WO2020096022A1 - Material for oxygen evolution (oer) electrode catalyst, and use thereof - Google Patents

Abstract

The present invention relates to: a Co oxide material which is a Co oxide nanocluster having an atomic arrangement structure that is identical or similar to a γ-CoOOH-type atomic arrangement structure and also having an oxygen defect, wherein some of Co atoms in the nanocluster may be substituted by Fe and/or Ni; and a method for producing the Co oxide material. The Co oxide nanocluster has a particle diameter of 10 nm or less. The Co oxide material according to the present invention is a transition metal oxide catalyst having a higher OER activity. The present invention also provides a catalyst for air electrodes, a catalyst for water electrolysis anodes, an air electrode and an air secondary battery, in each of which the above-mentioned catalyst is used.

Description

Oxygen generating (OER) electrode catalyst material and use thereof

The present invention relates to materials for oxygen generating (OER) electrocatalysts and uses thereof.
Cross Reference of Related Applications This application claims the priority of Japanese Patent Application No. 2018-210890 filed on Nov. 8, 2018, the entire description of which is specifically incorporated herein by reference.

Oxygen evolution (OER) electrocatalysts are important as anodes for alkaline electrolysis clean hydrogen production and as cathodes for metal-air batteries. Until now, various crystalline Co-based oxides have been studied as oxygen generating electrode catalysts (Non-Patent Documents 1-3), and their surface active species have been identified. Recently, it has been reported that Ba _0.5 Sr _0.5 Co _0.4 Fe _0.6 O _{3, which} is known as a highly oxidizing active catalyst, becomes amorphous when it becomes higher than the oxygen generation potential in an alkaline solution and becomes an active species (Non-Patent Document 4). Further, more recently, it has been reported that an amorphous Fe _1-x Co _x O _y solid solution exhibits high oxygen generating electrocatalytic activity (Non-Patent Document 5).

Furthermore, by using a brown mirrorlite-type transition metal oxide A ₂ B ₂ O ₅ that has not received much attention as an oxygen generation catalyst, it exhibits activity comparable to that of Pt catalysts for the OER reaction. It has been reported that the use of a material containing a metal has an activity exceeding that of a noble metal catalyst (Patent Document 1).

In addition, a material having a CoOOH nanosheet structure has been reported as an example of an OER catalyst having a new structure (Non-Patent Document 6). This material was prepared by sonicating an α-Co (OH) ₂ sheet in the presence of Cl anions and water to delaminate and then oxidize with NaClO. According to the TEM image and the AFFM image of 1c, the particle size is 200 to 300 nm. Furthermore, according to the XRD result of Fig. 1d, it has crystallinity.

Patent Document 1: WO2015 / 115592

Non-Patent Document 1: T. Maiyalagan, et al., Nature Commun., 5, 3949 (2014).
Non-Patent Document 2: A. Grimoud et al, Nature Chem., 9, 457 (2017).
Non-Patent Document 3: Y. Matsumoto et al, J. Electrochem. Soc., 127, 811 (1980).
Non-Patent Document 4: K. J. May et al, J. Phys. Chem. Lett., 3, 3264 (2012).
Non-Patent Document 5: L. Wei et al., Adv. Mater., 10.1002 / adma.201701410.
Non-Patent Document 6: 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 6 are specifically incorporated herein by reference.

The brown mirrorlite type transition metal oxide A ₂ B ₂ O ₅ containing two kinds of transition metals described in Patent Document 1 exhibits OER activity superior to that of a noble metal catalyst. However, in view of practical use, there is a need to develop a catalyst having a higher OER activity and a stable activity for a long period of time. Further, the material described in Non-Patent Document 3 has a complicated manufacturing method and its OER activity is not high, and thus there is room for further improvement.

Therefore, an object of the present invention is to develop a new transition metal oxide catalyst having a higher OER activity, and further provide a catalyst for an air electrode, a catalyst for a water electrolysis anode, an air electrode and an air secondary battery using this catalyst. Especially.

The present invention is as follows.
[1]
A Co oxide nanocluster having an atomic arrangement structure that is the same as or similar to that of a γ-CoOOH type and has an oxygen defect, in which a part of Co in the nanocluster is replaced with Fe and / or Ni. An optional Co oxide material.
[2]
The material according to [1], wherein the Co oxide nanocluster has a particle diameter of 10 nm or less.
[3]
CoO ₆ octahedra are formed by connecting two-dimensionally by Ling sharing [CoO _x] plane monolayer protons for charge compensation is coordinated [CoO _x H _y] plane monolayer n layer A Co oxide material containing nanoclusters of [CoO _x H _y ] _n molecular layer sheet material formed by stacking, wherein x is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, n is the number of layers stacked in the direction perpendicular to the plane of the planar monolayer (c-axis direction), and is in the range of 1 to 25. [CoO _x H _y ] Part of Co in the planar monolayer May be substituted with Fe and / or Ni, and the CoO ₆ octahedron may be partially deficient in oxygen.
[4]
The material according to [3], wherein one side of the [CoO _x H _y ] planar monolayer is 10 nm or less.
[5]
The material according to any one of [1] to [4], wherein the maximum outer diameter of the nanocluster observed in the TEM image is in the range of 0.3 to 10 nm.
[6]
The material according to any one of [1] to [5], wherein a part of Co in the nanocluster is replaced with Fe and / or Ni.
[7]
The substitution amount of Co for Fe and / or Ni is in the range of Co: Fe atomic ratio obtained by Auger spectroscopic analysis or Co: Fe atomic ratio obtained by elemental analysis by ICP analysis in the range of 100: 0.1 to 10 [ 6] The material according to [6].
[8]
The material according to any one of [1] to [7], which is for an OER catalyst.
[9]
A method for producing a material according to any one of [1] to [7], which comprises placing a raw material containing Ca ₂ CoFeO ₅ and / or Ca ₂ CoNiO ₅ under anode polarization or immersing the raw material in an alkaline aqueous solution. ..
[10]
Anode polarization is performed at a current density that gives a voltage in the range of 1.5 to 2.0 V with respect to RHE, and immersion in an alkaline aqueous solution is performed in an alkaline aqueous solution having a concentration of 1 M or more for one day or more, the production according to [9]. Method.
[11]
A step of adding an alkali to an aqueous solution containing Fe salt and / or Ni salt and Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and recovering the precipitate; Any of [1] to [7], which comprises firing an oxide precipitate containing Ni and Co in an oxygen-containing atmosphere to obtain an oxyhydroxide containing Fe and / or Ni and Co A method for producing the material according to item 1.
[12]
The Fe salt, the Ni salt, and the Co salt are nitrates, respectively, and the alkali is an alkali metal hydroxide [11].
[13]
A catalyst for an air electrode comprising the material according to any one of [1] to [7] or the material produced by the method according to any one of [9] to [12].
[14]
A catalyst for a water electrolysis anode containing the material according to any one of [1] to [7] or the material produced by the method according to any one of [9] to [12].
[15]
An air electrode for a metal-air secondary battery containing the catalyst according to [13] or [14].
[16]
The air electrode according to [15], wherein the material is contained as a catalyst for oxygen generation and further includes a catalyst for oxygen reduction.
[17]
A metal-air secondary battery comprising the air electrode according to [15] or [16], a negative electrode containing a negative electrode active material, and an electrolyte interposed between the air electrode and the negative electrode.
[18]
The metal-air secondary battery according to [17], further including an oxygen reduction air electrode containing an oxygen reduction catalyst.

According to the present invention, a new material useful as an OER catalyst having a high OER activity and stable activity for a long period of time is provided. Furthermore, by using this material, it is possible to provide a catalyst for an air electrode or a catalyst for a water electrolysis anode that exhibits excellent OER activity for a long period of time, and it is possible to provide an air electrode and an air secondary battery that are superior to conventional products.

3A is a high-resolution TEM image of (a) Brown mirror type Ca ₂ FeCoO _{5 + δ} (before OER polarization) and (b) Ca ₂ FeCoO _{5 + δ} after OER polarization for 1 hour at 1.6 V vs RHE. The lattice fringes in (a) correspond to the 110 plane spacing of the Brown mirror phase. In (b), nanoclusters having some periodic structures are surrounded by a yellow broken line. The interpolated figure shows the electron diffraction image measured near the center of the TEM image. Is an OER polarization cycle in which Ca ₂ FeCoO ₅ (sometimes abbreviated as CFC) supported on a carbon sheet is anodic polarized for 2 h at a constant current of 40 mA cm ^-2 and then held at an open circuit potential for 15 minutes. It is a current-time curve when repeated for a month. Shows the XRD pattern of the CFC-supported carbon electrode immediately after preparation (as-prepared), 1 hour (1 h) and 1 month (1 month) after OER polarization (1 month). The XRD pattern of CFC powder is also shown for reference. ▼ and ◯ indicate peaks derived from the carbon sheet and Nafion, respectively. Shows the Auger spectrum of CFC particles before and after one month OER polarization. Shows (a) Co K absorption edge and (b) Fe of anodic polarized Ca ₂ FeCoO ₅ for 1 hour (1 h) and 1 month (1 month) immediately after preparation (As prepared) and 20 mA cm ^-2 constant current condition. X-ray absorption spectrum (XANES) near the K absorption edge. Radial distributions around Co atoms ((c), (e)) and Fe atoms ((d), (f)) determined by broad-range X-ray absorption fine structure (EXAFS). (c) and (d) show comparison of As prepared and 1h samples, and (e) and (f) show comparison of As prepared and 1 month sample. In addition, (c) and (d) also show the fitting results (dotted line) using the γ-CoOOH structural model (FIG. 6). Shows a crystal structure model of γ-CoOOH (hexagonal). Red spheres (small), blue spheres (large) and white spheres (small, isolated between layers) represent oxygen, cobalt and hydrogen atoms, respectively. Is an OER equipotential polarization curve of CFC before and after one month OER polarization. The results of γ-CoOOH prepared by pyrolysis are also shown. _Shows the XRD patterns of Fe _0.05 Co _0.95 O _x H _y , Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y prepared in Example 2. The XRD pattern of γ-CoOOH is also shown. Shows an OER polarization curve of Fe _0.05 Co _0.95 O _x H _y , Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y prepared in Example 2. The OER polarization curve of CFC is also shown. Shows the XRD of the sample (CFC) before the KOH treatment prepared in Example 3 and the KOH-treated product. Shows the OER polarization curves of the sample (CFC) before KOH treatment prepared in Example 3 and the KOH-treated product. Shows a configuration example of the metal-air secondary battery of the present invention.

<Co oxide material of the present invention>
The Co oxide material of the present invention is a Co oxide nanocluster having an atomic arrangement structure that is the same as or similar to the γ-CoOOH type atomic arrangement structure and has an oxygen defect. It is a Co oxide material that may be partially substituted with Fe and / or Ni.

The Co oxide material of the present invention is a Co oxide nanocluster, and the Co oxide nanocluster is characterized by the following (1) to (3).
(1) It has an atomic arrangement structure that is the same as or similar to the atomic arrangement structure of γ-CoOOH type and has an oxygen defect:
The γ-CoOOH type atomic arrangement structure is an atomic arrangement structure of a γ-CoOOH (hexagonal) crystal structure model, and FIG. 6 shows a γ-CoOOH (hexagonal) crystal structure model. Red spheres (small), blue spheres (large) and white spheres (small, isolated between layers) in the figure represent oxygen atoms, cobalt atoms and hydrogen atoms, respectively. γ-CoOOH has a layered structure in which a [CoO ₂ ] planar molecular layer formed by stacking of CoO ₆ octahedra is laminated on the c-axis by hydrogen bonding via protons. The Co oxide material of the present invention has an atomic arrangement structure that is the same as or similar to the crystal structure model of γ-CoOOH (hexagonal) shown in FIG. The Co oxide material of the present invention has the same atomic arrangement structure as the crystal structure model of γ-CoOOH (hexagonal) in the case of [CoO ₂ ] planar molecular layer single layer, and in other cases, γ -It will have an atomic arrangement structure similar to the crystal structure model of CoOOH (hexagonal). Although such an atomic structure will be described later in the manufacturing method, rearrangement of atoms occurs due to OER polarization, and a Co-rich oxide portion is formed in the oxide matrix, which has an arrangement structure similar to γ-CoOOH. It is presumed that the FIG. 1 shows nanoclusters in the Co oxide of the present invention observed by high-resolution TEM. The nanoclusters have the same or similar atomic arrangement structure as the γ-CoOOH type atomic arrangement structure. Since the nanocluster of the present invention has an oxygen deficiency, the portion with the oxygen deficiency is not the same as the γ-CoOOH type atomic arrangement structure, and has an atomic arrangement structure similar to that of the γ-CoOOH type ,, is defined.

The Co oxide material of the present invention has oxygen deficiency. The degree of oxygen deficiency (less than stoichiometric ratio) is not particularly limited, but may be, for example, more than 0 and 25% or less of the total valence of elements other than oxygen. However, there may be more oxygen deficiencies than this.

(2) Co oxide nanoclusters:
Although the Co oxide nanoclusters have different diameters depending on the manufacturing method and conditions, for example, in the manufacturing methods in the following test examples and examples, the diameter can be 20 nm or less. The diameter can also be 10 nm or less.
FIG. 1 shows nanoclusters in the Co oxide of the present invention prepared from a raw material containing Ca ₂ CoFeO ₅ (CFC) observed by high-resolution TEM in Test Example 1. This nanocluster is a nanocluster having an atomic arrangement structure that is the same as or similar to the atomic arrangement structure of the γ-CoOOH type arrangement structure as described above. The high-resolution TEM image shown in FIG. 1 confirmed that these nanoclusters had a diameter of 10 nm or less. Specifically, the nanoclusters were about 0.5-2 nm. Further, in the XRD pattern of the Co oxide of the present invention, the fact that it can be observed and no natural molecular structure-derived peak can be confirmed supports that the cluster diameter is 10 nm or less.

In FIG. 8, the XRD patterns of Fe _0.05 Co _0.95 O _x H _y , Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y shown in (5) of Example 2 are very broad. The crystallite size is estimated to be about 8 to 15 nm from the 002 peak half-width of around 20 °, and the nanoclusters in the Co oxide of the present invention prepared from the raw materials prepared by the coprecipitation method are It can be a cluster having a diameter of 20 nm or less, preferably 5 nm or more and 15 nm or less.

The Co oxide of the present invention is a material according to Non-Patent Document 6 in which a clear X peak appears because at least a diffraction peak due to a crystal is not observed by these particle diameters and XRD, or is very broad even when observed. Is a material that is clearly different from.

(3) Co oxide material in which part of Co in the nanocluster may be substituted with Fe and / or Ni:
The Co oxide material of the present invention prepared in Example 1 shows that a part of Co in the nanocluster is replaced with Fe from the result of composition analysis by Auger spectroscopy. The substitution amount of Co for Fe is, for example, the upper limit substitution range of the Co: Fe atomic ratio obtained by Auger spectroscopic analysis, which is 100: 10 or less, preferably 100: 5 or less. The lower limit is 100: 0.1 or more, preferably 100: 1 or more. The range of 100: 0.1-10 is preferable, and the range of 100: 1-5 is more preferable.

As a result of elemental analysis by ICP, it is found that a part of Co in the nanocluster is replaced with Fe and / or Ni in the Co oxide material of the present invention prepared in Example 2. The substitution amount of Co for Fe and / or Ni is, for example, the upper limit substitution range of the Co: Fe and / or Ni atomic ratio by ICP of 100: 10 or less, preferably 100: 5 or less. The lower limit is 100: 0.1 or more, preferably 100: 1 or more. The range of 100: 0.1-10 is preferable, and the range of 100: 1-5 is more preferable.

Co oxide material of the present invention, more specifically, [CoO _x] protons for charge compensation is coordinated to the plane monolayer [CoO _x H _y] plane monolayer, through hydrogen bonds [CoO _x H _y ] _n molecular layer is a Co oxide material containing nanoclusters of a sheet-like material formed by stacking n layers vertically in the plane direction, x is in the range of 1.5 to 2.0, and y is 0.01 Is in the range of 1 to 1, n is the number of stacks of the plane monolayer in the direction perpendicular to the plane of the molecular layer (c-axis direction), and is in the range of 1 to 25, [CoO _x H _y ] plane monolayer. The above-mentioned material, in which a part of Co in the layer may be replaced with Fe and / or Ni.

Nanoclusters of Co oxide material of the present invention, [CoO _x] protons for charge compensation in the plane monolayer coordinated [CoO _x H _y] plane monolayer n layer laminated to a plane perpendicular It is a nanocluster of [CoO _x H _y ] _n molecular layer sheet material. From the EXAFS fitting results shown in Example 1, the oxygen coordination number around Co was 5.1 for 1-hour polarization and about 5.3 for 1-month polarization (Table 2). On the other hand, the Co coordination number in the [CoO ₂ ] _n molecular layer sheet having no oxygen deficiency is 6. Therefore, it is considered that the nanocluster of the Co oxide material of the present invention shown in the experimental example is a material having a [CoO _x H _y ] _n molecular layer sheet having oxygen deficiency as a basic skeleton. On the other hand, from the XRD results shown in FIG. 3, since the X-ray peak of γ-CoOOH does not appear in the Co oxide material of the present invention, this nanocluster does not grow even though stacking in the c-axis direction exists. It is considered not to. Therefore, the nano-cluster of the Co oxide material of the present invention was identified as a [CoO _X H _y ] _n molecular layer sheet-like substance in which stacks in the plane vertical direction are present but not developed. The atomic arrangement structure of such a [CoO _X H _y ] _n molecular layer sheet material is not the same as the γ-CoOOH type atomic arrangement structure, and has an atomic arrangement structure similar to the γ-CoOOH type atomic arrangement structure. Can be said.

In the [CoO _X H _y ] _n molecular layer sheet, x is in the range of 1.5 to 2.0, preferably 1.6 to 1.9, y is in the range of 0.01 to 1, preferably 0.05 to 0.5, and n is 1 The range is up to 25. The maximum outer diameter of the nanocluster of the Co oxide material of the present invention observed in the TEM image is in the range of 0.3 to 10 nm, preferably 0.6 to 7 nm, and more preferably 0.9 to 5 nm. The CoO ₆ octahedron has a diameter of about 0.29 nm (approximately 0.3 nm), and the [CoO _X H _y ] monolayer has an interlayer distance of about 0.4 nm. Assuming a cluster with 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 10 / 0.29 ( About 1200), 7 / 0.29 x 7 / 0.29 (about 580) in the maximum diameter range of 7 nm, and 5 / 0.29 x 5 / 0.29 (about 300) in the maximum diameter range of 5 nm.

As described above, the nano-cluster of the Co oxide material of the present invention is a [CoO _X H _y ] _n molecular layer sheet-like substance in which stacking in the direction perpendicular to the plane exists but has not been developed, and n is a plane single molecule. It is the number of layers stacked in the direction perpendicular to the molecular layer plane of the layer (c-axis direction). Assuming clusters with a maximum diameter of 0.3-10 nm, n is 1-10 / 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 diameter range of 0.6 to 7 nm, and n is 2 or 3 to 5 / 0.4 (about 12) in the diameter range of 0.9 to 5 nm.

The Co oxide material of the present invention is extremely useful as an OER catalyst. The catalyst will be described later.

<Method for producing Co oxide material of the present invention>
The Co oxide material of the present invention includes, for example, (a) a method including placing a raw material containing Ca ₂ CoFeO ₅ and / or Ca ₂ CoNiO ₅ under anodic polarization, or immersing the raw material in an alkaline aqueous solution, or ( b) a step of adding an alkali to an aqueous solution containing an Fe salt and / or a Ni salt and a Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and recovering the precipitate; And / or Ni and Co containing hydroxide precipitates in an oxygen containing atmosphere to obtain an oxyhydroxide containing Fe and / or Ni and Co. it can.

Manufacturing method (a)
Ca ₂ CoFeO ₅ and Ca ₂ CoNiO ₅ are one of the brown mirrorlite type transition metal oxides, and are prepared by the solid-state reaction method using each metal oxide as a raw material with reference to the method described in Patent Document 1. can do. In addition to the solid phase reaction method, the liquid phase reaction method can also be used for the synthesis. In the liquid phase reaction method, salts of respective metals such as nitrates, acetates and citrates are used as raw materials of respective metal oxides. For example, Ca salt _{(e.g., Ca (NO 3) 2)} , Fe salts _{(e.g., Fe (NO 3) 3)} · 9H 2 O), or Ni salts _{(e.g., Ni (NO 3) 3)} · 9H 2 O ), A Co salt (for example, Co (NO ₃ ) ₂ ) · 6H ₂ O), and using citric acid as a gelling agent as a solvent, for example, water (distilled water or ion-exchanged water), etc. Use and mix. 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 in the range of, for example, 10 to 1000 parts by mass with respect to 100 parts by mass of the metal salt. Other than citric acid, for example, EDTA (ethylenediaminetetraacetic acid), glycine, or the like can be used as the gelling agent. The mixture is gelled by heating the mixture to, for example, 50 to 90 ° C. to remove the solvent. The gelled product is 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 is calcined in the air at 600 to 800 ° C. for 1 to 24 hours, whereby Brown mirror light type Ca ₂ FeCoO ₅ or Ca ₂ CoNiO ₅ can be synthesized. As the firing conditions, for example, after firing at 600 ° C. for a predetermined time (1 to 12 hours), the temperature may be increased and firing at 800 ° C. for a predetermined time (6 to 12 hours) may be performed.

(1) Anodic polarization method Anode polarization is performed by using a raw material containing Ca ₂ CoFeO ₅ (CFC) and / or Ca ₂ CoNiO ₅ (CNC) as an electrode, and for a voltage in the range of 1.5 to 2.0 V with respect to RHE. It is appropriate to carry out an electric current of a predetermined amount or more at such a current density. The amount of electricity equal to or more than a predetermined value can be appropriately selected from the amount of electricity generated by a desired nanocluster, depending on the composition and concentration of the alkaline aqueous solution, the temperature, the structure of the electrode using the raw material as an electrode, and the like. In the examples, the amount of CFC applied was 10 mg cm ^-2 , the carbon sheet electrode was used as the electrode substrate, the platinum plate was the counter electrode (cathode), and the reference electrode for the anode electrode was used. In a three-electrode system using, the OER polarization was repeated for 2 hours in a KOH aqueous solution under an inert atmosphere of argon under the constant oxidation current condition of 40 mA cm ^-2 with the current being zero. The amount of electricity used for anodic polarization in this case is 288 coulombs per cm ² with OER polarization once for 2 hours. When CFC is applied to the anode electrode for polarization treatment, the polarization condition can be selected using this amount of electricity as a guide.

The alkaline aqueous solution used as an electrolytic solution for polarization in the alkaline aqueous solution can be, for example, an alkaline aqueous solution in the range of 0.1M to 10M, and preferably an alkaline aqueous solution in the range of 1M to 6M.

After the polarization treatment, the nanocluster material of the present invention can be recovered from the anode electrode, but the anode electrode formed with the nanocluster material of the present invention can also be used as a product as it is.

(2) Alkaline aqueous solution immersion method The alkaline aqueous solution immersion is performed by using a raw material containing Ca ₂ CoFeO ₅ (CFC) and / or Ca ₂ CoNiO ₅ (CNC), for example, an alkali metal hydroxide or an alkaline earth metal hydroxide. It can be carried out by immersing in an aqueous solution at a temperature range of 0 to 100 ° C., for example. The temperature is preferably in the range of 60 to 90 ° C. The concentration of the alkaline aqueous solution is not particularly limited, but can be, for example, 0.1 M to 10 M, preferably 1 M to 6 M. As the immersion time, the time until the desired nanoclusters are formed can be appropriately determined in consideration of the type of raw material, the immersion temperature, the concentration of the alkaline aqueous solution, and the like. For example, when the temperature is 80 ° C., the immersion in the alkaline aqueous solution is preferably performed in the alkaline aqueous solution having a concentration of 1 M or more for 1 day or more from the viewpoint of forming desired nanoclusters.

After the immersion in the alkaline aqueous solution, the immersed product can be collected and washed with water to obtain the nanocluster material of the present invention.

Manufacturing method (b)
In this production method, an alkali is added to an aqueous solution containing a Fe salt and / or a Ni salt and a Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and a precipitate is recovered. OH hydroxide containing Fe and / or Ni and Co by calcining the obtained precipitate of hydroxide containing Fe and / or Ni and Co in an oxygen-containing atmosphere To get

The Fe salt, Ni salt, and Co salt are not particularly limited as long as each salt is water-soluble, and for example, they can be nitrates, and chlorides can be used in addition to nitrates. The alkali is not particularly limited as long as it is water-soluble, and for example, alkali metal hydroxide can be used, and lithium hydroxide, sodium hydroxide, potassium hydroxide and the like can be used. It can be manufactured by a method including. The coprecipitation method can be performed at room temperature, but can also be performed under cooling or under heating. For the addition of the alkali to the aqueous solution containing the Fe salt and / or the Ni salt and the Co salt, it is appropriate to use an alkaline aqueous solution. The salt concentration of the aqueous solution containing the Fe salt and / or the Ni salt and the Co salt, and the alkali concentration of the alkaline aqueous solution can be appropriately determined.

The precipitate of hydroxide containing Fe and / or Ni and Co prepared by the coprecipitation method is fired in an oxygen-containing atmosphere. The oxygen-containing atmosphere may contain oxygen and may be pure oxygen or air which is an oxygen-containing atmosphere, but it is an oxygen atmosphere from the viewpoint of easily obtaining oxyhydroxide. Is preferred. The firing temperature may be any temperature at which oxyhydroxide can be obtained, and can be, for example, in the range of 50 to 200 ° C, preferably in the range of 80 to 150 ° C. The heating time can be appropriately determined in consideration of the heating temperature and the degree of the product of oxyhydroxide. By this firing, an oxyhydroxide containing Fe and / or Ni and Co is obtained, and the Co oxide material of the present invention can be obtained by using the raw material obtained by the coprecipitation method.

<Catalyst for electrode>
The present invention includes a cathode catalyst containing the material of the present invention.
Further, the present invention includes a catalyst for a water electrolysis anode containing the material of the present invention. The air electrode catalyst and the water electrolysis anode catalyst of the present invention may contain the above-mentioned CFC as a raw material in addition to the material of the present invention.

The air electrode catalyst and the water electrolysis anode catalyst containing the material of the present invention can have a surface area of, for example, 1 to 100 m ² / g, and preferably 10 to 100 m ² / g. However, it is not intended to be limited to this range.

The material of the present invention is extremely useful as an air electrode, and is extremely promising as an air electrode for hydrogen production by photo-water decomposition and a metal-air secondary battery expected as a next-generation high-capacity secondary battery.

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 material of the present invention has an excellent OER activity, and is extremely useful as a catalyst for a water electrolysis anode.

<Air electrode>
The air electrode usually has a porous structure and contains a conductive material in addition to the oxygen reaction catalyst. Further, the air electrode may include an oxygen reduction (ORR) catalyst, a binder, etc., if necessary. The air electrode in the secondary battery needs to have an OER catalytic activity as a function during charging and an ORR catalytic activity as a function during discharging. Since the catalyst of the present invention is an OER catalyst, the air electrode can contain an ORR catalyst in addition to this catalyst. The chemical formulas for charging and discharging in the air electrode are shown below.

The content of the catalyst of the present invention (OER catalyst) in the air electrode is not particularly limited, but from the viewpoint of enhancing the oxygen reaction performance of the air electrode, it is preferably 1 to 90% by mass, and particularly 10 to 60% by mass. %, And more preferably 30 to 50% by mass.

Examples of the ORR catalyst are not particularly limited, but include, for example, Pt or Pt-based materials (for example, PtCo, PtCoCr, Pt-W ₂ C, Pt-RuOx, etc.), Pd-based materials (for example, 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 by Suntivich et al. As high activity, and CoO / N-doped CNT (Nat. Commun. 4, 1805 (2013) reported by Li et al. )) Etc. can also be illustrated. However, it is not intended to be limited to these. Also, a plurality of catalysts may be used in combination in consideration of the performance and properties of each catalyst. Further, a promoter (for example, TiO _x , RuO ₂ , SnO ₂ etc.) can be used in combination with the above catalyst. When the ORR catalyst is used in combination, the content can be appropriately determined in consideration of the type of the ORR catalyst, catalytic activity, etc., and can be, for example, 1 to 90% by mass. However, it is not intended to be limited to this numerical range.

The conductive material is not particularly limited as long as it is a material that can be generally used as a conductive auxiliary agent, and a suitable material is conductive carbon. Specific examples include mesoporous carbon, graphite, acetylene black, carbon nanotubes and carbon fibers. Conductive carbon having a large specific surface area is preferable because it provides many reaction fields 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 air electrode may be supported on a conductive material.

The content of the electrically conductive material in the air electrode is not particularly limited, but from the viewpoint of increasing the discharge capacity, it is preferably 10 to 99% by mass, particularly preferably 20 to 80% by mass, and 20 to It is more preferably 50% by mass.

By including a binder in the air electrode, the catalyst and conductive material can be fixed and the cycle characteristics of the battery can be improved. The binder is not particularly limited, and examples thereof include polyvinylidene fluoride (PVDF) and its copolymer, polytetrafluoroethylene (PTFE) and its copolymer, styrene butadiene rubber (SBR), and the like. The content of the binder in the air electrode is not particularly limited, but from the viewpoint of the binding force between the carbon (conductive material) and the catalyst, it is preferably 1 to 40% by mass, particularly 5 to 35% by mass. It is preferable that the amount is 10 to 35% by mass.

The air electrode can be formed, for example, by applying a slurry prepared by dispersing the above-mentioned air electrode constituent materials in an appropriate solvent onto a base material and drying. 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 air electrode constituent material and the solvent is usually performed for 3 hours or more, preferably 4 hours. The mixing method is not particularly limited, and a general method can be adopted.

The base material to which the slurry is applied is not particularly limited, and examples thereof include a glass plate and a Teflon (registered trademark) plate. These base materials are peeled off from the obtained air electrode after the slurry is dried. Alternatively, the current collector of the air electrode or the solid electrolyte layer can be treated as the base material. In this case, the base material is used as it is as a constituent member of the metal-air secondary battery without being peeled off.

The method for applying the slurry and the method for drying the slurry are not particularly limited, and general methods can be adopted. For example, a coating method such as a spray method, a doctor blade method, 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 application of the metal-air secondary battery, etc., but is usually 5 to 100 μm, 10 to 60 μm, and particularly preferably 20 to 50 μm.

The air electrode is usually connected to an air electrode current collector that collects current from 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, and the like. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, a mesh (grid shape), a fibrous shape, and the like, and among them, a porous shape such as a mesh shape is preferable. This is because the porous collector has excellent oxygen supply efficiency to the air electrode.

<Metal air secondary battery>
The metal-air secondary battery of the present invention has an air electrode containing a catalyst containing the material of the present invention, 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 the material of the present invention, and this catalyst exhibits excellent OER catalytic properties. Therefore, by using the air electrode using this catalyst, the metal-air secondary battery of the present invention becomes excellent in charging speed and charging voltage.

Also, the air electrode can coexist with a catalyst having ORR catalytic activity as described above. Alternatively, an air electrode for oxygen reduction (ORR) containing a catalyst having an ORR catalytic activity can be provided separately from an air electrode for oxygen generation (OER) containing a catalyst containing the material of the present invention. 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). An air electrode for oxygen reduction is used during discharging, and an air electrode for oxygen generation is used during charging. The catalyst having the ORR catalytic activity is as described above, and an oxygen-generating air electrode can be obtained by using this catalyst and the conductive material, the binder and the like described in the description of the air electrode.

A configuration example of the metal-air secondary battery of the present invention will be described below. The metal-air secondary battery of the present invention is not limited to the configuration below. FIG. 12 is a cross-sectional view showing one example of the metal-air secondary battery of the present invention. The metal-air secondary battery 1 collects current from an air electrode 2 having oxygen as an active material, a negative electrode 3 containing a negative electrode active material, an electrolyte 4 that carries out ion conduction between the air electrode 2 and the negative electrode 3, and an air electrode 2. It is composed of an air electrode current collector 5 and a negative electrode current collector 6 that collects current from the negative electrode 3, and these are housed in a battery case (not shown). An air electrode current collector 5 that collects current from 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 A negative electrode current collector 6 that collects current from the negative electrode 3 is electrically connected to the negative electrode 3, and one of the ends of the air electrode current collector 5 and the negative electrode current collector 6 projects from the battery case. There is. Each functions as a positive electrode terminal (not shown) and a negative electrode terminal (not shown).

(Negative electrode)
The negative electrode contains a negative electrode active material. As the negative electrode active material, a negative electrode active material for general air batteries can be used, and it is not particularly limited. 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.

Among them, the zinc-air secondary battery is excellent in safety and is expected as a next-generation secondary battery. From the viewpoint of high voltage and high output, lithium-air secondary batteries and magnesium-air secondary batteries are promising.
An example of the zinc-air secondary battery will be described below, and the reaction formula is as follows.

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. As such a negative electrode, a zinc alloy can be used in addition to metallic zinc. Examples of the zinc alloy include a zinc alloy containing one or more elements selected from aluminum, indium, magnesium, tin, titanium, and copper.

Examples of the negative electrode active material of a lithium-air secondary battery include metallic lithium; lithium alloys such as lithium aluminum alloy, lithium tin alloy, lithium lead alloy, and lithium silicon alloy; 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, lithium manganese nitride; and graphite Examples thereof include carbon materials, and among them, metallic lithium is preferable.

Furthermore, 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 alloy such as magnesium aluminum, magnesium silicon, and magnesium gallium can be used in addition to magnesium metal.

When a foil-shaped or plate-shaped metal or alloy is used as the negative electrode active material, the foil-shaped or plate-shaped negative electrode active material can be used as the negative electrode itself.

The negative electrode only needs to contain at least the negative electrode active material, but may contain a binder that fixes the negative electrode active material, if necessary. Since the kind and amount of the binder used are the same as those of the above-mentioned air electrode, the description thereof is omitted here.

▽ The negative electrode is usually connected to a negative electrode current collector that collects the current of 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. Examples of the shape of the negative electrode current collector include a foil shape, a plate shape, and a mesh (grid shape).

(Electrolytes)
The electrolyte is arranged between the air electrode and the negative electrode. Metal ion conduction is performed between the negative electrode and the air electrode via the electrolyte. The form of the electrolyte is not particularly limited, and examples thereof include a liquid electrolyte, a gel electrolyte, and a solid electrolyte.

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, or zinc chloride or zinc perchlorate. An aqueous solution containing zinc perchlorate or a non-aqueous solvent containing zinc bis (trifluoromethylsulfonyl) imide may be used. If the negative electrode is magnesium or its alloy, for example, a non-aqueous solvent containing magnesium perchlorate or magnesium bis (trifluoromethylsulfonyl) imide may be used. Here, examples of the non-aqueous solvent include conventional secondary batteries such as ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), diethyl carbonate (DEC), and dimethyl carbonate (DMC). The organic solvent used for the capacitor may be used. These may be used alone or in combination of two or more. Alternatively, an ionic liquid such as N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (am) can be used.

In the secondary battery of the present invention, the electrolytic solution preferably contains a dendrite formation inhibitor. It is considered that the dendrite generation inhibitor is adsorbed on the surface of the negative electrode during charging to reduce the energy difference between the crystal planes and prevent preferential orientation, thereby suppressing generation of dendrites. The dendrite formation inhibitor is not particularly limited, but may be at least one selected from the group consisting of polyalkyleneimines, polyallylamines and asymmetric dialkylsulfones (for example, JP 2009 -93983). The amount of the dendrite formation inhibitor used is not particularly limited, but may be, for example, an amount sufficient to saturate the electrolytic solution at room temperature and normal pressure, or may be used as a solvent.

The liquid electrolyte having lithium ion conductivity is usually a non-aqueous electrolytic solution 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 , Examples thereof include organic lithium salts such as LiC (CF ₃ SO ₂ ) ₃ .

Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), butylene carbonate, γ-butyrolactone, sulfolane, acetonitrile, Examples thereof include 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and a mixture thereof. An ionic liquid can also be used as the non-aqueous solvent.

The concentration of the lithium salt in the non-aqueous electrolyte is not particularly limited, but is preferably in the range of 0.1 mol / L to 3 mol / L, and preferably 1 mol / L. In the present invention, a low-volatile 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 non-aqueous electrolyte and gelling the polymer. Specifically, a polymer such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF, product name Kynar manufactured by Arkema, etc.) polyacrylonitrile (PAN) or polymethylmethacrylate (PMMA) is added to the non-aqueous electrolyte solution. By doing so, gelation can be performed.

The solid electrolyte having lithium ion conductivity is not particularly limited, and a general solid electrolyte that can be used in a lithium metal air secondary battery can be used. For example, an oxide solid electrolyte such as Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ; Li ₂ S—P ₂ S ₅ compound, Li ₂ S—SiS ₂ compound, Li ₂ S—GeS ₂ Compounds such as sulfide solid electrolytes;

The thickness of the electrolyte varies greatly depending on the configuration of the battery, but it is preferably in the range of 10 μm to 5000 μm, for example.

(Attached structure)
In the metal-air secondary battery of the present invention, a separator is preferably arranged between the air electrode and the negative electrode in order to ensure electrical insulation between these electrodes. The separator is not particularly limited as long as it can ensure electrical insulation between the air electrode and the negative electrode and has a structure in which an electrolyte can intervene between the air electrode and the negative electrode.

Examples of the separator include porous membranes such as polyethylene, polypropylene, cellulose, polyvinylidene fluoride, and glass ceramics; and nonwoven fabrics such as resin nonwoven fabric and glass fiber nonwoven fabric. Of these, a glass ceramic separator is preferable.

Also, as the battery case for accommodating 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 air electrode, the negative electrode, and the electrolyte described above, but specific examples include a coin type, a flat plate type, a cylindrical type, and a laminated type. You 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. Examples of the oxygen supply source include oxygen gas and the like in addition to air, and oxygen gas is preferable. The pressure of air or oxygen gas to be supplied is not particularly limited and may be set appropriately.

The air electrode catalyst containing the material of the present invention is useful not only for metal-air secondary batteries, but also in other fields where OER electrode catalysts are used. OER electrocatalyst has been studied or used as a counter electrode reaction of various electrochemical reactions for a long time, and can be used for alkali metal plating, electrolytic degreasing, and cathodic protection technology. Further, recently, it is expected to be applied to a highly efficient and clean hydrogen production technology by combining with a solar cell or a photocatalyst.

Hereinafter, the present invention will be described in more detail based on examples. However, the examples are exemplifications of the present invention, and the present invention is not intended to be limited to the examples.

Example 1
Experimental method Ca ₂ CoFeO _{5 + δ} (CFC) was prepared by the following method. Ca (NO _{3) 2} hydrate, Co and (NO _{3) 2} hydrate and Fe (NO _{3) 2} hydrate Ca: Co: molar ratio of Fe 2: 1: 1 so as purified water After dissolution and addition of an appropriate amount of citric acid, the mixture was evaporated to dryness at 120 ° C and then calcined at 500 ° C. It was prepared by firing the finally fired powder in oxygen at 800 ° C. for 8 hours.
The prepared CFC, acetylene black (AB), and Nafion solution were dispersed in ethanol at a weight ratio of CFC: AB: Nafion = 5: 1: 1 to prepare a catalyst ink, which was used as a GC disk (5 mmφ) or carbon. It was applied on a sheet (15 mm x 5 mm, film thickness 0.2 mm) to make an electrode. The amount of ink applied was adjusted so that the amount of CFC catalyst was 10 mg cm ^-2 . A water resistant carbon sheet made by Tokai Carbon was used as the carbon sheet.

Preparation of Co Oxide Material For the preparation of Co oxide material by 1-hour OER polarization and 1-month OER polarization, a carbon sheet electrode was used. Hg / HgO / 4 mol dm ^-3 KOH was used as a reference electrode and a platinum plate was used as a counter electrode. In a 4 mol dm ^-3 KOH aqueous solution under argon inert atmosphere. First, OER polarization was carried out for 2 hours under a constant oxidation current condition of 40 mA cm ^-2 , and then left standing for 15 minutes under 0 current condition. OER polarization was performed by repeating the above two steps alternately for one month, and then the polarized material was recovered to obtain a Co oxide material by OER polarization for one month. For the 1-hour OER polarization, a Co oxide material was obtained by performing OER polarization for 1 hour under the same constant oxidation current condition as above and recovering the polarized material.

Further, the OER current-voltage curve was measured for the CFC electrode before and after the OER polarization for one month, and the OER activity was evaluated. The polarization measurement was performed in a 4 mol dm ^-3 KOH aqueous solution using a three-electrode system with Hg / HgO / 4 mol dm ^-3 KOH as a reference electrode and a platinum plate as a counter electrode. The ORR polarization measurement was performed in an oxygen saturated atmosphere, and the OER polarization measurement was performed in an argon saturated atmosphere.

Comparative Example 1
For comparison experiments, experiments were conducted using γ-CoOOH as a catalyst. γ-CoOOH was prepared by firing commercially available Co (OH) ₂ at 125 ° C for 6 hours. γ-CoOOH and AB, and Nafion solution were dispersed in ethanol in a weight ratio of γ-CoOOH: AB: Nafion = 5: 1: 1 to prepare a catalyst ink, which was applied on a GC disk (5 mmφ). It was used as an electrode. The amount of ink applied was adjusted so that the amount of γ-CoOOH catalyst was 10 mg cm ^-2 . OER and ORR polarization curves were measured using this electrode to evaluate the activity. The polarization measurement was performed in a 4 mol dm ^-3 KOH aqueous solution using a three-electrode system with Hg / HgO / 4 mol dm ^-3 KOH as a reference electrode and a platinum plate as a counter electrode. The ORR polarization measurement was performed in an oxygen saturated atmosphere, and the OER polarization measurement was performed in an argon saturated atmosphere.

Test example 1
The composition of CFC particles was analyzed by Auger spectroscopy for CFC electrodes before and after one month OER polarization. JEOL-2000A was used for spectroscopic measurement, and the electron beam probe system was narrowed down to about 10 nm to evaluate the CFC single particles exposed on the electrode surface. Further, the obtained spectrum was fitted based on the X-ray emission efficiency and emission energy of each element to determine the surface composition.

Also, EXAFS measurement was performed on the BL28XU line of spring 8 for the CFC electrode before and after OER polarization for one month. The measurement was performed by the transmission method.

(1) High-resolution TEM image (Co oxide nanocluster formation and particle size)
Fig. 1 shows high-resolution TEM images of the CFC catalyst before and after polarization when the CFC coated on the GC electrode was OER-polarized at 1.6 V vs. RHE for 1 hour. Pre-polarized samples showed a clean lattice fringe corresponding to the 110 plane spacing of the Brown mirror type phase, and electron diffraction also revealed spots that matched the Brown mirror type structure. You can see that it is being done. On the other hand, in the sample polarized for 1 hour, it is apparent that the bulk crystal structure collapses and the phase transitions to the amorphous phase. Combined with the results of potentiostatic polarization, it was confirmed that the OER activity of CFC was expressed by the amorphous phase formed during anodic polarization, not by the Brown mirror phase as the starting material. From the TEM image, it is clear that this amorphous phase has an apparently non-uniform structure, and nanoclusters of about 0.5-2 nm are dispersed and formed in the amorphous matrix. Furthermore, this nanocluster showed the characteristic of an ordered structure, and in this selected area electron diffraction, in addition to the halo derived from amorphous, a clear ring was observed.

(2) Voltage-time curve (Co oxide nanocluster stability)
FIG. 2 shows a voltage-time curve at the time of constant current repetitive polarization for one month. The potential gradually increased from 1.6 to 1.8 V vs RHE until 20 hours after the start of the current, but thereafter remained constant for one month. It was confirmed that this initial potential rise was an overvoltage rise due to poor conduction to the CFC due to the AB particles being consumed by oxidation. Therefore, it was confirmed that the nano-clustered CFC did not deteriorate the OER activity even if the OER reaction was carried out continuously for one month, and it was found that the CFC had excellent durability.

(3) XRD pattern FIG. 3 shows the XRD pattern after 1 hour and 1 month of polarization. The peak of the brown mirror type structure appearing in the sample before polarization (As prepared) disappeared completely after 1 hour and one month of polarization, and no peak other than the carbon sheet appeared. Therefore, nanoclustered CFCs after 1 hour and 1 month of anodic polarization are essentially amorphous and do not contain more than 10 nm of crystalline particles as expected to show XRD peaks. confirmed.

(4) Auger spectroscopy (chemical composition and structure of Co oxide nanoclusters)
Table 1 shows the results of composition analysis of sample particles before and after one month OER polarization by Auger spectroscopy. In both cases, a C signal derived from Nafion is seen around 240 eV. After one month of electrolysis, the Ca signal around 300 eV disappeared, and the Fe signal around 600 eV became very weak. On the other hand, over 640-800 eV, mixed signals of F, Co, and Fe appear, but their intensities appear to have hardly changed. The F signal here seems to be from Nafion. An increase in the K signal is observed after a further 1-month test, which is considered to be introduced when the Nafion protons are ion-exchanged. The composition of the substance particles before and after OER polarization was determined by fitting to each spectrum. The results are summarized in Table 1.

The CFC particles before OER polarization for one month showed a composition close to the Ca / Fe / Co ratio of the starting material, Brown mirror type phase, that is, 2/1/1. On the other hand, it can be seen that the Co oxide material of the present invention prepared by OER polarization for one month has almost no Ca and almost no Fe. In other words, it was shown that during polarization, Ca and Fe were eluted during the polarization of CFC and changed into oxides or hydrated oxides containing Co as the main component.

Note that this chemical composition was the composition obtained when the amorphous matrix disappeared and became nanoclusters alone, and the influence when the amorphous matrix was mixed was eliminated. The chemical composition of the Co oxide nanocluster immediately after generation (1 hour after polarization) is also considered to be similar to this composition from the results of the voltage-time curve, EXAFS fitting results, and OER current-voltage curve.

(5) EXAFS measurement In order to investigate the structure of the amorphous phase of the Co oxide material prepared by 1-hour OER polarization and the Co oxide material prepared by 1-month OER polarization, BL8XU in Spring 8 The EXAFS of the sample was measured and the local structure around Fe and Co was investigated. The results are shown in Figure 5. It can be seen that the radial distribution function around Fe and Co changes greatly due to one-month polarization, and that the bulk structure also changes like TEM. Due to the polarization, the periodicity of the Fe local structure decreased, and only the coordination sphere (1.6 Å) corresponding to the closest oxygen was observed. On the other hand, the symmetry of the Co local structure improved rather than after polarization, and a new peak appeared near 2.4Å, indicating the formation of the second coordination sphere. Therefore, it is suggested that Co oxide clusters with periodic structure are generated by the amorphization during the OER reaction.

Therefore, when fitting to EXAFS based on the crystal data of various Co oxides, hydroxides, and oxyhydroxides, the EXAFS vibration of the sample after polarization can be well fitted by the crystal model of γ-CoOOH. all right. The fitting results are shown in Fig. 5 (d) and Table 2. γ-CoOOH has a layered structure in which [CoO ₂ ] planar monolayers formed by the co-occurrence of CoO ₆ octahedra are stacked on the c-axis by hydrogen bonding via protons (Fig. 6). Therefore, the Co oxide material of the present invention causes the rearrangement of atoms by OER to form a Co-rich oxide portion in the oxide matrix, which forms an arrangement structure much like γ-CoOOH. Was shown. In other words, the nanoclusters observed by the high-resolution TEM in Fig. 1 were determined to be the nanoclusters having this γ-CoOOH type array structure or an array structure similar to it.

Furthermore, from the EXAFS fitting results, the oxygen coordination number around Co is 5.1 for 1-hour polarization and about 5.3 for 1-month polarization (Table 2). On the other hand, the Co coordination number in the [CoO ₂ ] planar monolayer having no oxygen deficiency is 6. Therefore, the nanoclusters formed in the Co oxide material of the present invention are considered to be materials having a basic skeleton of a [CoO _1.8 ] planar monolayer having oxygen deficiency. On the other hand, since the XRD peak of γ-CoOOH does not appear from the results of FIG. 3, the nanoclusters have some stacking in the c-axis direction, although it can be inferred from the particle size observed in the TEM image, but they do not develop. It is considered not to. Therefore, the nanoclusters formed in the Co oxide material of the present invention have some stacking in the direction perpendicular to the plane, but this stacking is not so well developed. [CoO _1.8 ] Planar monolayer and charge compensation Was identified as a [CoO _1.8 H _y ] _n molecular layer sheet material.

Based on the γ-CoOOH type structure, there are six Co atoms at approximately 2.8Å in the second coordination sphere of Co atoms. On the other hand, from the EXAFS fitting results (Table 2), the coordination number of Co in the second coordination sphere is about 4, and therefore, γ-CoOOH type planar molecular layers in which a part of Co has been substituted or deleted with different elements Nanoclusters are formed by stacking via hydrogen bonds. Together with the above results, it was suggested that Co in this [CoO _1.8 H _y ] _n molecular layer sheet was partially replaced by Fe.

(6) OER current-voltage curve (characteristics of Co oxide nanoclusters)
Figure 7 shows the OER current-voltage curves of the CFC sample and γ-CoOOH powder before and after the one month OER reaction. It was confirmed that the curves were almost the same before and after one month of polarization, and thus the OER activity was not changed at all. Furthermore, when the starting potential of OER is defined to be at 5 mA cm ^-2 current, the starting potentials of nanoclustered CFC and γ-CoOOH powder after one month polarization are 1.47 V vs RHE and 1.58 V vs RHE, respectively. The OER current values at 1.6 V vs RHE were 100 mA cm ^-2 and 12 mA cm ^-2 , respectively. Therefore, nanoclustered CFCs showed much higher activity than γ-CoOOH. From the above, it is suggested that the high activity cannot be obtained only by having the γ-CoOOH type structure, and that the size thereof is about several nm is important for exhibiting the high activity. Further, it is suggested that a part of Co is replaced with Fe.

Example 2
(1) Preparation of Fe- or Ni-dope CoOOH
Preparation of Fe-dope CoOOH and Ni-dope CoOOH were carried out by the coprecipitation method. _{Co (NO 3) 3 · 6H} 2 O and _{Fe (NO 3) 3 · 6H} 2 O or _{Ni (NO 3) 3 · 6H} 2 O were mixed dissolved in pure water at a predetermined molar ratio metal ions (Co + 50 cm ^{3 of a} solution containing 0.2 M of Fe or Co + Ni) was prepared. Subsequently, this mixed solution was gently added to 50 cm ³ of a 2M KOH aqueous solution while stirring at 200 rpm to obtain a hydroxide precipitate. After filtration, it was washed twice with 20 cm ³ of pure water, and then dried under reduced pressure overnight at room temperature. Finally, it was baked in an O ₂ stream at 120 ° C. for 6 hours, and Co was γCoOOH in which Fe was substituted. Oxyhydroxides Fe _0.05 Co _0.95 O _x H _y , Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _{x Hy} was obtained (hereinafter referred to as Fe-dope CoOOH or Ni-dope CoOOH.

(2) Elemental analysis In order to examine the Fe / Co or Ni / Co ratio of the obtained powder, the powder was dissolved in a 0.1 M KCl solution and analyzed by ICP. As a result, all the metal composition ratios matched the charged values.

(3) and the BET specific surface area of BET specific surface area obtained _{powder, Fe 0.05 Co 0.95 O x H} y, Fe 0.1 Co 0.9 O x H y and Ni _0.1 Co _0.95 O _x H _y, respectively 86,75 , 61 m ² g ^-1 . These BET specific surface areas were an order of magnitude higher than those of ordinary ceramics with micrometer-sized particles. From this, it was inferred that the obtained powder was a nanoparticulate substance.

(4) OER activity of Fe-dope CoOOH electrode and Ni-dope CoOOH electrode A carbon mixed electrode was prepared in the same manner as in Example 1 and measured in 4M KOH. That is, acetylene black (AB), and Nafion solution was dispersed in ethanol in a weight ratio of Fe-dope CoOOH or Ni-dope CoOOH: AB: Nafion = 5: 1: 1 to obtain a catalyst ink, which was used as a GC. A disk (5 mmφ) or a carbon sheet (15 mm x 5 mm, film thickness 0.2 mm) was applied to form an electrode. The amount of ink applied was adjusted so that the amount of Fe-dope CoOOH or Ni-dope CoOOH was 10 mg cm ^-2 .
(5) XRD
The Fe _0.05 Co _0.95 was prepared in (1) O _x H _y, the XRD of Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y is measured, and the results are shown in Fig. The XRD pattern of γ-CoOOH is also shown. Fe _0.05 Co _0.95 O _x H _y , Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y all showed the same XRD pattern as γ-CoOOH, and thus had a γ-CoOOH type layered structure. Was confirmed. The XRD patterns of the three oxyhydroxides are very broad, so the crystallite size is about 8-15 nm from the 002 peak half-width around 20 °.
(5) OER
The Fe _0.05 Co _0.95 was prepared in (1) O _x H _y, the OER polarization curves of Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y shown in FIG. In all cases, the current rose from 1.45 V vs RHE, and reached the current value of 5 mA cm ^-2 at 1.47, 1.46 and 1.49 V vs RHE, respectively. Moreover, both showed a current of 120 mA cm ^-2 or more at 1.6 V vs RHE.
(6)
As described above, the Fe- or Ni-dopeγ-CoOOH type nanocrystalline material produced by the coprecipitation method in this example exhibited the same structure and activity as the CFC shown in Example 1.

Example 3
Ca ₂ CoFeO _{5 + Δ} (CFC) was prepared in the same manner as in Example 1, the prepared CFC was immersed in 4 M KOH, and airtight Ar bubbling was performed at 50 ° C. for 3 days. After that, wash well with Milli-Q water,
A sample was obtained by filtration. The Ca / Fe / Co (ICP emission analysis) of the KOH-treated product was 0.03 / 0.21 / 0.76. The BET measured before KOH treatment was 2.92 m ² g ^-1 , whereas after BET treatment it increased to 230, about 80 times. FIG. 10 shows the XRD of the sample (CFC) before the KOH treatment and the KOH-treated product, and FIG. 11 shows the OER polarization curve. The EXAFS of the KOH-treated product was similar to that of the 1-hour OER-polarized product of Example 1 shown in FIG.

The results of EXAFS fitting are shown in Table 3 below. From the results in this table, it can be seen that the KOH-treated product is also a nanocluster having a γ-CoOOH type structure or an array structure similar to it.

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 photolysis.

Claims (18)

1. A Co oxide nanocluster having an atomic arrangement structure that is the same as or similar to that of a γ-CoOOH type and has an oxygen defect, in which a part of Co in the nanocluster is replaced with Fe and / or Ni. An optional Co oxide material.
2. The material according to claim 1, wherein the Co oxide nanocluster has a particle diameter of 10 nm or less.
3. CoO ₆ octahedra are formed by connecting two-dimensionally by Ling sharing [CoO _x] plane monolayer protons for charge compensation is coordinated [CoO _x H _y] plane monolayer n layer A Co oxide material containing nanoclusters of [CoO _x H _y ] _n molecular layer sheet material formed by stacking, wherein x is in the range of 1.5 to 2.0, y is in the range of 0.01 to 1, n is the number of layers stacked in the direction perpendicular to the plane of the planar monolayer (c-axis direction), and is in the range of 1 to 25. [CoO _x H _y ] Part of Co in the planar monolayer May be substituted with Fe and / or Ni, and the CoO ₆ octahedron may be partially deficient in oxygen.
4. The material according to claim 3, wherein one side of the [CoO _x H _y ] planar monolayer is 10 nm or less.
5. The material according to any one of claims 1 to 4, wherein the maximum outer diameter of the nanocluster observed in the TEM image is in the range of 0.3 to 10 nm.
6. The material according to any one of claims 1 to 5, wherein a part of Co in the nanocluster is replaced with Fe and / or Ni.
7. The substitution amount of Co for Fe and / or Ni is such that the Co: Fe and / or Ni atomic ratio obtained by Auger spectroscopic analysis or the Co: Fe atomic ratio obtained by elemental analysis by ICP analysis is 100: 0.1 to 10 The material according to claim 6, which is in the range of.
8. The material according to any one of claims 1 to 7, which is for an OER catalyst.
9. The method for producing a material according to any one of claims 1 to 7, which comprises placing a raw material containing Ca ₂ CoFeO ₅ and / or Ca ₂ CoNiO ₅ under anodic polarization or immersing the raw material in an alkaline aqueous solution.
10. 10. The production according to claim 9, wherein the anodic polarization is performed at a current density that gives a voltage in the range of 1.5 to 2.0 V with respect to RHE, and the immersion in the alkaline aqueous solution is performed for 1 day or more in an alkaline aqueous solution having a concentration of 1 M or more. Method.
11. A step of adding an alkali to an aqueous solution containing Fe salt and / or Ni salt and Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and recovering the precipitate; The method according to any one of claims 1 to 7, which comprises calcination of a hydroxide precipitate containing Ni and Co in an oxygen-containing atmosphere to obtain an oxyhydroxide containing Fe and / or Ni and Co. A method for producing the described material.
12. The manufacturing method according to claim 11, wherein each of the Fe salt, the Ni salt and the Co salt is a nitrate, and the alkali is an alkali metal hydroxide.
13. A catalyst for an air electrode comprising the material according to any one of claims 1 to 7 or the material produced by the method according to any one of claims 9 to 12.
14. A catalyst for a water electrolysis anode comprising the material according to any one of claims 1 to 7 or the material produced by the method according to any one of claims 9 to 12.
15. An air electrode for a metal-air secondary battery, which comprises the catalyst according to claim 13 or 14.
16. The air electrode according to claim 15, wherein the material is contained as a catalyst for oxygen generation and further includes a catalyst for oxygen reduction.
17. A metal-air secondary battery comprising the air electrode according to claim 15 or 16, a negative electrode containing a negative electrode active material, and an electrolyte interposed between the air electrode and the negative electrode.
18. The metal-air secondary battery according to claim 17, further comprising an oxygen reduction air electrode including an oxygen reduction catalyst.

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