JP2017157553A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell including a current collecting member or cathode layer which has a thermal expansion coefficient close to a thermal expansion coefficient of another member while having a large electric conductivity under a high-temperature working condition.SOLUTION: In a fuel cell (SOFC), a current collecting member (52) or cathode layer (2) includes a perovskite oxide expressed by the general formula, ABOwhich is included as a conductive material for the current collecting member or as a cathode material for the cathode layer. The perovskite oxide has a perovskite structure in which La and Sr are disposed at A sites, and Co is disposed at B sites; part of La which is one of La and Sr disposed at the A sites is substituted with Sm; and the composition ratio of Sm to the perovskite oxide in a mole basis is smaller than that of La before the substitution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell.

For example, in a solid oxide fuel cell operating at 600 to 800 ° C., lanthanum cobaltite-based perovskite oxide LaSrCoO ₃ (hereinafter also referred to as LSC) and LaSrCoFeO ₃ (hereinafter also referred to as LSCF) are frequently used as current collecting materials. Has been. Patent Document 1 discloses a fuel cell including a so-called horizontal stripe fuel cell stack. A plurality of fuel cells are arranged in a jumping island shape on the hollow flat cylindrical porous support of the fuel cell stack at predetermined intervals along the longitudinal direction. The fuel cell module is assembled by laminating and flattening flat surfaces of a large number of fuel cell stacks. Further, the fuel cell is assembled by housing the fuel cell module in a predetermined housing. Patent Document 2 discloses a fuel cell formed by stacking substantially square plate-shaped battery elements and a flat plate fuel cell formed by stacking fuel cells.

  The fuel cells adjacent to each other in Patent Literature 1 are connected along the longitudinal direction of the porous support via a current collector (interconnector) and a porous current collection layer. Specifically, the anode layer of one fuel battery cell and the cathode layer of the other fuel battery cell are electrically connected. Adjacent fuel cell stacks are connected to each other via a stack connecting member disposed on one end side. Specifically, the stack connecting member electrically connects a porous current collecting layer that conducts to the cathode layer of one fuel cell stack and a porous current collecting layer that conducts to the anode layer of the other fuel cell stack. Connect to. As described above, in the fuel cell, a large number of fuel cells (hereinafter also referred to as single cells) are electrically connected via predetermined current collecting members such as an interconnector, a bonding layer, a porous current collecting layer, and a stack connecting member. It is connected so that electricity can be taken out of the fuel cell device.

  In Patent Document 3, a bent metal sheet collecting current collecting member (current collecting member 76) is connected to a cathode layer (oxygen electrode 70) of one unit cell (fuel cell 62) and an interface between the other unit cell. A configuration example is disclosed in which a fuel cell stack is formed by interposing between a connector (72) and connecting a current collecting metal member and both single cells using an LSCF conductive bonding agent (see FIG. 4 etc.).

JP 2010-257744 A JP 2013-012473 A JP 2005-339904 A

  However, in general, the current collecting member is expected to have a high electrical conductivity in order to reduce current collection loss (voltage loss) due to its electrical resistance. Similarly, the cathode layer is expected to have a high electric conductivity in order to secure the electronic conductivity and increase the electrode reactivity. Further, in a solid oxide fuel cell operating at a high temperature, the material used for the current collecting member and the cathode layer is also required to have heat resistance.

Among the current collecting members shown in Patent Documents 1 and 2, lanthanum chromite perovskite oxide (LaCrO ₃ ) is cited as a main conductive material used for the interconnector. In addition, lanthanum cobaltite-based (lanthanum strontium cobaltite-based) perovskite oxides (LSC, LSCF, etc.) are cited as main conductive materials used for the porous current collecting layer. In addition, silver, a silver alloy, LSC, LSCF, or the like is given as a main conductive material used for the bonding layer.
As a main cathode material used for the cathode layer, lanthanum manganese nitrite (LaMnO ₃ ) is typically mentioned. Furthermore, perovskite oxides represented by the general formula LnMO ₃ (Ln: La, Sr, Pr or Sm, M: Fe, Co, Mn or Ni) are mentioned. When the metal material is excluded, among the above ceramic materials, the electrical conductivity of LSC is greatly excellent.

In addition, the current collecting member or the cathode layer is expected to exhibit a thermal expansion coefficient comparable to that of other constituent members of the single cell (hereinafter sometimes referred to as other members). This is because the degree of thermal expansion at a high temperature is different, so that it is possible to suppress the occurrence of defects such as peeling due to the occurrence of thermal stress at the joint location with other members to be joined.
In the case of using a current collecting member (interconnector 72) and a cathode layer mainly made of a ceramic material and joining to a current collecting metal member in order to connect single cells as in the example of Patent Document 3, Each of the current collecting member, the cathode layer, and the current collecting metal member is required to have the same thermal expansion coefficient. Although LSC has a large electrical conductivity and is excellent, LSC has a larger thermal expansion coefficient than general metal materials and ceramic materials. It is expected that a conductive material or a cathode material having a large electric conductivity and a coefficient of thermal expansion comparable to that of other members will appear.

  The present invention has been made to solve the above-described problems. In a fuel cell having a current collecting member and a cathode layer, a large amount of electricity is generated under conditions where at least one of the current collecting member and the cathode layer operates at a high temperature. An object of the present invention is to provide a fuel cell having conductivity and a thermal expansion coefficient close to that of other members.

The fuel cell of the present invention includes an electrolyte layer, a cathode layer provided on one side of the electrolyte layer, an anode layer provided on the other side of the electrolyte layer, and at least one of the cathode layer or the anode layer. And a current collecting member that collects electrons or collects electricity outside the fuel cell, and at least one of the current collecting member or the cathode layer is made of a perovskite oxide represented by the general formula ABO ₃ The perovskite type oxide has La and Sr arranged at the A site, Co is arranged at the B site, and part of one of La and Sr arranged at the A site is Sm. in substituted (LaSmSrCoO _3), molar ratio perovskite oxide Sm is less than a molar ratio perovskite oxide before substitution La, Perobu With a kite structure.

According to the fuel cell of the present invention, the perovskite oxide (LaSrCoO ₃ ) before substitution is an oxide in which La and Sr are arranged at the A site and Co is arranged at the B site, and the basic structure represented by LaSrCoO _3. Have LaSmSrCoO part of La perovskite type oxide (LaSrCoO ₃₎ is substituted with Sm ₃ shows a large electric conductivity than LaSrCoO ₃ before replacement. The thermal expansion coefficient of the LaSmSrCoO ₃ reduces than LaSrCoO _3, closer to the thermal expansion coefficient of the other member that, including metal material or ceramic material.

It is a figure which shows the SOFC cell of a present Example. It is a figure for demonstrating the crystal structure of a perovskite type oxide. It is a figure for demonstrating the crystal structure after substituting the A site element of FIG. 2A. 4 is a graph showing the relationship between the electrical conductivity of the oxide according to Example 1 and temperature. 6 is a graph showing the relationship between the substitution ratio of substitution elements and electrical conductivity according to Example 2. 6 is a graph showing a relationship between a substitution ratio of substitution elements and a thermal expansion coefficient according to Example 2. 6 is a graph showing the relationship between the substitution ratio of substitution elements and electrical conductivity according to Example 3. 6 is a graph showing a relationship between a substitution ratio of substitution elements and a thermal expansion coefficient according to Example 3. It is a graph which shows the relationship between the substitution ratio of the substitution element which concerns on Example 4, and cell voltage. 6 is a cross-sectional view of a coin-type cell C (disk) according to Embodiment 4. FIG. 6 is a cross-sectional view of a cylindrical cell C (cyl) according to Example 4. FIG.

  Hereinafter, a solid oxide fuel cell (hereinafter also simply referred to as “SOFC (Solid Oxide Fuel Cell)”) using an oxygen ion conductive electrolyte layer will be described in detail as an example of the fuel cell of the present invention. The fuel cell of the present invention includes a current collecting member 52 and a cathode layer 2, and the current collecting member 52 corresponds to a conductive material of the present embodiment (a material contained in the current collecting member 52) described later. Or the cathode layer 2 contains a cathode material (corresponding to a material contained in the cathode layer 2) described later. Therefore, matters other than the conductive material forming the current collecting member 52 and matters necessary for the implementation of the present invention (for example, the configuration and construction method of the single cell) can be obtained by those skilled in the art based on the prior art in this field. It can be grasped as a design matter.

(SOFC)
The configuration of the SOFC 100 of this embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing the structure of a flat plate-type SOFC 100 according to this embodiment. As shown in the figure, a flat plate-type SOFC 100 is formed by alternately laminating a plurality of flat single cells C and current collectors E along the normal direction with their respective surfaces (for example, an upper surface and a lower surface) facing each other. Has a multilayer structure. The unit cell C includes a flat thin-film electrolyte layer 3, a similarly flat thin-film cathode layer 2 provided on one side (upper side in the drawing) of the electrolyte layer 3, and the other side of the electrolyte layer 3 ( And a similarly flat anode layer 1 provided on the lower side in the figure.

The current collector E is interposed between adjacent single cells C and is sandwiched between the anode layer 1 of the single cell C stacked on one side and the cathode layer 2 of the single cell C stacked on the other side. 1 and 2 are joined. The current collector E also serves as a separator that separates the oxidizing gas supplied to the cathode layer 2 and the reducing fuel gas supplied to the anode layer 1. A flow path (not shown) through which the fuel gas flows is formed between the anode layer 1 and the current collector E, and an oxidizing gas is present between the cathode layer 2 and the current collector E. A flowing channel (not shown) is formed.
Furthermore, the current collector E collects electrons generated as a result of the electrode reaction in the anode layer 1 of the single cell C bonded to one side, and supplies it to the cathode layer 2 of the single cell C bonded to the other side. Therefore, it is electrically connected to each single cell C. Alternatively, the predetermined current collector E ₀₁ on one end side of the SOFC 100 is electrically connected to the stacked single cell C on the one end side, and electrons supplied via an external circuit are supplied to the cathode layer 2. Supply. The predetermined current collector E ₀₂ at the other end is electrically connected to the single cells C of most other end are stacked, supplying electrons generated in the anode layer 1 to an external circuit.

  Here, it is expected that the current collector E, the cathode layer 2, and other constituent members of the single cell C (hereinafter also referred to as other members) and the like exhibit the same thermal expansion coefficient. This is because the degree of thermal expansion at a high temperature is different, so that it is possible to suppress the occurrence of defects such as peeling due to the occurrence of thermal stress at the joint location with other members to be joined.

(Anode layer)
The anode layer 1 is a fuel electrode in which a fuel gas supplied by a predetermined method and an oxygen ion that has moved through the electrolyte layer 3 are in contact with each other, and an electrode reaction in which the fuel gas is oxidized to generate electrons proceeds. As the fuel gas, hydrogen can be typically used, but hydrocarbons such as methane and propane may be used.

  The anode layer 1 may have a conventionally known configuration and form, and is not particularly limited. Preferably, the anode material for forming the anode layer 1 is a metal material powder selected in consideration of catalytic activity, stability under a reducing atmosphere, cost, etc., and a ceramic material powder in an appropriate electrolyte layer A known cermet mixed with can be used. Typically, Ni-YSZ cermet in which yttria-stabilized zirconia (YSZ) as a ceramic material is mixed with nickel oxide (NiO) as a metal material can be given. As the ceramic material, scandia-stabilized zirconia (ScSZ), gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), or the like can be used instead of YSZ. As the metal material, Fe, Co, Ru, Pd, Pt, or the like can be used instead of Ni.

  The anode layer 1 is preferably composed of a porous body that can efficiently permeate the fuel gas. In addition, the anode layer 1 may have a function as a support for supporting the thin-film other layer of the single cell C. The thickness of the anode layer 1 may be, for example, about 10 μm to 300 μm. However, when the anode layer 1 is used as a support, the thickness of the anode layer 1 can be made larger than the thickness of other layers.

(Electrolyte layer)
The electrolyte layer 3 can move oxygen ions generated in the cathode layer 2 to the anode layer 1. The electrolyte layer 3 is formed of a material that satisfies the following conditions. The first condition is that it is stable at the operating temperature in both reducing and oxidizing atmospheres, and the second condition is that it has high oxygen ion conductivity and low electronic conductivity, and can easily form a dense electrolyte membrane. Can be formed.

The electrolyte layer 3 may have a conventionally known configuration and form, and is not particularly limited. Preferably, zirconia (ZrO ₂ ) stabilized by adding a heterovalent metal oxide such as Y can be used as a material for forming the electrolyte layer 3. Specifically, as the heterovalent metal oxide, one or more selected from Y ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O ₃ , Gd ₂ O ₃ , Sm ₂ O ₃ , CeO _{2 and the} like are used. Can do. Among them, yttria stabilized zirconia (YSZ) stabilized with Y ₂ O ₃ can be preferably used. Moreover, the thickness of the electrolyte layer 3 should just be about 30 micrometers, for example.

When a cobaltite-based perovskite oxide described later is selected as the cathode material and YSZ is selected as the electrolyte material, a high resistance component may be generated around the boundary surface between the cathode layer 2 and the electrolyte layer 3. There is. In such a case, a reaction inhibiting layer can be provided on the side of the electrolyte layer 3 where the cathode layer 2 is disposed. Examples of the material for forming the reaction suppression layer include ceria (CeO ₂ ) doped with gadolinia (Gd ₂ O ₃ ).

(Cathode layer)
The cathode layer 2 is an air electrode that reduces oxygen in the air by electrons conducted in the electrode and sends the oxygen as oxygen ions to the electrolyte layer 3. In the cathode layer 2, oxygen in the air receives electrons conducted in the electrode via a current collector E described later, and an electrode reaction for generating oxygen ions proceeds, so that the oxygen ions reach the electrolyte layer 3. The cathode layer 2 is preferably made of a porous body that has stability under an oxidizing atmosphere and can efficiently pass a gas. As the oxidizing gas, air can be typically used, but other oxidizing gases (for example, oxygen or the like) may be used.

The cathode layer 2 may have a conventionally known configuration and form and is not particularly limited, but the cathode material preferably contains LSSC (LaSmSrCoO ₃ ) according to the present invention. The LSSC is the same material as the conductive material forming the current collecting member 52 which will be described in detail later. LSSC is not necessarily the main material, but may be added to other cathode materials for forming the cathode layer 2 as a functional material that enhances electronic conductivity.

  As other cathode materials, at least one or more of La, Sr and Sm are contained in the A site, and at least one or more of Ca, Mn, Co, Fe, Cr and Ni are contained in the B site, An oxide having a perovskite structure can be used. As the A site element, at least one or more of lanthanoids of Ce, Pr, Nd, and Eu, alkaline earth metals of Ca, Ba, and Ra, Na, and Cd may be further contained.

  By the way, cobaltite-based perovskite oxide (hereinafter, also referred to as “cobaltite”) containing Co as a B-site element is a cathode material that can function as the cathode layer 2 even if it is an SOFC for lowering the temperature. Are known. Specific examples include LSC, LSCF, samarium strontium cobaltite (SSC), and the like. Cobaltite is highly evaluated for electrode reaction characteristics. In particular, in terms of conductivity under SOFC operating temperature conditions, LSC is a material having excellent electrical conductivity among ceramic materials, excluding metal materials. However, LSC has a larger coefficient of thermal expansion than general electrolyte materials and metal-based materials, and is under development to ensure the stability of SOFC. From the viewpoint of maintaining long-term stability and reliability, manganese night-based perovskite oxides containing Mn as the B-site element have obtained a certain evaluation. There is a tendency that LSCF is selected comprehensively by comparing stability and electrode reactivity.

In the cathode layer 2, gas phase oxygen is adsorbed / dissociated on the cathode material and bonded to electrons, and an electrode reaction in which the generated oxygen ions move into the electrolyte layer 3 proceeds. Therefore, from the viewpoint of promoting the electrode reaction, the cathode layer 2 has firstly a catalytic activity for adsorbing and dissociating oxygen, and secondly, has a function of transporting oxygen ions (ionic conductivity), and Third, it is formed of a cathode material that satisfies each condition having electronic conductivity.
The LSSC has the basic structure of the LSC like the LSCF. Therefore, it can be considered that the first and second conditions are satisfied and the oxygen activation catalyst function and oxygen ion conductivity are exhibited in the same way as LSC and LSCF. As will be described later, LSSC exhibits a higher electrical conductivity than LSC, which is superior in conductivity to LSCF, and is excellent in electronic conductivity performance.

In addition, from the viewpoint of maintaining long-term stability and reliability, the cathode layer 2 is firstly thermodynamically stable in an oxidizing atmosphere, and secondly, the electrolyte layer 3 and the current collector to be joined. It is desirable for the body E to be formed of a cathode material that is chemically stable under the SOFC operating temperature conditions and that exhibits a near thermal expansion coefficient.
LSSC satisfies the first condition in the same way as LSC, and is considered to have chemical stability even in relation to the joining member under the second condition. Moreover, LSSC shows a thermal expansion coefficient smaller than LSC so that it may approach the thermal expansion coefficient of electrolyte material or a metallic material so that it may mention later in an Example. Therefore, long-term stability and reliability can be maintained as compared with the LSC.

  In addition, LSSC can be preferably selected as a cathode material in the sense that the same material as that of a member mainly used for current collection bonded to the cathode layer 2 is used. For example, the current collecting member 52 described later is a member that covers the surface of the current collector E, is used by being joined to the cathode layer 2, and contains LSSC as a conductive material. Further, if the current collecting member 52 and the cathode layer 2 are formed of the same material, the current collector E (current collecting member 52) and the single cell C (cathode layer) even at a high temperature at which the SOFC operates. 2) A stable state can be maintained without any unexpected chemical interaction (reaction). Furthermore, since the thermal expansion coefficients of the conductive material and the cathode material are the same, long-term stability and reliability can be maintained.

(Current collector)
The current collector E separates an oxidizing gas supplied to the cathode layer 2 and a reducing fuel gas supplied to the anode layer 1 and collects electrons generated in the adjacent anode layer 1. Electrons are passed through the electrode reaction field of the adjacent cathode layer 2. The current collector E functions as a so-called interconnector. For example, the current collector E is formed by laminating a current collecting member 52 containing a conductive material according to the present invention on the surface of a dense separator layer 51 made of a metal material for separating an oxidizing gas and a reducing gas. The separator layer 51 can be sandwiched between both sides. The current collector E has a surface of one current collecting member 52 on the anode layer 1 of the single cell C adjacent to one side and a surface of the other current collecting member 52 on the cathode layer 2 of the single cell C adjacent to the other side. Are joined. The current collecting member 52 serves as a bonding layer for ensuring the bonding strength between the dense separator layer 51 made of a metal material, and the anode layer 1 and the cathode layer 2 which are porous bodies and are mainly made of ceramics. It also has. The current collecting member 52 is formed using the following perovskite oxide as a main conductive material.

  That is, in the perovskite type oxide, La and Sr are arranged at the A site, Co is arranged at the B site, and a part of one of La and Sr arranged at the A site is substituted with Sm. The molar composition ratio of Sm to the perovskite oxide is smaller than the molar composition ratio of La to the perovskite oxide before substitution.

Specifically, in the perovskite oxide according to the present embodiment, a part of La of LSC represented by the composition formula “La _z Sr _1-z CoO ₃ ” is replaced by Sm in terms of molar composition ratio by “x”. It is an oxide and is represented by the following formula (1) that satisfies the relationship of z−x> 0.
La _z-x Sm _x Sr _1-z CoO ₃ (1)
In the SOFC 100 of this embodiment, the current collecting member 52 (or the cathode layer 2) preferably contains the perovskite oxide of the above formula (1) as a conductive material (or cathode material).
As the conductive material, in the formula (1), x and z preferably satisfy the relationship of 0.01 ≦ x / z <0.5 and 0.3 ≦ z ≦ 0.8 as described later. .
As a cathode material, in the formula (1), x and z preferably satisfy the relationship of 0 <x / z <0.72 and z = 0.5.

The perovskite oxide according to the present invention is an oxide derived by a so-called computational materials design technique based on quantum mechanics. Here, the electronic structure of the object can be quantitatively calculated based on the electronic state theory (band theory), and the electronic conductivity of the object can be estimated based on the calculated value. Specifically, a simulation is performed using predetermined quantum calculation software, and the size of the band gap of the target perovskite oxide is obtained. As a result of the analysis, it was confirmed that the perovskite oxide having the basic structure of “LaSrCoO ₃ ” is a powerful material that can have high electronic conductivity. On the other hand, it is known that LaSrCoO ₃ has a larger coefficient of thermal expansion than a general metal.

Therefore, in order to identify a perovskite oxide that exhibits further excellent electronic conductivity, a part of the elements arranged at the A site of LaSrCoO ₃ was replaced with another element and recalculation was performed. In consideration of the ionic radii, ionic valence, and coordination number to be arranged at the A site of La and Sr, a candidate for element R ₁ that replaces La or element R ₂ that replaces Sr was selected. A simulation was performed using predetermined quantum calculation software, and the size of the band gap was calculated for the perovskite oxide LaR ₁ SrCoO ₃ or LaSrR ₂ CoO ₃ after substitution with candidate elements R ₁ and R ₂ . From the calculation results, it was possible to obtain an expectation that LaSmSrCoO ₃ substituted with La as R ₁ = Sm would have excellent electronic conductivity and a large electric conductivity. Actually, the perovskite oxide having a composition in which Sm is suppressed to a La or less before substitution in the molar composition ratio showed a larger electric conductivity than LaSrCoO ₃ .

Further, actually, the LaSmSrCoO _3, was measured thermal expansion coefficient under SOFC operating assumed temperature, the thermal conductivity is lower than LaSrCoO _3. It has been found that the thermal expansion coefficient approaches that of ceramic materials used for general metal materials, SOFC electrodes, and electrolytes.

The process of selecting candidate element R ₁ for substituting La or candidate element R ₂ for substituting Sr will be described. “LaSrCoO ₃ ” is a perovskite oxide having a basic structure in which a rare earth metal (ion) and an alkaline earth metal (ion) are arranged at the A site of the general formula ABO ₃ and a transition metal (ion) is arranged at the B site. It is. A perovskite oxide represented by the general formula ABO ₃ is known to have a basic structure described below. In addition, it is known that the electronic state changes when a change as described below is given to the metal ion arranged at the A site.

As shown in FIG. 2A, in the oxide having a perovskite structure, metal ions at the B site are arranged at the center of the cubic crystal. Oxygen ions are arranged at each face center of the cubic crystal centering on the metal ions at the B site. That is, the six oxygen ions regularly surround the B site metal ions to form a B—O ₆ octahedron. The octahedron is connected in the vertical, horizontal, and height directions while sharing the oxygen ions at the apex with the adjacent octahedron. The metal ions at the A site are arranged at the apexes of the cubic so as to fill the gaps around the octahedron.

  Therefore, as shown in FIG. 2B, if a change is made such that the radius of the metal ion arranged at the A site becomes small (labeled R in FIG. 2B), the ideal cubic lattice is distorted. There is a finding that the bond angle B-O-B between the face bodies is smaller than 180 ° (an example is shown by a thick straight line in FIG. 2B), and the bandwidth can be controlled. Further, there is a finding that when a part of the metal ions at the A site is replaced with metal ions R having different radii, the above-mentioned strain in the lattice can be locally varied, and the effect of local lattice strain can be introduced.

Further, when a part of the metal ions at the A site is replaced with metal ions having different valences, specifically, the n-valent metal ion at the A site is replaced by m with (n-1) or (n + 1) -valent ions. When replaced, it can be understood that it is similar to doping electrons or holes by m. Thus, there is a knowledge that the electronic state of metal ions and the interaction between electrons can be changed to enhance the electronic conductivity. In other words, if it is recognized that LaSrCoO ₃ has a certain doping effect, it can be inferred that it is preferable to maintain the current valence balance.

In this manner, focusing on the ionic radius, ionic valence, and coordination number, a plurality of candidates for the element R ₁ that replaces La in LaSrCoO ₃ or the element R ₂ that replaces Sr are selected. The simulation was performed using the wear. Among the plurality of candidate elements, LaSmSrCoO ₃ (hereinafter also referred to as “LSSC”) in the case where R ₁ is Sm was obtained to show a large electric conductivity.
In addition, the generalized gradient approximation functional (GGA method) which is a well-known density functional was used as quantum calculation software. Although simulation results were obtained for predetermined candidate elements R ₁ and R ₂ other than Sm (for example, Ce, Pr, Nd as R ₁ , Ca, Ba, Ra, etc. as R ₂ ), the most excellent predicted result with Sm was gotten.

Further, “x” in the above formula (1) is a molar composition ratio of Sm to the perovskite oxide. In the perovskite oxide LSC before substitution having the basic structure of “LaSrCoO ₃ ”, “z” is the molar composition of La and Sr arranged at the A site with respect to the perovskite oxide of La before substitution. Is the ratio. The molar composition ratio of Sr before substitution to the perovskite oxide is represented by “1-z”.

  Further, it is a parameter indicating the substitution ratio of Sm to La, and the possible range of the ratio “x / z” of the molar composition ratio “x” of Sm after substitution to the molar composition ratio “z” of La before substitution is From the viewpoint of the effect of increasing the electrical conductivity and obtaining an appropriate value of the thermal expansion coefficient, 0.01 ≦ x / z <0.5 is preferable. Furthermore, if x / z is in the range of 0.01 ≦ x / z ≦ 0.25, the electrical conductivity is obviously large and the thermal expansion coefficient approaches an appropriate value. From the viewpoint of ensuring the output characteristics of the SOFC. Is also preferable. Hereinafter, the above “x / z” is also simply referred to as “Sm substitution ratio”.

The amount of replacing La in LSC with Sm may be as small as possible, but if x / z is smaller than 0.01, the effect of increasing the electrical conductivity may not be sufficient. In addition, as shown in the examples described later, the relationship between the substitution ratio of Sm and the electrical conductivity is approximately a moderate inverse relationship with a downward slope (see FIGS. 4 and 6). Further, when the substitution ratio x / z of Sm increases, the thermal expansion coefficient tends to increase (see FIGS. 5 and 7). When x / z is larger than 0.5, the remarkable effect of increasing the electrical conductivity becomes dilute, and the risk of increasing the thermal expansion coefficient increases. If x / z is in the range of 0.01 ≦ x / z ≦ 0.25, it is particularly preferable from the viewpoint of clearly increasing the electrical conductivity and obtaining an appropriate value of the thermal expansion coefficient.
Further, from the viewpoint of obtaining a large electric conductivity, the molar composition ratio “x” of Sm is preferably smaller than the molar composition ratio “z” of La before substitution (z−x> 0).

  When used as a cathode material, the possible range of the substitution ratio “x / z” of Sm is preferably 0 <x / z <0.72. Compared with the case of using as the above conductive material, the possible range of “x / z” is different in the upper limit value. As shown in the examples described later, when x / z is 0.72 or more, it is recognized that the output characteristic (cell voltage) of SOFC tends to decrease compared to LSC (see FIG. 8). ). Furthermore, if x / z is in the range of 0.08 ≦ x / z ≦ 0.5, the electrical conductivity is clearly large (see FIG. 6), and the thermal expansion coefficient approaches an appropriate value (see FIG. 7). It is also preferable from the viewpoint of securing the output characteristics of SOFC.

Further, if the molar composition ratio “z” of La to the perovskite oxide before substitution is in the range of 0.3 ≦ z ≦ 0.8, “La _z Sr _1-z CoO ₃ ” before substitution is sufficient. This is preferable because it is known to exhibit a large electric conductivity. It is particularly preferable that “z” is in the range of 0.4 ≦ z ≦ 0.7 because it is known that a more preferable electric conductivity is exhibited. In other words, the molar composition ratio “1-z” of Sr to the perovskite oxide is preferably in the range of 0.2 ≦ 1-z ≦ 0.7, and 0.3 ≦ 1-z ≦ 0. If it is within the range of.

  As described above, the SOFC of the present invention contains LSSC, which is a perovskite oxide, as a conductive material in the current collecting member 52 or as a cathode material in the cathode layer 2. To do. The conductive material or cathode material containing LSSC according to the present invention has an effect of increasing the electric conductivity and the thermal expansion coefficient is reduced as compared with the conventional LSC, and general metal materials and SOFC ceramics. This has the effect of reducing the difference in thermal expansion coefficient of the system material. As long as this effect is recognized, the SOFC of the present invention is not limited by other sub-materials or elements other than the LSSC forming the current collecting member 52 or the cathode layer 2.

  In addition, the use of the conductive material that is the perovskite oxide as the current collecting member 52 is to cover the single cell C through the current collector E and cover the separator layer 51 of a metal material. It is not limited to the method used. For example, for the purpose of forming an inter-stack connection member for connecting cell stacks S in which single cells C are stacked, or for using a component of a conductive bonding agent for closely attaching an inter-stack connection member to both cell stacks S It can also be used as a conductive material. The inter-stack connection member is, for example, a member that joins the cathode layer of one cell stack S and the current collector of the other cell stack S. As a specific example, in the horizontal stripe fuel cell stack 1 of Patent Document 1, the inter-cell stack joining member 19 corresponds. Further, LSSC can be used as a component of the conductive bonding agent used for connection between the cell stack bonding member 19 and the porous current collecting layer 17.

  Further, in the present embodiment, the compatibility of the thermal expansion coefficient in consideration of the operation in the so-called intermediate temperature range (700 to 800 °) and considering the joining of the current collecting member 52 and the metal material (separator layer 51). However, the use of the conductive material (or the cathode material) containing LSSC is not limited to the purpose of joining the metal material. For example, it may be used for joining with a lanthanum chromite ceramic material generally used as a dense layer for forming an interconnector. As a specific example, in the example of the flat plate SOFC of Patent Document 2, LSSC is used as a material for forming the bonding layer 12 (also serving as the air electrode 31) bonded to the lanthanum chromite interconnector 1 via the protective layer 11. Can be used.

(Manufacture of SOFC)
Next, the manufacturing method of the fuel cell concerning the fuel cell of this invention is demonstrated. The manufacturing method of the single cell C of this embodiment is based on a well-known manufacturing method. For example, a half-cell laminate comprising an anode layer and an electrolyte layer obtained by laminating an anode layer precursor and an electrolyte layer precursor and co-firing in advance is obtained. The single cell C can be produced by a method of laminating and firing a cathode layer precursor on the electrolyte layer of the half cell laminate.

  The anode layer precursor can be produced, for example, as follows. A slurry is prepared by adding and mixing a binder, a pore forming agent, and a solvent to a mixed powder of a ceramic material powder and a metal material powder forming the anode layer. Next, a green sheet is produced from this slurry, cut into a predetermined shape, and then dried. Thereby, a green sheet-like anode layer precursor is obtained. As a binder for adjusting the slurry, polyvinyl butyral, ethyl cellulose, etc., pore forming agent, fine particles such as polymethyl methacrylate or carbon, and solvent, toluene, butanol or ethanol can be suitably used, which will be described later. The same applies to the adjustment of the slurry of each layer precursor.

  A slurry is prepared using the electrolyte layer material powder in the same manner as the anode layer precursor, and this slurry is laminated on the surface of the anode layer precursor by screen printing and dried. Then, the material obtained by laminating the anode layer precursor and the electrolyte layer precursor is co-fired over a temperature (for example, 1300 ° C. or more) suitable for sintering and time, and the anode layer 1 and the electrolyte layer 3 are laminated. A half-cell laminate is obtained.

Next, a cathode layer precursor is formed. Similar to the anode layer precursor, a slurry is prepared using the metal oxide powder for the cathode layer 2. When LSSC is used as the cathode material, the metal oxide powder can be synthesized. The raw material powder of LSSC can be synthesized from a predetermined compound containing each element of La, Sr, Sm, and Co. These predetermined compounds are weighed so as to have a desired molar composition ratio, mixed, and synthesized by, for example, a known solid phase reaction method to obtain LSSC raw material powder. If it is a solid-phase reaction method, the oxide, carbonate, nitrate, acetate, etc. of each said element can be used as a predetermined compound. The synthesis method is not limited to the solid phase reaction method, and may be a known synthesis method via a liquid phase. For example, known methods such as an alkali precipitation method, a coprecipitation method, a sol-gel method, and a citrate method can be exemplified.
A slurry is prepared by adding a binder, and if necessary, a pore-forming agent and a solvent to the obtained LSSC raw material powder and mixing the slurry, and this slurry is screen-printed on the surface on the electrolyte layer 3 side of the half-cell laminate. And a cathode layer precursor is formed and dried.
The precursor of the single cell C in which the cathode layer precursor is laminated on the upper surface of the half cell laminate is preferably sintered at a temperature of 900 ° C. or more and 1250 ° C. or less, preferably for 1 hour or more and 12 hours or less. Conclude. Thereby, the single cell C of SOFC can be manufactured. In addition, there is no limitation in particular about the method of laminating | stacking another precursor in order on each precursor, It can laminate | stack using a slurry coat method, a tape casting method, a doctor blade method etc. other than a screen printing method.

  Next, the manufacturing method of the electrical power collector E is demonstrated. As the separator layer 51 of the current collector E, for example, a metal plate having a predetermined shape such as Ni, Fe—Cr, or SUS can be used. Further, the raw material powder of LSSC used as the current collecting member 52 can be synthesized in the same manner as the raw material powder of the cathode material.

  The LSSC raw material powder can be molded by a known method such as uniaxial compression molding, isostatic pressing, or extrusion molding to obtain a compact of the current collecting member 52. Alternatively, a slurry is prepared by adding a predetermined binder and a solvent to the LSSC raw material powder and mixing them. Similarly to the method for manufacturing the battery element of the single cell C described above, a precursor having a desired shape can be formed from the slurry and fired to obtain a molded body of the current collecting member 52. A current collecting member 52 is interposed between the separator layer 51 and the single cell C, and an SOFC stack in which the single cells C are connected by stacking in order can be manufactured integrally. Alternatively, by preparing a slurry of LSSC in a paste form, applying this paste to a predetermined position on both surfaces of the separator layer 51 and the surface of the single cell C and connecting (connecting) the cells, drying and firing, The SOFC stack in which the single cells C are connected to each other can be manufactured integrally.

The current collecting member or the cathode layer according to the present invention can be used for SOFCs having various structures, and is not limited to a structure in which flat plate type single cells are stacked. The present invention can also be preferably applied to an SOFC including a cylindrical type or a hollow flat cylindrical single cell in which the peripheral surface of the cylinder is crushed. For example, in the case of a well-known hollow flat single cell described in Patent Document 3 at the beginning, the interconnector 72 joined to one fuel cell 62, the oxygen electrode 70 of the other fuel cell 62, and between the two cells. LSSC is used as a conductive material or cathode material for forming the current collecting member 76 interposed therebetween, the conductive bonding agent 120 for bonding them, the end side current collecting member 109 arranged at the end of the power generation unit, and the like. Can be used. In the example disclosed in Japanese Patent Application Laid-Open No. 2008-71712, the outer electrode (cathode) layer 20, the outer electrode terminal 22, the conductive sealing materials 32, 102, 120, the connecting member 55, the external terminal 56, the connecting member 72, LSSC can be used as a conductive material or a cathode material for forming the connection electrode terminals 96, 116 and the like. The fuel cell may be an SOFC that uses an H ⁺ conductive electrolyte layer. The type of the fuel cell is not limited to the solid oxide fuel cell, and can be used for various fuel cells such as a so-called phosphoric acid type and a solid polymer type.

  Examples of the present invention will be described below. In the first example, the result of mainly evaluating LSSC as the conductive material of the SOFC cell is shown, and in the second example, the result of evaluating mainly LSSC as the cathode material is shown. The following examples show specific examples of the present invention, and the present invention is not limited to the following examples.

<< First Example: Conductive Material >>
As a first example, evaluation using LSSC as a conductive material of SOFC was performed. The LSSC compacts of Examples 1 and 2 were prepared and evaluated for 1) electrical conductivity and 2) thermal expansion coefficient.
[Preparation of perovskite-type oxide compacts]
<Example 1>
As Example 1, a molded article of LSSC was obtained by the following procedure.
(LSSC compact)
The production of the LSSC raw material powder was performed by a solid phase reaction method. Various metal oxide or salt powders as raw materials were weighed so that LSSC having a desired molar composition ratio was obtained. Specifically, La ₂ O ₃ powder, SrCO ₃ powder, Sm ₂ O ₃ powder and Co ₃ O ₄ powder were used. The powder obtained by wet-mixing these in a solution and then removing the solvent was fired at 800 ° C. and pulverized to obtain an LSSC raw material powder having an average particle size of 0.5 μm (D50).

The obtained raw material powder is uniaxially compression-molded, and further compacted under pressure of 245 MPa using the CIP method (cold isostatic pressing), and further sintered at 1000 ° C. to form a pellet. To obtain an LSSC molded body. (1) In the formula [La _z-x Sm _x Sr _1-z CoO ₃ ], a plurality of LSSC molded body samples in which the molar composition ratio “x” of Sm in the case of z = 0.5 is within a predetermined range. It produced (refer No.1-1, 1-2 of Example 1 of Table 1).

<Example 2>
As Example 2, a molded article of LSSC was obtained by the following procedure.
(LSSC compact)
An LSSC molded body molded into a pellet shape by the same production method as in Example 1 was obtained. (1) In the formula [La _z-x Sm _x Sr _1-z CoO ₃ ], when the molar composition ratio “1-z” of Sr is a predetermined value, the substitution ratio “x / z” of Sm is a predetermined range A plurality of LSSC molded body samples were prepared (see Nos. 1 to 3 in Example 2 in Table 1).

<Comparative example 1>
(LSC compact)
The LSC molded object shape | molded by the manufacturing method similar to Example 1 at the pellet form was obtained. In [La _z Sr _1-z CoO ₃ ], an LSC molded product sample having a La molar composition ratio “z” of z = 0.5 was prepared (see No. 1 of Comparative Example 1 in Table 1).

<Comparative example 2>
(LSC compact)
The LSC molded object shape | molded by the manufacturing method similar to Example 1 at the pellet form was obtained. In [La _z Sr _1-z CoO ₃ ], LSC molded body samples were prepared when the molar composition ratio “1-z” of Sr was a predetermined value (see Nos. 1 to 3 in Comparative Example 2 in Table 1). .

[Evaluation of perovskite oxide compacts]
(Identification of perovskite oxide compacts)
X-ray diffraction spectrum data and ICP emission spectroscopic analysis data were obtained for each of the obtained LSSC molded body samples of Example 1 and each of the LSSC molded body samples of Example 2, and the crystal phase confirmation and composition of each molded body sample were obtained. Was identified.
It was found that each molded body sample obtained in Examples 1 and 2 was a molded body containing the perovskite oxide according to the present invention.

1) Evaluation of electric conductivity About each obtained molded object sample of LSSC of Example 1, 2, electrical conductivity was measured under predetermined | prescribed environmental temperature. In FIG. 3, the change of the electrical conductivity of the LSSC molded object of Example 1 (No.1-1, 1-2 of Table 1) with respect to environmental temperature (600-800 degreeC) was shown. FIG. 4 shows the change in electrical conductivity with respect to the Sm substitution ratio “x / z” at 650 ° C. for each LSSC molded body of Example 2 (Nos. 1 to 3 in Table 1). For each of FIGS. 3 and 4, the comparison results with the LSC compacts of Comparative Examples 1 and 2 are shown.
In addition, Table 1 shows the evaluation results of the electrical conductivities of the above Examples 1 and 2 in the form of relative evaluation with Comparative Examples 1 and 2. In Table 1, symbols ◎, ○, and △ indicate evaluation as a conductive material, ◎ is much better than the comparative example, ○ is better than the comparative example, and Δ is comparable to the comparative example ~ Slightly inferior, meaning evaluation. In addition, about evaluation of the test result of the comparative example itself which is a comparative reference, it abbreviate | omitted.

  From FIG. 3, it was confirmed that the electrical conductivity of the LSSC molded body was higher than that of LSC even when the temperature environment changed in the range of 600 to 800 ° C. It can be inferred that the electric conductivity is larger than that of LSC even in a wider temperature range of 600 ° C. or lower and 800 ° C. or higher. The inventors of the present invention pay attention to the tendency that the electrical conductivity tends to decrease as the environmental temperature increases. That is, the temperature dependence of electrical conductivity shows a metallic behavior. Therefore, it is understood that the material has conductive characteristics suitable as a metal substitute material from the viewpoint of electrical characteristics.

Further, as shown in FIG. 4, in the molar composition ratio (1-z) of a wide range of Sr to the perovskite oxide, the electric conductivity of the LSSC compact is generally larger than that of the LSC within a suitable Sm substitution ratio range. Thus, the effect of substituting part of La of LSC with Sm could be confirmed. From FIG. 4, the electrical conductivity of LSSC is about 20% higher than that of LSC in the range where the substitution ratio x / z of Sm is 0.01 ≦ x / z ≦ 0.25. The remarkable effect by substituting a part of La with Sm was recognized. It was found that when the molar composition ratio (1-z) of Sr is 0.2 ≦ 1-z ≦ 0.7, the electrical conductivity of the LSSC molded body will be larger than that of LSC.
When z = 0.3, the Sm substitution ratio x / z is in the range of 0.01 ≦ x / z ≦ 0.5, and the electrical conductivity of LSSC is larger than that of LSC. Further, when z = 0.5, the electrical conductivity of LSSC is larger than that of LSC in the range where the substitution ratio x / z of Sm is 0.01 ≦ x / z ≦ 0.72. Furthermore, when z = 0.8, the electrical conductivity of LSSC is larger than that of LSC when the substitution ratio x / z of Sm is in the range of 0.01 ≦ x / z <0.5.

As described above, the SOFC 100 (fuel cell) of the present invention uses the perovskite oxide described in this embodiment or the present example, and is provided on one side of the electrolyte layer 3 and the electrolyte layer 3. The cathode layer 2, the anode layer 1 provided on the other side of the electrolyte layer 3, and the electrons that are electrically connected to at least one of the cathode layer 2 or the anode layer 1 to collect the electrode reaction are collected, or the single cell C Or a current collector E for taking out electricity to the outside of the SOFC 100, and a current collector 52 constituting the current collector E contains a perovskite oxide represented by the general formula ABO ₃ as a conductive material, and a perovskite In the type oxide, La and Sr are arranged at the A site, and Co is arranged at the B site. Among La and Sr arranged at the A site, a part of one La is substituted with Sm, and S The molar composition ratio of m to the perovskite oxide is smaller than the molar composition ratio of La to the perovskite oxide before substitution, and has a perovskite structure.

Therefore, the electrical conductivity of the conductive material is larger than that of LaSrCoO _{3 of} the conventional material, so that the voltage loss due to the electrical resistance of the current collecting member 52 can be reduced, and the output characteristics of the SOFC 100 can be improved. it can. The SOFC 100 generally has a large effect of reducing electric resistance because a large number of single cells C are stacked and each unit cell C is electrically connected through a current collector E. Therefore, the output characteristics of the fuel cell can be improved.

  From the results of Example 2 above, when the molar composition ratio (1-z) of Sr in LSSC is 0.2 ≦ 1-z ≦ 0.7, the possible range of the substitution ratio x / z of Sm is as follows. It can be seen that 0.01 ≦ x / z <0.5 is preferable because the electric conductivity is higher than that of LSC before substitution with Sm. Further, it is particularly preferable that the substitution ratio x / z of Sm is 0.01 ≦ x / z ≦ 0.25, since it is clear that the above effect can be obtained.

  In addition, the range 0.2 ≦ 1-z ≦ 0.7 of the molar composition ratio (1-z) of Sr is 0.3 ≦ z ≦ 0.7 when the molar composition ratio “z” of La before substitution is used. Corresponds to a range of 0.8.

2) Evaluation of thermal expansion coefficient About each obtained molded object sample of LSSC of Example 2, the thermal expansion coefficient was measured under predetermined | prescribed environmental temperature. FIG. 5 shows changes in the thermal expansion coefficient with respect to the substitution ratio x / z of Sm in Example 2 (No. 2 in Table 1) at 650 ° C.
Moreover, similarly to the above-described evaluation of electrical conductivity, the evaluation results of the thermal expansion coefficient of Example 2 are shown in Table 1 in the form of relative evaluation with Comparative Example 2.

When the conductive material according to the present invention is used as a current collecting member that is joined to a predetermined other member, it is preferable that the thermal expansion coefficient of the mating member to be joined is close. The current collecting member is originally required to have high electrical conductivity as a characteristic, and a metal material is often selected as the counterpart member. As a coefficient of thermal expansion of the counterpart metal material, approximately 11 to 12 × 10 ⁻⁶ (K ⁻¹ ) is assumed as a standard value (assumed coefficient of thermal expansion). FIG. 5 reveals that the LSSC compact is closer to the assumed thermal expansion coefficient of the metal material than LSC at 650 ° C., and a favorable evaluation result was obtained.

By the way, although LSC is large and excellent in electrical conductivity, the thermal expansion coefficient is larger than that of a general metal material or ceramic material. It is expected that a conductive material or a cathode material having a large electric conductivity and a coefficient of thermal expansion comparable to that of other members will appear.
The present embodiment has been made to solve such a problem, and has a large electric conductivity under the condition of operating at a high temperature and a current collector having a thermal expansion coefficient close to that of other members. It can be aimed at providing a fuel cell provided with a member.

As described above, in the SOFC 100 (fuel cell) of the present invention, the current collecting member 52 according to the present embodiment contains the perovskite oxide LSSC according to the present example as a conductive material. Therefore, in addition to electrical conductivity of the conductive material increases, the thermal expansion coefficient of the LaSmSrCoO ₃ is smaller than the LaSrCoO _3, the thermal expansion coefficient between the ceramic material and the metallic material at a high temperature (under operating temperature) It is possible to prevent the current collecting member 52 and the separator layer 51 containing a metal material as a main component from being separated due to the mismatch. Therefore, the contact resistance can be reduced, so that the output characteristics of the fuel cell can be further improved.

Further, since the thermal expansion coefficient of the LaSmSrCoO ₃ is smaller than the LaSrCoO _3, the separator layer 51, the cathode layer 2, due to the mismatch in thermal expansion coefficient between the battery member such as the anode layer 1, the less likely the crack chipping Increases reliability.

  From the results of Example 2 above, when the molar composition ratio (1-z) of Sr in LSSC is 0.2 ≦ 1-z ≦ 0.7, the possible range of the substitution ratio x / z of Sm is as follows. If 0.01 ≦ x / z <0.5, it is preferable because the electric conductivity is larger than that of the LSC before substitution with Sm and the thermal expansion coefficient approaches an appropriate value. Further, it is particularly preferable that the substitution ratio x / z of Sm is 0.01 ≦ x / z ≦ 0.25, since it is clear that the above effect can be obtained.

<< Second Example: Cathode Material >>
As a second example, evaluation using LSSC as a cathode material of SOFC was performed. The LSSC molded body of Example 3 was manufactured and the LSSC molded body was evaluated in the same manner as in the first example, and a coin-type cell C (disk) according to Example 4 (corresponding to a single cell of SOFC) was manufactured. The output voltage when LSSC was used as the cathode material was measured. Based on the output voltage measurement value, the output voltage of the cylindrical cell C (cyl) corresponding to the coin cell C (disk) was obtained by simulation, and the power generation performance was evaluated as the SOFC cell of Example 4.

[Preparation of perovskite-type oxide compacts]
<Example 3>
As Example 3, a molded article of LSSC was obtained by the following procedure.
(LSSC compact)
A LSSC molded body molded into a pellet was obtained by the same production method as in Example 1. (1) In the formula [La _z-x Sm _x Sr _1-z CoO ₃ ], a plurality of types of LSSC raw material powders in which the molar composition ratio “x” of Sm in the case of z = 0.5 is within a predetermined range. It synthesize | combined and the some LSSC molded object sample was produced (refer No. 1-4 of Table 1).

<Comparative Example 3>
(LSC compact)
A molded sample of LSC [La _0.5 Sr _0.5 CoO ₃ ] in the case of z = 0.5, which was molded into a pellet by the same production method as in Comparative Example 1, was obtained.

[Evaluation of perovskite oxide compacts]
1) Evaluation of electrical conductivity In the same manner as in Examples 1 and 2, the obtained LSSC molded body samples of Example 3 were identified, and each molded body sample of Example 3 was subjected to perovskite oxidation according to the present invention. It confirmed that it was a molded object containing a thing. And about each obtained molded object sample of LSSC of Example 3, electrical conductivity was measured under predetermined | prescribed environmental temperature. FIG. 6 shows changes in electrical conductivity with respect to the Sm substitution ratio x / z of each LSSC of Example 3 at 700 ° C.

  From FIG. 6, it was confirmed by experiments as in Example 1 that each LSSC molded body of Example 3 had a higher electrical conductivity than that of Comparative Example 3 at 700 ° C. It was recognized that the electrical conductivity of each LSSC molded body was larger than that of the LSC molded body of Comparative Example 3 when the substitution ratio x / z of Sm was in the range of 0 <x / z ≦ 0.72.

2) Evaluation of thermal expansion coefficient About each obtained LSSC molded object sample of Example 3, the thermal expansion coefficient under 700 degreeC was measured. In FIG. 7, the change of the thermal expansion coefficient with respect to the substitution ratio x / z of Sm of each LSSC molded object of Example 3 was shown.

In SOFC, it is preferable that the thermal expansion coefficients of the cathode layer and the counterpart member bonded to the cathode layer are close. The cathode layer is assumed to be bonded to a mating member such as an electrolyte layer, a reaction suppressing layer or a current collecting member formed of a ceramic material, or a current collecting member formed of a metal material. As a coefficient of thermal expansion that can achieve consistency with these mating members, the approximate value of 11 to 12 × 10 ⁻⁶ (K ⁻¹ ) is assumed as in the case of Examples 1 and 2 (assumed thermal expansion). coefficient). From the graph of FIG. 7, at 700 ° C., each LSSC molded body of Example 3 has an Sm substitution ratio x / z in the range of 0 <x / z ≦ 0.5. The effect of becoming smaller than the thermal expansion coefficient and approaching the assumed thermal expansion coefficient was recognized.

[Production of coin cell]
<Example 4>
In order to evaluate the output characteristics of the SOFC of Example 4, a coin-type cell C (disk) using LSSC as a cathode material was manufactured by the following procedure. That is, using (1) a plurality of types of cathode layer pastes (cathode materials) containing LSSC powders having different molar composition ratios x in the formula [La _z-x Sm _x Sr _1-z CoO ₃ ], FIG. A plurality of coin-type cells C (disk) shown in the drawing were produced.
(Preparation of anode layer support precursor)
Commercially available nickel oxide (NiO) powder having a particle size of about 0.5 μm and 8YSZ (Y ₂ O ₃ : 8 [mol]%) powder having a particle size of about 0.5 μm are mixed at a weight ratio of 6: 4. Thus, a mixed powder was obtained. The mixed powder of the anode electrode support material, xylene as a solvent, polyvinyl butyral as an organic binder, an acrylic resin as a pore-forming material, and a phthalate ester as a plasticizer in a weight ratio of 48 to 58: The slurry was added at a ratio of 24: 8.5: 5 to 15: 4.5, dispersed in xylene, and kneaded with a ball mill to prepare a slurry. From this slurry, a sheet was formed on a PET substrate sheet by the doctor blade method, and the sheet was dried to prepare an anode layer support precursor having a thickness of 0.5 to 1.0 mm.

(Preparation of anode layer paste)
The same nickel oxide (NiO) powder that produced the anode layer support precursor, the same 8YSZ powder, α-terpineol as a solvent, and ethyl cellulose as a binder in a weight ratio of 48: 32: 18: 2. The mixture was added and mixed at a ratio, and kneaded sufficiently to prepare an anode layer paste.

(Preparation of electrolyte layer paste)
A commercially available YSZ (Y ₂ O ₃ : 8 [mol]% -ZrO ₂ : 92 [mol]%) powder having a particle size of about 0.5 μm, a terpineol-based solvent as a solvent, and ethyl cellulose as a binder in a weight ratio. , 65: 31: 4, and the mixture was sufficiently kneaded to prepare an electrolyte layer paste.

(Preparation of reaction suppression layer paste)
Commercially available 10 GDC (Gd ₂ O ₃ : 10 [mol]% -CeO ₂ : 90 [mol]%) powder having a particle diameter of about 0.5 μm, α-terpineol as a solvent, and ethyl cellulose as a binder in a weight ratio. , 65: 31: 4 were added and mixed, and kneaded thoroughly to prepare a reaction inhibiting layer paste.

(Preparation of cathode layer paste)
A plurality of types of cathode layer pastes containing LSSC raw material powders having different compositions as cathode materials were prepared by the following method. (1) In the formula [La _z-x Sm _x Sr _1-z CoO ₃ ], the molar composition ratio “x” of Sm when z = 0.5 is within a predetermined range (0 <x ≦ 0.36) LSSC raw material powder was used. Specifically, the LSSC powder having the same composition as the LSSC raw material powder having the respective composition from which each LSSC molded body of Example 3 was produced was used (see Table 1). To each LSSC powder having a predetermined molar composition ratio x, α-terpineol as a solvent and ethyl cellulose as a binder were added and mixed at a weight ratio of 80: 17: 3, and kneaded sufficiently to obtain a plurality of types. A paste for the cathode layer was obtained.

(Manufacture of coin cell C (disk))
Using the cathode layer pastes containing the LSSC powders having different molar composition ratios described above and the pastes for other members described above, etc., only the cathode material for forming the cathode layer is different by the following method. A plurality of coin-type cells C (disk) shown in FIG.
Using the anode layer support precursor described above, the anode layer paste is screen-printed concentrically on the surface of one side of the anode layer substrate and dried, and the anode layer precursor having a circular thin film shape having a diameter of about 30 mm and a thickness of about 10 μm is dried. The body was laminated. Further, the electrolyte layer paste was concentrically formed on the surface of the anode layer precursor by screen printing and dried to laminate a circular thin film electrolyte layer precursor having a diameter of about 30 mm and a thickness of about 10 μm. Furthermore, similarly, the above-mentioned paste for reaction suppression layer is screen-printed concentrically on the surface of the electrolyte layer precursor and dried to form a circular thin film-like reaction suppression layer precursor having a diameter of about 15 mm and a thickness of about 5 μm. Then, it was cut out into a disk shape having a diameter of about 25 mm. A laminate precursor was obtained in which the anode layer support / anode layer / electrolyte layer had substantially the same diameter, and only the reaction inhibiting layer had a small diameter and were laminated concentrically.

  Next, the laminate precursor of the anode layer support / anode layer / electrolyte layer / reaction inhibiting layer was fired at 1350 ° C. for 3 hours. A disc-shaped half cell laminate in which the anode layer support 12, the anode layer 11, the electrolyte layer 31, and the reaction suppression layer 32 were sequentially laminated was produced.

  Next, a cathode layer paste was screen-printed concentrically on the surface of the reaction suppression layer 32 of the half cell laminate and dried to laminate a cathode layer precursor having a diameter of about 10 mm. A laminated body precursor that was concentrically laminated with a small diameter was obtained in the order of the half cell laminated body / cathode layer.

  Next, the half cell laminate / cathode layer laminate precursor was fired at 1000 ° C. for 2 hours. As shown in FIG. 9, a coin-type cell C (disk) was fabricated in which the anode layer support 12, the anode layer 11, the electrolyte layer 31, the reaction suppression layer 32, and the cathode layer 21 were laminated in order. In the coin-type cell C (disk), the anode layer support 12, the anode layer 11, and the electrolyte layer 31 have substantially the same diameter, and the reaction suppression layer 32 and the cathode layer 21 have smaller diameters in this order, and these layers are laminated concentrically. In addition, the anode layer 11, the electrolyte layer 31, the reaction inhibition layer 32, and the cathode layer 21 as a whole have a circular flat plate configuration having a thickness of about 50 μm.

(Comparative Example 4)
(Manufacture of coin cell C (disk))
Using the LSC [La _0.5 Sr _0.5 CoO ₃ ] powder in the case of z = 0.5 in Comparative Example 3, the coin-type cell C (disk) having the same shape is manufactured by the same manufacturing method as in Example 4. Produced.

[Cell voltage evaluation]
(Power generation test)
Using the coin cell C (disk) according to Example 4 and Comparative Example 4, a power generation test was performed under the following conditions, and the cell voltage of each coin cell C (disk) was actually measured.
The coin-type cell C (disk) of Example 4 has an overall shape of a substantially circular flat plate type. As shown in FIG. 9, the coin-type cell C (disk) has the anode layer support 12, the anode layer 11, and the electrolyte layer 31 that have substantially the same diameter, and the reaction suppression layer 32 and the cathode layer 21 that have smaller diameters in this order. Each layer has a configuration in which concentric layers are stacked in the upper direction in the drawing.
Using a known power generation test device, an anode electrode side current is collected by bringing an electrode body made of a platinum mesh member into contact with the exposed portion of the anode layer support 12 at an ambient temperature of 700 ° C. In addition, the electrode body was brought into contact with the surface of the cathode layer 21 to collect current on the cathode electrode side. H ₂ was used as the fuel gas, air was used as the oxidizing gas, and each flowed at a flow rate of 200 (ml / min). The voltage between the electrode bodies at a predetermined current density of 0.2 (A / cm ² ) was measured.

(Cell voltage: Cylindrical cell)
From the voltage of the coin cell C (disk) measured in this way, the voltage of the cylindrical cell C (cyl) was estimated. Specifically, using the transmission line model (equivalent circuit) of the cylindrical cell C (cyl), based on the measured cell voltage of the coin cell C (disk) obtained in the power generation test, the cylindrical cell C ( cyl) to obtain the output voltage. Assuming that a predetermined virtual current collecting member (not shown) is attached to the cylindrical cell C (cyl), a voltage drop calculation for the current collection loss of the virtual current collecting member is performed from the above simulation values. Correction for subtracting the value was performed, and the voltage of the cylindrical cell C (cyl) was estimated.
As shown in FIG. 10, the cylindrical cell C (cyl) is composed of the anode layer support 12, the anode layer 11, and the electrolyte layer 31 of the coin cell C (disk) in order from the inside toward the outside along the radial direction. The anode layer support 120, the anode layer 110, the electrolyte layer 310, the reaction inhibition layer 320, and the cathode layer 210 correspond to the five layers of the reaction inhibition layer 32 and the cathode layer 21, respectively.

  The cylindrical cell C (cyl) has an electrode length of a predetermined length (for example, L = 50 mm) along the axial direction. Current collecting portions of the cylindrical cell C (cyl) connected to the external circuit are at one end and the other end along the axial direction of the anode layer 110 and the cathode layer 210. In addition, in order to perform a simulation in this transmission line model, a known numerical value is given as a physical property value of a material forming each layer. Among them, as the electrical conductivity of the cathode layer 210, a numerical value actually measured in each LSSC molded body according to Example 3 was given. The electrical conductivity of the virtual cathode current collector connected to the cathode layer 210 is a numerical value calculated as having a porosity of 30% based on the numerical value actually measured for each LSSC molded body according to Example 3. Gave.

FIG. 8 shows the cell voltage of the cylindrical cell C (cyl). The output voltage of each cylindrical cell C (cyl) calculated based on the actually measured voltage value of each coin type cell C (disk) according to Example 4 and Comparative Example 4, and the LSSC Sm replacement ratio x / z A graph showing the relationship is shown.
From FIG. 8, each cylindrical cell C (cyl) of Example 4 that contains LSSC as the cathode material of the cathode layer 21 and uses LSSC as the conductive material of the virtual cathode current collector is 700 ° C. Below, it was confirmed that the cell voltage was comparable to the cylindrical cell C (cyl) of Comparative Example 4. In the cylindrical cell C (cyl) in which the substitution ratio x / z of Sm is in the range of 0 <x / z <0.72, a cell voltage similar to that of the cell of Comparative Example 4 is obtained and can be evaluated. did it. In particular, in the cylindrical cell C (cyl) using the LSSC in the vicinity of the Sm substitution ratio x / z of 0.08, a cell voltage larger than that of the cylindrical cell C (cyl) in Comparative Example 4 is obtained. I was able to appreciate it.

[Comprehensive evaluation of cathode materials]
The evaluation results of Examples 3 and 4 using LSSC as the cathode material of the SOFC cell in the second example are shown in Table 1 in the form of relative evaluation with the comparative example.

  From Table 1 and FIGS. 6-8, it can judge comprehensively as follows. That is, if the possible range of the substitution ratio x / z of Sm to the perovskite oxide is 0 <x / z <0.72, the electrical conductivity is large and the thermal expansion coefficient approaches an appropriate value. This is preferable because a cell voltage comparable to the case of using LSC can be obtained. Further, it is particularly preferable that the range that the substitution ratio x / z can take is 0.08 ≦ x / z ≦ 0.5 because it is clear that the above-described effect can be obtained.

  In addition, in order to evaluate the output characteristics of the SOFC cell, a cylindrical cell C (cyl) having a structure in which a virtual cathode current collecting member is laminated on the cathode layer 21 and both the cathode material and the conductive material contain LSSC is used. Although examination was performed on the assumption, the present embodiment is not limited to this configuration. Even if the SOFC cell is configured so that at least the cathode material contains LSSC, the effect of improving electrical conductivity can be obtained. However, since the SOFC cell is configured as a joined body of different materials such as different ceramics or different materials such as metal-ceramics, an insulating reaction product is generated at the interface of different materials or the mutual diffusion of component elements proceeds. The possibility of reaction activity being impeded is included. It is preferable that the cathode layer and the cathode current collecting layer or current collector bonded to the cathode layer are made of the same material, because such a failure can be suppressed.

  In addition, although LSC is large and excellent in electrical conductivity, LSC has a larger thermal expansion coefficient than general metal materials and ceramic materials. It is expected that a cathode material having a large electric conductivity and a thermal expansion coefficient comparable to that of other members will appear. The present embodiment has been made in view of such problems, and includes a cathode layer having a large electrical conductivity under a condition of operating at a high temperature and a thermal expansion coefficient close to that of other members. It aims to provide a fuel cell.

As described above in detail, the SOFC 100 (fuel cell) of the present invention uses the perovskite oxide described in this embodiment or the present example, and is provided on one side of the electrolyte layer 3 and the electrolyte layer 3. The cathode layer 2, the anode layer 1 provided on the other side of the electrolyte layer 3, and the electron that is electrically connected to at least one of the cathode layer 2 or the anode layer 1 to collect an electrode reaction, or a single cell C or SOFC 100 and a current collector E for taking out electricity, and at least one of the current collector 52 or the cathode layer 2 constituting the current collector E is a perovskite oxide represented by the general formula ABO _3. A perovskite oxide, which is contained as a conductive material or a cathode material, arranges La and Sr at the A site, arranges Co at the B site, and arranges La and S at the A site. A part of one La in Sr is substituted with Sm, and the molar composition ratio of Sm to the perovskite oxide is smaller than the molar composition ratio of La to the perovskite oxide before substitution, and has a perovskite structure.

Therefore, the electrical conductivity of the conductive material is larger than that of LaSrCoO _{3 of} the conventional material, so that the voltage loss due to the electrical resistance of the current collecting member 52 can be reduced, and the output characteristics of the SOFC 100 can be improved. it can. The SOFC 100 generally has a large effect of reducing electric resistance because a large number of single cells C are stacked and each unit cell C is electrically connected through a current collector E. Sonouede, the thermal expansion coefficient of LaSmSrCoO ₃ reduces than LaSrCoO _3, closer to the thermal expansion coefficient of the other member that, including metal material or ceramic material. In other words. Since the thermal expansion coefficient of the LaSmSrCoO ₃ is smaller than the LaSrCoO _3, due to the mismatch in thermal expansion coefficient between the ceramic material and the metallic material at a high temperature (under operating temperature), mainly current collecting member 52 and the metal material It can suppress that the separator layer 51 used as a component tends to peel off. Therefore, the contact resistance can be reduced, so that the output characteristics of the fuel cell can be further improved.

Therefore, in addition to the effects described in the first embodiment, the electrical conductivity of the cathode material is larger than that of the conventional material LaSrCoO ₃ . LaSmSrCoO ₃ has an oxygen-activated catalyst function, oxygen ion conductivity, and electronic conductivity, similarly to LaSrCoO ₃ . Sonouede, the thermal expansion coefficient of the LaSmSrCoO ₃ is smaller than the LaSrCoO _3, with other ceramic material at a high temperature (under operating temperature), or due to mismatch in thermal expansion coefficient between the metallic material, the cathode layer 2 and the separator layer 51 having a metal material as a main component, or the cathode layer 2 and the electrolyte layer 3 and the current collector E having a ceramic material as a main component can be suppressed. The thermal expansion coefficient of the conventionally known LaSrCoO ₃ is considerably large compared to other materials of metals and ceramics generally used for SOFC, and there is a tendency that it is difficult to achieve consistency of the thermal expansion coefficient. The effect of reducing the thermal expansion coefficient while utilizing the conductive performance is conspicuous. Therefore, the contact resistance can be reduced, so that the output characteristics of the fuel cell can be further improved.
In the above-described embodiments, the preferred range of the composition of LaSrCoO _{3 that} is preferable as the cathode material has been described with the substitution ratio x / z of Sm as a parameter. However, the molar composition ratio x of Sm is used as a parameter. Can have the same preferred range.

Furthermore, the cylindrical current cell C (cyl) including the virtual current collecting member using LaSmSrCoO ₃ as the conductive material and the cathode material and the cathode layer 210 is more than the conventional material using LaSrCoO ₃ as the conductive material and the cathode material. , Can improve the output characteristics. In addition, a virtual current collecting member using LaSmSrCoO ₃ as a conductive material and a cathode material and a cylindrical cell C (cyl) including the cathode layer 210 are joined to the cathode layer and the cathode layer (virtual) cathode current collecting member; However, since they are the same material, it is possible to suppress the occurrence of the obstacle that hinders the electrode reaction activity described above, and to suppress the degradation of the output characteristics of the SOFC cell.

Further, since the thermal expansion coefficient of the LaSmSrCoO ₃ is smaller than the LaSrCoO _3, the separator layer 51, the collector E (current collecting member 52), by reducing the mismatch of thermal expansion coefficient between the battery member 3 such electrolyte layer Since cracks are less likely to occur, the reliability can be improved.

  DESCRIPTION OF SYMBOLS 1,11,110 ... Anode layer, 2, 21, 210 ... Cathode layer, 3, 31, 310 ... Electrolyte layer, 51 ... Separator layer, 52 ... Current collecting member, 100 ... SOFC (fuel cell), C ... Single cell , C (disk): coin cell (single cell), C (cyl): cylindrical cell (single cell), E: current collector.

Claims (3)

An electrolyte layer;
A cathode layer provided on one side of the electrolyte layer;
An anode layer provided on the other side of the electrolyte layer;
A current collecting member that is electrically connected to at least one of the cathode layer or the anode layer to collect electrons, or to take electricity out of the fuel cell;
With
At least one of the current collecting member or the cathode layer contains a perovskite oxide represented by the general formula ABO ₃ as a material,
The perovskite oxide is
La and Sr are arranged at the A site, and Co is arranged at the B site,
Of La and Sr arranged at the A site, a part of one La is substituted with Sm,
The molar composition ratio of Sm to the perovskite oxide is smaller than the molar composition ratio of La to the perovskite oxide before substitution.
A fuel cell having a perovskite structure. The material contained in the current collecting member is the perovskite oxide having a composition represented by the following formula (1):
La _z-x Sm _x Sr _1-z CoO ₃ (1)
In the formula (1), x / z indicating the ratio of the molar composition ratio x of Sm in the perovskite oxide to the molar composition ratio z of La in the perovskite oxide before substitution is 0.01 ≦ x / z <0.5,
2. The fuel cell according to claim 1, wherein a molar composition ratio (1-z) of Sr in the perovskite oxide is in a range of 0.2 ≦ 1-z ≦ 0.7.   3. The fuel cell according to claim 2, wherein the ratio x / z, which is a ratio of x to z, is in a range of 0.01 ≦ x / z ≦ 0.25.

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