Jongsik Park

Iridium-Based Multimetallic Nanoframe@Nanoframe Structure: An Efficient and Robust Electrocatalyst toward Oxygen Evolution Reaction

Nanoframe electrocatalysts have attracted great interest due to their inherently high active surface area per a given mass. Although recent progress has enabled the preparation of single nanoframe structures with a variety of morphologies, more complex nanoframe structures such as a double-layered nanoframe have not yet been realized. Herein, we report a rational synthetic strategy for a structurally robust Ir-based multimetallic double-layered nanoframe (DNF) structure, nanoframe@nanoframe. By leveraging the differing kinetics of dual Ir precursors and dual transition metal (Ni and Cu) precursors, a core-shell-type alloy@alloy structure could be generated in a simple one-step synthesis, which was subsequently transformed into a multimetallic IrNiCu DNF with a rhombic dodecahedral morphology via selective etching. The use of single Ir precursor yielded single nanoframe structures, highlighting the importance of employing dual Ir precursors. In addition, the structure of Ir-based nanocrystals could be further controlled to DNF with octahedral morphology and CuNi@Ir core-shell structures via a simple tuning of experimental factors. The IrNiCu DNF exhibited high electrocatalytic activity for oxygen evolution reaction (OER) in acidic media, which is better than Ir/C catalyst. Furthermore, IrNiCu DNF demonstrated excellent durability for OER, which could be attributed to the frame structure that prevents the growth and agglomeration of particles as well as in situ formation of robust rutile IrO2 phase during prolonged operation.

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.

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.

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.

Radially Phase Segregated PtCu@PtCuNi Dendrite@Frame Nanocatalyst for the Oxygen Reduction Reaction

Pt-based alloy nanoframes have shown great potential as electrocatalysts toward the oxygen reduction reaction (ORR) in fuel cells. However, the intrinsically infirm nanoframes could be severely deformed during extended electro-cyclings, which eventually leads to the loss of the initial catalytic activity. Therefore, the structurally robust nanoframe is a worthy synthetic target. Furthermore, ternary alloy phase electrocatalysts offer more opportunities in optimizing the stability and activity than binary alloy ones. Herein, we report a robust PtCuNi ternary nanoframe, structurally fortified with an inner-lying PtCu dendrite, which shows a highly active and stable catalytic performance toward ORR. Remarkably, the PtCu@PtCuNi catalyst exhibited 11 and 16 times higher mass and specific activities than those of commercial Pt/C.

Synthesis of bare Pt3Ni nanorods from PtNi@Ni core–shell nanorods by acid etching: one-step surfactant removal and phase conversion for optimal electrochemical performance toward oxygen reduction reaction

Pt–Ni alloy, most notably Pt3Ni phase, nanoparticles synthesized using a surfactant-assisted solution phase route have shown great promise as electrocatalysts toward the oxygen reduction reaction (ORR) for fuel cells. Surfactant removal without deteriorating the catalytic performance of alloy nanocrystals has been an ongoing issue in this research area. Herein, we report a convenient preparation route to surfactant-free Pt3Ni nanorods from PtNi@Ni nanorods assisted by acid etching as well as their excellent electrocatalytic activity for ORR.

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.

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.

Unexpected solution phase formation of hollow PtSn alloy nanoparticles from Sn deposition on Pt dendritic structures

Hollow nanoparticles with a high surface-to-volume ratio have found various applications in catalysis, sensors, and energy storage, and thus new synthetic routes to these structures are of great interest. One of the best-known synthetic routes to hollow nanostructures is the utilization of the Kirkendall effect, which, however, is not useful for systems with a slow diffusing-out core such as Pt and fast diffusing-in surface elements such as Sn. Herein, we report a counterintuitive formation of hollow PtSn nanostructures by reacting dendritic Pt nanostructures with Sn precursors.