Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2001-12-27
2004-06-08
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S150000, C502S159000, C423S44500R, C423S447100, C423S448000, C423S449100, C252S511000
Reexamination Certificate
active
06746982
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electrochemical cells such as fuel cells that are suited for usage in transportation vehicles, portable power plants, or as stationary power plants, and the invention especially relates to a porous carbon body that may be used within a fuel cell for transporting reactant, product and coolant fluids to, through and from the fuel cell, for conducting electricity from one cell to an adjacent cell, for providing a fluid barrier to gaseous reactants, for defining gaseous reactant distribution channels, and/or for providing mechanical integrity to the fuel cell.
BACKGROUND OF THE INVENTION
Fuel cells are well-known and are commonly used to produce electrical energy from reducing and oxidizing reactants fluids to power electrical apparatus such as apparatus on-board space vehicles, or on-site generators for buildings. A plurality of planar fuel cells are typically arranged in a stack surrounded by an electronically insulating frame structure that defines manifolds for directing flow of reducing, oxidant, coolant and product fluids as part of a fuel cell power plant. Each individual fuel cell generally includes an anode electrode and a cathode electrode separated by an electrolyte. A reducing fluid such as hydrogen is supplied to the anode electrode, and an oxidant such as oxygen or air is supplied to the cathode electrode. In a cell utilizing a proton exchange membrane (“PEM”) as the electrolyte, the hydrogen electrochemically reacts at a catalyst surface of the anode electrode to produce hydrogen ions and electrons. The electrons are conducted to an external load circuit and then returned to the cathode electrode, while the hydrogen ions transfer through the electrolyte to the cathode electrode, where they react with the oxidant and electrons to produce water and release thermal energy.
It is known to utilize one component of a fuel cell to assist in the accomplishment of a variety of water management and related tasks. Such a component is typically formed of a porous carbon body and is commonly referred to under various names including “cooler plate”, “water transport plate”, “separator plate”, “bi-polar plate”, “end plate”, among other names. For example, in U.S. Pat. No. 6,024,848 that issued on Feb. 15, 2000 to Dufner et al., which patent is owned by the assignee of all rights in the present invention and which patent is hereby incorporated herein by reference, a water transport plate is shown that defines a plurality of coolant water feed channels on a planar surface of the plate and on an opposed surface a network of reactant gas distribution channels is defined.
Such a water transport plate is a typical porous carbon body and the plate must perform a variety of functions. It must transport water from coolant channels through the body to gaseous reactant channels to humidify a reactant fluid within the gas reactant channels; it must remove product water generated at the cathode electrode across the body into the coolant water channels to prevent flooding of the cathode electrode; it must form a gaseous barrier to prevent mixing of fuel and oxidant reactant fluids on opposed sides of the plate; it must conduct electricity or electrons from one cell to an adjacent fuel cell in a fuel cell stack assembly; it must conduct waste heat generated at the cathode away from the cathode to the coolant fluid; it may provide a distribution network for oxidant and reducing fluid reactants; and, it must provide mechanical support and integrity to the fuel cell.
Therefore, a porous carbon body that makes up such a water transport plate must be porous, wettable to water, have a high rate of water permeability, have a high bubble pressure, be a good electrical and thermal conductor, have good compressive and flexural strength, and the porous carbon body must be chemically stable in the environment of an operating PEM fuel cell. Some of these qualities require characteristics that are inconsistent with characteristics appropriate for other such qualities. For example, to increase bubble pressure to thereby enhance a gaseous seal between gaseous oxidant and fuel reactants on opposed sides of the porous carbon body, it is appropriate to have a small mean pore size of the pores within the body. However, to enhance permeability of the body to coolant or product water, it is desirable to have a large mean pore size. Similarly, a high porosity, or percent open pore volume, is appropriate for enhancing flow of water through the porous carbon body, however a high porosity is detrimental to both electrical conductivity and mechanical strength.
Known porous carbon bodies utilized in fuel cells have been designed to reconcile such differing requirements. For example, it is known to render pores of a carbon body hydrophilic through incorporation of a hydrophilic rendering compound onto an interior surface of the pores, wherein the compound is a low solubility metal, such as shown in U.S. Pat. No. 6,258,476 that issued on Jul. 10, 2001 to Cipollini, which patent is owned by the assignee of all rights in the present invention and which patent is hereby incorporated herein by reference. In U.S. Pat. No. 5,840,414 that issued on Nov. 24, 1998 to Bett et al., which patent is owned by the assignee of all rights in the present invention and which patent is hereby incorporated herein by reference, a porous carbon body is shown that achieves increased wettability by incorporation of a metal oxide into the pores of the body, wherein the metal oxide has a solubility in water of less than about 10
−6
moles per liter. While Bett et al. makes the porous carbon body more hydrophilic, the process described in Bett includes a costly, and time consuming treatment to a graphitized carbon body. Normal manufacture of graphitized carbon bodies includes a very high temperature, lengthy process in order to produce a crystallized graphite structure. For example, to graphitize a mixture of a graphite powder and a resin into a porous carbon body acceptable for use in a PEM fuel cell, it is known to first compress the mixture in a mold to establish a pre-determined porosity at about 100-500 pounds per square inch (“p.s.i.”) and at about 325-375 degrees Fahrenheit (“° F.”), and to then heat the molded body in an inert atmosphere at about 3,600-5,400° F. As can be easily understood, such a process is quite expensive and time consuming often taking several weeks, and hence is a substantial problem in providing a cost effective porous carbon body for a PEM fuel cell.
Another approach to producing a porous carbon body for a PEM fuel cell is disclosed in U.S. Pat. No. 5,942,347 that issued on Aug. 24, 1999 to Koncar et al. wherein the body is described as a “bi-polar separator plate”. The plate includes 50% to about 95% by weight of a preferably carbonaceous “electronically conductive material”, at least 5% by weight of a resin, and at least one hydrophilic agent wherein the conductive material, resin and hydrophilic agent are substantially uniformly dispersed throughout the separator plate. In formation of the Koncar et al. plate, the hydrophilic or wetting agent is mixed together with the electronically conductive material and resin to produce a “uniform dispersion” of the wetting agent, and the mixture is then molded into a plate at 500-4,000 p.s.i. and 250-800° F. The hydrophilic or wetting agent is an oxide of titanium, aluminum or silica. Unfortunately however, the oxides of those substances are electronic insulators. Therefore, as shown in
FIG. 2
of Koncar et al., as the amount of the hydrophilic agent is increased, the conductivity of the resulting porous carbon body decreases. Hence, the carbon body of Koncar et al. necessarily results in a compromise between enhancing electrical conductivity of the body and making the body wettable to water. To increase wettability of the Koncar et al. porous carbon body, electrical conductivity must be decreased.
Accordingly, there is a need for a porous carbon body for a fuel cell that may be efficiently manufactured, and that in renderin
Bett John A. S.
Hertel Christopher J.
Lamm Foster P.
Reiser Carl A.
Bell Mark L.
Chisholm, Jr. Malcolm J.
Hailey Patricia L.
UTC Fuel Cells LLC
LandOfFree
Porous carbon body for a fuel cell having an electronically... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Porous carbon body for a fuel cell having an electronically..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Porous carbon body for a fuel cell having an electronically... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3306622