Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-03-30
2003-10-07
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S010000
Reexamination Certificate
active
06630266
ABSTRACT:
BACKGROUND OF THE INVENTION
Fuel cells directly transform chemical energy to electrical energy by reacting electrochemically gas or liquids in the presence of an electrolyte, electrodes and a catalyst. Our previous patents, U.S. Pat. No. 4,673,624 “Fuel Cell”, U.S. Pat. No. 5,631,099 “Surface Replica Fuel Cell, and U.S. Pat. No. 5,759,712 “Surface Replica Fuel Cell for Micro Fuel Cell Electrical Power Pack”, describe a method of forming a fuel cell that efficiently utilizes expensive catalysts, is easily mass produced, and can be packaged for portable electronics. A co-pending patent application, U.S. Ser. No. 09/208,745 (now U.S. Pat. No. 6,326,097), describes how the Micro-Fuel Cells™ can be packaged in portable electronics. A co-pending patent application, U.S. Ser. No. 09/210,792 (now U.S. Pat. No. 6.194.095), describes how the non-bipolar fuel cells can be packaged to form larger power supplies.
Applications of a small fuel cell include those devices currently powered by batteries, especially the rechargeable batteries. By directly utilizing alcohol fuels, the fuel cells can have higher energy per unit mass, higher energy per unit volume, be more convenient for the energy user, environmentally less harmful, and less expensive than conventional batteries.
RELATED ART
U.S. Pat. No. 5,364,711 and U.S. Pat. No. 5,432,023 describe miniature fuel cells to run “office automation (OA) equipment, audio equipment, and radio equipment.” Those patents describe the advantages of using miniature fuel cells built by a variety of techniques. They also describe a wick to introduce liquid fuel and electrolyte to the fuel cell and remove excess water from the fuel.
There are four fundamental problems of the wicking of input fuel and water in low power fuel cells. The first problem in delivering the methanol fuel to the fuel cell as a solution of sulfuric acid and methanol is the risk of shorting non-bipolar cells in a single membrane type fuel cell.
The second problem in low power applications is retaining water and maintaining water balance in the electrolyte. A mechanism for recovering water from the air electrode and recycling it back to the fuel electrode is not described in this patent. If water could be recovered it would allow the fuel cell to run on highly concentrated methanol. A wicking system alone may not be able to recover water if there is no condensed water.
The third problem is that by using a wicked delivery of fuel, impurities in the fuel are delivered to the fuel cell electrodes. The fourth problem is that, with a wicking system, physical liquid contact with the fuel reservoir and the wick needs to be made. This liquid contact and flow can be disturbed by gravitational orientation of the fuel source or poor mating of the fuel reservoir to the wick.
In our U.S. Pat. No. 5,631,099, water circulating and regulating membranes over the electrodes and water recovery from the exhaust are described. This patent uses wicking to recover the water and recycle it back to the fuel electrode.
In our U.S. Pat. No. 5,759,712, a vapor phase transport to a hydrophilic outer surface of a gas manifold is described. Selectively permeable membranes in proximity to the fuel cell are described for delivering reactants and products. Fueling is done by breaching a fuel tank and wicking fuel, which is then in the vapor phase transported to the fuel cells. This fuel tank breaching can lead to spilling of fuel while liquid contact needs to be maintained with the fuel in the fuel tank. Thus, as the fuel tank runs low on fuel some of the fuel may not be in liquid contact and will be unused.
To achieve wicking fuel delivery, the fuel needs to be fluid and mobile thus increasing the possibilities of leakage from the fuel ampoule. Gravity can affect the delivery of a liquid fuel. Achieving a good liquid seal on a methanol fuel can lead to complex and costly sealing mechanisms for the fueling system and the fuel cell system. Small leaks of liquid fuel compared to vapor loss through the same hole can have a far greater detrimental effect on the air electrode and total fuel loss.
In U.S. Pat. No. 4,931,168 a gas permeable electrode is described that is in contact with a methanol fuel. Its purpose is to prevent buildup of carbon dioxide bubbles on the fuel cell electrode. It uses a gas permeable resin and catalytic particle electrodes that allow reactants and ions to move in and out of the electrodes. The gas permeable membrane does not provide a means of transporting the fuel from the fuel source to the fuel cell.
In our co-pending patent application, U.S. Ser. No. 09/208,745 (now U.S. Pat. No. 6.326.097), the fuel cell and fueling ampoules are shown being placed in proximity to each other with a diffusion mat. The fuel tanks are described as a liquid wick or fluid motion fueling. Fuel diffusion from the fuel tanks is not described. Plastic blister packaging of the fuel tanks does not indicate the sealing properties of the package, nor individual sealing. Porous fillers are described as being in the fuel tanks, but not as a diffusion delivery means.
The present invention addresses existing problems.
SUMMARY OF THE INVENTION
The present invention includes a fuel tank that is permeable to the fuel and a container that is fuel impermeable for fuel storage. This system of fueling is used when small low power fuel cells need a steady controlled delivery of fuel. This fueling system is simple and may be easily packaged to be small compact fuel cell systems. There are several features that make this system enhance the performance of the fuel cell system.
We have discovered in building and testing these devices that some of the volatile hydrocarbons and hydrogen can diffuse through container walls at a sufficient rate that physical contact is not necessary. The fuel can also have impurities in it that would not be vaporized or transported through the container material thus protecting the fuel cell. We also discovered that some of the fuels in high concentrations can have debilitating effects on the fuel cells. Thus by devising a refueling scheme that avoids breaching containers and vapor fuel delivery, we found that safer and more convenient power devices may be realized.
The invention includes a fueling system having the fuel ampoules sealed in gas tight packages. When the package is opened the ampoule is inserted into the fuel cell application to deliver reactants through the selectively permeable wall of the ampoule. This permits a controlled release of fuel, keeps the fuel that is delivered to the fuel cells clean and avoids fuel spillage by the user, thus making small alcohol powered fuel cells practical.
Concentration Gradients
When fuel, such as concentrated methanol, is held behind a selectively permeable membrane, such as silicone rubber, and placed near a fuel cell gas manifold two concentration gradients are set up as the fuel cell consumes the fuel: concentration of fuel from high, at the fuel ampoule, to low, through the fuel cell; and concentration of the water from high, at the oxygen electrode of the fuel cell, to low, at the fuel tank.
These concentration gradients set up vapor pressure gradients also. Both have the effect of drawing fuel out of the fuel tank and drawing water from the oxygen electrode. Thus, it has the effect of recapturing product water from the air electrode and the fuel cells can run on highly concentrated methanol fuel.
Selectively Permeable Membranes
By having a selectively permeable fuel tank wall, such as silicone rubber, the fuel delivery has the advantageous effect of delivering fuel at a constant rate throughout its life cycle. If the membrane had similar permeability to fuel compared to water, the water would be diffusing in while the fuel was diffusing out. The water would drop the fuel vapor pressure and reduce the rate at which fuel can diffuse out. Thus, the rate of fuel delivery would gradually drop and the fuel tank would gradually fill with a mixture of fuel and water.
In product applications it is desirable to have the membrane be effectively much more permeabl
DeJohn Marc D.
Hockaday Robert G.
Navas Carlos J.
Turner Patrick S.
Vaz Heathcliff L.
Manhattan Scientifics, Inc.
Maples John S.
Narasimhan Meera P.
Wray James C.
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