JP4288485B2 - Solid oxide fuel cell - Google Patents

Description

  The present invention relates to a solid oxide fuel cell (SOFC) using a solid electrolyte.

  Conventionally, as a cell design of a solid oxide fuel cell, a flat plate type (stack type), a cylindrical type (tube type), and the like have been proposed.

  A flat cell is one in which a fuel electrode and an air electrode are respectively arranged on the front and back surfaces of a plate-like electrolyte, and a plurality of cells formed in this way are used in a state where they are stacked via separators. The separator plays a role of completely separating the fuel gas and air supplied to each cell, and a gas seal is provided between each cell and the separator (for example, Patent Document 1). However, this flat cell has a drawback that the cell is vulnerable to vibration, thermal cycle, etc. because it applies pressure to the cell to provide a gas seal, and has a big problem in practical use. Yes.

  On the other hand, a cylindrical cell has a fuel electrode and an air electrode arranged on the outer peripheral surface and inner peripheral surface of a cylindrical electrolyte, and a cylindrical vertical stripe type, a cylindrical horizontal stripe type, and the like have been proposed (for example, Patent Documents). 2). However, the cylindrical cell has an advantage of excellent gas sealing properties, but has a drawback that the manufacturing process is complicated and the manufacturing cost is high because the structure is more complicated than that of the flat plate cell.

  In addition, there are the following problems. In order to improve the performance of both the flat type cell and the cylindrical type cell, it is necessary to reduce the thickness of the electrolyte, and it is necessary to reduce the ohmic resistance of the electrolyte material. There was a problem that the durability and durability deteriorated.

  Therefore, as a fuel cell that replaces the flat plate type and the cylindrical type described above, the fuel electrode and the air electrode are arranged on the same surface of the substrate made of a solid electrolyte, and power generation is possible by supplying a mixed gas of fuel and air. Non-membrane type solid oxide fuel cells have been proposed (for example, Patent Document 3). According to this fuel cell, since it is not necessary to separate the fuel gas and air, the separator and the gas seal are not required, and the structure and the manufacturing process can be greatly simplified.

Further, in this non-membrane type solid oxide fuel cell, the conduction of oxygen ions occurs near the surface layer of the solid electrolyte, and the fuel electrode and the air electrode are formed close to each other on the same surface of the solid electrolyte. The thickness of the electrolyte does not directly affect the performance of the battery as in the case of the cylinder type. Therefore, the thickness of the electrolyte can be increased while maintaining the performance of the battery, thereby improving the vulnerability.
JP-A-5-3045 (first page, FIG. 6) Japanese Patent Laid-Open No. 5-94830 (first page, FIG. 1) JP-A-8-264195 (page 2-3, FIG. 1)

  As described above, in the fuel cell described in Patent Document 3, an electrolyte is used as a substrate, and a plurality of fuel electrodes and air electrodes are arranged on one surface thereof. However, since it is a portion near the electrode that is required for the battery reaction in the electrolyte, there are many portions that do not contribute to the battery reaction in the electrolyte used as the substrate as described above. Here, since the material cost of the electrolyte is not cheap, there is a problem that the cost performance is lowered if there is a portion that does not contribute to the battery reaction.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a solid oxide fuel cell capable of increasing cost performance without deteriorating battery performance.

  The present invention is a fuel cell including at least one single battery cell having an electrolyte, a fuel electrode, and an air electrode, and has been made to solve the above problem, and a substrate that supports the single battery cell. The electrolyte is disposed on one surface of the substrate, and one of the fuel electrode and the air electrode is disposed on the electrolyte, and the other electrode is not connected to the one electrode. In a contact state, at least a part of the substrate is disposed on one surface of the substrate and is in contact with the electrolyte.

  According to this configuration, one electrode is disposed on the electrolyte on the substrate, and the other electrode is disposed in contact with the electrolyte on the substrate. Thereby, since a single battery cell can be comprised, without using the electrolyte unnecessary for battery reaction as much as possible, the cost performance of a fuel cell can be improved.

  At this time, as long as the other electrode and the one electrode can maintain a non-contact state, the other electrode can be disposed on a part of the electrolyte. Further, when the other electrode is arranged on the substrate, a non-contact state between both electrodes can be formed only by adjusting the thickness of the other electrode. That is, since the non-contact state can be formed by making the thickness of the other electrode smaller than the thickness of the electrolyte, the distance between the two electrodes can be easily adjusted even if the fuel cell becomes minute. Moreover, the distance between both electrodes can be easily reduced by adjusting the thickness.

  Here, the following effects can be obtained by using one electrode as a fuel electrode and the other electrode as an air electrode. That is, by disposing the fuel electrode on the electrolyte, the interface between the fuel electrode and the electrolyte, that is, the three-phase interface that affects the cell reaction can be increased, so that stable battery performance can be obtained.

  It is also possible to arrange a plurality of unit cells configured as described above on a substrate and connect them with an interconnector. Accordingly, a large number of fuel electrodes and air electrodes can be formed on the same substrate, so that a high power generation output can be obtained. At this time, the plurality of single battery cells may be connected in series or in parallel, or may be connected in a mixed state of series and parallel.

  In particular, the following effects can be obtained when the battery cells are connected in series. For example, in the conventional example, since a plurality of electrode bodies composed of the fuel electrode and the air electrode are arranged on one substrate, there is a possibility that the electromotive force is canceled by the electrolyte between these electrode bodies. . On the other hand, in the present invention, even if a plurality of single battery cells are connected in series, there is no electrolyte between adjacent single battery cells. Obtainable.

  In the fuel cell, the electrolyte, the fuel electrode, and the air electrode are preferably formed by printing. By doing so, the thickness and dimensions can be precisely adjusted, and the distance between the electrodes can be accurately adjusted. In addition, because of this, it is possible to arbitrarily form an electrolyte for the part required for battery reaction, so the amount of electrolyte to be used can be minimized and further cost reduction is possible. It becomes.

  In the fuel cell described above, the single battery cell is disposed on one surface of the substrate, but can also be disposed on the other surface of the substrate. That is, in addition to one surface of the substrate, at least one single battery cell is disposed on the other surface, the electrolyte in this single battery cell is disposed on the other surface of the substrate, and either the fuel electrode or the air electrode is disposed. The electrode may be disposed on the electrolyte, and the other electrode may be in non-contact with the one electrode, and at least partly disposed on the other surface of the substrate so as to be in contact with the electrolyte. Thereby, since many single battery cells of the said structure can be formed on the same board | substrate, a high electric power generation output can be obtained, keeping a fuel cell compact.

  Moreover, it is preferable that the board | substrate used for this fuel cell is comprised with an insulating ceramic type material from a heat resistant viewpoint.

  According to the solid oxide fuel cell according to the present invention, it is possible to increase the cost performance without deteriorating the cell performance.

  Hereinafter, a first embodiment of a solid oxide fuel cell according to the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view of a fuel cell according to this embodiment.

  As shown in FIG. 1, the fuel cell includes a single battery cell C having an electrolyte 3, a fuel electrode 5, and an air electrode 7, and the single battery cell C is supported on a substrate 1.

  The electrolyte 3 is formed in a rectangular shape on the upper surface (one surface) of the substrate 1, and the fuel electrode 5 having substantially the same shape as the electrolyte 3 is formed on the upper surface. An air electrode 7 is formed at a position adjacent to the electrolyte 3 on the substrate 1. The air electrode 7 is in contact with the side surface of the electrolyte 3 and has a thickness smaller than that of the electrolyte 3. That is, the upper surface of the air electrode 7 is at a position lower than the upper surface of the electrolyte 3. As a result, the fuel electrode 5 and the air electrode 7 are arranged at a distance corresponding to the thickness difference D between the electrolyte 3 and the air electrode 7.

  Next, materials constituting the fuel cell will be described. The substrate 1 is preferably formed of a material having excellent adhesion to the electrolyte 3 and the air electrode 7 and having excellent heat resistance of 1500 ° C. or higher. Specifically, ceramic materials such as alumina materials, silica materials, and titanium materials can be preferably used. In addition, it is preferable that the thickness of the board | substrate 1 shall be 100 micrometers or more from a viewpoint of maintaining a certain amount of durability.

As the material of the electrolyte 3, those known as electrolytes for solid oxide fuel cells can be used. For example, (Ce, Sm) O ₃ , (Ce, Gd) O ₃ , (La, Sr) (Ga , Mg) O ₃ , scandia-stabilized zirconia (ScSZ), yttria-stabilized zirconia (YSZ), and other oxygen ion conductive ceramic materials can be used. Moreover, the thickness of the electrolyte 3 is preferably, for example, 100 μm to 1 mm, more preferably 10 to 500 μm, and particularly preferably 50 to 200 μm.

  The fuel electrode 5 and the air electrode 7 can be formed of a ceramic powder material. The particle size of the powder used at this time is usually 10 nm to 100 μm, preferably 100 nm to 10 μm.

As a ceramic powder material forming the fuel electrode 5, for example, a mixture of nickel and an oxygen ion conductive material can be used. Examples of the oxygen ion conductive material used at this time include ceria-based materials such as (Ce, Sm) O ₃ and (Ce, Gd) O _3, and lanthanum garades such as (La, Sr) (Ga, Mg) O _3. And oxygen ion conductive ceramic materials such as scandia-stabilized zirconia (ScSZ) and yttria-stabilized zirconia (YSZ), and the like. Is preferably formed. Among these, it is particularly preferable to form the fuel electrode 5 with a cermet of nickel-ceria-based oxide. The mixed form of the oxygen ion conductive ceramic material and nickel may be a physical mixed form or a form of powder modification to nickel. Moreover, the ceramic material mentioned above can be used individually by 1 type or in mixture of 2 or more types.

As a ceramic powder material forming the air electrode 7, for example, a perovskite metal oxide can be used. Specifically, (Sm, Sr) CoO ₃ , (La, Sr) MnO ₃ , (La, Sr) CoO ₃ , (La, Sr) (Fe, Co) O ₃ , (La, Sr) (Fe, Co , Ni) O _{3 and the} like. These ceramic powders can be used singly or in combination of two or more.

  The electrolyte 3, the fuel electrode 5, and the air electrode 7 are formed by adding appropriate amounts of varnish, photosensitive polymer, organic solvent, etc. with the above-described materials as main components. The film thickness of the air electrode 3 and the fuel electrode 5 is formed to be 1 μm to 500 μm after sintering, but is preferably 10 μm to 100 μm. However, the thickness of the air electrode 7 is preferably smaller than the thickness of the electrolyte 3 as described above.

Next, an example of a method for manufacturing the fuel cell will be described with reference to FIG. First, a substrate 1 that supports a single battery cell is prepared. The material of the substrate 1 is as described above. Subsequently, the above-described powder materials for the electrolyte 3, fuel electrode 5, and air electrode 7 are used as main components, and varnish, photosensitive polymer, organic solvent, and the like are added to each of these materials and kneaded to prepare an electrolyte paste, a fuel electrode. Create paste and air electrode paste respectively. The viscosity of each paste is preferably about 10 ³ to 10 ⁶ Pa · s so as to be compatible with screen printing described below.

  Next, after applying an electrolyte paste in a rectangular shape on the substrate 1 by a screen printing method, the electrolyte 3 is formed by drying at a predetermined time and temperature (FIG. 2A). And after apply | coating a fuel electrode paste on the electrolyte 3 by the screen printing method, it dries and sinters by predetermined time and temperature, and forms the fuel electrode 5 (FIG.2 (b)). At this time, the fuel electrode paste is applied to approximately the same size as the electrolyte 3. Subsequently, an air electrode paste is applied in a rectangular shape on the substrate 1 at a position adjacent to the electrolyte 3. At this time, the air electrode paste is applied so as to be in contact with the side surface of the electrolyte 3 and thinner than the thickness of the electrolyte 3. The air electrode paste thus applied is dried and sintered at a predetermined time and temperature to form the air electrode 7. Through the above steps, the fuel cell shown in FIG. 1 is formed.

  The fuel cell configured as described above generates power as follows. First, a mixed gas of a fuel gas composed of a hydrocarbon such as methane or ethane and air is supplied on one surface of each unit cell C in a high temperature state (for example, 400 to 1000 ° C.). As a result, oxygen ion conduction occurs in the electrolyte 3 between the fuel electrode 5 and the air electrode 7 to generate power.

  As described above, in the fuel cell according to the present embodiment, the air electrode 7 and the electrolyte 5 are disposed adjacent to each other, and the fuel electrode 5 is disposed on the electrolyte 3. Thereby, since the single battery cell can be configured without using the electrolyte 3 unnecessary for the battery reaction as much as possible as in the conventional example, the cost performance of the fuel cell can be improved.

  Further, in this fuel cell, the thickness of the electrolyte 3 is made larger than the thickness of the air electrode 7, thereby preventing the electrodes 5 and 7 from contacting each other. That is, the difference between the thickness of the electrolyte 3 and the thickness of the air electrode 7 is the distance between the electrodes 5 and 7. Therefore, since the distance between the electrodes 5 and 7 can be adjusted only by adjusting the thickness of the electrolyte 3 or the air electrode 7, for example, even if the fuel cell is miniaturized, the electrodes 5 and 7 can be easily brought into a non-contact state. The fuel cell can be easily manufactured.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this, A various change is possible unless it deviates from the meaning. For example, in the above embodiment, the non-contact state of the electrodes 5 and 7 is realized by making the thickness of the air electrode 7 smaller than the thickness of the electrolyte 3, but the non-contact state is realized by other forms. You can also For example, as shown in FIG. 3A, even if the electrolyte 3 and the air electrode 7 have substantially the same thickness, a gap S is formed from the air electrode 7 without applying the fuel electrode 5 to the entire upper surface of the electrolyte 3. If they are separated, the cost performance of the fuel cell can be improved as in the above embodiment. Alternatively, as shown in FIGS. 3B and 3C, if the fuel electrode 5 and the air electrode 7 are separated with a gap S therebetween, a part of the air electrode 7 is placed on the upper surface of the electrolyte 3. It may be formed. That is, as shown in FIG. 3B, the thickness of a part of the air electrode 7 is increased so that this part is disposed on the electrolyte 3, or as shown in FIG. 7, the entire thickness can be increased so that a portion thereof is disposed on the electrolyte 3. By doing so, as shown in FIG. 3A, it is not necessary to make the electrolyte 3 and the air electrode 7 have exactly the same thickness, so that it is easy to form a fuel cell by printing.

  Moreover, in the said embodiment, although the fuel cell is comprised using the single battery cell C, you may use two or more this. In this case, the plurality of single battery cells are connected by an interconnector. An example of this case is shown in FIG. As shown in the figure, in this example, two unit cells C are shown, but more unit cells can also be used. And between each unit cell C, the fuel electrode 5 of one unit cell C (right side of the figure) and the air electrode 7 of the other unit cell C (left side of the figure) are connected by an interconnector 9. is doing.

The interconnector 9 can be formed of a chromium-based material such as Pt, Au, Ag, Ni, SUS, or La (Cr, Mg) O ₃ , (La, Ca) CrO ₃ , (La, Sr) CrO _3. One of these may be used alone, or a mixture of two or more may be used. Further, like the above electrolytes, etc., it is preferable that these materials are the main components, and an appropriate amount of varnish, photosensitive polymer, organic solvent, etc. is added to form a thickness after sintering of 1 μm to 500 μm. More preferably, the thickness is 10 μm to 100 μm.

  Thus, a high power generation output can be obtained by using a plurality of single battery cells C. In addition, the several single battery cell C may be connected in series or in parallel, and can also be connected in the state in which series and parallel were mixed. However, connecting in series has the following advantages. For example, in the conventional example, since a plurality of electrode bodies composed of the fuel electrode and the air electrode are arranged on one substrate, there is a possibility that the electromotive force is canceled by the electrolyte between these electrode bodies. . On the other hand, in the present invention, even if a plurality of single battery cells are connected in series as described above, the single battery cells C are arranged at a predetermined interval, and the electrolyte 3 is interposed between the adjacent single battery cells C. There is no cancellation of electromotive force. Therefore, a higher output can be obtained than in the conventional example.

  Moreover, in the said embodiment, although the single battery cell C is formed only in the one surface of the board | substrate 1, you may form these in the other surface of the board | substrate 1. FIG. As a manufacturing method at this time, for example, in each step of forming the electrolyte 3, the fuel electrode 5, and the air electrode 7 on one surface of the substrate 1, the electrolyte, the fuel electrode, and the air electrode are respectively disposed on the other surface of the substrate 1. A single battery cell having the same configuration is formed on both sides of the substrate 3 in the same manner. By doing so, a high power generation output can be obtained while keeping the fuel cell compact.

  Moreover, in the said embodiment, although the fuel electrode 5 was formed in the upper surface of the electrolyte 3, and the air electrode 7 was formed in the position adjacent to the electrolyte 3, the formation position of the electrodes 5 and 7 can also be made reverse. . However, if the fuel electrode 5 is arranged on the upper surface of the electrolyte 3, the interface between the fuel electrode 5 and the electrolyte 3, that is, the three-phase interface that affects the cell reaction can be easily increased, so that a stable cell reaction is obtained. Can be advantageous.

  In the above-described embodiment, the screen printing method is used for applying each paste. However, the present invention is not limited to this, and the lithography method, the roll coating method, the gravure roll coating method, the dispenser coating method, and others. A general printing method can be used. Moreover, as a post-process after printing, a hydrostatic press, a hydraulic press, and other general press processes can be used.

Hereinafter, the present invention will be described in more detail with reference to examples. As an example, a solid oxide fuel cell shown in FIG. 1 is prepared. Al ₂ O ₃ having a thickness of 1 mm is used as the substrate. SDC [(Ce, Sm) O ₃ ] powder (0.1 to 10 μm, average particle size 5 μm) was used as an electrolyte material, and a cellulosic varnish was mixed to prepare an electrolyte paste. The viscosity of the electrolyte paste was 5 × 10 ⁵ mPa · s suitable for the screen printing method. Further, as the material of the fuel electrode, nickel oxide (NiO) powder (particle size 0.01 to 1 μm, average particle size 0.1 μm) and SDC [(Ce, Sm) O ₃ ] powder (particle size 1 to 10 μm, And an average particle size of 5 μm) were mixed so that the weight ratio was 7: 3, and then a cellulosic varnish was mixed to prepare a fuel electrode paste. The viscosity of the fuel electrode paste was 5 × 10 ⁵ mPa · s suitable for screen printing. Moreover, SSC [(Sm, Sr) CoO ₃ ] powder (0.1 to 10 μm, average particle size 3 μm) was used as a material for the air electrode, and a cellulosic varnish was mixed to prepare an air electrode paste. Similarly, the viscosity of the air electrode paste was set to 5 × 10 ⁵ mPa · s suitable for the screen printing method.

  Next, the electrolyte paste was applied on the substrate by screen printing in a range of 520 × 7000 μm and a thickness of 200 μm, and dried at 130 ° C. for 15 minutes. Subsequently, a fuel electrode paste was applied on the electrolyte in a range of 500 × 7000 μm and a thickness of 50 μm by screen printing, dried at 130 ° C. for 5 minutes, and then sintered at 1450 ° C. for 1 hour. Subsequently, the air electrode paste was applied so as to contact the side surface of the electrolyte, dried at 130 ° C. for 5 minutes, and then sintered at 1200 ° C. for 1 hour. At this time, the air electrode paste was applied to a thickness of 180 μm within a range of 500 × 7000 μm. As a result, a fuel cell in which the distance between the fuel electrode and the air electrode was 20 μm was formed.

  Moreover, the comparative example was manufactured as follows. As shown in FIG. 5, this fuel cell has a fuel electrode 53 and an air electrode 55 arranged on one surface of an electrolyte 51 at a predetermined interval. The fuel electrode 53 and the air electrode 55 have a rectangular shape of 500 × 7000 μm and a thickness of 50 μm, and the distance between the electrodes 53 and 55 is 500 μm. In addition, the material which comprises the electrolyte 51, the fuel electrode 53, and the air electrode 55 is the same as an Example.

Thus, the following evaluation experiment was performed with respect to the formed Example and the comparative example. That is, by introducing a mixed gas of methane and air at 800 ° C. and causing a reaction of CH ₄ + 1 / 2O ₂ → 2H ₂ + CO, the nickel oxide as the fuel electrode 5 is reduced, and then the current-voltage The characteristics were evaluated. In order to perform the reduction process, hydrogen gas may be introduced instead of the mixed gas.

As a result, in the example, an electromotive force of 800 ± 10 mV was obtained at an operating temperature of 800 ° C., and an output of 250 ± 10 mA / cm ² could be obtained. On the other hand, in the comparative example, an electromotive force of 600 ± 10 mV was obtained at the same operating temperature, and an output of 150 ± 10 mA / cm ² was obtained. Therefore, in the example, even when an electrolyte having an area of about 2/3 as compared with the comparative example is used, the distance between both electrodes can be reduced, so that high electromotive force and output can be obtained at low cost. It was.

1 is a cross-sectional view of an embodiment of a solid oxide fuel cell according to the present invention. It is a figure which shows an example of the manufacturing method of the fuel cell shown in FIG. It is sectional drawing which shows the other example of the fuel cell which concerns on this invention. It is sectional drawing which shows the other example of the fuel cell which concerns on this invention. It is the top view (a) and front view (b) which show a comparative example.

Explanation of symbols

1 Substrate 3 Electrolyte 5 Fuel electrode 7 Air electrode 9 Interconnector

Claims (7)

A fuel cell comprising at least one unit cell having an electrolyte, a fuel electrode, and an air electrode,
A substrate for supporting the unit cell,
The electrolyte is disposed on one surface of the substrate, and one of the fuel electrode and the air electrode is disposed on the electrolyte,
The other electrode is in a non-contact state with the one electrode, and at least a part of the other electrode is disposed on one surface of the substrate and is in contact with the electrolyte. The other electrode is disposed adjacent to the electrolyte on one surface of the substrate,
The solid oxide fuel cell according to claim 1, wherein a thickness of the electrolyte is larger than a thickness of the other electrode.   The solid oxide fuel cell according to claim 1 or 2, wherein the one electrode is a fuel electrode, and the other electrode is an air electrode.   4. The solid oxide fuel cell according to claim 1, wherein a plurality of the single battery cells are arranged on the substrate, and the plurality of single battery cells are connected via an interconnector. 5.   The solid oxide fuel cell according to claim 1, wherein the electrolyte, the fuel electrode, and the air electrode are formed by printing. The battery further includes at least one unit cell that is disposed on the other surface of the substrate and includes an electrolyte, a fuel electrode, and an air electrode.
The electrolyte is disposed on the other surface of the substrate, and one of the fuel electrode and the air electrode is disposed on the electrolyte,
6. The solid oxide according to claim 1, wherein the other electrode is in a non-contact state with the one electrode, and at least a part thereof is disposed on the other surface of the substrate and is in contact with the electrolyte. Physical fuel cell.   The solid oxide fuel cell according to claim 1, wherein the substrate is made of an insulating ceramic material.

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