Patent Application
20210075031
The present disclosure relates to electrochemical fuel cells and, in particular, to a novel design of the flow field plate landings.
Fuel cell systems convert reactants, namely fuel and oxidant, to electricity and are therefore used as power supplies in numerous applications, such as automobiles and stationary power plants. Such systems are a good solution for economically delivering power with environmental benefits.
Fuel cells generally employ an electrolyte disposed between two electrodes, namely a cathode and an anode. A catalyst typically induces the electrochemical reactions at the electrodes. Preferred fuel cell types include solid polymer electrolyte fuel cells that comprise a solid polymer electrolyte, for example a proton exchange membrane, and operate at relatively low temperatures. Proton exchange membrane fuel cells employ a membrane electrode assembly (“MEA”) having a proton exchange membrane (“PEM”) (also known as an ion-exchange membrane) interposed between an anode electrode and a cathode electrode. The anode electrode typically includes a catalyst and an ionomer, or a mixture of a catalyst, an ionomer and a binder. The presence of ionomer in the catalyst layer effectively increases the electrochemically active surface area of the catalyst, which requires an ionically conductive pathway to the cathode catalyst to generate electric current. The cathode electrode may similarly include a catalyst and a binder and/or an ionomer. Typically, the catalysts used in the anode and the cathode are platinum or platinum alloy. Each electrode generally includes a microporous, electrically conductive substrate, such as carbon fiber paper or carbon cloth, which provides mechanical support to the membrane and is employed for reactant distribution, thus serving as a gas diffusion layer (GDL).
The membrane electrode assembly is typically disposed between two electrically conductive flow field plates or separator plates and thereby forms a fuel cell. These flow field plates act as current collectors, provide support for the electrodes, and provide flow fields for the supply of reactants, such as fuel and oxidant, and removal of excess reactants and products that are formed during operation, such as product water. The flow fields comprise fluid distribution channels separated by landings which contact the electrodes of the MEA when assembled into a fuel cell. The landings act as mechanical supports for the gas diffusion layers and provide electrical contact thereto. A fuel cell stack comprises several fuel cells compressed between endplates.
In an effort to reduce the dimensions of the fuel cell stacks and to reduce the costs associated with the manufacturing of fuel cells while improving fuel cell performance, there is a trend to reduce the thickness of the flow field plates and/or to reduce the thickness of the membrane electrode assemblies by employing thinner, more porous materials for the gas diffusion layers (GDLs).
Reducing the thickness of the flow field plates might involve reducing the depth of the flow field channels which might require increasing the width of the flow field channels to ensure an adequate flow of reactants through the channels. This, in combination with the trend of employing thinner or more porous gas diffusion layers which are less stiff, might trigger the need to provide more support to the GDL material in order to prevent the material from deflecting into the flow field channels under compressive load and to ensure an appropriate contact pressure between the GDL and the membrane. If the deflection of the diffusion layer material is not prevented, channels become obstructed, thus impairing the distribution of reactants and/or removal of reaction products and adversely affecting fuel cell performance. Also, as discussed in “Characterisation of mechanical behavior and coupled electrical properties of polymer electrolyte membrane fuel cell gas diffusion layers” by J. Kleemann, F. Finsterwalder and W. Tillmetz (Journal of Power Sources 190 (2009) pg. 92-102) a minimum contact pressure between the GDL and the membrane in the area corresponding to the channel center is regarded as critical in terms of electrical losses within the fuel cell.
The problem of the gas diffusion layers intrusion into the flow field channels and maintaining an adequate contact pressure between the catalyst coated membrane (CCM) and the gas diffusion layers has been generally addressed by controlling the size (width) of the landings in the flow field plate and respectively the size of the flow channels. Simply increasing the landing area and/or the number of landings in a flow field design or decreasing the width of the flow channels may improve the mechanical support of the adjacent fluid diffusion layers but it also adversely affects fluid access to and from the fluid diffusion layer.
The problem of the intrusion of gas diffusion layers into the flow field channels is addressed for example in the U.S. Pat. No. 6,007,933 which describes the use of support members such as meshes or expanded metals to provide enhanced stability to the diffusion layers. A first side of a support member abuts the flow field plate face, and a second side of the support member abuts the resilient gas diffusion layer. The support member is formed with a plurality of openings. Because of the additional support member placed between the flow field plate and the gas diffusion layer, the resilient gas diffusion layer is restrained against entering the open-faced flow channels of the flow field plate under the compressive force applied to the fuel cell assembly. However, this approach involves using additional components which increase the cell thickness, its complexity and cost.
In another example, U.S. Pat. No. 6,541,145 describes a flow field design for a flow field plate comprising fluid flow channels having an average width W and separated by landings, the fluid flow channels being configured such that unsupported rectangular surfaces of the fluid diffusion layer have a length L and a width W with the ratio L/W being less than about 3. This approach solves the problem of improving the mechanical support for weak fluid diffusion layers, but involves a more complex configuration of the fluid flow field and does not address the problem of maintaining the contact pressure between the membrane and the electrodes.
Accordingly, there still remains a need for solving the problem of the gas diffusion layers intrusion into the flow field channels while ensuring an adequate contact pressure between the CCM and the gas diffusion layers. Embodiments of the present invention address this perceived need and provide further related advantages.
Briefly summarized, a flow field plate for an electrochemical fuel cell comprises a first flow field surface, an opposing second surface, at least one flow channel formed in the first flow field surface and at least one landing formed in the first flow field surface adjacent to the flow channel, wherein the landing comprises a main surface, a first protrusion extending from the main surface at a first edge thereof and a second protrusion extending from the main surface at the second edge thereof.
In particularly advantageous embodiments, the main surface of at least one of the landings of the first flow field surface has a curved shape. In some other embodiments, the main surface of at least one landing of the first flow field surface has a flat shape.
In particularly advantageous embodiments, the first protrusion extending from the main surface of the landing has a rounded shape with a predetermined radius of curvature. In some embodiments both protrusions extending from the main surface of the landing have a rounded shape with the first protrusion having a first predetermined radius of curvature and the second protrusion having a second predetermined radius of curvature. The first radius of the first protrusion is preferably equal to the second radius of the second protrusion.
In some other embodiments, the first protrusion extending from the main surface of at least one landing of the first flow field surface has a rounded shape and the second protrusion extending from the main surface of that landing has a flat shape. Alternatively both the first and the second protrusions extending from the main surface of at least one landing of the first flow field surface have a flat shape.
Furthermore, is some embodiments, at least one landing of the first flow field surface or each landing of the first flow field surface comprise at least one third protrusion extending from its main surface located between the first and the second protrusions. In some embodiments this third protrusion has a flat shape and in some other embodiments it can have a rounded shape. This third protrusion extending from the main surface of a landing can have the same size and shape as the first and the second protrusions extending from the main surface of the landing at its edges or it can have a different size and/or shape.
The flow field plate according to embodiments of the present invention can comprise a graphitic, carbonaceous or metallic material, or combinations thereof.
In some embodiments, the opposing second surface of the flow field plate is also provided with flow channels separated by landings, with at least one landing comprising a main surface, a first protrusion extending from the main surface at a first edge thereof and a second protrusion extending from the main surface at a second edge thereof.
The main surface of at least one landing on the opposing second surface of the flow field plate can have a curved or a flat shape and the first and the second protrusions on that landing can each have a rounded or a flat shape. The main surface of at least one landing on the opposing second surface of the flow field plate can further comprise at least one third protrusion between the first and the second protrusions, the third protrusion having a flat or a rounded shape. The third protrusion of each landing can have the same size and shape as the first or the second protrusion which extend from the main surface of that landing.
An electrochemical fuel cell is further disclosed, the fuel cell comprising:
The main surface of the landing can have a curved or a flat shape. The first or the second protrusion extending from the landing can have a rounded or a flat shape. In some embodiments, the first and the second protrusion can have the same shape and size.
In some embodiments, the main surface of the landing can further comprises at least one third protrusion between extending therefrom between the first and the second protrusions.
These and other aspects of embodiments of the invention will be evident upon reference to the following detailed description and attached drawings.
In the following description, certain specific details are set forth in order to provide a thorough understanding of the various embodiments. However, one skilled in the art will understand that embodiments of the invention may be practiced without these details. In other instances, well-known structures associated with fuel cells, fuel cell stacks, and fuel cell systems have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments.
Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to”. Also, reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
The flow field plate according to a particularly advantageous embodiment of the unit cell described in the present invention is illustrated in
According to the aspects of the present invention, the pressure created on the anode GDL and respectively on the cathode GDL by the protrusions of the flow field plate landings prevents the intrusion of the anode GDL and cathode GDL into the flow field channels. This is illustrated in
Another embodiment of the present invention refers to a flow field plate 508 having two flow field surfaces 503 and 505 provided with landings which have the shape illustrated in
A person skilled in the relevant art would easily understand that in other embodiments, the flow field plate landings can have more than three protrusions. The number of protrusions depends on the size of the flow field plate landing, with more protrusions being preferably used for landings having a larger width W. In some embodiments, the protrusions at the periphery of the landing can have a flat shape and the protrusion at the center of the landing can have a rounded shape. Any variations in the shape of the protrusions are possible with more or all protrusions having a rounded shape or with more or all protrusions having a flat shape.
The resulting contact pressure at the interface between the CCM and the anode and cathode GDLs for the embodiment illustrated in
Furthermore, the present flow field plate design diminishes the GDL intrusion into the flow field channels as shown by the modelling results illustrated in
In all the embodiments of the present invention, the illustrated flow field plates can be made of graphite or metal.
Similar to the embodiment illustrated in
In any of the described embodiments some protrusions on the landings of a flow field plate can have a flat surface while others can have a rounded shape. A person skilled in the relevant art would easily understand that the rounded shaped protrusions are preferred over the flat shaped protrusions because they allow a better contact between the GDL and the flow field plate.
In any of the described embodiments, the anode and the cathode catalysts can be deposited on the anode GDL and respectively on the cathode GDL instead of being deposited on the membrane (CCM) to form an MEA.
Embodiments of the present invention have the advantage that allows an increased contact pressure between the GDL and CCM independent of the GDL material (either soft or more rigid) which reduces the contact resistance between them and therefore improves the fuel cell operational performance.
Another advantage is that because the present design of embodiments of the flow field plates demonstrates an improved contact pressure between the GDL and the CCM, the flow channels can be made wider which allows a thinner construction of the flow field plates. Furthermore a smaller compression force is required for compressing the GDL and the CCM.
All the drawings referenced in the present description use the similar numbers for the elements having the same or similar function in the represented embodiments.
From the foregoing, it will be appreciated that, although specific embodiments have been described herein for the purpose of illustration, various modifications may be made without departing from the spirit and scope of the invention. U.S. Provisional Application 62/551,109, filed Aug. 28, 2017, is incorporated herein by reference, in its entirety. Accordingly, the invention is not limited except by the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/047822 | 8/23/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62551109 | Aug 2017 | US |
