Chemistry: electrical current producing apparatus – product – and – Having earth feature
Reexamination Certificate
2002-04-29
2004-12-07
Cantelmo, Gregg (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having earth feature
C429S006000, C429S006000
Reexamination Certificate
active
06828057
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to fuel cells. More particularly, the present invention relates to alkaline fuel cells wherein the electrodes are placed in frames to allow high air flow throughout the fuel cell while maintaining a low pressure within the fuel cell.
BACKGROUND OF THE INVENTION
Fuel cells use gaseous hydrogen streams, gaseous oxygen streams, and electrolyte streams to produce power. The oxygen stream may be pure oxygen, air, or another oxygen containing mixture. Air, however, is the most abundant and attainable source of oxygen. Due to air containing only 21% oxygen, a greater air flow rate is needed when air is used as a source of oxygen, as compared to a pure oxygen stream. As a result of the high flow rate of the oxygen stream, the pressure inside the fuel cell increases. The pressure increases inside fuel cells may cause design problems for other streams entering and exiting the fuel cell because the pressure of the streams will need to be adjusted according to the pressure within the fuel cell. As such, a fuel cell allowing for a high air flow rate while maintaining a low pressure within the fuel cell is very desirable.
The present invention utilizes parallel flow of an electrolyte solution with respect to the electrodes. The electrodes are placed in frames which distribute electrolyte solution and either air or hydrogen across the electrodes. The frames containing the electrodes are sealed together and flow channels in the frames distributes air, hydrogen, and electrolyte solution across the electrodes while maintaining low pressure throughout the fuel cell. The present invention provides a compacted fuel cell design while allowing for a high air flow while maintaining a low pressure throughout the fuel cell.
As the world's population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces the harmful gas. Experts say atmospheric levels of carbon dioxide may be double that of the pre-industrial era by the end of the next century, but they also say the levels would be much higher except for a trend toward lower-carbon fuels that has been going on for more than 100 years. Furthermore, fossil fuels cause pollution and are a causative factor in the strategic military struggles between nations. Furthermore, fluctuating energy costs are a source of economic instability worldwide.
In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. It had been predicted that this evolution will produce a carbon-free energy system by the end of the 21
st
century. The present invention is another product which is essential to shortening that period to a matter of years. In the near term, hydrogen will be used in fuel cells for cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But, with the problems of storage and infrastructure solved (see U.S. Pat. No. 6,305,442, entitled “A Hydrogen-based Ecosystem” filed on Nov. 22, 1999 for Ovshinsky, et al., which is herein incorporated by reference and U.S. Pat. No. 6,193,929, entitled “High Storage Capacity Alloys Enabling a Hydrogen-based Ecosystem”, filed on Nov. 6, 1999 for Ovshinsky et al., which is herein incorporated by reference), hydrogen will also provide a general carbon-free fuel to cover all fuel needs.
A dramatic shift has now occurred, in which the problems of global warming and climate change are now acknowledged and efforts are being made to solve them. Therefore, it is very encouraging that some of the world's biggest petroleum companies now state that they want to help solve these problems. A number of American utilities vow to find ways to reduce the harm done to the atmosphere by their power plants. DuPont, the world's biggest chemicals firm, even declared that it would voluntarily reduce its emissions of greenhouse gases to 35% of their level in 1990 within a decade. The automotive industry, which is a substantial contributor to emissions of greenhouse gases and other pollutants (despite its vehicular specific reductions in emissions), has now realized that change is necessary as evidenced by their electric and hybrid vehicles.
Hydrogen is the “ultimate fuel.” In fact, it is considered to be “THE” fuel for the future. Hydrogen is the most plentiful element in the universe (over 95%). Hydrogen can provide an inexhaustible, clean source of energy for our planet which can be produced by various processes. Utilizing the inventions of subject assignee, the hydrogen can be stored and transported in solid state form in trucks, trains, boats, barges, etc. (see the '810 and '497 applications).
A fuel cell is an energy-conversion device that directly converts the energy of a supplied gas into an electric energy. Researchers have been actively studying fuel cells to utilize the fuel cell's potential high energy-generation efficiency. The base unit of the fuel cell is a cell having an oxygen electrode, a hydrogen electrode, and an appropriate electrolyte. Fuel cells have many potential applications such as supplying power for transportation vehicles, replacing steam turbines and power supply applications of all sorts. Despite their seeming simplicity, many problems have prevented the widespread usage of fuel cells.
Presently most of the fuel cell R & D focus is on P.E.M. (Proton Exchange Membrane) fuel cells. The P.E.M. fuel cell suffers from relatively low conversion efficiency and has many other disadvantages. For instance, the electrolyte for the system is acidic. Thus, noble metal catalysts are the only useful active materials for the electrodes of the system. Unfortunately, not only are the noble metals costly, they are also susceptible to poisoning by many gases, and specifically carbon monoxide (CO). Also, because of the acidic nature of the P.E.M fuel cell, the remainder of the materials of construction of the fuel cell need to be compatible with such an environment, which again adds to the cost thereof. The proton exchange membrane itself is quite expensive, and because of its low conductivity, inherently limits the power performance and operational temperature range of the P.E.M. fuel cell (the PEM is nearly non-functional at low temperatures, unlike the fuel cell of the instant invention). Also, the membrane is sensitive to high temperatures, and begins to soften at 120° C. The membrane's conductivity depends on water and dries out at higher temperatures, thus causing cell failure. Therefore, there are many disadvantages to the P.E.M. fuel cell which make it somewhat undesirable for commercial/consumer use.
The conventional alkaline fuel cell has some advantages over P.E.M. fuel cells in that they have higher operating efficiencies, they use less expensive materials of construction, and they have no need for expensive membranes. The alkaline fuel cell also has relatively higher ionic conductivity in the electrolyte, therefore it has a much higher power capability. Unfortunately, conventional alkaline fuel cells still suffer from certain disadvantages. For instance, conventional alkaline fuel cells still use expensive noble metals catalysts in both electrodes, which, as in the P.E.M. fuel cell, are susceptible to gaseous contaminant poisoning. While the conventional alkaline fuel cell is less sensitive to temperature than the PEM fuel cell, the active materials of conventional alkaline fuel cell electrodes become very inefficient at low temperatures.
Fuel cells, like batteries, operate by utilizing electrochemical reactions. Unlike a battery, in which chemical energy is stored within the cell, fuel cells generally are
Aladjov Boyko
Dhar Subhash K.
Fok Kevin
Hopper Tom
Menjak Ana
Cantelmo Gregg
Energy Conversion Devices Inc.
Mau II Frederick W.
Schumaker David W.
Siskind Marvin S.
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