Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-05-21
2001-10-30
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S120000
Reexamination Certificate
active
06309774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a battery composed of at least two fuel cells that respectively comprise a negative pole plate, a membrane electrode unit and a positive pole plate that are connected to one another in a mechanically rigidly, gas-tight and electronically insulating manner by a frame element.
2. Description of the Related Art
Up to now, such batteries wherein every fuel cell of the battery respectively has a negative and a positive pole plate are disclosed, for example, by German Letters Patent 44 42 285; however, the problem of liquid cooling of such fuel batteries has not yet been solved. A liquid coolant is desirable for stationary applications wherein the waste heat is to be utilized in order to keep the required heat exchanger and the distribution of the heat compact.
Liquid-cooled fuel cell batteries are known that, however, respectively contain only individual contact or pole plates at the positive and at the negative end of the battery. Within the battery, these individual contact or pole plates are replaced by what are referred to as bipolar plates, which are often fashioned hollow. The liquid coolant of the known liquid-cooled batteries is located in the cavities of the bipolar plates. Previously known bipolar plates adjoin, on the one hand, the anode space and, on the other hand, the cathode space of the individual fuel cells to be connected to one another. When a traditional battery is assembled, the bipolar plates are stacked on top of one another with the membrane electrode units of the individual fuel cells and are mechanically joined to one another by screw bolts, tie rods or other clamp devices. A single pole or contact plate is then respectively located at the end. This system is also referred to as filter press technique (see, for example, W. Vielstich from “Brennstoffelemente”, Verlag Chemie GmbH, pages 171 and 201/202).
A significant disadvantage of filter press technique is that very high demands must be made of the edge seals of the fuel cell battery because the respective reaction agents, i.e. oxidant, fuel and coolant, must be reliably sealed from one another. Up to now, for example, an especially ticklish, direct sealing without buffer area that must assure that oxidant and fuel cannot overflow into one another is required at the edges of the bipolar plates. It is self-evident that such demands made of the edge seals are reflected in the manufacturing costs of the batteries. There is therefore a need to overcome the previously known filter press technique, not only given air-cooled fuel cells as in the above-cited German Letters Patent 44 42 285, but also given liquid-cooled fuel cell batteries.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to make a liquid-cooled battery of fuel cells available that is designed without direct edge sealing between cathode and anode space.
The general perception of the invention is that this is possible given employment of individual sealing of the fuel cell units of a battery disclosed by German Letters Patent 44 42 285 when a battery manufactured therefrom is immersed into a coolant bath.
The subject matter of the invention is a battery with liquid cooling composed of at least two fuel cells that respectively comprise a negative pole plate, a membrane electrode unit and a positive pole plate that are connected to one another mechanically rigidly, gas-tight and electronically insulating by a frame element, whereby the battery is immersed into a coolant bath.
A further subject matter of the present invention is a method for cooling a fuel cell battery, whereby the battery is cooled by immersion into a coolant bath.
In one embodiment of the invention and of the inventive method, the battery is completely immersed into a coolant bath.
In an advantageous development of the invention, the container for the coolant bath is integrated such in the battery housing that the battery housing itself is no longer surrounded by liquid coolant.
The electrolyte membrane, which is the heart of the membrane electrode unit of the fuel cell, extends up to the edge of the cell and could be washed out given employment of water as coolant. It is therefore provided in an advantageous development of the invention that it is not water but a hydrophobic, i.e. water-repellant coolant (for example, oil or transformer oil that does not wet the membrane that is employed. Alternatively to this advantageous embodiment, the electrolyte membrane can be prevented from being washed out by water as coolant in that a seal as offered, for example, by the Gore company in conjunction with the membrane electrolyte unit and that precludes this washing effect is employed in the individual sealing of the membrane electrode unit by the frame element. The costs of a battery constructed in this way nonetheless still lie below the costs for the seals of the known bipolar plates.
It is advantageous when the coolant flows through the coolant bath. The flow can thereby be effected solely by convection. As needed, the flow can also be generated by a pump or the convection can be intensified by a pump.
It is advantageous when the flow existing in the coolant bath is regulated such that it is uniformly distributed over the entire fuel cell battery. This can occur via a coolant distributor.
In an advantageous development of the method, the flow velocities and/or the flow distribution of the coolant in the coolant bath can be regulated. This is especially practical when the battery is intended to meet different power demands and has a differing cooling need over time as a result thereof.
What is referred to here as “battery” is an aggregate or stack of at least two senies-connected, individual fuel cells. One possible application of such a battery is, for example, decentralized power generating wherein aggregates having a far higher plurality of individual fuel cells are employed. For example, a battery must produce a power of approximately 10 kW for employment in a household energy supply system for a single-family house. Given an assumed cell area of approximately 300 cm
2
and a power of approximately 100 Watts per individual fuel cell, a battery employable therein comes out to about 100 individual cells.
The fuel cells that are disclosed in the above-cited German Letters Patent 44 42 285 are preferably referred to here as “individual fuel cell” or “fuel cell unit”. The full content of this Letters Patent is herewith referenced and the entire disclosure thereof is included in the subject matter of the present specification. Said fuel cells are units that can be individually handled and that respectively comprise a negative pole plate, a membrane electrode unit and a positive pole plate, whereby the aforementioned component parts are connected to one another mechanically fairly, gas-tight and electronically insulating by a respective frame element.
What is referred to here as “membrane electrode unit” is a membrane respectively having a negative and a positive electrode. All such units that are standard in this technology are included under the term “membrane electrode unit”. The electrodes preferably do not extend up to the edge of the membrane but leave an edge area of the membrane free, so that a frame element of the fuel cell embraces only the positive and negative pole plate of the fuel cell as well as the membrane itself.
What is fundamentally referred to as “frame element” is that part that is suitable for connecting at least negative pole plate, membrane and positive pole plate and, potentially, the electrodes or other component parts of the fuel cell as well to one another mechanically firmly, gas-tight and electronically insulating. The frame element can be composed of one piece; however, it can also be composed, for example, of a plurality of parts. The frame element preferably has a U-profile cross section, whereby the two U-legs press the two pole plates together with the membrane and thus close off the inside of this unit gas-tight from the penetration of gasses. Th
Buchner Peter
Helmolt Rittmar Von
Waidhas Manfred
Alejandro Raymond
Kalafut Stephen
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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