellent in practicality.

As the thermal expansion coefficients E _R and E _A in the above formula (3), for example, values obtained by measuring an increase in volume between room temperature and 1000 ° C. can be used. In the composition gradient type interconnector 10 having a two-layer structure having a reduction expansion coefficient in the above range, the values of x and y in the general formula (1) and / or the general formula (2) are within the above preferable range. It can be realized by adjusting. When such a two-layer composition graded interconnector 10 is formed of, for example, an LSTF oxide or an LSZF oxide, a composition suitable for the low reduction expansion layer 2 (preferable range of x and y) is 0.4 ≦ x ≦ 0.6 and 0.5 ≦ y ≦ 0.8 (for example, 0.6 ≦ y ≦ 0.8). Moreover, a suitable composition as the highly conductive layer 4 is 0.4 ≦ x ≦ 0.6 and 0.7 ≦ y ≦ 0.9 (for example, 0.8 ≦ y ≦ 0.9).

  The shape and dimensions of such a two-layer composition graded interconnector 10 can be appropriately changed according to the structure and size of various SOFCs applied, and are not particularly limited. For example, when the interconnector 10 is applied to a flat plate type SOFC (see FIG. 2), the interconnector 10 is formed into a flat plate shape (or layer shape) sandwiched between cells (single cells). Further, for example, in the case of a cylindrical SOFC having a configuration in which cylindrical single cells are connected in parallel via an interconnector, the slurry-like raw material forming each layer according to the interconnector 10 is added to the peripheral side surface of the single cell. It may be a form obtained by applying to a predetermined area and baking.

Such a two-layer composition graded interconnector 10 is manufactured, for example, as follows.
First, each of the low reduction expansion layer 2 and the highly conductive layer 4 constituting the interconnector 10 having a two-layer structure to be manufactured is prepared. That is, first, the perovskite oxide that forms the low reduction expansion layer 2 and the metal atom constituting the perovskite oxide represented by the general formula (1) (that is, Ln in the general formula (1) (for example, A powder (raw material powder) of a compound containing La), Ae (for example, Sr), and a metal element M (for example, Fe and Ti or Zr) that can form the B site of the perovskite oxide is prepared. Then, each raw material powder is mixed at a predetermined mixing ratio (that is, a mixing ratio determined so that each metal atom is included in a predetermined composition ratio with the whole perovskite oxide as 1 mol). This mixture is formed into a predetermined shape (plate or layer) and fired (oxidized) in an oxidizing atmosphere (for example, in the air) or an inert gas atmosphere to form a shaped body as the low reductive expansion layer 2. obtain. The molded body of the high conductive layer 4 is also produced in the same manner as the low reduction expansion layer 2 described above.
Here, as the raw material powder, an oxide containing each metal atom constituting the perovskite oxide or a compound that can be converted into an oxide by heating (a carbonate, nitrate, sulfate, phosphate, Acetates, oxalates, halides, hydroxides, oxyhalides, and the like) may be used. This raw material powder may contain a compound (a composite metal oxide, a composite metal carbonate, or the like) containing two or more metal atoms among the above metal atoms. The average particle diameter of each raw material powder is, for example, 0.5 μm to 3 μm (preferably about 1 μm to 2 μm). Here, the average particle diameter refers to D ₅₀ (median diameter) in the particle size distribution of the raw material powder. In addition, you may use the commercial item of the perovskite type oxide powder which consists of predetermined composition ratio instead of the said raw material powder.

  The appropriate firing (main firing) temperature is typically 1200 to 1800 ° C. (preferably 1400 to 1600 ° C.), although it varies depending on the composition of the perovskite oxide. Moreover, the firing step can include one or more calcination steps and a subsequent firing step. In this case, the main baking step is preferably performed at the baking temperature as described above, and the calcining step is preferably performed at a lower baking temperature (for example, 800 to 1500 ° C., preferably 1000 to 1300 ° C.) than the main baking step.

Moreover, when obtaining the said molded object using the raw material powder which has an average particle diameter smaller than the said range, it is obtained with the following method, for example. That is, the raw material powder is calcined, and the calcined raw material is pulverized using a wet ball mill or the like to obtain a calcined powder. Next, water and a molding aid such as an organic binder and a dispersing agent are added to and mixed with the calcined powder to prepare a slurry, and a desired particle size (for example, an average particle size is obtained by using a granulator such as a spray dryer). The raw powder for main firing granulated to 10 to 100 μm can be obtained. The molded body is obtained by molding and firing the raw powder for main firing thus obtained.
In addition, in the molding of the raw material powder or the calcined powder obtained by pulverizing the calcined product obtained after the calcining step, conventionally known molding methods such as uniaxial compression molding, isostatic pressing, and extrusion molding are used. Can be adopted. A conventionally well-known binder etc. can be used for this shaping | molding.
Note that the low reduction expansion layer 2 and the high conductivity layer 4 have the performance (battery deterioration prevention due to Cr poisoning, low reduction expansion, high conductivity, or distortion due to a thermal expansion coefficient similar to that of the cell material. Components other than the perovskite oxide represented by the general formula (1) may be contained within a range that does not significantly impair crack generation prevention properties and the like.

Next, the obtained compacts of the low reduction expansion layer 2 and the highly conductive layer 4 are polished to a desired thickness. Here, in order to keep the conductivity of the entire interconnector 10 as high as possible, each thickness may be adjusted so that the thickness of the high conductive layer 4 is larger than the thickness of the low reducing expansion layer. In this case, for example, the thickness of the highly conductive layer is preferably 2 to 10 times (more preferably 3 to 8 times, for example, about 4 times) the thickness of the low reduction expansion layer.
Next, the molded bodies of the low reduction expansion layer 2 and the highly conductive layer 4 whose thicknesses are adjusted as described above are opposed to each other, and these opposed surfaces are brought into contact with each other to be bonded. The joining method is not particularly limited as long as it can maintain high electrical conductivity and reduction expansion resistance as a whole interconnector. A diffusion bonding method in which bonding is performed by diffusing atoms in the bonded portion by pressing can be preferably employed. When the low reduction expansion layer 2 and the highly conductive layer 4 are bonded by diffusion bonding, it is preferable to heat to, for example, 1000 ° C. to 1400 ° C.
As described above, the composition gradient interconnector 10 having a two-layer structure in which the low reduction expansion layer 2 and the highly conductive layer 4 are laminated is manufactured.

  In addition, the manufacturing method of this interconnector 10 is not limited to the above manufacturing method, For example, the method of forming an interconnector and constructing | stacking simultaneously as follows may be sufficient. In such a method, first, a raw material powder for forming a low reduction expansion layer is prepared in a slurry form, and this is applied to the whole or a part of the surface of one cell (the fuel electrode side of the cell as will be described later). By drying and firing, a low reduction expansion layer is formed on the fuel electrode side of the cell. Next, a raw material powder for forming a highly conductive layer is prepared in a slurry form, and this is applied onto the low reduction expansion layer so that the applied portion and the air electrode side surface of another cell face each other. The other cells are connected (connected) and then dried and fired. As a result, the low reduction expansion layer and the highly conductive layer are laminated to form a two-layer interconnector, and at the same time, a stack in which a plurality of cells are connected via the interconnector. Can be built in one piece.

  The compositionally graded interconnector 10 having a two-layer structure obtained as described above is preferably provided in an SOFC as shown below, for example. Although not intended to be particularly limited, in the following, referring to FIG. 2 for a preferred embodiment of an SOFC including such an interconnector 10 as an example where the interconnector 10 is applied to a flat-plate SOFC. However, the present invention will be described in detail. FIG. 2 is an exploded perspective view schematically showing the structure of a flat plate type solid oxide fuel cell (SOFC) 100 according to an embodiment. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified.

As shown in FIG. 2, the flat plate type SOFC 100 according to this embodiment includes a cell (single cell) 20 including a layered solid electrolyte 22, an air electrode 24, and a fuel electrode 26, and the composition gradient interconnector 10. It is configured as a stack in which a plurality of layers are stacked. The cell 20 has a sandwich structure in which both surfaces of a solid electrolyte 22 are sandwiched between a layered air electrode 24 and a fuel electrode 26, respectively.
Here, the two-layer composition graded interconnector 10 provided in the SOFC 100 will be described with reference to FIG. 2 by taking an interconnector 10A as one of the interconnectors 10 as an example. The interconnector 10A is sandwiched between two cells 20A and 20B, and the cell facing surface 12 formed by the low reduction expansion layer 2 faces (adjacent) the fuel electrode 26 of one cell 20A. The cell facing surface 14 formed by the highly conductive layer 4 is opposed (adjacent) to the air electrode 24 of the other cell 20B. A plurality of grooves may be formed in the cell facing surface 12, and the grooves serve as fuel gas flow paths 13 through which the supplied fuel gas (for example, H ₂ gas) flows. Similarly, a plurality of grooves as the air flow path 15 through which the supplied air flows may be formed in the cell facing surface 14. In the interconnector 10 having such a configuration, as shown in FIG. 2, the fuel gas flow path 13 and the air flow path 15 are typically formed so that the directions of the flow paths are orthogonal to each other. The SOFC 100 typically has a sealed structure that is sealed with a sealing member such as glass sealing so that gas supplied into the stack does not leak.

The solid electrolyte 22 in the cell 20 according to the present embodiment may have a conventionally known configuration and form and is not particularly limited. As the constituent material, various conventionally known solid electrolyte materials can be preferably used. The solid electrolyte 22 is made of a material that has a high oxygen ion (oxide ion) conductivity in both an oxidizing (air) atmosphere and a reducing (fuel gas) atmosphere and can form a dense layer without gas permeability. Is preferred. For example, the solid electrolyte material is preferably a ceramic material such as yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), or lanthanum gallate (LaGaO ₃ ) in which yttria or scandia is dispersed and dissolved in zirconia.

Further, the air electrode 24 in the cell 20 may have a conventionally known configuration and form, and is not particularly limited. As the constituent material, various conventionally known air electrode materials can be preferably used. The air electrode 24 is preferably made of a porous body that is highly durable even in an oxidizing atmosphere and can efficiently pass a gas. For example, lanthanum manganite (LaAeMnO ₃ (where A is Sr or Ca), lanthanum cobaltite (LaSrCoO ₃ ), lanthanum ferrite (LaSrFeO ₃ ), lanthanum nickel oxide (LaNiO ₃ ), samarium cobaltite (SmSrCoO ₃ ) In addition, a perovskite oxide having a composition containing the same constituent elements as those of the highly conductive layer 4 constituting the cell facing surface 14 facing the air electrode 24 can also be used.

The fuel electrode 26 in the cell 20 may have a conventionally known configuration and form, and is not particularly limited. As the constituent material, various conventionally known fuel electrode materials can be preferably used. It is preferable to be composed of a porous body that is highly durable even in a reducing atmosphere and can efficiently pass gas. For example, NiO—YSZ, NiO—ScSZ, etc., a composite (composite material) of nickel oxide and typically a ceramic similar to the solid electrolyte material can be given.
The cell 20 is not limited to the above configuration, and a conventionally known configuration applicable to a general SOFC can be appropriately selected and used without particular limitation. Further, other configurations applicable to the SOFC (for example, an air electrode intermediate layer disposed between the air electrode 24 and the solid electrolyte 22, or a fuel electrode 26 and the solid electrolyte 22). A fuel electrode intermediate layer).

As a manufacturing method of the SOFC 100, for example, the SOFC 100 can be obtained by the following method. First, the cell 20 is manufactured. That is, the solid electrolyte 22 is prepared by a predetermined forming method (or a film forming method) using a conventionally known solid electrolyte material as described above. Next, a conventionally known air electrode material as described above is applied to one side surface of the solid electrolyte 22. Such an application method is not particularly limited, and a conventionally known method (for example, a wet film forming method) can be preferably used. Similarly for the fuel electrode, a conventionally known fuel electrode material as described above is applied to the other surface of the solid electrolyte 22.
Next, by firing the solid electrolyte 22 to which the air electrode material and the fuel electrode material are applied on both side surfaces, the cells 20 in which the fuel electrodes are formed on both side surfaces of the solid electrolyte 22 are obtained. The SOFC 100 is obtained by stacking a plurality of cells 20 using the composition gradient interconnector 10 obtained as described above.

  Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

<Preparation of perovskite oxide>
Commercially available lanthanum oxide (La ₂ O ₃ ) powder (average particle size about 2 μm), strontium carbonate (SrCO ₃ ) powder (average particle size about 2 μm), titanium oxide (TiO ₂ ) powder (average particle size about 1 μm) and oxidation Iron (Fe ₂ O ₃ ) powder (average particle size of about 2 μm) was mixed at a stoichiometric ratio of the composition of the fired body obtained after firing. In other words, La was 0.6, Sr was 0.4, Ti was 0.1, and Fe was 0.9 mol, and they were mixed using a ball mill. The mixed powder thus obtained was calcined at a firing temperature of 1200 ° C. for 6 hours. The calcined product thus obtained was pulverized by a wet ball mill to obtain a perovskite oxide raw material powder.
Next, this raw material powder was mixed with a binder and granulated into particles of about 80 μm. This granulated powder was formed into a disk shape having a diameter of about 30 mm and a thickness of about 4 mm by press molding at 100 MPa. The molded body was heated to 1400 ° C. to 1600 ° C. in the atmosphere, held for 6 hours, fired, and then mechanically polished to obtain a perovskite oxide LSTF1 (La _0.6 Sr _0.4 Ti) having a predetermined thickness. _0.1 Fe _0.9 O ₃ ) was obtained.
Perovskite oxides LSTF2 and LSTF3 were also obtained in the same manner as LSTF1.

For the perovskite oxides LSZF1 to LSZF4, zirconium oxide (ZrO ₂ ) powder (average particle size of about 1 μm) was prepared in place of the titanium oxide (TiO ₂ ) powder, and the perovskite oxides LSZF1 to LSZF4 were prepared in the same manner as the LSTF 1 described above.
The perovskite oxide LSCF was prepared in the same manner as the LSTF 1 by preparing chromium oxide (Cr ₂ O ₃ ) powder (average particle diameter of about 1 μm) instead of the titanium oxide (TiO ₂ ) powder.
For the perovskite oxide LSC, the chromium oxide (Cr ₂ O ₃ ) powder is prepared instead of the titanium oxide (TiO ₂ ) powder and the iron oxide (Fe ₂ O ₃ ) powder, and the perovskite oxide LSC is produced in the same manner as the LSTF 1 described above. did.
As described above, perovskite oxides having nine kinds of compositions were obtained. The composition of each perovskite oxide and the composition name (name) of each oxide are shown below.
LSTF1; La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O ₃
LSTF2; La _0.6 Sr _0.4 Ti _0.2 Fe _0.8 O ₃
LSTF3; La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃
LSZF1; La _0.6 Sr _0.4 Zr _0.1 Fe _0.9 O ₃
LSZF2; La _0.6 Sr _0.4 Zr _0.15 Fe _0.85 O ₃
LSZF3; La _0.6 Sr _0.4 Zr _0.2 Fe _0.8 O ₃
LSZF4; La _0.6 Sr _0.4 Zr _0.3 Fe _0.7 O ₃
LSCF; La _0.6 Sr _0.4 Cr _0.5 Fe _0.5 O ₃
LSC; La _0.6 Sr _0.4 CrO ₃

Next, the reduction expansion coefficient was evaluated for each of the nine types of perovskite oxides.
<Evaluation of reduction expansion coefficient>
In the obtained LSTF1, the LSTF1 was maintained from room temperature to 1000 ° C. under an air atmosphere (oxygen partial pressure of about 200 hPa (about 0.2 atm)). The increase in the volume of LSTF1 in the temperature region was measured, and the increase was expressed as a percentage of the volume at room temperature. This was a thermal expansion coefficient E _A under an air atmosphere. In the same way, a reducing atmosphere (hydrogen 5 vol%, containing 95 vol% of nitrogen) was determined thermal expansion coefficient _{E R} of LSTF1 under. These thermal expansion coefficients _{E A} and _{E R} was calculated reduction expansion coefficients of LSTF1 by fitting to the equation (3) [%].
For the other eight types of perovskite oxides, the reduction expansion coefficient [%] was determined in the same manner as in LSTF1. These results are shown in Table 1.

<Conductivity measurement>
Next, the electrical conductivity in the LSTF 1 was measured as follows. First, after applying a platinum paste serving as an electrode on the surface of the LSTF 1, a platinum wire for connecting a current terminal and a voltage terminal is attached to the electrode portion, and baked at 850 to 1100 ° C. for 10 to 60 minutes. The conductivity [S / cm] was determined by a direct current four-terminal method in a device that can be adjusted to a constant value. The conductivity of the other eight perovskite oxides was also determined in the same manner as described above. Table 1 shows the measurement results of the conductivity under a constant temperature condition (1000 ° C.).

<Fabrication of a two-layer composition graded interconnector>
Using the nine types of perovskite oxides having the reduction expansion coefficient and conductivity as shown in Table 1, two-layer composition graded interconnectors (samples) (1) to (9) were produced. .
First, the disk-like LSTF1 and LSTF3 obtained as described above were brought into contact with each other and pressurized at a predetermined pressure, and diffusion bonded under temperature conditions of 1000 ° C. to 1400 ° C. Thus, a composition gradient type interconnector (1) having a two-layer structure in which the LSTF1 and the LSTF3 are laminated is manufactured. At this time, the layer of LSTF1 having a relatively high reduction expansion coefficient functions as a highly conductive layer (high reduction expansion layer), and the layer of LSTF3 having a relatively low reduction expansion coefficient is a low reduction expansion. It shall function as a sex layer. Further, the LSTF 1 serving as a highly conductive layer is polished so that its thickness is about 0.4 mm, and the LSTF 3 serving as a low reduction expansion layer is 0.05 mm to 0.1 mm in shape. After polishing as described above, the interconnector (1) was produced by joining the two together.
Such interconnectors (2) to (9) were also produced in the same manner as the interconnector (1). Table 2 shows combinations of two perovskite oxides corresponding to the low reduction expansion layer and the high conductivity layer in each of the interconnectors (2) to (9). In the interconnectors (2) to (9), the thickness on the side that becomes the highly conductive layer is about 0.4 mm, and the thickness on the side that becomes the low reduction expansion layer is 0.05 to 0.1 mm. I made it.

<Measurement of conductivity of interconnectors (1) to (9)>
Similarly to the measurement of the conductivity of the nine types of perovskite oxides, the conductivity [S / cm] of the interconnectors (1) to (9) was determined by the direct current four-terminal method. The results are shown in Table 2.
As a result, the electrical conductivity of the interconnectors (6), (7) and (9) made of perovskite oxide having low electrical conductivity (having electrical conductivity of 50 S / cm or less) was lower than 50 S / cm. . In the interconnectors (1) to (9), the interconnector having a higher conductivity of the perovskite oxide itself serving as a highly conductive layer, and the conductivity of the perovskite oxide serving as a highly conductive layer It was found that interconnectors having a larger difference in conductivity of the perovskite oxide serving as the low reduction expansion layer tend to exhibit higher conductivity.

<Execution of leak test>
Next, with respect to the interconnectors (1) to (9), air is exposed to one surface of the interconnector and hydrogen (H ₂ ) gas (fuel gas) is exposed to the other surface, and a leak occurs after a predetermined time has elapsed. It was measured whether or not. The test method will be described with reference to FIG. FIG. 3 schematically shows an apparatus 60 for measuring the occurrence of leakage by exposing the interconnectors (1) to (9) having a two-layer structure formed in a disc shape to an air atmosphere and a reducing atmosphere. FIG.

<Measurement device>
The measuring device 60 includes a casing 30 that houses the interconnectors (1) to (9) (hereinafter also referred to as “sample 40”), and a heater 50 that maintains the sample 40 at a predetermined operating temperature. Is provided. The casing 30 includes an air electrode side outer tube 32 connected to one surface side of the sample 40, an air supply inner tube 34 inserted into the air electrode side outer tube 32, and the other surface side of the sample 40. It has a fuel electrode side outer tube 36 connected, and a fuel gas supply inner tube 38 inserted into the fuel electrode side outer tube 36. The inner pipes 34 and 38 and the outer pipes 32 and 36 are each formed of a dense ceramic (here, alumina) such as alumina or mullite. A glass seal 35 is formed in a ring shape on the outer periphery of the sample 40. The glass seal 35 hermetically seals one end of the outer tubes 32 and 36 to the sample 40 and hermetically seals the outer peripheral end of the sample 40. On the one surface side of the sample 40, an air supply space 33 is defined by the sample 40 and the air electrode side outer tube 32. Further, a fuel gas supply space 37 is defined on the other surface side of the sample 40 by the sample 40 and the fuel electrode side outer tube 36.

The measuring device 60 is configured such that the air supply inner pipe 34 is connected to an air supply means (not shown), and the air is supplied to the air supply space 33 through the air supply inner pipe 34. The measuring device 60 is configured such that the fuel gas supply inner pipe 38 is connected to a fuel gas supply means (not shown), and the fuel gas is supplied to the fuel gas supply space 37 through the fuel gas supply inner pipe 38. Has been.
By setting the sample 40 in the measuring device 60 having such a configuration, one surface of the sample 40 comes into contact with the air supplied to the air supply space 33, and the other surface of the sample 40 is fuel gas. The fuel gas supplied to the supply space 37 can be contacted. Thus, the sample 40 can be simulated in the state of an interconnector sandwiched between the air electrode of one cell and the fuel electrode of the other cell.

<Measurement method>
Next, a measurement method will be described.
The sample 40 was set in the measuring device 60, and air (oxygen partial pressure of about 200 hPa (about 0.2 atm)) was supplied to the air supply space 33 at a predetermined flow rate. In addition, a hydrogen (H ₂ ) -containing mixed gas ( ₅ vol% of H ₂ and 95 vol% of nitrogen (N ₂ )) was supplied to the fuel gas supply space 37 at a predetermined flow rate. In this state, the temperature of the measuring device 60 (sample 40) is maintained at 1000 ° C. for 10 hours, and then the composition of the gas discharged from the air supply space 33 is measured by a gas chromatograph. It was measured whether or not nitrogen (N ₂ ) gas supplied as a constituent component was included (that is, whether or not N ₂ gas was leaking).
Measurement was performed for each of the interconnectors (1) to (9) as described above.

As a result, N ₂ gas was recognized in the gas discharged from the air supply space 33 only in the interconnector (5) among the interconnectors (1) to (9). That is, in the interconnector (5), the measuring device 60 is maintained at 1000 ° C. with respect to the N ₂ gas content measured when air and fuel gas are supplied before the measuring device 60 is heated. The N ₂ gas content measured at the time was increased by 1% to 3%. In this interconnector (5), it was LSZF2 that was exposed to the fuel gas (reducing atmosphere) as a low reduction expansion layer, and this LSZF2 gave 0.15% in the above reduction expansion coefficient measurement.

<Evaluation of Cr diffusion>
Next, the possibility of Cr diffusion was evaluated. In the interconnectors (1) to (9) after the leakage test, whether or not Cr was diffused in each layer was observed by EDX. As a result, in the interconnector (8), it was confirmed that Cr contained in the LSCF serving as the high conductivity layer diffused into the LSZF3 of the adjacent low reduction expansion layer. Also in the interconnector (9), it was confirmed that Cr contained in the LSC serving as the highly conductive layer diffused into the LSTF 3 of the adjacent low-reductive expansion layer. In the other interconnectors (1) to (7), no Cr diffusion was observed.

<SOFC power generation performance evaluation>
Three types of simulated SOFCs (1) to (3) each including the interconnectors (1), (3), and (5) were produced, and the output density was evaluated as the power generation performance of each SOFC. Here, each SOFC (1) is composed of a 20 μm thick YSZ film as a solid electrolyte layer, a 1 mm thick NiO—YSZ layer as a fuel electrode layer, and a 50 μm thick LaSrMn oxide layer as an air electrode layer. 1 is a stack in which an interconnector (1) is arranged between the cells A. The SOFC (2) is a stack including one cell A and an interconnector (3). The SOFC (3) is a stack including one cell A and an interconnector (5).
The power density [W / cm ² ] of the SOFCs (1) to (3) was measured at 1000 ° C. within the operating temperature range of the SOFC using the same method as in the past. As a result, the output density of SOFC (1) was 0.3 W / cm ² . The power density of SOFC (2) was 0.3 W / cm ² . The power density of SOFC (3) was 0.2 W / cm ² . From the above, it was confirmed that the interconnectors (1), (3) and (5) are applicable as interconnectors provided in a practical SOFC.

According to such an embodiment, a composition gradient type interconnector having a two-layer structure composed of a low reduction expansion layer and a high conductivity layer, each layer is composed of La _0.6 Sr _0.4 Ti _1-y Fe. the _y O ₃ and _{La 0.6 Sr 0.4 Zr 1-y} Fe y O 3 (0.7 ≦ y ≦ 0.9) composition gradient type interconnector formed from perovskite type oxide represented by the Cr Since it does not contain, generation | occurrence | production of Cr poisoning accompanying Cr spreading | diffusion can be prevented and the electrical performance of SOFC can be maintained in a high state. Further, a low reductive expansion layer made of the above LSTF oxide or LSZF oxide having a reductive expansion coefficient of less than 0.15%, and a high conductivity (for example, 70 S / The composition gradient type interconnector having a two-layer structure composed of the above-described LSTF oxide or LSZF oxide and a highly conductive layer having a conductivity of at least cm) sandwiches the interconnector with the low reduction expansion layer. By disposing it facing the fuel electrode side of one cell, reducing expansion that can occur on the fuel electrode side is prevented, so that the SOFC has high durability and high electrical conductivity over the entire interconnector. Can do. Therefore, the composition-graded interconnector disclosed here (typically having a multilayer structure including a two-layer structure) is preferable because it exhibits the above effects and can maintain high battery performance and durability over a long period of time. Provision of SOFC can be realized.

  Although the present invention has been described in detail above, these are merely examples, and the present invention can be implemented in other modes, and various modifications can be made without departing from the spirit of the present invention.

2 Low-reduction expansive layer 4 High-conductivity layer 10 Composition gradient type interconnector 12 Cell facing surface formed by low-reduction expansible layer 13 Fuel gas flow path 14 Cell facing surface formed by high-conductivity layer 15 Air flow Path 22 Solid electrolyte 24 Air electrode 26 Fuel electrode 30 Casing 32 Air electrode side outer tube 33 Air supply space 34 Air supply inner tube 35 Glass seal 36 Fuel electrode side outer tube 37 Fuel gas supply space 38 Fuel gas supply inner tube 40 Sample 50 Heater 60 Measuring device 100 Solid oxide fuel cell (SOFC)

Claims (8)

To electrically connect a plurality of cells in a solid oxide fuel cell including a plurality of cells each composed of an air electrode as a positive electrode, a fuel electrode as a negative electrode, and a solid oxide electrolyte disposed between the two electrodes A solid oxide fuel cell interconnector disposed between the cells,
The reduction expansion coefficient is configured to gradually increase or decrease from one cell facing surface of the interconnector to the other cell facing surface,
Here, the interconnector has the following general formula:
Ln _1-x Ae _x MO _3-δ (1)
Here, Ln is at least one element selected from lanthanoids, Ae is one or more elements selected from the group consisting of Sr, Ba and Ca, and M is Ti, Zr. , Al, Ga, Nb, Ta , Fe, Co, Ni, Cu, Mn, Mg, Rh, Pd, a two or more elements that will be selected from the group consisting of Pt and Au, 0 ≦ x ≦ 1, δ Is a value determined to satisfy the charge neutrality condition. ;
The perovskite oxide is formed of a perovskite oxide and the perovskite oxide of the perovskite oxide constituting each portion is increased for each portion of the interconnector having a stepwise different reduction expansion coefficient . On the other hand, a composition-gradient type interface characterized in that the molar ratio of the element M that lowers the conductivity and the element M that increases the conductivity of the perovskite oxide while increasing the reduction expansion coefficient is different from each other. connector.   The one cell facing surface having a relatively high reduction expansion coefficient is a surface facing the air electrode of one cell sandwiching the interconnector, and the other cell facing surface having a relatively low reduction expansion coefficient is 2. The composition gradient type interconnector according to claim 1, wherein the composition inclined interconnector is disposed so as to face a fuel electrode of the other cell sandwiching the interconnector. A plurality of layers in which the molar ratio of the element M of the perovskite oxide is different from the one cell-facing surface toward the other cell-facing surface, and from the layer constituting the one cell-facing surface to the other Forming a multilayer structure composed of a plurality of layers laminated so that the reduction expansion coefficient gradually decreases toward the layer constituting the cell facing surface,
In the multilayer structure, the layer constituting the one cell facing surface having a high reduction expansion coefficient is disposed on the air electrode side of the cell, and the layer constituting the other cell facing surface having a low reduction expansion coefficient is the The composition gradient type interconnector according to claim 1, wherein the composition-graded interconnector is disposed on a fuel electrode side of the cell. Each of the perovskite type oxides having different molar ratios of the element M and constituting the portions having different reductive expansion coefficients in stages is represented by the following general formula:
La _1-x Sr _x M _1-y Fe _y O _3-δ (2)
Here, M in the general formula (2) is selected from the group consisting of Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, Mn, Mg, Rh, Pd, Pt, and Au. One or two or more elements, 0 ≦ x ≦ 1, 0.5 ≦ y ≦ 0.9, and δ is a value determined to satisfy the charge neutrality condition. ;
The composition gradient type interconnector according to claim 1 , wherein the composition-graded interconnector is included in a perovskite oxide represented by:   5. The structure according to claim 3, comprising a two-layer structure of a layer constituting one cell facing surface and a layer constituting the other cell facing surface having mutually different reduction expansion coefficients. Composition graded interconnector.   6. The reduction expansion coefficient of one layer of the two-layer structure is 0.15% or more, and the reduction expansion coefficient of the other layer is less than 0.15%. The composition gradient type interconnector as described.   The composition gradient type interconnector according to any one of claims 1 to 6, wherein the conductivity is 50 S / cm or more over the entire interconnector. A solid oxide fuel cell comprising a plurality of cells composed of an air electrode as a positive electrode, a fuel electrode as a negative electrode, and a solid oxide electrolyte disposed between the two electrodes,
A solid oxide fuel cell, wherein the composition gradient interconnector according to claim 1 is disposed between the plurality of cells.

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