Byeongyoon Kim

Skeletal Octahedral Nanoframe with Cartesian Coordinates via Geometrically Precise Nanoscale Phase Segregation in a Pt@Ni Core–Shell Nanocrystal

Catalytic properties of nanoparticles can be significantly enhanced by controlling nanoscale alloying and its structure. In this work, by using a facet-controlled Pt@Ni core-shell octahedron nanoparticle, we show that the nanoscale phase segregation can have directionality and be geometrically controlled to produce a Ni octahedron that is penetrated by Pt atoms along three orthogonal Cartesian axes and is coated by Pt atoms along its edges. This peculiar anisotropic diffusion of Pt core atoms along the ⟨100⟩ vertex, and then toward the ⟨110⟩ edges, is explained via the minimum strain energy for Ni-Ni pair interactions. The selective removal of the Ni-rich phase by etching then results in structurally fortified Pt-rich skeletal PtNi alloy framework nanostructures. Electrochemical evaluation of this hollow nanoframe suggests that the oxygen reduction reaction (ORR) activity is greatly improved compared to conventional Pt catalysts.

Facet-controlled hollow Rh2S3 hexagonal nanoprisms as highly active and structurally robust catalysts toward hydrogen evolution reaction

Developing highly active and structurally robust electrocatalysts for hydrogen evolution reaction (HER) is of paramount importance for sustainable and clean production of hydrogen. Metal sulphides exposing catalytically active sites, in particular, have been actively pursued as advanced HER catalysts. Herein we report high-performance Rh2S3-based HER catalysts with excellent activity and durability. Hollow Rh2S3 hexagonal nanoprisms with controlled size and thickness could be conveniently prepared by one-step formation of core–shell nanoprisms followed by the etching of the core, and they show high surface areas and highly exposed edge sites. The hollow Rh2S3 nanoprisms exhibit very high HER activity and excellent stability under harsh acidic conditions.

Rational design of Pt-Ni-Co ternary alloy nanoframe crystals as highly efficient catalysts toward the alkaline hydrogen evolution reaction

The rational design of highly efficient electrocatalysts for the hydrogen evolution reaction (HER) is of prime importance for establishing renewable and sustainable energy systems. The alkaline HER is particularly challenging as it involves a two-step reaction of water dissociation and hydrogen recombination, for which platinum-based binary catalysts have shown promising activity. In this work, we synthesized high performance platinum-nickel-cobalt alloy nanocatalysts for the alkaline HER through a simple synthetic route. This ternary nanostructure with a Cartesian-coordinate-like hexapod shape could be prepared by a one-step formation of core-dual shell Pt@Ni@Co nanostructures followed by a selective removal of the Ni@Co shell. The cobalt precursor brings about a significant impact on the control of size and shape of the nanostructure. The PtNiCo nanohexapods showed a superior alkaline HER activity to Pt/C and binary PtNi hexapods, with 10 times greater specific activity than Pt/C. In addition, the PtNiCo nanohexapods demonstrated excellent activity and durability for the oxygen reduction reaction in acidic media.

A highly crystalline manganese-doped iron oxide nanocontainer with predesigned void volume and shape for theranostic applications

Hollow Mn-doped iron oxide nanocontainers, formed by a novel one-pot synthetic process, fulfill the dual requirements of delivering an effective dose of an anticancer drug to tumor tissue and enabling image-contrast monitoring of the nanocontainer fate through T2 -weighted magnetic resonance imaging, thereby determining the optimal balance between diagnostic and therapeutic moieties in an all-in-one theranostic nanoplatform.

Axially twinned nanodumbbell with a Pt bar and two Rh@Pt balls designed for high catalytic activity

A fail-proof synthetic strategy has been developed for a multiply twinned dumbbell-shaped Rh@Pt nanostructure, which exhibits a superior electrocatalytic activity for methanol oxidation reaction. The unusually high electrocatalytic activity has been attributed to the synergistic effects of crystal twinning and core-shell structure.

MXene: An emerging two-dimensional material for future energy conversion and storage applications

The development of two-dimensional (2D) high-performance electrode materials is the key to new advances in the fields of energy conversion and storage. MXenes, a new intriguing family of 2D transition metal carbides, nitrides, and carbonitrides, have recently received considerable attention due to their unique combination of properties such as high electrical conductivity, hydrophilic nature, excellent thermal stability, large interlayer spacing, easily tunable structure, and high surface area. In this review, we discuss how 2D MXenes have emerged as efficient and economical nanomaterials for future energy applications. We highlight the promising potential of these materials in energy conversion and storage applications, such as water electrolyzers, lithium ion batteries, and supercapacitors. Finally, we present an outlook of the future development of MXenes for sustainable energy technologies.

Cactus-Like Hollow Cu2-xS@Ru Nanoplates as Excellent and Robust Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

The development of Pt-free electrocatalysts for the hydrogen evolution reaction (HER) recently is a focus of great interest. While several strategies are developed to control the structural properties of non-Pt catalysts and boost their electrocatalytic activities for the HER, the generation of highly reactive defects or interfaces by combining a metal with other metals, or with metal oxides/sulfides, can lead to notably enhanced catalytic performance. Herein, the preparation of cactus-like hollow Cu2-x S@Ru nanoplates (NPs) that contain metal/metal sulfide heterojunctions and show excellent catalytic activity and durability for the HER in alkaline media is reported. The initial formation of Ru islands on presynthesized Cu1.94 S NPs, via cation exchange between three Cu+ ions and one Ru3+ , induces the growth of the Ru phase, which is concomitant with the dissolution of the Cu1.94 S nanotemplate, culminating in the formation of a hollow nanostructure with numerous thin Ru pillars. Hollow Cu2-x S@Ru NPs exhibit a small overpotential of 82 mV at a current density of -10 mA cm-2 and a low Tafel slope of 48 mV dec-1 under alkaline conditions; this catalyst is among state-of-the-art HER electrocatalysts in alkaline media. The excellent performance of hollow Cu2-x S@Ru NPs originates from the facile dissociation of water in the Volmer step.

Synergistic Effect of Detection and Separation for Pathogen Using Magnetic Clusters.

Early diagnosis of infectious diseases is important for treatment; therefore, selective and rapid detection of pathogenic bacteria is essential for human health. We report a strategy for highly selective detection and rapid separation of pathogenic microorganisms using magnetic nanoparticle clusters. Our approach to develop probes for pathogenic bacteria, including Salmonella, is based on a theoretically optimized model for the size of clustered magnetic nanoparticles. The clusters were modified to provide enhanced aqueous solubility and versatile conjugation sites for antibody immobilization. The clusters with the desired magnetic property were then prepared at critical micelle concentration (CMC) by evaporation-induced self-assembly (EISA). Two different types of target-specific antibodies for H- and O-antigens were incorporated on the cluster surface for selective binding to biological compartments of the flagella and cell body, respectively. For the two different specific binding properties, Salmonella were effectively captured with the O-antibody-coated polysorbate 80-coated magnetic nanoclusters (PCMNCs). The synergistic effect of combining selective targeting and the clustered magnetic probe leads to both selective and rapid detection of infectious pathogens.

Ni@Ru and NiCo@Ru Core-Shell Hexagonal Nanosandwiches with a Compositionally Tunable Core and a Regioselectively Grown Shell

The development of highly active electrocatalysts is crucial for the advancement of renewable energy conversion devices. The design of core-shell nanoparticle catalysts represents a promising approach to boost catalytic activity as well as save the use of expensive precious metals. Here, a simple, one-step synthetic route is reported to prepare hexagonal nanosandwich-shaped Ni@Ru core-shell nanoparticles (Ni@Ru HNS), in which Ru shell layers are overgrown in a regioselective manner on the top and bottom, and around the center section of a hexagonal Ni nanoplate core. Notably, the synthesis can be extended to NiCo@Ru core-shell nanoparticles with tunable core compositions (Ni3 Cox @Ru HNS). Core-shell HNS structures show superior electrocatalytic activity for the oxygen evolution reaction (OER) to a commercial RuO2 black catalyst, with their OER activity being dependent on their core compositions. The observed trend in OER activity is correlated to the population of Ru oxide (Ru4+ ) species, which can be modulated by the core compositions.

Large-scale one pot synthesis of metal oxide nanoparticles by decomposition of metal carbonates or nitrates

This study identifies bulk metal carbonates and nitrates as cost-effective starting materials for a large-scale, one-pot synthesis of monodisperse metal oxide nanoparticles of MnO, Fe3O4, and CoO phases. The thermal decomposition of bulk metal carbonates or nitrates in hot fatty acid forms monodisperse metal oxide nanoparticles on a large scale. The release of carbon monoxide and nitrogen dioxide gas molecules from these precursors would in situ form molecular metal-oxo species, lightly stabilized by complexation with fatty acid, which would in turn undergo subsequent agglomeration to form metal oxide nanoparticles. The particle size and shape could be controlled simply by varying the reaction conditions, namely the amount and nature of added alkylamine. This general and convenient synthetic methodology would be greatly beneficial to the practical application of thermally synthesized metal oxide nanoparticles.