Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-08-22
2002-09-24
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000
Reexamination Certificate
active
06455184
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a fuel cell and more particularly to a gas distributor for a fuel cell.
The printed publication DE 44 30 958 C1 and the printed publication DE 195 31 852 C1 disclose fuel cells which include a cathode and an electrolyte as well as an anode. The cathode is disposed in a so-called cathode chamber. The anode is disposed in an anode chamber. An oxidation fluid such as air is supplied to the cathode chamber and fuel such as hydrogen is supplied to the anode chamber. The interface between an electrode and the electrolyte is called the active area. The two-dimensional surface area of the electrode, which is parallel to the active area is called electrode surface.
The German published patent application 197 15 256.7-45 discloses the provision of distribution structures in the electrode chambers. The distribution structures shown therein have a comb-like shape. They are said to provide for a uniform distribution of the operating fluid in the respective electrode chamber.
The operating fluids pass through the electrode chambers (anode and cathode chamber) and are consumed (depleted) in the process. Subsequently, the consumed or rather depleted operating media exit again from the respective electrode chambers.
On the cathode of the high temperature fuel cell disclosed in the printed publication DE 44 30 958 C1 oxygen ions are formed in the presence of the oxidation fluid. The oxygen ions travel through the solid electrolyte and recombine on the anode side with the hydrogen of the fuel so as to form water. With the recombination electrons are released which provide an electric energy potential.
The DE 195 31 852 C1 discloses a PEM-fuel cell at whose anode protons are generated by means of a catalyst in the presence of the fuel. The protons travel through the electrolyte membrane and combine at the cathode side with the oxygen from the oxidation fluid to form water. Electrons are released at the anode and consumed at the cathode whereby an electric potential between the electrode, that is electric energy, is generated. In order to achieve a good efficiency, the operating media must be distributed in the anode and cathode chambers uniformly over the electrode surfaces. Pressure losses of the operating fluids flowing through the fuel cell should be avoided or kept at a minimum. Pressure losses result in energy losses.
Generally, a mixture of gases and/or liquids is present in an electrode chamber of a fuel cell. The gas may be a mixture of a fuel gas and an inert gas. By the reformation or oxidation of a fuel such as a methanol-water mixture, other inert gases such as CO
2
may form in the respective electrode chamber. Air and, together therewith the inert gas nitrogen is generally supplied to the cathode.
The gases or liquids present at the respective electrodes must generally be kept well mixed in order to achieve a good performance.
If non-wetted gases, that is, gases, which have not been wetted in separate moistening apparatus, are to be supplied to a PEM fuel cell, the electrode surfaces have to be contacted by the operating fluid in a particularly uniform way. Otherwise, there is the danger that the electrode and, if applicable, the electrolyte membrane develop dried out areas. Local drying out may result in performance losses and in damages.
As the operating fluids flow parallel and adjacent to, the electrode surfaces over extended areas thereof they are increasingly depleted. In accordance therewith, the respective reactions differ locally in a qualitative respect.
It must be ensured that good electrical contacts are provided in the fuel cell. Thermal gradients must be avoided since they may have detrimental effects.
It is the object of the present invention to provide a fuel cell with an improved operating fluid supply and discharge system as compared to the fuel cells disclosed in the state of the art referred to above.
SUMMARY OF THE INVENTION
In a fuel cell comprising two electrodes, an electrolyte disposed between the electrodes and fluid conducting means for supplying an operating fluid to the electrodes and removing the depleted operating fluid from the electrodes, the fluid conducting means include fluid supply passages supplying the operating fluid to the electrodes in a direction normal to the electrode surface and depleted fluid discharge passages for removing the depleted operating fluid from the electrode surfaces also in a direction normal to the electrode surfaces.
The fuel cell includes an electrode with an open porosity. An electrolyte is disposed adjacent one side of the electrode. Adjacent the other side, a plurality of supply and discharge passages is disposed for supplying an operating fluid to the electrode.
A supply passage is a channel through which a fresh operating fluid is conducted to an active area of the electrode. A discharge passage is a channel by way of which the operating fluid depleted at the active area of the electrode is conducted out of the fuel cell. A channel to which fresh and depleted operating fluid is conducted is not a supply or discharge passage as defined in the claims.
The operating fluid for the electrode at one side of the electrolyte is fuel (hydrogen) and for the electrode at the opposite side of the electrolyte is oxygen (air).
Each supply passage joins a discharge passage. In contrast to the state of the art, the operating fluids are not discharged by way of the electrode chamber that is they do not pass through the whole electrode chamber into which they are introduced. Rather, the respective operating fluid leaves the supply passage and enters the electrode chamber fully in the direction normal to the respective electrode surface. As a result of the particular design, the operating fluid supplied by the supply passage then impinges essentially perpendicularly onto the electrode surface. It then flows into an adjacent discharge passage since this path provides the lowest flow resistance. Consequently, the operating fluid flows to the electrode essentially perpendicularly to the electrode surface and is discharged therefrom again essentially perpendicularly to the electrode surface in the opposite direction.
With the supply flows reaching the electrode essentially perpendicularly to the electrode surface fresh operating fluid is uniformly supplied to the whole electrode surface. The problems referred to in the introductory part of the specification are therefore avoided and the performance of the fuel cell is increased.
In a particular embodiment of the invention, the supply and discharge passages extend parallel to the electrode surfaces and are closed at one end. At the side adjacent the electrode, the supply and discharge passages have openings in the form of slots or gaps. In another embodiment, the supply passages extend parallel to the adjacent discharge passages. In this embodiment, it is ensured by simple design means that fresh operating fluid is supplied to a correspondingly large electrode surface essentially in a perpendicular direction.
In still another embodiment of the invention, a supply or discharge passage is provided with openings or bores, which extend between the adjacent electrode surface and the respective supply or discharge passage.
The operating fluid passes through the openings or bores of the supply passage into contact with the active surface and, after depletion at the active electrode surface, returns through the openings or bores in the discharge passage wall into the discharge passage. With the openings or bores, the flow of the operating fluid can be well controlled and dosed.
The diameters, the shapes and/or density (number of openings per passage length) of the openings, bores or slots in the supply and discharge passages may vary in accordance with still another embodiment of the arrangement according to the invention along the length of the passages. In this way, the flow resistances can be adjusted. Adjustment of the flow resistances by differently sizing the openings, bores or slots should be so made that the operating fluid is uniforml
Alejandro R
Bach Klaus J.
Forschungszentrum Jülich GmbH
Kalafut Stephen
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