JP2007239052A - Hydrogen storage alloy - Google Patents
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- JP2007239052A JP2007239052A JP2006064809A JP2006064809A JP2007239052A JP 2007239052 A JP2007239052 A JP 2007239052A JP 2006064809 A JP2006064809 A JP 2006064809A JP 2006064809 A JP2006064809 A JP 2006064809A JP 2007239052 A JP2007239052 A JP 2007239052A
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- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 90
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 90
- 239000001257 hydrogen Substances 0.000 title claims abstract description 90
- 238000003860 storage Methods 0.000 title claims abstract description 50
- 239000000956 alloy Substances 0.000 title claims abstract description 31
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 31
- 239000002105 nanoparticle Substances 0.000 claims abstract description 123
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims abstract description 115
- 229910052763 palladium Inorganic materials 0.000 claims abstract description 20
- 229910052741 iridium Inorganic materials 0.000 claims abstract description 15
- 239000013078 crystal Substances 0.000 claims abstract description 10
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 claims abstract description 10
- 229910052751 metal Inorganic materials 0.000 claims description 17
- 239000002184 metal Substances 0.000 claims description 17
- 238000000034 method Methods 0.000 claims description 17
- 125000004435 hydrogen atom Chemical group [H]* 0.000 claims description 3
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 abstract description 14
- 239000006104 solid solution Substances 0.000 abstract description 13
- 239000000243 solution Substances 0.000 abstract description 8
- 229910052697 platinum Inorganic materials 0.000 abstract description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 28
- 239000002245 particle Substances 0.000 description 24
- 239000011258 core-shell material Substances 0.000 description 22
- 238000010521 absorption reaction Methods 0.000 description 14
- 239000006185 dispersion Substances 0.000 description 8
- 238000002441 X-ray diffraction Methods 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 7
- 238000001914 filtration Methods 0.000 description 6
- 229920000620 organic polymer Polymers 0.000 description 6
- 238000003756 stirring Methods 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000002082 metal nanoparticle Substances 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- 229910021642 ultra pure water Inorganic materials 0.000 description 4
- 239000012498 ultrapure water Substances 0.000 description 4
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- WHNWPMSKXPGLAX-UHFFFAOYSA-N N-Vinyl-2-pyrrolidone Chemical compound C=CN1CCCC1=O WHNWPMSKXPGLAX-UHFFFAOYSA-N 0.000 description 3
- 239000003638 chemical reducing agent Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 239000003223 protective agent Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 101150003085 Pdcl gene Proteins 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000010948 rhodium Substances 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 229910001260 Pt alloy Inorganic materials 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 150000003950 cyclic amides Chemical group 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- PIBWKRNGBLPSSY-UHFFFAOYSA-L palladium(II) chloride Chemical compound Cl[Pd]Cl PIBWKRNGBLPSSY-UHFFFAOYSA-L 0.000 description 1
- 229920000058 polyacrylate Polymers 0.000 description 1
- 229920002239 polyacrylonitrile Polymers 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 229920001289 polyvinyl ether Polymers 0.000 description 1
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 1
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 150000005846 sugar alcohols Polymers 0.000 description 1
- 230000005469 synchrotron radiation Effects 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 229920003169 water-soluble polymer Polymers 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/32—Hydrogen storage
Abstract
Description
本発明は、パラジウム（Ｐｄ）とイリジウム（Ｉｒ）とを含むナノ粒子からなる新しい水素吸蔵合金に関する。 The present invention relates to a new hydrogen storage alloy composed of nanoparticles containing palladium (Pd) and iridium (Ir).
水素は、燃焼後の生成物が水であるために環境負荷が小さく、今後の主要燃料として期待されている。水素の貯蔵には、水素を可逆的に吸収／放出する水素吸蔵合金が必要となる。 Hydrogen has a low environmental impact because the product after combustion is water, and is expected as a future main fuel. Storage of hydrogen requires a hydrogen storage alloy that reversibly absorbs / releases hydrogen.
本発明者は、先に新たな合金ナノ粒子の製造方法を提案した（特許文献１）。この製造方法は、アルコール還元法により得たコア・シェル型構造を有するナノ粒子に水素吸収／放出サイクルを適用することにより、ナノ粒子の構造をコア・シェル型から固溶体型へと変化させるものである。コア・シェル型構造を有するナノ粒子は、まず、コアとなる金属ナノ粒子（特許文献１の実施例ではパラジウム（Ｐｄ）ナノ粒子）をアルコール還元法により形成し、次いでこの金属ナノ粒子の表面にシェルとなる金属（同実施例では白金（Ｐｔ）シェル）を析出させることにより作製される。 The inventor previously proposed a new method for producing alloy nanoparticles (Patent Document 1). This production method changes the nanoparticle structure from the core-shell type to the solid solution type by applying a hydrogen absorption / release cycle to the nanoparticles having a core-shell type structure obtained by the alcohol reduction method. is there. The nanoparticles having a core-shell structure are formed by first forming metal nanoparticles (palladium (Pd) nanoparticles in the example of Patent Document 1) as a core by an alcohol reduction method, and then forming the metal nanoparticles on the surface of the metal nanoparticles. It is produced by depositing a metal to be a shell (in this embodiment, platinum (Pt) shell).
アルコール還元法によるコア・シェル型のナノ粒子の作製は、種々の金属について試行されている（特許文献２；特に［０００３］［０００４］）。
特許文献１に開示されているように、コア・シェル型Ｐｄ／Ｐｔナノ粒子の水素吸蔵量は、水素吸収／放出サイクルの適用による固溶体型への構造変化に伴って増加する傾向を示す（特許文献１の図４）。しかし、このナノ粒子の水素吸蔵量は、完全な固溶体型となった後においても１気圧（約０．１ＭＰａ）の水素圧力で０．３Ｍ程度にとどまっており、さらに改善する必要がある。 As disclosed in Patent Document 1, the hydrogen occlusion amount of core-shell type Pd / Pt nanoparticles shows a tendency to increase with a structural change to a solid solution type by applying a hydrogen absorption / release cycle (patent) Reference 1 FIG. 4). However, the hydrogen occlusion amount of these nanoparticles is only about 0.3 M at a hydrogen pressure of 1 atm (about 0.1 MPa) even after becoming a complete solid solution type, and needs to be further improved.
そこで、本発明は、ナノ粒子からなる水素吸蔵合金のさらなる特性改善を図ることを目的とする。 Accordingly, an object of the present invention is to further improve the characteristics of a hydrogen storage alloy composed of nanoparticles.
特許文献２に開示されているように、アルコール還元法によるナノ粒子の作製は、種々の金属について試行されているが、イリジウム（Ｉｒ）についてはその作製例が報告されていない。 As disclosed in Patent Document 2, production of nanoparticles by an alcohol reduction method has been tried for various metals, but no example of production of iridium (Ir) has been reported.
本発明者は、アルコール還元法の改良によりＰｄ／Ｉｒナノ粒子の合成に成功し、このナノ粒子が他の金属種からなるナノ粒子を遙かに上回る水素吸蔵量を示すことを見いだした。 The present inventor has succeeded in synthesizing Pd / Ir nanoparticles by improving the alcohol reduction method, and found that the nanoparticles show a hydrogen storage capacity far exceeding that of nanoparticles composed of other metal species.
本発明は、ＰｄおよびＩｒを含むナノ粒子からなる水素吸蔵合金を提供する。 The present invention provides a hydrogen storage alloy comprising nanoparticles containing Pd and Ir.
本発明は、その別の側面から、ＰｄおよびＩｒを含むナノ粒子に、このナノ粒子中の金属のモル数に対して０．４モル％以上に相当する水素（水素原子換算）を吸収させる、当該ナノ粒子の水素吸蔵合金としての使用方法を提供する。この使用方法では、ナノ粒子に水素を吸収させる工程に引き続き、必要に応じ、吸収させた水素を放出させる工程、が実施される。 From another aspect of the present invention, a nanoparticle containing Pd and Ir absorbs hydrogen corresponding to 0.4 mol% or more with respect to the number of moles of metal in the nanoparticle (in terms of hydrogen atom). A method of using the nanoparticle as a hydrogen storage alloy is provided. In this method of use, subsequent to the step of absorbing hydrogen into the nanoparticles, a step of releasing the absorbed hydrogen is performed as necessary.
本発明による水素吸蔵合金は、Ｐｄナノ粒子やＰｄ−Ｐｔ合金ナノ粒子（特許文献１）を大幅に上回る水素吸蔵量を示す。この特異的に大きな水素吸蔵量は、Ｐｄを含むナノ粒子による水素貯蔵の実用化に大きな前進をもたらすものである。 The hydrogen storage alloy according to the present invention exhibits a hydrogen storage amount significantly exceeding that of Pd nanoparticles and Pd—Pt alloy nanoparticles (Patent Document 1). This specifically large amount of hydrogen occlusion provides a major advance in the practical application of hydrogen storage using nanoparticles containing Pd.
本発明の水素吸蔵合金を構成するナノ粒子は、Ｐｄからなるコアと、このコアを覆うＩｒからなるシェルと、を含むことが好ましい。ただし、このナノ粒子は、水素吸収／放出サイクルの適用により構造変化を起こすことがある。この構造変化により、上記ナノ粒子は、コア・シェル型から、最終的には固溶体型へと移行する。 The nanoparticles constituting the hydrogen storage alloy of the present invention preferably include a core made of Pd and an Ir shell covering the core. However, the nanoparticles may undergo structural changes upon application of a hydrogen absorption / release cycle. Due to this structural change, the nanoparticles move from a core / shell type to a solid solution type.
完全な固溶体型では、ナノ粒子が、ＰｄとＩｒとによる単一種の結晶格子を内包している。すなわち、本発明の水素吸蔵合金を構成するナノ粒子は、ナノ粒子において、ＰｄとＩｒとが単一種の結晶格子を形成していてもよい。 In the complete solid solution type, the nanoparticles contain a single type of crystal lattice of Pd and Ir. That is, in the nanoparticles constituting the hydrogen storage alloy of the present invention, Pd and Ir may form a single type of crystal lattice in the nanoparticles.
コア・シェル型から完全な固溶体型へと移行する間のナノ粒子も本発明の水素吸蔵合金を構成することができる。すなわち、本発明の水素吸蔵合金を構成するナノ粒子は、ＰｄがＩｒよりも豊富なＰｄリッチなコア部と、このコア部を覆う、ＩｒがＰｄよりも豊富なＩｒリッチなシェル部と、を含んでいてもよい。 The nanoparticles during the transition from the core-shell type to the complete solid solution type can also constitute the hydrogen storage alloy of the present invention. That is, the nanoparticles constituting the hydrogen storage alloy of the present invention have a Pd-rich core part rich in Pd than Ir and an Ir-rich shell part covering the core part and rich in Ir than Pd. May be included.
本明細書において、ナノ粒子とは、粒径が１００ｎｍ以下の粒子をいう。また、本明細書において、単一種の結晶格子を形成しているか否かはＸ線回折により確認するものとする。 In this specification, a nanoparticle means a particle | grain with a particle size of 100 nm or less. In this specification, whether or not a single type of crystal lattice is formed is confirmed by X-ray diffraction.
本発明による水素吸蔵合金を構成するナノ粒子は、Ｐｄを４０〜９０原子％、さらには７０〜８０原子％、Ｉｒを１０〜６０原子％、さらには２０〜３０原子％、の範囲で含有することが好ましい。Ｉｒの含有率が低すぎても高すぎても、水素吸蔵量増大の効果は十分に得られない。 The nanoparticles constituting the hydrogen storage alloy according to the present invention contain Pd in the range of 40 to 90 atomic%, further 70 to 80 atomic%, Ir in the range of 10 to 60 atomic%, and further 20 to 30 atomic%. It is preferable. If the Ir content is too low or too high, the effect of increasing the hydrogen storage amount cannot be obtained sufficiently.
本発明による水素吸蔵合金を構成するナノ粒子の粒径は、特に制限はないが、１００ｎｍ以下、例えば０．５ｎｍ〜１００ｎｍ、さらには１ｎｍ〜１００ｎｍ、特に２ｎｍ〜５０ｎｍ、とりわけ２ｎｍ〜２０ｎｍが好適であり、１０ｎｍ以下であってもよい。 The particle size of the nanoparticles constituting the hydrogen storage alloy according to the present invention is not particularly limited, but is preferably 100 nm or less, for example, 0.5 nm to 100 nm, more preferably 1 nm to 100 nm, particularly 2 nm to 50 nm, especially 2 nm to 20 nm. Yes, it may be 10 nm or less.
本発明による水素吸蔵合金が示す特異的に大きな水素吸蔵量は、温度３０３Ｋ、水素圧力０．１ＭＰａの条件において、０．４モル％（Ｍ）以上、０．５Ｍ以上、０．５５Ｍ以上、さらには０．６Ｍ以上にも達する。水素吸蔵量は、慣用に従い、ナノ粒子中の金属のモル数に対する吸蔵された水素原子のモル数の比率により示す。 The hydrogen storage amount that the hydrogen storage alloy according to the present invention shows is specifically 0.4 mol% (M) or more, 0.5 M or more, 0.55 M or more under the conditions of a temperature of 303 K and a hydrogen pressure of 0.1 MPa. Reaches 0.6M or more. The amount of hydrogen occlusion is indicated by the ratio of the number of moles of hydrogen atoms stored to the number of moles of metal in the nanoparticles, according to common practice.
本発明による水素吸蔵合金を構成するナノ粒子は、その製造方法に制限はないが、アルコール還元法により得ることができる。アルコール還元法は、従来から知られているように、有機高分子の存在下、アルコールを含む溶液中で金属イオンを還元するナノ粒子の製造方法である。 Although the nanoparticle which comprises the hydrogen storage alloy by this invention does not have a restriction | limiting in the manufacturing method, it can be obtained by the alcohol reduction method. As conventionally known, the alcohol reduction method is a method for producing nanoparticles in which metal ions are reduced in a solution containing alcohol in the presence of an organic polymer.
有機高分子としては、水溶性のポリマーが好ましく、具体的にはポリビニルピロリドン（ＰＶＰ）のような環状アミド構造を有するポリマーが好適であるが、これに限らず、目的とする金属粒子の種類等に応じ、例えばポリビニルアルコール、ポリビニルエーテル、ポリアクリレート、ポリアクリロニトリル等を用いてもよい。 As the organic polymer, a water-soluble polymer is preferable, and specifically, a polymer having a cyclic amide structure such as polyvinylpyrrolidone (PVP) is preferable. For example, polyvinyl alcohol, polyvinyl ether, polyacrylate, polyacrylonitrile, or the like may be used.
アルコールは、溶液中で還元剤として作用する。アルコールも、金属や有機高分子の種類等に応じて適宜選択するとよく、エタノール、プロパノール等を用いればよいが、エチレングリコール等の多価アルコールを用いてもよい。 Alcohol acts as a reducing agent in solution. The alcohol may be appropriately selected according to the type of metal or organic polymer, and ethanol, propanol, or the like may be used, but polyhydric alcohols such as ethylene glycol may be used.
溶液中における有機高分子の量を相対的に増やすと析出するナノ粒子の粒径は小さくなるため、これを利用すればナノ粒子の粒径を制御できる。添加する金属塩の濃度を調整することによっても、析出する金属の量、ひいてはナノ粒子の粒径を制御できる。得られる粒子の組成の均一性も高い。このように、アルコール還元法は、粒径等の制御性に優れており、ナノ粒子の製造方法として適している。 When the amount of the organic polymer in the solution is relatively increased, the particle size of the deposited nanoparticles becomes small, and this can be used to control the particle size of the nanoparticles. By adjusting the concentration of the metal salt to be added, it is possible to control the amount of the deposited metal and thus the particle size of the nanoparticles. The uniformity of the composition of the obtained particles is also high. Thus, the alcohol reduction method is excellent in controllability such as particle size, and is suitable as a method for producing nanoparticles.
後述する実施例のように、アルコール還元法では、まずコアを形成し、その後コアにシェルを付加することにより、コア・シェル型構造を実現するとよい。コア形成工程またはシェル形成工程を所定回数繰り返すことにより、所望の径のコアもしくは所望の厚さのシェルの形成、または所望のコア金属／シェル金属比を実現することも可能である。 As in the examples described later, in the alcohol reduction method, a core / shell structure may be realized by first forming a core and then adding a shell to the core. By repeating the core forming step or the shell forming step a predetermined number of times, it is possible to form a core having a desired diameter or a shell having a desired thickness, or to achieve a desired core metal / shell metal ratio.
アルコール還元法によるＩｒの還元には、本発明者が経験してきた限りにおいて、他の金属と比較して特異的に長い時間を要する。Ｐｄナノ粒子上へのＰｔシェルの被覆は、８時間程度の溶液の撹拌で実現できるが（特許文献１［００３１］）、Ｉｒシェルは、この程度の撹拌時間では形成できず、その形成には２４時間程度の撹拌を要した。このように、Ｉｒは極めて析出しにくい。また、ロジウム（Ｒｈ）のようにＰｄバルクとの合金化による水素吸蔵量の増大が報告されているわけでもない。これまでＰｄ／Ｉｒナノ粒子の水素吸蔵特性について報告がなかったのは、このような理由によるものと考えられる。 The reduction of Ir by the alcohol reduction method requires a particularly long time as compared with other metals as long as the present inventors have experienced. Although coating of Pt shells on Pd nanoparticles can be achieved by stirring the solution for about 8 hours (Patent Document 1 [0031]), Ir shells cannot be formed with this level of stirring time. Stirring for about 24 hours was required. Thus, Ir is extremely difficult to precipitate. Moreover, an increase in the hydrogen storage amount due to alloying with Pd bulk as in rhodium (Rh) has not been reported. It is thought that this is the reason why there has been no report on the hydrogen storage properties of Pd / Ir nanoparticles.
Ｐｄ／Ｉｒナノ粒子が、Ｐｄ／Ｐｔナノ粒子等よりも大きな水素吸蔵特性を示す理由の詳細は明らかではないが、現時点では、Ｐｄから電子を引き抜きやすいＩｒの特性がＰｄの水素吸蔵量を増大させている可能性を指摘することができる。 The details of the reason why Pd / Ir nanoparticles exhibit larger hydrogen storage properties than Pd / Pt nanoparticles are not clear, but at this time, the properties of Ir that easily extract electrons from Pd increase the amount of hydrogen stored in Pd. It is possible to point out the possibility that
これが正しければ、Ｉｒに代えて、あるいはＩｒとともに、ＡｕをＰｄとともに用いることによっても、水素吸蔵量の増大を図ることができると考えられる。Ａｕは、Ｉｒとともに、そのイオン化エネルギーがＰｄよりもかなり大きく（Ｐｄ：８．３４ｅＶ、Ｉｒ：９．０２ｅＶ、Ａｕ：９．２２５ｅＶ）、Ｐｄよりも電子を離しにくい特性、言い換えればＰｄの水素化に際してＰｄから電子を受け取りやすい特性を有すると考えられる。イオン化エネルギーを指標とする上記の推論は、イオン化エネルギーがＰｄとそれほど変わらないＰｔ（８．６１ｅＶ）とＰｄとからなるナノ粒子（Ｐｄ／Ｐｔナノ粒子）の水素吸蔵量が、Ｐｄナノ粒子とほぼ同じであったという実験結果とも一致する。これらの実験結果は、ＰｄおよびＡｕを含むナノ粒子からなる水素吸蔵合金、さらにはＰｄ、ＩｒおよびＡｕを含むナノ粒子からなる水素吸蔵合金の有用性を示唆するものである。 If this is correct, it is considered that the amount of hydrogen occlusion can be increased by using Au together with Pd instead of Ir or together with Ir. Au, together with Ir, has a significantly higher ionization energy than Pd (Pd: 8.34 eV, Ir: 9.02 eV, Au: 9.225 eV), and has characteristics that it is harder to release electrons than Pd, in other words, hydrogenation of Pd. At this time, it is considered that the material easily receives electrons from Pd. The above inference using ionization energy as an index indicates that the hydrogen occlusion amount of nanoparticles (Pd / Pt nanoparticles) composed of Pt (8.61 eV) and Pd whose ionization energy is not so different from Pd is almost the same as that of Pd nanoparticles. It agrees with the experimental result that it was the same. These experimental results suggest the usefulness of a hydrogen storage alloy composed of nanoparticles containing Pd and Au, and further a hydrogen storage alloy composed of nanoparticles containing Pd, Ir and Au.
上述のように、Ｐｄ／Ｉｒナノ粒子は、Ｐｄ／Ｐｔナノ粒子と同様、水素吸収／放出サイクルの適用により、コア・シェル型構造から完全な固溶体型へと移行する。Ｐｄ／Ｉｒナノ粒子については、３回の水素吸収／放出サイクルの適用により、コア・シェル型構造が完全に固溶体型へと移行した。 As described above, Pd / Ir nanoparticles, like Pd / Pt nanoparticles, transition from a core-shell type structure to a complete solid solution type by applying a hydrogen absorption / release cycle. For Pd / Ir nanoparticles, the core / shell structure was completely transformed into a solid solution type by applying three hydrogen absorption / release cycles.
コア・シェル型構造を有する金属ナノ粒子のＸ線回折パターンでは、通常、コア金属の結晶格子に由来する回折ピークと、シェル金属の結晶格子に由来する回折ピークとが重なり合って観察される。これに対し、完全に固溶体型へと移行したナノ粒子からは、コア金属とシェル金属とから構成された新たな結晶格子に由来する回折ピークのみが観察される。Ｘ線回折の結果から判断する限り、水素吸収／放出サイクルを十分な回数だけ適用した後、Ｐｄ／Ｉｒナノ粒子の内部では、ＰｄとＩｒとが単一種の結晶格子を形成していると考えられる。 In the X-ray diffraction pattern of metal nanoparticles having a core-shell structure, the diffraction peak derived from the core metal crystal lattice and the diffraction peak derived from the shell metal crystal lattice are usually observed overlapping each other. On the other hand, only the diffraction peak derived from the new crystal lattice composed of the core metal and the shell metal is observed from the nanoparticles completely transferred to the solid solution type. As far as judging from the results of X-ray diffraction, it is considered that Pd and Ir form a single type of crystal lattice inside the Pd / Ir nanoparticles after applying a sufficient number of hydrogen absorption / release cycles. It is done.
単一種の結晶格子を形成するための水素吸収／放出サイクルは、ナノ粒子を２０〜３００℃（２９３〜５７３Ｋ）、特に５０〜１００℃（３２３〜３７３Ｋ）に保持しながら行うとよい。上記のナノ粒子を水素吸蔵合金として使用する際における水素吸収過程および水素放出過程は、１５〜１５０℃（２８８〜４２３Ｋ）、特に３０〜８０℃（３０３〜３５３Ｋ）、の温度範囲で行うことが好ましい。 The hydrogen absorption / release cycle for forming a single type of crystal lattice may be performed while holding the nanoparticles at 20 to 300 ° C. (293 to 573 K), particularly 50 to 100 ° C. (323 to 373 K). When using the above nanoparticles as a hydrogen storage alloy, the hydrogen absorption process and the hydrogen release process are performed in a temperature range of 15 to 150 ° C. (288 to 423 K), particularly 30 to 80 ° C. (303 to 353 K). preferable.
本発明による水素吸蔵合金を構成するナノ粒子は、特に粒径が小さい場合には、有機高分子で被覆された状態で使用してもよい。この状態は微粒子の酸化防止に有効である。保護剤となる有機高分子は、特に制限されず、アルコール還元法で用いる各種ポリマーをそのまま用いてもよい。 The nanoparticles constituting the hydrogen storage alloy according to the present invention may be used in a state of being coated with an organic polymer, particularly when the particle size is small. This state is effective for preventing oxidation of fine particles. The organic polymer used as the protective agent is not particularly limited, and various polymers used in the alcohol reduction method may be used as they are.
以下、実施例により本発明をさらに具体的に説明するが、以下の実施例は、本欄における上記記載と同様、本発明の実施形態の例示に過ぎず、本発明を限定するものではない。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the following examples are only examples of the embodiments of the present invention, as described above in this section, and do not limit the present invention.
（Ｐｄナノ粒子の合成）
塩化パラジウム（ＰｄＣｌ2）を希塩酸に溶解し、２ｍＭのＨ2ＰｄＣｌ4水溶液を調製した。この水溶液８０ｍｌ（１６０μｍｏｌ）に保護剤としてポリ（Ｎ−ビニル−２−ピロリドン）（ＰＶＰ）１７７．７ｍｇ（モノマーユニットで１．６ｍｍｏｌ）および超純水５６０ｍｌを加えた溶液に、還元剤としてエタノール１６０ｍｌを撹拌しながら加えた。この溶液を９５℃で３時間還流することにより、ＰＶＰ保護Ｐｄナノ粒子（以下「Ｐｄ−ＰＶＰナノ粒子」という）を調製した。
(Synthesis of Pd nanoparticles)
Palladium chloride (PdCl 2 ) was dissolved in dilute hydrochloric acid to prepare a 2 mM H 2 PdCl 4 aqueous solution. To a solution obtained by adding 177.7 mg (1.6 mmol in monomer units) of poly (N-vinyl-2-pyrrolidone) (PVP) and 560 ml of ultrapure water as a protective agent to 80 ml (160 μmol) of this aqueous solution, 160 ml of ethanol as a reducing agent. Was added with stirring. The solution was refluxed at 95 ° C. for 3 hours to prepare PVP-protected Pd nanoparticles (hereinafter referred to as “Pd-PVP nanoparticles”).
このＰｄ−ＰＶＰナノ粒子分散液を出発粒子としＰｄ粒子の段階成長を行った。まず、Ｐｄ−ＰＶＰナノ粒子分散液２００ｍｌにＨ2ＰｄＣｌ4水溶液６０ｍｌ（１２０μｍｏｌ）、超純水４２０ｍｌおよびエタノール１２０ｍｌを撹拌しながら加え、９５℃で３時間還流を行って第二段階合成を行い、さらに同様の手順による第三段階合成により、Ｐｄ−ＰＶＰナノ粒子（この最終粒子を以下「Ｐｄナノ粒子」という）を得た。 Using this Pd-PVP nanoparticle dispersion as starting particles, Pd particles were grown in stages. First, 60 ml (120 μmol) of an H 2 PdCl 4 aqueous solution, 420 ml of ultrapure water and 120 ml of ethanol were added to 200 ml of the Pd-PVP nanoparticle dispersion with stirring, and the mixture was refluxed at 95 ° C. for 3 hours to perform the second stage synthesis. Further, Pd-PVP nanoparticles (the final particles are hereinafter referred to as “Pd nanoparticles”) were obtained by a third step synthesis according to the same procedure.
（Ｐｄ／Ｉｒコア・シェル型ナノ粒子の合成）
Ｐｄナノ粒子０．２ｇに超純水５０ｍｌおよびエタノール１００ｍｌを加え、これを保持するフラスコ内の空気を窒素置換して除去した。次いで、このＰｄナノ粒子分散液を水素雰囲気下で２時間撹拌を行った。引き続き、Ｐｄナノ粒子分散液の液温を７５℃に保持しながら、（ＮＨ4）2ＩｒＣｌ6０．２ｇ（０．５ｍｍｏｌ）を超純水１００ｍｌに溶解したものを６時間かけて等圧滴下ロートを用いて滴下した。さらに、反応を十分に進行させるために、分散液を７５℃に保持しながら２４時間撹拌した。この分散液を、メンブレンフィルタを用いて濾過し、Ｐｄ／Ｉｒコア・シェル型ナノ粒子を得た。
(Synthesis of Pd / Ir core / shell type nanoparticles)
50 ml of ultrapure water and 100 ml of ethanol were added to 0.2 g of Pd nanoparticles, and the air in the flask holding this was purged with nitrogen and removed. Subsequently, this Pd nanoparticle dispersion was stirred for 2 hours in a hydrogen atmosphere. Subsequently, while maintaining the liquid temperature of the Pd nanoparticle dispersion at 75 ° C., 0.2 g (0.5 mmol) of (NH 4 ) 2 IrCl 6 dissolved in 100 ml of ultrapure water was dropped at an equal pressure over 6 hours. It was dripped using a funnel. Furthermore, in order to fully advance the reaction, the dispersion was stirred for 24 hours while maintaining the temperature at 75 ° C. This dispersion was filtered using a membrane filter to obtain Pd / Ir core / shell type nanoparticles.
（透過型電子顕微鏡（ＴＥＭ）を用いた観察）
上記で得たＰｄナノ粒子およびＰｄ／Ｉｒコア・シェル型ナノ粒子の平均粒径を測定するため、ＴＥＭ観察を行なった。ＴＥＭ観察用試料は、カーボン支持膜の上にＰｄナノ粒子エタノール分散液およびＰｄ／Ｉｒナノ粒子エタノール分散液をパスツールピペットで６滴落とし、乾燥させて作製した。ＴＥＭ観察は、加速電圧２００ｋＶ、倍率１０万倍で行った。ＴＥＭ写真中の任意のエリアから約３００個の粒子を選出してその直径を測定し、その結果から平均粒径および標準偏差を算出した。
(Observation using transmission electron microscope (TEM))
In order to measure the average particle size of the Pd nanoparticles and Pd / Ir core / shell nanoparticles obtained above, TEM observation was performed. A sample for TEM observation was prepared by dropping 6 drops of Pd nanoparticle ethanol dispersion and Pd / Ir nanoparticle ethanol dispersion on a carbon support membrane with a Pasteur pipette and drying. TEM observation was performed at an acceleration voltage of 200 kV and a magnification of 100,000. About 300 particles were selected from an arbitrary area in the TEM photograph and the diameter thereof was measured, and the average particle size and standard deviation were calculated from the results.
結果を図１〜図３に示す。図１はＰｄナノ粒子についての結果であり、図２は濾過前のＰｄ／Ｉｒコア・シェル型ナノ粒子についての結果であり、図３は濾過後のＰｄ／Ｉｒコア・シェル型ナノ粒子についての結果である。Ｐｄナノ粒子は、平均粒径７．０ｎｍ、標準偏差１．３ｎｍであった。Ｐｄ／Ｉｒコア・シェル型ナノ粒子は、濾過前の状態で、平均粒径９．２ｎｍ、標準偏差１．２ｎｍ、濾過後の状態で、平均粒径９．０ｎｍ、標準偏差１．２ｎｍであった。Ｐｄナノ粒子とＰｄ／Ｉｒコア・シェル型ナノ粒子との粒径の差異は、Ｉｒシェルの厚みに相当する。 The results are shown in FIGS. FIG. 1 shows the results for Pd nanoparticles, FIG. 2 shows the results for Pd / Ir core / shell nanoparticles before filtration, and FIG. 3 shows the results for Pd / Ir core / shell nanoparticles after filtration. It is a result. The Pd nanoparticles had an average particle size of 7.0 nm and a standard deviation of 1.3 nm. The Pd / Ir core-shell nanoparticles had an average particle size of 9.2 nm and a standard deviation of 1.2 nm before filtration, and an average particle size of 9.0 nm and a standard deviation of 1.2 nm after filtration. It was. The difference in particle size between the Pd nanoparticles and the Pd / Ir core / shell nanoparticles corresponds to the thickness of the Ir shell.
Ｐｄナノ粒子の粒径およびＩｒシェルの厚みから見積もると、Ｐｄ／Ｉｒコア・シェル型ナノ粒子は、Ｐｄを７５原子％、Ｉｒを２５原子％、含んでいることになる。 As estimated from the particle size of the Pd nanoparticle and the thickness of the Ir shell, the Pd / Ir core / shell nanoparticle contains 75 atomic% of Pd and 25 atomic% of Ir.
（水素吸蔵能力の確認）
上記から得たＰｄ／Ｉｒコア・シェル型ナノ粒子について、ＰＣＴ（Hydrogen Pressure -Composition-Isotherms）曲線を測定した。測定には、ＰＣＴ自動特性測定装置（鈴木商館製）を用いた。水素雰囲気の最高圧力は０．１ＭＰａ（７６０Ｔｏｒｒ）、測定温度は３０３Ｋおよび３７３Ｋとした。結果を図４に示す。温度が高くなると、３０３Ｋの測定で明瞭であったプラトー領域が不明瞭になり、かつ水素吸蔵量が減少した。
(Confirmation of hydrogen storage capacity)
A PCT (Hydrogen Pressure-Composition-Isotherms) curve was measured for the Pd / Ir core-shell type nanoparticles obtained from the above. For the measurement, a PCT automatic characteristic measuring device (manufactured by Suzuki Shokan) was used. The maximum pressure in the hydrogen atmosphere was 0.1 MPa (760 Torr), and the measurement temperatures were 303K and 373K. The results are shown in FIG. As the temperature increased, the plateau region, which was clearly measured at 303K, became unclear and the hydrogen storage amount decreased.
図５に、Ｐｄ／Ｉｒコア・シェル型ナノ粒子のＰＣＴ曲線を、これまで測定されてきた、Ｐｄナノ粒子、Ｐｄ／Ｐｔナノ粒子、ＰｄバルクのＰＣＴ曲線とともに示す。Ｐｄ／Ｉｒコア・シェル型ナノ粒子は、温度３０３Ｋ、水素圧力０．１ＭＰａにおいて、０．７Ｍ程度の水素吸蔵量を示した。これは、Ｐｄナノ粒子およびＰｄ／Ｐｔナノ粒子の水素吸蔵量の３倍以上に相当し、Ｐｄバルクの水素吸蔵量を上回る。 FIG. 5 shows PCT curves of Pd / Ir core / shell nanoparticles together with PCT curves of Pd nanoparticles, Pd / Pt nanoparticles, and Pd bulk that have been measured so far. The Pd / Ir core-shell type nanoparticles exhibited a hydrogen storage amount of about 0.7 M at a temperature of 303 K and a hydrogen pressure of 0.1 MPa. This corresponds to more than three times the hydrogen storage capacity of Pd nanoparticles and Pd / Pt nanoparticles, and exceeds the hydrogen storage capacity of the Pd bulk.
なお、後述する水素吸収／放出サイクルを適用して固溶体型へと内部構造を変化させたＰｄ／Ｉｒ固溶体型ナノ粒子についても、コア・シェル型と同様、Ｐｄナノ粒子およびＰｄ／Ｐｔナノ粒子の水素吸蔵量を大きく上回る水素吸蔵量を有することが確認された。 In addition, Pd / Ir solid solution type nanoparticles whose internal structure was changed to a solid solution type by applying a hydrogen absorption / release cycle described later are similar to the core-shell type, as in the case of the core-shell type. It was confirmed that the hydrogen storage amount greatly exceeds the hydrogen storage amount.
（粉末Ｘ線回折による分析）
０．５ｍｍφのガラスキャピラリーに試料とする粒子を封入した。封入は真空で脱気した後に行った。測定は波長０．０６８８１８ｎｍの放射光を用いて行った。試料は、上記から得た、Ｐｄナノ粒子、Ｐｄ／Ｉｒコア・シェル型ナノ粒子、およびＩｒナノ粒子とした。Ｐｄ／Ｉｒコア・シェル型ナノ粒子は、水素吸収／放出サイクルを適用する前の試料を用いた。また、Ｉｒナノ粒子は、以下のようにして作製した。
(Analysis by powder X-ray diffraction)
Sample particles were encapsulated in a 0.5 mmφ glass capillary. The sealing was performed after deaeration in a vacuum. The measurement was performed using synchrotron radiation having a wavelength of 0.068818 nm. The samples were Pd nanoparticles, Pd / Ir core / shell type nanoparticles, and Ir nanoparticles obtained from the above. As the Pd / Ir core / shell type nanoparticles, a sample before applying a hydrogen absorption / release cycle was used. Ir nanoparticles were produced as follows.
（ＮＨ4）2ＩｒＣｌ6を水に溶解し、２ｍＭの（ＮＨ4）2ＩｒＣｌ6水溶液を調製した。この水溶液８０ｍｌ（１６０μｍｏｌ）に保護剤としてＰＶＰ１７７．７ｍｇ（モノマーユニットで１．６ｍｍｏｌ）に、還元剤としてエタノール４２０ｍｌを撹拌しながら加えた。この溶液を９５℃で２４時間還流し、Ｉｒナノ粒子を得た。 (NH 4 ) 2 IrCl 6 was dissolved in water to prepare a 2 mM (NH 4 ) 2 IrCl 6 aqueous solution. To 80 ml (160 μmol) of this aqueous solution, 420 ml of ethanol as a reducing agent was added with stirring to 177.7 mg (1.6 mmol in monomer units) as a protective agent. This solution was refluxed at 95 ° C. for 24 hours to obtain Ir nanoparticles.
図６にＸ線回折測定の結果を示す。この結果より、Ｐｄ／Ｉｒコア・シェル型ナノ粒子が面心立方（ｆｃｃ）格子構造を有することが確認された。Ｐｄ／Ｉｒコア・シェル型ナノ粒子における（０４２）面のピークに着目すると、高角度側のピークの強度がシェル部のＩｒ格子の影響を受けて高くなっていることがわかる。 FIG. 6 shows the results of X-ray diffraction measurement. From this result, it was confirmed that the Pd / Ir core-shell type nanoparticles have a face-centered cubic (fcc) lattice structure. When attention is paid to the peak of the (042) plane in the Pd / Ir core / shell type nanoparticles, it can be seen that the intensity of the peak on the high angle side is increased due to the influence of the Ir lattice in the shell portion.
引き続き、Ｐｄ／Ｉｒコア・シェル型ナノ粒子について水素の吸収／放出処理を３回適用した。この処理は、温度３７３Ｋ、水素圧力０．１ＭＰａの条件で行った。そして、水素吸収／放出サイクルを適用する前の試料および同サイクルを適用した後の試料それぞれについて、真空で脱気した試料とともに（水素圧力：０Ｔｏｒｒ）、０．０８６ＭＰａ（６５０Ｔｏｒｒ）の水素を導入してガラスキャピラリーを封じた試料を作製した。これらの試料について、上記と同様にしてＸ線回折測定を行った。結果を図７に示す。 Subsequently, hydrogen absorption / release treatment was applied three times to the Pd / Ir core-shell type nanoparticles. This treatment was performed under conditions of a temperature of 373 K and a hydrogen pressure of 0.1 MPa. For each of the sample before applying the hydrogen absorption / release cycle and the sample after applying the cycle, 0.086 MPa (650 Torr) of hydrogen was introduced together with the sample degassed in vacuum (hydrogen pressure: 0 Torr). A sample with a glass capillary sealed was prepared. These samples were subjected to X-ray diffraction measurement in the same manner as described above. The results are shown in FIG.
図７に示すように、水素吸収／放出サイクルを３回適用した後には、１つのｆｃｃ格子からのピークのみが観察された。これは、Ｐｄ／Ｉｒコア・シェル型ナノ粒子が完全な固溶体型へと変化したことを示している。 As shown in FIG. 7, after applying the hydrogen absorption / release cycle three times, only peaks from one fcc lattice were observed. This indicates that the Pd / Ir core-shell type nanoparticles have changed to a complete solid solution type.
本発明は、従来から知られていたナノ粒子からなる水素吸蔵合金の水素吸蔵特性を飛躍的に向上させるものとして、当該技術分野において多大な利用価値を有する。 INDUSTRIAL APPLICABILITY The present invention has a great utility value in the technical field as a material for dramatically improving the hydrogen storage characteristics of conventionally known hydrogen storage alloys composed of nanoparticles.
Claims (6)
Use of nanoparticles as a hydrogen storage alloy, wherein nanoparticles containing palladium and iridium absorb hydrogen (in terms of hydrogen atoms) equivalent to 0.4 mol% or more with respect to the number of moles of metal in the nanoparticles. Method.
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| CN113764698A (en) * | 2020-12-31 | 2021-12-07 | 厦门大学 | Hydrogen storage fuel and preparation method thereof |
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| JP2003226901A (en) * | 2002-02-05 | 2003-08-15 | Hitachi Maxell Ltd | Binary alloy fine particle and production method therefor |
| JP2005272970A (en) * | 2004-03-25 | 2005-10-06 | Kyushu Univ | Alloy particle and production method therefor |
| JP2008525638A (en) * | 2004-12-22 | 2008-07-17 | ブルックヘヴン サイエンス アソシエイツ | Metal deposition on palladium and palladium alloy particles induced by hydrogen absorption |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2003226901A (en) * | 2002-02-05 | 2003-08-15 | Hitachi Maxell Ltd | Binary alloy fine particle and production method therefor |
| JP2005272970A (en) * | 2004-03-25 | 2005-10-06 | Kyushu Univ | Alloy particle and production method therefor |
| JP2008525638A (en) * | 2004-12-22 | 2008-07-17 | ブルックヘヴン サイエンス アソシエイツ | Metal deposition on palladium and palladium alloy particles induced by hydrogen absorption |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113764698A (en) * | 2020-12-31 | 2021-12-07 | 厦门大学 | Hydrogen storage fuel and preparation method thereof |
| CN113764698B (en) * | 2020-12-31 | 2024-01-09 | 厦门大学 | Hydrogen storage fuel and preparation method thereof |
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