Abstract:
An example interconnector of a fuel cell repeater unit includes a dimpled interconnector of a fuel cell repeater unit. The dimpled interconnector establishes at least a portion of an interconnector flow path operative to communicate airflow through the fuel cell repeater unit, the dimpled interconnector having a plurality of dimples.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/770032, filed 29 Apr. 2010, which is a continuation-in-part of U.S. patent application Ser. No. 12/679772, filed 24 Mar. 2010, which is a National Phase application of International Application No. PCT/US2008/080671. These applications are each incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    This invention was made with United States Government support under Contract No. DE-FC26-01NT41246 awarded by the Department of Energy. The United States Government may have certain rights in this invention. 
     
    
     TECHNICAL FIELD 
       [0003]    This disclosure relates generally to fuel cells and, more particularly, to repeater units that facilitate fuel cell fluid communication through a fuel cell stack assembly. 
       DESCRIPTION OF RELATED ART 
       [0004]    Fuel cell stack assemblies are well known. Some fuel cell stack assemblies include multiple repeater units arranged in a stacked relationship. The repeater units each typically include a fuel cell, such as a solid oxide fuel cell (SOFC), that has an electrolyte layer positioned between a cathode electrode layer and an anode electrode layer. Providing the SOFC with a supply of fuel and air generates electrical power in a known manner. An interconnector near the anode electrode layer and another interconnector near the cathode electrode layer electrically connect the repeater unit to an adjacent repeater unit in the stack. 
         [0005]    As known, some fuel cell stack assemblies rely on complex arrangements for delivering supplies of fuel and air to the SOFC within each repeater unit. Adding more repeater units to the fuel cell stack assembly typically increases the size and complexity of the delivery arrangement because each repeater unit includes an SOFC requiring an evenly distributed supply of fuel and air. One example prior art arrangement includes multiple repeater units that each have a complex pattern of holes for fuel delivery and another pattern of holes for air delivery. Aligning these holes is difficult and time consuming. Achieving durable hermetic sealing between complex air and fuel holes is challenging. 
         [0006]    What is needed is a simplified arrangement for delivering supplies of fuel and air to an SOFC and for distributing air and fuel uniformly at the electrodes. 
       SUMMARY 
       [0007]    An example fuel cell repeater includes a separator plate and a frame establishing at least a portion of a flow path that is configured to fluidly couple a fuel supply with at least one fuel cell held by the frame relative to the separator plate. The flow path has a flow path perimeter. The flow path is within the flow path perimeter and configured to direct flow across the at least one fuel cell within a first plane. A dimpled interconnector portion establishes at least a portion of an interconnector flow path operative to communicate airflow through the fuel cell repeater. 
         [0008]    An example fuel cell repeater unit includes a separator plate. A frame establishes at least a portion of a fuel flow path that is configured to fluidly couple a fuel supply with at least one fuel cell held by the frame relative to the separator plate. The fuel flow path has a perimeter. the fuel flow path within the perimeter is configured to direct flow across the at least one fuel cell within a first plane. The separator plate, the frame, or both establish at least one conduit that is positioned outside the flow path perimeter and is fluidly coupled with the flow path. The at least one conduit is configured to direct flow within a second, different plane. The planes are nonparallel. A dimpled interconnector portion establishes at least a portion of an interconnector flow path that is operative to communicate airflow through the fuel cell repeater unit, the dimpled interconnector having a plurality of dimples. 
         [0009]    An example interconnector of a fuel cell repeater unit includes a dimpled interconnector of a fuel cell repeater unit. The dimpled interconnector establishes at least a portion of an interconnector flow path operative to communicate airflow through the fuel cell repeater unit, the dimpled interconnector having a plurality of dimples. 
         [0010]    These and other features of the disclosed examples can be best understood from the following specification and drawings. The following is a brief description of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a schematic sectional view of an example fuel cell arrangement having 6 fuel cells in a 2×3 matrix configuration. 
           [0012]      FIG. 2  shows an example fuel cell stack assembly. 
           [0013]      FIG. 3  shows a perspective view of an example repeater unit. 
           [0014]      FIG. 4  shows an exploded view of the  FIG. 3  repeater unit. 
           [0015]      FIG. 5  shows a sectional view through line  5 - 5  of  FIG. 3 . 
           [0016]      FIG. 6  shows an example stack of the  FIG. 3  repeater units. 
           [0017]      FIG. 7  shows a sectional view through a portion of the  FIG. 6  stack. 
           [0018]      FIG. 8  shows a perspective view of an example fuel cell arrangement having multiple fuel cell stack assemblies. 
           [0019]      FIG. 9  shows a top schematic view of  FIG. 8  fuel cell arrangement having multiple fuel cell stack assemblies. 
           [0020]      FIG. 10  shows an exploded view of another example repeater unit. 
           [0021]      FIG. 11  shows a top view of the  FIG. 10  repeater unit. 
           [0022]      FIG. 12  shows a section view through line  12 - 12  of  FIG. 11 . 
           [0023]      FIG. 13  shows an example stack assembly rig. 
           [0024]      FIG. 14  shows a section view of an example interconnector. 
           [0025]      FIG. 15  shows a section view of another example interconnector. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring to  FIG. 1 , an example fuel cell arrangement  10  includes a fuel cell stack assembly  14  housed within a duct  18 . The fuel cell stack assembly  14  includes multiple repeater units  22 . In this example, each of the repeater units  22  includes a plurality of tri-layer solid oxide fuel cells (SOFC)  26  that are arranged in a 2×3 matrix and aligned within the same plane. Other examples include different numbers of the SOFCs  26 , such as a single SOFC, and different arrangements, such as a 3×3 matrix or a 4×2 matrix. The SOFCs utilize supplies of fuel and air to generate electrical power in a known manner. The M×N matrix of fuel cells in a plane, where M, the number of rows, or N, the number of columns, is an integer equal or greater than 1, is referred to as the window frame design. 
         [0027]    The tri-layer solid oxide fuel cells  26  discussed herein are planar and comprise the anode electrode layer, the electrolyte layer, and the cathode electrode layer. The electrolyte layer is sandwiched between the anode electrode and the cathode electrode. In all the drawings,  FIG. 1-9 , the anode electrode faces down. The anode electrode may face up as another example. 
         [0028]    In this example, a fuel supply reservoir  30  provides fuel that is directed through at least one conduit  34   a  to the repeater unit  22 . The at least one conduit  34   a  is partially established by the repeater unit  22  in this example. Spent fuel is directed from the SOFC  26  to at least one second conduit  34   b  and then away from the repeater unit  22 . In this example, a spent fuel reservoir  38  holds spent fuel. A fuel pump  42  facilitates moving fuel through the repeater unit  22 . 
         [0029]    In this example, an air supply  44  provides air that is directed to the duct  18  through an air inlet  46 . Within the duct  18 , air moves across the repeater unit  22  and leaves the duct  18  through an air outlet  54 . Air inlet  46  and air outlet  54  can be located in a variety of duct  18 , any vertical face, bottom face, or top face. The SOFC  26  uses the oxygen in the air for the electrochemical reaction and releases spent air, i.e., air with reduced oxygen content, through the air outlet  54 . This example includes a spent air reservoir  56 . An air pump  50  facilitates moving air to the duct  18  and across the repeater unit  22 . In some examples, the fuel supply reservoir  30 , the spent fuel reservoir  38 , the air supply  44 , and the spent air reservoir  56  also denote piping connections or junctions between the fuel cell arrangement  10  and a fuel cell system or power plant comprising multiples of the fuel cell arrangement  10 . 
         [0030]    Referring to  FIGS. 2-5 , the fuel cell stack assembly  14  holds multiple repeater units  22  together between end plates  58 . Bolts  62 , or similar mechanical fasteners, or an external loading mechanism, secure the example components together. The corner portions  64  of the repeater units  22  and the end plates  58  establish the fuel cell conduits  34   a  and  34   b,  which have a generally circular cross-section in this example. The conduits  34   a  and  34   b  in the example of  FIG. 1  have a rectangular cross section. The length L of the conduits  34   a  and  34   b  corresponds generally to the height of the fuel cell stack assembly  14 . The conduits  34   a  and  34   b  will also be referred to as the primary fuel manifolds. 
         [0031]    The example individual repeater units  22  each include a cell frame  70  secured to separator plate  66  to form a cassette-like structure. In one example, the separator plate  66  and the cell frame  70  are welded at their outer perimeters to effectively hermetically seal the fuel gas space in the fuel cell stack assembly  14 . 
         [0032]    The separator plate  66  and the cell frame  70  include holes that establish a portion of the conduits  34   a  and  34   b  in this example. Together, a plurality of the separator plates  66  and cell frames  70 , and the sealant material  92  located therebetween and around conduits  34   a  and  34   b,  establish the conduits  34  when they are in a cell stack assembly  14 . 
         [0033]    The SOFCs  26  and corresponding flat wire mesh interconnects  74 , which is also referred to as the anode-side interconnect, are held between the cell frame  70  and the separator plate  66 . For the flat wire mesh interconnect the wire diameter ranges from 0.5 to 2 mm, and the wire composition is selected from the group of nickel, copper, and nickel-copper alloys. In another example, the flat wire mesh interconnects  74  comprise corrugated expanded metal. For the corrugated wire mesh, the wire diameter ranges from 0.125 mm to 0.250 mm, and the wire composition is selected from the group of nickel-based alloys, nickel-chromium alloys, including Haynes 230, Inconels, and Hastelloys. In yet another example, the flat wire mesh interconnects  74  are replaced with dimples extending from the separator plate  66 . In yet another example, the flat wire mesh interconnects  74  are replaced with sheets of metallic foam. For metallic foam, the material is selected from nickel foams, copper foams, or nickel-copper alloy foams. 
         [0034]    Each repeater unit  22  holds multiple SOFCs  26  within the same plane in this example. Openings  78  through the cell frame  70  leave a portion of the SOFCs  26  exposed. In this example, the openings  78  are larger than the cathode electrode layer of the SOFCs  26 . The example openings  78  have a rectangular profile. The cell frame  70  contacts the electrolyte surface of the SOFCs  26  at a joint  71  made of glass, glass ceramics, ceramics, metal oxides, metal brazes or a combination of them. 
         [0035]    Some portions of the cell frame  70  are spaced from the separator plate  66  to provide a fuel channel  72 , which comprises a trough-like cavity extending along the front and the back of the repeater unit  22 , the front being ahead of the first row of cells and the back being after the last row of cells in the repeater unit. Fuel moving within the repeater unit  22  flows within the fuel channel  72  and across the fuel cells  26 . The flow channel  72  will also be referred to as the secondary fuel manifold. 
         [0036]    In some examples, the cell frame  70  comprises a stamped piece. The equipment stamping the cell frame  70  is configured to deform the relatively planar stock material to establish the portion of the cell frame  70  that corresponds to the fuel channel  72  and accommodates the heights of the anode side interconnect  74 , the fuel cell  26 , the height of the bonding materials that may be used to bond the interconnect  74  to the anode electrode of the fuel cell  26 , and the height of the sealing materials that are used to bond and seal the top electrolyte surface at the periphery of the fuel cell  26  to the corresponding underside surface of cell frame  70 . The bonding and sealing materials are not shown in the drawings. The stamping operation moves a first portion  79  of the cell frame  70  away from a second portion  81 . In this example, the amount of movement, and relative deformation, between the first portion  79  and the second portion  81  corresponds to a height h, which is the approximate sum of the heights of the SOFC  26 , the anode side interconnect  74 , and any bonding materials that may be bond the anode side interconnect  74  to the separator plate  66  and to the anode electrode of the SOFCs  26 . 
         [0037]    The frame stamping operation moves second portion  181  and third portion  183 ,  FIG. 11 , around conduits  134   a  to essentially bridge the height between the top surface of a first separator plate  66  and the bottom surface of a second separator plate disposed of immediately above said first separator plate. 
         [0038]    The openings  78  and the openings  34   a  and  34   b  are formed either during the stamping step or by machining after the stamping operation by any suitable and cost-effective machining operations such as milling, electron discharge machining (EDM), laser slicing. The space created between the first portion  79  and the cell frame  70  receives portions of the SOFC  26  and the anode side interconnect  74 . The openings  78  are smaller than the dimensions of the anode electrode and electrolyte layer, and larger than the cathode of the SOFC  26 . Thus, the space created between the first portion  79  and the cell frame  70  receives the anode electrode and electrolyte layer of the SOFC  26 , and the cathode of the SOFC  26  extends into or through the opening. 
         [0039]    The second portion  81  of the cell frame  70  is then secured to the separator plate  66  by welding a continuous welding bead along the exterior perimeter of the separator plate  66  and the cell frame  70 . The second portion  81  of the cell frame  70  is secured to the separator plate  66  by a sufficient number of spot welds  93  between adjacent SOFCs  26 . 
         [0040]    A seal  92  seals the interface between adjacent repeater units  22  that combine to establish the conduits  34   a  and  34   b.  In one example, each seal  92  comprises an O-ring-like structure having a V-, C-, or ε-shaped cross-section. One side of the seal  92  is welded to the cell frame  70  in the openings  34   a  and  34   b.  The opposite side of the seal  92  is bonded to the underside of the separator plate  66  corresponding to the adjacent repeater unit  22  within the stack. This bonding is achieved by means of dielectric materials or through another set of materials and processes that ensure dielectric separation between adjacent repeater units  22 . The bonding dielectric materials for sealing may be glass, glass ceramics, glass-metal composites, glass-metal oxide composites or their combination. The bonding materials may also be chosen appropriate metallic materials provided that the seal  92  or the respective area of the separator plate  66  are equipped with a dielectric skin that has adequate voltage breakdown strength to ensure dielectric isolation of the repeater units  22  in a stack. These bonding materials will also be referred to as sealing materials. 
         [0041]    In another example, a plurality of inserts  94  that have a thickness essentially equal to the distance between the first portion  79  and the second portion  81  of the cell frame  70  are positioned between the cell frame  70  and the separator plate  66  each permit fuel flow between the respective conduit  34   a  and  34   b  and the fuel channel  72 . The inserts  94  do not seal a closed periphery and have an opening corresponding to the width of the fuel channel  72 . The example inserts  94  need only be spot-welded to either the cell frame  70  or the separator plate  66  in this example so as to keep the opening of the insert  94  aligned with the fuel channel  72 . The inserts  94  support the corresponding area of the cell frame  70  around the conduits  34   a  and  34   b  so that a compressive load can be applied to the seals  92  to achieve sealing around the conduits  34   a  and  34   b  and maintain the integrity of the seal  92  in a stack. 
         [0042]    In another example, the first portion  79  of the cell frame  70  is displaced, by the stamping process for example. The displacement is of a sufficient amount that the displaced portion, and associated bonding materials, spans between the cell frame  70  and the underside of the adjacent separator plate  66 . The inserts  94  in such an example have the appropriate thickness to provide structural support to the sealing portion of the cell frame sheet around the conduits  34   a  and  34   b.    
         [0043]    In this example, the conduits  34   a  and  34   b  are positioned near the perimeter corners of the cell frame  70  and the separator plate  66 , and the direction of fuel flow through the conduits  34   a  and  34   b  is perpendicular to the direction of fuel flow across the SOFCs  26 . Adjusting the cross-sectional area X 2  of the conduits  34   a  and  34   b  alters characteristics of flow through the conduits  34   a  and  34   b.  The value of X 2  is chosen so as to ensure near uniform distribution of fuel to the repeater units in a stack. For example, utilizing the round cross-sections of  FIGS. 2-8  may facilitate sealing the conduits  34   a  and  34   b  and lead to durable, robust seals with respect to thermal cycling. Utilizing the rectangular cross-sections of  FIG. 1  may desirably reduce the amount of material in the repeater unit  22 . 
         [0044]    The conduits  34   a  and  34   b  may include other cross-sectional geometries. Regardless the chosen geometry of the conduits  34   a  and  34   b,  the sum of the four conduit perimeters is smaller than the perimeter of other internally manifolded repeater units in the prior art that are sealed by dielectric materials, i.e., glass ceramics, in assembling a stack. 
         [0045]    A wire mesh interconnect  86  is secured to the underside of the separator plate  66  by means of welding, seam welding, brazing, diffusion bonding or a combination of these. The wire mesh interconnect  86  is corrugated and defines a plurality of channels  88  for directing air flow across cathode electrode side of the SOFCs  26  and of the repeater unit  22  through the stack assembly  14 . The channels  88  are open toward the SOFCs  26  to facilitate the transport of oxygen to the cathode electrode of the SOFCs  26  for the electrochemical reaction. In this example, the corrugated wire mesh interconnect  86  has a dovetail cross-sectional profile. 
         [0046]    The example wire mesh interconnect  86  is a compliant structure with well-defined deformation characteristics, which can be used to design the mechanical load that can be applied to the fuel cell  26 . This approach facilitates adequate contact between the wire mesh interconnect  86  and the SOFCs  26  and minimal interface ohmic resistance. The approach also lessens the potential for fracturing the SOFC  26  and accommodates the dimensional variability of production repeater units  22  of large footprint area, which reduces material and fabrication costs. 
         [0047]    The example wire mesh interconnect  86  is bonded to the cathode electrode by means of appropriate ceramic materials, such as perovskite or spinel materials. This approach lessens the ohmic resistance to electron flow and resists changes to the ohmic resistance across the wire mesh interconnect  86  and cathode electrode of the SOFC  26 . This approach also indirectly lessens the mechanical load across the stack. Changes in the ohmic resistance typically arise from potential thermal stresses during thermal cycling. Minimization of the mechanical load or stress also leads to minimization of the potential for interconnect creep under the operating conditions, since creep deformation is a function of material properties and stress. 
         [0048]    In this example, the metal alloy selected for the wire mesh interconnect  86  is a nickel-based alloy that exhibits excellent oxidation and creep resistance at the fuel cell operating temperatures of 650° C. to 900° C. thus ensuring good electrochemical performance stability and long lifetime for the fuel cell stack. The wire mesh interconnect  86  is coated with chromia-containment materials to further enhance performance stability and lifetime in some examples. 
         [0049]    In one example, the wire mesh interconnect  86  is compliant and is bonded to one side or extended surface of the separator plate  66  while the flat wire mesh interconnects  74  are bonded to the opposite side of the separator plate  66  to form a bipolar plate. Example bonding techniques include brazing, welding, seam welding, diffusion bonding and other metal bonding methods well known in the art. The wire mesh interconnect  86 , the flat wire mesh interconnect  74 , and the separator plate  66  are made from different metals or alloys to provide enhanced oxidation, corrosion, and creep resistance and mitigation of thermal stresses that may arise during thermal cycling. 
         [0050]    The example corrugated wire mesh interconnect  86  is made of a nickel based alloy, such as Haynes  230 , which has excellent oxidation and creep resistance in air at the fuel cell operating temperatures of 650° C. to 900° C., the flat wire mesh interconnects  74  is made of pure nickel wire which is very stable in the fuel environment, and the separator plate  66  is made of iron-chromium alloys that offer adequate matching of thermal expansion characteristics to those of the ceramic fuel cells to ensure the integrity of the fuel cell stack under thermal cycling between the ambient and fuel cell operating temperatures. For the wire mesh interconnect  86 , the wire diameter ranges from 0.125 to 0.250 mm. 
         [0051]    Referring now to  FIGS. 6 and 7 , stacking a plurality of repeater units  22  with another repeater unit  22  establishes a length L of the conduits  34   a  and  34   b.  Fuel is distributed from the conduits  34   a  through the space  98  in the inserts  94  into the fuel channels  72  to the SOFCs  26 . 
         [0052]    Each repeater unit  22  establishes a fuel channel perimeter  99  that surrounds all of the SOFCs  26  within that repeater unit  22 . In this example, the fuel channels  72  upstream, with regard to the direction of fuel flow, and downstream of the SOFCs  26  are positioned within the fuel channel perimeter  99 . That is, perimeter surrounds all of the fuel flow in a direction aligned with the SOFCs  26 . The conduits  34   a  and  34   b  are positioned outside the fuel channel perimeter  99 . The fuel channel perimeter  99  is aligned with the space  98  in this example, which establish the transition from the channels  34   a  and  34   b  to the fuel channels  72  adjacent the SOFCs  26  of the repeater unit  22 . The dimensions (the width and height) of the fuel channels  72  are designed so as to ensure essentially uniform flow distribution across the fuel cells  26  in each repeater unit  22  of a fuel cell  14 . 
         [0053]    Referring now to  FIGS. 8 and 9 , more than one fuel cell stack assembly  14  may be arranged within a duct  18 . In this example, air enters in the compartment or plenum  140  via inlets  46  between the first group  90  of fuel cell stack assemblies  14  and second group  91  of fuel cell stack assemblies  14  and splits into two streams flowing in opposite directions, one stream moving through the channels  88  of a first group  90  of fuel cell stack assemblies  14  before exiting the duct  18 , and the other stream moving through a second group  91  of fuel cell stack assemblies  14  before exiting the duct  18  via outlets  54 . 
         [0054]    Ring seals  96  seal the interfaces between the conduits  34   a  and  34   b  of adjacent ones of the cell stack assemblies  14  and the inlet and outlet pipes. The fuel cell stack assemblies  14  are packed in the duct  18  using air seals  100  configured to seal interfaces between the fuel cell stack assemblies  14  and the duct  18 . The air seals  100  are made of ceramic fibrous materials that are used to provide flow resistance and essentially block air flow around the fuel cell stack assemblies  14  and in areas other than channels  88 . 
         [0055]    In one example, the conduits  34   a  and  34   b  attach to pipes (not shown) that carry fuel from the fuel supply reservoir  30  to the conduits  34   a  and from the conduits  34   b  to the spent fuel reservoir  38  or to corresponding connection points in a fuel cell system (not shown). The air inlet  46  and the air outlet  54  also attach to pipes (not shown) that carry air from the air supply  44  to the duct  18 , and to the spent air reservoir  56 . A person skilled in the art that has the benefit of this disclosure would understand how to suitably connect the fuel cell arrangement  10  to the fuel supply reservoir  30 , the spent fuel reservoir  38 , the air supply  44 , and the spent air reservoir  56 . 
         [0056]    Manipulating the positions of the conduits  34   a  and  34   b  and the fuel channels  72  relative to the direction of air flow through the fuel cell stack assembly  14  provides several configurations, such as a co-flow arrangement where the fuel flows in the same direction as the air, counter-flow arrangement where the fuel flows in an opposite direction from the air, or cross-flow configurations where the fuel flows transverse to the air. 
         [0057]    Referring to  FIGS. 10-15 , an example repeater unit  122  includes cell frame  170 . The repeater unit  122  is stamped to establish the contours of the repeater unit  122 . The repeater unit  122  holds a single fuel cell  126  and thus has a 1×1 matrix. 
         [0058]    In this example, the cell frame  170  of the repeater unit  122  has a reinforcement zone having a first portion  179 , a second portion  181 , and a third portion  183  that are spaced relative to each other. The first portion  179 , the second portion  181 , and the third portion  183  are examples of the types of contours stamped into the repeater unit  122 . 
         [0059]    The first portion  179 , the second portion  181 , and the third portion  183  correspond to steps or tiers each having a different spacing of height relative to the separator plate  166 . Transitions  84  between the first portion  179 , the second portion  181 , and the third portion  183  are radiused in this example. Other reinforcement zones may include additional portions to accommodate different spacings or stamping requirements. 
         [0060]    To form the cell frame  170 , a stamping operation deforms or moves the second portion  181  of the cell frame  170  away from the third portion  183 , and the first portion  179  away from the third portion  183  and the second portion  181 . The stamping operation also forms the fuel channel  172 . The radiused transitions  84  facilitate material movement during the stamping operation. The multistep design of the frame stamping around the periphery of conduits  134   a  and  134   b,  eliminate the need to use C- or V-ring metallic structures for the formation of the primary fuel manifold conduits thus mitigating the possibility that the C- or V-ring structures may creep deform over time and lead to leakage. Similarly, this design reduces the thickness of the seal  192  to the range of 0.025 mm to 0.150 mm reduces the potential for catastrophic failure of the sealant material during thermal cycling. These features render the window frame stack design more durable and robust under both steady state conditions as well as under thermal cycling. 
         [0061]    In this example, the distance between the first portion  179  and the third portion  183  corresponds to a height h 1 , which is the approximate sum of the heights of the fuel cell  126 , the anode side interconnect  174 , any bonding materials that may be bond the anode side interconnect  174  to a separator plate  166  and to the anode electrode of the fuel cell  26 , plus the height of the cathode side interconnect minus the effective height of the seal  192  that seals the top portion of the frame to the bottom surface of the adjacent separator plate  166 . 
         [0062]    The example inserts  194  have a thickness essentially equal to the height h 1  minus the thickness of the separator place  166  and the seal  192 . The example inserts  194  establish a plurality of openings  95  configured to communicate flow between conduit  134   a,  the conduit  134   b,  and the fuel channel  172 . The openings  95  are positioned and sized to achieve a desired flow. 
         [0063]    During assembly, the example inserts  194  are spot-welded to the cell frame  170 , the separator plate  166  or both to ensure that the openings  95  are properly oriented relative to the fuel channel  172 . 
         [0064]    The example inserts  194  support the corresponding area of the cell frame  170  around the conduits  134   a  and  134   b  so that a compressive load can be applied to the seals  192  to achieve sealing around the conduits  134   a  and  134   b  and maintain the integrity of the seal  192  in a stack. At least a portion of the example inserts  194  extending circumferentially about the entire perimeter of the conduit  134   a  or  134   b.    
         [0065]    The example inserts  194  are formed from a planar sheet of metallic material and then bent into the cylindrical shape shown. In another example, the inserts  194  are cut from a cylinder or tube of material. Inserts  194  are made of alloys closely related to the alloys used for the separator  166  and frame  170 . 
         [0066]    The example repeater unit  122  includes a plurality of protrusions  97  located on both sides of the repeater unit  122 . A notch  130  is established on one side of the repeater unit. When assembling a fuel cell stack assembly  114 , the notch  130  and protrusions  97  are positioned against alignment rods  102  in a suitable stack assembly rig  103 . The notch  130  is received over the alignment rod  102  in this example. The notch  130  and protrusions  97  facilitate positioning the repeater unit  122  relative to another repeater unit  122   a  during assembly. Other examples of the repeater unit  122  may utilize cut-outs or other types of notches  130  and protrusions  97  to locating the repeater unit  122  during assembly. 
         [0067]    In this example, the alignment rods  102  are supported by the stack assembly rig  103 , which supports the weight of the rods and the repeater units  122  as they are stacked against the alignment rods  102 . Truss-like lattice work (not shown) provides further support to the rods  102  in some examples. 
         [0068]    In this example, the repeater unit  122  and  122   a  are sequentially stacked against a rig base plate  104  of the stack assembly rig  103  during assembly. The alignment rods  102  extend at right angles relative to the rig base plate  104 . A stack current collector plate and an end or compression plate, not shown, against which the repeater units are stacked are preferably the first stack components placed against rig base plate  104  during stack assembly. 
         [0069]    The example repeater unit  122  further includes notches  101 . In this example, the notches  101  relieve stress during operation by separating the thermal strain experienced by the stamped geometry that make up conduits  134   a  and  134   b  from exerting strain to the corners of fuel cell  126 . 
         [0070]    Referring to  FIG. 14 , an example interconnect  186  has a plurality of rounded or hemispherical dimples  106  and is laser welded to the separator plate  166 . The example dimples  106  have a radius of about 1.0 mm in this example, and each of the example dimples  106  is spaced about 3.0 mm from an adjacent one on the plurality of dimples  106 . The dimple radius ranges from 0.5 mm to 2.5 mm, while the spacing between dimples ranges from 1 mm to 4 mm. Other examples of the interconnect  186  include truncated hemispherical dimples, conical dimples, truncated conical dimples, prismatic, i.e., hexagonal footprint with a flat top, or prismatic with a spherical segment top. In general, the footprint of the dimple, that is the shape of the dimple at the flat base plane, can have a cylindrical, ellipsoid, square, tetragonal, or polygonal geometry. In these other examples of interconnect  186  geometry the height of the dimple ranges from 0.5 to 2.5 mm. Notably, the compliance of the interconnect  186  can be adjusted by modifying wire diameters, the wire design, and the geometry of the dimples  106 . The wire diameter for interconnect  186  ranges from 0.125 mm to 0.250 mm. 
         [0071]    The example interconnect  188  of  FIG. 15  has a circular arc cross-section with dimples  190  that are shallower than the dimples  106 . The dimples  190  are spaced about 2.0 mm apart in this example and have a radius of about 2.5 mm. The height of the dimples  190  is about 1.0 mm. The dimples  190  are shown as arcs from a circle in this example. In another example, the dimples  190  are arcs from parabolas, hyperbolas, or ellipses. 
         [0072]    Although a preferred embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.