Pengxian Han

Nitrogen-doped graphene nanosheets with excellent lithium storage properties

In this work, nitrogen-doped graphene nanosheets serving as lithium storage materials are presented. The nitrogen-doped graphene nanosheets were prepared by heat treatment of graphite oxide under an ammonia atmosphere at 800 degrees C for 2 h. Scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were employed to characterize the prepared product as nitrogen-doped graphene nanosheets with a doping level of ca. 2% nitrogen, where the N binding configuration of the graphene includes 57.4% pyridinic, 35.0% pyrrolic and 7.6% graphitic N atoms. Galvanostatic charge/discharge experiments revealed that these nitrogen-doped graphene nanosheets exhibited a high reversible capacity (900 mA h g(-1) at 42 mA g(-1) (1/20 C)), excellent rate performance (250 mA h g(-1) at a current density of 2.1 A g(-1) (2.5 C)), and significantly enhanced cycling stability, which demonstrated nitrogen-doped graphene nanosheets to be a promising candidate for anode materials in high rate lithium-ion batteries.

Synthesis of Nitrogen-Doped MnO/Graphene Nanosheets Hybrid Material for Lithium Ion Batteries

Nitrogen-doped MnO/graphene nanosheets (N-MnO/GNS) hybrid material was synthesized by a simple hydrothermal method followed by ammonia annealing. The samples were systematically investigated by X-ray diffraction analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy. N-doped MnO (N-MnO) nanoparticles were homogenously anchored on the thin layers of N-doped GNS (N-GNS) to form an efficient electronic/ionic mixed conducting network. This nanostructured hybrid exhibited a reversible electrochemical lithium storage capacity as high as 772 mAh g(-1) at 100 mA g(-1) after 90 cycles, and an excellent rate capability of 202 mA h g(-1) at a high current density of 5 A g(-1). It is expected that N-MnO/GNS hybrid could be a promising candidate material as a high capacity anode for lithium ion batteries.

One dimensional MnO2/titanium nitride nanotube coaxial arrays for high performance electrochemical capacitive energy storage

One dimensional MnO2/titanium nitride nanotube coaxial arrays have been designed for a high performance electrochemical capacitive energy storage system based on the concept of fabricating an efficient, fast charge separation network. This nanostructured composite material was prepared by electrodepositing mesoporous MnO2 into TiN nanotube arrays (TiN NTA), which are prepared by anodization of a Ti foil substrate and subsequent nitridation using ammonia annealing. The electrodeposited mesoporous MnO2 inside the electrically conductive framework of a TiN nanotube has been found to show high specific capacitance (681.0 F g−1 at 2 A g−1), excellent rate capability (55% capacitance retention from 2 to 2000 mV s−1), and a long cycle life (3% capacitance loss after 1000 cycles). These results demonstrate that this coaxial composite nanostructure is very promising for high performance supercapacitors.

Graphene oxide nanosheets/multi-walled carbon nanotubes hybrid as an excellent electrocatalytic material towards VO2+/VO2+ redox couples for vanadium redox flow batteries

A graphene oxide nanosheets/multi-walled carbon nanotubes (GO/MWCNTs) hybrid with excellent electrocatalytic redox reversibility towards VO2+/VO2+ redox couples for vanadium redox flow batteries (VRFB) has been prepared by an electrostatic spray technique after efficient ultrasonic treatment. The structures and electrochemical properties of GO/MWCNTs are investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and cyclic voltammetry. GO/MWCNTs are shown to be cross-linked and form an electrocatalytic hybrid with an effective mixed conducting network, leading to efficiently fast ion and electron transport characteristics. Compared with the pure GO nanosheets and MWCNTs, GO/MWCNTs deliver a much better electrocatalytic redox reversibility towards the positive VO2+/VO2+ couple, especially for the reduction from VO2+ to VO2+. The excellent experimental results demonstrate that the newly developed hybrid material holds great promise in the application of VRFB.

Coaxial NixCo2x(OH)(6x)/TiN Nanotube Arrays as Supercapacitor Electrodes

NixCo2x(OH)6x, as a precursor of intensively studied NiCo2O4, has been directly deposited into self-standing titanium nitride nanotube array (TiN NTA) grid monolithic supports to form a coaxial nanostructured electrode for supercapacitors. With TiN NTA substrates providing a large surface area, fast electron transport, and enhanced structure stability, this NixCo2x(OH)6x/TiN electrode exhibits superior pseudocapacitive performance with a high specific capacitance of 2543 F g(-1) at 5 mV s(-1), remarkable rate performance of 660 F g(-1) even at 500 mV s(-1), and promising cycle performance (about 6.25% capacitance loss for 5000 cycles). Interestingly, the NixCo2x(OH)6x/TiN NTA electrode outperforms the NiCo2O4/TiN NTA electrode, indicating that this self-standing NixCo2x(OH)6x/TiN NTA monolith is a promising candidate for high-performance supercapacitor applications.

Mesoporous Coaxial Titanium Nitride-Vanadium Nitride Fibers of Core–shell Structures for High-Performance Supercapacitors

In this study, titanium nitride-vanadium nitride fibers of core-shell structures were prepared by the coaxial electrospinning, and subsequently annealed in the ammonia for supercapacitor applications. These core-shell (TiN-VN) fibers incorporated mesoporous structure into high electronic conducting transition nitride hybrids, which combined higher specific capacitance of VN and better rate capability of TiN. These hybrids exhibited higher specific capacitance (2 mV s(-1), 247.5 F g(-1)) and better rate capability (50 mV s(-1), 160.8 F g(-1)), which promise a good candidate for high-performance supercapacitors. It was also revealed by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) characterization that the minor capacitance fade originated from the surface oxidation of VN and TiN.

Facile Preparation of Mesoporous Titanium Nitride Microspheres for Electrochemical Energy Storage

In this study, mesoporous TiN spheres with tunable diameter have been fabricated via a facile template-free strategy. Under ammonia atmosphere, mesoporous TiO₂ spheres are directly converted into mesoporous TiN spheres with the addition of cyanamide to retain the original morphology. The electrochemical performance of the resultant mesoporous TiN spheres demonstrates that this material can be a promising electrode material for nonaqueous supercapacitors with high energy densities.

Molybdenum nitride based hybrid cathode for rechargeable lithium-O2 batteries

Molybdenum nitride/nitrogen-doped graphene nanosheets (MoN/NGS) are synthesized and used as an alternative O(2) electrode for Li-O(2) batteries. In comparison with electrocatalysts proposed previously, this hybrid cathode exhibits a high discharge potential (around 3.1 V) and a considerable specific capacity (1490 mA h g(-1), based on carbon + electrocatalyst).

Nanostructured Titanium Nitride/PEDOT:PSS Composite Films As Counter Electrodes of Dye-Sensitized Solar Cells

The composite films of titanium nitride in conjunction with polystyrenesulfonate-doped poly (3,4-ethylene-dioxythiophene) (PEDOT:PSS) were prepared by a simple mechanical mixture of TiN and PEDOT:PSS under ultrasonication, which was demonstrated to deliver an effectively combined network of both high electrical conductivity and superior electrocatalytic activity. The composite films have been explored as an alternative for the counter electrodes of dye-sensitized solar cells. It was manifested that these nanostructured TiN-PEDOT:PSS composite films displayed excellent performance comparable to Pt-FTO counter electrode due to the combined network endowing more favorable and efficient interfacial active sites. Among them, the energy conversion efficiency of the cell with TiN(P)-PEDOT:PSS as counter electrode reached 7.06%, which was superior to 6.57% of the cell with Pt-FTO counter electrode under the same experimental conditions.

A hybrid material of vanadium nitride and nitrogen-doped graphene for lithium storage

Vanadium nitride and nitrogen-doped graphene nanosheet (G) hybrid materials were prepared by a facile sol–gel method combined with a thermal treatment at 800 °C under ammonia atmosphere. It was found that VN nanoparticles adhered to the surface of nitrogen-doped graphene nanosheets and/or were embedded in the graphene layers of the hybrid material (VN-G). This nanostructured material promises an efficient electronic and ionic conducting network, which exhibits dramatically increased specific capacities after rate capability test in comparison to the original value under the same current density. The most probable explanations for these distinct characteristics are deduced from observations by advanced transmission electron microscopy together with X-ray diffraction and electron energy-loss spectroscopy, which illustrate a gradual activation of nitride during lithiation/delithiation processes, owing to slow kinetics of VN reaction with lithium. The electrochemical results demonstrate that the weight ratio of VN to G has a significant effect on the performance and related kinetics of the materials.