Patent Application
20120009493
The embodiments herein generally relate to fuel cell stacks, and, more particularly, but not exclusively, to fuel cells employing an apparatus and a method for controlling swelling of a catalyst coated membrane and a MEA.
A fuel cell, like an ordinary battery, provides direct current electricity from two electrochemical reactions. The electrochemical reactions occur at electrodes to which reactants are fed. A fuel cell stack typically includes a series of individual fuel cells. Each cell includes an anode and a cathode. A voltage across each cell is determined by the type of electrochemical reaction occurring in the cell. For example, for a typical direct methanol fuel cell (DMFC), the voltage can vary from 0.2 V to 0.9 V, depending on a current being generated. The current being generated in the cell depends on the operating condition and design of the cell, such as electro-catalyst composition or distribution and active surface area of a membrane electrode assembly (MEA), characteristics of a gas diffusion layer (GDL), anode and cathode flow field designs, cell temperature, reactant concentration, reactant flow and pressure distribution, reaction by-product removal, and so forth. A reaction area of a cell, number of cells in series, and the type of electrochemical reaction in the fuel cell stack determine the current and hence the power supplied by the fuel cell stack. For example, typical power for a direct methanol fuel cell (DMFC) stack can range from a few watts to a few kilowatts. A fuel cell system typically integrates a fuel cell stack with different subsystems for the management of water, fuel, air, humidification, and thermal condition. These subsystems are sometimes collectively referred to as balance of the plant (BOP).
Further, when the catalyst coated membrane 12m formed of a PFSA-based material is included within the cell 10, the catalyst coated membrane 12m is typically compressed in a dry form along with the gas diffusion layers G and an elastomeric, compressible gasket 14, as illustrated in
Therefore, there is a need to develop fuel cells employing an apparatus and a method for controlling swelling of a catalyst coated membrane.
In view of the foregoing, an embodiment herein provides an apparatus to control a swelling of a catalyst coated membrane in a fuel cell. The apparatus includes an insulator layer provided at a perimeter of the fuel cell. The insulator layer has a plurality of insulator films and is secured to a flow field plate. The insulator layer has a less compressibility relative to a gasket used in the fuel cell.
Embodiments further disclose a method for controlling a swelling of a catalyst coated membrane in a fuel cell includes providing an insulator layer at a perimeter of each of fuel cells in a fuel cell stack. The fuel cell stack is compressed for a predetermined duration when the catalyst coated membrane is in a substantially dry state. The method further includes allowing passage of fuel inside the fuel cell thereby facilitating the catalyst coated membrane to swell. The method also includes allowing swollen catalyst coated membrane to contact the insulator layer thereby preventing further swelling of said catalyst coated membrane.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings.
The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The embodiments herein disclose an apparatus and a method for controlling swelling of a catalyst coated membrane in a fuel cell. Referring now to the drawings, and more particularly to
Information regarding the expected swelling of the catalyst coated membrane 12m in solution can be gathered beforehand. Given the expected membrane swell, compensation for the swell is made by setting a thickness of the insulator layer 40 based on, or corresponding to, a thickness of the swollen catalyst coated membrane 12m. The thickness of the insulator layer 40 can also take into account a desired gas diffusion layer G compression for smooth mass transport and low contact resistance. In such manner, the insulator layer 40 serves as a hard-stop to avoid over-compression of gas diffusion layers G. Nafion 115 and a hydrocarbon membrane were analyzed and tabulated. The values relating to membrane swelling in x, y, and z direction at 1M and 8M methanol, 80° C. is given below in table 1.
When assembling a fuel cell stack, the stack is initially compressed at a relatively low load based on the thickness of the insulator layer 40. At this point, the catalyst coated membrane 12m is substantially dry. Once the stack is assembled, a methanolic solution flows into the anode 12a side, while maintaining the stack within a desired temperature range. The catalyst coated membrane 12m swells and pushes against the gas diffusion layer G, thereby compressing the gas diffusion layer G in-situ. The gas diffusion layer G, upon being pushed by the swollen catalyst coated membrane 12m, contacts a plurality lands/ribs L provided on the flow field plate 13a.
Further, as there is adequate free volume provided by the insulator layer 40, there is reduced channel intrusion of the gas diffusion layer G as a result of membrane swell. The stack is thereafter compressed to a final load in one or more subsequent compression operations. As catalyst coated membrane 12m is already swollen, and a thickness of the compressed gas diffusion layers G is therefore set, subsequent compression operations reduce the contact resistance, while creating little or no mass transport restrictions in the channel areas C. The effect of the insulator layer 40 on membrane swell is illustrated in
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the claims as described herein.
This application claims priority from U.S. Provisional Application No. 61/363,048, filed on Jul. 9, 2010, the complete disclosure of which is incorporated fully herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61363048 | Jul 2010 | US |
