JP2009176675A - Electrolyte-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an oxide ion conductivity in an electrolyte-electrode assembly (MEA) having an apatite type oxide as an electrolyte. <P>SOLUTION: The MEA 10 includes an electrolyte 12 consisting of an apatite type oxide, intermediate layers 18, 20 which are formed at each end face of the electrolyte 12 and are made of a substance showing isotropy on the oxide ionic conduction, and an anode side electrode 14 and a cathode side electrode 16 which pinch the electrolyte 12 through each of these intermediate layers 18, 20. Any one of the electrodes 14, 16, for example, the anode side electrode 14 includes particles 28 (for example, Pt particles and SDC particles) with the particle size of 100 nm or less mutually bonded, and the thickness is established to be 1 μm or less. When the X-ray diffraction measurement is performed on the anode side electrode 14, a pattern showing that the particles 28 are amorphous is obtained. Further, in the jointing interface to the intermediate layer 18 in the anode side electrode 14, the interval distance of the particles 28, 28 adjoining jointing to the intermediate layer 18 is 1 μm or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrolyte / electrode assembly configured such that an electrolyte is sandwiched between an anode side electrode and a cathode side electrode.

  Fuel cells, oxygen sensors, oxygen loaded membrane devices, and the like have an electrolyte / electrode assembly in which an anode electrode and a cathode electrode are formed on each end face of an electrolyte capable of conducting oxide ions. In the thus configured electrolyte / electrode assembly, oxide ions generated as oxygen is ionized at the cathode side electrode move to the anode side electrode via the electrolyte.

  The movement of the above oxide ions becomes more active in a relatively high temperature range. Accordingly, in order to operate a fuel cell or the like having the electrolyte / electrode assembly, it is necessary to raise the temperature to such a temperature. For this reason, when electric power is required, electric power cannot be taken out from the fuel cell immediately.

  Therefore, in recent years, it has been proposed to employ a substance exhibiting excellent oxide ion conductivity as an electrolyte even at a relatively low temperature. Specific examples include fluorite oxides such as scandium stabilized zirconia (ScSZ) and samarium solid solution ceria (SDC), and perovskite oxides such as lanthanum gallate (LaSrGaMgO). Further, the present applicant has proposed an oxide ion conductor made of an apatite-type complex oxide (see, for example, Patent Document 1).

JP 2002-252005 A

  Despite the fact that apatite-type composite oxide is a substance that exhibits excellent oxide ion conductivity, sufficient power generation performance cannot be obtained if an electrolyte / electrode assembly is formed using the apatite-type composite oxide as an electrolyte. There is. The present applicant's earnest study has revealed that this is because the interfacial resistance between the electrode and the electrolyte is relatively large, so that the IR loss cannot be ignored.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electrolyte / electrode assembly that has a low internal resistance and can therefore improve the power generation characteristics of a fuel cell.

To achieve the above object, the present invention provides an electrolyte / electrode assembly in which an electrolyte is interposed between an anode electrode and a cathode electrode,
The electrolyte is a single crystal having a plane or direction in which oxide ions move, or a polycrystal oriented in the plane or direction in which oxide ions move, and the plane or direction is a thickness direction. An apatite-type oxide formed along
The anode side electrode or the cathode side electrode is configured by bonding particles having a particle size of 100 nm or less to each other, and the thickness is set to 1 μm or less.
The particles include at least amorphous metal particles;
The anode-side electrode or the cathode-side electrode has pores at a joint portion joined to the electrolyte or an intermediate layer interposed between the electrolyte and the anode-side electrode, and is adjacent to the pores. The separation distance between the particles is 1 μm or less. Here, the “separation distance” means a point that first contacts the electrolyte (or intermediate layer) at an arbitrary bonding site and a point that contacts the electrolyte (or intermediate layer) first at the bonding site adjacent to the bonding site. And the interval.

  In the present invention, since the particle size of the particles constituting the anode side electrode or the cathode side electrode is small, the particles are in close contact with each other, and the particles are also in close contact with the electrolyte (or intermediate layer). In combination with this, the separation interval is very small as described above, and oxide ions are transferred from the cathode side electrode to the electrolyte (or intermediate layer) and / or from the electrolyte (or intermediate layer) to the anode side electrode. The probability of being transferred to is increased. Moreover, since the thickness of the anode side electrode or the cathode side electrode is small, the internal resistance of the anode side electrode or the cathode side electrode is also small.

  For the above reasons, the internal resistance of the electrolyte / electrode assembly can be reduced.

  Furthermore, since the thickness of the anode side electrode or the cathode side electrode is small, it becomes easy for the reaction gas to diffuse in the anode side electrode or the cathode side electrode. Therefore, the advantage that the electrode reaction proceeds efficiently can also be obtained.

  The porosity of the anode side electrode or the cathode side electrode is preferably 5 to 40 vol%. When it exceeds 40 vol%, the probability that oxide ions are received from the electrolyte (or intermediate layer) to the anode side electrode or the probability that they are received from the cathode side electrode (or intermediate layer) to the electrolyte tends to decrease.

  The anode side electrode or cathode side electrode may contain oxide ceramic particles capable of conducting oxide ions in addition to the metal particles. In this case, the ratio of the oxide ceramic particles is less than 75 vol%. That is, in the present invention, metal particles: oxide ceramic particles = 100: 0 to more than 25: less than 75.

  According to the present invention, the distance between the particles constituting the anode-side electrode is set to a predetermined value or less. As a result, the anode-side electrode becomes dense, so that the contact area between the anode-side electrode and the electrolyte or intermediate layer increases, and the contact interval between the two decreases. As a result, oxide ions that have passed through the electrolyte or intermediate layer are efficiently received by the anode side electrode, the resistance between the electrolyte or intermediate layer and the electrode is reduced, and the oxide ion conductivity is improved. . In addition, since the thickness of the anode side electrode can be reduced, the reaction gas supplied to the anode side electrode is easily diffused.

  For the reasons described above, an electrolyte / electrode assembly having a low internal resistance and excellent oxide ion conductivity can be formed.

  Hereinafter, preferred embodiments of the electrolyte / electrode assembly according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an overall schematic longitudinal sectional view of an electrolyte / electrode assembly (hereinafter also referred to as MEA) 10 according to the present embodiment. The MEA 10 is configured by forming an anode side electrode 14 and a cathode side electrode 16 on each end face of the electrolyte 12. Intermediate layers 18 and 20 are interposed between the anode side electrode 14 and the electrolyte 12 and between the cathode side electrode 16 and the electrolyte 12, respectively.

  In this case, the electrolyte 12 is a single crystal made of an apatite complex oxide. This single crystal can be produced, for example, by a known single crystal production method such as the Czochralski method.

Here, as the apatite-type composite oxide, a composite oxide of lanthanum and silicon whose composition is represented by La _X Si ₆ O _{1.5X + 12} (however, 8 ≦ X ≦ 10; the same applies hereinafter) is exemplified. The structure of the unit cell will be described.

The structure of the unit cell of La _X Si ₆ O _{1.5X + 12} is shown in FIG. 2 with the viewpoint as the c-axis direction. This unit cell 21 has an apatite structure including six SiO ₄ tetrahedrons 22, O ²⁻ 24 occupying 2a sites, and La ³⁺ 26a and 26b occupying 4f sites or 6h sites, respectively. . Si ⁴⁺ and O ²⁻ in the SiO ₄ tetrahedron 22 are not shown.

  This unit cell 21 belongs to the hexagonal system. That is, in FIG. 2, the angle α at which the side AB in the a-axis direction and the side BF in the c-axis direction intersect with each other, the angle β at which the side BC in the b-axis direction intersects with the side BF, and the side AB and the side The angles γ at which BC intersects are 90 °, 90 °, and 120 °, respectively. The side AB and the side BC have the same length, and the lengths of the sides AB and BC are different from the side BF.

The reason why La _X Si ₆ O _{1.5X + 12} having such an apatite type structure is an oxide ion conductor is that O ²⁻ 24 occupying the 2a site corresponds to SiO ₄ tetrahedron 22 or La ³⁺ 26a. This is probably because it is not involved in binding. This is because the force acting on O ^2-24 is not strong, and therefore O ^2-24 can move relatively freely along the c-axis direction without being bound to the 2a site.

  That is, the oxide ions move along the c-axis direction in each crystal constituting the electrolyte 12. Therefore, the oxide ion conductivity increases in the direction along the c axis and decreases in the direction along the a axis and the b axis. In other words, anisotropy occurs in oxide ion conduction.

  In the present embodiment, as indicated by an arrow C in FIG. 1, the c-axis direction is the thickness direction of the electrolyte 12. That is, the anode-side electrode 14 and the cathode-side electrode 16 are disposed perpendicular to the direction in which the oxide ion conductivity is highest in the electrolyte 12, so that the oxide ions are transferred from the cathode-side electrode 16 to the anode. It can move quickly to the side electrode 14.

  The thickness of the electrolyte 12 configured in this way is set to 800 μm or less, preferably between 50 μm to 300 μm. When a support substrate type electrolyte / electrode assembly in which the electrolyte 12 is held by a support substrate is employed, the thickness of the electrolyte 12 can be set to be extremely small. For this reason, it becomes easy for oxide ions to move to the anode side electrode 14 side through the electrolyte 12, and the IR loss of the electrolyte 12 is also reduced. In the case of a support substrate type electrolyte / electrode assembly, a more preferable thickness of the electrolyte 12 is 50 nm to 10 μm. Even in this case, the strength of the electrolyte 12 is ensured.

Further, the electrolyte 12 preferably has a conductivity at 500 ° C. of 0.01 S / cm ^{2 according} to a direct current four-terminal method, and a conductivity at 300 ° C. of 0.001 S / cm ^2. Is more preferable. Of course, the above conductivity is in the c-axis direction, that is, in the thickness direction of the electrolyte 12 (arrow C in FIG. 1).

  When the electrolyte 12 has such a high conductivity, for example, a fuel cell incorporating the MEA 10 has excellent power generation characteristics even at a relatively low temperature. Therefore, the time for raising the fuel cell to the operating temperature is significantly shortened.

Anode 14 is in this case, the Pt is a metal, composite materials with an oxide ceramic Sm solute CeO ₂ (SDC) (hereinafter, also Pt-SDC notation to) a main, the sputtering , CVD (Chemical Vapor Deposition) method, ALD (Atomic Layer Deposition) method, PLD (Pulsed Laser Deposition) method and the like. When the anode side electrode 14 is observed with a scanning electron microscope (SEM) or the like, it is confirmed that Pt particles and SDC particles are bonded to each other while pores exist between the particles.

  Needless to say, Pt contained in the anode-side electrode 14 can conduct electrons, while SDC is an oxide ion conductor. That is, the anode side electrode 14 is a mixed conductor that contains an electron conductor and an oxide ion conductor, and thus exhibits both electron conductivity and oxide ion conductivity.

  In this case, the ratio between Pt and SDC is set so that SDC is less than 75 vol%. When the SDC exceeds 75 vol%, the electron conductivity of the anode side electrode 14 becomes insufficient.

  The thickness of the anode-side electrode 14 is set to about 50 nm to several hundred nm when manufactured by the various gas phase methods described above, and is 1 μm at the maximum. In this case, the porosity is about 5 to 40 vol%, typically about 30 vol%.

On the other hand, the cathode side electrode 16 may be made of the same material as the anode side electrode 14, but La _x Sr _1-x Co _y Fe _1-y Oα, Ba _x Sr _1-x Co _y More preferably, it is made of an oxide ceramic such as Fe _1-Y Oα, Sm _X Sr _1-X CoOα (where 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1). Alternatively, it may be composed of a cermet of these oxide ceramics and the above-described metal.

The intermediate layers 18 and 20 are preferably made of a fluorite-type oxide. Specific examples thereof include SDC, Y ₂ O ₃ solid solution CeO ₂ (YDC), Gd ₂ O ₃ solid solution CeO ₂ (GDC), La ₂ O ₃ solid solution CeO ₂ (LDC) is exemplified. These oxides are isotropic with respect to oxide ion conduction. Therefore, in the intermediate layers 18 and 20, the oxide ion conductivities are substantially equal both in the thickness direction (C direction in FIG. 1) and in the lateral direction (X direction in FIG. 1). Further, the oxide ion conductivity in the intermediate layers 18 and 20 is smaller than that in the thickness direction of the electrolyte 12.

  As will be described later, the presence of these intermediate layers 18 and 20 allows the number of oxide ions to move from the cathode side electrode 16 to the electrolyte 12 and the number of oxide ions to move from the electrolyte 12 to the anode side electrode 14. As a result, oxide ion conductivity can be improved.

  Note that SDC, YDC, GDC, LDC, and the like are mixed conductors that generate both oxide ion conduction and electron conduction. Such a mixed conductor contributes to rapid oxide ion conduction from the cathode-side electrode 16 to the anode-side electrode 14 as described above, as well as the ionization reaction of oxygen in the cathode-side electrode 16 and the anode-side electrode 14. It promotes the formation reaction of water and electrons that accompanies the bond between oxide ions and hydrogen. That is, the electrode reaction is promoted, and the power generation performance of the fuel cell is further improved.

  Here, FIG. 3 schematically shows the vicinity of the interface between the anode-side electrode 14 and the intermediate layer 18. Reference numeral 28 in FIG. 3 is a particle constituting the anode electrode 14. Each particle 28 may be either an SDC particle or a Pt particle. When X-ray diffraction measurement is performed on the anode side electrode 14, it is recognized that each peak appearing in the diffraction pattern is broad. That is, the particles 28 constituting the anode side electrode 14 are amorphous.

  As shown in FIG. 3, a plurality of pores 29 exist between the particles 28 on the end face of the anode side electrode 14 facing the intermediate layer 18. In other words, the anode side electrode 14 is microscopically bonded to the intermediate layer 18 by the point bonding or surface bonding of the particles 28.

  The particle size of the particles 28 is set to 100 nm or less. In this way, the fine particles 28 are in close contact with each other. Of course, the intermediate layer 18 (or the electrolyte 12) is also in intimate contact, and therefore the porosity of the anode electrode 14 is reduced.

  In the present embodiment, as shown in FIG. 3, the separation distance between the bonding portions facing each other across the pores 29 is 1 μm or less. The separation distance is more preferably 0.5 μm or less, and further preferably 0.1 μm or less. Here, the “separation distance” refers to an interval between points where the particles 28 first contact the intermediate layer 18.

  That is, in the present embodiment, the particles 28 constituting the anode side electrode 14 are in close contact with the intermediate layer 18. Moreover, as described above, the porosity of the anode-side electrode 14 is relatively small at 5 to 40 vol%. That is, there are more particles 28 than pores 29 near the interface with the intermediate layer 18 in the anode side electrode 14. Therefore, the anode side electrode 14 can receive a wide range of electrons that have moved from the electrolyte 12 through the intermediate layer 18.

  In addition, since the intermediate layer 18 is isotropic in terms of oxide ion conduction, the oxide ions move randomly in the intermediate layer 18. Accordingly, the probability that the oxide ions reach the particles 28 is higher than the probability that the oxide ions reach the pores 29 existing in the anode side electrode 14, and as a result, the anode side electrode 14 can easily receive the oxide ions. Thus, the interface resistance is reduced. In short, in the MEA 10 according to the present embodiment, the interface resistance between the anode side electrode 14 and the intermediate layer 18 is extremely small.

  In order to reduce the interface resistance, it is usually necessary to increase the thickness of the intermediate layer 18, but in this embodiment, as described above, the particles 28 constituting the anode side electrode 14 are densely packed in the intermediate layer. 18, and the porosity of the anode side electrode 14 is reduced, thereby improving the probability that the oxide ions reach the particles 28 constituting the anode side electrode 14, whereby the anode side electrode 14, the intermediate layer 18, The interface resistance is reduced. For this reason, the thickness of the intermediate layer 18 can be reduced.

  Furthermore, the MEA 10 including the anode side electrode 14 in which the Pt particles are amorphous has better power generation performance than the MEA including the anode side electrode in which a sharp peak of Pt particles appears in the X-ray diffraction measurement. It becomes.

  Of course, the same applies to the cathode side electrode 16 and the intermediate layer 20.

  The thickness of the intermediate layers 18 and 20 can be set to 1 μm or less, more preferably 500 nm or less, and still more preferably in the range of 50 to 200 nm. By making the thicknesses of the intermediate layers 18 and 20 extremely small in this way, it is possible to further reduce the IR loss.

  The thickness of the entire MEA 10 may be of a level that can ensure the strength, and specifically, 1 mm at the maximum is sufficient. When the thickness exceeds 1 mm, the MEA 10 has a large volume, and the energy efficiency per volume decreases.

  The thickness of the MEA 10 is preferably as small as possible. However, in order to ensure sufficient strength, the thickness is preferably 100 μm or more, and more preferably 200 μm or more. Moreover, in order to obtain high oxide ion conductivity while ensuring strength, the thickness of the MEA 10 is most preferably 200 to 600 μm.

  When configuring a unit cell of a fuel cell, as shown in FIG. 4, the MEA 10 configured as described above is interposed between a pair of separators 30a and 30b. In addition, current collecting electrodes 32a and 32b are disposed outside the separators 30a and 30b, respectively, and end plates 34a and 34b are disposed outside the current collecting electrodes 32a and 32b, respectively. The end plates 34a and 34b are connected to each other by bolts (not shown), and the MEA 10, the separators 30a and 30b, and the current collecting electrodes 32a and 32b are sandwiched between the end plates 34a and 34b, thereby forming a unit cell 36. . The separators 30a and 30b are provided with gas flow paths 38a and 38b for supplying fuel gas or oxygen-containing gas to the anode side electrode 14 or the cathode side electrode 16, respectively.

  The unit cell 36 is operated after being heated to a low to medium temperature range of about 300 to 700 ° C., preferably 500 ° C. That is, an oxygen-containing gas containing oxygen is circulated through the gas flow path 38b provided in the separator 30b, while a fuel gas containing hydrogen is circulated through the gas flow path 38a provided in the separator 30a.

Oxygen in the oxygen-containing gas is combined with electrons at the cathode-side electrode 16 to generate oxide ions (O ²⁻ ). The generated oxide ions move from the cathode side electrode 16 to the electrolyte 12 side.

  Here, the MEA 10 provided with the intermediate layers 18 and 20 is schematically shown in FIG. As shown in FIG. 5, oxide ions move from the cathode side electrode 16 to the intermediate layer 20, move randomly within the intermediate layer 20, and reach a site where the electrolyte 12 contacts the intermediate layer 20. Head. As described above, the intermediate layer 20 is made of a material that exhibits isotropic oxide ion conduction, such as SDC, YDC, GDC, and LDC. For this reason, not only the oxide ions moving straight in the intermediate layer 20 but also the oxide ions moving obliquely enter the electrolyte 12. That is, the number of oxide ions entering the electrolyte 12 is remarkably increased.

  Next, the oxide ions move in the electrolyte 12 toward the anode side electrode 14 side. Here, the electrolyte 12 has a thickness direction (arrow C direction), that is, a direction in which oxide ions can move most easily toward the anode electrode 14. For this reason, rapid movement of oxide ions occurs.

  In this way, a substance that exhibits anisotropy in oxide ion conduction (for example, apatite-type composite oxide) is used as the electrolyte 12, and the surface or direction in which the oxide ions are conducted is defined as the thickness direction. Ionic conductivity can be increased. In the electrolyte 12, oxide ions easily move even at a relatively low temperature. Therefore, the unit cell 36 exhibits sufficient power generation characteristics at a relatively low temperature.

  The oxide ions further move from the electrolyte 12 through the intermediate layer 18 to the anode side electrode 14. Also in this case, since the intermediate layer 18 is made of a material that exhibits isotropic oxide ion conduction such as SDC, YDC, GDC, and LDC, the oxide ions move randomly inside the intermediate layer 18, The intermediate layer 18 is directed to the anode side electrode 14, that is, a portion where Pt particles or SDC particles are in contact. Of course, since both the oxide ions moving straight in the intermediate layer 18 and the oxide ions moving obliquely are received by the anode side electrode 14, the number of oxide ions moving to the anode side electrode 14 is remarkably increased. To do.

  As described above, the intermediate layers 20 and 18 are interposed between the cathode side electrode 16 and the electrolyte 12 and between the electrolyte 12 and the anode side electrode 14, whereby the electrolyte 12 and the electrolyte 12 are changed from the cathode side electrode 16. The number of oxide ions that can move from the anode to the anode electrode 14 increases, and as a result, the oxide ion conductivity is improved.

  In this case, the particles 28 constituting the anode electrode 14 are in close contact with the intermediate layer 18. Therefore, the probability that the oxide ions that have moved to the intermediate layer 18 reach the pores 29 of the anode-side electrode 14 is low, and the probability that they reach the particles 28 is higher. Therefore, the interface resistance between the anode side electrode 14 and the intermediate layer 18 is significantly reduced.

  As described above, according to the present embodiment, the interfacial resistance between the electrodes 14 and 16 and the intermediate layers 18 and 20 is reduced, so that the overvoltage is reduced. Eventually, since the MEA 10 having excellent oxide ion conductivity is obtained, the unit cell 36 (fuel cell) exhibiting excellent power generation performance can be configured.

  The oxide ions finally reach the anode side electrode 14 and combine with hydrogen in the fuel gas supplied to the anode side electrode 14. As a result, water and electrons are released. Since the thickness of the anode side electrode 14 is as small as 1 μm at the maximum, the fuel gas (reactive gas) diffuses easily in the anode side electrode 14. Therefore, this electrode reaction proceeds efficiently.

  The emitted electrons are taken out to an external circuit electrically connected to the current collecting electrodes 32a and 32b, used as direct current electric energy for energizing the external circuit, and then to the cathode side electrode 16. To the oxygen supplied to the cathode side electrode 16.

  In the above reaction mechanism, since the intermediate layers 18 and 20 are made of SDC, YDC, GDC or the like as a mixed conductor, the ionization reaction at the cathode side electrode 16 and the water generation reaction at the anode side electrode 14 are promoted. In addition, since the thickness of the anode side electrode 14 is small, the internal resistance of the anode side electrode 14 is small. For this reason, the unit cell 36 exhibits even better power generation performance.

The MEA 10 can be manufactured as follows. First, obtained by a single crystal of La _X Si ₆ O _{1.5X +} apatite type oxides such as ₁₂ comprising an electrolyte 12 is grown by orienting the crystal growth direction in the c-axis direction. In order to align in this way, for example, a method described in JP-A-11-130595 may be employed.

  Next, various polishing processes such as a mirror polishing process, a fine polishing process, and a grindstone polishing process are performed on both end surfaces perpendicular to the c-axis direction of the obtained single crystal, and the arithmetic average height Ra of the end surface is determined. Set to a predetermined value.

  Next, the intermediate layers 18 and 20 are laminated on each end face subjected to the polishing treatment. In the present embodiment, the intermediate layers 18 and 20 are preferably formed by a vapor phase method so that the thickness of the intermediate layers 18 and 20 is 1 μm at the maximum. That is, for example, sputtering using an SDC target, a YDC target, a GDC target, an LDC target, or the like is performed.

  The fine active substance generated from the target adheres as fine particles to one end face of the single crystal. After the fine particles are adhered to the other end surface, the fine particles are bonded together to form the intermediate layers 18 and 20 by heat-treating the fine particles together with the single crystal.

Next, a perovskite type compound (for example, LaSrGaMgO, LaSrMnO, SmSrCoO, etc.), a fluorite type compound (for example, YDC, SDC, GDC, lanthanum solid solution ceria = LDC, etc.) or apatite with respect to the intermediate layer 20 A mold compound (for example, La _X Si ₆ O _{1.5X + 12} , La _X Ge ₆ O _{1.5X + 12} or the like) is applied by a screen printing method or the like. If this paste is baked, the cathode side electrode 16 is formed.

  Next, a composite material composed of Pt particles and SDC particles is deposited on the intermediate layer 18. In this deposition, for example, sputtering using a Pt target and an SDC target may be performed. In this case, sputtering for the Pt target and the SDC target is performed simultaneously.

  Fine active substances generated from each target also adhere to the intermediate layer 18 as fine particles. By subjecting the fine particles to heat treatment, the fine particles grow to form particles 28, and the anode electrode 14 in which the particles 28 are in close contact with the intermediate layer 18 is formed.

  If the sputtering conditions are adjusted, the particle size of the grown particles 28 can be 10 nm or less, whereby the distance between the pores 29 and 29 can be 1 μm or less. When the particles 28 constituting the anode side electrode 14 are made fine in this way, the probability that the oxide ions that have moved to the intermediate layer 18 reach the particles 28 is further improved.

  In order to make the SDC ratio less than 75 vol%, for example, when performing sputtering, the voltage with respect to the SDC target may be made smaller than that of the Pt target.

As described above, the anode electrode 14 made of Pt-SDC, the electrolyte 12 made of a single crystal such as La _x Si ₆ O _{1.5X + 12} having the c-axis direction as the thickness direction, the perovskite type compound (for example, LaSrGaMgO, LaSrMnO, SmSrCoO, etc.), fluorite type compounds (eg, YDC, SDC, GDC, LDC, etc.), or apatite type compounds (eg, La _X Si ₆ O _{1.5X + 12} , La _X Ge ₆ O _{1.5X + 12,} etc.) ), And intermediate layers 18 and 20 made of SDC, YDC, GDC or the like are interposed between the anode side electrode 14 and the electrolyte 12 and between the electrolyte 12 and the cathode side electrode 16. MEA 10 (see FIG. 1) is obtained.

  In order to construct the unit cell 36 from the MEA 10, the separators 30a and 30b, the current collecting electrodes 32a and 32b, and the end plates 34a and 34b are further disposed on the respective end faces of the anode side electrode 14 and the cathode side electrode 16. Good.

  In the above-described embodiment, the material of the anode side electrode 14 is Pt-SDC. However, Ni, Pt / Co, Ni / Co, Pt / Rd, etc. are used instead of Pt. You may make it employ | adopt 1 or more types of the metal element which belongs to. Further, the anode side electrode 14 may be made of only the metal as described above. Of course, even in such a case, the particle size of the metal particles is set to 10 nm or less.

  One cathode side electrode 16 may also be configured in accordance with the anode side electrode 14 described above. In this case, both the anode side electrode 14 and the cathode side electrode 16 may be configured as described above, or only the cathode side electrode 16 may be configured as described above. That is, in the present invention, it is only necessary that at least one of the anode side electrode 14 and the cathode side electrode 16 is configured as described above.

  The electrolyte / electrode assembly may be a support substrate type electrolyte / electrode assembly in which the electrolyte 12 is held by a support substrate. In this case, the thickness of the electrolyte 12 can be set to 50 μm or less. From the relationship between the power generation performance and strength of the electrolyte / electrode assembly, the thickness of the electrolyte 12 is preferably in the range of 200 nm to 10 μm.

The electrolyte 12 is not particularly limited to those consisting of _{La X Si 6 O 1.5X + 12} , if the substance having an anisotropic oxide ion conductivity, other apatitic oxides (e.g. La _X Ge ₆ O _{1.5X + 12} ), or a series of BIMEVOX compounds that are also layered compounds.

  Furthermore, the electrolyte 12 is not particularly limited to one made of a single crystal, and may be made of a sintered body in which crystals of each powder are oriented in the c-axis direction. Such a sintered body is, for example, a molded body obtained by adding apatite compound powder to a solvent to form a slurry, and then solidifying the slurry in the presence of a strong magnetic field of about 10 T (Tesla). It can be obtained by sintering the compact.

  Similarly, the intermediate layers 18 and 20 are not particularly limited to those made of SDC, YDC, or GDC, and may be other fluorite-type oxides as long as the oxide ion conduction is isotropic. It may be a perovskite oxide.

  Furthermore, in the above-described embodiment, the intermediate layers 18 and 20 are interposed between the anode side electrode 14 and the electrolyte 12 and between the cathode side electrode 16 and the electrolyte 12. Only the intermediate layer 20 between the side electrode 16 and the electrolyte 12 may be provided, or only the intermediate layer 18 between the anode side electrode 14 and the electrolyte 12 may be provided.

  Even in this case, the particles 28 constituting the anode electrode 14 are in intimate contact with the electrolyte 12. That is, the separation distance between the joint portions of the particles 28 and 28 facing each other across the pores 29 is set to 1 μm or less (see FIG. 3). Moreover, the porosity of the anode side electrode 14 is also ensured within a range of 5 to 40 vol%. Therefore, the probability that the oxide ions that have moved in the electrolyte 12 reach the particles 28 is higher than the probability that the oxide ions reach the pores 29. Therefore, the anode electrode 14 can efficiently receive the oxide ions. . Eventually, the interface resistance between the anode side electrode 14 and the electrolyte 12 is reduced, and the IR loss of the MEA 10 as a whole is reduced.

A single crystal of La _9.33 Si ₆ O ₂₆ (apatite compound) oriented in the c-axis direction was produced by the Czochralski method. The bottom surface of the single crystal was mirror-polished to obtain a disk-shaped body having a dimension along the c-axis direction (thickness direction) of 300 μm and a bottom surface diameter of 17 mm. Next, an SDC (Sm _0.8 Ce _0.2 O ₂ ) layer having a thickness of 200 nm is formed on both end faces of the disk-shaped body by sputtering, and then heat treatment is performed by holding at 1200 ° C. for 2 hours in the atmosphere. gave.

Next, La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ paste was applied to the end face of one SDC layer by screen printing so that the diameter was 8 mm, and then held at 1100 ° C. in the atmosphere for 1 hour. Heat treatment was performed to form a La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ layer.

Next, the Pt target and the SDC (Sm _0.8 Ce _0.2 O ₂ ) target were simultaneously sputtered to form a Pt-SDC layer having a thickness of 200 nm on the end face of the remaining SDC layer. Further, heat treatment was performed by holding at 500 ° C. for 2 hours. This Pt-SDC layer contained 75 vol% Pt.

As described above, La _9.33 Si ₆ O ₂₆ is the electrolyte, the Pt-SDC layer is the anode side electrode, the La _0.4 Sr _0.6 Co _0.8 Fe _0.2 O ₃ layer is the cathode side electrode, and the electrolyte and the anode side electrode An MEA in which an intermediate layer composed of an SDC layer was interposed between the cathode side electrode was obtained. When observed using a scanning electron microscope (SEM), the average distance between the bonding sites between the particles constituting the anode-side electrode was 20 nm. Moreover, the average interval between the bonding sites between the particles constituting the cathode side electrode was 500 nm. This is Example 1.

  FIG. 6 is an X-ray diffraction measurement pattern of an anode side electrode included in the MEA of Example 1. As can be seen from FIG. 6, only a broad peak appears in the heat treatment at 500 ° C. This means that both Pt particles and SDC particles are amorphous.

  Further, an MEA was produced in accordance with Example 1 except that the material and thickness of the intermediate layer, the material and thickness of the anode side electrode or cathode side electrode were changed as shown in FIG. Each is referred to as Examples 2-11. In FIG. 7, for example, a Pt-SDC layer containing 50 vol% Pt is expressed as “50% Pt-SDC” or the like. In Example 6, the intermediate layer is provided only on the cathode electrode side.

  Also in Examples 2 to 11 described above, the X-ray diffraction measurement of the anode side electrode was performed. In these cases, only a broad peak appeared as in Example 1.

  For comparison, the heat treatment temperature after forming the anode side electrode by sputtering was set to 700 ° C., or the heat treatment temperature after forming the anode side electrode by sintering was set to 900 ° C. or 1400 ° C. . These are referred to as Comparative Examples 1 to 5.

  FIG. 8 shows an X-ray diffraction measurement pattern of the anode side electrode included in the MEA of Comparative Example 1. It can be seen from FIG. 8 that a sharp peak derived from Pt appears when the heat treatment temperature is 700 ° C. That is, at this temperature, at least Pt becomes crystalline. Although not shown, similar results were obtained in Comparative Example 2.

  Moreover, the X-ray diffraction measurement of the anode side electrode was performed also about Comparative Examples 3-5. Although not shown, in these cases, sharp peaks derived from Pt and SDC appeared.

  In FIG. 7, the above results are shown as “electrode crystallinity” together with Examples 1-11. That is, “amorphous” in Examples 1 to 11 represents that only a broad peak appeared in the X-ray diffraction measurement pattern, and Comparative Examples 1 to 5 showed that a sharp peak of Pt or Pt and SDC appeared. Represents.

A unit cell of a fuel cell is configured by using each MEA of Examples 1 to 11 and Comparative Examples 1 to 5, and H ₂ is supplied to the anode side electrode at a flow rate of 15 cc / min, and compressed air is supplied to the cathode side electrode. Was supplied at a flow rate of 100 cc / min to generate electricity. The output power at 300 ° C. and 500 ° C. is also shown in FIG.

  It is clear that the output voltages at 300 ° C. and 500 ° C. are compared with each other, and the unit cells of Examples 1 to 11 are much more excellent in power generation performance than the unit cells of Comparative Examples 1 to 5. is there.

1 is an overall schematic longitudinal sectional view of an electrolyte / electrode assembly according to an embodiment. It is a structural view of the c-axis direction of the unit cell of _{La X Si 6 O 1.5X + 12} . FIG. 2 is a schematic structural explanatory view schematically showing an enlarged vicinity of an interface between an anode side electrode and an intermediate layer in the electrolyte-electrode assembly of FIG. 1. It is a schematic longitudinal cross-sectional view of the unit cell of the fuel cell which comprises the electrolyte electrode assembly of FIG. FIG. 2 is a schematic structural explanatory view schematically showing the electrolyte / electrode assembly of FIG. 1. 2 is an X-ray diffraction measurement pattern of an anode side electrode included in the MEA of Example 1. FIG. It is a chart which shows the anode side electrode in each unit cell of Examples 1-11 and Comparative Examples 1-5, the thickness and material of an intermediate | middle layer, and an output voltage. 3 is an X-ray diffraction measurement pattern of an anode side electrode included in the MEA of Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electrolyte electrode assembly (MEA) 12 ... Electrolyte 14 ... Anode side electrode 16 ... Cathode side electrode 18, 20 ... Intermediate | middle layer 21 ... Unit cell 28 ... Particle | grain 29 ... Pore 30a, 30b ... Separator 36 ... Unit cell 38a, 38b ... Gas flow path

Claims (4)

An electrolyte / electrode assembly in which an electrolyte is interposed between an anode side electrode and a cathode side electrode,
The electrolyte is a single crystal having a plane or direction in which oxide ions move, or a polycrystal oriented in the plane or direction in which oxide ions move, and the plane or direction is a thickness direction. An apatite-type oxide formed along
The anode side electrode or the cathode side electrode is configured by bonding particles having a particle size of 100 nm or less to each other, and the thickness is set to 1 μm or less.
The particles include at least amorphous metal particles;
The anode-side electrode or the cathode-side electrode has pores at a joint portion joined to the electrolyte or an intermediate layer interposed between the electrolyte and the anode-side electrode, and is adjacent to the pores. The electrolyte / electrode assembly is characterized in that the distance between the particles is 1 μm or less.   The electrolyte-electrode assembly according to claim 1, wherein the anode-side electrode or the cathode-side electrode has a porosity of 5 to 40 vol%.   3. The electrolyte / electrode assembly according to claim 1, wherein the anode side electrode or the cathode side electrode includes oxide ceramic particles capable of conducting oxide ions and metal particles capable of conducting electrons. An electrolyte / electrode assembly comprising:   4. The electrolyte / electrode assembly according to claim 3, wherein the ratio of the oxide ceramic particles is less than 75 vol%.

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