Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and rea...

Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures

A review of the oxygen reduction reaction (ORR) and its use in fuel-cell applications is presented. Discussed are mechanisms of the ORR and implementations of catalysts for this reaction. Specific catalysts discussed include nanoparticles, macrocycles and pyrolysis products, carbons, chalcogenides, enzymes, and coordination complexes. A prospectus for future efforts is provided.

Electroreduction of dioxygen for fuel-cell applications: materials and challenges.

Self-templated synthesis of hollow nanostructures

We report a facile synthesis of Pt–Pd bimetallic nanoparticles, named “metallic nanocages”, with a hollow interior and porous dendritic shell. This synthesis is easily achieved by selective chemical etching of Pd cores from dendritic Pt-on-Pd nanoparticles. The obtained Pt–Pd nanocages show superior catalytic activity for methanol oxidation reaction compared to other Pt-based materials reported previously.

Metallic nanocages: synthesis of bimetallic Pt-Pd hollow nanoparticles with dendritic shells by selective chemical etching.

The question of whether the metal chalcogenides (phosphides) that have been acknowledged to be efficient materials for bifunctional electrocatalysts really perform as the active species or just “pre-catalysts” has been debated Herein, a series of operando measurements, including in situ X-ray absorption spectroscopy, liquid-phase transmission electron microscopy, and in situ Raman spectroscopy, were conducted to unravel in real time the structural and chemical stability of P-substituted CoSe2 electrocatalysts under both hydrogen and oxygen evolution reactions (HER and OER, respectively) in an alkaline electrolyte It can be conclusively revealed that, in an alkaline electrolyte, the P-substituted CoSe2 electrocatalyst was acting as the “pre-catalyst” rather than the real reactive species The introduction of phosphorus is speculated to generate more vacancies or defects around Co cations in the initial CoSe2 and considerably facilitates the structural transformation into the “real reactive species”, such

Operando Unraveling of the Structural and Chemical Stability of P-Substituted CoSe2 Electrocatalysts toward Hydrogen and Oxygen Evolution Reactions in Alkaline Electrolyte

Hollow nanostructures are a particularly interesting class of materials that have unusual chemical and physical characteristics that are determined by their shape and composition. A facile procedure for the hollow Pt nanosphere catalysts with nanochannels was developed; the catalysts can be simply prepared at room temperature with silver nanoparticles as sacrificial templates. The incomplete shell of hollow nanospheres may provide the interior surface for the catalytic reaction, and the high surface area of Pt nanospheres leads to a higher catalytic activity. Consequently, these results demonstrate a simple route to enhance the catalytic efficiency of Pt catalysts by a simple improvement.

Li Duan Tsai

Papers

Operando Unraveling of the Structural and Chemical Stability of P-Substituted CoSe2 Electrocatalysts toward Hydrogen and Oxygen Evolution Reactions in Alkaline Electrolyte

Hollow Platinum Spheres with Nano-Channels: Synthesis and Enhanced Catalysis for Oxygen Reduction