Solid oxide electrochemical cell including ceria-free electrolyte

Abstract

A solid oxide electrochemical cell includes a fuel side electrode, an air side electrode, and an electrolyte disposed between the fuel side electrode and the air side electrode. The electrochemical cell can be an electrolyzer cell, a fuel cell, or a regenerative fuel cell. The electrolyte includes an electrolyte material formed of zirconia doped with Sc2O3 and at least one additional rare earth oxide dopant. The electrolyte material includes less than 0.1 atomic % CeO2.

Description

Attorney Docket No.: 7917-0789WO SOLID OXIDE ELECTROCHEMICAL CELL INCLUDING CERIA-FREE ELECTROLYTE FIELD

[0001] The embodiments of the present invention generally relate to solid oxide electrochemical cells, such as solid oxide electrolyzer cells (SOECs) and solid oxide fuel cells (SOFCs), and more particularly to cells containing a ceria-free electrolyte. BACKGROUND

[0002] A SOEC stack includes SOECs separated by interconnects. Similarly, a SOFC stack includes SOFCs separated by interconnects. Each SOEC and each SOFC comprises a solid oxide electrolyte, an air side electrode located on a first side of the solid oxide electrolyte and a fuel side electrode located on an opposite side of the solid oxide electrolyte. SUMMARY

[0003] In one embodiment, a solid oxide electrochemical cell includes: a fuel side electrode; an air side electrode; and an electrolyte disposed between the fuel side electrode and the air side electrode. The electrolyte comprises an electrolyte material formed of zirconia doped with Sc2O3and at least one additional dopant. The solid oxide electrochemical cell comprises an anode supported solid oxide electrochemical cell in which the fuel side electrode is thicker than the electrolyte and the air side electrode, or the solid oxide electrochemical cell comprises an electrolyte supported cell in which the electrolyte is thicker than the fuel side electrode and the air side electrode. The at least one additional dopant comprises at least one of gadolinium oxide, neodymium oxide, praseodymium oxide, or samarium oxide; and the electrolyte material comprises less than 0.1 atomic % of CeO2.Attorney Docket No.: 7917-0789WO

[0004] In another embodiment, an electrochemical cell stack includes stacked interconnects and electrochemical cells disposed between the interconnects. The cells utilize electrolytes that comprise less than 0.1 atomic % of CeO2.

[0005] In another embodiment, a solid oxide electrochemical cell comprises a fuel side electrode; an air side electrode; and an electrolyte disposed between the fuel side electrode and the air side electrode, the electrolyte comprising an electrolyte material formed of zirconia doped with Sc2O3and Pr6O11.

[0006] In another embodiment, a method of operating a solid oxide electrolyzer cell comprising a fuel side electrode, an air side electrode, and an electrolyte disposed between the fuel side electrode and the air side electrode, the method comprises providing steam to the fuel side electrode; providing air to the air side electrode; and applying a voltage between the fuel side electrode and the air side electrode to separate the steam into hydrogen and oxygen ions, and to transport the oxygen ions from the fuel side electrode to the air side electrode through the electrolyte. The electrolyte comprises an electrolyte material formed of zirconia doped with Sc2O3and at least one additional dopant; the at least one additional dopant comprises at least one of yttrium oxide, ytterbium oxide, gadolinium oxide, neodymium oxide, praseodymium oxide, or samarium oxide; and the electrolyte material comprises less than 0.1 atomic % of CeO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[0008] FIG.1A is a perspective view of an electrochemical cell stack according to various embodiments of the present invention.Attorney Docket No.: 7917-0789WO

[0009] FIG.1B is a cross-sectional view of a portion of the stack of FIG. 1A.

[0010] FIG.2A is a plan view of an air side of an interconnect according to various embodiments of the present invention.

[0011] FIG.2B is a plan view of a fuel side of the interconnect of FIG.2A.

[0012] FIG.3A is a plan view of an air side of an electrochemical cell according to various embodiments of the present invention.

[0013] FIG.3B is a plan view of a fuel side of the electrochemical cell of FIG.3A.

[0014] FIG.4 is a side cross-sectional views of an exemplary electrochemical cell stack portion according to various embodiments of the present invention. DETAILED DESCRIPTION

[0015] The various embodiments will be described in detail with reference to the accompanying drawings. 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.

[0016] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ).

[0017] Where a range of values is provided, it is understood that each intervening value between and including the upper and lower limit of that range and any otherAttorney Docket No.: 7917-0789WO stated or intervening value in that stated range is encompassed within the invention. In addition, weight percentages (wt.%) and atomic percentages (at.%) as used herein respectively refer to a percent of total weight or a percent of a total number of atoms of a corresponding composition.

[0018] 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.

[0019] Electrochemical cell systems include fuel cell and electrolyzer cell systems. In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is directed to the air side (which is the cathode side) of the fuel cell while a fuel flow is directed to the fuel side (which is the anode side) of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be hydrogen (H2) or a hydrocarbon fuel, such as methane, natural gas, ethanol, or methanol. The fuel cell, operating at a typical temperature between 750ºC and 950ºC, enables the transport 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 a hydrocarbon molecule to form water vapor and / or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ions 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.

[0020] In an electrolyzer system, such as a solid oxide electrolyzer cell (SOEC) system, water (e.g., steam) is separated into hydrogen and oxygen by applying a voltage across the electrolyzer cell. The steam is provided to the fuel side (e.g., the cathode side) of the SOEC and air may be provided to the air side (e.g., anode side) of the SOEC. A voltage is applied between the air and fuel electrodes to cause negatively charged oxygen ions to be transported from the fuel side of the electrolyteAttorney Docket No.: 7917-0789WO to the air side of the electrolyte, where the oxygen ions are provided into the air stream to generate an oxygen enriched air stream. The separated hydrogen is collected from the fuel side of the SOEC.

[0021] FIG.1A is a perspective view of an electrochemical cell stack 100, and FIG. 1B is a sectional view of a portion of the stack 100 according to various embodiments of the present invention. Referring to FIGS. 1A and 1B, the stack 100 may be a SOEC stack that includes solid oxide electrolyzer cells 1 separated by interconnects 10. Alternatively, the stack 100 may be a SOFC stack with fuel cells 1 separated by interconnects. Referring to FIG.1B, each electrochemical cell (e.g., SOEC or SOFC) 1 comprises an air side electrode 3, a solid oxide electrolyte 5, and a fuel side electrode 7.

[0022] Electrolyzer cell stacks are frequently built from a multiplicity of electrolyzer cells 1 in the form of planar elements, tubes, or other geometries. Although the electrolyzer cell stack 100 in FIG.1A is vertically oriented, electrolyzer cell stacks may be oriented horizontally or in any other direction. For example, water or steam may be provided through water conduits 22 (e.g., water / steam riser openings) formed in each interconnect 10 and electrolyzer cell 1, while oxygen (e.g., air) may be provided from the side of the stack and flow between air side ribs of the interconnects 10. Alternatively, in fuel cell stacks, fuel such as hydrogen or methane may be provided through fuel conduits 22 (e.g., fuel riser openings) formed in each interconnect 10 and fuel cell 1, while oxygen (e.g., air) may be provided from the side of the stack and flow between air side ribs of the interconnects 10.

[0023] Each interconnect 10 electrically connects adjacent cell 1 in the stack 100. In particular, an interconnect 10 may electrically connect the fuel side electrode 7 of one cell 1 to the air side electrode 3 of an adjacent cell 1. FIG.1B illustrates that the lower cell 1 is located between two interconnects 10. A Ni mesh (not shown) may be used to electrically connect the interconnect 10 to the fuel side electrode 7 of an adjacent cell 1. As noted above, cell 1 may be an electrolyzer cell or a fuel cell.Attorney Docket No.: 7917-0789WO

[0024] Each interconnect 10 includes fuel side ribs 12A that at least partially define fuel channels 8A and air side ribs 12B that at least partially define oxidant (e.g., air) channels 8B. Interconnect 10 may operate as a separator that separates water / steam flowing to the fuel side electrode of one electrolyzer cell 1 in the stack from oxygen flowing to the air side electrode of an adjacent electrolyzer cell 1 in the stack. Alternatively, interconnect 10 may separate hydrogen or methane flowing to the fuel side of the interconnect 10 from oxygen flowing to the air side electrode of an adjacent fuel cell 1 in the stack. At either end of stack 100, there may be an air end plate or fuel end plate (not shown).

[0025] Each interconnect 10 may be made of or may contain electrically conductive material, such as a metal alloy (e.g., chromium-iron alloy or a stainless steel containing a high amount of chromium) which has a similar coefficient of thermal expansion to that of the solid oxide electrolyte in the cells (e.g., a difference of 0- 10%). For example, the interconnects 10 may comprise a metal (e.g., a chromium- iron alloy, such as 4-6 weight percent iron (e.g., 5 wt.% iron), optionally 1 or less weight percent yttrium and balance chromium alloy) and may electrically connect the fuel side electrode 7 of one cell 1 to the air side electrode 3 of an adjacent cell 1.

[0026] FIG.2A is a top view of the air side of an interconnect 10, and FIG.2B is a top view of the fuel side of interconnect 10 according to various embodiments of the present invention. Referring to FIGS.1B and 2A, the air side includes the air channels 8B that extend from opposing first and second edges of the interconnect 10. Oxygen flows through the air channels 8B along the surface of the air side electrode 3 of an adjacent cell 1. Ring seals 20 may surround fuel holes 22A, 22B of the interconnect 10, to prevent water / steam or fuel from contacting the air side electrode 3. Strip-shaped peripheral seals 24 are located on peripheral portions of the air side of the interconnect 10. The seals 20, 24 may be formed of a glass or glass-ceramic material. The peripheral portions may be an elevated plateau which does not includeAttorney Docket No.: 7917-0789WO ribs or channels. The surface of the peripheral regions may be coplanar with tops of the ribs 12B.

[0027] Referring to FIGS.1B and 2B, the fuel side of interconnect 10 may include fuel channels 8A and fuel manifolds 28. Water / steam (or fuel) flows from one of the fuel holes 22A (e.g., inlet fuel hole that forms part of the fuel inlet riser), into the adjacent manifold 28, through the fuel channels 8A, and along the surface of a fuel side electrode 7 of an adjacent cell 1. Excess or unreacted water / steam (or fuel) may flow into the other fuel manifold 28 and then into the outlet fuel hole 22B. A frame 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 12A.

[0028] FIG.3A is a plan view of the air side of the SOFC or SOEC 1, and FIG.3B is a plan view of the fuel side of the cell 1 according to various embodiments of the present invention. Referring to FIGS.1A, 2A, 3A, and 3B, the cell 1 may include an inlet fuel hole 22A, an outlet fuel hole 22B, the electrolyte 5, and the air side electrode 3. The air side electrode 3 may be disposed on the air side of the electrolyte 5. The fuel side electrode 7 may be disposed on an opposing fuel (e.g., water) side of the electrolyte 5.

[0029] The fuel holes 22A, 22B may extend through the electrolyte 5 and may be arranged to overlap with the fuel holes 22A, 22B of the interconnects 10, when assembled in the SOFC or SOEC stack 100. The air side electrode 3 may be printed on the electrolyte 5 so as not to overlap with the ring seals 20 and the peripheral seals 24 when assembled in the stack 100. The fuel side electrode 7 may have a similar shape as the air side electrode 3. The fuel side electrode 7 may be disposed so as not to overlap with the frame seal 26, when assembled in the stack 100. In other words, the electrodes 3 and 7 may be recessed from the edges of the electrolyte 5, such that corresponding edge regions of the electrolyte 5 may directly contact the corresponding seals 20, 24, 26.Attorney Docket No.: 7917-0789WO

[0030] In one embodiment, electrochemical cell stack 100 may only be operated in the electrolysis mode. Thus, the electrochemical cell stack 100 comprises an electrolyzer cell stack that is not operated in a fuel cell mode to generate power from fuel and air provided to fuel side and air side electrodes, respectively. Alternatively, the electrochemical cell stack 100 may comprise a solid oxide regenerative (i.e., reversible) fuel cell (SORFC) stack. SORFCs can be operated in a fuel cell (FC) mode (e.g., power generation mode) in order to generate electricity from fuel and air provided to fuel side and air side electrodes, respectively, and may be operated in an electrolyzer cell (EC) mode (e.g., electrolysis mode) in order to produce hydrogen and oxygen from water / steam provided to the fuel side electrode 7. In the FC mode, oxygen ions are transported from the air side (e.g., cathode) electrode 3 to the fuel side (e.g., anode) electrode 7 of the SORFC to oxidize the fuel (e.g., hydrogen and / or hydrocarbon fuel, such as natural gas) and to generate electricity. In EC mode, a positive potential is applied to the air side of the cell, and oxygen ions are transported from the water / steam at the fuel side electrode 7 through the electrolyte 5 to the air side electrode 3. Thus, water is electrolyzed into hydrogen at the fuel side electrode 7 and oxygen at air side electrode 3.

[0031] The air side electrode 3 and the fuel side electrode 7 of a SORFC respectively operate as a cathode and an anode during FC mode, and respectively operate as an anode and a cathode during EC mode (i.e., a FC mode cathode is an EC mode anode, and a FC mode anode is an EC mode cathode). Accordingly, the SORFCs described herein may be referred to as having air side electrodes and fuel side electrodes.

[0032] During the EC mode, water / steam in the fuel stream is reduced (H2O + 2e- ^O2-+ H2) to form H2gas and O2-ions, the O2-ions are transported through the solid electrolyte, and then oxidized on the air side electrode (O2-oxidized to O2) to produce molecular oxygen. Since the open circuit voltage for a SORFC operating with air and wet fuel (e.g., hydrogen and / or reformed natural gas) may be from about 0.9 to 1.0V (depending on water content), the positive voltage applied to the air side electrode inAttorney Docket No.: 7917-0789WO EC mode increases the cell voltage to typical operating voltages from about 1.1 to 1.5V.

[0033] FIG.4 is a cross-sectional view of an electrochemical cell stack portion 400 including an electrochemical cell 402 according to various embodiments of the present invention. The electrochemical cell 402 may comprise a SOEC, a SORFC or a SOFC. While the stack portion 400 is described in the embodiments below as an electrolyzer cell stack, it should be noted that it may be a fuel cell stack or a reversible fuel cell stack instead. While the electrochemical cell 402 is described in the embodiments below as an electrolyzer cell, it should be noted that it may be a fuel cell (e.g., SOFC) or a reversible fuel cell (e.g., SORFC) instead.

[0034] Referring to FIG.4, the electrolyzer cell stack portion 400 includes a SOEC 402 disposed between two interconnects 10. The SOEC 402 may operate only in the electrolysis mode or may operate in both fuel cell and electrolysis modes (e.g., the SOEC 402 may comprise a SORFC). The SOEC 402 includes a solid oxide electrolyte 5, an air side electrode 3 disposed on an air side of the electrolyte 5, and a fuel side electrode 7 disposed on a fuel side of the electrolyte 5. Air may be provided to the air side electrode 3 by air channels 8B in the interconnect 10, and water / steam may be provided to the fuel side electrode 7 by fuel channels 8A in the interconnect 10 while operating in the electrolysis mode.

[0035] The air side electrode 3, electrolyte 5, and fuel side electrode 7 may be formed of various materials. For example, as discussed in detail below, the electrolyte may be formed of a ceria-free stabilized zirconia material.

[0036] The fuel side electrode 7 may comprise a cermet layer comprising a metal- containing phase and a ceramic phase. The metal-containing phase may include a metal catalyst, such as nickel (Ni), cobalt (Co), copper (Cu), alloys thereof, or the like, 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 whenAttorney Docket No.: 7917-0789WO it is in an oxidized state. Thus, the fuel side electrode 7 may be annealed in a reducing atmosphere prior to operation of the electrolyzer cell 1, to reduce the oxidized metal catalyst to a metallic state. In one embodiment, the metal-containing phase may be comprised entirely of nickel in a reduced state. This nickel-containing phase may form nickel oxide when it is in an oxidized state. Thus, the fuel side electrode 7 is preferably annealed in a reducing atmosphere prior to operation to reduce the nickel oxide to nickel.

[0037] The ceramic phase of the fuel side electrode 7 may include but is not limited to gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), ytterbia-doped ceria (YDC), ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ), or the like. In the case of 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 (e.g., at least 0.5 mol %) and equal to or less than 2.5 mol %, such as 1 mol %, and at least one of yttria and ytterbia may be present in an amount greater than 0 and equal to or less than 2.5 mol %, such as 1 mol %.

[0038] Alternatively, the ceramic phase of the fuel side electrode 7 may include a ceria-free phase, such as a stabilized zirconia phase. The ceria-free stabilized zirconia phase may comprise scandia-stabilized zirconia (SSZ) containing 9 to 11 atomic percent scandia, or SSZ which also includes bismuth oxide and / or one or more rare earth oxides such as Gd2O3, Pr2O3, Sm2O3, Y2O3, or Yb2O3. The ceria-free stabilized zirconia phase may have the following formula: (ZrO2)1-a-x(Sc2O3)a(MO)x, where 0.09 ≤ a ≤ 0.11, 0 ≤ x ≤0.025, such as 0.001 ≤ x ≤0.025; and MO representsGd2O3, Pr2O3, Sm2O3, Y2O3, or Yb2O3.

[0039] The fuel side electrode 7 may include from about 10 wt.% to about 90 wt.%, such as about 40 wt.% to about 60 wt.%, of the metal-containing phase described above, and from about 10 wt.% to about 90 wt.%, such as about 40 wt.% to about 60 wt.%, of the ceramic phase.Attorney Docket No.: 7917-0789WO

[0040] Furthermore, if desired, an additional contact or current collector layer may be placed over the fuel side electrodes 7. For example, a Ni or nickel oxide contact layer may be formed on the fuel side electrode 7.

[0041] The air side electrode 3 may include an optional barrier layer 30 located directly on an air side of the electrolyte 5, a functional layer 32 located on the barrier layer 30 (or directly on the air side of the electrolyte 5 if the barrier layer 30 is omitted), and a current collector layer 34 disposed on the functional layer 32. Thus, the functional layer 32 is located between the electrolyte 5 (or the barrier layer 30 if present) and the current collector layer 34.

[0042] The barrier layer 30 may be sintered to the air side of the electrolyte 5. The barrier layer 30 may be comprised of a single-phase ionic or majority-ionic conductor, and functions in part to prevent electrochemical delamination. The barrier layer 30 may comprise a doped ceria material. For example, the barrier layer may comprise from about 95 weight percent (wt.%) to about 100 wt.% of the doped ceria material, based on the total weight of the barrier layer 30. The doped ceria material may include samaria-doped ceria (SDC), gadolinia-doped ceria (GDC) and / or lanthana doped ceria (LDC).

[0043] The SDC portion may be represented by the formula: Ce1-xSmxO2-d, where x ranges from 0.05 to 0.4. For example, specific SDC materials may be represented by the formulas: Ce0.8Sm0.2O2-d, Ce0.9Sm0.1O2-d, and Ce0.7Sm0.3O2-d, where d ranges from 0 to 0.2, such as from 0 to 0.1.

[0044] The GDC portion may be represented by the formula Ce1-xGdxO2-d, where x ranges from 0.05 to 0.3 and d ranges from 0 to 0.2, such as from 0 to 0.1. For example, specific GDC materials may be represented by the formulas: Ce0.9Gd0.1O2-d, Ce0.8Gd0.2O2-d, and Ce0.7Gd0.3O2-d, where d ranges from 0 to 0.2, such as from 0 to 0.1. The LDC portion may be represented by the formula Ce1-xLaxO2-d, where x ranges from 0.05 to 0.6 and d ranges from 0 to 0.2, such as from 0 to 0.1.Attorney Docket No.: 7917-0789WO

[0045] The functional layer 32 may be comprised of a single-phase mixed-ionic electronic conductor (MIEC), a composite of a MIEC with a majority-ionic conductor, or a composite of a majority-ionic conductor with a majority-electronic conductor, the function of which is, in part, to facilitate an oxygen evolution reaction. The functional layer 32 may include a mixture of an electrically conductive perovskite metal oxide material and doped ceria material. The electrically conductive material may comprise an electrically conductive strontium containing perovskite material, such as 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., La0.85Sr0.15Co0.9Ni0.1O3), combinations thereof, or the like. In some embodiments, the electrically conductive material may preferably comprise LSM and / or LSCF. For example, the functional layer 32 may include from about 10 wt.% to about 90 wt.%, such as about 40 wt.% to about 60 wt.%, of the electrically conductive material described above, and from about 10 wt.% to about 90 wt.%, such as about 40 wt.% to about 60 wt.%, of the doped ceria material.

[0046] In various embodiments, the functional layer 32 may include the LSM as theelectrically conductive material. The LSM may be represented by the formula: (La1-zSrz)qMnO3-d, wherein z ranges from 0.1 to 0.4, q ranges from 0.94 to 1, such as 0.96 to 1, and d is the equilibrium oxygen deficiency which ranges from 0 to 0.2. For example, the LSM may comprise La0.8Sr0.2MnO3-dor A-site deficient LSM, such as (La0.8Sr0.2)0.98MnO3-d, wherein d ranges from 0 to 0.1.

[0047] In some embodiments, the functional layer 32 may include the LSCF as the electrically conductive material. The LSCF may be represented by the formula: (LaxSr1-x)yCozFe1-zO3-δ, wherein x ranges from 0.4 to 0.8, y ranges from 0.94 to 1.0, z ranges from 0.01 to 0.99, and δ is the equilibrium oxygen deficiency which ranges from 0 to 0.1. For example, the LSCF may comprise La0.58Sr0.4Co0.2Fe0.8O3-δ,Attorney Docket No.: 7917-0789WO (La0.6Sr0.4)0.98Co0.2Fe0.8O3-δ, or (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ, where δ is the equilibrium oxygen deficiency.

[0048] The barrier layer 30 and the functional layer 32 may include the same doped ceria material or different doped ceria materials. For example, the barrier layer 30 may include GDC and the functional layer 32 may include LSM and GDC, or LSM and SDC. In other embodiments, the barrier layer 30 may include SDC and the functional layer 32 may include LSM and SDC, or LSM and GDC. In other embodiments, the barrier layer may include SDC and the functional layer may include LSCF and SDC, or LSCF and GDC.

[0049] The current collector layer 34 may be comprised of a metal or metal oxide electronic conductor, a single phase MIEC, or composites of MIEC, majority- electronic conductors, and / or majority-ionic conductors; the function of which is, in part, to transport electronic charge and maintain electrical contact with the interconnect 10. The current collector layer 34 may include an electrically conductive material, such as an electrically conductive perovskite, such as LSM. However, other electrically conductive perovskites, such as LSC, LSCM, LSCF, LSF, LSCN, etc., or metals, such as Pt, may also be used.

[0050] In one embodiment, the solid oxide electrochemical cell 402 comprises an anode supported solid oxide electrochemical cell in which the fuel side electrode 7 is thicker than the electrolyte 5 and the air side electrode 3. In another embodiment, the solid oxide electrochemical cell 402 comprises an electrolyte supported cell in which the electrolyte 5 is thicker than the fuel side electrode 7 and the air side electrode 3. Electrolyte Materials

[0051] In various embodiments, the solid oxide electrolyte 5 may include an ionically conductive electrolyte material or phase, such as a stabilized zirconia electrolyte material, and in particular zirconia materials that are stabilized with (e.g., doped with)Attorney Docket No.: 7917-0789WO scandium(III) oxide (Sc2O3) (i.e., scandia) and at least one additional metal oxide dopant, such as a rare earth oxide dopant.

[0052] Prior stabilized zirconia electrolyte materials utilized cerium (IV) oxide (CeO2) (i.e., ceria) as a stabilizing dopant. For example, prior electrolyte materials include scandia-ceria-stabilized zirconia (SCSZ), scandia-ceria-yttria-stabilized zirconia (SCYSZ), and scandia-ceria-ytterbia-stabilized zirconia (SCYbSZ).

[0053] However, the present inventors discovered that the exposure of such electrolytes to relatively low oxygen partial pressures, such as oxygen partial pressures typically occurring during SOEC operation, may result in the reduction of the cerium (i.e., Ce4+→ Ce3+) present in the electrolyte. In particular, cerium (IV) oxide may be reduced to cerium (III) oxide according to the following reaction 2CeO2→ Ce2O3+ 0.5O2. The reduction of ceria may result in an undesirable electrolyte volume increase, which may result in mechanical damage and negatively affect device properties.

[0054] Accordingly, in various embodiments, the electrolyte 5 may be formed of various ceria-free stabilized zirconia materials. For example, the electrolyte 5 may comprise a ceramic electrolyte material formed of zirconia stabilized with (e.g., dopedwith) scandium (III) oxide (Sc2O3) (i.e., scandia) and at least one additional dopant.The electrolyte 5 may be free of ceria (e.g., contain less than about 0.1 atomic % ceria, such as less than about 0.01 atomic percent ceria, or less than about 0.001 atomic % ceria, including zero atomic % ceria).

[0055] In some embodiments, the electrolyte material may have an atomic percentage (at.%) of scandia that is greater than an atomic % of the additional dopant(s) included therein. For example, the atomic % of scandia may be greater than a total atomic % of all the included additional dopants.

[0056] In some embodiments, the additional dopants may include rare earth oxides such as gadolinium (III) oxide (Gd2O3) (i.e., gadolinia), neodymium (III) oxideAttorney Docket No.: 7917-0789WO (Nd2O3) praseodymium (III) oxide (Pr2O3), praseodymium (III,IV) oxide (Pr6O11), samarium(III) oxide (Sm2O3) (i.e., samaria), yttrium (III) oxide (Y2O3) (i.e., yttria), and / or ytterbium (III) oxide (Yb2O3) (i.e., ytterbia). In some embodiments, the secondary dopants may also include other metal oxides, such as bismuth (III) oxide (Bi2O3), indium (III) oxide (In2O3), and / or gallium (III) oxide (Ga2O3).

[0057] In some embodiments, the electrolyte material may be dual doped scandia- stabilized zirconia material represented by the formula: (ZrO2)1-a-x(Sc2O3)a(MO)x, wherein: 0.09 ≤ a ≤ 0.11; 0.001 ≤ x ≤0.025; and MO represents Bi2O3, Gd2O3, Pr2O3, Pr6O11, Sm2O3, Y2O3, or Yb2O3. In one embodiment, 0.003 ≤ x ≤0.015.

[0058] For example, various embodiments provide dual doped scandia-stabilized zirconia materials represented by the formulas: (ZrO2)1-a-x(Sc2O3)a(Bi2O3)x; (ZrO2)1-a-x(Sc2O3)a(Gd2O3)x; (ZrO2)1-a-x(Sc2O3)a(Pr2O3)x; (ZrO2)1-a-x(Sc2O3)a(Pr6O11)x; (ZrO2)1-a-x(Sc2O3)a(Sm2O3)x; (ZrO2)1-a-x(Sc2O3)a(Y2O3)x; or (ZrO2)1-a-x(Sc2O3)a(Yb2O3)x,wherein 0.09 ≤ a ≤ 0.11 and 0.001 ≤ x ≤0.025. In one embodiment, 0.003 ≤ x ≤0.015.

[0059] Specific examples of dual doped scandia-stabilized zirconia materials may include: (ZrO2)0.89(Sc2O3)0.1(Gd2O3)0.01; (ZrO2)0.885(Sc2O3)0.1(Gd2O3)0.015;Attorney Docket No.: 7917-0789WO (ZrO2)0.885(Sc2O3)0.1(Pr2O3)0.015; (ZrO2)0.897(Sc2O3)0.1(Pr6O11)0.003; (ZrO2)0.89(Sc2O3)0.1(Sm2O3)0.01; (ZrO2)0.8875(Sc2O3)0.1(Y2O3)0.0125; (ZrO2)0.887(Sc2O3)0.1(Y2O3)0.013; and (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.015.

[0060] In some embodiments, the electrolyte material is a tri-doped scandia-yttria- stabilized zirconia represented by the formula: (ZrO2)1-a-x(Sc2O3)a(Y2O3)x(MO)y, wherein: 0.09 ≤ a ≤ 0.11; 0.001 ≤ x ≤0.025; 0.001 ≤ y ≤ 0.02; and MO represents Ga2O3, Gd2O3, In2O3, Sm2O3, Pr2O3, Pr6O11,or Yb2O3. In one embodiment, 0.003 ≤ x ≤0.015 and 0.003 ≤ y ≤0.015. In one embodiment, 0.003 ≤ x ≤0.01 and 0.003 ≤ y ≤0.01.

[0061] For example, various embodiments provide tri-doped scandia-yttria-stabilized zirconia materials represented by the formulas: (ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(Ga2O3)y; (ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(Gd2O3)y; (ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(In2O3)y; (ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(Pr2O3)y;(ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(Pr6O11)y; and (ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(Yb2O3)y,Attorney Docket No.: 7917-0789WO wherein 0.09 ≤ a ≤ 0.11, 0.005 ≤ x ≤ 0.025, and 0.001 ≤ y ≤ 0.02. In one embodiment, 0.003 ≤ x ≤0.015 and 0.003 ≤ y ≤0.015. In one embodiment, 0.003 ≤ x ≤0.01 and 0.003 ≤ y ≤0.01.

[0062] In one embodiment, the tri-doped scandia-yttria-ytterbia stabilized zirconia materials may be represented by the formula (ZrO2)1-a-x-y(Sc2O3)a(Y2O3)x(Yb2O3)y, wherein 0.09 ≤ a ≤ 0.11, 0.005 ≤ x ≤ 0.015, and 0.005 ≤ y ≤ 0.015.

[0063] Specific examples of tri-doped scandia-yttria-stabilized zirconia materials may include: (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Gd2O3)0.005; (ZrO2)0.886(Sc2O3)0.1(Y2O3)0.007(Gd2O3)0.007; (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.008(Gd2O3)0.007; (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Sm2O3)0.005; (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Pr2O3)0.005; and (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Yb2O3)0.005.

[0064] Various embodiments provide tri-doped scandia-ytterbia-stabilized zirconia electrolyte materials represented by the formulas: (ZrO2)1-a-x-y(Sc2O3)a(Yb2O3)x(Ga2O3)y; (ZrO2)1-a-x-y(Sc2O3)a(Yb2O3)x(Gd2O3)y;(ZrO2)1-a-x-y(Sc2O3)a(Yb2O3)x(In2O3)y; and (ZrO2)1-a-x-y(Sc2O3)a(Yb2O3)x(Pr2O3)y, wherein 0.09 ≤ a ≤ 0.11, 0.005 ≤ x ≤ 0.025, and 0.001 ≤ y ≤ 0.02. In one embodiment, 0.003 ≤ x ≤0.015 and 0.003 ≤ y ≤0.015. In one embodiment, 0.003 ≤ x ≤0.01 and 0.003 ≤ y ≤0.01.Attorney Docket No.: 7917-0789WO

[0065] Various embodiments provide other tri-doped scandia-stabilized zirconia electrolyte materials represented by the formulas: (ZrO2)1-a-x-y(Sc2O3)a(Gd2O3)x(Sm2O3)y; (ZrO2)1-a-x-y(Sc2O3)a(Gd2O3)x(Y2O3)y; and (ZrO2)1-a-x-y(Sc2O3)a(Nd2O3)x(Sm2O3)y, wherein 0.09 ≤ a ≤ 0.11, 0.005 ≤ x ≤ 0.025, and 0.001 ≤ y ≤ 0.02. In one embodiment, 0.003 ≤ x ≤0.015 and 0.003 ≤ y ≤0.015. In one embodiment, 0.003 ≤ x ≤0.01 and 0.003 ≤ y ≤0.01.

[0066] Specific examples of tri-doped scandia-stabilized zirconia materials may include: (ZrO2)0.885(Sc2O3)0.1(Gd2O3)0.008(Sm2O3)0.007; (ZrO2)0.886(Sc2O3)0.1(Nd2O3)0.007(Sm2O3)0.007; and (ZrO2)0.884(Sc2O3)0.1(Gd2O3)0.009(Y2O3)0.007.

[0067] Various embodiments provide quad-doped scandia-stabilized zirconia electrolyte materials represented by the formulas: (ZrO2)1-a-x-y-z(Sc2O3)a(Y2O3)x(Gd2O3)y(Pr2O3)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Y2O3)x(Gd2O3)y(Pr6O11)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Y2O3)x(Gd2O3)y(Sm2O3)z;(ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Gd2O3)y(Pr2O3)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Gd2O3)y(Y2O3)z; and (ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Pr2O3)y(Y2O3)z,Attorney Docket No.: 7917-0789WO wherein 0.09 ≤ a ≤ 0.11, 0.003 ≤ x ≤ 0.025, 0.003 ≤ y ≤ 0.025, and 0.003 ≤ z ≤ 0.025. In one embodiment, 0.003 ≤ x ≤0.015, 0.003 ≤ y ≤0.015 and 0.003 ≤ z ≤0.015. In one embodiment, 0.003 ≤ x ≤0.01, 0.003 ≤ y ≤0.01 and 0.003 ≤ z ≤0.01.

[0068] Specific examples of quad-doped scandia-stabilized zirconia materials may include: (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.005(Gd2O3)0.005(Pr2O3)0.005; (ZrO2)0.887(Sc2O3)0.1(Y2O3)0.005(Gd2O3)0.005(Pr6O11)0.003; and (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.005(Gd2O3)0.005(Sm2O3)0.005.

[0069] Various embodiments provide penta-doped scandia-stabilized zirconia materials represented by the formulas: (ZrO2)1-a-x-y-z-w(Sc2O3)a(Yb2O3)x(Gd2O3)y(Y2O3)z(Pr2O3)w, or (ZrO2)1-a-x-y-z-w(Sc2O3)a(Yb2O3)x(Gd2O3)y(Y2O3)z(Pr6O11)w, wherein 0.09 ≤ a ≤ 0.11, 0.001 ≤ x ≤ 0.025, 0.001 ≤ y ≤ 0.025, 0.001 ≤ z ≤ 0.025, and 0.001 ≤ w ≤ 0.025.

[0070] Accordingly, in various embodiments the electrolyte 5 may be formed of various dual doped, tri-doped, quad-doped, or penta-doped scandia-stabilized zirconia materials that are free of ceria, in order to prevent cerium reduction when exposed to low oxygen partial pressure environments.

[0071] In another embodiment, the fuel electrode 7 also comprises a cermet containing a metal phase, such as Ni, and the ceria-free stabilized zirconia phase described above. Since the fuel electrode 7 may experience a volume expansion in a reducing atmosphere, forming the fuel electrode 7 from a ceria-free cermet can prevent cerium reduction in the fuel electrode 7 as well as in the electrolyte 5. The air electrode 3 is believed to remain stable during cell operation, and thus may include ceria.

[0072] It will be apparent to those skilled in the art that various modifications and variations can be made in the electrolytes of the present disclosure without departing from the spirit or scope of the invention. Similarly, those skilled in the art willAttorney Docket No.: 7917-0789WO recognize that other types of interconnects may be utilized with SOFCs and SOECs incorporating the inventive aspects of the present disclosure. For instance, the electrolytes of the embodiments of the present disclosure can be used with interconnects and SOEC and SOFC stacks configured like those disclosed in United States Patent Nos.11,355,762, 11,705,557, and 11,870,121, all of which are incorporated herein by reference in their entirety. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

Attorney Docket No.: 7917-0789WO What is claimed is:

1. A solid oxide electrochemical cell, comprising: a fuel side electrode; an air side electrode; and an electrolyte disposed between the fuel side electrode and the air side electrode, the electrolyte comprising an electrolyte material formed of zirconia doped with Sc2O3and at least one additional dopant, wherein: the solid oxide electrochemical cell comprises an anode supported solid oxide electrochemical cell in which the fuel side electrode is thicker than the electrolyte and the air side electrode, or the solid oxide electrochemical cell comprises an electrolyte supported cell in which the electrolyte is thicker than the fuel side electrode and the air side electrode; the at least one additional dopant comprises at least one of gadolinium oxide, neodymium oxide, praseodymium oxide, or samarium oxide; and the electrolyte material comprises less than 0.1 atomic % of CeO2.

2. The electrochemical cell of claim 1, wherein the electrolyte material is represented by the following formula: (ZrO2)1-a-x(Sc2O3)a(MO)x, wherein: 0.09 ≤ a ≤ 0.11; 0.001 ≤ x ≤0.025; and MO represents the gadolinium oxide, neodymium oxide, praseodymium oxide, or samarium oxide.

3. The electrochemical cell of claim 1, wherein the electrolyte material is represented by one of the following formulas: (ZrO2)0.89(Sc2O3)0.1(Gd2O3)0.01; (ZrO2)0.885(Sc2O3)0.1(Gd2O3)0.015;Attorney Docket No.: 7917-0789WO (ZrO2)0.886(Sc2O3)0.1(Nd2O3)0.007(Gd2O3)0.007; (ZrO2)0.885(Sc2O3)0.1(Pr2O3)0.015; (ZrO2)0.89(Sc2O3)0.1(Sm2O3)0.01; or (ZrO2)0.897(Sc2O3)0.1(Pr6O11)0.

003.

4. The electrochemical cell of claim 1, wherein the electrolyte material is represented by the following formula: (ZrO2)1-a-x(Sc2O3)a(Y2O3)x(MO)y, wherein: 0.09 ≤ a ≤ 0.11; 0.001 ≤ x ≤0.025; 0.001 ≤ y ≤ 0.02; and MO represents the gadolinium oxide, neodymium oxide, praseodymium oxide, or samarium oxide.

5. The electrochemical cell of claim 1, wherein the electrolyte material is represented by one of the following formulas: (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Gd2O3)0.005;(ZrO2)0.886(Sc2O3)0.1(Y2O3)0.007(Gd2O3)0.007; (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.008(Gd2O3)0.007; (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Sm2O3)0.005; or (ZrO2)0.888(Sc2O3)0.1(Y2O3)0.007(Pr2O3)0.

005.

6. The electrochemical cell of claim 1, wherein the electrolyte material is represented by one of the following formulas: (ZrO2)1-a-x-y(Sc2O3)a(Gd2O3)x(Sm2O3)y; (ZrO2)1-a-x-y(Sc2O3)a(Gd2O3)x(Y2O3)y; or (ZrO2)1-a-x-y(Sc2O3)a(Nd2O3)x(Sm2O3)y,Attorney Docket No.: 7917-0789WO wherein: 0.09 ≤ a ≤ 0.11; 0.001 ≤ x ≤0.025; and 0.001 ≤ y ≤ 0.

02.

7. The electrochemical cell of claim 1, wherein the electrolyte material is represented by one of the following formulas: (ZrO2)0.885(Sc2O3)0.1(Gd2O3)0.008(Sm2O3)0.007; (ZrO2)0.884(Sc2O3)0.1(Gd2O3)0.009(Y2O3)0.007; or (ZrO2)0.886(Sc2O3)0.1(Nd2O3)0.007(Sm2O3)0.

007.

8. The electrochemical cell of claim 1, wherein the electrolyte material is represented by one of the following formulas: (ZrO2)1-a-x-y-z(Sc2O3)a(Y2O3)x(Gd2O3)y(Pr2O3)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Y2O3)x(Gd2O3)y(Pr6O11)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Y2O3)x(Gd2O3)y(Sm2O3)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Gd2O3)y(Pr2O3)z; (ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Gd2O3)y(Pr6O11)z;(ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Gd2O3)y(Y2O3)z; or (ZrO2)1-a-x-y-z(Sc2O3)a(Yb2O3)x(Pr2O3)y(Y2O3)z, wherein: 0.09 ≤ a ≤ 0.11; 0.003 ≤ x ≤ 0.025; 0.003 ≤ y ≤ 0.025; and 0.003 ≤ z ≤ 0.025.Attorney Docket No.: 7917-0789WO 9. The electrochemical cell of claim 1, wherein the electrolyte material is represented by one of the following formulas: (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.005(Gd2O3)0.005(Pr2O3)0.005; (ZrO2)0.887(Sc2O3)0.1(Y2O3)0.005(Gd2O3)0.005(Pr6O11)0.003; or (ZrO2)0.885(Sc2O3)0.1(Y2O3)0.005(Gd2O3)0.005(Sm2O3)0.

005.

10. The electrochemical cell of claim 1, wherein the electrolyte material is represented by the following formulas: (ZrO2)1-a-x-y-z-w(Sc2O3)a(Yb2O3)x(Gd2O3)y(Y2O3)z(Pr2O3)w; or (ZrO2)1-a-x-y-z-w(Sc2O3)a(Yb2O3)x(Gd2O3)y(Y2O3)z(Pr6O11)w, wherein: 0.09 ≤ a ≤ 0.11; 0.001 ≤ x ≤ 0.025; 0.001 ≤ y ≤ 0.025; 0.001 ≤ z ≤ 0.025; and 0.001 ≤ w ≤ 0.

025.

11. The electrochemical cell of claim 1, wherein the electrochemical cell is a solid oxide electrolyzer cell.

12. The electrochemical cell of claim 1, wherein the electrochemical cell is a solid oxide fuel cell.

13. The electrochemical cell of claim 1, wherein the fuel side electrode comprises a cermet layer comprising a metal-containing phase and a ceramic phase.

14. The electrochemical cell of claim 13, wherein the metal-containing phase comprises nickel, and the ceramic phase comprises a ceria-free stabilized zirconia.Attorney Docket No.: 7917-0789WO 15. The electrochemical cell of claim 14, wherein the metal-containing phase comprises nickel, and the ceramic phase comprises a doped ceria.

16. The electrochemical cell of claim 1, wherein the air side electrode comprises: a barrier layer disposed on the electrolyte; a functional layer disposed on the barrier layer; and a current collector layer disposed on the functional layer.

17. An electrochemical cell stack, comprising: stacked interconnects; and electrochemical cells of claim 1 disposed between pairs of the interconnects.

18. A solid oxide electrochemical cell, comprising: a fuel side electrode; an air side electrode; and an electrolyte disposed between the fuel side electrode and the air side electrode, the electrolyte comprising an electrolyte material formed of zirconia dopedwith Sc2O3 and Pr6O11.

19. The electrochemical cell of claim 18, wherein the electrolyte material is represented by the following formula: (ZrO2)1-a-x(Sc2O3)a(Pr6O11), wherein: 0.09 ≤ a ≤ 0.11; and 0.001 ≤ x ≤0.

005.

20. A method of operating a solid oxide electrolyzer cell comprising a fuel side electrode, an air side electrode, and an electrolyte disposed between the fuel side electrode and the air side electrode, the method comprising:Attorney Docket No.: 7917-0789WO providing steam to the fuel side electrode; providing air to the air side electrode; and applying a voltage between the fuel side electrode and the air side electrode to separate the steam into hydrogen and oxygen ions, and to transport the oxygen ions from the fuel side electrode to the air side electrode through the electrolyte; wherein: the electrolyte comprises an electrolyte material formed of zirconia doped with Sc2O3and at least one additional dopant; the at least one additional dopant comprises at least one of yttrium oxide, ytterbium oxide, gadolinium oxide, neodymium oxide, praseodymium oxide, or samarium oxide; and the electrolyte material comprises less than 0.1 atomic % of CeO2.

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