金屬合金奈米材料的製備及其在生醫影像、催化和光電上之應用

Abstract

發展新型態合金金屬奈米晶體的催化劑對於未來燃料電池商品化是相當重要的一個步驟。在這個研究中，我們成功利用簡單的置換反應，發展出陽離子與奈米粒子發生離子交換反應，此新奇方法能夠合成含有Fe，Ru與Pt一系列之多重合金奈米晶體，並且進而由X光吸收光譜來確定其奈米粒子中所進行陽離子交換反應之機制，從EXAFS數據分析來了解其三合金奈米晶體之結構及表面組成。在觸媒催化活性之測試中，我們發現三合金Fe35Pt40Ru25, Fe31Pt40Ru29,以及 Fe17Pt40Ru43奈米晶體作為陽極觸媒，其主要對甲醇氧化過程中所產生之CO毒化有極佳的解毒能力。同時我們發現Fe31Pt40Ru29奈米晶體有最高的合金程度時，對於甲醇氧化產生最高之氧化電流以及最低的氧化起始電位。最後，我們利用density functional theory來建構出此三合金奈米晶體對於CO解毒之模型，來了解其三合金電子Fe31Pt40Ru29從3d 過度金屬傳遞到Pt的情形大於二合金FePt或PtRu，較大的電子傳遞量會導致減弱Pt-CO的鍵結，進而降低CO的毒化現象。最終，我們希望利用這樣一個簡單的反應對於尋找新型態並具有高催化性的奈米晶體可以大大降低貴金屬Pt or Ru的使用量，這對於燃料電池的發展是相當的重要的一環，而本篇工作將發表於JACS期刊。

The finding of new metal alloyed nanocrystals (NCs) with high catalytic activity and low cost to replace PtRu NCs is a critical step toward the commercialization of fuel cells. In this work, a simple cation replacement reaction was utilized to synthesize new type of ternary Fe1-xPtRux NCs from binary FePt NCs. The detailed structural transformation from binary FePt NCs to ternary Fe1-xPtRux NCs was analyzed by X-ray absorption spectroscopy (XAS). Ternary Fe35Pt40Ru25, Fe31Pt40Ru29 and Fe17Pt40Ru43 NCs exhibit superior catalytic ability to withstand CO poisoning in methanol oxidation reaction (MOR) than binary NCs (FePt and J-M PtRu). Also, the Fe31Pt40Ru29 NCs had the highest alloying extent and the lowest onset potential among the ternary NCs. Furthermore, the origin for the superior CO resistance of ternary Fe1-xPtRux NCs was investigated by determining the adsorption energy of CO on the NCs surfaces and the charge transfer from Fe/Ru to Pt using a simulation based on density functional theory. The simulation results suggested that by introducing a new metal into binary PtRu/PtFe NCs, the anti-CO poisoning ability of ternary Fe1-xPtRux NCs was greatly enhanced because the bonding of CO–Pt on the NC’s surface was weakened. Overall, our experimental and simulation results have indicated a simple route for the discovery of new metal alloyed catalysts with superior anti-CO poisoning ability and low usage of Pt and Ru for fuel cell applications. The work will be published in J. Am. Chem. Soc. on June, 2012.