Abstract:
A receptacle having an end cap, a pliable sidewall, and a fastener, for receiving and retaining a fuel cell stack in its stacked configuration during fabrication of a multi-stack fuel cell assembly, is shown and described. Methods of fabricating the assembly include stacking the fuel cell in the receptacle, compressing the fuel cell, and engaging the fastener to retain the stack in its stacked configuration and, or to retain the stack under at least partial compression.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to electrochemical energy converters with polymer electrolyte membranes, such as fuel cells or electrolyzer cells or stacks of such cells. In particular, the present invention relates to systems and methods for assembling, compressing, isolating, and/or retaining stacks during and/or following fabrication. 
   2. Description of the Related Art 
   Electrochemical cells comprising polymer electrolyte membranes (“PEM”s) may be operated as fuel cells wherein a fuel and an oxidant are electrochemically converted at the cell electrodes to produce electrical power, or as electrolyzers wherein an external electrical current is passed between the cell electrodes, typically through water, resulting in generation of hydrogen and oxygen at the respective electrodes.  FIGS. 1-4  collectively illustrate typical designs of a conventional membrane electrode assembly  5 , an electrochemical cell  10  comprising a PEM layer  2 , and a stack  100  of such cells. 
   Each cell  10  comprises a membrane electrode assembly (“MEA”)  5  such as that illustrated in an exploded view in FIG.  1 . MEA  5  comprises an ion-conducting PEM layer  2  interposed between first and second electrode layers 1/3 which are typically porous and electrically conductive, and each of which comprises an electrocatalyst at its interface with the PEM layer for promoting the desired electrochemical reaction. The electrocatalyst generally defines the electrochemically active area of the cell. The MEA  5  is typically consolidated as a bonded, laminated assembly. 
   In an individual cell  10 , illustrated in an exploded view in  FIG. 2 , an MEA  5  is interposed between first and second cell separator plates  11 / 12 , which are typically fluid impermeable and electrically conductive. The cell separator plates  11 / 12  are are manufactured from non-metals, such as graphite; from metals, such as certain grades of steel or surface treated metals; or from electrically conductive plastic composite materials. 
   Fluid flow spaces, such as passages or chambers, are provided between the cell separator plates  11 ,  12  and the adjacent electrode layers  1 ,  3  to facilitate access of reactants to the electrode layers and removal of products. Such spaces may, for example, be provided by means of spacers between the separator plates  11 ,  12  and the corresponding electrode layers  1 ,  3 , or by provision of a mesh or porous fluid flow layer between the cell separator plates and corresponding electrode layers. More commonly, channels are formed in the faces of the cell separator plates  11 ,  12  that face the electrode layers  1 ,  3 . Cell separator plates  11 ,  12  comprising such channels are commonly referred to as fluid flow field plates. In conventional cells  10 , resilient gaskets or seals are typically provided around the perimeter of the flow fields between the faces of the MEA  5  and each of the cell separator plates  11 ,  12  to prevent leakage of fluid reactant and product streams. 
   Electrochemical cells  10  with ion-conductive PEM layers  2 , sometimes called PEM cells, are advantageously stacked to form a stack  100  (see  FIG. 4 ) comprising a plurality of cells disposed between first and second end plates  17 ,  18 . A compression mechanism is typically employed to hold the cells  10  tightly together, to maintain good electrical contact between components, and to compress the seals. In the embodiment illustrated in  FIG. 3 , each cell  10  comprises a pair of cell separator plates  11 ,  12  in a configuration with two cell separator plates per MEA  5 . Cooling spaces or layers may be provided between some or all of the adjacent pairs of cell separator plates  11 ,  12  in the stack  100 . An alternate configuration (not shown) has a single separator plate, or “bipolar plate,” interposed between a pair of MEAs  5  contacting the cathode of one cell and the anode of the adjacent cell, thus resulting in only one separator plate per MEA  5  in the stack  100  (except for the end cell). Such a stack  100  may comprise a cooling layer interposed between every few cells  10  of the stack, rather than between each adjacent pair of cells. 
   The illustrated cell elements have openings  30  formed therein which, in the stacked assembly, align to form fluid manifolds for supply and exhaust of reactants and products and, if cooling spaces are provided, for a cooling medium. Again, resilient gaskets or seals are typically provided between the faces of the MEA  5  and each of the cell separator plates  11 ,  12  around the perimeter of these fluid manifold openings  30  to prevent leakage and intermixing of fluid streams in the operating stack  100 . 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention relates to apparatus, systems and methods for use in fabricating fuel cell stacks and multi-stack fuel cell assemblies. In one embodiment, the present invention incorporates a receptacle for receiving and retaining a fuel cell stack in its stacked configuration during fabrication of the multi-stack fuel cell assembly. The receptacle has an end cap, a pliable sidewall, and a fastener. The end cap has a plurality of openings configured to allow the fuel cell stack to communicate with a corresponding plurality of openings in a manifold and/or to electrically connect the fuel cell stack to other stacks in a multi-stack assembly. The pliable sidewall is sized and shaped to electrically insulate the fuel cell stack from at least one adjacent fuel cell stack when the multi-stack fuel cell has been assembled. The fastener is configured to extend from one location on the sidewall across the end of the fuel cell stack opposite the end cap, and to be attached to another location on the sidewall to retain the fuel cell stack in its stacked configuration. In particular embodiments, the sidewall can be coupled to the end cap, the sidewall can be sized to extend around at least substantially the entire perimeter of a fuel cell stack, the fastener can be a single band, the fastener can be a number of bands, or the fastener can be a portion of the sidewall itself. Other variations are also appreciated. The receptacle can be configured to retain the fuel cell stack in its stacked configuration, and, or can be configured to be tensioned around at least a portion of a compressed stack and adhered thereto to retain the stack under at least partial compression. 
   Another embodiment of the present invention is directed toward a method for fabricating a fuel cell stack. The method incorporates placing a stack of fuel cell elements in an open end of a pliable bag having the open end, an opposing closed end and a sidewall therebetween; compressing the fuel cell stack; extending a length of material over the compressed stack and across the open end of the bag; and attaching the length of material to the bag to retain the fuel cell stack in its stack configuration. Embodiments of this invention can be configured to retain the stack under at least partial compression. 
   Still another embodiment of the present invention is directed toward a method for assembling a plurality of fuel cells. The method incorporates compressing each of the fuel cell stacks; wrapping a pliable material around each of the stacks of fuel cells to retain the stacks in their stacked configuration; and placing the plurality of stacks between a pair of manifolds. Embodiments of this invention can be configured to insulate each fuel cell stack from adjacent fuel cell stacks, and, or to retain the fuel cell stacks under at least partial compression during assembly. Embodiments of this invention can also incorporate leak testing each fuel cell stack prior to assembly. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is an exploded isometric view of a membrane electrode assembly according to the prior art. 
       FIG. 2  is an exploded isometric view of an electrochemical cell according to the prior art. 
       FIG. 3  is an exploded isometric view of an electrochemical cell stack according to the prior art. 
       FIG. 4  is an isometric view of an electrochemical cell stack according to the prior art. 
       FIG. 5  is an exploded isometric view of a receptacle according to an embodiment of the present invention. 
       FIG. 6  is an elevation view of a lower portion of the receptacle of FIG.  5 . 
       FIG. 7  is a top view of the portion of the receptacle of FIG.  6 . 
       FIG. 8  is an end view of the portion of the receptacle of FIG.  6 . 
       FIG. 9  is an isometric view of four assembled receptacles and fuel cell stacks according to the embodiment of FIG.  5 . 
       FIG. 10  is an end view schematically illustrating one step in the insertion of a fuel cell stack into a receptacle according to another embodiment of the present invention. 
       FIG. 11  is an end view schematically illustrating another step in the insertion of the fuel cell stack into the receptacle of FIG.  10 . 
       FIG. 12  is an end view schematically illustrating still another step in the insertion of the fuel cell stack into the receptacle of FIG.  10 . 
       FIG. 13  is an exploded isometric view of a sidewall and a pair of opposing end caps according to yet another embodiment of the present invention. 
       FIG. 14  is an elevation view of a pattern for a receptacle according to still another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present detailed description is generally directed toward methods, systems, and apparatus for facilitating the stacking and compression of fuel cell stacks, and the assembly of multi-stack fuel cell assemblies. Various embodiments of the present invention can allow a fuel cell stack to be fabricated and compressed, then sealed in its compressed form for ease of handling and subsequent assembly. Further, embodiments of the invention can isolate adjacent fuel cell stacks in a multi-stack assembly to reduce the potential for electrical shorts. Still further, pre-compression of independent fuel cell stacks can allow the stacks to be leak tested prior to assembly into the multi-stack assembly. 
   Many specific details of certain embodiments of the invention are set forth in the following description and illustrated in  FIGS. 5-14  to provide a thorough understanding of such embodiments. Once skilled in the art, however, will understand that the present invention may have additional embodiments, or may be practiced without several of the details described in the following description. 
     FIG. 5  generally illustrates a receptacle assembly  20  according to one particular embodiment of the present invention. The receptacle assembly  20  incorporates a pair of opposing end assemblies  21  that engage a fuel cell stack  22  from opposing ends during use. In the illustrated embodiment, the end assemblies  21  are substantially identical to each other. Accordingly, the description of one end assembly  21  will serve to describe both end assemblies except where specifically described otherwise. 
   The end assembly  21  is fabricated from a convex sidewall  24 , a concave sidewall  26 , and an end cap  28 . The convex sidewall  24  and concave sidewall  26  can be fabricated from a thin, insulative material such as LEXAN or a similar material, and can be thermoplastically deformed to conform to a corresponding wall of the fuel cell stack  22 . Alternatively, convex sidewall  24  and concave sidewall  26  can be fabricated from an elastic insulative material that is capable of deforming to conform to a corresponding wall of the fuel cell stack  22 . The end cap  28  can also be fabricated from an insulative material such as LEXAN, and can be vacuum formed to conform with an end of the fuel cell stack  22 . The end cap  28  can contain a number of openings  30  configured to align with ports on the fuel cell stack  22  or to vent the receptacle assembly  20  during compression as discussed below. The opening configuration of  FIG. 5  is one particular example, but the inventor appreciates that the configuration can and will likely vary for each particular application. 
   Each of the sidewalls  24 ,  26  is slightly taller than one-half of the height of a fuel cell stack  22 . Consequently, when the end assemblies  21  are engaged with the fuel cell stack  22  from opposing ends, the concave sidewalls  26  overlap each other and the convex sidewalls  24  overlap each other. The respective lengths of the sidewalls  24 ,  26  can vary without deviating from the spirit of the invention. 
   The convex sidewall  24  approaches the concave sidewall  26  at opposing gaps  32  aligned with the ends of the fuel cell stack  22 . In the illustrated embodiment, the gaps  32  extend along the entire height of the end assembly  21 . The sizes and placements of the gaps  32  can vary and the gaps could be replaced with openings or other suitable features without deviating from the spirit of the invention. 
     FIGS. 6-8  further illustrate one particular end assembly  21  according to this embodiment of the present invention. When the end assembly  21  is assembled, the convex sidewall  24  and the concave sidewall  26  are each abutted against the end cap  28  and positioned internal to a raised rim  34  extending around the perimeter of the end cap. The sidewalls  24 ,  26  are attached to the end cap  28 , such as by high frequency welding or other suitable means. The inventor appreciates that the exact nature of the engagement between the sidewalls  24 ,  26  and the end caps  28  can vary without deviating from the spirit of the present invention. 
     FIG. 9  illustrates four receptacle assemblies  20  engaged with a manifold  36  according to this particular embodiment of the present invention. Prior to being configured as such, each receptacle assembly  20  and fuel cell stack  22  was assembled as discussed above and illustrated in FIG.  5 . Each receptacle assembly  20  and fuel cell stack  22  may be individually compressed in a vertical direction as oriented in  FIG. 9 , and may be individually pressure tested for leaks. Upon receiving confirmation that there are no leaks in a particular fuel cell stack  22 , the upper and lower end assemblies  21  can be affixed with adhesive  38  to the sides of the fuel cell stacks  22  through the gaps  32 . In the illustrated embodiment, the adhesive  38  is a high tensile strength tape. Accordingly, the adhesive  38  connects the sidewalls  24 ,  26  to each other and to the fuel cell stack  22 , and thus help retain the fuel cell stack in the stack configuration. The adhesive  38  can also retain the fuel cell stack  22  in at least a partially compressed state for a limited duration of time. During this duration, the receptacle assembly  20  can create an insulative barrier around the fuel cell stack  22  that allows the stack to be handled and moved without contaminating the stack or shorting a fuel cell. 
   The methods and systems of this particular embodiment have a number of advantages. For example, because the fuel cell stacks  22  can be compressed and pressure tested independently, a failed pressure test results in only a single stack being disassembled, as opposed to an entire multi-stack fuel cell assembly being disassembled. Further, the fuel stacks  22  act as uniform blocks for ease of handling and assembly. Further, the sidewalls  24 ,  26  serve to isolate the adjacent fuel cell stacks  22  electrically to reduce the potential for a short between the two. Further, because each end assembly  21  overlaps the other, if the fuel cell stack  22  is compressed within the receptacle assembly  20 , the end assemblies will not buckle, but will instead slide with respect to each other. 
     FIGS. 10-12  sequentially illustrate some of the steps in the assembly and compression of a receptacle assembly  120  and fuel cell stack  22  according to another embodiment of the present invention. The receptacle assembly  120  is in the form of a box having an open top for receiving the fuel cell stack  22 . The receptacle assembly  120  is shaped and sized to conform with the fuel cell stack  22 . As with the prior embodiment, the sides, bottom, and other portions of the receptacle assembly  120  can have openings therein for mating with external structures such as the manifold of  FIG. 9. A  number of straps  140  are spaced apart from each other along the width of the receptacle assembly  120 . 
   During assembly, the receptacle assembly  120  is retained from below such as by a foundation  142 . One or more pistons  144  extends through the foundation  142  and an opening in the receptacle assembly  120 , and projects upward toward the top of the receptacle assembly. The piston  144  is configured to support a buss plate  146  and the buss plate is configured to engage the fuel cell stack  22 . As illustrated in  FIG. 11 , the piston  144 , and with it the buss plate  146  and fuel cell stack  22 , move downward into the receptacle assembly  120 . 
   As illustrated in  FIG. 12 , once the fuel cell stack  22  has been completely received by the receptacle assembly  120 , an upper buss plate  148  is positioned on top of the fuel cell stack. A compression mechanism  150  compresses the fuel cell stack  22  against the foundation  142 . Depending on the circumstances, the compression mechanism  150  can compress the fuel cell stack  22  at a reduced force for pressure and leak testing, or the compression mechanism can compress the fuel cell stack to full operating compression. During compression, air may escape from the receptacle assembly  120  through openings such as those designated at  30  in FIG.  5 . 
   When the fuel cell stack  22  is compressed to the desired amount, the strap  140  or plurality of straps  140  are folded across the top of the fuel cell stack and are attached, such as by high frequency welding or other suitable means, to the opposing side of the receptacle assembly  120 . Once the straps  140  are welded to the opposing sidewall of the receptacle assembly  120 , the particular fuel cell stack is isolated and compressed for assembly into a multi-stack fuel cell. As discussed above, the receptacle assembly can be made from an electrically insulative material to facilitate handling and prevent the fuel cell from shorting, such as through contact with an adjacent fuel cell. In addition, the compressed fuel cell stack can be pressure-tested prior to assembly into the multi-stack fuel cell assembly. 
     FIG. 13  illustrates a receptacle assembly  220  according to another embodiment of the present invention. In this particular embodiment, the receptacle assembly  220  incorporates a pair of opposing end caps  228  and an intermediate sidewall  229 . In the illustrated embodiment, the end caps are vacuum formed thermoplastic polymers, such as those described above, and the sidewall  229  is a continuous, extruded tube cut to the length of a compressed fuel cell stack (not shown). As discussed above, the sidewall  229  can be vacuum formed to take the shape of a fuel cell stack. 
   Similar to those embodiments discussed above, the end caps  228  and sidewall  229  can have various openings therein to mate with complementary external ports or openings. Likewise, the end caps can contain openings for receiving pistons and compression mechanisms to compress the fuel cell stack. Once the fuel cell stack has been compressed the desired amount, the end caps  228  can be affixed to the sidewall  229  to retain the fuel cell stack in its stack configuration and, if desired, to retain the stack under compression. 
     FIG. 14  illustrates a receptacle assembly  320  according to another embodiment of the present invention. In this particular embodiment, the sidewall  329  is formed from a single sheet of material. The sidewall is punched or otherwise cut into a pattern that can be folded to conform to the external surface of a fuel cell stack (not shown). The folded receptacle assembly  320  can be vacuum formed and thermoplastically deformed to conform to the fuel cell stack during use. 
   The receptacle assembly  320  has a number of fasteners  340  oriented to extend over the top and bottom of the fuel cell stack. After being compressed in a manner similar to that described above, the fasteners  340  can be attached to opposing fasteners or to the opposing sidewall of the receptacle assembly  320  to retain the fuel cell stack in its stack configuration and, or under at least partial compression. 
   From the foregoing it will be appreciated that, all the specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.