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

electrochemical cell

[0001] The present invention relates to electrochemical cells.

[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).

[0003] JP 2013-241644 A

[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.

[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 hydrogen electrode-side surface and a second portion beyond 3 μm of the hydrogen electrode-side surface. The first portion and the second portion each contain yttria-stabilized zirconia. The yttrium concentration in the first portion is higher than the yttrium concentration in the second portion.

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

[0008] 1 is a perspective view of a fuel cell, FIG 2 is a cross-sectional view of the fuel cell, and FIG 3 is an enlarged view of a portion of FIG 2.

[0009] (Fuel Cell 10) A fuel cell 10 will be described as an example of an electrochemical cell. 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] 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 electron conductivity. For example, the support substrate 20 is made of calcia-stabilized zirconia (CSZ). Alternatively, the support substrate 20 may be made of nickel oxide (NiO) and yttria-stabilized zirconia (YSZ), or may be made of nickel oxide (NiO) and yttria-stabilized zirconia (YSZ). ２ O ３ (yttria), or MgO (magnesium oxide) and MgAl ２ O ４ The support substrate 20 may be composed of a magnesia alumina spinel. The porosity of the support substrate 20 may be, for example, 20% or more and 60% or less. In this specification, the porosity is the ratio of the area of ​​the gas phase to the total area of ​​the solid phase and the gas phase when a cross section is observed using a scanning electron microscope (SEM).

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

[0015] 1 , the support substrate 20 is covered with a dense layer 22. The dense layer 22 covers the areas of the surface of the support substrate 20 that are not covered by the power generation element sections 30. The dense layer 22 prevents gases 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 MgAlO ４ (magnesia alumina spinel), GDC (gadolinium-doped ceria) or LaCrO ３ (lanthanum chromite) or the like. 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] 1 , each power generating element unit 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 units 30 arranged on the first main surface S1 and the number of power generating element units 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 units 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 path 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 7 .

[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 portion 1 is made of a porous material having electron conductivity. For example, the first current collecting portion 1 is made of a material such as NiO (nickel oxide) and Y ２ O ３Alternatively, the first current collecting portion 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% to 50%. The thickness of the first current collecting part 1 can be, for example, 50 μm to 500 μm.

[0022] The hydrogen electrode 2 is disposed 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: H ２ +O ２－ →H ２ O + 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% to 50%. The thickness of the hydrogen electrode 2 can be, for example, more than 10 μm to 100 μm. 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 the interconnector 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 the formation of a reaction layer with high electrical resistance due to a reaction between the constituent materials of the electrolyte 3 and the oxygen electrode 5. The reaction prevention layer 4 can be made of an ion-conductive material. For example, the reaction prevention layer 4 is made of GDC=(Ce, Gd)O. ２ The reaction prevention layer 4 may be made of 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 collector 6. At the oxygen electrode 5, an electrode reaction occurs, which is expressed by the following formula (2): (1 / 2)·O ２ +2e － →O ２－ …(2)

[0027] The oxygen electrode 5 is made of a porous material having electron conductivity, for example, LSCF=(La, Sr)(Co, Fe)O ３ (lanthanum strontium cobalt ferrite), LSF = (La,Sr)FeO ３ (lanthanum strontium ferrite), LNF = La(Ni,Fe)O ３ (lanthanum nickel ferrite), LSC = (La,Sr)CoO ３ The oxygen electrode 5 may be made of, for example, lanthanum strontium cobaltite (lanthanum strontium cobaltite). The porosity of the oxygen electrode 5 may be, for example, 10% to 50%. The thickness of the oxygen electrode 5 may be, for example, 10 μm to 100 μm.

[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 length 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 is made of, for example, LaCrO ３ (Lanthanum chromite), (Sr,La)TiO ３ (strontium titanate), etc. 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. 2 .

[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 gradations 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 of the electrolyte 3 connected to the hydrogen electrode 2, thereby reducing the resistance overvoltage associated with ionic conduction in the vicinity of the hydrogen electrode 2 in the electrolyte 3. Furthermore, improving the ionic conductivity of the three-phase interface in the vicinity of the electrolyte 3 in 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 YSZ content 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 using atomic concentration profiles, i.e., element mapping using an EPMA (Electron Probe Micro Analyzer). Specifically, concentration distribution data for each element is obtained by performing line analysis in the z-axis direction using an EPMA on a cross section along the thickness direction (z-axis direction in FIG. 3). Note that EPMA is a concept that 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 is made of a ceria-based oxide and ZrO ２ The solid solution of ceria-based oxide and zirconia to which a rare earth element is added preferably contains Ni and has ionic conductivity derived from the ceria-based oxide and ZrO ２ In this way, the third portion 103 of the hydrogen electrode 2 where the electrode reaction is active is provided with ZrO ２By including a solid solution containing the above, the three-phase interface (reaction field) can be increased, and therefore the reaction resistance of the hydrogen electrode 2 can be reduced.

[0042] The solid solution is a mixture of ceria-based oxides containing rare earth elements and ZrO ２ 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 collector 1.

[0045] The fourth portion 104 includes 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 is a ZrO solid solution containing a rare earth element and a ceria-based oxide. ２ This strengthens the skeleton 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] The fourth portion 104 is ZrO ２ In the case where the third portion 103 contains Zr, the Zr concentration in the third portion 103 is preferably higher than the Zr concentration in the fourth portion 104. This can further increase 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] (Modifications of the Embodiment) Although the embodiment of the present invention has 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 ions) or protons may be used as carriers.

[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 a 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, Y ２ O ３ The powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for forming a support substrate, which was then extruded and cut to produce a molded body for the support substrate.

[0057] Next, NiO powder, Y ２ O ３ The powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the first current collector. The 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 a slurry for the hydrogen electrode, which was then 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 ３The powder and 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 molded body of 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 the 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 prepare 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, which was then applied to the reaction preventive film by screen printing to form a green body 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 the second current collector were fired (1050° C., 3 hours).

[0066] Examples 1 to 6 Fuel cells of Examples 1 to 6 (see FIGS. 1 to 3) were fabricated 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 first portion was adjusted by changing the Y concentration contained in the YSZ powder for each example, 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, a slurry for the second portion was prepared by mixing the YSZ powder and binder in a ball mill. The Y concentration in the YSZ powder was changed 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) The hydrogen electrode has a two-layer structure, and ZrO is used only in the third part. ２ A fuel cell of Example 7 was produced in the same manner as in Example 1, except that the above was added.

[0070] Specifically, NiO powder, YSZ powder, ZrO ２ The 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) ZrO was also used in the fourth part of the hydrogen electrode. ２ Fuel cells of Examples 8 to 12 were produced in the same manner as in Example 7, except that the above was added.

[0073] Specifically, NiO powder, YSZ powder, ZrO ２ The powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the third part. ２ The Zr concentration in the third portion was adjusted by changing the Zr concentration in the powder for each example, as shown in Table 1. The slurry for the third portion was then applied to the inside of 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 ２ The powder, binder, pore former, and dispersant were mixed in a ball mill to prepare a slurry for the fourth part. ２ The amount of powder added was the same as that of the third portion in Example 7. The slurry for the fourth portion was then applied onto 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 reference.

[0076] Reactive overvoltage suppression rate (%) of each example = 100 × ((reactive overvoltage of comparative example) - (reactive overvoltage of each example)) / (reactive overvoltage of comparative example) ... (3)

[0077] The calculated values ​​of the reactive overpotential inhibition rate and their evaluation are shown in Table 1. In Table 1, a reactive overpotential inhibition 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 was repeated 10 times, in which the temperature was increased from room temperature to 750°C over 2 hours and then decreased to room temperature over 4 hours.

[0079] The cross section of the hydrogen electrode was then observed with an FE-SEM to check 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 evaluated as "Good," and hydrogen electrodes with cracks of 3 μm or more were evaluated as "Poor."

[0080]

[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] The third part of the hydrogen electrode is made of ceria-based oxide and ZrO ２ In Examples 7 and 8, which contained a solid solution of ZrO2 and Ni, the initial performance was improved more than in Example 1. Such results were obtained because the three-phase interface (reaction field) was increased in the third portion 103. The presence of a solid solution of ZrO2 and a ceria-based oxide to which a rare earth element was added in the third portion was confirmed by elemental mapping by area analysis using EDX (energy dispersive X-ray analyzer). ２ This was confirmed by observing the same position.

[0084] The fourth part of the hydrogen electrode is made of ceria-based oxide and ZrO２ In Examples 8 to 12 containing a solid solution of ZrO and Ni, durability in the thermal cycle test was improved compared to Example 1. This result was obtained because ２ This is because the addition of ZrO strengthened the framework of the ceria-based oxide in the fourth portion. ２ The presence of a solid solution of Zr and CeO in the second portion was confirmed by elemental mapping using area analysis using EDX. ２ This was confirmed by observing the same position.

[0085] In addition, both the third and fourth portions of the hydrogen electrode are made of ZrO. ２ In Examples 9 to 12, in which the zirconium concentration in the third portion was higher than the zirconium concentration 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.

[0087] REFERENCE SIGNS LIST 10 fuel cell 20 support substrate 30 power generating element section 1 first current collecting section 2 hydrogen electrode 103 third section 104 fourth section 3 electrolyte 101 first section 102 second section 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 a 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 comprises yttria stabilized zirconia; a concentration of yttrium in the first portion is greater 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 ceria-based oxide and zirconia to which a rare earth element has been added.

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.

10. The electrochemical cell of claim 1.

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.