WO2019176511A1 - Carbon-based composite for oxygen reduction catalyst, method for producing carbon-based composite for oxygen reduction catalyst, and use of carbon-based composite for oxygen reduction catalyst - Google Patents

Carbon-based composite for oxygen reduction catalyst, method for producing carbon-based composite for oxygen reduction catalyst, and use of carbon-based composite for oxygen reduction catalyst Download PDF

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WO2019176511A1
WO2019176511A1 PCT/JP2019/006942 JP2019006942W WO2019176511A1 WO 2019176511 A1 WO2019176511 A1 WO 2019176511A1 JP 2019006942 W JP2019006942 W JP 2019006942W WO 2019176511 A1 WO2019176511 A1 WO 2019176511A1
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carbon
oxygen reduction
graphene oxide
based composite
nanosheet
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French (fr)
Japanese (ja)
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紳好 中川
宏和 石飛
佑輝 田中
大塚　喜弘
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国立大学法人群馬大学
株式会社ダイセル
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Priority claimed from JP2018079300A external-priority patent/JP2019155349A/en
Application filed by 国立大学法人群馬大学, 株式会社ダイセル filed Critical 国立大学法人群馬大学
Publication of WO2019176511A1 publication Critical patent/WO2019176511A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/18—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/10—Heat treatment in the presence of water, e.g. steam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/194—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/198—Graphene oxide
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/96—Carbon-based electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the method for oxidizing graphite is not particularly limited, and a conventional method can be used.
  • Examples of conventional production methods include the Hummers method, the Brodie method, the Staudenmaier method, and the like.
  • the Staudenmeier method may be a method described in L. Staudenmaier, Ber. Dtsch. Chem. Ges., 1898, ⁇ 31, 1481.
  • the oxidizing agent is sulfuric acid, nitric acid and chloric acid (potassium chlorate). Etc.) may be used.
  • the average diameter in the plane direction of graphene oxide may be selected from the range of about 0.1 to 1000 ⁇ m, for example, 1 to 500 ⁇ m (for example, 5 to 300 ⁇ m), preferably about 5 to 100 ⁇ m (for example, 10 to 100 ⁇ m). More preferably, it may be about 5 to 50 ⁇ m (particularly 10 to 30 ⁇ m).
  • an electron microscope, an optical microscope, or the like can be used to measure the average diameter in the surface direction of graphene oxide.
  • the average diameter can be calculated by calculating the average value of the long axis diameter and the short axis diameter for each graphene oxide and adding and averaging the average values of about 100 graphene oxides.
  • aqueous solution (precursor aqueous solution) containing the carbon source compound and the nitrogen source compound is heated at a temperature equal to or higher than the boiling point of water to obtain carbon quantum dots.
  • a heating method of the precursor aqueous solution it is preferable to heat the precursor aqueous solution in a sealed state in the pressure resistant reactor.
  • the method for removing the solvent is not particularly limited, and may be subjected to heat purification or natural drying after separation and purification treatment (for example, washing, centrifugation, filtration, etc.).
  • a conventional reduction method for example, a thermal reduction method, a photoreduction method, a reduction method by applying a voltage, a reduction method by microwave irradiation, a method using a reducing agent (hydrazine hydrate, etc.), electrochemical reduction, etc. Laws can be used.
  • a thermal reduction method, a photoreduction method, a reduction method by microwave irradiation, and the like are widely used, and a reduction method by microwave irradiation is preferable from the viewpoint of simplicity.
  • the reduction method by microwave irradiation for example, 100 to 1000 W, preferably 300 to 800 W, more preferably about 500 to 700 W, for example, 1 to 10 minutes, preferably 2 to 8 minutes, more preferably about 3 to 6 minutes. May be.
  • composition for battery cathode catalyst layer of the present invention contains the carbon-based composite for redox catalyst and a conductive additive.
  • the conductive auxiliary agent is not particularly limited as long as it is a conductive carbon material, and examples thereof include carbon black, graphite, conductive carbon fiber (carbon nanotube, carbon nanofiber, carbon fiber, carbon nanohorn, etc.) and the like. . These conductive assistants can be used alone or in combination of two or more. Of these, carbon black is preferred from the viewpoints of conductivity, availability, and cost.
  • the specific surface area (BET) determined from the nitrogen adsorption amount is 20 to 1500 m 2 / g, preferably 50 to 1500 m 2 / g, more preferably 100 to 1500 m 2 / g (for example, 500 to 1400 m 2).
  • / G preferably about 1000 to 1300 m 2 / g). If the specific surface area is too small, there is a risk that the electrical conductivity will decrease, and if it is too large, it will be difficult to obtain commercially available materials.
  • carbon blacks include, for example, Ketjen Black EC300J, EC600JD (manufactured by Akzo), Toka Black # 4300, # 4400, # 4500, # 5500 (manufactured by Tokai Carbon Co., Ltd., Furnace Black), Printex L Etc. (Degussa, Furnace Black), Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205 etc.
  • the oxygen reduction catalyst ink of the present invention includes the battery cathode catalyst layer composition, a binder, and a solvent.
  • the binder is preferably a resin having proton conductivity.
  • Proton conductive resins include, for example, vinyl resins introduced with sulfonic acid groups such as polystyrene sulfonic acid and polyvinyl sulfonic acid, polyimide resins introduced with sulfonic acid groups, phenol resins introduced with sulfonic acid groups, and sulfonic acid groups.
  • perfluorosulfonic acid resins that are chemically stable by introducing fluorine atoms having high electronegativity and that can realize high ionic conductivity by high dissociation of sulfonic acid groups are preferable.
  • Commercially available resins having such proton conductivity include “Nafion” manufactured by DuPont, “Flemion” manufactured by Asahi Glass Co., Ltd., “Aciplex” manufactured by Asahi Kasei Co., Ltd., and Gore manufactured by Gore. For example, “Gore ⁇ Select”.
  • a resin having proton conductivity is used as an aqueous polar solvent solution containing about 5 to 30% by weight as a solid content.
  • the polar solvent for example, alcohol such as methanol, propanol or ethanol, or ether such as diethyl ether is used.
  • the ratio of the binder is, for example, 30 parts by weight or less, preferably 1 to 20 parts by weight, and more preferably about 2 to 10 parts by weight with respect to 100 parts by weight of the carbon composite.
  • the solvent water or an aqueous solvent is preferable.
  • the aqueous solvent include alkanols such as ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, and t-butanol, and polyhydric alcohols such as propylene glycol and ethylene glycol. These solvents can be used alone or in combination of two or more.
  • the ratio of the solvent is, for example, about 1 to 200 parts by weight, preferably about 4 to 100 parts by weight with respect to 1 part by weight of the carbon-based composite.
  • the oxygen reduction catalyst ink of the present invention may be used by being applied as an oxygen reduction catalyst electrode used in a fuel cell or the like.
  • Example and the comparative example is as follows.
  • Example 1 (Synthesis of carbon quantum dots) 10 g of an aqueous precursor solution containing 0.96 g of citric acid as a hydroxy acid and 0.30 g of ethylenediamine as a nitrogen source compound was prepared and sealed in a 10 mL capacity SUS316 high-pressure vessel (reaction vessel). The reaction vessel was heated to 250 ° C. to react the precursor aqueous solution for 2 hours. Thereafter, the reaction solution was taken out and then air-cooled.
  • the cooled reaction solution containing carbon quantum dots (nanocarbon), which is a reaction product, is developed in ethanol, the supernatant liquid is recovered by filtration, the solvent is removed, and carbon having an average particle size of 1.8 nm is obtained. Quantum dots were obtained. The average particle diameter was measured by a transmission electron microscope observation method.
  • a working electrode was produced in the same manner as in Example 1 except that.
  • Example 4 In the preparation of a carbon-based composite having oxygen reduction catalytic ability, the obtained powdered carbon-based composite is dispersed in an ethylene glycol solvent and irradiated with microwaves for 5 minutes in a microwave device (600 W) to remove the solvent.
  • a working electrode was prepared in the same manner as in Example 2 except that a powdery carbon-based composite was obtained.
  • Example 5 In preparing a carbon-based composite having oxygen reduction catalytic ability, instead of the nanosheet-shaped graphene oxide aqueous solution A (“Exfoliated GO” manufactured by Nishina Materials Co., Ltd., 1 wt% aqueous solution), the nanosheet-shaped graphene oxide aqueous solution B (Graphenea) A working electrode was prepared in the same manner as in Example 2 except that “Graphene Oxide Water Dispersion” (0.4 wt% aqueous solution) was used.
  • “Graphene Oxide Water Dispersion” 0.4 wt% aqueous solution
  • Example 6 In the preparation of a carbon-based composite having oxygen reduction catalytic ability, the obtained powdered carbon-based composite is dispersed in an ethylene glycol solvent and irradiated with microwaves for 5 minutes in a microwave device (600 W) to remove the solvent. A working electrode was prepared in the same manner as in Example 5 except that a powdery carbon-based composite was obtained.
  • Example 7 In the production of the working electrode, the working electrode was prepared in the same manner as in Example 1 except that the working electrode obtained by drying at 100 ° C. for 30 minutes was reduced by applying a voltage of ⁇ 0.9 V (vs SCE) for 3000 seconds. Produced.
  • Comparative Example 1 In the preparation of oxygen reduction catalyst ink, it is obtained by removing the solvent of nanosheet-like graphene oxide aqueous solution A (“Exfoliated GO” manufactured by Nishina Materials Co., Ltd., 1 wt% aqueous solution) instead of powdery carbon-based composite A working electrode was prepared in the same manner as in Example 1 except that the powder was used.
  • Comparative Example 3 In the production of the working electrode, the working electrode was prepared in the same manner as in Comparative Example 2 except that the working electrode obtained by drying at 100 ° C. for 30 minutes was reduced by applying a voltage of ⁇ 0.9 V (vs SCE) for 4000 seconds. Produced.
  • Comparative Example 4 A working electrode was prepared in the same manner as in Example 1 except that an iron-graphene oxide composite was used instead of the powdery carbon-based composite in the preparation of the oxygen reduction catalyst ink.
  • the iron-graphene oxide composite was obtained as follows.
  • Comparative Example 5 In the production of the working electrode, the working electrode was reduced in the same manner as in Comparative Example 4 except that the working electrode obtained by drying at 100 ° C. for 30 minutes was reduced by applying a voltage of ⁇ 0.9 V (vs SCE) for 2000 seconds. Produced.
  • Example 8 Except for using 5 mg of powdery carbon-based composite and 4.5 mg of powdered carbon-based composite and 0.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink. A working electrode was produced in the same manner as in Example 1.
  • Example 9 Except for using 5 mg of powdery carbon-based composite and 4.5 mg of powdered carbon-based composite and 0.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink. A working electrode was produced in the same manner as in Example 2.
  • Example 10 Except for using 5 mg of powdery carbon-based composite and 2.5 mg of powdered carbon-based composite and 2.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink.
  • a working electrode was produced in the same manner as in Example 1.
  • Example 11 Except for using 5 mg of powdery carbon-based composite and 2.5 mg of powdered carbon-based composite and 2.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink.
  • a working electrode was produced in the same manner as in Example 2.
  • the oxygen reduction activity was evaluated using the working electrodes obtained in the examples and comparative examples.
  • the evaluation method is as follows.
  • An electrolytic solution (0.1 M KOH aqueous solution) was placed in an electrolytic cell equipped with working electrodes obtained in Examples and Comparative Examples, a counter electrode (platinum), and a reference electrode (Ag / AgCl), and an oxygen reduction activity test. was done.
  • the oxygen reduction starting potential as an index of the degree of oxygen reduction activity was measured by LSV (Linear Sweep Voltammetry) by bubbling with oxygen in the electrolytic solution and then rotating the working electrode at 1600 rpm in an oxygen atmosphere. Incidentally, after bubbling with nitrogen in the electrolyte, the numerical value obtained by performing LSV measurement in a nitrogen atmosphere was used as the background.
  • the oxygen reduction starting potential was calculated by reading a potential having a slope of 1.0 mA / (cm 2 V) as a starting potential in a region where current starts to flow, and converting it to a potential based on the reversible hydrogen electrode (RHE). (Catalytic ability).
  • the oxygen reduction start potential indicates that the higher the potential, the higher the oxygen reduction activity.
  • the current density at a potential lower by 0.3 V than the starting potential was determined (catalytic activity). The evaluation results are shown in Table 1. The lower the current density, the higher the catalytic activity.
  • the degree of oxygen reduction activity of platinum-supported carbon was evaluated by the above method.
  • the oxidation-reduction starting potential was 1.04 V (vs RHE) and the current density was ⁇ 5.0 mAcm ⁇ . 2 .
  • the carbon-based composite of the present invention can be used as an active material for various oxidation-reduction electrodes, and is suitable, for example, as an oxygen reduction catalyst electrode for an air electrode (cathode) such as a fuel cell or an air-metal cell.
  • an air electrode cathode

Abstract

The present invention addresses the problem of preparing a carbon-based composite for an oxygen reduction catalyst, the carbon-based composite comprising: a nanosheet-like graphene oxide or a reduction product thereof; and carbon quantum dots. The average particle diameter of the carbon quantum dots may be 20 nm or less. The nanosheet-like graphene oxide or the reduction product thereof, and the carbon quantum dots may be complexed in a uniformly mixed state. The carbon quantum dots may contain nitrogen atoms. The weight ratio of the nanosheet-like graphene oxide or the reduction product thereof to the carbon quantum dots may be 90/10 to 10/90 (the former/the latter). The carbon-based composite and a conductive aid may be combined to prepare a composite for a battery cathode catalyst layer. The conductive aid may be Ketjenblack. The carbon-based composite can be prepared simply and inexpensively, does not contain platinum, and can exhibit excellent oxygen reduction electrode characteristics.

Description

酸素還元触媒用炭素系複合体ならびにその製造方法および用途Carbon-based composite for oxygen reduction catalyst and production method and use thereof
　本発明は、燃料電池や金属－空気電池の空気極（カソード）の酸素還元触媒などに利用できる酸素還元触媒用炭素系複合体ならびにその製造方法および用途に関する。 The present invention relates to a carbon-based composite for an oxygen reduction catalyst that can be used as an oxygen reduction catalyst for an air electrode (cathode) of a fuel cell or a metal-air battery, and a production method and use thereof.
　燃料電池の電極は、空気極と燃料極とで構成されている。現在、空気極である酸素還元触媒電極には、白金や白金合金等を含む白金系触媒が使用されている。しかし、白金の埋蔵量は限られており、固体高分子形燃料電池（ＰＥＦＣ）においては白金の使用によってコストが高くなる上に、白金による電解質溶液の分解等の化学反応が起こることなど、解決すべき問題が多い。このため、高い酸素還元活性を有する白金や白金合金等を含む白金系触媒を使用しない代替技術の開発が求められている。その中で、現状の非白金系触媒の性能は、白金系触媒に比べて十分ではないため、白金の使用量を大幅に低減した触媒や、白金を含まない非白金系触媒の性能を高める技術開発が進められている。 The electrode of the fuel cell is composed of an air electrode and a fuel electrode. Currently, platinum-based catalysts containing platinum, platinum alloys and the like are used for oxygen reduction catalyst electrodes, which are air electrodes. However, platinum reserves are limited, and in polymer electrolyte fuel cells (PEFC), the use of platinum increases the cost and chemical reactions such as decomposition of the electrolyte solution by platinum occur. There are many problems to be done. For this reason, development of the alternative technique which does not use the platinum-type catalyst containing platinum, platinum alloy, etc. which have high oxygen reduction activity is calculated | required. Among them, the performance of current non-platinum-based catalysts is not sufficient compared to platinum-based catalysts, so technologies that significantly reduce the amount of platinum used and technologies that improve the performance of non-platinum-based catalysts that do not contain platinum Development is underway.
　特開２０１１－６２８３号公報（特許文献１）には、高い酸化還元活性を有し、燃料電池用電極触媒として用いられる炭素材料として、特定のハイパーブランチ金属フタロシアニンを不活性ガス雰囲気下、５００～１５００℃で焼成して得られる炭素材料が開示されている。 Japanese Patent Application Laid-Open No. 2011-6283 (Patent Document 1) discloses a specific hyperbranched metal phthalocyanine as a carbon material having a high redox activity and used as an electrode catalyst for a fuel cell in an inert gas atmosphere. A carbon material obtained by firing at 1500 ° C. is disclosed.
　特開２００８－２８２７２５号公報（特許文献２）には、炭素系燃料電池用電極触媒として、高分子金属錯体に炭素添加物を混合し熱処理して得られた炭素化物に、配位子として窒素原子をドープした炭素材料が開示されている。 Japanese Patent Application Laid-Open No. 2008-282725 (Patent Document 2) discloses a carbonized product obtained by mixing a carbon additive with a polymer metal complex and heat-treating it as a carbon-based fuel cell electrode catalyst. A carbon material doped with atoms is disclosed.
　特開２００９－１４８７０６号公報（特許文献３）には、燃料電池のカソードに有用な電極触媒として、ニオブ、チタン、タンタルおよびジルコニウムからなる群から選択される少なくとも二種以上の遷移金属元素を含み、かつ白金を含まない金属酸化物材料からなる電極触媒が開示されている。 JP 2009-148706 A (Patent Document 3) includes at least two kinds of transition metal elements selected from the group consisting of niobium, titanium, tantalum and zirconium as an electrode catalyst useful for a cathode of a fuel cell. An electrode catalyst made of a metal oxide material that does not contain platinum is disclosed.
　特開２０１５－９３２２３号公報（特許文献４）には、燃料電池の触媒層に含有させる触媒として、酸化物系非白金触媒と、導電性炭素材料と分散剤とを、含有する酸化物系非白金触媒造粒体であって、前記酸化物系非白金触媒造粒体の形状が、球状または楕円体状であり、かつ造粒体の平均粒子径が０．５～１００μｍである酸化物系非白金触媒造粒体が開示されている。 Japanese Patent Laid-Open No. 2015-93223 (Patent Document 4) discloses an oxide-based non-platinum containing an oxide-based non-platinum catalyst, a conductive carbon material, and a dispersant as a catalyst to be included in a catalyst layer of a fuel cell. A platinum catalyst granule, wherein the oxide-based non-platinum catalyst granule has a spherical or ellipsoid shape, and an average particle diameter of the granule is 0.5 to 100 μm. Non-platinum catalyst granules are disclosed.
　特開２０１４－９１０６１号公報（特許文献５）には、燃料電池の空気極として有用な酸素還元触媒として、酸化グラフェンを水に分散させた酸化グラフェン分散液と、鉄フタロシアニンをアルコールに分散させた鉄フタロシアニン分散液と、を混合して自己組織化させた鉄フタロシアニン／酸化グラフェン複合体を還元した鉄フタロシアニン／グラフェンナノ複合体酸素還元触媒が開示されている。 In JP 2014-91061 A (Patent Document 5), as an oxygen reduction catalyst useful as an air electrode of a fuel cell, a graphene oxide dispersion in which graphene oxide is dispersed in water and iron phthalocyanine are dispersed in alcohol. An iron phthalocyanine / graphene nanocomposite oxygen reduction catalyst obtained by reducing an iron phthalocyanine / graphene oxide composite that is self-organized by mixing with an iron phthalocyanine dispersion is disclosed.
　しかし、これらの触媒でも、調製が困難であったり、金属フタロシアニンなどの特殊で高価な化合物が必要であった。そのため、これらの非白金系触媒では、簡便で安価に、白金触媒と同等の優れた酸素還元触媒電極としての特性を実現できなかった。 However, even these catalysts are difficult to prepare or require special and expensive compounds such as metal phthalocyanine. Therefore, these non-platinum-based catalysts cannot realize the characteristics as an excellent oxygen reduction catalyst electrode equivalent to the platinum catalyst, simply and inexpensively.
特開２０１１－６２８３号公報（請求項１、段落［０００８］）JP2011-6283A (Claim 1, paragraph [0008]) 特開２００８－２８２７２５号公報（請求項１）JP 2008-282725 A (Claim 1) 特開２００９－１４８７０６号公報（請求項１、段落［０００４］）JP 2009-148706 A (Claim 1, paragraph [0004]) 特開２０１５－９３２２３号公報（請求項１および６）JP-A-2015-93223 (Claims 1 and 6) 特開２０１４－９１０６１号公報（請求項１、段落［００２３］）JP 2014-91061 A (Claim 1, paragraph [0023])
　従って、本発明の目的は、簡便で安価に調製でき、かつ白金を含まずに、優れた酸素還元電極特性を発現できる炭素系複合体ならびにその製造方法および用途を提供することにある。 Therefore, an object of the present invention is to provide a carbon-based composite that can be easily and inexpensively prepared and that can exhibit excellent oxygen-reducing electrode characteristics without containing platinum, and a method for producing the carbon-based composite.
　本発明者らは、前記課題を達成するため鋭意検討した結果、ナノシート状酸化グラフェンとカーボン量子ドットとを組み合わせることにより、簡便で安価に調製でき、かつ白金を含まずに、優れた酸素還元触媒電極特性を発現できることを見出し、本発明を完成した。 As a result of intensive studies to achieve the above-mentioned problems, the present inventors have been able to easily and inexpensively prepare a combination of nanosheet-like graphene oxide and carbon quantum dots, and are excellent in oxygen reduction without containing platinum. The inventors have found that electrode characteristics can be expressed and completed the present invention.
　すなわち、本発明の酸素還元触媒用炭素系複合体は、ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとを含む。前記カーボン量子ドットの平均粒子径は２０ｎｍ以下であってもよい。前記ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとは、均一に混合した状態で複合化していてもよい。前記カーボン量子ドットは窒素原子を含んでいてもよい。前記ナノシート状酸化グラフェンまたはその還元物と前記カーボン量子ドットとの重量比は、前者／後者＝９０／１０～１０／９０であってもよい。 That is, the carbon-based composite for oxygen reduction catalyst of the present invention includes nanosheet-like graphene oxide or a reduced product thereof and carbon quantum dots. The carbon quantum dots may have an average particle size of 20 nm or less. The nanosheet-like graphene oxide or reduced product thereof and the carbon quantum dots may be combined in a uniformly mixed state. The carbon quantum dots may contain nitrogen atoms. The weight ratio of the nanosheet-like graphene oxide or the reduced product thereof to the carbon quantum dots may be the former / the latter = 90/10 to 10/90.
　本発明には、炭素源化合物と窒素源化合物とを含む水溶液を水の沸点以上の温度で加熱してカーボン量子ドットを生成するカーボン量子ドット生成工程、得られたカーボン量子ドットとナノシート状酸化グラフェンとを水性溶媒中で混合する混合工程、得られた混合液から溶媒を除去する乾燥工程を含む、カーボン量子ドットとナノシート状酸化グラフェンとを含む酸素還元触媒用炭素系複合体の製造方法も含まれる。前記混合工程において、得られたカーボン量子ドットとナノシート状酸化グラフェンとを水性溶媒中で超音波処理してもよい。前記ナノシート状酸化グラフェンは、ハマーズ法により得られたナノシート状酸化グラフェンであってもよい。 The present invention includes a carbon quantum dot generating step for generating a carbon quantum dot by heating an aqueous solution containing a carbon source compound and a nitrogen source compound at a temperature equal to or higher than the boiling point of water, and the obtained carbon quantum dot and nanosheet-like graphene oxide And a method for producing a carbon-based composite for an oxygen reduction catalyst comprising carbon quantum dots and nanosheet-like graphene oxide, including a mixing step of mixing a carbon atom in an aqueous solvent and a drying step of removing the solvent from the obtained mixed solution It is. In the mixing step, the obtained carbon quantum dots and nanosheet-like graphene oxide may be subjected to ultrasonic treatment in an aqueous solvent. The nanosheet-like graphene oxide may be nanosheet-like graphene oxide obtained by the Hammers method.
　本発明には、前記方法で得られた炭素系複合体中のナノシート状酸化グラフェンを還元し、ナノシート状酸化グラフェンの還元物とカーボン量子ドットとを含む酸素還元触媒用炭素系複合体を製造する方法も含まれる。 In the present invention, the nanosheet-shaped graphene oxide in the carbon-based composite obtained by the above-described method is reduced to produce a carbon-based composite for oxygen reduction catalyst containing a reduced product of nanosheet-shaped graphene oxide and carbon quantum dots. A method is also included.
　本発明には、前記酸素還元触媒用炭素系複合体および導電助剤を含む電池カソード触媒層用組成物も含まれる。前記導電助剤はケッチェンブラックであってもよい。 The present invention also includes a composition for a battery cathode catalyst layer containing the carbon-based composite for oxygen reduction catalyst and a conductive additive. The conductive additive may be ketjen black.
　本発明には、前記組成物、バインダーおよび溶剤を含む酸素還元触媒インキも含まれる。また、本発明には、この触媒インキを含む酸素還元触媒電極も含まれる。 The present invention also includes an oxygen reduction catalyst ink containing the composition, binder and solvent. The present invention also includes an oxygen reduction catalyst electrode containing this catalyst ink.
　本発明では、ナノシート状酸化グラフェンとカーボン量子ドットとを組み合わせているため、簡便で安価に調製でき、かつ白金を含まずに、優れた酸素還元電極特性（または触媒電極特性）を発現できる。 In the present invention, since nanosheet-like graphene oxide and carbon quantum dots are combined, it can be prepared easily and inexpensively, and can exhibit excellent oxygen reduction electrode characteristics (or catalyst electrode characteristics) without containing platinum.
　［ナノシート状酸化グラフェンまたはその還元物］
　本発明の酸素還元触媒用炭素系複合体は、ナノシート状酸化グラフェンまたはその還元物を含む。ナノシート状酸化グラフェンは、天然または人工グラファイトを酸化し、単層または多層に剥離させることにより、ナノメータサイズの厚みのシート形状に調製された酸化グラフェンである。 [Nanosheet-like graphene oxide or its reduced product]
The carbon-based composite for oxygen reduction catalyst of the present invention contains nanosheet-like graphene oxide or a reduced product thereof. The nanosheet-like graphene oxide is graphene oxide prepared into a sheet shape having a thickness of nanometer size by oxidizing natural or artificial graphite and peeling it into a single layer or multiple layers.
　グラファイトの酸化方法としては、特に限定されず、慣用の方法を利用できる。慣用の製造方法としては、例えば、ハマーズ（Hummers）法、ブローディー（Brodie）法、スタウデンマイヤー（Staudenmaier）法などが挙げられる。 The method for oxidizing graphite is not particularly limited, and a conventional method can be used. Examples of conventional production methods include the Hummers method, the Brodie method, the Staudenmaier method, and the like.
　ハマーズ法は、W. S Hummers, Jr. et al., J. Am. Chem. Soc., 1958, 80, 1339.に記載の方法であってもよく、例えば、酸化剤として、硫酸、過マンガン酸塩（過マンガン酸カリウムなど）および硝酸塩（硝酸ナトリウムなど）を使用して酸化する方法であってもよい。 The Hammers method may be a method described in W. S Hummers, Jr. et al., J. Am. Chem. Soc., 1958, 80, 1339.For example, as an oxidizing agent, sulfuric acid, permanganese A method of oxidizing using an acid salt (such as potassium permanganate) and a nitrate (such as sodium nitrate) may be used.
　ブローディー法は、B. C. Brodie, Philos. Trans. R. Soc., London, 1859, 149, 249.やB. C. Brodie, Ann. Chim. Phys., 1860, 59, 46に記載の方法であってもよく、例えば、酸化剤として、発煙硝酸および塩素酸（塩素酸カリウムなど）を使用して酸化する方法であってもよい。 The Brodie method is described in B. C. Brodie, Philos. Trans. R. Soc., London, 1859, 149, 249. and B. C. Brodie, Ann. Chim. Phys., 1860, 59, 46 For example, a method of oxidizing using fuming nitric acid and chloric acid (such as potassium chlorate) as an oxidizing agent may be used.
　スタウデンマイヤー法は、L. Staudenmaier, Ber. Dtsch. Chem. Ges., 1898, 31, 1481.に記載の方法であってもよく、酸化剤として、硫酸、硝酸および塩素酸（塩素酸カリウムなど）を使用して酸化する方法であってもよい。 The Staudenmeier method may be a method described in L. Staudenmaier, Ber. Dtsch. Chem. Ges., 1898, 、 31, 1481. The oxidizing agent is sulfuric acid, nitric acid and chloric acid (potassium chlorate). Etc.) may be used.
　これらのうち、電極特性を向上できる点から、ハマーズ法が好ましい。 Of these, the Hammers method is preferable because electrode characteristics can be improved.
　得られた酸化グラファイトは、酸素含有官能基が付加されているため、親水性であり、かつ層間が拡大し易い性質に改質されている。そのため、酸化グラファイトは、水などの水性溶媒中で超音波を照射する方法や、遠心分離と再分散とを繰り返す方法などにより、層間を剥離して、単層または多層酸化グラフェンに分解できる。得られた酸化グラフェンは、酸素含有官能基として、カルボニル基、ホルミル基、ヒドロキシル基、カルボキシル基、エポキシ基などの酸素含有官能基を有していてもよい。 The obtained graphite oxide is modified to have a hydrophilic property and easily expand between layers because of the addition of an oxygen-containing functional group. Therefore, graphite oxide can be decomposed into single-layer or multilayer graphene oxide by peeling the layers by a method of irradiating ultrasonic waves in an aqueous solvent such as water or a method of repeating centrifugation and redispersion. The obtained graphene oxide may have an oxygen-containing functional group such as a carbonyl group, a formyl group, a hydroxyl group, a carboxyl group, or an epoxy group as an oxygen-containing functional group.
　酸化グラフェンの厚みは、原子１層の厚み（例えば、０．４ｎｍ程度）または複数層（例えば２～１０層、特に２～５層程度）の厚みを有していてもよい。酸化グラフェンは、炭素原子１個の厚みを有する単層構造であってもよく、複数の単層酸化グラフェンが所定の間隔で重なり合った多層（例えば２～１０層、好ましくは２～５層、さらに好ましくは２～３層）構造であってもよい。 The graphene oxide may have a thickness of one atomic layer (for example, about 0.4 nm) or a plurality of layers (for example, about 2 to 10 layers, particularly about 2 to 5 layers). The graphene oxide may have a single-layer structure having a thickness of one carbon atom, and a multilayer (for example, 2 to 10 layers, preferably 2 to 5 layers, in which a plurality of single-layer graphene oxides are overlapped at a predetermined interval, and The structure may preferably be 2 to 3 layers).
　酸化グラフェンの面方向の平均径は、０．１～１０００μｍ程度の範囲から選択してもよく、例えば１～５００μｍ（例えば５～３００μｍ）、好ましくは５～１００μｍ（例えば１０～１００μｍ）程度であり、さらに好ましくは５～５０μｍ（特に１０～３０μｍ）程度であってもよい。 The average diameter in the plane direction of graphene oxide may be selected from the range of about 0.1 to 1000 μm, for example, 1 to 500 μm (for example, 5 to 300 μm), preferably about 5 to 100 μm (for example, 10 to 100 μm). More preferably, it may be about 5 to 50 μm (particularly 10 to 30 μm).
　なお、本明細書および特許請求の範囲において、酸化グラフェンの面方向の平均径の測定には、電子顕微鏡、光学顕微鏡などが利用できる。なお、異形の酸化グラフェンにおいて、平均径は、各酸化グラフェンについて長軸径と短軸径との平均値を算出し、１００個程度の酸化グラフェンの平均値について加算平均することにより算出できる。 In the present specification and claims, an electron microscope, an optical microscope, or the like can be used to measure the average diameter in the surface direction of graphene oxide. In the irregular graphene oxide, the average diameter can be calculated by calculating the average value of the long axis diameter and the short axis diameter for each graphene oxide and adding and averaging the average values of about 100 graphene oxides.
　このような酸化グラフェンとしては、（株）仁科マテリアル製：品名「Rap GO (TQ-11)」、「GO-TQ2」、「Exfoliated GO」など、Graphenea社製：品名「Graphene Oxide Water Dispersion（０．４重量％濃度）」、「Highly Concentrated Graphene Oxide（２．５重量％濃度）」などの市販品で入手することができる。 Examples of such graphene oxide include those manufactured by Nishina Materials Co., Ltd .: product names “Rap GO (TQ-11)”, “GO-TQ2”, “Exfoliated GO”, etc., manufactured by Graphenea: product names “Graphene Oxide Water Dispersion (0 .4 wt% concentration) ”,“ Highly Concentrated Graphene Oxide (2.5 wt% concentration) ”and the like.
　酸化グラフェンの還元物は、還元処理により部分的に還元されたグラフェン（部分酸化グラフェン）であってもよく、還元処理により完全に還元されたグラフェンであってもよい。 The reduced product of graphene oxide may be graphene partially reduced by reduction treatment (partially graphene oxide) or graphene completely reduced by reduction treatment.
　［カーボン量子ドット］
　カーボン量子ドットは、Liu et al., Angew. Chem. Int. Ed. (2007).、Qu et al, Sci. Rep. (2014).、Ding et al, RSC Adv. (2015).などの文献に記載されているナノメータサイズの粒子状カーボンであり、粒子状ナノカーボンとも称される。 [Carbon quantum dots]
Carbon quantum dots are described in literature such as Liu et al., Angew. Chem. Int. Ed. (2007)., Qu et al, Sci. Rep. (2014)., Ding et al, RSC Adv. (2015). In the nanometer size, which is also referred to as particulate nanocarbon.
　カーボン量子ドットは、慣用の水熱反応により得られるカーボンであってもよく、例えば、炭素源化合物と窒素源化合物とを含む水溶液を水の沸点以上の温度で加熱して得られるカーボンであってもよい。 Carbon quantum dots may be carbon obtained by a conventional hydrothermal reaction, for example, carbon obtained by heating an aqueous solution containing a carbon source compound and a nitrogen source compound at a temperature equal to or higher than the boiling point of water. Also good.
　炭素源化合物としては、例えば、ヒドロキシ酸（クエン酸、リンゴ酸、酒石酸、ガラクタル酸（２，３，４，５－テトラヒドロキシアジピン酸）、キナ酸、グリセリン酸、グルコン酸、グルクロン酸、アスコルビン酸、没食子酸など）や糖酸等の有機酸；糖（グルコースなど）；ポリビニルアルコール等が挙げられる。これらの炭素源化合物は、単独でまたは二種以上組み合わせて使用できる。これらのうち、電極特性を向上できる点から、クエン酸やキナ酸などのヒドロキシ酸が好ましい。 Examples of the carbon source compound include hydroxy acid (citric acid, malic acid, tartaric acid, galactaric acid (2,3,4,5-tetrahydroxyadipic acid), quinic acid, glyceric acid, gluconic acid, glucuronic acid, ascorbic acid. , Gallic acid and the like) and organic acids such as sugar acid; sugar (glucose and the like); polyvinyl alcohol and the like. These carbon source compounds can be used alone or in combination of two or more. Of these, hydroxy acids such as citric acid and quinic acid are preferable from the viewpoint of improving electrode characteristics.
　窒素源化合物としては、例えば、脂肪族アミン（ヘキシルアミン、Ｎ，Ｎ－ジメチルエチレンジアミン等のモノアミン；エチレンジアミン等のジアミン等）、芳香族アミン（フェニレンジアミン等）、ヒドロキシアミン、ポリアミン、複素環式アミン等のアミン化合物、尿素等が挙げられる。これらのうち、電極特性を向上できる点から、エチレンジアミンなどの脂肪族ジアミンが好ましい。 Examples of nitrogen source compounds include aliphatic amines (hexylamine, monoamines such as N, N-dimethylethylenediamine; diamines such as ethylenediamine), aromatic amines (phenylenediamine, etc.), hydroxyamines, polyamines, and heterocyclic amines. And amine compounds such as urea and the like. Of these, aliphatic diamines such as ethylenediamine are preferred from the viewpoint that the electrode characteristics can be improved.
　窒素源化合物の割合は、炭素源化合物１００重量部に対して、例えば１０～１００重量部、好ましくは１５～５０重量部、さらに好ましくは２０～４０重量部（特に２５～３５重量部）程度である。水溶液中における炭素源化合物および窒素源化合物の総量の濃度は、例えば３～５０重量％、好ましくは５～３０重量％、さらに好ましくは８～２０重量％（特に１０～１５重量％）程度である。 The ratio of the nitrogen source compound is, for example, about 10 to 100 parts by weight, preferably 15 to 50 parts by weight, more preferably 20 to 40 parts by weight (particularly 25 to 35 parts by weight) with respect to 100 parts by weight of the carbon source compound. is there. The concentration of the total amount of the carbon source compound and the nitrogen source compound in the aqueous solution is, for example, about 3 to 50% by weight, preferably about 5 to 30% by weight, more preferably about 8 to 20% by weight (particularly 10 to 15% by weight). .
　前記炭素源化合物および前記窒素源化合物を含む水溶液（前駆体水溶液）は、水の沸点以上の温度で加熱されることによりカーボン量子ドットが得られる。前駆体水溶液の加熱方法としては、耐圧反応器内で密閉した状態で加熱するのが好ましい。 An aqueous solution (precursor aqueous solution) containing the carbon source compound and the nitrogen source compound is heated at a temperature equal to or higher than the boiling point of water to obtain carbon quantum dots. As a heating method of the precursor aqueous solution, it is preferable to heat the precursor aqueous solution in a sealed state in the pressure resistant reactor.
　反応容器内の前駆体水溶液は、気液平衡状態よりも高い密度となる量を仕込むのが好ましい。例えば、水の飽和密度（液相）は、反応温度１５０℃、２００℃、２５０℃および３００℃で、この順に０．９１７ｇ／ｃｍ３、０．８６４ｇ／ｃｍ３、０．７９９ｇ／ｃｍ３および０．７１２ｇ／ｃｍ３である。そのため、反応温度を２００～２５０℃に調整する場合、反応容器の容積の約９０％以上となる量の前駆体水溶液を仕込むのが好ましい。 The aqueous precursor solution in the reaction vessel is preferably charged in an amount that gives a higher density than the vapor-liquid equilibrium state. For example, the saturation density of water (liquid phase), the reaction temperature 0.99 ° C., 200 ° C., at 250 ° C. and 300 ° C., this order 0.917g / cm 3, 0.864g / cm 3, 0.799g / cm 3 and 0.712 g / cm 3 . Therefore, when the reaction temperature is adjusted to 200 to 250 ° C., it is preferable to charge the precursor aqueous solution in an amount that is about 90% or more of the volume of the reaction vessel.
　反応温度は、転化率を向上でき、不溶性成分を抑制できる点から、１５０～４００℃が好ましく、２００～３００℃がさらに好ましい。反応容器内の圧力は、反応温度における飽和蒸気圧以上となるように調整するのが好ましい。 The reaction temperature is preferably 150 to 400 ° C., more preferably 200 to 300 ° C. from the viewpoint that the conversion rate can be improved and insoluble components can be suppressed. The pressure in the reaction vessel is preferably adjusted to be equal to or higher than the saturated vapor pressure at the reaction temperature.
　このような水熱反応による製造方法は、例えば、Hydrothermal Synthesis of Photoluminescent Nanocarbon from Hydroxylic Acids and Amines, Journal of Solution Chemistry, 45, 1560-1570, 2016などの文献に記載の製造方法であってもよい。 Such a production method by a hydrothermal reaction may be, for example, a production method described in literatures such as Hydrothermal Synthesis of Photoluminescent Nanocarbon from Hydroxylic Acids and Amines, Journal of Solution Chemistry, 45, 1560-1570, 2016.
　カーボン量子ドットの形状は、粒子状であればよく、例えば、球状、楕円体状などであってもよい。 The shape of the carbon quantum dot is not particularly limited as long as it is particulate, and may be, for example, spherical or ellipsoidal.
　カーボン量子ドットの平均粒子径（一次粒径）は、２０ｎｍ以下（特に１５ｎｍ以下）であってもよく、例えば１～１０ｎｍ、好ましくは１．２～５ｎｍ、さらに好ましくは１．５～３ｎｍ程度である。カーボン量子ドットの平均粒子径が大きすぎると、電極特性が低下する虞がある。 The average particle size (primary particle size) of the carbon quantum dots may be 20 nm or less (particularly 15 nm or less), for example, 1 to 10 nm, preferably 1.2 to 5 nm, more preferably about 1.5 to 3 nm. is there. If the average particle size of the carbon quantum dots is too large, the electrode characteristics may deteriorate.
　なお、本明細書および特許請求の範囲において、平均粒子径とは、体積粒度分布において、粒子径の細かい粒子からその粒子の体積割合を積算していったときに、５０％となる粒子径（Ｄ５０）を意味する。 In the present specification and claims, the average particle size is a particle size (50%) when the volume fraction of particles is integrated from fine particles in a volume particle size distribution. D50).
　カーボン量子ドットは、窒素原子を含有していてもよい。窒素原子の原子割合は、カーボン量子ドットを構成する炭素原子に対して１０～４０％であってもよく、好ましくは１５～３５％程度である。なお、本明細書および特許請求の範囲において、窒素原子の割合は、Ｘ線光電子分光法（ＸＰＳ：X-ray Photoelectron Spectroscopy）や元素分析（ＣＨＮＯ）により測定された窒素元素の含有量で規定される。 The carbon quantum dots may contain nitrogen atoms. The atomic ratio of nitrogen atoms may be 10 to 40% with respect to the carbon atoms constituting the carbon quantum dots, and preferably about 15 to 35%. In the present specification and claims, the proportion of nitrogen atoms is defined by the content of nitrogen element measured by X-ray photoelectron spectroscopy (XPS) or elemental analysis (CHNO). The
　［酸素還元触媒用炭素系複合体およびその製造方法］
　本発明の酸素還元触媒用炭素系複合体は、前記ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとが複合化していればよいが、電極特性を向上できる点から、ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとが均一に混合した状態で複合化しているのが好ましい。このような状態の炭素系複合体は、炭素源化合物と窒素源化合物とを含む水溶液を水の沸点以上の温度で加熱してカーボン量子ドットを生成するカーボン量子ドット生成工程、得られたカーボン量子ドットとナノシート状酸化グラフェンとを水性溶媒中で混合する混合工程、得られた混合液から水性溶媒を除去する乾燥工程を経て製造してもよい。 [Carbon-based composite for oxygen reduction catalyst and method for producing the same]
The carbon-based composite for oxygen reduction catalyst of the present invention may be a composite of the nanosheet-shaped graphene oxide or its reduced product and carbon quantum dots. From the viewpoint of improving the electrode characteristics, the nanosheet-shaped graphene oxide or its It is preferable that the reduced product and the carbon quantum dots are combined in a uniformly mixed state. The carbon-based composite in such a state includes a carbon quantum dot generation step in which an aqueous solution containing a carbon source compound and a nitrogen source compound is heated at a temperature equal to or higher than the boiling point of water to generate carbon quantum dots, and the obtained carbon quantum You may manufacture through the mixing process which mixes a dot and nanosheet-like graphene oxide in an aqueous solvent, and the drying process which removes an aqueous solvent from the obtained liquid mixture.
　混合工程では、前記カーボン量子ドット生成工程で得られたカーボン量子ドットとナノシート状酸化グラフェンとを水性溶媒中で混合する方法は、特に限定されないが、両者を均一に混合し易い点から、水性溶媒中で超音波処理するのが好ましい。 In the mixing step, the method of mixing the carbon quantum dots obtained in the carbon quantum dot production step and the nanosheet-like graphene oxide in an aqueous solvent is not particularly limited, but it is easy to mix the two uniformly. Of these, ultrasonic treatment is preferred.
　水性溶媒としては、例えば、水、低級アルコール（メタノール、エタノール、イソプロパノールなどのＣ１－４アルカノールなど）、ケトン類（アセトンなど）、ジオキサン、テトラヒドロフランなどのエーテル類、セロソルブ類、セロソルブアセテート類、カルビトール類、カルビトールアセテート類、ニトリル類（アセトニトリルなど）、アミド類（Ｎ，Ｎ－ジメチルホルムアミド、Ｎ，Ｎ－ジメチルアセトアミドなど）などが挙げられる。これらの水性溶媒は、単独でまたは二種以上組み合わせて使用できる。これらのうち、水、エタノールなどのＣ１－４アルカノールが好ましい。 Examples of the aqueous solvent include water, lower alcohols (C 1-4 alkanols such as methanol, ethanol and isopropanol), ketones (such as acetone), ethers such as dioxane and tetrahydrofuran, cellosolves, cellosolve acetates, carbs. Tolls, carbitol acetates, nitriles (such as acetonitrile), amides (such as N, N-dimethylformamide, N, N-dimethylacetamide) and the like. These aqueous solvents can be used alone or in combination of two or more. Of these, C 1-4 alkanols such as water and ethanol are preferred.
　ナノシート状酸化グラフェンは、通常、水中に分散させた分散液の状態で混合に供されるのに対して、カーボン量子ドットは、水と分離しない水溶性溶媒（特に、エタノールなどの低級アルコール）に溶解または分散させた溶解液または分散液の状態で混合に供されるのが好ましい。水中にナノシート状酸化グラフェンを分散させた状態で、エタノールなどの水溶性溶媒にカーボン量子ドットを分散させた状態で混合することにより、ナノシート状酸化グラフェンを凝集させることなく、両者を混合できるため、ナノシート状酸化グラフェンとカーボン量子ドットとを均一に混合した状態で複合化できる。 Nanosheet-like graphene oxide is usually used for mixing in the form of a dispersion dispersed in water, whereas carbon quantum dots are used in water-soluble solvents that do not separate from water (particularly lower alcohols such as ethanol). It is preferable to be used for mixing in the state of a dissolved or dispersed solution or dispersion. In a state where nanosheet-like graphene oxide is dispersed in water, by mixing carbon quantum dots in a water-soluble solvent such as ethanol, both can be mixed without agglomerating nanosheet-like graphene oxide, Nanosheet-like graphene oxide and carbon quantum dots can be combined in a uniformly mixed state.
　ナノシート状酸化グラフェンを含む水分散体において、ナノシート状酸化グラフェンの濃度は、例えば０．１～１０重量％、好ましくは０．２～５重量％、さらに好ましくは０．３～３重量％程度である。一方、カーボン量子ドットを含む水性溶媒分散体において、カーボン量子ドットの濃度は、例えば０．１～１０重量％、好ましくは０．３～５重量％、さらに好ましくは０．５～３重量％程度である。 In the aqueous dispersion containing nanosheet-shaped graphene oxide, the concentration of nanosheet-shaped graphene oxide is, for example, about 0.1 to 10% by weight, preferably about 0.2 to 5% by weight, more preferably about 0.3 to 3% by weight. is there. On the other hand, in the aqueous solvent dispersion containing carbon quantum dots, the concentration of carbon quantum dots is, for example, about 0.1 to 10% by weight, preferably about 0.3 to 5% by weight, and more preferably about 0.5 to 3% by weight. It is.
　乾燥工程において、溶媒を除去する方法は、特に限定されず、分離精製処理（例えば、洗浄、遠心分離、濾過など）した後、加熱乾燥や自然乾燥を行ってもよい。 In the drying step, the method for removing the solvent is not particularly limited, and may be subjected to heat purification or natural drying after separation and purification treatment (for example, washing, centrifugation, filtration, etc.).
　得られた炭素系複合体は、ナノシート状酸化グラフェンとカーボン量子ドットとを含む複合体である。この複合体を還元して、ナノシート状酸化グラフェンの還元物とカーボン量子ドットとを含む炭素系複合体を製造してもよい。なお、炭素系複合体を作製する前に酸化グラフェンを還元処理すると水への溶解性が変化し不溶となり酸化グラフェン間での凝集が発生するため、カーボン量子ドットとの均一な複合化が困難となる。 The obtained carbon-based composite is a composite containing nanosheet-like graphene oxide and carbon quantum dots. This composite may be reduced to produce a carbon-based composite containing nanosheet-like graphene oxide reduction and carbon quantum dots. Note that if graphene oxide is reduced before the carbon-based composite is prepared, the solubility in water changes and becomes insoluble, causing aggregation between the graphene oxide, which makes it difficult to uniformly combine with carbon quantum dots. Become.
　還元方法としては、慣用の還元方法、例えば、熱還元法、光還元法、電圧印加による還元法、マイクロ波照射による還元法、還元剤（ヒドラジン水和物など）を用いる方法、電気化学的還元法などを利用できる。これらの還元方法のうち、熱還元法、光還元法、マイクロ波照射による還元法などが汎用され、簡便性などの点から、マイクロ波照射による還元法が好ましい。マイクロ波照射による還元法では、例えば１００～１０００Ｗ、好ましくは３００～８００Ｗ、さらに好ましくは５００～７００Ｗ程度で、例えば１～１０分間、好ましくは２～８分間、さらに好ましくは３～６分間程度照射してもよい。 As a reduction method, a conventional reduction method, for example, a thermal reduction method, a photoreduction method, a reduction method by applying a voltage, a reduction method by microwave irradiation, a method using a reducing agent (hydrazine hydrate, etc.), electrochemical reduction, etc. Laws can be used. Among these reduction methods, a thermal reduction method, a photoreduction method, a reduction method by microwave irradiation, and the like are widely used, and a reduction method by microwave irradiation is preferable from the viewpoint of simplicity. In the reduction method by microwave irradiation, for example, 100 to 1000 W, preferably 300 to 800 W, more preferably about 500 to 700 W, for example, 1 to 10 minutes, preferably 2 to 8 minutes, more preferably about 3 to 6 minutes. May be.
　ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとの重量比は、例えば、前者／後者＝９０／１０～１０／９０程度の範囲から選択でき、電極特性を向上できる点から、例えば８０／２０～２０／８０、好ましくは７０／３０～３０／７０、さらに好ましくは６０／４０～４０／６０程度である。 The weight ratio of the nanosheet-like graphene oxide or reduced product thereof to the carbon quantum dots can be selected, for example, from the range of the former / the latter = about 90/10 to 10/90, and the electrode characteristics can be improved. It is about 20/80, preferably 70/30 to 30/70, and more preferably about 60/40 to 40/60.
　［電池カソード触媒層用組成物］
　本発明の電池カソード触媒層用組成物は、前記酸化還元触媒用炭素系複合体および導電助剤を含む。導電助剤としては、導電性を有する炭素材料であれば特に限定されないが、例えば、カーボンブラック、グラファイト、導電性炭素繊維（カーボンナノチューブ、カーボンナノファイバー、カーボンファイバー、カーボンナノホーン等）等が挙げられる。これらの導電助剤は、単独でまたは二種以上組み合わせて使用できる。これらのうち、導電性、入手の容易さ、およびコスト面から、カーボンブラックが好ましい。 [Composition for battery cathode catalyst layer]
The composition for a battery cathode catalyst layer of the present invention contains the carbon-based composite for redox catalyst and a conductive additive. The conductive auxiliary agent is not particularly limited as long as it is a conductive carbon material, and examples thereof include carbon black, graphite, conductive carbon fiber (carbon nanotube, carbon nanofiber, carbon fiber, carbon nanohorn, etc.) and the like. . These conductive assistants can be used alone or in combination of two or more. Of these, carbon black is preferred from the viewpoints of conductivity, availability, and cost.
　カーボンブラックとしては、例えば、気体または液体の原料を反応炉中で連続的に熱分解して製造するファーネスブラック（特に、エチレン重油を原料としたケッチェンブラック）、原料ガスを燃焼させて、その炎をチャンネル鋼底面にあて急冷し析出させたチャンネルブラック、ガスを原料とし燃焼と熱分解とを周期的に繰り返して得られるサーマルブラック（特に、アセチレンガスを原料とするアセチレンブラック）等が挙げられる。また、カーボンブラックは、慣用の酸化処理がされたカーボンブラックや、中空カーボン等であってもよい。これらのカーボンブラックは、単独でまたは二種以上組み合わせて使用できる。これらのうち、電極特性に優れる点から、導電性カーボンブラック、例えば、ケッチェンブラックが好ましい。 As carbon black, for example, furnace black (particularly, ketjen black made from ethylene heavy oil as a raw material) produced by continuously pyrolyzing a gas or liquid raw material in a reaction furnace, Examples include channel black obtained by quenching the flame against the channel steel bottom surface and depositing it, thermal black obtained by periodically repeating combustion and thermal decomposition using gas as a raw material (particularly acetylene black using acetylene gas as a raw material), and the like. . The carbon black may be carbon black subjected to a conventional oxidation treatment, hollow carbon, or the like. These carbon blacks can be used alone or in combination of two or more. Of these, conductive carbon black, such as ketjen black, is preferred because of its excellent electrode characteristics.
　カーボンブラックの比表面積は、大きいほど、カーボンブラック粒子同士の接触点が増えるため、電極の内部抵抗を下げるのに有利となる。具体的には、窒素の吸着量から求められる比表面積（ＢＥＴ）が２０～１５００ｍ２／ｇ、好ましくは５０～１５００ｍ２／ｇ、さらに好ましくは１００～１５００ｍ２／ｇ（例えば、５００～１４００ｍ２／ｇ、好ましくは１０００～１３００ｍ２／ｇ）程度である。比表面積が小さすぎると、導電性が低下する虞があり、大きすぎると、市販材料での入手が困難となる。 The larger the specific surface area of the carbon black, the more the contact points between the carbon black particles increase, which is advantageous for lowering the internal resistance of the electrode. Specifically, the specific surface area (BET) determined from the nitrogen adsorption amount is 20 to 1500 m 2 / g, preferably 50 to 1500 m 2 / g, more preferably 100 to 1500 m 2 / g (for example, 500 to 1400 m 2). / G, preferably about 1000 to 1300 m 2 / g). If the specific surface area is too small, there is a risk that the electrical conductivity will decrease, and if it is too large, it will be difficult to obtain commercially available materials.
　カーボンブラックの平均粒子径（一次粒径）は、例えば０．００５～１μｍ程度が好ましく、特に、０．０１～０．２μｍ（好ましくは０．０１５～０．１μｍ、さらに好ましくは０．０２～０．０５μｍ）程度である。 The average particle size (primary particle size) of carbon black is preferably, for example, about 0.005 to 1 μm, particularly 0.01 to 0.2 μm (preferably 0.015 to 0.1 μm, more preferably 0.02 to About 0.05 μm).
　電池カソード触媒層用組成物中の導電助剤の平均粒子径（一次粒径又は二次粒径）は、０．０３～５μｍ程度に調整するのが好ましい。導電助剤の平均粒子径が小さすぎる組成物は、その作製が困難となる虞があり、逆に大きすぎる組成物は、触媒層の材料分布のバラつき、電極の抵抗分布のバラつき等の不具合が生じる虞がある。 The average particle size (primary particle size or secondary particle size) of the conductive additive in the battery cathode catalyst layer composition is preferably adjusted to about 0.03 to 5 μm. A composition having an average particle size of the conductive auxiliary agent that is too small may make it difficult to produce. May occur.
　市販のカーボンブラックとしては、例えば、ケッチェンブラックEC300J、EC600JD（アクゾ社製）、トーカブラック#4300、#4400、#4500、#5500等（東海カーボン（株）製、ファーネスブラック）、プリンテックスL等（デグサ社製、ファーネスブラック）、Raven7000、5750、5250、5000ULTRAIII、5000ULTRA等、Conductex SC ULTRA、Conductex 975 ULTRA等、PUER BLACK100、115、205等（コロンビヤン社製、ファーネスブラック）、#2350、#2400B、#2600B、#30050B、#3030B、#3230B、#3350B、#3400B、#5400B等（三菱化学（株）製、ファーネスブラック）、MONARCH1400、1300、900、VulcanXC-72R、BlackPearls2000等（キャボット社製、ファーネスブラック）、Ensaco250G、Ensaco260G、Ensaco350G、SuperP-Li（TIMCAL社製）、デンカブラック、デンカブラックHS-100、FX-35（デンカ（株）製、アセチレンブラック）等が挙げられる。 Commercially available carbon blacks include, for example, Ketjen Black EC300J, EC600JD (manufactured by Akzo), Toka Black # 4300, # 4400, # 4500, # 5500 (manufactured by Tokai Carbon Co., Ltd., Furnace Black), Printex L Etc. (Degussa, Furnace Black), Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205 etc. (Colombian, Furnace Black), # 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3230B, # 3350B, # 3400B, # 5400B, etc. (Mitsubishi Chemical Corporation, Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, etc. (Cabot Corporation) Manufactured by Furnace Black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denka Co., Ltd., acetylene black), etc.
　炭素系複合体と導電助剤との重量割合は、前者／後者＝９９／１～１／９９の範囲から選択でき、例えば９０／１０～１０／９０、好ましくは８０／２０～２０／８０、さらに好ましくは７０／３０～３０／７０（特に６０／４０～４０／６０）程度である。導電助剤の割合が少なすぎると、導電性の向上効果が小さくなる虞があり、逆に多すぎると、酸素還元触媒電極特性が低下する虞がある。 The weight ratio between the carbon-based composite and the conductive additive can be selected from the range of the former / the latter = 99/1 to 1/99, for example, 90/10 to 10/90, preferably 80/20 to 20/80, More preferably, it is about 70/30 to 30/70 (especially 60/40 to 40/60). If the proportion of the conductive aid is too small, the effect of improving the conductivity may be reduced, and conversely if too large, the oxygen reduction catalyst electrode characteristics may be reduced.
　［酸素還元触媒インキ］
　本発明の酸素還元触媒インキは、前記電池カソード触媒層用組成物、バインダーおよび溶剤を含む。バインダーは、プロトン伝導性を有する樹脂が好ましい。プロトン伝導性樹脂としては、例えば、ポリスチレンスルホン酸やポリビニルスルホン酸などスルホン酸基を導入したビニル系樹脂、スルホン酸基を導入したポリイミド系樹脂、スルホン酸基を導入したフェノール樹脂、スルホン酸基を導入したポリエーテルケトン系樹脂、スルホン酸基を導入したポリベンズイミダゾール系樹脂、イミダゾール部分で酸と塩形成したポリベンズイミダゾール系樹脂、スチレン・エチレン・ブチレン・スチレン共重合体のスルホン酸ドープ品、パーフルオロスルホン酸系樹脂等が挙げられる。これらのプロトン伝導性樹脂は、単独でまたは二種以上組み合わせて使用できる。 [Oxygen reduction catalyst ink]
The oxygen reduction catalyst ink of the present invention includes the battery cathode catalyst layer composition, a binder, and a solvent. The binder is preferably a resin having proton conductivity. Proton conductive resins include, for example, vinyl resins introduced with sulfonic acid groups such as polystyrene sulfonic acid and polyvinyl sulfonic acid, polyimide resins introduced with sulfonic acid groups, phenol resins introduced with sulfonic acid groups, and sulfonic acid groups. Polyether ketone resin introduced, polybenzimidazole resin introduced with sulfonic acid group, polybenzimidazole resin salted with acid at imidazole part, sulfonic acid dope product of styrene / ethylene / butylene / styrene copolymer, Examples include perfluorosulfonic acid resins. These proton conductive resins can be used alone or in combination of two or more.
　これらのうち、電気陰性度の高いフッ素原子の導入により化学的に安定性が高く、スルホン酸基の高い解離度により高いイオン導電性が実現可能なパーフルオロスルホン酸系樹脂が好ましい。このようなプロトン伝導性を有する樹脂の市販品としては、デュポン社製の「Ｎａｆｉｏｎ」、旭硝子（株）製の「Ｆｌｅｍｉｏｎ」、旭化成（株）製の「Ａｃｉｐｌｅｘ」、ゴア（Ｇｏｒｅ）社製の「Ｇｏｒｅ Ｓｅｌｅｃｔ」等が挙げられる。通常、プロトン伝導性を有する樹脂は、固形分として５～３０重量％程度含む極性溶媒水溶液として使用される。極性溶媒としては、例えば、メタノール、プロパノール、エタノールなどのアルコール、ジエチルエーテルなどのエーテルが使用される。 Among these, perfluorosulfonic acid resins that are chemically stable by introducing fluorine atoms having high electronegativity and that can realize high ionic conductivity by high dissociation of sulfonic acid groups are preferable. Commercially available resins having such proton conductivity include “Nafion” manufactured by DuPont, “Flemion” manufactured by Asahi Glass Co., Ltd., “Aciplex” manufactured by Asahi Kasei Co., Ltd., and Gore manufactured by Gore. For example, “Gore 等 Select”. Usually, a resin having proton conductivity is used as an aqueous polar solvent solution containing about 5 to 30% by weight as a solid content. As the polar solvent, for example, alcohol such as methanol, propanol or ethanol, or ether such as diethyl ether is used.
　バインダーの割合は、炭素系複合体１００重量部に対して、例えば３０重量部以下、好ましくは１～２０重量部、さらに好ましくは２～１０重量部程度である。 The ratio of the binder is, for example, 30 parts by weight or less, preferably 1 to 20 parts by weight, and more preferably about 2 to 10 parts by weight with respect to 100 parts by weight of the carbon composite.
　溶剤としては、水または水性溶媒が好ましい。水性溶媒としては、例えば、エタノール、１－プロパノール、イソプロパノール、１－ブタノール、２－ブタノール、ｔ－ブタノール等のアルカノール、プロピレングリコール、エチレングリコール等の多価アルコール等が挙げられる。これらの溶剤は、単独でまたは二種以上組み合わせて使用できる。 As the solvent, water or an aqueous solvent is preferable. Examples of the aqueous solvent include alkanols such as ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, and t-butanol, and polyhydric alcohols such as propylene glycol and ethylene glycol. These solvents can be used alone or in combination of two or more.
　溶剤の割合は、炭素系複合体１重量部に対して、例えば１～２００重量部、好ましくは４～１００重量部程度である。 The ratio of the solvent is, for example, about 1 to 200 parts by weight, preferably about 4 to 100 parts by weight with respect to 1 part by weight of the carbon-based composite.
　本発明の酸素還元触媒インキは、燃料電池などに利用される酸素還元触媒電極として塗布することにより利用してもよい。 The oxygen reduction catalyst ink of the present invention may be used by being applied as an oxygen reduction catalyst electrode used in a fuel cell or the like.
　以下に、実施例に基づいて本発明をより詳細に説明するが、本発明はこれらの実施例によって限定されるものではない。なお、実施例および比較例で使用した材料は以下の通りである。 Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the material used by the Example and the comparative example is as follows.
　実施例１
　（カーボン量子ドットの合成）
　ヒドロキシ酸としてクエン酸０．９６ｇと、窒素源化合物としてエチレンジアミン０．３０ｇとを含有する１０ｇの前駆体水溶液を調製し、容量１０ｍＬのＳＵＳ３１６製高圧容器（反応容器）に封入した。この反応容器を２５０℃に加熱して、前駆体水溶液を２時間反応させた。その後、反応溶液を取り出してから空冷した。 Example 1
(Synthesis of carbon quantum dots)
10 g of an aqueous precursor solution containing 0.96 g of citric acid as a hydroxy acid and 0.30 g of ethylenediamine as a nitrogen source compound was prepared and sealed in a 10 mL capacity SUS316 high-pressure vessel (reaction vessel). The reaction vessel was heated to 250 ° C. to react the precursor aqueous solution for 2 hours. Thereafter, the reaction solution was taken out and then air-cooled.
　反応生成物であるカーボン量子ドット（ナノカーボン）を含有する冷却後の反応溶液をエタノール中に展開し、濾過により上澄み液を回収した後、溶媒を除去して、平均粒子径１．８ｎｍのカーボン量子ドットを得た。なお、平均粒子径は、透過型電子顕微鏡観察の方法で測定した。 The cooled reaction solution containing carbon quantum dots (nanocarbon), which is a reaction product, is developed in ethanol, the supernatant liquid is recovered by filtration, the solvent is removed, and carbon having an average particle size of 1.8 nm is obtained. Quantum dots were obtained. The average particle diameter was measured by a transmission electron microscope observation method.
　（酸素還元触媒能を有する炭素系複合体の調製）
　ナノシート状酸化グラフェン水溶液Ａ（（株）仁科マテリアル製「Exfoliated GO」、１重量％水溶液）と、１重量％カーボン量子ドットエタノール溶液とを、固形分重量比率で、前者／後者＝１／１の比率で混合して１５分間超音波処理し、炭素系複合体分散液を調製した。得られた分散液から溶媒を１００℃、１０時間真空乾燥して除去し、粉末状の炭素系複合体を得た。 (Preparation of carbon-based composite with oxygen reduction catalytic ability)
A nanosheet-like graphene oxide aqueous solution A (“Exfoliated GO” manufactured by Nishina Materials Co., Ltd., 1 wt% aqueous solution) and a 1 wt% carbon quantum dot ethanol solution in a solid weight ratio of the former / the latter = 1/1 The mixture was mixed at a ratio and sonicated for 15 minutes to prepare a carbon-based composite dispersion. The solvent was removed from the obtained dispersion by vacuum drying at 100 ° C. for 10 hours to obtain a powdery carbon-based composite.
　（酸素還元触媒インキの調製）
　粉末状の炭素系複合体５ｍｇ、水１６０μＬ、エタノール１６０μＬ、バインダーとして５重量％ナフィオン分散液（エレクトロケム社製）２５μＬをマイクロチューブ（容量２ｍＬ）に入れ、超音波（４２ｋＨｚ）で１時間分散処理して触媒インキを調製した。 (Preparation of oxygen reduction catalyst ink)
5 mg of powdery carbon-based composite, 160 μL of water, 160 μL of ethanol, and 25 μL of 5 wt% Nafion dispersion (manufactured by Electrochem) as a binder are placed in a microtube (capacity 2 mL), and dispersed for 1 hour with ultrasound (42 kHz). Thus, a catalyst ink was prepared.
　（作用電極の作製）
　回転電極（グラッシーカーボン電極の直径５ｍｍ）表面上に触媒インキ７μＬを塗布した。触媒担持量は０．５ｍｇ・ｃｍ－２であった。触媒を塗布したグラッシーカーボン電極を室温で３０分間放置した後、１００℃で３０分乾燥し作用電極を作製した。 (Production of working electrode)
7 μL of catalyst ink was applied on the surface of the rotating electrode (glassy carbon electrode diameter: 5 mm). The amount of catalyst supported was 0.5 mg · cm −2 . The glassy carbon electrode coated with the catalyst was allowed to stand at room temperature for 30 minutes and then dried at 100 ° C. for 30 minutes to produce a working electrode.
　実施例２
　酸素還元触媒能を有する炭素系複合体の調製において、ナノシート状酸化グラフェン水溶液と、１重量％カーボン量子ドットエタノール溶液とを、固形分重量比率で、前者／後者＝３／１の比率で混合した以外は実施例１と同様にして作用電極を作製した。 Example 2
In the preparation of a carbon-based composite having oxygen reduction catalytic ability, a nanosheet-like graphene oxide aqueous solution and a 1 wt% carbon quantum dot ethanol solution were mixed at a solid content weight ratio of the former / the latter = 3/1. A working electrode was produced in the same manner as in Example 1 except that.
　実施例３
　酸素還元触媒能を有する炭素系複合体の調製において、得られた粉末状の炭素系複合体をエチレングリコール溶媒に分散させてマイクロ波装置（６００Ｗ）で５分間マイクロ波を照射し、溶媒を除去して粉末状の炭素系複合体を得た以外は実施例１と同様にして作用電極を作製した。 Example 3
In the preparation of a carbon-based composite having oxygen reduction catalytic ability, the obtained powdered carbon-based composite is dispersed in an ethylene glycol solvent and irradiated with microwaves for 5 minutes in a microwave device (600 W) to remove the solvent. A working electrode was prepared in the same manner as in Example 1 except that a powdery carbon composite was obtained.
　実施例４
　酸素還元触媒能を有する炭素系複合体の調製において、得られた粉末状の炭素系複合体をエチレングリコール溶媒に分散させてマイクロ波装置（６００Ｗ）で５分間マイクロ波を照射し、溶媒を除去して粉末状の炭素系複合体を得た以外は実施例２と同様にして作用電極を作製した。 Example 4
In the preparation of a carbon-based composite having oxygen reduction catalytic ability, the obtained powdered carbon-based composite is dispersed in an ethylene glycol solvent and irradiated with microwaves for 5 minutes in a microwave device (600 W) to remove the solvent. A working electrode was prepared in the same manner as in Example 2 except that a powdery carbon-based composite was obtained.
　実施例５
　酸素還元触媒能を有する炭素系複合体の調製において、ナノシート状酸化グラフェン水溶液Ａ（（株）仁科マテリアル製「Exfoliated GO」、１重量％水溶液）の代わりに、ナノシート状酸化グラフェン水溶液Ｂ（Graphenea社「Graphene Oxide Water Dispersion」、０．４重量％水溶液）を用いた以外は実施例２と同様にして作用電極を作製した。 Example 5
In preparing a carbon-based composite having oxygen reduction catalytic ability, instead of the nanosheet-shaped graphene oxide aqueous solution A (“Exfoliated GO” manufactured by Nishina Materials Co., Ltd., 1 wt% aqueous solution), the nanosheet-shaped graphene oxide aqueous solution B (Graphenea) A working electrode was prepared in the same manner as in Example 2 except that “Graphene Oxide Water Dispersion” (0.4 wt% aqueous solution) was used.
　実施例６
　酸素還元触媒能を有する炭素系複合体の調製において、得られた粉末状の炭素系複合体をエチレングリコール溶媒に分散させてマイクロ波装置（６００Ｗ）で５分間マイクロ波を照射し、溶媒を除去して粉末状の炭素系複合体を得た以外は実施例５と同様にして作用電極を作製した。 Example 6
In the preparation of a carbon-based composite having oxygen reduction catalytic ability, the obtained powdered carbon-based composite is dispersed in an ethylene glycol solvent and irradiated with microwaves for 5 minutes in a microwave device (600 W) to remove the solvent. A working electrode was prepared in the same manner as in Example 5 except that a powdery carbon-based composite was obtained.
　実施例７
　作用電極の作製において、１００℃で３０分乾燥して得られた作用電極に－０．９Ｖ（ｖｓ　ＳＣＥ）の電圧を３０００秒印加して還元した以外は実施例１と同様にして作用電極を作製した。 Example 7
In the production of the working electrode, the working electrode was prepared in the same manner as in Example 1 except that the working electrode obtained by drying at 100 ° C. for 30 minutes was reduced by applying a voltage of −0.9 V (vs SCE) for 3000 seconds. Produced.
　比較例１
　酸素還元触媒インキの調製において、粉末状の炭素系複合体の代わりに、ナノシート状酸化グラフェン水溶液Ａ（（株）仁科マテリアル製「Exfoliated GO」、１重量％水溶液）の溶媒を除去して得られた粉末を用いた以外は実施例１と同様にして作用電極を作製した。 Comparative Example 1
In the preparation of oxygen reduction catalyst ink, it is obtained by removing the solvent of nanosheet-like graphene oxide aqueous solution A (“Exfoliated GO” manufactured by Nishina Materials Co., Ltd., 1 wt% aqueous solution) instead of powdery carbon-based composite A working electrode was prepared in the same manner as in Example 1 except that the powder was used.
　比較例２
　酸素還元触媒インキの調製において、粉末状の炭素系複合体の代わりに、フタロシアニン鉄と、ナノシート状酸化グラフェン水溶液Ａ（（株）仁科マテリアル製「Exfoliated GO」、１重量％水溶液）とを、固形分重量比率で、前者／後者＝５／１の比率で混合した水分散液を調製し、溶媒を除去して得られた粉末を用いた以外は実施例１と同様にして作用電極を作製した。 Comparative Example 2
In the preparation of the oxygen reduction catalyst ink, instead of the powdery carbon-based composite, phthalocyanine iron and graphene oxide aqueous solution A (“Exfoliated GO” manufactured by Nishina Materials Co., Ltd., 1 wt% aqueous solution) A working electrode was prepared in the same manner as in Example 1 except that an aqueous dispersion was prepared by mixing the former / the latter = 5/1 at a weight ratio and using the powder obtained by removing the solvent. .
　比較例３
　作用電極の作製において、１００℃で３０分乾燥して得られた作用電極に－０．９Ｖ（ｖｓ　ＳＣＥ）の電圧を４０００秒印加して還元した以外は比較例２と同様にして作用電極を作製した。 Comparative Example 3
In the production of the working electrode, the working electrode was prepared in the same manner as in Comparative Example 2 except that the working electrode obtained by drying at 100 ° C. for 30 minutes was reduced by applying a voltage of −0.9 V (vs SCE) for 4000 seconds. Produced.
　比較例４
　酸素還元触媒インキの調製において、粉末状の炭素系複合体の代わりに、鉄－酸化グラフェン複合体を用いた以外は実施例１と同様にして作用電極を作製した。鉄－酸化グラフェン複合体は、次のようにして得た。 Comparative Example 4
A working electrode was prepared in the same manner as in Example 1 except that an iron-graphene oxide composite was used instead of the powdery carbon-based composite in the preparation of the oxygen reduction catalyst ink. The iron-graphene oxide composite was obtained as follows.
　すなわち、酸化グラフェン（（株）仁科マテリアル製「Exfoliated GO」）が１０ｍｇ／ｍＬの濃度となるように調製した３ｍＬの酸化グラフェン分散溶液に、５ｍｇの酢酸鉄を添加して混合溶液を作製した。この混合溶液に２０ｍＬのエタノールと２０ｍＬの蒸留水とを添加し、超音波を約２分間照射して十分に分散させた後、６０℃で約１時間、加熱撹拌を行って、鉄粒子を酸化グラフェンに担持させた鉄－酸化グラフェン複合体の分散液を作製した。この分散液から溶媒を除去し、粉末にした鉄－酸化グラフェン複合体を得た。 That is, 5 mg of iron acetate was added to 3 mL of graphene oxide dispersion solution prepared such that graphene oxide (“Exfoliated GO” manufactured by Nishina Material Co., Ltd.) had a concentration of 10 mg / mL, to prepare a mixed solution. To this mixed solution, 20 mL of ethanol and 20 mL of distilled water are added, and the mixture is sufficiently dispersed by irradiation with ultrasonic waves for about 2 minutes, and then heated and stirred at 60 ° C. for about 1 hour to oxidize the iron particles. A dispersion of iron-graphene oxide composite supported on graphene was prepared. The solvent was removed from this dispersion to obtain a powdered iron-graphene oxide composite.
　比較例５
　作用電極の作製において、１００℃で３０分乾燥して得られた作用電極に－０．９Ｖ（ｖｓ　ＳＣＥ）の電圧を２０００秒印加して還元した以外は比較例４と同様にして作用電極を作製した。 Comparative Example 5
In the production of the working electrode, the working electrode was reduced in the same manner as in Comparative Example 4 except that the working electrode obtained by drying at 100 ° C. for 30 minutes was reduced by applying a voltage of −0.9 V (vs SCE) for 2000 seconds. Produced.
　実施例８
　酸素還元触媒インキの調製において、粉末状の炭素系複合体５ｍｇの代わりに、粉末状の炭素系複合体４．５ｍｇおよびケッチェンブラック（アクゾ社製「EC600JD」）０．５ｍｇを用いた以外は実施例１と同様にして作用電極を作製した。 Example 8
Except for using 5 mg of powdery carbon-based composite and 4.5 mg of powdered carbon-based composite and 0.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink. A working electrode was produced in the same manner as in Example 1.
　実施例９
　酸素還元触媒インキの調製において、粉末状の炭素系複合体５ｍｇの代わりに、粉末状の炭素系複合体４．５ｍｇおよびケッチェンブラック（アクゾ社製「EC600JD」）０．５ｍｇを用いた以外は実施例２と同様にして作用電極を作製した。 Example 9
Except for using 5 mg of powdery carbon-based composite and 4.5 mg of powdered carbon-based composite and 0.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink. A working electrode was produced in the same manner as in Example 2.
　実施例１０
　酸素還元触媒インキの調製において、粉末状の炭素系複合体５ｍｇの代わりに、粉末状の炭素系複合体２．５ｍｇおよびケッチェンブラック（アクゾ社製「EC600JD」）２．５ｍｇを用いた以外は実施例１と同様にして作用電極を作製した。 Example 10
Except for using 5 mg of powdery carbon-based composite and 2.5 mg of powdered carbon-based composite and 2.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink. A working electrode was produced in the same manner as in Example 1.
　実施例１１
　酸素還元触媒インキの調製において、粉末状の炭素系複合体５ｍｇの代わりに、粉末状の炭素系複合体２．５ｍｇおよびケッチェンブラック（アクゾ社製「EC600JD」）２．５ｍｇを用いた以外は実施例２と同様にして作用電極を作製した。 Example 11
Except for using 5 mg of powdery carbon-based composite and 2.5 mg of powdered carbon-based composite and 2.5 mg of Ketjen Black ("EC600JD" manufactured by Akzo) in preparation of the oxygen reduction catalyst ink. A working electrode was produced in the same manner as in Example 2.
　実施例および比較例で得られた作用電極を用いて、酸素還元活性を評価した。評価方法は以下の通りである。 The oxygen reduction activity was evaluated using the working electrodes obtained in the examples and comparative examples. The evaluation method is as follows.
　実施例および比較例で得られた作用電極と、対極（白金）と、参照電極（Ａｇ／ＡｇＣｌ）とが取り付けられた電解槽に電解液（０．１Ｍ　ＫＯＨ水溶液）を入れ、酸素還元活性試験を行なった。 An electrolytic solution (0.1 M KOH aqueous solution) was placed in an electrolytic cell equipped with working electrodes obtained in Examples and Comparative Examples, a counter electrode (platinum), and a reference electrode (Ag / AgCl), and an oxygen reduction activity test. Was done.
　酸素還元活性度合いの指標となる酸素還元開始電位は、電解液中に酸素でバブリングを行ったあと、酸素雰囲気下、作用電極を１６００ｒｐｍで回転させＬＳＶ(リニアスイープボルタンメトリー）を測定した。ちなみに、電解液中に窒素でバブリングしたあと、窒素雰囲気下でＬＳＶ測定を行なって得られた数値をバックグランドとした。 The oxygen reduction starting potential as an index of the degree of oxygen reduction activity was measured by LSV (Linear Sweep Voltammetry) by bubbling with oxygen in the electrolytic solution and then rotating the working electrode at 1600 rpm in an oxygen atmosphere. Incidentally, after bubbling with nitrogen in the electrolyte, the numerical value obtained by performing LSV measurement in a nitrogen atmosphere was used as the background.
　酸素還元開始電位は、電流が流れはじめる領域において、傾きが１．０ｍＡ／（ｃｍ２Ｖ）となる電位を開始電位として読み取り、可逆水素電極（ＲＨＥ）を基準とした電位に換算して算出した（触媒能）。酸素還元開始電位は、その電位が高いほど酸素還元活性が高いことを示す。また、開始電位より０．３Ｖ低い電位での電流密度を求めた（触媒活性）。その評価結果を表１に示す。電流密度は低くなるほど高い触媒活性を示す。 The oxygen reduction starting potential was calculated by reading a potential having a slope of 1.0 mA / (cm 2 V) as a starting potential in a region where current starts to flow, and converting it to a potential based on the reversible hydrogen electrode (RHE). (Catalytic ability). The oxygen reduction start potential indicates that the higher the potential, the higher the oxygen reduction activity. Further, the current density at a potential lower by 0.3 V than the starting potential was determined (catalytic activity). The evaluation results are shown in Table 1. The lower the current density, the higher the catalytic activity.
　標準サンプルとして、白金担持カーボン（白金担持率５０重量％）の酸素還元活性度合いを前記方法で評価しところ、酸化還元開始電位は１．０４Ｖ（ｖｓ　ＲＨＥ）で、電流密度は－５．０ｍＡｃｍ－２であった。 As a standard sample, the degree of oxygen reduction activity of platinum-supported carbon (platinum support ratio 50% by weight) was evaluated by the above method. The oxidation-reduction starting potential was 1.04 V (vs RHE) and the current density was −5.0 mAcm −. 2 .
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１の結果から明らかなように、比較例に比べて、実施例のインキは、電極特性に優れていた。なお、表中、酸化グラフェンのＡは、（株）仁科マテリアル製酸化グラフェンを示し、ＢはGraphenea社製酸化グラフェンを示す。 As is clear from the results in Table 1, the inks of the examples were superior in electrode characteristics as compared with the comparative examples. In the table, A of graphene oxide indicates graphene oxide manufactured by Nishina Material Co., Ltd., and B indicates graphene oxide manufactured by Graphenea.
　本発明の炭素系複合体は、各種の酸化還元電極の活物質として利用でき、例えば、燃料電池や空気－金属電池などの空気極（カソード）の酸素還元触媒電極として好適である。 The carbon-based composite of the present invention can be used as an active material for various oxidation-reduction electrodes, and is suitable, for example, as an oxygen reduction catalyst electrode for an air electrode (cathode) such as a fuel cell or an air-metal cell.

Claims (13)

  1. 　ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとを含む、酸素還元触媒用炭素系複合体。 A carbon-based composite for oxygen reduction catalyst comprising nanosheet-like graphene oxide or a reduced product thereof and carbon quantum dots.
  2. 　カーボン量子ドットの平均粒子径が２０ｎｍ以下である請求項１記載の酸素還元触媒用炭素系複合体。 The carbon-based composite for oxygen reduction catalyst according to claim 1, wherein the average particle diameter of the carbon quantum dots is 20 nm or less.
  3. 　カーボン量子ドットが窒素原子を含む請求項１または２記載の酸素還元触媒用炭素系複合体。 The carbon-based composite for oxygen reduction catalyst according to claim 1 or 2, wherein the carbon quantum dots contain nitrogen atoms.
  4. 　ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとが均一に混合した状態で複合化している請求項１～３のいずれかに記載の酸素還元触媒用炭素系複合体。 The carbon-based composite for oxygen reduction catalyst according to any one of claims 1 to 3, wherein the nanosheet-like graphene oxide or reduced product thereof and the carbon quantum dots are combined in a uniformly mixed state.
  5. 　ナノシート状酸化グラフェンまたはその還元物とカーボン量子ドットとの重量比が、前者／後者＝９０／１０～１０／９０である請求項１～４のいずれかに記載の酸素還元触媒用炭素系複合体。 5. The carbon-based composite for oxygen reduction catalyst according to claim 1, wherein the weight ratio of the nanosheet-like graphene oxide or the reduced product thereof to the carbon quantum dots is the former / the latter = 90/10 to 10/90. .
  6. 　炭素源化合物と窒素源化合物とを含む水溶液を水の沸点以上の温度で加熱してカーボン量子ドットを生成するカーボン量子ドット生成工程、得られたカーボン量子ドットとナノシート状酸化グラフェンとを水性溶媒中で混合する混合工程、得られた混合液から溶媒を除去する乾燥工程を含む、カーボン量子ドットとナノシート状酸化グラフェンとを含む酸素還元触媒用炭素系複合体の製造方法。 A carbon quantum dot generating step for generating a carbon quantum dot by heating an aqueous solution containing a carbon source compound and a nitrogen source compound at a temperature equal to or higher than the boiling point of water, and the resulting carbon quantum dot and nanosheet-like graphene oxide in an aqueous solvent A method for producing a carbon-based composite for an oxygen reduction catalyst, comprising carbon quantum dots and nanosheet-like graphene oxide, comprising a mixing step of mixing in step 1 and a drying step of removing the solvent from the resulting mixture.
  7. 　混合工程において、得られたカーボン量子ドットとナノシート状酸化グラフェンとを水性溶媒中で超音波処理する請求項６記載の製造方法。 The production method according to claim 6, wherein in the mixing step, the obtained carbon quantum dots and the nanosheet-like graphene oxide are subjected to ultrasonic treatment in an aqueous solvent.
  8. 　ナノシート状酸化グラフェンが、ハマーズ法により得られたナノシート状酸化グラフェンである請求項６または７記載の製造方法。 The manufacturing method according to claim 6 or 7, wherein the nanosheet-shaped graphene oxide is nanosheet-shaped graphene oxide obtained by a Hammers method.
  9. 　請求項６～８のいずれかに記載の方法で得られた炭素系複合体中のナノシート状酸化グラフェンを還元し、ナノシート状酸化グラフェンの還元物とカーボン量子ドットとを含む酸素還元触媒用炭素系複合体を製造する方法。 9. A carbon-based carbon for oxygen reduction catalyst comprising a reduced nanosheet-like graphene oxide in the carbon-based composite obtained by the method according to claim 6 and comprising a reduced nanosheet-like graphene oxide and carbon quantum dots A method for producing a composite.
  10. 　請求項１～５のいずれかに記載の酸素還元触媒用炭素系複合体および導電助剤を含む電池カソード触媒層用組成物。 A composition for a battery cathode catalyst layer comprising the carbon-based composite for oxygen reduction catalyst according to any one of claims 1 to 5 and a conductive additive.
  11. 　導電助剤がケッチェンブラックである請求項１０記載の組成物。 The composition according to claim 10, wherein the conductive additive is ketjen black.
  12. 　請求項１０または１１記載の組成物、バインダーおよび溶剤を含む酸素還元触媒インキ。 An oxygen reduction catalyst ink comprising the composition according to claim 10 or 11, a binder and a solvent.
  13. 　請求項１２記載の触媒インキを含む酸素還元触媒電極。
          An oxygen reduction catalyst electrode comprising the catalyst ink according to claim 12.
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