Patent Publication Number: US-2023144742-A1

Title: Ni-Fe BASED CATHODE FUNCTIONAL LAYERS FOR SOLID OXIDE ELECTROCHEMICAL CELLS

Description:
FIELD 
     The present disclosure is directed to fuel cell stacks in general, and to electrochemical cell cathode materials in particular. 
     BACKGROUND 
     In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is passed through the cathode side of the fuel cell while a fuel flow is passed through the anode side of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. The fuel cell, operating at a typical temperature between 750° C. and 950° C., enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ion combines with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ion are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit. 
     Fuel cell stacks may be either internally or externally manifolded for fuel and air. In internally manifolded stacks, the fuel and air is distributed to each cell using risers contained within the stack. In other words, the gas flows through openings or holes in the supporting layer of each fuel cell, such as the electrolyte layer, and gas flow separator of each cell. In externally manifolded stacks, the stack is open on the fuel and air inlet and outlet sides, and the fuel and air are introduced and collected independently of the stack hardware. For example, the inlet and outlet fuel and air flow in separate channels between the stack and the manifold housing in which the stack is located. 
     Fuel cell stacks are frequently built from a multiplicity of cells in the form of planar elements, tubes, or other geometries. Fuel and air have to be provided to the electrochemically active surface, which can be large. One component of a fuel cell stack is the so called gas flow separator (referred to as a gas flow separator plate in a planar stack) that separates the individual cells in the stack. The gas flow separator plate separates fuel, such as hydrogen or a hydrocarbon fuel, flowing to the fuel electrode (i.e., anode) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e., cathode) of an adjacent cell in the stack. Frequently, the gas flow separator plate is also used as an interconnect which electrically connects the fuel electrode of one cell to the air electrode of the adjacent cell. In this case, the gas flow separator plate which functions as an interconnect is made of or contains an electrically conductive material. 
     SUMMARY 
     In one embodiment, a solid oxide electrochemical cell includes a solid oxide electrolyte, an anode located on a first side of the solid oxide electrolyte, and a cathode located on a second side of the solid oxide electrolyte, wherein the cathode comprises lanthanum nickel ferrite. 
     In another embodiment, a method of making a solid oxide electrochemical cell, comprises providing a solid oxide electrolyte, forming an anode on a first side of the solid oxide electrolyte, and forming a cathode on a second side of the solid oxide electrolyte, wherein the cathode comprises lanthanum nickel ferrite. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate example embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
         FIG.  1 A  is a perspective view of a conventional fuel cell column. 
         FIG.  1 B  is a perspective view of one counter-flow solid oxide fuel cell stack included in the column of  FIG.  1 A . 
         FIG.  1 C  is a side cross-sectional view of a portion of the stack of  FIG.  1 B . 
         FIG.  2 A  is a top view of the air side of a conventional interconnect of the stack of  FIG.  1 B . 
         FIG.  2 B  is a top view of the fuel side of the conventional interconnect of the stack of  FIG.  1 B . 
         FIG.  3 A  is a perspective view of a fuel cell stack, according to various embodiments of the present disclosure. 
         FIG.  3 B  is an exploded perspective view of a portion of the stack of  FIG.  3 A , according to various embodiments of the present disclosure. 
         FIG.  3 C  is a top view of the fuel side of an interconnect included in the stack of  FIG.  3 A , according to various embodiments of the present disclosure. 
         FIG.  3 D  is a schematic view of a fuel cell included in the stack of  FIG.  3 A , according to various embodiments of the present disclosure. 
         FIG.  4 A  is a plan view showing an air side of the cross-flow interconnect of  FIG.  3 C , according to various embodiments of the present disclosure. 
         FIG.  4 B  is a plan view showing a fuel side of the cross-flow interconnect of  FIG.  3 C , according to various embodiments of the present disclosure. 
         FIG.  5    is a schematic view of an electrochemical cell, according to various embodiments of the present disclosure. 
         FIG.  6    is a plot of normalized area specific resistance degradation of embodiment cells having lanthanum nickel ferrite based cathode functional layers (CFLs) and of comparative cells having lanthanum strontium manganate based CFLs, according to various embodiments of the present disclosure. 
         FIG.  7    is a plot of ohmic resistance for the embodiment and the comparative cells of  FIG.  6   , according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments are described in detail with reference to the accompanying drawings. The drawings are not necessarily to scale, and are intended to illustrate various features of the invention. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, examples include from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about” or “substantially” it will be understood that the particular value forms another aspect. In some embodiments, a value of “about X” may include values of +/−1% X. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Some embodiments of the present disclosure are directed to SOFCs containing a cathode functional layer (CFL) having Ni—Fe based perovskite materials, such as lanthanum nickel ferrite. Such materials have improved stability in the presence of water vapor and/or chromium vapor and exhibit reduced area specific resistance degradation in comparison with CFLs based on lanthanum strontium manganite (LSM). Disclosed embodiments include CFLs having Ni—Fe containing perovskite materials La Ni 1-y Fe y  O 3-δ  and La 1-x Ca), Ni 1-y Fe y  O 3-δ , and mixtures of such Ni—Fe containing perovskite materials with other non-perovskite ionically conductive ceramic materials, such as scandia stabilized zirconia (SSZ), samaria-doped ceria (SDC), gadolinia-doped ceria (GDC), or zirconia stabilized with Sc-Ce-Y or Sc-Ce-Yb. The weight percent ratio of the Ni—Fe perovskite phase to the other ceramic phase may vary between 3:7 and 7:3. Disclosed embodiments further include Ni—Fe perovskite based CFL combined in a SOFC cathode with a cathode current collecting layer (CCL) including higher electrical conductivity perovskite materials, such as LSM (e.g., (La 1-x Sr x ) y  MnO 3-δ ), lanthanum strontium cobaltite (LSCo) or lanthanum strontium cobalt ferrite (LSCF, e.g., La 1-x  Sr x Co 1-y  Fe y  O 3-δ ). 
       FIG.  1 A  is a perspective view of a conventional fuel cell column  30 ,  FIG.  1 B  is a perspective view of one counter-flow SOFC stack  20  included in the column  30  of  FIG.  1 A , and  FIG.  1 C  is a side cross-sectional view of a portion of the stack  20  of  FIG.  1 B . 
     Referring to  FIGS.  1 A and  1 B , the column  30  may include one or more stacks  20 , a fuel inlet conduit  32 , an anode exhaust conduit  34 , and anode feed/return assemblies  36  (e.g., anode splitter plates (ASP&#39;s)  36 ). The column  30  may also include side baffles  38  and a compression assembly  40 . The side baffles  38  may be connected to the compression assembly  40  and an underlying stack component (not shown) by ceramic connectors  39 . The fuel inlet conduit  32  is fluidly connected to the ASP&#39;s  36  and is configured to provide the fuel feed to each ASP  36 , and anode exhaust conduit  34  is fluidly connected to the ASP&#39;s  36  and is configured to receive anode fuel exhaust from each ASP  36 . 
     The ASP&#39;s  36  are disposed between the stacks  20  and are configured to provide a hydrocarbon fuel containing fuel feed to the stacks  20  and to receive anode fuel exhaust from the stacks  20 . For example, the ASP&#39;s  36  may be fluidly connected to internal fuel riser channels  22  formed in the stacks  20 , as discussed below. 
     Referring to  FIG.  1 C , the stack  20  includes multiple fuel cells  1  that are separated by interconnects  10 , which may also be referred to as gas flow separator plates or bipolar plates. Each fuel cell  1  includes a cathode electrode  3 , a solid oxide electrolyte  5 , and an anode electrode  7 . 
     Each interconnect  10  electrically connects adjacent fuel cells  1  in the stack  20 . 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 C  shows that the lower fuel cell  1  is located between two interconnects  10 . 
     Each interconnect  10  includes ribs  12  that at least partially define fuel channels  8 A and 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  20 , there may be an air end plate or fuel end plate (not shown) for providing air or fuel, respectively, to the end electrode. 
       FIG.  2 A  is a top view of the air side of the conventional interconnect  10 , and  FIG.  2 B  is a top view of a fuel side of the interconnect  10 . Referring to  FIGS.  1 C 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 . In particular, the air may flow across the interconnect  10  in a first direction A as indicated by the arrows. 
     Ring seals  23  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  23 ,  24  may be formed of a glass material. The peripheral portions may be in the form of 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 . 
     Referring to  FIGS.  1 C and  2 B , the fuel side of the interconnect  10  may include the fuel channels  8 A and fuel manifolds  28  (e.g., fuel plenums). Fuel flows from one of the fuel holes  22 A, 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 adjacent fuel hole  22 A. In particular, the fuel may flow across the interconnect  10  in a second direction B, as indicated by the arrows. The second direction B may be perpendicular to the first direction A (see  FIG.  2 A ). 
     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 . 
     Accordingly, a conventional counter-flow fuel cell column, as shown in  FIGS.  1 A,  1 B,  1 C,  2 A, and  2 B , may include complex fuel distribution systems (fuel rails and anode splitter plates). In addition, the use of an internal fuel riser may require holes in fuel cells and corresponding seals, which may reduce an active area thereof and may cause cracks in the ceramic electrolytes of the fuel cells  1 . 
     The fuel manifolds  28  may occupy a relatively large region of the interconnect  10 , which may reduce the contact area between the interconnect  10  and an adjacent fuel cell by approximately 10%. The fuel manifolds  28  are also relatively deep, such that the fuel manifolds  28  represent relatively thin regions of the interconnect  10 . Since the interconnect  10  is generally formed by a powder metallurgy compaction process, the density of fuel manifold regions may approach the theoretical density limit of the interconnect material. As such, the length of stroke of a compaction press used in the compaction process may be limited due to the high-density fuel manifold regions being incapable of being compacted further. As a result, the density achieved elsewhere in the interconnect  10  may be limited to a lower level by the limitation to the compaction stroke. The resultant density variation may lead to topographical variations, which may reduce the amount of contact between the interconnect  10  a fuel cell  1  and may result in lower stack yield and/or performance. 
     Another important consideration in fuel cell system design is in the area of operational efficiency. Maximizing fuel utilization is a key factor to achieving operational efficiency. Fuel utilization is the ratio of how much fuel is consumed during operation, relative to how much is delivered to a fuel cell. An important factor in preserving fuel cell cycle life may be avoiding fuel starvation in fuel cell active areas, by appropriately distributing fuel to the active areas. If there is a maldistribution of fuel such that some flow field channels receive insufficient fuel to support the electrochemical reaction that would occur in the region of that channel, it may result in fuel starvation in fuel cell areas adjacent that channel. In order to distribute fuel more uniformly, conventional interconnect designs include channel depth variations across the flow field. This may create complications not only in the manufacturing process, but may also require complex metrology to measure these dimensions accurately. The varying channel geometry may be constrained by the way fuel is distributed through fuel holes and distribution manifolds. 
     One possible solution to eliminate this complicated geometry and the fuel manifold is to have a wider fuel opening to ensure much more uniform fuel distribution across the fuel flow field. Since fuel manifold formation is a factor in density variation, elimination of fuel manifolds should enable more uniform interconnect density and permeability. Accordingly, there is a need for improved interconnects that provide for uniform contact with fuel cells, while also uniformly distributing fuel to the fuel cells without the use of conventional fuel manifolds. 
     Owing to the overall restrictions in expanding the size of a hotbox of a fuel cell system, there is also a need for improved interconnects designed to maximize fuel utilization and fuel cell active area, without increasing the footprint of a hotbox. 
       FIG.  3 A  is a perspective view of a fuel cell stack  300 , according to various embodiments of the present disclosure,  FIG.  3 B  is an exploded perspective view of a portion of the stack  300  of  FIG.  3 A ,  FIG.  3 C  is a top view of the fuel side of an interconnect  400  included in the stack  300 , and  FIG.  3 D  is a schematic view of a fuel cell included in the stack  300 . 
     Referring to  FIGS.  3 A- 3 D , the fuel cell stack  300 , which may also be referred to as a fuel cell column because it lacks ASP&#39;s, includes multiple fuel cells  310  that are separated by interconnects  400 , which may also be referred to as gas flow separator plates or bipolar plates. One or more stacks  300  may be thermally integrated with other components of a fuel cell power generating system (e.g., one or more anode tail gas oxidizers, fuel reformers, fluid conduits and manifolds, etc.) in a common enclosure or “hotbox.” 
     The interconnects  400  are made from an electrically conductive metal material. For example, the interconnects  400  may comprise a chromium alloy, such as a Cr—Fe alloy. The interconnects  400  may typically be fabricated using a powder metallurgy technique that includes pressing and sintering a Cr-Fe powder, which may be a mixture of Cr and Fe powders or an Cr—Fe alloy powder, to form a Cr-Fe interconnect in a desired size and shape (e.g., a “net shape” or “near net shape” process). A typical chromium-alloy interconnect  400  comprises more than about 90% chromium by weight, such as about 94-96% (e.g., 95%) chromium by weight. An interconnect  400  may also contain less than about 10% iron by weight, such as about 4-6% (e.g., 5%) iron by weight, may contain less than about 2% by weight, such as about zero to 1% by weight, of other materials, such as yttrium or yttria, as well as residual or unavoidable impurities. 
     Each fuel cell  310  may include a solid oxide electrolyte  312 , an anode  314 , and a cathode  316 . In some embodiments, the anode  314  and the cathode  316  may be printed on the electrolyte  312 . In other embodiments, a conductive layer  318 , such as a nickel mesh, may be disposed between the anode  314  and an adjacent interconnect  400 . The fuel cell  310  does not include through-holes, such as the fuel holes of conventional fuel cells. Therefore, the fuel cell  310  avoids cracks that may be generated due to the presence of such through-holes. 
     An upper most interconnect  400  and a lowermost interconnect  400  of the stack  300  may be different ones of an air end plate or fuel end plate including features for providing air or fuel, respectively, to an adjacent end fuel cell  310 . As used herein, an “interconnect” may refer to either an interconnect located between two fuel cells  310  or an end plate located at an end of the stack and directly adjacent to only one fuel cell  310 . Since the stack  300  does not include ASPs and the end plates associated therewith, the stack  300  may include only two end plates. As a result, stack dimensional variations associated with the use of intra-column ASPs may be avoided. 
     The stack  300  may include side baffles  302 , a fuel plenum  350 , and a compression assembly  306 . The side baffles  302  may be formed of a ceramic material and may be disposed on opposing sides of the fuel cell stack  300  containing stacked fuel cells  310  and interconnects  400 . The side baffles  302  may connect the fuel plenum  350  and the compression assembly  306 , such that the compression assembly  306  may apply pressure to the stack  300 . The side baffles  302  may be curved baffle plates, such each baffle plate covers at least portions of three sides of the fuel cell stack  300 . For example, one baffle plate may fully cover the fuel inlet riser side of the stack  300  and partially covers the adjacent front and back sides of the stack, while the other baffle plate fully covers the fuel outlet riser side of the stack and partially covers the adjacent portions of the front and back sides of the stack. The remaining uncovered portions for the front and back sides of the stack allow the air to flow through the stack  300 . The curved baffle plates provide an improved air flow control through the stack compared to the conventional baffle plates  38  which cover only one side of the stack. The fuel plenum  350  may be disposed below the stack  300  and may be configured to provide a hydrogen-containing fuel feed to the stack  300 , and may receive an anode fuel exhaust from the stack  300 . The fuel plenum  350  may be connected to fuel inlet and outlet conduits  320  which are located below the fuel plenum  350 . 
     Each interconnect  400  electrically connects adjacent fuel cells  310  in the stack  300 . In particular, an interconnect  400  may electrically connect the anode electrode of one fuel cell  310  to the cathode electrode of an adjacent fuel cell  310 . As shown in  FIG.  3 C , each interconnect  400  may be configured to channel air in a first direction A, such that the air may be provided to the cathode of an adjacent fuel cell  310 . Each interconnect  400  may also be configured to channel fuel in a second direction F, such that the fuel may be provided to the anode of an adjacent fuel cell  310 . Directions A and F may be perpendicular, or substantially perpendicular. As such, the interconnects  400  may be referred to as cross-flow interconnects. 
     The interconnect  400  may include fuel holes that extend through the interconnect  400  and that are configured for fuel distribution. For example, the fuel holes may include one or more fuel inlets  402  and one or more fuel (e.g., anode exhaust) outlets  404 , which may also be referred to as anode exhaust outlets  404 . The fuel inlets and outlets  402 ,  404  may be disposed outside of the perimeter of the fuel cells  310 . As such, the fuel cells  310  may be formed without corresponding through-holes for fuel flow. The combined length of the fuel inlets  402  and/or the combined length of the fuel outlets  404  may be at least 75% of a corresponding length of the interconnect  400  e.g., a length taken in direction A. 
     In one embodiment, each interconnect  400  contains two fuel inlets  402  separated by a neck portion  412  of the interconnect  400 , as shown in  FIG.  3 B . However, more than two fuel inlets  402  may be included, such as three to five inlets separated by two to four neck portions  412 . In one embodiment, each interconnect  400  contains two fuel outlets  404  separated by a neck portion  414  of the interconnect  400 , as shown in  FIG.  3 B . However, more than two fuel outlets  404  may be included, such as three to five outlets separated by two to four neck portions  414 . 
     The fuel inlets  402  of adjacent interconnects  400  may be aligned in the stack  300  to form one or more fuel inlet risers  403 . The fuel outlets  404  of adjacent interconnects  400  may be aligned in the stack  300  to form one or more fuel outlet risers  405 . The fuel inlet riser  403  may be configured to distribute fuel received from the fuel plenum  350  to the fuel cells  310 . The fuel outlet riser  405  may be configured to provide anode exhaust received from the fuel cells  310  to the fuel plenum  350 . 
     Unlike the flat related art side baffles  38  of  FIG.  1 A , the side baffles  302  may be curved around edges of the interconnects  400 . In particular, the side baffles  302  may be disposed around the fuel inlets  402  and outlets  404  of the interconnects  400 . Accordingly, the side baffles may more efficiently control air flow through air channels of the interconnects  400 , which are exposed between the side baffles  302  and are described in detail with regard to  FIGS.  4 A and  4 B . 
     In various embodiments, the stack  300  may include at least 30, at least 40, at least 50, or at least 60 fuel cells, which may be provided with fuel using only the fuel risers  403 ,  405 . In other words, as compared to a conventional fuel cell system, the cross-flow configuration allows for a large number of fuel cells to be provided with fuel, without the need for ASP&#39;s or external stack fuel manifolds, such as external conduits  32 ,  34  shown in  FIG.  1 A . 
     Each interconnect  400  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  400  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  310  to the cathode or air-side of an adjacent fuel cell  310 . An electrically conductive contact layer, such as a nickel contact layer (e.g., a nickel mesh), may be provided between anode and each interconnect  400 . Another optional electrically conductive contact layer may be provided between the cathode electrodes and each interconnect  400 . 
     A surface of an interconnect  400  that in operation is exposed to an oxidizing environment (e.g., air), such as the cathode-facing side of the interconnect  400 , may be coated with a protective coating layer in order to decrease the growth rate of a chromium oxide surface layer on the interconnect and to suppress evaporation of chromium vapor species which can poison the fuel cell cathode. Typically, the coating layer, which can comprise a perovskite such as LSM, may be formed using a spray coating or dip coating process. Alternatively, other metal oxide coatings, such as a spinel, such as an (Mn, Co) 3 O 4  spinel (MCO), can be used instead of or in addition to LSM. Any spinel having the composition Mn 2-x , Co 1+x O 4  (0≤x≤1) or written as z(Mn 3  O 4 )+(1−z)(Co 3  O 4 ), where (⅓≤z≤⅔) or written as (Mn, Co) 3  O 4  may be used. In other embodiments, a mixed layer of LSM and MCO, or a stack of LSM and MCO layers may be used as the coating layer. 
       FIGS.  4 A and  4 B  are plan views showing, respectively, an air side and a fuel side of the cross-flow interconnect  400 , according to various embodiments of the present disclosure. Referring to  FIG.  4 A , the air side of the interconnect  400  may include ribs  406  configured to at least partially define air channels  408  configured to provide air to the cathode of a fuel cell  310  disposed thereon. The air side of the interconnect  400  may be divided into an air flow field  420  including the air channels  408 , and riser seal surfaces  422  disposed on two opposing sides of the air flow field  420 . One of the riser seal surfaces  422  may surround the fuel inlets  402  and the other riser seal surface  422  may surround the fuel outlets  404 . The air channels  408  and ribs  406  may extend completely across the air side of the interconnect  400 , such that the air channels  408  and ribs  406  terminate at opposing peripheral edges of the interconnect  400 . In other words, when assembled into a stack  300 , opposing ends of the air channels  408  and ribs  406  are disposed on opposing (e.g., front and back) outer surfaces of the stack, to allow the blown air to flow through the stack. Therefore, the stack may be externally manifolded for air. 
     Riser seals  424  may be disposed on the riser seal surface  422 . For example, one riser seal  424  may surround the fuel inlets  402 , and one riser seal  424  may surround the fuel outlets  404 . The riser seals  424  may prevent fuel and/or anode exhaust from entering the air flow field  420  and contacting the cathode of the fuel cell  310 . The riser seals  424  may also operate to prevent fuel from leaking out of the fuel cell stack  100  (see  FIG.  3 A ). 
     Referring to  FIG.  4 B , the fuel side of the interconnect  400  may include ribs  416  that at least partially define fuel channels  418  configured to provide fuel to the anode of a fuel cell  310  disposed thereon. The fuel side of the interconnect  400  may be divided into a fuel flow field  430  including the fuel channels  418 , and an perimeter seal surface  432  surrounding the fuel flow field  430  and the fuel inlets and outlets  402 ,  404 . The ribs  416  and fuel channels  418  may extend in a direction that is perpendicular or substantially perpendicular to the direction in which the air-side channels  408  and ribs  406  extend. 
     A frame-shaped perimeter seal  434  may be disposed on the perimeter seal surface  432 . The perimeter seal  434  may be configured to prevent air entering the fuel flow field  430  and contacting the anode on an adjacent fuel cell  310 . The perimeter seal  434  may also operate to prevent fuel from exiting the fuel risers  403 ,  405  and leaking out of the fuel cell stack  300  (see  FIGS.  3 A and  3 B ). 
     The seals  424 ,  434  may comprise a glass or ceramic seal material. The seal material may have a low electrical conductivity. In some embodiments, the seals  424 ,  434  may be formed by printing one or more layers of seal material on the interconnect  400 , followed by sintering. 
       FIG.  5    is a schematic view of an electrochemical cell  500 , according to various embodiments of the present disclosure. The electrochemical cell  500  may comprise a solid oxide fuel cell (SOFC) or a solid oxide electrolyzer cell (SOEC). In a solid oxide electrolyzer cell, a voltage is applied between the anode and the cathode and a water containing stream is provided to the anode. The water is electrolyzed into hydrogen and oxygen at the anode. The oxygen ions are transported across the electrolyte to the cathode. An oxygen containing exhaust stream is provided from the cathode. A hydrogen containing stream is provided from the anode. 
     The electrochemical cell  500  contains a solid oxide electrolyte  312 , an anode  314  having an anode current collecting layer  314   a  and an anode functional layer  314   b , and a cathode  316  having a CFL  316   a  and a cathode current collecting layer (CCL)  316   b.    
     The electrolyte  312  may comprise an ionically conductive ceramic, such as doped zirconia, doped ceria, and/or any other suitable ionically conductive ceramic oxide material. For example, the electrolyte  312  may include yttria-stabilized zirconia (YSZ), yttria-ceria-stabilized zirconia (YCSZ), scandia-stabilized zirconia (SSZ), ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ), or blends thereof. In the YbCSSZ, scandia may be present in an amount equal to 9 to 11 mol %, such as 10 mol %, ceria may present in amount greater than 0 and equal to or less than 3 mol %, for example 0.5 mol % to 2.5 mol %, such as 1 mol %, and ytterbia may be present in an amount greater than 0 and equal to or less than 2.5 mol %, for example 0.5 mol % to 2 mol %, such as 1 mol %, as disclosed in U.S. Pat. No. 8,580,456, which is incorporated herein, by reference. In the YCSZ, yttria may be present in an amount equal to 8 to 10 mol %, and optionally ceria may be present in an amount equal to 0 to 3 mol %. In other embodiments, the electrolyte may include samaria, gadolinia, or yttria-doped ceria. 
     The anode  314  is located over a first side of the electrolyte  312 . The anode functional layer  314   b  is located between the anode current collecting layer  314   a  and the first side of the electrolyte  312 . The anode  314  may include at least one cermet that includes a metallic phase and a ceramic phase. The metallic phase may include a metal catalyst and the ceramic phase may include one or more ceramic materials. The ceramic phase of the anode  40  may comprise any suitable ionically conductive ceramic material, such as a doped ceria and/or a doped zirconia. For example, the ceramic phase may include, but is not limited to gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), praseodymia doped ceria (PDC), ytterbia-doped ceria (YDC), scandia-stabilized zirconia (SSZ), ytterbia-ceria-scandia-stabilized zirconia (YCSSZ), yttria stabilized zirconia (YSZ), or the like. For example, the ceramic material may comprise a doped ceria, such as samaria, gadolinia and/or praseodymia doped ceria, for example 10 to 20 mol % of Sm 2 O 3 , Gd 2 O 3 , and/or Pr 2 O 3  doped CeO 2 . The metallic phase may include a metal catalyst, such as nickel (Ni), which operates as an electron conductor. The metal catalyst may be in a metallic state or may be in an oxide state. For example, the metal catalyst forms a metal oxide when it is in an oxidized state. Thus, the anode may be annealed in a reducing atmosphere prior to and/or during operation of the fuel cell, to reduce the metal catalyst to a metallic state. The anode functional layer  314   b  contains a lower ratio of the nickel containing phase to the ceramic phase than the anode current collecting layer  314   a.    
     The cathode  316  is located over the second side of the electrolyte  312 . The CFL  316   a  is located between the CCL  316   b  and the second side of the electrolyte  312 . 
     Comparative (e.g., conventional) cathodes of SOFCs operating in the temperature range of 750° C.-850° C. may include a mixed electric-ionic conducting perovskite LSM phase, for example, La 0.8  Sr 0.2  Mn O 3-δ , where 0≤δ≤0.1, or an A-site deficient LSM perovskite phase, such as (La 0.8  Sr 0.2 ) 0.97  MnO 3-δ . While this material may be suitable for a CCL, there may be some stability issues associated with the use of LSM for a CFL. For example, water vapor or chromium vapor (CrO 2 (OH) 2 ) may degrade the electrocatalytic properties of LSM. Without wishing to be bound by a particular theory, it is believed that the surface of LSM may dissociate in the presence of water, leading to enriched strontium areas and deficient manganese regions, both of which may affect surface catalytic properties. Furthermore, it is believed that Mn in the LSM may react with chromium vapor to form Mn—Cr spinel phases, which may act to decrease surface catalytic properties and which may block three-phase boundaries in the CFL. Improved electrochemical properties (e.g., stability and/or catalytic activity) are desirable in the CFL where three-phase boundaries reside, and oxide-ion and charge-transfer processes occur. 
     Since both Sr and Mn in the LSM perovskite are prone to reactions with either water or chromium gas species, the present inventor realized that it may be desirable to use a CFL containing an electrochemically active and electrically conducting perovskite phase without Sr and Mn (other than unavoidable impurities or atoms diffused from the CCL during SOFC fabrication), or with decreased Sr and Mn content. The Sr and/or Mn may be replaced entirely or partially in the perovskite material with nickel and iron. Thus, Sr and/or Mn may be omitted entirely or at least partially in the CFL  316   a . Thus, the CFL  316   a  may comprise a lanthanum nickel ferrite perovskite material. 
     Two embodiment CFL lanthanum nickel ferrite perovskite material systems that exclude Sr and Mn comprise La Ni 1-y  Fe y  O 3-δ  and La 1-x Ca x  Ni 1-y  Fe y  O 3-δ , where 0≤δ≤0.1 In the first system, suitable compositions include La Ni 1-y  Fe y  O 3-δ  where 0.2&lt;y&lt;1, such as 0.2&lt;y&lt;0.8, for example 0.4&lt;y&lt;0.6. The materials of this system may have advantageous stability and electrochemical properties. Non-limiting examples include La Ni 0.4 Fe 0.6 O 3-δ , La Ni 0.5  Fe 0.5  O 3-δ , and La Ni 0.6  Fe 0.4  O 3-δ . In the second system, a portion of La may be substituted with Ca. Suitable compositions include La 1-x  Ca x  Ni 1-y  Fe y  O 3-δ  where 0.05&lt;x&lt;0.3, such as 0.1&lt;x&lt;0.2, and 0.3&lt;y&lt;0.7, such as 0.5&lt;y&lt;0.7. Non-limiting examples include La 0.8  Ca 0.2  Ni 0.3  Fe 0.7  O 3-δ  and La 0.9  Ca 0.1  Ni 0.4  Fe 0.6  O 3-δ . These lanthanum nickel ferrite perovskite materials may have a cubic perovskite lattice structure, and phases of La Ni 0.4  Fe 0.6  O 3-δ , La 0.8  Ca 0.2  Ni 0.3  Fe 0.7  O 3-δ , and La 0.9  Ca 0.1  Ni 0.4  Fe 0.6  O 3-δ  are confirmed by x-ray power diffraction spectroscopy to be cubic. 
     The electric conductivity of the above lanthanum nickel ferrite perovskite materials is lower than strontium containing perovskites materials, such as LSM, lanthanum strontium cobaltite (LSCo), and lanthanum strontium cobalt ferrite (LSCF). Therefore, the lanthanum nickel ferrite perovskite material is preferably used for the CFL  316   a  rather than for the CCL  316   b , while the above strontium containing perovskite materials (e.g., LSM, LSCo or LSCF) are used for the CCL  316   b . The lanthanum nickel ferrite perovskite material may be fabricated by forming a porous/sintered CFL  316   a  on the electrolyte  312 , followed by forming the CCL  316   b  on the CFL  316   a.    
     In another embodiment, the lanthanum nickel ferrite perovskite material may be mixed with a non-perovskite ionically conductive ceramic material, such as scandia stabilized zirconia (SSZ), Sm-doped ceria (SDC), Gd-doped ceria (GDC), or zirconia stabilized with Sc-Ce, Sc-Ce-Y or Sc-Ce-Yb. Specific examples of the non-perovskite ionically conductive ceramic material include 89 mol % ZrO 2 -10 mol % Sc 2  O 3 -1 mol % CeO 2  (“10Sc1Ce”), Ce 0.8  Sm 0.2  O 2-δ , Ce 0.8  Gd 0.2  O 2-δ , 88 mol % ZrO 2 -10 mol % Sc 2  O 3 -1 mol % Yb 2 O 3 -1 mol % CeO 2  (“10Sc1Ce1Yb”), and 88 mol % ZrO 2 -10 mol % Sc 2  O 3 -1 mol % YO 3 -1 mol % CeO 2  (“10Sc1Ce1Y”). In general the Sc-Ce-Y stabilized zirconia (“YbCSSZ”, which includes the above described 10Sc1Ce1Yb) may be mixed with the lanthanum nickel ferrite perovskite material. In the YbCSSZ stabilized zirconia, scandia may be present in an amount equal to 9 to 11 mol %, such as 10 mol %, ceria may present in amount greater than 0 and equal to or less than 3 mol %, for example 0.5 mol % to 2.5 mol %, such as 1 mol %, and ytterbia may be present in an amount greater than 0 and equal to or less than 2.5 mol %, for example 0.5 mol % to 2 mol %, such as 1 mol %. 
     The weight ratio of the lanthanum nickel ferrite perovskite material to the non-perovskite ionically conductive ceramic material in the CFL may be 3:7 to 7:3. For example, CFL compositions may include 30 wt. % lanthanum nickel ferrite and 70 wt. % 10Sc1Ce1Yb, 40 wt. % lanthanum nickel ferrite and 60 wt. % 10Sc1Ce1Yb, 50 wt. % lanthanum nickel ferrite and 50 wt. % 10Sc1Ce1Yb, and 60 wt. % lanthanum nickel ferrite and 40 wt. % 10Sc1Ce1Yb. In another example, CFL compositions with SDC may include 30 wt. % lanthanum nickel ferrite and 70 wt. % SDC, 40 wt. % lanthanum nickel ferrite and 60 wt. % SDC, 50 wt. % lanthanum nickel ferrite and 50 wt. % SDC, and 60 wt. % lanthanum nickel ferrite and 40 wt. % SDC. 
     The CFL  316   a  may be printed (e.g., screen printed using an ink) and sintered on top of the second side of the electrolyte  312 . The CCL  316   b  may be printed (e.g., screen printed using an ink) and sintered on top of the CFL  316   a  and may function largely as a current collecting layer. The CCL  316   b  may include LSM, LSCo, or LSCF. For example, LSM compositions may include A-site deficient (La 1-x  Sr x ) y  MnO 3-δ  where 0.1&lt;x&lt;0.3 and 0.94&lt;y&lt;0.99, such as (La 0.8  Sr 0.2 ) 0.98  MnO 3-δ . 
     Exemplary cathodes  316  may include a CCL  316   b  of (La 0.8 Sr 0.2 ) 0.98 MnO 3-δ  with a CFL  316   a  of LaNi 0.4  Fe 0.6  O 3-δ , a CCL of (La 0.8  Sr 0.2 ) 0.98  MnO 3-δ  with a CFL of La 0.8  Ca 0.2  Ni 0.3 Fe 0.7 , and a CCL of (La 0.8  Sr 0.2 ) 0.98  MnO 3-δ  with a CFL of La 0.9 Ca 0.1  Ni 0.4  Fe 0.6  O 3-δ . 
     Further examples of cathodes  316  with a composite CFL  316   a  include a CCL  316   b  of (La 0.8  Sr 0.2 ) 0.98  MnO 3-δ  with a CFL  316   a  including 50 wt. % La Ni 0.4  Fe 0.6  O 3-δ  and 50 wt. % Ce 0.8  Sm 0.2  O 2-δ , a CCL of (La 0.8 Sr 0.2 ) 0.98  MnO 3-δ  with a CFL including 50 wt. % LaNi 0.4  Fe 0.6  O 3-δ  and 50 wt. % of 89 mol % ZrO 2 -10 mol % Sc 2 O 3 -1 mol % CeO 2 , and a CCL of (La 0.8  Sr 0.2 ) 0.98  MnO 3-δ  with a CFL including 50 wt. % LaNi 0.4  Fe 0.6  O 3-δ  and 50 wt. % of 88 mol % ZrO 2 -10 mol % Sc 2 O 3 -1 mol % Yb 2 O 3 -1 mol % CeO 2 . 
     If the CCL  316   b  includes LSCo or LSCF, then CCL  316   b  may comprise La 0.8  Sr 0.2  Co O 3-δ , La 0.8  Sr 0.2  Co 0.4  Fe 0.6  O 3-δ , La 0.8  Sr 0.2  Co 0.2  Fe 0.8  O 3-δ , La 0.6  Sr 0.4  Co 0.4  Fe 0.6  O 3-δ , or La 0.6  Sr 0.4  Co 0.2  Fe 0.8  O 3-δ . 
     The embodiment CFL lanthanum nickel ferrite perovskite material systems may be used in SOFCs, SOECs or in reversible SOFCs which can operate in fuel cell mode to generate power from fuel and air provided to the respective anode and cathode, and in electrolyzer mode to electrolyze water when external electric power is applied to the cell. 
     SOFCs with a LSM based CCL  316   b  and lanthanum nickel ferrite based CFL  316   a  cathodes  316  have been tested in SOFC stacks in a temperature range between 700° C. and 850° C. for various time durations up to 2000 hrs. To evaluate the performance and degradation of the cathodes containing lanthanum nickel ferrite CFL, exemplary cathodes containing lanthanum nickel ferrite based CFL and LSM CCL were tested head-to-head with comparative LSM based cathodes containing a LSM based CFL and a LSM CCL in “rainbow” SOFC stacks that contain both types of SOFCs for direct comparison. In this non-limiting example, comparative “type A” SOFCs containing cathodes with a LSM CCL and CFL including 50 wt. % LSM and 50 wt. % 10Sc1Ce1Yb were compared to exemplary “type B” SOFCs containing cathodes with a LSM CCL and CFL including 50 wt. % La Ni 0.4  Fe 0.6  O 3-δ  and 50 wt. % 10Sc1Ce1Yb. 
     The cell degradation is measured in terms of a change in area specific resistance over a given time, and is designated as area specific resistance degradation (ASRD). ASRD is expressed in units of mohm-cm 2 /khr. Results of stack testing show that the exemplary type B cells had a lower average degradation rate compared to the comparative type A cells, with the median ASRD of exemplary type B cells being ˜1.5 mohm-cm 2 /khr lower than that of the comparative type A cells, as described in greater detail below with reference to  FIGS.  6  and  7   . 
       FIG.  6    is a plot  600  of normalized ASRD of SOFCs in a stack containing exemplary type B cell numbers 6 to 10, 16 to 20, and 26 to 30 and comparative type A cell numbers 1 to 5, 11 to 15, 21 to 25, and 31. The normalized ASRD data show that the exemplary type B cells had a lower average ASRD rate compared to the comparative type A cells. 
       FIG.  7    is a plot  700  of ohmic resistance (area specific resistance, ASR) obtained by electrochemical impedance spectroscopy for the SOFCs of the stack of  FIG.  6   . These measurements show that the lower ASRD of the exemplary type B cells relative to the comparative type A cells is largely ohmic (e.g., due to sheet resistance Rs) in nature. The data characterizes increases in Rs for each cell of the SOFC stack that occurred during operation of the SOFC stack over a 1500 hour time period. As shown in  FIG.  7   , the exemplary type B cells have a lower increase in Rs compared to the comparative type A cells. The results of  FIGS.  6  and  7    thus show improved performance of the exemplary cells compared to the comparative cells. 
     The foregoing descriptions are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the order of steps in the foregoing embodiments may be performed in any order. Words such as “thereafter,” “then,” “next,” etc. are not necessarily intended to limit the order of the steps; these words may be used to guide the reader through the description of the methods. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the” is not to be construed as limiting the element to the singular. 
     Further, any step or component of any embodiment described herein can be used in any other embodiment. 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. 
     The preceding description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.