Fuel cell elements with improved water handling capacity

Details Fuel cell elements with improved water handling capacity Fuel cell elements with improved water handling capacity

1998-11-23

2001-09-18

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

Reexamination Certificate

active

06291093

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the methods and apparatus of generating energy through low-cost, efficient processes. More specifically, the invention relates to components of a fuel cell for generating electricity.
BACKGROUND OF THE INVENTION
Methanol fuel cells promise to provide efficient and low-cost electrical current from methanol without burning the fuel. Therefore, pollution from combustion is not created by the use of such fuel cells. The fuel cells can be at least as efficient as gasoline engines; they run cool, without the need for insulation and structural reinforcement; and rely on a relatively inexpensive fuel. The methanol fuel cells which were designed initially produced about 100 W, running up to 200 continuous hours, and up to 3,000 intermittent hours, without suffering any loss in performance. The goal is to produce units which can generate up to 40 kW, which would be enough to power a full-size automobile, and which can run for at least 1,000 continuous hours.
The biplate is a two-sided component which is placed between the membrane electrode assemblies (MEAs) in a fuel cell stack. One side of the biplate is oriented to face the anode of one MEA, and the other side of the biplate is oriented to face the cathode of another MEA. The biplate provides electrical contact to the MEAs. It also acts to separate air or oxygen provided to the cathode of one MEA and the fuel provided to the anode of the other MEA. As such it forms part of the fuel cell compartment containing either fuel or air.
The endplate is a fuel cell component which forms part of the last fuel cell compartment in a stack, if a stack is present. If the cells are not stacked, the endplate is simply a wall of the fuel cell. The endplate provides electrical contact between an electrode of the fuel cell and the electrical load which spans the fuel cell or stack of fuel cells. The endplate is simply a single-ended biplate. Thus, both fuel cell components, biplates and endplates, are conductive elements.
Typical biplates and endplates are made of a graphite/polymer composite. The polymer is a polymer binder which has the functional effect of making the biplate an extremely hydrophobic surface.
At this time, cost is the major factor limiting methanol fuel cell commercialization. One difficulty in the operation of methanol fuel cells is the water that normally accumulates in the channels of the cathode side of the biplate. The source of this water can be from the chemical reaction of the fuel cell, it can be a result of electroosmosis from the anode side, or it can be a result of simple diffusion. If the accumulated water is not removed, the performance of the fuel cell can suffer. The traditional way to remove this accumulated water has been by pressurized air.
It is desirable to design fuel cell systems which work at temperatures between 25 and 45° C. However, the power output of methanol fuel cells at 25° C. is only about 15-20% of the same cell operating at 90° C. Thus, it becomes important to reduce the energy consumption of ancillary processes as much as possible. For example, power consumption of a pressurized air delivery system can unacceptably diminish the advantages of a room temperature methanol fuel cell. It is considered desirable to design such cells so as to minimize the air flow required to remove accumulated water.
SUMMARY OF THE INVENTION
The invention results from the use of a new fuel cell component assembly in liquid feed fuel cells. The fuel component assembly minimizes resistance to air flow which is required to remove accumulated water from biplates and endplates of the fuel cell. This aspect leads to specifically designed ports at the upper and lower edges of the plates, specifically fabricated plate surfaces, and a specific orientation and spatial arrangement of the conductive elements which are included in the plates.
The costs associated with ancillary systems, such as the power needed to operate water removal systems, are lower in the new plate assembly, for reasons directly attributable to the new design.
The new fuel cell component demonstrates that the improvements which are possible are extremely practical in nature, and can be used in fuel cells for automobiles, lawn mowers, portable electrical devices, stand-alone power generators, and in replacement of the internal combustion engine generally. This also finds use in fuel cells used in the space shuttle and other high-end applications.
As used herein, a “biplate” is a two-sided separator which prevents fluid communication between compartments of fuel cells which cannot be in fluid communication for the cell to function properly. For example, a biplate can prevent fluid communication between the adjacent negative and positive electrodes of a fuel cell. A biplate may also prevent fluid communication between the last compartment of a fuel cell in a stack and the exterior of the fuel cell. This last aspect of the definition of biplate includes the specific fuel cell components which are found at each end of a stack of cells, also referred to as the endplates. “Endplates” are merely biplates which are not between fuel cell compartments, but are found at the terminus of a fuel cell stack.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods and examples are illustrative only and not intended to be limiting.


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patent: WO 96/18216 (1996-06-01), None

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