ELECTROCHEMICAL CELL

Abstract

Electrochemical cell, which includes: a fuel electrode; an air electrode containing a perovskite structural oxide as a major component, wherein the perovskite structural oxide is represented by a general formula ABO3 and contains La and Sr at position A; and a solid electrolyte layer arranged between the fuel electrode and the air electrode, wherein the air electrode comprises a central section and an outer circumferential section, wherein the central section is located in a plane direction perpendicular to a thickness direction of the air electrode at a center of the air electrode, wherein the outer circumferential section surrounds the central section in the plane direction, and a first ratio of a La concentration to a Sr concentration, detected in the outer circumferential section by Auger electron spectroscopy, is at least 1.1 times a second ratio of a La concentration to a Sr concentration, detected in the central section by Auger electron spectroscopy.

Description

TECHNICAL FIELD

[0001] The present invention relates to an electrochemical cell. STATE OF THE ART

[0002] In recent years, fuel cells, a type of electrochemical cell, have attracted attention from the perspective of environmental issues and the effective utilization of energy resources. Fuel cells typically contain a fuel electrode, an air electrode, and a solid electrolyte layer sandwiched between the fuel electrode and the air electrode.

[0003] For the air electrode, perovskite structural oxides represented by the general formula ABO3 containing La (lanthanum) and Sr (strontium) at a site A are preferred (see, for example, Patent Literature 1 listed below). Examples of such perovskite structural oxides include (La, Sr)(Co, Fe)O3, (La, Sr)FeO3, (La, Sr)CoO3, and (La, Sr)MnO3.

[0004] Further prior art is also known from Patent Literature 2 and Patent Literature 3 listed below. LIST OF CITATIONS Patent literature Patent Literature 1: JP 2006-32132A Patent literature 2: DE 103 17 976 B4 Patent literature 3: US 9,520,597 B2 SUMMARYTECHNICAL PROBLEM

[0005] However, the output of a fuel cell may decrease as a result of repeated power generation. The present inventors have newly determined that a decrease in output is caused by deterioration of the air electrode, and that one cause of the deterioration of the air electrode is the formation of a compound by La contained in the air electrode and B (boron). It is noted that B reaches the air electrode by flying from a member located in a surrounding area, such as a support portion that supports the fuel cell.

[0006] An object of the present invention is to provide an electrochemical cell in which a reduction in output can be suppressed. SOLUTION TO THE PROBLEM

[0007] An electrochemical cell according to the present invention includes a fuel electrode, an air electrode containing a perovskite structural oxide as a main component, the perovskite structural oxide being represented by a general formula ABO3 and containing La and Sr at the A position, and a solid electrolyte layer disposed between the fuel electrode and the air electrode. The air electrode includes a central portion and an outer peripheral portion, the central portion being located at a center of the air electrode in an in-plane direction perpendicular to a thickness direction of the air electrode, and the outer peripheral portion surrounding the central portion in the in-plane direction.A first ratio of a La concentration to a Sr concentration detected in the outer peripheral portion by Auger electron spectroscopy is at least 1.1 times a second ratio of a La concentration to a Sr concentration detected in the central portion by Auger electron spectroscopy. BENEFICIAL EFFECTS

[0008] According to the present invention, it is possible to provide an electrochemical cell in which a reduction in output can be suppressed. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a perspective view showing a configuration of a fuel cell according to an embodiment. DESCRIPTION OF EMBODIMENTS Configuration of the fuel cell 100

[0009] A configuration of a fuel cell 100, which is an example of an electrochemical cell according to the present embodiment, will be described with reference to the accompanying drawings. Fig. 1 is a perspective view of the fuel cell 100.

[0010] The fuel cell 100 is a so-called solid oxide fuel cell (SOFC). The fuel cell 100 can be of various types, such as a flat tubular type, a series-segmented type, a flat plate type, and a cylindrical type.

[0011] The fuel cell 100 includes a fuel electrode 110, a solid electrolyte layer 120, and an air electrode 130. Although there is no particular limitation on the shape of the fuel cell 100, the fuel cell 100 may, for example, have a square or rectangular plate shape with sides having a length of 10 to 300 mm.

[0012] In the fuel cell 100, as a result of supplying a fuel gas (e.g., hydrogen) to the fuel electrode 110 and supplying an oxidant gas (e.g., air) to the air electrode 130, power is generated based on the following chemical reaction formulas (1) and (2). (1 / 2) · O2 + 2e - → O 2- (in the air electrode 130) (1) H2 + O 2- → H2O + 2e- (in the fuel electrode 110) (2)

[0013] The fuel electrode 110 is a porous body with good gas permeability. The fuel electrode 110 functions as an anode of the fuel cell 100. The fuel electrode 110 is formed from a substance that exhibits electron conductivity and a substance that exhibits oxygen ion conductivity. The fuel electrode 110 can be formed, for example, from NiO-8YSZ (yttria-stabilized zirconia) or NiO-GDC (gadolinium-doped ceria). Although there is no particular limitation on the thickness of the fuel electrode 110, the fuel electrode 110 can have a thickness of, for example, 50 to 2000 µm. Although there is no particular limitation on the porosity of the fuel electrode 110, the fuel electrode 110 can have a porosity of, for example, 15 to 55%.

[0014] The solid electrolyte layer 120 is arranged between the fuel electrode 110 and the air electrode 130. The solid electrolyte layer 120 is a compact body through which oxygen ions generated in the air electrode 130 can penetrate. The solid electrolyte layer 120 acts as a sealing film that prevents a fuel gas (e.g., hydrogen gas) from mixing with an oxygen-containing gas (e.g., air).

[0015] The solid electrolyte layer 120 may contain ZrO2 (zirconium dioxide) as a main component. Besides zirconium dioxide, the solid electrolyte layer 120 may also contain additives such as Y2O3 (yttrium oxide) and / or Sc2O3 (scandium oxide). These additives function as stabilizers. A molar composition ratio of the stabilizers to zirconium dioxide (stabilizers:zirconium dioxide) in the solid electrolyte layer 120 may be set to approximately 3:97 to 20:80. Accordingly, examples of materials of the solid electrolyte layer 120 include 3YSZ, 8YSZ, 10YSZ, and ScSZ (scandium oxide-stabilized zirconium dioxide). The solid electrolyte layer 120 may, for example, have a thickness of 3 μm to 50 μm. Although there is no particular limitation on the porosity of the solid electrolyte layer 120, the solid electrolyte layer 120 may have a porosity of, for example, 0 to 10%.

[0016] The air electrode 130 is a porous body with good gas permeability. The air electrode 130 functions as a cathode of the fuel cell 100. The air electrode 130 has a square or rectangular plate shape (external shape in a plan view).

[0017] The air electrode 130 includes, as a main component, a perovskite structural oxide represented by a general formula ABO3, which contains La (lanthanum) and Sr (strontium) at the A site. Examples of such perovskite structural oxides include, but are not limited to, (La,Sr)(Co,Fe)O3 (lanthanum strontium cobalt ferrite), (La,Sr)FeO3 (lanthanum strontium ferrite), (La,Sr)CoO3 (lanthanum strontium cobaltite), and (La,Sr)MnO3 (lanthanum strontium manganate). Although there is no particular limitation on the thickness of the air electrode 130, the air electrode 130 may have a thickness of, for example, 50 to 2000 μm. Although there is no particular limitation on the porosity of the air electrode 130, the air electrode 130 may, for example, have a porosity of 15 to 55%.

[0018] In the present embodiment, that a substance Y is “contained as a main component” in a composition X means that the substance Y constitutes at least 70% by weight of the total composition X.

[0019] As in Fig. 1, the air electrode 130 includes a central portion 130a and an outer peripheral portion 130b.

[0020] The central portion 130a is located in a plane direction perpendicular to a thickness direction at the center of the air electrode 130. The thickness direction is the same as a direction in which the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130 are layered. In the Fig.In the example shown in Figure 1, the central portion 130a has a circular planar shape, but the central portion 130a may also have an elliptical, rectangular, polygonal, or indeterminate planar shape. Although there is no particular limitation on the planar size of the central portion 130a, the central portion 130a may have a planar size that is at least 5% and no more than 50%, and preferably at least 10% and no more than 30%, of the total planar area of ​​the air electrode 130.

[0021] The outer peripheral portion 130b surrounds the central portion 130a in the plane direction. The outer peripheral portion 130b is a portion of the air electrode 130 that is different from the central portion 130a. The plane shape and plane size of the outer peripheral portion 130b are set in accordance with the plane shape and plane size of the central portion 130a. The outer peripheral portion 130b can also be formed together with the central portion 130a as a single part. That is, there need not be a boundary between the central portion 130a and the outer peripheral portion 130b. La / Sr ratio in the air electrode 130

[0022] A first ratio (La concentration / Sr concentration) Qb of a quantitative value of La (hereinafter referred to as a "La concentration") to a quantitative value of Sr (hereinafter referred to as a "Sr concentration") detected in the outer peripheral portion 130b by Auger electron spectroscopy is at least 1.1 times a second ratio (La concentration / Sr concentration) Qa of a La concentration to a Sr concentration detected in the central portion 130a by Auger electron spectroscopy. That is, Qb ≥ 1.1. Qa.

[0023] With this configuration, a composition ratio of La in the outer peripheral portion 130b can be made sufficiently higher than a composition ratio of La in the central portion 130a to cause B (boron) to preferentially react with La contained in the outer peripheral portion 130b during electrical conduction. As a result of B being trapped by La contained in the outer peripheral portion 130b as described above, B can be prevented from reacting with La in the central portion 130a and forming a compound. Accordingly, a reduction in catalyst reaction activity in the central portion 130a can be suppressed, and deterioration of the air electrode 130 as a whole can be suppressed. As a result, a reduction in the output of the fuel cell 100 can be suppressed.

[0024] The first ratio Qb in the outer peripheral portion 130b is preferably no greater than 1.6 times the second ratio Qa in the central portion 130a. This configuration can reduce the difference in reaction activity between the central portion 130a and the outer peripheral portion 130b during electrical conduction and can accordingly suppress local deterioration of the air electrode 130 due to the generation of a current density distribution. More preferably, the first ratio Qb in the outer peripheral portion 130b is no greater than 1.3 times the second ratio Qa in the central portion 130a.

[0025] Although there is no particular limitation on the numerical value range of the first ratio Qb in the outer circumferential portion 130b, the first ratio Qb is preferably, for example, at least 0.25 and not more than 0.55. Although there is no particular limitation on the numerical value range of the second ratio Qa in the central portion 130a, the second ratio Qa is preferably, for example, at least 0.18 and not more than 0.4. With this configuration, deterioration of the air electrode can be further suppressed.

[0026] A method for determining the first ratio Qb in the outer peripheral portion 130b and the second ratio Qa in the central portion 130a will be described below.

[0027] First, center points of four sides defining an outer edge of the air electrode 130 are determined in a plan view. Subsequently, an intersection point between a straight line connecting center points of two opposite sides and a straight line connecting center points of the remaining two opposite sides is determined as the center point. Subsequently, with respect to each line extending from the center to each center point, a position located at a distance of 3 / 4 of the total length of the line from the center is determined as a first measurement point (a total of four points) for calculating the first ratio Qb. Furthermore, with respect to each line extending from the center to each center point, a position located at a distance of 1 / 4 of the total length of the line from the center is determined as a second measurement point (a total of four points) for calculating the second ratio Qa.

[0028] Subsequently, La intensity data and Sr intensity data are obtained for each of the first four measurement points using a scanning Auger electron spectroscopy device (manufactured by ULVAC-PHI, Inc., Model 710, electron beam acceleration voltage: 10 kV). Subsequently, a La concentration is determined by dividing the La intensity data by a relative sensitivity factor of La for each first measurement point, and a Sr concentration is determined by dividing the Sr intensity data by a relative sensitivity factor of Sr for each first measurement point. Subsequently, an average La concentration is determined by calculating an arithmetic mean of the La concentrations of the first four measurement points, and an average Sr concentration is determined by calculating an arithmetic mean of the Sr concentrations of the first four measurement points.Then, a value obtained by dividing the mean La concentration by the mean Sr concentration is taken as the first ratio Qb.

[0029] Similarly, using the scanning Auger electron spectroscopy apparatus (manufactured by ULVAC-PHI, Inc., Model 710, electron beam acceleration voltage: 10 kV), La intensity data and Sr intensity data are obtained for each of the four second measurement points. Subsequently, a La concentration is determined for each second measurement point by dividing the La intensity data by the relative sensitivity factor of La, and a Sr concentration is determined for each second measurement point by dividing the Sr intensity data by the relative sensitivity factor of Sr. Subsequently, an average La concentration is determined by calculating an arithmetic mean of the La concentrations of the four second measurement points, and an average Sr concentration is determined by calculating an arithmetic mean of the Sr concentrations of the four second measurement points.Then, a value obtained by dividing the mean La concentration by the mean Sr concentration is taken as the second ratio Qa.

[0030] Note that the relative sensitivity factor of La and the relative sensitivity factor of Sr are determined according to the electron beam acceleration voltage of the scanning Auger electron spectroscopy device. If the electron beam acceleration voltage is 10 kV, the relative sensitivity factor of La is 0.652 and the relative sensitivity factor of Sr is 0.059. Method for producing the fuel cell 100

[0031] A method for manufacturing the fuel cell 100 is described.

[0032] First, a slurry is prepared by mixing a powder mixture (e.g., a mixture of NiO powder and YSZ powder) for forming the fuel electrode 110 with an organic binder and a solvent. Then, a fuel electrode sheet (a molded part for the fuel electrode 110) is formed using the slurry.

[0033] Subsequently, a slurry is prepared by mixing a powder (e.g., YSZ powder) for forming the solid electrolyte layer 120 with water and a binder. Then, a solid electrolyte layer sheet (a solid electrolyte layer 120 molded part) is formed by applying the slurry to the fuel electrode molded part 110.

[0034] Subsequently, a heat treatment is performed on the molded parts for the fuel electrode 110 and the solid electrolyte layer 120 to remove the binders, and then the molded parts are fired together at 1300 to 1600 °C in an oxygen-containing atmosphere to obtain a co-fired body of the fuel electrode 110 and the solid electrolyte layer 120.

[0035] Subsequently, powders (perovskite structural oxide powders represented by a general formula ABO3 and containing La and Sr at position A) are prepared to form the central portion 130a and the outer peripheral portion 130b of the air electrode 130. As the perovskite structural oxide powder for forming the outer peripheral portion 130b, a perovskite structural oxide powder having a higher composition ratio (La / Sr) of La to Sr than the perovskite structural oxide powder for forming the central portion 130a is used.

[0036] Subsequently, a molded part for the central portion 130a is formed on a central portion of the solid electrolyte layer 120 by dipping it into a coating liquid obtained by dispersing a material of a central portion for forming the central portion 130a into a solvent.

[0037] Subsequently, a molded part for the outer peripheral portion 130b is formed by dipping in an application liquid obtained by dispersing a material of the outer peripheral portion for forming the outer peripheral portion 130b in a solvent to surround the molded part for the central portion 130a.

[0038] Subsequently, the molded part for the air electrode 130 is fired at 1000 to 1300 °C to form the air electrode 130. Variations

[0039] The embodiment of the present invention has been described, but the present invention is not limited to this embodiment and various changes may be made without departing from the gist of the present invention.

[0040] In the above-described embodiment, the fuel cell 100 has been described as an example of the electrochemical cell, but the present invention can be applied to electrochemical cells such as solid oxide electrolysis cells as well as fuel cells.

[0041] In the embodiment described above, the fuel cell 100 includes the fuel electrode 110, the solid electrolyte layer 120, and the air electrode 130, but the present invention is not limited to this configuration. For example, the fuel cell 100 may further include a barrier layer to suppress the formation of a high-resistivity layer between the solid electrolyte layer 120 and the air electrode 130. The barrier layer may be formed using a ceria-based material, for example, containing ceria and a solid solution of ceria and a rare earth oxide. Examples of such ceria-based materials include GDC (gadolinium-doped ceria) and SDC (samarium-doped ceria). Examples

[0042] Examples of fuel cells according to the present invention are described below, but the present invention is not limited to the following examples. Preparation of samples No. 1 to No. 12

[0043] Fuel cells in accordance with samples No. 1 to No. 12 were fabricated as described below.

[0044] First, a slurry obtained by mixing a mixed powder of a NiO powder, a Y2O3 powder, and a pore-forming material (PMMA) with IPA was dried in a nitrogen atmosphere to prepare a powder mixture.

[0045] Subsequently, the powder mixture was pressed using a uniaxial press (compaction pressure: 50 MPa) to form a plate with a length of 30 mm, a width of 30 mm, and a thickness of 3 mm, and the plate was further consolidated using a CIP (compaction pressure: 100 MPa) to form a molded part for the fuel electrode power collection layer.

[0046] Subsequently, a slurry obtained by mixing a powder mixture of NiO-8YSZ and PMMA with IPA was applied to the fuel electrode power collection layer molding to form a fuel electrode active layer molding. Thus, a fuel electrode molding was obtained.

[0047] Subsequently, a slurry for the solid electrolyte layer was prepared by mixing 8YSZ with terpineol and a binder. The slurry for the solid electrolyte layer was then applied to the fuel electrode mold to form a solid electrolyte layer mold.

[0048] Subsequently, a GDC slurry was prepared and applied to the solid electrolyte layer mold to form a barrier layer mold.

[0049] Subsequently, the molded parts for the fuel electrode, the solid electrolyte layer, and the barrier layer were fired (5 hours at 1450 °C) to form a composite body consisting of the fuel electrode, the solid electrolyte layer, and the barrier layer.

[0050] Subsequently, a center section slurry was prepared by mixing a center section material shown in Table 1 with terpineol and a binder. The center section slurry was then applied in a circular shape to the center of the barrier layer to form a molded part for the center section of the air electrode.

[0051] Subsequently, an outer peripheral portion slurry was prepared by mixing an outer peripheral portion material shown in Table 1 with terpineol and a binder. As shown in Table 1, a material having a higher La to Sr composition ratio (La / Sr) than the center portion material was used as the outer peripheral portion material. Subsequently, the outer peripheral portion slurry was coated so as to surround the center portion molding to form an outer peripheral portion molding of the air electrode. Thus, an air electrode molding was obtained.

[0052] Subsequently, the preform for the air electrode was fired (1 hour at 1000 °C) to form the air electrode. The air electrode had a square plane shape with sides measuring 10 cm. The plane size of the center section of the air electrode constituted 50% of the total plane area of ​​the air electrode. La / Sr ratio of the central portion and outer peripheral portion of the air electrode

[0053] First, midpoints of four sides defining an outer edge of the air electrode were determined in a plan view. Subsequently, an intersection point between a straight line connecting midpoints of two opposite sides and a straight line connecting midpoints of the remaining two opposite sides was determined as the center. Subsequently, with respect to each line segment running from the center to each midpoint, a position located at a distance of 3 / 4 of the total length of the line from the center was determined as a first measurement point (a total of four points) for calculating the first ratio Qb. Furthermore, with respect to each line segment running from the center to each midpoint, a position located at a distance of 1 / 4 of the total length of the line from the center was determined as a second measurement point (a total of four points) for calculating the second ratio Qa.

[0054] Subsequently, La intensity data and Sr intensity data were obtained for each of the first four measurement points using a scanning Auger electron spectroscopy device (manufactured by ULVAC-PHI, Inc., Model 710, electron beam acceleration voltage: 10 kV). Subsequently, a La concentration was determined for each first measurement point by dividing the La intensity data by a relative sensitivity factor of La (= 0.652), and a Sr concentration was determined for each first measurement point by dividing the Sr intensity data by a relative sensitivity factor of Sr (= 0.059). Subsequently, an average La concentration was determined by calculating an arithmetic mean of the La concentrations of the first four measurement points, and an average Sr concentration was determined by calculating an arithmetic mean of the Sr concentrations of the first four measurement points.The first ratio Qb was then determined by dividing the mean La concentration by the mean Sr concentration.

[0055] Similarly, La intensity data and Sr intensity data were obtained for each of the four second measurement points using a scanning Auger electron spectroscopy device (manufactured by ULVAC-PHI, Inc., Model 710, electron beam acceleration voltage: 10 kV). Subsequently, a La concentration was determined for each second measurement point by dividing the La intensity data by the relative sensitivity factor of La (= 0.652), and a Sr concentration was determined for each second measurement point by dividing the Sr intensity data by the relative sensitivity factor of Sr (= 0.059). Subsequently, an average La concentration was determined by calculating an arithmetic mean of the La concentrations of the four second measurement points, and an average Sr concentration was determined by calculating an arithmetic mean of the Sr concentrations of the four second measurement points.The second ratio Qa was then determined by dividing the mean La concentration by the mean Sr concentration.

[0056] Table 1 shows the first ratio Qb, the second ratio Qa and the ratio of the first ratio Qb to the second ratio Qa. Durability test

[0057] Each of the samples from No. 1 to No. 12 was heated to 750 °C while supplying nitrogen gas to the fuel electrode side and air to the air electrode side, and when the temperature reached 750 °C, a reduction treatment was carried out for 3 hours while supplying hydrogen gas to the fuel electrode.

[0058] Subsequently, a voltage drop rate per 1000 hours was measured as a deterioration rate. A temperature of 750 °C and a nominal current density of 0.2 A / cm 2The obtained value is used. Table 1 shows the measurement results. In Table 1, samples with a deterioration rate of less than 1.0% are rated as "excellent," samples with a deterioration rate of at least 1.0% and less than 1.1% are rated as "good," samples with a deterioration rate of at least 1.1% and less than 1.2% are rated as "fair," and samples with a deterioration rate of at least 1.2% are rated as "poor." (Table 1) Material of the middle section Material of the outer peripheral section First ratio Qb in the outer circumference section t Second ratio Qa in the middle section Qb / Qa Quality deterioration rate (%) Evaluation 1 (La6, Sr4)(Co2, Fe8)O3 (La6, Sr4)(Co2, Fe3)O3 0,3 0,3 1,0 1,3 bad 2 (La 6,2 , Sr 3,8 )(Co2, Fe8)O3 (La6, Sr4)(Co2, Fe3)O3 0,33 0,3 1,1 0,9 excellent 3 (La 7,2 , Sr 2,8 )(Co2, Fe8)O3 (La 6,7 , Sr 3,3 )(Co2, Fe8)O3 0,5 0,4 1,3 0,75 excellent 4 (La 6,7 , Sr 3,3 )(Co2, Fe8)O3 (La 5,5 , Sr 4,5 )(Co2, Fe8)O3 0,4 0,25 1,6 1,08 good 5 (La 5,5 , Sr 4,5 )(Co2, Fe8)O3 (La 4,8 , Sr 5,2 )(Co2, Fe8)O3 0,25 0,18 1,4 1,05 good 6 (La 7,4 , Sr 2,6 )(Co2, Fe8)O3 (La 6,7 , Sr 3,3 )(Co2, Fe8)O3 0,55 0,4 1,4 1,0 good 7 (La 7,2 , Sr 2,8 )(Co2, Fe8)O3 (La6, Sr4)(Co2, Fe2)O3 0,5 0,3 1,7 1,1 mediocre 8 (The 6,4 , Mr 3,6 )FeO3 (The 6,4 , Mr 3,6 )FeO3 0,35 0,35 1,0 1,3 bad 9 (La6, Sr4)FeO3 (The 5,5 , Mr 4,5 )FeO3 0,3 0,25 1,2 0,9 excellent 10 (The 7,2 , Mr 2,8 )FeO3 (The 6,7 , Mr 3,3 )FeO3 0,5 0,4 1,3 0,8 excellent 11 (The 7,2 , Mr 2,8 )FeO3 (The 6,1 , Mr 3,9 )FeO3 0,5 0,32 1,6 1,05 good 12 (The 7,4 , Mr 2,6 )FeO3 (La6, Sr4)FeO3 0,55 0,3 1,8 1,15 mediocre

[0059] As shown in Table 1, the deterioration rate of the air electrode could be reduced in samples in which the first ratio Qb in the outer peripheral portion was at least 1.1 times the second ratio Qa in the central portion. This is because a reduction in catalyst reaction activity in the central portion due to B (boron) being trapped by La contained in the outer peripheral portion could be suppressed.

[0060] Furthermore, among the samples in which the first ratio Qb in the outer peripheral portion was at least 1.1 times the second ratio Qa in the inner portion, the deterioration rate of the air electrode could be further suppressed in samples in which the first ratio Qb was not greater than 1.6 times the second ratio Qa. This is because the generation of a current density distribution due to a difference in reaction activity between the central portion and the outer peripheral portion during electrical conduction could be suppressed, and accordingly, the local deterioration of the air electrode could be suppressed.

[0061] Furthermore, among the samples in which the first ratio Qb in the outer peripheral portion was at least 1.1 times the second ratio Qa in the central portion, in samples in which the first ratio Qb was not greater than 1.3 times the second ratio Qa, the deterioration rate of the air electrode could be further suppressed.

[0062] Although it is known that SrSO4, Co3O4, CoO, SrO and the like are substances that can cause deterioration of the air electrode, it is noted that it has been confirmed by experiments that the effects described above can be achieved even if the air electrode contains these substances. LIST OF REFERENCE SYMBOLS 100 fuel cells 110 Fuel electrode 120 solid electrolyte layer 130 Air electrode 130a middle section 130b Outer peripheral section

Claims

[1] Electrochemical cell comprising: a fuel electrode; an air electrode containing a perovskite structural oxide as a main component, wherein the perovskite structural oxide is represented by a general formula ABO3 and contains La and Sr at position A; and a solid electrolyte layer disposed between the fuel electrode and the air electrode, wherein the air electrode includes a central portion and an outer peripheral portion, the central portion being located at a center of the air electrode in a plane direction perpendicular to a thickness direction of the air electrode, the outer peripheral portion surrounding the central portion in the plane direction, and a first ratio of a La concentration to a Sr concentration detected in the outer peripheral portion by Auger electron spectroscopy is at least 1.1 times a second ratio of a La concentration to a Sr concentration detected in the central portion by Auger electron spectroscopy. [2] Electrochemical cell according to claim 1, wherein the first ratio is not greater than 1.6 times the second ratio. [3] Electrochemical cell according to claim 1 or 2, wherein the first ratio is not greater than 1.3 times the second ratio.

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