JP2002134137A - Cell of solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell of a solid electrolyte fuel cell, capable of generating electric power in a short time. SOLUTION: The cell 11 of the solid electrolyte fuel cell is formed, by stacking in order a solid electrolyte 2 and a fuel electrode 3 on an air electrode 1 comprising ceramics, and has an active part A contributing to power generation, where the air electrode 1, the solid electrolyte 2, and the fuel electrode 3 are piled up, and an inactive part B which does not contribute to power generation. A pair of terminal electrodes 5 are installed on the surface of the air electrode 1 in the inactive part B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell.

[0002]

2. Description of the Related Art In addition to being small in size, a solid oxide fuel cell has a high operating temperature of 1000 to 1050.degree. C. and can utilize heat, so that it has high energy efficiency and is greatly expected as a third generation power generation system. I have.

[0003] In general, solid oxide fuel cells include:
2 called a cylindrical fuel cell and a flat fuel cell
Different types of structures are known. Flat fuel cells have the feature that the power density per unit volume is high,
In practical use, there is a problem of thermal stress due to imperfect gas seal and non-uniform temperature distribution in the cell. On the other hand, the cylindrical fuel cell has the advantage of high mechanical strength due to its cylindrical shape, but generally has a problem of low power density. Hereinafter, a solid oxide fuel cell will be described using a cylindrical fuel cell as an example.

Conventionally, a cylindrical fuel cell has a support tube made of CaO-stabilized ZrO ₂ having an open porosity of about 30%, on which a porous air electrode made of a LaMnO ₃ material is formed. Is coated with a dense solid electrolyte made of ZrO ₂ stabilized with Y ₂ O ₃ , and a porous Ni /
A ZrO ₂ fuel electrode was provided.

In recent years, attempts have been made to use an air electrode directly as a support tube in order to simplify the manufacturing process of the cylindrical fuel cell. As a support tube having a function as an air electrode, a LaMnO ₃ material in which La and Ca are substituted by 10 to 20 atomic% is studied.

In a fuel cell module, a plurality of the cylindrical fuel cells are set in a cell storage container (power generation furnace), and the air electrode of one adjacent fuel cell and the fuel electrode of the other fuel cell are connected. The connection is made by forming a series circuit, or by connecting the fuel electrode of one fuel cell and the fuel electrode of the other fuel cell to form a parallel circuit.

The power generation of such a fuel cell uses an external heater provided so as to surround the power generating furnace, and is maintained at a temperature of about 1000 ° C. in order to electrochemically activate the fuel cell. This has been done by supplying air to the air electrode side and fuel gas such as hydrogen to the fuel electrode side.

[0008]

However, in the conventional solid oxide fuel cell, the starting of the power generation system, that is, the temperature rise to the operating temperature of 1000 ° C. is performed by the external heater surrounding the power generation furnace. The heating of the solid oxide fuel cell module by the external heater is performed by sandwiching a gas such as a fuel gas between the external heater, which is a heat source, and the fuel cell, and has a problem that the heating efficiency is extremely low.

That is, between the external heater and the fuel cell, in order to suppress reduction of the air electrode and oxidation of the fuel electrode,
An oxidizing gas such as air is interposed on the air electrode side, and a reducing gas such as hydrogen is interposed on the fuel electrode side. These gases have low thermal conductivity and are difficult to conduct heat. After that, since the gas is exhausted outside the furnace, there is a problem that the energy loss is large and the heating efficiency is very low.

For this reason, one solid oxide fuel cell is used.
There is a problem that it takes a very long time of several hours to heat up to 000 ° C., that is, several hours to start up the solid oxide fuel cell.

An object of the present invention is to provide a solid oxide fuel cell which can generate electric power in a short time.

[0012]

A solid oxide fuel cell according to the present invention comprises an air electrode made of ceramics, a solid electrolyte and a fuel electrode laminated in this order, and the air electrode, the solid electrolyte and the fuel In a solid oxide fuel cell having an active portion contributing to power generation with superposed poles and an inactive portion not contributing to power generation, a pair of terminal electrodes is provided on the surface of the air electrode in the non-active portion. is there.

According to the present invention, a terminal electrode is attached to the air electrode, which is a component part of the solid oxide fuel cell, and the air electrode can also be used as a heat source to cause the fuel cell to self-heat. Thermal energy can be directly supplied from the heat source to the fuel cell, the heating efficiency is dramatically improved, and the temperature rise time of the fuel cell to 1000 ° C., that is, the startup time of the fuel cell (the time until power generation) time)
Can be reduced from hours to minutes or seconds.

Further, the structure of the fuel cell is almost the same as that of the conventional fuel cell, and the heating can be performed only by providing a pair of terminal electrodes at the air electrode, so that the conventional cell structure can be used as it is.

In the solid oxide fuel cell according to the present invention, a pair of terminal electrodes is provided on the surface of the air electrode in the inactive portion that does not contribute to power generation, so that the air electrode, the solid electrolyte, and the fuel electrode overlap. Therefore, only the air electrode in the active portion contributing to power generation can be heated, and as a result, only the region related to the power generation reaction can be selectively heated, and the fuel cell is electrochemically activated. Can be greatly reduced, and the power consumption required for rapid startup of the power generation system can be reduced.

Further, since the heating area can be limited, the heat capacity of the cell can be reduced, and as a result, the time required for the cell to be heated up to 1000 ° C., that is, the startup time of the fuel cell can be further reduced.

Further, in the solid oxide fuel cell of the present invention, the terminal electrode is preferably formed on the entire surface of the air electrode in the inactive portion. As a result, only the air electrode in the active portion can generate heat, and the power consumption can be further reduced.

Further, according to the present invention, the air electrode has a cylindrical shape, and an end terminal electrode is provided on both end surfaces of the air electrode, and an inner terminal electrode is provided on the inner surfaces of both ends, so that the end terminal electrode and the inner terminal electrode are connected. It is desirable to have been.

In such a solid oxide fuel cell, a pair of terminal electrodes provided on the air electrode are first connected to a heater while supplying air to the air electrode side and fuel gas such as hydrogen to the fuel electrode side. Electrically connected to the power supply and apply voltage,
The air electrode is heated, the temperature is raised to about 1000 ° C. in order to electrochemically activate the solid oxide fuel cell, and then the terminal electrodes are electrically insulated. This is performed by connecting the fuel electrode to an external load to be supplied with electromotive force.

In the present invention, it is preferable that a resistor is provided on the surface of the air electrode in the active portion, and both ends of the resistor are connected to a pair of terminal electrodes, respectively.

This is because the resistance of the cathode material is high at low temperatures,
Due to the temperature dependence that decreases exponentially at high temperatures, the rate of temperature rise at startup is slow at low temperatures and fast at high temperatures. Therefore,
A resistor having a characteristic opposite to the temperature dependence of the air electrode material, that is, a resistance having a low resistance at a low temperature and a high resistance at a high temperature, forms a parallel circuit with an air electrode (can be regarded as a resistor) between terminal electrodes. In addition, by providing the surface of the air electrode in the active part and adjusting the resistance between the terminal electrodes to be low and constant from low to high temperatures, it is possible to achieve a reasonable and stable temperature increase from low to high temperatures. The rate of temperature rise at low temperatures can be dramatically increased.

That is, the resistor mainly generates heat in the low temperature region, and the air electrode in the active portion mainly generates heat in the high temperature region.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid oxide fuel cell according to the present invention has a cylindrical air electrode 1 as shown in FIGS.
The solid electrolyte 2 is formed on the outer surface of the solid electrolyte 2, and the fuel electrode 3 is formed on the outer surface of the solid electrolyte 2. As shown in FIG. 2, the solid electrolyte 2 is formed on almost the entire outer surface of the air electrode 1, and the fuel electrode 3 is formed at the center of the outer surface of the solid electrolyte 2 in the longitudinal direction. Is the air electrode 1,
The active portion A is composed of the solid electrolyte 2 and the active portion A which contributes to the power generation with the fuel electrode 3 superposed thereon, and the non-active portions B which are formed on both sides of the active portion A and do not contribute to the power generation.

End terminal electrodes 5 are provided on both end surfaces of the cell, that is, on both end surfaces of the cylindrical air electrode 1. Not paired with fuel electrode 3 (active part)
Inner terminal electrodes 6 are formed on inner surfaces of both ends of the air electrode 1, and the end terminal electrodes 5 and the inner terminal electrodes 6 are connected. still,
In FIG. 1, for easy understanding, the solid electrolyte 2 and the inner terminal electrode 6 are shown with diagonal lines, and in FIG. 2, the inner terminal electrode 6 is drawn with diagonal lines.

In the present invention, as shown in FIG. 3A, a resistor 7 is provided on the surface of the air electrode 1 in the active portion A, and both ends of the resistor 7 are connected to a pair of inner terminal electrodes 6, respectively. Is desirable. In order to facilitate understanding, FIG.
Only the end face terminal electrode 5, the inner face terminal electrode 6, and the resistor 7 are described. The resistor 7 is desirably a metal resistor, for example, having a characteristic opposite to the temperature dependence of the cathode material, that is, a temperature dependence in which the resistance is low at low temperatures and high at high temperatures. By connecting the resistor 7 and the air electrode 1 in the active portion A in parallel, the resistance can be adjusted so as to be low and constant from low to high temperatures.

The resistance of the resistor 7 may be adjusted by forming an electrode pattern of a meandering resistor 7a on the inner surface of the air electrode 1 in the active portion A, as shown in FIG. As shown in FIG. 3C, a uniform resistor 7b may be formed on the entire inner surface of the air electrode 1 in the active portion A, and the resistance may be adjusted by the electrode thickness. By using such a resistor, the resistance of the resistor can be adjusted.

The air electrode 1 can be made of a known shape and material. For example, first, a LaMnO ₃ -based or LaCoO ₃ -based air electrode material is formed into a cylindrical shape by extrusion molding or the like, and a predetermined temperature is obtained. And formed by firing. The air electrode 1 also serves as a support, and is in contact not only with air but also with oxygen or the like.

The solid electrolyte 2 is, for example, Y ₂ O ₃ , Yb ₂
ZrO ₂ containing O ₃ or the like, Y ₂ O ₃ , Yb ₂ O ₃ , S
Ce containing c ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , CaO, etc.
The outer surface of the air electrode 1 is coated with a solid electrolyte material of O ₂ by thermal spraying or EVD so as to have a thickness of 50 to 200 μm.

The fuel electrode 3 is formed, for example, by coating the outer surface of the solid electrolyte _{2 with} a fuel electrode material of ZrO ₂ containing NiO or Ru and firing it at a predetermined temperature.

The solid oxide fuel cell is not limited to the above example. For example, first, a cylindrical air electrode molded body is prepared, and then Y ₂ O ₃ , Yb ₂ O _{3 and the} like are formed. ZrO ₂ , Y ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O ₃ , Nd ₂
A solid electrolyte material of CeO ₂ containing O ₃ , Sm ₂ O ₃ , CaO and the like and a fuel electrode material of ZrO ₂ containing NiO or Ru are formed into green sheets by a doctor blade method or the like, and this is formed into a green sheet. It can also be formed by winding around an air electrode molded body and co-firing at a predetermined temperature. In the above example, the cylindrical fuel cell has been described, but the present invention can also be applied to a flat fuel cell.

The end face terminal electrodes 5 are formed on both end faces of the cylindrical air electrode 1, and the inner face terminal electrodes 6 are formed by applying a conductive paste on the inner surface of the air electrode 1 in the inactive portion B. The end face terminal electrode 5 and the inner face terminal electrode 6 are connected. In these conductive pastes, a non-oxidized electrode material such as Pt which is hardly oxidized is desirable as a metal material. Also,
Since the resistor 7 is formed on the inner surface of the air electrode in the active portion A, it is formed of a non-oxidized electrode material such as Pt which is not easily oxidized by oxygen such as air.

Such a solid oxide fuel cell has the following features:
As shown in FIG. 4, a circuit for connecting the end face terminal electrodes 5 and a circuit for power generation are formed. First, the end face terminal electrodes 5 are connected to each other to heat the solid oxide fuel cell, One of the end face terminal electrodes 5 is connected to the fuel electrode 3 to generate power.

Since the air electrode 1 and the resistor 7 between the end face terminal electrodes 5 in the active portion A are connected in parallel to the end face terminal electrode 5, the resistor 7 generates heat at a low temperature and becomes active at a high temperature. In the high temperature range, the air electrode 1 mainly generates heat in the active portion A, and the resistance between the end face terminal electrodes 5 is low and constant as a whole from low temperature to high temperature. The amount will be constant.

FIG. 5 shows a fuel cell module, in which a plurality of solid oxide fuel cells 11
, And these solid oxide fuel cells 11 are connected in series.

In the solid oxide fuel cell unit constructed as described above, in order to reduce the cathode 1 at high temperature and to suppress the oxidation of the anode 3, oxidizing gas and fuel
This is performed while flowing a reducing gas to the side. First, a heater power supply 13 is electrically connected between the pair of end face terminal electrodes 5 to apply a voltage, and only the air electrode 1 in the active part A, that is, only the power generation area of the fuel cell 11 is selectively electrochemically applied. The temperature is raised to about 1000 ° C., which is a temperature at which it becomes active.

Next, after electrically insulating the end face terminal electrodes 5 of the air electrode 1, the air electrode 1 and the fuel electrode 3 are connected to the external load 15 to which the electromotive force is supplied, and power generation is started. . After the start of power generation, 1000 ° C. at which the solid electrolyte 2 becomes electrochemically active is maintained by utilizing the reaction heat generated by the electrochemical reaction due to the power generation and the waste heat of the fuel gas.

Therefore, in the solid oxide fuel cell of the present invention, the end electrode 5 is electrically connected to the power source 13 for the heater, so that the air electrode 1 is also used as a heat source and the fuel cell 11 is self-contained. Heat can be generated, and as a result, the entire cell can be self-generated almost uniformly, and the temperature distribution in the fuel cell 11 at the time of temperature rise can be made substantially uniform. Heat energy can be supplied, the heating efficiency is dramatically improved, and the time for raising the temperature of the fuel cell 11 to 1000 ° C. can be greatly reduced.

The end terminal electrode 5 is connected to the heater power source 1.
3 and electrically connected to the air electrode 1 as a heat source,
When the fuel cell 11 self-generates heat, the air electrode 1 in the active part A can be selectively heated, and as a result, only the area related to the power generation reaction can be selectively heated, and the fuel cell 11 can be selectively heated. Power consumption required for electrochemically activating the compound can be greatly reduced.

In addition, since the heating region can be limited, the heat capacity of the cell can be reduced, and as a result, the time required to raise the temperature of the cell up to 1000 ° C., that is, the startup time of the fuel cell can be reduced.

Further, a resistor 7 having a characteristic opposite to the temperature dependence of the air electrode material, that is, a temperature dependence whose resistance is low at a low temperature and high at a high temperature, is connected to a parallel circuit with the air electrode 1 in the active part A. By providing the air electrode 1 such that the resistance is low and constant from low to high temperatures, the rate of temperature rise at low temperatures can be drastically increased.

In the above example, as shown in FIGS. 1 and 2, even if the resistor is not formed, the fuel cell 100
The time for raising the temperature to 0 ° C. can be shortened.

[0042]

According to the solid oxide fuel cell of the present invention, a terminal electrode is attached to the air electrode which is a constituent part of the fuel cell, and the terminal electrode is also used as a heat source, so that the air electrode can generate heat by itself. Therefore, heat energy can be directly supplied from the heat source to the fuel cell, the heating efficiency can be improved, and the time required to raise the temperature of the fuel cell up to 1000 ° C., that is, the startup time of the fuel cell, can be drastically reduced.

Further, since a pair of terminal electrodes is provided on the surface of the air electrode in the non-active portion which does not contribute to power generation, the air electrode, the solid electrolyte, and the fuel electrode are superposed, and only the air electrode in the active portion which contributes to power generation is provided. Can generate heat,
As a result, only the region related to the power generation reaction can be selectively heated, the power consumption required to activate the fuel cell electrochemically can be significantly reduced, and the power generation system can be quickly started. Required power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a solid oxide fuel cell unit of the present invention.

FIGS. 2A and 2B show the solid oxide fuel cell unit of FIG. 1, wherein FIG. 2A is a perspective view and FIG. 2B is a side view.

3A is a perspective view illustrating only an inner terminal electrode, an end terminal electrode, and a resistor, FIG. 3B is a cross-sectional view illustrating a meandering resistor, and FIG. 3C is uniform over the entire inner surface. It is sectional drawing in which the resistor was formed.

FIG. 4 is a diagram showing a heater circuit for starting a solid oxide fuel cell and a circuit for power generation.

FIG. 5 is an explanatory diagram of a solid oxide fuel cell module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Air electrode 2 ... Solid electrolyte 3 ... Fuel electrode 5 ... End terminal electrode 6 ... Inner terminal electrode 7, 7a, 7b ... Resistor 11 ... Solid electrolyte type fuel Battery cell A: Active part B: Inactive part

Claims (4)

[Claims] 1. An active part which is formed by sequentially laminating a solid electrolyte and a fuel electrode on an air electrode made of ceramics and which contributes to power generation in which the air electrode, the solid electrolyte and the fuel electrode are superimposed, and which contributes to power generation. A solid oxide fuel cell having a non-active portion, wherein a pair of terminal electrodes are provided on a surface of an air electrode in the non-active portion. 2. The solid oxide fuel cell according to claim 1, wherein the terminal electrode is formed on the entire surface of the air electrode in the inactive portion. 3. An air electrode having a cylindrical shape, an end surface terminal electrode provided on both end surfaces of the air electrode, and an inner surface terminal electrode provided on inner surfaces of both end portions, wherein the end surface terminal electrode and the inner surface terminal electrode are connected. The solid oxide fuel cell according to claim 1, wherein: 4. The device according to claim 1, wherein a resistor is provided on the surface of the air electrode in the active portion, and both ends of the resistor are connected to a pair of terminal electrodes, respectively. Solid electrolyte fuel cell.