JP5395303B1 - Current collecting member and fuel cell - Google Patents

Abstract

A current collecting member capable of suppressing separation of a second conductive ceramic film from a first conductive ceramic film of a base material and a fuel cell including the current collecting member are provided.
A current collecting member includes a substrate and a second conductive ceramic film. The substrate 210 includes an alloy member 211 containing Fe and Cr, and a first conductive ceramic film 212 formed on the alloy member 211 and containing Cr ₂ O ₃ as a main component. The second conductive ceramic film 220 is formed on the first conductive ceramic film 212 and is made of a ceramic material containing Mn and Co. The first conductive ceramic film 212 is composed of columnar particles.
[Selection] Figure 2

Description

  The present invention relates to a current collecting member and a fuel cell including the current collecting member.

Conventionally, an alloy base material containing iron (Fe) and chromium (Cr) has been used as a current collecting member for electrically connecting a plurality of fuel cells in series. A first conductive ceramic film made of Cr ₂ O ₃ is formed on the surface of the base material.
Here, for the purpose of suppressing the generation of chromium-containing gas from the base material at a high temperature, the second conductive ceramic film containing a material forming a composite oxide with chromium oxide (Cr ₂ O ₃ ) is used as the base material. There has been proposed a method of forming on the surface (see Patent Document 1).

JP 2001-196077 A

  However, during operation of the fuel cell, stress is generated at the interface between the base material and the second conductive ceramic film due to the expansion and contraction of the base material accompanying the temperature rise and fall. For this reason, the second conductive ceramic film may be peeled off from the substrate.

  This invention is made | formed in view of the above-mentioned situation, and is provided with the current collection member which can suppress that a 2nd conductive ceramic film peels from the 1st conductive ceramic film of a base material, and its current collection member. An object is to provide a fuel cell.

A current collecting member according to the present invention includes an alloy member containing Fe and Cr as main components, and a first conductive ceramic film formed on the alloy member and containing Cr ₂ O ₃ as a main component; And a second conductive ceramic film formed on the first conductive ceramic film and made of a conductive oxide ceramic material containing Mn and Co. The first conductive ceramic film is composed of columnar particles.

  ADVANTAGE OF THE INVENTION According to this invention, a fuel cell provided with the current collection member which can suppress that a 2nd conductive ceramic film peels from the 1st conductive ceramic film of a base material, and the current collection member can be provided.

Sectional view showing the configuration of the fuel cell Enlarged sectional view of current collector Schematic diagram of EBSD image Schematic diagram of the EBSD image of the first conductive ceramic film An example of an EBSD image

<Configuration of Solid Oxide Fuel Cell 100>
The configuration of a solid oxide fuel cell (hereinafter abbreviated as “fuel cell”) 100 will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of the fuel cell 100.

  The fuel cell 100 includes a power generation unit 10 and a current collecting member 20.

(Configuration of power generation unit 10)
The power generation unit 10 includes a fuel electrode 11, a solid electrolyte layer 12, and an air electrode 13. The power generation unit 10 is a thin plate made of a ceramic material. The power generation unit 10 can have a thickness of 30 μm to 3 mm and a diameter of 5 mm to 50 mm, for example.

The fuel electrode 11 functions as an anode of the power generation unit 10. The fuel electrode 11 may have a function as a substrate (in other words, “support”) that supports the solid electrolyte layer 12 and the air electrode 13. The thickness of the fuel electrode 11 can be set to, for example, 10 μm to 3 mm. When the fuel electrode 11 functions as a substrate, the thickness of the fuel electrode 11 may be larger than the thickness of the solid electrolyte layer 12 and the air electrode 13. The fuel electrode 11 includes an anode current collecting layer and an anode active layer. The anode current collecting layer can be made of, for example, NiO / Ni—Y ₂ O ₃ , and the anode active layer can be made of, for example, NiO / Ni-8YSZ.

The solid electrolyte layer 12 is disposed between the fuel electrode 11 and the air electrode 13. The solid electrolyte layer 12 has a function of transmitting oxygen ions generated at the air electrode 13. The solid electrolyte layer 12 contains zirconium. The solid electrolyte layer 12 may contain zirconium as zirconia (ZrO ₂ ). The solid electrolyte layer 12 may contain zirconia as a main component. As a material of the solid electrolyte layer 12, for example, 8YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), or the like can be used.

The air electrode 13 is disposed on the solid electrolyte layer 12. The air electrode 13 functions as a cathode of the power generation unit 10. The air electrode 13 is a porous layer including more pores than the dense solid electrolyte layer 12. The air electrode 13 may contain, for example, LSCF (lanthanum strontium cobalt ferrite: (LaSr) (CoFe) O ₃ ) as a main component. The thickness of the air electrode 13 can be set to 5 μm to 50 μm.

(Configuration of current collecting member 20)
As shown in FIG. 1, the current collecting member 20 has a recess 20 </ b> A. The recess 20 </ b> A is connected to the surface of the air electrode 13 via the conductive adhesive 21. During power generation, air is supplied to the air electrode 13 through the recess 20A.

  Here, FIG. 2 is an enlarged cross-sectional view of the current collecting member 20. As shown in FIG. 2, the current collecting member 20 includes a base material 210 and a second conductive ceramic film 220.

  The base 210 has an alloy member 211 and a first conductive ceramic film 212.

  The alloy member 211 is a plate-like member containing Fe and Cr. The alloy member 211 can be made of, for example, a ferritic stainless steel member. The thickness of the alloy member 211 can be 0.3 mm-1 mm, for example.

The first conductive ceramic film 212 is formed on the surface of the alloy member 211. The first conductive ceramic film 212 contains Cr ₂ O ₃ as a main component. Cr ₂ O ₃ may contain an element constituting the alloy member 211 or the second conductive ceramic film 220 as an impurity. The first conductive ceramic film 212 is formed by Ar sputtering a Cr target using an RF (radio-frequency) magnetron sputtering apparatus and depositing an oxide by reaction with a reactive gas (for example, oxygen). Can do. The thickness of the first conductive ceramic film 212 can be set to 1 μm to 20 μm, for example.

The second conductive ceramic film 220 is formed on the surface of the first conductive ceramic film 212. The second conductive ceramic film 220 is made of a spinel conductive oxide ceramic material containing Mn and Co. Specifically, the second conductive ceramic film 220 may be made of (Mn, Co) ₃ O ₄ . (Mn, Co) ₃ O ₄ includes Mn _1.5 Co _1.5 O ₄ and Mn ₂ Co ₂ O ₄ . Further, the second conductive ceramic film 220 may contain (Mn _X Fe _1-X ) Cr ₂ O ₄ .

  The second conductive ceramic film 220 includes a first dense layer 221, a porous layer 222, and a second dense layer 223.

The first dense layer 221 forms the outer surface 220S of the second conductive ceramic film 220. That is, the first dense layer 221 is the outermost layer of the second conductive ceramic film 220. The first dense layer 221 has a dense structure. The porosity of the first dense layer 221 is preferably lower than the porosity of the porous layer 222. Specifically, the porosity of the first dense layer 221 is preferably 0.5% to 15%, for example. The porosity of the first dense layer 221 is the area occupied by pores (including closed pores and open pores) per unit area in the cross section of the first dense layer 221. In other words, the porosity of the first dense layer 221 is the area occupancy rate of the pores in a predetermined range of the cross section (for example, about 500 μm ² ). The thickness of the first dense layer 221 can be, for example, 0.5 μm to 10 μm, and particularly preferably 1 μm or more.

The porous layer 222 is formed inside the first dense layer 221, that is, on the substrate 210 side of the first dense layer 221. The porous layer 222 includes a plurality of closed pores 222A. The closed porosity of the porous layer 222 is preferably 20% or more and 70% or less. The closed porosity is an area occupied by the plurality of closed pores 222A per unit area in the cross section of the porous layer 222. In other words, the closed porosity of the porous layer 222 is the area occupation ratio of the pores in a predetermined range (for example, about 500 μm ² ) of the cross section. The average equivalent circular diameter of the plurality of closed pores 222A is preferably 0.3 μm or more and 3.5 μm or less.

  In this embodiment, the equivalent circle diameter is a diameter of a circle having the same area as the cross-sectional area of the object, and the average equivalent circle diameter is an average value of equivalent circle diameters of a plurality of objects.

  Further, the porous layer 222 may include open pores separately from the plurality of closed pores 222A. However, the open porosity of the porous layer 222 is preferably smaller than the closed porosity of the porous layer 222. The open porosity is an area occupied by open pores per unit area in the cross section of the porous layer 222.

  The thickness of the porous layer 222 can be set to, for example, 0.5 μm to 10 μm, and particularly preferably 1.0 μm or more.

  The second dense layer 223 is formed inside the porous layer 222, that is, on the substrate 210 side of the porous layer 222. In the present embodiment, the second dense layer 223 is the innermost layer of the second conductive ceramic film 220. The second dense layer 223 has a dense structure similar to that of the first dense layer 221. The porosity of the second dense layer 223 is equivalent to the porosity of the first dense layer 221 and is preferably lower than the porosity of the porous layer 222. The thickness of the second dense layer 223 may be smaller than the thickness of the first dense layer 221. The thickness of the second dense layer 223 may be smaller than the thickness of the porous layer 222. Specifically, the thickness of the second dense layer 223 can be, for example, 0.1 μm to 5 μm, and particularly preferably 0.5 μm or more.

  Note that the interfaces of the first dense layer 221, the porous layer 222, and the second dense layer 223 can be recognized from the difference in porosity between the layers.

  Further, as shown in FIG. 2, the current collecting member 20 has a plurality of Kirkendall voids 230. The plurality of Kirkendall voids 230 are formed in the vicinity of the interface P between the substrate 210 and the second conductive ceramic film 220. In the present embodiment, the interface P is formed between the first conductive ceramic film 212 of the substrate 210 and the second dense layer 223 of the second conductive ceramic film 220. The plurality of Kirkendall voids 230 are arranged along the interface P. At least some of the plurality of Kirkendall voids 230 may be formed in the substrate 210 or may be formed in the second conductive ceramic film 220. The average equivalent circle diameter of the plurality of Kirkendall voids 230 is preferably 0.05 μm or more and 0.5 μm or less.

<Particles of First Conductive Ceramic Film 212 and Second Conductive Ceramic Film 220>
Next, the particles of the first conductive ceramic film 212 and the second conductive ceramic film 220 will be described with reference to the drawings. FIG. 3 is an EBSD image obtained by analysis using an electron backscatter diffraction (EBSD) method. According to the EBSD method, discontinuity of crystal orientation can be observed, and a particle image can be drawn by regarding a line where a predetermined crystal orientation difference is observed as a grain boundary. Although the predetermined crystal orientation difference can be arbitrarily set, it may be set to about 15 degrees, for example.

As shown in FIG. 3, the second conductive ceramic film 220 is composed of coarse particles compared to the first conductive ceramic film 212. That is, the average equivalent circle diameter of the ceramic particles constituting the second conductive ceramic film 220 is larger than the average equivalent circle diameter of Cr ₂ O ₃ constituting the first conductive ceramic film 212. Specifically, the average equivalent circular diameter of the ceramic particles constituting the second conductive ceramic film 220 is preferably 0.5 μm or more and 2.5 μm or less. The average equivalent circle diameter of Cr ₂ O ₃ constituting the first conductive ceramic film 212 is preferably 0.15 μm or more and 0.8 μm or less.

  As shown in FIG. 3, the average equivalent circle diameter of the ceramic particles constituting the first dense layer 221 is larger than the average equivalent circle diameter of the ceramic particles constituting the porous layer 222. Specifically, the average equivalent circular diameter of the ceramic particles constituting the first dense layer 221 is preferably 0.8 μm or more and 3.5 μm or less. The average equivalent circular diameter of the ceramic particles constituting the porous layer 222 is preferably 0.5 μm or more and 2.0 μm or less.

  Here, FIG. 4 is a schematic diagram of an EBSD image of the first conductive ceramic film 212.

  As shown in FIG. 4, the first conductive ceramic film 212 is composed of columnar particles. The columnar particles are arranged so as to extend along the thickness direction.

  The average major axis of the columnar particles is preferably from 0.5 μm to 3.0 μm, and the average minor axis of the columnar particles is preferably from 0.1 μm to 1.0 μm. In the columnar particles, the aspect ratio (average major axis / average minor axis) of the average major axis to the average minor axis is preferably 1.5 or more and 10 or less. The average equivalent circle diameter of the columnar particles is more preferably from 0.15 μm to 0.8 μm.

<The manufacturing method of the current collection member 20>
Next, a method for manufacturing the current collecting member 20 will be described.

  First, an alloy member 211 having a predetermined size made of ferritic stainless steel is prepared.

Next, Cr ₂ O ₃ is sputtered on the surface of the alloy member 211 using an RF sputtering apparatus, and then heat treatment (for example, 850 to 1050 ° C., 1 to 20 hours) is performed in an air atmosphere. As a result, columnar particles containing Cr ₂ O ₃ as a main component are grown on the surface of the alloy member 211 to form the first conductive ceramic film 212.

Next, a coating agent containing (Mn, Co) ₃ O ₄ is applied / dried a plurality of times on the surface of the first conductive ceramic film 212. At this time, a coating agent containing a pore forming agent is applied / dried a plurality of times, and then a coating agent not containing a pore forming agent is applied / dried a plurality of times. By adjusting the presence or absence of the pore former in this manner, two layers of the first dense layer 221 and the porous layer 222 are formed in the baking process described later. Further, the average equivalent circle diameter of the closed pores in the porous layer 222 can be adjusted by appropriately selecting the particle size of the pore former.

  Next, a multilayer coating agent is baked under predetermined conditions. The following three steps are examples of baking conditions for the coating agent.

900-1100 ° C., 1-20 hours, firing in air atmosphere 900-1100 ° C., 1-20 hours, reduction treatment in 1-10% humidified reducing atmosphere 900-1100 ° C., 1-10 hours Reoxidation treatment in the atmosphere <Action and effect>
(1) The first conductive ceramic film 212 of the substrate 210 according to the present embodiment is composed of columnar particles.

  Therefore, compared with the case where the first conductive ceramic film 212 is composed of, for example, spherical particles, the first conductive ceramic film 212 is easily deformed by receiving stress in the surface direction. Therefore, when the base material 210 expands and contracts as the temperature rises and falls during operation of the fuel cell 100, the stress generated at the interface between the base material 210 and the second conductive ceramic film 220 can be relaxed. Thereby, it is possible to suppress the second conductive ceramic film 220 from being peeled from the first conductive ceramic film.

<Other embodiments>
(A) In the above embodiment, the second conductive ceramic film 220 has the second dense layer 223, but may not have the second dense layer 223. In this case, the interface P between the substrate 210 and the second conductive ceramic film 220 is formed between the porous layer 222 and the first conductive ceramic film 212. Accordingly, the plurality of Kirkendall voids 230 are disposed between the porous layer 222 and the first conductive ceramic film 212.

  (B) Although not particularly mentioned in the above embodiment, the basic structure of the fuel cell 100 includes a fuel electrode support type, a flat plate type, a cylindrical shape, a vertical stripe type, a horizontal stripe type, a single-end holding type, and a double-end holding type. Can be adopted.

  (C) Although the configuration of the current collecting member 20 connected to the air electrode 13 has been described as an example of the current collecting member in the above embodiment, the present invention is not limited to this. The current collecting member according to the present invention may be a separator sandwiched between two fuel cells. In this case, the separator is connected to the air electrode of one fuel battery cell and the fuel electrode of the other fuel battery cell. According to the present invention, the durability of such a separator can also be improved.

  (D) In the above embodiment, the power generation unit 10 is configured by the fuel electrode 11, the solid electrolyte layer 12, and the air electrode 13. However, the present invention is not limited to this. For example, the power generation unit 10 may include a barrier layer for suppressing cation diffusion between the solid electrolyte layer 12 and the air electrode 13.

  (E) In the above embodiment, the alloy member 211 is a plate-like member, but is not limited thereto. The alloy member 211 may be a mesh member, for example.

(F) In the above embodiment, the Cr ₂ O ₃ columnar particles are formed by sputtering Cr ₂ O ₃ using an RF sputtering apparatus, but the present invention is not limited to this. Such columnar particles of Cr ₂ O ₃ can also be formed by oxidation treatment by subjecting the surface of the alloy member 211 to high-temperature heat treatment.

(Production of sample No. 1 to No. 19)
Sample no. Current collecting members and fuel cells according to 1 to 19 were produced.

  First, a ferritic stainless steel plate containing Fe and Cr as main components was prepared.

Next, a first conductive ceramic film mainly composed of Cr ₂ O ₃ was formed on the surface of the stainless steel plate. Sample No. 1, the first conductive ceramics composed of spherical particles by applying a slurry prepared using raw materials obtained by pulverizing and adjusting pre-synthesized Cr ₂ O ₃ particles to a predetermined particle size, followed by drying and firing. A film was formed. Sample No. 2 to No. 19, reactive sputtering (reaction gas: mixed gas of Ar + O ₂ (O ₂ / Ar ratio) using a metal Cr target (purity: 99.9% or more) using an RF magnetron sputtering apparatus (manufactured by Nidec Anelva, SPF-210H). : 0.2 to 0.6), sputtering pressure: 2 to 10 × 10 ⁻³ Torr, substrate temperature: normal temperature to 200 ° C., and then heat treatment (temperature: 600 to 700 ° C., treatment time: 1 to 5 hr) ) To form a first conductive ceramic film composed of columnar particles.

Next, (Mn, Co) ₃ O ₄ powder having an average particle size of 0.8 μm was prepared by removing coarse particles of 3 μm or more with an airflow classifier.

Next, terpineol as a solvent, a cellulose binder, a dispersant, and a pore former were added to the (Mn, Co) ₃ O ₄ powder to prepare a slurry for a porous layer. Further, a terpineol, a cellulose binder and a dispersant were added to the (Mn, Co) ₃ O ₄ powder to prepare a dense layer slurry.

  Next, a second conductive ceramic film was formed on the surface of the first conductive ceramic film. In Sample Nos. 1 to 10, only the dense layer slurry was applied / dried a plurality of times in order to form the second conductive ceramic film only with the dense layer. In Samples Nos. 11 to 16, in order to form the first dense layer on the porous layer, the porous layer slurry was applied / dried several times, and then the dense layer slurry was applied / dried several times. . In Samples Nos. 17 to 19, in order to form the porous layer and the second dense layer inside the first dense layer, the dense layer slurry, the porous layer slurry, and the dense layer slurry are sequentially applied a plurality of times. / Dried. In addition, application | coating was implemented by the slurry dipping method (immersion time 10-300 sec, raising / lowering speed 0.1-10 mm / sec), and drying was implemented by warm air drying (120 degreeC, 30 min). By using a hot air drier, the film formation surface is actively dried, and the solvent component remains in the film, so that it becomes easy to leave pores in the film after baking.

  Next, a second conductive ceramic film was formed by baking the applied / dried slurry. Specifically, the baking treatment includes degreasing treatment (600 ° C./2 hr), baking treatment in the air atmosphere (maximum temperature 1000 ° C./2 hr), reduction heat treatment in hydrogen atmosphere (maximum temperature 1000 ° C./10 hr, 4% humidification) ), And reoxidation treatment in an air atmosphere (maximum temperature 1000 ° C./5 hr). Thus, the current collecting members according to samples No. 1 to No. 19 were completed.

  Next, the current collecting members according to Samples No. 1 to No. 19 were connected to the air electrode of the power generation unit separately manufactured via a conductive adhesive. Thus, the fuel cells according to samples No. 1 to No. 19 were completed.

(First thermal cycle test)
Regarding the fuel cells according to sample Nos. 1 to 19, the temperature was raised to 750 ° C. while supplying nitrogen gas to the fuel electrode side and air to the air electrode side, and hydrogen gas was supplied to the fuel electrode when the temperature reached 750 ° C. The reduction treatment was performed for 3 hours. Subsequently, a cycle in which each sample was heated from room temperature to 750 ° C. at 200 ° C./hr and then cooled from 750 ° C. to room temperature at 100 ° C./hr was repeated 10 times.

(Second thermal cycle test)
For the fuel cells according to Samples Nos. 11 to 19, the cycle of raising the temperature from room temperature to 750 ° C. at 400 ° C./hr and then lowering the temperature from 750 ° C. to room temperature at 200 ° C./hr was repeated 5 times.

(EBSD measurement)
Next, five EBSD images were obtained by measuring five portions of the cross sections of sample Nos. 1 to 19 with an EBSD apparatus (TSL OIM). In the EBSD image, a line in which a crystal orientation difference of 15 degrees or more was observed was regarded as a grain boundary, and the particle was drawn. An example of an EBSD image according to sample Nos. 17 to 19 is shown in FIG.

  Then, by observing the EBSD images of samples No. 1 to No. 19, as shown in Table 1, the presence or absence of peeling at the interface between the first conductive ceramic film and the second conductive ceramic film was confirmed. Further, by observing the EBSD images of Sample Nos. 2 to 19, as shown in Table 1, the average major axis, the average minor axis, and the aspect ratio (average major axis / average) of the columnar particles constituting the first conductive ceramic film The minor axis) and the average equivalent circle diameter were measured. Furthermore, by observing SEM images of Sample Nos. 2 to 19, the thicknesses of the first dense layer, the porous layer, and the second dense layer were measured as shown in Table 1.

As shown in Table 1, Samples Nos. 2 to 19 were able to suppress enormous peeling after the first thermal cycle test. Such a result was obtained because the stress generated at the interface could be relaxed by the first conductive ceramic film constituted by the columnar particles.
Further, as shown in Table 1, Samples Nos. 3 to 9 and 11 to 19 were able to suppress slight peeling after the first thermal cycle test. Therefore, the average major axis of the columnar particles is 0.5 μm or more and 3.0 μm or less, the average minor axis of the columnar particles is 0.1 μm or more and 1.0 μm or less, and the aspect ratio is 1.5 or more and 10 or less. The following have been found to be preferred. From this, it was also found that the average equivalent circle diameter of the columnar particles is preferably 0.15 μm or more and 0.8 μm or less.
Moreover, as shown in Table 1, in Sample Nos. 12 to 15, slight peeling after the second thermal cycle test could be suppressed. Therefore, when the porous layer is formed inside the first dense layer, the thickness of the first dense layer is preferably 0.5 μm to 10 μm, and the thickness of the porous layer is 0.5 μm to 10 μm. The following were found to be preferred.

DESCRIPTION OF SYMBOLS 100 Solid oxide fuel cell 10 Power generation part 11 Fuel electrode 12 Solid electrolyte layer 13 Air electrode 20 Current collecting member 210 Base material 211 Alloy member 212 First conductive ceramic film 220 Second conductive ceramic film 221 First dense layer 222 Porous layer 223 second dense layer

Claims (9)

A base material comprising: an alloy member containing Fe and Cr as main components; and a first conductive ceramic film formed on the alloy member and containing Cr ₂ O ₃ as a main component;
A second conductive ceramic film formed on the first conductive ceramic film and made of a conductive oxide ceramic material containing Mn and Co;
With
The first conductive ceramic film is composed of a plurality of columnar particles.
Current collecting member. The average major axis of the plurality of columnar particles is 0.5 μm or more and 3.0 μm or less,
The average minor axis of the plurality of columnar particles is 0.1 μm or more and 1.0 μm or less,
The aspect ratio of the average major axis to the average minor axis is 1.5 or more and 10 or less.
The current collecting member according to claim 1. The average equivalent circle diameter of the plurality of columnar particles is 0.15 μm or more and 0.8 μm or less.
The current collecting member according to claim 2. The second conductive ceramic film includes a first dense layer that forms an outer surface, and a porous layer that is disposed inside the first dense layer and includes a plurality of closed pores.
The current collecting member according to claim 1. The thickness of the first dense layer is not less than 0.5 μm and not more than 10 μm.
The current collecting member according to claim 4. The thickness of the porous layer is 0.5 μm or more and 10 μm or less.
The current collecting member according to claim 4 or 5. The second conductive ceramic film has a second dense layer disposed inside the porous layer,
The second dense layer is thinner than the first dense layer;
The current collecting member according to claim 4. The thickness of the second dense layer is not less than 0.1 μm and not more than 5 μm.
The current collecting member according to claim 7. A current collecting member according to claim 1;
First and second power generation units each having a fuel electrode, an air electrode, and a solid electrolyte layer;
With
The current collecting member is electrically connected to the air electrode of the first power generation unit and the fuel electrode of the second power generation unit,
Fuel cell.