We have rationally synthesized and optimized catalytic nanoparticles consisting of a gold core, covered by a palladium shell, onto which platinum clusters are deposited (Au@Pd@Pt NPs). The amount of Pt and Pd used is extremely small, yet they show unusually high activity for electrooxidation of formic acid. The optimized structure has only 2 atomic layers of Pd and a half-monolayer equivalent of Pt (theta(Pt) approximate to 0.5) but a further increase in the loading of Pd or Pt will actually reduce catalytic activity, inferring that a synergistic effect exists between the three different nanostructure components (sphere, shell and islands). A combined electrochemical, surface-enhanced Raman scattering (SERS) and density functional theory (DFT) study of formic acid and CO oxidation reveals that our core-shell-cluster trimetallic nanostructure has some unique electronic and morphological properties, and that it could be the first in a new family of nanocatalysts possessing unusually high chemical reactivity. Our results are immediately applicable to the design of catalysts for direct formic acid fuel cells (DFAFCs).NSFC[20620130427]; MOST[2007DFC40440]; 973 Program[2009CB930703, 2007CB815303]; ENS; CNRS (UMR, LIA XiamENS)[8640

Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) based on Au@SiO 2 or Au@Al 2 O 3 nanoparticles (NPs)shows great potential to break the long-standing limitations of substrate and surface generality of surface-enhanced Raman scattering (SERS). However, the shell of SiO 2 or Al 2 O 3 can easily be dissolved in alkaline media, which limits the applications of SHINERS in alkaline systems. Besides that, the synthesis of Au@SiO 2 NPs can be further simplified and Au@Al 2 O 3 NPs be replaced by other NPs that are more amenable for mass production. In an attempt to make SHINERS NPs available in any systems practically, we report the synthesis of ultrathin and compact Au@MnO 2 NPs. The shell thickness of MnO 2 can be controlled down to about 1.2 nm without any pinhole. SHINERS based on such Au@MnO 2 NPs exhibits much higher Raman enhancement effect than Au@SiO 2 NPs and can be applied in alkaline systems in which Au@SiO 2 or Au@Al 2 O 3 NPs cannot be applied.

Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.

However, several severe obstacles, particularly the large overpotential and the limited capacity far less than theory, have hindered the practical application of Li-O 2 batteries. [2] Many authors have revealed that the high overpotential of Li-O 2 batteries is mainly attributed to the sluggish oxygen redox kinetics, [2a,3] electrical passivation of the cathode by the poorly conducting Li 2 O 2 , [4] inferior Li 2 O 2 /cathode contact interface, [5] and undesired parasitic reactions. [6] As a gas electrode, two factors, structural factor and catalytic factor, are crucial in the electrochemical performance. Although the two factors are interrelated and interplayed, basically, the structural factor will determine the O 2 electrode capacities and the O 2 active species diffusions, while the catalytic factor will determine the oxygen redox kinetics. In the past few years, tremendous efforts have been devoted to developing effective oxygen cathodes for improving the electrochemical performance of Li-O 2 batteries. [7] A variety of carbon catalysts with well-designed architecture have been proposed to serve as frameworks for insoluble Li 2 O 2 storage mainly for improving the discharge capacity but with very limited overpotential improvement. [7a-e] On the other hand, different kinds of noble metals [7f-i] and transition metal oxides (TMOs) [7j-q] were widely used to reduce the large overpotential of Li-O 2 batteries but with relatively low capacity. In fact, these investigations which only focused on either the structural factor or catalytic factor are not The nonaqueous lithium-oxygen (Li-O 2 ) battery is considered as one of the most promising candidates for next-generation energy storage systems because of its very high theoretical energy density. However, its development is severely hindered by large overpotential and limited capacity, far less than theory, caused by sluggish oxygen redox kinetics, pore clogging by solid Li 2 O 2 deposition, inferior Li 2 O 2 /cathode contact interface, and difficult oxygen transport. Herein, an open-structured Co 9 S 8 matrix with sisal morphology is reported for the first time as an oxygen cathode for Li-O 2 batteries, in which the catalyzing for oxygen redox, good Li 2 O 2 /cathode contact interface, favorable oxygen evolution, and a promising Li 2 O 2 storage matrix are successfully achieved simultaneously, leading to a significant improvement in the electrochemical performance of Li-O 2 batteries. The intrinsic oxygen-affinity revealed by density functional theory calculations and superior bifunctional catalytic properties of Co 9 S 8 electrode are found to play an important role in the remarkable enhancement in specific capacity and round-trip efficiency for Li-O 2 batteries. As expected, the Co 9 S 8 electrode can deliver a high discharge capacity of ≈6875 mA h g −1 at 50 mA g −1 and exhibit a low overpotential of 0.57 V under a cutoff capacity of 1000 mA h g −1 , outperforming most of the current metal-oxide-based cathodes.