Solid composite material for electrodes

Abstract

A solid composite material has been developed that may be used for various applications, including forming electrodes in electrochemical cells. The solid composite materials may comprise a double perovskite phase and a single perovskite phase, where the double perovskite phase comprises PrBaSrCoFeO (PBSCF) and the single perovskite phase comprises BaSrCoO (BSC). Due to its unique chemical formulation, the solid composite material of the present disclosure may be used to produce electrodes and electrochemical cells that exhibit superior performance.

Description

SOLID COMPOSITE MATERIAL FOR ELECTRODES RELATED APPLICATIONS

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial No. 63 / 598,330 entitled “SOLID COMPOSITE MATERIAL FOR ELECTRODES,” filed November 13, 2023, the entire disclosure of which is incorporated herein by reference. BACKGROUND 1. Field of the Invention

[0002] The present disclosure generally relates to solid composite materials for electrodes and to methods of forming the same. More particularly, the present disclosure generally relates to solid composite materials comprising a double perovskite phase and a single perovskite phase and to method of forming the same. 2. Description of the Related Art

[0003] The growing concern over global greenhouse effects and climate change has led to a surge in demands for clean and sustainable energy across the globe. This has generated significant interest in highly efficient energy technologies that produce considerably less greenhouse gas emissions. Among such technologies, electrolyzer cells have emerged as a promising option for next-generation electrochemical energy conversion and storage systems, due to their exceptional efficiency and minimal environmental impact. In fuel cell mode, electrolyzer cells convert fuels, such as hydrogen and hydrocarbons, into electricity with a higher efficiency than combustors. When there is excess electricity available, electrolyzer cells function as electrolyzers to produce hydrogen, carbon monoxide, or syngas with different reactants fed to the fuel electrode.

[0004] Electrolyzer technology has undergone drastic improvements over the past decade, but for its commercialization, further research and development are needed to increase performance (i.e., energy efficiency and durability). Therefore, extensive efforts have been invested in developing electrode materials to alleviate the restricted electrochemical activity and decreased performance. However, further advancements in the types of available electrode materials are needed.SUMMARY

[0005] One or more embodiments generally relate to a solid composite material comprising a double perovskite phase and a single perovskite phase.

[0006] One or more embodiments generally relate to a solid composite material comprising: (a) a double perovskite phase and (b) a single perovskite phase. The double perovskite phase has a formula PraBabSrcCodFeeO6-δ1, wherein a is from 1 to 1.75, b is from 0.05 to 0.5, c is from 0.3 to 0.7, d is from 1.25 to 1.75, e is from 0.4 to 0.9, and δ1 is greater than zero, but less than 1. Additionally, the single perovskite phase having a formula BaxSryCozO3-δ2, wherein x is from 0.4 to 0.75, y is from 0.25 to 0.5, z is from 0.75 to 1.25, and δ2 is greater than zero, but less than 0.5.

[0007] One or more embodiments generally relate to an article comprising the solid composite material described herein.

[0008] One or more embodiments generally relate to an electrode comprising the solid composite material described herein.

[0009] One or more embodiments generally relate to the use of the solid composite material described herein in an electrochemical cell.

[0010] One or more embodiments generally relate to an electrochemical cell. Generally, the electrochemical cell comprises: a first electrode comprising a first electrode material; a second electrode comprising a second electrode material; and a proton-conducting electrolyte positioned between the first electrode and the second electrode. Furthermore, the first electrode material and / or the second electrode material comprise a solid composite material, wherein the solid composite material comprises a double perovskite phase and a single perovskite phase.

[0011] One or more embodiments generally relate to a method of producing hydrogen. Generally, the method comprises: providing the electrochemical cell described herein; reacting water at the second electrode to generate oxygen and protons; causing the protons to pass through the proton-conducting electrolyte to the first electrode; and supplying an electrical current to the first electrode and reducing at least a portion of the protons to form hydrogen.

[0012] One or more embodiments generally relate to a method of generating electricity. Generally, the method comprises: providing the electrochemical cell described herein; supplying hydrogen to the electrochemical cell and oxidizing the hydrogen at the first electrode to form protons and electrons; causing the protons to pass through the proton-conducting electrolyte tothe second electrode; causing the electrons generated at the first electrode to induce an electrical current and passing the electrical current through an electrical load that is connected with the first electrode and the second electrode; and reacting the protons with oxygen at the second electrode to produce water. BRIEF DESCRIPTION OF THE FIGURES

[0013] Embodiments of the present invention are described herein with reference to the following drawing figures, wherein:

[0014] FIG. 1 depicts an exemplary electrochemical cell comprising an electrode formed from the solid composite materials described herein; and

[0015] FIG. 2 depicts an exemplary construct of a first electrode coated on a barrier layer. DETAILED DESCRIPTION

[0016] A solid composite material has been developed that may be used for various applications, including forming electrodes in electrochemical cells. The solid composite materials described herein may comprise a double perovskite phase and a single perovskite phase. Due to its unique chemical formulation, the solid composite material of the present disclosure may be used to produce electrodes and electrochemical cells that exhibit superior performance.

[0017] According to various embodiments, a solid composite material may be produced that comprises a double perovskite phase and a single perovskite phase. As described below in greater detail, the double perovskite phase comprises PrBaSrCoFeO (“PBSCF”) and the single perovskite phase comprises BaSrCoO (“BSC”).

[0018] As used herein, the term “perovskite” and “single perovskite phase” means any material with a crystal structure having the formula ABX3, wherein “A” and “B” refer to cations and “X” refers to an anion. Furthermore, as used herein a “double perovskite” refers to a complex perovskite material with a crystal structure of AA’BB’X6, wherein “A” and “A’” represent two or more cations, such as cations of alkaline earth metals and / or rare earth metals; “B” and “B’” represent two or more cations, such as those containing a transition metal; and “X” represents at least one anion. Generally, in various embodiments, a double phase perovskite mayhave a unit cell that is twice that of a single perovskite phase, with two cations ordered on the “B” site.

[0019] Generally, in one or more embodiments, the solid composite material, such as the double perovskite phase and the single perovskite phase, may be synthesized using a wet- chemistry method, wherein two or more cations and one or more anions are dissolved in water in stoichiometric amounts. Exemplary precursor reagents for the cations and / or anions may include, for example, Pr6O11, Ba(NO3)2, Sr(NO3)2, Co(NO3)•6H2O, Fe(NO3)3•9H2O, and / or Fe(NO3)3•6H2O.

[0020] During the wet-chemistry method, in one or more embodiments, Ba(NO3)2, Sr(NO3)2, Co(NO3)3•6H2O, and Fe(NO3)3•6H2O (or Fe(NO3)3•9H2O) may be at least partially dissolved in deionized water in stoichiometric amounts to form an initial reaction solution. Additionally, a specific amount of Pr6O11 may be dissolved in diluted nitric acid and subsequently added into the reaction solution. For example, a calculated amount of Pr6O11 may be dissolved in a about 20 weight percent diluted nitric acid solution at about 100°C to obtain a praseodymium nitrate solution. The praseodymium nitrate solution may be added to the reaction solution under stirring for 10 to 60 minutes, 15 to 45 minutes, or about 30 minutes at temperatures in the range of about 15 to about 100 °C, about 20 to about 80 °C, or about 20 to about 50 °C.

[0021] In one or more embodiments, the reaction solution comprises: (a) 0.05 to 0.5 moles, 0.1 to 0.4 moles, or 0.15 to 0.25 moles of Pr6O11; (b) 0.05 to 1.0 moles, 0.1 to 0.8, or 0.3 to 0.6 moles of Ba(NO3)2; (c) 0.05 to 1.0 moles, 0.1 to 0.8, or 0.3 to 0.6 moles of Sr(NO3)2; (d) 0.1 to 2.0 moles, 0.5 to 1.9 moles, or 1.0 to 1.7 moles of Co(NO3)3; and / or (e) 0.05 to 1.0 moles, 0.1 to 0.8, or 0.3 to 0.6 moles of Fe(NO3)3.

[0022] In one particular embodiment, the reaction solution comprises about 0.17 moles of Pr6O11, about 0.5 moles of Ba(NO3)2, about 0.5 moles of Sr(NO3)2, about 1.5 moles of Co(NO3)3, and about 0.5 moles of Fe(NO3)3.

[0023] After forming the initial reaction solution, one or more complexing and chelating agents, such as citric acid (“CA”) and / or ethylenediaminetetraacetic acid (“EDTA”), may be added to the reaction solution. The complexing and chelating agents may be added to the reaction solution under continuous stirring for 10 to 90 minutes, 15 to 75 minutes, or about 60minutes at temperatures in the range of about 15 to about 100 °C, about 20 to about 80 °C, about 20 to about 50 °C, or about 23°C in order to obtain complete complexation.

[0024] In one or more embodiments, after adding the complexing and chelating agents, the resulting reaction solution may have a CA:total cation molar ratio of at least 1:1, 1.5:1, or 2:1 and / or less than 4:1, 3.5:1, or 3:1. Additionally, or in the alternative, after adding the complexing and chelating agents, the resulting reaction solution may have an EDTA:total cation molar ratio of at least 1:1, 1.5:1, or 2:1 and / or less than 4:1, 3.5:1, or 3:1. In certain embodiments, after adding the complexing and chelating agents, the resulting reaction solution may have a CA:EDTA:total cation molar ratio of about 2:2:1.

[0025] Subsequently, after adding the complexing and chelating agents, the pH of the resulting reaction solution may be adjusted to about 9 via the addition of a pH adjustment agent (e.g., an aqueous NH4OH solution).

[0026] After adjusting the pH of the reaction solution, the reaction solution may then be heated to thereby form a gel. Generally, in one or more embodiments, the reaction solution may be heated at a temperature in the range of about 200 to about 400 °C, about 225 to about 350 °C, or about 250 to about 300 °C. The reaction solution may be heated using conventional equipment known in the art, such as via a hot plate or oven, until a gel is formed.

[0027] Once the gel has formed, at least a portion of the resulting gel may be immediately placed in a dryer, such as a drying oven, to further dry. In one or more embodiments, the drying step can occur at a temperature in the range of about 50 to about 250 °C, about 75 to about 225 °C, about 100 to about 200 °C, or about 175°C over a time period of about 3 to about 36 hours, about 6 to about 30 hours, or about 24 hours.

[0028] After drying, in various embodiments, the resulting powder may then be calcined under air at a temperature in the range of about 400 to about 700 °C, about 500 to about 675 °C, or about 600 to about 650 °C over a time period of 1 to 24 hours, 2 to 18 hours, 3 to 8 hours, or about 5 hours.

[0029] Afterwards, in various embodiments, at least a portion of the calcined powder may be subjected to milling, such as ball-milling, in an alcohol (e.g., ethanol) for 1 to 48 hours, 6 to 36 hours, or about 24 hours. Subsequently, at least a portion of the milled powder may be subjected to drying in a dryer (e.g., a drying oven) at a temperature in the range of about 50 to about 250 °C, about 75 to about 225 °C, about 100 to about 200 °C, about 100°C, or about175°C over a time period of about 3 to about 36 hours, about 6 to about 30 hours, or about 24 hours.

[0030] Finally, in various embodiments, the dried and calcined powder may be sintered at a temperature in the range of about 500 to about 900 °C, about 600 to about 800 °C, or about 750 to about 775 °C until the dried and calcined powder has crystallized into the solid composite material comprising a double perovskite phase and a single perovskite phase. In various embodiments, the resulting solid composite material may be in the form of a powder.

[0031] In one or more embodiments, the phase structures within the double perovskite phase and the single perovskite phase are such that each perovskite is a separately identifiable structure within the overall material with each phase having its own identifiable crystalline structure.

[0032] In one or more embodiments, solid composite material comprises a double perovskite phase having a formula PraBabSrcCodFeeO6-δ1 and a single perovskite phase having a formula BaxSryCozO3-δ2, wherein: a is from 1 to 1.75, 1.1 to 1.6, 1.2 to 1.5, or 1.3 to 1.5; b is from 0.05 to 0.5, 0.05 to 0.4, 0.05 to 0.3, or 0.1 to 0.2; c is from 0.3 to 0.7, 0.35 to 0.65, or 0.4 to 0.6; d is from 1.25 to 1.75, 1.3 to 1.7, or 1.35 to 1.65; e is from 0.4 to 0.9, 0.5 to 0.85, or 0.6 to 0.8; δ1 is greater than zero, but less than 1; x is from 0.4 to 0.75, 0.45 to 0.7, or 0.5 to 0.7; y is from 0.25 to 0.5, 0.3 to 0.45, or 0.3 to 0.4; z is from 0.75 to 1.25, 0.8 to 1.2, or 0.9 to 1.1; and / or δ2 is greater than zero, but less than 0.5.

[0033] In one or more embodiments, solid composite material comprises a double perovskite phase having a formula PraBabSrcCodFeeO6-δ1 and a single perovskite phase having a formula BaxSryCozO3-δ2, wherein: a is from 1 to 1.75; b is from 0.05 to 0.5; c is from 0.3 to 0.7; d is from 1.25 to 1.75;e is from 0.4 to 0.9; δ1 is greater than zero, but less than 1; x is from 0.4 to 0.75; y is from 0.25 to 0.5; z is from 0.75 to 1.25; and δ2 is greater than zero, but less than 0.5.

[0034] In one or more embodiments, the solid composite material has a molar ratio of barium to strontium in the double perovskite phase of from 0.1:1 to 1:1, 0.2:1 to 0.8:1, or 0.2:1 to 0.5:1; a molar ratio of praseodymium to barium in the double perovskite phase of from 1.5:1 to 15:1, 2:1 to 14:1, 3:1 to 13:1, or 4:1 to 12:1; a molar ratio of praseodymium to strontium in the double perovskite phase of from 1.5:1 to 3.5:1, 2:1 to 3.5:1, or 2.5:1 to 3.5:1; a molar ratio of praseodymium to cobalt in the double perovskite phase of from 0.5:1 to 1.5:1, 0.7:1 to 1.4:1, or 0.8 to 1.3:1; a molar ratio of praseodymium to iron in the double perovskite phase of from 1.5:1 to 2.5:1, 1.6:1 to 2.4:1, or 1.7:1 to 2.3:1; a molar ratio of barium to strontium in the single perovskite phase of from 1.5:1 to 2.0:1 or 1.6:1 to 1.95:1; a molar ratio of barium to cobalt in the single perovskite phase of from 0.5:1 to 0.75:1 or 0.6:1 to 0.7:1; and / or a molar ratio of strontium to cobalt in the single perovskite phase of from 0.25:1 to 0.5:1 or 0.3:1 to 0.45:1.

[0035] In one or more embodiments, the solid composite material has a molar ratio of barium to strontium in the double perovskite phase of from 0.1:1 to 1:1; a molar ratio of praseodymium to barium in the double perovskite phase of from 1.5:1 to 15:1; a molar ratio of praseodymium to strontium in the double perovskite phase of from 1.5:1 to 3.5:1; a molar ratio of praseodymium to cobalt in the double perovskite phase of from 0.5:1 to 1.5:1; a molar ratio of praseodymium to iron in the double perovskite phase of from 1.5:1 to 2.5:1; a molar ratio of barium to strontium in the single perovskite phase of from 1.5:1 to 2.0:1; a molar ratio of barium to cobalt in the single perovskite phase of from 0.5:1 to 0.75:1; and / or a molar ratio of strontium to cobalt in the single perovskite phase of from 0.25:1 to 0.5:1.

[0036] In an exemplary embodiment, the double perovskite phase has a formula of Pr1.44Ba0.11Sr0.45Co1.32Fe0.68O6-δ and the single perovskite phase has a formula of Ba0.62Sr0.38CoO3-δ-.

[0037] In another exemplary embodiment, the double perovskite phase has a formula of Pr1.39Ba0.14Sr0.53Co1.48Fe0.76O6-^- and the single perovskite phase has a formula of Ba0.66Sr0.34CoO3-^.

[0038] In one or more embodiments, the double perovskite phase has a tetragonal (P4 / mmm) crystal structure and / or the single perovskite phase has a hexagonal P63 / mmc crystal structure, as confirmed by transmission electron microscopy (“TEM”) and X-ray diffraction (“XRD”).

[0039] In one or more embodiments, the solid composite material comprises at least 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70 weight percent of the double perovskite phase. Additionally, or in the alternative, the solid composite material may comprise less than 99, 95, 90, 85, 80, or 75 weight percent of double perovskite phase. In certain embodiments, the solid composite material comprises about 70 or about 90 weight percent of double perovskite phase. These weight percentages and those disclosed below may be confirmed by XRD.

[0040] In one or more embodiments, the solid composite material comprises at least 1, 5, 10, 15, 20, or 25 weight percent of the single perovskite phase. Additionally, or in the alternative, the solid composite material may comprise less than 60, 50, 45, 40, or 35 weight percent of single perovskite phase. In certain embodiments, the solid composite material comprises about 10 or about 30 weight percent of single perovskite phase.

[0041] In one or more embodiments, the solid composite material may have an average particle size of at least 1, 5, 10, 15, or 20 nm and / or less than 100, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, or 40 nm, as confirmed by TEM. End Use Applications

[0042] The solid composite materials described herein may be used in a variety of applications. In one or more embodiments, the solid composite materials may be used to produce an electrode for power generation in an electrochemical cell, such as a fuel cell. Generally, a fuel cell is an electrochemical cell that reacts hydrogen fuel with oxygen or another oxidizing agent, to convert chemical energy to electricity. An exemplary fuel cell that may be produced from electrodes containing the solid composite materials described herein is a solid oxide electrolyzer cell (“SOEC”).

[0043] In one or more embodiments, and as shown in FIG. 1, an electrochemical cell 10 comprising an electrode formed from the solid composite materials described herein may comprise: a support layer 12 comprising a support layer material; an optional barrier layer 14 in contact with a surface of the support layer 12; a first electrode 16 in contact with the barrier layer 14 and comprising a first electrode material; an electrolyte 18 in contact with the first electrode 16; and a second electrode 20 in contact with the electrolyte 18. If present, the barrier layer 14 may inhibit chemical reactions between the support layer material and the electrode and electrolytes.

[0044] The present disclosure is also concerned with a method of forming an electrochemical cell 10 with the solid composite materials described herein. In one or more embodiments, the method comprises (a) forming an optional barrier layer 14 on a support layer 12; (b) forming a first electrode 16 on the optional barrier layer 14; (c) forming a electrolyte 18 on the first electrode 16, thereby forming a stack comprising the support layer 12, the barrier layer 14, the first electrode 16, and the electrolyte 18; and (d) sintering the stack to form a portion of the electrochemical cell 10. Additionally, in other embodiments, the method further comprises: (e) forming a second electrode 20 on the electrolyte 18, thereby forming a second stack comprising the support layer 12, the barrier layer 14, the first electrode 16, the electrolyte 18, and the second electrode 20; and (f) sintering the second stack to form the electrochemical cell 10.

[0045] In one or more embodiments, the electrochemical cell 10 comprises a support layer 12, which is permeable to H2, O2, and / or H2O. By including the support layer 12, the mechanical properties of the electrochemical cell 10 may be significantly improved. Thus, in most embodiments, the support layer 12 comprises any robust material that does not negatively affect the conductivity in the electrochemical cell 10. As used herein, the term “negatively affect” means that the material prevents, reduces, and / or causes a substantial reduction of proton conduction through the cell. In various embodiments, the support layer 12 comprises a crystalline substrate material. Examples of crystalline substrate materials include, but are not limited to, yttria-stabilized zirconia, nickel(II) oxide, ceria (CeO2), samarium-doped ceria (Sm- CeO2), gadolinium-doped ceria (Gd-CeO2), or combinations thereof. In these such embodiments, the crystalline substrate material can further comprise copper(II) oxide, nickel(II) oxide, or combinations thereof.

[0046] Once formed, the support layer 12 may have a thickness from about 10 mm to about 0.01 mm, about 7 mm to about 0.05 mm, about 3 mm to about 0.1 mm, or about 1 mm.

[0047] In one or more embodiments, the electrochemical cell 10 comprises a first electrode 16. It will be appreciated that, depending on the operating mode employed, the first electrode 16 can function as an anode or cathode in the cell 10. Particularly, when the cell 10 is operated in a hydrogen-producing mode, the first electrode 16 (functioning as a cathode) reduces protons to hydrogen, and when the cell is operated in an electricity-producing mode, the first electrode (functioning as an anode) forms protons from hydrogen.

[0048] In various embodiments, the first electrode 16 comprises, consists essentially of, or consists of the solid composite materials described herein. In such embodiments, the first electrode 16 may comprise at least 50, 75, 90, 95, or 99 weight percent of the solid composite materials.

[0049] Once formed, the first electrode 16 may have a thickness in a range of about 10 µm to about 70 µm, about 20 µm to about 60 µm, about 30 µm to about 50 µm, or about 40 µm.

[0050] In one or more embodiments, the electrochemical cell 10 comprises a proton- conducting electrolyte 18. The proton-conducting electrolyte 18 may comprise a perovskite oxide electrolyte material. Examples of perovskite oxide electrolyte materials include, but are not limited to, yttrium-doped barium cerate, yttrium-doped barium zirconate, yttrium-doped barium cerate-zirconate, ytterbium-doped barium cerate, ytterbium-doped barium zirconate, ytterbium-doped cerate-zirconate, yttrium- and ytterbium-doped barium cerate, yttrium- and ytterbium-doped barium zirconate, yttrium- and ytterbium-doped barium cerate-zirconate, or combinations thereof.

[0051] Once formed, the proton-conducting electrolyte 18 may have a thickness in a range of about 0.01 µm to about 75 µm, about 1 µm to about 25 µm, about 5 µm to about 15 µm, or about 10 µm.

[0052] In one or more embodiments, the electrochemical cell 10 comprises a second electrode 20. It will be appreciated that, depending on the operating mode employed, the second electrode 20 can function as an anode or cathode. Particularly, when the cell 10 is operated in hydrogen-producing mode, the second electrode 20 (functioning as an anode) forms protons and oxygen from water using an electrical current, and when the cell 10 is operated in electricity-producing mode, the second electrode 20 (functioning as a cathode) reacts protons and electrons with oxygen to form water.

[0053] In various embodiments, the second electrode 20 comprises, consists essentially of, or consists of the solid composite materials described herein. In such embodiments, the second electrode 20 may comprise at least 50, 75, 90, 95, or 99 weight percent of the solid composite materials.

[0054] Once formed, the second electrode 20 may have a thickness in a range of about 10 µm to about 70 µm, about 20 µm to about 60 µm, about 30 µm to about 50 µm, or about 40 µm.

[0055] The electrochemical cell 10 can be configured according to general methods in the art and / or methods known to one of skill in the art. In one or more embodiments, the cell 10 comprises a support layer 12 comprising a support layer material, a barrier layer 14, a first electrode 16 comprising the solid composite materials described herein, a proton-conducting electrolyte 18, and a second electrode 20 comprising the solid composite materials described herein. In such embodiments, the barrier layer 14 may be in contact with a surface of the support layer 12 and that the first electrode 16 may be in contact with the barrier layer 14 opposite of the support layer 12. Furthermore, the proton-conducting electrolyte 18 may be in contact with the first electrode 16 opposite of the barrier layer 14 and the second electrode 20 may be in contact with the proton-conducting electrolyte 18 opposite of the first electrode 16. As used herein, the term “in contact with” means that the layer, electrode, and / or electrolyte is sufficiently connected to at least one other layer, electrode, and / or electrolyte in the cell so that protons are allowed to move through the cell.

[0056] The present disclosure is also concerned with an electrical assembly. In one or more embodiments, the electrical assembly comprises an electrochemical cell operably connected to a source of electricity and / or an electrical load, such as a light bulb. In various embodiments, the electrochemical cell is operably connected to a source of water, such as steam.

[0057] The present disclosure is also concerned with a method of producing hydrogen. In one or more embodiments, the method comprises providing an electrochemical cell; reacting water at the second electrode to generate oxygen and protons; causing the protons to pass through the electrolyte to the first electrode; and supplying an electrical current to the first electrode and reducing at least a portion of the protons to form hydrogen.

[0058] In one or more embodiments, due to the inclusion of the first electrode, the electrical assembly may have an active area in a range of from about 150 cm2to about 350 cm2, about 175 cm2to about 300 cm2, about 200 cm2to about 250 cm2, or about 230 cm2. The electrochemical cell can be constructed in any suitable shape; however, in certain embodiments the cell may be tubular shape.

[0059] The electrochemical cell 10 as described above can be formed according to general methods in the art and / or methods known to one of skill in the art. For example, the cell 10 may be formed by successively depositing, in any order, the support layer 12, the barrier layer 14, the first electrode 16, the proton-conducting electrolyte 18, and the second electrode 20 to form a stack. Once the stack is formed, the stack is then sintered at a temperature of from about 500℃ to about 1950℃, about 800℃ to about 1650℃, or about 1200℃ to about 1450℃ for a time period of from about 1 hour to about 40 hours, about 2 hours to about 24 hours, or about 5 hours to about 15 hours.

[0060] To form the support layer 12, the support layer material may be prepared and formed into the support layer 12 using suitable methods, preferably by dry pressing or tape casting the material. In some embodiments, the support layer material is commercially available and formed directly into the support layer 12.

[0061] To form the barrier layer 14, if desired, the barrier layer material is prepared and coated on the support layer 12 using suitable coating methods, such as spray coating or screen printing the material on the support layer 12, to form the barrier layer 14. In some embodiments, the barrier layer material is commercially available and coated directly on the support layer 12.

[0062] To form the first electrode 16, the first electrode material may be prepared and coated on the barrier layer 14 using suitable coating methods, such as spray coating or screen printing the material on the barrier layer 14, to form the first electrode 16. This construct is demonstrated in FIG. 2. In one or more embodiments, the first electrode 16 from the solid composite materials may be formed by combining the solid composite materials with at least one dispersant and at least one binder, and then applying the mixture on the desired substrate (e.g., the barrier layer 14). This mixture of the solid composite materials, the dispersant, and the binder may be applied using any method known in the art, such as spray coating.

[0063] To form the proton-conducting electrolyte 18, the proton-conducting electrolyte material may be prepared and coated on the first electrode 16 using suitable coating methods,such as spray coating or screen printing the material on the first electrode 16, to form the proton- conducting electrolyte 18. In some embodiments, the proton-conducting electrolyte material is commercially available and coated directly on the first electrode 16.

[0064] To form the second electrode 20, the second electrode material is prepared and coated on the proton-conducting electrolyte 18 using suitable coating methods, such as spray coating or screen printing the material on the proton-conducting electrolyte 18, to form the second electrode 20. In one or more embodiments, the second electrode 20 from the solid composite materials may be formed by combining the solid composite materials with at least one dispersant and at least one binder, and then applying the mixture on the desired substrate. This mixture of the solid composite materials, the dispersant, and the binder may be applied using any method known in the art, such as spray coating.

[0065] Depending on the operating mode employed, the electrochemical cell 10 can produce hydrogen or generate electricity.

[0066] To produce hydrogen, the cell 10 operates in a hydrogen-producing configuration. While in this configuration, water, preferably in the form of steam, is reacted at the second electrode 20 to generate oxygen, electrons, and protons via an oxygen evolution reaction, which occurs at a temperature of from about 300℃ to about 700℃. The generated protons may then pass through the proton-conducting electrolyte 18 to the first electrode 16. Simultaneously, an electric current may be supplied to the first electrode 16 from an external source, such as a solar panel. The first electrode 16 may reduce at least a portion of the protons to form hydrogen via a hydrogen evolution reaction, which occurs at a temperature of from about 300℃ to about 700℃.

[0067] To generate electricity, the cell 10 operates in an electricity-producing configuration. In this configuration, hydrogen is supplied to the cell 10, which is oxidized at the first electrode 16 to generate electrons and protons via a hydrogen oxidation reaction occurring at a temperature of from about 300℃ to about 700℃. In most embodiments, the supplied hydrogen is hydrogen previously formed while the cell 10 operated in the hydrogen-producing configuration. Once generated, the protons pass through the proton-conducting electrolyte 18 to the second electrode 20 and react with oxygen to produce water via an oxygen reduction reaction, which occurs at a temperature of from about 300℃ to about 700℃. Simultaneously, the generated electrons induce an electrical current and pass the electrical current through an electrical load to the second electrode 20. The electrical load is connected with the first electrode16 and second electrode 20. In various embodiments, the electrons induce an open circuit voltage of the cell of from about 0.5 V to about 1.50 V, about 0.75 V to about 1.25 V, about 1.0 V to about 1.1 V, or about 1.05 V.

[0068] During operation, the cell 10 operates at a temperature of from about 200℃ to about 1000℃, about 350℃ to about 850℃, about 500℃ to about 700℃, or about 650℃.

[0069] The present disclosure is also concerned with a method of generating electricity. In one or more embodiments, the method comprises: (a) providing an electrochemical cell; (b) supplying hydrogen to the electrochemical cell and oxidizing the hydrogen at the first electrode to form protons and electrons; (c) causing the protons to pass through the electrolyte to the second electrode; (d) causing the electrons generated at the first electrode to induce an electrical current and passing the electrical current through an electrical load that is connected with the first electrode and the second electrode; and (e) reacting the protons with oxygen at the second electrode to produce water. DEFINITIONS

[0070] It should be understood that the following is not intended to be an exclusive list of defined terms. Other definitions may be provided in the foregoing description, such as, for example, when accompanying the use of a defined term in context.

[0071] As used herein, the terms “a,” “an,” and “the” mean one or more.

[0072] As used herein, the term “about” refers to a range within ±10% of the stated value. For example, “about 10” would cover a range of 9 to 11.

[0073] As used herein, the term “and / or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination.

[0074] As used herein, the terms “comprising,” “comprises,” and “comprise” are open- ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject.

[0075] As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

[0076] As used herein, the terms “including,” “include,” and “included” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above. NUMERICAL RANGES

[0077] The present description uses numerical ranges to quantify certain parameters relating to the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claim limitations that only recite the upper value of the range. For example, a disclosed numerical range of 10 to 100 provides literal support for a claim reciting “greater than 10” (with no upper bounds) and a claim reciting “less than 100” (with no lower bounds). CLAIMS NOT LIMITED TO DISCLOSED EMBODIMENTS

[0078] The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.

[0079] The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as it pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.

Claims

What is claimed is:

1. A solid composite material comprising a double perovskite phase and a single perovskite phase.

2. The solid composite material of claim 1, wherein the double perovskite phase comprises PrBaSrCoFeO (PBSCF) and the single perovskite phase comprises BaSrCoO (BSC).

3. The solid composite material of claim 2, wherein the molar ratio of barium to strontium in the double perovskite phase is from 0.1:1 to 1:

1.

4. The solid composite material of claim 3, wherein the molar ratio of praseodymium to barium in the double perovskite phase is from 1.5:1 to 15:

1.

5. The solid composite material of claim 4, wherein the molar ratio of praseodymium to strontium in the double perovskite phase is from 1.5:1 to 3.5:

1.

6. The solid composite material of claim 5, wherein the molar ratio of praseodymium to cobalt in the double perovskite phase is from 0.5:1 to 1.5:

1.

7. The solid composite material of claim 6, wherein the molar ratio of praseodymium to iron in the double perovskite phase is from 1.5:1 to 2.5:

1.

8. The solid composite material of claim 7, wherein the molar ratio of barium to strontium in the single perovskite phase is from 1.5:1 to 2.0:

1.

9. The solid composite material of claim 8, wherein the molar ratio of barium to cobalt in the single perovskite phase is from 0.5:1 to 0.75:

1.

10. The solid composite material of claim 9, wherein the molar ratio of strontium to cobalt in the single perovskite phase is from 0.25:1 to 0.5:1.

11. The solid composite material of claim 2, wherein the double perovskite phase has a formula of PraBabSrcCodFeeO6-δ1 and the single perovskite phase has a formula of BaxSryCozO3-δ2, wherein – a is from 1 to 1.75, b is from 0.05 to 0.5, c is from 0.3 to 0.7, d is from 1.25 to 1.75, e is from 0.4 to 0.9, δ1 is greater than zero, but less than 1, x is from 0.4 to 0.75, y is from 0.25 to 0.5, z is from 0.75 to 1.25, and / or δ2 is greater than zero, but less than 0.

5.

12. The solid composite material of claim 11, wherein the double perovskite phase has a tetragonal (P4 / mmm) crystal structure and / or the single perovskite phase has a hexagonal P63 / mmc crystal structure.

13. The solid composite material of claim 11, wherein the solid composite material comprises at least 50 weight percent of the double perovskite phase, based on the total weight of the solid composite material.

14. The solid composite material of claim 11, wherein the solid composite material comprises at least 10 weight percent and less than 50 weight percent of the single perovskite phase, based on the total weight of the solid composite material.

15. The solid composite material of claim 11, wherein the solid composite material has an average particle size of at least 1 nm and / or less than 100 nm, as confirmed by TEM.

16. An article comprising the solid composite material according to claim 1.

17. An electrode comprising the solid composite material according to claim 1.

18. Use of the solid composite material according to claim 1 in an electrochemical cell.

19. A solid composite material comprising: (a) a double perovskite phase having a formula PraBabSrcCodFeeO6-δ1, wherein a is from 1 to 1.75, b is from 0.05 to 0.5, c is from 0.3 to 0.7, d is from 1.25 to 1.75, e is from 0.4 to 0.9, and δ1 is greater than zero, but less than 1; (b) a single perovskite phase having a formula BaxSryCozO3-δ2, wherein x is from 0.4 to 0.75, y is from 0.25 to 0.5, z is from 0.75 to 1.25, and δ2 is greater than zero, but less than 0.

5.

20. The solid composite material of claim 19, wherein the double perovskite phase has a tetragonal (P4 / mmm) crystal structure and / or the single perovskite phase has a hexagonal P63 / mmc crystal structure.

21. The solid composite material of claim 19, wherein the solid composite material comprises at least 50 weight percent of the double perovskite phase, based on the total weight of the solid composite material.

22. The solid composite material of claim 19, wherein the solid composite material comprises at least 10 weight percent and less than 50 weight percent of the single perovskite phase, based on the total weight of the solid composite material.

23. The solid composite material of claim 19, wherein the solid composite material has an average particle size of at least 1 nm and / or less than 100 nm, as confirmed by TEM.

24. An article comprising the solid composite material according to claim 19.

25. An electrode comprising the solid composite material according to claim 19.

26. Use of the solid composite material according to claim 19 in an electrochemical cell.

27. An electrochemical cell comprising: a first electrode comprising a first electrode material; a second electrode comprising a second electrode material; and a proton-conducting electrolyte positioned between the first electrode and the second electrode, wherein the first electrode material and / or the second electrode material comprise a solid composite material, wherein the solid composite material comprises a double perovskite phase and a single perovskite phase.

28. The electrochemical cell of claim 27, wherein the double perovskite phase comprises PrBaSrCoFeO (PBSCF) and the single perovskite phase comprises BaSrCoO (BSC).

29. The electrochemical cell of claim 28, wherein the molar ratio of barium to strontium in the double perovskite phase is from 0.1:1 to 1:

1.

30. The electrochemical cell of claim 29, wherein the molar ratio of praseodymium to barium in the double perovskite phase is from 1.5:1 to 15:

1.

31. The electrochemical cell of claim 30, wherein the molar ratio of praseodymium to strontium in the double perovskite phase is from 1.5:1 to 3.5:

1.

32. The electrochemical cell of claim 31, wherein the molar ratio of praseodymium to cobalt in the double perovskite phase is from 0.5:1 to 1.5:

1.

33. The electrochemical cell of claim 32, wherein the molar ratio of praseodymium to iron in the double perovskite phase is from 1.5:1 to 2.5:

1.

34. The electrochemical cell of claim 33, wherein the molar ratio of barium to strontium in the single perovskite phase is from 1.5:1 to 2.0:

1.

35. The electrochemical cell of claim 34, wherein the molar ratio of barium to cobalt in the single perovskite phase is from 0.5:1 to 0.75:1.

36. The electrochemical cell of claim 35, wherein the molar ratio of strontium to cobalt in the single perovskite phase is from 0.25:1 to 0.5:

1.

37. The electrochemical cell of claim 27, wherein the double perovskite phase has a formula of PraBabSrcCodFeeO6-δ1 and the single perovskite phase has a formula of BaxSryCozO3-δ2, wherein – a is from 1 to 1.75, b is from 0.05 to 0.5, c is from 0.3 to 0.7, d is from 1.25 to 1.75, e is from 0.4 to 0.9, δ1 is greater than zero, but less than 1, x is from 0.4 to 0.75, y is from 0.25 to 0.5, z is from 0.75 to 1.25, and / or δ2 is greater than zero, but less than 0.

5.

38. The electrochemical cell of claim 27, wherein the double perovskite phase has a tetragonal (P4 / mmm) crystal structure and / or the single perovskite phase has a hexagonal P63 / mmc crystal structure.

39. The electrochemical cell of claim 27, wherein the solid composite material comprises at least 50 weight percent of the double perovskite phase, based on the total weight of the solid composite material.

40. The electrochemical cell of claim 27, wherein the solid composite material comprises at least 10 weight percent and less than 50 weight percent of the single perovskite phase, based on the total weight of the solid composite material.

41. An electrical assembly comprising the electrochemical cell of claim 27 operably connected to a source of electricity and / or an electrical load.

42. The electrical assembly of claim 41, wherein the electrical assembly is operably connected to a source of steam.

43. A method of producing hydrogen comprising: providing the electrochemical cell of any one of claim 27; reacting water at the second electrode to generate oxygen and protons; causing the protons to pass through the proton-conducting electrolyte to the first electrode; and supplying an electrical current to the first electrode and reducing at least a portion of the protons to form hydrogen.

44. A method of generating electricity comprising: providing the electrochemical cell of any one of claim 27; supplying hydrogen to the electrochemical cell and oxidizing the hydrogen at the first electrode to form protons and electrons; causing the protons to pass through the proton-conducting electrolyte to the second electrode; causing the electrons generated at the first electrode to induce an electrical current and passing the electrical current through an electrical load that is connected with the first electrode and the second electrode; and reacting the protons with oxygen at the second electrode to produce water.

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