Donghwan Yoon

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.

RhCu 3D nanoframe as a highly active electrocatalyst for oxygen evolution reaction under alkaline condition

One pot synthesis of RhCu alloy truncated octahedral nanoframes, Cu@Rh core–shell nanoparticles, and a bundle of five RhCu nanowires is demonstrated. The RhCu alloy 3D nanoframe, in particular, exhibits excellent catalytic activity toward the oxygen evolution reaction under alkaline conditions.

Scalable synthesis of djurleite copper sulphide (Cu1.94S) hexagonal nanoplates from a single precursor copper thiocyanate and their photothermal properties

Copper sulphide materials have received great attention due to their low bandgap semiconducting properties. As compared to other chalcogenides, few synthetic examples have been reported, and a simple and scalable synthetic method for preparing size- and shape-controlled copper sulphide nanoparticles is required for potential wide application of these materials. Herein, a facile one pot scalable synthetic route has been developed for preparing highly monodisperse djurleite Cu1.94S hexagonal nanoplates. The thermal decomposition of a single precursor CuSCN was found suitable for preparing a large quantity of highly monodisperse Cu1.94S hexagonal nanoplates; a multi-gram scale product could be obtained in a single step. Under the synthetic scheme developed, the width of Cu1.94S nanoplates with a thickness of ~ 10 nm could be easily tuned from 70 nm to 130 nm. Their optical properties were investigated and their photothermal effect was also studied by photothermal optical coherence reflectometry (PT OCR). Cu1.94S hexagonal nanoplates showed a considerable photothermal effect, which was found to depend on the nanoparticle concentration.

One pot synthesis of octahedral {111} CuIr gradient alloy nanocrystals with a Cu-rich core and an Ir-rich surface and their usage as efficient water splitting catalyst

A facile one pot synthetic route has been developed to obtain octahedral CuIr nanocrystals with Ir-rich {111} facets. Co-decomposition of Cu and Ir precursors in the presence of CTAC (cetyltrimethylammonium chloride) forms CuIr nanocrystals with an Ir-rich {111} facet. A mechanistic study reveals that the surface Cu atoms of the initially formed octahedral-shaped Cu-rich Cu–Ir alloy nanoparticles are replaced by Ir atoms via a galvanic replacement reaction. The formation of the Ir phase is rather slow, leading to the impermeable nature of the Ir shell, which does not allow the dissolution of the Cu phase. The CuIr nanocrystals with an Ir-rich shell show high catalytic activity toward oxygen evolution reaction.

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.

Formation of double layer hollow nanostars of Pd/CuIr by utilizing a Kirkendall effect and a facile Cu atom movement along twinning boundaries and their usage as efficient water splitting catalysts

Hollow nanostructures with an inherent high surface area per mass are attractive candidates as economically viable catalysts. Conceptually, a hollow nanostructure can be obtained by forming a desired material phase on a removable template and then by subsequently removing the template core. We recently reported the synthesis of a core–shell type structure with a Cu-rich core and Ir rich shell. However, the Cu phase could not be removed from the core due to the imperviousness of the single crystalline Ir-rich shell. In order to facilitate the Cu phase removal, we introduced the polycrystalline Pd seed into the growth of the CuIr nanocrystal, which resulted in the formation of Pd@CuIr nanocrystals with multiple radial grain boundaries. By placing the Pd@CuIr nanocrystal under oxidizing conditions, we could initiate the outward movement of the Cu phase along the grain boundaries. Herein we report the synthesis of an unusual bilayer hollow nanostructure with a CuIr surface layer and a Pd inner-coating layer, following a facile CuPd alloy phase formation and an outward movement of the Cu phase under oxidizing conditions. We also report the high catalytic performance of the hollow nanostructure in oxygen evolution reaction (OER).

Morphological evolution of 2D Rh nanoplates to 3D Rh concave nanotents, hierarchically stacked nanoframes, and hierarchical dendrites

Impurity doping has yielded a number of useful optical and catalytic alloy nanoparticles, by providing synthetic routes to unprecedented nanostructures. However, Zn is difficult to use as a dopant in alloy nanoparticles due to the difficulty in reduction, and therefore little has been reported on Zn-doped alloy nanoparticles and their potential applications. Herein we report an unusual role of the dopant Zn as a crystal growth modifying agent to cause the formation of novel concave Rh nanostructures, namely nanotents. We could further prepare unprecedented hierarchically stacked Rh nanoframes and dendritic nanostructures derived from them by understanding the role of various surface-stabilizing moieties. We also report the usage of new Rh nanostructures in selective hydrogenation of phthalimides.

Synthesis of size-controlled PtCu@Ru nanorattles via Pt seed-assisted formation of size-controlled removable Cu template

A facile synthetic strategy has been developed for size-controlled PtCu@Ru nanorattles via co-decomposition of Ru and Cu precursors in the presence of Pt nanoparticles. The presence of Pt nanoparticles induces a fast decomposition of Cu precursors, leading to the growth of the Cu phase on the Pt seeds. The Pt nanoparticle surface is partially alloyed with the Cu phase to form a PtCu alloy phase. Subsequent decomposition of Ru precursors leads to the formation of the Ru shell. The Cu layer between the core and shell of the intermediate PtCu@Cu@Ru nanoparticle, generated as a kinetic product, is then in situ removed by a CTAB (cetyltrimethylammonium bromide)-induced destabilization process to yield a novel nanorattle structure with a Pt-based core and a porous Ru shell. The diameter of the Ru shell could be conveniently controlled by varying the ratio of employed Cu and Ru precursors.

Plasmon Enhanced Direct Bandgap Emissions in Cu7S4@Au2S@Au Nanorings

Nanostructured copper sulfides, promising earth-abundant p-type semiconductors, have found applications in a wide range of fields due to their versatility, tunable low bandgap, and environmental sustainability. The synthesis of hexagonal Cu7 S4 @Au2 S@Au nanorings exhibiting plasmon enhanced emissions at the direct bandgap is reported. The synthesized Cu7 S4 @Au2 S@Au nanorings show greatly enhanced absorption and emission by local plasmons compared to pure copper sulfide nanoparticles.

Formation of a Cu@RhRu core–shell concave nanooctahedron via Ru-assisted extraction of Rh from the Cu matrix and its excellent electrocatalytic activity toward the oxygen evolution reaction

A facile one step route has been developed for the synthesis of trimetallic Cu@RhRu core-shell concave nanooctahedra by co-decomposition of Ru, Rh and Cu precursors. A mechanistic study reveals that nanoparticles with a CuRh alloy core and a Ru shell are initially formed and a subsequent migration of Rh to the shell results in the Cu@RhRu core-shell concave nanooctahedron. The shell exhibits atomically mixed Ru and Rh phases with an fcc atomic structure, although the hcp atomic structure is commonly found for the bulk Ru. We also report an unusually high catalytic activity of the Cu@RhRu octahedral nanocrystals toward the oxygen evolution reaction in alkaline solution.