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

Abstract

According to the present invention, a fuel electrode layer of an electrolysis cell has an intermediate layer that contains nickel, cerium, and zirconium, and includes a region which is in contact with a solid electrolyte layer that contains zirconium and in which the mass concentration of zirconium increases and the mass concentration of nickel decreases toward the solid electrolyte layer side along the thickness direction. The thickness of the intermediate layer is greater than 0.45 μm and less than 1.62 μm. 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 Zr / Ce concentration ratio of the mass concentration of zirconium to the mass concentration of cerium at the first position is greater than 1.8 and less than 6.3.

Description

Electrochemical cell, electrochemical cell stack, hot module, and electrolytic reactor

[0001] The present disclosure relates to an electrochemical cell, an electrochemical cell stack, a hot module, and an electrolytic reactor.

[0002] Conventionally, solid oxide-type electrochemical cells in which an ion-conductive oxide (for example, YSZ (yttria-stabilized zirconia)) is used as a solid electrolyte are known (see, for example, Patent Document 1). Solid oxide-type electrochemical cells are characterized by performing electrochemical reactions with high efficiency under high-temperature environments, and can be used as solid oxide electrolysis cells (SOECs) or solid oxide fuel cells (SOFCs).

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

[0004] It is known that the performance of an electrochemical cell is deeply related to the electrode structure in contact with a solid electrolyte, for example, the structure near the contact interface between the solid electrolyte and a fuel electrode in contact with the solid electrolyte. In particular, the catalytic performance of the fuel electrode near the contact interface is one of the factors that greatly affect the performance of the electrochemical cell, and the performance varies greatly depending on differences in the type, amount, particle size, and the like of particles constituting the fuel electrode. A material generally used as a fuel electrode consists of a mixture of metal particles and ion-conductive oxide particles, and the higher the ion conductivity of the ion-conductive oxide particles, the higher the performance of the electrochemical cell.

[0005] As the ion-conductive oxide particles in the fuel electrode, zirconium-containing oxide particles, for example YSZ (yttria-stabilized zirconia) particles, are typically used. Alternatively, cerium-containing oxide particles, for example GDC (gadolinium-doped ceria) particles, may be used in place thereof. Since GDC has higher ion conductivity than YSZ, further improvement in the performance of the electrochemical cell can be expected when GDC is used as the ion-conductive oxide for the fuel electrode.

[0006] However, when the solid electrolyte is a zirconium-containing oxide (e.g., YSZ) and the ion-conducting oxide in the fuel electrode is a cerium-containing oxide (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. If delamination or microcracks occur, the performance of the electrochemical cell will deteriorate. For this reason, it is not possible to sufficiently improve the performance of an electrochemical cell using a cerium-containing oxide 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 performance of an electrochemical cell comprising a zirconium-containing solid electrolyte and a cerium-containing fuel electrode.

[0008] The electrochemical cell (311) according to this disclosure comprises a solid electrolyte (311a) containing zirconium, a fuel electrode (311c) in contact with the solid electrolyte (311a), and an air electrode (311b). The fuel electrode (311c) contains nickel, cerium, and zirconium and has an intermediate layer (L12) in contact with the solid electrolyte (311a). The intermediate layer (L12) includes a region along its thickness direction in which the mass concentration of zirconium increases and the mass concentration of nickel decreases as it moves toward the solid electrolyte (311a) side. The thickness of the intermediate layer (L12) is expressed as the sum of the distance from the first position (P1), where the mass concentration of zirconium and nickel are the same, to the second position (P2), which is located along the thickness direction of the intermediate layer (L12) toward the solid electrolyte (311a) and where the mass concentration of nickel and cerium are the same, and the distance from the first position (P1) toward the fuel electrode (311c) and where the mass concentration of zirconium and cerium are the same, to the third position (P3), which is located along the thickness direction of the intermediate layer (L12) toward the fuel electrode (311c) and where the mass concentration of zirconium and cerium are the same. The thickness of the intermediate layer (L12) is greater than 0.45 μm and less than 1.62 μm. Furthermore, at the first position (P1), the Zr / Ce concentration ratio (R(Zr / Ce)), which is the ratio of the mass concentration of zirconium to the mass concentration of cerium, is greater than 1.8 and less than 6.3.

[0009] According to the electrochemical cell of this disclosure, the solid electrolyte contains zirconium, and the fuel electrode contains nickel, cerium, and zirconium. The fuel electrode also has an intermediate layer in the contact region with the solid electrolyte. The zirconium in the intermediate layer may be necking with the zirconium in the solid electrolyte. In the electrochemical cell of this disclosure, the mass concentration of zirconium at a predetermined position (first position) in the thickness direction of the intermediate layer is greater than 1.8 times the mass concentration of cerium. By including more zirconium in the intermediate layer than cerium in this way, the effect of improving adhesion due to necking between the solid electrolyte and the fuel electrode can be enhanced. Therefore, delamination of the fuel electrode is suppressed, as is the occurrence of microcracks, and the reduction of the ion conduction path between the solid electrolyte and the fuel electrode due to delamination or the occurrence of microcracks is suppressed. In addition, since the thickness of the intermediate layer is relatively thin, less than 1.62 μm, the increase in electrical resistance due to an intermediate layer that is too thick can also be suppressed. As a result, the performance of an electrochemical cell comprising a solid electrolyte containing zirconium and a fuel electrode containing cerium can be improved.

[0010] In another embodiment of the electrochemical cell according to this disclosure, the Zr / Ce concentration ratio (R(Zr / Ce)) at the first position (P1) is 2.1 or greater and 3.4 or less. This further improves the performance of the electrochemical cell.

[0011] In yet another embodiment of the electrochemical cell according to this disclosure, the mass concentration of zirconium (N(Zr0)) in the fuel electrode (311c) is less than 4.60 wt%. Here, the mass concentration of zirconium in the fuel electrode is the mass concentration of zirconium in the portion of the fuel electrode excluding the intermediate layer. Furthermore, if the fuel electrode includes a fuel electrode functional layer and a fuel electrode substrate layer, the mass concentration of zirconium in the fuel electrode is the mass concentration of zirconium in the portion of the fuel electrode functional layer excluding the intermediate layer. This prevents an unnecessary increase in the zirconium concentration in the fuel electrode, thereby suppressing a decrease in ionic conductivity due to the reaction between zirconium and cerium in the fuel electrode, and thereby suppressing a decrease in the performance of the electrochemical cell.

[0012] Furthermore, the electrochemical cell stack (1) according to this disclosure is formed by stacking electrochemical cells (311) having the above configuration. This makes it possible to provide an electrochemical cell stack with improved performance.

[0013] Furthermore, the hot module (6) according to this disclosure comprises an electrochemical cell stack (1) having the above configuration, 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 performance.

[0014] Furthermore, the electrolytic reactor (100) according to this disclosure includes a hot module (6) with the above configuration. This makes it possible to provide an electrolytic reactor equipped with an electrochemical cell with improved performance. An electrolytic reactor is a device in which an electrolysis reaction is carried out internally.

[0015] 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 the electrolytic cell cut in the thickness direction. Figure 7 is a diagram showing the distribution of mass concentrations of Ni, Ce, and Zr contained in the fuel electrode functional layer and its vicinity, along the thickness direction of the fuel electrode functional layer. Figure 7 is an enlarged view of part A in Figure 7.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 produced in the vaporizer 2, hydrogen for reduction, and air (Air) are introduced into the heat exchanger 3a. High-temperature hydrogen (H) produced in the electrochemical cell stack 1, which will be described later, is also introduced into the heat exchanger 3a. ２ ) and high-temperature oxygen (O ２ A heat exchanger is introduced. Then, in the heat exchanger 3a, these high-temperature gases are heated by exchanging heat with water vapor, reducing hydrogen, and air.

[0020] 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.

[0021] 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 into the heat exchanger 3a. These 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 these gases are then introduced into the heat exchanger 3a. These gases introduced into the heat exchanger 3a are used to heat the gas and air introduced from the vaporizer 2 into the heat exchanger 3a, and 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).

[0022] 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).

[0023] 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.

[0024] 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.

[0025] Each of the above-described components is formed in the shape of a rectangular plate with sides aligned in the width and depth directions. Furthermore, 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 (e.g., stainless steel). The upper insulating plate 20 and lower insulating plate 50 are plate-shaped components made of insulating material, such as mica or resin. Also, rectangular openings are formed in the central portions of the upper end plate 10 and upper insulating plate 20. Note that, for the sake of explanation, the proportions of each component in the drawings may differ from the actual proportions.

[0026] 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.

[0027] 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 via an upper insulating plate 20, a lower insulating plate 50, and a terminal plate 40.

[0028] 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.

[0029] 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, an air electrode layer 311b laminated on the upper surface (one side) of the solid electrolyte layer 311a, and a fuel electrode layer 311c laminated on the lower surface (the other side) of the solid electrolyte layer 311a. Furthermore, as shown in Figure 6, a reaction prevention layer 311d is formed between the solid electrolyte layer 311a and the air electrode layer 311b.

[0030] 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 contains YSZ (yttria-stabilized zirconia) as an ion-conducting oxide and is formed by sintering. Since YSZ contains Zr (zirconium), the solid electrolyte layer 311a contains Zr. 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.

[0031] 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 electron conductivity and collects electrons well in the current collector layer. The air electrode layer 311b is a porous layer and has many pores inside. Also, 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.

[0032] 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).

[0033] 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.

[0034] 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 the layer where the electrolytic reaction of water vapor mainly takes place. The fuel electrode substrate layer L2 is mainly a layer that supplies water vapor to the fuel electrode functional layer L1 and supports the electrolytic cell 311. 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. Note that if it is not a 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.

[0035] The main component of the fuel electrode substrate layer L2 is a cermet made of Ni and YSZ (yttria-stabilized zirconia). 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.

[0036] The main component of the fuel electrode functional layer L1 is a cermet of Ni and GDC (gadolinium-doped ceria). Like the fuel electrode substrate layer L2, the fuel electrode functional layer L1 is a porous layer containing multiple micropores (not shown). 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 fuel electrode functional layer L1 contains Zr (zirconium) in addition to Ni and GDC. GDC contains Ce (cerium). Therefore, the fuel electrode functional layer L1 contains Ni, Ce, and Zr.

[0037] 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 made of mica, for example. The plurality of conductors 312b are provided so as to cover the outer circumference of each elastic insulator 312a and may be made of metal foil, for example. 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] By stacking the cell cassettes 30 having the above configuration on a terminal plate 40, an electrochemical cell stack 1 is configured in which a plurality of electrochemical cell units 31 including an electrolytic cell 311 are stacked in the vertical direction. Further, a space between adjacent separators is partitioned by the separator section 32 (cell-side separator 321 and interconnector-side separator 322). As a result, inside the electrochemical cell stack 1, a plurality of fuel chambers Sf and air chambers Sa that mutually block gas flow therebetween are formed. Specifically, the fuel chamber Sf is formed by a 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. The air chamber Sa is formed by an 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. In the air chamber Sa, the air electrode layer 311b of the electrolytic cell 311 is exposed. Water vapor as fuel gas and hydrogen for reduction are supplied to the fuel chamber Sf. Air is supplied to the air chamber Sa.

[0043] Further, as shown in Fig. 3, the gas supply passage Pfi and the gas discharge passage Pfo are formed so as 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 via 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 via a lateral hole 331b formed in the fuel electrode frame 331 of each cell cassette 30.

[0044] Furthermore, the gas supply passage Pai and the gas discharge passage Pao are also formed so as to penetrate through 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 each in communication with the air chamber Sa via a lateral hole (not shown) formed in the air electrode frame 332 of each cell cassette 30.

[0045] Furthermore, the cell cassette 30 (30A) positioned at the top of the cell cassette group is a dummy cell cassette provided with a metal plate PL in place of the electrolytic cell 311. The fuel electrode frame 331 of this dummy cell cassette 30A functions as a terminal plate.

[0046] The operation of the electrochemical cell stack 1 will be described. First, a voltage is applied to the electrochemical cell stack 1. At this time, for example, the negative electrode of a power supply device 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. Subsequently, 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 lateral 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 via a lateral 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.

[0047] The water vapor and hydrogen for reduction that flow into the fuel chamber Sf flow from the front to the rear in the depth direction, as shown in Figure 3. The water vapor in the fuel chamber Sf comes into contact with 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. There, the water vapor reacts with electrons supplied via the interconnector 313 and the fuel electrode current collector 312, etc. in the fuel electrode functional layer L1. This decomposes the water vapor into hydrogen and oxide ions (water vapor electrolysis reaction). The hydrogen generated by the water vapor electrolysis reaction flows further to the rear in the depth direction within the fuel chamber Sf together with the unreacted water vapor and hydrogen for reduction, flows into the gas discharge passage Pfo through the lateral hole 331b, and is then discharged to the outside of the electrochemical cell stack 1 from the gas discharge passage Pfo. Meanwhile, oxide ions move via the solid electrolyte layer 311a to the air electrode layer 311b exposed to the air chamber Sa, where they release electrons in the functional layer of the air electrode layer 311b to become oxygen. The oxygen diffuses within the air chamber Sa and, together with the air flowing into the air chamber Sa, flows into the gas discharge passage Pao through a lateral hole (not shown), and is then discharged from the gas discharge passage Pao to the outside of the electrochemical cell stack 1.

[0048] Electrons emitted from the functional layer of the air electrode layer 311b are collected by the interconnector 313 via the current collector layer and then returned to the positive electrode of the power supply unit via the dummy cell cassette 30A.

[0049] Next, the solid electrolyte layer 311a and the fuel electrode functional layer L1 of the electrolytic cell 311 according to this embodiment will be described in detail. In this embodiment, the solid electrolyte layer 311a of the electrolytic cell 311 contains YSZ containing Zr, and the fuel electrode functional layer L1 contains Ni and GDC containing Ce. Since GDC has very good ionic conductivity, by using GDC as the ionic conductive oxide particles in the fuel electrode functional layer L1, an improvement in the performance of the electrolytic cell 311 can be expected.

[0050] However, since the GDC in the fuel electrode functional layer L1 is a different oxide from the YSZ in the solid electrolyte layer 311a, the difference in their thermal expansion coefficients (thermal contraction coefficients) may cause the solid electrolyte layer 311a and the fuel electrode layer 311c to delaminate or microcracks to occur at the contact interface during the manufacturing (sintering) of the electrolytic cell 311. If such delamination or microcracks occur, the ion conduction path between the solid electrolyte layer 311a and the fuel electrode layer 311c decreases, and the performance of the electrolytic cell 311 deteriorates.

[0051] In this regard, in this embodiment, in order to suppress delamination and the occurrence of microcracks caused by the difference in thermal expansion coefficient (difference in thermal contraction coefficient) between the solid electrolyte layer 311a and the fuel electrode functional layer L1, the fuel electrode functional layer L1 contains Zr (zirconium). Furthermore, the fuel electrode functional layer L1 has an intermediate layer in the region that is in contact with the solid electrolyte layer 311a, and is configured to contain a larger amount of zirconium in this intermediate layer.

[0052] As shown in Figure 6, the fuel electrode functional layer L1 and fuel electrode substrate layer L2 of the fuel electrode layer 311c are laminated on the solid electrolyte layer 311a in the order of fuel electrode functional layer L1 and fuel electrode substrate layer L2. The fuel electrode functional layer L1 is divided into a main layer L11 and an intermediate layer L12. The main layer L11 is the layer that makes up the majority of the fuel electrode functional layer L1, and its main components are Ni and GDC. The intermediate layer L12 is formed between the solid electrolyte layer 311a and the main layer L11, and is a layer that includes a region that contacts the solid electrolyte layer 311a. The main layer L11 and the intermediate layer L12 are laminated on the solid electrolyte layer 311a in the order of intermediate layer L12 and main layer L11. The main layer L11 and the intermediate layer L12 are distinguished by the relative mass concentrations of Ni, Zr, and Ce contained within them.

[0053] Figure 7 shows the distribution of mass concentrations (wt%) of Ni (nickel), Ce (cerium), and Zr (zirconium) contained in the fuel electrode functional layer L1 and its vicinity, along the thickness direction of the electrolytic cell 311. The horizontal axis of Figure 7 indicates the position in the thickness direction (thickness position). The thickness position shown on 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 7 represents the mass concentration (wt%). Graph G(Ni) in Figure 7 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 in a cross-section obtained by cutting the electrolytic cell 311 in the thickness direction using an EPMA (Electron Probe Micro Analyzer) device. Note that Ce is a rare earth element contained in GDC.

[0054] In Figure 7, 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 7, 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.

[0055] The fuel electrode functional layer L1 contains Ni, Ce, and Zr. The fuel electrode functional layer L1 is divided into a main layer L11 and an intermediate layer L12 along the thickness direction. The main components of the main layer L11 are Ni and GDC. Therefore, Ni and Ce are abundant in the main layer L11. Consequently, 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.

[0056] Since the main components of the fuel electrode substrate layer L2 are 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.

[0057] 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 7. Therefore, the region to the right of the fourth position in Figure 7 is the fuel electrode substrate layer L2.

[0058] Furthermore, the main component of the solid electrolyte layer 311a is 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.

[0059] The intermediate layer L12, located between the solid electrolyte layer 311a and the main body layer L11, 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 body layer L11 of the fuel electrode functional layer L1 (mass concentration of Ni > mass concentration of Ce > mass concentration of Zr).

[0060] Figure 8 is an enlarged view of the region indicated by part A in Figure 7, namely the intermediate layer L12 and its vicinity. As shown in Figure 8, the intermediate layer L12 is provided between the solid electrolyte layer 311a and the main layer L11 of the fuel electrode functional layer L1. 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.

[0061] 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 8. Therefore, the region to the left of the second position in Figure 8 is the solid electrolyte layer 311a.

[0062] 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 the same. This thickness position is the third position P3 in Figure 8. Consequently, the region from the second position P2 to the third position P3 in Figure 8 is the intermediate layer L12, and the region to the right of the third position P3 is the main layer L11.

[0063] Thus, the intermediate layer L12 is represented by the region from the second position P2 to the third position P3 in Figure 8. The thickness direction of this intermediate layer L12 coincides with the thickness direction of the electrolytic cell 311. Therefore, the distance from the second position P2 to the third position P3 represents the thickness of the intermediate layer L12. Furthermore, as shown in Figure 8, the intermediate layer L12 includes a region where the mass concentration of Zr increases and the mass concentration of Ni decreases as it moves toward 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 8.

[0064] When the mass concentration of Zr at the first position P1 is N(Zr) and the mass concentration of Ce is N(Ce), the ratio of the mass concentration N(Zr) to the mass concentration N(Ce) is defined as the Zr / Ce concentration ratio. In this embodiment, the Zr / Ce concentration ratio is expressed as R(Zr / Ce). In this embodiment, R(Zr / Ce) is greater than 1.8. In the example in Figure 8, R(Zr / Ce) is approximately 2.2 to 2.3.

[0065] A value of R(Zr / Ce) greater than 1.8 at the first position P1 indicates that there is more than 1.8 times the amount of Zr compared to Ce at a predetermined position (first position P1) in the intermediate layer L12. In other words, there is a large amount of Zr in the intermediate layer L12 that is in contact with the solid electrolyte layer 311a of the fuel electrode layer 311c. The Zr present in the intermediate layer L12 may be necking with the Zr present in the adjacent solid electrolyte layer 311a. Therefore, by having a large amount of Zr in the intermediate layer L12, the effect of improving the adhesion between the solid electrolyte layer 311a and the fuel electrode layer 311c due to Zr necking can be enhanced. This suppresses delamination of the fuel electrode layer 311c and the occurrence of microcracks at the contact interface between the solid electrolyte layer 311a and the fuel electrode layer 311c. By suppressing such delamination and the occurrence of microcracks, the reduction of ion conduction paths between the solid electrolyte layer 311a and the fuel electrode layer 311c is suppressed. By suppressing the reduction in ion conduction paths, the performance degradation of the electrolytic cell 311 is suppressed. Therefore, the effect of using GDC as the ion-conducting oxide in the fuel electrode functional layer L1 can be fully realized, and as a result, the performance of the electrochemical cell can be improved.

[0066] Furthermore, even in conventional technology where GDC is used as the ion-conducting oxide in the fuel electrode functional layer L1 and YSZ is used for the solid electrolyte layer, Zr diffuses to the fuel electrode functional layer side and Ce diffuses to the solid electrolyte layer side during manufacturing (sintering). Therefore, even in conventional electrolytic cells, an intermediate layer containing Zr can be formed in the region of the fuel electrode functional layer that is in contact with the solid electrolyte layer. However, since the amount of Zr diffused to the fuel electrode functional layer side by elemental diffusion alone is small, R(Zr / Ce) at the first position P1 is 1.8 or less. Therefore, the effect of improving adhesion by necking between Zr in the solid electrolyte layer and Zr in the fuel electrode functional layer is limited, and delamination and the occurrence of microcracks remain a concern. For this reason, the performance of the electrolytic cell cannot be sufficiently improved.

[0067] If R(Zr / Ce) is too large, adhesion improves, but the relative mass concentration of Ce in the intermediate layer L12 decreases. As a result, the effect of using GDC as the ion-conducting oxide in the fuel electrode functional layer L1 cannot be fully realized, and the performance of the electrolytic cell 311 cannot be sufficiently improved. Therefore, it is best if R(Zr / Ce) is not too large. Specifically, it is best if R(Ze / Ce) is less than 6.3.

[0068] From the above, in this embodiment, R(Zr / Ce) is greater than 1.8 and less than 6.3. When R(Zr / Ce) is within the above range, delamination and the occurrence of microcracks between the solid electrolyte layer 311a and the fuel electrode functional layer L1 can be sufficiently suppressed, and the effects of using GDC as the ion-conducting oxide in the fuel electrode functional layer L1 can be fully realized. Therefore, the performance of the electrolytic cell 311 comprising a solid electrolyte containing zirconium and a fuel electrode containing cerium can be improved.

[0069] Preferably, R(Zr / Ce) is 1.9 or more and 5.5 or less. When R(Zr / Ce) is within the above range, the performance of the electrolytic cell 311 can be further improved. Even more preferably, R(Zr / Ce) is 2.1 or more and 3.4 or less. When R(Zr / Ce) is within the above range, the performance of the electrolytic cell 311 can be further improved.

[0070] Furthermore, 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 8) 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 8), as shown in Figure 8. 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. The thickness of the intermediate layer L12 is preferably greater than 0.45 μm from the viewpoint of improving the adhesion between the solid electrolyte layer 311a and the fuel electrode layer 311c. However, if the intermediate layer L12 is too thick, the electrical resistance will increase and the performance of the electrolytic cell 311 will deteriorate. Therefore, the thickness of the intermediate layer L12 is preferably less than 1.62 μm from the viewpoint of improving the performance of the electrolytic cell 311. That is, the thickness of the intermediate layer L12 is greater than 0.45 μm and less than 1.62 μm. Preferably, the thickness of the intermediate layer L12 is 0.50 μm or more and 1.24 μm or less.

[0071] Furthermore, as shown in Figure 7, Zr is contained not only in the intermediate layer L12 but also in the main layer L11 of the fuel electrode functional layer L1. Therefore, Zr is present throughout the entire thickness of the fuel electrode functional layer L1. However, if the mass concentration of Zr contained in the fuel electrode functional layer L1 is too high, the effect of using GDC as the ion-conducting oxide of the fuel electrode functional layer L1 will be reduced. Also, if the mass concentration of Zr contained in the fuel electrode functional layer L1 is too high, there is a risk that the electrical resistance of the fuel electrode functional layer L1 will increase due to the products of the reaction between Zr and Ce. Therefore, it is preferable that the mass concentration of Zr contained in the fuel electrode functional layer L1 is not too high. Specifically, it is preferable that the mass concentration of Zr contained in the fuel electrode functional layer L1 be less than 4.60 wt%. Here, in this specification, the mass concentration of Zr contained in the fuel electrode functional layer L1 is defined as the mass concentration N(Zr0) of Zr at the midpoint in the thickness direction of the main layer L11, which accounts for the majority of the fuel electrode functional layer L1. The main body layer L11 is the region between the third position P3 and the fourth position P4, which are two points in Figure 7 where the mass concentration of Ce and the mass concentration of Zr coincide. Therefore, the midpoint is the fifth position P5, which is the midpoint between the third position P3 and the fourth position P4. Thus, the mass concentration of Zr at the fifth position P5 is, in this specification, the mass concentration N(Zr0) of Zr contained in the fuel electrode functional layer L1. It is preferable that this mass concentration N(Zr0) be less than 4.60 wt%.

[0072] The mass concentration N(ZrO) is preferably 3.48 wt% or less. More preferably, the mass concentration N(ZrO) is 2.35 wt% or less.

[0073] Furthermore, if the mass concentration of Zr N(Zr0) in the fuel electrode functional layer L1 is too low, the mass concentration of Zr in the intermediate layer L12 cannot be sufficiently increased. Therefore, it is preferable that the mass concentration of Zr N(Zr0) in the fuel electrode functional layer L1 is not too low. Specifically, it is preferable that N(Zr0) be greater than 0.32 wt%. Preferably, N(Zr0) is 1.33 wt% or more. Even more preferably, N(Zr0) is 2.33 wt% or more.

[0074] (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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] Subsequently, the laminate formed as described above was degreased at a predetermined temperature (for example, 200 to 300°C). Then, 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.

[0079] 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 a sample S1 of an electrolytic cell comprising a solid electrolyte layer, a fuel electrode layer laminated on the solid electrolyte layer so as to be in contact with one side of the solid electrolyte layer, and an air electrode layer laminated on the other side of the solid electrolyte layer via the reaction prevention layer.

[0080] [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.

[0081] [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.

[0082] [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.

[0083] [Preparation of Sample C1] Sample C1 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1330°C.

[0084] [Preparation of Sample C2] Sample C2 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1280°C.

[0085] [Preparation of Sample C3] Sample C3 was prepared under the same conditions as for Sample S1, except that the mixing ratio of GDC powder and YSZ powder was set to GDC powder:YSZ powder = 10:0 when forming the green sheet of the fuel electrode functional layer.

[0086] [Preparation of Sample C4] Sample C4 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1150°C.

[0087] [Preparation of Sample C5] Sample C5 was prepared under the same conditions as for Sample S3, except that the sintering temperature in the primary sintering was set to 1110°C.

[0088] [Preparation of Sample C6] Sample C6 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 = 6:4 when forming the green sheet of the fuel electrode functional layer.

[0089] [Preparation of Sample C7] Sample C7 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 = 1:9 when forming the green sheet of the fuel electrode functional layer.

[0090] [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.

[0091] 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 6.

[0092] [Identification of Positions P1, P2, P3, P4, and P5] 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, fourth position P4, and fifth position P5 were identified as shown in Figures 7 and 8. 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 in the region near the contact interface was identified as the second position, and the position where the mass concentration of Zr and the mass concentration of Ce are the same was identified as the third position P3. Furthermore, the position where the mass concentration of Zr and the mass concentration of Ce are the same in the region near the contact interface between the fuel electrode functional layer L1 and the fuel electrode substrate layer L2 was identified as the fourth position P4. Furthermore, the intermediate position in the thickness direction between the third position P3 and the fourth position P4 was identified as the fifth position P5.

[0093] [Identification of Solid Electrolyte Layer, Intermediate Layer, Fuel Electrode Functional Layer, and Fuel Electrode Substrate Layer] The region closer to the solid electrolyte layer than the second position P2 was identified as the solid electrolyte layer 311a, the region from the second position P2 to the third position P3 was identified as the intermediate layer L12, the region from the second position P2 to the fourth position P4 was identified as the fuel electrode functional layer L1, and the region further away from the solid electrolyte layer 311a than the fourth position P4 was identified as the fuel electrode substrate layer L2.

[0094] [Measurement of N(Zr) and N(Ce)] The mass concentration of Zr N(Zr) and Ce N(Ce) at the first position P1 were measured for each sample based on the mass concentration distribution graphs G(Zr) and G(Ce).

[0095] [Calculation of R(Zr / Ce)] For each sample, R(Zr / Ce) was calculated by dividing the measured N(Zr) by the measured N(Ce).

[0096] [Calculation of N(Zr+Ce)] The sum of the mass concentrations of Zr and Ce at the first position P1, N(Zr+Ce), was calculated by adding the measured N(Zr) and N(Ce) for each sample.

[0097] [Measurement of N(Zr0)] The mass concentration of Zr at position P5 was measured as the mass concentration of Zr contained in the fuel electrode layer (fuel electrode functional layer), N(Zr0).

[0098] [Measurement of the thickness T of the intermediate layer] The distance along the thickness direction between the second position P2 and the third position P3 was measured as the thickness T of the intermediate layer L12.

[0099] [Confirmation of the presence or absence of interfacial delamination] 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. Since the solid electrolyte layer is a dense layer and the fuel electrode layer is a porous layer, the contact interface between the two layers can be sufficiently identified by SEM images. If delamination of the contact interface was confirmed from the SEM image, it was determined that interfacial delamination was present; if it could not be confirmed, it was determined that there was no interfacial delamination.

[0100] [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. At this time, the voltage applied between the fuel electrode and the air electrode was measured as the initial electrolysis voltage V0. The measured initial electrolysis voltage V0 was used as an evaluation index for initial performance. A smaller initial electrolysis voltage V0 indicates better initial performance.

[0101] [Measurement Results] Table 1 shows the values ​​measured and calculated for each sample.

[0102] As can be seen from Table 1, no interfacial delamination was observed except for sample C5. Since sample C5 cracked during preparation, it was not possible to measure the concentrations of each element using EPMA or the electrolytic voltage. The reason for the cracking in sample C5 is presumed to be that the sintering temperature during the primary sintering was too low.

[0103] Furthermore, the initial electrolytic voltage V0 of samples S1 to S4 is 1.30V or less, while the initial electrolytic voltage V0 of samples C1 to C7 (excluding C5) is 1.38V or more. Here, the R(Zr / Ce) of samples S1 to S4 is greater than 1.8 and less than 6.3, and the thickness T of the intermediate layer L12 is greater than 0.45μm and less than 1.62μm. It is thought that the initial electrolytic voltage V0 is kept low and the initial performance is improved because the R(Zr / Ce) and the thickness T of the intermediate layer L12 are within the above ranges.

[0104] The ratio R(Zr / Ce) is preferably 1.9 or higher and 5.5 or lower, and more preferably 2.1 or higher and 3.4 or lower. When R(Zr / Ce) is within the above range, the performance of the electrolytic cell 311 can be further improved. The thickness T of the intermediate layer L12 is preferably 0.50 μm or higher and 1.24 μm or lower. When the thickness T is within the above range, the performance of the electrolytic cell 311 can be further improved.

[0105] Although the R(Zr / Ce) values ​​for samples C1 and C2 are both greater than 1.8 and less than 6.3, the thickness T of the intermediate layer L12 is 1.62 μm or greater in both cases. Therefore, it is thought that the electrical resistance of the intermediate layer L12 has increased, which in turn has resulted in a higher initial electrolysis voltage V0.

[0106] The R(Zr / Ce) values ​​for both samples C3 and C4 are 1.8 or less. Therefore, it is believed that the adhesion between the solid electrolyte layer and the fuel electrode layer could not be sufficiently improved, leading to the formation of microcracks and other issues, resulting in a high initial electrolysis voltage V0.

[0107] Although the thickness T of the intermediate layer L12 in samples C6 and C7 is greater than 0.45 μm and less than 1.62 μm, the R(Zr / Ce) ratio is 6.3 or higher in both cases. Therefore, it is thought that the GDC in the intermediate layer L12 is relatively low, reducing ionic conductivity and resulting in a high initial electrolysis voltage V0.

[0108] Furthermore, while the N(ZrO) content in samples S1 and S2 is less than 4.60 wt%, the N(ZrO) content in samples C6 and C7 is too high at 14.0 wt% or more. When the N(ZrO) content is too high, the frequency of reactions between Zr and Ce in the fuel electrode functional layer increases, leading to increased electrical resistance due to the generated reactants, which in turn increases the initial electrolysis voltage V0. Therefore, it is desirable for the N(ZrO) content to be less than 4.60 wt%.

[0109] Furthermore, N(ZrO) is preferably 3.5 wt% or less, and more preferably 2.35 wt% or less. Also, N(ZrO) is preferably greater than 0.32 wt%. More preferably, N(ZrO) is 1.33 wt% or more, and even more preferably, N(ZrO) is 2.33 wt% or more.

[0110] Furthermore, while the R(Zr / Ce) of samples S1 and S2 is 2.1 or greater and 3.4 or less, the R(Zr / Ce) of samples S3 and S4 is greater than 3.4. Here, the initial electrolysis voltage V0 of samples S1 and S2 is smaller than the initial electrolysis voltage V0 of samples S3 and S4. Therefore, it is more preferable that R(Zr / Ce) is 2.1 or greater and 3.4 or less.

[0111] Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the above 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 assuming that the entire fuel electrode is a fuel electrode functional layer. Furthermore, if there is no fuel electrode substrate layer, there is no boundary position between the fuel electrode functional layer and the fuel electrode substrate layer (the fourth position in Figure 7), so the fifth position P5 cannot be identified by the method shown in the above embodiments, and therefore the mass concentration N(Zr0) of Zr contained in the fuel electrode layer cannot be identified. In this case, the fifth position P5 can be identified as an intermediate position between the third position P3 and the thickness position corresponding to the end of the fuel electrode layer opposite to the solid electrolyte layer. The mass concentration of Zr at the fifth position P5 identified in this way can be determined as the mass concentration N(Zr0) of Zr contained in the fuel electrode layer.

[0112] 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.

[0113] Furthermore, this disclosure may include the following embodiments: [1] An electrochemical cell comprising: a solid electrolyte containing zirconium; a fuel electrode in contact with the solid electrolyte; and an air electrode, wherein the fuel electrode contains nickel, cerium, and zirconium, and has an intermediate layer in a region in contact with the solid electrolyte in which the mass concentration of zirconium increases and the mass concentration of nickel decreases as it moves toward the solid electrolyte side along the thickness direction, and when the position in the thickness direction of the intermediate layer in which the mass concentration of zirconium and the mass concentration of nickel are equal is taken as the first position, the thickness of the intermediate layer is expressed as the sum of the distance from the first position toward the solid electrolyte side along the thickness direction of the intermediate layer in which the mass concentration of nickel and the mass concentration of cerium are equal, and the distance from the first position toward the fuel electrode side along the thickness direction of the intermediate layer in which the mass concentration of zirconium and the mass concentration of cerium are equal, and the thickness of the intermediate layer is greater than 0.45 μm and less than 1.62 μm. [1] An electrochemical cell wherein the Zr / Ce concentration ratio, which is the ratio of the mass concentration of zirconium to the mass concentration of cerium at the first position, is greater than 1.8 and less than 6.3. [2] An electrochemical cell according to [1], wherein the Zr / Ce concentration ratio at the first position is 2.1 or greater and 3.4 or less. [3] An electrochemical cell according to [1] or [2], wherein the mass concentration of zirconium in the fuel electrode is less than 4.60 wt%. [4] An electrochemical cell stack comprising an electrochemical cell according to any one of [1] to [3] stacked on top of each other. [5] A hot module comprising the electrochemical cell stack according to [4], 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 disposed inside. [6] An electrolytic reaction apparatus comprising the hot module according to [5].

[0114] 1... Electrochemical cell stack, 2... Vaporizer, 3... Heating device, 4... Insulation material, 6... Hot module, 7... Condenser, 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, 100... Hydrogen production device (electrolytic reaction device), P1... 1st position, P2... 2nd position, P3... 3rd position, P4... 4th position, P5... 5th position

Claims

1. An electrochemical cell comprising: a solid electrolyte containing zirconium; a fuel electrode in contact with the solid electrolyte; and an air electrode, wherein the fuel electrode contains nickel, cerium, and zirconium, and has an intermediate layer in a region in contact with the solid electrolyte where the mass concentration of zirconium increases and the mass concentration of nickel decreases as it moves toward the solid electrolyte side along the thickness direction, and the thickness of the intermediate layer is 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 zirconium and the mass concentration of nickel 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, and the thickness of the intermediate layer is greater than 0.45 μm and less than 1.62 μm. An electrochemical cell in which the Zr / Ce concentration ratio, which is the ratio of the mass concentration of zirconium to the mass concentration of cerium at the first position, is greater than 1.8 and less than 6.

3.

2. An electrochemical cell according to claim 1, wherein the Zr / Ce concentration ratio at the first position is 2.1 or greater and 3.4 or less.

3. An electrochemical cell according to claim 1, wherein the mass concentration of zirconium in the fuel electrode is less than 4.60 wt%.

4. An electrochemical cell stack comprising an electrochemical cell according to any one of claims 1 to 3.

5. A hot module comprising: an electrochemical cell stack according to claim 4; 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.

6. An electrolytic reaction apparatus comprising the hot module described in claim 5.

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