Abstract:
High temperature polymer electrolyte membrane fuel cells and techniques related thereto that involve alternative materials. For example, in one aspect, a device includes a high temperature polymer electrolyte membrane fuel cell comprising one or more metal anodes or cathodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. Provisional Application Ser. No. 60/914,685, filed on Apr. 27, 2007, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to high temperature polymer electrolyte membrane fuel cells. 
         [0003]    A fuel cell is a galvanic electrochemical cell that oxidizes a fuel at an anode and reduces an oxidant (typically, oxygen from air) at a cathode to generate electricity. The fuel and the oxidant are different chemical species and therefore the electrodes have different chemical potentials. Accordingly, a potential difference (i.e., the electromotive force) can be generated between an anode and a cathode even when the anode and the cathode are made from the same material. For example, anodes and cathodes can include a platinum catalyst that is neither consumed nor produced by the oxidation or reduction reactions but instead remains largely intact. If the electrodes remain intact, the electromotive force for the generation of electricity can, in principal, continue indefinitely provided that the fuel and oxidant are supplied to the cell. 
         [0004]    In general, the oxidation and reduction reactions will occur in the presence of an electrolyte. Proton conducting electrolytes, such a polymer electrolyte membranes (also known as “proton-exchange membranes”) can act as the electrolyte in a fuel cell. Polymer electrolyte membranes in fuel cells are preferentially permeable to cations such as the protons generated by the oxidation of the fuel. The reduced permeability to the electrons generated by the oxidation of the fuel can be used to direct energized electrons from the anode through an external load and then to the cathode, where electrons and protons combine with oxygen to form water. The directed current flow of energized electrons through the external load can be used to do work. 
         [0005]    One source of protons is from the oxidation of hydrogen gas from reformed hydrocarbons. Hydrogen gas from reformed hydrocarbons is less expensive than hydrogen gas from water electrolysis but generally includes higher concentrations of contaminants such as carbon monoxide. At low temperatures (e.g., between room temperature and 140° C.), even trace amounts of carbon monoxide can poison a platinum catalyst and impair or even halt the generation of electricity. At higher temperatures (e.g., above 140° C., such as between 160° C. and 200° C.), platinum catalysts can tolerate higher levels of carbon monoxide and other contaminants in gaseous hydrogen fuel. For example, a platinum catalyst can tolerate up to 2% CO without crippling performance loss. 
         [0006]    In addition to facilitating the use of reformed hydrocarbon feedstocks, high temperature polymer electrolyte membrane fuel cells have other advantages. For example, high temperature polymer electrolyte membrane fuel cells have been shown to operate for relatively long periods (e.g., in excess of 10,000 hours) and with a relatively low amount of performance degradation over time (e.g., less than about 0.0045 mV/h). Many high temperature polymer electrolyte membrane fuel cells also have relatively favorable design characteristics, including relatively high shock and vibration tolerance, gas phase reactants and products (which provides simplified one-phase fluid handling and relatively simple water management issues), fewer thermal control issues (e.g., smaller radiators and simplified reformer integration into fuel cells), and increased catalytic activity associated with higher temperatures. 
         [0007]    Because high temperature polymer electrolyte membrane fuel cells operate at relatively high temperatures, there are certain fundamental limitations on the materials that are used in high temperature polymer electrolyte membrane fuel cells. For example, commercially available NAFION, which is a common polymer electrolyte membrane in low temperature applications, is generally only conductive below 120° C. and hence not used in high temperature polymer electrolyte membrane fuel cells. Instead, polybenzimidazole fiber that is loaded with phosphoric or other acid can be formed into a polymer electrolyte membrane and is used in high temperature polymer electrolyte membrane fuel cells. The acidic, high temperature environment created by this use is relatively highly corrosive and places other limitations on material properties of other fuel cell components, such as the bipolar plates. Bipolar plates collect the current while funneling chemicals to and products from the anode and cathode. 
         [0008]    Bipolar plates in high temperature polymer electrolyte membrane fuel cells can be made from conducting carbon, such as POCO graphite plates. Graphite is a conducting carbon that oxidizes slowly. The conducting surface of graphite plates thus remains suitable even for high temperature polymer electrolyte membrane fuel cells for relatively long periods. However, graphite is relatively bulky and difficult to fabricate into the forms convenient for use as bipolar plates. 
         [0009]    Nitrided metals, such as stainless steel, are candidate materials for bipolar plates in room temperature fuel cells. 
       SUMMARY 
       [0010]    The present inventors have recognized that conducting carbon bipolar plates are heavy, difficult to machine, and relatively brittle. Experimental investigations have shown that certain metals may be suitable replacements for conducting carbon in the bipolar plates of high temperature polymer electrolyte membrane fuel cells. Also, the inventors have recognized that certain polymeric materials may be suitable for making endplates of high temperature polymer electrolyte membrane fuel cell stacks. These materials can thus lead to fuel cells stacks with higher specific and volumetric power densities. 
         [0011]    Accordingly, the inventors have developed high temperature polymer electrolyte membrane fuel cells and techniques related thereto that involve alternative materials. 
         [0012]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a schematic representation of a high temperature polymer electrolyte membrane fuel cell. 
           [0014]      FIGS. 2-4  are graphs that illustrate aspects of the corrosion resistance provided by HASTELLOYS. 
           [0015]      FIG. 5  shows another implementation of anodes and/or cathodes in the high temperature polymer electrolyte membrane fuel cell of  FIG. 1 . 
           [0016]      FIG. 6  is a schematic representation of a high temperature polymer electrolyte membrane fuel cell stack. 
           [0017]      FIG. 7  illustrates a system for generating electricity that includes high temperature polymer electrolyte membrane fuel cells. 
           [0018]      FIG. 8  is a graph that illustrates the operational characteristics of one implementation of the system  FIG. 7 . 
           [0019]      FIG. 9  is a graph that illustrates the operational characteristics of a PEMEAS MEA housed by Hastelloy bipolar plates before and after soaking the plates in phosphoric acid at 150° C. for 12 hours. 
       
    
    
       [0020]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0021]      FIG. 1  is a schematic representation of one implementation of a high temperature polymer electrolyte membrane fuel cell  100 . Fuel cell  100  includes an anode  105  and a cathode  110  that are separated by a proton conducting electrolyte  115 . Proton conducting electrolyte  115  preferentially conducts protons from anode  105  to cathode  110 . For example, proton conducting electrolyte  115  can be a polymer electrolyte membrane such as polybenzimidazole fiber that is loaded with phosphoric or other acid. 
         [0022]    Anode  105  and cathode  110  each include a catalyst  120  and a conductive plate  125 . Catalyst  120  can be one or more materials that catalyze oxidation and reduction reactions that occur at anode  105  and cathode  110 . In some implementations, catalyst  120  can be identical in both anode  105  and cathode  110 . In other implementations, catalyst  120  in anode  105  can differ in composition and/or treatment from catalyst  120  in cathode  110 . Catalyst  120  in can be porous platinum catalysts that are poisoned by carbon monoxide at low temperatures. 
         [0023]    Conductive plate  125  can be self-supporting solid member that defines an outer boundary of the region where reactions occur in fuel cell  100 . Each conductive plate  125  can be in electrical contact with a corresponding catalyst  120  so that electrons released from fuel in anode  105  are provided a conductive path  130  to cathode  110  for the reduction of oxidant. The electrons flowing along path  130  can be used to perform work W. Fuel and oxidant can be supplied to cell  100  over any of a number of different flow paths. For example, anode  105  and cathode  110  can be separated by a distance D that is larger than a thickness T of proton conducting electrolyte  115 . Fuel and oxidant can be supplied to cell  100  through the resulting gap. As another example, one or more of conductive plates  125  and catalysts  120  can include channels (not shown) for the supply of fuel and oxidant to cell  100 . 
         [0024]    Please note that although conductive plates  125  can be separated from proton conducting electrolyte  115  by catalysts  120  and/or the gap discussed above, in practical terms, conductive plates  125  are likely to be exposed to proton conducting electrolyte  115  during operation. For example, the movement of fuel cell  100 , the generation of gaseous species, the use of porous catalysts  120 , and/or defects and other vagaries in the construction of fuel cell  100  will result in contact between conductive plates  125  and fluids in proton conducting electrolyte  115 . Such fluids can include acids that load a polybenzimidazole proton conducting electrolyte  115 . 
         [0025]    High temperature polymer electrolyte membrane fuel cell  100  can be designed to operate at temperatures in excess of 140° C., such as between 160° C. and 200° C. or between 160° C. and 190° C. This design can be implemented using thermal management systems, as discussed further below. Despite these relatively high operational temperatures and the corrosive environment created by acidic proton conducting electrolytes  115 , one or more conductive plates  125  can be made from a metal. For example, conductive plates  125  can include high nickel-content steel alloys such as HASTELLOYS (Haynes International, Inc., Kokomo, Ind., U.S.A.). For example, conductive plates  125  can be made from HASTELLOY C276, HASTELLOY C22, HASTELLOY C2000, and combinations thereof. As another example, conductive plates  125  can be made from low chromium HASTELLOYS, such as HASTELLOY B3 and HASTELLOY C242. 
         [0026]    The composition of HASTELLOY C276, HASTELLOY C22, HASTELLOY C2000 is presented in Table 1. The composition of HASTELLOY B3 is presented in Table 2 and HASTELLOY C242 is presented in Table 3. 
         [0027]    When conductive plates  125  are made from metals, they can be made relatively thin, for example, about 0.1 mm (4 mil) thick. This relative thinness decreases the weight of conductive plates  125  and hence the volume and weight of fuel cell  100 . Such decreases in volume and weight are of particular importance when fuel cell  100  is to be moved, such as when fuel cell  100  is part of a vehicle. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Alloy 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Designation 
                 UNS# 
                 C 
                 Co 
                 Cr 
                 Cu 
                 Fe 
                 Mn 
                 Mo 
                 Ni 
                 P 
                 S 
                 Si 
                 V 
                 W 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Hastelloy(R) 
                 N10275 
                 4e−3 
                 1.45 
                 15.74 
                 n/a 
                 5.58 
                 0.50 
                 15.53 
                 57.55 
                 0.008 
                 0.003 
                 0.02 
                 0.163 
                 3.45 
               
               
                 C276 
               
               
                 Hastelloy(R) 
                 N06022 
                 4e−3 
                 0.72 
                 21.00 
                 n/a 
                 3.90 
                 0.23 
                 13.30 
                 57.90 
                 0.011 
                 0.004 
                 0.026 
                 0.013 
                 2.90 
               
               
                 C22 
               
               
                 Hastelloy(R) 
                 N06200 
                 1e−3 
                 0.05 
                 22.71 
                 1.54 
                 0.65 
                 0.23 
                 15.64 
                 59.12 
                 0.003 
                 0.004 
                 0.043 
                 n/a 
                 n/a 
               
               
                 C2000 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Alloy 
                 Ni 
                 Mo 
                 Cr 
                 Fe 
                 Co 
                 W 
                 Mn 
                 Al 
                 Ti 
                 Si 
               
               
                   
               
             
             
               
                 B3 
                 65 b   
                 28.5 
                 1.5 
                 1.5 
                 3* 
                 3* 
                 3* 
                 0.5* 
                 0.2* 
                 0.1* 
               
               
                   
               
               
                   b Minimum 
               
               
                 *Maximum 
               
             
          
         
       
     
         [0000]    
       
         
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 ALLOY C242 
               
               
                   
               
             
             
               
                 65Ni a —25Mo—8Cr—2.5Co*—2Fe*—0.8Mn*—0.8Si*—0.5Al*0.5Cu*—0.03C*—0.006B* 
               
               
                   
               
               
                   a As Balance 
               
               
                 *Maximum 
               
             
          
         
       
     
         [0028]    When conductive plates  125  are made from metals, they can be fabricated using metal fabrication techniques, such as stamping. Such stamping can be used to pattern or otherwise form features in conductive plates  125 . For example, channels for the supply of fuel and oxidant to cell  100  can be stamped in conductive plates  125 . 
         [0029]      FIG. 2  is a graph  200  that illustrates one aspect of the corrosion resistance provided by HASTELLOYS. In particular, graph  200  includes an X-axis  205  and a Y-axis  210 . The position of ordinates along Y-axis  210  reflects the weight-% of metal coupons that remain after exposure to 85% H 3 PO 4  at 150° C. in air. The position of abscissae along X-axis  205  reflects the time after such exposure commenced. The behavior of the samples under these conditions is believed to reflect the relative stability of conductive plates  125  formed from these metals under operational conditions in high temperature polymer electrolyte membrane fuel cells. 
         [0030]    These measurement results, and the results illustrated in  FIGS. 3 and 4  below, were made using HASTELLOY were obtained from Haynes International. Other metal samples were donated by GenCell (Southbury, Conn.). Weight measurements were made by weighing metal samples of approximately 1 cm×2 cm×0.1 cm in size and approximately 1 g to 2 g in weight, submerging the samples in 85% phosphoric acid at 150° C. in air, removing selected samples at known intervals, rinsing the removed samples in water and alcohol, and then drying the rinsed samples in an oven at 100° C. in air for 1 minute. The samples were then reweighed. Metal resistance was measure in plane using a DC ohmmeter with probes in the middle of the sample and separated by 1 cm along the 2 cm length of the metal strip. 
         [0031]    As can be seen, HASTELLOY C22, HASTELLOY C2000, and two different samples of HASTELLOY C276 (i.e., “C276-a” and “C276-b”) retain over 80% of their weight after 200 hours. On the other hand, titanium, nickel, and stainless steels SS316 and SS310 lose weight much quicker. The weight retention of HASTELLOY C22, HASTELLOY C2000, and/or HASTELLOY C276 is due to the rapid passivation of HASTELLOY C22, HASTELLOY C2000, and/or HASTELLOY C276 through the formation of a passivation layer on the exposed surfaces thereof. Since the amount of weight lost from HASTELLOY C22, HASTELLOY C2000, and HASTELLOY C276 is relatively low, conductive plates  125  made therefrom can be thin and light weight. 
         [0032]    A resistance of 0.6 Ohms was measured on 1 cm by 2 cm by 0.1 cm HASTELLOY C22 and C276 plates with probes that were 1 cm apart on long side. Such a conductivity is believed to be sufficient to allow conductive plates  125  made from HASTELLOY C22, HASTELLOY C2000, and/or HASTELLOY C276 to be in electrical contact with a corresponding catalyst  120 . This conductivity remains despite the rapid repassivation of HASTELLOY C22, HASTELLOY C2000, and/or HASTELLOY C276. In particular, the passivations layers retain and electron conductivity that is similar to metals such as copper and aluminum. 
         [0033]      FIG. 3  is a graph  300  that illustrates another aspect of the corrosion resistance provided by HASTELLOYS. In particular, graph  300  includes an X-axis  305  and a Y-axis  310 . The position of ordinates along Y-axis  210  reflects the weight-% of metal coupons that remain after exposure to 85% H 3 PO 4  at 150° C. in air. The position of abscissae along X-axis  205  reflects the time after such exposure commenced. The behavior of the samples under these conditions is believed to reflect the relative stability of conductive plates  125  formed from these metals under operational conditions in high temperature polymer electrolyte membrane fuel cells. 
         [0034]    As can be seen, HASTELLOY C22 and HASTELLOY C276 retain over 70% of their weight after 1200 hours. Moreover, the rate of decrease in weight become negligible. On the other hand, titanium, nickel, and stainless steels SS316 and SS310 lose weight much quicker. The weight retention of HASTELLOY C22 and HASTELLOY C276 is due to the rapid passivation of HASTELLOY C22 and HASTELLOY C276 through the formation of a passivation layer on the exposed surfaces thereof. Since the amount of weight lost from HASTELLOY C22 and HASTELLOY C276 is relatively low, conductive plates  125  made therefrom can be thin and light weight. Since the dissolution rate of HASTELLOY C22 and HASTELLOY C276 is relatively low, conductive plates  125  made therefrom can have long operational lifespans. 
         [0035]      FIG. 4  is a graph  400  that illustrates another aspect of the corrosion resistance provided by HASTELLOYS. In particular, graph  400  includes an X-axis  405  and a Y-axis  410 . The position of ordinates along Y-axis  210  reflects the weight-% of metal coupons that remain after exposure to 85% H 3 PO 4  at 150° C. in air. The position of abscissae along X-axis  205  reflects the time after such exposure commenced. The behavior of the samples under these conditions is believed to reflect the relative stability of conductive plates  125  formed from these metals under operational conditions in high temperature polymer electrolyte membrane fuel cells. 
         [0036]    As can be seen, HASTELLOY C22 and HASTELLOY C276 retain over 60% of their weight after 2560 hours. On the other hand, titanium, nickel, stainless steels SS316 and SS310, and dimensionally stable anode (DSA), a ruthenium oxide coated titanium sheet lose weight much quicker. The weight retention of HASTELLOY C22 and HASTELLOY C276 is due to the rapid passivation of HASTELLOY C22 and HASTELLOY C276 through the formation of a passivation layer on the exposed surfaces thereof. Since the amount of weight lost from HASTELLOY C22 and HASTELLOY C276 is relatively low, conductive plates  125  made therefrom can be thin and light weight. Since the dissolution rate of HASTELLOY C22 and HASTELLOY C276 is relatively low, conductive plates  125  made therefrom can have long operational lifespans. 
         [0037]      FIG. 5  shows another implementation of either of anode  105  and/or cathode  110 . In addition to catalyst  120  and conductive plate  125 , these implementations of electrodes  105 ,  110  also includes a layer  505  of corrosion resistant material between catalyst  120  and conductive plate  125 . 
         [0038]    Layer  505  can have a corrosion resistance that exceeds that of conductive plate  125 , even if conductive plate  125  is formed from one or more HASTELLOY&#39;s, as discussed above. Layer  505  can be formed from a material having a low electrical sheet resistance. For example, layer  505  can be formed from a graphite or noble metal paint, ruthenium oxide, and/or sputtered, evaporated, or plated noble metals. In one implementation, layer  505  can be formed from a dispersion of semi-colloidal graphite in a thermoset binder, such as DAG EB-023 or DAG EB-030 (Acheson Colloid U.S., Port Huron, Mich. USA). In another implementation, layer  505  can be formed from gold electroplate. For example, a gold layer can be electroplated to have a thickness that is thicker than 10 nanometers, e.g., up to several microns. 
         [0039]    Layer  505  can be so thin that it is not self-supporting. In other words, layer  505  can require support from conductive plate  125  to retain mechanical stability. For example, layer  505  can be applied as a paint, using spraying and or brushing. As another example, layer  505  can be applied using thin film deposition techniques such as spin or dip coating. 
         [0040]    Please note that layer  505  need not be free from defects. Rather, layer  505  can include one or more defects that allow catalyst  120  and conductive plate  125  to contact. 
         [0041]      FIG. 6  is a schematic representation of a high temperature polymer electrolyte membrane fuel cell stack  600 . A fuel cell stack is a collection of fuel cells that are electrically connected in series. High temperature polymer electrolyte membrane fuel cell stack  600  includes a collection of anodes  105 , proton conducting electrolytes  115 , and cathodes  110  that are connected in series. Please note that a single element can act both as an anode  105  and a cathode  110  in fuel cell stack  600 . In particular, as shown, fuel cell stack  600  can include one or more bipolar plates  105 , 110 . One side of bipolar plate  105 , 110  can act as anode while the other side acts as a cathode in adjacent high temperature polymer electrolyte membrane fuel cells. Bipolar plates  105 , 110  thus form the electrical series connection between these adjacent cells. 
         [0042]    Fuel cell stack  600  can also include sealing members  605 , cooling plates  610 , and end plates  615 . Sealing members  605  can seal cells in stack  600  to prevent undesired mixing of fuels and oxidants. Sealing members  605  can be, e.g., thermoplastic members that are compression fit between adjacent anodes  105 , proton conducting electrolytes  115 , and cathodes  110 . 
         [0043]    Cooling plates  610  can be part of a thermal management system for stack  600 . For example, cooling plates  610  can include a radiator element with a fluid flow path for removing heat from stack  600 . In some implementations, the heat removed from stack  600  can be used to elevate the temperature of a reformer, as discussed further below. Cooling plates  610  can be electrically conductive and can electrically connect an anode  105  in one high temperature polymer electrolyte membrane fuel cell to a cathode  110  in another such cell, as shown. Cooling plates  610  can thus be part of the electrical series connection between adjacent high temperature polymer electrolyte membrane fuel cells. 
         [0044]    End plates  615  are part of the mechanical structure of fuel cell stack  600 . For example, end plates  615  can serve to isolate fuel cell stack  600  from the outside environment. End plates  615  can also be part of a mechanism for compressing fuel cell stack  600  laterally, e.g., so that compression seals can be formed by sealing members  605 . 
         [0045]    The present inventors have recognized that end plates  615  can include certain polymeric materials. For example, the inventors have recognized that end plates  615  can include polyimide composites such as AVIMID-N (DuPont de Nemours, E. I., Co., Wilmington, Del., U.S.A.). The inventors have recognized that AVIMID-N provides sufficient stiffness and mechanical strength combined with sufficient resistance to thermal oxidation and has a sufficient stability to endure long term exposure to the operational temperatures of high temperature polymer electrolyte membrane fuel cells. 
         [0046]    High temperature polymer electrolyte membrane fuel cells can be incorporated into a system for generating electricity either individually or as part of a fuel cell stack.  FIG. 7  illustrates such a system, namely, a system  700  that includes one or more fuel cells  705  and one or more reformers  710 . Fuel cells  705  can include one or more fuel cells  100  ( FIG. 1 ). For example, fuel cells  705  can include several fuel cells  100  arranged in electrical series in a fuel cell stack  600  ( FIG. 6 ). Reformers  710  can include one or more reformers to crack hydrocarbons and form a fuel such as hydrogen gas. For example, reformers  710  can be one or more methanol steam reformers, such as those described in U.S. Patent Publication No. 2004/0179980 to A. Pattekar and M. Kothare, the contents of which are incorporated herein by reference. 
         [0047]    In operation, a hydrocarbon-containing feedstock  715  (such as methanol and water) can be fed into reformers  710 . Reformers  710  can crack feedstock  715  to yield fuel  720  (such as hydrogen) that is fed into fuel cells  705 . Please note that, given that fuel cells  705  can be high temperature polymer electrolyte membrane fuel cells, fuel  720  can include carbon monoxide and other contaminants and yet platinum catalysts in fuel cells  705  can remain operational. Fuel cells  705  can oxidize fuel  720  to generate electrical power  725  that can be used to do work. As a consequence of the reactions associated with oxidizing fuel  720 , fuel cells  705  can also generate excess heat  730  that can be returned to reformers  710  for use in cracking feedstock  715 . For example, heat  730  can be used to vaporize feedstock  715 . 
         [0048]      FIG. 8  is a graph  800  that illustrates the operational characteristics of one implementation of a system  700  ( FIG. 7 ). In this implementation, a four cell, 10 watt stack that operated at 170° C. was fed air and hydrogen from a pair of methanol steam reformers that operated in parallel. The methanol reformers have been described in the article entitled “A Microreactor for Hydrogen Production in Micro-Fuel Cell Applications” by A. Pattekar and M. Kothare in the Journal of Microelectromechanical Systems, Vol. 13: 7-18 (2004), the contents of which are incorporated herein by reference. The reformers were loaded with Sud Chemie C18-7 Cu/ZnO/Al 2 O 3  catalyst, heated on a hot plate to a temperature of approximately 180° C. The reformers were &lt;0.02 liter in volume and weighed 0.05 kilogram. A liquid feedstock of 1 part methanol to 1.25 part water was fed to the reformers at 8 ml per hour (152 sccm hydrogen gas) using a precision syringe pump and a 10 ml Hamilton μL Gastight syringe. Fluid connections between the feedstock source and the reformers, and from the reformers to the fuel cell stack, were made using Teflon tubing. 
         [0049]    As the liquid feedstock reached the reformer inlets, pressures of 3 to 15 psig start to accumulate. A condenser was used to remove liquid water and trace amounts of methanol from the reformate and the dry reformate was input into the fuel cell stack. The fuel cell stack used a polybenzimidazole proton electrolyte membrane (PEM), as described in the publication entitled “A H 2 /O 2  Fuel Cell Using Acid Doped Polybenzimidazole as a Polymer Electrolyte” by J-T. Wang, et al. in Electrochimica Acta, Vol. 41, pp. 193-197 (1996), the contents of which are incorporated herein by reference. Platinum-catalyzed porous electrodes with a loading of about 1 mg-Pt/cm2 were used to make membrane electrode assemblies. Such assemblies have been demonstrated to have long term operational lifespans (&gt;10,000 hours) with a performance degradation rate of only ˜0.0045 mV/h. The fuel cell stack included four phosphoric acid loaded PBI MEAs (Area per MEA=25 cm2; Total area per 4-cell stack=100 cm2) (available from PEMEAS, Murray Hill, N.J.) in an commercial graphite four cell stack housing fitted with a resistance heater (Electrochem Inc, Woburn Mass.). The resistance heater was controlled by a thermocouple fitted to feedback electrical controller (Omega). 
         [0050]    The internal resistance of the four cell in series stack at open circuit conditions at 150° C. was 0.5 Ohm per 25 cm 2 , and was obtained from the real and imaginary plot of the stack impedance as the high frequency intercept of impedance on the real axis using a Solartron 1286 electrochemical interface (potentiostat) coupled to a Solartron 1250 frequency response analyzer (FRA). The measurement parameters included a potentiostatic amplitude of 10 mV and a frequency of 0.1 to 50,000 Hz. 
         [0051]    The performance of the system as a power source was measured by connecting resistors between the anode and cathode and measuring the voltage across the resistors. The cell current was measured using an ammeter connected in series with the load. 
         [0052]    Graph  800  includes an X-axis  805  and a pair of Y-axes  810 ,  815 . The position of ordinates along Y-axis  810  reflects the voltage in volts that was output from this system. The position of ordinates along Y-axis  815  reflects the power in watts that was output from this system. The position of abscissae along X-axis  805  reflects the current in amps that that was output from this system. 
         [0053]    In some implementations, metal conductive plates  125  can be preconditioned for use in a high temperature polymer electrolyte membrane fuel cell  100 . For example, high nickel-content steel alloys such as HASTELLOYS can be preconditioned to improve stability under high temperature polymer electrolyte membrane fuel cell conditions. In one implementation, HASTELLOYS such as HASTELLOY C22 can be preconditioned by soaking in phosphoric acid at 150° C. overnight. After removal, the surface can be abraded (e.g., using 600 SiC sandpaper) and the stability of the metal conductive plate in a high temperature polymer electrolyte membrane fuel cell can be improved. 
         [0054]      FIG. 9  is a graph  900  that illustrates the operational characteristics of an implementation of a system  700  ( FIG. 7 ) in which metal conductive plates  125  can be preconditioned. In this implementation, the fuel cell operates above 170° C. using a PEMEAS membrane electrode assembly having a commercial phosphoric acid loaded polybenzimidazole membrane sandwiched between platinum catalyzed porous gas-fed electrodes (i.e., oxygen was fed to the cathode and hydrogen was fed to the anode). 
         [0055]    Graph  900  includes an X-axis  905  and a Y-axis  910 . The position of ordinates along Y-axis  910  reflects the voltage that the fuel cell produced. The position of abscissae along X-axis  905  reflects the time that the fuel cell was operated. A pair of traces  915 ,  920  are plotted on graph  900 . Trace  915  shows the voltage generated with HASTELLOY C22 plates that were not preconditioned at a current density of 20 mA/cm 2 . Trace  9205  shows the voltage generated at a current density of 50 mA/cm 2  using HASTELLOY C22 plates that were preconditioned by soaking in phosphoric acid at 150° C. overnight and abraded using 600 SiC sandpaper. As can be seen, HASTELLOY C22 plates without preconditioning are stable for about 60,000 seconds and fail after about 80,000 seconds. Preconditioned HASTELLOY C22 plates are stable beyond the period illustrated in the graph. 
         [0056]    Although the physical mechanism underlying the effectiveness of such preconditioning is still being investigated, it is suspected that preconditioning depletes one or more impurities from the plates  125 . For example, it is suspected that chromium impurities may be depleted. 
         [0057]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, proton conducting electrolyte  115  and catalysts  120  can be purchased as a unit, such as the polymer electrolyte membrane electrode assemblies available from PEMEAS (Murray Hill, N.J., U.S.A.). In cases such as these, there is no need for a seal between proton conducting electrolyte  115  and catalysts  120 . Instead a seal can be positioned between catalysts  120  and a conductive plate  125  to prevent undesired mixing of fuels and oxidants. Accordingly, other implementations are within the scope of the following claims.