JP2006008472A - Nano-structured graphite, its composite material, conductive material and catalyst material using them - Google Patents
Nano-structured graphite, its composite material, conductive material and catalyst material using them Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 169
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 138
- 239000010439 graphite Substances 0.000 title claims abstract description 138
- 239000003054 catalyst Substances 0.000 title claims abstract description 47
- 239000004020 conductor Substances 0.000 title claims abstract description 23
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- 150000004706 metal oxides Chemical class 0.000 claims description 15
- 229910052697 platinum Inorganic materials 0.000 claims description 10
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- 229910052782 aluminium Inorganic materials 0.000 claims description 5
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- 229910052758 niobium Inorganic materials 0.000 claims description 5
- 229910052763 palladium Inorganic materials 0.000 claims description 5
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- KQNVWRXGMSYLDH-UHFFFAOYSA-N 2-methyl-3-propyl-1h-imidazol-3-ium;iodide Chemical compound [I-].CCC[N+]=1C=CNC=1C KQNVWRXGMSYLDH-UHFFFAOYSA-N 0.000 description 1
- UUIMDJFBHNDZOW-UHFFFAOYSA-N 2-tert-butylpyridine Chemical compound CC(C)(C)C1=CC=CC=N1 UUIMDJFBHNDZOW-UHFFFAOYSA-N 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
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- 229910052741 iridium Inorganic materials 0.000 description 1
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- 238000004898 kneading Methods 0.000 description 1
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- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- HLBBKKJFGFRGMU-UHFFFAOYSA-M sodium formate Chemical compound [Na+].[O-]C=O HLBBKKJFGFRGMU-UHFFFAOYSA-M 0.000 description 1
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Classifications
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- 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
Abstract
Description
この発明は、導電材料や触媒材料などに広く利用できるナノ構造化した黒鉛、その複合材料並びにこれらを用いた導電材料及び触媒材料に関する。 The present invention relates to nanostructured graphite that can be widely used for conductive materials, catalyst materials, and the like, composite materials thereof, and conductive materials and catalyst materials using these.
現在、炭素材料は、エネルギー分野、電子・情報・通信分野、機械・航空・宇宙分野、光学分野、化学・環境分野、医療・福祉分野など広範囲に使用されている。しかしながら、炭素材料の機能性を発現させるためには、結晶構造の制御、高比表面積化、一次粒子の凝集状態の制御、細孔構造の制御などが必要であり、更に、それらの炭素材料への金属元素の坦持や複合化が高機能性を発現するための有効な手段となるにもかかわらず充分に研究されていないのが現状であり、係る分野の開発が望まれていた。具体的には、炭素材料の現状は以下のとおりである。 Currently, carbon materials are used in a wide range of fields such as energy, electronics / information / communication, machinery / aviation / space, optics, chemistry / environment, and medical / welfare. However, in order to develop the functionality of carbon materials, it is necessary to control the crystal structure, increase the specific surface area, control the aggregation state of the primary particles, control the pore structure, etc. In spite of the fact that the loading and complexing of these metal elements are effective means for expressing high functionality, they have not been fully studied, and the development of such a field has been desired. Specifically, the current status of carbon materials is as follows.
前記炭素材料の中で導電材料に用いられる炭素材料としては、カーボンブラック、黒鉛、カーボンファイバー、カーボンナノチューブなどがある。従来の導電材料であるカーボンブラックは、（１１０）面の結晶子の大きさＬaが１.７ｎｍ程度、（００２）面の結晶子の大きさＬcが１.２ｎｍ程度の結晶子よりなり、これらの結晶子は、炭素網平面が、概ね３〜４層積層したものからなり、その層面間距離は０.３４〜０.３６ｎｍである。また、導電性に優れるカーボンブラックは小さな結晶子が凝集し、更にストラクチャー構造を作っているのが一般的である。 Among the carbon materials, carbon materials used as conductive materials include carbon black, graphite, carbon fiber, and carbon nanotube. Carbon black, which is a conventional conductive material, consists of crystallites having a crystallite size La of (110) plane of about 1.7 nm and a crystallite size Lc of (002) plane of about 1.2 nm. The crystallites are composed of approximately 3 to 4 layers of carbon network planes, and the distance between the layer surfaces is 0.34 to 0.36 nm. In addition, carbon black, which is excellent in electrical conductivity, generally has small crystallites aggregated to form a structure structure.
カーボンブラックの導電機構には次の二説がある。一つはカーボンブラック粒子の連鎖（カーボン・ストラクチャー）が互いに接触し、その連鎖をπ電子が伝わって流れる導電通路説である。もう一つは、カーボンブラック粒子間のギャップ間距離が１０ｎｍ程度の間隔に縮まるとπ電子がジャンプして導電性を示すトンネル効果説である。 There are the following two the conduction mechanisms of carbon black. One is a conductive path theory in which a chain of carbon black particles (carbon structure) contacts each other and π electrons flow through the chain. The other is a tunnel effect theory in which π-electrons jump and exhibit conductivity when the gap distance between carbon black particles is reduced to an interval of about 10 nm.
黒鉛としては一般に粒子径３〜２０μm程度のものが導電材料として用いられており、結晶性の発達したリン状またはリン片状の黒鉛は電気抵抗値が低い。結晶性の高いリン状またはリン片状の黒鉛はＬcが１００ｎｍ以上に発達し、ａ軸方向での体積固有抵抗値は１０−３Ω・ｃｍと非常に低い。しかし、ｃ軸方向の抵抗はその1０００倍程度に達するため、塗膜中の接触抵抗を低減するには、一般的にカーボンブラックと併用される。 In general, graphite having a particle diameter of about 3 to 20 μm is used as a conductive material, and phosphorus-like or flake-like graphite having developed crystallinity has a low electric resistance value. Phosphorous or scaly graphite with high crystallinity develops Lc to 100 nm or more, and its volume resistivity value in the a-axis direction is as low as 10 −3 Ω · cm. However, since the resistance in the c-axis direction reaches about 1,000 times, it is generally used together with carbon black in order to reduce the contact resistance in the coating film.
また、カーボンファイバーやカーボンナノチューブは、長さ方向に結晶が発達しているため電気伝導性が良く、樹脂に練り込んで導電性樹脂としての検討が進められている。具体的には、導電性が１０−４〜１０−５Ω・ｃｍと高く、生成法によっては金属導電性のレベルまで期待できること、アスペクト比（Ｌ／Ｄ）が１００〜１０００と大きく塗膜中で導電回路を形成できるなど従来のカーボン系導電性フィラーと比べきわめて高い優位性が認められる。しかしながら、炭素材料の高機能性を発現するには充分なものとは言えない。 In addition, carbon fibers and carbon nanotubes have good electrical conductivity because crystals are developed in the length direction, and studies are being conducted as conductive resins by kneading them into resins. Specifically, the conductivity is as high as 10 −4 to 10 −5 Ω · cm, and depending on the production method, it can be expected to a level of metal conductivity, and the aspect ratio (L / D) is as large as 100 to 1000 in the coating film. It is recognized that it has an extremely superior advantage over conventional carbon-based conductive fillers, such as being capable of forming a conductive circuit. However, it cannot be said that it is sufficient for expressing the high functionality of the carbon material.
炭素材料は、坦持触媒の担体としても用いられる。触媒適用例としては、活性炭、カーボンブラックに代表される素材料に白金（Ｐｔ）等を担持させたＰｔ坦持触媒がある。例えば、キャボット社製のカーボンブラックであるバルカン（ＶａＬｃａｎ）Ｘ−７２は、粒子径が２９ｎｍ、比表面積が１８０ｍ２／ｇで、導電性に優れるものであり、Ｐｔ坦持用触媒の坦体としても用いられている。Ｐｔ坦持触媒は粒子径の小さいＰｔをカーボンブラックに坦持させたものであり、またカーボンブラック上でＰｔが凝集を起こさないことが必要である。このためには担体となる炭素材の構造が重要となる。また、Pｔ坦持用触媒の坦体として使用する場合には、Ｐｔをいかに小さく炭素材表面に分散・坦持させるかが重要であり、特殊な構造をもつ炭素材料が必要になる。 The carbon material is also used as a support for the supported catalyst. Examples of catalyst applications include Pt-supported catalysts in which platinum (Pt) or the like is supported on a raw material typified by activated carbon or carbon black. For example, Cabot's carbon black, VaLcan X-72, has a particle diameter of 29 nm, a specific surface area of 180 m 2 / g, and is excellent in conductivity, and is used as a carrier for a Pt-supporting catalyst. Are also used. The Pt-supported catalyst is obtained by supporting Pt having a small particle diameter on carbon black, and it is necessary that Pt does not aggregate on the carbon black. For this purpose, the structure of the carbon material used as a carrier is important. Further, when used as a carrier for a Pt-supporting catalyst, it is important how small Pt is dispersed and supported on the surface of the carbon material, and a carbon material having a special structure is required.
また、電池における炭素系材料は、電解液と接する部分で導電材として用いられることが多い。電池中での導電性向上に当たっては、炭素材料と電解液が接した状態で、炭素中のπ電子が電解液中をスムーズに移動する必要があり、そのためには、π電子が移動し易い塗膜構造や、電解液を包含できる炭素材料の細孔構造、また金属と炭素材料との複合体が必要になる。 In addition, the carbon-based material in the battery is often used as a conductive material in a portion in contact with the electrolytic solution. In order to improve conductivity in a battery, it is necessary for π electrons in carbon to move smoothly in the electrolyte solution while the carbon material and the electrolyte solution are in contact with each other. A membrane structure, a pore structure of a carbon material that can contain an electrolytic solution, and a composite of a metal and a carbon material are required.
以上のように、電池内で使用される炭素系材料においては、目的とする導電性を確保するにはπ電子の移動性が充分でなく発電効率が低い点、更に、炭素系材料上でＰｔ等触媒が凝集を起こし易く、比表面積が減少し、それに伴って触媒能力が低下する点などが問題である。 As described above, in the carbon-based material used in the battery, the π-electron mobility is not sufficient to secure the target conductivity, and the power generation efficiency is low. The problem is that the catalyst is likely to agglomerate, the specific surface area is reduced, and the catalyst capacity is reduced accordingly.
なお、従来技術の一例として、触媒担体に用いられる炭素材料について以下に例を挙げる。一般的に、触媒担体として用いられる炭素材料としては、カーボンブラック以外に、カーボンナノホーン、カーボンナノチューブなどがある。
たとえば特許文献１には、固体高分子電解質型燃料電池のような電気化学的装置に用いられる電極における反応ガスの触媒への拡散性を向上させる細孔構造を有し触媒用担体として使用可能なカーボンブラックが提案されている。電極触媒の担体として使用可能なカーボンブラック、並びに該担体を用いた電極触媒および電気化学的装置について開示されている。使用されるカーボンブラックは、ＤＢＰ吸油量が170〜300ｃｍ3／100ｇ、ＢＥＴ法による比表面積が250〜400ｍ2／ｇ、一次粒子径が10〜17ｎｍ、かつ、表面に開口している半径が10〜30ｎｍである細孔の合計容積が0.40〜2.0ｃｍ3／ｇである。
また、特許文献２には、単層カーボンナノフォーン（ＳＷＮＨｓ）の構造を基本とし、活性化処理が不要で、吸着容量の極めて大きな単層カーボンナノホーンの吸着材と、単層カーボンナノホーンの触媒および触媒担体が提案されている。そして、単層カーボンナノホーンが球状に集合してなる単層カーボンナノホーン集合体であって、近接する単層カーボンナノホーンの円錐部により形成される空間に有機物を吸着する単層カーボンナノホーン吸着材や、単層カーボンナノホーンを液相反応における酸化触媒としする単層カーボンナノホーン触媒、および単層カーボンナノホーンの表面に金属触媒を担持させる単層カーボンナノホーン触媒担体とする。
また、特許文献３には、中空の炭素材料の細孔内に貴金属を導入し、前記貴金属が導入された炭素材料を酸化物担体に固定した後、焼成することを特徴とする貴金属触媒の製造方法であって、好ましくは、前記炭素材料がカーボンナノチューブ又はカーボンナノホーンであり、前記貴金属が、白金、ロジウム、パラジウム、金、及びイリジウムから選択された少なくとも１種であることが開示されている。
As an example of the prior art, examples of carbon materials used for the catalyst carrier will be given below. In general, carbon materials used as a catalyst carrier include carbon nanohorns and carbon nanotubes in addition to carbon black.
For example, Patent Document 1 discloses a pore structure that improves the diffusibility of a reaction gas to a catalyst in an electrode used in an electrochemical device such as a solid polymer electrolyte fuel cell, and can be used as a catalyst carrier. Carbon black has been proposed. Carbon black that can be used as an electrode catalyst carrier, and an electrode catalyst and an electrochemical device using the carrier are disclosed. The carbon black used has a DBP oil absorption of 170 to 300 cm 3/100 g, a specific surface area by BET method of 250 to 400 m 2 / g, a primary particle size of 10 to 17 nm, and a radius opening on the surface of 10 to 30 nm. The total volume of the pores is 0.40 to 2.0 cm 3 / g.
Patent Document 2 discloses a structure of single-walled carbon nanophones (SWNHs), which does not require an activation process, and has a very large adsorption capacity for a single-walled carbon nanohorn, a catalyst for the single-walled carbon nanohorn, A catalyst support has been proposed. And a single-walled carbon nanohorn assembly formed by spherically assembling single-walled carbon nanohorns, and a single-walled carbon nanohorn adsorbent that adsorbs organic matter in the space formed by the conical portion of the adjacent single-walled carbon nanohorn, A single-walled carbon nanohorn catalyst that uses the single-walled carbon nanohorn as an oxidation catalyst in a liquid phase reaction, and a single-walled carbon nanohorn catalyst carrier that supports a metal catalyst on the surface of the single-walled carbon nanohorn.
Patent Document 3 discloses the production of a noble metal catalyst characterized by introducing a noble metal into pores of a hollow carbon material, fixing the carbon material into which the noble metal has been introduced to an oxide support, and then firing it. Preferably, the carbon material is a carbon nanotube or a carbon nanohorn, and the noble metal is at least one selected from platinum, rhodium, palladium, gold, and iridium.
本発明は、電池内で導電材料として使用した場合、炭素材料中および炭素材料から電解液への電子の移動性を向上し、Ｐｔ等金属坦持触媒への適用においては、金属の担持粒子径を小さくして比表面積を増加することによって触媒能力を向上し、特徴のあるナノ構造化黒鉛、その複合材料、これらを用いた導電材料及び触媒材料を提供することを目的としたものである。 The present invention improves the mobility of electrons in the carbon material and from the carbon material to the electrolyte when used as a conductive material in a battery. The object is to provide a characteristic nanostructured graphite, a composite material thereof, a conductive material using the same, and a catalyst material by improving the catalytic capacity by reducing the specific surface area.
前記の課題を解決するために、本発明は、結晶子の大きさが１〜２０ｎｍであるナノ構造化した黒鉛の一次粒子が凝集した黒鉛凝集体からなり、該黒鉛凝集体の平均粒子径が０.５〜５０μｍであることを特徴とするナノ構造化黒鉛とする（請求項１）。 In order to solve the above problems, the present invention comprises a graphite aggregate in which primary particles of nanostructured graphite having a crystallite size of 1 to 20 nm are aggregated, and the average particle diameter of the graphite aggregate is The nanostructured graphite is 0.5 to 50 μm (claim 1).
また、前記の課題を解決するために、本発明は、前記ナノ構造化黒鉛の比表面積が２００〜２０００ｍ２／ｇであり、平均細孔半径０.８〜１５０ｎｍの細孔容積が０.３ｃｍ３／ｇ以上であることを特徴とする前記のナノ構造化黒鉛とすることが好ましい（請求項２）。 In order to solve the above problems, the present invention provides a nanostructured graphite having a specific surface area of 200 to 2000 m 2 / g and an average pore radius of 0.8 to 150 nm and a pore volume of 0.3 cm. The nanostructured graphite is preferably 3 / g or more (claim 2).
また、前記の課題を解決するために、本発明は、前記ナノ構造化黒鉛のラマンバンドの強度比（Ｉ１３６０／Ｉ１５８０）が０.４〜１.７であることを特徴とする前記のナノ構造化黒鉛とすることが好ましい（請求項３）。 In order to solve the above problem, the present invention is characterized in that the Raman band intensity ratio (I 1360 / I 1580 ) of the nanostructured graphite is 0.4 to 1.7. Nanostructured graphite is preferred (Claim 3).
また、前記の課題を解決するために、本発明は、前記の何れかに記載のナノ構造化黒鉛に金属または金属酸化物の何れかを含有、担持または複合化させたことを特徴とするナノ構造化黒鉛の複合材料とすることが好ましい（請求項４）。 In order to solve the above problems, the present invention is directed to a nanostructured graphite according to any one of the above, wherein the nanostructured graphite contains, supports, or is compounded with either a metal or a metal oxide. A composite material of structured graphite is preferred (Claim 4).
また、前記の課題を解決するために、本発明は、前記金属がＦｅ、Ｃｏ、Ｎｉ、Ｒｕ、Ｒｈ、Ｐｄ、Ｏｓ、Ｐｔから選ばれる少なくとも何れか一種の元素である前記のナノ構造化黒鉛の複合材料とすることが好ましい（請求項５）。 In order to solve the above-described problems, the present invention provides the nanostructured graphite, wherein the metal is at least one element selected from Fe, Co, Ni, Ru, Rh, Pd, Os, and Pt. It is preferable to use a composite material of (Claim 5).
また、前記の課題を解決するために、本発明は、前記金属酸化物がＴｉ、Ａｌ、Ｓｉ、Ｚｒ、Ｖ、Ｎｂから選ばれる少なくとも何れか一種の元素からなる金属の酸化物であることを特徴とする前記のナノ構造化黒鉛の複合材料とすることが好ましい（請求項６）。 In order to solve the above problems, the present invention is that the metal oxide is an oxide of a metal composed of at least one element selected from Ti, Al, Si, Zr, V, and Nb. Preferably, the nanostructured graphite composite material is characterized.
また、前記の課題を解決するために、本発明は、前記のナノ構造化黒鉛または前記のナノ構造化黒鉛の複合材料を用いたことを特徴とする導電材料とすることが好ましい（請求項７）。 In order to solve the above problems, the present invention is preferably a conductive material using the nanostructured graphite or the composite material of the nanostructured graphite. ).
また、前記の課題を解決するために、本発明は、前記のナノ構造化黒鉛または前記のナノ構造化黒鉛の複合材料を用いたことを特徴とする触媒材料とすることが好ましい（請求項８）。 In order to solve the above problems, the present invention is preferably a catalyst material characterized by using the nanostructured graphite or the composite material of the nanostructured graphite. ).
本発明のナノ構造化黒鉛、ナノ構造化黒鉛の複合材料、これらを用いた導電材料及び触媒材料は、上記のように、導電材として、電解液への電子の移動が更に改善できることから、ナノ構造化黒鉛の複合材料を色素増感型太陽電池の導電材料として使用した場合、発電効率を向上する効果を発揮する。また、貴金属担持触媒の坦体として用いた場合、担持貴金属の粒子径を小さくして比表面積を増加することによって、触媒活性乃至触媒能力が向上する効果を発揮する。このように貴重な貴金属の使用量を低減し、資源の有効利用と経済的効果に寄与するところは極めて大きなものがある。 The nanostructured graphite of the present invention, the composite material of nanostructured graphite, and the conductive material and the catalyst material using these, as described above, can further improve the transfer of electrons to the electrolytic solution as a conductive material. When a composite material of structured graphite is used as a conductive material for a dye-sensitized solar cell, the effect of improving power generation efficiency is exhibited. Further, when used as a carrier for a noble metal-supported catalyst, the effect of improving the catalytic activity or the catalyst ability is exhibited by reducing the particle size of the supported noble metal and increasing the specific surface area. In this way, the amount of valuable precious metals used is greatly reduced, contributing to effective use of resources and economic effects.
以下、この発明のナノ構造化黒鉛およびナノ構造化黒鉛担持材料について説明する。
この発明に係るナノ構造化黒鉛の第１の特徴は、結晶子の大きさが１〜２０ｎｍであるナノ構造化した黒鉛の一次粒子が凝集した黒鉛凝集体からなり、該黒鉛凝集体の平均粒子径が０.５〜５０μｍである。詳細には、結晶性の良い黒鉛に粉砕処理等を施すことで、結晶子の大きさが１〜２０ｎｍの結晶子が結合した一次粒子が凝集した凝集体の平均粒子径が０.５〜５０μｍの範囲の粒子になることにより、ナノ構造化された黒鉛が形成される。ナノ構造化された黒鉛結晶子間の導電性は、π電子のトンネル効果で良好に保たれ、また黒鉛の結晶性が残っているため結晶子内のπ電子の移動もスムーズである。
Hereinafter, the nanostructured graphite and the nanostructured graphite supporting material of the present invention will be described.
A first feature of the nanostructured graphite according to the present invention is a graphite aggregate in which primary particles of nanostructured graphite having a crystallite size of 1 to 20 nm are aggregated, and the average particle of the graphite aggregate The diameter is 0.5 to 50 μm. Specifically, the average particle size of the aggregate in which primary particles having crystallites with a crystallite size of 1 to 20 nm are aggregated by a pulverization process or the like on graphite having good crystallinity is 0.5 to 50 μm. By becoming particles in this range, nanostructured graphite is formed. The conductivity between the nanostructured graphite crystallites is well maintained by the tunneling effect of π electrons, and the crystallinity of graphite remains, so that the π electrons move smoothly in the crystallites.
これらのナノ構造化された黒鉛は、１〜２０ｎｍの結晶子からなる集合体が、２０〜１００nm程度の球状の一次粒子として強固に結合しているため、ナノ構造化黒鉛の表面の球状な一次粒子間は、数ｎｍ前後の均一な間隙が生じ、Ｐｔを坦持させた場合、ナノ構造化黒鉛の表面に数ｎｍ程度の微粒子となってＰｔが均一に分散して存在できる。この現象はナノ構造化黒鉛の外観、構造に起因するものであり、黒鉛表面へのＰｔの微細な担時が可能になりＰｔ比表面積の向上、Ｐｔ担持量の削減に貢献できる。さらに、Ｐｔはナノ構造化された黒鉛の表面に分散しているため、Ｐｔの表面を有効に活用でき、Ｐｔの回収も容易である。 In these nanostructured graphite, aggregates composed of crystallites of 1 to 20 nm are firmly bonded as spherical primary particles of about 20 to 100 nm, so that the spherical primary on the surface of the nanostructured graphite. A uniform gap of about several nm is generated between the particles, and when Pt is supported, fine particles of about several nm are formed on the surface of the nanostructured graphite, and Pt can be uniformly dispersed. This phenomenon is attributed to the appearance and structure of the nanostructured graphite, which enables fine loading of Pt on the graphite surface and contributes to the improvement of the Pt specific surface area and the reduction of the Pt loading. Further, since Pt is dispersed on the surface of the nanostructured graphite, the surface of Pt can be used effectively, and the recovery of Pt is easy.
この発明に係るナノ構造化黒鉛の第２の特徴は、ナノ構造化黒鉛の比表面積が２００〜２０００ｍ２／ｇであり、平均細孔半径０.８〜１５０ｎｍの細孔容積が０.３ｃｍ３／ｇ以上であることにある。比表面積が２００ｍ２／ｇ〜２０００ｍ２／ｇであり、平均細孔半径が０.８〜１５０ｎｍの細孔容積が０.３ｃｍ３／ｇ以上であることにより、電池用の導電材料として使用する場合、ナノ構造化した結晶子及び凝集体の表面への電解液の濡れ性がよくなるとともに、ナノ構造化した結晶子の凝集体間に電解液が浸透して、この電解液が保持されることも電子移動性の向上に寄与している。 The second feature of the nanostructured graphite according to the present invention is that the specific surface area of the nanostructured graphite is 200 to 2000 m 2 / g, and the pore volume with an average pore radius of 0.8 to 150 nm is 0.3 cm 3. / G or more. Specific surface area of 200m 2 / g~2000m 2 / g, the average pore radius is a pore volume of 0.8~150nm is 0.3 cm 3 / g or more, for use as a conductive material for a battery In this case, the wettability of the electrolyte solution to the surface of the nanostructured crystallites and aggregates is improved, and the electrolyte solution permeates between the nanostructured crystallite aggregates and the electrolyte solution is retained. Contributes to the improvement of electron mobility.
この発明に係るナノ構造化黒鉛の第３の特徴は、ナノ構造化された黒鉛のラマンバンドの強度比（Ｉ１３６０／Ｉ１５８０）が０.４〜１.７とすることにある。レーザーラマン分光分析により得られる結晶性の尺度となるＲ値は、レーザーラマン分光の１５８０ｃｍ−１付近と、１３６０ｃｍ−１付近のラマンバンドの強度比（Ｒ＝Ｉ１３６０／Ｉ１５８０）からの算出値であり、通常、このＲ値を黒鉛結晶構造のパラメーターにしている。例えば、天然黒鉛では１５８０ｃｍ−１付近に炭素網状平面を形成する二次元六方格子に起因する一本のラマンバンドが存在するのに対し、結晶性が低い黒鉛では１５８０〜１６００ｃｍ−１にシフトすると共に、構造欠陥によって六方格子の対称性が低下したか、失われたことに起因する１３５５〜１３６０ｃｍ−１のバンドが現れる。したがって、１３６０ｃｍ−１付近のバンド強度が強いものほど炭素欠陥の構造が多い黒鉛と言える。 The third feature of the nanostructured graphite according to the present invention is that the intensity ratio (I 1360 / I 1580 ) of the Raman band of the nanostructured graphite is 0.4 to 1.7. Laser R value which is a crystalline measure obtained by Raman spectroscopy, and around 1580 cm -1 of the laser Raman spectroscopy, the calculated value from the intensity ratio of the Raman band near 1360cm -1 (R = I 1360 / I 1580) Usually, this R value is used as a parameter of the graphite crystal structure. For example, natural graphite has a single Raman band due to a two-dimensional hexagonal lattice forming a carbon network plane in the vicinity of 1580 cm −1 , while graphite having low crystallinity shifts to 1580 to 1600 cm −1. A band of 1355 to 1360 cm −1 appears due to the symmetry of the hexagonal lattice being reduced or lost due to structural defects. Therefore, it can be said that the stronger the band intensity in the vicinity of 1360 cm −1 , the more the structure of carbon defects.
また、レーザーラマン分光分析は、材料の表層から数１０ｎｍの深さ方向の情報が得られるものであるから、バルクの結晶構造が得られるＸ線回折より求めた結晶子の大きさとは、必ずしも相関関係は無い。例えば、結晶性の高い黒鉛を粉砕したものでも粉体表層から格子欠陥やアモルファス化が進行した場合では、Ｘ線回折で評価する結晶性は高いにもかかわらず、レーザーラマン分光分析で評価すると結晶性が低いことがある。このため、ナノ構造化された黒鉛材料の特定としては両者の解析を同時に行うことが重要である。特に、黒鉛のような層状結晶は、粉砕から生じるクラックや格子欠陥が黒鉛の表層部分から発生し、また、アモルファス化も同時に進行する虞のあるときにはなおさらである。このような点から、本発明者らは、粉砕後また粉砕及び賦活後の黒鉛試料の表面状態を結晶構造的に把握することがナノ構造化された黒鉛材料の調製には有効と判断し、種々の材料を試作して、導電材料、Ｐｔ担時触媒などに適する最適なＲ値を試験的に検証した。即ち、前記試験結果に基づいて、上記の粉砕処理及び賦活処理条件にて得られるナノ構造化黒鉛を、その結晶性の尺度となるＲ値を０.４〜１.７に特定することで、導電性向上やＰｔの微粒子担持材料として最適な構造を備えた炭素材料としたものである。 In addition, since laser Raman spectroscopy can obtain information in the depth direction of several tens of nanometers from the surface layer of a material, it does not necessarily correlate with the crystallite size obtained by X-ray diffraction that can obtain a bulk crystal structure. There is no relationship. For example, in the case of pulverized graphite with high crystallinity, when lattice defects and amorphization progress from the powder surface layer, the crystallinity evaluated by laser Raman spectroscopic analysis is high even though the crystallinity evaluated by X-ray diffraction is high. May be low. For this reason, it is important to analyze both of them simultaneously in order to identify the nanostructured graphite material. In particular, in a layered crystal such as graphite, cracks and lattice defects resulting from pulverization are generated from the surface layer portion of graphite, and amorphization is likely to proceed at the same time. From these points, the present inventors determined that grasping the surface state of the graphite sample after pulverization and after pulverization and activation in terms of crystal structure is effective in preparing a nanostructured graphite material, Various materials were prototyped, and the optimal R value suitable for a conductive material, a catalyst for supporting Pt, and the like was experimentally verified. That is, based on the test results, the nanostructured graphite obtained under the above pulverization treatment and activation treatment conditions is specified by specifying an R value as a measure of crystallinity of 0.4 to 1.7, This is a carbon material having an optimum structure as a material for improving conductivity and supporting fine particles of Pt.
この発明に係るナノ構造化黒鉛の複合材料の特徴は、前記の構造を持つナノ構造化黒鉛に金属または金属酸化物を含有、担持または複合化させたことにある。ここで、含有、坦持または複合化させる金属としては、Ｆｅ、Ｃｏ、Ｎｉ、Ｒｕ、Ｒｈ、Ｐｄ、Ｏｓ、Ｐｔから選ばれる少なくとも何れか一種の元素であることが好ましい。これらを含有することにより、水素分子がプロトンへ解離しやすく、また水素の吸着量も増加することが確認された。また、ＰｔやＲｕを坦持させたものは、燃料電池用電極触媒として使用でき、微粒子で担持が可能なため、Ｐｔ量乃至Ｒｕ量の削減が可能となる。 A feature of the composite material of nanostructured graphite according to the present invention is that the nanostructured graphite having the structure described above contains, supports or composites a metal or a metal oxide. Here, the metal to be contained, supported or complexed is preferably at least one element selected from Fe, Co, Ni, Ru, Rh, Pd, Os, and Pt. By containing these, it was confirmed that hydrogen molecules were easily dissociated into protons, and the amount of hydrogen adsorption was increased. Moreover, what carried Pt and Ru can be used as an electrode catalyst for a fuel cell and can be supported by fine particles, so that the amount of Pt or Ru can be reduced.
また、含有、坦持または複合化させる金属酸化物としては、Ｔｉ、Ａｌ、Ｓｉ、Ｚｒ、Ｖ、Ｎｂから選ばれる少なくとも何れか一種の元素からなる金属の酸化物であることが好ましい。これらは触媒又は導電材料として有用である。複合化させる酸化物は、遷移元素からなるものが特に好ましい。遷移元素は、d軌道またはf軌道が電子で満たされておらず、種々の酸化数をとることのできる元素であり、充填される電子軌道によって、第一遷移元素から第四遷移元素まで分類される。そして、この遷移元素からなる酸化物を色素増感型太陽電池の導電材料として使用する場合、電解液であるヨウ素溶液中で安定であるＴｉ、Ａｌ、Ｓｉ、Ｚｒ、Ｖ、Ｎｂのいずれかの遷移金属を用いた金属酸化物が好ましい。そして、これらの遷移金属からなる金属酸化物は、電池用の導電材料以外に触媒としても有効である。 In addition, the metal oxide to be contained, supported or complexed is preferably a metal oxide composed of at least one element selected from Ti, Al, Si, Zr, V, and Nb. These are useful as catalysts or conductive materials. The oxide to be combined is particularly preferably made of a transition element. Transition elements are elements whose d orbitals or f orbitals are not filled with electrons and can take various oxidation numbers, and are classified from the first transition element to the fourth transition element depending on the electron orbit to be filled. The And when using the oxide which consists of this transition element as a conductive material of a dye-sensitized solar cell, any of Ti, Al, Si, Zr, V, and Nb which are stable in the iodine solution which is electrolyte solution Metal oxides using transition metals are preferred. And the metal oxide which consists of these transition metals is effective also as a catalyst other than the electrically conductive material for batteries.
この発明のナノ構造化黒鉛並びにナノ構造化黒鉛の複合材料は、色素増感型太陽電池の導電材料として特に効果を発揮する。具体的には、ポリエチレンテレフタレート（ＰＥＴ）フィルム上にインジウム錫酸化物（Indium-Tin Oxide、ＩＴＯ）膜を形成した導電性プラスチック集電体（以下「ＩＴＯ−ＰＥＴフィルム」と略称する）を使用した色素増感型太陽電池の場合、発電効率を上げるためにはＩＴＯ膜から電解液であるヨウ素溶液へ電子が抵抗なく移動できることが必要がある。しかしＩＴＯ膜は電子を出す時の抵抗が高く、発電効率を大幅に低下させることがわかっている。本発明のナノ構造化黒鉛をＩＴＯ表面に被覆することで発電効率が１％から３％に向上することが確認できており、さらにナノ構造化黒鉛と金属酸化物の複合化物においてもＩＴＯ膜に被覆することで３％以上の発電効率が得られる。導電性が１０２〜１０４Ω・cmであるにもかかわらず、ＩＴＯ膜からの電子放出に対する抵抗が低減され、ナノ構造化黒鉛の複合化物は電解液へ電子を移動させやすい特性を具備することが分かる。 The nanostructured graphite and the composite material of the nanostructured graphite of the present invention are particularly effective as a conductive material for a dye-sensitized solar cell. Specifically, a conductive plastic current collector (hereinafter abbreviated as “ITO-PET film”) in which an indium tin oxide (ITO) film was formed on a polyethylene terephthalate (PET) film was used. In the case of a dye-sensitized solar cell, in order to increase the power generation efficiency, it is necessary that electrons can move without resistance from the ITO film to the iodine solution that is the electrolytic solution. However, it has been found that the ITO film has a high resistance when emitting electrons and greatly reduces power generation efficiency. It has been confirmed that the power generation efficiency is improved from 1% to 3% by coating the surface of ITO with the nanostructured graphite of the present invention. Further, in the composite of nanostructured graphite and metal oxide, the ITO film is also formed. By coating, power generation efficiency of 3% or more can be obtained. Despite having a conductivity of 10 2 to 10 4 Ω · cm, the resistance to electron emission from the ITO film is reduced, and the composite of nanostructured graphite has the property of easily transferring electrons to the electrolyte. I understand that.
なお、金属または金属酸化物を複合化させる手段としては、例えば、メカニカルミリング（Mechanical milling）による調整手段がある。ナノ構造化された黒鉛の調整方法としては、粉砕工程、粉砕・賦活工程または粉砕・酸化工程のいずれかの工程を経る方法がある。すなわち、結晶性の高い黒鉛を用い、粉砕雰囲気を制御して、材料の細孔や比表面積などを最適形態に調整するものである。まず、ナノ構造化された比表面積の大きい黒鉛系材料の調整方法については、粉砕雰囲気を制御し、最適な粉砕時間を操作することで、機能性が発現できるナノ構造化された黒鉛を調整する。更に比表面積を増大させるため、粉砕処理で黒鉛の結晶子を小さく（２０ｎｍ以下）し、また、黒鉛表面の黒鉛化度を下げた後に賦活処理や酸化処理を施すことで、比表面積の増大や細孔の制御を行うことが好ましい。 In addition, as a means to make a metal or a metal oxide compound, there exists an adjustment means by mechanical milling (Mechanical milling), for example. As a method for adjusting the nanostructured graphite, there is a method of passing through any one of a pulverization step, a pulverization / activation step, or a pulverization / oxidation step. That is, graphite having high crystallinity is used and the pulverizing atmosphere is controlled to adjust the pores, specific surface area, etc. of the material to the optimum form. First, regarding the method of adjusting the nanostructured graphite-based material having a large specific surface area, the nanostructured graphite capable of expressing the functionality is adjusted by controlling the pulverization atmosphere and operating the optimal pulverization time. . In order to further increase the specific surface area, the crystallites of the graphite are reduced (20 nm or less) by the pulverization treatment, and activation treatment or oxidation treatment is performed after the graphitization degree of the graphite surface is lowered, thereby increasing the specific surface area. It is preferable to control the pores.
すなわち、この発明においては、結晶性の高い原料黒鉛を用い、その比表面積を上げ、細孔構造、表面形状を最適化するためには粉砕雰囲気の制御と粉砕時間の最適化が有効である。更に、粉砕処理と賦活処理または粉砕処理・酸化処理を組み合わせることによって、黒鉛の粉砕により生じるアモルファス部分が賦活処理や酸化処理で更に除去されので、より好ましい。 That is, in the present invention, control of the pulverization atmosphere and optimization of the pulverization time are effective for using raw material graphite having high crystallinity, increasing its specific surface area, and optimizing the pore structure and surface shape. Furthermore, by combining the pulverization treatment with the activation treatment or the pulverization treatment / oxidation treatment, the amorphous part generated by the pulverization of graphite is further removed by the activation treatment or the oxidation treatment, which is more preferable.
ここで、原料黒鉛、つまり粉砕前の黒鉛としては結晶性の高いものが望ましく、（１１０）面の結晶子の大きさＬaが２５ｎｍ以上、（００２）面の結晶子の大きさＬcが２０ｎｍ以上のものを用いることが好ましい。これは、粉砕効果として、特に粉砕処理過程での細孔の容積向上が期待でき、粉砕時間も短くできるからである。具体的な原料黒鉛としては、鱗片状黒鉛、鱗状黒鉛、土状黒鉛などの天然黒鉛、コークスなどを焼成して製造する人造黒鉛、メソフェーズピッチを原料として焼成するメソフェーズピッチ系黒鉛など結晶性の発達した黒鉛が好適である。粉砕後の前記結晶子の大きさの最適な範囲は、黒鉛の（１１０）面の結晶子の大きさＬａ及び（００２）面の結晶子の大きさＬcを１ｎｍ以上に収めることが好ましい。これは、結晶性の高い原料黒鉛を粉砕すると、結晶子の大きさが減少し、それに伴い比表面積や細孔容積が増大するものの、前記結晶子の大きさが１ｎｍ以下となるような長時間の粉砕により、ナノ粒子乃至結晶子の縮合等が起こる結果、逆に比表面積や細孔容積が減少することを防止するためである。 Here, it is desirable that the raw material graphite, that is, the graphite before pulverization is highly crystalline, the crystallite size La of the (110) plane is 25 nm or more, and the crystallite size Lc of the (002) plane is 20 nm or more. It is preferable to use those. This is because, as a pulverizing effect, an improvement in the volume of pores can be expected particularly during the pulverization process, and the pulverization time can be shortened. Specific raw material graphites include natural graphite such as flake graphite, scaly graphite and earthy graphite, artificial graphite produced by firing coke, etc., mesophase pitch-based graphite fired using mesophase pitch as a raw material, and the development of crystallinity Graphite is preferred. The optimum range of the crystallite size after pulverization is preferably such that the crystallite size La on the (110) plane and the crystallite size Lc on the (002) plane are 1 nm or more. This is because, when the highly crystalline raw material graphite is pulverized, the size of the crystallites decreases, and the specific surface area and pore volume increase accordingly, but the crystallite size becomes 1 nm or less for a long time. This is to prevent the specific surface area and pore volume from decreasing as a result of the condensation of the nanoparticles or crystallites due to the pulverization.
以上のナノ構造化黒鉛を調整するため、粉砕機としてはボールミル、振動ミル、遊星ボールミル、ジェットミルなどを単独、又は、これらを組み合わせた粉砕態様が好ましい。また、粉砕雰囲気は大気、アルゴン、窒素、水素、真空粉砕などから選択することが好ましい。粉砕機の選定は粉砕後の黒鉛構造を決定するために重要である。ボールミルではボールによる衝撃、圧縮粉砕と摩砕で粉砕が進行する。ジェットミルでは気流による衝撃粉砕と摩砕により粉砕が進行する。振動ボールミルでは、粉砕媒体に挟まれた粒子の衝撃粉砕と摩砕により粉砕が進行する。また、遊星ボールミルでは、ポットの公転と自転により粉体媒体による加速度を与え、圧縮・衝撃破砕と摩砕で粉砕が進行する。特に黒鉛の粉砕では、圧縮・衝撃破砕の他に摩砕効果の大きい遊星ボールミルの適用によって、より速く粉砕を進めることができ、短時間で黒鉛の結晶子を小さくできる。しかし、比表面積が高く、細孔構造の発達した黒鉛を得るためには、粉砕媒体に挟まれた粒子の衝撃粉砕と摩砕で粉砕がおこる振動ボールミルや回転ボールミルなどの方が、結晶性を保ち、比表面積が高く、細孔容積の大きい粉砕物を調製できるので好ましい。以上から、ナノ構造化された黒鉛の黒鉛構造を最適化するには、原料の粒径、粉砕時間、粉砕雰囲気などに応じ、前記粉砕態様の中の何れかを単独又は組み合わせて用いることが好ましい。 In order to adjust the above-mentioned nanostructured graphite, a pulverizing mode in which a ball mill, a vibration mill, a planetary ball mill, a jet mill or the like is used alone or in combination is preferable as a pulverizer. The pulverizing atmosphere is preferably selected from air, argon, nitrogen, hydrogen, vacuum pulverization and the like. The selection of the pulverizer is important for determining the graphite structure after pulverization. In a ball mill, pulverization proceeds by impact with balls, compression pulverization and grinding. In a jet mill, pulverization proceeds by impact pulverization and grinding with an air stream. In the vibration ball mill, pulverization proceeds by impact pulverization and grinding of particles sandwiched between pulverization media. In the planetary ball mill, acceleration by the powder medium is given by the revolution and rotation of the pot, and the pulverization proceeds by compression, impact crushing and grinding. In particular, in the pulverization of graphite, by applying a planetary ball mill having a large grinding effect in addition to compression / impact pulverization, the pulverization can be accelerated more quickly and the crystallites of graphite can be reduced in a short time. However, in order to obtain graphite with a high specific surface area and developed pore structure, the vibration ball mill and the rotating ball mill, which are pulverized by impact pulverization and attrition of particles sandwiched between pulverization media, have better crystallinity. This is preferable because a pulverized product having a large specific surface area and a large pore volume can be prepared. From the above, in order to optimize the graphite structure of the nanostructured graphite, it is preferable to use any one of the above pulverization modes alone or in combination depending on the particle size of the raw material, the pulverization time, the pulverization atmosphere, and the like. .
この発明の実施例について、次に詳細に説明する。試料の調整は以下の通りである。
〈ナノ構造化された黒鉛の調製〉
平均粒径２〜１００μｍの天然黒鉛（鱗片状黒鉛）、メソフェーズピッチ系黒鉛、人造黒鉛を振動ボールミル、回転ボールミルを用いて、２４〜９６時間、真空中で粉砕し、結晶子の大きさ、凝集体の平均粒径等の異なる試料を作製した。（実施例１〜３）
〈Ｐｔ担持法〉
Ｐｔ（白金）化合物として塩化白金酸（Ｈ６ＰｔＣｌ６）を用いた。白金の必要量を溶解した水溶液に試料を入れ、撹拌した。Ｐｔの７倍モル数のＮａＯＨ水溶液で加水分解した後、スラリーに２倍過剰量の蟻酸ナトリウム（ＮａＨＣｏ２）を入れ、７０℃で３時間撹拌し還元処理した。次いで、温水による濾過を十分に行い、乾燥してＰｔ担持触媒を調整した。（実施例１〜３、比較例２，３）
〈金属との複合物及び金属酸化物との複合化物（複合材料）の調整方法〉
Ｆｅ、Ｃｏ、Ｎｉ、Ｒｕ、Ｒｈ、Ｐｄ、Ｏｓ、Ｐｔの金属およびＴｉ、Ａｌ、Ｓｉ、Ｚｒ、Ｖ、Ｎｂの金属酸化物のいずれかと平均粒子径５０μｍの天然黒鉛を混合し、回転ボールミルを用い９６時間真空中で粉砕し、ナノ構造化された黒鉛の複合化物を作製した。（実施例５〜８）
〈賦活処理〉
真空雰囲気中で９６時間粉砕したナノ構造化黒鉛（ＮＳＧ）を用い、水酸化カリウム（ＫＯＨ）と４：１の割合（ＫＯＨ：ＮSG＝４：１）で混合しアルゴン（Ａｒ）雰囲気中で７００℃、１時間の賦活処理を行った。賦活処理後、純水で十分洗浄、乾燥し、評価用試料とした。
〈酸化処理〉
真空雰囲気中で９６時間粉砕したナノ構造化された黒鉛を用い１５質量％過酸化水素（Ｈ２Ｏ２）水溶液中で７０℃、３時間混合し酸化処理を行った。その後、純水で充分洗浄、乾燥し、評価用試料とした。
Embodiments of the invention will now be described in detail. Sample preparation is as follows.
<Preparation of nanostructured graphite>
Natural graphite (flaky graphite) with an average particle diameter of 2 to 100 μm, mesophase pitch graphite, and artificial graphite are pulverized in a vacuum for 24 to 96 hours using a vibrating ball mill and a rotating ball mill, and the crystallite size, Samples having different average particle diameters of the aggregates were prepared. (Examples 1-3)
<Pt loading method>
Chloroplatinic acid (H 6 PtCl 6 ) was used as the Pt (platinum) compound. The sample was put into an aqueous solution in which the required amount of platinum was dissolved and stirred. After hydrolysis with an aqueous NaOH solution having a 7-fold molar number of Pt, a 2-fold excess amount of sodium formate (NaHCo 2 ) was added to the slurry, and the mixture was stirred at 70 ° C. for 3 hours for reduction treatment. Subsequently, filtration with warm water was sufficiently performed and dried to prepare a Pt-supported catalyst. (Examples 1 to 3, Comparative Examples 2 and 3)
<Method of adjusting composite with metal and composite with metal oxide (composite material)>
One of Fe, Co, Ni, Ru, Rh, Pd, Os, Pt metal and Ti, Al, Si, Zr, V, Nb metal oxide and natural graphite having an average particle diameter of 50 μm are mixed, and a rotating ball mill is prepared. It was pulverized in a vacuum for 96 hours to produce a nanostructured graphite composite. (Examples 5 to 8)
<Activation treatment>
Nanostructured graphite (NSG) ground for 96 hours in a vacuum atmosphere was mixed with potassium hydroxide (KOH) at a ratio of 4: 1 (KOH: NSG = 4: 1) and 700 in an argon (Ar) atmosphere. The activation treatment was performed at 1 ° C. for 1 hour. After the activation treatment, the sample was sufficiently washed with pure water and dried to obtain a sample for evaluation.
<Oxidation treatment>
The nanostructured graphite ground for 96 hours in a vacuum atmosphere was mixed in a 15 mass% hydrogen peroxide (H 2 O 2 ) aqueous solution at 70 ° C. for 3 hours for oxidation treatment. Thereafter, the sample was sufficiently washed with pure water and dried to obtain a sample for evaluation.
〈試料の評価〉
窒素（Ｎ２）吸着法による細孔構造、Ｘ線回折による構造解析、ラマンスペクトルからの構造解析、粒度分布の測定方法は以下のとおりである。また、ナノ構造化された黒鉛複合体、担持物の特性はカソード電極触媒としてのＭＥＡ（Membrane−Electrode−Assembly）試験方法、色素増感光電池のカソード電極を用いた発電効率評価で行った。
〈細孔構造の測定〉
各試料の比表面積［ｍ２／ｇ］の測定は、窒素吸着法を用い、解析にはBrunauer−Emmett−TellerによるＢＥＴ式より求めた（準拠規格ＩＳＯ９２７７）。細孔分布の測定は、液体窒素温度における毛管凝縮を利用するもので、Ｋｅｌｖｉｎの式が基礎になる。吸着平衡圧を広い範囲にわたり変えて吸着等温線を描き、解析すると細孔分布が求まる。この細孔分布の解析方法は、Ｂａｒｅｔｔ、ＪｏｙｅｒおよびＨａｌｅｎｄａによって提案された方法（ＢＪＨ法）により解析した。細孔径と細孔容積の関係を把握し、細孔半径０.８ｎｍから１５０ｎｍまでの細孔容積を積算して求め、細孔容積とした。
比表面積、細孔系分布（細孔径及び細孔容積）の測定装置はマイクロメトリックス社製のＡＳＡＰ２０１０を使用した。
〈Ｘ線回折分析〉
Ｘ線回折装置を用いて、学振法より結晶子の大きさＬｃ（００２）を求めた。測定装置はマックサイエンス社製ＭＸＰ１８ＶＡＨＦを用いた。
〈Ｒ値〉
このＲ値は、顕微ラマン分光器にて、各試料（賦活後の試料）のラマンスペクトルを計測し、Ｄバンドと呼ばれるアモルファス化した黒鉛に起因する１３６０ｃｍ−１ 付近のスペクトル強度（Ｉ１３６０）と、Ｇバンドと呼ばれる黒鉛の結晶質炭素に起因する１５７５ｃｍ−１付近のスペクトル強度（Ｉ１５７５）との相対的強度比、つまりピーク面積比（Ｉ１３６０／Ｉ１５７５）を算出し、黒鉛化度の評価に用いた。ラマン分析装置には日本分光製ＮＲ−１８００を使用した。
〈粒度分布〉
レーザー回折型粒度分布計を用いて、黒鉛凝集体の粒度分布を測定し平均粒子径を求めた。測定では、各試料を界面活性剤を用いて水中に均一に分布させ、超音波分散状態で粒度を計測した。屈折率は１.７０−０.２０ｉを用いた。
〈ＴＥＭ像観察〉
Ｐｔ担持ナノ構造化カーボンのＰｔ粒子径、Ｐｔ分散状態を８０万倍のＴＥＭ像より観察した。
〈カソード電極触媒、ＭＥＡ（Membrane−Electrode−Assembly）試験方法〉
Ｐｔ３０質量％担持カーボン材料をカソード触媒とし、ナフィオン（Nafion 登録商標）溶液とを混合しカソード電極触媒スラリーを調整した。膜面積６.２５ｃｍ２、アノード電極触媒の白金使用量０.０４〜０.０５ｍｇ／ｃｍ３、電解質膜ナフィオン１１２（Nafion 登録商標）は厚さ５０μｍ、ＭＥＡ温度８０℃、水素条件は０.１ＭＰａ（８５℃飽和蒸気圧）、酸素条件は純酸素０.１ＭＰａ（７５℃飽和水蒸気）にて試験した。そして電流密度０.０１Ａ／ｃｍ２における出力電圧で触媒性能を評価した。
〈色素増感光電池評価〉
平均粒子径２５ｎｍの酸化チタン（ＴｉＯ２）とポリエチレングリコールを含む粘性の水性ペーストを酸化スズ（ＳｎＯ）透明導電性ガラスに塗布し、４５０℃で３０分焼成して厚みが１５μｍの多孔質ＴｉＯ２膜を被覆した電極を作製した。ＴｉＯ２膜電極をＲｕ色素Ｎ７１９の０.００３モルのエタノール溶液に室温で一昼夜浸漬して色素を吸着させ、色素増感作用極（アノード）を作製した。対極カソードとして、ＩＴＯ−ＰＥＴフィルムのＩＴＯ表面にナノ黒鉛またはナノ黒鉛複合化物をｔｅｒｔ−ブタノールに分散したペーストをドクターブレード法で塗布し、ナノ黒鉛またはナノ黒鉛複合化物を含む導電性薄膜を形成した。溶媒系電解液の組成は、０.０５モルのヨウ素、０.１モルのヨウ化リチウム、０.５モルのTert−ブチルピリジン、０.６モルのヨウ化ジメチルプロピルイミダゾリウムを含むメトキシアセトニトリル、溶融塩電解液には、ヨウ化メチルプロピルイミダゾリウムを主体とする常温溶融塩と０.０２モルのヨウ素からなる混合物を用いた。光電変換特性は、ソーラーシミュレータによる１ｓｕｎ照射下で光電流−電圧特性を計測にもとづくエネルギー変換効率で評価した。
〈表面活性の評価〉
調整した試料を２００℃で焼成後、Ｈ２ガスを吸着させ、常温、常圧におけるＨ２吸着量を測定し、試料表面の活性度を評価した。
<Evaluation of sample>
The pore structure by the nitrogen (N 2 ) adsorption method, the structural analysis by X-ray diffraction, the structural analysis from the Raman spectrum, and the particle size distribution measuring method are as follows. Further, the characteristics of the nanostructured graphite composite and the support were evaluated by the MEA (Membrane-Electrode-Assembly) test method as a cathode electrode catalyst and the power generation efficiency evaluation using the cathode electrode of the dye-sensitized photocell.
<Measurement of pore structure>
The specific surface area [m 2 / g] of each sample was measured using a nitrogen adsorption method, and the BET formula by Brunauer-Emmett-Teller was used for analysis (compliance standard ISO 9277). The measurement of the pore distribution utilizes capillary condensation at liquid nitrogen temperature and is based on the Kelvin equation. Drawing and analyzing the adsorption isotherm while changing the adsorption equilibrium pressure over a wide range, the pore distribution can be obtained. The analysis method of the pore distribution was analyzed by the method proposed by Barett, Joyer and Halenda (BJH method). The relationship between the pore diameter and the pore volume was grasped, and the pore volume from the pore radius of 0.8 nm to 150 nm was obtained by integration and determined as the pore volume.
A measurement apparatus for specific surface area and pore system distribution (pore diameter and pore volume) used ASAP2010 manufactured by Micrometrics.
<X-ray diffraction analysis>
The crystallite size Lc (002) was determined by the Gakushin method using an X-ray diffractometer. The measuring device used was MXP18VAHF manufactured by Mac Science.
<R value>
This R value is obtained by measuring the Raman spectrum of each sample (sample after activation) with a micro-Raman spectrometer, and the spectral intensity (I 1360 ) near 1360 cm −1 due to amorphous graphite called D band. The relative intensity ratio to the spectral intensity (I 1575 ) near 1575 cm −1 due to the crystalline carbon of graphite called the G band, that is, the peak area ratio (I 1360 / I 1575 ) is calculated, and the graphitization degree is calculated. Used for evaluation. As a Raman analyzer, NR-1800 manufactured by JASCO was used.
<Particle size distribution>
Using a laser diffraction type particle size distribution meter, the particle size distribution of the graphite aggregate was measured to determine the average particle size. In the measurement, each sample was uniformly distributed in water using a surfactant, and the particle size was measured in an ultrasonic dispersion state. The refractive index used was 1.70-0.20i.
<TEM image observation>
The Pt particle diameter and Pt dispersion state of the Pt-supported nanostructured carbon were observed from a 800,000 times TEM image.
<Cathode electrode catalyst, MEA (Membrane-Electrode-Assembly) test method>
A cathode electrode catalyst slurry was prepared by mixing a Nafion (registered trademark) solution with a Pt 30 mass% supported carbon material as a cathode catalyst. Membrane area 6.25 cm 2 , platinum usage of anode electrocatalyst 0.04 to 0.05 mg / cm 3 , electrolyte membrane Nafion 112 (Nafion registered trademark) 50 μm thick, MEA temperature 80 ° C., hydrogen conditions 0.1 MPa (85 ° C. saturated vapor pressure) and oxygen conditions were tested with pure oxygen of 0.1 MPa (75 ° C. saturated water vapor). The catalyst performance was evaluated based on the output voltage at a current density of 0.01 A / cm 2 .
<Dye-sensitized photocell evaluation>
A viscous aqueous paste containing titanium oxide (TiO 2 ) having an average particle size of 25 nm and polyethylene glycol is applied to tin oxide (SnO) transparent conductive glass, and baked at 450 ° C. for 30 minutes, and porous TiO 2 having a thickness of 15 μm. An electrode coated with a membrane was prepared. The TiO 2 film electrode was immersed in a 0.003 molar ethanol solution of Ru dye N719 at room temperature for 24 hours to adsorb the dye, thereby preparing a dye-sensitized working electrode (anode). As a counter electrode, a paste in which nanographite or nanographite composite was dispersed in tert-butanol was applied to the ITO surface of the ITO-PET film by a doctor blade method to form a conductive thin film containing nanographite or nanographite composite. . The composition of the solvent-based electrolyte solution is 0.05 mole iodine, 0.1 mole lithium iodide, 0.5 mole Tert-butylpyridine, 0.6 mole dimethylacetonitrile iodide containing methoxyacetonitrile, As the molten salt electrolyte, a mixture of a room temperature molten salt mainly composed of methylpropyl imidazolium iodide and 0.02 mol of iodine was used. Photoelectric conversion characteristics were evaluated by energy conversion efficiency based on measurement of photocurrent-voltage characteristics under 1 sun irradiation by a solar simulator.
<Evaluation of surface activity>
After the adjusted sample was fired at 200 ° C., H 2 gas was adsorbed, and the amount of H 2 adsorption at normal temperature and normal pressure was measured to evaluate the activity of the sample surface.
前記評価による評価結果は以下のとおりである。ナノ構造化された黒鉛の実施例についての評価結果を表１に示す。 The evaluation results based on the evaluation are as follows. The evaluation results for the examples of nanostructured graphite are shown in Table 1.
〈評価結果〉
実施例１〜３及び比較例１〜３は発明対象となるナノ構造化黒鉛の有効性を調べた一例である。比較例３は粉砕を行わない黒鉛にＰｔを３０質量％担持した例であり、実施例１〜３は真空粉砕で調整したナノ構造化黒鉛にＰｔを担持した例である。比較例３と比較して、結晶子の大きさが低下し細孔容積及びＲ値の増加が確認できる。また、粒子径は３.５〜８μｍの造粒粉を形成している。つまり、ナノ構造化された黒鉛は、特殊な条件での粉砕を進めることで、黒鉛構造を形成する炭素の六角網面の端部に生じるダングリングボンド（dangling bond 未結合手）が活性点となり黒鉛の結晶子間が結合され一次粒子を形成し、更にこの一次粒子が強固に凝集して数μｍの造粒粉を形成する。このような構造を有するナノ構造化された黒鉛に、Ｐｔを担持させると、ナノ構造化黒鉛は表面構造の特異性よりＰｔを均一に分散できることが確認できた。
<Evaluation results>
Examples 1 to 3 and Comparative Examples 1 to 3 are examples of examining the effectiveness of the nanostructured graphite that is the subject of the invention. Comparative Example 3 is an example in which 30% by mass of Pt is supported on graphite that is not pulverized, and Examples 1-3 are examples in which Pt is supported on nanostructured graphite prepared by vacuum pulverization. Compared with Comparative Example 3, the size of the crystallites decreases, and increases in pore volume and R value can be confirmed. Moreover, the particle diameter forms the granulated powder of 3.5-8 micrometers. In other words, when nanostructured graphite is pulverized under special conditions, dangling bonds (dangling bonds that are not dangling bonds) generated at the ends of the hexagonal surface of carbon forming the graphite structure become active sites. The crystallites of graphite are bonded to form primary particles, and the primary particles are firmly aggregated to form a granulated powder of several μm. It was confirmed that when Pt is supported on the nanostructured graphite having such a structure, the nanostructured graphite can uniformly disperse Pt due to the specificity of the surface structure.
ナノ構造化された黒鉛を用いた実施例２，３は、Ｐｔ担持カーボンとして知られているカーボンブラック担体（バルカンＶＸＣ７２）を用いた試料（比較例２）より良好な分散を示した。また、カソード電極触媒、ＭＥＡ（Membrane−Electrode−Assembly）試験においても電流密度０.０１Ａ／ｃｍ２、０.１Ａ／ｃｍ２における出力電圧が高く、Ｐｔの分散が良好で、水素をプロトンに解離させる触媒特性またカソード電極触媒としての特性が良好であることが確認できた。また、色素増感光電池評価では、対極カソードとして、ＩＴＯ−ＰＥＴフィルムのＩＴＯ表面にナノ構造化された黒鉛複合化物を塗布することで、エネルギー変換効率が向上し、特性が大幅に向上した。これは、ナノ構造化された黒鉛をＩＴＯ上に塗布することで、ＩＴＯから電解液への電子の移動がスムーズに行われることになることを意味しており、つまり本発明材料は、電池内での電極と電解液間の電子移動速度改善に大きな効果があることが確認できた。なお、ナノ構造化された黒鉛は結晶子の大きさが１〜２０ｎｍであり、これらの結晶子が集合して２０〜１００ｎｍ程度の一次粒子を形成し、この一次粒子は強固に凝集し平均粒径０.５〜５０μmになっていることが重要である。平均粒子径は粉砕条件のほか、粉砕媒体の大きさ、材質などの変更により所望（０.５〜５０μｍ）に調整することが可能である。 Examples 2 and 3 using nanostructured graphite showed better dispersion than the sample (Comparative Example 2) using a carbon black support (Vulcan VXC72) known as Pt-supported carbon. Also in cathode electrode catalyst and MEA (Membrane-Electrode-Assembly) tests, the output voltage is high at current densities of 0.01 A / cm 2 and 0.1 A / cm 2 , Pt dispersion is good, and hydrogen is dissociated into protons. It was confirmed that the catalytic characteristics to be used and the characteristics as a cathode electrode catalyst were good. Moreover, in dye-sensitized photovoltaic cell evaluation, energy conversion efficiency improved and the characteristic improved significantly by apply | coating the nanostructured graphite composite material to the ITO surface of ITO-PET film as a counter electrode cathode. This means that by applying the nanostructured graphite on the ITO, the movement of electrons from the ITO to the electrolyte solution is performed smoothly. It was confirmed that there was a great effect in improving the electron transfer speed between the electrode and the electrolyte solution. The nanostructured graphite has a crystallite size of 1 to 20 nm, and these crystallites aggregate to form primary particles of about 20 to 100 nm. It is important that the diameter is 0.5 to 50 μm. The average particle diameter can be adjusted to a desired value (0.5 to 50 μm) by changing the size and material of the grinding medium in addition to the grinding conditions.
また、黒鉛の表面構造のパラメータであるラマン分光スペクトルのＲ値は、黒鉛表面の黒鉛化度、黒鉛エッジ比率と相関するが、ナノ構造化された黒鉛の表面はエッジ比率が増加し、黒鉛化度が少し低下しておりＲ値が上昇する。この表面状態がＰｔなどの担持、分散性に効果があり、また電極と電解液間で導電材として使用した場合に電子移動速度改善に効果を発揮する。黒鉛表面のＲ値は０．４以上であることが好ましく、より好ましくは０．５以上である。なお、Ｒ値は粉砕条件を変更して検討した結果１.７に漸近することが確認できており、以上から、黒鉛表面のＲ値は０.４〜１.７の範囲内にあることが好ましい。 The R value of the Raman spectrum, which is a parameter of the surface structure of graphite, correlates with the degree of graphitization of the graphite surface and the graphite edge ratio, but the edge ratio increases on the surface of the nanostructured graphite. The degree is slightly decreased and the R value is increased. This surface state is effective for supporting and dispersing Pt and the like, and when used as a conductive material between the electrode and the electrolyte, it is effective for improving the electron transfer speed. The R value of the graphite surface is preferably 0.4 or more, more preferably 0.5 or more. The R value has been confirmed to be asymptotic to 1.7 as a result of studying by changing the pulverization conditions. From the above, the R value of the graphite surface is in the range of 0.4 to 1.7. preferable.
ナノ構造化された黒鉛に金属元素、金属酸化物を複合化させた実施例についての評価結果を表２に示す。 Table 2 shows the evaluation results for Examples in which metal elements and metal oxides were combined with nanostructured graphite.
表２において、実施例４は粒径５０μｍの天然黒鉛を用い、真空粉砕で調整したナノ構造化された黒鉛の例であり、実施例５〜８は粒子径５０μｍの天然黒鉛と金属酸化物及び金属（ＴｉＯ２，ＳｉＯ２，Ｆｅ，Ｎｉ）を複合した例である。金属酸化物を添加して調整したナノ構造化された黒鉛複合化物である実施例５、６は、色素増感光電池評価でエネルギー変換効率の増加が確認できる。これより、ナノ構造化された黒鉛の複合化物を電解液中で導電材として使用した場合、電解液への電子の移動が更に改善できることが確認できた。また、金属元素を複合化した実施例を実施例７、８に示す。実施例４と比較して、実施例７，８の複合化物はH2の吸着量が多く、表面活性が高いことが確認できた。これより、ナノ構造化された黒鉛に金属元素を複合化することにより、触媒活性の向上が認められた。 In Table 2, Example 4 is an example of nanostructured graphite prepared by vacuum pulverization using natural graphite having a particle size of 50 μm, and Examples 5 to 8 are natural graphite and metal oxide having a particle size of 50 μm and This is an example in which metals (TiO 2 , SiO 2 , Fe, Ni) are combined. In Examples 5 and 6, which are nanostructured graphite composites prepared by adding metal oxides, an increase in energy conversion efficiency can be confirmed by dye-sensitized photocell evaluation. From this, it was confirmed that when the composite of the nanostructured graphite is used as the conductive material in the electrolyte, the transfer of electrons to the electrolyte can be further improved. Examples where metal elements are combined are shown in Examples 7 and 8. Compared with Example 4, it was confirmed that the composites of Examples 7 and 8 had a higher H2 adsorption amount and higher surface activity. From this, the catalytic activity was improved by compounding the metal element with the nanostructured graphite.
黒鉛の種類を変えて真空粉砕で調整したナノ構造化黒鉛に酸化処理と賦活処理を施し、細孔構造及び比表面積を変化させ、これにＰｔを担持させて特性を確認した実施例についての評価結果を表３に示す。 Evaluation of examples in which nanostructured graphite prepared by changing the type of graphite and vacuum pulverizing was subjected to oxidation treatment and activation treatment, the pore structure and specific surface area were changed, and Pt was supported on this to confirm the characteristics. The results are shown in Table 3.
表２の実施例４と表３の実施例９を比較すると、酸化処理では比表面積の増加は少ない。しかし、表３の実施例９と実施例１０〜１３を比較すると、酸化処理した実施例９は、賦活処理した実施例１０〜１３に比較して、担持Ｐｔの分散状態が良く、カソード電極触媒評価の特性が向上する。また、ＫＯＨ賦活処理は比表面積の増加に効果があり、特に粉砕後の賦活処理（実施例１２）で比表面積２０００ｍ２／ｇ近くまでの増加が確認できた。実施例１０〜１３にその結果が示されるように、KOH賦活処理において比表面積を増加でき、さらにPt担持後の出力特性も良好である。以上により、ナノ構造化黒鉛の比表面積は、２０００ｍ２／ｇ程度まで増加させることが可能なことが分かり、またＰｔ担持触媒としての特性を確認すると、ナノ構造化黒鉛調整後の処理としてはKOH賦活処理のほか酸化処理も有効であることが確認できた。
When Example 4 in Table 2 and Example 9 in Table 3 are compared, the increase in specific surface area is small in the oxidation treatment. However, when Example 9 in Table 3 and Examples 10 to 13 are compared, Example 9 subjected to the oxidation treatment has a better dispersion state of the supported Pt than Examples 10 to 13 subjected to the activation treatment, and the cathode electrode catalyst. Evaluation characteristics are improved. In addition, the KOH activation treatment was effective in increasing the specific surface area, and in particular, the activation treatment after pulverization (Example 12) was confirmed to increase up to a specific surface area of about 2000 m 2 / g. As the results are shown in Examples 10 to 13, the specific surface area can be increased in the KOH activation treatment, and the output characteristics after supporting Pt are also good. From the above, it can be seen that the specific surface area of the nanostructured graphite can be increased to about 2000 m 2 / g, and the characteristics as a Pt-supported catalyst are confirmed. It was confirmed that the oxidation treatment was effective in addition to the activation treatment.
Claims (8)
A catalyst material comprising the nanostructured graphite according to any one of claims 1 to 3 or the composite material of the nanostructured graphite according to any one of claims 4 to 6.
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