Electrochemical cell, solid oxide electrolysis cell, cell stack, hot module, and hydrogen production device

Abstract

An electrolysis cell 21 comprises: a solid electrolyte layer 211 including ion-conductive oxide particles; a fuel electrode layer 213 laminated on the back surface 211A side of the solid electrolyte layer 211; and an air electrode layer 212 laminated on the upper surface 211B side of the solid electrolyte layer 211. The average particle diameter of the ion-conductive oxide particles in the solid electrolyte layer 211 is 0.40-1.24 µm.

Description

Electrochemical cells, solid oxide electrolysis cells, cell stacks, hot modules, and hydrogen production devices

[0001] The present disclosure relates to an electrochemical cell, a solid oxide electrolysis cell, a cell stack, a hot module, and a hydrogen production device.

[0002] Solid oxide electrochemical cells using a solid oxide as an electrolyte have been known for some time (see, for example, Patent Document 1). Solid oxide electrochemical cells are characterized by performing electrochemical reactions with high efficiency in high-temperature environments and can be used as solid oxide electrolysis cells (SOECs) or solid oxide fuel cells (SOFCs). Solid oxide electrolysis cells are electrolysis devices that use electrical energy to decompose water vapor into hydrogen and oxygen. Solid oxide fuel cells are power generation devices that generate electrical energy through a chemical reaction between hydrogen and oxygen.

[0003] Japanese Patent Application Laid-Open No. 2019-8914

[0004] Electrochemical cells are required to have high durability so that they can maintain a predetermined performance even after being operated for a predetermined period of time.

[0005] The present disclosure aims to solve the above-mentioned problems, that is, one of the aims of the present disclosure is to improve the durability of electrochemical cells.

[0006] The electrochemical cell (21) according to the present disclosure includes a solid electrolyte layer (211) containing ion-conductive oxide particles, a fuel electrode layer (213) laminated on one surface (211A) of the solid electrolyte layer (211), and an air electrode layer (212) laminated on the other surface (211B) of the solid electrolyte layer (211). The average particle size (D) of the ion-conductive oxide particles in the solid electrolyte layer (211) is 0.40 μm or more and 1.24 μm or less.

[0007] According to the above configuration, the durability of the electrochemical cell can be improved.

[0008] In one embodiment of the electrochemical cell according to the present disclosure, the standard deviation (σ) of the particle size of the ion-conductive oxide particles in the solid electrolyte layer (211) is 0.31 or less.

[0009] According to the above configuration, the performance of the electrochemical cell can be improved.

[0010] In another embodiment of the electrochemical cell according to the present disclosure, the average particle size (D) of the ion-conductive oxide particles in the solid electrolyte layer (211) is 0.55 μm or more and 1.01 μm or less.

[0011] According to the above configuration, the durability and performance of the electrochemical cell can be improved.

[0012] In yet another embodiment of the electrochemical cell according to the present disclosure, the fuel electrode layer (213) is a CeO ２ and the ion-conductive oxide particles in the solid electrolyte layer are YSZ (yttria-stabilized zirconia).

[0013] According to the above configuration, durability can be improved in an electrochemical cell in which elements interdiffuse between the solid electrolyte layer and the fuel electrode layer.

[0014] Furthermore, the solid oxide electrolysis cell (21) according to the present disclosure is comprised of the electrochemical cell according to the present disclosure.

[0015] According to the above configuration, it is possible to provide a solid oxide electrolysis cell with improved durability.

[0016] The cell stack (20) according to the present disclosure is formed by stacking a plurality of solid oxide electrolysis cells (21) according to the present disclosure.

[0017] According to the above configuration, a cell stack with improved durability can be provided.

[0018] The hot module (10) according to the present disclosure includes a cell stack (20) according to the present disclosure, a vaporizer (30) that generates steam to be supplied to the cell stack (20), a heat exchanger (40) that exchanges heat with gas supplied to the cell stack (20), a heater (50) that heats the cell stack (20), and a heat insulating material (60) in which the cell stack (20), the vaporizer (30), the heat exchanger (40), and the heater (50) are disposed.

[0019] According to the above configuration, it is possible to provide a hot module with improved durability.

[0020] The hydrogen production device (1) according to the present disclosure includes the hot module (10) according to the present disclosure.

[0021] According to the above configuration, it is possible to provide a hydrogen production device with improved durability.

[0022] It is a block diagram of the hydrogen production device. It is a perspective view of the cell stack. It is a cross-sectional view taken along the line III-III in Figure 2. It is a cross-sectional view in the thickness direction of the electrolysis cell.

[0023] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a block diagram of a hydrogen production device 1 according to this embodiment. The hydrogen production device 1 according to this embodiment is a device that produces hydrogen by electrolyzing water vapor. As shown in Fig. 1, the hydrogen production device 1 includes a hot module 10 and a condenser 90.

[0024] The hot module 10 is constructed by covering with insulating material the main components that become hot among the elements that make up the hydrogen production device 1, and is a device in which the main components are concentrated within the insulating material so that the high temperature state of the main components is maintained. This hot module 10 includes a cell stack 20, a vaporizer 30, a heat exchanger 40, a heater 50, and insulating material 60.

[0025] The vaporizer 30 contains water (H ２0) is supplied to the vaporizer 30. The vaporizer 30 heats the supplied water to a temperature of 100°C or higher by a heat source (not shown). Therefore, the water supplied to the vaporizer 30 evaporates within the vaporizer 30, generating water vapor. The water vapor generated in the vaporizer 30 is introduced into the heat exchanger 40.

[0026] In addition to the water vapor, air is introduced into the heat exchanger 40. The heat exchanger 40 also receives high-temperature hydrogen (H ２ ) and high-temperature oxygen (O ２ ) is introduced into the heat exchanger 40. The high-temperature gas exchanges heat with the steam and air in the heat exchanger 40, thereby heating the steam and air introduced from the vaporizer 30.

[0027] The water vapor and air heated by the heat exchanger 40 are further heated by the heater 50 to the operating temperature of the cell stack 20 (i.e., the temperature required to operate the cell stack 20).The water vapor and air are then introduced into the cell stack 20.

[0028] The cell stack 20 is formed by stacking solid oxide electrolysis cells. The cell stack 20 is heated to an operating temperature by a heat source (such as a burner) not shown. A predetermined voltage is applied to the cell stack 20. As a result, water vapor introduced into the cell stack 20 is electrolyzed to produce hydrogen and oxygen. The hydrogen produced in the cell stack 20 is introduced into the heat exchanger 40 together with unreacted water vapor, where it is used to heat the water vapor and air introduced into the heat exchanger 40 from the vaporizer 30, and then introduced into the condenser 90. The unreacted water vapor is condensed in the condenser 90. The condensed water produced in the condenser 90 is introduced into the vaporizer 30. Meanwhile, hydrogen separated by the condensation of the water vapor in the condenser 90 is recovered. The oxygen produced in the cell stack 20 is introduced into the heat exchanger 40, where it is used to heat the water vapor and air, and then introduced into the vaporizer 30 to heat the water supplied to the vaporizer 30. The oxygen discharged from the vaporizer 30 is then recovered (or released to the atmosphere).

[0029] The cell stack 20, vaporizer 30, heat exchanger 40, and heater 50 are disposed inside a thermal insulation material 60. This suppresses heat radiation from each of the components 20, 30, 40, and 50. Heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), and biosoluble fiber (AES), and / or a heat-resistant container formed from these heat-resistant fibers, may be used for the thermal insulation material 60. The heat-resistant fibers are disposed so as to fill gaps between the cell stack 20, vaporizer 30, heat exchanger 40, and heater 50.

[0030] FIG. 2 is a perspective view of the cell stack 20, and FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . As shown in FIGS. 2 and 3 , the cell stack 20 comprises an electrolysis unit group including a plurality of rectangular flat-plate-shaped electrolysis units Ue stacked in the thickness direction (vertical direction), and a pair of end plates 27, 28 disposed on the upper and lower surfaces of the electrolysis unit group, respectively. The end plates 27, 28 are rectangular flat-plate-shaped members having the same outer shape as the electrolysis units Ue, and each has a rectangular opening formed in its center. The electrolysis unit group and the end plates 27, 28 are fastened to each other at their four corners by bolts B inserted through the electrolysis units 27, 28 in the thickness direction and nuts (not shown). The end plates 27, 28 are made of metal (for example, stainless steel) and function as an anode and a cathode, respectively, when a voltage is applied. Note that for ease of explanation, the proportions of the components in the drawings may differ from the actual proportions.

[0031] The electrolysis unit Ue will be described with reference to Fig. 3. As shown in Fig. 3, the electrolysis unit Ue comprises a solid oxide electrolysis cell 21 (hereinafter simply referred to as an electrolysis cell 21), an interconnector 22, a separator 23, a cathode frame 24, an anode frame 25, and a current collector 26.

[0032] The electrolysis cell 21 is the smallest unit of the SOEC and includes a solid electrolyte layer 211, an air electrode layer 212, and an anode layer 213. The air electrode layer 212 is laminated on the upper surface of the solid electrolyte layer 211 so as to contact the upper surface of the solid electrolyte layer 211. The air electrode layer 212 has a smaller outer shape than the solid electrolyte layer 211 and the anode layer 213, and is disposed in the center of the upper surface of the solid electrolyte layer 211 in a plan view of the electrolysis cell 21. Therefore, the upper surface of the outer periphery of the solid electrolyte layer 211 is exposed. The anode layer 213 is laminated on the back surface (lower surface) of the solid electrolyte layer 211.

[0033] The interconnector 22 is a rectangular metal (for example, stainless steel) member that has a rectangular current collecting part 22a that protrudes downward from the centre of its lower surface. A pair of interconnectors 22 is arranged on both sides of the electrolysis cell 21 in the thickness direction. Two adjacent electrolysis units Ue share one interconnector 22. The interconnector 22 also functions as a separator that separates the two adjacent electrolysis units Ue, Ue. The lower surface of the current collecting part 22a is in contact with the upper surface of the air cathode layer 212 of the electrolysis cell 21. The lower electrolysis unit Ue includes a pair of interconnectors 22, 29 instead of the pair of interconnectors 22, 22. The interconnector 29 is arranged at the bottom end of the cell stack 20 and differs from the interconnector 22 in that it does not have a current collecting part 22a.

[0034] The separator 23 is a rectangular plate-shaped metal (e.g., stainless steel) member with a rectangular opening formed in its center. The periphery of the opening of the separator 23 is brazed to the upper surface of the outer periphery of the solid electrolyte layer 211 of the electrolysis cell 21 with a brazing material (e.g., Ag brazing) (not shown). The separator 23 prevents mixing of oxygen generated in the air electrode layer 212 by electrolysis of water vapor and hydrogen generated in the fuel electrode layer 213.

[0035] The cathode frame 24 is a rectangular plate-shaped insulating member and may be formed of, for example, a mica sheet. A rectangular opening is formed in the center of the cathode frame 24. The cathode frame 24 is disposed between the separator 23 and the interconnector 22 above it.

[0036] The fuel electrode frame 25 is a rectangular plate-shaped metal (e.g., stainless steel) member having a rectangular opening at its center, and is disposed between the separator 23 and the interconnector 22 below it.

[0037] The internal space of the electrolysis unit Ue is partitioned by the separator 23 into an air chamber Sa and a fuel chamber Sf. The air chamber Sa is a space that allows the flow of oxygen generated in the air electrode layer 212, and is defined by a space surrounded by the separator 23, the interconnector 22 above the separator 23, the air electrode frame 24, and the electrolysis cell 21. The fuel chamber Sf is a space that allows the flow of hydrogen generated in the fuel electrode layer 213, and is defined by a space surrounded by the separator 23, the interconnector 22 (or interconnector 29) below the separator 23, the fuel electrode frame 25, and the electrolysis cell 21.

[0038] The current collector 26 is a rectangular porous member made of metal (for example, nickel) that is smaller than the anode layer 213 in a plan view and allows hydrogen to pass through. The current collector 26 is arranged in the fuel chamber Sf so as to be in contact with the lower surface of the anode layer 213 and the upper surface of the lower interconnector 22. Two adjacent electrolysis cells 21 are stacked in the thickness direction so as to share the interconnector 22 via the current collector 26, thereby electrically connecting the multiple electrolysis cells 21 in series.

[0039] 2 and 3 , four paths Pfi, Pfo, Pai, and Pao are formed as gas flow paths around the outer periphery of the cell stack 20. These paths Pfi, Pfo, Pai, and Pao are each formed to penetrate through members of the cell stack 20 in the thickness direction, excluding the "end plate 27" and the "upper interconnector 22 of the upper electrolysis unit Ue."

[0040] The path Pfi is formed near one corner of the side E1, which is one of the four sides that make up the outer periphery of the cell stack 20. The path Pfo is formed near the other corner of the side E2 that faces the side E1 (the corner located diagonally from the one corner of the side E1). As shown in FIG. 3 , the path Pfi communicates with the fuel chamber Sf via a horizontal hole 25a formed in the anode frame 25 of each electrolysis unit Ue. The path Pfo communicates with the fuel chamber Sf via a horizontal hole 25b formed in the anode frame 25 of each electrolysis unit Ue.

[0041] The path Pai is formed near one corner of the side E2. The path Pao is formed near the other corner of the side E1. The path Pai and the path Pao each communicate with the air chamber Sa via a horizontal hole (not shown) formed in the air electrode frame 24 of each electrolysis unit Ue.

[0042] Next, the configuration of the electrolysis cell 21 will be described in more detail with reference to FIG. 4 . FIG. 4 is a cross-sectional view of the electrolysis cell 21 in the thickness direction. As described above, the electrolysis cell 21 includes a solid electrolyte layer 211, an air cathode layer 212, and an anode layer 213. In this embodiment, the solid electrolyte layer 211 is a rectangular flat layer measuring approximately 150 mm square and approximately 6 μm thick, and is made of YSZ (yttria-stabilized zirconia) as an ion-conductive oxide. The solid electrolyte layer 211 is formed by sintering YSZ powder. Therefore, the solid electrolyte layer 211 has a structure in which multiple YSZ particles (ion-conductive oxide particles) are bonded together. The solid electrolyte layer 211 has high oxide ion conductivity. The solid electrolyte layer 211 is a dense layer and is designed to prevent leakage between the atmosphere on the air cathode layer 212 side (air atmosphere) and the atmosphere on the anode layer 213 side (reducing atmosphere).

[0043] The air electrode layer 212 is laminated on the upper surface 211B side of the solid electrolyte layer 211 so as to contact the upper surface 211B of the solid electrolyte layer 211. The air electrode layer 212 is a rectangular flat layer with a thickness of approximately 100 μm, is configured to contain a perovskite oxide such as LSCF (lanthanum strontium cobalt iron oxide), and is formed by sintering. The air electrode layer 212 has a functional layer and a current collecting layer. The current collecting layer is thicker than the functional layer and is disposed on the upper surface of the functional layer. The air electrode layer 212 has high electronic conductivity and effectively collects electrons from the current collecting layer. The air electrode layer 212 is a porous layer with pores inside.

[0044] The anode layer 213 is a rectangular flat layer measuring approximately 150 mm on each side, and is formed to have a thickness greater than the thicknesses of the solid electrolyte layer 211 and the air cathode layer 212, for example, approximately 400 μm. The solid electrolyte layer 211 and the air cathode layer 212 are supported by the anode layer 213. In other words, the electrolysis cell 21 is an anode-supported cell. The anode layer 213 has an anode functional layer 213 a and an anode support layer 213 b. The anode support layer 213 b is formed to be significantly thicker than the anode functional layer 213 a, and the thickness ratio can be set to, for example, approximately 16 to 40 times.

[0045] The anode layer 213 is laminated on the back surface 211A side, which is the lower surface of the solid electrolyte layer 211 in Fig. 4. As described above, the anode layer 213 has the anode functional layer 213a and the anode support layer 213b. The anode functional layer 213a and the anode support layer 213b are in contact with each other, and are laminated in this order on the back surface 211A side of the solid electrolyte layer 211.

[0046] The main component of the anode support layer 213b is a cermet of Ni as a catalytic metal and YSZ as an ion-conductive oxide. The anode support layer 213b is a porous layer that is configured to have a porous shape including a plurality of micropores (not shown). The diameter of the micropores is on the order of several μm, which ensures the permeability of water vapor (gas diffusibility).

[0047] The main component of the anode functional layer 213a is a cermet of Ni as a catalytic metal and GDC (gadolinia-doped ceria), an ion-conductive oxide. GDC is CeO containing Gd (gadolinium). ２ The anode functional layer 213a is made of ceria (ceria). Like the anode support layer 213b, the anode functional layer 213a is also a porous layer configured to have a porous shape including a plurality of micropores (not shown). The anode functional layer 213a is formed to be denser than the anode support layer 213b. In other words, the porosity of the anode functional layer 213a is smaller than the porosity of the anode support layer 213b. Like the solid electrolyte layer 211 and the air cathode layer 212, the anode layer 213 including the anode functional layer 213a and the anode support layer 213b is also formed by sintering.

[0048] The operation of the cell stack 20 will be described. First, a voltage is applied between the end plates 27, 28 of the cell stack 20. Next, high-temperature steam is supplied from the path Pfi. The steam supplied to the path Pfi flows into the fuel chamber Sf of each electrolysis unit Ue via the horizontal holes 25a. In addition, high-temperature air is supplied from the path Pai. The air supplied to the path Pai flows into the air chamber Sa of each electrolysis unit Ue via a horizontal hole (not shown). The reason for supplying high-temperature air to the air chamber Sa is to control the temperature of the cell stack 20.

[0049] The water vapor that flows into the fuel chamber Sf passes through the anode support layer 213b of the anode layer 213 and travels to the anode functional layer 213a. In the anode functional layer 213a, the water vapor reacts with electrons supplied from the end plate 28 via the current collector 26 to decompose into hydrogen and oxide ions (water vapor electrolysis reaction). The hydrogen generated by the water vapor electrolysis reaction diffuses within the fuel chamber Sf, is discharged through the horizontal hole 25b via path Pfo, and is recovered by a well-known method. At this time, unreacted water vapor can be discharged along with the hydrogen via path Pfo. Meanwhile, the oxide ions travel through the solid electrolyte layer 211 to the air cathode layer 212 in the air chamber Sa, release electrons in the functional layer of the air cathode layer 212, and become oxygen. The oxygen diffuses within the air chamber Sa and, together with the air that flowed into the air chamber Sa, is discharged through path Pao via a horizontal hole (not shown) and is recovered (or released to the atmosphere) by a well-known method. Electrons emitted from the functional layer of the air electrode layer 212 are collected by the current collecting portion 22a of the interconnector 22 via the current collecting layer, and circulate from the end plate 27 to the end plate 28 via the external power source.

[0050] The cell stack 20 operates as described above, and hydrogen is produced in the hydrogen production device 1 .

[0051] It is known that when the ion-conductive oxide in the anode functional layer is the same as the ion-conductive oxide in the solid electrolyte layer, YSZ, Ni in the anode functional layer migrates and aggregates, resulting in a decrease in the performance of the electrolysis cell. In contrast, when the ion-conductive oxide in the anode functional layer is GDC, as in this embodiment, Ni migration and aggregation in the anode functional layer are suppressed to some extent, thereby preventing a decrease in performance. However, when the ion-conductive oxide in the solid electrolyte layer is YSZ and the ion-conductive oxide in the anode layer (anode functional layer) is GDC, the ion-conductive oxides in the two layers are different. In this case, during the production (sintering) of the electrolysis cell, Zr in the YSZ in the solid electrolyte layer diffuses to the anode layer (anode functional layer), and Ce in the GDC in the anode layer (anode functional layer) diffuses into the solid electrolyte layer. In other words, Zr in the solid electrolyte layer and Ce in the anode layer (anode functional layer) interdiffuse. Such interdiffusion reduces the durability of the electrolysis cell. Therefore, improving the durability of the electrolysis cell is desirable. In particular, it is desirable to improve the durability of electrolysis cells in which elements interdiffuse between the solid electrolyte layer and the fuel electrode layer (fuel electrode functional layer).

[0052] In this regard, in the electrolysis cell 21 according to this embodiment, the average particle size of the YSZ particles, which are ion-conductive oxide particles, in the solid electrolyte layer 211 is set to 1.24 μm or less to improve durability. Conventionally, the average particle size of YSZ particles in a solid electrolyte layer is approximately 1.5 μm. Therefore, the average particle size of the YSZ particles in the solid electrolyte layer 211 of the electrolysis cell 21 according to this embodiment is smaller than the average particle size of YSZ particles in a conventional solid electrolyte layer. Setting the average particle size of the YSZ particles in the solid electrolyte layer 211 to 1.24 μm or less can improve the durability of the electrolysis cell 21.

[0053] Although the exact mechanism by which a small average particle size of the YSZ particles, which are ion-conductive oxide particles in the solid electrolyte layer, improves the durability of the electrolysis cell is unclear, it can be inferred as follows: The smaller the ion-conductive oxide particles in the solid electrolyte layer, the more grain boundaries are formed in the solid electrolyte layer. Furthermore, when elements in the solid electrolyte layer migrate (diffuse) toward the fuel electrode layer, or when elements in the fuel electrode layer migrate (diffuse) toward the solid electrolyte layer, the grain boundaries in the solid electrolyte layer act as a barrier to the migration of the elements. Therefore, the more grain boundaries there are in the solid electrolyte layer, i.e., the smaller the average particle size of the ion-conductive oxide particles in the solid electrolyte layer, the more the diffusion of elements into the solid electrolyte layer is suppressed, thereby improving durability.

[0054] The average particle size of the YSZ particles in the solid electrolyte layer 211 can be set to 1.24 μm or less by pre-pulverizing the YSZ powder during the production of the electrolytic cell 21 or by sintering at a sintering temperature lower than conventional sintering temperatures. Here, the average particle size of the YSZ particles in the solid electrolyte layer refers to the average value of the diameters of the YSZ particles (sintered particles) separated by the grain boundaries of YSZ in the solid electrolyte layer formed by sintering.

[0055] When the YSZ powder is pre-pulverized, it is preferable to reduce the particle size of the YSZ powder to 0.20 μm or less by pre-pulverization. In the examples described below, samples were prepared using YSZ particles whose average particle size after pre-pulverization was 0.20 μm or less and YSZ particles whose average particle size after pre-pulverization was greater than 0.20 μm. Hereinafter, the YSZ powder used to form the electrolytic cell 21 (solid electrolyte layer 211) and whose particle size has been reduced by pre-pulverization will be referred to as pulverized YSZ powder.

[0056] Furthermore, if the average particle size of the YSZ particles in the solid electrolyte layer is less than 0.40 μm, the YSZ particles will not grow sufficiently by sintering, resulting in a decrease in the strength of the solid electrolyte layer. In contrast, the average particle size of the YSZ particles in the solid electrolyte layer 211 according to this embodiment is set to 0.40 μm or more. This makes it possible to prevent a decrease in the strength of the solid electrolyte layer 211.

[0057] Thus, the average particle size of the YSZ particles, which are ion-conductive oxide particles in the solid electrolyte layer 211 according to this embodiment, is 0.40 μm or more and 1.24 μm or less, which allows the durability of the electrolysis cell 21 to be improved while maintaining the strength of the solid electrolyte layer 211.

[0058] The average particle size of the YSZ particles in the solid electrolyte layer is preferably 0.55 μm or more and 1.01 μm or less. When the average particle size of the YSZ particles in the solid electrolyte layer is within the above range, the durability and performance of the electrolysis cell can be improved.

[0059] Furthermore, in the electrolysis cell 21 according to this embodiment, the standard deviation σ of the particle size of the YSZ particles in the solid electrolyte layer 211 is 0.31 or less. If the standard deviation σ exceeds 0.31, the particle size variation is large, resulting in localized areas in the solid electrolyte layer where oxygen ions flow easily and areas where they do not. In this case, excessive voltage is applied in the areas where oxygen ions flow easily, and in areas where they do not flow easily, the reaction field where a reaction could occur is not effectively utilized, preventing efficient flow of oxygen ions, resulting in reduced performance. In contrast, if the standard deviation σ of the particle size of the YSZ particles is 0.31 or less, oxide ions flow evenly throughout the solid electrolyte layer, improving the performance of the electrolysis cell.

[0060] (Examples) 1. Sample Preparation NiO powder and GDC powder were mixed in a predetermined ratio and stirred for a predetermined time using a ball mill or the like. Next, butyral resin, polyvinyl acetal resin (G-260, manufactured by Sekisui Chemical Co., Ltd.) as a plasticizer, a known dispersant, a mixed solvent of toluene and MEK (methyl ethyl ketone), and optionally a pore-forming agent (typically organic beads) were added to the mixed powder in predetermined ratios, and mixed in a ball mill to prepare a slurry. Then, a green sheet of an anode functional layer having a predetermined thickness was formed from the slurry using a doctor blade method.

[0061] NiO powder and YSZ powder were mixed in a predetermined ratio and stirred for a predetermined time using a ball mill or the like. Next, butyral resin, polyvinyl acetal resin as a plasticizer, a known dispersant, a mixed solvent of toluene and MEK, and optionally a pore-forming agent (typically organic beads) were added to the mixed powder in predetermined ratios and mixed in a ball mill to prepare a slurry. Then, a green sheet of the anode support layer having a predetermined thickness was formed from the slurry using a doctor blade method.

[0062] In addition, butyral resin, polyvinyl acetal resin as a plasticizer, a known dispersant, and a mixed solvent of toluene and MEK were added to the crushed YSZ powder in predetermined proportions and mixed in a ball mill to prepare a slurry, which was then molded into a green sheet of a solid electrolyte layer having a predetermined thickness using a doctor blade method.

[0063] The crushed YSZ powder used to form the green sheets for the solid electrolyte layers was prepared by crushing commercially available YSZ powder in advance so that the powder had a predetermined average particle size or less.

[0064] Next, the green sheet for the anode functional layer and the green sheet for the anode support layer were laminated in this order on one side of the green sheet for the solid electrolyte layer. These laminated green sheets were then pressed together under high pressure using a press while heating and evacuating. This produced a laminate including the green sheet for the solid electrolyte layer, the green sheet for the anode functional layer, and the green sheet for the anode support layer.

[0065] The laminate formed as described above was then degreased at a predetermined temperature (e.g., 200 to 300°C). The laminate was then fired at a predetermined first temperature t0 for a predetermined time (e.g., 1 to 5 hours) (primary firing). This resulted in the formation of a primary sintered body having a solid electrolyte layer and a fuel electrode layer stacked on one side of the solid electrolyte layer.

[0066] Subsequently, a material containing LSCF was screen-printed onto the other surface of the solid electrolyte layer of the formed primary sintered body, and the resulting primary sintered body was fired at a predetermined second temperature (e.g., 900 to 1000°C) for a predetermined time (e.g., 1 to 5 hours) (secondary firing). This produced a sample electrolysis cell including a solid electrolyte layer, an anode layer (anode functional layer and anode support layer) laminated on one surface of the solid electrolyte layer, and an air cathode layer laminated on the other surface of the solid electrolyte layer.

[0067] Furthermore, by varying the firing temperature (first temperature t0) during the primary firing between 1000°C and 1400°C, for example, multiple electrolytic cell samples (Samples 1 to 8) with different average particle diameters D and particle diameter standard deviations σ of the YSZ particles in the solid electrolyte layer were produced. Specifically, the first temperatures t0 for each sample were as follows: Sample 1: 1290°C; Sample 2: 1240°C; Sample 3: 1190°C; Sample 4: 1170°C; Sample 5: 1140°C; Sample 6: 1340°C; Sample 7: 1090°C; and Sample 8: 1340°C. Note that the lower the firing temperature (first temperature t0), the smaller the average particle diameter D and the smaller the standard deviation σ tend to be. Furthermore, the amount of pore-forming material was adjusted during molding of these layers so that the porosity in the anode functional layer of each sample was smaller than the porosity in the anode support layer.

[0068] When the firing temperature (first temperature t0) of the primary sintered body is low, there is a concern that the strength and performance may be reduced due to insufficient sintering. However, by controlling the particle size of the YSZ powder (pulverized YSZ powder) used to form the green sheet of the solid electrolyte layer, good sinterability can be maintained even when the firing temperature (first temperature t0) is low. Specifically, since the smaller the particle size of the pulverized YSZ powder, the better the sinterability. Therefore, by using a pulverized YSZ powder with a small average particle size for samples with a low firing temperature (first temperature t0) and a pulverized YSZ powder with a large average particle size for samples with a high firing temperature (first temperature t0), the sinterability of the primary sintered body of each sample can be maintained good. In this example, for samples (samples 2, 3, 4, 5, and 7) having a firing temperature (first temperature t0) of 1240°C or less, the YSZ powder was pre-ground so that the average particle diameter (median diameter) PD of the pulverized YSZ powder was 0.20 μm or less (specifically, 0.16 μm), and for samples (samples 1, 6, and 8) having a firing temperature (first temperature t0) of more than 1240°C, the YSZ powder was pre-ground so that the average particle diameter (median diameter) PD of the pulverized YSZ powder was more than 0.20 μm (specifically, 0.27 μm).

[0069] 2. Calculation of the average particle size D of YSZ particles in the solid electrolyte layer Each sample was cut along a plane along the thickness direction of the electrolytic cell, and the cut surface was photographed using a FIB-SEM device (Thermo Fisher Scientific: Model Helios NanoLab 600i). Ten YSZ particles in the solid electrolyte layer shown in the photographed image were selected, and the particle size of each of the selected 10 particles was calculated using the intercept method. The average particle size D of the sample related to the photographed image was calculated by arithmetically averaging the particle sizes calculated for each particle. Then, the average particle size D of each sample was calculated using the above method.

[0070] The intercept method used in this example is as follows: Using predetermined software (ImageJ software), 10 random YSZ particles are selected from the FIB-SEM image, and lines are drawn vertically and horizontally at 1-pixel intervals for each selected particle. The two points where each line intersects with the grain boundary of the YSZ particle are determined, and the distance between the two intersections determined for each line is calculated. The arithmetic mean value of the distances between the intersections calculated for all lines is used as the particle diameter of the YSZ particle, and the arithmetic mean value of the particle diameters determined for the 10 YSZ particles is used as the average particle diameter of the YSZ particles. The average particle diameter of YSZ particles can also be determined by methods other than those described above. For example, multiple straight lines are drawn at equal intervals in the width direction (horizontal direction) and height direction (vertical direction) on the image of multiple YSZ particles shown in the FIB-SEM image of the cross section of the solid electrolyte layer, and the points where each line intersects with the grain boundaries of multiple YSZ particles are determined, and the average values ​​of the width (horizontal distance) and height (vertical distance) of each particle determined from the determined intersection points can be used as the average particle size of the YSZ particles.

[0071] 3. Calculation of the standard deviation σ of particle diameters of YSZ particles in the solid electrolyte layer For each sample, the particle diameter variance σ was calculated from the average particle diameter D calculated as above and the particle diameters of the 10 particles used to calculate the average particle diameter D. ２ Calculate the calculated variance σ ２ The standard deviation σ was calculated by calculating the square root of

[0072] 4. Measurement of Durability Degradation Rate A voltage was applied between the fuel electrode layer and the air electrode layer of each sample so that a constant current flowed through each sample. A durability degradation test was then conducted in which a constant current was continuously flowing for a predetermined time while a constant flow rate of water vapor was supplied to the fuel electrode layer side to continuously perform a steam electrolysis reaction. When a constant current was continuously flowing during the durability degradation test, the applied voltage increased over time due to an increase in internal resistance within the sample. The difference ΔV (= V1 - V0) between the initially applied voltage (V0) and the voltage (V1) applied after a predetermined time (e.g., 400 hours) was calculated, and the calculated value was converted into the difference between the voltage that would be applied after 1000 hours and the initially applied voltage. The converted value was then divided by the initially applied voltage to calculate the durability degradation rate as a percentage. It can be said that the smaller the durability degradation rate, the higher the durability.

[0073] 5. Measurement of Current Density For each sample, the current per unit area (current density) was measured when a constant voltage (1 to 1.3 V) was applied between the fuel electrode layer and the air electrode layer while a constant flow rate of water vapor was supplied to the fuel electrode layer side to perform a steam electrolysis reaction. The measured current density was used as an index for evaluating performance. It can be said that the higher the current density, the better the performance. 8. Evaluation Table 1 shows the average particle size D, standard deviation σ, durability deterioration rate, current density, and overall evaluation results obtained for Samples 1 to 8.

[0074] In Table 1, t0 indicates the firing temperature (first temperature) of the primary sintered body, and PD indicates the average particle diameter (median diameter D50) of the pulverized YSZ powder used in preparing the green sheet for the solid electrolyte layer. In Table 1, durability was evaluated as good (◯) when the durability degradation rate was 2.8% or less, and as poor (×) when the durability degradation rate was more than 2.8%. Furthermore, when the current density was 0.90 A / cm ２ When the current density was 0.80 A / cm or more, the performance was evaluated as very good (◎). ２ 0.90A / cm or more ２ When the current density is less than 0.80 A / cm, the performance is evaluated as good (◯). ２If the durability was good (◯) and the performance was very good (◎), the overall judgment was rated as very good (◎). If both the durability and the performance were good (◯), the overall judgment was rated as good (◯). If the durability was poor (×), the overall judgment was rated as poor (×). Note that in Sample 7, the strength of the sample was very low due to the particle size of the YSZ particles in the solid electrolyte layer being too small, and the sample broke before the evaluation of the performance and durability degradation rate, so the performance and durability could not be evaluated. In Sample 7, the strength was very low, so the overall judgment was determined to be poor (×).

[0075] As can be seen from Table 1, the durability evaluations for Samples 1, 2, 3, 4, and 5 are all good (◯). In contrast, the durability evaluations for Samples 6 and 8 are all poor (×). Here, the average particle size D for Samples 1 to 5 is 1.24 μm or less, while the average particle size D for Samples 6 and 8 exceeds 1.24 μm. This shows that durability is improved when the average particle size D of the YSZ particles in the solid electrolyte layer is 1.24 μm or less.

[0076] Furthermore, the average particle size D of Samples 1 to 5 was 0.40 μm or more, and no cracks occurred in these samples. In contrast, the average particle size D of Sample 7 was less than 0.40 μm (0.32 μm), and this sample experienced cracks due to insufficient strength, as described above. From these findings, it can be seen that when the average particle size D of the YSZ particles in the solid electrolyte layer is 0.40 μm or more, the desired strength can be maintained.

[0077] From the above, when the average particle size D of the YSZ particles in the solid electrolyte layer is 0.40 μm or more and 1.24 μm or less, the durability of the electrolysis cell can be improved while maintaining its strength.

[0078] The standard deviation σ for Samples 2 to 5 is 0.31 or less, while the standard deviation σ for Sample 1 is greater than 0.31 (0.46). Here, the current density for Samples 2 to 5 is 0.87 A / cm ２or more, while the current density for Sample 1 was 0.87 A / cm ２ Less than (0.82 A / cm ２ ) Therefore, when the standard deviation σ of the particle diameters of the YSZ particles in the solid electrolyte layer is 0.31 or less, the performance of the electrolysis cell can be improved.

[0079] Furthermore, the current density evaluation for Samples 2 to 4 is very good (◎). On the other hand, the current density evaluation for Samples 1 and 5 is good (◯). Here, the average particle size D for Samples 2 to 4 is 0.55 μm or more and 1.01 μm or less, while the average particle size D for Sample 1 is more than 1.01 μm (1.24 μm), and the average particle size D for Sample 5 is less than 0.55 μm (0.40 μm). From this, it can be seen that when the average particle size D of the YSZ particles in the solid electrolyte layer is 0.55 μm or more and 1.01 μm or less, both durability and performance can be improved.

[0080] Furthermore, the smaller the average particle size D of the YSZ particles in the solid electrolyte layer, the lower the firing temperature (first temperature t0) of the primary sintered body can be, thereby reducing the thermal energy required to fabricate the electrolytic cell and, as a result, the manufacturing cost of the electrolytic cell. Therefore, from the perspective of reducing the manufacturing cost of the electrolytic cell, it is desirable that the average particle size D of the YSZ particles in the solid electrolyte layer be as small as possible. Specifically, the average particle size D of the YSZ particles in the solid electrolyte layer may be 1.13 μm or less. Preferably, the average particle size D is 1.01 μm or less, more preferably, the average particle size D is 0.88 μm or less, and even more preferably, the average particle size D is 0.74 μm or less.

[0081] Although the embodiments of the present disclosure have been described above, the technology according to the present disclosure is not limited to the above embodiments. For example, in the above embodiments, an example was shown in which the anode layer includes an anode functional layer and an anode support layer, and the ion-conductive oxides in each layer are different. However, the ion-conductive oxide in the anode functional layer and the ion-conductive oxide in the anode support layer may be the same. Furthermore, in the above embodiments, an electrolytic cell in which elements interdiffuse between the solid electrolyte layer and the anode functional layer was described. However, the present technology can also be applied to electrochemical cells in which interdiffusion does not occur, for example, electrochemical cells in which the ion-conductive oxide in the solid electrolyte layer and the ion-conductive oxide in the anode layer (anode functional layer) are the same. Furthermore, in the above embodiments, an example was shown in which YSZ was used as the ion-conductive oxide in the solid electrolyte layer, but other ion-conductive oxides may also be used. Furthermore, in the above embodiments, an anode-supported electrolytic cell, i.e., an electrolytic cell including an anode support layer, was described. However, the present technology can also be applied to other electrochemical cells. In this manner, the technology according to the present disclosure can be modified without departing from its spirit.

[0082] The present invention may further include the following aspects. [1] An electrochemical cell comprising: a solid electrolyte layer containing ion-conductive oxide particles; a fuel electrode layer laminated on one side of the solid electrolyte layer; and an air electrode layer laminated on the other side of the solid electrolyte layer, wherein the average particle size of the ion-conductive oxide particles in the solid electrolyte layer is 0.40 μm or more and 1.24 μm or less. [2] The electrochemical cell according to [1], wherein the standard deviation of the particle sizes of the ion-conductive oxide particles in the solid electrolyte layer is 0.31 or less. [3] The electrochemical cell according to [1] or [2], wherein the average particle size of the ion-conductive oxide particles in the solid electrolyte layer is 0.55 μm or more and 1.01 μm or less. [4] The electrochemical cell according to any of [1] to [3], wherein the fuel electrode layer is made of CeO containing Gd. ２an electrochemical cell comprising: the ion-conductive oxide particles in the solid electrolyte layer being YSZ; [5] a solid oxide electrolysis cell comprising the electrochemical cell according to any one of [1] to [4]; [6] a cell stack comprising a stack of electrochemical cells according to any one of [1] to [4] or the solid oxide electrolysis cells according to [5]; [7] a hot module comprising: the cell stack according to [6]; a vaporizer generating water vapor to be supplied to the cell stack; a heat exchanger performing heat exchange with gas supplied to the cell stack; a heater for heating the cell stack; and a thermal insulator in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed; [8] a hydrogen production device comprising the hot module according to [7].

[0083] 10...hot module, 20...cell stack, 21...solid oxide electrolysis cell (electrochemical cell), 211...solid electrolyte layer, 211A...rear surface (one side), 211B...upper surface (other side), 212...air electrode layer, 213...fuel electrode layer, 213a...fuel electrode functional layer, 213b...fuel electrode support layer, 22, 29...interconnector, 23...separator, 24...air electrode frame, 25...fuel electrode frame, 26...current collector, 27, 28...end plate, 30...evaporator, 40...heat exchanger, 50...heater, 60...insulating material, 90...condenser, D...average particle size, σ...standard deviation

Claims

1. An electrochemical cell comprising: a solid electrolyte layer containing ion-conductive oxide particles; a fuel electrode layer laminated on one side of the solid electrolyte layer; and an air electrode layer laminated on the other side of the solid electrolyte layer, wherein the average particle size of the ion-conductive oxide particles in the solid electrolyte layer is 0.40 μm or more and 1.24 μm or less.

2. An electrochemical cell according to claim 1, wherein the standard deviation of the particle size of the ion-conductive oxide particles in the solid electrolyte layer is 0.31 or less.

3. An electrochemical cell according to claim 1 or 2, wherein the average particle size of the ion-conductive oxide particles in the solid electrolyte layer is 0.55 μm or more and 1.01 μm or less.

4. The electrochemical cell according to claim 1, wherein the fuel electrode layer is made of CeO containing Gd. ２ wherein the ion-conducting oxide particles in the solid electrolyte layer are YSZ.

5. A solid oxide electrolysis cell comprising the electrochemical cell according to claim 1.

6. A cell stack comprising a stack of solid oxide electrolysis cells according to claim 5.

7. A hot module comprising: a cell stack according to claim 6; a vaporizer that generates steam to be supplied to the cell stack; a heat exchanger that exchanges heat with gas supplied to the cell stack; a heater that heats the cell stack; and a heat insulating material in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed.

8. A hydrogen production device comprising the hot module according to claim 7.

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