Electrochemical cell, solid oxide electrolytic cell, cell stack, hot module, and gas manufacturing device

Abstract

An electrochemical cell (electrolytic cell) has a solid electrolyte layer, an air electrode layered on the front surface side of the solid electrolyte layer, and a fuel electrode layered on the rear surface side of the solid electrolyte layer. The fuel electrode has a functional layer containing a Ni alloy and a conductive solid oxide, and the average particle diameter of the Ni alloy contained in the functional layer is 0.77 μm-1.00 μm inclusive.

Description

Electrochemical cells, solid oxide electrolysis cells, cell stacks, hot modules, and gas production equipment

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

[0002] Conventionally, solid oxide electrochemical cells using a solid oxide as an electrolyte have been known (see 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] JP 2015-92459 A

[0004] The electrochemical cell can be configured to include a solid electrolyte layer, a fuel electrode layer laminated on one side of the solid electrolyte layer, and a cathode layer laminated on the other side of the solid electrolyte layer. The fuel electrode layer can be configured to contain Ni (nickel) as an electrode catalyst and an oxide having ion conductivity (e.g., YSZ (yttria-stabilized zirconia)).

[0005] When an electrochemical cell containing Ni in the fuel electrode layer is operated for a long time under a harsh operating environment (high temperature, high humidity, high current), Ni migration and aggregation occurs within the fuel electrode layer. When Ni migrates or aggregates within the fuel electrode layer, the internal resistance of the fuel electrode layer increases, and the three-phase interface (the boundary between the fuel gas, Ni, and the electrolyte (YSZ)) serving as a reaction field decreases. This reduces the electrical characteristics of the electrochemical cell, making it impossible to achieve the desired performance. Therefore, there is a need for an electrochemical cell with improved durability that can maintain the desired performance even when operated for a long time.

[0006] The present disclosure has an object to solve the above-mentioned problems, that is, one object of the present disclosure is to improve the durability of electrochemical cells.

[0007] The electrochemical cell according to the present disclosure comprises a solid electrolyte layer, an air electrode laminated on a front surface side of the solid electrolyte layer, and an anode laminated on a back surface side of the solid electrolyte layer, wherein the anode has a functional layer containing a Ni alloy and a conductive solid oxide, and the Ni alloy contained in the functional layer has an average particle size of 0.77 μm or more and 1.00 μm or less.

[0008] The functional layer of the electrochemical cell according to the present disclosure contains a Ni alloy and a conductive solid oxide. The metal element that bonds with Ni to form the Ni alloy suppresses Ni migration and aggregation. However, if the average particle size of the Ni alloy is less than 0.77 μm, the metal element is less effective in suppressing Ni migration and aggregation. On the other hand, if the average particle size of the Ni alloy exceeds 1.0 μm, the metal element promotes densification of the interior of the fuel electrode layer during molding (sintering) of the fuel electrode layer, thereby reducing gas diffusivity in the fuel electrode layer and resulting in reduced initial performance. If the average particle size of the Ni alloy contained in the functional layer is 0.77 μm or more and 1.00 μm or less, the durability of the electrochemical cell can be improved while suppressing a decrease in initial performance.

[0009] In addition, when the fuel electrode layer contains a metal element other than Ni, particles of elemental Ni may be present in the functional layer in addition to particles of an alloy of Ni and the metal. Therefore, in the present disclosure, the average particle size of the Ni alloy may be the "average particle size of the Ni alloy and elemental Ni."

[0010] The Ni alloy may be a NiFe alloy.

[0011] Fe has the property of being highly effective in suppressing the migration and aggregation of Ni by forming a NiFe alloy, so when the Ni alloy is a NiFe alloy, it is possible to suppress the deterioration of the initial performance of the electrochemical cell and enhance the effect of improving durability.

[0012] The average particle size of the Ni alloy may be smaller than the average particle size of the conductive solid oxide.

[0013] One cause of deterioration of the functional layer of the fuel electrode layer is the disconnection of the conduction path (pathway of ion conduction) in the conductive solid oxide. The larger the average particle size of the conductive solid oxide, the less likely the conduction path in the conductive solid oxide is to be disconnected, and therefore the less likely deterioration progresses. Therefore, when the relationship between the average particle size of the Ni alloy and the average particle size of the conductive solid oxide is specified as described above, the conduction path in the conductive solid oxide is stabilized. Therefore, the effect of improving durability can be enhanced.

[0014] A pore size ratio, which is a ratio of the average particle size of the conductive solid oxide to the average size of the pores contained in the functional layer, may be 1.5 or more and 2.6 or less.

[0015] If the average diameter of the pores contained in the functional layer is too small, the functional layer will be dense, resulting in low gas diffusibility in the functional layer. This will result in a decrease in the initial performance of the electrochemical cell. Furthermore, if the average diameter of the pores contained in the functional layer is too large, Ni will be more likely to migrate and aggregate, resulting in a decrease in durability. Therefore, a pore diameter ratio of 1.5 or more and 2.6 or less can enhance the effect of improving durability while suppressing a decrease in the initial performance of the electrochemical cell.

[0016] A solid oxide electrolysis cell according to the present disclosure comprises an electrochemical cell according to the present disclosure.

[0017] Such a configuration makes it possible to provide a solid oxide electrolysis cell that is improved in durability while suppressing deterioration in initial performance.

[0018] The cell stack according to the present disclosure is formed by stacking a plurality of solid oxide electrolysis cells according to the present disclosure.

[0019] With this configuration, it is possible to provide a cell stack that has improved durability while suppressing deterioration in initial performance.

[0020] The hot module according to the present disclosure comprises a cell stack according to the present disclosure, a vaporizer that generates water vapor to be supplied to the cell stack, a heat exchanger that exchanges heat with gas supplied to the cell stack, a heater for heating the cell stack, and an insulating material in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed.

[0021] With this configuration, a hot module with improved durability can be provided.

[0022] The gas production apparatus according to the present disclosure includes the hot module according to the present disclosure.

[0023] With this configuration, it is possible to provide a gas production device with improved durability.

[0024] Fig. 1 is a block diagram of a hydrogen production device including a hot module. Fig. 2 is a perspective view of a cell stack of a solid oxide electrolysis cell (SOEC) according to an embodiment of the present invention. Fig. 3 is a cross-sectional view taken along line II-II in Fig. 2. Fig. 4 is a cross-sectional view in the thickness direction of a unit cell included in the electrolysis unit of Fig. 1. Fig. 5 is a graph showing the relationship between the average particle size of a NiFe alloy and the durability deterioration rate.

[0025] Hereinafter, embodiments 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 from water vapor. The hydrogen production device 1 according to this embodiment is an example of a gas production device of the present invention. As shown in FIG. 1, the hydrogen production device 1 includes a hot module 10 and a condenser 90.

[0026] 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.

[0027] 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.

[0028] In addition to the water vapor, air is introduced into the heat exchanger 40. The heat exchanger 40 also receives high-temperature hydrogen (H ) generated in the cell stack 20 (described later). 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.

[0029] 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.

[0030] 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, and then introduced into the condenser 90. The unreacted water vapor is condensed in the condenser 90. The water condensed in the condenser 90 is introduced into the vaporizer 30. Meanwhile, the 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 recovered (or released into the atmosphere).

[0031] The cell stack 20, vaporizer 30, heat exchanger 40, and heater 50 are disposed inside the thermal insulation 60. This suppresses heat radiation from the cell stack 20, vaporizer 30, heat exchanger 40, and heater 50 to the outside of the thermal insulation 60. Heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), and biosoluble fiber (AES), and / or heat-resistant containers formed from these heat-resistant fibers, may be used for the thermal insulation 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.

[0032] 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 (up-down 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 end plates 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.

[0033] 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 sometimes simply referred to as the electrolysis cell 21), an interconnector 22, a separator 23, a cathode frame 24, an anode frame 25, and a current collector 26.

[0034] The electrolysis cell 21 is an example of an electrochemical cell of the present invention. The electrolysis cell 21 is the smallest unit of an SOEC and includes a solid electrolyte layer 211, an air electrode layer 212 laminated on the upper surface of the solid electrolyte layer 211, and an anode layer 213 laminated on the lower 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 to the outside.

[0035] 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. 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 other interconnectors 22 in that it does not have a current collecting part 22a.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 upper interconnector 22, separator 23, air electrode frame 24, and 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 lower interconnector 22, separator 23, fuel electrode frame 25, and electrolysis cell 21.

[0040] 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.

[0041] 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."

[0042] 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.

[0043] 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.

[0044] Next, the configuration of the electrolytic cell 21 will be described in more detail with reference to FIG. 4 . FIG. 4 is a cross-sectional view of the electrolytic cell 21 in the thickness direction. As described above, the electrolytic cell 21 includes a solid electrolyte layer 211, an air electrode layer 212, and an anode layer 213. In this embodiment, the solid electrolyte layer 211 is a rectangular flat layer measuring 150 mm square and 6 μm thick, and is configured to contain YSZ (yttria-stabilized zirconia). The solid electrolyte layer 211 has high oxide ion conductivity. The solid electrolyte layer 211 is a dense layer designed to prevent leakage between the air atmosphere at the air electrode and the reducing atmosphere at the anode. The solid electrolyte layer 211 is formed by sintering.

[0045] The air electrode layer 212 is laminated on the upper surface 211B (other surface) of the solid electrolyte layer 211. The air electrode layer 212 is a rectangular flat layer with a thickness of 108 μm, and 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.

[0046] The anode layer 213 is a rectangular flat layer measuring 150 mm on each side, and is formed to be thicker than the solid electrolyte layer 211 and the air cathode layer 212, for example, approximately 400 μm. The thick anode layer 213 supports the solid electrolyte layer 211 and the air cathode layer 212. In other words, the electrolysis cell 21 is an anode-supported cell. The anode layer 213 has a functional layer 213 a and a support layer 213 b. The support layer 213 b is formed to be significantly thicker than the functional layer 213 a, and the thickness ratio can be set to be approximately 16 to 40 times, for example.

[0047] The anode layer 213 is laminated on the back surface 211A (one side), which is the bottom surface in Fig. 4, of the solid electrolyte layer 211. Specifically, the functional layer 213a of the anode layer 213 is laminated on the back surface 211A of the solid electrolyte layer 211, and the support layer 213b is laminated on the back surface (bottom surface in Fig. 4) of the functional layer 213a. In other words, the functional layer 213a and the support layer 213b are laminated on the back surface 211A of the solid electrolyte layer 211 in this order. The anode layer 213 is also formed by sintering.

[0048] The main component of the support layer 213b is a cermet of Ni (nickel) and YSZ. The support layer 213b is configured to be porous, 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. The main component of the functional layer 213a is also a cermet of Ni and YSZ. Like the support layer 213b, the functional layer 213a is also configured to be porous, including a plurality of micropores (not shown), but is denser than the support layer 213b. In other words, the porosity of the functional layer 213a is smaller than the porosity of the support layer 213b.

[0049] 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.

[0050] The water vapor that flows into the fuel chamber Sf passes through the support layer 213b of the fuel electrode layer 213 and travels to the functional layer 213a. In the functional layer 213a, the water vapor reacts with electrons supplied from the end plate 28 via the current collector 26 and is decomposed into hydrogen and oxide ions (water electrolysis reaction). The hydrogen 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 electrode layer 212 in the air chamber Sa, release electrons in the functional layer of the air electrode 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.

[0051] The cell stack 20 operates as described above, and hydrogen is produced in the hydrogen production device 1 .

[0052] It has been confirmed that when the cell stack 20 operates for a long time, Ni in the fuel electrode layer 213 migrates and aggregates within the fuel electrode layer 213. When Ni migrates and aggregates within the fuel electrode layer 213, the Ni concentration near the interface between the functional layer 213a and the solid electrolyte layer 211 decreases, and the reaction efficiency of the water electrolysis reaction decreases. Furthermore, when Ni migrates and aggregates within the fuel electrode layer 213, the conduction path (pathway for ion conduction) within the fuel electrode layer 213 decreases, and the internal resistance increases. This decrease in reaction efficiency and increase in internal resistance deteriorates the fuel electrode layer 213.

[0053] In the present disclosure, durability is improved by alloying Ni with other metal elements (Ni alloying) in the functional layer 213a of the fuel electrode layer 213 and specifying the average particle size of this alloy within a predetermined range. Furthermore, by making the average particle size of the Ni alloy smaller than the average particle size of the YSZ in the functional layer 213a, the effect of improving durability can be enhanced while suppressing a decrease in initial performance. Furthermore, by setting the pore size ratio, which is the ratio of the average particle size of the YSZ in the functional layer 213a to the average diameter of the pores contained in the functional layer 213a, within a predetermined range, the effect of improving durability can be enhanced while suppressing a decrease in initial performance.

[0054] (Ni Alloy) In the present disclosure, a NiFe alloy is used as the Ni alloy. By including Fe (iron) in the fuel electrode layer 213, the progression of deterioration of the fuel electrode layer 213 can be suppressed. Fe also serves as a sintering aid, and can improve the sinterability of YSZ and Ni when manufacturing the fuel electrode layer 213. However, the metal element added to the fuel electrode layer 213 to generate the Ni alloy is not limited to Fe.

[0055] (Average particle size of Ni alloy) Figure 5 is a graph showing the relationship between the average particle size of the NiFe alloy and the durability deterioration rate. The average particle size was measured as follows. First, the functional layer 213a was cut along a plane along the thickness direction of the fuel electrode layer 213 (thickness direction of the electrolysis cell 21), and the cut surface was photographed using a scanning electron microscope (SEM). The obtained SEM image was ternary-coded into white, black, and gray. This resulted in an SEM image in which YSZ was white, pores were black, and the metal was gray. The gray areas in the ternary-coded SEM image were then considered to be particles of the NiFe alloy, and the average particle size of the gray areas of the ternary-coded SEM image was measured using the intercept method.

[0056] In the ternary SEM image, it is impossible to distinguish whether the gray region represents a NiFe alloy, pure Ni, or pure Fe. However, since almost all of the Ni and Fe contained in the functional layer 213a can be considered to be alloyed, the average particle size of the gray region in the SEM image was considered to be the average particle size of the NiFe alloy. Note that if the total volume of Fe in the functional layer 213a is smaller than the total volume of Ni, there is a possibility that pure Ni not alloyed with Fe is present. Therefore, if pure Ni is present, the average particle size of the NiFe alloy may be the "average particle size of the NiFe alloy and pure Ni." The "average particle size of the NiFe alloy" can also be described as the "average particle size of metal particles present in the fuel electrode layer 213 obtained by sintering a material in which a small amount of Fe (i.e., a metal element other than Ni) (specifically, a smaller volume than Ni) is added to Ni and the conductive solid oxide YSZ."

[0057] However, when the inventors measured the "average particle size of metal particles present in a fuel electrode layer obtained by sintering a material consisting of Ni and YSZ, a conductive solid oxide, with no added Fe" and the "average particle size of metal particles present in a fuel electrode layer obtained by sintering a material consisting of Ni and YSZ, a conductive solid oxide, with added Fe," they found that the metal particles in the fuel electrode layer consisting of a material consisting of Fe-added material were larger in size than the metal particles in the fuel electrode layer consisting of a material consisting of No added Fe, and no metal particles with a size comparable to that of the metal particles in the fuel electrode layer consisting of a material consisting of No added Fe were found. This is thought to be because, when the Fe-added material was sintered, all of the Ni and Fe were alloyed into NiFe, and the NiFe alloy particles grew. Therefore, it is thought that almost all of the "metal particles present in a fuel electrode layer obtained by sintering a material consisting of Ni and YSZ, a conductive solid oxide, with added a small amount of Fe" are NiFe alloy particles.

[0058] Whether the metal particles contained in the functional layer 213a are particles of simple Ni or particles of a NiFe alloy can be analyzed by X-ray diffraction (XRD). Specifically, if the metal particles contained in the functional layer 213a are particles of simple Ni, a peak derived from Ni appears in the diffraction profile (diffraction pattern) obtained by X-ray diffraction. Similarly, if the metal particles contained in the functional layer 213a are particles of a NiFe alloy, a peak derived from the NiFe alloy appears in the diffraction profile. The peak derived from the NiFe alloy appears at a position shifted by a predetermined angle (e.g., 0.02° or more) relative to the peak derived from simple Ni. Therefore, by identifying the angle at which the peak appears, it is possible to analyze whether the metal particles contained in the functional layer 213a are particles of simple Ni or particles of a NiFe alloy. In addition, whether the metal particles that appear on the cross section of the functional layer 213a are particles of simple Ni or particles of a NiFe alloy can also be analyzed (identified) using an electron probe micro analyzer (EPMA).

[0059] The durability deterioration rate is calculated as follows: durability deterioration rate = (((voltage after 1000 hours) - (initial voltage)) / (initial voltage)) × 100 [%]. Note that the "initial voltage" is the "voltage applied to pass a predetermined current through the electrolytic cell," and the "voltage after 1000 hours" is the "voltage applied to pass the predetermined current through the electrolytic cell after the predetermined current has been passed through the electrolytic cell for 1000 hours." Since the internal resistance of an electrolytic cell increases as it deteriorates, the "voltage applied to pass a predetermined current through the electrolytic cell" increases with continued use. For this reason, a smaller value of the durability deterioration rate indicates less deterioration and higher durability.

[0060] As shown in Figure 5, when the average particle size of the NiFe alloy is in the range of 0.779 to 1.00 μm, the durability degradation rate is in the range of 5.7 to 7.5%. In contrast, when the average particle size of the NiFe alloy is less than 0.779 μm or more than 1.00 μm, the durability degradation rate is 15% or more. Thus, when the average particle size of the NiFe alloy is in the range of 0.779 to 1.00 μm, durability is high. For this reason, the average particle size of the NiFe alloy is set to the range of 0.77 to 1.00 μm.

[0061] Here, it was confirmed that there is a positive correlation between the "volume fraction of Fe relative to the total volume of Ni and Fe in the functional layer 213a" (hereinafter referred to as the Fe volume fraction) and the average particle size of the NiFe alloy. Therefore, by specifying the Fe volume fraction, the average particle size of the NiFe alloy can be controlled within the range of this embodiment, i.e., 0.779 to 1.00 μm.

[0062] (Relationship between the average particle size of the Ni alloy and the average particle size of the YSZ) In the present disclosure, assuming that the average particle size of the NiFe alloy is in the range of 0.779 μm or more and 1.00 μm or less, it is preferable that the average particle size of the YSZ be larger than the average particle size of the NiFe alloy. One cause of deterioration of the functional layer 213a of the fuel electrode layer 213 is the disconnection of the conductive paths of the YSZ during use. Furthermore, if the average particle size of the YSZ is small, the conductive paths are more likely to be disconnected during endurance, and deterioration is more likely to progress. Conversely, the larger the average particle size of the YSZ, the less likely the conductive paths are to be disconnected, and therefore deterioration is less likely to progress. Therefore, in order to improve the durability of the functional layer 213a, it is preferable that the average particle size of the YSZ be large. The average particle size of the YSZ can be measured using the same method as the average particle size of the NiFe alloy. That is, the white area in the ternary SEM image of the cross section of the functional layer 213a is regarded as YSZ, and the average particle size in the gray area of ​​the ternary SEM image can be measured by the intercept method.

[0063] The relationship between the average particle size of YSZ and the average particle size of the NiFe alloy in the functional layer 213a is affected by the particle size of the YSZ starting material. Specifically, if the particle size of the YSZ starting material is small, the average particle size of YSZ will be smaller than the average particle size of the NiFe alloy. In this case, as mentioned above, the conductive paths are more likely to be broken, resulting in lower durability. Furthermore, if the volume fraction of Fe is small and the average particle size of the NiFe alloy is larger than the average particle size of YSZ, the effect of Fe as a sintering aid is reduced. If the particle size of the YSZ starting material is large, the average particle size of YSZ will be larger than the average particle size of the NiFe alloy. However, if the volume fraction of Fe is too large, the average particle size of the NiFe alloy will be larger than the average particle size of YSZ. This is thought to be because Fe is present between the YSZ particles, inhibiting the growth of the YSZ particles by bonding them together.

[0064] Specifically, by making the particle size of the YSZ starting material smaller than that of the NiFe precursor starting material, the average particle size of the YSZ in the functional layer 213a can be made smaller than that of the NiFe alloy. Conversely, by making the particle size of the YSZ starting material larger than that of the NiFe precursor starting material, the average particle size of the YSZ in the functional layer 213a can be made larger than that of the NiFe alloy.

[0065] (Pore Diameter Ratio) The pore diameter ratio of the functional layer 213a is 1.5 or more and 2.6 or less. The pore diameter ratio is the ratio of the average particle diameter of YSZ to the average diameter of pores contained in the functional layer 213a, and is calculated as follows: Pore diameter ratio = (average particle diameter of YSZ contained in the functional layer 213a) / (average diameter of pores contained in the functional layer 213a). When the pore diameter ratio is small, i.e., when the average diameter of pores is large, YSZ tends to become brittle. On the other hand, when the pore diameter ratio is large, i.e., when the average diameter of pores is small, Ni becomes less likely to move, improving durability. On the other hand, when the average diameter of pores is small, gas diffusibility in the functional layer 213a decreases, resulting in a decrease in initial performance. In the present disclosure, by setting the pore diameter ratio to 1.5 or more and 2.6 or less, durability can be improved while maintaining (or preventing a decrease in) initial performance. Furthermore, by setting the pore size ratio in this range, embrittlement of the YSZ can be prevented. The average pore size can be measured using a method similar to that for measuring the average particle size of a NiFe alloy. That is, in an SEM image of a cross section of the ternary-valued functional layer 213a, the black areas are considered to be pores, and the average diameter of the black areas calculated using the intercept method can be used as the average pore size.

[0066] (Example) 1. Preparation of sample NiO powder and Fe ２ O ３The powder was mixed in a predetermined compounding ratio and stirred for a predetermined time using a ball mill or the like. The mixture was then washed with alcohol, and the liquid mixture was poured into a bowl. The mixture was dried by volatilizing the alcohol in the bowl and formed into a powder. The powder was calcined at approximately 800°C. This produced a composite oxide powder containing Ni and Fe (NiFe precursor powder). The produced composite oxide 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 (G-260, manufactured by Sekisui Chemical Co., Ltd.) as a plasticizer, a known dispersant, a mixed solvent of toluene and ethanol, and optionally a pore-forming agent (typically organic beads) were added to the mixed powder in predetermined ratios, and the mixture was mixed in a ball mill to prepare a slurry. Then, a green sheet of the functional layer of the fuel electrode layer having a predetermined thickness was formed from the slurry using a doctor blade method. This green sheet is sintered to form a functional layer of the fuel electrode layer in which the NiFe alloy is uniformly dispersed.

[0067] 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 ethanol, 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 support layer for the fuel electrode layer having a predetermined thickness was formed from the slurry using a doctor blade method. This green sheet was sintered to form the support layer for the fuel electrode layer.

[0068] In addition, butyral resin, polyvinyl acetal resin as a plasticizer, a known dispersant, and a mixed solvent of toluene and ethanol were added to the YSZ powder in predetermined proportions and mixed in a ball mill to prepare a slurry. A doctor blade method was then used to form a green sheet of a solid electrolyte layer having a predetermined thickness from the slurry. The green sheet was sintered to form the solid electrolyte layer.

[0069] Next, a green sheet for the functional layer of the fuel electrode layer and a green sheet for the support layer of the fuel electrode layer were stacked in this order on one side of the green sheet for the solid electrolyte layer. These stacked green sheets were then pressed together under high pressure using a press while being heated and evacuated. This resulted in the formation of a laminate including the green sheet for the solid electrolyte layer, the green sheet for the functional layer of the fuel electrode layer, and the green sheet for the support layer of the fuel electrode layer.

[0070] 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 (e.g., 1300 to 1400°C) for a predetermined time (e.g., 1 to 5 hours) (primary firing). This resulted in a primary sintered body having a solid electrolyte layer and a fuel electrode layer stacked on one side of the solid electrolyte layer.

[0071] 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 product 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 laminated on one surface of the solid electrolyte layer, and an cathode layer laminated on the other surface of the solid electrolyte layer.

[0072] Furthermore, by changing the volume fraction (compound ratio) of Fe when forming the green sheet for the functional layer of the fuel electrode layer, the average particle size of the NiFe alloy contained in the formed fuel electrode layer can be changed. By setting the volume fraction of Fe in the range of 5.0 to 20.0%, these can be within the range of this embodiment. Therefore, by changing the volume fraction of Fe within the range of 5.0 to 20.0%, example samples with different average particle sizes of the NiFe alloy contained in the fuel electrode layer were created. Furthermore, by changing the volume fraction of Fe outside the range of 5.0 to 20.0%, comparative example samples were created.

[0073] Furthermore, when forming the green sheet of the functional layer of the fuel electrode layer, the particle size of the YSZ to be mixed can be changed to change the size relationship between the average particle size of the NiFe alloy and the average particle size of the YSZ. ｏ C. The pore size ratio can be changed by changing the time between 1 and 5 hours. Therefore, by changing the particle size of the YSZ to be mixed and the primary firing conditions, several example samples were created that had different pore size ratios and different size relationships between the average particle size of the NiFe alloy contained in the anode and the average particle size of the YSZ.

[0074] 2. Measurement of the average particle size of the NiFe alloy Each sample was cut along the thickness direction of the fuel electrode layer (thickness direction of the cell), and the cut surface was photographed using an SEM. The obtained SEM image was tri-leveled into white, black, and gray, and the gray area was considered to be the NiFe alloy area, and the average particle size of the NiFe alloy was measured using the intercept method. The white area was considered to be the YSZ area, and the average particle size of the YSZ was measured using the intercept method. The black area was considered to be the pore, and the average diameter of the pore was measured using the intercept method.

[0075] 3. Measurement of Initial Performance and Durability Degradation Rate The current per unit area (current density) flowing when a constant voltage (1 to 1.3 V) was applied between the fuel electrode layer and the air electrode layer of each sample was measured. The measured current density was used as an evaluation index for initial performance. The higher the current density, the better the initial performance. Furthermore, 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. The applied voltage increased over time due to an increase in the internal resistance within the sample. The difference between the voltage applied initially and the voltage applied after a predetermined time (e.g., 400 hours) was calculated, and this calculated value was converted to the difference between the voltage that would be applied after 1,000 hours. The converted value was then divided by the initially applied voltage to calculate the durability degradation rate as a percentage. The smaller the durability degradation rate, the higher the durability.

[0076] 4. Measurement Results Table 1 shows the initial performance (current density) and its evaluation, the durability deterioration rate and its evaluation, and an overall evaluation, measured for the samples of each Example and Comparative Example.

[0077]

[0078] In Table 1, when the durability degradation rate was less than 8%, the durability was evaluated as very good (◎), when the durability degradation rate was 8% or more and less than 12%, the durability was evaluated as good (◎), when the durability degradation rate was 12% or more and less than 15%, the durability was evaluated as fairly good (◯), and when the durability degradation rate was 15% or more, the durability was evaluated as poor (×). ２ When the current density was 1.0 mA / cm or more, the initial performance was evaluated as good (◯). ２ If the evaluation result of durability was less than 1 / 3, the initial performance was evaluated as poor (×). If the evaluation result of durability was very good (◎◎) and the evaluation result of initial performance was good (◯), the overall judgment was judged to be very good (◎◎). If the evaluation result of durability was good (◎) and the evaluation result of initial performance was good (◯), the overall judgment was judged to be good (◎). If the evaluation result of durability was fairly good (◯) and the evaluation result of initial performance was good (◯), the overall judgment was judged to be fairly good (◯). Furthermore, if the evaluation result of durability was poor (×), the overall judgment was judged to be poor (×) regardless of the evaluation result of initial performance.

[0079] (Particle size of NiFe alloy) As can be seen from Table 1, the overall evaluations for all Examples 1 to 18 were fairly good (◯), good (◎), and very good (◎◎). On the other hand, Comparative Examples 1 to 3, i.e., samples in which the average particle size of the NiFe alloy was outside the range, all received an overall evaluation of poor (×). Specifically, for samples in which the average particle size of the NiFe alloy was smaller than the range of this embodiment (Comparative Example 1 and Comparative Example 2), the initial performance was maintained at good (◯), but the durability was poor (×). This is thought to be because when the average particle size of the NiFe alloy was smaller than the range of this embodiment, the alloying effect was absent (or small). On the other hand, for a sample in which the average particle size of the NiFe alloy was larger than the range of this embodiment (Comparative Example 3), both the initial performance and durability were poor (×). This is thought to be because the effect of Fe as a sintering aid was too high, making the functional layer too dense and making it difficult for gas to pass through. This shows that when the average particle size of the NiFe alloy is in the range of 0.779 to 1.00 μm, the durability is improved while maintaining the initial performance.

[0080] (Relationship between the average particle size of NiFe and the average particle size of YSZ particles) As can be seen from a comparison between Examples 1 to 3 and Examples 4 to 6, when the average particle size of the NiFe alloy is 0.779 μm and the pore size ratio is the same, the samples (Examples 1 to 3) in which the size relationship between the average particle size of NiFe and the average particle size of YSZ particles satisfies the range of this embodiment (Examples 4 to 6) do not satisfy this range, and the durability is improved without a significant decrease in initial performance. Furthermore, as can be seen from a comparison between Examples 7 to 9 and Examples 10 to 12, when the average particle size of the NiFe alloy is 0.808 μm and the pore size ratio is the same, the samples (Examples 7 to 9) in which the size relationship satisfies the range of this embodiment (Examples 10 to 12) show slightly improved initial performance and significantly improved durability. As can be seen from a comparison between Examples 13 to 15 and Examples 16 to 18, when the average particle size of the NiFe alloy is 1.000 μm and the pore size ratio is the same, the samples (Examples 13 to 15) in which the size relationship of the average particle size satisfies the range of this embodiment maintain the initial performance and have significantly improved durability compared to the samples (Examples 16 to 18) that do not satisfy this range. This shows that when the average particle size of the NiFe alloy is within the range of this embodiment and the size relationship between the average particle size of NiFe and the average particle size of YSZ is within the range of this embodiment, durability is improved while maintaining the initial performance.

[0081] (Pore diameter ratio) As can be seen from a comparison of Example 2 with Examples 1 and 3, when the average particle diameter of the FeNi alloy is 0.779 μm and the size relationship between the average particle diameter of the NiFe alloy and the average particle diameter of the YSZ is within the range of this embodiment, the sample (Example 2) in which the pore diameter ratio satisfies the range of this embodiment shows improved durability while maintaining initial performance compared to the samples (Examples 1 and 3) that do not satisfy the range. A similar tendency is also seen in samples (Examples 7 to 9) in which the average particle diameter of the NiFe alloy is 0.808 μm and the size relationship is within the range of this embodiment, and samples (Examples 13 to 15) in which the average particle diameter of the NiFe alloy is 1.00 μm and the size relationship is within the range of this embodiment.

[0082] As can be seen from the comparison of Example 5 with Examples 4 and 6, when the average particle size of the NiFe alloy is 0.779 μm and the size relationship between the average particle size of the NiFe alloy and the average particle size of the YSZ is outside the range of this embodiment, the sample (Example 5) in which the pore size ratio satisfies the range of this embodiment shows improved durability while maintaining initial performance compared to samples (Examples 4 and 6) in which the pore size ratio does not satisfy the range of this embodiment. A similar trend was observed for samples (Examples 10-12) in which the average particle size of the NiFe alloy is 0.808 μm and the size relationship is outside the range of this embodiment, and samples (Examples 16-18) in which the average particle size of the NiFe alloy is 1.00 μm and the size relationship is outside the range of this embodiment. From this, it can be seen that when the pore size ratio satisfies the range of this embodiment, durability is improved while maintaining initial performance.

[0083] As described above, it can be seen that when the average particle size of the NiFe alloy satisfies the range specified in this embodiment, durability can be improved while maintaining initial performance. Furthermore, it can be seen that when the average particle size of the NiFe alloy satisfies the range specified in this embodiment and the relationship between the average particle size of the NiFe alloy and the average particle size of the YSZ particles satisfies the range specified in this embodiment, durability can be further improved. Similarly, it can be seen that when the average particle size of the NiFe alloy satisfies the range specified in this embodiment and the relationship between the average particle size of the YSZ particles and the pore size satisfies the range specified in this embodiment, durability can be further improved. Furthermore, it can be seen that when the particle size of the NiFe alloy satisfies the range specified in this embodiment and the relationship between the average particle size of the NiFe alloy and the average particle size of the YSZ particles and the pore size ratio satisfies the range specified in this embodiment, durability is most improved.

[0084] As can be seen from Comparative Examples 1 to 3, even if the relationship between the average particle size of the NiFe alloy and the average particle size of the YSZ particles, or the pore size ratio, satisfies the range of this embodiment, if the average particle size of the NiFe alloy does not satisfy the range of this embodiment, durability is low.

[0085] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and various modifications are possible.

[0086] For example, in the above embodiment, the Ni alloy is a NiFe alloy, but the Ni alloy is not limited to a NiFe alloy.

[0087] The present invention may include the following configurations.

[0088] [1] An electrochemical cell comprising: a solid electrolyte layer; an air electrode laminated on a front surface side of the solid electrolyte layer; and an anode laminated on a back surface side of the solid electrolyte layer, wherein the anode has a functional layer containing a Ni alloy and a conductive solid oxide, and the Ni alloy contained in the functional layer has an average particle size of 0.77 μm or more and 1.00 μm or less.

[0089] [2] The electrochemical cell according to [1], wherein the Ni alloy is a NiFe alloy.

[0090] [3] The electrochemical cell according to [1] or [2], wherein the average particle size of the Ni alloy is smaller than the average particle size of the conductive solid oxide.

[0091] [4] The electrochemical cell according to any one of [1] to [3], wherein a pore size ratio, which is a ratio of an average particle size of the conductive solid oxide to an average size of pores contained in the functional layer, is 1.5 or more and 2.6 or less.

[0092] [5] A solid oxide electrolysis cell comprising the electrochemical cell according to any one of [1] to [4].

[0093] [6] A cell stack comprising a plurality of solid oxide electrolysis cells according to [5] stacked together.

[0094] [7] A hot module comprising: a cell stack according to [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.

[0095] [8] A gas production device comprising the hot module according to [7].

[0096] The present invention relates to an electrochemical cell, a solid oxide electrolysis cell, a cell stack, a hot module, and a gas production device.

Claims

1. An electrochemical cell comprising: a solid electrolyte layer; an air electrode laminated on a front side of the solid electrolyte layer; and an anode laminated on a back side of the solid electrolyte layer, wherein the anode has a functional layer containing a Ni alloy and a conductive solid oxide, and the Ni alloy contained in the functional layer has an average particle size of 0.77 μm or more and 1.00 μm or less.

2. The electrochemical cell according to claim 1, wherein the Ni alloy is a NiFe alloy.

3. The electrochemical cell according to claim 1, wherein the average particle size of the Ni alloy is smaller than the average particle size of the conductive solid oxide.

4. An electrochemical cell according to claim 1, wherein the pore size ratio, which is the ratio of the average particle size of the conductive solid oxide to the average size of the pores contained in the functional layer, is 1.5 or more and 2.6 or less.

5. A solid oxide electrolysis cell comprising the electrochemical cell according to any one of claims 1 to 4.

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

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 thermal insulator in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed.

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

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