Abstract:
A fuel cell is described. The fuel cell includes current collectors, each of which includes a substrate of lightweight material, such as Kapton material. Micro channels are formed via laser machining or chemical etching into the substrate. The current collectors further include conductive layers sputtered on the substrate, and protective coating on the conductive layers. A variety of materials are available for the conductive layers. The fuel cell so developed is particularly well suited to mobile applications, such as electronic devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims priority to Markoski&#39;s U.S. provisional patent application No. 60/547,618, filed Feb. 24, 2004, entitled FUEL CELL APPARATUS AND METHOD OF FABRICATION, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to fuel cells. More specifically, the present invention teaches a variety of in-plane fuel cell current collectors embedded on flexible lightweight substrates and coupled to lightweight flow distributors, and methods for manufacturing same. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Existing renewable power sources for low-power devices, such as handheld electronics or other portable devices, have failed to keep pace with the increasing sophistication of such electronics. The power sources currently employed in mobile devices, including various types of chemical batteries such as lithium ion or nickel cadmium batteries, are unwieldy, generate insufficient power for inadequately short duration, and require untenably long recharge periods. These limitations impose severe restrictions on the functionality of the devices they power: e.g., users are forced to recharge units at untenably short intervals, and the weight of existing batteries renders mobile devices much larger and heavier than desirable. The dichotomy between the rapid progress in electronics and the relative torpor in power technologies grows progressively more pronounced, as electronics technology continue to advance at geometric rates for the foreseeable future. 
         [0006]    Efforts have been undertaken to replace or enhance existing, antiquated battery technologies for the types of applications discussed above. Amongst the more promising candidates for renewable, portable energy provision are miniature, or “micro” fuel cells, and in particular, Polymer Electrolyte Membrane (PEM) fuel cells due to their low operating temperature (i.e. &lt;120° C.) and potential for high energy density due to the use of atmospheric oxygen as the oxidant which does not add to the overall system weight. 
         [0007]    PEM fuel cells can be broken down into different types depending on the chemical composition of the fuel that is used in the system. If pure hydrogen is used as the fuel the type is hydrogen PEM. If a hydrocarbon fuel such as butane or methanol is 
         [0000]                                  TABLE 1               ½ Cell potentials of oxidants and fuels that can be utilized directly in       PEM based fuel cells                                    O 2 (g) + 4H +  + 4e −                2H 2 O   +1.23 V           H 2 (g)            2H +  + 2e   +0.00 V           CO 2 (g) + 6H +  + 6e −                CH 3 OH + H 2 O   +0.02 V           CO 2 (g) + 2H +  + 2e −                HCOOH   −0.20 V                    
reformed to produce hydrogen from an onboard reformer, the type is a reformed hydrogen PEM. If a hydrocarbon based fuel such as methanol or formic acid is used as fuels without reforming to hydrogen, the type is direct liquid PEMs. A liquid methanol fuel cell, the most popular type fuel used directly without reforming, is typically referred to as a direct methanol fuel cell (DMFC). However, formic acid has been also shown to be a good direct fuel for PEMs.
 
         [0008]    Prior Art  FIG. 1  illustrates a cross-sectional schematic diagram of an assembled and sealed single polymer electrolyte membrane (PEM) fuel cell  100 . Table 1 (shown above) shows the half-cell potentials for the fuels discussed above, whose potential energy can be converted into electric energy when combined with oxygen within the PEM fuel cell  100 . The PEM fuel cell  100  includes a membrane electrode assembly (MEA)  102 , an anode current collector/flow distributor  104 , and a cathode current collector/flow distributor  106 . The MEA  102  is where all of the electric energy is released. 
         [0009]    The current collectors/flow distributors  104  and  106  are electrically conductive and resistant to the corrosive fuel cell environment and are typically machined graphite with various flow channels (such as anode flow channel  108  and cathode flow channel  110 ) and patterns known in the art. The current collectors/flow distributors  104  and  106  can be used as both end plates and bipolar plates in PEM stacks. The channel dimensions and flow patterns can vary depending upon the application but for the most part both anode and cathode channels are 1.0-2.5 mm in height and width and the anode and cathode shoulders are typically 1.0-2.5 mm in height and width. The thickness between the bottom of the anode and cathode channels, called the web thickness needs to be 1 mm or greater to ensure mechanical robustness of the brittle graphite material and also ensure that the fuel and oxidant don&#39;t mix through the somewhat porous graphite web. This produces an overall thickness of 3-7.5 mm for the graphite based bi-polar plate design. Those skilled in the art will recognize that the majority of the volume and weight of the PEM stack comes from the current collectors/flow distributors  104  and  106 . 
         [0010]    As shown in Prior Art  FIG. 2 , the MEA  102  includes a polymer electrolyte membrane  120  capable of conducting protons and insulating electrons is sandwiched between two platinum based catalyst layers  122  and  124 , and two porous gas/fuel diffusion electrodes (GDEs)  126  and  128 . The PEM  120  can take any suitable form, such as a Nafion ionmer based material with thickness ranging from 25-250 micrometers. The anode catalyst layer  122  is typically supported or unsupported Pt or Pt alloy with precious metal loadings ranging from 0.1-10 mg/cm 2  depending on fuel used and desired current density. The cathode catalyst layer  124  is typically supported or unsupported Pt with loadings ranging from 0.1-10 mg/cm 2  depending on fuel used and desired current density. The GDEs  126  and  128  are typically graphite based (Torray paper) with coatings added to increase or decrease hydrophobiticy and porosity ranging from 5-80% and thickness ranging from 50-350 micrometers in thickness. 
         [0011]    In a fully assembled and operational single cell PEM fuel cell  102  (see  FIGS. 1-2 ), electricity is created as a result of fuel coming in contact with the anode catalyst where the fuel is decomposed into protons, electrons, and carbon dioxide if a carbon based fuel is used (see Table 1.) These protons flow through the PEM  120  while the electrons can only flow via the anode current collector  104  out through an external load  112  and into the cathode current collector  106  where the electrons recombine in the cathode catalyst layer with protons and oxygen to produce water; this completes the electric circuit, in so doing performing electrochemical work. 
         [0012]    By stacking numerous PEM cells  100  together as shown in Prior Art  FIG. 3 , a fuel cell stack power source system  150  capable of use in aerospace and automotive applications can be built. Such power systems have been studied widely at power levels of 10,000 watts and above and have been engineered to produce high power density systems. These systems consist of three components, the fuel, the fuel cell stack  150  and the balance of plant (BOP). The BOP is responsible for controlling the performance of the fuel cell stack by distributing and conditioning the fuel, air, and cooling streams that run through the fuel cell stack. 
         [0013]    The fuel cell stack  150  of  FIG. 3  can be controlled to operate at high power density or high energy density (high fuel efficiency). This is illustrated graphically in a current/voltage plot  160  as shown graphically in  FIG. 4 . Here the potential losses fall into three regimes: an activation region  162 , an Ohmic region  164  and a transport region  166 . The shape and slope of the activation region  162  is determined by the activity and performance of the catalyst layers. The shape and slope of the Ohmic region  164  is determined by the sum of the internal cell resistances (ionic and electrical). The shape and slope of the transport region  166  is determined by the rate at which fuel and oxidant are supplied to the fuel cell stack. 
         [0014]    Prior Art  FIG. 5  provides a graphical representation  170  of how increasing the fuel to system ratio for a given power requirement (e.g., 20 Watts) serves to increase the specific energy density for a PEM based power system  150 . As will be appreciated, at a given temperature and BOP operating conditions, the maximum power (watts) a fuel cell stack  150  can deliver occurs at the maximum product value of the potential (volts) and the current density (mA/cm 2 ). To increase the energy density of the system, the stack  150  can be operated at higher voltage, at an optimal point between the open circuit voltage (zero current), and the maximum power voltage. Alternatively or in conjunction with, for a given stack power output and system weight/volume,  FIG. 9  illustrates how the energy density can be increased by decreasing the size and weight of the BOP and fuel cell stack while increasing the amount of fuel. 
         [0015]    While increasing the energy density for PEM systems is relative easy to achieve for large systems, decreasing the size and weight of the BOP and fuel cell stack  150  has been shown to be somewhat problematic for sub 100 Watt levels. Inefficiency can be at least partially attributed to the volume of the fuel cell stack within these low power PEM fuel cell systems. Moreover, such stacks are physically weighty, by virtue of the thick machined graphite bipolar plates and end plates typically used in construction. This feature of the prior art PEM fuel cell technology is particularly problematic for mobile devices, for which low weight/volume form factors constitute a critical selling feature. 
         [0016]    Thus, the prior art evinces a need for reducing the size and weight of PEM fuel cell stacks and systems for application to low power products, such as handheld mobile devices, laptop computers, or other such applications. More specifically the prior art evinces a need for reducing the size and weight of PEM fuel cell stacks by replacing machined graphite bipolar plates and end plates with flexible lightweight, low density composites of corrosion resistant materials with adequate electrical conductivity (See table 2). Such fuel cell systems should produce power efficiently (e.g., have high energy density), in order to support sufficiently lengthy operational duration. Moreover, to enhance the suitability of fuel cells for intended applications (such as mobile electronic devices), it is desirable that such fuel cell systems be lightweight and inexpensive. Moreover, it is desirable for such devices to be manufacturable through low cost, efficient processes. These and other objectives of the present invention are addressed as further discussed herein. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 List of electrically conductive materials and  
               
               
                 corresponding physical properties 
               
             
          
           
               
                   
                   
                   
                   
                 Conduct- 
                 Resis- 
               
               
                   
                   
                 Atomic 
                 Density 
                 ivity 
                 tivity 
               
               
                 Metal 
                 Symbol 
                 Weight 
                 (gcm −3 ) 
                 (S/cm) 
                 (Ωm) 
               
               
                   
               
             
          
           
               
                 Silver 
                 Ag 
                 107.868 
                 10.49 
                 630100 
                 1.59E-08 
               
               
                 Copper 
                 Cu 
                 63.546 
                 8.92 
                 596100 
                 1.68E-08 
               
               
                 Gold 
                 Au 
                 196.9665 
                 19.3 
                 452100 
                 2.21E-08 
               
               
                 Aluminum 
                 Al 
                 26.98152 
                 2.7 
                 377100 
                 2.65E-08 
               
               
                 Rhodium 
                 Rh 
                 102.9055 
                 12.45 
                 211100 
                 4.51E-08 
               
               
                 Molybdenum 
                 Mo 
                 95.94 
                 10.28 
                 187100 
                 5.34E-08 
               
               
                 Tungsten 
                 W 
                 183.85 
                 19.25 
                 18910 
                 5.40E-08 
               
               
                 Nickel 
                 Ni 
                 58.6934 
                 8.908 
                 143100 
                 6.99E-08 
               
               
                 Ruthenium 
                 Ru 
                 101.07 
                 12.37 
                 137100 
                 7.10E-08 
               
               
                 Iron 
                 Fe 
                 55.847 
                 7.874 
                 99310 
                 9.71E-08 
               
               
                 Palladium 
                 Pd 
                 106.42 
                 12.023 
                 95010 
                 1.05E-07 
               
               
                 Platinum 
                 Pt 
                 195.08 
                 21.45 
                 96610 
                 1.06E-07 
               
               
                 Chromium 
                 Cr 
                 51.996 
                 7.14 
                 77410 
                 1.29E-07 
               
               
                 Tantalum 
                 Ta 
                 180.9479 
                 16.65 
                 76110 
                 1.35E-07 
               
               
                 Niobium 
                 Nb 
                 92.9064 
                 8.57 
                 69310 
                 1.44E-07 
               
               
                 Rhenium 
                 Re 
                 186.207 
                 21.02 
                 54210 
                 1.84E-07 
               
               
                 Titanium 
                 Ti 
                 47.88 
                 4.507 
                 23410 
                 4.20E-07 
               
               
                 Graphite 
                 C 
                 12.0107 
                 1.25 
                 500-700 
                 2.00E-05 
               
               
                   
               
             
          
         
       
     
       SUMMARY OF THE INVENTION 
       [0017]    The invention teaches a variety of fuel cell, fuel cell stack systems, and fuel cell power systems, as well as techniques and mechanisms for manufacturing such devices. Certain embodiments of the present invention offer dramatic improvements over prior art fuel cell technologies in system performance, usability, and expense. In particular, certain fuel cells of the present invention demonstrate efficiency, are lightweight, relatively easy to manufacture, and cost-effective to produce and distribute. These embodiments are particularly well-suited to micro fuel cell applications (100 watt and below) such as portable electronic devices, including lap top computers, personal digital assistants, mobile phones, and other such products. Other suitable applications for the fuel cells described herein shall be readily apparent to those skilled in the art. 
         [0018]    In embodiments of the invention, the fuel cell power source may comprise a PEM based fuel cell stack. Some such embodiments include a current collector layer further comprised of a support layer, with a series of micro-channels etched through the support layer and current collector layer. In some such embodiments, the support layer may be comprised of a lightweight material; in embodiments, this lightweight material may be comprised of a Kapton-type material or other chemically resistant polymer thermoplastic films such as Imidex, PEEK, Vectra, PET, Teflon, Tefzel, HDPE Ultem or any other polymer films typically used in or compatible with the manufacture of flexible circuits. In some embodiments, the micro-channels are patterned onto the support layer through a lithographic photoresist process. In other embodiments, the micro-channels are etched through the support layer using a chemical etching process. In still other embodiments, the micro-channels are cut into the support layer through a photo machining process (i.e., laser cutting). In further embodiments, the micro-channels are punched into the support layer through a die cutting process. 
         [0019]    The present invention also teaches a current collector having a thin adhesion layer opposite of the support layer. In certain embodiments, the adhesion layer may be a conductive metal layer or multilayer (10-2000 angstroms). The adhesion layer may be comprised partially of a platinum group metal such as platinum, palladium, ruthenium or rhodium, a coinage metal such as silver, gold, or copper a refractory metal such as niobium, rhenium, molybdenum, tungsten or tantalum, a metal such as aluminum, iron, nickel, or chromium, or a metal alloy such as Inconel, Monel, or stainless steels or any other such metallic based adhesive layer commonly employed or compatible with the metallization process in the flexible and/or printed circuit board manufacturing process. The adhesion layer deposition process may include sputtering, e-beam, or chemical vapor deposition processes. In alternative embodiments, the adhesion layer may be a chemically and thermally substantially stable polymer-based adhesive ranging in thickness from 25-250 um. The polymer-based adhesive can be a B-stage epoxy bond-ply layer, a thermo-setting liquid crystal polymer resin, a Teflon-like FEP or PFA film or any other polymer-based solid or liquid state adhesive commonly employed or compatible with the flexible and or printed circuit board manufacturing process. 
         [0020]    In embodiments of the invention, the current collector further includes a thicker highly conductive metallic layer or multilayer adhered/bonded/deposited onto the adhesion surface of the support layer. In some such embodiments, the conductive layer may be comprised at least partially of a platinum group metal such as platinum, palladium, ruthenium or rhodium, a coinage metal such as silver, gold, or copper a refractory metal such as niobium, rhenium, molybdenum, tungsten or tantalum, a metal such as aluminum, iron, nickel, or chromium, a metal alloy such as Inconel, Monel, or stainless steels or any other such metallic based adhesive layer commonly employed or compatible with the metallization and electrodeposition processes in the flexible and/or printed circuit board manufacturing process 
         [0021]    According to certain manufacturing aspects of the invention, the conductive layer is deposited onto the adhesion layer via a sputtering or e-beam deposition process. In alternative aspects, the conductive layer is deposited onto the adhesion layer via or in conjunction with an electrodepostion process. In other embodiments, the conductive layer is a thin metal or metal alloy or thin low density flexible graphite bonded or clad to the opposite surface of the support layer through a cladding process commonly employed or compatible in the flexible and or printed circuit board manufacturing process. 
         [0022]    In embodiments of the invention, the current collector further includes a conductive protective layer, formed on a surface of the highly conductive layer opposite the surface of the support layer. Such a protective layer protects the highly conductive layer of the current collector from at least one of oxidation and/or corrosion. In some such embodiments, the conductive protective layer may be comprised at least partially of a platinum group metal such as platinum, palladium, ruthenium or rhodium, a coinage metal such as silver or gold, a refractory metal such as niobium, rhenium, molybdenum, tungsten or tantalum. In alternative embodiments, the protective layer may be comprised at least partially of carbon or metallic particles dispersed within a polymer matrix. In some embodiments, the protective layer may be comprised at least partially of a conductive polymer. In other embodiments, the conductive polymer may be a polypyrrole, polythiophene or polyaniline. 
         [0023]    According to certain manufacturing aspects of the invention, the protective conductive layer is deposited onto the highly conductive layer via a sputtering or e-beam deposition process. In alternative aspects, the conductive layer is deposited onto the adhesion layer via or in conjunction with an electrodepostion process In alternative embodiments of the present invention, the protective conductive layer is deposited onto the adhesion layer via a spray coating, dip coating or painting type process. 
         [0024]    In embodiments of the invention, the fuel cell includes two lightweight flow distributors and two current collectors, with a membrane electrode assembly sandwiched between the two current collectors and lightweight flow distributors, such that one surface of the electrode assembly is in direct contact with one of the current collectors, and an opposite surface of the electrode assembly is in contact with the other current collectors. In embodiments of the invention the lightweight flow distributors are composed of chemically and thermally stable thermoplastics such as HDPE, Teflon, PEEK, Ultem, Kapton, or any other suitable thermoplastic. In other embodiments of the invention, the lightweight flow distributors are mechanically machined, alternatively, these flow distributors may be injection molded or blow molded. Alternatively, these flow distributors may be laser machined, or chemically etched. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0025]    Prior Art  FIG. 1  is a cross-sectional schematic diagram of an assembled and sealed single polymer electrolyte membrane (PEM) fuel cell. 
           [0026]    Prior Art  FIG. 2  is a blow up of a cross-section of the membrane electrode assembly of  FIG. 1 . 
           [0027]    Prior Art  FIG. 3  is a diagram of a fuel cell stack of the prior art. Prior Art  FIG. 4  is a graphical illustration of fuel cell potential versus current density. 
           [0028]    Prior Art  FIG. 5  is a graphical illustration of how increasing the fuel to system ration for a given power requirement serves to increase the specific energy density for a PEM based power system. 
           [0029]      FIG. 6  is a schematic of a fuel cell stack according to one embodiment of the present invention. 
           [0030]      FIG. 7  is an illustration of a 4-channel in-plane conductive composite end plate, anode or cathode. 
           [0031]      FIG. 7A  is a cross-sectional diagram of the end plate of  FIG. 7 . 
           [0032]      FIG. 8  is an illustration of a 4-channel in-plane conductive composite bipolar plate. 
           [0033]      FIG. 8A  is a cross-sectional diagram of the bipolar plate of  FIG. 8 . 
           [0034]      FIG. 9  is a cross-sectional view of a composite based current collector in accordance with one embodiment of the present invention. 
           [0035]      FIG. 10  is a top view of a substrate of a current collector according to yet another embodiment of the present invention. 
           [0036]      FIG. 11  is a flow chart of a method for the manufacture of a current collector in accordance with one aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]      FIG. 6  illustrates schematically a design of a fuel cell stack  200  according to one embodiment of the present invention. The fuel cell stack  200  includes an anode end plate  202 , a cathode end plate  204 , two membrane electrode assemblies  206  and  208 , and a bipolar plate  210 . Opposite surfaces  212  and  214  of the MEA  206  are flush with conductive surfaces of the anode end plate  202  and the bipolar plate  210 , respectively. Opposite surfaces  216  and  218  of the MEA  208  are flush with conductive surfaces of the cathode end plate  204  and the bipolar plate  210 , respectively. (number). 
         [0038]      FIG. 7  illustrates a 4-channel in-plane conductive composite end plate  230  in accordance with one embodiment of the present invention.  FIG. 7A  provides a cross-sectional (side profile) schematic diagram of the 4-channel in-plane conductive composite end plate  230  of  FIG. 7 . As will be appreciated, the end plate  230  represents one possible generic configuration for both anode and cathode end plates such as anode end plate  202  and cathode end plate  204  of  FIG. 6 . The end plate  230  includes a current collector (anode or cathode)  232 , a plurality of flow channels  234 , a thermoplastic flow distributor  236 , and a thermoplastic film web or separator  238 . 
         [0039]    With further reference to  FIGS. 7 and 7A , the dimensions of the end plate  230  will depend upon the specific application. For example, the applicant contemplates a width W in the range of 2 cm-100 cm and a length L in the range of 2 cm-20 cm. The application further contemplates a channel height  240  in the range of 25 micrometers-2.5 mm, a channel width  242  in the range of 0.25 mm 2.5 mm, a shoulder width  244  in the range of 0.25 mm-2.5 mm, an overall thickness in the range of 75 micrometers-6.5 mm, and a web thickness  248  in the range of 25 micrometers-2.5 mm. 
         [0040]      FIG. 8  illustrates a 4-channel in-plane conductive composite bipolar plate  210  in accordance with another embodiment of the present invention.  FIG. 8A  provides a cross-sectional (side profile) schematic diagram of the 4-channel in-plane conductive composite bipolar plate  210  of  FIG. 8 . The bipolar plate  210  includes an anode current collector  250 , a plurality of anode flow channels  252  etched into the anode current collector  250 , an anode thermoplastic flow distributor  254 , a thermoplastic film web or separator  256 , a cathode thermoplastic flow distributor  258 , a cathode current collector  260 , a plurality of cathode flow channels  262  (not fully shown in  FIG. 8 ), and a low resistance external current collector connector  264 . 
         [0041]    With further reference to  FIGS. 8 and 8A , the dimensions of the bipolar plate  210  will depend upon the specific application. For example, the Applicant contemplates an anode channel height  270  of 25 um-2.5 mm, a web thickness  272  of about 25 um-2.5 mm, a shoulder width  274  of about 0.25 mm-2.5 mm, a cathode channel height  276  of about 1.0 mm-2.5 mm, a channel width  278  of about 1.0 mm-2.5 mm and an overall thickness  280  of about 75 um-6.5 mm. 
         [0042]      FIG. 9  illustrates a cross-sectional view of a composite based current collector  300  in accordance with one embodiment of the present invention. The current collector  300  includes a substrate (polymer film support layer)  302 , an adhesive layer  304 , a highly conductive layer  306 , and a conductive protective layer  308 . 
         [0043]    The substrate  302  is preferably comprised of a lightweight material, i.e., a material lighter in weight than a comparable semiconductor, ceramic, metal, or high density graphite substrate. For example, the substrate  302  may include a thermoplastic film material such as Kapton, Imidex, PEEK, Vectra or any other lightweight suitable thermoplastic film material. Thermoplastic film materials are well understood in the art, and are used extensively for deployment in flexible circuits. Amongst other features, they are distinguished for their low manufacturing cost, high yield processing, and superior fatigue resistance. The thickness of the substrate  302  will depend upon the specific implementation, however the present invention contemplates substrate thickness of about 12 um-500 um. 
         [0044]    The adhesive layer  304  may include any suitable conductive metal, metal alloy, or metal multilayer, such as platinum, palladium, ruthenium rhodium, silver, gold, copper niobium, rhenium, molybdenum, tungsten or tantalum, aluminum, iron, nickel, chromium, such as Inconel, Monel, or stainless steels. Many different non-conductive organic materials such as b-stage epoxies, bond-ply layers etc., may be suitable for inclusion in the adhesion layer. The thickness of the adhesive layer  304  will depend upon the specific implementation, and the present invention contemplates thicknesses of about 500 A-250 um. 
         [0045]    The highly conductive layer  306  may be made including any suitable conductive metal, metal alloy, or metal multilayer, such as platinum, palladium, ruthenium rhodium, silver, gold, copper niobium, rhenium, molybdenum, tungsten or tantalum, aluminum, iron, nickel, chromium, such as Inconel, Monel, or stainless steels. The present invention contemplates thicknesses of the highly conductive layer  306  to be about 1 um-100 um. 
         [0046]    The protective conductive layer  308  serves to protect the otherwise exposed surface of the current collector  300  from corrosion in the hostile fuel cell environment. The protective conductive layer  308  may be made including any suitable corrosion resistant conductive metal, metal alloy, or metal multilayer, such as platinum, palladium, ruthenium rhodium, gold, niobium, rhenium, molybdenum, tungsten or tantalum. Many different conductive organic coatings with carbon or metal particles dispersed within the polymer matrix may be suitable for inclusion in the protective conductive layer. The present invention contemplates thicknesses of the protective conductive layer  308  to be about 0.25 um-25 um. 
         [0047]      FIG. 10  illustrates a top view of a substrate  320  of a current collector in accordance with one embodiment of the present invention. The substrate  320  includes a series  322  of embedded microchannels. While the present invention contemplates any suitable shape and design for the microchannels,  FIG. 10  illustrates a non-limiting single pass serpentine example formed into a Kapton-based substrate  320 . 
         [0048]      FIG. 11  illustrates a flow chart of a method  350  for the manufacture of a current collector in accordance with one aspect of the present invention. The manufacture commences with a process  352 , which forms microchannels into the surface of a substrate of the current collector. As described above, the substrate includes a lightweight material, such as a Kapton material, and the process  352  is customized to the specific material. As will be appreciated, the microchannels may be formed via a laser machining process, a chemical etching process, a die stamp process, or any other process suitable to the material of the substrate. In some embodiments of the invention, the microchannels may comprise a serpentine microchannel  322  as illustrated in  FIG. 10 . 
         [0049]    With further reference to  FIG. 11 , upon completion of the process  352 , a next process  354  aligns the microchannels with feedholes such as feedholes  324  of  FIG. 10 . In certain embodiments of the invention, such alignment may be undertaken through a lithographic process. A subsequent process  356  sputters or forms a conductive layer the substrate. As described above with reference to  FIG. 9 , the conductive layer may be comprised of metals such as gold, platinum, or silver; alternatively, the conductive layer may be comprised of a conductive polymer, such as polypyrrole. In embodiments of the invention, a process  358  deposits a protective coating on the conductive layer, to protect from oxidation and/or corrosion. Note that these processes are offered as examples only, and alternative processes for manufacturing current collectors according to the present invention shall be apparent to those skilled in the art. 
       Flow Distributors 
       [0050]    In certain embodiments of the invention, the flow distributor of the plate is comprised of a lightweight material, i.e., a material lighter in weight than a comparable silicon, ceramic, semiconductor, graphite or metal, substrate such as HDPE, Teflon, PEEK, Ultem, Kapton, or any other suitable thermoplastic. The lightweight flow distributors may be mechanically machined, alternatively, these flow distributors may be injection molded or blow molded. Alternatively, these flow distributors may be laser machined, or chemically etched as previously described. 
       Web/Separator 
       [0051]    In certain embodiments of the invention, the web/separator of the plate is comprised of a lightweight material, i.e., a material lighter in weight than a comparable silicon, ceramic, semiconductor, graphite or metal, substrate such as HDPE, Teflon, PEEK, Ultem, Kapton, or any other suitable thermoplastic. The lightweight flow distributors may be mechanically machined, alternatively, these flow distributors may be injection molded or blow molded. Alternatively, these flow distributors may be laser machined, or chemically etched as previously described. 
       CONCLUSION 
       [0052]    The examples of fuel cells and manufacturing techniques discussed herein are for example, illustrative purposes only, and are not intended to limit the scope of the invention. Many modifications, alternative embodiments, and equivalents shall be apparent to those skilled in the art. In particular, substrates employed in current collectors according to embodiments of the present invention are not limited to Kapton or Kapton-type material, and may be comprised of any type of suitable, lightweight material.