Electrochemical cell

Abstract

According to the present invention, an electrolysis cell (1) is provided with a hydrogen electrode layer (5), an electrolyte layer (6), an intermediate layer (7), and a reaction prevention layer (8). The electrolyte layer (6) is composed of YSZ. The reaction prevention layer (8) is composed of GDC. The intermediate layer (7) has a first intermediate layer (71) that is formed on the electrolyte layer (6), and a second intermediate layer (72) that is sandwiched between the first intermediate layer (71) and the reaction prevention layer (8). Each of the first intermediate layer (71) and the second intermediate layer (72) is composed of YSZ and GDC. In the first intermediate layer (71), the Zr content is higher than the cerium content. In the second intermediate layer (72), the Zr content is equal to or less than the Ce content. When the Gd content is subjected to line analysis along the thickness direction of the intermediate layer (7), the position at which the highest Gd content is acquired is present in the first intermediate layer (71).

Description

electrochemical cell

[0001] The present invention relates to electrochemical cells.

[0002] Conventionally, there has been known an electrochemical cell (electrolysis cell or fuel cell) that includes a hydrogen electrode layer, an oxygen electrode layer, an electrolyte layer disposed between the hydrogen electrode layer and the oxygen electrode layer, and a reaction prevention layer disposed between the oxygen electrode layer and the electrolyte layer (see, for example, Patent Document 1).

[0003] The electrolyte layer is made of YSZ (yttria-stabilized zirconia) or ScSZ (scandia-stabilized zirconia). The reaction prevention layer is made of GDC (gadolinium-doped ceria) or SDC (samarium-doped ceria). The reaction prevention layer prevents the formation of a high-resistance layer between the oxygen electrode layer and the electrolyte layer.

[0004] JP 2017-174813 A

[0005] When the compacts for the electrolyte layer and the reaction prevention layer are simultaneously formed by firing or heat treatment, an intermediate layer is formed between the two layers due to the mutual diffusion of the constituent materials of the two layers. In the region of this intermediate layer facing the electrolyte layer, the zirconium content is higher than the cerium content, which tends to result in particularly low ionic conductivity, limiting the improvement of the performance of the electrochemical cell.

[0006] An object of the present invention is to provide an electrochemical cell that can improve performance.

[0007] An electrochemical cell according to a first aspect of the present invention includes a hydrogen electrode layer, an oxygen electrode layer, an electrolyte layer disposed between the hydrogen electrode layer and the oxygen electrode layer, a reaction prevention layer disposed between the oxygen electrode layer and the electrolyte layer, and an intermediate layer disposed between the electrolyte layer and the reaction prevention layer. The electrolyte layer is made of zirconia stabilized with yttria or scandia. The reaction prevention layer is made of ceria doped with gadolinium or samarium. The intermediate layer includes a first intermediate layer formed on the electrolyte layer and a second intermediate layer sandwiched between the first intermediate layer and the reaction prevention layer. The first intermediate layer and the second intermediate layer are each made of zirconia stabilized with yttria or scandia and ceria doped with gadolinium or samarium. The zirconium content in the first intermediate layer is higher than the cerium content. The zirconium content in the second intermediate layer is equal to or lower than the cerium content. When the content of the doping element is analyzed line-wise along the thickness direction of the intermediate layer, the position where the highest content of the doping element is obtained is located within the first intermediate layer.

[0008] An electrochemical cell according to a second aspect of the present invention is the electrochemical cell according to the second aspect, wherein the thickness of the first intermediate layer is 5 μm or less.

[0009] According to the present invention, it is possible to provide an electrochemical cell that can improve performance.

[0010] Fig. 1 is a cross-sectional view of an electrolytic cell according to an embodiment. Fig. 2 is a graph showing the content of elements contained in the electrolyte layer, intermediate layer, and reaction prevention layer. Fig. 3 is a graph showing the relationship between the thickness of the first intermediate layer and the rate of increase in sheet resistance in the electrolyte layer for examples and comparative examples.

[0011] (Electrolysis Cell 1) FIG. 1 is a cross-sectional view of an electrolysis cell 1 according to an embodiment.

[0012] The electrolysis cell 1 has a hydrogen electrode layer 5 (cathode), an electrolyte layer 6, an intermediate layer 7, a reaction prevention layer 8, and an oxygen electrode layer 9 (anode).

[0013] The hydrogen electrode layer 5, electrolyte layer 6, intermediate layer 7, reaction prevention layer 8, and oxygen electrode layer 9 are stacked in this order in the Z-axis direction, which is perpendicular to the X-axis direction and the Y-axis direction. The Z-axis direction is substantially the same as the thickness direction, which will be described later.

[0014] [Hydrogen Electrode Layer 5] The hydrogen electrode layer 5 functions as a support for the electrolytic cell 1. The thickness of the hydrogen electrode layer 5 may be greater than the thickness of each of the electrolyte layer 6, the intermediate layer 7, the reaction prevention layer 8, and the oxygen electrode layer 9. The thickness of the hydrogen electrode layer 5 is not particularly limited, but may be, for example, 1 μm or more and 500 μm or less.

[0015] A source gas is supplied to the hydrogen electrode layer 5. The source gas contains at least H ２ Contains O.

[0016] The raw material gas is H ２ When only O is contained, the hydrogen electrode layer 5 converts H from the raw material gas according to the electrochemical reaction of water electrolysis shown in the following formula (1): ２ Generate.

[0017] Hydrogen electrode layer 5: H ２ O + 2e － →H ２ +O ２－ ...(1)

[0018] The raw material gas is H ２ O plus CO ２ In this case, the hydrogen electrode layer 5 converts H from the source gas according to the co-electrolytic electrochemical reactions shown in the following formulas (2), (3), and (4). ２ , CO and O ２－ Generate.

[0019] Hydrogen electrode layer 5: CO ２ +H ２ O+4e － →CO+H ２ +20 ２－ ... (2) H ２ Electrochemical reaction of O: H ２ O + 2e － →H ２ +O ２－ ... (3) CO ２ Electrochemical reaction of: CO ２ +2e － →CO+O ２－ ...(4)

[0020] The hydrogen electrode layer 5 is a porous body having gas diffusibility and electrical conductivity, and contains an electrically conductive material and an oxide ion conductive material.

[0021] As the conductive material, metal materials such as Ni (nickel) and Fe (iron), conductive ceramic materials, etc. can be used. In the case of co-electrolysis, Ni is used as the catalyst for the generated H ２ and CO contained in the raw material gas ２ It also functions as a thermal catalyst, promoting the thermal reaction with HCl to maintain an appropriate gas composition for methanation and reverse water-gas shift reactions.

[0022] When the hydrogen electrode layer 5 contains a metal material as a conductive material, the metal material exists in an oxide state (for example, NiO) in an oxidizing atmosphere and in a metallic state (for example, Ni) in a reducing atmosphere.

[0023] Examples of oxide ion conductive materials include YSZ (yttria-stabilized zirconia), CSZ (calcia-stabilized zirconia), ScSZ (scandia-stabilized zirconia), GDC (gadolinium-doped ceria), SDC (samarium-doped ceria), and (La,Sr)(Cr,Mn)O. ３ , (La,Sr)TiO ３ , Sr ２ (Fe, Mo) ２ O ６ , (La, Sr)VO ３ , (La,Sr)FeO ３ , LDC (lanthanum doped ceria), LSGM (lanthanum gallate), and a mixed material of two or more of these can be used.

[0024] The hydrogen electrode layer 5 may have a multilayer structure composed of different compositions. For example, the hydrogen electrode layer 5 may have a two-layer structure composed of a hydrogen electrode active layer disposed on the electrolyte layer 6 side and a hydrogen electrode current collecting layer disposed on the opposite side of the electrolyte layer 6.

[0025] The porosity of the hydrogen electrode layer 5 is not particularly limited, but can be, for example, 5% or more and 70% or less.

[0026] The method for forming the hydrogen electrode layer 5 is not particularly limited, and may be a firing method, a spray coating method (such as a thermal spraying method, an aerosol deposition method, an aerosol gas deposition method, a powder jet deposition method, a particle jet deposition method, or a cold spray method), a PVD method (such as a sputtering method or a pulsed laser deposition method), or a CVD method.

[0027] [Electrolyte Layer 6] The electrolyte layer 6 is disposed between the hydrogen electrode layer 5 and the oxygen electrode layer 9. More specifically, the electrolyte layer 6 is sandwiched between the hydrogen electrode layer 5 and a first intermediate layer (described later). The electrolyte layer 6 is connected to both the hydrogen electrode layer 5 and the first intermediate layer.

[0028] The electrolyte layer 6 absorbs the O generated in the hydrogen electrode layer 5. ２－ The electrolyte layer 6 is made of yttria-stabilized zirconia (YSZ). Examples of YSZ that can be used include 3YSZ, 4YSZ, 8YSZ, 10YSZ, 6ScSz, and 10ScCeSZ, as well as mixtures of two or more of these.

[0029] The porosity of the electrolyte layer 6 is not particularly limited, but may be, for example, 0.1% to 7%. The thickness of the electrolyte layer 6 is not particularly limited, but may be, for example, 1 μm to 100 μm.

[0030] [Intermediate Layer 7] The intermediate layer 7 is disposed between the electrolyte layer 6 and the reaction prevention layer 8. As shown in FIG.

[0031] The first intermediate layer 71 is formed on the electrolyte layer 6. The first intermediate layer 71 is sandwiched between the electrolyte layer 6 and the second intermediate layer 72. The first intermediate layer 71 is connected to both the electrolyte layer 6 and the second intermediate layer 72.

[0032] The second intermediate layer 72 is formed on the first intermediate layer 71. The second intermediate layer 72 is sandwiched between the first intermediate layer 71 and the reaction prevention layer 8. The second intermediate layer 72 is connected to both the first intermediate layer 71 and the reaction prevention layer 8.

[0033] The first intermediate layer 71 and the second intermediate layer 72 are each made of the constituent material of the electrolyte layer 6 and the constituent material of the reaction prevention layer 8. Specifically, the first intermediate layer 71 and the second intermediate layer 72 are each made of zirconia stabilized with yttria or scandia (YSZ or ScSZ) and ceria doped with gadolinium or samarium (CeO ２ ) and is composed of.

[0034] The porosity of the first intermediate layer 71 is not particularly limited, but may be, for example, 0.1% to 15%. The porosity of the second intermediate layer 72 is not particularly limited, but may be, for example, 0.1% to 50%.

[0035] The detailed configurations of the first intermediate layer 71 and the second intermediate layer 72 will be described later.

[0036] [Reaction prevention layer 8] The reaction prevention layer 8 is disposed between the electrolyte layer 6 and the oxygen electrode layer 9. More specifically, the reaction prevention layer 8 is sandwiched between the intermediate layer 7 and the oxygen electrode layer 9. The reaction prevention layer 8 is connected to both the second intermediate layer 72 of the intermediate layer 7 and the oxygen electrode layer 9. The reaction prevention layer 8 prevents the constituent elements of the electrolyte layer 6 from reacting with the constituent elements of the oxygen electrode layer 9 to form a layer with high electrical resistance.

[0037] The reaction prevention layer 8 is made of ceria doped with gadolinium or samarium as a doping element. Specifically, the reaction prevention layer 8 can be made of gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), or a mixed material of two or more of these.

[0038] The porosity of the reaction prevention layer 8 is not particularly limited, but may be, for example, 0.1% to 50%. The thickness of the reaction prevention layer 8 is not particularly limited, but may be, for example, 1 μm to 50 μm.

[0039] The method for forming the reaction prevention layer 8 is not particularly limited, and may be a baking method, a spray coating method, a PVD method, a CVD method, or the like.

[0040] [Oxygen Electrode Layer 9] The oxygen electrode layer 9 is disposed on the opposite side of the electrolyte layer 6 from the hydrogen electrode layer 5. The oxygen electrode layer 9 is formed on the reaction prevention layer 8.

[0041] The oxygen electrode layer 9 reacts with O 2 transferred from the hydrogen electrode layer 5 through the electrolyte layer 6 in accordance with the chemical reaction of the following formula (5): ２－ From O ２ Generate.

[0042] Oxygen electrode layer 9: 2O ２－ →O ２ +4e － ...(5)

[0043] The oxygen electrode layer 9 is made of a porous material having oxide ion conductivity and electron conductivity, such as (La, Sr)(Co, Fe)O. ３ , (La,Sr)FeO ３ , La(Ni,Fe)O ３ , (La,Sr)CoO ３ , and (Sm,Sr)CoO ３ The insulating layer 10 may be made of a composite material of one or more of the above and an oxide ion conductive material (such as GDC).

[0044] The porosity of the oxygen electrode layer 9 is not particularly limited, but may be, for example, 20% to 60%. The thickness of the oxygen electrode layer 9 is not particularly limited, but may be, for example, 1 μm to 100 μm.

[0045] The method for forming the oxygen electrode layer 9 is not particularly limited, and may be a firing method, a spray coating method, a PVD method, a CVD method, or the like.

[0046] (Configuration of Intermediate Layer 7) The intermediate layer 7 is composed of a first intermediate layer 71 and a second intermediate layer 72. The first intermediate layer 71 is connected to the electrolyte layer 6, and the second intermediate layer 72 is connected to the reaction prevention layer 8.

[0047] 2 is a graph showing the contents of elements contained in the electrolyte layer 6, intermediate layer 7, and reaction prevention layer 8. FIG. 2 illustrates an example in which the electrolyte layer 6 is mainly composed of YSZ (yttria-stabilized zirconia), the reaction prevention layer 8 is mainly composed of GDC (ceria doped with gadolinium), and the intermediate layer 7 is mainly composed of YSZ and GDC. Accordingly, FIG. 2 shows the respective contents of Zr (zirconium), Ce (cerium), Y (yttrium), and Gd (gadolinium). Gd is an example of a doping element added to the ceria that constitutes the reaction prevention layer 8.

[0048] The content of each element shown in Fig. 2 is obtained by performing line analysis in the thickness direction using EDS (Energy Dispersive X-ray Spectroscopy) on cross sections along the thickness direction of the electrolyte layer 6, intermediate layer 7, and reaction prevention layer 8. The direction is perpendicular to the surface of the electrolyte layer 6 on the side of the hydrogen electrode layer 5. When specifying the thickness direction, an approximate straight line representing the surface on the side of the hydrogen electrode layer 5, which is obtained by the least squares method, is used.

[0049] The electrolyte layer 6 is a region where the Zr content is 75 mol% or more. The reaction prevention layer 8 is a region where the Ce content is 75 mol% or more. The intermediate layer 7 is a region where the Zr content is less than 75 mol% and the Ce content is also less than 75 mol%. When the Zr content passes through 75 mol% multiple times, the line where the Zr content first passes through 75 mol% as viewed from the reaction prevention layer 8 side is defined as the boundary between the electrolyte layer 6 and the intermediate layer 7. When the Ce content passes through 75 mol% multiple times, the line where the Ce content first passes through 75 mol% as viewed from the electrolyte layer 6 side is defined as the boundary between the intermediate layer 7 and the reaction prevention layer 8.

[0050] The first intermediate layer 71 is a region of the intermediate layer 7 where the Zr content is higher than the Ce content. Therefore, as shown in FIG. 2 , the first intermediate layer 71 is a region of the intermediate layer 7 that is closer to the electrolyte layer 6 than the intersection P1 between the curves showing the Zr content and the Ce content. The second intermediate layer 72 is a region of the intermediate layer 7 where the Zr content is lower than the Ce content. Therefore, as shown in FIG. 2 , the second intermediate layer 72 is a region of the intermediate layer 7 that is closer to the reaction prevention layer 8 than the intersection P1 between the curves showing the Zr content and the Ce content. Note that the intersection P1 is included in the second intermediate layer 72.

[0051] In the first intermediate layer 71, the Zr content tends to increase toward the electrolyte layer 6, and the Ce content tends to decrease toward the electrolyte layer 6. In the second intermediate layer 72, the Zr content tends to decrease toward the reaction prevention layer 8, and the Ce content tends to increase toward the reaction prevention layer 8.

[0052] 2 , when the content of Gd, a doping element added to the ceria constituting the reaction prevention layer 8, is analyzed line-by-line along the thickness direction of the intermediate layer 7, the position P2 at which the highest Gd content is obtained is located within the first intermediate layer 71. Thus, by highly doping the first intermediate layer 71, which has a relatively higher Zr content than the second intermediate layer 72, with Gd, which has a large ionic radius, the lattice distortion in the first intermediate layer 71 can be increased. Therefore, many oxygen vacancies can be introduced into the first intermediate layer 71, thereby improving the ionic conductivity of the first intermediate layer 71. As a result, the performance of the electrolysis cell 1 can be improved.

[0053] This effect is not limited to when Gd is added to the ceria that constitutes the reaction prevention layer 8, but is also obtained when Sm (samarium) is added to the ceria. The same effect is also obtained when the electrolyte layer 6 is made of ScSZ, not just when it is made of YSZ. Furthermore, the same effect is also obtained when the intermediate layer 7 is made of ScSZ and GDC, or when it is made of YSZ and SDC, not just when it is made of YSZ and GDC.

[0054] The thickness of the first intermediate layer 71 is not particularly limited, but can be set to 0.1 μm or more and 6.5 μm or less. The thickness of the first intermediate layer 71 is preferably 5 μm or less. This reduces the high-resistance layer, thereby further improving the ionic conductivity of the first intermediate layer 71. The thickness of the first intermediate layer 71 is particularly preferably 2 μm or less. This further improves the ionic conductivity of the first intermediate layer 71.

[0055] The thickness of the second intermediate layer 72 is not particularly limited, but may be 0.1 μm or more and 6.5 μm or less. The thickness of the second intermediate layer 72 is preferably 2 μm or less. This can reduce the high resistance layer.

[0056] The intermediate layer 7 can be formed together with the electrolyte layer 6 as follows. First, a paste containing YSZ, the constituent material of the electrolyte layer 6, is applied to the hydrogen electrode layer 5 to form a green body of the electrolyte layer 6. Next, a paste containing GDC, the constituent material of the reaction prevention layer 8, is applied to the green body of the electrolyte layer 6 to form a green body of the reaction prevention layer 8. Next, the green bodies of the electrolyte layer 6 and the reaction prevention layer 8 are subjected to primary firing (1200°C to 1500°C, 1 hour to 5 hours), followed by secondary firing (1000°C to 1100°C, 1 hour to 5 hours). The primary firing forms the electrolyte layer 6 and the reaction prevention layer 8, and the intermediate layer 7 is formed between them, in which the constituent materials of the two layers are interdiffused. Then, the secondary firing preferentially diffuses the doping element (gadolinium or samarium) added to the ceria constituting the reaction prevention layer 8 toward the electrolyte layer 6, thereby highly doping the first intermediate layer 71 of the intermediate layer 7 with Gd.

[0057] (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.

[0058] [Variation 1] In the above embodiment, the electrolytic cell 1 is described as an electrode-supported type in which the hydrogen electrode layer 5 functions as the support, but the electrolytic cell 1 may also be an electrode-supported type in which the oxygen electrode layer 9 functions as the support. Furthermore, the electrolytic cell 1 is not limited to an electrode-supported type. The electrolytic cell 1 may also be a metal-supported type or an electrolyte-supported type.

[0059] [Variation 2] In the above embodiment, the present invention has been described as being applied to an electrolysis cell, but the present invention can be applied to electrochemical cells in general. An electrochemical cell is a general term for an element in which a pair of electrodes are arranged so that an electromotive force is generated from an overall oxidation-reduction reaction to convert electrical energy into chemical energy, and an element for converting chemical energy into electrical energy. Therefore, the present invention is also useful for fuel cell cells that use oxide ions or protons as carriers.

[0060] An example of an electrochemical cell according to the present invention will be described below. In this example, the relationship between the position P2 (the position where the maximum Gd content is obtained) in the intermediate layer 7 and the performance of the electrolytic cell 1 will be examined. However, the present invention is not limited to the example described below.

[0061] Examples 1 to 16 Electrolytic cells according to Examples 1 to 16 (see FIGS. 1 and 2) were fabricated in the following manner.

[0062] First, a laminate was formed consisting of a green body for the hydrogen electrode layer 5, a green body for the electrolyte layer 6, and a green body for the reaction prevention layer 8. NiO-8YSZ was commonly used as the constituent material for the hydrogen electrode layer 5. As shown in Table 1, YSZ (8YSZ) or ScSZ (6ScSZ) was used as the constituent material for the electrolyte layer 6. As shown in Table 1, GDC (10 mol % gadolinium-doped ceria) or SDC (10 mol % samarium-doped ceria) was used as the constituent material for the reaction prevention layer 8.

[0063] Next, the laminate was subjected to primary firing under the following firing conditions.

[0064] Examples 1, 5, 9, and 13: 1500°C, 5 hours Examples 2, 6, 10, and 14: 1450°C, 5 hours Examples 3, 7, 11, and 15: 1350°C, 5 hours Examples 4, 8, 12, and 16: 1250°C, 5 hours

[0065] Next, the laminated body after the primary firing was subjected to secondary firing, which was performed under the same firing conditions of 1000° C. and 5 hours in all examples.

[0066] Next, a green body of the oxygen electrode layer 9 was formed on the reaction prevention layer 8. LSCF was commonly used as the constituent material of the oxygen electrode layer 9. Then, the green body of the oxygen electrode layer 9 was fired (1000°C, 1 hour).

[0067] Comparative Examples 1 to 16 As described below, electrolytic cells according to Comparative Examples 1 to 16 were fabricated using the same steps as in Examples 1 to 16, except that secondary firing was not performed.

[0068] First, a laminate was formed consisting of a green body for the hydrogen electrode layer 5, a green body for the electrolyte layer 6, and a green body for the reaction prevention layer 8. NiO-8YSZ was commonly used as the constituent material for the hydrogen electrode layer 5. As shown in Table 1, YSZ (8YSZ) or ScSZ (6ScSZ) was used as the constituent material for the electrolyte layer 6. As shown in Table 1, GDC (10 mol % gadolinium-doped ceria) or SDC (10 mol % samarium-doped ceria) was used as the constituent material for the reaction prevention layer 8.

[0069] Next, the laminate was subjected to primary firing under the following firing conditions.

[0070] Comparative Examples 1, 5, 9, and 13: 1500°C, 5 hours Comparative Examples 2, 6, 10, and 14: 1450°C, 5 hours Comparative Examples 3, 7, 11, and 15: 1350°C, 5 hours Comparative Examples 4, 8, 12, and 16: 1250°C, 5 hours

[0071] Next, a green body of the oxygen electrode layer 9 was formed on the reaction prevention layer 8 of the laminate after the primary firing. LSCF was commonly used as the constituent material of the oxygen electrode layer 9. Then, the green body of the oxygen electrode layer 9 was fired (1000°C, 1 hour).

[0072] (Identification of Position P2) First, a cross section along the thickness direction of the electrolysis cells according to Examples 1 to 16 and Comparative Examples 1 to 16 was exposed.

[0073] Next, the cross section was subjected to line analysis in the thickness direction using EDS to measure the content of each element shown in FIG.

[0074] 2 , the region with a Zr content of 75 mol % or more was identified as the electrolyte layer 6, the region with a Ce content of 75 mol % or more was identified as the reaction prevention layer 8, and the space between the electrolyte layer 6 and the reaction prevention layer 8 was identified as the intermediate layer 7. The thicknesses of the electrolyte layer 6 and the reaction prevention layer 8 were as shown in Table 1.

[0075] Next, the region of the intermediate layer 7 where the Zr content was higher than the Ce content was designated as the first intermediate layer 71, and the region of the intermediate layer 7 where the Zr content was equal to or lower than the Ce content was designated as the second intermediate layer 72. The thicknesses of the first intermediate layer 71 and the second intermediate layer 72 were as shown in Table 1.

[0076] Next, it was determined whether position P2, at which the highest Gd content in the intermediate layer 7 was obtained, was located within the first intermediate layer 71. As shown in Table 1, in Examples 1 to 16 in which secondary firing was performed, position P2 was located within the first intermediate layer 71, while in Comparative Examples 1 to 16 in which secondary firing was not performed, position P2 was not located within the first intermediate layer 71.

[0077] (Evaluation) The sheet resistance values ​​of the electrolytic cells according to Examples 1 to 16 and Comparative Examples 1 to 16 were evaluated as follows.

[0078] First, the electrolytic cell was heated to 750° C., and hydrogen was supplied to the hydrogen electrode layer 5 to reduce the NiO contained in the hydrogen electrode layer 5 to Ni.

[0079] Next, while the electrolytic cell was maintained at 750° C., H ２ Air was supplied to the oxygen electrode layer 9 while supplying the O-containing raw material gas.

[0080] Next, the impedance of the open circuit voltage (OCV) of the electrolytic cell was measured in the range of 0.1 Hz to 1 MHz, and a complex impedance plane plot (Cole-Cole plot) was obtained.

[0081] Next, the resistance value was read from the intercept of the real axis on the high frequency side of the Cole-Cole plot, and the measured sheet resistance was determined from the read resistance value.

[0082] Next, assuming that the first intermediate layer 71 and the second intermediate layer 72 do not exist, the theoretical sheet resistance (Ωcm) calculated from the film thickness of the electrolyte layer 6 and the reaction prevention layer 8 and the conductivity of each material is ２ ) was sought.

[0083] The increase rate of the measured sheet resistance relative to the theoretical sheet resistance was then calculated. In Table 1, the increase rate of the sheet resistance in the electrolyte layer 6 was evaluated as "◎" when it was 200% or less, "◯" when it was more than 200% and 1000% or less, and "Δ" when it was more than 1000%.

[0084]

[0085] FIG. 3 is a graph showing the relationship between the thickness of the first intermediate layer 71 and the rate of increase in sheet resistance of the electrolyte layer 6 for Examples 1 to 16 and Comparative Examples 1 to 16 shown in Table 1.

[0086] 3 , in Examples 1 to 16, the rate of increase in sheet resistance in the electrolyte layer 6 was able to be reduced compared to Comparative Examples 1 to 16. Such results were obtained because the ionic conductivity of the first intermediate layer 71 was improved by highly doping the first intermediate layer 71, which has a relatively higher Zr content than the second intermediate layer 72, with Gd.

[0087] Furthermore, as shown in FIG. 3, in Examples 1 to 16, it was found that by setting the thickness of the first intermediate layer 71 to 5.0 μm or less, the rate of increase in the sheet resistance of the electrolyte layer 6 could be suppressed to 1000% or less, and the slope of the rate of increase could be made smaller.

[0088] Furthermore, as shown in FIG. 3, in Examples 1 to 16, it was found that the increase rate of the sheet resistance in the electrolyte layer 6 could be suppressed to 200% or less by setting the thickness of the first intermediate layer 71 to 2.0 μm or less.

[0089] REFERENCE SIGNS LIST 1 electrolytic cell 5 hydrogen electrode layer 6 electrolyte layer 7 intermediate layer 71 first intermediate layer 72 second intermediate layer 8 reaction prevention layer 9 oxygen electrode layer

Claims

1. A cathode layer comprising: a hydrogen electrode layer; an oxygen electrode layer; an electrolyte layer disposed between the hydrogen electrode layer and the oxygen electrode layer; a reaction prevention layer disposed between the oxygen electrode layer and the electrolyte layer; and an intermediate layer disposed between the electrolyte layer and the reaction prevention layer, wherein the electrolyte layer is made of zirconia stabilized with yttria or scandia, the reaction prevention layer is made of ceria doped with gadolinium or samarium, the intermediate layer has a first intermediate layer formed on the electrolyte layer and a second intermediate layer sandwiched between the first intermediate layer and the reaction prevention layer, the first intermediate layer and the second intermediate layer are each made of zirconia and ceria, the zirconium content in the first intermediate layer is higher than the cerium content, and the zirconium content in the second intermediate layer is equal to or lower than the cerium content, and when the content of the doping element is analyzed line-by-line along the thickness direction of the intermediate layer, the position at which the maximum content of the doping element is obtained is within the first intermediate layer. Electrochemical cell.

2. The electrochemical cell according to claim 1, wherein the thickness of the first intermediate layer is 5 μm or less.

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