JP2021197332A - Electrochemical cell - Google Patents

Abstract

To provide an electrochemical cell capable of suppressing reaction unevenness in the cell surface.SOLUTION: An electrochemical cell 1 includes a solid electrolyte layer 2 having oxygen ion conductivity, a first electrode 3 that is arranged on one surface side of the solid electrolyte layer 2, and to which fuel F is supplied, a second electrode 4 arranged on the other surface side of the solid electrolyte layer 2 and paired with the first electrode 3. The second electrode 4 includes a metal oxide 41 having an oxygen indefinite ratio, and a decomposition product 42 of the metal oxide having an oxygen indefinite ratio. The metal oxide 41 having an oxygen indefinite ratio can include an oxygen-deficient metal oxide 411. The metal oxide 41 having an oxygen indefinite ratio can further include an oxygen-rich metal oxide 412.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrochemical cell.

Conventionally, electrochemical cells such as water electrolysis cells and fuel cell cells using a solid electrolyte layer having oxygen ion conductivity are known. For example, Patent Document 1 discloses a water electrolysis cell in which a part of an oxygen electrode feeder that supplies an electric current is embedded inside an oxygen electrode. According to the same document, with such a configuration, the adhesion between the oxygen electrode and the oxygen electrode feeder can be maintained for a long period of time, the electrolytic current is uniformly supplied to the oxygen electrode, and the increase in contact resistance is suppressed. Is said to be possible.

Japanese Unexamined Patent Publication No. 2008-0455152

In the above-mentioned conventional technique, as long as the materials of the oxygen electrode and the oxygen electrode feeder are different, it is inevitable that poor contact will occur due to a difference in thermal expansion or the like. That is, in the prior art, in the oxygen electrode, a contact portion and a non-contact portion are locally generated between the oxygen electrode and the oxygen electrode feeder. Therefore, in the prior art, it is not possible to obtain a uniform reaction in the cell surface, and reaction unevenness is likely to occur in the cell surface.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrochemical cell capable of suppressing reaction unevenness in the cell surface.

One aspect of the present invention is a solid electrolyte layer (2) having oxygen ion conductivity and a first electrode (3) arranged on one side of the solid electrolyte layer and supplied with fuel (F, F1, F2). ) And a second electrode (4) arranged on the other side of the solid electrolyte layer and paired with the first electrode.
The second electrode contains a metal oxide having an oxygen indefinite ratio (41) and a decomposition product of the metal oxide having an oxygen indefinite ratio (42).
It is in the electrochemical cell (1).

The electrochemical cell has the above configuration. Therefore, according to the electrolytic chemical cell, it is possible to suppress reaction unevenness in the cell surface.

The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

FIG. 1 is an explanatory diagram schematically showing the microstructure of the electrochemical cell according to the first embodiment. In FIG. 2, a part of the metal oxide having oxygen non-stoichiometricity is converted into a decomposition product of the metal oxide having oxygen non-stoichiometricity in the portion in the second electrode where current easily flows locally, and the others. It is a figure schematically showing how the reaction moves to the reaction field of (a) before decomposition of a metal oxide having an oxygen non-stoichiometric ratio, and (b) is a decomposition of a metal oxide having an oxygen non-stoichiometric ratio. It is the figure which showed the latter. FIG. 3 is an explanatory diagram for explaining a case (SOEC mode) in which the electrochemical cell according to the first embodiment is operated as a solid oxide electrolyzer cell. FIG. 4 is an explanatory diagram for explaining a case (SOFC mode) in which the electrochemical cell according to the first embodiment is operated as a solid oxide fuel cell. FIG. 5 is an explanatory diagram schematically showing the microstructure of the electrochemical cell according to the second embodiment. It is a figure which showed the XRD analysis result of the 2nd electrode which the electrochemical cell produced in the experimental example has.

The electrochemical cell of the present embodiment is arranged on one side of the solid electrolyte layer having oxygen ion conductivity and the solid electrolyte layer, the first electrode to which fuel is supplied, and the other side of the solid electrolyte layer. It is provided with a second electrode that is paired with the first electrode.
The second electrode contains a metal oxide having an oxygen indefinite ratio and a decomposition product of the metal oxide having an oxygen indefinite ratio.

In an electrochemical cell using a solid electrolyte layer having oxygen ion conductivity, an electrochemical reaction occurring at a three-phase interface is often used in the first electrode to which fuel is supplied, and the cell is not taken any measures. In-plane reaction unevenness is likely to occur. In the above electrolytic chemical cell, when a portion where an electrolytic current or a power generation current tends to flow locally occurs due to non-uniformity of the microstructure of the first electrode, the second electrode paired with the first electrode may have a portion. A high oxygen concentration atmosphere or a low oxygen concentration atmosphere is locally generated by a local overload electrolytic reaction or an overload power generation reaction (hereinafter, collectively referred to as an overload reaction). In the portion of the second electrode where such a high oxygen concentration atmosphere or a low oxygen concentration atmosphere is generated, the metal compound having an oxygen indefinite specificity is decomposed, and a decomposition product having reduced activity or an inert decomposition product is generated. Therefore, the reaction shifts to another reaction field, and the local overload reaction is suppressed. Therefore, according to the electrolytic chemical cell, the reaction unevenness in the cell surface can be suppressed. Further, by suppressing the reaction unevenness in the cell surface, deterioration due to microstructural failure in the first electrode is also suppressed, and a highly reliable electrochemical cell can be obtained.

Hereinafter, the electrochemical cell of the present embodiment will be described in detail with reference to the drawings. The electrochemical cell of the present embodiment is not limited to the following examples.

(Embodiment 1)
The electrochemical cell of the first embodiment will be described with reference to FIGS. 1 to 4. As illustrated in FIG. 1, the electrochemical cell 1 of the present embodiment includes a solid electrolyte layer 2, a first electrode 3, and a second electrode 4. The first electrode 3 is arranged on one side of the solid electrolyte layer 2. The second electrode 4 is arranged on the other side of the solid electrolyte layer 2. Specifically, FIG. 1 shows an example in which the first electrode 3, the solid electrolyte layer 2, and the second electrode 4 are laminated in this order and bonded to each other.

The electrochemical cell 1 may further include an intermediate layer (not shown) between the solid electrolyte layer 2 and the second electrode 4. The intermediate layer is mainly a layer for suppressing the reaction between the material of the solid electrolyte layer 2 and the material of the second electrode 4. In this case, specifically, the electrochemical cell 1 can be configured such that the first electrode 3, the solid electrolyte layer 2, the intermediate layer, and the second electrode 4 are laminated in this order and joined to each other. Further, the electrochemical cell 1 can have a flat plate-shaped cell structure. Further, the electrochemical cell 1 may be configured such that the first electrode 3 also functions as a support, or the solid electrolyte layer 2 may also serve as a support. However, it may be configured to be supported by another support (not shown) such as a metal member.

The solid electrolyte layer 2 has oxygen ion conductivity. Specifically, the solid electrolyte layer 2 can be formed in a layered state from the solid electrolyte having oxygen ion conductivity. The solid electrolyte layer 2 is usually formed to be dense in order to ensure gas tightness. As the solid electrolyte constituting the solid electrolyte layer 2, for example, from the viewpoint of excellent strength and thermal stability, zirconium oxide-based oxides such as yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) are used. It can be suitably used. The solid electrolyte constituting the solid electrolyte layer 2 includes yttria-stabilized zirconia from the viewpoints of oxygen ion conductivity, mechanical stability, compatibility with other materials, and chemical stability from an oxidizing atmosphere to a reducing atmosphere. Etc. are suitable.

When the solid electrolyte layer 2 is not allowed to function as a support, the thickness of the solid electrolyte layer 2 is preferably 3 to 20 μm, more preferably 3.5 to 15 μm, still more preferably 4 to 4 to the thickness of the solid electrolyte layer 2 from the viewpoint of electrical resistance and the like. It can be 10 μm. When the solid electrolyte layer 2 functions as a support, the thickness of the solid electrolyte layer 2 is preferably 30 to 300 μm, more preferably 50 to 200 μm, still more preferably 100 to 100, from the viewpoint of strength, electrical resistance, and the like. It can be 150 μm.

The first electrode 3 is a portion to which fuel is supplied. The first electrode 3 can be formed porously. The first electrode 3 can be formed in a layered shape, and may be composed of a single layer or a plurality of layers. FIG. 1 shows an example in which the first electrode 3 is composed of a single layer. When the first electrode 3 is composed of a plurality of layers, specifically, for example, the first electrode 3 has an active layer (not shown) arranged on the solid electrolyte layer 2 side and a solid electrolyte layer 2 side. It may be configured to include a diffusion layer (not shown) arranged on the opposite side. The active layer is a layer for enhancing the electrochemical reaction in the first electrode 3. Further, the diffusion layer is a layer capable of diffusing the supplied fuel F in the in-plane direction of the first electrode 3.

Specifically, as illustrated in FIG. 1, the first electrode 3 has a configuration including an electron conductive material 31 having electron conductivity and an oxygen ion conductive material 32 having oxygen ion conductivity. be able to. Examples of the electronically conductive material 31 include metal materials having catalytic activity such as Ni and Ni alloys. These can be used alone or in combination of two or more. Further, as the oxygen ion conductive material used for the first electrode 3, for example, zirconium oxide-based oxides such as yttria-stabilized zirconia and scandia-stabilized zirconia can be exemplified. These can be used alone or in combination of two or more. In this embodiment, the first electrode 3 can be specifically composed of a mixture of Ni and yttria-stabilized zirconia. In FIG. 1, reference numeral 30 is a pore. Further, the electron conductive material 31 and the oxygen ion conductive material 32 in the first electrode 3 can both be in the form of particles.

When the first electrode 3 functions as a support, the thickness of the first electrode 3 is, for example, preferably 100 to 800 μm, more preferably 150 to 700 μm, from the viewpoints of strength, electrical resistance, gas diffusivity, and the like. More preferably, it can be 200 to 600 μm. When the first electrode 3 is not made to function as a support, the thickness of the first electrode 3 is, for example, preferably 10 to 40 μm, more preferably 15 to 35 μm, still more preferably, from the viewpoint of electrical resistance, gas diffusivity, and the like. Can be 20 to 30 μm.

The second electrode 4 is an electrode paired with the first electrode 3. Specifically, as shown in FIG. 1, the second electrode 4 can be arranged so as to face the first electrode 3 with the solid electrolyte layer 2 interposed therebetween. The outer shape of the second electrode 4 may be formed to have the same size as the outer shape of the first electrode 3, or may be formed smaller than the outer shape of the first electrode 3. The second electrode 4 can be formed porously. The second electrode 4 can be formed in a layered shape, and may be composed of a single layer or a plurality of layers. FIG. 1 shows an example in which the second electrode 4 is composed of a single layer.

Here, the second electrode 4 contains a metal oxide 41 having an oxygen indefinite specificity and a decomposition product 42 of the metal oxide having an oxygen indefinite specificity. The metal oxide 41 having an oxygen indefinite specificity is a composite metal oxide, which is a material capable of having a point defect at an oxygen position by containing a metal element having a different valence. The decomposition product 42 of the metal oxide having an oxygen indefinite ratio is a substance produced by the decomposition of the metal oxide 41 having an oxygen indefinite ratio. The metal oxide 41 having an oxygen indefinite specificity may be contained alone or in combination of two or more in the second electrode 4. Further, the decomposition product 42 of the metal oxide having an oxygen indefinite specificity may be contained alone or in combination of two or more in the second electrode 4.

The metal oxide 41 having an oxygen indefinite specificity can be configured to contain an oxygen-deficient metal oxide 411. The oxygen-deficient metal oxide 411 is a metal oxide with oxygen vacancies, and the above-mentioned point defect position is vacant. The oxygen-deficient metal oxide 411 becomes unstable when excess oxygen enters, and tends to change to a more stable oxide or the like. Therefore, according to the configuration in which the metal oxide 41 having oxygen indefinite specificity contains the oxygen-deficient metal oxide 411, there are the following advantages. That is, the oxygen-deficient metal oxide 411 increases the sensitivity to a high oxygen concentration atmosphere, and as shown in FIG. 2A, in the portion where the high oxygen concentration atmosphere is generated, the oxygen-deficient metal due to the excess oxygen has entered. Oxide 411 decomposes to produce degraded or inactive degradation products. That is, as shown in FIG. 2B, a decomposition product 421 of the oxygen-deficient metal oxide is produced. Since the decomposition product 421 of the oxygen-deficient metal oxide has poor electrode activity, the reaction shifts to another reaction field 44 as shown in FIGS. 2 (a) and 2 (b), and a local overload reaction ( In the SOEC mode described later, a local overloaded water electrolysis reaction is suppressed, and in the SOFC mode described later, a local overloaded power generation reaction) is suppressed, and reaction unevenness in the cell surface is suppressed.

The metal oxide 41 having an oxygen indefinite specificity can be configured to have a perovskite structure or a double perovskite structure. According to this configuration, metal elements having different valences are fixed, so that solid oxide electrochemical cells (hereinafter referred to as SOC) such as water electrolysis cells (including steam electrolysis cells, hereinafter omitted) can be referred to as SOEC. In the steady operating environment of solid oxide fuel cells (Solid Oxide Fuel Cell: hereinafter referred to as SOFC), oxygen is maintained while maintaining a structure having oxygen indefinite specificity. With respect to concentration fluctuations, the structure can be changed to form a stable compound. Therefore, according to this configuration, it becomes easy to secure the electrode activity even when the second electrode 4 is placed in an environment where the oxygen concentration is different in the steady operation of the electrochemical cell 1. The metal oxide 41 having an oxygen non-stoichiometric property can preferably be configured to have a perovskite structure. According to this configuration, the A-site or B-site metal can form a stable compound due to the fluctuation of oxygen concentration. Therefore, according to this configuration, it is advantageous to realize a uniform electrolytic reaction while maintaining the power generation performance.

Examples of the oxygen-deficient metal oxide 411 include (La, Sr) CoO _3-δ , (La, Sr) (Co, Fe) O _3-δ , and (La, Sr) (Mn, Fe) O _3-. Examples thereof _{include δ} , (La, Sr) FeO _3-δ , (Sm, Sr) CoO _3-δ , (La, Ca) CrO _3-δ , and (Ba, La) CoO _3-δ. These can be used alone or in combination of two or more. In addition, δ indicates an oxygen indefinite ratio amount. Further, the above (A, B) contains at least one of the A element and the B element, and the A element and the B element can be partially replaced with each other so that the total chemical composition of the A element and the B element becomes 1. It means that (the same applies hereinafter). _{Among the above-mentioned oxygen-deficient metal oxides 411, (La, Sr) CoO 3-δ} , (La,) are preferable from the viewpoints of electrical resistivity, low toxicity to other functional layers, raw material cost, and the like. Sr) (Co, Fe) O _3-δ , (Sm, Sr) CoO _{3-δ and the} like, and more preferably (La, Sr) CoO _3-δ .

Specific examples of the (La, Sr) CoO _{3-δ include La 1-x} Sr _x CoO _3-δ (0 ≦ x ≦ 1, preferably 0.1 ≦ x ≦ 0.5), (La). , Sr) (Co, Fe) O _3-δ , specifically, La _1-x Sr _x Co _1-y F _y O _3-δ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, preferably. 0.1 ≦ x ≦ 0.5, 0.5 ≦ y ≦ 0.9), (La, Sr) (Mn, Fe) O _3-δ , specifically, La _1-x Sr. _x Mn _{1-y F y} O _3-δ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, preferably 0.1 ≦ x ≦ 0.5, 0.5 ≦ y ≦ 0.9), (La , Sr) FeO _3-δ , specifically, La _1-x Sr _x FeO _3-δ (0 ≦ x ≦ 1, preferably 0.1 ≦ x ≦ 0.5), (Sm, Sr). ) CoO _3-δ specifically includes Sm _1-x Sr _x CoO _3-δ (0 ≦ x ≦ 1, preferably 0.4 ≦ x ≦ 0.6), (La, Ca) CrO. Specific examples of _{3-δ include La 1-x} Ca _x CoO _3-δ (0 ≦ x ≦ 1, preferably 0.1 ≦ x ≦ 0.5), (Ba, La) CoO _3-δ. Specifically, as _{δ , Ba 1-x} La _x CoO _3-δ (0 ≦ x ≦ 1, preferably 0.1 ≦ x ≦ 0.5) and the like can be exemplified. These can be used alone or in combination of two or more. These metal oxides have a perovskite structure.

Specific examples of the decomposition product 421 of the oxygen-deficient metal oxide include inactive oxides containing one or more metal elements constituting the oxygen-deficient metal oxide 411 described above. .. Examples of the decomposition product of (La, Sr) CoO _3-δ include oxides containing Sr and Co such as Sr ₃ Co ₂ O _6.6 and Sr ₂ Co ₂ O _5. Examples of the decomposition product of (La, Sr) (Co, Fe) O _3-δ include Sr and Co and / or Fe _{such as Sr 3} Co ₂ O _6.6 , Sr ₂ Co ₂ O ₅ , _{and Sr FeO 2.} An oxide containing carbon dioxide and the like can be exemplified. Examples of the decomposition product of (Sm, Sr) CoO _3-δ include oxides containing Sr and Co such as Sr ₃ Co ₂ O _6.6 and Sr ₂ Co ₂ O _5.

FIG. 1 shows an example in which the metal oxide 41 having an oxygen indefinite specificity is composed of an oxygen-deficient metal oxide 411. Therefore, in the present embodiment, as illustrated in FIG. 1, the second electrode 4 contains an oxygen-deficient metal oxide 411 and a decomposition product 421 of the oxygen-deficient metal oxide. The decomposition product 421 of the oxygen-deficient metal oxide is a substance produced by decomposing a part of the oxygen-deficient metal oxide 411 contained in the second electrode 4. The above-mentioned metal oxide 41 having indefinite oxygen specificity, the decomposition product 42 of the metal oxide having indefinite oxygen specificity, the oxygen-deficient metal oxide 411, and the decomposition product 421 of the oxygen-deficient metal oxide are any of them. Can also be in the form of particles.

The metal oxide 41 having an oxygen indefinite specificity is preferably a material that decomposes at an ^{oxygen partial pressure of 10-6} bar or less, or ^{10-0.5 bar or more.} Usually, during the steady operation of the SOEC and SOFC, oxygen concentration oxygen electrode and SOFC of the air electrode of SOEC (oxidant electrode) is exposed ^is less than ^{10 -1} bar~10 -0.5 bar. Therefore, according to the above configuration, when the electrochemical cell 1 is constantly operated as at least one of SOEC and SOFC, the metal oxide 41 having oxygen indefinite specificity is present in the oxygen concentration atmosphere to which the second electrode 4 is exposed. Hard to disassemble. Therefore, according to the above configuration, the electrochemical cell 1 that can easily secure a stable output during steady operation can be obtained.

For example, the above-mentioned (La, Sr) CoO _3-δ , (La, Sr) (Co, Fe) O _{3-δ and the} like can be found in the literature “K.Kendall, M.Kendall,“ Chapter 6-Cathodes ”High. -As understood from "temperature Solid Oxide Fuel Cells for the 21st Century, p166, Figure 6.4 (2015)", decomposition occurs at an oxygen concentration of ^{10-8 bar.} Further, (La, Sr) MnO _{3 + δ} described later in the second embodiment is understood from the document “T. Ishihara“ Perovskite Oxide for Cathode of SOFCs ”Perovskite Oxide for Solid Oxide Fuel Cells, p160, Fig7.9 (2009)”. Decomposition occurs at an oxygen concentration of ^{10-7 bar.}

As illustrated in FIG. 1, the second electrode 4 can also include an oxygen ion conductive material 43 having oxygen ion conductivity. The oxygen ion conductive material 43 used for the second electrode 4 is, for example, _{one or two selected from Celia (CeO 2} ), Gd, Y, Sm, La, Nd, Yb, Ca, and Ho. Celia, Y, Ca, which is doped with the above elements and the like, and zirconia, which is doped with one or more elements selected from Sc, (La, Sr) (Ga, Mg) O ₃ , ( Examples thereof include La, Sr) (Sc, Mg) O ₃ and (La, Sr) (Al, Mg) O _3. These can be used alone or in combination of two or more. Specific examples of the (La, Sr) (Ga, Mg) O _{3 include La 1-x} Sr _x Ga _1-y Mg _y O ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, preferably. 0.1 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.3), (La, Sr) (Sc, Mg) O ₃ is specifically La _1-x Sr _x Sc _{1-. y} Mg _y O ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, preferably 0.1 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.3), (La, Sr) (Al, Mg) O ₃ is La _1-x Sr _x Al _1-y Mg _y O ₃ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, preferably 0.1 ≦ x ≦ 0.5, 0.1. ≦ y ≦ 0.5) and the like can be exemplified.

Among the above-mentioned oxygen ion conductive materials 43 used for the second electrode 4, preferably, Gd has a small temperature dependence of oxygen ion conduction, electron conductivity, and suppression of reaction with other functional layers. Dope ceria is preferred. In FIG. 1, reference numeral 40 is a pore. Further, the oxygen ion conductive material 43 used for the second electrode 4 can be in the form of particles.

In the second electrode 4, the amount of the metal oxide 41 having oxygen indefiniteness in the total of the metal oxide 41 having oxygen indefiniteness and the decomposition product 42 of the metal oxide having oxygen indefiniteness is the electrolytic reaction / power generation reaction. From the viewpoint of ensuring a sufficient amount of reaction points, 95% by volume or more is preferable. The volume% can be calculated using a 3D element mapping result using FIB-SEM-EDS (energy dispersive X-ray spectroscopic analysis using a focused ion beam scanning electron microscope) or the like.

The thickness of the second electrode 4 can be 5 μm or more. In the electrochemical cell 1, in addition to the metal oxide 41 having an oxygen indefinite ratio, the second electrode 4 contains a decomposition product 42 of the metal oxide having an oxygen indefinite ratio. That is, the second electrode 4 is a metal having an oxygen indefinite ratio as compared with an electrode containing a metal oxide 41 having an oxygen indefinite ratio and not containing a decomposition product 42 of the metal oxide having an oxygen indefinite ratio. It can be said that the electrode activity is partially lost due to the partial decomposition of the oxide 41. Therefore, when the thickness of the second electrode 4 is within the above range, it becomes easy to secure a reaction point where a sufficient reaction can be obtained by securing the electrode thickness, and it becomes easy to suppress deterioration in the performance of the second electrode 4.

The thickness of the second electrode 4 is preferably 10 μm or more, more preferably 15 μm or more, still more preferably 20 μm or more, still more preferably 25 μm or more, from the viewpoint of ensuring a sufficient reaction point. can. The thickness of the second electrode 4 can be preferably 100 μm or less, more preferably 60 μm or less, still more preferably 50 μm or less, from the viewpoint of gas diffusivity, electrical resistance, and the like.

When the electrochemical cell 1 has an intermediate layer, the intermediate layer can be specifically formed in a layered state from a solid electrolyte having oxygen ion conductivity. Examples of the solid electrolyte used for the intermediate layer include ceria (CeO ₂ ), gd, Sm, Y, La, Nd, Yb, Ca, and one or more elements selected from Ho for ceria. Can be exemplified by ceria doped with. These 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 suitable.

The thickness of the intermediate layer can be preferably 1 to 20 μm, more preferably 2 to 10 μm, from the viewpoint of reducing ohmic resistance and suppressing element diffusion from the second electrode.

The thickness of each part of the electrochemical cell 1 described above is a thickness measurement value of 10 points at each part measured by observing a cross section perpendicular to the cell surface of the electrochemical cell 1 with a scanning electron microscope (SEM). It is the arithmetic average value of.

The electrochemical cell 1 can be manufactured, for example, as follows.

A solid electrolyte layer 2 having oxygen ion conductivity, a first electrode 3 arranged on one side of the solid electrolyte layer 2, and a metal oxidation arranged on the other side of the solid electrolyte layer 2 and having an oxygen indefinite specificity. A cell (not shown) having a second electrode precursor (not shown) containing the substance 41 and not containing the decomposition product 42 of the metal oxide having an oxygen indefinite specificity is produced. Specifically, in the present embodiment, a second electrode precursor containing oxygen-deficient metal oxide 411 and not containing the decomposition product 421 of oxygen-deficient metal oxide can be used. Next, the cell is subjected to a leveling process of operating in a current density higher than the current density of the electrochemical cell 1 during steady operation, that is, in a current density region where a non-uniform reaction becomes more apparent. As a result, the metal oxide 41 having oxygen non-stoichiometricity is decomposed in the portion of the second electrode precursor where the current easily flows locally, and the metal oxide decomposition product 42 having oxygen non-stoichiometricity is generated. On the other hand, in the portion of the second electrode precursor where no local current flow occurs, the decomposition of the metal oxide 41 having oxygen non-stoichiometricity hardly proceeds. By the above leveling treatment, the second electrode precursor is converted into the second electrode 4 containing the metal oxide 41 having an oxygen indefinite specificity and the decomposition product 421 of the metal oxide having an oxygen indefinite ratio. The obtained electrochemical cell 1 is obtained. That is, in this method of producing the electrochemical cell 1, it is obtained by performing a leveling treatment on the cell and deliberately decomposing a part of the metal oxide 41 having an oxygen non-stoichiometric ratio in the state of the cell. The reaction distribution in the cell plane of the electrochemical cell 1 is relaxed. That is, the reaction in the cell plane of the electrochemical cell 1 is leveled. As the leveling treatment, for example, _{a mixed gas of H 2} and H ₂ O is supplied to the first electrode 3, air is supplied to the second electrode precursor, and the leveling temperature is 650 ° C to 850 ° C. , A process of operating in a current density region higher than the current density during steady operation can be exemplified. Examples of the current density region higher than the current density during steady operation include, for example, a range of current densities of 2 to 4 times the current density (described later) when the electrochemical cell 1 is operated for steady power generation. be able to. Further, the processing time for the power generation operation can be, for example, 2 hours to 10 hours. The above process may be performed once, or may be performed a plurality of times under the same conditions or different conditions. It is preferable that the electrochemical cell 1 thus obtained is constantly operated at a current density equal to or lower than the current density at the time of the leveling treatment.

The electrochemical cell 1 can be used as at least one of SOEC and SOFC. That is, the electrochemical cell 1 may be operated as SOEC, may be operated as SOFC, and may be further switched between an SOEC mode operated as SOEC and an SOFC mode operated as SOFC. It may be operated as SOEC and SOFC. Hereinafter, an operation example of the electrochemical cell 1 will be described.

First, an example of operating the electrochemical cell 1 as SOEC will be described with reference to FIG. In this case, the first electrode 3 is used as a hydrogen electrode, and the second electrode 4 is used as an oxygen electrode. The first electrode 3, as a fuel F, for example, can supply water (H 2 _O) containing gas F1 such as water vapor gas. Gas A1 such as air may be supplied to the second electrode 4, or gas A1 may not be supplied. Note that FIG. 3 shows an example of supplying the gas A1 to the second electrode 4. On the first electrode 3 side, the gas flow path 5 on the first electrode side can be arranged in contact with the first electrode 3. On the second electrode 4 side, the gas flow path 6 on the second electrode side can be arranged in contact with the second electrode 4. As illustrated in FIG. 3, a power source 7 is connected between the first electrode 3 and the second electrode 4. In the SOIC mode, the fuel F supplied from the supply port 51 of the gas flow path 5 on the first electrode side passes through the gas flow path 5 on the first electrode side and reaches the first electrode 3. At the first electrode 3, an electrode reaction of _{H 2} O + 2e ⁻ → H ₂ + O ^{2- occurs.} The surplus fuel F is _{discharged from the discharge port 52 together with the generated hydrogen gas (H 2} ) through the gas flow path 5 on the first electrode side. On the other hand, the second electrode _{^{4, O 2- → 1 / 2O}} 2 + 2e - → electrode reaction occurs in. The generated oxygen gas (O ₂ ) is discharged from the discharge port 62. When the gas A1 is not supplied to the second electrode 4, the generated oxygen gas is discharged from the discharge port 62 due to the difference in oxygen concentration from the outside. When the gas A1 is supplied to the second electrode 4, the generated oxygen gas has an advantage that its concentration is diluted by the gas A1 and discharged to the outside. ^{In the solid electrolyte layer 2, oxygen ions (O2-} ) move from the first electrode 3 side to the second electrode 4 side. In this way, the electrochemical cell 1 can be operated as SOEC. The first electrode 3 may be mixed with a water-containing gas F1 as a fuel F and a adjusting gas (reducing gas) (not shown) such as hydrogen gas. In this case, it is possible to suppress the oxidation of the metal material that may be contained in the first electrode 3 during the SOIC operation.

Next, an example of operating the electrochemical cell 1 as an SOFC will be described with reference to FIG. In this case, the first electrode 3 is used as a fuel electrode, and the second electrode 4 is used as an air electrode (oxidizing agent electrode). A hydrogen-containing gas F2 such as hydrogen gas can be supplied to the first electrode 3 as the fuel F. An oxygen-containing gas A2 such as air or oxygen gas can be supplied to the second electrode 4 as an oxidizing agent. On the first electrode 3 side, the gas flow path 5 on the first electrode side can be arranged in contact with the first electrode 3. On the second electrode 4 side, the gas flow path 6 on the second electrode side can be arranged in contact with the second electrode 4. As illustrated in FIG. 4, a load 8 is connected between the first electrode 3 and the second electrode 4. In the SOFC mode, the fuel F supplied from the supply port 51 of the gas flow path 5 on the first electrode side passes through the gas flow path 5 on the first electrode side and reaches the first electrode 3. At the first electrode 3, an electrode reaction of _{H 2} + O ^2- → H ₂ O + 2e ^{− occurs.} The surplus fuel F is _{discharged from the discharge port 52 together with the generated water vapor (H 2} O) through the gas flow path 5 on the first electrode side. On the other hand, the oxygen-containing gas A2 supplied from the supply port 61 of the second electrode side gas flow path 6 passes through the second electrode side gas flow path 6 and reaches the second electrode 4. At the second electrode 4, a 1/2O ₂ + 2e ⁻ → O ^2- electrode reaction occurs. The excess oxygen-containing gas A2 is discharged from the discharge port 62 through the gas flow path 6 on the second electrode side. ^{In the solid electrolyte layer 2, oxygen ions (O2-} ) move from the second electrode 4 side to the first electrode 3 side. In this way, the electrochemical cell 1 can be operated as an SOFC. In addition, water vapor or the like (not shown) can be mixed with the hydrogen-containing gas F2 as the fuel F in the first electrode 3.

Next, an example in which the electrochemical cell 1 is operated as SOEC and SOFC (the electrochemical cell 1 is operated in a reversible manner) will be described. In this case, the electrochemical cell 1 may be configured to be operable as SOEC and SOFC as described above. According to this configuration, the electrochemical cell 1 is operated as a SOC by using electricity generated by surplus electricity, renewable energy, etc., and the generated hydrogen gas is separately stored and the stored hydrogen gas is used as fuel. It is possible to obtain an electrolysis / power generation device capable of operating the electrochemical cell 1 as an SOFC to generate power.

Examples of the steady operating temperature of the electrochemical cell 1 can be, for example, 400 ° C. or higher and 800 ° C. or lower when functioning as SOEC, and 400 ° C. or higher and 800 ° C. or lower when functioning as SOFC. The current density of the electrochemical cell 1 during steady operation is, specifically, 0.4 A / cm ² or more and 2.0 A / cm ² or less when functioning as SOEC, and 0.2 A when functioning as SOFC. / cm ² or more 1.0A / cm ² can be less.

(Embodiment 2)
The electrochemical cell of the second embodiment will be described with reference to FIG. In addition, among the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-mentioned embodiments represent the same components and the like as those in the above-mentioned embodiments, unless otherwise specified.

As illustrated in FIG. 5, the electrochemical cell 1 of the present embodiment has a different configuration of the second electrode 4 from the electrochemical cell 1 of the first embodiment. Specifically, in the present embodiment, the metal oxide 41 having an oxygen indefinite ratio in the second electrode 4 can be further configured to contain an oxygen-rich metal oxide 412.

The oxygen-rich metal oxide 412 is a metal oxide with interstitial oxygen, and the above-mentioned point defect positions are excessively filled. The oxygen-rich metal oxide 412 becomes unstable when interstitial oxygen is released, and tends to change to a more stable oxide or the like. Therefore, according to the configuration in which the metal oxide 41 having an oxygen indefinite specificity contains not only the oxygen-deficient metal oxide 411 but also the oxygen-rich metal oxide 412, there are the following advantages. That is, even when the oxygen-deficient metal oxide 411 contained in the second electrode 4 is excessively decomposed when a high oxygen concentration atmosphere is locally generated in the second electrode 4, the oxygen excess type Metal oxide 412 does not decompose. On the contrary, when a low oxygen concentration atmosphere is locally generated in the second electrode 4, oxygen is excessively decomposed even when the oxygen-rich metal oxide 412 contained in the second electrode 4 is excessively decomposed. The defective metal oxide 411 does not decompose. Therefore, according to the above configuration, it is possible to suppress the amount of the catalytically active substance in the second electrode 4 from becoming excessively small, and it is possible to suppress the decrease in the electrode activity of the second electrode 4. That is, according to the above configuration, the excess of the metal oxide 41 having oxygen indeterminacy that exerts catalytic activity regardless of whether a high oxygen concentration atmosphere or a low oxygen concentration atmosphere is locally generated in the second electrode 4. Decomposition can be suppressed.

Examples of the oxygen-rich metal oxide 412 include (La, Sr) MnO _{3 + δ} , PrBaCo ₂ O _{5 + δ} , PrBaFe ₂ O _{5 + δ, and the} like. These can be used alone or in combination of two or more. In addition, δ indicates an oxygen indefinite ratio amount. Among the above-mentioned oxygen-rich metal oxides 412, (La, Sr) MnO _{3 + δ} , PrBaCo ₂ O _{5 + δ,} etc. are preferable, and (La, Sr) MnO 3 + δ, and more preferably, (La, Sr) MnO 3 + δ, etc. La, Sr) MnO _{3 + δ} .

Specific examples of the (La, Sr) MnO _{3 + δ include La 1-x} Sr _x MnO _{3 + δ} (0 ≦ x ≦ 1, preferably 0.1 ≦ x ≦ 0.4). .. These can be used alone or in combination of two or more. These metal oxides have a perovskite structure or a double perovskite structure.

Specific examples of the decomposition product 422 of the oxygen-rich metal oxide include inactive oxides containing one or more metal elements constituting the oxygen-rich metal oxide 412 described above. .. Examples of the decomposition product of (La, Sr) MnO _{3 + δ} include oxides containing Sr and Mn such as Sr ₂ Mn ₂ O ₅ and Sr ₂ MnO _4.

In the present embodiment, the second electrode 4 may contain an oxygen-deficient metal oxide 411, a decomposition product 421 of the oxygen-deficient metal oxide, and an oxygen-rich metal oxide 412, or oxygen. It may contain a defective metal oxide 411, a decomposition product 421 of the oxygen-deficient metal oxide, an oxygen-rich metal oxide 412, and a decomposition product 422 of the oxygen-rich metal oxide. The decomposition product 422 of the oxygen-rich metal oxide is a substance produced by decomposition of a part of the oxygen-rich metal oxide 412 contained in the second electrode 4. The above-mentioned metal oxide 41 having an indefinite oxygen specificity, a decomposition product 42 of a metal oxide having an indefinite oxygen specificity, an oxygen-deficient metal oxide 411, a decomposition product of an oxygen-deficient metal oxide 421, and an excess of oxygen. Both the type metal oxide 412 and the decomposition product 422 of the oxygen excess type metal oxide can be in the form of particles. Further, the electrochemical cell 1 having the second electrode 4 in the present embodiment can be manufactured, for example, as follows. Specifically, as the second electrode precursor described above in the first embodiment, the oxygen-deficient metal oxide 411 and the oxygen-rich metal oxide 412 are contained, and the decomposition product 421 of the oxygen-deficient metal oxide and the decomposition product 421 of the oxygen-deficient metal oxide are contained. The structure does not contain the decomposition product 422 of the oxygen-rich metal oxide. Then, as described above in the first embodiment, after the electrochemical cell 1 is operated in the range of the current density of 2 times or more and 4 times or less of the current density at the time of steady power generation operation, the electrochemical cell 1 is further operated. It is possible to exemplify a process of operating the current in a range of a current density of 2 times or more and 4 times or less of the current density when the steady electrolytic operation is performed. The processing time for the electrolysis operation can be, for example, 2 hours to 10 hours.

The second electrode 4 can also include the oxygen ion conductive material 43 having oxygen ion conductivity as described above in the first embodiment. In FIG. 5, the second electrode 4 is an oxygen-deficient metal oxide 411, a decomposition product 421 of an oxygen-deficient metal oxide, an oxygen-rich metal oxide 412, and a decomposition product 422 of an oxygen-rich metal oxide. And an example including the oxygen ion conductive material 43 are shown.

Other configurations and effects are the same as in the first embodiment.

(Experimental example)
<Material preparation>
NiO powder (average particle size: 1.0 .mu.m) and yttria-stabilized zirconia containing _Y 2 _{O 3} of 8 mol% (hereinafter, YSZ) powder (average particle size: 0.5 [mu] m) and, the carbon (pore forming agent) , Polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed in a ball mill to prepare a slurry. The mass ratio of NiO powder and YSZ powder was 65:35. Using the doctor blade method, the slurry was applied in layers on the resin sheet, dried, and then the resin sheet was peeled off to prepare a first electrode forming sheet. The average particle diameter is the particle diameter (diameter) d50 when the volume-based cumulative frequency distribution measured by the laser diffraction / scattering method shows 50% (hereinafter, the same applies).

A slurry was prepared by mixing YSZ powder (average particle size: 0.5 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol with a ball mill. After that, the solid electrolyte layer forming sheet was prepared in the same manner as in the preparation of the first electrode forming sheet.

A slurry is prepared by mixing Gd-doped CeO ₂ (hereinafter, GDC) powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol with a ball mill. did. In this experimental example, CeO ₂ doped with 10 mol% Gd was used as the GDC. After that, the intermediate layer forming sheet was prepared in the same manner as in the preparation of the first electrode forming sheet.

A mixture of (La, Sr) CoO _3-δ powder (average particle size: 1.5 μm) as an oxygen-deficient metal oxide and GDC powder (average particle size: 2.0 μm) as an oxygen ion conductive material. Then, this was dispersed in terpineol as a solvent together with a dispersant. Ethyl cellulose as a binder was added to the obtained dispersion and mixed to prepare a paste for forming a second electrode. As the above (La, Sr) CoO _3-δ powder, specifically, La _0.6 Sr _0.4 CoO _3-δ powder was used. The mass ratio of the (La, Sr) CoO _3-δ powder to the GDC powder was 50:50.

<Preparation of electrochemical cell>
A plurality of first electrode forming sheets, a solid electrolyte layer forming sheet, and an intermediate layer forming sheet were laminated in this order and pressure-bonded using a hydrostatic pressure press (WIP) molding method. The WIP molding conditions were a temperature of 85 ° C., a pressing force of 50 MPa, and a pressurizing time of 10 minutes. Further, the obtained molded product was degreased.

Then, the obtained molded product was calcined at 1350 ° C. for 2 hours in the air atmosphere. As a result, a fired body in which the layered first electrode (thickness 400 μm), the solid electrolyte layer (3.5 μm), and the intermediate layer (3 μm) were laminated in this order was obtained.

Next, a paste for forming a second electrode is applied to the surface of the intermediate layer in the fired body by a screen printing method, and the paste is fired (baked) at 950 ° C. for 2 hours in an air atmosphere to form a layered second electrode. A precursor (thickness 50 μm) was formed. The outer shape of the second electrode precursor was formed to be smaller than the outer shape of the first electrode. This formed a flat cell. The formed cell is usually assembled to a metal stack member so that it can operate as a system. In this experimental example, in order to exclude various environmental factors such as toxic substances scattered from metal members and temperature distribution due to the increase in size, a small cell is formed, only this cell is used, and an element evaluation bench is used. The following processing and evaluation were performed.

Then, the sealing glass was applied to the end face of the obtained cell. The temperature of this cell was raised to 850 ° C. in the atmosphere, and the first electrode and the fuel pipe were sealed with glass to form a gas seal structure. Next, the first electrode was reduced. The reduction treatment conditions were a reduction temperature: 800 ° C., a reduction treatment gas: hydrogen gas, and a reduction time: 3 hours.

Next, after the above reduction treatment, the temperature is lowered a little to reach the power generation temperature, and the current density is twice the current density at the time of steady power generation operation (specifically, 1.5 A / cm ² ) with respect to the cell. The process of operating the time power generation was carried out. At this time, a mixed gas of _{H 2} and H _{2 O (H 2} : H ₂ O = 6: 4 in volume ratio) was supplied to the first electrode, and air was supplied to the second electrode precursor. .. The power generation temperature was 700 ° C. In this experimental example, the cell subjected to the power generation operation was further subjected to a process of electrolyzing for 4 hours at the same current density as described above. At this time, a mixed gas of _{H 2} and H _{2 O (H 2} : H ₂ O = 6: 4 in volume ratio) was supplied to the first electrode, and air was supplied to the second electrode precursor. .. The water electrolysis temperature was 700 ° C. Then, the temperature was lowered while maintaining the atmosphere of the first electrode. As a result, the electrochemical cell according to this experimental example was produced. In this experimental example, as the leveling treatment, both the treatment by the power generation operation and the treatment by the electrolysis operation were performed. This is because the reaction distribution caused by the non-uniformity of the voids in the plane of the cell is difficult to react if there is a rate-determining part of the hydrogen supply during the power generation operation, whereas the water vapor supply is performed during the electrolysis operation. This is to ensure that a uniform reaction can be obtained in either mode because there is a part that is difficult to react if there is a rate-determining part of.

<XRD analysis of the second electrode>
The structure of the second electrode of the electrochemical cell taken out from the element evaluation bench was analyzed using an X-ray diffractometer (fully automatic multipurpose X-ray diffractometer "SmartLab" manufactured by RIGAKU). Here, in this experimental example, in order to exclude various environmental factors at the time of producing the electrochemical cell, the leveling treatment is performed using only the small cell. Therefore, the substances that can be contained in the second electrode are basically (La, Sr) CoO _3-δ and GDC (including impurities in the raw material) used as the raw material of the second electrode, and other substances. That is, it can be roughly classified into compounds formed at the time of production.

FIG. 6 shows the XRD analysis result of the second electrode. According to FIG. 6, in the second electrode of the electrochemical cell, in addition to the peaks of _{(La, Sr) CoO 3-δ and GDC used as the raw materials of the second electrode, La 2} O ₃ and Sr ₂ Co ₂ O _{Peak 5} was detected. The peaks of La ₂ O ₃ and Sr ₂ Co ₂ O ₅ were detected because the oxygen non-stoichiometric metal oxide (La, Sr) CoO _3-δ was decomposed by the above leveling treatment and La. _{This is because 2} O ₃ and Sr ₂ Co ₂ O ₅ were generated. For comparison, the same XRD analysis was performed on the second electrode precursor in the cell not subjected to the leveling treatment. As a result, the second electrode precursor was La ₂ O ₃ , Sr ₂ Co ₂ O _5. Peak was not detected.

The electrochemical cell and the cell not subjected to the leveling treatment were used as SOFCs and were constantly operated at ^{700 ° C. and a current density of 0.5 A / cm 2.} As a result, the reaction temperature distribution in the cell surface of the electrochemical cell was reduced as compared with the cell not subjected to the leveling treatment. The reason why the electrochemical cell was made to function as SOFC and the reaction temperature distribution in the cell surface was confirmed is that SOFC causes a power generation reaction, so that the reaction temperature distribution in the cell surface can be easily confirmed as compared with SOEC. .. From this result, it was confirmed that the electrochemical cell can suppress the reaction unevenness in the cell surface.

The present invention is not limited to each of the above embodiments and experimental examples, and various modifications can be made without departing from the gist thereof. In addition, each configuration shown in each embodiment and each experimental example can be arbitrarily combined.

1 Electrochemical cell 2 Solid electrolyte layer 3 1st electrode 4 2nd electrode F Fuel F1 Water-containing gas F2 Hydrogen-containing gas

Claims (7)

A solid electrolyte layer (2) having oxygen ion conductivity, a first electrode (3) arranged on one side of the solid electrolyte layer and supplied with fuel (F, F1, F2), and the solid electrolyte layer. A second electrode (4) arranged on the other side of the above-mentioned first electrode and paired with the first electrode is provided.
The second electrode contains a metal oxide having an oxygen indefinite ratio (41) and a decomposition product of the metal oxide having an oxygen indefinite ratio (42).
Electrochemical cell (1). The metal oxide having an oxygen indefinite specificity includes an oxygen-deficient metal oxide (411).
The electrochemical cell according to claim 1. The metal oxide having an oxygen indefinite specificity further includes an oxygen excess type metal oxide (412).
The electrochemical cell according to claim 2. The metal oxide having an oxygen indefinite specificity has a perovskite structure.
The electrochemical cell according to any one of claims 1 to 3. The metal oxide having an oxygen indefinite specificity is a material that decomposes at an ^{oxygen partial pressure of 10-6} bar or less, or ^{10-0.5 bar or more.}
The electrochemical cell according to any one of claims 1 to 4. The thickness of the second electrode is 5 μm or more.
The electrochemical cell according to any one of claims 1 to 5. Used as at least one of a solid oxide electrolytic cell and a solid oxide fuel cell,
The electrochemical cell according to any one of claims 1 to 6.

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