Ion-conductive oxide material

Abstract

An ion-conductive oxide material comprising: one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances represented by the following formula: MQaOb wherein M is at least one element selected from the group consisting of Groups 3, 4, 5, 6, or 7, Q is at least one element selected from the group consisting of Groups 12, 13, 14, 15, or 16, provided that O is excluded, and a is 0 or more and 2 or less, and b is greater than 0 and 2 or less; and two or more ions selected from the group consisting of H+, metal ions, organic ions, or OH- in an interlayer.

Description

ION-CONDUCTIVE OXIDE MATERIAL

[0001] The present disclosure relates to an ion-conductive oxide material.

[0002] There is an increasing demand for renewable energy, and development of fuel cells and water electrolysis technologies has attracted attention. There is an ion-conductive solid electrolyte / separator as a constituent member of the above technology, and Nafion (registered trademark), which is a fluorocarbon polymer, is used as the solid electrolyte / separator, as shown in Non-patent Document 1. Characteristics required for the solid electrolyte include: (1) ion conductivity, (2) film-forming property / flexibility, and (3) chemical resistance. Nafion (registered trademark) as the fluorocarbon polymer is used to satisfy the characteristics of (1) to (3).

[0003] Conventionally, for example, TiO2is known as an oxide containing metal. Non-patent Document 2 proposes a method for converting 12 types of Ti including harmless precursors (TiC, TiN, etc.) abundantly present in the Earth into a TiO2-based one-dimensional (1D) nanofilament (NF). It has also been shown that the TiO2-based 1D NF may be applied in the fields of photocatalysts, dye decomposition, batteries, supercapacitors, etc.

[0004] Yoshitsugu Sone et al., "Proton Conductivity of Nafion 117 as Measured by a Four-Electrode AC Impedance Method" J. Electrochem. Soc. 143, 1254, 1996Hussein O. Badr et al., "On the structure of one-dimensional TiO2 lepidocrocite" Matter 6, 128-141, January 4, 2023

[0005] The conventional fluorocarbon polymer contains fluorine, which is non-deal from the viewpoint of environmental considerations, and so substitution is desired. Due to the fluorine regulation, a hydrocarbon polymer without F having low stability and the like may become the mainstream, but there is a problem in chemical stability.

[0006] When the TiO2-based one-dimensional (1D) nanofilament (NF) is used as a solid electrolyte for a fuel cell or water electrolysis, it is necessary to impregnate a solid electrolyte film with an electrolytic solution such as an acid aqueous solution. However, when the TiO2-based one-dimensional (1D) nanofilament (NF) is immersed, for example, in a 0.01 M aqueous sulfuric acid solution, they are dissolved or the NF structure is lost, and they are not self-supported films.

[0007] An object of the present disclosure is to provide an ion-conductive oxide material having sufficient ion conductivity as the solid electrolyte for a fuel cell or water electrolysis, or the like.

[0008] According to one gist of the present disclosure, provided is an ion-conductive oxide material comprising: one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances represented by the following formula: MQaOb wherein M is at least one element selected from the group consisting of Groups 3, 4, 5, 6, or 7, Q is at least one element selected from the group consisting of Groups 12, 13, 14, 15, or 16, provided that O is excluded, and a is 0 or more and 2 or less, and b is greater than 0 and 2 or less; and two or more ions selected from the group consisting of H+, metal ions, organic ions, or OH-in an interlayer.

[0009] According to the present disclosure, it is possible to provide an ion-conductive oxide material having sufficient ion conductivity as the solid electrolyte for a fuel cell or water electrolysis, or the like.

[0010] Fig. 1A is a schematic explanatory view for explaining a form of a material of the present embodiment.Fig. 1B is a schematic explanatory view for explaining another form of the material of the present embodiment.Fig. 1C is a schematic explanatory view for explaining another form of the material of the present embodiment.Fig. 2 is an explanatory view of a representative atomic model of the material of the present embodiment.Fig. 3 is another explanatory view of a representative atomic model of the material of the present embodiment.Fig. 4 is another explanatory view of a representative atomic model of the material of the present embodiment.Fig. 5 is an explanatory view of a representative atomic model of a conventional material.

[0011] The present embodiment relates to an ion-conductive oxide material containing one or more selected from the group consisting of nanofibers, nanowires, or two-dimensional substances of a predetermined material, and containing two or more ions selected from the group consisting of H+, metal ions, organic ions, or OH-in the interlayer. In the present disclosure, simply referring to “material” means “material containing one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances” (in other words, a material containing at least one or more materials selected from the group consisting of nanofibers, nanowires, and two-dimensional substances). The term “oxide material” simply means a compound composed of oxygen and other elements. In the present embodiment, the material containing one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances typically means a material that is solid and does not contain a binder or the like (for example, a polymer). The material containing one or more materials selected from the group consisting of nanofibers, nanowires, and two-dimensional substances can mean, in a narrow sense, a material substantially containing one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances (which may contain other objects, impurities, and the like that may be inevitably mixed). However, the material containing one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances is not limited thereto.

[0012] The material of the present embodiment is one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances of a predetermined material (substance). The predetermined material that can be used in the present embodiment is represented by the following Formula (1): MQaOb(1) wherein M is at least one element selected from the group consisting of Groups 3, 4, 5, 6 or 7, and may contain a so-called early transition metal, for example, at least one element selected from the group consisting of Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and Mn, and preferably at least one element selected from the group consisting of Ti, V, Cr, Mo and Mn, Q is at least one element, provided that O is excluded, selected from the group consisting of Groups 12, 13, 14, 15, or 16, and may contain, for example, at least one element selected from the group consisting of B, C, N, Si, P, and S, a is 0 or more and 2 or less, b is greater than 0 and 2 or less.

[0013] Hereinafter, the predetermined material is also simply referred to as “MQO”. Examples of MQO include those represented by formulas such as TiO2, TiCO, TiCON, VO2, VCO, VCON, CrO2, CrCO, CrCON, MoO2, MoCO, MoCON, MnO2, MnCO, and MnCON. For example, in Formula (1), M may be Ti, and the Q may be C. For example, in Formula (1), a may not be 0. The a may be 1 or more.

[0014] MQO has a crystal structure different from that of a hexagonal system. Although the present embodiment is not bound by any theory, it can be considered that the crystal structure of MQO is an anatase type, a lepidocrocite type, or a mixture thereof at present. For example, the crystal structure of MQO may be a lepidocrocite type.

[0015] MQO can be produced using a first raw material and a second raw material, for example, as follows. The first raw material contains at least M, the second raw material contains at least Q, and the first raw material and the second raw material can react in a protic solvent to generate MQO.

[0016] As the first raw material, a material represented by the following Formula (2) can be used: McA1d(2) wherein M is as described above, A1is at least one element selected from the group consisting of Groups 12, 13, 14, 15, or 16, and may contain, for example, at least one element selected from the group consisting of B, C, N, O, Si, P, and S, c and d are each independently 1 or more and 5 or less, however, the material represented by Formula (2) needs to be different from the MQO of the product. Typically, the material represented by Formula (2) may not have a peak in a range in which a diffraction angle 2θ is not less than 2° and not more than 12° in an X-ray diffraction (XRD) pattern.

[0017] Examples of the first raw material represented by Formula (2) include TiB2, TiB, TiC, TiN, TiO2, Ti5Si3, Ti2SbP, VO2, V2O4, NbC, Nb2O5, MoO2, MoO3, MoS2, MnO2, Mn3O4, and MnCO3. MnO2that can be used as the first raw material has a peak in the vicinity of 2θ = 13° and does not have a peak in the range where 2θ is not less than 2° and not more than 12° in the XRD pattern.

[0018] Alternatively, or in addition to the above, a material represented by the following Formula (3) (hereinafter, also simply referred to as "MAX phase" or "MAX raw material") can be used as the first raw material: MmA2Xn(3) wherein M is as described above, X is at least one element selected from the group consisting of C and N, n is 1 or more and 4 or less, m is greater than n and or less 5, A2is at least one element selected from the group consisting of Groups 12, 13, 14, 15, or 16, is usually a Group A element, typically Group IIIA and Group IVA, and more particularly may include at least one selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S, and Cd, and is preferably Al. The MAX phase has a crystal structure in which a layer constituted by A2atoms is located between two layers represented by MmXn(each X may have a crystal lattice located in an octahedral array of M). In the case of m = n + 1, the MAX phase typically includes repeating units in which each one layer of X atoms is disposed in between adjacent layers of n + 1 layers of M atoms (these are also collectively referred to as an “MmXnlayer”), and a layer of A2atoms ("A2atom layer") is disposed as a layer next to the (n + 1)th layer of M atoms. However, the MAX phase is not limited thereto.

[0019] Examples of the first raw material represented by Formula (3) include Ti3AlC2, Ti3GaC2, and Ti3SiC2.

[0020] As the first raw material, the material represented by Formula (2) and the material represented by Formula (3) may be used together (for example, as a mixture).

[0021] As the second raw material, an ion-binding substance having a carbon-containing group can be used. The ion-binding substance having a carbon-containing group contains C. Examples of the ion-binding substance include an ammonium salt, a phosphate salt, and a sulfate salt.

[0022] More specifically, a quaternary ammonium salt can be used as the second raw material. Examples of the quaternary ammonium salt include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH or TBAOH), benzyltrimethylammonium hydroxide, tetrabutylammonium fluoride (TBAF), tetrabutylammonium chloride (TBACl), tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI), benzyltriethylammonium chloride (BTEAC), hexadecyltrimethylammonium bromide, cetyltrimethylammonium bromide (CTAB), benzetonium chloride, benzalkonium chloride, and cetylpyridinium chloride (CPC). Among them, TMAH and TBAOH are preferable.

[0023] Alternatively, or in addition to the above, other ion-binding substances containing P and / or S etc. may be used as the second raw material.

[0024] The protic solvent may be any solvent that can at least partially dissolve the first raw material and the second raw material, and may be particularly an aqueous solvent. As the protic solvent, water, an alcohol (for example, ethanol, 1-propanol, isopropanol), or a carboxylic acid (for example, acetic acid, formic acid) or the like is used. The aqueous solvent may be composed of water and optionally a liquid substance compatible with water (for example, a protic solvent other than water), and is preferably water.

[0025] The first raw material and the second raw material are reacted in the protic solvent. The second raw material can be added to the protic solvent in advance. The ratio of the second raw material to the total of the protic solvent and the second raw material may be, for example, 5% by mass or more, particularly 20% by mass or more, and / or may be, for example, 80% by mass or less, particularly 50% by mass or less. The first raw material can be further added to and mixed with the protic solvent to which the second raw material has been added. In such a mixture, a reaction for producing MQO proceeds. The temperature (reaction temperature) of the mixture (which may contain the reaction product) may be, for example, 15°C or higher, particularly 40°C or higher, and / or, for example, 100°C or lower, particularly 80°C or lower. A mixing time (reaction time) may, for example, be 1 day or more, particularly 2 days or more, and / or may, for example, be 10 days or less, particularly 7 days or less. The mixing can be performed, for example, by rotating and stirring a magnetic stirring bar charged into a container using a magnetic stirrer while the reaction temperature is maintained by a hot plate stirrer and a hot water bath. However, the treatment operation and conditions (temperature and time and the like) under which the reaction can proceed are not limited to the above, and may be appropriately selected according to the first raw material, the second raw material, and the protic solvent and the like to be used.

[0026] By the above reaction, MQO is generated and can eventually grow into nanofibers of MQO. Figs. 1A to 1C are schematic explanatory views for explaining a form of the material of the present embodiment. Without limiting the present disclosure, the nanofibers of the resulting MQO may be in the form of nanoribbons (extending in the

[0001] direction in Fig. 1A) extending with a nanoscale width (width in the

[0100] direction in Fig. 1A) as schematically illustrated in Fig. 1A, for example. In addition, a plurality of nanofibers (or nanoribbons) of MQO may overlap each other by bonding and / or intermolecular interaction (for example, van der Waals force) to constitute a laminate (layered nanofibers) as schematically illustrated in Fig. 1B. In addition, as schematically illustrated in Fig. 1C, they may be grown into layered nanoflakes extending two-dimensionally. In addition, as a higher order structure, a porous body (for example, a particle shape or a film shape) in which layered nanofibers are entangled with each other, or a layer structure in which layered nanoflakes are layered in the thickness direction can be obtained. Although the present disclosure is not bound by any theory, such generation and growth of MQO can be considered to be due to a bottom-up type synthesis reaction.

[0027] The mixture after the reaction (also referred to as a reaction mixture) may be appropriately subjected to post-treatment. Examples of the post-treatment include washing, impact application (including shear force application), drying (for example, freeze dry, heat dry), and pulverization.

[0028] The washing may be performed using a protic solvent. The same description as above may apply to the protic solvent, and the protic solvent may be washed with, for example, water or an alcohol. After washing, a separation operation (centrifugation and / or decantation) may be performed. The washing and separation operations may be repeated until the pH of a supernatant liquid after centrifugation is, for example, 8 or less.

[0029] Optionally, washing may be performed using an aqueous solution of a metal salt instead of or in addition to the above washing. The metal salt may be, for example, a halide (fluoride, chloride, bromide, or iodide) of an alkali metal (Li, Na, or K or the like), typically LiCl, NaCl, or KCl or the like. Specifically, for example, washing may be performed using an aqueous solution of a metal salt having a molar concentration of 1 to 10. After washing, a separation operation (centrifugation and / or decantation) may be performed. Also in this case, the washing and separation operations may be repeated as necessary until the pH of the supernatant liquid after centrifugation is, for example, 8 or less.

[0030] During and / or after washing, an impact such as vibration and / or ultrasound may be applied. This makes it possible to promote the dispersion or the like of MQO particles (for example, nanofibers / nanoflakes, and so on). When the MQO particles are aggregated, they can be crushed. Such an effect is remarkably obtained when an impact is applied during washing using an aqueous solution of a metal salt (it is considered that metal cations derived from the metal salt can enter gaps of the aggregates and the aggregates can be crushed). The impact can be achieved using, for example, any one or more of a handshake, an automatic shaker, a mechanical shaker, a vortex mixer, a homogenizer, an ultrasonic bath, and the like.

[0031] Since the MQO particles are solid, a separation operation may be performed at any suitable timepoint to remove unwanted liquid components, if present. As a final separation operation, for example, a drying operation, typically freeze drying or heat drying, may be performed. The freeze-drying may be performed, for example, by freezing a mixture containing MQO particles and a liquid component at any suitable temperature (for example, -40°C), followed by drying under a reduced pressure atmosphere. The heat drying can be performed, for example, by drying a mixture containing MQO particles and a liquid component at a temperature of 25°C or higher (for example, 200°C or lower) under a normal pressure or a reduced pressure atmosphere. The pulverization is not particularly limited, but can be performed using, for example, a combination of a mortar and a pestle, or an IKA mill or the like. The pulverization may be performed after drying.

[0032] As described above, the MQO particles can be obtained as a material containing MQO. According to the present embodiment, as described above, a material containing MQO can be easily produced, and a material containing MQO or a material containing the material can be realized.

[0033] In the present disclosure, the cross-sectional outer dimension of the MQO nanofibers means the shortest distance passing through the center in the cross section crossing the longitudinal direction of the MQO nanofibers. The shape of the cross section of the MQO nanofibers is not particularly limited, but can be approximated by, for example, a rectangle (rectangle and square and the like) or an ellipse (flat circle and true circle and the like). When the MQO nanofibers are in the form of nanoribbons, the shape of the cross-section thereof can be approximated by the rectangle, and the cross-sectional outer dimension can correspond to the short side length of the rectangle. When the MQO nanofibers are in the form of nanofilaments, the shape of the cross section thereof can be approximated by the flat circle, and the cross-sectional outer dimension can correspond to the short diameter length of the flat circle.

[0034] In the present disclosure, MQO is a solid content. MQO can be typically a particle (or powder).

[0035] Although MQO is represented by Formula (1), the material containing MQO (typically, MQO particles) does not need to be composed of only the constituent elements of Formula (1). Although the present disclosure is not limited, the material containing MQO may optionally contain at least one selected from the group consisting of a hydroxyl group, a chlorine atom, an oxygen atom, a hydrogen atom, and a nitrogen atom as modification or termination T present on the surface. The material containing MQO (typically, MQO particles) may have two or more layers, and as described later, and at least one selected from the group consisting of ammonium ions (for example, quaternary ammonium cations) or metal cations (for example, alkali metal ions and alkaline earth metal ions) may be present between these layers.

[0036] The particle diameter of the MQO particles may be, for example, 0.01 nm or more, particularly 0.1 nm or more, and 1 nm or more, and / or may be, for example, less than 1000 nm, particularly 100 nm or less, and 50 nm or less. Such particles may also be referred to as nanoparticles.

[0037] The form of the MQO particles is one or more selected from the group consisting of nanofibers, nanowires, and two-dimensional substances. The two-dimensional substance includes one or more of nanoflake and a laminate of nanoflake. In the present embodiment, the two-dimensional substance is not limited to only the nanoflake and the laminate of nanoflake.

[0038] The nanofibers may also be referred to as nanowires. In the present disclosure, the “nanofiber” means, as described above, for example, as shown in Fig. 1A, a solid material extending in a longitudinal direction, and an outer dimension (cross-sectional outer dimension) of a cross section perpendicular to the longitudinal direction is on the nano order (that is, not less than 1 nm and less than 1000 nm) or on the sub-nano order smaller than the nano order (less than 1 nm, for example, not less than 0.1 nm and less than 1 nm). The longitudinal length of the nanofiber is not limited to the nano order (that is, not less than 1 nm and less than 1000 nm), and may be in the micron order (not less than 1 μm and less than 1000 μm). The cross-sectional outer dimension of the nanofiber may be, for example, 0.1 nm or more, and particularly 1 nm or more, and may be, for example, 100 nm or less, particularly 50 nm or less, and preferably 15 nm or less.

[0039] In the present disclosure, a “two-dimensional substance” means, for example, as shown in Fig. 1C, and a solid having a two-dimensionally extended surface (also referred to as a plane or a two-dimensional sheet surface) and having a thickness relatively small with respect to a maximum dimension of the surface (which may correspond to an“ in-plane dimension” of a particle), and having a thickness on the order of nanometers (that is, 1 nm or more and less than 1000 nm) or sub-nanometers (less than 1 nm, for example, 0.1 nm or more and less than 1 nm) smaller than the order of nanometers. The in-plane dimension is not limited to the nano order (that is, not less than 1 nm and less than 1000 nm), and may be the micron order (not less than 1 μm and less than 1000 μm). The two-dimensional substance includes one or more of nanoflake and a laminate of nanoflake as described above. The nanoflake may also be referred to as a nanosheet or a two-dimensional (nano) sheet. The thickness of one layer of the nanoflake may be, for example, 0.01 nm or more, particularly 0.8 nm or more and, for example, 20 nm or less, particularly 3 nm or less. The in-plane dimension of the nanoflake may be, for example, 0.1 μm or more, particularly 1 μm or more, and may be, for example, 200 μm or less, particularly 40 μm or less. The nanoflake can be constituted by the aggregation of nanofibers.

[0040] The stack of the nanoflakes may also be referred to as a multilayer MQO. A distance (interlayer distance or void dimension) between two adjacent nanoflakes (or MQO of two adjacent layers) is not particularly limited.

[0041] A representative atomic model of the material of the present embodiment (more specifically, MQO) is shown along

[0100] ,

[0010] , and

[0001] , for example, in Figs. 2 to 4. These figures are representative polyhedral views (TiO2) of TiCO. In these drawings, the number of atoms in each direction is not limited to this drawing, and will be described later as a suitable range of the length in each direction. In Fig. 2, a TiO6octahedron is arranged to form one layer.

[0042] The length in the

[0100] direction may be 10 nm to 10 μm. In addition, the length in the

[0100] direction is, for example, preferably 20 nm to 5 μm, and most preferably 30 nm to 3 μm so that handling of the water dispersion becomes easy, that is, the viscosity of the water dispersion falls within an appropriate range.

[0043] The length in the

[0010] direction may be between 1 nm and 5 μm. In addition, the length in the

[0010] direction is, for example, preferably 3 nm to 1 μm, and more preferably 5 nm to 100 nm so that handling of the water dispersion becomes easy, that is, the viscosity of the water dispersion falls within an appropriate range.

[0044] The length in the

[0001] direction may be between 0.1 nm and 100 nm. In addition, the length in the

[0001] direction is, for example, preferably 0.5 nm to 50 nm, and more preferably 1 nm to 30 nm so that handling of the water dispersion becomes easy, that is, the viscosity of the water dispersion falls within an appropriate range. This range is also preferable because the specific surface area of MQO is increased.

[0045] Without limiting the present disclosure, the resulting nanofibers of the MQO may be in the form of nanoribbons extending at nanoscale widths as previously described. In addition, the nanoparticles may be grown into nanoflakes extending two-dimensionally, and for example, the length in the

[0100] direction and the length in the

[0010] direction may be about the same (within an error of 20%).

[0046] In the present disclosure, the “interlayer” refers to a space between one layer in the

[0010] direction in Figs. 1A to 1C and 2 to 4 and another adjacent layer. The interlayer distance is 0.01 nm to 100 nm. If the interlayer distance is too small, the specific surface area decreases, and if the interlayer distance is too large, the van der Waals force in the interlayer decreases, and the structural stability decreases. Therefore, the interlayer distance is preferably 0.1 nm to 50 nm, and more preferably 0.3 nm to 20 nm.

[0047] Although the present disclosure is not limited, in the obtained MQO, the length in the

[0010] direction and the length in the

[0001] direction may be on the order of nm. This is completely different from the conventional layered material, and the interlayer may be almost exposed to the surface. Therefore, the reaction efficiency can be higher than that of the conventional layered material in physical phenomena such as adsorption and all chemical reactions. Furthermore, in a case where the

[0100] direction is the longitudinal direction on the order of μm, a one-dimensional material having a layer structure in the

[0010] direction can be obtained.

[0048] The atomic structure of lepidocrocite-type TiO2, which is a representative example of MQO, has been described above. MQO may undergo phase transition to anatase type TiO2due to heat treatment or the like. At that time, as shown in Fig. 5, the interlayer presenting in the

[0010] direction disappears, the specific surface area decreases, and the efficiency of all physical phenomena and chemical reactions may decrease.

[0049] Each dimension described above can be obtained as a number average dimension (number average of at least 40) based on a photograph observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an atomic force microscope (AFM) (if necessary, processing is performed by a method such as a focused ion beam (FIB)), or a distance in a real space calculated from a position on a reciprocal lattice space of a (002) plane measured by an X-ray diffraction (XRD) method.

[0050] However, it should be noted that in the present disclosure, MQO is not limited to the above-described form, and may have any suitable form.

[0051] According to the study of the present inventors, it has been found that when two or more ions selected from the group consisting of H+(proton), metal ions, organic ions, or OH-(hydroxide anion) are contained in the interlayer of the ion-conductive oxide material, for example, in the interlayer of MQO, an ion-conductive oxide material having high ionic conductivity is obtained. Examples of the metal ions include ions of main group metal elements and transition metal elements of Groups 1 (excluding hydrogen) to 15 of the periodic table. Examples of the organic ions include ammonium ions and an ionized organic substance.

[0052] The ions present in the interlayer are protons, organic ions such as ammonium ions (for example, quaternary ammonium cations), and metal ions (also referred to as metal cations). Examples thereof include alkali metal ions and alkaline earth metal ions) and OH anions. Typical control factors of the ionic conductivity include an ion diffusion rate, an amount of crystal water, a proton conductivity, and an interlayer distance. Since each factor has a trade-off relationship, it is preferable to include a plurality of ions in an arbitrary weight ratio. Preferably, two or more metal ions are included in the interlayer. More preferably, metal cations having different valences are included. In either case, protons or hydroxide anions may be included. The solid electrolyte for a fuel cell or water electrolyzer preferably contains metal cations and protons.

[0053] The solid electrolyte for a fuel cell or water electrolyzer are often degraded by OH radicals derived from hydrogen peroxide. Ions such as Ce, Nb, Mn, and V can scavenge radicals by changing the oxidation number to change the radicals to a more stable state. Therefore, it is preferable that at least one of Ce, Nb, Mn, and V ions is further included between the layers as the solid electrolyte. Here, examples of the radical scavenger include ions such as Ce, Nb, Mn, and V, but the ion-conductive oxide material of the present embodiment may include at least one selected from the group consisting of oxides of Ce, Nb, Mn, and V, carbon-based materials such as graphene and carbon dots, MXenes such as Ti3C2and nitrogen-doped Ti3C2, antioxidant organic substances such as vitamin C, vitamin E, and glutathione, and enzymes such as catalase, superoxide dismutase, and peroxidase.

[0054] The diffusion rate of the ions (particularly metal ions) depends on the mass and size of the ions. For example, ions having a smaller mass and a smaller size have a higher diffusion rate. For example, the order of fastest diffusion rate is H+, Li+, Mg2+, and Al3+. This affects not only the ionic conductivity of the ion itself, but also the ion diffusion of other competing ions, for example, the proton conductivity.

[0055] Examples of the control factor of the ionic conductivity include the metal ion size, the diffusion rate of the metal ions, the amount of crystal water, the mobility of H+, the amount of H+, the hydration E of the metal ions, and the interlayer distance. Among these, the smaller the metal ion size is, the more the ionic conductivity is improved, and for example, the ionic conductivity of Li ions is higher than that of Al ions. The higher the diffusion rate of metal ions, the higher the ionic conductivity. The larger the amount of crystal water, the higher the ionic conductivity. The higher the mobility of H+is, the higher the ionic conductivity is. The larger the amount of H+, the higher the ionic conductivity. The smaller the hydration E of the metal ions, the higher the ionic conductivity. The lower the interlayer distance, the higher the ionic conductivity. The hydration E of the metal ion has a correlation with the amount of crystal water, to be described later.

[0056] The amount of ions present in the interlayer is preferably 0.001 to 10% by mass. The amount is more preferably 0.1 to 8% by mass, and still more preferably 1 to 6% by mass.

[0057] (Crystalline water) Water molecules (hereinafter, referred to as crystal water) may be present in the interlayer. The crystal water may interact with the ions. The amount of crystal water is preferably 0.001 to 10% by mass, more preferably 0.1 to 8% by mass, and still more preferably 1 to 6% by mass. As the solid electrolyte for a fuel cell or water electrolysis, ion conductivity of protons and the like is increased when the amount of crystal water is in an appropriate range, which is suitable.

[0058] The larger the amount of crystal water, the larger the ionic conductivity. There are two typical factors. One is called an electrostatic shielding effect, in which a water molecule relaxes an interaction ion’s potential to be conducted in the interlayer of TICO, so that ionic conductivity increases. The other is that the presence of crystal water improves the charge transfer rate, resulting in improved ionic conductivity. The amount of crystal water is correlated with the valence of ions, and the amount of crystal water increases as the valence increases, so that, for example, the order of the amount of crystal water increases when considering metal cations such as Al3+, Mg2+, and Li+. However, if the amount of the crystal water is too large, the van der Waals force in the interlayer is reduced, so that the crystal water is easily deteriorated. Therefore, it is preferable that a plurality of ions is included and the amount of crystal water is controlled within an appropriate range.

[0059] The proton conductivity is proportional to the amount of protons and inversely proportional to the hydration E of ions. The hydration energy of ions such as metal cations affects the proton conductivity by, for example, a competitive adsorption action. In the competitive adsorption, when metal ions have high hydration energy, there is a possibility that these ions are strongly associated with water molecules and are adsorbed by competing with protons in the interlayer or the like. As a result, movement of protons is hindered, and the proton conductivity is lowered.

[0060] (Interlayer distance) For example, the ionic conductivity increases as the interlayer distance in the layered material increases so that the proton conductivity increases as the free volume in the proton-conductive polymer increases. When the interlayer distance is large, protons pass easily, which is preferable. However, if the interlayer distance is too large, the structural stability is deteriorated, and thus it is preferable to control the interlayer distance to an appropriate range.

[0061] The interlayer distance at which the ions (and crystal water that may be present) are present is preferably 1 to 20 angstroms, more preferably 3 to 15 angstroms, and still more preferably 5 to 13 angstroms. As the solid electrolyte for a fuel cell or water electrolysis, when the interlayer distance is in an appropriate range, ion conductivity of protons and the like is increased, which is suitable.

[0062] The ion-conductive oxide material may contain, for example, a polymer such as Nafion (registered trademark) which is a fluorocarbon polymer within a range in which the action and effect according to the present embodiment are not inhibited.

[0063] The material containing MQO may typically have a peak in a range in which a diffraction angle 2θ is 2° or more and 12° or less in an X-ray diffraction (XRD) pattern. Although the present disclosure is not bound by any theory, the fact that the material containing MQO has a peak in a range of 2θ not less than 2° and not more than 12° in the XRD pattern is considered to mean that MQO has a crystal structure different from that of a well-known metal oxide. For example, the above-described peak means that a periodic structure presents in the [0k0] direction. In addition, by having peaks at 2θ = 26°, 2θ = 48°, and 2θ = 63°, it can be confirmed that MQO has a crystal structure of lepidocrocite. Furthermore, it is also possible to additionally confirm the identification of ion species in the interlayer by the size of d-spacing obtained from the peak in the range of 2θ = 2° or more and 12° or less.

[0064] In the present disclosure, an XRD pattern is a pattern obtained by scanning in a θ-axis direction with an XRD analyzer (wherein the vertical axis represents strength and the horizontal axis represents 2θ) using a CuKα ray (= about 1.54 angstrom) as a characteristic X-ray, and may also be referred to as an “XRD profile”. The peaks in the XRD pattern can be identified visually or using a software used with the XRD analyzer.

[0065] Although the present embodiment is not limited, for example, the material of the present embodiment (more specifically, MQO) may have a Raman shift with peaks at positions of at least 275 to 295 cm-1, 435 to 455 cm-1, and 665 to 745 cm-1in a Raman spectrum using a laser with a wavelength of 532 nm.

[0066] Although the present embodiment is not limited, for example, the material of the present embodiment (more specifically, MQO) may have a Raman shift with peaks at positions of 140 to 160 cm-1, 275 to 295 cm-1, 435 to 455 cm-1, and 665 to 745 cm-1in a Raman spectrum using a laser with a wavelength of 532 nm. Incidentally, at the position of 140 to 160 cm-1, an anatase type peak may be present.

[0067] Although the present embodiment is not limited, for example, the material of the present embodiment (more specifically, MQO) has a crystal structure of an anatase type, a lepidocrocite type, or a mixture thereof. More preferably, the material has a lepidocrocite type crystal structure.

[0068] Although the present embodiment is not limited, for example, the material of the present embodiment (more specifically, MQO) may have an aspect in which a Raman shift has peaks at positions of at least 275 to 295 cm-1, 435 to 455 cm-1, and 665 to 745 cm-1in a Raman spectrum using a laser with a wavelength of 532 nm, and X is the largest when the intensity of each of the peaks is X, Y, and Z.

[0069] Although the present embodiment is not limited, more preferably, the material of the present embodiment (more specifically, MQO) may have an aspect in which in a Raman spectrum using a laser with a wavelength of 532 nm, a Raman shift has peaks at positions of at least 180 to 200 cm-1, 275 to 295 cm-1, 375 to 395 cm-1, 435 to 455 cm-1, and 665 to 745 cm-1, and X is the largest when the intensity of each of the peaks is V, X, Y, Z, and W.

[0070] In the present disclosure, the Raman spectrum is measured by a Raman spectrometer using a laser beam having a wavelength of 532 nm as an excitation light source (the vertical axis represents intensity, and the horizontal axis represents a Raman shift). The peaks in the Raman spectrum can be identified visually or using a software used with the Raman spectrometer.

[0071] In addition, the material containing MQO may contain unreacted first raw material and / or second raw material as impurities, and may contain a substance derived from the first raw material, the second raw material and / or the protic solvent. For example, when a quaternary ammonium salt is used as the second raw material, N may present (remain) in arbitrary form in the material containing MQO. Although the present embodiment is not limited, the material containing MQO may contain ammonium ions and tetramethylammonium ions. For example, when the MAX raw material is used as the first raw material, in the present disclosure, the material containing MQO may contain a relatively small amount of remaining A atoms, for example, 10% by mass or less with respect to the original A atoms. The remaining amount of A atoms can be preferably 8% by mass or less, and more preferably 6% by mass or less. However, even if the remaining amount of A atoms exceeds 10% by mass, there may be no problem depending on the use conditions or the like.

[0072] In order to obtain a material containing MQO with higher purity, it is preferable to repeat washing and centrifugation multiple times and to recover the supernatant liquid after final centrifugation. Such a supernatant liquid can be formed into a slurry containing MQO particles as it is, appropriately diluted with a liquid medium, or mixed with a liquid medium after drying.

[0073] According to the present embodiment, as an ion-conductive oxide material having sufficient ion conductivity, for example, a TiO2-based one-dimensional (1D) nanofilament (NF) or solid electrolyte film having sufficient ion conductivity can be provided.

[0074] Although the materials in certain embodiments of the present disclosure have been described in detail above, the present disclosure can be modified in various ways. It should be noted that the material of the present disclosure may be manufactured by a method different from the manufacturing method in the above-described embodiment.

[0075] <Preparation of sample> (Example 1) (Preparation of slurry containing TiCO) First, a container (100 mL I Boy) was charged with 1 g of titanium diboride (TiB2, manufactured by Alfa Aesar) and 10 mL of a 25% by mass aqueous tetramethylammonium hydroxide (TMAH) solution (manufactured by Alfa Aesar). Thereto was placed a stirrer chip having a length substantially equal to the inner diameter of the circular bottom surface of the container (35 mm). While the container was kept at 80°C in an oil bath, the mixture in the container was stirred with a stirrer chip and maintained for 120 hours, thereby allowing the reaction to proceed. The reaction mixture in the container was then transferred to a centrifuge tube. Centrifugation was performed using a centrifuge under conditions of 3500 G and 5 minutes to precipitate the solid content. (i) After centrifugation, the supernatant was discarded, (ii) 40 mL of ethanol (manufactured by Fisher Chemical Co., Ltd.) was added to the remaining precipitate in the centrifuge tube, dispersion treatment using a Vortex mixer was performed for 5 minutes (reslurry), and (iii) centrifugation was performed under the same conditions as described above. The operations (i) to (iii) were repeated until the pH of the supernatant liquid was 8 or less. When the operations were repeated three times, the pH of the supernatant liquid became 8 or less. Therefore, this supernatant liquid was discarded, and the repeated operations were terminated. 40 mL of pure water was added to the remaining precipitate in the centrifuge tube, and the mixture was shaken and stirred for 5 minutes using a Vortex mixer. Thereafter, centrifugation was performed using a centrifuge under the conditions of 3500 G and 30 minutes, and the supernatant liquid was recovered as a sample slurry. The obtained sample slurry corresponds to a slurry containing TiCO.

[0076] (Preparation of TiCO film) A TiCO film was produced as follows using the slurry containing TiCO. 1 mL of the slurry containing TiCO was collected, mixed with 20 mL of pure water, and then vibrated with a vortex mixer for 5 minutes. The resulting mixture was filtered with suction overnight using Nutsche. A porous membrane (Celgard 3501, Gurley permeation test 200 seconds based on JIS (Japanese Industrial Standard), manufactured by Asahi Kasei Corp.) was used as a filter for suction filtration. After suction filtration, the precursor film on the filter was dried in a vacuum oven at 80°C overnight to obtain a TiCO film (self-supported film).

[0077] (Immersion in electrolytic solution) Using the TiCO film, a film for ion conductivity measurement was prepared as follows. Ion-exchanged water having a pH of 7 was placed in a Petri dish, and the TiCO film (self-supported film) was immersed therein for 30 minutes. Thereafter, the film was taken out from the ion-exchanged water having a pH of 7, and water droplets on the film surface were lightly wiped with a waste cloth to obtain a film containing TMA (tetramethylammonium) ions and H+as ionic species.

[0078] (Example 2) A TiCO film (self-supported film) was prepared in the same manner as in Example 1.

[0079] (Preparation of aqueous lithium chloride (LiCl) solution-immersed film) An aqueous lithium chloride solution having a concentration of 1 M was placed in a Petri dish, and the film (self-supported film) was immersed therein for 10 minutes. Thereafter, the film was taken out from the aqueous lithium chloride solution, and the film surface was washed away with pure water for the purpose of removing excessive lithium chloride on the film surface. The washing was repeated until the pH of the washing liquid reached 7. Thereafter, water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous lithium chloride solution-immersed film containing 2.7% by mass of Li ions.

[0080] (Immersion in electrolytic solution) Using the above aqueous LiCl solution-immersed film, an aqueous LiCl-sulfuric acid solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous sulfuric acid solution having a concentration of 0.05 M was placed in a Petri dish, and the film (self-supported film) was immersed therein for 30 minutes. Thereafter, the film was taken out from the aqueous sulfuric acid solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous LiCl-sulfuric acid solution-immersed film containing 2.2% by mass of Li ions (monovalent) as ions and H+.

[0081] (Example 3) In the same manner as in Example 2, an aqueous lithium chloride solution-immersed film containing 2.7% by mass of Li was prepared.

[0082] (Immersion in electrolytic solution) Using the aqueous lithium chloride solution-immersed film, an aqueous LiCl solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous LiCl solution having a concentration of 0.5 M was placed in a Petri dish, and the aqueous lithium chloride solution-immersed film was immersed therein for 30 minutes. Thereafter, the film was taken out from the LiCl aqueous solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous LiCl solution-immersed film containing 3.0% by mass of Li ions (monovalent) and H+as ions.

[0083] (Example 4) A TiCO film (self-supported film) was prepared in the same manner as in Example 1.

[0084] (Preparation of aqueous magnesium chloride (MgCl2) solution-immersed film) Using the TiCO film, ion-exchanged TiCO was prepared as follows. An aqueous MgCl2solution having a concentration of 0.5 M was placed in a Petri dish, and the film (self-supported film) was immersed therein for 30 minutes. Thereafter, the film was taken out from the MgCl2aqueous solution, and for the purpose of removing excessive MgCl2on the film surface, washing of washing the film surface 4 times with pure water was repeated, and then water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous MgCl2solution-immersed film containing 2.3% by mass of Mg ions.

[0085] (Immersion in electrolytic solution) Using the aqueous MgCl2solution-immersed film, an aqueous MgCl2-sulfuric acid solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous sulfuric acid solution having a concentration of 0.05 M was placed in a Petri dish, and the aqueous MgCl2solution-immersed film was immersed therein for 30 minutes. Thereafter, the film was taken out from the aqueous sulfuric acid solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous MgCl2-sulfuric acid solution-immersed film containing 2.2% by mass of Mg ions (divalent) as ions and H+.

[0086] (Example 5) A magnesium chloride (MgCl2) aqueous solution-immersed film was prepared in the same manner as in Example 4.

[0087] (Preparation of aqueous MgCl2-lithium chloride (LiCl) solution-immersed film) An aqueous lithium chloride solution having a concentration of 0.5 M was placed in a Petri dish, and an aqueous magnesium chloride (MgCl2) solution-immersed film was immersed therein for 10 minutes. Thereafter, the film was taken out from the aqueous lithium chloride solution, and the film surface was washed away with pure water for the purpose of removing excessive lithium chloride on the film surface. Washing was repeated 10 times until excess lithium chloride was removed. Thereafter, water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous MgCl2-lithium chloride (LiCl) solution-immersed film containing 1.2% by mass of Li ions. (Immersion in electrolytic solution) Using the aqueous MgCl2-lithium chloride solution-immersed film, an aqueous MgCl2-LiCl-sulfuric acid solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous sulfuric acid solution having a concentration of 0.05 M was placed in a Petri dish, and the aqueous MgCl2-lithium chloride solution-immersed film was immersed therein for 30 minutes. Thereafter, the film was taken out from the aqueous sulfuric acid solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous MgCl2-LiCl-sulfuric acid solution-immersed film containing 1.3% by mass of Mg ions (divalent), 1.2% by mass of Li ions (monovalent) as ions, and H+.

[0088] (Example 6) A TiCO film (self-supported film) was prepared in the same manner as in Example 1.

[0089] (Preparation of aqueous aluminum chloride (AlCl3) solution-immersed film) Using the TiCO film, ion-exchanged TiCO was prepared as follows. An aqueous AlCl3solution having a concentration of 0.5 M was placed in a Petri dish, and the film (self-supported film) was immersed therein for 30 minutes. Thereafter, the film was taken out from the aqueous AlCl3solution, and for the purpose of removing excessive AlCl3on the film surface, washing of the film surface with pure water was repeated 4 times, and then water droplets on the film surface were lightly wiped off with a waste cloth to complete an aqueous AlCl3solution-immersed film containing 1.8% by mass of Al ions (trivalent).

[0090] (Immersion in electrolytic solution) Using the aqueous AlCl3solution-immersed film, an aqueous AlCl3-sulfuric acid solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous sulfuric acid solution having a concentration of 0.05 M was placed in a Petri dish, and the aqueous AlCl3solution-immersed film was immersed therein for 30 minutes. Thereafter, the film was taken out from the aqueous sulfuric acid solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous AlCl3-sulfuric acid solution-immersed film containing 1.6% by mass of Al ions (trivalent) as ions and H+.

[0091] (Example 7) An aqueous aluminum chloride (AlCl3) solution-immersed film was prepared in the same manner as in Example 4.

[0092] (Immersion in electrolytic solution) Using the aqueous aluminum chloride solution-immersed film, an aqueous aluminum chloride-LiCl solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous LiCl solution having a concentration of 0.5 M was placed in a Petri dish, and the aqueous aluminum chloride solution-immersed film was immersed therein for 30 minutes. Thereafter, the film was taken out from the LiCl aqueous solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous AlCl3-LiCl solution-immersed film containing 1.6% by mass of Al (trivalent), 2.0% by mass of Li ions (monovalent), and H+as ions.

[0093] (Example 8) An aqueous aluminum chloride (AlCl3) solution-immersed film was prepared in the same manner as in Example 4.

[0094] (Preparation of aqueous AlCl3-lithium chloride (LiCl) solution-immersed film) An aqueous lithium chloride solution having a concentration of 1 M was placed in a Petri dish, and the aqueous aluminum chloride (AlCl3) solution-immersed film was immersed therein for 10 minutes. Thereafter, the film was taken out from the aqueous lithium chloride solution, and the film surface was washed away with pure water for the purpose of removing excessive lithium chloride on the film surface. Washing was repeated 10 times until excess lithium chloride was removed. Thereafter, water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous AlCl3-lithium chloride (LiCl) solution-immersed film containing 1.9% by mass of Li ions.

[0095] (Immersion in electrolytic solution) Using the aqueous AlCl3-lithium chloride (LiCl) solution-immersed film, an aqueous AlCl3-LiCl-sulfuric acid solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous sulfuric acid solution having a concentration of 0.05 M was placed in a Petri dish, and the aqueous AlCl3-lithium chloride (LiCl) solution-immersed film was immersed therein for 30 minutes. Thereafter, the film was taken out from the aqueous sulfuric acid solution, and water droplets on the film surface were lightly wiped with a waste cloth to complete an aqueous AlCl3-LiCl-sulfuric acid solution-immersed film containing 1.2% by mass of Al ions (trivalent), 1.4% by mass of Li ions (monovalent) as ions, and H+.

[0096] (Comparative Example 1) A TiCO film (self-supported film) was prepared in the same manner as in Example 1.

[0097] Using the TiCO film (self-supported film), an aqueous sulfuric acid solution-immersed film for ion conductivity measurement was prepared as follows. An aqueous sulfuric acid solution having a concentration of 0.05 M was placed in a Petri dish, and the TiCO film (self-supported film) was immersed therein for 30 minutes. Thereafter, the shape of the film was deformed by the aqueous sulfuric acid solution, and the self-supported film could not be maintained, and as a result, a film could not be obtained. As a reason for this, it is considered that when immersed in an acid in a state where TMA presents as an interlayer ion, the phase transition occurs to an anatase type, and at that time, the interlayer disappears, a self-supported film is not obtained, and the powder is obtained.Evaluation of sample

[0098] Raman spectroscopic analysis, ion conductivity measurement, the measurement of the interlayer distance, and measurement of the amount of crystal water of the produced film as a sample were performed as follows. In Comparative Example 1, a film could not be obtained, and any measurement could not be performed.

[0099] (Raman spectroscopic analysis measurement) A Raman spectrum of each immersion film was obtained by performing measurement using a laser beam having a wavelength of 532 nm as an excitation light source in a Raman spectrometer (Renishaw, product number: InVia). In the Raman spectrum, since the Raman shift had peaks at positions of 202, 290, 453, 677, and 922 cm-1, it is considered that the crystal structure has a lepidocrocite type crystal structure.

[0100] (Measurement of ion conductivity) The ion conductivity in the thickness direction of a sample (each of the above films prepared assuming a solid electrolyte sample) was measured as follows.

[0101] A pair of electrodes was disposed on a surface orthogonal to the thickness direction of each film (solid electrolyte sample). A direct current or alternating current voltage was applied between the sample and the pair of electrodes, and an ion current flowing in the sample at that time was measured. The resistance value (impedance) generated in the sample was obtained from the relationship between the measured ion current and the applied voltage. The ion conductivity generated in the sample was calculated from the thickness and area of the sample and the obtained resistance value (impedance). Specifically, a cylindrical sample having a diameter of 10 mm and a thickness of 100 μm was prepared as a solid electrolyte sample. A pair of metal disc-shaped electrodes (diameter: 10 mm) was disposed on both end surfaces of the sample, and each electrode was brought into close contact with the sample surface. An alternating current signal (amplitude: 10 mV) was applied between the pair of electrodes at an alternating current frequency in the range of 20 Hz to 50 MHz. Then, an alternating current response signal (impedance) flowing between the pair of electrodes was measured by an impedance analyzer.

[0102] The resistance component (R) was obtained from the measured impedance data by equivalent circuit analysis. The ion conductivity (σ) was calculated from the sample thickness (d = 100 μm), the sample cross-sectional area (A = 78.5mm2), and the obtained resistance component (R) by the following equation. The case where the ionic conductivity (σ) was 0.001 mS or more at 30°C and 95%RH was evaluated to be useful as the solid electrolyte for a fuel cell or water electrolyzer. The calculated ionic conductivity (σ) is shown in Table 1. σ = (1 / R) * (d / A)

[0103] In the measurement of the ion conductivity, the electrolytic solution may be impregnated into the solid electrolyte. Examples of a protic electrolytic solution include sulfuric acid, hydrochloric acid, and nitric acid. Examples of an electrolytic solution near neutrality include ion-exchanged water. Examples of an alkaline electrolytic solution include at least one electrolytic solution selected from the group consisting of ionic compounds such as KOH and NaOH.

[0104] (Measurement of interlayer distance) The interlayer distance was determined using each film (solid electrolyte sample). First, a CuKα ray (= about 1.54 angstrom) was used as a characteristic X-ray in an XRD analyzer (MiniFlex manufactured by Rigaku Holdings Corporation), and an X-ray diffraction (XRD) pattern was obtained by θ-axis direction scanning. The above-described interlayer distance of the solid electrolyte sample (each film) is calculated from the XRD pattern. Specifically, for the peak of 2θ = 2° or more and 12° or less, the value of 2θ was substituted into the Bragg’s equation to calculate the interlayer distance. Bragg's equation (Bragg's Law) is an equation for describing the diffraction phenomenon of a wave such as an X-ray, and for representing the relationship between the crystal lattice plane spacing (d), the incident angle (θ), and the wavelength (λ). Bragg’s equation is expressed as follows. nλ = 2dsinθ In the above equation, n represents an integer (diffraction order), λ represents an incident wavelength, d represents a crystal lattice plane spacing, and θ represents a diffraction angle. The calculated interlayer distance is shown in Table 1.

[0105] (Measurement of amount of crystal water) The amount of crystal water (molecular weight of water in the interlayer) was calculated by thermogravimetry-mass spectrometry (TG-MS) as follows. Each film was heated from 50°C to 500°C at a heating rate of 10°C / min in a He atmosphere (flow rate: 70 mL / min). The weight % of crystal water was determined from the amount of crystal water calculated from the integral value of the peak of H2O gas present at the position of 300 to 500°C at the time of temperature rise and the weight of the sample (excluding water molecules adsorbed outside the interlayer) at 300°C. The results are shown in Table 1.

[0106]

[0107] In Comparative Example 1, a film could not be formed in the first place. On the other hand, in Examples 1 to 8, a film could be formed, and the ionic conductivity was measurable. In particular, in Examples 5 to 8, the value of the ionic conductivity was higher than that in Example 4. From this, in Examples 5 to 8, H+and crystal water are considered to have a good balance in the interlayer.

[0108] This application claims priority to Application No. 63 / 669706, filed in the United States on July 11, 2024, the entire contents of which are incorporated herein by reference.

[0109] The ion-conductive oxide material of the present disclosure can be used as the solid electrolyte for a fuel cell or water electrolyzer. In addition, it can be used as the solid electrolyte of an ion battery such as in modern lithium-ion batteries (LiBs). In the above applications, the solid electrolyte can be used not only as a solid electrolyte but also as an additive to an electrode.

Claims

1. An ion-conductive oxide material comprising: one or more materials selected from the group consisting of nanofibers, nanowires, or two-dimensional substances represented by the following formula: MQaOb wherein M is at least one element selected from the group consisting of Groups 3, 4, 5, 6, or 7, Q is at least one element selected from the group consisting of Groups 12, 13, 14, 15, or 16, provided that O is excluded, and a is 0 or more and 2 or less, and b is greater than 0 and 2 or less; and two or more ions selected from the group consisting of H+, metal ions, organic ions, or OH-in an interlayer.

2. The ion-conductive oxide material according to claim 1, comprising two or more metal ions in the interlayer.

3. The ion-conductive oxide material according to claim 1 or 2, wherein each of the metal ions is a trivalent or higher metal ion.

4. The ion-conductive oxide material according to any one of claims 1 to 3, wherein the metal ions are ions of main group metal elements and transition metal elements of Groups 1 (excluding hydrogen) to 15 of the periodic table.

5. The ion-conductive oxide material according to any one of claims 1 to 4, wherein the organic ions are ammonium ions and an ionized organic substance.

6. The ion-conductive oxide material according to any one of claims 1 to 5, wherein the two or more ions include metal cations having different valences.

7. The ion-conductive oxide material according to any one of claims 1 to 6, wherein the amount of ions present in the interlayer is 0.001 to 10% by mass.

8. The ion-conductive oxide material according to any one of claims 1 to 7, wherein an interlayer distance at which the ions (and crystal water that may be present) are present is 1 to 20 angstroms.

9. The ion-conductive oxide material according to any one of claims 1 to 8, wherein the two or more ions include TMA (tetramethylammonium) ions and H+.

10. The ion-conductive oxide material according to any one of claims 1 to 9, wherein the two or more ions include Li ions (monovalent) and H+.

11. The ion-conductive oxide material according to any one of claims 1 to 10, wherein the two or more ions include Mg ions (divalent) and H+.

12. The ion-conductive oxide material according to any one of claims 1 to 11, wherein the two or more ions include Mg ions (divalent), Li ions (monovalent) and H+.

13. The ion-conductive oxide material according to any one of claims 1 to 12, wherein the two or more ions include Al ions (trivalent) and H+.

14. The ion-conductive oxide material according to any one of claims 1 to 13, wherein the two or more ions include Al ions (trivalent), Li ions (monovalent) and H+.

Images