Electrode

Abstract

An electrode includes electrolyte particles and Ni-based particles. The electrolyte particles comprise CeO2 (GDC) doped with Gd and / or CeO2 (La-GDC) doped with Gd and La. The Ni-based particles are composed of core-shell particles in which the surface of a core composed of Ni or an Ni-based alloy is partially or completely covered with a shell composed of a composite oxide containing Ni O or Ni.

Description

Technical Field

[0001] The present disclosure relates to an electrode. More particularly, the present disclosure relates to an electrode suitable for use as a fuel electrode in a solid oxide electrolysis cell (SOEC) or a fuel electrode in a solid oxide fuel cell (SOFC). Background Art

[0002] SOFCs are fuel cells that use an oxygen ion conductor as their electrolyte. When a fuel gas such as H₂, CO, or CH₄ is ​​supplied to the SOFC's anode (fuel electrode) and O₂ is supplied to the cathode (oxygen electrode), an electrode reaction occurs, generating electricity. The CO₂ and H₂O generated by the electrode reaction are discharged outside the SOFC.

[0003] However, although SOEC is structurally the same as SOFC, it produces the opposite reaction to SOFC. That is, CO2 and H2O can be supplied to the cathode (fuel electrode) of SOEC, and CO and H2 are produced by passing current between the electrodes.

[0004] An SOEC includes a unit cell in which an anode (air electrode) is connected to one surface of an electrolyte and a cathode (fuel electrode) is connected to the other surface. As materials constituting components of such an SOEC, the following materials are generally used (see Non-Patent Documents 1 to 5 below).

[0005] (a) Electrolytes: yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), scandia-yttria-stabilized zirconia (ScYSZ), samarium-doped ceria (SDC), lanthanum strontium gallium magnesium oxide (LSGM), etc.

[0006] (b) Air electrodes: lanthanum strontium manganese oxide (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium cobaltate (LSC), etc.

[0007] (c) Fuel electrode: Ni / YSZ, Ni / ScYSZ, Ni-Cu / YSZ, etc.

[0008] [Non-patent document 1] Ebbesen, SD; Hansen, JB; Mogensen, MB. The Electrochemical Society Transactions 2013, 57, 3217.

[0009] [Non-patent document 2] Jensen, SH; Larsen, PH; Mogensen, M. International Journal of Hydrogen Energy 2007, 32, 3253.

[0010] [Non-patent document 3] Ullman, H.; Trofimenko, N.; Stoever, D.; Ahmad-Khanlou, A. Solid State Ionics 2000, 138, 79.

[0011] [Non-patent document 4] Laguna-Bercero, MA; Skinner, SJ; Kilner, JA Journal of Power Sources 2009, 192, 126.

[0012] [Non-patent document 5] Ebbesen, SD; Jensen, SH; Hauch, A.; Mogensen, MB Chemical Reviews 2014, 114, 10697.

[0013] Although not a fuel electrode, JP 2018-142419A discloses an anti-reaction layer for a solid oxide fuel cell, in which ceria is doped with more than 10 mol% and less than 30 mol% of GdO 1.5 .

[0014] Although not intended to optimize fuel electrode materials, JP 2018-085200A discloses an active layer including a gas flow path for diffusing gas from a diffusion layer to an electrolyte layer.

[0015] Ni / YSZ cermets are commonly used for fuel electrodes of SOECs. However, steam, which is used as a raw material for hydrogen production, is supplied to the fuel electrode at high temperatures (700°C or higher). Therefore, when SOECs using Ni / YSZ as fuel electrodes are used for a long time, it is known that electrolysis performance gradually decreases. This is believed to be because the fuel electrode is exposed to high-temperature steam, causing the Ni particles to be oxidized and turned into nickel hydroxide with a low vapor pressure. The nickel hydroxide then volatilizes and disperses. Therefore, it is believed that the structure of the fuel electrode will change.

[0016] In order to solve the above-mentioned problems, various proposals have been made so far.

[0017] For example, JP 2020-155349A, JP 2021-085061A, JP 2020-167052A, and JP 2021-161467A propose a fuel electrode comprising Ni-containing particles and ACZ particles having a composite oxide (ACZ) composed of A2O3 (wherein A=Y, La and / or Sc), CeO2, and ZrO2.

[0018] Furthermore, JP 2022-074189 A proposes an active layer composed of a cermet containing Ni-containing particles and YScCZ particles composed of ZrO 2 doped with Y, Sc, and Ce.

[0019] However, there are limitations in improving the durability of SOECs by simply optimizing the electrolyte used in the fuel electrode alone. Summary of the Invention

[0020] Therefore, it is desirable to provide an electrode whose structure undergoes minimal changes even when exposed to high-temperature steam.

[0021] One aspect of the present disclosure provides an electrode comprising electrolyte particles and Ni-based particles. The electrolyte particles comprise Gd-doped CeO2 (GDC) and / or Gd and La-doped CeO2 (La-GDC). The Ni-based particles are composed of core-shell particles in which the surface of a core composed of Ni or a Ni-based alloy is partially or completely covered by a shell composed of a composite oxide containing NiO or Ni.

[0022] When used as a fuel electrode in an electrolytic cell, Ni / YSZ electrodes tend to degrade easily over time. This is believed to be due to changes in the morphology of the electrode reaction sites caused by the gas phase diffusion of Ni during use.

[0023] In contrast, in an electrode comprising electrolyte particles consisting of GDC and / or La-GDC and Ni-based particles, if a shell consisting of a composite oxide containing NiO or Ni (hereinafter also referred to as "Ni-based oxide") is formed on the surface of the Ni-based particles in advance, the degradation of the electrode over time can be suppressed without compromising electrode performance. This is believed to be because in the region (three-phase interface) where Ni-based particles, GDC or La-GDC and voids overlap, GDC or La-GDC extracts oxygen from the Ni-based oxide, thereby always forming a Ni layer or a Ni-based alloy layer near the three-phase interface, and can continue to play a role as an electrode reaction site. In addition, in the region outside the three-phase interface, the shell consisting of the Ni-based oxide can suppress the gas phase diffusion of Ni, thereby suppressing the morphological change of the electrode reaction site. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the attached figure:

[0025] Figure 1 is a schematic diagram illustrating electrode degradation in a conventional fuel electrode.

[0026] Figure 2 Schematic diagram showing a process of maintaining electrode activity by Ni-based particles having a core-shell structure.

[0027] Figure 3 is a schematic diagram of the electrolytic cell used for resistance measurement.

[0028] Figure 4 is a diagram showing an example of resistance analysis results.

[0029] Figure 5 1 is a graph showing an example of the resistance change rate of sample No. 1 changing with time.

[0030] Figure 6 Graph showing the degradation rates of the electrodes of Sample No. 1 and Sample No. 2 at each temperature.

[0031] Figure 7 This is a SEM image of a cross section (partial) of the electrode of Sample No. 1 after the durability test (800° C.).

[0032] Figure 8 is an example showing SEM / EDS mapping of the electrode cross section (total: from the electrolyte interface to the electrode surface) of sample No. 1 after the durability test (800° C.).

[0033] Figure 9 This is a graph showing the area ratios of the electrode constituent materials of Sample No. 1 after the durability test (800° C.).

[0034] Figure 10 This is a graph showing the area ratios of the electrode constituent materials of Sample No. 1 after the durability test (850° C.).

[0035] Figure 11 The TEM image (left) and EDS mapping (right) of sample No. 1 after the durability test (800°C) are shown.

[0036] Figure 12A is shown along Figure 11 This is a diagram showing the results of line analysis when line analysis is performed in the direction of arrow A. Figure 12B is shown along Figure 11 This is a diagram showing the results of line analysis when line analysis is performed in the direction of arrow B in FIG.

[0037] Figure 13 Graph showing the oxygen storage capacity of the electrodes of Sample No. 1 and Sample No. 2 at each temperature.

[0038] Figure 14 This is a graph showing the Ni particle change rate of the electrode of sample No. 1 at each temperature.

[0039] Figure 15 It is a graph showing the electrode degradation rates of Sample No. 3 (La-GDC) and Sample No. 1 (GDC) at various temperatures.

[0040] Figure 16 It is a graph showing the oxygen storage capacity of La-GDC and GDC.

[0041] Figure 17 This is a SEM image of a cross section (partial) of the electrode of Sample No. 3 after the durability test (700° C.).

[0042] Figure 18 This is an example of SEM / EDS mapping of the electrode cross section (a region of approximately 20 μm from the electrolyte interface toward the electrode surface) of sample No. 3 after a durability test (700° C.).

[0043] Figure 19 This is a graph showing the area ratios of the electrode constituent materials of Sample No. 3 after the durability test (700° C.).

[0044] Figure 20 This is a graph showing the area ratios of the electrode constituent materials of Sample No. 3 after the durability test (800° C.). DETAILED DESCRIPTION

[0045] Hereinafter, embodiments of the present disclosure will be described in detail.

[0046] [1. Electrode]

[0047] The electrode of the present disclosure includes electrolyte particles and Ni-based particles.

[0048] [1.1. Electrolyte particles]

[0049] The electrolyte particles include CeO 2 doped with Gd (GDC) and / or CeO 2 doped with Gd and La (La-GDC).

[0050] [1.1.1.GDC]

[0051] GDC not only acts as an oxygen ion conductor but also as an oxygen storage material. Therefore, when GDC is used as an electrolyte particle, it can not only exchange oxygen ions with Ni-based particles during the use of the electrode, but also suppress the morphological changes of the electrode reaction sites.

[0052] In the present disclosure, the Gd content in GDC is not particularly limited, and an optimal value can be selected depending on the intended purpose.

[0053] Here, the Gd content refers to the ratio of the number of moles of Gd to the total number of moles of Ce and Gd contained in GDC.

[0054] Generally speaking, the oxygen ion conductivity and oxygen storage capacity of GDC increase with increasing Gd content. To achieve such effects, the Gd content is preferably greater than 0 mol%, more preferably equal to or greater than 4 mol%, or further preferably equal to or greater than 8 mol%.

[0055] Meanwhile, if the Gd content becomes too high, the oxygen ion conductivity may be reduced or the oxygen storage capacity may be reduced. Therefore, the Gd content is preferably equal to or less than 20 mol%, more preferably equal to or less than 15 mol%, or further preferably equal to or less than 10 mol%.

[0056] In particular, GDC preferably has a Gd content of equal to or greater than 4 mol % and equal to or less than 15 mol %.

[0057] [1.1.2.LaGDC]

[0058] Similarly, La-GDC functions not only as an oxygen ion conductor but also as an oxygen storage material. Therefore, when La-GDC is used as an electrolyte particle, it not only exchanges oxygen ions with Ni-based particles during electrode use but also suppresses morphological changes at the electrode reaction sites. Furthermore, La-GDC is more effective than GDC in suppressing morphological changes at the electrode reaction sites.

[0059] In the present disclosure, the Gd content and the La content in La-GDC are not particularly limited, and optimal values ​​can be selected depending on the intended purpose.

[0060] Here, the “Gd content” refers to the ratio of the number of moles of Gd to the total number of moles of Ce, Gd, and La contained in La-GDC.

[0061] The “La content” refers to the ratio of the number of moles of La to the total number of moles of Ce, Gd, and La contained in La-GDC.

[0062] In La-GDC, the oxygen ion conductivity of La-GDC increases with the increase of Gd content. To achieve this effect, the Gd content is preferably greater than 0 mol%, more preferably equal to or greater than 1 mol%, or further preferably equal to or greater than 2.5 mol%.

[0063] Meanwhile, if the Gd content becomes too high, the oxygen storage capacity may decrease or the oxygen ion conductivity may reach an upper limit. Therefore, the Gd content is preferably less than 10 mol%, more preferably equal to or less than 8.5 mol%, or further preferably equal to or less than 7.5 mol%.

[0064] In La-GDC, the oxygen storage capacity of La-GDC increases with the increase of La content. This is believed to be because La 3+ (ion radius: 0.116nm) is doped into the CeO2 lattice. 4+ (ion radius: 0.097nm) reduced to Ce 3+ (ion radius: 0.114 nm) reduces the strain generated on the lattice. To achieve this effect, the La content is preferably greater than 0 mol%, more preferably equal to or greater than 1 mol%, or further preferably equal to or greater than 2.5 mol%.

[0065] Meanwhile, if the La content becomes too high, the oxygen storage capacity may be reduced. Therefore, the La content is preferably less than 10 mol%, more preferably equal to or less than 8.5 mol%, or further preferably equal to or less than 7.5 mol%.

[0066] In particular, La-GDC preferably has a Gd content of 2.5 mol% or more and 7.5 mol% or less and a La content of 2.5 mol% or more and 7.5 mol% or less.

[0067] [1.2.Ni-based particles]

[0068] In the present disclosure, the Ni-based particles are composed of core-shell particles in which the surface of a core composed of Ni or a Ni-based alloy is partially or completely covered with a shell composed of a composite oxide containing NiO or Ni.

[0069] [1.2.1. Core]

[0070] In the electrode, the core serves as a catalyst and an electron conductor. In the present disclosure, the core is composed of Ni or a Ni-based alloy.

[0071] When the core is composed of a Ni-based alloy, the type of alloying element is not particularly limited and may be Fe or Co, for example.

[0072] Furthermore, when the core is composed of a Ni-based alloy, the Ni content in the core is preferably equal to or greater than 90 wt %, more preferably equal to or greater than 95 wt %.

[0073] In particular, the core is preferably Ni or a Ni—Fe alloy.

[0074] [1.2.2. Shell]

[0075] [A. Shell composition]

[0076] The surface of the core is partially or completely covered with a shell. The shell serves to suppress the gas phase diffusion of Ni contained in the Ni-based particles.

[0077] Here, “gas phase diffusion” of Ni refers to a phenomenon in which, when an electrode containing Ni is exposed to high-temperature steam, Ni reacts with the steam to form nickel hydroxide, and the nickel hydroxide or its decomposition product diffuses through the gas phase within the electrode.

[0078] As described below, the shell is formed from an electrode containing Ni-based particles that have been reduced to a metallic state by oxidation treatment in a controlled oxidizing atmosphere. Therefore, the shell is composed of an oxide containing the metal element that constitutes the core. More specifically, the shell is composed of a composite oxide containing NiO or Ni (Ni-based oxide).

[0079] Here, in the initial state, the entire surface of the core is likely covered by the shell. This is believed to be because when current is applied to the electrode, in the region (three-phase interface) where Ni-based particles, GDC or La-GDC, and voids (gas phase) overlap, GDC or La-GDC extracts oxygen from the shell, and a Ni layer or Ni-based alloy layer is always formed near the three-phase interface.

[0080] [B. Shell thickness]

[0081] The thickness of the shell may vary depending on the position. The shell does not necessarily have to completely cover the surface of the core, but may cover a portion of the core. Even when a portion of the core is covered by the shell, the gas phase diffusion of Ni can be effectively suppressed depending on the coverage of the shell.

[0082] At the same time, when the entire surface of the core is covered by a thick shell, the electrode activity may be excessively reduced. Therefore, the shell preferably includes a region that is thinner than its surroundings (hereinafter referred to as a "thin film region"). In order to achieve high electrode activity, the thickness of the thin film region is preferably equal to or less than 200 nm, more preferably equal to or less than 150 nm, or further preferably equal to or less than 100 nm, or still further preferably equal to or less than 50 nm, or still further preferably equal to or less than 40 nm, or yet further preferably equal to or greater than 30 nm.

[0083] In particular, the thin film region is preferably formed in the three-phase interface portion. If the thin film region is formed in the three-phase interface portion, the vicinity of the three-phase interface portion can continue to serve as an electrode active site due to the oxygen storage capacity of the electrolyte particles.

[0084] Here, the "three-phase interface portion" refers to the electrolyte particle / Ni-based particle interface near the three-phase interface or the Ni-based particle / gas phase interface near the three-phase interface.

[0085] “Near the three-phase interface” refers to a region that is 300 nm or less from an electrode reaction site where three phases, namely, electrolyte particles, Ni-based particles, and a gas phase, meet.

[0086] [C. Shell area ratio]

[0087] The “shell area ratio” refers to the area of ​​the shell in the cross section of the electrode (S shell ) and the area of ​​the core (S core ) of the ratio (S shell / S core ). S core and S shell It can be calculated by scanning electron microscopy (SEM) / energy dispersive X-ray spectroscopy (EDS) mapping relative to the cross section of the electrode, respectively.

[0088] The area ratio of the shell is related to the coverage of the shell on the core surface. If the area ratio of the shell becomes too small, the proportion of the exposed core will increase. Therefore, it may become difficult to suppress the gas phase diffusion of Ni. Therefore, the area ratio of the shell is preferably greater than 0, more preferably equal to or greater than 0.30, or further preferably equal to or greater than 0.40, or even more preferably equal to or greater than 0.50, or even more preferably equal to or greater than 0.56.

[0089] Meanwhile, if the shell area ratio becomes too large, the proportion of the Ni-based oxide occupying the electrode increases, and the electrode characteristics may be reduced. Therefore, the shell area ratio is preferably equal to or less than 0.98, more preferably equal to or less than 0.95, or further preferably equal to or less than 0.90.

[0090] [1.3. Electrode composition]

[0091] [1.3.1. Ni-based particle content]

[0092] The “Ni-based particle content” 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.

[0093] If the content of Ni-based particles becomes too small, the total resistance of the battery will increase and the efficiency of the electrode reaction will decrease. Therefore, the content of Ni-based particles is preferably 30% by weight or more, more preferably 40% by weight or more.

[0094] Meanwhile, if the Ni-based particle content becomes excessive, the electrolyte particle content decreases, and the efficiency of the electrolyte reaction may decrease. Therefore, the Ni-based particle content is preferably equal to or less than 70 wt%.

[0095] [1.3.2.La-GDC content]

[0096] The “La-GDC content” refers to the ratio of the mass of La-GDC to the total mass of GDC and La-GDC contained in the electrode.

[0097] In the present disclosure, the La-GDC content is not particularly limited, and an appropriate content can be selected depending on the intended purpose. That is, the electrodes of the present disclosure may include only either GDC or La-GDC as electrolyte particles, or may include both. To achieve high durability, the La-GDC content is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 70% by weight, and even more preferably equal to or greater than 90% by weight.

[0098] [1.3.3. Total content of GDC and La-GDC]

[0099] The “total content of GDC and La-GDC” refers to the ratio of the total mass of GDC and La-GDC to the total mass of the electrolyte particles contained in the electrode.

[0100] The electrolyte particles may consist solely of GDC and / or La-GDC, or may contain other components. Generally speaking, electrode durability increases with increasing the combined content of GDC and La-GDC. To achieve high durability, the combined content of GDC and La-GDC is preferably 80% by weight or greater, more preferably 90% by weight or less, further preferably 95% by weight or greater, and even more preferably 99% by weight or greater.

[0101] [1.4. Porosity]

[0102] The "porosity" refers to a value measured by a mercury porosimeter.

[0103] The porosity of the electrode affects its properties. If the porosity of the electrode is too low, gas diffusivity decreases, and the efficiency of the electrode reaction may be reduced. Therefore, the porosity of the electrode is preferably equal to or greater than 20%, and more preferably equal to or greater than 25%.

[0104] At the same time, if the porosity of the electrode is too high, the three-phase interface is relatively reduced, and the efficiency of the electrode reaction may be reduced. Therefore, the porosity of the electrode is preferably equal to or less than 40%, more preferably equal to or less than 35%, or further preferably equal to or less than 30%.

[0105] [1.5. Characteristics: Degradation Rate]

[0106] "Degradation rate" refers to the slope A of the straight line ΔR=A×t, which is determined by setting the vertical axis to the resistance change rate ΔR (%) of the electrode before and after the durability test, setting the horizontal axis to the durability test time t (h), and connecting the values ​​of t=0h and 40h.

[0107] The resistance change rate ΔR (%) refers to a value represented by the following expression (1).

[0108] ΔR(%)={Rct2(t)–Rct2(0)}×100 / Rct2(0)···(1)

[0109] Here, Rct2(0) is the electrode reaction resistance before the durability test, and Rct2(t) is the electrode reaction resistance after the durability test time (t).

[0110] “Electrode reaction resistance (Rct2)” refers to the reaction resistance at the three-phase interface in the fuel electrode, and is the diameter of the arc (second arc) contributing to the electrode reaction obtained by resistance measurement of an electrolytic cell using the electrode as a fuel electrode.

[0111] The “durability test” refers to a test in which water vapor electrolysis is performed for a predetermined period of time under the conditions shown in Table 1 using an electrolytic cell using the above-described electrode as a fuel electrode.

[0112] [Table 1]

[0113] temperature 650、700、750、800、850℃ Fuel electrode* <![CDATA[H2O / H2 = 4 (volume %), and diluted with nitrogen]]> Current <![CDATA[30mA(0.06A / cm 2 ) and controlled by constant current]]>

[0114] *Counter electrode (air electrode): 80% nitrogen + 20% oxygen

[0115] Conventional fuel electrodes (Ni / YSZ) are prone to changes in the morphology of electrode reaction sites. Consequently, they degrade at a higher rate. In contrast, the electrodes disclosed herein use core-shell particles as Ni-based particles. Consequently, during durability testing, regardless of temperature, they degraded at a lower rate than conventional electrodes.

[0116] For example, the degradation rate of a conventional electrode at 700°C is 17.18% / h. In contrast, when the electrolyte particles consist only of GDC, the degradation rate of the electrode of the present disclosure at 700°C is equal to or less than 10% / h. If the manufacturing conditions are further optimized, the degradation rate at 700°C is preferably equal to or less than 9% / h, or more preferably equal to or less than 8% / h.

[0117] Similarly, the degradation rate of a conventional electrode at 750°C is 10.25% / h. In contrast, when the electrolyte particles consist only of GDC, the degradation rate of the electrode of the present disclosure at 750°C is equal to or less than 6% / h. If the manufacturing conditions are further optimized, the degradation rate at 750°C is equal to or less than 5% / h.

[0118] Furthermore, conventional electrodes degrade at a rate of 2.67% / h at 800°C. In contrast, when the electrolyte particles consist solely of GDC, the electrode of the present disclosure degrades at a rate of 2% / h or less at 800°C. Further optimization of manufacturing conditions results in a degradation rate of 1.5% / h or less at 800°C. In contrast, when the electrolyte particles consist solely of La-GDC, the electrode of the present disclosure degrades at a rate of 5% / h or less at 700°C.

[0119] If the manufacturing conditions are further optimized, the degradation rate at 700° C. is equal to or less than 4% / h, or more preferably, equal to or less than 3% / h.

[0120] Furthermore, when the electrolyte particles consisted only of La-GDC, the degradation rate of the electrode of the present disclosure was equal to or less than 1% / h at 800° C. If the manufacturing conditions were further optimized, the degradation rate at 800° C. was equal to or less than 0.5% / h.

[0121] The same applies when the electrolyte particles are a mixture of GDC and La-GDC. When the composition is optimized, an electrode with a slow degradation rate is obtained.

[0122] [1.6. Intended Use]

[0123] SOECs and SOFCs generally include an electrolyte layer containing a solid oxide electrolyte, a fuel electrode coupled to one surface of the electrolyte layer, an air electrode coupled to the other surface of the electrolyte layer, and an intermediate layer (anti-reaction layer) interposed between the electrolyte layer and the air layer.

[0124] Furthermore, the fuel electrode side current collecting layer may be arranged outside the fuel electrode, or the air electrode side current collecting layer may be arranged outside the air electrode.

[0125] In particular, the electrode of the present disclosure is suitable as a fuel electrode of a SOEC or a fuel electrode of a SOFC.

[0126] When the electrode of the present disclosure is used as a fuel electrode of an SOEC or a fuel electrode of an SOFC, the materials of other constituent elements are not particularly limited, and optimal materials can be selected according to the intended purpose.

[0127] For example, among the solid oxide electrolytes constituting the electrolyte layer, yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), scandia-yttria-stabilized zirconia (ScYSZ), samarium-doped ceria (SDC), lanthanum strontium gallium magnesium oxide (LSGM), etc. can be used.

[0128] Lanthanum strontium manganese oxide (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium cobaltate (LSC), or the like can be used for the air electrode.

[0129] The intermediate layer prevents the reaction that occurs when the electrolyte layer and the air electrode are in direct contact, and is inserted as needed. For example, when the electrolyte layer is YSZ and the air electrode is LSC, Gd-doped CeO2 (GDC) is preferably used in the intermediate layer.

[0130] The materials of the fuel electrode side current collecting layer and the air electrode side current collecting layer are not particularly limited as long as they can transfer electrons, supply reactants, and discharge reaction products. Generally, materials with the same or similar composition as the electrode and higher porosity than the electrode are used in the current collecting layer.

[0131] [2. Electrode Manufacturing Method]

[0132] The electrodes of the present disclosure can be manufactured by the following methods:

[0133] (a) manufacturing a molded article using a raw material mixture containing a raw material of Ni-based particles and a raw material of electrolyte particles;

[0134] (b) sintering the obtained molded part;

[0135] (c) subjecting the obtained sintered body to a reduction treatment; and

[0136] (d) subjecting the obtained reduced product to oxidation treatment in a controlled oxidizing atmosphere.

[0137] [2.1. Molded Part Forming Step]

[0138] First, a molded article is manufactured using a raw material mixture including a raw material for Ni-based particles and a raw material for electrolyte particles;

[0139] "Ni-based particle raw material" refers to the raw material that forms Ni-based particles after sintering, reduction, and controlled oxidation. In the present disclosure, the type of raw material for Ni-based particles is not particularly limited, and the optimal raw material can be selected based on the intended purpose. For example, as the raw material for Ni-based particles, NiO powder, Fe2O3 powder, Fe3O4 powder, a mixture of metallic Fe and NiO or metallic Ni, CoO powder, and Co2O3 powder can be used.

[0140] "Electrolyte particle raw material" refers to the raw material that forms electrolyte particles after sintering, reduction, and controlled oxidation. In the present disclosure, GDC powder and / or La-GDC powder are used as the electrolyte particle raw material. The compositions of GDC and La-GDC are as described above. Therefore, their description is omitted.

[0141] The raw material mixture may include 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 subjected to a reduction treatment after the manufacture of the sintered body. At this point, volume shrinkage occurs and pores are introduced into the sintered body. Therefore, a pore-forming material is not necessarily required. However, if a pore-forming material is added to the raw material mixture, the degree of freedom of control of the porosity will increase.

[0142] Furthermore, the feedstock is preferably formulated to yield a fuel electrode having a target composition after sintering, reduction, and controlled oxidation treatments.

[0143] The method for manufacturing the molded article is not particularly limited, and the best method can be selected according to the intended purpose. For example, as a method for manufacturing the molded article, there are the following methods:

[0144] (a) a method of tape-forming a slurry containing a raw material mixture, laminating the obtained green sheet onto a substrate (e.g., a molded article to be used as a fuel electrode side current collecting layer after sintering or a molded article to be used as an electrolyte layer after re-sintering), and pressing the laminate by hydrostatic pressure; and

[0145] (b) A method of preparing a paste containing a raw material mixture and screen-printing the paste onto a substrate surface.

[0146] [2.2. Sintering step]

[0147] The resulting molded part is then sintered (sintering step). Optimal sintering conditions are preferably selected based on the raw material composition. Sintering is typically performed in an air atmosphere at 1000°C to 1500°C (preferably 1000°C to 1300°C) for one to five hours. If the raw material mixture contains pore-forming material, the pore-forming material is burned off during sintering, forming pores in the sintered body.

[0148] [2.3. Restoration steps]

[0149] Next, the obtained sintered body is subjected to a reduction treatment (reduction step). The reduction treatment is performed to reduce the metal oxide contained in the sintered body, such as NiO, and to produce Ni-based particles in a metallic state (i.e., core particles). The reduction conditions are not particularly limited as long as they can produce core particles.

[0150] [2.4. Oxidation step]

[0151] The resulting reduced product is then subjected to an oxidation treatment in a controlled oxidizing atmosphere. As a result, the electrode of the present disclosure is obtained. The controlled oxidation treatment is performed to form a shell on the surface of the core particles. The conditions of the controlled oxidation treatment are not particularly limited, as long as the surface layer of the core particles can be selectively oxidized.

[0152] As a method for forming core-shell particles, the following method can be given.

[0153] In the first method,

[0154] (a) manufacturing a battery using an electrode (electrode containing nuclear particles) immediately after reduction as a fuel electrode;

[0155] (b) While the cell is heated to a temperature equal to or higher than 650° C., the gas atmosphere on the fuel electrode side is adjusted to H 2 O / H 2 = 4 (volume ratio);

[0156] (c) in this state, applying a current of 30 mA to the battery for at least 50 hours; and

[0157] (d) Filling the interior of the fuel electrode with an inert gas (eg, N2 gas) after stopping the application of current.

[0158] In the second method,

[0159] (a) manufacturing a battery using an electrode (electrode containing nuclear particles) immediately after reduction as a fuel electrode;

[0160] (b) in a state where the cell is heated to a temperature equal to or higher than 400° C., the gas atmosphere on the fuel electrode side is adjusted to H 2 O / H 2 = 1.0 or more (volume ratio);

[0161] (c) Maintaining the battery without applied current for at least 1 hour;

[0162] (d) After the maintenance, the fuel electrode is filled with an inert gas (such as N2 gas) and maintained in this state.

[0163] In the present disclosure, any method can be used. Whichever method is used, the shell area ratio can be controlled by optimizing temperature, atmosphere, current, processing time, etc.

[0164] Here, as described above, the electrolytic cell is composed of a combination of a fuel electrode (cathode) / electrolyte layer / anti-reaction layer / air electrode (anode). In addition, the fuel electrode side collector layer may be further combined on the outside of the fuel electrode. In addition or in lieu of the foregoing, the air electrode side collector layer may be further combined on the outside of the air electrode. After the stacking of the molded parts, the sintering and bonding of the layers are performed by heating the stack to a predetermined temperature. In addition, if the optimal sintering temperatures are different between the layers, the sintering is generally carried out in a plurality of stages. In addition, the reduction of the fuel electrode is generally performed after all the layers are bonded.

[0165] When the electrode of the present disclosure is used as a fuel electrode for an electrolytic cell, after all layers are bonded and the fuel electrode undergoes a reduction process, the fuel electrode is subjected to a controlled oxidation process.

[0166] [3. Function]

[0167] [3.1. Deterioration of electrodes]

[0168] Figure 1 Schematic diagram showing electrode degradation in a conventional fuel electrode. In a conventional electrolytic cell using Ni / YSZ in the fuel electrode, it is believed that the degradation of the fuel electrode over time is caused by the gas phase diffusion of Ni.

[0169] It is believed that the degradation of the fuel electrode over time due to the gas phase diffusion of Ni proceeds in the following manner. That is, as Figure 1 As shown, when the fuel electrode is exposed to high-temperature steam, nickel reacts with the steam to produce nickel hydroxide. The resulting nickel hydroxide or its decomposition products diffuse through the gas phase within the electrode and aggregate on the surfaces of larger nickel particles. As a result, the morphology of the electrode reaction sites changes, which is believed to cause electrode degradation.

[0170] [3.2. Maintaining electrode activity through core-shell particles]

[0171] In contrast, in an electrode comprising electrolyte particles composed of GDC and / or La-GDC and Ni-based particles, if a shell composed of a composite oxide containing NiO or Ni (Ni-based oxide) is formed on the surface of the Ni-based particles in advance, degradation of the electrode over time can be suppressed without impairing electrode performance. This is believed to be due to the following reasons.

[0172] 3.2.1. Maintenance of GDC and La-GDC Electrode Reaction Sites

[0173] Figure 2A schematic diagram showing the process of maintaining electrode activity by Ni-based particles having a core-shell structure. First, when an electrode containing pure Ni particles and GDC is subjected to an oxidation treatment in a controlled oxidizing atmosphere, only the surface portion of the pure Ni particles is selectively oxidized. As a result, core-shell particles are obtained in which the surface of the core composed of pure Ni is covered. Figure 2 The upper left picture in .

[0174] GDC has oxygen storage capacity. Therefore, in the "NiO / GDC / void overlap region (three-phase interface)", GDC extracts oxygen from NiO. Therefore, near the three-phase interface, NiO may be reduced to metallic Ni. However, in other regions, the surface of the core is mostly still covered with NiO. Figure 2 The upper right and lower right images in .

[0175] When current is applied to the electrode (e.g., during electrolysis operation), oxygen stored in the GDC diffuses within the GDC, forming lattice vacancies that serve as a source of oxygen storage capacity. As a result, even when the electrode is exposed to high-temperature steam, a Ni layer is always formed in the "NiO / GDC / void overlap region" and continues to function as an electrode reaction site. Figure 2 The lower left image in .

[0176] The same applies to:

[0177] (a) when the electrolyte particles are La-GDC or a mixture of GDC and La-GDC; or

[0178] (b) When the core of the Ni-based particle is composed of a Ni-based alloy and the shell is composed of a composite oxide containing Ni.

[0179] [3.2.2. Suppressing morphological changes at electrode reaction sites by using a shell]

[0180] It is believed that the gas phase diffusion of Ni occurs due to direct contact between Ni and high temperature steam. In contrast, when the Ni surface in the area other than the vicinity of the three-phase interface is covered with NiO, the generation of nickel oxide that causes electrode degradation can be suppressed in this area (i.e., the "area where NiO and voids overlap"). As a result, it is believed that the gas phase diffusion of Ni is suppressed. Figure 2 The lower left image in .

[0181] The same applies when the core of the Ni-based particle is a Ni-based alloy and the shell is a Ni-containing composite oxide.

[0182] In an electrode composed of Ni-based particles and GDC and / or La-GDC, the electrode functions as an electrode even when the Ni-based particles do not have a shell. However, when the Ni-based particles do not have a shell, if the electrode is used under harsh conditions immediately after use, the morphological changes at the electrode reaction sites may occur excessively. In contrast, when the Ni-based particles have a shell, the risk of this problem is extremely small.

[0183] [3.3. Effect of La]

[0184] The electrode containing La-GDC exhibited higher durability than the electrode containing GDC alone. This is believed to be because a portion of the Gd contained in GDC was replaced by La, resulting in an increase in oxygen storage capacity.

[0185] [Example]

[0186] [A. Experiment 1]

[0187] [1. Manufacture of electrolytic cell]

[0188] 1.1. Sample No. 1

[0189] A GDC sheet (anti-reaction layer, diameter: 22 mm) was placed on one surface of an 8YSZ electrolyte core block (diameter: 22 mm, thickness: 500 μm) to the side of which a reference electrode was attached, and sintered at 1380°C.

[0190] Next, a fuel electrode was formed on the other surface of the 8YSZ electrolyte core block (the surface opposite to the surface where the anti-reaction layer was sintered). Specifically, a NiO / GDC slurry (NiO:GDC mass ratio = 1:1) was applied by screen printing and sintered at 1340°C. GDC powder with a Gd content of 10 mol% was used.

[0191] Furthermore, LSC / GDC paste was coated on the anti-reaction layer by a screen printing method and sintered at 1125° C., thereby forming an air electrode.

[0192] The obtained electrolytic cell was subjected to a fuel electrode reduction treatment by maintaining the obtained electrolytic cell in a 100% hydrogen atmosphere at 700° C. for 20 minutes.

[0193] [1.2. Sample No. 2]

[0194] An electrolytic cell was manufactured in a manner similar to Sample No. 1, except that NiO / 8YSZ slurry was used to manufacture the fuel electrode.

[0195] [2. Test methods]

[0196] [2.1. Degradation rate]

[0197] Figure 3 A schematic diagram of an electrolytic cell used for resistance measurement is shown. 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 current V2 between the electrolyte layer and the fuel electrode. Because the reference electrode is attached to the electrolyte layer, the fuel electrode and air electrode can be evaluated separately.

[0198] Under the conditions shown in Table 1, using Figure 3 The electrolytic cell shown was subjected to a 100-hour steam electrolysis test (durability test). During the durability test, resistance measurement was performed and the electrode reaction resistance (Rct2) was measured. In addition, the resistance change rate represented by expression (1) was calculated using the electrode reaction resistance (Rct2) before the durability test and after the durability test was performed for a predetermined amount of time. In addition, the degradation rate was calculated based on the resistance change rate.

[0199] [2.2. Shell area ratio]

[0200] Before and after the 100-hour durability test, cross-sections of the fuel electrode were observed using a scanning electron microscope (SEM) and subjected to EDS mapping. Based on the EDS mapping results, the area of ​​each constituent material contained in the fuel electrode was calculated, and their area ratios were determined. The calculation process for the area ratios is shown below.

[0201] That is, the cross section of the electrode was observed at a magnification of 2000 to 3500 times, and the electrode cross section was divided into eight regions (thickness: 5 μm) along the thickness direction. For each region, the Ni (core) area ratio, NiO area ratio, void area ratio, and electrolyte area ratio were calculated.

[0202] Next, the average area ratio of each constituent material is calculated for each region. Furthermore, the average area ratio of each constituent material calculated for each area is used to calculate the average area ratio of each constituent material for the entire electrode.

[0203] 2.3.TEM / EDS analysis

[0204] After the durability test, the fuel electrodes were subjected to TEM / EDS analysis.

[0205] [3. Results]

[0206] [3.1. Degradation rate]

[0207] Figure 4 An example of the resistance analysis results is shown. Figure 4In the graph, the second arc (Rct2) represents the electrochemical reaction resistance of the fuel electrode. The results show that as the diameter of the second arc increases, the electrochemical reaction resistance increases. The arc to the left of the second arc is the first arc (Rct1), which represents the resistance of the electrolyte ion path within the hydrogen electrode.

[0208] Figure 5 An example of the resistance change rate of sample No. 1 over time is shown. Figure 5 It can be clearly seen that when the durability test time exceeds 40 hours, the rate of change of the resistance change rate decreases.

[0209] Figure 6 The degradation rates of sample No. 1 and sample No. 2 at each temperature are shown. For sample No. 1, the degradation rates at each temperature are 7.44% / h (650°C), 6.22% / h (700°C), 3.99% / h (750°C), 0.86% / h (800°C), and 0.79% / h (850°C). Figure 6 It can be clearly seen that the degradation rate of Sample No. 1 is approximately half that of Sample No. 2. Furthermore, this result is believed to indicate that when the fuel electrode immediately after manufacture undergoes oxidation treatment in a controlled oxidizing atmosphere and Ni-based particles having a core-shell structure are formed in advance, degradation of the Ni-based particles during electrolysis can be suppressed.

[0210] [3.2. Shell area ratio]

[0211] Figure 7 An SEM image of a cross section (partial) of the electrode of Sample No. 1 after the durability test (800° C.) is shown. Figure 8 An example of SEM / EDS mapping of the electrode cross section (total: cross section from the electrolyte interface to the electrode surface) of sample No. 1 after the durability test (800° C.) is shown. Figure 9 The area ratio of the electrode constituent materials of sample No. 1 after the durability test (800°C) is shown. Figure 10 The area ratios of the electrode constituent materials of Sample No. 1 after the durability test (850° C.) are shown.

[0212] In the case of sample No. 1, the ratio of Ni particles (core) to NiO layer (shell) in the entire cross section of the electrode after the durability test (800°C) was 17.7:9.9 (=1:0.56). Figure 9 In the first row of the “whole”. In addition, the ratio of Ni particles (core) to NiO layer (shell) in the cross section of the entire electrode after the durability test (850°C) is 14.3:13.9 (=1:0.97). Please refer to Figure 10The first row in the "whole".

[0213] Furthermore, the region actually used as the electrode reaction site is the region 20 μm from the fuel electrode / electrolyte interface ( Figures 8 to 10 The ratio of the Ni particles (core) to the NiO layer (shell) in this region after the durability test (800°C) was 17.9:8.8 (=1:0.49). Furthermore, the ratio of the Ni particles (core) to the NiO layer (shell) in this region after the durability test (850°C) was 14.4:13.0 (=1:0.90).

[0214] 3.3.TEM / EDS analysis

[0215] Figure 11 Shown are a TEM image (left) and EDS mapping (right) of the electrode of Sample No. 1 after a durability test (800° C.). Figure 12A Shown along Figure 11 The line analysis results when the line analysis is performed in the direction of arrow A in the figure. Figure 12B Shown along Figure 11 The line analysis results when the line analysis is performed in the direction of arrow B in the figure. Figure 13 The oxygen storage capacity of the electrodes of Sample No. 1 and Sample No. 2 at each temperature is shown.

[0216] like Figure 11 As shown in the left figure in , NiO layers are confirmed at both the Ni particle / gas phase interface and the Ni particle / GDC particle interface. However, the thickness of the NiO layer formed at the Ni particle / gas phase interface and the Ni particle / GDC particle interface is inconsistent. Figure 11 It can be clearly seen that there is an area with a significantly thinner NiO layer near the three-phase interface.

[0217] In the case of sample No. 1, a Ni-rich layer (approximately 5 nm in size) was observed in the NiO region near the three-phase interface (electrode reaction site). See Figure 12. This Ni-rich layer is believed to be a trace of GDC absorbing oxygen from NiO.

[0218] This result indicates that the NiO layer is in a Ni-rich state due to the absorption of oxygen by GDC from the NiO layer (refer to Figure 13 ). In addition, it is considered that this also shows that the function as an electrode reaction site is maintained on the surface of the Ni-based particles even when the Ni-based particles are exposed to high-temperature steam.

[0219] Figure 14The Ni particle change rate of the electrode of sample No. 1 at each temperature is shown. "Ni particle change rate" refers to the change ratio of the average particle size of Ni particles before and after the durability test. Figure 14 It can be clearly seen that during the durability test, the Ni particle change rate decreases with increasing temperature.

[0220] This result is considered to indicate that if the treatment temperature of the controlled oxidation treatment is increased, it is easier to form a shell on the surface of the Ni-based particles.

[0221] Furthermore, it is considered that this result also shows that if the treatment temperature of the controlled oxidation treatment is increased, the morphological change in the three-phase interface can be suppressed, and the electrode activity can be more easily maintained due to the suppression of the generation of Ni(OH)2.

[0222] [B. Experiment 2]

[0223] [1. Manufacture of electrolytic cell]

[0224] 1.1. Sample No. 3

[0225] An anti-reaction layer was formed on one surface of an 8-YSZ electrolytic core block in a manner similar to Sample No. 1. La-GDC was used as the electrolyte powder for the fuel electrode, and a NiO / La-GDC slurry (NiO:La-GDC = 36:64 mass ratio) was applied to the other surface of the 8YSZ electrolyte core block by screen printing. An electrolytic cell was then fabricated in a manner similar to Sample No. 1. La-GDC powder containing 5 mol% La and 5 mol% Gd was used.

[0226] [2. Test methods]

[0227] [2.1. Degradation rate]

[0228] The measurement of the electrode reaction resistance (Rct2), the calculation of the resistance change rate, and the calculation of the degradation rate were performed in a manner similar to that of Sample No. 1.

[0229] [2.2. Shell area ratio]

[0230] The area ratio of the shell was determined in a manner similar to that of Sample No.1.

[0231] [3. Results]

[0232] [3.1. Degradation rate]

[0233] Figure 15 The electrode degradation rates of sample No. 3 (La-GDC) and sample No. 1 (GDC) at each temperature are shown. Figure 15It can be clearly seen that the degradation rate of sample No. 3 is equal to or less than half of that of sample No. 1.

[0234] Figure 16 The oxygen storage capacity of La-GDC and GDC is shown. Figure 16 As can be clearly seen from the graph, La-GDC has a higher oxygen storage capacity than GDC. Since part of the Gd contained in GDC is replaced by La, the oxygen storage capacity increases. Therefore, it is believed that the durability of sample No. 3 is significantly improved compared to the durability of sample No. 1.

[0235] [3.2. Shell area ratio]

[0236] Figure 17 An SEM image of a cross section (partial) of the electrode of Sample No. 3 after the durability test (700° C.) is shown. Figure 18 An example of SEM / EDS mapping of the electrode cross section (region of about 20 μm from the electrolyte interface to the electrode surface side) of sample No. 3 after the durability test (700° C.) is shown. Figure 19 The area ratio of the electrode constituent materials of sample No. 3 after the durability test (700°C) is shown. Figure 20 The area ratios of the electrode constituent materials of Sample No. 3 after the durability test (800° C.) are shown.

[0237] In the case of Sample No. 3, the average ratio of the Ni particles (core) to the NiO layer (shell) after the durability test (700°C) was 14.5:5.0 (=1:0.34). Furthermore, the average ratio of the Ni particles (core) to the NiO layer (shell) after the durability test (800°C) was 10.9:10.3 (=1:0.94).

[0238] The embodiments of the present disclosure are described in detail above. However, the present disclosure is not limited to the embodiments described above in any way, and various modifications can be made without departing from the spirit of the present disclosure.

[0239] The electrode of the present disclosure may be used as a fuel electrode of a SOEC or a fuel electrode of a SOFC.

[0240] Characteristic configurations extracted from the embodiment and modified examples described above are described below.

[0241] [Structure 1]

[0242] An electrode comprises electrolyte particles and Ni-based particles, wherein the electrolyte particles contain Gd-doped CeO2 (GDC) and / or Gd and La-doped CeO2 (La-GDC), and the Ni-based particles consist of core-shell particles in which the surface of a core composed of Ni or a Ni-based alloy is partially or completely covered by a shell composed of NiO or a composite oxide containing Ni.

[0243] [Construction 2]

[0244] The electrode according to configuration 1, wherein the area ratio of the shell is greater than 0 and equal to or less than 0.98, the area ratio of the shell referring to the area of ​​the shell in the cross section of the electrode (S shell ) and the area of ​​the core (S core ) of the ratio (S shell / S core ).

[0245] [Construction 3]

[0246] The electrode according to configuration 1 or 2, wherein the shell includes a region having a thickness equal to or less than 200 nm.

[0247] [Structure 4]

[0248] An electrode according to any one of constructions 1 to 3, wherein the degradation rate at 700°C is equal to or less than 10% / h, the degradation rate refers to the slope A of the straight line ΔR=a×t, which is determined by setting the resistance change rate ΔR(%) of the electrode before and after the durability test as the vertical axis, setting the durability test time t(h) as the horizontal axis, and connecting the values ​​of t=0h and 40h.

[0249] [Structure 5]

[0250] The electrode according to any one of Configurations 1 to 4, wherein the Gd content of the GDC is greater than 0 mol % and equal to or less than 20 mol %, the Gd content referring to a ratio of the number of moles of Gd relative to the total number of moles of Ce and Gd contained in the GDC.

[0251] [Construction 6]

[0252] An electrode according to any one of Configurations 1 to 5, wherein the Gd content of La-GDC is greater than 0 mol% and less than 10 mol%, and the La content is greater than 0 mol% and less than 10 mol%, the Gd content refers to the ratio of the molar number of Gd to the total molar number of Ce, Gd, and La contained in GDC, and the "La content" refers to the ratio of the molar number of La to the total molar number of Ce, Gd, and La contained in GDC.

[0253] [Construction 7]

[0254] The electrode according to any one of Configurations 1 to 6, wherein the Ni-based particle content is equal to or greater than 30 wt % and equal to or less than 70 wt %, the Ni-based particle content referring to the ratio of the mass of the Ni-based particles to the total mass of the electrolyte particles and the Ni-based particles.

[0255] [Construction 8]

[0256] The electrode according to any one of Configurations 1 to 7, wherein the porosity of the electrode is equal to or greater than 20% and equal to or less than 40%, the porosity being a value measured by a mercury porosimeter.

[0257] [Construction 9]

[0258] The electrode according to any one of Configurations 1 to 8, wherein the electrode is used as a fuel electrode of a solid oxide electrolysis cell (SOEC) or a fuel electrode of a solid oxide fuel cell (SOFC).

Claims

1. An electrode comprising: electrolyte particles; as well as Ni-based particles, wherein the electrolyte particles comprise CeO2 doped with Gd, i.e., GDC, and / or CeO2 doped with Gd and La, i.e., La-GDC, The Ni-based particles are composed of core-shell particles in which the surface of a core composed of Ni or a Ni-based alloy is partially or completely covered with a shell composed of a composite oxide containing NiO or Ni.

2. The electrode according to claim 1, wherein The area ratio of the shell is greater than 0 and equal to or less than 0.98, The area ratio of the shell refers to the ratio of the area of ​​the shell to the area of ​​the core in the cross section of the electrode.

3. The electrode according to claim 1, wherein The shell includes a region having a thickness equal to or less than 200 nm.

4. The electrode according to claim 1, wherein The degradation rate at 700°C is equal to or less than 10% / h, The degradation rate refers to the slope A of the straight line ΔR=a×t, which is determined by setting the resistance change rate ΔR of the electrode expressed in % before and after the durability test as the vertical axis, setting the durability test time t in units of h as the horizontal axis, and connecting the values ​​of t=0h and 40h.

5. The electrode according to claim 1, wherein The Gd content of GDC is greater than 0 mol% and equal to or less than 20 mol%, The Gd content refers to the ratio of the number of moles of Gd to the total number of moles of Ce and Gd contained in GDC.

6. The electrode according to claim 1, wherein The Gd content of La-GDC is greater than 0 mol% and less than 10 mol%, and the La content is greater than 0 mol% and less than 10 mol%. The Gd content refers to the ratio of the molar number of Gd to the total molar number of Ce, Gd, and La contained in GDC, and the La content refers to the ratio of the molar number of La to the total molar number of Ce, Gd, and La contained in GDC.

7. The electrode according to claim 1, wherein The content of Ni-based particles is equal to or greater than 30 wt % and equal to or less than 70 wt %, The Ni-based particle content 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. The electrode according to claim 1, wherein The porosity of the electrode is equal to or greater than 20% and equal to or less than 40%, The porosity refers to a value measured by a mercury porosimeter.

9. The electrode according to claim 1, wherein The electrode is used as a fuel electrode of a solid oxide electrolysis cell or a fuel electrode of a solid oxide fuel cell.

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