ionic conductor

Abstract

Solid, ionically conductive materials for use in electrochemical devices include oxyhydroxides or hydrated oxides derived from oxides having a perovskite structure, a brownmillerite structure, a layered oxide structure, and / or a KCdCl structure, where the elemental composition of the initial oxide is selected to impart suitable conductive properties to the derived anhydrous or hydrated oxyhydroxide or hydrated oxide. Methods for making such solid, ionically conductive materials, including treatment with water, and electrochemical devices incorporating such solid, ionically conductive materials (optionally as an electrolyte) are also disclosed.

Description

[Technical Field]

[0001] The present invention relates to novel solid, ionically conductive materials for use in electrochemical devices such as fuel cells and electrolyzers, methods for their manufacture, and electrochemical devices employing layers of such materials. In particular, the present invention relates to the use of various ceramic oxide oxyhydroxides and / or hydrated oxides (thus sometimes described as ceramic ionically conductive materials) with suitable structure and reactivity as solid, ionically conductive materials. In some embodiments, such materials may be purely or primarily ionic conductors and may be useful as electrolytes. Such materials may also be described as electrolyte materials. In other embodiments, such materials may be mixed ionic and electronic conductors and may be suitable as electrode materials. [Background technology]

[0002] Ionically conductive materials are used as electrolytes in electrochemical devices, such as fuel cells, electrolyzers, batteries, flow batteries, electrochemical synthesis cells, gas separation cells, and sensors. Challenges with electrochemical devices are typically poor durability and high cost, which are attributable to the materials used. The development of robust, inexpensive solid-state, ionically conductive materials could improve durability and reduce cost, making large-scale applications economically feasible. While electrolytes are a particularly important research focus, it will be understood that their use as electrolytes is only one example of the wide range of applications for ionically conductive materials in electrochemical devices. Summary of the Invention [Problem to be solved by the invention]

[0003] For example, proton exchange membrane fuel cells (PEMFCs) are widely used in the field of fuel cells for electric vehicles (e.g., as developed in the Toyota Mirai and Hyundai IX35). However, Nafion® membrane electrolytes, generally considered the best membrane available today, lack stability due to oxidation by H2O2 generated at the cathode and short-circuiting caused by diffusion of platinum electrodes into the polymer membrane. Hydrogen fuel cells using Nafion® membranes typically have a lifespan of less than 2000 hours, making them unsuitable for automobiles, which typically have a lifespan of around 10 years. Furthermore, the cost of Nafion® is very high (often around US$800 per square meter). Therefore, the identification of cheaper membranes is desirable. Furthermore, because Nafion® is a polymer membrane, its density is not very high. Therefore, H2 at the anode of a hydrogen fuel cell can diffuse through the Nafion® membrane to the cathode. This results in hydrogen loss at the cathode. Hydrogen is flammable, which not only reduces efficiency but also poses potential safety concerns. Therefore, it would be desirable to develop a denser alternative to polymeric Nafion® membranes, ideally while maintaining the membrane's flexibility. Similarly, in flow batteries, cross-diffusion of vanadium ions through Nafion® can lead to self-discharge and reduced efficiency.

[0004] Changing the type of fuel cell, OH is used as the electrolyte in alkaline membrane fuel cells (AMFCs). - Alkaline membranes based on ion-conducting polymer electrolytes have been investigated. The reported alkaline membranes have limited applicability to AMFCs due to their low stability. Therefore, a robust OH-based electrolyte is being developed to be used as the electrolyte for new alkaline fuel cells. -The discovery of an ion-conducting membrane is desirable. Replacing the liquid KOH solution electrolyte in conventional alkaline fuel cells with a solid electrolyte would also allow the use of air (which does not remove CO2) as the oxidant at the cathode, reducing operating costs. The same would also be true for some metal-air batteries, such as Zn-air batteries, which currently use KOH solution as the electrolyte.

[0005] Those skilled in the art can enumerate many other examples in the fields of electrochemical synthesis, wastewater treatment, gas separation, etc., and also in the field of improved H + ions and OH - It will be appreciated that the need for ionically conductive materials is emphasized. Accordingly, new ionically conductive materials for use as electrolytes are desired. [Means for solving the problem]

[0006] According to a first aspect of the present invention, there is provided a solid electrolyte for use in an electrochemical device, the electrolyte comprising an oxyhydroxide derived from an oxide having a perovskite or brownmillerite structure, the oxyhydroxide having the general formula (A 1-x A' x ) 1-a B 1-y B y (O 3-z-d C z )(OH) m nH2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta, and include at least one of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu; C is selected from N, Cl, F, Br, S and Se; 0≦x≦1, 0≦y≦1, a≦0.15, z≦0.2, d≦2, m≧0.01, and n≧0.

[0007] B and B' may be selected from Co, Fe, Mn, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta. In particular, indium may be excluded because its properties do not justify its relatively high cost compared to other compositions. B and B' may both be selected from the following elements: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. B and B' may include at least one of Mn, Fe, Co, Ni, and Cu, and optionally, at least one of B and B' is cobalt (Co) or iron (Fe).

[0008] Optionally, at least one of A and A' may be strontium (Sr).

[0009] Examples of materials include Sr2Fe2O5 and SrCo 0.5 Ti 0.5 O 3-δ Includes.

[0010] When n=0, the oxyhydroxide may be described as an anhydrate. When n>0, the oxyhydroxide may be described as a hydrate.

[0011] The oxide having a perovskite or brownmillerite structure from which the electrolyte material is made may be referred to as the starting material. Optionally, the starting material may have a brownmillerite structure and may be Sr2Co2O5, more precisely Sr2Co2O 5±δ , or Sr2Fe2O5, more precisely Sr2Fe2O 5±δ Therefore, the electrolyte may be Sr2Co2O with a brownmillerite structure. 5±δ or Sr2Fe2O 5±δ Oxyhydroxides derived from each of these may be included. Oxides having an oxygen-deficient brownmillerite structure may be selected (i.e., O5-δ Optionally, the starting material may have a perovskite structure, SrCoO3, more precisely SrCoO 3-δ , or SrFeO3, more precisely SrFeO 3-δ Therefore, the electrolyte may be SrCoO 3-δ or SrFeO 3-δ When a perovskite oxide is used, an oxygen-deficient perovskite oxide may be selected (i.e., δ>0, unlike the case of a brownmillerite oxide where ±δ is acceptable in various embodiments). 3-δ (It is).

[0012] The value of m may range from 0.01 to 2, optionally from 0.2 to 1.5, and further optionally from 0.5 to 1. The value of n may range from 0 to 12, optionally from 0.1 to 2, and further optionally from 0.2 to 1.5.

[0013] The oxides having a perovskite structure or a brownmillerite structure are (i) SrCoO 5±δ (ii) SrCoO 5-x N x (iii) Ca2Co2O 5±δ (iv) SrCoO 3-δ (v) CaCoO 3-δ (vi) SrCaFeCoO 5±δ (vii) SrCaCoO 5±δ or (viii) SrCo 0.5 Ti 0.5 O 3-δ (ix) SrFeO 5±δ (x)SrFeO 5-x N x (xi)Ca2Fe2O 5±δ or (xii) SrCaFeO 5±δ It may be one or more of the above.

[0014] Thus, the A-sites and / or B-sites may be occupied by mixed elements, and the oxide may be a pure oxide (containing no C-site elements other than oxygen) or a doped oxide (e.g., an oxynitride such as those listed as examples in (ii) above).

[0015] The starting material may comprise a single oxide composition (without impurities) or a number of different oxides selected according to the above criteria.

[0016] The oxyhydroxide (whether anhydrous or hydrated) may form the major component of the electrolyte, and optionally the only ion-conducting material of the electrolyte. In some cases, the electrolyte may be composed of the oxyhydroxide material (without any impurities or remaining binder material).

[0017] According to a second aspect, there is provided a solid electrolyte for use in an electrochemical device, the electrolyte comprising a hydrated oxide derived from an oxide having a Brownmillerite structure, the hydrated oxide having the general formula (A 2-x A' x ) 1-a B 2-y B y (O 1-z C z ) 5±δ ·n'H2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Co, Fe, Mn, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta; C is selected from N, Cl, F, Br, S and Se; a≦0.15, 0≦x≦1, 0≦y≦1, z≦0.04, and n′≧0.01.

[0018] The value of a may be less than or equal to 0.10. The composition may be more narrowly selected as recited for the first embodiment.

[0019] Oxides with a brownmillerite structure are (i) Sr2Fe2O5 (ii) Sr2Co2O5 or (iii) Sr2Co2O 5-x N x (iv) Sr2FeCoO5 or (v) Sr2Fe2O 5-x N x It may be one or more of the above.

[0020] The starting material may comprise a single oxide composition (without impurities) or multiple different oxides selected according to the criteria above. The hydrated oxide may form the major component of the electrolyte, and optionally the only ionically conductive material of the electrolyte. In some cases, the electrolyte may be comprised of hydrated oxide materials (without any impurities).

[0021] According to a third aspect, there is provided a solid electrolyte for use in an electrochemical device, the electrolyte comprising a hydrated oxide derived from an oxide having a perovskite structure, the hydrated oxide having the general formula (A 1-x A' x ) 1-a B 1-y B' y O 3-z-d’ C z n''H2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta, and include at least one of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu; C is selected from N, Cl, F, Br, S and Se; 0≦x≦1, 0≦y≦1, a≦0.15, z≦0.2, d≦2, and n″≧0.01.

[0022] The value of a may be 0.1 or less. The composition may be more narrowly selected as listed for the first embodiment. For example, oxides having a perovskite structure may be SrCoO 3-δ or SrCo 0.5 Ti 0.5 O 3-δ One or more of the above may be used. An oxide having an oxygen-deficient perovskite structure may be selected.

[0023] The starting material may comprise a single oxide composition (without impurities) or multiple different oxides selected according to the criteria above. The hydrated oxide forms the major component of the electrolyte, and optionally the only ionically conductive material of the electrolyte. In some cases, the electrolyte may be comprised of hydrated oxide materials (without any impurities).

[0024] According to a fourth aspect, there is provided a solid electrolyte for use in an electrochemical device, the electrolyte comprising a hydrated oxide or a hydrated or non-hydrated oxyhydroxide derived from an oxide having the K4CdCl6 structure, the oxide having the K4CdCl6 structure being represented by the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z wherein: A and A' are selected from Ca, Sr, Ba, Na, K, Rb, Cs, Ln, Y, Pb and Bi; B and B' are selected from Co, Fe, Mn, Ni, Cu, Ti, V, Cr, alkaline earths, lanthanides, Y, Zn, Cd, Na, B, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Ir and Ru, and contain at least one element of Ti, V, Cr, Mn, Fe, Co, Ni and Cu; C is selected from N, Cl, F, Br, S and Se; y ranges from 0 to 2, z ranges from 0 to 0.5, and x ranges from 0 to 1.

[0025] B and B' may be selected from Co, Fe, Mn, Ni, Cu, Ti, V, Cr, alkaline earths, lanthanides, Y, Zn, Cd, Na, B, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta. In particular, Pt, Ir, and Ru may be excluded because they may be too costly. At least one of B and B' may be selected from Co, Fe, Mn, Ni, and Cu.

[0026] The oxide may be Ca3Co2O6. The solid electrolyte may be a compound represented by the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z nH2O, where n is 0.01 or greater, x is in the range of 0 to 1, y is in the range of 0 to 2, and z is in the range of 0 to 0.5.

[0027] The solid electrolyte is represented by the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z (OH) m nH2O, where x ranges from 0 to 1, y ranges from 0 to 2, z ranges from 0 to 0.5, and m ranges from 0.01 to 6. For hydrated oxyhydroxides, the value of n may be 0.01 or greater.

[0028] The starting material may comprise a single oxide composition (without impurities) or multiple different oxides selected according to the criteria above. The oxyhydroxide or hydrated oxide generally forms the major component of the electrolyte, and optionally forms the only ionically conductive material of the electrolyte. In some cases, the electrolyte may be comprised of an oxyhydroxide material or a hydrated oxide material (without any impurities).

[0029] The solid electrolyte according to any of the preceding aspects may be a pure ceramic electrolyte.

[0030] The solid electrolyte of any of the preceding embodiments may alternatively be a composite electrolyte comprising at least one hydrated oxide or hydrated or non-hydrated (anhydrous) oxyhydroxide described above mixed with one or more polymers. The composite electrolyte may comprise several different polymers. The composite electrolyte may be in the form of a flexible membrane. The composite electrolyte may comprise between 1% and 99% by volume, optionally 10% to 80% by volume, and even optionally 30% to 50% by volume of at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide. The volume percentage of ceramic may be at least 30% to 33%. The volume percentage of ceramic may be at most 85%. The density of the composite may be significantly higher than the density of its polymer component. The polymer may be or may include a hydrophilic polymer. The major composition of the polymer may be hydrophilic (e.g., greater than 50% by volume, optionally greater than 70% or 90% by volume). A small amount of a hydrophobic polymer, such as PTFE, may be included. The polymer may be selected so that the ceramic-polymer composite as a whole is hydrophilic, thereby promoting the diffusion of water into the composite and wetting the ceramic component.

[0031] According to a fifth aspect, there is provided a method of producing a solid electrolyte for use in an electrochemical device, the method comprising: obtaining a ceramic oxide material, which is an oxide having a perovskite structure, a brownmillerite structure or a K4CdCl6 structure, and which contains A-site ions of one or more elements selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi, and B-site ions of one or more elements selected from Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Ir and Ru; The obtained ceramic oxide material, (i) firing the ceramic oxide material in an atmosphere having a partial pressure of oxygen lower than that of air; (iii) immersing the ceramic oxide material in a reducing liquid; or (iv) electrochemically reducing the calcined ceramic oxide material; introducing additional oxygen vacancies; and treating the ceramic oxide material with water, wherein the water treatment comprises immersing the calcined ceramic oxide material in water or exposing it to an atmosphere containing at least 1 vol % water to form a hydrated oxide or a hydrated or non-hydrated oxyhydroxide.

[0032] The electrolyte formed may be as described in any of the preceding embodiments. Accordingly, the A-site ions and B-site ions of the resulting ceramic oxide material may be selected appropriately using the criteria described above.

[0033] The atmosphere having a lower partial pressure of oxygen than air may have an oxygen partial pressure (pO2) of 0.01 atm or less.

[0034] An atmosphere having a partial pressure of oxygen lower than that of air may, in some embodiments, be substantially free of oxygen. An atmosphere having a partial pressure of oxygen lower than that of air may be (i) an inert atmosphere (e.g., nitrogen or argon) or (ii) a reducing atmosphere (e.g., a mixture of an inert gas and a reducing gas, such as hydrogen or 5 vol% H2 / Ar). Alternatively, the atmosphere may contain oxygen or a mixture of air and an inert gas. Typical pO2 for commercial Ar or N2 is non-zero, often 0.00001 atm (10 -5 It will be understood that the pressure in an "inert" atmosphere is on the order of 1000-15000 atm. Thus, an "inert" atmosphere may contain trace amounts of oxygen. Any trace amounts of oxygen in a reducing atmosphere are likely to be burned off during firing. In embodiments in which the ceramic oxide material is fired in an atmosphere having a lower partial pressure of oxygen than air, the firing temperature may be selected to be between 200°C and 1200°C, optionally in the range of 300°C to 1000°C, and further optionally in the range of 400°C to 800°C.

[0035] The obtained ceramic oxide material is (i) an oxide having a perovskite structure, optionally SrCoO 3-δ or SrCo 0.5 Ti 0.5 O 3-δ It may be an oxide having a perovskite structure as described for the first and / or third aspects, etc. (ii) an oxide having a brownmillerite structure, optionally Sr2Co2O 5±δ or Sr2Fe2O 5±δ or an oxide having a Brownmillerite structure as described for the first and / or second aspect, such as (iii) an oxide having the KCdCl structure, optionally an oxide having the KCdCl structure as described for the fourth embodiment, such as CaCoO; At least one of the above may be used.

[0036] The water treatment may be carried out for a period of at least 2 hours, optionally for a period of at least 48 hours, and further optionally for a period of at least 96 hours.

[0037] The obtained ceramic oxide material may be an oxide having a perovskite structure, a brownmillerite structure, or a K4CdCl6 structure, and may include A-site ions of one or more elements selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi, and B-site ions of one or more elements selected from Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta.

[0038] The solid electrolyte produced by the present method may be a pure ceramic electrolyte. In such embodiments, a single firing step may be provided to sinter the ceramic material to form the sintered material so as to retain the desired shape for the electrolyte and to introduce additional oxygen vacancies. Alternatively, the material may be sintered in air in a first firing step before firing the sintered material in an atmosphere having a lower partial pressure of oxygen than air to introduce additional oxygen vacancies. Alternatively, the material may be sintered in air and then treated to introduce oxygen vacancies (e.g., treatment with a reducing liquid) without further firing.

[0039] In particular, in embodiments where a single-step firing procedure simultaneously sinters the material and introduces additional oxygen vacancies, the temperature selected for firing may be in the range of 300°C or 500°C to 1700°C, optionally in the range of 500°C to 1500°C or in the range of 700°C to 1400°C, and optionally in the range of 800°C or 900°C to 1200°C.

[0040] The method may include forming a fired ceramic oxide material by firing the ceramic oxide material at a temperature 50° C. to 700° C. below the melting point of the ceramic oxide material, optionally at a temperature 50° C. to 300° C. below the melting point. The firing may be sintering the ceramic oxide material. The temperature selected for firing may be 50° C. to 300° C. below the melting point of the ceramic oxide material.

[0041] Thus, the solid electrolyte may be a pure ceramic electrolyte, and a firing process may sinter the ceramic material to form a sintered material that retains the desired shape for the electrolyte. Firing, if present, may be a single-step (one-stage) process or a multi-step (e.g., using two or more different firing temperatures and / or two or more different firing atmospheres). The residence time of the firing process may be selected to produce a sintered ceramic material that has sufficient mechanical strength to maintain the desired shape after firing.

[0042] In some embodiments, a sintered oxide material (e.g., in the form of one or more pellets or a film) may be obtained, after which a (second) calcination step may be performed to generate oxygen vacancies. For example, the sintered oxide may be calcined in a reducing atmosphere, such as pure H. The calcination temperature for this step may be lower than that of the sintering step. The calcination temperature for this step may be 200°C to 1000°C or 1200°C, optionally 300°C to 700°C or 1000°C, and further optionally 400°C to 500°C or 700°C. A dilute H atmosphere, e.g., 5 vol% H in Ar or N, may be used in other embodiments, potentially allowing for better control of calcination conditions by reducing oxide decomposition compared to pure H. Alternatively, the method may include mixing one or more polymers with the ceramic material to form a composite ceramic-polymer electrolyte.

[0043] The solid electrolyte produced by the method may alternatively be a ceramic-polymer composite electrolyte. The method may further include blending one or more polymers with the ceramic material to form a composite ceramic-polymer electrolyte prior to the aqueous treatment. Blending one or more polymers with the ceramic material is, in many embodiments, performed after the step of introducing additional oxygen vacancies. It will be appreciated that the use of post-blending calcination on the polymer will generally be limited by the melting or decomposition temperature of the polymer. Similarly, some reducing liquids or reducing treatments may damage the polymer film, but some treatments, for example, with reducing liquids, may be preferable to apply after blending the ceramic with one or more polymers.

[0044] In the embodiments described herein, it is generally desirable to sinter the material for use as a pure ceramic electrolyte. However, it is generally not desirable to sinter the ceramic to full density (compact) in order to leave space to accommodate volume expansion and to allow water diffusion through formed pellets, membranes, etc. Therefore, the sintering temperature can be selected to be significantly lower than the melting point of the oxide material.

[0045] In the embodiments described herein, it is generally desirable not to sinter materials for use as composite polymer-ceramic electrolytes, as finer powders may be preferable for incorporation into polymer composites, particularly when thin films are being made. Therefore, when ceramic materials are used to form such composite electrolytes, firing conditions may be selected to avoid sintering, such as by using lower firing temperatures (e.g., more than 300°C below the melting point of the ceramic oxide material, and even more than 700°C below the melting point) and / or shorter firing times, or by dispersing the fired powder so that the particles do not separate and bond upon heating. For oxide powders used to make ceramic-polymer composite electrolytes, firing temperatures should generally be high enough to generate more oxygen vacancies while avoiding decomposition and / or sintering of the oxide powder. Instead of avoiding sintering, in some embodiments, the sintered material may be ground into powder for use in the composite electrolyte.

[0046] In summary, when sintering a pure ceramic electrolyte, for example in the form of one or more pellets or a film, the firing temperature for sintering is generally selected to be high enough to impart sufficient mechanical strength to the formed ceramic electrolyte, and this temperature is generally also high enough to introduce oxygen vacancies if a suitable atmosphere is selected. When preparing oxides for use in ceramic-polymer composite electrolytes, the firing temperature is generally selected to be high enough to add oxygen vacancies to the brownmillerite, perovskite, or KCdCl structures while avoiding sintering of these powders.

[0047] After treatment to introduce more oxygen vacancies, the ceramic oxide material may be immersed in water or exposed to an atmosphere containing at least 1 vol% water. This water treatment may be carried out for a period of at least 2 hours, optionally at least 48 hours, and even optionally at least 96 hours. Those skilled in the art will appreciate that this period may be selected based on the structure and composition of the oxide and / or based on the size, porosity, and tortuosity of the electrolyte, among other characteristics. The water may be provided as liquid water, water vapor (e.g., using a humidified gas stream), and / or steam.

[0048] In some embodiments, the oxide material may have insufficient oxygen vacancies even after calcination in an atmosphere having a low oxygen partial pressure. In such cases, the method may further include immersing the calcined ceramic oxide material in a reducing liquid or electrochemically reducing the calcined ceramic oxide material. This treatment may be performed before immersing the material in water or exposing it to an environment containing at least 1 vol% water, or may be performed simultaneously with these. In other embodiments, the reducing liquid treatment and / or electrochemical reduction treatment is performed in place of calcination in an atmosphere having a low oxygen partial pressure.

[0049] The method may be used to prepare a solid electrolyte according to any of the preceding aspects.

[0050] The method may include mixing the ceramic material with one or more polymers to form a composite electrolyte.

[0051] According to a sixth aspect, there is provided a solid electrolyte for use in an electrochemical device, the electrolyte being made by the method of the fifth aspect, and the electrolyte may be a ceramic electrolyte or a composite electrolyte including a ceramic component.

[0052] According to a seventh aspect, there is provided an electrochemical device comprising a solid electrolyte according to any of the first to fourth or sixth aspects and / or made by the method of the fifth aspect. The electrochemical device may be configured to keep the electrolyte hydrated in use, particularly where a hydrated oxide or hydrated oxyhydroxide is used.

[0053] The electrochemical device may be a fuel cell, an electrolyzer, or a battery. For example, the electrochemical device may be a redox flow battery, an aqueous battery, or a Zn-air battery. The electrochemical device may be an electrochemical synthesis cell or a gas separation cell.

[0054] The starting oxide material may not be pure / single phase. Due to the relatively high conductivity of certain materials such as Sr2Fe2O5 after reaction with water, contamination with as little as 30 vol% insulating ceramic impurities (such as Al2O3 or TiO2) may still provide a final material with ionic conductivity high enough for use as an electrolyte in electrochemical devices. Similarly, secondary phases may be created during the preparation of oxide materials. For example, the desired SrCo 0.5 Ti 0.5 O 3-δ In parallel, smaller amounts of Sr3Ti2O7 may be formed. However, this small amount (e.g., up to 30 vol%) of Sr3Ti2O7 may not prevent the material from being used as an electrolyte.

[0055] If current electrolyte membranes were replaced with the electrolytes described herein, it is anticipated that the lifetime of hydrogen fuel cells could be extended from 2,000 to 20,000 hours. Because pure ceramic electrolytes or composite membranes contain relatively inexpensive inorganic materials, the cost of the electrolyte may also be reduced. Thus, hydrogen or liquid fueled fuel cells could become more competitive with battery technology in various applications, such as electric vehicles. In particular, the electrolytes described herein may offer one or more of improved stability, reduced cost, and comparable or better ionic conductivity (testing has shown comparable conductivity to Nafion® membranes, as described in more detail below).

[0056] The electrolytes and electrochemical devices described herein may have many diverse applications. Solid-state electrolytes may be used to solve problems with existing electrochemical devices, such as fuel cells (e.g., PEMFCs, alkaline fuel cells, alkaline membrane fuel cells), electrolyzers, supercapacitors, batteries (e.g., flow batteries, metal-air batteries, and aqueous batteries), gas separation / purification, gas sensors, electrochemical synthesis, and the like. A typical hydrogen fuel cell based on a polymer electrolyte membrane fuel cell (PEMF) typically contains a Nafion® membrane as the electrolyte, and requires humidification of both the anode H2 and the cathode air / O2 to keep the Nafion® membrane hydrated to maintain high proton conductivity of the electrolyte membrane. Some of the materials described herein (in both preceding and subsequent embodiments) utilize H + / OH - When they are used as electrolytes in hydrogen fuel cells, protons can be generated at the anode and migrate to the cathode to further react with O2, forming H2O at the cathode and hydrating the electrolyte. Meanwhile, H2O formed at the cathode can react in situ with O2, e.g., from air, to form OH. -The electrolyte may form ions that can then migrate to the anode and react with H to form H2O again, hydrating the electrolyte. Because water is generated at both the anode and cathode, this may reduce the need to humidify the H2 at the anode and the O2 / air at the cathode. Therefore, various embodiments may use H2 as the electrolyte. + Ionic conductor or OH - This may offer advantages over conventional PEMFCs that use any of the ionic conductors.

[0057] When ceramic ion-conducting materials are used as electrolytes in electrochemical devices such as fuel cells, electrolyzers, or redox flow cells, either as pure ceramic layers of ion-conducting materials or in combination with other materials, such as other ceramic materials or polymers, to form composite dense membranes, cross-diffusion of chemicals, ions, and gases can be effectively avoided. It will be appreciated that cross-over is a major problem for conventional fuel cells, electrolyzers, and redox flow cells (e.g., vanadium redox flow batteries) when traditional polymer-based membranes are used as electrolytes. SrZr 0.8 Y 0.2 O 3-δ Polymer-ceramic composites, including polymers such as HDPE combined with conductive oxide materials such as SiO2, have excellent mechanical strength and are sufficiently dense to reduce cross-diffusion of chemicals and gases. Membranes made from such materials can be much denser than Nafion®.

[0058] The electrolyzers discussed herein may be configured to perform the electrolysis of water to produce H2 and O2, or the electrolysis of aqueous ammonia or urea solutions to produce H2 and N2. In the chloralkali industry, ion exchange membranes such as Nafion® are used as electrolytes for the electrolysis of aqueous NaCl solutions to produce NaOH, H2, and Cl2. However, the long-term stability of ion exchange membranes presents challenges. Membranes made with the ionic conductors described herein, either in pure form or when mixed with other ceramics or polymers to form composites with improved mechanical strength, exhibit sufficient ionic conductivity to make them ideal electrolytes for the electrolysis of aqueous NaCl or KCl solutions for the chloralkali industry. These membranes also exhibit high ionic conductivity for the electrolysis of aqueous NaCl or KCl solutions for the chloralkali industry. + or / and OH - It can also be used in other industrial chemical production processes via electrolysis or electrodialysis, as long as the process involves the transport of ions.

[0059] Low-temperature electrolyzers often have alkaline electrolytes, typically using aqueous KOH as the electrolyte, while CO2 must be removed from the water. The materials described herein can replace the aqueous KOH solution, reducing the need for CO2 removal. The development of electrolyzers based on polymer membranes is desirable due to their rapid start-up and reduced response time compared to conventional alkaline electrolyzers based on aqueous KOH electrolytes. Due to the intermittent nature of wind, solar, and other renewable energy sources, a short response time is crucial for using renewable electricity in water electrolysis for renewable energy storage. Electrolyzers based on acidic membranes, such as Nafion®, require the use of precious metal catalysts, such as Pt and Ir, in the electrodes, making them too costly for large-scale applications. Replacing the acidic membrane with an alkaline membrane would allow the use of cheaper electrodes, but the durability of current alkaline membranes is not sufficient. Therefore, H is being developed for use as an electrolyte in electrolyzers. + Or OH -It is desirable to develop robust membranes capable of conducting either or both of these ions. The materials described herein provide an enabling solution for these new technologies. With regard to alkaline electrolyzers or alkaline membrane electrolyzers, the ability to use inexpensive non-precious metal catalysts as electrodes in electrolyzers based on the ion-conducting electrolytes described herein could significantly reduce the cost of the electrolyzers and advance them toward large-scale applications. In other electrochemical processes, such as the electrochemical reduction of N2 or CO2 to produce ammonia or hydrocarbons, desalination, and wastewater treatment, the process requires the use of H + ions and / or OH - Insofar as ion transport is involved, these ionic conductors may be used again as electrolytes.

[0060] In the chemical industry, there are many processes that require the separation of H2 from a mixture or the purification of impure H2 to purer H2. + / OH - The ionic conductors described herein, which have ionic conductivity, can be used for separating or purifying H. When wet (humid) H or a mixture containing H is supplied to the positive electrode side of an electrochemical device and a direct current voltage is applied, the H at the positive electrode is converted into H. + ions that can be transported to the other side of the electrolyte, i.e., the negative electrode, where they gain electrons to form pure H2 again. All other gases / chemicals can be converted to H2 by dense pure ceramic electrolytes or composite (e.g., ceramic-ceramic or ceramic-polymer composite) electrolytes. + Because conduction is blocked, the H2 generated at the negative electrode is very pure. Because electrodes are present and a DC voltage is applied via wires, this process may also be called a "wired" process.

[0061] Some of these oxides, when hydrated, form H +In this case, when used as a dense membrane for gas separation, application of a DC voltage will cause a short circuit due to electronic conduction in the dense separation membrane. However, if one side is exposed to a mixture containing H2 (pure or impure) and the other side is exposed to pure steam or wet H2 at low pressure, then H2 from the mixture will diffuse into the other side at low pressure (which can be achieved by a vacuum pump), and the separation / purification of H2 can also be achieved by using H2. + / e' mixed conducting dense membrane (H + / OH - Again, all other gases / chemicals are encapsulated by a dense pure ceramic layer, a polymer-ceramic composite layer, or a ceramic-ceramic composite layer. + Because conduction is blocked, the H2 produced on the low-pressure side can be very pure. Because there is no applied DC potential, there are no wires, and the process may be called a "wireless" process.

[0062] "Wireless" and "wireless" processes for H2 separation / purification, as well as O 2- The ionic conductors described herein having ionic conductivity are formed by dissolving H in a dense ceramic or ceramic-ceramic or ceramic-polymer composite membrane with sufficient mechanical strength. + Instead of ions, O 2- While the ions are being transported, a similar mechanism can also be used to separate O2 from mixtures containing O2, such as humid air, or to purify low-quality O2 into very pure O2. - / e' mixed conductor (optionally O 2- / H + When using a mixed conductor (e'), the difference in partial pressure of O2 between different sides of a dense ceramic or composite membrane allows for O2 separation / purification via a "wireless" process. 2- / e' (or O 2- / H +When one side of an electrochemical separator using a mixed conductor is exposed to humid air and the other side is exposed to low-pressure steam or humid O2, O2 diffuses from the humid air to the other side, while high-purity humid O2 is generated on the low-pressure side, achieving separation of O2 from air. O2 generators are widely used in hospitals to treat patients with respiratory distress, such as those suffering from Covid-19.

[0063] To capture the CO2 generated in gas / coal-fired power plants, researchers have proposed burning coal / natural gas with pure O2 instead of air to generate relatively pure CO2 without the N2 / inert gases from the air, simplifying / bypassing the separation process. This process is called the oxy-fuel (oxygen-fuel) combustion process. The main challenge is the lack of technology to efficiently separate O2 from air. 2- Ionic conductor (optionally O 2- / H + Mixed conductor) and O 2- / e' mixed conductor (optionally O 2- / H + / e' mixed conductors) can be used for the separation or purification of O via "wired" and "wireless" processes, respectively, similar to the separation / purification process of H. Such materials can also separate O from moist air for oxy-fuel combustion processes in coal / gas-fired power plants or other similar processes.

[0064] ions (H + / OH - ) conduction or ion / e'(H + / OH - Oxide-polymer composites with mixed conductivity can also be used in the H / O separation / purification processes described above, although the resulting H / O purity levels may be lower due to the potential for cross-diffusion of gases / chemicals through the polymer portion of the composite. However, this may not be an issue when gas purity requirements are not too high, such as O for oxy-fuel combustion, or when sufficiently dense polymers are used.

[0065] Some oxides, such as Sr2Co2O5, form mixed ionic / electronic conductors when calcined in air followed by treatment in water or further calcined briefly in Ar. These materials can be used for H2 or O2 separation / purification via a "wireless" process, as described. Pure ionic conductors can be mixed with electronic conductors such as metals (steel, titanium, etc.) or nonmetals (carbon, graphene, etc.) or electronically conducting polymers (polypyrrole (PPY), polyaniline (PAN), etc.) to form mixed ionic / electronic composites for use in H2 / O2 separation. H + / OH - The / e' mixed conductors, either in a pure phase such as Sr2Co2O5 or when mixed with other materials to form composites, can also be used as electrodes in electrochemical devices such as fuel cells, electrolyzers, batteries or supercapacitors. For example, SrZr 0.8 Y 0.2 O 3-δ When used as an electrolyte in a fuel cell, electrolyzer, battery, or supercapacitor, it improves the ionic conductivity of the electrode and promotes the dissociation of H + / OH - SrZr is used in both the negative and positive electrodes of these devices to facilitate ion transport and reduce the overpotential at both electrodes, making electrochemical devices function more efficiently. 0.8 Y 0.2 O 3-δ Of course, you can add other H + / OH - Conductor (SrCe 0.8 Y 0.2 O 3-δ etc.) or H + / OH - / e' mixed conductors (such as Sr2Co2O5 when fired in air) can also be added to the electrode, and SrZr 0.8 Y 0.2 O 3-δ Therefore, H + / OH - The / e' mixed conductors can also be used as components of electrodes in various electrochemical devices.

[0066] Reducing cross-diffusion of chemicals or gases between the anode and cathode compartments in electrochemical devices is a major challenge in current electrochemical devices. For example, in all vanadium redox flow batteries, when a polymer membrane such as Nafion® is used as the electrolyte, different vanadium ions cross-diffuse between the two compartments, leading to self-discharge. This poses a major challenge for the large-scale application of all vanadium redox flow batteries. Furthermore, in direct methanol fuel cells, cross-diffusion of methanol from the anode to the cathode is a major problem. Conventional hydrogen fuel cells with polymer electrolytes can also experience the same problem: cross-diffusion of hydrogen from the anode to the cathode within the fuel cell. This cross-diffusion can sometimes be resolved by using a pure, dense ceramic membrane, a ceramic-ceramic composite (containing no or only a small percentage of polymer), or a ceramic-polymer composite (when the polymer is carefully selected, such as various plastics) as the electrolyte. The ceramic, ceramic-ceramic composite, or ceramic-polymer composite electrolytes described herein may offer the advantage of reducing or eliminating cross-diffusion. In some specific applications, such as "wireless" gas separation, dense ceramic-metal composite membranes may be used to avoid cross-diffusion of chemicals or gases.

[0067] According to a further aspect, there is provided an electrochemical device comprising a solid ionically conductive layer, the ionically conductive layer comprising an oxyhydroxide derived from an oxide having a perovskite or brownmillerite structure, the oxyhydroxide having the general formula (A 1-x A' x ) 1-a B 1-y B y (O 3-z-d C z )(OH) m nH2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, As, Sb, Zr, Hf, Nb, Mo, W, Cd and Ta; C is selected from N, Cl, F, Br, S, Te and Se; 0≦x≦1, a≦0.15, z≦0.2, y≦1, d≦2, m≧0.01, and n≧0. The electrochemical device is also arranged (configured) so that, in use, the ion-conducting layer is exposed to liquid water or to a gas containing at least 5 vol % water.

[0068] The water may be provided as liquid water, water in a humidified gas, or in the form of steam. The water may be provided at a temperature above room temperature, for example, at a temperature of 80°C or higher, or at a temperature of 90°C or higher.

[0069] As used herein and elsewhere in the scientific literature, Ln is the informal chemical symbol for lanthanide, which refers to the 15 metallic chemical elements, from lanthanum to lutetium, having atomic numbers 57 through 71. Of these, cerium (Ce) has been found to have particularly favorable properties in some embodiments. Thus, B or B' may be Ce in some embodiments. Of the lanthanide materials usable at the B site, Ce and Y are of particular interest. Other important lanthanide elements at the B site include Yb, Sm, and Gd.

[0070] In various embodiments, m ranges from 0.01 to 2, optionally from 0.2 to 1.5, and further optionally from 0.5 to 1. In various embodiments, n ranges from 0 to 12, optionally from 0.1 to 2, and further optionally from 0.2 to 1.5.

[0071] The solid ionically conductive layer may be one or more of the following: (i) a pure ionic conductor, optionally an electrolyte; (ii) an OH - ions and / or H + Ionic conductors and (iii) mainly OH - ionic conductor

[0072] Oxides having a perovskite or brownmillerite structure include: (i) Sr2Co2O 5±δ (ii) SrCoO 5-x N x (iii) Ca2Co2O 5±δ (iv) SrCoO 3-δ (v) CaCoO 3-δ (vi) SrCaFeCoO 5±δ (vii) SrCaCoO 5±δ or (viii) SrCo 0.5 Ti 0.5 O 3-δ (mixed ionic / electronic conductor in water) or SrTi 0.7 Co 0.3 O 3-δ (Ionic conductor in water) (ix) Sr2Fe2O 5±δ (x)SrFeO 5-x N x (xi)Ca2Fe2O 5±δ (xii) SrZr 0.8 Y 0.2 O 3-δ (xiii) SrCe 0.8 Y 0.2 O 3-δ or SrCe 0.85 Y 0.15 O 3-δ (xiv) SrCeO 3-δ or (xv) SrCaFeO 5±δ The value of δ may be 0 or greater. Optionally, 0≦δ≦1. According to a further aspect, there is provided a solid ionically conductive layer for use in an electrochemical device. The solid ionically conductive layer comprises a hydrated oxide derived from an oxide having a Brownmillerite structure. The hydrated oxide may be of the general formula (A 2-x A' x ) 1-aB 2-y B y (O 1-z C z ) 5±δ ·n'H2O wherein A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Ln, Co, Fe, Mn, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, As, Y, In, Sc, Sr, Ca, Mg, Li, Na, Cd and Ta; C is selected from N, Cl, F, Br, S, Te and Se; a≦0.15, 0≦x≦1, 0≦y≦1, z≦0.04, and n′≧0.01.

[0073] Oxides with the brownmillerite structure are: (i) Sr2Fe2O5 (ii) Sr2FeCoO5 (iii) Sr2Fe2O 5-x N x and (iv) Ba2InCe 0.5 La 0.5 The solid ion conducting layer may be one or more of: (i) a pure ionic conductor, optionally the solid ion conducting layer is an electrolyte; (ii) OH - ions and / or H + Ionic conductors and (iii) mainly OH - ionic conductor

[0074] According to a further aspect, there is provided a solid ionically conductive layer for use in an electrochemical device, the solid ionically conductive layer comprising a hydrated oxide derived from an oxide having a perovskite structure, the hydrated oxide having the general formula (A 1-x A' x ) 1-a B 1-y B' y O 3-z-d’ C z n''H2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Ln, Y, In, Sc, Sr, Ca, Mg, Li, Na, Co, Fe, Mn, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, As and Ta; C is selected from N, Cl, F, Br, S, Te and Se; 0≦x≦1, a≦0.15, z≦0.2, d≦2, and n″≧0.01.

[0075] Oxides with a perovskite structure include (i) SrCoO 3-δ or (ii) SrCo 0.5 Ti 0.5 O 3-δ (iii) SrZr 0.8 Y 0.2 O 3-δ (iv) SrCe 0.8 Y 0.2 O 3-δ (v) SrTi 0.7 Co 0.3 O 3-δ or (vi) SrCeO 3-δ It may be one or more of the above.

[0076] The solid ionically conductive layer may be one or more of the following: (i) a pure ionically conductive material, optionally the solid ionically conductive layer is an electrolyte; (ii) OH - ions and / or H + Ionic conductors and (iii) mainly OH - ionic conductor

[0077] According to a further aspect, there is provided a solid ionically conductive layer for use in an electrochemical device, the solid ionically conductive layer comprising a hydrated oxide or a hydrated or non-hydrated oxyhydroxide derived from an oxide having the K4CdCl6 structure, the oxide having the K4CdCl6 structure being represented by the general formula (A 1-x A' x )3B 2-y B'y O 6-z C z wherein: A and A' are selected from Ca, Sr, Ba, Na, K, Rb, Cs, Ln, Y, Pb, In, Tl and Bi; B and B' are selected from Co, Fe, Mn, Ni, Cu, Ti, V, Cr, alkaline earths, Mg, Ca, Sr, B, lanthanides (Ln), Y, Zn, Cd, Li, Sc, Na, B, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Rh, Ir, and Ru (optionally, B and B' may comprise at least one element of Ti, V, Cr, Mn, Fe, Co, Ni, Ce, Zr, Y, Sc, and Cu); C is selected from N, Cl, F, Br, I, S, Te and Se; y ranges from 0 to 2, z ranges from 0 to 0.5, and x ranges from 0 to 1.

[0078] At least one of B and B' may be selected from Ti, Ce, Zr, Y, Sc, Co, Fe, Mn, Ni, and Cu. Optionally, the oxide may be Ca3Co2O6. Of the lanthanide materials that can be used at the B site, Ce and Y may be of particular interest. Other important lanthanide elements at the B site include Yb, Sm, and Gd.

[0079] The solid ion conducting layer is formed of (i) a compound represented by the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z nH2O, where n is 0.01 or greater, x is in the range of 0 to 1, y is in the range of 0 to 2, and z is in the range of 0 to 0.5; or (ii) a hydrated oxide having the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z (OH) mnH2O, where x ranges from 0 to 1, y ranges from 0 to 2, z ranges from 0 to 0.5, and m ranges from 0.01 to 6.

[0080] The solid ion conducting layer of any of the preceding embodiments may be a composite solid ion conducting layer comprising at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide described for this embodiment, mixed with a polymer. The solid ion conducting layer may comprise at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide in a volume percentage of 1% to 99%, optionally 10% to 80%, and even optionally 30% to 50%. The polymer may be a hydrophilic or hydrophobic polymer, or may comprise a hydrophilic or hydrophobic polymer. In various embodiments, the plastic used in the ceramic-polymer composite may be a hydrophobic polymer, such as HDPE, PEEK, or PTFE. This type of composite film has excellent mechanical strength while allowing the ceramic component of the composite to remain hydrated to maintain its high ionic conductivity. The use of hydrophilic polymers, such as PVA or PAA, can enhance water absorption at the expense of mechanical strength. If a hydrophobic polymer is used, it may be necessary to ensure that the ceramic is based to provide sufficient water absorption for hydration of the ionically conductive material.

[0081] Alternatively or additionally, a metallic or non-metallic material may be mixed with at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide described in any of the various embodiments, in addition to or instead of a polymer. Non-metallic materials can be classified as ceramics, polymers, glasses, pure (non-metallic) elements, salts, etc., thus covering a wide range of materials. A ceramic-graphite composite is one example of a composite containing such a non-metallic material. The solid ion-conducting layer may be a flexible membrane, for example, when the mixed material is a polymer or graphite. Salts such as CaCO3 and BaSO4 are also non-metallic materials that can be used in such composites. The added material can increase mechanical strength when mixed with the ceramic ion conductor to form the composite. Similar volume ratios as listed above may be applied to composites formed from a ceramic conductive material and a metallic or non-metallic material mixed therewith. Whether an ion-conducting material is a pure ionic conductor or a mixed ionic / electronic conductor depends on its chemical composition and pre-treatment history. The properties of the composite will also depend on the amount and nature of the materials mixed with the initial ion-conducting material.

[0082] The composite material formed by the blend may have improved mechanical strength compared to the unblended ion-conducting material. Typically, a polymer, oxide, or ceramic binder or glass compatible with the ion-conducting material may be used to form the composite. The composite material may form a high-density ion conductor with excellent mechanical strength. This high-density ion-conducting material may beneficially prevent cross-diffusion of chemicals between the negative and positive chambers of an electrochemical device during use, for example. This is particularly useful in redox flow cells / batteries, electrolyzers, and fuel cells.

[0083] The solid ion conducting layer may be one or more of the following: (i) a pure ion conductor, optionally the solid ion conducting layer is an electrolyte; (ii) OH -ions and / or H + Ionic conductors (iii) Mainly OH - Ionic conductors and (iv) H + / OH - / e' mixed conductors, optionally solid ion-conducting layers, are used as membranes for "wireless" gas separations or as electrodes for electrochemical devices

[0084] According to a further aspect, there is provided a method for producing a solid ionically conductive layer for use in an electrochemical device, the method comprising: obtaining a ceramic oxide material, which is an oxide having a perovskite structure, a brownmillerite structure or a K4CdCl6 structure, and which contains A-site ions of one or more elements selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi, and B-site ions of one or more elements selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Cd, Co, Fe, Mn, In, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Ir and Ru; The obtained ceramic oxide material, (i) firing the ceramic oxide material in air; (ii) firing the ceramic oxide material in an atmosphere having a partial pressure of oxygen lower than that of air; (iii) immersing the ceramic oxide material in a reducing liquid; or (iv) electrochemically reducing the calcined ceramic oxide material; introducing additional oxygen vacancies; treating the ceramic oxide material with water; Treatment with water involves immersing the calcined ceramic oxide material in liquid water or exposing it to an atmosphere containing at least 5 vol% water to form hydrated oxides or hydrated or non-hydrated oxyhydroxides.

[0085] While options (ii) through (iv) are expected to produce more oxygen vacancies in the unwetted material, for many of the oxides described herein, treatment with water has been found to produce sufficiently high levels of ionic conductivity, even when the material is calcined in air (option (i)). In particular, SrZr 0.8 Y 0.2 O3, SrCe 0.8 Y 0.2 O3, SrCeO3, SrTi 0.7 Fe 0.3 Materials such as O3 were calcined in air without further treatment in a reducing atmosphere, but were found to function well as ionic conductors after treatment with water. In fact, most of the materials described herein can achieve high ionic or mixed ionic / electronic conductivity simply by calcining in air followed by treatment in water. For some materials, particularly those containing polyvalent elements in their chemical composition, increasing the concentration of anion vacancies (typically oxygen vacancies) by treating them in a reducing atmosphere (lower oxygen partial pressure than in air) or a reducing liquid, or by applying an electrochemical reduction process, has been found to be beneficial for achieving high ionic transference numbers upon exposure to liquid water or a humidified atmosphere. Water may be provided as liquid water, water in a humidified gas, or in the form of steam. Water may be provided at temperatures above room temperature, for example, at temperatures above 80°C or above 90°C.

[0086] The atmosphere having a lower partial pressure of oxygen than air can be (i) an inert atmosphere (eg, Ar), or (ii) a reducing atmosphere (eg, 5% H2 / 95% Ar).

[0087] The obtained ceramic oxide material may be as described in the previous embodiment, and / or may be (i) SrCe 0.8 Y 0.2 O 3-δ , SrZr 0.8 Y 0.2 O 3-δ or SrCo 0.5 Ti0.5 O 3-δ (ii) oxides with perovskite structure such as SrFeO 5±δ or (iii) an oxide having a K4CdCl6 structure such as Ca3Co2O6.

[0088] The water treatment may be performed for a period of at least 1 or 2 hours, optionally for a period of at least 48 hours, and optionally for a period of at least 96 hours, prior to use of the solid ion conducting layer. The duration of the water treatment may depend on the composition and thickness of the material and the temperature. Typically, at room temperature, pellets having a thickness on the order of 2 mm may be treated for a period of at least 1 hour prior to use of the solid ion conducting layer. In embodiments where the solid ion conducting layer is in the form of a thin film or membrane, the time may be shortened. Indeed, for sufficiently thin and / or porous samples, a treatment time of only a few minutes may be sufficient. The solid ion conducting layer remains hydrated between the water treatment and use, regardless of whether the water treatment is performed in situ. Ideally, the water treatment may be performed in situ just before the device is turned on.

[0089] The solid ion conducting layer may be a pure ceramic solid ion conducting layer. The ceramic material may be sintered in a single firing step to form a sintered material configured to retain the solid ion conducting layer in a desired shape and introduce additional oxygen vacancies. Alternatively, the material may be fired in air in a first firing step before firing the sintered material in an atmosphere having a lower partial pressure of oxygen than air to introduce additional oxygen vacancies.

[0090] The method may further include blending the ceramic material with one or more polymers to form a composite ceramic-polymer solid ionically conductive layer prior to treatment with the water. In alternative or additional embodiments, the ceramic material may be blended with another material to form a composite ceramic-polymer or ceramic-ceramic solid ionically conductive layer, e.g., for use as an electrolyte. In other embodiments, aceramic-polymer composite, ceramic-carbon (e.g., graphite) composite, ceramic-ceramic composite, or even ceramic-metal composite may be formed for use as a mixed ionic / electronically conductive layer (e.g., for use as an electrode or separation membrane for "wireless" gas separation, e.g., H2 and O2). Formation of a composite may enhance mechanical strength and / or increase mixed ionic / electronic conductivity (e.g., by providing some / more electronic conductivity) for specific applications, such as as an electrode for an electrochemical device or as a separation membrane for "wireless" gas separation, as described above.

[0091] According to a further aspect, there is provided a solid ionically conductive layer for use in an electrochemical device, the solid ionically conductive layer being made by the method of the preceding aspect. These materials may be suitable for use as electrolytes if they are pure ionic conductors, or may be used as electrodes or for gas separation membranes if the pure material, or the composite material formed after mixing with a metallic or non-metallic material (e.g., a polymer, ceramic, pure element such as carbon), is a mixed ionic / electronic conductor.

[0092] According to a further aspect, there is provided an electrochemical device comprising the solid ionically conductive layer of any of the preceding aspects. In use, the solid ionically conductive layer is exposed to liquid water or to a gas comprising at least 5 vol% water. As noted above, "water" as used herein refers to HO, whether present as liquid water, water vapor, or steam.

[0093] The electrochemical device of any of the preceding embodiments may be configured to operate at an operating temperature of 250°C or less, optionally below 235°C, and further optionally at an operating temperature of 120°C or less. Optionally, if the operating temperature is above 100°C, pressurized steam or water may be provided to maintain exposure to liquid water or a gas containing at least 5 vol% water. The electrochemical device of any of the preceding embodiments is configured to operate in the presence of liquid water or in the presence of at least 5 vol% water or water vapor in the surrounding gas. Thus, temperatures and pressures may be selected accordingly. At elevated pressures, the operating temperature can be much higher than 100°C (the boiling point of liquid water at ambient pressure) and still retain liquid water.

[0094] The electrochemical device may be a fuel cell, an electrolyzer, or a battery. The solid ion conducting layer may be an electrolyte. The electrochemical device may be configured to keep the solid ion conducting layer (which may be a pure ionic conductor or a mixed ionic / electronic conductor) hydrated during use. The solid ion conducting layer may be a H + / OH - / e' mixed conductors, and such materials may be used as membranes for "wireless" gas separations or as electrodes for electrochemical devices.

[0095] The solid ion conducting layer of any of the preceding aspects may be composed of or include a ceramic oxide material, which in some embodiments may be lightly doped with one or more other anions, typically N, Cl, F, Br, S, Te, and Se.

[0096] According to a further aspect, there is provided a method of operating an electrochemical device according to any of the preceding aspects, the method comprising continuously exposing the electrochemical device, and more particularly the ion conductor layer, to liquid water or to a gas containing at least 5 vol % water (as water vapor or steam) while the electrochemical device, and more particularly the ion conductor layer, is in use. [Brief explanation of the drawings]

[0097] Those skilled in the art will appreciate that features described with respect to one aspect of the invention may be applied mutatis mutandis to other aspects of the invention. A detailed description of embodiments of the invention will now be given, by way of example only, with reference to the accompanying drawings, in which:

[0098] [Figure 1] FIG. 1 is a schematic diagram of an electrochemical device. [Figure 2] FIG. 2 is a graph of conductivity and ionic transport number with temperature for a Sr2Fe2O5 (brownmillerite structure) sample after immersion in water for 6 days at room temperature. [Figure 3] FIG. 3 is a diagram showing the brownmillerite structure. [Figure 4] FIG. 4 is a diagram showing the perovskite structure. [Figure 5] Figure 5 is a diagram showing the structure of K4CdCl6. [Figure 6] FIG. 6 is a graph of conductivity and ionic transport number with temperature for a SrCo0.5Ti0.5O3-δ (perovskite structure) sample after immersion in water for 3 days at room temperature. [Figure 7] FIG. 7 is a graph of conductivity and ionic transport number with temperature for a Ca3Co2O6 (K4CdCl6 structure) sample after immersion in water for 3 days at room temperature. [Figure 8A] 8A and 8B are graphs of fuel cell performance of Sr2Fe2O5-based electrolyte materials measured with three different fuels. [Figure 8B] 8A and 8B are graphs of fuel cell performance of Sr2Fe2O5-based electrolyte materials measured with three different fuels. [Figure 9] FIG. 9 is a diagram illustrating a method according to an embodiment. [Figure 10] FIG. 10 shows X-ray diffraction (XRD) data for the Sr2Fe2O5 sample calcined at 1200° C. in Ar. [Figure 11] FIG. 11 shows XRD data for the sample of FIG. 10 after treatment in water and conductivity measurement. [Figure 12] FIG. 12 shows XRD data for the SrCo0.5Ti0.5O3-δ sample calcined at 1100°C in Ar. [Figure 13] FIG. 13 shows XRD data for the Ca3Co2O6-δ sample calcined at 1000° C. in air. [Figure 14] FIG. 14 shows the XRD patterns of the as-prepared SrZrO.8YO.2O3-δ pellet, the pellet after conductivity measurements in H2O at temperatures up to 90 °C, and the pellet after conductivity measurements in D2O. [Figure 15] FIG. 15 shows the conductivity (filled symbols) and ion transference number (open symbols) of SrZrO3, SrZr0.9Y0.1O3-δ, and SrZr0.8Y0.2O3-δ in water measured upon cooling. [Figure 16] FIG. 16 shows the conductivity (solid symbols) and ionic transport number (open symbols) of MZr0.8Y0.2O3-δ when M=Ca, Sr, or Ba. [Figure 17] FIG. 17 shows the stability of conductivity of SrZrO.8YO.2O3-δ in water at 90°C after treatment in water at 90°C, including changing the water three times before measurement. [Figure 18] FIG. 18 shows the ionic conductivity of SrZrO.8YO.2O3-δ in humid air at different temperatures, with an inset showing the conductivity above 100 °C (air was passed through water at 100 °C). [Figure 19]FIG. 19 shows the ionic conductivity and ionic transport number of SrZr0.8Y0.2O3-δ in humid air from 20 to 100°C (the air was humidified by passing it through boiling water at 100°C). [Figure 20] FIG. 20 is a plot of conductivity stability for SrZr0.8Y0.2O3-δ samples in humid air at 70 °C (air was humidified by passing water at 100 °C). [Figure 21] FIG. 21 shows the conductivity and ionic transport number of SrZr0.8Y0.2O3-δ pellets in H2O and D2O measured upon cooling. [Figure 22] FIG. 22 shows 1H-magic angle spinning (MAS) solid-state NMR of hydrated (solid line) and deuterated (dashed line) SrZr0.8Y0.2O3-δ measured at room temperature. [Figure 23] Figure 23 shows the XRD patterns of Sr2Co2O5 calcined in air and Sr2Co2O5 after conductivity measurements in water at temperatures up to 90°C. The sample is in a single phase after calcining in air, and this phase remains after the conductivity measurements, meaning it is stable (since XRD is insensitive to elemental hydrogen, the reaction of Sr2Co2O5 with H2O to form oxyhydroxides cannot be detected or ruled out by XRD). [Figure 24] FIG. 24 shows the conductivity (measured upon cooling) and ionic transport number of SrCoO in water for samples calcined in air and not further processed (e.g., no reduction by calcination in different atmospheres or treatment with reducing liquids). [Figure 25] Figure 25 shows the XRD patterns of SrCoO calcined in air, then in Ar, and after conductivity measurements in water up to 90 °C, showing that a single phase is formed after calcination in air and persists (albeit with lower crystallinity) after calcination in Ar, and that this phase persists after conductivity measurements in water, although some Co(OH) peaks appear. [Figure 26]Figure 26 shows the conductivity and transport number of Sr2Co2O5 in water measured upon cooling. The sample was calcined in air, then in Ar, and washed twice with water before the conductivity measurements. [Figure 27] Figure 27 shows the conductivity and ionic transport number of pure Co(OH) pellets in water, which under the same conditions results in a conductivity two orders of magnitude lower than that of SrCoO pellets calcined in Ar. [Figure 28] Figure 28 shows the conductivity and transport number of Sr2Co2O5 in water measured upon cooling for a sample that was calcined in air and then treated with a reducing agent (1 M NaOH + 7 M NaBH4) for 8 hours before conductivity measurement. [Figure 29] Figure 29 shows the XRD patterns of pure Sr2Co2O5, with conductivity measurements in water, before and after electrochemical reduction at -1.14 V (vs. Ag / AgCl) for 10 hours, indicating that the main phase remains but is poorly crystalline. [Figure 30] FIG. 30 shows the conductivity data of Sr2Co2O5 pellets in water during the heating process, where the pellets were electrochemically reduced for 10 hours before conductivity measurements and then immersed in water at 90°C for 3 days. [Figure 31] FIG. 31 shows the conductivity and transference number of a Sr2Co2O5 sample in water, calcined in air, then treated with a reducing agent (1 M NaOH + 7 M NaBH4) for 8 hours, and measured upon cooling. DETAILED DESCRIPTION OF THE INVENTION

[0099] In the drawings, like or corresponding reference numerals are used for like or corresponding elements.

[0100] FIG. 1 illustrates a simplified electrochemical device 100. An electrochemical device 100, such as a fuel cell, typically includes two electrodes 102, 106 (anode and cathode) and an electrolyte 104 separating the anode from the cathode. The electrolyte 104 is selected as an ionic conductor to allow ion transport between the electrodes 102, 106, but as an electrical insulator to prevent or minimize short circuits / leakage currents. The electrolyte 104 described herein may provide stable ionic conductivity. In alternative embodiments, the electrochemical device 100 may include a solid ionically conductive layer that does not function as an electrolyte. Those skilled in the art will appreciate that while the electrolyte 104 is one example of a solid ionically conductive layer 104, the materials and processes described herein are also useful for solid ionically conductive layers that are not electrolytes. While the following description generally refers to the electrolyte 104 for ease of reading, it will be understood that the present invention is not limited to the electrolyte 104. Indeed, in some instances, the ion conducting layer may be a mixed ionic and electronic conductor and therefore not suitable for use as an electrolyte in, for example, a battery or fuel cell 100. The ionic conductors described herein (pure or mixed ionic / electronic conductors) may be added to electrodes in electrochemical devices or used as separation membranes for the separation / purification of gases, such as H2 and O2, in "wired" or "wireless" type gas separation devices.

[0101] While the embodiments described herein may be described specifically with respect to a fuel cell 100, those skilled in the art will understand that the described electrolyte 104 (or indeed other ion-conducting layer) may be equally applicable to other electrochemical devices 100 and many different types of fuel cells 100. By way of non-limiting example, suitable electrochemical devices 100 that may use the electrolyte (or other ion-conducting layer) 104 as described herein include: ·Electrolytic cell For example, electrolyzers used to split water to produce "green" H2, or ammonia / urea electrolyzers to split ammonia / urea into hydrogen and nitrogen, or electrolyzers used in the chlor-alkali industry to electrolyze aqueous NaCl / KCl solutions to produce NaOH / KOH, H2 and Cl2. Gas or liquid fuel cells Typical fuels are hydrogen, methanol, ethanol, ammonia, hydrazine, urea, and methane. Such fuel cells may be used solely for the purpose of generating electricity, or may have a dual purpose. For example, an ammonia / urea fuel cell using the electrolyte 104 described herein may be used to remove ammonia from ammonia / urea-containing wastewater, with electricity generation not being the primary purpose but rather a beneficial by-product. Redox flow battery or other flow cell Metal-air batteries (e.g., Zn-air batteries or OH - Ionic conductor or H + / OH - Other metal-air batteries using mixed ionic conductors as electrolytes), aqueous rechargeable batteries (aqueous secondary batteries), and H + or / and OH - Batteries such as any aqueous batteries based on ion-conducting electrolytes Electrochemical devices for electrochemically synthesizing chemical substances such as ammonia and hydrocarbons Supercapacitor Electrodialysis equipment, e.g. for wastewater treatment or desalination to produce fresh water from seawater Gas separators (especially H2 and O2), gas purifiers, or other separation units Sensors

[0102] In general, the materials described herein can be used in any suitable electrochemical device 100 requiring an ion conducting layer. The ion conducting layer can be any ionic conductive material required for the electrolyte (e.g., OH - Conduction or H + / OH -mixed conduction), or ionic-electronic mixed conduction (e.g., OH - / e' mixed conductor or H + / OH - / e' mixed conductor). When used as a membrane for gas separation, the material of choice is H + / OH - For hydrogen separation, H + Only the / e' conductivity characteristics may be used, and in the case of O2 separation, OH - Only the / e' conductivity characteristics may be used.

[0103] All of the materials described and claimed herein are ionic conductors, and some are also electronic conductors (i.e., mixed ionic / electronic conductors). In particular, the materials generally + / OH - It is a mixed ionic conductor, and mixed ionic-electronic conductor (MIEC) is H + / OH - / e' mixed conductor. Generally, ionic conduction is mainly due to OH - conduction, but in some cases H + Conduction is OH - It may even exceed conduction.

[0104] The SrZr prepared and described herein and processed in water 0.8 Y 0.2 O 3-δ , SrCe 0.8 Y 0.2 O 3-δ and SrCe 0.85 Y 0.15 O 3-δ These perovskite oxides only become O at high temperatures (>500°C). 2- Conductors and H + Conductor or O 2- / H + Contrary to prior expectations that it could operate as a mixed conductor, even at relatively low temperatures (e.g., below 120°C), + / OH -It has been found that these oxides act as mixed ionic conductors. Therefore, even if perovskite oxides with similar chemical compositions are used, the conduction mechanism is significantly different (charge carriers are different) depending on the environment (e.g., the material is in contact with liquid water or exposed to a gas containing at least 5 vol% water vapor) and / or pretreatment. When such oxides are used in contact with liquid water or exposed to a gas containing at least 5 vol% water, the high OH - Ionic conduction or H + / OH - It has been found to provide mixed ionic conduction (typically at temperatures below 100° C., but the temperature can be higher if device 100 is pressurized).

[0105] The following guidelines can be used when selecting ceramic materials that may have high ionic conductivity in water, steam, or in a hydrated state. A. The material contains many negative ion vacancies (anion vacancies), typically oxygen vacancies. B. When the material is exposed to water or steam, suitable materials are capable of reacting with water or steam to form oxyhydroxides or hydrated oxides, otherwise known as OH. - Ions can be incorporated into the material. C. The material has high H + / OH - H in the lattice to provide ionic conductivity + / OH - They may be selected to have a structure that contains continuous pathways that facilitate ion movement. Exemplary crystal structures that contain the required pathways are perovskite and perovskite-related structures, including the primitive ABO3-type perovskite block structure, the brownmillerite structure, and the K4CdCl6 structure.

[0106] In some cases, materials that meet only two of the three guidelines above may exhibit favorable behavior. For example, undoped SrCeO3, despite not being classified as a material rich in oxygen vacancies, has been found to exhibit high ionic conductivity when in contact with liquid water or when exposed to a gaseous atmosphere containing at least 5 vol% steam. This primitive perovskite-structured material meets the second and third guidelines listed above, but not the first.

[0107] The electrolyte 104 described herein includes a ceramic component. The electrolyte 104 may be a pure ceramic electrolyte or may be, for example, a ceramic-polymer composite electrolyte or a ceramic-ceramic composite electrolyte. For use in the electrochemical device 100, the structure and properties of the electrolyte 104 are selected and controlled to provide suitable conductivity and other parameters.

[0108] A family of oxide materials has been identified that, when properly prepared, exhibits high ionic conductivity (e.g., the room temperature conductivity of processed Sr2Fe2O5 is 1.9 × 10 -2 (The conductivity is measured in water to ensure that the hydrated state of the material is tested.) Unlike prior work on related oxide materials that uses the oxide material itself as the electrolyte material, the inventors have recognized that by forming a hydrated oxide or a hydrated or non-hydrated oxyhydroxide of a specifically selected oxide, improved properties are obtained when the resulting hydrated oxide or oxyhydroxide material is used to form the electrolyte 104. The oxide material used to form the electrolyte 104 may be specially formulated to promote the formation of the hydrated oxide or hydrated or non-hydrated oxyhydroxide (e.g., by the introduction of oxygen vacancies and / or by selecting a composition with suitable reactivity with water).

[0109] For example, SrFeO between 25°C and 90°C 2.5 (OH) mThe ionic conductivity and ion transfer number of the nH2O material are shown in graph 200 of Figure 2. The ionic transfer number 202 is around 0.998, indicating that the material is a pure ionic conductor and suitable for use as the electrolyte 104 for the electrochemical device 100. The ionic conductivity 204 is 0.041 S / cm at 90°C, which is comparable to that of a commercial Nafion® membrane (0.04 S / cm at 96°C). The data shown in Figure 2 for the SrFeO 2.5 (OH) m To form the nHO material, SrFeO was prepared by a standard solid-state reaction method. Specifically, 14.91 g of SrCO and 8.03 g of FeO (analytical grade) were mixed for 12 hours at 300 rpm using a ball mill (Ortoalresa OABM 255) and then calcined at 1100 °C for 55 hours in air with a heating / cooling rate of 5 °C / min. This powder was finely ground and pelletized, then calcined in argon at 1200 °C for 8 hours. XRD data for the pelletized material after calcination in argon is shown in Figure 10 and confirms the expected brownmillerite structure. Unless otherwise specified, disc-shaped pellets with a diameter of 13 mm and a thickness of 2.2 mm were the default for the tests described herein. Those skilled in the art will recognize that pellets of any suitable size and shape can be used in other embodiments.

[0110] To test the ionic conductivity of Sr2Fe2O5 pellets in water, two flat sides of the pellets were coated with silver conductive ink (Fisher Scientific) to form Ag electrodes. The coated pellets were dried at 130 °C for 150 minutes. The sandwich cell, consisting of the pellet sandwiched between two layers of silver mesh, was then fixed in a fixture while submerged in liquid water. Electrochemical impedance spectroscopy (EIS) was performed using a Solartron 1470 / 1455 with an amplitude of 10 mV and a frequency range of 10,000-0.01 Hz. The DC voltage applied to the pellet and the current flowing through it were recorded to calculate the resistance to electronic conduction. Figure 2 shows the conductivity results. The highest ionic conductivity was 0.041 S / cm in water at 90 °C, where the ionic transport number (t i ) was found to be 99.8%. As the temperature decreased, the conductivity decreased. Figure 11 shows the XRD data for electrolyte 104 after immersion in water, showing that its structure is affected by hydration (compare with Figure 10).

[0111] Those skilled in the art will appreciate that there are diverse and complex interactions between structure and composition to provide the reactivity and conductivity of the initial oxide and the resulting oxyhydroxide or hydrated oxide, and therefore extensive research and experimentation has been conducted to identify a suitable family of ceramic oxide starting materials. Furthermore, reaction with water to produce the oxyhydroxide or hydrated oxide may alter the structure of the material, resulting in an electrolyte material having a different structure than the starting oxide. Data has been collected to demonstrate the use of such materials as electrolytes in fuel cells.

[0112] Figure 8A shows the current-voltage (IV) plots for fuel cells using electrolytes prepared from SrFeO, comparing methanol and ethanol under the same conditions (operating temperature 60 °C, using a 1 molar (1 M) liquid fuel). Figure 8B shows the IV plots for the same fuel cell at different temperatures, using a 1 M ammonia solution as the fuel. For these fuel cell tests, a 15 mm diameter, 0.8 mm thick circular SrFeO pellet preheated to 1200 °C in argon was used as the electrolyte. The anode and cathode were made of 20 wt% Pt / C with PAP-BP-100 ionomer added, and carbon cloth was used as the substrate. (PAP-BP-100 refers to poly(allylpiperidinium) polymer with N-methyl-4-piperidone, 2,2,2-trifluoroacetophenone, and biphenyl, where the molar ratio between N-methyl-4-piperidone and the aryl monomer is 1:1.) To fabricate the Pt / C electrode, 68 mg of commercial Pt / C (20 wt% Pt) was ultrasonically dispersed in a mixture of 125 μL of deionized water, 125 μL of isopropanol, and 385 μL of 5 wt% PAP-BP-100 ionomer solution in a Fisherbrand FB15051 ultrasonic bath for 1 h. Carbon cloth was pretreated with 5 wt% HCl and isopropanol to remove impurities and contaminants. After ultrasonication, ink was applied by brush to the clean carbon cloth and the electrode, which was then dried in a dry oven at 80 °C for 8 h. The Pt content of the electrode was 0.77 mg / cm. 2 The fuel cell 100 was assembled in a fuel cell fixture. The SrFeO electrolyte 104 was sandwiched between the cathode and anode. The active area of ​​the fuel cell was 1 × 1 cm. 2In the tests, 1 molar aqueous solutions of methanol, ethanol, and ammonia were used as fuels. The fuel solution was slowly injected into the anode chamber, and humidified compressed air (obtained using a bubbling setup) was introduced into the cathode chamber from the opposite direction. The flow rate of the fuel solution was controlled by a pump rotating at 10 rpm, generating a solution flow rate of approximately 0.5 mL / min. The air flow rate was controlled to be 20 mL / min. In the described embodiment, the electrolyte was not treated with water before insertion into the fuel cell. Instead, the electrolyte was left in the fuel cell with the fuel and humidified air overnight before fuel cell testing to allow reaction with water. Thus, the water treatment was performed in situ before use. In embodiments using gaseous fuels instead of aqueous fuels, the fuel cell 100 may be soaked in water before use, and / or the electrolyte 104 may be soaked in water before insertion into the fuel cell 100, to allow sufficient time for the electrolyte to react with water and achieve sufficient ionic conductivity.

[0113] The performance of the fuel cell 100 was tested using a Solartron 1287A electrochemical interface controlled by the electrochemical software Corr-Ware / CorrView. Fuel cell performance data are shown in Figures 8A and 8B. In summary, increasing the temperature and ammonia concentration was found to increase the open-circuit voltage (OCV) of the fuel cell. Therefore, the SrFeO-based electrolyte 104 is a promising electrolyte material for methanol, ethanol, and ammonia fuel cells. In particular, when concentrated ammonia was used as the fuel, the fuel cell was found to have an OCV of 0.44 V, demonstrating its suitability for ammonia fuel cell applications. The electrolyte 104 in this fuel cell is a solid, relatively dense, sintered pellet with relatively low porosity and high tortuosity, thereby avoiding fuel crossover.

[0114] The family of identified oxides to which Sr2Fe2O5 belongs has the general formula A2B2O 5±δand Brownmillerite structure. This family includes compounds in which either or both of the A and B sites contain a mixture of elements rather than a single element (i.e., A in the general formula can be replaced with A and A', and / or B can be replaced with B and B', resulting in A 2-x A' x B 2-y B y O 5±δ (which can be expressed as a mixed brownmillerite-type oxide) 5±δ or similar formulas may be used, although one skilled in the art will understand that this is not intended to exclude oxides having a mixture of A-site and / or B-site elements. Similarly, the more generalized formulas are not intended to exclude oxides having a single A-site and / or B-site element. As used herein, A and A' are used for A-site elements, and B and B' are used for B-site elements. However, one skilled in the art will understand that there may be only one A-site element or one B-site element, or there may be more than one A-site element or one B-site element (e.g., three, four, or five different elements at each site). The general formula used is chosen merely to emphasize that mixed elements may occupy both the A-site and B-site, and is not intended to limit the described embodiments to having only one or two elements at each site.

[0115] In the described brownmillerite-type oxides, A and A' (if present) are selected from Ca, Sr, Ba, Ln (i.e., any lanthanide element), Y, Na, K, Rb, Cs, Pb, and Bi. More particularly, one or both of A and A' may be Ca, Sr, or Ba.

[0116] In the described Brownmillerite-type oxides, B and B' (if present) are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, Te, and Ta. In some such embodiments, B and B' (if present) may be selected from Zr, Ce, In, Y, La, Te, Co, Fe, Mn, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, As, and Ta (optionally, indium may also be included in this list), including at least one of Zr, Ce, Y, Ti, V, Cr, Mn, Fe, Co, Ni, Te, and Cu. More specifically, one or both of B and B' may be Zr, Ce (lanthanides, Ln), Y, Ti, Mn, Fe, or Co.

[0117] Additionally, some of the oxygen may be substituted with N, Cl, F, Br, S, and / or Se to provide doped oxides (e.g., oxynitrides when N substitutes for some of the oxygen). For example, SrFeO 5-x N y or SrFeO 2.5-x N y (OH) m Oxynitrides such as nH2O may also be used as electrolyte materials. 5±δ O 5-z±δ C z where C represents the doping element(s). Thus, the term "oxide" as used herein is intended to include doped oxides such as oxynitrides. The general formula for Brownmillerite-type oxides, which explicitly shows optional doping, is: (A 2-x A' x ) 1-a B 2-y B y (O 1-z C z ) 5±δThe dopant element C, which replaces a portion of the oxygen, is generally selected from N, Cl, F, Br, S and Se.

[0118] The value of a is typically 0.3 or less, optionally ≦0.2, and optionally ≦0.1 (particularly likely for A-site deficient Brownmillerite-type oxides). In various embodiments, the value of a is 0.15 or less, optionally ≦0.10, and optionally ≦0.05. The value of z is typically 0.04 or less, optionally ≦0.02, for anion-doped Brownmillerite-type oxides (anion-doped Brownmillerite-type oxides). In various embodiments, the value of z is 0.02 or less, optionally ≦0.01.

[0119] After reaction with water, oxyhydroxides and / or hydrated oxides may be formed. The general formula for hydrated Brownmillerite-type oxides is: 2-x A' x ) 1-a B 2-y B y (O 1-z C z ) 5±δ n'H2O, where n' > 0.01. Oxyhydroxides are described in more detail below.

[0120] Figure 3 shows a typical Brownmillerite structure, and more specifically, the structure of Sr2Co2O5. The A-site ions (in this case, strontium) are represented by dark gray spheres. The B-site ions (in this case, cobalt) are represented by polyhedra. The oxygen ions (in this case, unmixed with other C-site ions) are represented by light gray spheres. These types of oxides (or doped oxides, such as oxynitrides) are rich in oxygen vacancies and can absorb water to form A2B2O5(OH). m (non-hydrated oxyhydroxide) or A2B2O5(OH) m ·nH2O (hydrated oxyhydroxide) may be formed. OH - ions and / or H +The ion is A2B2O5(OH) m nH2O lattice, resulting in high ionic conductivity (non-hydrated oxyhydroxides with n=0). As mentioned above, this formula is 2-x A' x B 2-y B' y O 5-z C z (OH) m Selected families of oxides may have a relatively high density of oxygen or anion vacancies. Treatment of these oxides with water, under appropriate conditions and even at relatively low temperatures (below 100°C to 200°C, optionally around 25°C), can result in the formation of lattice water or OH vacancies at or near the original locations of these vacancies. - Using H + ions and / or OH - It is capable of conducting ions.

[0121] Generally, when these materials are used as electrolytes 104 (or other ion-conducting layers) for electrochemical devices 100 such as fuel cells, electrolyzers, gas separators / gas purifiers, etc., a minimum required ionic conductivity is 1.0×10 -2S / cm. For battery use, the minimum required ionic conductivity is generally slightly lower. While ionic conductivity generally increases at higher temperatures, even temperatures around room temperature (20°C to 25°C) have been shown to exceed this minimum. Thus, these materials can be used for electrolytes 104 operating at around room temperature as well as at higher temperatures. Room-temperature fuel cells and electrolyzers 100 may therefore use these ceramic electrolyte materials. Advantageously, the materials may be used at temperatures below 500°C, and optionally below 100°C or below 60°C. For example, the electrolytes 104 described herein may have operating temperatures between 0°C and 600°C, optionally between 0°C and 400°C, and even optionally between 0°C and 200°C. In some embodiments, a lower operating temperature limit may be applied, such as 10°C, 15°C, or 20°C. Thus, at relatively low and room temperatures, electrochemical devices 100 may use the electrolyte 104 (or other ion-conducting layer) described herein.

[0122] Pure ceramic electrolytes 104 made from these materials are solid-state and can be made dense and robust using standard manufacturing techniques, thus addressing the crossover issues associated with currently used polymer membrane electrolytes or KOH-based alkaline electrolytes.

[0123] It has been previously stated that a high density of oxygen or anion vacancies results in high ionic conductivity and high ionic transport numbers. However, it has been discovered that this is not the only factor. In particular, the following interrelated factors are considered herein:

[0124] (1) Structure of the starting material: High ionic conductivity is related to the structure of the starting oxide. For example, doped CeO2 (doped CeO2) with a fluorite structure has a relatively high density of oxygen vacancies, but the CeO2 can be prepared according to the preparation method described below. 0.5La 0.5 O 2-δ Experiments using this method have resulted in materials with excessively low conductivity and mixed ionic / electronic conduction rather than pure ionic conduction. Therefore, a high concentration of oxygen vacancies does not guarantee high ionic conductivity.

[0125] (2) The location of oxygen vacancies in the starting material: Ordered (regular) oxygen vacancies that form continuous channels, such as in brownmillerite-type oxides, or at least local ordering (as in perovskites), have been found to improve ionic conductivity.

[0126] (3) Composition of the Starting Materials: Experiments have shown that it is desirable for the starting oxide to have a relatively high reactivity with water, particularly a tendency to form (optionally hydrated) oxyhydroxides and hydrated oxides. The reactivity with water is related to the structure and composition of the starting oxide and has been found to be an important property for forming pure ionic conductors with high ionic conductivity. Starting materials capable of forming oxyhydroxides have been found to be particularly beneficial in some embodiments.

[0127] (4) Hydration process: Forming hydrated oxides or oxyhydroxides has been found to have a strong influence on the formation of ionically conductive materials with sufficiently high ionic transport numbers. 0.8 Y 0.2 O 3-δ and SrCe 0.8 Y 0.2 O 3-δ In some oxides, such as SrZr, extrinsic oxygen vacancies exist due to doping with low-valent elements at the B site. In some cases, oxygen vacancies or anion vacancies can also be introduced when forming A-site deficient oxides by doping with low-valent elements at the A site. 0.8 Y 0.2 O 3-δ , SrCe 0.8 Y 0.2 O 3-δ , SrTi 0.7 Fe 0.3 O3-δ and SrTi 0.7 Co 0.3 O 3-δ Many materials, such as SrTi, exhibit high ionic conductivity and high ionic transport numbers when calcined in air to obtain the perovskite phase (which may contain small amounts of secondary phases) and then processed in water. Ionic conductivity is highly dependent on chemical composition. In general, oxides composed of elements with fixed valence are likely to be good pure ionic conductors when in contact with liquid water, while oxides composed of elements with multiple valences are likely to be electronic conductors or mixed ionic / electronic conductors when in contact with liquid water. The exact chemical composition of the material is also very important. For example, SrTi, when calcined only in air, exhibits high ionic conductivity and high ionic transport numbers. 0.5 Fe 0.5 O 3-δ becomes a mixed ionic / electronic conductor in water, while SrTi 0.7 Fe 0.3 O 3-δ SrTi is primarily an ionic conductor in water. 1-x Fe x O 3-δ Increasing the Ti content in the series changes the material from an electronic conductor to a mixed ionic / electronic conductor, and then to a material that is primarily an ionic conductor. The unprocessed oxides of the family selected as starting materials often have perovskite or brownmillerite structures and are generally electronic conductors, semiconductors, or ionic and electronic insulators, and only acquire ionic conducting properties when prepared and processed as described herein. The ionic conductivity is generally not high enough for use as an electrolyte 104. Upon hydration with water, the structure of the ceramic material is affected. By starting with a material with the listed structure, the ions (OH) are released in the hydrated material. - ions or H + It was found that sufficient paths were provided for the diffusion of OH ions. - The presence of ions or new OH bonds - ions and / or H +The continuous diffusion of ions is promoted, thereby improving ionic conductivity. In particular, the reaction between the oxide and water forms new (hydrated or non-hydrated) oxyhydroxides, which form new bonds and cut off potential electron transport paths in the starting material (thus reducing or eliminating electronic conductivity). In samples with a lower concentration of oxygen vacancies, the electron pathways are not completely blocked, and the material may become an electronic conductor or a mixed electronic / ionic conductor. Therefore, a higher concentration of oxygen vacancies is desirable, especially when the ionically conductive layer is used as an electrolyte and minimal or no electronic conduction is desired. Calcining the oxide under different conditions, e.g., at different temperatures and in different atmospheres (optionally reducing), can tailor the material's composition and / or the number of oxygen vacancies. It has been shown that various ceramics with a moderately high concentration of oxygen vacancies can yield nearly pure ionically conductive materials after reacting the calcined oxide material with water. These materials are suitable for use as the electrolyte 104 in the electrochemical device 100. If the oxygen vacancy concentration is not high enough, mixed ionic / electronic conductors may be formed after reacting with water. In such cases, the electronic conductivity becomes too high for use as an electrolyte. However, these mixed ionic / electronic conductors may have applications as electrode materials in some electrochemical devices or gas separation membranes.

[0128] (5) Ion size: Ionic conductivity has been found to be related to the size of the cations at the A site, especially in oxides with perovskite structure or brownmillerite structure. Oxides with (relatively small) Sr cations at the A site tend to exhibit higher ionic conductivity. Oxides with (larger) Ba cations at the A site tend to exhibit lower ionic conductivity. In general, oxides with large Ba cations at the A site tend to exhibit lower ionic conductivity. 2+ In the presence of ions, the lattice constant increases, and therefore the spacing between adjacent OH - The gap between ions becomes larger. OH - OH via ion or lattice H2O - ions or H +The larger the spacing, the more difficult it is for ions to jump or diffuse, leading to poor ionic conduction. However, if the A-site ions are too small, e.g., Ca in some structures, 2+ In the case of Ba2Fe2O, the oxyhydroxides formed have generally been found to have too high an electronic conductivity for use as the electrolyte 104 in the electrochemical device 100. Therefore, the size of the A-site ions is selected to be large enough to block the electron pathway, but small enough to allow ion "hopping" for ionic conduction. In particular, the size of the A-site ions is believed to affect the separation of O-H bonds in the electrolyte material. 5±δ The ionic conductivity of the oxyhydroxide formed from SrFeO 5±δ It was found that the ionic conductivity of the oxyhydroxide formed from BaFeO was lower than that of the oxyhydroxide formed from BaFeO. 5±δ In the oxyhydroxide formed from the OH bond, the lattice constant is large due to the presence of large cations in the A site, and the distance / spacing between adjacent OH bonds is longer. - Ion / H + It is believed that this is because it becomes more difficult for the ions to jump. Oxides with the compositions detailed herein may form oxyhydroxides with diffusion channels of appropriate size for the ions. If the channels are too narrow (when smaller A-site cations are used), the ions (OH - ions and / or H + If the channel is too large, e.g., Ba 2+ In the case of larger A-site cations such as Sr, it becomes difficult for the ion to jump from one site to the next available site, which can lead to a decrease in ionic conductivity. 2+It has been shown that samples with cations exhibit the highest ionic conductivity. However, the size of the channels through which ions pass is also related to the size of the B-site ions and the crystal structure. Therefore, the size of the channels can be tuned by doping cations into the A and / or B sites. The effect of cation size may also differ between different crystal structures.

[0129] Those skilled in the art will appreciate that careful tailoring of the composition and structure of the starting oxide is necessary to create a material with suitable properties for the electrolyte 104. In particular, materials with a suitably high number density of oxygen vacancies and a layered structure, or where the formed (hydrated or anhydrous) oxyhydroxide (after treatment with water) has a high OH - Ion / H + It may be desirable to create materials with channels or pathways for ion diffusion, particularly starting oxides with ordered oxygen vacancies (such as the Brownmillerite structure), or starting oxides rich in oxygen vacancies with locally ordered oxygen vacancies (such as various perovskite-type oxides), or layered oxides with oxygen vacancies (e.g., various K4CdCl6 structure oxides).

[0130] As described in detail below, the preparation method of the electrolyte material is adjusted to obtain the desired properties. For example, in the case of oxides having a perovskite or brownmillerite structure, the starting material is generally fired in an atmosphere with a low oxygen partial pressure, such as pure N, pure Ar, or a mixed N / Ar. A reducing gas, typically H, but optionally other reducing gases such as CO, may be added to the atmosphere. Firing in an atmosphere with a low oxygen partial pressure, optionally a reducing atmosphere, may help increase the oxygen vacancy concentration in the resulting fired material. An increase in the number of oxygen vacancies results in more OH groups in the oxyhydroxides formed in the hydration process. - This may promote the formation of ions and also result in more H2O being incorporated into the lattice, leading to higher ionic conductivity.

[0131] Therefore, the solid-state H + and / or OH - Ion-conducting materials may be used as the electrolyte 104, replacing, for example, state-of-the-art Nafion® membranes or alkaline membranes or KOH solutions. The ceramic oxide starting materials described are generally stable in air, miscible with CO2, and can be densified to avoid fuel crossover. Also, relatively inexpensive oxide materials are used to form the electrolyte 104, keeping the cost of the electrolyte low.

[0132] The Brownmillerite structural material described above is an example of one family of materials with suitable characteristics. To date, the family of starting materials identified that meet these criteria and provide electrolyte materials when hydrated are as follows, from a structural standpoint: A. Oxide with brownmillerite structure, as shown in Figure 3 B. Oxides with a perovskite structure, as shown in Figure 4 C. Oxides with the K4CdCl6 structure, such as Ca3Co2O6, as shown in Figure 5

[0133] Those skilled in the art of crystallography will understand that the term "K4CdCl6 structure" is used broadly to refer to the known K4CdCl6 structure, whatever the elemental composition of the material. K4CdCl6 itself is not an oxide, and therefore is not included in "oxides having the K4CdCl6 structure." As shown in Figure 5, the K4CdCl6 structure is a one-dimensional layered structure. This structure contains one-dimensional channels, and OH - Ions and H + This provides a potential pathway for the diffusion of ions such as ions.

[0134] As noted above, the elemental composition of the starting material also affects properties, and not all oxides having the structures listed above form part of a specified family. Further limitations to each family are provided elsewhere herein. For ease of reference, a list of structural definitions for each family is provided here. Subsequent hydration further alters the structure and composition of the starting material to form the electrolyte material. Typically, a starting material ceramic oxide with ordered oxygen vacancies (e.g., Brownmillerite structure), or a starting material ceramic oxide with locally ordered high concentrations of oxygen vacancies (e.g., oxygen-vacancy-rich perovskite-type oxides), or a layered oxide with oxygen vacancies is selected. Often, after reaction with water, water molecules and / or OH groups are formed at or near the B-site tetrahedrons. - Anions are taken up and OH - ions and H + A continuous channel is formed through which ions, such as ions, can pass.

[0135] For example, in the case of family A of starting materials, i.e., brownmillerite structure oxides, the general formula for a simple, undoped brownmillerite ceramic containing only three elements is A 2-a B2O 5±δ where A is selected from Ca, Sr, Ba, Ln (i.e., any lanthanide), Y, Na, K, Rb, Cs, Pb, and Bi. B may be selected from Ce, Zr, In, Y, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu, and more typically is selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, As, and Ta. In the above general formula, the value of a is typically 0.3 or less, often 0.2 or less, and optionally 0.1 or less for A-site deficient brownmillerite-type oxides.

[0136] In doped brownmillerite, one or more of A, B, and O can be partially substituted with one or more other elements, selected from the list to provide the desired properties. The general formula for doped oxides is: (A 2-x A' x ) 1-a B 2-y B y (O 1-z C z ) 5±δ A and A' are one or more elements selected from the list provided above for A in the undoped oxide, i.e., Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi. B and B' are one or more elements selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, As, and Ta. Optionally, B and B' are one or more elements selected from Ce, Zr, Y, Co, Fe, Mn, In, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta, and at least one of B and B' may be selected from the list provided for B in the undoped oxide, i.e., Ce, Zr, Y, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The value of a is generally as described for the undoped oxide. The value of z is generally 0.04 or less, and optionally 0.02 or less, for anion-doped Brownmillerite-type oxides. C, which replaces a portion of the oxygen in the undoped oxide, is one or more elements selected from N, Cl, F, Br, S, Te, and Se.

[0137] An example of this family is SrFeO after reaction with water to form an oxyhydroxide. 5±δThe ionic conductivity of the membrane is 0.041 S / cm at 90°C, which is the same as that of commercial Nafion® membranes (0.04 S / cm at 96°C), and the ionic transport number is 0.998, providing strong electrolytic performance.

[0138] The brown millerite structure is A n B n O 3n-1 (n ≥ 2). This structure contains (n-1) rows of perovskite-type layers of corner-sharing BO6 octahedra alternating with a single layer of BO4 tetrahedra. In the brownmillerite structure (A2B2O5, i.e., when n = 2), oxygen vacancies are ordered along the (010) plane, forming one-dimensional (1D) diffusion paths for the migration of oxygen ions within the tetrahedral layers.

[0139] Turning to family B of starting materials, i.e., perovskite structure oxides, Figure 4 shows a diagram of the perovskite structure, more specifically SrCoO 2.64 1 shows the structure of (III) of the perovskite-structured oxide material of the present invention. This structure is typical of simple perovskites. The A-site ions (in this case, strontium) are represented by dark gray spheres. The B-site ions (in this case, cobalt) are represented by polyhedra (in this case, CoO octahedra, with some oxygen sites unoccupied). The oxygen ions (which may be mixed with other C-site ions in other embodiments) are represented by light gray spheres. In many embodiments, Family B oxygen-deficient perovskite-structured oxide materials can be reacted with water to form oxyhydroxides for use as electrolyte materials.

[0140] The simplest general formula for perovskite is ABO3, which is SrCoO 2.64 It should be noted that the oxygen stoichiometry in is just 2.64 instead of 3, which means there is an oxygen deficiency. The general formula is ABO 3-δwhere the value of δ indicates the level of oxygen vacancy. The value of δ may be 0 in some embodiments, but in various embodiments may be selected to be 0.1 or greater, 0.2 or greater, 0.3 or greater, 0.4 or greater, or 0.5 or greater. More specifically, "simple" perovskite oxides have the general formula ABO 3-δ As with brownmillerite oxides, A, B, and O can all be partially substituted with one or more other elements, e.g., the terms "double perovskite oxide" or "triple perovskite oxide" are used for perovskites with two or three different A-site and B-site elements, respectively, which further complicates the general formula. Double perovskite oxide: (A 2-x A' x ) a B 2-y B' y O 6-δ Triple perovskite oxide: (A 3-x-x’ A' x A'' x’ ) a B 3-y-y’ B' y B'' y’ O 9-δ Doped double perovskite oxides: (A 1-x-x’ A' x A'' x’ ) 2-a B 2-y-y’ B' y B'' y’ (O 1-z C z ) 6-δ

[0141] In this family of starting materials, the one or more A-site elements are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi. The one or more B-site elements are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, and Ta. Optionally, the one or more B-site elements are selected from Zr, Ce, Y, Co, Fe, Mn, In, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta, and may include at least one of Zr, Ce, Y, Ti, Mn, Fe, Co, Ni, and Cu. When present, C is selected from N, Cl, F, Br, S, and Se. The value of a in the above general formula is typically 0.15 or less, often 0.1 or less, and optionally 0.05 or less for A-site deficient perovskite oxides. The value of z is typically 0.2 or less, and optionally 0.05 or less, for anion-doped perovskite oxides. The value of z is zero for undoped oxides. The simplified formula ABO 3-δ It will be understood that when used, this is used to refer to a doped perovskite having any suitable number of A-site and B-site elements, optionally with partial oxygen substitution.

[0142] In oxides with a perovskite structure, when the oxygen vacancy concentration increases to a certain level, the oxygen vacancies may not be fully ordered, as is generally the case with brownmillerite structure oxides. However, partial, local ordering is thought to occur, providing some channels for ion migration after reaction with water. Other factors remaining constant, a higher concentration of oxygen vacancies generally leads to higher ionic conductivity. For example, the ionic conductivity of hydrated SrCo at temperatures between 25°C and 90°C is 0.5 Ti 0.5 O 3-δThe ionic conductivity and ionic transport number of perovskite materials are shown in graph 200 of Figure 6. Figure 6 shows the conductivity and transport number of SrCo after immersion in water at room temperature for three days. 0.5 Ti 0.5 O 3-δ The graph shows the conductivity and ionic transport number of the SrCo alloy used in the tested samples. At room temperature, the ionic conductivity is 0.016 S / cm and the ionic transport number is 0.997. When the temperature is increased to 90°C, the ionic conductivity increases to 0.05 S / cm and the ionic transport number is 0.988. This ionic conductivity exceeds that of Nafion (registered trademark) (0.04 S / cm at 96°C). 0.5 Ti 0.5 O 3-δ was synthesized by the standard Pechini method. 21.60 g of Sr(NO3)2, 14.90 g of Co(NO3)2·6H2O, and 14.93 g of titanium isopropanol (Ti(C3H7O)4) were dissolved in deionized water to prepare a mixed solution. 46.58 g of citric acid (C6H8O7) was then added to the mixed solution to achieve a molar ratio of citric acid to the total molar concentration of metal ions of 1.2:1. 10.03 g of ethylene glycol (C2H6O2) was added to the mixed solution in a molar ratio of 2:3 to citric acid. The mixture was then magnetically stirred on a hot plate at 150 °C for 6 hours to form a gel. The gel was then dried at a constant temperature of 450 °C for 1 hour to burn off the organic components. After removing the organic components, the powder was ground and calcined in air at 600 °C for 5 h with a heating / cooling rate of 5 °C / min. The powder was then ground again and calcined in air at 900 °C for 9 h to give SrCo 0.5 Ti 0.5 O 3-δ The prepared powder was then pelletized and sintered in argon at 1100 °C for 12 hours with a heating / cooling rate of 2 °C / min. Figure 12 shows the XRD data for the pellet after sintering in argon, which confirms the expected perovskite structure. SrCo 0.5 Ti 0.5 O 3-δTo test the ionic conductivity of the pellets in water, silver conductive ink (Fisher Scientific) was applied to both sides of the pellet to form Ag electrodes. The Ag-ink-coated pellets were dried at 130°C for 150 minutes. The pellets were then sandwiched between two layers of silver mesh to form a sandwich cell, which was then fixed in a fixture. Electrochemical impedance spectroscopy (EIS) was then performed using a Solartron 1470 / 1455 with an amplitude of 10 mV and a frequency range of 100,000-0.01 Hz. A constant DC voltage of 1 V was applied to the pellets, and the DC conductivity of the pellets was measured using a pseudo-four-probe method while recording the sample current. The conductivity and ionic transport number are shown in Figure 6. SrCo 0.5 Ti 0.5 O 3-δ The highest ionic conductivity of 0.050 S / cm was obtained in water at 90°C, and the ionic transference number (t i ) is 98.8%. The conductivity was measured during the cooling process.

[0143] General formula (A 1-x A' x ) 1-a B 1-y B' y O 3-z-d C z may be reacted with water to form a hydrated perovskite oxide having the formula: (A 1-x A' x ) 1-a B 1-y B' y O 3-z-d’ C z n''H2O n'' is non-zero and generally n''≧0.01. A, A', B, B', and C are as defined above. Among other parameters, 0≦x≦1, 0≦y≦1, a≦0.15, z≦0.2, and d≦2.

[0144] The starting brownmillerite-structure oxides or perovskite-structure oxides (doped or otherwise) of Family A and Family B may be selected to contain elements with multiple valences at the B site to accommodate oxygen vacancies, as these have been found to be relevant to the electrolytic performance of the processed materials. However, monovalent elements may also be used. For example, in some embodiments, SrZr 0.8 Y 0.2 O3 may provide better performance than Sr2Co2O5. For example, when pretreated Sr2Co2O5 is used as the electrolyte 104 in an ammonia fuel cell or an ammonia electrolyzer, cobalt reacts with ammonia to form complexes, resulting in the gradual loss of Sr2Co2O5 during this time. 0.8 Y 0.2 Materials such as O3 can offer improved stability by avoiding this problem.

[0145] All oxides in Family A and Family B can be prepared from powders by calcination. Calcination can be performed in air, N2, Ar, or He, or in a reducing atmosphere, optionally with H2, CH4, or CO. To prepare N-doped oxides, samples can be calcined in NH3 and nitrogen can be introduced. Optionally, an atmosphere with a relatively low oxygen partial pressure compared to air, such as air mixed with an inert gas such as argon, can be used. These doped or undoped oxides (doped or undoped oxides) with brownmillerite or perovskite structures are typically electronic conductors, semiconductors, or insulators before reaction with water. Reacting these oxides with water forms the desired electrolyte materials. To react the oxides with water, the oxides can be immersed in liquid water or placed in an atmosphere containing at least 1 vol% water (as steam and / or water vapor). The oxide may react with H2O to form a hydrated or non-hydrated oxyhydroxide, or may form a hydrated oxide.

[0146] The general formula for the hydrated or non-hydrated oxyhydroxides formed from the perovskite or brownmillerite starting materials is: (A 1-x A' x ) 1-a B 1-y B y (O 3-z-d C z )(OH) m nH2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi, and B and B' are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, and Ta, and optionally As. Optionally, B and B' are selected from Ce, Zr, Y, In, Co, Fe, Mn, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta, and may include at least one of Ce, Zr, Y, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. C is selected from N, Cl, F, Br, S, and Se, and optionally Te, and 0≦x≦1, a≦0.15, z≦0.2, 0≦y≦1, d≦2, m≧0.01, and n≧0.

[0147] Optionally, for A-site deficient perovskite or brownmillerite oxides, a may be 0.1 or 0.05 or less. Optionally, for anion-doped perovskite or brownmillerite oxides, z may be 0.1 or less. The value of m generally varies depending on the valence of the B-site ions and the oxygen vacancy concentration. Those skilled in the art will understand that the values ​​of z and d generally vary with the value of m. The concentration of anion vacancies depends at least in part on the value of (z + d); as the value of z + d increases, there are more anion vacancies (usually oxygen vacancies) and, correspondingly, the value of m increases. A larger value of m indicates more charge carriers in the resulting material, resulting in higher conductivity. The value of n generally varies depending on the chemical composition of the material and the presence of ambient steam / water vapor concentration or liquid water. For non-hydrated (anhydrous) oxyhydroxides, whether doped or undoped, n = 0. The value of n in hydrated oxyhydroxides depends on the structure and composition of the material and may vary widely between embodiments, ranging from near zero to relatively high values. In various embodiments, the value of n may be up to 15 or 12, and optionally up to 6. The value of n in various embodiments may range from 0.1 to 4, and optionally from 1 to 2. Higher values ​​of n may be obtained with more porous / less dense oxide materials and / or longer treatment times with water.

[0148] In these cases, the ionically conductive material (or other ionically conductive layer) useful as the electrolyte is or includes a material having the form of a hydrated or non-hydrated doped or undoped oxyhydroxide. In additional or alternative embodiments, the formed ionically conductive material may be or include a hydrated oxide (doped or undoped) formed from the original (original) starting material.

[0149] For ceramic oxide starting materials having a brownmillerite structure, the hydrated oxides are of the general formula (A 2-x A' x ) 1-a B 2-y B y (O 1-z C z ) 5±δ ·n'H2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi. B and B' are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, and Ta. Optionally, B and B' are selected from Ce, Zr, Y, In, Co, Fe, Mn, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, As, and Ta. C is selected from N, Cl, F, Br, S, Te, and Se. a≦0.15, 0≦x≦1, 0≦y≦1, z≦0.04, and n′≧0.01. In some embodiments, a≦0.10 and z≦0.02. In various embodiments, for A-site deficient Brownmillerite-type oxides, a≦0.2, and often a≦0.1. Optionally, a≦0.15. In various embodiments, for anion-doped Brownmillerite-type oxides, z≦0.02, and optionally z≦0.01.

[0150] For ceramic oxide starting materials having a perovskite structure, the hydrated oxides are represented by the general formula (A 1-x A' x ) 1-a B 1-y B' y O 3-z-d’ C z n''H2O wherein: A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi. B and B' are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, As, and Ta. Optionally, B and B' are selected from Ce, Zr, Y, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, and Ta, and may include at least one of Ce, Zr, Y, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. C is selected from N, Cl, F, Br, S, Te and Se. 0≦x≦1, 0≦y≦1, a≦0.15, z≦0.2, d≦2, and n″≧0.01.

[0151] In some cases, a mixture of oxyhydroxides and hydrated oxides may be formed from Family A and / or B starting materials.

[0152] Family C starting materials include oxides having the K4CdCl6 structure, as shown in Figure 5. Family C oxide materials, such as Ca3Co2O6 and Sr3Co2O6, can be reacted in water (e.g., by immersion in liquid water or by treatment with water vapor and / or steam) to produce oxyhydroxides and / or hydrated oxides for use as electrolyte materials. More specifically, Figure 5 shows a typical K4CdCl6 structure, and more specifically, the structure of Sr3Co2O6. A-site ions (in this case, strontium) are represented by dark gray spheres. B-site ions (in this case, cobalt) are represented by polyhedra. Oxygen ions (which may be mixed with one or more other C-site ions in other embodiments) are represented by light gray spheres. This structure has a distinct one-dimensional character, with Co-O chains along the c-axis and Co atoms forming face-coordinated polyhedra alternating between triangular prisms and octahedra. One-dimensional channels through the structure are provided by adjacent polyhedra.

[0153] As an example of this family, the A-site deficient Ca3Co2O6 oxide material was found to have an ionic conductivity of 0.053 S / cm at 90°C when immersed in water. While this conductivity is higher than that of Nafion®, the ionic transport number is only about 0.91, providing more electronic conduction than is desired in the electrolyte 104 (although this is inferior to the performance obtained from perovskite- or brownmillerite-structure starting materials, it may be acceptable for some applications). By adjusting the chemical composition, the ionic transport number can be further improved.

[0154] Oxides with the K4CdCl6 structure have the general formula shown below, noting that the previous comments regarding doping and number of A-site and B-site elements also apply to this family. (A 1-x A' x )3B 2-y B' y O 6-z C z A and A' are selected from Ca, Sr, Ba, Na, K, Rb, Cs, Ln, Y, Pb, In, Tl, and Bi. B and B' are selected from Co, Fe, Mn, Ni, Cu, Ti, V, Cr, alkaline earths, Mg, Ca, Sr, Ba, lanthanides, Ln (e.g., Ce), Zr, Sc, Y, Zn, Cd, Na, B, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Ir, Ru, Li, and Rh, and may optionally include at least one of Ce, Zr, Y, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. C is selected from N, Cl, F, Br, S, I, Te, and Se. y ranges from 0 to 2, z ranges from 0 to 0.5, and x ranges from 0 to 1.

[0155] It will be understood that, as in the structures described above, the amount of oxygen may not be exactly equal to that predicted by ideal stoichiometry. For example, in the case of undoped oxides, the oxygen stoichiometry may be greater or less than 6 by an amount delta (δ), i.e., Ca3Co2O 6±δ In the described embodiments, generally, Ca3Co2O is used to provide oxygen vacancies. 6-δ is preferred. Therefore, the above formula is more generally (A 1-x A' x )3B 2-y B' y O 6-z-δ C z The simplified formula above is not intended to exclude non-zero deltas, it just does not show them for clarity.

[0156] As an example of Family C, the ionic conductivity and ionic transport number of a Ca3Co2O6 material immersed in water for three days at temperatures ranging from 25°C to 90°C are shown in the graph in Figure 7. Figure 7 shows the ionic conductivity and ionic transport number of a Ca3Co2O6 sample after three days of immersion in water at room temperature. The ionic conductivity is 0.021 S / cm and the ionic transport number is 0.881 at room temperature. When the temperature is increased to 90°C, the ionic conductivity increases to 0.053 S / cm and the ionic transport number also increases to 0.91. This ionic conductivity is higher than that of Nafion® (0.04 S / cm at 96°C).

[0157] A-site deficient Ca3Co2O6 was prepared for testing by the following method. δwas synthesized by the sol-gel method. 19.50 g of Ca(NO3)2 4H2O, 20.36 g of Co(CH3COO)2 4H2O, and 37.25 g of citric acid (C6H8O7) were dissolved in deionized water in a molar ratio of 1:1:2.4 to form a mixed solution. The mixed solution was magnetically stirred on a hot plate at 125°C for 12 hours to form a gel. The gel was then dried at a constant temperature of 450°C for 1 hour to burn off the organic components in the mixture. The resulting powder was crushed and calcined in air at 600°C for 8 hours. The powder was then crushed again, pelletized, and calcined in air at 800°C for 10 hours to form the Ca2Co2O5 phase. The pellets were then heated in air at 1000°C for 10 hours at a heating / cooling rate of 5°C / min to form the Ca3Co2O6 phase. X-ray diffraction (XRD) analysis showed the formation of a Ca3Co2O6 phase with a K4CdCl6 structure (data shown in Figure 13). These XRD data confirmed that the resulting pellets were a single Ca3Co2O6 phase.

[0158] The Ca-deficient Ca3Co2O6 phase is believed to form because the starting material does not contain enough Ca to form Ca3Co2O6. After water treatment (immersion in liquid water at room temperature for 3 days), this material was found to exhibit a relatively high ionic conductivity of 0.053 S / cm in water at 90 °C, with an ionic transport number of approximately 0.91. While not as high as the values ​​obtained for Sr2Co5O5-based oxides, this level of conductivity is viable as an electrolyte material. Furthermore, a large family of oxides with the K4CdCl6 structure exists, and by tailoring the composition of the A and B sites in accordance with the principles described herein, it is possible to further improve the ionic conductivity and ionic transport number. To test the conductivity of Ca3Co2O6 pellets in water, silver conductive ink (Fisher Scientific) was applied to both sides of the pellet to form Ag electrodes. The coated pellets were dried at 130 °C for 150 minutes. The pellets were then sandwiched between two layers of silver mesh and clamped in a jig. Electrochemical impedance spectroscopy (EIS) was then performed using a Solartron 1470 / 1455 with an amplitude of 10 mV and a frequency range of 100,000 Hz-0.01 Hz. The DC conductivity of the pellets was measured by the pseudo four-probe method by applying a constant DC voltage of 1 V to the pellets while recording the sample current to calculate the resistance. The conductivity results are shown in Figure 7. The highest ionic conductivity of Ca3Co2O6 was 0.053 S / cm, obtained at 90 °C in water, and the ionic transport number (t i ) is 0.91. The conductivity was measured while the sample was cooling.

[0159] It will be understood that stoichiometric Ca3Co2O6 will generally have a low concentration of oxygen vacancies. However, due to the preparation methods described herein, the prepared oxide exhibits the Ca3Co2O6 structure but is Ca deficient, and therefore has an increased concentration of oxygen vacancies. The oxygen vacancy concentration may be further increased if the precursor is calcined at 800 °C in Ar or N2 rather than in air. Because the Ca vacancies introduce oxygen vacancies, calcination in air may produce a material with sufficient ionic conductivity without subsequent steps, such as treatment with a reducing liquid or calcination in a different atmosphere.

[0160] Hydrated oxides or hydrated or non-hydrated oxyhydroxides derived from oxides (doped or otherwise) having the KCdCl structure described above may be formed by treatment with water for use as electrolyte materials. In particular, one or more of the following may be formed: (i) a compound of the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z nH2O, where n is 0.01 or greater, or (ii) a hydrated oxide having the general formula (A 1-x A' x )3B 2-y B' y O 6-z C z (OH) m Oxyhydroxides having the formula nH2O, where m ranges from 0.01 to 6. For anhydrous oxyhydroxides, n is equal to 0. For hydrated oxyhydroxides, the value of n generally depends on the structure and composition of the material and may vary widely among embodiments, from values ​​near zero to relatively high values. For hydrated oxyhydroxides, n is generally 0.01 or greater.

[0161] In various embodiments, the value of n may be 15 or less, or 12 or less, and optionally 6 or less. In various embodiments, the value of n may range from 0.1 to 4, and optionally range from 1 to 2.

[0162] Example of perovskite oxide - SrZr 0.8 Y 0.2 O 3-δ and related materials

[0163] 1. SrZr 0.8 Y 0.2 O 3-δ -1300 Air - Experimental Process

[0164] SrZr 0.8 Y 0.2 O 3-δ was synthesized by the sol-gel method. 10.80 g of Sr(NO3)2, 3.83 g of Y(NO3)3·6H2O, 13.15 g of ZrOCl2·8H2O, 5 mL of nitric acid (70%), and 38.81 g of citric acid were dissolved in deionized water in a molar ratio of 1:0.2:0.8:1.6:4. The mixture was then magnetically stirred on a hot plate at 90°C for 12 hours to form a gel. The gel was then dried at a constant temperature of 400°C for 1 hour and ignited. After the organic components in the mixture were burned off, the powder was crushed and calcined in air at 400°C for 3 hours, followed by calcination at 1000°C for 2 hours. The powder was then re-ground and pelletized, and calcined in air at 1300°C for 24 hours with a heating / cooling rate of 5°C / min to give SrZr 0.8 Y 0.2 O 3-δ The XRD pattern showed the formation of a single phase.

[0165] SrZr 0.8 Y 0.2 O 3-δTo test the pellets' conductivity in water, silver conductive ink (Fisher Scientific) was applied to both sides of the pellets to form Ag electrodes. The Ag paste was dried at 130°C for 150 minutes. The Ag-coated pellets were then treated twice in fresh water at 90°C before conductivity testing to ensure the material was hydrated. The resulting sandwich cell was assembled with the pellet sandwiched between two layers of silver mesh and secured in a fixture. Electrochemical impedance spectroscopy (EIS) was then performed using a Solartron 1470 / 1455 with an amplitude of 10 mV and a frequency range of 1 MHz–0.01 Hz. The DC conductivity of the pellets was measured using a pseudo-four-probe method, applying a constant DC voltage of 1 V to the pellets and recording the current to calculate the resistance to electronic conduction. This approach will be referred to as "Method 1" for ease of reference below, as conductivity tests were prepared and performed using the same method for various pellets.

[0166] 2. MZr 0.8 Y 0.2 O 3-δ (M=Ca, Sr, Ba) Pellets - Experimental Process

[0167] MZr 0.8 Y 0.2 O 3-δ (M = Ca, Sr, Ba) were synthesized by the sol-gel method. M(NO3)2 (M = Ca, Sr, Ba), Y(NO3)3·6H2O, ZrOCl2·8H2O, nitric acid, and citric acid were dissolved in deionized water in a molar ratio of 1:0.2:0.8:1.6:4 to prepare a mixed solution. The mixed solution was then magnetically stirred on a hot plate at 90 °C overnight to form a gel. The gel was then dried at a constant temperature of 400 °C for 1 h and ignited for combustion. After burning off the organic components in the mixture, the powder was crushed and calcined in air at 400 °C for 3 h, then at 1000 °C for 2 h. The powder was then crushed again, pelletized, and calcined in air. SrZr was obtained by treating at 1300 °C for 24 h. 0.8 Y 0.2 O 3-δThe CaZr phase was formed and treated at 1300°C for 4 hours. 0.8 Y 0.2 O 3-δ The BaZr phase was formed and treated at 1500°C for 4 hours. 0.8 Y 0.2 O 3-δ A phase was formed.

[0168] MZr 0.8 Y 0.2 O 3-δ For testing the conductivity of (M=Ba, Ca, Sr) pellets in water, Method 1 defined above was again carried out.

[0169] 3. SrZr 1-x Y x O 3-δ -1300 air (x=0 to 0.2) pellets - experimental process

[0170] SrZr 1-x Y x O 3-δ The -1300°C air (x = 0 to 0.2) materials were synthesized by the sol-gel method. Sr(NO3)2, Y(NO3)3·6H2O, ZrOCl2·8H2O, nitric acid, and citric acid were dissolved in deionized water in molar ratios of 1:0.2:0.8:1.6:4, 1:0.1:0.9:1.8:4, and 1:0:1:2:4 for x = 0.2, 0.1, and 0, respectively. The mixture was then magnetically stirred on a hot plate overnight at 90°C to form a gel. The gel was then dried at a constant temperature of 400°C for 1 hour and ignited. After the organic components in the mixture were burned off, the powder was crushed and calcined in air at 400°C for 3 hours, followed by calcination at 1000°C for 2 hours. The powder was then re-ground and pelletized, and calcined in air at 1300°C for 24 hours with a heating / cooling rate of 5°C / min to give SrZr 0.8 Y 0.2 O 3-δ The XRD pattern shows that a single phase was obtained.

[0171] SrZr 1-x Yx O 3-δ Method 1 was repeated to test the conductivity of the −1300 air (x=0 to 0.2) pellets in water.

[0172] result

[0173] As-prepared SrZr 0.8 Y 0.2 O 3-δ The main phase of the SrZrO3 (PDF Card No. 31-1365) solid solution contains a trace of SrY2O4 (PDF Card No. 32-1272). 0.8 Y 0.2 O 3-δ The XRD pattern of the present invention indicates that the product is a nearly pure solid solution phase.

[0174] Each of the various samples was heated in water at 90°C for one day and then cooled to room temperature. The water was then replaced and the samples were again heated to 90°C and cooled to room temperature. This process was repeated three times. This process was intended to remove unreacted impurities such as SrO and Sr(OH)2 that may have formed when SrO reacted with HO. The conductivity data shown in Figure 15 was obtained after the first treatment and during the subsequent cooling process. In general, SrZr 1-x Y x O 3-δ In the series, as the value of x increases, more oxygen vacancies are introduced into the lattice. After treatment in water, SrZr 0.8 Y 0.2 O 3-δ The highest ionic conductivity of the sample is due to the highest doping level at the B site. However, this is not the only factor. For example, SrCe 1-x Y x O 3-δ In the series, undoped SrCeO was obtained after treatment in boiling water at 90 °C. 3-δ The ionic conductivity of SrCe 0.9 Y 0.1 O 3-δTherefore, even undoped materials with few oxygen or anion vacancies may exhibit high ionic conductivity after treatment in water, especially boiling water. However, SrCeO 3-δ The ionic conductivity of the highly doped SrCe sample measured in water is 0.8 Y 0.2 O 3-δ This indicates that the introduction of additional oxygen vacancies is still a good strategy to obtain materials with high ionic conductivity.

[0175] These experiments, the results of which are shown in Figure 15, 1-x Y x O 3-δ In solid solution, the greater the Y-doping (the higher the Y doping amount), the more oxygen vacancies the sample has, resulting in higher ionic conductivity. The ionic conductivity is related to the oxygen vacancies. Furthermore, as shown in Figure 16, at the same doping level, the ionic conductivity is related to the size of the A-site cations in the perovskite oxide. SrZr 0.8 Y 0.2 O 3-δ The sample exhibits the highest ionic conductivity of those tested.

[0176] MZr 0.8 Y 0.2 O 3-δ For conventional proton conductors in the (M=Ca, Sr, Ba) series, the sample BaZr 0.8 Y 0.2 O 3-δ has the largest cell volume and H + / O 2- The highest H at temperatures above 500°C is achieved due to the large "free volume" (space not occupied by ions within the lattice) that allows ion transport. + or H + / O 2- However, in the water treatment studies reported here, the SrZr0.8 Y 0.2 O 3-δ However, CaZr 0.8 Y 0.2 O 3-δ and BaZr 0.8 Y 0.2 O 3-δ Higher than MZr 0.8 Y 0.2 O 3-δ It was found that the (M = Ca, Sr, Ba) series exhibited the highest ionic conductivity. This indicates that the type of ion that moves (H + / O 2- H instead of ions + / OH - ions), suggesting that the materials may offer different transport mechanisms. 0.8 Y 0.2 O 3-δ is H in liquid water + / OH - It is a mixed ionic conductor, and it was found that its proton conductivity at high temperatures is significantly different from that of the conventional ionic conductor.

[0177] Therefore, it was speculated that if the lattice constant is too large, the distance between adjacent vacancy sites is too long, making it difficult for ions to jump or diffuse. If the lattice constant is too small, the free volume (unoccupied space) becomes too small, which also makes it difficult for ions to jump or diffuse. BaZr 0.8 Y 0.2 O 3-δ The excessively large "free volume" in CaZr 0.8 Y 0.2 O 3-δ Too small a "free volume" in SrZr also does not lead to high ionic conductivity in water. Instead, there is an optimum lattice size or "free volume" between the two. In particular, SrZr 0.8 Y 0.2 O 3-δ The sample exhibited the highest ionic conductivity among the samples tested. + / OH - To form a continuous pathway for ion transport, H + / OH -The distance between two adjacent sites available for jumping / moving should not be too long. 0.8 Y 0.2 O 3-δ While the sample has a large "free volume," the SrZr 0.8 Y 0.2 O 3-δ This may be the reason why the ionic conductivity is lower than that of the CaZr sample. 0.8 Y 0.2 O 3-δ The ionic conductivity of SrZr 0.8 Y 0.2 O 3-δ The ionic conductivity of CaZr is lower than that of 0.8 Y 0.2 O 3-δ has a smaller "free volume". Therefore, there is an optimum ion size at the A site, and the "free volume" and H + / OH - By balancing this with the jump / travel distance of the ions, the highest ionic conductivity can be achieved.

[0178] As shown in Figure 17, the SrZr 0.8 Y 0.2 O 3-δ The ionic conductivity of the was found to decrease slightly initially and stabilize after 75 h, indicating excellent stability.

[0179] Figure 18 shows the results of SrZr in humid air at different temperatures. 0.8 Y 0.2 O 3-δ It was found that at temperatures below 100°C, the conductivity increased with increasing temperature. However, when the temperature exceeded 100°C, the conductivity decreased significantly, reaching 10 -6 S / cm to 10 -5 This experiment was carried out in the range of S / cm. 0.8 Y 0.2The high ionic conductivity of O3 is associated with water or steam at low temperatures, typically below 100 °C. This suggests that proton or H conductivity of perovskite oxides at high temperatures, typically above 500 °C, can be improved for use as electrolytes in solid oxide fuel cells and solid oxide electrolysis cells. + / OH - This is quite different from reports of mixed ionic conduction. Figure 19 shows in more detail the change in ionic conductivity and ionic transport number at temperatures below 100°C. The ionic transport number is greater than 99.6%, indicating that the material is a good ionic conductor and suitable for use as an electrolyte in various electrochemical devices.

[0180] Figure 20 provides conductivity data over time. From this experiment, SrZr 0.8 Y 0.2 O 3-δ It can be seen that the conductivity of the materials is stable in humid air. This indicates that the materials are suitable for use as electrolytes in fuel cells or other electrochemical devices where water can be supplied not as a liquid but as steam or a humidified (moist) gas atmosphere. High ionic conductivity is maintained when exposed to a humidified atmosphere. This is particularly useful for use as an electrolyte membrane (optionally as part of a composite to enhance flexibility and mechanical strength) for direct hydrogen fuel cells, where humidified hydrogen is supplied to the anode and humidified air (moist air) or O2 is supplied to the cathode. Such electrode membranes can replace the state-of-the-art Nafion® membrane electrolyte for hydrogen fuel cells with polymer exchange membrane electrolytes, reducing costs. Unlike the acidic Nafion® membrane, the materials described herein are very weakly acidic, and some may even be alkaline. Therefore, the materials can also be used as electrolyte membranes in alkaline membrane fuel cells. Most of these oxides are chemically miscible with CO2 in air, which reduces the risk of CO2 poisoning of conventional alkaline membranes, i.e., OH ions. -This reduction in ionic conductivity would not be an issue for these electrolyte membranes, and therefore the disclosed materials may be able to overcome the biggest challenge of conventional alkaline membrane fuel cells and electrolyzers: avoiding CO poisoning.

[0181] SrZr in DO 0.8 Y 0.2 O 3-δ -1300 Air Pellets Testing - Experimental Process

[0182] SrZr in H2O and D2O 0.8 Y 0.2 O 3-δ To test the conductivity of the pellets, Method 1 described above was repeated. The results of the conductivity test are shown in FIG.

[0183] SrZr in D2O 0.8 Y 0.2 O 3-δ The conductivity of SrZr in H2O is 0.8 Y 0.2 O 3-δ This is because the ionic conduction is much lower than that of H + or OH - This indicates that the transport of hydrogen-containing species, such as ions, ions, or both, is involved. Concentration cell measurements, as described below, show that this material exhibits H + / OH - It is a mixed ionic conductor, but mainly contains OH - It was suggested that the material is an ionic conductor. + Conductor and OH - Which conductor dominates may depend on one or more of structure, chemical composition, temperature and hydration level.

[0184] Figure 22 shows the hydrated (solid line) and deuterated (dashed line) SrZr measured at room temperature. 0.8 Y 0.2 O 3-δ of 1The H-MAS solid-state NMR data are shown. The two peaks at chemical shifts of 3.52 ppm and 0.71 ppm correspond to Zr-OH-Zr and Zr-OH-Y, respectively. The hydrogen at chemical shift 0.71 ppm corresponds to H + ions or OH - It was confirmed that the material migrates in either its ionic form or its ionic form. The peak at 0.71 ppm becomes significantly weaker when the sample is dehydrated, indicating the involvement of physically or chemically adsorbed water, or both. This indicates that a humidified (wet) environment that keeps the material hydrated is crucial to maintaining high ionic conductivity, which can be achieved by direct contact with liquid water or exposure to an atmosphere containing at least 5 vol% water (e.g., as steam). The same material may exhibit significantly different conduction properties when placed in different environments.

[0185] The material is H + Ionic conductor, OH - Ionic conductors, and H + / OH - To determine whether the ceramic oxide electrolyte was SrZr, a concentration cell was used according to the method described in J. Am. Chem. Soc. 2013, 135, 1112-11130. 0.8 Y 0.2 O 3-δ After immersion in water at room temperature and 30 minutes in an H-cell, - The transference number was found to be 0.80.

[0186] This measurement revealed that SrZr 0.8 Y 0.2 O 3-δ is H + / OH - It is a mixed ionic conductor, but mainly contains OH - It has been shown to be an ionic conductor, which means that at temperatures above 500°C, + Ionic conductor or H + / OH -These are significantly different from similar oxides, such as doped BaZrO3 and BaCeO3, which are known as mixed ionic conductors and have been used as electrolytes in fuel cells or electrolysis cells under these conditions. On the other hand, the operating temperatures selected for the ion-conducting layers described herein are generally much lower, typically below 100°C, and water or a humidified atmosphere is provided. The conducting species is H + / OH - ions, whereas at temperatures above 500°C the same material becomes O 2- / H + As shown in Figure 18, SrZr in humid air at temperatures above 200°C can act as an ionic conductor. 0.8 Y 0.2 O 3-δ The conductivity of -6 Scm -1 However, when in contact with liquid water or exposed to moist air (Figures 16 to 20), the ionic conductivity is about 10 at temperatures below 100°C. -3 Scm -1 From 10 -2 Scm -1 It also exhibits good stability. -3 Scm -1 From 10 -2 Scm -1 The ionic conductivity of this oxide is high enough to be used as an electrolyte in electrochemical devices, making it a practically useful material.

[0187] Sr2Co2O5

[0188] Sr2Co2O5 pellets fired in air - experimental process

[0189] Sr2Co2O5 was prepared by standard solid-state techniques. 21.59 g of Sr(NO3)2 and 29.79 g of Co(NO3)2·6H2O were ground to form a mixture and then calcined in air at 600 °C for 8 hours with a cooling rate of 1 °C / min. This powder was then ground and calcined in air at 1100 °C for 3 hours with a cooling rate of 1 °C / min to give SrCoO 2.5 The as-prepared powder was then pelletized and sintered in air at 1100 °C for 3 hours with a cooling rate of 1 °C / min. The XRD pattern, shown in Figure 23, indicated that a single phase was formed. Method 1 described above was again used to test the conductivity of the SrCoO pellets in water. The conductivity data, shown in Figure 24, indicate that pure SrCoO calcined in air is primarily an electronic conductor in water. XRD showed that a single phase remained after the conductivity test, suggesting that this phase is stable. However, the possibility that SrCoO reacts with HO to form oxyhydroxides cannot be ruled out, as this cannot be detected by XRD, which is insensitive to the hydrogen element.

[0190] Sr2Co2O5 pellets fired in air and then treated with argon - experimental process

[0191] Sr2Co2O5 was prepared by standard solid-state techniques. 21.59 g of Sr(NO3)2 and 29.79 g of Co(NO3)2·6H2O were ground to form a mixture, which was then calcined in air at 600 °C for 8 h at a cooling rate of 1 °C / min. This powder was then ground and calcined in air at 1100 °C for 3 h at a cooling rate of 1 °C / min to form the Sr2Co2O5 phase. The as-prepared powder was then pelletized and heated in argon at 1100 °C for 8 h to increase oxygen vacancies in the solid structure. Method 1 was repeated to test the conductivity of the Sr2Co2O5-1100Ar pellet in water. As shown in Figure 25, the XRD pattern of the sample after the conductivity test showed several Co(OH)2 peaks.

[0192] Co(OH) powder was prepared by coprecipitation from CoCl and NaOH, directly pressed into pellets, and its conductivity in water was tested. XRD data, shown in Figure 25, confirmed that the synthesized Co(OH) was a single phase. Figure 26 shows the conductivity data of SrCoO in water measured upon cooling. Figure 27 shows the conductivity data of a pure Co(OH) sample in water, showing a conductivity two orders of magnitude lower than that of SrCoO pellets calcined in Ar under the same conditions. This experiment indicates that the high ionic conductivity of SrCoO after calcination in Ar is not due to the formation of Co(OH).

[0193] Sr2Co2O5 pellets calcined in air and then treated in reducing liquid - experimental process

[0194] Sr2Co2O5 was again prepared by standard solid-state techniques. 21.59 g of Sr(NO3)2 and 29.79 g of Co(NO3)2·6H2O were ground to form a mixture, which was then calcined in air at 600 °C for 8 hours at a cooling rate of 1 °C / min. This powder was then ground and calcined in air at 1100 °C for 3 hours at a cooling rate of 1 °C / min to form the SrCo2O5 phase. The as-prepared powder was then pelletized and sintered in air at 1100 °C for 3 hours at a cooling rate of 1 °C / min. The XRD pattern indicates the formation of a single phase.

[0195] To increase the oxygen vacancies in the solid structure, the Sr2Co2O5-1100 air pellet was soaked in a reducing agent consisting of 2 M NaOH and 14 M NaBH4 at room temperature for 5 days. The pellet was then rinsed with deionized water several times and soaked in deionized water for 12 hours to wash off any remaining reducing agent in the pellet.

[0196] Method 1 was repeated to test the conductivity of SrCoO-NaBH pellets in water. As shown in Figure 28, the conductivity data for the treated pellets confirmed that treatment of oxides in reducing liquids can convert normal electronic conductors, such as SrCoO, into ionic conductors when the material is exposed to liquid water or humidified conditions. This method may also be applied to other materials, particularly those containing multivalent elements in their composition.

[0197] Sr2Co2O5 pellets calcined in air and then electrochemically reduced (ER) - Experimental process

[0198] Sr2Co2O5 was again prepared by standard solid-state techniques. 21.59 g of Sr(NO3)2 and 29.79 g of Co(NO3)2·6H2O were ground to form a mixture, which was then calcined in air at 600 °C for 8 hours at a cooling rate of 1 °C / min. This powder was then ground and calcined in air at 1100 °C for 3 hours at a cooling rate of 1 °C / min to form the SrCo2O5 phase. The as-prepared powder was then pelletized and sintered in air at 1100 °C for 3 hours at a cooling rate of 1 °C / min. The XRD pattern indicates the formation of a single phase.

[0199] To increase the oxygen vacancies in the solid structure, an electrochemical reduction process was applied to Sr2Co2O5 pellets. Silver conductive ink (Fisher Scientific) was applied to two sides of the pellet to form Ag electrodes. The Ag paste was dried at 130 °C for 150 min. A supersaturated Sr(OH)2 solution consisting of 8 g of Sr(OH)2·8H2O and 30 mL of deionized water was used as the electrolyte. The Sr2Co2O5-1100 air pellet coated with Ag paste, a Pt mesh, and an Ag / AgCl electrode served as the working, counter, and reference electrodes, respectively. The electrochemical reduction potential was controlled at -1.14 V vs. Ag / AgCl for 10 h using an electrochemical interface (Solartron 1287A). Next, the pellet was rinsed with deionized water several times and then immersed in deionized water for 2 h to wash off the residual Sr(OH)2 on the pellet. The pellets were then dried at room temperature and reapplied with silver conductive ink (RS Components) for further conductivity testing. To test the conductivity of Sr2Co2O5-ER pellets in water, Method 1 was performed, but without the addition of a silver ink layer. Instead, the pre-added silver ink was used. Figure 29 shows the XRD pattern of the electrochemically reduced Sr2Co2O5 pellet after conductivity testing in water. The major phase remains, but is poorly crystallized. Figure 30 shows conductivity data obtained by immersing the pellets in water. After electrochemical reduction, the ionic transport number of Sr2Co2O5 in water exceeds 0.9, indicating that this material is primarily an ionic conductor. This experiment demonstrates that the electrochemical reduction process can also convert electronic conductors into predominantly ionic conductors when exposed to water. This method may also be applied to other materials, especially those containing multivalent elements in their composition.

[0200] In some embodiments, for any of the described families and materials, a pure ceramic electrolyte 104 is formed. This electrolyte 104 may be at least substantially composed of one or more hydrated oxides and / or hydrated or non-hydrated oxyhydroxides as described above. These materials may be formed by sintering prepared powders in a selected atmosphere and at a selected temperature to form a solid ceramic electrolyte 104 with desired properties. In alternative embodiments, a composite ceramic-polymer electrolyte 104 is formed.

[0201] The solid ion-conducting layer 104 may be a composite solid ion-conducting layer comprising at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide described herein, mixed with one or more polymeric materials to form a composite material. Alternatively or additionally, the oxide or oxyhydroxide may be mixed with one or more crystallized or amorphous metallic or ceramic materials to form a composite material with good mechanical strength while retaining sufficient ionic conductivity. When an ionic conductor is mixed with a polymeric material, a ceramic material, or a non-metallic material such as carbon / graphite in the appropriate volume ratio, the resulting composite material becomes a pure ionic conductor suitable for use as an electrolyte in an electrochemical device, unless the polymeric material or non-metallic material is itself an electronic conductor. When an ionic conductor is mixed with an electronically conducting polymer such as polypyrrole (PPY) or polyaniline (PAN), a metallic or electronically conducting non-metallic material such as carbon, graphene, or graphite, and / or one or more electronically conducting oxides / nitrides / carbides, the resulting composite becomes a mixed ionic / electronic conductor. For example, SrTi in the appropriate volume ratio. 0.5 Fe 0.5 O 3-δ When a mixed ionic / electronic conductor such as ZnO is mixed with another electronic conductor or insulator, the newly formed composite is potentially a mixed conductor.

[0202] The composite ceramic-polymer electrolyte 104 may include one or more hydrated oxides and / or hydrated or non-hydrated oxyhydroxides, as described above, mixed with one or more polymers. In some embodiments, the one or more hydrated oxides and / or hydrated or non-hydrated oxyhydroxides are the sole ionic conductors of the ceramic-polymer electrolyte 104, while the selected polymer may provide some ionic conductivity in other embodiments. The polymer component may provide a flexible support matrix for the ceramic. The ceramic may be provided as a powder for combination with the polymer. Sintering of the ceramic powder is generally not necessary, and indeed undesirable, when preparing the ceramic-polymer composite electrolyte 104. However, firing the powder at relatively high temperatures, typically in a reducing atmosphere or an atmosphere with a low oxygen partial pressure, has been found to be beneficial in some embodiments for the formation of desired oxygen vacancies in the oxide powder.

[0203] A typical method for preparing a ceramic-polymer composite electrolyte may be as follows: Obtain a suitable ceramic oxide starting material. If the material has an insufficient concentration of oxygen vacancies, the material may be calcined in an atmosphere with a low oxygen partial pressure, or optionally in a reducing atmosphere, to introduce more oxygen vacancies. For example, the material may be calcined in 5 vol% H2 / Ar or 5 vol% H2 / N2. The calcination temperature in this step may range from 200°C to 1200°C, optionally from 200°C to 700°C, and this temperature is selected based on the composition and structure of the material. Alternatively, or similar to this calcination step, the material may be treated with a reducing liquid or electrochemically reduced to introduce more oxygen vacancies. If the material is a sintered material rather than a powder, the material may be crushed to a powder to facilitate the fabrication of the polymer-ceramic composite. Dissolve one or more selected polymers in a suitable solvent, or prepare a polymer suspension. The oxide powder is then mixed with a polymer-containing liquid in a selected ratio. A ceramic-polymer membrane, pellet, or other article of the desired shape, size, and thickness is then formed, for example, by molding or printing. The composite article is then dried, for example, at room temperature or slightly warmer temperatures, to remove the solvent. The prepared ceramic-polymer article is then processed in water to react the ceramic components and achieve the desired ionic conduction properties, thereby forming a composite ionic conductor, such as an electrolyte.

[0204] The polymer(s) used to form the oxide-polymer composite electrolyte material are, in some embodiments, selected from the following list, although one skilled in the art will recognize that other suitable polymers may be used in place of or in addition to those listed. Nafion®, Nafion® Ionomer, high density polyethylene (HDPE), low density polyethylene (LDPE), polyether ether ketone (PEEK), polybenzimidazole (PBI), polyvinyl alcohol (PVA), poly(acrylic acid) (PAA), poly(arylpiperidinium) (PAP), poly(ethylene oxide) (PEO), polypropylene oxide (PPO), poly(ethylene glycol) (PEG), polysulfone (PS), poly(arylene ether sulfone) (PESF), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), poly(acrylonitrile) (PAN), polyurethane (PU), polyvinylpyrrolidone (PVP), polyacrylamide (PAAm), poly-(diallyldimethylammonium) (PDADMA), poly(vinylidene dimethicone) (PVdF), polyvinylidene fluoride (PVdF), polyvinylidene dimethicone ... Examples of suitable oxide-polymer composites include PVDF-HFP, polytetrafluoroethylene (PTFE), polybenzimidazole (PBI), polyvinyl chloride (PVC), chitosan, and alkaline ionomers. Those skilled in the art will appreciate that any polymer material previously investigated for proton exchange membrane fuel cells (PEMF) or alkaline membrane fuel cells (AMFC) may be suitable for forming oxide-polymer composites as described herein. In many embodiments, the polymer is selected to be water-insoluble because it may come into contact with water during use. However, when used as a battery electrolyte, for example, in a sealed environment without running water to dissolve the polymer, water-soluble polymers such as poly(vinyl alcohol) (PVA) or poly(acrylic acid) (PAA) may also be used.

[0205] SrFeO 5±δThe water-treated oxide powders described herein, such as those described herein, can therefore be mixed with one or more polymers to form, for example, polymer / oxyhydroxide composite electrolytes. Because the primary conduction relies on the conductive (hydrated or anhydrous) oxyhydroxide, the stability of these composite membranes can be very good. Therefore, the membranes can be thin, e.g., 25 μm to 100 μm thick, facilitating wetting of the material. A single polymer or a mixture of polymers may be used in the composite. In some embodiments, PVA and / or PEO are selected. Low-cost polymers, such as PVA, PEG, and PS, may be of particular interest to reduce the cost of the composite membrane.

[0206] In most embodiments, the polymer component is selected to be hydrophilic. However, a relatively small amount of a hydrophobic polymer may be used with another polymer; for example, a small amount of PTFE (which is generally hydrophobic) may be used to improve the mechanical strength of the composite. In embodiments in which the Nafion®-ceramic oxide electrolyte 104 is prepared, for example, in the form of a membrane, ionic conductivity is provided by both the Nafion® and the ceramic material. Thus, the overall ionic conductivity may be higher than that of a non-conductive polymer of the same volume percentage. The presence of the ceramic oxide in the membrane may reduce the level of oxidation of the Nafion® (e.g., by H2O2 generated at the fuel cell cathode), potentially reducing fuel cell degradation, since the oxide provides the desired ionic conductivity. The ceramic phase is primarily composed of OH. - When ionic conductors, the ceramic Nafion® membranes made therefrom generally + / OH - It is an ionic hybrid conductor. When used as the electrolyte 104 in a hydrogen fuel cell, water / steam can be generated at both the anode and cathode to wet the ceramic-polymer composite membrane, reducing the need for H2 on the anode side or air / O2 on the cathode side.

[0207] In various embodiments, the oxide powder may be mixed with a polymeric alkali ionomer to create an alkaline polymer-ceramic oxide composite membrane. The alkaline polymer in the ceramic oxide-polymer composite is an OH group, similar to Nafion®-ceramic oxide membranes. - Since they also conduct ions, the overall ionic conductivity can be higher than that of the same vol% non-conducting polymer. If the ceramic oxide is primarily a proton conductor, alkaline polymer-ceramic oxide membranes can also conduct H + / OH - When used as the electrolyte 104 in a hydrogen fuel cell 100, water / steam can again be generated on both the anode and cathode sides to wet the ceramic-polymer composite membrane, alleviating the need to wet H on the anode side or air / O on the cathode side.

[0208] In various embodiments, a wide range of ceramic volume percentages can be used. For example, a composite electrolyte 104 with only 1 vol% ceramic may function but may not offer any particular benefit in terms of performance and may be less efficient, especially if the polymer is an ion conductor (e.g., a protic or alkaline polymer). Above a ceramic volume percentage of approximately 33 vol%, the ceramic particles begin to form continuous pathways, improving conductivity. When using a strong polymer such as PMMA, the ceramic volume can be 80% or more to maximize ionic conductivity. For other polymers, more polymer matrix material may be required for structural integrity. In various embodiments, the ceramic (oxyhydroxide or hydrated oxide) is the primary conductive phase. In various embodiments, the ceramic (oxyhydroxide or hydrated oxide) comprises at least 30 vol% of the electrolyte. While the polymer used in the composite can be an insulator or an ion conductor, if an ion-conducting material is used as the electrolyte 104, it should be electrically insulating.

[0209] Ceramic-polymer composites using these ceramic materials may be produced using manufacturing techniques already known to those skilled in the art. For example, Nafion® membranes contain CeO (typically less than 20 wt%) to protect against oxidation / damage from HO generated in fuel cell cathodes, and reliable composite polymer-ceramic electrolyte membrane manufacturing techniques are known. Typical plastics known for use in molding may be used to form ceramic-polymer composites that result in very low cross-diffusion (examples of such polymers are provided here: https: / / www.plastikcity.co.uk / useful-stuff / material-melt-mould-temperatures). This may be very important in some embodiments to avoid chemical or gas crossover, for example, when used as an electrolyte membrane or gas separation membrane. The ionic or mixed ionic / electronic conductors described herein can be blended with polymers such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyamide (Nylon), polyvinyl chloride (PVC), poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK), polyvinylidene fluoride or polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), and fabricated into thin films (e.g., using hot pressing) or into different shapes by model casting or the like for different specific applications. The approaches described herein are not limited to hot pressing, model casting, or any particular forming technique. Any suitable technique for producing ceramic-polymer composites can be applied to the materials described herein.

[0210] Ceramic-polymer composite membranes made from some polymers, such as HDPE, may effectively minimize cross-diffusion of chemicals and gases between two compartments at the anode and cathode in electrochemical devices such as redox flow batteries / cells, fuel cells, electrolyzers, gas separation / purification, etc. Material properties may be tailored by forming composites with different polymers and / or other materials. The oxide / oxyhydroxide-polymer composite electrolytes described herein may provide one or more of the following advantages: Good mechanical strength and shape flexibility compared to pure ceramic electrolytes Ease of manufacturing (e.g. for continuous production of membranes / thin films) - Use of thin films reduces electrolyte resistance and increases fuel cell power density Better wettability of oxides / oxyhydroxides to maintain high ionic conductivity: For example, in fuel cells where aqueous liquid fuels are used as the anode but the cathode is exposed to dry or humid air, the wettability of the ceramic material in the electrolyte on the cathode side of dense pure ceramics may not be sufficient to achieve high ionic conductivity, especially when ionic conductivity relies on hydrated oxides. However, replacing the pure ceramic membrane with an oxide / oxyhydroxide-polymer composite membrane may maintain higher ionic conductivity because the polymer allows water at the anode to more easily diffuse into the membrane and wet the ceramic material.

[0211] Although less flexible, pure ceramic electrolytes or ceramic-ceramic composite electrolytes have unique advantages, such as avoiding cross-diffusion of chemicals or gases between the two sides of an electrochemical device, and may be preferred in various applications, such as many electrolyzers and flow batteries, and fuel cells with liquid fuels on both sides. A method 900 for forming the solid electrolyte 104 of the above embodiment will now be described with reference to Figure 9. In summary, the method 900 includes: Obtaining a ceramic oxide material (902). The ceramic oxide material is the starting material for forming the solid electrolyte 104 and may be as described above. Creating further (additional) oxygen vacancies in the ceramic oxide material (904). This may be done by calcination, where the temperature and atmosphere may be selected to suit the material in question in order to introduce oxygen vacancies into the material. Alternatively or additionally, this may be done by treatment with a reducing liquid (904) or by electrochemical reduction (904). Treating the ceramic oxide material with water to form hydrated oxides, hydrated oxyhydroxides, and / or anhydrous oxyhydroxides (906).

[0212] Obtaining step 902 may include obtaining (902) a ceramic oxide material from one of the three families described above. Those skilled in the art will appreciate that for some of the materials described herein (e.g., Ca3Co2O6), the material may have sufficient oxygen vacancies to provide good ionic conductivity after treatment with water even without performing step 904, for example, if the material is prepared by standard techniques including calcination in air. Thus, while step 904 is not believed to be necessary for the formation of all electrolytes 104 as described herein, it can further improve performance even when viable electrolyte properties are obtained without intentionally adding additional oxygen vacancies. In some embodiments, a ceramic-ceramic composite material may be desired. To create a ceramic-ceramic composite, precursors for preparing a ceramic material from one of the three families described above may be mixed with one or more ceramic materials selected to be non-reactive with the precursor or the resulting ceramic ionic conductor. Alternatively, a ceramic ionic conductor of one of the above three families may be made first, for example by firing in air, and then mixed with another ceramic material (or optionally multiple other ceramic materials) to form a mixture, which may then be shaped and fired again in air (or fired in a controlled atmosphere such as N, Ar, or 5% H / Ar) to form a ceramic-ceramic composite.

[0213] Step 906 of treating the material with water before use may involve a relatively long water treatment, for example, from 1 to 2 hours to 2 weeks, depending on the material, the temperature, and the type of water exposure (e.g., steam or liquid water). After the first treatment 906, the ionically conductive material is then preferably kept in a humidified environment until and during use. If the material is kept in a dry / non-humidified environment, a second treatment may be performed to restore ionic conductivity. This second treatment may take only a few minutes, especially if performed at a relatively high temperature (e.g., 90°C). Again, the suitable treatment time may depend on the material structure and composition.

[0214] In particular, the ceramic oxide material is an oxide having a perovskite, brownmillerite, or K4CdCl6 structure, and includes A-site ions of one or more elements selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb, and Bi, In, and Tl, and B-site ions of one or more elements selected from Ln (e.g., Ce, La), Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, As, Sb, Zr, Hf, Nb, Mo, W, Cd, Rh, Mg, Ba, and Ta, and optionally Pt, Ir, and Ru. The ceramic oxide material may be a single phase (without impurities) or may include multiple different phases. The ceramic oxide material may be in the form of a powder, optionally a fine powder. Ceramic oxide materials may be prepared by any suitable technique known in the art, such as solid-state reactions, sol-gel processes, co-precipitation, PVD (physical vapor deposition), CVD (chemical vapor deposition), spray pyrolysis (NSP), combustion synthesis, solvothermal synthesis, microwave synthesis, or pulsed laser deposition (PLD). Typically, oxide materials are prepared using solid-state reactions with precursors such as oxides, carbonates, and / or nitrates. However, any other method known to be suitable, such as those listed above, may also be used. When preparing Cl-, Br-, S-, or Se-doped oxides, solution thermal synthesis with the addition of Cl-, Br-, S-, or Se-precursors may be used.

[0215] The obtained ceramic oxide material is then treated (904) to introduce additional oxygen vacancies. If treatment 904 is performed by calcination, the calcination atmosphere may be air, or may be N, Ar, H, mixed H / N, mixed H / Ar, NH, CH, or other inert or reducing atmosphere. The atmosphere may be selected based on the chemical composition and / or structure of the oxide material. In various embodiments, the principle is to maximize the oxygen vacancy concentration while avoiding destruction of the crystalline structure or decomposition of the oxide.

[0216] In various embodiments where a pure ceramic electrolyte 104 is desired, the ceramic oxide material is sintered. This sintering may occur simultaneously with or before the calcination 904 to introduce oxygen vacancies. The sintering process involves suitably shaping the powder (e.g., pellet formation or tape casting) and firing at a temperature selected to provide sufficient mechanical strength for the sintered material to maintain its shape (e.g., pellet or film). The firing temperature may be 50°C to 300°C below the melting point of the ceramic oxide material, and optionally, 50°C to 200°C below the melting point. In some embodiments involving certain materials, sintering may be achieved even below the melting point, e.g., 50°C to 700°C below the melting point. The use of sintering aids, such as H3BO3, can be effective for sintering at lower relative temperatures; such sintering aids can lower the minimum temperature required for sintering.

[0217] For the various oxides tested, the optimum calcination temperature was found to be between 800° C. and 1200° C. More generally, in various embodiments, the calcination temperature may be in the range of 300° C. to 1700° C. or 500° C. to 1700° C., optionally in the range of 500° C. to 1500° C. or 700° C. to 1400° C., and further optionally in the range of 800° C. to 1200° C.

[0218] In embodiments in which the electrolyte 104 is fabricated by PVD, CVD, or other methods of forming structured solids, an oxide material film or pellet may be formed directly, and sintering may not be necessary. If the formed material does not have a sufficiently high concentration of oxygen vacancies, a subsequent calcination step may be performed in a reducing, inert, or other atmosphere with a low oxygen partial pressure to introduce more oxygen vacancies. Additionally or alternatively, the formed material may be treated with a reducing liquid (904) or electrochemically reduced (904). In embodiments in which the formed oxide material contains sufficient oxygen vacancies, the calcination step or other treatment step 904 may not be necessary. In the case of oxide materials made by physical vapor deposition (PVD) and pulsed laser deposition (PLD), preparation is often performed under vacuum or in an inert gas atmosphere, and it will be appreciated that such materials may have a sufficient concentration of oxygen vacancies without further processing.

[0219] In embodiments where a pure ceramic electrolyte 104 is desired, the sintered material may be in the form of a ceramic membrane, film, pellet, or block, optionally formed into the shape and size desired for the target electrochemical device 100. The ceramic membrane or film may be made by any suitable method known in the art, such as, for example, pressing into pellets, screen printing, tape casting, gel casting, slip coating, dip coating, spin coating, sol-gel processing, PVD, or CVD. The obtained oxide material may be shaped prior to sintering so that it retains the desired shape after firing / sintering.

[0220] In embodiments in which a composite polymer-ceramic electrolyte 104 is desired, sintering is generally not performed. The ceramic oxide material is provided as a powder to facilitate blending (908) with one or more polymers to form a homogeneous film (e.g., having a thickness on the order of 100 μm). The powder particle size may be selected to be fine enough to easily produce a film of the desired thickness and coarse enough to provide good contact with the oxide phase (it will be understood that having more grain boundaries will decrease ionic conductivity, as ion migration through grain boundaries is generally more difficult than through bulk material). Thus, the powder particle size may be selected as appropriate for the material and the desired electrolyte shape. Blending (908) of the ceramic and polymer components of the composite electrolyte 104 may be performed before or after treatment with water (906) and before or after adding oxygen vacancies to the ceramic material (904). The order shown in FIG. 9 may be representative of various embodiments and is not intended to be limiting. Step 908 is generally not performed at all for pure ceramic electrolytes 104.

[0221] In various embodiments, loose powder (i.e., the powder is not pressed or otherwise compacted, as may be done for pure ceramic electrolytes) is fired (904) at a selected temperature in a selected atmosphere to introduce oxygen vacancies. While the temperature and atmosphere selection may be as described above, lower temperatures (and / or shorter firing times) may be preferred in some embodiments to avoid sintering. The use of lower firing temperatures may also reduce energy costs. In some embodiments, firing oxide materials at lower temperatures in air, Ar, or nitrogen may result in fired materials with oxygen vacancy concentrations that are not high enough to form good ionic conductors. However, firing samples in a reducing atmosphere, such as pure H, may promote the formation of single-phase oxides with sufficient oxygen vacancy concentrations at much lower temperatures (e.g., 400°C to 500°C or more below the melting temperature).

[0222] To minimize costs, the simplest method for preparing oxide materials is generally to prepare and calcinate them in air rather than in an inert or reducing atmosphere. However, it has been found that oxides produced by calcination in air often do not have a sufficiently high concentration of oxygen vacancies (although in some cases, such as the Ca-deficient Ca3Co2O6 example mentioned above, the concentration is sufficient). In fact, many oxides having the brownmillerite structure cannot be formed by calcination in air, but can be formed by calcination at high temperatures in Ar or N2. Therefore, in some embodiments, the oxide material is calcined in air. It will be appreciated that calcination in air is generally less expensive and requires less equipment than calcination in other environments. When oxide materials are calcined in air, the oxygen vacancy concentration is often relatively low. The calcined oxide material (e.g., in the form of oxide pellets or powder) may be treated (904) with a reducing agent, such as a reducing liquid, to increase the concentration of oxygen vacancies. The concentration and temperature of the reducing liquid can be carefully controlled so that some of the lattice oxygen in the oxide is removed and additional oxygen vacancies are created. If calcination 904 is not performed in air, treatment with a reducing liquid 904 may still be used if it is desired to further increase the oxygen vacancy concentration.

[0223] The reducing liquid may be an aqueous solution, in which case the reducing liquid treatment 904 may also serve as the water treatment 906. In such embodiments, the formed oxygen vacancy-rich oxide may simultaneously react with HO in the reducing liquid to form a hydrated oxide or a hydrated or anhydrous oxyhydroxide. In additional or alternative embodiments, the material may be subjected to the water treatment 906 after the reducing liquid treatment. The use of a reducing liquid may serve to convert an electronic conductor to an ionic conductor. For example, sodium borohydride or potassium borohydride may be used as the reducing agent.

[0224] The reducing agent may be a mixture of NaBH4 / NaOH, or a mixture of KBH4 / KOH, or similar. The use of NaOH (or KOH) avoids the hydrolysis of NaBH4 (or KBH4, if applicable). For example, Sr2Co2O5 becomes an electronic conductor in water when calcined in air. After calcining in Ar, it becomes an ionic conductor in water, but high-temperature calcination in Ar is costly, so the use of a reducing agent instead is preferred. Sr2Co2O5 material can be converted to an ionic conductor by placing it in a bath of a NaBH4 / NaOH aqueous mixture and treating it at room temperature or by heating (e.g., to 45°C or 90°C), thereby avoiding more costly high temperatures. The preparation of Sr2Co2O5 pellets ("Sr2Co2O5-1100 air pellets") following such a reduction treatment and calcining in air at 1100°C is described below. Sr2Co2O5 was prepared by standard solid-state techniques. 21.59 g of Sr(NO3)2 and 29.79 g of Co(NO3)2 6H2O were ground to form a mixture and then calcined in air at 600 °C for 8 hours with a cooling rate of 1 °C / min. This powder was then ground and calcined in air at 1100 °C for 3 hours with a cooling rate of 1 °C / min to give SrCoO 2.5The as-prepared powder was then pelletized and sintered in air at 1100 °C for 3 h with a cooling rate of 1 °C / min. XRD patterns indicated the formation of a single phase. The Sr2Co2O5-1100 air pellet was then immersed in a reducing agent of 1 M NaOH + 7 M NaBH4 at room temperature (RT) for 2 h, followed by immersion in deionized water overnight at room temperature. The pellet was then immersed in the same reducing agent at room temperature for 3 h and heated in water at 90 °C overnight. This process was repeated twice, so the total chemical reduction time (total time in reducing agent) of the pellet was 8 h (at room temperature). The pellet was then rinsed with deionized water to remove any remaining reducing agent, dried at room temperature, and coated with silver conductive ink (RS Components) to facilitate conductivity testing. To test the conductivity of the Sr2Co2O5 pellets in water after the above treatment process, silver conductive ink (RS Components) was applied to both sides of the pellets to form Ag electrodes. The Ag paste was allowed to dry at room temperature for 40 minutes. The resulting sandwich cell, consisting of a layer of pellets sandwiched between two layers of silver mesh, was then fixed in a fixture. The Ag-coated pellets were then treated in fresh water at 90°C prior to conductivity testing to allow the pellets to absorb water. Electrochemical impedance spectroscopy (EIS) was then performed using a Solartron 1470 / 1455 with an amplitude of 10 mV and a frequency range of 1 MHz–0.01 Hz. The DC conductivity of the pellets was measured using a pseudo-four-probe method, applying a constant DC voltage of 10 mV to the pellets and recording the current to determine the electrical resistance. Figure 31 shows the conductivity data for the sample prepared as described above, demonstrating high conductivity at temperatures above 60°C.

[0225] Another process 904 that can be used to generate oxygen vacancies in oxides at ambient temperature (room temperature), either as an alternative to or similar to the reducing liquid treatment, is electrochemical reduction 904. It is well known that graphene oxide can be reduced to graphene by an electrochemical reduction process. The same process 904 can be applied to partially reduce oxides prepared in air in an electrochemical cell to form oxides rich in oxygen vacancies (removing lattice oxygen). The partially reduced oxide can then be reacted with water (906) to simultaneously or subsequently form oxyhydroxides and / or hydrated oxides. Process 904 can be performed at ambient temperature and pressure on a benchtop / without a controlled atmosphere, thereby maintaining low costs.

[0226] In other embodiments, the oxide material is fired (904) in an atmosphere with a reduced oxygen partial pressure relative to air, such as nitrogen, argon, or another inert gas, or a mixture of air and an inert gas. In various cases, particularly if sintering is desired, the lower the oxygen partial pressure of the atmosphere in which the material is fired, the higher the firing temperature required for the same material. As used herein, the term "low oxygen partial pressure" refers to a partial pressure of oxygen lower than that of air (which is approximately 21% oxygen, resulting in a partial pressure of approximately 0.21 atmospheres, or approximately 21 kPa). In some embodiments, an oxygen partial pressure of approximately 0.01 atmospheres (approximately 1 kPa) is preferred. In some embodiments, the oxide material is fired in a reducing atmosphere containing a reducing agent, such as H or CO. For example, atmospheres containing 5 vol% H in Ar, or pure H, or different concentrations of H in Ar or N may be used. In general, for a given oxide material, the higher the concentration of H, the lower the firing temperature. High temperature itself can be considered a reducing agent. Thus, for the same material, higher calcination temperatures generally result in higher concentrations of oxygen vacancies and therefore higher ionic conductivity after reaction with water. If the calcination temperature is too high, the oxides can be over-reduced, causing lattice collapse and further decomposition into other mixed oxides, metals, and oxides that are more stable under reducing conditions.

[0227] As mentioned above, if the oxide calcined in air (for example) does not have a sufficiently high concentration of oxygen vacancies, the calcined material can be placed in a liquid reducing environment prior to the water treatment 906 to simultaneously reduce and water treat, or it can be treated with an aqueous reducing solution 906. For example, a mixture of hydrazine (NH) or NaBH / KBH with an alkaline solution such as NaOH(aq) or KOH(aq) can be used to partially remove lattice oxygen atoms to produce an oxide rich in oxygen vacancies. The reducing liquid can partially reduce any polyvalent elements (e.g., Mn, Fe, Co, Ni, Cu) in the B site of the oxide, generating oxygen vacancies. This can be simpler and more cost-effective than calcining in 5% H / Ar or 5% H / N. The length of time selected for immersion in the reducing environment generally depends on the chemical composition of the oxide, the concentration, reactivity, and temperature of the liquid reducing agent. For ceramic materials, suitable parameters may be selected to create more oxygen vacancies without destroying the structure.

[0228] In various embodiments, the oxides are prepared by solid-state reaction methods, as described above. For example, to prepare SrFeO, SrCO and FeO were mixed in a ball mill at 300 rpm for 12 hours and then calcined in air at 1100 °C for 55 hours with a heating / cooling rate of 5 °C / min. The powder was crushed and pelletized, and then calcined in argon at 1200 °C for 8 hours (904).

[0229] When preparing ceramic films by tape casting, for example, the obtained oxide material can be first prepared in air and then mixed with one or more binders to prepare a thin film by tape casting. This thin film can then be fired in air at temperatures up to 700°C to burn out the organic binders in the tape-cast film. A further firing step can then be performed in an atmosphere with a low oxygen partial pressure, such as N2 or Ar (inert gas), optionally at a higher temperature. Some sintering may occur in the first firing step. A second firing step can be used to ensure the material is sintered to the desired level and to introduce oxygen vacancies.

[0230] Thus, calcination may be performed in one or two steps. In the single-step process, when preparing oxide materials by a solid-state reaction method, the oxide / carbonate precursors may be pre-calcined to decompose the carbonate precursors, and the pre-calcined powder may then be pressed into pellets. The pellets may then be directly calcined in air or (for example) in N or Ar. The temperature for calcining the pellets depends on the melting point of the material and is typically between 700°C and 1300°C. This calcination 904, in some embodiments, both sinters the material and introduces any additional oxygen vacancies as desired; alternatively, a subsequent non-calcination step (e.g., electrochemical reduction) may be used to introduce additional oxygen vacancies. In the two-step calcination process, the pellets may first be calcined in air to obtain sufficient mechanical strength, typically with a relative density of ≥ 70%. These pellets can then be fired at relatively low temperatures (e.g., 50°C to 600°C) in a reducing atmosphere (e.g., 5% H2 / Ar or 5% H2 / N2) to remove some of the lattice oxygen to create more oxygen vacancies.

[0231] For a one-stage (single-step) firing process 904, the residence time typically varies from a few hours to 48 hours, often on the order of 4 to 10 hours. For many of the oxide materials described herein, 4 hours is sufficient to obtain pellets with good mechanical strength, provided the temperature is very close to the melting point of the material. For a two-stage (two-step) firing process, firing in a reducing atmosphere 904 is typically carried out for up to 48 or 72 hours. The firing temperature is typically determined from simultaneous thermal analysis (STA) in the atmosphere and is selected to indicate the temperature at which the ceramic material begins to lose oxygen / mass. It should be noted that too high a firing temperature or too long a firing time can lead to oxide decomposition.

[0232] The calcined material is then treated with water (906) to form hydrated oxides and / or oxyhydroxides (which may be hydrated or anhydrous) from the oxide starting material. The water treatment 906 may also be carried out in a variety of ways. For example, oxygen-vacancy-rich oxide pellets (e.g., calcined in Ar or N, or calcined in air and then optionally reduced) may be immersed in (liquid) water at room temperature for 4 days. Alternatively, the oxide material may be treated in an atmosphere containing at least 1 vol.% water, optionally containing at least 3 vol.% to 4 vol.% water (e.g., as water vapor in a humidified gas stream or as steam), and optionally containing at least 5 vol.% water to form the desired hydrated or unhydrated metal oxyhydroxides and / or hydrated oxides. In embodiments where the oxide material was calcined in air but did not undergo any reduction treatment after calcination, treatment with liquid water or an atmosphere containing at least 5 vol.% water may be required. For example, air or another carrier gas may be passed through water at 25°C (e.g., using a gas bubbler). The resulting air stream may have a moisture content of around 3 vol%. Alternatively or additionally, steam may be used.

[0233] The duration selected for treatment 906 depends on the porosity / relative density and tortuosity of the material, the size and shape of the material (e.g., pellet or thin film), and the nature / composition of the oxide. Increasing the temperature of the water may promote a reaction between oxygen-vacancy-rich oxides and water to form hydrated or unhydrated metal oxyhydroxides and / or hydrated oxides, so the duration may be shortened for higher temperature water treatment 906. Too high a temperature (e.g., hot steam) may cause material degradation. Also, shorter durations may be used for thinner and / or more porous materials and materials that are more reactive with water. For example, a duration of less than 1 hour, or a duration equal to or about 2, 8, 10, 24, 48, or 72 hours may be selected. At the same temperature, the exposure time selected in a humid atmosphere may be longer than that in liquid water, although increasing the temperature of the atmosphere and / or using steam instead of water vapor in the humidifying gas stream may change that balance. When steam is used to produce ionically conductive (optionally hydrated) oxyhydroxides or hydrated oxides, the exposure temperature is limited to be below the decomposition temperature of the desired (optionally hydrated) oxyhydroxide or hydrated oxide. Increasing the volume percentage of water may also shorten the time.

[0234] In embodiments where the material is treated in an atmosphere containing at least 1 vol% water (and optionally at least 5 vol% water), steam (at temperatures above 100°C at standard pressure) or water vapor (e.g., humidified air flow at ambient pressure and temperature) may be selected depending on the material. For example, SrFeO 2.5-x (OH) 2x In the case of nH2O, the material is stable in liquid water at temperatures below 100 °C, or in an atmosphere saturated with water vapor at such temperatures (e.g., 80 °C). Thus, the hydrated oxyhydroxide SrFeO 2.5-x (OH) 2xnH2O is formed and remains stable. When the temperature rises above 100°C, this phase may begin to lose hydration water from the lattice. The charge carriers are the hydration water in the lattice and the OH - ions, the loss of HO means the loss of charge carriers. + and / or OH - For ionic charge carriers, the conduction path may rely on lattice HO, and the loss of hydrated HO in the lattice leads to the formation of H + ions and / or OH - In either case, the loss of lattice water is undesirable because it reduces ionic conductivity. Therefore, liquid water or water vapor may be used instead of steam. + ions and / or OH - When ion transport is less dependent on lattice HO, the loss of HO does not significantly affect conductivity, so the anhydrous phase SrFeO 2.5-x (OH) 2x Ionic conductivity of (n=0) may be maintained. 2.5-x (OH) 2x nH2O and SrFeO 2.5-x (OH) 2x The temperature range over which is stable depends on the partial pressure of H2O, pH2O. The higher the pH2O, the higher the decomposition temperature of the material. 2.5-x (OH) 2x At this point, the material changes from an ionic conductor to an electronic conductor or semiconductor and is no longer useful as an electrolyte material.

[0235] For most materials described herein, an atmosphere of at least 1 vol% to 3 vol% (and optionally at least 5 vol%) water at standard pressure (1 atmosphere) is sufficient for the reaction, eliminating the need for pressurization. The selected temperature may be room temperature or the operating temperature of the electrochemical device 100. A saturated air flow at a predetermined temperature may be used. These conditions may be relatively easy to achieve in situ within the device 100 (e.g., in a PEMFC 100), so that the correct phase can be generated and maintained in situ by heat exchange with the device 100, for example, if the selected temperature is higher than room temperature. For example, if the operating temperature of a hydrogen fuel cell is 80°C, the air or O supplied to the cathode may be supplied at 80°C and saturated at that temperature. These conditions are already provided in commercial hydrogen fuel cells based on Nafion® electrolyte. The operating temperatures of other electrochemical devices 100, such as fuel cells using pure ceramic membranes 104 or ceramic-polymer composite membranes 104, can exceed 100°C, optionally as high as 200°C. A steam saturated air stream at 200°C may be supplied to the cathode at ambient pressure, or a combination of steam and water vapor may be present. High pressure is not necessary. If the temperature is further increased, increased pressure may be desirable. As mentioned above, H + / OH - When the hybrid membrane is used as the electrolyte in a hydrogen fuel cell, the need for deliberate / additional wetting of the electrolyte may be reduced, as water / steam can be generated on both the anode and cathode sides to provide sufficient wetting.

[0236] In various embodiments, the operating temperature may be 120°C or less. At temperatures above 100°C, the electrochemical device 100 may be pressurized or supplied with pressurized steam, if applicable, to maintain hydration of the ion-conducting layer. Most electrochemical devices operate at pressures close to ambient. However, in some electrochemical devices, such as water electrolyzers, outlet H2 and O2 pressures may be as high as 30 bar (3000 kPa) or even as high as 50 bar (5000 kPa). At 120°C, with a pressure of 2 bar (200 kPa), water is still in a liquid state and may play a role in hydrating the oxide-ion conductor. When used in a water electrolyzer, if the outlet gas pressure is 5000 kPa, water will still be in a liquid state even at temperatures as low as 250°C. As long as the operating temperature of such an electrolyzer does not exceed 250°C, e.g., 230°C or 250°C, liquid water can be used to provide smooth operation of the ion-conducting layer. The equilibrium pressure of water at 265°C is approximately 5000 kPa. If the outlet pressure of the H2 and O2 outlets from the electrolyzer is 5000 kPa, the operating temperature of the water electrolyzer will be high, for example, 265°C. Therefore, by adjusting the pressure appropriately, a liquid water working environment at elevated temperatures (above 100°C) can be provided. Alternatively, for ion-conducting materials that require hydration for sufficiently strong ion-conducting performance, a gaseous environment containing at least 5 vol% steam may be provided at elevated temperatures.

[0237] For various oxides in the three identified families, we found that a water immersion period of at least 48 hours yielded the highest ionic conductivity. However, acceptable conductivity can be achieved in shorter time frames. For example, Ca3Co2O6 immersed in water for approximately 2 hours had an ionic conductivity of 0.001 S / cm, but after immersion in water for 3 days at room temperature, this increased to 0.053 S / cm at 90°C. Other oxides with higher water reactivity or in different forms (e.g., thinner films or granules for use in composite electrolytes) may be able to obtain acceptable conductivity with even shorter immersion periods. For many oxides, the conductivity of the tested ceramic pellets was found to increase during immersion in water and then reach a plateau. For samples with higher relative densities (i.e., lower porosity) (compared to theoretical density), longer immersion periods were required due to slower water diffusion into the pellet's center. For most pellets tested (with diameters on the order of 12–13 mm and thicknesses on the order of 2 mm), 4 days at room temperature is sufficient to reach a steady state. Increasing the temperature promotes the formation of oxyhydroxides (hydrated or anhydrous), allowing for shorter periods. It will be appreciated that shorter periods are sufficient for smaller / thinner pellets. The composition and reactivity of the oxide material also influence the time required to reach a steady state. For some relatively reactive materials, such as Ca6Co2O6, it takes only a few minutes for the reaction with water to convert the semiconductor to an ionic conductor, but longer times are required to achieve ionic conductivity high enough for use in electrochemical devices, sometimes requiring 48 hours of immersion in water at room temperature.

[0238] When forming a pure ceramic electrolyte, the sintered ceramic oxide may have a relative density of 60% to 99% (i.e., a density that is 60% to 99% of the theoretical density at that structure), optionally a relative density of 70% to 85%. After reaction with water, the relative density may increase to 70% to 99%, optionally to 85% to 99%. After reaction with water (906), the formed (hydrated or anhydrous) oxyhydroxide or hydrated oxide may have a porosity of 1% to 30%, optionally 1% to 15%, and even optionally 1% to 5%. Generally, lower porosity (and therefore higher density) is preferred, for example, to minimize or avoid hydrogen or other fuel / reactant crossover and maximize available ionic conduction paths. If the ionic conductivity is high enough, thicker films / layers can be used as the electrolyte, and a lower relative density can be tolerated (i.e., sufficient to minimize or avoid crossover of, for example, hydrogen or other fuels / reactants). Closed pores tend to reduce conductivity but generally do not affect the tightness of the electrolyte 104. Open pores reduce conductivity and also affect the tightness of the electrolyte 104 (enabling potentially harmful crossover). Therefore, the desired porosity boundary is related to both the thickness of the electrolyte 104 and the properties of the pores (e.g., tortuosity). The upper thickness limit of the electrolyte 104 may be based on ionic conductivity.

[0239] It has also been found that the mechanical strength of ceramic materials can be adjusted by changing their composition. For example, SrCoO 3-δ The mechanical strength of the oxyhydroxide derived from the reaction between SrCo and water was found to be relatively low, but by doping the B site with Ti, it was possible to obtain SrCo 0.5 Ti 0.5 O 3-δ Instead, forming a polymer-composite electrolyte improved the mechanical strength, which may be more important for dense ceramic membranes or films than for polymer-composite electrolytes.

[0240] In the described embodiment, the sintered ceramic material is treated 906 uniformly on all exposed surfaces, allowing time for the water to diffuse throughout the structure.

[0241] Therefore, to obtain higher ionic conductivity, ceramic oxide materials having oxygen vacancies are reacted with water to form hydrated oxides and / or (optionally hydrated) oxyhydroxides, generally by immersing the ceramic oxide in water for several days, typically 2 to 4 days.

[0242] As-prepared oxides generally lack water of hydration as a result of the relatively high temperature calcination process 904 used in many embodiments. When these oxides are treated with water 906, four main possibilities exist for the electrolyte materials described herein: ·Oxides absorb water to form hydrated oxides, and the water molecules become incorporated into the lattice. For example, Sr2Fe2O5 in the brownmillerite structure can react to form Sr2Fe2O5·nH2O. ·Oxides react with water to form anhydrous oxyhydroxides. For example, Sr2Fe2O with the brownmillerite structure 5±δ , or SrFeO with a large δ value 3-δ Perovskite structures of similar composition with relatively high concentrations of oxygen vacancies, such as SrFeO x (OH) y Anhydrous oxyhydroxides such as: ·Oxides react to form hydrated oxyhydroxides. The oxides react to form mixtures of metal hydroxides with one or more of the above (especially in the case of oxides that are not chemically stable).

[0243] For a given oxide material, the temperature, water concentration, and duration of treatment 906 can all affect the resulting product. In some embodiments, a mixed-phase product may be formed, including, for example, both hydrated and anhydrous oxyhydroxides, optionally with one or more metal oxides or hydroxides intermixed with the desired oxyhydroxides and / or hydrated oxides. If suitable hydrated oxides or oxyhydroxides are not formed, or if inadequate amounts of such compositions are formed, the conditions of calcination 904 or water treatment 906 may be adjusted, and / or an additional step 904 to introduce oxygen vacancies, such as treatment with a reducing liquid, may be performed.

[0244] For many oxide materials tested, treatment with water at temperatures around 25°C produced hydrated oxyhydroxides. Heating the samples slowly lost water of hydration, forming anhydrous oxyhydroxides. Further heating resulted in further water loss, returning the oxides to the oxygen-deficient forms initially formed. This process was therefore shown to be reversible. In rare cases, treatment of sintered ceramic materials with water was found to directly form anhydrous oxyhydroxides. When heating was performed in humid air rather than ambient air, the loss of HO generally occurred at slightly higher temperatures due to the higher pH.

[0245] At temperatures above 100°C, most hydrated oxyhydroxides become anhydrous; that is, n=0 for many of the materials tested. Despite the loss of water, the anhydrous oxyhydroxides tested were found to maintain good ionic conductivity. This is believed to be, at least in part, because ionic mobility increases at high temperatures, compensating for the lost water pathways. At low to intermediate temperatures (e.g., between 10°C and 200-300°C), the hydrated and / or anhydrous oxyhydroxides of the materials described herein may be good ionic conductors. Decomposition of the oxyhydroxide phase into oxygen-deficient oxides converts the material from an ionic conductor to an electronic conductor or semiconductor, as observed for most oxides with first-row transition elements in the B-site.

[0246] The electrochemical device 100 may be configured to operate at relatively low temperatures, for example below 200°C, optionally below 100°C, and even optionally below 90°C or 60°C.

[0247] The electrochemical device 100 may be configured to keep the electrolyte 104 humidified (wet). For example, steam may be supplied to both the anode and cathode sides of the fuel cell, or room temperature water may be passed through the gaseous fuel (e.g., H2 or NH3, or indeed CO or CH4) and oxidant (air or O2 or HO2) as they approach the electrolyte 104 to provide water vapor. At operating temperatures below 100°C, a supply of water at the saturation vapor pressure at that temperature is generally sufficient to maintain the electrolyte 104 in the desired phase. At temperatures above 100°C, the vapor pressure for saturation at 100°C is generally sufficient to maintain the electrolyte 104 in the desired phase. The electrolyte 104 of the hydrogen fuel cell 100 is typically composed of primarily OH. - When an oxyhydroxide electrolyte, which is an ion conductor, is used, water is generated at the anode, wetting the electrolyte membrane on the anode side. When the electrolyte is a proton conductor, water is generated at the cathode. + / OH - As a mixed conductor, water / steam can be generated at both the anode and cathode of a hydrogen fuel cell, allowing the electrolyte to be automatically wetted. By adjusting the composition, oxides with brownmillerite, perovskite, or K4CdCl6 structures treated with water can be used to automatically wet the electrolyte. + / OH - They may exhibit mixed conductivity, which may be particularly beneficial for the electrolyte 104 for hydrogen fuel cells.

[0248] In the case of aqueous batteries, electrolysis cells, redox flow batteries, etc., the electrolyte 104 often remains in liquid water and may not require humidification during use. In fuel cells 100 using liquid fuels such as methanol, ethanol, ammonia solution, urea solution, hydrazine, or aqueous borohydride solutions, water is often present in the fuel solution and may be sufficient to keep the entire electrolyte 104 wet. For example, it may wet the ceramic membrane if it is thin enough, or it may diffuse into the hydrophilic polymer of a ceramic-polymer composite membrane. Wetting the gas in the cathode compartment may be unnecessary or a minimum requirement in such embodiments; for example, passing air / O2 through room-temperature water may be sufficient without the need for any steam introduction. Performance can be improved by using waste heat or a separate heater to heat the water to a temperature close to or equal to the cell's operating temperature and passing the gas through the heated water.

[0249] Some fuel cells use aqueous hydrogen peroxide (HO) solutions as the oxidant at the cathode. This can be particularly useful in fuel cells based on the hydrated oxide electrolytes described herein because the water in the HO solution can maintain the electrolyte's high ionic conductivity. Such electrochemical devices may be particularly useful in certain (niche) applications where air / O is not readily available, such as submarines and space shuttles, because this type of fuel cell can generate electricity without O or air. For example, aqueous ammonia, urea, hydrazine, methanol, or ethanol solutions may be supplied to the anode, and aqueous HO may be supplied to the cathode. The fuel and oxygen can be replaced as they deplete, providing a fast alternative to battery recharging. Ammonia / HO, urea / HO, NH / HO, methanol / HO, or ethanol / HO fuel cells could potentially be used in portable applications and to power electric vehicles. The aqueous fuel at the anode is not limited to ammonia, urea, hydrazine, methanol, and / or ethanol, and similarly, the aqueous oxidant is not limited to aqueous H2O2, as examples only.

[0250] In some electrochemical devices 100, such as water electrolyzers, aqueous batteries, and some flow batteries, the electrolyte 104 is exposed to liquid water on both the anode and cathode sides during use. In some embodiments, the liquid water may be provided as part of a liquid mixture or solution that also includes, for example, alcohol, ammonia, urea, hydrazine, or borohydride. This exposure to liquid water can be beneficial in developing and maintaining the ionic conduction properties of the materials described herein. At drier operating conditions, conductivity is slightly lower (although still sufficient for an electrolyte), so measurements of the conductivity of the various materials described herein in water may most accurately reflect their conductivity in this working environment.

[0251] In various embodiments where the solid oxide ion conducting layer 104 is exposed at the anode to liquid water (e.g., most cases when used as an electrolyte in an electrolytic cell) or a fuel containing liquid water (such as aqueous solutions of ammonia, urea, hydrazine, borohydride, methanol, and / or ethanol), or at the cathode to an oxidant containing liquid water (such as aqueous HO), the water content need not necessarily be as high as 5%. For example, a direct ethanol fuel cell using a 98 vol% ethanol / 2 vol% HO mixture may have the solid oxide ion conducting layer described herein as the electrolyte, and 2 vol% liquid water may be sufficient, even for ion-conducting materials that require at least 5 vol% water in the gas stream to ensure good ionic conductivity. As long as the oxide is in contact with a medium containing “liquid” water, the volume percentage of water may be lower than the amount selected for a gas stream containing steam (a minimum of 5 vol% is preferred to maintain high ionic conductivity). For operating temperatures above 100° C., the electrochemical device may be pressurized above ambient pressure if it is intended to maintain exposure to liquid water. Also, if a humidified gas stream / atmosphere is used instead of a mixture of steam and gas stream / atmosphere, a minimum of 5 vol% HO may be selected.

[0252] When the solid oxide ion conducting layer described herein is used in an environment containing multiple gases, such as when used as the electrolyte in a hydrogen fuel cell, both the hydrogen (or other fuel) at the anode and the O / air (or other oxidant) at the cathode may be humidified to include at least 5 vol% HO in the H / H0 mixture at the anode and the air / H0 mixture at the cathode to provide high ionic conductivity for smooth operation of the electrochemical device.

[0253] When the solid oxide ion conducting layers described herein are used in a sealed environment, such as a battery or supercapacitor, contact with a flow or supply of water or humidified gas may not be necessary to achieve the desired level of hydration. Liquid water or steam (depending on temperature and pressure) is contained inside the sealed battery / supercapacitor, providing hydration without the need for replacement. For example, pretreated SrZr 0.8 Y 0.2 O 3-δ Thin ceramic film or SrZr 0.8 Y 0.2 O 3-δ -polymer composite or SrZr 0.8 Y 0.2 O 3-δ -ceramic composites have OH as charge carriers - or H + The materials described herein can be used as electrolytes in batteries or supercapacitors using oxygen (O2) or oxygen-containing electrolytes (or both). When the various materials described herein are used in sealed electrochemical devices, such as batteries or supercapacitors, it is necessary to keep the materials hydrated to maintain high ionic conductivity (optionally, high mixed ionic / electronic conductivity when the material is used as or as part of an electrode). The electrolyte and / or electrodes are placed in contact with liquid water or a sealed environment containing at least 5 vol% steam in the equilibrium gas within the sealed electrochemical device during use. Not all batteries are sealed systems. For example, in metal-air batteries, such as Zn-air and Mg-air batteries, the cathode is exposed to air. A porous membrane may be used to allow O2 to reach the cathode of a Zn-air battery from the ambient air. This membrane can prevent water loss from the Zn-air battery and keep the ion-conducting layer of the Zn-air battery hydrated to maintain high ionic conductivity.

[0254] In the special case of wastewater treatment, if the anode of a fuel cell is fed with reduced wastewater and the cathode is fed with oxidized wastewater, electricity can be beneficially generated as a by-product while simultaneously treating the wastewater.

[0255] When the ceramic or ceramic-polymer membranes described herein are used as the electrolyte 104 in a fuel cell 100 configured to remove ammonia from ammonia-containing wastewater, the membrane 104 is more resistant to impurities in the wastewater than Nafion® and, therefore, can exhibit greater durability than current fuel cells based on Nafion® or alkaline membrane electrolytes.

[0256] The electrochemical device 100 of the described embodiments is configured to have a maximum operating temperature below the temperature at which the hydrated oxide or hydrated oxyhydroxide begins to lose lattice water or the anhydrous oxyhydroxide begins to lose water to form the original starting oxide (if applicable). This temperature depends on the chemical composition and structure of the hydrated oxide or hydrated or anhydrous oxyhydroxide, and the partial pressure of water (pH2O) within the electrochemical device. The higher the pH2O, the higher the maximum operating temperature of the ionic conductor while still maintaining sufficient ionic conductivity.

[0257] As described herein, three families of oxides have been identified that can be used to form oxyhydroxides and / or hydrated oxides that have properties suitable for use as the electrolyte 104 in electrochemical devices 100. Various methods 900 for making these materials have also been described. It will be understood that the specific compositions mentioned herein are examples of the identified classes of oxides and should not be construed as limiting the scope of the present disclosure.

Claims

1. 1. An electrochemical device comprising a solid ion conducting layer, the solid ion conducting layer comprising an oxyhydroxide derived from an oxide having a perovskite structure or a brownmillerite structure, the oxyhydroxide having the general formula (A １－ｘ A’ ｘ ) １－ａ B １－ｙ B’ y(O ３－ｚ－ｄ C ｚ )(OH) ｍ ・nH ２ O wherein A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Sc, Ti, V, Cr, Ga, Ge, Al, Si, Sn, As, Sb, Zr, Hf, Nb, Mo, W, Cd and Ta, C is selected from N, Cl, F, Br, S, Te and Se; 0≦x≦1 a≦0.15 z≦0.2 y≦1 d≦2 0 < (z + d) m≧0.01 n≧0 and wherein the solid ion conducting layer is configured to be exposed in use to liquid water or to a gas containing at least 5 vol% H2O; An electrochemical device configured to operate at an operating temperature of 300°C or less.

2. (i) m is in the range of 0.01 to 2; and / or (ii) n is in the range of 0 to 12; 2. The electrochemical device according to claim 1, wherein at least one of the following is applied.

3. The solid ion conducting layer is (i) pure ionic conductors; (ii) OH － ions and / or H ＋ a conductor of ions, and (iii) Mainly OH － ionic conductors, 3. The electrochemical device according to claim 1, wherein the electrochemical device is one or more of the following:

4. The oxide having a perovskite structure or a brownmillerite structure is (i)Sr ２ Co ２ O ５±δ (ii)Sr ２ Co ２ O ５－ｘ N ｘ (yy)Ca ２ Co ２ O ５±δ (iv)SrCoO ３－δ (v)CaCoO ３－δ (vi)SrCadeCoO ５±δ (vii) SrCaCo ２ O ５±δ or (vifi)SrCo ０．５ Till ０．５ Oh ３－δ (ix)Sr ２ Fe ２ O ５±δ (x)Sr ２ Fe ２ O ５－ｘ N ｘ (xi)Ca ２ Fe ２ O ５±δ (xii)SrZr ０．８ Y ０．２ O ３－δ (xiiiiｳrCe ０．８ Y ０．２ 9 ３－δ (xiv) SrCeO ３－δ or (xv)SrCaFe ２ O ５±δ One or more of 4. The electrochemical device according to claim 1, wherein δ is a value indicating a level of oxygen vacancy, and δ≧0.

5. An electrochemical device comprising a solid ion conducting layer, the solid ion conducting layer comprising a hydrated oxide derived from an oxide having a Brownmillerite structure, the hydrated oxide having the general formula (A ２－ｘ A’ ｘ ) １－ａ B ２－ｙ B’ y(O １－ｚ C ｚ ) ５±δ ・n’H ２ O wherein A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Ln, Y, Sc, Mg, Ca, Sr, Li, Na, Co, Fe, Mn, In, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, As and Ta, C is selected from N, Cl, F, Br, S, Te and Se; a≦0.15 0≦x≦1 0≦y≦1 0 < z ≦ 0.04 and n′≧0.01; δ is a value indicating the level of oxygen deficiency, and δ≧0; 10. An electrochemical device, wherein the solid, ionically conductive layer is configured to be exposed, in use, to liquid water or to a gas containing at least 5 vol % H2O.

6. The oxide having a brownmillerite structure is (i)r ２ Fe ２ O ５ (｡｡)｡ ２ FeCoO ５ (iii) Sr ２ Fe ２ O ５－ｘ N ｘ or (iv)Ba ２ InCe ０．５ La ０．５ O ５ 6. The electrochemical device according to claim 5, wherein the electrochemical device is one or more of the following:

7. An electrochemical device comprising a solid ion conducting layer, the solid ion conducting layer comprising a hydrated oxide derived from an oxide having a perovskite structure, the hydrated oxide having a general formula (A １－ｘ A’ ｘ ) １－ａ B １－ｙ B’ ｙ O ３－ｚ－ｄ’ C ｚ ・n’’H ２ O wherein A and A' are selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi; B and B' are selected from Ln, Y, In, Sc, Sr, Ca, Mg, Li, Na, Co, Fe, Mn, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Cd, As and Ta, C is selected from N, Cl, F, Br, S and Se; 0≦x≦1 a≦0.15 z≦0.2 d≦2 0 < (z + d) and n″≧0.01 and An electrochemical device configured to operate at an operating temperature of 300°C or less.

8. The oxide having a perovskite structure is (i)SrCoO ３－δ (ii) Sr. ０．５ Till ０．５ Oh ３－δ (iii)SrZr ０．８ Y ０．２ O ３－δ (iv) SrCe ０．８ Y ０．２ O ３－δ or (v)SrCeO ３－δ One or more of 8. The electrochemical device according to claim 7, wherein δ is a value indicating a level of oxygen vacancy, and δ≧0.

9. 1. A solid ion conducting layer for use in an electrochemical device, said solid ion conducting layer comprising: ４ CdCl ６ The K includes hydrated oxides or hydrated or non-hydrated oxyhydroxides derived from oxides having the structure ４ CdCl ６ The oxide having the structure is represented by the general formula (A １－ｘ A’ ｘ ) ３ B ２－ｙ B’ ｙ O ６－ｚ C ｚ wherein A and A' are selected from Ca, Sr, Ba, Na, K, Rb, Cs, Ln, Y, Pb, In, Tl and Bi; B and B' are selected from Co, Fe, Mn, Ni, Cu, Ti, V, Cr, Mg, Ca, Sr, Ba, Ln, Y, Zn, Cd, Li, Na, B, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Rh, Ir and Ru, C is selected from N, Cl, F, Br, I, S, Te and Se; 0≦y≦2 0 < z ≦ 0.5 0≦x≦1 A solid ion conducting layer characterized by:

10. 10. The solid ion conducting layer of claim 9, wherein at least one of B and B' is selected from Ce, Zr, Ti, Y, Sc, Co, Fe, Mn, Ni, and Cu.

11. The oxide is Ca ３ Co ２ O ６ 11. The solid ion conducting layer according to claim 9 or claim 10, wherein

12. The solid ion conducting layer is (i) General formula (A １－ｘ A' ｘ ) ３ B ２－ｙ B' ｙ O ６－ｚ C ｚ ・nH ２ O, where n≧0.01, 0≦x≦1, 0≦y≦2, and 0<z≦0.5; or (ii) General formula (A １－ｘ A' ｘ ) ３ B ２－ｙ B' ｙ O ６－ｚ C ｚ (OH) ｍ ・nH ２ O (wherein 0≦x≦1, 0≦y≦2, 0<z≦0.5, 0.01≦m≦6) 12. The solid ion conducting layer according to claim 9, comprising:

13. 13. The solid ion conducting layer according to any one of claims 9 to 12, wherein the solid ion conducting layer is a composite solid ion conducting layer formed by mixing at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide according to any one of claims 5 to 12 with at least one of the following materials: (i) a polymer and (ii) a ceramic; (iii) a pure non-metallic element such as graphite; or (iv) CaCO3 or BaSO4.

14. 14. The solid ion conducting layer of claim 13, wherein the material is a polymer or graphite, and the composite solid ion conducting layer is in the form of a flexible membrane.

15. 15. The solid ion conducting layer of claim 13 or claim 14, wherein the composite solid ion conducting layer comprises the at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide in a volume percentage between 1% and 99%.

16. The solid ion conducting layer is (i) pure ionic conductors; (ii) OH － Ion conductor and / or H ＋ an ionic conductor, and (iii) Mainly OH － ionic conductors, 16. The solid ion conducting layer according to claim 9, wherein the layer is one or more of the following:

17. An electrochemical device as described in any one of claims 5 to 8, characterized in that the solid ion conducting layer is a composite solid ion conducting layer formed by mixing at least one hydrated oxide or hydrated or non-hydrated oxyhydroxide as described in any one of claims 5 to 12 with at least one material selected from the group consisting of (i) a polymer and (ii) a ceramic, (iii) a pure non-metallic element such as graphite, or (iv) CaCO3 or BaSO4.

18. 1. A method of making a solid ionically conductive layer for use in an electrochemical device, comprising: Perovskite structure, Brownmillerite structure, or K ４ CdCl ６ obtaining a ceramic oxide material which is an oxide having a structure and which comprises A-site ions of one or more elements selected from Ca, Sr, Ba, Ln, Y, Na, K, Rb, Cs, Pb and Bi, and B-site ions of one or more elements selected from Ln, Y, Sc, Mg, Ca, Sr, Ba, Li, Na, Cd, Co, Fe, Mn, In, Ni, Cu, Zn, Ti, V, Cr, Ga, Ge, Al, Si, Sn, Sb, Zr, Hf, Nb, Mo, W, Ta, Pt, Rh, Ir and Ru; The obtained ceramic oxide material is (i) firing the ceramic oxide material in air; (ii) firing the ceramic oxide material in an atmosphere having an oxygen partial pressure lower than that of air; (iii) immersing the ceramic oxide material in a reducing liquid; or (iv) electrochemically reducing the calcined ceramic oxide material; introducing additional oxygen vacancies; treating the ceramic oxide material with water; The method of claim 1, wherein the treatment with water comprises immersing the calcined ceramic oxide material in water or exposing it to an atmosphere containing at least 5 vol.% water vapor to form a hydrated oxide or a hydrated or non-hydrated oxyhydroxide.

19. The atmosphere has an oxygen partial pressure lower than that of air, (i) an inert atmosphere, or (ii) a reducing atmosphere; 19. The method of claim 18, wherein the method is any one of the following:

20. The obtained ceramic oxide material comprises: (i) SrZr ０．８ Y ０．２ O ３－δ , SrCe ０．８ Y ０．２ O ３－δ , or SrCo ０．５ Ti ０．５ O ３－δ oxides having a perovskite structure, such as (ii) Sr ２ Fe ２ O ５±δ oxides having a brownmillerite structure such as (iii) Ca ３ Co ２ O ６ etc. ４ CdCl ６ an oxide having the structure At least one of 20. The method according to claim 18 or 19, wherein δ is a value indicating the level of oxygen deficiency, and δ≧0.

21. 21. The method of any of claims 18-20, wherein the water treatment is carried out for a period of at least 1 hour prior to use of the solid ion conducting layer.

22. the solid ion conducting layer is a pure ceramic solid ion conducting layer; (i) sintering the ceramic oxide material to form a sintered material in a single firing step to hold the solid ion conducting layer in a desired shape and to introduce the additional oxygen vacancies; or (ii) sintering the ceramic oxide material in air in a first firing step to introduce the additional oxygen vacancies before firing the sintered material in an atmosphere with an oxygen partial pressure lower than that in air; 22. The method according to claim 18, wherein the method is any one of the following:

23. 23. The method of any of claims 18 to 22, further comprising mixing the ceramic oxide material with one or more polymers prior to the treatment with water to form a composite ceramic-polymer solid ionically conductive layer.

24. 18. A method of using an electrochemical device comprising a solid ion conducting layer according to any one of claims 5 to 17, comprising exposing the solid ion conducting layer to liquid water or to a gas containing at least 5 vol% H2O.

25. 5. The electrochemical device according to claim 1, wherein the electrochemical device is configured to operate at an operating temperature of 250° C. or less.

26. (i) the electrochemical device is a fuel cell, an electrolyzer, or a battery; (ii) the solid ion-conducting layer is an electrolyte; and / or (iii) the electrochemical device is configured to maintain the solid ionically conductive layer in a hydrated state during use; 26. The electrochemical device according to claim 1, wherein at least one of the following is applied:

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