Xiangcun Li

Electrodeposition of high-capacitance 3D CoS/graphene nanosheets on nickel foam for high-performance aqueous asymmetric supercapacitors

Electrochemical energy storage devices that encompass the capability of offering both excellent capacitance and rate performance have always be in high demand. Herein, we present a simple and green two-step electrodeposition process to fabricate a high-performance 3D CoS/graphene hybrid network with a nanosheet structure on Ni foam. The nanosheet-like CoS is tightly wrapped and anchored by the graphene layer and the two different material species are nicely integrated together, leading to increased conductivity and enlarged electroactive surface area of the electrode materials. The CoS/graphene composites exhibit an impressive specific capacitance of 3785 F g−1 at a current density of 1 A g−1, a favorable rate capability with 82% retention at 20 A g−1. A CoS/graphene‖activated carbon asymmetric supercapacitor fabricated in 2 M KOH solution exhibits a maximum energy density of 29 Wh kg−1 at the power density of 800 W kg−1, and a power density of 40.0 kW kg−1 (at the energy density of 11.0 Wh kg−1). Furthermore, 70% capacitance retention was obtained after 10 000 cycles within the potential window of 0–1.6 V. The excellent performance of the CoS/graphene composites demonstrated in this work has revealed the promising potential of adopting the CoS/graphene hybrid network for high performance supercapacitors.

Synthesis and morphology control of ZnO nanostructures in microemulsions

ZnO nanostructures with different morphologies and optical properties were prepared by a simple microemulsion process, and PEG400 was used as a directing agent. The samples were characterized by TEM, XRD, FTIR, and TG-DTA analysis. The XRD spectra indicate that the ZnO crystal has a hexagonal wurtzite structure. Needle-like, columnar, and spherical ZnO samples were synthesized respectively with the increase of PEG400 concentration in Zn(NO(3))(2) solution. TEM images and thermogravimetric analysis reveal that the microemulsion interface and the PEG400 agent have a synergistic effect on the morphology and crystalline size transition of ZnO nanostructures. The optical properties of the samples were investigated by measuring the UV-Vis absorbance spectra at room temperature. All the samples exhibit strong UV absorption at around 365 nm. ZnO products with band gap energies at 3.06, 3.02, 2.95, and 2.85 eV were obtained with 0, 12.5, 25.0, and 50.0% of PEG400 in Zn(NO(3))(2) solution, respectively. The formation mechanism of the ZnO nanostructures was proposed and discussed in detail. The synergistic control of the microemulsion interface and the agent on the growth of crystal nuclei reported here provides an alternative approach for preparation of other well-defined nanostructures.

The Synthesis of Mesoporous TiO2/SiO2/Fe2O3 Hybrid Particles Containing Micelle- Induced Macropores through an Aerosol Based Process

Mesoporous SiO(2)/TiO(2)/Fe(2)O(3) particles containing macropores of about 50 nm in diameter have been prepared by an aerosol process using cetyltrimethylammonium bromide (CTAB) as a templating agent. In contrast to the traditional templating effect of CTAB to form ordered mesoporous silicas, the morphology here is vastly different due to the presence of precursor iron salts. The particles have mesoporosity templated by CTAB but additionally have large voids leading to a combined macroporous and mesoporous structure. The morphology is explained through the formation of colloidal structures containing species such as CTA(+)X(-1)Fe(3+) colloids in the aerosol droplets, indicating of a salt bridging effect. This dual porosity has applied implications, as the macropores provide easy entry to the particle interior in potentially diffusion limited situations. Furthermore, the particles encapsulate Fe(2)O(3) and contain TiO(2) leading to the dual functional properties of magnetic response and photocatalytic activity.

Multishelled Nickel-Cobalt Oxide Hollow Microspheres with Optimized Compositions and Shell Porosity for High-Performance Pseudocapacitors.

Nickel-cobalt oxides/hydroxides have been considered as promising electrode materials for a high-performance supercapacitor. However, their energy density and cycle stability are still very poor at high current density. Moreover, there are few reports on the fabrication of mixed transition-metal oxides with multishelled hollow structures. Here, we demonstrate a new and flexible strategy for the preparation of hollow Ni-Co-O microspheres with optimized Ni/Co ratios, controlled shell porosity, shell numbers, and shell thickness. Owing to its high effective electrode area and electron transfer number (n(3/2) A), mesoporous shells, and fast electron/ion transfer, the triple-shelled Ni-Co1.5-O electrode exhibits an ultrahigh capacitance (1884 F/g at 3A/g) and rate capability (77.7%, 3-30A/g). Moreover, the assembled sandwiched Ni-Co1.5-O//RGO@Fe3O4 asymmetric supercapacitor (ACS) retains 79.4% of its initial capacitance after 10 000 cycles and shows a high energy density of 41.5 W h kg(-1) at 505 W kg(-1). Importantly, the ACS device delivers a high energy density of 22.8 W h kg(-1) even at 7600 W kg(-1), which is superior to most of the reported asymmetric capacitors. This study has provided a facile and general approach to fabricate Ni/Co mixed transition-metal oxides for energy storage.

Shear Induced Formation of Patterned Porous Titania with Applications to Photocatalysis

Patterned macroporous titania (TiO2) materials have been synthesized via a shear-aligned rigid crystalline surfactant mesophase. The macropores inherit the hexagonal geometry of the water channels of the template. Scanning electron microscopy (SEM) and cut-section transmission electron microscopy (TEM) images show that the macropores templated by the sheared mesophase attain considerably greater alignment than pores templated by the nonsheared mesophase. The mean pore diameter, the crystalline size of TiO2 particles, and the photoactivity of the materials increase with the increase of water content in the template. The sheared TiO2 samples exhibit higher photocatalytic activity for the degradation of Rhodamine B than the corresponding materials synthesized in the nonsheared template. The improvement in photocatalytic activity of the sheared TiO2 materials is attributed to its higher photoabsorption efficiency and the patterned channels which facilitate the diffusion and transport of reactant molecules within the frameworks. Such patterned porous materials may have promise as advanced catalytic supports and photocatalytic materials.

Magnetic titania-silica composite–Polypyrrole core–shell spheres and their high sensitivity toward hydrogen peroxide as electrochemical sensor

A novel core-shell sphere with controlled shell thickness was synthesized by in situ chemical oxidative polymerization of pyrrole on FTS (Fe(2)O(3)/TiO(2)/SiO(2) composite) surface. The dual porosity of 2-3 nm and 40-50 nm in FTS core particle provides the hybrids with a high surface area to volume ratio, which enormously facilitates the molecule diffusion process. Furthermore, the porous FTS particle encapsulate Fe(2)O(3) and TiO(2) leading to its synergetic interaction with the PPy coating based on FTIR analysis. The unique structure and composition of the hybrid spheres result in new sensing property that is not available from their single counterparts. Cyclic voltammetry results demonstrate that the spheres with appropriate concentration of PPy exhibit enhanced electrocatalytic activity toward the reduction of H(2)O(2) in 0.1 M phosphate buffer solution. The sensing performance tests show that the hybrids possess good linear response in wide H(2)O(2) concentration range (10-4000 μM) and high sensitivity to H(2)O(2) (0.653 AM(-1) cm(-2)) at room temperature. The formation mechanism of the spheres was proposed based on the fact that the FTS core was coated firstly by a smooth PPy layer and then PPy nanoparticles. The work reported here provides an alternative concept for preparation of functional materials with new nanostructures and properties.

Multishelled NiO Hollow Microspheres for High-performance Supercapacitors with Ultrahigh Energy Density and Robust Cycle Life.

Multishelled NiO hollow microspheres for high-performance supercapacitors have been prepared and the formation mechanism has been investigated. By using resin microspheres to absorb Ni2+ and subsequent proper calcinations, the shell numbers, shell spacing and exterior shell structure were facilely controlled via varying synthetic parameters. Particularly, the exterior shell structure that accurately associated with the ion transfer is finely controlled by forming a single shell or closed exterior double-shells. Among multishelled NiO hollow microspheres, the triple-shelled NiO with an outer single-shelled microspheres show a remarkable capacity of 1280 F g−1 at 1 A g−1, and still keep a high value of 704 F g−1 even at 20 A g−1. The outstanding performances are attributed to its fast ion/electron transfer, high specific surface area and large shell space. The specific capacitance gradually increases to 108% of its initial value after 2500 cycles, demonstrating its high stability. Importantly, the 3S-NiO-HMS//RGO@Fe3O4 asymmetric supercapacitor shows an ultrahigh energy density of 51.0 Wh kg−1 at a power density of 800 W kg−1, and 78.8% capacitance retention after 10,000 cycles. Furthermore, multishelled NiO can be transferred into multishelled Ni microspheres with high-efficient H2 generation rate of 598.5 mL H2 min−1 g−1Ni for catalytic hydrolysis of NH3BH3 (AB).

Highly Active Nanoreactors: Patchlike or Thick Ni Coating on Pt Nanoparticles Based on Confined Catalysis.

Catalyst-containing nanoreactors have attracted considerable attention for specific applications. Here, we initially report preparation of PtNi@SiO2 hollow microspheres based on confined catalysis. The previous encapsulation of dispersed Pt nanoparticles (NPs) in hollow silica microspheres ensures the formation of Pt@Ni coreshell NPs inside the silica porous shell. Thus, the Pt NPs not only catalyze the reduction of Ni ions but also direct Ni deposition on the Pt cores to obtain Pt@Ni core-shell catalyst. It is worthy to point out that this synthetic approach helps to form a patchlike or thick Ni coating on Pt cores by controlling the penetration time of Ni ions from the bulk solution into the SiO2 microspheres (0.5, 1, 2, or 4 h). Notably, the Pt@Ni core-shell NPs with a patch-like Ni layer on Pt cores (0.5 and 1 h) show a higher H2 generation rate of 1221-1475 H2 mL min(-1) g(-1)cat than the Pt@Ni NPs with a thick Ni layer (2 and 4 h, 920-1183 H2 mL min(-1) g(-1)cat), and much higher than that of pure Pt NPs (224 H2 mL min(-1) g(-1)cat). In addition, the catalyst possesses good stability and recyclability for H2 generation. The Pt@Ni core-shell NPs confined inside silica nanocapsules, with well-defined compositions and morphologies, high H2 generation rate, and recyclability, should be an ideal catalyst for specific applications in liquid phase reaction.

Shape-Controlled Synthesis of Magnetic Iron Oxide@SiO2–Au@C Particles with Core–Shell Nanostructures

The preparation of nonspherical magnetic core-shell nanostructures with uniform sizes still remains a challenge. In this study, magnetic iron oxide@SiO2-Au@C particles with different shapes, such as pseduocube, ellipsoid, and peanut, were synthesized using hematite as templates and precursors of magnetic iron oxide. The as-obtained magnetic particles demonstrated uniform sizes, shapes, and well-designed core-shell nanostructures. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) analysis showed that the Au nanoparticles (AuNPs) of ∼6 nm were uniformly distributed between the silica and carbon layers. The embedding of the metal nanocrystals into the two different layers prevented the aggregation and reduced the loss of the metal nanocrystals during recycling. Catalytic performance of the peanut-like particles kept almost unchanged without a noticeable decrease in the reduction of 4-nitrophenol (4-NP) in 8 min even after 7 cycles, indicating excellent reusability of the particles. Moreover, the catalyst could be readily recycled magnetically after each reduction by an external magnetic field.

A highly responsive UV photodetector based on hierarchical TiO2 nanorod/nanoparticle composite

Hierarchical TiO2 nanorod/nanoparticle composites were successfully prepared by TiCl4 modification of vertically aligned TiO2 nanorod (NR) arrays. After the hydrolysis of TiCl4 at room temperature, TiO2 nanoparticles (NPs) were deposited on the surface of TiO2 NRs. Morphology and structure analysis demonstrated that the TiO2 NPs were distributed around the entire surface of TiO2 NRs due to the easy permeation of TiCl4 solution between the NR space. Moreover, the high concentration of TiCl4 and long reaction time are favorable for the generation of more TiO2 NPs, which correspondingly increases the surface area of the composite to a large extent. Compared with most reported TiO2-based UV photodetectors (PDs), the present TiO2 NR/NP composite-based PDs simultaneously exhibit an extremely high response and a relatively fast response speed. The maxima of responsivity and response speed, which are 1973 A W−1 and 0.47 s (rise time) and 1.02 s (decay time), respectively, are obtained from the sample of TiO2 NR/NP-0.4 M-72 h. The fast and high photoresponses are ascribed to the large surface area provided by TiO2 NPs, the well-defined electron transport pathway offered from TiO2 NRs and the homojunction formed at the interface between them. Moreover, together with the high responsivity and the relatively fast response speed, significant UV light selectivity and a very good linear relationship between a photoresponse and the UV light intensity suggest that the present UV PDs are very competitive and highly applicable in UV light detection.