Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-12-20
2002-08-06
Kalafut, Stephen J. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S006000
Reexamination Certificate
active
06428916
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to a coolant treatment system for a fuel cell assembly, and deals more particularly with a coolant treatment system for a fuel cell assembly which is in direct communication with an antifreeze coolant solution.
BACKGROUND OF THE INVENTION
Electrochemical fuel cell assemblies are known for their ability to produce electricity and a subsequent reaction product through the interaction of a fuel being provided to an anode and an oxidant being provided to a cathode, thereby generating an external current flow between these substrates. Such fuel cell assemblies are very useful and sought after due to their high efficiency, as compared to internal combustion fuel systems and the like. Fuel cell assemblies are additionally advantageous due to the environmentally friendly chemical reaction by-products that are produced, such as water. In order to control the temperature within the fuel cell assembly, a water coolant is typically provided to circulate about the fuel cell assembly. The use of reformed fuels within fuel cell assemblies makes them particularly sensitive to possible water contaminants.
Electrochemical fuel cell assemblies typically employ hydrogen as the fuel and oxygen as an oxidant where the reaction by-product is water. Such fuel cell assemblies may employ a membrane consisting of a solid polymer electrolyte, or ion exchange membrane, disposed between the two substrates formed of porous, electrically conductive sheet material—typically, carbon fiber paper. The ion exchange membrane is also known as a proton exchange membrane (hereinafter PEM), such as sold by DuPont under the trade name NAFION™. Catalyst layers are formed between the membrane and the substrates to promote the desired electrochemical reaction. The combination of the PEM, the two catalyst layers and the substrates are referred to as a membrane electrode assembly.
In operation, hydrogen fuel permeates the porous substrate material of the anode and reacts with the catalyst layer to form hydrogen ions and electrons. The hydrogen ions migrate through the membrane to the cathode and the electrons flow through an external circuit to the cathode. At the cathode, the oxygen-containing gas supply also permeates through the porous substrate material and reacts with the hydrogen ions and the electrons from the anode at the catalyst layer to form the by-product water. Not only does the ion exchange membrane facilitate the migration of these hydrogen ions from the anode to the cathode, but the ion exchange membrane also acts to isolate the hydrogen fuel from the oxygen-containing gas oxidant. The reactions taking place at the anode and cathode catalyst layers are represented by the equations:
Anode reaction: H
2
→2H
+
+2
e
Cathode reaction: ½O
2
+2H
+
+2
e
→H
2
O
Conventional PEM fuels cells have the ion exchange membrane positioned between two gas-permeable, electrically conductive plates, referred to as the anode and cathode plates. The plates are typically formed from graphite, a graphite-polymer composite, or the like. The plates act as a structural support for the two porous, electrically conductive substrates, as well as serving as current collectors and providing the means for carrying the fuel and oxidant to the anode and cathode, respectively. They are also utilized for carrying away the reactant by-product water during operation of the fuel cell.
When flow channels are formed within these plates for the purposes of feeding either fuel or oxidant to the anode and cathode plates, they are referred to as “fluid flow field plates”. These plates may also function as water transfer plates in certain fuel cell configurations. When these plates simply overlay channels formed in the anode and cathode porous material, they are referred to as “separator plates”. Moreover, the plates may have formed therein reactant feed manifolds which are utilized for supplying fuel to the anode flow channels or, alternatively, oxidant to the cathode flow channels. They also have corresponding exhaust manifolds to direct unreacted components of the fuel and oxidant streams, and any water generated as a by-product, from the fuel cell. Alternatively, the manifolds may be external to the fuel cell itself, as shown in commonly owned U.S. Pat. No. 3,994,748, issued to Kunz et al., and incorporated herein by reference in its entirety.
The catalyst layer in a fuel cell assembly is typically a carbon supported platinum or platinum alloy, although other noble metals or noble metal alloys may be utilized. Multiple electrically connected fuel cells consisting of two or more anode plate/membrane electrode assembly/cathode plate combinations are referred to as a “fuel cell stack”. A fuel cell stack is typically electrically connected in series.
Recent efforts at producing the fuel for fuel cell assemblies have focused on utilizing a hydrogen rich gas produced from the chemical conversion of hydrocarbon fuels, such as methane, natural gas, gasoline or the like, into hydrogen. This process requires that the hydrogen produced must be efficiently converted to be as pure as possible, thereby ensuring that a minimal amount of carbon monoxide and other undesirable chemical byproducts are produced. This conversion of hydrocarbons is generally accomplished through the use of a steam reformer or an autothermal reformer. Reformed hydrocarbon fuels frequently contain quantities of ammonia, NH
3
, as well as significant quantities of carbon dioxide, CO
2
. These gases tend to dissolve and dissociate into the water which is provided to, and created within, the fuel cell assembly. The resultant contaminated water supply may cause the conductivity of the water to increase to a point where shunt current corrosion occurs in the coolant channels and manifold leading to degradation of fuel cell materials, as well as reducing the conductivity of the PEM and thereby reducing the efficiency of the fuel cell assembly as a whole.
As disclosed above, the anode and cathode plates provide coolant channels for the circulation of a water coolant, as well as for the wicking and carrying away of excessive water produced as a by-product of the fuel cell assembly operation. The water so-collected and circulated through a fuel cell assembly is susceptible to water contamination and may therefore damage and impair the operation of the fuel cell assembly as the contaminated water circulates throughout the fuel cell assembly.
It is therefore necessary to provide a system which may protect the fuel cell assembly from water contamination, such as is described in commonly owned U.S. Pat. No. 4,344,850, issued to Grasso, and incorporated herein by reference in its entirety. Grasso's system for treating the coolant supply of a fuel cell assembly, as illustrated in FIG. 1 of 4,344,850, utilizes a filter and demineralizer for purifying a portion of the coolant supplied to the fuel cell assembly. A deaerator is also utilized to process the condensed water obtained from a humidified cathode exit stream. As discussed in Grasso, the heat exchange occurring between the coolant stream and the body of the fuel cell assembly is accomplished according to commonly assigned U.S. Pat. No. 4,233,369, issued to Breault et al., incorporated herein by reference in its entirety.
It is important to note that Grasso's coolant system does not provide for the cleansing of the coolant stream as a whole. This is due to the fact that the coolant conduits in Grasso, being fashioned from copper or the like, are not in diffusable communication with the body of the fuel cell assembly and as such, the coolant stream does not receive contamination from, inter alia, the CO
2
or NH
3
present in the reformed fuel stream. The burden of cleansing the coolant stream in Grasso is therefore born solely by the filter and demineralizer and results in greater wear on these components and hence greater repairs and replacements. Grasso also utilizes two distinct coolant pumps for circulating the coolant.
Another coolant trea
Breault Richard D.
Grasso Albert P.
Van Dine Leslie L.
Kalafut Stephen J.
McCormick, Paulding & Huber
UTC Fuel Cells LLC
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