Shengjie Peng

Cobalt Sulfide Nanosheet/Graphene/Carbon Nanotube Nanocomposites as Flexible Electrodes for Hydrogen Evolution

Flexible three-dimensional (3D) nanoarchitectures have received tremendous interest recently because of their potential applications in wearable electronics, roll-up displays, and other devices. The design and fabrication of a flexible and robust electrode based on cobalt sulfide/reduced graphene oxide/carbon nanotube (CoS2 /RGO-CNT) nanocomposites are reported. An efficient hydrothermal process combined with vacuum filtration was used to synthesize such composite architecture, which was then embedded in a porous CNT network. This conductive and robust film is evaluated as electrocatalyst for the hydrogen evolution reaction. The synergistic effect of CoS2 , graphene, and CNTs leads to unique CoS2 /RGO-CNT nanoarchitectures, the HER activity of which is among the highest for non-noble metal electrocatalysts, showing 10 mA cm(-2) current density at about 142 mV overpotentials and a high electrochemical stability.

The facile synthesis of hierarchical porous flower-like NiCo2O4 with superior lithium storage properties

In this work, we demonstrate the facile fabrication of 3-dimensional (3D) hierarchical porous flower-like NiCo2O4 and its application as an anode material in high-performance lithium ion batteries (LIBs). The uniform flower-like NiCo2O4 is built from porous nanoplates with thicknesses of approximately 25 nm. A detailed investigation reveals that PVP plays an important role, not only in controlling the formation of the delicate hierarchical flower-like structure, but also in creating the uniform pores of each nanoplate. Furthermore, a possible formation mechanism for this unique structure is proposed based on the experimental results. As a virtue of its beneficial structural features, the as-prepared NiCo2O4 exhibits an enhanced lithium storage capacity and excellent cycling stability (∼939 mA h g−1 at 100 mA g−1 after 60 cycles). This remarkable electrochemical performance can be attributed to the hierarchical structure and sufficient void space within the surface of the nanoplates, which effectively increases the contact area between the active materials and the electrolyte, reducing the Li+ diffusion pathway and buffering the volume change during cycling.

Electrospun Porous NiCo2O4 Nanotubes as Advanced Electrodes for Electrochemical Capacitors

Novel, porous NiCo2O4 nanotubes (NCO-NTs) are prepared by a single-spinneret electrospinning technique followed by calcination in air. The obtained NCO-NTs display a one-dimensional architecture with a porous structure and hollow interiors. The effect of precursor concentration on the morphologies of the products is investigated. Due to their unique structure, the prepared NCO-NT electrode exhibits a high specific capacitance (1647 F g(-1) at 1 A g(-1)), excellent rate capability (77.3 % capacity retention at 25 A g(-1)), and outstanding cycling stability (6.4 % loss after 3000 cycles), which indicates it has great potential for high-performance electrochemical capacitors. The desirable enhanced capacitive performance of NCO-NTs can be attributed to the relatively large specific surface area of these porous and hollow one-dimensional nanostructures.

Ultrathin S-doped MoSe2 nanosheets for efficient hydrogen evolution

We report the synthesis of ultrathin S-doped MoSe2 nanosheets demonstrating enhanced HER catalysis with a low onset overpotential of 90 mV and a Tafel slope of 58 mV per decade. We attribute the improved catalytic effects to the proliferation of unsaturated HER active sites in MoSe2 resulting from S-doping.

Fabrication of spinel one-dimensional architectures by single-spinneret electrospinning for energy storage applications.

A facile and general method is developed to fabricate one-dimensional (1D) spinel composite oxides with complex architectures by using a facile single-spinneret electrospinning technique. It is found that precursor polymers and heating rates could control the structures of the products, such as 1D solid, nanotube and tube-in-tubes structures. Especially, the tube-in-tube structures have been successfully fabricated for various mixed metal oxide, including CoMn2O4, NiCo2O4, CoFe2O4, NiMn2O4 and ZnMn2O4. Benefiting from the unique structure features, the tube-in-tube hollow nanostructures possess superior electrochemical performances in asymmetric supercapacitors and Li-O2 batteries.

Unique Cobalt Sulfide/Reduced Graphene Oxide Composite as an Anode for Sodium-Ion Batteries with Superior Rate Capability and Long Cycling Stability

Exploitation of high-performance anode materials is essential but challenging to the development of sodium-ion batteries (SIBs). Among all proposed anode materials for SIBs, sulfides have been proved promising candidates due to their unique chemical and physical properties. In this work, a facile solvothermal method to in situ decorate cobalt sulfide (CoS) nanoplates on reduced graphene oxide (rGO) to build CoS@rGO composite is described. When evaluated as anode for SIBs, an impressive high specific capacity (540 mAh g(-1) at 1 A g(-1) ), excellent rate capability (636 mAh g(-1) at 0.1 A g(-1) and 306 mAh g(-1) at 10 A g(-1)), and extraordinarily cycle stability (420 mAh g(-1) at 1 A g(-1) after 1000 cycles) have been demonstrated by CoS@rGO composite for sodium storage. The synergetic effect between the CoS nanoplates and rGO matrix contributes to the enhanced electrochemical performance of the hybrid composite. The results provide a facile approach to fabricate promising anode materials for high-performance SIBs.

Controlled Synthesis of BiOCl Hierarchical Self-Assemblies with Highly Efficient Photocatalytic Properties

Herein, we report the controlled synthesis of bismuth oxychloride (BiOCl) hierarchical self-assemblies under hydrothermal conditions and demonstrate their high photocatalytic properties. An interesting morphological evolution from microplates to nanoplate assemblies with microsphere-, microdisk-, and microflower-like structures is investigated by adjusting the amounts of surfactant poly(vinyl pyrrolidone) (PVP). It has been found that three types of three-dimensional (3D) BiOCl micromaterials are formed layer-by-layer from a large number of interconnected 2D nanoplates with a mean side length of about 20 nm. A possible crystal growth and formation mechanism is proposed as a plausible mechanistic interpretation for the self-assembly of nanoplates into the observed microstructures that is based on the detailed experiments. Furthermore, the photocatalytic properties of the obtained samples are investigated by the photodegradation analysis of Rhodamine B and methylene orange (RhB and MO) dyes, thus indicating that the microspherelike BiOCl hierarchical structure has a higher photocatalytic activity than the microdisk-like and microflower-like BiOCl structures, owing to its novel structure with a high surface area. Introduction

Monodispersed Ag nanoparticles loaded on the PVP-assisted synthetic Bi2O2CO3 microspheres with enhanced photocatalytic and supercapacitive performances

Uniform 1 μm-sized Bi2O2CO3 microspheres constructed by nanoplates with a thickness of about 12 nm have been obtained through a facile hydrothermal method. Ag is deposited on the surface of Bi2O2CO3via a subsequent facile photoreduction process. In the synthesis process, polyvinylpyrrolidone (PVP) is used as a reactant that not only provides C and O sources but also serves as a template to induce the nanoplate-assembly to form microspheres. With the addition of KCl in the synthesis, the size of the Bi2O2CO3 microspheres can be reduced from ∼6 μm to ∼1 μm. It is demonstrated that PVP and KCl play key roles in the formation of such hierarchical microspheres. The obtained Bi2O2CO3 and novel Ag/Bi2O2CO3 composites are evaluated for photocatalytic and supercapacitive applications. The test result of the photocatalytic activity demonstrates that 0.6 wt% loading of Ag on the Bi2O2CO3 microspheres exhibits significantly enhanced activity for the photodegradation of methyl orange (MO) dye, compared with Bi2O2CO3. The enhanced photocatalytic activity can be attributed to the Ag deposits acting as electron traps and the high surface area of Bi2O2CO3. Furthermore, the Ag/Bi2O2CO3 composites are primarily evaluated as supercapacitor electrodes, which deliver specific capacities of 620 and 361 F g−1 at current densities of 1 and 5 A g−1, respectively.

Hollow nanospheres constructed by CoS2 nanosheets with a nitrogen-doped-carbon coating for energy-storage and photocatalysis.

Hierarchical CoS2 hollow nanospheres (HSs) with a nitrogen-doped-carbon coating (NC@CoS2 ) are fabricated by a simple solution method. The uniform 300 nm-sized NC@CoS2 HSs are composed of ultrathin nanosheet subunits with a thickness of around 2 nm. It was found that polyvinylpyrrolidone and ethylenediamine not only controlled the morphology of the products, but also provided the sources of nitrogen-doped carbon. Benefiting from their unique structural characteristics, hierarchical NC@CoS2 HSs can be applied in lithium-ion batteries, supercapacitors, and photocatalysis. When evaluated as an electrode material, NC@CoS2 with a coating of optimal thickness showed a high lithium-storage capability with a good cycling stability. Moreover, NC@CoS2 had a remarkable supercapacitive performance and photocatalytic activity. The attractive electrochemical and photocatalytic performances were attributed to the overall structural features of the NC@CoS2 hollow spheres: the N-doped-carbon (NC) coating, hollow interior, and ultrathin nanosheets.

Polypyrrole Nanorod Networks/Carbon Nanoparticles Composite Counter Electrodes for High-Efficiency Dye-Sensitized Solar Cells

Polypyrrole(PPy) nanorod networks with a high electrical conductivity of 40 S cm(-1) have been obtained in a high yield by employing an ion association of heparin-methylene blue as a new morphology-directing agent. The polypyrrole nanorod networks are mixed with different content of carbon nanoparticles to make PPy nanorod networks/carbon nanoparticles(PPy/C) counter electrodes. It is found that the PPy/C composite with 10% carbon content shows a lower charge transfer resistance and better catalytic performance for the reduction of I(3)(-), compared with the pristine PPy and carbon electrodes. The better catalytic performance is attributed to the interaction of the superior electrocatalytic activity of the unique polypyrrole nanorod networks and the carbon nanoparticles, which can accelerate triiodide reduction and electron transfer in the electrode. Under standard AM 1.5 sunlight illumination, the dye-sensitized solar cell based on the PPy/C composite with 10% carbon content as the counter electrode demonstrates a high efficiency of 7.2%, which is much higher than that of pristine PPy and carbon electrode-based DSCs and comparable to that of the thermal decomposed Pt-based DSC.