JPWO2020096022A1 - Oxygen Evolution (OER) Electrode Catalyst Materials and Their Use - Google Patents

Abstract

The present invention is a Co oxide nanocluster having the same or similar atomic arrangement structure as the γ-CoOOH type atomic arrangement structure and having an oxygen defect, and a part of Co in the nanocluster is Fe and / Alternatively, the present invention relates to a Co oxide material and a method for producing the same, which may be substituted with Ni. The particle size of the Co oxide nanocluster is 10 nm or less. The Co oxide material of the present invention is a transition metal oxide catalyst having a higher OER activity, and the present invention also provides a catalyst for an air electrode, a catalyst for a water electrolysis anode, an air electrode and an air secondary battery using this catalyst. do.

Description

The present invention relates to materials for oxygen evolution (OER) electrode catalysts and their use.
Cross-reference to related applications This application claims the priority of Japanese Patent Application No. 2018-210890 filed on November 8, 2018, the entire description of which is incorporated herein by reference in particular.

Oxygen evolution (OER) electrode catalysts are important as anodes for alkaline electrolytic clean hydrogen production and as air electrodes for metal-air batteries. So far, various crystalline Co-based oxides have been studied as oxygen-evolving 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 oxidative activity catalyst, becomes amorphous when it exceeds the oxygen evolution potential in an alkaline solution, and this becomes an active species (Non-Patent Document 4). More recently, _{it has been reported that an amorphous Fe 1-x} Co _x O _y solid solution exhibits high oxygen-evolving electrode catalytic activity (Non-Patent Document 5).

Furthermore, by using the brown mirror light type transition metal oxide A ₂ B ₂ O ₅ , which has not been attracting attention as an oxygen evolution catalyst, the activity is comparable to that of the Pt catalyst for the OER reaction, and two types of transitions are among them. It has been reported that the use of a metal-containing catalyst exhibits an activity superior to that of a noble metal catalyst (Patent Document 1).

Further, as an example of an OER catalyst having a new structure, a material having a CoOOH nanosheet structure has been reported (Non-Patent Document 6). This material was prepared by sonicating an α-Co (OH) ₂ sheet in the presence of Cl anion and water to peel off the layers, and then oxidizing it with NaClO. Fig.1b According to the TEM image of 1c and the AFMM image of 1c, it has a particle size of 200 to 300 nm. Furthermore, according to the XRD result in 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: KJ 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 description of Patent Document 1 and Non-Patent Documents 1 to 6 is incorporated herein by reference in particular.

_{The brown mirror light 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, it is necessary to develop a catalyst having higher OER activity and stable activity for a long period of time. In addition, the materials described in Non-Patent Document 3 have a complicated manufacturing method and do not have high OER activity, so there is room for further improvement.

Therefore, an object of the present invention is to develop a new transition metal oxide catalyst having higher OER activity, and further to 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. There is.

The present invention is as follows.
[1]
A Co oxide nanocluster having the same or similar atomic arrangement structure as the γ-CoOOH type atomic arrangement structure and having an oxygen defect, and a part of Co in the nanocluster is replaced with Fe and / or Ni. Co-oxide material, which may be.
[2]
The material according to [1], wherein the Co oxide nanocluster has a particle size 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 can be laminated to a [CoO _x H _y] Co oxide material containing nano-clusters of _n molecular layer sheet material, 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 stacked direction perpendicular to the molecular layer planes of monomolecular layer (c-axis direction) in the range of 1 to 25, a portion of [CoO _x H _y] plane Co monomolecular layer The material may be substituted with Fe and / or Ni, and may lack some of the oxygen in the _{CoO 6 octahedron.}
[4]
Material according to the one side of the [CoO _x H _y] plane monomolecular layer is 10nm or less, [3].
[5]
The material according to any one of [1] to [4], wherein the maximum outer diameter of the nanoclusters 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 amount of Co substituted for Fe and / or Ni has a Co: Fe atomic ratio obtained by Auger spectroscopic analysis or a 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.
[8]
The material according to any one of [1] to [7] for an OER catalyst.
[9]
The 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 anodic polarization or immersing it in an alkaline aqueous solution.} ..
[10]
The production according to [9], wherein the anodic polarization is carried out at a current density having 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 carried out in the alkaline aqueous solution having a concentration of 1 M or more for 1 day or more. Method.
[11]
A step of adding an alkali to an aqueous solution containing a Fe salt and / or Ni salt and a Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and recovering the precipitate. Any of [1] to [7], which comprises calcining a precipitate of a hydroxide containing Ni and Co in an oxygen-containing atmosphere to obtain an oxyhydroxide containing Fe and / or Ni and Co. The method for producing the material described in Crab.
[12]
The production method according to [11], wherein the Fe salt, the Ni salt and the Co salt are nitrates, respectively, and the alkali is an alkali metal hydroxide.
[13]
An air electrode catalyst 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].
[14]
A catalyst for a water electrolytic 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 an oxygen evolution catalyst and further contains an oxygen reduction catalyst.
[17]
A metal-air secondary battery having an 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 comprising an oxygen-reducing air electrode including an oxygen-reducing catalyst.

According to the present invention, there is provided a new material useful as an OER catalyst, which has high OER activity and its activity is stable for a long period of time. Further, by using this material, it is possible to provide a catalyst for an air electrode and a catalyst for a water electrolysis anode that exhibit 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.

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 1 hour OER polarization at 1.6 V vs RHE.} The plaid in (a) corresponds to the 110-plane spacing of the brown mirror phase. In (b), nanoclusters having several periodic structures are surrounded by a yellow dashed line. The inset 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 hours 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 the month is repeated. Shows the XRD pattern of CFC-supported carbon electrodes immediately after fabrication (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 〇 indicate peaks derived from carbon sheet and Nafion, respectively. Shows Auger spectroscopic spectra of CFC particles before and after one month OER polarization. The (a) Co K absorption edge and (b) Fe of _{Ca 2} FeCoO ₅ anodic polarized immediately after preparation (As prepared) and under 20 mA cm ^-2 constant current conditions for 1 hour (1 h) and January (1 month). X-ray absorption spectrum near the K-edge (XANES). Radial distribution around Co atoms ((c), (e)) and Fe atoms ((d), (f)) determined from extended X-ray absorption fine structure (EXAFS). (c) and (d) show a comparison of As prepared and 1h samples, and (e) and (f) show a comparison of As prepared and 1 month samples. The fitting results (dotted line) using the γ-CoOOH structure model (Fig. 6) are also shown in (c) and (d). 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 the OER equipotential polarization curve of CFC before and after one month OER polarization. The results of γ-CoOOH prepared by the thermal decomposition method are also shown. Shows the XRD pattern of the as prepared in Example _{2 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} . The XRD pattern of γ-CoOOH is also shown. Shows OER polarization curves 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 KOH treatment and the KOH-treated product prepared in Example 3. Shows the OER polarization curves of the sample (CFC) before KOH treatment and the KOH-treated product prepared in Example 3. 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 the same or similar atomic arrangement structure as the γ-CoOOH type atomic arrangement structure and having an oxygen defect, and is a Co oxide nanocluster in the nanocluster. 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 the same or similar atomic arrangement structure as the γ-CoOOH type atomic arrangement structure and has an oxygen defect:
The γ-CoOOH type atomic arrangement structure is an atomic arrangement structure possessed by a γ-CoOOH (hexagonal) crystal structure model, and FIG. 6 shows a γ-CoOOH (hexagonal) crystal structure model. The red spheres (small), blue spheres (large), and white spheres (small, isolated between layers) in the figure indicate oxygen atoms, cobalt atoms, and hydrogen atoms, respectively. γ-CoOOH has _{a layered structure in which [CoO 2} ] planar molecular layers formed by the ridge sharing of _{CoO 6} octahedrons are laminated on the c-axis by hydrogen bonds via protons. The Co oxide material of the present invention has an atomic arrangement structure that is the same as or similar to the γ-CoOOH (hexagonal) crystal structure model shown in FIG. The Co oxide material of the present invention has the same atomic arrangement structure as the γ-CoOOH (hexagonal) crystal structure model in the case _{of a [CoO 2] planar molecular layer single layer, and in other cases, γ.} -It will have an atomic arrangement structure similar to the CoOOH (hexagonal) crystal structure model. Such an atomic structure will be described later in the production method, but the rearrangement of atoms occurs due to OER polarization, and a Co-rich oxide portion is formed in the oxide matrix, which is an arrangement structure very similar to γ-CoOOH. Is presumed to have formed. FIG. 1 shows the nanoclusters in the Co oxide of the present invention observed by the high-resolution TEM. The nanoclusters are nanoclusters having 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 having the oxygen deficiency is not the same as the γ-CoOOH type atomic arrangement structure, but has an atomic arrangement structure similar to the γ-CoOOH type atomic arrangement structure. , Is defined as.

The Co oxide material of the present invention has an oxygen deficiency. The degree of oxygen deficiency (less than the stoichiometric ratio) is not particularly limited, but can 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 deficiency than this.

(2) Co oxide nanocluster:
The diameter of the Co oxide nanocluster differs depending on the production method and conditions. For example, in the production methods in the following test examples and examples, the diameter can be 20 nm or less, and the Co oxide nanocluster can be used. The diameter can 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 a high-resolution TEM in Test Example 1. As described above, 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 for this nanocluster, a cluster having a diameter of 10 nm or less is confirmed by the high-resolution TEM image shown in FIG. 1, and specifically, it is a nanocluster of about 0.5-2 nm. Further, in the XRD pattern of the Co oxide of the present invention, the fact that a peak derived from a molecular structure that can be observed cannot be confirmed supports that the cluster diameter is 10 nm or less.

8, shown in Example _{2 (5), Fe 0.05 Co} 0.95 O x H y, XRD pattern of Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y is very be broad The crystallite size is estimated to be about 8-15 nm from the full width at half maximum of 002 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 with a diameter of 20 nm or less, preferably 5 nm or more and 15 nm or less.

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

(3) A Co oxide material in which a part of Co in the nanocluster may be substituted with Fe and / or Ni:
From the results of composition analysis by Auger spectroscopy, it can be seen that the Co oxide material of the present invention prepared in Example 1 has a part of Co in the nanocluster replaced with Fe. The amount of Co substituted to Fe is such that the Co: Fe atomic ratio obtained by Auger spectroscopic analysis is in the upper limit substitution range, 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 to 10 is preferable, and the range of 100: 1 to 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 amount of Co substituted with Fe and / or Ni is, for example, a substitution range in which the Co: Fe and / or Ni atomic ratio by ICP is the upper limit, and is in the range 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 to 10 is preferable, and the range of 100: 1 to 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 can be laminated on the n layer plane perpendicular Te a Co oxide material containing nanoclusters [CoO _x H _{y] n} molecules layer sheet material, x is in the range of 1.5 to 2.0, y is 0.01 ranges from to 1, n is the number of stacked direction perpendicular to the molecular layer planes of monomolecular layer (c-axis direction) in the range of 1~25, [CoO _x H _y] plane monomolecular The material in which a portion of Co in the layer may be substituted 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 Te is nanoclusters [CoO _x H _{y] n} molecules layer sheet material. From the EXAFS fitting results shown in Example 1, the oxygen coordination number around Co was 5.1 in the case of 1-hour polarization and about 5.3 in the case of 1-month polarization (Table 2). On the other hand, the Coordination number in the _{[CoO 2} ] _{n molecular layer sheet having no oxygen deficiency is 6.} Therefore, nanoclusters of Co oxide material of the present invention shown in Experimental Example is believed to [CoO _x H _{y] n} molecules layer sheet having an oxygen deficiency is a material having the basic skeleton. On the other hand, from the XRD results shown in FIG. 3, since the XRD peak of γ-CoOOH does not appear in the Co oxide material of the present invention, this nanocluster is laminated in the c-axis direction, but it has developed. It is considered that it is not. Therefore, nanoclusters of Co oxide material of the present invention there are laminated in the plane vertical Although not developed to, it was identified as [CoO _X H _{y] n} molecules layer sheet material. Such [CoO _X H _y] atomic arrangement of _n molecular layer sheet material is not the same as the atomic arrangement of gamma-CoOOH type, having the atomic arrangement structure similar to gamma-CoOOH type atomic arrangement structure It can be said that.

[CoO _X H _y] is the _n range of molecular layer x in the sheet 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 from 0.05 to 0.5, n is 1 It is in the range of ~ 25. In the nanoclusters of the Co oxide material of the present invention, the maximum outer diameter of the nanoclusters 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, and more preferably 0.9 to 5 nm. CoO ₆ octahedra diameter is about 0.29 nm (approximately 0.3 nm), also [CoO _X H _y] interlayer distance monolayer is about 0.4 nm. Assuming a maximum diameter 10nm cluster to configure the clusters of the particle diameter, [CoO _X H _y] number of CoO _X H _y octahedral molecules in monolayer, 10 / 0.29 x 10 / 0.29 ( It is about 1200), 7 / 0.29 x 7 / 0.29 (about 580) in the range of the maximum diameter of 7 nm, and 5 / 0.29 x 5 / 0.29 (about 300) in the range of the maximum diameter of 5 nm.

Nanoclusters of Co oxide material of the present invention as described above is [CoO _X H _{y] n} molecules layer sheet material is laminated planar vertical presence is not Developmental, n represents plan monomolecular The number of layers stacked in the direction perpendicular to the molecular layer plane (c-axis direction). 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, in the range of 0.6 to 7 nm in diameter, n is 2 to 7 / 0.4 (about 18), and in the range of 0.9 to 5 nm in diameter, n is 2 or 3 to 5 / 0.4 (about 12).

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

<Method for producing Co oxide material of the present invention>
The Co oxide material of the present invention comprises, for example, (a) _{placing a raw material containing Ca 2} CoFeO ₅ and / or Ca ₂ CoNiO ₅ under anodic polarization or immersing it in an alkaline aqueous solution, or ( b) A step of adding an alkali to an aqueous solution containing a Fe salt and / or Ni salt and a Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and recovering the precipitate. It can be produced by a method comprising calcining a precipitate of a hydroxide containing / or Ni and Co in an oxygen-containing atmosphere to obtain an oxyhydroxide containing Fe and / or Ni and Co. can.

Manufacturing method (a)
Ca ₂ CoFeO ₅ and Ca ₂ CoNiO ₅ are a kind of brown mirror light type transition metal oxides, and are prepared by a solid phase reaction method using each metal oxide as a raw material with reference to the method described in Patent Document 1. can do. It can also be synthesized by using a liquid phase reaction method in addition to the solid phase reaction method. In the liquid phase reaction method, salts of each metal, for example, nitrates, acetates, citrates and the like are used as raw materials for each metal oxide. For example, Ca salt (eg Ca (NO ₃ ) ₂ ), Fe salt (eg Fe (NO ₃ ) ₃ ) · 9H ₂ O), or Ni salt (eg Ni (NO ₃ ) ₃ ) · 9H ₂ O ), Co salt (for example, Co (NO ₃ ) ₂ ), 6H ₂ O), and using a mixture to which citric acid is added as a gelling agent as a solvent, for example, water (distilled water or ion-exchanged water), etc. Use to 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 the 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 the gelling agent, for example, EDTA (ethylenediaminetetraacetic acid), glycine and the like can be used in addition to citric acid. The mixture is gelled by heating the mixture to, for example, 50-90 ° C. to remove the solvent. The gelled product is calcined in air at 300 to 500 ° C. (for example, 450 ° C.) for 10 minutes to 6 hours (for example, 1 hour) to synthesize a precursor. Next, the precursor can be calcined in the air at 600 to 800 ° C. for 1 to 24 hours to synthesize _{brown mirror light type Ca 2} FeCoO ₅ or Ca ₂ CoNiO _5. As for the firing conditions, for example, after firing at 600 ° C. for a predetermined time (1 to 12 hours), the temperature may be raised, and for example, firing may be performed at 800 ° C. for a predetermined time (6 to 12 hours).

(1) Anode 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 adjusting the voltage to a voltage in the range of 1.5 to 2.0 V with respect to RHE, for example. It is appropriate to carry out energization of a predetermined amount of electricity or more with a current density. The amount of electricity above a predetermined level 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 embodiment, the amount applied to the anode electrode is such that the amount of CFC is 10 mg cm ^-2 , the carbon sheet electrode is used as the electrode base material, the platinum plate is used as the counter electrode (cathode), and the reference electrode for the anode electrode is further used. In a three-electrode system using the above, OER polarization is repeated for 2 hours ^{under a constant oxidation current condition of 40 mA cm -2} in an argon-inert atmosphere in a KOH aqueous solution for a time of zero current. The amount of electricity used for anodic polarization in this case is ^{288 coulons per cm 2} for OER polarization for 2 hours at a time. 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 the electrolytic solution for polarization in the alkaline aqueous solution can be, for example, an alkaline aqueous solution in the range of 0.1 M to 10 M, preferably an alkaline aqueous solution in the range of 1 M to 6 M.

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

(2) Alkaline aqueous solution immersion method In alkaline aqueous solution immersion, _{raw materials containing Ca 2} CoFeO ₅ (CFC) and / or Ca ₂ CoNiO ₅ (CNC) are used, for example, alkali metal hydroxides and alkaline earth metal hydroxides. It can be carried out by immersing in an aqueous solution in a temperature range of 0 to 100 ° C., for example. The temperature is preferably in the range of 60-90 ° C. The concentration of the alkaline aqueous solution is not particularly limited, but can be, for example, in the range of 0.1M to 10M, preferably in the range of 1M to 6M. The immersion time 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 until the desired nanoclusters are formed. For example, when the temperature is 80 ° C., the immersion in the alkaline aqueous solution is preferably carried out in an 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 recovered 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 Ni salt and a Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and a co-precipitate is used to recover the precipitate. Raw materials are prepared by the method, and the obtained precipitate of hydroxide containing Fe and / or Ni and Co is calcined in an oxygen-containing atmosphere to oxyhydroxide containing Fe and / or Ni and Co. To get.

The Fe salt, Ni salt and Co salt are not particularly limited as long as each salt is water-soluble. For example, a nitrate can be used, and a chloride can be used in addition to the nitrate. The alkali is not particularly limited as long as it is water-soluble, and can be, for example, an alkali metal hydroxide, and lithium hydroxide, sodium hydroxide, potassium hydroxide, or the like can be used. It can be manufactured by the method including. The coprecipitation method can be carried out at room temperature, but can also be carried out under cooling or heating. For the addition of alkali to the aqueous solution containing Fe salt and / or Ni salt and Co salt, it is appropriate to use an alkaline aqueous solution. The salt concentration of the aqueous solution containing the Fe salt and / or 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 calcined 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 from the viewpoint that oxyhydroxide can be easily obtained, the oxygen-containing atmosphere is an oxygen atmosphere. Is preferable. 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, the degree of the product of oxyhydroxide, and the like. 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 electrodes>
The present invention includes a catalyst for an air electrode containing the material of the present invention.
Further, the present invention includes a catalyst for a water electrolytic anode containing the material of the present invention. The catalyst for an air electrode and the catalyst for a water electrolysis anode of the present invention may contain the above-mentioned CFC as a raw material in addition to the material of the present invention.

The catalyst for the air electrode and the catalyst for the water electrolysis anode containing the material of the present invention can have a surface area of, for example, 1 to 100 m ² / g, 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 for an air electrode, and is extremely promising as an air electrode for a metal-air secondary battery, which is expected to produce hydrogen by photo-water decomposition and 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 (OERs). The material of the present invention has excellent OER activity and is extremely useful as a catalyst for a water electrolytic anode.

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

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

Examples of the ORR catalyst are not particularly limited, but are, 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). , PdCoAu, etc.), metal oxides (eg, ZrO _2-x , TiO _x , TaN _x O _y , IrMO _x, etc.), complex systems (Co-porphyrin complexes), and others (PtMoRuSeO _x , RuSe, etc.) can. _{In addition, LaNiO 3} (Nat. Chem. 3, 546 (2011)) reported by Suntivich et al. And CoO / N-doped CNT (Nat. Commun. 4, 1805 (2013)) reported by Li et al. )) Etc. can also be exemplified. However, the intention is not limited to these. Further, a plurality of catalysts can be used in combination in consideration of the performance and properties of each catalyst. Further, a co-catalyst (for example, TiO _x , RuO ₂ , SnO _2, etc.) can be used in combination with the above catalyst. The content when the ORR catalyst is used in combination can be appropriately determined in consideration of the type of the ORR catalyst, the catalytic activity, and the like, 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 can be generally used as a conductive auxiliary agent, and conductive carbon is preferable. Specific examples thereof include mesoporous carbon, graphite, acetylene black, carbon nanotubes, and carbon fiber. Conductive carbon with a large specific surface area is preferred because it provides many reaction fields at the air electrode. Specifically, the specific surface area of 1~3000m ² / g, which conductive carbon is particularly preferably 500 to 1500 ² / g. The catalyst of the air electrode may be supported on a conductive material.

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

By including the binder in the air electrode, the catalyst and the 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, and styrene-butadiene rubber (SBR). The content of the binder in the air electrode is not particularly limited, but is preferably 1 to 40% by mass, particularly 5 to 35% by mass, from the viewpoint of the binding force between carbon (conductive material) and the catalyst. It is preferably 10 to 35% by mass, and more preferably 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 material in an appropriate solvent on a substrate and drying it. 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 preferably carried out 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 on which the slurry is applied is not particularly limited, and examples thereof include a glass plate and a Teflon (registered trademark) plate. These substrates are stripped from the resulting air electrode after the slurry has dried. Alternatively, an air electrode current collector or a solid electrolyte layer can be treated as the base material. In this case, the base material is not peeled off and is used as it is as a component of the metal-air secondary battery.

The method for applying the slurry and the method for drying 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, a gravure printing method, or a drying method such as heat drying or vacuum drying can be adopted.

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.

An air electrode current collector that collects electricity 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, 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 current 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 is excellent in charging speed and charging voltage.

Further, as described above, the air electrode can coexist with a catalyst having ORR catalytic activity. Alternatively, an air electrode for oxygen evolution (ORR) containing a catalyst having ORR catalytic activity may be provided separately from the air electrode for oxygen evolution (OER) containing the catalyst containing the material of the present invention. In this case, the metal-air secondary battery has an air electrode for reducing oxygen and an air electrode for generating oxygen (3-electrode method). An air electrode for reducing oxygen is used during discharge, and an air electrode for generating oxygen is used during charging. The catalyst having ORR catalytic activity is as described above, and an air electrode for oxygen evolution can be obtained by using this catalyst and the conductive material and binder described in the above description of the air electrode.

Hereinafter, a configuration example of the metal-air secondary battery of the present invention will be described. The metal-air secondary battery of the present invention is not limited to the following configuration. FIG. 12 is a cross-sectional view showing an example of a form of the metal-air secondary battery of the present invention. The metal-air secondary battery 1 collects electricity from 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 an air electrode 2. It is composed of an air electrode current collector 5 and a negative electrode current collector 6 that collects electricity from the negative electrode 3, and these are housed in a battery case (not shown). An air electrode current collector 5 that collects electricity 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 electricity 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 protrudes from the battery case. There is. They function as positive electrode terminals (not shown) and negative electrode terminals (not shown), respectively.

(Negative electrode)
The negative electrode contains a negative electrode active material. As the negative electrode active material, a negative electrode active material of a general air battery can be used, and is not particularly limited. The negative electrode active material is usually one that can occlude and release metal ions. Specific examples of the negative electrode active material include metals such as Li, Na, K, Mg, Ca, Zn, Al, and Fe, alloys, oxides, and nitrides of these metals, carbon materials, and the like.

Among them, the zinc-air secondary battery is excellent in terms of 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 a zinc-air secondary battery will be described below. The reaction formula is as follows.

In the zinc-air secondary battery of the present invention, a material capable of occluding and releasing 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 zinc alloys containing one or more elements selected from aluminum, indium, magnesium, tin, titanium, and copper.

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

Further, as the negative electrode active material of the magnesium-air secondary battery, a material capable of occluding and releasing magnesium ions is used. As such a negative electrode, in addition to metallic magnesium, magnesium alloys such as magnesium aluminum, magnesium silicon, and magnesium gallium can be used.

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 may contain at least the negative electrode active material, but may also contain a binder for immobilizing the negative electrode active material, if necessary. Since the type of binder, the amount used, and the like are the same as those of the above-mentioned air electrode, the description thereof is omitted here.

A negative electrode current collector that collects current from the negative electrode is usually connected to 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. Further, examples of the shape of the negative electrode current collector include a foil shape, a plate shape, a mesh (grid shape), and the like.

(Electrolytes)
The electrolyte is placed between the air electrode and the negative electrode. Metal ion conduction between the negative electrode and the air electrode is performed 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.

As an example of the case where the negative electrode is zinc or an alloy thereof, an alkaline aqueous solution such as a potassium hydroxide aqueous solution containing zinc oxide or a sodium hydroxide aqueous solution may be used as the electrolytic solution, or zinc chloride or zinc perchlorate may be used. An aqueous solution containing zinc perchlorate may be used, or a non-aqueous solution containing zinc perchlorate or a non-aqueous solvent containing zinc bis (trifluoromethylsulfonyl) imide may be used. Further, for example, when the negative electrode is magnesium or an alloy thereof, 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). Examples include organic solvents used in capacitors. 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 to suppress the generation of dendrites. The dendrite formation inhibitor is not particularly limited, but may be, for example, at least one selected from the group consisting of polyalkyleneimines, polyallylamines and asymmetric dialkylsulphons (for example, JP-A-2009). -Refer to Gazette No. 93983). The amount of the dendrite formation inhibitor used is not particularly limited, but for example, it may be used only in an amount that saturates in the electrolytic solution at normal temperature and pressure, or may be used as a solvent.

The liquid electrolyte having lithium ion conductivity is usually a non-aqueous electrolyte 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), ethyl methyl carbonate (EMC), butylene carbonate, γ-butyrolactone, sulfolane, acetonitrile, and the like. Examples thereof include 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and mixtures thereof. An ionic liquid can also be used as the 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, preferably 1 mol / L. In the present invention, a low volatile liquid such as an ionic liquid may be used as the non-aqueous electrolytic solution.

A gel electrolyte having lithium ion conductivity can be obtained, for example, by adding a polymer to the non-aqueous electrolytic solution to gel. Specifically, a polymer such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF, trade 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} SP ₂ S ₅ compound, Li ₂ S-SiS ₂ compound, Li ₂ S-GeS ₂ Sulfide solid electrolytes such as compounds;

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

(Attached configuration)
In the metal-air secondary battery of the present invention, it is preferable that a separator is 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 has a structure capable of ensuring electrical insulation between the air electrode and the negative electrode and allowing an electrolyte to intervene between the air electrode and the negative electrode.

Examples of the separator include porous films such as polyethylene, polypropylene, cellulose, polyvinylidene fluoride, and glass ceramics; and non-woven fabrics such as resin non-woven fabric and glass fiber non-woven fabric. Of these, a separator made of glass ceramics is preferable.

Further, 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 above-mentioned air electrode, negative electrode, and electrolyte, but specific examples thereof include a coin type, a flat plate type, a cylindrical type, and a laminated type. Can be done.

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 the air or oxygen gas to be supplied is not particularly limited and may be appropriately set.

In addition to being useful for metal-air secondary batteries, the air electrode catalyst containing the material of the present invention is also useful in other fields where OER electrode catalysts are used. OER electrode catalysts have long been studied or used as counter-polar reactions in various electrochemical reactions, and can be used for alkali metal plating, electrolytic degreasing, and electrolytic protection technology. Recently, by combining with solar cells and photocatalysts, it is expected to be applied to highly efficient and clean hydrogen production technology.

Hereinafter, the present invention will be described in more detail based on examples. However, the examples are examples 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 dissolving and further adding an appropriate amount of citric acid, the mixture was evaporated to dryness at 120 ° C. and then fired at 500 ° C. The last calcined powder was produced by calcining in oxygen at 800 ° C. for 8 hours.
The prepared CFC, acetylene black (AB), and Nafion solution were dispersed in ethanol so that the weight ratio was CFC: AB: Nafion = 5: 1: 1 to form 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, thickness 0.2 mm) to form 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
The Co oxide material is prepared by 1-hour OER polarization and 1-month OER polarization using a carbon sheet electrode ^{, a reference electrode of Hg / HgO / 4 mol dm -3} KOH, and a three-electrode system with a platinum plate as the counter electrode. , 4 mol dm ^-3 KOH aqueous solution, under an argon inert atmosphere. First, OER polarization was performed for 2 hours under a constant oxidation current condition of 40 mA cm ^-2 , and then the mixture was allowed to stand for 15 minutes under a 0 current condition. OER polarization was performed by alternately repeating the above two steps for one month, and then the polarized material was recovered to obtain a Co oxide material by OER polarization for one month. For 1-hour OER polarization, a Co-oxide material was obtained by performing OER polarization for 1 hour under the same constant oxidation current conditions as described above and recovering the polarized material.

In addition, the OER current-voltage curve was measured for the CFC electrodes before and after the one-month OER polarization, and the OER activity was evaluated. The polarization measurement was carried out in a ^{4 mol dm -3} KOH aqueous solution using a three-electrode system with Hg / HgO / 4 mol dm ^-3 KOH as the reference electrode and a platinum plate as the 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
An experiment was conducted using γ-CoOOH as a catalyst for a comparative experiment. γ-CoOOH was prepared by calcining commercially available Co (OH) ₂ at 125 ° C. for 6 hours. γ-CoOOH, AB, and Nafion solutions are dispersed in ethanol so that the weight ratio is γ-CoOOH: AB: Nafion = 5: 1: 1 to form a catalyst ink, which is applied onto 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. The 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 the reference electrode and a platinum plate as the 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 on the CFC electrodes before and after OER polarization for one month. JEOL-2000A was used for spectroscopic measurement, and the probe system of the electron beam was narrowed down to about 10 nm to evaluate 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.

In addition, EXAFS measurements were performed on the BL28XU line of spring 8 for the CFC electrodes before and after OER polarization for one month. The measurement was performed by the transmission method.

(1) High-resolution TEM image (formation of Co oxide nanoclusters and particle size)
FIG. 1 shows a high-resolution TEM image 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. In the sample before polarization, clear lattice fringes corresponding to the 110-plane spacing of the Brown mirror type phase were observed, and spots matching the Brown mirror type structure appeared in the electron diffraction, so a highly crystalline sample was obtained. You can see that it is done. On the other hand, in the sample polarized for 1 hour, it can be seen that the bulk crystal structure is clearly broken and the sample is transferred to the amorphous phase. Combined with the results of constant potential polarization, it was confirmed that the OER activity of CFC is expressed not by the brown mirror phase, which is the starting material, but by the amorphous phase formed during anodic polarization. From the TEM image, it can be seen that this amorphous phase has a clearly non-uniform structure, and nanoclusters of about 0.5-2 nm are dispersed and formed in the amorphous matrix. Furthermore, the nanoclusters were characterized by an ordered structure, and in this limited-field electron diffraction, a clear ring was observed in addition to the amorphous-derived halo.

(2) Voltage-time curve (stability of Co oxide nanocluster)
FIG. 2 shows a voltage-time curve when constant current is repeatedly polarized 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 remained constant for one month thereafter. It was confirmed that this initial potential increase was an overvoltage increase due to poor conduction to the CFC due to oxidative consumption of the AB particles. Therefore, it was confirmed that the OER activity of the nano-clustered CFC did not deteriorate 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 polarization. The peak of the brown mirror type structure appearing in the pre-polarization sample (As prepared) disappeared completely after 1 hour and 1 month of polarization, and no peak other than the carbon sheet appeared. Therefore, the nanoclustered CFCs after 1 hour and 1 month anodic polarization are essentially amorphous and do not contain crystal particles above 10 nm that would be 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 OER polarization for one month by Auger spectroscopy. In both cases, a C signal derived from Nafion can be seen around 240 eV. After one month of electrolysis, the Ca signal around 300 eV was clearly lost, and the Fe signal around 600 eV was also very weak. On the other hand, at 640-800 eV, a mixed signal of F, Co and Fe appears, but its intensity does not seem to change much. Here, the F signal seems to be derived from Nafion. An increase in K signal is observed after an additional month of testing, which is believed to have been introduced during ion exchange of Nafion protons. The composition of the material particles before and after OER polarization was determined by fitting to each spectrum. The results are summarized in Table 1.

The CFC particles before one month OER polarization showed a Ca / Fe / Co ratio of the brown mirror type phase, which is the starting material, that is, a composition close to 2/1/1. On the other hand, it can be seen that in the Co oxide material of the present invention prepared by OER polarization for one month, Ca is almost eliminated and Fe is also almost eliminated. In other words, it was shown that Ca and Fe were eluted during polarization of CFC, and the oxide or hydrated oxide was changed to an oxide containing almost Co as a main component.

It should be noted that this chemical composition is the composition obtained when the amorphous matrix disappears and the nanocluster becomes a single substance, and the influence when the amorphous matrix is mixed is excluded. From the results of the voltage-time curve, the EXAFS fitting result, and the OER current-voltage curve, it is considered that the chemical composition of the Co oxide nanocluster immediately after formation (1 hour after polarization) is similar to this composition.

(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 in more detail, EXAFS of the sample before and after OER polarization was measured by BL28XU of Spring8. Then, the local structures around Fe and Co were investigated. The results are shown in Fig. 5. It can be seen that the radial distribution function around Fe and Co changes significantly due to one-month polarization, and the bulk structure changes as in TEM. The periodicity of the Fe local structure was reduced by polarization, and only the coordination sphere (1.6 Å) corresponding to the most recent oxygen contact was observed. On the other hand, the symmetry of the Co local structure was rather improved after polarization, and a new peak indicating the formation of the second coordination sphere appeared around 2.4 Å. Therefore, it is suggested that amorphization during the OER reaction produces Co-oxide clusters with a periodic structure.

Therefore, when fitting to EXAFS was performed based on the crystal data of various Co oxides, hydroxides and oxyhydroxides, it was found that the EXAFS vibration of the sample after polarization can be well fitted with 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 _{coherence of CoO 6} octahedrons are laminated on the c-axis by hydrogen bonds via protons (Fig. 6). Therefore, in the Co oxide material of the present invention, atoms are rearranged by OER, and a Co-rich oxide moiety is formed in the oxide matrix, which forms an arrangement structure very similar to γ-CoOOH. Was shown. In other words, the nanoclusters observed by the high-resolution TEM in Fig. 1 were determined to be nanoclusters with this γ-CoOOH type sequence structure or a similar sequence structure.

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 Coordination number in the _{[CoO 2] planar monatomic layer without any oxygen deficiency is 6.} Therefore, the nanoclusters formed in the Co oxide material of the present invention _{are considered to be a material having an oxygen-deficient [CoO 1.8} ] plane monolayer as a basic skeleton. On the other hand, since the XRD peak of γ-CoOOH does not appear from the result of FIG. 3, this nanocluster is laminated in the c-axis direction to some extent, which is inferred from the particle size observed in the TEM image, but it has developed. It is considered that it is not. Therefore, the nanoclusters formed in the Co oxide material of the present invention have some stacking in the vertical plane, but this stacking is not so well developed, [CoO _1.8 ] plane monolayer and charge compensation. proton for were identified as coordinating [CoO _1.8 H _{y] n} molecules layer sheet material.

Based on the γ-CoOOH type structure, there are 6 Co atoms at the position of about 2.8 Å in the second coordination sphere of Co atoms. On the other hand, from the EXAFS fitting results (Table 2), the coordination number of the second coordination sphere of Co is about 4, and therefore, the γ-CoOOH type planar molecular layers in which a part of Co is substituted or deleted by different elements are formed. It produces nanoclusters that are stacked and formed via hydrogen bonds. Combined with the above results, it was suggested that this [CoO _1.8 H _{y] n} molecules layer sheet of Co is partially substituted with Fe.

(6) OER current-voltage curve (characteristics of Co oxide nanocluster)
FIG. 7 shows the OER current-voltage curves of the CFC sample and the γ-CoOOH powder before and after the one-month OER reaction. Around the same curve before and after one-month polarization, it was confirmed that the OER activity did not change at all. If the starting potential of OER is defined as 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 high activity cannot be obtained only by having a γ-CoOOH type structure, and that its size of about several nm is important for showing high activity. Furthermore, it is suggested that it is also effective that a part of Co is replaced with Fe.

Example 2
(1) Preparation of Fe- or Ni-dope CoOOH
The preparation of Fe-dope CoOOH and the preparation of 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 + A solution having Fe or Co + Ni) of 0.2 M was prepared in ^{50 cm 3. Subsequently, this mixed solution was gently added to 50 cm 3} of a 2 M KOH aqueous solution while stirring at 200 rpm to obtain a hydroxide precipitate. After filtration, the mixture ^{was washed twice with 20 cm 3} of pure water, and then dried under reduced pressure overnight at room temperature. Finally, 6h calcined in an O ₂ gas stream 120 ° C., oxyhydroxide Fe _0.05 Co _0.95 Co is γCoOOH substituted with _{Fe 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 were in agreement with 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 orders of magnitude higher than those of ordinary micrometer-sized particles of ceramics. From this, it was inferred that the obtained powder was a nano-granular 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 are dispersed in ethanol so that Fe-dope CoOOH or Ni-dope CoOOH: AB: Nafion = 5: 1: 1 by weight to form a catalytic ink, which is used as GC. It was applied on a disk (5 mmφ) or a carbon sheet (15 mm x 5 mm, film thickness 0.2 mm) 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} , since showed Fe _0.1 Co _0.9 O _x H _y and Ni _0.1 Co _0.95 O _x H _y are both the same XRD pattern as gamma-CoOOH, has a gamma-CoOOH type layered structure It was confirmed that The XRD pattern of the three oxyhydroxides is very broad, so the crystallite size is about 8-15 nm from the 002 peak full width at 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 each case, the current increased from 1.45 V vs RHE and reached a current value of ^{5 mA cm -2 at 1.47, 1.46 and 1.49 V vs RHE, respectively.} All of them 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 nanocrystal material prepared by the coprecipitation method in this example showed 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 4M KOH, and airtight Ar bubbling was performed at 50 ° C. for 3 days. Then wash well with Milli-Q water and
A sample was obtained by filtration. The Ca / Fe / Co (ICP emission spectrometry) of the KOH-treated product was 0.03 / 0.21 / 0.76. The BET measured before the KOH treatment was 2.92 m ² g ^-1 , but after the KOH treatment it was 230, which was an increase of about 80 times. The XRD of the sample (CFC) before KOH treatment and the KOH treated product is shown in FIG. 10, and the OER polarization curve is shown in FIG. The EXAFS of the KOH-treated product was the same as that of the 1-hour OER polarized product of FIG. 5 in Example 1.

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 a similar sequence structure.

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 photo-water decomposition.

Claims (18)

A Co oxide nanocluster having the same or similar atomic arrangement structure as the γ-CoOOH type atomic arrangement structure and having an oxygen defect, and a part of Co in the nanocluster is replaced with Fe and / or Ni. Co-oxide material, which may be. The material according to claim 1, wherein the Co oxide nanocluster has a particle size of 10 nm or less. 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 can be laminated to a [CoO _x H _y] Co oxide material containing nano-clusters of _n molecular layer sheet material, 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 stacked direction perpendicular to the molecular layer planes of monomolecular layer (c-axis direction) in the range of 1 to 25, a portion of [CoO _x H _y] plane Co monomolecular layer The material may be substituted with Fe and / or Ni, and may lack some of the oxygen in the _{CoO 6 octahedron.} Wherein [CoO _x H _y] one side of the planar monolayer is 10nm or less, the material according to claim 3. The material according to any one of claims 1 to 4, wherein the maximum outer diameter of the nanoclusters observed in the TEM image is in the range of 0.3 to 10 nm. 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. The amount of Co substituted 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 within the scope of. The material according to any one of claims 1 to 7, which is for an OER catalyst. 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 it in an alkaline aqueous solution.} The production according to claim 9, wherein the anodic polarization is carried out at a current density having 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 carried out in the alkaline aqueous solution having a concentration of 1 M or more for 1 day or more. Method. A step of adding an alkali to an aqueous solution containing a Fe salt and / or Ni salt and a Co salt to precipitate a hydroxide containing Fe and / or Ni and Co, and recovering the precipitate. One of claims 1 to 7, which comprises calcining a precipitate of a hydroxide containing Ni and Co in an oxygen-containing atmosphere to obtain an oxyhydroxide containing Fe and / or Ni and Co. The method for producing the material described. The production method according to claim 11, wherein the Fe salt, the Ni salt and the Co salt are nitrates, respectively, and the alkali is an alkali metal hydroxide. An air electrode catalyst 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. A catalyst for a water electrolytic 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. An air electrode for a metal-air secondary battery comprising the catalyst according to claim 13 or 14. The air electrode according to claim 15, wherein the material is contained as an oxygen evolution catalyst and further includes an oxygen reduction catalyst. A metal-air secondary battery having an 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. The metal-air secondary battery according to claim 17, further comprising an oxygen-reducing air electrode including an oxygen-reducing catalyst.

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