Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-03-10
2002-09-10
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S010000, C429S120000
Reexamination Certificate
active
06447941
ABSTRACT:
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 10-278759, filed Sep. 30, 1998; and No. 11-162630, field Jun. 9, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, particularly, to a fuel cell readily available in a reduced size.
Fuel cells are nowadays attracting attentions because of their efficient energy conversion into electricity.
Fuel cells are classified according to the kind of electrolyte and fuel employed. Those which depend on a gaseous fuel are classified as phosphoric acid fuel cells, molten carbonate salt fuel cells, solid electrolyte fuel cells, and alkaline electrolyte fuel cells. Those which depend on liquid fuel are classified as methanol fuel cells and hydrazine fuel cells. These fuel cells are intended to supply electric power to large machines, and they need auxiliary equipment such as compressors and pumps to introduce a fuel gas or liquid and an oxidant gas into them. In addition to their complex structure, they consume electric power for the introduction of fuel and oxidant into them.
The current trend in the fields of office automation (OA) equipment, audio systems, and radio sets is toward miniaturization and portability resulting from the development of semiconductor technologies. This goal is achieved by using handy primary or secondary batteries as the power source. However, batteries are inherently limited in operating time and hence OA equipment depending on them for power supply is necessarily limited in operating time. Primary batteries are rather short in operating time for their weight and hence they do not suit portable equipment. On the other hand, secondary batteries need a power source for recharging which takes a long time. This limit the site where OA equipment can be used and also limits the length of service time. Thus, conventional primary and secondary batteries cannot run small machines for a long period of time, and there is an increasing demand for long-life batteries.
In order to meet this requirement, the present inventors propose that conventional primary and secondary batteries be replaced by fuel cells. Fuel cells offer the advantage of generating electricity continuously as long as they are supplied with fuel and oxidant. Therefore, they contribute to the size reduction and power saving of OA equipment.
Fuel cells employ air as the oxidant and hence they are not restricted in site and time for their use as far as the oxidant is concerned. However, they need a large volume of gaseous fuel with a low density even though the power consumption of OA equipment is small. This is unfavorable to the size reduction of power source. By contrast, liquid fuel has a higher density than gaseous fuel and hence extremely favorable to fuel cells for small-size machines. If fuel cells using liquid fuel are available in small size, they would be able to run small-sized machines for a long time. A hindrance to realization of such a small-sized power system is the necessity for pumps and blowers to feed liquid fuel to the fuel cell proper. The resulting power system is complex in structure and large in size.
Methanol fuel cells (which use methanol as liquid fuel) are explained below. They are broadly classified into liquid feed type and vapor feed type according to the type of fuel feeding. The former is so designed as to feed liquid fuel in the form of liquid, and the latter is so designed as to feed liquid fuel in the form of gas after evaporation. A fuel cell of liquid feed type is supplied with methanol which is circulated under pressure by a pump through the methanol tank and fuel cell proper. Therefore, it necessarily needs a pump for fuel supply. By contrast, in the case of a fuel cell of vapor feed type, methanol (as a liquid fuel) is introduced into a vaporizer by a pump and then methanol vapor is fed to the fuel cell proper by a blower. Unconsumed methanol vapor discharged from the outlet of the fuel electrode is recycled to the methanol tank through a condenser. This process needs a complex system which is not suitable for small-sized machines. By the way, a fuel cell for practical use is usually composed of stacked unit cells. The disadvantage of this construction is that the fuel being fed under pressure by a pump or blower fluctuates in flow through stacked unit cells, causing variation in performance from one cell to another.
One way to address this problem is to utilize capillary action to feed liquid fuel. In a fuel cell of this type, liquid fuel is fed to the fuel electrode from the fuel tank by capillary action. Therefore, it dispenses with a fuel pump, unlike fuel cells of liquid feed type, and hence is suitable for size reduction.
However, a fuel cell of this type still has the disadvantage of being poor in performance due to low electrode reactivity. In addition, it poses another problem of cross-over, which is a phenomenon that an organic liquid fuel (such as methanol) passes through the electrolyte membrane to reach the oxidant electrode, if a proton-conducting solid polymer such as perfluorosulfonic acid (available under a trade name of “Nafion” from Du Pont) is used as electrolyte.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a fuel cell fed with liquid fuel by capillary action, which is characterized by the increased fuel electrode reactivity and the reduced cross-over (a phenomenon that an organic liquid fuel passes through the electrolyte membrane to reach the oxidant electrode).
Another object is to provide a fuel cell that permits simplifying the liquid fuel supply system and also permits miniaturizing the cell size while maintaining a high performance.
According to a first aspect of the present invention, there is provided a fuel cell to produce an electromotive force through the reaction between a liquid fuel and an oxidant gas, the fuel cell comprising a fuel electrode, an electrolyte plate positioned adjacent to the fuel electrode, an oxidant electrode positioned adjacent to the electrolyte plate and opposite to the fuel electrode, and a fuel evaporating portion positioned adjacent to the surface opposite to that surface of the fuel electrode which is in contact with the electrolyte plate.
According to a second aspect of the present invention, there is provided a fuel cell to produce an electromotive force through the reaction between a liquid fuel and an oxidant gas, the fuel cell comprising a first power generating section and a second power generating section, which are placed on top of the other, with a separator interposed therebetween, the first power generating section being composed of a first fuel electrode, a first fuel evaporating layer, a first electrolyte plate, and a first oxidant electrode, which are placed sequentially one over another, the second power generating section being composed of a second fuel electrode, a second fuel evaporating layer, a second electrolyte plate, and a second oxidant electrode, which are placed sequentially one over another, the first and second fuel evaporating layers being fed with the liquid fuel through a liquid fuel passage which is formed adjacently to both of the first and second power generating sections.
According to a third aspect of the present invention, there is provided a fuel cell, comprising:
an oxidant electrode;
an electrolyte plate laminated on the oxidant electrode;
a fuel electrode laminated on the electrolyte plate;
a liquid fuel holding section laminated on the fuel electrode; and
a liquid fuel evaporating portion positioned to be in contact with both the fuel electrode and the liquid fuel holding portion.
According to a fourth aspect of the present invention, there is provided a fuel cell, comprising:
an oxidant electrode;
an electrolyte plate laminated on the oxidant electrode;
a fuel electrode laminated on the electrolyte plate;
a liquid fuel holding portion;
a plurality of unit cells each having a liquid fuel evaporating portion positioned in co
Akasaka Yoshihiro
Ohzu Hideyuki
Takashita Masahiro
Tomimatsu Norihiro
Yasuda Kazuhiro
Alejandro R.
Kabushiki Kaisha Toshiba
Kalafut Stephen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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