WO2019039538A1 - Conductivity aid for oxygen generating electrode, and utilization of same - Google Patents

Conductivity aid for oxygen generating electrode, and utilization of same Download PDF

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WO2019039538A1
WO2019039538A1 PCT/JP2018/031116 JP2018031116W WO2019039538A1 WO 2019039538 A1 WO2019039538 A1 WO 2019039538A1 JP 2018031116 W JP2018031116 W JP 2018031116W WO 2019039538 A1 WO2019039538 A1 WO 2019039538A1
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pcnf
electrode
carbon
edge
catalyst
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PCT/JP2018/031116
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French (fr)
Japanese (ja)
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浩樹 幅▲ざき▼
芳尚 青木
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国立大学法人北海道大学
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    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a conductive aid for an oxygen generating electrode made of a carbon material having excellent oxidation resistance, and use thereof.
  • the water-based air battery is a battery using a base metal as a negative electrode, an air electrode as a positive electrode, and a water-based electrolyte (electrolytic solution) as an electrolyte, and utilizes oxygen in air as a positive electrode active material. Therefore, the volume and weight occupied by the air electrode in the battery are small, and a large amount of negative electrode active material can be accommodated in the battery, which is promising as a high energy density battery.
  • the water-based air battery is advantageous in that the output can be easily obtained with high ion conductivity and an inexpensive and safe battery can be formed by using a water-based electrolyte, particularly an alkaline aqueous solution as the electrolyte.
  • the zinc-air battery is a battery which has strong reducing power, is abundant in resources, is inexpensive, and has zinc as an anode active material established industrially and which can be charged and discharged in an aqueous solution.
  • Patent Document 1 WO 2015/115592
  • Patent Document 2 Japanese Patent Application Laid-Open No. 2005-47763
  • Non-Patent Document 1 E. Tsuji, T. Motohashi, H. Noda, D. Kowalski, Y. Aoki, H. Tanida, J. Niikura, Y. Koyama, M. Mori, H. Arai, T. Ioroi, N. Fujiwara, Y. Uchimoto, Z. Ogumi, H. Habazaki; ChemSusChem, 10, 2864 (2017). 10.1002 / cssc. 201700499
  • Non-Patent Document 2 H. Konno, S. Sato, H. Habazaki, M. Inagaki; Carbon, 42, 2756 (2004).
  • Non-Patent Document 3 H. Habazaki, M.
  • Patent Documents 1 and 2 and Non-Patent Documents 1 to 3 are specifically incorporated herein by reference.
  • the high activity oxide catalyst as described above is not sufficiently conductive, it is necessary to add carbon as a conductive aid to produce an electrode, but carbon is oxidized and consumed in the OER environment. Therefore, in order to improve the durability of the oxygen electrode for zinc-air batteries, it is necessary to develop a carbon material that is resistant to oxidative consumption and use it as a conductive aid.
  • the problem to be solved by the present invention is to improve the durability of the oxygen electrode for zinc-air battery, a conductive support agent made of a carbon material resistant to oxidative consumption, and an oxygen electrode for zinc-air battery using this conductive support agent. It is an object of the present invention to solve these problems.
  • pCNF platelet carbon nanofibers
  • Patent Document 2 Non-Patent Document 2
  • pCNF was also revealed to have a unique orientation in which the carbon hexagonal network plane was laminated in the fiber direction.
  • pCNF has a structure in which the edge of the active carbon hexagonal network face is exposed on the side of the fiber, but heat treatment at a high temperature such as 2800 ° C forms a loop with several layers on the edge face and exposes the edge face It also became clear that there is no longer (non-patent document 3).
  • the inventors of the present invention found in the subsequent examination that the fiber in which the loop was formed and the exposure of the edge surface was removed had higher oxidation resistance than that of the untreated pCNF, based on this finding. Completed. Furthermore, it has been newly found that pCNF has a platelet structure even at heating temperatures of 1500 ° C. and 2400 ° C., and a loop consisting of several graphene layers can be seen on the side of the fiber. The present invention is also completed based on these new findings.
  • Carbon nanofibers having a platelet structure of a carbon hexagonal network surface (hereinafter sometimes referred to as platelet carbon nanofibers, sometimes abbreviated as pCNF), At least a part of the edge of the carbon hexagonal surface exposed to the side of the fiber has a loop structure between the edge of the adjacent carbon hexagonal surface, sometimes called pCNF (loop edge-pCNF, lpe- A conductive aid for an oxygen generating electrode, which may be abbreviated as pCNF.
  • lpe-pCNF is a conductive aid as described in [1], wherein the intensity of G band (near 1580 cm -1 ) in Raman spectrum is stronger than the intensity of D band (near 1380 cm -1 ).
  • the conductive auxiliary according to any one of [1] to [3], wherein lpe-pCNF has a weight reduction onset temperature of 500 ° C. or more or 600 ° C. or more in a temperature rising test in the air.
  • An ink for producing an oxygen generating electrode which contains the conductive auxiliary agent according to any one of [1] to [5], an OER catalyst and an organic solvent, and can further contain an ORR catalyst.
  • a reversible air electrode comprising the conductive auxiliary according to any one of [1] to [5], an ORR catalyst and an OER catalyst.
  • the reversible air electrode according to [7] which is an oxygen electrode for a zinc-air battery.
  • a zinc-air battery comprising the reversible air electrode according to [8].
  • the conductive support agent which consists of a carbon material excellent in oxidation resistance can be provided, and this conductive support agent has high oxidation resistance in OER environment.
  • the conductive aid of the present invention greatly contributes to the improvement of the durability of the oxygen electrode for zinc air battery.
  • FIG. 1 is a TEM photograph of pCNF heat-treated at 2800 ° C.
  • FIG. 2 is a SEM photograph of (a) pCNF isolated after heat treatment at 600 ° C. and (b) pCNF heat treated at 2400 ° C.
  • FIG. 3 shows XRD patterns of pCNF synthesized in Reference Example 1 and commercially available acetylene black.
  • FIG. 4 is a Raman spectrum of pCNF synthesized in Reference Example 1 and commercially available acetylene black.
  • FIG. 1 is a TEM photograph of pCNF heat-treated at 2800 ° C.
  • FIG. 2 is a SEM photograph of (a) pCNF isolated after heat treatment at 600 ° C. and (b) pCNF heat treated at 2400 ° C.
  • FIG. 3 shows XRD patterns of pCNF synthesized in Reference Example 1 and commercially available acetylene black.
  • FIG. 4 is a Raman spectrum of
  • FIG. 5 is a TEM photograph of pCNF synthesized in Reference Example 1, heat-treated at (a) 600 ° C., (b) 1100 ° C., (c) 1500 ° C., (d) 2400 ° C.
  • FIG. 6 is a TG curve of pCNF synthesized in Reference Example 1 and commercial acetylene black in the atmosphere.
  • FIG. 7 is an oxygen generation current-potential curve when the various carbon / CFCO electrodes in Example 1 are anodically polarized.
  • FIG. 8 shows changes in current when the various carbon / CFCO electrodes in Example 1 are subjected to constant potential polarization at 1.7 V vs RHE.
  • FIG. 9 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of AB / CFCO electrode.
  • FIG. 10 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of pCNF2400 / CFCO electrode.
  • FIG. 11 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of pCNF1500 / CFCO electrode.
  • FIG. 12 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of pCNF1100 / CFCO electrode.
  • FIG. 13 shows OER polarization curves before and after 1-month OER endurance test of CFCO / pCNF2400 and CFCO / AB electrodes.
  • FIG. 14 is a SEM photograph of the electrode before the test, 3 days after the start of the test and 1 month after the start of the test in the 1-month OER durability test of the CFCO / pCNF2400 and the CFCO / AB electrode.
  • the loop edge-pCNF used for the conductive additive of the present invention is a carbon nanofiber (platelet carbon nanofiber or pCNF) having a platelet structure of a carbon hexagonal network, and the carbon hexagonal network exposed to the side of the fiber At least a part of the edge of p is a pCNF having a loop structure between it and the edge of the adjacent carbon hexagonal network surface, which may be called loop edge-pCNF, and may be abbreviated as lpe-pCNF.
  • PCNF (hereinafter referred to simply as pCNF or untreated pCNF) described in Patent Document 2 and Non-patent Document 2 is a carbon nanofiber having a platelet structure of a carbon hexagonal network plane, and the carbon hexagonal network plane on the side of the fiber The edge of is exposed.
  • lpe-pCNF is a pCNF that has a loop structure between at least part of the edge of the carbon hexagonal surface exposed to the side of the fiber in the untreated pCNF and the edge of the adjacent carbon hexagonal surface.
  • the edge of the hexagonal carbon network exposed on the fiber side of untreated pCNF is chemically active, and in the presence of oxygen, under certain conditions, it reacts and consumes carbon.
  • Non-patent Document 3 It has been found that heat treatment of untreated pCNF at a high temperature such as 2800 ° C. forms loops on the edge surface and loses the exposure of the edge surface (Non-patent Document 3).
  • the loop structure of the edge face is shown in FIG. From the study of the inventors of the present invention, it was found that lpe-pCNF having no edge surface exposure was excellent in oxidation resistance and had high oxidation resistance when it was used as a conductive aid for an oxygen generating electrode. .
  • the ratio of having a loop structure can be, for example, 10% or more, 20% or more, 50% or more, 80% or more, 90% or more. From the viewpoint of excellent oxidation resistance, the higher the proportion of the loop structure, the better. However, since it is necessary to increase the temperature and heat treatment conditions for forming the loop structure to increase the proportion of the loop structure, the proportion of the loop structure is appropriately selected according to the oxidation resistance required practically. It can be selected.
  • the loop structure of lpe-pCNF can be a loop structure between the edges of a plurality of laminated carbon hexagonal mesh faces and the edges of a plurality of adjacent laminated carbon hexagonal mesh faces as in the case of FIG. 1 .
  • the loop structure can be confirmed by preparing a sample for observation by the method described in the examples and performing TEM observation (for example, magnification 300,000 times or more).
  • the proportion of lpe-pCNF having a loop structure can also be identified using a TEM observation (for example, magnification of 300,000 ⁇ or more) image within a specific observation range.
  • the weight loss start temperature in the temperature rising test in the air is 500 ° C. or higher, preferably 550 ° C. or higher, and more preferably 600 ° C. or higher.
  • the temperature rising rate in the temperature rising test is 10 ° C./min.
  • lpe-pCNF is prepared by heat treating untreated pCNF at high temperature during manufacture as described later. Therefore, graphitization of the carbon which comprises by heat processing advances.
  • the Raman spectrum of the carbon material is observed only for the D band (around 1380 cm ⁇ 1 ) for amorphous carbon.
  • a G band (around 1580 cm -1 ) is observed.
  • the lpe-pCNF can have a higher G band intensity than the D band intensity in the Raman spectrum, and if the G band intensity is higher than the D band intensity, the heat resistance tends to be better.
  • PCNF in which the edge of the carbon hexagonal mesh surface is exposed on the side surface of the raw material fiber can be produced by the methods described in Patent Document 2 and Non-Patent Document 2.
  • the heat treatment of pCNF is carried out at a temperature higher than 1100 ° C. in a non-oxidative atmosphere, as long as the atmosphere does not contain oxygen, for example, an inert gas atmosphere such as an argon atmosphere. be able to.
  • the heating temperature is higher than 1100.degree. With heating above 1100 ° C., the formation of loop structures is observed. However, heating is preferably performed at a higher temperature from the viewpoint of efficiently generating the loop structure (in a relatively short time), for example, 1300 ° C. or more, 1500 ° C. or more, 2000 ° C. or more, 2500 ° C. or more, It can be 2700 ° C or more.
  • the heating temperature there is no particular upper limit to the heating temperature, and if it can be achieved as a device, it can be a higher temperature, and practically it can be heating at a temperature of around 3000 ° C.
  • the heating rate is suitably, for example, in the range of 5 to 15 K min -1 , but there is no problem if it is slower than this.
  • the holding time can be appropriately determined in consideration of the heating temperature, for example, about one hour is appropriate, but depending on the heating temperature, it can be shorter than this, and the influence of the holding time is smaller than the influence of the holding temperature Tend.
  • At least a part of the edge of the carbon hexagonal surface exposed to the side of the fiber by heating can form a loop structure between adjacent edges to obtain lpe-pCNF.
  • the heating time is not particularly limited, and can be appropriately determined in consideration of the formation condition (amount and structure) of the loop structure.
  • lpe-pCNF has high oxidation resistance when used in an oxygen generating electrode, it is useful as a conductive aid for the oxygen generating electrode, and the present invention relates to a conductive for an oxygen generating electrode comprising lpe-pCNF Regarding the auxiliary agent. Furthermore, the oxygen generating electrode in which this conductive support agent is used can be a reversible air electrode.
  • the present invention includes an ink containing a conductive aid comprising lpe-pCNF, which is, for example, an ink for producing an oxygen generating electrode containing an OER catalyst and an organic solvent in addition to the conductive aid of the present invention.
  • a conductive aid comprising lpe-pCNF
  • the ink may further contain an ORR catalyst.
  • the ORR catalyst, the OER catalyst and the organic solvent contained in the ink can be known, and the OER catalyst can be, for example, the OER catalyst described in Patent Document 1 and Non-Patent Document 1.
  • the OER catalyst can be, for example, a brown mullite light transition metal oxide, but is not intended to be limited thereto.
  • the present invention includes a reversible air electrode comprising the conductive aid of lpe-pCNF of the present invention, the ORR catalyst and the OER catalyst.
  • ORR catalysts and OER catalysts can be known. Typical examples of ORR catalysts include, but are not intended to be limited to, Pt or Pt based materials.
  • the reversible air electrode of the present invention can be, for example, an oxygen electrode for a zinc-air battery.
  • the recovered pCNF was further heat-treated at 1100 ° C., 1500 ° C. or 2400 ° C. in an Ar atmosphere to change the microstructure and the degree of graphitization.
  • the heating rate was 10 K min -1 and the holding time at each temperature was 1 hour (2400 ° C. only 10 min), and after holding, natural cooling was performed (about 13 K min -1 ).
  • FIG. 2 is a SEM image of pCNF heat treated (a) immediately after isolation from the AAO template and (b) heat treated at 2400 ° C. Looking at the fiber immediately after isolation, all have uniform diameters of 40-50 nm. This diameter is consistent with the pore diameter of the AAO template, so the template method allows one to make pCNF with a uniform diameter. When this is heat-treated at 2400 ° C., the fiber diameter hardly changes, but it can be seen that the fiber length is shortened. The fibers were shortened but the fiber morphology was maintained, and lpe-pCNF (high temperature heat treated pCNF) could be produced.
  • FIG. 4 is a Raman spectrum of each carbon material.
  • pCNF pCNF 1100, pCNF 1500 and acetylene black after heat treatment at 600 ° C.
  • a broad peak is observed around 1380 cm -1 . This is due to the vibration of the D band derived from the disorder of the structure of the graphite, and the integrated intensity is stronger than the 1580 cm -1 peak derived from the regular graphitic structure, which indicates that the degree of graphitization is low.
  • the G band is stronger than the D band, and the improvement of the degree of graphitization can also be confirmed from the Raman spectrum.
  • FIG. 5 Shown in FIG. 5 is a TEM image of each carbon material.
  • a TEM sample was prepared by ultrasonically dispersing about 100 ⁇ g of each sample in ethanol and dropping it on a carbon-coated Cu grid for TEM observation. This was observed using a field emission type transmission electron microscope with an accelerating voltage of 200 kV.
  • the presence or absence of the loop structure can be confirmed at a magnification of 300,000 or more.
  • FIG. 5 (a) no plaid is found in the sample, and it is guessed from TEM that the degree of graphitization is low.
  • crystal stripes can be clearly seen in pCNF1100 (FIG.
  • Oxidation resistance The weight change of pCNF1100, pCNF1500 and pCNF2400, and acetylene black (AB) when heated to 1000 ° C. in the atmosphere is shown in FIG. 6 (heating rate: 10 ° C./min). .
  • Electrode durability test (1) 1) Method of electrode preparation: 50 mg of Ca 2 FeCoO 5 (CFCO) which is an OER highly active catalyst and 10 mg of a carbon conductive aid (pCNF 1100, pCNF 1500 or pCNF 2400 or AB synthesized in Reference Example 1), 5% Nafion (R 2.) 0.2 mL of the dispersion solution was dispersed in 4.8 mL of ethanol as a catalyst ink.
  • CFCO Ca 2 FeCoO 5
  • FIG. 7 shows the evaluation results of electrode activity. It is a current-potential curve when anodic polarization is performed with a sweep rate of 1 mV s -1 from 1.1 V to 1.7 V in a 4 moldm -3 KOH aqueous solution in which a catalyst layer is formed on a glassy carbon electrode and used as an electrode. In the same way, the current rises at 1.47 V and oxygen generation starts. Thus, the onset potential of oxygen evolution does not depend on the type of carbon. Further sweeping the potential to the anode side increases the current.
  • the AB, pCNF1500, and pCNF2400 samples have sufficient current of 100 mA cm -2 or more at 1.7 V, but pCNF1100 has a small current at 1.7 V and the difference in current with other samples is also 1.52 V Be This is because graphitization does not progress so much because the heat treatment temperature is low, and the conductivity of the pCNF1100 sample is insufficient.
  • FIG. 8 shows a change in current when a catalyst layer is formed on a carbon sheet to form an electrode and polarized at +1.7 V for 20 h.
  • AB samples show a large current drop due to the oxidative consumption of carbon.
  • pCNF1100 also showed a current drop similar to that of the AB sample.
  • pCNF1500 and pCNF2400 which showed high oxidation resistance in the TG test, the current drop is very small compared to AB and pCNF1100, suggesting that pCNF1500 and pCNF2400 are difficult to oxidize even when used as an electrode.
  • Ru
  • pCNF1500 also has no clear change in fiber diameter, and is considered to be highly resistant to oxidative consumption. This is also consistent with the fact that the change in current in FIG. 8 does not greatly differ between pCNF1500 and pCNF2400. Therefore, the conductive aid of the present invention consisting of lpe-pCNF which is pCNF heat treated at high temperature can be said to be a carbon conductive aid having high oxidation resistance under the OER environment.
  • the excellent oxidation resistance of not only pCNF2400 but also pCNF1500 appears to be due to the formation of loops on the side of the fiber as shown in FIG. 5 (c).
  • An electrode prepared by mixing pCNF1100 having no loop edge structure (FIG. 5 (b)) with CFCO was subjected to the same test. As in the case of AB.sub.2, the form of the electrode was largely changed. This is considered to be attributable to the oxidative consumption of the carbon material, and it has been confirmed that the fiber diameter is actually partially reduced (FIG. 12).
  • Example 2 Electrode durability test (2) 1) A carbon sheet electrode (CFCO / pCNF2400 electrode, CFCO / AB electrode) using pCNF2400 or AB as a carbon conductive aid was produced by the method similar to the method described in 1) Electrode production method of Example 1.
  • OER endurance test One month OER endurance test using carbon sheet electrode using pCNF2400 or AB prepared in 1), Hg / HgO / 4 mol dm -3 KOH as a reference electrode and platinum plate as a counter electrode, It was carried out in a 4 mol dm -3 KOH aqueous solution under an inert atmosphere of argon. First, OER polarization was performed for 2 hours under a constant oxidation current condition of 40 mA cm ⁇ 2 , followed by standing for 15 minutes under 0 current condition. The above two steps were alternately repeated for one month.
  • the OER current-potential curves of the CFCO / pCNF2400 electrode and the CFCO / AB electrode before and after one month of electrolysis are shown in FIG.
  • the results in FIG. 13 indicate that the OER current-potential curve of the CFCO / pCNF2400 electrode shows almost no change before and after electrolysis.
  • the OER current-potential curve of the CFCO / AB electrode shifted to the high voltage side after electrolysis compared to before the electrolysis, and the resistance increased.
  • the rising potential of the current in the OER current-potential curve of the CFCO / pCNF2400 electrode is almost the same as the rising potential of the current in the OER current-potential curve of the CFCO / AB electrode, and changes even after 1 month has passed It was not.
  • the present invention is useful in the field of carbon conductive aids and the use thereof.

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Abstract

The present invention relates to: a loop edge-pCNF containing conductivity aid for an oxygen generating electrode, in which conductivity aid at least a part of the edge of a carbon hexagonal net plane exposed on a side surface of the fiber of a carbon nanofiber (platelet carbon nanofiber, pCNF) having a platelet structure of carbon hexagonal net planes forms a loop structure with the edge of a proximate carbon hexagonal net plane; an ink for fabricating an oxygen generating electrode which contains the conductivity aid, an OER catalyst, and an organic solvent, and which may further contain an ORR catalyst; and a reversible air electrode which contains the conductivity aid, an ORR catalyst, and an OER catalyst. The conductivity aid of the present invention is a conductivity aid made of a carbon material that contributes to the improvement of the durability of an oxygen electrode for zinc air battery and that is resistant to oxidative consumption. It is possible to provide an oxygen electrode for zinc air battery in which the conductivity aid is utilized.

Description

酸素発生電極用導電助剤及びその利用Conductive auxiliary for oxygen generating electrode and use thereof
　本発明は、優れた耐酸化性を有する炭素材料からなる酸素発生電極用導電助剤及びその利用に関する。
関連出願の相互参照
　本出願は、２０１７年８月２５日出願の日本特願２０１７－１６１９３３号の優先権を主張し、その全記載は、ここに特に開示として援用される。 The present invention relates to a conductive aid for an oxygen generating electrode made of a carbon material having excellent oxidation resistance, and use thereof.
This application claims the priority of Japanese Patent Application No. 2017-161933, filed on Aug. 25, 2017, the entire disclosure of which is incorporated herein by reference in particular.
　水系空気電池は、卑金属を負極、空気極を正極、水系電解質（電解液）を電解質とした電池であり、正極活物質として空気中の酸素を利用する。そのため、空気極が電池内に占める体積・重量が少なく、電池内に多量の負極活物質を収納することができ、高エネルギー密度電池として有望である。水系空気電池は、水系電解質、特にアルカリ水溶液を電解質に用いることにより、高イオン伝導率で出力が取りやすく、安価で安全な電池を構成できるメリットがある。水系空気電池の空気極は、酸素の4電子反応が利用でき、還元生成物である水酸化物イオン（OH-）が電解質の構成成分であるため、リチウム空気電池において見られる空孔閉塞が起こらない利点を有する。亜鉛空気電池は、強い還元力を持ち、資源的に豊富で安価、かつ工業的に取り扱いの確立した亜鉛を負極活物質とする電池であり、水溶液中で充放電可能である。亜鉛空気電池は、理論電圧1.65 V×理論容量（金属ベース）820 Ah/kg＝1350 Wh/kgの重量当たりの理論エネルギー密度と、高い亜鉛の嵩密度（g/cc）のため、リチウム空気電池を凌ぐ体積当たりの理論エネルギー密度を有する。 The water-based air battery is a battery using a base metal as a negative electrode, an air electrode as a positive electrode, and a water-based electrolyte (electrolytic solution) as an electrolyte, and utilizes oxygen in air as a positive electrode active material. Therefore, the volume and weight occupied by the air electrode in the battery are small, and a large amount of negative electrode active material can be accommodated in the battery, which is promising as a high energy density battery. The water-based air battery is advantageous in that the output can be easily obtained with high ion conductivity and an inexpensive and safe battery can be formed by using a water-based electrolyte, particularly an alkaline aqueous solution as the electrolyte. Cathode aqueous air battery, four-electron reaction of oxygen available, the hydroxide ion is a reduction product (OH -) because it is a component of the electrolyte, it occurs vacancies obstruction seen in lithium-air batteries Not have advantages. The zinc-air battery is a battery which has strong reducing power, is abundant in resources, is inexpensive, and has zinc as an anode active material established industrially and which can be charged and discharged in an aqueous solution. The zinc-air battery is a lithium-air battery because of its theoretical energy density per weight of theoretical voltage 1.65 V × theoretical capacity (metal base) 820 Ah / kg = 1350 Wh / kg and high bulk density of zinc (g / cc). Higher than the theoretical energy density per volume.
　金属空気二次電池の実現には、電池の動作環境である強アルカリ条件で、酸素還元(ORR)および酸素発生反応(OER)の過電圧を十分に抑制し、かつ繰り返しの充放電に耐えうる可逆空気電極が必要である。酸素発生に高活性な触媒として、RuO2やIrO2などの貴金属酸化物がよく知られており、また、酸素還元触媒としては炭素に担持したPt触媒が高活性である。しかしながら、このような貴金属触媒は高価であり、資源も乏しいことから、最近は貴金属を含まない様々な酸化物のORR/OER活性評価が進められている。なかでもペロブスカイト型酸化物は多くの研究が行われ、高活性OER触媒としてBa0.8Sr0.2Co0.6Fe0.4O3-δ(BSCF)が見出されてきた。さらに、最近、充電電圧2.0 Vで100 mA cm-2の電流を取り出せるCa2FeCoO5（CFCO）ブラウンミラーライト触媒も新しいBCSFを上回る高活性触媒として発見されている(特許文献1、非特許文献1)。 To realize a metal-air secondary battery, it is reversible enough to sufficiently suppress overpotentials of oxygen reduction (ORR) and oxygen evolution reaction (OER) under strong alkaline conditions, which is the operating environment of the battery, and withstand repeated charging and discharging. An air electrode is required. Noble metal oxides such as RuO 2 and IrO 2 are well known as highly active catalysts for oxygen generation, and Pt catalysts supported on carbon are highly active as oxygen reduction catalysts. However, since such noble metal catalysts are expensive and resources are scarce, ORR / OER activity evaluation of various oxides not containing noble metals has recently been advanced. Above all, many studies have been conducted on perovskite oxides, and Ba 0.8 Sr 0.2 Co 0.6 Fe 0.4 O 3- δ (BSCF) has been found as a highly active OER catalyst. Furthermore, recently, a Ca 2 FeCoO 5 (CFCO) brown mirror light catalyst capable of extracting a current of 100 mA cm −2 at a charge voltage of 2.0 V has also been discovered as a highly active catalyst over new BCSF (Patent Document 1, Non-patent Document) 1).
特許文献１：WO2015/115592
特許文献２：特開2005-47763号公報 Patent Document 1: WO 2015/115592
Patent Document 2: Japanese Patent Application Laid-Open No. 2005-47763
非特許文献１：E. Tsuji, T. Motohashi, H. Noda, D. Kowalski, Y. Aoki, H. Tanida, J. Niikura, Y. Koyama, M. Mori, H. Arai, T. Ioroi, N. Fujiwara, Y. Uchimoto, Z. Ogumi, H. Habazaki; ChemSusChem, 10, 2864 (2017). 10.1002/cssc.201700499
非特許文献２：H.  Konno, S. Sato, H. Habazaki, M. Inagaki; Carbon, 42, 2756 (2004).
非特許文献３：H. Habazaki, M. Kiriu, M. Hayashi, H. Konno; Mater. Chem. Phys., 105, 367 (2007).
特許文献１及び２並びに非特許文献１～３の全記載は、ここに特に開示として援用される。 Non-Patent Document 1: E. Tsuji, T. Motohashi, H. Noda, D. Kowalski, Y. Aoki, H. Tanida, J. Niikura, Y. Koyama, M. Mori, H. Arai, T. Ioroi, N. Fujiwara, Y. Uchimoto, Z. Ogumi, H. Habazaki; ChemSusChem, 10, 2864 (2017). 10.1002 / cssc. 201700499
Non-Patent Document 2: H. Konno, S. Sato, H. Habazaki, M. Inagaki; Carbon, 42, 2756 (2004).
Non-Patent Document 3: H. Habazaki, M. Kiriu, M. Hayashi, H. Konno; Mater. Chem. Phys., 105, 367 (2007).
The entire descriptions of Patent Documents 1 and 2 and Non-Patent Documents 1 to 3 are specifically incorporated herein by reference.
　前記のような高活性酸化物触媒は導電性が充分でないため、導電助剤として炭素を添加して電極を作製する必要があるが、炭素はOER環境で酸化消耗してしまう。したがって、亜鉛空気電池用酸素電極の耐久性向上には酸化消耗に強い炭素材料を開発し、それを導電助剤として利用する必要がある。 Since the high activity oxide catalyst as described above is not sufficiently conductive, it is necessary to add carbon as a conductive aid to produce an electrode, but carbon is oxidized and consumed in the OER environment. Therefore, in order to improve the durability of the oxygen electrode for zinc-air batteries, it is necessary to develop a carbon material that is resistant to oxidative consumption and use it as a conductive aid.
　本発明が解決しようとする課題は、亜鉛空気電池用酸素電極の耐久性向上に寄与する、酸化消耗に強い炭素材料からなる導電助剤及びこの導電助剤を利用する亜鉛空気電池用酸素電極を提供することであり、これらの課題を解決することを本発明の目的とする。 The problem to be solved by the present invention is to improve the durability of the oxygen electrode for zinc-air battery, a conductive support agent made of a carbon material resistant to oxidative consumption, and an oxygen electrode for zinc-air battery using this conductive support agent. It is an object of the present invention to solve these problems.
　本発明者らは、先に、プレートレット構造を有するカーボンナノファイバー（以下、プレートレットカーボンナノファイバー(pCNF)と呼ぶことがある）を開発した(特許文献2、非特許文献2)。さらに、pCNFは、炭素六角網面がファイバー方向に積層した特異な配向性をもつことも明らかにした。さらに、pCNFは、ファイバーの側面に活性な炭素六角網面のエッジが露出した構造になっているが、2800℃などの高温で熱処理すると、エッジ面数層でループを形成してエッジ面の露出がなくなることも明らかにした(非特許文献3)。本発明者らは、その後の検討で、ループを形成してエッジ面の露出がなくなったファイバーは、耐酸化性が未処理のpCNFに比べて高くなることを見いだし、この知見に基づいて本発明を完成させた。さらに、pCNFは、加熱温度が1500℃および2400℃においても、プレートレット構造であり、かつファイバー側面にグラフェン数層からなるループが見られることを新たに見出した。本発明は、これら新たな知見に基づいて完成させたものでもある。 The present inventors previously developed carbon nanofibers having a platelet structure (hereinafter sometimes referred to as platelet carbon nanofibers (pCNF)) (Patent Document 2, Non-Patent Document 2). Furthermore, pCNF was also revealed to have a unique orientation in which the carbon hexagonal network plane was laminated in the fiber direction. Furthermore, pCNF has a structure in which the edge of the active carbon hexagonal network face is exposed on the side of the fiber, but heat treatment at a high temperature such as 2800 ° C forms a loop with several layers on the edge face and exposes the edge face It also became clear that there is no longer (non-patent document 3). The inventors of the present invention found in the subsequent examination that the fiber in which the loop was formed and the exposure of the edge surface was removed had higher oxidation resistance than that of the untreated pCNF, based on this finding. Completed. Furthermore, it has been newly found that pCNF has a platelet structure even at heating temperatures of 1500 ° C. and 2400 ° C., and a loop consisting of several graphene layers can be seen on the side of the fiber. The present invention is also completed based on these new findings.
　本発明は以下のとおりである。
［１］
炭素六角網面のプレートレット構造を有するカーボンナノファイバー（以下、プレートレットカーボンナノファイバーと呼ぶことがあり、ｐＣＮＦと略記することがある）であって、
ファイバーの側面に露出した炭素六角網面のエッジの少なくとも一部が、近接する炭素六角網面のエッジとの間でのループ構造を有する、ｐＣＮＦ（ループエッジ－ｐＣＮＦと呼ぶことがあり、ｌｐｅ－ｐＣＮＦと略記することがある）を含む酸素発生電極用導電助剤。
［２］
ｌｐｅ－ｐＣＮＦは、ラマンスペクトルにおけるＧバンド（１５８０ｃｍ-1付近）の強度がＤバンド（１３８０ｃｍ-1付近）の強度より強い、［１］に記載の導電助剤。
［３］
ループ構造が、複数の積層炭素六角網面のエッジと、近接する複数の積層炭素六角網面のエッジとの間でのループ構造である、［１］又は［２］に記載の導電助剤。
［４］
ｌｐｅ－ｐＣＮＦは、大気中での昇温試験における重量減少開始温度が５００℃以上又は６００℃以上である、［１］～［３］のいずれかに記載の導電助剤。
［５］
酸素発生電極が可逆空気電極である［１］～［４］のいずれかに記載の導電助剤。
［６］
［１］～［５］のいずれかに記載の導電助剤、ＯＥＲ触媒及び有機溶媒を含有し、さらにＯＲＲ触媒を含有することができる、酸素発生電極作製用インク。
［７］
［１］～［５］のいずれかに記載の導電助剤、ＯＲＲ触媒及びＯＥＲ触媒を含有する可逆空気電極。
［８］
亜鉛空気電池用の酸素電極である、［７］に記載の可逆空気電極。
［９］
［８］に記載の可逆空気電極を含む亜鉛空気電池。 The present invention is as follows.
[1]
Carbon nanofibers having a platelet structure of a carbon hexagonal network surface (hereinafter sometimes referred to as platelet carbon nanofibers, sometimes abbreviated as pCNF),
At least a part of the edge of the carbon hexagonal surface exposed to the side of the fiber has a loop structure between the edge of the adjacent carbon hexagonal surface, sometimes called pCNF (loop edge-pCNF, lpe- A conductive aid for an oxygen generating electrode, which may be abbreviated as pCNF.
[2]
lpe-pCNF is a conductive aid as described in [1], wherein the intensity of G band (near 1580 cm -1 ) in Raman spectrum is stronger than the intensity of D band (near 1380 cm -1 ).
[3]
The conductive aid according to [1] or [2], wherein the loop structure is a loop structure between an edge of the plurality of laminated carbon hexagonal network faces and an edge of the adjacent plurality of laminated carbon hexagonal network faces.
[4]
The conductive auxiliary according to any one of [1] to [3], wherein lpe-pCNF has a weight reduction onset temperature of 500 ° C. or more or 600 ° C. or more in a temperature rising test in the air.
[5]
The conductive auxiliary according to any one of [1] to [4], wherein the oxygen generating electrode is a reversible air electrode.
[6]
An ink for producing an oxygen generating electrode, which contains the conductive auxiliary agent according to any one of [1] to [5], an OER catalyst and an organic solvent, and can further contain an ORR catalyst.
[7]
A reversible air electrode comprising the conductive auxiliary according to any one of [1] to [5], an ORR catalyst and an OER catalyst.
[8]
The reversible air electrode according to [7], which is an oxygen electrode for a zinc-air battery.
[9]
A zinc-air battery comprising the reversible air electrode according to [8].
　本発明によれば、耐酸化性に優れた炭素材料からなる導電助剤を提供することができ、この導電助剤はＯＥＲ環境下において高い耐酸化性を有する。本発明の導電助剤は、亜鉛空気電池用酸素電極の耐久性向上に大いに貢献する。 ADVANTAGE OF THE INVENTION According to this invention, the conductive support agent which consists of a carbon material excellent in oxidation resistance can be provided, and this conductive support agent has high oxidation resistance in OER environment. The conductive aid of the present invention greatly contributes to the improvement of the durability of the oxygen electrode for zinc air battery.
図１は、2800℃にて熱処理したpCNFのTEM写真。FIG. 1 is a TEM photograph of pCNF heat-treated at 2800 ° C. 図２は、(a)600℃熱処理後単離したpCNFおよび(b)2400℃熱処理したpCNFのSEM写真。FIG. 2 is a SEM photograph of (a) pCNF isolated after heat treatment at 600 ° C. and (b) pCNF heat treated at 2400 ° C. 図３は、参考例1で合成したpCNFと市販アセチレンブラックのXRDパターン。FIG. 3 shows XRD patterns of pCNF synthesized in Reference Example 1 and commercially available acetylene black. 図４は、参考例1で合成したpCNFと市販アセチレンブラックのRamanスペクトル。FIG. 4 is a Raman spectrum of pCNF synthesized in Reference Example 1 and commercially available acetylene black. 図５は、参考例1で合成し、(a)600℃、(b)1100℃、(c)1500℃、(d)2400℃で熱処理したpCNFのTEM写真。FIG. 5 is a TEM photograph of pCNF synthesized in Reference Example 1, heat-treated at (a) 600 ° C., (b) 1100 ° C., (c) 1500 ° C., (d) 2400 ° C. 図６は、参考例1で合成したpCNFと市販アセチレンブラックの大気中におけるTG曲線。FIG. 6 is a TG curve of pCNF synthesized in Reference Example 1 and commercial acetylene black in the atmosphere. 図７は、実施例1における各種炭素／CFCO電極をアノード分極したときの酸素発生電流-電位曲線。FIG. 7 is an oxygen generation current-potential curve when the various carbon / CFCO electrodes in Example 1 are anodically polarized. 図８は、実施例1における各種炭素／CFCO電極を1.7 V vs RHEで定電位分極したときの電流変化。FIG. 8 shows changes in current when the various carbon / CFCO electrodes in Example 1 are subjected to constant potential polarization at 1.7 V vs RHE. 図９は、AB/CFCO電極の1.7 V vs RHEで20時間電解前後のSEM写真。FIG. 9 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of AB / CFCO electrode. 図１０は、pCNF2400/CFCO電極の1.7 V vs RHEで20時間電解前後のSEM写真。FIG. 10 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of pCNF2400 / CFCO electrode. 図１１は、pCNF1500/CFCO電極の1.7 V vs RHEで20時間電解前後のSEM写真。FIG. 11 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of pCNF1500 / CFCO electrode. 図１２は、pCNF1100/CFCO電極の1.7 V vs RHEで20時間電解前後のSEM写真。FIG. 12 is a SEM photograph before and after 20 hours of electrolysis at 1.7 V vs RHE of pCNF1100 / CFCO electrode. 図１３は、CFCO/pCNF2400およびCFCO/AB電極の１ヶ月OER耐久試験前後におけるＯＥＲ分極曲線。FIG. 13 shows OER polarization curves before and after 1-month OER endurance test of CFCO / pCNF2400 and CFCO / AB electrodes. 図１４は、CFCO/pCNF2400およびCFCO/AB電極の１ヶ月OER耐久性試験において、試験前、試験開始3日後および試験開始１ヶ月後の電極のSEM写真。FIG. 14 is a SEM photograph of the electrode before the test, 3 days after the start of the test and 1 month after the start of the test in the 1-month OER durability test of the CFCO / pCNF2400 and the CFCO / AB electrode.
＜ループエッジ－ｐＣＮＦ＞
　本発明の導電助剤に用いるループエッジ－ｐＣＮＦは、炭素六角網面のプレートレット構造を有するカーボンナノファイバー（プレートレットカーボンナノファイバー又はｐＣＮＦ）であって、ファイバーの側面に露出した炭素六角網面のエッジの少なくとも一部が、近接する炭素六角網面のエッジとの間でのループ構造を有する、ｐＣＮＦであり、ループエッジ－ｐＣＮＦと呼ぶことがあり、ｌｐｅ－ｐＣＮＦと略記することがある。 <Loop edge-pCNF>
The loop edge-pCNF used for the conductive additive of the present invention is a carbon nanofiber (platelet carbon nanofiber or pCNF) having a platelet structure of a carbon hexagonal network, and the carbon hexagonal network exposed to the side of the fiber At least a part of the edge of p is a pCNF having a loop structure between it and the edge of the adjacent carbon hexagonal network surface, which may be called loop edge-pCNF, and may be abbreviated as lpe-pCNF.
　特許文献２及び非特許文献２に記載のｐＣＮＦ（以下、単にｐＣＮＦ又は未処理ｐＣＮＦと呼ぶ）は、炭素六角網面のプレートレット構造を有するカーボンナノファイバーであり、ファイバーの側面に炭素六角網面のエッジが露出している。それに対してｌｐｅ－ｐＣＮＦは、未処理ｐＣＮＦにおいてファイバーの側面に露出した炭素六角網面のエッジの少なくとも一部が、近接する炭素六角網面のエッジとの間でのループ構造を有するｐＣＮＦである。未処理ｐＣＮＦのファイバー側面に露出した炭素六角網面のエッジは化学的に活性であり、酸素が存在すると、条件によっては反応して炭素が消耗する。未処理ｐＣＮＦを2800℃などの高温で熱処理すると、エッジ面でループを形成してエッジ面の露出がなくなることを見いだした（非特許文献３）。エッジ面のループ構造を図１に示す。その後の本発明者らの検討から、エッジ面の露出がなくなったｌｐｅ－ｐＣＮＦは耐酸化性に優れ、これを酸素発生電極用の導電助剤として用いると高い耐酸化性を有することを見いだした。ｌｐｅ－ｐＣＮＦの中で、ループ構造を有する割合は、例えば、１０％以上、２０％以上、５０％以上、８０％以上、９０％以上であることができる。耐酸化性に優れるという観点からは、ループ構造の割合は、高いほど好ましい。但し、ループ構造の割合を高めるにはループ構造形成のための熱処理条件を高温化及び長時間化する必要があることから、実用的には求められる耐酸化性に応じてループ構造の割合を適宜選択することができる。 PCNF (hereinafter referred to simply as pCNF or untreated pCNF) described in Patent Document 2 and Non-patent Document 2 is a carbon nanofiber having a platelet structure of a carbon hexagonal network plane, and the carbon hexagonal network plane on the side of the fiber The edge of is exposed. In contrast, lpe-pCNF is a pCNF that has a loop structure between at least part of the edge of the carbon hexagonal surface exposed to the side of the fiber in the untreated pCNF and the edge of the adjacent carbon hexagonal surface. . The edge of the hexagonal carbon network exposed on the fiber side of untreated pCNF is chemically active, and in the presence of oxygen, under certain conditions, it reacts and consumes carbon. It has been found that heat treatment of untreated pCNF at a high temperature such as 2800 ° C. forms loops on the edge surface and loses the exposure of the edge surface (Non-patent Document 3). The loop structure of the edge face is shown in FIG. From the study of the inventors of the present invention, it was found that lpe-pCNF having no edge surface exposure was excellent in oxidation resistance and had high oxidation resistance when it was used as a conductive aid for an oxygen generating electrode. . In lpe-pCNF, the ratio of having a loop structure can be, for example, 10% or more, 20% or more, 50% or more, 80% or more, 90% or more. From the viewpoint of excellent oxidation resistance, the higher the proportion of the loop structure, the better. However, since it is necessary to increase the temperature and heat treatment conditions for forming the loop structure to increase the proportion of the loop structure, the proportion of the loop structure is appropriately selected according to the oxidation resistance required practically. It can be selected.
　ｌｐｅ－ｐＣＮＦのループ構造は、図１の場合のように、複数の積層炭素六角網面のエッジと、近接する複数の積層炭素六角網面のエッジとの間でのループ構造であることができる。ループ構造を形成する炭素六角網面の積層数には特に制限はないが、例えば、２～１０の範囲である。但し、この範囲に制限される意図ではない。ループ構造は、実施例に記載する方法で観察用の試料を調製し、TEM観察（例えば、倍率30万倍以上）することで確認することができる。ｌｐｅ－ｐＣＮＦのループ構造を有する割合も、特定観察範囲内のTEM観察（例えば、倍率30万倍以上）画像を用いて特定することができる。 The loop structure of lpe-pCNF can be a loop structure between the edges of a plurality of laminated carbon hexagonal mesh faces and the edges of a plurality of adjacent laminated carbon hexagonal mesh faces as in the case of FIG. 1 . There is no particular limitation on the number of laminations of carbon hexagonal network faces forming the loop structure, but it is, for example, in the range of 2 to 10. However, it is not the intention limited to this range. The loop structure can be confirmed by preparing a sample for observation by the method described in the examples and performing TEM observation (for example, magnification 300,000 times or more). The proportion of lpe-pCNF having a loop structure can also be identified using a TEM observation (for example, magnification of 300,000 × or more) image within a specific observation range.
　ｌｐｅ－ｐＣＮＦは、上記ようにループエッジ構造を有し、化学的に活性な炭素六角網面のエッジの少なくとも一部がファイバー側面に露出しておらず、そのため、耐酸化性に優れる。具体的には、大気中での昇温試験における重量減少開始温度が５００℃以上であり、好ましくは５５０℃以上であり、より好ましくは６００℃以上である。尚、昇温試験における昇温速度は10℃/minとする。 As described above, lpe-pCNF has a loop edge structure, and at least a part of the edge of the chemically active carbon hexagonal network face is not exposed to the side of the fiber, and hence is excellent in oxidation resistance. Specifically, the weight loss start temperature in the temperature rising test in the air is 500 ° C. or higher, preferably 550 ° C. or higher, and more preferably 600 ° C. or higher. The temperature rising rate in the temperature rising test is 10 ° C./min.
　ｌｐｅ－ｐＣＮＦは、後述するように、製造の際に未処理ｐＣＮＦを高温で熱処理して調製される。そのため、熱処理により構成する炭素の黒鉛化が進行する。炭素材料のラマンスペクトルは、無定形炭素ではＤバンド（１３８０ｃｍ-1付近）のみが観測される。それに対して、黒鉛では、Ｄバンドに加えてＧバンド（１５８０ｃｍ-1付近）が観測される。ｌｐｅ－ｐＣＮＦは、ラマンスペクトルにおいてＧバンドの強度がＤバンドの強度より強いものであることができ、Ｇバンドの強度がＤバンドの強度より強ければそれだけ耐熱性に優れる傾向がある。 lpe-pCNF is prepared by heat treating untreated pCNF at high temperature during manufacture as described later. Therefore, graphitization of the carbon which comprises by heat processing advances. The Raman spectrum of the carbon material is observed only for the D band (around 1380 cm −1 ) for amorphous carbon. On the other hand, in graphite, in addition to the D band, a G band (around 1580 cm -1 ) is observed. The lpe-pCNF can have a higher G band intensity than the D band intensity in the Raman spectrum, and if the G band intensity is higher than the D band intensity, the heat resistance tends to be better.
＜ｌｐｅ－ｐＣＮＦの製造方法＞
　ｌｐｅ－ｐＣＮＦは、ファイバーの側面に炭素六角網面のエッジが露出したｐＣＮＦを非酸化性雰囲気中１１００℃超の温度で加熱して、ファイバーの側面に露出した炭素六角網面のエッジの少なくとも一部が、近接するエッジ間でのループ構造を形成することで調製できる。原料とするファイバーの側面に炭素六角網面のエッジが露出したｐＣＮＦは、特許文献２及び非特許文献２に記載の方法で製造することができる。 <Method for producing lpe-pCNF>
lpe-pCNF heats pCNF in which the edge of the carbon hexagonal surface is exposed at the side of the fiber at a temperature of more than 1100 ° C. in a non-oxidizing atmosphere to at least one edge of the carbon hexagonal surface exposed at the side of the fiber Parts can be prepared by forming a loop structure between adjacent edges. PCNF in which the edge of the carbon hexagonal mesh surface is exposed on the side surface of the raw material fiber can be produced by the methods described in Patent Document 2 and Non-Patent Document 2.
　ｐＣＮＦの加熱処理は、非酸化性雰囲気中１１００℃超の温度で行う非酸化性雰囲気は、酸素を含有しない雰囲気であれば特に制限はなく、例えば、不活性ガス雰囲気、例えば、アルゴン雰囲気であることができる。加熱温度は、１１００℃超とする。１１００℃超の温度での加熱であれば、ループ構造の生成は観測される。但し、ループ構造を効率的に（比較的短時間で）生成させるという観点からより高い温度での加熱であることが好ましく、例えば、１３００℃以上、１５００℃以上、２０００℃以上、２５００℃以上、２７００℃以上とすることができる。加熱温度の上限は特になく、装置的に達成可能であれば、より高い温度であることもでき、現実的には３０００℃前後の温度での加熱であることができる。昇温速度は、例えば、5～15 K min-1の範囲であることが適当であるが、これよりも遅くても問題はない。保持時間は、加熱温度を考慮して適宜決定でき、例えば、1時間程度が適当であるが、加熱温度によってはこれよりも短くすることができ、保持時間の影響は保持温度の影響よりも小さい傾向がある。 The heat treatment of pCNF is carried out at a temperature higher than 1100 ° C. in a non-oxidative atmosphere, as long as the atmosphere does not contain oxygen, for example, an inert gas atmosphere such as an argon atmosphere. be able to. The heating temperature is higher than 1100.degree. With heating above 1100 ° C., the formation of loop structures is observed. However, heating is preferably performed at a higher temperature from the viewpoint of efficiently generating the loop structure (in a relatively short time), for example, 1300 ° C. or more, 1500 ° C. or more, 2000 ° C. or more, 2500 ° C. or more, It can be 2700 ° C or more. There is no particular upper limit to the heating temperature, and if it can be achieved as a device, it can be a higher temperature, and practically it can be heating at a temperature of around 3000 ° C. The heating rate is suitably, for example, in the range of 5 to 15 K min -1 , but there is no problem if it is slower than this. The holding time can be appropriately determined in consideration of the heating temperature, for example, about one hour is appropriate, but depending on the heating temperature, it can be shorter than this, and the influence of the holding time is smaller than the influence of the holding temperature Tend.
　加熱によりファイバーの側面に露出した炭素六角網面のエッジの少なくとも一部が、近接するエッジ間でのループ構造を形成して、ｌｐｅ－ｐＣＮＦを得ることができる。加熱時間は特に制限はなく、ループ構造の形成具合（量と構造）を考慮して適宜決定することができる。 At least a part of the edge of the carbon hexagonal surface exposed to the side of the fiber by heating can form a loop structure between adjacent edges to obtain lpe-pCNF. The heating time is not particularly limited, and can be appropriately determined in consideration of the formation condition (amount and structure) of the loop structure.
＜導電助剤＞
　ｌｐｅ－ｐＣＮＦは、酸素発生電極に用いた場合に高い耐酸化性を有することから、酸素発生電極用の導電助剤として有用であり、本発明は、ｌｐｅ－ｐＣＮＦからなる酸素発生電極用の導電助剤に関する。さらに、この導電助剤が用いられる酸素発生電極は、可逆空気電極であることができる。 <Conductive agent>
Since lpe-pCNF has high oxidation resistance when used in an oxygen generating electrode, it is useful as a conductive aid for the oxygen generating electrode, and the present invention relates to a conductive for an oxygen generating electrode comprising lpe-pCNF Regarding the auxiliary agent. Furthermore, the oxygen generating electrode in which this conductive support agent is used can be a reversible air electrode.
＜インク＞
　本発明は、ｌｐｅ－ｐＣＮＦからなる導電助剤を含むインクを包含し、このインクは、例えば、本発明の導電助剤に加えて、ＯＥＲ触媒及び有機溶媒を含有する酸素発生電極作製用インクであることができ、このインクはさらに、ＯＲＲ触媒を含有することもできる。インクに含有されるＯＲＲ触媒、ＯＥＲ触媒及び有機溶媒は公知のものであることができ、ＯＥＲ触媒は、例えば、特許文献１及び非特許文献１に記載のＯＥＲ触媒であることができる。ＯＥＲ触媒は、例えば、ブラウンミューラライト型遷移金属酸化物であることができるが、これらに限定される意図ではない。 <Ink>
The present invention includes an ink containing a conductive aid comprising lpe-pCNF, which is, for example, an ink for producing an oxygen generating electrode containing an OER catalyst and an organic solvent in addition to the conductive aid of the present invention. There may be, and the ink may further contain an ORR catalyst. The ORR catalyst, the OER catalyst and the organic solvent contained in the ink can be known, and the OER catalyst can be, for example, the OER catalyst described in Patent Document 1 and Non-Patent Document 1. The OER catalyst can be, for example, a brown mullite light transition metal oxide, but is not intended to be limited thereto.
　本発明は、本発明のｌｐｅ－ｐＣＮＦからなる導電助剤、ＯＲＲ触媒及びＯＥＲ触媒を含有する可逆空気電極を包含する。ＯＲＲ触媒及びＯＥＲ触媒は公知のものであることができる。ＯＲＲ触媒の典型例としてはPt又はPt系材料等を挙げることができるが、これらに限定される意図ではない。本発明の可逆空気電極は、例えば、亜鉛空気電池用の酸素電極であることができる。 The present invention includes a reversible air electrode comprising the conductive aid of lpe-pCNF of the present invention, the ORR catalyst and the OER catalyst. ORR catalysts and OER catalysts can be known. Typical examples of ORR catalysts include, but are not intended to be limited to, Pt or Pt based materials. The reversible air electrode of the present invention can be, for example, an oxygen electrode for a zinc-air battery.
　以下、本発明を実施例に基づいて更に詳細に説明する。但し、実施例は本発明の例示であって、本発明は実施例に限定される意図ではない。 Hereinafter, the present invention will be described in more detail based on examples. However, the examples are illustrative of the present invention, and the present invention is not intended to be limited to the examples.
参考例１
・pCNFの作製
　pCNFの作製は、アノード酸化アルミナ（AAO）をテンプレートとする液相鋳造法により行った。AAOテンプレートは、0.3 mol dm-3 シュウ酸水溶液中、40 VにてAl箔を2時間アノード酸化し、さらに30分間 5 wt%リン酸水溶液に浸漬してポア径を50 nm程度に制御することで作製した。テンプレートとポリ塩化ビニル（PVC）粉末とを Ar 雰囲気下、300℃で0.5 h、600℃で1 h熱処理することにより、PVCを溶融状態にし、テンプレートポア内で黒鉛化した。これを20 wt% NaOH 水溶液中で処理することにより、テンプレートを溶解し、プレートレット炭素ナノファイバー（pCNF）をテンプレートから回収した。 Reference Example 1
Preparation of pCNF Preparation of pCNF was carried out by a liquid phase casting method using anodized alumina (AAO) as a template. In the AAO template, anodize the Al foil at 40 V in 0.3 mol dm -3 aqueous oxalic acid solution for 2 hours, and immerse in a 5 wt% phosphoric acid aqueous solution for 30 minutes to control the pore diameter to about 50 nm. Made in Heat treatment of the template and polyvinyl chloride (PVC) powder at 300 ° C. for 0.5 h and 600 ° C. for 1 h under Ar atmosphere brought the PVC into a molten state and was graphitized in the template pore. The template was dissolved by treating it in a 20 wt% aqueous NaOH solution, and platelet carbon nanofibers (pCNF) were recovered from the template.
・pCNFの熱処理
　回収したpCNFはAr雰囲気中で1100℃、1500℃又は2400℃でさらに熱処理することで、微細構造及び黒鉛化度を変化させた。昇温速度は10 K min-1で各温度での保持時間は1時間（2400℃のみ10 min）であり，保持後は自然冷却とした（約13 K min-1）。 Heat Treatment of pCNF The recovered pCNF was further heat-treated at 1100 ° C., 1500 ° C. or 2400 ° C. in an Ar atmosphere to change the microstructure and the degree of graphitization. The heating rate was 10 K min -1 and the holding time at each temperature was 1 hour (2400 ° C. only 10 min), and after holding, natural cooling was performed (about 13 K min -1 ).
・pCNFのキャラクタリゼーション
　図2は、(a)AAOテンプレートから単離した直後、および(b)2400℃で熱処理したpCNFのSEM像である。単離直後のファイバーを見ると、いずれもその径が40 - 50 nmと均一である。この径はAAOテンプレートのポア径と一致しており、したがって、本テンプレート法により均一な径を有するpCNFを作製できる。これを2400℃で熱処理すると、ファイバー径がほとんど変化しないが、ファイバーの長さは短くなっているのがわかる。ファイバーは短くなるがファイバー形態を維持しており、lpe-pCNF(高温熱処理 pCNF)が作製できた。 Characterization of pCNF FIG. 2 is a SEM image of pCNF heat treated (a) immediately after isolation from the AAO template and (b) heat treated at 2400 ° C. Looking at the fiber immediately after isolation, all have uniform diameters of 40-50 nm. This diameter is consistent with the pore diameter of the AAO template, so the template method allows one to make pCNF with a uniform diameter. When this is heat-treated at 2400 ° C., the fiber diameter hardly changes, but it can be seen that the fiber length is shortened. The fibers were shortened but the fiber morphology was maintained, and lpe-pCNF (high temperature heat treated pCNF) could be produced.
　図3は、AAOテンプレートから単離した直後、および1100℃、1500℃、2400℃で熱処理したpCNF(それぞれpCNF1100、pCNF1500及びpCNF2400と表示。以下同様)、そして比較材料として用いた市販導電助剤アセチレンブラック(AB)のXRDパターンである。いずれの材料においても2θ= 26.4°付近に 炭素の002回折線がみられる。その半値幅は熱処理温度の上昇とともに小さくなっており、高温熱処理により黒鉛化度が高くなっている。 FIG. 3 shows pCNF heat-treated at 1100 ° C., 1500 ° C. and 2400 ° C. immediately after being isolated from the AAO template (represented as pCNF 1100, pCNF 1500 and pCNF 2400 respectively, and so forth), and commercially available conductive aid acetylene used as a comparison material It is a XRD pattern of black (AB). The 002 diffraction line of carbon is observed around 2θ = 26.4 ° in any of the materials. The half width becomes smaller as the heat treatment temperature rises, and the degree of graphitization is increased by the high temperature heat treatment.
　図4は各炭素材料のRamanスペクトルである。600℃熱処理後のpCNFおよびpCNF1100、pCNF1500、アセチレンブラックのものには、1380 cm-1付近にブロードなピークがみられる。これは黒鉛の構造の乱れに由来するDバンドの振動によるものであり、規則的な黒鉛構造に由来する1580 cm-1ピークよりも積分強度が強いことから、黒鉛化度が低いことがわかる。一方、pCNF2400には、GバンドがDバンドよりも強くなっており、黒鉛化度の向上がRamanスペクトルからも確認できる。 FIG. 4 is a Raman spectrum of each carbon material. In pCNF, pCNF 1100, pCNF 1500 and acetylene black after heat treatment at 600 ° C., a broad peak is observed around 1380 cm -1 . This is due to the vibration of the D band derived from the disorder of the structure of the graphite, and the integrated intensity is stronger than the 1580 cm -1 peak derived from the regular graphitic structure, which indicates that the degree of graphitization is low. On the other hand, in pCNF2400, the G band is stronger than the D band, and the improvement of the degree of graphitization can also be confirmed from the Raman spectrum.
　ループ構造の形成はTEM観察で確認することができる。図5に示すのは、各炭素材料のTEM 像である。TEM試料は、各試料約100μgをエタノール中に超音波分散し、これをカーボン被覆したTEM観察用Cuグリッド上に滴下して準備した。これを加速電圧200 kVの電界放射型透過電子顕微鏡を用いて観察した。ループ構造の有無は倍率30万倍以上で確認可能である。600℃焼成直後試料(図5(a))では、格子縞が試料内に見受けられず、TEMからも黒鉛化度が低いことが推察される。一方、pCNF1100(図5(b))、pCNF1500(図5(c))およびpCNF2400(図5(d))でははっきりと結晶縞が確認でき、黒鉛化度が熱処理によって向上したことは明らかである。その格子縞はファイバー軸にほぼ直行しており、プレートレット構造であることが明瞭である。さらにpCNF2400においてはファイバー側面にグラフェン数層からなるループが見られる。これは、2800℃で処理したpCNFの構造と類似しており、今回2400℃での処理によって耐久性が高いと予想されるpCNFのループ構造の構築に成功したといえる。また、pCNF1500でもファイバー側面にループ形成が起こり始めている様子もみられる（エッジ面の約50％）。一方，pCNF1100ではループ構造は見られない。pCNF2400のファイバー側面のループ構造の割合はほぼ１００%であった。 The formation of the loop structure can be confirmed by TEM observation. Shown in FIG. 5 is a TEM image of each carbon material. A TEM sample was prepared by ultrasonically dispersing about 100 μg of each sample in ethanol and dropping it on a carbon-coated Cu grid for TEM observation. This was observed using a field emission type transmission electron microscope with an accelerating voltage of 200 kV. The presence or absence of the loop structure can be confirmed at a magnification of 300,000 or more. In the sample immediately after firing at 600 ° C. (FIG. 5 (a)), no plaid is found in the sample, and it is guessed from TEM that the degree of graphitization is low. On the other hand, crystal stripes can be clearly seen in pCNF1100 (FIG. 5 (b)), pCNF 1500 (FIG. 5 (c)) and pCNF 2400 (FIG. 5 (d)), and it is clear that the degree of graphitization is improved by heat treatment . The checkerboard is almost perpendicular to the fiber axis and it is clear that it is a platelet structure. Furthermore, in pCNF2400, a loop consisting of several graphene layers can be seen on the side of the fiber. This is similar to the structure of pCNF treated at 2800 ° C., and it can be said that the treatment at 2400 ° C. succeeded in constructing the loop structure of pCNF expected to have high durability. In addition, it is also seen that loop formation is beginning to occur on the side of the fiber also in pCNF1500 (about 50% of the edge surface). On the other hand, no loop structure is found in pCNF1100. The percentage of loop structure on the fiber side of pCNF2400 was almost 100%.
・耐酸化性
　図6に示すのは、pCNF1100、pCNF1500及びpCNF2400、並びにアセチレンブラック(AB)を大気中で1000℃まで昇温加熱した際の重量変化である（昇温速度:10℃/min）。pCNFとABとを比べると、ABでは200℃付近から重量減少が始まり、酸化分解が生じているのに対し、pCNFでは600℃付近までほぼ重量の変化がないことから、pCNFは高い耐酸化性を有することがわかる。但し、pCNF1100は、500℃付近から重量減少が始まるのに対して、pCNF1500の重量減少開始温度は600℃付近であり、pCNF2400の重量減少開始温度は600℃を超えている。pCNF1500及びpCNF2400は、pCNF1100よりもさらに100 K程度質量減少の始まる温度が高くなっており、一層耐酸化性が高いことがわかる。したがって、高温熱処理したpCNF(lpe-pCNF)であるpCNF1500及びpCNF2400は、大気中加熱下での耐酸化性に優れていることが分かる。 Oxidation resistance The weight change of pCNF1100, pCNF1500 and pCNF2400, and acetylene black (AB) when heated to 1000 ° C. in the atmosphere is shown in FIG. 6 (heating rate: 10 ° C./min). . When pCNF and AB are compared, weight loss starts at around 200 ° C in AB and oxidative degradation occurs, while pCNF has almost no weight change up to around 600 ° C, so pCNF has high oxidation resistance It can be seen that However, while the weight loss of pCNF1100 starts at around 500 ° C., the weight loss start temperature of pCNF1500 is around 600 ° C., and the weight loss start temperature of pCNF2400 exceeds 600 ° C. pCNF1500 and pCNF2400 have a higher temperature at which the mass loss starts about 100 K higher than that of pCNF1100, indicating that the oxidation resistance is higher. Therefore, it can be seen that pCNF1500 and pCNF2400, which are pCNF (lpe-pCNF) subjected to high-temperature heat treatment, are excellent in oxidation resistance under atmospheric heating.
実施例１
・電極耐久性試験（１）
1)電極作製方法
　OER高活性触媒であるCa2FeCoO5（CFCO）50 mgと炭素導電助剤（参考例１でそれぞれ合成したpCNF1100、pCNF1500、若しくはpCNF2400又はAB）10 mg、5% Nafion(R)分散溶液0.2 mLをエタノール4.8 mL中に分散させ、触媒インクとした。この触媒インクをグラッシーカーボン電極（φ = 5 mm、以下GC）上に20μL塗布したもの（触媒密度 = 1.0 mg cm-3）を電極活性評価に、カーボンシート上に20μL塗布したもの（触媒密度 = 0.1 mg cm-3）を電極耐久性評価に供した。電気化学測定は、4 mol/L KOH aq 中、酸素飽和雰囲気下で実施した。なお、使用したABはStern Chemical製（CAS#1333-86-4、純度99.99％）で、使用前に濃硝酸中80℃で12時間撹拌する酸処理を行った。なお、1500℃以上で熱処理したpCNFは乳鉢を用いた機械的粉砕と超音波分散を用い1μm以下のサイズに調整した。 Example 1
・ Electrode durability test (1)
1) Method of electrode preparation: 50 mg of Ca 2 FeCoO 5 (CFCO) which is an OER highly active catalyst and 10 mg of a carbon conductive aid (pCNF 1100, pCNF 1500 or pCNF 2400 or AB synthesized in Reference Example 1), 5% Nafion (R 2.) 0.2 mL of the dispersion solution was dispersed in 4.8 mL of ethanol as a catalyst ink. What applied 20 μL of this catalyst ink on a glassy carbon electrode (φ = 5 mm, GC below) (catalyst density = 1.0 mg cm -3 ) was applied 20 μL on a carbon sheet for electrode activity evaluation (catalyst density = 0.1 mg cm -3 was used for electrode durability evaluation. Electrochemical measurements were performed in an oxygen saturated atmosphere in 4 mol / L KOH aq. The AB used was Stern Chemical (CAS # 1333-86-4, purity 99.99%), and was acid-treated in concentrated nitric acid at 80 ° C. for 12 hours before use. In addition, pCNF heat-treated at 1500 ° C. or more was adjusted to a size of 1 μm or less using mechanical pulverization and ultrasonic dispersion using a mortar.
2)図7に、電極活性評価結果を示す。グラッシーカーボン電極上に触媒層を形成し電極としたものを4 moldm-3 KOH水溶液中、1.1 Vから1.7 Vまで掃引速度1 mV s-1でアノード分極したときの電流・電位曲線であり、いずれの試料も同じように1.47 Vで電流が立ち上がり、酸素発生が始まる。したがって、酸素発生の開始電位は炭素の種類に依存しない。さらに電位をアノード側に掃引すると、電流が増大する。AB試料、pCNF1500、pCNF2400試料は1.7 Vで100 mA cm-2以上の十分な電流が得られるが、pCNF1100は明らかに1.7 Vでの電流が小さく、他の試料との電流の差も1.52 Vからみられる。これは熱処理温度が低いために黒鉛化があまり進行しておらず、pCNF1100試料の導電性が不十分なためである。 2) FIG. 7 shows the evaluation results of electrode activity. It is a current-potential curve when anodic polarization is performed with a sweep rate of 1 mV s -1 from 1.1 V to 1.7 V in a 4 moldm -3 KOH aqueous solution in which a catalyst layer is formed on a glassy carbon electrode and used as an electrode. In the same way, the current rises at 1.47 V and oxygen generation starts. Thus, the onset potential of oxygen evolution does not depend on the type of carbon. Further sweeping the potential to the anode side increases the current. The AB, pCNF1500, and pCNF2400 samples have sufficient current of 100 mA cm -2 or more at 1.7 V, but pCNF1100 has a small current at 1.7 V and the difference in current with other samples is also 1.52 V Be This is because graphitization does not progress so much because the heat treatment temperature is low, and the conductivity of the pCNF1100 sample is insufficient.
3)電極耐久性
　図8に、カーボンシート上に触媒層を形成し電極としたものを+1.7 Vで20 h分極したさいの電流変化を示す。このように高い酸化電位に保持すると、AB試料は炭素の酸化消耗のため大きな電流降下がみられる。また、pCNF1100もAB試料と同様の電流降下がみられた。一方、TG試験において高い耐酸化性を示したpCNF1500及びpCNF2400を用いた場合、電流降下量が AB 及びpCNF1100に比べ非常に小さく、pCNF1500及びpCNF2400は電極とした場合にも酸化しにくいことが示唆される。 3) Electrode Durability FIG. 8 shows a change in current when a catalyst layer is formed on a carbon sheet to form an electrode and polarized at +1.7 V for 20 h. When held at such a high oxidation potential, AB samples show a large current drop due to the oxidative consumption of carbon. In addition, pCNF1100 also showed a current drop similar to that of the AB sample. On the other hand, when using pCNF1500 and pCNF2400, which showed high oxidation resistance in the TG test, the current drop is very small compared to AB and pCNF1100, suggesting that pCNF1500 and pCNF2400 are difficult to oxidize even when used as an electrode. Ru.
　実際に炭素の消耗を確認するために、SEMにより分極前後の電極状態を評価した。ABを用いた場合（図9）には、電極の形態が大きく変化しているのが明瞭であり、炭素材料ABが酸化消耗によって径が小さくなったり、消失したためと考えられる。また、炭素材料が消耗したためにNafion(R)の露出も一部起こっている。一方、pCNF2400を用いた場合（図10）には、その径・形状がほぼ変化しておらず、かつにNafion(R)の露出も少ないことから、分極による酸化消耗がほとんど起こっていないといえる。pCNF1500も図11に示すようにファイバー径に明瞭な変化はなく、酸化消耗耐性は高いと考えられる。なお、これは図8の電流変化がpCNF1500とpCNF2400が大きく違わないこととも一致している。したがって、高温熱処理したpCNFであるlpe-pCNFからなる本発明の導電助剤は、OER環境下で高い耐酸化性を有する炭素導電助剤といえる。 In order to actually confirm the consumption of carbon, the electrode states before and after polarization were evaluated by SEM. In the case of using AB (FIG. 9), it is clear that the form of the electrode is largely changed, and it is considered that the carbon material AB is reduced in diameter due to oxidative consumption or is lost. In addition, exposure to Nafion (R) has also occurred partly due to exhaustion of the carbon material. On the other hand, when pCNF2400 is used (FIG. 10), the diameter and shape are almost unchanged, and the exposure of Nafion (R) is also small, so it can be said that oxidation consumption due to polarization hardly occurs. . As shown in FIG. 11, pCNF1500 also has no clear change in fiber diameter, and is considered to be highly resistant to oxidative consumption. This is also consistent with the fact that the change in current in FIG. 8 does not greatly differ between pCNF1500 and pCNF2400. Therefore, the conductive aid of the present invention consisting of lpe-pCNF which is pCNF heat treated at high temperature can be said to be a carbon conductive aid having high oxidation resistance under the OER environment.
　pCNF2400のみならずpCNF1500も優れた酸化耐性を示すのは、図5(c)に示すようにファイバー側面でループが形成されていることに基因すると思われる。ループエッジ構造を有さないpCNF1100（図5(b)）をCFCOと混和し作製した電極を同様の試験に供したところ、AB の場合同様に、電極の形態が大きく変化していた。これは、炭素材料の酸化消耗に起因すると考えられ、実際にファイバー径も一部で小さくなっていたことを確認している（図12）。 The excellent oxidation resistance of not only pCNF2400 but also pCNF1500 appears to be due to the formation of loops on the side of the fiber as shown in FIG. 5 (c). An electrode prepared by mixing pCNF1100 having no loop edge structure (FIG. 5 (b)) with CFCO was subjected to the same test. As in the case of AB.sub.2, the form of the electrode was largely changed. This is considered to be attributable to the oxidative consumption of the carbon material, and it has been confirmed that the fiber diameter is actually partially reduced (FIG. 12).
実施例２
・電極耐久性試験（２）
1)実施例１の1)電極作製方法に記載の方法と同様の方法により、炭素導電助剤としてpCNF2400又はABを用いたカーボンシート電極(CFCO/pCNF2400電極、CFCO/AB電極)を作製した。 Example 2
・ Electrode durability test (2)
1) A carbon sheet electrode (CFCO / pCNF2400 electrode, CFCO / AB electrode) using pCNF2400 or AB as a carbon conductive aid was produced by the method similar to the method described in 1) Electrode production method of Example 1.
2) １ヶ月OER耐久試験
1)で調製したpCNF2400 又はABを用いたカーボンシート電極を用いて１ヶ月OER耐久試験を、Hg/HgO/4 mol dm-3 KOH を参照電極，白金板を対極とする三電極系にて， 4 mol dm-3 KOH水溶液中，アルゴン不活性雰囲気下で行った。まず40 mA cm-2の一定酸化電流条件で2時間OER分極を行い、続いて0電流条件で15分静置した。以上の2つのステップを交互に１ヶ月繰り返した。電解前と１ヶ月電解後のCFCO/pCNF2400電極およびCFCO/AB電極のOER電流－電位曲線を図13に示す。図13の結果は、CFCO/pCNF2400電極のOER電流－電位曲線は電解前後でほとんど変化がないことを示す。CFCO/AB電極のOER電流－電位曲線は電解前に比べて電解後は、高電圧側にシフトし、抵抗が増大した。尚、CFCO/pCNF2400電極のOER電流－電位曲線における電流の立ち上がりの電位は、CFCO/AB電極のOER電流－電位曲線における電流の立ち上がりの電位とほぼ同様であり、かつ１ヶ月経過後でも変化は無かった。 2) 1 month OER endurance test
One month OER endurance test using carbon sheet electrode using pCNF2400 or AB prepared in 1), Hg / HgO / 4 mol dm -3 KOH as a reference electrode and platinum plate as a counter electrode, It was carried out in a 4 mol dm -3 KOH aqueous solution under an inert atmosphere of argon. First, OER polarization was performed for 2 hours under a constant oxidation current condition of 40 mA cm −2 , followed by standing for 15 minutes under 0 current condition. The above two steps were alternately repeated for one month. The OER current-potential curves of the CFCO / pCNF2400 electrode and the CFCO / AB electrode before and after one month of electrolysis are shown in FIG. The results in FIG. 13 indicate that the OER current-potential curve of the CFCO / pCNF2400 electrode shows almost no change before and after electrolysis. The OER current-potential curve of the CFCO / AB electrode shifted to the high voltage side after electrolysis compared to before the electrolysis, and the resistance increased. The rising potential of the current in the OER current-potential curve of the CFCO / pCNF2400 electrode is almost the same as the rising potential of the current in the OER current-potential curve of the CFCO / AB electrode, and changes even after 1 month has passed It was not.
耐久性試験開始前、3日後および１ヶ月後の電極のSEM写真を図14に示す。CFCO/AB電極の場合、3日のOER試験により、AB粒子がほぼ焼失し、CFCO粒子間にNafion膜が露出した状態になっている。一方、CFCO/pCNF2400電極の場合、3日後及び１ヶ月後でもファイバー形状に変化は見られなかった。 SEM photographs of the electrode before, 3 days and 1 month after the start of the durability test are shown in FIG. In the case of the CFCO / AB electrode, according to the 3-day OER test, the AB particles are almost burned out, and the Nafion film is exposed between the CFCO particles. On the other hand, in the case of the CFCO / pCNF2400 electrode, no change in the fiber shape was observed even after 3 days and 1 month.
　以上より、pCNFを用い、これを1100℃超の高温熱処理することで、金属空気電池空気極に適した高耐久性を有する炭素導電助剤を得ることができた。この高い耐久性は、熱処理によるループ形成により、酸化消耗優先サイトと考えられるグラフェンエッジを消滅させるという、炭素担体の微細構造制御によりもたらされたものである。 From the above, it was possible to obtain a carbon conductive aid having high durability suitable for a metal-air battery air electrode by heat treating it at high temperature of over 1100 ° C. using pCNF. This high durability is brought about by the fine structure control of the carbon support in which the graphene edge which is considered to be the oxidation consumption priority site is annihilated by the loop formation by the heat treatment.
　本発明は、炭素導電助剤及びこれを用いる分野において有用である。 The present invention is useful in the field of carbon conductive aids and the use thereof.

Claims (9)

  1. 炭素六角網面のプレートレット構造を有するカーボンナノファイバー（以下、ｐＣＮＦと略記する）であって、
    ファイバーの側面に露出した炭素六角網面のエッジの少なくとも一部が、近接する炭素六角網面のエッジとの間でのループ構造を有する、ｐＣＮＦ（ｌｐｅ－ｐＣＮＦと略記する）を含む酸素発生電極用導電助剤。     A carbon nanofiber (hereinafter abbreviated as pCNF) having a platelet structure of a carbon hexagonal network surface,
    An oxygen generating electrode comprising pCNF (abbreviated as lpe-pCNF), wherein at least a part of the edge of the exposed carbon hexagonal surface on the side of the fiber has a loop structure between the edge of the adjacent carbon hexagonal surface. Conductive aids.
  2. ｌｐｅ－ｐＣＮＦは、ラマンスペクトルにおけるＧバンド（１５８０ｃｍ-1付近）の強度がＤバンド（１３８０ｃｍ-1付近）の強度より強い、請求項１に記載の導電助剤。 The conductive aid according to claim 1, wherein lpe-pCNF has an intensity of G band (near 1580 cm -1 ) in the Raman spectrum higher than that of D band (near 1380 cm -1 ).
  3. ループ構造が、複数の積層炭素六角網面のエッジと、近接する複数の積層炭素六角網面のエッジとの間でのループ構造である、請求項１又は２に記載の導電助剤。 The conductive support agent according to claim 1 or 2, wherein the loop structure is a loop structure between an edge of the plurality of laminated carbon hexagonal network faces and an edge of the adjacent plurality of laminated carbon hexagonal network faces.
  4. ｌｐｅ－ｐＣＮＦは、大気中での昇温試験における重量減少開始温度が５００℃以上又は６００℃以上である、請求項１～３のいずれかに記載の導電助剤。 The conductive aid according to any one of claims 1 to 3, wherein lpe-pCNF has a weight loss start temperature in a temperature rising test in the atmosphere of 500 ° C or more or 600 ° C or more.
  5. 酸素発生電極が可逆空気電極である請求項１～４のいずれかに記載の導電助剤。 The conductive aid according to any one of claims 1 to 4, wherein the oxygen generating electrode is a reversible air electrode.
  6. 請求項１～５のいずれかに記載の導電助剤、ＯＥＲ触媒及び有機溶媒を含有し、さらにＯＲＲ触媒を含有することができる、酸素発生電極作製用インク。 An ink for producing an oxygen generating electrode, comprising the conductive auxiliary according to any one of claims 1 to 5, an OER catalyst and an organic solvent, and further containing an ORR catalyst.
  7. 請求項１～５のいずれかに記載の導電助剤、ＯＲＲ触媒及びＯＥＲ触媒を含有する可逆空気電極。 A reversible air electrode comprising the conductivity assistant according to any one of claims 1 to 5, an ORR catalyst and an OER catalyst.
  8. 亜鉛空気電池用の酸素電極である、請求項７に記載の可逆空気電極。 The reversible air electrode according to claim 7, which is an oxygen electrode for a zinc-air battery.
  9. 請求項８に記載の可逆空気電極を含む亜鉛空気電池。 A zinc-air battery comprising the reversible air electrode according to claim 8.
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CN113646953A (en) * 2019-04-01 2021-11-12 昭和电工材料株式会社 Catalyst for air electrode, and metal-air secondary battery

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JP2006240958A (en) * 2005-03-07 2006-09-14 Kyushu Univ Ultrahigh graphitization degree carbon nanofiber having many carbon hexagonal edge faces on surface and its manufacturing method
JP2014519152A (en) * 2011-05-16 2014-08-07 フィナジー リミテッド Zinc air storage battery

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JP2006240958A (en) * 2005-03-07 2006-09-14 Kyushu Univ Ultrahigh graphitization degree carbon nanofiber having many carbon hexagonal edge faces on surface and its manufacturing method
JP2014519152A (en) * 2011-05-16 2014-08-07 フィナジー リミテッド Zinc air storage battery

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Publication number Priority date Publication date Assignee Title
CN113646953A (en) * 2019-04-01 2021-11-12 昭和电工材料株式会社 Catalyst for air electrode, and metal-air secondary battery

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