Electrode material and electrochemical cell

Abstract

To provide an electrode material capable of suppressing deterioration over time of electrode performance.SOLUTION: There is provided an electrode material having a composition represented by the following expression (1), Ce1-x-yZrxMyO2-α (1), provided that 0<x<0.1, 0.05<y<0.2, α is a value at which electrical neutrality is maintained, M is at least one element selected from the group consisting of Gd, La, Nd, Y and Sm. Both the maintenance of oxide ion conductivity and the improvement of OSC can be achieved by co-doping CeO2 with Zr and M. As a result, the deterioration over time of electrode performance can be suppressed while securing oxide ion conductivity.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electrode material and an electrochemical cell, and more particularly to an electrode material that can suppress deterioration of electrode performance over time, and an electrochemical cell that includes this electrode material in the fuel electrode. [Background technology]

[0002] A solid oxide fuel cell (SOFC) is a fuel cell that uses an oxide ion conductor as an electrolyte. When fuel gases such as H2, CO, and CH4 are supplied to the anode (fuel electrode) of the SOFC and O2 is supplied to the cathode (oxygen electrode), an electrode reaction occurs and electricity can be extracted. The CO2 and H2O produced by the electrode reaction are discharged outside the SOFC. On the other hand, solid oxide electrolysis cells (SOECs) have the same structure as SOFCs, but they operate in the opposite direction to SOFCs: by supplying CO2 or H2O to the cathode (fuel electrode) of an SOEC and passing an electric current between the electrodes, CO and H2 can be produced.

[0003] An SOEC is a single cell in which a cathode (fuel electrode) is formed on one side of a solid electrolyte layer and an anode (air electrode) is formed on the other side. The following materials are generally used as materials for the components that make up such an SOEC.

[0004] (a) Solid electrolyte layer: yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), lanthanum strontium gallium magnesium oxide (LSGM), etc. (b) Fuel electrode: Ni / YSZ, Ni-Fe / YSZ, etc. (c) Air electrode: lanthanum strontium manganite (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium cobaltite (LSC), etc.

[0005] The anode of an SOEC is generally made of Ni / YSZ cermet. However, because YSZ has low oxide ion conductivity at low temperatures, CeO2-based materials such as gadolinium-doped ceria (GDC), which have higher oxide ion conductivity at low temperatures, have been attracting attention in recent years.

[0006] For example, Patent Document 1 discloses the following as a solid electrolyte: A configuration is disclosed that uses ZrO2, CeO2 doped with at least one element selected from the group consisting of ZrO2, Y, Sc, Sm, Gd, and La, or CeO2 doped with at least one element selected from the group consisting of Gd, Sm, Y, La, Nd, Yb, Ca, and Ho.

[0007] In addition, in Patent Document 2, the reaction prevention layer on the air electrode side is A configuration is disclosed in which CeO2 is doped with a rare earth element and the doping amount when the rare earth element is converted into an oxide is more than 10 mol % and less than 30 mol %.

[0008] In addition, in Patent Document 3, a solution containing Ce alkoxide and Sm alkoxide is impregnated into the fuel electrode of a solid oxide fuel cell, and Ce is deposited in the fuel electrode. 0.9 Sm 0.1 O 1.95 A configuration capable of depositing such an electrode active oxide is disclosed.

[0009] Furthermore, Patent Document 4 discloses the configuration of a solid oxide fuel cell equipped with an air electrode made of a perovskite oxide containing manganese. The document states that such a solid oxide fuel cell is excellent in output performance and durability.

[0010] However, even if a CeO2-based material is used as the solid electrolyte, the operating temperature of SOECs and other devices is still high, and the temperature of the water vapor that is supplied to the anode as a raw material for hydrogen production is currently over 700°C. In such a harsh environment, the hydroxide species generated during HO electrolysis oxidize (convert to hydroxide) the active species, such as Ni-based particles, causing them to evaporate, resulting in deterioration of the electrode performance of the anode over time. For this reason, some kind of countermeasure is urgently needed. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2018-085200 A [Patent Document 2] JP 2018-142419 A [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-352809 [Patent Document 4] International Publication No. 2005 / 015671 Summary of the Invention [Problem to be solved by the invention]

[0012] The problem to be solved by the present invention is to provide an electrode material capable of suppressing deterioration of electrode performance over time. Another problem to be solved by the present invention is to provide an electrochemical cell using an electrode material that can suppress deterioration of electrode performance over time. [Means for solving the problem]

[0013] In order to solve the above problems, the electrode material according to the present invention has a composition represented by the following formula (1). Ce 1―x―y Zr x M y O 2-α …(1) however, 0 <x<0.1 0.05 <y<0.2 α is the value at which electroneutrality is maintained M is at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm.

[0014] The electrochemical cell according to the present invention further comprises: an electrolyte layer made of a solid oxide electrolyte; a fuel electrode formed on one side of the electrolyte layer; an air electrode formed on the other side of the electrolyte layer; Equipped with The fuel electrode is Electrolyte particles made of the electrode material according to the present invention; Ni-based particles and Includes: [Effects of the Invention]

[0015] CeO2 has an oxygen storage capacity (Oxygen Storage Capacity: OSC) that absorbs and releases oxygen depending on the ambient oxygen partial pressure. This is because Ce ions can easily absorb and release oxygen depending on the ambient oxygen partial pressure. 3+ →Ce 4+ , Ce 4+ →Ce 3+ (See formula (a)). Ce(IV)O2⇔Ce2(III)O3+1 / 4O2…(a)

[0016] Here, Ce 3+ , Ce 4+ The ionic radii of Ce are 1.14 Å and 0.97 Å, respectively. 4+ →Ce 3+ During the reduction reaction, the ionic radius increases by approximately 1.2 times. This is a very large change from a crystallographic perspective, and the steric repulsion caused by the increase in the ionic radius of Ce destabilizes the lattice, making this reduction reaction energetically unfavorable and usually not proceeding easily. This is the rate-limiting factor, limiting the OSC.

[0017] On the other hand, Zr 4+ The ionic radius of Zr is 0.84 Å, and the small ionic radius of Zr is present in the crystal lattice of CeO2. 4+ By introducing Ce 4+ →Ce 3+This locally alleviates the steric repulsion that accompanies the increase in ionic radius during the reduction reaction, and reduces the destabilization of the crystal lattice, thereby improving the OSC.

[0018] In other words, Zr with a small ionic radius is added to the crystal lattice of CeO2. 4+ By introducing this, the OSC of the electrolyte particles made of the electrode material is improved, the oxidation (hydroxide formation) of Ni-based particles and other particles that also make up the electrode is suppressed, and the evaporation of Ni-based particles and other particles can be prevented. As a result, deterioration of the electrode performance over time can be suppressed.

[0019] Furthermore, M (at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm) is doped to ensure the conductivity of oxide ions. From the viewpoint of oxide ion conductivity, it is more preferable to dope the oxide with Gd and / or Sm.

[0020] Therefore, by co-doping CeO2 with Zr and M, it is possible to maintain the conductivity of oxide ions and improve the OSC at the same time. As a result, it is possible to suppress deterioration of the electrode performance over time while ensuring the conductivity of oxide ions. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is an explanatory diagram of OSC improvement. [Figure 2] FIG. 10 is an explanatory diagram of electrode deterioration suppression. [Figure 3] FIG. 1 is a schematic diagram of an electrochemical cell used for impedance measurements. [Figure 4] FIG. 1 is a graph showing the relationship between the amount of Zr doping and the specific oxygen storage capacity (OSC / SSA). [Figure 5] FIG. 10 is a diagram showing an example of an impedance analysis result. [Figure 6] FIG. 10 is a graph showing the relationship between the oxide ion conductivity and the deterioration rate of the fuel electrode. [Figure 7] FIG. 1 is a graph showing the relationship between the specific oxygen storage capacity (OSC / SSA) and the degradation rate of the anode. DETAILED DESCRIPTION OF THE INVENTION

[0022] [Configuration 1] An electrode material having a composition represented by the following formula (1): Ce 1―x―y Zr x M y O 2-α …(1) however, 0 <x<0.1 0.05 <y<0.2 α is the value at which electroneutrality is maintained M is at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm.

[0023] [Configuration 2] Specific oxygen storage capacity (OSC / SSA) at 700°C is 1.5 mg / m 2 10. The electrode material of claim 1, wherein the electrode material is ultrathin. However, "specific oxygen storage capacity (OSC / SSA)" refers to the oxygen storage capacity (OSC) (mg / g) per 1g of electrode material divided by the specific surface area (SSA) (m 2 / g).

[0024] [Configuration 3] Conductivity is 1.0 x 10 -3 3. The electrode material of claim 1 or 2, wherein the electrical conductivity is greater than 1000 kJ / cm. Here, "electrical conductivity" refers to a value calculated from bulk resistance obtained by measuring AC impedance at 700°C in the atmosphere.

[0025] [Configuration 4] 0.01≦x≦0.05 0.05 <y≦0.15 4. The electrode material according to any one of configurations 1 to 3, which satisfies the above.

[0026] [Configuration 5] 5. The electrode material according to any one of configurations 1 to 4, which is used as a solid oxide electrolyte for an anode of a solid oxide electrolysis cell (SOEC) or a solid oxide fuel cell (SOFC).

[0027] [Configuration 6] an electrolyte layer made of a solid oxide electrolyte; a fuel electrode formed on one side of the electrolyte layer; an air electrode formed on the other side of the electrolyte layer; Equipped with The fuel electrode is Electrolyte particles made of the electrode material according to any one of configurations 1 to 5; Ni-based particles and Contains Electrochemical cell.

[0028] [Configuration 7] 7. The electrochemical cell according to aspect 6, wherein the content of Ni-based particles in the fuel electrode is 20 mass % or more and 70 mass % or less. Here, the "content of Ni-based particles" refers to the ratio of the mass of Ni-based particles to the total mass of the electrolyte particles and Ni-based particles.

[0029] [Configuration 8] 8. The electrochemical cell of claim 6 or 7, wherein the porosity of the anode is greater than 25% and less than 40%. Here, the "porosity" refers to the ratio of the difference between the theoretical specific gravity of the fuel electrode and the actually measured specific gravity of the fuel electrode to the theoretical specific gravity of the fuel electrode.

[0030] [Configuration 9] 9. The electrochemical cell according to any one of configurations 6 to 8, which is used as a solid oxide electrolysis cell (SOEC) or a solid oxide fuel cell (SOFC).

[0031] An embodiment of the present invention will be described in detail below. [1.1. Electrode material] The electrode material according to the present invention comprises: It has a composition represented by the following formula (1). Ce 1―x―y Zr x My O 2-α …(1) however, 0 <x<0.1 0.05 <y<0.2 α is the value at which electroneutrality is maintained M is at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm.

[0032] [1.1.1. CeO2] CeO2 has an OSC that absorbs and releases oxygen depending on the ambient oxygen partial pressure. This means that Ce ions can easily absorb and release oxygen depending on the ambient oxygen partial pressure. 3+ →Ce 4+ , Ce 4+ →Ce 3+ Because it can change into

[0033] Here, Ce 3+ , Ce 4+ The ionic radii of Ce are 1.14 Å and 0.97 Å, respectively. 4+ →Ce 3+ During the reduction reaction, the ionic radius increases by approximately 1.2 times. This is an extremely large change from a crystallographic perspective, and the steric repulsion caused by the increase in the Ce ionic radius destabilizes the lattice, making this reduction reaction energetically unfavorable and normally not proceeding easily. This is the rate-limiting factor, limiting the OSC (see Figure 1(a)).

[0034] [1.1.2. Zr] On the other hand, Zr 4+ The ionic radius of Zr is 0.84 Å, and the small ionic radius of Zr is present in the crystal lattice of CeO2. 4+ By introducing Ce 4+ →Ce 3+ This locally alleviates the steric repulsion that accompanies the increase in ionic radius during the reduction reaction, and reduces the destabilization of the crystal lattice, thereby improving the OSC (see Figure 1(b)).

[0035] And, Ce due to the improvement of OSC 4+ →Ce 3+As the reduction reaction of CeO2 increases, the number of oxygen vacancies formed in CeO2 to satisfy the electroneutrality condition also increases. For this reason, Zr 4+ When considering an SOEC using CeO2-based materials containing hydroxyl groups as electrolyte particles, the hydroxide species O2 generated during H2O electrolysis 2― Ions tend to be trapped by the electrolyte particles. In other words, oxidation (conversion to hydroxide) of the Ni-based particles and the like that constitute the electrodes is suppressed, and evaporation of the Ni-based particles and the like can be prevented (see FIG. 2). As a result, deterioration of the electrode performance over time can be suppressed.

[0036] Generally, the higher the Zr content, the better the OSC of the electrode material. Here, the "Zr content" refers to the ratio of the number of moles of Zr to the total number of moles of Ce, Zr, and M (at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm) contained in the electrode material. To obtain such an effect, the Zr content must be greater than 0 mol %, preferably 0.5 mol % or more, and more preferably 1 mol % or more.

[0037] On the other hand, if the Zr content is excessive, the oxide ion conductivity or OSC may decrease. Therefore, the Zr content must be less than 10 mol%. The content is preferably 7.5 mol% or less, and more preferably 5 mol% or less.

[0038] [1.1.3. M (an element selected from the group consisting of Gd, etc.)] The electrode material is doped with trivalent M (at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm) to form oxygen vacancies for oxide ion conduction.

[0039] Generally, the oxide ion conductivity of an electrode material improves as the content of M increases. Here, the "content of M" refers to the ratio of the number of moles of M to the total number of moles of Ce, Zr, and M contained in the electrode material. To achieve such an effect, the content of M must exceed 5 mol %, preferably 7.5 mol % or more, and more preferably 10 mol % or more.

[0040] On the other hand, if the content of M is excessive, the oxide ion conductivity or OSC may decrease. Therefore, the content of M must be less than 20 mol%. The content is preferably 17.5 mol% or less, and more preferably 15 mol% or less.

[0041] From the viewpoint of oxide ion conductivity, it is more preferable to incorporate Gd and / or Sm, because the incorporation of Gd and / or Sm makes it easier to create a lattice structure in which oxygen ions can move most easily.

[0042] Therefore, by co-doping CeO2 with Zr and M as an electrode material, it is possible to maintain the conductivity of oxide ions while improving the OSC. As a result, it is possible to suppress deterioration of the electrode performance over time while ensuring the conductivity of oxide ions.

[0043] [1.2.1. Electrode Material Characteristics (OSC)] The oxygen storage capacity (OSC) refers to the mass change ΔW (mg) of a given weight of electrode material heated to a given temperature T before and after oxygen storage. In the present invention, ΔW specifically refers to the difference in mass between 15 mg of electrode material heated to 700°C and exposed to an O2 (5%) / N2 atmosphere for 5 minutes, and the mass of the electrode material heated to temperature T and exposed to an H2 (5%) / N2 atmosphere. ΔW can be measured using a thermogravimetric analyzer. The OSC of an electrochemical cell, which will be described later, can be estimated by detecting changes in the Ce_K absorption edge energy through X-ray absorption spectroscopy using synchrotron radiation or the like.

[0044] [1.2.2. Electrode material characteristics (specific surface area)] The specific surface area (SSA) of an electrode material is the surface area per 1 g of the electrode material, and is a value measured by the BET method using a specific surface area measuring device.

[0045] In the case of SOEC, etc., active species particles such as Ni-based particles and electrolyte particles are physically mixed on a submicron to micron scale to form an electrode. As shown in Figure 2, the OSC of the electrolyte particles functions near the contact interface between the active species particles and the electrolyte particles. Therefore, the particle size and / or specific surface area (SSA (m 2 The value of OSC relative to the saturation temperature (Tc) is important.

[0046] [1.2.3. Electrode material characteristics (specific oxygen storage capacity (OSC / SSA)] Therefore, the value of the OSC (mg / g) of the electrode material was calculated as the SSA (m 2 The value obtained by dividing the OSC capacity by the value of the oxygen storage capacity (OSC / SSA) is used as an index for evaluating the OSC performance of the electrode material. Here, the OSC (mg / g) of the electrode material represents the OSC per 1 g of the electrode material, and can be calculated from ΔW.

[0047] The electrode material according to the present invention exhibits a higher OSC / SSA than conventional solid oxide electrolytes. When the manufacturing conditions are optimized, the OSC / SSA at 700°C is 1.5 mg / m 2 Further optimization of the manufacturing conditions resulted in an OSC / SSA of 1.60 mg / m 2 Ultra, 1.70mg / m 2 More than 2.00mg / m 2 More than 3.00mg / m 2 More than 4.00mg / m 2 or more, or 5.00 mg / m 2 That's all. Further optimization of the manufacturing conditions resulted in an OSC / SSA of 10 mg / m 2It is possible to manufacture the electrode from such an electrode material.

[0048] [1.2.4. Electrode material properties (conductivity)] "Conductivity" refers to a value calculated from bulk resistance obtained by AC impedance measurement at 700°C in air. The electrode material according to the present invention not only exhibits a high OSC / SSA but also maintains a relatively high electrical conductivity. When the manufacturing conditions are optimized, the electrical conductivity is 1.0×10 -3 Further optimization of the manufacturing conditions will result in a conductivity of 2.0×10 -3 S / cm or more, 5.0×10 -3 S / cm or more, or 1.0 x 10 -2 S / cm or more.

[0049] [1.2.5. Uses of electrode materials] The electrode material according to the present invention is suitable as a solid oxide electrolyte used in the anode of an SOEC or the anode of an SOFC.

[0050] [1.2.6. Manufacturing method of electrode material] The electrode material is (a) A mixed aqueous solution is prepared by mixing an aqueous solution of cerium nitrate, an aqueous solution of zirconium nitrate, and an aqueous solution of gadolinium nitrate pentahydrate dissolved in pure water; (b) The mixed solution is added to an aqueous ammonia solution prepared by diluting aqueous ammonia with pure water to prepare hydroxide precipitate solutions of each cation. (c) The hydroxide precipitate solution is dried in a degreasing furnace in an air atmosphere at 150°C for 7 hours, and then calcined at 400°C for 5 hours to produce an oxide solid solution powder. (d) The oxide solid solution powder is fired in air at 1100°C for 5 hours. It is produced by

[0051] [2. Electrochemical Cell] The electrochemical cell according to the present invention comprises: an electrolyte layer made of a solid oxide electrolyte; an air electrode formed on one side of the electrolyte layer; a fuel electrode formed on the other side of the electrolyte layer; Equipped with The fuel electrode is Electrolyte particles made of the electrode material according to the present invention; Ni-based particles and Includes:

[0052] [2.1. Electrolyte layer] The solid oxide electrolyte that constitutes the electrolyte layer can be yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), samaria-doped ceria (SDC), lanthanum strontium gallium magnesium oxide (LSGM), or the like.

[0053] 2.2. Air electrode For the air electrode, lanthanum strontium manganite (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium cobaltite (LSC), or the like can be used.

[0054] A reaction prevention layer may be inserted between the electrolyte layer and the air electrode to prevent a reaction that occurs due to direct contact between the electrolyte layer and the air electrode. Here, when the electrolyte layer is YSZ and the air electrode is LSC, it is preferable to use gadolinium-doped ceria (GDC) as the reaction prevention layer.

[0055] [2.3. Fuel electrode] The fuel electrode is Electrolyte particles made of the electrode material according to the present invention; Ni-based particles and It is equipped with:

[0056] [2.3.1. Electrolyte particles] The electrolyte particles are made of the electrode material according to the present invention. The details of the electrode material are as described above, and therefore will not be described here.

[0057] [2.3.2. Ni-based particles] The Ni-based particles are made of Ni or a Ni-based alloy and function as a catalyst and an electron conductor within the fuel electrode. When the Ni-based particles are made of a Ni-based alloy, the type of alloying element is not particularly limited, and examples of the alloying element include Fe, Co, and the like. When the Ni-based particles are made of a Ni-based alloy, the Ni content is preferably 90 mass % or more, and more preferably 95 mass % or more. The Ni-based particles are particularly preferably Ni or a Ni—Fe alloy.

[0058] 2.3.3. Fuel electrode composition The "content of Ni-based particles" refers to the ratio of the mass of Ni-based particles to the total mass of the electrolyte particles and Ni-based particles.

[0059] If the content of Ni-based particles is too low, the total cell resistance increases and the reaction efficiency at the fuel electrode also decreases. Therefore, the content of Ni-based particles is preferably 20 mass % or more, and more preferably 30 mass % or more. On the other hand, if the content of Ni-based particles is excessive, the content of electrolyte particles will be reduced, which may result in a decrease in reaction efficiency at the fuel electrode. Therefore, the content of Ni-based particles is preferably 70 mass% or less, and more preferably 60 mass% or less.

[0060] [2.3.4. Fuel electrode characteristics (porosity)] The term "porosity" refers to the ratio of the difference between the theoretical specific gravity of the anode and the actually measured specific gravity of the anode to the theoretical specific gravity of the anode. Here, the "theoretical specific gravity" is a value calculated from the specific gravity of each material that constitutes the fuel electrode, and the "measured specific gravity" is the specific gravity of the fuel electrode calculated by actual measurement. The "specific gravity" is the ratio of density to water.

[0061] The porosity of the anode affects the characteristics of the anode. If the porosity of the anode is too small, the gas diffusion property may decrease, and the reaction efficiency at the anode may decrease. Therefore, the porosity of the anode is preferably more than 25%, and more preferably 30% or more. On the other hand, if the porosity of the anode is too high, the number of three-phase interfaces becomes relatively small, which may actually reduce the reaction efficiency at the anode. Therefore, the porosity of the anode is preferably less than 40%, and more preferably 35% or less.

[0062] [2.3.5. Fuel electrode characteristics (degradation rate)] "Deterioration rate" refers to the slope A of the line (ΔR=A×t+B) that approximates the relationship between ΔR and t within the range of t=0 hr to 40 hr, with the vertical axis representing the resistance change rate of the anode before and after the durability test: ΔR (%) and the horizontal axis representing the durability test time: t (hr).

[0063] The resistance change rate: ΔR (%) refers to the value expressed by the following formula (2). ΔR(%)={Rct2(t)−Rct2(0)}×100 / Rct2(0)…(2) however, Rct2(0) is the electrochemical reaction resistance of the anode before the durability test. Rct2(t) is the electrochemical reaction resistance of the anode after the durability test at time t.

[0064] "Electrochemical reaction resistance (Rct2)" is obtained by measuring the impedance of an electrochemical cell using an electrolytic cell. It is the reaction resistance of the three-phase interface in the anode, and is the diameter of the arc (second arc) that contributes to the electrochemical reaction. The "durability test" refers to a test in which the electrochemical cell is used as an electrolysis cell and steam electrolysis is carried out for a predetermined time under the conditions shown below.

[0065] Temperature: 700℃ Air electrode atmosphere: 20% O2 / N2 Fuel electrode atmosphere: 30% H2O / 7.5% H2 / 62.5% N2 Electrolytic current: 30mA (60mA / cm 2 )

[0066] The anode of the present invention has a lower degradation rate than conventional anodes (e.g., Ni / YSZ). When the manufacturing conditions are optimized, the degradation rate at 700°C is 5.5% / hr or less. When the manufacturing conditions are further optimized, the degradation rate at 700°C is 5.0% / hr or less, or even 4.5% / hr or less.

[0067] 2.4. Fuel electrode manufacturing method The fuel electrode is (a) preparing a compact using a raw material mixture containing raw materials for Ni-based particles and raw materials for electrolyte particles; (b) sintering the obtained green body; (c) The obtained sintered body is subjected to a reduction treatment. It can be produced by

[0068] [2.4.1. Molded object forming process] First, a compact is produced using a raw material mixture containing raw materials for Ni-based particles and raw materials for electrolyte particles.

[0069] The term "raw material for Ni-based particles" refers to a raw material that becomes Ni-based particles after sintering and reduction. The type of raw material for Ni-based particles is not particularly limited, and an optimal raw material can be selected depending on the purpose. Examples of raw materials for Ni-based particles include NiO powder, Fe2O3 powder, Fe3O4 powder, a mixture of metallic Fe and NiO or metallic Ni, CoO powder, and Co2O3 powder.

[0070] The term "raw material for electrolyte particles" refers to a raw material that becomes electrolyte particles after sintering and reduction. In the present invention, an electrode material is used as the raw material for the electrolyte particles. Details of the electrode material are as described above, and therefore will not be described here.

[0071] The raw material mixture may contain a pore-forming material (e.g., carbon powder). The metal oxide (e.g., NiO powder) contained in the raw material of the Ni-based particles added to the raw material mixture is reduced after the sintered body is produced. During this process, volumetric shrinkage occurs, and pores are introduced into the sintered body. For this reason, a pore-forming material is not necessarily required. However, adding a pore-forming material to the raw material mixture increases the degree of freedom in controlling the porosity. Furthermore, it is preferable that the raw materials are blended so as to obtain a fuel electrode having the desired composition after sintering and reduction.

[0072] The method for producing the molded body is not particularly limited, and an optimum method can be selected depending on the purpose. Examples of the method for producing the molded body include: (a) A method in which a slurry containing a raw material mixture is tape-cast, the resulting green sheet is laminated on a substrate (e.g., a molded body that will become a solid electrolyte layer after sintering), and the laminate is isostatically pressed to bond the laminate; (b) A method of preparing a slurry containing the raw material mixture and screen printing the slurry onto the surface of a substrate; etc.

[0073] 2.4.2. Sintering process Next, the obtained molded body is sintered (sintering step). It is preferable to select the optimum sintering conditions depending on the raw material composition. Sintering is usually carried out in an air atmosphere at 1000°C to 1500°C (preferably 1000°C to 1350°C) for 1 hour to 5 hours. If a pore-forming material is contained in the raw material mixture, the pore-forming material disappears during sintering, and pores are formed in the sintered body.

[0074] [2.4.3. Reduction process] Next, the obtained sintered body is subjected to a reduction treatment (reduction step). The reduction treatment is carried out to reduce metal oxides such as NiO contained in the sintered body and generate metallic Ni-based particles. The reduction conditions are not particularly limited as long as they are capable of generating Ni-based particles.

[0075] 2.5. Applications of Electrochemical Cells The electrochemical cell according to the present invention can be suitably used in a solid oxide electrolysis cell (SOEC) or a solid oxide fuel cell (SOFC).

[0076] [3. Effect] The electrode material according to the present invention comprises: It has a composition represented by the following formula (1). Ce 1―x―y Zr x M y O 2-α …(1) however, 0 <x<0.1 0.05 <y<0.2 α is the value at which electroneutrality is maintained M is at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm.

[0077] CeO2 has an OSC that absorbs and releases oxygen depending on the ambient oxygen partial pressure. This means that Ce ions can easily absorb and release oxygen depending on the ambient oxygen partial pressure. 3+ →Ce 4+ , Ce 4+ →Ce 3+ Because it can change into

[0078] Here, Ce 3+ , Ce 4+ The ionic radii of Ce are 1.14 Å and 0.97 Å, respectively. 4+ →Ce 3+ During the reduction reaction, the ionic radius increases by approximately 1.2 times. This is a very large change from a crystallographic perspective, and the steric repulsion caused by the increase in the ionic radius of Ce destabilizes the lattice, making this reduction reaction energetically unfavorable and usually not proceeding easily. This is the rate-limiting factor, limiting the OSC.

[0079] On the other hand, Zr 4+ The ionic radius of Zr is 0.84 Å, and the small ionic radius of Zr is present in the crystal lattice of CeO2. 4+ By introducing Ce 4+ →Ce 3+This locally alleviates the steric repulsion that accompanies the increase in ionic radius during the reduction reaction, and reduces the destabilization of the crystal lattice, thereby improving the OSC.

[0080] And, Ce due to the improvement of OSC 4+ →Ce 3+ As the reduction reaction of CeO2 increases, the number of oxygen vacancies formed in CeO2 to satisfy the electroneutrality condition also increases. For this reason, Zr 4+ When considering an SOEC using CeO2-based materials containing hydroxyl groups as electrolyte particles, the hydroxide species O2 generated during H2O electrolysis 2― Ions tend to be trapped by the electrolyte particles. In other words, oxidation (conversion to hydroxide) of the Ni-based particles and the like that constitute the electrodes is suppressed, and evaporation of the Ni-based particles and the like can be prevented. As a result, deterioration of the electrode performance over time can be suppressed.

[0081] The electrode material is doped with trivalent M (at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm) to form oxygen vacancies for oxide ion conduction.

[0082] From the viewpoint of oxide ion conductivity, it is more preferable to incorporate Gd and / or Sm, because the incorporation of Gd and / or Sm makes it easier to create a lattice structure in which oxygen ions can move most easily.

[0083] Therefore, by co-doping CeO2 with Zr and M as an electrode material, it is possible to maintain the conductivity of oxide ions while improving the OSC. As a result, it is possible to suppress deterioration of the electrode performance over time while ensuring the conductivity of oxide ions. [Example]

[0084] [1. Electrolyte particles] 1.1. Preparation of electrolyte particles 1.1.1. Example 1 The electrolyte particles according to Example 1 were prepared as follows. First, 218.7 g of an aqueous solution of cerium nitrate with a concentration of 28 wt% in terms of CeO2, 2.7 g of an aqueous solution of zirconium nitrate with a concentration of 18 wt% in terms of ZrO, and an aqueous solution in which 18.1 g of gadolinium nitrate pentahydrate was dissolved in 100 ml of pure water were mixed to prepare a mixed aqueous solution.

[0085] Next, the mixed aqueous solution was added to an aqueous ammonia solution prepared by diluting 97.6 g of 25% aqueous ammonia with 900 ml of pure water, and hydroxide precipitate solutions of each cation were prepared by reverse coprecipitation. Next, the hydroxide precipitate solution was placed in a 2 L beaker and dried in a degreasing furnace in an air atmosphere at 150°C for 7 hours, and then calcined at 400°C for 5 hours to produce an oxide solid solution powder.

[0086] The oxide solid solution powder was then fired in air at 1100° C. for 5 hours, and then pulverized to obtain electrolyte particles according to Example 1. Here, the composition of the electrolyte particles is Ce 0.89 Zr 0.01 Gd 0.1 O 1.95 It was.

[0087] [1.1.2. Examples 2 and 3, Comparative Examples 1 to 3] The composition of the electrolyte particles in Example 2 was Ce 0.875 Zr 0.025 Gd 0.1 O 1.95 , The composition of the electrolyte particles in Example 3 was Ce 0.85 Zr 0.05 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Comparative Example 1 was Ce 0.9 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Comparative Example 2 was Ce 0.8 Zr 0.1 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Comparative Example 3 was Ce 0.75 Zr0.15 Gd 0.1 O 1.95 It was. The procedure for preparing each of the electrolyte particles was similar to that of Example 1, except that the amounts of the cerium nitrate aqueous solution, the zirconium nitrate aqueous solution, and the gadolinium nitrate pentahydrate were adjusted.

[0088] [1.2.1. Electrolyte particle characteristics (SSA)] The specific surface area (SSA) of the electrolyte particles of Examples 1 to 3 and Comparative Examples 1 to 3 was measured by the BET single-point method using a fully automatic specific surface area measuring device (MODEL-4232III, manufactured by Microdata). Pretreatment for the measurement was carried out in air at 250°C for 20 minutes.

[0089] 1.2.2. Electrolyte particle characteristics (OSC (mg / 15 mg of material) Pt (1 mass %) was supported on the electrolyte particles of Examples 1 to 3 and Comparative Examples 1 to 3 using a dinitrodiamine Pt solution to prepare Pt-supported particles for OSC measurement. The Pt-supported particles were placed in a thermogravimetric analyzer (TGA-50, Shimadzu Corporation), and the weight increase / decrease was measured under a fluctuating atmosphere in which an H2 (5%) / N2 atmosphere and an O2 (5%) / N2 atmosphere were switched three times every five minutes. The average weight loss during the second and third H2 (5%) / N2 reduction was taken as the OSC (mg / 15 mg of material) for 15 mg of electrolyte particles in Examples 1-3 and Comparative Examples 1-3.

[0090] It should be noted that Pt improves the reaction rate of the oxygen storage / release reaction and does not affect the OSC of the electrolyte particles. The OSC for 15 mg of electrolyte particles is defined as OSC (mg / 15 mg of material), which is the average value of the weight loss measured directly for 15 mg of electrolyte particles.

[0091] The details of the OSC measurement conditions are as follows: Electrolyte particle amount: 15mg Gas flow rate: 100 mL / min Measurement temperature: 700℃ Reducing gas: H2 (5%) / N2 (balance) Oxidizing gas: O2 (5%) / N2 (balance)

[0092] [1.2.3. Electrolyte particle characteristics (OSC / SSA)] In the case of SOECs and the like, electrodes are formed by physically mixing Ni-based particles and electrolyte particles on a submicron to micron scale. As shown in Figure 2, the OSC of the electrolyte particles functions near the contact interface between the Ni-based particles and the electrolyte particles. Therefore, the particle size and / or the value of OSC relative to the specific surface area (SSA) of the electrolyte particles are important.

[0093] Therefore, the value of the OSC (mg / g) of the electrolyte particles is calculated as the SSA (m 2 The value obtained by dividing the OSC / SSA by the value of the specific oxygen storage capacity (OSC / SSA) was used as an index for evaluating the OSC performance of the electrode material.

[0094] [2. Electrolysis Cell] 2.1. Preparation of electrolytic cell First, a GDC sheet (reaction prevention layer, diameter 22 mm) was pressed onto one side of an 8YSZ electrolyte pellet (diameter: 22 mm, thickness: 500 μm) with a reference electrode attached to the side using a hot isostatic press, and then fired at 1350°C. The thickness of the reaction prevention layer after firing was about 3 μm.

[0095] Next, a paste made by mixing electrolyte particles and NiO in a specified ratio was applied by screen printing to the other side of the 8YSZ electrolyte pellet (the side opposite the reaction prevention layer), and then fired at 1340°C to form the fuel electrode. The shape of the paste printing area was a circle with a diameter of approximately 8 mm. The mass ratio of electrolyte particles to NiO was 64:36 or 50:50.

[0096] Next, the LSC / GDC paste was applied onto the reaction prevention layer by screen printing and fired at 1125° C. to form the air electrode. The shape of the paste printing area was a circle with a diameter of approximately 18 mm. The resulting electrolytic cell was then subjected to a reduction treatment, which was carried out by holding it in a 100% hydrogen atmosphere at 700°C for 20 minutes.

[0097] 2.2. Composition of electrolyte particles The compositions of the electrolyte particles in the electrolytic cells of Examples 11 to 15 and Comparative Examples 11 to 13 are shown below. The composition of the electrolyte particles of Example 11 was Ce 0.89 Zr 0.01 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Example 12 was Ce 0.89 Zr 0.01 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Example 13 was Ce 0.875 Zr 0.025 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Example 14 was Ce 0.85 Zr 0.05 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Example 15 was Ce 0.85 Zr 0.05 Sm 0.1 O 1.95 , The composition of the electrolyte particles of Comparative Example 11 was Ce 0.9 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Comparative Example 12 was Ce 0.8 Zr 0.1 Gd 0.1 O 1.95 , The composition of the electrolyte particles of Comparative Example 13 was Ce 0.75 Zr 0.15 Gd 0.1 O 1.95 It was.

[0098] The electrolyte particles of Examples 11 and 12 were from the same lot as the electrolyte particles of Example 1, the electrolyte particles of Example 13 were from the same lot as the electrolyte particles of Example 2, and the electrolyte particles of Example 14 were from the same lot as the electrolyte particles of Example 3. Similarly, the electrode materials of Comparative Examples 11 to 13 were from the same lot as the electrode materials of Comparative Examples 1 to 3, respectively.

[0099] Here, the electrolyte particles of Example 15 were newly prepared by a preparation procedure similar to that of Example 1, except that the gadolinium nitrate pentahydrate in Example 1 was replaced with samarium nitrate hexahydrate, and the amounts of the cerium nitrate aqueous solution, the zirconium nitrate aqueous solution, and the samarium nitrate hexahydrate were adjusted.

[0100] 2.2.1. Conductivity of electrolyte particles The oxide ion conductivity was determined using the electrolyte particles of Examples 11 to 15 and Comparative Examples 11 to 13. The conductivity of the electrolyte particles was measured by compressing the electrolyte particles into a disk, forming Pt electrodes on both sides of the disk, and measuring the AC impedance of the disk at 700°C in air. The conductivity was calculated using the bulk resistance of the disk.

[0101] [2.3. Porosity] The porosity of the fuel electrode was calculated from the ratio of the difference between the theoretical specific gravity of the fuel electrode and the actually measured specific gravity of the fuel electrode to the theoretical specific gravity of the fuel electrode. More specifically, (1): Measure the mass of the 8YSZ electrolyte pellet. (2): The fuel electrode raw material paste was applied to an 8YSZ electrolyte pellet, and the mass was measured after firing and reduction. (3): Calculate the mass of the fuel electrode from the mass difference between (1) and (2). (4): Measure the diameter of the fuel electrode using a microscope. (5): The thickness of the anode was measured by cross-sectional SEM observation. (6): Calculate the volume of the fuel electrode from (4) and (5), (7): The actual specific gravity was calculated from (3) and (6). The theoretical specific gravity was calculated from the specific gravity of the electrolyte particles and Ni, and the mixing ratio thereof.

[0102] [2.4. Deterioration rate] Figure 3 shows a schematic diagram of the electrolytic cell used for impedance measurements. A reference electrode is attached to the side of the electrolyte layer. The reference electrode is used to measure the voltage V1 between the electrolyte layer and the air electrode, and the voltage V2 between the electrolyte layer and the fuel electrode. By attaching the reference electrode to the electrolyte layer, the fuel electrode and the air electrode can be evaluated separately.

[0103] Specifically, by providing a reference electrode, it becomes possible to measure the phase difference between the electrolytic current and the voltage V2 between the electrolyte layer and the fuel electrode when the frequency of the electrolytic current is changed, which makes it possible to measure the AC impedance characteristics of just the fuel electrode.

[0104] Using the electrolytic cell shown in Figure 3, a 100-hour steam electrolysis test (durability test) was conducted under the conditions described above. During the durability test, impedance measurements were performed every 10 hours to measure the electrode reaction resistance (Rct2). Furthermore, the electrode reaction resistance (Rct2) before the durability test and after the durability test for a predetermined period was used to calculate the resistance change rate, expressed by equation (2). Furthermore, the degradation rate was calculated from the resistance change rate.

[0105] [3. Results] [3.1. Specific oxygen storage capacity (OSC / SSA)] For each of the electrolyte particles in Examples 1 to 3 and Comparative Examples 1 to 3, the OSC (mg / 15 mg of material) and SSA (m 2 / g) was measured. The obtained OSC (mg / 15 mg of material), SSA (m 2 / g), the specific oxygen storage capacity OSC / SSA (mg / m 2 ) was calculated. The results are shown in Table 1 and FIG.

[0106] [Table 1]

[0107] From FIG. 4, it was found that the OSC / SSA value relative to the Zr doping amount had a maximum value in Example 1 where the Zr doping amount was 1 mol %. It was also found that both Example 2 with a Zr doping amount of 2.5 mol % and Example 3 with a Zr doping amount of 5 mol % had higher OSC / SSA values ​​than Comparative Example 1 with a Zr doping amount of 0 mol %.

[0108] Furthermore, it was found that both Comparative Example 2 with a Zr doping amount of 10 mol % and Comparative Example 3 with a Zr doping amount of 15 mol % had lower OSC / SSA values ​​than Comparative Example 1 with a Zr doping amount of 0 mol %.

[0109] From the above, it was found that the range in which the Zr doping amount has a significant effect, in other words, the range in which Zr doping has the effect of relaxing the distortion of the crystal lattice during the reduction of Ce ions, is a Zr doping amount greater than 0 mol% and less than 10 mol%.

[0110] [3.2. Deterioration rate] Figure 5 shows an example of the impedance analysis results. In Figure 5, the second arc (Rct2) represents the magnitude of the electrochemical reaction resistance of the anode. The larger the diameter of the second arc, the greater the electrochemical reaction resistance. The arc to the left of the second arc is the first arc (Rct1), which represents the magnitude of the resistance of the electrolyte ion path in the anode.

[0111] The results of the deterioration rate of the fuel electrode in the electrolytic cells of Examples 11 to 15 and Comparative Examples 11 to 13 are shown in Table 2, FIGS. FIG. 6 shows the relationship between the oxide ion conductivity of the electrolyte particles and the degradation rate of the anode, and FIG. 7 shows the relationship between the OSC / SSA of the electrolyte particles and the degradation rate of the anode.

[0112] [Table 2]

[0113] From Table 2 and Figures 6 and 7, it was found that the rate of deterioration of the anode of the electrolytic cell varies depending on the amount of Zr doped. It was also found that in Examples 11 to 15, in which the doping amount of Zr was more than 0 mol % and less than 10 mol %, the deterioration rate of the fuel electrode was 5% / hr or less. The deterioration rate of the fuel electrode in Comparative Example 11 was 5.52% / hr.

[0114] Furthermore, from Table 2 and FIG. 6, in Examples 11 to 15 in which the doping amount of Zr was more than 0 mol% and less than 10 mol%, the conductivity of the electrolyte particles was 1.0 × 10 -3 S / cm super 2.0×10 -2 It was found that the density was less than S / cm. In other words, if the conductivity of the electrolyte particles is 1.0 × 10 -3 S / cm super 2.0×10 -2 If it is less than S / cm, the deterioration rate of the fuel electrode is 5% / hr or less.

[0115] Generally, in CeO2-based materials, the oxide ion conductivity decreases as the amount of Zr doped increases. This is because the addition of Zr, which has a small ionic radius, causes lattice contraction, narrowing the oxide ion migration channel. Therefore, increasing the amount of Zr added decreases the oxide ion conductivity and deteriorates the electrode properties.

[0116] Furthermore, from Table 2 and Figure 7, the OSC / SSA of the electrolyte particles is 1.5 mg / m 2 It can be seen that when the temperature exceeds 5000 K, the deterioration rate of the fuel electrode is 5% / hr or less. Furthermore, it is clear from Examples 11, 13, and 14 that the rate of deterioration of the fuel electrode decreases as the OSC / SSA value increases. The deterioration rate of Example 12 is slightly slower (higher) because the amount of electrolyte particles is relatively small.

[0117] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0118] The electrode material according to the present invention can be used as an anode for a solid oxide electrolysis cell (SOEC) or an anode for a solid oxide fuel cell (SOFC). The electrochemical cell according to the present invention can be used as a solid oxide electrolysis cell or a solid oxide fuel cell.

Claims

1. An electrode material having a composition represented by the following formula (1): Yes １―ｘ―ｙ Zr ｘ M ｙ O ２－α …(1) however, 0<x<0.10 0.05<y<0.20 α is the value at which electroneutrality is maintained M is at least one element selected from the group consisting of Gd, La, Nd, Y, and Sm.

2. Specific oxygen storage capacity (OSC / SSA) at 700°C is 1.5 mg / m ２ The electrode material according to claim 1, wherein the Here, the "specific oxygen storage capacity (OSC / SSA)" refers to the oxygen storage capacity (OSC) (mg / g) per 1 g of the electrode material relative to the specific surface area (SSA) (m ２ / g).

3. Conductivity is 1.0 x 10 －３ 2. The electrode material according to claim 1, wherein the electrical conductivity is greater than 100 S / cm. The "electrical conductivity" refers to a value calculated from bulk resistance obtained by measuring AC impedance at 700°C in the atmosphere.

4. 0.01≦x≦0.05 0.05<y≦0.15 The electrode material according to claim 1 , which satisfies the above formula:

5. 2. The electrode material according to claim 1, which is used as an anode of a solid oxide electrolysis cell (SOEC) or a solid oxide electrolyte of an anode of a solid oxide fuel cell (SOFC).

6. an electrolyte layer made of a solid oxide electrolyte; an air electrode formed on one side of the electrolyte layer; a fuel electrode formed on the other side of the electrolyte layer; Equipped with The fuel electrode is Electrolyte particles made of the electrode material according to claim 1; Ni-based particles and Contains Electrochemical cell.

7. 7. The electrochemical cell according to claim 6, wherein the content of the Ni-based particles in the fuel electrode is 20 mass % or more and 70 mass % or less. Here, the "content of Ni-based particles" refers to the ratio of the mass of the Ni-based particles to the total mass of the electrolyte particles and the Ni-based particles.

8. 7. The electrochemical cell of claim 6, wherein the anode has a porosity of greater than 25% and less than 40%. Here, the "porosity" refers to the ratio of the difference between the theoretical specific gravity of the fuel electrode and the actually measured specific gravity of the fuel electrode to the theoretical specific gravity of the fuel electrode.

9. 7. The electrochemical cell according to claim 6, which is used as a solid oxide electrolysis cell (SOEC) or a solid oxide fuel cell (SOFC).

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