JP3646038B2 - Solid oxide fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid oxide fuel cell, and in particular, when a heat-resistant alloy containing chromium is used as a constituent member of a solid oxide fuel cell, and the chromium-containing gas is generated from the constituent member, the chromium-containing gas is a cause. The present invention relates to a solid oxide fuel cell that does not cause problems such as a decrease in power generation capacity.
[0002]
[Prior art]
Fuel cells such as solid oxide fuel cells are attracting attention as new energy sources from the viewpoint of resource saving and environmental impact.
[0003]
A solid oxide fuel cell includes a solid electrolyte layer, a unit cell including a fuel electrode provided on one surface of the solid electrolyte layer, and an air electrode provided on the opposite surface, and the unit cell. It is composed of an interconnector or the like that is electrically connected, and power is generated by supplying fuel gas to the fuel electrode and oxidant gas to the air electrode to generate power.
[0004]
Such a solid oxide fuel cell has a relatively high operating temperature of 700 to 1000 ° C. among the fuel cells, so that various fuels can be used, power generation efficiency is high, and all are made of solid materials. Therefore, there are advantages such as easy handling, and research and development for practical use is underway.
[0005]
The solid electrolyte layer is mainly composed of 8YSZ (YSZ: stabilized zirconia doped with yttria), 3YSZ, or the like.
[0006]
As the air electrode, LaSrMnO ₃ (referred to as LSM) is used as a representative material, and La-based materials in which La in LSM is replaced with other elements and Co-based materials in which Mn is replaced with Co are also proposed. . The fuel electrode is made of a material typified by Ni / YSZ cermet. For the air electrode and the fuel electrode, for example, first, a raw material to be a fuel electrode is applied to one surface of the solid electrolyte layer, fired at a high temperature of about 1450 ° C., and then the raw material of the air electrode is applied to the opposite surface. It is formed by firing at a low temperature of about ℃. Thus, an interface is formed between the air electrode and the solid electrolyte layer, and between the fuel electrode and the solid electrolyte layer.
[0007]
For interconnectors, doped LaCrO ₃ ceramics are generally used, but the use of heat-resistant alloys containing chromium due to the high cost of ceramics and the recent reduction in operating temperature. Has been considered.
[0008]
[Problems to be solved by the invention]
However, the use of a chromium-containing heat-resistant alloy for the interconnector has the following disadvantages.
[0009]
In other words, when an interconnector made of a heat-resistant alloy containing chromium is used in a solid oxide fuel cell, when the power generation operation is started in the solid oxide fuel cell, the interconnector used is exposed to a high temperature in an oxidizing atmosphere. As a result, chromium contained in the interconnector is oxidized, and a chromium oxide layer (Cr ₂ O ₃ ) is formed on the surface of the interconnector. When the chromium oxide layer (Cr ₂ O ₃ ) is formed on the surface, the chromium oxide in the chromium oxide layer further reacts with oxygen and water, and gaseous CrO ₂ (OH) ₂ is generated and emitted. CrO ₂ (OH) ₂ emitted from the interconnector comes into contact with the air electrode provided facing the interconnector and is reduced at the interface between the air electrode and the electrolyte layer. Chromium oxide is deposited at the interface.
[0010]
Chromium oxide deposited at the interface between the air electrode and the electrolyte layer inhibits the reaction between the oxidant gas and the air electrode, and increases the overvoltage between the air electrode and the electrolyte layer within 2 to 300 minutes from the start of power generation. The power generation performance of was significantly reduced. Thus, there is a problem when a chromium-containing heat-resistant alloy is used for an interconnector, and the problem caused by such chromium is called chromium poisoning.
[0011]
As a method for solving such a problem, the surface of the interconnector made of a heat-resistant alloy is coated with a coating agent so that the chromium-containing gas does not evaporate, or a trapping layer for capturing the emitted chromium-containing gas is provided inside the fuel cell. Although a method of providing a coating on the interconnector is limited and costly, the method of providing a trapping layer is a chromium-containing gas when the trapping capability of the trapping layer is exceeded. Could not be captured, and the effect did not last for a long time.
[0012]
The present invention has been made in view of the above points, and even when a chromium-containing heat-resistant alloy is used for a component member such as an interconnector, a problem caused by a chromium-containing gas occurs between the air electrode and the electrolyte layer. An object of the present invention is to provide a solid oxide fuel cell that is not allowed to flow.
[0013]
[Means for Solving the Problems]
Therefore, in the present invention, in order to solve the above problems, a solid oxide fuel cell is configured as follows. That is, the material of the air electrode and the electrolyte of the unit cell constituting the solid oxide fuel cell is a combination that is not affected by the chromium-containing gas at the interface between the air electrode and the electrolyte. For example, the air electrode is made of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (LSCF) and the electrolyte is a samarium-doped ceria-based oxide such as Ce _0.8 Sm _0.2 O. _1.9 . According to such a configuration of the air electrode and the electrolyte, even in the atmosphere of the chromium-containing gas, at the interface between the air electrode and the electrolyte, the influence of chromium poisoning, that is, the power generation capability may be reduced due to the deposition of chromium oxide. In addition, problems such as performance degradation do not occur in the solid oxide fuel cell.
[0014]
Not being affected by chromium poisoning means that the energization resistance generated between the air electrode and the electrolyte does not increase greatly when power generation is performed using an interconnector made of a heat-resistant alloy containing chromium. I understand. The reason is that when chromium-containing gas is generated from the interconnector and comes into contact with the air electrode, no chromium oxide is formed at the interface between the air electrode and the electrolyte layer, or even when chromium oxide is formed at the interface. This is considered to prevent problems such as an increase in resistance.
[0015]
Further, the present invention is not limited to the combination of the above examples, and the electrolyte may be at least a ceria-based oxygen ion conductive fluorite type, and the air electrode may be a perovskite oxide. In addition, the fuel electrode can use the material similar to the material used conventionally.
[0016]
Alternatively, the electrolyte may be composed of a plurality of layers, and at least the electrolyte on the side where the air electrode is provided may be composed of components that are not affected by the chromium-containing gas at the interface with the air electrode. In that case, the electrolyte on the other side can be a commonly used electrolyte such as a ZrO ₂ system or a LaGaO ₃ system.
[0017]
By constructing a solid oxide fuel cell in this way, there is no problem with chromium oxide at the interface between the air electrode and the electrolyte, and various components such as an interconnector are manufactured with a heat-resistant alloy containing chromium. Even so, it is possible to provide a solid oxide fuel cell that does not cause a decrease in power generation performance.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of a solid oxide fuel cell (flat solid electrolyte fuel cell) according to the present invention will be described.
[0019]
The solid oxide fuel cell is configured by laminating a plurality of fuel cells 20 including separators 10 and unit cells 12 as interconnectors.
[0020]
As shown in FIG. 1, the unit cell 12 includes a fuel electrode 14, a solid electrolyte layer 16, and an air electrode 18, and the fuel electrode 14 and the air electrode 18 are formed on the front and back of the solid electrolyte layer 16, respectively. As shown in FIG. 1, the solid electrolyte layer 16 is formed of two layers of a first electrolyte 4 made of a zirconia sintered body (YSZ) doped with yttria and the like, and a second electrolyte 6 of ceria-based oxide doped with samaria. The second electrolyte 6 has an appropriate thickness such as 0.05 mm and is laminated on the surface of the first electrolyte 4.
[0021]
The air electrode 18 is La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ and is formed on the surface of the second electrolyte 6, and the Ni / YSZ cermet is formed on the surface of the first electrolyte 4. A fuel electrode 14 is formed.
[0022]
As shown in FIG. 5, the separator 10 includes an alloy separator 22 and a ceramic separator 24. At the four corners of the separator 10, an oxidant gas supply hole for flowing an oxidant gas such as air, and an oxidant gas exhaust hole. A fuel gas supply hole for supplying a fuel gas such as city gas and a fuel gas exhaust hole (not shown) are formed. These holes are continuous when the fuel cells 20 are stacked, and form respective supply passages and exhaust passages. In addition, formation of each channel | path is not restricted to this.
[0023]
The alloy separator 22 is formed of an Inconel 600 heat resistant alloy and contains a predetermined amount of chromium. A groove portion 15 is formed on the contact surface side with the air electrode 18, and an oxidant gas passage that connects the oxidant gas supply hole and the oxidant gas exhaust hole is formed by the groove portion 15.
[0024]
The ceramic separator 24 is made of ceramic, and a recess 25 for accommodating the unit cell 12 is formed at the center. A groove portion 17 (fuel passage) communicating with the fuel gas supply hole and the fuel gas exhaust hole is formed at the bottom of the recess 25, and a nickel mesh 32 is provided on the groove portion 17.
[0025]
In addition, although the separator 10 was formed from two types of materials, the alloy separator 22 and the ceramic separator 24, this invention is not limited to this, You may form the separator 10 only from heat resistant alloys, such as Inconel600.
[0026]
Further, the separator 10 may be formed only of ceramic made of lanthanum chromite doped with strontium. In that case, when a chromium-containing alloy containing chromium is used in the fuel cell 20 or a part of its surrounding components, such as a gas passage gasket, the chromium coating caused by such a component is used. The problem of poison can be sufficiently prevented.
[0027]
Next, the operation of the fuel cell 20 will be described.
[0028]
First, the unit cell 12 is accommodated in the recess 25 of the ceramic separator 24, and the alloy separator 22 is covered from above to constitute the fuel cell 20. Then, the air electrode 18 comes into contact with the alloy separator 22, and is conducted to a fuel cell (not shown) stacked on the upper portion through the alloy separator 22, and the fuel electrode 14 has a nickel mesh 32 provided at the bottom of the recess 25. And through a current collecting hole 34, it conducts to a fuel cell (not shown) stacked below.
[0029]
When the fuel cells 20 are sequentially stacked to constitute a solid oxide fuel cell, the temperature is raised to a predetermined temperature, air is supplied from the oxidant gas passage, and fuel gas such as city gas is supplied from the fuel gas passage. Is brought into contact with the air electrode 18 and the fuel electrode 14 to start power generation. Then, since the alloy separator 22 has Inconel 600 as a base material, it is exposed to a high-temperature oxidizing atmosphere by the power generation action of the fuel cell 20, and chromium contained in the alloy is oxidized, and chromium oxide is formed on the surface of the alloy separator 22. A layer is formed.
[0030]
Further, the formed chromium oxide reacts with oxygen and water, and gaseous CrO ₂ (OH) ₂ is generated and emitted to come into contact with the air electrode 18. However, the material of the air electrode 18 is La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ , and the second electrolyte 6 in contact with the air electrode 18 is composed of a ceria-based oxide doped with samaria. Therefore, the interface between the _two is not affected by the chromium-containing gas (CrO ₂ (OH) ₂ ) generated from the alloy separator 22. For this reason, the solid oxide fuel cell does not cause a decrease in power generation action or the like, and power generation is performed stably for a long time.
[0031]
In the above example, the solid electrolyte layer 16 is formed of two layers of the first electrolyte 4 and the second electrolyte 6. However, the present invention is not the two layers of the solid electrolyte layer 16, but the predetermined components equivalent to the second electrolyte 6. You may form only. For example, the solid electrolyte layer 16 may be formed of ceria-based oxide doped with samaria, and the air electrode 18 and the fuel electrode 14 may be formed on the front and back surfaces thereof. Even in this case, since the interface between the air electrode 18 and the solid electrolyte layer 16 is maintained under a predetermined condition, it is possible to prevent a decrease in power generation capacity due to the chromium-containing gas.
[0032]
In the above example, the alloy separator 22 is made of Ni-based alloy Inconel 600. However, the present invention is a separator made of other alloys such as an Fe-based alloy, and is also effective for a separator that generates a chromium-containing gas. is there.
[0033]
(Experimental example)
Hereinafter, experimental examples of the solid oxide fuel cell will be described. The experimental apparatus is shown in FIG. 4, and the experimental results are shown in FIGS.
[0034]
As shown in FIG. 4, the experimental apparatus includes a ceramic container 52, a lid 56 that presses the test piece 54 accommodated in the container 52, and the like, and a supply port 58 that introduces air into the lid 56. A discharge port 60 for discharging air is formed. In addition, 78 is a platinum electrode and 80 is a mesh-shaped platinum electrode.
[0035]
As the test piece 54, the first test piece according to the present invention and the second test piece of the conventional example were prepared, and the lid 56 was made of Inconel 600 alloy and ceramic.
[0036]
The first test piece is an electrolyte 16 and an air electrode 18 provided thereon. The electrolyte 16 is composed of a first electrolyte 4 (8YSZ pellet (diameter 20 mm, thickness 2 mm)) and a second electrolyte 6 (Samaria). The air electrode 18 is made of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _{3. The} air electrode 18 is made of a ceria (SDC) film (thickness 20 μm) doped with (LSCF) powder was dispersed in hexylene glycol, and the solution was applied on the second electrolyte 6 by a screen method and baked at 1100 ° C. for 4 hours. Then, an electrode 62 was wound around the first electrolyte 4.
[0037]
The second test piece of the prior art (not shown), the electrolyte is formed by 8YSZ, the La _{0. 6} Sr _0. In ₄ MnO _{3 + δ (LSM)} powders hexylene glycol having an average particle diameter of 2μm thereon The dispersion was applied, the solution was applied by a screen method, fired at 1150 ° C. to form the air electrode 18, and the electrode 62 was wound around the electrolyte.
[0038]
In the experiment, the test piece 54 is put in the container 52, and a current is passed in the vertical direction of the test piece 54 with the lid 56 covering the top of the test piece 54, and the whole is heated to a predetermined temperature (800 ° C.) and supplied. Air is allowed to flow from the port 58 toward the discharge port 60, and energized at a current density of 0.3 A / cm ² in the vertical direction under the same conditions as the fuel cell operating conditions, and the air electrode 18 and the electrolyte 16 (electrode 62). The polarization (overvoltage) was measured.
[0039]
The results are shown in FIG. As shown in FIG. 2, in the first test piece according to the present invention, the overvoltage hardly changes even after 2500 minutes, and is almost the same as the case where the ceramic lid 56 that does not generate the chromium-containing gas is used. It is a value and it turns out that it is not influenced by chromium containing gas. On the other hand, in the experiment using the second test piece, it can be seen that the overvoltage rose to −2000 mV within 100 minutes, and chromium poisoning from the lid 56 was received.
[0040]
FIG. 3 shows the results of another experimental example.
[0041]
The table of FIG. 3 shows the value of the overvoltage when the material of the air electrode and the second electrolyte is changed and measured in the same manner as in the above experiment for each combination. From the results, when a chromium-containing heat-resistant alloy is used for the separator, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ is used as the air electrode for the combination that is least susceptible to chromium poisoning. and, it can be seen that a combination using _Ce 0.8 _Sm 0.2 _{O 1.9} in the second electrolyte.
[0042]
In the above example, a flat solid electrolyte fuel cell has been described as an example. However, the present invention is not limited to a flat plate type, but is a cylindrical solid electrolyte fuel cell or other shape solid oxide fuel cell. It may be.
[0043]
Furthermore, the chromium-containing alloy is not only used for an interconnector such as a separator, but may also be a supporting member for supporting a solid oxide fuel cell, a container, a pipe, or other constituent member. Not specific.
[0044]
【The invention's effect】
According to the solid electrolyte fuel cell of the present invention, since the air electrode and the electrolyte of the unit cell are made of a combination material that does not cause a decrease in power generation capability due to the chromium-containing gas at the interface between the air electrode and the electrolyte, a separator or the like A chromium-containing alloy can be used as a constituent member of a solid oxide fuel cell, and an inexpensive solid oxide fuel cell that performs stable power generation for a long time can be provided.
[0045]
In addition, since the electrolyte is composed of at least two layers, and the electrolyte on the air electrode side is a component that does not cause poisoning of the air electrode and chromium, a predetermined electrolyte is formed only in a necessary portion that forms an interface with the air electrode, and other electrolytes are used. Since the base portion of this can be configured with a general electrolyte that is easy to handle, efficiency, price, performance, etc. can be set satisfactorily.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a unit cell according to the present invention.
FIG. 2 is a graph showing experimental results.
FIG. 3 is a diagram showing a table of experimental results.
FIG. 4 is a diagram showing an experimental apparatus.
FIG. 5 is a cross-sectional view showing a fuel cell.
[Explanation of symbols]
4 First electrolyte 6 Second electrolyte 10 Separator (interconnector)
12 Cell 14 Fuel Electrode 15, 17 Groove 16 Solid Electrode 18 Air Electrode 20 Fuel Cell 22 Alloy Separator 24 Ceramic Separator 25 Recess 32 Nickel Mesh 34 Collecting Hole 54 Test Piece 56 Lid 58 Supply Port 60 Discharge Port 62 Electrode 78 Platinum Electrode 80 mesh platinum electrode

Claims (4)

At the interface between the air electrode and the electrolyte, the solid electrolyte side is the Ce _1-x Sm _x O _2-δ and the air electrode side is La _1-y Sr _y Fe. A solid oxide fuel cell characterized by being _1-z Co _z O ₃ . However, x = 0.1 to 0.5, y = 0.05 to 0.6, z = 0.01 to 0.95, and δ are deficient oxygen. The solid body electrolyte and the first electrolyte and the second layer of the second electrolyte, and the second electrolyte layer _{Ce 1-x Sm x O 2} -δ, the air electrode _{La 1-y Sr y Fe 1} -z Co z O _3. A solid oxide fuel cell, wherein the solid electrolyte fuel cell is formed on the second electrolyte as ₃ . However, x = 0.1 to 0.5, y = 0.05 to 0.6, z = 0.01 to 0.95, and δ are deficient oxygen. The _{Ce 1-x Sm x O 2} -δ is _Ce 0.8 _Sm 0.2 _{O 1.9,} the _{La 1-y Sr y Fe 1} -z Co z O 3 is _La 0.6 _{Sr 0.} The solid oxide fuel cell according to claim 1, which is ₄ Co _0.2 Fe _0.8 O ₃ .   The solid oxide fuel cell according to claims 1 to 3, wherein a chromium-containing alloy is used for at least a part of the constituent members of the solid oxide fuel cell.

Images