JP2007131926A - Platinum nanoparticle, production method therefor, and electrode for fuel cell using the same - Google Patents
Platinum nanoparticle, production method therefor, and electrode for fuel cell using the same Download PDFInfo
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 title claims abstract description 375
- 229910052697 platinum Inorganic materials 0.000 title claims abstract description 188
- 239000002105 nanoparticle Substances 0.000 title claims abstract description 143
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 27
- 239000000446 fuel Substances 0.000 title claims description 11
- 239000013078 crystal Substances 0.000 claims abstract description 38
- 239000013626 chemical specie Substances 0.000 claims abstract description 30
- 229920000642 polymer Polymers 0.000 claims abstract description 22
- 150000003058 platinum compounds Chemical class 0.000 claims abstract description 20
- 150000001450 anions Chemical class 0.000 claims abstract description 8
- 150000001768 cations Chemical class 0.000 claims abstract description 7
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 238000000151 deposition Methods 0.000 claims abstract 2
- 238000001179 sorption measurement Methods 0.000 claims description 35
- 229920001495 poly(sodium acrylate) polymer Polymers 0.000 claims description 21
- NNMHYFLPFNGQFZ-UHFFFAOYSA-M sodium polyacrylate Chemical group [Na+].[O-]C(=O)C=C NNMHYFLPFNGQFZ-UHFFFAOYSA-M 0.000 claims description 21
- 239000002245 particle Substances 0.000 claims description 15
- 230000000087 stabilizing effect Effects 0.000 claims description 15
- 239000003054 catalyst Substances 0.000 claims description 12
- 125000005210 alkyl ammonium group Chemical group 0.000 claims description 3
- 230000000274 adsorptive effect Effects 0.000 abstract 2
- 230000006641 stabilisation Effects 0.000 abstract 1
- 238000011105 stabilization Methods 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 29
- 238000006243 chemical reaction Methods 0.000 description 18
- -1 platinum ions Chemical class 0.000 description 17
- 239000011259 mixed solution Substances 0.000 description 15
- 238000000034 method Methods 0.000 description 14
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 13
- 238000006722 reduction reaction Methods 0.000 description 13
- 239000002253 acid Substances 0.000 description 11
- 239000007864 aqueous solution Substances 0.000 description 11
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 8
- 238000003756 stirring Methods 0.000 description 8
- 238000002484 cyclic voltammetry Methods 0.000 description 7
- 238000003917 TEM image Methods 0.000 description 6
- 239000000654 additive Substances 0.000 description 6
- 230000000996 additive effect Effects 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 5
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 5
- 230000002776 aggregation Effects 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 5
- 230000003197 catalytic effect Effects 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 229910052700 potassium Inorganic materials 0.000 description 5
- 239000011591 potassium Substances 0.000 description 5
- 229910052938 sodium sulfate Inorganic materials 0.000 description 5
- 235000011152 sodium sulphate Nutrition 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 238000004220 aggregation Methods 0.000 description 4
- 229910052786 argon Inorganic materials 0.000 description 4
- 238000007664 blowing Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- FVAUCKIRQBBSSJ-UHFFFAOYSA-M sodium iodide Chemical compound [Na+].[I-] FVAUCKIRQBBSSJ-UHFFFAOYSA-M 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- DBMJMQXJHONAFJ-UHFFFAOYSA-M Sodium laurylsulphate Chemical compound [Na+].CCCCCCCCCCCCOS([O-])(=O)=O DBMJMQXJHONAFJ-UHFFFAOYSA-M 0.000 description 3
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 3
- 238000000862 absorption spectrum Methods 0.000 description 3
- 230000008034 disappearance Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000011734 sodium Substances 0.000 description 3
- 235000019333 sodium laurylsulphate Nutrition 0.000 description 3
- 238000002336 sorption--desorption measurement Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000005227 gel permeation chromatography Methods 0.000 description 2
- 229910021397 glassy carbon Inorganic materials 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- XMBWDFGMSWQBCA-UHFFFAOYSA-M iodide Chemical compound [I-] XMBWDFGMSWQBCA-UHFFFAOYSA-M 0.000 description 2
- 229940006461 iodide ion Drugs 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- 230000000877 morphologic effect Effects 0.000 description 2
- 239000005518 polymer electrolyte Substances 0.000 description 2
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 2
- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 2
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 2
- XAEFZNCEHLXOMS-UHFFFAOYSA-M potassium benzoate Chemical compound [K+].[O-]C(=O)C1=CC=CC=C1 XAEFZNCEHLXOMS-UHFFFAOYSA-M 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 239000004094 surface-active agent Substances 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- VBWYZPGRKYRKNV-UHFFFAOYSA-N 3-propanoyl-1,3-benzoxazol-2-one Chemical compound C1=CC=C2OC(=O)N(C(=O)CC)C2=C1 VBWYZPGRKYRKNV-UHFFFAOYSA-N 0.000 description 1
- 229920000557 Nafion® Polymers 0.000 description 1
- 239000004793 Polystyrene Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical group 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 229910001410 inorganic ion Inorganic materials 0.000 description 1
- 150000008040 ionic compounds Chemical class 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002159 nanocrystal Substances 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 239000003002 pH adjusting agent Substances 0.000 description 1
- UPIXZLGONUBZLK-UHFFFAOYSA-N platinum Chemical compound [Pt].[Pt] UPIXZLGONUBZLK-UHFFFAOYSA-N 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 229920002223 polystyrene Polymers 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 235000009518 sodium iodide Nutrition 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
Description
本発明は、白金ナノ粒子の面方位を選択的かつ簡便に制御するための白金ナノ粒子の製造方法、および該製造方法によって得られる白金ナノ粒子、ならびに該白金ナノ粒子を用いた燃料電池用電極に関する。 The present invention relates to a method for producing platinum nanoparticles for selectively and simply controlling the plane orientation of platinum nanoparticles, platinum nanoparticles obtained by the production method, and an electrode for a fuel cell using the platinum nanoparticles. About.
白金は、様々な化合物を吸着し、適度な結合力を持つことから、化学反応を促進する触媒としての機能に優れ、燃料電池の電極等種々の用途に利用されており、たとえば固体高分子型燃料電池の電極触媒としては多結晶白金ナノ粒子が使用されている。しかし、白金はきわめて高価であるため、たとえば触媒として利用される際には、できるだけ少量で効果が発揮されるよう比表面積を大きくすること、すなわち粒子径をできるだけ小さくすることがコストの面で有効である。よってナノメートルレベルの粒径を有する白金ナノ粒子の作製は重要な課題となっている。また、白金は幾つかの結晶面を持ち、結晶面により触媒活性に違いがあることが知られていることから、バルク体としての白金の結晶面を揃える試みがこれまで行なわれている。 Since platinum adsorbs various compounds and has an appropriate binding force, it has an excellent function as a catalyst for promoting chemical reactions, and is used for various applications such as fuel cell electrodes. Polycrystalline platinum nanoparticles are used as an electrode catalyst for fuel cells. However, since platinum is extremely expensive, for example, when used as a catalyst, it is effective in terms of cost to increase the specific surface area, that is, to make the particle diameter as small as possible so that the effect can be exerted in as little amount as possible. It is. Therefore, the production of platinum nanoparticles having a nanometer level particle size is an important issue. Further, since platinum has several crystal planes, and it is known that the catalytic activity varies depending on the crystal plane, attempts have been made so far to align the crystal planes of platinum as a bulk body.
たとえば非特許文献１には、塩化白金酸水溶液に安定化ポリマーを添加することにより白金ナノ粒子を製造する方法が報告されている。この方法においては、塩化白金酸水溶液中の白金イオンを、水素ガスを用いて、下記の式、
ＰｔＣｌ4 2-＋２Ｈ2→Ｐｔ0＋４Ｈ+＋４Ｃｌ-
に従い還元し、生成した白金の結晶核から白金ナノ粒子を成長させる。非特許文献１の方法はポリマーによる立体障害を利用するものであり、ポリアクリル酸ナトリウムの分子量、添加量、ｐＨ、温度、撹拌速度を制御することにより該立体障害の度合いを調整し、白金の特定の面方位を発現させる。たとえば、ポリアクリル酸ナトリウムの添加量を比較的多くした場合には（１１１）面の面方位を有する四面体状の白金ナノ粒子が生成し易く、一方、ポリアクリル酸ナトリウムの添加量を比較的少なくした場合には（１００）面および（１１１）面の面方位を有する白金ナノ粒子、および／または、（１００）面の面方位を有する白金ナノ粒子が生成し易い傾向がある。しかし、この方法においては白金ナノ粒子を生成する際の反応条件によって白金ナノ粒子の形状が大きく左右されてしまうため、所望の面方位を有する白金ナノ粒子を確実に生成することは困難である。また、白金（１１１）面においては、Ｐｔ2+→Ｐｔ0の還元反応の反応速度が速いため、結晶核が持つ（１１１）面の結晶構造が乱れ易い。よって、（１１１）面の面方位を有する白金ナノ粒子を確実に生成することは特に困難である。
For example, Non-Patent Document 1 reports a method for producing platinum nanoparticles by adding a stabilizing polymer to a chloroplatinic acid aqueous solution. In this method, platinum ions in an aqueous chloroplatinic acid solution are converted into the following formula using hydrogen gas:
PtCl 4 2- + 2H 2 → Pt 0 + 4H + + 4Cl −
Then, platinum nanoparticles are grown from the generated platinum crystal nucleus. The method of Non-Patent Document 1 utilizes steric hindrance by a polymer, and the degree of the steric hindrance is adjusted by controlling the molecular weight, added amount, pH, temperature, and stirring speed of sodium polyacrylate. A specific plane orientation is expressed. For example, when the amount of sodium polyacrylate added is relatively large, tetrahedral platinum nanoparticles having a (111) plane orientation are likely to be formed, while the amount of sodium polyacrylate added is relatively small. When the number is decreased, platinum nanoparticles having a (100) plane orientation and (111) plane orientation and / or platinum nanoparticles having a (100) plane orientation tend to be generated. However, in this method, since the shape of the platinum nanoparticles greatly depends on the reaction conditions when generating the platinum nanoparticles, it is difficult to reliably generate platinum nanoparticles having a desired plane orientation. In addition, on the platinum (111) plane, the reaction rate of the Pt 2+ → Pt 0 reduction reaction is fast, so that the crystal structure of the (111) plane of the crystal nucleus tends to be disturbed. Therefore, it is particularly difficult to reliably generate platinum nanoparticles having a (111) plane orientation.
特許文献１には、レーザー光源からのレーザー光を集光レンズで集光し、白金ナノ粒子を含むラウリル硫酸ナトリウム（ＳＤＳ）水溶液の表面に該レーザ光をパルス照射する方法が提案されている。レーザー光の照射により白金ナノ粒子が断片化し、ＳＤＳの濃度に応じて微粒子状またはネットワーク状の白金ナノ構造体が生成する。しかしこの方法によっては特定の面方位を持つ白金ナノ粒子を選択的に生成することは困難である。 Patent Document 1 proposes a method of condensing laser light from a laser light source with a condensing lens and irradiating the surface of an aqueous sodium lauryl sulfate (SDS) solution containing platinum nanoparticles with pulses. The platinum nanoparticles are fragmented by laser light irradiation, and fine or network-like platinum nanostructures are generated according to the concentration of SDS. However, it is difficult to selectively generate platinum nanoparticles having a specific plane orientation by this method.
特許文献２には、（ａ）１以上の金属カチオンを含有する溶液を調製するステップ、（ｂ）ステップ（ａ）の溶液を１以上の界面活性剤と混合し、界面活性剤／液体混合物を生成するステップ、（ｃ）ステップ（ｂ）の混合物を加熱して、粒子を生成するステップ、を含む、ナノサイズの結晶粒を有する粒子の製造方法が提案されている。しかし特許文献２では、生成する粒子の結晶方位を制御する方法については考慮されず、特定の面方位を持つ白金ナノ粒子を選択的に生成することはできない。
本発明は上記の課題を解決し、得られる白金ナノ粒子の面方位を選択的かつ簡便に制御可能な白金ナノ粒子の製造方法、および該製造方法によって得られる白金ナノ粒子、ならびに該白金ナノ粒子を用いた燃料電池用電極を提供することを目的とする。 The present invention solves the above-mentioned problems, and a method for producing platinum nanoparticles capable of selectively and simply controlling the plane orientation of the obtained platinum nanoparticles, platinum nanoparticles obtained by the production method, and the platinum nanoparticles It aims at providing the electrode for fuel cells using this.
本発明は、特定の面方位を有する白金ナノ粒子を生成するための白金ナノ粒子の製造方法であって、イオン性白金化合物の溶液と特異吸着化学種と安定化ポリマーとを混合する工程と、該イオン性白金化合物の溶液からの析出により白金結晶を成長させる工程とを含み、該特異吸着化学種が陽イオンおよび／または陰イオンである白金ナノ粒子の製造方法に関する。 The present invention is a method for producing platinum nanoparticles for producing platinum nanoparticles having a specific plane orientation, which comprises mixing a solution of an ionic platinum compound, a specific adsorption chemical species, and a stabilizing polymer; And a step of growing platinum crystals by precipitation from a solution of the ionic platinum compound, and a method for producing platinum nanoparticles in which the specific adsorption chemical species is a cation and / or an anion.
本発明において使用されるイオン性白金化合物としては、ハロゲン化白金酸塩が好ましい。 The ionic platinum compound used in the present invention is preferably a halogenated platinate.
また、特異吸着化学種の白金に対する当量比が０．０１〜１０当量の範囲内であることが好ましい。 Moreover, it is preferable that the equivalence ratio with respect to platinum of a specific adsorption chemical species exists in the range of 0.01-10 equivalent.
本発明において使用される安定化ポリマーは、特にポリアクリル酸ナトリウムであることが好ましい。 The stabilizing polymer used in the present invention is particularly preferably sodium polyacrylate.
本発明はまた、特定の面方位として（１１１）面を有する白金ナノ粒子の製造方法に関する。この場合、特異吸着化学種が、Ｃｌ-、Ｂｒ-、Ｉ-、ＳＯ4 2-、ＰＯ4 3-から選択される少なくとも１種の陰イオンであることが好ましい。また、特異吸着化学種が、アルキルアンモニウムイオンであることも好ましい。 The present invention also relates to a method for producing platinum nanoparticles having a (111) plane as a specific plane orientation. In this case, the specific adsorption species is preferably at least one anion selected from Cl − , Br − , I − , SO 4 2− and PO 4 3− . It is also preferred that the specific adsorption chemical species is an alkyl ammonium ion.
本発明はまた、上述の製造方法により得られる白金ナノ粒子に関する。
本発明に係る白金ナノ粒子の平均粒径は１〜２０ｎｍの範囲内であることが好ましい。
The present invention also relates to platinum nanoparticles obtained by the production method described above.
The average particle diameter of the platinum nanoparticles according to the present invention is preferably in the range of 1 to 20 nm.
本発明はさらに、上述の白金ナノ粒子を触媒として用いた燃料電池用電極に関する。 The present invention further relates to a fuel cell electrode using the above-mentioned platinum nanoparticles as a catalyst.
本発明の白金ナノ粒子の製造方法によれば、特異吸着化学種を共存させた状態で白金結晶を成長させるため、特定の結晶面における白金結晶の成長が該特異吸着化学種によって阻害される。よって本発明によれば、特異吸着化学種の選択により面方位を任意かつ簡便に制御し、所望の特定の面方位を有する白金ナノ粒子を選択的に得ることが可能となる。 According to the method for producing platinum nanoparticles of the present invention, platinum crystals are grown in the presence of specific adsorption chemical species. Therefore, the growth of platinum crystals on a specific crystal plane is inhibited by the specific adsorption chemical species. Therefore, according to the present invention, it is possible to selectively and easily obtain platinum nanoparticles having a desired specific plane orientation by arbitrarily and simply controlling the plane orientation by selecting specific adsorption chemical species.
本発明は、特定の面方位を有する白金ナノ粒子を生成するための白金ナノ粒子の製造方法であって、イオン性白金化合物の溶液と特異吸着化学種と安定化ポリマーとを混合する工程と、該イオン性白金化合物の溶液からの析出により白金結晶を成長させる工程とを含む。本発明において、特定の面方位を有する白金ナノ粒子とは、目的の面方位を有する白金ナノ粒子の数の生成した白金ナノ粒子の数に占める割合が４０％以上であるものを指す。該割合が４０％以上であれば、白金ナノ粒子が目的の面方位を有することによる所望の触媒活性の発現が可能となる。目的の面方位を有する白金ナノ粒子の数は、生成した白金ナノ粒子の数の５０％以上、さらに６０％以上であることが好ましい。なお、目的の面方位を有する白金ナノ粒子の数が全白金ナノ粒子の数に占める割合は、たとえば透過型電子顕微鏡（ＴＥＭ）による形態観察において、画像計測により生成した白金ナノ粒子の数および目的の面方位を有する白金ナノ粒子の数を計測したときの計測値から算出することができる。なお白金ナノ粒子が目的の面方位を有しているか否かは、立方体状、角切り八面体状、角切り四面体状、四面体状等の、白金ナノ粒子の面方位を反映した形状から判断することができる。 The present invention is a method for producing platinum nanoparticles for producing platinum nanoparticles having a specific plane orientation, which comprises mixing a solution of an ionic platinum compound, a specific adsorption chemical species, and a stabilizing polymer; And a step of growing platinum crystals by precipitation from a solution of the ionic platinum compound. In the present invention, platinum nanoparticles having a specific plane orientation refer to those having a ratio of the number of platinum nanoparticles having a target plane orientation to the number of generated platinum nanoparticles of 40% or more. If the ratio is 40% or more, the desired catalytic activity can be expressed by the platinum nanoparticles having a desired plane orientation. The number of platinum nanoparticles having a desired plane orientation is preferably 50% or more, and more preferably 60% or more of the number of platinum nanoparticles produced. The ratio of the number of platinum nanoparticles having a target plane orientation to the total number of platinum nanoparticles is, for example, the number of platinum nanoparticles generated by image measurement and the purpose in morphological observation with a transmission electron microscope (TEM). It can be calculated from the measured value when the number of platinum nanoparticles having the plane orientation is measured. Whether or not the platinum nanoparticles have the desired plane orientation depends on the shape reflecting the plane orientation of the platinum nanoparticles, such as a cubic shape, a truncated octahedral shape, a truncated tetrahedral shape, and a tetrahedral shape. Judgment can be made.
本発明において用いられる特異吸着化学種は陽イオンおよび／または陰イオンである。該特異吸着化学種により、白金を含有するイオン性化合物における白金イオンが反応性良く還元され、所望の面方位を有する白金結晶からなる白金ナノ粒子が生成する。本発明においては、白金結晶の特定の結晶面に特異的に吸着する特異吸着化学種を用いるため、白金結晶の成長工程において特定の結晶面の結晶成長が阻害され、これにより特定の面方位を有する白金結晶を成長させることができる。 The specific adsorption species used in the present invention is a cation and / or an anion. By the specific adsorption chemical species, platinum ions in the ionic compound containing platinum are reduced with good reactivity, and platinum nanoparticles composed of platinum crystals having a desired plane orientation are generated. In the present invention, since a specific adsorption chemical species that specifically adsorbs on a specific crystal plane of the platinum crystal is used, the crystal growth of the specific crystal plane is inhibited in the growth process of the platinum crystal. The platinum crystal which has can be grown.
本発明において用いられるイオン性白金化合物とは、溶液中で白金イオンを供給するものを指し、該イオン性白金化合物を用いることにより、白金イオンの還元反応により白金結晶を析出させることができる。有機イオンは還元反応後に触媒を被毒する成分を生成するおそれがあるため、イオン性白金化合物としては特に無機イオン化合物が好ましい。具体的には、ハロゲン化白金酸塩等が挙げられる。 The ionic platinum compound used in the present invention refers to a substance that supplies platinum ions in a solution. By using the ionic platinum compound, platinum crystals can be precipitated by a reduction reaction of platinum ions. Since organic ions may generate a component that poisons the catalyst after the reduction reaction, an inorganic ion compound is particularly preferable as the ionic platinum compound. Specific examples include halogenated platinates.
ハロゲン化白金酸塩の好ましい例としては、ヨウ化白金酸、臭化白金酸、塩化白金酸、フッ化白金酸のそれぞれのナトリウム塩、カリウム塩、リチウム塩等が挙げられるが、反応性の点で塩化白金酸のカリウム塩が特に好ましい。 Preferred examples of the halogenated platinate include sodium salt, potassium salt, lithium salt and the like of iodoplatinic acid, bromoplatinic acid, chloroplatinic acid, and fluorinated platinic acid. In particular, the potassium salt of chloroplatinic acid is particularly preferred.
白金ナノ粒子を生成する際には、特異吸着化学種の白金に対する当量比が０．０１〜１０当量の範囲内となるように該特異吸着化学種を供給することが好ましい。該当量比が０．０１当量以上であれば、所望の面方位を有する白金結晶からなる白金ナノ粒子を選択的に得ることができ、１０当量以下であれば白金の還元反応速度が阻害され難く、特定の面方位を持つ白金ナノ粒子が純度良く形成され得る。該当量比は０．０５〜１０当量の範囲内とされることがさらに好ましい。たとえば特異吸着化学種が硫酸イオン（ＳＯ4 2-）である場合、該当量比は０．０５〜３当量が特に好ましく、たとえば特異吸着化学種がヨウ化物イオン（Ｉ-）である場合、該当量比は３〜１０当量が特に好ましい。 When producing platinum nanoparticles, it is preferable to supply the specific adsorption chemical species so that the equivalent ratio of the specific adsorption chemical species to platinum is in the range of 0.01 to 10 equivalents. If the amount ratio is 0.01 equivalent or more, platinum nanoparticles composed of platinum crystals having a desired plane orientation can be selectively obtained. If the equivalent ratio is 10 equivalents or less, the reduction reaction rate of platinum is hardly inhibited. Platinum nanoparticles having a specific plane orientation can be formed with high purity. More preferably, the relevant amount ratio is in the range of 0.05 to 10 equivalents. For example, when the specific adsorption chemical species is sulfate ion (SO 4 2− ), the corresponding amount ratio is particularly preferably 0.05 to 3 equivalents. For example, when the specific adsorption chemical species is iodide ion (I − ), The amount ratio is particularly preferably 3 to 10 equivalents.
本発明において用いられる安定化ポリマーは、成長した白金結晶により形成される白金ナノ粒子の凝集を防止して、該白金ナノ粒子の表面が効率良く触媒作用に寄与するようにするために用いられる。安定化ポリマーとしては、ポリマー分子内に白金ナノ粒子の表面に吸着し易い構造を含んでいるものが好ましく、このような構造としては−ＣＯＯＮａ基等の親水性基が挙げられる。たとえば分子内に−ＣＯＯＮａ基を有する安定化ポリマーを用いた場合には、該−ＣＯＯＮａ基の−ＣＯＯ-構造が白金と静電的な相互作用をするか、または結合することにより、白金ナノ粒子のキャッピング作用が得られ、白金ナノ粒子間にポリマー鎖が介在することにより白金ナノ粒子の凝集が抑制される。これにより白金ナノ粒子の凝集による触媒活性の低下を防止できる。 The stabilizing polymer used in the present invention is used to prevent the aggregation of platinum nanoparticles formed by the grown platinum crystals and to efficiently contribute to the catalytic action of the surface of the platinum nanoparticles. As the stabilizing polymer, those containing a structure that is easily adsorbed on the surface of the platinum nanoparticles in the polymer molecule are preferable, and examples of such a structure include hydrophilic groups such as a —COONa group. For example, when a stabilizing polymer having a —COONa group in the molecule is used, the —COO 2 — structure of the —COONa group interacts electrostatically with or binds to the platinum nanoparticles. The capping action is obtained, and the aggregation of platinum nanoparticles is suppressed by interposing polymer chains between the platinum nanoparticles. Thereby, the fall of the catalyst activity by aggregation of a platinum nanoparticle can be prevented.
本発明において使用される安定化ポリマーの好ましい具体例としては、ポリアクリル酸ナトリウム、ポリビニルピロリドン（ＰＶＰ）等が挙げられ、特にポリアクリル酸ナトリウムが好ましく用いられる。 Preferable specific examples of the stabilizing polymer used in the present invention include sodium polyacrylate, polyvinylpyrrolidone (PVP) and the like, and sodium polyacrylate is particularly preferably used.
安定化ポリマーとしてポリアクリル酸ナトリウムが用いられる場合、該ポリアクリル酸ナトリウムの重量平均分子量が３０００〜１００００の範囲内とされることが好ましい。重量平均分子量が３０００以上である場合、安定化ポリマーが嵩高であり、分子鎖中の親水性基部分がループまたはテールとなって、白金ナノ粒子の凝集を効果的に防止するため好ましく、１００００以下である場合、白金ナノ粒子の成長過程における核生成が抑制され、白金の無定形物の生成が抑制される点で好ましい。なお、ポリアクリル酸ナトリウムの重量平均分子量は、たとえばＧＰＣ（ゲル浸透クロマトグラフィー）を用い、ポリスチレン換算により求めることができる。 When sodium polyacrylate is used as the stabilizing polymer, the weight average molecular weight of the sodium polyacrylate is preferably in the range of 3000 to 10,000. When the weight average molecular weight is 3,000 or more, the stabilizing polymer is bulky, and the hydrophilic group part in the molecular chain is preferably a loop or tail, which effectively prevents aggregation of platinum nanoparticles, and is preferably 10,000 or less. Is preferable in that nucleation in the growth process of platinum nanoparticles is suppressed, and generation of amorphous platinum is suppressed. In addition, the weight average molecular weight of sodium polyacrylate can be calculated | required by polystyrene conversion, for example using GPC (gel permeation chromatography).
本発明の白金ナノ粒子の面方位は、特異吸着化学種の種類および／または量の調整により目的に応じて任意に制御することができる。白金ナノ粒子の面方位としては、（１００）面、（１１０）面、（１１１面）が選択でき、白金ナノ粒子を電極用触媒として使用する場合の所望される触媒活性等によって選択すれば良い。 The plane orientation of the platinum nanoparticles of the present invention can be arbitrarily controlled according to the purpose by adjusting the type and / or amount of the specific adsorption chemical species. The plane orientation of the platinum nanoparticles can be selected from (100) plane, (110) plane, and (111 plane), and may be selected depending on the desired catalytic activity when using the platinum nanoparticles as an electrode catalyst. .
たとえば、面方位として（１１１）面を有する白金ナノ粒子を作製する場合、特異吸着化学種としては、陰イオンとして、Ｃｌ-、Ｂｒ-、Ｉ-、ＳＯ4 2-、ＰＯ4 3-から選択される少なくとも１種、中でも特にＣｌ-が好ましく採用され、また、陽イオンとして、アルキルアンモニウムイオンが好ましく用いられる。上述の陰イオン、陽イオンはそれぞれ白金の（１１１）面に対する特異吸着力が強く、（１１１）面の面方位を有する白金ナノ粒子を選択的に作製することが可能である。 For example, when producing platinum nanoparticles having a (111) plane as the plane orientation, the specific adsorption chemical species is selected from Cl − , Br − , I − , SO 4 2− , and PO 4 3− as anions. at least one element, among others Cl - is preferably used, and as cations, alkyl ammonium ion is preferably used. Each of the above anions and cations has a strong specific adsorption force with respect to the (111) plane of platinum, and it is possible to selectively produce platinum nanoparticles having a (111) plane orientation.
本発明において、イオン性白金化合物からの還元反応により白金結晶を析出させ、白金ナノ粒子を成長させる典型的な方法について以下に説明するが、本発明はこれに限定されない。まず、撹拌手段を備えた密閉可能な反応器の内部をたとえば５〜５０℃の範囲内、好ましくは２５℃に設定し、該反応器内でイオン性白金化合物の溶液と特異吸着化学種と安定化ポリマーとを混合し、混合溶液を調製する。このとき、適切なｐＨ調整剤を用いて混合溶液のｐＨが６．５〜７．５程度になるよう調整することが好ましい。次いで、反応器内にアルゴン（Ａｒ）ガス等の不活性ガスを９０分間導入して反応基内を不活性ガスで置換した後、水素（Ｈ2）ガスを反応器内に１０分間導入して反応器内を水素ガスで満たす。次いで、水素ガスで置換された該反応器を密閉し、２５℃程度で１８〜２４時間撹拌する。これにより、水素ガス存在下の白金イオンの還元反応により、該イオン性白金化合物の溶液から白金結晶が析出し、白金ナノ粒子が成長する。ここで、イオン性白金化合物としてたとえばハロゲン化白金酸塩を用いる場合の反応を表すと、下記の反応式、
ＰｔＢ4 2-＋２Ｈ2→Ｐｔ0＋４Ｈ+＋４Ｂ-
（ただしＢはハロゲンを示す）
のようになる。
In the present invention, a typical method for growing platinum nanoparticles by precipitating platinum crystals by a reduction reaction from an ionic platinum compound will be described below, but the present invention is not limited thereto. First, the inside of a sealable reactor equipped with a stirring means is set within a range of, for example, 5 to 50 ° C., preferably 25 ° C., and the ionic platinum compound solution, the specific adsorption chemical species, and the The mixed polymer is mixed to prepare a mixed solution. At this time, it is preferable to adjust the pH of the mixed solution to about 6.5 to 7.5 using an appropriate pH adjusting agent. Next, after introducing an inert gas such as argon (Ar) gas into the reactor for 90 minutes to replace the inside of the reactive group with an inert gas, hydrogen (H 2 ) gas is introduced into the reactor for 10 minutes. Fill the reactor with hydrogen gas. Next, the reactor substituted with hydrogen gas is sealed and stirred at about 25 ° C. for 18 to 24 hours. Thus, platinum crystals are precipitated from the solution of the ionic platinum compound by the reduction reaction of platinum ions in the presence of hydrogen gas, and platinum nanoparticles grow. Here, a reaction in the case of using, for example, a halogenated platinate as the ionic platinum compound is represented by the following reaction formula:
PtB 4 2− + 2H 2 → Pt 0 + 4H + + 4B −
(B represents halogen)
become that way.
成長させた白金ナノ粒子は、たとえば溶液を遠心沈降させ、得られた沈殿を凍結乾燥する方法により回収できる。 The grown platinum nanoparticles can be recovered by, for example, a method in which the solution is centrifuged and the obtained precipitate is freeze-dried.
図１〜４は、本発明に係る白金ナノ粒子の形状の例を示す図である。本発明の白金ナノ粒子は、図１に示すような（１００）面の面方位を有する立方体状の他、図２に示すような（１００）面および（１１１）面の面方位を有する角切り八面体（ＴＯ）状、図３に示すような（１００）面および（１１１）面の面方位を有する角切り八面体（ＴＯ）状、図４に示すような（１１１）面の面方位を有する四面体状等のナノ粒子とされることができ、形状は所望される面方位に応じて適宜選択され得る。白金イオンの還元反応による白金結晶の成長においては、（１１１）面における白金イオンの還元反応、すなわち結晶成長の速度は特に大きい。よってたとえば安定化ポリマーのみを用いて白金ナノ粒子の形状を制御する方法を用いた場合には、（１１１）面における結晶構造が乱れ易い傾向があり、（１１１）面の面方位を有する白金ナノ粒子を選択的に生成することは一般に困難である。しかし、本発明の製造方法においては、白金結晶の特定の結晶面に対して選択的に吸着する特異吸着化学種を用い、該結晶面上での結晶成長速度を制御できるため、たとえば（１１１）面の面方位を有する白金ナノ粒子を選択的に生成する場合にも、（１１１）面の結晶構造の乱れが抑制され、かつ粒径が均一な白金ナノ粒子を生成することが可能となる。なお白金ナノ粒子の面方位における（１００）面と（１１１）面との比率は、立方体（（１００）面のみ）、角切り八面体（（１００）面および（１１１）面）、角切り四面体（（１００）面および（１１１）面）、四面体（（１１１）面のみ）の順に変化する。 1-4 is a figure which shows the example of the shape of the platinum nanoparticle which concerns on this invention. The platinum nanoparticle of the present invention has a cubic shape having a (100) plane orientation as shown in FIG. 1, and also has a (100) and (111) plane orientation as shown in FIG. Octagonal (TO) shape, square-cut octahedron (TO) shape having (100) plane and (111) plane orientation as shown in FIG. 3, and (111) plane orientation as shown in FIG. It can be made into nanoparticles, such as a tetrahedral shape, and the shape can be appropriately selected according to the desired plane orientation. In the growth of platinum crystals by the reduction reaction of platinum ions, the reduction rate of platinum ions on the (111) plane, that is, the rate of crystal growth is particularly high. Therefore, for example, when a method for controlling the shape of platinum nanoparticles using only a stabilizing polymer is used, there is a tendency that the crystal structure in the (111) plane tends to be disturbed, and platinum nanocrystals having a (111) plane orientation. It is generally difficult to selectively produce particles. However, in the production method of the present invention, a specific adsorption chemical species that selectively adsorbs to a specific crystal plane of the platinum crystal can be used, and the crystal growth rate on the crystal plane can be controlled. For example, (111) Even when the platinum nanoparticles having the plane orientation are selectively generated, it is possible to suppress the disorder of the crystal structure of the (111) plane and to generate platinum nanoparticles having a uniform particle size. The ratio of the (100) plane to the (111) plane in the plane orientation of the platinum nanoparticles is as follows: a cube ((100) plane only), a square octahedron ((100) plane and (111) plane), and a square plane. It changes in the order of the body ((100) plane and (111) plane) and tetrahedron (only (111) plane).
上記の方法で製造される本発明の白金ナノ粒子の平均粒径は、１〜２０ｎｍの範囲内であることが好ましい。この場合、電極用触媒として優れた触媒活性を有するという効果を有する。該平均粒径は、特に２〜１０ｎｍの範囲内とされることが好ましい。なお白金ナノ粒子の平均粒径は、たとえばＴＥＭ（透過型電子顕微鏡）による形態像から画像計測により測定した白金ナノ粒子の最大径の数平均値として評価することができる。 The average particle size of the platinum nanoparticles of the present invention produced by the above method is preferably in the range of 1 to 20 nm. In this case, it has the effect of having excellent catalytic activity as an electrode catalyst. The average particle diameter is particularly preferably in the range of 2 to 10 nm. In addition, the average particle diameter of platinum nanoparticles can be evaluated as, for example, the number average value of the maximum diameters of platinum nanoparticles measured by image measurement from a morphological image using a TEM (transmission electron microscope).
本発明の白金ナノ粒子は燃料電池用電極等に対する電極用触媒として用いることができる。白金ナノ粒子を用いた燃料電池用電極を作製する方法としては従来公知の方法が好ましく採用され得る。具体的には、白金ナノ粒子のコロイド溶液に、担体としてカーボンブラック（カーボン担体）を入れ、白金ナノ粒子をまずカーボン担体上に担持させる。これをポリマー電解質の溶液（たとえばＮａｆｉｏｎ（登録商標）溶液）と混ぜてスラリーとし、ポリマー電解質上に該スラリーを塗布した後、ホットプレスをする方法等により燃料電池用電極とすることができる。 The platinum nanoparticles of the present invention can be used as an electrode catalyst for fuel cell electrodes and the like. As a method for producing an electrode for a fuel cell using platinum nanoparticles, a conventionally known method can be preferably employed. Specifically, carbon black (carbon carrier) is added as a carrier to a colloidal solution of platinum nanoparticles, and the platinum nanoparticles are first supported on the carbon carrier. This can be mixed with a polymer electrolyte solution (for example, Nafion (registered trademark) solution) to form a slurry, and after applying the slurry on the polymer electrolyte, a fuel cell electrode can be obtained by hot pressing or the like.
［実施例］
以下、実施例を挙げて本発明をより詳細に説明するが、本発明はこれらに限定されるものではない。
[Example]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.
＜白金ナノ粒子の合成＞
（参照例１）
イオン性白金化合物として塩化白金酸カリウムを用いた。１．０×１０-4Ｍの塩化白金酸カリウム（Ｋ2ＰｔＣｌ4、和光純薬工業社製）水溶液１００ｍｌを用意し、暗所にて２０〜２４時間保存して、イオン性白金化合物の溶液を調製した。安定化ポリマー溶液として、０．１Ｍのポリアクリル酸ナトリウム（［−ＣＨ2ＣＨ（ＣＯ2Ｎａ）−］n、Ａｌｄｒｉｃｈ社製、分子量Ｍｗ＝５１００、分子量についてはモノマーユニットで計算）水溶液を調製した。
<Synthesis of platinum nanoparticles>
(Reference Example 1)
Potassium chloroplatinate was used as the ionic platinum compound. Prepare 100 ml of 1.0 × 10 −4 M potassium chloroplatinate (K 2 PtCl 4 , Wako Pure Chemical Industries, Ltd.) aqueous solution and store it in the dark for 20-24 hours to obtain a solution of an ionic platinum compound. Was prepared. An aqueous solution of 0.1 M sodium polyacrylate ([—CH 2 CH (CO 2 Na)-] n, manufactured by Aldrich, molecular weight Mw = 5100, molecular weight calculated in monomer units) was prepared as a stabilizing polymer solution. .
上記の塩化白金酸カリウム水溶液にポリアクリル酸ナトリウム水溶液を添加し、混合溶液を調製した。ここで、混合溶液における−ＣＯＯ-イオンの当量比は白金イオン（Ｐｔ2+）に対して１当量となるようにした。該混合溶液を反応器内に入れ、反応温度を２５℃に設定した。この混合溶液を２５０ｒｐｍで十分に撹拌しながら、該混合溶液にアルゴンガス（太陽東洋酸素、Ｇ２、純度９９．９９９５％）を流量２００ｍｌｍｉｎ-1で９０分間吹き込むことにより脱気を十分に行なった後、水素ガス（太陽東洋酸素、Ｇ２、純度９９．９９９％）を流量３００ｍｌｍｉｎ-1で１０分間吹き込むことにより塩化白金酸イオン（ＰｔＣｌ4 2-）の還元を行なった。反応を完全に進行させるため、水素ガス流通後、反応容器を密閉し、１８〜２４時間撹拌を続けた。反応の終了は、紫外可視吸収スペクトルを用い、ＰｔＣｌ4 2-由来のピーク（２１４ｎｍ）の消失を確認することにより判断した。 A sodium polyacrylate aqueous solution was added to the above potassium chloroplatinate aqueous solution to prepare a mixed solution. Here, the equivalent ratio of —COO − ions in the mixed solution was set to 1 equivalent with respect to platinum ions (Pt 2+ ). The mixed solution was put in a reactor and the reaction temperature was set to 25 ° C. After sufficiently stirring the mixed solution at 250 rpm, degassing was sufficiently performed by blowing argon gas (solar oriental oxygen, G2, purity 99.9995%) into the mixed solution at a flow rate of 200 mlmin −1 for 90 minutes. Then, chloroplatinic acid ions (PtCl 4 2− ) were reduced by blowing hydrogen gas (Taiyo Toyo Oxygen, G2, purity 99.999%) at a flow rate of 300 mlmin −1 for 10 minutes. In order to allow the reaction to proceed completely, the reaction vessel was sealed after flowing hydrogen gas, and stirring was continued for 18 to 24 hours. The completion of the reaction was judged by confirming the disappearance of the peak (214 nm) derived from PtCl 4 2− using an ultraviolet-visible absorption spectrum.
（参照例２）
ポリアクリル酸ナトリウムにおける−ＣＯＯ-イオンの当量比が白金イオン（Ｐｔ2+）に対して２．５当量となるようにポリアクリル酸ナトリウム水溶液を添加した他は参照例１と同様の方法で白金ナノ粒子の合成を行なった。
(Reference Example 2)
Platinum was prepared in the same manner as in Reference Example 1 except that an aqueous solution of sodium polyacrylate was added so that the equivalent ratio of —COO − ions in sodium polyacrylate was 2.5 equivalents with respect to platinum ions (Pt 2+ ). Nanoparticles were synthesized.
（参照例３）
ポリアクリル酸ナトリウムにおける−ＣＯＯ-イオンの当量比が白金イオン（Ｐｔ2+）に対して５当量となるようにポリアクリル酸ナトリウム水溶液を添加した他は参照例１と同様の方法で白金ナノ粒子の合成を行なった。
(Reference Example 3)
Platinum nanoparticles in the same manner as in Reference Example 1 except that an aqueous sodium polyacrylate solution was added so that the equivalent ratio of —COO − ions in sodium polyacrylate was 5 equivalents to platinum ions (Pt 2+ ). Was synthesized.
（参照例４）
ポリアクリル酸ナトリウムにおける−ＣＯＯ-イオンの当量比が白金イオン（Ｐｔ2+）に対して１２当量となるようにポリアクリル酸ナトリウム水溶液を添加した他は参照例１と同様の方法で白金ナノ粒子の合成を行なった。
(Reference Example 4)
Platinum nanoparticles in the same manner as in Reference Example 1 except that an aqueous sodium polyacrylate solution was added so that the equivalent ratio of —COO − ions in sodium polyacrylate was 12 equivalents relative to platinum ions (Pt 2+ ). Was synthesized.
（実施例１〜１１）
１．０×１０-4Ｍの塩化白金酸（Ｋ2ＰｔＣｌ4、和光純薬工業社製）水溶液１００ｍｌを用意し、暗所にて２０〜２４時間保存して、塩化白金酸溶液を調製した。安定化ポリマー溶液として、０．１Ｍのポリアクリル酸ナトリウム（［−ＣＨ2ＣＨ（ＣＯ2Ｎａ）−］n、Ａｌｄｒｉｃｈ社製、分子量Ｍｗ＝５１００、分子量についてはモノマーユニットで計算）水溶液を調製した。特異吸着化学種を含む添加剤の溶液として、表１に示す添加剤水溶液を調製した。
(Examples 1 to 11)
100 ml of an aqueous solution of 1.0 × 10 −4 M chloroplatinic acid (K 2 PtCl 4 , manufactured by Wako Pure Chemical Industries) was prepared and stored in the dark for 20 to 24 hours to prepare a chloroplatinic acid solution. . As a stabilizing polymer solution, an aqueous solution of 0.1 M sodium polyacrylate ([—CH 2 CH (CO 2 Na)-] n, manufactured by Aldrich, molecular weight Mw = 5100, molecular weight calculated in monomer units) was prepared. . As an additive solution containing specific adsorption species, an aqueous additive solution shown in Table 1 was prepared.
上記の塩化白金酸溶液に、ポリアクリル酸ナトリウムにおける−ＣＯＯ-イオンの当量比が白金イオン（Ｐｔ2+）に対して１２当量となるように上記のポリアクリル酸ナトリウム水溶液を加え、さらに表１に示す添加剤を反応器内に入れ、反応温度を２５℃に設定し、混合溶液を調製した。ここで該添加剤の添加量は、特異吸着化学種の当量比が白金イオン（Ｐｔ2+）に対して表１に示す値となる量に調整し、さらにそれぞれ０．１Ｍ塩酸を滴下して混合溶液のｐＨを７．０に調整した。 To the above chloroplatinic acid solution, the above sodium polyacrylate aqueous solution was added so that the equivalent ratio of —COO − ions in sodium polyacrylate was 12 equivalents with respect to platinum ions (Pt 2+ ). Were added to the reactor, the reaction temperature was set to 25 ° C., and a mixed solution was prepared. Here, the addition amount of the additive is adjusted so that the equivalent ratio of the specific adsorption chemical species becomes the value shown in Table 1 with respect to platinum ions (Pt 2+ ), and 0.1 M hydrochloric acid is further added dropwise. The pH of the mixed solution was adjusted to 7.0.
上記で調製した混合溶液を２５０ｒｐｍで十分に撹拌しながら、該混合溶液にアルゴンガス（太陽東洋酸素、Ｇ２、純度９９．９９９５％）を流量２００ｍｌｍｉｎ-1で９０分間吹き込むことにより脱気を十分に行なった後、水素ガス（太陽東洋酸素、Ｇ２、純度９９．９９９％）を流量３００ｍｌｍｉｎ-1で１０分間吹き込むことにより塩化白金酸の還元を行なった。反応を完全に進行させるため、水素ガス流通後、反応容器を密閉し、１８〜２４時間撹拌を続けた。反応の終了は、紫外可視吸収スペクトルを用い、ＰｔＣｌ4 2-由来のピーク（２１４ｎｍ）の消失を確認することにより判断した。 While thoroughly stirring the mixed solution prepared above at 250 rpm, argon gas (solar oriental oxygen, G2, purity 99.9995%) was blown into the mixed solution at a flow rate of 200 mlmin −1 for 90 minutes to sufficiently degas. Thereafter, hydrogen chloroplatinic acid was reduced by blowing hydrogen gas (solar oriental oxygen, G2, purity 99.999%) at a flow rate of 300 mlmin −1 for 10 minutes. In order to allow the reaction to proceed completely, the reaction vessel was sealed after flowing hydrogen gas, and stirring was continued for 18 to 24 hours. The completion of the reaction was judged by confirming the disappearance of the peak (214 nm) derived from PtCl 4 2− using an ultraviolet-visible absorption spectrum.
（比較例１）
１．０×１０-4Ｍの塩化白金酸カリウム（Ｋ2ＰｔＣｌ4、和光純薬工業社製）水溶液１００ｍｌを用意し、暗所にて２０〜２４時間保存して、イオン性白金化合物の溶液を調製した。特異吸着化学種を含む添加剤の溶液として、表２に示す０．０５Ｍ硫酸ナトリウム水溶液を調製した。
(Comparative Example 1)
Prepare 100 ml of 1.0 × 10 −4 M potassium chloroplatinate (K 2 PtCl 4 , Wako Pure Chemical Industries, Ltd.) aqueous solution and store it in the dark for 20 to 24 hours to obtain a solution of an ionic platinum compound. Was prepared. As an additive solution containing specific adsorption species, 0.05M aqueous sodium sulfate solution shown in Table 2 was prepared.
上記の塩化白金酸カリウム水溶液と硫酸ナトリウム水溶液とを反応器内に入れ、反応温度を２５℃に設定し、混合溶液を調製した。ここで、硫酸ナトリウム水溶液の添加量は、特異吸着化学種である硫酸イオン（ＳＯ4 2-）の当量比が白金イオン（Ｐｔ2+）に対して５当量となるように調整し、さらに０．１Ｍ塩酸を滴下して混合溶液のｐＨを７．０に調整した。 The aqueous potassium chloroplatinate solution and the aqueous sodium sulfate solution were placed in a reactor, the reaction temperature was set to 25 ° C., and a mixed solution was prepared. Here, the amount of sodium sulfate aqueous solution added was adjusted so that the equivalent ratio of sulfate ions (SO 4 2− ), which is a specific adsorption chemical species, was 5 equivalents with respect to platinum ions (Pt 2+ ). 0.1M hydrochloric acid was added dropwise to adjust the pH of the mixed solution to 7.0.
上記で調製した混合溶液を２５０ｒｐｍで十分に撹拌しながら、該混合溶液にアルゴンガス（太陽東洋酸素、Ｇ２、純度９９．９９９５％）を流量２００ｍｌｍｉｎ-1で９０分間吹き込むことにより脱気を十分に行なった後、水素ガス（太陽東洋酸素、Ｇ２、純度９９．９９９％）を流量３００ｍｌｍｉｎ-1で１０分間吹き込むことにより白金イオンの還元を行なった。反応を完全に進行させるため、水素ガス流通後、反応容器を密閉し、１８〜２４時間撹拌を続けた。反応の進行および終了は、紫外可視吸収スペクトルを用い、ＰｔＣｌ4 2-由来のピーク（２１４ｎｍ）の消失を確認することにより判断した。 While thoroughly stirring the mixed solution prepared above at 250 rpm, argon gas (solar oriental oxygen, G2, purity 99.9995%) was blown into the mixed solution at a flow rate of 200 mlmin −1 for 90 minutes to sufficiently degas. Then, platinum ions were reduced by blowing hydrogen gas (solar oriental oxygen, G2, purity 99.999%) at a flow rate of 300 mlmin −1 for 10 minutes. In order to allow the reaction to proceed completely, the reaction vessel was sealed after flowing hydrogen gas, and stirring was continued for 18 to 24 hours. The progress and completion of the reaction were judged by confirming the disappearance of the peak (214 nm) derived from PtCl 4 2− using an ultraviolet-visible absorption spectrum.
注１：硫酸ナトリウム（Ｎａ2ＳＯ4）は、Ｗａｋｏ社製である。
注２：ヨウ化ナトリウム（ＮａＩ）は、Ｗａｋｏ社製である。
Note 1: Sodium sulfate (Na 2 SO 4 ) is manufactured by Wako.
Note 2: Sodium iodide (NaI) is manufactured by Wako.
＜白金ナノ粒子の粒径および形状＞
上記の還元反応により析出させた白金ナノ粒子を含む溶液の１滴を、透過型電子顕微鏡用メッシュ（応研商事製、フォルマール支持膜メッシュ）に滴下し、自然乾燥させて透過型電子顕微鏡（ＴＥＭ）（日立製、Ｈ−９０００、Ｈ−８１００）を用いて１０万倍で観察し、観察像を得た。また、画像計測により面方位を有する白金ナノ粒子の数を計測し、全白金ナノ粒子の数に占める割合（％）を算出した。結果を表１および表２に示す。
<Particle size and shape of platinum nanoparticles>
One drop of the solution containing platinum nanoparticles precipitated by the above reduction reaction is dropped on a transmission electron microscope mesh (manufactured by Oken Shoji Co., Ltd., a formal support membrane mesh), allowed to dry naturally, and then a transmission electron microscope (TEM). ) (Manufactured by Hitachi, H-9000, H-8100) was observed at a magnification of 100,000 to obtain an observation image. In addition, the number of platinum nanoparticles having a plane orientation was measured by image measurement, and the ratio (%) to the total number of platinum nanoparticles was calculated. The results are shown in Tables 1 and 2.
＜サイクリックボルタモグラム＞
実施例２および１０の白金ナノ粒子について、下記の条件でサイクリックボルタモグラムを測定した。電解液中に下記に示す作用極を設け、下記の条件、
電解液 ０．０５ＭＨ2ＳＯ4
作用極 実施例２：Ａｕ板にキャスト法によってＰｔナノ粒子を担持
実施例１０：グラッシーカーボン（ＧＣ）にＰｔナノ粒子を担持
参照極 Ｐｔ
電位範囲 ０．０５〜０．８５Ｖ
スキャン速度 ５０ｍＶ-Ｓ-1
に従い、酸化還元電位を測定した。
<Cyclic voltammogram>
For the platinum nanoparticles of Examples 2 and 10, cyclic voltammograms were measured under the following conditions. Provide the working electrode shown below in the electrolyte, the following conditions,
Electrolyte 0.05MH 2 SO 4
Working electrode Example 2: Pt nanoparticles supported on Au plate by casting method
Example 10: Pt nanoparticles supported on glassy carbon (GC) Reference electrode Pt
Potential range 0.05 to 0.85V
Scan speed 50 mV-S -1
The redox potential was measured according to
参照例１〜３においては、白金ナノ粒子が観察されたものの、特定の結晶面を有するものは認められなかった。図５は、参照例４で生成させた白金ナノ粒子の形状を示すＴＥＭ像である。参照例４においては、特定の結晶面として（１００）面の面方位を有する立方体状の白金ナノ粒子が多く認められた。画像計測により該立方体状の白金ナノ粒子の数を計測し、全白金ナノ粒子の数に占める割合を算出したところ、（１００）面の面方位を有する立方体状の白金ナノ粒子が全白金ナノ粒子に占める割合は４７％であった。 In Reference Examples 1 to 3, although platinum nanoparticles were observed, those having a specific crystal plane were not recognized. FIG. 5 is a TEM image showing the shape of the platinum nanoparticles produced in Reference Example 4. In Reference Example 4, many cubic platinum nanoparticles having a (100) plane orientation as a specific crystal plane were observed. The number of the platinum platinum particles was measured by image measurement, and the proportion of the total platinum nanoparticles was calculated. As a result, the cubic platinum nanoparticles having the (100) plane orientation were all platinum nanoparticles. The proportion of the total was 47%.
なお、安定性ポリマーの添加量によって白金ナノ粒子の形状を制御した参照例１〜４においては、他の結晶面の面方位を有する粒子が４０％以上含まれる白金ナノ粒子を選択的に生成することはできなかった。 In Reference Examples 1 to 4 in which the shape of the platinum nanoparticles is controlled by the addition amount of the stability polymer, platinum nanoparticles containing 40% or more of particles having a plane orientation of other crystal planes are selectively generated. I couldn't.
図６は、実施例４で生成させた白金ナノ粒子の形状を示すＴＥＭ像である。添加剤として硫酸ナトリウムを用いた実施例１〜６においては、特定の面方位として（１００）面と（１１１）面との面方位を有する角切り八面体（ＴＯ）状の白金ナノ粒子が多く認められた。 FIG. 6 is a TEM image showing the shape of platinum nanoparticles produced in Example 4. In Examples 1 to 6 using sodium sulfate as an additive, there are many square-cut octahedral (TO) -shaped platinum nanoparticles having a plane orientation of (100) plane and (111) plane as a specific plane orientation. Admitted.
図７は、実施例１０で生成させた白金ナノ粒子の形状を示すＴＥＭ像である。添加剤としてヨウ化ナトリウムを用いた実施例７〜１１においては、(１１１)面の面方位を有する四面体状の白金ナノ粒子が比較的多く認められた他、（１００）面と（１１１）面との面方位を有する角切り八面体（ＴＯ）状の白金ナノ粒子も相当量認められた。特異吸着化学種としてのヨウ化物イオンの当量比が０．０５当量および０．５当量と小さい実施例７、８においては白金ナノ粒子の凝集が若干見られたのに対し、該当量比が３．０、５．０、１０当量の範囲内である実施例９〜１１においては白金ナノ粒子の分散性が良好であった。 FIG. 7 is a TEM image showing the shape of the platinum nanoparticles produced in Example 10. In Examples 7 to 11 using sodium iodide as an additive, a relatively large number of tetrahedral platinum nanoparticles having a (111) plane orientation were observed, and (100) plane and (111) A considerable amount of rounded octahedron (TO) -shaped platinum nanoparticles having a plane orientation with respect to the surface was also observed. In Examples 7 and 8 in which the equivalent ratio of iodide ions as specific adsorption chemical species was as small as 0.05 equivalent and 0.5 equivalent, agglomeration of platinum nanoparticles was slightly observed, while the corresponding ratio was 3 In Examples 9 to 11 in the range of 0.0, 5.0, and 10 equivalents, the dispersibility of the platinum nanoparticles was good.
図８は、実施例２において生成させた白金ナノ粒子について測定したサイクリックボルタモグラムの結果を示す図であり、図９は、実施例１０において生成させた白金ナノ粒子について測定したサイクリックボルタモグラムの結果を示す図である。図９に示すように、実施例２で生成させた白金ナノ粒子においては、（１００）面での水素の吸脱着に由来する０．２７Ｖの還元電位、および、（１１１）面での水素の吸脱着に由来する０．５Ｖ付近の還元電位のピークがそれぞれ認められた。一方、図９に示すように、実施例１０で生成させた白金ナノ粒子においては、（１１１）面での水素の吸脱着に由来する０．５Ｖ付近の還元電位のピークが認められた。透過型電子顕微鏡（ＴＥＭ）による観察像に加え、サイクリックボルタモグラムの結果からも、硫酸イオン（ＳＯ4 2-）を特異吸着化学種とした実施例２においては、（１００）面および（１１１）面の面方位を有する白金ナノ粒子、ヨウ化物イオン（Ｉ-）を特異吸着化学種とした実施例１０においては、（１１１）面の面方位を有する白金ナノ粒子がそれぞれ生成していることが分かる。 FIG. 8 is a diagram showing the results of cyclic voltammograms measured for the platinum nanoparticles produced in Example 2, and FIG. 9 is the results of cyclic voltammograms measured for the platinum nanoparticles produced in Example 10. FIG. As shown in FIG. 9, in the platinum nanoparticles produced in Example 2, the reduction potential of 0.27 V derived from the adsorption / desorption of hydrogen on the (100) plane and the hydrogen potential on the (111) plane A reduction potential peak around 0.5 V derived from adsorption / desorption was observed. On the other hand, as shown in FIG. 9, in the platinum nanoparticle produced | generated in Example 10, the peak of the reduction potential of 0.5V derived from the adsorption / desorption of hydrogen on the (111) plane was recognized. In addition to the observation image by the transmission electron microscope (TEM), from the result of the cyclic voltammogram, in Example 2 in which sulfate ion (SO 4 2− ) was used as the specific adsorption chemical species, the (100) plane and (111) In Example 10 in which platinum nanoparticles having a plane orientation of plane and iodide ion (I − ) as a specific adsorption chemical species are used, platinum nanoparticles having a plane orientation of (111) plane are generated respectively. I understand.
これらの結果から、安定性ポリマーおよび特異吸着化学種の存在下で白金イオンの還元反応により白金ナノ粒子を生成させた各実施例においては、所望の面方位を有する白金ナノ粒子が任意かつ簡便に製造されていることが分かる。 From these results, in each Example in which platinum nanoparticles were generated by the reduction reaction of platinum ions in the presence of a stable polymer and a specific adsorption chemical species, platinum nanoparticles having a desired plane orientation could be arbitrarily and simply It can be seen that it is manufactured.
今回開示された実施の形態および実施例はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。 It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
本発明によれば、使用する特異吸着化学種の種類および量の選択により面方位を任意かつ簡便に制御し、所望の特定の面方位を有する白金ナノ粒子を選択的に得ることが可能となる。これにより、燃料電池用電極等において所望される種々の触媒特性に対応した電極用触媒を提供することが可能である。 According to the present invention, the plane orientation can be arbitrarily and easily controlled by selecting the type and amount of the specific adsorption chemical species to be used, and platinum nanoparticles having a desired specific plane orientation can be selectively obtained. . As a result, it is possible to provide an electrode catalyst corresponding to various catalyst characteristics desired in a fuel cell electrode or the like.
Claims (10)
イオン性白金化合物の溶液と特異吸着化学種と安定化ポリマーとを混合する工程と、
前記イオン性白金化合物の溶液から白金結晶を析出させる工程と、
を含み、前記特異吸着化学種が陽イオンおよび／または陰イオンである、白金ナノ粒子の製造方法。 A method for producing platinum nanoparticles for forming platinum nanoparticles having a specific plane orientation,
Mixing a solution of an ionic platinum compound, a specific adsorption species and a stabilizing polymer;
Depositing platinum crystals from a solution of the ionic platinum compound;
And the method for producing platinum nanoparticles, wherein the specific adsorption chemical species is a cation and / or an anion.
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