Electrochemical cell stacks, hot modules, and electrolytic reactors

Abstract

The present invention provides an electrochemical cell stack that can suppress internal temperature inhomogeneity. [Solution] The electrochemical cell stack 20A comprises a conductive central plate 22, a first cell cassette group 24A stacked on one side of the central plate 22, and a second cell cassette group 25A stacked on the other side. The first cell cassette group 24A and the second cell cassette group 25A are arranged symmetrically across the central plate 22 such that an interconnector 113, which is stacked on the electrochemical cell 111 closest to the central plate 22, is in contact with the central plate 22, and the air electrode layer of the electrochemical cell 111 furthest from the central plate 22 is electrically connected to the first terminal 241 or the second terminal 251.

Description

Technical Field

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

Background Art

[0002] A solid oxide type electrolysis cell (SOEC) is an electrochemical cell that generates gases such as hydrogen and carbon monoxide by performing an electrolysis reaction of water vapor using a solid oxide type electrolyte having oxide ion conductivity. When generating a gas using an SOEC, in practice, an electrochemical cell stack formed by laminating a plurality of cell cassettes having a reaction part including an SOEC, a frame part arranged around the reaction part, and a separator part connecting the reaction part and the frame part is used. Patent Document 1 discloses an electrochemical cell stack formed by laminating a plurality of cell cassettes.

[0003] Since the electrolysis voltage of water decreases as the temperature of water increases, the higher the temperature of the electrochemical cell stack, the lower the energy required for the electrolysis reaction of water. Therefore, for each SOEC of the electrochemical cell stack, for example, a gas (water vapor and air) heated to 700 to 800°C is supplied.

[0004] By the way, the electrolysis reaction of water is an endothermic reaction. Therefore, a part of the heat received by each SOEC of the electrochemical cell stack from the gas and the outside (specifically, other members in contact with the electrochemical cell or the gas in the space where the electrochemical cell is arranged) is taken away by the electrolysis reaction of water. Since heat is difficult to transfer to the central part of the electrochemical cell stack, the temperature may be lower than that of the outer peripheral part. When the temperature of the central part of the electrochemical cell stack decreases, the efficiency of the electrolysis reaction of water decreases. Therefore, in order to improve (or suppress the decrease) in the efficiency of the electrolysis reaction of water, it is required to prevent or suppress the temperature of the electrochemical cell stack from becoming non-uniform (particularly, to prevent or suppress the temperature decrease of the central part).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-34249 [Overview of the Initiative]

[0006] This disclosure aims to solve the problems described above. Specifically, one of the objectives of this disclosure is to provide an electrochemical cell stack that can prevent or suppress temperature non-uniformity between the interior (center) and the outer periphery, a hot module including the electrochemical cell stack, and an electrolytic reaction apparatus including the hot module.

[0007] To solve the above problems, the electrochemical cell stack relating to this disclosure is A terminal configured to exchange power with the outside is provided, and the device has a first surface and a second surface opposite to the first surface, and includes a conductive central plate, A group of first cell cassettes stacked on the side of the first surface of the central plate, A group of second cell cassettes stacked on the side of the second surface of the central plate, A first terminal is located on the opposite side of the central plate of the first cell cassette group and is configured to be able to exchange power with the outside, A second terminal is located on the opposite side of the central plate of the second cell cassette group and is configured to be able to exchange power with the outside, Equipped with, The first cell cassette group and the second cell cassette group each comprise a plurality of cell cassettes arranged in a stack, The plurality of stacked cell cassettes include an electrochemical cell which is a solid oxide type electrolytic cell or a reversible solid oxide type fuel cell-steam electrolytic cell comprising a solid oxide type electrolyte layer, an air electrode layer stacked on one side of the electrolyte layer, and a fuel electrode layer stacked on the side of the electrolyte layer opposite to the air electrode layer; an electrochemical cell cassette which comprises a current collector stacked on the side of the fuel electrode layer opposite to the electrolyte layer, and an interconnector stacked on the side of the current collector opposite to the fuel electrode layer; and a cover cell cassette which is located furthest from the central plate and has a conductive cover member in place of the electrochemical cell. The first cell cassette group and the second cell cassette group are arranged symmetrically on either side of the central plate, such that the fuel electrode layer of the electrochemical cell is located closer to the central plate than the electrolyte layer. The interconnector, which is stacked on the electrochemical cell closest to the central plate of the first cell cassette group, is in contact with the first surface of the central plate, and the cover cell cassette is in contact with or includes the first terminal. The interconnector, which is stacked on the electrochemical cell closest to the central plate in the second cell cassette group, is in contact with the second surface of the central plate, and the cover cell cassette is in contact with or includes the second terminal.

[0008] Furthermore, the electrochemical cell stack related to this disclosure is A terminal configured to exchange power with the outside is provided, and the device has a first surface and a second surface opposite to the first surface, and includes a conductive central plate, A group of first cell cassettes stacked on the side of the first surface of the central plate, A group of second cell cassettes stacked on the side of the second surface of the central plate, A first terminal is located on the opposite side of the central plate of the first cell cassette group and is configured to be able to exchange power with the outside, A second terminal is located on the opposite side of the central plate of the second cell cassette group and is configured to be able to exchange power with the outside, Equipped with, The first cell cassette group and the second cell cassette group each comprise a plurality of cell cassettes arranged in a stack, The plurality of stacked cell cassettes include an electrochemical cell which is a solid oxide type electrolytic cell or a reversible solid oxide type fuel cell-steam electrolytic cell comprising a solid oxide type electrolyte layer, an air electrode layer stacked on one side of the electrolyte layer, and a fuel electrode layer stacked on the side of the electrolyte layer opposite to the air electrode layer; an electrochemical cell cassette which comprises a current collector stacked on the side of the fuel electrode layer opposite to the electrolyte layer, and an interconnector stacked on the side of the current collector opposite to the fuel electrode layer; and a cover cell cassette which is located furthest from the central plate and has a conductive cover member in place of the electrochemical cell. The first cell cassette group and the second cell cassette group are arranged symmetrically on either side of the central plate, such that the air electrode layer of the electrochemical cell is located closer to the central plate than the electrolyte layer. The air electrode layer of the electrochemical cell closest to the central plate in the first cell cassette group is in contact with the first surface of the central plate, and the cover cell cassette is in contact with or includes the first terminal. The air electrode layer of the electrochemical cell closest to the central plate in the second cell cassette group is in contact with the second surface of the central plate, and the cover cell cassette is in contact with or includes the second terminal.

[0009] According to this disclosure, it is possible to prevent or suppress temperature non-uniformity between the inside (center) and the outer periphery of the electrochemical cell stack. That is, since heat is transferred from the outside to the inside (center) of the electrochemical cell stack via the central plate, it is possible to prevent or suppress the temperature drop inside the electrochemical cell stack due to endothermic reactions during operation. Therefore, it is possible to prevent or suppress temperature non-uniformity between the inside (center) and the outer periphery of the electrochemical cell stack. [Brief explanation of the drawing]

[0010] [Figure 1] It is a block diagram of a hydrogen production device. [Figure 2] It is a perspective view showing a schematic configuration of an electrochemical cell stack according to the first embodiment. [Figure 3] It is a top view showing a schematic configuration of an electrochemical cell stack according to the first embodiment. [Figure 4] It is a sectional view taken along line IV-IV of FIG. 3. [Figure 5] It is a sectional view of a cell cassette. [Figure 6] It is a sectional view taken along line VI-VI of FIG. 3. [Figure 7] It is a sectional view showing a schematic configuration of an electrochemical cell stack according to the second embodiment. [Figure 8] It is a schematic sectional view of a conventional electrochemical cell stack. [Figure 9] It is a view showing a state in which cell cassettes of a conventional electrochemical cell stack are stacked on plates. [Figure 10] It is a view showing a state in which cell cassettes of a conventional electrochemical cell stack are stacked on plates and then fastened.

Mode for Carrying Out the Invention

[0011] <First Embodiment> FIG. 1 is a block diagram of a hydrogen production device 1 as an electrolysis reaction device according to the present disclosure. The hydrogen production device 1 is a device that produces hydrogen by electrolyzing water vapor. As shown in FIG. 1, the hydrogen production device 1 includes a hot module 10 and a condenser 90.

[0012] The hot module 10 is configured by covering main components that become high temperature among the components constituting the hydrogen production device 1 as an electrolysis reaction device with a heat insulating material 60, and is a device in which the main components are aggregated in the heat insulating material so that the high temperature state of the main components is maintained. This hot module 10 includes an electrochemical cell stack 20A, a vaporizer 30, a heat exchanger 40, a heater 50, and a heat insulating material 60.

[0013] As shown in FIG. 1, water (H2O) is supplied to the vaporizer 30. The vaporizer 30 is configured to heat the supplied water to a temperature of 100° C. or higher by a heating source (not shown). Then, the water supplied to the vaporizer 30 evaporates in the vaporizer 30 to generate water vapor. The water vapor generated in the vaporizer 30 is supplied to the heat exchanger 40.

[0014] In addition to the above-described water vapor, air is supplied to the heat exchanger 40. Further, high-temperature hydrogen (H2) and high-temperature oxygen (O2) generated in the electrochemical cell stack 20A are supplied to the heat exchanger 40. Then, these high-temperature gases exchange heat with water vapor and air in the heat exchanger 40, so that the water vapor and air supplied from the vaporizer 30 to the heat exchanger 40 are heated (temperature increased).

[0015] The water vapor and air heated in the heat exchanger 40 are further heated (temperature increased) to the operating temperature of the electrochemical cell stack 20A (that is, the temperature required to operate the electrochemical cell stack 20A. For example, 700 to 800° C.) by the heater 50. Then, the water vapor and air are supplied to the electrochemical cell stack 20A. Note that the heat exchanger 40 and the heater 50 are temperature increasing devices for increasing the temperature of the gas (water vapor and air) supplied to the electrochemical cell stack 20A to the operating temperature of the electrochemical cell stack 20A.

[0016] The electrochemical cell stack 20A is heated to the operating temperature by a heating source (such as a burner) not shown. Further, a predetermined voltage is applied to the electrochemical cell stack 20A from a power source (not shown). Then, the water vapor supplied to the electrochemical cell stack 20A is electrolyzed to generate hydrogen and oxygen. The details of the configuration of the electrochemical cell stack 20A will be described later.

[0017] The hydrogen produced in the electrochemical cell stack 20A is supplied to the heat exchanger 40 along with unreacted water vapor, and after being used to heat the water vapor and air supplied from the vaporizer 30 to the heat exchanger 40, it is introduced to the condenser 90. In the condenser 90, the unreacted water vapor is condensed. The condensed water produced in the condenser 90 is supplied to the vaporizer 30. Meanwhile, the hydrogen separated by the condensation of water vapor in the condenser 90 is recovered. In addition, the oxygen produced in the electrochemical cell stack 20A is supplied to the heat exchanger 40, and after being used to heat the water vapor and air, it is supplied to the vaporizer 30, where it heats the water supplied to the vaporizer 30. The oxygen discharged from the vaporizer 30 is then recovered or released into the atmosphere.

[0018] The electrochemical cell stack 20A, vaporizer 30, heat exchanger 40, and heater 50 are placed inside the insulation material 60. This suppresses heat dissipation from each component 20A, 30, 40, and 50. The insulation material 60 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 20A, vaporizer 30, heat exchanger 40, and heater 50.

[0019] Figure 2 is a perspective view showing the schematic configuration of the electrochemical cell stack 20A according to the first embodiment. In Figure 2, the upper side of the electrochemical cell stack 20A is indicated by the arrow Up, and the lower side is indicated by the arrow Dw (the same applies to other figures). The electrochemical cell stack 20A includes an upper end plate 21, a central plate 22, a lower end plate 23, a first cell cassette group 24A, and a second cell cassette group 25A. As shown in Figure 2, the electrochemical cell stack 20A is formed in a substantially rectangular parallelepiped shape.

[0020] The upper end plate 21 and the lower end plate 23 are spaced apart in the vertical direction (plate thickness direction). The upper end plate 21 is positioned at the top of the rectangular parallelepiped electrochemical cell stack 20A. The lower end plate 23 is positioned at the bottom of the electrochemical cell stack 20A. Both the upper end plate 21 and the lower end plate 23 are approximately quadrilateral flat plate members, positioned with their plate thickness direction approximately parallel to the vertical direction, and exhibiting approximately the same external shape and dimensions when viewed in the vertical direction.

[0021] The central plate 22 is a flat plate-shaped member. The central plate 22 is positioned at an intermediate vertical position between the upper end plate 21 and the lower end plate 23. The central plate 22 is positioned so that its thickness direction is substantially parallel to the vertical direction. The central plate 22 is provided with a central terminal 225 that allows for the exchange of power with the outside. The central plate 22 is made of a material that is conductive and has high thermal conductivity. Furthermore, it is preferable that the central plate 22 has substantially the same coefficient of thermal expansion as the interconnector 113, which will be described later. For this reason, for example, a configuration in which the central plate 22 is made of the same material (metal material) as the interconnector 113 can be applied.

[0022] The first cell cassette group 24A and the second cell cassette group 25A are both laminates formed by stacking multiple substantially flat cell cassettes 100. The stacking direction of the multiple cell cassettes 100 constituting the first cell cassette group 24A and the stacking direction of the multiple cell cassettes 100 constituting the second cell cassette group 25A coincide with the thickness direction of the upper end plate 21, the central plate 22, and the lower end plate 23. Therefore, the first cell cassette group 24A is composed of multiple cell cassettes 100 stacked in the thickness direction from the upper surface of the central plate 22 toward the upper end plate 21. Similarly, the second cell cassette group 25A is composed of multiple cell cassettes 100 stacked in the thickness direction from the lower surface of the central plate 22 toward the lower end plate 23.

[0023] Of the multiple cell cassettes 100 included in the first cell cassette group 24A, all cell cassettes 100 other than the one located at the top (i.e., the furthest from the central plate 22) are normal cell cassettes 101. Of the multiple cell cassettes 100 included in the second cell cassette group 25A, all cell cassettes 100 other than the one located at the bottom (i.e., the furthest from the central plate 22) are also normal cell cassettes 101. A normal cell cassette 101 is an example of the electrochemical cell cassette of the present invention. A normal cell cassette 101 comprises an electrolytic cell 111 and a frame portion 120 configured to surround the electrolytic cell 111.

[0024] Of the multiple cell cassettes 100 included in the first cell cassette group 24A, the cell cassette 100 located at the top (i.e., the position furthest from the central plate 22) is a dummy cell cassette 102. Of the multiple cell cassettes 100 included in the second cell cassette group 25A, the cell cassette 100 located at the bottom (i.e., the position furthest from the central plate 22) is also a dummy cell cassette 102. The dummy cell cassette 102 is an example of a cover cell cassette of the present invention. The dummy cell cassette 102 has a configuration in which the electrolytic cells 111 of a normal cell cassette 101 are replaced with a metal plate 133 (see Figure 4). The metal plate 133 of the dummy cell cassette 102 (cover cell cassette) is an example of a cover member of the present invention. Thus, the multiple cell cassettes 100 included in the first cell cassette group 24A and the multiple cell cassettes 100 included in the second cell cassette group 25A each include multiple normal cell cassettes 101 and one dummy cell cassette 102 located furthest from the central plate 22.

[0025] The first cell cassette group 24A is positioned between the upper end plate 21 and the central plate 22. The second cell cassette group 25A is positioned between the lower end plate 23 and the central plate 22. Both the first cell cassette group 24A and the second cell cassette group 25A are positioned such that the dummy cell cassette 102 is located as far away from the central plate 22 as possible. In other words, the first cell cassette group 24A and the second cell cassette group 25A are positioned symmetrically across the central plate 22 such that the dummy cell cassette 102 is located on the upper end plate 21 and the lower end plate 23, respectively (or they are positioned mirror-symmetrically with respect to the central plate 22).

[0026] At least a portion of the central plate 22 is exposed to the outside of the electrochemical cell stack 20A (or it can be said that it is exposed to the outer surface of the electrochemical cell stack 20A). The central plate 22 is provided with a central terminal 225 that is electrically conductive with the central plate 22. The terminal plate TP (described later) of the dummy cell cassette 102 of the first cell cassette group 24A is provided with an upper terminal 241 that is electrically conductive with the terminal plate TP. The upper terminal 241 is an example of the first terminal of the present invention. The terminal plate TP (described later) of the dummy cell cassette 102 of the second cell cassette group 25A is provided with a lower terminal 251 that is electrically conductive with the terminal plate TP. The lower terminal 251 is an example of the second terminal of the present invention.

[0027] The central terminal 225 may be integrally provided with the central plate 22 (i.e., the central terminal 225 is part of the central plate 22), or it may be a separate component from the central plate 22. The configuration in which the central terminal 225 is integrally provided with the central plate 22 can also be described as "the central plate 22 includes the central terminal 225." Furthermore, if the central terminal 225 is a separate component from the central plate 22, the central terminal 225 is in contact with the central plate 22 so as to be electrically conductive. Similarly, the upper terminal 241 and the lower terminal 251 may each be integrally provided with the terminal plate TP, or they may be separate components from the terminal plate TP. The configuration in which the upper terminal 241 and the lower terminal 251 are integrally provided with the terminal plate TP can also be described as "the dummy cell cassette 102 of the first cell cassette group 24A includes the upper terminal 241," and "the dummy cell cassette 102 of the second cell cassette group 25A includes the lower terminal 251." Furthermore, if the upper terminal 241 and the lower terminal 251 are separate components from the terminal plate TP, the upper terminal 241 and the lower terminal 251 are in contact with the terminal plate TP of the dummy cell cassette 102 so as to be electrically conductive.

[0028] The central terminal 225 is connected to the negative terminal of the power supply. The upper terminal 241 and lower terminal 251 are connected in parallel to the positive terminal of the power supply. As a result, the water vapor supplied to the electrochemical cell stack 20A is electrolyzed to produce hydrogen and oxygen.

[0029] The upper end plate 21 and the lower end plate 23 each have a quadrilateral opening of the same shape in their central portions when viewed in the vertical direction. The central plate 22 is also a roughly quadrilateral flat plate member. However, the central plate 22 differs from the upper end plate 21 and the lower end plate 23 in that it does not have an opening in its central portion. The plate thicknesses of the upper end plate 21, the central plate 22, and the lower end plate 23 may be the same or different. Furthermore, the outer shapes of the upper end plate 21, the central plate 22, and the lower end plate 23 when viewed in the vertical direction may be different from each other.

[0030] In the upper end plate 21 and the multiple cell cassettes 100 constituting the first cell cassette group 24A, through holes are formed coaxially at their four corners, penetrating them in the thickness direction. These through holes are connected in the thickness direction to form the first bolt insertion hole 261. The first fastening bolt BT1 is inserted through the first bolt insertion hole 261. Similarly, in the lower end plate 23 and the multiple cell cassettes 100 constituting the second cell cassette group 25A, through holes are formed coaxially at their four corners, penetrating them in the thickness direction. These through holes are connected in the thickness direction to form the second bolt insertion hole 262. The second fastening bolt BT2 is inserted through the second bolt insertion hole 262.

[0031] Furthermore, the multiple cell cassettes 100 constituting the first cell cassette group 24A and the second cell cassette group 25A, the central plate 22, and the lower end plate 23 have two gas supply passages Pfi, Pai and two gas discharge passages Pfo, Pao that penetrate in a direction substantially parallel to the stacking direction. As shown in Figure 2, 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 20A. 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. 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 supplied to the electrochemical cell stack 20A passes, and the gas supply passage Pai forms a passage through which air supplied to the electrochemical cell stack 20A passes. Gas discharge passage Pfo forms a passage through which hydrogen and water vapor discharged from the electrochemical cell stack 20A passes, and gas discharge passage Pao forms a passage through which oxygen and air discharged from the electrochemical cell stack 20A passes.

[0032] Figure 3 is a top view showing the schematic configuration of the electrochemical cell stack 20A. An opening for the first bolt insertion hole 261 is formed on the upper surface of the upper end plate 21 shown in Figure 3, and the bolt head of the first fastening bolt BT1, which is inserted through the first bolt insertion hole 261, is positioned on this surface. An opening for the second bolt insertion hole 262 is formed on the lower surface of the lower end plate 23 of the electrochemical cell stack 20A, and the bolt head of the second fastening bolt BT2, which is inserted through the second bolt insertion hole 262, is positioned on this surface.

[0033] Figure 4 is a schematic cross-sectional view of the line IV-IV in Figure 3. More specifically, Figure 4 is a schematic cross-sectional view of the electrochemical cell stack 20A cut so that the cross-sections of the first bolt insertion hole 261 and the second bolt insertion hole 262 are visible. As shown in Figure 4, the central plate 22 has an upper surface 221 (first surface) and a lower surface 222 (second surface) opposite to the upper surface 221. A first cell cassette group 24A, consisting of multiple stacked cell cassettes 100, is arranged on the upper surface 221 side of the central plate 22. A second cell cassette group 25A, consisting of multiple stacked cell cassettes 100, is arranged on the lower surface 222 side of the central plate 22. An upper end plate 21 is arranged above the first cell cassette group 24A, and a lower end plate 23 is arranged below the second cell cassette group 25A.

[0034] Figure 4 shows an example in which the first cell cassette group 24A and the second cell cassette group 25A are each composed of stacks of three cell cassettes 100. However, the first cell cassette group 24A and the second cell cassette group 25A can be composed of stacks of more than three cell cassettes 100. For example, the first cell cassette group 24A and the second cell cassette group 25A can each be composed of stacks of 50 cell cassettes. Furthermore, the number of stacks of cell cassettes 100 constituting the first cell cassette group 24A and the number of stacks of cell cassettes 100 constituting the second cell cassette group 25A may be different, but in this embodiment, the number of stacks of cell cassettes 100 constituting the first cell cassette group 24A and the number of stacks of cell cassettes 100 constituting the second cell cassette group 25A are the same.

[0035] Figure 5 is a schematic cross-sectional view of the cell cassette 100 (normal cell cassette 101) shown in Figure 4. The cell cassette 100 shown in Figure 5 is shown in the same orientation as the cell cassette 100 that constitutes the first cell cassette group 24A shown in Figure 4. The orientation of the cell cassette 100 that constitutes the second cell cassette group 25A is the same as the orientation of the cell cassette 100 shown in Figure 5 rotated 180° vertically. Therefore, the cell cassette 100 that constitutes the second cell cassette group 25A has a configuration in which the direction described using Figure 5 is reversed below.

[0036] As shown in Figure 5, the cell cassette 100 comprises a reaction section 110, a frame section 120, and a separator section 130. The reaction section 110 includes a solid oxide type electrolytic cell 111 (hereinafter referred to as the electrolytic cell). Specifically, the reaction section 110 includes the electrolytic cell 111, a current collector 112, and an interconnector 113. The electrolytic cell 111 may be a reversible solid oxide type fuel cell-steam electrolytic cell.

[0037] In this embodiment, the electrolytic cell 111 is a substantially quadrilateral plate-shaped member. The electrolytic cell 111 comprises a solid electrolyte layer 111a, a fuel electrode layer 111c arranged on one side thereof, and an air electrode layer 111b arranged on the other side, and is formed by stacking these in the thickness direction of the electrolytic cell 111. The air electrode layer 111b has smaller external dimensions than the solid electrolyte layer 111a and the fuel electrode layer 111c when viewed in the vertical direction, and is positioned in the center of the upper surface of the solid electrolyte layer 111a when viewed in the vertical direction of the electrolytic cell 111. For this reason, the upper surface of the outer periphery of the solid electrolyte layer 111a is exposed.

[0038] The solid electrolyte layer 111a is a layer made of a solid oxide electrolyte. The solid electrolyte layer 111a is a roughly quadrilateral, flat layer, and is constructed to contain YSZ (yttria-stabilized zirconia) and formed by sintering. The solid electrolyte layer 111a has high oxide ion conductivity. The solid electrolyte layer 111a is a dense layer and is designed so that the atmosphere on the air electrode layer 111b side (atmospheric atmosphere) and the atmosphere on the fuel electrode layer 111c side (reducing atmosphere) do not leak from each other through the solid electrolyte layer 111a.

[0039] The air electrode layer 111b is also a roughly quadrilateral, flat layer, composed of perovskite-type oxides such as LSCF (lanthanum strontium cobalt iron oxide), and is formed by sintering. The air electrode layer 111b has a functional layer and a current collector layer. The current collector layer is thicker than the functional layer and is positioned on the upper surface of the functional layer. The air electrode layer 111b has high electron conductivity and collects electrons well in the current collector layer. This air electrode layer 111b is a porous layer and has pores inside.

[0040] The fuel electrode layer 111c is also a roughly quadrilateral, flat layer. The fuel electrode layer 111c is molded to be thicker than the solid electrolyte layer 111a and the air electrode layer 111b. The fuel electrode layer 111c supports the solid electrolyte layer 111a and the air electrode layer 111b. In other words, the electrolytic cell 111 is a fuel electrode-supported electrochemical cell. The external shape of the fuel electrode layer 111c in a vertical view matches the external shape of the solid electrolyte layer 111a. The fuel electrode layer 111c also has a fuel electrode functional layer and a fuel electrode support layer. The thickness of the fuel electrode support layer is formed to be significantly thicker than that of the fuel electrode functional layer, and the ratio can be set to, for example, about 16 to 40 times. The fuel electrode functional layer and the fuel electrode support layer are stacked on the lower surface of the solid electrolyte layer 111a, in the order of fuel electrode functional layer, followed by fuel electrode support layer.

[0041] The main component of the fuel electrode support layer is a cermet of Ni and YSZ (yttria-stabilized zirconia). The fuel electrode support layer is a porous layer configured to be porous, containing multiple micropores (not shown). The diameter of the micropores is on the order of several μm, which ensures water vapor permeability (gas diffusion). The main component of the fuel electrode functional layer is also a cermet of Ni and YSZ. The fuel electrode functional layer is a porous layer configured to be porous, containing multiple micropores (not shown), similar to the fuel electrode support layer. The fuel electrode functional layer is formed more densely than the fuel electrode support layer. That is, the fuel electrode functional layer and the fuel electrode support layer are formed such that the porosity of the fuel electrode functional layer is smaller than that of the fuel electrode support layer. The fuel electrode layer 111c is also formed by sintering, similar to the solid electrolyte layer 111a and the air electrode layer 111b. Note that the components of the fuel electrode functional layer and the fuel electrode support layer are not limited to those described above. For example, the main components of the fuel electrode functional layer can be composed of Ni and GDC (gadolinia-doped ceria).

[0042] The current collector 112 is positioned below the electrolytic cell 111 and above the interconnector 113. That is, the current collector 112 is positioned between the electrolytic cell 111 and the interconnector 113. The current collector 112 includes a plurality of insulators 112a and a plurality of conductors 112b. The insulators 112a have a long, rod-like shape in the direction perpendicular to the plane of the paper in Figure 5, and can be made of, for example, mica. The plurality of insulators 112a are arranged parallel to each other at equal intervals. The insulators 112a are configured to exert a predetermined elastic force.

[0043] The conductor 112b is formed in a sheet-like shape so as to surround the outer circumference of each insulator 112a. For example, nickel material can be used as the conductor 112b. A conductor 112b is provided for each insulator 112a, so that the outer circumference of all insulators 112a is covered by the conductor 112b. As can be seen from Figure 5, each conductor 112b, in the portion that covers the upper surface of the insulator 112a, is in contact with the fuel electrode layer 111c of the electrolytic cell 111 located directly above it.

[0044] The interconnector 113 is a metal (for example, stainless steel) component and has a roughly quadrilateral flat body portion 113a and a projection portion 113b that protrudes downward from the lower surface of the body portion 113a. The projection portion 113b is formed by a plurality of protrusions that extend in a direction parallel to the plane of the paper in Figures 4 and 5 and are arranged in a direction perpendicular to the plane of the paper. These protrusions are formed in a downward convex shape, extending from left to right in Figure 5.

[0045] Furthermore, as can be seen in Figure 4, the portion of the conductor 112b of the current collector 112 that covers the lower surface of the insulator 112a contacts the upper surface of the main body 113a of the interconnector 113. The protruding portion 113b of the interconnector 113 contacts the air electrode layer 111b of the electrolytic cell 111 of the adjacent cell cassette 100, as shown in Figure 4. The interconnector 113 functions as an inter-cell connecting member that electrically connects adjacent electrolytic cells 111, 111. The protruding portion 113b of the interconnector 113 of the cell cassette 100 adjacent to the central plate 22 among the cell cassettes 100 constituting the first cell cassette group 24A contacts the upper surface 221 of the central plate 22. Similarly, the protruding portion 113b of the interconnector 113 of the cell cassette 100 adjacent to the central plate 22 among the cell cassettes 100 constituting the second cell cassette group 25A contacts the lower surface 222 of the central plate 22.

[0046] The frame portion 120 includes a fuel electrode frame 121 and an air electrode frame 122. The fuel electrode frame 121 is a roughly quadrilateral plate-shaped metal (e.g., stainless steel) member, with a roughly quadrilateral opening formed in its central portion. The air electrode frame 122 is positioned below the fuel electrode frame 121. The air electrode frame 122 is a roughly quadrilateral plate-shaped insulating member, formed, for example, from a mica sheet. A roughly quadrilateral opening is also formed in the central portion of the air electrode frame 122, similar to that of the fuel electrode frame 121. In a vertical view, the shape of the frame portion 120 matches the shape of the upper end plate 21 and the lower end plate 23.

[0047] Furthermore, as can be seen from Figures 4 and 5, the reaction section 110 is positioned inside an opening formed in the central part of the frame section 120. In other words, the frame section 120 is positioned around the reaction section 110 so as to surround its outer periphery. A predetermined gap is formed between the frame section 120 and the reaction section 110, and the separator section 130 is positioned to close this gap. The separator section 130 includes a cell-side separator 131 and an interconnector-side separator 132. The cell-side separator 131 is a roughly quadrilateral plate-shaped metal (e.g., stainless steel) member, with a roughly quadrilateral opening formed in its central part. The periphery (i.e., inner periphery) of the opening of the cell-side separator 131 is brazed to the upper surface of the outer periphery of the solid electrolyte layer 111a of the electrolytic cell 111 using a brazing material (e.g., Ag brazing material) not shown. On the other hand, the outer peripheral portion of the cell-side separator 131 is positioned on the upper surface of the fuel electrode frame 121 and is joined to the fuel electrode frame 121 by, for example, welding.

[0048] The interconnector-side separator 132, like the cell-side separator 131, is a roughly quadrilateral plate-shaped metal (for example, stainless steel) member with a roughly quadrilateral opening formed in its central portion. The periphery (i.e., inner periphery) of the opening of the interconnector-side separator 132 is joined to the upper surface of the main body portion 113a of the interconnector 113, for example, by welding. The outer periphery portion of the interconnector-side separator 132 is sandwiched between the lower surface of the fuel electrode frame 121 and the upper surface of the air electrode frame 122, and is joined to the fuel electrode frame 121 above it, for example, by welding. In this way, the separator portion 130 (cell-side separator 131 and interconnector-side separator 132) is configured to connect the reaction portion 110 and the frame portion 120.

[0049] When the cell cassettes 100 configured as described above are stacked on the upper surface 221 of the central plate 22, a first cell cassette group 24A is formed by stacking multiple cell cassettes 100. Furthermore, when the cell cassettes 100 configured as described above are stacked on the lower surface 222 of the central plate 22 in the opposite direction (downward) to the stacking direction (upward) of the first cell cassette group 24A, a second cell cassette group 25A is formed by stacking multiple cell cassettes 100. When the cell cassettes 100 are stacked in this manner, each cell cassette 100 is stacked in the thickness direction of the electrolytic cell 111. Also, as shown in Figure 4, the frame portion 120 of each cell cassette 100 is stacked, and the reaction portion 110 of each cell cassette 100 is stacked. In addition, the cell-side separator 131 and the interconnector-side separator 132 are arranged alternately at predetermined intervals in the stacking direction.

[0050] Furthermore, each separator section 130 (cell-side separator 131 and interconnector-side separator 132) partitions the space between adjacent separators. As a result, multiple fuel chambers Sf and air chambers Sa are formed inside the first cell cassette group 24A and the second cell cassette group 25A, with gas flow being blocked from each other. The fuel chambers Sf are spaces that allow the flow of hydrogen generated in the fuel polar layer 111c. The air chambers Sa are spaces that allow the flow of oxygen generated in the air polar layer 111b.

[0051] The fuel chamber Sf is the space where the fuel electrode layer 111c of the electrolytic cell 111 exists. The fuel chamber Sf is formed by the fuel electrode frame 121, the cell-side separator 131 joined to the fuel electrode frame 121, the electrolytic cell 111 connected to the cell-side separator 131, the interconnector-side separator 132 joined to the fuel electrode frame 121, and the interconnector 113 connected to the interconnector-side separator 132.

[0052] The air chamber Sa is the space where the air electrode layer 111b of the electrolytic cell 111 exists. The air chamber Sa is formed by the air electrode frame 122, the interconnector-side separator 132 connected to the air electrode frame 122, the interconnector 113 connected to the interconnector-side separator 132, the cell-side separator 131 of the cell cassette 100 adjacent to the air electrode frame 122, and the electrolytic cell 111 connected to the cell-side separator 131.

[0053] Furthermore, all cell cassettes 100 constituting the first cell cassette group 24A are arranged such that the fuel electrode layer 111c of the electrolytic cell 111 faces the upper surface 221 of the central plate 22, and all cell cassettes 100 constituting the second cell cassette group 25A are arranged such that the fuel electrode layer 111c of the electrolytic cell 111 faces the lower surface 222 of the central plate 22. In other words, in all cell cassettes 100, of the fuel electrode layer 111c and the air electrode layer 111b, the layer facing the central plate 22 is the fuel electrode layer 111c. Thus, the first cell cassette group 24A and the second cell cassette group 25A are arranged symmetrically (mirror symmetric with respect to the central plate 22) with respect to the central plate 22, with the fuel electrode layer 111c of the electrolytic cell 111 of the cell cassettes 100 constituting them located closer to the central plate 22 than the electrolyte layer 111a and the air electrode layer 111b.

[0054] As shown in Figure 4, the frame portion 120 and upper end plate 21 of each cell cassette 100 stacked on the upper surface 221 of the central plate 22 have coaxial through holes extending in a direction substantially parallel to the stacking direction. These through holes connect in the stacking direction (axial direction) to form a first bolt insertion hole 261. A first fastening bolt BT1, which serves as the first fastening member, is inserted from above into this first bolt insertion hole 261. As a result, the first fastening bolt BT1 penetrates the upper end plate 21 and the frame portion 120 of each cell cassette 100 constituting the first cell cassette group 24A in the stacking direction of the cell cassettes 100. In addition, a first screw hole 223 is formed on the upper surface 221 of the central plate 22 on the extension of the first bolt insertion hole 261. Therefore, the tip of the first fastening bolt BT1 that has passed through the first bolt insertion hole 261 is screwed into the first screw hole 223 of the central plate 22, thereby fastening the first cell cassette group 24A to the central plate 22.

[0055] Similarly, the frame portion 120 and lower end plate 23 of each cell cassette 100 stacked on the lower surface 222 of the central plate 22 have coaxial through holes extending in a direction substantially parallel to the stacking direction. These through holes connect in the stacking direction (axial direction) to form a second bolt insertion hole 262. A second fastening bolt BT2, which serves as a second fastening member, is inserted from below into this second bolt insertion hole 262. As a result, the second fastening bolt BT2 penetrates the lower end plate 23 and the frame portion 120 of each cell cassette 100 constituting the second cell cassette group 25A in the stacking direction of the cell cassettes 100. In addition, a second screw hole 224 is formed on the lower surface 222 of the central plate 22 on the extension of the second bolt insertion hole 262. Therefore, the tip of the second fastening bolt BT2 that has passed through the second bolt insertion hole 262 is screwed into the second screw hole 224 of the central plate 22, thereby fastening the second cell cassette group 25A to the central plate 22.

[0056] Figure 6 is a schematic cross-sectional view of the line VI-VI in Figure 3. Figure 6 is a schematic cross-sectional view of the electrochemical cell stack 20A cut to reveal the cross-sections of the gas supply passage Pfi and the gas discharge passage Pfo. As shown in Figure 6, the gas supply passage Pfi and the gas discharge passage Pfo are formed to penetrate the lower end plate 23, the frame portion 120 of each cell cassette 100 constituting the second cell cassette group 25A, the central plate 22, and the frame portion 120 of each cell cassette 100 constituting the first cell cassette group 24A in the stacking direction. The gas supply passage Pfi communicates with the fuel chamber Sf via a lateral hole 121a formed in the fuel electrode frame 121 of each cell cassette 100. The gas discharge passage Pfo communicates with the fuel chamber Sf via a lateral hole 121b formed in the fuel electrode frame 121 of each cell cassette 100.

[0057] Furthermore, the gas supply passage Pai and the gas discharge passage Pao are formed to penetrate the lower end plate 23, the frame portion 120 of each cell cassette 100 constituting the second cell cassette group 25A, the central plate 22, and the frame portion 120 of each cell cassette 100 constituting the first cell cassette group 24A in the stacking direction. The gas supply passage Pai and the gas discharge passage Pao communicate with the air chamber Sa, respectively, through transverse holes (not shown) formed in the air electrode frame 122 of each cell cassette 100.

[0058] As shown in Figure 4, the cell cassette 100 located at the top of the first cell cassette group 24A is a dummy cell cassette 102 in which a metal plate 133 is provided in place of the electrolytic cell 111. Similarly, the cell cassette 100 located at the bottom of the second cell cassette group 25A is also a dummy cell cassette 102 in which a metal plate 133 is provided in place of the electrolytic cell 111. The fuel electrode frame 121 of these dummy cell cassettes 102 is the terminal plate TP. The terminal plate TP of the dummy cell cassette 102 in the first cell cassette group 24A is provided with an upper terminal 241 configured to be connectable to a power supply. Similarly, the terminal plate TP of the dummy cell cassette 102 in the second cell cassette group 25A is provided with a lower terminal 251 configured to be connectable to a power supply. An insulating plate IP is interposed between the terminal plate TP and the upper end plate 21 of the uppermost dummy cell cassette 102 in the first cell cassette group 24A. Similarly, an insulating plate IP is interposed between the terminal plate TP of the dummy cell cassette 102 at the bottom of the second cell cassette group 25A.

[0059] The operation of the electrochemical cell stack 20A will now be explained. First, a voltage is applied to the electrochemical cell stack 20A. In this case, the central terminal 225 of the central plate 22 is connected to the negative terminal of the power supply, and the upper terminal 241 and lower terminal 251 of both terminal plates TP are connected in parallel to the positive terminal. That is, the central plate 22 is used as the negative terminal, and both terminal plates TP are used as the anodes. Next, high-temperature steam is supplied from the gas supply passage Pfi. The steam supplied to the gas supply passage Pfi flows into the fuel chamber Sf of each cell cassette 100 through the side hole 121a. High-temperature air is also supplied from the gas supply passage Pai. The air supplied to the gas supply passage Pai flows into the air chamber Sa of each cell cassette 100 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 20A.

[0060] Water vapor flowing into the fuel chamber Sf reacts with electrons supplied via the central plate 22, interconnector 113, current collector 112, etc., in the fuel electrode layer 111c to decompose into hydrogen and oxide ions (water vapor electrolysis). The hydrogen produced by the water vapor electrolysis diffuses within the fuel chamber Sf and is discharged from the gas exhaust passage Pfo through the lateral hole 121b. At this time, unreacted water vapor is discharged from the gas exhaust passage Pfo along with the hydrogen. Meanwhile, oxide ions move via the solid electrolyte layer 111a to the air electrode layer 111b in the air chamber Sa, where they release electrons in the functional layer of the air electrode layer 111b to become oxygen. The oxygen diffuses within the air chamber Sa and is discharged from the gas exhaust passage Pao through a lateral hole (not shown) along with the air flowing into the air chamber Sa.

[0061] Electrons emitted in the functional layer of the air electrode layer 111b are collected by the interconnector 113 via the current collector layer and circulate from the terminal plate TP through the power supply to the central plate 22.

[0062] Furthermore, all cell cassettes 100 constituting the first cell cassette group 24A and all cell cassettes 100 constituting the second cell cassette group 25A are arranged so that the fuel electrode layer 111c of the electrolytic cell 111 faces the central plate 22. In other words, all cell cassettes 100 stacked on both sides of the central plate 22 are arranged so that the fuel electrode layer 111c of the electrolytic cells 111 contained within them becomes the facing layer that faces the central plate 22. Therefore, when a voltage is applied, the central plate 22 is used as the negative electrode, and by supplying electrons from the central plate 22 to the fuel electrode layer 111c, a water vapor electrolysis reaction can be caused in the electrolytic cell 111 of each cell cassette 100. In this way, hydrogen can be produced by the electrochemical cell stack 20A in which cell cassettes 100 are stacked on both sides of the central plate 22.

[0063] This configuration prevents or suppresses temperature unevenness inside the electrochemical cell stack 20A. Specifically, the electrochemical cell stack 20A is supplied with steam and air heated to a predetermined temperature. Heat is also transferred to the electrochemical cell stack 20A through other components that are joined to or in contact with the electrochemical cell stack 20A. As a result, the electrochemical cell stack 20A is heated by the steam and air, as well as the heat transferred from the outside. On the other hand, since the electrolysis reaction of steam is an endothermic reaction, heat is absorbed inside the electrochemical cell stack 20A during its operation due to this endothermic reaction.

[0064] Therefore, in conventional configurations where the central plate 22 is not provided, the temperature of the central part of the electrochemical cell stack 20A is lower than the temperature of the outer periphery during operation. In contrast, according to this embodiment, the central plate 22 is exposed to the outside of the electrochemical cell stack 20A. Therefore, heat transferred from the outside of the electrochemical cell stack 20A to the central plate 22 is transferred to the inside of the electrochemical cell stack 20A via the central plate 22. That is, the inside of the electrochemical cell stack 20A (especially the central part) is heated by the heat transferred from the outside via the central plate 22. Thus, it is possible to prevent or suppress the temperature inside the electrochemical cell stack 20A from being lower than that inside the outer periphery. This makes it possible to improve the efficiency of the electrolysis reaction of water vapor in the central part of the electrochemical cell stack 20A (prevent or suppress a decrease in efficiency).

[0065] Furthermore, according to this embodiment, since current flows through the central plate 22 during the operation of the electrochemical cell stack 20A, the central plate 22 generates Joule heat. As a result of the heat generated by the central plate 22, the central part of the electrochemical cell stack 20A is heated, which prevents or suppresses the internal temperature of the electrochemical cell stack 20A from being lower than that of the outer periphery. In particular, according to this embodiment, since twice the current flows through the central plate 22 as through each terminal plate TP, the heat generated by the central plate 22 can be made greater than the heat generated by the terminal plates TP at both ends. Therefore, the amount of heat supplied to the center of the electrochemical cell stack 20A can be increased compared to the amount of heat supplied to the outer periphery.

[0066] In this embodiment, the number of cell cassettes 100 included in the first cell cassette group 24A is the same as the number of cell cassettes 100 included in the second cell cassette group 25A. Furthermore, the structure of the cell cassettes 100 included in the first cell cassette group 24A and the cell cassettes 100 included in the second cell cassette group 25A is substantially the same. In other words, the first cell cassette group 24A and the second cell cassette group 25A have substantially the same configuration and are arranged mirror-symmetrically with respect to the central plate 22. Therefore, with this configuration, the central plate 22 is located in the center of the electrochemical cell stack 20A. In a conventional configuration without a central plate 22, the center of the electrochemical cell stack 20A is less susceptible to heat transfer from the outside, resulting in the lowest temperature in the center of the electrochemical cell stack. In contrast, according to this embodiment, since the central plate 22 is located in the center of the electrochemical cell stack 20A, the center of the electrochemical cell stack 20A (i.e., the area where the temperature is most likely to be lowest due to endothermic reactions) can be heated.

[0067] Furthermore, the central plate 22 and the interconnectors 113 of the electrolytic cells 111 of the first cell cassette group 24A and the second cell cassette group 25A have approximately the same coefficient of thermal expansion (coefficient of linear expansion). With this configuration, the thermal expansion behavior of each cell cassette 100 equipped with the central plate 22 and the interconnectors 113 is synchronized. Therefore, the thermal stress generated in the electrochemical cell stack 20A can be reduced. Consequently, delamination between the central plate 22 and the interconnectors 113 in contact with the central plate 22 can be prevented or suppressed. In this embodiment, a configuration in which the central plate 22 and the interconnectors 113 are formed from the same material is shown, but it is sufficient that the materials have approximately the same coefficient of thermal expansion, and the configuration is not limited to being formed from the same material. It is preferable that the coefficients of thermal expansion of the central plate 22 and the interconnectors 113 be the same, but they do not have to be the same. That is, it is sufficient that the thermal stress caused by the difference in the coefficients of thermal expansion when the electrochemical cell stack 20A is heated from room temperature to operating temperature remains within an acceptable range.

[0068] Furthermore, according to this embodiment, for the reasons shown below, it is possible to increase the number of stacked cell cassettes 100 included in the first cell cassette group 24A and the second cell cassette group 25A while preventing or suppressing damage to the electrolytic cell 111 during manufacturing.

[0069] Figure 8 is a schematic cross-sectional view of a conventional electrochemical cell stack. As shown in Figure 8, in a conventional electrochemical cell stack SS, cell cassettes CC are stacked only on the upper surface of plate PL. An upper end plate EP is placed above the stacked cell cassettes CC. Bolts BT are inserted through bolt insertion holes that penetrate these stacks in the stacking direction, and nuts NT are screwed onto these bolts BT from below. In this way, each cell cassette CC is fastened to plate PL.

[0070] Figure 9 shows the state in which cell cassettes CC of a conventional electrochemical cell stack SS are stacked on a plate PL. As shown in Figure 9, each cell cassette CC is sequentially stacked on the upper surface of the plate PL. Here, when stacking each cell cassette CC, a conductive paste is applied between the conductive part ST1 of the current collector ST of each cell cassette CC and the interconnector IC below it to ensure electrical connection between them. The conductive paste contains organic matter, which is present when the electrochemical cell stack SS is fastened.

[0071] The organic matter contained in the conductive paste is removed during the evaluation process after the fastening of the electrochemical cell stack SS, when the electrochemical cell stack SS is heated to approximately 700°C. The thickness of the reaction section RE and the frame section FL of each cell cassette CC are designed so that no unnecessary stress acts on the reaction section RE of the cell cassette CC after the evaluation process, i.e., after the removal of the organic matter. Therefore, before the evaluation process, the thickness of the reaction section RE of the cell cassette CC is slightly greater than the thickness of the frame section FL by the amount of organic matter contained in the conductive paste.

[0072] Therefore, as shown in Figure 9, when cell cassettes CC are stacked and then fastened together with bolts BT and nuts NT, the height of the reaction section RE of the same cell cassette CC becomes relatively higher than the height of the frame section FL of the same cell cassette CC, as shown in Figure 10. In other words, the reaction section RE bulges out relative to the frame section FL. The degree of this bulge, i.e., the deviation between the height of the reaction section RE and the height of the frame section FL, increases as the number of stacked cell cassettes CCs increases, as shown by the range indicated by the arrows in Figure 10. Therefore, as shown in Figure 10, the deviation between the height of the frame section FR and the reaction section RE is largest in the uppermost cell cassette CC1.

[0073] The difference in height between the reaction section RE and the frame section FL (the degree of elevation of the reaction section RE) is absorbed by the deformation of the separator SP connecting the frame section FL and the reaction section RE. However, the deformation of the separator SP causes a restoring force of the separator SP to act on the reaction section RE connected to the separator SP. As a result, unnecessary stress acts on the reaction section RE, and if this stress is large, the electrolytic cell inside the reaction section RE may crack.

[0074] Therefore, to prevent the electrolytic cells from cracking due to unnecessary stress acting on them during fastening as the number of layers increases, conventionally, the number of cell cassettes stacked on the plate PL was limited to a predetermined number or less. However, since a larger number of cell cassettes stacked allows for a larger amount of hydrogen to be produced per unit time, measures were needed to increase the number of cell cassettes stacked.

[0075] In this regard, in the electrochemical cell stack 20A according to this embodiment, a central plate 22 is provided between the upper end plate 21 and the lower end plate 23. Cell cassettes 100 are stacked on both sides of the central plate 22, one side (upper surface 221) and the other side (lower surface 222). Therefore, even if the number of cell cassettes 100 stacked on one side of the central plate 22 is limited to a number that does not cause cracking of the electrolytic cells, the number of stacked cell cassettes can be increased by stacking cell cassettes 100 on the other side of the central plate 22 as well.

[0076] Furthermore, in the electrochemical cell stack 20A according to this embodiment, as can be seen from Figure 4, the axial position of the first fastening bolt BT1 and the axial position of the second fastening bolt BT2 are different when viewed in the vertical direction. Therefore, interference between the first fastening bolt BT1 and the second fastening bolt BT2 can be avoided. Also, if the axial position of the first fastening bolt BT1 and the axial position of the second fastening bolt BT2 were the same, it would be necessary to form the central plate 22 thicker to prevent interference between the tips of both bolts. However, by shifting the axial positions of both bolts, the central plate 22 can be formed thinner. Therefore, the electrochemical cell stack 20A can be constructed compactly.

[0077] In addition, in the electrochemical cell stack 20A according to this embodiment, the number of stacked cell cassettes 100 constituting the first cell cassette group 24A, which is located on the upper surface 221 side of the central plate 22, is the same as the number of stacked cell cassettes 100 constituting the second cell cassette group 25A, which is located on the lower surface 222 side of the central plate 22 (in this embodiment, including the dummy cell cassette 102, the number of stacked cell cassettes constituting each cell cassette group is 3). By making the number of stacked cell cassettes 100 constituting each cell cassette group the same, the current flowing through each cell cassette 100 during operation can be evenly distributed. Furthermore, the number of cell cassettes 100 stacked in both cell cassette groups can be maximized to the extent that the cell cassettes 100 do not break, thus maximizing the number of stacked cell cassettes 100.

[0078] <Second Embodiment> Next, a second embodiment will be described. Components identical to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted. Figure 7 is a schematic cross-sectional view showing the configuration of the electrochemical cell stack 20B according to the second embodiment, and corresponds to Figure 4, which shows the electrochemical cell stack 20A according to the first embodiment.

[0079] As shown in Figure 7, the central plate 22 has an upper surface 221 (first surface) and a lower surface 222 (second surface) opposite to the upper surface 221. The upper surface 221 and lower surface 222 of the central plate 22 are provided with protrusions 226 (multiple protrusions) which have substantially the same configuration as the protrusions 113b (multiple protrusions) of the interconnector 113 of the electrolytic cell 111.

[0080] The first cell cassette group 24B is positioned on the upper surface 221 side of the central plate 22, and the second cell cassette group 25B is positioned on the lower surface 222 side of the central plate 22. The upper end plate 21 is positioned above the first cell cassette group 24B, and the lower end plate 23 is positioned below the second cell cassette group 25B.

[0081] The first cell cassette group 24B and the second cell cassette group 25B each comprise a plurality of cell cassettes 100 arranged in a stacked configuration. Of the plurality of cell cassettes 100 included in the first cell cassette group 24B, all cell cassettes 100 except for the one located at the top (the position furthest from the central plate 22) are normal cell cassettes 101. Of the plurality of cell cassettes 100 included in the first cell cassette group 24B, the one located at the top is a dummy cell cassette 102. Of the plurality of cell cassettes 100 included in the second cell cassette group 25B, all cell cassettes 100 except for the one located at the bottom (the position furthest from the central plate 22) are normal cell cassettes 101. Of the plurality of cell cassettes 100 included in the second cell cassette group 25B, the cell cassette 100 located at the bottom is a dummy cell cassette 102.

[0082] As is clear from the comparison between Figure 7 and Figure 4, each normal cell cassette 100 in the electrochemical cell stack 20B according to the second embodiment has the same configuration as each normal cell cassette 101 in the electrochemical cell stack 20A according to the first embodiment. However, in the electrochemical cell stack 20B according to the second embodiment, each normal cell cassette 101 is stacked on top of each other with the air electrode layer 111b of the electrolytic cell 111 located on the side of the central plate 22 and the fuel electrode layer 111c located on the opposite side. In other words, in the electrochemical cell stack 20B according to the second embodiment, the orientation of the normal cell cassettes 100 included in the first cell cassette group 24B and the second cell cassette group 25B is opposite to the orientation of the normal cell cassettes 100 in the electrochemical cell stack 20A according to the first embodiment in terms of the vertical direction.

[0083] Furthermore, the protrusion 226 on the upper surface 221 of the central plate 22 is in contact with the air electrode layer 111b of the electrolytic cell 111 of the cell cassette 100 in the first cell cassette group 24B that is closest to the central plate 22. Similarly, the protrusion 226 on the lower surface 222 of the central plate 22 is in contact with the air electrode layer 111b of the electrolytic cell 111 of the cell cassette 100 in the second cell cassette group 25B that is closest to the central plate 22. The central plate 22 is electrically connected to the air electrode layer 111b of the electrolytic cell 111 of the cell cassette 100 in the first cell cassette group 24B and the second cell cassette group 25B that is closest to the central plate 22.

[0084] The dummy cell cassette 102 of the electrochemical cell stack 20B according to the second embodiment has a configuration in which the interconnector 113 of the dummy cell cassette 102 of the electrochemical cell stack 20A according to the first embodiment is replaced with a metal plate 134 which is a conductive plate-shaped member. That is, the dummy cell cassette 102 according to the second embodiment comprises two metal plates 133, 134 and a current collector 112 placed between them. In addition, the air electrode frame 122 of these dummy cell cassettes 102 is a terminal plate TP. An upper terminal 241 is provided on the terminal plate TP of the dummy cell cassette 102 of the first cell cassette group 24B. A lower terminal 251 is provided on the terminal plate TP of the dummy cell cassette 102 of the second cell cassette group 25B.

[0085] Furthermore, in both the first cell cassette group 24B and the second cell cassette group 25B, the metal plate 133 located on the side of the dummy cell cassette 102 closest to the central plate 22 is in contact with the interconnector 113 of the electrolytic cell 111 of the normal cell cassette 101 located furthest from the central plate 22. Therefore, the metal plate 133 of the dummy cell cassette 102 and the interconnector 113 of the normal cell cassette 101 located furthest from the central plate 22 are electrically conductive.

[0086] Thus, in the second embodiment as well, the first cell cassette group 24B and the second cell cassette group 25B have substantially the same configuration. The first cell cassette group 24B and the second cell cassette group 25B are arranged in opposite directions with respect to the central plate 22 (so as if they are mirror images of each other with respect to the central plate 22).

[0087] However, in the second embodiment, the first cell cassette group 24B and the second cell cassette group 25B are arranged symmetrically with respect to the central plate 22 (mirror symmetric with respect to the central plate 22), in the opposite orientation to the first embodiment, such that the air electrode layer 111b of the electrolytic cell 111 of the cell cassette 100 that constitutes them is located closer to the central plate 22 than the electrolyte layer 111a and the fuel electrode layer 111c. In the hydrogen production apparatus 1 to which the electrochemical cell stack 20B according to the second embodiment is applied, the central terminal 225 (central plate 22) is connected to the positive electrode of the power supply, and the upper terminal 241 and lower terminal 251 are connected to the negative electrode of the power supply.

[0088] The electrochemical cell stack 20B according to the second embodiment can achieve the same effects as the electrochemical cell stack 20A according to the first embodiment.

[0089] While embodiments of this disclosure have been described above, the technology relating to this disclosure is not limited to the embodiments described above. For example, although the embodiments described above describe a hydrogen production apparatus for producing hydrogen, this technology can be applied to apparatuses for producing gases other than hydrogen, such as carbon monoxide, or both hydrogen and carbon monoxide. Thus, the technology relating to this disclosure is modifiable as long as it does not depart from the spirit of the disclosure.

[0090] Furthermore, this disclosure may include the following aspects:

[0091] [1] A terminal configured to exchange power with the outside is provided, and the device has a first surface and a second surface opposite to the first surface, and includes a conductive central plate, A group of first cell cassettes stacked on the side of the first surface of the central plate, A group of second cell cassettes stacked on the side of the second surface of the central plate, A first terminal is located on the opposite side of the central plate of the first cell cassette group and is configured to be able to exchange power with the outside, A second terminal is located on the opposite side of the central plate of the second cell cassette group and is configured to be able to exchange power with the outside, Equipped with, The first cell cassette group and the second cell cassette group each comprise a plurality of cell cassettes arranged in a stack, The plurality of stacked cell cassettes include an electrochemical cell which is a solid oxide type electrolytic cell or a reversible solid oxide type fuel cell-steam electrolytic cell comprising a solid oxide type electrolyte layer, an air electrode layer stacked on one side of the electrolyte layer, and a fuel electrode layer stacked on the side of the electrolyte layer opposite to the air electrode layer; an electrochemical cell cassette which comprises a current collector stacked on the side of the fuel electrode layer opposite to the electrolyte layer, and an interconnector stacked on the side of the current collector opposite to the fuel electrode layer; and a cover cell cassette which is located furthest from the central plate and has a conductive cover member in place of the electrochemical cell. The first cell cassette group and the second cell cassette group are arranged symmetrically on either side of the central plate, such that the fuel electrode layer of the electrochemical cell is located closer to the central plate than the electrolyte layer. The interconnector, which is stacked on the electrochemical cell closest to the central plate of the first cell cassette group, is in contact with the first surface of the central plate, and the cover cell cassette is in contact with or includes the first terminal. The interconnector, which is stacked on the electrochemical cell closest to the central plate of the second cell cassette group, is in contact with the second surface of the central plate, and the cover cell cassette is in contact with or includes the second terminal. Electrochemical cell stack.

[0092] [2] A terminal configured to exchange power with the outside is provided, and the device has a first surface and a second surface opposite to the first surface, and includes a conductive central plate, A group of first cell cassettes stacked on the side of the first surface of the central plate, A group of second cell cassettes stacked on the side of the second surface of the central plate, A first terminal is located on the opposite side of the central plate of the first cell cassette group and is configured to be able to exchange power with the outside, A second terminal is located on the opposite side of the central plate of the second cell cassette group and is configured to be able to exchange power with the outside, Equipped with, The first cell cassette group and the second cell cassette group each comprise a plurality of cell cassettes arranged in a stack, The plurality of stacked cell cassettes include an electrochemical cell which is a solid oxide type electrolytic cell or a reversible solid oxide type fuel cell-steam electrolytic cell comprising a solid oxide type electrolyte layer, an air electrode layer stacked on one side of the electrolyte layer, and a fuel electrode layer stacked on the side of the electrolyte layer opposite to the air electrode layer; an electrochemical cell cassette which comprises a current collector stacked on the side of the fuel electrode layer opposite to the electrolyte layer, and an interconnector stacked on the side of the current collector opposite to the fuel electrode layer; and a cover cell cassette which is located furthest from the central plate and has a conductive cover member in place of the electrochemical cell. The first cell cassette group and the second cell cassette group are arranged symmetrically on either side of the central plate, such that the air electrode layer of the electrochemical cell is located closer to the central plate than the electrolyte layer. The air electrode layer of the electrochemical cell closest to the central plate in the first cell cassette group is in contact with the first surface of the central plate, and the cover cell cassette is in contact with or includes the first terminal. The air electrode layer of the electrochemical cell closest to the central plate in the second cell cassette group is in contact with the second surface of the central plate, and the cover cell cassette is in contact with or includes the second terminal. Electrochemical cell stack.

[0093] [3] An electrochemical cell stack according to [1] or [2] above, The thermal expansion coefficient of the central plate and the thermal expansion coefficient of the interconnectors of the first cell cassette group and the second cell cassette group are approximately the same. Electrochemical cell stack.

[0094] [4] An electrochemical cell stack according to any one of the above [1] to [3], The central plate and the interconnectors of the first cell cassette group and the second cell cassette group are formed from the same material. Electrochemical cell stack.

[0095] [5] An electrochemical cell stack according to any one of the above [1] to [4], The number of electrochemical cells in the first cell cassette group is the same as the number of electrochemical cells in the second cell cassette group. Electrochemical cell stack.

[0096] [6] An electrochemical cell stack according to any one of the above [1] to [5], A heating device for heating the gas supplied to the electrochemical cell stack, The electrochemical cell stack and the heating device are insulated from an insulating material placed inside them. Equipped with, Hot module.

[0097] [7] The hot module described in [6] above is provided, Electrolytic reaction apparatus. [Explanation of Symbols]

[0098] 1...Hydrogen production equipment (electrolytic reaction apparatus), 10...Hot module, 20A, 20B...Electrochemical cell stack, 22...Central plate, 221...Upper surface of central plate (first surface), 222...Lower surface of central plate (second surface), 225...Central terminal, 24...First cell cassette group, 241...Upper terminal, 25...Second cell cassette group, 251...Lower terminal, 30...Vaporizer, 40...Heat exchanger (heating device) ), 50…Heater (heating device), 60…Insulation material, 90…Condenser, 100…Cell cassette, 110…Reaction section of cell cassette, 111…Electrolytic cell (electrochemical cell), 111a…Solid electrolyte layer, 111b…Air electrode layer, 111c…Fuel electrode layer, 112…Current collector, 112a…Insulator, 112b…Conductor, 113…Interconnector, Sa…Air chamber, Sf…Fuel chamber, TP…Terminal plate

Claims

1. A terminal configured to exchange power with the outside is provided, and the device has a first surface and a second surface opposite to the first surface, and includes a conductive central plate, A group of first cell cassettes stacked on the side of the first surface of the central plate, A group of second cell cassettes stacked on the side of the second surface of the central plate, A first terminal is located on the opposite side of the central plate of the first cell cassette group and is configured to be able to exchange power with the outside, A second terminal is located on the opposite side of the central plate of the second cell cassette group and is configured to be able to exchange power with the outside, Equipped with, The first cell cassette group and the second cell cassette group each comprise a plurality of cell cassettes arranged in a stack, The plurality of stacked cell cassettes include an electrochemical cell which is a solid oxide type electrolytic cell or a reversible solid oxide type fuel cell-steam electrolytic cell, comprising a solid oxide type electrolyte layer, an air electrode layer stacked on one side of the electrolyte layer, and a fuel electrode layer stacked on the side of the electrolyte layer opposite to the air electrode layer; an electrochemical cell cassette which comprises a current collector stacked on the side of the fuel electrode layer opposite to the electrolyte layer, and an interconnector stacked on the side of the current collector opposite to the fuel electrode layer; and a cover cell cassette which is located furthest from the central plate and has a conductive cover member in place of the electrochemical cell. The first cell cassette group and the second cell cassette group are arranged symmetrically on either side of the central plate, such that the fuel electrode layer of the electrochemical cell is located closer to the central plate than the electrolyte layer. The interconnector, which is stacked on the electrochemical cell closest to the central plate of the first cell cassette group, is in contact with the first surface of the central plate, and the cover cell cassette is in contact with or includes the first terminal. The interconnector, which is stacked on the electrochemical cell closest to the central plate of the second cell cassette group, is in contact with the second surface of the central plate, and the cover cell cassette is in contact with or includes the second terminal. Electrochemical cell stack.

2. A terminal configured to exchange power with the outside is provided, and the device has a first surface and a second surface opposite to the first surface, and includes a conductive central plate, A group of first cell cassettes stacked on the side of the first surface of the central plate, A group of second cell cassettes stacked on the side of the second surface of the central plate, A first terminal is located on the opposite side of the central plate of the first cell cassette group and is configured to be able to exchange power with the outside, A second terminal is located on the opposite side of the central plate of the second cell cassette group and is configured to be able to exchange power with the outside, Equipped with, The first cell cassette group and the second cell cassette group each comprise a plurality of cell cassettes arranged in a stack, The plurality of stacked cell cassettes include an electrochemical cell which is a solid oxide type electrolytic cell or a reversible solid oxide type fuel cell-steam electrolytic cell, comprising a solid oxide type electrolyte layer, an air electrode layer stacked on one side of the electrolyte layer, and a fuel electrode layer stacked on the side of the electrolyte layer opposite to the air electrode layer; an electrochemical cell cassette which comprises a current collector stacked on the side of the fuel electrode layer opposite to the electrolyte layer, and an interconnector stacked on the side of the current collector opposite to the fuel electrode layer; and a cover cell cassette which is located furthest from the central plate and has a conductive cover member in place of the electrochemical cell. The first cell cassette group and the second cell cassette group are arranged symmetrically on either side of the central plate, such that the air electrode layer of the electrochemical cell is located closer to the central plate than the electrolyte layer. The air electrode layer of the electrochemical cell closest to the central plate in the first cell cassette group is in contact with the first surface of the central plate, and the cover cell cassette is in contact with or includes the first terminal. The air electrode layer of the electrochemical cell closest to the central plate in the second cell cassette group is in contact with the second surface of the central plate, and the cover cell cassette is in contact with or includes the second terminal. Electrochemical cell stack.

3. An electrochemical cell stack according to claim 1 or claim 2, The thermal expansion coefficient of the central plate and the thermal expansion coefficient of the interconnectors of the first cell cassette group and the second cell cassette group are approximately the same. Electrochemical cell stack.

4. The electrochemical cell stack according to claim 3, The central plate and the interconnectors of the first cell cassette group and the second cell cassette group are formed from the same material. Electrochemical cell stack.

5. An electrochemical cell stack according to claim 1 or claim 2, The number of electrochemical cells in the first cell cassette group is the same as the number of electrochemical cells in the second cell cassette group. Electrochemical cell stack.

6. An electrochemical cell stack according to claim 1 or claim 2, A heating device for heating the gas supplied to the electrochemical cell stack, The electrochemical cell stack and the heating device are insulated from an insulating material placed inside them. Equipped with, Hot module.

7. A hot module comprising the hot module described in claim 6, Electrolytic reaction apparatus.

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