Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-06-01
2003-11-11
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C422S236000, C048S061000, C048S198200, C048SDIG005
Reexamination Certificate
active
06645651
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 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” described a method of forming a fuel cell that efficiently utilizes expensive catalysts, is easily mass produced, and can be packaged for portable electronics.
A variety of methods for production and/or delivery of hydrogen gas into fuel cells are known. Some of them include pressurized hydrogen storage in cylinders and storage into metal hydride alloys, such as those used in Ni—MH rechargeable batteries.
Needs exist to provide safe and convenient sources of hydrogen fuel for fuel cells at a low cost, especially in portable power applications.
A different way of creating and delivering this hydrogen is to use chemical hydride compounds that absorb water or other liquids or gases which react with the chemical hydride to form hydrogen. The hydrogen then diffuses out and is delivered to the fuel cell or hydrogen consuming device.
There are a variety of chemical hydrides which release hydrogen when combined with water. Their reaction with water can be described by the following general equation:
MH
x
+x
H
2
O→M(OH)
x
+x
H
2
where M is a metal of valence x. Examples of these chemical hydrides include LiH, LiAlH
4
, LiBH
4
, NaH, NaAlH
4
, NaBH
4
, MgH
2
, Mg(BH
4
)
2
, KH, KBH
4
, CaH
2
and Ca(BH
4
)
2
(Kong et. al). Kong et al. showed that LiH, LiAlH
4
, LiBH
4
, NaH, NaBH
4
and CaH
2
all deliver a large fraction of their hydrogen capacity upon reaction with water vapor. Conversely, LiBH
4
and NaBH
4
were observed not to react with water vapor and there was no reaction with water until the powders were effectively dissolved. The U.S. Army Mobility Equipment Research and Development Command developed a system in which liquid water flows from a reservoir into a chamber where it contacts a porous hydrophobic membrane. In this system, water vapor diffuses through the membrane and spontaneously reacts with the hydride to release hydrogen, which then flows out of the reaction chamber to the anode of the fuel cell. Hydrogen production is controlled by virtue of water being forced back into the water reservoir during periods of no load, when the hydrogen is not being consumed.
As another example, Millennium Cell has developed a chemical hydrogen generator based on basic solutions of sodium borohydride (Amendola et al.). The generation of hydrogen is based on the reaction:
NaBH
4
+2H
2
O→NaBO
2
+4H
2
(1)
Basic solutions of sodium borohydride were shown to be stable. A catalyst (Ru) releases hydrogen when in contact with the solution and therefore requires mechanical means to bring the solution into contact with the catalyst. This adds complexity to the system.
This last case is a particular example of the more general case where NaBH
4
and water are chosen from a larger class of compounds A and B, respectively.
This new invention addresses the pre-existing problems.
SUMMARY OF THE INVENTION
A subject of this invention is to advance fueling systems such as described in our U.S. Pat. No. 5,759,712 that has the fuel ampoules sealed in gas tight packages. An advance is to arrange a system of two ampoules or components (A and B) such that when placed together produce hydrogen and when separated do not. Diffusion regulation mechanisms are used to regulate the production rates, as well as the choice of both A and B components. An objective is to make hydrogen fueling system safer for hydrogen consuming systems such as fuel cells. In products, an A ampoule and a B ampoule are placed in a cavity and sealed together. Reactants diffuse through the walls of one of the ampoules into the other ampoule through the walls of the second ampoule. The reaction then produces hydrogen gas which diffuses out of the second ampoule.
Obvious applications of a small fuel cell are in those that are currently powered by batteries, especially rechargeable batteries. By safely encapsulating intrinsically energetic fuels with an interactive hydrogen release reaction, the fuel cells can have higher energy per unit mass, higher energy per unit volume, and be more convenient for the energy user.
Our invention provides a safe, convenient, inexpensive and portable hydrogen generator which can be used to fuel a PEM fuel cell. Component A is chosen from chemical hydrides such as LiH, NaH, NaBH
4
CaH
2
and LiAlH
4
, among others. Component B may include, but is not limited to, substances such as water, alcohols, organic and inorganic acids (e.g. acetic acid, sulfuric acid), aldehydes, ketones, esters, nitrites and superacids (e.g. polyoxotungstates), and combinations thereof. Depending on the choice of component B, an appropriate selectively permeable membrane should be selected (e.g. silicone rubber for methanol).
Our recently issued patent U.S. Pat. No. 6,194,095 describes how the non-bipolar fuel cells can be packaged to form larger power supplies. Our pending patent no. U.S. Ser. No. 09/821,053 describes an ampoule of fuel that can be delivered at a controlled and constant rate by using the selective permeability of the fuel tank. In some fuel cells a controlled release of hydrogen or other gas is also needed.
This patent describes a recipe where the choice of A and B influences the rate of hydrogen gas generation. More importantly, this patent discloses a method for combining both chemicals without the aid of any mechanical means, thus resulting in a chemical hydrogen generator which is safe, portable and inexpensive.
In our patent application No. U.S. Ser. No. 09/821,053, a liquid hydride solution is immobilized and its contact is controlled with capillary wicking material. It does not have the feature of two components in diffusion contact, instead describing physical contact of a single fuel with a catalyst. Capillary wicking can be used to immobilize any liquid reactants in a two component diffusion delivery system.
In our patent 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 transported to the fuel cells in the vapor phase. Breaching this fuel tank 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 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 our 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 diffusion delivery means.
Hydrogen Gas Generation
Chemical hydrides are known to react with water and give off hydrogen gas as a product. Reaction (1) shown above serves as an example. In general, hydrogen generation occurs when the hydride ion reacts with a proton from another source. Water is the most common source of protons used, and hen
Bradford Zachary R.
DeJohn Marc D.
Hockaday Robert G.
Navas Carlos J.
Turner Patrick S.
Creighton Wray James
Maples John S.
Narasimhan Meera P.
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