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

Abstract

An electrolysis cell 21 comprises: a solid electrolyte layer 211 that includes oxide particles containing Zr; a fuel electrode layer 213 that is stacked and arranged on one surface side of the solid electrolyte layer 211 and includes metal particles and oxide particles containing Ce; and an air electrode layer 212 that is stacked and arranged on the other surface side of the solid electrolyte layer 211. A Raman spectrum of Stokes scattered light of each of the solid electrolyte layer 211 and the fuel electrode layer 213 (213a) has a peak in a wave number region of 334 cm-1 or more and 531 cm-1 or less. When the half widths of the peaks of the Raman spectra of the solid electrolyte layer 211 and the fuel electrode layer 213 (213a) in the wave number region are defined as an electrolyte half width and a fuel electrode half width, respectively, the ratio of the electrolyte half width to the fuel electrode half width is 3.5 or more and 5.7 or less.

Description

Electrochemical cells, solid oxide electrolysis cells, cell stacks, hot modules, and hydrogen production devices

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

[0002] Solid oxide electrochemical cells using a solid oxide as an electrolyte have been known for some time (see, for example, Patent Document 1). Solid oxide electrochemical cells are characterized by performing electrochemical reactions with high efficiency in high-temperature environments and can be used as solid oxide electrolysis cells (SOECs) or solid oxide fuel cells (SOFCs). Solid oxide electrolysis cells are electrolysis devices that use electrical energy to decompose water vapor into hydrogen and oxygen. Solid oxide fuel cells are power generation devices that generate electrical energy through a chemical reaction between hydrogen and oxygen.

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

[0004] The electrochemical cell can be configured to include a solid electrolyte layer, a fuel electrode layer laminated on one side of the solid electrolyte layer, and a cathode layer laminated on the other side of the solid electrolyte layer. Generally, the solid electrolyte layer contains an ion-conductive oxide (also referred to as an oxide ion conductor). For example, YSZ (yttria-stabilized zirconia) is used as the ion-conductive oxide. The fuel electrode layer can be configured to include Ni (nickel) as an electrode catalyst and YSZ as an ion-conductive oxide.

[0005] When an electrochemical cell having an anode layer containing Ni and YSZ is operated for a long time under a severe operating environment (high temperature, high humidity, high current), Ni in the anode layer migrates and aggregates. When Ni in the anode layer migrates or aggregates, the internal resistance of the anode layer increases and the three-phase interface (the boundary between the fuel gas, Ni, and the electrolyte (YSZ)) serving as a reaction field decreases, resulting in a problem of reduced performance of the electrochemical cell.

[0006] Therefore, instead of YSZ, gadolinia-doped ceria (GDC) has been used as the ion-conductive oxide in the fuel electrode layer. Because GDC has the property of reducing the degree of Ni migration and aggregation compared to YSZ, using GDC as the ion-conductive oxide in the fuel electrode layer can improve the performance degradation of electrochemical cells due to Ni migration and aggregation. However, when an electrochemical cell having such a structure is manufactured in a conventional sintering temperature range (a relatively high temperature range), the crystalline morphologies of the solid electrolyte layer and the fuel electrode layer change. Specifically, when the precursor of the electrochemical cell (i.e., a laminate of green sheets for each layer) is sintered in the above-mentioned sintering temperature range, Ni in the fuel electrode layer diffuses into the solid electrolyte layer and dissolves in YSZ. This causes a phase transition of the crystalline structure of YSZ from cubic to tetragonal, reducing the ionic conductivity of the solid electrolyte layer (because tetragonal YSZ has lower ionic conductivity than cubic YSZ). Furthermore, when the precursor of the electrochemical cell is fired within the above firing temperature range, Ni in the fuel electrode layer diffuses and dissolves in the surrounding GDC. This causes a solid solution phase (Ni phase) to form in the fuel electrode layer, disrupting the crystal structure and resulting in a deterioration in electrical properties. This change in the crystal morphology of the solid electrolyte layer and the fuel electrode layer, respectively, leads to a deterioration in ionic conductivity and electrical properties, resulting in a problem of reduced durability of the electrochemical cell.

[0007] On the other hand, if an electrochemical cell having the above structure is manufactured at a temperature range significantly lower than the conventional firing temperature range, the materials of the solid electrolyte layer and the fuel electrode layer will not be sufficiently sintered, resulting in a problem of reduced adhesion between the two layers.

[0008] Thus, when the ion-conductive oxide in the solid electrolyte layer is YSZ and the ion-conductive oxide in the fuel electrode layer is GDC, the problem caused by the configuration in which both layers contain YSZ ion-conductive oxides (performance degradation due to Ni migration and aggregation) can be improved, but another problem caused by the firing temperature (reduced durability or adhesion) occurs. This problem is thought to occur regardless of the type of additive to the ion-conductive oxide in each layer of the solid electrolyte layer and the fuel electrode layer. That is, it is thought to occur in common when the ion-conductive oxide in the solid electrolyte layer is oxide particles containing Zr (zirconium) and the ion-conductive oxide in the fuel electrode layer is oxide particles containing Ce (cerium).

[0009] The present invention has been made to address the above-mentioned problems, and an object of the present invention is to provide a technique that can prevent a decrease in durability while ensuring adhesion of an electrochemical cell.

[0010] The electrochemical cell (21) according to the present invention comprises: a solid electrolyte layer (211) containing oxide particles containing Zr; a fuel electrode layer (213 (213a)) laminated on one side of the solid electrolyte layer and containing metal particles and oxide particles containing Ce; and an air electrode layer (212) laminated on the other side of the solid electrolyte layer. The Raman spectrum of the Stokes scattered light of the solid electrolyte layer and the fuel electrode layer shows a peak at 334 cm －１ Above and 531 cm －１ The Raman spectra of the solid electrolyte layer and the anode layer have peaks in the following wave number regions, respectively: when the half widths of the peaks in the Raman spectra of the solid electrolyte layer and the anode layer in the wave number regions are defined as an electrolyte half width (d1) and an anode half width (d2), respectively, the ratio (R (= d1 / d2)) of the electrolyte half width to the anode half width is 3.5 or more and 5.7 or less.

[0011] The Raman spectrum of Stokes scattered light obtained by Raman spectroscopy of an electrochemical cell provides various physical properties including the crystalline morphology of the electrochemical cell. －１ Above and 531 cm －１In the following wave number range, a peak of tetragonal Zr-containing oxide particles among "oxide particles containing Zr (hereinafter also referred to as "Zr-containing oxide particles")," which are ion-conductive oxides in the solid electrolyte layer, is observed. In addition, in the above wave number range, a peak of "oxide particles containing Ce (hereinafter also referred to as "Ce-containing oxide particles")," which are ion-conductive oxides in the fuel electrode layer, is observed.

[0012] The half-width ratio R, which is the ratio of the electrolyte half-width (i.e., the half-width of the peak in the Raman spectrum of the solid electrolyte layer (tetragonal Zr-containing oxide particles) in the above wavenumber range) to the fuel electrode half-width (i.e., the half-width of the peak in the Raman spectrum of the fuel electrode layer (Ce-containing oxide particles) in the above wavenumber range), tends to decrease as the firing temperature of the electrochemical cell increases. If the half-width ratio R is less than 3.5, the firing temperature is excessively high, resulting in reduced durability. If the half-width ratio R exceeds 5.7, the firing temperature is excessively low, resulting in reduced adhesion and a high likelihood of peeling between the solid electrolyte layer and the fuel electrode layer. In contrast, the electrochemical cell according to the present invention has a half-width ratio R of 3.5 or more and 5.7 or less, which ensures adhesion of the electrochemical cell and suppresses a decrease in durability. In addition, a decrease in the initial performance of the electrochemical cell due to reduced adhesion can be suppressed. In other words, by manufacturing an electrochemical cell at a firing temperature that results in a full width at half maximum ratio R within the above range, the crystal morphology of the solid electrolyte layer and the fuel electrode layer can be optimized. The initial performance refers to the performance of the electrochemical cell after an initial reduction treatment. The initial reduction treatment is a process for reducing oxides of metal particles (e.g., NiO (nickel oxide)) contained in the green sheet of the fuel electrode layer to metal particles (e.g., Ni) during the manufacturing process of the electrochemical cell.

[0013] The fuel electrode layer may include a functional layer and a support layer located farther from the solid electrolyte layer than the functional layer (in other words, the electrochemical cell may be a fuel electrode-supported type). In this case, the "fuel electrode layer containing metal particles and oxide particles containing Ce" corresponds to the functional layer, and the "fuel electrode half-width" refers to the half-width of the peak in the Raman spectrum of the functional layer (the Ce-containing oxide particles therein) in the above wavenumber region. Therefore, in a fuel electrode-supported electrochemical cell, the type of ion-conductive oxide in the support layer does not matter as long as the ion-conductive oxide in the functional layer is Ce-containing oxide particles.

[0014] In one aspect of the present invention, the electrolyte half-width (d1) is 81.3 cm －１ or more and 123.1 cm －１ The following is the result.

[0015] The electrolyte half-width (i.e., the half-width of the peak in the Raman spectrum of tetragonal Zr-containing oxide particles) tends to narrow (become smaller) as the firing temperature increases. This will be explained in detail below. When the firing temperature of the electrochemical cell is relatively high, metal particles in the fuel electrode layer diffuse into the solid electrolyte layer and dissolve in the Zr-containing oxide particles. Then, the crystal structure of the Zr-containing oxide particles undergoes a phase transition from cubic to tetragonal, increasing the proportion of tetragonal Zr-containing oxide particles relative to cubic Zr-containing oxide particles, thereby increasing the peak intensity of the Zr-containing oxide particles (i.e., the tetragonal Zr-containing oxide particles) in the above wavenumber range. Generally, the half-width of the peak in the Raman spectrum of particles becomes narrower as the intensity of the peak increases. Therefore, the electrolyte half-width becomes narrower as the firing temperature of the electrochemical cell increases.

[0016] Electrolyte half-width is 81.3 cm －１ If the firing temperature is less than 123.1 cm, the proportion of tetragonal Zr-containing oxide particles will be excessively high due to phase transition, resulting in a decrease in ionic conductivity. －１ If the firing temperature is too low, the solid electrolyte layer will not be sintered sufficiently (i.e., the density will be low), and the adhesion to the fuel electrode layer will be reduced.－１ or more and 123.1 cm －１ Since the value is within the following range, it is possible to suppress a decrease in ionic conductivity in the solid electrolyte layer while ensuring adhesion to the fuel electrode layer.

[0017] In one aspect of the present invention, the fuel electrode half width (d2) is 20.0 cm －１ or more, and 23.4 cm －１ The following is the result.

[0018] The fuel electrode half-width (i.e., the half-width of the peak in the Raman spectrum of the Ce-containing oxide particles) tends to decrease as the firing temperature increases, and then to increase midway. This will be explained in detail below. Increasing the firing temperature of the electrochemical cell densifies the fuel electrode layer. However, at a certain temperature, the metal particles in this layer diffuse and dissolve into the surrounding Ce-containing oxide particles. This forms a solid solution phase in the fuel electrode layer, and the crystal structure collapses. In general, the peak shape of the Raman spectrum of the particles becomes sharper as the crystal structure becomes denser, and broader as the crystal structure collapses. Therefore, the fuel electrode half-width gradually narrows in the temperature region where the crystal structure becomes denser (the region from a relatively low temperature to an intermediate temperature), and gradually widens in the temperature region where the crystal structure collapses (the region from an intermediate temperature to a relatively high temperature). Therefore, the fuel electrode half-width changes from decreasing to increasing at the above-mentioned "intermediate temperature." In this specification, the "intermediate temperature" is referred to as the "transition temperature."

[0019] Fuel electrode half-width is 20.0 cm －１ The firing temperature at this time is the conversion temperature (or a temperature close to it). In other words, this value is the minimum value of the fuel electrode half-width. On the other hand, when the fuel electrode half-width is 23.4 cm －１ There are two cases where the anode full width at half maximum exceeds 20.0 cm: when the firing temperature is excessively high and when it is excessively low. When the firing temperature is excessively high, the crystal structure of the anode layer is destroyed due to the formation of a solid solution phase, resulting in a deterioration in electrical properties. When the firing temperature is excessively low, the sinterability decreases, resulting in a decrease in adhesion to the solid electrolyte layer. In contrast, according to one aspect of the present invention, －１ or more, and 23.4 cm －１Since the value is within the following range, the degree of denseness of the fuel electrode layer is appropriately maintained, deterioration of electrical characteristics due to collapse of the crystalline structure of the fuel electrode layer is suppressed, and adhesion to the solid electrolyte layer can be ensured.

[0020] The solid oxide electrolysis cell (21) according to the present invention comprises an electrochemical cell according to the present invention.

[0021] According to the above configuration, it is possible to provide a solid oxide electrolysis cell in which adhesion is ensured and a decrease in durability is suppressed.

[0022] The cell stack (20) according to the present invention is formed by stacking the solid oxide electrolysis cells (21) according to the present invention.

[0023] According to the above configuration, it is possible to provide a cell stack in which the adhesion of the solid oxide electrolysis cells is ensured and a decrease in durability is suppressed.

[0024] The hot module (10) of the present invention comprises a cell stack (20) of the present invention, a vaporizer (30) that generates steam to be supplied to the cell stack, a heat exchanger (40) that exchanges heat with gas supplied to the cell stack, a heater (50) that heats the cell stack, and a thermal insulator (60) in which the cell stack, the vaporizer, the heat exchanger, and the heater are arranged.

[0025] According to the above configuration, it is possible to provide a hot module in which the adhesion of the solid oxide electrolysis cell is ensured and a decrease in durability is suppressed.

[0026] The hydrogen production device (1) according to the present invention comprises the hot module (10) according to the present invention.

[0027] According to the above configuration, it is possible to provide a hydrogen production device in which the adhesion of the solid oxide electrolysis cell is ensured and a decrease in durability is suppressed.

[0028] 4 is a block diagram of a hydrogen production device. It is a perspective view of a cell stack. It is a cross-sectional view taken along line III-III in FIG. 2. It is a cross-sectional view in the thickness direction of an electrolysis cell. It is a schematic diagram showing peaks of a Raman spectrum. It is a partial enlarged view of region R in FIG. 4, showing measurement points of the solid electrolyte layer and the functional layer by Raman spectroscopy. It is a diagram showing the half-width d1 of the YSZ peak in the solid electrolyte layer and the half-width d2 of the GDC peak in the functional layer for each of seven samples with different firing temperatures. It is a diagram showing the half-width ratio R (d1 / d2) for each of seven samples with different firing temperatures.

[0029] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram of a hydrogen production device 1 according to this embodiment. The hydrogen production device 1 according to this embodiment is a device that produces hydrogen by electrolyzing water vapor. As shown in Fig. 1, the hydrogen production device 1 includes a hot module 10 and a condenser 90.

[0030] The hot module 10 is constructed by covering with insulating material the main components that become hot among the elements that make up the hydrogen production device 1, and is a device in which the main components are concentrated within the insulating material so that the high temperature state of the main components is maintained. This hot module 10 includes a cell stack 20, a vaporizer 30, a heat exchanger 40, a heater 50, and insulating material 60.

[0031] The vaporizer 30 contains water (H ２ 0) 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 heat source. Therefore, the water supplied to the vaporizer 30 evaporates within the vaporizer 30, generating water vapor. The water vapor generated in the vaporizer 30 is introduced into the heat exchanger 40.

[0032] In addition to the water vapor, air is introduced into the heat exchanger 40. The heat exchanger 40 also receives high-temperature hydrogen (H ２ ) and high-temperature oxygen (O ２) is introduced into the heat exchanger 40. The high-temperature gas exchanges heat with the steam and air in the heat exchanger 40, thereby heating the steam and air introduced from the vaporizer 30.

[0033] The water vapor and air heated by the heat exchanger 40 are further heated by the heater 50 to the operating temperature of the cell stack 20 (i.e., the temperature required to operate the cell stack 20).The water vapor and air are then introduced into the cell stack 20.

[0034] The cell stack 20 is formed by stacking solid oxide electrolysis cells. The cell stack 20 is heated to an operating temperature by a heat source (such as a burner) not shown. A predetermined voltage is applied to the cell stack 20. As a result, water vapor introduced into the cell stack 20 is electrolyzed to produce hydrogen and oxygen. The hydrogen produced in the cell stack 20 is introduced into the heat exchanger 40 together with unreacted water vapor, where it is used to heat the water vapor and air introduced into the heat exchanger 40 from the vaporizer 30, and then introduced into the condenser 90. The unreacted water vapor is condensed in the condenser 90. The condensed water produced in the condenser 90 is introduced into the vaporizer 30. Meanwhile, hydrogen separated by condensation of the water vapor in the condenser 90 is recovered. The oxygen produced in the cell stack 20 is introduced into the heat exchanger 40, where it is used to heat the water vapor and air, and then introduced into the vaporizer 30 to heat the water supplied to the vaporizer 30. The oxygen discharged from the vaporizer 30 is then recovered (or released to the atmosphere).

[0035] The cell stack 20, vaporizer 30, heat exchanger 40, and heater 50 are disposed inside a thermal insulation material 60. This suppresses heat radiation from each of the components 20, 30, 40, and 50. Heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), and biosoluble fiber (AES), and / or a heat-resistant container formed from these heat-resistant fibers, may be used for the thermal insulation material 60. The heat-resistant fibers are disposed so as to fill gaps between the cell stack 20, vaporizer 30, heat exchanger 40, and heater 50.

[0036] FIG. 2 is a perspective view of the cell stack 20, and FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . As shown in FIGS. 2 and 3 , the cell stack 20 comprises an electrolysis unit group including a plurality of rectangular flat-plate-shaped electrolysis units Ue stacked in the thickness direction (up-down direction), and a pair of end plates 27, 28 disposed on the upper and lower surfaces of the electrolysis unit group, respectively. The end plates 27, 28 are rectangular flat-plate-shaped members having the same outer shape as the electrolysis units Ue, and each has a rectangular opening formed in its center. The electrolysis unit group and the end plates 27, 28 are fastened to each other at their four corners by bolts B inserted through the electrolysis units 27, 28 in the thickness direction and nuts (not shown). The end plates 27, 28 are made of metal (for example, stainless steel) and function as an anode and a cathode, respectively, when a voltage is applied. Note that for ease of explanation, the proportions of the components in the drawings may differ from the actual proportions.

[0037] The electrolysis unit Ue will be described with reference to Fig. 3. As shown in Fig. 3, the electrolysis unit Ue comprises a solid oxide electrolysis cell 21 (hereinafter simply referred to as an electrolysis cell 21), an interconnector 22, a separator 23, a cathode frame 24, an anode frame 25, and a current collector 26.

[0038] The electrolysis cell 21 is the smallest unit of the SOEC and includes a solid electrolyte layer 211, a cathode layer 212, and an anode layer 213. The cathode layer 212 is laminated on the upper surface of the solid electrolyte layer 211 so as to contact the upper surface of the solid electrolyte layer 211. The cathode layer 212 has a smaller outer shape than the solid electrolyte layer 211 and the anode layer 213, and is disposed in the center of the upper surface of the solid electrolyte layer 211 in a plan view of the electrolysis cell 21. Therefore, the upper surface of the outer periphery of the solid electrolyte layer 211 is exposed. The anode layer 213 is laminated on the lower surface of the solid electrolyte layer 211.

[0039] The interconnector 22 is a rectangular metal (for example, stainless steel) member that has a rectangular current collecting part 22a that protrudes downward from the center of its lower surface. A pair of interconnectors 22 is arranged on both sides of the electrolysis cell 21 in the thickness direction. Two adjacent electrolysis units Ue, Ue share one interconnector 22. The interconnector 22 also functions as a separator that separates the two adjacent electrolysis units Ue, Ue. The lower surface of the current collecting part 22a is in contact with the upper surface of the air cathode layer 212 of the electrolysis cell 21. The lower electrolysis unit Ue includes a pair of interconnectors 22, 29 instead of the pair of interconnectors 22, 22. The interconnector 29 is arranged at the bottom end of the cell stack 20 and differs from the interconnector 22 in that it does not have a current collecting part 22a.

[0040] The separator 23 is a rectangular plate-shaped metal (e.g., stainless steel) member with a rectangular opening formed in its center. The periphery of the opening of the separator 23 is brazed to the upper surface of the outer periphery of the solid electrolyte layer 211 of the electrolysis cell 21 with a brazing material (e.g., Ag brazing) (not shown). The separator 23 prevents mixing of oxygen generated in the air electrode layer 212 by electrolysis of water vapor and hydrogen generated in the fuel electrode layer 213.

[0041] The cathode frame 24 is a rectangular plate-shaped insulating member and may be formed of, for example, a mica sheet. A rectangular opening is formed in the center of the cathode frame 24. The cathode frame 24 is disposed between the separator 23 and the interconnector 22 above it.

[0042] The fuel electrode frame 25 is a rectangular plate-shaped metal (e.g., stainless steel) member having a rectangular opening at its center, and is disposed between the separator 23 and the interconnector 22 below it.

[0043] The internal space of the electrolysis unit Ue is partitioned into an air chamber Sa and a fuel chamber Sf by the separator 23. The air chamber Sa is a space that allows the flow of oxygen generated in the air electrode layer 212, and is defined by a space surrounded by the separator 23, the interconnector 22 above the separator 23, the air electrode frame 24, and the electrolysis cell 21. The fuel chamber Sf is a space that allows the flow of hydrogen generated in the fuel electrode layer 213, and is defined by a space surrounded by the separator 23, the interconnector 22 (or interconnector 29) below the separator 23, the fuel electrode frame 25, and the electrolysis cell 21.

[0044] The current collector 26 is a rectangular porous member made of metal (for example, nickel) that is smaller than the anode layer 213 in a plan view and allows hydrogen to pass through. The current collector 26 is arranged in the fuel chamber Sf so as to be in contact with the lower surface of the anode layer 213 and the upper surface of the lower interconnector 22. Two adjacent electrolysis cells 21 are stacked in the thickness direction so as to share the interconnector 22 via the current collector 26, thereby electrically connecting the multiple electrolysis cells 21 in series.

[0045] 2 and 3 , four paths Pfi, Pfo, Pai, and Pao are formed as gas flow paths around the outer periphery of the cell stack 20. These paths Pfi, Pfo, Pai, and Pao are each formed to penetrate members of the cell stack 20 in the thickness direction, excluding the "end plate 27" and the "upper interconnector 22 of the upper electrolysis unit Ue."

[0046] The path Pfi is formed near one corner of the side E1, which is one of the four sides that make up the outer periphery of the cell stack 20. The path Pfo is formed near the other corner of the side E2 that faces the side E1 (the corner located diagonally from the one corner of the side E1). As shown in FIG. 3 , the path Pfi communicates with the fuel chamber Sf via a horizontal hole 25a formed in the anode frame 25 of each electrolysis unit Ue. The path Pfo communicates with the fuel chamber Sf via a horizontal hole 25b formed in the anode frame 25 of each electrolysis unit Ue.

[0047] The path Pai is formed near one corner of the side E2. The path Pao is formed near the other corner of the side E1. The path Pai and the path Pao each communicate with the air chamber Sa via a horizontal hole (not shown) formed in the air electrode frame 24 of each electrolysis unit Ue.

[0048] Next, the configuration of the electrolytic cell 21 will be described in more detail with reference to FIG. 4 . The sizes and thicknesses of each layer of the electrolytic cell 21 shown below are merely examples and are not limited to these values. FIG. 4 is a cross-sectional view of the electrolytic cell 21 in the thickness direction. More precisely, FIG. 4 is a cross-sectional view of the electrolytic cell 21 cut along a cut plane including the center of the top surface of the electrolytic cell 21 in a plan view. As described above, the electrolytic cell 21 includes a solid electrolyte layer 211, an air electrode layer 212, and an anode layer 213. The solid electrolyte layer 211 is a rectangular flat layer measuring 150 mm square and 6 μm thick. It is configured to contain YSZ, an ion-conductive oxide, and is formed by sintering. The solid electrolyte layer 211 has high oxide ion conductivity. The solid electrolyte layer 211 is a dense layer and is designed to prevent leakage between the atmosphere on the air electrode layer 212 side (air atmosphere) and the atmosphere on the anode layer 213 side (reducing atmosphere).

[0049] The ion-conductive oxide in the solid electrolyte layer 211 is not limited to YSZ, and any type of additive may be used as long as it is an oxide particle containing Zr. For example, CSZ (calcia-stabilized zirconia) or ScSZ (scandia-stabilized zirconia) may be used as the ion-conductive oxide in the solid electrolyte layer 211. CSZ is ZrO with CaO (calcium oxide) added. ２ and ScSZ is Sc ２ O ３ (Scandium oxide) doped ZrO ２ is.

[0050] The air electrode layer 212 is laminated on the upper surface of the solid electrolyte layer 211 so as to contact the upper surface of the solid electrolyte layer 211. The air electrode layer 212 is a rectangular flat layer with a thickness of 108 μm, and is configured to contain a perovskite-type oxide such as LSCF (lanthanum strontium cobalt iron oxide), and is formed by sintering. The air electrode layer 212 has a functional layer and a current collecting layer. The current collecting layer is thicker than the functional layer and is disposed on the upper surface of the functional layer. The air electrode layer 212 has high electronic conductivity and effectively collects electrons from the current collecting layer. The air electrode layer 212 is a porous layer and has pores inside.

[0051] The anode layer 213 is a rectangular flat layer measuring 150 mm on each side, and is formed to have a thickness greater than that of the solid electrolyte layer 211 and that of the air cathode layer 212, for example, approximately 400 μm. The anode layer 213 supports the solid electrolyte layer 211 and the air cathode layer 212. In other words, the electrolysis cell 21 is an anode-supported cell. The anode layer 213 has a functional layer 213 a and a support layer 213 b. The functional layer 213 a is laminated on the lower surface side of the solid electrolyte layer 211. The support layer 213 b is located below the functional layer 213 a (i.e., on the side away from the solid electrolyte layer 211). In other words, the functional layer 213 a and the support layer 213 b are laminated in this order on the lower surface side of the solid electrolyte layer 211. The thickness of the support layer 213b is formed to be significantly thicker than that of the functional layer 213a, and the ratio can be set to, for example, about 16 to 40 times.

[0052] The main component of the support layer 213b is a cermet of Ni as a catalytic metal and YSZ as an ion-conductive oxide. The support layer 213b is a porous layer configured to have a porous shape including a plurality of micropores (not shown). The diameter of the micropores is on the order of several μm, which ensures the permeability of water vapor (gas diffusibility). The ion-conductive oxide in the support layer 213b is not limited to YSZ and may be, for example, GDC.

[0053] The main component of the functional layer 213a is a cermet of Ni as a catalytic metal and GDC, an ion-conductive oxide. Like the support layer 213b, the functional layer 213a is a porous layer configured to have a porous shape including a plurality of micropores (not shown). However, the functional layer 213a is formed more densely than the support layer 213b. That is, the porosity of the functional layer 213a is smaller than the porosity of the support layer 213b. Like the solid electrolyte layer 211 and the air electrode layer 212, the fuel electrode layer 213 is formed by sintering.

[0054] The ion-conductive oxide in the functional layer 213 a is not limited to GDC, and any type of additive may be used as long as it is an oxide particle containing Ce. For example, YDC (yttria-doped ceria), SDC (samaria-doped ceria), LDC (lanthania-doped ceria), or the like may be used as the ion-conductive oxide in the functional layer 213 a.

[0055] The Raman spectrum of the Stokes scattered light obtained by Raman spectroscopy of the electrolytic cell 21 provides various physical property information, including the crystalline morphology of each layer of the electrolytic cell 21. The physical properties of each layer can be controlled by adjusting the firing temperature (strictly speaking, the firing temperature during the manufacture of the electrolytic cell 21). Raman spectroscopy is a spectroscopic method that evaluates the physical properties of a target using Raman scattered light. When light is irradiated onto a target, the incident light collides with molecules in the target and some of the light is emitted as scattered light. Most of the scattered light has the same wavelength as the incident light (i.e., Rayleigh scattered light), but the scattered light also contains a small amount of light having a wavelength different from that of the incident light (i.e., Raman scattered light). In this embodiment, Stokes scattered light, which is Raman scattered light with a longer wavelength than the incident light, is used for analysis.

[0056] 5 is a schematic diagram showing the peak Pr of the Raman spectrum Sr. The horizontal axis of the Raman spectrum Sr is the wave number (in other words, the Raman shift) (cm －１) The Raman shift is the amount of wavenumber shift from the excitation wavelength. The vertical axis of the Raman spectrum Sr represents the intensity of the Stokes scattered light. Various physical property information can be obtained from the Raman spectrum Sr. For example, information on chemical bonds can be obtained from the top position of peak Pr. Information on molecular structure and information on differences in crystalline structure can be obtained from the overall waveform of the Raman spectrum Sr. Information on differences in crystallinity can be obtained from the half-width d of peak Pr (the width of peak Pr at half the intensity Imax / 2 of the top of peak Pr).

[0057] In this embodiment, Raman spectroscopy of the ion-conductive oxide in the solid electrolyte layer 211 and the functional layer 213a was performed using a laser Raman spectrophotometer (model: NRS-5100) manufactured by JASCO Corporation. The laser light used had an excitation wavelength of 532.38 nm and an intensity of 4.7 mW. The exposure time was 60 seconds, and the number of integrations was two.

[0058] FIG. 6 is a partial enlarged view of region R in FIG. 4 , showing measurement points for Raman spectroscopy. As is clear from FIG. 4 , region R is a region including the center in a direction perpendicular to the thickness direction of the cross-sectional view in FIG. 4 . As shown in FIG. 6 , measurement point p1 indicates the position where laser light is irradiated on the cross-section of the solid electrolyte layer 211, and measurement point p2 indicates the position where laser light is irradiated on the cross-section of the functional layer 213a. Five measurement points p1 are arranged at equal intervals in the thickness direction, with three equally spaced points at the same thickness position. That is, for the solid electrolyte layer 211, Raman spectroscopy is performed at 15 measurement points p1. Six measurement points p2 are arranged at equal intervals in the thickness direction, with three equally spaced points at the same thickness position. That is, for the functional layer 213a, Raman spectroscopy is performed at 18 measurement points p2. Measurement point p1 is set in advance so as not to be located in the vicinity of interface S1 between solid electrolyte layer 211 and cathode layer 212, or in the vicinity of interface S2 between solid electrolyte layer 211 and functional layer 213a. Measurement point p2 is set in advance so as not to be located in the vicinity of interface S2 or in the vicinity of interface S3 between functional layer 213a and support layer 213b. Note that interfaces S1, S2, and S3 can all be identified by differences in porosity.

[0059] When analyzing the solid electrolyte layer 211 by Raman spectroscopy, the measurement point p1 is irradiated with laser light, and the resulting Stokes scattered light is separated using a diffraction grating to generate a Raman spectrum of the solid electrolyte layer 211. The Raman spectrum of tetragonal YSZ, which is one of the YSZ components constituting the solid electrolyte layer 211, is expressed by a Raman spectrum of 334 cm －１ Above and 531 cm －１ The Raman spectrum of the solid electrolyte layer 211 has a peak in the following wavenumber region. Hereinafter, this wavenumber region will be referred to as the "wavenumber region of interest." In this embodiment, the average value of the half-widths of the peaks of tetragonal YSZ measured at each measurement point p1 is defined as the half-width d1 of the peak in the Raman spectrum of the solid electrolyte layer 211 in the wavenumber region of interest. The half-width d1 corresponds to an example of the "electrolyte half-width."

[0060] Similarly, when analyzing the functional layer 213a by Raman spectroscopy, the Stokes scattered light obtained by irradiating the measurement point p2 with laser light is dispersed using a diffraction grating to generate a Raman spectrum of the functional layer 213a. The Raman spectrum of the GDC constituting the functional layer 213a has a peak in a wavenumber region of interest. In this embodiment, the average value of the half-width of the GDC peak measured at each measurement point p2 is defined as the half-width d2 of the peak of the Raman spectrum of the functional layer 213a in the wavenumber region of interest. The half-width d2 corresponds to an example of the "fuel electrode half-width."

[0061] In this embodiment, the electrolytic cell 21 is manufactured so that the half-value width ratio R (= d1 / d2), which is the ratio of the half-value width d1 to the half-value width d2, is a value in the range of 3.5 or more and 5.7 or less. In addition, the electrolytic cell 21 has a half-value width d1 of 81.3 cm －１ or more and 123.1 cm －１ The value is within the following range, and the half width d2 is 20.0 cm －１ or more, and 23.4 cm －１ It is manufactured to have values ​​within the following ranges.

[0062] The operation of the cell stack 20 will be described. First, a voltage is applied between the end plates 27, 28 of the cell stack 20. Next, high-temperature steam is supplied from the path Pfi. The steam supplied to the path Pfi flows into the fuel chamber Sf of each electrolysis unit Ue via the horizontal holes 25a. In addition, high-temperature air is supplied from the path Pai. The air supplied to the path Pai flows into the air chamber Sa of each electrolysis unit Ue via a horizontal hole (not shown). The reason for supplying high-temperature air to the air chamber Sa is to control the temperature of the cell stack 20.

[0063] The water vapor that flows into the fuel chamber Sf passes through the support layer 213b of the fuel electrode layer 213 and travels to the functional layer 213a. In the functional layer 213a, the water vapor reacts with electrons supplied from the end plate 28 via the current collector 26 and is decomposed into hydrogen and oxide ions (water vapor electrolysis reaction). The hydrogen generated by the water vapor electrolysis reaction diffuses within the fuel chamber Sf, is discharged through the horizontal hole 25b via path Pfo, and is recovered by a well-known method. At this time, unreacted water vapor can be discharged along with the hydrogen via path Pfo. Meanwhile, the oxide ions travel through the solid electrolyte layer 211 to the air electrode layer 212 in the air chamber Sa, release electrons in the functional layer of the air electrode layer 212, and become oxygen. The oxygen diffuses within the air chamber Sa and, together with the air that flowed into the air chamber Sa, is discharged through path Pao via a horizontal hole (not shown) and is recovered (or released to the atmosphere) by a well-known method. Electrons emitted from the functional layer of the air electrode layer 212 are collected by the current collecting portion 22a of the interconnector 22 via the current collecting layer, and circulate from the end plate 27 to the end plate 28 via the external power source.

[0064] The cell stack 20 operates as described above, and hydrogen is produced in the hydrogen production device 1 .

[0065] As described above, the ion-conductive oxide in the solid electrolyte layer 211 of the electrolytic cell 21 according to this embodiment is YSZ. Meanwhile, the ion-conductive oxide in the functional layer 213a of the electrolytic cell 21 according to this embodiment is GDC. Thus, when the solid electrolyte layer 211 contains YSZ and the functional layer 213a contains Ni and GDC, the performance degradation of the electrolytic cell 21 due to Ni migration and aggregation can be improved, but another problem due to the firing temperature occurs. Specifically, if the firing temperature is excessively high, durability decreases, and if the firing temperature is excessively low, adhesion decreases (and in some cases, initial performance also decreases).

[0066] The full width at half maximum ratio R tends to decrease as the firing temperature of the electrolytic cell 21 increases. In the electrolytic cell 21 according to this embodiment, the full width at half maximum ratio R is set to a value within a range of 3.5 or more and 5.7 or less. The full width at half maximum ratio R of 3.5 or more prevents the firing temperature from becoming excessively high, thereby suppressing a decrease in durability. Furthermore, the full width at half maximum ratio R of 5.7 or less prevents the firing temperature from becoming excessively low, thereby ensuring the adhesion of the electrolytic cell 21. Therefore, the electrolytic cell 21 according to this embodiment can suppress a decrease in durability while ensuring adhesion. In addition, it can suppress a decrease in the initial performance of the electrolytic cell 21 due to a decrease in adhesion. In other words, by manufacturing the electrolytic cell 21 at a firing temperature that results in a value of the full width at half maximum ratio R within the above range, the crystal morphology of the solid electrolyte layer 211 and the functional layer 213a can be optimized.

[0067] Furthermore, the half-value width d1 tends to become narrower (smaller) as the firing temperature increases. In the electrolysis cell 21 according to this embodiment, the half-value width d1 is 81.3 cm －１ or more and 123.1 cm －１ The value is set to be within the following range: According to this configuration, it is possible to suppress a decrease in ion conductivity in the solid electrolyte layer 211 while ensuring adhesion to the functional layer 213a (described in detail in Examples).

[0068] Furthermore, the half-value width d2 tends to decrease as the calcination temperature increases and then increase at the conversion temperature.－１ or more, and 23.4 cm －１ The half width d2 is set to a value within the following range. －１ The firing temperature at this time is the conversion temperature (or a temperature close to it). That is, this value is the minimum value of the half-value width d2 when Raman spectroscopy is performed under the above conditions. －１ The firing temperature at this time can be either higher or lower than the conversion temperature. Therefore, this configuration can appropriately maintain the density of the fuel electrode layer, suppress deterioration of electrical characteristics due to collapse of the crystalline structure of the fuel electrode layer, and ensure adhesion to the solid electrolyte layer (described in detail in the Examples).

[0069] The physical properties of each layer of the electrolytic cell 21 can be controlled by adjusting the firing temperature. In the following examples, multiple samples of the electrolytic cell 21 were produced at different firing temperatures, and the relationships among the firing temperature, the half-value width ratio R, and the half-value widths d1 and d2 were investigated.

[0070] (Examples) 1. Sample Preparation NiO powder and GDC powder were mixed in a predetermined ratio and stirred for a predetermined time using a ball mill or the like. Next, butyral resin, polyvinyl acetal resin (G-260, manufactured by Sekisui Chemical Co., Ltd.) as a plasticizer, a known dispersant, a mixed solvent of toluene and MEK (methyl ethyl ketone), and optionally a pore-forming agent (typically organic beads) were added to the mixed powder in predetermined ratios and mixed in a ball mill to prepare a slurry. Then, a green sheet of a functional layer having a predetermined thickness was formed from the slurry using a doctor blade method.

[0071] NiO powder and YSZ powder were mixed in a predetermined ratio and stirred for a predetermined time using a ball mill or the like. Next, butyral resin, polyvinyl acetal resin as a plasticizer, a known dispersant, a mixed solvent of toluene and MEK, and optionally a pore-forming agent (typically organic beads) were added to the mixed powder in predetermined ratios and mixed in a ball mill to prepare a slurry. Then, a green sheet of a support layer having a predetermined thickness was formed from the slurry using a doctor blade method.

[0072] A butyral resin, a polyvinyl acetal resin as a plasticizer, a known dispersant, and a mixed solvent of toluene and MEK were added to the YSZ powder in predetermined proportions and mixed in a ball mill to prepare a slurry, which was then molded into a green sheet of a solid electrolyte layer having a predetermined thickness using a doctor blade method.

[0073] Next, a green sheet for the functional layer and a green sheet for the support layer were stacked in this order on one side of the green sheet for the solid electrolyte layer. These stacked green sheets were then pressed together under high pressure using a press while being heated and evacuated. This resulted in the formation of a laminate including the green sheet for the solid electrolyte layer, the green sheet for the functional layer, and the green sheet for the support layer.

[0074] The laminate formed as described above was then degreased at a predetermined temperature (e.g., 200 to 300°C). The laminate was then fired at a predetermined first temperature t0 for a predetermined time (primary firing). This resulted in a primary sintered body having a solid electrolyte layer and a fuel electrode layer stacked on one side of the solid electrolyte layer.

[0075] Subsequently, a material containing LSCF was screen-printed onto the other surface of the solid electrolyte layer of the formed primary sintered body, and the resulting product was fired at a predetermined second temperature (e.g., 900 to 1000°C) for a predetermined time (e.g., 1 to 5 hours) (secondary firing). This produced a sample electrolysis cell including a solid electrolyte layer, an anode layer laminated on one surface of the solid electrolyte layer, and an cathode layer laminated on the other surface of the solid electrolyte layer.

[0076] In this example, seven electrolytic cell samples (Samples 1 to 7) were prepared, each with different full widths at half maximum (d1) and full width at half maximum (d2) and different full width at half maximum (R) ratios, by changing the firing temperature (first temperature t0) and firing time of the primary firing for each sample. For Samples 1 to 7, the first temperature t0 increases and the firing time increases as the sample number (1 to 7) increases. The first temperature t0 for each sample is specifically as follows: for Sample 1, the first temperature t0 is 1090°C; for Sample 2, the first temperature t0 is 1120°C; for Sample 3, the first temperature t0 is 1190°C; for Sample 4, the first temperature t0 is 1240°C; for Sample 5, the first temperature t0 is 1290°C; for Sample 6, the first temperature t0 is 1340°C; and for Sample 7, the first temperature t0 is 1390°C.

[0077] Furthermore, if the first temperature t0 is low, the electrolytic cell may not be sufficiently sintered. Therefore, in this embodiment, the particle size of the YSZ powder used to form the green sheet for the solid electrolyte layer is controlled so that the electrolytic cell can be sufficiently sintered even when the first temperature t0 is low. Specifically, a commercially available YSZ powder is pre-pulverized to reduce its particle size (average particle size), and the resulting YSZ powder is used to form the green sheet for the solid electrolyte layer. It is known that the smaller the particle size of the YSZ powder used, the better the sinterability. Therefore, even when the first temperature t0 is low, sufficient sinterability can be maintained by reducing the particle size of the YSZ powder used to form the green sheet for the solid electrolyte layer. Hereinafter, the pre-pulverized YSZ powder used to form the green sheet for the solid electrolyte layer is referred to as pulverized YSZ powder.

[0078] In this example, for samples (samples 1, 2, 3, and 4) having a firing temperature (first temperature t0) of 1240°C or less, the YSZ powder was pre-ground so that the average particle diameter (median diameter) PD of the pulverized YSZ powder was 0.20 μm or less (specifically, 0.16 μm), and for samples (samples 5, 6, and 7) having a firing temperature (first temperature t0) of more than 1240°C, the YSZ powder was pre-ground so that the average particle diameter (median diameter) PD of the pulverized YSZ powder was more than 0.20 μm (specifically, 0.27 μm).

[0079] 2. Measurement of the half-value width d1 of the solid electrolyte layer and the half-value width d2 of the functional layer Samples 1 to 7 were cut in plan view along the thickness direction of the electrolytic cell, and the half-value width d1 of the solid electrolyte layer and the half-value width d2 of the functional layer in region R (see FIG. 4 ) were measured by Raman spectroscopy using the method described above. The half-value width d1 is the half-value width of the YSZ (i.e., tetragonal YSZ) peak in the wavenumber region of interest, and the half-value width d2 is the half-value width of the GDC peak in the wavenumber region of interest.

[0080] 3. Calculation of Half Width Ratio R For Samples 1 to 7, the half width ratio R was calculated by dividing the half width d1 by the half width d2.

[0081] 4. Measurement of Current Density For Samples 1 to 7, the samples were heated to 700°C, and a constant voltage (1.3 V in this example) was applied between the anode layer and the cathode layer while a constant flow rate of steam was supplied to the anode layer side to perform a steam electrolysis reaction. The current per unit area (current density) flowing during the steam electrolysis reaction was measured, and the measured current density was used as an index for evaluating performance. That is, Samples 1 to 7 were operated as SOECs. It can be said that the higher the current density, the better the initial performance.

[0082] 5. Measurement of Durability Degradation Rate For Samples 1 to 7, a durability degradation test was conducted in which the samples were heated to 700°C, a constant flow rate of water vapor was supplied to the anode layer side so that a constant current flowed between the anode layer and the cathode layer, and a voltage was applied between the anode layer and the cathode layer to continuously perform a steam electrolysis reaction. That is, Samples 1 to 7 were operated as an SOEC. When a constant current was continuously flowed during the durability degradation test, the applied voltage increased over time due to an increase in internal resistance within the sample. The difference ΔV (= V1 - V0) between the initially applied voltage (V0) and the voltage (V1) applied after a predetermined time (e.g., 400 hours) was calculated, and the calculated value was converted to the difference between the voltage that would be applied after 1000 hours and the initially applied voltage. The converted value was then divided by the initially applied voltage to calculate the durability degradation rate as a percentage. It can be said that the smaller the durability degradation rate, the higher the durability.

[0083] 6. Evaluation Table 1 shows the half-value widths d1 and d2, half-value width ratio R, current density, and durability deterioration rate obtained for Samples 1 to 7.

[0084] In Table 1, t0 indicates the firing temperature (first temperature) of the primary sintered body, and PD indicates the average particle diameter (median diameter D50) of the pulverized YSZ powder used to form the green sheet for the solid electrolyte layer. ２ When the current density was 0.7 A / cm or more, the initial performance was evaluated as very good (◎). ２ 0.9A / cm or more ２ When the current density is less than 0.5 A / cm, the initial performance is evaluated as good (◯). ２ 0.7A / cm or more ２ When the current density is less than 0.5 A / cm, the initial performance is evaluated as fair (△). ２When the current density was less than 3.0%, the initial performance was evaluated as poor (×). When the current density could not be measured, the initial performance was evaluated as ineligible for evaluation (-). Regarding the durability degradation rate, when the durability degradation rate was less than 3.0%, the durability was evaluated as good (◯), and when the durability degradation rate was 3.0% or more, the durability was evaluated as poor (×). When the durability degradation test could not be continued for the specified time, the durability was evaluated as ineligible for evaluation (-).

[0085] For samples 3 to 5, the initial performance is very good (◎) and the durability is good (◯). In contrast, for sample 1, both the initial performance and durability are unassessable (-). For sample 2, the initial performance is good (◯), but the durability is unassessable (-) because the durability degradation test showed rapid deterioration in less than 400 hours, forcing the test to be discontinued. For samples 6 and 7, the initial performance is very good (◎), but the durability is poor (×).

[0086] Fig. 7 is a graph plotting the half-widths d1 and d2 of Samples 1 to 7 for each sample. Fig. 8 is a graph plotting the half-width ratio R of Samples 1 to 7 for each sample. The half-widths d1 and d2 of Sample 1 could not be measured, and the half-width ratio R could not be calculated. For this reason, the values ​​for Sample 1 are both set to 0 in Figs. 7 and 8 .

[0087] As can be seen from Table 1 and FIG. 7, in Samples 2 to 7, the half-width d1 decreases as the sample number increases (i.e., the firing temperature increases). Also, the half-width d2 decreases from Samples 2 to 4 and increases from Samples 4 to 7. That is, the firing temperature of Sample 4 is the conversion temperature. Furthermore, as can be seen from Table 1 and FIG. 8, in Samples 2 to 7, the half-width ratio R decreases as the sample number increases.

[0088] The initial performance and durability of Sample 1 were rated "unassessable" (-) because the firing temperature was excessively low, and even when the YSZ powder used to form the green sheet for the solid electrolyte layer was pre-pulverized to reduce the average particle size, the solid electrolyte layer and functional layer were not sufficiently sintered (i.e., low density), resulting in reduced adhesion between the two layers. The initial performance of Sample 2 was rated "good" (i.e., improved compared to Sample 1) because the firing temperature was higher than that of Sample 1, resulting in slightly improved density between the solid electrolyte layer and functional layer, and slightly improved adhesion between the two layers. However, because the density was still insufficient, adhesion decreased over the course of long-term operation, which is thought to be the reason for the durability rating of "unassessable" (-).

[0089] As can be seen from Table 1 and FIG. 7 , the half-width ratios d1 and d2 of Sample 2 are larger than the half-width ratios d1 and d2 of Sample 3. This is thought to be because Sample 2 had a lower firing temperature than Sample 3, resulting in lower density of the solid electrolyte layer and functional layer, and as a result, the peak shapes of both tetragonal YSZ and GDC are broader. As mentioned above, in the Raman spectroscopy measurement of the solid electrolyte layer, the Raman spectrum of tetragonal YSZ is analyzed. However, in the region where the firing temperature is relatively low, no phase transition occurs and the proportion of tetragonal YSZ is low, so the peak intensity is naturally low. This is also thought to be the reason why Sample 2 has a larger half-width d1 than Sample 3.

[0090] On the other hand, the poor durability (×) of Samples 6 and 7 is thought to be due to changes in the crystalline morphology of the solid electrolyte layer and the functional layer caused by excessively high firing temperatures. Specifically, the high firing temperature causes Ni in the functional layer to diffuse into the solid electrolyte layer and dissolve in the YSZ, resulting in a phase transition from cubic to tetragonal. This change in the crystalline morphology of the solid electrolyte layer causes a decrease in ionic conductivity. Furthermore, the high firing temperature causes Ni in the functional layer to diffuse and dissolve in the surrounding GDC, forming a solid solution phase (Ni phase) in the functional layer, which disrupts the crystalline structure of the functional layer. This change in the crystalline morphology of the functional layer causes a decrease in electrical properties. It is thought that the poor durability (×) was due to the changes in the crystalline morphology of the solid electrolyte layer and the functional layer, resulting in a decrease in ionic conductivity and electrical properties. The reason why the initial performance of Samples 6 and 7 is very good (◎) is thought to be that what affects the initial performance is the high adhesion between the solid electrolyte layer and the functional layer, and the phase transition in the solid electrolyte layer and the collapse of the crystalline structure in the functional layer do not have much effect on the initial performance.

[0091] As can be seen from Table 1 and FIG. 7 , the half-value widths d1 of Samples 6 and 7 are smaller than that of Sample 5. This is thought to be because Samples 6 and 7 were fired at a higher temperature than Sample 5, resulting in a greater amount of Ni dissolved in the solid electrolyte layer and more phase transitions, resulting in a higher peak intensity of tetragonal YSZ (generally, the higher the peak intensity, the narrower the half-value width of the peak). On the other hand, the half-value widths d2 of Samples 6 and 7 are larger than that of Sample 5. This is thought to be because Samples 6 and 7 were fired at a higher temperature than Sample 5, resulting in a greater amount of solid solution phase being formed in the functional layer, causing the crystal structure to collapse, resulting in a broader GDC peak shape.

[0092] From the above, as long as the full width at half maximum ratios R (see Table 1 and FIG. 8 ) for Samples 3 to 5 are within the range, adhesion is ensured and deterioration in durability is suppressed. That is, when the full width at half maximum ratio R is 3.5 or more and 5.7 or less, adhesion of the electrolysis cell can be ensured and deterioration in durability can be suppressed. In other words, the crystal morphologies of the solid electrolyte layer and the functional layer can be optimized.

[0093] Furthermore, the larger the half-width ratio R, the lower the firing temperature (first temperature t0) of the primary sintered body can be, thereby reducing the thermal energy required to produce the electrolytic cell and, as a result, reducing the manufacturing cost of the electrolytic cell. Therefore, from the perspective of reducing the manufacturing cost of the electrolytic cell, it is desirable that the half-width ratio R be as large as possible. Specifically, the half-width ratio R is preferably 4.0 or more, more preferably 4.5 or more, and even more preferably 5.1 or more.

[0094] Furthermore, within the range of the half-value width d1 (see Table 1 and FIG. 7) in Samples 3 to 5, the decrease in ion conductivity in the solid electrolyte layer is suppressed and adhesion to the functional layer is ensured. －１ By setting the value to 1 or more, the firing temperature is prevented from becoming excessively high, and therefore, a decrease in ion conductivity due to a phase transition of YSZ in the solid electrolyte layer is prevented. －１ By setting the half width d1 to 81.3 cm or less, the firing temperature is prevented from becoming excessively low, thereby ensuring the density of the solid electrolyte layer and the adhesion with the functional layer. －１ or more and 123.1 cm －１ When the ratio is equal to or less than 1, the adhesion to the functional layer can be ensured while suppressing a decrease in ionic conductivity in the solid electrolyte layer.

[0095] Furthermore, within the range of the half-value width d2 (see Table 1 and FIG. 7) in Samples 3 to 5, the degree of denseness of the functional layer is appropriately maintained, deterioration of the electrical properties due to the collapse of the crystalline structure of the functional layer is suppressed, and adhesion to the solid electrolyte layer is ensured. －１The firing temperature at this time is the conversion temperature. That is, this value is the minimum value of the half-value width d2 when Raman spectroscopy is performed under the above conditions. －１ The firing temperature at this time can be either higher or lower than the conversion temperature (firing temperature of sample 4). －１ By keeping the half-value width d2 at 23.4 cm or less, the firing temperature is prevented from becoming excessively high, and therefore, deterioration of the electrical characteristics due to the breakdown of the crystalline structure of the functional layer caused by the formation of a solid solution phase is prevented. －１ By keeping the half width d2 at 20.0 cm or less, the firing temperature is prevented from becoming excessively low, and therefore, a decrease in adhesion to the solid electrolyte layer due to a decrease in sinterability is prevented. －１ or more, and 23.4 cm －１ When the thickness is below this value, the degree of density of the functional layer can be appropriately maintained, deterioration of electrical properties due to breakdown of the crystalline structure of the functional layer can be suppressed, and adhesion to the solid electrolyte layer can be ensured.

[0096] In the above examples, the performance of the electrolytic cell was evaluated by operating it as an SOEC, but similar results were obtained when Samples 1 to 7 were fabricated as fuel cells (the cell configuration was the same) and operated as SOFCs. That is, for Samples 3 to 5, the initial performance was very good (◎) and the durability was good (◯).

[0097] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the object of the present invention.

[0098] For example, the type of metal particles in the functional layer 213a is not limited to Ni. The same applies to the support layer 213b.

[0099] The present invention may further include the following aspects: [1] An electrochemical cell comprising: a solid electrolyte layer containing oxide particles containing Zr; a fuel electrode layer laminated on one surface of the solid electrolyte layer and containing metal particles and oxide particles containing Ce; and an air electrode layer laminated on the other surface of the solid electrolyte layer, wherein the Raman spectra of the Stokes scattered light of the solid electrolyte layer and the fuel electrode layer are －１ Above and 531 cm －１ [2] The electrochemical cell according to [1], wherein the electrolyte half width is 81.3 cm or less, and wherein the half widths of the peaks of the Raman spectra of the solid electrolyte layer and the anode layer in the wave number ranges are defined as the electrolyte half width and the anode half width, respectively, and the ratio of the electrolyte half width to the anode half width is 3.5 or more and 5.7 or less. －１ or more and 123.1 cm －１ [3] The electrochemical cell according to [1] or [2], wherein the fuel electrode half width is 20.0 cm or less. －１ or more, and 23.4 cm －１ An electrochemical cell comprising the following: [4] A solid oxide electrolysis cell comprising the electrochemical cell according to any one of [1] to [3]. [5] A cell stack comprising a stack of solid oxide electrolysis cells according to [4]. [6] A hot module comprising: the cell stack according to [5]; a vaporizer that generates water vapor to be supplied to the cell stack; a heat exchanger that exchanges heat with gas supplied to the cell stack; a heater for heating the cell stack; and a thermal insulator in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed. [7] A hydrogen production device comprising the hot module according to [6].

[0100] 1... Hydrogen production device, 10... Hot module, 20... Cell stack, 21... Solid oxide electrolysis cell (electrochemical cell), 22, 29... Interconnector, 23... Separator, 24... Cathode frame, 25... Anode frame, 26... Current collector, 27, 28... End plate, 30... Vaporizer, 40... Heat exchanger, 50... Heater, 60... Insulator, 90... Condenser, 211... Solid electrolyte layer, 212... Cathode layer, 213... Anode layer, 213a... Functional layer, 213b... Support layer

Claims

1. An electrochemical cell comprising: a solid electrolyte layer containing oxide particles containing Zr; a fuel electrode layer laminated on one side of the solid electrolyte layer and containing metal particles and oxide particles containing Ce; and an air electrode layer laminated on the other side of the solid electrolyte layer, wherein the Raman spectrum of the Stokes scattered light of the solid electrolyte layer and the fuel electrode layer has a wavelength of 334 cm －１ Above and 531 cm －１ wherein the half widths of the peaks of the Raman spectra of the solid electrolyte layer and the anode layer in the wave number ranges below are defined as an electrolyte half width and an anode half width, respectively, and the ratio of the electrolyte half width to the anode half width is 3.5 or more and 5.7 or less.

2. The electrochemical cell according to claim 1, wherein the electrolyte half-width is 81.3 cm －１ or more and 123.1 cm －１ The following is an electrochemical cell.

3. An electrochemical cell according to claim 1 or 2, wherein the fuel electrode half width is 20.0 cm －１ or more, and 23.4 cm －１ The following is an electrochemical cell.

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

5. A cell stack comprising a stack of solid oxide electrolysis cells according to claim 4.

6. A hot module comprising: a cell stack according to claim 5; a vaporizer that generates steam to be supplied to the cell stack; a heat exchanger that exchanges heat with gas supplied to the cell stack; a heater that heats the cell stack; and a heat insulating material in which the cell stack, the vaporizer, the heat exchanger, and the heater are disposed.

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

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