WO2019093441A1 - Amorphous transition metal oxide and use thereof - Google Patents

Amorphous transition metal oxide and use thereof Download PDF

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WO2019093441A1
WO2019093441A1 PCT/JP2018/041555 JP2018041555W WO2019093441A1 WO 2019093441 A1 WO2019093441 A1 WO 2019093441A1 JP 2018041555 W JP2018041555 W JP 2018041555W WO 2019093441 A1 WO2019093441 A1 WO 2019093441A1
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metal oxide
transition metal
catalyst
range
oxygen
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PCT/JP2018/041555
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French (fr)
Japanese (ja)
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芳尚 青木
浩樹 幅▲ざき▼
ダミアン コヴァルスキー
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国立大学法人北海道大学
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/02—Hydrogen or oxygen
    • C25B1/04—Hydrogen or oxygen by electrolysis of water
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Definitions

  • the present invention relates to amorphous transition metal oxides and their use. Further, the present invention relates to a catalyst for an air electrode using an amorphous transition metal oxide and a catalyst for a water electrolysis anode. In addition, the present invention relates to a metal air secondary battery using the catalyst for the air electrode.
  • a perovskite type transition metal oxide ABO 3 has been reported as a non-precious metal OER catalyst containing no precious metal.
  • the perovskite oxide has a transition metal at the B site and is composed of an octahedral structure bonded to six oxygens.
  • e g electron number of the B site transition metal is associated with its OER activity, e g the number of electrons 1 near La 0.5 Ca 0.5 CoO 3- ⁇ , such as a high activity (1.5 It is reported that mA / cm 2 @ 1.6 V vs RHE, 0.1 mol dm ⁇ 3 in a NaOH aqueous solution) [Non-patent document 2].
  • the material which has a CoOOH nanosheet structure is reported as an example of the OER catalyst which has a novel structure (nonpatent literature 3).
  • This material was prepared by layer peeling by sonicating an ⁇ -Co (OH) 2 sheet in the presence of Cl anion and water, followed by oxidation using NaClO, as shown in FIG.
  • the TEM image of and the AFFM image of 1c it has a particle size of 200-300 nm.
  • the result of XRD in FIG. 1 d it has crystallinity.
  • Patent Document 1 WO 2015/115592
  • Non-Patent Document 1 Y. Lee, et al., J. Phys. Chem. Lett. 2012, 3, 399.
  • Non-patent document 2 Suntivich Science 2011, 334, 1383.
  • Non-Patent Document 3 J. Huang, et al., Angewandte_Chemie_International_Edition 2015, 54, 8722-8727 The entire descriptions of Patent Document 1 and Non-Patent Documents 1 to 3 are specifically incorporated herein by reference.
  • the brown mirror light type transition metal oxide A 2 B 2 O 5 containing two types of transition metals described in Patent Document 1 exhibits OER activity superior to that of a noble metal catalyst.
  • the materials described in Non-Patent Document 3 have a complicated manufacturing method and there is room for further improvement because the OER activity is not high.
  • an object of the present invention is to develop a new transition metal oxide catalyst having higher OER activity, and further provide an air electrode catalyst, a water electrolytic anode catalyst, an air electrode and an air secondary battery using this catalyst. It is.
  • the present invention is as follows.
  • Amorphous, non-oxygen-deficient or oxygen-deficient transition metal oxide containing one or more elements selected from the following group A, one or more elements selected from group B, and cobalt Yes However, A group consists of Ca, Sr, Ba and rare earth elements (RE), Group B consists of 3d transition elements other than Co, And an oxide in which a cluster structure having a particle size in the range of 0.1 to 10 nm is observed in high resolution transmission electron microscopy, wherein the cluster structure portion has an element arrangement structure of ⁇ -CoOOH type or an element arrangement structure similar thereto. Having transition metal oxide.
  • An element arrangement structure of ⁇ -CoOOH type or an element arrangement structure similar to this is formed for charge compensation in a [CoO x ] planar monolayer formed by two-dimensionally connecting CoO 6 octahedra by sharing a ring.
  • protons coordinated [CoO x H y] plane monolayer can be n layer laminated to a [CoO x H y] n molecules layer, [CoO x H y] one side of the planar monolayer 10nm or less X is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, and n is the number of laminations in the direction (c-axis direction) perpendicular to the molecular layer plane of the planar monolayer, In the range of ⁇ 25, a part of Co in the [CoO x H y ] planar monolayer may be substituted with Fe, or a part of oxygen of the CoO 6 octahedron may be deficient Transition metal oxides described in [1].
  • Amorphous, non-oxygen-depleted type having an element arrangement structure of ⁇ -CoOOH type or an element arrangement structure similar thereto and having a cluster structure with a particle size in the range of 0.1 to 10 nm in high resolution transmission electron microscopy Or a method of producing an oxygen deficient transition metal oxide.
  • a x B 1 2-y B 2 y O 5 (1)
  • A represents Ca, Sr, Ba or a rare earth element (RE)
  • B 1 represents Co
  • B 2 represents a 3d transition element other than Co
  • x is a numerical value in the range of 1.5 to 2.0
  • y is a numerical value in the range of 0 to 1.0.
  • the metal air secondary battery which has an air electrode as described in [11] or [12], the negative electrode containing a negative electrode active material, and the electrolyte interposed between the said air electrode and the said negative electrode.
  • the metal-air secondary battery according to [13] further including an oxygen reduction air electrode containing a catalyst for oxygen reduction.
  • a novel oxide which is an amorphous transition metal oxide and in which a cluster structure having a particle size in the range of 0.1 to 10 nm can be found in a matrix structure. Since the ORR activity is higher than light type transition metal oxide A 2 B 2 O 5 , an excellent catalyst for air electrode and a catalyst for water electrolytic anode can be provided. Further, according to the present invention, it is possible to provide an air electrode for a metal air secondary battery using the catalyst for the air electrode and a metal air secondary battery using the air electrode.
  • FIG. 1 is a current-time curve when a Ca 2 FeCoO 5 carbon sheet electrode sample is subjected to constant-potential polarization at 1.7 V vs RHE for 20 h and oxygen generation reaction (OER).
  • (a) shows the current-voltage curve when the potential scan from 1.2 V vs RHE to 1.7 V vs RHE and OER is performed for the sample before and after the 20 h constant potential OER in FIG.
  • (b) shows a current-voltage curve when a potential scan from 1.0 V vs RHE to 0.6 V vs RHE is performed and oxygen reduction reaction (ORR) is performed for the sample before and after the 20 h constant potential OER in FIG.
  • ORR oxygen reduction reaction
  • FIG 1 shows a 20 h polarization before and after Ca 2 FeCoO 5 electrode sample XRD pattern.
  • TEM transmission electron microscope
  • TEM High resolution transmission electron microscope
  • TEM High resolution transmission electron microscope
  • the present invention is an amorphous non-oxygen-deficient or oxygen-deficient transition including one or more elements selected from the following group A, one or more elements selected from group B, and cobalt.
  • the cluster structure portion is a transition metal oxide having an element arrangement structure of ⁇ -CoOOH type or an element arrangement structure similar thereto.
  • the amorphous transition metal oxide of the present invention has a structure in which a cluster structure portion is dispersed in a matrix portion which is a portion other than the cluster structure portion. This structure can be observed and confirmed by high resolution transmission electron microscopy. Furthermore, the cluster structure portion had a particle size in the range of 0.1 to 10 nm, and the cluster structure shown in the example had a particle size in the range of approximately 0.5 to 5 nm.
  • the amorphous transition metal oxide of the present invention is an amorphous oxide because no diffraction pattern is observed in the limited field electron diffraction pattern and the halo pattern is exhibited.
  • the amorphous transition metal oxide of this invention is an amorphous oxide also in this point.
  • the matrix portion is amorphous, it does not matter whether the cluster structure portion is amorphous or not.
  • Amorphous in the oxide of the present invention means that a diffraction pattern can not be seen in a limited field electron diffraction image and a halo pattern is shown.
  • the amorphous transition metal oxide of the present invention is a material which is clearly different from the material described in Non-patent Document 3 because at least the particle diameter and diffraction peaks due to crystals are not observed by XRD.
  • the cluster structure part of the transition metal oxide of the present invention has an atomic arrangement structure that is the same as or similar to the atomic arrangement structure of ⁇ -CoOOH type.
  • the atomic arrangement structure of the ⁇ -CoOOH type is an atomic arrangement structure possessed by the crystal structure model of ⁇ -CoOOH (hexagonal), and FIG. 8 shows a crystal structure model of ⁇ -CoOOH (hexagonal). Red spheres (small), blue spheres (large) and white spheres (small, isolated between layers) in the figure indicate oxygen atom, cobalt atom and hydrogen atom, respectively.
  • the ⁇ -CoOOH has a layered structure in which a [CoO 2 ] planar molecular layer formed by the sharing of CoO 6 octahedra is stacked on the c-axis by hydrogen bonding via protons.
  • the transition metal oxide of the present invention has an atomic arrangement structure identical or similar to the crystal structure model of ⁇ -CoOOH (hexagonal crystal) shown in FIG. Such an atomic structure will be described later in the manufacturing method, but OER polarization causes rearrangement of the atoms to form a Co-rich oxide portion in the oxide matrix, which is similar to ⁇ -CoOOH. It is guessed that it formed.
  • the cluster structure in the oxide of the present invention observed by high resolution TEM is shown in FIG. 4b.
  • This cluster structure is a cluster structure having an atomic arrangement structure identical or similar to that of the ⁇ -CoOOH type atomic arrangement structure. is there.
  • the cluster structure part of the present invention may have oxygen vacancies, the part having oxygen vacancies is not identical to the atomic arrangement structure of ⁇ -CoOOH type, and an atom similar to the atomic arrangement structure of ⁇ -CoOOH type It is defined as having an array structure.
  • protons for charge compensation are arranged in a [CoO x ] planar monolayer formed by two-dimensionally connecting CoO 6 octahedra by ring sharing. It is a transition metal oxide containing a cluster structure portion of a [CoO x H y ] n molecular layer sheet-like substance formed by n-layer lamination of layered [CoO x H y ] planar monolayers, and [CoO x H]
  • One side of the [1] planar monolayer is 10 nm or less, x is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, and n is the direction perpendicular to the molecular layer plane of the planar monolayer (c Number of layers in the axial direction, in the range of 1 to 25, and a part of Co in the [CoO x H y ] planar monolayer may be substituted with Fe, and the CoO 6 octahedron It is an
  • Cluster structure of transition metal oxides of the present invention is a [CoO x] protons for charge compensation in the plane monolayer coordinated [CoO x H y] cluster structure of the n molecules layer sheet material .
  • the oxygen coordination number around Co was 5.1 for 1 hour polarization (Table 2).
  • the Co coordination number in the [CoO 2 ] n plane molecular layer sheet having no oxygen deficiency is six. Therefore, the cluster structure portion of the transition metal oxide of the present invention shown in the experimental example is considered to be a material having, as a basic skeleton, a [CoO x ] n molecular layer sheet having oxygen deficiency.
  • the atomic arrangement structure of such [CoO x H y ] n molecular sheet material is not identical to the atomic arrangement structure of the ⁇ -CoOOH type, but has an atomic arrangement structure similar to that of the ⁇ -CoOOH type It can be said that.
  • x is in the range of 1.5 to 2.0, preferably in the range of 1.6 to 1.9
  • y is in the range of 0.01 to 1, preferably in the range of 0.05 to 0.5
  • n is 1 It is in the range of ⁇ 25.
  • the maximum outer diameter of the cluster structure portion observed in the TEM image is in the range of 0.3 to 10 nm, preferably in the range of 0.6 to 7 nm, more preferably 0.9 to 5 nm.
  • the diameter of the CoO 6 octahedron is about 0.29 nm (approximately 0.3 nm), and the interlayer distance of the [CoO x H y ] monolayer is about 0.4 nm.
  • the number of CoO X H y octahedral molecules in the [CoO X H y ] monolayer is 10 / 0.29 x in order to form a cluster structure of this particle diameter.
  • the cluster structure portion of the oxide of the present invention is a [CoO X H y ] n molecular layer sheet-like material in which a stack in the plane vertical direction exists but is not developed, and n is a plane monolayer Is the number of layers stacked in the direction (c-axis direction) perpendicular to the molecular layer plane.
  • n is 1 to 10 / 0.4 (about 25). Therefore, the above n is in the range of 1 to 25.
  • n is 2 to 7 / 0.4 (about 18) in the range of 0.6 to 7 nm in diameter
  • n is 2 or 3 to 5 / 0.4 (about 12) in the range of 0.9 to 5 nm in diameter.
  • Group A consists of Ca, Sr, Ba and rare earth elements (RE), Group B consists of 3d transition elements other than Co.
  • the A group element consists of Ca, Sr, Ba and a rare earth element (RE).
  • the rare earth elements (RE) are two elements of Sc and Y and 15 elements of lanthanoid, and the lanthanoid is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.
  • the rare earth element (RE) is preferably, for example, La, Pr, Nd, Sm, Eu, Gd, etc., which have a relatively large ion radius.
  • Group B elements are 3d transition elements other than Co.
  • the 3d transition element represented by B is, for example, at least one metal element selected from the group consisting of Fe, Mn, Cr, Ni, Ti, Cu, and Zn.
  • the group B element is preferably iron from the viewpoint of providing a new transition metal oxide catalyst with higher OER activity.
  • the molar ratio of the group A element, the group B element and cobalt in the cluster structure part is in the range of 0 to 1.99: 0.01 to 1.0: 1.0. And preferably in the range of 0.01 to 1.0: 0.1 to 1.0: 1.0.
  • the molar ratio of the group A element, the group B element and cobalt in the matrix part which is the part other than the cluster structure part is 0.01 or more, 2.0 or less: 0.5 or more: 1.0, preferably 0.01 or more, 2.0 or less: 1 or more: 1.0, more preferably 0.5 to 1.9: 0.5 to 2.0: 1.0.
  • the molar ratio of the elements can be determined by electron energy loss spectroscopy.
  • the amorphous transition metal oxide of the present invention is non-oxygen deficient or oxygen deficient.
  • the ratio of oxygen to other elements is a stoichiometric ratio, while in the oxygen-deficient oxide, oxygen is more chemically related to the amount of other elements. Less than stoichiometric ratio.
  • the degree of oxygen deficiency is not particularly limited, but for example, it is more than 0 and 25% or less of the total valence of elements other than oxygen it can. However, there may be more oxygen deficiency than this.
  • the transition metal oxide of the present invention can be produced by amorphizing a brown mirror light type transition metal oxide.
  • a x B 1 2-y B 2 y O 5 (1)
  • A represents Ca, Sr, Ba or a rare earth element (RE)
  • B 1 represents Co
  • B 2 represents a 3d transition element other than Co
  • B 1 and B 2 consist of different elements
  • x is a numerical value in the range of 1.5 to 2.0
  • y is a numerical value in the range of 0 to 1.0.
  • Amorphization can be carried out, for example, by immersing a brown mirrorlite type transition metal oxide in an aqueous alkaline solution or polarization treatment in an aqueous alkaline solution.
  • the alkaline aqueous solution immersion can be carried out, for example, by immersion in an aqueous solution of an alkali metal hydroxide and an alkaline earth metal hydroxide at a temperature range of 0 to 80 ° C., for example.
  • concentration of the aqueous alkaline solution is not particularly limited, but should be, for example, in the range of 0.1 M to 10 M in consideration of the type of transition metal oxide of brown mirror light type, the immersion temperature, the time required for amorphization, etc. Can.
  • the immersion time can be appropriately determined in consideration of the type of brown mirror light type transition metal oxide, the immersion temperature, the concentration of the aqueous alkali solution, and the like.
  • the polarization treatment in the alkaline aqueous solution can be carried out by applying an electric potential of, for example, 1.0 to 2.0 V based on RHE, using the same alkaline aqueous solution as that shown in the alkaline aqueous solution immersion as an electrolytic solution.
  • the temperature of the electrolytic solution and the electrolysis time can be appropriately determined in consideration of the type of the brown mirror light type transition metal oxide and the progress of the amorphization. If the polarization process in the alkaline aqueous solution is the same as in alkaline aqueous solution immersion, the treatment in a short time may be possible if the concentration of the alkaline aqueous solution is the same.
  • the brown mirror light type transition metal oxide to be subjected to amorphization can be, for example, a crystalline transition metal oxide represented by the following general formula (1).
  • a x B 1 2-y B 2 y O 5 (1)
  • A represents Ca, Sr, Ba or a rare earth element (RE)
  • B 1 represents Co
  • B 2 represents a 3d transition element other than Co
  • B 1 and B 2 consist of different elements
  • x is a numerical value in the range of 1.5 to 2.0
  • y is a numerical value in the range of 0 to 1.0.
  • the brown mirror light type transition metal oxide can be synthesized by a solid phase reaction method using each metal oxide as a raw material with reference to the method described in Patent Document 1 and the method described in the following document.
  • the following Non-patent documents 4 to 7 can be referred to for a synthesis method for Ca 2 FeCoO 5 .
  • Non-patent document 4 P. Berastegui et al., Mater. Res. Bull. 1999, 34, 303.
  • the brown mirror light type transition metal oxide can also be synthesized using a liquid phase reaction method.
  • the liquid phase reaction method salts of the respective metals, for example, nitrates, acetates, citrates and the like are used as raw materials of the respective metal oxides.
  • a Ca salt eg, Ca (NO 3 ) 2
  • an Fe salt eg, Fe (NO 3 ) 3 .9H 2 O
  • a Co salt eg, Co (NO) 3 ) 2
  • a mixture to which citric acid is added as a gelling agent are mixed as a solvent, for example, using water (distilled water or ion exchanged water) or the like.
  • the ratio of each metal salt is appropriately determined in consideration of the composition of the target metal oxide.
  • the amount of citric acid used as a gelling agent can be, for example, in the range of 10 to 1000 parts by mass with respect to 100 parts by mass of the metal salt.
  • EDTA ethylenediaminetetraacetic acid
  • glycine glycine
  • the mixture is heated, for example, to 50 to 90 ° C. to remove the solvent to gelate the mixture.
  • the gelled product is, for example, calcined in air at 300 to 500 ° C. (eg, 450 ° C.) for 10 minutes to 6 hours (eg, 1 hour) to synthesize a precursor.
  • this precursor can be baked, for example, in the air at 600 to 800 ° C. for 1 to 24 hours to synthesize brown mirror light type Ca 2 FeCoO 5 .
  • the firing conditions may be, for example, firing at 600 ° C. for a predetermined time (1 to 12 hours), and then raising the temperature, for example, firing at 800 ° C. for a predetermined time (6 to 12 hours).
  • the amorphous transition metal oxide of the present invention when used as a catalyst, the Braun Millerite type transition metal oxide having the same or similar composition and the OER activity are equivalent and higher ORR activity Indicates
  • Brown mirror light type Ca 2 FeCoO 5 as a raw material which was amorphous Ca
  • amorphous oxides containing Fe and Co as compared to brown mirror light type Ca 2 FeCoO 5 as a raw material It shows high ORR activity.
  • OER activity is equivalent.
  • the present invention includes a catalyst for an air electrode comprising the amorphous transition metal oxide of the present invention. Furthermore, the present invention includes a catalyst for a water electrolysis anode comprising the amorphous transition metal oxide of the present invention.
  • the catalyst for air electrode of the present invention and the catalyst for water electrolysis anode contain brown mirror light type transition metal oxide represented by the above general formula (1) in addition to the amorphous transition metal oxide of the present invention. You can also.
  • Amorphous transition metal oxide cathode catalyst and water electrolysis anode catalyst including the present invention can range from 1 ⁇ 100m 2 / g, preferably, 10 ⁇ 100 m 2 / It is in the range of g. However, it is not the intention limited to this range.
  • the amorphous transition metal oxide of the present invention is extremely useful as an air electrode, and is an air electrode of a metal-air secondary battery expected as hydrogen production by light water decomposition and as a next-generation high-capacity secondary battery. It is very promising as
  • the reaction at the anode of water electrolysis is represented by the following reaction formula.
  • Both reactions are oxygen evolution reactions (OER).
  • the amorphous transition metal oxide of the present invention is one having excellent OER activity, and is extremely useful as a catalyst for water electrolysis anode.
  • the cathode usually has a porous structure and contains a conductive material in addition to an oxygen reaction catalyst.
  • the air electrode may contain an oxygen reduction (ORR) catalyst, a binder, and the like, as necessary.
  • ORR oxygen reduction
  • the air electrode in the secondary battery needs to have OER catalyst activity as a function at the time of charge and ORR catalyst activity as a function at the time of discharge. Since the catalyst of the present invention is an OER catalyst, the air electrode can also contain an ORR catalyst in addition to the catalyst.
  • ORR oxygen reduction
  • the content of the catalyst (OER catalyst) of the present invention in the air electrode is not particularly limited, but it is preferably, for example, 1 to 90% by mass, particularly 10 to 60 mass, from the viewpoint of enhancing the oxygen reaction performance of the air electrode. % Is preferable, and 30 to 50% by mass is more preferable.
  • ORR catalysts include, but are not limited to, Pt or Pt-based materials (eg, PtCo, PtCoCr, Pt-W 2 C, Pt-RuOx, etc.), Pd-based materials (eg, PdTi, PdCr, PdCo) , etc.), metal oxides PdCoAu (e.g., ZrO 2-x, TiO x , TaN x O y, etc. Irmo x), complex type (Co- porphyrin complexes), and the like other (PtMoRuSeO x, etc. RuSe) it can. Furthermore, LaNiO 3 (Nat. Chem.
  • the conductive material is not particularly limited as long as it can be generally used as a conductive aid, and conductive carbon is preferably mentioned. Specifically, mesoporous carbon, graphite, acetylene black, carbon nanotubes, carbon fibers and the like can be mentioned. Conductive carbon having a large specific surface area is preferred because it provides many reaction sites at the air electrode. Specifically, conductive carbon having a specific surface area of 1 to 3000 m 2 / g, particularly 500 to 1500 m 2 / g is preferable.
  • the catalyst of the cathode may be supported on a conductive material.
  • the content of the conductive material in the air electrode is not particularly limited, but is preferably 10 to 99% by mass, particularly preferably 20 to 80% by mass, from the viewpoint of enhancing the discharge capacity. More preferably, it is 50% by mass.
  • the binder is not particularly limited, and examples thereof include polyvinylidene fluoride (PVDF) and copolymers thereof, polytetrafluoroethylene (PTFE) and copolymers thereof, and styrene butadiene rubber (SBR).
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • SBR styrene butadiene rubber
  • the content of the binder in the air electrode is not particularly limited, it is preferably, for example, 1 to 40% by mass, particularly 5 to 35% by mass from the viewpoint of the binding ability between carbon (conductive material) and the catalyst. Is preferably 10 to 35% by mass.
  • the air electrode can be formed, for example, by applying and drying a slurry prepared by dispersing the above-described air electrode constituent material in a suitable solvent on a substrate.
  • the solvent is not particularly limited, and examples thereof include acetone, N, N-dimethylformamide, N-methyl-2-pyrrolidone (NMP) and the like.
  • the mixing of the cathode constituent material and the solvent is preferably carried out usually for 3 hours or more, preferably 4 hours.
  • the mixing method is not particularly limited, and a general method can be adopted.
  • the substrate to which the slurry is applied is not particularly limited, and examples thereof include a glass plate, a Teflon (registered trademark) plate, and the like. These substrates are peeled off from the obtained air electrode after drying of the slurry.
  • the current collector of the air electrode or the solid electrolyte layer can be treated as the above-mentioned base material.
  • the base material is used as it is as a constituent member of the metal-air secondary battery without peeling off.
  • the coating method and the drying method of the slurry are not particularly limited, and a general method can be adopted.
  • a coating method such as a spray method, a doctor blade method, or a gravure printing method, or a drying method such as heat drying or reduced pressure drying can be employed.
  • the thickness of the air electrode is not particularly limited and may be appropriately set according to the use of the metal-air secondary battery etc., but usually 5 to 100 ⁇ m, 10 to 60 ⁇ m, particularly preferably 20 to 50 ⁇ m.
  • An air electrode current collector for collecting current from the air electrode is usually connected to the air electrode.
  • the material and shape of the air electrode current collector are not particularly limited. Examples of the material of the air electrode current collector include stainless steel, aluminum, iron, nickel, titanium, carbon (carbon) and the like. Further, the shape of the air electrode current collector may be a foil shape, a plate shape, a mesh (grid shape), a fiber shape or the like, and among them, a porous shape such as a mesh shape is preferable. The porous current collector is excellent in the efficiency of oxygen supply to the air electrode.
  • the metal-air secondary battery of the present invention comprises an air electrode containing a catalyst containing the above amorphous transition metal oxide, a negative electrode containing a negative electrode active material, and an electrolyte interposed between the air electrode and the negative electrode.
  • the air electrode of the metal-air secondary battery of the present invention contains a catalyst containing an amorphous transition metal oxide transition metal oxide, which exhibits excellent OER catalytic properties. Therefore, by using an air electrode using this catalyst, the metal-air secondary battery of the present invention becomes excellent in charge rate and charge voltage.
  • the air electrode can also coexist a catalyst having ORR catalytic activity as described above.
  • an air electrode for oxygen reduction (ORR) containing a catalyst having ORR catalytic activity can be provided separately from an air electrode for oxygen generation (OER) containing a catalyst containing amorphous transition metal oxide.
  • the metal-air secondary battery has an air electrode for oxygen reduction and an air electrode for oxygen generation (three-electrode system). At the time of discharge, an air electrode for oxygen reduction is used, and at the time of charge, an air electrode for oxygen generation is used.
  • the catalyst having ORR catalytic activity is as described above, and an air electrode for oxygen generation can be obtained using this catalyst and the conductive material and the binder described in the explanation of the air electrode.
  • FIG. 10 is a cross-sectional view showing an embodiment of the metal-air secondary battery of the present invention.
  • the metal-air secondary battery 1 includes an air electrode 2 using oxygen as an active material, a negative electrode 3 containing a negative electrode active material, an electrolyte 4 responsible for ion conduction between the air electrode 2 and the negative electrode 3, and a current collector of the air electrode 2.
  • An air electrode current collector 5 to be performed and a negative electrode current collector 6 to collect current from the negative electrode 3 are accommodated in a battery case (not shown).
  • An air electrode current collector 5 for collecting current of the air electrode 2 is electrically connected to the air electrode 2, and the air electrode current collector 5 has a porous structure capable of supplying oxygen to the air electrode 2.
  • the negative electrode current collector 6 for collecting current of the negative electrode 3 is electrically connected to the negative electrode 3, and one of the end portions of the air electrode current collector 5 and the negative electrode current collector 6 protrudes from the battery case There is. It functions as a positive electrode terminal (not shown) and a negative electrode terminal (not shown), respectively.
  • the negative electrode contains a negative electrode active material.
  • a negative electrode active material the negative electrode active material of a common air battery can be used, It does not specifically limit.
  • the negative electrode active material is usually capable of inserting and extracting metal ions.
  • Specific examples of the negative electrode active material include metals such as Li, Na, K, Mg, Ca, Zn, Al, and Fe, alloys of these metals, oxides and nitrides, and carbon materials.
  • zinc-air secondary batteries are excellent in terms of safety, and are expected as next-generation secondary batteries.
  • Lithium-air secondary batteries and magnesium-air secondary batteries are promising from the viewpoint of high voltage and high output.
  • An example of the zinc-air secondary battery will be described below, and the reaction formula is as follows.
  • a material capable of inserting and extracting zinc ions is used as the negative electrode.
  • a zinc alloy can also be used as such a negative electrode.
  • the zinc alloy include zinc alloys containing one or more elements selected from aluminum, indium, magnesium, tin, titanium, and copper.
  • metal lithium As a negative electrode active material of a lithium-air secondary battery, for example, metal lithium; lithium alloy such as lithium aluminum alloy, lithium tin alloy, lithium lead alloy, lithium silicon alloy, etc .; tin oxide, silicon oxide, lithium titanium oxide, Metal oxides such as niobium oxide and tungsten oxide; metal sulfides such as tin sulfide and titanium sulfide; metal nitrides such as lithium cobalt nitride, lithium iron nitride and lithium manganese nitride; and graphite A carbon material etc. can be mentioned and metal lithium is preferable among them.
  • metal lithium is preferable among them.
  • the negative electrode active material of the magnesium-air secondary battery a material capable of inserting and extracting magnesium ions is used.
  • a negative electrode magnesium aluminum, magnesium silicon, magnesium alloys such as magnesium gallium and the like can be used besides metal magnesium.
  • the foil-like or plate-like negative electrode active material can be used as the negative electrode itself.
  • the negative electrode may contain at least a negative electrode active material, but may contain a binder for immobilizing the negative electrode active material, if necessary.
  • the type of binder, the amount used, and the like are the same as those of the above-described air electrode, and thus the description thereof is omitted here.
  • the negative electrode is usually connected to a negative electrode current collector for collecting current from the negative electrode.
  • the material and shape of the negative electrode current collector are not particularly limited. Examples of the material of the negative electrode current collector include stainless steel, copper, nickel and the like. Moreover, as a shape of a negative electrode collector, foil shape, plate shape, mesh (grid shape) etc. are mentioned.
  • An electrolyte is disposed between the air electrode and the negative electrode. Metal ion conduction between the negative electrode and the air electrode takes place via the electrolyte.
  • the form of the electrolyte is not particularly limited, and examples thereof include a liquid electrolyte, a gel electrolyte, a solid electrolyte and the like.
  • the electrolytic solution may be an alkaline aqueous solution such as an aqueous solution of potassium hydroxide containing zinc oxide or an aqueous solution of sodium hydroxide, for example, when the negative electrode is zinc or an alloy thereof, or zinc chloride or zinc perchlorate.
  • An aqueous solution may be used, or a non-aqueous solvent containing zinc perchlorate or a non-aqueous solvent containing zinc bis (trifluoromethylsulfonyl) imide may be used.
  • a negative electrode is magnesium or its alloy is mentioned as an example, you may use the non-aqueous solvent containing magnesium perchlorate and magnesium bis (trifluoromethyl sulfonyl) imide.
  • non-aqueous solvent for example, conventional secondary batteries such as ethylene carbonate (EC), propylene carbonate (PC), ⁇ -butyrolactone ( ⁇ -BL), diethyl carbonate (DEC), dimethyl carbonate (DMC) or the like
  • EC ethylene carbonate
  • PC propylene carbonate
  • ⁇ -BL ⁇ -butyrolactone
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • ionic liquids such as N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (am) can also be used.
  • the electrolyte preferably contains a dendrite formation inhibitor. It is believed that the dendrite formation inhibitor suppresses the generation of dendrite by adsorbing to the negative electrode surface at the time of charge to reduce the energy difference between crystal planes and preventing preferential orientation.
  • the dendrite formation inhibitor is not particularly limited, and may be, for example, at least one selected from the group consisting of polyalkyleneimines, polyallylamines and asymmetric dialkyl sulfones (for example, JP-A-2009 -93983)).
  • the amount of the dendrite formation inhibitor used is not particularly limited, but may be used, for example, as an amount that saturates the electrolyte at normal temperature and pressure, or as a solvent.
  • the liquid electrolyte having lithium ion conductivity is usually a non-aqueous electrolyte containing a lithium salt and a non-aqueous solvent.
  • the lithium salt include inorganic lithium salts such as LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 ; and LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , Organic lithium salts such as LiC (CF 3 SO 2 ) 3 and the like can be mentioned.
  • non-aqueous solvent examples include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butylene carbonate, ⁇ -butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and mixtures thereof can be mentioned.
  • An ionic liquid can also be used as a non-aqueous solvent.
  • the concentration of the lithium salt in the non-aqueous electrolytic solution is not particularly limited, but is preferably in the range of, for example, 0.1 mol / L to 3 mol / L, and preferably 1 mol / L.
  • a low volatility liquid such as an ionic liquid may be used as the non-aqueous electrolyte.
  • the gel electrolyte having lithium ion conductivity can be obtained, for example, by adding a polymer to the above-mentioned non-aqueous electrolyte and gelling it.
  • a polymer such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF, trade name Kynar manufactured by Arkema, etc.) polyacrylonitrile (PAN) or polymethyl methacrylate (PMMA) is added to the non-aqueous electrolyte. Gelation can be performed by carrying out.
  • the solid electrolyte having lithium ion conductivity is not particularly limited, and a general solid electrolyte usable in a lithium metal air secondary battery can be used.
  • oxide solid electrolytes such as Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 ; Li 2 S—P 2 S 5 compounds, Li 2 S—SiS 2 compounds, Li 2 S—GeS 2 And compounds such as sulfide solid electrolytes.
  • the thickness of the electrolyte varies depending on the configuration of the battery, but is preferably in the range of, for example, 10 ⁇ m to 5000 ⁇ m.
  • a separator is preferably disposed between the air electrode and the negative electrode in order to ensure electrical insulation between the electrodes.
  • the separator is not particularly limited as long as it has a structure in which electrical insulation between the air electrode and the negative electrode can be secured and an electrolyte can be interposed between the air electrode and the negative electrode.
  • separator examples include porous films such as polyethylene, polypropylene, cellulose, polyvinylidene fluoride, and glass ceramics; and nonwoven fabrics such as resin nonwoven fabrics and glass fiber nonwoven fabrics. Among them, a separator made of glass ceramic is preferable.
  • a battery case for housing the metal air secondary battery a battery case of a general metal air secondary battery can be used.
  • the shape of the battery case is not particularly limited as long as it can hold the above-described air electrode, negative electrode, and electrolyte, but specific examples include coin type, flat type, cylindrical type, laminate type, etc. Can.
  • the metal-air secondary battery of the present invention can be discharged by supplying oxygen, which is an active material, to the air electrode.
  • oxygen supply source in addition to air, oxygen gas etc. may be mentioned, preferably oxygen gas.
  • oxygen gas preferably oxygen gas.
  • the pressure of the supplied air or oxygen gas is not particularly limited, and may be set as appropriate.
  • the catalyst for air electrode containing the amorphous transition metal oxide of the present invention is useful not only in the metal air secondary battery but also in the field where other OER electrode catalysts are used.
  • OER electrode catalysts have long been studied or used as counter electrodes for various electrochemical reactions, and can be used for alkali metal plating, electrolytic degreasing, and cathodic protection technology.
  • it is expected to be applied to highly efficient and clean hydrogen production technology by combining with solar cells and photocatalysts.
  • x 1.0
  • catalyst ink Ca 2 Fe 2-x Co x O 5 catalyst and amorphous Ca 1 Fe m Co n O k catalyst, carbon powder and Nafion binder in a weight ratio of 5: 1: 1 respectively It was added to 5 ml of ethanol and well dispersed by an ultrasonic mixer. From the above, a catalyst ink having a catalyst concentration of 5 mg cm -3 was prepared.
  • the catalyst ink was collected by a pipette and applied onto a glassy carbon disk or a carbon sheet so as to be 1 mg cm ⁇ 2 to prepare an electrode sample.
  • a 4 M KOH solution was used as an electrolyte, and the above-mentioned electrode sample was used as a working electrode.
  • RHE is a relative standard electrode potential.
  • FIG. 1 is a current-time curve when Ca 2 FeCoO 5 carbon sheet electrode sample is subjected to constant-potential polarization at 1.7 V vs RHE for 20 h and oxygen evolution reaction (OER).
  • the current value decreased with the passage of time, and the current after 20 h decreased by about 40% compared to the initial current. This is because at 1.7 V, carbon which plays a role of current collection is oxidized and consumed.
  • FIG. 2 (a) shows a current-voltage curve when a potential scan from 1.2 V vs RHE to 1.7 V vs RHE and OER is performed for the sample before and after the 20 h constant potential OER in FIG.
  • the potential at which the OER current starts to rise is approximately equal around 1.48 V vs RHE, and that the OER catalytic activity has not changed.
  • FIG. 2 (b) shows a current-voltage curve when the potential reduction scan (ORR) is performed from 1.0 V vs RHE to 0.6 V vs RHE for the sample before and after the 20 h constant potential OER in FIG. There is.
  • ORR potential reduction scan
  • FIG. 3 shows the XRD pattern of the Ca 2 FeCoO 5 electrode sample before and after 20 h polarization at 1.7 V vs RHE in FIG. It can be seen that the brown mirror light type structure collapses and an amorphous phase is formed.
  • FIG. 4 shows high resolution TEM photographs before and after 1 h OER polarization at 1.7 V vs RHE.
  • a clean checkerboard derived from the brown mirror light type crystal structure is observed.
  • the limited field electron diffraction pattern also showed a diffraction pattern showing a brown mirror light structure.
  • the lattice disappears and an amorphous phase is formed, and the electron diffraction pattern also shows only the halo pattern.
  • dark clusters of about 0.5-1 nm in size were observed, and it was found that they had a nonuniform structure.
  • Table 1 shows the results of metal composition analysis of this dark cluster and the other light colored portions by EELS.
  • the dark portion has a relatively higher Co concentration than the composition of the base material, and lower Ca and Fe instead.
  • Ca was slightly lower than the composition of the base material, but the ratio of Fe / Co remained almost 1/1.
  • FIG. 5 (a) shows that OER was subjected to potential scanning from 1.2 V vs RHE to 1.7 V vs RHE for the amorphization sample by KOH aqueous solution immersion (80 ° C. 24 h) Current-voltage curve.
  • the potential at which the OER current starts to rise is approximately equal around 1.48 V vs RHE, which indicates that the OER catalytic activity has not changed.
  • Fig. 5 (b) shows the current-voltage curve when the potential reduction scan from 1.0 V vs RHE to 0.6 V vs RHE and the oxygen reduction reaction (ORR) were performed on the amorphized sample by KOH aqueous solution immersion (80 ° C 24 h). Is shown. In the sample before the KOH aqueous solution immersion, the onset potential of the negative ORR current is 0.78 V vs RHE, but after the KOH aqueous solution immersion, the current rises from 0.82 V vs RHE, and thus the KOH aqueous solution immersion sample has a higher potential. It was shown that more ORR reaction occurred, that is, ORR high activity.
  • FIG. 6 shows the XRD pattern of the amorphized sample by KOH aqueous solution immersion (80 ° C. 24 h). It can be seen that the brown mirror light type structure collapses and an amorphous phase is formed.
  • EXAFS oscillations of the sample after polarization can be well fitted by the crystal model of ⁇ -CoOOH.
  • the fitting results are shown in FIG. 7 (d) and Table 2.
  • the ⁇ -CoOOH has a layered structure in which a [CoO 2 ] n plane molecular layer sheet formed by the sharing of CoO 6 octahedra is laminated on the c-axis by hydrogen bonding via protons (FIG. 8).
  • the oxide of the present invention undergoes atomic rearrangement by OER to form a Co-rich oxide portion in the oxide matrix, which forms an ordered structure similar to ⁇ -CoOOH. Indicated. That is, the nanoclusters observed by the high resolution TEM in FIG. 4 were determined to be nanoclusters having this ⁇ -CoOOH type array structure or an array structure similar thereto.
  • the oxygen coordination number around Co is 5.1 for 1 hour polarization (Table 2).
  • the coordination number of Co in the [CoO 2 ] planar monolayer having no oxygen deficiency is six. Therefore, the nanoclusters formed in the oxide of the present invention are considered to be materials having a [CoO 1.8 ] planar monolayer sheet having oxygen deficiency as a basic skeleton.
  • the stacking in the c-axis direction of this nanocluster is to some extent inferred from the particle diameter observed in the TEM image.
  • the cluster structure in the oxide of the present invention has some stacking in the direction perpendicular to the plane, this stacking is not so developed, [CoO 1.8 ] planar monolayer and charge compensation For [CoO 1.8 H y ] n molecular sheet with coordinated protons.
  • the present invention is useful in the fields of secondary batteries, metal-air secondary batteries expected as next-generation high-capacity secondary batteries, and hydrogen production by water electrolysis and light water decomposition.

Abstract

The present invention pertains to an amorphous transition metal oxide that comprises a group-A (Ca, Sr, Ba, and rare-earth elements (RE)) element, cobalt, and a group-B (3d transition element other than Co) element. Observation with a high-resolution transmission electron microscope reveals that this amorphous transition metal oxide has a cluster structure with a particle diameter falling within a range of 0.1-10 nm. The cluster structural part has a γ-CoOOH-type element array structure or an element array structure similar thereto. In the cluster structural part, the molar ratio of the group-A element, cobalt, and the group-B element falls in the range of 0 to 1.99 : 0.01 to 1.0 : 1.0. In a matrix part, the molar ratio of the group-A element, cobalt, and the group-B element falls in the range of not less than 1.0 but less than 2.0 : not less than 1 : 1.0. The present invention also pertains to a water electrolysis positive electrode catalyst and an air electrode catalyst comprising said amorphous transition metal oxide. Disclosed are: an air electrode for a metal-air secondary battery comprising the catalyst mentioned above; and a metal-air secondary battery that has an air electrode comprising the catalyst mentioned above, a negative electrode comprising a negative electrode active material, and an electrolyte interposed between the air electrode and the negative electrode.

Description

非晶質遷移金属酸化物及びその利用Amorphous transition metal oxide and use thereof
　本発明は、非晶質遷移金属酸化物及びその利用に関する。さらに本発明は、非晶質遷移金属酸化物を用いる空気極用触媒及び水電解陽極用触媒に関する。加えて本発明は、前記空気極用触媒を用いる金属空気二次電池に関する。
関連出願の相互参照
　本出願は、２０１７年１１月１０日出願の日本特願２０１７－２１７７７８号の優先権を主張し、その全記載は、ここに特に開示として援用される。 The present invention relates to amorphous transition metal oxides and their use. Further, the present invention relates to a catalyst for an air electrode using an amorphous transition metal oxide and a catalyst for a water electrolysis anode. In addition, the present invention relates to a metal air secondary battery using the catalyst for the air electrode.
This application claims the priority of Japanese Patent Application No. 2017-217778 filed on Nov. 10, 2017, the entire description of which is incorporated herein by reference in particular.
　近年、太陽エネルギーを利用した水分解による水素製造や金属空気二次電池の開発が盛んに行われている。中でも金属空気二次電池は、現在主流であるリチウムイオン二次電池に代わる新たな高容量蓄電池として期待されており、2030年頃の普及を目指して研究開発が進められている。しかしながら現状では実用化に向けて解決すべき課題が種々挙げられており、その1つとして高活性酸素発生反応（OER）触媒の開発が挙げられる。 BACKGROUND ART In recent years, hydrogen production by water decomposition using solar energy and development of metal-air secondary batteries have been actively conducted. Above all, metal air secondary batteries are expected as new high-capacity storage batteries to replace currently mainstream lithium ion secondary batteries, and research and development are being promoted aiming for the spread around 2030. However, under the present circumstances, various issues to be solved for practical use are listed, and one of them is the development of a high active oxygen generation reaction (OER) catalyst.
　一般にOERには大きな過電圧が生じることが知られており、このために十分な充放電効率が得られていないのが現状である。そのため、充電時の電圧を大きく左右する高活性OER触媒の開発が急務となっている。一般的にOERに対して高活性な触媒として、PtやIrO2、RuO2（2.5～3.0 mA/cm2@1.6 V vs RHE、0.1 mol dm-3 NaOH水溶液中）[非特許文献1]などの貴金属触媒が知られている。しかしながら、これら貴金属はコストが高く埋蔵量も少ないため、広く普及させるためには貴金属を含まないOER触媒の開発が必要である。 In general, it is known that a large overvoltage occurs in OER, and for this reason, sufficient charge and discharge efficiency is not obtained at present. Therefore, there is an urgent need to develop a highly active OER catalyst that largely affects the voltage at the time of charging. Generally, Pt, IrO 2 , RuO 2 (2.5 to 3.0 mA / cm 2 @ 1.6 V vs RHE, in 0.1 mol dm −3 NaOH aqueous solution) [Non-patent document 1], etc., as highly active catalysts for OER Precious metal catalysts are known. However, since these precious metals are expensive and have low reserves, the development of an OER catalyst that does not contain precious metals is necessary for widespread use.
　最近では貴金属を含まない非貴金属OER触媒として、ペロブスカイト型遷移金属酸化物ABO3が報告されている。ペロブスカイト型酸化物はBサイトに遷移金属を有し、酸素6つと結合した八面体構造から成る。最近ではこのBサイト遷移金属のeg電子数がそのOER活性と関連していることが報告されており、eg電子数が1付近のLa0.5Ca0.5CoO3-δなどが高活性（1.5 mA/cm2@1.6 V vs RHE、0.1 mol dm-3 NaOH水溶液中）[非特許文献2]であることが報告されている。 Recently, a perovskite type transition metal oxide ABO 3 has been reported as a non-precious metal OER catalyst containing no precious metal. The perovskite oxide has a transition metal at the B site and is composed of an octahedral structure bonded to six oxygens. Recently, it has been reported that e g electron number of the B site transition metal is associated with its OER activity, e g the number of electrons 1 near La 0.5 Ca 0.5 CoO 3-δ, such as a high activity (1.5 It is reported that mA / cm 2 @ 1.6 V vs RHE, 0.1 mol dm −3 in a NaOH aqueous solution) [Non-patent document 2].
　さらに、これまで酸素発生触媒として注目されてこなかったブラウンミラーライト型遷移金属酸化物A2B2O5を用いることによりOER反応に対してPt触媒に匹敵する活性を示し、中でも2種類の遷移金属を含むものを用いることにより、貴金属触媒を凌ぐ活性を示すことが報告されている（特許文献１）。 Furthermore, by using the brown mirror light type transition metal oxide A 2 B 2 O 5 which has not been noted as an oxygen generation catalyst so far, it exhibits an activity comparable to a Pt catalyst for the OER reaction, among which two types of transitions It has been reported that by using a metal-containing one, the activity over noble metal catalysts is shown (Patent Document 1).
　また、新たな構造を有するOER触媒の例として、CoOOHナノシート構造を有する材料が報告されている（非特許文献3）。この材料は、α-Co(OH)2シートをClアニオン及び水の存在下で超音波処理することで、層の剥離を行い次いで、NaClOを用いて酸化処理することで調製され、Fig.1bのTEM像及び1cのAFMＭ像によれば、200～300nmの粒子サイズを有する。さらに、Fig.1dのXRDの結果によれば、結晶性を有する。 Moreover, the material which has a CoOOH nanosheet structure is reported as an example of the OER catalyst which has a novel structure (nonpatent literature 3). This material was prepared by layer peeling by sonicating an α-Co (OH) 2 sheet in the presence of Cl anion and water, followed by oxidation using NaClO, as shown in FIG. According to the TEM image of and the AFFM image of 1c, it has a particle size of 200-300 nm. Furthermore, according to the result of XRD in FIG. 1 d, it has crystallinity.
特許文献１：ＷＯ２０１５／１１５５９２ Patent Document 1: WO 2015/115592
非特許文献１：Y. Lee, et al., J. Phys. Chem. Lett. 2012, 3,399.
非特許文献２：SuntivichScience 2011, 334, 1383.
非特許文献３：J.Huang, et al., Angewandte_Chemie_International_Edition 2015, 54, 8722-8727
特許文献１及び非特許文献１～３の全記載は、ここに特に開示として援用される。 Non-Patent Document 1: Y. Lee, et al., J. Phys. Chem. Lett. 2012, 3, 399.
Non-patent document 2: Suntivich Science 2011, 334, 1383.
Non-Patent Document 3: J. Huang, et al., Angewandte_Chemie_International_Edition 2015, 54, 8722-8727
The entire descriptions of Patent Document 1 and Non-Patent Documents 1 to 3 are specifically incorporated herein by reference.
　特許文献１に記載されている2種類の遷移金属を含むブラウンミラーライト型遷移金属酸化物A2B2O5は、貴金属触媒を凌ぐOER活性を示すものである。しかし、OER活性がより高い触媒の開発が必要とされている。また、非特許文献3に記載の材料は製造方法が複雑であり、OER活性も高くないことからさらに改善の余地がある。 The brown mirror light type transition metal oxide A 2 B 2 O 5 containing two types of transition metals described in Patent Document 1 exhibits OER activity superior to that of a noble metal catalyst. However, there is a need to develop catalysts with higher OER activity. In addition, the materials described in Non-Patent Document 3 have a complicated manufacturing method and there is room for further improvement because the OER activity is not high.
　そこで本発明の目的は、OER活性がより高い新たな遷移金属酸化物触媒を開発し、さらにこの触媒を用いた空気極用触媒や水電解陽極用触媒、空気極及び空気二次電池を提供することにある。 Therefore, an object of the present invention is to develop a new transition metal oxide catalyst having higher OER activity, and further provide an air electrode catalyst, a water electrolytic anode catalyst, an air electrode and an air secondary battery using this catalyst. It is.
　上記のように非貴金属OER触媒は今後の新規エネルギー材料として期待されているが、特許文献１で報告されているブラウンミラーライト型遷移金属酸化物においても未だそのOER活性は十分とは言えない。本発明では、ブラウンミラーライト型遷移金属酸化物A2B2O5よりも、さらに高いOER活性を示す酸化物触媒を見出し、本発明を完成した。 As described above, although non-precious metal OER catalysts are expected as new energy materials in the future, the OER activity of the brown mirror light type transition metal oxides reported in Patent Document 1 is not sufficient yet. In the present invention, the present inventors have completed the present invention by finding an oxide catalyst which exhibits a higher OER activity than the brown mirror light type transition metal oxide A 2 B 2 O 5 .
　本発明は以下の通りである。
［１］
下記A群から選ばれる1種又は2種以上の元素、B群から選ばれる1種又は2種以上の元素及びコバルトを含む非晶質の酸素非欠損型又は酸素欠損型の遷移金属酸化物であり、
但し、A群は、Ca、Sr、Ba及び希土類元素(RE)からなり、
B群は、Co以外の3d遷移元素からなり、
かつ高分解能透過電子顕微鏡観察において粒径が0.1～10nmの範囲のクラスター構造が見られる酸化物であって、前記クラスター構造部はγ-CoOOH型の元素配列構造又はこれに類似する元素配列構造を有する遷移金属酸化物。
［２］
γ-CoOOH型の元素配列構造又はこれに類似する元素配列構造は、CoO6八面体が陵共有により二次元的に連結して形成する[CoOx]平面単分子層に、電荷補償のためのプロトンが配位した[CoOxHy]平面単分子層がn層積層してできる[CoOxHy]n分子層であって、[CoOxHy]平面単分子層の一辺が10nm以下であり、xは1.5～2.0の範囲であり、ｙは0.01～1の範囲であり、nは平面単分子層の分子層平面に垂直な方向（c軸方向）への積層数であり、1～25の範囲であり、[CoOxHy]平面単分子層中のCoの一部がFeで置換されていてもよく、またCoO6八面体の酸素の一部が欠損していてもよい、［１］に記載の遷移金属酸化物。
［３］
前記クラスター構造部が前記マトリクス部に分散している［１］又は［２］に記載の酸化物。
［４］
制限視野電子線回折像において回折パターンは見られず、ハローパターンを示す、［１］～［３］のいずれかに記載の酸化物。
［５］
前記元素のモル比は、電子エネルギー損失分光法により求める［１］～［４］のいずれかに記載の酸化物。
［６］
下記一般式(1)で示されるブラウンミラーライト型遷移金属酸化物を非晶質化することを含む、
γ-CoOOH型の元素配列構造又 はこれに類似する元素配列構造を有し、高分解能透過電子顕微鏡観察において粒径が0.1～10nmの範囲のクラスター構造を有する、非晶質の酸素非欠損型又は酸素欠損型の遷移金属酸化物の製造方法。
AxB1 2-yB2 yO5  (1)
式中、Aは、Ca、Sr、Ba又は希土類元素(RE)を表し、
B1は、Coを表し、
B2は、Co以外の3d遷移元素を表し、
ｘは、1.5～2.0の範囲の数値であり、
ｙは、0～1.0の範囲の数値である。
［７］
非晶質化は、ブラウンミラーライト型遷移金属酸化物を、アルカリ水溶液に浸漬すること、又はアルカリ水溶液中で分極処理することを含む、［６］に記載の製造方法。
［８］
［１］～［５］のいずれかに記載の非晶質遷移金属酸化物又は［６］若しくは［７］に記載の方法で製造された非晶質遷移金属酸化物を含む空気極用触媒。
［９］
［１］～［５］のいずれかに記載の非晶質遷移金属酸化物又は［６］若しくは［７］に記載の方法で製造された非晶質遷移金属酸化物を含む水電解陽極用触媒。
［１０］
表面積が0.1～100m2/gの範囲である［８］又は［９］に記載の触媒。
［１１］
［８］又は［１０］に記載の触媒を含む金属空気二次電池用空気極。
［１２］
前記非晶質金属酸化物は酸素発生用触媒として含有され、酸素還元用触媒をさらに含む［１１］に記載の空気極。
［１３］
［１１］又は［１２］に記載の空気極と、負極活物質を含有する負極と、前記空気極と前記負極との間に介在する電解質とを有する金属空気二次電池。
［１４］
酸素還元用触媒を含む酸素還元用空気極をさらに含む［１３］に記載の金属空気二次電池。 The present invention is as follows.
[1]
Amorphous, non-oxygen-deficient or oxygen-deficient transition metal oxide containing one or more elements selected from the following group A, one or more elements selected from group B, and cobalt Yes,
However, A group consists of Ca, Sr, Ba and rare earth elements (RE),
Group B consists of 3d transition elements other than Co,
And an oxide in which a cluster structure having a particle size in the range of 0.1 to 10 nm is observed in high resolution transmission electron microscopy, wherein the cluster structure portion has an element arrangement structure of γ-CoOOH type or an element arrangement structure similar thereto. Having transition metal oxide.
[2]
An element arrangement structure of γ-CoOOH type or an element arrangement structure similar to this is formed for charge compensation in a [CoO x ] planar monolayer formed by two-dimensionally connecting CoO 6 octahedra by sharing a ring. protons coordinated [CoO x H y] plane monolayer can be n layer laminated to a [CoO x H y] n molecules layer, [CoO x H y] one side of the planar monolayer 10nm or less X is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, and n is the number of laminations in the direction (c-axis direction) perpendicular to the molecular layer plane of the planar monolayer, In the range of ̃25, a part of Co in the [CoO x H y ] planar monolayer may be substituted with Fe, or a part of oxygen of the CoO 6 octahedron may be deficient Transition metal oxides described in [1].
[3]
The oxide according to [1] or [2], wherein the cluster structure part is dispersed in the matrix part.
[4]
The oxide according to any one of [1] to [3], wherein a diffraction pattern is not seen in the limited field electron diffraction image but shows a halo pattern.
[5]
The molar ratio of the elements is determined by electron energy loss spectroscopy [1] to [4].
[6]
Including amorphizing a brown mirror light type transition metal oxide represented by the following general formula (1):
Amorphous, non-oxygen-depleted type having an element arrangement structure of γ-CoOOH type or an element arrangement structure similar thereto and having a cluster structure with a particle size in the range of 0.1 to 10 nm in high resolution transmission electron microscopy Or a method of producing an oxygen deficient transition metal oxide.
A x B 1 2-y B 2 y O 5 (1)
In the formula, A represents Ca, Sr, Ba or a rare earth element (RE),
B 1 represents Co,
B 2 represents a 3d transition element other than Co,
x is a numerical value in the range of 1.5 to 2.0,
y is a numerical value in the range of 0 to 1.0.
[7]
The production method according to [6], wherein the amorphization includes immersing the brown mirrorlite type transition metal oxide in an aqueous alkaline solution or polarization treatment in an aqueous alkaline solution.
[8]
A catalyst for an air electrode comprising the amorphous transition metal oxide according to any one of [1] to [5] or the amorphous transition metal oxide produced by the method according to [6] or [7].
[9]
Catalyst for water electrolysis anode containing amorphous transition metal oxide according to any one of [1] to [5] or amorphous transition metal oxide produced by the method according to [6] or [7] .
[10]
The catalyst according to [8] or [9], which has a surface area in the range of 0.1 to 100 m 2 / g.
[11]
The air electrode for metal air secondary batteries containing the catalyst as described in [8] or [10].
[12]
The air electrode according to [11], wherein the amorphous metal oxide is contained as an oxygen generation catalyst and further includes an oxygen reduction catalyst.
[13]
The metal air secondary battery which has an air electrode as described in [11] or [12], the negative electrode containing a negative electrode active material, and the electrolyte interposed between the said air electrode and the said negative electrode.
[14]
The metal-air secondary battery according to [13], further including an oxygen reduction air electrode containing a catalyst for oxygen reduction.
　本発明によれば、非晶質遷移金属酸化物であって、マトリクス構造中に粒径が0.1～10nmの範囲のクラスター構造が見られる新規な酸化物が提供され、この酸化物は、ブラウンミラーライト型遷移金属酸化物A2B2O5より高いORR活性を示すことから、優れた空気極用触媒や水電解陽極用触媒を提供することができる。さらに本発明によれば上記空気極用触媒を用いた金属空気二次電池用空気極、及びこの空気極を用いた金属空気二次電池も提供できる。 According to the present invention, there is provided a novel oxide which is an amorphous transition metal oxide and in which a cluster structure having a particle size in the range of 0.1 to 10 nm can be found in a matrix structure. Since the ORR activity is higher than light type transition metal oxide A 2 B 2 O 5 , an excellent catalyst for air electrode and a catalyst for water electrolytic anode can be provided. Further, according to the present invention, it is possible to provide an air electrode for a metal air secondary battery using the catalyst for the air electrode and a metal air secondary battery using the air electrode.
図１はCa2FeCoO5カーボンシート電極試料を，1.7V vs RHEで20 h定電位分極し酸素発生反応（OER）させたときの電流－時間曲線である。FIG. 1 is a current-time curve when a Ca 2 FeCoO 5 carbon sheet electrode sample is subjected to constant-potential polarization at 1.7 V vs RHE for 20 h and oxygen generation reaction (OER). (a)は，図１の20 h定電位OER前後の試料について，1.2 V vs RHEから1.7 V vs RHEまで電位走査しOERさせたときの電流－電圧曲線を示す。(b)は，図１の20 h 定電位OER前後の試料について，1.0 V vs RHEから0.6 V vs RHEまで電位走査し酸素還元反応(ORR)させたときの電流－電圧曲線を示す。(a) shows the current-voltage curve when the potential scan from 1.2 V vs RHE to 1.7 V vs RHE and OER is performed for the sample before and after the 20 h constant potential OER in FIG. (b) shows a current-voltage curve when a potential scan from 1.0 V vs RHE to 0.6 V vs RHE is performed and oxygen reduction reaction (ORR) is performed for the sample before and after the 20 h constant potential OER in FIG. 図1の1.7 V vs RHEで20 h分極前後のCa2FeCoO5電極試料のXRDパターンを示す。In 1.7 V vs RHE in FIG 1 shows a 20 h polarization before and after Ca 2 FeCoO 5 electrode sample XRD pattern. (a)1.7 V vs RHEで1 h OER分極前の高分解能透過電子顕微鏡(TEM)像と制限視野電子線回折像を示す。(b)1.7 V vs RHEで1 h OER分極後の高分解能透過電子顕微鏡(TEM)像と制限視野電子線回折像を示す。アモルファス中に濃色のナノクラスターが分散していることがわかる。いくつかの例を黄点線で囲って示してある。(a) A high resolution transmission electron microscope (TEM) image and a limited field electron diffraction image before 1 h OER polarization at 1.7 V vs RHE are shown. (b) High resolution transmission electron microscope (TEM) image and limited field electron diffraction image after 1 h OER polarization at 1.7 V vs RHE. It can be seen that dark nanoclusters are dispersed in the amorphous state. Some examples are shown surrounded by a yellow dotted line. Ca2FeCoO5をKOHで80℃24ｈ化学処理したときの(a)OER分極曲線および(b)ORR分極曲線を示す。(A) OER polarization curve and (b) ORR polarization curve when Ca 2 FeCoO 5 is chemically treated with KOH at 80 ° C. for 24 h are shown. Ca2FeCoO5をKOHで80℃24ｈ化学処理したときのXRDパターンを示す。An XRD pattern when Ca 2 FeCoO 5 is chemically treated with KOH at 80 ° C. for 24 h is shown. 分極前(As prepared)および20 mA cm-2定電流条件で1時間アノード分極したCa2FeCoO5試料の(a) Co K吸収端および(b) Fe K吸収端近傍X線吸収スペクトル(XANES)。広域X線吸収微細構造(EXAFS)より決定したCo原子((c))およびFe原子((d))周囲の動径分布。(c)および(d)はAs preparedおよび1時間アノード分極したCa2FeCoO5試料の比較、また(c)および(d)にはγ-CoOOH構造モデル(図8)を用いたFitting結果(点線)を併せて示した。(A) Co K absorption edge and (b) Fe K absorption edge near-X-ray absorption spectrum (XANES) of Ca 2 FeCoO 5 samples anodically polarized (As prepared) and anodically polarized for 1 hour at 20 mA cm -2 constant current conditions . Radial distribution around Co atoms ((c)) and Fe atoms ((d)) determined from wide area X-ray absorption fine structure (EXAFS). (c) and (d) compare the As prepared and 1-hour anodically polarized Ca 2 FeCoO 5 samples, and (c) and (d) fit results (dotted line) using the γ-CoOOH structural model (FIG. 8) ) Is also shown. γ-CoOOH(六方晶)の結晶構造モデルを示す。赤球(小)、青球(大)および白球(小、層の間に孤立)は、それぞれ酸素原子、コバルト原子および水素原子を示している。1 shows a crystal structure model of γ-CoOOH (hexagonal crystal). Red spheres (small), blue spheres (large) and white spheres (small, isolated between layers) indicate oxygen atom, cobalt atom and hydrogen atom, respectively. カーボンシート上に担持したCa2FeCoO5を、40 mA cm-2定電流で2ｈアノード分極し、その後15分開回路電位で保持するOER分極サイクルを一か月繰り返した時の電流－時間曲線である。It is a current-time curve when one cycle of OER polarization cycle, in which Ca 2 FeCoO 5 supported on a carbon sheet is anodically polarized at 40 mA cm −2 constant current for 2 h and then held at open circuit potential for 15 minutes, is repeated one month . 本発明の金属空気二次電池の一構成例を示す。BRIEF DESCRIPTION OF THE DRAWINGS One structural example of the metal air secondary battery of this invention is shown.
＜非晶質遷移金属酸化物＞
　本発明は、下記A群から選ばれる1種又は2種以上の元素、B群から選ばれる1種又は2種以上の元素及びコバルトを含む非晶質の酸素非欠損型又は酸素欠損型の遷移金属酸化物であり、かつ高分解能透過電子顕微鏡観察において粒径が0.1～10nmの範囲のクラスター構造が見られる酸化物であって、
前記クラスター構造部はγ-CoOOH型の元素配列構造又はこれに類似する元素配列構造を有する遷移金属酸化物である。 <Amorphous transition metal oxide>
The present invention is an amorphous non-oxygen-deficient or oxygen-deficient transition including one or more elements selected from the following group A, one or more elements selected from group B, and cobalt. An oxide which is a metal oxide and in which a cluster structure having a particle diameter in the range of 0.1 to 10 nm is observed in high resolution transmission electron microscopy,
The cluster structure portion is a transition metal oxide having an element arrangement structure of γ-CoOOH type or an element arrangement structure similar thereto.
　本発明の非晶質遷移金属酸化物は、クラスター構造部がクラスター構造部以外の部分であるマトリクス部に分散した構造を有する。この構造は、高分解能透過電子顕微鏡観察により観察確認することができる。さらに、クラスター構造部は粒径が0.1～10nmの範囲であり、実施例で示したクラスター構造は、粒径が約0.5～5nmの範囲であった。本発明の非晶質遷移金属酸化物は、制限視野電子線回折像において回折パターンは見られず、かつハローパターンを示すことから、非晶質の酸化物である。また、本発明の非晶質遷移金属酸化物は、ＸＲＤによっても、結晶による回折ピークが観察されず、この点でも、非晶質の酸化物である。但し、マトリクス部は非晶質であるが、クラスター構造部が非晶質であるか否かは問わない。本発明の酸化物における非晶質とは、制限視野電子線回折像において回折パターンは見られず、かつハローパターンを示すことを意味する。本発明の非晶質遷移金属酸化物は、少なくともこれら粒径及びＸＲＤによって結晶による回折ピークが観察されないことから、非特許文献3に記載の材料とは明らかに異なる材料である。 The amorphous transition metal oxide of the present invention has a structure in which a cluster structure portion is dispersed in a matrix portion which is a portion other than the cluster structure portion. This structure can be observed and confirmed by high resolution transmission electron microscopy. Furthermore, the cluster structure portion had a particle size in the range of 0.1 to 10 nm, and the cluster structure shown in the example had a particle size in the range of approximately 0.5 to 5 nm. The amorphous transition metal oxide of the present invention is an amorphous oxide because no diffraction pattern is observed in the limited field electron diffraction pattern and the halo pattern is exhibited. Moreover, the diffraction peak by a crystal | crystallization is not observed also by XRD, and the amorphous transition metal oxide of this invention is an amorphous oxide also in this point. However, although the matrix portion is amorphous, it does not matter whether the cluster structure portion is amorphous or not. Amorphous in the oxide of the present invention means that a diffraction pattern can not be seen in a limited field electron diffraction image and a halo pattern is shown. The amorphous transition metal oxide of the present invention is a material which is clearly different from the material described in Non-patent Document 3 because at least the particle diameter and diffraction peaks due to crystals are not observed by XRD.
　本発明の遷移金属酸化物のクラスター構造部は、γ-CoOOH型の原子配列構造と同一又は類似する原子配列構造を有する。γ-CoOOH型の原子配列構造とは、γ-CoOOH(六方晶)の結晶構造モデルが有する原子配列構造であり、図８にγ-CoOOH(六方晶)の結晶構造モデルを示す。図中の赤球(小)、青球(大)および白球(小、層の間に孤立)は、それぞれ酸素原子、コバルト原子および水素原子を示している。γ-CoOOHは、CoO6八面体の陵共有によって形成する[CoO2]平面分子層が、プロトンを介した水素結合によってc軸上積層した層状構造をもつ。本発明の遷移金属酸化物は、図８に示すγ-CoOOH(六方晶)の結晶構造モデルと同一又は類似する原子配列構造を有する。このような原子構造は、製造方法において後述するが、OER分極により原子の再配列が起り、酸化物マトリクス中にCoリッチな酸化物部分が形成され、それがγ-CoOOHによく似た配列構造を形成したものと推察される。図４ｂに高分解能TEMにより観測された本発明の酸化物におけるクラスター構造部を示すが、このクラスター構造部は、γ-CoOOH型の原子配列構造と同一又は類似する原子配列構造もつクラスター構造部である。尚、本発明のクラスター構造部は酸素欠損を有することがあることから、酸素欠損がある部分はγ-CoOOH型の原子配列構造と同一ではなく、γ-CoOOH型の原子配列構造と類似する原子配列構造を有する、と定義する。 The cluster structure part of the transition metal oxide of the present invention has an atomic arrangement structure that is the same as or similar to the atomic arrangement structure of γ-CoOOH type. The atomic arrangement structure of the γ-CoOOH type is an atomic arrangement structure possessed by the crystal structure model of γ-CoOOH (hexagonal), and FIG. 8 shows a crystal structure model of γ-CoOOH (hexagonal). Red spheres (small), blue spheres (large) and white spheres (small, isolated between layers) in the figure indicate oxygen atom, cobalt atom and hydrogen atom, respectively. The γ-CoOOH has a layered structure in which a [CoO 2 ] planar molecular layer formed by the sharing of CoO 6 octahedra is stacked on the c-axis by hydrogen bonding via protons. The transition metal oxide of the present invention has an atomic arrangement structure identical or similar to the crystal structure model of γ-CoOOH (hexagonal crystal) shown in FIG. Such an atomic structure will be described later in the manufacturing method, but OER polarization causes rearrangement of the atoms to form a Co-rich oxide portion in the oxide matrix, which is similar to γ-CoOOH. It is guessed that it formed. The cluster structure in the oxide of the present invention observed by high resolution TEM is shown in FIG. 4b. This cluster structure is a cluster structure having an atomic arrangement structure identical or similar to that of the γ-CoOOH type atomic arrangement structure. is there. In addition, since the cluster structure part of the present invention may have oxygen vacancies, the part having oxygen vacancies is not identical to the atomic arrangement structure of γ-CoOOH type, and an atom similar to the atomic arrangement structure of γ-CoOOH type It is defined as having an array structure.
　本発明の遷移金属酸化物は、より具体的には、CoO6八面体が陵共有により二次元的に連結して形成する[CoOx]平面単分子層に、電荷補償のためのプロトンが配位した[CoOxHy]平面単分子層がn層積層してできる[CoOxHy]n分子層シート状物質のクラスター構造部を含有する遷移金属酸化物であって、[CoOxHy]平面単分子層の一辺が10nm以下であり、xは1.5～2.0の範囲であり、ｙは0.01～1の範囲であり、nは平面単分子層の分子層平面に垂直な方向（c軸方向）への積層数であり、1～25の範囲であり、[CoOxHy]平面単分子層中のCoの一部がFeで置換されていてもよく、またCoO6八面体の酸素の一部が欠損していてもよい、酸化物である。 More specifically, in the transition metal oxide of the present invention, protons for charge compensation are arranged in a [CoO x ] planar monolayer formed by two-dimensionally connecting CoO 6 octahedra by ring sharing. It is a transition metal oxide containing a cluster structure portion of a [CoO x H y ] n molecular layer sheet-like substance formed by n-layer lamination of layered [CoO x H y ] planar monolayers, and [CoO x H] One side of the [1] planar monolayer is 10 nm or less, x is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, and n is the direction perpendicular to the molecular layer plane of the planar monolayer (c Number of layers in the axial direction, in the range of 1 to 25, and a part of Co in the [CoO x H y ] planar monolayer may be substituted with Fe, and the CoO 6 octahedron It is an oxide in which part of oxygen may be lost.
　本発明の遷移金属酸化物のクラスター構造部は、[CoOx]平面単分子層に電荷補償のためのプロトンが配位した[CoOxHy]n分子層シート状物質のクラスター構造部である。実施例に示すEXAFSフィッティング結果より、Co周りの酸素配位数は1時間分極の場合5.1であた（表2）。一方酸素欠損が全くない [CoO2]ｎ平面分子層シートにおけるCo配位数は6となる。従って、実験例で示した本発明の遷移金属酸化物のクラスター構造部は、酸素欠損を有する[CoOX]n分子層シートを基本骨格にもつ材料であると考えられる。一方、図3 に示すXRDの結果より本発明の遷移金属酸化物にはγ-CoOOH のXRDピークが現れないことから、このクラスター構造部はc軸方向への積層は、存在はするが発達はしていないと考えられる。従って本発明の遷移金属酸化物のクラスター構造部は平面垂直方向の積層が存在はするが発達はしていない、[CoOX]n分子層と電荷補償のためのプロトンが配位した[CoOXHy]n分子層シート状物質であると同定された。このような[CoOXHy]n分子層シート状物質の原子配列構造は、γ-CoOOH型の原子配列構造と同一ではなく、γ-CoOOH型の原子配列構造と類似する原子配列構造を有する、と言える。 Cluster structure of transition metal oxides of the present invention is a [CoO x] protons for charge compensation in the plane monolayer coordinated [CoO x H y] cluster structure of the n molecules layer sheet material . According to the EXAFS fitting results shown in the examples, the oxygen coordination number around Co was 5.1 for 1 hour polarization (Table 2). On the other hand, the Co coordination number in the [CoO 2 ] n plane molecular layer sheet having no oxygen deficiency is six. Therefore, the cluster structure portion of the transition metal oxide of the present invention shown in the experimental example is considered to be a material having, as a basic skeleton, a [CoO x ] n molecular layer sheet having oxygen deficiency. On the other hand, according to the results of XRD shown in FIG. 3, since the XRD peak of γ-CoOOH does not appear in the transition metal oxide of the present invention, this cluster structure portion has a stack in the c-axis direction but development is It is thought that it does not do. Therefore, the cluster structure part of the transition metal oxide according to the present invention has a stack in the plane vertical direction but does not develop, [CoO x ] n molecular layer and proton for charge compensation are coordinated [CoO x The substance was identified as H y ] n molecular sheet material. The atomic arrangement structure of such [CoO x H y ] n molecular sheet material is not identical to the atomic arrangement structure of the γ-CoOOH type, but has an atomic arrangement structure similar to that of the γ-CoOOH type It can be said that.
　[CoOXHy]n分子層シートにおけるxは1.5～2.0の範囲、好ましくは1.6～1.9の範囲であり、ｙは0.01～1の範囲、好ましくは0.05～0.5の範囲であり、nは1～25の範囲である。本発明の酸化物のクラスター構造部は、ＴＥＭ像において観察されるクラスター構造部の最大外径は0.3～10nmの範囲であり、好ましくは0.6～7nmの範囲、より好ましくは0.9～5nmである。CoO6八面体の直径は約0.29 nm(ほぼ0.3nm)であり、また[CoOXHy]単分子層の層間距離は0.4 nm程度である。最大直径10nmのクラスター構造部を想定するとこの粒子径のクラスター構造部を構成するためには、[CoOXHy]単分子層内のCoOXHy八面体分子の数は、10/0.29 x 10/0.29 （約1200）であり、最大直径7nmの範囲の場合は7/0.29 x 7/0.29（約580）であり、最大直径5nmの範囲の場合は5/0.29 x 5/0.29（約300）である。 In the [CoO X H y ] n molecular layer sheet, x is in the range of 1.5 to 2.0, preferably in the range of 1.6 to 1.9, y is in the range of 0.01 to 1, preferably in the range of 0.05 to 0.5, and n is 1 It is in the range of ̃25. In the cluster structure portion of the oxide of the present invention, the maximum outer diameter of the cluster structure portion observed in the TEM image is in the range of 0.3 to 10 nm, preferably in the range of 0.6 to 7 nm, more preferably 0.9 to 5 nm. The diameter of the CoO 6 octahedron is about 0.29 nm (approximately 0.3 nm), and the interlayer distance of the [CoO x H y ] monolayer is about 0.4 nm. Assuming a cluster structure having a maximum diameter of 10 nm, the number of CoO X H y octahedral molecules in the [CoO X H y ] monolayer is 10 / 0.29 x in order to form a cluster structure of this particle diameter. 10 / 0.29 (about 1200), 7 / 0.29 x 7 / 0.29 (about 580) in the range of the maximum diameter of 7 nm, 5 / 0.29 x 5 / 0.29 (about 300 in the range of the maximum diameter of 5 nm) ).
　上記のように本発明の酸化物のクラスター構造部は平面垂直方向の積層が存在はするが発達はしていない[CoOXHy]n分子層シート状物質であり、nは平面単分子層の分子層平面に垂直な方向（c軸方向）への積層数である。最大直径0.3～10nmのクラスターを想定するとnは1～10/0.4（約25）である。従って、上記ｎは1～25の範囲である。さらに、直径0.6～7nmの範囲の場合、nは2～7/0.4（約18）であり、直径0.9～5nmの範囲の場合、nは2または3～5/0.4（約12）である。 As described above, the cluster structure portion of the oxide of the present invention is a [CoO X H y ] n molecular layer sheet-like material in which a stack in the plane vertical direction exists but is not developed, and n is a plane monolayer Is the number of layers stacked in the direction (c-axis direction) perpendicular to the molecular layer plane. Assuming a cluster with a maximum diameter of 0.3 to 10 nm, n is 1 to 10 / 0.4 (about 25). Therefore, the above n is in the range of 1 to 25. Further, n is 2 to 7 / 0.4 (about 18) in the range of 0.6 to 7 nm in diameter, and n is 2 or 3 to 5 / 0.4 (about 12) in the range of 0.9 to 5 nm in diameter.
　本発明の酸化物において、
A群は、Ca、Sr、Ba及び希土類元素(RE)からなり、
B群は、Co以外の3d遷移元素からなる。 In the oxide of the present invention,
Group A consists of Ca, Sr, Ba and rare earth elements (RE),
Group B consists of 3d transition elements other than Co.
　A群元素は、Ca、Sr、Ba及び希土類元素(RE)からなる。希土類元素(RE)は、Sc、Yの2元素とランタノイドの15元素であり、ランタノイドは、La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Luである。希土類元素(RE)は、好ましくは、比較的イオン半径の大きなLa、Pr、Nd、Sm、Eu、Gdなどを例示できる。 The A group element consists of Ca, Sr, Ba and a rare earth element (RE). The rare earth elements (RE) are two elements of Sc and Y and 15 elements of lanthanoid, and the lanthanoid is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. The rare earth element (RE) is preferably, for example, La, Pr, Nd, Sm, Eu, Gd, etc., which have a relatively large ion radius.
　B群元素は、Co以外の3d遷移元素。Bで表される3d遷移元素は、例えば、Fe、Mn、Cr、Ni、Ti、Cu、Znから成る群から選ばれる少なくとも1種の金属元素である。B群元素は、OER活性がより高い新たな遷移金属酸化物触媒を提供するという観点から好ましくは、鉄である。 Group B elements are 3d transition elements other than Co. The 3d transition element represented by B is, for example, at least one metal element selected from the group consisting of Fe, Mn, Cr, Ni, Ti, Cu, and Zn. The group B element is preferably iron from the viewpoint of providing a new transition metal oxide catalyst with higher OER activity.
　OER活性がより高い新たな遷移金属酸化物触媒を提供するという観点から、前記クラスター構造部におけるA群元素、B群元素及びコバルトのモル比は、0～1.99:0.01～1.0: 1.0の範囲であり、好ましくは0.01～1.0:0.1～1.0: 1.0の範囲である。同様に、OER活性がより高い新たな遷移金属酸化物触媒を提供するという観点から好ましくは、前記クラスター構造部以外の部分であるマトリクス部におけるA群元素、B群元素及びコバルトのモル比は、0.01以上、2.0未満:0.5以上: 1.0の範囲であり、好ましくは0.01以上、2.0未満:1以上: 1.0の範囲であり、より好ましくは0.5～1.9:0.5～2.0: 1.0の範囲である。 From the viewpoint of providing a new transition metal oxide catalyst having higher OER activity, the molar ratio of the group A element, the group B element and cobalt in the cluster structure part is in the range of 0 to 1.99: 0.01 to 1.0: 1.0. And preferably in the range of 0.01 to 1.0: 0.1 to 1.0: 1.0. Similarly, from the viewpoint of providing a new transition metal oxide catalyst having higher OER activity, preferably, the molar ratio of the group A element, the group B element and cobalt in the matrix part which is the part other than the cluster structure part is 0.01 or more, 2.0 or less: 0.5 or more: 1.0, preferably 0.01 or more, 2.0 or less: 1 or more: 1.0, more preferably 0.5 to 1.9: 0.5 to 2.0: 1.0.
　前記元素のモル比は、電子エネルギー損失分光法により求めることができる。 The molar ratio of the elements can be determined by electron energy loss spectroscopy.
　本発明の非晶質の遷移金属酸化物は酸素非欠損型又は酸素欠損型である。酸素非欠損型の酸化物は、酸素とその他の元素との比が化学量論比であるのに対して、酸素欠損型の酸化物では、酸素は、その他の元素の量に比べて、化学量論比より少ない。酸素欠損型である場合、酸素欠損の程度（化学量論比より少ない程度）には特に制限はないが、例えば、酸素以外の元素の価数の総量の0を超え25%以下であることができる。但し、これより多い酸素欠損が有ってもよい。 The amorphous transition metal oxide of the present invention is non-oxygen deficient or oxygen deficient. In the non-oxygen-depleted oxide, the ratio of oxygen to other elements is a stoichiometric ratio, while in the oxygen-deficient oxide, oxygen is more chemically related to the amount of other elements. Less than stoichiometric ratio. In the case of the oxygen deficient type, the degree of oxygen deficiency (less than the stoichiometric ratio) is not particularly limited, but for example, it is more than 0 and 25% or less of the total valence of elements other than oxygen it can. However, there may be more oxygen deficiency than this.
＜製造方法＞
　本発明の遷移金属酸化物はブラウンミラーライト型遷移金属酸化物を非晶質化することで製造することができる。 <Manufacturing method>
The transition metal oxide of the present invention can be produced by amorphizing a brown mirror light type transition metal oxide.
　さらに本発明は、下記一般式(1)で示されるブラウンミラーライト型遷移金属酸化物を非晶質化することを含む、γ-CoOOH型の元素配列構造又はこれに類似する元素配列構造の平面分子層シート状物質であり、高分解能透過電子顕微鏡観察において粒径が0.1～10nmの範囲のクラスター構造を有する、非晶質の酸素非欠損型又は酸素欠損型の遷移金属酸化物の製造方法を包含する。
AxB1 2-yB2 yO5　　(1)
式中、Aは、Ca、Sr、Ba又は希土類元素(RE)を表し、
B1は、Coを表し、
B2は、Co 以外の3d遷移元素を表し、
B1及びB2は異なる元素からなり、
ｘは、1.5～2.0の範囲の数値であり、
ｙは、0～1.0の範囲の数値である。 Furthermore, according to the present invention, a plane of an element arrangement structure of γ-CoOOH type or an element arrangement structure similar thereto including amorphizing a brown mirror light type transition metal oxide represented by the following general formula (1) A method for producing an amorphous non-oxygen-deficient or oxygen-deficient transition metal oxide which is a molecular layer sheet-like substance and has a cluster structure having a particle size in the range of 0.1 to 10 nm in high resolution transmission electron microscopy. Include.
A x B 1 2-y B 2 y O 5 (1)
In the formula, A represents Ca, Sr, Ba or a rare earth element (RE),
B 1 represents Co,
B 2 represents a 3d transition element other than Co,
B 1 and B 2 consist of different elements,
x is a numerical value in the range of 1.5 to 2.0,
y is a numerical value in the range of 0 to 1.0.
　非晶質化は、ブラウンミラーライト型遷移金属酸化物を、例えば、アルカリ水溶液に浸漬すること、又はアルカリ水溶液中で分極処理することで実施できる。 Amorphization can be carried out, for example, by immersing a brown mirrorlite type transition metal oxide in an aqueous alkaline solution or polarization treatment in an aqueous alkaline solution.
　アルカリ水溶液浸漬は、例えば、アルカリ金属水酸化物、アルカリ土類金属水酸化物の水溶液に、例えば、０～８０℃の温度範囲で浸漬することで実施できる。アルカリ水溶液の濃度は特に限定はないが、ブラウンミラーライト型遷移金属酸化物の種類、浸漬温度、非晶質化に要する時間等を考慮して、例えば、０．１Ｍ～１０Ｍの範囲とすることができる。浸漬時間は、ブラウンミラーライト型遷移金属酸化物の種類、浸漬温度、アルカリ水溶液濃度等を考慮して、適宜決定できる。 The alkaline aqueous solution immersion can be carried out, for example, by immersion in an aqueous solution of an alkali metal hydroxide and an alkaline earth metal hydroxide at a temperature range of 0 to 80 ° C., for example. The concentration of the aqueous alkaline solution is not particularly limited, but should be, for example, in the range of 0.1 M to 10 M in consideration of the type of transition metal oxide of brown mirror light type, the immersion temperature, the time required for amorphization, etc. Can. The immersion time can be appropriately determined in consideration of the type of brown mirror light type transition metal oxide, the immersion temperature, the concentration of the aqueous alkali solution, and the like.
　アルカリ水溶液中での分極処理は、アルカリ水溶液浸漬で示したと同様のアルカリ水溶液を電解液として用い、ＲＨＥ基準で例えば、１．０～２．０Ｖの電位を印加することで実施できる。電解液の温度や電解時間は、ブラウンミラーライト型遷移金属酸化物の種類と非晶質化の進捗を考慮して適宜決定できる。アルカリ水溶液浸漬に比べて、アルカリ水溶液中での分極処理の方が、アルカリ水溶液の濃度が同一であれば、短時間での処理が可能な場合がある。 The polarization treatment in the alkaline aqueous solution can be carried out by applying an electric potential of, for example, 1.0 to 2.0 V based on RHE, using the same alkaline aqueous solution as that shown in the alkaline aqueous solution immersion as an electrolytic solution. The temperature of the electrolytic solution and the electrolysis time can be appropriately determined in consideration of the type of the brown mirror light type transition metal oxide and the progress of the amorphization. If the polarization process in the alkaline aqueous solution is the same as in alkaline aqueous solution immersion, the treatment in a short time may be possible if the concentration of the alkaline aqueous solution is the same.
　非晶質化に供されるブラウンミラーライト型遷移金属酸化物は、例えば、下記一般式(1)で示される結晶質の遷移金属酸化物であることができる。
AxB1 2-yB2 yO5　　(1)
式中、Aは、Ca、Sr、Ba又は希土類元素(RE)を表し、
B1は、Coを表し、
B2は、Co 以外の3d遷移元素を表し、
B1及びB2は異なる元素からなり、
ｘは、1.5～2.0の範囲の数値であり、
ｙは、0～1.0の範囲の数値である。 The brown mirror light type transition metal oxide to be subjected to amorphization can be, for example, a crystalline transition metal oxide represented by the following general formula (1).
A x B 1 2-y B 2 y O 5 (1)
In the formula, A represents Ca, Sr, Ba or a rare earth element (RE),
B 1 represents Co,
B 2 represents a 3d transition element other than Co,
B 1 and B 2 consist of different elements,
x is a numerical value in the range of 1.5 to 2.0,
y is a numerical value in the range of 0 to 1.0.
　一般式(1)で示される遷移金属酸化物の例としては、例えば、組成式としては、Ca2FeCoO5を挙げることができる。ブラウンミラーライト型遷移金属酸化物は、特許文献１に記載されている方法や下記文献に記載の方法を参照して、それぞれの金属酸化物を原料として固相反応法により合成することができる。例えば、Ca2FeCoO5についての合成方法は、下記非特許文献4～7を参照できる。
[非特許文献4] P.Berastegui et al., Mater. Res. Bull. 1999, 34, 303.
[非特許文献5] F.Ramezanipour et al., Chem. Mater. 2010, 22, 6008.
[非特許文献6]F. Ramezanipour et al., J. Solid State Chem. 2009, 182,153.
[非特許文献7]F. Ramezanipour et al., J. Am. Chem. Soc. 2012, 134,3215. Examples of the transition metal oxide represented by the general formula (1), for example, the formula can be mentioned Ca 2 FeCoO 5. The brown mirror light type transition metal oxide can be synthesized by a solid phase reaction method using each metal oxide as a raw material with reference to the method described in Patent Document 1 and the method described in the following document. For example, the following Non-patent documents 4 to 7 can be referred to for a synthesis method for Ca 2 FeCoO 5 .
[Non-patent document 4] P. Berastegui et al., Mater. Res. Bull. 1999, 34, 303.
[Non-patent document 5] F. Ramezanipour et al., Chem. Mater. 2010, 22, 6008.
[Non-patent document 6] F. Ramezanipour et al., J. Solid State Chem. 2009, 182, 153.
[Non-patent document 7] F. Ramezanipour et al., J. Am. Chem. Soc. 2012, 134, 3215.
　ブラウンミラーライト型遷移金属酸化物は、固相反応法に加えて、液相反応法を用いても合成することができる。液相反応法には、それぞれの金属酸化物の原料としてそれぞれの金属の塩、例えば、硝酸塩、酢酸塩、クエン酸塩等を用いる。例えば、Ca2FeCoO5を合成する場合、Ca塩(例えば、Ca(NO3)2)、Fe塩(例えば、Fe(NO3)3)・9H2O)、Co塩(例えば、Co(NO3)2)・6H2O)を用い、かつゲル化剤としてクエン酸を添加した混合物を溶媒として、例えば、水（蒸留水またはイオン交換水）等を用いて混合する。各金属塩の比率は、目的とする金属酸化物の組成を考慮して適宜決定する。ゲル化剤として用いるクエン酸の量は、金属塩100質量部に対して、例えば、10～1000質量部の範囲とすることができる。ゲル化剤としてはクエン酸以外に、例えば、EDTA（エチレンジアミン四酢酸）やグリシン等を用いることもできる。上記混合物を、例えば、50～90℃に加熱して溶媒を除去することで混合物をゲル化させる。このゲル化物を、例えば、空気中、300～500℃(例えば、450℃)で10分～6時間(例えば、1時間)仮焼成して前駆体を合成する。次にこの前駆体を、例えば、大気中、600～800℃で1～24時間焼成することで、ブラウンミラーライト型のCa2FeCoO5を合成することができる。焼成条件は、例えば、600℃で所定時間(1～12時間)焼成した後、温度を上げて、例えば、800℃で所定時間(6～12時間)焼成することもできる。 In addition to the solid phase reaction method, the brown mirror light type transition metal oxide can also be synthesized using a liquid phase reaction method. In the liquid phase reaction method, salts of the respective metals, for example, nitrates, acetates, citrates and the like are used as raw materials of the respective metal oxides. For example, when Ca 2 FeCoO 5 is synthesized, a Ca salt (eg, Ca (NO 3 ) 2 ), an Fe salt (eg, Fe (NO 3 ) 3 .9H 2 O), a Co salt (eg, Co (NO) 3 ) 2 ) · 6H 2 O) and a mixture to which citric acid is added as a gelling agent are mixed as a solvent, for example, using water (distilled water or ion exchanged water) or the like. The ratio of each metal salt is appropriately determined in consideration of the composition of the target metal oxide. The amount of citric acid used as a gelling agent can be, for example, in the range of 10 to 1000 parts by mass with respect to 100 parts by mass of the metal salt. As a gelling agent, for example, EDTA (ethylenediaminetetraacetic acid), glycine or the like can be used besides citric acid. The mixture is heated, for example, to 50 to 90 ° C. to remove the solvent to gelate the mixture. The gelled product is, for example, calcined in air at 300 to 500 ° C. (eg, 450 ° C.) for 10 minutes to 6 hours (eg, 1 hour) to synthesize a precursor. Next, this precursor can be baked, for example, in the air at 600 to 800 ° C. for 1 to 24 hours to synthesize brown mirror light type Ca 2 FeCoO 5 . The firing conditions may be, for example, firing at 600 ° C. for a predetermined time (1 to 12 hours), and then raising the temperature, for example, firing at 800 ° C. for a predetermined time (6 to 12 hours).
　実施例において詳細を示すが、本発明の非晶質遷移金属酸化物を触媒として用いると同一又は類似する組成を有するブラウンミラーライト型遷移金属酸化物とOER活性は同等であり、より高いORR活性を示す。例えば、ブラウンミラーライト型Ca2FeCoO5を原料に、これを非晶質化したCa、Fe及びCoを含有する非晶質酸化物は、原料としたブラウンミラーライト型Ca2FeCoO5に比べて高いORR活性を示す。OER活性は同等である。 Although the details are shown in the examples, when the amorphous transition metal oxide of the present invention is used as a catalyst, the Braun Millerite type transition metal oxide having the same or similar composition and the OER activity are equivalent and higher ORR activity Indicates For example, Brown mirror light type Ca 2 FeCoO 5 as a raw material, which was amorphous Ca, amorphous oxides containing Fe and Co, as compared to brown mirror light type Ca 2 FeCoO 5 as a raw material It shows high ORR activity. OER activity is equivalent.
＜電極用触媒＞
　本発明は、本発明の非晶質遷移金属酸化物を含む空気極用触媒を包含する。
　さらに本発明は、本発明の非晶質遷移金属酸化物を含む水電解陽極用触媒を包含する。本発明の空気極用触媒及び水電解陽極用触媒は、本発明の非晶質遷移金属酸化物に加えて、上記一般式(1)で示されるブラウンミラーライト型遷移金属酸化物を含有することもできる。 <Catalyst for electrode>
The present invention includes a catalyst for an air electrode comprising the amorphous transition metal oxide of the present invention.
Furthermore, the present invention includes a catalyst for a water electrolysis anode comprising the amorphous transition metal oxide of the present invention. The catalyst for air electrode of the present invention and the catalyst for water electrolysis anode contain brown mirror light type transition metal oxide represented by the above general formula (1) in addition to the amorphous transition metal oxide of the present invention. You can also.
　本発明の非晶質遷移金属酸化物を含む空気極用触媒及び水電解陽極用触媒は、表面積が例えば、1～100m2/gの範囲であることができ、好ましくは、10～100m2/gの範囲である。但し、この範囲に限定される意図ではない。 Amorphous transition metal oxide cathode catalyst and water electrolysis anode catalyst including the present invention, the surface area, for example, can range from 1 ~ 100m 2 / g, preferably, 10 ~ 100 m 2 / It is in the range of g. However, it is not the intention limited to this range.
　本発明の非晶質遷移金属酸化物は、空気極用として極めて有用であり、光水分解による水素製造や、次世代型高容量二次電池として期待されている金属空気二次電池の空気極として極めて有望である。 The amorphous transition metal oxide of the present invention is extremely useful as an air electrode, and is an air electrode of a metal-air secondary battery expected as hydrogen production by light water decomposition and as a next-generation high-capacity secondary battery. It is very promising as
　水電解の陽極における反応は、下記の反応式で表される。
Ｈ２Ｏ→Ｏ２＋４Ｈ＋＋４ｅ－（中性から酸性）
４ＯＨ－→Ｏ２＋２Ｈ２Ｏ＋４ｅ－（塩基性）
　いずれの反応も、酸素発生反応（OER）である。本発明の非晶質遷移金属酸化物は優れたOER活性を有する物であり、水電解陽極用触媒として、極めて有用である。 The reaction at the anode of water electrolysis is represented by the following reaction formula.
H 2 O → O 2 + 4H + + 4e − (neutral to acidic)
4OH - → O 2 + 2H 2 O + 4e - ( basic)
Both reactions are oxygen evolution reactions (OER). The amorphous transition metal oxide of the present invention is one having excellent OER activity, and is extremely useful as a catalyst for water electrolysis anode.
＜空気極＞
　空気極は、通常、多孔質構造を有し、酸素反応触媒の他、導電性材料を含む。また、空気極は、必要に応じて、酸素還元(ORR)触媒、バインダー等を含んでいてもよい。二次電池における空気極には、充電時の機能としてOER触媒活性と、放電時の機能としてORR触媒活性を有することを要する。本発明の触媒はOER触媒であるので、空気極には、この触媒に加えて、ORR触媒を含有させることもできる。空気極における充電及び放電時の化学式を以下に示す。
Figure JPOXMLDOC01-appb-C000001
 <Air electrode>
The cathode usually has a porous structure and contains a conductive material in addition to an oxygen reaction catalyst. In addition, the air electrode may contain an oxygen reduction (ORR) catalyst, a binder, and the like, as necessary. The air electrode in the secondary battery needs to have OER catalyst activity as a function at the time of charge and ORR catalyst activity as a function at the time of discharge. Since the catalyst of the present invention is an OER catalyst, the air electrode can also contain an ORR catalyst in addition to the catalyst. The chemical formulas at the time of charge and discharge at the air electrode are shown below.
Figure JPOXMLDOC01-appb-C000001
　空気極における本発明の触媒(OER触媒)の含有量は、特に限定されないが、空気極の酸素反応性能を高める観点から、例えば、１～９０質量％であることが好ましく、特に１０～６０質量％であることが好ましく、３０～５０質量％であることがより好ましい。 The content of the catalyst (OER catalyst) of the present invention in the air electrode is not particularly limited, but it is preferably, for example, 1 to 90% by mass, particularly 10 to 60 mass, from the viewpoint of enhancing the oxygen reaction performance of the air electrode. % Is preferable, and 30 to 50% by mass is more preferable.
　ORR触媒の例としては、特に制限はないが、例えば、PtまたはPt系材料(例えば、PtCo、PtCoCr、Pt-W2C、Pt-RuOxなど)、Pd系材料(例えば、PdTi、PdCr、PdCo、PdCoAuなど)、金属酸化物(例えば、ZrO2-x、TiOx、TaNxOy、IrMOxなど)、錯体系(Co-ポルフィリン錯体)、その他(PtMoRuSeOx、RuSeなど)を挙げることができる。さらに、Suntivichらが高活性と報告しているLaNiO3(Nat. Chem. 3, 546 (2011))、Liらが報告しているCoO/N-doped CNT(Nat. Commun. 4, 1805 (2013)) なども例示できる。但し、これらに限定される意図ではない。また、各触媒の性能や性質を考慮して複数の触媒を組み合わせて用いることもできる。さらに上記触媒には、助触媒(例えば、TiOx、RuO2、SnO2など)を組み合わせて用いる事もできる。ORR触媒を併用する場合の含有量は、ORR触媒の種類や触媒活性等を考慮して適宜決定することができ、例えば、１～９０質量％であることができる。但し、この数値範囲に限定される意図ではない。 Examples of ORR catalysts include, but are not limited to, Pt or Pt-based materials (eg, PtCo, PtCoCr, Pt-W 2 C, Pt-RuOx, etc.), Pd-based materials (eg, PdTi, PdCr, PdCo) , etc.), metal oxides PdCoAu (e.g., ZrO 2-x, TiO x , TaN x O y, etc. Irmo x), complex type (Co- porphyrin complexes), and the like other (PtMoRuSeO x, etc. RuSe) it can. Furthermore, LaNiO 3 (Nat. Chem. 3, 546 (2011)) reported as highly active by Suntivich et al., CoO / N-doped CNT reported by Li et al. (Nat. Commun. 4, 1805 (2013) ) Can also be illustrated. However, it is not the intention limited to these. In addition, a plurality of catalysts can be used in combination in consideration of the performance and properties of each catalyst. Furthermore, a co-catalyst (for example, TiO x , RuO 2 , SnO 2 or the like) can be used in combination with the above-mentioned catalyst. The content in the case of using the ORR catalyst in combination can be appropriately determined in consideration of the type of the ORR catalyst, the catalyst activity and the like, and can be, for example, 1 to 90% by mass. However, it is not the intention limited to this numerical range.
　導電性材料としては、特に限定されず、導電助剤として一般的に使用可能なものであればよいが、好適なものとして導電性カーボンが挙げられる。具体的には、メソポーラスカーボン、グラファイト、アセチレンブラック、カーボンナノチューブ、カーボンファイバー等が挙げられる。空気極において多くの反応場を提供することから、比表面積が大きい導電性カーボンが好ましい。具体的には、比表面積が１～３０００ｍ２／ｇ、特に５００～１５００ｍ２／ｇである導電性カーボンが好ましい。空気極の触媒は、導電性材料に担持させてもよい。 The conductive material is not particularly limited as long as it can be generally used as a conductive aid, and conductive carbon is preferably mentioned. Specifically, mesoporous carbon, graphite, acetylene black, carbon nanotubes, carbon fibers and the like can be mentioned. Conductive carbon having a large specific surface area is preferred because it provides many reaction sites at the air electrode. Specifically, conductive carbon having a specific surface area of 1 to 3000 m 2 / g, particularly 500 to 1500 m 2 / g is preferable. The catalyst of the cathode may be supported on a conductive material.
　空気極における導電性材料の含有量は、特に限定されないが、放電容量を高める観点から、例えば、１０～９９質量％であることが好ましく、特に２０～８０質量％であることが好ましく、２０～５０質量％であることがより好ましい。 The content of the conductive material in the air electrode is not particularly limited, but is preferably 10 to 99% by mass, particularly preferably 20 to 80% by mass, from the viewpoint of enhancing the discharge capacity. More preferably, it is 50% by mass.
　空気極にバインダーを含有させることで、触媒や導電性材料を固定化し、電池のサイクル特性を向上させることができる。バインダーとしては特に限定されず、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）及びその共重合体、ポリテトラフルオロエチレン（ＰＴＦＥ）及びその共重合体、スチレンブタジエンゴム（ＳＢＲ）等が挙げられる。空気極におけるバインダーの含有量は、特に限定されないが、カーボン（導電性材料）と触媒との結着力の観点から、例えば、１～４０質量％であることが好ましく、特に５～３５質量％であることが好ましく、１０～３５質量％であることがより好ましい。 By including the binder in the air electrode, the catalyst and the conductive material can be fixed to improve the cycle characteristics of the battery. The binder is not particularly limited, and examples thereof include polyvinylidene fluoride (PVDF) and copolymers thereof, polytetrafluoroethylene (PTFE) and copolymers thereof, and styrene butadiene rubber (SBR). Although the content of the binder in the air electrode is not particularly limited, it is preferably, for example, 1 to 40% by mass, particularly 5 to 35% by mass from the viewpoint of the binding ability between carbon (conductive material) and the catalyst. Is preferably 10 to 35% by mass.
　空気極は、例えば、上記した空気極構成材料を適当な溶媒に分散させて調製したスラリーを基材上に塗布、乾燥することで形成することができる。溶媒としては、特に限定されず、例えば、アセトン、Ｎ，Ｎ－ジメチルホルムアミド、Ｎ－メチル－２－ピロリドン（ＮＭＰ）等が挙げられる。空気極構成材料と溶媒との混合は、通常、３時間以上、好ましくは４時間行うことが好ましい。混合方法は特に限定されず、一般的な方法を採用することができる。 The air electrode can be formed, for example, by applying and drying a slurry prepared by dispersing the above-described air electrode constituent material in a suitable solvent on a substrate. The solvent is not particularly limited, and examples thereof include acetone, N, N-dimethylformamide, N-methyl-2-pyrrolidone (NMP) and the like. The mixing of the cathode constituent material and the solvent is preferably carried out usually for 3 hours or more, preferably 4 hours. The mixing method is not particularly limited, and a general method can be adopted.
　スラリーを塗布する基材は、特に限定されず、ガラス板、テフロン（登録商標）板等が挙げられる。これら基材は、スラリーの乾燥後、得られた空気極から剥離される。或いは、空気極の集電体や、固体電解質層を、上記基材として扱うこともできる。この場合、基材は剥離せずに、金属空気二次電池の構成部材としてそのまま利用する。 The substrate to which the slurry is applied is not particularly limited, and examples thereof include a glass plate, a Teflon (registered trademark) plate, and the like. These substrates are peeled off from the obtained air electrode after drying of the slurry. Alternatively, the current collector of the air electrode or the solid electrolyte layer can be treated as the above-mentioned base material. In this case, the base material is used as it is as a constituent member of the metal-air secondary battery without peeling off.
　スラリーの塗布方法、乾燥方法は、特に限定されず、一般的な方法を採用することができる。例えば、スプレー法、ドクターブレード法、グラビア印刷法等の塗布方法、加熱乾燥、減圧乾燥等の乾燥方法を採用することができる。 The coating method and the drying method of the slurry are not particularly limited, and a general method can be adopted. For example, a coating method such as a spray method, a doctor blade method, or a gravure printing method, or a drying method such as heat drying or reduced pressure drying can be employed.
　空気極の厚さは、特に限定されず、金属空気二次電池の用途等に応じて適宜設定すればよいが、通常、５～１００μｍ、１０～６０μｍ、特に２０～５０μｍであることが好ましい。 The thickness of the air electrode is not particularly limited and may be appropriately set according to the use of the metal-air secondary battery etc., but usually 5 to 100 μm, 10 to 60 μm, particularly preferably 20 to 50 μm.
　空気極には、通常、空気極の集電を行う空気極集電体が接続される。空気極集電体の材料、形状は特に限定されない。空気極集電体の材料としては、例えば、ステンレス、アルミニウム、鉄、ニッケル、チタン、炭素（カーボン）等が挙げられる。また、空気極集電体の形状としては、箔状、板状、メッシュ（グリッド状）、繊維状等が挙げられ、中でもメッシュ状等の多孔質形状であることが好ましい。多孔質形状の集電体は、空気極への酸素供給効率に優れているからである。 An air electrode current collector for collecting current from the air electrode is usually connected to the air electrode. The material and shape of the air electrode current collector are not particularly limited. Examples of the material of the air electrode current collector include stainless steel, aluminum, iron, nickel, titanium, carbon (carbon) and the like. Further, the shape of the air electrode current collector may be a foil shape, a plate shape, a mesh (grid shape), a fiber shape or the like, and among them, a porous shape such as a mesh shape is preferable. The porous current collector is excellent in the efficiency of oxygen supply to the air electrode.
＜金属空気二次電池＞
　本発明の金属空気二次電池は、上記非晶質遷移金属酸化物を含む触媒を含有する空気極と、負極活物質を含有する負極と、空気極と負極との間に介在する電解質と、を有する。本発明の金属空気二次電池の空気極には、非晶質遷移金属酸化物遷移金属酸化物を含む触媒が含有され、この触媒は優れたOER触媒特性を示す。従って、この触媒を用いた空気極を用いることで、本発明の金属空気二次電池は、充電速度及び充電電圧に優れたものとなる。 <Metal-air rechargeable battery>
The metal-air secondary battery of the present invention comprises an air electrode containing a catalyst containing the above amorphous transition metal oxide, a negative electrode containing a negative electrode active material, and an electrolyte interposed between the air electrode and the negative electrode. Have. The air electrode of the metal-air secondary battery of the present invention contains a catalyst containing an amorphous transition metal oxide transition metal oxide, which exhibits excellent OER catalytic properties. Therefore, by using an air electrode using this catalyst, the metal-air secondary battery of the present invention becomes excellent in charge rate and charge voltage.
　また、空気極は前記のようにORR触媒活性を有する触媒を共存させることもできる。あるいは、非晶質遷移金属酸化物を含む触媒を含有する酸素発生(OER)用の空気極とは別に、ORR触媒活性を有する触媒を含む酸素還元(ORR)用の空気極を設けることもできる。この場合、金属空気二次電池は、酸素還元用の空気極と酸素発生用の空気極とを有することになる(3電極方式)。放電時には酸素還元用の空気極が用いられ、充電時には酸素発生用の空気極が用いられる。ORR触媒活性を有する触媒は前述の通りであり、この触媒と上記空気極の説明で記載した導電性材料及びバインダー等を用いて酸素発生用の空気極を得ることができる。 In addition, the air electrode can also coexist a catalyst having ORR catalytic activity as described above. Alternatively, an air electrode for oxygen reduction (ORR) containing a catalyst having ORR catalytic activity can be provided separately from an air electrode for oxygen generation (OER) containing a catalyst containing amorphous transition metal oxide. . In this case, the metal-air secondary battery has an air electrode for oxygen reduction and an air electrode for oxygen generation (three-electrode system). At the time of discharge, an air electrode for oxygen reduction is used, and at the time of charge, an air electrode for oxygen generation is used. The catalyst having ORR catalytic activity is as described above, and an air electrode for oxygen generation can be obtained using this catalyst and the conductive material and the binder described in the explanation of the air electrode.
　以下、本発明の金属空気二次電池の一構成例について説明する。尚、本発明の金属空気二次電池は、以下の構成に限定されるものではない。図１０は、本発明の金属空気二次電池の一形態例を示す断面図である。金属空気二次電池１は、酸素を活物質とする空気極２、負極活物質を含有する負極３、空気極２及び負極３の間でイオン伝導を担う電解質４、空気極２の集電を行う空気極集電体５、及び負極３の集電を行う負極集電体６からなり、これらが図示しない電池ケースに収容されている。空気極２には、該空気極２の集電を行う空気極集電体５が電気的に接続され、空気極集電体５は、空気極２への酸素供給が可能な多孔質構造を有している。負極３には、該負極３の集電を行う負極集電体６が電気的に接続され、空気極集電体５及び負極集電体６の端部のうち一方は、電池ケースから突出している。それぞれ、正極端子（図示せず）、負極端子（図示せず）として機能する。 Hereinafter, one structural example of the metal air secondary battery of the present invention will be described. In addition, the metal air secondary battery of this invention is not limited to the following structures. FIG. 10 is a cross-sectional view showing an embodiment of the metal-air secondary battery of the present invention. The metal-air secondary battery 1 includes an air electrode 2 using oxygen as an active material, a negative electrode 3 containing a negative electrode active material, an electrolyte 4 responsible for ion conduction between the air electrode 2 and the negative electrode 3, and a current collector of the air electrode 2. An air electrode current collector 5 to be performed and a negative electrode current collector 6 to collect current from the negative electrode 3 are accommodated in a battery case (not shown). An air electrode current collector 5 for collecting current of the air electrode 2 is electrically connected to the air electrode 2, and the air electrode current collector 5 has a porous structure capable of supplying oxygen to the air electrode 2. Have. The negative electrode current collector 6 for collecting current of the negative electrode 3 is electrically connected to the negative electrode 3, and one of the end portions of the air electrode current collector 5 and the negative electrode current collector 6 protrudes from the battery case There is. It functions as a positive electrode terminal (not shown) and a negative electrode terminal (not shown), respectively.
（負極）
　負極は、負極活物質を含有する。負極活物質としては、一般的な空気電池の負極活物質を用いることができ、特に限定されるものではない。負極活物質は、通常、金属イオンを吸蔵・放出することができるものである。具体的な負極活物質としては、例えば、Ｌｉ、Ｎａ、Ｋ、Ｍｇ、Ｃａ、Ｚｎ、Ａｌ、及びＦｅ等の金属、これら金属の合金、酸化物及び窒化物、並びに炭素材料等が挙げられる。 (Negative electrode)
The negative electrode contains a negative electrode active material. As a negative electrode active material, the negative electrode active material of a common air battery can be used, It does not specifically limit. The negative electrode active material is usually capable of inserting and extracting metal ions. Specific examples of the negative electrode active material include metals such as Li, Na, K, Mg, Ca, Zn, Al, and Fe, alloys of these metals, oxides and nitrides, and carbon materials.
　中でも、亜鉛－空気二次電池は安全面において優れており、次世代の二次電池として期待されている。尚、高電圧高出力という観点からはリチウム－空気二次電池及びマグネシウム空気二次電池が有望である。
　亜鉛－空気二次電池の例を以下に説明すると、反応式は以下の通りである。
Figure JPOXMLDOC01-appb-C000002
 Among them, zinc-air secondary batteries are excellent in terms of safety, and are expected as next-generation secondary batteries. Lithium-air secondary batteries and magnesium-air secondary batteries are promising from the viewpoint of high voltage and high output.
An example of the zinc-air secondary battery will be described below, and the reaction formula is as follows.
Figure JPOXMLDOC01-appb-C000002
　本発明の亜鉛－空気二次電池において、負極としては、亜鉛イオンを吸蔵・放出可能な材料を用いる。このような負極としては、金属亜鉛のほかに、亜鉛合金を用いることもできる。亜鉛合金としては、例えば、アルミニウム、インジウム、マグネシウム、スズ、チタン、銅、から選択される一種または二種以上の元素を含有する亜鉛合金を挙げることができる。 In the zinc-air secondary battery of the present invention, a material capable of inserting and extracting zinc ions is used as the negative electrode. Besides such metallic zinc, a zinc alloy can also be used as such a negative electrode. Examples of the zinc alloy include zinc alloys containing one or more elements selected from aluminum, indium, magnesium, tin, titanium, and copper.
　リチウム－空気二次電池の負極活物質としては、例えば金属リチウム；リチウムアルミニウム合金、リチウムスズ合金、リチウム鉛合金、リチウムケイ素合金等のリチウム合金；スズ酸化物、ケイ素酸化物、リチウムチタン酸化物、ニオブ酸化物、タングステン酸化物等の金属酸化物；スズ硫化物、チタン硫化物等の金属硫化物；リチウムコバルト窒化物、リチウム鉄窒化物、リチウムマンガン窒化物等の金属窒化物；並びにグラファイト等の炭素材料等を挙げることができ、中でも金属リチウムが好ましい。 As a negative electrode active material of a lithium-air secondary battery, for example, metal lithium; lithium alloy such as lithium aluminum alloy, lithium tin alloy, lithium lead alloy, lithium silicon alloy, etc .; tin oxide, silicon oxide, lithium titanium oxide, Metal oxides such as niobium oxide and tungsten oxide; metal sulfides such as tin sulfide and titanium sulfide; metal nitrides such as lithium cobalt nitride, lithium iron nitride and lithium manganese nitride; and graphite A carbon material etc. can be mentioned and metal lithium is preferable among them.
　さらに、マグネシウム－空気二次電池の負極活物質としては、マグネシウムイオンを吸蔵・放出可能な材料を用いる。このような負極としては、金属マグネシウムのほかに、マグネシウムアルミニウム、マグネシウムシリコン、マグネシウムガリウムなどのマグネシウム合金などを用いることができる。 Further, as the negative electrode active material of the magnesium-air secondary battery, a material capable of inserting and extracting magnesium ions is used. As such a negative electrode, magnesium aluminum, magnesium silicon, magnesium alloys such as magnesium gallium and the like can be used besides metal magnesium.
　箔状や板状の金属や合金等を負極活物質として用いる場合には、該箔状や板状の負極活物質を負極そのものとして使用することができる。 When a foil-like or plate-like metal or alloy is used as the negative electrode active material, the foil-like or plate-like negative electrode active material can be used as the negative electrode itself.
　負極は、少なくとも負極活物質を含有してればよいが、必要に応じて、負極活物質を固定化する結着材を含有していてもよい。結着材の種類、使用量等については、上述した空気極と同様であるため、ここでの説明は省略する。 The negative electrode may contain at least a negative electrode active material, but may contain a binder for immobilizing the negative electrode active material, if necessary. The type of binder, the amount used, and the like are the same as those of the above-described air electrode, and thus the description thereof is omitted here.
　負極には、通常、負極の集電を行う負極集電体が接続される。負極集電体の材料、形状は特に限定されない。負極集電体の材料としては、例えば、ステンレス、銅、ニッケル等が挙げられる。また、負極集電体の形状としては、箔状、板状、メッシュ（グリッド状）等が挙げられる。 The negative electrode is usually connected to a negative electrode current collector for collecting current from the negative electrode. The material and shape of the negative electrode current collector are not particularly limited. Examples of the material of the negative electrode current collector include stainless steel, copper, nickel and the like. Moreover, as a shape of a negative electrode collector, foil shape, plate shape, mesh (grid shape) etc. are mentioned.
（電解質）
　電解質は、空気極と負極との間に配置される。電解質を介して、負極と空気極との間の金属イオン伝導が行われる。電解質の形態は、特に限定されるものではなく、液体電解質、ゲル電解質、固体電解質等を挙げることができる。 (Electrolytes)
An electrolyte is disposed between the air electrode and the negative electrode. Metal ion conduction between the negative electrode and the air electrode takes place via the electrolyte. The form of the electrolyte is not particularly limited, and examples thereof include a liquid electrolyte, a gel electrolyte, a solid electrolyte and the like.
　電解液は、負極が亜鉛又はその合金の場合を例に挙げれば、酸化亜鉛を含む水酸化カリウム水溶液や水酸化ナトリウム水溶液などのアルカリ水溶液を用いてもよいし、塩化亜鉛や過塩素酸亜鉛を含む水溶液を用いてもよいし、過塩素酸亜鉛を含む非水系溶媒や亜鉛ビス（トリフルオロメチルスルフォニル）イミドを含む非水系溶媒を用いてもよい。また、負極がマグネシウム又はその合金の場合を例に挙げれば、過塩素酸マグネシウムやマグネシウムビス（トリフルオロメチルスルフォニル）イミドを含む非水系溶媒を用いてもよい。ここで、非水系溶媒としては、例えば、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、γ－ブチロラクトン（γ－ＢＬ）、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）など従来の二次電池やキャパシタに使われる有機溶媒が挙げられる。これらは単独で用いてもよいし、複数を混合して用いてもよい。あるいは、Ｎ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシエチル）アンモニウムビス（トリフルオロメチルスルホニル）イミド（ａｍ）などのイオン性液体を用いることもできる。 The electrolytic solution may be an alkaline aqueous solution such as an aqueous solution of potassium hydroxide containing zinc oxide or an aqueous solution of sodium hydroxide, for example, when the negative electrode is zinc or an alloy thereof, or zinc chloride or zinc perchlorate. An aqueous solution may be used, or a non-aqueous solvent containing zinc perchlorate or a non-aqueous solvent containing zinc bis (trifluoromethylsulfonyl) imide may be used. Moreover, if the case where a negative electrode is magnesium or its alloy is mentioned as an example, you may use the non-aqueous solvent containing magnesium perchlorate and magnesium bis (trifluoromethyl sulfonyl) imide. Here, as the non-aqueous solvent, for example, conventional secondary batteries such as ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), diethyl carbonate (DEC), dimethyl carbonate (DMC) or the like The organic solvent used for a capacitor is mentioned. These may be used alone or in combination of two or more. Alternatively, ionic liquids such as N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (am) can also be used.
　本発明の二次電池において、電解液は、デンドライト生成防止剤を含むことが好ましい。デンドライト生成防止剤は、充電時に負極表面に吸着して結晶面間のエネルギー差を小さくし、優先配向を防ぐことによりデンドライトの発生を抑制すると考えられる。デンドライト生成防止剤については特に限定はないが、例えば、ポリアルキレンイミン類、ポリアリルアミン類及び非対称ジアルキルスルフォン類からなる群より選ばれた少なくとも１種のものであることができる(例えば、特開2009-93983号公報参照)。また、デンドライト生成防止剤の使用量は、特に限定されるものではないが、例えば常温常圧で電解液に飽和する量だけ用いてもよいし、溶媒として用いてもよい。 In the secondary battery of the present invention, the electrolyte preferably contains a dendrite formation inhibitor. It is believed that the dendrite formation inhibitor suppresses the generation of dendrite by adsorbing to the negative electrode surface at the time of charge to reduce the energy difference between crystal planes and preventing preferential orientation. The dendrite formation inhibitor is not particularly limited, and may be, for example, at least one selected from the group consisting of polyalkyleneimines, polyallylamines and asymmetric dialkyl sulfones (for example, JP-A-2009 -93983)). The amount of the dendrite formation inhibitor used is not particularly limited, but may be used, for example, as an amount that saturates the electrolyte at normal temperature and pressure, or as a solvent.
　リチウムイオン伝導性を有する液体電解質は、通常、リチウム塩及び非水溶媒を含有する非水電解液である。上記リチウム塩としては、例えばＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４及びＬｉＡｓＦ６等の無機リチウム塩；並びにＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３等の有機リチウム塩等を挙げることができる。 The liquid electrolyte having lithium ion conductivity is usually a non-aqueous electrolyte containing a lithium salt and a non-aqueous solvent. Examples of the lithium salt include inorganic lithium salts such as LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 ; and LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , Organic lithium salts such as LiC (CF 3 SO 2 ) 3 and the like can be mentioned.
　上記非水溶媒としては、例えばエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ブチレンカーボネート、γ－ブチロラクトン、スルホラン、アセトニトリル、１，２－ジメトキシメタン、１，３－ジメトキシプロパン、ジエチルエーテル、テトラヒドロフラン、２－メチルテトラヒドロフラン及びこれらの混合物等を挙げることができる。非水溶媒としては、イオン液体を用いることもできる。 Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butylene carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and mixtures thereof can be mentioned. An ionic liquid can also be used as a non-aqueous solvent.
　非水電解液におけるリチウム塩の濃度は、特に限定されないが、例えば０．１ｍｏｌ／Ｌ～３ｍｏｌ／Ｌの範囲内であることが好ましく、好ましくは１ｍｏｌ／Ｌである。尚、本発明においては、非水電解液として、例えばイオン性液体等の低揮発性液体を用いてもよい。 The concentration of the lithium salt in the non-aqueous electrolytic solution is not particularly limited, but is preferably in the range of, for example, 0.1 mol / L to 3 mol / L, and preferably 1 mol / L. In the present invention, as the non-aqueous electrolyte, for example, a low volatility liquid such as an ionic liquid may be used.
　リチウムイオン伝導性を有するゲル電解質は、例えば、上記非水電解液にポリマーを添加してゲル化することで得ることができる。具体的には、上記非水電解液に、ポリエチレンオキシド（ＰＥＯ）、ポリビニリデンフルオライド（ＰＶＤＦ、Ａｒｋｅｍａ社製商品名Ｋｙｎａｒなど）ポリアクリロニトリル（ＰＡＮ）またはポリメチルメタクリレート（ＰＭＭＡ）等のポリマーを添加することにより、ゲル化を行うことができる。 The gel electrolyte having lithium ion conductivity can be obtained, for example, by adding a polymer to the above-mentioned non-aqueous electrolyte and gelling it. Specifically, a polymer such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF, trade name Kynar manufactured by Arkema, etc.) polyacrylonitrile (PAN) or polymethyl methacrylate (PMMA) is added to the non-aqueous electrolyte. Gelation can be performed by carrying out.
　リチウムイオン伝導性を有する固体電解質としては、特に限定されず、リチウム金属空気二次電池で使用可能な一般的な固体電解質を用いることができる。例えば、Ｌｉ１．５Ａｌ０．５Ｇｅ１．５（ＰＯ４）３等の酸化物固体電解質；Ｌｉ２Ｓ－Ｐ２Ｓ５化合物、Ｌｉ２Ｓ－ＳｉＳ２化合物、Ｌｉ２Ｓ－ＧｅＳ２化合物等硫化物固体電解質；を挙げることができる。 The solid electrolyte having lithium ion conductivity is not particularly limited, and a general solid electrolyte usable in a lithium metal air secondary battery can be used. For example, oxide solid electrolytes such as Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 ; Li 2 S—P 2 S 5 compounds, Li 2 S—SiS 2 compounds, Li 2 S—GeS 2 And compounds such as sulfide solid electrolytes.
　電解質の厚さは、電池の構成によって大きく異なるものであるが、例えば１０μｍ～５０００μｍの範囲内であることが好ましい。 The thickness of the electrolyte varies depending on the configuration of the battery, but is preferably in the range of, for example, 10 μm to 5000 μm.
（付属構成）
　本発明の金属空気二次電池において、空気極と負極との間には、これら電極間の電気的絶縁を確実に行うために、セパレータが配置されることが好ましい。セパレータは、空気極と負極との間の電気的絶縁が確保可能であると共に、空気極と負極との間に電解質が介在することが可能な構造を有していれば特に限定されない。 (Attachment configuration)
In the metal-air secondary battery of the present invention, a separator is preferably disposed between the air electrode and the negative electrode in order to ensure electrical insulation between the electrodes. The separator is not particularly limited as long as it has a structure in which electrical insulation between the air electrode and the negative electrode can be secured and an electrolyte can be interposed between the air electrode and the negative electrode.
　セパレータとしては、例えば、ポリエチレン、ポリプロピレン、セルロース、ポリフッ化ビニリデン、ガラスセラミックス等の多孔膜；及び樹脂不織布、ガラス繊維不織布等の不織布等を挙げることができる。中でも、ガラスセラミックス製のセパレータが好ましい。 Examples of the separator include porous films such as polyethylene, polypropylene, cellulose, polyvinylidene fluoride, and glass ceramics; and nonwoven fabrics such as resin nonwoven fabrics and glass fiber nonwoven fabrics. Among them, a separator made of glass ceramic is preferable.
　また、金属空気二次電池を収納する電池ケースとしては、一般的な金属空気二次電池の電池ケースを用いることができる。電池ケースの形状としては、上述した空気極、負極、及び電解質を保持することができれば特に限定されるものではないが、具体的にはコイン型、平板型、円筒型、ラミネート型等を挙げることができる。 Further, as a battery case for housing the metal air secondary battery, a battery case of a general metal air secondary battery can be used. The shape of the battery case is not particularly limited as long as it can hold the above-described air electrode, negative electrode, and electrolyte, but specific examples include coin type, flat type, cylindrical type, laminate type, etc. Can.
　本発明の金属空気二次電池は、空気極に活物質である酸素が供給されることにより、放電が可能となる。酸素供給源としては、空気の他、酸素ガス等が挙げられ、好ましくは酸素ガスである。供給する空気又は酸素ガスの圧力は特に限定されず、適宜設定すればよい。 The metal-air secondary battery of the present invention can be discharged by supplying oxygen, which is an active material, to the air electrode. As the oxygen supply source, in addition to air, oxygen gas etc. may be mentioned, preferably oxygen gas. The pressure of the supplied air or oxygen gas is not particularly limited, and may be set as appropriate.
　本発明の非晶質遷移金属酸化物を含む空気極用触媒は、金属空気二次電池に有用であることに加えて、それ以外のOER電極触媒が用いられる分野においても有用である。OER電極触媒は古くからさまざまな電気化学反応の対極反応として研究あるいは利用されており、アルカリ金属メッキや電解脱脂、電気防食技術への転用が可能である。また、最近では太陽電池や光触媒と組み合わせることで、高効率でクリーンな水素製造技術への応用も期待される。 The catalyst for air electrode containing the amorphous transition metal oxide of the present invention is useful not only in the metal air secondary battery but also in the field where other OER electrode catalysts are used. OER electrode catalysts have long been studied or used as counter electrodes for various electrochemical reactions, and can be used for alkali metal plating, electrolytic degreasing, and cathodic protection technology. In addition, recently, it is expected to be applied to highly efficient and clean hydrogen production technology by combining with solar cells and photocatalysts.
　以下に、実施例を挙げて、本発明を更に具体的に説明するが、本発明は、これらの実施例のみに限定されるものではない。 EXAMPLES The present invention will be more specifically described below with reference to examples, but the present invention is not limited to these examples.
実施例１
（１）試料調製１：ブラウンミラーライト型Ca2Fe2-xCoxO5触媒(x=1.0)の調製
　硝酸カルシウム２水和物（Ca(NO3)2・2H2O），硝酸鉄(II)6水和物（Fe(NO3)2・6H2Oおよび硝酸コバルト(II)６水和物（Co(NO3)2・6H2O）をそれぞれ適量純粋に溶かした。さらにそれにクエン酸を金属イオン総量とクエン酸分子のモル量が1:1になるよう加え、溶解させた。60℃に保ちながら数時間水を飛ばし、ゲルを調製した。得られたゲルを大気中５００℃で8hか焼し、前駆体粉末を得た。最後に前駆体粉末を大気中６００℃以上で６時間焼成し、Ca2Fe2-xCoxO5粉末を得た。 Example 1
(1) Preparation of sample 1: Preparation of brown mirror light type Ca 2 Fe 2-x Co x O 5 catalyst (x = 1.0) Calcium nitrate dihydrate (Ca (NO 3 ) 2 · 2H 2 O), iron nitrate (II) Hexahydrate (Fe (NO 3 ) 2 · 6H 2 O and cobalt (II) hexahydrate (Co (NO 3 ) 2 · 6H 2 O) were each dissolved in an appropriate amount pure respectively. Citric acid was added and dissolved so that the total amount of metal ions and molar amounts of citric acid molecules became 1: 1 Water was removed while maintaining at 60 ° C. for several hours to prepare a gel. The precursor powder was calcined for 8 h at 0 ° C. Finally, the precursor powder was calcined in air at 600 ° C. or higher for 6 hours to obtain a Ca 2 Fe 2-x Co x O 5 powder.
（２）試料調製２：化学処理によるアモルファスCalFemConOk触媒の調製
　（１）で調製したブラウンミラーライト型Ca2Fe2-xCoxO5触媒(x=0, 0.25, 0.5 and 1.0)を，4MのKOH水溶液に加え、室温から８０℃で１２時間以上静置した。得られたアモルファスCalFemConOk触媒の表面積は10～30 m2 g-1であった。
　尚、化学処理は1 M以上の塩濃度を持つ水溶液（例えば、1-8M KOH，1M Na2SO4溶液および1M KClなど）で行うことができる。 (2) Sample preparation 2: Amorphous by chemical treatment Ca l Fe m Co n O k Preparation of the catalyst (1) Brown mirror light type was prepared in Ca 2 Fe 2-x Co x O 5 catalyst (x = 0, 0.25, 0.5 and 1.0) were added to 4 M KOH aqueous solution and allowed to stand at room temperature to 80 ° C. for 12 hours or more. Surface area of the obtained amorphous Ca l Fe m Co n O k catalyst was 10 ~ 30 m 2 g -1.
The chemical treatment can be carried out with an aqueous solution having a salt concentration of 1 M or more (eg, 1-8 M KOH, 1 M Na 2 SO 4 solution, 1 M KCl, etc.).
（３）触媒インクの調製
　Ca2Fe2-xCoxO5触媒およびアモルファスCalFemConOk触媒、炭素粉末およびナフィオンバインダーを、それぞれ重量比で5:1:1となるようにエタノール5mlに添加し、超音波混合機でよく分散させた。以上より触媒濃度5 mg cm-3の触媒インクを調製した。 (3) Preparation of catalyst ink Ca 2 Fe 2-x Co x O 5 catalyst and amorphous Ca 1 Fe m Co n O k catalyst, carbon powder and Nafion binder in a weight ratio of 5: 1: 1 respectively It was added to 5 ml of ethanol and well dispersed by an ultrasonic mixer. From the above, a catalyst ink having a catalyst concentration of 5 mg cm -3 was prepared.
（４）分極処理による非晶質化実験
　触媒インクをピペットで採取し、グラッシーカーボンディスクまたはカーボンシート上に、1 mg cm-2となるように塗布し、電極試料を作製した。4 M KOH溶液を電解液とし、作用極に上述の電極試料を用いた。さらに参照電極にKOH飽和Hg/HgO電極、また対極にPt電極を用い、0.6-1.8 V vs RHEの範囲で電位を操作することにより行った。RHEは相対標準電極電位である。 (4) Amorphization Experiment by Polarizing Treatment The catalyst ink was collected by a pipette and applied onto a glassy carbon disk or a carbon sheet so as to be 1 mg cm −2 to prepare an electrode sample. A 4 M KOH solution was used as an electrolyte, and the above-mentioned electrode sample was used as a working electrode. Furthermore, it carried out by manipulating the potential in the range of 0.6-1.8 V vs RHE, using a KOH-saturated Hg / HgO electrode as a reference electrode and a Pt electrode as a counter electrode. RHE is a relative standard electrode potential.
結果
　図１はCa2FeCoO5カーボンシート電極試料を、1.7V vs RHEで20 h定電位分極し酸素発生反応（OER）させたときの電流－時間曲線である。時間の経過とともに電流値が減少し、初期電流に比べ20 h後の電流は約４０％ほど減少した。これは1.7 Vでは集電の役割を担うカーボンが酸化消耗するためである。 Results FIG. 1 is a current-time curve when Ca 2 FeCoO 5 carbon sheet electrode sample is subjected to constant-potential polarization at 1.7 V vs RHE for 20 h and oxygen evolution reaction (OER). The current value decreased with the passage of time, and the current after 20 h decreased by about 40% compared to the initial current. This is because at 1.7 V, carbon which plays a role of current collection is oxidized and consumed.
　図２（a）は、図１の20 h 定電位OER前後の試料について、1.2 V vs RHEから1.7 V vs RHEまで電位走査しOERさせたときの電流－電圧曲線を示す。定電位分極前後を比較すると、OER電流が上昇し始める電位は、1.48 V vs RHE付近でほぼ等しいことから、OER触媒活性は変化していないことがわかる。 FIG. 2 (a) shows a current-voltage curve when a potential scan from 1.2 V vs RHE to 1.7 V vs RHE and OER is performed for the sample before and after the 20 h constant potential OER in FIG. When comparing before and after constant potential polarization, it can be seen that the potential at which the OER current starts to rise is approximately equal around 1.48 V vs RHE, and that the OER catalytic activity has not changed.
　図２（b）は、図１の20 h 定電位OER前後の試料について、1.0 V vs RHEから0.6 V vs RHEまで電位走査し酸素還元反応(ORR)させたときの電流－電圧曲線を示している。定電位分極前の試料では、負のORR電流の開始電位は0.78 V vs RHEであるが、定電位分極後の試料は0.82 V vs RHEより電流が立ち上がり、よって20 h OER後の試料のほうが、高電位よりORR反応が起こる、つまりORR高活性であることが示された。 FIG. 2 (b) shows a current-voltage curve when the potential reduction scan (ORR) is performed from 1.0 V vs RHE to 0.6 V vs RHE for the sample before and after the 20 h constant potential OER in FIG. There is. In the sample before potentiostatic polarization, the onset potential of the negative ORR current is 0.78 V vs RHE, but in the sample after potentiostatic polarization, the current rises from 0.82 V vs RHE, so the sample after 20 h OER It was shown that ORR reaction occurs from high potential, that is, ORR activity is high.
　図３は、図１の1.7 V vs RHEで20 h分極前後のCa2FeCoO5電極試料のXRDパターンを示している．ブラウンミラーライト型構造が崩れ、アモルファス相が形成していることがわかる。 FIG. 3 shows the XRD pattern of the Ca 2 FeCoO 5 electrode sample before and after 20 h polarization at 1.7 V vs RHE in FIG. It can be seen that the brown mirror light type structure collapses and an amorphous phase is formed.
　図４は1.7 V vs RHEで1 h OER分極前後の高分解能TEM写真を示している。分極前はブラウンミラーライト型結晶構造に由来するきれいな格子縞が観察される。さらに制限視野電子回折パターンも、ブラウンミラーライト構造を示す回折パターンを示した。一方1 h分極すると格子縞は消失し、アモルファス相とが形成し、電子線回折パターンもハローパターンのみを示した。さらにアモルファスマトリクス中には、0.5-1 nm程度の大きさ濃色のクラスターが観察され、不均一構造を有していることがわかった。 FIG. 4 shows high resolution TEM photographs before and after 1 h OER polarization at 1.7 V vs RHE. Before the polarization, a clean checkerboard derived from the brown mirror light type crystal structure is observed. Furthermore, the limited field electron diffraction pattern also showed a diffraction pattern showing a brown mirror light structure. On the other hand, when polarized for 1 h, the lattice disappears and an amorphous phase is formed, and the electron diffraction pattern also shows only the halo pattern. Furthermore, in the amorphous matrix, dark clusters of about 0.5-1 nm in size were observed, and it was found that they had a nonuniform structure.
　この濃色のクラスターとそれ以外の淡色の部分をEELSにより金属組成分析した結果を表１に示した。この結果濃色部分は母材の組成に比べ、相対的にCo濃度が高く、代わりにCaおよびFeが低いことが分かる。一方淡色部分は、母材の組成に比べCaはわずかに低いがFe/Coの比は、ほぼ1/1のままであった。 Table 1 shows the results of metal composition analysis of this dark cluster and the other light colored portions by EELS. As a result, it can be seen that the dark portion has a relatively higher Co concentration than the composition of the base material, and lower Ca and Fe instead. On the other hand, in the light color portion, Ca was slightly lower than the composition of the base material, but the ratio of Fe / Co remained almost 1/1.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　以上からブラウンミラーライト型Ca2FeCoO5はOER分極によって0.5 nm－数 nmのCoリッチクラスターをもつ不均一構造を有したアモルファス相に転移し、これがOERおよびORR両反応に対する高活性相であることが示唆された。 From the above, it is found that the brown mirror light type Ca 2 FeCoO 5 is transformed by OER polarization to an amorphous phase having a heterogeneous structure with 0.5 nm to several nm Co-rich clusters, which is a highly active phase for both OER and ORR reactions. Was suggested.
　（５）KOH水溶液浸漬による非晶質化実験
図５（a）は、KOH水溶液浸漬（80℃ 24ｈ）による非晶質化試料について、1.2 V vs RHEから1.7 V vs RHEまで電位走査しOERさせたときの電流－電圧曲線を示す。KOH水溶液浸漬の有無を比較すると、OER電流が上昇し始める電位は、1.48 V vs RHE付近でほぼ等しいことから、OER触媒活性は変化していないことがわかる。 (5) Amorphization experiment by immersion in KOH aqueous solution FIG. 5 (a) shows that OER was subjected to potential scanning from 1.2 V vs RHE to 1.7 V vs RHE for the amorphization sample by KOH aqueous solution immersion (80 ° C. 24 h) Current-voltage curve. When the presence or absence of KOH aqueous solution immersion is compared, the potential at which the OER current starts to rise is approximately equal around 1.48 V vs RHE, which indicates that the OER catalytic activity has not changed.
　図５（b）は、KOH水溶液浸漬（80℃ 24ｈ）による非晶質化試料について、1.0 V vs RHEから0.6 V vs RHEまで電位走査し酸素還元反応(ORR)させたときの電流－電圧曲線を示している。KOH水溶液浸漬前の試料では、負のORR電流の開始電位は0.78 V vs RHEであるが、KOH水溶液浸漬後の試料は0.82 V vs RHEより電流が立ち上がり、よってKOH水溶液浸漬試料のほうが、高電位よりORR反応が起こる、つまりORR高活性であることが示された。 Fig. 5 (b) shows the current-voltage curve when the potential reduction scan from 1.0 V vs RHE to 0.6 V vs RHE and the oxygen reduction reaction (ORR) were performed on the amorphized sample by KOH aqueous solution immersion (80 ° C 24 h). Is shown. In the sample before the KOH aqueous solution immersion, the onset potential of the negative ORR current is 0.78 V vs RHE, but after the KOH aqueous solution immersion, the current rises from 0.82 V vs RHE, and thus the KOH aqueous solution immersion sample has a higher potential. It was shown that more ORR reaction occurred, that is, ORR high activity.
　図６は、KOH水溶液浸漬（80℃ 24ｈ）による非晶質化試料のXRDパターンを示している。ブラウンミラーライト型構造が崩れ、アモルファス相が形成していることがわかる。 FIG. 6 shows the XRD pattern of the amorphized sample by KOH aqueous solution immersion (80 ° C. 24 h). It can be seen that the brown mirror light type structure collapses and an amorphous phase is formed.
　（４）の分極処理（1.7 V vs RHE、1h）を行うことで非晶質化により調製したアモルファス相を有する試料について、様々なCo酸化物、水酸化物およびオキシ水酸化物の結晶データを基に、EXAFSへのフィッティングを行ったところ、分極後試料のEXAFS振動は、γ-CoOOHの結晶モデルでよくフィットできることがわかった。フィッティング結果を図7(d)および表2に示した。γ-CoOOHは、CoO6八面体の陵共有によって形成する[CoO2]n平面分子層シートが、プロトンを介した水素結合によってc軸上積層した層状構造をもつ(図8)。従って、本発明の酸化物はOERにより原子の再配列を起こし、酸化物マトリクス中にCoリッチな酸化物部分が形成され、それがγ-CoOOHによく似た配列構造を形成していることが示された。つまり図4の高分解能TEMにより観測されたナノクラスターは、このγ-CoOOH型配列構造またそれに類似する配列構造をもつナノクラスターであると決定された。 Crystal data of various Co oxides, hydroxides and oxyhydroxides for samples with amorphous phase prepared by amorphization by polarization treatment (1.7 V vs RHE, 1 h) of (4) When fitting to EXAFS was performed based on the results, it was found that EXAFS oscillations of the sample after polarization can be well fitted by the crystal model of γ-CoOOH. The fitting results are shown in FIG. 7 (d) and Table 2. The γ-CoOOH has a layered structure in which a [CoO 2 ] n plane molecular layer sheet formed by the sharing of CoO 6 octahedra is laminated on the c-axis by hydrogen bonding via protons (FIG. 8). Therefore, the oxide of the present invention undergoes atomic rearrangement by OER to form a Co-rich oxide portion in the oxide matrix, which forms an ordered structure similar to γ-CoOOH. Indicated. That is, the nanoclusters observed by the high resolution TEM in FIG. 4 were determined to be nanoclusters having this γ-CoOOH type array structure or an array structure similar thereto.
　さらにEXAFSフィッティング結果より、Co周りの酸素配位数は１時間分極の場合5.1である（表2）。一方酸素欠損が全くない [CoO2]平面単分子層におけるCo配位数は6となる。従って本発明の酸化物中に形成されるナノクラスターは、酸素欠損を有する[CoO1.8]平面単分子層シートを基本骨格にもつ材料であると考えられる。一方、図3の結果よりγ-CoOOH のXRDピークが現れないことから、このナノクラスターはc軸方向への積層は、ＴＥＭ像で観察される粒子径から推察してある程度あるが、発達はしていないと考えられ、従って、本発明の酸化物中のクラスター構造部は平面垂直方向に多少の積層はあるが、この積層はそれほど発達していない、[CoO1.8]平面単分子層と電荷補償のためのプロトンが配位した[CoO1.8Hy]n分子層シート状物質であると同定された。 Furthermore, according to the EXAFS fitting results, the oxygen coordination number around Co is 5.1 for 1 hour polarization (Table 2). On the other hand, the coordination number of Co in the [CoO 2 ] planar monolayer having no oxygen deficiency is six. Therefore, the nanoclusters formed in the oxide of the present invention are considered to be materials having a [CoO 1.8 ] planar monolayer sheet having oxygen deficiency as a basic skeleton. On the other hand, according to the result in FIG. 3, since the XRD peak of γ-CoOOH does not appear, the stacking in the c-axis direction of this nanocluster is to some extent inferred from the particle diameter observed in the TEM image. Although the cluster structure in the oxide of the present invention has some stacking in the direction perpendicular to the plane, this stacking is not so developed, [CoO 1.8 ] planar monolayer and charge compensation For [CoO 1.8 H y ] n molecular sheet with coordinated protons.
　γ-CoOOH 型構造に基づくと、Co原子の第二配位圏には、およそ2.8Åの位置に6個のCo原子が存在する。一方EXAFSフィッティング結果より（表2）、Coの第二配位圏の配位数はおよそ4であり、従ってCoの一部が異種元素置換または欠損しているγ-CoOOH 型平面分子層同士が水素結合を介して積層して形成されるナノクラスターを生成する。以上の結果と合わせると、この[CoO1.8Hy]n分子層シートのCoが一部Feで置換されていることが示唆された。 Based on the γ-CoOOH type structure, six Co atoms exist at about 2.8 Å in the second coordination category of Co atoms. On the other hand, according to the EXAFS fitting results (Table 2), the coordination number of the second coordination sphere of Co is approximately 4, and therefore, γ-CoOOH type planar molecular layers in which part of Co is substituted or deficient with another element are It forms nanoclusters formed by stacking through hydrogen bonds. Taken together with the above results, it was suggested that Co of this [CoO 1.8 H y ] n molecular layer sheet is partially substituted by Fe.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
（６）耐久性試験
　（４）で用いたと同様のCa2FeCoO5カーボンシート電極試料について、Hg/HgO/4 mol dm-3 KOH を参照電極，白金板を対極とする三電極系にて，4 mol dm-3 KOH水溶液中，アルゴン不活性雰囲気下で、40 mA cm-2の一定酸化電流条件で2時間のOER分極及び続いての0電流条件で15分の静置を繰り返すことで一か月間定電流耐久性試験を行った。結果を図した際の、電圧-時間曲線を示す。電流開始後20時間まで電位が1.6 から1.8 V vs RHEまで徐々に上昇するが、その後は一カ月間一定となった。この初期の電位上昇は、AB粒子が酸化消耗したため、CFCへの導通が悪くなったための過電圧上昇であることが確認された。従ってCFCは一か月連続してOER反応を行っても、活性は劣化しないことが確認された。 (6) Durability test For the same Ca 2 FeCoO 5 carbon sheet electrode sample as used in (4), Hg / HgO / 4 mol dm −3 KOH in a three-electrode system using a reference electrode and a platinum plate as a counter electrode, One cycle by repeating OER polarization for 2 hours under a constant oxidation current condition of 40 mA cm -2 in 4 mol dm -3 KOH aqueous solution under argon inert atmosphere and then standing for 15 minutes under 0 current conditions The constant current durability test was conducted for a month. The voltage-time curve when drawing a result is shown. The potential gradually increased from 1.6 to 1.8 V vs RHE until 20 hours after the current started, but remained constant for one month thereafter. It was confirmed that this initial potential rise was an overvoltage rise due to poor conduction to the CFC because the AB particles were oxidized and consumed. Therefore, it has been confirmed that the activity of CFC does not deteriorate even if the OER reaction is performed for one month continuously.
　本発明は、二次電池、次世代型高容量二次電池として期待されている金属空気二次電池や、水電解、光水分解による水素製造の分野において有用である。 The present invention is useful in the fields of secondary batteries, metal-air secondary batteries expected as next-generation high-capacity secondary batteries, and hydrogen production by water electrolysis and light water decomposition.

Claims (14)

  1. 下記A群から選ばれる1種又は2種以上の元素、B群から選ばれる1種又は2種以上の元素及びコバルトを含む非晶質の酸素非欠損型又は酸素欠損型の遷移金属酸化物であり、
    但し、A群は、Ca、Sr、Ba及び希土類元素(RE)からなり、
    B群は、Co以外の3d遷移元素からなり、
    かつ高分解能透過電子顕微鏡観察において粒径が0.1～10nmの範囲のクラスター構造が見られる酸化物であって、前記クラスター構造部はγ-CoOOH型の元素配列構造又はこれに類似する元素配列構造を有する、前記酸化物。     Amorphous, non-oxygen-deficient or oxygen-deficient transition metal oxide containing one or more elements selected from the following group A, one or more elements selected from group B, and cobalt Yes,
    However, A group consists of Ca, Sr, Ba and rare earth elements (RE),
    Group B consists of 3d transition elements other than Co,
    And an oxide in which a cluster structure having a particle size in the range of 0.1 to 10 nm is observed in high resolution transmission electron microscopy, wherein the cluster structure portion has an element arrangement structure of γ-CoOOH type or an element arrangement structure similar thereto. The said oxide.
  2. γ-CoOOH型の元素配列構造又はこれに類似する元素配列構造は、CoO6八面体が陵共有により二次元的に連結して形成する[CoOx]平面単分子層に、電荷補償のためのプロトンが配位した[CoOxHy]平面単分子層がn層積層してできる[CoOxHy]n分子層であって、[CoOxHy]平面単分子層の一辺が10nm以下であり、xは1.5～2.0の範囲であり、ｙは0.01～1の範囲であり、nは平面単分子層の分子層平面に垂直な方向（c軸方向）への積層数であり、1～25の範囲であり、[CoOxHy]平面単分子層中のCoの一部がFeで置換されていてもよく、またCoO6八面体の酸素の一部が欠損していてもよい、請求項１に記載の金属酸化物。 An element arrangement structure of γ-CoOOH type or an element arrangement structure similar to this is formed for charge compensation in a [CoO x ] planar monolayer formed by two-dimensionally connecting CoO 6 octahedra by sharing a ring. protons coordinated [CoO x H y] plane monolayer can be n layer laminated to a [CoO x H y] n molecules layer, [CoO x H y] one side of the planar monolayer 10nm or less X is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, and n is the number of laminations in the direction (c-axis direction) perpendicular to the molecular layer plane of the planar monolayer, In the range of ̃25, a part of Co in the [CoO x H y ] planar monolayer may be substituted with Fe, or a part of oxygen of the CoO 6 octahedron may be deficient The metal oxide according to claim 1.
  3. 前記クラスター構造部が前記マトリクス部に分散している請求項１又は２に記載の酸化物。 The oxide according to claim 1 or 2, wherein the cluster structure portion is dispersed in the matrix portion.
  4. 制限視野電子線回折像において回折パターンは見られず、ハローパターンを示す、請求項１～３のいずれかに記載の酸化物。 The oxide according to any one of claims 1 to 3, wherein no diffraction pattern is seen in the limited field electron diffraction image but a halo pattern is shown.
  5. 前記元素のモル比は、電子エネルギー損失分光法により求める請求項１～４のいずれかに記載の酸化物。 The oxide according to any one of claims 1 to 4, wherein the molar ratio of the elements is determined by electron energy loss spectroscopy.
  6. 下記一般式(1)で示されるブラウンミラーライト型遷移金属酸化物を非晶質化することを含む、
    γ-CoOOH型の元素配列構造又はこれに類似する元素配列構造を有し、高分解能透過電子顕微鏡観察において粒径が0.1～10nmの範囲のクラスター構造を有する、非晶質の酸素非欠損型又は酸素欠損型の遷移金属酸化物の製造方法。
    AxB1 2-yB2 yO5  (1)
    式中、Aは、Ca、Sr、Ba又は希土類元素(RE)を表し、
    B1は、Coを表し、
    B2は、Co以外の3d遷移元素を表し、
    ｘは、1.5～2.0の範囲の数値であり、
    ｙは、0～1.0の範囲の数値である。     Including amorphizing a brown mirror light type transition metal oxide represented by the following general formula (1):
    Amorphous, non-oxygen-depleted type having an element arrangement structure of γ-CoOOH type or an element arrangement structure similar thereto, and having a cluster structure in the range of 0.1 to 10 nm in particle diameter in high resolution transmission electron microscopy Method for producing an oxygen deficient transition metal oxide.
    A x B 1 2-y B 2 y O 5 (1)
    In the formula, A represents Ca, Sr, Ba or a rare earth element (RE),
    B 1 represents Co,
    B 2 represents a 3d transition element other than Co,
    x is a numerical value in the range of 1.5 to 2.0,
    y is a numerical value in the range of 0 to 1.0.
  7. 非晶質化は、ブラウンミラーライト型遷移金属酸化物を、アルカリ水溶液に浸漬すること、又はアルカリ水溶液中で分極処理することを含む、請求項６に記載の製造方法。 The manufacturing method according to claim 6, wherein the amorphization includes immersing the brown mirror light type transition metal oxide in an aqueous alkali solution or polarization treatment in an aqueous alkali solution.
  8. 請求項１～５のいずれかに記載の非晶質遷移金属酸化物又は請求項６若しくは７に記載の方法で製造された非晶質遷移金属酸化物を含む空気極用触媒。 A catalyst for an air electrode, comprising the amorphous transition metal oxide according to any one of claims 1 to 5 or the amorphous transition metal oxide produced by the method according to claim 6 or 7.
  9. 請求項１～５のいずれかに記載の非晶質遷移金属酸化物又は請求項６若しくは７に記載の方法で製造された非晶質遷移金属酸化物を含む水電解陽極用触媒。 A catalyst for a water electrolysis anode comprising the amorphous transition metal oxide according to any one of claims 1 to 5 or the amorphous transition metal oxide produced by the method according to claim 6 or 7.
  10. 表面積が0.1～100m2/gの範囲である請求項８又は９に記載の触媒。 The catalyst according to claim 8 or 9, wherein the surface area is in the range of 0.1 to 100 m 2 / g.
  11. 請求項８又は１０に記載の触媒を含む金属空気二次電池用空気極。 An air electrode for a metal air secondary battery comprising the catalyst according to claim 8 or 10.
  12. 前記非晶質金属酸化物は酸素発生用触媒として含有され、酸素還元用触媒をさらに含む請求項１１に記載の空気極。 The air electrode according to claim 11, wherein the amorphous metal oxide is contained as an oxygen generation catalyst and further includes an oxygen reduction catalyst.
  13. 請求項１１又は１２に記載の空気極と、負極活物質を含有する負極と、前記空気極と前記負極との間に介在する電解質とを有する金属空気二次電池。 A metal air secondary battery comprising the air electrode according to claim 11 or 12, a negative electrode containing a negative electrode active material, and an electrolyte interposed between the air electrode and the negative electrode.
  14. 酸素還元用触媒を含む酸素還元用空気極をさらに含む請求項１３に記載の金属空気二次電池。
          The metal-air secondary battery according to claim 13, further comprising an oxygen reduction air electrode containing an oxygen reduction catalyst.
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