Patent Publication Number: US-2019190052-A1

Title: Fuel cell tube with laterally segmented fuel cells

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 15/847,456, filed Dec. 19, 2017, all of which is hereby incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates to fuel cell tubes. More specifically, the present disclosure relates to fuel cell tubes including one or more laterally segmented fuel cells. 
     BACKGROUND 
     A fuel cell is an electrochemical conversion device that produces electricity by oxidizing a fuel. A fuel cell may be one of an electrochemically active fuel cell and an electrochemically inactive fuel cell (i.e. a dummy cell). An electrochemically active fuel cell typically includes an anode, a cathode, and an electrolyte between the anode and the cathode. A fuel cell tube usually includes multiple fuel cells disposed on a substrate and electrically connected to one another in series via primary interconnects. A fuel cell stack typically includes multiple fuel cell tubes electrically connected to one another in series via tube interconnects. A fuel cell system includes multiple fuel cell stacks electrically connected to one another in series and several components configured to provide the fuel to the anodes of the fuel cells and an oxidant to the cathodes of the fuel cells. The oxygen in the oxidant is reduced at the cathode into oxygen ions that diffuse through the electrolyte layers into the anodes. The fuel is oxidized at the anodes, which gives off electrons that flow through an electrical load. 
     SUMMARY 
     Various embodiments of the present disclosure provide a fuel cell tube including one or more laterally segmented electrochemically active fuel cells or dummy cells each including lateral electrochemically active fuel cell or dummy cell portions that are electrically isolated from one another such that there is no continuous electrical path across the width of the tube. When assembled into a fuel cell stack, tube interconnects electrically connect adjacent fuel cell tubes via their respective laterally segmented fuel cells. The use of laterally segmented electrochemically active fuel cells or dummy cells to effect the fuel cell tube-to-fuel cell tube electrical connection enables more accurate testing of the electrical connection between adjacent fuel cell tubes. 
     In some examples, a segmented-in-series solid-oxide fuel cell system includes a first fuel cell tube, a second fuel cell tube and a first tube interconnect. The first fuel cell tube can include a substrate having a first end and an opposing second end, a first major surface extending between the first and second ends, and a second opposing major surface extending between the first and second ends. The first fuel cell tube can also include a plurality of fuel cells disposed on the first major surface, each fuel cell extending laterally across the first major surface and being positioned between the first and second ends. In some examples, a first selected one of the plurality of fuel cells on the first major surface proximate the first end is laterally segmented so that a first lateral end of the first selected fuel cell is electrically isolated from a second lateral end of the first selected fuel cell. In some examples, the fuel cell tube may comprise a “dummy” cell, i.e., a cell comprising only the cathode layer or the cathode layer with a cathode current collector layer. In some examples, an interior selected one of the plurality of fuel cells is a fuel cell adjacent the first selected fuel cell. The interior selected one of the plurality of fuel cells may be laterally segmented so that a first lateral end of the interior selected fuel cell is electrically isolated from a second lateral end of the interior selected fuel cell. 
     The second fuel cell tube can include a substrate having a first end and an opposing second end, a first major surface extending between the first and second ends, and a second opposing major surface extending between the first and second ends. The second fuel cell tube can also include a plurality of fuel cells disposed on the first major surface, each fuel cell extending laterally across the first major surface and being positioned between the first and second ends. In some examples, a first selected one of the plurality of fuel cells on the first major surface proximate the second end is laterally segmented so that a first lateral end of the first selected fuel cell is electrically isolated from a second lateral end of the first selected fuel cell. In some examples, the fuel cell tube may comprise a “dummy” cell, i.e., a cell comprising only the cathode layer or the cathode layer with a cathode current collector layer. 
     The segmented-in-series solid-oxide fuel cell system can also include a first tube interconnect electrically connecting the first lateral end of the first selected fuel cell of the first fuel cell tube to the second lateral end of the first selected fuel cell of the second fuel cell tube. 
     In some examples, a fuel cell tube includes a substrate defining one or more fuel conduits therethrough, the substrate having a first end and an opposing second end, a first major surface extending between the first and second ends, and a second opposing major surface extending between the first and second ends. The fuel cell tube can also include a plurality of fuel cells disposed on the first major surface, each fuel cell extending laterally across the first major surface and being positioned between the first and second ends. In some examples, a first selected one of the plurality of fuel cells on the first major surface proximate the first end is laterally segmented so that a first lateral end of the first selected fuel cell is electrically isolated from a second lateral end of the first selected fuel cell. In some examples, a first interior selected one of the plurality of fuel cells disposed on the first major surface is a fuel cell adjacent the first selected fuel cell. The first interior selected one of the plurality of fuel cells may be laterally segmented so that a first lateral end of the first interior selected fuel cell is electrically isolated from a second lateral end of the first interior selected fuel cell. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a top plan view of one embodiment of a fuel cell tube of the present disclosure. 
         FIG. 2  is a side elevational view of the fuel cell tube of  FIG. 1 . 
         FIG. 3  is a front elevational cross-sectional view of the fuel cell tube of  FIG. 1  taken substantially along line  3 - 3  of  FIG. 1 . 
         FIG. 4  is a side elevational cross-sectional view of part of one of the fuel cells of the fuel cell tube of  FIG. 1  taken substantially along line  4 - 4  of  FIG. 1 . 
         FIG. 5  is a side elevational view of six fuel cell tubes of one embodiment of a fuel cell stack of the present disclosure. 
         FIG. 6  is a front elevational cross-sectional view of the fuel cell tubes of the fuel cell stack of  FIG. 5  taken substantially along line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a rear elevational cross-sectional view of the fuel cell tubes of the fuel cell stack of  FIG. 5  taken substantially along line  7 - 7  of  FIG. 5 . 
         FIGS. 8A-8D  are front elevational cross-sectional views of two prior art fuel cell tubes of a prior art fuel cell stack during resistance testing. 
         FIGS. 9A-9D  are front elevational cross-sectional views of two the fuel cell tubes of the fuel cell stack of  FIG. 5  during resistance testing taken substantially along line  6 - 6  of  FIG. 5 . 
         FIGS. 10A and 10B  are schematics showing a side view of one embodiment of a fuel cell tube of the present disclosure along the length of the tube.  FIG. 10A  shows the anode side of the tube and  FIG. 10B  shows the cathode side of the tube. 
         FIGS. 11A and 11B  are schematics showing a top view of one embodiment of a fuel cell tube of the present disclosure.  FIGS. 11C and 11D  are schematics showing a bottom view of one embodiment of a fuel cell tube of the present disclosure.  FIGS. 11A and 11C  show the anode side of the tube, and  FIGS. 11B and 11D  show the cathode side of the tube. 
         FIG. 12  is a top plan view of one embodiment of a fuel cell tube of the present disclosure. 
         FIG. 13  is a side elevational view of the fuel cell tube of  FIG. 12 . 
         FIG. 14A  is a front elevational cross-sectional view of the fuel cell tube of  FIG. 12  taken substantially along line  8 - 8  of  FIG. 12 .  FIG. 14B  is a front elevational cross-sectional view of the fuel cell tube of  FIG. 12  taken substantially along line  9 - 9  of  FIG. 12 . 
         FIGS. 15A and 15B  are front elevational cross-sectional views of three fuel cell tubes of one embodiment of a fuel cell stack of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     While the features, methods, devices, and systems described herein may be embodied in various forms, the drawings show and the detailed description describes some exemplary and non-limiting embodiments. Not all of the components shown and described in the drawings and the detailed descriptions may be required, and some implementations may include additional, different, or fewer components from those expressly shown and described. Variations in the arrangement and type of the components; the shapes, sizes, and materials of the components; and the manners of attachment and connections of the components may be made without departing from the spirit or scope of the claims as set forth herein. This specification is intended to be taken as a whole and interpreted in accordance with the principles of the invention as taught herein and understood by one of ordinary skill in the art. 
       FIGS. 1-4  illustrate one example embodiment of a fuel cell tube  100  of the present disclosure and components thereof.  FIGS. 5-7  illustrate part of one example embodiment of a fuel cell stack  10  of the present disclosure including the fuel cell tube  100  and fuel cell tubes  200 ,  300 ,  400 ,  500 , and  600  electrically connected to one another. 
     The fuel cell tube  100  includes a porous substrate  110  having a width W, a length L, a thickness T, a generally planar upper major surface  110   a,  and a generally planar lower major surface  110   b.  As shown in  FIG. 3 , multiple fuel conduits  110   c  extend through the substrate  110  along the length L of the substrate  110 . The fuel cell tube  100  is fluidly connectable to a manifold (not shown) that is fluidly connectable to a fuel source such that fuel can flow from the fuel source through the manifold and into and through the fuel conduits  110   c.  In this example embodiment, the substrate  110  is formed of MgO—MgAl 2 O 4  (MMA), though in other embodiments the substrate  110  may be formed of any suitable material(s) in addition to or instead of MMA (such as doped zirconia and/or forsterite). 
     First and second porous anode barriers  120   a  and  120   b  are disposed on the upper and lower major surfaces  110   a  and  110   b,  respectively, of the substrate  110 . The first and second porous anode barriers  120   a  and  120   b  are configured to prevent reactions between the anodes of the fuel cells (described below) and the substrate  110 , and are not configured to provide electrical conduction within a given fuel cell or between two fuel cells. Additionally, the first and second porous anode barriers  120   a  and  120   b  are not configured to partake in the electrochemical reactions that generate electrical power from the fuel. In this example embodiment, the first and second porous anode barriers  120   a  and  120   b  are formed of an inert porous ceramic material that is not an electronic conductor such as 3YSZ or another suitable doped zirconia, though in other embodiments the first and second porous anode barriers  120   a  and  120   b  may be formed of any suitable material(s) in addition to or instead of doped zirconia, such as SrZrO 3  or SrTiO 3 -doped zirconia composite. In other embodiments, the fuel cell tube  100  does not include the first and second porous anode barriers  120   a  and  120   b.    
     Multiple fuel cells  130 , a first laterally segmented fuel cell  140 , and a second laterally segmented fuel cell  150  are disposed on the first porous anode barrier  120   a.  Each fuel cell  130 , the first laterally segmented fuel cell  140 , and the second laterally segmented fuel cell  150  generally extend laterally in the direction of the width W of the substrate  110  and terminate in opposing first and second lateral ends (not labeled). The fuel cells  130  are positioned between the first and second laterally segmented fuel cells  140  and  150 , which are generally positioned at opposing ends of the first porous anode barrier  120   a  in the direction of the length L of the substrate  110 . The fuel cells  130 , the first laterally segmented fuel cell  140 , and the second laterally segmented fuel cell  150  on the first porous anode barrier  120   a  are electrically connected in series via primary interconnects (not shown). 
     As best shown in  FIGS. 1 and 3 , the first laterally segmented fuel cell  140  includes first and second fuel cell portions  140   a  and  140   b.  The first and second fuel cell portions  140   a  and  140   b  are laterally separated in the direction of the width W of the substrate  110  by a space  140   c  such that the first and second fuel cell portions  140   a  and  140   b  are electrically isolated such that there is no continuous electrical path in the fuel cell across the width of the fuel cell tube. Put differently, no continuous direct electrical path exists between the first and second fuel cell portions  140   a  and  140   b  in the direction of the width W of the substrate  110 . In this example embodiment, the space  140   c  is 0.5 millimeters in the direction of the width W of the substrate  110 , though the space  140   c  may be of any suitable size sufficient to ensure the first and second fuel cell portions  140   a  and  140   b  are electrically isolated. 
     As best shown in  FIGS. 1 and 3 , the second laterally segmented fuel cell  150  includes first and second fuel cell portions  150   a  and  150   b.  The first and second fuel cell portions  150   a  and  150   b  are laterally separated in the direction of the width W of the substrate  110  by a space  150   c  such that the first and second fuel cell portions  150   a  and  150   b  are electrically isolated such that there is no continuous electrical path in the fuel cell across the width of the fuel cell tube. Put differently, no continuous direct electrical path exists between the first and second fuel cell portions  150   a  and  150   b  in the direction of the width W of the substrate  110 . In this example embodiment, the space  150   c  is 0.5 millimeters in the direction of the width W of the substrate  110 , though the space  150   c  may be of any suitable size sufficient to ensure the first and second fuel cell portions  150   a  and  150   b  are electrically isolated. 
     Similarly, multiple fuel cells  130 , a third laterally segmented fuel cell  160 , and a fourth laterally segmented fuel cell  170  are disposed on the second porous anode barrier  120   b.  Each fuel cell  130 , the third laterally segmented fuel cell  160 , and the fourth laterally segmented fuel cell  170  generally extend laterally in the direction of the width W of the substrate  110 . The fuel cells  130  are positioned between the third and fourth laterally segmented fuel cells  160  and  170 , which are generally positioned at opposing ends of the second porous anode barrier  120   b  in the direction of the length L of the substrate  110 . The fuel cells  130 , the third laterally segmented fuel cell  160 , and the fourth laterally segmented fuel cell  170  on the second porous anode barrier  120   b  are electrically connected in series via primary interconnects (not shown). 
     As best shown in  FIGS. 1 and 3 , the third laterally segmented fuel cell  160  includes first and second fuel cell portions  160   a  and  160   b.  The first and second fuel cell portions  160   a  and  160   b  are separated in the direction of the width W of the substrate  110  by a space  160   c  such that the first and second fuel cell portions  160   a  and  160   b  are electrically isolated such that there is no continuous electrical path in the fuel cell across the width of the fuel cell tube. Put differently, no continuous direct electrical path exists between the first and second fuel cell portions  160   a  and  160   b  in the direction of the width W of the substrate  110 . In this example embodiment, the space  160   c  is 0.5 millimeters in the direction of the width W of the substrate  110 , though the space  160   c  be of any suitable size sufficient to ensure the first and second fuel cell portions  160   a  and  160   b  are electrically isolated. 
     As best shown in  FIGS. 1 and 3 , the fourth laterally segmented fuel cell  170  includes first and second fuel cell portions  170   a  and  170   b.  The first and second fuel cell portions  170   a  and  170   b  are laterally separated in the direction of the width W of the substrate  110  by a space  170   c  such that the first and second fuel cell portions  170   a  and  170   b  are electrically isolated such that there is no continuous electrical path in the fuel cell across the width of the fuel cell tube. Put differently, no continuous direct electrical path exists between the first and second fuel cell portions  170   a  and  170   b  in the direction of the width W of the substrate  110 . In this example embodiment, the space  170   c  is 0.5 millimeters in the direction of the width W of the substrate  110 , though the space  170   c  be of any suitable size sufficient to ensure the first and second fuel cell portions  170   a  and  170   b  are electrically isolated. 
     As shown in  FIG. 4 , each fuel cell  130  and each fuel cell portion of each laterally segmented fuel cell  140 ,  150 ,  160 ,  170 ,  181 ,  190 , and  191  includes an anode current collector  130   a,  an anode  130   b,  an electrolyte  130   c,  a cathode  130   d,  and a cathode current collector  130   e.  The anode  130   b  is disposed between the anode current collector  130   a  and the electrolyte  130   c.  The electrolyte  130   c  is disposed between the anode  130   b  and the cathode  130   d.  The cathode  130   d  is disposed between the electrolyte  130   c  and the cathode current collector  130   e.  The anode current collector  130   a  is electrically connected to the anode  130   b,  and the cathode current collector  130   e  is electrically connected to the cathode  130   d.  The anode and cathode current collectors  130   a  and  130   e  provide a higher electrical conductivity path for the transfer of electrons than is possible by the anode and cathode along. 
     In this example embodiment, the anode current collector  130   a  is an electrode conductive layer formed of a nickel cermet. Examples of suitable materials include Ni—YSZ (yttria doping in zirconia is 3-8 mol %); Ni—ScSZ (scandia doping is 4-10 mol %, preferably second doping for phase stability for 10 mol % scandia-ZrO 2 ); Ni-doped ceria (such as Gd or Sm doping); cermet of Ni and doped lanthanum chromite (such as Ca doping on A site and Zn doping on B site); cermet of Ni and doped strontium titanate (such as La doping on A site and Mn doping on B site) and/or La 1-x Sr x Mn y Cr 1-y O 3 . In other embodiments, the anode current collector may be formed of cermets based at least in part on one or more precious metals and/or one or more precious metal alloys in addition to retaining Ni content. Precious metals in the cermet may include, for example, Pt, Pd, Au, Ag, and/or alloys thereof. The ceramic phase may include, for example, an inactive non-electrically conductive phase, including, for example, YSZ, ScSZ, and/or one or more other inactive phases, e.g., having desired coefficients of thermal expansion (CTE) to control the CTE of the layer to match the CTE of the substrate  110  and the electrolyte  130   c.  In some embodiments, the ceramic phase may include Al 2 O 3  and/or a spinel such as NiAl 2 O 4 , MgAl 2 O 4 , MgCr 2 O 4 , or NiCr 2 O 4 . In other embodiments, the ceramic phase may be electrically conductive, e.g., doped lanthanum chromite, doped strontium titanate, and/or one or more forms of LaSrMnCrO. One specific example of the anode current collector  130   a  material is 76.5% Pd, 8.5% Ni, 15% 3YSZ. 
     In this example embodiment, the anode  130   b  is formed of xNiO-(100-x)YSZ (x is from 55 to 75 in weight ratio), yNiO-(100-y)ScSZ (y is from 55 to 75 in weight ratio), NiO-gadolinia stabilized ceria (such as 55 wt % NiO-45 wt % GDC), and/or NiO samaria stabilized ceria. In other embodiments, the anode may be formed of doped strontium titanate, La 1-x Sr x Mn y Cr 1-y O 3  (e.g., La 0.75 Sr 0.25 Mn 0.5 Cr 0.5 O 3 ) and/or other ceramic-based anode materials. 
     In this example embodiment, the electrolyte  130   c  is formed of a ceramic material. In some embodiments, the electrolyte  130   c  is formed of a proton and/or oxygen ion conducting ceramic. In other embodiments, the electrolyte  130   c  is formed of YSZ, such as 3YSZ and/or 8YSZ. In other embodiments, the electrolyte  130   c  is formed of ScSZ, such as 4ScSZ, 6ScSz, and/or 10ScSZ in addition to or in place of YSZ. In other embodiments, the electrolyte  130   c  may be formed of doped ceria and/or doped lanthanum gallate. The electrolyte  130   c  is essentially impervious to diffusion therethrough of the oxidant (e.g., air or O 2 ) and the fuel (e.g., H 2 ) flowed through or past the fuel cell tube  100 , but enables diffusion of oxygen ions and/or protons, depending upon the particular embodiment and its application. 
     In this example embodiment, the cathode  130   d  is formed of a mixture of an electrochemically catalytic ceramic and an ionic phase. The electrochemically catalytic phase consists of at least one of LSM (La 1-x Sr x MnO 3 , x=0.1 to 0.3), La 1-x Sr x FeO 3 , (such as x=0.3), La 1-x Sr x Co y Fe 1-y O 3 (such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 ) and/or Pr 1-x Sr x MnO 3 (such as Pr 0.8 Sr 0.2 MnO 3 ), although other materials may be employed. For example, in some embodiments, the cathode  130   d  is formed of Ruddlesden-Popper nickelates and La 1-x Ca x MnO 3  (such as La 0.8 Ca 0.2 MnO 3 ) materials. The ionic phase may be YSZ containing from 3-8 mole percent yttria, or ScSZ containing 4-10 mole percent scandia and optionally a second dopant of Al, Y or ceria at minor content (about 1 mole percent) for high scandia stabilized zirconias (8-10ScSZ) to prevent formation of the rhombohedral phase. The electrochemically catalytic ceramic phase can comprise 40-60% by volume of the cathode. 
     In this example embodiment, the cathode current collector  130   e  is an electrode conductive layer formed of an electronically conductive ceramic and in many cases is similar in its chemistry to that of the electrochemically catalytic ceramic phase of the cathode. For example, a LSM+YSZ cathode will generally employ a LSM (La1-xSrxMnO3, x=0.1 to 0.3) cathode current collector. Other embodiments of the cathode current collector  130   e  may include at least one of LaNi x Fe 1-x O 3  (such as LaNi 0.6 Fe 0.4 O 3 ), La 1-x Sr x MnO 3  (such as La 0.75 Sr 0.25 MnO 3 ), doped lanthanum chromites (such as La 1-x Ca x CrO 3-δ , x=0.15-0.3), and/or Pr 1-x Sr x CoO 3 , such as Pr 0.8 Sr 0.2 CoO 3 . In other embodiments, the cathode current collector  130   e  may be formed of a precious metal cermet. The precious metals in the precious metal cermet may include, for example, Pt, Pd, Au, Ag, and/or alloys thereof. Non electrically conducting ceramic phase may also be included, for example, YSZ, ScSZ, and Al 2 O 3 , or other ceramic materials. One specific example of cathode current collector  130   e  material is 80 wt % Pd-20 wt % LSM. 
     In this example embodiment, the fuel cells  130  and the laterally segmented fuel cells  140 ,  150 ,  160 ,  170 ,  181 ,  190 , and  191  are formed by depositing films/layers onto the upper and lower major surfaces  110   a  and  110   b  of the substrate  110 , such as by screen printing and/or inkjet printing, to form the porous anode barriers, the primary interconnects, the anode current collectors, and anodes, the electrolytes, the cathodes, and the cathode current collectors. In other embodiments, the films/layers may be deposited by one or more other techniques in addition to or instead of screen printing and/or inkjet printing. In various embodiments, one or more firing/sintering cycles are performed subsequent to depositing one or more films/layers. Other embodiments may not require any firing/sintering for one or more films/layers deposition. 
     A first fuel cell connector  145   a  is electrically connected to (and electrically connects) the first fuel cell portion  140   a  of the first laterally segmented fuel cell  140  and the first fuel cell portion  160   a  of the third laterally segmented fuel cell  160 . A second fuel cell connector  145   b  is electrically connected to (and electrically connects) the second fuel cell portion  140   b  of the first laterally segmented fuel cell  140  and the second fuel cell portion  160   b  of the third laterally segmented fuel cell  160 . A third fuel cell connector  155   a  is electrically connected to (and electrically connects) the first fuel cell portion  150   a  of the second laterally segmented fuel cell  150  and the first fuel cell portion  170   a  of the fourth laterally segmented fuel cell  170 . A fourth fuel cell connector  155   b  is electrically connected to (and electrically connects) the second fuel cell portion  150   b  of the second laterally segmented fuel cell  150  and the second fuel cell portion  170   b  of the fourth laterally segmented fuel cell  170 . 
     In this example embodiment, the first fuel cell connector  145   a  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the first fuel cell portions  140   a  and  160   a,  and the second fuel cell connector  145   b  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the second fuel cell portions  140   b  and  160   b.  Since the first and second fuel cell portions  140   a  and  140   b  are electrically isolated and the first and second fuel cell portions  160   a  and  160   b  are electrically isolated, the first and second fuel cell connectors  145   a  and  145   b  are electrically isolated such that there is no continuous electrical path across the width W of the tube (substrate  110 ). 
     In this example embodiment, the third fuel cell connector  155   a  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the first fuel cell portions  150   a  and  170   a,  and the fourth fuel cell connector  155   b  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the second fuel cell portions  150   b  and  170   b.  Since the first and second fuel cell portions  150   a  and  150   b  are electrically isolated and the first and second fuel cell portions  170   a  and  170   b  are electrically isolated, the third and fourth fuel cell connectors  155   a  and  155   b  are electrically isolated such that there is no continuous electrical path across the width W of the tube (substrate  110 ). 
       FIGS. 5-7  show six fuel cell tubes  100 ,  200 ,  300 ,  400 ,  500 , and  600  of the fuel cell stack  10 . While the fuel cell stack  10  may include any suitable quantity of fuel cell tubes electrically connected to one another in series, only six are shown here for clarity and brevity. In this example embodiment, the fuel cell tubes  200 ,  300 ,  400 ,  500 , and  600  are identical to the fuel cell tube  100  and are therefore not separately described (though in other embodiments the fuel cell tubes may differ from one another). The element numbering schemes of the fuel cell tubes  200 ,  300 ,  400 ,  500 , and  600  correspond to the element numbering scheme used to describe the fuel cell tube  100  such that like element numbers correspond to like components. 
     The first fuel cell tube  100  is electrically connected to the second fuel cell tube  200  via: (1) a first tube interconnect  12   a  that electrically connects the third fuel cell connector  155   a  of the first fuel cell tube  100  to the third fuel cell connector  255   a  of the second fuel cell tube  200 ; and (2) a second tube interconnect  12   b  that electrically connects the fourth fuel cell connector  155   b  of the first fuel cell tube  100  to the fourth fuel cell connector  255   b  of the second fuel cell tube  200 . Generally, the fuel cell tubes are connected in series with direction of the flow of fuel through the tubes. 
     The second fuel cell tube  200  is electrically connected to the third fuel cell tube  300  via: (1) a third tube interconnect  23   a  that electrically connects the first fuel cell connector  245   a  of the second fuel cell tube  200  to the first fuel cell connector  345   a  of the third fuel cell tube  300 ; and (2) a fourth tube interconnect  23   b  that electrically connects the second fuel cell connector  245   b  of the second fuel cell tube  200  to the second fuel cell connector  345   b  of the third fuel cell tube  300 . 
     The third fuel cell tube  300  is electrically connected to the fourth fuel cell tube  400  via: (1) a fifth tube interconnect  34   a  that electrically connects the third fuel cell connector  355   a  of the third fuel cell tube  300  to the third fuel cell connector  455   a  of the fourth fuel cell tube  400 ; and (2) a sixth tube interconnect  34   b  that electrically connects the fourth fuel cell connector  355   b  of the third fuel cell tube  300  to the fourth fuel cell connector  455   b  of the fourth fuel cell tube  400 . 
     The fourth fuel cell tube  400  is electrically connected to the fifth fuel cell tube  500  via: (1) a seventh tube interconnect  45   a  that electrically connects the first fuel cell connector  445   a  of the fourth fuel cell tube  400  to the first fuel cell connector  545   a  of the fifth fuel cell tube  500 ; and (2) a eighth tube interconnect  45   b  that electrically connects the second fuel cell connector  445   b  of the fourth fuel cell tube  400  to the second fuel cell connector  545   b  of the fifth fuel cell tube  500 . 
     The fifth fuel cell tube  500  is electrically connected to the sixth fuel cell tube  600  via: (1) a ninth tube interconnect  56   a  that electrically connects the third fuel cell connector  555   a  of the fifth fuel cell tube  500  to the third fuel cell connector  655   a  of the sixth fuel cell tube  600 ; and (2) a tenth tube interconnect  56   b  that electrically connects the fourth fuel cell connector  555   b  of the fifth fuel cell tube  500  to the fourth fuel cell connector  655   b  of the sixth fuel cell tube  600 . 
     Although not shown here, the first fuel cell tube  100  may be electrically connected to another fuel cell tube of the fuel cell stack  10  or to another fuel cell stack via the tube interconnects shown but not labeled in  FIGS. 5 and 7 . Similarly, the sixth fuel cell tube  600  may be electrically connected to another fuel cell tube of the fuel cell stack  10  or to another fuel cell stack via the tube interconnects shown but not labeled in  FIGS. 5 and 7 . 
     In operation, as oxidant is flowed past the cathodes of the fuel cells of the fuel cell tubes and as fuel is flowed through the fuel conduits of the substrates of the fuel cell tubes, the electrochemical reactions that occur at the cathodes and the anodes produce free electrons at the anodes. Within a particular fuel cell tube, those free electrons flow as electrical current from one fuel cell to the next (via the anode current collectors, the primary interconnects, and the cathode current collectors) in a particular direction. Once the electrical current reaches the final fuel cell in the fuel cell tube (here, a laterally segmented fuel cell), the electrical current flows via the fuel cell connectors and the tube interconnects to the next fuel cell tube, and so on until reaching the electrical load. 
     For instance, as shown in  FIG. 5 , in this example embodiment, the electrical current I flows: (1) within the fuel cell tube  100  from the laterally segmented fuel cells  140  and  160  through the fuel cells  130  and to the laterally segmented fuel cells  150  and  170 ; (2) from the laterally segmented fuel cells  150  and  170  of the fuel cell tube  100  to the laterally segmented fuel cells  250  and  270  of the fuel cell tube  200  via the fuel cell connectors  155   a,    155   b,    255   a,  and  255   b  and the tube interconnects  12   a  and  12   b;  (3) within the fuel cell tube  200  from the laterally segmented fuel cells  250  and  270  through the fuel cells  230  and to the laterally segmented fuel cells  240  and  260 ; (4) from the laterally segmented fuel cells  240  and  260  of the fuel cell tube  200  to the fuel cells  340  and  360  of the fuel cell tube  300  via the fuel cell connectors  245   a,    245   b ,  345   a,  and  345   b  and the tube interconnects  23   a  and  23   b;  (5) within the fuel cell tube  300  from the laterally segmented fuel cells  340  and  360  through the fuel cells  330  and to the laterally segmented fuel cells  350  and  370 ; (6) from the laterally segmented fuel cells  350  and  370  of the fuel cell tube  300  to the laterally segmented fuel cells  450  and  470  of the fuel cell tube  400  via the fuel cell connectors  355   a,    355   b,    455   a,  and  455   b  and the tube interconnects  34   a  and  34   b;  (7) within the fuel cell tube  400  from electrically isolated the fuel cells  450  and  470  through the fuel cells  430  and to the laterally segmented fuel cells  440  and  460 ; (8) from the laterally segmented fuel cells  440  and  460  of the fuel cell tube  400  to the laterally segmented fuel cells  540  and  560  of the fuel cell tube  500  via the fuel cell connectors  445   a,    445   b,    545   a,  and  545   b  and the tube interconnects  45   a  and  45   b;  (9) within the fuel cell tube  500  from the laterally segmented fuel cells  540  and  560  through the fuel cells  530  and to the laterally segmented fuel cells  550  and  570 ; (10) from the laterally segmented fuel cells  550  and  570  of the fuel cell tube  500  to the laterally segmented fuel cells  650  and  670  of the fuel cell tube  600  via the fuel cell connectors  555   a,    555   b,    655   a,  and  655   b  and the tube interconnects  56   a  and  56   b;  ( 11 ) within the fuel cell tube  600  from the laterally segmented fuel cells  650  and  670  through the fuel cells  630  and to the laterally segmented fuel cells  640  and  660 ; and (12) from the laterally segmented fuel cells  640  and  660  of the fuel cell tube  600  to the electrical load (or to another fuel cell tube or fuel cell stack) via the fuel cell connectors  645   a  and  645   b.    
     For the fuel cell stack to conduct electrical current from one fuel cell tube to another, the tube interconnects must be in working order, i.e., provide a path for the electrical current to flow from one fuel cell tube to the other. One way of checking whether a given tube interconnect is in working order is by using an ohmmeter to attempt to flow an electrical current across that tube interconnect and to calculate the resistance across that tube interconnect. If the resistance is relatively low (e.g., negligible), the electrical current is able to flow across the tube interconnect. But if the resistance is relatively high (e.g., infinite), the electrical current is not able to flow across the tube interconnect, and the tube interconnect is damaged and must be repaired or replaced to ensure proper fuel cell stack operation. 
     Since prior art fuel cell tubes do not include laterally segmented fuel cells, their fuel cell connectors are electrically connected to laterally continuous fuel cells. As described below, this leads to ohmmeters generating false positive readings in certain instances when calculating the resistance across a particular tube interconnect. That is, in certain instances, the ohmmeter calculates a relatively low resistance across a given tube interconnect—and thus indicates a working tube interconnect—when in reality that tube interconnect is damaged such that it electrical current cannot flow through it. 
       FIGS. 8A-8D  show a negative ohmmeter probe N and a positive ohmmeter probe P positioned to attempt to flow an electrical current I across a tube interconnect  1012   b  that electrically connects prior art fuel cell tubes  1100  and  1200 . Opposing tube interconnect  1012   a  also electrically connects the prior art fuel cells  1100  and  1200 . The fuel cell connectors (not labeled) of the fuel cell tubes  1100  and  1200  are electrically connected to laterally continuous fuel cells. 
     In the scenario shown in  FIG. 8A , the tube interconnects  1012   a  and  1012   b  are both in working order. The ohmmeter calculates a low resistance because the tube interconnect  1012   b  is in working order and the electrical current I can flow across the tube interconnect  1012   b  from the negative probe N to the positive probe P. 
     In the scenario shown in  FIG. 8B , the tube interconnect  1012   a  is in working order while the tube interconnect  1012   b  is damaged such that electrical current cannot flow through it. But rather than calculate a high resistance that correspond to electrical current not being able to flow across the tube interconnect  1012   b,  the ohmmeter calculates a low resistance because the electrical current flows from the negative probe N across the laterally continuous fuel cells of the fuel cell tube  1100 , across the tube interconnect  1012   a,  and across the laterally continuous fuel cells of the fuel cell tube  1200  to the positive probe P. In other words, the laterally continuous fuel cells provide a low-resistance path for the electrical current Ito flow from the negative probe N to the positive probe P, so the electrical current does so and causes the ohmmeter to calculate a low resistance that does not reflect the damaged state of the tube interconnect  1012   b.    
     In the scenario shown in  FIG. 8C , the tube interconnect  1012   a  is damaged such that electrical current cannot flow through it while the tube interconnect  1012   b  is in working order. The ohmmeter calculates a low resistance because the tube interconnect  1012   b  is in working order and the electrical current I can flow across the tube interconnect  1012   b  from the negative probe N to the positive probe P. 
     In the scenario shown in  FIG. 8D , the tube interconnects  1012   a  and  1012   b  are damaged such that electrical current cannot flow through them. The ohmmeter calculates a high resistance because electrical current cannot flow through either of the tube interconnects  1012   a  or  1012   b  from the negative probe N to the positive probe P. 
     The fuel cell tubes with laterally segmented fuel cells of the present disclosure solve this problem. As explained above, the fuel cell connectors of the fuel cell tubes of the present disclosure are electrically connected to laterally segmented fuel cells, which means only one low-resistance electrical path exists when attempting to flow electrical current across a tube interconnect during resistance testing. 
       FIGS. 9A-9D  show negative probe N and positive probe P of the ohmmeter described above positioned to attempt to flow an electrical current across the tube interconnect  12   b.    
     In the scenario shown in  FIG. 9A , the tube interconnects  12   a  and  12   b  are both in working order. The ohmmeter calculates a low resistance because the tube interconnect  12   b  is in working order and the electrical current I can flow across the tube interconnect  12   b  from the negative probe N to the positive probe P. 
     In the scenario shown in  FIG. 9B , the tube interconnect  12   a  is in working order while the tube interconnect  12   b  is damaged such that electrical current cannot flow through it. The ohmmeter calculates a high resistance because electrical current cannot flow through the tube interconnect  12   b  from the negative probe N to the positive probe P. Additionally, electrical current cannot flow from the negative probe N to the positive probe P through the tube interconnect  12   a  because a low-resistance electrical path does not exist between the negative probe N and the positive probe P through the tube interconnect  12   a  due to the laterally segmented fuel cells. 
     In the scenario shown in  FIG. 9C , the tube interconnect  12   a  is damaged such that electrical current cannot flow through it while the tube interconnect  12   b  is in working order. The ohmmeter calculates a low resistance because the tube interconnect  12   b  is in working order and the electrical current I can flow across the tube interconnect  12   b  from the negative probe N to the positive probe P. 
     In the scenario shown in  FIG. 9D , the tube interconnects  12   a  and  12   b  are damaged such that electrical current cannot flow through them. The ohmmeter calculates a high resistance because electrical current cannot flow through either of the tube interconnects  12   a  or  12   b  from the negative probe N to the positive probe P. 
     Another benefit is that the use of laterally segmented fuel cells has a negligible effect on the performance of a given fuel cell tube because the electrical current density at the location of the space between the fuel cell portions is low because the electrical current is concentrated at the fuel cell connectors (through which the electrical current flows to the next fuel cell tube). 
       FIGS. 10A and 10B  are schematics showing a side view of fuel cell tube  2100  along the length of the tube.  FIG. 10A  shows schematics of the anode-side of a fuel cell tube, including a tube interconnect connection region at laterally segmented dummy cell portion  2180   b.  Laterally segmented dummy cell portion  2180   b  includes cathode current collector  2130   e  and cathode  2130   d.  Laterally segmented dummy cell portion  2180   b  is electrically connected to a laterally segmented fuel cell portion  2181   b  by a primary interconnect within primary interconnect region  2111 , which may overlay dense barrier  2120   c.  Dense barrier  2120   c  may be formed from yttria stabilized zirconia, preferably 3YSZ. Dense barrier  2120   c  could be formed of 8YSZ or ScSz as well and could have additional impurities, compositing to reduce its ionic conductivity. Dense barrier  2120   c  could also be formed of non-zirconia ceramics not having electrical conductivity. The lateral segmentation extends into the primary interconnect region  2111  connected to dummy cell  2180  and into the fuel cell  2181  to allow for electrical isolation of an operated fuel cell. 
     Laterally segmented fuel cell portion  2181   b  includes cathode current collector  2130   e,  cathode  2130   d,  electrolyte  2130   c,  anode  2130   b,  and anode current collector  2130   a.  The anode  2130   b  is disposed between the anode current collector  2130   a  and the electrolyte  2130   c.  The electrolyte  2130   c  is disposed between the anode  2130   b  and the cathode  2130   d.  The cathode  2130   d  is disposed between the electrolyte  2130   c  and the cathode current collector  2130   e.  The anode current collector  2130   a  is electrically connected to the anode  2130   b,  and the cathode current collector  2130   e  is electrically connected to the cathode  2130   d.  The anode current collector  2130   a  and cathode current collector  2130   e  provide a higher electrical conductivity path for the transfer of electrons than is possible by the anode and cathode alone. Laterally segmented fuel cell portion  2181   b  is electrically connected to fuel cell  2130  by a primary interconnect within primary interconnect region  2111 , which may overlay dense barrier  2120   c.  Dense barrier  2120   c  may be formed from yttria stabilized zirconia, preferably 3YSZ. Dense barrier  2120   c  could be formed of 8YSZ or ScSz as well and could have additional impurities, compositing to reduce its ionic conductivity. Dense barrier  2120   c  could also be formed of non-zirconia ceramics not having electrical conductivity. 
     Fuel cell  2130  may be further electrically connected to other fuel cells  2130  by a primary interconnect within primary interconnect region  2111 . Porous anode barrier  2120   a  is printed over the upper major surface  2110   a  (not shown) of the tube  2100  and overlaid by laterally segmented dummy cell portion  2180   b,  laterally segmented fuel cell portion  2181   b,  fuel cell  2130 , primary interconnect regions  2111 , and optional dense barrier  2120   c.  Fuel passes through the porous anode barrier  2120   a  to reach the active cell. 
     In fuel cell  2130  and laterally segmented fuel cell portion  2181   b,  the anode  2130   b  is disposed between the anode current collector  2130   a  and the electrolyte  2130   c.  The electrolyte  2130   c  is disposed between the anode  2130   b  and the cathode  2130   d.  The cathode  2130   d  is disposed between the electrolyte  2130   c  and the cathode current collector  2130   e.  The anode current collector  2130   a  is electrically connected to the anode  2130   b,  and the cathode current collector  2130   e  is electrically connected to the cathode  2130   d.  The anode current collector  2130   a  and cathode current collector  2130   e  provide a higher electrical conductivity path for the transfer of electrons than is possible by the anode and cathode alone. 
       FIG. 10B  shows schematics of the cathode-side of fuel cell tube  2100 , including a tube interconnect connection region at laterally segmented fuel cell portion  2190   b.  Laterally segmented fuel cell portion  2190   b  includes cathode current collector  2130   e,  cathode  2130   d,  electrolyte  2130   c,  anode  2130   b,  and anode current collector  2130   a,  where the cathode current collector  2130   e,  cathode  2130   d,  and electrolyte  2130   c  extend past anode  2130   b  and anode current collector  2130   a  into the tube interconnect connection region. The anode  2130   b  is disposed between the anode current collector  2130   a  and the electrolyte  2130   c.  The electrolyte  2130   c  is disposed between the anode  2130   b  and the cathode  2130   d.  The cathode  2130   d  is disposed between the electrolyte  2130   c  and the cathode current collector  2130   e.  The anode current collector  2130   a  is electrically connected to the anode  2130   b,  and the cathode current collector  2130   e  is electrically connected to the cathode  2130   d.  The anode current collector  2130   a  and cathode current collector  2130   e  provide a higher electrical conductivity path for the transfer of electrons than is possible by the anode and cathode alone. Laterally segmented fuel cell portion  2190   b  may be further electrically connected to fuel cell  2130  by a primary interconnect within primary interconnect region  2111 , which may overlay dense barrier  2120   c.  Dense barrier  2120   c  may be formed from yttria stabilized zirconia, preferably 3YSZ. Dense barrier  2120   c  could be formed of 8YSZ or ScSz as well and could have additional impurities, compositing to reduce its ionic conductivity. 
     Fuel cell  2130  may be further electrically connected to other fuel cells  2130  by a primary interconnect within primary interconnect region  2111 , which may overlay dense barrier  2120   c.  Porous anode barrier  2120   a  is printed over the upper major surface  2110   a  (not shown) of the tube  2100  and overlaid by laterally segmented fuel cell portion  2190   b,  fuel cells  2130 , primary interconnect regions  2111 , and optional dense barrier  2120   c.  Fuel passes through the porous anode barrier  2120   a  to reach the active cell. 
     In this example embodiment, the anode current collector  2130   a  is an electrode conductive layer formed of a nickel cermet. Examples of suitable materials include Ni—YSZ (yttria doping in zirconia is 3-8 mol %); Ni—ScSZ (scandia doping is 4-10 mol %, preferably second doping for phase stability for 10 mol % scandia-ZrO 2 ); Ni-doped ceria (such as Gd or Sm doping); cermet of Ni and doped lanthanum chromite (such as Ca doping on A site and Zn doping on B site); cermet of Ni and doped strontium titanate (such as La doping on A site and Mn doping on B site) and/or La 1-x Sr x Mn y Cr 1-y O 3 . In other embodiments, the anode current collector may be formed of cermets based at least in part on one or more precious metals and/or one or more precious metal alloys in addition to retaining Ni content. Precious metals in the cermet may include, for example, Pt, Pd, Au, Ag, and/or alloys thereof. The ceramic phase may include, for example, an inactive non-electrically conductive phase, including, for example, YSZ, ScSZ, and/or one or more other inactive phases, e.g., having desired coefficients of thermal expansion (CTE) to control the CTE of the layer to match the CTE of the substrate  2110  and the electrolyte  2130   c.  In some embodiments, the ceramic phase may include Al 2 O 3  and/or a spinel such as NiAl 2 O 4 , MgAl 2 O 4 , MgCr 2 O 4 , or NiCr 2 O 4 . In other embodiments, the ceramic phase may be electrically conductive, e.g., doped lanthanum chromite, doped strontium titanate, and/or one or more forms of LaSrMnCrO. One specific example of the anode current collector  2130   a  material is NiO—NiAl 2 O 4 -8YSZ. 
     In this example embodiment, the anode  2130   b  is formed of xNiO-(100-x)YSZ (x is from 55 to 75 in weight ratio), yNiO-(100-y)ScSZ (y is from 55 to 75 in weight ratio), NiO-gadolinia stabilized ceria (such as 55 wt % NiO-45 wt % GDC), and/or NiO samaria stabilized ceria. In other embodiments, the anode  2130   b  may be formed of doped strontium titanate, La 1-x Sr x Mn y Cr 1-y O 3 (e.g., La 0.75 Sr 0.25 Mn 0.5 Cr 0.5 O 3 ) and/or other ceramic-based anode materials. 
     In this example embodiment, the electrolyte  2130   c  is formed of a ceramic material. In some embodiments, the electrolyte  2130   c  is formed of a proton and/or oxygen ion conducting ceramic. In other embodiments, the electrolyte  2130   c  is formed of YSZ, such as 3YSZ and/or 8YSZ. In other embodiments, the electrolyte  2130   c  is formed of ScSZ, such as 4ScSZ, 6ScSz, and/or 10ScSZ in addition to or in place of YSZ. In other embodiments, the electrolyte  2130   c  may be formed of doped ceria and/or doped lanthanum gallate. The electrolyte  2130   c  is essentially impervious to diffusion therethrough of the oxidant (e.g., air or O 2 ) and the fuel (e.g., H 2 ) flowed through or past the fuel cell tube  2100 , but enables diffusion of oxygen ions and/or protons, depending upon the particular embodiment and its application. 
     In this example embodiment, the cathode  2130   d  is formed of a mixture of an electrochemically catalytic ceramic and an ionic phase. The electrochemically catalytic phase consists of at least one of LSM (La 1-x Sr x MnO 3 , x=0.1 to 0.3), La 1-x Sr x FeO 3 , (such as x=0.3), La 1-x Sr x Co y Fe 1-y O 3  (such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 ) and/or Pr 1-x Sr x MnO 3  (such as Pr 0.8 Sr 0.2 MnO 3 ), although other materials may be employed. For example, in some embodiments, the cathode  2130   d  is formed of Ruddlesden-Popper nickelates and La 1-x Ca x MnO 3  (such as La 0.8 Ca 0.2 MnO 3 ) materials. The ionic phase may be YSZ containing from 3-8 mole percent yttria, or ScSZ containing 4-10 mole percent scandia and optionally a second dopant of Al, Y or ceria at minor content (about 1 mole percent) for high scandia stabilized zirconias (8-10ScSZ) to prevent formation of the rhombohedral phase. The electrochemically catalytic ceramic phase can comprise 40-60% by volume of the cathode. 
     In this example embodiment, the cathode current collector  2130   e  is an electrode conductive layer formed of an electronically conductive ceramic and in many cases is similar in its chemistry to that of the electrochemically catalytic ceramic phase of the cathode. For example, a LSM+YSZ cathode will generally employ a LSM (La1-xSrxMnO3, x=0.1 to 0.3) cathode current collector. Other embodiments of the cathode current collector  2130   e  may include at least one of LaNi x Fe 1-x O 3  (such as LaNi 0.6 Fe 0.4 O 3 ), La 1-x Sr x MnO 3  (such as La 0.75 Sr 0.25 MnO 3 ), doped lanthanum chromites (such as La 1-x Ca x CrO 3-δ , x=0.15-0.3), and/or Pr 1-x Sr x CoO 3 , such as Pr 0.8 Sr 0.2 CoO 3 . In other embodiments, the cathode current collector  2130   e  may be formed of a precious metal cermet. The precious metals in the precious metal cermet may include, for example, Pt, Pd, Au, Ag, and/or alloys thereof. Non electrically conducting ceramic phase may also be included, for example, YSZ, ScSZ, and Al 2 O 3 , or other ceramic materials. One specific example of cathode current collector  2130   e  material is (La0.8Sr0.2)0.95MnOx. 
     In this example embodiment, the fuel cells  2130 , laterally segmented dummy cells  2180  and  2185 , and the laterally segmented fuel cells  2181 ,  2186 ,  2190 , and  2195  are formed by depositing films/layers onto the upper and lower major surfaces  2110   a  and  2110   b  of the substrate  2110 , such as by screen printing and/or inkjet printing, to form the porous anode barriers, the primary interconnects, the anode current collectors, and anodes, the electrolytes, the cathodes, and the cathode current collectors. In other embodiments, the films/layers may be deposited by one or more other techniques in addition to or instead of screen printing and/or inkjet printing. In various embodiments, one or more firing/sintering cycles are performed subsequent to depositing one or more films/layers. Other embodiments may not require any firing/sintering for one or more films/layers deposition. 
       FIGS. 11A and 11B  are schematics showing a top view of fuel cell tube  2100 .  FIG. 11A  shows schematics of the anode-side of a fuel cell tube, including tube interconnect connection regions at laterally segmented dummy cell portions  2180   a  and  2180   b.  Laterally segmented dummy cell portions  2180   a  and  2180   b  are electrically connected to laterally segmented fuel cell portions  2181   a  and  2181   b,  respectively, via primary interconnects within laterally spaced primary interconnect regions  2111 . The primary interconnect regions  2111  between the laterally segmented dummy cell portions and the laterally segmented fuel cell portions are laterally separated. The lateral segmentation extends into the primary interconnect region  2111  connected to dummy cell  2180  and into the fuel cell  2181  to allow for electrical isolation of an operated fuel cell. Laterally segmented fuel cell portions  2181   a  and  2181   b  are electrically connected to fuel cell  2130  via a primary interconnect within primary interconnect region  2111 . Fuel cell  2130  may be further electrically connected to fuel cells  2130  via a primary interconnect within primary interconnect region  2111 . 
       FIG. 11B  shows schematics of the cathode-side of a fuel cell tube, including tube interconnect connection regions at laterally segmented fuel cell portions  2190   a  and  2190   b.  Laterally segmented fuel cell portions  2190   a  and  2190   b  are electrically connected to fuel cell  2130 , via a primary interconnect within primary interconnect region  2111 . Fuel cell  2130  may be further electrically connected to fuel cells  2130  (not shown) by a primary interconnect within primary interconnect region  2111 . 
     The addition of a laterally segmented fuel cell  2181  connected to laterally segmented dummy cell  2180  on the anode-side of the fuel cell tube allows for the inspection of the side-to-side and tube-to-tube connections for cells that have been operated and have reduced anodes in the Ni-cermet highly conductive state. These additions prevent false readings when the cells are fired and there is a broken tube interconnect. 
       FIGS. 11C and 11D  are schematics showing a bottom view of fuel cell tube  2100 .  FIG. 11C  shows schematics of the anode-side of a fuel cell tube, including tube interconnect connection regions at laterally segmented dummy cell portions  2185   a  and  2185   b.  Laterally segmented dummy cell portions  2185   a  and  2185   b  are electrically connected to laterally segmented fuel cell portions  2186   a  and  2186   b , respectively, via primary interconnects within primary interconnect regions  2111 . The primary interconnect regions  2111  between the laterally segmented dummy cell portions and the laterally segmented fuel cell portions are laterally separated. The lateral segmentation extends into the primary interconnect region  2111  connected to dummy cell  2185  and into the fuel cell  2186  to allow for electrical isolation of an operated fuel cell. Laterally segmented fuel cell portions  2186   a  and  2186   b  are electrically connected to fuel cell  2130  via a primary interconnect within primary interconnect region  2111 . Fuel cell  2130  may be further electrically connected to fuel cells  2130  via a primary interconnect within primary interconnect region  2111 . 
       FIG. 11D  shows schematics of the cathode-side of fuel cell tube  2100 , including tube interconnect connection regions at laterally segmented fuel cell portions  2195   a  and  2195   b.  Laterally segmented fuel cell portions  2195   a  and  2195   b  are electrically connected to fuel cell  2130 , via a primary interconnect within primary interconnect region  2111 . Fuel cell  2130  may be further electrically connected to fuel cells  2130  (not shown) by a primary interconnect within primary interconnect region  2111 . 
     The addition of a laterally segmented fuel cell  2186  connected to laterally segmented dummy cell  2185  on the anode-side of the fuel cell tube allows for the inspection of the side-to-side and tube-to-tube connections for cells that have been operated and have reduced anodes in the Ni-cermet highly conductive state. These additions prevent false readings when the cells are fired and there is a broken tube interconnect. 
       FIGS. 10-14  illustrate one example embodiment of a fuel cell tube  2100  of the present disclosure and components thereof. The fuel cell tube  2100  includes a porous substrate  2110  having a width W, a length L, a thickness T, a generally planar upper major surface  2110   a,  and a generally planar lower major surface  2110   b.  The fuel cell tube  2100  is fluidly connectable to a manifold (not shown) that is fluidly connectable to a fuel source such that fuel can flow from the fuel source through the manifold and into and through fuel conduits  2110   c.  In this example embodiment, the substrate  2110  is formed of MgO—MgAl 2 O 4  (MMA), though in other embodiments the substrate  2110  may be formed of any suitable material(s) in addition to or instead of MMA (such as doped zirconia and/or forsterite). Glass edge seal  2146  is not shown in  FIG. 12  in order to clarify the structure of components underneath it. In  FIG. 13 , electrolyte  2130   c,  first and second porous anode barriers  2120   a  and  2120   b,  and substrate  2110  are represented by dashed lines as they are behind the glass edge seal  2146 . 
     First and second porous anode barriers  2120   a  and  2120   b  are disposed on the upper and lower major surfaces  2110   a  and  2110   b,  respectively, of the substrate  2110 . The first and second porous anode barriers  2120   a  and  2120   b  are configured to prevent reactions between the anodes of the fuel cells (described below) and the substrate  2110 , and are not configured to provide electrical conduction within a given fuel cell or between two fuel cells. Additionally, the first and second porous anode barriers  2120   a  and  2120   b  are not configured to partake in the electrochemical reactions that generate electrical power from the fuel. In this example embodiment, the first and second porous anode barriers  2120   a  and  2120   b  are formed of an inert porous ceramic material such as 3YSZ or another suitable doped zirconia, though in other embodiments the first and second porous anode barriers  2120   a  and  2120   b  may be formed of any suitable material(s) in addition to or instead of doped zirconia, such as SrZrO 3 . In other embodiments, the fuel cell tube  2100  does not include the first and second porous anode barriers  2120   a  and  2120   b.    
     Multiple fuel cells  2130 , laterally segmented dummy cell  2180 , and laterally segmented fuel cells  2181  and  2190  are disposed on the first porous anode barrier  2120   a.  Each fuel cell  2130 , laterally segmented dummy cell  2180 , and laterally segmented fuel cells  2181  and  2190  generally extend laterally in the direction of the width W of the substrate  2110  and terminate in opposing first and second lateral ends (not labeled). The fuel cells  2130  are positioned between laterally segmented fuel cells  2181  and  2190 , which are generally positioned proximate opposing ends of the first porous anode barrier  2120   a  in the direction of the length L of the substrate  2110 . The fuel cells  2130 , the laterally segmented dummy cell  2180 , and the laterally segmented fuel cells  2181  and  2190  on the first porous anode barrier  2120   a  are electrically connected in series via primary interconnects within primary interconnect regions  2111 . 
     As best shown in  FIGS. 11A and 12 , the laterally segmented dummy cell  2180  includes first and second dummy cell portions  2180   a  and  2180   b.  First and second dummy cell portions  2180   a  and  2180   b  are electrically connected to first and second fuel cell portions  2181   a  and  2181   b,  respectively, via primary interconnects within primary interconnect regions  2111 . The first and second dummy cell portions  2180   a  and  2180   b  are laterally separated in the direction of the width W of the substrate  2110  such that the first and second dummy cell portions are electrically isolated. No continuous direct electrical path exists between the dummy cell portions  2180   a  and  2180   b,  which are separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . The primary interconnect regions  2111 , which dummy cell portions  2180   a  and  2180   b  are connected to, are also separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . As shown in  FIG. 14A , the space between first and second dummy cell portions  2180   a  and  2180   b  includes dense barrier  2120   c  overlaid by electrolyte  2130   c.    
     As best shown in  FIGS. 11A and 12 , the interior laterally segmented fuel cell  2181  includes first and second fuel cell portions  2181   a  and  2181   b . First and second fuel cell portions  2181   a  and  2181   b  are electrically connected to fuel cell  2130  via a primary interconnect within primary interconnect region  2111 . The first and second fuel cell portions  2181   a  and  2181   b  are laterally separated in the direction of the width W of the substrate  2110  such that the first and second fuel cell portions are electrically isolated. No continuous direct electrical path exists between the fuel cell portions  2181   a  and  2181   b,  which are separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . 
     As best shown in  FIGS. 11B and 12 , the laterally segmented fuel cell  2190  includes first and second fuel cell portions  2190   a  and  2190   b.  First and second fuel cell portions  2190   a  and  2190   b  are electrically connected to fuel cell  2130  via a primary interconnect within primary interconnect region  2111 . The first and second fuel cell portions  2190   a  and  2190   b  are laterally separated in the direction of the width W of the substrate  2110  such that the first and second fuel cell portions are electrically isolated. No continuous direct electrical path exists between the fuel cell portions  2190   a  and  2190   b,  which are separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . As shown in  FIG. 14B , the space between fuel cell portions  2190   a  and  2190   b  includes dense barrier  2120   c  overlaid by electrolyte  2130   c.    
     Multiple fuel cells  2130 , laterally segmented dummy cell  2185 , and laterally segmented fuel cells  2186  and  2195  are disposed on the second porous anode barrier  2120   b.  Each fuel cell  2130 , laterally segmented dummy cell  2185 , and laterally segmented fuel cells  2186  and  2195  generally extend laterally in the direction of the width W of the substrate  2110 . The fuel cells  2130  are positioned between laterally segmented fuel cells  2186  and  2195 , which are generally positioned proximate opposing ends of the second porous anode barrier  2120   b  in the direction of the length L of the substrate  2110 . The fuel cells  2130 , the laterally segmented dummy cell  2185 , and the laterally segmented fuel cells  2186  and  2195  on the second porous anode barrier  2120   b  are electrically connected in series via primary interconnects within primary interconnect regions  2111 . 
     As best shown in  FIGS. 11C and 14A , the laterally segmented dummy cell  2185  includes first and second dummy cell portions  2185   a  and  2185   b.  First and second dummy cell portions  2185   a  and  2185   b  are electrically connected to first and second fuel cell portions  2186   a  and  2186   b,  respectively, via primary interconnects within primary interconnect regions  2111 . The first and second dummy cell portions  2185   a  and  2185   b  are laterally separated in the direction of the width W of the substrate  2110  such that the first and second dummy cell portions  2185   a  and  2185   b  are electrically isolated. No continuous direct electrical path exists between the first and second dummy cell portions  2185   a  and  2185   b,  which are separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . The primary interconnect regions  2111 , which dummy cell portions  2185   a  and  2185   b  are connected to, are also separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . As shown in  FIG. 14A , the space between dummy cell portions  2185   a  and  2185   b  includes dense barrier  2120   c  overlaid by electrolyte  2130   c.    
     As best shown in  FIG. 11C , the interior laterally segmented fuel cell  2186  includes first and second fuel cell portions  2186   a  and  2186   b.  First and second fuel cell portions  2186   a  and  2186   b  are electrically connected to fuel cell  2130  via a primary interconnect within primary interconnect region  2111 . The first and second fuel cell portions  2186   a  and  2186   b  are laterally separated in the direction of the width W of the substrate  2110  such that the first and second fuel cell portions  2186   a  and  2186   b  are electrically isolated. No continuous direct electrical path exists between the first and second fuel cell portions  2186   a  and  2186   b,  which are separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . 
     As best shown in  FIGS. 11D and 14B  the laterally segmented fuel cell  2195  includes first and second fuel cell portions  2195   a  and  2195   b.  First and second fuel cell portions  2195   a  and  2195   b  are electrically connected to fuel cell  2130  via a primary interconnect within primary interconnect region  2111 . The first and second fuel cell portions  2195   a  and  2195   b  are separated in the direction of the width W of the substrate  2110  such that the first and second fuel cell portions  2195   a  and  2195   b  are electrically isolated. No continuous direct electrical path exists between the first and second fuel cell portions  2195   a  and  2195   b,  which are separated by a space of 1.5 mm in the direction of the width W of the substrate  2110 . As shown in  FIG. 14B , the space between fuel cell portions  2195   a  and  2195   b  includes dense barrier  2120   c  overlaid by electrolyte  2130   c.    
     As shown in  FIG. 14A , a first fuel cell connector  2145   a  is electrically connected to (and electrically connects) the first dummy cell portion  2180   a  of laterally segmented dummy cell  2180  and the first dummy cell portion  2185   a  of laterally segmented dummy cell  2185 . As shown in  FIGS. 13 and 14A , second fuel cell connector  2145   b  is electrically connected to (and electrically connects) the second dummy cell portion  2180   b  of laterally segmented dummy cell  2180  and the second dummy cell portion  2185   b  of laterally segmented dummy cell  2185 . 
     In this example embodiment, the first fuel cell connector  2145   a  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the first dummy cell portions  2180   a  and  2185   a,  and the second fuel cell connector  2145   b  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the second dummy cell portions  2180   b  and  2185   b . Since the first and second dummy cell portions  2180   a  and  2180   b  are electrically isolated, and the first and second dummy cell portions  2185   a  and  2185   b  are electrically isolated, the first and second fuel cell connectors  2145   a  and  2145   b  are electrically isolated such that there is no continuous electrical path across the width W of the substrate  2110 . A glass edge seal  2146  fills the space between the fuel cell connector  2145   a  and the rest of fuel cell tube  2100 . This glass edge seal  2146  extends down the full length of the fuel cell tube  2100  and prevents fuel from escaping the fuel cell structure, separating air and fuel. A glass edge seal  2146  also fills the space between fuel cell connector  2145   b  and the rest of fuel cell tube  2100 . This glass edge seal  2146  extends down the full length of the fuel cell tube  2100  and prevents fuel from escaping the fuel cell structure, separating air and fuel. 
     As shown in  FIG. 14B , a third fuel cell connector  2155   a  is electrically connected to (and electrically connects) the first fuel cell portion  2190   a  of laterally segmented fuel cell  2190  and the first fuel cell portion  2195   a  of laterally segmented fuel cell  2195 . As shown in  FIGS. 13 and 14B , a fourth fuel cell connector  2155   b  is electrically connected to (and electrically connects) the second fuel cell portion  2190   b  of laterally segmented fuel cell  2190  and the second fuel cell portion  2195   b  of laterally segmented fuel cell  2195 . 
     In this example embodiment, the third fuel cell connector  2155   a  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the first fuel cell portions  2190   a  and  2195   a,  and the fourth fuel cell connector  2155   b  is electrically connected to (and in this example embodiment contacts) the cathode current collectors of the second fuel cell portions  2190   b  and  2195   b.  Since the first and second fuel cell portions  2190   a  and  2190   b  are electrically isolated and the first and second fuel cell portions  2195   a  and  2195   b  are electrically isolated, the third and fourth fuel cell connectors  2155   a  and  2155   b  are electrically isolated such that there is no continuous electrical path across the width W of the substrate  2110 . A glass edge seal  2146  fills the space between the fuel cell connector  2155   a  and the rest of fuel cell tube  2100 . This glass edge seal  2146  extends down the full length of the fuel cell tube  2100  and prevents fuel from escaping the fuel cell structure, separating air and fuel. A glass edge seal  2146  also fills the space between fuel cell connector  2155   b  and the rest of fuel cell tube  2100 . This glass edge seal  2146  extends down the full length of the fuel cell tube  2100  and prevents fuel from escaping the fuel cell structure, separating air and fuel. 
       FIGS. 15A and 15B  show three fuel cell tubes  2100 ,  2200 , and  2300  of the fuel cell stack  20 . While the fuel cell stack  20  may include any suitable quantity of fuel cell tubes electrically connected to one another in series, only three are shown here for clarity and brevity. In this example embodiment, the fuel cell tubes  2200  and  2300  are identical to the fuel cell tube  2100  and are therefore not separately described (though in other embodiments the fuel cell tubes may differ from one another). The element numbering schemes of the fuel cell tubes  2200  and  2300  correspond to the element numbering scheme used to describe the fuel cell tube  2100  such that like element numbers correspond to like components. 
     As shown in  FIG. 15A , the first fuel cell tube  2100  is electrically connected to the second fuel cell tube  2200  via: (1) a first tube interconnect  2122   a  that electrically connects fuel cell connector  2145   a  of the first fuel cell tube  2100  to fuel cell connector  2255   b  of the second fuel cell tube  2200 ; and (2) a second tube interconnect  2122   b  that electrically connects fuel cell connector  2145   b  of the first fuel cell tube  2100  to fuel cell connector  2255   a  of the second fuel cell tube  2200 . First tube interconnect  2122   a  electrically connects laterally segmented dummy cell portions  2180   a  and  2185   a  of the first fuel cell tube to laterally segmented fuel cell portions  2290   b  and  2295   b  of the second fuel cell tube. Second tube interconnect  2122   b  electrically connects laterally segmented dummy cell portions  2180   b  and  2185   b  to laterally segmented fuel cell portions  2290   a  and  2295   a.  Generally, the fuel cell tubes are connected in series with direction of the flow of fuel through the tubes. 
     As shown in  FIG. 15B , the second fuel cell tube  2200  is electrically connected to the third fuel cell tube  2300  via: (1) a third tube interconnect  2223   a  that electrically connects fuel cell connector  2245   a  of the second fuel cell tube  2200  to fuel cell connector  2355   b  of the third fuel cell tube  2300 ; and (2) a fourth tube interconnect  2223   b  that electrically connects the fuel cell connector  2245   b  of the second fuel cell tube  2200  to fuel cell connector  2355   a  of the third fuel cell tube  2300 . Third tube interconnect  2223   a  electrically connects laterally segmented dummy cell portions  2280   a  and  2285   a  of the second fuel cell tube to laterally segmented fuel cell portions  2390   b  and  2395   b  of the third fuel cell tube. Fourth tube interconnect  2223   b  electrically connects laterally segmented dummy cell portions  2280   b  and  2285   b  of the second fuel cell tube to laterally segmented fuel cell portions  2390   a  and  2395   a  of the third fuel cell tube. 
     The tube interconnects shown in the various embodiments (for example  2122   a  and  2122   b  in  FIG. 15A ) are illustrated as wires for exemplary purposes only. The present disclosure pertains to other designs for tube (secondary) interconnects such as the designs disclosed in the following co-pending applications: U.S. patent application Ser. No. 15/816,918, filed Nov. 17, 2017, entitled “Improved Fuel Cell Secondary Interconnect”; U.S. patent application Ser. No. 15/816,931, filed Nov. 17, 2017, entitled “Improved Fuel Cell Secondary Interconnect”; and U.S. patent application Ser. No. 15/816,948, filed Nov. 17, 2017, entitled “Multiple Fuel Cell Secondary Interconnect Bonding Pads And Wires”. 
     Various modifications to the embodiments described herein will be apparent to those skilled in the art. These modifications can be made without departing from the spirit and scope of the present disclosure and without diminishing its intended advantages. It is intended that such changes and modifications be covered by the appended claims.