JP2024122245A - Electrochemical Cell - Google Patents

Abstract

[Problem] To provide an electrolytic cell capable of suppressing sheet resistance and improving electrolysis efficiency. [Solution] The electrolytic cell 1 includes a cell body 20. The cell body 20 includes a hydrogen electrode layer 5, an intermediate layer 6 having ionic conductivity and electronic conductivity in a reducing atmosphere, and an electrolyte layer 7 having ionic conductivity. The density of the hydrogen electrode layer 5 is 35% or more and 65% or less. The density of the intermediate layer 6 is 86% or more. [Selected Figure] Figure 3

Description

The present invention relates to an electrochemical cell.

Conventionally, electrolysis cells have been known that include a cell body having an electrolyte layer disposed between a hydrogen electrode layer and an oxygen electrode layer (see, for example, Patent Document 1). A source gas containing water is supplied to the hydrogen electrode, and _O2 (oxygen) is produced at the oxygen electrode.

JP 2020-155337 A

The inventors have investigated the insertion of an intermediate layer between the hydrogen electrode layer and the electrolyte layer in an electrolysis cell in order to suppress the stress that occurs in the electrolyte layer due to the difference in thermal expansion coefficient between the hydrogen electrode layer and the electrolyte layer.

As a result of intensive research, the inventors have discovered that when an intermediate layer is made of a mixed conductive material that has ionic conductivity and exhibits electronic conductivity in a reducing atmosphere, the density of the hydrogen electrode layer and the intermediate layer has a significant effect on the sheet resistance and electrolysis rate.

The present invention was made based on the above-mentioned new findings, and aims to achieve both suppression of sheet resistance and improvement of electrolysis rate in an electrolytic cell.

The electrolysis cell according to the first aspect of the present invention includes a cell body. The cell body has a first electrode layer, an intermediate layer, an electrolyte layer, and a second electrode layer. The intermediate layer is formed on the first electrode layer and has ionic conductivity and electronic conductivity in a reducing atmosphere. The electrolyte layer is formed on the intermediate layer and has ionic conductivity. The second electrode layer is disposed on the opposite side of the intermediate layer with respect to the electrolyte layer. The density of the first electrode layer is 35% or more and 65% or less. The density of the intermediate layer is 86% or more.

The electrolytic cell according to the second aspect of the present invention is the same as the first aspect, in which the density of the first electrode layer is 40% or more and 62% or less, and the density of the intermediate layer is 88% or more.

The electrolysis cell according to the third aspect of the present invention is related to the first or second aspect and further includes a metal support that supports the cell body. The metal support has a main surface on which the first electrode layer is disposed and a plurality of supply holes formed in the main surface.

The present invention provides an electrolysis cell that can simultaneously suppress sheet resistance and improve electrolysis efficiency.

FIG. 1 is a plan view of an electrolysis cell according to an embodiment. FIG. 2 is a cross-sectional view taken along line AA of FIG. 3 is a graph showing the evaluation of sheet resistance of Samples No. 1 to 46. 4 is a graph showing the evaluation of the electrolysis rate of Samples No. 1 to 46. 5 is a graph showing the overall evaluation of Samples No. 1 to 46.

(Electrolysis Cell 1)
Fig. 1 is a plan view of an electrolysis cell 1 according to an embodiment of the present invention, and Fig. 2 is a cross-sectional view taken along line AA of Fig. 1.

The electrolytic cell 1 is an example of an "electrochemical cell" according to the present invention. The electrolytic cell 1 is a so-called metal-supported electrolytic cell.

The electrolytic cell 1 is formed in a plate shape extending in the X-axis and Y-axis directions. In this embodiment, the electrolytic cell 1 is formed in a rectangular shape extending in the Y-axis direction when viewed in a plan view from the Z-axis direction perpendicular to the X-axis and Y-axis directions. However, the planar shape of the electrolytic cell 1 is not particularly limited, and may be a polygon other than a rectangle, an ellipse, a circle, etc.

As shown in FIG. 2, the electrolysis cell 1 includes a metal support 10, a cell body 20, and a flow path member 30.

[Metal support 10]
The metal support 10 supports the cell main body 20. The metal support 10 is formed in a plate shape. The metal support 10 may be in the shape of a flat plate or a curved plate.

The metal support 10 only needs to be able to support the cell body 20, and there are no particular limitations on its thickness, but it can be, for example, 0.1 mm or more and 2.0 mm or less.

As shown in FIG. 2, the metal support 10 has a plurality of supply holes 11, a first main surface 12, and a second main surface 13.

Each supply hole 11 penetrates the metal support 10 from the first main surface 12 to the second main surface 13. Each supply hole 11 opens to the first main surface 12 and the second main surface 13. In this embodiment, the opening of each supply hole 11 on the first main surface 12 side is covered by the hydrogen electrode layer 5 described later. The opening of each supply hole 11 on the second main surface 13 side is connected to a flow path 30a described later.

Each supply hole 11 can be formed by mechanical processing (e.g., punching), laser processing, or chemical processing (e.g., etching).

In this embodiment, each supply hole 11 is formed linearly along the Z-axis direction. However, each supply hole 11 may be inclined with respect to the Z-axis direction, and may not be linear. Furthermore, the supply holes 11 may be connected to each other.

The first main surface 12 is provided on the opposite side of the second main surface 13. The cell main body 20 is disposed on the first main surface 12. The flow path member 30 is bonded to the second main surface 13.

The metal support 10 is made of a metal material. For example, the metal support 10 is made of an alloy material containing Cr (chromium). Examples of such metal materials include Fe-Cr alloy steel (stainless steel, etc.) and Ni-Cr alloy steel. The Cr content in the metal support 10 is not particularly limited, but can be 4% by mass or more and 30% by mass or less.

The metal support 10 may contain Ti (titanium) and Zr (zirconium). The Ti content in the metal support 10 is not particularly limited, but may be 0.01 mol% or more and 1.0 mol% or less. The Al content in the metal support 10 is not particularly limited, but may be 0.01 mol% or more and 0.4 mol% or less. The metal support 10 may contain Ti as _TiO2 (titania) and may contain Zr as _ZrO2 (zirconia).

The metal support 10 may have an oxide film on its surface that is formed by oxidation of the constituent elements of the metal support 10. A typical example of the oxide film is a chromium oxide film. The chromium oxide film covers at least a portion of the surface of the metal support 10. The chromium oxide film may also cover at least a portion of the inner wall surface of each supply hole 11.

[Cell body 20]
The cell body 20 is disposed on the metal support 10. The cell body 20 is supported by the metal support 10. The cell body 20 has a hydrogen electrode layer 5 (cathode), an intermediate layer 6, an electrolyte layer 7, a reaction prevention layer 8, and an oxygen electrode layer 9 (anode).

The hydrogen electrode layer 5, intermediate layer 6, electrolyte layer 7, reaction prevention layer 8, and oxygen electrode layer 9 are stacked in this order from the metal support 10 side in the Z-axis direction. The hydrogen electrode layer 5, intermediate layer 6, electrolyte layer 7, and oxygen electrode layer 9 are required components, while the reaction prevention layer 8 is optional.

[Hydrogen electrode layer 5]
The hydrogen electrode layer 5 is an example of a “first electrode layer” according to the present invention. The hydrogen electrode layer 5 is disposed on the first main surface 12 of the metal support 10.

A source gas is supplied to the hydrogen electrode layer 5 through each supply hole 11 of the metal support 10. The source gas contains at least moisture (H ₂ O).

When the source gas contains only H ₂ O, the hydrogen electrode layer 5 produces H ₂ from the source gas in accordance with the electrochemical reaction of water electrolysis shown in the following formula (1).

Hydrogen electrode layer 5: H ₂ O+2e ⁻ →H ₂ +O ²⁻ (1)

When the source gas contains CO ₂ in addition to H ₂ O, the hydrogen electrode layer 5 produces H ₂ , CO, and O ²⁻ from the source gas in accordance with the co-electrochemical reactions shown in the following formulas (2), (3), and (4).

Hydrogen electrode layer 5: CO ₂ + H ₂ O + 4e ⁻ → CO + H ₂ + 2O ²⁻ (2)
Electrochemical reaction of H ₂ O: H ₂ O + 2e ⁻ → H ₂ + O ²⁻ (3)
Electrochemical reaction of _CO2 : _CO2 + ^2e- → CO + O2 ^-... (4)

The hydrogen electrode layer 5 is a porous body having electronic conductivity. The hydrogen electrode layer 5 contains nickel (Ni). In the case of co-electrolysis, Ni functions as an electronic conductor and also functions as a thermal catalyst that promotes a thermal reaction between the generated H ₂ and CO ₂ contained in the raw material gas to maintain a gas composition suitable for methanation, Fischer-Tropsch (FT) synthesis, etc. The Ni contained in the hydrogen electrode layer 6 is basically present in the form of metallic Ni during operation of the electrolysis cell 1, but may also be partially present in the form of nickel oxide (NiO).

The hydrogen electrode layer 5 may contain an ion-conductive material such as yttria-stabilized zirconia (YSZ), calcia-stabilized zirconia (CSZ), scandia-stabilized zirconia (ScSZ), gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), (La, Sr)(Cr, Mn) _O3 , (La, Sr) _TiO3 , _Sr2 (Fe, Mo) _{2O6 ,} (La, Sr) _VO3 , (La, Sr) _FeO3 , or a mixture of two or more of these.

The thickness of the hydrogen electrode layer 5 is not particularly limited, but may be, for example, 1 μm or more and 100 μm or less. The thermal expansion coefficient of the hydrogen electrode layer 5 is not particularly limited, but may be, for example, 12×10 ⁻⁶ /° C. or more and 20×10 ⁻⁶ /° C. or less.

The method for forming the hydrogen electrode layer 5 is not particularly limited, and may be a sintering method, a spray coating method (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), a PVD method (sputtering, pulsed laser deposition, etc.), a CVD method, etc.

[Intermediate layer 6]
The intermediate layer 6 is formed on the hydrogen electrode layer 5. The intermediate layer 6 is disposed between the hydrogen electrode layer 5 and the electrolyte layer 7. The intermediate layer 6 is sandwiched between the hydrogen electrode layer 5 and the electrolyte layer 7 and is connected to both of them.

The intermediate layer 6 has ionic conductivity and electronic conductivity (so-called mixed conductivity) in a reducing atmosphere. The intermediate layer 6 does not have to substantially exhibit at least one of ionic conductivity and electronic conductivity in an oxidizing atmosphere. The intermediate layer 6 is made of a material that can exhibit mixed conductivity in a reducing atmosphere. The intermediate layer 6 can be made of GDC, SDC, YDC (yttrium-doped ceria), etc., with GDC being particularly suitable.

The thickness of the intermediate layer 6 is not particularly limited, but can be, for example, 1 μm or more and 100 μm or less.

The thermal expansion coefficient of the intermediate layer 6 is smaller than that of the hydrogen electrode layer 5 and larger than that of the electrolyte layer 7. This makes it possible to suppress the stress that occurs in the electrolyte layer 7 due to the difference in thermal expansion coefficient between the hydrogen electrode layer 5 and the electrolyte layer 7. This makes it possible to suppress the occurrence of breakage or cracks in the electrolyte layer 7.

The method for forming the intermediate layer 6 is not particularly limited, and a firing method, a spray coating method, a PVD method, a CVD method, etc. can be used.

[Electrolyte layer 7]
The electrolyte layer 7 is formed on the intermediate layer 6. The electrolyte layer 7 is connected to the intermediate layer 6. The electrolyte layer 7 is disposed between the intermediate layer 6 and the oxygen electrode layer 9. In this embodiment, the electrolyte layer 7 is sandwiched between the intermediate layer 6 and the reaction prevention layer 8 and is connected to both of them.

The electrolyte layer 7 covers the intermediate layer 6 and also covers the area of the first main surface 12 of the metal support 10 that is exposed from the hydrogen electrode layer 5.

The electrolyte layer 7 is a dense body having oxide ion conductivity. The electrolyte layer 7 transmits O ^2- generated in the hydrogen electrode layer 5 to the oxygen electrode layer 9. The electrolyte layer 7 is made of an oxide ion conductive material. The electrolyte layer 7 can be made of, for example, YSZ, GDC, ScSZ, SDC, LSGM (lanthanum gallate), etc., with YSZ being particularly suitable.

The thickness of the electrolyte layer 7 is not particularly limited, but may be, for example, 1 μm or more and 100 μm or less. The thermal expansion coefficient of the electrolyte layer 7 is not particularly limited, but may be, for example, 10×10 ⁻⁶ /° C. or more and 12×10 ⁻⁶ /° C. or less.

The method for forming the electrolyte layer 7 is not particularly limited, and a baking method, a spray coating method, a PVD method, a CVD method, etc. can be used.

[Reaction prevention layer 8]
The reaction prevention layer 8 is disposed between the electrolyte layer 7 and the oxygen electrode layer 9. The reaction prevention layer 8 is disposed on the opposite side of the intermediate layer 6 with respect to the electrolyte layer 7. The reaction prevention layer 8 prevents the constituent elements of the electrolyte layer 7 from reacting with the constituent elements of the oxygen electrode layer 9 to form a layer with high electrical resistance.

The reaction prevention layer 8 is made of an oxide ion conductive material. The reaction prevention layer 8 can be made of GDC, SDC, etc.

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

The method for forming the reaction prevention layer 8 is not particularly limited, and a baking method, a spray coating method, a PVD method, a CVD method, etc. can be used.

[Oxygen electrode layer 9]
The oxygen electrode layer 9 is an example of a "second electrode layer" according to the present invention. The oxygen electrode layer 9 is disposed on the opposite side of the intermediate layer 6 with respect to the electrolyte layer 7. In this embodiment, the reaction prevention layer 8 is disposed between the electrolyte layer 7 and the oxygen electrode layer 9, and therefore the oxygen electrode layer 9 is connected to the reaction prevention layer 8. If the reaction prevention layer 8 is not disposed between the electrolyte layer 7 and the oxygen electrode layer 9, the oxygen electrode layer 9 is connected to the electrolyte layer 7.

The oxygen electrode layer 9 produces O ₂ from O ²⁻ transferred from the hydrogen electrode layer 5 via the electrolyte layer 7 in accordance with the chemical reaction of the following formula (5).

Oxygen electrode layer 9: 2O ²⁻ →O ₂ +4e ⁻ (5)

The oxygen electrode layer 9 is a porous body having oxide ion conductivity and electron conductivity, and may be made of a composite material of one or more of (La,Sr)(Co,Fe) _O3 , (La,Sr) _FeO3 , La(Ni,Fe) _O3 , (La,Sr) _CoO3 , and (Sm,Sr) _CoO3 and an oxide ion conductive material (such as GDC).

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

The method for forming the oxygen electrode layer 9 is not particularly limited, and a firing method, a spray coating method, a PVD method, a CVD method, etc. can be used.

[Flow path member 30]
The flow path member 30 is joined to the second main surface 13 of the metal support 10. The flow path member 30 forms a flow path 30a between itself and the metal support 10. A source gas is supplied to the flow path 30a. The source gas supplied to the flow path 30a is supplied to the hydrogen electrode layer 5 of the cell main body 20 through each supply hole 11 of the metal support 10.

The flow path member 30 can be made of, for example, an alloy material. The flow path member 30 may be made of the same material as the metal support 10. In this case, the flow path member 30 may be substantially integral with the metal support 10.

The flow path member 30 has a frame body 31 and an interconnector 32. The frame body 31 is an annular member that surrounds the side of the flow path 30a. The frame body 31 is joined to the second main surface 13 of the metal support body 10. The interconnector 32 is a plate-shaped member for electrically connecting an external power source or another electrolysis cell in series with the electrolysis cell 1. The interconnector 32 is joined to the frame body 31.

In this embodiment, the frame body 31 and the interconnector 32 are separate components, but the frame body 31 and the interconnector 32 may be an integrated component.

[Density of hydrogen electrode layer 5, intermediate layer 6 and electrolyte layer 7]
The density of the hydrogen electrode layer 5 is 35% or more and 65% or less, and the density of the intermediate layer 6 is 86% or more. By optimizing the density of each of the hydrogen electrode layer 5 and the intermediate layer 6 in this manner, the sheet resistance of the electrolytic cell 1 can be suppressed and the electrolysis rate in the electrolytic cell 1 can be improved.

The sheet resistance of the electrolytic cell 1 can be significantly suppressed because the resistance value of the hydrogen electrode layer 5 can be reduced by setting the density of the hydrogen electrode layer 5 to 35% or more, and the resistance value of the intermediate layer 6 can be reduced by setting the density of the intermediate layer 6 to 86% or more.

The electrolysis rate in the electrolysis cell 1 can be significantly improved because the diffusivity of the raw material gas in the hydrogen electrode layer 5 can be improved by setting the density of the hydrogen electrode layer 5 to 65% or less.

It is preferable that the density of the hydrogen electrode layer 5 is 40% or more and 62% or less, and that the density of the intermediate layer 6 is 88% or more. This significantly reduces the sheet resistance of the electrolysis cell 1 and significantly improves the electrolysis rate in the electrolysis cell 1.

The density of the electrolyte layer 7 must be 96% or more to ensure gas sealing properties. The upper limit of the density of the intermediate layer 6 is not particularly limited and can be, for example, 99%.

In this specification, density refers to the proportion of the area occupied by the solid phase in the cross section of each layer. Specifically, density can be obtained as follows. Since the method for measuring porosity is common to each layer, the following explanation will be given using an example of obtaining the porosity of the intermediate layer 6.

First, the electrolytic cell 1 is heated to 750°C and hydrogen is supplied to the hydrogen electrode layer 5, thereby reducing the NiO contained in the hydrogen electrode layer 5 to Ni.

Next, the temperature of the electrolytic cell 1 is lowered while still in the reducing atmosphere, and the electrolytic cell 1 is cut along the thickness direction (Z-axis direction) to expose the cross sections of the hydrogen electrode layer 5, intermediate layer 6, and electrolyte layer 7.

Next, the cross section is precision machine polished and then ion milling processing is performed using Hitachi High-Technologies Corporation's IM4000.

Next, an FE-SEM (Field Emission Scanning Electron Microscope) using an in-lens secondary electron detector is used to obtain an enlarged SEM image of the cross section of the intermediate layer 6 at a magnification (e.g., 5,000 to 30,000 times) that allows the boundaries between the constituent materials of the intermediate layer 6 and the pores to be confirmed.

Next, the brightness of the SEM image is classified into 256 gradations, and the brightness difference between the constituent materials and the pores is binarized. For example, the constituent materials are displayed in gray and the pores in black.

Next, the SEM image is analyzed using image analysis software HALCON made by MVTec (Germany) to obtain an analysis image in which the constituent materials are highlighted.

Next, the total area of the constituent materials is obtained from the analysis image, and the density of each analysis image is calculated by dividing the total area of the constituent materials by the area of the entire analysis image.

The above analysis is then performed at five randomly selected locations on the same cross section of the intermediate layer 6, and the arithmetic mean value of the density calculated at the five locations is taken as the density of the intermediate layer 6.

(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.

[Modification 1]
In the above embodiment, the hydrogen electrode layer 5 functions as a cathode and the oxygen electrode layer 9 functions as an anode, but the hydrogen electrode layer 5 may function as an anode and the oxygen electrode layer 9 may function as a cathode. In this case, the constituent materials of the hydrogen electrode layer 5 and the oxygen electrode layer 9 are switched, and a source gas is passed over the outer surface of the hydrogen electrode layer 5.

[Modification 2]
In the above embodiment, the electrolysis cell 1 has been described as an example of an electrochemical cell, but the electrochemical cell is not limited to the electrolysis cell. 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 in order to convert electrical energy into chemical energy, and an element for converting chemical energy into electrical energy. Therefore, the electrochemical cell includes, for example, a fuel cell that uses oxide ions or protons as a carrier.

[Modification 3]
In the above embodiment, the metal support type electrolytic cell 1 has been described as an example of an electrolytic cell, but the electrolytic cell according to the present invention can also be applied to a flat plate type that does not have a metal support 10.

Below, we will explain examples of the electrolysis cell according to the present invention, but the present invention is not limited to the examples described below.

(Sample No. 1 to 46)
Electrolytic cells for Samples No. 1 to 46 were prepared as follows.

First, a metal support was prepared, in which multiple supply holes (hole diameter 1 mm, pitch 2.5 mm, aperture ratio 12.56%) were formed in the central region (length 5 cm x width 5 cm) of a metal plate (length 7 cm x width 7 cm x thickness 0.5 mm) made of Fe-Cr-Mn alloy steel.

Next, a slurry for the hydrogen electrode layer was prepared by mixing GDC powder, NiO powder, butyral resin, polymethyl methacrylate beads as a pore-forming material, a plasticizer, a dispersant, and a solvent. At this time, the density of the hydrogen electrode layer was changed for each sample by adjusting the amount of pore-forming material added, as shown in Table 1. Then, a molded body for the hydrogen electrode layer was formed by printing the slurry for the hydrogen electrode layer on the first main surface of the metal support by the doctor blade method.

Next, the intermediate layer slurry was prepared by mixing GDC powder, butyral resin, polymethyl methacrylate beads as a pore former, plasticizer, dispersant, and solvent. At this time, the density of the intermediate layer was changed for each sample by adjusting the amount of pore former added, as shown in Table 1. The intermediate layer slurry was then printed on the hydrogen electrode layer compact by the doctor blade method to form an intermediate layer compact.

Next, a slurry for the electrolyte layer was prepared by mixing YSZ powder, butyral resin, plasticizer, dispersant, and solvent. The electrolyte slurry was then printed by a doctor blade method so as to cover the intermediate layer compact, thereby forming an electrolyte layer compact.

Next, a slurry for the reaction prevention layer was prepared by mixing GDC powder, polyvinyl alcohol, and a solvent. The slurry for the reaction prevention layer was then printed on the electrolyte layer compact by a doctor blade method to form a reaction prevention layer compact.

Next, the hydrogen electrode layer, intermediate layer, electrolyte layer, and reaction prevention layer molded bodies arranged in sequence on the metal support were sintered in air (1050°C, 1 hour) to form a hydrogen electrode layer (length 5 cm x width 5 cm x thickness 20 μm), intermediate layer (length 5 cm x width 5 cm x thickness 10 μm), electrolyte layer (length 5.4 cm x width 5.4 cm x thickness 10 μm), and reaction prevention layer (length 5.2 cm x width 5.2 cm x thickness 10 μm).

Next, a slurry for the oxygen electrode layer was prepared by mixing (La, Sr) (Co, Fe) _O3 powder, polyvinyl alcohol, and a solvent. The slurry for the oxygen electrode layer was then printed on the reaction prevention layer by a doctor blade method to form a compact for the oxygen electrode layer.

Next, the oxygen electrode layer compact was sintered in air (1000°C, 1 hour) to form an oxygen electrode (length 5 cm x width 5 cm x thickness 15 μm).

As a result of the above, the electrolytic cells for samples No. 1 to 46 were completed. Note that the electrolytic cells for samples No. 1 to 46 did not have the flow path member 30 shown in FIG. 2.

(Measurement of sheet resistance)
First, the electrolytic cell of each sample was heated to 750° C., and hydrogen was supplied to the hydrogen electrode layer, thereby reducing NiO contained in the hydrogen electrode layer to Ni.

Next, with the electrolytic cell held at 750° C., a source gas containing H ₂ O was supplied to the hydrogen electrode layer, while air was supplied to the oxygen electrode layer.

Next, an AC voltage (1.3 V) was applied to the electrolytic cell in the range of 0.1 Hz to 1 MHz to measure the impedance, and a complex impedance plane plot (Cole-Cole plot) was obtained.

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

In Table 1, the sheet resistivity was evaluated as "◎" when it was ^0.32 Ωcm2 or less, as "◯" when it was more than ^0.32 Ωcm2 and ^0.35 Ωcm2 or less, and as "×" when it was more than ^0.35 Ωcm2.

(Measurement of electrolysis rate)
First, the electrolytic cell of each sample was heated to 750° C., and hydrogen was supplied to the hydrogen electrode layer, thereby reducing NiO contained in the hydrogen electrode layer to Ni.

Next, air was supplied to the oxygen electrode layer while a source gas containing H ₂ O was supplied to the hydrogen electrode layer while the electrolysis cell was maintained at 750° C. In this case, the current density was fixed under conditions of a voltage of 1.3 V and an electrolysis rate of 60%.

Next, the flow rate of the raw gas was reduced and the electrolysis rate was measured when the voltage reached 1.35 V.

In Table 1, the electrolysis rate was rated as "◎" when it was 75% or more, "〇" when it was 65% or more but less than 75%, and "×" when it was less than 65%.

Figure 3 shows the sheet resistance evaluation (◎, ◯, ×) of samples No. 1 to 46 on a graph with the density of the intermediate layer on the horizontal axis and the density of the hydrogen electrode layer on the vertical axis.

Figure 4 shows the electrolysis rate evaluation (◎, ◯, ×) for samples No. 1 to 46 on a graph with the density of the intermediate layer on the horizontal axis and the density of the hydrogen electrode layer on the vertical axis.

Figure 5 shows the overall evaluations (◎, ◯, ×) of samples No. 1 to 46 on a graph with the horizontal axis representing the density of the intermediate layer and the vertical axis representing the density of the hydrogen electrode layer. In Figure 5, those for which both the sheet resistance and the electrolytic rate were evaluated as "◎" were marked as "◎", those for which one was evaluated as "◎" and the other as "◯" were marked as "◯", and those for which at least one was evaluated as "×" were marked as "×".

As shown in Figure 3, in samples in which the density of the hydrogen electrode layer was 35% or more and the density of the intermediate layer was 86% or more, the sheet resistance of the electrolytic cell was suppressed. This result was obtained because the resistance value of the hydrogen electrode layer could be reduced by setting the density of the hydrogen electrode layer to 35% or more, and the resistance value of the intermediate layer could be reduced by setting the density of the intermediate layer to 86% or more.

As shown in Figure 3, in samples in which the density of the hydrogen electrode layer was 40% or more and the density of the intermediate layer was 88% or more, the sheet resistance of the electrolytic cell was further suppressed.

As shown in Figure 4, in samples in which the density of the hydrogen electrode layer was set to 65% or less, the electrolysis rate in the electrolysis cell was improved. This result was obtained because the diffusion of the raw material gas in the hydrogen electrode layer was improved by setting the density of the hydrogen electrode layer to 65% or less.

And, as shown in Figure 4, in samples where the density of the hydrogen electrode layer was 62% or less, the electrolysis rate in the electrolysis cell was further improved.

As a result of the above, as shown in Figure 5, it was found that by setting the density of the hydrogen electrode layer to 35% or more and 65% or less, and the density of the intermediate layer to 86% or more, the sheet resistance of the electrolytic cell can be suppressed and the electrolysis rate in the electrolytic cell can be improved.

Furthermore, as shown in Figure 5, it was found that by setting the density of the hydrogen electrode layer to 40% or more and 62% or less, and the density of the intermediate layer to 88% or more, the sheet resistance of the electrolytic cell can be significantly suppressed and the electrolysis rate in the electrolytic cell can be significantly improved.

Reference Signs List 1 Electrolysis cell 10 Metal support 11 Supply hole 12 First main surface 13 Second main surface 20 Cell body 5 Hydrogen electrode layer 6 Intermediate layer 7 Electrolyte layer 8 Reaction prevention layer 9 Oxygen electrode layer 30 Flow path member 30a Flow path

Claims (3)

A first electrode layer;
an intermediate layer formed on the first electrode layer and having ionic conductivity and electronic conductivity in a reducing atmosphere;
an electrolyte layer having ion conductivity formed on the intermediate layer;
a second electrode layer disposed on the opposite side of the intermediate layer with respect to the electrolyte layer;
a cell body having
The density of the first electrode layer is 35% or more and 65% or less,
The density of the intermediate layer is 86% or more.
Electrolysis cell.
The density of the first electrode layer is 40% or more and 62% or less,
The density of the intermediate layer is 88% or more.
2. The electrolysis cell of claim 1.
Further comprising a metal support for supporting the cell body portion,
the metal support has a main surface on which the first electrode layer is disposed and a plurality of supply holes formed in the main surface;
3. An electrolytic cell according to claim 1 or 2.

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