Zhangpeng Li

Flexible graphene/MnO2 composite papers for supercapacitor electrodes

Graphene/manganese dioxide (MnO2) composite papers (GMCP) are fabricated via a simple three-step route: preparation of graphene oxide/MnO2 composite (GOMC) dispersion, subsequent vacuum filtration of GOMC dispersion to achieve graphene oxide/MnO2 composite paper (GOMCP), and finally thermal reduction of GOMCP to generate GMCP. The morphology and microstructure of the prepared samples are characterized by field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transformation infrared spectroscopy, thermal gravimetric analysis and X-ray photoelectron spectroscopy. Moreover, as a binder-free and flexible electrode material for supercapacitors, the electrochemical properties of the prepared GMCP are evaluated by cyclic voltammetry and galvanostatic charge/discharge tests. As a result, the specific capacitance of the GMCP with the MnO2 weight ratio of 24% (GMCP-24) reaches 256 F g−1 at a current density of 500 mA g−1 and also shows good cycle stability, indicating a promising potential application as an effective electrode material for supercapacitors.

Electrostatic layer-by-layer self-assembly multilayer films based on graphene and manganese dioxide sheets as novel electrode materials for supercapacitors

A new class of multilayer films was constructed by electrostatic layer-by-layer self-assembly, using poly(sodium 4-styrenesulfonate) mediated graphene sheets (PSS-GS), manganese dioxide (MnO2) sheets, and poly(diallyldimethylammonium) (PDDA) as building blocks. UV-vis spectroscopy, field-emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the microstructures and morphologies of the multilayer films. Capacitive properties of the synthesized multilayer film electrodes were studied using cyclic voltammetry and galvanostatic charge/discharge in 0.1 M Na2SO4 electrolyte. The specific capacitance of the ITO/(PDDA/PSS-GS/PDDA/MnO2)10electrode reached 263 F g−1 at a discharge current density of 0.283 A g−1; moreover, this film electrode also shows a good cyclic stability and high Coulombic efficiency. Anticipatedly, the synthesized multilayer films will find promising applications as a novel electrode material in supercapacitors and other devices in virtue of their outstanding characteristics of controllable capacitance, good cycle stability, low cost and environmentally benign nature.

Simple synthesis of amorphous NiWO4 nanostructure and its application as a novel cathode material for asymmetric supercapacitors.

This study reports a simple synthesis of amorphous nickel tungstate (NiWO4) nanostructure and its application as a novel cathode material for supercapacitors. The effect of reaction temperature on the electrochemical properties of the NiWO4 electrode was studied, and results demonstrate that the material synthesized at 70 °C (NiW-70) has shown the highest specific capacitance of 586.2 F g(-1) at 0.5 A g(-1) in a three-electrode system. To achieve a high energy density, a NiW-70//activated carbon asymmetric supercapacitor is successfully assembled by use of NiW-70 and activated carbon as the cathode and anode, respectively, and then, its electrochemical performance is characterized by cyclic voltammetry and galvanostatic charge-discharge measurements. The results show that the assembled asymmetric supercapacitor can be cycled reversibly between 0 and 1.6 V with a high specific capacitance of 71.1 F g(-1) at 0.25 A g(-1), which can deliver a maximum energy density of 25.3 Wh kg(-1) at a power density of 200 W kg(-1). Furthermore, this asymmetric supercapacitor also presented an excellent, long cycle life along with 91.4% specific capacitance being retained after 5000 consecutive times of cycling.

Fabrication of free-standing graphene/polyaniline nanofibers composite paper via electrostatic adsorption for electrochemical supercapacitors

Flexible graphene sheet (GS)/polyaniline (PANi) nanofibers composite paper was prepared via a facile and fast two-step route composed of electrostatic adsorption between negatively-charged poly(sodium 4-styrenesulfonate) (PSS) mediated GS (coded as PSS-GS) and positively-charged PANi nanofibers and the follow-up vacuum filtration of the as-prepared PSS-GS/PANi nanofibers suspension. By observations of field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM), it is clearly seen that representative and highly ordered layered PSS-GS/PANi composite papers have been achieved and PANi nanofibers are coated by PSS-GS. In addition, the synthesized PSS-GS/PANi composite papers are also characterized by Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy, and the results further confirm the successful synthesis of PSS-GS/PANi composites and the existence of strong interaction between PSS-GS and PANi nanofibers. The most interesting thing is the effective synergy can remarkably improve electrochemical properties of GS by introducing PANi nanofibers, which can ascribe to high surface area of GS and good combination between PSS-GS and PANi nanofibers. The highest specific capacitance of the composites reaches 301 F/g. Thermogravimetry analysis (TGA) indicates that the thermal stability of the PSS-GS/PANi composites is obviously improved compared to the pure PSS-GS and PANi.

One-pot sonochemical preparation of fluorographene and selective tuning of its fluorine coverage

Fluorographene (FG), which inherits the properties of graphene and fluorographite (FGi), holds great promise for applications in high-performance materials and devices, including lubricants, nanocomposites, batteries, and nanoelectronics. However, challenges for realizing large-scale preparation and little knowledge concerning FGs physicochemical properties hinder its practical applications. Here, a novel and feasible method is developed to prepare FG through a simple sonochemical exfoliation process in N-methyl-2-pyrrolidone (NMP). Interestingly, FG at a high concentration in NMP displays dramatic stability without any additional stabilizer or modifier, and the C/F ratio of FG can be facilely tuned just by adjusting the sonochemical time. Furthermore, the electrochemical and thermal properties of the prepared FG have been systematically investigated and exhibited regularity with variation of fluorine coverage. On the other hand, based on the solubility of FG in various solvents, a possible dispersion mechanism is proposed to guide FGs further applications in films or polymer-based composites as a mechanical reinforcement.

Pyrite FeS2 microspheres wrapped by reduced graphene oxide as high-performance lithium-ion battery anodes

A composite of pyrite FeS2 microspheres wrapped by reduced graphene oxide (FeS2/rGO) has been synthesized by a facile one-step solvothermal method and applied as an anode in lithium ion batteries (LIBs). Impedance measurements and transmission electron microscopy show that incorporation of rGO significantly decreases the charge transfer resistance and improves the structural stability of the composite. As an anode material for LIBs, the composite exhibits a high capacity of 970 mA h g−1 at a current density of 890 mA g−1 after 300 cycles. Additionally, this composite anode shows impressive performance especially at high current densities. The LIB shows a capacity of 380 mA h g−1 even at a high current density of 8900 mA g−1 (10C) over 2000 cycles, demonstrating its potential for applications in LIBs with long cycling life and high power density.

Synthesis of Honeycomb‐like Mesoporous Pyrite FeS2 Microspheres as Efficient Counter Electrode in Quantum Dots Sensitized Solar Cells

Honeycomb-like mesoporous pyrite FeS2 microspheres, with diameters of 500-800 nm and pore sizes of 25-30 nm, are synthesized by a simple solvothermal approach. The mesoporous FeS2 microspheres are demonstrated to be an outstanding counter electrode (CE) material in quantum dot sensitized solar cells (QDSSCs) for electrocatalyzing polysulfide electrolyte regeneration. The cell using mesoporous FeS2 microspheres as CE shows 86.6% enhancement in power conversion efficiency (PCE) than the cell using traditional noble Pt CE. Furthermore, it also shows 11.4% enhancement in PCE than the cell using solid FeS2 microspheres as CE, due to the mesoporous structure facilitating better contact with polysulfide electrolyte and fast diffusion of redox couple species in electrolyte.

A simple and feasible in-situ reduction route for preparation of graphene lubricant films applied to a variety of substrates

In this work, we present a simple and feasible method with broad applicability for the in-situ reduction and assembly of graphene lubricant films on various substrates. We adopt graphene oxide hydrosol as the precursor solution and creatively introduce an adherent coating of polydopamine that can be firmly bonded onto a wide range of substrates and acts as an active transition layer and in-situ reducing agent, aiming at obtaining the reduced graphene oxide (rGO) films thereon without addition of exogenous reducing agent. Experimental results prove that rGO nanosheets have been successfully assembled onto the substrates and the in-situ synthesized rGO film presents excellent morphology, outstanding friction reduction and wear resistance properties.

Facile fabrication and electrochemical properties of high-quality reduced graphene oxide/cobalt sulfide composite as anode material for lithium-ion batteries

A reduced graphene oxide (rGO)/cobalt sulfide composite is synthesized with a simple and efficient ultrasound-assisted wet chemical method. The morphology and microstructure of the composite are examined with field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results confirm that cobalt sulfide nanoparticles are homogeneously and tightly attached on the surfaces of rGO. As an anode material for lithium-ion batteries, this composite delivers a high reversible capacity of 994 mA h g−1 after 150 cycles at a current density of 200 mA g−1. A synergistic effect combining the merits of rGO and cobalt sulfide nanoparticles endows the composite with superior electrochemical performances over those of pure cobalt sulfide.

Cooperatively exfoliated fluorinated graphene with full-color emission

We report a novel and effective method to prepare fluorinated graphene sheets (FGS) by the cooperative exfoliation of graphite fluoride using cetyl-trimethyl-ammonium bromide and dopamine. This facile, scalable preparation route results in wide (about 2 μm in width), long (at least 3 μm in length) and ultrathin (1–2 layers) FGS with uniform morphology. The chemical composition of FGS was characterized by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The obtained FGS exhibits full-color emission when excited by near ultraviolet (NUV) rays, suggesting its potential applications in luminescence devices, such as NUV-pumped FGS-based flexible light-emitting diodes.