Strontium-rich lsm air electrode for solid oxide electrochemical cell

Abstract

To provide an air electrode for a solid oxide electrochemical cell improved in electrical conductivity.SOLUTION: A solid oxide electrochemical cell 500 includes a solid oxide electrolyte 312, a fuel electrode 314 located on a first side of the solid oxide electrolyte, and an air electrode 316 located on a second side of the solid oxide electrolyte. The air electrode includes strontium-rich lanthanum strontium manganite.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure is directed generally to electrochemical cells, and more particularly to electrochemical cell cathode materials. [Background technology]

[0002] In high-temperature fuel cell systems, such as solid oxide fuel cell (SOFC) systems, an oxidant stream is delivered to the cathode side of the fuel cell and a fuel stream is delivered to the anode side of the fuel cell. The oxidant stream is typically air, and the fuel stream can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol, as well as hydrocarbon fuels blended with pure hydrogen. SOFCs operate at temperatures between 750°C and 950°C and allow the transfer of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ions combine with either free hydrogen or hydrogen in hydrocarbon molecules to form water vapor and / or with carbon monoxide to form carbon dioxide. Excess electrons from the negatively charged ions are returned to the cathode side of the fuel cell via an electrical circuit completed between the anode and cathode, resulting in electrical current flowing through the circuit.

[0003] Fuel cell stacks can have either internal or external manifolding for fuel and air. In an internal manifold stack, fuel and air are distributed to each cell using risers contained within the stack. In other words, gas flows through openings or holes in the support layers, e.g., electrolyte layers, of each fuel cell and through the gas flow separators of each cell.

[0004] Fuel cell stacks are often constructed from multiple cells in the form of planar elements, tubes, or other geometries. Fuel and air must be provided to electrochemically active surfaces, which can be large. One of the components of a fuel cell stack is a so-called gas flow separator (called a gas flow separator plate in a planar stack) that separates the individual cells in the stack. The gas flow separator plate separates the fuel, e.g., hydrogen or hydrocarbon fuel, flowing to the anode (i.e., anode) of one cell in the stack from the oxidant, e.g., air, flowing to the cathode (i.e., cathode) of an adjacent cell in the stack. Often, the gas flow separator plate also serves as an interconnect, electrically connecting the anode of one cell to the cathode of an adjacent cell. In this case, the gas flow separator plate, which functions as an interconnect, is made of or includes an electrically conductive material. Summary of the Invention

[0005] 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. The cathode has a first formula: (La 1-z Sr z ) q MnO 3-d wherein z is in the range of 0.3 to 0.8, q is in the range of 0.9 to 1, and d is an equilibrium oxygen deficiency in the range of 0 to 0.2.

[0006] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain features of the invention. [Brief explanation of the drawings]

[0007] [Figure 1A]1 is a perspective view of a fuel cell column according to various embodiments of the present disclosure. [Figure 1B] FIG. 1B is a perspective view of one counter-flow solid oxide fuel cell stack included in the column of FIG. 1A according to various embodiments of the present disclosure. [Figure 1C] 1C is a cross-sectional side view of a portion of the stack of FIG. 1B according to various embodiments of the present disclosure. [Figure 2A] FIG. 1C is a top view of the air side of the interconnect of the stack of FIG. 1B. [Figure 2B] FIG. 1C is a top view of the fuel side of the interconnect of the stack of FIG. 1B. [Figure 3A] 1 is a perspective view of a fuel cell stack according to various embodiments of the present disclosure. [Figure 3B] 3B is an exploded perspective view of a portion of the stack of FIG. 3A according to various embodiments of the present disclosure. [Figure 3C] FIG. 3B is a top view of the fuel side of a cross-flow interconnect included in the stack of FIG. 3A. [Figure 3D] 3B is a schematic diagram of a fuel cell included in the stack of FIG. 3A according to various embodiments of the present disclosure. [Figure 4A] FIG. 3D is a plan view showing the air side of the cross-flow interconnect of FIG. 3C. [Figure 4B] FIG. 3D is a plan view of the fuel side of the cross-flow interconnect of FIG. 3C. [Figure 5] FIG. 1 is a schematic diagram of an electrochemical cell according to one embodiment of the present disclosure. [Figure 6] FIG. 2 is a schematic diagram of an electrochemical cell according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] Various embodiments will be described in detail with reference to the accompanying drawings. The drawings, which are not necessarily to scale, are intended to illustrate various features of the present disclosure. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References to specific examples and implementations are for illustrative purposes only and are not intended to limit the scope of the invention or the claims.

[0009] Ranges may 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 immediately preceding "about" or "substantially," it will be understood that the particular value constitutes another embodiment. In some embodiments, a value of "about X" may include + / - 1% of the value of X. Additionally, it will be understood that the endpoints of each range are significant both in relation to the other endpoint, and independently of the other endpoint.

[0010] Electrochemical cell systems include fuel cells and electrolyzer cell systems. In high-temperature fuel cell systems, such as solid oxide fuel cell (SOFC) systems, an oxidant stream is delivered to the cathode side of the fuel cell and a fuel stream is delivered to the anode side of the fuel cell. The oxidant stream is typically air, and the fuel stream is hydrogen (H2) or a hydrocarbon fuel, e.g., methane, natural gas, ethanol, or methanol, ammonia, or a hydrocarbon fuel blended with hydrogen. Fuel cells operate at temperatures between 750°C and 950°C and allow the transfer of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the oxygen ions combine with either free hydrogen or hydrogen in hydrocarbon molecules to form water vapor and / or with carbon monoxide to form carbon dioxide. Excess electrons from the negatively charged ions are returned to the cathode side of the fuel cell via an electrical circuit completed between the anode and cathode, resulting in electrical current flowing through the circuit. In electrolyzer systems, such as solid oxide electrolyzer systems, water (eg, steam) is separated into hydrogen and oxygen by applying a voltage across the electrolyzer cells.

[0011] FIG. 1A is a perspective view of an electrochemical cell column 30 with an external manifold, FIG. 1B is a perspective view of one counterflow solid oxide electrochemical cell stack 20 contained in the column 30 of FIG. 1A, and FIG. 1C is a cross-sectional side view of a portion of the stack 20 of FIG. 1B.

[0012] In various embodiments, the column 30 can be described as being operated as a solid oxide fuel cell (SOFC) column 30. However, it should be noted that the electrochemical column 30 can also be operated as an electrolyzer column (e.g., a solid oxide electrolyzer cell (SOEC) column). In an SOEC column, the anode is the air electrode and the cathode is the fuel (e.g., steam) electrode, while in an SOFC column, the anode is the anode and the cathode is the air electrode. Thus, in both SOFC and SOEC cells, the electrode supplied with fuel (e.g., hydrogen or hydrocarbon fuel in an SOFC, steam in an SOEC) is sometimes referred to as the anode, and the opposing electrode is sometimes referred to as the air electrode.

[0013] 1A and 1B, a column 30 may include one or more stacks 20, a fuel inlet conduit 32, an anode exhaust conduit 34, and an anode feed / return assembly 36 (e.g., an anode splitter plate (ASP) 36). The column 30 may also include a side baffle 38 and a compression assembly 40. The side baffle 38 may be connected to the compression assembly 40 and to a lower stack component (not shown) by a ceramic connector 39. The fuel inlet conduit 32 is fluidly connected to the ASPs 36 and configured to provide a fuel feed to each ASP 36, and the anode exhaust conduit 34 is fluidly connected to the ASPs 36 and configured to receive an anode fuel exhaust from each ASP 36.

[0014] The ASP 36 is disposed between the stacks 20 and is configured to provide a fuel feed comprising a hydrocarbon fuel to the stacks 20 and to receive anode fuel exhaust from the stacks 20. For example, the ASP 36 may be fluidly connected to an internal fuel riser channel 22 formed within the stacks 20, as described below.

[0015] 1C, stack 20 includes multiple fuel cells 1 separated by interconnects 10, sometimes called 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.

[0016] Each interconnect 10 electrically connects adjacent fuel cells 1 in the stack 20. In particular, an interconnect 10 can electrically connect the anode electrode 7 of one fuel cell 1 to the cathode electrode 3 of an adjacent fuel cell 1. FIG. 1C shows the lower fuel cell 1 positioned between two interconnects 10.

[0017] Each interconnect 10 includes ribs 12 that at least partially define fuel channels 8A and air channels 8B. The interconnects 10 can operate as gas-fuel separators that separate fuel, e.g., a hydrocarbon fuel, flowing to the anode (i.e., anode 7) of one cell in the stack from oxidant, e.g., air, flowing to the cathode (i.e., cathode 3) of an adjacent cell in the stack. At one end of the stack 20, there may be an air end plate or a fuel end plate (not shown) for providing air or fuel, respectively, to the end electrodes.

[0018] Figure 2A is a plan view of the air side of an exemplary interconnect 10, and Figure 2B is a plan view of the fuel side of the interconnect 10. With reference to Figures 1C and 2A, the air side includes air channels 8B. Air flows through the air channels 8B to the cathode electrodes 3 of adjacent fuel cells 1. In particular, air can flow across the interconnect 10 in a first direction A, as indicated by the arrows.

[0019] A ring seal 23 may surround the fuel holes 22A of the interconnect 10 to prevent fuel from contacting the cathode electrode. A band-shaped perimeter seal 24 is located on the perimeter of the air side of the interconnect 10. The seals 23, 24 may be formed from a glass material. The perimeter may be in the form of a raised plateau without ribs or channels. The surface of the perimeter region may be flush with the tops of the ribs 12.

[0020] 1C and 2B, the fuel side of the interconnect 10 may include a fuel channel 8A and a fuel manifold 28 (e.g., a fuel plenum). Fuel flows from one of the fuel holes 22A into the adjacent manifold 28, through the fuel channel 8A, and to the anode 7 of the adjacent fuel cell 1. Excess fuel and anode exhaust can flow into the other fuel manifold 28 and then into the adjacent fuel hole 22A. In particular, fuel can flow across the interconnect 10 in a second direction B, as indicated by the arrows. The second direction B may be orthogonal to the first direction A (see FIG. 2A).

[0021] A frame-like seal 26 is disposed in the peripheral region on the fuel side of the interconnect 10. The peripheral region may be a raised plateau that does not include ribs or channels. The surface of the peripheral region may be flush with the tops of the ribs 12. The surface of the manifold 28 may be flush with the bottom of the fuel channels or, optionally, may be below the surface of the bottom of the fuel channels.

[0022] FIG. 3A is a perspective view of a fuel cell stack 300 according to various embodiments of the present disclosure, FIG. 3B is an exploded perspective view of a portion of the stack 300 of FIG. 3A, FIG. 3C is a top view of the fuel side of an interconnect 400 included in the stack 300, and FIG. 3D is a schematic diagram of a fuel cell included in the stack 300.

[0023] 3A-3D, a fuel cell stack 300, sometimes called a fuel cell column because it does not have an ASP, includes multiple fuel cells 310 separated by interconnects 400, sometimes called gas flow separator plates or bipolar plates. One or more stacks 300 may be thermally integrated with other components of the fuel cell power generation system (e.g., one or more anode tail gas oxidizers, fuel reformers, fluid conduits and manifolds, etc.) within a common enclosure or "hot box."

[0024] The interconnect 400 is made from a conductive metallic material. For example, the interconnect 400 may include a chromium alloy, such as a Cr—Fe alloy. The interconnect 400 is typically manufactured using powder metallurgy techniques, including pressing and sintering a Cr—Fe powder, which may be a mixture of Cr and Fe powders or a Cr—Fe alloy powder, to form a Cr—Fe interconnect of a desired size and shape (e.g., a “net shape” or “near net shape” process). A typical chromium alloy interconnect 400 includes greater than about 90% chromium by weight, such as about 94-96% (e.g., 95%) chromium by weight. The interconnect 400 may also include less than about 10% iron by weight, such as about 4-6% (e.g., 5%) iron by weight, and less than about 2% by weight, such as about 0-1% by weight, of other materials, such as yttrium or yttria, as well as residual or unavoidable impurities.

[0025] 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 cathode 316 can 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 that extend through the electrolyte layer of the fuel cell shown in FIG. 1B. Thus, the fuel cell 310 may avoid cracks that may occur due to the presence of such through-holes.

[0026] The top and bottom interconnects 400 of the stack 300 may be different interconnects, air end plates or fuel end plates, each including features for providing air or fuel to the adjacent end fuel cells 310. As used herein, "interconnect" can refer to either an interconnect located between two fuel cells 310 or an end plate located at the end of the stack and directly adjacent to only one fuel cell 310. Because the stack 300 does not include an ASP and its associated end plate, the stack 300 may include only two end plates. As a result, the dimensional variability of the stack associated with the use of intra-column ASP can be avoided.

[0027] 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 positioned on opposite sides of the fuel cell stack 300, which includes stacked fuel cells 310 and interconnects 400. The side baffles 302 may connect the fuel plenum 350 and the compression assembly 306 so that the compression assembly 306 can apply pressure to the stack 300. The side baffles 302 may be curved baffle plates, each covering at least a portion of three sides of the fuel cell stack 300. For example, one baffle plate may completely cover the fuel inlet riser side of the stack 300 and partially cover the adjacent top and back sides of the stack, while the other baffle plate completely covers the fuel outlet riser side of the stack and partially covers adjacent portions of the top and back sides of the stack. The remaining uncovered portions of the top and bottom sides of the stack allow air to flow through the stack 300. The curved baffle plates provide improved airflow control through the stack. A 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 a fuel inlet and outlet conduit 320 located below the fuel plenum 350.

[0028] Each interconnect 400 electrically connects adjacent fuel cells 310 in the stack 300. In particular, the 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. 3C , each interconnect 400 may be configured to allow air to flow in a first direction A to provide air to the cathode of the adjacent fuel cell 310. Each interconnect 400 may also be configured to allow fuel to flow in a second direction F to provide fuel to the anode of the adjacent fuel cell 310. Directions A and F may be orthogonal to each other or substantially orthogonal to each other. Thus, the interconnect 400 may be referred to as a cross-flow interconnect.

[0029] The interconnect 400 may include fuel holes extending therethrough and 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, sometimes referred to as anode exhaust outlets 404. The fuel inlets 402 and fuel outlets 404 may be located outside the periphery of the fuel cell 310. Thus, the fuel cell 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 the corresponding length of the interconnect 400, e.g., the length in direction A.

[0030] 3B, each interconnect 400 includes two fuel inlets 402 separated by a neck portion 412 of the interconnect 400. 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, as shown in FIG. 3B, each interconnect 400 includes two fuel outlets 404 separated by a neck portion 414 of the interconnect 400. However, more than two fuel outlets 404 may be included, such as three to five outlets separated by two to four neck portions 414.

[0031] The fuel inlets 402 of adjacent interconnects 400 may be aligned within the stack 300 to form one or more fuel inlet risers 403. The fuel outlets 404 of adjacent interconnects 400 may be aligned within the stack 300 to form one or more fuel outlet risers 405. The fuel inlet risers 403 may be configured to distribute fuel received from the fuel plenum 350 to the fuel cells 310. The fuel outlet risers 405 may be configured to provide anode exhaust received from the fuel cells 310 to the fuel plenum 350.

[0032] 1A, the side baffles 302 may be curved to surround the edges of the interconnect 400. In particular, the side baffles 302 may be positioned to surround the fuel inlet 402 and the fuel outlet 404 of the interconnect 400. Thus, the side baffles may more efficiently control airflow through the air channels of the interconnect 400 that are exposed between the side baffles 302 and are described in detail with respect to FIGS.

[0033] In various embodiments, stack 300 may include approximately 200-400 fuel cells, such as approximately 250-350 fuel cells, and more particularly, approximately 275-325 fuel cells, which may be provided with fuel using only fuel risers 403, 405. The cross-flow configuration may provide fuel to a large number of fuel cells without requiring an external fuel manifold, such as external conduits 32, 34, of the ASP or stack shown in FIG. 1A.

[0034] Each interconnect 400 may be made of or include a conductive material, such as a metal alloy (e.g., a chromium-iron alloy) having a thermal expansion coefficient similar to that of the solid oxide electrolyte in the cell (e.g., a difference of 0-10%). For example, the interconnect 400 may include a metal (e.g., a chromium-iron alloy, such as 4-6 wt. % iron, optionally 1 wt. % or less yttrium, and the balance chromium alloy) and may electrically connect the anode side, i.e., fuel side, of one fuel cell 310 to the cathode side, i.e., air side, of an adjacent fuel cell 310. A conductive contact layer, such as a nickel contact layer (e.g., nickel mesh), may be provided between the anode and each interconnect 400. Another optional conductive contact layer may be provided between the cathode electrode and each interconnect 400.

[0035] Surfaces of the interconnect 400 that are exposed to an oxidizing environment (e.g., air) during operation, such as the cathode-facing side of the interconnect 400, may be coated with a protective coating layer to reduce the growth rate of the interconnect's chromium oxide surface layer and inhibit the evaporation of chromium vapor species that would otherwise degrade the fuel cell cathode. Typically, the coating layer, which may include a perovskite, e.g., LSM, may be formed using a thermal spray or dip coating process. Alternatively, other metal oxide coatings, such as spinels, e.g., manganese cobalt spinel oxide (MCO), may be used instead of or in addition to LSM. Mn 2-x Co 1+xAny spinel having a composition written as O4 (0≦x≦1), or y(Mn3O4)+(1−y)(Co3O4), where (1 / 3≦y≦2 / 3), or written as (Mn,Co)3O4, can be used. In other embodiments, a mixed layer of LSM and MCO, or a stack of LSM and MCO layers, can be used as the coating layer.

[0036] 4A and 4B are plan views illustrating the air side and fuel side, respectively, of a cross-flow interconnect 400 according to various embodiments of the present disclosure. Referring to FIG. 4A, 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 cathodes of the mounted fuel cells 310. The air side of the interconnect 400 may be divided into an air flow field 420 including the air channels 408 and riser sealing surfaces 422 disposed on two opposing sides of the air flow field 420. One of the riser sealing surfaces 422 may surround the fuel inlet 402, and the other riser sealing surface 422 may surround the fuel outlet 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 peripheries of the interconnect 400. In other words, when assembled into stack 300, opposing ends of air channels 408 and ribs 406 are positioned on opposite (e.g., top and bottom) exterior surfaces of the stack to allow blown air to flow through the stack. Thus, the stack may be provided with an external air manifold.

[0037] Riser seals 424 may be disposed on the riser seal surface 422. For example, one riser seal 424 may surround the fuel inlet 402 and one riser seal 424 may surround the fuel outlet 404. The riser seals 424 may prevent fuel and / or anode exhaust from entering the air flow field 420 and contacting the cathodes of the fuel cells 310. The riser seals 424 may also operate to prevent fuel from leaking out of the fuel cell stack 100 (see FIG. 3A).

[0038] 4B , 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 anodes of the mounted fuel cells 310. The fuel side of the interconnect 400 may be divided into a fuel flow area 430 that includes the fuel channels 418 and a peripheral sealing surface 432 that surrounds the fuel flow area 430 and the fuel inlets 402 and fuel outlets 404. The ribs 416 and fuel channels 418 may extend in a direction that is orthogonal or substantially orthogonal to the direction in which the air-side channels 408 and ribs 406 extend.

[0039] A frame-shaped perimeter seal 434 may be disposed on the perimeter sealing surface 432. The perimeter seal 434 may be configured to prevent air from entering the fuel flow field 430 and contacting the anodes of adjacent fuel cells 310. The perimeter seal 434 may also function to prevent fuel from exiting the fuel risers 403, 405 and leaking out of the fuel cell stack 300 (see FIGS. 3A and 3B).

[0040] The seals 424, 434 may include a glass or ceramic seal material. The seal material may have low electrical conductivity. In some embodiments, the seals 424, 434 may be formed by printing one or more layers of the seal material onto the interconnect 400 and then sintering.

[0041] 5 is a schematic diagram of an electrochemical cell 500 according to one embodiment of the present disclosure. The electrochemical cell 500 may include 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 cathode, and a stream containing water (e.g., steam) is provided to the anode. The water is electrolyzed at the anode into hydrogen and oxygen. The oxygen ions are transported across the electrolyte to the cathode. An exhaust stream containing oxygen is provided from the cathode. A stream containing hydrogen is provided from the anode.

[0042] Electrochemical cell 500 includes a solid oxide electrolyte 312, an anode 314, and a cathode 316. In the embodiment described below, electrochemical cell 500 is an SOFC, and anode 314 is referred to as the anode 314 and cathode 316 is referred to as the cathode 316. However, in alternative embodiments in which electrochemical cell 500 is an SOEC, anode 314 functions as the cathode and cathode 316 functions as the anode.

[0043] The anode 314 includes an anode current collecting layer 314a and an anode functional layer 314b, and the cathode 316 includes a cathode functional layer (CFL) 316a and a cathode current collecting layer (CCL) 316b.

[0044] The electrolyte 312 can include an ion-conducting ceramic, such as doped zirconia, doped ceria, and / or any other suitable ion-conducting ceramic oxide material. For example, the electrolyte 312 can 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 case of YbCSSZ, as disclosed in U.S. Pat. No. 8,580,456 (which is incorporated herein by reference), scandia can be present in an amount equal to 9-11 mol%, e.g., 10 mol%, ceria can be present in an amount greater than 0 mol% and less than or equal to 3 mol%, e.g., 0.5 mol% to 2.5 mol%, e.g., 1 mol%, and ytterbia can be present in an amount greater than 0 mol% and less than or equal to 2.5 mol%, e.g., 0.5 mol% to 2 mol%, e.g., 1 mol%. In the case of YCSZ, yttria may be present in an amount equal to 8-10 mol%, and optionally ceria may be present in an amount equal to 0-3 mol%. In other embodiments, the electrolyte may include samaria, gadolinia, or yttria-doped ceria.

[0045] The anode 314 is located on a first side of the electrolyte 312. The anode functional layer 314b is located between the anode current collecting layer 314a and the first side of the electrolyte 312. The anode 314 can include at least one cermet including a metallic phase and a ceramic phase. The metallic phase can include a metal catalyst, and the ceramic phase can include one or more ceramic materials. The ceramic phase of the anode 314 can include any suitable ion-conducting ceramic material, such as doped ceria and / or doped zirconia. For example, the ceramic phase can 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 can include doped ceria, such as ceria doped with samaria, gadolinia, and / or praseodymia, e.g., CeO doped with 10-20 mol% SmO, GdO, and / or PrO. The metal phase can include a metal catalyst, such as nickel (Ni), that acts as an electronic conductor. The metal catalyst can be in either a metallic or oxidized state. For example, a metal catalyst forms a metal oxide when it is in an oxidized state. Therefore, the anode can be annealed in a reducing atmosphere before and / or during fuel cell operation to reduce the metal catalyst to the metallic state. The anode functional layer 314b includes a lower ratio of nickel-containing phase and ceramic phase than the anode current collecting layer 314a.

[0046] The cathode 316 is located on the second side of the electrolyte 312. The CFL 316a is located between the CCL 316b and the second side of the electrolyte 312. The electrode 316 comprises the air electrode in both the SOEC and the SOFC.

[0047] In one embodiment, the CFL 316a comprises a composite of a majority electron conductor and a majority ion conductor. The CFL 316a can comprise a mixture of a conductive perovskite metal oxide material and an ionically conductive stabilized zirconia or doped ceria material. The conductive material can be lanthanum strontium manganite (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium cobaltite (LSC), lanthanum strontium cobalt manganite (LSCM), lanthanum strontium ferrite (LSF), lanthanum strontium cobalt nickel oxide (LSCN) (e.g., La 0.85 Sr 0.15 Co 0.9 Ni 0.1 O3), combinations thereof, or the like.

[0048] In one embodiment, the conductive material can include LSM, which has the formula: (La 1-z Sr z ) q MnO 3-d where z is in the range of 0.1 to 0.2, q is in the range of 0.9 to 1, for example, 0.95 to 1, and d is an equilibrium oxygen deficiency in the range of 0 to 0.2, for example, 0 to 0.1. For example, the low strontium content LSM may be La 0.8 Sr 0.2 MnO 3-d or A-site deficient low strontium content LSM, where q is in the range of 0.9 to 0.99, for example 0.95 to 0.99, such as (La 0.8 Sr 0.2 ) 0.97 MnO 3-d where d is in the range of 0 to 0.1.

[0049] In one embodiment, the ionically conductive material can include stabilized zirconia, such as yttria-stabilized zirconia (YSZ), yttria-ceria-stabilized zirconia (YCSZ), scandia-stabilized zirconia (SSZ), ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ), or blends thereof. In the case of YbCSSZ, scandia can be present in an amount equal to 9-11 mol%, e.g., 10 mol%, ceria can be present in an amount greater than 0 mol% and less than or equal to 3 mol%, e.g., 0.5 mol% to 2.5 mol%, e.g., 1 mol%, and ytterbia can be present in an amount greater than 0 mol% and less than or equal to 2.5 mol%, e.g., 0.5 mol% to 2 mol%, e.g., 1 mol%. In another embodiment, the ionically conductive material can include doped ceria, such as samaria-, gadolinia-, or yttria-doped ceria.

[0050] CFL316a can include about 10% to about 90% by weight, e.g., about 40% to about 60% by weight, of the above-described conductive material and about 10% to about 90% by weight, e.g., about 40% to about 60% by weight, of an ion-conducting stabilized zirconia or doped ceria material. For example, CFL316a can be a composite of low-strontium-content LSM and YbCSSZ.

[0051] CCL316b includes a majority-electron conductor and may or may not include a majority-ion conductor. If a majority-ion conductor, such as stabilized zirconia or doped ceria, is included in CCL316b, the ratio of majority-electron conductor to majority-ion conductor in CCL316b will be higher than in CFL316a. Alternatively, CCL316 may consist essentially of a majority-electron conductor and include no majority-ion conductor, or may include an unavoidable amount of majority-ion conductor that diffuses from CFL316a to CCL316b during cell fabrication or cell operation.

[0052] In one embodiment, CCL316b comprises or consists essentially of high strontium content LSM (e.g., strontium-rich LSM) that comprises a higher strontium content than the low strontium content LSM of CFL316a. The high strontium content LSM has the formula: (La 1-z Sr z ) q MnO 3-d In the formula, z is in the range of 0.3 to 0.8, q is in the range of 0.9 to 1, for example, in the range of 0.95 to 1, and d is an equilibrium oxygen deficiency in the range of 0 to 0.2, for example, in the range of 0 to 0.1. In one embodiment, z is in the range of 0.3 to 0.7, for example, 0.35 to 0.6 (including 0.4 to 0.6 or 0.4 to 0.5). For example, the high strontium content LSM is an A-site deficient high strontium content LSM in which q is in the range of 0.9 to 0.99, for example, 0.94 to 0.98, such as (La 0.7 Sr 0.3 ) 0.95 MnO 3-d , (La 0.65 Sr 0.35 ) 0.95 MnO 3-d , (La 0.6 Sr 0.4 ) 0.95 MnO 3-d Or (La 0.5 Sr 0.5 ) 0.95 MnO 3-d (wherein d is in the range of 0 to 0.1).

[0053] CCL316b can include about 90 wt. % to about 100 wt. %, e.g., about 95 wt. % to about 99 wt. % of the conductive high strontium content LSM material described above, and 0 wt. % to about 10 wt. %, e.g., about 0.01 wt. % to about 1 wt. % of an ionically conductive stabilized zirconia or doped ceria material.

[0054] Although not conclusive, it is believed that a lower strontium content (e.g., z in the range of 0.1 to 0.2 in the LSM formula above) reduces the reactivity of the LSM with stabilized zirconia, thereby reducing the formation of strontium zirconate (SrZrO), which is insulating and detrimental to electrochemical cell performance. Therefore, a low-strontium-content LSM can be used with CFL316a, which may also contain stabilized zirconia. In contrast, a higher strontium content (e.g., z in the range of 0.3 to 0.8 inclusive) is believed to increase the electrical conductivity of the LSM. For example, the electrical conductivity of the LSM is believed to increase above z=0.2, e.g., from z=0.3 to z=0.5, peak near z=0.5, and then decrease from z=0.5 to z=0.8. However, when z is greater than 0.5 and less than 0.8, the conductivity of the LSM is still relatively high compared to low-strontium-content LSMs with z in the range of 0.1 to 0.2. Therefore, because CCL316b contains little or no stabilized zirconia, high-strontium-content LSMs can be used in CCL316b to enhance the conductivity of CCL316b without significant concerns about the formation of strontium zirconate. Furthermore, although not conclusive, the additional strontium in the high-strontium-content LSM may act as a chromium getter, capturing chromium vapor diffusing from adjacent interconnects 10 within the column 30 before the chromium reaches CFL316a and / or electrolyte 312.

[0055] The inventors tested SOFC stacks containing both a comparative SOFC and an exemplary SOFC. The comparative SOFC and exemplary SOFC were identical except that the comparative SOFC contained low strontium content LSM in both CLF316a and CCL316b, while the exemplary SOFC contained low strontium content LSM in CLF316a and high strontium content in CCL316b. The low strontium content LSM is represented by the formula (La 0.8 Sr 0.2 ) 0.97 MnO 3-dwhere d is in the range of 0 to 0.1, and the high strontium LSM has the formula (La 0.65 Sr 0.35 ) 0.95 MnO 3-d where d ranges from 0 to 0.1. The inventors observed higher average cell voltages (e.g., 6 to 8 mV higher average cell voltages) in the exemplary SOFC than in the comparative SOFC while operating the SOFC stack with hydrogen fuel and partially externally reformed hydrocarbon fuel. While not conclusive, the improved performance of the exemplary SOFC may be attributed to the higher electrical conductivity of the high strontium content of CCL316b in the exemplary SOFC.

[0056] 6 is a schematic diagram of an electrochemical cell 600 according to another embodiment of the present disclosure. The electrochemical cell 600 may be similar to the electrochemical cell 500 of the previous embodiment, except for the presence of an additional chromium getter layer 316c at the air electrode 316 (e.g., in the cathode of an SOFC). The chromium getter layer 316c is configured to capture chromium vapor that diffuses from the adjacent interconnect 10 during operation.

[0057] The chromium getter layer 316c is located on the CCL 316b such that the CCL 316b is located between the CFL 316a and the chromium getter layer 316c. The chromium getter layer 316c can include a perovskite, such as lanthanum strontium manganite (LSM). For example, the chromium getter layer 316c can include a composite of a perovskite (e.g., LSM) and a spinel, such as manganese cobalt spinel oxide (MCO). MCO has the composition Mn 2-x Co 1+x % to about 90 wt. %, e.g., about 60 wt. % to about 80 wt. % LSM and about 10 wt. % to about 50 wt. % to about 50 wt. % to about 20 wt. % MCO.

[0058] The LSM of the chromium getter layer 316c is represented by the formula: (La 1-z Sr z ) q MnO 3-d where z is in the range of 0.3 to 0.8, q is in the range of 0.9 to 1, e.g., 0.95 to 1, and d is the equilibrium oxygen vacancy in the range of 0 to 0.2. In one embodiment, z is in the range of 0.3 to 0.7, e.g., 0.35 to 0.6, including 0.4 to 0.6 or 0.4 to 0.5. Although not conclusive, it is believed that the high strontium content improves the chromium getter properties of the LSM, as discussed above.

[0059] Fuel cell systems incorporating SOFCs of the presently disclosed embodiments benefit the climate by reducing greenhouse gas emissions.

[0060] The foregoing description is provided by way of example only and is not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be understood by one of ordinary skill in the art, the order of steps in the foregoing embodiments may be performed in any order. Words such as "then," "then," and "next" are not intended to necessarily limit the order of the steps; rather, these words may be used to guide the reader through the method description. Additionally, any reference to a claim element in the singular, for example, using the article "a," "an," or "the," should not be construed as limiting the element to the singular.

[0061] Furthermore, any step or component of any embodiment described herein may be used in any other embodiment.

[0062] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. 1. A solid oxide electrochemical cell comprising: a solid oxide electrolyte; an anode located on a first side of the solid oxide electrolyte; a cathode located on a second side of the solid oxide electrolyte, the cathode having a first formula: <h2 style=";text-align:left;direction:ltr">((La<h2 style=";text-align:left;direction:ltr"> １－ｚ <h2 style=";text-align:left;direction:ltr"> 25<h2 style=";text-align:left;direction:ltr"> ｚ <h2 style=";text-align:left;direction:ltr"> )<h2 style=";text-align:left;direction:ltr"> ｑ <h2 style=";text-align:left;direction:ltr"> MnO<h2 style=";text-align:left;direction:ltr"> ３－ｄ wherein z is in the range of 0.3 to 0.8, q is in the range of 0.9 to 1, and d is the equilibrium oxygen deficiency in the range of 0 to 0.

2. An air electrode containing lanthanum strontium manganate (LSM) represented by 1. A solid oxide electrochemical cell comprising:

2. 2. The solid oxide electrochemical cell of claim 1, wherein z is in the range of 0.35 to 0.6, q is in the range of 0.95 to 1, and d is in the range of 0 to 0.

1.

3. 3. The solid oxide electrochemical cell of claim 2, wherein z is in the range of 0.4 to 0.

6.

4. 10. The solid oxide electrochemical cell of claim 1, wherein the solid oxide electrochemical cell comprises a solid oxide fuel cell (SOFC) and the air electrode comprises a cathode of the SOFC.

5. the cathode includes a cathode current collecting layer and a cathode functional layer positioned between the cathode current collecting layer and the second side of the solid oxide electrolyte; the cathode current collecting layer comprises an LSM represented by the first formula; 5. The solid oxide electrochemical cell of claim 4.

6. 6. The solid oxide electrochemical cell of claim 5, wherein the cathode current collecting layer consists essentially of the LSM represented by the first formula.

7. The cathode functional layer has a second formula: <h2 style=";text-align:left;direction:ltr">((La<h2 style=";text-align:left;direction:ltr"> １－ｚ <h2 style=";text-align:left;direction:ltr"> 25<h2 style=";text-align:left;direction:ltr"> ｚ <h2 style=";text-align:left;direction:ltr"> )<h2 style=";text-align:left;direction:ltr"> ｑ <h2 style=";text-align:left;direction:ltr"> MnO<h2 style=";text-align:left;direction:ltr"> ３－ｄ wherein z is in the range of 0.1 to 0.2, q is in the range of 0.9 to 1, and d is the equilibrium oxygen deficiency in the range of 0 to 0.

2.

6. The solid oxide electrochemical cell of claim 5, comprising an LSM represented by the formula:

8. 8. The solid oxide electrochemical cell of claim 7, wherein the cathode functional layer comprises a composite of the LSM represented by the second formula and a non-perovskite ion-conducting ceramic material.

9. 9. The solid oxide electrochemical cell of claim 8, wherein the non-perovskite ion-conducting ceramic material comprises a stabilized zirconia material.

10. 10. The solid oxide electrochemical cell of claim 9, wherein the stabilized zirconia material comprises zirconia stabilized with 9 to 11 mol% scandia, greater than 0 mol% and less than or equal to 3 mol% ceria, and greater than 0 mol% and less than or equal to 2.5 mol% ytterbia.

11. 9. The solid oxide electrochemical cell of claim 8, wherein the non-perovskite ion-conducting ceramic material comprises a doped ceria material.

12. 9. The solid oxide electrochemical cell of claim 8, wherein the weight percent ratio of the LSM represented by the second formula to the non-perovskite ion-conducting ceramic material is from 3:7 to 7:

3.

13. 6. The solid oxide electrochemical cell of claim 5, wherein the cathode further comprises a chromium getter layer.

14. 14. The solid oxide electrochemical cell of claim 13, wherein the cathode current collecting layer is located between the cathode functional layer and the chromium getter layer.

15. 15. The solid oxide electrochemical cell of claim 14, wherein the chromium getter layer comprises the lanthanum strontium manganate (LSM) represented by the first formula.

16. 15. The solid oxide electrochemical cell of claim 14, wherein the chromium getter layer comprises a composite of the lanthanum strontium manganate (LSM) represented by the first formula and a manganese cobalt spinel oxide material.

17. 17. The solid oxide electrochemical cell of claim 16, wherein the weight percent ratio of the LSM represented by the first formula to the manganese cobalt spinel oxide material is from 1:1 to 9:

1.

18. 2. The solid oxide electrochemical cell according to claim 1, wherein the LSM represented by the first formula is A-site deficient and q is in the range of 0.94 to 0.

99.

19. The solid oxide electrochemical cell of claim 1 , wherein the solid oxide electrochemical cell comprises a solid oxide electrolyzer cell (SOEC).

20. a plurality of the solid oxide electrochemical cells of claim 1; Multiple interconnects and A solid oxide electrochemical cell column comprising:

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