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

Abstract

To suppress deterioration of durability while maintaining initial performance of an electrochemical cell.SOLUTION: The electrolytic cell 21 includes a solid electrolyte layer 211, a fuel electrode layer 213 laminated on one surface side of the solid electrolyte layer 211, and an air electrode layer 212 laminated on the other surface side of the solid electrolyte layer 211. The fuel electrode layer includes a Ni simple substance particle 100 which is a particle made of Ni simple substance, and a ceramic particle 101. Mg-containing particles 102, 103 which are particles containing Mg exist in grains or grain boundaries of the Ni simple substance particles, and the concentration of Mg at the interface on the anode layer side between the solid electrolytic layer and the anode layer is 0. 01wt% or more and 0. 31wt% or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Solid oxide electrochemical cells, which use solid oxide as an electrolyte, have been known for some time. Solid oxide electrochemical cells are characterized by their ability to perform 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] An electrochemical cell can be configured with a solid electrolyte layer, 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. Various studies have been conducted on the structure of each layer to improve the characteristics of electrochemical cells. For example, Patent Document 1 describes an electrochemical cell in which the fuel electrode layer (referred to as a "hydrogen electrode" in Patent Document 1) contains, on its surface, metal fine particles, magnesium (Mg) oxide sintered particles covered with a mixed conductive film, and ion-conductive oxide sintered particles. It is described that this configuration can provide a highly active fuel electrode layer with low overvoltage and high power density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-44966 Summary of the Invention

[0005] Typically, a fuel electrode layer contains nickel (Ni) as an electrode catalyst and ceramic particles. The ceramic particles are ionically conductive oxide particles, such as yttria-stabilized zirconia (YSZ). When an electrochemical cell including a fuel electrode layer containing Ni and ceramic particles is operated for a long period of time under harsh operating conditions (high temperature, high humidity, and high current), migration and aggregation of Ni occurs within the fuel electrode layer. Migration of Ni within the fuel electrode layer reduces the number of conduction paths within the fuel electrode layer, increasing internal resistance. On the other hand, aggregation of Ni within the fuel electrode layer increases the particle size of the Ni, reducing the number of three-phase interfaces (boundaries between fuel gas, Ni, and ceramic particles) that serve as reaction fields. This reduces the surface area of ​​the Ni, reducing its catalytic performance and ultimately increasing the reaction resistance in the electrochemical reaction (in other words, reducing reaction efficiency). This increase in internal resistance and reaction resistance leads to a problem of reduced durability of the electrochemical cell.

[0006] One possible solution to this problem is to increase the number of three-phase interfaces by reducing the Ni particle size. However, because Ni easily aggregates under the operating environment (particularly a reducing atmosphere) described above, the number of three-phase interfaces decreases in a relatively short period of time even if the Ni particle size is reduced. Therefore, this method can only delay the timing of the deterioration of durability, but it cannot suppress the deterioration of durability itself.

[0007] Alternatively, another possible solution to the above problem is to add additives such as Mn2O3 (manganese(III) oxide) or Co3O4 (tricobalt tetroxide) to the fuel electrode layer. While this can improve durability to some extent, adding these additives increases the internal resistance and reaction resistance of the fuel electrode layer, making it impossible to maintain initial performance. Note that initial performance refers to the performance of an electrochemical cell after an initial reduction treatment. The initial reduction treatment is a process in the electrochemical cell manufacturing process that reduces NiO (nickel oxide) contained in the green sheet of the fuel electrode layer to Ni.

[0008] The present invention has been made to address the above-mentioned problems, and an object of the present invention is to provide a technique that can suppress a decrease in durability while maintaining the initial performance of an electrochemical cell.

[0009] The electrochemical cell (21) according to the present invention comprises: a solid electrolyte layer (211); a fuel electrode layer (213) laminated on one side of the solid electrolyte layer; an air cathode layer (212) laminated on the other side of the solid electrolyte layer; Equipped with. The fuel electrode layer includes Ni particles (100) which are particles made of Ni alone and ceramic particles (101), Mg-containing particles (102, 103) that contain Mg are present within or at the grain boundaries of the Ni particles, The Mg concentration at the interface (S) between the solid electrolyte layer and the fuel electrode layer on the fuel electrode layer side is 0.01 wt % or more and 0.31 wt % or less.

[0010] In the electrochemical cell according to the present invention, the fuel electrode layer contains Ni particles and ceramic particles, and Mg-containing particles are present within or at the grain boundaries of the Ni particles. The Mg-containing particles have the property of suppressing the migration and aggregation of the Ni particles. However, if the Mg concentration at the interface between the solid electrolyte layer and the fuel electrode layer on the fuel electrode layer side is less than 0.01 wt%, the Mg-containing particles are less effective in suppressing the migration and aggregation of the Ni particles, causing the Ni particles to migrate and aggregate, resulting in a decrease in the durability of the electrochemical cell. Furthermore, if the Mg concentration at the interface exceeds 0.31 wt%, some of the excess Mg-containing particles (or the Mg particles in the Mg-containing particles) will migrate to the reaction field (the region where the electrochemical reaction is particularly active) during operation of the electrochemical cell. This reduces the number of three-phase interfaces and reduces durability. In contrast, in the electrochemical cell according to the present invention, the Mg concentration at the interface is in the range of 0.01 wt% or more and 0.31 wt% or less, thereby appropriately suppressing the migration and aggregation of Ni particles and suppressing a decrease in the number of three-phase interfaces due to the migration of Mg-containing particles (or Mg particles). The addition of Mg to the fuel electrode layer does not affect the conduction paths within the fuel electrode layer, and the number of three-phase interfaces and catalytic performance do not change, so internal resistance and reaction resistance do not increase. Therefore, the addition of Mg does not reduce the initial performance of the electrochemical cell. Therefore, the configuration of the present invention can maintain the initial performance of the electrochemical cell while suppressing a decrease in durability. The reaction field is the region located at and near the interface between the solid electrolyte layer and the fuel electrode layer on the fuel electrode layer side (in other words, the interface of the fuel electrode layer on the solid electrolyte layer side and its vicinity).

[0011] In one aspect of the invention, The Mg-containing particles include composite oxide particles (102) of Ni and Mg.

[0012] The Ni and Mg composite oxide particles have the property of particularly suppressing the aggregation of the Ni simple particles. Therefore, when the Mg-containing particles contain Ni and Mg composite oxide particles (i.e., the Ni and Mg composite oxide particles are present within or at the grain boundaries of the Ni simple particles), the aggregation of the Ni simple particles is further suppressed, and as a result, the initial performance of the electrochemical cell can be maintained better while the deterioration of durability can be more appropriately suppressed.

[0013] In one aspect of the invention, The ceramic particles (101) contain stabilized zirconia or partially stabilized zirconia.

[0014] When the ceramic particles in the fuel electrode layer contain stabilized zirconia or partially stabilized zirconia, their catalytic performance is excellent when their crystal structure is cubic, thereby maintaining the performance of the electrochemical cell favorably. However, the crystal structure of stabilized zirconia or partially stabilized zirconia tends to undergo a phase transition from cubic to tetragonal relatively easily. In this case, there is a problem that the phase transition increases the volume of the fuel electrode layer and damages the electrochemical cell. In contrast, in an electrochemical cell according to one aspect of the present invention, Mg-containing particles are present within or at the grain boundaries of simple Ni particles contained in the fuel electrode layer. This means that Mg is present around the stabilized zirconia or partially stabilized zirconia. Mg has the property of stably maintaining the crystal structure of stabilized zirconia or partially stabilized zirconia in a cubic form. Therefore, according to the configuration of one aspect of the present invention, the phase transition of the crystal structure of the ceramic particles from cubic to tetragonal is suppressed, thereby further appropriately suppressing deterioration in the performance of the electrochemical cell.

[0015] The solid oxide electrolysis cell (21) according to the present invention comprises: It consists of an electrochemical cell according to the present invention.

[0016] According to the above configuration, it is possible to provide a solid oxide electrolysis cell in which the initial performance is maintained while deterioration in durability is suppressed.

[0017] The cell stack (20) according to the present invention comprises: The solid oxide electrolysis cell (21) according to the present invention is stacked.

[0018] According to the above configuration, it is possible to provide a cell stack in which the initial performance of the solid oxide electrolysis cell is maintained while deterioration in durability is suppressed.

[0019] The hot module (10) according to the present invention comprises: A cell stack (20) according to the present invention; a vaporizer (30) for generating water vapor to be supplied to the cell stack; a heat exchanger (40) for exchanging heat with the gas supplied to the cell stack; a heater (50) for heating the cell stack; a heat insulating material (60) in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed; Equipped with.

[0020] According to the above configuration, it is possible to provide a hot module in which the initial performance of the solid oxide electrolysis cell is maintained while deterioration in durability is suppressed.

[0021] The hydrogen production device (1) according to the present invention comprises: The hot module (10) according to the present invention is provided.

[0022] According to the above configuration, it is possible to provide a hydrogen production device in which the initial performance of the solid oxide electrolysis cell is maintained while deterioration in durability is suppressed.

[0023] In the above description, in order to facilitate understanding of the invention, the symbols used in the embodiments are added in parentheses to the constituent elements of the invention corresponding to the embodiments, but each constituent element of the invention is not limited to the embodiments defined by the symbols. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a block diagram of a hydrogen production device. [Figure 2] FIG. 2 is a perspective view of a cell stack. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 2 is a cross-sectional view of the electrolysis cell in the thickness direction. [Figure 5] FIG. 2 is a partially enlarged view of a functional layer, and is a diagram schematically illustrating particles contained in the functional layer. [Figure 6] 1 is a graph showing the results of a qualitative analysis of the functional layer by XRD. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention 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.

[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 they can be kept at a high temperature. This hot module 10 includes a cell stack 20, a vaporizer 30, a heat exchanger 40, a heater 50, and insulating material 60.

[0027] Water (H2O) is supplied to the vaporizer 30 as shown in Fig. 1. The vaporizer 30 is configured to heat the supplied water to a temperature of 100°C or higher using a heat source. 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 described above, air is introduced into the heat exchanger 40. High-temperature hydrogen (H2) and high-temperature oxygen (O2) generated in the cell stack 20, which will be described later, are also introduced into the heat exchanger 40. These high-temperature gases exchange heat with the water vapor and air in the heat exchanger 40, thereby heating the water vapor and air introduced from the vaporizer 30 in the heat exchanger 40.

[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 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 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. Then, the oxygen discharged from the vaporizer 30 is recovered (or released to the atmosphere).

[0031] 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.

[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 (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 each a rectangular flat-plate-shaped member having the same outer shape as the electrolysis units Ue, and each have a rectangular opening formed in their 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.

[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 simply referred to as "electrolysis cell 21"), an interconnector 22, a separator 23, a cathode frame 24, a fuel electrode frame 25, and a current collector 26.

[0034] 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 lower surface of the solid electrolyte layer 211 so as to contact the lower surface of the solid electrolyte layer 211.

[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 center 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, 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.

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

[0039] The internal space of the electrolysis unit Ue is partitioned into an air chamber Sa and a fuel chamber Sf by the separator 23. 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.

[0040] The current collector 26 is a rectangular porous member made of metal (for example, nickel) that is smaller than the fuel electrode layer 213 in 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 fuel electrode 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 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 side E2 that faces side E1 (the corner located diagonally from the one corner of 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 electrolysis cell 21 will be described in more detail with reference to FIG. 4. The size and thickness of each layer of the electrolysis cell 21 shown below are merely examples and are not limited to these values. 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. The solid electrolyte layer 211 is a rectangular flat layer measuring 150 mm square and 6 μm thick. The solid electrolyte layer 211 is configured to contain ceramic particles and is formed by sintering. The ceramic particles are oxide particles with ion conductivity (hereinafter simply referred to as "ion-conductive oxide particles"). In this embodiment, YSZ is used. 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). The ceramic particles (ion-conductive oxide particles) in the solid electrolyte layer 211 are not limited to YSZ, but may be, for example, GDC (gadolinia-doped ceria).

[0045] 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 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 and has pores inside.

[0046] The anode layer 213 is a rectangular flat layer measuring 150 mm on each side, and is formed to have a thickness greater than that of the solid electrolyte layer 211 and the air cathode layer 212, for example, 420 μm. The 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 includes a functional layer 213 a and a support layer 213 b. The functional layer 213 a is laminated on the lower surface of the solid electrolyte layer 211 so as to contact the lower surface of the solid electrolyte layer 211. The support layer 213 b is located below the functional layer 213 a. In other words, the functional layer 213 a and the support layer 213 b are laminated in this order on the lower surface of the solid electrolyte layer 211. The support layer 213 b is formed to be significantly thicker than the functional layer 213 a. In this embodiment, the functional layer 213a has a thickness of 20 μm, and the support layer 213b has a thickness of 400 μm. However, the thicknesses of the functional layer 213a and the support layer 213b are not limited to these values, and the ratio of the thickness of the support layer 213b to the thickness of the functional layer 213a can be set to, for example, approximately 16 to 40 times.

[0047] The configuration of the fuel electrode layer 213 will be described in more detail with reference to FIG. 5. FIG. 5 is a partially enlarged view of the functional layer 213a, and is a diagram schematically illustrating particles contained in the functional layer 213a. As shown in FIG. 5, the functional layer 213a contains a cermet of simple Ni particles 100 and ceramic particles 101 as a main component, with small amounts of NiMg composite oxide particles 102 and MgO particles 103 as other components. The simple Ni particles 100 are particles made of simple Ni as a catalytic metal. The ceramic particles 101 are ion-conductive oxide particles, and YSZ is used in this embodiment. The NiMg composite oxide particles 102 are oxide particles containing a composite of two metals, Ni and Mg. The MgO particles 103 are Mg oxide particles. Both the NiMg composite oxide particles 102 and the MgO particles 103 contain Mg and are produced during the manufacturing process of the electrolysis cell 21 (described below).

[0048] The particle sizes of the Ni simple particle 100 and the ceramic particle 101 are both on the order of several μm, whereas the particle sizes of the NiMg composite oxide particle 102 and the MgO particle 103 are approximately one-tenth of those of the particles 100 and 101. The NiMg composite oxide particle 102 and the MgO particle 103 are both present within and at the grain boundaries of the Ni simple particle 100. That is, the NiMg composite oxide particle 102 and the MgO particle 103 are located inside the Ni simple particle 100 and attached to the outer surface of the Ni simple particle 100. Micropores p are formed in the gaps between the particles 100, 101, 102, and 103. That is, the functional layer 213a is a porous layer configured to have a porous shape including a plurality of micropores p.

[0049] Although not shown in the figure, the support layer 213b, like the functional layer 213a, contains a cermet of Ni simplex particles 100 and ceramic particles 101 (YSZ) as its main component, with small amounts of NiMg composite oxide particles 102 and MgO particles 103 as other components. The particle size of each of the particles 100 to 103 is approximately equal to the particle size of each of the particles 100 to 103 in the functional layer 213a. In the support layer 213b, the NiMg composite oxide particles 102 and the MgO particles 103 are both present within and at the grain boundaries of the Ni simplex particles 100. However, the proportions of the NiMg composite oxide particles 102 and the MgO particles 103 in the support layer 213b are significantly lower than those in the functional layer 213a. Furthermore, the support layer 213b is also a porous layer configured to have a porous shape including a plurality of micropores p (not shown).

[0050] The diameter of the micropores p in the functional layer 213a and the support layer 213b is on the order of several μm, thereby ensuring water vapor permeability (gas diffusibility). However, the functional layer 213a is formed more densely than the support layer 213b. That is, the porosity of the functional layer 213a is smaller than the porosity of the support layer 213b. Like the solid electrolyte layer 211 and the air cathode layer 212, the fuel electrode layer 213 is also formed by sintering. The YSZ in the fuel electrode layer 213 is an example of "stabilized zirconia." The NiMg composite oxide particles 102 and the MgO particles 103 are an example of "Mg-containing particles."

[0051] The type of particles contained in the fuel electrode layer 213 can be identified by XRD. Figure 6 is a graph showing the results of qualitative analysis of the functional layer 213a by XRD. The horizontal axis 2θ [deg.] of the graph represents the diffraction angle (the angle between the direction of incident X-rays and the direction of diffracted X-rays), and the vertical axis I 1 / 2 [Counts] represents the square root of the diffraction intensity I. As shown in Figure 6, when multiple peaks measured by XRD were qualitatively analyzed using library data, it was confirmed that the functional layer 213a contained YSZ, NiMg composite oxide, MgO, and Ni. Although not shown in the figure, the presence of the same types of particles was also confirmed when the support layer 213b was qualitatively analyzed by XRD.

[0052] The ceramic particles 101 in the fuel electrode layer 213 are not limited to YSZ, and other stabilized zirconia or partially stabilized zirconia may be used. In other words, any type of additive may be used to stabilize zirconia. Examples of other stabilized zirconia or partially stabilized zirconia include CSZ (calcia-stabilized zirconia) and ScSZ (scandia-stabilized zirconia). CSZ is zirconia to which CaO (calcium oxide) is added, and ScSZ is zirconia to which Sc2O3 (scandium oxide) is added. Furthermore, an ion-conductive oxide other than stabilized zirconia or partially stabilized zirconia (e.g., GDC) may be used for the ceramic particles 101. Furthermore, different ion-conductive oxides may be used for the ceramic particles 101 in the functional layer 213a and the ceramic particles 101 in the support layer 213b.

[0053] Additionally, in this embodiment, the NiMg composite oxide particles 102 and the MgO particles 103 are both present within and at the grain boundaries of the Ni simplex particles 100, but they may be configured to be present only at one of them. Furthermore, in the manufacturing process of the electrolysis cell 21, the fuel electrode layer 213 may be formed to include only either the NiMg composite oxide particles 102 or the MgO particles 103.

[0054] The Mg concentration in the fuel electrode layer 213 can be controlled by adjusting the Mg compounding ratio added to the slurry when forming the green sheet of the functional layer 213a. In this embodiment, the Mg compounding ratio is adjusted so that the Mg concentration at the interface between the solid electrolyte layer 211 and the functional layer 213a on the functional layer 213a side is 0.01 wt% or more and 0.31 wt% or less. Hereinafter, the interface between the solid electrolyte layer 211 and the functional layer 213a on the functional layer 213a side will be simply referred to as "interface S."

[0055] The Mg concentration at the interface S can be calculated by measuring the mass percent concentration of Mg at multiple locations on a cross section of the electrolytic cell 21 cut along the thickness direction at the interface S and averaging these measurements. The mass percent concentration of Mg at any given location can be measured from an element mapping image obtained by area analysis using an EPMA device (in this embodiment, a device manufactured by JEOL Ltd. is used).

[0056] 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 horizontal holes (not shown). The reason for supplying high-temperature air to the air chamber Sa is to control the temperature of the cell stack 20.

[0057] 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 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 is discharged through path Pao via a horizontal hole (not shown) together with the air that flowed into the air chamber Sa, 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 supply.

[0058] The cell stack 20 operates as described above, and hydrogen is produced in the hydrogen production device 1.

[0059] As described above, when an electrolysis cell with an anode layer containing Ni and ceramic particles is operated for a long time under a severe operating environment (high temperature, high humidity, high current), migration and aggregation of Ni occurs within the anode layer, resulting in a decrease in the durability of the electrolysis cell. Possible solutions to this problem include increasing the number of three-phase interfaces by reducing the Ni particle size or adding additives such as Mn2O3 or Co3O4 to the anode layer, but it is difficult with either method to maintain initial performance while suppressing a decrease in durability.

[0060] In the electrolysis cell 21 according to this embodiment, NiMg composite oxide particles 102 and MgO particles 103 are present as Mg-containing particles within or at the grain boundaries of the Ni simplex particles 100 in the fuel electrode layer 213. The NiMg composite oxide particles 102 and MgO particles 103 have the property of suppressing the migration and aggregation of the Ni simplex particles 100. In addition, the fuel electrode layer 213 (strictly speaking, the functional layer 213a) is configured so that the Mg concentration at the interface S is 0.01 wt% or more and 0.31 wt% or less. The Mg concentration at the interface S being 0.01 wt% or more appropriately suppresses the migration and aggregation of the Ni simplex particles 100. Furthermore, the Mg concentration at the interface S being 0.31 wt% or less suppresses the reduction in the number of three-phase interfaces caused by the migration of some of the NiMg composite oxide particles 102 and MgO particles 103 (or the Mg simplex particles in these particles) to the reaction field. The initial performance of the electrolysis cell 21 does not decrease due to the addition of Mg to the fuel electrode layer 213. Therefore, the electrolysis cell 21 according to this embodiment can suppress a decrease in durability while maintaining the initial performance.

[0061] Furthermore, the NiMg composite oxide particles have the property of particularly suppressing aggregation of the simple Ni particles 100. Therefore, the presence of the NiMg composite oxide particles 102 within and at the grain boundaries of the simple Ni particles 100 further suppresses aggregation of the simple Ni particles 100, and as a result, the initial performance of the electrolysis cell 21 can be maintained better while more appropriately suppressing a decrease in durability.

[0062] Furthermore, in the electrolysis cell 21, the ceramic particles 101 in the fuel electrode layer 213 are YSZ (i.e., stabilized zirconia). Therefore, Mg is present around the YSZ in the fuel electrode layer 213. Mg has the property of stably maintaining the crystal structure of YSZ in a cubic form. Therefore, this configuration suppresses the phase transition of the crystal structure of the ceramic particles 101 from a cubic to a tetragonal crystal, and as a result, the performance degradation of the electrolysis cell 21 can be further appropriately suppressed.

[0063] (Example) 1. Sample Preparation NiO powder, YSZ powder, and MgO 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 functional layer having a predetermined thickness was formed from the slurry using a doctor blade method.

[0064] 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 a support layer having a predetermined thickness was formed from the slurry using a doctor blade method.

[0065] 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 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.

[0066] Next, a green sheet for the functional layer and a green sheet for the support 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 produced a laminate including the green sheet for the solid electrolyte layer, the green sheet for the functional layer, and the green sheet for the support layer.

[0067] The laminate formed as described above was then degreased at a predetermined temperature (e.g., 200 to 300°C). The laminate was then fired (primary firing) at a predetermined first temperature (e.g., 1300 to 1500°C) for a predetermined time (e.g., 1 to 5 hours). 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. The Mg added to the functional layer slurry chemically reacted during the primary firing, resulting in the production of NiMg composite oxide particles and MgO particles in the functional layer and support layer.

[0068] Next, a material containing LSCF was screen-printed onto the other side 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 comprising a solid electrolyte layer, an anode layer laminated on one side of the solid electrolyte layer, and an cathode layer laminated on the other side of the solid electrolyte layer.

[0069] In this example, six electrolytic cell samples (Samples 1 to 6) with different Mg concentrations at the interface S were prepared by adjusting the Mg content added to the slurry during green sheet formation of the functional layer. In Samples 1 to 6, the Mg content in the slurry increases as the sample number (1 to 6) increases. Specifically, the Mg content in the slurry for each sample was 0 wt% (=0 vol%) for Sample 1, 0.7 wt% (=1 vol%) for Sample 2, 1.9 wt% (=3 vol%) for Sample 3, 3.2 wt% (=5 vol%) for Sample 4, 7.0 wt% (=10 vol%) for Sample 5, and 13.0 wt% (=20 vol%) for Sample 6.

[0070] 2. Measurement of Mg concentration Samples 1 to 6 were cut at a plane along the thickness direction of the electrolytic cell, and the Mg concentrations at the interfaces S of Samples 1 to 6 were measured using the method described above.

[0071] 3. Current Density Measurement For Samples 1 to 6, the samples were heated to 700°C, and a constant voltage (1.3 V in this example) was applied between the fuel electrode layer and the air electrode layer while a constant flow rate of steam was supplied to the fuel electrode layer side to perform a steam electrolysis reaction. The current per unit area (current density) flowing during the steam electrolysis reaction was measured, and the measured current density was used as an index for evaluating performance. That is, Samples 1 to 6 were operated as SOECs. It can be said that the higher the current density, the better the initial performance.

[0072] 4. Measurement of durability deterioration rate For Samples 1 to 6, a durability degradation test was conducted by heating the samples to 700°C, supplying a constant flow of water vapor to the anode layer side so that a constant current flows between the anode layer and the cathode layer, and applying a voltage between the anode layer and the cathode layer to continuously perform a steam electrolysis reaction. In other words, Samples 1 to 6 were operated as SOECs. When a constant current is continuously applied during the durability degradation test, the applied voltage increases 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 this calculated value was converted to 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. A smaller durability degradation rate indicates higher durability.

[0073] 5. Evaluation Table 1 shows the Mg concentration, current density, and durability deterioration rate at the interface S obtained for Samples 1 to 6. [Table 1]

[0074] Regarding the current density, the current density was 0.9 A / cm 2 If the current density is 0.7 A / cm or more, the initial performance is evaluated as very good (◎). 2 More than 0.9A / cm 2When the current density is less than 0.5 A / cm, the initial performance is evaluated as good (◯). 2 More than 0.7A / cm 2 If the current density is less than 0.5A / cm, the initial performance is evaluated as fair (△). 2 When the durability degradation rate was less than 3.0%, the durability was evaluated as good (◯), and when the durability degradation rate was 3.0% or more, the durability was evaluated as poor (×).

[0075] As can be seen from Table 1, for Samples 1 to 6, the Mg concentration at the interface S increases as the sample number (1 to 6) increases. For Samples 2 to 5, the initial performance is very good (◎) and the durability is good (◯). In contrast, for Samples 1 and 6, the initial performance is very good (◎) but the durability is poor (×).

[0076] The reason why Sample 1 had poor durability (×) is thought to be because the Mg concentration at the interface S in Sample 1 was 0.00 wt%, and no Mg-containing particles (NiMg composite oxide particles and / or MgO particles) were present in the fuel electrode layer. In other words, this is thought to be because Sample 1 did not achieve the effect of the Mg-containing particles suppressing the migration and aggregation of simple Ni particles. The reason why Sample 6 had poor durability (×) is thought to be because the Mg concentration at the interface S in Sample 6 was 0.75 wt%, and this is thought to be because excess Mg-containing particles were present in the fuel electrode layer (particularly the functional layer). In other words, this is thought to be because, in Sample 6, some of the excess Mg-containing particles (or simple Mg particles in the Mg-containing particles) migrated to the reaction field during operation of the electrolysis cell, thereby reducing the number of three-phase interfaces.

[0077] In addition, the initial performance of all samples 1 to 6 is very good (◎), which is thought to be because samples 1 to 6 do not contain additives such as Mn2O3 or Co3O4 in the functional layer slurry, and therefore the internal resistance and reaction resistance of the fuel electrode layer do not increase due to these additives.

[0078] Therefore, when the Mg concentration at the interface S is within the range of Samples 2 to 5, it is possible to appropriately suppress the migration and aggregation of Ni particles and to suppress a decrease in the number of three-phase interfaces caused by the migration of Mg-containing particles (or Mg particles). That is, when the Mg concentration at the interface S is 0.01 wt% or more and 0.31 wt% or less, it is possible to suppress a decrease in durability while maintaining the initial performance of the electrolytic cell.

[0079] In the above examples, the performance of the electrolytic cell was evaluated by operating it as an SOEC, but similar results were obtained when Samples 1 to 6 were fabricated as fuel cells (the cell configuration was the same) and operated as SOFCs. That is, Samples 2 to 5 showed very good initial performance (◎) and good durability (◯).

[0080] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the object of the present invention.

[0081] Furthermore, the present invention may include the following aspects. [1] a solid electrolyte layer; a fuel electrode layer disposed on one side of the solid electrolyte layer; an air electrode layer disposed on the other surface of the solid electrolyte layer; An electrochemical cell comprising: the fuel electrode layer includes simple Ni particles, which are particles made of simple Ni, and ceramic particles, Mg-containing particles, which are particles containing Mg, are present within or at the grain boundaries of the Ni simple particle, the Mg concentration at the interface between the solid electrolyte layer and the fuel electrode layer on the fuel electrode layer side is 0.01 wt% or more and 0.31 wt% or less; Electrochemical cell. [2] [1] The electrochemical cell according to [1], The Mg-containing particles include composite oxide particles of Ni and Mg. Electrochemical cell. [3] The electrochemical cell according to [1] or [2], The ceramic particles include stabilized zirconia or partially stabilized zirconia. Electrochemical cell. [4] A solid oxide electrolysis cell comprising the electrochemical cell according to any one of [1] to [3]. [5] A cell stack formed by stacking the solid oxide electrolysis cells according to [4]. [6] [5] The cell stack according to [5], a vaporizer that generates water vapor to be supplied to the cell stack; a heat exchanger that exchanges heat with the gas supplied to the cell stack; a heater for heating the cell stack; a heat insulating material in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed; Equipped with Hot module. [7] A hydrogen production device comprising the hot module according to [6]. [Explanation of symbols]

[0082] 1...hydrogen production device, 10...hot module, 20...cell stack, 21...solid oxide electrolysis cell (electrochemical cell), 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...insulation material, 90...condenser, 100...Ni single particle, 101...ceramic particle, 102...NiMg composite oxide particle, 103...MgO particle, 211...solid electrolyte layer, 212...air electrode layer, 213...fuel electrode layer, 213a...functional layer, 213b...support layer

Claims

1. a solid electrolyte layer; a fuel electrode layer disposed on one side of the solid electrolyte layer; an air electrode layer disposed on the other surface of the solid electrolyte layer; An electrochemical cell comprising: the fuel electrode layer includes simple Ni particles that are particles made of simple Ni and ceramic particles, Mg-containing particles, which are particles containing Mg, are present within or at the grain boundaries of the Ni simple particle, a Mg concentration at the interface between the solid electrolyte layer and the fuel electrode layer on the fuel electrode layer side is 0.01 wt % or more and 0.31 wt % or less; Electrochemical cell.

2. 10. The electrochemical cell of claim 1, The Mg-containing particles include composite oxide particles of Ni and Mg. Electrochemical cell.

3. 3. The electrochemical cell according to claim 1 or claim 2, The ceramic particles include stabilized zirconia or partially stabilized zirconia. Electrochemical cell.

4. A solid oxide electrolysis cell comprising the electrochemical cell of claim 1.

5. A cell stack formed by stacking the solid oxide electrolysis cells according to claim 4 .

6. The cell stack according to claim 5; a vaporizer that generates water vapor to be supplied to the cell stack; a heat exchanger that exchanges heat with the gas supplied to the cell stack; a heater for heating the cell stack; a heat insulating material in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed; Equipped with Hot module.

7. A hydrogen production device comprising the hot module according to claim 6.

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