Hui-Hui Li

Octahedral PtNi Nanoparticle Catalysts: Exceptional Oxygen Reduction Activity by Tuning the Alloy Particle Surface Composition

We demonstrate how shape selectivity and optimized surface composition result in exceptional oxygen reduction activity of octahedral PtNi nanoparticles (NPs). The alloy octahedra were obtained by utilizing a facile, completely surfactant-free solvothermal synthesis. We show that the choice of precursor ligands controls the shape, while the reaction time tunes the surface Pt:Ni composition. The 9.5 nm sized PtNi octahedra reached a 10-fold surface area-specific (~3.14 mA/cm(Pt)(2)) as well as an unprecedented 10-fold Pt mass based (~1.45 A/mg(Pt)) activity gain over the state-of-art Pt electrocatalyst, approaching the theoretically predicted limits.

Nitrogen-Doped Graphene/ZnSe Nanocomposites: Hydrothermal Synthesis and Their Enhanced Electrochemical and Photocatalytic Activities

Nitrogen-doped graphene (GN) has great potential applications in many fields because doping with nitrogen can alter the electrical properties of graphene. It is still a challenge to develop a convenient method for synthesis of GN sheets. In this paper, we first report the synthesis of a nitrogen-doped graphene/ZnSe nanocomposite (GN-ZnSe) by a one-pot hydrothermal process at low temperature using graphene oxide nanosheets and [ZnSe](DETA)(0.5) nanobelts as precursors. ZnSe nanorods composed of ZnSe nanoparticles were found to deposit on the surface of the GN sheets. The results demonstrated that [ZnSe](DETA)(0.5) nanobelts were used not only as the source of ZnSe nanoparticles but also as the nitrogen source. Interestingly, it was found that the as-prepared nanocomposites exhibit remarkably enhanced electrochemical performance for oxygen reduction reaction and photocatalytic activities for the bleaching of methyl orange dye under visible-light irradiation. This facile and catalyst-free approach for depositing ZnSe nanoparticles onto the graphene sheets may provide an alternative way for preparation of other nanocomposites based on GN sheets under mild conditions, which show their potential applications in wastewater treatment, fuel cells, energy storage, nanodevices, and so on.

Facile synthesis of silver@graphene oxide nanocomposites and their enhanced antibacterial properties

Uniform and water-soluble Ag@reduced graphene oxide (Ag@rGO) nanocomposites can be prepared by a facile approach in the absence of additional reductants, which display much better antibacterial properties than that of pure silver nanoparticles synthesized by microwave irradiation, and an equivalent antibacterial effect in comparison with that of the general antibacterial drug ampicillin. Their skin irritation tests with the use of rat models are taken in order to explore the toxicity of this nanocomposite, which confirm that no oedema or erythema appears on the injured rat skin after exposure to the as-prepared Ag@rGO nanocomposites.

An Efficient CeO2/CoSe2 Nanobelt Composite for Electrochemical Water Oxidation

CeO2 /CoSe2 nanobelt composite for electrochemical water oxidation: A new CeO2 /CoSe2 nanobelt composite is developed as a highly effective water oxidation electrocatalyst by growing CeO2 nanoparticle CoSe2 nanobelts in situ via a simple polyol reduction route. The constructed hybrid catalyst shows extremely high oxgen evolution reaction (OER) activity, even beyond the state-of-the-art RuO2 catalyst in alkaline media.

Ultrathin PtPdTe Nanowires as Superior Catalysts for Methanol Electrooxidation

Ultrathin and ultralong: Highly uniform, ultrathin (diameter 5-7 nm), and ultralong (aspect ratio >10(4)) PtPdTe nanowires (NWs) were synthesized by using a facile method employing Te NWs as both sacrificial templates and reducing agents. Fine-tuning of the molar ratios of Pt and Pd precursors afforded PtPdTe NWs with different compositions and enhanced electroactivity in the methanol oxidation reaction in comparison with a commercial Pt/C catalyst.

Scalable Bromide-Triggered Synthesis of Pd@Pt Core–Shell Ultrathin Nanowires with Enhanced Electrocatalytic Performance toward Oxygen Reduction Reaction

This article reports a novel scalable method to prepare ultrathin and uniform Pd@Pt nanowires (NWs) with controllable composition and shell thickness, high aspect ratio, and smooth surface, triggered by bromide ions via a galvanic replacement reaction between PtCl6(2-) and Pd NWs. It was found that bromide ions played a vital role in initiating and promoting the galvanic reaction. The bromide ions served as capping and oxidized etching agents, counterbalancing the Pt deposition and Pd etching on the surface to give final Pd@Pt core-shell nanostructures. Such a counterbalance and the formation PtBr6(2-) with lower redox potential could lower the reaction rate and be responsible for full coverage of a smooth Pt shell. The full coverage of Pt deposited on Pd NWs is important for the enhancement of the activity and stability, which depend strongly on the Pt content and Pt shell thickness. Significantly, the Pd@Pt NWs with Pt content of 21.2% (atomic ratio) exhibited the highest mass activity (810 mA mg(-1)(Pt)) and specific activity (0.4 mA cm(-2)). Interestingly, the mass activity (1560 mA mg(-1)(Pt)) and specific activity (0.98 mA cm(-2)) of Pd@Pt (21.2%) NWs increased to 2.45 and 1.95 times the initial values after 60k cycles tests, 8.5 and 9.0 times greater than those of Pt/C catalysts. In addition, these ultrathin NW electrocatalysts with large aspect ratio are easy to form into a freestanding film, which improves the mass transport, electrical conductivity, and structure stability.

Ultrathin W18O49 Nanowire Assemblies for Electrochromic Devices

Ordered W18O49 nanowire thin films were fabricated by Langmuir-Blodgett (LB) technique in the presence of poly(vinyl pyrrolidone) coating. The well-organized monolayer of W18O49 nanowires with periodic structures can be readily used as electrochromic sensors, showing reversibly switched electrochromic properties between the negative and positive voltage. Moreover, the electrochromism properties of the W18O49 nanowire films exhibit significant relationship with their thickness. The coloration/bleaching time was around 2 s for the W18O49 nanowire monolayer, which is much faster than the traditional tungsten oxide nanostructures. Moreover, the nanowire devices display excellent stability when color switching continues, which may provide a versatile and promising platform for electrochromism device, smart windows, and other applications.

Remarkable enhancement of electrocatalytic activity by tuning the interface of Pd-Au bimetallic nanoparticle tubes.

The interface, which formed in a bimetallic system, is a critical issue to investigate the fundamental mechanism of enhanced catalytic activity. Here, we designed unsupported Pd-Au bimetallic nanoparticle tubes with a tunable interface, which was qualitatively controlled by the proportion of Pd and Au nanoparticles (NPs), to demonstrate the remarkably enhanced effect of Pd and Au NPs in electro-oxidation of ethanol. The results demonstrated that the electrocatalytic activity is highly relative to the interface and has no direct relation with individual metal component in the Pd-Au system. This effect helps us in achieving a fundamental understanding of the relationship between their activity and the interface structure and chemical properties and, consequently, is helpful in designing new catalysts with high performances.

Large scale restructuring of porous Pt-Ni nanoparticle tubes for methanol oxidation: A highly reactive, stable, and restorable fuel cell catalyst

We report a large scale restructuring of porous Pt-Ni nanoparticle tubes for electrocatalytic oxidation of methanol, showing high catalytic activity, stability and resistance to poisoning. The surface restructuring highly improved the electrochemical active surface area (ECSA) by potential cycling in a strong acid electrolyte at room temperature. After a long-time stability test, the ECSA can be restored to its initial value after another potential cycling, thus this kind of electrocatalyst shows the potential possibility for next-generation highly restorable catalysts in direct methanol fuel cells.

Ternary heterostructured nanoparticle tubes: a dual catalyst and its synergistic enhancement effects for O2/H2O2 reduction.

The ability to control the chemical composition and the interface structure of multicomponent heterogeneous metallic catalysts without the support of porous carbon materials and foreign oxides is a challenging catalyst design area and can be aided by understanding the respective function of the metallic components. Generally, the alloy surface has an unusual electronic structure and arrangement of surface atoms in the near-surface region. A monolayer of noble metals, such as Pt or Pd, deposited on a host metal or alloy may induce strain and ligand effects, which can improve the activities. The promising strategies to change activities concern introducing a guest metal to form near-surface alloys and heterogeneous interfaces that endow the surface and interface with improved catalytic properties. However, the active metals, including Au, Fe, Ni, Cu, are usually alloyed or protected by noble metal layer, the naked-state effect of these active metals on the catalytic activity is unknown, but it is fascinating because of the unique interface and different oxidation state of the active metal. Recently, some research work focused on the unique catalytic activity of dispersed metal nanoparticles supported on oxides and the metal/oxide support interface boundary sites has provided evidence for the enhancement of the catalytic activity. However, these support oxides are usually impossible to reverse, which means that the oxides cannot be reduced into metallic state, and the oxidation state cannot be adjusted. Herein, we describe a Pd-Au/CuO@Cu heterostructured nanoparticle tube (HNT) catalyst, in which the CuO layer can be formed at lower potential when a metal (gold) component is added into the bimetallic PdCu system. The CuO layer formation is aided by the potential difference of the Au/Cu system. At negative potential, the CuO layer can be reduced and the PdAuCu catalyst is restored. The PdAuCu HNT was synthesized by a facile, nonaqueous solution electrodeposition method. Unlike the seeded-growth method or metallic-precursor reduction for the synthesis of heterostructure nanoparticle materials, which require a mass of surfactants that will hinder the catalytic activity of metal surface, this strategy just uses dimethyl sulfoxide (DMSO) as a solvent and as a surfactant, which is bound to the metal surface by the sulfur atom in an inverted pyramid configuration and can be washed away easily owing to it weak absorption on the surface. We synthesized a family of PdAuCu HNT catalysts by a one-step electrodeposition route onto an anodic aluminum oxide (AAO) template in anhydrous DMSO solution without the addition of any other surfactants (see Supporting Information). The aim of designing a tubular structure is to enhance the performance durability, eliminate the supporteffect problem, and relax the Ostwald ripening and aggregation in contrast to the situation for particles. The scanning electron microscopy (SEM) images in Figures 1a and 1b show that the as-synthesized PdAuCu HNTs have lengths of several micrometers and a diameter of about 300 nm. The PdAuCu HNTs were completely dispersed and provided a three-dimensional space for the mass transfer of O2 and H2O2 molecules. A typical transmission electron microscopy