Li Wan

Hubei University, Wu-han-shih, Hubei, China

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Publications (37)81.77 Total impact

  • No preview · Article · Feb 2016 · Coloration Technology
  • [Show abstract] [Hide abstract] ABSTRACT: A double-layer TiO2 (Ag–TiO2-DL) photoanode with various loading amounts of Ag nanoparticles were designed with an underlayer composed of P25 TiO2 nanoparticles and an overlayer of 3D flower-like TiO2 hierarchical microstructures (TiO2-HS) and used to make a serious of dye-sensitized solar cells (DSSCs). The resulting nanostructures are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible spectroscopy, N2 adsorption–desorption isotherms, and Raman spectroscopy. The influences of different loading amounts of Ag on the structure and performance of the DSSCs are investigated. Results indicate that the short current density (Jsc), open-circuit voltage (Voc) and charge lifetime of DSSCs containing Ag nanoparticles are significantly improved. Especially, the as-prepared Ag–TiO2-DL film at the nominal Ag loading of 0.8 wt% showed the highest photoelectric conversion efficiency of 8.98%, which exceeds that of pure TiO2-DL of 6.22%. Thus superior cell efficiency is mostly due to the increase of current density, attributed to that (i) a higher efficiency of light harvesting through the light scattering of overlayer; (ii) the efficient separation of photo-induced electrons and holes due to these novel hierarchical microstructures; (iii) the surface Plasmon resonance effect of Ag nanoparticles, which enhance the efficient charge separation and high carrier mobility.
    No preview · Article · Oct 2015 · Journal of Power Sources
  • [Show abstract] [Hide abstract] ABSTRACT: Low Pt-loaded graphene nanocomposites were prepared using a two-step reduction process. Graphene dispersion was first prepared from graphene oxide using hydrazine hydrate as a reducing agent. Pt-reduced graphene oxide composites were then synthesized in the aqueous graphene dispersion at 90 °C without the need for another reductant. Pt/graphene composite films were then deposited on fluorine-doped tin oxide substrates using a simple drop-casting method at room temperature and subsequently used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Cyclic voltammetry and electrical impedance analysis show that the composite electrodes have high electrocatalytic activity toward iodide/triiodide reduction. The energy conversion efficiency of the Pt/graphene CE-based DSSC was found to be 1.9 % lower than that of cells with a Pt-based CE.
    No preview · Article · Jun 2015 · Journal of Materials Science
  • [Show abstract] [Hide abstract] ABSTRACT: In this study, one- and two-step chemical reduction methods were compared in terms of the production of Pt/graphene nanocomposites with low platinum (Pt)-loadings. Cyclic voltammetry and electrical impedance analysis indicated that the composites displayed high electrocatalytic activity with respect to the reduction of iodide/triiodide. Furthermore, the Pt/RGO composites were deposited on fluorine-doped tin oxide substrates by drop coating and were applied as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The energy conversion efficiency of the DSSCs based on Pt/RGO CEs (prepared using the one-step reduction method) was only 0.9% lower than that of the Pt CE-based cell.
    No preview · Article · Mar 2015 · Composites Science and Technology
  • [Show abstract] [Hide abstract] ABSTRACT: Vertically ordered single-crystalline TiO2 nanorod arrays (NRAs) grown directly on transparent conductive substrates are of considerable interest for overcoming the limitations of current nanoparticle-based dye-sensitized solar cells (DSSCs) with the disordered network structure. However, the synthesis of such structures with high internal surface area is still challenging and desirable for highly efficient DSSCs. Herein, by introduction of a TiO2 nanocrystal seed layer, growth of long single-crystalline rutile TiO2 NRAs with high surface area has been demonstrated by a mild hydrothermal method combined with a chemical etching route. The chemical etching treatment developed here can effectively enlarge the surface area of rutile TiO2 NRAs for more dye-loading by splitting of original TiO2 nanorods into secondary nanowires with a reduced diameter. Accordingly, a DSSC constructed by 7 h-etched rutile TiO2 NRAs exhibits markedly enhanced efficiency of 4.69 %, compared to that of 1.30 % in the DSSCs based on un-etched TiO2 NRAs.
    No preview · Article · Mar 2015 · Journal of Materials Science Materials in Electronics
  • [Show abstract] [Hide abstract] ABSTRACT: Preparation of graphene composite material suitable for drop-coating on FTO conductive glasses in ambient conditions is reported. Highly dispersed PEDOT:PSS/graphene composites were synthesized by in situ polymerization of 3,4-ethylenedioxythiophene (EDOT) using aqueous graphene dispersions as a precursor without the need for further reducing steps. The structural properties of the PEDOT:PSS/graphene were investigated by transmission electron microscope and FT-IR spectrometry. Graphene sheets as the support material likely provided increased active sites for the polymerization of EDOT. The graphene sheets were homogeneously coated by PEDOT:PSS. Drop-coating the solution of PEDOT:PSS/graphene nanocomposites onto FTO glass yielded graphene composite counter electrodes (CEs) useful for dye-sensitized solar cells (DSSCs). Both in cyclic voltammetry measurements and electrochemical impedance spectroscopy, the composite CEs exhibited good catalytic activity. The DSSCs based on PEDOT:PSS/graphene CEs showed a conversion efficiency of 4.66 %, comparable to platinum CE-based cells which showed a conversion efficiency of 5.94 %.
    No preview · Article · Dec 2014 · Journal of Materials Science
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    [Show abstract] [Hide abstract] ABSTRACT: A TiO2 double-layer composite film consisting of hollow TiO2 boxes (HB-TiO2) as overlayer and commercial-grade TiO2 nanoparticles (P25) as underlayer is designed as the photoelectrode of dye-sensitized solar cells (DSSCs). The hollow TiO2 box has been employed as light-scattering part to increase the optical length in the film and enhance light-harvesting. It was found that the double-layer film cell with lower absorbed dye achieved the highest conversion efficiency and reach up to a maximum value of 6.4%, which is 226% higher than that of pure HB-TiO2 film cell (eta = 1.96%) and 57.2% higher than that of pure P25 particles film cell under identical film thickness at a constant irradiation of 100 mW cm(-2). The enhanced efficiency of double-layer film can be attributed to its light-scattering capability.
    Full-text · Article · Nov 2014 · Materials Research Bulletin
  • [Show abstract] [Hide abstract] ABSTRACT: Water-soluble polyaniline/graphene nanocomposites have been prepared via a simple in-situ polymerization of aniline in graphene dispersion. TEM measurement confirmed that polyaniline was homogeneously coated on the graphene sheets. The nanocomposites solution can be used for film fabrication by common technology, such as drop coating. When these different polyaniline/graphene nanocomposites were applied as the counter electrode materials for dye-sensitized solar cells, the short-circuit current density and power-conversion efficiency of the devices were measured to be 12.19 mA cm-2 and 4.46%, respectively, which was comparable to 5.71% for the cell with a Pt counter electrode under the same experimental conditions.
    No preview · Article · Jun 2014 · Reactive and Functional Polymers
  • [Show abstract] [Hide abstract] ABSTRACT: Pure anatase, pure rutile and the mixed TiO2 crystals with different amounts of rutile and anatase were prepared by a hydrothermal method using Ti (OBu)4 as starting material. The effect of anions on crystal phase and morphology of TiO2 synthesized by the hydrothermal method was investigated, and the relevant mechanism was also discussed. The X-ray diffraction (XRD) results indicate that Cl- ion was in favor of the formation of rutile, while NO3- and CH3COO- were beneficial for the formation of anatase. The hydrothermal conditions have significant effects on the phase component, morphology, and particle size of obtained titania products. Additionally, mixed TiO2 crystals with different amounts of rutile and anatase could be prepared by adjusting the reaction conditions, such as the concentration of Cl- ion, hydrothermal time, the amount of citric acid and the concentration of tetrabutyl titanate.
    No preview · Article · Feb 2014
  • [Show abstract] [Hide abstract] ABSTRACT: The dependence of the absorbance of few-layer graphene oxide on reduction level is shown to originate from different inter- and intra-band transitions using infrared-visible spectroscopy. In addition, the band-gap of reduced graphene oxide is tunable from 2 to 0.02 eV depending on its reduction level. These results indicate that reduced graphene oxide possesses great potential as a candidate for photodetection in the mid-infrared range by controlling its band-gap. This study not only gives further insight into the absorption mechanism of graphene oxide reduced to different levels, but also reveals a way to tune and measure the band-gap of graphene-based materials using a simple, economical, and nondestructive approach. This approach should be readily adapted for use in photodetection applications. (c) 2013 Elsevier Ltd. All rights reserved.
    No preview · Article · Oct 2013 · Carbon - Science and Technology
  • [Show abstract] [Hide abstract] ABSTRACT: The TiO2 film electrodes sensitized with CdS quantum dots (QDs) via chemical bath deposition method were successfully prepared as the photoanode of dye-sensitized solar cells (DSSCs). Microstructural characterizations by XRD, SEM, TEM and EDX show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO2 films. The amount of CdS QDs can be controlled by varying the dipping time. The experiment results demonstrate that the CdS QDs-sensitized solar cells show a wider absorption in the solar spectrum and an enhanced surface photovoltage response. The maximal photoelectric conversion efficiency of 5.57% was achieved by the DSSC based on CdS QDs-sensitized TiO2 film with 4 min. The performance improvement is ascribed to the enhancement of electron transport, the reduction of electron recombination and the long electron lifetime.
    No preview · Article · Jul 2013 · Materials Research Bulletin
  • Xuyu Yang · Xianbao Wang · Jia Yang · Jing Li · Li Wan
    [Show abstract] [Hide abstract] ABSTRACT: Functionalized reduced graphene oxide (RGO) was obtained by reaction of graphene oxide with dodecyl (12C), octyl (8C) and propyl (3C) trimethoxysilane and subsequent reduction using hydrazine hydrate. The results showed the successful grafting of the alkyl groups onto the surface of RGO, and that the longer alkylated chains made graphene more lipophilic. Furthermore, the RGO-12C was incorporated into polypropylene matrix as a reinforcing component by solution mixing. The resulting nanocomposites displayed a significant improvement in thermal stability, crystallinity and mechanical properties. This work suggests a new route to improve the solubility and dispersion of graphene in polymer matrix.
    No preview · Article · May 2013 · Chemical Physics Letters
  • J. Li · X.-B. Wang · J. Yang · X.-Y. Yang · L. Wan
    [Show abstract] [Hide abstract] ABSTRACT: A series nGs with different electrocatalytic abilities toward oxygen reduction reaction(ORR) was prepared via a two-steps pyrolysis method by controlling the reaction temperature on the physical mixture of graphene oxideand urea. Transmission electron microscopy and scanning electron microscopy display nG with highly wrinkled and overlapping structures. X-ray photoelectron spectroscopy shows that nitrogen is successfully doped in graphene with the formation of pyridinic N, pyrrolic N and graphitic N, and the maximum nitrogen content is 6.6%(molar fraction). Cyclic voltammogram and rotating disk electrode measurement show that nGs exhibit high electrocatalytic activity with an onset potential of 0.1 V in an acid electrolyte. Moreover, the nGs catalyzed oxygen reduction revealed a favorable formation of water via a four-electron pathway and excellent stability over Pt/C catalyst. Furthermore, the nG obtained at 200°C in the first pyrolysis step displays the best catalytic performance.
    No preview · Article · Apr 2013 · Chemical Journal of Chinese Universities -Chinese Edition-
  • [Show abstract] [Hide abstract] ABSTRACT: A facile means to generate carbon dots/ionic liquids (ILs) blend using ionic liquid-assisted electrochemical exfoliation was demonstrated. Two kinds of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), were used in this work. Transmission electron microscopy and UV–vis spectrum were employed to characterize the formed carbon dots/ILs. The carbon dots/ILs were used for fabricating quasi-solid-state dye-sensitized solar cells (DSSCs), where 1-butyl-3-methylimidazolium iodide and LiI/I2 were added to enhance the performance of DSSCs. Effects of the varied contents of components in the complex on the performance of DCCSs have been studied in detail at ambient temperature. The electrochemical impedance spectroscopy showed that the introduction of carbon dots into ionic liquids can enhance the electrical properties by facilitating charge transfer processes of the electrolytes. The overall energy-conversion efficiency (η) was 2.71% and 2.41% for carbon dots/[bmim][PF6] and carbon dots/[bmim][BF4] based blend electrolytes, respectively. A 82% enhancement in η was obtained by introduction of carbon dots into [bmim][PF6] comparing with pure [bmim][PF6] (η = 1.49%). In addition, the cells exhibited good stability under continuous illumination in room temperature without any further sealing.
    No preview · Article · Jan 2013 · Electrochimica Acta
  • [Show abstract] [Hide abstract] ABSTRACT: Bi2O3 nanostructures with high surface-to-volume ratio are attracting particular interest in catalysis, gas sensors, solar-energy conversion, and so on. In this paper, we present the impact of annealing on morphology, structure, and optical properties of Bi2O3 nanotube-based urchin-like microarchitectures, which is very important to determine before their applications in many potential fields. Our results showed that below 400 °C, the microarchitectures possessed good thermal stability. While annealing at 500 °C, jointed nanoparticles with an average size of 350 nm were formed. On further increasing the annealing temperature to 600 °C, the microarchitectures were transformed into stable α-Bi2O3 microcrystal film with a larger particle size of about 800 nm. The optical bandgaps of the annealed products were also changed according to their changes of morphology and structure.
    No preview · Article · Nov 2012 · physica status solidi (a)
  • X.-Y. Yang · X.-B. Wang · J. Li · J. Yang · L. Wan · J.-C. Wang
    [Show abstract] [Hide abstract] ABSTRACT: Graphene with different reduction degree was prepared by controlling the reduction time. The structures and properties of graphene were characterized systematically by Fourier transform infrared spectroscopy(FTIR), UV-Vis spectroscopy, Raman spectroscopy, X-ray diffractions(XRD), thermo-gravimetric analysis(TGA) and electrical conductivity measurements. Moreover, transmission electron microscopy(TEM), scanning electron microscopy(SEM) and atomic force microscopy(AFM) were employed to compare the morphologies of graphene oxide with those of graphene. The results showed that with the increase of reduction time, the oxygen-containing groups were removed gradually and the absorption peak of ultraviolet displayed a gradual red-shift, besides, the ratio of the Raman intensities(I D/I G) of graphene increased markedly, and the thermal stability was improved significantly. The characterization of microstructures reveals that graphene consists of thicker layer structures and more crumples than those of graphene oxide.
    No preview · Article · Sep 2012 · Chemical Journal of Chinese Universities -Chinese Edition-
  • [Show abstract] [Hide abstract] ABSTRACT: A controllable preparation of novel graphene-based inorganic semi-conducting composites has aroused great attention in the optoelectronic device and powerful electronic anode materials. In this article, we demonstrate a simple two-step strategy for the synthesis of cadmium sulfide/reduced graphene oxide (CdS/RGO) nanocomposites, of which the preparing process includes modification of the exfoliated graphene oxide acylated with thionyl chloride, immobilization of the CdS nanoparticles on the graphene oxide (GO) surface by an amide reaction between the amino groups located on the CdS particles and the acyl chloride bound to the GO surface, and reduction by hydrazine and ammonia. Our results showed that the CdS nanoparticles with an average size of 20 nm were homogeneously dispersed on the surface of RGO sheets. The CdS/RGO nanocomposites can form a homogeneous and stable solution in dimethylformamide, and CV analysis indicated a remarkable increase for the CdS/RGO modified electrode in the electrochemical current relative to that at a glass carbon electrode.
    No preview · Article · Aug 2012 · Materials Chemistry and Physics
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    [Show abstract] [Hide abstract] ABSTRACT: This work reports a facile and rapid method assisted by microwave irradiation for the synthesis of hemin functionalized reduced graphene oxide (hemin–RGO) materials. Our investigation confirmed that the hemin molecules were covalently grafted to the surface of graphene by the amidation reaction of the NH2 groups on the edges of ethylenediamine functionalized graphene oxide with the COOH groups of hemin. Hemin–RGO exhibits a homogeneous dispersion in water, dimethylformamide, and acetone after more than one month, indicating that hemin can effectively improve the dispersion and solubility of RGO in the solvent. Hemin–RGO was used as a counter electrode in dye-sensitized solar cells and exhibited preferable electrocatalytic activity for I3− to I− reduction compared with RGO.
    Full-text · Article · Feb 2012 · Materials Chemistry and Physics
  • [Show abstract] [Hide abstract] ABSTRACT: Graphene nanosheets–gold (GNS-Au) nanocomposites have been successfully prepared by microwave radiation in aqueous media via a rapid one-step method. The as-obtained nanocomposites were characterized by Fourier transform infrared spectra, X-ray power diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry, Raman spectrum and UV-visible absorption spectra. The results show that Au nanoparticles with a mean diameter of 9.3 nm are densely coated on the surface of graphene nanosheets, which disturbs the van der Waals interactions and prevents graphene nanosheets from approaching each other. Cyclic voltammetry measurements reveal that GNS–Au modified glassy carbon electrode (GNS–Au/GCE) has a greatly enhanced electrochemical response compared with bare GCE and the GNS modified glassy carbon electrode (GNS/GCE), suggesting that the GNS–Au nanocomposites may be a promising nanomaterial for highly sensitive electrochemical sensors.
    No preview · Article · Jan 2012 · Fullerenes Nanotubes and Carbon Nanostructures
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    [Show abstract] [Hide abstract] ABSTRACT: Spectroscopic ellipsometry was used to characterize the optical response of few layer reduced graphene oxide and graphene oxide in visible range. Lorentz oscillator model is added to analyze the ellipsometric parameters. The experiment shows the optical response of few layer reduced graphene oxide and monolayer exfoliated graphene in visible range is quite similar with slight difference due to the structure defects. The Lorentz oscillator model gives experimental support to investigate the band-gap tuning through the reduction process in details.
    Full-text · Article · Oct 2011 · Applied Physics Letters