Electrochemical cell, electrochemical cell stack, hot module, and electrolytic reaction device

Abstract

This electrochemical cell comprises: a solid electrolyte (311a) comprising stabilized zirconia; a fuel electrode (311c) that contains nickel and is in contact with the solid electrolyte (311a); and an air electrode (311b). A cermet of nickel and ceria and a cermet of nickel and a stabilized zirconia-ceria solid solution are present inside the fuel electrode (311c).

Description

Electrochemical cells, electrochemical cell stacks, hot modules, and electrolytic reactors

[0001] This disclosure relates to electrochemical cells, electrochemical cell stacks, hot modules, and electrolytic reactors.

[0002] Conventionally, solid oxide type electrochemical cells containing a solid electrolyte made of an ion-conducting oxide (e.g., YSZ (yttria-stabilized zirconia)) have been known (see, for example, Patent Document 1). Solid oxide type 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).

[0003] Japanese Patent Publication No. 2019-8914

[0004] The performance of an electrochemical cell is known to be deeply related to the electrode structure in contact with the solid electrolyte, for example, the structure near the contact interface between the solid electrolyte and the fuel electrode that contacts this solid electrolyte. In particular, the catalytic performance of the fuel electrode near the contact interface is one of the factors that greatly influence the performance of the electrochemical cell, and the performance changes greatly depending on the type, amount, and particle size of the particles that make up the fuel electrode. Generally, the material used as a fuel electrode consists of a mixture of metal particles and ion-conducting oxide particles, and the higher the ion conductivity of the ion-conducting oxide particles, the higher the performance of the electrochemical cell.

[0005] Typically, stabilized zirconia-containing oxide particles, such as YSZ (yttria-stabilized zirconia) particles, are used as ion-conducting oxide particles in the fuel electrode. However, ceria-containing oxide particles, such as GDC (gadolinium-doped ceria) particles, can sometimes be used instead. Since GDC has higher ion conductivity than YSZ, using GDC as the ion-conducting oxide in the fuel electrode can be expected to further improve the performance of the electrochemical cell.

[0006] However, when the solid electrolyte is an oxide containing stabilized zirconia (e.g., YSZ) and the ion-conducting oxide in the fuel electrode is an oxide containing ceria (e.g., GDC), the difference in thermal expansion coefficients between the two may cause delamination or microcracks at the contact interface between the solid electrolyte and the fuel electrode during manufacturing or use. If delamination or microcracks occur, the adhesion between the solid electrolyte and the fuel electrode decreases, thereby degrading the performance of the electrochemical cell. For this reason, it is not possible to sufficiently improve the performance of an electrochemical cell using an oxide containing ceria as the ion-conducting oxide in the fuel electrode.

[0007] This disclosure aims to solve the problems described above. Specifically, one of the objectives of this disclosure is to improve the adhesion of an electrochemical cell comprising a solid electrolyte containing stabilized zirconia and a fuel electrode containing ceria.

[0008] The electrochemical cell according to this disclosure is an electrochemical cell (311) comprising a solid electrolyte (311a) made of stabilized zirconia, a fuel electrode (311c) containing nickel and in contact with the solid electrolyte (311a), and an air electrode (311b), wherein a cermet of nickel and ceria and a cermet of nickel and stabilized zirconia ceria solid solution are present inside the fuel electrode (311c).

[0009] According to the electrochemical cell described herein, the solid electrolyte is made of stabilized zirconia, and inside the fuel electrode there are cermets of nickel and ceria, and cermets of nickel and stabilized zirconia-ceria solid solution. As a result, the thermal shrinkage rate of the fuel electrode can be brought closer to that of the solid electrolyte, and delamination and the generation of microcracks at the contact interface between the solid electrolyte and the fuel electrode caused by the difference in thermal shrinkage rates can be suppressed. As a result, the adhesion of an electrochemical cell comprising a solid electrolyte containing stabilized zirconia and a fuel electrode containing ceria can be improved.

[0010] In the above, "stabilized zirconia-ceria solid solution" means a solid solution of either or both of the following: stabilized zirconia in which cerium is solidly dissolved in the zirconium within the stabilized zirconia, or ceria in which zirconium is solidly dissolved in the cerium within the ceria.

[0011] Furthermore, in the above, "a cermet of nickel and ceria and a cermet of nickel and stabilized zirconia-ceria solid solution exist inside the fuel electrode" means that when the fuel electrode is divided into three equal parts (three sections) perpendicular to the contact interface with the solid electrolyte layer (thickness direction), the cermet of nickel and ceria and the cermet of nickel and stabilized zirconia-ceria solid solution exist in the intermediate region in the thickness direction of each of the three divided regions. For example, in the above intermediate region, if the ratio of the amount of nickel and ceria cermet A to the amount of nickel and stabilized zirconia-ceria solid solution cermet B is in the range of A:B = 20:80 to 80:20, then it can also be said that "a cermet of nickel and ceria and a cermet of nickel and stabilized zirconia-ceria solid solution exist inside the fuel electrode." Note that the ratio A:B may be set to any ratio. Therefore, in this specification, even if a nickel-ceria cermet and a nickel-stabilized zirconia-ceria solid solution cermet are present only in the vicinity of the surface of the fuel electrode, these cermets are not considered to be present inside the fuel electrode. Furthermore, "fuel electrode" refers to the region that is formed primarily for the purpose of forming the reaction field of the fuel electrode. Accordingly, if the fuel electrode has a fuel electrode functional layer and a fuel electrode substrate layer as described later, "fuel electrode" refers to the "fuel electrode functional layer," and "inside the fuel electrode" refers to "inside the fuel electrode functional layer."

[0012] According to one embodiment of the electrochemical cell of this disclosure, in a region within 5 μm from the contact interface between the fuel electrode (311c) and the solid electrolyte (311a) toward the fuel electrode (311c), the ratio (R) of the amount of nickel-stabilized zirconia-ceria solid solution cermet to the amount of nickel-ceria cermet is greater than 0.16. When the ratio (R) is greater than 0.16, there is a high probability that nickel-ceria cermet and nickel-stabilized zirconia-ceria solid solution cermet are present inside the fuel electrode layer. Therefore, in this case, the adhesion of the electrochemical cell can be improved.

[0013] In another embodiment of the electrochemical cell according to the present disclosure, the fuel electrode (311c) has an intermediate layer (L12) that is in contact with the solid electrolyte (311a) and includes a region in which the mass concentration of zirconium increases and the mass concentration of nickel decreases as it moves toward the solid electrolyte (311c) side along the thickness direction. Furthermore, when the position in the thickness direction of the intermediate layer (L12) where the mass concentration of zirconium and the mass concentration of nickel are the same is defined as the first position (P1), the thickness (T1) of the intermediate layer (L12), which is expressed as the sum of the distance from the first position (P1) to the second position (P2) along the thickness direction of the intermediate layer (L12) toward the solid electrolyte (311a) side where the mass concentration of nickel and the mass concentration of cerium are the same, and the distance from the first position (P1) toward the fuel electrode (311c) side along the thickness direction of the intermediate layer (L12) toward the third position (P3) where the mass concentration of zirconium and the mass concentration of cerium are the same, is greater than 0.50 μm and less than 1.62 μm. According to this, it is possible to maintain the initial performance of the electrochemical cell while improving the adhesion of the electrochemical cell.

[0014] In yet another embodiment of the electrochemical cell relating to this disclosure, the distance (T2) from the first position (P1) to the third position (P3) is less than 0.50 μm, which allows for further improvement of the initial performance of the electrochemical cell.

[0015] The electrochemical cell stack (1) relating to this disclosure is made up of stacked electrochemical cells (311) as described above. This makes it possible to provide an electrochemical cell stack equipped with electrochemical cells with improved adhesion.

[0016] The hot module (6) according to this disclosure comprises the electrochemical cell stack (1) described above, a heating device (3) for heating the gas supplied to the electrochemical cell stack (1), and an insulating material (4) in which the electrochemical cell stack (1) and the heating device (3) are arranged. This makes it possible to provide a hot module equipped with an electrochemical cell with improved adhesion.

[0017] The electrolytic reactor (100) according to this disclosure includes the hot module (6) described above. This makes it possible to provide an electrolytic reactor equipped with an electrochemical cell with improved adhesion.

[0018] Figure 1 is a block diagram of the hydrogen production apparatus according to this embodiment. Figure 2 is a perspective view of the electrochemical cell stack. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a cross-sectional view of the cell cassette shown in Figure 3. Figure 5 is a cross-sectional view taken along line VV in Figure 4. Figure 6 is a schematic diagram showing a part of the cross-section of an electrolytic cell cut in the thickness direction. Figure 7 is a cermet mapping image of the electrolytic cell according to this embodiment. Figure 8 is a cermet mapping image of a conventional electrolytic cell. Figure 9 is a diagram showing the distribution of mass concentrations of Ni, Ce, and Zr contained in the fuel electrode functional layer and its vicinity, across the thickness direction of the fuel electrode functional layer. This is an enlarged view of part A in Figure 9.

[0019] Embodiments of the present disclosure will be described below with reference to the drawings. Figure 1 is a block diagram of a hydrogen production apparatus 100 as an electrolytic reaction apparatus according to this embodiment. The hydrogen production apparatus 100 according to this embodiment is an apparatus that produces hydrogen by electrolyzing water vapor. As shown in Figure 1, the hydrogen production apparatus 100 comprises a hot module 6 and a condenser 7.

[0020] The hot module 6 is constructed by covering the main components of the hydrogen production apparatus 100 that become hot with an insulating material. In other words, the hot module 6 is a device that concentrates the main components of the hydrogen production apparatus 100 within an insulating material so that the high temperature state of the main components of the hydrogen production apparatus 100 is maintained. This hot module 6 comprises an electrochemical cell stack 1, a vaporizer 2, a heating device 3, and an insulating material 4.

[0021] As shown in Figure 1, the vaporizer 2 contains water (H ２ O) and hydrogen for reduction (H ２ ) is supplied. The vaporizer 2 is designed to heat the supplied water to a temperature of 100°C or higher. As a result, water vapor is generated when the water supplied to the vaporizer 2 evaporates within the vaporizer 2. The water vapor generated in the vaporizer 2 and the reducing hydrogen heated in the vaporizer 2 are introduced into the heating device 3.

[0022] The heating device 3 is a device for heating the gas introduced into the electrochemical cell stack 1. The heating device 3 comprises a heat exchanger 3a and a heater 3b. Water vapor, hydrogen for reduction, and air (Air) generated in the vaporizer 2 are introduced into the heat exchanger 3a. High-temperature gas from the electrochemical cell stack 1 is also introduced into the heat exchanger 3a. The high-temperature gas from the electrochemical cell stack 1 exchanges heat with the water vapor, hydrogen for reduction, and air in the heat exchanger 3a. As a result, the water vapor, hydrogen for reduction, and air are heated.

[0023] The gas heated in the heat exchanger 3a is further heated by the heater 3b to the operating temperature of the electrochemical cell stack 1 (i.e., the temperature required to operate the electrochemical cell stack 1). The heated gas is then introduced into the electrochemical cell stack 1.

[0024] The electrochemical cell stack 1 is formed by stacking solid oxide electrolytic cells (hereinafter referred to as electrolytic cells). The electrochemical cell stack 1 is heated to its operating temperature by a heating source (burner, etc.) not shown. A predetermined voltage is also applied to the electrochemical cell stack 1. As a result, the water vapor introduced into the electrochemical cell stack 1 is electrolyzed to produce hydrogen and oxygen. The produced hydrogen, along with unreacted water vapor and hydrogen for reduction, is discharged from the electrochemical cell stack 1 and then introduced as a high-temperature gas into the heat exchanger 3a. These high-temperature gases are then used to heat the gas and air introduced from the vaporizer 2 to the heat exchanger 3a before being introduced into the condenser 7. In the condenser 7, the unreacted water vapor is condensed. The condensed water produced in the condenser 7 is introduced into the vaporizer 2. Meanwhile, the hydrogen separated by the condensation of water vapor in the condenser 7 is recovered. Furthermore, the oxygen generated in the electrochemical cell stack 1 is discharged from the electrochemical cell stack 1 along with the air introduced into the electrochemical cell stack 1, and is then introduced into the heat exchanger 3a as a high-temperature gas. These high-temperature gases introduced into the heat exchanger 3a are used to heat the gas and air introduced into the heat exchanger 3a from the vaporizer 2, and are then introduced into the vaporizer 2, where they heat the water and hydrogen for reduction supplied to the vaporizer 2, before being discharged from the vaporizer 2. These gases discharged from the vaporizer 2 are recovered (or released into the atmosphere).

[0025] The electrochemical cell stack 1, vaporizer 2, and heating device 3 are arranged inside the thermal insulation material 4. This suppresses heat dissipation from each component 1, 2, and 3. The thermal insulation material 4 may be made of heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), biosoluble fiber (AES), and / or heat-resistant containers formed from these heat-resistant fibers. The heat-resistant fibers are arranged to fill the gaps between the electrochemical cell stack 1, vaporizer 2, and heating device 3 (heat exchanger 3a and heater 3b).

[0026] Figure 2 is a perspective view of the electrochemical cell stack 1. Here, when directions are used to describe the electrochemical cell stack 1 and its components, the three directions shown in Figure 2—the vertical direction, the width direction, and the depth direction—are used. The vertical direction, the width direction, and the depth direction are orthogonal to each other. The planes extending in the width direction and the depth direction are horizontal planes perpendicular to the vertical direction. Furthermore, one direction in the depth direction is defined as the front, and the other as the back.

[0027] As shown in Figure 2, the electrochemical cell stack 1 comprises a cell cassette group consisting of multiple rectangular flat cell cassettes 30 stacked in the thickness direction, an upper insulating plate 20 stacked on the upper surface of the cell cassette group, an upper end plate 10 stacked on the upper surface of the upper insulating plate 20, a terminal plate 40 stacked on the lower surface of the cell cassette group, a lower insulating plate 50 stacked on the lower surface of the terminal plate 40, and a lower end plate 60 stacked on the lower surface of the lower insulating plate 50, and is a laminate formed by stacking these plate-like members in the thickness direction. The thickness direction of each member coincides with the vertical direction in Figure 2. Therefore, each of the above-mentioned members is stacked in the vertical direction.

[0028] Each of the above-described components is formed in the shape of a rectangular plate with sides along the width and depth directions. Each of the above-described components is fastened to one another by bolts B and nuts (not shown) inserted through their four corners in the stacking direction. The upper end plate 10, upper insulating plate 20, terminal plate 40, lower insulating plate 50, and lower end plate 60 have the same external shape as the cell cassette 30 when viewed from above or below. The upper end plate 10, terminal plate 40, and lower end plate 60 are all made of metal (for example, stainless steel). The upper insulating plate 20 and lower insulating plate 50 are formed in the shape of plates from an insulating material, such as mica or resin. In addition, a rectangular opening is formed in the central part of the upper end plate 10 and upper insulating plate 20. For the sake of explanation, the proportions of each component in the drawings may differ from the actual proportions.

[0029] Multiple cell cassettes 30, terminal plates 40, lower insulating plates 50, and lower end plates 60 constituting the cell cassette group have two gas supply passages Pfi and Pai and two gas discharge passages Pfo and Pao that penetrate in the stacking direction. The gas supply passage Pfi is formed near one corner of side E1, which is one of the four sides constituting the outer periphery of the electrochemical cell stack 1. The gas discharge passage Pfo is formed near the other corner of side E2, which is opposite side E1 (the corner located diagonally opposite to one corner of side E1). The gas supply passage Pai is formed near one corner of side E2, and the gas discharge passage Pao is formed near the other corner of side E1. The gas supply passage Pfi forms a passage through which water vapor and hydrogen for reduction supplied to the electrochemical cell stack 1 pass, and the gas supply passage Pai forms a passage through which air supplied to the electrochemical cell stack 1 passes. The gas exhaust passage Pfo forms a passage through which hydrogen and water vapor discharged from the electrochemical cell stack 1 passes, and the gas exhaust passage Pao forms a passage through which oxygen and air discharged from the electrochemical cell stack 1 passes.

[0030] Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 3 is a cross-sectional view of the electrochemical cell stack 1 cut in the depth direction so that the cross-sections of the gas supply passage Pfi and the gas discharge passage Pfo are visible. As shown in Figure 3, the multiple cell cassettes 30 constituting the cell cassette group are stacked between the upper end plate 10 and the lower end plate 60. An upper insulating plate 20 is interposed between the cell cassette group and the upper end plate 10. A terminal plate 40 and a lower insulating plate 50 are interposed between the cell cassette group and the lower end plate 60.

[0031] Figure 4 shows a cross-sectional view of the cell cassette 30 shown in Figure 3. Note that the gas supply passage Pfi and gas discharge passage Pfo shown in Figure 3 are omitted in Figure 4. As shown in Figure 4, the cell cassette 30 comprises an electrochemical cell unit 31, a separator section 32, and a frame section 33. The electrochemical cell unit 31 is a reaction section in which an electrochemical reaction takes place, and includes a solid oxide type electrolytic cell (hereinafter referred to as an electrolytic cell) as an electrochemical cell. Specifically, the electrochemical cell unit 31 includes an electrolytic cell 311, a fuel electrode current collector 312, and an interconnector 313. In Figure 4, the fuel electrode current collector 312 is positioned below the electrolytic cell 311, and the interconnector 313 is positioned below the fuel electrode current collector 312.

[0032] In this embodiment, the electrolytic cell 311 is a substantially rectangular plate-like member having a predetermined thickness. Figure 6 is a schematic diagram showing a part of the cross-section of the electrolytic cell 311 cut in the thickness direction. As shown in Figures 4 and 6, the electrolytic cell 311 comprises a solid electrolyte layer 311a (solid electrolyte), an air electrode layer 311b (air electrode) laminated on the upper surface (one side) of the solid electrolyte layer 311a, and a fuel electrode layer 311c (fuel electrode) laminated on the lower surface (the other side) of the solid electrolyte layer 311a, and is formed by laminating these in the thickness direction. Furthermore, as shown in Figure 6, a reaction prevention layer 311d may be formed between the solid electrolyte layer 311a and the air electrode layer 311b.

[0033] The solid electrolyte layer 311a is a layer made of a solid oxide type electrolyte. The solid electrolyte layer 311a is a rectangular, flat layer. The solid electrolyte layer 311a is made of stabilized zirconia as an ion-conducting oxide and is formed by sintering. The solid electrolyte layer 311a has good oxide ion conductivity. The solid electrolyte layer 311a is a dense layer and is designed so that the atmosphere on the air electrode layer 311b side and the atmosphere on the fuel electrode layer 311c side do not leak to each other through the solid electrolyte layer 311a.

[0034] The air electrode layer 311b is a rectangular, flat layer, composed of a perovskite-type oxide such as LSCF (lanthanum strontium cobalt iron oxide), and is formed by sintering. The air electrode layer 311b has a functional layer and a current collector layer. The current collector layer is thicker than the functional layer and is located on the upper surface of the functional layer. The air electrode layer 311b has high electronic conductivity and collects electrons well in the current collector layer. The air electrode layer 311b is a porous layer and has many pores inside. As shown in Figure 4, the air electrode layer 311b has a smaller outer shape than the solid electrolyte layer 311a and the fuel electrode layer 311c, and is located in the center of the upper surface of the solid electrolyte layer 311a in a plan view of the electrolytic cell 311. For this reason, the upper surface of the outer periphery of the solid electrolyte layer 311a is exposed and not covered by the air electrode layer 311b.

[0035] The reaction prevention layer 311d is provided to prevent the reaction between the components in the solid electrolyte layer 311a and the components in the air electrode layer 311b. The reaction prevention layer 311d can be formed, for example, by GDC (gadolinium-doped ceria).

[0036] The fuel electrode layer 311c is a rectangular, flat layer. The fuel electrode layer 311c is molded to be thicker than the solid electrolyte layer 311a and the air electrode layer 311b. The fuel electrode layer 311c supports the solid electrolyte layer 311a and the air electrode layer 311b. In other words, the electrolytic cell 311 is a fuel electrode-supported electrochemical cell. In plan view, the external shape of the fuel electrode layer 311c matches the external shape of the solid electrolyte layer 311a.

[0037] As shown in Figure 6, the fuel electrode layer 311c has a fuel electrode functional layer L1 and a fuel electrode substrate layer L2. The fuel electrode functional layer L1 is a layer in which the electrolytic reaction of water vapor mainly takes place. The fuel electrode substrate layer L2 is a layer that mainly supplies water vapor to the fuel electrode functional layer L1 and supports the electrolytic cell 311. The electrolytic reaction of water vapor may also take place in the fuel electrode substrate layer L2. The thickness of the fuel electrode substrate layer L2 is formed to be significantly thicker than that of the fuel electrode functional layer L1, and the ratio can be set to, for example, about 16 to 40 times. The fuel electrode functional layer L1 and the fuel electrode substrate layer L2 are stacked on the lower surface of the solid electrolyte layer 311a in the order of fuel electrode functional layer L1, then fuel electrode substrate layer L2. In the case of a non-fuel electrode-supported electrochemical cell, the fuel electrode substrate layer can be omitted. In this case, the fuel electrode functional layer becomes the fuel electrode layer.

[0038] The main components of the fuel electrode substrate layer L2 are Ni and stabilized zirconia (ZrO ２ The fuel electrode substrate layer L2 is a cermet made of the same material as the fuel electrode substrate layer L2. The fuel electrode substrate layer L2 is a porous layer containing multiple micropores (not shown). The diameter of the micropores is on the order of several micrometers. The formation of multiple micropores ensures the permeability (gas diffusion) of water vapor within the fuel electrode layer 311c.

[0039] The main components of the fuel electrode functional layer L1 are Ni and CeO ２ It is a cermet with (ceria). The fuel electrode functional layer L1 is a porous layer containing multiple micropores (not shown), similar to the fuel electrode substrate layer L2. However, the fuel electrode functional layer L1 is formed more densely than the fuel electrode substrate layer L2. That is, the porosity of the fuel electrode functional layer L1 is smaller than that of the fuel electrode substrate layer L2. The fuel electrode layer 311c is also formed by sintering, similar to the solid electrolyte layer 311a and the air electrode layer 311b. As will be described later, the interior of the fuel electrode functional layer L1 contains Ni and CeO ２ In addition to cermets, Ni and ZrO ２ (Zirconia) - CeO ２ A cermet exists with a (ceria) solid solution. Therefore, the fuel electrode functional layer L1 contains Ni, Ce, and Zr.

[0040] Figure 5 is a cross-sectional view taken along the line V-V in Figure 4. As shown in Figure 5, the fuel electrode current collector 312 is disposed between the electrolytic cell 311 and the interconnector 313. In this embodiment, the fuel electrode current collector 312 is composed of a plurality of elastic insulators 312a and a plurality of conductors 312b. Each of the plurality of elastic insulators 312a is formed in an elongated shape extending in the depth direction and is arranged in parallel with a predetermined interval in the width direction. The elastic insulators 312a may be, for example, mica. The plurality of conductors 312b are provided so as to cover the outer circumference of each elastic insulator 312a. The plurality of conductors 312b may be, for example, metal foil. Each conductor 312b contacts the interconnector 313 with the portion covering the lower surface of the elastic insulator 312a and contacts the fuel electrode layer 311c of the electrolytic cell 311 with the portion covering the upper surface of the elastic insulator 312a.

[0041] The interconnector 313 is a metal (for example, stainless steel) component and, as shown in Figure 4, has a rectangular flat body portion 313a and a projection portion 313b that protrudes downward from the lower surface of the body portion 313a. The projection portion 313b is formed by a plurality of protrusions that are arranged parallel to each other along the direction perpendicular to the plane of the paper (width direction) in Figures 3 and 4. As shown in Figure 3, the interconnector 313 is positioned such that the body portion 313a contacts the conductor 312b of the fuel electrode current collector 312 disposed above it, and the projection portion 313b connects to the air electrode layer 311b of the adjacent electrolytic cell 311 disposed below it.

[0042] The frame portion 33 includes a fuel electrode frame 331 and an air electrode frame 332. The fuel electrode frame 331 is a rectangular plate-shaped metal (for example, stainless steel) member with a rectangular opening formed in its center. The air electrode frame 332 is positioned below the fuel electrode frame 331. The air electrode frame 332 is a rectangular plate-shaped insulating member, which may be formed from, for example, a mica sheet. The air electrode frame 332 also has a rectangular opening in its center, similar to that of the fuel electrode frame 331.

[0043] Furthermore, as can be seen from Figures 4 and 5, the electrochemical cell unit 31 is disposed inside an opening formed in the center of the frame portion 33. In other words, the frame portion 33 is disposed around the electrochemical cell unit 31 so as to surround its outer periphery. A predetermined gap is formed between the frame portion 33 and the electrochemical cell unit 31, and the separator portion 32 is disposed to close this gap. The separator portion 32 includes a cell-side separator 321 and an interconnector-side separator 322. The cell-side separator 321 is a rectangular plate-shaped metal (for example, stainless steel) member, with a rectangular opening formed in its center. The periphery (i.e., inner periphery) of the opening of the cell-side separator 321 is brazed to the upper surface of the outer periphery of the solid electrolyte layer 311a of the electrolytic cell 311 with a brazing material (for example, Ag brazing material) not shown. On the other hand, the outer periphery of the cell-side separator 321 is positioned on the upper surface of the fuel electrode frame 331 and is joined to the fuel electrode frame 331 by, for example, welding.

[0044] The interconnector-side separator 322, like the cell-side separator 321, is a rectangular plate-shaped metal (for example, stainless steel) member with a rectangular opening formed in its center. The periphery (i.e., inner periphery) of the opening of the interconnector-side separator 322 is joined to the upper surface of the main body portion 313a of the interconnector 313, for example, by welding. The outer periphery of the interconnector-side separator 322 is sandwiched between the lower surface of the fuel electrode frame 331 and the upper surface of the air electrode frame 332, and is joined to the fuel electrode frame 331 above it, for example, by welding. In this way, the separator portion 32 (cell-side separator 321 and interconnector-side separator 322) is configured to connect the electrochemical cell unit 31 and the frame portion 33.

[0045] When the cell cassettes 30 configured as described above are stacked on the terminal plate 40, an electrochemical cell stack 1 is formed in which multiple electrochemical cell units 31, including an electrolytic cell 311, are stacked vertically. In addition, the separator section 32 (cell-side separator 321 and interconnector-side separator 322) partitions the space between adjacent separators. As a result, multiple fuel chambers Sf and air chambers Sa are formed inside the electrochemical cell stack 1, with gas flow being blocked from each other. Specifically, the fuel chamber Sf is formed by the fuel electrode frame 331, the cell-side separator 321 joined to the fuel electrode frame 331, the electrolytic cell 311 connected to the cell-side separator 321, the interconnector-side separator 322 joined to the fuel electrode frame 331, and the interconnector 313 connected to the interconnector-side separator 322. The fuel chamber Sf is formed between the electrolytic cell 311 and the interconnector 313. Furthermore, the fuel electrode layer 311c of the electrolytic cell 311 is exposed in the fuel chamber Sf. In addition, an air chamber Sa is formed by the air electrode frame 332, the interconnector-side separator 322 in contact with the air electrode frame 332, the interconnector 313 connected to the interconnector-side separator 322, the cell-side separator 321 of the cell cassette 30 adjacent to the air electrode frame 332, and the electrolytic cell 311 connected to the cell-side separator 321. The air electrode layer 311b of the electrolytic cell 311 is exposed in the air chamber Sa. Water vapor as fuel gas and hydrogen for reduction are supplied to the fuel chamber Sf. Air is supplied to the air chamber Sa.

[0046] As shown in Figure 3, the gas supply passage Pfi and the gas discharge passage Pfo are formed to penetrate the lower end plate 60, the lower insulating plate 50, the terminal plate 40, and the frame portion 33 of each cell cassette 30 constituting the cell cassette group in the stacking direction. The gas supply passage Pfi communicates with the fuel chamber Sf through a lateral hole 331a formed in the fuel electrode frame 331 of each cell cassette 30. The gas discharge passage Pfo communicates with the fuel chamber Sf through a lateral hole 331b formed in the fuel electrode frame 331 of each cell cassette 30.

[0047] The gas supply passage Pai and the gas discharge passage Pao are also formed to penetrate the lower end plate 60, the lower insulating plate 50, the terminal plate 40, and the frame portion 33 of each cell cassette 30 constituting the cell cassette group in the stacking direction. The gas supply passage Pai and the gas discharge passage Pao are in communication with the air chamber Sa, respectively, through lateral holes (not shown) formed in the air electrode frame 332 of each cell cassette 30.

[0048] The cell cassette 30 (30A), located at the top of the cell cassette group, is a dummy cell cassette in which a metal plate PL is provided in place of the electrolytic cell 311. The fuel electrode frame 331 of this dummy cell cassette 30A functions as a terminal plate.

[0049] The operation of the electrochemical cell stack 1 will now be explained. First, a voltage is applied to the electrochemical cell stack 1. At this time, for example, the negative electrode of the power supply is connected to the terminal plate 40, and the positive electrode is connected to the fuel electrode frame 331 of the dummy cell cassette 30A. This causes current to flow through the electrochemical cell stack 1. Next, high-temperature steam and hydrogen for reduction are supplied to the gas supply passage Pfi. The steam and hydrogen for reduction supplied to the gas supply passage Pfi flow into the fuel chamber Sf of each cell cassette 30 through the side hole 331a. High-temperature air is supplied to the gas supply passage Pai. The air supplied to the gas supply passage Pai flows into the air chamber Sa of each cell cassette 30 through a side hole (not shown). The reason for supplying high-temperature air to the air chamber Sa is to control the temperature of the electrochemical cell stack 1.

[0050] The water vapor flowing into the fuel chamber Sf and the hydrogen for reduction flow through the fuel chamber Sf from the front side to the rear side in the depth direction as shown in Figure 3. The water vapor in the fuel chamber Sf contacts the fuel electrode layer 311c exposed in the fuel chamber Sf, and reaches the fuel electrode functional layer L1 via the fuel electrode substrate layer L2. Then, the water vapor reacts with electrons supplied via the interconnector 313, the fuel electrode current collector 312 and the like in the fuel electrode functional layer L1. Thereby, water vapor is decomposed into hydrogen and oxide ions (steam electrolysis reaction). The hydrogen generated by the steam electrolysis reaction flows further toward the rear side in the depth direction in the fuel chamber Sf together with unreacted water vapor and hydrogen for reduction, flows into the gas discharge passage Pfo through the lateral hole 331b, and is further discharged to the outside of the electrochemical cell stack 1 from the gas discharge passage Pfo. On the other hand, the oxide ions move to the air electrode layer 311b exposed in the air chamber Sa via the solid electrolyte layer 311a, and release electrons in the functional layer of the air electrode layer 311b to form oxygen. Oxygen diffuses in the air chamber Sa, flows into the gas discharge passage Pao through a lateral hole (not shown) together with the air flowing into the air chamber Sa, and is further discharged to the outside of the electrochemical cell stack 1 from the gas discharge passage Pao.

[0051] The electrons released in the functional layer of the air electrode layer 311b are collected by the interconnector 313 via the current collecting layer, and further return to the positive electrode of the power supply device through the dummy cell cassette 30A.

[0052] Next, the solid electrolyte layer 311a and the fuel electrode functional layer L1 of the electrolysis cell 311 according to the present embodiment will be described in detail. In the present embodiment, the solid electrolyte layer 311a of the electrolysis cell 311 is made of stabilized zirconia.

[0053] Stabilized zirconia is zirconia (ZrO ２ ) added with a small amount of oxide (stabilizing material). In the present specification, stabilized zirconia includes partially stabilized zirconia. Stabilized zirconia is a material that is less prone to cracking due to phase transition accompanying temperature change. As the stabilizing material to be added, yttrium oxide (Y ２ O ３ ), scandium oxide (Sc ２ O ３ ), ytterbium oxide (Yb ２O ３ Examples include ), etc. When the stabilizing material is yttrium oxide, the stabilized zirconia is YSZ (yttria stabilized zirconia); when the stabilizing material is scandium oxide, the stabilized zirconia is SSZ (scandia stabilized zirconia); and when the stabilizing material is ytterbium oxide, the stabilized zirconia is YbSZ (ytterbium stabilized zirconia). In this embodiment, the solid electrolyte layer 311a is made of YSZ.

[0054] As shown in Figure 6, the fuel electrode functional layer L1 is in contact with the solid electrolyte layer 311a. The fuel electrode functional layer L1 contains a cermet of nickel and ceria. The ceria is doped with a rare earth element. Examples of dopants include samarium (Sm) and gadolinium (Gd). When the dopant is Gd, the ceria is GDC (gadolinium-doped ceria). Since GDC has very good ionic conductivity, using GDC as the ionic conductive oxide particles in the fuel electrode functional layer L1 is expected to improve the performance of the electrolytic cell 311.

[0055] However, the GDC in the fuel electrode functional layer L1 is a different oxide from the YSZ in the solid electrolyte layer 311a. Therefore, due to the difference in thermal shrinkage rates between the two, thermal stress acts between the solid electrolyte layer 311a and the fuel electrode layer 311c during the manufacturing (sintering) or use of the electrolytic cell 311. As a result, there is a risk that the two layers may delaminate or microcracks may occur at the contact interface between the solid electrolyte layer 311a and the fuel electrode functional layer L1. If such interfacial delamination or microcracks occur, the adhesion between the solid electrolyte layer 311a and the fuel electrode layer 311c decreases, reducing the ion conduction paths between the two layers and degrading the performance of the electrolytic cell 311. Therefore, there is a need to improve the adhesion between the solid electrolyte layer 311a and the fuel electrode layer 311c.

[0056] In this regard, in this embodiment, in addition to the nickel-ceria cermet, a nickel-stabilized zirconia-ceria solid solution cermet is present inside the fuel electrode functional layer L1. Hereinafter, the nickel-ceria cermet will be referred to as Ni / CeO ２The term "cermet" is used, and the cermet made of nickel and stabilized zirconia-ceria solid solution is referred to as Ni / (ZrO ２ - CEO ２ ) It is written as cermet.

[0057] A stabilized zirconia-ceria solid solution is a solid solution of either stabilized zirconia in which cerium is dissolved in zirconium, or ceria in which zirconium is dissolved in cerium. Therefore, Ni / (ZrO ２ - CEO ２ A cermet is a cermet consisting of either or both of the following: a cermet of stabilized zirconia in which cerium is dissolved in zirconium and nickel, and a cermet of ceria in which zirconium is dissolved in cerium and nickel.

[0058] Figure 7 shows a cermet mapping image created based on an elemental mapping image obtained by surface analysis of the fuel electrode functional layer L1, which is part of a cross-section of the electrolytic cell 311 according to this embodiment, cut along the thickness direction, using an EPMA (Electron Probe Micro Analyzer) device. This cermet mapping image shows the Ni / CeO present in the fuel electrode functional layer. ２ Cermet and Ni / (ZrO ２ - CEO ２ ) Shows the distribution of cermet.

[0059] Figure 7 shows a portion of the cross-section of the solid electrolyte layer 311a and the fuel electrode functional layer L1. The solid electrolyte layer 311a and the fuel electrode functional layer L1 are in contact with each other at the contact interface S. The region above the contact interface S is the solid electrolyte layer 311a, and the region below is the fuel electrode functional layer L1. The cermet mapping image shown in Figure 7 maps the cermet within the fuel electrode functional layer L1.

[0060] The measurement points shown in dark gray in Figure 7 are those where the mass concentration of Zr (zirconium) is less than 3 wt%, the mass concentration of Ce (cerium) is 10 wt% or more, and the mass concentration of Ni (nickel) is 40 wt% or less. The measurement points shown in light gray in Figure 7 are those where the mass concentration of Zr is 3 wt% or more, the mass concentration of Ce is 10 wt% or more, and the mass concentration of Ni is 40 wt% or less. In other words, the positions shown in dark gray in Figure 7 are those where Zr is low and Ce is high, while the positions shown in light gray are those where both Zr and Ce are high.

[0061] Ni / CeO ２ The presence of cermet is presumed. Therefore, the measurement points shown in dark gray are Ni / CeO ２ It is presumed that cermet is present at these points. Also, Ni / (ZrO) is found at locations where Zr and Ce are abundant. ２ - CEO ２ ) It is presumed that cermet is present. Therefore, the measurement points shown in light gray are Ni / (ZrO ２ - CEO ２ ) These are presumed to be points where cermet exists. Thus, as shown in Figure 7, the Ni / CeO within the fuel electrode functional layer L1 is shown by the light gray and dark gray areas. ２ Location of cermet and Ni / (ZrO ２ - CEO ２ The location of the cermet is shown. It can be determined from the EPMA elemental mapping image that the areas shown in light gray and dark gray are areas that contain cermet, respectively. For example, from the elemental mapping images of Ce and Ni, a region has been identified where a region with a high concentration of Ce and a low concentration of Ni (high-Ce concentration region) is adjacent to a region with a high concentration of Ni and a low concentration of Ce (high-Ni concentration region). In this region, Ni / CeO ２ Cermet or Ni / (ZrO ２ - CEO ２ ) It can be determined that cermet is present.

[0062] As can be seen from Figure 7, the dark gray and light gray portions within the fuel electrode functional layer L1 extend to a position away from the contact interface S between the solid electrolyte layer 311a and the fuel electrode functional layer L1 in the thickness direction (downward in Figure 7). Therefore, within the fuel electrode functional layer L1 of the electrolytic cell 311 according to this embodiment, Ni / CeO extends to a position away from the contact interface S in the thickness direction. ２ Cermet and Ni / (ZrO ２ - CEO ２ ) This indicates that cermet and cermet coexist simultaneously.

[0063] Figure 8 shows a solid electrolyte layer SE made of stabilized zirconia and Ni / CeO ２ This is a cermet mapping image of a conventional electrolytic cell equipped with a fuel electrode functional layer FE containing cermet. Similar to Figure 7, the measurement points shown in dark gray in Figure 8 are Ni-CeO ２ The points where cermet is present are indicated, and the measurement points shown in light gray are Ni / (ZrO ２ - CEO ２ ) Indicates the presence of cermet.

[0064] As can be seen from Figure 8, the dark gray portion within the fuel electrode functional layer FE extends to a position away from the contact interface S between the solid electrolyte layer SE and the fuel electrode functional layer FE in the thickness direction (downward in Figure 8). On the other hand, the light gray portion within the fuel electrode functional layer FE is found to exist only in the vicinity region in the thickness direction from the contact interface S. Therefore, in conventional electrolytic cells, the fuel electrode functional layer FE contains Ni / CeO only in the vicinity region of the contact interface S. ２ Cermet and Ni / (ZrO ２ - CEO ２ ) A cermet is present, and beyond that point, at a position away from the contact interface S, Ni / CeO ２ Cermet exists on its own (i.e., Ni / ZrO ２ - CEO ２ It can be seen that cermet is not present.

[0065] In this specification, the fuel electrode functional layer is divided into three equal parts in the thickness direction, and the cermet detected in the middle region of the three divided regions, that is, the region second furthest from the contact interface between the solid electrolyte layer and the fuel electrode functional layer (the region adjacent to the region in contact with the contact interface), is defined as the cermet present inside the fuel electrode functional layer.

[0066] In Figure 7, since the thickness of the fuel electrode functional layer is 10 μm, when the fuel electrode functional layer is divided into three equal parts in the thickness direction, the position of the dividing line B in the thickness direction, which indicates the boundary between the region in contact with the contact interface S and the intermediate region adjacent to that region, is 3.3 μm away from the contact interface S towards the fuel electrode functional layer L1. In Figure 7, the region below the dividing line B is the intermediate region. This intermediate region has a dark gray area and a light gray area. Therefore, inside the fuel electrode functional layer L1 of the electrolytic cell 311 according to this embodiment, Ni / CeO ２ Cermet and Ni / (ZrO ２ - CEO ２ ) It can be said that cermet exists.

[0067] Furthermore, in Figure 8, the thickness of the fuel electrode functional layer is 10 μm, so the position of the dividing line B in the thickness direction is 3.3 μm away from the contact interface S towards the fuel electrode functional layer FE. In Figure 8, the region below this dividing line B is the intermediate region. In this intermediate region, only the dark gray area exists, and the light gray area does not. Therefore, inside the fuel electrode functional layer FE of a conventional electrolytic cell, Ni / CeO ２ Cermet and Ni / (ZrO ２ - CEO ２ ) It cannot be said that cermet exists.

[0068] From the above, the inside of the fuel electrode functional layer L1 of the electrolytic cell 311 according to this embodiment contains Ni / CeO ２ Cermet and Ni / (ZrO ２ - CEO ２ ) A cermet is present. On the other hand, inside the fuel electrode functional layer of a conventional electrolytic cell, Ni / CeO ２ Although cermets exist, Ni / (ZrO ２- CEO ２ Cermet does not exist.

[0069] In this embodiment, the fuel electrode functional layer L1 of the electrolytic cell 311 contains Ni / CeO not only in the region near the contact interface with the solid electrolyte layer 311a, but also inside the fuel electrode functional layer L1, away from the contact interface. ２ Cermet and Ni / (ZrO ２ - CEO ２ ) cermet and exist. In other words, Ni / (ZrO ２ - CEO ２ ) The amount of cermet present in the thickness direction is greater than in conventional electrolytic cells. For this reason, the material composition of the fuel electrode functional layer containing GDC is stabilized with zirconia (ZrO ２ By bringing the solid electrolyte layer, which is made of stabilized zirconia, closer to the solid electrolyte layer, the difference between the thermal shrinkage rate of the fuel electrode functional layer and the thermal shrinkage rate of the solid electrolyte layer made of stabilized zirconia can be reduced. Therefore, the possibility of interfacial delamination between the solid electrolyte layer and the fuel electrode layer due to the difference in thermal shrinkage rates, and the possibility of microcracks occurring can be reduced. As a result, the adhesion of the electrochemical cell can be improved.

[0070] Ni / CeO in the fuel electrode functional layer ２ Ni / (ZrO) as a function of the abundance (volume) of cermet ２ - CEO ２ From the viewpoint of improving adhesion, a larger ratio of cermet volume is preferable. Here, in Figures 7 and 8, Ni / CeO is found in a region up to 5 μm on the fuel electrode functional layer side along the thickness direction from the contact interface S between the solid electrolyte layer and the fuel electrode functional layer (hereinafter referred to as the measurement region). ２ Let N1 be the number of points (pixels) where the presence of cermet is detected by the EPMA device, and in the measurement area, Ni / (ZrO ２ - CEO ２ Let N2 be the number of points (pixels) where the presence of cermet is detected. N1 is Ni / CeO ２ It is thought to be proportional to the abundance (volume) of cermet. The score N2 is Ni / (ZrO ２ - CEO ２It is thought to be proportional to the amount (volume) of cermet present. If the ratio of score N2 to score N1 is the ratio R (= N2 / N1), then the ratio R is Ni / CeO ２ Ni / (ZrO) for cermet ２ - CEO ２ This can be considered as the ratio of cermet to be present. The larger the ratio R, the greater the amount of Ni / (ZrO) inside the fuel electrode functional layer. ２ - CEO ２ ) It is thought that there is a larger amount of cermet present. In Figure 7, the ratio R = 1.12, and in Figure 8, the ratio R = 0.16. If the ratio R is larger than that of the conventional electrolytic cell shown in Figure 8, then there is a larger amount of Ni / (ZrO) inside the fuel electrode functional layer than in the conventional cell. ２ - CEO ２ ) It can be determined that cermet is present, and it is thought that the adhesion of the electrolytic cell will be improved compared to conventional methods. Therefore, it is preferable that the ratio R (= N2 / N1) is greater than 0.16. Preferably, the ratio R is 0.64 or higher. Even more preferably, the ratio R is 1.12 or higher.

[0071] Incidentally, the fuel electrode functional layer L1 can be considered as being divided into a main layer L11 and an intermediate layer L12, as shown in Figure 6, depending on the composition ratio of Ni, Ce, and Zr. The intermediate layer L12 is a layer that includes a region in contact with the solid electrolyte layer 311a. The main layer L11 is a layer that contacts the intermediate layer L12 on the side opposite to the contact interface between the intermediate layer L12 and the solid electrolyte layer 311a. The main layer L11 is in contact with the fuel electrode substrate layer L2 on the side opposite to the contact interface with the intermediate layer L12. The main layer L11 and the intermediate layer L12 are stacked on the solid electrolyte layer 311a in the thickness direction in the order of intermediate layer L12, then main layer L11. The main layer L11 and the intermediate layer L12 can be distinguished by the relative mass concentrations of Ni, Zr, and Ce contained within them, as shown below.

[0072] Figure 9 shows the distribution of mass concentrations (wt%) of Ni, Ce, and Zr contained in the fuel electrode functional layer L1 and its vicinity, along the thickness direction of the fuel electrode functional layer L1. The horizontal axis of Figure 9 indicates the position in the thickness direction (thickness position). The thickness position indicated by the horizontal axis is such that moving to the left brings it closer to the solid electrolyte layer 311a, and moving to the right brings it closer to the fuel electrode substrate layer L2. The vertical axis of Figure 9 represents the mass concentration (wt%). Graph G(Ni) in Figure 9 is an example of a Ni mass concentration distribution graph measured along the thickness direction, graph G(Ce) is an example of a Ce (cerium) mass concentration distribution graph measured along the thickness direction, and graph G(Zr) is an example of a Zr (zirconium) mass concentration distribution graph measured along the thickness direction. These graphs can be obtained by measuring the concentration of each element along the thickness direction using an EPMA device in a cross-section obtained by cutting the electrolytic cell 311 in the thickness direction.

[0073] In Figure 9, the thickness region represented by 311a represents the solid electrolyte layer 311a, the thickness region represented by L1 represents the fuel electrode functional layer L1, and the thickness region represented by L2 represents the fuel electrode substrate layer L2. As shown in Figure 9, the fuel electrode functional layer L1 contacts the solid electrolyte layer 311a at one end in the thickness direction and contacts the fuel electrode substrate layer L2 at the other end.

[0074] The fuel electrode functional layer L1 contains Ni, Ce, and Zr. As described above, the fuel electrode functional layer L1 is divided into a main layer L11 and an intermediate layer L12 along the thickness direction. The main component of the main layer L11 is Ni / CeO ２ It is a cermet. Therefore, the main layer L11 contains a large amount of Ni and Ce. As a result, within the main layer L11, the mass concentrations of Ni, Ce, and Zr satisfy the relationship: mass concentration of Ni > mass concentration of Ce > mass concentration of Zr.

[0075] Since the main components of the fuel electrode substrate layer L2 are a cermet of Ni and YSZ, Ni and Zr are abundant in the fuel electrode substrate layer L2. Therefore, within the fuel electrode substrate layer L2, the mass concentrations of Ce and Zr satisfy the relationship: mass concentration of Zr > mass concentration of Ce.

[0076] Since the main body layer L11 and the fuel electrode substrate layer L2 are in contact, the relationship between the mass concentrations of Ce and Zr is reversed at the contact interface. Therefore, the boundary position between the two layers can be determined to be the position where the mass concentrations of Ce and Zr are equal. This position is the fourth position P4 in Figure 9. The region to the right of the fourth position in Figure 9 is the fuel electrode substrate layer L2.

[0077] Furthermore, the main component of the solid electrolyte layer 311a is stabilized zirconia (YSZ), and Ni and Ce are not included in the components blended during manufacturing. Therefore, the mass concentration of Zr should be the highest within the solid electrolyte layer 311a. In this specification, the solid electrolyte layer 311a is defined as the layer in which the mass concentration of Zr is highest and the mass concentration of Ni is lower than the mass concentration of Ce. Accordingly, within the solid electrolyte layer 311a, the mass concentrations of Ni, Ce, and Zr satisfy the relationship: mass concentration of Zr > mass concentration of Ce > mass concentration of Ni.

[0078] An intermediate layer L12 exists between the solid electrolyte layer 311a and the main layer L11. Therefore, the intermediate layer L12 is the layer of the fuel electrode functional layer L1 that is in contact with the solid electrolyte layer 311a. This intermediate layer L12 is a layer that appears during the transition from the relationship between the mass concentrations of each element (Zr, Ce, Ni) present in the solid electrolyte layer 311a (mass concentration of Zr > mass concentration of Ce > mass concentration of Ni) to the relationship between the mass concentrations of each element (Ni, Ce, Zr) present in the main layer L11 of the fuel electrode functional layer L1 (mass concentration of Ni > mass concentration of Ce > mass concentration of Zr).

[0079] Figure 10 is an enlarged view of the region shown as part A in Figure 9, i.e., the intermediate layer L12 and its vicinity. As shown in Figure 10, the intermediate layer L12 contains Ni, Ce, and Zr. Within the intermediate layer L12, the mass concentration of Ce is the lowest among the mass concentrations of Zr, Ni, and Ce.

[0080] Within the solid electrolyte layer 311a, the mass concentration of Ce is higher than that of Ni, while within the intermediate layer L12, the mass concentration of Ce is lowest. Since the solid electrolyte layer 311a and the intermediate layer L12 are in contact, the relationship between the mass concentrations of Ce and Ni is reversed at the contact interface. Therefore, the boundary position between the two layers can be determined by the thickness position where the mass concentrations of Ce and Ni are equal. This thickness position is the second position P2 in Figure 10. The second position P2 corresponds to the contact interface between the solid electrolyte layer 311a and the fuel electrode functional layer L1. Therefore, the region to the left of the second position P2 in Figure 10 is the solid electrolyte layer 311a.

[0081] Within the main layer L11, the mass concentration of Ce is higher than that of Zr, while within the intermediate layer L12, the mass concentration of Ce is lowest. Since the intermediate layer L12 is in contact with the main layer L11 at the end opposite to the contact interface with the solid electrolyte layer 311a, the relative magnitudes of the mass concentrations of Ce and Zr are reversed at this contact interface. Therefore, the boundary position between the two layers can be determined by the thickness position where the mass concentrations of Ce and Zr are equal. This thickness position is the third position P3 in Figure 10. Thus, the region from the second position P2 to the third position P3 in Figure 10 is the intermediate layer L12, and the region to the right of the third position P3 is the main layer L11. Note that the third position P3 is the thickness position where, when comparing the mass concentrations of Zr and Ce from the first position P1 toward the fuel electrode substrate layer, the mass concentrations of Zr and Ce first become equal.

[0082] As shown in Figure 10, the intermediate layer L12 includes a region where the mass concentration of Zr increases and the mass concentration of Ni decreases as it approaches the solid electrolyte layer. At a specific thickness position in the thickness direction of the intermediate layer L12 (the thickness direction of the electrolytic cell 311), the mass concentrations of Ni and Zr are equal. The thickness position in the intermediate layer L12 where the mass concentrations of Ni and Zr are equal is the first position P1 in Figure 10.

[0083] The thickness of the intermediate layer L12 can be expressed as the sum of the distance along the thickness direction from the first position P1 to the second position P2 (i.e., the thickness of region L121 in Figure 10) and the distance along the thickness direction from the first position P1 to the third position P3 (i.e., the thickness of region L122 in Figure 10), as shown in Figure 10. Here, the second position P2 is a position that is toward the solid electrolyte layer 311a side along the thickness direction of the intermediate layer L12 (the thickness direction of the electrolytic cell 311) from the first position P1, and is a thickness position where the mass concentration of Ni and the mass concentration of Ce are the same. The third position P3 is a position that is toward the fuel electrode layer side (opposite side from the solid electrolyte layer 311a) along the thickness direction of the intermediate layer L12 (the thickness direction of the electrolytic cell 311) from the first position P1, and is a thickness position where the mass concentration of Zr and the mass concentration of Ce are the same.

[0084] Since the intermediate layer L12 is a layer that contacts the contact interface between the solid electrolyte layer 311a and the fuel electrode functional layer L1, the thickness of the intermediate layer L12 affects the adhesion of the electrolytic cell 311. From the viewpoint of improving adhesion, a thicker intermediate layer L12 is preferable. Preferably, the thickness T1 of the intermediate layer L12 is greater than 0.50 μm. However, if the intermediate layer L12 is too thick, the electrical resistance increases and the initial performance of the electrolytic cell 311 deteriorates. Therefore, from the viewpoint of maintaining the initial performance of the electrolytic cell 311, a thinner intermediate layer is preferable. Preferably, the thickness T1 of the intermediate layer L12 is less than 1.62 μm. That is, the thickness T1 is greater than 0.50 μm and less than 1.62 μm. By controlling the thickness of the intermediate layer L12 so that the thickness T1 is within the above range, it is possible to improve the adhesion of the electrolytic cell 311 while maintaining the initial performance of the electrolytic cell 311. The thickness T1 is more preferably 0.53 μm or more and 1.24 μm or less. Even more preferably, the thickness T1 is more than 0.56 μm or more and 0.86 μm or less.

[0085] Furthermore, it is preferable that the thickness T2 of the intermediate layer L12, specifically the distance from the first position P1 to the third position P3, i.e., the region L122 in Figure 10 (hereinafter, region L122 may be referred to as the functional layer-side intermediate layer), be thin. Since the functional layer-side intermediate layer contains roughly equal amounts of Zr and Ce, it is considered to be a layer with a large amount of stabilized zirconia ceria solid solution. Stabilized zirconia ceria solid solution has high electrical resistance. Therefore, the thinner the thickness T2 of the functional layer-side intermediate layer, the lower the electrical resistance of the electrolytic cell 311 can be, thereby improving the initial performance of the electrolytic cell 311. Specifically, it is preferable that the thickness T2 be less than 0.50 μm. Preferably, the thickness T2 is 0.49 μm or less, and more preferably, the thickness T2 is 0.47 μm or less.

[0086] (Example) [Preparation of Sample S1] NiO powder, GDC powder, and YSZ powder were mixed in predetermined proportions. At this time, the mixing ratio of GDC powder to YSZ powder was GDC powder:YSZ powder = 9:1. Next, the mixed powder was stirred for a predetermined time using a ball mill or the like. Then, butyral resin, polyvinyl acetal resin (G-260, manufactured by Sekisui Chemical Co., Ltd.) as a plasticizer, a well-known dispersant, a mixed solvent of toluene and ethanol, and a pore-forming agent as needed were added to the mixed powder in predetermined proportions and mixed in a ball mill to prepare a slurry. Then, a green sheet of fuel electrode functional layer having a predetermined thickness was formed from the slurry using the doctor blade method.

[0087] Furthermore, NiO powder and YSZ powder were mixed in predetermined proportions and stirred for a predetermined time using a ball mill or the like. Next, butyral resin, polyvinyl acetal resin as a plasticizer, a well-known dispersant, a mixed solvent of toluene and ethanol, and, if necessary, a pore-forming agent (typically organic beads) were added to the mixed powder in predetermined proportions and mixed in a ball mill to prepare a slurry. Then, a green sheet of fuel electrode substrate layer having a predetermined thickness was formed from the slurry using the doctor blade method.

[0088] Furthermore, butyral resin, polyvinyl acetal resin as a plasticizer, a well-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. Then, a green sheet of solid electrolyte layer having a predetermined thickness was formed from the slurry using the doctor blade method.

[0089] Next, the green sheet for the fuel electrode functional layer and the green sheet for the fuel electrode substrate layer were laminated on one side of the green sheet for the solid electrolyte layer, in that order. Then, these laminated green sheets were pressed together under high pressure using a press machine while heating and vacuuming. This formed a laminate containing the green sheet for the solid electrolyte layer, the green sheet for the fuel electrode functional layer, and the green sheet for the fuel electrode substrate layer.

[0090] The laminate formed as described above was degreased at a predetermined temperature (for example, 200 to 300°C). Next, the laminate was fired at a sintering temperature of 1230°C for a predetermined time (for example, 1 to 5 hours) (primary sintering). This formed a primary sintered body having a solid electrolyte layer and a fuel electrode layer laminated on one side of the solid electrolyte layer.

[0091] Next, a paste containing GDC was screen printed onto the other side of the solid electrolyte layer of the molded primary sintered body, and it was fired at a predetermined temperature (1000°C to 1200°C) (secondary sintering). This formed a reaction prevention layer on the other side of the solid electrolyte layer. Then, a material containing LSCF was screen printed onto the surface of the reaction prevention layer, and it was fired at a predetermined temperature (e.g., 900 to 1000°C) for a predetermined time (e.g., 1 to 5 hours) (tertiary sintering). This produced sample S1 of an electrolytic cell comprising a solid electrolyte layer, a fuel electrode layer laminated on one side of the solid electrolyte layer, and a reaction prevention layer and an air electrode layer laminated on the other side of the solid electrolyte layer.

[0092] [Preparation of Sample S2] Sample S2 was prepared under the same conditions as for Sample S1, except that the sintering temperature in the primary sintering was set to 1190°C.

[0093] [Preparation of Sample S3] Sample S3 was prepared under the same conditions as for Sample S1, except that the mixing ratio of GDC powder to YSZ powder was set to GDC powder:YSZ powder = 8:2 when forming the green sheet of the fuel electrode functional layer.

[0094] [Preparation of Sample S4] Sample S4 was prepared under the same conditions as for Sample S2, except that the mixing ratio of GDC powder to YSZ powder was set to GDC powder:YSZ powder = 8:2 when forming the green sheet of the fuel electrode functional layer.

[0095] [Preparation of Sample S5] Sample S5 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1330°C.

[0096] [Preparation of Sample S6] Sample S6 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1280°C.

[0097] [Preparation of Sample S7] Sample S7 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1150°C.

[0098] [Preparation of Sample S8] Sample S8 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1110°C.

[0099] [Preparation of Sample C1] Sample C1 was prepared under the same conditions as for Sample S1, except that the sintering temperature in the primary sintering was set to 900°C to 950°C. It is considered that no solid solution is formed during sintering when the sintering temperature in the primary sintering is 900°C to 950°C. Therefore, Ni and ZrO are present in the fuel electrode functional layer of Sample C1. ２ Cermet and Ni and CeO ２ There are cermets for Ni / (ZrO ２ - CEO ２ Cermet does not exist.

[0100] [Preparation of Sample C2] Before forming the green sheet of the fuel electrode functional layer, GDC powder and YSZ powder were mixed in a predetermined ratio (GDC powder:YSZ powder = 9:1), and the mixed powder was calcined (temperature: approximately 1000°C, time: approximately 6 hours). After that, the calcined powder was pulverized to obtain post-calcined powder. This post-calcined powder was used when forming the green sheet of the fuel electrode functional layer. Sample C2 was prepared under the same conditions as Sample S1.

[0101] [Preparation of Sample C3] Sample C3 was prepared under the same conditions as for Sample S1, except that the mixing ratio of GDC powder to YSZ powder was set to GDC powder:YSZ powder = 10:0 when forming the green sheet of the fuel electrode functional layer.

[0102] [Preparation of Sample C4] Sample C4 was prepared under the same conditions as for Sample S2, except that the mixing ratio of GDC powder to YSZ powder was set to GDC powder:YSZ powder = 10:0 when forming the green sheet of the fuel electrode functional layer.

[0103] [Creation of Mass Concentration Distribution Graphs G(Ni), G(Zr), G(Ce) for Ni, Zr, and Ce] Each sample was cut along a plane in the thickness direction, and the cut surface was subjected to surface analysis using an EPMA instrument (manufactured by JEOL Ltd.). From the elemental mapping images obtained from the surface analysis, the mass concentration distributions of Ni, Zr, and Ce in the thickness direction of the sample were calculated. In this case, the mass concentrations of Ni, Zr, and Ce present at each thickness position at 0.06 μm intervals were calculated. In order to calculate the concentration of each element present at each thickness position, the average value of the mass concentration of each element measured at multiple locations on the line corresponding to that thickness position was calculated, and the average value of the calculated mass concentrations of each element was taken as the mass concentration of each element present at that thickness position.

[0104] Next, based on the mass concentrations of each element (Ni, Zr, Ce) at each thickness position, mass concentration distribution graphs G(Ni), G(Zr), and G(Ce), which represent the change in mass concentration along the thickness position, were created for each sample, as shown in Figure 9.

[0105] [Identification of Positions P1, P2, P3, and P4] Based on the mass concentration distribution graphs G(Ni), G(Zr), and G(Ce) created for each sample, the first position P1, second position P2, third position P3, and fourth position P4 were identified as shown in Figures 9 and 10. In this case, the position where the mass concentration of Zr and the mass concentration of Ni are the same in the region near the contact interface between the solid electrolyte layer 311a and the fuel electrode functional layer L1 was identified as the first position P1, the position where the mass concentration of Ce and the mass concentration of Ni are the same for the first time, located away from the first position P1 toward the solid electrolyte layer, was identified as the second position, and the position where the mass concentration of Zr and the mass concentration of Ce are the same for the first time, located away from the first position P1 toward the fuel electrode substrate layer, was identified as the third position P3. Furthermore, in the region near the contact interface between the fuel electrode functional layer L1 and the fuel electrode substrate layer L2, the position where the mass concentration of Zr and the mass concentration of Ce are the same (i.e., the position where the mass concentration of Zr and the mass concentration of Ce are the same, located toward the fuel electrode substrate layer from the third position P3) was identified as the fourth position P4. The second position P2 corresponds to the contact interface S between the solid electrolyte layer and the fuel electrode functional layer.

[0106] [Measurement of Fuel Electrode Functional Layer Thickness] For each sample, the distance along the thickness direction between the second position P2 and the fourth position P4 was measured as the thickness of the fuel electrode functional layer.

[0107] [Measurement of Intermediate Layer Thickness T1] For each sample, the distance along the thickness direction between the second position P2 and the third position P3 was measured as the intermediate layer thickness T1.

[0108] [Measurement of the thickness T2 of the functional layer-side intermediate layer] For each sample, the distance along the thickness direction between the first position P1 and the third position P3 was measured as the thickness T2 of the functional layer-side intermediate layer.

[0109] [Identification of cermets present inside the fuel electrode functional layer] Based on the elemental mapping images obtained for samples S1 and C3, Ni / CeO was identified within the fuel electrode functional layer. ２ Location of cermet and Ni / (ZrO ２ - CEO ２) A cermet mapping image showing the location of cermet was created. Fig. 7 is a cermet mapping image created for sample S1, and Fig. 8 is a cermet mapping image created for sample C3.

[0110] A contact interface line representing the contact interface between the solid electrolyte layer and the fuel electrode functional layer was drawn on the produced cermet mapping image. The contact interface line is a line corresponding to the second position P2 specified as described above based on each mass concentration distribution graph, and corresponds to the line indicating the contact interface S in Fig. 7 and Fig. 8. Further, a line separated toward the fuel electrode functional layer side along the thickness direction by a distance of one third of the thickness of the fuel electrode functional layer from the contact interface line was drawn. This line is a dividing line between a region in contact with the contact interface and an intermediate region adjacent to said region among the regions obtained by dividing the fuel electrode functional layer into three equal parts in the thickness direction, and corresponds to the dividing line B in Fig. 7 and Fig. 8.

[0111] In the cermet mapping image, a region farther from the contact interface than the dividing line is the intermediate region when the fuel electrode functional layer is divided into three equal parts in the thickness direction. The cermet detected in this intermediate region is the cermet existing inside the fuel electrode functional layer. As shown in Fig. 7, inside the fuel electrode functional layer of sample S1, there is Ni / CeO ２ cermet and Ni / (ZrO ２ -CeO ２ ) were confirmed to exist.

[0112] When forming the green sheet of the fuel electrode functional layer of sample S1, a mixed powder obtained by mixing GDC powder and YSZ powder is used. Therefore, during sintering, part of cerium in GDC forms a solid solution in YSZ and / or part of zirconium in YSZ forms a solid solution in GDC. Therefore, inside the fuel electrode functional layer, Ni / CeO ２ cermet and Ni / (ZrO ２ -CeO ２ ) cermet is considered to exist. Therefore, similarly to sample S1, for samples S2 to S7 that also use a mixed powder of GDC powder and YSZ powder when forming the green sheet of the fuel electrode functional layer, Ni / CeO is also present inside the fuel electrode functional layer ２cermet and Ni / (ZrO ２ -CeO ２ ) cermet is considered to exist.

[0113] Sample C1 also uses a mixed powder obtained by mixing GDC powder and YSZ powder when molding the green sheet for the fuel electrode functional layer. However, the sintering temperature in primary sintering is as low as 900°C to 950°C, and it is considered that in this case, stabilized zirconia and ceria do not form a solid solution during sintering. Therefore, inside the fuel electrode functional layer of Sample C1, there is Ni / CeO ２ cermet and Ni / ZrO ２ cermet, and Ni / (ZrO ２ -CeO ２ ) cermet is considered not to exist.

[0114] When molding the green sheet for the fuel electrode functional layer of Sample C2, powder obtained by pre-calcining a mixed powder of GDC powder and YSZ powder is used. This powder is considered to be GDC powder in which Zr is already solid-dissolved or YSZ powder in which Ce is solid-dissolved. Therefore, Ni / (ZrO ２ -CeO ２ ) only this cermet is considered to exist inside the fuel electrode functional layer of Sample C2.

[0115] Regarding Sample C3, as shown in FIG. 8, in a region farther from the contact interface S than the dividing line B, that is, the intermediate region when the fuel electrode functional layer is divided into three equal parts in the thickness direction, only a dark gray region is detected. Therefore, inside the fuel electrode functional layer of Sample C3, Ni / CeO ２ it was confirmed that only cermet exists. When molding the green sheet for the fuel electrode functional layer of Sample C3, only GDC powder is used, and YSZ powder is not used. Therefore, inside the fuel electrode functional layer of Sample C3, there is Ni / (ZrO ２ -CeO ２) It is considered that no cermet is present. Also, similar to sample C3, only GDC powder was used when forming the green sheet of the fuel electrode functional layer of sample C4, and YSZ powder was not used. Therefore, the interior of the fuel electrode functional layer of sample C4 contains Ni / CeO ２ Only cermets exist, Ni / (ZrO ２ - CEO ２ It is believed that cermet does not exist.

[0116] [Confirmation of the presence or absence of interfacial delamination and microcracks] Each sample was cut in cross-section along the thickness direction, and the cut surface was observed using SEM to confirm whether or not delamination occurred at the interface between the solid electrolyte layer and the fuel electrode layer.

[0117] [Measurement of initial electrolysis voltage V0] With hydrogen and water vapor supplied to the fuel polar layer side and air supplied to the air polar layer side of each sample at a constant flow rate, a constant current (1.0 A / cm²) is applied between the fuel polar layer and the air polar layer. ２ A steam electrolysis reaction was carried out by flowing a vapor (V0) through the system. The voltage applied between the fuel electrode and the air electrode at this time was measured as the initial electrolysis voltage V0. A smaller initial electrolysis voltage V0 indicates better initial performance.

[0118] [Measurement Results] Table 1 shows the cermet present inside the fuel electrode functional layer, the evaluation results of adhesion, the measurement results of the intermediate layer thickness T1, the measurement results of the functional layer side intermediate layer thickness T2, the initial electrolysis voltage, and the overall judgment for each sample.

[0119] Regarding adhesion in Table 1, adhesion was judged as passing (○) if no delamination or microcracks were observed at the contact interface from the SEM image, and as failing (△) if delamination or microcracks were observed at the contact interface. Regarding the initial electrolytic current V0, initial performance was evaluated as excellent (◎) if V0 was less than 1.26V, initial performance was evaluated as good (○) if V0 was 1.26V or more and less than 1.36V, and initial performance was evaluated as average (△) if V0 was 1.36V or more. Regarding the overall judgment, if adhesion was passing (○) and initial performance was excellent (◎), the overall judgment was evaluated as excellent (○) if adhesion was passing (○) and initial performance was excellent (○), the overall judgment was evaluated as average (△) if adhesion was passing (○) and initial performance was average (△), and the overall judgment was evaluated as poor (×) if adhesion was failing (△).

[0120] As can be seen from Table 1, in all of samples S1 to S8, the inside of the fuel electrode functional layer contains Ni / CeO ２ Cermet and Ni / (ZrO ２ - CEO ２ A cermet is present. Inside the fuel electrode functional layer of sample C1, Ni / CeO ２ Cermet and Ni / ZrO ２ A cermet is present. Inside the fuel electrode functional layer of sample C2, there is Ni / (ZrO ２ - CEO ２ ) Only cermet is present. Inside the fuel electrode functional layer of sample C3 and sample C4, Ni / CeO ２ Only cermet exists.

[0121] Furthermore, the adhesion evaluation was satisfactory (○) for all samples S1 to S8. On the other hand, the adhesion evaluation was unsatisfactory (△) for all of samples C1, C2, C3, and C4. From this, it can be concluded that Ni / CeO cermet and Ni / (ZrO) are present inside the fuel electrode layer. ２ It is evident that the presence of CeO cermet improves adhesion.

[0122] In sample C1, the low sintering temperature during primary sintering prevented sufficient necking growth between particles at the contact interface between the solid electrolyte layer and the fuel electrode functional layer, resulting in poor adhesion in sample C1. In sample C2, the powder used to form the green sheet of the fuel electrode functional layer was obtained by calcining a mixed powder of GDC powder and YSZ powder, as described above. Once calcined, the powder has high hardness and is difficult to pulverize sufficiently. Therefore, the particle size of the powder used when forming the green sheet of the fuel electrode functional layer is considered to be larger than that of powders normally used. When the particle size of the powder used is large, sufficient necking growth between particles occurs at the contact interface between the solid electrolyte layer and the fuel electrode functional layer during primary sintering. For this reason, poor adhesion in sample C2 is considered to be the cause. In samples C3 and C4, Ni / (ZrO) is present inside the fuel electrode. ２ - CEO ２ Because a cermet is not present, there is a large difference in thermal shrinkage between the solid electrolyte layer and the fuel electrode functional layer. As a result, delamination or microcracks occur at the contact interface between the solid electrolyte layer and the fuel electrode functional layer during primary sintering. For this reason, the adhesion between samples C3 and C4 is considered to be low.

[0123] Furthermore, the initial electrolytic voltage V0 of samples S1 to S4 is all less than 1.36V, while the initial electrolytic voltage V0 of samples S5 to S8 is all 1.36V or greater. Here, the thickness T1 of the intermediate layer in samples S1 to S4 is greater than 0.50 μm and less than 1.62 μm. On the other hand, the thickness T1 of the intermediate layer in samples S5 and S6 is 1.62 μm or greater, and the thickness T1 of the intermediate layer in samples S7 and S8 is 0.50 μm or less. Therefore, it can be seen that by adjusting the thickness of the intermediate layer so that the thickness T1 is greater than 0.50 μm and less than 1.62 μm, the initial electrolytic voltage V0 can be kept low, and the initial performance can be maintained or improved.

[0124] The thickness T1 of the intermediate layer is preferably 0.53 μm or more and 1.24 μm or less. More preferably, the thickness T1 of the intermediate layer is 0.56 μm or more and 0.86 μm or less.

[0125] Furthermore, the initial electrolytic voltages of samples S1 and S2 are both less than 1.26V, while the initial electrolytic voltages of samples S3 and S4 are both 1.26V or higher. Here, the thickness T2 of the functional layer-side intermediate layer of samples S1 and S2 is less than 0.50 μm, while the thickness T2 of the functional layer-side intermediate layer of samples S3 and S4 is 0.50 μm or higher. Therefore, by molding the intermediate layer so that the thickness T2 of the functional layer-side intermediate layer is less than 0.50 μm, the initial performance can be further improved.

[0126] The thickness T2 of the functional layer-side intermediate layer is preferably 0.49 μm or less, and more preferably 0.47 μm or less.

[0127] Furthermore, for sample S1, as shown in Figure 7, Ni / CeO is present in a region of 5 μm or less along the thickness direction from the contact interface between the solid electrolyte layer and the fuel electrode functional layer towards the fuel electrode functional layer. ２ Let N1 be the number of points where cermet was detected, and within the above region, Ni / (ZrO ２ - CEO ２ The number of points where cermet was detected was denoted as point number N2, and the ratio R (= N2 / N1) of points N2 to points N1 was calculated to be R = 1.12. Similarly, for sample C3, the ratio R was calculated based on Figure 8 and was R = 0.16. The adhesion of sample S1 was satisfactory (○), while the adhesion of sample C3 was unsatisfactory (△). From this, it can be concluded that when the ratio R is greater than 0.16, the adhesion is improved compared to the conventional method. Preferably, the ratio R is 0.64 or higher. More preferably, the ratio R is 1.12 or higher.

[0128] While embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments. For example, in the above embodiments, an example was described in which the fuel electrode layer comprises a fuel electrode functional layer and a fuel electrode substrate layer, but the technology of the present disclosure can also be applied to fuel electrodes that do not have a fuel electrode substrate layer. In this case, the technology of the present disclosure can be applied by assuming that the entire fuel electrode is a fuel electrode functional layer. Furthermore, in the above embodiments, an electrolytic cell was given as an example of an electrochemical cell, but the technology of the present disclosure can also be applied to fuel cell cells.

[0129] Furthermore, although the above embodiment shows an example in which YSZ is used for the solid electrolyte layer, any stabilized zirconia other than YSZ may be used. Also, although the above embodiment describes an example in which GDC is used as the ion-conducting oxide for the fuel electrode functional layer, ceria doped with rare earth elements other than Gd can be used as the ion-conducting oxide for the fuel electrode functional layer.

[0130] Furthermore, although the above embodiment discloses a hydrogen production apparatus as an electrolytic reactor, the electrolytic reactor may be an apparatus other than a hydrogen production apparatus, for example, a co-electrolytic apparatus of water vapor and carbon dioxide. Also, although the above embodiment shows an example in which the hot module 6 includes a vaporizer 2, a hot module without a vaporizer 2 is also possible. In addition, in the electrochemical cell stack 1 shown in Figures 2 and 3, the number of stacked cell cassettes 30 is four, including the dummy cell cassette, but a larger number of cell cassettes, for example 20 to 30 cell cassettes, may be stacked. Thus, this disclosure is modifiable as long as it does not depart from its spirit.

[0131] Furthermore, this disclosure may include the following embodiments: [1] An electrochemical cell comprising a solid electrolyte made of stabilized zirconia, a fuel electrode containing nickel and in contact with the solid electrolyte, and an air electrode, wherein a cermet of nickel and ceria and a cermet of nickel and stabilized zirconia ceria solid solution are present inside the fuel electrode. [2] The electrochemical cell according to [1] above, wherein in a region within 5 μm from the contact interface between the fuel electrode and the solid electrolyte toward the fuel electrode, the ratio of the amount of cermet of nickel and stabilized zirconia ceria solid solution to the amount of cermet of nickel and ceria is greater than 0.16. [3] An electrochemical cell according to [1] or [2] above, wherein the fuel electrode has an intermediate layer that is in contact with the electrolyte and includes a region in the thickness direction toward the electrolyte side in which the mass concentration of zirconium increases and the mass concentration of nickel decreases, and when a position in the thickness direction of the intermediate layer where the mass concentration of zirconium and the mass concentration of nickel are the same is defined as a first position, the thickness of the intermediate layer expressed as the sum of the distance from the first position toward the solid electrolyte side along the thickness direction of the intermediate layer where the mass concentration of nickel and the mass concentration of cerium are the same and the distance from the first position toward the fuel electrode side along the thickness direction of the intermediate layer where the mass concentration of zirconium and the mass concentration of cerium are the same is greater than 0.50 μm and less than 1.62 μm. [4] An electrochemical cell according to [3] above, wherein the distance from the first position to the third position is less than 0.50 μm. [5] An electrochemical cell stack comprising an electrochemical cell stack according to any one of [1] to [4] above. [6] A hot module comprising the electrochemical cell stack according to [5] above, a heating device for heating the gas supplied to the electrochemical cell stack, and an insulating material in which the electrochemical cell stack and the heating device are arranged inside. [7] An electrolytic reaction apparatus comprising the hot module according to [6] above.

[0132] 1... Electrochemical cell stack, 2... Vaporizer, 3... Heating device, 4... Insulation material, 6... Hot module, 7... Condenser, 30... Cell cassette, 31... Electrochemical cell unit, 311... Electrolytic cell (Electrochemical cell), 311a... Solid electrolyte layer (Solid electrolyte), 311b... Air electrode layer (Air electrode), 311c... Fuel electrode layer (Fuel electrode), L1... Fuel electrode functional layer, L11... Main body layer, L12... Intermediate layer, L2... Fuel electrode substrate layer, 311d... Reaction prevention layer, 312... Fuel electrode current collector, 313... Interconnector, 32... Separator section, 33... Frame section, 100... Hydrogen production apparatus

Claims

1. An electrochemical cell comprising a solid electrolyte made of stabilized zirconia, a fuel electrode containing nickel and in contact with the solid electrolyte, and an air electrode, wherein a cermet of nickel and ceria and a cermet of nickel and stabilized zirconia ceria solid solution are present inside the fuel electrode.

2. An electrochemical cell according to claim 1, wherein in a region within 5 μm from the contact interface between the fuel electrode and the solid electrolyte toward the fuel electrode, the ratio of the amount of cermet of nickel and stabilized zirconia ceria solid solution to the amount of cermet of nickel and ceria is greater than 0.

16.

3. An electrochemical cell according to claim 1 or 2, wherein the fuel electrode has an intermediate layer that is in contact with the solid electrolyte and includes a region in the thickness direction toward the electrolyte side in which the mass concentration of zirconium increases and the mass concentration of nickel decreases, and the thickness of the intermediate layer, expressed as the sum of the distance from the first position to a second position toward the solid electrolyte side in the thickness direction of the intermediate layer in which the mass concentration of nickel and the mass concentration of cerium are the same, and the distance from the first position toward the fuel electrode side in the thickness direction of the intermediate layer in which the mass concentration of zirconium and the mass concentration of cerium are the same, is greater than 0.50 μm and less than 1.62 μm.

4. An electrochemical cell according to claim 3, wherein the distance from the first position to the third position is less than 0.50 μm.

5. An electrochemical cell stack comprising an electrochemical cell stacked according to claim 1.

6. A hot module comprising: an electrochemical cell stack according to claim 5; a heating device for heating a gas supplied to the electrochemical cell stack; and an insulating material in which the electrochemical cell stack and the heating device are disposed.

7. An electrolytic reaction apparatus comprising the hot module described in claim 6.

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