Aram Oh

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.

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.

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.

Dendrite-Embedded Platinum–Nickel Multiframes as Highly Active and Durable Electrocatalyst toward the Oxygen Reduction Reaction

Pt-based nanoframe catalysts have been explored extensively due to their superior activity toward the oxygen reduction reaction (ORR). Herein, we report the synthesis of Pt-Ni multiframes, which exhibit the unique structure of tightly fused multiple nanoframes and reinforced by an embedded dendrite. Rapid reduction and deposition of Ni atoms on Pt-Ni nanodendrites induce the alloying/dealloying of Pt and Ni in the overall nanostructures. After chemical etching of Ni, the newly formed dendrite-embedded Pt-Ni multiframes show an electrochemically active surface area (ECSA) of 73.4 m2 gPt-1 and a mass ORR activity of 1.51 A mgPt-1 at 0.93 V, which is 30-fold higher than that of the state-of-the-art Pt/C catalyst. We suggest that high ECSA and ORR performances of dendrite-embedded Pt-Ni multiframes/C can be attributed to the porous nanostructure and numerous active sites exposed on surface grain boundaries and high-indexed facets.

Cancer theranosis using mono-disperse, mesoporous gold nanoparticles obtained via a robust, high-yield synthetic methodology

Porous noble metal nanoparticles exhibit many attractive nanoplasmonic features, and these structures have potential applications in many fields. However, such applications have been hindered by a lack of synthetic methods with the ability to mass-produce mono-disperse nanoparticles. Current synthetic approaches to porous gold nanostructure fabrication involve galvanic replacement approaches or electrochemical deposition methods that are generally limited by stringent multi-step protocols and relatively low yields. Here, we introduce the facile synthesis of scalable, mono-disperse, mesoporous gold nanoparticles (MPGNs) using an acidic emulsification method. This method facilitates high synthetic yields (>93%) and tunable particle sizes (130–400 nm). MPGNs exhibit enhanced payloads of gadolinium (Gd), a contrast agent for magnetic resonance imaging. Additionally, they permit photo-thermal conversion under near-infrared light (NIR) irradiation due to the increased surface area to volume ratio and the unique, structure-mediated LSPR effect. Specifically, MPGNs fabricated using our method provided Gd payloads 2–4 orders of magnitude greater than previously reported theranostic nano-probes. We believe that our novel synthetic technique will not only contribute to large-scale production of homogeneous porous gold nanoparticles, but will also promote further research in porous noble metal nanostructures.

A facet-controlled Rh3Pb2S2 nanocage as an efficient and robust electrocatalyst toward the hydrogen evolution reaction

Highly active and durable electrocatalysts for the hydrogen evolution reaction (HER) may play a pivotal role in commercial success of electrolytic water splitting technology. Among various material classes, binary metal sulphides show a great promise as HER catalysts because of their tunable energy levels conducive to a high catalytic activity and high robustness under harsh operating conditions. On the other hand, facet-controlled nanoparticles with controlled surface energies have gained great recent popularity as active and selective catalysts. However, binary metal sulphide nanoparticles with well-defined facets and high surface areas are very rare. Herein we report the synthesis of a facet-controlled hollow Rh3Pb2S2 nanocage as a new catalytic material and its excellent activity (overpotential: 87.3 mV at 10 mA cm-2) and robustness toward HER under harsh acidic conditions.

NiOOH Exfoliation-Free Nickel Octahedra as Highly Active and Durable Electrocatalysts Toward the Oxygen Evolution Reaction in an Alkaline Electrolyte

A layered β-NiOOH crystal with undercoordinated facets is an active and economically viable nonnoble catalyst for the oxygen evolution reaction (OER) in alkaline electrolytes. However, it is extremely difficult to enclose the β-NiOOH crystal with undercoordinated facets because of its inevitable crystal transformation to γ-NiOOH, resulting in the exfoliation of the catalytic surfaces. Herein, we demonstrate {111}-faceted Ni octahedra as the parent substrates whose surfaces are easily transformed to catalytically active β-NiOOH during the alkaline OER. Electron microscopic measurements demonstrate that the horizontally stacked β-NiOOH on the surfaces of Ni octahedra has resistance to further oxidation to γ-NiOOH. By contrast, significant crystal transformation and thus the exfoliation of the γ-NiOOH sheets can be observed on the surfaces of Ni cubes and rhombic dodecahedra (RDs). Electrocatalytic measurements show that the β-NiOOH formed on Ni octahedra exhibits highly enhanced OER durability compared to the Ni cubes, Ni RDs, and the state-of-the-art Ir/C catalysts.

RuOx-decorated Multimetallic Hetero-nanocage as Highly Efficient Electrocatalyst toward the Methanol Oxidation Reaction

Direct methanol fuel cell technology awaits the development of highly efficient and robust nanocatalysts driving the methanol oxidation reaction (MOR) in a CO poisoning-free fashion. Thus far, various Pt-based alloy nanoparticles have been studied as electrocatalysts toward the MOR, and it has been found that the introduction of dopants such as Ru and Cu to Pt has been particularly successful in mitigating the CO poisoning problem. Herein, we report a facile synthesis of Ru-branched RuPtCu nanocages that involves in situ formation of Ru-doped PtCu nanoparticles and subsequent outgrowth of Ru branches by insertion of additional Ru precursors. We show that the electrocatalytic activity and stability of Ru branched RuPtCu ternary nanocages toward the MOR are greatly improved compared to those of PtCu/C and RuPtCu/C counterparts and state-of-the-art PtRu/C and Pt/C catalysts, mainly due to the synergy between the CO-tolerant RuOx phase and the highly open and robust RuPtCu nanoframe.

An IrRu alloy nanocactus on Cu2−xS@IrSy as a highly efficient bifunctional electrocatalyst toward overall water splitting in acidic electrolytes

Development of highly active and durable bifunctional electrocatalysts for overall water splitting is vital for the economical production of H2 as an alternative energy source. Herein, we report the synthesis of Cu2−xS@IrSy@IrRu nanoparticles (CIS@IrRu NPs), which show excellent catalytic performances for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an acidic electrolyte. Benefiting from the optimal composition of IrRu and the stable IrSy shell, the cactus-like IrRu NPs show high electrocatalytic activity and stability. The cactus-like IrRu NPs exhibit optimal HER and OER performances and high stability at a ratio of Ir/Ru 1.00 : 1.07. In overall water splitting, the CIS@Ir48Ru52 NPs achieve a current density of 10 mA cm−2 at a cell voltage of only 1.47 V in 0.1 M HClO4 electrolyte and show negligible degradation after 100 h of continuous operation in the stability test.