Size‐Controlled Synthesis of Sub‐10 nm PtNi3 Alloy Nanoparticles and their Unusual Volcano‐Shaped Size Effect on ORR Electrocatalysis

Dealloyed Pt bimetallic core–shell catalysts derived from low‐Pt bimetallic alloy nanoparticles (e.g, PtNi₃) have recently shown unprecedented activity and stability on the cathodic oxygen reduction reaction (ORR) under realistic fuel cell conditions and become today's catalyst of choice for commercialization of automobile fuel cells. A critical step toward this breakthrough is to control their particle size below a critical value (≈10 nm) to suppress nanoporosity formation and hence reduce significant base metal (e.g., Ni) leaching under the corrosive ORR condition. Fine size control of the sub‐10 nm PtNi₃ nanoparticles and understanding their size dependent ORR electrocatalysis are crucial to further improve their ORR activity and stability yet still remain unexplored. A robust synthetic approach is presented here for size‐controlled PtNi₃ nanoparticles between 3 and 10 nm while keeping a constant particle composition and their size‐selected growth mechanism is studied comprehensively. This enables us to address their size‐dependent ORR activities and stabilities for the first time. Contrary to the previously established monotonic increase of ORR specific activity and stability with increasing particle size on Pt and Pt‐rich bimetallic nanoparticles, the Pt‐poor PtNi₃ nanoparticles exhibit an unusual “volcano‐shaped” size dependence, showing the highest ORR activity and stability at the particle sizes between 6 and 8 nm due to their highest Ni retention during long‐term catalyst aging. The results of this study provide important practical guidelines for the size selection of the low Pt bimetallic ORR electrocatalysts with further improved durably high activity.     

Nonspherical Noble Metal Nanoparticles: Colloid‐Chemical Synthesis and Morphology Control

Metal nanoparticles have been the subject of widespread research over the past two decades. In recent years, noble metals have been the focus of numerous studies involving synthesis, characterization, and applications. Synthesis of an impressive range of noble metal nanoparticles with varied morphologies has been reported. Researchers have made a great progress in learning how to engineer materials on a nanometer length scale that has led to the understanding of the fundamental size‐ and shape‐dependent properties of matter and to devising of new applications. In this article, we review the recent progress in the colloid‐chemical synthesis of nonspherical nanoparticles of a few important noble metals (mainly Ag, Au, Pd, and Pt), highlighting the factors that influence the particle morphology and discussing the mechanisms behind the nonspherical shape evolution. The article attempts to present a thorough discussion of the basic principles as well as state‐of‐the‐art morphology control in noble metal nanoparticles.     

Chemical Valence‐Dependent Electrocatalytic Activity for Oxygen Evolution Reaction: A Case of Nickel Sulfides Hybridized with N and S Co‐Doped Carbon Nanoparticles

Exploration of the relationship between electrocatalytic activities and their chemical valence is very important in rational design of high‐efficient electrocatalysts. A series of porous nickel sulfides hybridized with N and S co‐doped carbon nanoparticles (Ni_xS_y‐NSCs) with different chemical valences of Ni, Ni₉S₈‐NSCs, Ni₉S₈‐NiS_1.03‐NSCs, and NiS_1.03‐NSCs are successfully fabricated, and their electrocatalytic performances as oxygen evolution reaction electrocatalysts are systematically investigated. The Ni_xS_y‐NSCs are obtained via a two‐step reaction including a low‐temperature synthesis of Ni‐Cys precursor followed by thermal decomposing of the precursor in Ar atmosphere. By controlling the sulfidation process during the formation of Ni_xS_y‐NSCs, Ni₉S₈‐NSCs, Ni₉S₈‐NiS_1.03‐NSCs, and NiS_1.03‐NSCs are obtained, respectively, giving rise to the increase of high‐valence Ni component, and resulting in gradually enhanced oxygen evolution reaction electrocatalytic activities. In particular, the NiS_1.03‐NSCs show an exceptional low overpotential of ≈270 mV versus reversible hydrogen electrode at a current density of 10 mA cm^?2 and a small Tafel slope of 68.9 mV dec^?1 with mass loading of 0.25 mg cm^?2 in 1 m KOH and their catalytic activities remained for at least 10 h, which surpass the state‐of‐the‐art IrO₂, RuO₂, and Ni‐based electrocatalysts.     

Cover Picture: Functionalized Gold Nanoparticles Mimic Catalytic Activity of a Polysiloxane‐Synthesizing Enzyme (Adv. Mater. 10/2005)

A system that acts as a biomimetic of the silica‐synthesizing enzyme found in a marine sponge is reported by Morse and co‐workers on p. 1234. Gold nanoparticles (GNPs) are functionalized with the same organic moieties that are found in the enzyme's catalytic site. Interaction between the nucleophilic (OH‐terminated) and hydrogen‐bonding (imidazole‐terminated) GNPs, as shown on the cover, is required for the hydrolysis of a silicon alkoxide precursor and subsequent polycondensation to form silica at a low temperature and near‐neutral pH. Replacement of either of the required functional groups by a non‐reactive methyl group abolishes catalysis in this synthetic system, as it does in the biological enzyme. Cover art provided by Peter Allen.     

Bright Quantum‐Dot‐Sized Single‐Chain Conjugated Polyelectrolyte Nanoparticles: Synthesis,Characterization and Application for Specific Extracellular Labeling and Imaging

We report a simple method to fabricate quantum‐dot‐sized nanoparticles (NPs) from poly[9,9‐bis((6‐N,N,N‐trimethylammonium)hexyl)fluorene‐alt‐co‐2,1,3‐benzo­xadiazole dibromide] (PFBD). The transmission electron microscope results reveal that the obtained NPs have a mean diameter of ≈4 nm, which is composed of a single PFBD chain. The NPs show bright fluorescence with an emission maximum at ≈636 nm and a quantum yield of ≈26% in water. The fluorescence properties of the NPs are characterized by steady fluorescence microscopy, fluorescence dynamic study and single nanoparticle microscopy, which show superior brightness over commercial quantum dots QD655. The NPs are further conjugated with streptavidin to yield PFBD‐SA NPs, which serve as a specific extracellular labeling and imaging probe with high specificity and good photostability.