JP2009021181A - Battery cell for solid oxide fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery cell for a SOFC composed of a chrome containing alloy or the like bonded with an air electrode in which the occurrence of chrome poisoning in the air electrode is favorably controlled and an increase of contact resistance between the alloy or the like and the air electrode can be favorably controlled, and to provide its manufacturing method. <P>SOLUTION: Before conducting a calcination process while an alloy or the like and an air electrode are jointed, a coat forming process in which a TiO2 coat in which a dope element of a pentavalent element is doped on the surface of the alloy or the like is formed, and a Cr (VI) oxide control state is obtained where the generation of an oxide of Cr (VI) in the alloy or the like is controlled. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell that performs a firing process in which an alloy or oxide containing Cr (chromium) (hereinafter sometimes referred to as “alloy or the like”) and an air electrode are joined together. The present invention relates to a method for manufacturing a cell for SOFC and a cell for SOFC manufactured by the manufacturing method.

Such an SOFC cell has a single cell in which an air electrode is joined to one surface side of an electrolyte membrane and a fuel electrode is joined to the other surface side of the electrolyte membrane. It has a structure sandwiched between a pair of electron conductive alloys and the like.
And in such a cell for SOFC, for example, it operates at an operating temperature of about 700 to 900 ° C., and with the movement of oxide ions through the electrolyte membrane from the air electrode side to the fuel electrode side, the pair of electrodes An electromotive force is generated in the meantime, and the electromotive force can be taken out and used.

An alloy used in such a SOFC cell is made of a material containing Cr that is excellent in electronic conductivity and heat resistance. Further, the heat resistance of such an alloy is derived from a dense film of chromia (Cr ₂ O ₃ ) formed on the surface of the alloy.

  In addition, in the manufacturing process of the SOFC cell, for the purpose of minimizing the contact resistance between the alloy, etc., the air electrode and the fuel electrode as much as possible, in a state where they are laminated, the operating temperature is higher than 1000 ° C. There is a case where a baking treatment is performed at a baking temperature of about 1250 ° C. (see, for example, Patent Document 1).

JP 2004-259634 A

As described above, in an SOFC cell formed by joining an alloy containing Cr and the air electrode, when the alloy is exposed to a high temperature during operation or the like, Cr contained in the alloy or the like is moved to the air electrode side. There is a problem that air poisoning causes Cr poisoning.
Such Cr poisoning of the air electrode inhibits the oxygen reduction reaction for the generation of oxide ions in the air electrode, increases the electrical resistance of the air electrode, and further decreases the Cr concentration of alloys and the like. This may cause problems such as a decrease in the heat resistance of the alloy itself, resulting in a decrease in SOFC performance.

Further, even when the SOFC is manufactured, when performing a firing process in which the alloy or the like and the air electrode are joined, the Cr (VI) (hereinafter, referred to as the following) is exposed to a firing temperature higher than the operating temperature. Cr having a valence of 6+ is described as “Cr (VI)”), and it is evaporated to react with the air electrode to produce a Cr compound, resulting in Cr poisoning of the air electrode. There is a case. In this firing treatment, the oxygen partial pressure is reduced as much as possible in a vacuum or an inert gas atmosphere, so that the chromia (Cr ₂ O ₃ ) on the surface of the alloy is converted to Cr (VI) or the surface of the alloy or the like is oxidized. Oxidation of Cr (III) (hereinafter, Cr having a valence of 3+ is referred to as “Cr (III)”) to Cr (VI) is suppressed, and the occurrence of Cr poisoning during production is suppressed. Even in the case of suppression, during the subsequent operation, exposure to high temperature in an oxidizing atmosphere in which air supplied to the air electrode exists causes oxidation to Cr (VI) to proceed, and the Cr poisoning occurs. There is a case.

  In addition, in order to suppress Cr poisoning of the air electrode as described above, when the surface of an alloy or the like is coated, there is a concern that the contact resistance between the alloy and the air electrode is increased by the coating layer. .

  The present invention has been made in view of the above-mentioned problems, and the object thereof is to improve the occurrence of Cr poisoning of the air electrode in a SOFC cell formed by joining an alloy containing Cr and the air electrode. The object of the present invention is to provide an SOFC cell and a method for manufacturing the same that can satisfactorily suppress an increase in contact resistance between an alloy or the like and an air electrode.

The SOFC cell manufacturing method according to the present invention for achieving the above object is a method for manufacturing a solid oxide fuel cell cell obtained by joining an alloy or oxide containing Cr and an air electrode. The characteristic configuration is that the surface of the alloy or oxide is doped with a dope element which is a pentavalent element before firing the alloy or oxide and the air electrode in a joined state. By performing a film forming process for forming a TiO ₂ film, the alloy or oxide is in a Cr (VI) oxide suppressed state that suppresses the generation of Cr (VI) oxide.

According to the above characteristic configuration, in performing the firing process at the time of manufacturing the SOFC cell, the alloy containing Cr is brought into the Cr (VI) oxide suppressed state, so that the alloy electrode side or the air electrode side or It is possible to suppress the occurrence of Cr poisoning of the air electrode satisfactorily by suppressing the diffusion of the oxide (or oxyhydroxide) of the gas phase Cr (VI) to the interface between the air electrode and the electrolyte.
That is, by forming a TiO ₂ film on the surface of the alloy or the like in the film forming process, the equilibrium dissociation pressure of the oxygen partial pressure at the boundary between the TiO ₂ film and the alloy or the like is very small (10 at 1000 ° C. ⁻²⁶ atm or less), and the oxide state of Cr (VI) that can more effectively suppress the formation of Cr (VI) oxide can be obtained.

In addition, the TiO ₂ film is an n-type semiconductor film made of an oxide having a standard generation free energy of WO ₃ or less and a low oxidizing power, and therefore, such an n-type semiconductor film is formed on the surface of an alloy or the like. Thus, the equilibrium dissociation pressure of the oxygen partial pressure at the boundary between the n-type semiconductor film and the alloy or the like can be made extremely small so that Cr contained in the alloy or the like is not easily oxidized to Cr (VI). . Therefore, even if an oxide of Cr (III) is generated under the n-type semiconductor film having a small oxidizing power, at least a Cr (VI) oxide suppressed state that suppresses generation of an oxide of Cr (VI). In the firing process after the film forming process, the occurrence of Cr poisoning of the air electrode can be satisfactorily suppressed. Furthermore, by forming an n-type semiconductor film having a small oxidizing power on the alloy or the like in this way, generation of Cr (VI) oxide can be suppressed not only during the firing process but also during operation. The progress of Cr poisoning of the air electrode can also be satisfactorily prevented. Moreover, since the fall of Cr content, such as an alloy, can also be suppressed, the heat resistance of alloy itself etc. can be hold | maintained in a favorable state.
That is, as the n-type semiconductor film, an oxide such as the TiO ₂ film having a standard free energy of formation of oxide and WO ₃ or less at the operating temperature has a low oxidizing power, and Cr (III) to Cr ( It can be estimated that this is because oxidation to VI) can be suppressed.

Further, since the TiO ₂ film is an n-type semiconductor film made of an oxide having a standard electrode potential in an aqueous solution of −0.029 V or less and a small oxidizing power, similarly to the above, firing after the film forming treatment is performed. Even during processing and operation, it is possible to suppress the formation of Cr (VI) oxides, and to suppress the Cr poisoning of the air electrode, and to suppress the decrease in the Cr content of alloys and the like. Further, the heat resistance of the alloy itself can be maintained in a good state.
That is, as the n-type semiconductor film, an oxide such as the TiO ₂ film having a standard electrode potential in an aqueous solution of −0.029 V or less has a low oxidizing power, and the Cr (III) to Cr (VI) It can be estimated that this is because oxidation can be suppressed.

Furthermore, by doping the TiO ₂ film formed on the surface of the alloy or the like with the doping element that is a pentavalent element in the film forming process, the electrical resistance of the TiO ₂ film can be made as small as possible, While suppressing the occurrence of Cr poisoning of the air electrode, it is possible to satisfactorily suppress an increase in contact resistance between the alloy and the air electrode.

The SOFC cell according to the present invention for achieving the above object is a solid oxide fuel cell cell formed by joining an alloy or oxide containing Cr and an air electrode, and its characteristic configuration it is the surface of the alloy or oxide, in that by forming a pentavalent TiO ₂ coating the doping element doped an element.
According to the characteristic configuration of the SOFC cell according to the present invention, the SOFC cell has the same configuration as that of the SOFC cell manufactured by the SOFC cell manufacturing method having the above characteristic configuration, so that it is formed on the surface of an alloy or the like. by been oxidizing power of the TiO ₂ coating small n-type semiconductor film, doped in the firing process and during operation, while well suppressing the occurrence of Cr poisoning of the air electrode, the doping element to the TiO ₂ coating As a result, an increase in contact resistance between the alloy or the like and the air electrode can be satisfactorily suppressed.

In addition, pentavalent elements such as Nb and Ta can be used as the doping element, but by using Nb as the doping element, the electrical resistance of the TiO ₂ film can be satisfactorily reduced, and an alloy or the like can be used. An increase in contact resistance between the air electrode and the air electrode can be suppressed even better.

Embodiments of an SOFC cell and a manufacturing method thereof according to the present invention will be described with reference to the drawings.
The SOFC cell C shown in FIGS. 1 and 2 has an air electrode made of an oxide ion and an electron conductive porous body on one side of an electrolyte membrane 30 made of a dense oxide oxide conductive solid oxide. 31 and a single cell 3 formed by bonding a fuel electrode 32 made of an electron conductive porous body to the other surface side of the electrolyte membrane 30.
Further, the SOFC cell C exchanges electrons with the single cell 3 with respect to the air electrode 31 or the fuel electrode 32, and at the same time, a pair of electronically conductive elements in which grooves 2 for supplying air and hydrogen are formed. It has a structure in which a gas seal body is appropriately sandwiched between outer peripheral edges by an interconnect 1 made of an alloy or an oxide. The groove 2 on the air electrode 31 side functions as an air flow path 2a for supplying air to the air electrode 31 by arranging the air electrode 31 and the interconnect 1 in close contact, while the fuel electrode The groove 2 on the 32 side functions as a fuel flow path 2 b for supplying hydrogen to the fuel electrode 32 by arranging the fuel electrode 32 and the interconnect 1 in close contact with each other.

In addition, when a general material used in each element constituting the SOFC cell C is described, for example, the material of the air electrode 31 is LaMO ₃ (for example, M = Mn, Fe, Co). A perovskite oxide of (La, AE) MO ₃ in which a part of La of Al is substituted with an alkaline earth metal AE (AE = Sr, Ca) can be used. And yttria-stabilized zirconia (YSZ) can be used, and yttria-stabilized zirconia (YSZ) can be used as the material of the electrolyte membrane 30.

Furthermore, in the SOFC cell C described so far, the material of the interconnect 1 is a perovskite oxide such as LaCrO ₃ that is excellent in electronic conductivity and heat resistance, or ferritic stainless steel. Alloys or oxides containing Cr are used, such as Fe—Cr alloys, Fe—Cr—Ni alloys that are austenitic stainless steels, and Ni—Cr alloys that are nickel-based alloys.

Then, in a state where the plurality of SOFC cells C are arranged in a stacked manner, a pressing force is applied in the stacking direction by a plurality of bolts and nuts to form a cell stack.
In this cell stack, the interconnects 1 arranged at both ends in the stacking direction may be any one in which only one of the fuel flow path 2b or the air flow path 2a is formed, and the other interconnect arranged in the middle. 1 may use a fuel channel 2b formed on one surface and an air channel 2a formed on the other surface. In such a stacked cell stack, the interconnect 1 may be called a separator.
An SOFC having such a cell stack structure is generally called a flat-plate SOFC. In the present embodiment, a flat SOFC will be described as an example. However, the present invention is applicable to SOFCs having other structures.

When the SOFC including the SOFC cell C is operated, air is supplied through the air flow path 2a formed in the interconnect 1 adjacent to the air electrode 31, as shown in FIG. At the same time, hydrogen is supplied through the fuel flow path 2b formed in the interconnect 1 adjacent to the fuel electrode 32, and operates at an operating temperature of, for example, about 800 ° C. Then, the air electrode 31 O ₂ electrons e ^- are reacting with O ^2- is generated, the O ^2- passes through the electrolyte membrane 30 to move to the fuel electrode 32, H ₂ supplied in the fuel electrode 32 Reacts with the O ²⁻ to generate H ₂ O and e ⁻ , so that an electromotive force E is generated between the pair of interconnects 1 and the electromotive force E can be taken out and used outside. it can.

  In addition, the SOFC cell C has an operating temperature in a state in which they are stacked in order to reduce the contact resistance between the interconnect 1 and the air electrode 31 and the fuel electrode 32 as much as possible in the manufacturing process. There is a case where a baking treatment is performed at a higher baking temperature of about 1000 ° C. than that.

  In the SOFC cell C in which the interconnect 1 made of an alloy containing Cr or the like and the air electrode 31 are joined as described above, the interconnect is exposed to a high temperature during firing or operation. There is a problem that Cr contained in 1 is oxidized and evaporated and scattered to the air electrode 31 side, and Cr poisoning of the air electrode 31 occurs.

In addition, such Cr poisoning includes Cr ₂ O ₃ which is an oxide of Cr contained in the interconnect 1 and Cr (III) generated by oxidation of the Cr on the air electrode 31 side or the like. Oxidized by O ₂ or H ₂ O, CrO ₃ or CrO ₂ (OH) ₂ , which is an oxide of Cr (VI) in a gas phase, is generated, and the oxide of Cr (VI) is on the air electrode 31 side. And is reduced in the vicinity of the interface with the electrolyte membrane 30 or in the electrode and precipitated as Cr ₂ O ₃ or as a Cr compound by reaction with the air electrode 31. In the presence of water vapor, CrO ₂ (OH) ₂ is likely to be generated and Cr (VI) is likely to be scattered.
When Cr poisoning of the air electrode 31 occurs in this way, during the operation, the oxygen reduction reaction for the production of O ²⁻ occurs at the interface between the air electrode 31 and the electrolyte membrane 30 or inside the electrode. Furthermore, high resistance compounds such as SrCr ₂ O ₄ , SrCrO ₄ , CaCr ₂ 0 ₄ , and CaCrO ₄ are formed by depriving Sr, Ca, etc., in which the Cr is doped in the air electrode 31, The increase in electrical resistance of the air electrode 31 itself due to the disappearance of Sr and Ca may cause a decrease in SOFC performance. In addition, the amount of Cr contained in the alloy or the like may decrease, and the heat resistance of the alloy or the like itself may decrease.

  And in the manufacturing method of the cell C for SOFC which concerns on this invention, while suppressing generation | occurrence | production of Cr poisoning of the air electrode 31 satisfactorily, the characteristic for suppressing the increase in contact resistance with an alloy etc. and an air electrode favorably. Details thereof will be described below.

In such a SOFC manufacturing method, the Cr (VI) oxide suppression state that suppresses the generation of Cr (VI) oxide in Cr contained in the interconnect 1 is set, and the interconnect 1 and the air electrode 31 are joined. A baking treatment is performed at a baking temperature of about 1000 ° C. to 1150 ° C.
Therefore, in this firing treatment, Cr contained in the interconnect 1 is suppressed to be oxidized as Cr (VI) having a valence of 6+, and thus is an oxide of Cr (VI) in a gas phase state. The generation of CrO ₃ and CrO ₂ (OH) ₂ is sufficiently suppressed, and the occurrence of Cr poisoning of the air electrode 31 due to the movement of the oxide of Cr (VI) toward the air electrode 31 is satisfactorily suppressed. be able to. Moreover, since the fall of Cr content, such as an alloy, can also be suppressed, the fall of heat resistance of alloy etc. itself can also be suppressed.

In addition, details of methods for achieving a Cr (VI) oxide suppression state that suppresses the generation of Cr (VI) oxide in Cr included in the interconnect 1 will be described below.
That is, the n-type semiconductor film having a small oxidizing power is formed on the surface including at least the boundary surface 1a (see FIG. 2) with respect to the air electrode 31 of the interconnect 1 before performing the firing treatment in the Cr (VI) oxide suppression state. This is realized by forming a TiO ₂ film (titania film) that functions as:

That is, in the SOFC cell C TiO ₂ film is formed on the boundary surface 1a of the interconnect 1, because of its dense structure on the TiO ₂ film is excellent in heat resistance, via the TiO ₂ coating As a result, the supply of oxygen or water vapor as an oxidant to the interconnect 1 side is blocked, and further, the movement of Cr (VI) oxide to the air electrode 31 side through the TiO ₂ coating is blocked. As a result, Cr poisoning of the air electrode 31 can be satisfactorily suppressed even when the interconnect 1 is exposed to a high temperature during firing or operation during manufacturing.

Further, this TiO ₂ film is doped with a dope element which is a pentavalent element such as Nb, Ta, Sb or the like in the range of 0.5 to 5%, for example, in order to make the electric resistance as small as possible. The increase in the contact resistance between the air electrode 31 and the interconnect 1 due to the TiO ₂ film is well suppressed.

〔Example〕
A simulated SOFC cell manufactured by forming a TiO ₂ film doped with Nb by dip coating on the surface of an alloy used for an interconnect or the like before firing as in the above embodiment (Example) The experimental results of observing the Cr distribution in the cross section near the joint between the alloy and the air electrode are shown below.
In the simulated SOFC cell of this example, the alloy is an Fe—Cr alloy (Cr content: 22 wt%), and the air electrode is (La, Sr) (Co, Fe) O ₃ .

In the dip coating method, as shown in FIG. 3, the coating liquid was prepared with a Ti: Nb molar ratio of 0.99875: 0.00125 to form a TiO ₂ film. Then, TiO ₂ coating with a thickness of thus formed was about 2 [mu] m.

Further, the coating liquid dispensing method will be described below with reference to FIG.
Commercially available TiO ₂ nanoparticles (average particle size of about 70 nm) were mixed with alcohol and binder (cellulose) and dispersed using a paint shaker (this is referred to as “Coating Liquid 1”).
Further, titanium alkoxide Ti (OC ₃ H ₇ ⁱ ) ₄ , niobium alkoxide Nb (OC ₂ H ₅ ) ₅ , and alcohol are mixed, and a mixture of water and alcohol is added to cause hydrolysis (this is referred to as “ Called Coating Solution 1 ”).
Then, the coating liquid 1, the coating liquid 2, a binder (cellulose) and niobium alkoxide Nb (OC ₂ H _{5) 5} were mixed and dispersed to prepare a film-forming TiO ₂ slurry.
The slurry was dip-coated with an alloy substrate, pulled up at a predetermined rate of 1 mm / sec, dried, and fired at 1000 ° C. for 1 hour to obtain a Nb-doped TiO ₂ coating.

In this experiment, the simulated SOFC cell of the example was subjected to a firing process at a firing temperature of 1000 ° C. to 1100 ° C. for 2 hours in an air atmosphere, and then assumed to be in operation, at a temperature of 750 ° C. in an air atmosphere. and held for 20 hours in a state of continuous flow a direct current of 0.96A / cm ² at the operating temperature. It was confirmed that the sheet resistance after adding the alloy and the TiO ₂ film after 20 hours was 47 mΩ · cm ² .

On the other hand, for a simulated SOFC cell (comparative example) produced by forming a TiO ₂ film not doped with Nb, an experiment similar to the above was conducted. resistance is 70mΩ · cm ^2, the surface resistance from the typically temperature increases and decreases, confirmed that the surface resistance at the operating temperature of 750 ° C. in an air atmosphere is 70mΩ · cm ² or more It was.

From the above experimental results, the sheet resistance with the addition of the alloy and the TiO ₂ film was decreased in the simulated SOFC cell manufactured by forming the TiO ₂ film doped with Nb than in the cell not doped with Nb. You can see that

Further, for the simulated SOFC cell of the above example, the Cr distribution in the cross section near the joint between the alloy and the air electrode was analyzed by EPMA (electron beam microanalyzer).
In addition, in FIG. 4, the analysis result of Cr distribution after the baking process of the cell for simulation SOFC of an Example is shown. In these drawings, the Cr concentration in the alloy is about 22%, and the Cr concentration in the lightest color region in the air electrode is approximately 0% (in the drawings, the light gray region in the air electrode). In the drawings showing these distributions, the lateral width of the photographic diagram corresponds to about 130 μm.

As a result of the above analysis of the Cr distribution, in the simulated SOFC cell in which the Nb-doped TiO ₂ film of the example was formed on the surface of the alloy, as shown in FIG. It can be seen that scattering is suppressed. This slight Cr scattering, believed to be due to the thickness of the TiO ₂ film is thin, such Cr scattering by increasing the film thickness is considered to be effectively suppressed.

In the above embodiment, in order to realize the Cr (VI) oxide suppression state and suppress Cr poisoning, the interface 1 includes at least the boundary surface 1a (see FIG. 2) with respect to the air electrode 31. The film formed on the surface is preferably an n-type semiconductor film having a small oxidizing power, stable at room temperature, and from the viewpoint of conductivity. Furthermore, from the viewpoint of low oxidizing power, the n-type semiconductor film preferably satisfies at least one of the following first condition, second condition, and third condition like TiO ₂ .

(First condition)
As the n-type semiconductor film, an oxide having a WO ₃ or lower at the operating temperature in the Ellingham diagram relating to the standard free energy of formation (equilibrium dissociation pressure of oxygen), such as TiO ₂ , is desirable.
That is, in the Ellingham diagram shown in FIG. 5, it was confirmed that Cr poisoning occurred in the compound above WO ₃ . From this, it can be seen that the presence or absence of the effect of suppressing Cr scattering can be determined by the magnitude of the equilibrium dissociation pressure of oxygen. The reason for this can be presumed that the smaller the standard free energy of formation, the smaller the oxidizing power, and the more the oxidation from Cr (III) to Cr (VI) can be suppressed.

As the n-type semiconductor film satisfying the first condition, specifically, TiO ₂ , Y ₂ O ₃ and WO ₃ are preferable, but Ta ₂ O ₅ , Al ₂ O ₃ , BaO, and MoO ₂ are separately used. Nb ₂ O ₅ , ZrO ₂ , BeO, MgO, SrO, In ₂ O ₃ , SiO ₂ , MgAl ₂ O ₄ , MgSiO ₃ , CaTiO ₃ , SrTiO ₃ , BaTiO ₃ , Ce ₂ O ₃ , Sm ₂ O ₃ , MgTiO _3, may be a n-type semiconductor such as an oxide of a rare earth. However, the thermal expansion coefficient is desirably 7.5 × 10 ^{−6 to} 13.5 × 10 ⁻⁶ / ° C. due to the characteristics of SOFC, and if it exceeds this range, peeling of the coating due to thermal expansion and thermal shrinkage tends to occur. . Furthermore, considering the low toxicity, vapor pressure, hygroscopicity, TiO _2, Y ₂ O ₃ and _{WO 3, Al 2 O 3,} MoO 2, ZrO 2, BeO, In 2 O 3, SiO 2, MgAl 2 O ₄ , MgSiO ₃ , CaTiO ₃ , SrTiO ₃ , BaTiO ₃ , Ce ₂ O ₃ , Sm ₂ O ₃ , MgTiO _{3 and the} like are desirable.

(Second condition)
As the n-type semiconductor film, an oxide having a standard electrode potential in an aqueous solution (25 ° C.) of −0.029 V or less, such as TiO ₂ , is desirable.
That is, as a result of evaluating the standard electrode potential E ° / V of various oxides, as shown in FIG. 6, when the standard electrode potential E ° / V is −0.029 (standard electrode potential of WO ₃ ) or less. No Cr poisoning occurred, but it was confirmed that Cr poisoning occurred when the standard electrode potential E ° / V was larger than WO ₃ . From this, it can be seen that the presence or absence of the effect of suppressing Cr scattering can be determined by the value of the standard electrode potential. This can be presumed to be because the lower the standard electrode potential, the smaller the oxidizing power, and the more the oxidation from Cr (III) to Cr (VI) can be suppressed.

(Third condition)
The n-type semiconductor film is desirably an oxide such as TiO ₂ whose vapor pressure at 800 ° C. is 1/100 or less of the CrO ₃ vapor pressure from Cr ₂ O ₃ at the same temperature.
This is because when the vapor pressure is increased, the coating material is scattered on the air electrode, which may affect the physical properties.
As an n-type semiconductor film satisfying the third condition, as shown in FIG. 7 (only a part is shown), TiO ₂ , Y ₂ O ₃ , WO ₃ , Al ₂ O ₃ , MoO ₂ , ZrO ₂ , _{BeO, MgO, SiO 2, MgAl} 2 O 4, MgSiO 3, Ce 2 O 3, CaTiO 3, BaTiO 3, Sm 2 O 3, MgTiO 3, and desirable. Since the vapor pressure of CaTiO ₃ , which is a composite oxide of CaO and TiO ₂ , is not expected to exceed the higher one of the respective oxides, the vapor pressure is below the vapor pressure of TiO _2. Presumed to be. Similarly, the vapor pressure of BaTiO ₃ , which is a composite oxide of BaO and TiO ₂ , is estimated to be lower than the vapor pressure of BaO, and the vapor pressure of MgTiO ₃ , which is a composite oxide of MgO and TiO ₂ , is It is presumed that it is lower than the vapor pressure of MgO.

From the above, it can be said that it is desirable to use a TiO ₂ film as the n-type semiconductor film that satisfies all of the first condition, the second condition, and the third condition.

By doping TiO ₂ that satisfies the above various conditions with a pentavalent doping element such as Nb or Ta, the electrical resistance can be lowered.
For example, a powder having the composition shown in Table 1 below is prepared, subjected to uniaxial pressing and cold isotropic pressing (CIP), and then subjected to a baking treatment at a baking temperature of 1300 ° C. for 2 hours in an air atmosphere. A sintered body was obtained. About the sample for a measurement cut out from the sintered compact, the electroconductivity was measured in air atmosphere at 850 ° C., 750 ° C., and 650 ° C. by the four-terminal method. The results are shown in Table 1 below.

As a result, the sheet resistance when a 10 μm TiO ₂ film is formed on the surface of the alloy can be estimated as shown in Table 2 below.

From this, it is considered that resistance can be reduced by doping a small amount of doping element into TiO ₂ .
Further, the TiO _2, By Ti (IV) and the mixed oxides of Ti (III), it is also possible to reduce the resistance.

Further, as a film forming method for forming the TiO ₂ film, in order to form a dense and thin film with few defects and cracks, a dry film forming method such as the sputtering method, vapor deposition method, CVD method, It is desirable to employ a wet film formation method such as a sol-gel method. In addition, adopting a wet film formation method such as a dip method can also obtain a certain degree of Cr poisoning suppression effect. Moreover, when raising the temperature to the firing temperature, it is desirable that there is no transformation or that the degree of damage to the coating film due to transformation is small. Further, as the n-type semiconductor film, not only a single film of TiO ₂ but also a plurality of kinds such as Y ₂ O ₃ , WO ₃ , SiO ₂ , CaTiO ₃ , BaTiO ₃ , Sm ₂ O ₃ , MgTiO _3, etc. Even if the coating is combined, it is considered that the effect of suppressing Cr poisoning can be obtained.

  The SOFC cell and the manufacturing method thereof according to the present invention include an alloy or the like while satisfactorily suppressing the occurrence of Cr poisoning of the air electrode in the SOFC cell formed by joining an alloy containing Cr and the air electrode. It can be effectively used as an SOFC cell capable of satisfactorily suppressing an increase in contact resistance between the air electrode and the air electrode, and a manufacturing method thereof.

The schematic perspective view which shows the decomposition | disassembly state of each element of the cell for SOFC Diagram explaining the operating principle of SOFC cell Flow chart showing TiO ₂ coating formation method The figure which shows Cr distribution after the holding | maintenance at the operating temperature of the cell for simulated SOFC of an Example Graph showing the characteristics of the standard free energy of oxide formation Table showing the standard electrode potential characteristics of oxides Graph showing the vapor pressure characteristics of oxides

Explanation of symbols

1: Interconnect (alloy or oxide)
1a: Interface 2a: Air channel 2: Groove 2b: Fuel channel 3: Single cell 30: Electrolyte membrane 31: Air electrode 32: Fuel electrode C: Cell for SOFC (cell for solid oxide fuel cell)

Claims (4)

A method for producing a solid oxide fuel cell, comprising a Cr-containing alloy or oxide joined with an air electrode,
Before performing a firing treatment in which the alloy or oxide and the air electrode are joined, a TiO ₂ film doped with a doping element that is a pentavalent element is formed on the surface of the alloy or oxide. A solid oxide fuel cell having a Cr (VI) oxide-suppressed state in which the formation of Cr (VI) oxide in the alloy or oxide is suppressed by performing a film forming process. Production method.   The method for producing a solid oxide fuel cell according to claim 1, wherein the doping element is Nb. A solid oxide fuel cell unit formed by joining an alloy or oxide containing Cr and an air electrode,
A cell for a solid oxide fuel cell, wherein a TiO ₂ film doped with a doping element which is a pentavalent element is formed on the surface of the alloy or oxide.   The solid oxide fuel cell according to claim 3, wherein the doping element is Nb.

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