The Electrochemical Energy, Catalysis, and Materials Science Laboratory, Department of Chemistry, Chemical Engineering Division, Technical University Berlin, Sekr. TC03, Strasse des 17. Juni 124, 10623 Berlin, Germany.
J Am Chem Soc. 2012 Jan 11;134(1):514-24. doi: 10.1021/ja2088162. Epub 2011 Dec 28.
Chemical dealloying of Pt binary alloy precursors has emerged as a novel and important preparation process for highly active fuel cell catalysts. Dealloying is a selective (electro)chemical leaching of a less noble metal M from a M rich Pt alloy precursor material and has been a familiar subject of macroscale corrosion technology for decades. The atomic processes occurring during the dealloying of nanoscale materials, however, are virtually unexplored and hence poorly understood. Here, we have investigated how the morphology and intraparticle composition depend on the particle size of dealloyed Pt-Co and Pt-Cu alloy nanoparticle precursor catalysts. To examine the size-morphology-composition relation, we used a combination of high-resolutionscanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), electron energy loss (EEL) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), and surface-sensitive cycling voltammetry. Our results indicate the existence of three distinctly different size-dependent morphology regimes in dealloyed Pt-Co and Pt-Cu particle ensembles: (i) The arrangement of Pt shell surrounding a single alloy core ("single core-shell nanoparticles") is exclusively formed by dealloying of particles below a characteristic diameter d(multiple cores) of 10-15 nm. (ii) Above d(multiple cores), nonporous bimetallic core-shell particles dominate and show structures with irregular shaped multiple Co/Cu rich cores ("multiple cores-shell nanoparticles"). (iii) Above the second characteristic diameter d(pores) of about 30 nm, the dealloyed Pt-Co and Pt-Cu particles start to show surface pits and nanoscale pores next to multiple Co/Cu rich cores. This structure prevails up to macroscopic bulklike dealloyed particles with diameter of more than 100 nm. The size-morphology-composition relationships link the nano to the macro scale and provide an insight into the existing material gap of dealloyed nanoparticles and highly porous bulklike bimetallic particles in corrosion science.
化学脱合金法已成为一种新兴的、重要的制备高活性燃料电池催化剂的方法。脱合金是一种从富含 M 的 Pt 合金前驱体材料中选择性（电）化学浸出较不活泼金属 M 的过程，几十年来一直是宏观腐蚀技术领域的一个熟悉课题。然而，纳米材料脱合金过程中发生的原子过程实际上尚未得到探索，因此了解甚少。在这里，我们研究了脱合金的 Pt-Co 和 Pt-Cu 合金纳米颗粒前驱体催化剂的颗粒尺寸如何影响其形态和颗粒内组成。为了研究尺寸-形态-组成关系，我们使用高分辨率扫描透射电子显微镜（STEM）、透射电子显微镜（TEM）、电子能量损失（EEL）光谱、能量色散 X 射线光谱（EDS）和表面敏感循环伏安法相结合的方法。我们的结果表明，在脱合金的 Pt-Co 和 Pt-Cu 颗粒中存在三种明显不同的尺寸依赖性形态区域：（i）由单个合金核周围的 Pt 壳排列而成的“单核壳纳米颗粒”仅由直径 d（多核）小于 10-15nm 的颗粒脱合金形成。（ii）在 d（多核）以上，无孔双金属核壳颗粒占主导地位，并具有具有不规则形状的多个富 Co/Cu 核的结构（多核壳纳米颗粒）。（iii）在第二个特征直径 d（孔）约 30nm 以上，脱合金的 Pt-Co 和 Pt-Cu 颗粒开始在多个富 Co/Cu 核旁边显示表面凹坑和纳米级孔。这种结构一直持续到直径大于 100nm 的宏观块状脱合金颗粒。尺寸-形态-组成关系将纳米尺度与宏观尺度联系起来，深入了解了腐蚀科学中脱合金纳米颗粒和高度多孔的块状双金属颗粒之间存在的材料差距。
