Doped scandia stabilized zirconia electrolyte compositions

Information

  • Patent Grant
  • 10381673
  • Patent Number
    10,381,673
  • Date Filed
    Tuesday, November 1, 2016
    8 years ago
  • Date Issued
    Tuesday, August 13, 2019
    5 years ago
Abstract
A solid oxide fuel cell (SOFC) electrolyte composition includes zirconia stabilized with scandia, and at least one of magnesia, zinc oxide, indium oxide, and gallium oxide, and optionally ceria in addition to the oxides above.
Description
FIELD

The present invention is generally directed to fuel cell components, and to solid oxide fuel cell electrolyte materials in particular.


BACKGROUND OF THE INVENTION

Fuel cells are electrochemical devices which can convert chemical energy stored in fuels to electrical energy with high efficiencies. They comprise an electrolyte between electrodes. Solid oxide fuel cells (SOFCs) are characterized by the use of a solid oxide as the electrolyte.


In 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 650° 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.


In recent years considerable interest has been shown towards the development of SOFC electrolyte compositions of high ionic conductivity. Doped cerium oxide, lanthanum gallate and zirconium oxide are the most suitable candidates. However, in order to achieve sufficient ionic conductivity high operation temperature is often required, deteriorating the life of the fuel cell components and requiring the use of expensive materials in the fuel cell stack, such as chromium alloy interconnects. Therefore, it is highly desirable to lower the operation temperature of SOFCs and one important step to achieve this is the development of an electrolyte composition with higher ionic conductivity than yttria-stabilized zirconia (YSZ), the state of the art SOFC electrolyte material.


Doping zirconia with aliovalent dopants stabilizes the high temperature cubic fluorite phase at room temperature leading to an increase in oxygen vacancy concentration, oxygen mobility and ionic conductivity. Complex studies have demonstrated a correlation between the dopant and host ionic radii and the existence of a critical dopant cation radius that can ensure maximum conductivity. It has been suggested that a good evaluation of the relative ion mismatch between dopant and host would be to compare the cubic lattice parameter of the host oxide and the pseudocubic lattice parameter of the dopant oxide, a smaller size mismatch being preferred for obtaining high ionic conductivity.


Numerous attempts to find the appropriate dopant for stabilizing the cubic phase have been made (Y, Yb, Ce, Bi, etc). Among these, scandia stabilized zirconia shows the highest ionic conductivity with Sc3+ concentration of 11 mole % (2-3 higher than YSZ at 800° C.) due to a lower activation energy than YSZ. The complex phase diagram in the Sc2O3—ZrO2 system is still under debate, with several phases identified in the dopant rich segment of the phase diagram, as monoclinic, tetragonal and rhombohedral intermediate phases appear at low temperatures. One example is the distorted rhombohedral β phase (Sc2Zr7O17), that undergoes a rhombohedral-cubic phase transition around 600-700° C. and induces a steep decrease in conductivity in this temperature region. This transition is not favorable from the point of view of thermal expansion mismatch and may be related to order-disorder transition of oxygen vacancies.


Co-doping in zirconia systems may produce cheaper, stable compositions with enhanced ionic conductivity. Co-dopants in the scandia zirconia system include Ce, Y, Yb and Ti, the former (1 mole % CeO2) being the most successful to date in stabilizing the cubic phase at room temperature and very high conductivity values have been measured by Lee et al, 135 mS/cm at 800° C. in air (SSI 176 (1-2) 33-3 (2005)). However, concerns about long term stability, especially at the interface with the fuel electrode, due to Ce3+ presence, have been reported.


In general, CaO or MgO are used for improving the toughness of zirconia ceramics by stabilizing the tetragonal phase at room temperature.


However, previous studies for doping zirconia with alkaline earth metal cations alone have been unsuccessful in improving the conductivity because of a high tendency of defect association and a lower thermodynamic stability of cubic fluorite ZrO2—CaO and ZrO2—MgO solid solutions.


SUMMARY OF THE INVENTION

A solid oxide fuel cell (SOFC) electrolyte composition includes zirconia stabilized with scandia, and at least one of magnesia, zinc oxide, indium oxide, and gallium oxide, and optionally ceria.


Another embodiment of the invention provides an electrolyte composition for a solid oxide fuel cell that includes zirconia stabilized with scandia and indium oxide, in which scandia and indium oxide are present in total amount that is greater than or equal to 10 mol % and less than or equal to 13 mol %. Another embodiment of the invention provides zirconia stabilized with scandia, indium oxide, and ceria, in which scandia, indium oxide, and ceria are present in a total amount that is greater than or equal to 8 mol % and less than or equal to 14 mol %, such as 11 mol %.





BRIEF DESCRIPTION OF THE DRAWINGS


FIGS. 1A-1D are ternary phase diagrams illustrating embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIGS. 2A-2D are plots showing x-ray diffraction patterns for compositions in embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIG. 3 is a ternary phase diagram illustrating the structures of compositions in embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIGS. 4A and 4B are back scattered electron images from sample compositions in embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIG. 5A is a graph showing D.C. conductivity versus atomic percent of magnesium ions at 850° C. for embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIGS. 5B-5G are graphs showing electrical impedance spectroscopy results for sample compositions in embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIG. 6A is a graph showing D.C. conductivity versus atomic percent of scandium ions at 850° C. for embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIG. 6B is a graph showing D.C. conductivity versus oxygen stoichiometry at 850° C. for embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIG. 6C is a ternary phase diagram showing D.C. conductivity results at 850° C. for embodiment series of magnesia doped scandia stabilized zirconia compositions.



FIG. 7A is a ternary phase diagram of two embodiment series of yttria and magnesia doped scandia stabilized zirconia compositions.



FIGS. 7B and 7C are plots showing x-ray diffraction patterns for compositions in two embodiment series of yttria and magnesia doped scandia stabilized zirconia compositions.



FIG. 8A is a graph showing D.C. conductivity versus atomic percentage of yttrium ions at 850° C. for two embodiment series of yttria and magnesia doped scandia stabilized zirconia compositions.



FIGS. 8B-8E are graphs showing electrical impedance spectroscopy results for sample compositions in an embodiment series of yttria and magnesia doped scandia stabilized zirconia compositions.



FIGS. 9A-9D are graphs showing electrical impedance spectroscopy results for sample compositions in two embodiment series of yttria and magnesia doped scandia stabilized zirconia compositions.



FIG. 10A is a graph showing D.C. conductivity versus atomic percentage of scandium ions at 850° C. for embodiment series of magnesia doped scandia stabilized zirconia compositions and yttria and magnesia doped scandia stabilized zirconia compositions.



FIG. 10B is a graph showing D.C. conductivity versus oxygen stoichiometry at 850° C. for embodiment series of magnesia doped scandia stabilized zirconia compositions and yttria and magnesia doped scandia stabilized zirconia compositions.



FIG. 11A is a plot showing x-ray diffraction patterns for sample compositions in an embodiment series of zinc oxide doped scandia stabilized zirconia compositions.



FIG. 11B is an expanded view of the x-ray diffraction patterns of FIG. 11A for angles within the range of 2θ=25-50.



FIG. 11C is an expanded view of the x-ray diffraction patterns of FIG. 11A for angles within the range of 2θ=80-88.



FIG. 12A is a graph comparing D.C. conductivities at 850° C. of an embodiment series of magnesia doped scandia stabilized zirconia compositions and a similar series of zinc oxide doped scandia stabilized zirconia compositions.



FIG. 12B is a plot showing x-ray diffraction patterns for an embodiment series of indium oxide doped scandia stabilized zirconia compositions.



FIG. 12C is a graph showing D.C. conductivity versus mole percent of indium oxide at 850° C. for an embodiment series of indium oxide doped scandia stabilized zirconia compositions.



FIG. 13A is plot showing electron diffraction spectroscopy patterns for an embodiment series of indium oxide and magnesia doped scandia stabilized zirconia compositions and an embodiment series of indium oxide doped scandia stabilized zirconia compositions.



FIG. 13B is a plot showing x-ray diffraction patterns for sample compositions in embodiment series of scandia stabilized zirconia compositions doped with varying amounts of indium oxide and magnesia.



FIGS. 14A-14D are graphs showing electrical impedance spectroscopy results for sample compositions in embodiment series of scandia stabilized zirconia compositions doped with varying amounts of yttria, magnesia, indium oxide, and/or zinc oxide.



FIG. 15 is a ternary phase diagram of embodiment series of scandia stabilized zirconia compositions doped with varying amounts of yttria and gallium oxide.



FIG. 16A is a plot showing x-ray diffraction patterns for sample compositions in embodiment series of scandia stabilized zirconia compositions doped with varying amounts of yttria and gallium oxide.



FIG. 16B is an expanded view of the x-ray diffraction patterns of FIG. 16A for angles within the range of 2θ=82-85.



FIG. 17A is a graph showing D.C. conductivity versus atomic percentage of yttrium and gallium ions at 850° C. for embodiment series of scandia stabilized zirconia compositions doped with varying amounts of yttria and gallium oxide.



FIG. 17B is a graph showing D.C. conductivity versus atomic percentage of scandium ions at 850° C. for embodiment series of scandia stabilized zirconia compositions doped with varying amounts of yttria and gallium oxide.



FIG. 18 is a graph showing D.C. conductivity versus atomic percentage of gallium ions at 850° C. for an embodiment series of scandia stabilized zirconia compositions doped with yttria, gallium oxide, and magnesia.



FIG. 19A is a graph showing D.C. conductivities as a function of scandium content for sample compositions of various series of scandia stabilized zirconia doped with indium oxide and ceria at 850° C.



FIG. 19B is a graph showing D.C. conductivities as a function of indium content for sample compositions of various series of scandia stabilized zirconia doped with indium oxide and ceria at 850° C.



FIG. 19C is a graph showing D.C. conductivities as a function of the ratio of scandium to indium for sample compositions of various series of scandia stabilized zirconia doped with indium oxide and ceria at 850° C.



FIG. 20A is a graph showing D.C. conductivity as a function of scandium content at 850° C. for embodiment series of scandia stabilized zirconia compositions with various dopant combinations.



FIG. 20B is a graph showing D.C. conductivity as a function of oxygen stoichiometry at 850° C. for embodiment series of scandia stabilized zirconia compositions with various dopant combinations.



FIG. 21 is a ternary phase diagram showing sample high conductivity compositions of two embodiment series of scandia stabilized zirconia compositions doped with magnesia.





DETAILED DESCRIPTION OF THE EMBODIMENTS

The various embodiments provide compositions of an electrolyte for a SOFC which includes a doped scandia stabilized zirconia. In an embodiment, zirconia is co-doped with scandium and aliovalent atoms and is made by co-precipitation.


As both phase composition and conductivity may be very much dependant on the synthesis conditions, numerous studies have focused on developing technologies for synthesis and sintering. Solid state synthesis is known to lead to phase inhomogeneity due to the slow kinetics for cation migration, therefore high sintering temperatures may be required for phase formation. Alternative techniques such as co-precipitation, combustion and sol-gel may prove to be more successful in achieving compositional homogeneity and high extent of densification.


In the various embodiments, powder may be obtained using co-precipitation, which includes dissolving stoichiometric amounts of scandium, and at least one of magnesium oxide or carbonate, zinc oxide, indium oxide and/or gallium oxide (and optionally yttrium oxide in addition to the above oxides depending on the composition) in hot HNO3 followed by mixing with and aqueous solution in which zirconium acetylacetonate or other Zr precursor compound has been dissolved. The mixture may be stirred under heating on a hot plate then cooled down to room temperature and precipitated with ammonia until pH=9. The formed precipitate may be filtrated, dried and calcined at 1200° C. for 5 hours. The resulting powder may be crushed, ball milled and pressed into pellets and bars to be sintered to dense bodies at 1500-1550° C. for 7 hours. The sintered product may be characterised using X-ray diffraction, particle size analysis, SEM, TEM and conductivity measurements. To obtain an accurate value of the ionic conductivity at high temperatures, the bulk and grain boundary contributions to the total resistance of the sample may be separated out.


In preparing these new electrolyte compositions, a parent electrolyte material may have a molar ratio of zirconia (ZrO2):scandia (Sc2O3) that is around 89:11, such as 87-91:13-9. In an embodiment, zirconia may be doped with magnesia (MgO), or other ionic oxide with an aliovalent cation (e.g., Mg2+), up to 11% mole percent (mol %), while keeping the atomic percent of either Sc or Zr constant. In other embodiments, zirconia may be doped with a combination of one or more of magnesia, yttria, zinc oxide, and/or indium oxide. In other embodiments, zirconia may be doped with a combination of one or more of magnesia, yttria, and gallium oxide.


In an embodiment, magnesia may be used as a dopant that replaces scandia in scandia stabilized zirconia. Four example series of compositions are discussed in further detail below.


One example series of compositions (“A-series”) may be prepared based on the composition of 11 mol % Sc2O3, and may have a formula of Zr0.802Sc0.198-xMgxO1.90-0.5x. A ternary phase diagram showing the compositions of this example A-series is illustrated in FIG. 1A. In the A-series compositions, Sc3+ ions may be replaced by Mg2+ ions in a 1:1 ratio, thereby lowering scandium and oxygen content of the composition, while keeping zirconia content constant. The x values in the above formula that may be used to form the A-series are: 0, 0.009, 0.018, 0.027 and 0.036, thereby creating the following compositions:

  • A0: Zr0.802Sc0.198O1.90
  • A1: Zr0.802Sc0.189Mg0.009O1.90
  • A2: Zr0.802Sc0.180Mg0.018O1.89
  • A3: Zr0.802Sc0.171Mg0.027O1.89
  • A4: Zr0.802Sc0.162Mg0.036O1.88


In this example series, at x=0, no Sc3+ ions are replaced, and therefore the atomic percent of Sc3+ ions is equal to the atomic percent in the parent material (i.e., 19.8%). At the highest x value tested (x=0.36), the atomic percent of scandium ions becomes the lowest (i.e., 16.2%).


Another example series of compositions (“B-series”) may be prepared based on the composition of 11 mol % Sc2O3. A formula for the B-series compositions may be Zr0.802+xSc0.198-2xMgxO1.90 FIG. 1B is a ternary phase diagram showing the compositions of the B-series. In this example series, two Sc3+ ions may be replaced by one Zr4+ and one Mg2+ ion, thereby lowering scandium content while keeping the oxygen content and stoichiometry constant at 1.90. The x values that may be used to form this B-series are: 0, 0.009, 0.0135, 0.018 0.027 and 0.036, thereby creating the following compositions:

  • B0: Zr0.802Sc0.198O1.90
  • B1: Zr0.811Sc0.18Mg0.009O1.90
  • B1.5: Zr0.815Sc0.171Mg0.0135O1.90
  • B2: Zr0.820Sc0.162Mg0.018O1.90
  • B3: Zr0.829Sc0.144Mg0.027O1.90
  • B4: Zr0.838Sc0.126Mg0.036O1.90


In this example series, at x=0, no Sc3+ ions are replaced, and therefore the atomic percent of Sc3+ ions is equal to the atomic percent in the parent material (i.e., 19.8%). At the highest x value tested (x=0.036), the atomic percent of scandium ions is the lowest (i.e., 12.6%). A ternary phase diagram showing the compositions of this example B-series is illustrated in FIG. 1B.


Other example series of compositions (“G-series” and “H-series”) may maintain constant scandia content and increase magnesia levels by replacing Zr ions with Mg ions, thereby lowering the levels of zirconium and oxygen. The example G-series of compositions may be prepared based on a parent composition with 5.3 mol % Sc2O3, and may have a formula of Zr0.9-xSc0.1MgxO1.95-x. A ternary phase diagram showing the compositions in this example G-series is illustrated in FIG. 1C. The x values that may be used to form the G-series compositions are: 0, 0.025, 0.05, 0.075 and 0.10, thereby creating the following compositions:

  • G0: Zr0.9Sc0.1O1.95
  • G1: Zr0.875Sc0.1Mg0.025O1.925
  • G2: Zr0.85Sc0.1Mg0.05O1.90
  • G3: Zr0.825Sc0.1Mg0.075O1.875
  • G4: Zr0.80Sc0.1Mg0.10O1.85


At x=0, no Mg2+ ions are added, and therefore the atomic percent of Sc3+ ions is equal to the atomic percent in the parent material (i.e., 10.0%). At the highest x value (x=0.10), the atomic percent of zirconium ions is the lowest (i.e., 80.0%).


Another example series of compositions (“H-series”) may be prepared based on a parent composition of 8.1 mol % Sc2O3. The H-series compositions may have a formula Zr0.85-xSc0.15MgxO1.925-x. A ternary phase diagram showing the example H-series compositions is illustrated in FIG. 1D. The x values that may be used to form the H-series compositions are: 0, 0.025, 0.05, 0.075 and 0.10, thereby creating the following compositions:

  • H0: Zr0.85Sc0.15O1.925
  • H1: Zr0.825Sc0.15Mg0.025O1.90
  • H2: Zr0.80Sc0.15Mg0.05O1.875
  • H3: Zr0.775Sc0.15Mg0.075O1.85
  • H4: Zr0.75Sc0.15Mg0.10O1.825


X-ray diffraction patterns may determine the stable phase at room temperature for each magnesia doped scandia stabilized zirconia composition. The phases at room temperature for compositions in the example A-, B-, G-, and H-series of compositions are shown in Table 1 below:

















Composition
Phases Present
Spacegroup









A0, B0
Rhombohedral
R-3C



A1
Rhombohedral
R-3C



A2
Cubic
Fm-3m



A3
Cubic
Fm-3m



A4
Cubic
Fm-3m



B1
Tetragonal
P42 nmc



B1-5
Tetragonal
P42 nmc



B2
Tetragonal
P42 nmc



B3
Tetragonal
P42 nmc



B4
Tetragonal
P42 nmc



G0
Tetragonal + monoclinic
P42 nmc+



G1
Tetragonal + monoclinic
P42 nmc+



G2
Tetragonal + monoclinic
P42 nmc+



G3
Tetragonal + monoclinic
P42 nmc+



G4
Tetragonal + monoclinic
P42 nmc+



H0
Tetragonal
P42 nmc



H1
Tetragonal
P42 nmc



H2
Cubic
Fm-3m



H3
Cubic
Fm-3m



H4
Tetragonal
P42 nmc











Previous studies of the parent composition A0, B0 of the A and B-series, 11 mol % Sc2O3, have found it to have a rhombohedral structure at room temperature. At the lowest level of doping in the A-series of compositions (x=0.09), the structure may remain rhombohedral, while at all other doping levels the cubic fluorite structure may be stable. For the example B-series, all compositions may have a tetragonal fluorite structure. FIG. 2A illustrates an x-ray diffraction patterns for the example B-Series compositions.


X-ray analysis of the magnesium free G0 sample showed both tetragonal and monoclinic fluorite phases to be present, consistent with findings by Ruh et al. (Ruh 1977), in their study. FIG. 2B illustrates x-ray diffraction (XRD) patterns for G-series compositions, which show that increasing the magnesia content across the G-Series leads to a reduction in the amount of monoclinic phase present. For example, FIG. 2C, which is a close up view of the low angle region in FIG. 2B illustrates x-ray diffraction patterns for G-series compositions, which show relative peak heights of the monoclinic reflections reduce with increasing magnesia content.


With respect to the H-series of compositions, additions of MgO with between 2.5 and 7.5 at. % magnesium stabilize the cubic phase. When the magnesium content is increased to 2.5 at. % the structure may remain tetragonal, but when the magnesium content is further increased to 5.0 and 7.5 at. %, the cubic structure may be stabilized. A further increase in magnesium content to 10 at. % tetragonal structure may become stable. This is shown in FIG. 2D which is an XRD pattern series for the H-series compositions. A ternary phase diagram showing as fired phases for the B-, G- and H-series compositions is illustrated in FIG. 3.



FIGS. 4A and 4B are back scattered electron (BSE) images from samples B2 and H2 respectively, taken using a scanning electron microscope (SEM). As shown by the data, sample G2 may have a much finer grain structure, which is consistent with the presence of tetragonal and monoclinic zirconia. In contrast sample H2 may have a much coarser microstructure, typical of cubic zirconia.



FIG. 5A illustrates the variation of example D.C. conductivity measurements with magnesia content (measured atomic percent of magnesium) at 850° C. for the B, G and H-Series of compositions. Peak conductivity may be measured at or above 200 mS/cm, such as 200-210 mS/cm for the B1.5 composition (Zr0.815Sc0.171Mg0.0135O1.90).


Regarding the G-series of compositions, conductivity may remain less than 100 m/Scm across the entire range of compositions. These relatively low conductivities may be consistent with XRD results that show the presence of unwanted low conductivity monoclinic phases at room temperature. These low results may also indicate that G-series levels of magnesia and scandia are likely insufficient to stabilize the more conductive cubic phase of zirconia at 850° C. In contrast, the example H-series of compositions may show conductivities above 150 mS/cm, such as 150-199 mS/cm at compositions with 5.0 at. % magnesium or less. The conductivity may increase approximately linearly with magnesia content to a peak value of 199 mS/cm for the H2 sample, (5.0 at. % magnesium). A further increase to 7.5 at. % magnesium may lead to a large drop in conductivity to 79 mS/cm.



FIG. 5B illustrates electrical impedance spectroscopy (EIS) measurements showing bulk conductivity for the sample G2 and H2 compositions with 5 at. % magnesium. FIG. 5C illustrates EIS measurements showing conductivity across the grain boundary of the sample G2 and H2 compositions. At 400° C. the low scandia G2 sample may have a higher bulk conductivity but lower grain boundary conductivity than the higher scandia H2 sample. As temperature increases the bulk and grain boundary component of the conductivity may increase faster for the higher scandia sample, leading to the far superior conductivity at 850° C. Without wishing to be bound by a particular theory, the large grain boundary resistance of the G-series phase may be the result of the presence of the lower conductivity monoclinic phase.


When the magnesium content of the H-series of compositions is increased from 5 at. % to 7.5 at. % or higher, a large decrease in conductivity may be observed. FIG. 5D illustrates EIS measurements showing total conductivity for H2 and H3 samples, which have 5 at. % and 7.5 at. % magnesium, respectively. FIG. 5E illustrates EIS measurements showing conductivity across the grain boundary for H2 and H3. FIG. 5F illustrates EIS measurements showing bulk conductivity for H2 and H3 samples, while FIG. 5G illustrates bulk resistivity measurements for the H2 and H3 samples. It may be observed from these measurements that H2 and H3 samples may have very similar bulk conductivities, while H3 may have a much lower grain boundary conductivity. Thus, 1-6 atomic percent MgO, such as 1.3-5 atomic percent are preferred.



FIG. 6A illustrates the variation of D.C. conductivity measurements with scandia content (measured as atomic percent of scandia) at 850° C. for the B, G and H-Series of compositions. FIG. 6B illustrates the variation of D.C. conductivity measurements with oxygen stoichiometry at 850° C. for the B, G and H-Series of compositions. FIG. 6C illustrates the D.C. conductivity results at 850° C. are presented on a ternary composition diagram. These plots indicate that peak values of conductivity may be achieved at scandia contents between 15 and 19 at. %, magnesia contents less than 5 at. % (e.g., 2-5 at. %), and oxygen stoichiometries between 1.875 and 1.9.


In order to further decrease the level of scandia, two additional series of compositions based on the B1.5 and B3 compositions may be developed.


In another embodiment, scandia stabilized zirconia compositions may be co-doped with magnesia and yttria. An example series of compositions (“E-series”) may be prepared based on a parent composition of 10.7 mol % Sc2O3. The E-series may have a formula Zr0.815Sc0.171-xYxMg0.0135O1.90. In this series of compositions, one Y3+ ion replaces one scandium ion, while zirconium, magnesium and oxygen levels remain constant. The x values that may be used to form the E-series compositions were: 0, 0.018, 0.036, 0.054, and 0.072, thereby creating the following E-series compositions:

  • E0: Zr0.815Sc0.171Mg0.0135O1.90. (Same as B1.5)
  • E1: Zr0.815Sc0.153Y0.018Mg0.0135O1.90
  • E2: Zr0.815Sc0.135Y0.036Mg0.0135O1.90
  • E3: Zr0.815Sc0.117Y0.054Mg0.0135O1.90
  • E4: Zr0.815Sc0.099Y0.072Mg0.0135O1.90

    At x=0, no scandium ions are replaced, and the atomic percent of scandium is equal to the parent composition (i.e., 17.1%). At the highest x value, x=0.072, atomic percent of scandium is lowest of the series (i.e., 9.9%).


Another example series of compositions (“F-series”) may be prepared based on a parent composition of 7.9 mol % Sc2O3. The F-series may have a formula Zr0.829Sc0.144-xYxMg0.027O1.90. The x values that may be used to prepare the F-series compositions are: 0, 0.018, 0.036, 0.054, and 0.072, thereby creating the following compositions:

  • F0: Zr0.829Sc0.144Mg0.027O1.90 (Same as B3)
  • F1: Zr0.829Sc0.126Y0.018Mg0.027O1.90
  • F2: Zr0.829Sc0.108Y0.036Mg0.027O1.90
  • F3: Zr0.829Sc0.09Y0.054Mg0.027O1.90
  • F4: Zr0.829Sc0.072Y0.072Mg0.027O1.90


In this series of compositions, like in the E-series, one Y3+ ion replaces one scandium ion, while zirconium, magnesium and oxygen levels remain constant. At x=0, no scandium ions are replaced, and the atomic percent of scandium is equal to the parent composition (i.e., 14.4%). At the highest x value, x=0.072, atomic percent of scandium is lowest of the series (i.e., 7.2%). A ternary phase diagram of the example E- and F-series compositions is illustrated in FIG. 7A (yttria not shown).


The XRD patterns of the example in the E-series and F-series compositions are shown in FIGS. 7B and 7C, respectively. The E-series of compositions may be tetragonal at yttrium contents of 5.4 at. % or less and may be cubic at 7.2 at. %. The F-series compositions may remain tetragonal. At 5.4 at. % and 7.2 at. % yttrium, the F-series samples may also have small amounts of monoclinic phase. Table 2 shows the room temperature phases of example compositions E0 through E4, and F0 through F4.

















Composition
Phases Present
Spacegroup









E0 (B1-5)
Tetragonal
P42 nmc



E1
Tetragonal
P42 nmc



E2
Tetragonal
P42 nmc



E3
Tetragonal
P42 nmc



E4
Cubic
Fm3m



F0
Tetragonal
P42 nmc



F1
Tetragonal



F2
Tetragonal
P42 nmc



F3
Tetragonal + monoclinic
P42 nmc



F4
Tetragonal + monoclinic
P42 nmc











FIG. 8A illustrates the variation in D.C. conductivity with yttria content measured for the E and F series of compositions at 850° C. As the data show, an approximately linear decrease in conductivity may occur with increasing content. The highest conductivity for a yttria-containing sample may be 199 mS/cm for E1, which has 1.8 at. % yttrium.



FIG. 8B illustrates EIS measurements showing total conductivity for the E-series compositions E1, E3 and E4. FIG. 8C illustrates EIS measurements showing bulk conductivity for E1, E3 and E4. FIG. 8D illustrates EIS measurements showing conductivity across the grain boundary plane for E1, E3 and E4. FIG. 8E illustrates bulk resistivity values at 400° C. for E1, E3 and E4.



FIG. 9A illustrates EIS measurements showing total conductivity for the samples E1 and F1, each of which have 1.8 at. % yttrium. FIG. 9B illustrates EIS measurements showing bulk conductivity for E1 and F1. FIG. 9C illustrates EIS measurements showing conductivity across the grain boundary plane for E and F1. FIG. 9D illustrates bulk resistivity values at 400° C. for E1 and F1.



FIG. 10A illustrates D.C. conductivity at 850° C. versus scandia content for series A, B, G and H (ZrO2—Sc2O3—MgO), and E and F (ZrO2—Sc2O3—Y2O3—MgO) at 850° C. Further, FIG. 10 B illustrates D.C. conductivity at 850° C. versus oxygen stoichiometry for each of these series. The conditions for high conductivity in the yttria containing samples are consistent with those found for the yttria free samples. The highest values of conductivity may be found for scandium contents between 15 and 19 at. % magnesium contents less than 5 at. % and oxygen stoichiometries between 1.875 and 1.9.


In another embodiment, scandia stabilized zirconia compositions that are similar to the B-series compositions may be doped with either zinc oxide (ZnO) or indium oxide (In2O3), instead of or in addition to magnesia.


In an example series of compositions (“B—Zn series”), which may be based on the B1.5 sample composition discussed above, zinc ions may replace magnesium ions. The B—Zn series may have a formula of Zr0.802+xSc0.198-2xZnxO1.90. X values that may be used to prepare this B—Zn series of compositions are: 0, 0.0135 (corresponding to B1.5) and 0.027 (corresponding to B3), thereby creating the following compositions:

  • B1.5Zn: Zr0.815Sc0.171Zn0.0135O1.90
  • B3Zn: Zr0.829Sc0.144Zn0.0270O1.90


Specifically, in this series, two Sc3+ ions may be replaced by one Zn2+ and one Zr4+ ion. The oxygen stoichiometry remains constant as Sc3+ is replaced by these ions. XRD patterns for sample compositions in this B—Zn series of compositions are illustrated in FIGS. 11A-11C, where FIGS. 11B and 11C are close ups of low and high angle regions of FIG. 11A.


The conductivities at 850° C. of the B—Zn series compositions, compared to corresponding B-series compositions and the parent composition with 11 mol % Sc2O3, are provided in Table 3 below:
















σ850° C. (mS · cm−1)











B-Zn series
B-series















11Sc2O3
140
140



B1.5
127
199, 232



B3
105
159











FIG. 12A illustrates D.C. conductivity at 850° C. versus ZnO content (measured as atomic percent of zinc) for the B—Zn series of compositions, overlaid onto a plot of D.C. conductivity at 850° C. versus magnesium content for B1.5 and B3.


In another example series of compositions, indium oxide may be used as a co-dopant with scandia. Similar to the A-series of compositions in which Mg2+ is a co-dopant that replaces Sc3+, in an In2O3 co-doped composition the In3+ ions may replace Sc3+ ions in a 1:1 ratio, with the oxygen content remaining fixed. This series may be based on a parent composition of 11 mol % Sc2O3, and may have a formula of: Zr0.802Sc0.198-xInxO1.90 where 0≤x≤0.198, such as 0.018≤x≤0.18.


Sample compositions of this embodiment may have 0-11 mol % Sc2O3, such as 1-9 mol % Sc2O3, and 0-11 mol % In2O3, such as 2-10 mol % In2O3, with a total doping range (i.e., sum of Sc2O3 and In2O3 mole percentages) of 11 mol %. In one example, the composition may have 9 mol % Sc2O3 and 2 mol % In2O3, and therefore have a formula of Zr0.802Sc0.162In0.036O1.90.



FIG. 12B illustrates XRD patterns for this series, in which sample compositions have discreet integer indium oxide contents varying from 0 to 11 mol % and discreet integer scandia contents varying from 11 to 0 mol %. FIG. 12C illustrates the variation in D.C. conductivity of these sample compositions as a function of discrete integer indium oxide content (measured as mole percent of In2O3), where indium oxide content varies from 0 to 11 mol %. As shown by the data plot, D.C. conductivity of the samples may be a value between 80 mS/cm and 220 mS/cm. As also shown by the data plot, a peak D.C. conductivity level of at least 215 mS/cm, such as between 215 and 220 mS/cm, may be achieved at about 3 mol % In2O3, which corresponds to a sample formula of around Zr0.802Sc0.144In0.054O1.90. Thus, this series may be described as having a formula Zr1-w-yScwInyOd, in which 0.018≤w≤0.18, in which 0.018≤y≤0.18, and in which 1.8≤d≤2. In an embodiment, scandium ion concentration (w) may be characterized by w=0.198−y. In another embodiment, indium ion concentration (y) may be characterized by y=0.054.


In another embodiment, scandia stabilized zirconia compositions that are similar to the H-series compositions may be doped with indium oxide (In2O3) in addition to magnesia. In an example series of compositions (“H—In series”), which may be based on the H2 sample composition discussed above, Sc3+ ions may be replaced by Mg2+ ions in a 1:1 ratio, thereby lowering scandium and oxygen content of the composition while keeping zirconia and indium content constant. The H—In series may have a formula of Zr0.8Sc0.15-xIn0.05MgxO2-d, in which 0≤x≤0.05. The formula for the H—In series may also be written as Zr0.8Sc0.15-xIn0.05MgxOd, in which 1.8≤d≤2 and 0≤x≤0.05. At x=0, no magnesia is present and a sample composition has a formula Zr0.8Sc0.15In0.05O2-d. At x=0.05, a sample composition has a formula Zr0.8Sc0.10In0.05Mg0.05O2-d.


Another set of examples involves variants of the E1 sample composition, discussed above. In one example composition, zinc oxide may replace magnesia as a dopant, producing a composition “E1-Zn” that may have a formula Zr0.815Sc0.153Y0.0153Zn0.0135O1.90. In another example, In2O3 may be used as a co-dopant that replaces yttria, producing a composition “E1-In” that may have a formula Zr0.815Sc0.153In0.018Mg0.0135O1.90.



FIG. 13A illustrates energy-dispersive x-ray (EDX) spectroscopy analysis of the sample compositions E1-In and 9Sc2O3-2In2O3. FIG. 13B illustrates x-ray diffraction (XRD) patterns for these compositions, with an expanded view region for angles of 2θ=80-88°. At 850° C., the D.C. conductivity of E1-In at 850° C. may be around 195 mS/cm, while the D.C. conductivity of 9Sc2O3-2In2O3 may be around 170 mS/cm. Thus, these compositions have a conductivity of at least 170, such as 180-195 mS/cm.



FIG. 14A shows bulk impedance values of the E1 sample composition with the E1 variants E1-Zn and E1-In at 400° C. FIG. 14B shows bulk conductivity measurements for E1, E1-Zn and E1-In. FIG. 14C shows the total conductivity measurements for E1, E1-Zn and E1-In, and FIG. 14D shows the conductivity across the grain boundary plane for E1, E1-Zn and E1-In.


In further embodiments, scandia stabilized zirconia may be co-doped with gallium oxide and yttria. Without wishing to be bound to a particular theory, the combination of the smaller radius Ga3+ ion and the larger radius Y3+ may lead to less distortion of the crystal structure.


An example series of compositions (“I-series”) may be created with a formula Zr0.8018Sc0.1782Y0.02-xGaxO1.90. In this series of compositions, one Ga3+ ion replaces one Y3+ ion, while zirconium, scandium and oxygen levels remain constant. The x values that may be used to form the I-series compositions are: 0, 0.005, 0.01, 0.015 and 0.02, thereby creating the following compositions:

  • I0: Zr0.802Sc0.178Y0.02O1.90
  • I1: Zr0.802Sc0.171Y0.015Ga0.005O1.90
  • I2: Zr0.802Sc0.171Y0.01Ga0.01O1.90
  • I3: Zr0.802Sc0.171Y0.005Ga0.015O1.90
  • I4: Zr0.802Sc0.171Ga0.02O1.90


At x=0, no yttrium ions are replaced, and no gallium ions are present. At the highest x value, x=0.02, all yttrium ions are replaced by gallium ions.


Another example series of compositions (“J-series”) may be prepared with a formula Zr0.802Sc0.188Y0.01-xGaxO1.90. In the J-series, one Ga3+ ion replaces one Y3+ ion, while zirconium, scandium and oxygen levels remain constant. The x values that may be used to form the J-series compositions are: 0, 0.0025, 0.005, 0.0075, thereby creating the following compositions:

  • J0: Zr0.802Sc0.188Y0.01O1.90
  • J1: Zr0.802Sc0.188Y0.0075Ga0.0025O1.90
  • J2: Zr0.802Sc0.188Y0.005Ga0.005O1.90
  • J3: Zr0.802Sc0.188Y0.0025Ga0.0075O1.90


At x=0, no yttrium ions are replaced, and no gallium ions are present. At the highest x value, x=0.0075, the composition contains 2.5 at. % Y3+ and 7.5 at. % Ga3+ ions.


Another example series of compositions (“K-series”) may be prepared with a formula Zr0.8018Sc0.1682Y0.03-xGaxO1.90. In this series of compositions, one Ga3+ ion replaces one Y3+ ion, while zirconium, scandium and oxygen levels remain constant. An x value that may be used to form an example K-series composition is 0.015, which may create a K2 sample composition having a formula Zr0.8018Sc0.1682Y0.015Ga0.015O1.90. At this x value, the atomic percentages of Y3+ ions and Ga3+ ions are equal.


Another example series of compositions (“L-series”) may be prepared with a formula Zr0.8018Sc0.1582Y0.04-xGaxO1.90. In this series of compositions, one Ga3+ ion replaces one Y3+ ion, while zirconium, scandium and oxygen levels remain constant. An x value that may be used to form an example L-series composition is 0.02, which may create a L2 sample composition having a formula Zr0.8018Sc0.1582Y0.02Ga0.02O1.90. At this x value, the atomic percentages of Y3+ ions and Ga3+ ions are equal.



FIG. 15 is a ternary phase diagram showing the example I-, J-, K- and L-series of compositions. FIG. 16A illustrates XRD patterns for sample compositions in these series, I2, J2, K2, and L2. FIG. 16B is an expansion of the XRD patterns over the range of 2θ=82-85°. FIG. 17A illustrates the variation in D.C conductivity with total gallium oxide and yttria content (measured as atomic percent of gallium or yttrium) for the I, J, K and L series of compositions at 850° C. FIG. 17B illustrates the variation in D.C. conductivity with scandium content (measured as atomic percent of scandium). As the data show, the K-series composition, which has 0.015 at. % Y3+ ions and 0.015 at. % Ga3+ ions, has the highest conductivity, such as above 200 mS/cm, for example 221 mS/cm.


D.C. conductivities of sample compositions I2, I3, J2, J3, K2 and L2 at 850° C. are provided in Table 4 below:
















Composition
σ850° C.









I2
132



I3
126



J2
118



J3
129



K2
221



L3
106










Another example series of compositions (“M-series”) may be prepared with a formula Zr0.815Sc0.15 Y0.02-xGaxMg0.015O1.9. In this series of compositions, one Ga3+ ion replaces one Y3+ ion, while zirconium, scandium, magnesium and oxygen levels remain constant. The x values that may be used to prepare the M-series are 0, 0.01 and 0.02, thereby creating the following compositions:

  • M0: Zr0.815Sc0.15Y0.02Mg0.015O1.9
  • M1: Zr0.815Sc0.15Y0.01Ga0.01Mg0.015O1.9
  • M2: Zr0.815Sc0.15Ga0.02Mg0.015O1.9

    At x=0, no yttrium ions are replaced, and no gallium is present, and at x=0.02, all yttrium ions are replaced with gallium ions.


    D.C. conductivity results of the M-series compositions at 850° C. are provided in Table 5 below:
















Composition
σ850° C.









M0
179



M1
154



M2
162











FIG. 18 is a graph illustrating the D.C. conductivity for the M-series compositions with varying gallium oxide content (measured as atomic percent gallium).


Another example series of compositions (“N-series”) may be created with a formula Zr0.815SC0.13Y0.04-xGaxMg0.015O1.90. In this series of compositions, one Ga3+ ion replaces one Y3+ ion, while zirconium, scandium, magnesium and oxygen levels remain constant. The x values that may used to make the N-series are 0, 0.01, 0.02, 0.03, and 0.04, thereby creating the following compositions:

  • N0: Zr0.815Sc0.13Y0.04Mg0.015O1.90
  • N1: Zr0.815Sc0.13Y0.03Ga0.01Mg0.015O1.90
  • N2: Zr0.815Sc0.13Y0.02Ga0.02Mg0.015O1.90
  • N3: Zr0.815Sc0.13Y0.01Ga0.03Mg0.015O1.90
  • N4: Zr0.815Sc0.13Ga0.04Mg0.015O1.90


At x=0, no yttrium ions are replaced, and no gallium is present, and at x=0.04, all yttrium ions are replaced with gallium ions.


In further embodiments, scandia stabilized zirconia may be co-doped with indium oxide and ceria. An example series of compositions (“O-series”) may be created with a formula Zr0.8o9Sc0.182-xCe0.009InxO2-d, where 0≤x≤0.164. This series may also be written as Zr0.809Sc0.182-xCe0.009InxOd, where 1.8≤d≤2 and 0≤x≤0.164. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium, cerium, and oxygen levels remain constant. A parent dopant material for the O-series of compositions may be 10Sc2O3-1CeO2. Sample compositions may be created by replacing Sc2O3 with up to 9 mol % In2O3 (e.g., 9Sc2O3-1In2O3-1CeO2 to 1Sc2O3-9In2O3-1CeO2).


Other example compositions may be created with total dopant amounts lower than 11 mol %. For example, one series of compositions may be created with at least 8 mol %, such as 9 mol % of total dopant, and a formula Zr0.843Sc0.0926-xCe0.009In0.0556+xO2-d, where 0≤x≤0.0741. The formula for this series may also be written as Zr0.843Sc0.0926-xCe0.009In0.0556+xOd, where 1.8≤d≤2 and 0≤x≤0.0741. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium, cerium, and oxygen levels remain constant. A parent dopant material may comprise 5Sc2O3-3In2O3-1CeO2. Sample compositions may be created by replacing Sc2O3 with up to 4 mol % In2O3 (e.g., 5Sc2O3-3In2O3-1CeO2 to 1Sc2O3-7In2O3-1CeO2). In another example, a series of compositions (“P-series”) may be created with 10 mol % of total dopant, and a formula Zr0.825Sc0.110-xCe0.009In0.055+xO2-d, where 0≤x≤0.0917. The formula for the P-series may also be written as Zr0.825Sc0.110-xCe0.009In0.055+xOd, where 1.8≤d≤2 and 0≤x≤0.0917. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium, cerium, and oxygen levels remain constant. A parent dopant material may be 6Sc2O3-3In2O3-1CeO2. Sample compositions may be created by replacing Sc2O3 with up to 5 mol % In2O3 (e.g., 6Sc2O3-3In2O3-1CeO2 to 1Sc2O3-8In2O3-1CeO2). Some x values that may used to make the P-series are 0 and 0.018, thereby creating the following compositions:

  • P0: Zr0.825Sc0.110Ce0.009In0.055O1.92
  • P1: Zr0.825Sc0.092Ce0.009In0.073O1.92


At x=0, no additional scandium ions are replaced, and the amount of indium present is the same as in the parent dopant material.


Other embodiment compositions may be created with total dopant amounts that are higher than 11 mol %, such as up to 14 mol %. For example, one series of compositions (“Q-series”) may be created with 11.5 mol % of total dopant, and a formula Zr0.801Sc0.10-xCe0.009In0.091+xO2-d, where 0≤x≤0.082. The formula for the Q-series may also be written as Zr0.801Sc0.10-xCe0.009In0.091+xOd, where 1.8≤d≤2 and 0≤x≤0.082. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium, cerium, and oxygen levels remain constant. A parent dopant material may be 5.5Sc2O3-5In2O3-1CeO2. Sample compositions may be created by replacing Sc2O3 with up to 4.5 mol % In2O3 (e.g., 5.5Sc2O3-5In2O3-1CeO2 to 1Sc2O3-9.5In2O3-1CeO2). Some x values that may used to make the Q-series are 0 and 0.010, thereby creating the following compositions:

  • Q0: Zr0.801Sc0.10Ce0.009In0.091O1.91
  • Q1: Zr0.825Sc0.091Ce0.09In0.10O1.91


At x=0, no additional scandium ions are replaced, and the amount of indium present is the same as in the parent dopant material.


In another example, a series of compositions (“R-series”) may be created with 12 mol % of total dopant, and a formula Zr0.793Sc0.110-xCe0.009In0.090+xO2-d, where 0≤x≤0.09. The formula for the R-series may also be written as Zr0.793Sc0.110-xCe0.009In0.090+xOd, where 1.8≤d≤2 and 0≤x≤0.09. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium, cerium, and oxygen levels remain constant. A parent dopant material may be 6Sc2O3-5In2O3-1CeO2. Sample compositions may be created by replacing Sc2O3 with up to 5 mol % In2O3 (e.g., 6Sc2O3-5In2O3-1CeO2 to 1Sc2O3-10In2O3-1CeO2). Some x values that may used to make the R-series are 0, 0.009, and 0.018, thereby creating the following compositions:

  • R0: Zr0.793Sc0.110Ce0.009In0.090O1.90
  • R1: Zr0.793Sc0.101Ce0.009In0.099O1.90
  • R2: Zr0.793Sc0.092Ce0.009In0.108O1.90


At x=0, no additional scandium ions are replaced, and the amount of indium present is the same as in the parent dopant material.


In another embodiment, a related series of compositions (R′-series) also having a total of 12 mol % dopant may be created with scandia stabilized zirconia that is co-doped only with indium, and lacks cerium or ceria. The R′-series may have a formula Zr0.786Sc0.143-xIn0.071+xO2-d, where 0≤x≤0.125. The formula for the R′-series may also be written as Zr0.786Sc0.143-xIn0.071+xOd, where 1.8≤d≤2 and 0≤x≤0.125. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium and oxygen levels remain constant. A parent dopant material may be 8Sc2O3-4In2O3. Sample compositions may be created by replacing Sc2O3 with up to 7 mol % In2O3 (e.g., 8Sc2O3-4In2O3 to 1Sc2O3-11In2O3). Some x values that may used to make the R-series are 0 and 0.036, thereby creating the following compositions:

  • R′0: Zr0.786Sc0.143In0.071O1.89
  • R′1: Zr0.786Sc0.107In0.107O1.89


At x=0, no additional scandium ions are replaced, and the amount of indium present is the same as in the parent dopant material. At x=0.036, the amounts of indium and scandium are equal in the dopant material.


In another example, a series of compositions (“S-series”) having 13 mol % of total dopant may be created using scandia stabilized zirconia co-doped with indium oxide and ceria. The S-series may have a formula Zr0.777Sc0.107-xCe0.009In0.107+xO2-d, where 0≤x≤0.089. The formula for the S-series may also be written as Zr0.777Sc0.107-xCe0.009In0.107+xOd, where 1.8≤d≤2 and 0≤x≤0.089. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium, cerium, and oxygen levels remain constant. A parent dopant material may be 6Sc2O3-6In2O3-1CeO2. Sample compositions may be created by replacing Sc2O3 with up to 5 mol % In2O3 (e.g., 6Sc2O3-6In2O3-1CeO2 to 1Sc2O3-11In2O3-1CeO2). Some x values that may used to make the S-series are 0 and 0.018, thereby creating the following compositions:

  • S0: Zr0.777Sc0.107Ce0.009In0.090O1.87
  • S1: Zr0.793Sc0.101Ce0.009In0.099O1.87


In another embodiment, a related series of compositions (S′-series) also having a total of 13 mol % dopant may be created with scandia stabilized zirconia that is co-doped only with indium. The S′-series may have a formula Zr0.770Sc0.142-xIn0.088+xO2-d, where 0≤x≤0.125. The formula for the S′-series may also be written as Zr0.770Sc0.142-xIn0.088+xOd, where 1.8≤d≤2 and 0≤x≤0.125. In this series of compositions, In3+ ions replace Sc3+ ions in a 1:1 ratio, while zirconium and oxygen levels remain constant. A parent dopant material may be 8Sc2O3-5In2O3. Sample compositions may be created by replacing Sc2O3 with up to 7 mol % In2O3 (e.g., 8Sc2O3-5In2O3 to 1Sc2O3-12In2O3).



FIGS. 19A-19C are graphs illustrating the variation in D.C. conductivity for sample compositions of the O-series, P-series, Q-series, R-series, and S-series. FIG. 19A shows D.C. conductivity of sample compositions in these series as a function of discrete integer scandium content (measured as at. % Sc3+), where scandium content varies from 7.2 to 18.2 at. %. FIG. 19B shows the variation in D.C. conductivity of the sample compositions as a function of indium content (measured as at. % In3+), where indium content varies from 0 to 10.9 at. %. FIG. 19C shows the variation in D.C. conductivity of the sample compositions as a function of the ratio of scandium content to indium content (excluding an O-series sample in which dopant composition had 0% indium oxide).


As shown by the data plots, D.C. conductivity of the samples may be a value between 80 mS/cm and 220 mS/cm. As also shown by the data plot, a peak D.C. conductivity level of at least 215 mS/cm, such as between 215 and 220 mS/cm, may be achieved in the O-series in a sample with around 16.3 at. % scandium, and around 1.8 at % indium, which has a sample formula of around Zr0.809Sc0.163Ce0.009In0.018O1.9. The amounts of scandium and indium at the peak D.C. conductivity level correspond to a dopant material of 9 mol % Sc2O3, 1 mol % In2O3, and 1 mol % CeO2. Thus, the O-series this series may be described as having a formula Zr1-w-y-zScwCezInyOd, in which 0.072≤w≤0.182, in which 0≤y≤0.1098, in which 0.008≤z≤0.1, and in which 1.8≤d≤2. In an embodiment, scandium ion concentration (w) may be characterized by w=0.182−y, and cerium ion concentration (z) may be characterized by z=0.009. In another embodiment, indium ion concentration (y) may be characterized by y=0.018.



FIGS. 20A and 20B are graphs illustrating summaries of the D.C. conductivity results for various example series of scandia stabilized zirconia compositions that may have the properties discussed above. FIG. 20A shows D.C. conductivity of sample compositions in these series as a function of discrete integer scandium content (measured as at. % Sc3+). FIG. 20B shows D.C. conductivity of the sample compositions in these series as a function of oxygen stoichiometry.



FIG. 21 is a ternary phase diagram showing sample high conductivity compositions of embodiment B- and H-series scandia stabilized zirconia that is doped with magnesia.


As demonstrated in the various example series of scandia stabilized zirconia compositions, the B- and H-series compositions may have high relative conductivities. For example, a sample B1.5 composition may have a D.C. conductivity of 232 mS/cm. In another example, sample H2 and H1 compositions may have D.C. conductivities of 199 mS/cm and 171 mS/cm, respectively.


In another example, a sample K2 composition may have a relatively high conductivity of 145 mS/cm. In another example, a sample L2 composition may also have a relatively high conductivity of 145 mS/cm. In another example, compositions doped In2O3 may have relatively high conductivities around 195 mS/cm.


The compositions above may be used for a solid oxide fuel cell electrolyte. The electrolyte may be plate shaped with an anode electrode on one side (e.g., a nickel and stabilized zirconia and/or doped ceria cermet) and a cathode electrode (e.g., lanthanum strontium manganate) on the opposite side. The fuel cell comprising the electrolyte, anode and cathode electrodes may be located in a fuel cell stack. The term “fuel cell stack,” as used herein, means a plurality of stacked fuel cells separated by interconnects which may share common air and fuel inlet and exhaust passages, manifolds or risers. The “fuel cell stack,” as used herein, includes a distinct electrical entity which contains two end plates which are connected to power conditioning equipment and the power (i.e., electricity) output of the stack. Thus, in some configurations, the electrical power output from such a distinct electrical entity may be separately controlled from other stacks. The term “fuel cell stack” as used herein, also includes a part of the distinct electrical entity. For example, the stacks may share the same end plates. In this case, the stacks jointly comprise a distinct electrical entity, such as a column. In this case, the electrical power output from both stacks cannot be separately controlled.


The formulas that represent the compositions above are not intended to limit the scope of the invention to particular atomic or mole percentages, but are provided to facilitate disclosure of the various series of related compositions. For example, the representation of oxygen as “O2-d” or “Od” provides for a variable amount of oxygen that may depend, for example, on the total amount of doping, valence of cations in the composition, etc. Example amounts of oxygen that may be present in series of compositions discussed above include, without limitation: 1.92 at % oxygen in the P-series; 1.91 at % oxygen in the Q-series, 1.90 at % oxygen in the R-series; 1.89 at % oxygen in the R′-series; and 1.87 at % oxygen in the S-series.


The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The description was chosen in order to explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

Claims
  • 1. An electrolyte composition for a solid oxide fuel cell, having a formula Zr1-w-x-zScwMgxYzOd, wherein: 0.1≤w≤0.18,0<x≤0.03,0<z≤0.08, and1.8≤d≤2.
  • 2. The electrolyte composition of claim 1, wherein w=0.171−z, wherein 0.013≤x≤0.014.
  • 3. The electrolyte composition of claim 2, wherein z=0.018.
  • 4. The electrolyte composition of claim 1, wherein w=0.144−z, and wherein 0.02≤x≤0.03.
  • 5. The electrolyte composition of claim 1, wherein 0.018≤z≤0.072.
US Referenced Citations (152)
Number Name Date Kind
4052532 Tannenberger et al. Oct 1977 A
4272353 Lawrance et al. Jun 1981 A
4426269 Brown et al. Jan 1984 A
4459340 Mason Jul 1984 A
4575407 Diller Mar 1986 A
4686158 Nishi et al. Aug 1987 A
4791079 Hazbun Dec 1988 A
4792502 Trocciola et al. Dec 1988 A
4804592 Vanderborgh et al. Feb 1989 A
4847173 Mitsunaga et al. Jul 1989 A
4898792 Singh et al. Feb 1990 A
4913982 Kotchick et al. Apr 1990 A
4917971 Farooque Apr 1990 A
4925745 Remick et al. May 1990 A
4983471 Reichner et al. Jan 1991 A
5034287 Kunz Jul 1991 A
5047299 Shockling Sep 1991 A
5143800 George et al. Sep 1992 A
5162167 Minh et al. Nov 1992 A
5169730 Reichner et al. Dec 1992 A
5170124 Blair et al. Dec 1992 A
5171645 Khandkar Dec 1992 A
5192334 Rohr et al. Mar 1993 A
5213910 Yamada May 1993 A
5215946 Minh Jun 1993 A
5256499 Minh et al. Oct 1993 A
5273837 Aiken et al. Dec 1993 A
5290323 Okuyama et al. Mar 1994 A
5290642 Minh et al. Mar 1994 A
5302470 Okada et al. Apr 1994 A
5342705 Minh et al. Aug 1994 A
5368667 Minh et al. Nov 1994 A
5441821 Merritt et al. Aug 1995 A
5498487 Ruka et al. Mar 1996 A
5501914 Satake et al. Mar 1996 A
5505824 McElroy Apr 1996 A
5518829 Satake et al. May 1996 A
5527631 Singh et al. Jun 1996 A
5573867 Zafred et al. Nov 1996 A
5589017 Minh Dec 1996 A
5589285 Cable et al. Dec 1996 A
5601937 Isenberg Feb 1997 A
5686196 Singh et al. Nov 1997 A
5688609 Rostrup-Nielsen et al. Nov 1997 A
5733675 Dederer et al. Mar 1998 A
5741406 Barnett et al. Apr 1998 A
5741605 Gillett et al. Apr 1998 A
5922488 Marucchi-Soos et al. Jul 1999 A
5942349 Badwal et al. Aug 1999 A
5955039 Dowdy Sep 1999 A
5993989 Baozhen Nov 1999 A
6013385 DuBose Jan 2000 A
6051125 Pham et al. Apr 2000 A
6106964 Voss et al. Aug 2000 A
6228521 Kim et al. May 2001 B1
6238816 Cable et al. May 2001 B1
6280865 Eisman et al. Aug 2001 B1
6287716 Hashimoto et al. Sep 2001 B1
6329090 McElroy et al. Dec 2001 B1
6361892 Ruhl et al. Mar 2002 B1
6403245 Hunt Jun 2002 B1
6436562 DuBose Aug 2002 B1
6451466 Grasso et al. Sep 2002 B1
6489050 Ruhl et al. Dec 2002 B1
6495279 Bogicevic et al. Dec 2002 B1
6558831 Doshi et al. May 2003 B1
6582845 Helfinstine et al. Jun 2003 B2
6592965 Gordon Jul 2003 B1
6605316 Visco Aug 2003 B1
6623880 Geisbrecht et al. Sep 2003 B1
6677070 Kearl Jan 2004 B2
6682842 Visco et al. Jan 2004 B1
6767662 Jacobson et al. Jul 2004 B2
6787261 Ukai Sep 2004 B2
6803141 Pham et al. Oct 2004 B2
6811913 Ruhl Nov 2004 B2
6821663 McElroy et al. Nov 2004 B2
6854688 McElroy et al. Feb 2005 B2
6924053 McElroy Aug 2005 B2
6972161 Beatty et al. Dec 2005 B2
6979511 Visco et al. Dec 2005 B2
7150927 Hickey et al. Dec 2006 B2
7157173 Kwon Jan 2007 B2
7255956 McElroy et al. Aug 2007 B2
7494732 Roy et al. Feb 2009 B2
7550217 Kwon et al. Jun 2009 B2
7563503 Gell et al. Jul 2009 B2
7601183 Larsen Oct 2009 B2
8580456 Armstrong et al. Nov 2013 B2
20010049035 Haltiner, Jr. et al. Dec 2001 A1
20020012825 Sasahara et al. Jan 2002 A1
20020014417 Kuehnle et al. Feb 2002 A1
20020028362 Prediger et al. Mar 2002 A1
20020028367 Sammes et al. Mar 2002 A1
20020058175 Ruhl May 2002 A1
20020098406 Huang et al. Jul 2002 A1
20020106544 Noetzel et al. Aug 2002 A1
20020127455 Pham et al. Sep 2002 A1
20020132156 Ruhl et al. Sep 2002 A1
20030162067 McElroy Aug 2003 A1
20030165732 McElroy Sep 2003 A1
20030196893 McElroy et al. Oct 2003 A1
20040081859 McElroy et al. Apr 2004 A1
20040191595 McElroy et al. Sep 2004 A1
20040191597 McElroy Sep 2004 A1
20040191598 Gottmann et al. Sep 2004 A1
20040202914 Sridhar et al. Oct 2004 A1
20040224193 Mitlitsky et al. Nov 2004 A1
20040229031 Gell et al. Nov 2004 A1
20040265484 Pham et al. Dec 2004 A1
20040265663 Badding et al. Dec 2004 A1
20050048334 Sridhar et al. Mar 2005 A1
20050074650 Sridhar et al. Apr 2005 A1
20050164051 Venkataraman et al. Jul 2005 A1
20050214616 Kumar et al. Sep 2005 A1
20050227134 Nguyen Oct 2005 A1
20050271919 Hata et al. Dec 2005 A1
20060008682 McLean et al. Jan 2006 A1
20060040168 Sridhar Feb 2006 A1
20060110633 Ukai et al. May 2006 A1
20060166070 Hickey et al. Jul 2006 A1
20060199057 Hiwatashi Sep 2006 A1
20060216575 Cassidy Sep 2006 A1
20060222929 Hickey et al. Oct 2006 A1
20070045125 Hartvigsen et al. Mar 2007 A1
20070082254 Hiwatashi Apr 2007 A1
20070141422 Brown Jun 2007 A1
20070141423 Suzuki et al. Jun 2007 A1
20070141443 Brown Jun 2007 A1
20070141444 Brown Jun 2007 A1
20070224481 Suzuki et al. Sep 2007 A1
20070237999 Donahue et al. Oct 2007 A1
20070275292 Sin Xicola et al. Nov 2007 A1
20070287048 Couse et al. Dec 2007 A1
20080029388 Elangovan et al. Feb 2008 A1
20080075984 Badding et al. Mar 2008 A1
20080076006 Gottmann et al. Mar 2008 A1
20080096080 Batawi et al. Apr 2008 A1
20080102337 Shimada May 2008 A1
20080254336 Batawi Oct 2008 A1
20080261099 Nguyen et al. Oct 2008 A1
20090029195 Gauckler et al. Jan 2009 A1
20090068533 Fukusawa et al. Mar 2009 A1
20090186250 Narendar et al. Jul 2009 A1
20090214919 Suzuki Aug 2009 A1
20090291347 Suzuki Nov 2009 A1
20090305106 Gell et al. Dec 2009 A1
20110039183 Armstrong et al. Feb 2011 A1
20110183233 Armstrong et al. Jul 2011 A1
20120231368 Hata Sep 2012 A1
20140051010 Armstrong et al. Feb 2014 A1
20140141344 Miller et al. May 2014 A1
Foreign Referenced Citations (27)
Number Date Country
101147285 Mar 2008 CN
101295792 Oct 2008 CN
102725902 Oct 2012 CN
1048839 Nov 1966 GB
3196465 Aug 1991 JP
H06150943 May 1994 JP
6215778 Aug 1994 JP
2000-340240 Aug 2000 JP
2000-281438 Oct 2000 JP
2003068324 Mar 2003 JP
2004087490 Mar 2004 JP
2007-026874 Feb 2007 JP
2007026874 Feb 2007 JP
2008502113 Jan 2008 JP
2008189838 Aug 2008 JP
2008-305804 Dec 2008 JP
2009059699 Mar 2009 JP
20020092223 Dec 2002 KR
20070095440 Sep 2007 KR
20080010737 Jan 2008 KR
20080097971 Nov 2008 KR
100886239 Feb 2009 KR
20090061870 Jun 2009 KR
WO2004093214 Oct 2004 WO
WO2005041329 May 2005 WO
WO2008019926 Feb 2008 WO
WO2009097110 Aug 2009 WO
Non-Patent Literature Citations (36)
Entry
JPH06150943 A—Machine Translation (Year: 1992).
Republic of China (Taiwan) Office Communication for Taiwanese Patent Application No. 102142390, dated Jan. 19, 2017, 5 pages.
State Intellectual Property Office (SIPO) issued a Third Office Action for PRC (China) Patent Application No. 201380060253.1, dated Dec. 21, 2017, 4 pages.
Second Office Action Issued by State Intellectual Property Office for Chinese Patent Application No. 201380060253.1, dated Apr. 27, 2017, 14 pages including English-language translation.
Ahmad-Khantou et al., “Electrochemical & Microstructural Study of SOFC Cathodes Based on La0.5Sr0.3MnO3 and Pro0.65Sr0.3MnO3,” Electrochemical Society Proceedings, 2001, p. 476-485, vol. 2001-16.
Mori et al., “Lanthanum Alkaline-Earth Manganites as a Cathode Material in High-Temperature Solid Oxide Fuel Cells,” Journal of the Electrochemical Society, 1999, p. 4041-4047, vol. 146.
L.G. Austin, “Cell & Stack Construction: Low Temperature Cells,” NASA SP-120, 1967.
EG & G Services, Parsons, Inc., SAIC, Fuel Cell Handbook, 5th Edition, USDOE, Oct. 2000, p. 9-1-9.4, and 9-12-9-14.
J.M. Sedlak, et al., “Hydrogen Recovery and Purification Using the Solid Polymer Electrolyte Electrolysis Cell,” Int. J. Hydrogen Energy, vol. 6, p. 45-51, 1981.
Dr. Ruhl, “Low Cost Reversible Fuel Cell System,” Proceedings of the 2000 U.S. DOE Hydrogen Program Review, Jun. 15, 2000, NREL/CP-570-30535.
Low Cost, Compact Solid Oxide Fuel Cell Generator, NASA Small Business Innovation Research Program, 2001.
Low Cost, High Efficiency Reversible Fuel Cell (and Electrolyzer) Systems, Proceedings of the 2001 DOE Hydrogen Program Review NREL/CP-570-30535.
Milliken et al., “Low Cost, High Efficiency Reversible Fuel Cell Systems,” Proceedings of the 2002 U.S. DOE Hydrogen Program Review, NREL/CP-610-32405.
K. Eguchi et al., Power Generation and Steam Electrolysis Characteristics of an Electrochemical Cell with a Zirconia or Ceria based Electrode, Solid State Ionics, 86 88, 1996, p. 1245-49.
F. Mitlitsky et al., “Regenerative Fuel Cells for High Altitude Long Endurance Solar Powered Aircraft,” 28th Intersociety Energy Conversion Engineering Conference (IECED), Jul. 28, 1993, UCRL-JC-113485.
Small, Ultra Efficient Fuel Cell Systems, Advanced Technology Program, ATP 2001 Competition, Jun. 2002.
F. Mitlitsky et al., Unitized Regenerative Fuel Cells for Solar Rechargeable Aircraft and Zero Emission Vehicles, 1994 Fuel Cell Seminar, Sep. 6, 1994, UCRL-JC-117130.
Ralph et al., “Cathode Materials for Reduced-Temperature SOFCs,” Journal of the Electrochemical Society, 2003, p. A1518-A1522, vol. 150.
Simmer et al., “Development of Fabrication Techniques and Electrodes for Solid Oxide Fuel Cells,” Electrochemcial Society Proceedings, p. 1050-1061, vol. 2001-16.
Yamamoto et al., “Electrical Conductivity of Stabilized Zirconia with Ytterbia and Scandia,” Solid State Ionics, v79, p. 137-142, Jul. 1995.
Araki et al., “Degradation Mechanism of Scandia-Stabilized Zirconia Electrolytes: Discussion based on Annealing Effects on Mechanical Strength, Ionic Conductivity, and Raman Spectrum,” Solid State Ionics, v180, n28-31, p. 1484-1489, Nov. 2009.
Lybye et al., “Effect of Transition Metal Ions on the Conductivity and Stability of Stabilized Zirconia,” Ceramic Engineering and Science Proceedings, v27, n4, p. 67-78, 2006.
International Preliminary Report on Patentability, International Application No. PCT/US2011/021664, dated Aug. 9, 2012.
International search report and written opinion received in connection with International Application No. PCT/US2013/070783, dated Mar. 10, 2014.
Chinese Office Action received in connection with Chinese Patent Application No. 201180006935.5, dated Jun. 13, 2014 (English translation also provided).
Taiwan Office Action received in connection with Taiwan Patent Application No. 100102963, dated May 6, 2014 (English translation also provided).
Taiwan Search Report received in connection with Taiwan Patent Application No. 100102963, dated May 6, 2014 (English translation also provided).
International Search Report, International Application No. PCT/US2011/021664, dated Sep. 28, 2011.
International preliminary report on patentability received in connection with International Application No. PCT/US2013/070783, dated Jun. 4, 2015.
State Intellectual Property Office (SIPO) First Office Action for PRC (China) Patent Application No. 201380060253.1, dated Sep. 2, 2016, 11 pages.
Office Action from the Republic of China (Taiwan) Intellectual Property Office for Taiwanese Patent Application No. 106134369, dated Mar. 7, 2018, 2 pages.
English-language Translation of the Search Report from Republic of China (Taiwan) Office Communication for Taiwanese Patent Application No. 106134369, dated Mar. 7, 2018, 1 page.
Japan Patent Office, Office Communication, Notice of Reasons for Rejection for Japanese Patent Application No. 2015-543115, dated Sep. 7, 2017, 4 pages.
Taiwanese Office Action from the Intellectual Property Office of ROC (Taiwan) for Patent Application No. 106134369, dated Sep. 25, 2018, and English Translation thereof.
The Fourth Office Action from the State Intellectual Property Office (SIPO) for PRC (China) Patent Application No. 201380060253.1, dated May 28, 2018, 3 pages.
Japan Office Communication, Notice of Reasons for Rejection and Its Brief Summary for Japanese Patent Application No. 2018-091247, dated May 22, 2019, 5 pages including English-language translation.
Related Publications (1)
Number Date Country
20170117567 A1 Apr 2017 US
Provisional Applications (2)
Number Date Country
61792699 Mar 2013 US
61728270 Nov 2012 US
Divisions (1)
Number Date Country
Parent 14083708 Nov 2013 US
Child 15340625 US