Patent Description:
In the context of solid oxide fuel and electrolyzer cells, operating temperatures greater than <NUM> are desirable for the more facile kinetics of the gas reactants and lower resistance of the ionic membrane. High operating temperatures also allow internal reformation of hydrocarbon fuels, which can reduce the system size significantly compared to systems with external reforming. However, the high operating temperatures can reduce electrode performance. <NPL> relates to a composite cathode including Ln<NUM>NiO<NUM> and Sm doped ceria, Ce<NUM>-xSmxO<NUM>-δ. <NPL>addresses issues of the reaction between electrolyte of a doped lanthanum gallium oxide (LSGM) and composite anode formed of CeO<NUM> and NiO.

A need exists for an improved electrode material.

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.

The following description in combination with the figures is provided to assist in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This focus is provided to assist in describing the teachings and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other embodiments can be used based on the teachings as disclosed in this application.

Unless otherwise stated, the term "vol%," when used herein to describe the composition of a layer, refers to a percentage of the total volume of the solids, e.g., excluding porosity, of the layer. Further, unless otherwise stated, the term "mol%," when used herein to describe a dopant concentration, refers to a percentage of the total amount, in moles, of cations in a given compound. Furthermore, the oxygen stoichiometry in any of the formulas provided below may vary slightly and, thus, is considered to include a delta (excess or deficiency), referred to as "d", of +/- <NUM>. In particular, a doped ceria (CeABO(<NUM>-d)) can have oxygen understoichiometry (oxygen deficiency) where d is a deficiency of at most <NUM>, at most <NUM>, or at most <NUM>; and an Ln<NUM>MO<NUM>+d can have oxygen overstoichiometry (oxygen excess) where d is an excess of at most <NUM>, at most <NUM>, or at most <NUM>. For example, La<NUM>Ce<NUM>O<NUM> would include, e.g., La<NUM>Ce<NUM>O<NUM>-d, where d is at at most <NUM>, and La<NUM>NiO<NUM>+d would include, e.g., La<NUM>NiO<NUM>+d, where d is at most <NUM>.

The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing acts are conventional and may be found in textbooks and other sources within the electrochemical arts.

An electrode can include a composite functional layer including a heavily-doped ceria that is suitable for operating temperatures of greater than <NUM>. As used herein, the term "heavily-doped" refers to a dopant concentration of at least <NUM> mol%. In an embodiment, the electrode can include a first phase comprising the heavily-doped ceria and a second phase including an Ln<NUM>MO<NUM> phase, where Ln is at least one lanthanide optionally doped with a metal and M is at least one 3d transition metal, without the reactivity problems encountered with existing composite electrode materials. The concepts are better understood in view of the embodiments described below that illustrate and do not limit the scope of the present invention.

High temperature electrochemical cells can include a number of requirements for high performance. Ideally, the materials should withstand processing temperatures of at least <NUM> without decomposing or forming resistive phases and maintain a stable composition and crystal structure at operating conditions. In addition, the functional layers should retain porosity and facile electron transfer reaction kinetics.

Ln<NUM>MO<NUM> materials can generally provide high electrode performance, where Ln is any of the lanthanide elements and M is a 3d transition metal. In particular, the Ln<NUM>MO<NUM> family of materials can offer a wider operating temperature range (e.g., <NUM> to <NUM>) as compared to other materials only suitable for either higher or lower temperatures. The Ln<NUM>MO<NUM> family of materials provides the additional advantage of mixed ionic electronic conductivity.

However, the Ln<NUM>MO<NUM> family of materials can be reactive with common high temperature electrolytes. Moreover, Ln<NUM>MO<NUM> materials have a high coefficient of thermal expansion (referred to herein as "CTE"), reducing mechanical stability in a multilayer architecture.

A rare earth-doped ceria can form a composite with the Ln<NUM>MO<NUM> materials to form a composite electrode with a reduced CTE. However, a lightly-doped ceria can react with Ln<NUM>MO<NUM> when in intimate contact at elevated temperatures. As used herein, the term "lightly-doped" refers to a dopant concentration of less than <NUM> mol%.

Applicants have discovered that an Ln<NUM>MO<NUM>:ceria composite including a heavily-doped ceria, especially near the solubility limit of ceria, surprisingly does not exhibit the same reactivity as the lightly-doped ceria. The solubility limit is the amount of rare earth oxide that can be incorporated into the ceria lattice while maintaining its fluorite structure. Further, diffusional transport of the lanthanide element from the Ln<NUM>MO<NUM> into the ceria is suppressed since the dopant concentration is close to the solubility limit of Ln in ceria.

As discussed above, the Ln of the Ln<NUM>MO<NUM> phase includes at least one lanthanide. In an embodiment, the Ln of the Ln<NUM>MO<NUM> phase includes at least one lanthanide selected from the group consisting of La, Sm, Er, Pr, Nd, Gd, Dy, or any combination thereof. Further, the at least one lanthanide or combination thereof can be doped with a metal. The metal dopant can include an alkaline earth metal. In a particular embodiment, the alkaline earth metal can include at least one alkaline earth selected from the group consisting of Sr, Ca, Ba, or any combination thereof to increase hole conductivity.

Further, as discussed above, the M of the Ln<NUM>MO<NUM> phase includes a 3d transition metal. In an embodiment, the M of the Ln<NUM>MO<NUM> phase includes at least one 3d transition metal selected from the group consisting of Ni, Cu, Co, Fe, Mn or any combination thereof.

The heavily-doped ceria phase includes a ceria and at least one dopant such that the total dopant concentration is at least <NUM> mol% and no greater than the solubility limit of ceria. The heavily-doped ceria has the general formula:
Ce(<NUM>-x)AxO<NUM>, where A is at least one rare earth dopant, x is greater than <NUM> and no greater than the solubility limit of ceria.

In an embodiment, the rare earth dopant A includes at least one dopant selected from the group consisting of La, Gd, Nd, Sm, Dy, Er, Y, Yb, Ho, or any combination thereof. In a more particular embodiment, the rare earth dopant A includes at least one of La, Gd, Nd, or Sm. It would be expected that the use of heavily-doped ceria for cathode functional layers would lead to lower ionic conductivity. In addition, current literature indicates that electrode performance decreases as x increases up to <NUM>. See, for example, Figure <NUM> of Perez-Coll, et al. , "Optimization of the interface polarization of the La<NUM>NiO<NUM>-based cathode working with the Ce<NUM>-xSmxO<NUM>-δ electrolyte system. " However, Applicant has discovered that, contrary to Perez-Coll et al. , as x increases to <NUM> mol% or greater, even up to the solubility limit of ceria, the more thermodynamically stable the phase is and the diffusion of the lanthanide element from Ln<NUM>MO<NUM> is reduced. That being said, the benefits of increasing the dopant concentration begin to deteriorate beyond the solubility limit of ceria.

As mentioned previously, a lightly-doped ceria phase can be reactive with an Ln<NUM>MO<NUM> phase. Such a reaction can cause diffusion of the Ln into the lightly-doped ceria, leading to a reduction or even a complete removal of the Ln from the Ln<NUM>MO<NUM> phase. In addition, such a reaction can lead to the presence of a metal oxide (MO) and/or a free rare earth oxide (RE<NUM>O<NUM>), which were not initially present in the electrode, particularly when M is Ni. However, in the composite electrode described herein, the reactivity is reduced or avoided such that, in an embodiment, less than <NUM> vol% of free RE<NUM>O<NUM> rare earth oxide is detectable in the functional layer of the electrode. In an embodiment, less than <NUM> vol% of MO metal oxide is detectable in the functional layer of the electrode. The detection method is x-ray diffraction having a detection limit of <NUM> vol%.

In an embodiment, the ceria phase can be present in the functional layer of the electrode in an amount of at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, based on a total volume of the functional layer minus the volume occupied by porosity. For a lightly-doped ceria phase, increasing the volume percent of the ceria phase would increase the likelihood of rare earth diffusion. Thus, higher performance for composite electrodes including a lightly-doped ceria phase would be exhibited at lower concentrations of the ceria phase. On the other hand, as the heavily-doped ceria is near the solubility limit of ceria, the thermodynamic stability is increased and, thus, the volume percent of the ceria phase can be increased without increasing the likelihood of rare earth diffusion.

In an embodiment, the functional layer of the electrode has a porosity of at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, based on a total volume of the functional layer. Further, in an embodiment, the functional layer of the electrode has a porosity of at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, based on a total volume of the functional layer. The porosity is determined by image analysis of the cross section of the layer using an image analysis tool such as ImageJ to view and measure the porosity by contrast.

In an embodiment, the functional layer of the electrode has the functional layer has a thickness of at least <NUM> micron, or at least <NUM> microns, or at least <NUM> microns, or at least <NUM> microns, or at least <NUM> microns. Further, in an embodiment, the functional layer of the electrode has a thickness of at most <NUM> microns, at most <NUM> microns, at most <NUM> microns, or at most <NUM> microns.

The electrode described herein is made by providing starter materials, mixing the starter materials, and sintering the mixture. The starter materials include an Ln<NUM>MO<NUM> material, where Ln is at least one lanthanide optionally doped with a metal and M is at least one 3d transition metal, and a ceria material comprising doped ceria having the general formula Ce(<NUM>-x-y)AxByO<NUM>, where A is at least one rare earth dopant, B is at least one alkaline earth dopant, x is at least <NUM>, y is in a range of <NUM> to <NUM>, and x+y is at least <NUM> and no greater than the solubility limit of ceria.

In an embodiment, a binder system can be added to the Ln<NUM>MO<NUM> material and the ceria material to form a slurry. In an embodiment, the binder system can include at least one polymer. The slurry can be deposited by a ceramic forming technique such as spraying, tape casting or screen printing and then sintered to form an electrode having an Ln<NUM>MO<NUM> phase and a ceria phase. The sintering temperature can be greater than the operating temperature. For example, the sintering temperature can be at least <NUM>, or at least <NUM><NUM>, or at least <NUM>, or at least <NUM>. In an embodiment, the sintering temperature can be no greater than <NUM>, or no greater than <NUM>, or no greater than <NUM>.

The electrode described herein can be utilized as a component in a variety of devices including electrochemical devices, sensor devices, and the like.

In an embodiment, the electrochemical device including the electrode described herein comprises an electrolyte layer, an optional barrier layer, and an anode layer. The electrolyte layer can comprise at least one electrolyte material selected from the group consisting of ceria, zirconia, lanthanum gallate, or a combination thereof.

In a particular embodiment, the electrolyte material includes a stabilized zirconia.

In a particular embodiment, the electrolyte layer includes a doped ceria having the general formula:
Ce(<NUM>-x-y)AxByO<NUM>, where A is at least one rare earth dopant, B is at least one alkaline earth dopant, x is at least <NUM>, y is in a range of <NUM> to <NUM>, and x+y is greater than <NUM> and less than <NUM>. In a particular embodiment, A is La, Gd, Nd, Sm, Dy, Er, Y, Yb, Ho, or any combination thereof. In a particular embodiment, B is Sr, Ca, Ba, or any combination thereof.

The electrolyte layer can have a thickness of at most <NUM> microns, or at most <NUM> microns, or at most <NUM> microns, or at most <NUM> microns, or at most <NUM> microns. Further, the electrolyte layer can have a thickness of at least <NUM> micron, at least <NUM> microns, or at least <NUM> microns.

The electrolyte layer can have a porosity of at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, based on a total volume of the electrolyte layer. Further, while the electrolyte may be completely dense, it is possible that some porosity can exist, such as at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%.

In an embodiment, the electrochemical device includes a barrier layer disposed between the electrode and the electrolyte layer. In a particular embodiment, the barrier layer includes doped ceria having the general formula:
Ce(<NUM>-x-y)AxByO<NUM>, where A is at least one rare earth dopant, B is at least one alkaline earth dopant, x is at least <NUM>, y is in a range of <NUM> to <NUM>, and x+y is greater than <NUM> and no greater than the solubility limit of ceria. In a particular embodiment, A is La, Gd, Nd, Sm, Dy, Er, Y, Yb, Ho, Pr, or any combination thereof. In a particular embodiment, B is Sr, Ca, Ba, or any combination thereof.

In an embodiment, the barrier layer has a porosity of at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, based on a total volume of the barrier layer. In an embodiment, the barrier layer has a porosity of at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, based on a total volume of the barrier layer.

In an embodiment, the barrier layer has a thickness less than the electrolyte layer and the functional layer.

In a particular embodiment, the electrochemical device includes a solid oxide fuel cell (also referred to as "SOFC"), a solid oxide electrolyzer cell (also referred to as "SOEC"), or a reversible SOFC-SOEC. In a particular embodiment, electrode can be an oxygen electrode.

Moreover, the device can be a sensor device comprising the electrode described herein. In a particular embodiment, the sensor device is an amperometric sensor. In another embodiment, the sensor device is a potentiometric sensor.

Many different aspects and embodiments are possible. Some of those aspects and embodiments are described below. After reading this specification, skilled artisans will appreciate that those aspects and embodiments are only illustrative. Embodiments may be in accordance with any one or more of the items as embodiments below.

Embodiment <NUM>. An electrode as defined in claim <NUM>.

Embodiment <NUM>. A method as defined in claim <NUM>.

Embodiment <NUM>. The method of embodiment <NUM>, wherein the sintering temperature is at least <NUM>, or at least <NUM>, or at least <NUM>.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the lanthanide of the Ln<NUM>MO<NUM> phase includes at least one of La, Sm, Er, Pr, Nd, Gd, Dy or any combination thereof.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the lanthanide of the Ln<NUM>MO<NUM> phase is doped with an alkaline earth metal.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the lanthanide of the Ln<NUM>MO<NUM> phase is doped with an alkaline earth metal including at least one of Sr, Ca, Ba, or any combination thereof.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the 3d transition metal of the Ln<NUM>MO<NUM> phase includes at least one of Ni, Cu, Co, Fe, Mn or any combination thereof.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein A is La, Gd, Nd, Sm, Dy, Er, Y, Yb, Ho, or any combination thereof.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein x is at least <NUM>, or at least <NUM>, or at least <NUM>, or at least <NUM>, or at least <NUM>, or at least <NUM>, or at least <NUM>.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein x is at most <NUM>.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein less than <NUM> vol% free rare earth oxide is detectable in the functional layer.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein less than <NUM> vol% of 3d transition metal oxide is detectable in the functional layer.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the ceria phase is present in the functional layer in an amount of at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, based on a total volume of the functional layer minus porosity.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the functional layer has a porosity of at least <NUM> vol%, or at least <NUM> vol%, or at least <NUM> vol%, based on a total volume of the functional layer.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the functional layer has a porosity of at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, based on a total volume of the functional layer.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the functional layer has a thickness of at least <NUM> micron, or at least <NUM> microns, or at least <NUM> microns, or at least <NUM> microns, or at least <NUM> microns.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the functional layer has a thickness of at most <NUM> microns, at most <NUM> microns, at most <NUM> microns, or at most <NUM> microns.

Embodiment <NUM>. The electrode or method of any one of the preceding embodiments, wherein the functional layer includes the Ln<NUM>MO<NUM> phase in an initial composition.

Embodiment <NUM>. An electrochemical device comprising the electrode of any one of the preceding embodiments.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein the electrochemical device is an SOFC, an SOEC, or a reversible SOFC-SOEC.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> and <NUM>, further comprising an electrolyte layer.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein the electrolyte layer has a thickness of at most <NUM> microns, or at most <NUM> microns, or at most <NUM> microns, or at most <NUM> microns, or at most <NUM> microns.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> and <NUM>, wherein the electrolyte layer has a porosity of at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%, based on a total volume of the electrolyte layer.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> to <NUM>, wherein the electrolyte layer comprises at least one of ceria, zirconia, lanthanum gallate or a combination thereof.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein the electrolyte layer includes a doped ceria having the general formula Ce(<NUM>-x-y)AxByO<NUM>, where A is at least one rare earth dopant, B is at least one alkaline earth dopant, x is at least <NUM>, y is in a range of <NUM> to <NUM>, and x+y is greater than <NUM> and less than <NUM>.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein the electrolyte layer includes a stabilized zirconia.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, further comprising a barrier layer disposed between the functional layer and the electrolyte layer.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein the barrier layer includes doped ceria having the general formula Ce(<NUM>-x-y)AxByO<NUM>, where A is at least one rare earth dopant, B is at least one alkaline earth dopant, x is at least <NUM>, y is in a range of <NUM> to <NUM>, and x+y is greater than <NUM> and no greater than the solubility limit of ceria.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein A is La, Gd, Nd, Sm, Dy, Er, Y, Yb, Ho, Pr, or any combination thereof.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> to <NUM>, wherein the barrier layer has a porosity of at most <NUM> vol%, or at most <NUM> vol%, or at most <NUM> vol%.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> to <NUM>, wherein the barrier layer has a thickness less than the electrolyte layer and the functional layer.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> to <NUM>, wherein the electrochemical device is a solid oxide fuel cell and the electrode is an oxygen electrode.

Embodiment <NUM>. The electrochemical device of embodiment <NUM>, wherein the fuel electrode comprises a Ni-YSZ anode electrode.

Embodiment <NUM>. The electrochemical device of any one of embodiments <NUM> to <NUM>, wherein the electrochemical device is a solid oxide electrolyzer cell and the electrode is an anode electrode.

Embodiment <NUM>. A sensor device comprising the electrode of any one of embodiments <NUM> to <NUM>.

Embodiment <NUM>. The sensor device of embodiment <NUM>, wherein the sensor device is an amperometric sensor.

Embodiment <NUM>. The sensor device of embodiment <NUM>, wherein the sensor device is a potentiometric sensor.

The CTE of various samples were measured.

For Sample <NUM>, SDC:LNO mixtures were mixed poly(ethylene glycol) <NUM> and poly(vinyl alcohol) <NUM> as a binder system to form a slurry. Each sample was prepared with <NUM> of the slurry pressed at room temperature in a <NUM> diameter cylinder. After sintering, they were heated up to <NUM> and back down to room temperature at <NUM>/min to measure the CTE. The CTE reported in Table <NUM> is the value over the cooling down cycle in the range of <NUM> to <NUM>. The CTE of LNO-SDC mixtures described in Table <NUM> is low enough to be used for SOFC cathodes with YSZ as the electrolyte. For Sample <NUM>, the initial composition included SDC as Sm<NUM>Ce<NUM>O<NUM> and LNO as La<NUM>NiO<NUM>.

Sample <NUM> was prepared identically to Sample <NUM> except SDC was replaced with LDC40, where the initial composition included LDC40 as La<NUM>Ce<NUM>O<NUM> and LNO as La<NUM>NiO<NUM>. The results for Sample <NUM> are provided in Table <NUM>.

Advantageously, the use of heavily-doped ceria lowers the CTE of the LNO phase, similar to Sample <NUM>. However, unlike Sample <NUM>, the CTE values for heavily-doped ceria in Sample <NUM> follow here the rule of mixture, which further indicates that the phases for Sample <NUM> are thermodynamically stable.

Sample <NUM> included SDC-LNO compositions at <NUM>:<NUM> vol% SDC:LNO, <NUM>:<NUM> vol% SDC:LNO, and <NUM>:<NUM> vol% SDC:LNO, each after annealing at <NUM> for <NUM> hrs. The initial composition for Sample <NUM> included a lightly-doped SDC phase (Sm<NUM>Ce<NUM>O<NUM>), and an LNO phase (La<NUM>NiO<NUM>). The X-ray diffraction (XRD) patterns for Sample <NUM> are provided in the graph of <FIG>. In the case of the <NUM>:<NUM> vol% SDC:LNO mixture, the amount of La incorporated in the ceria lattice could be estimated, by measuring lattice parameters from XRD patterns, as Sm<NUM>La<NUM>Ce<NUM>O<NUM>-δ. Because of the adsorption of La<NUM>O<NUM> in the ceria lattice, LNO is La<NUM>O<NUM> depleted, which leads to its decomposition and the formation of NiO.

Sample <NUM> included LDC30-LNO compositions at <NUM>:<NUM> vol% LDC30:LNO, <NUM>:<NUM> vol% LDC30:LNO, and <NUM>:<NUM> vol% LDC30:LNO, each after annealing at <NUM> for <NUM> hrs. The initial composition for Sample <NUM> included LDC30 as La<NUM>Ce<NUM>O<NUM> and LNO as La<NUM>NiO<NUM>. The XRD patterns for Sample <NUM> are provided in the graph of <FIG>, and shows that the peaks (more specifically (<NUM>) and (<NUM>)) of the lightly-doped ceria, which had been introduced as single-phase ceria, were split. This was not desirable as it indicated significant diffusion of La<NUM>O<NUM> from the LNO phase into the LDC lattice, meaning that the LNO phase is decomposed.

However, when LDC (lanthanum-doped ceria) was introduced with a concentration of dopant at or above <NUM> vol%, and below the solubility limit of ceria, around <NUM> mol%, the peaks of doped ceria are not split, as it can be seen below in the case of <NUM> mol% (Sample <NUM> and <NUM> below), and <NUM> mol% (Sample <NUM> below). The closer the dopant concentration was to the solubility limit, the results were more desirable, as the XRD patterns indicated the composite was more thermodynamically stable.

Sample <NUM> included LDC40-LNO compositions at <NUM>:<NUM> vol% LDC40:LNO, <NUM>:<NUM> vol% LDC40:LNO, and <NUM>:<NUM> vol% LDC40:LNO, each after annealing at <NUM> for <NUM> hrs. The initial composition for Sample <NUM> included LDC40 as La<NUM>Ce<NUM>O<NUM> and LNO as La<NUM>NiO<NUM>. The XRD patterns for Sample <NUM> are provided in the graph of <FIG>, showing there is no split peak.

Sample <NUM> is similar to Sample <NUM> except that it included LDC40-LNO compositions at <NUM>:<NUM> vol% LDC40:LNO, <NUM>:<NUM> vol% LDC40:LNO, <NUM>:<NUM> vol% LDC40:LNO, and <NUM>:<NUM> vol% LDC40:LNO. Like Sample <NUM>, the initial composition for Sample <NUM> included LDC40 as La<NUM>Ce<NUM>O<NUM> and LNO as La<NUM>NiO<NUM>. The XRD patterns for Sample <NUM> are provided in the graph of <FIG>, and are measured at a scale sufficient to show there was no extra peak indicating any decomposition of LNO or formation of NiO.

Sample <NUM> included LDC48-LNO compositions at <NUM>:<NUM> vol% LDC48:LNO, <NUM>:<NUM> vol% LDC48:LNO, and <NUM>:<NUM> vol% LDC48:LNO, each after annealing at <NUM> for <NUM> hrs. The initial composition of Sample <NUM> includes LDC48 as La<NUM>Ce<NUM>O<NUM> and LNO as La<NUM>NiO<NUM>. The XRD patterns are provided in the graph of <FIG>.

Samples <NUM>, <NUM> and <NUM> below showed the stability of NNO and LSNO phases in the presence of a heavily-doped ceria phase.

Sample <NUM> included NDC43-NNO compositions at <NUM>:<NUM> vol% NDC43:NNO and <NUM>:<NUM> vol% NDC43:NNO, each after annealing at <NUM> for <NUM> hrs. The initial composition of Sample <NUM> included NDC43 as Nd<NUM>Ce<NUM>O<NUM> and NNO as Nd<NUM>NiO<NUM>. The X-ray diffraction results are provided in the graph of <FIG>, and show the stability of NNO even in low NNO volume fractions, using a composite having a heavily-doped ceria phase.

Sample <NUM> included LDC40-LSNO compositions at <NUM>:<NUM> vol% LDC40:LSNO, <NUM>:<NUM> vol% LDC40:LSNO, <NUM>:<NUM> vol% LDC40:LSNO, and <NUM>:<NUM> vol% LDC40:LSNO, each after annealing at <NUM> for <NUM> hrs. The initial composition of Sample <NUM> included LDC40 as La<NUM>Ce<NUM>O<NUM> and LSNO as La<NUM>Sr<NUM>NiO<NUM>. The X-ray diffraction patterns are provided in the graph of <FIG>, and show the stability of LSNO, even in low LSNO volume fractions, using a composite having a heavily-doped ceria phase.

Sample <NUM> included LDC48-NNO compositions at <NUM>:<NUM> vol% LDC48:NNO, <NUM>:<NUM> vol% LDC48:NNO, and <NUM>:<NUM> vol% LDC48:NNO, each after annealing at <NUM> for <NUM> hrs. The initial composition for Sample <NUM> included LDC48 as La<NUM>Ce<NUM>O<NUM> and NNO as Nd<NUM>NiO<NUM>. The X-ray diffraction patterns are provided in the graph of <FIG>, and show the stability of NNO, even in low NNO volume fractions, using a composite having a heavily-doped ceria phase with a different rare earth dopant.

For each of Samples <NUM> to <NUM>, the densities listed in Table <NUM> were calculated based on XRD patterns of the single phase materials, and used in the calculations for the vol% of the different mixtures.

Claim 1:
An electrode comprising:
a functional layer comprising an Ln<NUM>MO<NUM> phase, where Ln is at least one lanthanide optionally doped with a metal and M is at least one 3d transition metal;
the functional layer further comprising a ceria phase comprising doped ceria having the general formula Ce(<NUM>-x)AxO<NUM>, where A is at least one rare earth dopant, x is greater than <NUM> and no greater than the solubility limit of ceria.