Patent Application
20230395813
The present disclosure relates to a fuel electrode and an electrochemical cell.
Conventionally, there has been known electrochemical cells such as a solid oxide fuel cell (hereinafter also referred to as SOFC) and a solid oxide electrolysis cell (hereinafter also referred to as SOEC) each including a solid electrolyte layer having oxygen ion conductivity. In general, a fuel electrode of an SOFC is supplied with hydrogen gas as fuel, and a power generation reaction of H2+O2−→H2O+2e− occurs. A fuel electrode of an SOEC is supplied with water vapor gas as fuel, and a water electrolysis reaction of H2O+2e−→H2+O2− occurs.
A fuel electrode according to an aspect of the present disclosure is configured to be adopted to an electrochemical cell that includes a solid electrolyte layer having oxide ion conductivity, and to be supplied with a fuel. The fuel electrode includes ion conductive particles having oxide ion conductivity, metal particles, oxygen storage particles having oxygen storage capacity, and pores.
An electrochemical cell according to another aspect of the present disclosure includes a solid electrolyte layer having oxide ion conductivity, the fuel electrode disposed on one surface of the solid electrolyte layer, and an electrode disposed on another surface of the solid electrolyte layer and paired with the fuel electrode.
Objects, features and advantages of the present disclosure will become apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:
Next, a relevant technology is described only for understanding the following embodiments. A solid oxide fuel cell may adopt a fuel electrode having an electrode skeleton composed of an ion conductive oxide and a Ni-based metal alloy. In the solid oxide fuel cell, destruction of an electrode due to oxidation and reduction of a metal constituting the electrode can be restricted and excellent electrode performance can be obtained.
In short, the solid oxide fuel cell may use a Ni alloy instead of metal Ni conventionally used for a fuel electrode. However, this technique has an issue that an electrode activity of the fuel electrode is lowered because Ni is alloyed. On the other hand, when a non-alloyed metal such as metal Ni is used as it is, water vapor oxidation of the metal occurs due to water vapor gas generated by the power generation reaction or water vapor gas supplied for the water electrolysis reaction, and the fuel electrode deteriorates.
A fuel electrode according to an aspect of the present disclosure is configured to be adopted to an electrochemical cell that includes a solid electrolyte layer having oxide ion conductivity, and to be supplied with a fuel. The fuel electrode includes ion conductive particles having oxide ion conductivity, metal particles, oxygen storage particles having oxygen storage capacity, and pores.
An electrochemical cell according to another aspect of the present disclosure includes a solid electrolyte layer having oxide ion conductivity, the fuel electrode disposed on one surface of the solid electrolyte layer, and an electrode disposed on another surface of the solid electrolyte layer and paired with the fuel electrode.
The above-described fuel electrode has the above configuration. Therefore, when the above-described fuel electrode is adopted as a fuel electrode of an SOFC or an SOEC, deterioration of the fuel electrode due to water vapor gas can be restricted while restricting decrease in electrode activity.
In addition, the above-described electrochemical cell includes the above-described fuel electrode. Therefore, when the electrochemical cell is adopted as an SOFC or an SOEC, deterioration of the fuel electrode due to water vapor gas can be restricted while restricting decrease in electrode activity of the fuel electrode, and thus the electrochemical cell is excellent in long-term stability.
Reference numerals in parentheses described in claims indicate a correspondence relationship with specific means described in embodiments described later, and do not limit a technical scope of the present disclosure.
A fuel electrode and an electrochemical cell according to a first embodiment will be described with reference to
When the fuel electrode 2 of the present embodiment is adopted as the fuel electrode 2 of the SOFC or the SOEC, deterioration of the fuel electrode 2 due to water vapor gas can be restricted while restricting decrease in electrode activity. An estimation mechanism by which such an effect is obtained will be described with reference to
As illustrated in
On the other hand, in the fuel electrode 2 of the present embodiment, at the time of power generation of the SOFC shown in
In addition, in the fuel electrode 2 of the present embodiment, at the time of the water electrolysis of the SOEC shown in
The electrochemical cell 1 of the present embodiment includes the fuel electrode 2 of the present embodiment. Therefore, when the electrochemical cell 1 of the present embodiment is adopted as the SOFC or the SOEC, deterioration of the fuel electrode 2 due to water vapor gas can be restricted while restricting decrease in electrode activity of the fuel electrode 2, and thus the electrochemical cell 1 is excellent in long-term stability. Note that, in the electrochemical cell 1 of the present embodiment, a part of the metal constituting the metal particles 22 is not prevented from being inevitably alloyed at the time of manufacturing the fuel electrode 2 or the like.
Hereinafter, the fuel electrode 2 of the present embodiment and the electrochemical cell 1 of the present embodiment will be described in more detail.
The fuel electrode 2 is an electrode to which the fuel F is supplied. Specifically, when the electrochemical cell 1 is operated as the SOFC, a hydrogen-containing gas F1 such as hydrogen gas is supplied to the fuel electrode 2 as the fuel F. On the other hand, when the electrochemical cell 1 is operated as the SOEC, a water (H2O)-containing gas F2 such as a water vapor gas is supplied to the fuel electrode 2 as the fuel F. The hydrogen-containing gas F1 may contain water vapor for humidification or the like. The water-containing gas F2 may include a reducing gas such as hydrogen gas. The fuel electrode 2 is usually formed to be porous so that a gaseous fuel can spread.
As described above, the fuel electrode 2 includes the ion conductive particles 21, the metal particles 22, the oxygen storage particles 23, and the pores 24.
The ion conductive particles 21 have oxide ion conductivity. Examples of an oxide ion conductive material constituting the ion conductive particles 21 include zirconium oxide-based oxides such as yttria-stabilized zirconia and scandia-stabilized zirconia. The ion conductive particles 21 may include one or more kinds of oxide ion conductive material.
As a metal material constituting the metal particles 22, various metals having catalytic activity can be used. Examples of such a metal include Ni (nickel), Cu (copper), and Co (cobalt). The metal particles 22 may include one or more kinds of metal. Specifically, at least one selected from the group consisting of Ni particles, Cu particles, and Co particles can be suitably used as the metal particles 22 from the viewpoint of high electrical conductivity, high catalytic activity, and the like.
The oxygen storage particles 23 have an oxygen storage capacity (OSC). As an oxygen storage material constituting the oxygen storage particles 23, an oxide containing Zr (zirconium) and at least one element selected from the group consisting of Al (aluminum), Ce (cerium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Y (yttrium), and Sc (scandium) can be suitably used. According to this configuration, it is easy to increase the oxygen storage capacity of the oxygen storage particles 23, and it is possible to more reliably restrict the water vapor oxidation of the metal particles 22 having catalytic activity. Specific examples of the oxygen storage material include an oxide containing Zr and at least one element selected from the group consisting of Al, Ce, La, Pr, Nd, Y, and Sc, and an oxide containing Ce and Zr and at least one element selected from the group consisting of Al, La, Pr, Nd, Y, and Sc. More specifically, examples of the oxygen storage material include an Al—Ce—Zr oxide containing Al, Ce, and Zr, an Y—Ce—Zr oxide containing Y, Ce, and Zr (hereinafter, also simply referred to as YCZ), a Sc—Ce—Zr oxide containing Sc, Ce, and Zr (hereinafter, also simply referred to as SCZ), and a La—Ce—Zr oxide containing La, Ce, and Zr (hereinafter, also simply referred to as LCZ). The oxygen storage particles 23 may include one or more kinds of the oxygen storage material.
The oxygen storage particles 23 can be synthesized, for example, as follows. An Al source, a Ce source, a La source, a Pr source, a Nd source, an Y source, a Sc source, a Zr source, and the like, which are starting materials of the oxygen storage material constituting the oxygen storage particles 23, are weighed so as to have a predetermined mol ratio. Each starting material can be provided in the form of nitrate or the like. Next, the starting material is dissolved in an aqueous solution, a target material precursor is precipitated with a base such as ammonia water or sodium hydroxide aqueous solution (coprecipitation method), and then the target material precursor is recovered by filtration. Next, the obtained precursor powder is dried, placed in an alumina crucible or the like, and fired at, for example, 300° C. to 1500° C. in an air atmosphere, a reducing atmosphere such as H2, or an inert atmosphere such as nitrogen and argon. Accordingly, the oxygen storage particles 23 described above can be obtained.
The oxygen storage capacity of the oxygen storage particles 23 can be measured by thermogravimetric analysis (TGA) of the oxygen storage material constituting the oxygen storage particles 23. When the amount of weight loss by thermogravimetric analysis per 15 mg of the oxygen storage material constituting the oxygen storage particles 23 is 0.02 mg or more, the oxygen storage particles 23 are considered to have oxygen storage capacity. The thermogravimetric analysis is performed under the following conditions: measurement sample powder weight, 15 mg; measurement temperature, 700° C.; measurement gas, hydrogen-containing gas consisting of 5 volume % hydrogen and 95 volume % nitrogen and oxygen-containing gas consisting of 5 volume % oxygen and 95 volume % nitrogen are switched every 5 minutes; and gas flow rate, 100 m L/min.
The amount of weight reduction by thermogravimetric analysis per 15 mg of the oxygen storage material constituting the oxygen storage particles 23 can be set to preferably 0.03 mg or more, more preferably 0.035 mg or more, and even more preferably 0.04 mg or more from the viewpoint of enhancing the effect of restricting water vapor oxidation of the metal particles 22. The amount of weight reduction is preferably large from the viewpoint of enhancing the effect of restricting water vapor oxidation of the metal particles 22. Therefore, the upper limit of the amount of weight loss is not particularly limited, but the amount of weight loss can be, for example, 2.00 mg or less from the viewpoint of inhibition of oxide ion conduction or the like.
It is important that the above-described oxygen storage material is present as particles (can be disposed as particles) in the fuel electrode 2. This is because it is difficult to restrict water vapor oxidation of the metal particles 22 in a state in which the oxygen storage material is not present as particles and elements such as Ce constituting the oxygen storage material are substantially dissolved in the metal particles 22 and the ion conductive particles 21. Note that it is difficult for a Ce—Zr oxide including Ce, Zr, and O (oxygen) to maintain a crystal structure after firing of the fuel electrode 2, and to be present in the form of particles in the fuel electrode 2. In addition, the fuel electrode 2 may have a configuration that does not have a concentration distribution of the oxygen storage particles 23, that is, a configuration in which the concentration of the oxygen storage particles 23 can be considered to be constant. The fuel electrode 2 may have a concentration distribution of the oxygen storage particles 23. The latter example will be described later in the second embodiment to the fourth embodiment.
The fuel electrode 2 preferably has a microstructure in which the oxygen storage particles 23 are in contact with the ion conductive particles 21, the metal particles 22, and the pores 24. According to this configuration, since the oxygen storage particles 23 are present at positions where the water vapor gas is in contact with the metal particles 22, the effect of restricting the water vapor oxidation of the metal particles 22 is easily exerted. It is not required that all of the oxygen storage particles 23 contained in the fuel electrode 2 are in contact with all of the ion conductive particles 21, the metal particles 22, and the pores 24 as long as the fuel electrode 2 can exhibit the above-described effects.
The oxygen storage particles 23 preferably have a crystal structure of a pyrochlore structure or a fluorite structure. According to this configuration, it is easy to exhibit high oxygen storage capacity, and it is possible to more reliably restrict water vapor oxidation of the metal particles 22.
The ratio of the ion conductive particles 21 to the metal particles 22 contained in the fuel electrode 2 can be set to preferably 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30 in terms of the mass ratio from the viewpoint of the formability of an oxide ion conductive path and an electron conductive path, a balance between the oxide ion conductivity and the electron conductivity, and the like. In addition, the content of the oxygen storage particles 23 contained in the fuel electrode 2 can be set to preferably 1 mass % or more, more preferably 2 mass % or more, even more preferably 3 mass % or more, even more preferably 4 mass % or more, and even more preferably 5 mass % or more with respect to the total mass of the ion conductive particles 21 and the metal particles 22 from the viewpoint of ensuring the above-described action and effect. The content of the oxygen storage particles 23 contained in the fuel electrode 2 can be set to preferably 30 mass % or less, more preferably 25 mass % or less, and even more preferably 20 mass % or less with respect to the total mass of the ion conductive particles 21 and the metal particles 22 from the viewpoint of restricting decrease in the electron conductivity and the oxide ion conductivity of the fuel electrode 2. The ratio between the ion conductive particles 21 and the metal particles 22 and the content of the oxygen storage particles 23 can be measured by inductively coupled plasma (ICP) emission spectrometry of a solution obtained by dissolving the fuel electrode 2 in a strong acid.
In the fuel electrode 2, the average particle diameter of the oxygen storage particles 23 may be preferably 100 nm or more, more preferably 300 nm or more, and even more preferably 500 nm or more from the viewpoint of ensuring the oxygen storage capacity. The average particle diameter of the oxygen storage particles 23 can be set to preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 5 μm or less from the viewpoint of preventing the conduction of oxide ions from being hindered during the electrode reaction such as the power generation reaction or the water electrolysis reaction.
In the fuel electrode 2, the average particle diameter of the ion conductive particles 21 may be preferably 50 nm or more, more preferably 75 nm or more, and even more preferably 100 nm or more from the viewpoint of strength, oxide ion conductivity, and the like. The average particle diameter of the ion conductive particles 21 can be set to preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less from the viewpoint of increasing the density of the three-phase interface in the fuel electrode 2 in order to ensure the electrode performance.
In the fuel electrode 2, the average particle diameter of the metal particles 22 may be preferably 50 nm or more, more preferably 75 nm or more, and even more preferably 100 nm or more from the viewpoint of electron conductivity and the like. The average particle diameter of the metal particles 22 may be preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less from the viewpoint of increasing the density of the three-phase interface in the fuel electrode 2 in order to ensure the electrode performance.
The average particle diameter of the oxygen storage particles 23 is an arithmetic average value of particle diameters measured for any ten oxygen storage particles 23 specified in a cross section along the thickness direction of the fuel electrode 2 by TEM-EDX analysis (transmission electron microscope-energy dispersive X-ray analysis). Similarly, the average particle diameter of the ion conductive particles 21 is an arithmetic average value of particle diameters measured for any ten ion conductive particles 21 specified in the cross section. The average particle diameter of the metal particles 22 is an arithmetic average value of particle diameters measured for any ten metal particles 22 specified in the cross section.
The fuel electrode 2 may be formed in a layer shape, and may be composed of a single layer or multiple layers.
When the fuel electrode 2 functions as a support (described in detail later), the thickness of the fuel electrode 2 may be, for example, preferably 100 to 800 μm, more preferably 150 to 700 μm, and even more preferably 200 to 600 μm from the viewpoint of strength, oxide ion conductivity, electron conductivity, gas diffusivity, and the like. When the fuel electrode 2 is not made to function as a support, the thickness of the fuel electrode 2 can be, for example, preferably 10 to 500 μm, more preferably 15 to 300 μm, and even more preferably 20 to 200 μm from the viewpoint of oxide ion conductivity, electron conductivity, gas diffusivity, and the like.
The electrochemical cell 1 of the present embodiment can be configured to include the solid electrolyte layer 10 having oxide ion conductivity, the fuel electrode 2 of the present embodiment disposed on one surface of the solid electrolyte layer 10, and an electrode 3 disposed on another surface of the solid electrolyte layer 10 and paired with the fuel electrode 2. Specifically,
The electrochemical cell 1 may further include an intermediate layer (not illustrated) between the solid electrolyte layer 10 and the electrode 3. The intermediate layer is a layer mainly for restricting the reaction between the material of the solid electrolyte layer 10 and the material of the electrode 3. In this case, specifically, the electrochemical cell 1 may have a configuration in which the fuel electrode 2, the solid electrolyte layer 10, the intermediate layer, and the electrode 3 are stacked in this order and joined to each other. The electrochemical cell 1 may have a flat cell structure. In addition, the electrochemical cell 1 may be configured such that the fuel electrode 2 functions as both an electrode and a support, may be configured such that the solid electrolyte layer 10 functions as a support, or may be configured to be supported by another support (not illustrated) such as a metal member.
The solid electrolyte layer 10 has oxide ion conductivity. Specifically, the solid electrolyte layer 10 may be formed in a layer shape from a solid electrolyte having oxide ion conductivity. The solid electrolyte layer 10 is usually formed to be dense in order to ensure gas tightness. As the solid electrolyte forming the solid electrolyte layer for example, zirconium oxide based oxides such as yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) may be preferably used from the viewpoints of excellent strength and thermal stability, for example. As the solid electrolyte forming the solid electrolyte layer 10, yttria-stabilized zirconia may be preferably used from the viewpoints of the oxide ion conductivity, the mechanical stability, the compatibility with other materials, and the chemical stability from an oxidizing atmosphere to a reducing atmosphere, for example.
When the solid electrolyte layer 10 is not made to function as a support, the thickness of the solid electrolyte layer 10 can be set to preferably 3 to 20 μm, more preferably 3.5 to 15 μm, and even more preferably 4 to 10 μm from the viewpoint of electrical resistance and the like. When the solid electrolyte layer 10 functions as a support, the thickness of the solid electrolyte layer 10 can be set to preferably 30 to 300 μm, more preferably 50 to 200 μm, and even more preferably 100 to 150 μm from the viewpoint of strength, electric resistance, and the like.
The electrode 3 is used as an air electrode (oxidant electrode) when the electrochemical cell 1 is used as an SOFC. In this case, an oxygen-containing gas such as air or oxygen gas is supplied to the electrode 3 as an oxidizing agent. On the other hand, when the electrochemical cell 1 is used as an SOEC, the electrode 3 is used as an oxygen electrode. In this case, a gas such as air may or may not be supplied to the electrode 3.
Specifically, as shown in
Examples of the electrode 33 include transmission metal perovskite-type oxides and mixtures of the transmission metal perovskite-type oxides and ceria (CeO2) or ceria-based solid solutions. Examples of the transition metal perovskite-type oxides include lanthanum-strontium-cobalt oxide, lanthanum-strontium-cobalt-iron oxide, and lanthanum-strontium-manganese-iron oxide. The ceria-based solid solutions are obtained by doping one or more elements selected from the group consisting of Gd, Sm, Y, La, Nd, Yb, Ca, and Ho to ceria. These materials can be used alone or in combination of two or more.
The thickness of the electrode 3 may be preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and even more preferably 25 μm or more, from the viewpoint of securing a sufficient reaction point or the like. The thickness of the electrode 3 can be preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less from the viewpoint of gas diffusivity, electric resistance, and the like.
In a case where the electrochemical cell 1 has an intermediate layer, the intermediate layer may specifically be configured as a layer of a solid electrolyte having oxide ion conductivity. Examples of the solid electrolyte used for the intermediate layer include ceria (CeO2) and ceria-based solid solutions in which one or more elements selected from the group consisting of Gd, Sm, Y, La, Nd, Yb, Ca, and Ho are doped to ceria. These materials can be used alone or in combination of two or more. As the solid electrolyte used for the intermediate layer, ceria doped with Gd is preferable.
The thickness of the intermediate layer can be set to preferably 1 to 20 μm, more preferably 2 to 10 μm, from the viewpoint of reduction of ohmic resistance, restriction of element diffusion from the electrode 3, and the like.
The electrochemical cell 1 can be adopted as at least one of the SOFC and the SOEC. That is, the electrochemical cell 1 may be operated as the SOFC, may be operated as the SOEC, and may be configured to be switchable between an SOFC mode operated as the SOFC and an SOEC mode operated as the SOEC.
A fuel electrode and an electrochemical cell according to a second embodiment will be described with reference to
As illustrated in
In the fuel electrode 2, a region close to the solid electrolyte layer 10, which is a region having a certain depth from the surface 20a on the solid electrolyte layer 10 toward an inner side in the thickness direction, is a region in which the power generation reaction or the water electrolysis reaction is more likely to occur than a remaining region, which is a region excluding the region close to the solid electrolyte layer 10.
Therefore, according to the above configuration, it is possible to efficiently restrict the water vapor oxidation of the metal particles 22 involved in the power generation reaction and the water electrolysis reaction in the fuel electrode 2.
In the present embodiment, for example, as illustrated in
In the present embodiment, for example, as illustrated in
An electrochemical cell 1 of the present embodiment includes the fuel electrode 2 of the present embodiment. Therefore, in the electrochemical cell 1 of the present embodiment, deterioration of the fuel electrode 2 due to the water vapor gas can be efficiently restricted while restricting decrease in the electrode activity of the fuel electrode 2, and long-term stability can be improved.
Other configurations and effects are similar to those of the first embodiment.
A fuel electrode and an electrochemical cell according to a third embodiment will be described with reference to
As illustrated in
In general, when the SOFC is operated, a fuel electrode side gas flow path (not illustrated) is disposed so as to be in contact with the fuel electrode 2. The hydrogen-containing gas F1 as the fuel F supplied from a supply port (not illustrated) of the fuel electrode side gas flow path flows in the fuel electrode side gas flow path along the surface 20b of the fuel electrode 2 that is located opposite the surface 20a located on the solid electrolyte layer 10. As illustrated in
Therefore, according to the above configuration, it is possible to efficiently restrict the water vapor oxidation of the metal particles 22 involved in the power generation reaction in the fuel electrode 2.
In the present embodiment, for example, as illustrated in
The electrochemical cell 1 of the present embodiment includes the fuel electrode 2 of the present embodiment. Therefore, in the electrochemical cell 1 of the present embodiment, deterioration of the fuel electrode 2 due to the water vapor gas can be efficiently restricted while restricting decrease in the electrode activity of the fuel electrode 2, and long-term stability can be improved.
Other configurations and effects are similar to those of the first and second embodiments.
A fuel electrode and an electrochemical cell according to a fourth embodiment will be described with reference to
As illustrated in
In general, when the SOEC is operated, a fuel electrode side gas flow path (not illustrated) is disposed so as to be in contact with the fuel electrode 2. The water-containing gas F2 as the fuel F supplied from the supply port (not illustrated) of the fuel electrode side gas flow path flows in the fuel electrode side gas flow path along the surface 20b of the fuel electrode 2 that is located opposite the surface 10a located on the solid electrolyte layer 10. As illustrated in
Therefore, according to the above configuration, it is possible to efficiently restrict the water vapor oxidation of the metal particles 22 involved in the water electrolysis reaction in the fuel electrode 2.
In the present embodiment, for example, as illustrated in
The electrochemical cell 1 of the present embodiment includes the fuel electrode 2 of the present embodiment. Therefore, in the electrochemical cell 1 of the present embodiment, deterioration of the fuel electrode 2 due to the water vapor gas can be efficiently restricted while restricting decrease in the electrode activity of the fuel electrode 2, and long-term stability can be improved.
Other configurations and effects are similar to those of the first and second embodiments.
NiO powder (average particle size: 0.5 μm), yttria-stabilized zirconia (hereinafter, YSZ) powder containing 8 mol % of Y2O3 (average particle size: 0.2 μm), LCZ powder (average particle size: 0.5 μm), carbon (pore former), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed and crushed with a ball mill to prepare a slurry. As the LCZ powder, specifically, La1.5Ce0.5Zr2O7 powder as La—Ce—Zr oxide powder was used. In addition, the mixing and crushing were performed for 24 hours or more in order to sufficiently disperse the respective materials. The mass ratio of the NiO powder to the YSZ powder was 65:35. The addition amount of the LCZ powder was 10 mass % with respect to the total mass of the NiO powder and the YSZ powder. Using a doctor blade method, the slurry was applied in layers on a resin sheet and dried, and then the resin sheet was peeled off to prepare a fuel electrode forming sheet. The average particle diameter is a particle diameter d50 when the volume-based cumulative frequency distribution measured by the laser diffraction and scattering method shows 50% (the same applies hereinafter). In the present example, the average particle diameter of the LCZ powder is set to 0.5 μm, but the average particle diameter of the LCZ powder can be selected from a range of, for example, 0.1 to 1 μm. In the present example, the addition amount of the LCZ powder is set to 10 mass %, but the addition amount of the LCZ powder can be selected from a range of, for example, 1 to 20 mass %.
YSZ powder (average particle size: 0.2 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed with a ball mill to prepare a slurry. Thereafter, a solid electrolyte layer forming sheet was prepared in a manner similar to the preparation of fuel electrode forming sheet.
Gd-doped CeO2 (hereinafter, GDC) powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed with a ball mill to prepare a slurry. In this experimental example, CeO2 doped with 10 mol % Gd was used as the GDC. Thereafter, an intermediate layer forming sheet was prepared in a manner similar to the preparation of the fuel electrode forming sheet.
LSC (La0.6Sr0.4CoO3) powder (average particle size: 2.0 μm), ethyl cellulose, and terpineol were kneaded with three rolls to prepare an electrode forming paste.
The fuel electrode forming sheet, the solid electrolyte layer forming sheet, and the intermediate layer forming sheet were laminated in this order, and pressure-bonded using a hydrostatic pressing (WIP) molding method. The WIP molding was performed under conditions of a temperature of 85° C., a pressurizing force of 50 MPa, and a pressurizing time of 10 minutes. The obtained molded body was fired at about 500° C. and degreased.
Next, the obtained molded body was fired at 1400° C. for 2 hours in an air atmosphere. As a result, a fired body in which a layered fuel electrode (thickness: 200 μm), a solid electrolyte layer (thickness: 3.5 μm), and an intermediate layer (thickness: 3 μm) were laminated in this order was obtained.
Next, the electrode forming paste was applied to the surface of the intermediate layer in the fired body by a screen printing method, and the resultant was fired (baked) at 950° C. for 2 hours in an air atmosphere to form a layered electrode (thickness: 50 μm) paired with the fuel electrode. The outer shape of the electrode was formed to be smaller than the outer shape of the fuel electrode. Accordingly, a flat cell was formed.
Next, the cell was appropriately sealed with glass to form a gas seal structure. Thereafter, the fuel electrode of this cell was subjected to a reduction treatment at 800° C. for 3 hours in a hydrogen atmosphere. As described above, the fuel electrode and the electrochemical cell of Sample 1 were obtained. The electrochemical cell produced in this example is a coin-shaped single cell.
A fuel electrode and an electrochemical cell of Sample 1C were produced in a similar manner to the production of the fuel electrode and the electrochemical cell of Sample 1 except that CeZr3O8 (hereinafter, CZ) powder (average particle diameter: 1.0 μm) as Ce—Zr oxide powder was used instead of the LCZ powder at the time of producing the fuel electrode forming sheet. A fuel electrode and an electrochemical cell of Sample 2C were produced in a manner similar to the production of the fuel electrode and the electrochemical cell of Sample 1 except that the LCZ powder was not added at the time of producing the fuel electrode forming sheet.
For Sample 1 and Sample 1C, TEM-EDX analysis was performed on a cross section along the thickness direction of the fuel electrode, and EDX mapping of each fuel electrode was acquired.
As shown in
The electrochemical cells of Sample 1, Sample 1C, and Sample 2C were operated as SOECs, and the deterioration of each fuel electrode was investigated. Specifically, water electrolysis was carried out at a constant voltage of 1.3 V using each electrochemical cell 1. At this time, a mixed gas of H2O, H2, and N2 (H2O:H2:N2=30:30:40 in volume ratio) was supplied to the fuel electrode, and air was supplied to the electrode to be the oxygen electrode. The cell operating temperature was 700° C. The results are shown in
Oxygen storage capacities of various oxygen storage materials were measured by the thermogravimetric analysis (TGA) described above. In this example, specifically, CeZr3O8 (CZ) powder as Ce—Zr oxide powder, La1.5Ce0.5Zr2O7 (LCZ) powder as La—Ce—Zr oxide powder, Y0.13Ce0.10Zr0.77O2 (YCZ) powder as Y—Ce—Zr oxide powder, and Sc0.13Ce0.10Zr0.77O2 (SCZ) powder as the Sc—Ce—Zr oxide powder were used as the oxygen storage materials. As a thermogravimetric analyzer, TGA2 manufactured by Mettler Toledo was used. The results are shown in
As shown in
An influence of high temperature firing on YSZ, NiO, LCZ, and CZ used as raw materials for the fuel electrode in Experimental Example 1 was examined. Specifically, a mixed powder pellet obtained by mixing LCZ and NiO at a mass ratio of 10:35, a mixed powder pellet obtained by mixing LCZ and YSZ at a mass ratio of 10:65, a powder pellet formed of LCZ alone, a powder pellet formed of YSZ alone, and a powder pellet formed of NiO alone were fired at a cell firing temperature of 1400° C., and X-ray diffraction (XRD) measurement was performed using an X-ray diffraction apparatus (full automatic multipurpose X-ray diffractometer “SmartLab” manufactured by Rigaku Corporation). Similarly, a mixed powder pellet obtained by mixing CZ and NiO at a mass ratio of 10:35, a mixed powder pellet obtained by mixing CZ and YSZ at a mass ratio of 10:65, a powder pellet formed of CZ alone, a powder pellet formed of YSZ alone, and a powder pellet formed of NiO alone were fired at 1400° C., and X-ray diffraction (XRD) measurement was performed. The results are shown in
As shown in
The present disclosure is not limited to each of the above-described embodiments and experimental examples, and various modifications can be made without departing from the gist of the present disclosure. In addition, each configuration shown in each embodiment and each experimental example can be optionally combined. That is, although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to the embodiments, structures, and the like. The present disclosure encompasses various modifications and variations within the scope of equivalents. In addition, various combinations and configurations, as well as other combinations and configurations that include only one element, more, or less, fall within the scope and spirit of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-030030 | Feb 2021 | JP | national |
The present application is a continuation application of International Patent Application No. PCT/JP2021/044663 filed on Dec. 6, 2021, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2021-030030 filed on Feb. 26, 2021. The entire disclosures of all of the above applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/044663 | Dec 2021 | US |
| Child | 18453301 | US |
