Effect of Mo Doping and Heat Treatment on Microstructure and Electrochemical Performance of Vanadium Oxide Nanotubes
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Effect of Mo Doping and Heat Treatment on Microstructure and Electrochemical Performance of Vanadium Oxide Nanotubes Liqiang Mai, Wen Chen *, Congsheng Jiang, Qing Xu, Junfeng Peng, Quanyao Zhu Institute of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070 Hubei, P. R. China ABSTRACT Mo doped vanadium oxide nanotubes (VONT) were formed via a rheological phase reaction followed by self-assembling process and were heated at 400 in an inert atmosphere. The nanotubes were characterized by SEM, HRTEM, XRD, FTIR, electrochemical investigation, etc. In contrast to the undoped VONTs, the interlayer distance between oxide layers in the (V0.99Mo0.01)xONTs increases owing to replacement of some V in nanotubes by Mo with a larger ionic radius, resulting in a shorten diffusion length of Li ions and an improved electrochemical performance. The electrochemical performance of (V0.99Mo0.01)xONTs is further enhanced by removing the residual organic template by heating in an inert atmosphere. INTRODUCTION Since Iijima discovered carbon nanotubes in 1991 [1], nanotubes with one-dimensional structure attract much scientific interests for electrochemical insertion because they offer four different contact regions, namely, the tube ends, the inner and outer wall surfaces as well as the inter-walls spaces. Moreover, they can provide electrolyte-filled channels for faster transport of the ions to the insertion sites [2]. Mo doped vanadium oxides have found a wide range of applications because of their selective oxidation as well as the unique interaction between V2O5 and MoO3 owing to the similarity of ionic radii and the structure in their highest oxidation state [3-4]. These similarities enable the formation of substitutional solid solutions with different oxidation states of cations [4, 6]. In the present work, Mo doped vanadium oxide nanotubes (VONT) were prepared by modified sol-gel process from layered oxide precursor and organic molecules as structure-directing templates and then heated in an inert atmosphere. The nanotubes were characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), electrochemical investigation, etc. Experiments are performed in order to study the effect of Mo doping and heat treatment on the microstructure and electrochemical performance of vanadium oxide nanotubes. EXPERIMENTAL The vanadium oxide nanotubes were prepared according to literature method with modifications where necessary [2, 7]. V2O5, MoO3 and hexadecylamine were mixed in the molar ratio (0.5-0.5x)∶x∶0.5 (x=0, 0.01, 0.05, 0.09, 0.10) in distilled water and the mixture stirred for * The corresponding author. Fax: +86-27-87642079.
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48 hours in air. The resulting rheological suspension was transferred into a Teflon-lined autoclave with a stainless steel shell. The autoclave was kept at 180 ℃ for about a week. The final black product was washed with distilled water and dried at 80 ℃ for 8 h. T
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