Electrochemical cell

Abstract

Electrochemical cell containing an anode (20), a cathode (50) and a solid electrolyte layer (30) arranged between the anode (20) and the cathode (50), wherein the cathode (50) contains a main phase and a second phase, wherein the main phase is configured with a perovskite oxide designated by the general formula ABO3 and contains at least one element of Sr and La at position A, and the second phase is configured with SrSO4 and (Co, Fe)3O4, and a ratio of the occupied surface area of ​​the second phase in a cross-section of the cathode (50) is less than or equal to 10.5%, wherein a ratio of the occupied surface area of ​​(Co, Fe)3O4 in the cross-section of the cathode (50) is greater than a ratio of the occupied surface area of ​​SrSO4.

Description

Technical area

[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 increasing attention due to environmental concerns and their effective use as an energy source. A fuel cell typically contains an anode, a cathode, and a solid electrolyte layer sandwiched between the anode and cathode.

[0003] The cathode is configured with, for example, a perovskite oxide such as (La,Sr)(Co,Fe)O3 (lanthanum strontium cobalt ferrite) or the like (for example, reference is made to Patent Literature 1).

[0004] Furthermore, DE 11 2016 000 041 T5 describes a fuel cell comprising an anode, a cathode, and a solid electrolyte layer. The cathode contains a perovskite composite oxide as a main component and contains a compound containing S and / or Cr as a secondary component. The cathode has a surface on a side opposite the solid electrolyte layer. The surface of the cathode contains a first region and a second region positioned downstream of the first region with respect to the direction of the oxidant gas flow in which the oxidant gas flows over the surface. The first region and the second region, respectively, contain a main phase configured by a perovskite composite oxide and a secondary phase configured by the compound. The proportion of the occupied surface of the secondary phase in the first region is greater than the proportion of the occupied surface of the secondary phase in the second region. List of publicationsPatent literature

[0005] [Patent Literature 1] Japanese Patent Application Laid-Open No. JP 2006-32132 A Brief description of the inventionTechnical problem

[0006] However, fuel cell performance can degrade with repeated power generation. The present inventors have discovered that one cause of performance degradation is cathode damage, and that such cathode damage is related to the total amount of SrSO4 and (Co, Fe)3O4 introduced into the cathode.

[0007] The present invention is proposed on the basis of the above novel finding and has an object to provide an electrochemical cell configured to prevent a decline in fuel cell performance. Problem solving

[0008] An electrochemical cell according to claim 1 includes an anode, a cathode, and a solid electrolyte layer disposed between the anode and the cathode. The cathode includes a main phase and a second phase. The main phase is configured with a perovskite oxide represented by the general formula ABO3 and containing at least one of Sr and La at site A. The second phase is configured with SrSO4 and (Co, Fe)3O4. A ratio of the occupied surface area of ​​the second phase in a cross section of the cathode is less than or equal to 10.5%. A ratio of the occupied surface area of ​​(Co, Fe)3O4 in the cross section of the cathode is greater than a ratio of the occupied surface area of ​​SrSO4.

[0009] An electrochemical cell according to claim 4 includes an anode, a cathode, and a solid electrolyte layer disposed between the anode and the cathode. The cathode includes a main phase and a second phase. The main phase is configured with a perovskite oxide represented by the general formula ABO3 and containing at least one of Sr and La at position A. The second phase is configured with SrSO4 and (Co, Fe)3O4. A ratio of the occupied surface area of ​​the second phase in a cross section of the cathode is less than or equal to 10.5%. The cathode includes a first region on a side opposite the solid electrolyte layer and a second region on a side with the solid electrolyte layer. A ratio of the occupied surface area of ​​SrSO4 in the cross section of the first region is greater than a ratio of the occupied surface area of ​​SrSO4 in the cross section of the second region.A ratio of the occupied surface of (Co, Fe)3O4 in the cross section of the second region is larger than a ratio of the occupied surface of (Co, Fe)3O4 in the cross section of the first region. Advantageous effects of the invention

[0010] The present invention provides an electrochemical cell configured to prevent a decline in fuel cell performance. Brief description of the drawings Fig. 1 is a sectional view illustrating a configuration of a fuel cell. Description of embodimentsConfiguration of the fuel cell 10

[0011] The configuration of the fuel cell 10 will now be described with reference to the drawings. The fuel cell 10 is configured as a so-called solid oxide fuel cell (SOFC). Possible configurations of the fuel cell 10 include a flat-tubular type, a series-segmented type, an anode-supported type, a flat-plate electrolyte type, a tubular type, or the like.

[0012] The fuel cell 10 contains an anode 20, a solid electrolyte layer 30, a barrier layer 40 and a cathode 50.

[0013] The anode 20 acts as an anode for the fuel cell 10. As in Fig. 1, the anode 20 includes an anode current collecting layer 21 and an anode active layer 22.

[0014] The anode current collecting layer 21 is configured as a porous body with excellent gas permeability. The material of the anode current collecting layer 21 includes the use of a material used in the anode current collecting layer of a conventional SOFC, and includes, for example, NiO (nickel oxide)-8YSZ (8 mol% yttria-stabilized zirconia) or NiO-Y2O3 (yttrium oxide). However, when NiO is included in the anode current collecting layer 21, at least a portion of the NiO may be reduced to Ni during operation of the fuel cell 10. The thickness of the anode current collecting layer 21 may be configured, for example, to be 0.1 mm to 5.0 mm.

[0015] The anode active layer 22 is disposed on the anode current collecting layer 21. The anode active layer 22 is configured as a porous body that is denser than the anode current collecting layer 21. The base material for the anode active layer 22 includes the use of a material used in an anode active layer of a conventional SOFC and includes, for example, NiO-8YSZ. However, when NiO is included in the anode active layer 22, at least a portion of the NiO may be reduced to Ni during operation of the fuel cell 10. The thickness of the anode active layer 22 may be configured, for example, as 5.0 µm to 30 µm.

[0016] The solid electrolyte layer 30 is disposed between the anode 20 and the cathode 50. The solid electrolyte layer 30 in the present embodiment is disposed between the anode 20 and the barrier layer 40. The solid electrolyte layer 30 provides permeability to oxide ions produced by the cathode 50. The solid electrolyte layer 30 is configured with a material that is denser than either the anode 20 or the cathode 50.

[0017] The solid electrolyte layer 30 may contain ZrO2 (zirconium dioxide) as a main component. In addition to zirconium dioxide, the solid electrolyte layer 30 may contain an additive such as Y2O3 (yttrium oxide) and / or Sc2O S(scandium oxide). These additives function as a stabilizer. The molar composition ratio (stabilizer:zirconium dioxide) of the stabilizer to zirconia in the solid electrolyte layer 30 can be configured to approximately 3:97 to 20:80. Therefore, the material used in the solid electrolyte layer 30 includes 3YSZ, 8YSZ, 10YSZ, or ScSZ (scandium oxide-stabilized zirconia), or the like. The thickness of the solid electrolyte layer 30 can be configured, for example, to be 3 µm to 30 µm.

[0018] In the present embodiment, the phrase "Composition X contains as a main component Composition Y" means that Composition Y preferably constitutes at least 70% by weight of the total amount of Composition X, and more preferably constitutes at least 90% by weight.

[0019] The barrier layer 40 is disposed between the solid electrolyte layer 30 and the cathode 50. The barrier layer 40 prevents the formation of a high-resistivity layer between the solid electrolyte layer 30 and the cathode 50. The barrier layer 40 is configured with a material that is denser than the anode 20 or the cathode 50. The barrier layer 40 may contain a primary component of a ceria-based material such as GDC (gadolinium-doped ceria), SDC (samarium-doped ceria), or the like. The thickness of the barrier layer 40 may be configured, for example, as 3 µm to 20 µm.

[0020] The cathode 50 is arranged on the barrier layer 40. The cathode 50 functions as a cathode for the fuel cell 10. The cathode 50 is configured as a porous body. There is no particular limitation on the porosity of the cathode 50, and it can be configured to between 20% and 60%. There is no particular limitation on the thickness of the cathode 50, and it can be configured to between 2 µm and 100 µm.

[0021] The cathode 50 includes a main phase configured with a perovskite oxide represented by the general formula ABO3 and containing at least one of Sr and La at site A. The perovskite oxide may appropriately use, for example, a composite perovskite oxide containing lanthanum or SSC (samarium strontium cobaltite (Sm, Sr)CoO3) or the like that does not contain lanthanum. However, there is no limitation in this regard. The lanthanum-containing composite perovskite oxide contains LSCF (Lanthanum-Strontium-Cobalt-Ferrite): (La, Sr)(Co, Fe)O3), LSF: (Lanthanum-Strontium-Ferrite: (La, Sr)FeO3), LSC: (Lanthanum-Strontium-Cobaltite: (La, Sr)CoO3), and LNF (Lanthanum-Nickel-Ferrite: (La(Ni, Fe)O3)) or the like. The density of the main phase configured with a perovskite oxide can be expressed as 5.5 g / cm 3 up to 8.5 g / cm 3 be configured.

[0022] The occupied surface area ratio of the main phase in a cross-section of the cathode 50 can be configured to be greater than or equal to 89.5% and less than or equal to 99.5%. In the present embodiment, the term "occupied surface area ratio of the substance Z in the cross-section" refers to the ratio of the total area of ​​a substance Z phase to the gross area of ​​a solid phase in a cross-section. The method for calculating the occupied surface area ratio is described in detail below.

[0023] The cathode 50 contains a second phase configured with (Co, Fe)3O4 and SrSO4. In the second phase, SrSO4 and (Co, Fe)3O4 are in a mixed configuration. More specifically, a phrase such as "SrSO4 and (Co, Fe)3O4 are mixed" refers to a configuration in which an EDX spectrum detecting Sr, S, and O and an EDX spectrum detecting Co, Fe, and O are acquired separately at different locations, and SrSO4 and (Co, Fe)3O4 are literally mixed (= present in a combined state). (Co, Fe)3O4 contains Co2FeO4, Co 1,5 Fe 1,5 O4 and CoFe2O4 or the like. The density of the second phase can be estimated as 5.2 g / cm 3 up to 6.2 g / cm 3 The density of the second phase is lower than the density of the main phase.

[0024] The occupied surface area ratio of the second phase in the cross section of the cathode 50 is less than or equal to 10.5%. The occupied surface area ratio of the second phase is the sum of the occupied surface area ratio of SrSO4 and the occupied surface area ratio of (Co, Fe)3O4. More specifically, the occupied surface area ratio of the second phase includes the occupied surface area ratio of the particles configured with SrSO4, the occupied surface area ratio of the particles configured with (Co, Fe)3O4, the occupied surface area ratio of the particles configured with a mixture of SrSO4 and (Co, Fe)3O4, and the occupied surface area ratio of SrSO4 and / or (Co, Fe)3O4 mixed into the main phase particles.

[0025] Since the inactive part of the inner part of the cathode is reduced by a configuration in which the occupied surface area ratio of the second phase is less than or equal to 10.5%, it is possible to suppress a decrease in the performance of the fuel cell 10 during power supply.

[0026] More preferably, the occupied surface area ratio of the second phase in a cross-section of the cathode 50 is greater than or equal to 0.2%. In this way, since the sintering properties of the cathode 50 are improved by appropriately incorporating the second phase, the porous framework structure can be strengthened. Consequently, since changes in the microstructure of the cathode 50 can be prevented, it is possible to suppress the formation of cracks in the cathode 50 during current delivery.

[0027] Although there is no particular limitation on the ratio of the occupied surface area of ​​SrSO4 and the occupied surface area of ​​(Co, Fe)3O4 to the occupied surface area of ​​the second phase, a configuration in which (Co, Fe)3O4 is added in a larger amount than SrSO4 is effective for strengthening the framework structure of the cathode 50. For this purpose, the occupied surface area of ​​(Co, Fe)3O4 is preferably larger than the occupied surface area of ​​SrSO4. The occupied surface area of ​​SrSO4 in a cross section of the cathode 50 may be configured to be less than or equal to 5%, and the occupied surface area of ​​(Co, Fe)3O4 in a cross section of the cathode 50 may be configured to be less than or equal to 9.5%.

[0028] Although there is no particular restriction on the distribution of the main phase and the second phase in a cross section of the cathode 50, both components are preferably generally present in a uniform distribution.

[0029] Preferably, SrSO4 in the second phase is more distributed in a region on the side of the cathode 50 opposite the solid electrolyte layer. More specifically, in a configuration in which the cathode 50 is divided into a "first region" on the side opposite the solid electrolyte layer and a "second region" on the side with the solid electrolyte layer, with respect to the center in the thickness direction of the cathode 50, the occupied surface area ratio of SrSO4 in the first region is preferably larger than the occupied surface area ratio of SrSO4 in the second region. In this way, an activity in the second region, where activity reactions tend to increase more than in the first region, can be increased.

[0030] Preferably, (Co, Fe)3O4 in the second phase is more distributed in a region on the side of the cathode 50 near the solid electrolyte layer. More specifically, in a configuration in which the cathode 50 is divided into a "first region" on the side opposite the solid electrolyte layer and a "second region" on the side with the solid electrolyte layer with respect to the center in the thickness direction of the cathode 50, the occupied surface area ratio of (Co, Fe)3O4 in the second region is preferably larger than the occupied surface area ratio of (Co, Fe)3O4 in the first region. In such a configuration, the occupied surface area ratio of (Co, Fe)3O4 in the first region is more preferably smaller than the occupied surface area ratio of SrSO4 in the first region, and the occupied surface area ratio of (Co, Fe)3O4 in the second region is preferably larger than the occupied surface area ratio of SrSO4 in the second region.

[0031] Although there is no particular limitation on the average equivalent circular diameter of the second phase in the cross section of the cathode 50, it is preferably greater than or equal to 0.05 µm and less than or equal to 2.0 µm. In this way, it is possible to suppress a decrease in the performance of the fuel cell 10 during power delivery. The average equivalent circular diameter is the arithmetic mean value of 50 randomly selected circular diameters having the same surface area as the second phase. The 50 second phases subject to equivalent circular diameter measurement are preferably randomly selected from five or more locations in an FE-SEM image (10,000x magnification) of a cross section of the cathode 50.The second phase selected for calculating the equivalent circle diameter can be a region containing both (Co, Fe)3O4 and SrSO4, a region containing only SrSO4, or a region containing only (Co, Fe)3O4.

[0032] The cathode 50 may contain a third phase other than the main phase and the second phase described above. The components constituting the third phase may include, for example, Co3O4 (tricobalt tetraoxide), CoO (cobalt oxide), SrO (strontium oxide), and an oxide of an element constituting the main phase. However, there is no limitation in this regard. The total occupied surface area ratio of the third phase in the cross-section of the cathode 50 is preferably less than 10%. Method for calculating the occupied surface

[0033] Now, the method for calculating the ratio of the occupied surface of the second phase in a cross section of the cathode 50 will be described.

[0034] First, a cross-section of the cathode 50 is polished with a precision machine, and then an ion thinning process is performed using an IM4000 manufactured by Hitachi High-Technologies Corporation.

[0035] Then, using a field emission scanning electron microscope (FE-SEM), which works with a secondary electron detector in the lens, an SEM image of a cross-section of the cathode 50 is obtained, which is magnified 10,000 times.

[0036] Then, by dividing the brightness of the SEM image into 256 levels, three values ​​are assigned corresponding to the contrast of the main phase, the secondary phase, and the pores. For example, the main phase is displayed in light gray, the secondary phase in gray, and the pores in black. However, there are no restrictions in this regard.

[0037] Then, by analyzing an SEM image using the HALCON image analysis software produced by MVTec GmbH (Germany), an analysis image highlighting SrSO4 and (Co, Fe)3O4 is obtained. The total area of ​​SrSO4 and (Co, Fe)3O4 in the analysis image is considered the total area of ​​the second phase, and the occupied surface area ratio of the second phase is calculated by dividing the total area of ​​the second phase by the gross area of ​​the solid phase in the analysis image. The above-described analysis is performed at five locations on the same cross-section of the cathode 50, and the arithmetic mean value of the total area ratio of the second phase calculated at each of the five locations is the occupied surface area ratio of the second phase in the cathode 50.

[0038] It should be noted that the respective ratio of the occupied surface of SrSO4 and (Co, Fe)3O4 can be confirmed by a constituent analysis as described below.

[0039] First, the position of the second phase is confirmed by referring to the SEM image used to calculate the occupied surface area ratio of the second phase. Then, an EDX spectrum at the second phase position is obtained using energy-dispersive X-ray spectroscopy (EDX). The elements present at the second phase position are identified by semi-quantitative analysis of the EDX spectrum. This confirms that SrSO4 and (Co, Fe)3O4 exist in a mixed configuration in the second phase, and the occupied surface area ratio of SrSO4 and the occupied surface area ratio of (Co, Fe)3O4 in the second phase can be obtained separately.

[0040] Whether (Co, Fe)3O4 as one of CoFe2O4, Co 1,5 Fe 1,5 O4 or Co2FeO4 can be confirmed by analyzing the crystal structure of the second phase (lattice constant, lattice type, crystal orientation) using selected area electron diffraction (SAED) of a transmission electron microscope (TEM).

[0041] Although the method for calculating the occupied surface area ratio for the second phase has been described above, the occupied surface area ratio for the main phase can also be calculated in the same way. Cathode material

[0042] The cathode material used to configure the cathode 50 is a mixture in which an SrSO4 raw material powder and a (Co, Fe)3O4 raw material powder are added to a perovskite oxide raw material powder represented by the general formula ABO3.

[0043] The composite perovskite oxide feedstock powder contains a feedstock powder such as LSCF, LSF, LSC, LNF, SSC, or the like. (Co, Fe)3O4 contains a feedstock powder of Co2FeO4, Co 1,5 Fe 1,5 O4 or CoFe2O4 or the like.

[0044] The total amount of SrSO4 starting material powder and (Co, Fe)3O4 starting material powder added to the cathode material is less than or equal to 9.5 wt%. This makes it possible to reduce the occupied surface area ratio of the second phase in a cross-section of the cathode 50 to a value less than or equal to 10.5%.

[0045] The total addition amount of SrSO4 and (Co, Fe)3O4 in the cathode material is preferably greater than or equal to 0.18 wt%. This makes it possible to control the ratio of the occupied surface area of ​​the second phase in a cross-section of the cathode 50 to a value greater than or equal to 0.2%.

[0046] The occupied surface area ratio of the second phase can be precisely controlled by adjusting the grain size of each starting material powder or the configuration of the SrSO4 starting material powder and the (Co, Fe)3O4 starting material powder.

[0047] Adjusting the grain size of the SrSO4 feedstock powder and the (Co,Fe)3O4 feedstock powder allows for adjusting the average equivalent circular diameter of the second phase in a cross-section of the cathode 50. Adjusting the grain size of the SrSO4 feedstock powder and the (Co,Fe)3O4 feedstock powder is preferably performed using an air classifier. Such a configuration enables precise classification, which includes an upper and lower limit for the grain diameter. Method for producing the fuel cell 10

[0048] An example of a manufacturing process for the fuel cell 10 will now be described. In the following description, the term "green body" refers to an element before firing.

[0049] First, an anode current-collecting layer slurry is prepared by adding a binder (e.g., polyvinyl alcohol) to a mixture of an anode current-collecting layer powder (e.g., NiO powder and YSZ powder) and a pore-forming agent (e.g., PMMA (polymethyl methacrylate resin)). Then, an anode current-collecting layer powder is obtained by drying and granulating the anode current-collecting layer slurry in a spray dryer. A green body for the anode current-collecting layer 21 is formed by molding the anode powder using a compression molding method. A tape lamination method may also be used as a substitute for the compression molding method.

[0050] Next, an anode active layer slurry is prepared by adding a binder (e.g., polyvinyl alcohol) to a mixture of an anode active layer powder (e.g., NiO powder and YSZ powder) and a pore-forming agent (e.g., PMMA). Then, a green body for the anode active layer 22 is formed by printing the anode active layer slurry onto the green body for the anode current collecting layer 21 using a printing method. In this way, a green body for the anode 20 is formed. At this time, a tape lamination method, a coating method, or the like can also be used as a substitute for the printing method.

[0051] Then, a solid electrolyte layer slurry is prepared by mixing a mixture of water and a binder into a solid electrolyte layer powder (for example, YSZ powder) in a ball mill. Then, a solid electrolyte layer green body 30 is formed by coating and drying the solid electrolyte layer slurry onto the anode green body 20. A tape lamination method, a printing method, or the like can also be used as a substitute for the coating method.

[0052] Then, a barrier layer slurry is prepared by mixing a mixture of water and a binder into a barrier layer powder (for example, a GDC powder) in a ball mill. Then, a barrier layer green body 40 is formed by coating and drying the barrier layer slurry onto the solid electrolyte layer green body 30. A tape lamination method, a printing method, or the like can also be used as a substitute for the coating method.

[0053] Then, a laminated body using the green bodies for the anode 20, the solid electrolyte layer 30, and the barrier layer 40, respectively, is co-fired at 1300 to 1600 degrees C for 2 to 20 hours to form a co-fired body of the anode 20, the solid electrolyte layer 30, and the barrier layer 40.

[0054] Then, a cathode slurry is prepared by mixing water and a binder with the above-described cathode material in a ball mill. A cathode green body 50 is then formed by applying and drying the cathode slurry onto the barrier layer 40 of the co-fired body. The cathode green body 50 is then fired in an electric furnace (oxygen-containing atmosphere) (1000 to 1100 degrees C, for 1 to 10 hours), thereby forming the cathode 50 on the barrier layer 40. Further embodiments

[0055] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various changes and modifications can be made within a scope that does not deviate from the spirit of the invention.

[0056] Although a configuration in which the cathode 50 according to the present invention is used for the fuel cell 10 has been described, the cathode of the present invention can also be used for a solid oxide type electrochemical cell such as a solid oxide electrolysis cell in addition to a fuel cell.

[0057] In the present embodiment, although the fuel cell 10 includes the anode 20, the solid electrolyte layer 30, the barrier layer 40, and the cathode 50, there is no limitation in this regard. The fuel cell 10 may also include the anode 20, the solid electrolyte layer 30, and the cathode 50, or another layer may be disposed between the anode 20 and the solid electrolyte layer 30 or between the solid electrolyte layer 30 and the cathode 50. Examples

[0058] Although examples of a cell according to the present invention are described below, the present invention is not limited to the following examples. Production of samples No. 1 to No. 20

[0059] A fuel cell according to samples No. 1 to No. 20 was manufactured as described below.

[0060] First, an anode current collecting layer (NiO:8YSZ = 50:50 (Ni volume % conversion)) with a thickness of 500 µm was formed by a press-molding process, and an anode active layer (NiO:8YSZ = 45:55 (Ni volume % conversion)) with a thickness of 20 µm was formed on this layer by a printing process.

[0061] Then, using a deposition process, green bodies for a GDC layer and an 8YSZ layer were successively formed on the anode active layer and fired together (1400 degrees C, 2 hours).

[0062] Then, as shown in Table 1, a cathode material was prepared containing a main phase (LSCF, LSF, or SSC) and a second phase (SrSO4 and (Co, Fe)3O4). As shown in Table 1, the ratio of the occupied surface area of ​​the second phase in the cathode was varied by varying the addition amount of the second phase in each sample. Furthermore, the grain size of the SrSO4 raw material powder and the (Co, Fe)3O4 raw material powder were adjusted so that the mean equivalent circular diameter of the second phase matched the values ​​shown in Table 1. In samples No. 1, No. 2, No. 10, and No. 11, Co2FeO4 was used as (Co, Fe)3O4; in samples No. 3 to No. 5, No. 12, No. 13, and No. 16, Co was used. 1,5 Fe 1,5 O4 was used as (Co, Fe)3O4, and in sample No. 6 to No. 9, No. 14, No. 15 and No. 17 to No. 20, CoFe2O4 was used as (Co, Fe)3O4.

[0063] A cathode slurry was then prepared by mixing the cathode material, water, and PVA in a ball mill for 24 hours.

[0064] Then, after applying and drying the slurry for the cathode on the GDC layer of the co-fired body, a cathode was formed by firing for one hour in an electric furnace (oxygen-containing atmosphere, 1000 degrees C). Measurement of the ratio of the occupied surface of the second phase

[0065] First, after polishing a cross-section of the cathode in each sample with a precision machine, ion thinning processing was performed using an IM4000 manufactured by Hitachi High-Technologies Corporation.

[0066] Then, using an FESEM with a secondary electron detector in the lens, a 10,000x magnification SEM image was obtained from five positions in a cross-section of the cathode. The SEM image was acquired using an FESEM (model: ULTRA55, manufactured by Zeiss AG) with a working distance of 3 mm and an accelerating voltage of 1.5 kV. In the SEM image, three values ​​corresponding to the contrast of the main phase, the secondary phase, and the pores were assigned by dividing the image brightness into 256 levels.

[0067] Then, the SEM image was configured as an analysis image using the image analysis software HALCON produced by MVTec GmbH (Germany) to obtain an analysis image highlighting SrSO4 and (Co, Fe) 3O4.

[0068] Then, the occupied surface area ratio of the second phase was calculated at five locations each by dividing the total area of ​​SrSO4 and (Co, Fe)3O4 in the analysis image by the gross area of ​​the solid phase in the analysis image, and then calculating the arithmetic mean of these values ​​as the occupied surface area ratio for the second phase. Furthermore, a occupied surface area ratio of SrSO4 and a occupied surface area ratio of (Co, Fe)3O4 in the second phase were separately obtained by acquiring an EDX spectrum at the position of the second phase with reference to the SEM image. The calculation results for the occupied surface area ratio of the second phase in a cross-section of the cathode are shown in Table 1. Average equivalent circle diameter of the second phase

[0069] The mean equivalent circular diameter of the second phase at 50 randomly selected locations was calculated based on the five analysis images used to calculate the occupied surface area ratio. The calculation results for the mean equivalent circular diameter of the second phase are shown in Table 1. Measuring fuel cell performance

[0070] While nitrogen gas was supplied to the anode side of each sample and air was supplied to the cathode side of each sample, the temperature was raised to 750 degrees C. Once a temperature of 750 degrees C was reached, hydrogen gas was supplied to the anode for three hours to carry out a reduction process.

[0071] Then a nominal current density value of 0.2 A / cm 2and power generation was performed for 1000 hours while measuring cell voltage. The voltage drop ratio per 1000 hours was calculated as a degradation rate.

[0072] After 1000 hours of power generation, a cross-section of the cathode was examined using an electron microscope to detect cracks in the cathode. Those samples in which cracks smaller than or equal to 5 µm were detected, which have a minor impact on the fuel cell's properties, are labeled "present (minor)" in Table 1. Table 1 Sample No. Main phase of the cathode Secondary phase of the cathode Ratio of the occupied surface of the secondary phase in the cross section of the cathode (%) Ratio of the covered surface of SrSO4 in the cross section of the cathode (%) Ratio of the covered surface of (Co,Fe)3O4 in the cross section of the cathode (%) Mean equivalent circular diameter of the secondary phase (µm) Deterioration rate (%) Presence / absence of microscopic cracks Evaluation Nr. 1 LSCF Co2FeO4+SrSO4 0,18 0,03 0,15 0,14 0,54 present (minor) ◯ Nr.2 LSCF Co2FeO4+SrSO4 0,21 0,04 0,17 0,17 0,37 unavailable ⊚ Nr.3 LSCF What 1.5 Fe 1.5 O4 +SrSO4 0,40 0,06 0,34 0,35 0,45 unavailable ⊚ Nr.4 LSCF What 1.5 Fe1.5O4+SrSO4 1,4 0,2 1,2 0,80 0,49 unavailable ⊚ Nr.5 LSCF What 1.5 Fe 1.6 O4+SrSO4 3,7 0,4 3,3 1,4 0,51 unavailable ⊚ Nr.6 LSCF CoFe2O4+SrsO4 5,1 0,5 4,6 1,5 0,80 unavailable ⊚ Nr.7 LSCF CoFe2O4+SrSO4 7,3 0,6 6,7 1,7 0,88 unavailable ⊚ Nr.8 LSCF CoFe2O4+SrSO4 10,3 2,8 7,5 2,0 1,4 unavailable ⊚ Nr.9 LSCF CoFe2O4+SrSO4 11,5 1,8 9,7 2,4 2,4 unavailable × Nr.10 SPF Co2FeO4+SrSO4 0,16 0,03 0,13 0,14 0,55 present (minor) ◯ Nr.11 SPF Co2FeO4+SrSO4 4,5 0,7 3,8 1,5 0,66 unavailable ⊚ Nr.12 SPF What 1.5 Fe 1.6 O4+SrSO4 7,2 0,5 6,7 1,6 0,78 unavailable ⊚ Nr.13 SPF What 1.5 Fe 1.6 O4+SrSO4 9,3 0,8 8,5 1,8 1,0 unavailable ⊚ Nr. 14 SPF CoFe2O4+SrSO4 10,1 1,5 8,6 2,1 1,5 unavailable ⊚ Nr.15 SPF CoFe2O4+SrSO4 11,1 2,2 8,9 2,3 2,9 unavailable × Nr.16 SSC What 1.5 Fe 1.6 O4+SrSO4 0,15 0,03 0,12 0,16 0,62 present (minor) ◯ Nr.17 SSC CoFe2O4+SrSO4 2,4 0,3 2,1 1,1 0,77 unavailable ⊚ Nr.18 SSC CoFe2O4+SrSO4 6,2 0,5 5,7 1,6 0,82 unavailable ⊚ Nr.19 SSC CoFe2O4+SrSO4 10,0 2,1 7,9 1,8 1,1 unavailable ⊚ Nr.20 SSC CoFe2O4+SrSO4 11,9 3,2 8,7 2,5 2,9 unavailable ×

[0073] As shown in Table 1, fuel cell performance degradation was suppressed in samples No. 1 to No. 8, No. 10 to No. 14, and No. 16 to No. 19, in which the occupied surface area ratio of the second phase in a cross-section of the cathode was kept below or equal to 10.5%. This feature is due to the reduction of the inactive part in an internal part of the cathode.

[0074] In the present embodiment, the effect of the present invention was confirmed simply by manufacturing a cathode into which a second phase was incorporated and measuring a deterioration rate after 1000 hours of power generation immediately after the fuel cell was manufactured. However, the results of the present embodiment show that regardless of the manufacturing method or the extent to which the fuel cell is used, it is possible to suppress a fuel cell's performance deterioration by suppressing the occupied surface area ratio of a second phase in a cross section of the cathode to a value less than or equal to 10.5%.

[0075] Furthermore, the occurrence of cracks in the cathode was suppressed in samples No. 2 to No. 8, No. 11 to No. 14, and No. 17 to No. 19, in which the occupied surface area ratio of the second phase in a cross-section of the cathode was configured to be greater than or equal to 0.20%. This feature is due to the strengthening of the porous framework structure by improving the sintering properties of the cathode with the second phase.

[0076] The occupied surface area ratio of (Co, Fe)3O4 in these samples is generally larger than the occupied surface area ratio of SrSO4, and therefore, such a feature exerts a more beneficial effect on strengthening the cathode framework structure. However, even if the occupied surface area ratio of (Co, Fe)3O4 is smaller than the occupied surface area ratio of SrSO4, or even if they are equal, the cathode framework structure can be strengthened by a configuration in which the occupied surface area ratio of the second phase is greater than or equal to 0.20%.

[0077] In the present embodiment, the effect of the present invention was confirmed simply by manufacturing a cathode into which a second phase was incorporated and observing cracks after 1000 hours of power generation immediately after the fuel cell was manufactured. However, the results of the present embodiment show that regardless of the manufacturing method or the extent to which the fuel cell is used, it is possible to suppress the occurrence of cracks in a cathode if the occupied surface area ratio of the second phase in a cross section of the cathode is configured to be greater than or equal to 0.20%.

[0078] Furthermore, in Sample Nos. 1 to No. 8, No. 10 to No. 13, and No. 16 to No. 19, in which the mean equivalent circular diameter of the second phase in a cross section of the cathode was configured to be greater than or equal to 0.05 µm and less than or equal to 2.0 µm, further suppression of a decline in fuel cell performance was enabled. List of reference symbols 10 fuel cell 20 Anode 21 Anode current collecting layer 22 Anode active layer 30 Solid electrolyte layer 40 barrier layer 50 cathode

Claims

[1] Electrochemical cell containing an anode (20), a cathode (50) and a solid electrolyte layer (30) arranged between the anode (20) and the cathode (50), wherein the cathode (50) contains a main phase and a second phase, wherein the main phase is configured with a perovskite oxide denoted by the general formula ABO3 and containing at least one of Sr and La at position A, and the second phase is configured with SrSO4 and (Co, Fe)3O4, and a ratio of the occupied surface of the second phase in a cross-section of the cathode (50) is less than or equal to 10.5%, wherein a ratio of the occupied surface of (Co, Fe)3O4 in the cross section of the cathode (50) is greater than a ratio of the occupied surface of SrSO4. [2] The electrochemical cell of claim 1, wherein the ratio of the occupied surface of the second phase in the cross section of the cathode (50) is greater than or equal to 0.20%. [3] The electrochemical cell of claim 1 or 2, wherein a mean equivalent circular diameter of the second phase in the cross section of the cathode (50) is greater than or equal to 0.05 µm and less than or equal to 2.0 µm. [4] Electrochemical cell containing an anode (20), a cathode (50) and a solid electrolyte layer (30) arranged between the anode (20) and the cathode (50), wherein the cathode (50) contains a main phase and a second phase, wherein the main phase is configured with a perovskite oxide denoted by the general formula ABO3 and containing at least one of Sr and La at position A, and the second phase is configured with SrSO4 and (Co, Fe)3O4, and a ratio of the occupied surface of the second phase in a cross-section of the cathode (50) is less than or equal to 10.5%, wherein the cathode (50) includes a first region on a side opposite the solid electrolyte layer (30), and a second region on a side with the solid electrolyte layer (30), a ratio of the occupied surface of SrSO4 in the cross section of the first region is greater than a ratio of the occupied surface of SrSO4 in the cross section of the second region, and a ratio of the occupied surface of (Co, Fe)3O4 in the cross section of the second region is greater than a ratio of the occupied surface of (Co, Fe)3O4 in the cross section of the first region.

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