JP2018010740A - Electrochemical cell, electrochemical stack, and method for manufacturing electrochemical cell - Google Patents

Abstract

Dispersion of a transition metal element into an electrolyte layer is suppressed, and a decrease in power generation capacity of an electrochemical cell is suppressed. An electrochemical cell includes an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in a first direction with the electrolyte layer interposed therebetween. The lanthanum gallate-based perovskite oxide is included, the thickness of the fuel electrode in the first direction is larger than the thickness of the electrolyte layer in the first direction, and the average particle size of the particles constituting the electrolyte layer is 2.0 ( μm) or more and 8.0 (μm) or less. [Selection] Figure 3

Description

  The technology disclosed herein relates to an electrochemical cell.

  A solid oxide fuel cell (hereinafter referred to as “SOFC”) is known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. A cell for SOFC (hereinafter referred to as “cell”) includes an electrolyte layer containing a solid oxide, an air electrode and a fuel electrode facing each other in a predetermined direction (hereinafter referred to as “arrangement direction”) with the electrolyte layer interposed therebetween. Is provided.

As a solid oxide, a lanthanum gallate-based perovskite oxide ((La (lanthanum), Sr (strontium)) (Ga (gallium), Mg (magnesium)) O ₃ ( Hereinafter, “LSGM”)) may be used. SOFCs using LSGM as a solid oxide are known in which transition metal elements are contained in the air electrode and the fuel electrode (see, for example, Patent Documents 1 and 2).

JP 2003-173801 A JP 2012-156007 A

When a transition metal element (for example, Sr or La) is included in the air electrode, the transition metal element diffuses to the electrolyte layer side and reacts with an element (for example, Zr (zirconium)) included in the electrolyte layer, thereby causing a high resistance layer (for example, SrZrO ₃ ) is formed, and as a result, the power generation performance of the cell may be reduced. Further, when the fuel electrode contains a transition metal element (for example, Ni (nickel), Mn (manganese)), for example, in the process of firing the precursor before firing of the electrolyte layer and the molded body for the fuel electrode in the manufacturing stage, Transition metal elements (for example, Ni (nickel), Mn (manganese)) contained in the molded article for electrodes diffuse to the pre-firing precursor side of the electrolyte layer, and the elements (eg, La) contained in the pre-firing precursor of the electrolyte layer By reacting, an insulating layer (for example, LaNiO ₃ ) is formed at the interface between the electrolyte layer and the fuel electrode, and as a result, the power generation performance of the cell may be reduced.

  Such a problem is common to solid oxide electrolysis cells (hereinafter referred to as “SOEC”) that generate hydrogen using an electrolysis reaction of water. In this specification, the SOFC cell and the SOEC cell are collectively referred to as an electrochemical cell, and the SOFC stack and the SOEC stack are collectively referred to as an electrochemical stack.

  In this specification, the technique which can solve the subject mentioned above is disclosed.

  The technology disclosed in this specification can be implemented as the following forms.

(1) An electrochemical cell disclosed in the present specification includes an electrolyte layer containing a solid oxide, and an air electrode and a fuel electrode facing each other in a first direction with the electrolyte layer interposed therebetween. The solid oxide includes a lanthanum gallate perovskite oxide, and the thickness of the fuel electrode in the first direction is larger than the thickness of the electrolyte layer in the first direction. The average particle size of the constituent particles is 2.0 (μm) or more and 8.0 (μm) or less. According to this electrochemical cell, the average particle diameter of the particles constituting the electrolyte layer is 2.0 (μm) or more and 8.0 (μm) or less. For this reason, compared with the case where the average particle diameter of the particle | grains which comprise an electrolyte layer is less than 2.0 (micrometer), the grain boundary which is a boundary between the particle | grains used as the diffusion path | route of a transition metal element in an electrolyte layer Accordingly, the diffusion of the transition metal element into the electrolyte layer can be suppressed by the amount of decrease, and as a result, it is possible to suppress a decrease in the power generation capability of the electrochemical cell.

(2) In the electrochemical cell, the thickness of the electrolyte layer in the first direction may be 15 (μm) or more and 30 (μm) or less. According to this electrochemical cell, the thickness of the electrolyte layer in the first direction is 15 (μm) or more and 30 (μm) or less. For this reason, compared with the case where the thickness of the electrolyte layer in the first direction is less than 15 (μm), the air electrode and the fuel electrode are prevented from being electrically short-circuited by the transition metal element diffused in the electrolyte layer. be able to. Moreover, compared with the case where the thickness of the electrolyte layer in the first direction is larger than 30 (μm), the electrical resistance of the electrolyte layer itself can be suppressed. Thereby, it can suppress more effectively that the power generation capability of an electrochemical cell falls.

(3) In the electrochemical cell, the air electrode may include a cobaltite perovskite oxide. According to this electrochemical cell, since the air electrode contains a cobaltite-based perovskite oxide having excellent conductivity and electrocatalytic activity, it is possible to more effectively suppress a decrease in the power generation capacity of the electrochemical cell. Can do.

(4) In the electrochemical cell, the cobaltite-based perovskite oxide may include Ba. According to the present electrochemical cell, the cobaltite-based perovskite oxide constituting the air electrode contains Ba (barium). Thereby, the electrocatalytic activity in an air electrode becomes high, and can improve the power generation capability of an electrochemical cell.

(5) In the method for producing an electrochemical cell, a step of preparing a fuel electrode molded body, a step of forming a precursor before firing of an intermediate layer in the fuel electrode molded body, and the fuel electrode molded body, A step of simultaneously firing the precursor before firing of the intermediate layer formed in the molded body for the fuel electrode to produce a first fired body, and an electrolyte on the intermediate layer side of the first fired body The step of forming a precursor before firing of the layer, the first fired body, and the precursor before firing of the electrolyte layer formed on the first fired body are simultaneously fired to form a second fired body. It is good also as a structure provided with the process to produce. In order to increase the average particle size of the particles constituting the electrolyte layer, it is necessary to increase the firing temperature. Here, if the molded body for the fuel electrode, the precursor before firing of the intermediate layer and the precursor before firing of the electrolyte layer are simultaneously fired, by increasing the firing temperature, before the intermediate layer becomes dense, There is a possibility that the transition metal element contained in the fuel electrode passes through the intermediate layer and diffuses to the electrolyte layer side. On the other hand, according to the manufacturing method of the electrochemical cell, first, the molded body for the fuel electrode and the precursor before firing of the intermediate layer formed in the molded body for the fuel electrode are fired. A fired body is produced. Thereafter, the precursor before firing of the electrolyte layer is disposed on the intermediate layer side of the first fired body and fired. As a result, when the electrolyte layer is fired, even if the firing temperature is increased in order to increase the average particle size of the particles constituting the electrolyte layer, it is included in the fuel electrode by the intermediate layer that is already dense by firing. It is possible to suppress the transition metal element from diffusing to the electrolyte layer side.

(6) In the above electrochemical cell manufacturing method, the firing temperature of the precursor before firing of the electrolyte layer may be 1400 (° C.) or more and 1450 (° C.) or less. According to this method for producing an electrochemical cell, the firing temperature of the electrolyte layer is 1400 (° C.) or higher and 1450 (° C.) or lower, so that the average particle size of the particles constituting the electrolyte layer is changed to transition metal. The size can be more reliably reduced to suppress the diffusion of elements.

  The technology disclosed in this specification can be realized in various forms. For example, a fuel cell power generation unit, a fuel cell stack including a plurality of fuel cell power generation units, and a power generation module including a fuel cell stack It can be realized in the form of a fuel cell system including a power generation module, an electrolytic cell unit, an electrolytic cell stack including a plurality of electrolytic cell units, a hydrogen generation module including an electrolytic cell stack, a hydrogen generation system including a hydrogen generation module, etc. It is.

1 is a perspective view showing an external configuration of a fuel cell stack 100 in the present embodiment. It is explanatory drawing which shows XY cross-section structure of the fuel cell stack 100 in the position of II-II of FIG. FIG. 3 is an explanatory diagram showing an XZ cross-sectional configuration of a fuel cell stack 100 at a position of III-III in FIG. 1. FIG. 4 is an explanatory diagram showing an XZ cross-sectional configuration of a part of the cell 110 (an electrolyte layer 112, a fuel electrode 116, and a diffusion prevention layer 200). 3 is a flowchart showing a method for manufacturing the cell 110. It is explanatory drawing which shows the result of the performance evaluation of the cell 110. FIG.

A. Embodiment:
A-1. Constitution:
(Configuration of fuel cell stack 100)
FIG. 1 is a perspective view showing an external configuration of a fuel cell stack 100 in the present embodiment, and FIG. 2 is an explanatory diagram showing an XY cross-sectional configuration of the fuel cell stack 100 at a position II-II in FIG. FIG. 3 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 100 at the position of III-III in FIG. FIG. 4 is an explanatory diagram showing an XZ sectional configuration of a part of the cell 110 (the electrolyte layer 112, the fuel electrode 116, and the diffusion prevention layer 200). In each figure, XYZ axes orthogonal to each other for specifying the direction are shown. In this specification, for convenience, the positive direction of the Z axis is referred to as the upward direction, and the negative direction of the Z axis is referred to as the downward direction. However, the fuel cell stack 100 is actually installed in a direction different from such a direction. May be. The fuel cell stack 100 corresponds to the electrochemical stack and the solid oxide fuel cell stack in the claims.

  As shown in FIGS. 1 to 3, the fuel cell stack 100 includes a plurality (24 in this embodiment) of cells 110, a current collecting member 104, an insulating porous body 106, and a pair of glass seal members 108. Is provided. The 24 cells 110 are arranged in a lattice pattern with a space therebetween. Specifically, the 24 cells 110 are arranged in a predetermined direction (three in the horizontal direction (X-axis direction) in the present embodiment), and the direction perpendicular to the predetermined direction (the vertical direction in the present embodiment). (Z-axis direction)) are arranged side by side.

(Configuration of cell 110)
The cell 110 is a cylindrical (tube-shaped) member, and includes an electrolyte layer 112, an air electrode (cathode) 114 and a fuel electrode (anode) 116 facing each other in the radial direction of the cell 110 with the electrolyte layer 112 interposed therebetween. Prepare. Note that the cell 110 of this embodiment is a fuel electrode-supported cell in which the electrolyte layer 112 and the air electrode 114 are supported by the fuel electrode 116. Specifically, as shown in FIG. 3, the radial thickness D1 of the fuel electrode 116 is thicker than the radial thickness D2 of the electrolyte layer 112, and more than the radial thickness D3 of the air electrode 114. It is thick. The radial direction of the cell 110 corresponds to the first direction in the claims. The cell corresponds to an electrochemical cell and a stack for a solid oxide fuel cell in the claims.

  The fuel electrode 116 is a substantially cylindrical member, and the fuel gas FG is introduced from the outside of the fuel cell stack 100 into the through hole extending in the longitudinal direction (Y-axis direction) of the cell 110, and the fuel gas FG is supplied to each cell 110. This is a fuel gas conduction hole 117 to be supplied. The fuel electrode 116 includes a substrate layer (not shown) that constitutes the fuel gas conduction hole 117 and an active layer (not shown) that is located on the outer peripheral side of the substrate layer and is adjacent to the electrolyte layer 112. Both the active layer and the substrate layer are, for example, Ni (nickel) and a ceria-based oxide (for example, GDC (gadolinium doped ceria), LDC (lanthanum doped ceria), SDC (samarium doped ceria), YDC (yttrium doped ceria). )). Ni is a catalyst and plays a role of improving electron conductivity in the fuel electrode 116. Ni is an example of a transition metal element.

  The active layer mainly functions to generate electrons and water vapor by reacting oxide ions supplied from the electrolyte layer 112 with hydrogen or the like contained in the fuel gas FG, and the substrate layer is mainly active. The layer, the electrolyte layer 112, and the air electrode 114 are supported. In order to increase the activity of the active layer, the Ni content (mol%) in the active layer is preferably higher than the Ni content in the substrate layer. In order to increase the strength of the substrate layer, the thickness of the substrate layer in the radial direction is preferably larger than the thickness of the active layer in the radial direction. In order to improve the gas diffusibility of the substrate layer, the porosity of the substrate layer is preferably higher than the porosity of the active layer.

The electrolyte layer 112 is a thin-walled cylindrical member disposed on the outer peripheral surface side of the fuel electrode 116, and as a solid oxide, a lanthanum gallate-based perovskite oxide having a higher oxide ion conductivity than stabilized zirconia (( La (lanthanum), Sr (strontium)) (Ga (gallium), Mg (magnesium)) O ₃ (hereinafter referred to as “LSGM”)). The detailed configuration of the electrolyte layer 112 will be described later. The air electrode 114 is a thin-walled cylindrical member disposed on the outer peripheral surface side of the electrolyte layer 112, and is formed of, for example, a perovskite oxide. Examples of the perovskite oxide include LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide), LNF (lanthanum nickel iron), and cobaltite perovskite oxide (for example, La _0.6 Sr _0.4 CoO ₃ , Ba _0.4 La _0.6 CoO ₃ , La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ). Thus, the cell 110 of the present embodiment is a solid oxide fuel cell (SOFC) that uses a solid oxide as an electrolyte. Note that La (lanthanum), Sr (strontium), Ba (barium), and Co (cobalt) are examples of transition metal elements.

  As shown in FIG. 2, a part of one end side (Y-axis positive direction side) or the other end side (Y-axis negative direction side) of each fuel electrode 116 is covered with the electrolyte layer 112 and the air electrode 114 over the entire circumference. There are no exposed parts. And the formation position of the exposed part in the longitudinal direction (Y-axis direction) of the fuel electrode 116 differs between cells 110 adjacent to each other in the X-axis direction. That is, the formation position of the exposed part in the two cells 110 located at both ends in the X-axis direction is the one end side (Y-axis positive direction side) of the fuel electrode 116 and in the cell 110 located in the center in the X-axis direction. The formation position of the exposed portion is the other end side (Y-axis negative direction side) of the fuel electrode 116. A metal seal member 109 is formed on the exposed portion of each fuel electrode 116 so as to cover the exposed portion. The metal sealing member 109 functions as a current collecting terminal for the fuel electrode 116 while preventing gas from flowing.

(Configuration of current collecting member 104)
As shown in FIGS. 2 and 3, the current collecting member 104 is a conductive member including a plurality of cylindrical portions 142 and a plurality of connecting portions 144. Each cylindrical portion 142 is spaced apart from the first cylindrical portion 142A and the first cylindrical portion 142A that are disposed on the side where the exposed portion of the cell 110 is formed, and between the first cylindrical portion 142A and the cell 110. And a second cylindrical portion 142B arranged side by side in the longitudinal direction (Y-axis direction). The second cylindrical portion 142B is formed so as to surround the entire circumference of the air electrode 114 of each cell 110. The insulating member 105 is disposed between the first cylindrical portion 142A and the second cylindrical portion 142B, whereby the first cylindrical portion 142A and the second cylindrical portion 142B are electrically insulated. ing. As shown in FIG. 2, the connecting portion 144 connects the first cylindrical portion 142A of one cylindrical portion 142 adjacent to each other in the X-axis direction and the second cylindrical portion 142B of the other cylindrical portion 142. Yes. Thereby, the cells 110 adjacent to each other in the X-axis direction are electrically connected.

  The insulating porous body 106 is a flat porous body capable of flowing the oxidant gas OG, and is formed of, for example, ceramics. The insulating porous body 106 is disposed between the eight current collecting members 104 arranged in the vertical direction (Z-axis direction) and the upper and lower ends of the eight current collecting members 104.

  The glass seal members 108 are arranged on both sides in the longitudinal direction (Y-axis direction) of the 24 cells 110, and the end portions of the respective cells 110 are inserted into a plurality of through holes 108A formed in the glass seal member 108. ing. The glass seal member 108 prevents the oxidant gas OG flowing through the insulating porous body 106 from leaking.

A-2. Operation of the fuel cell stack 100:
As shown in FIGS. 1 and 2, when the fuel gas FG is supplied through a pipe (not shown) connected to the cell 110, the fuel gas FG is supplied to the fuel gas conduction hole 117, and the fuel electrode 116, the hydrogen in the fuel gas FG reacts with oxide ions carried from the electrolyte layer 112, and water is generated. On the other hand, as shown in FIG. 3, when the oxidant gas OG is supplied into the insulating porous body 106 from the outside of the fuel cell stack 100, the oxidant gas OG passes through the insulating porous body 106 and the current collecting member 104. In contact with the air electrode 114, oxide ions are generated from oxygen molecules contained in the oxidant gas OG. As described above, power generation is performed in the cell 110 by an electrochemical reaction of the oxidant gas OG and the fuel gas FG. This power generation reaction is an exothermic reaction. 2 indicates a conductive path between the three cells 110.

A-3. Configuration of diffusion preventing layer 200:
As shown in FIG. 4, the cell 110 further includes a diffusion prevention layer 200 disposed between the electrolyte layer 112 and the fuel electrode 116. The diffusion preventing layer 200 includes, for example, the above-mentioned ceria-based oxide. For example, in the process of firing the precursor before firing of the electrolyte layer and the precursor before firing of the fuel electrode in the manufacturing stage, the diffusion prevention layer 200 forms La and the fuel electrode molded body in the precursor before firing of the electrolyte layer. Reaction of Ni contained therein to suppress the formation of an insulating layer (for example, LaNiO ₃ ) at the interface between the electrolyte layer 112 and the fuel electrode 116 is suppressed. The diffusion preventing layer 200 corresponds to the intermediate layer in the claims.

A-4. Detailed configuration of the electrolyte layer 112:
In this embodiment, the average particle diameter of the particles constituting the electrolyte layer 112 is 2.0 (μm) or more and 8.0 (μm) or less. The particles constituting the electrolyte layer 112 here are particles constituting a grain boundary that can be a diffusion path of the transition metal element in the electrolyte layer 112. The radial thickness D2 (see FIG. 3) of the electrolyte layer 112 is 15 (μm) or more and 30 (μm) or less.

A-5. Method for manufacturing cell 110:
FIG. 5 is a flowchart showing a method for manufacturing the cell 110. As shown in FIG. 5, first, a cylindrical fuel electrode molded body containing Ni or the like is prepared (S110), and the precursor before firing of the diffusion preventing layer is formed on the outer peripheral surface of the fuel electrode molded body by the dip coating method. Form (S120). At this time, the precursor before firing of the electrolyte layer is not yet formed on the molded article for the fuel electrode. Next, the first fired body is produced by simultaneously firing the fuel electrode compact and the pre-firing precursor of the diffusion prevention layer formed on the fuel electrode compact (S130). The first fired body includes the fuel electrode 116 and the diffusion prevention layer 200, but does not include the electrolyte layer 112.

  Next, a second fired body is manufactured by forming a precursor before firing of the electrolyte layer on the outer peripheral surface of the diffusion preventing layer 200 of the first fired body by dip coating and firing (S140). The firing temperature at the time of producing this second fired body is preferably 1400 (° C.) or more and 1450 (° C.) or less. The second fired body includes an electrolyte layer 112 in addition to the fuel electrode 116 and the diffusion prevention layer 200. Next, a third fired body is manufactured by forming a pre-fired precursor of the air electrode on the outer peripheral surface of the electrolyte layer 112 of the second fired body by dip coating and firing (S150). Thereby, the above-described cell 110 can be manufactured.

A-6. Cell 110 performance evaluation:
FIG. 6 is an explanatory diagram showing the results of performance evaluation of the cell 110. As shown in FIG. 6, eight samples (Examples 1 to 7 and Comparative Example) were used for performance evaluation. Among the eight samples, Examples 1 to 7 have the same layer structure as the cell 110 described above, and the average particle diameter of the particles constituting the electrolyte layer 112 and the thickness in the radial direction of the electrolyte layer 112. Both the length D2 and the length D2 are included in the specified range defined by the cell 110. On the other hand, the comparative example has the same layer configuration as the cell 110 described above, but the average particle size of the particles constituting the electrolyte layer 112 and the radial thickness D2 of the electrolyte layer 112 are defined as above. Not included in the range. The eight samples have different combinations of the material for forming the air electrode 114, the average particle diameter of the particles constituting the electrolyte layer 112, and the radial thickness of the electrolyte layer 112. In all eight samples, the material for forming the fuel electrode 116 is Ni and GDC.

(Sample preparation)
Examples 1 to 7 are manufactured by the above-described manufacturing method. On the other hand, the comparative example is manufactured by a manufacturing method different from the above-described manufacturing method in that the molded body for a fuel electrode, the precursor before firing of the diffusion preventing layer, and the precursor before firing of the electrolyte layer are fired simultaneously. In this performance evaluation, for each sample, a part of the electrolyte layer 112 is removed, and a silver wire is wound around the exposed portion of the fuel electrode 116 to form a fuel electrode side terminal. In addition, the air electrode 114 is covered with a platinum mesh, a silver wire is connected to the platinum mesh, and a conductive paste for current collection is applied onto the platinum mesh and baked in an electric furnace to form an air electrode side terminal. ing.

(Performance evaluation method)
First, the power generation output (W / cm ² ) of each sample is acquired. Specifically, after each prepared sample is installed in an electric furnace, the fuel electrode side terminal and the air electrode side terminal are electrically connected via a voltmeter and an impedance measuring device (manufactured by solartron, SI1287 / 1255B). Connect. Next, the supply of nitrogen gas to the fuel gas conduction hole 117 of the fuel electrode 116 and the start of supply of air to the air electrode 114 raise the temperature of the electric furnace to 700 (° C.). After raising the temperature to 700 (° C.), the fuel electrode 116 is subjected to a reduction process by starting to supply hydrogen gas instead of nitrogen gas to the fuel gas conduction hole 117. After performing the reduction treatment, the temperature of the electric furnace is lowered to 600 (° C.), and an IV curve (current voltage curve) at 600 (° C.) is measured by an impedance measuring device. The voltage value (V) at 1 (A / cm ² ) is read, and the power generation output (W / cm ² ) of each sample is obtained using the following formula 1.
<Formula 1>
Cell power generation output (W / cm ² ) = Current density (0.1 (A / cm ² )) × Voltage value (V)

Next, the voltage drop rate (%) of each sample is acquired as an index of durability of each sample. Specifically, the open circuit electromotive force of each sample when the temperature of the electric furnace is 600 (° C.) is measured by a voltmeter, and the measured value is set as an initial open circuit electromotive force V0. Next, from the time when the initial open circuit electromotive force V0 was measured, the temperature of the electric furnace was 600 (° C.), and each sample was maintained in an open circuit state (non-energized state) for 100 hours, and 100 hours had elapsed. The open circuit electromotive force of each sample is measured with a voltmeter, and the measured value is defined as an open circuit electromotive force V1 after operation. Then, the voltage drop rate (% / 100 hr) per 100 hours is obtained for each sample using the following formula 2.
<Formula 2>
Voltage drop rate (%) = [(initial open circuit electromotive force V0−post-operation open circuit electromotive force V1) / initial open circuit electromotive force V0] × 100

  Next, the average particle diameter of the particles constituting the electrolyte layer of each sample is obtained. Specifically, the temperature of the electric furnace is lowered to room temperature while hydrogen gas is supplied to the fuel gas conduction hole 117. After the sample taken out from the electric furnace is cured by being embedded in an epoxy resin, each sample is cut along a plane perpendicular to the gas supply direction to obtain a cut surface including an electrolyte layer. Then, the cut surface is polished to make a smooth surface. After carbon deposition is performed on the smooth cut surface, an SEM image of the cut surface is acquired using an SEM (scanning electron microscope). About the acquired SEM image, the average particle diameter of the particle | grains which comprise an electrolyte layer is acquired using an intercept method.

(Results of performance evaluation)
As shown in FIG. 6, in the comparative example, the average particle diameter of the particles constituting the electrolyte layer 112 is 1.4 (μm). In the evaluation result of the comparative example, the power generation output is 0.042 (W / cm ² ), which is lower than those in Examples 1 to 7, and the voltage drop rate is 1.17 (% / 100 hr). Higher than Examples 1-7 (low durability). On the other hand, in each of Examples 1 to 7, the average particle diameter of the particles constituting the electrolyte layer 112 is 2.0 (μm) or more and 8.0 (μm) or less. In any of the evaluation results of Examples 1 to 7, the power generation output was 0.080 (W / cm ² ) or more, and the voltage drop rate was 0.37 (% / 100 hr) or less, which was favorable. It was.

  The cause of the difference in the evaluation results between Examples 1 to 7 and the comparative example is considered to be mainly due to the difference in the average particle diameter of the particles constituting the electrolyte layer 112. The diffusion path of the transition metal (for example, Co from the air electrode 114 and Ni from the fuel electrode 116) in the electrolyte layer 112 is at a grain boundary that is a boundary between particles constituting the electrolyte layer 112. The larger the average particle size of the particles constituting the electrolyte layer 112, the smaller the number of grain boundaries. That is, there are fewer diffusion paths. Conversely, the smaller the average particle size of the particles constituting the electrolyte layer 112, the greater the number of grain boundaries. That is, the number of diffusion paths increases.

  In the comparative example, since the average particle diameter of the particles constituting the electrolyte layer 112 is relatively small, the transition metal element is easily diffused by the presence of many diffusion paths of the transition metal element in the electrolyte layer 112. Therefore, in the comparative example, many transition metal elements diffuse from the air electrode 114 and the fuel electrode 116 to the electrolyte layer 112 even though the radial thickness of the electrolyte layer 112 is thicker than those of the first to seventh embodiments. . As a result, an electrical short circuit is likely to occur between the air electrode 114 and the fuel electrode 116, and the power generation output is reduced due to a decrease in the open circuit electromotive force of the cell, and the voltage drop rate is increased. It is done.

  On the other hand, in Examples 1-7, since the average particle diameter of the particles constituting the electrolyte layer 112 is relatively large, the transition metal element diffuses due to the small number of diffusion paths of the transition metal element in the electrolyte layer 112. It is difficult to do. Therefore, in Examples 1 to 7, it is considered that good evaluation results were obtained even though the radial thickness of the electrolyte layer 112 was thinner than that of the comparative example. In other words, since the diffusion of the transition metal element into the electrolyte layer 112 can be suppressed by setting the average particle size of the particles constituting the electrolyte layer 112 to 2.0 (μm) or more, the thickness of the electrolyte layer 112 in the radial direction is reduced. The thickness D2 can be made thinner than that of the comparative example.

  Next, in Examples 1 to 3, the material for forming the fuel electrode 116, the material for forming the air electrode 114, and the radial thickness D2 of the electrolyte layer 112 are the same. However, in Example 1, the average particle diameter of the particles constituting the electrolyte layer 112 is 8.0 (μm), the largest, and the voltage drop rate is 0.28 (% / 100 hr), the lowest. . In Example 2, the average particle diameter of the particles constituting the electrolyte layer 112 is 6.2 (μm), which is smaller than that of Example 1, and the voltage drop rate is 0.31 (% / 100 hr). Higher than Example 1. In Example 3, the average particle size of the particles constituting the electrolyte layer 112 is 2.0 (μm), which is even smaller than Example 2, and the voltage drop rate is 0.37 (% / 100 hr). Even higher than in Example 2. From this, it can be seen that the durability of the cell 110 is improved as the average particle diameter of the particles constituting the electrolyte layer 112 is increased. This is because, as the average particle diameter of the particles constituting the electrolyte layer 112 is larger, an electrical short circuit between the air electrode 114 and the fuel electrode 116 is suppressed, so that the power generation operation of the cell 110 (below the firing temperature) However, it is considered that the voltage drop of the cell 110 is suppressed.

Next, in Examples 1, 4 and 5, the material for forming the fuel electrode 116 and the material for forming the air electrode 114 are the same, and the average particle size of the particles constituting the electrolyte layer 112 is about 8 in all cases. 0.0 (μm). However, in Example 5, the thickness D2 in the radial direction of the electrolyte layer 112 is 30 (μm), the thickest, and the power generation output is 0.095 (W / cm ² ), which is the lowest. In Example 1, the radial thickness D2 of the electrolyte layer 112 is 20 (μm), which is thinner than that of Example 5, and the power generation output is 0.100 (W / cm ² ). high. In Example 4, the thickness D2 in the radial direction of the electrolyte layer 112 is 15 (μm), which is the thinnest, but the power generation output is 0.103 (W / cm ² ), which is the highest. From these facts, by setting the average particle size of the particles constituting the electrolyte layer 112 to 8.0 (μm), the air electrode 114 is formed at the manufacturing stage of the cell 110 (S150 in FIG. 5 above). The diffusion of Co from the electrode 114 to the electrolyte layer 112 is suppressed. For this reason, it can be said that even if the thickness D2 in the radial direction of the electrolyte layer 112 is reduced, a high power generation output can be obtained.

Next, for Examples 3, 6, and 7, the material for forming the fuel electrode 116 and the radial thickness D2 of the electrolyte layer 112 are the same, and the average particle size of the particles constituting the electrolyte layer 112 is Both are about 2.0 (μm). However, in Examples 6 and 7, Ba is not included in the material for forming the air electrode 114, and the power generation outputs are 0.085 (W / cm ² ) and 0.080 (W / cm ² ), respectively. In Example 3, Ba is contained in the material for forming the air electrode 114, and the power generation output is 0.098 (W / cm ² ), which is the highest. In Example 3, it is considered that a higher power output than in Examples 6 and 7 was obtained due to the high electrocatalytic activity of Ba.

A-7. Effects of this embodiment:
According to the present embodiment, the average particle diameter of the particles constituting the electrolyte layer 112 is 2.0 (μm) or more and 8.0 (μm) or less. For this reason, compared with the case where the average particle diameter of the particle | grains which comprise the electrolyte layer 112 is less than 2.0 (micrometer), it is a boundary of the particle | grains used as the diffusion path | route of a transition metal element in the electrolyte layer 112 As the grain boundary is reduced, the diffusion of the transition metal element into the electrolyte layer 112 is suppressed, and as a result, it is possible to suppress a decrease in the power generation capability of the cell 110.

  The thickness of the electrolyte layer 112 in the radial direction is 15 (μm) or more and 30 (μm) or less. For this reason, the air electrode 114 and the fuel electrode 116 are electrically short-circuited by the transition metal element diffused in the electrolyte layer 112 as compared with the case where the thickness of the electrolyte layer 112 in the radial direction is less than 15 (μm). Can be suppressed. In addition, the electrical resistance of the electrolyte layer 112 itself can be suppressed as compared with the case where the thickness of the electrolyte layer 112 in the radial direction is larger than 30 (μm). Thereby, it can suppress more effectively that the power generation capability of the cell 110 falls.

  In addition, since the air electrode 114 includes a cobaltite-based perovskite oxide having excellent conductivity and electrocatalytic activity, it is possible to more effectively suppress a decrease in the power generation capacity of the cell 110.

  Further, the cobaltite-based perovskite oxide that forms the air electrode 114 contains Ba. Thereby, the electrode catalyst activity in the air electrode 114 becomes high, and the power generation capability of the cell 110 can be improved.

  Further, in order to increase the average particle diameter of the particles constituting the electrolyte layer 112, it is necessary to increase the firing temperature. Here, if the molded body for the fuel electrode, the precursor before firing of the diffusion preventing layer 200 and the precursor before firing of the electrolyte layer 112 are simultaneously fired, the diffusion preventing layer 200 becomes dense by increasing the firing temperature. There is a possibility that the transition metal element contained in the fuel electrode 116 passes through the diffusion prevention layer 200 and diffuses toward the electrolyte layer 112 before becoming. On the other hand, according to the manufacturing method of this embodiment (FIG. 5), the molded body for the fuel electrode and the precursor before firing of the intermediate layer formed in the molded body for the fuel electrode are first fired. A first fired body is produced (S130 in FIG. 5). Thereafter, the precursor before firing of the electrolyte layer 112 is disposed on the diffusion preventing layer 200 side of the first fired body and fired (S140 in FIG. 5). Thus, when the electrolyte layer 112 is fired, even if the firing temperature is increased in order to increase the average particle size of the particles constituting the electrolyte layer 112, the diffusion preventing layer 200 that has already been dense due to the firing enables the fuel The transition metal element contained in the electrode 116 can be prevented from diffusing to the electrolyte layer 112 side.

  In addition, the firing temperature of the electrolyte layer 112 in S140 is 1400 (° C.) or higher and 1450 (° C.) or lower, so that the average particle size of the particles constituting the electrolyte layer 112 is suppressed and diffusion of transition metal elements is suppressed. The possible size can be made more reliable.

B. Variations:
The technology disclosed in the present specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the gist thereof. For example, the following modifications are possible.

  In the above embodiment, the cell 110 is configured to include the diffusion prevention layer 200 between the electrolyte layer 112 and the fuel electrode 116, but the present invention is not limited to this, and an intermediate layer is provided between the electrolyte layer 112 and the air electrode 114. The structure provided with may be sufficient. Further, the cell 110 may be configured not to include an intermediate layer such as the diffusion prevention layer 200.

  In the above embodiment, the thickness D2 of the electrolyte layer 112 in the radial direction may be less than 15 (μm) or thicker than 30 (μm).

  In the above-described embodiment, the air electrode 114 includes a cobaltite-based perovskite oxide containing Ba, but is not limited thereto, and the cobaltite-based perovskite-type oxide not containing Ba or a perovskite-type oxide other than the cobaltite-based oxide. In addition, oxides other than the perovskite type may be included.

  In the above-described embodiment, the number of cells 110 included in the fuel cell stack 100 is merely an example, and the number of cells 110 is appropriately determined according to the output voltage required for the fuel cell stack 100 or the like.

  Moreover, the material which forms each member in the said embodiment is an illustration to the last, and each member may be formed with another material.

  In the above embodiment, the city gas is reformed to obtain the hydrogen-rich fuel gas FG, but the fuel gas FG may be obtained from other raw materials such as LP gas, kerosene, methanol, gasoline, Pure hydrogen may be used as the fuel gas FG.

  In the present specification, the fact that the member B and the member C are opposed to each other across the member (or a part having the member, the same applies hereinafter) A is not limited to the form in which the member A and the member B or the member C are adjacent to each other. It includes a form in which another component is interposed between member A and member B or member C. For example, even in a configuration in which another layer is provided between the electrolyte layer 112 and the air electrode 114, it can be said that the air electrode 114 and the fuel electrode 116 face each other with the electrolyte layer 112 interposed therebetween.

  In the above embodiment (or a modified example, the same applies hereinafter), the average particle size of the particles constituting the electrolyte layer 112 is 2.0 (μm) or more for all the cells 110 included in the fuel cell stack 100, and However, if at least one cell 110 included in the fuel cell stack 100 has such a configuration, an effect of suppressing a decrease in power generation capacity of the cell 110 is obtained. Play.

  In the above embodiment, the SOFC that generates electricity using the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas is targeted. The present invention can be similarly applied to a solid oxide electrolytic cell (SOEC) that generates hydrogen by using hydrogen and an electrolytic cell stack including a plurality of electrolytic cells. The configuration of the electrolytic cell stack is well known as described in, for example, Japanese Patent Application Laid-Open No. 2006-81813, and thus will not be described in detail here. However, it is schematically the same as the fuel cell stack 100 in the above-described embodiment. It is a configuration. That is, the fuel cell stack 100 in the above-described embodiment may be read as an electrolytic cell stack, and the cell 110 may be read as an electrolytic cell. However, when the electrolysis cell stack is operated, a voltage is applied between both electrodes so that the air electrode 114 is positive (anode) and the fuel electrode 116 is negative (cathode). Thereby, an electrolysis reaction of water occurs in each electrolysis cell, hydrogen gas is generated at the fuel electrode, and hydrogen is taken out of the electrolysis cell stack. Also in the electrolytic cell and the electrolytic cell stack having such a configuration, the average particle diameter of the particles constituting the electrolyte layer 112 is 2.0 (μm) or more and 8.0 (μm), as in the above embodiment. Adopting the configuration described below provides an effect of suppressing a decrease in the power generation capacity of the cell 110.

  Further, the present invention is not limited to the cylindrical type, but can be applied to a flat plate type cell or the like.

DESCRIPTION OF SYMBOLS 100: Fuel cell stack 104: Current collecting member 105: Insulating member 106: Insulating porous body 108: Glass sealing member 108A: Through hole 109: Metal sealing member 110: Cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 117: Fuel gas conduction hole 142: cylindrical portion 142A: first cylindrical portion 142B: second cylindrical portion 144: connection portion 200: diffusion preventing layer D1: radial thickness of fuel electrode 116 D2: radial direction of electrolyte layer 112 Thickness D3: radial thickness of the air electrode 114 FG: fuel gas OG: oxidant gas

Claims (9)

An electrolyte layer comprising a solid oxide;
In an electrochemical cell comprising an air electrode and a fuel electrode facing each other in a first direction across the electrolyte layer,
The solid oxide includes a lanthanum gallate perovskite oxide,
The thickness of the fuel electrode in the first direction is thicker than the thickness of the electrolyte layer in the first direction,
The electrochemical cell having an average particle diameter of 2.0 (μm) or more and 8.0 (μm) or less, which constitutes the electrolyte layer. The electrochemical cell according to claim 1.
The thickness of the said electrolyte layer of the said 1st direction is 15 (micrometer) or more and 30 (micrometer) or less, The electrochemical cell characterized by the above-mentioned. The electrochemical cell according to claim 1 or 2,
The electrochemical cell according to claim 1, wherein the air electrode includes a cobaltite-based perovskite oxide. The electrochemical cell according to claim 3,
The electrochemical cell according to claim 1, wherein the cobaltite-based perovskite oxide contains Ba. The electrochemical cell according to any one of claims 1 to 4, wherein
The electrochemical cell is a cell for a solid oxide fuel cell or a cell for a solid oxide electrolytic cell. In an electrochemical stack comprising a plurality of electrochemical cells,
The electrochemical stack according to claim 1, wherein at least one of the plurality of electrochemical cells is the electrochemical cell according to claim 1. The electrochemical stack according to claim 6,
The electrochemical stack is a stack for a solid oxide fuel cell or a stack for a solid oxide electrolytic cell. In the manufacturing method of the electrochemical cell as described in any one of Claim 1- Claim 5,
A step of preparing a molded article for the fuel electrode;
Forming a precursor before firing of the intermediate layer in the molded article for the fuel electrode;
A step of simultaneously firing the molded body for a fuel electrode and the precursor before firing of the intermediate layer formed in the molded body for the fuel electrode to produce a first fired body;
Forming a pre-fired precursor of the electrolyte layer on the intermediate layer side of the first fired body;
A step of simultaneously firing the first fired body and the precursor before firing of the electrolyte layer formed on the first fired body to produce a second fired body, Electrochemical cell manufacturing method. The method for producing an electrochemical cell according to claim 8,
The method for producing an electrochemical cell, wherein a firing temperature of the precursor before firing of the electrolyte layer is 1400 (° C.) or more and 1450 (° C.) or less.

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