JP2008071594A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell capable of improving output power while improving gas permeability. <P>SOLUTION: This solid oxide fuel cell is provided with a porous substrate 2, a fuel electrode 4 formed on the upper surface 23 of the porous substrate 2, an electrolyte 5 formed on the fuel electrode 4, and an air electrode 6 formed on the electrolyte 5. The porous substrate 2 is structured such that porosity is reduced toward the upper surface 23 side from its undersurface 24 side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell.

A fuel cell is a cell that can directly convert chemical energy generated when fuel is oxidized into electric energy while continuously supplying fuel from the outside and exhausting combustion products. The types of fuel cells are classified according to the electrolyte, and those using a solid oxide having ionic conductivity for the electrolyte are called solid oxide fuel cells. Various types of solid oxide fuel cells have been proposed. For example, in Patent Document 1, in order to improve the strength and thermal shock resistance, a fuel electrode (anode), electrolyte, air, and the like are supported by a support. A single-chamber fuel cell that supports a single cell composed of an electrode (cathode) is disclosed.
JP 2005-174661 A

  In the fuel cell, the support is made porous, and the mixed gas is supplied to the fuel electrode formed on the support through the pores of the support. Such a porous support has a problem of how much the porosity should be. That is, if the porosity of the support is lowered, the gas permeability is deteriorated. On the other hand, if the porosity is increased, the gas permeability is improved, but the support and the fuel electrode formed on the support are formed. The contact area becomes smaller. As a result, there arises a problem that the resistance between the support and the fuel electrode is increased, and as a result, the output of the fuel cell is lowered. Further, when the porosity of the support is increased, the penetration of the electrode paste when printing the electrode paste on the support becomes severe, and it becomes difficult to form the fuel electrode paste with a uniform film thickness. For this reason, irregularities occur on the upper surface of the fuel electrode, and it becomes difficult to form an electrolyte formed on the upper surface. As a result, the stability and reproducibility of the battery performance during mass production becomes poor, and as a result, the yield decreases.

  Therefore, an object of the present invention is to provide a solid oxide fuel cell capable of improving gas permeability and improving power generation efficiency.

  A solid oxide fuel cell according to the present invention has been made to solve the above-described problems, and includes any one of a porous substrate and a fuel electrode and an air electrode formed on one surface of the porous substrate. One electrode, an electrolyte formed on the one electrode, and the other electrode formed on the electrolyte, and the porous substrate has pores from the other side toward the one side. It is comprised so that a rate may become low.

  In this way, the porous substrate is not configured with a uniform porosity, but is configured so that the porosity decreases from the other surface side toward the one surface side. While increasing the porosity on the direction side, the porosity on one side of the porous substrate can be decreased. Thus, since the porosity of the other surface side of the porous substrate is high, the gas permeability can be improved. And even if the porosity of the other surface side of the porous substrate is high, the porosity of the one surface side of the porous substrate is low, so one electrode formed on one surface of the porous substrate and the porous substrate The contact area can be increased, and the resistance between one electrode and the porous substrate can be reduced. Therefore, the output of the solid oxide fuel cell can be improved. Further, by reducing the porosity, it is possible to reduce the penetration of the electrode paste. As a result, the battery performance can be stabilized and the yield can be improved. As described above, in the solid oxide fuel cell according to the present invention, it is possible to obtain both conflicting effects of improving gas permeability and improving power generation efficiency.

  There are various methods for changing the porosity of the porous substrate as described above. For example, the first plate member disposed on one side of the porous substrate and the first plate disposed on the other surface side thereof are available. The porosity of the porous substrate can be changed by laminating the second plate-like member having a higher porosity than the shaped member to constitute the porous substrate.

  In order to improve the conductivity between the one electrode and the porous substrate, the porosity of the first plate member is set to 10 to 30%, and in order to improve the gas permeability, a second value is used. The porosity of the plate member is preferably 50 to 70%.

  According to the present invention, it is possible to provide a solid oxide fuel cell capable of improving gas permeability and improving power generation efficiency.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a front sectional view of a solid oxide fuel cell according to this embodiment, and FIG. 2 is a plan view of the solid oxide fuel cell according to this embodiment.

  As shown in FIGS. 1 and 2, the solid oxide fuel cell 1 includes a porous substrate 2 having a rectangular shape in plan view, and a single cell C having a rectangular shape in plan view formed slightly smaller on the porous substrate 2. Yes. The porous substrate 2 is configured by laminating a first plate-like member 21 and a second plate-like member 22, and the porosity of the first plate-like member 21 is 10 to 30%, The porosity of the plate-like member 22 is 50 to 70%. Thereby, the porous substrate 2 is configured such that the porosity on the upper surface 23 side is lower than the porosity on the lower surface (other surface) 24 side. On the other hand, in the single cell C, the fuel electrode 4, the electrolyte 5, and the air electrode 6 are formed in this order on the upper surface (one surface) 23 of the porous substrate 2, that is, on the first plate member 21.

  Next, materials constituting the fuel cell 1 will be described. The first and second plate-like members 21 and 22 constituting the porous substrate 2 are, for example, Pt, Au, Ag, Cu, Pd, Al, Ni, Ti, Cu, Fe, and Cr from the viewpoint of heat resistance. It may be made of at least one metal selected from conductive metal materials such as, and may be alloyed with other metal types. The thickness of the first plate-like member 21 is preferably 10 to 1000 μm, and more preferably 100 to 500 μm. The thickness of the second plate-like member 22 is preferably 100 to 5000 μm, and more preferably 500 to 3000 μm.

  The fuel electrode 4 can use, for example, a mixture of a metal catalyst and a ceramic powder material made of an oxide ion conductor. As the metal catalyst used at this time, a material that is stable in a reducing atmosphere, such as nickel, iron, cobalt, or a noble metal (platinum, ruthenium, palladium, etc.) and has hydrogen oxidation activity can be used. In addition, as the oxide ion conductor, one having a fluorite structure or a perovskite structure can be preferably used. Examples of those having a fluorite structure include ceria-based oxides doped with samarium, gadolinium, and the like, and zirconia-based oxides containing scandium and yttrium. In addition, examples of those having a perovskite structure include lanthanum galide oxides doped with strontium and magnesium. Among the above materials, the fuel electrode 4 is preferably formed of a mixture of an oxide ion conductor and nickel. The mixed form of the ceramic material made of the oxide ion conductor 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. The fuel electrode 4 can also be configured using a metal catalyst alone.

  As the material of the electrolyte 5, those known as electrolytes for solid oxide fuel cells can be used. For example, ceria-based oxides doped with samarium or gadolinium, lanthanum galade doped with strontium or magnesium Oxygen ion conductive ceramic materials such as oxides, zirconia-based oxides containing scandium and yttrium can be used.

As the ceramic powder material forming the air electrode 6, for example, a metal oxide made of Co, Fe, Ni, Cr, Mn, or the like having a perovskite structure or the like 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, and (La, Sr) MnO ₃ is preferable. The ceramic material mentioned above can be used individually by 1 type or in mixture of 2 or more types.

  When the fuel electrode 4, the electrolyte 5 and the air electrode 6 are formed from a ceramic powder material, the average particle size of the powder used is preferably 10 nm to 100 μm, more preferably 50 nm to 50 μm, and particularly preferably 100 nm. 10 μm. In addition, an average particle diameter can be measured according to JISZ8901, for example.

  The fuel electrode 4 and the air electrode 6 are formed by adding appropriate amounts of a binder resin, an organic solvent, and the like with the above-described material as a main component. More specifically, it is preferable to add a binder resin or the like so that the main component is 50 to 95% by weight in the mixing of the main component and the binder resin. Similarly to the fuel electrode 4 and the air electrode 6, the electrolyte 5 is molded by adding an appropriate amount of a binder resin, an organic solvent, or the like with the above-described material as a main component. In the mixing, it is preferable to mix so that the ratio of the main component is 80% by weight or more. The film thickness of the fuel electrode 4 and the air electrode 6 is preferably formed to be 5 μm to 100 μm after sintering, and more preferably 10 μm to 30 μm. The thickness of the electrolyte 5 is preferably 1 to 100 μm, and more preferably 10 to 50 μm.

  Next, a method for manufacturing the above-described fuel cell 1 will be described with reference to FIG. FIG. 3 is an explanatory view showing a method for manufacturing the fuel cell 1.

  First, the 2nd plate-shaped member 22 which consists of the material mentioned above is prepared (FIG. 3 (a)). And the 1st plate-shaped member 21 is laminated | stacked on this 2nd plate-shaped member 22, and these 1st and 2nd plate-shaped members 21 and 22 are carried out by diffusion bonding, and a porous board | substrate is carried out. 2 is formed (FIG. 3B).

Subsequently, the above-described powder materials for the electrolyte 5, the fuel electrode 4, and the air electrode 6 are used as main components, and an appropriate amount of a binder resin, an organic solvent, and the like are added and kneaded to each of them, and the electrolyte paste, fuel electrode paste, air electrode Each paste is prepared. The viscosity of each paste is preferably about 10 ³ to 10 ⁶ mPa · s so as to be compatible with the screen printing method described below.

  Next, the fuel electrode paste is applied on the upper surface 23 of the porous substrate 2 by screen printing, and then dried and sintered at a predetermined time and temperature to form the fuel electrode 4 (FIG. 3C).

  Subsequently, after applying an electrolyte paste onto the fuel electrode 4 by screen printing, the electrolyte 5 is formed by drying and sintering at a predetermined time and temperature (FIG. 3D). The electrolyte 5 can be formed by various methods. In order to form the fuel electrode 4 and the air electrode 6 as a porous body using the metal porous substrate 2, the temperature is lower than these, that is, about 1200 ° C. It is preferable to sinter at the following temperatures, and for example, it can be formed by a low-temperature firing method such as a vacuum method or a thermal spray method.

  Subsequently, an air electrode paste is applied on the electrolyte 5 by a screen printing method, and dried and sintered at a predetermined time and temperature to form the air electrode 6 (FIG. 3E). Through the above steps, the fuel cell 1 as shown in FIGS. 1 and 2 is completed.

  Next, the power generation operation of the fuel cell 1 configured as described above will be described with reference to FIGS. 1 and 2. First, a mixed gas of a fuel gas composed of hydrogen or a hydrocarbon such as methane or ethane and an oxidant gas such as air is supplied to the battery at a high temperature (for example, 400 to 1000 ° C.). At this time, the mixed gas is supplied to both sides of the upper surface 23 and the lower surface 24 of the substrate 2. The mixed gas on the upper surface 23 side is supplied to the air electrode 6 formed on the electrolyte 5 and is also supplied to the fuel electrode 4 exposed from the side surface. The mixed gas on the lower surface 24 side enters from the second plate member 22 having a high porosity, passes through the first plate member 21, and is supplied to the fuel electrode 4. Thus, since the fuel electrode 4 and the air electrode 6 of the single cell 3 are in contact with the mixed gas, oxygen ion conduction through the electrolyte 5 occurs between the fuel electrode 4 and the air electrode 6 in the single cell 3 to generate power. Is done.

  As described above, according to the present embodiment, the upper surface 23 side of the porous substrate 2 is constituted by the first plate-like member 21 having a low porosity, so that the contact between the porous substrate 2 and the fuel electrode 4 is achieved. The area can be increased, the resistance between the porous substrate 2 and the fuel electrode 4 can be reduced, and as a result, the output of the solid oxide fuel cell 1 can be improved. Moreover, since the lower surface 24 side of the porous substrate 2 is composed of the second plate-like member 22 having a high porosity, the permeability of the mixed gas supplied from the lower surface 24 side of the porous substrate 2 is improved. Can be planned. Accordingly, it is possible to obtain both conflicting effects of improving gas permeability and improving power generation efficiency.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to these, A various change is possible unless it deviates from the meaning of this invention.

  For example, in the said embodiment, although the porous board | substrate 2 is comprised with two members, the 1st plate-shaped member 21 and the 2nd plate-shaped member 22, it can also comprise with three or more members. . In this case, the members are arranged in descending order of porosity from the lower surface 24 side of the porous substrate 2. In addition, the porous substrate 2 can also be configured by a single member formed such that the porosity decreases from the lower surface 24 side toward the upper surface 23 side. In addition, the porosity of the porous substrate 2 after baking can be changed by changing the addition amount of the foaming agent contained in the powder when the porous substrate 2 is molded. It is possible to configure so that the porosity decreases from the 24 side toward the upper surface 23 side.

  Moreover, in the said embodiment, although it is set as the single chamber type solid oxide fuel cell 1, it can also be used as a two-chamber type solid oxide fuel cell. In this case, as shown in FIG. 4, the periphery of the electrolyte 5 formed on the fuel electrode 4 extends downward so as to cover the periphery of the fuel electrode 4 and is connected to the upper surface 23 of the porous substrate 2. Then, the fuel electrode 4 and the air electrode 6 are separated vertically by the partition wall 25 and the electrolyte 5 by a known method such as providing the partition wall 25. If the solid oxide fuel cell 1 is configured in this way and the fuel gas is supplied to the lower surface 24 side of the porous substrate 2 and the oxidant gas is supplied to the upper surface 23 side, the two-chamber solid oxide fuel cell 1 is provided. Can be used as Further, by forming the electrolyte 5 so as to cover the entire fuel electrode 4 as described above, the fuel electrode 4 and the air electrode 6 can be connected to each other even if the positional accuracy when the air electrode 6 is formed on the electrolyte 5 is low. Contact can be prevented, and it is possible to reliably prevent a short circuit from occurring.

  Moreover, in the said embodiment, although the screen printing method is used for application | coating of each paste, it is not limited to this, A doctor blade method, a spray coat method, a spin coat method, an electrophoresis method, CVD, EVD, Other general printing methods such as a sputtering method and a printing method such as a transfer method can be used. Moreover, as a post-process after printing, CIP (hydrostatic pressure press), HIP (hot isostatic press), hot press, and other general press processes can be used. In addition to etching, various methods such as photolithography and cutting can be used as a method for forming the gas flow path.

  In the above embodiment, only one single cell is formed on the porous substrate 2, but a plurality of single cells can also be formed.

1 is a front sectional view showing an embodiment of a solid oxide fuel cell according to the present invention. 1 is a plan view showing an embodiment of a solid oxide fuel cell according to the present invention. It is explanatory drawing which shows the manufacturing method of the solid oxide fuel cell which concerns on this embodiment. It is front sectional drawing which shows other embodiment of the solid oxide fuel cell which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid oxide fuel cell 2 Porous substrate 21 1st plate-shaped member 22 2nd plate-shaped member 23 Upper surface (one side)
24 Lower surface (the other surface)
4 Fuel electrode 5 Electrolyte 6 Air electrode

Claims (3)

A conductive porous substrate;
Formed on one surface of the porous substrate, either one of a fuel electrode and an air electrode;
An electrolyte formed on the one electrode;
The other electrode formed on the electrolyte,
The said porous substrate is a solid oxide fuel cell comprised so that a porosity may become low toward the one surface side from the other surface side.   The porous substrate includes a first plate member disposed on the one surface side, a second plate member disposed on the other surface side and having a higher porosity than the first plate member, The solid oxide fuel cell according to claim 1, comprising: The first plate-like member has a porosity of 10 to 30%,
The solid oxide fuel cell according to claim 2, wherein the second plate-shaped member has a porosity of 50 to 70%.

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