JP2005046702A - Graphite hydrogen occluding material and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a graphite hydrogen occluding material which is capable of efficiently occluding a larger amount of hydrogen, is light in weight and is excellent in repeated use, and to provide a producing method of the graphite hydrogen occluding material. <P>SOLUTION: The graphite hydrogen occluding material which occludes or releases hydrogen is made of graphite intercalating compound in which the layer to layer distance is enlarged by inserting atoms or molecules by 5 wt.% to 70 wt.% between layers and has sites for hydrogen occlusion which are formed by removing the inserted atoms or molecules all or partially. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３４】
【表２】

【００３５】
まず、表１から次のようなことが分かる。まず、実施例１〜３は、黒鉛層間化合物としてＫ−ＴＨＦ−ＧＩＣ、ＦｅＣｌ_３−ＧＩＣ、酸化黒鉛を用い、層間にインタ−カラントした元素を一部、又は全部取り除いた試料である。比較例１は、黒鉛層間化合物としてＦｅＣｌ_３−ＧＩＣを用い、層間にインタ−カラントした元素を一部、又は全部取り除いた試料である。比較例２は酸化黒鉛の未処理の試料である。ここで、ＦｅＣｌ_３と黒鉛の層間化合物の場合（実施例２と比較例１）、第１ステージの層間化合物はＣ_６−ＦｅＣｌ_３の組成を持ち、層間に挿入されたインターカラントは６９．３ｗｔ％である。この状態では、黒鉛層間にＦｅＣｌ_３が一杯詰まった状態であり、水素が吸蔵するナノスペースはほとんど無く、比較例１に示すように水素吸蔵量は０．１ｗｔ％である。しかし、層間からＦｅＣｌ_３、ＦｅやＣｌ_２を取り除き、例えば、６０％取り除いた実施例２の試料では水素吸蔵量が０．９ｗｔ％と大きな値を示している。また、酸化黒鉛は、一般にＣ_８Ｏ_５Ｈ_２程度の組成を持ち、黒鉛層間に酸素や水素が約４６ｗｔ％共有結合された状態である。比較例２の酸化黒鉛についても、酸素や水素を除かない状態では水素吸蔵能は少なく０．１ｗｔ％となるが、８５ｗｔ％除いた実施例３の試料では２．２ｗｔ％の水素吸蔵能となる。また、実施例１は、Ｋとテトラヒドロフラン（ＴＨＦ）が黒鉛の層間内に３８．９ｗｔ％インターカラントした三元系黒鉛層間化合物であるが、ＴＨＦをガス化させて層間より取り除くことで水素吸蔵能は２．６ｗｔ％となる。
【００３６】
また、他の実施例として、実施例２の層間化合物であるＦｅＣｌ_３−ＧＩＣと、実施例３の層間化合物である酸化黒鉛とを用い、還元温度、熱処理温度を変えて、層間から炭素以外の元素を取り除く検討を詳細に行った。その結果例を図２及び図３に示す。これらの結果より、黒鉛層間化合物は、黒鉛の層間に挿入された炭素原子以外の元素を全部または一部分取り除くことで水素吸蔵能を発現すること、多く取り除くほど水素吸蔵量が大きくなること分かる。これらの結果より、実用上は、少なくとも５％以上つまり５〜１００％の範囲で除去したものが好ましい。
【００３７】
ところで、実施例２及び図１の試料は、イオン結合を有するＦｅＣｌ_３をインターカラントとして用いているイオン結合型層間化合物であり、還元処理を適度に制御することで、層間内でＦｅ等の微粒子を析出させ、水素吸蔵能の高いナノスペースを創生し易いことが分かる。また、実施例３及び図２の試料は、酸化黒鉛を用いており、黒鉛層間に酸素などを共有結合させて層間を広げた共有結合型であり、加熱処理で炭素と結合した元素を除去することでナノスペースを創生し易いことが分かる。また、実施例４は層間のインターカラントを全て除いた後、炭素網平面間に働く分散力が作用し層間の広がりを維持している分散力型の例である。このように、層間内に水素吸蔵用ナノスペースを創生させるためには、黒鉛層間化合物にけるイオン結合型、分散力型、共有結合型のいずれかをの結合力を利用することが必要である。
【００３８】
以上の黒鉛系水素吸蔵材料において、炭素原子以外の元素を全てあるいは部分的に取り除く操作は、加熱処理か還元処理のいずれかである。実施例１、３、４は熱処理、実施例２は還元処理の例である。熱処理方法として、実施例１ではバーナーを用いたが、実施例４では層間のＴＨＦを急激にガス化させるためにＣＯ_２レーザーを照射した。還元処理は、黒鉛の層間にインターカラントした金属塩化物などを還元し層間内に出来るだけメタル状態で残すナノスペースを確保するための処理法であり、実施例２は３００℃での水素還元の例である。
【００３９】
また、黒鉛系水素吸蔵材料の物性特性として、ボイル・シャルルの法則に基づいてＨｅの圧力が２気圧と８気圧の条件で算出した試料の密度（Ｈｅ平衡圧密度）が０．２５ｇ／ｃｍ^３から３．３ｇ／ｃｍ^３であり、原料となる黒鉛層間化合物と比較したＨｅ平衡圧密度比が約０．７以下に低下していることが水素を吸蔵するナノスペース量を確保するのに重要である。しかし、Ｈｅ平衡圧密度比が０．１以下に低下すると、層間が大きく広がりすぎて嵩高い材料となるため、一定容器内に充填できる重量が減少し、実用上使用が難しい。そこで、水素吸蔵材料のＨｅ平衡圧密度比としては０．７から０．１に低下していることが重要となる。
【００４０】
すなわち、実施例１の場合はＫとＴＨＦの三元系黒鉛層間化合物をバーナーで加熱することにより、黒鉛の層間内にインターカラントしていたＴＨＦが一気にガス化し、層間を拡張させ、黒鉛内に多数のナノスペースを創生する。この材料の加熱前のＨｅ平衡圧密度は１．２５ｇ／ｃｍ^３であるに対し、加熱後のＨｅ平衡圧密度は０．３９ｇ／ｃｍ^３（密度比０．３１）と大きく低下し、層間の拡張とともにナノスペースが発現し、密度が低下したものと推察される。実施例２つまりＦｅＣｌ_３と黒鉛の第１ステージの層間化合物ＦｅＣｌ_３−Ｃ_６は、Ｈｅ平衡圧での密度が２．６５ｇ／ｃｍ^３であるが、３００℃での水素還元後の密度は１．３４ｇ／ｃｍ^３（密度比０．５１）まで低下し、層間にナノスペースが発現している。このときの水素吸蔵量は、還元処理前０ｗｔ％に対し、３００℃還元後に０．９ｗｔ％まで向上している。また、実施例３と比較例２つまり酸化黒鉛を使用し、４００℃熱処理前後のＨｅ平衡圧密度を比較すると、熱処理前２．０９ｇ／ｃｍ^３に対し、実施例３の熱処理後０．４７ｇ／ｃｍ^３（密度比０．２３）と大幅な密度低下をきたし、ナノスペースの創生が認められる。このときの水素吸蔵量は、熱処理前０．１ｗｔ％に対し、熱処理後２．２ｗｔ％と水素吸蔵性の向上が認められる。
【００４１】
ここで、比較例１はＦｅＣｌ_３−ＧＩＣを５００℃で水素還元したものの特性、比較例２は酸化黒鉛の特性である。比較例１は還元温度が高すぎるため、ＦｅＣｌ_３が還元されると同時に、Ｆｅがほぼすべて層間外に排出され、黒鉛の層間距離が０．３６ｎｍに戻り、ナノスペースが消失したことが推察される。その結果、Ｈｅ平衡圧密度比は０．８と高い値を示し、水素吸蔵能もほとんど消失している。比較例２は熱処理前の酸化黒鉛のため、ナノスペース創生の度合いを表す密度比は１．０であり、水素を吸蔵するサイトであるナノスペース及び水素吸蔵能がほとんど無い。
【００４２】
次に、透過型電子顕微鏡の像（ＴＥＭ像）より解析した結果から、次のようなことが分かる。ＴＥＭ像での観察からは、熱処理試料である実施例１と３は０．３７〜０．４ｎｍの層間、還元処理試料である実施例２は０．９４ｎｍの層間が残されている。また、黒鉛の規則的な層間は、実施例２つまりＦｅＣｌ_３−ＧＩＣを用いた水素還元において、黒鉛層間内でメタルの凝集が発生した場合、表１に示さなかったが２ｎｍ程度の間隔まで広がることもある。従って、本発明での黒鉛の規則的な層間は０．３５ｎｍ以上かつ２ｎｍ以下とし、併せて、実施例１において規則的な層間を形成する結晶子の間隙は２ｎｍ〜５０ｎｍであることから、規則的な層間を形成する結晶子の間隙が１ｎｍ〜１００ｎｍの範囲で開いている部分を有している点を特定した。これらの物性は発明材料を特定する上で重要な目安となる。
【００４３】
また、粉末Ｘ線回折法（入射Ｘ線：ＣｕＫα）において、層間が広がっていること、つまりディフラクトメ−タ法による回折角度（２θ）が２４．５°以下にピークを持つことが必要である。層間化合物や酸化黒鉛は一般に２４．５°以下に明確なピークを持ち、層間の広がりが認められるが、熱処理や還元処理を施すことで、層間内にナノスペースを創生し、層間の均一な広がりは低下する。そして、それら処理を過度に施し、層間内のインターカラントや酸化物を多く除いたものは層間が３．３５Åまで戻ってしまう。水素吸蔵能が高い材料は、これらの処理後も黒鉛の層間距離までは戻らず、特に回折角度（２θ）が２４．５°以下にピークを持っていることが重要である。このような材料は層間内にナノスペースが発生していることを確認している。また、特に層間が広がっているものは、回折角度（２θ）が１０°以下にピークや隆起を検出される。すなわち、実施例１，２の試料は０〜１０°に隆起が発生し、実施例２の試料は１８．９°と９．４２°にピークが発生しており、熱処理や還元処理後も層間が広がっていることが分かる。
【００４４】
他の物性としては、５１４．５ｎｍ波長のラマン分光スペクトルで１５８５〜１６３０ｃｍ^−１にピークが発現することである。黒鉛層間化合物を熱処理や還元処理した試料において、黒鉛の層間に挿入した原子あるいは分子が部分的に残りナノスペースが創生された場合、Ｇバンドの１５８０ｃｍ^−１のピークに対し、１５８５〜１６３０ｃｍ^−１にシフトしたピークが現れることが分かっている。しかし、ラマン分光分析は試料の表面から数ｎｍの深さまでの表面分析法であるため、この分析結果で１５８５〜１６３０ｃｍ^−１にピークが現れないものでも試料内部の層間に挿入した原子あるいは分子が残っていることがある。実施例１と２の試料では１６０６〜１６１６ｎｍにピークが確認される。実施例３の試料では、熱処理によりＧバンドピークにほぼ戻っているが、Ｘ線回折結果より１０°以下に隆起を持ち、層間の拡張が確認される。つまり、上記黒鉛系水素吸蔵材料において、回折角度２θが２４．５°以下にピークを持つものか、又は、１５８５〜１６３０ｃｍ^−１にラマンピークを発現するものが本発明の水素吸蔵材料として重要な指標となる。
【００４５】
（その他）実施例５はＰｔを約１０ｗｔ％坦持した試料の特性である。水素吸蔵量としては、未坦持品である実施例４より約１ｗｔ％増加しており、Ｐｔ坦持の効果が認められる。このような効果は、Ｐｔ以外のＰｄやＮｉなどでも同様な傾向になることが確認されている。また、Ｋ，Ｃｓ，Ｒｂ等のアルカリ金属は黒鉛と層間化合物を作り易く、水素吸蔵能を向上させるのに効果があり、Ｔｉ，Ｃｒ，Ｆｅ，Ｃｕ，Ｃｏ，Ｚｒ，Ｎｂは塩化物の形で黒鉛と層間化合物を調整でき、還元などにより層間にメタル状態で残し、また層間内にナノスペースを創生することで水素吸蔵能の優れた材料を調整できる。実施例６と７は、黒鉛層間化合物を調整するための黒鉛原料としてキッシュ黒鉛、メソフェーズピッチ系黒鉛であるＭＣＦを用いた例である。これ以外にも、人造黒鉛やＢを添加した黒鉛も原料黒鉛として使用できる。
【００４６】
【発明の効果】
以上のように、発明の黒鉛系水素吸蔵材料及びその製造方法は、黒鉛の層間に原子あるいは分子を挿入し層間距離を拡大した黒鉛層間化合物を用いること、黒鉛層間化合物より前記挿入した原子あるいは分子を熱処理や還元処理等によりすべてあるいは部分的に取り除くことを特徴とし、それにより、黒鉛層間化合物により多くの水素吸蔵用サイトつまり水素吸蔵能に優れたナノスペースを創生できる。この結果、この発明は、大量の水素を効率的に吸蔵でき、軽量で、繰り返し使用できる上、製造方法が容易なことから製造費を抑えて実用化に寄与できる。
【図面の簡単な説明】
【図１】発明材料例について水素還元温度と水素吸蔵量（取り除いた量）の関係を示した図である。
【図２】発明材料例について熱処理温度と水素吸蔵量（取り除いた量）の関係を示した図である。
【図３】Ｈｅ平衡圧密度の測定方法を説明するための参考模式図である。
【符号の説明】
１と２は圧力容器
▲１▼〜▲３▼は開閉用弁[0001]
[Technical field to which the invention belongs]
The present invention relates to a graphite-based hydrogen storage material and a method for producing the same. In this specification, Pt, Pd, Ni, Li, K, Cs, Rb, Ti, Cr, Fe, Cu, Co, Zr, Nb, etc. are element symbols.
[0002]
[Prior art]
Fuel cells are attracting attention from the viewpoints of global warming and air pollution countermeasures, and the stabilization and efficiency of energy supply. In order to mount fuel cells on transportation equipment, it is important to study hydrogen storage methods, which are cheap, lightweight, have a high volumetric hydrogen storage density, have a fast hydrogen filling / release rate, and are safe. Development of easy-to-handle hydrogen storage materials and storage methods is desired. Currently, as a method for mounting hydrogen on a transport device, four types of methods of high-pressure hydrogen gas, liquid hydrogen, a hydrogen storage alloy, and a carbon-based material have been proposed. Here, the use of a hydrogen cylinder in a fuel cell vehicle is essentially no problem, and it has been studied to increase the filling amount to about 750 atm in order to increase the hydrogen storage amount. However, the cylinder has a problem that it is thickened to withstand a high pressure and its weight increases. Next, in transport storage using liquid hydrogen, liquefied hydrogen can be produced by making the temperature lower than the boiling point of hydrogen (−253 ° C.). Liquefied hydrogen is an excellent storage method for hydrogen because its volume is about 1/800 compared to gas. However, there are problems such as vaporization (boil-off) due to the small heat of vaporization of hydrogen and the need for a container that can withstand ultra-low temperatures. On the other hand, in the hydrogen storage alloy, hydrogen dissociates into atoms and enters between the lattices of metal atoms, so that the volume hydrogen density is high and energy comparable to gasoline can be stored in the same volume at room temperature. Some structural alloys have a hydrogen storage capacity approaching 3 wt%. However, it is necessary to remove the heat generated during filling as well as to reduce the weight and cost of the storage alloy and storage container for mounting in automobiles. is there.
[0003]
On the other hand, research on hydrogen storage using carbon-based materials has been actively conducted in recent years. Carbon materials include activated carbon, graphite intercalation compounds, carbon nanotubes (CNT), graphite nanofibers (GNF), fullerenes, etc., and problems with occlusion / release characteristics at normal temperature, production cost, mass productivity, yield, etc. However, further studies are underway to overcome this problem. Specifically, it is as follows. Of the carbon-based materials, the hydrogen storage method using CNTs has received the most attention, and it has been reported that the storage capacity of about 4 wt%, which is superior to the storage capacity of hydrogen storage alloys, is achieved.
Single-walled CNTs have a cylindrical shape with a diameter of several to several tens of nanometers in which a single graphene sheet in which carbon atoms are arranged in a hexagonal network is formed, and has a bundle shape (bundle shape). It is said that a strong physical potential acts inside or between tubes, and a large amount of hydrogen molecules are physically adsorbed there. Multi-walled CNTs are graphene sheets concentrically stacked in multiple layers at equal intervals, and since the tube wall is multilayered, the proportion of surface carbon atoms that come into contact with hydrogen molecules decreases, but hydrogen enters the space between graphene sheets. It is said that a high hydrogen storage function can be expected. Moreover, the thing with a high orientation degree is synthesize | combined by the development of the synthesis | combining method of multilayer CNT, As a result, the high hydrogen storage amount has been reported. For example, Patent Document 1 proposes a technique for storing hydrogen in a carbon material having pores such as CNT, CNF, and activated carbon. However, in general, in nanotubes, high hydrogen occlusion can be achieved at a low temperature near liquid nitrogen, and the occlusion capability at room temperature is as low as 0.2 to 0.4 wt%, and it is also significant for practical use. There are many problems such as cost reduction and improvement of production capacity. In Patent Document 2, a proposal is made to mechanically pulverize graphite in a hydrogen atmosphere to store hydrogen in nanostructured graphite, and 7.4 wt% hydrogen release is confirmed. By pulverizing graphite in a hydrogen atmosphere, hydrogen is stored in graphite particles without a covalent bond or without a covalent bond, and a large occlusion is confirmed. This technique is also described in detail in the literature (Carbon TANSO 2001 “No. 200” pp 261-268). As an example, “the amount of hydrogen inside the nanostructured graphite increases significantly with the increase of the milling time, that is, the development of the defect structure, and the amount of hydrogen after 80 hours can reach 7.4 wt%. Recognize. Specific surface area after milling for 80 hours is only 10m ² The amount of physical adsorption on the sample surface is extremely small. Further, the temperature programmed desorption spectrum of the hydrogen molecule having a mass number of 2 showed two peaks starting at about 600K and 950K. ”And other interesting analyzes have been made. However, in actual use, it is necessary to lower the hydrogen release temperature and to ensure cycleability (repeated use). The hydrogen occlusion in the hydrogen atmosphere is dangling bonds caused by pulverization, and structural defects are the driving force, and the location of hydrogen is hydrogen bonded to dangling bonds of graphite from neutron diffraction experiments, The other is reported to be hydrogen located between graphite layers. Therefore, when hydrogen is put into the material once heated and released, hydrogen hardly enters by pressurization, and even if pulverized again in a hydrogen atmosphere, the crystallites of the graphite are small and become amorphous. The problem is that almost no hydrogen storage is observed. That is, in the hydrogen storage method by pulverization in a hydrogen atmosphere, it is a big issue how to reduce the discharge temperature and how to use it repeatedly.
[0004]
[Patent Document 1]
JP 2001-220101 A
[Patent Document 2]
JP 2001-302224 A
[0005]
[Problems to be solved by the invention]
The above carbon-based materials show a higher hydrogen storage capacity than hydrogen storage alloys depending on the storage and release conditions, but the release temperature is high, the storage mechanism cannot be used repeatedly, There are many problems such as being unable to produce in large quantities. Accordingly, the object of the present invention is to provide a graphite-based hydrogen storage material that can efficiently store a larger amount of hydrogen, is lightweight, can be repeatedly used, and is easy to manufacture, and a method for manufacturing the same. is there.
[0006]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors have conducted earnest research from the viewpoint of how to use the graphite layer as a raw material, using graphite that is easy to obtain and manufacture. Using graphite with good properties, it has been found that by extending the interlayer between the graphite to an optimum distance, and forming a hydrogen storage site in the interlayer, the physical and chemical potentials work and high hydrogen storage can be achieved. Invented. That is, the invention of claim 1 is a graphite intercalation compound in which 5- to 70% by weight of atoms or molecules are inserted between layers to expand the interlayer distance in a graphite-based hydrogen storage material that absorbs and releases hydrogen. It is characterized by having a hydrogen storage site from which all or part of the atoms or molecules are removed. On the other hand, the invention of claim 12 captures the above graphite-based hydrogen storage material from the production method, and includes a first process of creating an intercalation compound by inserting atoms or molecules between graphite layers, It is characterized by going through a second process that removes all or part of the inserted atoms or molecules.
[0007]
When the graphite intercalation compound is used for hydrogen storage, the above invention outlines the use of graphite with good crystallinity as the raw material graphite, and inserts atoms and molecules between the graphite layers, that is, between the carbon network planes, to control the expansion of the interlayer distance. Then, all or part of the atoms and molecules inserted into the graphite intercalation compound are partially removed to create more hydrogen storage sites. The inventions of claims 2 to 11 specify details or physical properties, and the inventions of claims 13 to 14 specify details of the manufacturing method.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the graphite-based hydrogen storage material and the production method thereof according to the present invention will be described for each main part, and then the usefulness will be clarified by giving examples.
(Claim 1) The graphite-based hydrogen storage material according to the present invention is a graphite intercalation compound in which atoms or molecules are inserted between graphite layers in an amount of 5 wt% to 70 wt%, and the interlayer distance is expanded. It has a hydrogen storage site where all or part of the atoms or molecules are removed. First, in order to adjust a graphite material having a large amount of hydrogen storage, it is necessary to create a nanospace for storing hydrogen by expanding the graphite layer. From this point, the inventors of the present invention, after repeated testing, inserted a graphite intercalation compound between the graphite intercalation compounds with an interlaminar distance increased by inserting at least 5 wt% or more of atoms or molecules between the graphite intercalation layers. It was found that by removing all or part of the atoms or molecules, nanospaces were developed between the layers and more hydrogen could be stored by increasing the number of hydrogen storage sites.
[0009]
Specifically, for example, KC, which is a first stage intercalation compound of potassium in which potassium is contained between graphite layers, that is, between all carbon network surfaces. ₈ Contains 28.9 wt% of K. FeCl ₃ C, the first stage intercalation compound of ₆ -FeCl ₃ Is FeCl ₃ 69.2 wt%. CuCl ₂ C, the first stage intercalation compound ₅ -CuCl ₂ Is CuCl ₂ 69.2 wt%. In addition, PtCl ₄ Forms a third stage intercalation compound with graphite, the compositional formula being C ₂₄ -PtCl ₄ And PtCl ₄ 66.8 wt%. Graphite oxide is generally C ₈ O ₅ H ₂ It has a composition of the order, and oxygen and hydrogen are about 46 wt% covalently bonded between the graphite layers. However, these graphite intercalation compounds are in a state in which atoms or molecules are fully packed in the interlayer, the nanospace in the interlayer is insufficient, and hydrogen storage properties are hardly expected. However, the present inventors have confirmed that it is most preferable to improve the hydrogen storage properties by using these graphite intercalation compounds to remove all or part of the other elements other than carbon atoms and to make the material exhibit nanospace. Obtained.
[0010]
In the present invention, by using a graphite intercalation compound, an acid intercalation compound, graphite oxide with an alkali metal or a transition metal element chloride, which is a graphite intercalation compound, a nanospace is expressed between the layers, It is a graphite-based hydrogen storage material having a structure or structure in which molecules and hydrogen atoms are easily adsorbed physically and chemically. The physical and chemical potential of hydrogen storage can be expressed by removing all or part of the inclusions inserted between the layers of the graphite intercalation compound and expanding the layers to create nanospaces within the layers. . As the usable graphite intercalation compound, when the number of atoms or molecules inserted between the graphite layers is 5 wt% or less, there is little spread between the layers, and even if the hydrogen storage material is adjusted, the hydrogen storage amount is small. Further, no material having a composition of 70 wt% or more has been confirmed as atoms or molecules inserted between graphite layers. For the above reasons, in the present invention, the graphite intercalation compound that can be used practically is limited to those in which 5 to 70 wt% of atoms or molecules are inserted between graphite layers.
[0011]
Here, usable graphite intercalation compounds include halogen-based graphite intercalation compounds using graphite-fluorine compounds, ICI, IBr, Br, BrCl, Cl, etc. as intercalants, TiCl. ₄ , CrCl ₃ , MnCl ₂ , FeCl ₃ , CoCl ₂ , NiCl ₂ , CuCl ₂ , ZnCl ₂ , ZrCl ₄ , NdCl ₅ , MoCl ₅ , RuCl ₃ , RhCl ₃ , PdCl ₂ , CdCl ₂ , InCl ₃ , SnCl ₄ , SbCl ₅ , TaCl ₅ , WCl ₆ , OsCl ₃ , IrCl ₄ , PtCl ₄ , AuCl ₃ Examples include chloride-based intercalant compounds using, for example, an intercalant, and alkali metal and alkaline earth metal-based graphite intercalation compounds, such as Li, K, Na, Rb, Cs, Ba, Sr, and Ca. In addition, ternary graphite intercalation compounds with two or more of these as intercalants can be used, and alkali metal and alkaline earth metal graphite intercalation compounds absorb organic molecules (tetrahydrofuran, benzene, ammonia, ethylene, etc.). There are many combinations, such as two types of chloride systems, and chloride and acid systems. HNO as an acid that reacts with graphite ₃ , H ₂ SO ₄ , H ₃ PO ₄ , H ₃ AsO ₄ , HF, H ₂ SeO ₄ , HClO ₄ , CF ₃ Acid-based graphite intercalation compounds using COOH or the like, and graphite oxide that forms a covalent bond between carbon and oxygen by invading oxygen between graphite layers can also be used as a material for developing nanospace. Further, when graphite oxide is reacted with dibutyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, p-tri-sulfoxide, tetramethylene sulfoxide, n-hexadecylamine, hexamethylammonium salt, an inter-layer compound is formed. The interlayer distance extends from 0.7 nm to 2.0 nm, and nanospace can be expressed. A material obtained by reacting an organic substance in the interlayer using graphite oxide can also be used as a graphite interlayer compound for improving the hydrogen storage performance.
[0012]
(Regarding Claim 2) The graphite-based hydrogen storage material of the present invention essentially requires that atoms or molecules inserted between the above-mentioned graphite intercalation compounds are removed in a range of 5 to 100 wt%. This is based on the following test results. First, FeCl ₃ In the case of an intercalation compound of graphite and graphite, the intercalation compound of the first stage is C ₆ -FeCl ₃ And the intercalant inserted between the layers is 69.3 wt%.
In this state, FeCl is interposed between the graphite layers. ₃ There is almost no nanospace for storing hydrogen. However, in the test, FeCl ₃ As hydrogen, Fe, and Cl were removed, more hydrogen was occluded. For example, by removing 2 wt%, the hydrogen occlusion amount was 0.1 wt%, and by removing 60 wt%, the hydrogen occlusion amount reached a maximum value of 0.9 wt%. In addition, graphite oxide is generally C ₈ O ₅ H ₂ It has a composition of the order, and oxygen and hydrogen are about 46 wt% covalently bonded between the graphite layers. Graphite oxide also has a low hydrogen storage capacity in the state where oxygen and hydrogen are not removed, but in the test, a hydrogen storage capacity of 0.4 wt% was obtained by removing 5 wt%, and 2 wt% was obtained by removing all. Further, in the graphite intercalation compound of K and tetrahydrofuran (hereinafter referred to as THF), the hydrogen storage capacity is increased by gasifying THF and removing it from the interlayer. In this case, the graphite having the maximum hydrogen storage capacity. The intercalation compound was in a form in which 2% of K remained in the interlaminar. As a result of repeated studies, as a graphite intercalation compound that exhibits hydrogen storage capacity, it is possible to express hydrogen storage capacity by removing all or part of the atoms or molecules inserted between graphite layers, more specifically, It is necessary to remove in the range of 5 to 100 wt%.
[0013]
(Claim 3) In the graphite-based hydrogen storage material of the present invention, atoms or molecules inserted between the above-mentioned graphite intercalation compounds are in contact with one surface of the two graphite layers sandwiching the atoms or molecules. That is essential. As described above, in order to increase the hydrogen storage capacity, it is indispensable to optimally widen the graphite layers and further form hydrogen storage sites in the layers. Usually, the interlayer distance of an interlayer compound is often equal to the size of the inserted atom or molecule. However, the graphite-based hydrogen storage material of the present invention has an extended interlayer distance starting from atoms or molecules inserted between layers, and forms a storage space wider than the size of the inserted atoms or molecules. Therefore, it is important for formation of a wide hydrogen storage site that the inserted atom or molecule is in contact with one surface of the two graphite layers sandwiching the atom or molecule.
[0014]
(Regarding Claim 4) The graphite-based hydrogen storage material of the present invention requires that the graphite intercalation compound is of an ionic bond type, a dispersion force type, or a covalent bond type. As described above, in order to increase the hydrogen storage capacity, it is indispensable to use a graphite intercalation compound in which the graphite interlayer is expanded. Therefore, the graphite-based hydrogen storage material of the invention is a dispersion force type in which the dispersive force acting between the carbon network planes acts to maintain the spread between the layers, and the common layer in which the layers are spread by covalently bonding oxygen or the like between the graphite layers. A bond type or an ion bond type in which a metal chloride composed of an ion bond is inserted between layers can be used. When removing all or part of the atoms or molecules inserted between the graphite layers, decompose the covalent bonds between the layers, remove the ion-bonded molecules, or expand the carbon network planes all at once. After that, it is necessary to maintain the spread between the layers by the dispersion force. As described above, by using a graphite intercalation compound of a dispersion force type, a covalent bond type, or an ion bond type, a site having a strong hydrogen adsorption force is formed, and the hydrogen storage ability can be enhanced.
[0015]
(Regarding Claim 5) The graphite-based hydrogen storage material of the present invention requires that the inserted atoms or molecules are completely or partially removed by heat treatment or reduction treatment. A ternary intercalation compound (K and THF or K and NH ₃ And graphite oxide) and graphite oxide must be removed by gasifying the solvent in the interlayer by heat treatment, or oxygen covalently bonded in the interlayer must be removed by thermal decomposition. The heat treatment may be any form in which the sample can be heated by laser irradiation, microwave irradiation, or the like, in addition to direct heating with a heater or burner. In the operation of removing all or part of the atoms or molecules inserted by the heat treatment, it is also effective to carbonize organic substances that have reacted between the layers. In contrast, the reduction treatment is a treatment method that reduces metal chlorides intercalated between graphite layers and leaves them in the metal state as much as possible in the layers, and is useful for expressing nanospaces with the layers expanded. is there. As a specific reduction treatment, in addition to reduction at 150 ° C. to 500 ° C. using hydrogen gas, reduction can be performed at a high temperature using an organic substance such as ethylene. Further, there are a method using an alkali metal such as K or Na and a method using a solution-like reducing agent such as an aqueous hydrazine solution. Of course, depending on the object to be removed, a combination of reduction treatment and heat treatment is also effective.
[0016]
(Claim 6) In the present invention, in the above graphite-based hydrogen storage material, the density of the sample (He equilibrium pressure density) calculated based on Boyle-Charle's law under the conditions that the He pressure is 2 atm and 8 atm. Is 0.25 g / cm ³ To 3.3 g / cm ³ Compared with the graphite intercalation compound used as a raw material, it is essential that the He equilibrium pressure density ratio is reduced to 0.7 to 0.1. This is a characteristic based on, for example, finding the following tendency.
(A) First, the ternary graphite intercalation compound of K and THF is heated with a burner to gasify the THF intercalated into the graphite layer at once, expanding the interlayer, and a large number in the graphite. Create a nanospace. In the case of this graphite intercalation compound, the He equilibrium pressure density before heating is 1.25 g / cm. ³ On the other hand, the He equilibrium pressure density after heating is 0.39 g / cm. ³ It can be considered that the density was greatly reduced to (density ratio 0.31), nanospace was developed with the expansion between layers, and the density was reduced. The hydrogen storage property of this material was 2.6 wt%.
(I) FeCl ₃ And graphite first stage intercalation compound FeCl ₃ -C ₆ Has a density at He equilibrium pressure of 2.65 g / cm ³ However, the density after hydrogen reduction at 300 ° C. is 1.34 g / cm. ³ The density decreases to (density ratio 0.51), and creation of nanospaces is recognized between the layers. That is, the hydrogen storage amount is improved to 0.9 wt% after reduction at 300 ° C. with respect to 0 wt% before reduction.
(C) Using graphite oxide and comparing the He equilibrium pressure density before and after the heat treatment at 400 ° C., it is 2.09 g / cm before the heat treatment. ³ In contrast, 0.474 g / cm after heat treatment ³ (Density ratio is 0.22) and the density is greatly reduced, and the creation of nanospace is recognized. That is, the hydrogen occlusion amount is improved to 0.1 wt% before heat treatment to 2.2 wt% after heat treatment.
[0017]
From the above, the He equilibrium pressure density is 0.20 g / cm. ³ The following materials have a reduced hydrogen storage amount per unit volume and become bulky materials. Therefore, in practice, the He equilibrium pressure density is 0.20 g / cm. ³ That is important. Further, in order to increase the hydrogen storage property, it is necessary to expand the graphite layer, and it is possible to intercalate up to the first stage between the graphite layers, and CuCl as a material that can expand the layer to about 1 nm. ₂ And FeCl ₃ Graphite intercalation compounds can be mentioned, but by reducing these to metallization, a maximum of 3.3 g / cm ³ Up to the He equilibrium pressure density. Thus, in order to increase the hydrogen storage amount, it is indispensable to have a nanospace that easily absorbs hydrogen by removing atoms or molecules inserted from the graphite intercalation compound. As a specific index, the He equilibrium pressure density is 0.20 to 3.3 g / cm. ³ It is important to be a hydrogen storage material. In addition, it is also important that these hydrogen storage materials have a He equilibrium pressure density ratio reduced to 0.7 to 0.1 with respect to the graphite intercalation compound before at least heat treatment or reduction treatment. When the He equilibrium pressure density ratio is 0.7 or more, the amount of nanospace is still small and a sufficient hydrogen storage amount cannot be secured. On the other hand, when it falls to 0.1 or less, it becomes a bulky material, the hydrogen storage amount per volume falls, and it becomes difficult to use practically.
[0018]
(Regarding Claim 7) The present invention specifies the above-mentioned graphite-based hydrogen storage material from the structure, and the regular graphite interlayer is 0.35 nm or more and 2 nm or less from the observation of an image of a transmission electron microscope. Alternatively, it is essential that the crystallites forming the regular layers have a portion opened between 1 nm and 100 nm. That is, as a result of analyzing the material having a large amount of hydrogen occlusion in more detail than the image of the transmission electron microscope, the inventors have found that the regular interlayer of graphite is 0.35 nm or more and 2 nm or less. It has been found that the gap between the crystallites forming the interlayer has an open portion of 1 nm or more and 100 nm or less. Usually, in order to occlude hydrogen, it is necessary to spread between layers of 0.5 nm or more. From this point, when an inclusion is inserted into the interlayer and then the interlayer is expanded by gasifying the inclusion in the interlayer, the interlayer is restored by van der Waals force between the carbon network planes forming the interlayer. There are many cases. However, the graphite-based hydrogen storage material of the present invention has a structure in which a graphite layer is deformed and maintains a nanospace in a structure portion where a lattice defect or a structural shift occurs in a crystal structure, and a fan is formed in a structure portion that is greatly expanded The nanospace is maintained without returning to the original interlayer state due to the decrease in Delwars force, and it can be used as a hydrogen storage site. The above value is important in specifying a graphite-based hydrogen storage material having a hydrogen storage site formed as described above and having a high hydrogen storage capacity.
[0019]
(Embodiments 8 and 9) Each invention specifies the above-mentioned graphite-based hydrogen storage material from the structure. In the powder X-ray diffraction method (incident X-ray: CuKα), the diffraction angle (2θ ) Has a peak at 24.5 ° or less, more preferably, it is essential that the peak or bulge be detected when the diffraction angle (2θ) by the diffractometer method is 10 ° or less. In other words, intercalation compounds and graphite oxide generally have a clear peak at 24.5 degrees or less, and spread between the layers is recognized. However, by applying heat treatment or reduction treatment, nanospaces are created in the interlayers, Uniform spread is reduced. And the thing which processed excessively and remove | excluded the intercalant and oxide in an interlayer will return an interlayer to 3.35cm. Even after these treatments, the material having a high hydrogen storage capacity does not return crystallinity to the interlayer distance of graphite. Particularly, the diffraction angle (2θ) is 24.5 degrees or less and the (002) plane spacing is 3.6 mm or more. It is indispensable to have such a structure, and such a material creates a nanospace suitable for hydrogen storage between layers. In particular, this phenomenon is remarkable in a material obtained by heat-treating graphite oxide. Also, for example, when graphite oxide is heat treated, the diffraction angle (2θ) by the diffractometer method is 10 ° or less, and peaks and bumps appear, and the first stage FeCl 3 and graphite intercalation compound is reduced at 300 ° C. Shows a peak at a diffraction angle (2θ) of 9.4 °. This is because the reduction of FeCl3 proceeds with the interlayer spread to 0.94 nm, and it becomes a material with a high hydrogen storage capacity.
[0020]
(About Claim 10) This invention also specifies the above graphite-type hydrogen storage material from the Raman spectroscopic analysis, and it is 1585 cm in the Raman spectroscopic spectrum of a wavelength of 514.5 nm. ^-1 To 1630cm ^-1 It is essential that a peak appears in That is, the present inventors, in a material obtained by heat treatment or reduction treatment of a graphite intercalation compound, intercalant is inserted between graphite layers, the layers are expanded, atoms or molecules inserted between the layers remain, nanospace When the Raman spectroscopic analysis is performed, 1580 cm of the G band is obtained. ^-1 For the peak of 1585-1630cm ^-1 It was discovered that a shifted peak appears. This Raman spectroscopic analysis is effective for information in the depth direction of several tens of nanometers from the surface layer of the material, and is not necessarily correlated with the size of the crystallite obtained by X-ray diffraction. For this reason, it is important to analyze the Raman spectroscopic analysis together with the X-ray diffraction for specifying the graphite-based hydrogen storage material.
[0021]
(About Claim 11) In the present invention, the above-described graphite-based hydrogen storage material is any one of Pt, Pd, Ni, Li, K, Cs, Rb, Ti, Cr, Fe, Cu, Co, Zr, Nb, and B. It is essential to contain at least one kind. Among these contained elements, the transition metal element can form an intercalation compound with graphite as a chloride, and can be contained by metalation by a method such as reduction. Alkali metals can be intercalated as graphite intercalation compounds and can also be used as graphite intercalation compounds. It can also be adjusted by subjecting the graphite intercalation compound to heat treatment or reduction treatment, expanding the interlayer, allowing nanospaces to develop, and then supporting the necessary elements. Pt, Pd, and Ni have the effect of adsorbing hydrogen and increasing the amount of hydrogen storage. In particular, Pt, Pd, Ni chloride and an intercalation compound of graphite are used, and metallization within the interlayer by reduction, or graphite oxide After heat-treating etc. to develop nanospace, a fine support in units of several nm has a great effect. Alkali metals such as K, Cs, and Rb are easy to form an intercalation compound with graphite, and are effective in improving the hydrogen storage capacity. Ti, Cr, Fe, Cu, Co, Zr, and Nb can adjust the graphite and intercalation compounds in the form of chlorides, leave them in metal between the layers by reduction, and create nanospaces for hydrogen storage sites in the interlaminar Make it easier.
[0022]
(About Claim 12) This invention makes it essential that the graphite raw material for adjusting the above graphite intercalation compounds is any of natural graphite, artificial graphite, quiche graphite, and mesophase pitch graphite. As the raw material graphite for adjusting the graphite intercalation compound, one having high crystallinity is desirable. Specifically, natural graphite such as scaly graphite, scaly graphite, earthy graphite, artificial graphite produced by firing coke, etc., graphite with improved crystallinity such as quiche graphite and mesophase pitch graphite are suitable. The graphite to which B is added is also included in the raw material graphite.
[0023]
(About Claims 13-15) Each invention inserted as a manufacturing method of the above graphite-type hydrogen storage material, the 1st process which inserts elements other than a carbon atom between the layers of graphite, and creates an intercalation compound. It goes through a second process that removes all or part of the atoms or molecules. Here, the first process for creating an intercalation compound by inserting atoms or molecules includes a liquid phase method for reacting with a liquid substance, a gas phase method for reacting with a gaseous substance, and a mixed powder of reactants. It can be carried out by either a heat treatment mixing method or a dipping method in which the reaction is carried out by dipping in a molten salt. As the gas phase method, for example, a graphite raw material and a substance to be intercalated are set in different places in a reaction tube, and the reactant is contacted and reacted with graphite in a gas state. Alkali metal graphite intercalation compounds such as K, FeCl ₃ And CuCl ₃ Intercalation compounds of chloride such as can be produced by a gas phase method. The liquid phase method is a method for producing an intercalation compound using a required solution. For example, in an embodiment in which an alkali metal is dissolved, it is necessary to add an aromatic hydrocarbon such as naphthalene. About this, it is thought that an alkali metal and an aromatic hydrocarbon make an ion pair, and solvent molecules such as THF are coordinated to this to dissolve it. When graphite is immersed in this solution, the ternary graphite intercalation compound can be adjusted. NH liquefied K ₃ K-NH by dissolving in graphite and reacting with graphite ₃ -It is possible to adjust ternary intercalation compounds of GIC. Other than this, graphite and chloroplatinic acid are reacted in thionyl chloride to form PtCl. ₃ A method for adjusting GIC, graphite oxide for adjusting by reacting with a strong acid or a strong oxidizing agent, and the like are also included in the liquid phase method. In addition, a method of heat-treating a mixed powder of graphite and a reactant, and a mixing method and a dipping method in which graphite is immersed in a molten salt are effective for mass production. In contrast, the second process of removing all or part of the inserted atoms or molecules can be performed by heat treatment or reduction treatment. Ternary intercalation compounds (K and THF, K and NH, etc.) with solvent in between layers ₃ It is effective to remove the intercalation compound between graphite and graphite) and graphite oxide by gasifying the solvent in the interlayer by heat treatment, or removing oxygen covalently bonded in the interlayer by thermal decomposition. Any heat treatment method may be used as long as it can heat the sample, such as laser irradiation or microwave irradiation, in addition to direct heating by a heater or burner. In the operation of removing all or part of the atoms or molecules inserted by the heat treatment, a treatment for carbonizing organic substances reacted between layers is also effective. The reduction treatment method is a treatment method that reduces metal chlorides intercalated between graphite layers and leaves them in the metal state as much as possible in the layers, and is necessary to develop nanospace with the layers expanded. . That is, as a reduction method, in addition to reduction at 150 ° C. to 500 ° C. using hydrogen gas, reduction can be performed at a high temperature using an organic substance such as ethylene. Further, there are a method using an alkali metal such as K or Na and a method using a solution-like reducing agent such as an aqueous hydrazine solution. As a matter of course, a combination of reduction treatment and heat treatment is also effective.
[0024]
【Example】
Hereinafter, the usefulness of the invention will be clarified by test examples. In this test example (Examples 1 to 8 in Tables 1 and 2 and Comparative Examples 1 and 2), graphite intercalation compounds in which atoms or molecules were inserted between 5 wt% and 70 wt% between the graphite layers were expanded as three layers. Using elemental graphite intercalation compound, transition metal chloride-graphite intercalation compound, and graphite oxide, 5 to 100 wt% of elements other than carbon atoms are removed by either heat treatment or reduction treatment to express nanospace This is an example of examining the effectiveness of the hydrogen storage material. The raw material graphite used is natural graphite (flaky graphite) with an average particle diameter of 300 μm, good natural graphite (flaky graphite) with an average particle diameter of 8 μm, quiche graphite with an average particle diameter of 20 μm, and mesophase pitch system. There are four types of graphite and MCF with an average particle size of 10 μm. An intermediate graphite intercalation compound is referred to as an intermediate sample.
[0025]
<Preparation of Intercalation Compound> The graphite intercalation compound was prepared by the following method using the raw material graphite (first process of the invention).
The intermediate samples of Examples 1, 4 and 5 are the natural graphite (flaky graphite having an average particle size of 300 μm), the intermediate sample of Example 6 is the MCF, the intermediate sample of Example 7 is the Kish graphite. As a ternary graphite intercalation compound of K and THF (K-THF-GIC), the liquid phase method was used. In this adjustment, 50 ml of THF and 1.6 g of naphthalene were mixed in a container, and then K1.1 g was added and mixed and dissolved. The mixed solution was charged with 2 g of natural graphite in Examples 1, 4, and 5, 2 g of MCF in Example 6, and 2 g of Kish graphite in Example 7, and allowed to react for 72 hours with stirring. . After completion of the reaction, the undissolved portion of naphthalene and THF were filtered and removed by vacuum drying to prepare K-THF-GIC which is an intercalation compound of K-THF.
As an intermediate sample between Examples 2 and 8 and Comparative Example 1, natural graphite (flaky graphite having an average particle size of 300 μm) was used, and FeCl ₃ And graphite intercalation compound (FeCl ₃ -GIC). In this adjustment, in Example 2 and Comparative Example 1, first, 8 g of natural graphite and FeCl in an argon purged glove box. ₃ 19.3 g of was put into a two-valve tube and evacuated, and then the two-valve tube was sealed. Then, the 2-valve tube is reacted at 300 ° C. for 7 days to obtain the first stage FeCl. ₃ -GIC was prepared by a vapor phase method. In Example 8, 8 g of the natural graphite was previously melted with FeCl. ₃ The first stage of FeCl ₃ -GIC was produced by a dipping method.
The samples of Example 3 and Comparative Example 2 were made of natural graphite (flaky graphite) having an average particle diameter of 8 μm, and graphite oxide was prototyped by the liquid phase method as follows. First, 8 g of the natural graphite was put into 150 ml of fuming nitric acid, and 64.4 g of potassium chlorate was further added to react for 3 hours. The reaction temperature was 55 ° C. After completion of the reaction, it was diluted, filtered and dried to produce graphite oxide.
[0026]
<Preparation of hydrogen storage material> The intermediate samples described above were prepared by applying the following treatment except for Comparative Example 2 (second process of the invention).
(Application of heat treatment)
In the case of the intercalation compound of Example 1 (K-THF-GIC), the intermediate sample is placed in a glass tube and evacuated, heated with a gas burner, and THF is gasified from the intercalation and discharged. A hydrogen storage material was prepared.
In the case of each intercalation compound (K-THF-GIC) of Examples 4 to 7, as an example in which the heating method was changed, microwaves (CO ₂ The hydrogen storage material was produced by gasifying and extracting THF inserted between the layers.
-The graphite oxide of Example 3 produced the hydrogen storage material by heating the said intermediate sample at 200 degreeC-400 degreeC in air | atmosphere, and decomposing | disassembling the oxygen covalently bonded between layers.
(Application of reduction treatment)
Example 2 and Comparative Example 1 and Interlayer Compound of Example 8 (FeCl ₃ -GIC), the intermediate sample is brought into contact with hydrogen gas at 200 ° C. to 500 ° C., and FeCl in the graphite layer. ₃ A hydrogen storage material was produced by reducing Specifically, FeCl in the interlayer was heated by hydrogen gas at 300 ° C. in Example 2, 500 ° C. in Comparative Example 1 and 300 ° C. in Example 8. ₃ The amount was changed.
[0027]
<Physical Properties of Sample> With respect to the samples of Examples 1 to 8 and Comparative Examples 1 and 2 prepared as described above, powder X-ray diffraction analysis, Raman spectroscopic analysis, and He equilibrium pressure density were measured as follows.
[0028]
(Powder X-ray diffraction) In this diffraction, MXP18VAHF manufactured by Mac Science Co., Ltd. was used as an X-ray diffraction apparatus utilizing an automatic recording method (diffractometer) using a counter (counter tube). In the measurement, the applied voltage and current to the X-ray tube were 40 kV and 150 mA, and CuKα was used as the incident X-ray. The X-ray powder pattern of each sample was measured, and the 2θ on the (002) plane and the interlayer distance on the (002) plane were measured.
(Micro Raman spectroscopy) In this analysis, RM2000 manufactured by RENISHAW was used as a Raman analyzer. In the measurement, an Ar + laser − having a wavelength of 514.5 nm was used, and the Raman spectrum of each sample was examined.
(Observation with Transmission Electron Microscope) In the image observation with this microscope, a Tecnai G2 manufactured by EFI was used as a transmission electron microscope, and the acceleration voltage was set to 200 kV to investigate the spread between layers of each sample.
[0029]
(Measurement of He Equilibrium Pressure Density) In this measurement, as schematically shown in FIG. 3, the He equilibrium pressure density was measured as follows using a measuring apparatus including the pressure vessels 1 and 2. First, approximately 1 g of the measurement sample is accurately put into the pressure vessel 2. Next, after evacuating the pressure vessels 1 and 2, about 0.2 MPa of He is put into the vessel 2 to accurately adjust the pressure P _0.2 Measure. In addition, with the valve (1) on the pressure vessel 2 side closed, the pressure vessel 1 is filled with He at a pressure of 0.8 Mpa and the pressure P is accurately measured. _0.8 Measure. Further, with the valve (2) provided in the upstream piping section of the pressure vessel 2 closed, the valves (1) and (3) are opened, and the He equilibrium pressure P of the pressure vessel 1 and the pressure vessel 2 is opened. _E Measure. And the He equilibrium pressure density of the sample is V ₀ Ask for.
[0030]
[Formula 1]
[(P _0.8 ・ V ₂ ) / T _0.8 ] + [(P _0.2 ・ (V ₁ -V _s ) / T _0.2 ) = [(P _E ・ V ₂ ) / T _E ] + [P _E ・ (V ₁ -V _s ) / T _E ]
[0031]
The He equilibrium pressure density (A) is the sample weight W / sample volume V. ₀ Ask more. Here, the volume V of the reaction vessel ₁ , V ₂ Measure in advance. In addition, the temperature in the pressure vessel (T _0.8 , T _0.2 , T _E ) Was set to 30 ° C., but actual values were used for measuring the He equilibrium pressure density.
[0032]
<Sample Evaluation> The samples of Examples 1 to 8 and Comparative Examples 1 and 2 were measured for hydrogen storage amount and hydrogen release amount by a test method according to JIS7201 and 7203. In this measurement, each sample was precisely weighed, placed in a sample tube and evacuated, and then the hydrogen pressure was increased to 12 MPa and the hydrogen storage amount [wt%] was measured by the volume method. Next, the hydrogen release amount was confirmed by returning to room temperature. As the cycle characteristics, the hydrogen occlusion amount [wt%] after repeating the above occlusion and release five times was measured. In addition, the sample of Example 5 is a value in the aspect which carried about 10 wt% Pt. This adjustment is ₂ PtCI ₆ Was dissolved in pure water, the sample of Example 5 was added, mixed and dried, and then hydrogen reduced at 400 ° C. to disperse Pt on the material surface. Table 1 lists the evaluation results of the above Examples 1 to 3 and Comparative Examples 1 and 2 together with the material constitution / physical properties, and Table 2 lists the evaluation results of the above Examples 4 to 8 together with the material constitution / physical properties. It is.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
First, Table 1 shows the following. First, Examples 1-3 are K-THF-GIC, FeCl as graphite intercalation compounds. ₃ -A sample using GIC and graphite oxide and removing some or all of the elements intercalated between layers. Comparative Example 1 uses FeCl as a graphite intercalation compound. ₃ -A sample using GIC to remove some or all of the elements intercalated between layers. Comparative Example 2 is an untreated sample of graphite oxide. Where FeCl ₃ In the case of an interlayer compound of graphite and graphite (Example 2 and Comparative Example 1), the interlayer compound of the first stage is C ₆ -FeCl ₃ And the intercalant inserted between the layers is 69.3 wt%. In this state, FeCl is interposed between the graphite layers. ₃ As shown in Comparative Example 1, the hydrogen occlusion amount is 0.1 wt%. However, from the interlayer FeCl ₃ Fe and Cl ₂ For example, in the sample of Example 2 from which 60% was removed, the hydrogen storage amount showed a large value of 0.9 wt%. In addition, graphite oxide is generally C ₈ O ₅ H ₂ It has a composition of the order, and oxygen and hydrogen are about 46 wt% covalently bonded between the graphite layers. The graphite oxide of Comparative Example 2 also has a low hydrogen storage capacity of 0.1 wt% when oxygen and hydrogen are not removed, but the sample of Example 3 excluding 85 wt% has a hydrogen storage capacity of 2.2 wt%. . Further, Example 1 is a ternary graphite intercalation compound in which K and tetrahydrofuran (THF) are intercalated with 38.9 wt% in the graphite layer, but the hydrogen storage capacity can be obtained by gasifying THF and removing it from the layer. Is 2.6 wt%.
[0036]
As another example, FeCl which is an intercalation compound of Example 2 is used. ₃ Using -GIC and graphite oxide, which is an intercalation compound of Example 3, the reduction temperature and the heat treatment temperature were changed to examine in detail the elements other than carbon from the interlaminar. Examples of the results are shown in FIGS. From these results, it is understood that the graphite intercalation compound exhibits hydrogen storage ability by removing all or part of elements other than carbon atoms inserted between the graphite layers, and the hydrogen storage capacity increases as the element is removed more. From these results, those practically removed at least 5% or more, that is, in the range of 5 to 100% are preferable.
[0037]
By the way, the sample of Example 2 and FIG. 1 is FeCl having an ionic bond. ₃ Is an ion-bonded intercalant compound that uses intercalant as an intercalant, and it is easy to create nanospaces with high hydrogen storage capacity by appropriately controlling the reduction treatment to deposit fine particles such as Fe in the interlayer. I understand. The samples of Example 3 and FIG. 2 use graphite oxide, and are of a covalent bond type in which oxygen or the like is covalently bonded between the graphite layers to expand the layers, and the elements bonded to carbon are removed by heat treatment. This shows that it is easy to create nanospace. Further, Example 4 is an example of a dispersion force type in which all the intercalant between layers is removed, and then the dispersion force acting between the carbon network planes acts to maintain the spread between the layers. As described above, in order to create a nanospace for hydrogen storage in the interlayer, it is necessary to use the bond strength of any of the ion bond type, dispersion force type, and covalent bond type in the graphite intercalation compound. is there.
[0038]
In the above graphite-based hydrogen storage material, the operation of removing all or part of the elements other than carbon atoms is either heat treatment or reduction treatment. Examples 1, 3, and 4 are examples of heat treatment, and Example 2 is an example of reduction treatment. As a heat treatment method, a burner was used in Example 1, but CO2 was used in Example 4 in order to rapidly gasify THF between layers. ₂ The laser was irradiated. The reduction treatment is a treatment method for ensuring a nanospace in which metal chlorides intercalated between graphite layers are reduced and remain in a metal state as much as possible in the layers. Example 2 is a hydrogen reduction at 300 ° C. It is an example.
[0039]
In addition, as a physical property of the graphite-based hydrogen storage material, the density of the sample (He equilibrium pressure density) calculated under the conditions of He pressure of 2 atm and 8 atm based on Boyle-Charles' law is 0.25 g / cm. ³ To 3.3 g / cm ³ It is important to secure the amount of nanospace for storing hydrogen that the He equilibrium pressure density ratio as compared with the graphite intercalation compound as a raw material is reduced to about 0.7 or less. However, when the He equilibrium pressure density ratio is reduced to 0.1 or less, the interlayer is too widened to become a bulky material, so that the weight that can be filled in a certain container is reduced and practical use is difficult. Therefore, it is important that the He equilibrium pressure density ratio of the hydrogen storage material is reduced from 0.7 to 0.1.
[0040]
That is, in the case of Example 1, by heating the ternary graphite intercalation compound of K and THF with a burner, the THF intercalated in the graphite interlayer was gasified at once, expanding the interlayer, Create many nanospaces. The He equilibrium pressure density before heating of this material is 1.25 g / cm. ³ On the other hand, the He equilibrium pressure density after heating is 0.39 g / cm. ³ It is presumed that the density is greatly reduced to (density ratio 0.31), the nanospace is developed with the expansion between layers, and the density is lowered. Example 2, ie FeCl ₃ And graphite first stage intercalation compound FeCl ₃ -C ₆ Has a density at He equilibrium pressure of 2.65 g / cm ³ However, the density after hydrogen reduction at 300 ° C. is 1.34 g / cm. ³ The density decreases to (density ratio 0.51), and nanospace is developed between the layers. The amount of hydrogen occluded at this time is improved to 0.9 wt% after reduction at 300 ° C. with respect to 0 wt% before the reduction treatment. Further, when Example 3 and Comparative Example 2, that is, graphite oxide was used and the He equilibrium pressure density before and after the heat treatment at 400 ° C. was compared, 2.09 g / cm before heat treatment was compared. ³ In contrast, 0.47 g / cm after the heat treatment of Example 3 ³ (Density ratio is 0.23) and the density is greatly reduced, and the creation of nanospace is recognized. The amount of hydrogen occlusion at this time is 2.2 wt% after heat treatment with respect to 0.1 wt% before heat treatment, and an improvement in hydrogen occlusion is recognized.
[0041]
Here, Comparative Example 1 is FeCl ₃ -Characteristics of GIC obtained by hydrogen reduction at 500 ° C, Comparative Example 2 is a characteristic of graphite oxide. In Comparative Example 1, since the reduction temperature is too high, FeCl ₃ At the same time, the Fe is exhausted to the outside of the interlayer, and the interlayer distance of the graphite returns to 0.36 nm, which suggests that the nanospace has disappeared. As a result, the He equilibrium pressure density ratio is as high as 0.8, and the hydrogen storage capacity is almost lost. Since Comparative Example 2 is graphite oxide before heat treatment, the density ratio representing the degree of creation of nanospace is 1.0, and there is almost no nanospace and hydrogen storage capacity that are sites for storing hydrogen.
[0042]
Next, the following can be understood from the result of analysis from the transmission electron microscope image (TEM image). From the observation with the TEM image, the heat treatment samples of Examples 1 and 3 have 0.37 to 0.4 nm interlayer, and the reduction sample of Example 2 has 0.94 nm interlayer. Further, the regular interlayer of graphite is in Example 2, that is, FeCl. ₃ In the hydrogen reduction using -GIC, when metal agglomeration occurs between the graphite layers, although not shown in Table 1, it may spread to an interval of about 2 nm. Therefore, the regular interlayer of graphite in the present invention is 0.35 nm or more and 2 nm or less, and the gap between crystallites forming the regular interlayer in Example 1 is 2 nm to 50 nm. It was determined that the gap between the crystallites forming a typical interlayer had a portion opened in the range of 1 nm to 100 nm. These physical properties are an important measure for specifying the inventive material.
[0043]
Further, in the powder X-ray diffraction method (incident X-ray: CuKα), it is necessary that the interlayer is spread, that is, the diffraction angle (2θ) by the diffractometer method has a peak at 24.5 ° or less. Interlayer compounds and graphite oxide generally have a clear peak at 24.5 ° or less, and broadening of the interlayer is observed, but by applying heat treatment or reduction treatment, nanospaces are created in the interlayer, and the interlayer is uniform. The spread decreases. And when those processes are performed excessively and the intercalant and oxide in the interlayer are largely removed, the interlayer returns to 3.35 mm. A material having a high hydrogen storage capacity does not return to the interlayer distance of graphite after these treatments, and it is important that the diffraction angle (2θ) has a peak at 24.5 ° or less. It has been confirmed that such materials have nanospaces between the layers. In particular, in the case where the interlayer is spread, a peak or a bulge is detected when the diffraction angle (2θ) is 10 ° or less. That is, the samples of Examples 1 and 2 were raised at 0 to 10 °, and the samples of Example 2 were peaked at 18.9 ° and 9.42 °. It can be seen that is spreading.
[0044]
Other physical properties include 1585 to 1630 cm in a 514.5 nm Raman spectrum. ^-1 It is that a peak appears. In a sample obtained by heat treatment or reduction treatment of a graphite intercalation compound, when atoms or molecules inserted between the graphite layers partially remain to create nanospaces, the G band 1580 cm ^-1 For the peak of 1585-1630cm ^-1 It is known that a shifted peak appears. However, since Raman spectroscopic analysis is a surface analysis method from the surface of the sample to a depth of several nanometers, the result of this analysis is 1585 to 1630 cm. ^-1 Even if no peak appears, atoms or molecules inserted between the layers inside the sample may remain. In the samples of Examples 1 and 2, a peak is confirmed at 1606 to 1616 nm. In the sample of Example 3, it almost returned to the G band peak by the heat treatment, but it has a bulge at 10 ° or less from the X-ray diffraction result, and the expansion between layers is confirmed. That is, in the graphite-based hydrogen storage material, the diffraction angle 2θ has a peak at 24.5 ° or less, or 1585 to 1630 cm. ^-1 Those exhibiting a Raman peak are important indicators for the hydrogen storage material of the present invention.
[0045]
(Others) Example 5 shows the characteristics of a sample carrying about 10 wt% Pt. The hydrogen storage amount is increased by about 1 wt% from the unsupported Example 4 and the effect of Pt support is recognized. It has been confirmed that such an effect tends to be the same with Pd, Ni, and the like other than Pt. Alkali metals such as K, Cs, and Rb can easily form an intercalation compound with graphite, and are effective in improving the hydrogen storage capacity. Ti, Cr, Fe, Cu, Co, Zr, and Nb are in the form of chloride. It is possible to adjust the graphite and intercalation compound by leaving it in a metal state between the layers by reduction or the like, and by creating nanospaces in the interlaminar layer, it is possible to adjust a material with excellent hydrogen storage capacity. Examples 6 and 7 are examples in which MCF, which is Kish graphite and mesophase pitch-based graphite, was used as a graphite raw material for adjusting the graphite intercalation compound. In addition to this, artificial graphite and graphite to which B is added can also be used as raw material graphite.
[0046]
【The invention's effect】
As described above, the graphite-based hydrogen storage material of the invention and the method for producing the same use the graphite intercalation compound in which atoms or molecules are inserted between the graphite layers to increase the interlayer distance, and the atoms or molecules inserted from the graphite intercalation compound. Is removed entirely or partially by heat treatment, reduction treatment, or the like, thereby making it possible to create more hydrogen storage sites, that is, nanospaces excellent in hydrogen storage capacity, due to the graphite intercalation compound. As a result, the present invention can efficiently store a large amount of hydrogen, is lightweight, can be used repeatedly, and can be used in a practical manner with a reduced manufacturing cost because the manufacturing method is easy.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between a hydrogen reduction temperature and a hydrogen storage amount (amount removed) in an inventive material example.
FIG. 2 is a graph showing the relationship between the heat treatment temperature and the hydrogen storage amount (removed amount) for the inventive material examples.
FIG. 3 is a reference schematic diagram for explaining a method of measuring He equilibrium pressure density.
[Explanation of symbols]
1 and 2 are pressure vessels
▲ 1 to ▲ 3 ▼ are valves for opening and closing

Claims (15)

A graphite intercalation compound in which atoms or molecules are inserted in an amount of 5 to 70% by weight between graphite layers to increase the interlayer distance, and a hydrogen storage site in which all or part of the inserted atoms or molecules are removed. A graphite-based hydrogen storage material characterized by comprising: 2. The graphite-based hydrogen storage material according to claim 1, wherein the graphite-based hydrogen storage material is removed in a range of 5 to 100% with respect to the amount of the inserted atom or molecule. 2. The graphite-based hydrogen storage material according to claim 1, wherein atoms or molecules remaining between the graphite layers are in contact with one surface of the two graphite layers sandwiching the atoms or molecules. The graphite-based hydrogen storage material according to any one of claims 1 to 3, wherein the graphite intercalation compound is one of an ionic bond type, a dispersion force type, and a covalent bond type. The graphite-based hydrogen storage material according to any one of claims 1 to 4, wherein the inserted atoms or molecules are all or partly removed by heat treatment or reduction treatment. Sample density (He equilibrium pressure density) calculated based on Boyle-Charle's law under the conditions of He pressure of 2 atm and 8 atm is 0.20 to 3.3 g / cm ³ and is a raw material The graphite-based hydrogen storage material according to any one of claims 1 to 5, wherein a He equilibrium pressure density ratio is reduced to 0.7 to 0.1 as compared with the graphite intercalation compound. From a transmission electron microscope image, it has a portion where the regular graphite interlayer is open in the range of 0.35 to 2 nm, or the crystallites forming the regular interlayer are in the range of 1 to 100 nm. The graphite-based hydrogen storage material according to any one of 1 to 6. The graphite-based hydrogen according to any one of claims 1 to 7, wherein in a powder X-ray diffraction method (incident X-ray: CuKα), a diffraction angle (2θ) by a diffractometer method has a peak at 24.5 ° or less. Occlusion material. The graphite-based hydrogen according to any one of claims 1 to 7, wherein in a powder X-ray diffraction method (incident X-ray: CuKα), a peak or a bump is detected when a diffraction angle (2θ) by a diffractometer method is 10 ° or less. Occlusion material. 8. The graphite-based hydrogen storage material according to claim 1, wherein a peak appears at 1585 to 1630 cm −1 in a Raman spectroscopic spectrum at a wavelength of 514.5 nm. One or more elements of Pt, Pd, Ni, Li, K, Cs, Rb, Ti, Cr, Fe, Cu, Co, Zr, Nb, and B are contained in the black smoke layer. Item 8. The graphite-based hydrogen storage material according to any one of Items 1 to 7. The graphite-based hydrogen storage material according to claim 1, wherein a graphite raw material for adjusting the graphite intercalation compound is any one of natural graphite, artificial graphite, quiche graphite, and mesophase pitch-based graphite. Graphite-based hydrogen characterized by undergoing a first process of creating an intercalation compound by inserting atoms or molecules between graphite layers and a second process of removing all or part of the inserted atoms or molecules. Manufacturing method of occlusion material. The first process to create an intercalation compound by inserting the atoms or molecules includes the liquid phase method for reacting with a liquid substance, the gas phase method for reacting with a gaseous substance, and the mixing of heat treating the mixed powder of the reactants. The method for producing a graphite-based hydrogen storage material according to claim 13, wherein the method is carried out by any one of a method and a dipping method in which the reaction is performed by dipping in a molten salt. The method for producing a graphite-based hydrogen storage material according to claim 13 or 14, wherein the second process of removing all or part of the inserted atoms or molecules is performed by heat treatment or reduction treatment.

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