Patent Publication Number: US-2023155143-A1

Title: Fuel cell interconnect optimized for operation in hydrogen fuel

Description:
FIELD 
     The present invention is directed to fuel cell stack components, specifically to interconnects and methods of making interconnects for fuel cell stacks. 
     BACKGROUND 
     A typical solid oxide fuel cell stack includes multiple fuel cells separated by metallic interconnects (IC) which provide both electrical connection between adjacent cells in the stack and channels for delivery and removal of fuel and oxidant. The metallic interconnects are commonly composed of a Cr based alloy, such as an alloy known as CrFe which has a composition of 95 wt. % Cr-5 wt. % Fe, or Cr—Fe—Y having a 94 wt. % Cr-5 wt. % Fe-1 wt. % Y composition. The CrFe and CrFeY alloys retain their strength and are dimensionally stable at typical solid oxide fuel cell (SOFC) operating conditions, e.g., 700-900C in both air and wet fuel atmospheres. 
     SUMMARY 
     According to various embodiments, a fuel cell interconnect includes fuel ribs disposed on a first side of the interconnect and a least partially defining fuel channels, and air ribs disposed on an opposing second side of the interconnect and at least partially defining air channels. The fuel channels include central fuel channels disposed in a central fuel field and peripheral fuel channels disposed in peripheral fuel fields disposed on opposing sides of the central fuel field. The air channels include central air channels disposed in a central air field and peripheral air channels disposed in peripheral air fields disposed on opposing sides of the central air field. At least one of the central fuel channels or the central air channels has at least one of a different cross-sectional area or length than at least one of the respective peripheral fuel channels or the respective peripheral air channels to increase hydrogen fuel flow through the central fuel channels or to increase air flow through the peripheral air channels. 
     According to various embodiments, a method of operating a fuel cell stack containing the above described interconnect includes providing hydrogen fuel into the fuel channels, wherein more of the hydrogen fuel flows through the central fuel channels than through the peripheral fuel channels; and providing air into the air channels, wherein more of the air fuel flows through the central air channels than through the peripheral air channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a perspective view of a SOFC stack, according to various embodiments of the present disclosure. 
         FIG.  1 B  is a cross-sectional view of a portion of the stack of  FIG.  1 A . 
         FIG.  2 A  is a top view of an air side of an interconnect, according to various embodiments of the present disclosure. 
         FIG.  2 B  is a top view of a fuel side of the interconnect of  FIG.  2 A . 
         FIGS.  3 A- 3 D  are top views of the fuel sides of interconnects, according to various embodiments of the present disclosure. 
         FIGS.  4 A- 4 D  are top views of the air sides of interconnects, according to various embodiments of the present disclosure 
         FIG.  5 A  is a top view of a fuel side of a crossflow interconnect, according to various embodiments of the present disclosure, and  FIG.  5 B  is a top view of the air side of the interconnect of  FIG.  5 A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1 A  is a perspective view of a solid oxide fuel cell (SOFC) stack  100 , and  FIG.  1 B  is a sectional view of a portion of the stack  100 , according to various embodiments of the present disclosure. Referring to  FIGS.  1 A and  1 B , the stack  100  includes fuel cells  1  separated by interconnects  10 . Referring to  FIG.  1 B , each fuel cell  1  comprises a cathode electrode  3 , a solid oxide electrolyte  5 , and an anode electrode  7 . 
     Various materials may be used for the cathode electrode  3 , electrolyte  5 , and anode electrode  7 . For example, the anode electrode  7  may comprise a cermet comprising a nickel containing phase and a ceramic phase. The nickel containing phase may consist entirely of nickel in a reduced state. This phase may form nickel oxide when it is in an oxidized state. Thus, the anode electrode  7  is preferably annealed in a reducing atmosphere prior to operation to reduce the nickel oxide to nickel. The nickel containing phase may include other metals in additional to nickel and/or nickel alloys. The ceramic phase may comprise a stabilized zirconia, such as yttria and/or scandia stabilized zirconia and/or a doped ceria, such as gadolinia, yttria and/or samaria doped ceria. 
     The electrolyte may comprise a stabilized zirconia, such as scandia stabilized zirconia (SSZ) or yttria stabilized zirconia (YSZ). Alternatively, the electrolyte may comprise another ionically conductive material, such as a doped ceria. 
     The cathode electrode  3  may comprise an electrically conductive material, such as an electrically conductive perovskite material, such as lanthanum strontium manganite (LSM). Other conductive perovskites, such as LSCo, etc., or metals, such as Pt, may also be used. The cathode electrode  3  may also contain a ceramic phase similar to the anode electrode  7 . The electrodes and the electrolyte may each comprise one or more sublayers of one or more of the above described materials. 
     Fuel cell stacks are frequently built from a multiplicity of SOFC&#39;s  1  in the form of planar elements, tubes, or other geometries. Although the fuel cell stack in  FIG.  1 A  is vertically oriented, fuel cell stacks may be oriented horizontally or in any other direction. Fuel and air may be provided to the electrochemically active surface, which can be large. For example, fuel may be provided through fuel conduits  22  (e.g., fuel riser openings) formed in each interconnect  10 . 
     Each interconnect  10  electrically connects adjacent fuel cells  1  in the stack  100 . In particular, an interconnect  10  may electrically connect the anode electrode  7  of one fuel cell  1  to the cathode electrode  3  of an adjacent fuel cell  1 .  FIG.  1 B  shows that the lower fuel cell  1  is located between two interconnects  10 . An optional Ni mesh may be used to electrically connect the interconnect  10  to the anode electrode  7  of an adjacent fuel cell  1 . 
     Each interconnect  10  includes fuel ribs  12 A that at least partially define fuel channels  8 A and air ribs  12 B that at least partially define oxidant (e.g., air) channels  8 B. The interconnect  10  may operate as a gas-fuel separator that separates a fuel, such as a hydrocarbon fuel, flowing to the fuel electrode (i.e., anode  7 ) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e., cathode  3 ) of an adjacent cell in the stack. At either end of the stack  100 , there may be an air end plate or fuel end plate (not shown) for providing air or fuel, respectively, to the end electrode. 
     Each interconnect  10  may be made of or may contain electrically conductive material, such as a metal alloy (e.g., chromium-iron alloy) which has a similar coefficient of thermal expansion to that of the solid oxide electrolyte in the cells (e.g., a difference of 0-10%). For example, the interconnects  10  may comprise a metal (e.g., a chromium-iron alloy, such as 4-6 weight percent iron, optionally 1 or less weight percent yttrium and balance chromium alloy) and may electrically connect the anode or fuel-side of one fuel cell  1  to the cathode or air side of an adjacent fuel cell  1 . An electrically conductive contact layer, such as a nickel contact layer, may be provided between anode electrodes  7  and each interconnect  10 . Another optional electrically conductive contact layer, such as a lanthanum strontium manganite and/or a manganese cobalt oxide spinel layer, may be provided between the cathode electrodes  3  and each interconnect  10 . 
       FIG.  2 A  is a top view of the air side of the interconnect  10 , and  FIG.  2 B  is a top view of a fuel side of the interconnect  10 , according to various embodiments of the present disclosure. Referring to  FIGS.  1 B and  2 A , the air side includes the air channels  8 B. Air flows through the air channels  8 B to a cathode electrode  3  of an adjacent fuel cell  1 . Ring seals  20  may surround fuel holes  22 A of the interconnect  10 , to prevent fuel from contacting the cathode electrode. Peripheral strip-shaped seals  24  are located on peripheral portions of the air side of the interconnect  10 . The seals  20 ,  24  may be formed of a glass or glass-ceramic material. The peripheral portions may be an elevated plateau which does not include ribs or channels. The surface of the peripheral regions may be coplanar with tops of the ribs  12 B. 
     Referring to  FIGS.  1 B and  2 B , the fuel side of the interconnect  10  may include the fuel channels  8 A and fuel manifolds  28 . Fuel flows from one of the fuel holes  22 A (e.g., inlet hole that forms part of the fuel inlet riser), into the adjacent manifold  28 , through the fuel channels  8 A, and to an anode  7  of an adjacent fuel cell  1 . Excess fuel may flow into the other fuel manifold  28  and then into the outlet fuel hole  22 B. A frame-shaped seal  26  is disposed on a peripheral region of the fuel side of the interconnect  10 . The peripheral region may be an elevated plateau which does not include ribs or channels. The surface of the peripheral region may be coplanar with tops of the ribs  12 . 
     As shown in  FIGS.  2 A and  2 B , one of the fuel holes  22 A,  22 B delivers fuel to each cell in the stack and a corresponding manifold  28  distributes fuel to each fuel channel  8 A. Fuel flows straight down each fuel channel  8 A, and unreacted fuel is collected in the other manifold  28  and exits the stack via the other fuel hole  28 A,  28 B. This flow channel geometry is optimized for operation on natural gas with partial external pre-reforming. 
     The present inventors found that while the interconnect  10  shown in  FIGS.  2 A and  2 B  provides a high fuel utilization when a hydrocarbon fuel (e.g., natural gas) is used, the interconnect  10  may not provide a sufficiently high fuel utilization when hydrogen is used as a fuel. Without wishing to be bound by a particular theory, it is believed that using hydrogen as a fuel produces an increased thermal gradient. For example, in a natural gas-fueled system, an endothermic steam reformation reaction occurs at the anode and partially cools the fuel cell. However, with a pure hydrogen fuel, no reformation cooling occurs, and most of the heat generated by the fuel cell is removed by reactant flow (e.g., primarily air flow). This results in higher thermal gradient within the cell  1  (e.g., in the area which corresponds to the center of the interconnects  10  near the fuel inlet hole  22 A), and therefore poorer fuel distribution, as fuel flows preferentially to the cooler areas adjacent the edges (i.e., periphery) of the interconnects  10 , where the specific volume and viscosity of the gas are lower. 
     The embodiments of the present disclosure provide interconnects configurations that distribute hydrogen and/or air in a manner that increases fuel utilization and/or reduces thermal gradients. 
       FIG.  3 A  is a top view of the fuel side of an interconnect  300 A, according to various embodiments of the present disclosure. The interconnect  300 A may be similar to the interconnect  10 . As such, only the differences therebetween will be discussed in detail. 
     Referring to  FIG.  3 A , the fuel-side of the interconnect  300 A may include a frame seal region  302 , opposing fuel manifolds  304 , fuel holes  306 , fuel ribs  312 , and fuel channels  310 . The frame seal region  302  may be a planar surface that extends alone the perimeter of the interconnect  300 A. The frame seal region  302  may be coplanar with the tops of the fuel ribs  312 . The fuel manifolds  304  may be disposed inside of the frame seal region  302 , at opposing edges of the interconnect  300 . The fuel holes  306  may be formed in the center of each of the fuel manifolds  304 , adjacent to opposing first and second edges  301 ,  303  of the interconnect  300 A. 
     The fuel ribs  312  and fuel channels  310  may extend between the fuel manifolds  304 , in a direction parallel to opposing third and fourth edges  305 ,  307  of the interconnect  300 A. The fuel channels  310  and fuel ribs  312  may be configured to guide fuel flow across the interconnect  300  between the fuel manifolds  304 . The interconnect  300 A may be divided into a central fuel field  314  and peripheral fuel fields  316  disposed on opposing sides of the central fuel field  314 , adjacent to the third and fourth edges  305 ,  307 . The fuel channels  310  may include central fuel channels  310 C disposed in the central fuel field  314  and peripheral fuel channels  310 P disposed in the peripheral fuel fields  316 . In various embodiments, from about 25% to about 50%, such as from about 30% to about 40% of the fuel channels  310  may be the central fuel channels  310 C, and a remainder of the fuel channels  310  may be the peripheral fuel channels  310 P. 
     The interconnect  300 A may be configured to provide higher fuel (e.g., hydrogen) mass flows through the central fuel channels  310 C than through the peripheral fuel channels  310 P. In particular, the central fuel channels  310 C may have a larger cross-sectional area, taken in a direction perpendicular to the third and fourth edges  305 ,  307 , than a cross-sectional area of the peripheral fuel channels  310 P. For example, the central fuel channels  310 C may be wider and/or deeper than the peripheral fuel channels  310 P. In some embodiments, the cross-sectional areas of the central fuel channels  310 C may be from 5% to 40%, such as from 8% to 30%, or from 10% to 20% larger than the cross-sectional areas of the peripheral fuel channels  310 P. Accordingly, more fuel mass flow may be provided to a central portion of an adjacent fuel cell via the central fuel channels  310 C than is provided to peripheral portions of the fuel cell via the peripheral fuel channels  310 P. As such, the interconnect  300 A may be configured to direct more hydrogen fuel to areas having higher operating temperatures and corresponding higher fuel flow resistance, due to using hydrogen as a fuel. 
     In various embodiments, the cross-sectional areas of the fuel channels  310  may vary incrementally, such that the fuel channels  310  closest to the third and fourth edges  305 ,  307  of the interconnect  300 A have the smallest cross-sectional area and the fuel channels  310  that extend through the middle of the interconnect  300 A (e.g., that extend between the fuel holes  306 ) have the largest cross-sectional area. 
     In some embodiments, the depths of the fuel manifolds  304  may be varied in a lengthwise direction, such that the fuel manifolds  304  have a maximum depth adjacent to the fuel holes  306  and a minimum depth adjacent the third and fourth edges  305 ,  307  of the interconnect  300 A. The variation in depth may result in lower fuel mass flow through the peripheral fuel channels  310 P and a higher mass flow through the central fuel channels  310 C. The variable depth fuel manifolds  304  may be used with the relatively large central fuel channels  310 C and the relatively small peripheral fuel channels  310 P or may be used with fuel channels that are all the same size. 
       FIG.  3 B  is a top view of a fuel side of an interconnect  300 B, according to various embodiments of the present disclosure. The interconnect  300 B may be similar to the interconnect  300 A. As such, only the differences therebetween will be described in detail. 
     Referring to  FIG.  3 B , at least some of the peripheral fuel channels  310 P may be longer than the central fuel channels  310 C. In other words, the lengths of the fuel ribs  312  and the fuel channels  310  may increase continuously or step-wise as a distance between the fuel ribs  312  and the fuel channels  310  and the third and fourth edges  305 ,  307  decreases. In some embodiments, at least some of the peripheral fuel channels  310 P and the corresponding fuel ribs  312  may extend into the fuel manifolds  304 . 
     Increasing the lengths of the peripheral fuel channels  310 P may increase the fuel flow resistance therethrough. As such, the relatively short central fuel channels  310 C may have a higher fuel mass flow (e.g., a lower flow resistance) than the relatively long peripheral fuel channels  310 P. 
     In one embodiment of the interconnect  300 B, the shorter central fuel channels  310 C may have a larger cross-sectional area (i.e., a larger width and/or depth) than the longer peripheral fuel channels  310 P. In another embodiment of the interconnect  300 B, the shorter central fuel channels  310 C may have the same cross-sectional area (i.e., the same width and depth) as the longer peripheral fuel channels  310 P. 
     The variation in the lengths of the fuel channels  310  may advantageously increase the active area of an adjacent fuel cell, which may provide improved electrochemical performance. In one embodiment, a nickel mesh current collector (not shown) may be used to improve contact between the fuel ribs  312  and the anode of the adjacent fuel cell. To realize the benefit of the higher active area, the Ni mesh may be shaped to correspond to the shape of the longer fuel ribs  312 . In other words, the Ni mesh may be configured to completely overlap with the central fuel field  314  and the peripheral fuel fields  316 . 
       FIG.  3 C  is a top view of a fuel side of an interconnect  300 C, according to various embodiments of the present disclosure. The interconnect  300 C may be similar to the interconnect  300 A. As such, only the differences therebetween will be described in detail. 
     Referring to  FIG.  3 C , the interconnect  300 C may include fuel blockers or bumpers  318  that extend across one or more of the peripheral fuel channels  310 P. The fuel blockers  318  may extend lengthwise in a direction perpendicular to the fuel channels  310 . The fuel blockers  318  may be and configured to reduce fuel mass flow through the peripheral fuel channels  310 P, such that fuel mass flow through the central fuel channels  310 C is higher than the fuel mass flow through the peripheral fuel channels  310 P. In some embodiments, the fuel blockers  318  may be configured to generate a fuel mass flow gradient, such that the peripheral fuel channels  310 P further from the central fuel field  314  have a lower mass flow that the peripheral fuel channels  310 P closer to the central fuel field  314 , thereby increasing the fuel utilization in central portions of an adjacent fuel cell. 
     In some embodiments, in addition to or instead of the fuel blockers  318 , manifold diverters  320  may be disposed in the fuel manifolds  304  to redirect fuel through the fuel manifolds  304  and into the fuel channels  310 . For example, the diverters  320  may be configured to direct a higher fuel mass flow into the central fuel channels  310 C than into the peripheral fuel channels  310 P. The diverters  320  may comprise ribs located in the fuel manifolds  304 , and which extend perpendicular to the fuel channels  310  and ribs  312 . This configuration may provide the additional benefit of increasing the active area of an adjacent fuel cell. 
     In various embodiments, spaces S may be formed between the fuel holes  306  and adjacent fuel ribs  312  in the central fuel field  314 , in a fuel flow direction. The spaces S may be configured to increase fuel mass flow through the central fuel channels  310 C adjacent to the fuel holes  306 . 
     In some embodiments of interconnect  300 C, the cross-sectional areas of the central fuel channels  310 C may be larger than the cross-sectional areas of the peripheral fuel channels  310 P, in order to further increase fuel mass flow through the central fuel channels  310 C. However, in other embodiments, the fuel channels  310  may all have substantially the same cross-sectional area. 
       FIG.  3 D  is a top view of a fuel side of an interconnect  300 D, according to various embodiments of the present disclosure. The interconnect  300 D may be similar to the interconnect  300 C. As such, only the differences therebetween will be described in detail. 
     Referring to  FIG.  3 D , the interconnect  300 D may include multiple fuel holes  306  in each fuel manifold  304 . The multiple fuel holes  306  may improve fuel distribution and/or increase fuel mass flow through the central fuel channels  310 C and to a central portion of an adjacent fuel cell. 
     In various embodiments, spaces S may be formed between the fuel holes  306  and adjacent fuel ribs  312  in the central fuel field  314 , in a fuel flow direction. The spaces S may be configured to increase fuel mass flow within the central fuel channels  310 C, between the fuel holes  306  on opposing sides of the interconnect  300 D. 
     In some embodiments of interconnect  300 D, the cross-sectional areas of the central fuel channels  310 C may be larger than the cross-sectional areas of the peripheral fuel channels  310 P, in order to further increase fuel mass flow through the central fuel channels  310 C. However, in other embodiments, the fuel channels  310  may all have substantially the same cross-sectional area. 
       FIG.  4 A  is a top view of the air side of an interconnect  400 A, according to various embodiments of the present disclosure. Referring to  FIG.  4 A , the airside of the interconnect  400 A may include strip seal regions  402 , ring seal regions  404 , air (e.g., oxidant) channels  410 , air ribs  412 , and fuel holes  306 . The ring seal regions  404  may be planar regions that surround the fuel holes  306 . The strip seal regions  402  may be planar regions disposed on opposing edges of the interconnect  400 A. The ring seal regions  404  and the strip seal regions  402  may be coplanar with the tops of the air ribs  412 . 
     The air ribs  412  may at least partially define the air channels  410 . The air channels  410  may be configured to guide air across the interconnect between the strip seal regions  402 . The air side of the interconnect  400 A may be divided into a central air field  414  and peripheral air fields  416  that are disposed on opposing sides of the central air field  414 , adjacent to third and fourth edges  305 ,  307  of the interconnect  400 A. The air channels  410  may include central air channels  410 C disposed in the central air field  414  and peripheral air channels  410 P disposed in the peripheral air fields  416 . 
     In one embodiment, all air channels  410  may have a larger cross-sectional area than the air channels  8 B of the comparative interconnect  10  shown in  FIG.  2 A . This increases the air cooling of the air side of the interconnect  400 A when hydrogen is used as a fuel in the fuel side of the interconnect  400 A. 
     In another embodiment, the cross-sectional areas of the central air channels  410 C may be larger than the cross-sectional areas of the peripheral air channels  410 P of interconnect  400 A. For example, the central air channels  410 C may be wider and/or deeper than the peripheral air channels  410 P. In some embodiments, the cross-sectional areas of the central air channels  410 C may be from 5% to 40%, such as from 8% to 30%, or from 10% to 20% larger than the cross-sectional areas of the peripheral air channels  410 P. As such, air mass flows through the central air channels  410 C may be correspondingly larger than air mass flows through the peripheral air channels  410 P. More air mass flow in the central air channels  410 C increases cooling of the center of an adjacent fuel cell and reduces thermal gradients in the fuel cell and the interconnect  400 A when hydrogen is used as a fuel. 
     In some embodiments, the cross-sectional areas of the air channels  410  may increase continuously or step-wise as distance to the adjacent third and fourth edges  305 ,  307  decreases. In some embodiments, the cross-sectional areas of the central air channels  410 C may vary incrementally, such that the central air channels  410 C closer to the middle of the central air field  414  may have larger cross-sectional areas than central air channels  410 C disposed closer to the peripheral air fields  416 . However, in various embodiments, at least some of the central air channels  410 C may have larger cross-sectional areas than the peripheral air channels  410 P. 
     In some embodiments, the air ribs  412  located in the central air field  414  adjacent to the ring seal regions  404  may be relatively short (i.e., shorter than the air ribs  412  located in the peripheral air field  416 ), to provide air spaces S to increase air flow around the ring seal regions  404 , thereby increase air mass flows through the central air channels  410 C extending between the ring seal regions  404  on the opposite side of the interconnect  400 A. In other words, at least some of the air ribs  412  in the central air field  414  may be shorter than the remaining air ribs  412 , in order to increase air flow through the central air channels  410 C in the central air field  414 , thereby increasing cooling of corresponding portions of the interconnect  400 A and an adjacent fuel cell. In some embodiments in which the air ribs  412  have a different length in the central and peripheral air fields, the cross-sectional areas of the central air channels  410 C may be larger than the cross-sectional areas of the peripheral air channels  410 P, in order to further increase air mass flow through the central air channels  410 C of the central air field  414 . In other embodiments, the cross-sectional areas of the central air channels  410 C may the same as the cross-sectional areas of the peripheral air channels  410 P. 
       FIG.  4 B  is a top view of the air side of an interconnect  400 B, according to various embodiments of the present disclosure. The interconnect  400 B may be similar to the interconnect  400 A. As such, only the differences therebetween will be discussed in detail. 
     Referring to  FIG.  4 B , the air side of the interconnect  400 B may include curved or bent peripheral air channels  410 BP and corresponding curved or bent air ribs  412 B. In particular, end portions of the bent air ribs  412 B may be shaped so as to form air spaces S adjacent to the ring seal regions  404 . In other words, edge portions of the bent peripheral air channels  410 BP located near the edges  301  and  303  of the interconnect  400 B are not parallel to the edges  305  and  307  of the interconnect and are not parallel to the central air channels  410 C. For example, edge portions of the bent peripheral air channels  410 BP located near the edges  301  and  303  of the interconnect  400 B extend at an angle of  30  to  60  degrees relative to the edges  305  and  307  of the interconnect and to the central air channels  410 C. In contrast, middle portions of the bent peripheral air channels  410 BP at the middle of the interconnect  400 B are parallel to the edges  305  and  307  of the interconnect and the central air channels  410 C. 
     The air spaces S may be configured to increase air mass flow into the central channels  410 C of the central air field  414 . In particular, the spaces S may operate to compensate for an air blockage resulting from the ring seal regions  404 . The bent air ribs  412 B may also be configured to reduce air mass flow through peripheral air channels  410 P adjacent to the strip seal regions  402 . For example, the end portions of the bent air ribs  412 B may partially block air flow to the outermost peripheral air channels  410 P. 
     In some embodiments, the cross-sectional areas of the central air channels  410 C may be larger than the cross-sectional areas of the peripheral air channels  410 P, in order to further increase air mass flow through the central air channels  410 C of the central air field  414  of interconnect  400 B. In other embodiments, the cross-sectional areas of the central air channels  410 C may the same as the cross-sectional areas of the peripheral air channels  410 P of interconnect  400 B. 
       FIG.  4 C  is a top view of the air side of an interconnect  400 C, according to various embodiments of the present disclosure. The interconnect  400 C may be similar to the interconnect  400 B. As such, only the differences therebetween will be discussed in detail. 
     Referring to  FIG.  4 C , the airside of the interconnect  400 C may include multiple fuel holes  306  and ring seal regions  404  disposed on opposing top and bottom sides of the interconnect  400 C. The ring seal regions  404  may be disposed outside of the central air field  414 , such that the central air channels  410 C of the central air field  414  are not obstructed by fuel seals. As such, air mass flow through the central air field  414  may be increased since it is not obstructed by fuel seals. 
     In some embodiments, the cross-sectional areas of the central air channels  410 C may be larger than the cross-sectional areas of the peripheral flow channels  410 P, in order to further increase air flow through the central air channels  410 C. However, in other embodiments, all the air channels  410  may have substantially the same cross-sectional area. 
       FIG.  4 D  is a top view of the air side of an interconnect  400 D, according to various embodiments of the present disclosure. The interconnect  400 D may be similar to the interconnect  400 A. As such, only the differences therebetween will be discussed in detail. 
     Referring to  FIG.  4 D , at least some of the central air channels  410 C may be shorter than the peripheral air channels  410 P. Furthermore, the central air channels  410  in the middle of the central air field  414  maybe shorter than the central air channels  410  at the peripheral parts of the central air field  414 . Furthermore, the central air channels  410  in the middle of the central air field  414  may have an increasing length (in the direction between the ring seal regions  404 ) as a function of distance from the middle of the interconnect  400 D. For example, the edges of the central air channels  410  in the middle of the central air field  414  may form a semi-circular shape around the ring seal regions  404 . In contrast, the central air channels  410  at the peripheral parts of the central air field  414  may have the same length and their edges facing the interconnect  400 D edges  301  and  303  form a straight line. 
     In particular, air spaces S may be formed around the ring seal regions  404  due the shortening of air ribs  412  in the central air field  414 . The air spaces S are located between the air ribs  412  in the peripheral air fields  416  and the ring seal regions  404 . The air spaces S may be configured to increase air mass flow through the central air channels  410 C, by providing additional space for air to flow around the ring seal regions  404 . The spaces S may also reduce an air mass flow variation among the central air channels  410 C. For example, air mass flow through variation between the central air channels  410 C may be less than 25%, such as 20 to 25%. Furthermore, the air flow through the central air channels  410 C may be at least 25% greater, such as 30 to 35% greater than through the peripheral flow channels  410 P. 
     In some embodiments, the cross-sectional areas of the central air channels  410 C may be larger than the cross-sectional areas of the peripheral air flow channel  410 P, in order to further increase air flow through the central air flow channels  410 C. However, in other embodiments, all the air flow channels  410  may have substantially the same cross-sectional area. 
     Referring to  FIGS.  3 A- 3 D and  4 A- 4 D , various embodiments may include interconnects having any combination of the described air and fuel side features. For example, the interconnects  300 A- 300 D may include any of the air side features shown in  FIGS.  4 A- 4 D , and the interconnects  400 A- 400 D may include any of the fuel side features shown in  FIGS.  3 A- 3 D . However, in some embodiments, the interconnect having plural fuel holes  306  may have the fuel side features of interconnect  300 D and the air side features of interconnect  400 C. 
     According to various embodiments, the thickness of an interconnect may be increased, as compared to the comparative interconnect  10  shown in  FIGS.  2 A and  2 B , in order to increase lateral heat conduction. In other embodiments, the aspect ratio of an interconnect may be modified, in order to increase a perimeter to active area ratio and decrease a thermal conduction distance from the center to edges of the interconnect. 
     In some embodiments, the thermal conductivity of an interconnect may be increased. For example, the density may be increased by modifying a starting chromium powder (e.g., direct-reduced chromium, different particle size, etc.). In some embodiments, the Fe-content is of an interconnect material powder may be increased, such as from 5% to from about 7 to about 10 wt. % Fe. Thus, the interconnect comprises an alloy of 7 wt. % Fe to 10 wt.% Fe and balance Cr (e.g. 7 wt. % to 10 wt. % iron and 90 wt. % to 93 wt. % chromium). The increased iron content may allow for the formation of a denser interconnect via powder metallurgy, which may improve thermal conduction and increase temperature uniformity. 
     In various embodiments the aspect ratio of an interconnect may be increased, such that the interconnect is more rectangular rather than a square, in order to increase the ratio of perimeter to active area and decrease the thermal conduction distance from the center to the edges of the interconnect. This configuration may be beneficial to the co-flow interconnects of  FIGS.  3 A- 3 D and  4 A- 4 D , where fuel and air flow in parallel directions. In addition, this configuration may be even more beneficial to crossflow interconnects, where fuel and air flows are perpendicular to one another across the interconnect. 
       FIG.  5 A  is a top view of a fuel side of a crossflow interconnect  500 , according to various embodiments of the present disclosure.  FIG.  5 B  is a top view of the air side of the interconnect  500  of  FIG.  5 A . The interconnect  500  may be similar to the previously described interconnects. As such, only the differences therebetween will be described in detail. 
     Referring to  FIGS.  5 A and  5 B , the interconnect  500  may include enlarged fuel holes  308  that operate as fuel manifolds  304  (shown in  FIG.  3 A ). The fuel holes  308  may optionally include supports (e.g., separators)  308 S configured to increase the structural integrity of the interconnect  500  and/or fuel holes  308 . The interconnect  500  may include fuel ribs  312  that at least partially define fuel channels that extend in a length direction L, which may be co-linear with a fuel flow direction, and air ribs  412  that at least partially define air channels  410  than extend in a width direction W, which may be colinear with an air flow direction and may be substantially perpendicular to the length direction L. 
     The interconnect  500  may have a length, taken the length direction L, of greater than 100 mm, such as 110 mm to 150 mm, and a fuel channel  310  length of at least 100 mm, such as 100 mm to 115 mm. The interconnect  500  may have a width, taken in the width W direction, of less than 100 mm, such as from 70 mm to 90 mm. Thus, the interconnect  500  may have a length to width ratio of greater than 1, such as from 1.05 to 2.75. or from 1.25 to 2.5. 
     Thus, in some embodiments, interconnects that include fuel channels having larger cross-sectional areas in a central fuel field than in peripheral fuel fields, by increasing the width, depth, or both the width and depth of the fuel channels in the central fuel field. 
     In various embodiments, interconnects provide improved thermal uniformity when operating on hydrogen fuel, which leads to higher fuel utilization and system efficiency. In some embodiments, a higher active area decreases current density and improves fuel cell performance. 
     Fuel cell systems of the embodiments of the present disclosure are designed to reduce greenhouse gas emissions and have a positive impact on the climate. 
     Although the foregoing refers to particular preferred embodiments, it will be understood that the invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.