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Abstract In addition to the conventional knobs such as composition, size, shape, and defect structure, the crystal structure (or phase) of metal nanocrystals offers a new avenue for engineering their properties. Various strategies have recently been developed for the fabrication of colloidal metal nanocrystals in metastable phases different from their bulk counterparts. With a focus on noble metals, we begin with a brief introduction to their atomic packing, followed by a discussion about five major synthetic approaches to their colloidal nanocrystals in unconventional phases. We then highlight the success of synthesis in terms of mechanistic insights and experimental controls, as well as the enhanced catalytic properties. We end this Minireview with perspectives on the remaining issues and future opportunities.
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Abstract In addition to the conventional knobs such as composition, size, shape, and defect structure, the crystal structure (or phase) of metal nanocrystals offers a new avenue for engineering their properties. Various strategies have recently been developed for the fabrication of colloidal metal nanocrystals in metastable phases different from their bulk counterparts. With a focus on noble metals, we begin with a brief introduction to their atomic packing, followed by a discussion about five major synthetic approaches to their colloidal nanocrystals in unconventional phases. We then highlight the success of synthesis in terms of mechanistic insights and experimental controls, as well as the enhanced catalytic properties. We end this Minireview with perspectives on the remaining issues and future opportunities.
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Abstract A relatively unexplored aspect of noble‐metal nanomaterials is polymorphism, or their ability to crystallize in different crystal phases. Here, a method is reported for the facile synthesis of Ru@Pd core–shell nanocrystals featuring polymorphism, with the core made of hexagonally close‐packed (
hcp) ‐Ru while the Pd shell takes either anhcp or face‐centered cubic (fcc) phase. The polymorphism shows a dependence on the shell thickness, with shells thinner than ≈1.4 nm taking thehcp phase whereas the thicker ones revert tofcc . The injection rate provides an experimental knob for controlling the phase, with one‐shot and drop‐wise injection of the Pd precursor corresponding tofcc ‐Pd andhcp ‐Pd shells, respectively. When these nanocrystals are tested as catalysts toward formic acid oxidation, the Ru@Pdhcp nanocrystals outperform Ru@Pdfcc in terms of both specific activity and peak potential. Density functional theory calculations are also performed to elucidate the origin of this performance enhancement. -
Abstract Oberflächenstabilisatoren werden eingesetzt, um das Wachstum von Keimen zu Nanokristallen mit gut kontrollierbaren Formen zu steuern. Hier wird eine Übersicht über diese Mittel gegeben, wobei der Schwerpunkt auf dem mechanistischen Verständnis ihrer Rolle bei der Steuerung der Formentwicklung metallischer Nanokristalle liegt. Begonnen wird mit einer Einführung in die frühe Geschichte der Oberflächenstabilisatoren, gefolgt von einer Diskussion darüber, wie an der Synthese von Metall‐Nanokristallen beteiligte Stabilisatoren die Thermodynamik und Kinetik beeinflussen. Danach werden Beispiele für Oberflächenstabilisatoren diskutiert, einschließlich ihrer Bindungsselektivität, Wechselwirkung auf molekularer Ebene mit einer Metalloberfläche und Auswirkungen auf das Wachstum metallischer Nanokristalle. Es werden Fortschritte bei der Nutzung von Oberflächenstabilisatoren zur Erzeugung von Nanokristallen mit komplexen Strukturen und/oder zur Verbesserung ihrer katalytischen Eigenschaften beschrieben. Schließlich werden Strategien zum Austausch und zur Entfernung der Stabilisatoren sowie Perspektiven für die zukünftige Entwicklung diskutiert.
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Surface Capping Agents and Their Roles in Shape‐Controlled Synthesis of Colloidal Metal Nanocrystals
Abstract Surface capping agents have been extensively used to control the evolution of seeds into nanocrystals with diverse but well‐controlled shapes. Here we offer a comprehensive review of these agents, with a focus on the mechanistic understanding of their roles in guiding the shape evolution of metal nanocrystals. We begin with a brief introduction to the early history of capping agents in electroplating and bulk crystal growth, followed by discussion of how they affect the thermodynamics and kinetics involved in a synthesis of metal nanocrystals. We then present representative examples to highlight the various capping agents, including their binding selectivity, molecular‐level interaction with a metal surface, and impacts on the growth of metal nanocrystals. We also showcase progress in leveraging capping agents to generate nanocrystals with complex structures and/or enhance their catalytic properties. Finally, we discuss various strategies for the exchange or removal of capping agents, together with perspectives on future directions.