JP6524434B2 - Solid oxide fuel cell air electrode, solid oxide fuel cell, and method of manufacturing solid oxide fuel cell air electrode - Google Patents

Description

  The present invention relates to a solid oxide fuel cell air electrode, a solid oxide fuel cell, and a method of manufacturing a solid oxide fuel cell air electrode.

  In recent years, as the demand for clean and renewable energy has grown, solid oxide fuel cells (SOFCs) have received great attention due to their high energy efficiency, environmental friendliness and excellent fuel flexibility . The SOFC comprises an air electrode, an electrolyte, and a fuel electrode as main components. In the operation, first, at the air electrode, oxygen in the air at the surface receives electrons from the air electrode material and becomes oxide ions. The oxide ions are taken into the cathode material and diffuse through the crystal lattice to reach the electrolyte interface. The oxide ions further transfer and diffuse into the electrolyte, reach the fuel electrode disposed on the opposite surface of the electrolyte, and further diffuse within the fuel electrode material to reach the fuel electrode surface. The oxide ions react with hydrogen of the fuel at the surface of the fuel electrode to generate water while passing electrons to the fuel electrode. Thus, multistage reactions occur. Electrons flow from the fuel electrode to the air electrode through an external circuit to operate as a battery.

  In SOFC, the manufacturing cost is one of the major issues, and the method for this is to lower the operating temperature so that cheaper materials can be used in structural materials, sealing materials, and electrical connection materials. Is being sought. Although the operating temperature is conventionally about 1000 ° C., it is desirable that the temperature can be lowered to an intermediate operating temperature of 600 ° C. to 750 ° C., and further to a lower temperature (<600 ° C.). However, when using SOFC in the said middle-low temperature area | region, the problem that the characteristic material falls in the conventional SOFC constituent material arises.

Low temperature operation is a major issue for any of the main components of the fuel cell, that is, the air electrode, the electrolyte and the fuel electrode. In the electrolyte, in addition to reducing the thickness of the electrolyte, a material having higher ion conductivity is required. Examples of such materials include samarium (Sm) substituted ceria (SDC), gadolinium (Gd) substituted ceria (GDC), and lanthanum gallate (LaGaO ₃ ) as part of strontium (Sr) or magnesium ( Mg) substituted materials (LSGM). In the fuel electrode, cermets containing nickel (Ni) or YSZ have been considered.

  In medium- and low-temperature operation, it is believed that the air electrode accounts for the majority of the total resistance of the battery and is the main cause of performance degradation. It is the biggest challenge for practical use. That is, the reaction in which oxygen molecules in the air are ionized on the surface of the air electrode and the speed at which the ionized oxide ions diffuse in the material lattice of the air electrode are slow, and these faster high-performance air electrodes are required. It is done.

One of the SOFC air electrodes is one containing a perovskite oxide. Early The air electrode for SOFC, e.g. _{La 1-x Sr x MnO 3-} δ, La 1-x Sr x CrO 3- δ etc. B site of Mn and Cr in the perovskite (oxygen octahedral center position) The materials contained therein have been used, which are the air electrodes used in SOFCs of zirconia electrolytes such as YSZ, but are usually operated at high temperatures above 700.degree. On the other hand, as the air electrode of the SOFC is used at medium low temperature region, as described in Non-Patent Documents 1 and _{2, Ln 1-x Sr x CoO} 3- δ, La 1-x Sr x Co 1-y Fe _y O _{3- [delta],} and _{Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2} O 3- δ etc., to exhibit good properties in combination with ceria based electrolyte have been reported. In order for these air electrode materials to exhibit desirable properties in the middle and low temperature region, it is considered that the key is that Co (Co) or iron (Fe) is contained at the B site of the perovskite structure.

  As described in Non-Patent Document 3, the Co, Fe-based perovskite oxide has been focused on the feature of having high oxide ion conductivity and high electron (or hole) conductivity. Co, Fe-based perovskite oxides have been considered as an oxygen separation membrane material for separating oxygen from the air before being considered for application to SOFCs.

  In the oxygen separation membrane, oxygen in air at the membrane surface on the high oxygen partial pressure side receives electrons from the membrane material to form oxide ions, and oxide ions diffuse in the material lattice of the separation membrane to the other side of the membrane The surface (low oxygen partial pressure side surface) is reached. At the surface, two oxide ions react, leaving electrons in the film material, and are separated again as oxygen molecules. Thus, the reaction taking place in the oxygen separation membrane is similar to the air electrode of SOFC. The difference between the two is that electrons (or holes) flow from the fuel electrode to the air electrode through the external connection in the case of SOFC, while in the case of the oxygen separation membrane, the inside of the separation membrane is low. It is a point flowing from the oxygen partial pressure side (oxygen permeation side) surface toward the high oxygen partial pressure side (oxygen inlet side) surface. The dissociation reaction rate of oxygen on the electrode surface, the oxide ion conductivity in the electrode material, the electron (or hole) conductivity, which are important as an air electrode, are all important factors that determine the separation characteristics in the oxygen separation membrane is there. Therefore, it is inevitable that an oxygen separation membrane material has been considered as a high performance cathode material candidate.

  Among the oxygen separating materials, particularly those having high oxide ion conductivity contain Co and Fe at the B site, and the content of Co is particularly high. Even when iron is contained in the B site, good oxide ion conductivity can be obtained, but the oxide ion conductivity is inferior to that of Co. On the other hand, the perovskite-type oxide having a high Co content has a problem that the material is unstable. There are two types of the instability, one of which is that oxygen vacancies in the crystal of the oxide having a perovskite structure are regularly arranged by interaction, and the structure changes to a structure represented by so-called brownmillerite. It is transformation. The other is transformation to hexagonal crystals, which is very different from the perovskite structure. In any structural transformation, there arises a problem that the oxide ion conductivity is greatly impaired if it occurs. Many oxygen separation membrane materials have been developed to solve these material instability problems.

  Among these oxygen separation membrane materials, the material disclosed in Patent Document 1 has high stability of the material and high oxygen permeation rate in the composition range where the content of barium (Ba) at A site is large. That is, it is a perovskite-type mixed conductor having high oxide ion conductivity. This material is characterized in that it contains Ba at the A site, and contains indium (In), yttrium (Y), etc. in addition to Co and Fe at the B site. In particular, as for Y, in Patent Document 1, as a way of including it in the perovskite-type mixed conductor, the stabilization of the perovskite is strong when it is contained in the B site, not in the conventionally known A site. It is disclosed that an effect can be obtained. Moreover, it is also shown that the fact that Y is not at the A site but at the B site can be confirmed by measuring the lattice constant of the perovskite-type mixed conductor by X-ray powder diffraction method or the like. That is, in the case where Y substitutes the A site, the ion radius of Y is smaller than that of Ba or strontium (Sr) at the A site, and therefore no increase in lattice constant due to substitution is observed. On the other hand, when Y substitutes the B site, the ion radius of Y is larger than Co or Fe of the B site, so an increase in lattice constant is observed, and it is believed that B site substitution can be confirmed.

  For example, Patent Document 2 discloses an oxide ion conductor as a technology of an oxide mixed conductor having a composition that looks similar to that of Patent Document 1 or an air electrode of SOFC; Containing Al), In, etc. to produce oxygen vacancies and to express oxide ion conductivity, and Al, Co, etc., to improve the mechanical strength by reducing the size of matrix crystal grains. It is stated that it can. However, this oxide ion conductor is a Ga-based perovskite-type oxide, and Al and In as well as Co are only one of the selection elements, and the crystal structure of a Co-based perovskite-type oxide is It does not disclose the effect on stability.

  Further, Patent Document 3 discloses an air electrode material of SOFC, which indicates that B site can contain Co, Al, In in addition to titanium (Ti). However, this air electrode material is a Ti-based perovskite-type oxide, and Al and In as well as Co are only one of the selection elements, and the crystal structure of the Co-based perovskite-type oxide is stable. It does not disclose the effect on sexuality.

  Further, Patent Document 4 discloses an air electrode material of SOFC, and it is shown that, in addition to manganese (Mn), B can contain Al, In, etc. in addition to Co as an arbitrary element. There is. However, this cathode material is a Mn-based perovskite-type oxide, and Al and In, of course, Co is only one of the selection elements, and the crystal structure of the Co-based perovskite-type oxide is stable. It does not disclose the effect on sexuality.

  Further, Patent Document 5 discloses an SOFC air electrode material, and a composite material including perovskite particles and ceramic coating particles in which the surface of metal core particles such as silver (Ag) is ceramic-coated. There is. In this composite material, it is disclosed that the perovskite particles may contain Co or Mn, and may contain Al, In, or Y as an arbitrary element. This optional element is disclosed to have high oxide ion conductivity as its effect. However, Patent Document 5 may optionally contain Al, In, or Y at the B site, but does not disclose the effect on the stability of the crystal structure of the Co-based perovskite oxide by these elements. .

  Patent Document 6 discloses a SOFC air electrode material, which is a composite material of a perovskite oxide and a cerium oxide. It is said that this perovskite type oxide can contain Co, Al, In, Y and the like for the purpose of obtaining high oxide ion conductivity, in addition to containing cerium. However, in Patent Document 6, Al, In, and Y are only one of the optional elements which are not essential. Moreover, the effect on the stability of the crystal structure of the Co-based perovskite oxide due to the inclusion of these elements in the B site is not disclosed.

Patent No. 4074452 JP 2001-332122 A JP, 2009-263225, A Japanese Patent Application Publication No. 2011-510892 JP, 2012-230795, A JP, 2013-143242, A

Shao, Z. P .; Haile, S. M. Nature 2004, 431, 170 Xia, C. R. et al. Solid State Ionics 2002, 149, 1 Teraoka et al., Chemistry Letters 1985, 1743

In order to enable SOFC operation in the middle and low temperature range, perovskite electrode oxides containing manganese (Mn) and chromium (Cr) in the air electrode material that can obtain sufficient characteristics at high temperatures have performance degradation in the middle and low temperature ranges It is essential to solve the problem of A possible solution to this problem is to change the cathode material to a Co-containing perovskite-type oxide which is superior to Mn and Cr in diffusion of oxide ions and has high properties. In particular, a perovskite-type oxide containing Ba at the A site is excellent in diffusion of oxide ions, and the possibility of obtaining high characteristics as an air electrode material is expected. However, studies using Co-containing perovskite oxides for the air electrode have only just begun, and it is a stage where primarily the initial properties immediately after being manufactured are mainly discussed.

  From the past developmental experience with Co-containing perovskite-type oxides, the present inventors derive from the instability of the material possessed by this material, and in the use of SOFCs in the middle and low temperature range, particularly after long-term use It has been noted that phase transformations and the associated loss of properties and durability problems result. Since such transformation progresses slowly in the long term at low temperatures, the device performance is in the form of deterioration of fuel cell durability accompanied by electrode deterioration and lack of long-term reliability, regardless of how high the initial performance is. Affect.

  In other application fields where Co-containing perovskite oxides have already been studied as potential materials, ie, in the field of oxygen separation membranes, efforts have been made to stabilize the crystal structure of this oxide. It has However, the development of conventional oxygen separation materials is mainly premised on the use at 800 ° C to 900 ° C, and the durability has been studied according to this, but the operating temperature of SOFC for middle and low temperature is 750 It is less than ° C and will be used at lower temperature than oxygen separation. In this way, in the application to SOFC operating in the middle to low temperature region where the use temperature is lower, the instability of the crystal structure of the Co-containing perovskite-type mixed conductor becomes larger than the application to oxygen separation. Therefore, development of a Co-containing perovskite-type oxide as an air electrode of SOFC requires the development of a dedicated material that can not be simply used for the conventional oxygen separation material.

Was developed as an oxygen separation materials, along with containing Ba in the A site, in addition to Co or Fe at the B site, the perovskite-type mixed conductor containing In or Y _{etc., Ba 1-x Sr x Co} 1-y In _y O _{3- [delta],} represented by _{Ba 1-x Sr x Co 1} -y Y y O 3- δ like. These are mixed conductors that exhibit excellent oxide ion conductivity. However, the development premise was that the operating temperature of SOFC was 800 ° C. to 900 ° C., like other oxygen separation materials. Material development from the viewpoint of long-term reliability considering the material instability peculiar to the SOFC application of middle and low temperature operation has not been made in the In and Y containing Co based perovskite type mixed conductors.

  As a result of studies by the present inventors, even if it is attempted to apply the oxygen separation material to the air electrode of an SOFC operating at low and medium temperatures, it has been found that coexistence of durability and high characteristics is difficult as feared. . However, the high performance of this oxygen separation material as an oxide ion conductor is still attractive, and it is effective to improve this oxygen separation material to solve the problems of SOFC operating in the middle and low temperature range. Was expected to be a candidate for a successful solution. That is, as a material of an air electrode for SOFC aiming at long-term use in the middle and low temperature range, a Co-based perovskite containing Ba at the A site and Co or Fe and In at Y site at the B site disclosed in Patent Document 1 There has been a demand for the development of more superior materials specialized for the air electrode of SOFCs for middle and low temperatures while being based on a mixed conductor.

  The present invention has been made in view of the above problems, and exhibits excellent characteristics in the use environment of the middle and low temperature range of the solid oxide fuel cell, and has high fuel cell characteristics even when the medium and low temperature range is used. Solid oxide type that can obtain (for example, maximum power density), exhibit high stability as a perovskite crystal structure even under the use environment, and can exhibit characteristics stably for a long period of time An object of the present invention is to provide an air electrode of a fuel cell, a solid oxide fuel cell, and a method of manufacturing the air electrode of a solid oxide fuel cell.

The air electrode of the solid oxide fuel cell of the present invention is an oxide ion mixed conductor having a perovskite crystal structure, and the composition is
[L n _1-ab A _a (Ba) _b ] [B _x B ' _y B " _z (Al) _w ] O _{(3- δ )} (1)
The ceramic composition represented by the general formula of
In the above equation (1),
Ln is a combination of one or more elements selected from lanthanoid elements La, Pr, Nd, Pm, Sm, Eu, Gd, Tb and Dy;
A is a combination of one or two elements selected from Sr and Ca,
B is a combination of one or two elements selected from Co and Fe, and the mole number of Co is 50% or more with respect to the mole number x of all B elements,
B ′ is a combination of one or two elements selected from In and Y,
B "is a combination of one or two elements selected from Nb and Ta,
However,
When B ′ is In, 0.7 ≦ b ≦ 1.0, 0.05 ≦ y ≦ 0.2,
When B ′ is Y, 0.5 ≦ b ≦ 1.0, 0.06 ≦ y ≦ 0.2,
When B 'is a combination of In and Y, the range of b and y is the same as the range for elements containing more moles of In and Y,
0.8 ≦ a + b ≦ 1,
0 <x,
0 ≦ z ≦ 0.1,
0 <w ≦ 0.2,
0.98 ≦ x + y + z + w ≦ 1.02,
δ is a value defined to satisfy the charge neutral condition.

  The solid oxide fuel cell of the present invention comprises the above-mentioned air electrode.

  The method for producing an air electrode of a solid oxide fuel cell according to the present invention comprises using a powder of carbonate or oxide containing Ln, A, Ba, B, B ', B ", and Al in the formula (1). And mixing the powders and firing in an oxidizing atmosphere or an inert gas atmosphere to form a raw material powder consisting of a single phase of a perovskite structure, and pulverizing the raw material powder and grinding the raw material powder The maximum temperature of the heat treatment experienced as the sintering heat history when firing the air electrode into the shape of the air electrode is a temperature of 1150 ° C. or more and 1200 ° C. or less.

  According to the present invention, the solid oxide fuel cell can exhibit excellent characteristics in the use environment of the middle and low temperature range, and can obtain high fuel cell characteristics (for example, maximum power density) even when the middle and low temperature range is used. The air electrode of a highly reliable solid oxide fuel cell, which exhibits high stability as a perovskite crystal structure even under the use environment and can exhibit characteristics stably for a long period of time To realize.

It is a figure which shows the table | surface which described the composition etc. as each sample as Example 1-21 and Comparative Examples 1-9. It is a figure which shows the table | surface which described the evaluation result of the accelerated test of durability, etc. by making each sample into Examples 1-21 and Comparative Examples 1-9.

Hereinafter, specific embodiments of the present invention will be described.

[Specific material composition of air electrode for SOFC]
The air electrode for SOFC according to the present embodiment is for achieving excellent SOFC characteristics particularly in the middle and low temperature range. Here, the “mid-low temperature range” refers to a temperature range (500 ° C. to 750 ° C.) obtained by combining an intermediate temperature range within the range of 600 ° C. to 750 ° C. and a low temperature range within the range of 500 ° C. to 600 ° C. I assume.

  The material of the air electrode according to the present embodiment is based on the study of the perovskite-type mixed conductor containing Ba at the A site and In and Y in addition to Co and Fe at the B site disclosed in Patent Document 1 Was developed. In the process of the said examination, it turned out that the perovskite type mixed conductor disclosed by patent document 1 can exhibit the outstanding characteristic in the initial stage of use start as SOFC air electrode material. On the other hand, the material is likely to deteriorate in characteristics in the middle to low temperature range, particularly in long-term use at 500 ° C. to 600 ° C., mainly due to destabilization of the cathode material during use at the temperature. It was also revealed that the phase transition to the characteristic phase. In order to prevent the characteristic deterioration due to the phase transition, it is possible to increase the content of In and Y contained in the cathode material by one method. However, as a side effect, the characteristics as the air electrode are lowered due to the decrease in the oxide ion conductivity and the electron (or hole) conductivity of the material, and the maximum power density of the fuel cell is lowered, etc. A problem arises.

  The inventors of the present invention have long-term characteristics in the middle and low temperature region while maintaining the inherent high characteristics of the Perovskite-type mixed conductor containing Ba at the A site and In and Y in addition to Co and Fe at the B site. We have also continued to search for cathode materials that can stably maintain the perovskite-type crystal structure and use less deterioration of the characteristics. As a result, it is found that the material disclosed in this embodiment, that is, containing Al in addition to Co, Fe and In and Y at Ba site and B site at A site is extremely effective for solving the problem. The The examination of the conventional perovskite-type mixed conductor containing Co as a main component is premised on use at a higher temperature of about 800 ° C. to 900 ° C. in an oxygen separation application, and in this case, containing Al improves the characteristics It was not considered as a means or crystal structure stabilization means.

  On the other hand, the present inventors added Al on the premise that In and / or Y are contained in the perovskite type mixed conductor in which Ba at the A site and Co at the B site are main components. I thought about containing it. In this case, the stability of the perovskite-type crystal structure in the middle and low temperature range is improved without increasing the content of In and Y and without reducing the characteristics as the air electrode, and the characteristics are deteriorated even in long-term use. I found that I could suppress it. Based on this finding, the present inventors have identified a range of materials that can obtain particularly high effects by the addition of Al for use as an air electrode for SOFC operation at medium and low temperatures, and completed the present invention .

  The mechanism by which the above-mentioned favorable effect is obtained by the addition of Al is not clear yet. The stabilizing effect of the perovskite-type crystal structure obtained by the addition of Al is not strong, and a single addition does not produce a remarkable function. For this reason, it is considered that, conventionally, Al has not received much attention as an additive element for stabilizing the crystal structure of the perovskite-type mixed conductor containing Co as a main component. On the other hand, under the conditions where a certain degree of stabilization is obtained by In and Y, a further improvement in stability is obtained by the addition of Al, in addition to the effects already obtained by In and Y. It is presumed that this additional stability improvement helps to improve the reliability in long-term use in the middle and low temperature range. While the stability of the crystal structure can be improved even if Al is added, the reason why the characteristics do not decrease as in the case of increasing the amount of In and Y is considered as follows. That is, it is speculated that Al has an ion radius relatively close to that of Co at the B site of the perovskite oxide, and the larger distortion is more likely to occur in the arrangement of oxide ions as In and Y having a larger ion radius. Ru.

  On the other hand, the excellent air electrode characteristics can be obtained with a perovskite-type mixed conductor mainly composed of Co because this material has high oxide ion conductivity. It is considered that this is because Co ions have high flexibility and help the movement of oxygen (or oxygen vacancies) in the crystal. In order to reflect this and to realize high cathode characteristics, the content of Co in the B site needs to be a certain level or more. If the amount of Co in the material is too small, even if In is replaced by In, Y, or Al, a region which becomes rate-limiting for the diffusion of oxide ions is generated, and the electrode characteristics are degraded. Problems such as a decrease in the maximum power density of the fuel cell occur.

Based on the above, Configuration 1 of the SOFC air electrode according to the present embodiment is an oxide ion mixed conductor having a perovskite crystal structure, and the composition is
[L n _1-ab A _a (Ba) _b ] [B _x B ' _y B " _z (Al) _w ] O _{(3- δ )} (1)
It contains the porcelain composition represented by the general formula of

  Here, in the formula (1), Ln is a combination of one or more elements selected from lanthanoid elements La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, and Dy. is there. A is a combination of one or two elements selected from Sr and Ca. B is a combination of one or two elements selected from Co and Fe, and the mole number of Co is 50% or more with respect to the mole number x of all B elements. B ′ is a combination of one or two elements selected from In and Y. B ′ ′ is a combination of one or more elements selected from Nb and Ta. However, when B ′ is In, 0.7 ≦ b ≦ 1.0, 0.05 ≦ y ≦ If B ′ is Y, then 0.5 ≦ b ≦ 1.0, 0.06 ≦ y ≦ 0.2 If B ′ is a combination of In and Y The ranges of b and y correspond to the ranges for elements containing more moles of In and Y.

  Furthermore, 0.8 ≦ a + b ≦ 1, 0 <x, 0 ≦ z ≦ 0.1, 0 <w ≦ 0.2, 0.98 ≦ x + y + z + w ≦ 1.02, and δ satisfies the charge neutrality condition To be determined. That is, the sum of the valences of the cations (Ln, A, Ba, B, B ′, B ′ ′, Al) is a value determined to be equal to the valence of the anion (O).

  As described above, the porcelain composition in the present embodiment mainly contains Co as B, and further, In, Y and Al represented by B ′, niobium (Nb) and tantalum represented by B ′ ′ in some cases. The air electrode of the present embodiment has particularly high characteristics when the mole number of Co is 50% or more with respect to the mole number x of all B elements, and In, Y and Al When the mole number of Co is less than 50% with respect to the mole number x of all B elements, conductivity of oxide ions in the material can be obtained. As a result, the power density in the case of SOFC is generally reduced to half or less of the value obtained in the present invention. Y may be used alone or in combination. When B 'is In, the content of B' is 0.05 or more and 0.2 or less as y, and when B 'is Y, y or more is 0.06 or more and 0.2 or less If B 'is a combination of In and Y, the range of y follows the range of y of the element containing more moles of In and Y. Beyond this range B' In addition, the oxide ion conductivity and the electron (or hole) conductivity of the air electrode decrease, and as a result, the output density of the fuel cell decreases to about half or less of the value obtained in the present invention. In addition, if the content is less than the above range, the effect of adding In and Y is difficult to be obtained, and the stability of the perovskite structure may be insufficient. If the content of Al exceeds this range, the fuel cell output Deterioration of the characteristics occurs such that the force density is reduced to about half or less of the value obtained in the present invention, and the content is preferably 0.05 or more as w. In some cases, it is difficult to obtain the effect of adding Al.

  The stability of the oxide ion mixed conductor having the perovskite-type crystal structure in the constitution 1 is mainly used as an air electrode in the middle and low temperature region by the coexistence of Al and B 'of In and Y. Are well secured. In addition, even if the high characteristics of the air electrode are somewhat compromised, it is effective to contain Nb and Ta as B "as an additional crystal structure stabilizing element, when it is desired to use with emphasis on durability even if it gives some emphasis on durability. The content of B ′ ′ is in the range of 0.1 or less as z. If the content of B ′ ′ exceeds this range, the oxide ion conductivity in the material decreases and the characteristics of the electrode decrease, and the power density of the fuel cell falls to half or less of the value obtained in the present invention. In order to expect the additive effect of B ", it is desirable that z be 0.02 or more.

  Ln is a lanthanoid element which is a trivalent ion capable of substituting the A site, and one or more elements selected from La, Pr, Nd, Pm, Sm, Eu, Gd, Tb and Dy It is a combination. Further, A is a divalent alkaline earth element of Sr and Ca, and mainly constitutes an A site together with Ba. In the air electrode of Configuration 1, in order to obtain high characteristics, A is a and Ba is b, and 0.8 or more is added as a + b obtained by adding. When the total content of A and Ba becomes lower than this range, the oxide ion conductivity of the mixed conductor constituting the air electrode decreases, and the power density of the fuel cell is about half or less of the value obtained in the present invention To decline. The addition of the lanthanoid element has the effect of stabilizing the perovskite structure, but in the present embodiment, the stability can be secured by the addition of In, Y, or Al. Therefore, the content of the lanthanoid element is not necessarily essential. Further, in the air electrode of configuration 1, the range of the content b of Ba, which is suitable for keeping the structure of the perovskite structure stable, in which the B ′ elements are In and Y, is different. That is, when B 'is In, b is 0.7 or more, and when B' is Y, b is 0.5 or more. When B ′ is a combination of In and Y, the range of b is in accordance with the range of b of the element containing a larger number of moles of In and Y. When the content of Ba is less than the above range, the stabilizing effect of the perovskite structure by In and Y is reduced, and it may not be sufficient as an air electrode used in the middle and low temperature range.

  In Configuration 1, x + y + z + w represents the ratio of the sum of B-site ions to the sum of A-site ions, and is in the range of 0.98 to 1.02. In the region of less than 0.98, the amount of A-site ions becomes too large to contain an impurity phase, which causes a problem of deterioration of electrode characteristics. In addition, in the region of more than 1.02, the amount of B site ions becomes too large, and it becomes difficult to properly maintain the porosity when the electrode is formed.

  The point of the structure 1 is that the stability of the perovskite crystal structure under the conditions of use in order to make it possible to utilize the Co-based mixed-type mixed conductor having excellent properties as an air electrode of SOFC in the middle and low temperature range. It is possible to achieve both improvement and securing high characteristics. Including Co at the B site is, of course, characterized in that both In or Y and Al are contained in specific amounts in the B site. Furthermore, the above effects can be realized by disclosing the configuration such as the Ba content of A site suitable for In and Y respectively. The inclusion of Ga, Ti, Mn, cerium, etc., or the coexistence of metal particles such as Ag, which are regarded as essential in the prior art perovskite-type oxides that formally resemble similar technologies, is not necessary for the manifestation of effects in the present disclosure. It is. Also, the prior art does not discuss or disclose any means for keeping the Co-based perovskite structure stable under the conditions of use of SOFC in the air electrode of the medium-low temperature region, and these prior art It is difficult to utilize the present invention.

  In this embodiment, the more preferable structure 2 in the air electrode for SOFC is disclosed. In this configuration 2, in the above configuration 1, B is limited to Co. Due to the limitation of the elements used, the oxide ion conductivity of the mixed conductor constituting the air electrode is further improved, and the output density of the fuel cell is improved.

  In the present embodiment, a more preferable configuration 3 in the air electrode for SOFC is disclosed. In this configuration 3, in the above configuration 2, Ln is limited to La and A is limited to Sr. Due to the limitation of the elements used, the oxide ion conductivity of the mixed conductor constituting the air electrode is further improved, and the output density of the fuel cell is improved.

  In this embodiment, the more preferable structure 4 in the air electrode for SOFC is disclosed. In this structure 4, in said structure 3, it limits to a + b = 1, ie, limits to the range which does not contain La. By not containing La, the oxide ion conductivity of the mixed conductor constituting the air electrode is improved. Usually, this side effect causes the problem that the stability of the perovskite crystal structure is further reduced, but in the configuration 1, in addition to the effects of In and Y, Al is contained. As a result, even in the case of operating the SOFC at low to medium temperatures, it is possible to achieve both high battery output characteristics and durability that does not cause deterioration of the characteristics even in long-term use.

  In this embodiment, more preferable configurations 5 and 6 in the SOFC air electrode are disclosed. In configuration 5, in the above configuration 4, B ′ is limited to In, and the content of In represented by y is limited to the range of 0.1 ≦ y ≦ 0.14. Further, the content of Ba at the A site represented by b is limited to 0.85 ≦ b ≦ 0.95. On the other hand, in the configuration 6, in the above configuration 4, B ′ is limited to Y, and the content of Y represented by y is limited to the range of 0.08 ≦ y ≦ 0.15. In addition, the content of Ba at the A site represented by b is limited to 0.5 ≦ b ≦ 0.8. By limiting the content of Ba to the above range, the perovskite stabilization effect by In or Y and Al can be further enhanced. Further, by further limiting the range of y, both the improvement of the battery output and the long-term characteristic stability can be achieved, which is more suitable for SOFC at low and middle temperatures.

  In this embodiment, the more preferable structure 7 in the air electrode for SOFC is disclosed. In this configuration 7, it is desirable that the porosity of the air electrode be 15% or more and 40% or less as a mode in which the air electrodes of the above-described structures 1 to 6 are incorporated into a fuel cell and used. If the porosity is out of this range, the rate of exchange of oxygen with air is reduced to lower the cell output, or the mechanical strength of the air electrode is reduced to cause cracks in the process of using as a fuel cell and break A problem arises. The porosity can be controlled in a method of manufacturing an air electrode described later. The porosity of the cathode can be evaluated by densitometry such as Archimedes when the cathode material is in a single bulk state. Further, when the air electrode is laminated and integrally formed as a part of the fuel cell stack, a cross-sectional photograph of the formed fuel cell sample is taken with a scanning electron microscope or the like, and this photograph is subjected to image processing or the like. It can evaluate from the ratio by dividing into an electrode part and a pore part and quantifying.

In the present embodiment, an SOFC of a configuration 8 provided with the above-described configurations 1 to 7 of the air electrode is disclosed. In this configuration 8, the electrolyte for forming the SOFC may be of a known configuration and form, and is not particularly limited. Moreover, well-known various solid electrolyte materials can be preferably used also about the constituent material. The electrolyte is made of a material that has high oxide ion conductivity, low electron and hole conductivity, and can form a dense layer without gas permeability in any of an oxidizing (air) atmosphere and a reducing (fuel gas) atmosphere. Is preferred. Examples of the material include yttria stabilized zirconia (YSZ) in which yttria and scandia are dispersed in zirconia and solid solution, or scandia stabilized zirconia (ScSZ). In addition, particularly for middle and low temperature use, as described above, Sm-substituted ceria (SDC), Gd-substituted ceria (GDC), and lanthanum gallate (LaGaO ₃ ) are partially substituted with strontium (Sr) or magnesium ( Preferred are ceramic materials such as Mg) substituted materials (LSGM).

  In the SOFC of configuration 8, the fuel electrode used in combination with the air electrode according to the present embodiment may be of a known configuration and form, and is not particularly limited. Moreover, various well-known fuel electrode materials can be preferably used also about the constituent material. It is preferable to be made of a porous body that is highly durable even in a reducing atmosphere and that can efficiently transmit gas. For example, a cermet (metal / ceramic composite material) of nickel oxide and the same oxide as the electrolyte layer, such as NiO-YSZ, NiO-ScSZ, etc. may be mentioned. Ni and YSZ cermets (NiO changes to metallic nickel during fuel cell operation) are commonly used as fuel electrode materials for solid electrolyte fuel cells, but Ni and SDC cermets are also used in medium and low temperature applications It is preferably used.

  In this embodiment, a further preferable configuration 9 in SOFC is disclosed. In the SOFC of this configuration 9, the above-mentioned configuration 8 operates at a temperature of 500 ° C. or higher, which is the middle low temperature range, to 750 ° C. or lower. In this middle and low temperature region, stable and excellent SOFC characteristics can be exhibited even in long-term use.

  The fuel cell to which the present invention is applied is not limited to the above-described configuration, and a known configuration applicable to a general SOFC can be appropriately selected and used without particular limitation. In addition, other configurations applicable to SOFC, for example, an air electrode intermediate layer disposed between the air electrode and the electrolyte, and a fuel electrode intermediate layer disposed between the fuel electrode and the electrolyte May be In particular, when YSZ is used as the solid electrolyte layer, if the SDC layer or the GDC layer is formed with a thickness of about 1 μm as the air electrode intermediate layer, the formation of undesirable reactants at the interface between the electrolyte and the air electrode is suppressed. Can be preferred.

[Specific production method of air electrode for SOFC]
In the present embodiment, configuration 10 is disclosed as a method of manufacturing an air electrode for SOFC.
The raw material powder | flour of the SOFC air electrode in the structure 10 is manufactured as follows, for example. First, a powder of a compound containing constituent elements Ln, A, B, B ′, B ′ ′, and Al of the perovskite-type mixed conductor oxide contained in the air electrode to be manufactured is prepared. The mixture is mixed at a mixing ratio, and the mixture is fired in an oxidizing atmosphere (for example, in the atmosphere) or in an inert gas atmosphere to produce a raw material powder composed of a single phase of a perovskite oxide having a desired composition. Here, as the above-mentioned compound powder, an oxide containing the above-mentioned respective metal atoms constituting such a perovskite type oxide, or a compound which can be an oxide by heating (carbonates of the metal atoms, nitrates, sulfates, phosphorus Acid salts, acetates, oxalates, halides, hydroxides, oxyhalides, etc.) can be used.

In particular, Ln, B, B ′, B ′ ′ and Al are Ln ₂ O ₃ , CoO, Co ₂ O ₃ , and Co ₃ as raw materials that are inexpensive and easy to handle and that the composition can be easily synthesized accurately in configuration 10 Oxide powder such as O ₄ , Fe ₂ O ₃ , F ₃ O ₄ , Nb ₂ O ₅ , Ta ₂ O ₅ , Al ₂ O ₃ etc. For A, carbonate powder such as BaCO ₃ , SrCO ₃ , CaCO ₃ etc. The average particle diameter of each compound powder is preferably, for example, about 0.5 μm to 3 μm, where the average particle diameter means D50 (median diameter) in the particle size distribution of the raw material powder.

  The above-mentioned calcination can be carried out only once, but more preferably it is divided into a plurality of times, and a grinding process by a mortar, a dry ball mill, a wet ball mill, a jet mill or the like is inserted. By inserting this pulverization process during the calcination process, it is possible to obtain a raw material powder of uniform and good characteristics. For example, it is preferable that the firing be divided into two steps of temporary firing and main firing, and the temporary firing be performed at a temperature lower by about 100 ° C. to 300 ° C. than the main firing.

  In the present embodiment, in the process of forming the air electrode as a member of SOFC, the maximum temperature of heat treatment experienced as a sintering heat history is preferably a temperature of 1150 ° C. or more and 1200 ° C. or less. If the temperature is lower than 1150 ° C., the formation of the perovskite phase may be insufficient. Insufficient formation of the perovskite phase causes deterioration of the characteristics during use of the fuel cell. When the heat treatment is performed at a temperature exceeding 1200 ° C., the electrode characteristics may be degraded due to the volatilization of the components of the perovskite and the phase separation.

  Here, with regard to the above-described configuration 10, the firing temperature when forming the air electrode using the raw material powder may be lower than the preferable maximum temperature of 1150 ° C. or more and 1200 ° C. or less. In such a case, it is preferable to carry out main firing in the production process of the raw material powder at 1150 ° C. or more and 1200 ° C. or less.

  In the present embodiment, a preferred configuration 11 in a method of manufacturing an air electrode for SOFC is disclosed. In this configuration 11, the fired powder from which the perovskite single phase is obtained is pulverized using balls of the ceramic according to the above configuration 9, and the average particle diameter described by D50 (median diameter) is 0.5 μm or more It is preferable to use for formation of an air electrode, after setting it as 3 micrometers or less. This makes it possible to obtain an air electrode of sufficient strength. It is preferable to use a zirconia ball as the ceramic ball used for the pulverization in order to avoid mixing of impurities accompanying the pulverization.

  As described above, there is a preferred range of porosity for the air electrode according to the present embodiment. Also, in general, it is desirable that the fuel electrode also have an appropriate porosity as with the air electrode. The porosity can be controlled, for example, by the firing temperature or firing time when firing the air electrode, but can also be controlled by mixing a pore-forming material with the air electrode at the time of firing. The pore-forming material may be one that volatilizes at the time of formation of the air electrode, and may be, for example, a powder of a carbon material such as graphite or a powder of a resin such as polyvinyl alcohol. However, when the pore-forming material is used, it is necessary to take sufficient heat treatment time or the like so that the pore-forming material is volatilized in the process of forming the air electrode.

  There are several types of fuel cell structures (cell stack structures). Specifically, there are a solid electrolyte self-supporting membrane method, an air electrode supporting method, a fuel electrode supporting method, a support supporting method and the like as a classification focusing mainly on which part the strength of the cell stack is given. Further, as a classification focusing on the shape of the laminated structure of cells, there are a cylindrical type, a flat type, and a flat cylindrical type in between. The air electrode according to the present embodiment can be favorably used in any of these cell stacks.

  As a method of manufacturing a fuel cell, in the following, a method of manufacturing a cell stack will be illustrated by taking an anode supporting method of NiO-SDC cermet as an example, but a method of manufacturing a fuel cell using the air electrode of this embodiment Is not limited to the following method. The fuel electrode NiO-SDC cermet as the base material is prepared, for example, by adding a forming agent such as methyl cellulose or polyvinyl alcohol to a mixture of nickel oxide powder and SDC powder as a raw material, and optionally a pore forming material. Press forming. Alternatively, the mixture is clay-like and extruded. Alternatively, the mixed material is made into a slurry and sheet-formed into a flat plate by a tape casting method such as a doctor blade method. Then, the obtained molding material is sintered at about 1300 ° C. to 1450 ° C. to form a porous fuel electrode. Here, the production conditions such as the presence or absence of the pore forming material, the addition amount, the strength of the pressure of pressing and extrusion, the sheet forming condition of the doctor blade, the sintering temperature and time, the formed porous fuel electrode It is set to have a porosity that allows easy passage. Usually, the porosity is adjusted to 15% to 40%.

  Subsequently, on the obtained fuel electrode, a fuel electrode intermediate layer, a solid electrolyte, an air electrode intermediate layer, an air electrode, and the like are sequentially deposited. For the film formation, a slurry coating method, a coating thermal decomposition method, a slurry spray decomposition method, a sol gel method, a dipping method (dip coating method), a spin coating method, a tape casting method, a screen printing method, a chemical vapor deposition method (CVD Physical vapor deposition (PVD), electrophoresis (EPD), electrochemical deposition (EVD), EVD-CVD, vacuum deposition, ion plating, sputtering, laser ablation, plasma spraying A known or new film forming method such as an atmospheric plasma spraying method or a low pressure spraying method may be used. Alternatively, an unsintered film prepared by a tape casting method is attached to an unsintered fuel electrode, or the raw material of the electrolyte layer is filled in layers at the time of press forming of the fuel electrode and integrally molded, co-sintering these simultaneously The film may be formed by a method or the like.

  As an example, in the case of forming a film by a slurry coating method, for example, first, a fuel electrode is prepared, the raw material of the fuel intermediate layer is made into a slurry, and this slurry is applied to a fuel electrode as a substrate and baked. Furthermore, in the same manner, the solid electrolyte, the air electrode intermediate layer, and the air electrode are sequentially formed into a film by repeatedly slurrying, applying and baking the raw materials. The slurry coating method is less expensive than the physical vapor deposition method, the chemical vapor deposition method, the electrochemical vapor deposition method, the thermal spraying method, etc. because it does not require large-scale equipment, and moreover the concentration of the slurry and the number of times of application and firing of the slurry There is an advantage that the film thickness can be easily controlled by adjusting. The powder of the raw material for obtaining the slurry may be synthesized by the same method as the above-mentioned raw material powder of the air electrode, or may be used when a commercially available powder is available. However, caution is required for the particle size of the powder. In general, the particle size of the powder to be slurried is preferably in the range of, for example, about 0.1 μm to 5 μm, and since the theoretically high packing ratio is ideal in order to obtain a dense film, it is to some extent Preferably, small particles and large particles are mixed. Therefore, for example, for the powder of the electrolyte layer material, the volume ratio of particles having an average particle diameter of about 0.4 μm and particles having an average particle diameter of about 2 μm is set to 9: 1. In addition, for the powder of the intermediate layer material, the average particle diameter is made to be about 0.7 μm. Further, for the raw material powder of the air electrode, the average particle diameter is made to be about 0.9 μm. The solvent used to slurry the raw material powder for film formation is not particularly limited. For example, either water or an organic solvent (eg, toluene, isopropanol, etc.) may be selected. In particular, utilization of an organic solvent is preferable because removal of the solvent after film formation is easy. Moreover, when using an organic solvent, you may add additives, such as a binder, an antifoamer, and a dispersing agent. Moreover, when using water as a solvent, you may add additives, such as a binder, an antifoamer, a dispersing agent, and a thickener.

  Generally, the denser the film, the higher the baking temperature of each layer, the more dense the film obtained. However, if the treatment is performed at an excessively high temperature, the porosity and the like of the component layers including the fuel electrode may change, or the component phase may change. Care must be taken because the function as a fuel cell may deteriorate. The solid electrolyte layer is preferably fired at about 1300 ° C. to about 1400 ° C., the intermediate layer at about 1000 ° C. to about 1250 ° C., and the air electrode at about 950 ° C. to about 1050 ° C. In particular, for the air electrode according to the present embodiment, as described above, it is important to select the firing conditions and temperature so that the porosity of the air electrode is 5% or more and 40% or less. Further, as to the maximum temperature experienced by the air electrode is in the range of 1150 ° C. or more and 1200 ° C. or less, consideration must be given to the heat treatment after the air electrode baking. The baking time is about 1 hour to 10 hours, preferably about 1 hour to 3 hours, and the temperature raising and lowering rate is about 100 ° C. to 250 ° C./hour, preferably about 200 ° C./hour.

When the fuel cell obtained in this manner is operated, the definition of whether the operation is good or not can not generally be determined. However, in the present embodiment, a single cell is formed, and the range of good operation is defined with reference to the maximum output density calculated from the current-voltage characteristics measured by changing the external load. That is, the air to the air electrode side, under the condition of supplying 3% humidified hydrogen to the fuel electrode side, in the 600 ° C. as the middle low temperature region 1000W / cm ² or more, 500 W / cm ² or more power density at 500 ° C. When obtained, the fuel cell shows particularly excellent characteristics, and a case where 70% or more of the power density is achieved is defined as showing good characteristics. As the durability after long-term use, in the present embodiment, the degree of maintenance of characteristics after 10,000 hours of low-temperature experience corresponding to use for one year or more is taken as a standard.

  As described above, according to the present embodiment, the SOFC exhibits excellent characteristics under the use environment in the middle and low temperature range, and high fuel cell characteristics (for example, maximum power density) are obtained even when the medium and low temperature range is used. Thus, a highly reliable SOFC air electrode is realized which exhibits high stability as a perovskite crystal structure even under the use environment, and can exhibit characteristics stably for a long period of time.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

<Preparation of Perovskite Phase and Accelerated Test of Durability>
Powdered Ln ₂ O ₃ , BaCO ₃ , SrCO ₃ , CaCO ₃ , Co ₃ O ₄ , Fe as raw materials of Ln, Ba, Sr, Ca, Co, Fe, In, Y, Nb, Ta and Al ₂ O ₃ , In ₂ O ₃ , Y ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and Al ₂ O ₃ were used. Further, powdery CeO ₂ was used as a raw material of Ce used in the comparative example, and powdery MnO was used as a raw material of Mn. The above raw materials were weighed so that each element had a predetermined molar ratio, added to ethyl alcohol (dispersion medium), and wet mixed while being ground by a ball mill to obtain a slurry. The solids were separated from the slurry on a rotary evaporator and dried at about 120 ° C. for 1 hour. Next, the obtained dried product was crushed, placed in a square ceramic container made of MgO ceramic, and fired in an electric furnace at 900 ° C. in the atmosphere for 5 hours to obtain a porous lump-shaped fired product. The fired product was crushed, then dry-pulverized using an automatic mortar, placed again in a square ceramic container made of MgO ceramic, and fired at a predetermined temperature for 5 hours in the air in an electric furnace to obtain an oxide powder. This firing temperature is the maximum heat treatment temperature in this test. The obtained oxide powder was ball milled in ethanol solvent using zirconia balls. The average particle size D50 of the pulverized powder was measured by the particle size distribution diameter by a laser scattering method. Qualitative analysis was conducted by powder X-ray diffraction using an X-ray diffractometer using a Cu-based radiation source as a constituent phase of the obtained oxide pulverized powder. As a result, no peak of any phase other than the perovskite phase appears or, if it appears, the integrated intensity of the strongest peak is 1% or less of the integrated intensity of the main peak (110 peak) of the perovskite phase. It was judged that the formation of the perovskite phase was good. On the other hand, when the integrated intensity of the strongest peak was 1% or less of the integrated intensity of the main peak of the perovskite phase, it was judged that the formation of the perovskite phase was poor.

  The obtained samples were subjected to an accelerated durability test. The obtained oxide powder was placed in a boat made of alumina, and heat treatment was performed in an oxygen atmosphere pressurized at 2 atm for 100 hours at 600 ° C. in an electric furnace capable of atmospheric firing. The constituent phase of the oxide powder after heat treatment was evaluated by qualitative analysis by powder X-ray diffraction method. Among the diffraction peaks of the main phase (110 peak) of the perovskite phase and the diffraction phase of the impurity phase such as a hexagonal crystal which appeared by baking in an oxygen atmosphere, the integral intensity of the strongest peak not overlapping with the diffraction peak of the perovskite phase was determined. The strongest peak of the impurity phase was in the range of 20 ° to 35 ° at the diffraction angle 2θ. The relative strength of the hexagonal peak with respect to the perovskite phase main peak is ◎ when it is less than 1%, ○ when it is more than 1% and less than 5%, △ when it is more than 5% and less than 10%, and it is more than 10% The durability was evaluated as x.

  This durability evaluation is expected to be a 10-fold accelerated durability test for heat treatment in the normal atmosphere by pressurizing the oxygen partial pressure to 2 atm, which is about 10 times that in the normal atmosphere. That is, by keeping the medium temperature of 600 ° C. for 100 hours in an oxygen atmosphere at the operating temperature, it is simulated how much the main peak of the perovskite phase decreases after 1000 hours of operation at 600 ° C. under normal pressure. By doing this, it is possible to know the durability of the composition of each cathode.

<Air electrode performance test-1>
The performance test of the air electrode was conducted by preparing a fuel electrode supported type three-layer cell of a fuel electrode / electrolyte / air electrode. The fuel electrode is a 60:40 wt% cermet of Ni and SDC (Ce: 0.8, Sm: 0.2, O: 1.9), the thickness is about 0.7 mm, the porosity is about 40%, and the electrolyte is thick The thickness of the air electrode was set to about 20 μm. The fuel cell was produced by the following method. First, 54: 36: 10% by weight mixed powder of nickel oxide powder, SDC powder, and polyvinyl alcohol powder was filled in a 30 mmφ molding die and uniaxially molded. Furthermore, SDC powder was filled on the molded body and uniaxially molded again. The molded body was fired at 1350 ° C. for 5 hours. An air electrode was formed on the surface of the obtained sintered body. As the raw material powder, an oxide powder which was prepared by the above-mentioned "Perovskite phase preparation and durability accelerated test" and used before the durability accelerated test was used. The oxide powder for air electrode was adjusted to an average particle diameter D50 by ball milling and dispersed in isopropanol to prepare a slurry for slurry coating. The oxide powder-containing slurry was slurry coated on the surface of the sintered body. The slurry coated air electrode was baked in the air. The porosity of the obtained air electrode was obtained by cutting a sample and taking a photograph of a cross-sectional structure with a scanning electron microscope after a fuel cell characteristic measurement test to be described later. The area ratio of the pore portion in this cross-sectional structure photograph was calculated, and the value of the 3/2 power of the area ratio was determined as the porosity.

  Hydrogen was supplied to the fuel electrode side of the obtained cell and air was supplied to the air electrode side, and the change in voltage when changing the current at 600 ° C. was measured to measure the initial maximum power density. After the power generation test, the fuel cell was recovered and subjected to heat treatment at 600 ° C. in the atmosphere for 10000 hours. The fuel cell after the heat treatment was subjected to the same fuel cell performance evaluation at 600 ° C. again to measure the maximum power density after the heat treatment. The case where the maximum power density was 1000 mW or more was evaluated as ◎, the case of 700 mW or more and less than 1000 mW as ○, the case of 500 mW or more and less than 700 mW as Δ, and the case less than 500 mW as x.

The samples are given as Examples 1 to 21 and Comparative Examples 1 to 9 and their compositions etc. are shown in the table of FIG. 1, the evaluation results of the accelerated durability test and the evaluation results of the cathode performance test etc. in the table of FIG. Show.
As shown in FIG. 1, Examples 1 to 3 satisfy the composition range defined by Configurations 1 to 5 of the present embodiment. Examples 4-6 satisfy the composition range which the structures 1-4 and 6 prescribe. The composition ranges defined in Examples 7 to 10 are Configurations 1 to 4, Examples 11 to 13 are Configurations 1 to 3, Examples 14 to 17 are Configurations 1 and 2, and Examples 18 to 21 are Configuration 1 Each meets.

  As shown in FIG. 2, the sample within the scope of the present invention has good formation of the perovskite phase, is also ◎ or 耐久 in durability, and is excellent in stability of the perovskite phase in the middle and low temperature range. Furthermore, in the cell within the scope of the present invention, there is no cross in the judgment result of the performance in the initial stage and after the heat treatment, and good initial characteristics and durability are compatible. However, in Example 20, the amount w of Al is set to 0.03, which is less than 0.05, which is the lower limit of the desirable addition amount of the present invention, relative to Example 19. For this reason, in Example 20, the maximum power density after heat treatment is 500 mW which is the lower limit value of the allowable range of the present invention. Further, in the present invention, the durability of the air electrode can be enhanced by containing Nb and Ta as B "as described above. Embodiments 7, 8, 15, 18 and 21 containing B" In each case, the durability judgment by X-ray is ◎. On the other hand, in Example 21 in which B ′ is contained in the upper limit of allowable amount z = 0.1, the initial characteristic determination is Δ, and in exchange for stability and durability, the output characteristics of the battery are slightly It's getting lower.

  On the other hand, in each of Comparative Examples 1 and 2, the values of b and y, w, x + y + z + w are values immediately outside the range of the present invention, and the maximum heat treatment temperature, the particle size after crushing, and the baking conditions of the air electrode Also, the porosity of the air electrode is out of the scope of the present invention. For this reason, problems occur in the formation and durability of the perovskite phase, and the initial maximum power density and the maximum power density after heat treatment are low. In Comparative Example 3, the values of y and w are values immediately outside the scope of the present invention, and in Comparative Example 4, the value of y is a value immediately outside the scope of the present invention, and they are out of the scope of the present invention. ing. The samples out of the scope of the present invention have problems such as poor formation of the perovskite phase, low durability with respect to the scope of the present invention, and low initial fuel cell characteristics and post heat treatment characteristics. . In Comparative Example 5, the composition ratio of Ln element, 1-ab and a + b and B elements is out of the range of the present invention, and the stability of the perovskite phase is good, but the initial maximum power density and the maximum power after heat treatment Low density. In Comparative Example 6, the composition ratio of the element of B and z are respectively outside the range of the present invention, and in particular, the value of z is a value immediately outside the range of the present invention. In Comparative Example 6, although the stability of the perovskite phase is good, the output characteristics of the battery further deteriorate compared to Example 21, and there is a problem that the initial characteristics of the fuel cell and the characteristics after heat treatment deteriorate to outside the allowable range of the present invention. ing. The comparative example 7 has y, x + y + z + w and the maximum heat treatment temperature outside the range of the present invention, and there is a problem in formation of the perovskite phase and its durability. In Comparative Example 8, the Mn-based air electrode material used in the conventional SOFC used at high temperature is used. Although this air electrode has good stability of the perovskite phase, it can be seen that the output characteristics at 600 ° C. are already low from the initial characteristics and not suitable for use at medium and low temperatures. Moreover, in Comparative Example 9, a Co-based material which is studied for the purpose of improving the Mn-based material is used, and this is an example of a material other than the present invention. Since the material is a Co-based material, the initial output characteristics are greatly improved compared to the Mn-based material, but the durability is insufficient, and the determination of the durability and the determination of the characteristics after heat treatment are both bad.

  In FIG. 1 and FIG. 2, all of the judgment items described above are good and の も の good, も の even one 良 good, even one △ good, even one bad or x It shows the result of the general judgment that some things are not acceptable. The scope of the present invention was all judged to be excellent, and out of the scope of the present invention was judged to be impossible including conventional materials. From these results, it has been found that the SOFC air electrode material provided by the present invention can exhibit excellent characteristics in the middle and low temperature range, and can obtain high fuel cell characteristics and the highest power density. At the same time, it has been revealed that the air electrode material exhibits high perovskite type crystal structure stability, so that it can exhibit characteristics stably for a long period of time and can contribute to the improvement of the durability for fuel cells.

<Air electrode performance test-2>
The performance test of the air electrode was conducted by changing the manufacturing method of the cell for evaluation to the air electrode performance test-1. In this test, a fuel electrode supported type three layer cell of fuel electrode / electrolyte / air electrode was manufactured by the doctor blade method and the screen printing method. The configurations of the fuel electrode and the electrolyte were the same as those of the cathode performance test-1. That is, 60: 40 wt% cermet of Ni and SDC (Ce: 0.8, Sm: 0.2, O: 1.9), thickness about 0.7 mm, porosity about 40%, electrolyte about 20 μm thick SDC. The raw material powder of each fuel electrode is a 54: 36: 10% by weight mixed powder of nickel oxide powder, SDC powder, polyvinyl alcohol powder, and the raw material powder of electrolyte is SDC powder, and these are respectively slurried by the doctor blade method. Sheet molded. The obtained sheets were laminated and uniaxially pressed, and then pressure-bonded by CIP molding. The molded body was fired at 1350 ° C. for 5 hours. On the surface of the obtained sintered body, an air electrode was formed by screen printing to a thickness of about 20 μm. The ink used for screen printing is, as a raw material powder, the same (Sr _0.1 Ba _0.9 ) {Co _0.87 In _0.1 Al _0.05 } O _{3-as in} Example 1 prepared in the above-mentioned “Perovskite phase preparation and durability accelerated test”. _[delta], and example 5 and the same _{(Sr 0.35 Ba 0.65) {Co} 0.85 Y 0.08 Al 0.05} of O _{3- [delta]} powder, the powder prior to the acceleration test of durability were used, respectively. The oxide powder for air electrode was adjusted to an average particle diameter of about 0.9 μm by ball milling, and dispersed in a solvent in which isopropanol and toluene were mixed at 1: 1, to prepare an ink for screen printing. The oxide powder-containing ink was formed into an electrode on the surface of the sintered body by screen printing. The air electrode was baked in air at 1000 ° C. for 2 hours. The porosity of the obtained air electrode was determined in the same manner as air electrode performance test 1 after the fuel cell characteristic measurement test described later. As a result, both the composition of Example 1 and the composition of Example 5 were about 35% Met.

  Hydrogen was supplied to the fuel electrode side of the obtained cell, air was supplied to the air electrode side, and the change in voltage when changing the current at 600 ° C. was measured, and the initial maximum power density was measured. The composition of Example 1 and the composition of Example 5 were 1250 mW and 1200 mW, respectively. After the power generation test, the fuel cell was recovered and heat treated at 600 ° C. in the atmosphere for 10000 hours. The fuel cell after this heat treatment was subjected to the same fuel cell performance evaluation at 600 ° C. again, and the maximum power density after heat treatment was measured. The composition of Example 1 and the composition of Example 5 were 1000 mW and 1100 mW, respectively. Met. According to the same evaluation criteria as those of the cathode performance test 1, the characteristics of the initial stage and after the heat treatment were both ◎ for the composition of Example 1 and the composition of Example 5. From this result, it is clear that even if the manufacturing method of the air electrode of the present invention is changed, excellent fuel cell characteristics can be obtained.

Claims (11)

An oxide ion mixed conductor having a perovskite crystal structure, wherein the composition is
[L n _1-ab A _a (Ba) _b ] [B _x B ' _y B " _z (Al) _w ] O _{(3- δ )} (1)
And an air electrode of a solid oxide fuel cell characterized by containing the ceramic composition represented by the general formula:
In the above equation (1),
Ln is a combination of one or more elements selected from lanthanoid elements La, Pr, Nd, Pm, Sm, Eu, Gd, Tb and Dy;
A is a combination of one or two elements selected from Sr and Ca,
B is a combination of one or two elements selected from Co and Fe, and the mole number of Co is 50% or more with respect to the mole number x of all B elements,
B ′ is a combination of one or two elements selected from In and Y,
B "is a combination of one or two elements selected from Nb and Ta,
However,
When B ′ is In, 0.7 ≦ b ≦ 1.0, 0.05 ≦ y ≦ 0.2,
When B ′ is Y, 0.5 ≦ b ≦ 1.0, 0.06 ≦ y ≦ 0.2,
When B 'is a combination of In and Y, the range of b and y is the same as the range for elements containing more moles of In and Y,
0.8 ≦ a + b ≦ 1,
0 <x,
0 ≦ z ≦ 0.1,
0 <w ≦ 0.2,
0.98 ≦ x + y + z + w ≦ 1.02,
δ is a value defined to satisfy the charge neutral condition.   The air electrode of a solid oxide fuel cell according to claim 1, wherein B is Co. Ln is La,
The air electrode of a solid oxide fuel cell according to claim 2, wherein A is Sr.   4. The solid oxide fuel cell air electrode according to claim 3, wherein a + b = 1. B 'is In,
0.85 ≦ b ≦ 0.95
5. The solid oxide fuel cell air electrode according to claim 4, wherein 0.1 ≦ y ≦ 0.14. B 'is Y,
0.5 ≦ b ≦ 0.8,
5. The solid oxide fuel cell air electrode according to claim 4, wherein 0.08 ≦ y ≦ 0.15.   The air electrode of a solid oxide fuel cell according to any one of claims 1 to 6, wherein the porosity is 15% or more and 40% or less.   A solid oxide fuel cell comprising the air electrode of the solid oxide fuel cell according to any one of claims 1 to 7.   9. The solid oxide fuel cell according to claim 8, wherein the solid oxide fuel cell is operated at a temperature of 500 ° C. or more and 750 ° C. or less. A method of manufacturing an air electrode of a solid oxide fuel cell according to any one of claims 1 to 7,
Powders of carbonates or oxides containing Ln, A, Ba, B, B ′, B ′ ′, and Al in the formula (1) are used as raw materials, and the powders are mixed to obtain an oxidizing atmosphere or an inert gas atmosphere. The raw material powder consisting of a single phase having a perovskite structure is formed by firing in the following step, and the raw material powder is crushed, and the heat treatment experienced as a sintering heat history when firing the crushed raw material powder into an air electrode shape A method for producing an air electrode of a solid oxide fuel cell, characterized in that the maximum temperature of is a temperature of 1150 ° C. to 1200 ° C.   The method of manufacturing an air electrode of a solid oxide fuel cell according to claim 10, wherein the step of grinding the raw material powder sets an average particle diameter of the raw material powder to 0.5 μm or more and 3 μm or less.

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