JP2004256860A - Hydrogen storage body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage body having large hydrogen desorption capacity, capable of desorbing hydrogen at ≤150°C, and suitable for mass production. <P>SOLUTION: The hydrogen storage body 10 is constituted of: a hydrogen absorbing powder 1 composed of Mg or Mg alloy and performing the absorption and desorption of hydrogen; and a coating layer 2 having a composition different from that of the powder 1 and formed on the surface of the powder 1 by the vapor-phase process. The coating layer 2 can be composed of at least one kind among Pd, V and Ti-Cr alloys. By depositing the coating layer 2 by the vapor-phase process, a thin film of uniform thickness can be deposited onto the surface of the powder 1 and stress can be uniformly applied to the powder 1. When stress, particularly compressive stress, is applied from the coating layer 2 to the powder 1, the hydrogen located in a hydrogen occlusion site in the powder 1 is moved and the desorption of hydrogen from the powder 1 can be accelerated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

なお、本発明において、ｂｃｃ相のほかに存在し得る相は、ラーべス相である。
【００２０】
さて、図１に示したように、被覆層２は、水素吸蔵粉体１のほぼ表面全体を覆うようにして形成されている。本発明では、この被覆層２を気相法により形成することを推奨する。気相法によれば、被覆層２を、水素吸蔵粉体１の表面に薄くかつ厚さ均一に形成することができる。なお、従来技術として、Ｐｄ／Ｍｇ／Ｐｄ等の膜構造をすべてスパッタ法で作製する例を示したが、本発明では水素吸蔵粉体１は気相法で作製する必要はない。つまり本発明では、水素吸蔵粉体１については通常の溶解・鋳造法で得ることができるため、水素吸蔵体１０の製造コストを低減できるとともに、量産性に優れる。
【００２１】
ここで、気相法を用いて水素吸蔵粉体１の表面全体に厚さの均一な被覆層２を形成させるには、水素吸蔵粉体１を転動させることが有効である。水素吸蔵粉体１を転動させるには、例えば、水素吸蔵粉体１をトレーに収容している場合に、このトレーに振動を加える手段を設ければよい。この場合の振動は、例えば超音波〜１Ｈｚとすることができる。また、市販の振動器を用いて、１〜５００Ｈｚの振動を加えるようにしてもよい。さらには、振動器に限らず、トレー内に収容された水素吸蔵粉体１を撹拌棒で撹拌させるような方法を用いることもできる。なお、水素吸蔵粉体１を転動させることができれば、これらの振動または撹拌手段に限られるものではない。
また、気相法で被覆層２を形成する場合の他の利点として、電解メッキまたは無電解メッキのような方法に比べて、水素吸蔵粉体１の表面を清浄に保ちやすいということが挙げられる。すなわち、気相法で被覆層２を形成する場合には、水素吸蔵粉体１の表面を清浄化するための処理、例えば、粉体表面へのイオンボンバード処理やレーザービーム照射、減圧（または真空）下での粉体の加熱処理を併用することができる。また、水素吸蔵粉体１を作製してから被覆層２を形成し終えるまで、水素吸蔵粉体１を大気に一切暴露させないということも、水素吸蔵粉体１の表面を清浄化する上で有効である。
【００２２】
ここで、気相法とは、真空またはガス中に原子、分子、またはそれらの数ｎｍから数百ｎｍの微粒子化したもの、イオン、帯電粒子、を発生させ対象物に堆積させる方法である。気相法としては、例えば、イオンプレーティング法、スパッタ法、レーザーアブレーション法、高周波プラズマＣＶＤ法、等が挙げられる。なかでも、複数のターゲットを個々に、かつ同時に制御できるレーザーアブレーション法が特に好ましい。なお、気相法を用いて被覆層２を水素吸蔵粉体１の表面につける際に好ましい装置例については後述する。
【００２３】
上述したように、被覆層２は、水素吸蔵粉体１のほぼ表面全体を覆うようにして形成されており、その被覆率は９０％以上、さらには９３％以上、より望ましくは９５％以上である。
被覆層２の膜厚は、水素吸蔵粉体１を構成する粉体の形状にもよるが、数ｎｍ〜５００ｎｍとすることが望ましい。被覆層２の膜厚が数ｎｍを下回ると、水素吸蔵粉体１に付与される応力が小さくなるため、水素吸蔵粉体１からの水素放出が促進されにくい。一方、被覆層２の膜厚が５００ｎｍを超えると、水素吸蔵粉体１の占める割合が相対的に減少してしまうため、水素吸蔵体１０の単位体積あたりの水素吸蔵量が減ってしまう。よって、被覆層２の膜厚は、数ｎｍ〜５００ｎｍとすることが望ましい。より望ましい被覆層２の膜厚は２０〜２００ｎｍ、さらに望ましい被覆層２の膜厚は５０〜１００ｎｍである。
【００２４】
次に、水素吸蔵粉体１と被覆層２とからなる第１の実施形態に係る水素吸蔵体１０の水素放出メカニズムについて説明する。
水素吸蔵粉体１および被覆層２は、水素原子の移動（吸蔵または透過）に伴って、その体積が膨張、収縮する。つまり、水素原子が水素吸蔵体１０内に侵入すると、水素吸蔵体１０は膨脹し、一方、水素原子が水素吸蔵体１０の外部に放出されると、水素吸蔵体１０は収縮する。但し、被覆層２と水素吸蔵粉体１はその組成が異なるとともに、被覆層２は水素吸蔵体１０の最外周に設けられているために、被覆層２が収縮し、この収縮による圧縮応力が図２に示すように水素吸蔵粉体１に付与されることとなる。そして、この圧縮応力の発生により、水素吸蔵粉体１内に貯蔵されていた水素原子の放出が促進されると推測される。このように、本実施の形態に係る水素吸蔵体１０では、水素吸蔵粉体１からの水素放出環境が改善されるため、水素放出温度が１５０℃以下という比較的低温の状態でも、水素吸蔵粉体１からの水素放出がスムーズに行われる。よって、第１の実施形態に係る水素吸蔵体１０によれば、１５０℃以下で３ｍａｓｓ％以上、さらには４ｍａｓｓ％以上の水素放出量を得ることができる。
なお、被覆層２は、水素ガスを原子状に解離させる触媒作用を発現し、かつ解離した水素原子を内部拡散させる作用を有する。そして、被覆層２を構成する金属または合金は、水素分子を解離する触媒能が、水素吸蔵粉体１を構成するＭｇまたはＭｇ合金よりも優れていると推測される。つまり、水素吸蔵体１０の水素吸蔵メカニズムについては定かではないが、被覆層２は水素分子を低温（１５０℃以下）で原子に分解する触媒的な働きをしていると考えられる。
【００２５】
以上、水素タンク用として好適に用いられる水素吸蔵体１０の構成について詳述した。次に、本発明の水素吸蔵体１０を得るための望ましい製造方法を説明する。
本発明の水素吸蔵体１０の製造方法は、水素吸蔵粉体１を構成するＭｇ母材を得る工程（以下、「Ｍｇ母材作製工程」という）と、得られたＭｇ母材の表面に被覆層２を形成する工程（以下、「被覆層２形成工程」という）とを含む。なお、Ｍｇ母材作製工程では、Ｍｇ合金粉末を作製する場合を例にして説明する。
以下、各工程を詳述する。
【００２６】
＜Ｍｇ母材作製工程＞
Ｍｇ合金は、出発原料金属を例えばルツボ内で高周波等によって溶解することにより作製することができる。こうして得られたＭｇ合金のインゴットを、ディスクミル、乳鉢等を用いて例えば５００μｍ以下の粉体とする。続いて、５００μｍ以下のＭｇ合金粉末を水素化粉砕する。水素化粉砕されたＭｇ合金粉末は、さらに微粉砕され、フルイ（例えば５μｍ以下）で分級される。上述した理由から、水素吸蔵粉体１を構成するＭｇ合金粉末は、被覆層２が形成される前段階で、その平均粒径が数十ｎｍ〜数十μｍであることが好ましい。よって、Ｍｇ合金粉末をフルイで分級した後、試験管ミキサー等を用いてその平均粒径が数十ｎｍ〜数十μｍになるまで調整することが望ましい。なお、アトマイズ法を用いた場合には、こうした粉砕処理を経ることなく、所望の平均粒径を有するＭｇ合金粉末を得ることができる。
【００２７】
Ｍｇ合金粉末は、大気に曝されたりして、表面が不純物ガスで汚染されている場合がある。よって、Ｍｇ合金粉末の表面を清浄化するための処理を予め行った後に、以下の被覆層２形成工程に進むことが望ましい。Ｍｇ合金粉末の表面を清浄化するための処理としては、上述したように、粉体表面へのイオンボンバード処理やレーザービーム照射、減圧（または真空）下での粉体の加熱処理等が挙げられる。また、Ｍｇ母材作製工程と後述する被覆層２形成工程を、Ｍｇ合金粉末を大気に一切暴露させることなく一貫して行うことも有効である。
【００２８】
＜被覆層２形成工程＞
被覆層２形成工程では、Ｍｇ合金粉末またはＭｇ粉末を、Ｐｄ，Ｖ，Ｔｉ−Ｃｒ系合金の少なくとも１種で被覆する。Ｐｄ等の被覆方法としては、気相法を用いる。気相法によれば、Ｍｇ合金粉末またはＭｇ粉末の表面に薄くかつ厚さの均一な被覆層２を形成することができ、また被覆層２の厚さ制御も容易である。また、上述したようにＭｇ合金粉末またはＭｇ粉末に適度な振動を加えるなどして、被覆層２形成時にＭｇ合金粉末またはＭｇ粉末を転動させることにより、Ｍｇ合金粉末またはＭｇ粉末の表面全体に厚さ均一に被覆層２を形成させることができる。さらに、気相法は、無電解メッキ法等と比較して、Ｍｇ合金粉末またはＭｇ粉末の表面を比較的清浄に保ちやすいという利点をそもそも有しているが、上述した表面清浄化処理を併用することで、より一層、粉体表面の清浄化を図ることができる。なお、気相法を用いて被覆層２を形成する場合に用いられる装置の例は、後述の実施例で示す。
【００２９】
以上のＭｇ母材作製工程、被覆層２形成工程を経ることにより、Ｍｇ粉末の表面に被覆層２が形成された第１の実施形態に係る水素吸蔵体１０を得ることができる。なお、被覆層２と、水素吸蔵粉体１を構成するＭｇ粉末（またはＭｇ合金粉末）の間の水素原子の移動を容易にするという理由から、被覆層２を形成した後に、１００〜４００℃で０．５〜２時間程度、加熱保持する熱処理を施すことが望ましい。
【００３０】
被覆層２として、ｂｃｃを主相とするＴｉ−Ｃｒ系合金を選択する場合には、以下の方法を採用することができる。例えば、Ｔｉ−Ｃｒ−Ｖ系合金を被覆層２としたい場合には、Ｔｉ，Ｃｒ，Ｖそれぞれの単体ターゲットを準備する。そして、これらの単体ターゲットを用いて交互に、又は同時に、水素吸蔵粉体１としてのＭｇ粉末またはＭｇ合金粉末に被覆させればよい。被覆時に加熱するか、もしくは被覆後に加熱することによって、Ｔｉ−Ｃｒ−Ｖ系合金とすることができる。つまり、被覆層２形成後に、目的の組成比を有するＴｉ−Ｃｒ系合金になるように合金化すればよい。なお、加熱温度は、５００℃以下とすればよい。また、複数の単体ターゲットに限らず、合金ターゲットを使用してもよい。さらに、周知のアーク溶解法により、ｂｃｃを主相とするＴｉ−Ｃｒ系合金を作製してもよい。
【００３１】
次に、水素吸蔵体１０に対し、水素を吸蔵・放出させるための処理について簡単に述べる。水素吸蔵体１０に水素を吸蔵させる水素化処理は、水素雰囲気中で行う。また、水素化処理を行う際には、水素吸蔵体１０を入れた容器を減圧し、真空引きした後に水素を導入することが有効である。導入される水素の純度は、好ましくは９９．９９９９％以上である。
【００３２】
水素吸蔵体１０から水素を取り出すには、加熱条件または／および減圧条件を調整する。第１の実施形態に係る水素吸蔵体１０によれば、水素吸蔵体１０を１００〜１５０℃の範囲で加熱することによって、水素吸蔵体１０中の水素を容易に放出させることができる。また、水素吸蔵体１０を入れた容器を、その温度における放出曲線のプラトー圧以下の圧力に減圧することにより、水素吸蔵体１０中の水素を容易に取り出すことができる。ここで、減圧条件を示すと、５ｋＰａ以下に減圧することが望ましい。
【００３３】
＜第２の実施形態＞
水素タンク用として用いる場合に好適な、第２の実施形態に係る水素吸蔵体２０の断面を図３に模式的に示す。
図３に示す水素吸蔵体２０は、コア体（コア相）３、コア体３の周囲を取り囲む水素吸蔵相１ａ、水素吸蔵相１ａの表面に形成された被覆相２ａ、被覆相２ａとコア体３を連結するとともに、被覆相２ａからコア体３に水素原子を流通させる連結部（通路）４とで構成される。なお、水素吸蔵相１ａは、上述した水素吸蔵粉体１と同様の組成で構成することができる。また、被覆相２ａ、コア体３、連結部４を形成するには、いずれも被覆層２の箇所で挙げたもの、つまり、Ｐｄ，Ｖ，Ｔｉ−Ｃｒ系合金のいずれかを採用することができる。被覆相２ａ、コア体３および連結部４は、同一の金属または合金で構成することが望ましいが、異なる金属または合金で構成してもよい。
【００３４】
図３に示すように、第２の実施形態に係る水素吸蔵体２０は、水素吸蔵相１ａ、被覆相２ａ、コア体３とで構成された３層構造となっている。水素吸蔵相１ａは、被覆相２ａと、コア体３とで挟まれた構造となっており、被覆相２ａとコア体３との間には両者を連結する連結部４が確保されている。コア体３を設けているのは、水素吸蔵相１ａの内側からも、水素吸蔵相１ａに対して応力を付与するためである。この作用を発現するために、被覆相２ａと、コア体３とを連結する連結部４を設けている。
【００３５】
図４は、水素吸蔵体２０を模式的に示す部分断面図であり、水素吸蔵体２０内で発生する応力の状態を示す説明図である。
水素吸蔵体２０の最外周に位置する被覆相２ａにおいて水素原子が放出されると、被覆相２ａの体積が収縮する。これにより、被覆相２ａと隣接する水素吸蔵相１ａに圧縮応力が付与される。一方、水素吸蔵相１ａの内側に位置するコア体３において水素原子が放出されると、コア体３の体積が収縮する。これにより、コア体３と隣接する水素吸蔵相１ａに圧縮応力が付与される。また、被覆相２ａとコア体３とを連結する連結部４から水素原子が放出されると、連結部４も体積が収縮する。連結部４の体積収縮の一形態として、図４中白抜き矢印で示したように連結部４の高さが縮むと、被覆相２ａおよびコア体３に取り囲まれている水素吸蔵相１ａには、被覆相２ａおよびコア体３の両側から圧縮応力が付与されることとなる。このようにして、水素吸蔵相１ａには被覆相２ａ側およびコア体３側から、つまり１以上の側から応力が付与される。そして、この付与された応力により、水素吸蔵相１ａ中の水素吸蔵サイトに位置していた水素が移動し、水素吸蔵相１ａの水素放出が促進されることとなる。
【００３６】
すなわち、第１の実施形態では、水素吸蔵粉体１の周囲に応力が付与されていたのに対し、第２の実施形態では、水素吸蔵相１ａの周囲とさらにその内側から応力が付与される。このため、図３に示した形態を採用することで、水素吸蔵相１ａに付与される応力が大きくなり、水素吸蔵相１ａからの水素放出がより促進される。これにより、水素吸蔵相１ａの１５０℃以下での水素放出量が多くなる。
【００３７】
ここで、第２の実施形態の水素吸蔵体２０の作製方法の具体例を図５を用いて説明する。
まず、図５（ａ）に示すように、コア体３を構成する金属または合金を準備する。次に、このコア体３に対して、図５（ｂ）に示すように、水素吸蔵相１ａを構成する金属粉末（合金粉末）を被覆させる。この被覆は、スタンプミル等を用いて機械的な方法で行うことができる。ここで、水素吸蔵相１ａは粉状であるから、隣接する水素吸蔵相１ａの間には隙間が存在することになる。
図５（ｂ）に示した、コア体３の表面に水素吸蔵相１ａが形成された複合体の表面に対し、さらに被覆相２ａを形成して、図５（ｃ）に示す形態の水素吸蔵体２０を作製する。この被覆相２ａの形成は気相法を用いて行う。このとき、被覆相２ａの一部は水素吸蔵相１ａの間の隙間に侵入し、コア体３に到達する。これにより、コア体３と被覆相２ａとを連結する連結部４が構成される。ここで、図５（ｃ）の断面図を模式的に示すと、図３のようになる。なお、コア体３は、板状のものとしてもよい。
【００３８】
【実施例】
以下本発明の水素吸蔵体について、具体的な実施例に基づいて説明する。
（実施例１）
実施例１では、気相法の１種であるレーザーアブレーション法を用いて、水素吸蔵粉体１としてのＭｇ粉末にＰｄを被覆させる例について説明する。ここで、レーザーアブレーション法とは、強力なレーザービームを固体表面に照射することにより、固体構成物質そのものを爆発的に放出させる方法である。
実施例１で使用したコーティング装置１００の概要を、図６を用いて説明する。
コーティング装置１００は、内部が減圧可能な容器１２と、容器１２の下方に設置されたトレー１１と、容器１２の上方に設置されるターゲットに対してレーザービームを照射するレーザー装置１３とを主な構成要素としている。
【００３９】
トレー１１にはＭｇ粉末（水素吸蔵粉体１）が収容される。この状態で、被覆されるＰｄからなるターゲット１４に向けて、レーザー装置１３からレーザービームを照射する。レーザービームが照射されたターゲット１４の表面から蒸気化されたＰｄが放出される。蒸気化されたＰｄは下方に向けて飛散しトレー１１に収容されたＭｇ粉末（水素吸蔵粉体１）の表面に被覆する。なお、蒸気化したＰｄは飛散している過程で凝集し、数ｎｍ〜数十ｎｍに成長すると考えられる。
Ｍｇ粉末の表面に、被覆層２を構成するＰｄを厚さ均一に被覆させるために、トレー１１には、例えば超音波振動装置のような振動装置を設けることが望ましい。トレー１１に振動を付与することにより、トレー１１内に収容されているＭｇ粉末を転動させて、その表面に厚さ均一にＰｄを被覆させることができる。振動装置としては、超音波振動装置に限らず、公知のタップ装置を用いることができる。また、振動は１〜５００Ｈｚ程度の周波数を有していればよい。Ｍｇ粉末へのＰｄの被覆率を向上させるために、Ｍｇ粉末を加熱するための加熱装置をトレー１１に設けることも有効である。
【００４０】
蒸気化したＰｄを効率的にトレー１１に導くために、Ｐｄをイオン化し、かつターゲット１４とトレー１１との間に電位差を与えることが有効である。蒸気化したＰｄを効率的にトレー１１に導くために、容器１２内に、ターゲット１４からトレー１１に向けたガス流（例えば、アルゴンガス流）を形成することも有効である。
なお、Ｍｇ粉末の表面が不純物ガスで汚染されているような場合には、その表面を清浄化するために、例えば粉体表面へのイオンボンバード処理やレーザービーム照射、減圧（または真空）下での粉体の加熱処理等を予め行うことも有効である。
【００４１】
次に、本実施例の水素吸蔵体の具体的な作製手順およびその評価結果を説明する。
機械的に粉砕された平均粒径９００ｎｍのＭｇ粉末を用意した。
図６に示したコーティング装置１００（レーザーアブレーション法）を用いて、用意したＭｇ粉末（水素吸蔵粉体１）の表面にＰｄを被覆させた。これにより、Ｍｇ粉末からなる水素吸蔵粉体１の表面にＰｄからなる被覆層が形成された水素吸蔵体を得た。
次いで、この水素吸蔵体に対し、真空（１０^−２Ｐａ）下で２００℃で１時間保持する熱処理を行った。熱処理後、水素吸蔵体をＥＤＳ（エネルギー分散型Ｘ線分析装置）で観察したところ、Ｍｇ粉末に対するＰｄの被覆率は、平均すると９５％以上であった。また、水素吸蔵体の断面をＴＥＭ（透過型電子顕微鏡）で観察したところ、Ｐｄの平均厚さは９０ｎｍであった。
得られた水素吸蔵体（１ｇ）に対して、１３０℃で水素の放出量を測定したところ、３．９ｍａｓｓ％であった。なお、測定はジーベルツ法に基づいて行った。
【００４２】
（実施例２）
実施例２では、気相法の１種であるアーク蒸発法を用いて、水素吸蔵粉体１としてのＭｇ粉末にＰｄを被覆させた例について説明する。ここで、アーク蒸発法とは、電圧を印加することにより被覆させたい金属から構成されるターゲット上にアーク放電を発生させ、当該金属が蒸気化すると同時に蒸気化した金属粒子をイオン化させ、ターゲットとの間に電位差を設けた部位にイオン化された金属を導く方法である。なお、アーク蒸発法はイオンプレーティング法の１種である。
【００４３】
実施例２で使用したコーティング装置２００の概要を、図７を用いて説明する。
コーティング装置２００は、内部が減圧可能な容器１２と、容器１２の下方に設置されたトレー１１と、アーク放電を発生させる電源を主な構成要素としている。
トレー１１にはＭｇ粉末（水素吸蔵粉体１）が収容される。この状態で、電源を駆動することにより、被覆されるＰｄからなるターゲット１４に対して電圧を印加してアーク放電を発生させる。そうすると、ターゲット１４の表面でターゲット１４を構成するＰｄが蒸気化される。ターゲット１４とトレー１１との間には電位差が与えられているために、蒸気化したＰｄはトレー１１に誘導され、トレー１１に収容されたＭｇ粉末の表面に被覆される。トレー１１に振動装置、加熱装置を設ける点は、実施例１と同様である。
【００４４】
次に、本実施例の水素吸蔵体の具体的な作製手順およびその評価結果を説明する。
高周波プラズマＣＶＤ法により得た平均粒径１μｍのＭｇ粉末を用意した。
図７に示したコーティング装置２００（アーク蒸発法）のトレー１１に用意したＭｇ粉末（水素吸蔵粉体１）を収容し、かつＰｄからなるターゲット１４を用いることにより、Ｍｇ粉末からなる水素吸蔵粉体１の表面にＰｄからなる被覆相が形成された水素吸蔵体を得た。
続いて、この水素吸蔵体に対し、真空（１０^−２Ｐａ）下で２００℃で１時間保持する熱処理を行った。熱処理後、水素吸蔵体をＥＤＳで観察したところ、Ｍｇ粉末に対するＰｄの被覆率は、平均すると９５％以上であった。また、水素吸蔵体の断面をＴＥＭで観察したところ、Ｐｄの平均厚さは３０ｎｍであった。
得られた水素吸蔵体（１ｇ）に対して、１３０℃で水素の放出量を測定したところ、５．２ｍａｓｓ％であった。
【００４５】
（実施例３）
実施例３では、気相法の１種である高周波プラズマＣＶＤ法を用いて、水素吸蔵粉体１としてのＭｇ粉末に、ｂｃｃを主相とするＴｉ−Ｃｒ−Ｖ合金を被覆させた例について説明する。なお、Ｔｉ−Ｃｒ−Ｖ合金はアーク溶解法で作製したものである。ここで、高周波プラズマＣＶＤ法では、まずプラズマ源としてガス（基本的にはＡｒガス）を保持、あるいはフローさせた領域に高周波によってプラズマを発生させる。そして、発生したプラズマ内に金属粉末を投入すると、プラズマ出力や粉末の濃度または流量（ｇ／ｍｉｎ）によって、数ｎｍから数百μｍまでのさまざまな粒径の粒子が得られる。被覆対象となる金属粉末を収容するトレーの位置（高さ）や加熱装置の設置によって、プラズマ通過により微粒化された金属粒子（微粒化金属）がトレーに到達するときの微粉化粒子の温度を制御することができる。また、微粒化金属をイオン化しておくことによって、微粒化金属を効率的にトレー内に導くことができる。
【００４６】
実施例３で使用したコーティング装置３００の概要を、図８を用いて説明する。
Ｍｇ粉末（水素吸蔵粉体１）は、減圧可能な容器１２の下方に設置されたトレー１１に収容される。一方、Ｔ−Ｃｒ−Ｖ合金粉末は、容器１２の上方に設けられた粉末供給口３２から容器１２内に導入される。粉末供給口３２の近傍には、プラズマＦを発生するための加熱コイル３１が設けられている。また、トレー１１の上方かつプラズマＦの下方には、プラズマＦを通過して蒸気化されたＴ−Ｃｒ−Ｖ合金を加熱する加熱装置３４が設置されている。加熱装置３４としては、高周波、赤外線等により加熱を行うものが好ましい。蒸気化されたＴ−Ｃｒ−Ｖ合金は、トレー１１に向けて飛散し、トレー１１に収容されたＭｇ粉末（水素吸蔵粉体１）の表面に被覆するようになっている。なお、実施例１と同様に、トレー１１に振動装置、加熱装置を設けることが望ましい。
【００４７】
次に、本実施例の水素吸蔵体の具体的な作製手順およびその評価結果を説明する。
実施例２と同様のＭｇ粉末を用意した。このＭｇ粉末をトレー１１内に収容する一方、コーティング装置３００の粉末供給口３２からＴｉ−Ｃｒ−Ｖ合金をプラズマＦ中に向けて投入することにより、Ｍｇ粉末の表面にＴｉ−Ｃｒ−Ｖ合金を被覆させて水素吸蔵体を得た。この水素吸蔵体に対し、３００℃で１時間保持する熱処理を行った。
熱処理後、水素吸蔵体をＥＤＳで観察したところ、Ｍｇ粉末に対するＴｉ−Ｃｒ−Ｖ合金の被覆率は、平均して９５％以上であり、またＭｇ粉末の表面に被覆されているＴｉ−Ｃｒ−Ｖ合金の組成はＴｉ_２５Ｃｒ_４５Ｖ_３０であった。また、水素吸蔵体の断面をＴＥＭで観察したところ、Ｔｉ−Ｃｒ−Ｖ合金からなる被覆層の平均厚さは５０ｎｍであった。
得られた水素吸蔵体（１ｇ）に対して、１１０℃で水素の放出量を測定したところ、５．４ｍａｓｓ％であった。実施例１、２よりも低い放出温度でも、５．４ｍａｓｓ％という高い水素放出量が確認できたことから、Ｔｉ−Ｃｒ−Ｖ合金を用いた場合には、Ｐｄを用いた場合よりもＭｇ粉末に対して大きな応力を与えることができるものと考えられる。
【００４８】
なお、高周波プラズマＣＶＤ法による水素吸蔵体の製造は、図８に示す形態に限定されない。例えば、図９に示す構成の装置によっても本発明による水素吸蔵体を製造することができる。図９に示すコーティング装置４００の基本構成はコーティング装置３００と同様であるが、Ｍｇ粉末をトレー１１に収容するのではなく、容器１２の下方に設けた粉末供給口３３から容器１２内に向けて噴出させる。容器１２内に噴出されたＭｇ粉末の表面には、高周波プラズマで蒸気化されたＰｄが被覆することにより、本発明の水素吸蔵体を得ることができる。
【００４９】
また、実施例１〜３では、気相法としてレーザーアブレーション法、イオンプレーティング法の１種であるアーク蒸発法、高周波プラズマＣＶＤ法を用いて水素吸蔵体を作製する例を示したが、水素吸蔵体を作製方法はこれらの方法に限定されるものではない、例えば、スパッタ法も適用できることはもちろんである。スパッタ法を用いて水素吸蔵体を作製する場合について、図１０を用いて簡単に説明する。図１０は、スパッタ法を用いて水素吸蔵体１０を作製する場合に適したコーティング装置５００の構成を簡略化して示す図である。まず、容器１２内にＡｒガスやその他の目的に応じたガスを導入する。そして、ターゲット１４近傍にプラズマを発生させ、そのイオン化したガスをターゲット１４に衝突させる。この衝突によって飛び出した微粒化金属を、トレー１１上のＭｇ粉末（水素吸蔵粉体１）に被覆させればよい。この場合も、上述した例と同様に、トレー１１を振動可能な構成にしておくことによって、Ｍｇ粉末の表面に厚さ均一に微粒化金属を被覆させることができる。また、上述した例と同様に、トレー１１を加熱可能な構成としておくことが望ましい。
【００５０】
なお、実施例１〜３では、水素吸蔵粉体１としてＭｇ粉末を用いる場合を示したが、Ｍｇ合金粉末を用いた場合も、上述した場合と同等の水素放出量を示す水素吸蔵体を得ることができる。同様に、実施例１〜３では、被覆層２を構成する金属または合金として、Ｐｄ，Ｔｉ−Ｃｒ系合金を用いた例を示したが、これはあくまで一例であって、Ｐｄ，Ｔｉ−Ｃｒ系合金に代えて（またはＰｄ，Ｔｉ−Ｃｒ系合金と併用して）Ｖを用いた場合にも、同様の効果を期待できる。
【００５１】
【発明の効果】
本発明によれば、水素放出量が大きく、かつ１５０℃以下で水素を放出する、量産に適した水素吸蔵体を得ることができる。また、このような水素吸蔵体を安価で作製することができる。
【図面の簡単な説明】
【図１】第１の実施形態に係る水素吸蔵体の構成を模式的に示す断面図である。
【図２】水素原子の移動に伴って、被覆層、水素吸蔵粉体の体積が収縮する様子を模式的に示す図である。
【図３】第２の実施形態に係る水素吸蔵体の構成を模式的に示す断面図である。
【図４】水素吸蔵体を模式的に示す部分断面図であり、水素吸蔵体内で発生する応力の状態を示す説明図である。
【図５】第２の実施形態の水素吸蔵体の作製方法の具体例を示す図である。
【図６】実施例１で使用したコーティング装置の構成を簡略化して示す図である。
【図７】実施例２で使用したコーティング装置の構成を簡略化して示す図である。
【図８】実施例３で使用したコーティング装置の構成を簡略化して示す図である。
【図９】高周波プラズマＣＶＤ法を用いて水素吸蔵体を作製する場合に適したコーティング装置の他の例を簡略化して示す図である。
【図１０】スパッタ法を用いて水素吸蔵体を作製する場合に適したコーティング装置の構成を簡略化して示す図である。
【符号の説明】
１…水素吸蔵粉体、１ａ…水素吸蔵相、２…被覆層、２ａ…被覆相、３…コア体（コア相）、４…連結部（通路）、１０，２０…水素吸蔵体[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hydrogen storage body which has a large amount of hydrogen release, releases hydrogen at 150 ° C. or lower, and is excellent in mass productivity.
[0002]
[Prior art]
At present, acid rain caused by NOx (nitrogen oxide) increased by the use of fossil fuels and CO2 ₂ There is a concern about global warming caused by these, and these environmental destructions have become a serious problem. Among them, the practical use of hydrogen energy as clean energy has been attracting worldwide attention. Hydrogen is an inexhaustible constituent element of water on the earth.It can be produced using various primary energies, and because by-products are only water, there is no concern about environmental destruction. It also has excellent characteristics such as relatively easy storage compared to electric power.
[0003]
For this reason, in recent years, research and development of hydrogen storage alloys as a storage and transport medium for these hydrogen and studies on their practical use have been actively conducted. These hydrogen storage alloys are alloys that can absorb and release hydrogen under appropriate conditions. By using this alloy, it is possible to store hydrogen at a lower pressure and at a higher density than in a conventional hydrogen gas cylinder. The volume density is almost equal to or higher than that of liquid hydrogen or solid hydrogen, and the handling safety is remarkably excellent.
[0004]
As these hydrogen storage alloys, LaNi ₅ AB such as ₅ Type alloy or TiMn ₂ AB such as ₂ Mold alloys have been put to practical use. However, the hydrogen storage amount is at most around 1.4 mass%, and the hydrogen release amount is insufficient at 1.4 mass% or less. Therefore, a hydrogen storage alloy having a larger hydrogen release amount is required, and in recent years, Mg metal having a high hydrogen release amount of 7 mass% or more has been attracting attention.
[0005]
[Non-patent document 1]
Mater Tran, Jim (vol. 43 No. 7 p. 1732-1736, 2002).
[Non-patent document 2]
J. Am. Chem. Soc. 2002, 123, p. 6193-6194
[Non-Patent Document 3]
j. Alloy. Compd vol. 330/332 p. 526-530, 2002
[Non-patent document 4]
17th “University and Science” Public Symposium Preliminary Collection of Hydrogen World Opening the 21st Century p. 44-46, 2002
[0006]
[Problems to be solved by the invention]
By the way, when a hydrogen storage alloy is used for a hydrogen tank, not only the large amount of hydrogen storage and release but also the capability of storing and releasing hydrogen at 150 ° C. or lower, preferably near room temperature, is an important factor. Although the above-mentioned Mg metal has a high hydrogen release amount, its hydride (MgH ₂ ) Is thermodynamically stable, so the hydrogen release temperature is as high as 300 ° C. or higher. Such a drawback of the temperature characteristics is an obstacle in putting Mg metal to practical use for a hydrogen tank. In view of such a current situation, many studies have been made to improve the defect of the temperature characteristics of Mg metal. For example, Mater Tran, Jim (vol. 43 No. 7 p. 1732-1736, 2002) discloses Mg produced by melt spanning. ₈₆ Ni ₁₀ Nd ₄ It is reported that the (at%) alloy gives a release of about 2 mass% at 150 ° C. Also, J.I. Am. Chem. Soc. 2002, 123, p. No. 6193-6194, the Mg produced by a method using a high-pressure technique is used. _1.0 Ni _1.02 H _2.2 It has been reported that (at%) alloys release 2.6 mass% hydrogen from room temperature to 200 ° C. In addition, Orimo et al. Of Tohoku University (Mg _0.5 Y _0.5 ) Ni ₂ (At%) It was shown that the alloy releases hydrogen at 40 ° C, but the release amount is very small, about 1 mass%. (The 17th “University and Science” Open Symposium The World of Hydrogen Opening the 21st Century Pp. 44-46, 2002).
As described above, Mater Tran, Jim (vol. 43 No. 7 p. 1732-1736, 2002), J. Am. Am. Chem. Soc. 2002, 123, p. 6193-6194, the hydrogen storage alloy by Orimo et al. Of Tohoku University is effective in improving the temperature characteristics of Mg metal, but has a lower hydrogen release amount than the original hydrogen release amount of Mg metal. It is enough.
On the other hand, Fujii et al. Alloy. Compd vol. 330/332 p. In 526-530 and 2002, about 5 mass% of hydrogen is released at 130 ° C. or less by forming a Pd / Mg / Pd film by a sputtering method. However, this method is inferior in mass productivity because all three layers of Pd / Mg / Pd are formed by a sputtering method.
Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hydrogen storage body which emits hydrogen at a large amount of 150 ° C. or less and is suitable for mass production. It is another object of the present invention to provide a technique for manufacturing such a hydrogen storage material at low cost.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present inventor has made various studies. As a result, they found that it is effective to form a coating layer having a composition different from that of the hydrogen storage powder on the surface of the hydrogen storage powder by a gas phase method. That is, the present invention relates to a hydrogen storage powder composed of Mg or a Mg alloy and responsible for storing and releasing hydrogen, and having a composition different from that of the hydrogen storage powder. And a covering layer formed by the method. Here, the coating layer can be composed of at least one of Pd, V, and a Ti—Cr alloy. In the hydrogen storage body of the present invention, since a coating layer having a composition different from that of the hydrogen storage powder is formed on the surface of the hydrogen storage powder, stress is generated in the hydrogen storage powder. In order for this stress to effectively act on the hydrogen storage powder, it is extremely effective to form the coating layer by a gas phase method. By forming the coating layer by the gas phase method, it is possible to form a thin and uniform film on the surface of the hydrogen storage powder, and it is possible to uniformly apply stress to the hydrogen storage powder. It becomes. When stress, especially compressive stress, is applied to the hydrogen storage powder from the coating layer, the hydrogen located at the hydrogen storage site in the hydrogen storage powder moves, that is, the hydrogen in the hydrogen storage powder becomes unstable. It is considered that the state is reached, and the release of hydrogen from the hydrogen storage powder is promoted. For this reason, according to the hydrogen storage body of the present invention, the hydrogen release temperature of the Mg powder or Mg alloy powder as the hydrogen storage powder, which is known to have a high hydrogen release temperature, is significantly reduced as compared with the related art. be able to. Moreover, the Mg powder or the Mg alloy powder as the hydrogen storage powder can be obtained by a usual melting and casting method, and thus is suitable for mass production.
[0008]
Further, in the hydrogen storage body of the present invention, it is preferable that the metal or alloy constituting the above-mentioned coating layer has a larger volume change due to the movement of hydrogen atoms. Specifically, the volume change rate is preferably 10% or more. In particular, it is preferable to use a metal or an alloy whose volume change due to the movement of hydrogen atoms is larger than that of the hydrogen storage powder. Such metals or alloys include, for example, V, Ti-Cr alloys. When such a metal or alloy is used as the coating layer, when the coating layer releases and contracts hydrogen, compressive stress can be applied to the hydrogen storage powder, and the coating layer stores hydrogen. When the hydrogen storage powder expands, it is possible to apply a tensile stress to the hydrogen storage powder, which is presumed to be effective in making the hydrogen in the hydrogen storage powder unstable. Note that, in the present invention, as one form of the "movement of hydrogen atoms", the hydrogen atoms penetrate the inside of the hydrogen storage body, the hydrogen atoms penetrated inside the hydrogen storage body are released to the outside of the hydrogen storage body, Including both. Specifically, hydrogen atoms are occluded in the hydrogen storage powder or the coating layer, hydrogen atoms pass through (pass through) the hydrogen storage powder or the coating layer, the hydrogen storage powder or the coating layer From the inside of the hydrogen storage body to the outside of the hydrogen storage body.
[0009]
The compressive or tensile stress applied from the coating layer to the hydrogen storage powder can be applied from the periphery of the hydrogen storage powder or from inside the hydrogen storage powder. The present invention also provides a hydrogen storage material that realizes the form of applying the stress. That is, the present invention includes a core phase, a hydrogen storage phase covering the surface of the core phase, a coating phase covering the surface of the hydrogen storage phase, and a passage for flowing hydrogen atoms from the coating phase to the core phase. Disclosed is a hydrogen storage body characterized in that stress is applied to a hydrogen storage phase by expansion or contraction of a core phase and a coating phase when the phase stores or releases hydrogen.
According to the hydrogen storage body of the present invention described above, the amount of released hydrogen under an environment of 150 ° C. or less can be 3.0 mass% or more.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The hydrogen storage body according to the present invention is composed of a hydrogen storage powder for storing and releasing hydrogen, and a coating layer having a composition different from that of the hydrogen storage powder and formed on the surface of the hydrogen storage powder. Is done. In the hydrogen storage body according to the present invention, the release of hydrogen from the hydrogen storage powder is promoted by applying a stress from the coating layer to the hydrogen storage powder by utilizing the volume change of the coating layer. By forming a coating layer having such a function by a gas phase method, it is possible to apply stress uniformly to the hydrogen storage powder. Hydrogen in the hydrogen storage powder to which a uniform stress has been applied from the coating layer falls into an unstable state, and it is possible to release hydrogen from the hydrogen storage powder even at a lower temperature than before. The term “volume change” in the present invention refers to a volume expansion when a hydrogen atom enters the inside and a volume contraction when a hydrogen atom that has entered the inside is released to the outside.
[0011]
<First embodiment>
FIG. 1 is a cross-sectional view schematically showing a configuration of a hydrogen storage body according to the first embodiment, which is suitable for use in a hydrogen tank.
As shown in FIG. 1, the hydrogen storage body 10 according to the first embodiment includes a hydrogen storage powder 1 and a coating layer 2 formed so as to cover almost the entire surface of the hydrogen storage powder 1. It has a two-layer structure.
[0012]
First, the hydrogen storage powder 1 will be described.
The hydrogen storage powder 1 mainly functions to store and release hydrogen. In the present embodiment, the hydrogen storage powder 1 is made of a powder made of Mg or a Mg alloy. Since Mg has a large amount of hydrogen absorption and desorption of about 7 mass% or more, when the hydrogen storage body 10 is used for a hydrogen tank, it is desirable that the hydrogen storage powder 1 be made of Mg or a Mg alloy.
[0013]
When the hydrogen storage powder 1 is made of an Mg alloy, an Mg-RE alloy (RE: rare earth element), an Mg-Ni alloy, an Mg-Ni-RE alloy, or the like can be used. Specifically, Mg ₂ Ni alloy, La-Mg-Ni _x (X = 3 to 3.5) alloy, La ₂ MgNi ₉ Alloy, LaMgNi alloy, LaMgNi ₁₄ Alloys and the like. The hydrogen storage powder 1 composed of the above Mg alloy or Mg alone has a high hydrogen release temperature of 300 ° C. or higher. However, by forming the coating layer 2 made of a predetermined metal or alloy on almost the entire surface of the hydrogen storage powder 1 by a gas phase method, the hydrogen storage body 3 can be used even under an environment of 150 ° C. or less. 0 mass% or more, and more preferably 4.0 mass% or more of hydrogen can be released.
[0014]
FIG. 1 shows an example in which the hydrogen storage powder 1 is composed of a spherical powder, but the shape of the powder is not limited to this. Not only spherical but also elliptical or amorphous powder can be used as the powder constituting the hydrogen storage powder 1. However, when the shape of the powder is nearly spherical, there is an advantage that the thickness of the coating layer 2 can be made more uniform. Further, the particle diameter of the powder constituting the hydrogen storage powder 1 is preferably several tens nm to several tens μm. If the particle size is smaller than several tens of nanometers, the amount of hydrogen absorbed and released per particle will be small. On the other hand, when the particle size is larger than several tens of μm, it is necessary to increase the thickness of the coating layer 2 in order to apply an appropriate stress from the coating layer 2. However, an increase in the thickness of the coating layer 2 is not preferable because the hydrogen storage amount per unit volume of the hydrogen storage body 10 decreases. Therefore, in order to secure the hydrogen absorption / desorption amount and to enjoy the effect of lowering the hydrogen release temperature of the hydrogen storage powder 1 by the stress applied by the coating layer 2, the powder constituting the hydrogen storage powder 1 must be used. Is from several tens nm to several tens μm. A desirable particle size is 100 nm to 5 μm, and a more desirable particle size is 500 nm to 2 μm.
[0015]
Next, the coating layer 2 will be described.
The coating layer 2 is made of a metal or an alloy having a composition different from that of the hydrogen storage powder 1. Here, the coating layer 2 can be made of, for example, Pd (or a Pd alloy), V (or a V alloy), or a Ti—Cr-based alloy. Each of these has a catalytic action capable of dissociating hydrogen gas into atoms, and functions as a port for hydrogen atoms to enter and exit the hydrogen storage powder 1. In particular, the V, Ti—Cr-based alloy has a larger volume change than Mg or the Mg alloy constituting the hydrogen storage powder 1. Therefore, when the coating layer 2 is made of V or a Ti—Cr alloy, the stress applied to the hydrogen storage powder 1 increases, that is, the hydrogen release at a relatively low temperature (150 ° C. or lower) becomes more difficult. There is an advantage that it is performed smoothly.
Here, the form in the case of forming the coating layer 2 using two or more of Pd, V, and Ti-Cr alloys includes the following forms. As a first mode, for example, there is a mode in which a coating layer 2 made of V is further formed on a coating layer 2 made of a Pd layer (the coating layer 2 made of Pd is formed on the coating layer 2 made of V). Good). As a second mode, there is a mode in which a coating layer 2 made of a Pd-V alloy is formed. Not limited to the combination of Pd and V, the same applies to the combination of Pd and Ti-Cr alloy, V and Ti-Cr alloy, and Pd, V and Ti-Cr alloy.
[0016]
When the coating layer 2 is made of a Ti—Cr-based alloy, its composition is desirably determined so as to have a body-centered cubic structure (hereinafter referred to as “bcc phase” or “bcc”) as a main phase. Even if the coating layer 2 is made of a Ti-Cr-based alloy having a bcc phase as a main phase but not as much as Mg, 3.5 mass% or more alone (3.5 mass% or more is a value in the first cycle. From the second cycle onward) Indicates a hydrogen storage amount of 1.6 mass% or more, and often 2 mass% or more.) When the coating layer 2 is made of a Ti—Cr alloy, the hydrogen storage amount of the hydrogen storage body 10 as a whole is Can be increased. Further, according to the Ti-Cr alloy, there is an advantage that the plateau pressure can be set to an arbitrary value by appropriately setting the Ti amount and the Cr amount.
When the coating layer 2 is composed of a Ti—Cr-based alloy, it is desirable that the composition is represented by the following formula (1).
Ti _(100-abcde) Cr _a X _b X ' _c T _d L _e ... Equation (1)
[0017]
However, in equation (1),
20 ≦ a (at%) ≦ 80, 0 ≦ b (at%) ≦ 10, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 30, 0 ≦ e (at%) ≦ 10 Represented,
X is at least one element of Ru, Rh, Os, Ir, Pd, Pt, and Re;
X ′ is at least one element of V, Mo, W, and Al;
T is at least one element of Mn, Fe, Co, Ni, Cu, Nb, Ta, B and C;
L is at least one of Y and lanthanoid elements.
[0018]
The element X has a high bcc phase forming ability only by containing a small amount in the Ti—Cr alloy, ₁₄ Type, C _Fifteen A bcc single phase alloy containing almost no Laves phase such as a mold can be obtained. By simultaneously containing the X element and the X 'element, the content of the expensive X element can be kept low, and a hydrogen storage alloy having high practicality balanced in cost and hydrogen storage amount per unit weight can be obtained. Can be. Further, by containing the T element, it is possible to control arbitrary control of the plateau pressure, control of the flatness of the plateau pressure, control of the heat treatment temperature, improvement of the corrosion resistance of the alloy, and the like. Since the L element has a strong affinity for oxygen, it has an effect of removing oxygen present in the alloy as an L element oxide. As a result, it is possible to stabilize the hydrogen storage amount and to effectively use a raw material having a relatively large amount of oxygen industrially.
[0019]
The case where the coating layer 2 is made of a Ti—Cr-based alloy has been described above in detail. By employing the above composition, the Ti—Cr-based alloy as the coating layer 2 can have the bcc phase as the main phase. Whether or not the alloy has the bcc phase as the main phase can be determined by X-ray diffraction. In the present invention, an alloy having a bcc phase as a main phase is defined as an alloy having a ratio (%) of 50% or more according to the following equation (2) based on the integrated intensity of the diffraction line.

In the present invention, a phase that can exist in addition to the bcc phase is a Laves phase.
[0020]
Now, as shown in FIG. 1, the coating layer 2 is formed so as to cover almost the entire surface of the hydrogen storage powder 1. In the present invention, it is recommended that the coating layer 2 be formed by a gas phase method. According to the vapor phase method, the coating layer 2 can be formed thinly and uniformly on the surface of the hydrogen storage powder 1. As an example of the prior art, an example is shown in which a film structure such as Pd / Mg / Pd is entirely formed by a sputtering method. However, in the present invention, it is not necessary to manufacture the hydrogen storage powder 1 by a gas phase method. That is, in the present invention, since the hydrogen storage powder 1 can be obtained by a normal melting and casting method, the manufacturing cost of the hydrogen storage body 10 can be reduced and the mass productivity is excellent.
[0021]
Here, in order to form the coating layer 2 having a uniform thickness on the entire surface of the hydrogen storage powder 1 by using the gas phase method, it is effective to roll the hydrogen storage powder 1. In order to roll the hydrogen storage powder 1, for example, when the hydrogen storage powder 1 is stored in a tray, means for applying vibration to the tray may be provided. The vibration in this case can be, for example, an ultrasonic wave to 1 Hz. Moreover, you may make it apply vibration of 1-500 Hz using a commercially available vibrator. Furthermore, not only the vibrator but also a method of stirring the hydrogen storage powder 1 stored in the tray with a stirring rod can be used. The vibration or stirring means is not limited as long as the hydrogen storage powder 1 can be rolled.
Another advantage of the case where the coating layer 2 is formed by a vapor phase method is that the surface of the hydrogen storage powder 1 is easily kept clean as compared with a method such as electrolytic plating or electroless plating. . That is, when the coating layer 2 is formed by a gas phase method, a treatment for cleaning the surface of the hydrogen storage powder 1, for example, ion bombardment treatment, laser beam irradiation, decompression (or vacuum) on the surface of the powder. ) The following powder heat treatment can be used in combination. Further, the fact that the hydrogen storage powder 1 is not exposed to the air at all from the time when the hydrogen storage powder 1 is produced until the formation of the coating layer 2 is also effective in cleaning the surface of the hydrogen storage powder 1 is effective. It is.
[0022]
Here, the gas phase method is a method in which atoms, molecules, or fine particles of several to hundreds of nm, ions, and charged particles are generated in a vacuum or gas and deposited on an object. Examples of the gas phase method include an ion plating method, a sputtering method, a laser ablation method, and a high-frequency plasma CVD method. Above all, a laser ablation method capable of controlling a plurality of targets individually and simultaneously is particularly preferable. An example of a preferred apparatus for applying the coating layer 2 to the surface of the hydrogen storage powder 1 using a gas phase method will be described later.
[0023]
As described above, the coating layer 2 is formed so as to cover almost the entire surface of the hydrogen storage powder 1, and its coverage is 90% or more, further 93% or more, and more preferably 95% or more. is there.
The thickness of the coating layer 2 depends on the shape of the powder constituting the hydrogen storage powder 1, but is preferably several nm to 500 nm. When the thickness of the coating layer 2 is less than several nm, the stress applied to the hydrogen storage powder 1 becomes small, so that the hydrogen release from the hydrogen storage powder 1 is not easily promoted. On the other hand, when the film thickness of the coating layer 2 exceeds 500 nm, the proportion of the hydrogen storage powder 1 relatively decreases, so that the hydrogen storage amount per unit volume of the hydrogen storage body 10 decreases. Therefore, it is desirable that the film thickness of the coating layer 2 be several nm to 500 nm. The more preferable thickness of the coating layer 2 is 20 to 200 nm, and the more preferable thickness of the coating layer 2 is 50 to 100 nm.
[0024]
Next, the hydrogen release mechanism of the hydrogen storage body 10 according to the first embodiment, which includes the hydrogen storage powder 1 and the coating layer 2, will be described.
The volume of the hydrogen storage powder 1 and the coating layer 2 expands and contracts with the movement (occlusion or permeation) of hydrogen atoms. That is, when a hydrogen atom enters the hydrogen storage body 10, the hydrogen storage body 10 expands. On the other hand, when a hydrogen atom is released to the outside of the hydrogen storage body 10, the hydrogen storage body 10 contracts. However, since the coating layer 2 and the hydrogen storage powder 1 have different compositions, and since the coating layer 2 is provided on the outermost periphery of the hydrogen storage body 10, the coating layer 2 contracts, and the compressive stress due to the contraction is reduced. As shown in FIG. 2, it is applied to the hydrogen storage powder 1. It is presumed that the generation of the compressive stress promotes the release of the hydrogen atoms stored in the hydrogen storage powder 1. As described above, in the hydrogen storage body 10 according to the present embodiment, since the environment for releasing hydrogen from the hydrogen storage powder 1 is improved, even if the hydrogen release temperature is relatively low at 150 ° C. or less, the hydrogen storage powder is not required. Hydrogen release from the body 1 is performed smoothly. Therefore, according to the hydrogen storage body 10 according to the first embodiment, a hydrogen release amount of 3 mass% or more, and more preferably 4 mass% or more can be obtained at 150 ° C. or less.
In addition, the coating layer 2 has a catalytic action of dissociating hydrogen gas into atoms and has an action of diffusing dissociated hydrogen atoms inside. It is presumed that the metal or alloy constituting the coating layer 2 is superior in catalytic ability to dissociate hydrogen molecules to Mg or Mg alloy constituting the hydrogen storage powder 1. That is, although the hydrogen storage mechanism of the hydrogen storage body 10 is not clear, it is considered that the coating layer 2 has a catalytic function of decomposing hydrogen molecules into atoms at a low temperature (150 ° C. or lower).
[0025]
As above, the configuration of the hydrogen storage body 10 suitably used for the hydrogen tank has been described in detail. Next, a desirable manufacturing method for obtaining the hydrogen storage body 10 of the present invention will be described.
The method for producing the hydrogen storage body 10 of the present invention includes a step of obtaining a Mg base material constituting the hydrogen storage powder 1 (hereinafter, referred to as a “Mg base material preparation step”) and a step of coating the surface of the obtained Mg base material. Forming a layer 2 (hereinafter, referred to as a “coating layer 2 forming step”). In the Mg base material manufacturing process, a case where an Mg alloy powder is manufactured will be described as an example.
Hereinafter, each step will be described in detail.
[0026]
<Mg base material manufacturing process>
The Mg alloy can be produced by melting the starting material metal by, for example, high frequency in a crucible. The Mg alloy ingot obtained in this manner is formed into a powder having a size of, for example, 500 μm or less using a disc mill, a mortar or the like. Subsequently, the Mg alloy powder of 500 μm or less is pulverized by hydrogenation. The hydrogenated and pulverized Mg alloy powder is further finely pulverized and classified with a sieve (for example, 5 μm or less). For the above-mentioned reason, it is preferable that the average particle diameter of the Mg alloy powder constituting the hydrogen storage powder 1 is several tens nm to several tens μm before the coating layer 2 is formed. Therefore, after classifying the Mg alloy powder with a sieve, it is desirable to adjust the average particle size using a test tube mixer or the like until the average particle size becomes several tens nm to several tens μm. When the atomizing method is used, a Mg alloy powder having a desired average particle size can be obtained without performing such a pulverizing treatment.
[0027]
The surface of the Mg alloy powder may be contaminated with an impurity gas due to exposure to the air or the like. Therefore, it is desirable that the process for cleaning the surface of the Mg alloy powder be performed in advance, and then proceed to the following coating layer 2 forming step. Examples of the treatment for cleaning the surface of the Mg alloy powder include, as described above, ion bombardment treatment, laser beam irradiation, and heat treatment of the powder under reduced pressure (or vacuum) on the powder surface. . It is also effective to perform the Mg base material manufacturing step and the later-described coating layer 2 forming step consistently without exposing the Mg alloy powder to the air at all.
[0028]
<Coating layer 2 forming step>
In the coating layer 2 forming step, the Mg alloy powder or the Mg powder is coated with at least one of Pd, V, and a Ti—Cr alloy. A vapor phase method is used as a coating method of Pd or the like. According to the vapor phase method, the coating layer 2 having a thin and uniform thickness can be formed on the surface of the Mg alloy powder or the Mg powder, and the thickness of the coating layer 2 can be easily controlled. Further, as described above, the Mg alloy powder or the Mg powder is rolled at the time of forming the coating layer 2 by applying appropriate vibration to the Mg alloy powder or the Mg powder, so that the entire surface of the Mg alloy powder or the Mg powder is The coating layer 2 can be formed with a uniform thickness. Furthermore, the vapor phase method has an advantage that the surface of the Mg alloy powder or the Mg powder can be kept relatively clean as compared with the electroless plating method or the like. By doing so, the powder surface can be further cleaned. An example of an apparatus used when forming the coating layer 2 by using a vapor phase method will be described in Examples described later.
[0029]
Through the above-described Mg base material preparation step and coating layer 2 forming step, the hydrogen storage body 10 according to the first embodiment in which the coating layer 2 is formed on the surface of the Mg powder can be obtained. After the coating layer 2 is formed, 100 to 400 ° C. is used to facilitate the transfer of hydrogen atoms between the coating layer 2 and the Mg powder (or Mg alloy powder) constituting the hydrogen storage powder 1. For about 0.5 to 2 hours.
[0030]
When a Ti—Cr-based alloy having bcc as a main phase is selected as the coating layer 2, the following method can be adopted. For example, when it is desired to use a Ti—Cr—V-based alloy as the coating layer 2, individual targets of Ti, Cr, and V are prepared. Then, the Mg powder or the Mg alloy powder as the hydrogen storage powder 1 may be coated alternately or simultaneously with these single targets. By heating at the time of coating or heating after coating, a Ti-Cr-V-based alloy can be obtained. That is, after forming the coating layer 2, alloying may be performed to obtain a Ti—Cr-based alloy having a desired composition ratio. Note that the heating temperature may be 500 ° C. or lower. In addition, not only a plurality of single targets but also an alloy target may be used. Further, a Ti-Cr-based alloy containing bcc as a main phase may be produced by a well-known arc melting method.
[0031]
Next, a process for storing and releasing hydrogen in the hydrogen storage body 10 will be briefly described. The hydrogenation treatment for storing hydrogen in the hydrogen storage body 10 is performed in a hydrogen atmosphere. When performing the hydrogenation treatment, it is effective to reduce the pressure of the vessel containing the hydrogen storage body 10 and to evacuate the vessel, and then to introduce hydrogen. The purity of the hydrogen introduced is preferably at least 99.9999%.
[0032]
In order to extract hydrogen from the hydrogen storage body 10, heating conditions and / or depressurizing conditions are adjusted. According to the hydrogen storage body 10 according to the first embodiment, the hydrogen in the hydrogen storage body 10 can be easily released by heating the hydrogen storage body 10 in the range of 100 to 150 ° C. Further, by reducing the pressure of the container containing the hydrogen storage body 10 to a pressure equal to or lower than the plateau pressure of the release curve at that temperature, hydrogen in the hydrogen storage body 10 can be easily taken out. Here, the pressure reduction condition is desirably reduced to 5 kPa or less.
[0033]
<Second embodiment>
FIG. 3 schematically shows a cross section of a hydrogen storage body 20 according to the second embodiment, which is suitable for use as a hydrogen tank.
The hydrogen storage body 20 shown in FIG. 3 includes a core body (core phase) 3, a hydrogen storage phase 1a surrounding the periphery of the core body 3, a coating phase 2a formed on the surface of the hydrogen storage phase 1a, a coating phase 2a and a core body. 3 and a connecting portion (passage) 4 for flowing hydrogen atoms from the coating phase 2a to the core body 3. In addition, the hydrogen storage phase 1a can be composed of the same composition as the hydrogen storage powder 1 described above. Further, in order to form the coating phase 2a, the core body 3, and the connecting portion 4, it is possible to employ any of the coating layers 2 mentioned above, that is, any one of Pd, V, and Ti-Cr alloys. it can. It is desirable that the covering phase 2a, the core body 3 and the connecting portion 4 are made of the same metal or alloy, but may be made of different metals or alloys.
[0034]
As shown in FIG. 3, the hydrogen storage body 20 according to the second embodiment has a three-layer structure including a hydrogen storage phase 1a, a covering phase 2a, and a core body 3. The hydrogen storage phase 1a has a structure sandwiched between the covering phase 2a and the core body 3, and a connecting portion 4 for connecting the covering phase 2a and the core body 3 is provided between the covering phase 2a and the core body 3. The reason why the core body 3 is provided is to apply stress to the hydrogen storage phase 1a even from the inside of the hydrogen storage phase 1a. In order to exhibit this effect, a connecting portion 4 connecting the covering phase 2a and the core body 3 is provided.
[0035]
FIG. 4 is a partial cross-sectional view schematically showing the hydrogen storage body 20, and is an explanatory diagram showing a state of stress generated in the hydrogen storage body 20.
When hydrogen atoms are released from the covering phase 2a located at the outermost periphery of the hydrogen storage body 20, the volume of the covering phase 2a shrinks. Thereby, compressive stress is applied to the hydrogen storage phase 1a adjacent to the coating phase 2a. On the other hand, when hydrogen atoms are released from the core body 3 located inside the hydrogen storage phase 1a, the volume of the core body 3 shrinks. Thereby, compressive stress is applied to the hydrogen storage phase 1a adjacent to the core body 3. Further, when hydrogen atoms are released from the connecting portion 4 connecting the covering phase 2a and the core body 3, the connecting portion 4 also contracts in volume. As one form of the volume contraction of the connecting portion 4, when the height of the connecting portion 4 is reduced as shown by a white arrow in FIG. 4, the hydrogen storage phase 1 a surrounded by the covering phase 2 a and the core body 3 Thus, compressive stress is applied from both sides of the coating phase 2 a and the core body 3. Thus, stress is applied to the hydrogen storage phase 1a from the coating phase 2a side and the core body 3 side, that is, from one or more sides. Then, the hydrogen applied to the hydrogen storage site in the hydrogen storage phase 1a moves due to the applied stress, and the hydrogen release of the hydrogen storage phase 1a is promoted.
[0036]
That is, in the first embodiment, stress is applied around the hydrogen storage powder 1, whereas in the second embodiment, stress is applied from around the hydrogen storage phase 1a and further from the inside. . For this reason, by employing the configuration shown in FIG. 3, the stress applied to the hydrogen storage phase 1a increases, and the release of hydrogen from the hydrogen storage phase 1a is further promoted. Thereby, the amount of hydrogen released at 150 ° C. or lower in the hydrogen storage phase 1a increases.
[0037]
Here, a specific example of a method for manufacturing the hydrogen storage body 20 of the second embodiment will be described with reference to FIG.
First, as shown in FIG. 5A, a metal or an alloy constituting the core body 3 is prepared. Next, as shown in FIG. 5B, the core body 3 is coated with a metal powder (alloy powder) constituting the hydrogen storage phase 1a. This coating can be performed by a mechanical method using a stamp mill or the like. Here, since the hydrogen storage phase 1a is powdery, a gap exists between the adjacent hydrogen storage phases 1a.
A covering phase 2a is further formed on the surface of the composite in which the hydrogen storage phase 1a is formed on the surface of the core body 3 shown in FIG. 5 (b), and the hydrogen storage in the form shown in FIG. The body 20 is manufactured. The formation of the coating phase 2a is performed using a gas phase method. At this time, a part of the covering phase 2a enters the gap between the hydrogen storage phases 1a and reaches the core body 3. Thereby, the connection part 4 which connects the core body 3 and the coating phase 2a is formed. Here, a schematic cross-sectional view of FIG. 5C is as shown in FIG. In addition, the core body 3 may be in a plate shape.
[0038]
【Example】
Hereinafter, the hydrogen storage body of the present invention will be described based on specific examples.
(Example 1)
In the first embodiment, an example will be described in which Mg powder as the hydrogen storage powder 1 is coated with Pd by using a laser ablation method, which is a kind of gas phase method. Here, the laser ablation method is a method in which a solid constituent material itself is explosively emitted by irradiating a strong laser beam to a solid surface.
An outline of the coating apparatus 100 used in the first embodiment will be described with reference to FIG.
The coating apparatus 100 mainly includes a container 12 whose interior can be depressurized, a tray 11 installed below the container 12, and a laser device 13 for irradiating a laser beam to a target installed above the container 12. It is a component.
[0039]
The tray 11 stores Mg powder (hydrogen storage powder 1). In this state, a laser beam is irradiated from the laser device 13 toward the target 14 made of Pd to be coated. The vaporized Pd is emitted from the surface of the target 14 irradiated with the laser beam. The vaporized Pd scatters downward and covers the surface of the Mg powder (hydrogen storage powder 1) stored in the tray 11. The vaporized Pd is considered to aggregate during the scattering process and grow to several nm to several tens nm.
In order to uniformly cover the surface of the Mg powder with Pd constituting the coating layer 2, the tray 11 is desirably provided with a vibration device such as an ultrasonic vibration device. By applying vibration to the tray 11, the Mg powder contained in the tray 11 can be rolled, and its surface can be coated with Pd with a uniform thickness. The vibration device is not limited to an ultrasonic vibration device, and a known tap device can be used. The vibration may have a frequency of about 1 to 500 Hz. In order to improve the coverage of Pd on the Mg powder, it is also effective to provide a heating device for heating the Mg powder on the tray 11.
[0040]
In order to efficiently guide the vaporized Pd to the tray 11, it is effective to ionize Pd and to apply a potential difference between the target 14 and the tray 11. In order to efficiently guide the vaporized Pd to the tray 11, it is also effective to form a gas flow (for example, an argon gas flow) from the target 14 toward the tray 11 in the container 12.
If the surface of the Mg powder is contaminated with an impurity gas, for example, ion bombardment treatment, laser beam irradiation, or reduced pressure (or vacuum) may be applied to the powder surface to clean the surface. It is also effective to perform heat treatment of the powder in advance.
[0041]
Next, a specific manufacturing procedure of the hydrogen storage body of this example and evaluation results thereof will be described.
A mechanically pulverized Mg powder having an average particle diameter of 900 nm was prepared.
Using a coating apparatus 100 (laser ablation method) shown in FIG. 6, the surface of the prepared Mg powder (hydrogen storage powder 1) was coated with Pd. As a result, a hydrogen storage body in which a coating layer made of Pd was formed on the surface of the hydrogen storage powder 1 made of Mg powder was obtained.
Then, a vacuum (10 ^-2 Under Pa), heat treatment at 200 ° C. for 1 hour was performed. After the heat treatment, when the hydrogen storage material was observed with an EDS (energy dispersive X-ray analyzer), the coverage of Pd on the Mg powder was 95% or more on average. When the cross section of the hydrogen storage material was observed with a TEM (transmission electron microscope), the average thickness of Pd was 90 nm.
The amount of released hydrogen was measured at 130 ° C. with respect to the obtained hydrogen storage material (1 g), and it was 3.9 mass%. The measurement was performed based on the Siebert's method.
[0042]
(Example 2)
In the second embodiment, an example will be described in which Mg powder as the hydrogen storage powder 1 is coated with Pd by using an arc evaporation method, which is a kind of gas phase method. Here, the arc evaporation method is to generate an arc discharge on a target composed of a metal to be coated by applying a voltage, ionize the vaporized metal particles at the same time that the metal is vaporized, and form a target with the target. This is a method of guiding the ionized metal to a portion where a potential difference is provided between the two. The arc evaporation method is one type of ion plating method.
[0043]
The outline of the coating apparatus 200 used in the second embodiment will be described with reference to FIG.
The main components of the coating apparatus 200 are a container 12 whose inside can be depressurized, a tray 11 installed below the container 12, and a power supply for generating arc discharge.
The tray 11 stores Mg powder (hydrogen storage powder 1). In this state, by driving the power supply, a voltage is applied to the target 14 made of Pd to be coated, and an arc discharge is generated. Then, Pd constituting the target 14 is vaporized on the surface of the target 14. Since a potential difference is applied between the target 14 and the tray 11, the vaporized Pd is guided to the tray 11 and is coated on the surface of the Mg powder stored in the tray 11. The vibration device and the heating device are provided on the tray 11 as in the first embodiment.
[0044]
Next, a specific manufacturing procedure of the hydrogen storage body of this example and evaluation results thereof will be described.
Mg powder having an average particle diameter of 1 μm obtained by a high-frequency plasma CVD method was prepared.
By storing the prepared Mg powder (hydrogen storage powder 1) in the tray 11 of the coating apparatus 200 (arc evaporation method) shown in FIG. 7 and using the target 14 made of Pd, the hydrogen storage powder made of Mg powder is used. A hydrogen storage body in which a coating phase made of Pd was formed on the surface of the body 1 was obtained.
Subsequently, a vacuum (10 ^-2 Under Pa), heat treatment at 200 ° C. for 1 hour was performed. After the heat treatment, when the hydrogen storage material was observed by EDS, the coverage of Pd on the Mg powder was 95% or more on average. When the cross section of the hydrogen storage material was observed with a TEM, the average thickness of Pd was 30 nm.
The amount of released hydrogen was measured at 130 ° C. with respect to the obtained hydrogen storage material (1 g), and it was 5.2 mass%.
[0045]
(Example 3)
Example 3 relates to an example in which a Mg powder as the hydrogen storage powder 1 is coated with a Ti—Cr—V alloy having bcc as a main phase by using a high-frequency plasma CVD method, which is a kind of a gas phase method. explain. Note that the Ti-Cr-V alloy was produced by an arc melting method. Here, in the high frequency plasma CVD method, first, a plasma (generally an Ar gas) is held as a plasma source, or plasma is generated by a high frequency in a region where the gas flows. Then, when the metal powder is introduced into the generated plasma, particles having various particle sizes from several nm to several hundred μm can be obtained depending on the plasma output and the concentration or flow rate (g / min) of the powder. Depending on the position (height) of the tray containing the metal powder to be coated and the installation of a heating device, the temperature of the finely divided metal particles (micronized metal) when the particles pass through the plasma and reach the tray can be adjusted. Can be controlled. Further, by ionizing the atomized metal, the atomized metal can be efficiently guided into the tray.
[0046]
The outline of the coating apparatus 300 used in the third embodiment will be described with reference to FIG.
The Mg powder (hydrogen storage powder 1) is stored in a tray 11 installed below a container 12 that can be decompressed. On the other hand, the T-Cr-V alloy powder is introduced into the container 12 from a powder supply port 32 provided above the container 12. In the vicinity of the powder supply port 32, a heating coil 31 for generating the plasma F is provided. Above the tray 11 and below the plasma F, a heating device 34 that heats the vaporized T-Cr-V alloy through the plasma F is installed. As the heating device 34, a device that performs heating by high frequency, infrared light, or the like is preferable. The vaporized T-Cr-V alloy scatters toward the tray 11 and covers the surface of the Mg powder (hydrogen storage powder 1) stored in the tray 11. It is desirable to provide the tray 11 with a vibration device and a heating device, as in the first embodiment.
[0047]
Next, a specific manufacturing procedure of the hydrogen storage body of this example and evaluation results thereof will be described.
The same Mg powder as in Example 2 was prepared. While storing the Mg powder in the tray 11, the Ti-Cr-V alloy is injected into the plasma F from the powder supply port 32 of the coating apparatus 300, so that the surface of the Mg powder has a Ti-Cr-V alloy. To obtain a hydrogen storage material. This hydrogen storage body was subjected to heat treatment at 300 ° C. for 1 hour.
After the heat treatment, the hydrogen storage material was observed by EDS. The coverage of the Ti—Cr—V alloy with respect to the Mg powder was 95% or more on average, and the Ti—Cr— The composition of the V alloy is Ti ₂₅ Cr ₄₅ V ₃₀ Met. When the cross section of the hydrogen storage body was observed with a TEM, the average thickness of the coating layer made of the Ti—Cr—V alloy was 50 nm.
The amount of hydrogen released from the obtained hydrogen storage material (1 g) at 110 ° C. was 5.4 mass%. Since a high hydrogen release amount of 5.4 mass% was confirmed even at a release temperature lower than those of Examples 1 and 2, Mg powder was more likely to be used when using a Ti—Cr—V alloy than when using Pd. It can be considered that a large stress can be applied to.
[0048]
The production of the hydrogen storage body by the high-frequency plasma CVD method is not limited to the embodiment shown in FIG. For example, the hydrogen storage body according to the present invention can also be manufactured by an apparatus having a configuration shown in FIG. The basic configuration of a coating apparatus 400 shown in FIG. 9 is the same as that of the coating apparatus 300 except that the Mg powder is not stored in the tray 11 but is directed from a powder supply port 33 provided below the container 12 into the container 12. Let it squirt. By coating the surface of the Mg powder ejected into the container 12 with Pd vaporized by high-frequency plasma, the hydrogen storage body of the present invention can be obtained.
[0049]
Further, in the first to third embodiments, an example in which a laser absorber is used as a gas phase method, an arc evaporation method which is one kind of an ion plating method, and a high-frequency plasma CVD method is used to produce a hydrogen storage body. The method for manufacturing the occlusion body is not limited to these methods. For example, it goes without saying that a sputtering method can also be applied. A case where a hydrogen storage body is manufactured by a sputtering method will be briefly described with reference to FIGS. FIG. 10 is a diagram schematically illustrating a configuration of a coating apparatus 500 suitable for producing the hydrogen storage body 10 by using a sputtering method. First, Ar gas or a gas according to another purpose is introduced into the container 12. Then, plasma is generated near the target 14 and the ionized gas is caused to collide with the target 14. The atomized metal ejected by the collision may be coated on the Mg powder (hydrogen storage powder 1) on the tray 11. Also in this case, similarly to the above-described example, the surface of the Mg powder can be uniformly coated with the atomized metal by forming the tray 11 into a vibrating configuration. It is desirable that the tray 11 be configured to be heatable as in the above-described example.
[0050]
In Examples 1 to 3, the case where Mg powder was used as the hydrogen storage powder 1 was described. However, even when Mg alloy powder was used, a hydrogen storage body having the same amount of hydrogen release as that described above was obtained. be able to. Similarly, in the first to third embodiments, an example in which a Pd, Ti—Cr-based alloy is used as the metal or alloy constituting the coating layer 2 has been described, but this is merely an example, and Pd, Ti—Cr The same effect can be expected when V is used instead of the alloy (or in combination with the Pd, Ti-Cr alloy).
[0051]
【The invention's effect】
According to the present invention, it is possible to obtain a hydrogen storage material that emits hydrogen at a temperature of 150 ° C. or less and is suitable for mass production. Further, such a hydrogen storage material can be manufactured at low cost.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically illustrating a configuration of a hydrogen storage body according to a first embodiment.
FIG. 2 is a diagram schematically showing a state in which the volumes of a coating layer and a hydrogen storage powder shrink with the movement of hydrogen atoms.
FIG. 3 is a cross-sectional view schematically illustrating a configuration of a hydrogen storage body according to a second embodiment.
FIG. 4 is a partial cross-sectional view schematically showing a hydrogen storage body, and is an explanatory diagram showing a state of stress generated in the hydrogen storage body.
FIG. 5 is a diagram showing a specific example of a method for manufacturing a hydrogen storage body of the second embodiment.
FIG. 6 is a diagram showing a simplified configuration of a coating apparatus used in Example 1.
FIG. 7 is a diagram showing a simplified configuration of a coating apparatus used in Example 2.
FIG. 8 is a diagram showing a simplified configuration of a coating apparatus used in Example 3.
FIG. 9 is a simplified view of another example of a coating apparatus suitable for producing a hydrogen storage body by using a high-frequency plasma CVD method.
FIG. 10 is a simplified diagram showing a configuration of a coating apparatus suitable for producing a hydrogen storage body by using a sputtering method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... hydrogen storage powder, 1a ... hydrogen storage phase, 2 ... coating layer, 2a ... coating phase, 3 ... core body (core phase), 4 ... connection part (passage), 10, 20 ... hydrogen storage body

Claims (5)

A hydrogen storage powder made of Mg or an Mg alloy and responsible for storing and releasing hydrogen;
A coating layer having a composition different from that of the hydrogen storage powder and formed on the surface of the hydrogen storage powder by a gas phase method,
Hydrogen storage body provided with. The hydrogen storage body according to claim 1, wherein the coating layer is made of at least one of Pd, V, and a Ti-Cr alloy. 2. The hydrogen storage body according to claim 1, wherein the coating layer has a larger volume change due to movement of hydrogen atoms than the hydrogen storage powder. 3. A core phase,
A hydrogen storage phase covering the surface of the core phase,
A coating phase covering the surface of the hydrogen storage phase,
A passage for flowing hydrogen atoms from the coating phase to the core phase,
With
A hydrogen storage body, wherein a stress is applied to the hydrogen storage phase by expansion or contraction of the core phase and the coating phase when the hydrogen storage phase stores or releases hydrogen. 5. The hydrogen storage body according to claim 1, wherein the hydrogen storage body has a hydrogen release amount of 3.0 mass% or more in an environment of 150 ° C. or less.

Images