Note: Descriptions are shown in the official language in which they were submitted.
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GR 95 P 3655
FUEL CELL SYSTEM
Backqround of the Invention:
Field of the Invention:
The invention relates to a fuel cell system having an
electrolyzer with a hydrogen-yielding side being connected to
a fuel cell.
Such a system is known from German Published, Non-Prosecuted
Patent Application DE 38 40 517 Al. In that system, oxygen
lo and hydrogen are generated from water, using a conventional
electrolysis cell. The energy required therefor is furnished
by a power plant. The oxygen and the hydrogen are stored in
collecting devices and can be supplied as needed to a fuel
cell that furnishes electrical energy. The fuel cell can be
operated only at a temperature that is markedly higher than
100C. It is accordingly quite clear that its thermal energy
must be supplied both from a unit-type power station and from
a hydrogen burner.
The commercially available electrolysis cell being used
contains a liquid electrolyte. As a result, it can be
operated only in a particular position in three-dimensional
terms.
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The reservoirs for oxygen and hydrogen disposed between the
electrolysis cell and the fuel cell store the gases at a high
pressure, which by way of example is a multiple of the
ambient atmospheric pressure. Such reservoirs are expensive
because they have to withstand the high pressure. They are
always very heavy in weight and must meet special safety
regulations.
Summary of the Invention:
It is accordingly an object of the invention to provide a
fuel cell system, which overcomes the hereinafore-mentioned
disadvantages of the heretofore-known devices of this general
type and which can be operated at relatively low temperature,
that by way of example is markedly lower than 100C. More-
over, the fuel cell should be supplied continuously with
oxygen and hydrogen, without having to hold gases at high
pressure, which would require expensive and heavy gas reser-
voirs. In particular, a replenishable source for electrical
energy is to be furnished, which only occupies little space
and can be used instead of a battery for grid-independent
supply to a consumer.
With the foregoing and other objects in view there is provid-
ed, in accordance with the invention, a fuel cell system,
comprising a fuel cell being a low-temperature polymer
electrolyte membrane fuel cell; and an electrolyzer being an
inversely operated low-temperature polymer electrolyte
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membrane fuel cell having a hydrogen-yielding side being
connected to the fuel cell.
This has the advantage that the fuel cell requires no supply
lines for thermal energy. Moreover, the fuel cell can be
supplied continuously with oxygen and hydrogen without gases
having to be held at high pressure. By way of example, the
ambient pressure need not be exceeded. Finally, the
electrolyzer, as well as the fuel cell, are distinguished in
that they contain solid electrolytes, which assure operation
in a way that is largely independent of position.
In accordance with another feature of the invention, the
operating temperature of the PEM is lower than 100C. The
fuel cell system can accordingly be used in a simple way. At
an operating temperature that is in the vicinity of the
ambient temperature, the system requires no insulators and
can nevertheless be transported at any time without danger.
In accordance with a further feature of the invention, water
and/or water vapor (moisture in air) is present or stored in
the electrolyzer. No permanent water supply line is then
necessary. The stored water supply is adequate for furnish-
ing hydrogen and oxygen, which are then available to the fuel
cell, for a first operating phase. Subsequently, the water
supply can be supplemented with water that is formed in the
fuel cell.
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.
In accordance with an added feature of the invention, a
water-storing medium is disposed in the electrolyzer. Thus a
particular advantage is attained which is that the entire
fuel cell system can be operated regardless of position,
without water being able to run out of the electrolyzer.
This kind of water-storing medium may be a sponge or a
sponge-like body.
In accordance with an additional feature of the invention,
the water-storing medium for introducing the water into the
electrolyzer has wicks of absorbent material. These wicks
can absorb water that is given off by the fuel cell and carry
it into the electrolyzer regardless of the position of the
fuel cell system. The outflow of the oxygen generated in the
electrolyzer is not hindered thereby, because the wicks and
the outlets for gases in the electrolyzer are located at
different positions.
In accordance with yet another feature of the invention, the
electrolyzer is connected to a solar cell array, so as to be
supplied with electrical energy. For generating hydrogen and
oxygen, this has the advantage of permitting recourse to
photovoltaically generated electrical energy, so that the
system can then be used as a voltage source during periods of
darkness, for example.
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However, the electrolyzer can also be connected to the public
power-supply grid (grid adaptor).
In accordance with yet a further feature of the invention,
the hydrogen-yielding side of the electrolyzer borders the
side of the fuel cell that receives hydrogen. As a result,
the hydrogen generated in the electrolyzer can reach the
hydrogen-consuming fuel cell directly. The transport of
oxygen from the electrolyzer to the fuel cell must then be
carried out through a line. In particular, the fuel cell is
disposed above the electrolyzer.
In accordance with yet an added feature of the invention, the
hydrogen-yielding side of the electrolyzer is connected to
the fuel cell through a hydrogen reservoir that serves to
store hydrogen temporarily. In the hydrogen reservoir, the
hydrogen generated in the electrolyzer can be stored tempo-
rarily until it is needed in the fuel cell. It is also
possible, however, for the hydrogen-yielding side of the
electrolyzer to communicate directly through a line with the
fuel cell. In the event that a line, which may contain a
hydrogen reservoir, is available for the transport of hydro-
gen from the electrolyzer to the fuel cell, the electrolyzer
in the fuel cell can be disposed in such a way that the
oxygen-yielding or donor side of the electrolyzer borders the
oxygen-receiving or receptor side of the fuel cell. As a
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result, oxygen is advantageously supplied directly to the
fuel cell.
In accordance with yet an additional feature of the inven-
tion, the hydrogen reservoir which may possibly be present a
metal hydride reservoir. This kind of hydrogen reservoir is
distinguished by the fact that depending on the alloy being
used, which can be chosen suitably, it can be charged with
hydrogen even in the vicinity of the ambient pressure. The
stored quantity of gas can be so great that under normal
conditions it would occupy a volume that can be considerably
larger than the inherent volume of the reservoir, for in-
stance 400 to 500 times the inherent volume. This would be
equivalent to a pressure reservoir of an identical volume,
but with an internal pressure of up to 4 x 107 to 5 x 10 Pa
(400 to 500 bar). Depending on the alloy used for the metal
hydride reservoir, the reservoir can operate at largely
constant pressure within wide pressure ranges (both negative
and overpressure). Due to the large holding capacity at a
small volume, a fuel cell system equipped with a metal
hydride reservoir can be accommodated in a small housing.
Moreover, the system is very light in weight. As a result,
for the first time it is advantageously possible to use the
fuel cell system as a substitute for conventional accumula-
tors and batteries, such as in small electrical appliances
and equipment, among other uses.
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21 65742 GR 95 P 3655
In accordance with again another feature of the invention,
the metal hydride reservoir is connected to a cooling device
or a heating device. It can be connected to a water supply
which, for instance, is disposed in a water bath, for cooling
or for heating. Cooling increases the storage capacity of
the hydrogen reservoir.
In accordance with again a further feature of the invention,
a dryer is disposed upstream of the hydrogen reservoir. This
has the advantage of ensuring that only dry hydrogen reaches
the reservoir, and can be stored in the reservoir in greater
quantity within the same reservoir volume in the form of wet
hydrogen.
In accordance with again an added feature of the invention, a
moistener is disposed downstream of the hydrogen reservoir.
This improves the operation of the fuel cell downstream of
it, since this cell functions better with wet hydrogen.
In accordance with again an additional feature of the inven-
tion, the dryer is combined with the moistener. Thus advan-
tageously the water given off by the dryer can be utilized to
operate the moistener. However, the water given off by the
dryer may also be drained off or fed to the electrolyzer.
The dryer and the moistener can also be combined into a unit.
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In accordance with still another feature of the invention,
the oxygen-yielding side of the electrolyzer can be connected
to the fuel cell through an oxygen reservoir, which serves to
store oxygen temporarily. This assures that as a result of
the temporary storage of oxygen, adequate oxygen is always
available to the fuel cell.
In accordance with still a further feature of the invention,
in the event that a hydrogen reservoir and an oxygen reser-
voir are present, they are constructed, for example, in such
a way that the hydrogen reservoir can hold approximately
twice as large a volume as the oxygen reservoir. To that
end, the hydrogen reservoir can be twice as large as the
oxygen reservoir. This assures that adequate hydrogen and
oxygen will always be available in the fuel cell, since twice
as much hydrogen as oxygen is needed.
In accordance with still an added feature of the invention,
the electrolyzer and the fuel cell are surrounded by a
gas-tight housing that serves as the oxygen reservoir. The
oxygen generated by the electrolyzer then accumulates in the
housing and is received as needed by the fuel cell. Besides
the oxygen generated in the electrolyzer, the oxygen compo-
nent of the air present in the housing is also located in the
housing.
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In the event that the oxygen can accumulate inside the
housing, a separate hydrogen reservoir is always necessary,
which communicates with the hydrogen-yielding or donor side
of the electrolyzer and the hydrogen-receiving or receptor
side of the fuel cell. The hydrogen reservoir is necessary
so that no mixture of hydrogen and oxygen can form in the
housing.
In accordance with still a further feature of the invention,
the electrolyzer and the fuel cell are surrounded by a
housing provided with an air inlet. The air inlet can be
realized by providing the housing with openings. If the
housing is to store water, these openings must not be dis-
posed in the lower region of the housing, because otherwise
the water would drain out. The oxygen required in the fuel
cell can then be drawn through the openings from the ambient
air.
In accordance with still an added feature of the invention,
the fuel cell and the electrolyzer can be air-breathing low-
temperature polymer electrolyte membrane fuel cells (PEMs).
These fuel cells are distinguished in that, not only can they
draw the required oxygen from the air when operated in their
inherent function, but when operated as electrolyzers they
can moreover extract the required water solely from the
moisture in air.
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The advantage attained with the use of such fuel cells is
that no water supply is necessary for operating the
electrolyzer. There is then no liquid in the fuel cell
system aside from the moisture from air, and thus it becomes
possible to operate the system in any position three-dimen-
sionally. Such a system can be used even in small portable
devices, such as flashlights.
In accordance with still an additional feature of the inven-
tion, a differential pressure regulator, which regulates
lo pressure differences through valves, is disposed at the
electrolyzer and/or the fuel cell between a hydrogen-yielding
or hydrogen-receiving side on one hand, and an oxygen-yield-
ing or oxygen-receiving side on the other hand. With this
regulator, a pressure difference between the hydrogen and the
air/oxygen side can be avoided through the valves.
In accordance with another feature of the invention, the
hydrogen reservoir, the electrolyzer and/or the fuel cell can
be operated in the negative-pressure range and/or in the
overpressure range. These components can also be operated in
the negative pressure range and the overpressure range in
alternation. If a metal hydride reservoir is to be operated
in the negative pressure range, it must be equipped with a
suitable alloy.
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In accordance with a concomitant feature of the invention,
the electrolyzer and the fuel cell can form a unit, which is
to be operated in alternation as an electrolyzer or as a fuel
cell. In that case, control of the supply of electric
current is important. That is, a voltage can be allowed to
be applied to the unit only when the unit is intended to
operate as an electrolyzer. Moreover, when used as an
electrolyzer, the unit must not contain too much water, so
that when used as a fuel cell, it is not blocked by the water
for oxygen and hydrogen. In the case of this embodiment, a
device in which the required water is extracted from the
moisture in the air is especially suitable.
Instead of the electrolyzer, a chemically operated hydrogen
generator can also be used, in which by way of example
organic compounds are decomposed (cracked) in such a way that
hydrogen is produced. The required hydrogen can also be
generated in any other conventional way. The requisite
oxygen can then be obtained from the ambient air, for in-
stance, or can also derive from a chemical process.
In particular, the fuel cell system of the invention attains
the advantage of being lightweight and only occupying little
space. It can be operated at low pressure near the ambient
pressure.
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Other features which are considered as characteristic for the
invention are set forth in the appended claims.
Although the invention is illustrated and described herein as
embodied in a fuel cell system, it is nevertheless not
intended to be limited to the details shown, since various
modifications and structural changes may be made therein
without departing from the spirit of the invention and within
the scope and range of equivalents of the claims.
The construction and method of operation of the invention,
however, together with additional objects and advantages
thereof will be best understood from the following descrip-
tion of specific embodiments when read in connection with the
accompanying drawing.
Brief Description of the Drawinq:
The figure of the drawing is an embodiment of a fuel cell
system according to the invention.
Description of the Preferred Embodiments:
Referring now in detail to the single figure of the drawing,
there is seen a diagrammatic illustration of a housing 1, in
which an electrolyzer 2 that is an inversely operated fuel
cell, is disposed. This electrolyzer 2 is connected to an
electrical voltage source 3 and gives up oxygen through
openings 4 and hydrogen through a line 5. Water 6 which is
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located in the electrolyzer 2 was originally fed-in a single
time, and is subsequently reproduced during operation in a
fuel cell 8 to be described below.
The line 5 for the hydrogen communicates with the fuel cell 8
through a hydrogen reservoir 7, which is a metal hydride
reservoir. Hydrogen which has been generated in the
electrolyzer 2 is stored in the hydrogen reservoir 7 until
needed in the fuel cell 8. Since on one hand dry hydrogen is
to be supplied to the hydrogen reservoir 7, and on the other
hand the fuel cell 8 functions better when the hydrogen
supplied to it is wet than when it is not wet, the line 5
includes a dryer 16 upstream of the hydrogen reservoir 7 and
a moistener 17 downstream of the hydrogen reservoir 7. In
order to ensure that the water recovered in the dryer 16 can
be used in the moistener 17, the dryer 16 communicates with
the moistener 17 through a connecting line 18.
The fuel cell 8 draws the required oxygen from the housing 1
which serves as an oxygen reservoir. The oxygen can also be
temporarily stored in a non-illustrated reservoir.
The direct voltage generated by the fuel cell 8 can, if
necessary, be supplied at a tap 9, for instance through a
DC/AC converter 10, to a consumer 11.
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The water formed in the fuel cell 8 flows into the water
supply of the electrolyzer 2. The water in the electrolyzer
can be stored there in some water-storing medium 12, such as
a sponge. In order to provide better feeding of water into
this medium 12, wicks 15 of absorbent material, which extend
in the direction of the water-yielding fuel cell 8, can be
formed onto this medium.
The voltage source 3 for the electrolyzer 2 can be connected
permanently or temporarily to a power supply grid 13 or also
to a solar cell array 14. Moreover, if the consumer 11
requires less electrical energy than is generated in the fuel
cell 8, the excess can be carried to the electrolyzer 2
through a non-illustrated electrical line.
A differential pressure regulator 19 is disposed at the fuel
cell 8, between the hydrogen side and the oxygen side/air
side. The differential pressure regulator 19 regulates
pressure differences through valves 20 and 21. These valves
20 and 21 are disposed in outgoing lines, which respectively
originate at the hydrogen side and the oxygen/air side or in
the interior of the air-containing housing 1, and terminate
outside the housing 1.
The fuel cell system accommodated in the housing 1 is very
light in weight and can be used instead of accumulators and
batteries. The advantage which is attained in particular is
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that an environmentally friendly electrical energy source is
furnished. In contrast to conventional batteries and accumu-
lators, no heavy metals to be disposed of are involved.
Moreover, the energy source according to the invention is
operationally ready over a markedly longer time than known
accumulators.
Furthermore, the fuel cell system can be operated with a
closed process or, with respect to the oxygen, with a half-
open process. In addition, it can be operated in the vicini-
ty of the ambient pressure.
The electrolyzer 2 can also obtain the required water solely
from the moisture in air. In this case and also whenever the
water is stored in a water-storing medium 12, the fuel cell
system can be operated in any three-dimensional position.
This makes it especially suitable for small equipment.
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