Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-07-26
2002-12-10
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06492055
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a stack for polymer electrolyte fuel cells that use, as an electrolyte, a solid polymer having ion conductivity, and more particularly to a polymer electrolyte fuel cell stack improved to have a large electrode area.
Attention is now being paid to fuel cells that serve as highly efficient energy converting devices. These fuel cells are roughly divided into a low-temperature operable fuel cell such as an alkali fuel cell, a polymer electrolyte fuel cell, a phosphoric acid fuel cell, etc., and a high-temperature operable fuel cell such as a molten carbonate fuel cell, a solid oxide fuel cell, etc.
Among the above-mentioned fuel cells, a polymer electrolyte fuel cell (hereinafter referred to as a “PEFC”), which uses a solid polymer electrolyte membrane having proton conductivity, is expected to be used as a power supply for space or vehicle equipment, since it has a compact structure, provides a high output density and is operable by a simple system.
As the polymer electrolyte membrane (hereinafter referred to as a “polymer membrane”), a perfluorocarbon sulfonic acid membrane (e.g. Nafion: name of commodity, produced by Dupont Company), for example, is used. This polymer membrane is held between a pair of porous electrodes (an anode and a cathode) having a catalyst such as platinum, thereby constituting a membrane/electrode assembly. The polymer membrane and the porous electrodes are in the shape of a sheet, and have a thickness of about 1 mm or less so as to reduce the internal resistance thereof.
Further, the polymer membrane and electrode sheets are usually rectangular. The area of each electrode is determined on the basis of a current required for power generation and a current value per unit area, i.e. the current density. Most of the electrodes are set to have an area of about 100 cm
2
or more, i.e. to have one side of 10 cm or more. The polymer membrane also has a function of preventing mixture of gasses supplied to the anode and the cathode, and hence is set to have a larger area than the electrodes.
To extract a current from the membrane/electrode assembly, current collectors are provided outside the anode and the cathode. The current collectors have a large number of grooves extending parallel to the surfaces of the anode and the cathode. These grooves serve as gas passages for supplying the anode and the cathode with a fuel gas and an oxidant gas required for reaction in the cell, respectively. Moreover, since voltage generated by a single membrane/electrode assembly is as small as 1V or less, a PEFC stack structure is formed by stacking a plurality of membrane/electrode assemblies and connecting them in series. This structure needs a cathode current collector and a cathode current collector, and therefore a separator is used, which includes collectors respectively provided at the anode side and the cathode side of the adjacent membrane/electrode assemblies, and formed integral as one body.
Each membrane/electrode assembly generates heat during reaction in the cell. It is a usually used cooling method to insert a cooling plate between a plurality of membrane/electrode assemblies and circulate cooling water in the cooling plate. This method, however, requires a separator for supplying the cooling water, in addition to a separator for supplying gases. This results in an increase in the thickness in the direction of stacking.
Japanese Patent Application KOKAI Publication No. 10-21949 discloses, as a method for solving the problem, a method for forming cooling water passages around the gas passages to dispense with the cooling plate inserted between the membrane/electrode assemblies. More specifically, in the technique disclosed in this publication, passages
202
for circulating cooling water are formed in upper, lower, left and right four portions of a separator
200
which has grooves
21
formed as gas passages at a central portion thereof, as is shown in
FIG. 1
, and cooling water is circulated in the passages
202
to eliminate reaction heat.
However, the above cooling method has the following problems:
A first problem is that the reaction area cannot be enlarged. In the above-mentioned cooling method, heat generated from the membrane/electrode assemblies that hold the separator
200
is transferred to the separator
200
conducted in a direction perpendicular to the thickness direction of the separator, and is removed by cooling water flowing through the passages
202
. In other words, the temperature of a central reaction portion of the separator becomes higher than its peripheral portion.
Accordingly, if the reaction area is increased, the distance between the center of the reaction portion and each cooling passage increases, and a temperature difference, as above, also increases. On the other hand, increasing the thickness of the separator to thereby increase the cross section, i.e. the heat transfer area, can be contrived in order to reduce the temperature difference. This method, however, inevitably increases the thickness of the cell and hence the entire cell size.
A second problem is that a three-dimensional temperature distribution occurs in the separator plane. Specifically, in the above-described cooling method, the temperature is so distributed in the separator plane that it is higher at a central portion than at peripheral four sides. Therefore, even if the gas passages are formed flat, moisture created as a result of reaction condenses at a peripheral portion of the separator, and hence cannot be efficiently collected.
A third problem is that supply manifold and exhaust manifold for the fuel gas and the oxidant gas cannot be enlarged. Where cooling water passages are arranged around gas passages as shown in
FIG. 21
, the supply manifold and the exhaust manifold for the fuel gas and the oxidant gas must be arranged at the four corners, thereby reducing the cross sections of the supply manifold and the exhaust manifold than those of the cooling water passages.
This means that when the reaction area is enlarged and a great amount of fuel gas or oxidant gas is required, the fuel gas or the oxidant gas cannot uniformly be distributed to each cell of a fuel cell stack, since the cross section of the supply port, i.e. the cross section of a gas distributing manifold, inevitably reduces.
BRIEF SUMMARY OF THE INVENTION
It is the object of the invention to provide a polymer electrolyte fuel cell stack, which is compact but has a large reaction area, and can smoothly supply gas.
To attain the object, there is provided a polymer electrolyte fuel cell stack including a plurality of cells stacked on each other, each cell having an anode, a cathode and a solid polymer electrolyte membrane held between the anode and the cathode, the cells being stacked on each other via separators that each have at least one of a fuel gas passage for supplying the anode with a fuel gas, and an oxidant gas passage for supplying the cathode with an oxidant gas, characterized in that: each of the separators has a rectangular outline; and a coolant passage is formed in a portion of each separator, which is located around the fuel gas passage and the oxidant gas passage and is substantially parallel to a long side of each separator, such that a coolant flows in a direction perpendicular to a surface of each separator.
Since in the invention constructed as above, each separator has a rectangular outline and has a coolant passage in a portion thereof substantially parallel to its long side, the distance between a central portion and the upper or the lower end of each electrode can be reduced. Accordingly, the temperature difference between the central portion and the upper or lower end of each electrode can be minimized. Further, heat generated during reaction is transferred vertically, and hence the temperature is almost constant horizontally. This means that even when the reaction area is enlarged, the temperature difference in each separator can be minimized. Furthermore, since it is not required to insert a cooling member in a dire
Hori Michio
Saito Kazuo
Shimotori Soichiro
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ryan Patrick
Wills M.
LandOfFree
Polymer electrolyte fuel stack does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer electrolyte fuel stack, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer electrolyte fuel stack will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2944737