electrochemical cell

Abstract

A fuel battery cell (10) comprises a hydrogen electrode (2), an oxygen electrode (5), and an electrolyte (3). The electrolyte (3) has: a first portion (101) within 3 μm from a hydrogen electrode-side surface (S3); and a second portion (102) which is more than 3 μm away from the hydrogen electrode-side surface (S3). The first portion (101) and the second portion (102) each contain YSZ. The Y concentration in the first portion (101) is higher than the Y concentration in the second portion (102).

Description

[Technical Field]

[0001] The present invention relates to electrochemical cells. [Background technology]

[0002] A fuel cell is known as an example of an electrochemical cell (see, for example, Patent Document 1). A fuel cell includes a hydrogen electrode, an oxygen electrode, and an electrolyte disposed between the hydrogen electrode and the oxygen electrode. The electrolyte is made of an ion-conductive material. A typical example of the ion-conductive material is YSZ (yttria-stabilized zirconia). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-241644 Summary of the Invention [Problem to be solved by the invention]

[0004] In fuel cells, it is expected that the cell performance can be improved by reducing the resistance overvoltage of the electrolyte near the hydrogen electrode. Furthermore, reducing the resistance overvoltage of the electrolyte near the hydrogen electrode is useful not only for fuel cells but also for electrochemical cells in general, such as electrolysis cells.

[0005] An object of the present invention is to provide an electrochemical cell capable of reducing the resistance overvoltage of the electrolyte in the vicinity of the hydrogen electrode. [Means for solving the problem]

[0006] The electrochemical cell according to the present invention includes a hydrogen electrode, an oxygen electrode, and an electrolyte disposed between the hydrogen electrode and the oxygen electrode. The electrolyte has a first portion within 3 μm of the surface facing the hydrogen electrode and a second portion beyond 3 μm of the surface facing the hydrogen electrode. The first and second portions each contain yttria-stabilized zirconia. The yttrium concentration in the first portion is higher than the yttrium concentration in the second portion. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an electrochemical cell capable of reducing the resistance overvoltage in the vicinity of the hydrogen electrode in the electrolyte. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a fuel cell. [Figure 2] FIG. 2 is a cross-sectional view of a fuel cell. [Figure 3] FIG. 3 is a partially enlarged view of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Fuel cell 10) As an example of an electrochemical cell, a fuel cell 10 will be described. Fig. 1 is a perspective view of the fuel cell 10. Fig. 2 is a cross-sectional view of the fuel cell 10 taken along a gas flow path 21, which will be described later.

[0010] As shown in FIGS. 1 and 2, the fuel cell 10 includes a support substrate 20 and a plurality of power generating element sections 30.

[0011] [Support substrate 20] 1, the support substrate 20 is formed in a flat plate shape. In the support substrate 20 according to this embodiment, the dimension in the length direction (x-axis direction) is longer than the dimension in the width direction (y-axis direction), but the dimension in the width direction may be longer than the dimension in the length direction.

[0012] 2, the support substrate 20 has a first main surface S1 and a second main surface T1. The first main surface S1 and the second main surface T1 face opposite each other in the thickness direction (z-axis direction) of the support substrate 20. The first main surface S1 and the second main surface T1 support each power generation element portion 30.

[0013] The support substrate 20 is made of a porous material that does not have electronic conductivity. The support substrate 20 is made of, for example, CSZ (calcia-stabilized zirconia). Alternatively, the support substrate 20 may be made of NiO (nickel oxide) and YSZ (yttria-stabilized zirconia), NiO (nickel oxide) and YO (yttria), or MgO (magnesium oxide) and MgAlO (magnesia-alumina spinel). The porosity of the support substrate 20 can be, for example, 20% or more and 60% or less. In this specification, the porosity refers to the ratio of the area of ​​the gas phase to the total area of ​​the solid phase and the gas phase in cross-sectional observation using an SEM (scanning electron microscope).

[0014] A plurality of gas flow paths 21 are formed inside the support substrate 20. A fuel gas such as hydrogen gas is supplied to each gas flow path 21. In this embodiment, each gas flow path 21 extends in the length direction (x-axis direction) within the support substrate 20. Each gas flow path 21 penetrates the support substrate 20. It is preferable that each gas flow path 21 is arranged at substantially equal intervals.

[0015] As shown in FIG. 1, the support substrate 20 is covered with a dense layer 22. The dense layer 22 covers the surface of the support substrate 20 in areas not covered by the power generation element sections 30. The dense layer 22 prevents gas diffused within the support substrate 20 from being discharged to the outside. The dense layer 22 is made of, for example, CSZ (calcia-stabilized zirconia), YSZ (8YSZ) (yttria-stabilized zirconia), LSGM (lanthanum gallate), MgO (magnesium oxide) and MgAlO4 (magnesia-alumina spinel), GDC (gadolinium-doped ceria), or LaCrO3 (lanthanum chromite). The dense layer 22 is denser than the support substrate 20. The porosity of the dense layer 22 can be, for example, 0% or more and 7% or less.

[0016] [Power generating element section 30] 1, each power generating element section 30 is supported on the first main surface S1 or the second main surface T1 of the support substrate 20. The number of power generating element sections 30 arranged on the first main surface S1 and the number of power generating element sections 30 arranged on the second main surface T1 may be the same as or different from each other. Furthermore, the sizes of the power generating element sections 30 may be the same as or different from each other.

[0017] The power generation element sections 30 are arranged at intervals along the longitudinal direction (x-axis direction) of the gas flow channel 21. The power generation element sections 30 are electrically connected in series to one another by electrical connectors 9, which will be described later.

[0018] The power generating element section 30 includes a first current collecting section 1, a hydrogen electrode 2, an electrolyte 3, a reaction prevention layer 4, an oxygen electrode 5, a second current collecting section 6, and an interconnector .

[0019] The first current collector 1 is disposed in a recess 23 of the support substrate 20. The first current collector 1 has a first recess 11 and a second recess 12. The hydrogen electrode 2 is disposed in the first recess 11. The interconnector 7 is disposed in the second recess 12.

[0020] The first current collecting part 1 is made of an electron-conductive porous material. The first current collecting part 1 can be made of, for example, NiO (nickel oxide) and Y2O3 (yttria). Alternatively, the first current collecting part 1 may be made of NiO (nickel oxide) and 8YSZ (yttria-stabilized zirconia), or may be made of NiO (nickel oxide) and CSZ (calcia-stabilized zirconia).

[0021] The porosity of the first current collecting part 1 can be, for example, 10% or more and 50% or less. The thickness of the first current collecting part 1 can be, for example, 50 μm or more and 500 μm or less.

[0022] The hydrogen electrode 2 is placed in the first recess 11 of the first current collector 1. A fuel gas is supplied to the hydrogen electrode 2 from a gas flow channel 21 via a support substrate 20 and the first current collector 1. An electrode reaction represented by the following formula (1) occurs in the hydrogen electrode 2. H2+O 2- →H2O+2e - …(1)

[0023] The hydrogen electrode 2 is made of a porous material having electronic and ionic conductivity. The porosity of the hydrogen electrode 2 can be, for example, 10% or more and 50% or less. The thickness of the hydrogen electrode 2 can be, for example, more than 10 μm and 100 μm or less. The configuration of the hydrogen electrode 2 will be described later.

[0024] The electrolyte 3 is disposed so as to cover the hydrogen electrode 2. Both ends of the electrolyte 3 in the longitudinal direction (x-axis direction) are connected to interconnectors 7. The electrolyte 3 is made of a dense material that has ionic conductivity but no electronic conductivity. The porosity of the electrolyte 3 can be, for example, 0% or more and 7% or less. The thickness of the electrolyte 3 can be, for example, 3 μm or more and 50 μm or less. The configuration of the electrolyte 3 will be described later.

[0025] The reaction prevention layer 4 is disposed between the electrolyte 3 and the oxygen electrode 5. The reaction prevention layer 4 is in contact with both the electrolyte 3 and the oxygen electrode 5. The reaction prevention layer 4 is disposed at a position corresponding to the hydrogen electrode 2 across the electrolyte 3. The reaction prevention layer 4 is provided to prevent a reaction between the constituent materials of the electrolyte 3 and the oxygen electrode 5, resulting in the formation of a reaction layer with high electrical resistance. The reaction prevention layer 4 may be made of an ion-conductive material. The reaction prevention layer 4 may be made of, for example, GDC=(Ce,Gd)O2 (gadolinium-doped ceria). The porosity of the reaction prevention layer 4 may be, for example, 0.1% or more and 50% or less. The thickness of the reaction prevention layer 4 may be, for example, 1 μm or more and 50 μm or less.

[0026] The oxygen electrode 5 is disposed on the reaction prevention layer 4. A gas containing oxygen (e.g., air) is supplied to the oxygen electrode 5 via the second current collecting part 6. In the oxygen electrode 5, an electrode reaction represented by the following formula (2) occurs. (1 / 2)·O2+2e - →O 2- …(2)

[0027] The oxygen electrode 5 is made of an electron-conductive porous material. The oxygen electrode 5 can be made of, for example, LSCF=(La,Sr)(Co,Fe)O3 (lanthanum strontium cobalt ferrite), LSF=(La,Sr)FeO3 (lanthanum strontium ferrite), LNF=La(Ni,Fe)O3 (lanthanum nickel ferrite), or LSC=(La,Sr)CoO3 (lanthanum strontium cobaltite). The porosity of the oxygen electrode 5 can be, for example, 10% or more and 50% or less. The thickness of the oxygen electrode 5 can be, for example, 10 μm or more and 100 μm or less.

[0028] The second current collector 6 is connected to the oxygen electrode 5 and the interconnector 7. The second current collector 6 is made of a porous material having electronic conductivity. The second current collector 6 may or may not have oxygen ion conductivity. The second current collector 6 can be made of, for example, LSCF, LSC, Ag (silver), Ag-Pd (silver-palladium alloy), etc. The porosity of the second current collector 6 can be, for example, 25% or more and 50% or less. The thickness of the second current collector 6 can be, for example, 50 μm or more and 500 μm or less.

[0029] The interconnector 7 is disposed in the second recess 12 of the first current collector 1. Both ends of the interconnector 7 in the longitudinal direction (x-axis direction) are connected to the electrolyte 3. The interconnector 7 is made of a dense material having electronic conductivity. The interconnector 7 can be made of, for example, LaCrO3 (lanthanum chromite), (Sr,La)TiO3 (strontium titanate), or the like. The porosity of the interconnector 7 can be, for example, 0% or more and 7% or less. The thickness of the interconnector 7 can be, for example, 10 μm or more and 100 μm or less.

[0030] (Configuration of electrolyte 3 and hydrogen electrode 2) Next, the configuration of the electrolyte 3 and the hydrogen electrode 2 will be described. FIG. 3 is a partially enlarged view of FIG.

[0031] [Electrolyte 3] As shown in FIG. 3, the electrolyte 3 has a first portion 101 and a second portion 102.

[0032] The first portion 101 is a region of the electrolyte 3 on the hydrogen electrode 2 side. Specifically, the first portion 101 is a region of the electrolyte 3 within 3 μm of the hydrogen electrode side surface S3. Therefore, the thickness of the first portion 101 is 3 μm. The first portion 101 is connected to the hydrogen electrode 2. The hydrogen electrode side surface S3 of the electrolyte 3 is in direct contact with the electrolyte side surface S2 of the hydrogen electrode 2.

[0033] The interface between the hydrogen electrode 2 and the electrolyte 3 (i.e., the electrolyte-side surface S2 of the hydrogen electrode 2 and the hydrogen-electrode-side surface S3 of the electrolyte 3) is defined as follows. First, the brightness of a cross-sectional SEM image parallel to the thickness direction (z-axis direction in FIG. 3 ) is classified into 256 gray levels to identify the interface between the reaction prevention layer 4 and the oxygen electrode 5. Next, on the cross-sectional SEM image, a line (hereinafter referred to as the "reference line") having the same shape as the interface between the reaction prevention layer 4 and the oxygen electrode 5 is translated toward the hydrogen electrode 2. Next, the reference line is stopped at the position where it first comes into contact with nickel (Ni) contained in the hydrogen electrode 2. This reference line is the interface between the hydrogen electrode 2 and the electrolyte 3.

[0034] The second portion 102 is a region of the electrolyte 3 on the opposite side to the hydrogen electrode 2. Specifically, the second portion 102 is a region of the electrolyte 3 that is more than 3 μm from the hydrogen electrode-side surface S3. In other words, the second portion 102 is a region of the electrolyte 3 excluding the first portion 101. The second portion 102 is formed integrally with the first portion 101. The second portion 102 is connected to the reaction prevention layer 4.

[0035] The first portion 101 and the second portion 102 each contain YSZ (yttria-stabilized zirconia). The Y (yttrium) concentration in the first portion 101 is higher than the yttrium concentration in the second portion 102. This improves the ionic conductivity of the first portion 101, which is connected to the hydrogen electrode 2, of the electrolyte 3, thereby reducing the resistance overvoltage associated with ionic conduction in the vicinity of the hydrogen electrode 2 of the electrolyte 3. Furthermore, the improvement in the ionic conductivity of the three-phase interface in the vicinity of the electrolyte 3 of the hydrogen electrode 2 reduces the reaction overvoltage of the hydrogen electrode 2.

[0036] Each of the first portion 101 and the second portion 102 preferably contains YSZ as a main component. In this specification, "containing YSZ as a main component" means that the content of YSZ is 70 mol % or more.

[0037] The Y concentration in the first portion 101 can be 3.0 mol% or more and 8.0 mol% or less. The Y concentration in the first portion 101 is particularly preferably 4.5 mol% or more and 7.0 mol% or less. The Y concentration in the second portion 102 can be 2.0 mol% or more and 7.0 mol% or less. The Y concentrations in the first portion 101 and the second portion 102 can be adjusted by using a YSZ raw material containing the desired Y concentration.

[0038] The Zr concentration and Y concentration in the first portion 101 and the second portion 102 are obtained by line analysis based on atomic concentration profiles, i.e., element mapping using an EPMA (Electron Probe Micro Analyzer). Specifically, in a cross section along the thickness direction (z-axis direction in FIG. 3), line analysis is performed in the z-axis direction using the EPMA to obtain concentration distribution data for each element. Note that the concept of EPMA includes EDS (Energy Dispersive x-ray Spectroscopy).

[0039] [Hydrogen electrode 2] As shown in FIG. 3, the hydrogen electrode 2 has a third portion 103 and a fourth portion 104.

[0040] The third portion 103 is a region of the hydrogen electrode 2 on the electrolyte 3 side. Specifically, the third portion 103 is a region of the hydrogen electrode 2 within 10 μm of the electrolyte-side surface S2. Therefore, the thickness of the third portion 103 is 10 μm. The third portion 103 is connected to the electrolyte 3. The electrolyte-side surface S2 of the hydrogen electrode 2 is in direct contact with the hydrogen-electrode-side surface S3 of the electrolyte 3.

[0041] The third portion 103 preferably contains a solid solution of rare earth-added ceria-based oxide and ZrO2 (zirconia), and Ni. The solid solution of rare earth-added ceria-based oxide and zirconia has both the ionic conductivity inherent to the ceria-based oxide and the electronic conductivity inherent to ZrO2. By including a solid solution containing ZrO2 in the third portion 103 of the hydrogen electrode 2, where the electrode reaction is active, the three-phase interface (reaction field) can be increased, thereby reducing the reaction resistance of the hydrogen electrode 2.

[0042] The solid solution refers to a solid solution in which a ceria-based oxide to which a rare earth element has been added and ZrO2 are dissolved together to form a uniform solid phase. Examples of ceria-based oxides to which a rare earth element has been added include, but are not limited to, gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), and yttrium-doped ceria (YDC).

[0043] The Ce (cerium) concentration in the third portion 103 may be 8.0 mol% or more and 30 mol% or less. The rare earth element concentration in the third portion 103 may be 0.5 mol% or more and 10 mol% or less. The Zr (zirconium) concentration in the third portion 103 may be 1.0 mol% or more and 20 mol% or less. The Zr concentration in the third portion 103 is particularly preferably 5.0 mol% or more and 15 mol% or less. In the third portion 103, the Zr concentration may be lower than the Ce concentration. The Ni concentration in the third portion 103 may be 12 mol% or more and 50 mol% or less.

[0044] The fourth portion 104 is a region of the hydrogen electrode 2 on the opposite side to the electrolyte 3. Specifically, the fourth portion 104 is a region of the hydrogen electrode 2 that is more than 10 μm from the electrolyte-side surface S2. In other words, the fourth portion 104 is a region of the hydrogen electrode 2 excluding the third portion 103. The fourth portion 104 is formed integrally with the third portion 103. The fourth portion 104 is connected to the first current collecting part 1.

[0045] The fourth portion 104 contains a ceria-based oxide doped with a rare earth element and Ni. Examples of ceria-based oxides doped with a rare earth element include, but are not limited to, GDC, SDC, and YDC. The ceria-based oxide doped with a rare earth element contained in the fourth portion 104 is preferably the same as the ceria-based oxide doped with a rare earth element contained in the fourth portion 104, but may be different.

[0046] The fourth portion 104 may have a Ce concentration of 10 mol% or more and 35 mol% or less, a rare earth element concentration of 1.0 mol% or more and 15 mol% or less, and a Ni concentration of 12 mol% or more and 50 mol% or less.

[0047] The fourth portion 104 preferably contains ZrO2, which forms a solid solution with ceria-based oxide to which a rare earth element has been added. This strengthens the framework of the ceria-based oxide, which tends to become unstable in an atmosphere where hydrogen and water vapor coexist, thereby improving the durability of the hydrogen electrode 2. The Zr concentration in the fourth portion 104 can be set to 0.0 mol% or more and 15 mol% or less.

[0048] When the fourth portion 104 contains ZrO2, the Zr concentration in the third portion 103 is preferably higher than the Zr concentration in the fourth portion 104. This further increases the three-phase interface in the third portion 103, thereby further reducing the reaction resistance of the hydrogen electrode 2.

[0049] The Ce concentration, rare earth element concentration, Zr concentration, and Ni concentration in the third portion 103 and the fourth portion 104 are obtained by line analysis using the above-mentioned atomic concentration profile.

[0050] (Modification of the embodiment) Although the embodiments of the present invention have been described above, the present invention is not limited to these, and various modifications are possible without departing from the spirit of the present invention.

[0051] In the above embodiment, a so-called horizontal stripe type fuel cell has been described as an example of a fuel cell, but the electrochemical cell is not limited to this. The present invention can also be applied to an electrochemical cell in which a hydrogen electrode and an oxygen electrode are arranged on either side of an electrolyte layer.

[0052] An electrochemical cell is a general term for an element in which a pair of electrodes is arranged so that an electromotive force is generated from an overall oxidation-reduction reaction in order to convert electrical energy into chemical energy, and an element for converting chemical energy into electrical energy.

[0053] Examples of electrochemical cells include horizontally striped fuel cells, vertically striped fuel cells, flat plate fuel cells, cylindrical fuel cells, and electrolysis cells that generate hydrogen by utilizing the electrolysis reaction of water. 2- (oxygen ion) was used as the carrier, but OH - (hydroxide ion) or proton may be used as the carrier. [Example]

[0054] Examples of the electrochemical cell according to the present invention will be described below, but the present invention is not limited to these examples.

[0055] (Comparative Example) A fuel cell of the comparative example was fabricated as follows: In the fuel cell described below, ten power generating element portions were formed on each main surface of the support substrate.

[0056] First, MgO powder, Y2O3 powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for forming the support substrate. This slurry for forming the support substrate was extruded and cut to produce a green body for the support substrate.

[0057] Next, NiO powder, YO powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the first current collector. This slurry for the first current collector was applied to the first recess of the molded body of the support substrate by screen printing to form a molded body for the first current collector.

[0058] Next, NiO powder, YSZ powder, binder, pore former, and dispersant were mixed in a ball mill to prepare slurry for the hydrogen electrode. This slurry for the hydrogen electrode was applied to the second recess of the first current collector by screen printing to form a green body for the hydrogen electrode.

[0059] Next, LaCrO powder and a binder were added and mixed in a ball mill to prepare a slurry for the interconnector. This slurry for the interconnector was applied to the third recess of the first current collector by screen printing to form a green body for the interconnector.

[0060] Next, the YSZ powder and the binder were mixed in a ball mill to prepare a slurry for the electrolyte, which was then applied to a support substrate by screen printing to cover the substrate, thereby forming a green body for the electrolyte.

[0061] Next, the GDC powder and binder were mixed in a ball mill to prepare a slurry for the reaction prevention layer, which was then applied to the electrolyte compact by screen printing to form a reaction prevention film.

[0062] Next, the laminate of each compact was co-fired (1300°C, 5 hours) to produce a co-fired body of the support substrate, first current collector, hydrogen electrode, interconnector, electrolyte, and reaction prevention layer.

[0063] Next, the LSCF powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the oxygen electrode. This slurry for the oxygen electrode was applied to the reaction preventive film by screen printing to form a compact for the oxygen electrode.

[0064] Next, the LSCF powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the second current collector. This slurry for forming the second current collector was applied by screen printing from the oxygen electrode to the interconnector to form a green body for the second current collector.

[0065] Next, the compacts of the oxygen electrode and second current collecting part were fired (1050°C, 3 hours).

[0066] Examples 1 to 6 Fuel cells of Examples 1 to 6 (see FIGS. 1 to 3) were produced in the same manner as in the comparative example, except that the electrolyte had a two-layer structure.

[0067] Specifically, a slurry for the first portion was prepared by mixing YSZ powder and a binder in a ball mill. At this time, the Y concentration in the YSZ powder was changed for each example, thereby adjusting the Y concentration in the first portion as shown in Table 1. The slurry for the first portion was then applied by screen printing to cover a support substrate, thereby forming a compact for the first portion of the electrolyte.

[0068] Next, the YSZ powder and binder were mixed in a ball mill to prepare a slurry for the second portion. The Y concentration in the YSZ powder was varied for each example, so that the Y concentration in the second portion of Examples 1 to 5 was the same as that in the electrolyte of the comparative example, and the Y concentration in the second portion of Example 6 was lower than that in the electrolyte of the comparative example, as shown in Table 1. The slurry for the second portion was then applied to the compact of the first portion by screen printing to form a compact of the second portion of the electrolyte.

[0069] Example 7 A fuel cell of Example 7 was fabricated in the same manner as in Example 1, except that the hydrogen electrode had a two-layer structure and ZrO2 was added only to the third portion.

[0070] Specifically, NiO powder, YSZ powder, ZrO powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the third portion, which was then applied to the second recess of the first current collector by screen printing to form a compact for the third portion of the hydrogen electrode.

[0071] Next, NiO powder, YSZ powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the fourth portion, which was then applied to the green body for the third portion by screen printing to form a green body for the fourth portion of the hydrogen electrode.

[0072] Examples 8 to 12 Fuel cells of Examples 8 to 12 were produced in the same manner as in Example 7, except that ZrO2 was also added to the fourth portion of the hydrogen electrode.

[0073] Specifically, a slurry for the third portion was prepared by mixing NiO powder, YSZ powder, ZrO2 powder, a binder, a pore-forming material, and a dispersing material in a ball mill. The Zr concentration in the third portion was adjusted by changing the Zr concentration in the ZrO2 powder for each example, as shown in Table 1. The slurry for the third portion was then applied to the second recess of the first current collector by screen printing to form a compact for the third portion of the hydrogen electrode.

[0074] Next, NiO powder, YSZ powder, ZrO powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the fourth portion. The amount of ZrO powder added was the same as that for the third portion of Example 7. The slurry for the fourth portion was then applied to the green body for the third portion by screen printing to form a green body for the fourth portion of the hydrogen electrode.

[0075] (Initial performance evaluation) The fuel cells of the comparative example and examples 1 to 12 were heated to 750°C, and a mixed gas of water vapor and hydrogen (mixing ratio 50:50) was supplied to the hydrogen electrode, and air was supplied to the oxygen electrode.2 While sweeping the current value, the reactive overvoltage was obtained by subtracting the resistive overvoltage from the total overvoltage using the current interruption method. Then, the reactive overvoltage suppression rate was calculated using the following formula (3) with the reactive overvoltage of the comparative example as the standard.

[0076] Reaction overvoltage suppression rate (%) of each example = 100 × ((reaction overvoltage of comparative example) - (reaction overvoltage of each example)) / (reaction overvoltage of comparative example) (3)

[0077] The calculated values ​​of the reaction overpotential suppression rate and their evaluation are shown in Table 1. In Table 1, a reaction overpotential suppression rate of 25% or more was evaluated as "A," a rate of 20% or more but less than 25% was evaluated as "B," a rate of 10% or more but less than 20% was evaluated as "C," and a rate of less than 10% was evaluated as "D."

[0078] (Thermal cycle test) A mixed gas of Ar and hydrogen (hydrogen was 4% relative to Ar) was supplied to the hydrogen electrode to maintain a reducing atmosphere. One cycle consisted of heating from room temperature to 750°C in 2 hours and then cooling to room temperature in 4 hours, and this was repeated 10 times.

[0079] The cross section of the hydrogen electrode was then observed using an FE-SEM to determine whether cracks of 3 μm or more in length had occurred in the hydrogen electrode. In Table 1, hydrogen electrodes with no cracks or with cracks of less than 3 μm in length were rated "Good," and hydrogen electrodes with cracks of 3 μm or more were rated "Poor."

[0080] [Table 1]

[0081] As shown in Table 1, in Examples 1 to 12 in which the electrolyte had a two-layer structure and the Y concentration in the first portion was higher than that in the second portion, the initial performance was improved compared to the comparative example. This result was achieved because the ionic conductivity of the first portion of the electrolyte connected to the hydrogen electrode was improved, and the ionic conductivity of the three-phase interface in the hydrogen electrode near the electrolyte was also improved.

[0082] Furthermore, in Examples 2 to 4 and 6 in which the Y concentration in the first portion was set to 4.5 mol % or more and 7.0 mol % or less, the initial performance was improved more than in Examples 1 and 5.

[0083] Furthermore, in Examples 7 and 8, in which the third portion of the hydrogen electrode contained Ni and a solid solution of a ceria-based oxide and ZrO2 with a rare earth element added thereto, the initial performance was improved more than in Example 1. This result was obtained because the three-phase interface (reaction field) was increased in the third portion 103. The presence of a solid solution of a ceria-based oxide and ZrO2 with a rare earth element added thereto in the third portion was confirmed by observing Zr and CeO2 at the same position in element mapping by area analysis using EDX (energy dispersive X-ray analyzer).

[0084] Furthermore, in Examples 8 to 12, in which the fourth portion of the hydrogen electrode contained Ni and a solid solution of a ceria-based oxide and ZrO2 to which a rare earth element had been added, durability in a thermal cycle test was improved compared to Example 1. This result was obtained because the framework of the ceria-based oxide in the fourth portion was strengthened by the addition of ZrO2. The presence of a solid solution of a ceria-based oxide and ZrO2 to which a rare earth element had been added in the second portion was confirmed by the fact that Zr and CeO2 were observed at the same position in elemental mapping by area analysis using EDX.

[0085] Furthermore, in Examples 9 to 12, in which both the third and fourth portions of the hydrogen electrode contained ZrO2 and the zirconium concentration in the third portion was higher than that in the fourth portion, the initial performance was improved more than in Examples 7 and 8. This result was obtained because the three-phase interface in the third portion was increased.

[0086] Furthermore, among Examples 9 to 12, Examples 10 and 11 in which the zirconium concentration in the third portion was set to 5 mol % or more and 15 mol % or less were able to further improve the initial performance. [Explanation of symbols]

[0087] 10 Fuel cell 20 Support substrate 30 Power generating element section 1 First current collecting section 2 Hydrogen electrode 103 Part 3 104 Part 4 3 Electrolytes 101 Part 1 102 Part 2 4. Reaction prevention layer 5 Oxygen electrode 6 Second current collecting section 7 Interconnector

Claims

1. A hydrogen electrode, an oxygen electrode; an electrolyte disposed between the hydrogen electrode and the oxygen electrode; a reaction prevention layer disposed between the oxygen electrode and the electrolyte; Equipped with the electrolyte has a first portion within 3 μm from the hydrogen electrode side surface and a second portion more than 3 μm from the hydrogen electrode side surface, each of the first portion and the second portion contains 70 mol% or more of yttria-stabilized zirconia; a concentration of yttrium in the first portion is higher than a concentration of yttrium in the second portion; The yttrium concentration in the first portion is 4.5 mol% or more and 7.0 mol% or less. Electrochemical cell.

2. the hydrogen electrode has a third portion within 10 μm from the electrolyte-side surface and a fourth portion more than 10 μm from the electrolyte-side surface, the third portion contains nickel and a solid solution of a rare earth element-added ceria-based oxide and zirconia; 10. The electrochemical cell of claim 1.

3. the fourth portion contains nickel and a solid solution of a ceria-based oxide and zirconia to which a rare earth element has been added; 3. The electrochemical cell of claim 2.

4. the zirconium concentration in the third portion is higher than the zirconium concentration in the fourth portion; 4. The electrochemical cell of claim 3.

5. The zirconium concentration in the third portion is 5.0 mol% or more and 15 mol% or less.

5. The electrochemical cell of claim 4.

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