Abstract:
One exemplary embodiment includes a method of selectively electroplating an electrically conductive coating on selected portions of lands of a bipolar plate leaving portions of the lands uncoated by the electrically conductive coating. Thus, allowing for reducing cost of bipolar plates for PEM fuel cells considerably.

Description:
TECHNICAL FIELD 
       [0001]    The field to which the disclosure generally relates includes bipolar plates for fuel cells and methods of making and using the same. 
       BACKGROUND 
       [0002]    Heretofore bipolar plates for fuel cells have been known to include at least one reaction gas flow path defined in a surface of a bipolar plate by a plurality of lanes and at least one channel. To reduce contact resistance between a diffusion media layer and a bipolar plate, the surface defining the reaction gas flow path of the bipolar plate has heretofore been coated with gold. 
       SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
       [0003]    One exemplary embodiment of the invention includes a method including providing a bipolar plate including at least one reacting gas flow path defined in a surface of the bipolar plate by a plurality of lands and at least one channel, selectively electroplating an electrically conductive coating over a plurality of first locations on the lands, and so that a plurality of second locations on the lands are free of the electrically conductive coating, and so that the channels are substantially free of the electrically conductive coating. In one exemplary embodiment the electrically conductive coating may include gold. 
         [0004]    Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0006]      FIG. 1  illustrates an electroplating system useful in a method according to one exemplary embodiment of the invention. 
           [0007]      FIG. 2  is a plan view of a sponge having a plurality of through-holes useful in a method according to one exemplary embodiment. 
           [0008]      FIG. 2A  is an enlarged view of a portion  2 A of  FIG. 2 . 
           [0009]      FIG. 3  is a sectional view of a bipolar plate including a first substrate and a second substrate onto which an electrically conductive coating may be selectively electroplated according to one embodiment of the invention. 
           [0010]      FIG. 4  illustrates an alternative embodiment of a fuel cell bipolar plate onto which an electrically conductive coating may be selectively electroplated according to one embodiment of the invention. 
           [0011]      FIG. 5  is an enlarged, partial, plan view of a surface of a fuel cell bipolar plate including a plurality of lands and a reacting gas flow channel, and wherein an electrically conductive coating has been electroplated selectively on portions of the lands leaving portions of the lands uncoated, as well as the channels uncoated according to one exemplary embodiment. 
           [0012]      FIG. 6  illustrates an alternative method of electroplating selected portions of the lands of a fuel cell bipolar plate utilizing a sponge having a plurality of raised features or projections for contact with portions of the lands of the fuel cell bipolar plate according to one exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0013]    The following description of the embodiment(s) is merely exemplary (illustrative) in nature and is in no way intended to limit the invention, its application, or uses. 
         [0014]    Referring now to  FIG. 1-2A , one embodiment of the invention may include a method including providing an electroplating system  10  including a container  12  which may include sidewalls  14 , a top  16  and a bottom  18  each of which may be an insulative material such as a polymeric material. The bottom  18  may be a polymeric sheet including a plurality of through-holes  21  best seen in  FIG. 2A . The through-holes  21  may each be of and arranged in a variety of designs. In one embodiment, the through-hole may have a cross-sectional area ranging from 1 nm to 100 nm, and may be spaced apart a distance from center-to-center ranging from 1 nm to 100 nm. A material for slowing the flow of the electrolyte solution through the through-holes  21 , such as, but not limited to, a sponge  20  may be provided in the container overlying the bottom  18 . A positive electrode (anode)  22  may be provided in the container and connected to an electrical source such as a battery  28 . The positive electrode  22  may be made from any of a variety of electrically conductive materials, such as but not limited to low contact resistant materials. A suitable low contact resistant material or coating may include, but is not limited to, gold, palladium, platinum, iridium, ruthenium, silver, alloys or mixtures thereof may be suitable for the positive electrode  22 . An electrolytic solution  24  may be provided in the container which is complementary to the positive electrode  22 . A charge pipe  26  may be provided and connected to the container  12  to replenish the electrolytic solution from a reservoir. 
         [0015]    At least a first substrate  30  for a fuel cell bipolar plate may be positioned under the bottom  18  and connected to the electrical source (battery)  28 . The first substrate  30  includes a first face  31  having a fuel cell reactant gas flow field defined therein by a plurality of lands  32  and channels  34 . The first substrate  30  may also include a second opposite face  33  which may include a plurality of portions of a coolant fluid channel  40  defined therein. When the first substrate  30  and the positive electrode  22  are connected to the battery  28  electrons flow from the first substrate  30  to the positive electrode  22  and so that material from the positive electrode enters the electrolytic solution and travels through the plurality of through-holes  36  in the bottom  18  to be selectively electroplated on portions of the lands  32  of the first substrate leaving portions of the lands uncovered. 
         [0016]      FIG. 3  illustrates an alternative embodiment showing a first substrate  30  including a first face  31  defining a plurality of lands  32  and channels  34 . A second substrate  38  which includes a first face  37  also defining a plurality of lands  32  and channels  34  is joined to the first substrate  30 . A plurality of coolant fluid flow channels  40  may be defined between the first substrate  30  and second substrate  38 . The first substrate  30  may have a second face  33  which also defines a plurality of lands and channels. Likewise, the second substrate  38  may have a second face  39  defining a plurality of lands and channels.  FIG. 4  illustrates an alternative embodiment of a fuel cell bipolar plate wherein the first substrate  30  and second substrate  38  may be substantially thicker. 
         [0017]      FIG. 5  is an enlarged, partial, plan view of a portion of the first face  31  of a first substrate  30  of a fuel cell bipolar plate. The first face  31  includes at least one reacting gas flow channel  34  defined by a plurality of lands  32 . An electrically conductive material  42  is selectively deposited over portions of the lands  32  leaving portions  44  uncovered by the electrically conductive material. Furthermore, the channels  40  may be substantially free of the electrically conductive material  42 . 
         [0018]    Referring now to  FIG. 6 , in another embodiment of the invention, the container  12  may be modified to remove the bottom  18  and the sponge  20  may be provided with a plurality of raised features or projections  46  extending downwardly with the adjacent projections  46  spaced apart by a recess  48  so that the projections  46  selectively contact portions of the lands  32  to electrically plate the electrically conductive material thereon. 
         [0019]    In one embodiment electrically conductive coating is a gold alloy having up to 90 Wt % gold and the balance including an unstable metal. The unstable metal can be zinc, magnesium, aluminum or mixtures thereof. In one embodiment the alloy may include a reactive component, and the reactive component may be dissolved in an acid such as sulfuric acid or a base such as sodium or potassium hydroxide leaving behind gold islands on the lands. The above described designs may be constructed and arranged and operated so that less than 30% of the area of the lands is electroplated. 
         [0020]    The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.