Electrodes and electrochemical cells

Abstract

Disclosed is an electrode for an electrochemical cell having a first layer comprising a first electrode material of formula Pr(1-x)LnxO(2-0.5x-δ), where Ln is selected from at least one rare earth metal and δ is the degree of oxygen deficiency, 0.01≦x≦0.4. The rare earth metal can be a lanthanide, scandium or yttrium. Also disclosed is an electrochemical cell having such an electrode and a method of making such an electrochemical cell. The electrochemical cell can be an electrolyzer, an oxygen separator, a sensor or a fuel cell. Also disclosed are materials of formula Pr(1-x)LnxO(2-0.5x-δ) and Pr(1-x)SmxO(2-0.5x-δ).

Description

[Technical field]

[0001] The present invention relates to electrodes for electrochemical cells, electrochemical cells containing such electrodes, methods of producing such electrochemical cells and materials for use in such electrodes. [Background technology]

[0002] Electrochemical cells formed with oxide layers (often known as solid oxide batteries: SOC) may be used as fuel cells or electrolysis cells.

[0003] SOC fuel cell units generate electricity using an electrochemical conversion process to oxidize a fuel. SOC fuel cell units can also or instead operate as regenerative fuel cell (or reverse fuel cell) units, often known as solid oxide electrolyzer fuel cell units, for example to separate hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide.

[0004] Solid oxide fuel cells (SOFCs) generate electrical energy through the electrochemical oxidation of a fuel gas (usually hydrogen-based), and the devices are generally ceramic-based and use an oxygen-ion conducting metal oxide-containing ceramic as their electrolyte. Because many ceramic oxygen-ion conductors (e.g., doped zirconium oxide or doped cerium oxide) have useful ionic conductivity at temperatures above 500° C. (for cerium oxide-based electrolytes) or 650° C. (for zirconium oxide-based ceramics), SOFCs tend to be operated at high temperatures.

[0005] In operation, the electrolyte of the SOFC transfers oxygen ions from the cathode to the anode, located on the opposite side of the electrolyte. A fuel, for example from the reformation of a hydrocarbon or alcohol, contacts the anode (usually known as the "anode"), and an oxidant, such as air or an oxygen-rich fluid, contacts the cathode (usually known as the "air electrode"). Conventional ceramic-supported (e.g. anode-supported) SOFCs have low mechanical strength and are vulnerable to fracture. Therefore, metal-supported SOFCs, which have active fuel cell component layers supported on a metal substrate, have been developed in recent years. In these cells, since they only perform an electrochemical function, the ceramic layers can be very thin: i.e., they are not free-standing, but rather are thin coatings / films laid down on and supported by a metal substrate. Such metal-supported SOFC stacks are more robust, less expensive, have better thermal properties than ceramic-supported SOFCs, and can be sealed using conventional metal welding techniques.

[0006] Applicant's previous patent application WO 2015 / 136295 discloses a metal-supported SOFC in which electrochemically active layers (or active fuel cell component layers) including anode, electrolyte and cathode layers are each deposited (e.g. as a thin coating / film) on and supported by a metal support plate (e.g. foil). The metal support plate has porous regions surrounded by non-porous regions with the active layers deposited on the porous regions, so that gas can pass through the pores from one side of the metal support plate to the other side to access the active layers coated thereon. The porous regions include small openings (holes through the metal foil substrate) that extend through the support plate and overlie the anode (or cathode, depending on the orientation of the electrochemically active layers).

[0007] A solid oxide electrolysis cell (SOEC) may have the same structure as a SOFC, but is actually a SOFC operated in reverse, or regenerative, mode to accomplish the electrolysis of water and / or carbon dioxide.

[0008] The anode, electrolyte, and cathode of an SOC may each be formed of one or more layers to optimize operation. Effective cathode materials allow diffusion of oxygen to the cathode / electrolyte interface and have a thermal expansion coefficient similar to that of the electrolyte. Practical cathode materials often have the perovskite structure ABX3, where A and B are different metal ions (there may be more than one A and B metal ion), and X may be O. In some SOFCs, the cathode is formed of an active layer close to the electrolyte that has high activity for the electrochemical reduction of oxygen, and a bulk layer that may be a metallic conductor. There are many known cathode materials.

[0009] Cruz Pacheco et al., (J. Phys: Conference Series, vol. 687, no. 1, 2016) disclose the synthesis of praseodymium-doped cerium oxide by polymerization combustion method for application as an anode component in SOFC devices.

[0010] Doped praseodymium oxide has been investigated for reasons unrelated to SOC. For example, Zoellner et al. (J. Crystal Growth, vol. 355, no. 1, 2012, p. 159-165) disclose the stoichiometry-structure correlation of epitaxial cerium-doped praseodymium oxide films on Si(111). Knauth et al. (J. European Ceramic Society, vol. 19, no. 6-7, 1999, p. 831-836) disclose the non-stoichiometry and relaxation kinetics of nanocrystalline mixed praseodymium-cerium oxide. Popescu Ione et al. (Applied Catalysis A: General, vol. 578, 2019, p. 30-39) disclose a study on the catalytic oxidation performance of Ce-Pr mixed oxides. Simona Somacescu et al. (J. Nanoparticle Research; vol. 14, no. 6, 2012, p. 1-17) disclose the CePrO structure, morphology, interfacial chemistry, and catalytic performance. Kang et al. (J. Alloys and Compounds, vol. 207-208, 1994, p. 420-423) disclose the structure and structural defects in colloidal particles modified in situ in HREM.

[0011] U.S. Patent No. 6,117,582 discloses a cathode composition for solid oxide fuel cells having a cathode made from a transition metal perovskite such as PrCoO3 or praseodymium manganite. Nicollet, C, et al., International Journal of Hydrogen Energy, September 2016, Vol. 41, Issue 34, pages 15538-15544, discloses the use of Pr6O3 as an electrocatalyst for the oxygen reduction reaction. 11and its use as a cathode in SOFCs. CN-A-106 057 641 discloses La, Nd and Gd doped Pr semiconducting oxides. Wang et al 2017 Meet.Abstr.(MA2017-02)1730 discloses Pr,Nd)2NiO4 in combination with (Pr,Nd)2NiO4 (PNNO) to improve the activity and phase stability of PNNO used as a cathode for solid oxide fuel cells. 1-x Nd x O 2-d Biswas, R. et al. (1997) Journal of Materials Science Letters. 16. 1089-1091 discloses Pr 1-x La x O 2-δ (x=0.05, 0.1, 0.2) discloses the preparation, structure and electrical conductivity. Zhu, et al. Advanced Materials Research, vol. 1065-1069, (2014), pp. 1921-1925 discloses Ce 0.8 Pr 0.2-x Nd x O 2-δ (x=0.02, 0.05, 0.1) is disclosed. WO 2006 / 106334 A1 discloses a solid oxide fuel cell (SOFC) in which the cathode material comprises a doped material having a perovskite structure that may include praseodymium. This structure has the conventional notation ABX3, where cerium is substituted on the "B" site.

[0012] However, there remains a need to provide electrode materials that have suitable properties for use in electrochemical cells.

[0013] It is an object of the present invention to address such a need. Summary of the Invention

[0014] The present invention therefore relates in a first aspect to an electrode for an electrochemical cell, the electrode having the formula Pr (1-x) Ln x O(2-0.5x-δ) wherein Ln is selected from at least one rare earth metal, δ is the degree of oxygen deficiency, and 0.01≦x≦0.4.

[0015] δ may vary depending on the environment and the history of the first electrode material. In oxidizing environments in many praseodymium-containing oxides, praseodymium is in thermodynamic equilibrium with its +3 to +4 oxidation states, depending on temperature and oxygen partial pressure. Pr 4+ But, Pr 3+ When praseodymium is reduced to 0, an oxygen vacancy is created. The oxygen vacancy induced by praseodymium reduction is known as an additional vacancy. Using Kroger-Bink notation, the equilibrium can be expressed as:

[0016]

number

[0017] (In the formula, V O ’’ is an oxygen vacancy.)

[0018] In the first electrode material, δ may be 0.25 or less, suitably 0.2 or less, more suitably ≦0.15.

[0019] δ may have a lower limit of 0.0001, sometimes 0.001, sometimes 0.005, sometimes 0.01, and sometimes 0.05.

[0020] The addition of (eg trivalent) dopant cations to praseodymium oxide creates inherent oxygen vacancies within the structure. In the first electrode material, suitably, a rare earth metal may function as a dopant.

[0021] The rare earth metal may be selected from the lanthanides, Sc, Y and mixtures thereof.

[0022] Suitably the rare earth metal is not cerium.

[0023] Suitably, the rare earth metal may be selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof.

[0024] More suitably, the rare earth metal may be selected from La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof.

[0025] Most suitably, the rare earth metal may be selected from La, Nd, Sm, Eu, Gd, and Yb; preferably Nd, Sm, Eu, Gd, more preferably Gd or Sm, most preferably Sm.

[0026] As used herein, Ln refers to a dopant, and thus Ln excludes Pr.

[0027] The oxides of praseodymium represent a system of phases with some variation in composition. Single phase PrO2 is typically formed in pure oxygen at high pressures (>20,000 kPa). Among the various oxides, PrO 11 is particularly stable. At ambient temperature and pressure, PrO 11 is a mixed valence state of Pr(III) and Pr(IV) with additional oxygen vacancies, promoting oxygen ion conductivity. 11 It is believed (without wishing to be bound) that this forms a cubic fluorite type structure with the praseodymium ion in the complex providing the catalytic activity.

[0028] Advantageously, the presence of a rare earth metal dopant in the first electrode material may result in the formation of additional intrinsic oxygen vacancies, which may stabilize the cubic fluorite structure of the material.

[0029] Suitably, the ionic radius of Ln may be similar to that of praseodymium(IV). This is advantageous as it may reduce lattice distortion and result in a more stable structure. The ionic radius of Pr(IV) (8 coordinates) is 110 picometers.

[0030] Thus, as disclosed herein, particularly suitable rare earths include La, Nd, Sm, Eu, and Gd, or mixtures thereof. Selected Ln(III) ionic radii are shown in Table 1 below.

[0031] [Table 1]

[0032] In the first electrode material, x may be selected to achieve a balance between oxygen vacancy concentration and ion mobility, for example 0.02-0.25. Advantageously, x may be in the range of 0.02≦x≦0.3; 0.03≦x≦0.3; 0.04≦x≦0.3; 0.05≦x≦0.3; 0.05≦x≦0.27; 0.05≦x≦0.25; 0.05≦x≦0.25; or 0.05≦x≦0.3. Suitably, x may be 0.08-0.2 or 0.08-0.12, more suitably x may be about 0.1; about 0.15; or about 0.2.

[0033] Therefore, preferably, the first electrode material has the formula Pr 0.9 Ln 0.1 O (1.95-δ) ,Pr 0.85 Ln 0.15 O (1.925-δ) ,Pr 0.8 Ln 0.2 O (1.9-δ) or mixtures thereof, where Ln is La, Nd, Sm, Eu, Gd, or Yb; preferably Sm.

[0034] The first layer of the electrode can consist essentially of a first electrode material. Optionally, the first layer may include a composite layer containing the first electrode material and at least one additional material. The additional material may include, for example, doped ceria or doped zirconia or a mixture thereof. Doped ceria may include cerium gadolinium oxide (CGO). Doped zirconia may be a solid solution corresponding to the formula Zr (1-x) Y x O (2-0.5x δ )(where 0 < x ≦ 0.2).

[0035] Thus, the first layer may include 20 wt% or more of the first electrode material; optionally 25 wt% or more of the first electrode material; optionally 30 wt% or more of the first electrode material; optionally 35 wt% or more of the first electrode material; optionally 40 wt% or more of the first electrode material; optionally 45 wt% or more of the first electrode material; optionally 50 wt% or more of the first electrode material; optionally 55 wt% or more of the first electrode material; optionally 60 wt% or more of the first electrode material.

[0036] Alternatively, the first layer may include 80 wt% or more of the first electrode material; optionally 85 wt% or more of the first electrode material; optionally 90 wt% or more of the first electrode material; optionally 95 wt% or more of the first electrode material.

[0037] Advantageously, the first electrode material may have a cubic microcrystalline structure; preferably a fluorite-type microcrystalline structure. Thus, at least one phase of the first electrode material may have a fluorite-type crystal structure and may have a lattice constant in the range of a = 5.4 - 5.5 Å; and / or may have a microcrystalline size of, for example, 20 - 85 nM. The first electrode material essentially includes or consists of a single phase having a cubic fluorite-type structure. Such a structure may be more stable and may have more predictable oxygen ion transport properties than a plurality of different phases having various degrees of oxygen non-stoichiometry.

[0038] The first electrode material has a size d in the range of 0.5 μm to 1.5 μm. 90 As used herein, d 90 , d90, d(90) or D90 is the number of particles in a tested sample that are 90% of the size 90 Smaller than particle size or d 90 The particle size is such that the percentage of smaller particles is 90%.

[0039] The first electrode material is ≧7m 2 / g; appropriately 10m 2 / g, more appropriately 12m 2 / g, most appropriately 20m 2 / g or more (eg, BET: Brunauer, Emmett, Teller, specific surface area).

[0040] The first electrode layer advantageously has a resistivity of ≦100 mΩcm at 600° C. 2 or <300mΩcm at 500℃ 2 The activation energy for oxygen reduction / exhaustion is about 100-110 kJmol -1 may be in the range.

[0041] The first layer may have a thickness in the range of 1 μm to 7 μm, optionally 1 μm to 6 μm; 1 μm to 5 μm; 1 to 4 μm or about 3 μm.

[0042] The electrodes may be multi-layered electrode systems that provide additional and / or improved properties for the electrochemical cell. For example, the electrodes may be two-layer, three-layer, four-layer or five-layer systems, or may have more than five layers. In general, each layer of the electrode system may be the same or different, and if different, may be made of different materials, and the electrode system as a whole may have different properties and applications.

[0043] Thus, the electrode may include at least a second layer that includes a second electrode material. In some cases, the second electrode material may be electrically conductive, and in some cases, may be a conductive ceramic material.

[0044] The second layer may have a thickness in the range of 10 μm to 80 μm; 15 μm to 75 μm; 17 μm to 73 μm; 20 μm to 70 μm; 20 μm to 65 μm; 20 μm to 60 μm; 25 μm to 55 μm; 30 μm to 50 μm; or 35 μm to 45 μm.

[0045] The thickness ratio of the first electrode layer to the second electrode layer may be in the range of 1-20; suitably 1-10, more suitably 1-6, and optionally 1-5.

[0046] Thus, in a second aspect, the present invention provides an electrode for an electrochemical cell, comprising a compound of formula Pr (1-x) Ln x O (2-0.5x-δ) wherein Ln is selected from at least one rare earth metal, δ is the degree of oxygen deficiency, and 0.01≦x≦0.4, and at least one second layer comprising a second electrode material.

[0047] As an example, the first and second layers of the electrode system may each include a first layer as described above for use as a cathode active layer (also known as a cathode active layer CAL in SOFCs) and a second layer as a cathode bulk layer (also known as a cathode bulk layer CBL in SOFCs). The cathode bulk layer may have a higher electrical (i.e., electronic) conductivity than the first layer and therefore may function as a current collector.

[0048] The first layer may be located next to the electrolyte (which may itself be an electrolyte system comprised of multiple layers) with either an intermediate layer between the first layer of electrode and the electrolyte (e.g. a further layer of electrode) or the first layer is in direct contact with (i.e. immediately adjacent to) a layer of electrolyte.

[0049] The second layer (e.g., cathode bulk layer) may advantageously be formed of or include a second electrode material that is electrically conductive, e.g., may be a metallic conductor at the operating temperatures of the electrochemical cell and may have a relatively high electronic conductivity at those temperatures. The material of the second layer is preferably chemically and mechanically stable. The second layer, e.g., cathode bulk layer, is usually porous (as is usually the first layer) to allow good interaction with oxygen on the air side of the cell. The electrocatalytic activity of the second layer (e.g., cathode bulk layer) may be less than that of the first layer (which may have a high electrocatalytic activity as described above).

[0050] The second electrode material may comprise an electronically conductive ceramic material, preferably having a perovskite structure, ABX3.

[0051] Suitable second electrode materials include lanthanum cobaltite, lanthanum ferrite, lanthanum nickel ferrite, La 0.99 Co 0.4 Ni 0.6 O (3-δ) (LCN60) and mixtures thereof.

[0052] In some cases, the second layer may be a composite layer further comprising at least one additional second electrode material. The additional electrode material may optionally comprise strontium, including materials selected from rare earth strontium cobaltite; rare earth strontium ferrite, rare earth strontium cobalt ferrite, and the rare earth component may optionally be Pr, La, Gd and / or Sm, preferably Pr.

[0053] The composite second electrode layer may contain the second electrode material and an additional electrode material in a ratio of 1:10 to 10:1 by weight, optionally 1:5 to 5:1 by weight, and optionally 1:1 to 5:1 by weight. Optionally, the composite second electrode layer may contain 60 wt% or more of the second electrode material; optionally 65 wt% or more of the second electrode material; optionally 70 wt% or more of the second electrode material; optionally 75 wt% or more of the second electrode material.

[0054] The electrode may further include a third layer that may contain a third electrode material.

[0055] To improve the adhesion between the first electrode layer and the second electrode layer, if necessary, the third layer may optionally be located between the first layer and the second layer.

[0056] Optionally, the third electrode material may include an oxygen ion conductor. The oxygen ion conductor may preferably include doped ceria, or doped zirconia or a mixture thereof. The doped ceria may preferably include cerium gadolinium oxide (CGO) which is a solid solution having the formula Ce (1-x) Gd x O (2-0.5x-δ) (where 0 < x ≦ 0.5). The doped zirconia may be a solid solution corresponding to the formula Zr (1-x) Y x O (2-0.5x δ )(where 0 < x ≦ 0.2).

[0057] Furthermore or alternatively, the third electrode material may optionally include a material selected from rare earth strontium cobaltite; rare earth strontium ferrite, rare earth strontium cobalt ferrite, and may contain strontium, and the rare earth component may optionally be Pr, La, Gd, and / or Sm; preferably Pr.

[0058] In some cases, the third electrode material may comprise a mixture of rare earth strontium cobaltite or rare earth strontium ferrite and rare earth doped ceria (REDC). The ratio of such a mixture may be 70:30 by weight to 30:70 by weight, for example 60:40 by weight of rare earth strontium cobaltite, rare earth strontium ferrite or rare earth strontium cobalt ferrite to REDC, for example 60:40 rare earth strontium cobaltite to REDC. A particularly suitable third electrode material is 60:40 by weight of praseodymium strontium cobaltite (e.g. PSC 551:Pr 0.5 Sr 0.5 It may also comprise a mixture of CoO3) and CGO.

[0059] The third electrode material can promote good adhesion between the first and second electrode layers and can reduce any reaction under cell conditions between the second electrode material (e.g., LCN60) and the first electrode material that can result in the formation of secondary phases, which can lead to poor adhesion and potentially increased ohmic resistance.

[0060] The third electrode layer may further act as a poison getter for the first electrode layer, since contaminants in the cell may react with the third electrode material (including, for example, strontium cobaltite / cobalt ferrite) before contacting the first electrode layer. This advantageously protects the first electrode material and layer from decomposition. Such contaminants may include chromium, which tends to vaporize stainless steel components at high temperatures and react to form stable chromate phases across the active surface of the cathode; silicon, which physically blocks the active surface of the cathode; and sulfur from SO2 in the air, which tends to react to form sulfates.

[0061] The third layer may have a thickness in the range of 1 μm to 5 μm; 1 μm to 4 μm; 2 μm to 5 μm; or 2 μm to 4 μm.

[0062] Thus, the electrode is advantageously of formula Pr(1-x) Ln x O (2-0.5x-δ) and at least a third layer comprising a third electrode material as previously described.

[0063] The electrode advantageously has at least one of the formula Pr (1-x) Ln x O (2-0.5x-δ) In some cases, the electrode composition may include multiple layers, including a first layer including a first electrode material as described above, a third layer including a third electrode material as described above, and a second layer including a second electrode material as described above.

[0064] The layers of the electrode may be pressed, and possibly isostatically pressed, while being sintered to improve adhesion and other properties.

[0065] Typically, the electrode may be a cathode in an electrochemical cell, such as a SOC, SOFC or SOEC.

[0066] Thus, in a third aspect, the present invention provides an electrochemical cell comprising an electrode according to any one of the preceding claims, and optionally further comprising one or more electrolytes, a second electrode and a substrate. The second electrode may be a second anode.

[0067] The first electrode material has excellent activity and other properties, in contrast to some electrode materials, and does not need to include alkaline earth metal oxides (e.g., strontium oxide), which can be problematic in electrochemical cells, especially since they can react with zirconia-based electrolytes.

[0068] Thus, in a fourth aspect, the present invention provides an electrochemical cell comprising an electrode having the formula Pr (1-x) Ln x O (2-0.5x-δ)wherein Ln is selected from at least one rare earth metal, δ is the degree of oxygen deficiency, and 0.01≦x≦0.4; and the first layer comprising the first electrode material is in direct contact with the material comprising zirconia.

[0069] The zirconia-containing material can be a layer of an electrolyte in an electrochemical cell.

[0070] Thus, the electrochemical cell typically further comprises an electrolyte, and the zirconia-containing material may form a layer of the electrolyte.

[0071] The layer with the zirconia-containing layer can be a main electrolyte layer or an intermediate layer (e.g., a thin intermediate layer) on another main electrolyte layer (which may contain ceria, for example). Due to the degree of electrical conductivity of ceria-based electrolytes, a thin zirconia electron blocking layer may be applied to the SOC as an electrical insulating layer for the electrolyte.

[0072] Thus, materials containing zirconia may form a substantial electronically insulating layer for the electrolyte.

[0073] In known electrochemical cells, a buffer (or protective) layer of doped ceria (e.g., CGO) between the cathode and the zirconia layer is often deposited to avoid reactions between zirconia and alkaline earth metal oxides.

[0074] Avoiding the need for a buffer layer is highly advantageous as it can significantly reduce the manufacturing costs of the cell due to potentially lower processing temperatures and fewer sintering / deposition steps for the cell overall, and can also improve the quality of the final zirconia-containing layer after processing.

[0075] The zirconia-containing material may be selected from scandia-stabilized zirconia (ScSZ), yttria-stabilized zirconia (YSZ), scandia-ceria-co-stabilized zirconia (ScCeSZ), ytterbia-stabilized zirconia (YbSZ), scandia-yttria-co-stabilized zirconia (ScYSZ), and mixtures thereof.

[0076] The electrochemical cell may include a multi-layer electrolyte, and thus may optionally further include an electrolyte layer comprising doped ceria selected from samarium-doped ceria (SDC), gadolinium-doped ceria (GDC or CGO), samaria-gadolinia doped ceria (SGDC) and mixtures thereof.

[0077] The electrochemical cell may further comprise a substrate; optionally a metal substrate, preferably a steel substrate. The substrate may be porous.

[0078] The metal substrate may be a metal foil (i.e., solid metal) that is provided with openings. This has the advantage that the porosity can be tailored and located in specific areas of the substrate. Alternatively or additionally, the metal substrate may have inherent porosity (e.g., isotropic porosity) formed, for example, as a tape molded by powder depositing a film and then sintering to form a porous substrate. References herein to a metal substrate or porous steel plate may refer to either of these.

[0079] The electrochemical cell may be an electrolyser, an oxygen separator, a sensor or a fuel cell, or an electrolysis cell, preferably a SOFC.

[0080] Thus, the electrochemical cell may be a fuel cell, or an electrolysis cell. The cell may be based on a solid oxide electrolyte, possibly a metal-supported solid oxide battery. In fuel cell mode, the fuel is in contact with the anode (fuel electrode) and an oxidant, such as air or an oxygen-rich fluid, is in contact with the cathode (air electrode), so that in fuel cell mode operation, the air electrode is the cathode. A solid oxide electrolysis cell (SOEC) may have the same structure as a SOFC, but is essentially a SOFC operated in reverse or regenerative mode to achieve electrolysis of water and / or carbon dioxide by using a solid oxide electrolyte to produce hydrogen gas and / or carbon monoxide and oxygen.

[0081] Thus, in a fifth aspect, the present invention provides a method of producing an electrochemical cell, the method comprising the steps of optionally providing a substrate having an anode layer and a layer comprising an electrolyte deposited thereon, applying a source of Pr and Ln to the substrate (with or without optional layers comprising an anode layer and one or more electrolyte layers) to form a cathode layer, where Ln is selected from at least one rare earth metal, optionally drying, and optionally sintering the cathode layer; thereby forming a cathode.

[0082] In some cases, the method may further include applying material to the substrate to form at least one electrolyte layer, applying sources of Pr and Ln over the electrolyte layer to form a cathode layer, optionally drying, and co-sintering the electrolyte layer and the cathode layer.

[0083] For example, a cathode layer (e.g., active cathode layer, CAL) may be co-fired (i.e., co-sintered) with an underlying electrolyte material layer, where both layers have been laid down (and possibly pressed) sequentially as green layers. At least one electrolyte layer (and there may of course be other electrolyte layers) may be a layer comprising zirconia (e.g., an electron blocking layer). Co-sintering is highly advantageous as it allows for production in fewer steps.

[0084] In a sixth aspect, the present invention provides a compound of formula Pr (1-x) Ln x O (2-0.5x-δ) where Ln is selected from at least one rare earth metal, δ is the degree of oxygen deficiency, and 0.01≦x≦0.4.

[0085] In a seventh aspect, the present invention provides a compound of formula Pr (1-x) Sm x O (2-0.5x-δ) where δ is the degree of oxygen deficiency and 0.01≦x≦0.4.

[0086] A method of producing a material according to the sixth or seventh aspect of the invention comprises: (a) preparing a first solution comprising a soluble Pr salt, preferably Pr nitrate, and a soluble Ln salt, preferably Ln nitrate; (b) mixing the first solution of (a) with a second solution capable of reacting with the salt of (a) to form an insoluble precipitate, whereby the insoluble precipitate may be thermally decomposed; (c) sintering the insoluble precipitate to decompose the insoluble precipitate and produce a material according to the first aspect of the invention. may include:

[0087] A method of forming an electrode including at least a first electrode layer may include the steps of preparing a suitable dispersion in a carrier of the first electrode layer material, applying a coating of the dispersion to a substrate; and sintering the coating to form a cathode.

[0088] Sintering may be carried out at a temperature in the range of 750° C. to 900° C., preferably 800° C. to 870° C. Sintering may be carried out in an air atmosphere.

[0089] definition As used herein, the terms "lanthanoid" and "lanthanide" are used interchangeably to refer to metallic chemical elements having atomic numbers 57-71.

[0090] The term "dopant" as used herein is not intended to be limited to a maximum percentage of an element, ion, or compound added to a chemical structure. Similarly, the term "doping" is intended to mean the addition of a certain amount of an element, ion, or compound to a material. There is no maximum amount of material limited, beyond which further addition of material is not considered doping.

[0091] The term "perovskite structure" as used herein generally refers to a single network of chemically bonded crystalline structures having a perovskite (ABX3) structure. This does not mean that this single network needs to have a single uniform crystalline structure throughout the entire structure. However, when different crystalline structures occur between different regions of the network, these regions often have complementary structures that allow chemical bonds to form between them more easily.

[0092] The term "solid oxide cell" (SOC) is intended to encompass both solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs).

[0093] The term "atomic percent" or "atomic percentage" (abbreviated herein as "at. %") refers to the percentage of atoms for a specified dopant site.

[0094] The term "source of" an element, compound or other material refers to a material that contains that element, compound or other material, whether or not it is chemically bound to the source. The source of an element, compound or other material may be an elemental source (e.g., Ln, Sm, Pr, or O2) or may be in the form of a compound or a mixture that contains the element, compound, or other material that contains one or more of those elements, compounds, or materials.

[0095] References herein to electrochemical cells, SOCs, SOFCs and SOECs may refer to cylindrical or planar cells. The electrochemical cell units may be cylindrical or planar in configuration. Planar fuel cell units may be arranged on top of each other in a stack arrangement, for example 100-200 fuel cell units in a stack with the individual fuel cell units electrically arranged in series.

[0096] An electrochemical cell can be a fuel cell, a reversible fuel cell or an electrolysis cell. In general, these cells may have the same structure, and a reference to an electrochemical cell may refer to any of these types of cells (unless the context suggests otherwise).

[0097] As used herein, the terms "oxidant electrode" or "air electrode" and "fuel electrode" may be used interchangeably to refer to the cathode and anode, respectively, of a SOFC, due to potential confusion between fuel cells and electrolysis cells.

[0098] Although cells are described herein in which the fuel electrode (eg, anode) is laid down first on the substrate, the invention also encompasses cells in which the cathode is laid down first on the substrate.

[0099] The cells described herein include metal-supported cells, in which the layers of the cell are supported by a metal substrate, although the invention also encompasses anode-supported, electrolyte-supported, or cathode-supported cells, in which each layer provides structural support for all other layers coated thereon.

[0100] The electrochemical cell encompassed by the present invention comprises: a) Two flat components welded together with a volume of fluid between them (e.g. a substrate with an electrochemical layer and an interconnect (separate plate)). b) Three flat components welded together with a volume of fluid between them (e.g., a substrate with electrochemical layers and interconnects (separate plates) and a spacer that provides the volume of fluid). may include:

[0101] The various features of the aspects of the disclosure described herein may be used in combination with any other feature in the same or other aspects of the disclosure, with appropriate modifications as necessary, as will be understood by those skilled in the art.

[0102] Moreover, it is specifically envisaged that any aspect of the present invention or disclosure may "comprise" the features described in relation to that aspect, but may "consist of" or "consist essentially of" those features outlined in the claims.

[0103] The invention will now be described with reference to the accompanying drawings and examples. [Brief description of the drawings]

[0104] [Figure 1] FIG. 1 illustrates a scanning electron micrograph (SEM) cross-section of a SOFC including a cathode active layer (CAL) comprising a material according to the present invention. [Diagram 2] FIG. 2 illustrates the X-ray diffraction (XRD) spectrum (Cu K-α radiation) of Pr0.9Gd0.1O(1.95-δ). [Diagram 3] FIG. 3 illustrates the XRD spectrum (Cu K-α radiation) of Pr0.8Gd0.2O(1.90-δ). [Figure 4] FIG. 4 illustrates the XRD spectrum (Cu K-α radiation) of Pr0.9Sm0.1O(1.95-δ). [Diagram 5]FIG. 5 illustrates the XRD spectrum (Cu K-α radiation) of Pr0.85Sm0.15O(1.925-δ). [Figure 6] FIG. 6 illustrates the XRD spectrum (Cu K-α radiation) of PrLaO(1.95-δ). [Figure 7] FIG. 7 illustrates the XRD spectrum (Cu K-α radiation) of Pr0.8La0.2O(1.90-δ). [Figure 8] FIG. 8 illustrates the XRD spectrum (Cu K-α radiation) of PrYbO(1.95-δ). [Figure 9] FIG. 9 illustrates the XRD spectrum (Cu K-α radiation) of Pr0.8Yb0.2O(1.90-δ). [Figure 10] FIG. 10 illustrates the XRD spectrum (Cu K-α radiation) of undoped Pr6O11. [Figure 11] FIG. 11 shows curves of cubic lattice constant calculated from XRD as a function of dopant and dopant level. [Figure 12] Figure 12 shows the curves of normalized polarization resistance as a function of temperature for cells in a 17-layer stack. A variety of cathode variations are compared to a standard composite cathode. [Figure 13] Figure 13 shows the curves of normalized polarization resistance as a function of temperature for cells in a 17-layer stack. A larger selection (than in Figure 12) of different cathode variants is compared to the standard composite cathode. [Figure 14] FIG. 14 shows a box plot of the OCV of the cells in Example 6 compared to the standard cell at 570° C. [Figure 15] FIG. 15 shows the average OCV of the cells of Example 6 as a function of temperature compared to the standard cells and theoretical values. [Figure 16] FIG. 16 shows a scanning electron micrograph (SEM) cross section of the SOC according to Example 5. [Figure 17] FIG. 17 shows a detailed SEM cross section of the cathode-electrolyte interface of the SOC according to Example 5. [Figure 18] FIG. 18 shows an SEM cross-section of the cathode-electrolyte interface of an SOC according to Example 6. [Figure 19] FIG. 19 shows the average OCV of the Example 7 cells compared to the standard cells at 570° C. [Figure 20] FIG. 20 shows a graph of polarization resistance as a function of temperature for cells using the composite CAL in Example 9 normalized to the standard cell with a PSC / CGO composite cathode active layer (standard cell=1.0). [Figure 21] 21(a) and 21(b) show scanning electron micrograph (SEM) cross-sections at different magnifications of a SOC according to Example 9 having a cathode co-fired with a ceria interfacial layer. [Figure 22] FIG. 22 shows a scanning electron micrograph (SEM) cross section of an SOC according to Example 9 having a ceria interfacial layer and a separately sintered cathode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0105] FIG. 1 shows an anode (10), a doped ceria electrolyte layer (20), a zirconia layer (30), PGO10 (Pr 0.9 Gd 0.1 O 1.95-δ 1 illustrates an SOC that includes a cathode active layer, a CAL (40), and a perovskite cathode bulk layer (50), a CBL. Although not shown, the SOC in FIG. 1 may be deposited on a metal surface, such as the surface of a metal, particularly a steel, and more particularly a ferritic stainless steel layer, typically a foil layer.

[0106] The CAL (40) comprises a material according to the invention. The anode (10), the doped ceria interlayer (20), the zirconia interlayer (30) and the cathode bulk layer (50) are types of layers whose compositions are known to those skilled in the art, as are the methods of manufacture and application. See, for example, WO 2009 / 090419 A2, which discusses methods for the laying down of these types of layers, and their representative compositions, along with methods for laying down such layers on metal substrates, in particular stainless steel substrates. The layers (including the cathode layer) may exhibit good adhesion or may be isopressed to improve adhesion.

[0107] Materials according to the invention have been prepared, analyzed and tested. Figures 2 to 9 show the following materials according to the first embodiment of the invention: 0.9 Gd 0.1 O (1.95-δ)、 Pr 0.8 Gd 0.2 O (1.90-δ)、 Pr 0.9 Sm 0.1 O (1.95-δ)、 Pr 0.85 Sm 0.15 O (1.925-δ)、 Pr 0.9 La 0.1 O (1.95-δ)、 Pr 0.8 La 0.2 O (1.90-δ)、 Pr 0.9 Yb 0.1 O (1.95-δ)、 Pr 0.8 Yb 0.2 O (1.90-δ) The XRD spectrum (Cu K-α radiation) of

[0108] Each of these XRD spectra indicates the presence of a single-phase cubic fluorite structure. This is in contrast to the XRD spectrum in FIG. 10 (undoped PrO 119). The phase with the larger lattice constant (and therefore the smaller diffraction angle for all peaks) has a higher proportion of trivalent praseodymium. This information can be derived from the fact that each peak is not a single peak, as is the case in Figures 2 to 9, but a doublet containing two closely adjacent peaks. This phase instability can be explained by the fact that, as mentioned above, PrO 11 is specific to.

[0109] FIG. 11 shows the curves of cubic lattice constant calculated from XRD as a function of dopant and dopant level, with PrO2 provided as a reference. As previously discussed, Pr 3+ The ion is Pr 4+ ions (113 picometers vs. 110 pm). 11 contains both of these ions in thermodynamic equilibrium, so PrO 11 has a larger lattice constant than PrO2. The effects observed in Figure 11 are consistent with this. For example, the small Yb 3+ When ions (ionic radius: 100.8 pm) are added, their presence is reflected by the oversized Pr 3+ The effect of the La ions is nullified, and the lattice constant decreases, tending towards that of pure PrO2. Conversely, the presence of the oversized La ions (ionic radius: 117 pm) causes an increase in the lattice constant with increasing dopant levels. Doping with Gd and Sm ions reduces the ionic radii of these materials (107.8 pm and 109.8 pm, respectively) to a level close to that of Pr 4+ Since the ionic radius of the doped ZnO ions is close to that of the doped Yb and La ions (110 pm), the effect is smaller than that of doping with Yb and La ions.

[0110] FIG. 12 shows the curves of normalized polarization resistance as a function of temperature for cells in a 17-layer stack with various cathode modifications compared to a standard composite cathode (a rare earth strontium cobaltite / CGO composite with high catalytic activity), in which: PG010 is a Pr 0.9 Gd 0.1 O 1.95-δ)Refers to, PG020 is a Pr 0.8 Gd 0.2 O 1.90-δ) Refers to, PLa010 is Pr 0.9 La 0.1 O 1.95-δ) Refers to, PLa020 is Pr 0.8 La 0.2 O 1.90-δ) Refers to...

[0111] To measure the polarization resistance in an operating stack (in this example operating in SOFC mode), the stack was supplied with a fuel mixture mimicking partially externally steam reformed natural gas at a flow rate such that 75% of the easily oxidized fuel was consumed by electrochemical reactions within the stack. To minimize internal temperature gradients, air was supplied to the cathode side of the stack at a flow rate significantly in excess of the stoichiometric requirement for oxygen. -2 The temperature of the stack was varied by controlling the temperature of the furnace in which the tests were performed.

[0112] At each temperature, once the stack had reached thermal equilibrium, the impedance of all 17 cells was measured using AC impedance spectroscopy. This technique allows the internal cell impedance to be separated into ohmic (non-frequency deformation) and non-ohmic components. The electrochemical impedance of the cathode is classified as the non-ohmic part of the impedance, hereafter described as the polarization resistance. Since it is not generally possible to separate the cathode contribution from the anode in a complete fuel cell, the polarization resistance is for the entire cell. The polarization resistance is calculated based on the voltage drop from an open circuit minus the voltage drop contributed by the ohmic resistance (which does not change significantly with current at a given temperature). The values ​​quoted are normalized to that of a cell with a standard cathode at 625°C and are overall averages from at least three cells. Since the anode and the external environment of the cells were all the same, any difference in the polarization resistance can be attributed to a change in the electrochemical activity of the cathode for oxygen reduction. Any value less than 1 means that the cathode is more active for oxygen reduction than the standard cathode.

[0113] These curves show that all four tested materials according to the invention function as electrode (cathode) materials.

[0114] FIG. 13 shows curves of normalized polarization resistance (measured in the same manner as described above in connection with FIG. 12) as a function of temperature for cells in a 17-layer stack having more diverse cathode modifications (than FIG. 12) compared to a standard composite cathode, in which: PGO10 is Pr 0.9 Gd 0.1 O 1.95-δ) Refers to, PGO20 is Pr 0.8 Gd 0.2 O 1.90-δ) Refers to, PLaO10 is Pr 0.9 La 0.1 O 1.95-δ) Refers to, PLaO20 is Pr 0.8 La 0.2 O 1.90-δ)Refers to, PYbO10 is Pr 0.9 Yb 0.1 O 1.95-δ) Refers to, PYbO20 is Pr 0.8 Yb 0.2 O 1.90-δ) Refers to, PSmO15 is Pr 0.85 Sm 0.15 O 1.925-δ) Refers to...

[0115] Provided below are Examples 1-4, which are general methods for synthesizing doped praseodymia in accordance with the present invention (Examples 1 and 2), for synthesizing printable inks using such doped praseodymium powders (Example 3), and for using such inks to print CALs (Example 4).

[0116] Example 5 relates to the use of an electrode layer according to the invention in a multi-layer cathode system.

[0117] Example 6 relates to the use of an electrode layer according to the invention in direct contact with a scandia-yttria stabilized zirconia-containing layer of an electrolyte system.

[0118] Example 7 relates to the use of an electrode layer according to the invention in direct contact with an ytterbia-stabilized zirconia-containing layer of an electrolyte system.

[0119] Example 8 relates to the use of a composite cathode bulk layer.

[0120] Example 1: Synthesis of doped praseodymium oxide powder Preparation of solutions A stoichiometric mixture of praseodymium nitrate hexahydrate and the nitrate of the desired dopant is dissolved in deionized (DI) water to give a solution with a molarity of 0.4M.

[0121] Under a fume hood, in a separate container, dissolve oxalic acid dihydrate in the same amount of DI water used to dissolve the nitrates to give an oxalic acid to nitrates molar ratio of 1.7 (slightly above the stoichiometric requirement of 1.5 to ensure all metal ions are precipitated).

[0122] Once the oxalic acid has completely dissolved, concentrated ammonium hydroxide solution is added while monitoring the pH until the acid is neutralized (pH 7) leaving a solution of ammonium oxalate.

[0123] Precipitation The nitrate solution is added to the ammonium oxalate solution while the mixture is vigorously stirred, resulting in a light green precipitate of insoluble praseodymium and the dopant oxalate.

[0124] filtration Prepare a Buchner funnel with heavy duty filter paper and an aquarium pump. With the aquarium pump running, pour the precipitation mixture onto the filter and allow it to pass for a sufficient time until most of the supernatant solution has been removed, leaving a cake of precipitate on the filter paper.

[0125] Washing The precipitate is washed three times with DI water and then once with ethanol.

[0126] Drying The damp filter cake is transferred from the funnel to a suitable container and dried in a solvent-rated oven overnight at 70°C.

[0127] Micronization The dried precipitate cake is pulverized using a pestle and mortar and the resulting powder is then transferred to an alumina crucible.

[0128] Sintering The finely ground precipitate is transferred to an alumina crucible and placed in an airtight tube furnace through which various gas mixtures can be fed. A water bubbler is provided in the gas exhaust line from the furnace, both to allow gas to flow through the furnace and to prevent backflow of air into the furnace even if the gas supply is cut off during cooling.

[0129] A flow of a mixture of 5% H2 in Ar is applied, ensuring that gas bubbles up from the furnace exhaust. The furnace is heated at 5°C / min to 710°C with a dwell of 1 hour. The furnace is then cooled to <300°C under a reducing atmosphere and then purged with nitrogen for 10 minutes.

[0130] Air flow is provided to ensure the finished material is of the desired oxide phase. Ensure that gas is rising from the furnace exhaust. The furnace is heated at 5°C / min to 710°C with a dwell time of 1 hour. The furnace is then cooled to room temperature.

[0131] Example 2: Alternative synthesis of doped praseodymium oxide powder Preparation of solutions A stoichiometric mixture of praseodymium nitrate hexahydrate and the nitrate of the desired dopant is dissolved in deionized (DI) water to give a solution of 0.15 M molarity.

[0132] Under the fume hood, in a separate container, dilute concentrated ammonium hydroxide solution with DI water to give an equal volume of a 0.45 M solution as the nitrate solution.

[0133] Precipitation The nitrate solution is added to the ammonium hydroxide solution while the mixture is vigorously stirred, resulting in a pale green gelatinous precipitate of insoluble praseodymium and dopant hydroxide.

[0134] filtration Prepare a Büchner funnel with heavy duty filter paper and an aquarium pump. With the aquarium pump running, pour the precipitation mixture onto the filter and allow it to pass for a sufficient time until most of the supernatant solution has been removed, leaving a cake of precipitate on the filter paper.

[0135] Washing The precipitate is washed three times with DI water and then once with ethanol.

[0136] Drying The damp filter cake is transferred from the funnel to a suitable container and dried in a solvent-rated oven overnight at 70°C.

[0137] Micronization The dried precipitate cake is pulverized using a pestle and mortar and the resulting powder is then transferred to an alumina crucible.

[0138] Sintering The finely ground precipitate is transferred to an alumina crucible which is placed in a suitable furnace and heated in air to a temperature of 650° C. to decompose the hydroxide precipitate to the desired mixed oxides.

[0139] Example 3: Synthesis of printable ink Dispersion and grinding of doped praseodymium oxide powders. Doped praseodymium oxide powder, produced as discussed in Examples 1 or 2, is weighed out and mixed with a carrier, a dispersant, and an antifoaming agent to form a slurry containing the target amount of 46 wt% powder.

[0140] The slurry is transferred to a basket mill where 1 mm YSZ grinding media is also added in an amount twice the weight of the slurry.

[0141] d <0.9 μm 90 The slurry is milled at about 7000 rpm until a particle size distribution is achieved. The particle size distribution may be measured using a Malvern Mastersizer® 2000 laser diffraction particle size analyzer.

[0142] The slurry is then removed from the basket mill.

[0143] Ink manufacturing The dispersed and milled praseodymium oxide powder slurry produced in the previous section is transferred to a small high shear disperser (HSD) pot and placed on the HSD.

[0144] Weigh out an amount of binder powder equivalent to 2.5-3.5 wt% of the finished ink.

[0145] The binder is added to the slurry which is actively dispersed on the HSD.

[0146] The ink is left on the HSD until the binder is completely dissolved in the ink.

[0147] Transfer the ink to a three-roll mill (TRM) for final homogenization and run four passes through the mill using a 5 μm front nip to ensure that the binder is fully homogenized into the ink and that no particles larger than 5 μm remain in the finished ink.

[0148] Example 4: Printing of ink and formation of active layer The substrate included an electrolyte layer deposited on a metal supported SOFC. The ink was screen printed using an automated screen printer in a single pass onto the electrolyte layer of the metal supported SOFC. It was then dried in an oven. The combination of ink solids and screen mesh was selected to give a thin print of approximately 3 μm. Following the addition of the CBL, the layer was then sintered together with the CBL at a temperature of 820-870° C. to form the CAL. Following sintering, the X-ray diffraction and BET analysis were repeated. After sintering, there was a slight increase in crystallite size and a decrease in BET surface area, but no change in crystal structure. The layer still consisted of a single phase with a cubic fluorite structure.

[0149] Example 5: Cathode using a layer of CAL and a further layer of PrLnO. The first electrode materials described herein and illustrated in Examples 1-4 above perform as well as or better than the standard and are less susceptible to poisoning from airborne contaminants, particularly airborne sulfur and water vapor. To further improve performance, a three-layer SOFC cathode was produced. The three-layer electrode advantageously reduces the effects of chromium contamination (praseodymium oxide can react with chromia to form perovskite) and ensures better adhesion between the bulk layer and the active layer.

[0150] The three layers of the electrode are a bulk layer of LCN60, which gives it good stability and thermal expansion, matched with the rest of the cell, an interfacial composite layer of rare-earth strontium cobaltite (or LSCF) / CGO and a catalytic active layer of rare-earth doped praseodymium oxide. The interfacial layer ensures good adhesion between the active layer and the bulk, while also acting as a poison getter for the active layer, where poisons such as chromium and sulfur react with the rare-earth strontium cobaltite / cobalt ferrite before obtaining a strontium-free active layer (which may be susceptible to chromium poisoning). The interfacial layer has a similar thermal coefficient as the cathode bulk layer. It protects the active layer from decomposition (it is not affected by water vapor, carbon dioxide or sulfur dioxide).

[0151] The cathode was produced by screen printing as three layers: a thin layer (~3 microns) of the first electrode material (e.g., PSmO10), a thin layer (~3 microns) of rare earth strontium cobaltite / CGO (e.g., ReSC / CGO10 60:40, where "Re" refers to rare earth), and a final thicker (~40 microns) bulk layer (LCN60).

[0152] Optionally, these layers can be fired and isostatically or uniaxially pressed to increase their green density, and then finally sintered at 800-850° C. in air to form the finished cathode.

[0153] In general, adhesion can be improved without the need to isopress the layers by printing two layers, where the electrochemically active layer is PLnO, e.g. PGO10 or PSmO10, on top of which is an interfacial layer of PSC / CGO.

[0154] The described cathode was provided in a standard metal-supported SOFC and assembled into a stack of 17 cells. For each cell the anode was a ceria-nickel cermet and the electrolyte included CGO with a doped zirconia electron blocking layer. As discussed in Example 5 below, the active layer may be in direct contact with the zirconia electron blocking layer or, for example, a layer of CGO may be sandwiched between the active layer and the zirconia electron blocking layer.

[0155] Using airflow on the air side and simulated steam reformed natural gas fuel on the fuel side, the stack was heated for 2.19 kh, had a temperature of 570°C (stack air outlet temperature), and was charged to 17.81 (227 mA cm -2 The stack was operated at a current of 1000 kWh, with a fuel usage rate (Uf) of 80%, an air usage rate (Ua) of 20%, and water vapor in the air of 1.5%.

[0156] The results for voltage and ASR degradation rate versus time for the standard cell (as described above but with the standard composite cathode) and for PSmO10 sintered at 800°C or 820°C and either pressed (isopressed at a pressure of 300 MPa) or unpressed are shown in Table 2.

[0157] [Table 2]

[0158] The results show that all tested PSmO10 cathode active layers (CALs) show low or very low degradation after 2200 hours at 1.5 kh. The stacks were subjected to several deep thermal cycles without significant performance changes. The conclusion is that the cathodes according to the examples are superior, showing good activity, adhesion and being almost immune to contamination.

[0159] A cross section of the SOC of Example 5 is shown in Figure 16 and details are shown in Figure 17. In Figures 16 and 17, the layers of the SOC are a bulk cathode layer (CBL) 200, an interfacial cathode layer of ReSC / CGO 210, a cathode active layer (CAL) of PSmO10 220, a zirconia electron blocking layer 230, a doped ceria barrier layer 235, a doped ceria electrolyte layer 240, and an anode 250. The anode is supported on a metal substrate (not shown).

[0160] Example 6. PrLnO electrode material in direct contact with a scandia-yttria stabilized zirconia-containing layer of the electrolyte. This example investigates the performance of PrLnO CALs in direct contact with a zirconia electron blocking layer in an electrolyte system.

[0161] The cathode was produced by screen printing three layers on top of the electrolyte: a thin layer (~3 microns) of the first electrode material (e.g. PSmO10), a thin layer (~3 microns) of rare earth strontium cobaltite / CGO (e.g. ReSC / CGO10 60:40), and a final thicker (~40 microns) bulk layer (LCN60).

[0162] The described cathode was applied to a standard metal-supported SOFC and assembled into a stack. For each cell the anode was a ceria-nickel cermet and the electrolyte comprised CGO with a scandia-yttria-stabilized zirconia electron blocking layer.

[0163] Two types of cells were produced: Cell 1 had a doped ceria protective layer deposited directly on top of the zirconia electron blocking layer, and Cell 2 did not have a doped ceria protective layer, so the PSmO10 CAL was in direct contact with the zirconia electron blocking layer.

[0164] The cell was tested at a temperature of 570°C in an open circuit with air flow on the air side and a fuel of 44% H2 in N2 on the fuel side.

[0165] The cells were compared to a standard cell.

[0166] FIG. 14 shows a box plot of the open circuit voltage (OCV) of the cells compared to the standard cell at 570° C.

[0167] All variants showed a higher OCV than the standard cell, and the two variants of the cell also showed slight variations.

[0168] Figure 15 shows the average OCV of the cells as a function of temperature compared to the standard cells. The tested cells, Cell 1 and Cell 2, each show good results. The cells with the doped ceria layer (STD and Cell 1) show a trend towards accelerating OCV decay with temperature, while the results for Cell 2 are reasonably linear.

[0169] The electrochemical performance of Cell 1 and Cell 2 was also evaluated and found to be comparable to the standard cell, indicating that omission of the doped ceria buffer layer in Cell 2 did not adversely affect performance.

[0170] The excellent results for the tested cells indicate that simplification of cell design by removing protective layers is possible. Thus, rare earth doped praseodymia air electrode catalysts, e.g. PSmO10, may give cell performance at least equivalent to CALs deposited directly on the zirconia electron blocking layer of the cell, avoiding the need for a doped ceria barrier layer. A small amount of interdiffusion between zirconia and praseodymia is likely to result in ionically conducting phases on both sides of the interface, so that a non-conductive interfacial layer is unlikely to form between these materials. This could significantly reduce the manufacturing costs of the cell.

[0171] A cross-sectional detail of the SOC of Example 6 is shown in Figure 18, in which the layers of the SOC are bulk cathode layer 300, ReSC / CGO interfacial cathode layer 310, PSmO10 cathode active layer 320, zirconia electron blocking layer 330, and doped ceria electrolyte layer 340. The anode layer and substrate are not shown.

[0172] Other tests were performed to evaluate the co-sintering of the doped zirconia-containing layers of the electrolyte and the PrLnO electrode material. Co-sintering simplifies production and results in fewer sintering steps. The ScYSZ and PrLnO layers were sequentially deposited as green layers on top of the substrate and co-sintered at 800°C-850°C (the layers may be pressed in some cases). The OCV results of the cells were acceptable.

[0173] Example 7. PrLnO electrode material in direct contact with the ytterbia-stabilized zirconia-containing layer of the electrolyte. This example investigates the performance of PrLnO CALs in direct contact with a zirconia electron blocking layer in an electrolyte system.

[0174] The cathode was produced by screen printing three layers on top of the electrolyte: a thin layer (~3 microns) of the first electrode material (e.g. PSmO10), a thin layer (~3 microns) of rare earth strontium cobaltite / CGO (e.g. ReSC / CGO10 60:40), and a final thicker (~40 microns) bulk layer (LCN60).

[0175] The described cathode was applied to a standard metal-supported SOFC and assembled into a stack. For each cell, the anode was a ceria-nickel cermet and the electrolyte contained CGO with an ytterbia-stabilized zirconia (YbSZ) electron blocking layer.

[0176] 19 shows a box plot of the open circuit voltage (OCV) of a cell (listed as Cell 3) compared to the standard cell at 570° C. As with Example 6, it can be seen that the OCV of the cell made according to this example is significantly higher than the standard cell.

[0177] The electrochemical performance of Cell 3 was also evaluated and found to be comparable to, or under some conditions better than, the standard cell, indicating that omission of the doped ceria buffer layer did not adversely affect performance.

[0178] Example 8. Two-layer cathode of PLnO active cathode and composite bulk cathode A bilayer cathode with a first layer of PSmO10 and a second layer of 25 wt% PSC / 75 wt% LCN60 composite, with no buffer layer between the first and second layers, was printed on top of an otherwise standard configuration cell as described above in Example 5. The printed layers were then sintered to form a completed cell.

[0179] It was found that adhesion of the two layers in this case was improved compared to the single component bulk cathode layer illustrated in FIG. 1 and no isostatic pressing was required to achieve sufficient interfacial bonding.

[0180] Example 9. PSmO10 / CGO10 composite cathode active layer. Two types of cells were investigated, each with a cathode produced by screen printing as three layers: a thin layer of a first electrode composite of PSmO10 / CGO10 (60%:40% by weight), a thin layer of rare earth strontium cobaltite / CGO (e.g., ReSC / CGO10 60:40, where "Re" refers to rare earth), and a final thicker bulk cathode layer (LCN60).

[0181] For each cell the anode was a ceria-nickel cermet and the electrolyte included CGO with a doped zirconia electron blocking layer and an interfacial doped ceria layer on top of the zirconia blocking layer. A thin layer of the first electrode composite was printed on top of the ceria layer.

[0182] Figure 20 shows the current at 133mAcm -2 Figure 1 shows a graph of test data from cells in a 17-layer stack operating at 70% and 75% fuel utilization. The graph shows polarization resistance as a function of temperature normalized to a standard cell with a PSC / CGO composite cathode active layer (standard cell = 1.0). The results show improved electrode performance (lower polarization resistance) for the PSmO10 / CGO10 composite.

[0183] FIG. 21(a) and FIG. 21(b) show cross-sectional SEM images of a PSmO10-CGO (60:40) composite cathode active layer (CAL) with a co-fired cathode with a ceria interfacial layer and twice the other layers of the stack.

[0184] 21(a) and 21(b), the layers of the SOC are a bulk cathode layer (CBL) 400, a ReSC / CGO interfacial cathode layer 410, a PSmO10 / CGO10 (60:40 wt%) cathode active layer (CAL) 420, a zirconia electron blocking layer 430, a doped ceria barrier layer 435, a doped ceria electrolyte layer 440, and an anode 450. The anode 450 is supported on a metal substrate (not shown).

[0185] FIG. 22 shows a cross-sectional SEM image of a PSmO10-CGO (60:40) composite cathode active layer (CAL) with the cathode sintered separately from the ceria interfacial layer and other layers of the stack.

[0186] 22, the layers of the SOC are a bulk cathode layer (CBL) 500, a ReSC / CGO interfacial cathode layer 510, a PSmO10 / CGO10 (60:40 wt%) cathode active layer (CAL) 520, a zirconia electron blocking layer 530, a doped ceria barrier layer 535, a doped ceria electrolyte layer 540, and an anode 550. The anode 550 is supported on a metal substrate (not shown).

[0187] In Figures 21 and 22, the two phases within the CAL have little contrast in SEM imaging because the density and morphology of the materials are very similar. [Explanation of symbols]

[0188] 10-Anode (fuel electrode) 20-Doped ceria electrolyte layer 30-Zirconia electron blocking layer 40-Air electrode active layer (cathode active layer, CAL) 50-Bulk Cathode Layer 200-Bulk cathode layer (CBL) 210-ReSC / CGO interface air electrode layer 220-PSmO10 Cathode Active Layer (CAL) 230-zirconia electron blocking layer with a thin doped ceria barrier layer between the zirconia and the cathode active layer 235-Thin doped ceria interfacial layer 240-Doped ceria electrolyte layer 250-Fuel electrode 300-Bulk Air Cathode Layer 310-ReSC / CGO interface air electrode layer 320-PSmO10 air electrode active layer 330-zirconia electron blocking layer 340-Doped ceria electrolyte layer 400-Bulk Air Cathode Layer 410-ReSC / CGO interface air electrode layer 420-PSmO10 / CGO cathode active composite layer 430-zirconia electron blocking layer 435-Thin doped ceria barrier / interface layers 440-Doped ceria electrolyte layer 450-fuel electrode 500-Bulk Air Cathode Layer 510-ReSC / CGO interface air electrode layer 520-PSmO10 / CGO cathode active composite layer 530-zirconia electron blocking layer 535-Thin doped ceria barrier / interface layers 540-Doped ceria electrolyte layer 550-fuel electrode

[0189] All publications mentioned in the above specification are incorporated herein by reference. Although illustrative embodiments of the present invention are described in detail herein with reference to the accompanying drawings, it is understood that the present invention is not limited to the precise embodiments, and various changes and modifications can be made therein by those skilled in the art without departing from the scope of the present invention, which is defined by the appended claims and their equivalents.

Claims

1. 1. An electrode for an electrochemical cell, comprising: （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） wherein Ln is selected from at least one rare earth metal; δ is the degree of oxygen deficiency, 0.01≦x≦0.4) an electrode comprising at least one first layer comprising a first electrode material of

2. 2. The electrode of claim 1, wherein the rare earth metal is selected from the lanthanides, Sc, Y, and mixtures thereof.

3. 3. The electrode of claim 2, wherein the rare earth metal is selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof.

4. 4. The electrode of claim 3, wherein the rare earth metal is selected from La, Sm, Gd, and Yb; preferably Sm.

5. 2. The electrode of claim 1, wherein 0.02≦x≦0.

25.

6. The first electrode material has the formula Pr ０．９ Ln ０．１ O （１．９５－δ） , Pr ０．８５ Ln ０．１５ O （１．９２５－δ） , Pr ０．８ Ln ０．２ O （１．９－δ） 2. The electrode of claim 1, wherein Ln is La, Sm, Gd, or Yb; or a mixture thereof; and wherein Ln is La, Sm, Gd, or Yb; preferably Sm.

7. 10. The electrode of claim 1, wherein the first layer comprises 20% or more by weight of the first electrode material; optionally 30% or more by weight of the first electrode material; optionally 40% or more by weight of the first electrode material; or optionally 55% or more by weight of the first electrode material.

8. The electrode of claim 1 , wherein the first layer has a thickness in the range of 1 μm to 7 μm.

9. The electrode of claim 1 , comprising at least one second layer comprising a second electrode material.

10. 1. An electrode for an electrochemical cell, comprising: （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） wherein Ln is selected from at least one rare earth metal; δ is the degree of oxygen deficiency, 0.01≦x≦0.4) and at least one second layer comprising a second electrode material.

11. 11. An electrode according to claim 9 or claim 10, wherein the second electrode material is electrically conductive, optionally a conductive ceramic material.

12. The second electrode material is lanthanum cobaltite, lanthanum ferrite, lanthanum nickel ferrite, La ０．９９ Co ０．４ Ni ０．６ Co ０ O （３－δ） 11. The electrode according to claim 9 or claim 10, wherein the electrode is selected from the group consisting of (LCN60), (LCN60), and mixtures thereof.

13. 11. The electrode of claim 9 or claim 10, wherein the second layer is a composite layer further comprising at least one additional second electrode material, optionally the additional electrode material optionally comprising strontium comprising a material selected from rare earth strontium cobaltite; rare earth strontium ferrite, rare earth strontium cobalt ferrite, the rare earth component optionally being Pr, La, Gd and / or Sm.

14. 14. The electrode of claim 13, wherein the composite layer comprises the second electrode material and the additional electrode material in a ratio of 1:10 to 10:1 by weight, optionally 1:5 to 5:1 by weight, optionally 1:1 to 5:1 by weight.

15. 14. The electrode of claim 13, wherein the second layer comprises 60% or more by weight of the second electrode material; optionally 65% ​​or more by weight of the second electrode material; optionally 70% or more by weight of the second electrode material; or optionally 75% or more by weight of the second electrode material.

16. 11. The electrode of claim 9 or claim 10, further comprising a third layer optionally comprising a third electrode material located between the first layer and the second layer.

17. 17. The electrode of claim 16, wherein the third electrode material optionally comprises strontium comprising a material selected from rare earth strontium cobaltite; rare earth strontium ferrite, rare earth strontium cobalt ferrite; and the rare earth component may optionally be Pr, La, Gd and / or Sm.

18. 17. The electrode of claim 16, wherein the third layer has a thickness in the range of 1 μm to 5 μm.

19. 11. The electrode of claim 1 or claim 10, wherein the electrode is a cathode.

20. 11. An electrochemical cell comprising the electrode of claim 1 or claim 10; and optionally further comprising one or more electrolytes, a second anode, and a substrate.

21. 1. An electrochemical cell comprising an electrode, the electrode comprising: Formula Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） at least one first layer comprising a first electrode material of the formula: where Ln is selected from at least one rare earth metal, δ is the degree of oxygen deficiency, and 0.01≦x≦0.4; the first layer comprising the first electrode material is in direct contact with a material comprising zirconia; Electrochemical cell.

22. 22. The electrochemical cell of claim 21 further comprising an electrolyte, wherein the material comprising zirconia forms a layer of the electrolyte.

23. 22. The electrochemical cell of claim 21, wherein the zirconia-containing material is selected from scandia-stabilized zirconia (ScSZ), yttria-stabilized zirconia (YSZ), ytterbia-stabilized zirconia (YbSZ), scandia-ceria-co-stabilized zirconia (ScCeSZ), scandia-yttria-co-stabilized zirconia (ScYSZ), and mixtures thereof.

24. 22. The electrochemical cell of claim 21 further comprising an electrolyte layer optionally further comprising doped ceria selected from samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), praseodymium-doped ceria (PDC), samaria-gadolinia-doped ceria (SGDC), and mixtures thereof.

25. 22. The electrochemical cell of claim 21 further comprising a substrate; optionally a metal substrate, preferably a steel substrate.

26. 22. The electrochemical cell of claim 21, which is an electrolyzer, an oxygen separator, a sensor or a fuel cell, and optionally comprises a solid oxide electrochemical cell.

27. 1. A method of producing an electrochemical cell, comprising: providing a substrate on which layers including an anode and an electrolyte are optionally deposited; applying a source of Pr and Ln, where Ln is selected from at least one rare earth metal, to the substrate to form a cathode layer; Optionally, a drying step; and Optionally, sintering the cathode layer; Thereby forming the electrode according to claim 1 or claim 10. A method comprising:

28. moreover, applying a material to the substrate to form at least one electrolyte layer; applying the source of Pr and Ln onto the electrolyte layer to form a cathode layer; Optionally, a drying step; and Co-sintering the electrolyte layer and the cathode layer 28. The method of claim 27, comprising:

29. Formula Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） wherein Ln is selected from at least one rare earth metal; δ is the degree of oxygen deficiency, 0.01≦x≦0.4) Ingredients.

30. Formula Pr （１－ｘ） Sm ｘ O （２－０．５ｘ－δ） (wherein δ is the degree of oxygen deficiency, 0.01≦x≦0.4) Ingredients.

Images