Xuxu Wang

Synthesis and photoluminescence of single-crystalline In2O3 nanowires

Single-crystalline In2O3 nanowires have been successfully synthesized from indium grains by a vapor–solid method at 1030 °C in 90% Ar and 10% O2 atmosphere. These nanowires are uniform with diameters of 40–120 nm and lengths of about 15–25 µm, and crystallize in a cubic structure. The growth of these nanowires is controlled by a spiral growth mechanism. Photoluminescence (PL) measurements show a green–blue PL band in the wavelength range of 400–700 nm with a peak at 470 nm (2.64 eV), caused by oxygen vacancies in the In2O3 nanowires.

Micro-Raman investigation of GaN nanowires prepared by direct reaction Ga with NH3

Abstract Ordered crystalline GaN nanowires embedded in the nanochannels of anodic alumina membrane (AAM) were achieved by direct reaction Ga with NH 3 . The impact of reaction temperatures on Raman spectroscopic properties of GaN nanowires is investigated. X-ray diffraction and transmission electron microscopy (TEM) observations demonstrate that the crystalline GaN nanowires have hexagonal wurtzite structure. The hexagonal wurtzite structure GaN nanowires prepared at 960 °C are about 40 nm in diameter and up to several hundreds of micrometers in length.

Polymer electrolytes from PEO and novel quaternary ammonium iodides for dye-sensitized solar cells

Polymer electrolytes were prepared by blending high molecular weight poly(ethylene oxide) (PEO) and a series of novel quaternary ammonium iodides, the polysiloxanes with oligo(oxyethylene) side chains and quaternary ammonium groups. X-ray diffraction (XRD) measurements ensured relatively low crystallinity when the quaternary ammonium iodides were incorporated into the PEO host. The ionic conductivity of these complexes was improved with the addition of plasticizers. The improvement in the ionic conductivity was determined by the polarity, viscosity and amounts of plasticizers. A plasticized electrolyte containing the novel quaternary ammonium iodide was successfully used in fabricating a quasi-solid-state dye-sensitized solar cell for the first time. The fill factor and energy conversion efficiency of the cell were calculated to be 0.68 and 1.39%, respectively.

Gel polymer electrolytes based on a novel quaternary ammonium salt for dye-sensitized solar cells

Gel polymer electrolytes were prepared with polyacrylonitrile (PAN) and solutions of a novel quaternary ammonium salt, polysiloxane with quaternary ammonium side groups (PSQAS), in a mixture of ethylene carbonate (EC) and propylene carbonate (PC). The influences of PAN content and salt concentration on the ionic conductivity have been investigated. The ionic conductivity can be further improved with the use of the mixtures of KI and PSQAS, which can be expected as inorganic-organic salts. The gel polymer electrolytes were used in the fabrication of the dye-sensitized solar cells with a nanoporous TiO2 working electrode, cis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) complex dye and a counter electrode based on platinized conducting glass. The cells showed open-circuit voltages (Voc) around 0.6 V and short-circuit current densities (Jsc) larger than 7.5 mA cm−2 under 60 mW cm−2 irradiation. The fill factors (FF) and energy conversion efficiencies (η) of the cells were calculated to be higher than 0.56 and 4.4%, respectively.

Sulfur-impregnated core-shell hierarchical porous carbon for lithium-sulfur batteries.

Core-shell hierarchical porous carbon spheres (HPCs) were synthesized by a facile hydrothermal method and used as host to incorporate sulfur. The microstructure, morphology, and specific surface areas of the resultant samples have been systematically characterized. The results indicate that most of sulfur is well dispersed over the core area of HPCs after the impregnation of sulfur. Meanwhile, the shell of HPCs with void pores is serving as a retard against the dissolution of lithium polysulfides. This structure can enhance the transport of electron and lithium ions as well as alleviate the stress caused by volume change during the charge-discharge process. The as-prepared HPC-sulfur (HPC-S) composite with 65.3 wt % sulfur delivers a high specific capacity of 1397.9 mA h g(-1) at a current density of 335 mA g(-1) (0.2 C) as a cathode material for lithium-sulfur (Li-S) batteries, and the discharge capacity of the electrode could still reach 753.2 mA h g(-1) at 6700 mA g(-1) (4 C). Moreover, the composite electrode exhibited an excellent cycling capacity of 830.5 mA h g(-1) after 200 cycles.

Metal-Organic Framework Template Synthesis of NiCo2S4@C Encapsulated in Hollow Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage

Owing to its richer redox reaction and remarkable electrical conductivity, bimetallic nickel cobalt sulfide (NiCo2S4) is considered as an advanced electrode material for energy-storage applications. Herein, nanosized NiCo2S4@C encapsulated in a hollow nitrogen-doped carbon cube (NiCo2S4@D-NC) has been fabricated using a core@shell Ni3[Co(CN)6]2@polydopamine (PDA) nanocube as the precursor. In this composite, the NiCo2S4 nanoparticles coated with conformal carbon layers are homogeneously embedded in a 3D high-conduction carbon shell from PDA. Both the inner and the outer carbon coatings are helpful in increasing the electrical conductivity of the electrode materials and prohibit the polysulfide intermediates from dissolving in the electrolyte. When researched as electrode materials for lithium storage, owing to the unique structure with double layers of nitrogen-doped carbon coating, the as-obtained NiCo2S4@D-NC electrode maintains an excellent specific capacity of 480 mAh g-1 at 100 mA g-1 after 100 cycles. Even after 500 cycles at 500 mA g-1, a reversible capacity of 427 mAh g-1 can be achieved, suggesting an excellent rate capability and an ultralong cycling life. This remarkable lithium storage property indicates its potential application for future lithium-ion batteries.

Magnetic and microwave-absorption properties of SnO-coated α-Fe(Sn) nanocapsules

A series of SnO-coated alpha-Fe solid-solution nanocapsules were fabricated by a modified arc-discharge technique from Fe(1-x)Sn(x) targets with x = 0, 2, 3, 4 and 5 at%. The core and shells change with changing Sn concentration (0, 2, 3, 4 and 5 at%) in the Fe(1-x)Sn(x) targets used in the preparation. An in-depth study of the complex permittivity and permeability reveals that the SnO-coated alpha-Fe solid-solution nanocapsules with 3 at% Sn exhibit excellent microwave-absorption properties among the present SnO-coated Fe solid-solution nanocapsules, due to a proper electromagnetic match in the microstructure, the strong natural resonance as well as dipolar polarization mechanisms.

Strong Quantum Confinement in Ordered PbSe Nanowire Arrays

Ordered PbSe crystalline nanowire arrays have been successfully fabricated in the nanochannels of porous anodic alumina membrane by direct current electrodeposition. X-ray diffraction and selected area electron diffraction investigations demonstrate that the PbSe nanowires have a uniform cubic structure. Electromicroscopy results show that the nanowires are quite ordered with diameters of about 50 nm and lengths up to 5 micrometers. X-ray energy dispersion analysis indicate that Pb:Se is very close to 1:1. The optical absorption spectrum of these PbSe nanowires show that there exist two peaks at 280 and 434 nm, respectively, attribute to excitonic absorption peaks.

Formation of Mo–Polydopamine Hollow Spheres and Their Conversions to MoO2/C and Mo2C/C for Efficient Electrochemical Energy Storage and Catalyst

Highly uniform hierarchical Mo-polydopamine hollow spheres are synthesized for the first time through a liquid-phase reaction under ambient temperature. A self-assembly mechanism of the hollow structure of Mo-polydopamine precursor is discussed in detail, and a determined theory is proposed in a water-in-oil system. Via different annealing process, these precursors can be converted into hierarchical hollow MoO2 /C and Mo2 C/C composites without any distortion in shape. Owing to the well-organized structure and nanosize particle embedding, the as-prepared hollow spheres exhibit appealing performance both as the anode material for lithium-ion batteries and as the catalyst for hydrogen evolution reaction (HER). Accordingly, MoO2 /C delivers a high reversible capacity of 940 mAh g-1 at 0.1 A g-1 and 775 mAh g-1 at 1 A g-1 with good rate capability and long cycle performance. Moreover, Mo2 C/C also exhibits an enhanced electrocatalytic performance with a low overpotential for HER in both acidic and alkaline conditions, as well as remarkable stability.

Tin dioxide as a high-performance catalyst towards Ce(VI)/Ce(III) redox reactions for redox flow battery applications

A novel SnO2-modified graphite felt electrode with a high-performance and non-precious electrocatalyst of SnO2 deposited onto the graphite felt surface is prepared for cerium-based redox flow batteries (RFBs). Through a facile and one-pot solvothermal route, a thin and uniform SnO2 coating layer could be successfully introduced onto the surfaces of graphite felt fibers for the first time. The electrochemical reactivity of the SnO2 decorated graphite felt toward the redox reactions of Ce(IV)/Ce(III) could be substantially enhanced, which is ascribed to the superior electrocatalytic activity of this SnO2 catalyst. What is more, the undesirable side reaction of oxygen evolution can be suppressed by introducing the SnO2 coating layer that possesses a high oxygen evolution overpotential. The charge/discharge test with the catalyzed electrode exhibits a 41.2% and 25.1% increase in energy efficiency as compared with the pristine graphite felt and acid treated graphite felt at a high current density of 30 mA cm−2. Also, the long-term cycling performance confirms the outstanding stability of the as-prepared SnO2 catalyst enhanced electrode. These results suggest that the graphite felt modified by the low-cost and uniform SnO2 coating layer could serve as a highly promising electrode towards the Ce(IV)/Ce(III) redox couple for cerium-based RFB applications.