Patent Application
20080138665
This invention relates in general to fuel cells, and in particular to fuel cells using membrane electrode assembly stacks.
A typical fuel cell system includes a power section in which one or more fuel cells generate electrical power. A fuel cell is an energy conversion device that converts hydrogen and oxygen into water, producing electricity and heat in the process. Each fuel cell unit may include a proton exchange member (PEM) at the center with gas diffusion layers on either side of the proton exchange member. Anode and cathode catalyst layers are respectively positioned at the inside of the gas diffusion layers. This unit is referred to as a membrane electrode assembly (MEA). Separator plates (also referred to herein and flow field plates or bipolar plates) are respectively positioned on the outside of the gas diffusion layers of the membrane electrode assembly. This type of fuel cell is often referred to as a PEM fuel cell.
The reaction in a single MEA typically produces less than one volt. Therefore, to obtain operating voltages useful in most applications, a plurality of the MEAs may be stacked and electrically connected in series to achieve a desired voltage. Electrical current is collected from the fuel cell stack and used to drive a load. Fuel cells may be used to supply power for a variety of applications, ranging from automobiles to laptop computers.
It is recognized that for certain applications, such as stacks used for automotive drives, there are limitations with existing PEM Fuel Cells due to excessive weight, volume, and cost. One reason for this is due to the thickness and weight of the flow field separators. Machined graphite, carbon composite, and metals are materials commonly used for flow field separators. These material options may suffer from either excessive volume or weight. This limitation leads to heavy or bulky fuel cell stacks, as typically there are many separators in each stack. Furthermore, it is difficult to make these separators thin and robust. Breakage and cracking have been issues with graphite and carbon composite based separators. Small defects can lead to breakage and catastrophic failures. Thin, light weight metal plate separators can bend easily and remain deformed. There have been many attempts to improve the performance of flow field separators, but it has been difficult to find a good balance between cost, thickness, weight, and toughness.
Even where the thickness of the flow field separators can be reduced, there are still space constraints in some applications that make it difficult to adapt fuel cells to practical designs. For example, some electric drive motors used in automobile applications may require electrical potentials as high as 100 volts or more. In order for a fuel cell system to provide this potential without expensive power conversions, the fuel cell stack would require a large number of MEAs stacked together, making the fuel cell stack larger than desirable.
Other design requirements limit how compact a fuel cell system can be. For example, gases and fluids need to flow through the stack in order to power the cells and to regulate the cell temperature. The internal flow passages and external plumbing needed to accommodate these gases and fluids may make it difficult to produce a fuel cell assembly that is easy to integrate in a space-constrained environment such as an automobile. However, the potential benefit resulting from practical, fuel cell powered automobiles is great, so cost effective and robust solutions to these limitations are desirable.
The present disclosure is directed to methods, systems, and apparatus for forming a proton exchange membrane (PEM) fuel cell stack. In one embodiment of the invention, a fuel cell assembly includes a membrane electrode assembly (MEA) stack which has a plurality of stacked planar membranes. The MEA stack further includes gas passageways arranged so that anode and cathode gases flow perpendicular to the planar membranes between a first side and a second side of the fuel cell assembly. Anode gas inlet and outlet ports and cathode gas inlet and outlet ports are disposed on the first side of the fuel cell assembly and coupled to the gas passageways of the MEA stack.
In more particular embodiments, the planar membranes are arranged substantially perpendicular to the ground in an operational configuration of the fuel cell assembly. In such an arrangement, the anode gas outlet port may be closer to the ground than the anode gas inlet port in the operational configuration, and/or the cathode gas inlet port may be closer to the ground than the cathode gas outlet port in the operational configuration.
In other, more particular embodiments, the (MEA) stack further includes coolant passageways arranged so that coolant flows perpendicular to the planar membranes. In such a case, the fuel cell assembly may further include coolant inlet and outlet ports disposed on the second end of the fuel cell assembly and coupled to the coolant passageways. In another arrangement, the fuel cell assembly further includes an anode gas manifold and a cathode gas manifold disposed on the first side of the fuel cell assembly. In one arrangement, the anode gas manifold is disposed between the MEA stack and the cathode gas manifold, and the MEA stack may further include a first compression member proximate the anode gas manifold.
In another arrangement, the cathode gas manifold is disposed between the MEA stack and the anode gas manifold, and the MEA stack may further include a first compression member proximate the cathode gas manifold. In one arrangement, the fuel cell assembly further includes a coolant manifold disposed on a second end of the fuel cell assembly, and the MEA stack further includes a second compression member proximate the coolant manifold. The MEA stack may further include a fastening member connecting the first and second compression members, and the fastening member is disposed in one of the gas passageways. The cathode gas manifold may include upper and lower plenums respectively coupled to the cathode gas outlet and inlet ports. Liquid drainage ports may be included in at least one of the upper and lower plenums of the cathode gas manifold. The anode gas manifold may also include upper and lower plenums respectively coupled to the anode gas inlet and outlet ports, and liquid drainage ports may be included in at least one of the upper and lower plenums of the anode gas manifold.
In other, more particular embodiments, the MEA stack includes a plurality of plate assemblies stacked together. Each plate assembly includes an anode plate, a cathode plate, and an MEA disposed between the anode and cathode plates. One of the anode and cathode plates is thinner than the other one. In one configuration, the MEA stack comprises a plurality of plate assemblies stacked together, each plate assembly comprising an anode plate, a cathode plate, and an MEA disposed between the anode and cathode plates, and wherein at least one the anode and cathode plates have first flow field features of a first uniform depth on a side facing the MEA and second flow field features of a second uniform depth on a side facing away from the MEA. In one configuration, the first and second uniform depths are substantially equal.
In another embodiment of the invention, a fuel cell assembly includes a membrane electrode assembly (MEA) stack having stacked planar membranes. The stacked planar membranes are arranged substantially perpendicular the ground in an operational configuration of the fuel cell assembly. The MEA stack further includes anode and cathode gas passageways arranged so that anode and cathode gases flow perpendicular to the planar membranes. Anode gas inlet and outlet ports are capable of being respectively coupled to external anode gas sources and sinks. The anode gas outlet port is closer to the ground than the anode gas inlet port in the operational configuration. Cathode gas inlet and outlet ports are capable of being respectively coupled to external cathode gas sources and sinks. The cathode gas inlet port is closer to the ground than the cathode gas outlet port in the operational configuration. An anode gas manifold couples the anode gas inlet and outlet ports to the anode gas passageways of the MEA stack, and a cathode gas manifold couples the cathode gas inlet and outlet ports to the cathode gas passageways of the MEA stack.
In more particular embodiments, the cathode gas manifold includes upper and lower plenums respectively coupled to the cathode gas outlet and inlet ports, and may include liquid drainage ports in at least one of the upper and lower plenums of the cathode gas manifold. In another arrangement, the anode gas manifold includes upper and lower plenums respectively coupled to the anode gas inlet and outlet ports, and may include liquid drainage ports in at least one of the upper and lower plenums of the anode gas manifold.
In other, more particular embodiments, the anode gas manifold and cathode gas manifold are both coupled to a first end of the fuel cell assembly. The (MEA) stack may further include coolant passageways arranged so that coolant flows perpendicular to the planar membranes. A coolant manifold may be coupled to a second end of the fuel cell assembly opposite the first end of the fuel cell assembly. In one arrangement, the anode gas manifold is between the MEA stack and the cathode gas manifold and the MEA stack may further include a first compression member proximate the anode gas manifold. In another arrangement, the cathode gas manifold is between the MEA stack and the anode gas manifold, and the MEA stack may further include a first compression member proximate the cathode gas manifold. In such an arrangement, a coolant manifold is coupled to a second end of the fuel cell assembly opposite the first end of the fuel cell assembly, and the MEA stack further includes a second compression member proximate the coolant manifold. The MEA stack may further include fastening members connecting the first and second compression members, and the fastening members are disposed in at least one of the anode and cathode gas passageways. In this arrangement, the cathode gas manifold may further include conduits coupling the anode gas inlet and outlet ports with the anode gas manifold.
In other, more particular embodiments, the MEA stack includes a plurality of plate assemblies stacked together. Each plate assembly includes an anode plate, a cathode plate, and an MEA disposed between the anode and cathode plates. One of the anode and cathode plates is thinner than the other one and/or at least one the anode and cathode plates have first flow field features of a first uniform depth on a side facing the MEA and second flow field features of a second uniform depth on a side facing away from the MEA. In one configuration, the first and second uniform depths are substantially equal.
In another embodiment of the invention, a method of making a fuel cell assembly involves stacking a plurality of planar membranes into a membrane electrode assembly (MEA) stack so that anode and cathode gases flow perpendicular to the planar membranes between a first side and a second side of the fuel cell assembly. Anode gas inlet and outlet ports and cathode gas inlet and outlet ports are placed on the first side of the fuel cell assembly so that the anode gas inlet and outlet ports and the cathode gas inlet and outlet ports are coupled to the gas passageways of the MEA stack.
In more particular embodiments, the method further involves operating the fuel cell assembly in a configuration where the planar membranes are arranged substantially perpendicular the ground. In such an arrangement, placing the anode gas inlet and outlet ports on the first side of the fuel cell assembly involves placing the anode gas outlet port closer to the ground than the anode gas inlet port in the operational configuration. Placing the cathode gas inlet and outlet ports on the first side of the fuel cell assembly may also involve placing the cathode gas inlet port closer to the ground than the cathode gas outlet port in the operational configuration. The method may also involve placing coolant inlet and outlet ports on the second end of the fuel cell assembly so that the coolant inlet and outlet ports are coupled to coolant passageways of the MEA stack.
In other, more particular embodiments, the method further involves attaching an anode gas manifold and a cathode gas manifold on the first side of the fuel cell assembly. Attaching the anode gas manifold and the cathode gas manifold on the first side of the fuel cell assembly may involve attaching the cathode gas manifold between the MEA stack and the anode gas manifold. In one arrangement, stacking the planar membranes into the MEA stack involves placing each membrane between an anode and a cathode plate to form a plate assembly (where one of the anode and cathode plates is thinner than the other), and stacking the plate assemblies to form the MEA stack.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described representative examples of systems, apparatuses, and methods in accordance with the invention.
The invention is described in connection with the embodiments illustrated in the following diagrams.
In the following description of various exemplary embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, as structural and operational changes may be made without departing from the scope of the present invention.
The present invention relates to fuel cell assemblies, and particular embodiments are described in the context of proton exchange member (PEM) fuel cell systems that are suitable for applications requiring high power densities and compact, lightweight packaging. Such applications include, but are not limited to, electric vehicle drive power, portable generators, vehicle power generators, or any other situation where the fuel cell stack might need to be small and light. In particular, mobile applications often require that the fuel cell system be compact and lightweight, and may impose form factors on the system that cannot be satisfied using traditional fuel cell stack designs.
Some features described in relation to embodiments of the present invention are intended to optimize the form factor of a fuel cell by reducing the dimension in the direction perpendicular to the plane of the fuel cell membranes. The size of this dimension is driven in part by the thickness of the stack of membrane electrode assemblies (MEAs) and separator plates positioned between the MEAs that form the fuel cell stack. This stack has a thickness defined by the nominal voltage of a single MEA, the required stack voltage, the thickness of the bipolar plates, and the thickness of the MEAs. Other components that may also add to the dimension of the final product. These components include current collectors electrically coupled to the ends of the stack, compression members that hold the stack together, and manifolds or other fluid-transport structures that deliver fuel, air, and coolant to the stack.
An example of how the dimensions of the stack components and voltage drive the ultimate stack system dimension, consider a hypothetical stack that must deliver approximately 100 volts using MEAs that nominally deliver 0.7 volts each. This will require 100/0.7=143 MEAs. Each plate assembly has an MEA sandwiched between a cathode plate and an anode plate. Except for plate assemblies at the end of the stack, the cathode plate of each plate assembly touches the anode plate of the adjacent plate assembly on one side, and the anode plate of the plate assembly touches the cathode plate of the plate assembly on the other side. Coolant is introduced between the touching cathode-anode plates of adjacent plate assembly. If the thickness of the plate assembly is 0.100 inches (0.254 cm) when compressed into the stack, then the thickness of the entire stack would be 143*0.10=14.3 inches (36.3 cm).
One approach to reducing the size of the stack is to reduce the thickness of the bipolar plates. Even reducing the thickness of each plate in the above example by 0.001 inches (0.00254 cm) will result in the total stack being reduced by (0.001+0.001)*143=0.286 inches (0.726 cm). However, there is a practical limit of how thin the plates can be made. The plates must contain small, closely spaced channels that distribute fluids to the gas diffusion layers (GDL) of the MEA, and must be thick enough to accommodate these channels. The plates must also have sufficient strength to prevent damage during assembly and failure during use. Some aspects of the present disclosure are directed towards reducing the thickness of the bipolar plates, and towards making the plates easier and cheaper to manufacture.
Even when thickness of the plates is reduced, the design parameters may still cause the thickness of fuel cell stack to be larger than desired. This is true where the stack voltage is relatively high, but the dimension of the system that includes the stack height (e.g., measured from positive to negative end of the stack) must be relatively small. Therefore, in order to accommodate such a design, the present disclosure describes a fuel cell that includes two or more stacks within a single pressure plate. The stacks may be arranged so that adjacent stacks have opposite polarities. One current collector is coupled to one end of a stack, and the other current collector is coupled to one end of another of the stacks. The stacks may be arranged so that adjacent stacks have opposite polarity. This allows the ends of adjacent stacks (or at least those ends not coupled to a current collector) to be electrically shunted together, such as by using a coupling plate or bar. In this arrangement, the current stays within the stack assembly at all points except where it exits at the current collectors. Depending on the number of stacks used, the current collectors may be both on the same end of the fuel cell assembly, or there may be one collector on the first end, and the other collector on the second end.
Turning now to
As seen in
The anode gas ports 136, 138 are connected to the anode gas manifold 110 by way of the cathode gas manifold 112, therefore features are provided in the manifolds 110, 112 that allow flow of anode gases through the outer cathode gas manifold 112 and into the inner anode gas manifold 110. These features are discussed in greater detail in relation to
The cathode gases take a similar path from the cathode inlet port 142, into the cathode gas manifold 112, through the anode gas manifold 110, compression plate 108, and finally stack assembly 106. One difference is that the incoming cathode gases are first distributed to a plurality of passageways 149 through the anode gas manifold 110. These passages 149 are coupled to passages 151 in the compression member 108. The stack assembly 106 contains passages 153 that receive the cathode gases from the passages 151 and distribute the gases to the cathode gas flow fields in the separation plates. Cathode gases exit the flow fields at passages 152 where they are carried through passages 150 in the compression member 108, and eventually into the cathode gas manifold 112 by way of the passages 148 in the anode gas manifold 110. Cathode gases exit the cathode gas manifold 112 at the exit port 140.
As will be apparent in light of the above description, the gas ports 136, 138, 140, 142 are placed on one side of the fuel cell system 100. This may provide advantages in some installations, particularly where it is desirable to minimize the length and complexity of gas lines routed to the system 100. The coolant side of the system is similarly arranged, with all inlets and outlets placed on one side of the assembly. Generally, the coolant manifold 102 includes ports 120 and 122 (see
The compression member 104 contains fluid passageways 128, 130 used to carry respective incoming and outgoing coolant to the stack assembly 106. As these passageways 128, 130 distribute/collect fluids from/to the plenums 126, 124, they may be referred to herein as manifold passages, even though they are not formed in the manifold 102 itself. The stack assembly 106 contains inlet coolant passages 132 (see
In the illustrated system 100, coolant is routed through the stack assembly 106, compression plate 104, and coolant manifold 102. One advantage to this is that the coolant supply and return lines are connected on a single side of the system 100, the exterior portion of the coolant manifold 102. There may be additional benefits in having the coolant restricted to these components, and this is due in part to the design of the stack assembly 106.
As was described above, the stack assembly 106 contains more than one stack, two stacks in this particular embodiment. In reference now to
The arrangement of stacks 202, 204 in the stack assembly 106 results in current flow in a U-shaped path, as indicated by arrow 212. It will be appreciated that the stacks 202, 204 will have substantially different potentials at all locations except at the coupling plate 210. Therefore, it may be preferable in some situations to dispose an electrical insulator 214 between the stacks 202, 204 and/or their respective collector plates 206, 208. Under the ideal situation, physical separation is provided by placement of the stacks 202, 204 which are held apart by the non-conductive compression plates (e.g., plates 104 and 108 if
As was previously mentioned, the coolant does not flow through both ends of the stack assembly 106, but enters and exits through the same end. This is shown in
Because the anode and cathode flows are both primarily gaseous, there is minimal risk in these fluid transfer passages having a short fluid coupling path between the collectors 206, 208. The fluid path of the cathode gases (e.g., air) is indicated by arrows 218 and 220 in
As seen in
However, this use of multiple stacks as described herein need not be limited to two stacks. For example,
The stack assembly 230 may include two insulators 246 and 248, and have two points of high potential difference, indicated by areas 250 and 252. Note that, because the areas of closely spaced conductors in regions 250, 252 of electrical potential are on both sides of the stack 230, the advantage of having the coolant flow on just one side of the stack (see, e.g.,
The concepts incorporated in the stack assembly 230 of
As described above in relation to
This view of the cathode gas manifold 112 also shows the configuration of the input and output plenums 146, 144 (also seen in
The gases moving through the manifold plenums 144, 146 may include water vapor. As such, there may be conditions where some of the moisture condenses and collects in the gas flow paths. Because the plenums 144, 146 may have low points in their respective return and feed paths, drain features may be included in the manifold 112. As indicated by broken lines, locations 312 and 314 may be used to place drain ports in the supply plenum 146, and location 316 may be used to place a drain support for the return plenum 144.
As discussed above, the conduits 302, 304 provide a passageway to couple anode gases from the external ports 136, 138 to the anode gas manifold 110. In reference now to
The manifold 110 also includes passages 148, 149 that allow cathode gases to flow between the cathode manifold 112 and manifold passages 150, 151 of the compression member 108, where they are eventually coupled to distribution passages 152, 153 of the stack assembly 106 (see
The other side of the anode gas manifold 110 is shown in the perspective view of
Turning now to
The compression plates 104, 108, are typically designed to be electrically isolated from the stack assembly 106, and therefore may be formed from a material that is not electrically conductive. For example, the plates 104, 108 could be machined from a polymer resin or similar material, which also reduces weight and machining costs. In other embodiments, the compression members 104, 108 could be formed from metal and/or other conductive materials, and an electrical insulator placed between the plates 104, 108 and the stack assembly 106. The compression plates 104, 108 are clamped around the stack 106, thus sealing off the gas flow passages to prevent leakage. In many stack/compression plate systems, these clamping forces are provided by hardware such as bolts or tie rods that pass through both the stack and compression plates. To accommodate this hardware, the stack and compression plates may include dedicated holes/voids for passing the compression hardware. One disadvantage to this, however, is that each of these voids provided for the compression hardware must include their own seals. These seals are needed to prevent leakage from gas and cooling manifolds into the hardware voids, which could result in these gases and/or fluids leaking from the fuel cell stack assembly. These seals may also help ensure there are no cross manifold leakages, particularly between the anode and cathode gas sections.
Systems that have dedicated voids through which to pass compression hardware must increase the size of the fuel cell stack assembly to accommodate the compression hardware, additional space to account for manufacturing tolerances, and the area needed to place a seal. For example, assume a stack design used 0.375 in. (0.953 cm) diameter compression hardware members (e.g., tie rods), that each take up 0.110 sq. in. (0.710 sq cm) of cross sectional space. The hole used to accommodate the hardware would have a 0.406 in. (1.03 cm) diameter, and would require an additional 0.25 in. (0.64 cm) of sealing surface, thus making the space consumed 0.906 in. (2.30 cm) diameter, or 0.645 sq. in (4.16 sq cm). In any design that uses compression hardware that goes through the stack, the 0.110 sq. in. (0.710 sq cm) of space consumed by the compression hardware must be accommodated for, so the additional space needed to accommodate seals for dedicated hardware voids is 0.645−0.110=0.545 sq. in (3.52 sq cm). If the design used 10 compression hardware members, then the total cross sectional area increase for the stack is 5.45 sq. in (35.2 sq cm).
The use of dedicated compression hardware void also impacts the total volumetric dimension of the system as well. For example, if it was assumed that the compression plates and fuel cell stack assembly were 15 inches (38 cm) thick/high, then the total volume needed to accommodate such a design is 5.45 sq. in.*15 in=80.3 cubic inches (1316 cubic cm). It will also be appreciated that with this increased volume comes increased weight, both because of the weight of gaskets, and the weight associated with increase peripheral sealing areas needed for the hardware voids.
Both volume and weight are at a premium in fuel cells that are designed for mobile environments. Therefore, to economize on this space consumed by dedicated compression hardware voids, the compression plates 104, 108, and stack assembly 106 shown in
As shown in
Special design considerations may be required when deploying compression hardware 600, 602, 604 inside fluid or gas passageways. For example, the compression plate may require attachment surfaces 606, 608 may be provided in the gas passages 147, 150 of the compression plate 108 in order to transfer compressive forces from the nut 604 and tie rod 600 to the rest of the compression plate 608. The inclusion of these attachment surfaces 606, 608 may require enlarging the respective passageways 147, 150 to compensate for the lost cross-sectional fluid flow area.
Another factor to consider when using the gas passageways as hardware throughways is that the compression hardware 600, 602, 604 must not allow the fluids or gases to escape. For example, this may involve using a fluid seal at hardware attachment points that might leak gas outside the respective flow transfer paths. For example, the illustrated inserts 602 may be exposed to air or fluid on the back side of compression plate 104, and therefore may include an o-ring or other compliant seal on the surface 610 that contacts the compression plate 104. In the illustrated example, however, the nuts 604 do not require sealing, because this end of the tie rod 600 is encompassed within the anode gas flow area that includes the voids 147, 158, and anode gas plenum 502 (see
One factor to take into account, particularly when deploying metal hardware within the anode gas passageway 147, 158, is to guard against hydrogen embrittlement or corrosive effects that may occur to metals that are exposed to hydrogen gas in the anode gas passageways 147, 158. One way to overcome these effects is to use a material such as titanium or corrosion-resistant steel that is resistant to corrosive effects of hydrogen at the temperatures, pressures, and fastener tensile stresses seen in a PEM-type fuel cell. In other configurations, the hardware 600, 602, 604, 605 may be coated or sealed (e.g., using a heat shrinkable material) for protection against the effects of hydrogen gas exposure. Additionally, it may be possible to use other fluid passageways instead of the anode gas passageways 147, 158, such as the cathode passageways 152, 153 or coolant passages 132.
It will be appreciated that the nuts and inserts 604, 602 that retain the compression hardware 600 in the illustrated arrangement are not accessible from the exterior of the fuel cell system 100, because the cooling manifold 102 and anode gas manifold 108 prevent immediate access to this hardware. This arrangement has some advantages, because it prevents inadvertent gas leaks that might be caused by somebody unknowingly loosening the compression hardware from the outside of the fuel cell 100 and thereby causing a gas or fluid leak.
The compression member 108 includes mounting features 620, 622 (e.g., inserts) that receive hardware fastening the anode and cathode gas manifolds 110, 112. Features 620 receive hardware that is passed through holes 320, 420 of manifolds 112, 110. Similarly, compression member 104 includes features 630 (e.g., a threaded hole or an insert on the opposite side of member 104) for fastening the coolant manifold 102 to the compression member 104.
As previously described regarding
The MEA 702 includes a PEM-type membrane 704 which is sandwiched between an anode gas diffusion layer (GDL) 706 and a cathode GDL 708, which are located on respective anode and cathode sides of the membrane 704. An anode plate 710 includes flow field features, seen here as channels 712, for evenly distributing hydrogen to the anode GDL 706. Besides distributing hydrogen, the anode plate 710 is electrically conductive, and removes electrons from the MEA 702 to either a current collector, adjacent plate assembly 700, or some other current carrying element (e.g., coupling plate or current shunt). The side 714 of the anode plate 710 facing away from the MEA 702 is flat/smooth. This can reduce manufacturing costs of the plate 710, because the plate 710 only needs flow field features 712 formed on the side of the plate 710 that faces the MEA 702.
Adjacent to the cathode GDL 708 is the cathode plate 716, which also includes flow field features 718 for distributing air to the cathode GDL 706. The cathode plate 716 is conductive and delivers electrons to the MEA 702. The opposite side 722 of the cathode plate 716 includes coolant flow field features 720 for carrying coolant between adjacent plate assemblies 700. The far side 722 of the cathode plate 716 is in physical and electrical contact with the anode plate 710 of an adjacent plate assembly 700. The exception to this is when the plate assembly 700 is at the end of the stack, then it may be coupled to a current collector or some other current carrying element.
The coolant flow field 720 delivers coolant that cools both the cathode plate 716 in which the flow field 720 is etched/machined, but also the anode plate 710 of the adjacent plate assembly 700. Because the cathode plate 716 includes features on both sides, the cathode plate 716 is typically thicker than the anode plate 714. One advantage of including the cooling flow fields 720 on the cathode plate 716 only is that the features on both sides of the cathode plate can be made the same depth. Therefore, in situations where the flow fields are formed via etching, this requires only a single precision etching operation to form the features on the entire plate 716. If other features such as manifold holes and voids are etched (e.g., instead of machining or stamping the holes) this may require additional etching steps. However creating holes by etching requires far less precision than is required to etch flow fields 718, 720, therefore cost savings can still be realized. As will be described in greater detail elsewhere herein, the anode plate 710 also can be formed with flow fields 712 of a single depth, and includes gas distribution features that allow the thickness of the anode plate 710 to remain near its theoretical minimum, given design considerations of strength and heat transfer.
In order to gain a better understanding of features of the anode and cathode plates 710, 716,
The anode plate 710 also includes anode gas manifold holes 804 that facilitate distribution of hydrogen through all plates of the stack. In addition, the plate 710 includes features that allow distribution of hydrogen from the manifold holes 804 to the flow field 712, while still allowing for sealing between the plate 710 and an MEA. Generally, this involves coupling the manifold holes 804 to the flow field 712 via a path that causes the gas to contact both sides of the plate 710. That flow path includes distribution voids 806 disposed between the flow fields 712 and the manifold holes 804. The voids 806 are coupled to the flow fields 712 via channels 808 and allow hydrogen to pass therebetween. Note that the flow field channels 808 do not pass directly to the manifold holes 804. Further, as will be described in greater detail below, there are no channels on either side of plate 710 that couple the distribution voids 806 to the manifold holes 804.
By terminating the channels 808 at the distribution voids 806, the area immediately surrounding the perimeter of the anode gas manifold holes 804 can remain free of flow channels to facilitate a tighter perimeter seal. This also allows for the anode gas manifold holes 804 to retain a consistent sealing surface on the other side, as will be seen further hereinbelow. Alternatively, the area surrounding the gas manifold holes 804 (and other manifold holes in the plates) may include features (e.g., a 10 mil (0.25 mm) channel) for containing a gasket that seals the holes 804 from the MEA while allowing the coolant sides of the plates 710, 716 to contact each other in the assembly and the other sides of the plates 710,716 to contact the MEA.
Also seen in
In reference now to
Turning now to
In
Also visible in this view are the coolant flow fields 720 and channels 1104 that directly couple the flow fields 720 to the coolant manifold holes 1000. The coolant manifold holes 1000 on this side 722 of the cathode plate 716 are sealed by one or more gaskets seal around the gas manifold holes 1002, 1004 and the around the coolant manifold holes 1000 and flow field 720 together. Note that channels 1100, 1102 are formed on slightly thicker material, as represented by steps 1106 and 1108. In this way channels 1100, 1102 can interface tightly against the adjacent anode plate while allowing space for coolant flow/manifold seals and gas manifold seals on this side 722.
In order to better illustrate the flow of the gases and coolant between and into the plates,
The anode flow field 712 contacts the distribution void 806, which creates a flow connection from the first side of the plate 710 (e.g., the side facing the MEA 702) and the second side 714 of the plate 710 (e.g., the side facing away from the MEA 702, and facing the cathode plate 716a of an adjacent plate assembly 700a). Recall that from
Another advantage of using the illustrated arrangement relates to sealing between the plates 710, 716, and the MEA 702. Regarding the anode gas flow, the use of the void 806 and channels 1100, 808 allows a tight seal between adjacent members of the stack, represented by blocks 1206, 1208 representing seals created between the cathode plate 716 and the MEA 702. These sealing areas 1206, 1208 are made tight to prevent anode gases from leaking into the cathode flow fields 718. These blocks 1206, 1208 may represent a compliant sealing member, or may just indicate areas that allow smooth surface-to-surface interfaces (e.g., no machined flow channels) around the passage 1200. Similar sealing features 1202, 1204 are shown between the anode plate 710 and MEA 702, although preventing leakage here may not be as critical. Also features 1210, 1212 indicated sealing between the anode plate 710 and adjacent cathode plate 716a, which prevent leakage between anode gas and coolant flows.
Similar features in the cathode plates 716 provide of sealing around the cathode gas passages 1300 formed by manifold holes 1004, 802, as is shown in
The use of the void 1006 and channels 1102, 1108 allows a tight seal, represented by blocks 1306, 1308, to be created between the anode plate 710 and the MEA 702. These sealing areas 1306, 1308 need to be tight to prevent cathode gases from leaking into the anode flow fields 712. The blocks 1306, 1308 may represent a compliant sealing member, or may just indicate areas that allow smooth surface-to-surface interfaces (e.g., no machined flow channels) around the passage 1300. Other cathode passage sealing features 1302, 1304 are shown between the cathode plate 716 and MEA 702, as well as features 1310, 1312 between the cathode plate 716 and adjacent anode plate 710b that is part of adjacent plate assembly 700b.
In reference now to
It will be appreciated that the gas/fluid flow features shown in
The foregoing description of the exemplary embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather determined by the claims appended hereto.
