Electrodes and electrochemical cells

Abstract

An electrode for an electrochemical cell. An electrode comprising at least a first layer containing a first electrode composition, wherein the first electrode composition is Pr (1-x) Ln x O (2-0.5x-δ) and a lithium source. Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof, and δ is the oxygen deficiency degree, 0.01 ≤ x ≤ 0.4. An electrochemical cell comprising the electrode and a stack of electrochemical cells, a method for manufacturing the electrode, and the composition.

Description

Technical Field

[0001] The present invention relates to an electrode for an electrochemical cell, an electrochemical cell including such an electrode, a method of manufacturing such an electrochemical cell, and a material used for such an electrode.

Background Art

[0002] An electrochemical cell formed of an oxide layer (also called a solid oxide cell: SOC) can be used as a fuel cell or an electrolysis cell.

[0003] The SOC fuel cell unit produces electricity using an electrochemical conversion process that oxidizes a fuel. The SOC fuel cell unit can also operate as a regenerative fuel cell (or reverse fuel cell) unit and is often also known as a solid oxide electrolyzer fuel cell unit, for example, separating hydrogen and oxygen from water or separating carbon monoxide and oxygen from carbon dioxide.

[0004] A solid oxide fuel cell (SOFC) generates electrical energy by the electrochemical oxidation of a fuel gas (usually hydrogen-based), and this device generally uses a ceramic-based ceramic containing an oxygen ion-conductive metal oxide as an electrolyte. Many ceramic oxygen ion conductors (e.g., doped zirconium oxide or doped cerium oxide) have useful ion conductivity at temperatures above 500 °C (for cerium oxide-based electrolytes) or 650 °C (for zirconium oxide-based ceramics), so SOFCs tend to operate at high temperatures.

[0005] During operation, the electrolyte of the SOFC conducts oxygen ions from the cathode to the anode on the opposite side of the electrolyte. A fuel (e.g., a fuel obtained from the reforming of hydrocarbons or alcohols) contacts the anode (usually called the "fuel electrode"), and an oxidant such as air or a fluid rich in oxygen contacts the cathode (usually called the "air electrode"). Conventional ceramic-supported (e.g., anode-supported) SOFCs have low mechanical strength and are vulnerable to damage. Therefore, in recent years, metal-supported SOFCs in which the active fuel cell component layers are supported on a metal substrate have been developed. In these cells, the ceramic layer can be made very thin because it only performs an electrochemical function. That is, the ceramic layer is not self-supporting but is a thin coating / film placed on and supported by the metal substrate. Such a metal-supported SOFC stack is more robust, less costly, has excellent thermal properties, and can be sealed using conventional metal welding techniques.

[0006] In the applicant's previous Patent Application International Publication No. A-2015 / 136295, a metal-supported SOFC is disclosed that includes an anode layer, an electrolyte layer, and a cathode layer in which an electrochemically active layer (or an active fuel cell component layer) is respectively deposited (e.g., as a thin coating / film) on a metal-supported plate (e.g., a foil) and supported by the metal support plate. The metal-supported plate has a porous region surrounded by a non-porous region, and since the active layer is deposited on the porous region, gas can pass through the pores from one side of the metal-supported plate to the opposite side and access the active layer coated thereon. The porous region extends through the support plate and includes small openings (holes drilled in the metal foil substrate) that overlap the anode (or the cathode depending on the direction of the electrochemically active layer).

[0007] A solid oxide electrolysis cell (SOEC) may have the same structure as an SOFC, but in fact, it is an SOFC that operates in the reverse direction, i.e., in the regeneration mode, to achieve the electrolysis of water and / or carbon dioxide.

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

[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 for application as an anode component in SOFC devices.

[0010] Doped praseodymium oxides have been investigated for reasons unrelated to state of complexity (SOC). For example, Zoellner et al. (J. Crystal Growth, vol.355, no.1, 2012, pp.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, pp.831-836) elucidate the non-stoichiometry and relaxation kinetics of nanocrystalline mixed praseodymium-cerium oxides. Popescu Ione et al. (Applied Catalysis A:General, vol.578, 2019, pp.30-39) disclose studies on the catalytic oxidation performance of Ce-Pr mixed oxides. Simona Somacescu et al. (J. Nanoparticle Research; vol. 14, no. 6, 2012, pp. 1-17) have clarified the structure, morphology, surface chemistry, and catalytic performance of CePrO. ​​Kang et al. (J. Alloys and Compounds, vol. 207-208, 1994, pp. 420-423) have clarified the structure and structural defects of colloidal particles that have changed in situ using HREM.

[0011] Tuller et al; (Energy Environ.Sci.,2022,15,4038) found that cerium-based solid oxides Pr 0.1 Ce 0.9 O 2-δ It has been reported that the oxygen exchange rate in chromia poisoning is reactivated by continuous infiltration of lithium oxide.

[0012] U.S. Patent No. B-6,117,582 describes a cathode composition for a solid oxide fuel cell having a cathode made from a transition metal perovskite such as PrCoO3 or praseodymium manganite. U.S. Patent Application No. A-2017 / 149067 discloses a fuel cell and a cathode that may include a nickelate compound (e.g., Pr2NiO4). Nicollet, C, et al., (International Journal of Hydrogen Energy, September 2016, Vol. 41, Issue 34, pages 15538-15544) describes Pr6O 11 as an electrocatalyst for the oxygen reduction reaction and its use as a cathode in a SOFC. Chinese Patent No. A-106 057 641 discloses Pr semiconductor oxides doped with La, Nd, and Gd. Wang et al 2017 232nd ECS Meet. Abstr. (MA2017-02 / 39 / 1730) discloses combining Pr 1-x NdxO 2-d with (Pr, Nd)2NiO4 (PNNO) to improve the activity and phase stability of PNNO used as a cathode in a solid oxide fuel cell. Biswas, R.et al. (1997) Journal of Materials Science Letters. 16.1089-1091 discloses the preparation, structure, and electrical conductivity of Pr 1-x La x O 2-δ (x = 0.05, 0.1, 0.2). 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-δThe preparation and characterization of (x=0.02,0.05,0.1) are disclosed. International Publication No. A-2006 / 106334(A1) describes a solid oxide fuel cell (SOFC) containing a doped material having a perovskite structure in which praseodymium can be included in the cathode material. This structure has the conventional notation ABX3, in which cerium is substituted at site "B".

[0013] However, the need remains to provide electrode materials with properties suitable for use in electrochemical cells.

[0014] The objective of this invention is to address these needs. [Overview of the Initiative]

[0015] The present invention therefore provides, in a first aspect, an electrode for an electrochemical cell, the electrode comprising a first layer comprising at least a first electrode composition, the first electrode composition being Pr (1-x) LnxO (2-0.5x-δ) and a lithium source (wherein Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof) δ represents the degree of oxygen deficiency, (0.01 ≤ x ≤ 0.4).

[0016] Li-containing Pr (1-x) Ln xO(2-0.5x-δ) The first electrode composition containing Li is highly advantageous because the applicant has discovered that, surprisingly, it can increase the average cell potential, especially at low temperatures, and act as a sintering aid. (1-x) Ln x O (2-0.5x-δ) This may mitigate the effects of chromium poisoning during SOC use and may also increase the surface reaction rate at the air electrode / electrolyte interface (although this is not something we would like to be restricted by).

[0017] The first electrode material may be a mixture of materials. However, a solid solution (e.g., Li in RE-doped praseodymia) may be present, or under certain conditions (e.g., during or after sintering, or during use), particles or nanoparticles of lithium oxide (or other lithium compounds such as lithium carbonate) may be present in the composition. Thus, the first electrode material having an overall composition may consist of one or more phases or mixtures of materials, and different parts of the electrode may have different local compositions or mixtures of materials or phases.

[0018] δ can vary depending on the environment and history of the first electrode material. In the oxidizing environment of many praseodymium-containing oxides, praseodymium is in thermodynamic equilibrium between oxidation states +3 and +4, depending on temperature and oxygen partial pressure. Pr 4+ It is reduced to Pr 3+ This creates oxygen vacancies. Oxygen vacancies induced by the reduction of praseodymium are known as extrinsic vacancies. Using Kroger-Vink notation, the equilibrium can be expressed as follows: Pr 4+ +O O <->Pr 3+ +V O ’’ +0.5O2(g) Here, V O ’’ These are oxygen vacancies.

[0019] In the first electrode material, δ is 0.25 or less, preferably 0.2 or less, and more preferably 0.15 or less.

[0020] δ may have lower bounds of 0.0001, 0.001 (optionally), 0.005 (optionally), 0.01 (optionally), and 0.05 (optionally).

[0021] By adding a dopant cation (e.g., trivalent) to praseodymium oxide, unique oxygen vacancies are created within the structure. In the first electrode material, a rare earth metal can preferably act as the dopant.

[0022] Preferably, the upper limit of lithium in the composition may be 7 cation%, optionally 6 cation%, or optionally 5 cation%.

[0023] Preferably, the lower limit of lithium in the composition may be 0.001 cation%, optionally 0.01 cation%, optionally 0.1 cation%, or optionally 1 cation%.

[0024] The cation percentage represents the atomic percentage (equivalent to mole percentage) of cations (e.g., cations Pr, Li, Ln) in the first electrode composition.

[0025] Lithium can be present in the first electrode composition in an amount of 0.001 to 5 cation%. Optionally, lithium can be present in the first electrode composition in an amount of 0.01 to 5 cation%.

[0026] Preferably, the lithium source can be present in the first electrode composition in an amount of 0.1 to 5 cation%. More preferably, the lithium source can be present in the first electrode composition in amounts of 0.2 to 5 cation%, 0.3 to 5 cation%, 0.5 to 5 cation%, 0.5 to 4 cation%, and 0.5 to 3 cation%.

[0027] The rare earth metal may be selected from lanthanides, Sc, Y, and mixtures thereof, excluding cerium.

[0028] Preferably, the rare earth metal may be selected from La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, and mixtures thereof. More preferably, the rare earth metal may be selected from La, Nd, Sm, Eu, Gd, and Yb, with optional selection from La, Sm, Gd, and Yb, preferably Nd, Sm, Eu, Gd, more preferably Gd or Sm, and most preferably Sm.

[0029] As used herein, Ln indicates a dopant, and therefore Ln excludes Pr.

[0030] Praseodymium oxides represent a system of phases with somewhat variable composition. Single-phase PrO2 is typically formed with pure oxygen and high pressure (>20,000 kPa). Among the various oxides, Pr6O 11 It is particularly stable. Under normal temperature and pressure, Pr6O 11 It adopts a cubic fluorite structure, Pr6O 11 The praseodymium ions inside are thought to be in a mixed valence state of Pr(III) and Pr(IV) with exogenous oxygen vacancies, promoting oxygen ion conduction and providing catalytic activity (although they do not wish to be constrained).

[0031] Advantageously, the presence of rare-earth metal dopants in the first electrode material can result in the formation of additional unique oxygen vacancies, thereby stabilizing the cubic fluorite structure of the material.

[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 to 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. Preferably, x may be 0.08 to 0.2 or 0.08 to 0.12, and more preferably x may be about 0.1, about 0.15, or about 0.2.

[0033] Preferably, 0.02 ≤ x ≤ 0.25.

[0034] Therefore, preferably, the first electrode material is 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 a mixture thereof, and a lithium source may be included.

[0035] The first layer of the electrode may be essentially composed of a first electrode material.

[0036] 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 that can conform to the chemical formula Zr(1-x)YxO(2-0.5xδ) (0 < x ≤ 0.2).

[0037] Thus, the first layer may contain 20% by weight or more of the first electrode material, optionally 25% by weight or more of the first electrode material, optionally 30% by weight or more of the first electrode material, optionally 35% by weight or more of the first electrode material, optionally 40% by weight or more of the first electrode material, optionally 45% by weight or more of the first electrode material, optionally 50% by weight or more of the first electrode material, optionally 55% by weight or more of the first electrode material, optionally 60% by weight or more of the first electrode material.

[0038] The thickness of the first layer ranges from 1 μm to 7 μm, optionally 1 μm to 6 μm, 1 μm to 5 μm, 1 to 4 μm, or approximately 3 μm.

[0039] The lithium source may include any suitable lithium compound, such as lithium oxide, lithium hydroxide, lithium salts (e.g., lithium nitrate, lithium carbonate), lithium salts of organic acids (e.g., lithium citrate, lithium acetate, or lithium oxalate), and / or lithium as a dopant.

[0040] The electrodes may be multilayer electrode systems that provide additional and / or improved properties to the electrochemical cell. For example, the electrodes may be a two-layer, three-layer, four-layer, or five-layer system, or more than five layers. Generally, each layer of the electrode system may be the same or different, and if different, may be formed of different materials, and the electrode system as a whole may have different properties and uses.

[0041] Therefore, the electrode may comprise at least a second layer containing a second electrode material. Optionally, the second electrode material may be conductive, or optionally, a conductive ceramic material.

[0042] 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.

[0043] Therefore, in a second aspect, the present invention provides an electrode for an electrochemical cell, the electrode being Pr (1-x) Ln x O (2-0.5x-δ) The device comprises at least a first layer containing a first electrode material having a composition including a lithium source, and at least a second layer containing a second electrode material, where Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof, and δ is the oxygen deficiency degree, where 0.01 ≤ x ≤ 0.4.

[0044] As an example, the first and second layers of the electrode system may include the aforementioned first layer for use as the air electrode active layer (also called the cathode active layer or CAL in SOFCs) and the second layer for use as the air electrode bulk layer (also called the cathode bulk layer or CBL in SOFCs), respectively. The air electrode bulk layer has higher electrical (i.e., electronic) conductivity than the first layer and can therefore function as a current collector.

[0045] The first layer may be located next to the electrolyte (which itself may be an electrolyte system composed of multiple layers), with an intermediate layer (e.g., another layer of the electrode) located between the first layer of the electrode and the electrolyte, or the first layer may be in direct contact with (i.e., right next to) the electrolyte layer.

[0046] The second layer (e.g., the air electrode bulk layer) may be advantageously formed from or contain a conductive second electrode material, which may be, for example, a metallic conductor at the operating temperature of the electrochemical cell, and which may have relatively high electronic conductivity at such temperatures. The material of the second layer is preferably chemically and mechanically stable. The second layer, e.g., the air electrode bulk layer, is usually porous (the first layer is usually similar) to allow for good interaction with oxygen on the air side of the cell. The electrocatalytic activity of the second layer (e.g., the air electrode bulk layer) may be lower than that of the first layer (which may have high electrocatalytic activity as described above).

[0047] The second electrode material may optionally include an electronically conductive ceramic material having a perovskite structure ABX3.

[0048] Suitable second electrode materials include lanthanum cobaltite, lanthanum ferrite, lanthanum nickel ferrite, La 0.99 Co 0.4 Ni0.6O (3-δ) Examples include (LCN60) and mixtures thereof.

[0049] Optionally, the second layer may be a composite layer further comprising at least one additional second electrode material. The additional electrode material may include a strontium-containing material optionally selected from rare earth strontium cobaltite, rare earth strontium ferrite, and rare earth strontium cobalt ferrite, and the rare earth component may optionally be Pr, La, Gd and / or Sm, preferably Pr.

[0050] Optionally, the second composite electrode layer may contain 60% by weight or more of the second electrode material, optionally 65% by weight or more of the second electrode material, optionally 70% by weight or more of the second electrode material, and optionally 75% by weight or more of the second electrode material.

[0051] The electrode may further include a third layer containing a third electrode material.

[0052] To improve the adhesion between the first electrode layer and the second electrode layer, a third layer may be disposed between the first layer and the second layer as necessary.

[0053] 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 chemical formula Ce (1-x) GdxO (2-0.5x-δ) (0 < x ≤ 0.5). The doped zirconia may be a solid solution conforming to the chemical formula Zr (1-x) YxO (2-0.5xδ) (0 < x ≤ 0.2).

[0054] Additionally or alternatively, the third electrode material may include a strontium-containing material optionally selected from rare earth strontium cobaltite, rare earth strontium ferrite, and rare earth strontium cobalt ferrite, where the rare earth constituent may optionally be Pr, La, Gd, and / or Sm, and is preferably Pr.

[0055] Optionally, the third electrode material may include a mixed material of rare earth strontium cobaltite or rare earth strontium ferrite and rare earth doped ceria (REDC). A particularly preferred third electrode material may include a mixture of 60:40% by weight of praseodymium strontium cobaltite (e.g., PSC551: Pr 0.5 Sr 0.5 CoO3) and CGO.

[0056] The third electrode material may promote good adhesion between the first electrode layer and the second electrode layer, and may reduce any reactions under cell conditions between the second electrode material (such as LCN60) and the first electrode material, which may lead to the formation of a secondary phase, resulting in insufficient adhesion and potentially increased ohmic resistance.

[0057] Furthermore, since contaminants within the cell may react with the third electrode material (e.g., strontium cobaltite / cobalt ferrite) before contacting the first electrode layer, the third electrode layer can act as a poison getter for the first electrode layer. This advantageously protects the first electrode material and layer from degradation. Such contaminants may include chromium, silicon, and sulfur derived from SO2 in the air.

[0058] 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.

[0059] The electrode layers (e.g., a first electrode layer, a second electrode layer, and / or a third electrode layer) are pressed during sintering and optionally subjected to isotropic pressing to improve adhesion and other properties.

[0060] The electrode in the first or second embodiment may be an air electrode.

[0061] The electrode in the first or second embodiment may be, for example, an air electrode in an electrochemical cell such as an SOC, SOFC, or SOEC.

[0062] Accordingly, in a third aspect, the present invention provides an electrochemical cell comprising an electrode according to any one of the above-described aspects, and optionally further comprising one or more of an electrolyte, a second electrode, and a substrate. The second electrode may be a second fuel electrode.

[0063] The electrolyte may include at least one electrolyte layer containing doped ceria optionally selected from samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), praseodymium-doped ceria (PDC), samarium-gadolinia-doped ceria (SGDC), and mixtures thereof.

[0064] The electrolyte may include at least one electrolyte layer comprising zirconia optionally selected from scandia-stabilized zirconia (ScSZ), yttria-stabilized zirconia (YSZ), ytterbium-stabilized zirconia (YbSZ), scandia-celia-costabilized zirconia (ScCeSZ), scandia-yttria-costabilized zirconia (ScYSZ), and mixtures thereof.

[0065] The electrochemical cell may further comprise a substrate, optionally a metal substrate, preferably a steel substrate. The substrate may be porous.

[0066] The metal substrate may be a metal foil (i.e., a solid metal) with openings. This has the advantage of being able to adjust the porosity to be located in specific areas of the substrate. Alternatively or additionally, the metal substrate may have inherent porosity (e.g., isotropic porosity) formed by, for example, tape casting of a powder-deposited film and then sintering to form a porous substrate. In this specification, when the terms metal substrate or porous steel sheet are used, either of these may be referred to.

[0067] The electrochemical cell may be an electrolytic cell, oxygen separator, sensor, or fuel cell, and preferably a solid oxide electrochemical cell (fuel cell, SOFC, or electrolytic cell, SOEC).

[0068] In fuel cell mode, the fuel is in contact with the anode (fuel electrode), and the oxidant, such as air or an oxygen-rich fluid, is in contact with the cathode (air electrode). Therefore, in fuel cell mode, the air electrode becomes the cathode. A solid oxide electrolytic cell (SOEC) may have the same structure as a solid oxide fuel cell (SOFC), but essentially operates like an SOFC in reverse, i.e., in regenerative mode, using a solid oxide electrolyte to achieve the electrolysis of water and / or carbon dioxide, producing hydrogen gas and / or carbon monoxide and oxygen.

[0069] The electrodes are printed onto the substrate on which the layers are deposited, or applied by other means.

[0070] In a fourth aspect, the present invention provides a method for manufacturing an electrode for an electrochemical cell, the method comprising providing a substrate on which a layer comprising a fuel electrode and an electrolyte is optionally deposited, and applying at least a first layer comprising a first electrode composition, wherein the first electrode composition is Pr (1-x) Ln x O (2-0.5x-δ) The method comprises applying a first layer containing a lithium source, optionally drying at least the first layer, and optionally sintering at least the first layer to form an electrode, wherein Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof, and δ is the degree of oxygen depletion, where 0.01 ≤ x ≤ 0.4.

[0071] This is advantageous because the applicant has surprisingly found that the presence of a lithium source greatly improves sintering, and as a result, the average cell voltage of electrochemical cells such as SOFCs can be greatly improved.

[0072] Optionally, this method may further include applying a material to a substrate to form at least one electrolyte layer, applying a first electrode composition on the electrolyte layer to form an air electrode layer, optionally drying the air electrode layer, and co-sintering the electrolyte layer and the air electrode layer.

[0073] The air electrode layer (e.g., an activated air electrode layer, CAL) may be fired (i.e., co-sintered) together with the underlying electrolyte material layer, where both layers are sequentially placed as green layers (optionally pressed). At least one electrolyte layer (there may be other electrolyte layers) may be a zirconia-containing layer (e.g., an electron block layer). Co-sintering is highly advantageous because it allows for manufacturing in fewer steps.

[0074] Sintering, or co-sintering, may be carried out at a temperature of 750°C to 900°C, preferably 790°C to 900°C. Sintering may also be carried out in an air atmosphere.

[0075] In this method, the first electrode composition is Pr (1-x) Ln x O (2-0.5x-δ) The lithium salts may optionally include lithium nitrate, lithium carbonate, lithium citrate, lithium acetate, and / or lithium oxalate, preferably lithium nitrate.

[0076] A method for preparing the material for the first electrode composition is: (a)Pr (1-x) Ln x O (2-0.5x-δ) The process involves mixing a lithium source, and optionally, a lithium source (e.g., a lithium compound) in a solvent, preferably an alcohol. (b) an optional drying step, (c) Li-containing Pr (1-x) Ln x O (2-0.5x-δ)The process may include the step of firing (for example, at a temperature of 450°C to 600°C) to produce the material for the first electrode composition (for example, decomposing a lithium salt to produce lithium oxide).

[0077] A method for forming an electrode including at least a first electrode layer may include the steps of: applying a suitable dispersion liquid into a carrier of the first electrode layer material; applying a coating of the dispersion liquid to a substrate; and sintering the coating to form an air electrode.

[0078] In a fifth aspect, the present invention provides a composition comprising Pr(1-x)LnxO(2-0.5x-δ) and a lithium source, where Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof, and δ is the degree of oxygen deficiency, where 0.01 ≤ x ≤ 0.4.

[0079] In a sixth aspect, the present invention relates to Pr (1-x) Sm x O (2-0.5x-δ) The present invention provides a composition comprising a lithium source, where δ is the degree of oxygen deficiency and 0.01 ≤ x ≤ 0.4.

[0080] In a seventh aspect, the present invention provides a stack of electrochemical cells according to the electrochemical cell of the third aspect.

[0081] definition In this specification, the terms "lanthanide" and "lanthanide" are used interchangeably and refer to metallic chemical elements with atomic numbers 57–71.

[0082] As used herein, the term “dopant” is not intended to be limited to the maximum percentage of an element, ion, or compound added to a chemical structure. Similarly, the term “doping” means adding a certain amount of an element, ion, or compound to any material. It does not limit the maximum amount of material that can be added further without it ceasing to be doping.

[0083] As used herein, the term “perovskite structure” generally refers to a single network of chemically bonded crystalline structures having a perovskite (ABX3) structure. This does not mean that this single network must have a single, uniform crystalline structure throughout its entirety. However, if different crystalline structures arise between different regions of the network, these regions often have complementary structures, allowing for easier formation of chemical bonds between them.

[0084] The term "solid oxide cell" (SOC) is intended to encompass both solid oxide fuel cells (SOFCs) and solid oxide electrolytic cells (SOECs).

[0085] The term "cation percentage" or "cation percentage" (abbreviated as "cation%" or "%cation" herein) refers to the proportion of cations in a composition.

[0086] The term “source” of an element, compound, or other material refers to a material containing an element, compound, or other material, whether or not it is chemically bonded within the source. A source of an element, compound, or other material may be an elemental source (e.g., Ln, Sm, Pr, or O2), or it may be in the form of an element (e.g., lithium nitrate), a compound, or a compound or mixture containing one or more of those elements, compounds, or materials.

[0087] In this specification, electrochemical cells, SOCs, SOFCs, and SOECs may refer to tubular cells or planar cells. Electrochemical cell units may have tubular or planar configurations. Planar fuel cell units can be stacked on top of each other, for example, 100 to 200 fuel cell units can be stacked, and the individual fuel cell units are electrically connected in series.

[0088] An electrochemical cell may be a fuel cell, a reversible fuel cell, or an electrolytic cell. Generally, these cells may have the same structure, and a reference to an electrochemical cell may refer to any of these types of cells (unless otherwise indicated by the context).

[0089] In this specification, the terms "oxidant electrode" or "air electrode" and "fuel electrode" are used interchangeably to refer to the cathode and anode, respectively, of a SOFC, in order to avoid confusion between fuel cells and electrolytic cells.

[0090] While this specification describes cells in which a fuel electrode (e.g., an anode) is initially placed on the substrate, the present invention also encompasses cells in which an air electrode is initially placed on the substrate.

[0091] The cells described herein include metal-supported cells in which the layers of the cell are supported by a metal substrate, but the present invention also includes anode-supported cells, electrolyte-supported cells, or cathode-supported cells, each of which provides structural support for all other layers on which the other layers are coated.

[0092] The electrochemical cell included in the present invention may include the following: a) Two planar components welded together with a fluid volume between them (e.g., a substrate with an electrochemical layer and an interconnector (another plate)), b) Three planar components welded together via a fluid volume section between them (e.g., a substrate with an electrochemical layer and an interconnector (another plate) and a spacer providing the fluid volume section).

[0093] Various features of the embodiments of the disclosure described herein may be used in combination with any other features of the same embodiment or other embodiments of the disclosure, at the discretion of those skilled in the art, with appropriate modifications.

[0094] Furthermore, it is specifically assumed that all aspects of the present invention or the present disclosure preferably "include" the features described in relation to such aspects, but may "consist" or "consist essentially" of these features outlined in the claims.

[0095] The present invention will be described below with reference to the attached figures and examples. [Brief explanation of the drawing]

[0096] [Figure 1] This image shows a scanning electron microscope (SEM) cross-section of an SOFC equipped with the cathode active layer (CAL) of the material according to this disclosure. [Figure 2] Figure 1 shows a cross-sectional scanning electron microscope (SEM) image of the SOFC, illustrating the details of the CAL and adjacent layers. [Figure 3] The average cell potential, corresponding to the temperature of a cell containing the 2% lithium-containing material according to this disclosure and sintered at 870°C with CAL (133 mAcm-2, 75% Uf, under conditions of reforming equilibrium at 545°C), is shown normalized to a standard cell in the same stack. [Figure 4] The average cell potential corresponding to the temperature of a cell containing the 2% lithium-containing material according to this disclosure and sintered at 870°C with CAL (225 mAcm-2, 75% Uf, under conditions of reforming equilibrium at 545°C) is shown, normalized to a standard cell in the same stack. Embodiments for carrying out the present invention

[0097] Figure 1 shows a state of affairs (SOC) with a cathode active layer (CAL) 30 containing a lithium source (e.g., Li-containing PSmO10) and Ln-doped praseodymium oxide (PLnO).

[0098] In Figure 1, the SOC layers consist of a bulk air electrode layer (CBL) 10, a ReSC / CGO interfacial air electrode layer 20, an air electrode active layer (CAL) 30 containing the composition according to this disclosure (e.g., lithium source and PrLnO, e.g., 2LiPSmO10), a doped ceria barrier layer 35, a zirconia electron block layer 40, a CGO electrolyte layer 50, and a fuel electrode 60. The fuel electrode 60 is supported on a metal substrate (not shown).

[0099] Metal substrates are metal substrates, especially steel, especially ferritic stainless steel substrates, and usually foil substrates.

[0100] CAL30 includes the material according to this disclosure. Other layers are of a type whose composition is known to those skilled in the art, and whose methods of preparation and application are also known. For example, refer to International Publication No. 2009 / 090419(A2), which describes methods for laying these types of layers, exemplary configurations of these types of layers, and laying such layers on metal substrates, in particular stainless steel substrates. The layers (including air electrode layers) may exhibit good adhesion and / or may be isobaric pressed to further improve adhesion.

[0101] Figure 2 shows a scanning electron microscope (SEM) cross-section of the CAL30 of the SOFC in Figure 1 in more detail. The microstructure is generally consistent throughout the main portion of CAL30, and good adhesion exists with adjacent layers. Porosity and grain size are consistent throughout the depth of CAL30. Densification occurs at the interface with the ReSC / CGO interface air electrode layer.

[0102] Figure 3 shows sintering at 870°C (133 mAcm²). -2 The curve 4 shows the average cell potential corresponding to temperature, comparing a cell (curve 5) containing the material according to the present invention, modified under conditions of 75% Uf and 545°C reforming equilibrium, with a standard cell (curve 5) in the same stack. The performance of the Li-containing PSmO10CAL cell is far superior to that of the standard cell, especially at low temperatures.

[0103] Figure 4 shows sintering at 870°C (225 mAcm²). -2 The curve shows the average cell potential corresponding to temperature, comparing a cell containing CAL (curve 6) made from the 2% Li-containing PSmO10 material according to the present invention (under the conditions of 75% Uf and 545°C reforming equilibrium) with a standard cell (curve 7) in the same stack. Under these conditions, the Li-containing PSmO10CAL has a very high average cell voltage of 0.867V at 570°C.

[0104] To investigate the stack in operation (in this example, operating in SOFC mode), a fuel mixture simulating partially externally steam-reformed natural gas was supplied to the stack at a flow rate such that 75% of the oxidizable fuel was consumed by electrochemical reactions within the stack. To minimize the internal temperature gradient, air was supplied to the air electrode side of the stack at a flow rate far exceeding the stoichiometric requirement for oxygen. A constant current density of 133 mAcm² was maintained. -2 or 225mAcm -2 The stack temperature was varied by controlling the temperature of the furnace in which the test was being conducted.

[0105] The following examples illustrate a general method for synthesizing lithium-containing rare earth element-doped praseodymium according to the present invention (Examples 1, 2, and 3), a method for synthesizing a printable ink using such lithium-containing praseodymium powder (Example 4), and a method for printing CAL using such ink (Example 5).

[0106] Example 1: Synthesis of rare earth element (RE) doped praseodymium oxide powder Solution preparation A stoichiometric mixture of praseodymium nitrate hexahydrate and the desired RE dopant nitrate is dissolved in deionized (DI) water to obtain a 0.4 M molar solution.

[0107] In a separate container within the fume hood, dissolve the oxalic acid dihydrate in the same amount of DI water used to dissolve the nitrate, so that the molar ratio of oxalic acid to nitrate is 1.7 (slightly exceeding the stoichiometric requirement of 1.5 to ensure that all metal ions precipitate).

[0108] Once the oxalic acid is completely dissolved, add concentrated ammonium hydroxide solution while monitoring the pH, and continue until the acid is neutralized (pH 7) and ammonium oxalate solution remains.

[0109] subsidence While vigorously stirring the mixture, the nitrate solution is added to the ammonium oxalate solution, yielding a pale green precipitate of insoluble praseodymium and dopant oxalate.

[0110] filtration Prepare a Buchner funnel equipped with high-strength filter paper and a water tank pump. While the pump is running, pour the sediment mixture onto the filter and allow sufficient time for most of the supernatant to be removed and a sediment cake to remain on the filter paper.

[0111] Cleaning Wash the precipitate three times with DI water, then wash it once with ethanol.

[0112] dry Transfer the moist filtered cake from the funnel to a suitable container and dry it overnight in a solvent-resistant oven at 70°C.

[0113] Crushing The dried precipitate cake is ground using a mortar and pestle, and the resulting powder is transferred to an alumina crucible.

[0114] Example 2: Alternative synthesis of RE-doped praseodymium oxide powder Solution preparation A stoichiometric mixture of praseodymium nitrate hexahydrate and the target RE dopant nitrate is dissolved in deionized (DI) water to obtain a 0.15 M molar solution.

[0115] In a separate container inside a fume hood, dilute the concentrated ammonium hydroxide solution with DI water to obtain a 0.45 M solution of the same volume as the nitrate solution.

[0116] subsidence When the nitrate solution is added to the ammonium hydroxide solution while vigorously stirring the mixture, a pale green, gelatinous precipitate of insoluble praseodymium and dopant hydroxide is obtained.

[0117] filtration Prepare a Buchner funnel equipped with high-strength filter paper and a water tank pump. While the pump is running, pour the sediment mixture onto the filter and allow sufficient time for most of the supernatant to be removed and a sediment cake to remain on the filter paper.

[0118] Cleaning Wash the precipitate three times with DI water, then wash it once with ethanol.

[0119] dry Transfer the moist filtered cake from the funnel to a suitable container and dry it overnight in a solvent-resistant oven at 70°C.

[0120] Crushing The dried precipitate cake is ground using a mortar and pestle, and the resulting powder is transferred to an alumina crucible.

[0121] Example 3: Infiltration of a lithium source into RE-doped praseodymium oxide powder Samples of co-precipitated RE-doped praseodymium oxide powder were obtained for use in subsequent procedures. The samples were brought into contact with a lithium source according to the following method.

[0122] 10% Sm praseodymium oxide (Pr 0.9 Ln 0.1 O (1.95-δ) Samples of "PSmO10" were processed to produce two compositions in which lithium was present as a 1% cation and a 2% cation.

[0123] Using a high-precision pipette, a 0.5 M lithium nitrate solution in ethanol was slowly added to the PSmO10 powder, ensuring that the powder was not visibly wetted. The resulting powder was then mixed using a mortar and pestle.

[0124] Li-containing PSmO10 powder was dried in an oven, and then calcined at 500°C for 2 hours to decompose lithium nitrate into lithium oxide.

[0125] Samples of PSmO10, PSmO10 containing 1 cation %Li, and PSmO10 containing 2 cations %Li were calcined in a tubular furnace at 850°C for 1 hour to simulate cathode ignition.

[0126] Pellets made from the same powder were uniaxially pressed and simultaneously fired to evaluate sintering.

[0127] Sintering shrinkage was evaluated, and the results are shown in Table 1 below.

[0128] [Table 1]

[0129] Example 4: Synthesis of printable ink Dispersion and milling of Li-containing RE-doped praseodymium oxide powder The lithium-containing RE-doped praseodymium oxide powder, prepared as described in Examples 1-3, is weighed and mixed with a carrier, dispersant, and defoamer to form a slurry containing a target amount of approximately 46% by weight of the powder.

[0130] The slurry is transferred to a basket mill, and twice the weight of the slurry is added as 1 mm YSZ milling medium.

[0131] Slurry is d 90 Milling is performed at approximately 7000 rpm until a particle size of <0.9 μm is achieved. The particle size distribution can be measured using a Malvern Mastersizer® 2000 laser diffraction particle size analyzer.

[0132] The slurry is then removed from the basket mill.

[0133] Ink manufacturing Transfer the dispersed and pulverized Li-containing RE-doped praseodymium oxide powder slurry, prepared in the previous section, to a small high-shear disperser (HSD) pot and place it on the HSD.

[0134] Weigh out an amount of binder powder equivalent to 2.5-3.5% by weight of the finished ink.

[0135] The binder is added to the slurry, which is actively dispersed on the HSD.

[0136] The ink remains on the HSD until the binder has completely dissolved within it.

[0137] The ink is then transferred to a triple-roll mill (TRM) for final homogenization, passing through the mill four times with a 5μm front nip. This ensures that the binder is completely homogenized with the ink, guaranteeing that no particles larger than 5μm remain in the finished ink.

[0138] Example 5: Print ink and form an active layer The printing substrate consisted of an electrolyte layer deposited on a metal-supported SOFC. The ink was screen printed onto the electrolyte layer of the metal-supported SOFC in a single pass using an automatic screen printing machine. It was then dried in a drying oven. A combination of ink solids and screen mesh was selected to obtain a thin print of approximately 3 μm. After adding CBL, the layer was sintered with the CBL at a temperature of 820-870°C to form CAL. After sintering, X-ray diffraction and BET analysis were repeated. After sintering, the crystal grain size increased slightly and the BET surface area decreased, but the crystal structure remained unchanged. This layer still consisted of a single phase with a cubic fluorite structure.

[0139] Example 6: SOFC cell using a Li-containing PrLnO air electrode CAL. The Li-containing RE-doped praseodymium oxide powder slurry described herein and illustrated in Examples 1-4 above has performance equal to or better than that of the standard.

[0140] A three-layer SOFC air electrode was produced. The three-layer electrode advantageously reduces the effects of chromium contamination (praseodymium oxide can react with chromia to form perovskites) and ensures further strengthening of adhesion between the bulk layer and the active layer.

[0141] The electrode consists of three layers: a bulk layer of LCN60, which provides excellent stability and thermal expansion matching with the rest of the cell; an interfacial composite layer of rare-earth strontium cobaltite / CGO; and a catalytic active layer of rare-earth doped praseodymium oxide. The interfacial layer ensures sufficient adhesion between the active layer and the bulk layer, and also acts as a toxin getter for the active layer, as toxins such as chromium and sulfur react with the rare-earth strontium cobaltite / cobalt ferrite before reaching the strontium-free active layer (which may be susceptible to chromium poisoning). The interfacial layer has a similar thermal coefficient to the air electrode bulk layer. This protects the active layer from degradation (it is unaffected by water vapor, carbon dioxide, or sulfur dioxide).

[0142] The air electrode was manufactured by screen printing as three layers: a thin layer (approximately 3 microns) of a first electrode material (e.g., 2-cation %LiPSmO10), a thin layer (approximately 3 microns) of rare earth strontium cobaltite / CGO (e.g., ReSC / CGO1060:40, where "Re" refers to a rare earth element), and finally a much thicker (approximately 40 microns) bulk layer (LCN60).

[0143] Optionally, these layers may be burned away, hydrostatic or uniaxial pressure applied to increase the green density, and finally sintered in air at 800-900°C to form the finished air electrode.

[0144] The described air electrodes were supplied to a standard metal-supported SOFC and incorporated into a 17-cell stack. The anode of each cell consisted of a ceria-nickel cermet, and the electrolyte consisted of CGO with a doped zirconia electron-blocking layer. The CAL may be in direct contact with the zirconia electron-blocking layer, or, for example, a layer of CGO may be interposed between the active layer and the zirconia electron-blocking layer.

[0145] Under the above conditions, the stack can operate with an airflow on the air side and simulated steam-reformed natural gas as fuel on the fuel side.

[0146] All publications referenced in the above specification are incorporated herein by reference. While exemplary embodiments of the present invention have been disclosed in detail with reference to the accompanying drawings, it will be understood that the present invention is not limited to such embodiments, and that various modifications and alterations are possible by those skilled in the art without departing from the scope of the invention as defined by the accompanying claims and their equivalents.

Claims

1. An electrode for an electrochemical cell, wherein the electrode comprises a first layer containing at least a first electrode composition, and the first electrode composition is Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） and electrodes including a lithium source (wherein Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof) δ represents the degree of oxygen deficiency, (0.01 ≤ x ≤ 0.4).

2. The electrode according to claim 1, wherein the lithium source is present in the first electrode composition in an amount of 0.001 to 5 cation percent.

3. The electrode according to claim 2, wherein the lithium source is present in the first electrode composition in an amount of 0.01 to 5 cation percent.

4. The electrode according to any one of the prior claims, wherein the rare earth metal is selected from La, Sm, Gd, and Yb, and preferably Sm.

5. An electrode according to any one of the prior claims, wherein 0.02 ≤ x ≤ 0.

25.

6. where the first electrode composition is 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 a mixture thereof, and a lithium source, the electrode according to any one of the preceding claims.

7. The electrode according to any one of the prior claims, wherein the first layer comprises 20% by weight or more of the first electrode composition, 25% by weight or more of the first electrode composition, optionally 30% by weight or more of the first electrode composition, optionally 40% by weight or more of the first electrode composition, and optionally 55% by weight or more of the first electrode composition.

8. The electrode according to any one of the prior claims, wherein the first layer has a thickness in the range of 1 μm to 7 μm.

9. The electrode according to any one of the prior claims, wherein the electrode comprises at least a second layer containing a second electrode material.

10. The electrode according to any one of the prior claims, wherein the electrode is an air electrode.

11. The electrode according to any one of the prior claims, wherein the lithium source comprises lithium oxide, lithium hydroxide, lithium salts, lithium salts of organic acids, and / or lithium as a dopant.

12. An electrochemical cell comprising the electrode described in any one of the prior claims, and optionally further comprising one or more of an electrolyte, a second fuel electrode, and a substrate.

13. The electrochemical cell according to claim 12, further comprising an electrolyte, wherein the electrolyte comprises at least one electrolyte layer comprising a doped ceria optionally selected from samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), praseodymium-doped ceria (PDC), samarium-gadolinia-doped ceria (SGDC), and mixtures thereof.

14. The electrochemical cell according to claim 12 or 13, wherein the electrochemical cell is an electrolytic cell, an oxygen separator, a sensor, or a fuel cell, and optionally the electrochemical cell includes a solid oxide electrochemical cell.

15. A method for manufacturing electrodes for an electrochemical cell, wherein the method is To provide a substrate, wherein a layer containing a fuel electrode and an electrolyte is optionally deposited thereon. Applying at least a first layer comprising a first electrode composition, wherein the first electrode composition is Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） And applying a first layer including a lithium source, Optionally, drying at least the first layer, Optionally, sinter at least the first layer, A method including forming electrodes thereafter. (wherein Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof) δ represents the degree of oxygen deficiency, (0.01 ≤ x ≤ 0.4).

16. The method according to claim 15, Applying a material to the substrate to form at least one electrolyte layer, The above-described first electrode composition is applied to the electrolyte layer to form an air electrode layer, Optionally, drying the air electrode layer, A method further comprising co-sintering the electrolyte layer and the air electrode layer.

17. The method according to claim 15 or 16, wherein the sintering or co-sintering is performed at a temperature in the range of 750°C to 900°C.

18. The first electrode composition is Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） The method according to any one of claims 15 to 17, comprising and a lithium salt, preferably lithium nitrate.

19. Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） The method according to any one of claims 15 to 18, further comprising the step of preparing a first electrode composition by mixing with a lithium source, wherein optionally the lithium source is dissolved or dispersed in a solvent, optionally in an alcohol.

20. Pr （１－ｘ） Ln ｘ O （２－０．５ｘ－δ） A composition comprising a lithium source. (wherein Ln is selected from at least one rare earth metal selected from La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y and mixtures thereof) δ represents the degree of oxygen deficiency, (0.01 ≤ x ≤ 0.4).

21. Pr （１－ｘ） Sm ｘ O （２－０．５ｘ－δ） A composition comprising a lithium source. (Here, δ is the degree of oxygen deficiency, (0.01 ≤ x ≤ 0.4).

22. A stack of electrochemical cells according to any one of claims 12 to 14.

Images