Abstract:
A system and method for aligning and reducing the relative movement between adjacent fuel cells within a fuel cell stack. The inter-cell cooperation between fuel cells along a stacking dimension is enhanced by one or more datum placed along the edge of a bipolar plate that makes up a part of a cell-containing assembly. The datum is shaped along a thickness that substantially coincides with the cell stacking dimension to avoid shifting between adjacently-stacked cells that may otherwise arise out of the occurrence of a significant acceleration along the dimension that defines the major surfaces of the plates, cells and their respective assemblies. By having the datum be integrally formed with numerous stacked cells, the need to affix individual tabs each plate is avoided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present disclosure relates generally to an improved design for assembling a fuel cell stack, and more particularly to a way to distribute an acceleration load over a fuel cell stack to secure and maintain the relative position of the fuel cells within the stack after exposure to impacts and other high acceleration loads. 
         [0002]    A significant benefit to using fuel cells to convert a fuel into usable electricity via electrochemical reaction is that it is achieved without reliance upon combustion as an intermediate step. As such, fuel cells have several environmental advantages over internal combustion engines (ICEs) for propulsion and related motive applications. In a typical fuel cell—such as a proton exchange membrane or polymer electrolyte membrane (in either event, PEM) fuel cell—a pair of catalyzed electrodes are separated by an ion-transmissive medium (such as Nafion™) in what is commonly referred to as a membrane electrode assembly (MEA). The electrochemical reaction occurs when a gaseous reducing agent (such as hydrogen, H 2 ) is introduced to and ionized at the anode and then made to pass through the ion-transmissive medium such that it combines with a gaseous oxidizing agent (such as oxygen, O 2 ) that has been introduced through the other electrode (the cathode); this combination of reactants form water as a byproduct. The electrons that were liberated in the ionization of the hydrogen proceed in the form of direct current (DC) to the cathode via external circuit that typically includes a load (such as an electric motor) where useful work may be performed. The power generation produced by this flow of DC electricity can be increased by combining numerous such cells into a larger current-producing assembly. In one such construction, the fuel cells are connected along a common stacking dimension—much like a deck of cards—to form a fuel cell stack. 
         [0003]    The delivery of the reactants to the MEA—as well as the removal of the byproduct water and the delivery of the cell-generated electrical current to the load—is facilitated through stacked engagement of the MEA, a gas-permeable diffusion medium (also called a gas diffusion medium (GDM)) and a multi-channeled bipolar plate. In addition to establishing a planar facing relationship with the MEA and GDM, the bipolar plate defines a manifold as part of a frame-like structure that is sized to be placed about the periphery of the MEA and GDM to facilitate the reactant, coolant and byproduct movement within the stack. 
         [0004]    Fuel cell stacks placed within vehicles must be able to withstand severe load changes from acceleration and deceleration of the vehicle, as well as from crashes, accidents and related impacts. In particular, in order to continue to perform after exposure to high acceleration loads (for example, up to 160 g or more) during disruptive events such as a vehicle crash, the position of the fuel cells that make up the stack must be retained relative to one another. In such events, a high shearing force may cause sliding between adjacent cells of the stack (especially within the X-Z plane of the aforementioned Cartesian coordinate system). Small displacements between individual cells is magnified over the height of a large stack assembly (for example, a 100 micron cell shift can result in a 30 mm cell block shift for a 300 cell stack assembly). Such problems may be exacerbated by cold start conditions where thermally-induced contraction may reduce the Y-axis compressive retention load that was placed on the cells during stack assembly, as well as by reduced inter-cell friction brought about by the use of surface treatments or inserts that may have low coefficient of friction attributes. 
         [0005]    One way to avoid automotive fuel cell inter-plate or inter-cell shifting during these high-acceleration events is to leave datum pins that are used in stack assembly coupled to the stack even after the assembling process is complete; in this way, the pins provide additional resistance to the shearing movement between the adjacently-stacked plates or cells. In the present context, these shearing or in-plane shifts between adjacent cells or plates are premised on the understanding that the cell or plate stacking axis is orthogonal to the direction of travel of the vehicle being powered by such stack. As such, the stacking axis may be along a substantially vertical (i.e., Y) Cartesean axis so that the majority of inter-cell or inter-plate movement sought to be minimized is in the X-Z plane. It will be appreciated by those skilled in the art that the particular orientation of the cells, plates and stack isn&#39;t critical, but rather that the means used to avoid or reduce such inter-cell or inter-plate shifting are preferably arranged in an orientation that maximizes such avoidance. While the use of conventional datum pins and related structures are effective at maintaining the relative stacking alignment of the cells or plates when exposed to a high acceleration in-plane load, they can significantly add to the cost of assembly of the stack. Their continued presence within the stack also militates against disassembly in the event one of the cells or other stack components needs to be removed for service. 
         [0006]    Another way to avoid automotive fuel cell inter-plate or inter-cell shifting during such a disruptive event is through the use of adhesives or supplemental support structure that can be formed between a housing wall and the stack. An example of this may be found in U.S. patent application Ser. No. 13/803,098 that was filed on Mar. 14, 2013 and entitled CELL RETENTION DESIGN AND PROCESS that is owned by the Assignee of the present application and incorporated herein by reference in its entirety; the approach taught therein uses an insertable adhesive-like potting compound between the lateral edges of the stacked plates and a rigid housing or related enclosure. Nevertheless, this approach is only applied after the cells and plates have been aligned and stacked, and therefore does nothing to help with the alignment of the cells and plates during the stacking process. Moreover, the permanent nature of the compound being used is not conducive to subsequent stack disassembly for repair or diagnostic analysis. 
         [0007]    Yet another approach involves welding (or otherwise attaching) a tab that projects laterally from one or more of the edges of the generally rectangular bipolar plate. These tabs may be made to engage with one another along the through-the-thickness (i.e., Y-axis) dimension such that the tendency of each cell or plate within the stack to move in response to a shearing (i.e., in-plane) force is resisted by the interfering contact of the tab and cutout. While effective at preventing inter-cell/inter-plate movement, each tab must be individually joined to its corresponding plate. 
       SUMMARY OF THE INVENTION 
       [0008]    According to one aspect of the present disclosure, a method of assembling a fuel cell stack that has an improved resistance to inter-cell shifting in response to a disruptive event is disclosed. The method includes arranging numerous bipolar plates along a stacking dimension and adding a potting material to at least one peripheral edge that is formed by the stacked plates; the resulting datum (also called datum structure) is possessive of an enhanced thickness dimension along the cell stacking dimension; the enhanced thickness corresponds to the number of stacked cells and plates of a particular group. Thus, an 8-plate group would have a corresponding 8-datum thickness, while a 16-plate or a 32-plate group would have a corresponding datum thickness. Preferably, the plates define at least one edgewise undulation to accommodate the complementary shape of the potting material. This way, the datum is secured to the stacked cells within a multi-cell group such that a snug, cooperative fit is formed between them. In the present context, the securing of the datum to the stacked cells within a group is via the cured potting material forming a bond with, around or otherwise coupled to the edge undulation on each of the cells. In one preferred from, the undulation is an outwardly-projecting tab that can be overmolded by the potting material. In turn, the potting material defines a shape such the outward projection formed thereby may fit into a complementary-shaped cutout or recess formed within a stack housing or related enclosure. In a preferred form, the potting material is built up along the stacking dimension to be as thick as numerous plates. In a more preferred form, the cooperation between the datum that is formed by the potting material and the various plates is through an overmolding of the potting material onto integrally-formed tabs that extend edgewise from the plate periphery. In this last embodiment, the multilayer thick datum formed by the potting material may be shaped to cooperate with a complementary-shaped lateral undulation formed within the stack enclosure or housing such that any shearing motion imparted to the various stacked plates is passed through the thick datum an into the housing to provide the increased resistance. One or more fixtures may be used to facilitate the stacking process, as well as form a mold cavity or shape at the plate lateral edge into which the potting material may be poured. In the present context, either the singular or plural recitation of such a fixture is deemed to be within the scope of the present invention. 
         [0009]    According to another aspect of the present disclosure, a method of assembling numerous fuel cells together is disclosed. Each cell includes an MEA placed facingly-adjacent to a bipolar plate that defines at least one integrally-formed edge extension therein. The method includes defining within a stacking fixture one or more mold shapes that are configured to receive a potting material. The fuel cells are arranged along a stacking dimension within the stacking fixture such that a liquid form of the potting material is poured into the mold such that upon curing, the potting material forms a datum that is secured to the various arranged fuel cells along their stacking dimension, thereby providing an increased resistance to inter-cell movement of the arranged fuel cells along a dimension that is substantially orthogonal to the stacking dimension. As discussed elsewhere, the number of cells that may be stacked into a module with a datum acting as the affixing or connecting point may be determined by other stacking needs of the fuel cell system; in one form, the number of cells within each arranged module may be in multiples of 8, such as 8, 16, 24 or 32, where limits on the upper bound of cells is dictated by the mechanical properties (such as shear strength) of the potting material. 
         [0010]    According to yet another aspect of the present disclosure, a fuel cell stack is disclosed. The stack includes numerous fuel cells arranged in an adjacently facing relationship along a stacking dimension (for example, the aforementioned Y-axis in a conventional Cartesian coordinate system), and a respective bipolar plate for each of the cells. A potting material is secured to the stacked, arranged fuel cells along their stacking dimension to provide an increased resistance to inter-cell movement along a dimension that has at least a component that is substantially orthogonal to the stacking dimension. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    The following detailed description of the preferred 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 and in which: 
           [0012]      FIG. 1  is a simplified exploded view of a fuel cell stack; 
           [0013]      FIG. 2  is a perspective cutaway view of a vehicle with the fuel cell stack of  FIG. 1 ; 
           [0014]      FIG. 3  is a simplified exploded view of a bipolar plate that is used in the fuel cell stack of  FIG. 1 ; 
           [0015]      FIG. 4  is a perspective view of a stacked fuel cell block prior to placement of a housing support structure therearound, where the protruding tabs and overmolded datum are placed along a lateral edge of the corresponding bipolar plates; 
           [0016]      FIG. 5A  shows an alternate embodiment of the placement of the protruding tabs and overmolded datum along the corners of a bipolar plate that is placed within a stacking fixture according to an aspect of the present invention; 
           [0017]      FIG. 5B  shows a detailed portion of the corner-placed datum of  FIG. 5A ; and 
           [0018]      FIG. 6  shows the use of a housing with a feature shaped to cooperate with the datum of  FIG. 4  in order to provide another form of supplemental inter-cell sliding resistance. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring first to  FIGS. 1 and 3 , a fuel cell stack  1  is shown, and includes a dry end unit plate  5 , a wet end unit plate  10  and a block of fuel cells  15  placed in stacking alignment between the end unit plates  5 ,  10 . Although not shown in detail, each fuel cell  15  within the block generally includes the anode, cathode, and membrane arranged together to form the generally planar sandwich structure of the MEA that is pressed between a pair of the gas-permeable electrically conductive diffusion media that serve to both deliver reactants (i.e., H 2  on the anode side of the MEA and O 2  (typically in the form of air) on the cathode side of the MEA as well as collect electrical current that is catalytically produced at the anode and cathode. Fuel cell  15  also includes bipolar plates (also referred to herein as bipolar plate assemblies)  17  that provide supporting structure to the MEA and diffusion media. Within the present context, the stacking dimension that corresponds to the height of the assembled stack  1  is defined along the Y-axis as shown, although it will be appreciated by those skilled in the art that such is a matter of convenience, and that any suitable linear dimension is equally suitable, depending on the orientation of the stack  1  during the assembly process. 
         [0020]    The numerous individual cells  15  within stack  1  are kept in place via enclosure or housing  20  made up of a pair of opposing end caps  25 ,  30 , sidewalls  35 ,  40  and rigid bracketing elements  45  disposed vertically along each of the sidewalls  35 ,  40  for securing the wet end unit plate  10  to the dry end unit plate  5 . In one form, the wet end unit plate  10  is fixedly secured to the opposing end caps  25 ,  30  while the dry end unit plate  5  is adjustably secured. This latter connection is particularly useful in stack forming situations, as the end-point secured position is not known until final assembly; this in turn allows the securing to be adapted to accommodate a range of possible end-point securing positions. By contrast, the fixed securing of the wet end plate  10  means that the positional relationship of the secured components to one another is substantially invariant. Additional details associated with shaped features that may be formed into one of more of end caps  25 ,  30  and sidewalls  35 ,  40  will be discussed in conjunction with  FIG. 6  below. 
         [0021]    Referring next to  FIG. 2 , vehicle  100  (for example, a car, van, bus, truck, or motorcycle) includes a fuel-cell based propulsion system  110  made up of an electric motor  120  that receives its electric power from the fuel cell stack  1  of  FIG. 1  that includes numerous individual fuel cells  15 . The propulsion system  110  may include one or more fuel storage gas vessels  130 ,  140 , as well as power converters or related electronics  150 , electrical storage devices (e.g., batteries, ultra-capacitors or the like)  160  and controllers that provide operational management, and any number of valves, compressors, tubing, temperature regulators, and other ancillary equipment. 
         [0022]    Any number of different types of fuel cells  15  may be used to make up the stack  1  of the propulsion system  110 ; these cells  15  may be of the metal hydride, alkaline, electrogalvanic, or other variants. In one preferred (although not necessary) form, the cells  15  are PEM fuel cells as discussed above, and it is with this configuration that the remainder of the present disclosure is based. In one preferred form, the cells  15  within stack  1  are combined in series, parallel or a combination of the two in order to produce a higher voltage or current yield, depending on the needs of vehicle  100 . It will be understood that stack  1  may be used for purposes other than motor vehicles. 
         [0023]    Referring again to  FIG. 3 , as with the MEAs and diffusion media (not shown) to which they are attached, each bipolar plate assembly  17  defines a generally rectangular planar face portion  17 A with four edge portions  17 B that form a periphery around the face portion  17 A. Between the face portion  17 A and the two edge portions  17 B along the elongate dimension are a pair of header (or manifold) portions  17 C,  17 D, each disposed on opposing edges such that introduced reactant passes through the numerous serpentine flow field channels formed on the face portion  17 A. In one form, one of the header portions  17 C,  17 D defines a supply (or inlet) header, while the other defines an exhaust header. In an alternate configuration (not shown), the supply and exhaust header portions  17 C,  17 D can be situated side-by-side adjacent the same edge of the plate assembly  17 ; either variant is compatible with the present invention. In one form, the bipolar plate assembly  17  may be made of separate sheets  17 E,  17 F (typically between about 75 and 100 microns along the thickness (i.e., stacking) dimension) of a suitable corrosion-resistant material (such as 304 stainless steel) that can be joined together through brazing, laser welding or related operation; in such configuration, the flow channels formed with each face portion  17 A may define generally mirror images of one another such that upon stacking of two adjacent cells  15 , the face portions  17 A of the two within a single assembly  17  are in a back-to-back arrangement. In addition to these sheets that include the flow channels for the reactant gas flow field, similarly-shaped sheets (not shown) may be stackingly interspersed to provide a separate coolant-flow circuit; such coolant flow circuits may define any suitable flow channel shape (such as the serpentine shape depicted in flow channels. As with the sheets  17 E,  17 F, any such additional sheet coolant-flow circuit may also be joined through brazing or some other suitable joining technique. In the present context, the bipolar plate assembly  17  may or may not have the serpentine flow channels formed on both opposing planar faces; for example, when such plate forms the last plate in a stack  1 , it would not be necessary to have channels formed in the side that faces the end unit plates (such as end unit plates  5 ,  10  of  FIG. 1 ). 
         [0024]    An edgewise undulation (also called an edgewise extension, lateral extension or the like) in the form of a tab  17 G is integrally formed within the plane of each assembly  17 . Although tab  17 G is presently shown as being outwardly-extending, it will be appreciated by those skilled in the art that various inwardly-projecting tabs (not shown) may also be formed; either variant is deemed to be within the scope of the present invention as long as it provides an integrally-formed member with which the poured potting material may be affixed, bonded or otherwise secured. In the present context, the integral connection between the plate and the tab  17 G differs from those that require separate attachment, such as through securing, welding or the like. In this way, additional fabrication steps are avoided. Datum  18  is overmolded over tab  17 G with a suitable potting material such that it defines a thickness along the stacking dimension (i.e., the Y axis as shown). As will be discussed in more detail below, a conical cutout  18 A helps provide resistance to inter-plate sliding or related relative movement. Other forms besides the conical shape  18 A may also be used, including a post or pintle (not shown) that mimics the projection of an assembly (i.e., datum) pin along the stacking dimension; these and other forms are deemed to be within the scope of the present invention. 
         [0025]    Referring next to  FIG. 4  in conjunction with  FIG. 3 , details associated with the formation of a datum  18  along two of the lateral edges  17 B of numerous stacked cells (shown presently in simplified form as only containing the bipolar plate assemblies  17 ) are shown. As shown, apertures may be formed in tabs  17 G to further help the overmolding of the poured potting material that makes up datum  18 . Although the tabs  17 G (as well as the overmolded datum formed thereon) are shown disposed along the elongate edges of the bipolar plate assemblies  17 , it will appreciated by those skilled in the art that other locations on the plate periphery may also be used. For example, as discussed in conjunction with  FIGS. 5A and 5B  below, placement of the tabs  17 G and their overmolded datum on the corners is also within the scope of the present invention. Likewise, while the shape of the tabs  17 G are shown as rectangular, it will be appreciated that other shapes (for example, trapezoidal, semicricular or the like) may also be used, especially if they are helpful in forming the overmolded datum  18 . In the particular form shown in  FIG. 3 , datum  18  defines a conical or related thickness feature  18 A that by being substantially hollow within the region defined by the cone allows for nesting of two or more data  18  upon stacking of adjacently-facing groups of assemblies  17 . The conical feature  18 A of datum  18  is discussed in more detail in related U.S. patent application Ser. No. 14/482,000 that was filed on Sep. 10, 2014 and entitled FUEL CELL STACK ASSEMBLY—DATUM DESIGN FOR FUEL CELL STACKING AND COLLISION PROTECTION that is owned by the Assignee of the present application and incorporated herein by reference in its entirety. Significantly, the use of datum  18  ensures that no pins are required for assembly of stack  1 . 
         [0026]    In particular, datum  18  can be used to alleviate concerns over recent design increases in inter-cell sliding resistance (for example, being able to withstand up to about  160   g  loads whereas previous designs only required about  40   g ) as a way to provide out-of-plane support. In one particular form, datum  18  may be made from a rigid, load-bearing plastic (such as an epoxy or elastomeric material) that may be overmolded onto the thin tabs  17 G that form integral extensions from the edges  17 B or corners of the individual plates that make up assembly  17 . In this way, a shape (shown and discussed in more detail below in conjunction with  FIG. 6 ) that acts as a mold for the pouring of the potting material during the stack assembly process helps to build up the datum  18  in a columnar configuration for a complementary resistance fit between the datum  18  and the housing  20 . Although  FIG. 3  presently shows two datum  18  (one each on opposing edges  17 B) per bipolar plate assembly  17 , it will be understood that a greater or fewer number may be formed, depending on the stack  1  configuration. In a preferred form, multiple datum  18  per each grouped assembly  17  are preferred, as not only will this help promote better alignment during stack  1  assembly, but it may also provide additional shearing movement resistance between adjacent cell  15  layers within the stack  1  in situations where higher levels of the sliding resistance may be required. 
         [0027]    Severe load changes due to a disruptive event, which includes high acceleration or deceleration of the vehicle  100 , an impact involving the vehicle  100 , or similar impact to the fuel cell stack  1  itself, such as a vertical fall, can damage the fuel cell stack  1  or disassemble the stack  1  by causing the individual fuel cells  15  therein to move relative to one another. The mechanical properties of the datum  18  must be sufficient to carry the maximum acceleration that is attendant to such load changes. In one exemplary form, the datum  18  for each corresponding bipolar plate of the assembly  17  within the stack  1  would have a shear strength of about 150 N as a way to absorb the 160 g loading. 
         [0028]    Referring next to  FIGS. 5A and 5B , a variation on the placement and shape of datum  18  is shown. In particular, a fixture  200  used to stack the individual fuel cells  15  includes upper and lower plates  210 ,  220 , as well as the corner-mounted datum forms  230  and guide pins  240 . Flange mounted bearings  250  are secured to the top plate  210  to accept the ends of the linear guide pins  240  that are mounted at their opposing ends to lower plate  220 . Additional dowels or related alignment pins (not shown) may also be used. In this variation, the lower plate  220  of fixture  200  includes a generally trapezoidal-shaped mold or related preform  230  that is situated on the four corners of the lower plate  220  to accept the liquid potting material precursor that will (upon curing) become datum  18 . The corner of bipolar plate assembly  17  is shaped such that a tab-like extension (that is generally similar to tab  17 G of  FIG. 3 ) may engage the datum  18 . As mentioned above, the number, shape and placement of the datum  18  may be varied depending on the needs of the fuel cell system that employs stack  1 . 
         [0029]    Referring next to  FIG. 6  in conjunction with  FIG. 4 , other supplemental means may be used to promote improved resistance to shearing and the related inter-cell sliding. For example,  FIG. 6  shows with particularity indentations  20 A that may be molded or affixed to housing  20 . In the version shown, the housing  20  may be of a substantially integral structure (based for example, on extruded aluminum) that is robust enough to provide support to the cell block  1  during collision and to maintain it in compression along the stacking axis. These shapes define a complementary resistance fit between the molded datum  18  and the indentations  20 A formed within housing  20 . In such event, the molded indentations  20 A are sized to allow a close-tolerance fit along at least one sliding direction S within the X-Z plane of each assembly  17  within stack  1 , and are spaced to coincide with the edgewise placement of the stacked groups of datum  18  (which are presently shown in an embodiment devoid of the conical feature  18 A of the embodiment in  FIG. 3 ). In one preferred form, the indentations  20 A are integrally-formed into the extruded aluminum housing  20 , although in another variant, the indentations  20 A may be separately formed and subsequently attached to housing  20 . Moreover, the indentations  20 A may define a generally C-shaped profile (when viewed from above) such that any tendency of inter-cell sliding movement along sliding direction S is additionally resisted by the columnar shape that extends a substantial entirety of the height (which coincides with the stacking dimension of the Y-axis of  FIG. 1 ) of the housing  20 . As such, the shape of the molded indentations  20 A help them act as a bulkhead against movement in the X-direction of  FIG. 1 , as well as provide such additional resistance along one movement elsewhere within the X-Z plane. Insulation  20 B may be placed in the interstitial region between the periphery of the stack  1  and the internal housing  20  wall to provide electrical isolation. 
         [0030]    As mentioned above, in the embodiment depicted in  FIG. 6 , datum  18  may not include the conical feature  18 A. Likewise, such variant (As well as the variant of  FIG. 3 ) may avoid having a pin-accepting aperture, as the unitary built-up structure formed by the molding of datum  18  according to an aspect of the present invention onto multiple stacked fuel cells  15  promotes secure, accurate placement of each of the cells  15  in the stacking dimension without having to rely upon pins or other supplemental structure. Moreover, the tabs  17 G that are formed in the peripheral structure of each bipolar plate or assembly  17  may be made to engage with the complementary-shaped cutouts or recesses of the housing  20  such that the tendency of each cell or plate within the stack to move in response to a shearing (i.e., in-plane) force is resisted by the unitary nature of the datum  18  and tab  17 G to form a composite-like through-the-thickness inter-plate structure. 
         [0031]    Referring again to  FIG. 4 , in another structural reinforcement embodiment, a vertically elongate retainer  50  (preferably made from aluminum or steel) may extend between the end unit plates  5 ,  10  of  FIG. 1  such that it substantially envelopes or otherwise covers the projecting stacked datum  18  in a manner that mimics the C-shaped indentations  20 A that are integrally-formed into the embodiment of the extruded aluminum housing  20  of  FIG. 6 . Such retainer may be bolted or otherwise secured to the end unit plates  5 ,  10  as a way to achieve the structural rigidity without having to form a separate housing  20 . In yet another variation, instead of being secured directly to the end unit plates  5 ,  10 , the retainer may be secured to a box-like frame that is formed around the stack  1 . Such a frame may additionally include shims  55  to help adjust for variations in the height of the individual cells  15  that make up stack  1 . Additional equipment is also depicted, including current collector plates  60 ,  65  that extend laterally out of the respective end plates  5 ,  10  to connect to electrical circuitry (not shown). Insulator plates  70  may be placed between the lower surface of the end plates  5 ,  10  and a facingly-adjacent upper surface of stack  1  to promote electrical and thermal insulation between them. 
         [0032]    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. Likewise, 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 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. 
         [0033]    For the purposes of describing and defining the present invention it is noted that the terms “fuel cell” or the like are utilized herein to represent a one or more individual cells used to provide electric current, preferably for vehicular, propulsive or related purposes. Furthermore, variations on the terms “automobile”, “automotive”, “vehicular” or the like are meant to be construed generically unless the context dictates otherwise. As such, reference to an automobile will be understood to cover cars, trucks, buses, motorcycles and other similar modes of transportation unless more particularly recited in context. 
         [0034]    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.