Patent Application
20110254198
The present invention relates generally to electrochemical conversion cells, and specifically electrochemical conversion cells disposed between bipolar plates.
Electrochemical conversion cells, commonly referred to as fuel cells, which produce electrical energy by processing first and second reactants, e.g., through oxidation and reduction of hydrogen and oxygen. By way of illustration and not limitation, a typical polymer electrolyte fuel cell comprises a polymer membrane (e.g., a proton exchange membrane) that is positioned between a pair of gas diffusion media layers and catalyst layers. A cathode plate and an anode plate are positioned at the outermost sides adjacent the gas diffusion media layers, and the preceding components are tightly compressed to form the cell unit.
The voltage provided by a single cell unit is typically too small for useful applications. Accordingly, a plurality of cells are typically arranged and connected consecutively in a “stack” to increase the electrical output of the electrochemical conversion assembly or fuel cell. In this arrangement, two adjacent cell units can share a common polar plate, which serves as the anode and the cathode for the two adjacent cell units it connects in series. Such a plate is commonly referred to as a bipolar plate and typically includes a flow field defined therein to enhance the delivery of reactants and coolant to the associated cells. Bipolar plates for fuel cells are typically required to be electrochemically stable, and electrically conductive.
In a first embodiment of the present invention, a device comprising an electrochemical conversion assembly is provided. The electrochemical conversion assembly comprises a plurality of electrochemical conversion cells, and a plurality of electrically conductive bipolar plates, wherein the electrochemical conversion cells are disposed between adjacent bipolar plates. The electrochemical conversion assembly further comprises a plurality of conversion assembly gaskets, wherein the respective conversion assembly gaskets are molded onto corresponding ones of the plurality of bipolar plates. The conversion assembly gaskets comprise a mixture including polyvinylidene fluoride (PVDF).
In a second embodiment of the present invention, a device comprising an electrochemical conversion assembly is provided. The electrochemical conversion assembly comprises a plurality of electrochemical conversion cells, wherein each conversion cell comprises membrane electrode assemblies. The electrochemical conversion assembly further comprises a plurality of electrically conductive bipolar plates, wherein the electrochemical conversion cells are disposed between adjacent bipolar plates. The electrochemical conversion assembly also comprises a plurality of conversion assembly gaskets molded onto the membrane electrode assemblies, wherein the conversion assembly gaskets comprise a mixture including polyvinylidene fluoride (PVDF).
In a third embodiment of the present invention, a method of fabricating an electrochemical conversion assembly is provided. The method comprises providing a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates. The method further comprises forming a mixture comprising polyvinylidene fluoride (PVDF) and a solvent by dissolving the PVDF in the solvent, applying the mixture onto the plurality of bipolar plates, and heating the mixture under pressure at a temperature and duration sufficient to form a plurality of conversion assembly gaskets on the plurality of bipolar plates.
In a fourth embodiment of the present invention, a method of fabricating an electrochemical conversion assembly is provided. The method comprises providing a plurality of electrochemical conversion cells comprising electrode membrane assemblies, and a plurality of electrically conductive bipolar plates. The method further comprises forming a mixture comprising polyvinylidene fluoride (PVDF) and a solvent by dissolving the PVDF in the solvent, applying the mixture onto the membrane electrode assemblies, and heating the mixture under pressure at a temperature and duration sufficient to form a plurality of conversion assembly gaskets on the membrane electrode assemblies.
Other features and advantages of the present invention will be apparent in light of the description of the invention embodied herein.
The following detailed description of specific embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals, where various components of the drawings are not necessarily illustrated to scale, and in which:
Referring generally to
Many aspects of the specific configuration of the bipolar plates 30 according to the present invention are also beyond the scope of the present invention. For example, referring specifically to
As is illustrated in
As shown in
Referring to
The conversion assembly gaskets comprise a mixture including polyvinylidene fluoride (PVDF). In one embodiment, the mixture comprises a PVDF homopolymer, for example,
Hylar® 461, which is produced by Solvay Solexis®. In yet another embodiment, the mixture comprises at least one solvent. The solvent may comprise any suitable material effective to dissolve a PVDF material. In an exemplary embodiment, the solvent is a carbonate solvent comprising propylene carbonate, ethylene carbonate, or combinations thereof. The PVDF material may be selected such that it dissolves well in carbonates. Upon dissolving, a paste is formed, which may be molded on or onto a membrane of an electrode membrane assembly or a bipolar plate. For example, and not by way of limitation, the paste may comprise a composition of 60% by wt. PVDF homopolymer, and 40% by wt. propylene carbonate.
It is contemplated that any suitable PVDF material may be used; however, a PVDF homopolymer, such as Hylar® 461, may provide additional benefits. Unlike typical fluorocarbons, Hylar® dissolves in an ethylene/propylene carbonate, which enables Hylar® to be injection molded into a bipolar plate. Further, since it is from the Teflon family, it is chemically inert and can be applied directly to the membrane of the MEA.
In contrast, Hylar® has superior chemical stability which facilitates its effectiveness in the gasket. Hylar® has a density of about 1.76 cm3 and a melting point of about 158 to about 160° C. Hylar® exhibits excellent thermal stability. For example, at high temperatures, Hylar® only exhibits a 1% mass loss in N2 at a temperature of 410° C. High temperature stability enables Hylar to be used as a gasket material in high temperature proton exchange membrane fuel cell stacks, wherein Hylar gaskets may contact membranes with operating temperatures of between about 120° C. to about 150° C., and temperatures much greater.
Hylar® also is thermally stable at lower temperatures, e.g. at temperatures below freezing. For example, Hylar® exhibits a glass transition temperature of about −39° C. Hylar® is also desirable for use in a gasket seal because it is an electrically insulating material. For example, Hylar® has a volume resistivity of about 1×1015 ohm-cm at 23° C., and a dielectric strength of about 6 kV/mm. Unlike other fluoropolymers or other gaskets such as rubber or silicone based gaskets, Hylar® is chemically inert. For example, Hylar® does not react or absorb water as demonstrated by a water absorption of only about 0.02% by weight. Since the Hylar® will typically be compressed in a fuel cell gasket, the water absorption of the gasket may be even less than 0.02% by weight. Furthermore, Hylar® exhibits sound mechanical properties, which contribute to its long term stability. For instance, Hylar® exhibits an elongation at breakage of about 100%, and an elongation at yield of about 10%. Moreover, Hylar® has a tensile modulus of about 190000 psi or about 1310 Mpa.
Fabricating an electrochemical conversion assembly, wherein a gasket 40 is provided on the bipolar plate 30 as in
As is noted above, the specific structure of the conversion assembly 10 and the individual conversion cells 20, is beyond the scope of the present invention. However, it is noted that typical conversion assemblies comprise respective membrane electrode assemblies that are configured to operate with hydrogenous gas and air as the respective reactant supplies. Again by way of illustration and not limitation, the electrochemical conversion cells 20 may comprise respective electrolytic membranes, gaseous diffusion layers, catalytic components, carbonaceous components, electrically conductive components, and combinations thereof. Finally, although the bipolar plates 30 illustrated in
Referring to
Although the present invention is not limited to any specific reactant compositions, it will be appreciated by those practicing the present invention and generally familiar with fuel cell technology that the first reactant supply R1 typically comprises oxygen and nitrogen while the second reactant supply R2 comprises hydrogen.
It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention.
For the purposes of describing and defining the present invention it is noted that the term “device” is utilized herein to represent a combination of components and individual components, regardless of whether the components are combined with other components. For example, a “device” according to the present invention may comprise an electrochemical conversion assembly or fuel cell, a vehicle incorporating an electrochemical conversion assembly according to the present invention, etc.
For the purposes of describing and defining the present invention it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.
This application is a divisional of U.S. Utility application Ser. No. 11/368,057, filed Mar. 3, 2006.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11368057 | Mar 2006 | US |
| Child | 13166939 | US |
