Synthesis of composition-tunable octahedral Pt–Cu alloy nanocrystals by controlling reduction kinetics of metal precursors

Facile synthesis of clean PtAg dendritic nanostructures with enhanced electrochemical properties

PtAg dendritic nanocrystals were synthesized by a one-step and surfactant-free route and exhibited excellent activities in both MOR and ORR.

Monocrystalline platinum-nickel branched nanocages with enhanced catalytic performance towards the hydrogen evolution reaction

Single crystalline noble metal nanocages are the most promising candidates for heterogeneous catalysis due to their large specific surface area, well-defined structure and enhanced structural stability. Herein, based on the observation of an unexpected phenomenon that the alloying of Pt and transition metals by co-reduction is more preferential than the formation of pure Pt NCs, we propose a feasible one-pot strategy to synthesize a uniformly epitaxial core-shell Pt-Ni structure with a Ni-rich alloy as the core and a Pt-rich alloy as the shell. The as-prepared Pt-Ni core-shell structures are subsequently etched into monocrystalline Pt-Ni branched nanocages with the wall thickness being 2.8 nm. This unique structure exhibits excellent catalytic performance and stability for the hydrogen evolution reaction (HER) in alkaline solution which is of great significance for the energy-intensive water-alkali and chlor-alkali industry.

Surfactant dependent evolution of Au-Pd alloy nanocrystals from trisoctahedron to excavated rhombic dodecahedron and multipod: a matter of crystal growth kinetics

In wet chemical syntheses of noble metal nanocrystals, surfactants play crucial roles in regulating their morphology. To date, more attention has been paid to the effect of the surfactant on the surface energy of crystal facets, while less attention has been paid to its effect on the growth kinetics. In this paper, using the growth of Au-Pd alloy nanocrystals as an example, we demonstrate that different concentration of surfactant hexadecyltrimethyl ammonium chloride (CTAC) may cause the different packing density of CTA⁺ bilayers on different sites (face, edge or vertex) of crystallite surface, which would change the crystal growth kinetics and result in preferential crystal growth along the edge or vertex of crystallites. The unique shape evolution from trisoctahedron to excavated rhombic dodecahedron and multipod structure for Au-Pd alloy nanocrystals was successfully achieved by simply adjusting the concentration of CTAC. These results help to understand the effect of surfactants on the shape evolution of nanocrystals and open up avenues to the rational synthesis of nanocrystals with the thermodynamically unfavorable morphologies.

Platinum-nickel alloy excavated nano-multipods with hexagonal close-packed structure and superior activity towards hydrogen evolution reaction

Crystal phase regulations may endow materials with enhanced or new functionalities. However, syntheses of noble metal-based allomorphic nanomaterials are extremely difficult, and only a few successful examples have been found. Herein, we report the discovery of hexagonal close-packed Pt-Ni alloy, despite the fact that Pt-Ni alloys are typically crystallized in face-centred cubic structures. The hexagonal close-packed Pt-Ni alloy nano-multipods are synthesized via a facile one-pot solvothermal route, where the branches of nano-multipods take the shape of excavated hexagonal prisms assembled by six nanosheets of 2.5 nm thickness. The hexagonal close-packed Pt-Ni excavated nano-multipods exhibit superior catalytic property towards the hydrogen evolution reaction in alkaline electrolyte. The overpotential is only 65 mV versus reversible hydrogen electrode at a current density of 10 mA cm^-2, and the mass current density reaches 3.03 mA μgPt^-1 at -70 mV versus reversible hydrogen electrode, which outperforms currently reported catalysts to the best of our knowledge.

Facet Energy versus Enzyme-like Activities: The Unexpected Protection of Palladium Nanocrystals against Oxidative Damage

To develop nanomaterials as artificial enzymes, it is necessary to better understand how their physicochemical properties affect their enzyme-like activities. Although prior research has demonstrated that nanomaterials exhibit tunable enzyme-like activities depending on their size, structure, and composition, few studies have examined the effect of surface facets, which determine surface energy or surface reactivity. Here, we use electron spin-resonance spectroscopy to report that lower surface energy {111}-faceted Pd octahedrons have greater intrinsic antioxidant enzyme-like activity than higher surface energy {100}-faceted Pd nanocubes. Our in vitro experiments found that those same Pd octahedrons are more effective than Pd nanocubes at scavenging reactive oxygen species (ROS). Those reductions in ROS preserve the homogeneity of mitochondrial membrane potential and attenuate damage to important biomolecules, thereby allowing a substantially higher number of cells to survive oxidative challenges. Our computations of molecular mechanisms for the antioxidant activities of {111}- and {100}-faceted Pd nanocrystals, as well as their activity order, agree well with experimental observations. These findings can guide the design of antioxidant-mimicking nanomaterials, which could have therapeutic or preventative potential against oxidative stress related diseases.

Free-standing iridium and rhodium-based hierarchically-coiled ultrathin nanosheets for highly selective reduction of nitrobenzene to azoxybenzene under ambient conditions

The fabrication of atom-layered two dimensional (2D) noble metal nanosheets (NSs) in a face-centered cubic (fcc) structure is of broad scientific and technological importance, yet this remains a challenge due to the intrinsic cubic symmetry and high surface energy of fcc noble metals. Herein, we report a solid-liquid interface mediated 2D growth method towards the synthesis of hierarchically-coiled ultrathin Ir NSs (thickness <2 nm) and Rh NSs (0.8 nm thick), and bimetallic Ir-Rh NSs (1.2 nm thick) and Pt-Rh NSs (1.2 nm thick) using the benzyl alcohol solvothermal approach. The formation of NSs was attributed to the 2D oriented attachment of tiny seeds through the lateral growth stemming from the abundant defect sites of the seeds produced in the heterogeneous system. The free-standing Ir NSs, Rh NSs and Ir-Rh NSs exhibited high selectivities (from 83.9% to 88.5%) towards the selective reduction of nitrobenzene to azoxybenzene in ethanol at room temperature with 1 atm of hydrogen, because the condensation step of nitrosobenzene (PhNO) and phenylhydroxylamine (PhNHOH) was more exothermic than the dissociation step of Ph-NHOH on the (111) facets of the NSs under alkaline conditions, as indicated by density functional theory (DFT) calculations.